| @c Copyright (C) 1988-2022 Free Software Foundation, Inc. |
| @c This is part of the GCC manual. |
| @c For copying conditions, see the file gcc.texi. |
| |
| @ignore |
| @c man begin INCLUDE |
| @include gcc-vers.texi |
| @c man end |
| |
| @c man begin COPYRIGHT |
| Copyright @copyright{} 1988-2022 Free Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.3 or |
| any later version published by the Free Software Foundation; with the |
| Invariant Sections being ``GNU General Public License'' and ``Funding |
| Free Software'', the Front-Cover texts being (a) (see below), and with |
| the Back-Cover Texts being (b) (see below). A copy of the license is |
| included in the gfdl(7) man page. |
| |
| (a) The FSF's Front-Cover Text is: |
| |
| A GNU Manual |
| |
| (b) The FSF's Back-Cover Text is: |
| |
| You have freedom to copy and modify this GNU Manual, like GNU |
| software. Copies published by the Free Software Foundation raise |
| funds for GNU development. |
| @c man end |
| @c Set file name and title for the man page. |
| @setfilename gcc |
| @settitle GNU project C and C++ compiler |
| @c man begin SYNOPSIS |
| gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}] |
| [@option{-g}] [@option{-pg}] [@option{-O}@var{level}] |
| [@option{-W}@var{warn}@dots{}] [@option{-Wpedantic}] |
| [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}] |
| [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}] |
| [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}] |
| [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{} |
| |
| Only the most useful options are listed here; see below for the |
| remainder. @command{g++} accepts mostly the same options as @command{gcc}. |
| @c man end |
| @c man begin SEEALSO |
| gpl(7), gfdl(7), fsf-funding(7), |
| cpp(1), gcov(1), as(1), ld(1), gdb(1), dbx(1) |
| and the Info entries for @file{gcc}, @file{cpp}, @file{as}, |
| @file{ld}, @file{binutils} and @file{gdb}. |
| @c man end |
| @c man begin BUGS |
| For instructions on reporting bugs, see |
| @w{@value{BUGURL}}. |
| @c man end |
| @c man begin AUTHOR |
| See the Info entry for @command{gcc}, or |
| @w{@uref{https://gcc.gnu.org/onlinedocs/gcc/Contributors.html}}, |
| for contributors to GCC@. |
| @c man end |
| @end ignore |
| |
| @node Invoking GCC |
| @chapter GCC Command Options |
| @cindex GCC command options |
| @cindex command options |
| @cindex options, GCC command |
| |
| @c man begin DESCRIPTION |
| When you invoke GCC, it normally does preprocessing, compilation, |
| assembly and linking. The ``overall options'' allow you to stop this |
| process at an intermediate stage. For example, the @option{-c} option |
| says not to run the linker. Then the output consists of object files |
| output by the assembler. |
| @xref{Overall Options,,Options Controlling the Kind of Output}. |
| |
| Other options are passed on to one or more stages of processing. Some options |
| control the preprocessor and others the compiler itself. Yet other |
| options control the assembler and linker; most of these are not |
| documented here, since you rarely need to use any of them. |
| |
| @cindex C compilation options |
| Most of the command-line options that you can use with GCC are useful |
| for C programs; when an option is only useful with another language |
| (usually C++), the explanation says so explicitly. If the description |
| for a particular option does not mention a source language, you can use |
| that option with all supported languages. |
| |
| @cindex cross compiling |
| @cindex specifying machine version |
| @cindex specifying compiler version and target machine |
| @cindex compiler version, specifying |
| @cindex target machine, specifying |
| The usual way to run GCC is to run the executable called @command{gcc}, or |
| @command{@var{machine}-gcc} when cross-compiling, or |
| @command{@var{machine}-gcc-@var{version}} to run a specific version of GCC. |
| When you compile C++ programs, you should invoke GCC as @command{g++} |
| instead. @xref{Invoking G++,,Compiling C++ Programs}, |
| for information about the differences in behavior between @command{gcc} |
| and @command{g++} when compiling C++ programs. |
| |
| @cindex grouping options |
| @cindex options, grouping |
| The @command{gcc} program accepts options and file names as operands. Many |
| options have multi-letter names; therefore multiple single-letter options |
| may @emph{not} be grouped: @option{-dv} is very different from @w{@samp{-d |
| -v}}. |
| |
| @cindex order of options |
| @cindex options, order |
| You can mix options and other arguments. For the most part, the order |
| you use doesn't matter. Order does matter when you use several |
| options of the same kind; for example, if you specify @option{-L} more |
| than once, the directories are searched in the order specified. Also, |
| the placement of the @option{-l} option is significant. |
| |
| Many options have long names starting with @samp{-f} or with |
| @samp{-W}---for example, |
| @option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of |
| these have both positive and negative forms; the negative form of |
| @option{-ffoo} is @option{-fno-foo}. This manual documents |
| only one of these two forms, whichever one is not the default. |
| |
| Some options take one or more arguments typically separated either |
| by a space or by the equals sign (@samp{=}) from the option name. |
| Unless documented otherwise, an argument can be either numeric or |
| a string. Numeric arguments must typically be small unsigned decimal |
| or hexadecimal integers. Hexadecimal arguments must begin with |
| the @samp{0x} prefix. Arguments to options that specify a size |
| threshold of some sort may be arbitrarily large decimal or hexadecimal |
| integers followed by a byte size suffix designating a multiple of bytes |
| such as @code{kB} and @code{KiB} for kilobyte and kibibyte, respectively, |
| @code{MB} and @code{MiB} for megabyte and mebibyte, @code{GB} and |
| @code{GiB} for gigabyte and gigibyte, and so on. Such arguments are |
| designated by @var{byte-size} in the following text. Refer to the NIST, |
| IEC, and other relevant national and international standards for the full |
| listing and explanation of the binary and decimal byte size prefixes. |
| |
| @c man end |
| |
| @xref{Option Index}, for an index to GCC's options. |
| |
| @menu |
| * Option Summary:: Brief list of all options, without explanations. |
| * Overall Options:: Controlling the kind of output: |
| an executable, object files, assembler files, |
| or preprocessed source. |
| * Invoking G++:: Compiling C++ programs. |
| * C Dialect Options:: Controlling the variant of C language compiled. |
| * C++ Dialect Options:: Variations on C++. |
| * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C |
| and Objective-C++. |
| * Diagnostic Message Formatting Options:: Controlling how diagnostics should |
| be formatted. |
| * Warning Options:: How picky should the compiler be? |
| * Static Analyzer Options:: More expensive warnings. |
| * Debugging Options:: Producing debuggable code. |
| * Optimize Options:: How much optimization? |
| * Instrumentation Options:: Enabling profiling and extra run-time error checking. |
| * Preprocessor Options:: Controlling header files and macro definitions. |
| Also, getting dependency information for Make. |
| * Assembler Options:: Passing options to the assembler. |
| * Link Options:: Specifying libraries and so on. |
| * Directory Options:: Where to find header files and libraries. |
| Where to find the compiler executable files. |
| * Code Gen Options:: Specifying conventions for function calls, data layout |
| and register usage. |
| * Developer Options:: Printing GCC configuration info, statistics, and |
| debugging dumps. |
| * Submodel Options:: Target-specific options, such as compiling for a |
| specific processor variant. |
| * Spec Files:: How to pass switches to sub-processes. |
| * Environment Variables:: Env vars that affect GCC. |
| * Precompiled Headers:: Compiling a header once, and using it many times. |
| * C++ Modules:: Experimental C++20 module system. |
| @end menu |
| |
| @c man begin OPTIONS |
| |
| @node Option Summary |
| @section Option Summary |
| |
| Here is a summary of all the options, grouped by type. Explanations are |
| in the following sections. |
| |
| @table @emph |
| @item Overall Options |
| @xref{Overall Options,,Options Controlling the Kind of Output}. |
| @gccoptlist{-c -S -E -o @var{file} @gol |
| -dumpbase @var{dumpbase} -dumpbase-ext @var{auxdropsuf} @gol |
| -dumpdir @var{dumppfx} -x @var{language} @gol |
| -v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help --version @gol |
| -pass-exit-codes -pipe -specs=@var{file} -wrapper @gol |
| @@@var{file} -ffile-prefix-map=@var{old}=@var{new} @gol |
| -fplugin=@var{file} -fplugin-arg-@var{name}=@var{arg} @gol |
| -fdump-ada-spec@r{[}-slim@r{]} -fada-spec-parent=@var{unit} -fdump-go-spec=@var{file}} |
| |
| @item C Language Options |
| @xref{C Dialect Options,,Options Controlling C Dialect}. |
| @gccoptlist{-ansi -std=@var{standard} -aux-info @var{filename} @gol |
| -fallow-parameterless-variadic-functions -fno-asm @gol |
| -fno-builtin -fno-builtin-@var{function} -fcond-mismatch @gol |
| -ffreestanding -fgimple -fgnu-tm -fgnu89-inline -fhosted @gol |
| -flax-vector-conversions -fms-extensions @gol |
| -foffload=@var{arg} -foffload-options=@var{arg} @gol |
| -fopenacc -fopenacc-dim=@var{geom} @gol |
| -fopenmp -fopenmp-simd @gol |
| -fpermitted-flt-eval-methods=@var{standard} @gol |
| -fplan9-extensions -fsigned-bitfields -funsigned-bitfields @gol |
| -fsigned-char -funsigned-char -fsso-struct=@var{endianness}} |
| |
| @item C++ Language Options |
| @xref{C++ Dialect Options,,Options Controlling C++ Dialect}. |
| @gccoptlist{-fabi-version=@var{n} -fno-access-control @gol |
| -faligned-new=@var{n} -fargs-in-order=@var{n} -fchar8_t -fcheck-new @gol |
| -fconstexpr-depth=@var{n} -fconstexpr-cache-depth=@var{n} @gol |
| -fconstexpr-loop-limit=@var{n} -fconstexpr-ops-limit=@var{n} @gol |
| -fno-elide-constructors @gol |
| -fno-enforce-eh-specs @gol |
| -fno-gnu-keywords @gol |
| -fno-implicit-templates @gol |
| -fno-implicit-inline-templates @gol |
| -fno-implement-inlines @gol |
| -fmodule-header@r{[}=@var{kind}@r{]} -fmodule-only -fmodules-ts @gol |
| -fmodule-implicit-inline @gol |
| -fno-module-lazy @gol |
| -fmodule-mapper=@var{specification} @gol |
| -fmodule-version-ignore @gol |
| -fms-extensions @gol |
| -fnew-inheriting-ctors @gol |
| -fnew-ttp-matching @gol |
| -fno-nonansi-builtins -fnothrow-opt -fno-operator-names @gol |
| -fno-optional-diags -fpermissive @gol |
| -fno-pretty-templates @gol |
| -fno-rtti -fsized-deallocation @gol |
| -ftemplate-backtrace-limit=@var{n} @gol |
| -ftemplate-depth=@var{n} @gol |
| -fno-threadsafe-statics -fuse-cxa-atexit @gol |
| -fno-weak -nostdinc++ @gol |
| -fvisibility-inlines-hidden @gol |
| -fvisibility-ms-compat @gol |
| -fext-numeric-literals @gol |
| -flang-info-include-translate@r{[}=@var{header}@r{]} @gol |
| -flang-info-include-translate-not @gol |
| -flang-info-module-cmi@r{[}=@var{module}@r{]} @gol |
| -stdlib=@var{libstdc++,libc++} @gol |
| -Wabi-tag -Wcatch-value -Wcatch-value=@var{n} @gol |
| -Wno-class-conversion -Wclass-memaccess @gol |
| -Wcomma-subscript -Wconditionally-supported @gol |
| -Wno-conversion-null -Wctad-maybe-unsupported @gol |
| -Wctor-dtor-privacy -Wno-delete-incomplete @gol |
| -Wdelete-non-virtual-dtor -Wno-deprecated-array-compare @gol |
| -Wdeprecated-copy -Wdeprecated-copy-dtor @gol |
| -Wno-deprecated-enum-enum-conversion -Wno-deprecated-enum-float-conversion @gol |
| -Weffc++ -Wno-exceptions -Wextra-semi -Wno-inaccessible-base @gol |
| -Wno-inherited-variadic-ctor -Wno-init-list-lifetime @gol |
| -Winvalid-imported-macros @gol |
| -Wno-invalid-offsetof -Wno-literal-suffix @gol |
| -Wmismatched-new-delete -Wmismatched-tags @gol |
| -Wmultiple-inheritance -Wnamespaces -Wnarrowing @gol |
| -Wnoexcept -Wnoexcept-type -Wnon-virtual-dtor @gol |
| -Wpessimizing-move -Wno-placement-new -Wplacement-new=@var{n} @gol |
| -Wrange-loop-construct -Wredundant-move -Wredundant-tags @gol |
| -Wreorder -Wregister @gol |
| -Wstrict-null-sentinel -Wno-subobject-linkage -Wtemplates @gol |
| -Wno-non-template-friend -Wold-style-cast @gol |
| -Woverloaded-virtual -Wno-pmf-conversions -Wsign-promo @gol |
| -Wsized-deallocation -Wsuggest-final-methods @gol |
| -Wsuggest-final-types -Wsuggest-override @gol |
| -Wno-terminate -Wuseless-cast -Wno-vexing-parse @gol |
| -Wvirtual-inheritance @gol |
| -Wno-virtual-move-assign -Wvolatile -Wzero-as-null-pointer-constant} |
| |
| @item Objective-C and Objective-C++ Language Options |
| @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling |
| Objective-C and Objective-C++ Dialects}. |
| @gccoptlist{-fconstant-string-class=@var{class-name} @gol |
| -fgnu-runtime -fnext-runtime @gol |
| -fno-nil-receivers @gol |
| -fobjc-abi-version=@var{n} @gol |
| -fobjc-call-cxx-cdtors @gol |
| -fobjc-direct-dispatch @gol |
| -fobjc-exceptions @gol |
| -fobjc-gc @gol |
| -fobjc-nilcheck @gol |
| -fobjc-std=objc1 @gol |
| -fno-local-ivars @gol |
| -fivar-visibility=@r{[}public@r{|}protected@r{|}private@r{|}package@r{]} @gol |
| -freplace-objc-classes @gol |
| -fzero-link @gol |
| -gen-decls @gol |
| -Wassign-intercept -Wno-property-assign-default @gol |
| -Wno-protocol -Wobjc-root-class -Wselector @gol |
| -Wstrict-selector-match @gol |
| -Wundeclared-selector} |
| |
| @item Diagnostic Message Formatting Options |
| @xref{Diagnostic Message Formatting Options,,Options to Control Diagnostic Messages Formatting}. |
| @gccoptlist{-fmessage-length=@var{n} @gol |
| -fdiagnostics-plain-output @gol |
| -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol |
| -fdiagnostics-color=@r{[}auto@r{|}never@r{|}always@r{]} @gol |
| -fdiagnostics-urls=@r{[}auto@r{|}never@r{|}always@r{]} @gol |
| -fdiagnostics-format=@r{[}text@r{|}json@r{]} @gol |
| -fno-diagnostics-show-option -fno-diagnostics-show-caret @gol |
| -fno-diagnostics-show-labels -fno-diagnostics-show-line-numbers @gol |
| -fno-diagnostics-show-cwe @gol |
| -fdiagnostics-minimum-margin-width=@var{width} @gol |
| -fdiagnostics-parseable-fixits -fdiagnostics-generate-patch @gol |
| -fdiagnostics-show-template-tree -fno-elide-type @gol |
| -fdiagnostics-path-format=@r{[}none@r{|}separate-events@r{|}inline-events@r{]} @gol |
| -fdiagnostics-show-path-depths @gol |
| -fno-show-column @gol |
| -fdiagnostics-column-unit=@r{[}display@r{|}byte@r{]} @gol |
| -fdiagnostics-column-origin=@var{origin} @gol |
| -fdiagnostics-escape-format=@r{[}unicode@r{|}bytes@r{]}} |
| |
| @item Warning Options |
| @xref{Warning Options,,Options to Request or Suppress Warnings}. |
| @gccoptlist{-fsyntax-only -fmax-errors=@var{n} -Wpedantic @gol |
| -pedantic-errors @gol |
| -w -Wextra -Wall -Wabi=@var{n} @gol |
| -Waddress -Wno-address-of-packed-member -Waggregate-return @gol |
| -Walloc-size-larger-than=@var{byte-size} -Walloc-zero @gol |
| -Walloca -Walloca-larger-than=@var{byte-size} @gol |
| -Wno-aggressive-loop-optimizations @gol |
| -Warith-conversion @gol |
| -Warray-bounds -Warray-bounds=@var{n} -Warray-compare @gol |
| -Wno-attributes -Wattribute-alias=@var{n} -Wno-attribute-alias @gol |
| -Wno-attribute-warning @gol |
| -Wbidi-chars=@r{[}none@r{|}unpaired@r{|}any@r{|}ucn@r{]} @gol |
| -Wbool-compare -Wbool-operation @gol |
| -Wno-builtin-declaration-mismatch @gol |
| -Wno-builtin-macro-redefined -Wc90-c99-compat -Wc99-c11-compat @gol |
| -Wc11-c2x-compat @gol |
| -Wc++-compat -Wc++11-compat -Wc++14-compat -Wc++17-compat @gol |
| -Wc++20-compat @gol |
| -Wno-c++11-extensions -Wno-c++14-extensions -Wno-c++17-extensions @gol |
| -Wno-c++20-extensions -Wno-c++23-extensions @gol |
| -Wcast-align -Wcast-align=strict -Wcast-function-type -Wcast-qual @gol |
| -Wchar-subscripts @gol |
| -Wclobbered -Wcomment @gol |
| -Wconversion -Wno-coverage-mismatch -Wno-cpp @gol |
| -Wdangling-else -Wdangling-pointer -Wdangling-pointer=@var{n} @gol |
| -Wdate-time @gol |
| -Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init @gol |
| -Wdisabled-optimization @gol |
| -Wno-discarded-array-qualifiers -Wno-discarded-qualifiers @gol |
| -Wno-div-by-zero -Wdouble-promotion @gol |
| -Wduplicated-branches -Wduplicated-cond @gol |
| -Wempty-body -Wno-endif-labels -Wenum-compare -Wenum-conversion @gol |
| -Werror -Werror=* -Wexpansion-to-defined -Wfatal-errors @gol |
| -Wfloat-conversion -Wfloat-equal -Wformat -Wformat=2 @gol |
| -Wno-format-contains-nul -Wno-format-extra-args @gol |
| -Wformat-nonliteral -Wformat-overflow=@var{n} @gol |
| -Wformat-security -Wformat-signedness -Wformat-truncation=@var{n} @gol |
| -Wformat-y2k -Wframe-address @gol |
| -Wframe-larger-than=@var{byte-size} -Wno-free-nonheap-object @gol |
| -Wno-if-not-aligned -Wno-ignored-attributes @gol |
| -Wignored-qualifiers -Wno-incompatible-pointer-types @gol |
| -Wimplicit -Wimplicit-fallthrough -Wimplicit-fallthrough=@var{n} @gol |
| -Wno-implicit-function-declaration -Wno-implicit-int @gol |
| -Winfinite-recursion @gol |
| -Winit-self -Winline -Wno-int-conversion -Wint-in-bool-context @gol |
| -Wno-int-to-pointer-cast -Wno-invalid-memory-model @gol |
| -Winvalid-pch -Wjump-misses-init -Wlarger-than=@var{byte-size} @gol |
| -Wlogical-not-parentheses -Wlogical-op -Wlong-long @gol |
| -Wno-lto-type-mismatch -Wmain -Wmaybe-uninitialized @gol |
| -Wmemset-elt-size -Wmemset-transposed-args @gol |
| -Wmisleading-indentation -Wmissing-attributes -Wmissing-braces @gol |
| -Wmissing-field-initializers -Wmissing-format-attribute @gol |
| -Wmissing-include-dirs -Wmissing-noreturn -Wno-missing-profile @gol |
| -Wno-multichar -Wmultistatement-macros -Wnonnull -Wnonnull-compare @gol |
| -Wnormalized=@r{[}none@r{|}id@r{|}nfc@r{|}nfkc@r{]} @gol |
| -Wnull-dereference -Wno-odr @gol |
| -Wopenacc-parallelism @gol |
| -Wopenmp-simd @gol |
| -Wno-overflow -Woverlength-strings -Wno-override-init-side-effects @gol |
| -Wpacked -Wno-packed-bitfield-compat -Wpacked-not-aligned -Wpadded @gol |
| -Wparentheses -Wno-pedantic-ms-format @gol |
| -Wpointer-arith -Wno-pointer-compare -Wno-pointer-to-int-cast @gol |
| -Wno-pragmas -Wno-prio-ctor-dtor -Wredundant-decls @gol |
| -Wrestrict -Wno-return-local-addr -Wreturn-type @gol |
| -Wno-scalar-storage-order -Wsequence-point @gol |
| -Wshadow -Wshadow=global -Wshadow=local -Wshadow=compatible-local @gol |
| -Wno-shadow-ivar @gol |
| -Wno-shift-count-negative -Wno-shift-count-overflow -Wshift-negative-value @gol |
| -Wno-shift-overflow -Wshift-overflow=@var{n} @gol |
| -Wsign-compare -Wsign-conversion @gol |
| -Wno-sizeof-array-argument @gol |
| -Wsizeof-array-div @gol |
| -Wsizeof-pointer-div -Wsizeof-pointer-memaccess @gol |
| -Wstack-protector -Wstack-usage=@var{byte-size} -Wstrict-aliasing @gol |
| -Wstrict-aliasing=n -Wstrict-overflow -Wstrict-overflow=@var{n} @gol |
| -Wstring-compare @gol |
| -Wno-stringop-overflow -Wno-stringop-overread @gol |
| -Wno-stringop-truncation @gol |
| -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{|}malloc@r{]} @gol |
| -Wswitch -Wno-switch-bool -Wswitch-default -Wswitch-enum @gol |
| -Wno-switch-outside-range -Wno-switch-unreachable -Wsync-nand @gol |
| -Wsystem-headers -Wtautological-compare -Wtrampolines -Wtrigraphs @gol |
| -Wtrivial-auto-var-init -Wtsan -Wtype-limits -Wundef @gol |
| -Wuninitialized -Wunknown-pragmas @gol |
| -Wunsuffixed-float-constants -Wunused @gol |
| -Wunused-but-set-parameter -Wunused-but-set-variable @gol |
| -Wunused-const-variable -Wunused-const-variable=@var{n} @gol |
| -Wunused-function -Wunused-label -Wunused-local-typedefs @gol |
| -Wunused-macros @gol |
| -Wunused-parameter -Wno-unused-result @gol |
| -Wunused-value -Wunused-variable @gol |
| -Wno-varargs -Wvariadic-macros @gol |
| -Wvector-operation-performance @gol |
| -Wvla -Wvla-larger-than=@var{byte-size} -Wno-vla-larger-than @gol |
| -Wvolatile-register-var -Wwrite-strings @gol |
| -Wzero-length-bounds} |
| |
| @item Static Analyzer Options |
| @gccoptlist{ |
| -fanalyzer @gol |
| -fanalyzer-call-summaries @gol |
| -fanalyzer-checker=@var{name} @gol |
| -fno-analyzer-feasibility @gol |
| -fanalyzer-fine-grained @gol |
| -fno-analyzer-state-merge @gol |
| -fno-analyzer-state-purge @gol |
| -fanalyzer-transitivity @gol |
| -fanalyzer-verbose-edges @gol |
| -fanalyzer-verbose-state-changes @gol |
| -fanalyzer-verbosity=@var{level} @gol |
| -fdump-analyzer @gol |
| -fdump-analyzer-callgraph @gol |
| -fdump-analyzer-exploded-graph @gol |
| -fdump-analyzer-exploded-nodes @gol |
| -fdump-analyzer-exploded-nodes-2 @gol |
| -fdump-analyzer-exploded-nodes-3 @gol |
| -fdump-analyzer-exploded-paths @gol |
| -fdump-analyzer-feasibility @gol |
| -fdump-analyzer-json @gol |
| -fdump-analyzer-state-purge @gol |
| -fdump-analyzer-stderr @gol |
| -fdump-analyzer-supergraph @gol |
| -fdump-analyzer-untracked @gol |
| -Wno-analyzer-double-fclose @gol |
| -Wno-analyzer-double-free @gol |
| -Wno-analyzer-exposure-through-output-file @gol |
| -Wno-analyzer-file-leak @gol |
| -Wno-analyzer-free-of-non-heap @gol |
| -Wno-analyzer-malloc-leak @gol |
| -Wno-analyzer-mismatching-deallocation @gol |
| -Wno-analyzer-null-argument @gol |
| -Wno-analyzer-null-dereference @gol |
| -Wno-analyzer-possible-null-argument @gol |
| -Wno-analyzer-possible-null-dereference @gol |
| -Wno-analyzer-shift-count-negative @gol |
| -Wno-analyzer-shift-count-overflow @gol |
| -Wno-analyzer-stale-setjmp-buffer @gol |
| -Wno-analyzer-tainted-allocation-size @gol |
| -Wno-analyzer-tainted-array-index @gol |
| -Wno-analyzer-tainted-divisor @gol |
| -Wno-analyzer-tainted-offset @gol |
| -Wno-analyzer-tainted-size @gol |
| -Wanalyzer-too-complex @gol |
| -Wno-analyzer-unsafe-call-within-signal-handler @gol |
| -Wno-analyzer-use-after-free @gol |
| -Wno-analyzer-use-of-pointer-in-stale-stack-frame @gol |
| -Wno-analyzer-use-of-uninitialized-value @gol |
| -Wno-analyzer-write-to-const @gol |
| -Wno-analyzer-write-to-string-literal @gol |
| } |
| |
| @item C and Objective-C-only Warning Options |
| @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol |
| -Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol |
| -Wold-style-declaration -Wold-style-definition @gol |
| -Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol |
| -Wdeclaration-after-statement -Wpointer-sign} |
| |
| @item Debugging Options |
| @xref{Debugging Options,,Options for Debugging Your Program}. |
| @gccoptlist{-g -g@var{level} -gdwarf -gdwarf-@var{version} @gol |
| -gbtf -gctf -gctf@var{level} @gol |
| -ggdb -grecord-gcc-switches -gno-record-gcc-switches @gol |
| -gstabs -gstabs+ -gstrict-dwarf -gno-strict-dwarf @gol |
| -gas-loc-support -gno-as-loc-support @gol |
| -gas-locview-support -gno-as-locview-support @gol |
| -gcolumn-info -gno-column-info -gdwarf32 -gdwarf64 @gol |
| -gstatement-frontiers -gno-statement-frontiers @gol |
| -gvariable-location-views -gno-variable-location-views @gol |
| -ginternal-reset-location-views -gno-internal-reset-location-views @gol |
| -ginline-points -gno-inline-points @gol |
| -gvms -gxcoff -gxcoff+ -gz@r{[}=@var{type}@r{]} @gol |
| -gsplit-dwarf -gdescribe-dies -gno-describe-dies @gol |
| -fdebug-prefix-map=@var{old}=@var{new} -fdebug-types-section @gol |
| -fno-eliminate-unused-debug-types @gol |
| -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol |
| -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol |
| -fno-eliminate-unused-debug-symbols -femit-class-debug-always @gol |
| -fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol |
| -fvar-tracking -fvar-tracking-assignments} |
| |
| @item Optimization Options |
| @xref{Optimize Options,,Options that Control Optimization}. |
| @gccoptlist{-faggressive-loop-optimizations @gol |
| -falign-functions[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] @gol |
| -falign-jumps[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] @gol |
| -falign-labels[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] @gol |
| -falign-loops[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] @gol |
| -fno-allocation-dce -fallow-store-data-races @gol |
| -fassociative-math -fauto-profile -fauto-profile[=@var{path}] @gol |
| -fauto-inc-dec -fbranch-probabilities @gol |
| -fcaller-saves @gol |
| -fcombine-stack-adjustments -fconserve-stack @gol |
| -fcompare-elim -fcprop-registers -fcrossjumping @gol |
| -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules @gol |
| -fcx-limited-range @gol |
| -fdata-sections -fdce -fdelayed-branch @gol |
| -fdelete-null-pointer-checks -fdevirtualize -fdevirtualize-speculatively @gol |
| -fdevirtualize-at-ltrans -fdse @gol |
| -fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects @gol |
| -ffast-math -ffinite-math-only -ffloat-store -fexcess-precision=@var{style} @gol |
| -ffinite-loops @gol |
| -fforward-propagate -ffp-contract=@var{style} -ffunction-sections @gol |
| -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity @gol |
| -fgcse-sm -fhoist-adjacent-loads -fif-conversion @gol |
| -fif-conversion2 -findirect-inlining @gol |
| -finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol |
| -finline-small-functions -fipa-modref -fipa-cp -fipa-cp-clone @gol |
| -fipa-bit-cp -fipa-vrp -fipa-pta -fipa-profile -fipa-pure-const @gol |
| -fipa-reference -fipa-reference-addressable @gol |
| -fipa-stack-alignment -fipa-icf -fira-algorithm=@var{algorithm} @gol |
| -flive-patching=@var{level} @gol |
| -fira-region=@var{region} -fira-hoist-pressure @gol |
| -fira-loop-pressure -fno-ira-share-save-slots @gol |
| -fno-ira-share-spill-slots @gol |
| -fisolate-erroneous-paths-dereference -fisolate-erroneous-paths-attribute @gol |
| -fivopts -fkeep-inline-functions -fkeep-static-functions @gol |
| -fkeep-static-consts -flimit-function-alignment -flive-range-shrinkage @gol |
| -floop-block -floop-interchange -floop-strip-mine @gol |
| -floop-unroll-and-jam -floop-nest-optimize @gol |
| -floop-parallelize-all -flra-remat -flto -flto-compression-level @gol |
| -flto-partition=@var{alg} -fmerge-all-constants @gol |
| -fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves @gol |
| -fmove-loop-invariants -fmove-loop-stores -fno-branch-count-reg @gol |
| -fno-defer-pop -fno-fp-int-builtin-inexact -fno-function-cse @gol |
| -fno-guess-branch-probability -fno-inline -fno-math-errno -fno-peephole @gol |
| -fno-peephole2 -fno-printf-return-value -fno-sched-interblock @gol |
| -fno-sched-spec -fno-signed-zeros @gol |
| -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol |
| -fomit-frame-pointer -foptimize-sibling-calls @gol |
| -fpartial-inlining -fpeel-loops -fpredictive-commoning @gol |
| -fprefetch-loop-arrays @gol |
| -fprofile-correction @gol |
| -fprofile-use -fprofile-use=@var{path} -fprofile-partial-training @gol |
| -fprofile-values -fprofile-reorder-functions @gol |
| -freciprocal-math -free -frename-registers -freorder-blocks @gol |
| -freorder-blocks-algorithm=@var{algorithm} @gol |
| -freorder-blocks-and-partition -freorder-functions @gol |
| -frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol |
| -frounding-math -fsave-optimization-record @gol |
| -fsched2-use-superblocks -fsched-pressure @gol |
| -fsched-spec-load -fsched-spec-load-dangerous @gol |
| -fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol |
| -fsched-group-heuristic -fsched-critical-path-heuristic @gol |
| -fsched-spec-insn-heuristic -fsched-rank-heuristic @gol |
| -fsched-last-insn-heuristic -fsched-dep-count-heuristic @gol |
| -fschedule-fusion @gol |
| -fschedule-insns -fschedule-insns2 -fsection-anchors @gol |
| -fselective-scheduling -fselective-scheduling2 @gol |
| -fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol |
| -fsemantic-interposition -fshrink-wrap -fshrink-wrap-separate @gol |
| -fsignaling-nans @gol |
| -fsingle-precision-constant -fsplit-ivs-in-unroller -fsplit-loops@gol |
| -fsplit-paths @gol |
| -fsplit-wide-types -fsplit-wide-types-early -fssa-backprop -fssa-phiopt @gol |
| -fstdarg-opt -fstore-merging -fstrict-aliasing -fipa-strict-aliasing @gol |
| -fthread-jumps -ftracer -ftree-bit-ccp @gol |
| -ftree-builtin-call-dce -ftree-ccp -ftree-ch @gol |
| -ftree-coalesce-vars -ftree-copy-prop -ftree-dce -ftree-dominator-opts @gol |
| -ftree-dse -ftree-forwprop -ftree-fre -fcode-hoisting @gol |
| -ftree-loop-if-convert -ftree-loop-im @gol |
| -ftree-phiprop -ftree-loop-distribution -ftree-loop-distribute-patterns @gol |
| -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol |
| -ftree-loop-vectorize @gol |
| -ftree-parallelize-loops=@var{n} -ftree-pre -ftree-partial-pre -ftree-pta @gol |
| -ftree-reassoc -ftree-scev-cprop -ftree-sink -ftree-slsr -ftree-sra @gol |
| -ftree-switch-conversion -ftree-tail-merge @gol |
| -ftree-ter -ftree-vectorize -ftree-vrp -ftrivial-auto-var-init @gol |
| -funconstrained-commons -funit-at-a-time -funroll-all-loops @gol |
| -funroll-loops -funsafe-math-optimizations -funswitch-loops @gol |
| -fipa-ra -fvariable-expansion-in-unroller -fvect-cost-model -fvpt @gol |
| -fweb -fwhole-program -fwpa -fuse-linker-plugin -fzero-call-used-regs @gol |
| --param @var{name}=@var{value} |
| -O -O0 -O1 -O2 -O3 -Os -Ofast -Og -Oz} |
| |
| @item Program Instrumentation Options |
| @xref{Instrumentation Options,,Program Instrumentation Options}. |
| @gccoptlist{-p -pg -fprofile-arcs --coverage -ftest-coverage @gol |
| -fprofile-abs-path @gol |
| -fprofile-dir=@var{path} -fprofile-generate -fprofile-generate=@var{path} @gol |
| -fprofile-info-section -fprofile-info-section=@var{name} @gol |
| -fprofile-note=@var{path} -fprofile-prefix-path=@var{path} @gol |
| -fprofile-update=@var{method} -fprofile-filter-files=@var{regex} @gol |
| -fprofile-exclude-files=@var{regex} @gol |
| -fprofile-reproducible=@r{[}multithreaded@r{|}parallel-runs@r{|}serial@r{]} @gol |
| -fsanitize=@var{style} -fsanitize-recover -fsanitize-recover=@var{style} @gol |
| -fasan-shadow-offset=@var{number} -fsanitize-sections=@var{s1},@var{s2},... @gol |
| -fsanitize-undefined-trap-on-error -fbounds-check @gol |
| -fcf-protection=@r{[}full@r{|}branch@r{|}return@r{|}none@r{|}check@r{]} @gol |
| -fharden-compares -fharden-conditional-branches @gol |
| -fstack-protector -fstack-protector-all -fstack-protector-strong @gol |
| -fstack-protector-explicit -fstack-check @gol |
| -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol |
| -fno-stack-limit -fsplit-stack @gol |
| -fvtable-verify=@r{[}std@r{|}preinit@r{|}none@r{]} @gol |
| -fvtv-counts -fvtv-debug @gol |
| -finstrument-functions @gol |
| -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol |
| -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}} @gol |
| -fprofile-prefix-map=@var{old}=@var{new} |
| |
| @item Preprocessor Options |
| @xref{Preprocessor Options,,Options Controlling the Preprocessor}. |
| @gccoptlist{-A@var{question}=@var{answer} @gol |
| -A-@var{question}@r{[}=@var{answer}@r{]} @gol |
| -C -CC -D@var{macro}@r{[}=@var{defn}@r{]} @gol |
| -dD -dI -dM -dN -dU @gol |
| -fdebug-cpp -fdirectives-only -fdollars-in-identifiers @gol |
| -fexec-charset=@var{charset} -fextended-identifiers @gol |
| -finput-charset=@var{charset} -flarge-source-files @gol |
| -fmacro-prefix-map=@var{old}=@var{new} -fmax-include-depth=@var{depth} @gol |
| -fno-canonical-system-headers -fpch-deps -fpch-preprocess @gol |
| -fpreprocessed -ftabstop=@var{width} -ftrack-macro-expansion @gol |
| -fwide-exec-charset=@var{charset} -fworking-directory @gol |
| -H -imacros @var{file} -include @var{file} @gol |
| -M -MD -MF -MG -MM -MMD -MP -MQ -MT -Mno-modules @gol |
| -no-integrated-cpp -P -pthread -remap @gol |
| -traditional -traditional-cpp -trigraphs @gol |
| -U@var{macro} -undef @gol |
| -Wp,@var{option} -Xpreprocessor @var{option}} |
| |
| @item Assembler Options |
| @xref{Assembler Options,,Passing Options to the Assembler}. |
| @gccoptlist{-Wa,@var{option} -Xassembler @var{option}} |
| |
| @item Linker Options |
| @xref{Link Options,,Options for Linking}. |
| @gccoptlist{@var{object-file-name} -fuse-ld=@var{linker} -l@var{library} @gol |
| -nostartfiles -nodefaultlibs -nolibc -nostdlib @gol |
| -e @var{entry} --entry=@var{entry} @gol |
| -pie -pthread -r -rdynamic @gol |
| -s -static -static-pie -static-libgcc -static-libstdc++ @gol |
| -static-libasan -static-libtsan -static-liblsan -static-libubsan @gol |
| -shared -shared-libgcc -symbolic @gol |
| -T @var{script} -Wl,@var{option} -Xlinker @var{option} @gol |
| -u @var{symbol} -z @var{keyword}} |
| |
| @item Directory Options |
| @xref{Directory Options,,Options for Directory Search}. |
| @gccoptlist{-B@var{prefix} -I@var{dir} -I- @gol |
| -idirafter @var{dir} @gol |
| -imacros @var{file} -imultilib @var{dir} @gol |
| -iplugindir=@var{dir} -iprefix @var{file} @gol |
| -iquote @var{dir} -isysroot @var{dir} -isystem @var{dir} @gol |
| -iwithprefix @var{dir} -iwithprefixbefore @var{dir} @gol |
| -L@var{dir} -no-canonical-prefixes --no-sysroot-suffix @gol |
| -nostdinc -nostdinc++ --sysroot=@var{dir}} |
| |
| @item Code Generation Options |
| @xref{Code Gen Options,,Options for Code Generation Conventions}. |
| @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol |
| -ffixed-@var{reg} -fexceptions @gol |
| -fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables @gol |
| -fasynchronous-unwind-tables @gol |
| -fno-gnu-unique @gol |
| -finhibit-size-directive -fcommon -fno-ident @gol |
| -fpcc-struct-return -fpic -fPIC -fpie -fPIE -fno-plt @gol |
| -fno-jump-tables -fno-bit-tests @gol |
| -frecord-gcc-switches @gol |
| -freg-struct-return -fshort-enums -fshort-wchar @gol |
| -fverbose-asm -fpack-struct[=@var{n}] @gol |
| -fleading-underscore -ftls-model=@var{model} @gol |
| -fstack-reuse=@var{reuse_level} @gol |
| -ftrampolines -ftrapv -fwrapv @gol |
| -fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]} @gol |
| -fstrict-volatile-bitfields -fsync-libcalls} |
| |
| @item Developer Options |
| @xref{Developer Options,,GCC Developer Options}. |
| @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol |
| -dumpfullversion -fcallgraph-info@r{[}=su,da@r{]} |
| -fchecking -fchecking=@var{n} |
| -fdbg-cnt-list @gol -fdbg-cnt=@var{counter-value-list} @gol |
| -fdisable-ipa-@var{pass_name} @gol |
| -fdisable-rtl-@var{pass_name} @gol |
| -fdisable-rtl-@var{pass-name}=@var{range-list} @gol |
| -fdisable-tree-@var{pass_name} @gol |
| -fdisable-tree-@var{pass-name}=@var{range-list} @gol |
| -fdump-debug -fdump-earlydebug @gol |
| -fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links @gol |
| -fdump-final-insns@r{[}=@var{file}@r{]} @gol |
| -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol |
| -fdump-lang-all @gol |
| -fdump-lang-@var{switch} @gol |
| -fdump-lang-@var{switch}-@var{options} @gol |
| -fdump-lang-@var{switch}-@var{options}=@var{filename} @gol |
| -fdump-passes @gol |
| -fdump-rtl-@var{pass} -fdump-rtl-@var{pass}=@var{filename} @gol |
| -fdump-statistics @gol |
| -fdump-tree-all @gol |
| -fdump-tree-@var{switch} @gol |
| -fdump-tree-@var{switch}-@var{options} @gol |
| -fdump-tree-@var{switch}-@var{options}=@var{filename} @gol |
| -fcompare-debug@r{[}=@var{opts}@r{]} -fcompare-debug-second @gol |
| -fenable-@var{kind}-@var{pass} @gol |
| -fenable-@var{kind}-@var{pass}=@var{range-list} @gol |
| -fira-verbose=@var{n} @gol |
| -flto-report -flto-report-wpa -fmem-report-wpa @gol |
| -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report @gol |
| -fopt-info -fopt-info-@var{options}@r{[}=@var{file}@r{]} @gol |
| -fprofile-report @gol |
| -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol |
| -fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol |
| -fstats -fstack-usage -ftime-report -ftime-report-details @gol |
| -fvar-tracking-assignments-toggle -gtoggle @gol |
| -print-file-name=@var{library} -print-libgcc-file-name @gol |
| -print-multi-directory -print-multi-lib -print-multi-os-directory @gol |
| -print-prog-name=@var{program} -print-search-dirs -Q @gol |
| -print-sysroot -print-sysroot-headers-suffix @gol |
| -save-temps -save-temps=cwd -save-temps=obj -time@r{[}=@var{file}@r{]}} |
| |
| @item Machine-Dependent Options |
| @xref{Submodel Options,,Machine-Dependent Options}. |
| @c This list is ordered alphanumerically by subsection name. |
| @c Try and put the significant identifier (CPU or system) first, |
| @c so users have a clue at guessing where the ones they want will be. |
| |
| @emph{AArch64 Options} |
| @gccoptlist{-mabi=@var{name} -mbig-endian -mlittle-endian @gol |
| -mgeneral-regs-only @gol |
| -mcmodel=tiny -mcmodel=small -mcmodel=large @gol |
| -mstrict-align -mno-strict-align @gol |
| -momit-leaf-frame-pointer @gol |
| -mtls-dialect=desc -mtls-dialect=traditional @gol |
| -mtls-size=@var{size} @gol |
| -mfix-cortex-a53-835769 -mfix-cortex-a53-843419 @gol |
| -mlow-precision-recip-sqrt -mlow-precision-sqrt -mlow-precision-div @gol |
| -mpc-relative-literal-loads @gol |
| -msign-return-address=@var{scope} @gol |
| -mbranch-protection=@var{none}|@var{standard}|@var{pac-ret}[+@var{leaf} |
| +@var{b-key}]|@var{bti} @gol |
| -mharden-sls=@var{opts} @gol |
| -march=@var{name} -mcpu=@var{name} -mtune=@var{name} @gol |
| -moverride=@var{string} -mverbose-cost-dump @gol |
| -mstack-protector-guard=@var{guard} -mstack-protector-guard-reg=@var{sysreg} @gol |
| -mstack-protector-guard-offset=@var{offset} -mtrack-speculation @gol |
| -moutline-atomics } |
| |
| @emph{Adapteva Epiphany Options} |
| @gccoptlist{-mhalf-reg-file -mprefer-short-insn-regs @gol |
| -mbranch-cost=@var{num} -mcmove -mnops=@var{num} -msoft-cmpsf @gol |
| -msplit-lohi -mpost-inc -mpost-modify -mstack-offset=@var{num} @gol |
| -mround-nearest -mlong-calls -mshort-calls -msmall16 @gol |
| -mfp-mode=@var{mode} -mvect-double -max-vect-align=@var{num} @gol |
| -msplit-vecmove-early -m1reg-@var{reg}} |
| |
| @emph{AMD GCN Options} |
| @gccoptlist{-march=@var{gpu} -mtune=@var{gpu} -mstack-size=@var{bytes}} |
| |
| @emph{ARC Options} |
| @gccoptlist{-mbarrel-shifter -mjli-always @gol |
| -mcpu=@var{cpu} -mA6 -mARC600 -mA7 -mARC700 @gol |
| -mdpfp -mdpfp-compact -mdpfp-fast -mno-dpfp-lrsr @gol |
| -mea -mno-mpy -mmul32x16 -mmul64 -matomic @gol |
| -mnorm -mspfp -mspfp-compact -mspfp-fast -msimd -msoft-float -mswap @gol |
| -mcrc -mdsp-packa -mdvbf -mlock -mmac-d16 -mmac-24 -mrtsc -mswape @gol |
| -mtelephony -mxy -misize -mannotate-align -marclinux -marclinux_prof @gol |
| -mlong-calls -mmedium-calls -msdata -mirq-ctrl-saved @gol |
| -mrgf-banked-regs -mlpc-width=@var{width} -G @var{num} @gol |
| -mvolatile-cache -mtp-regno=@var{regno} @gol |
| -malign-call -mauto-modify-reg -mbbit-peephole -mno-brcc @gol |
| -mcase-vector-pcrel -mcompact-casesi -mno-cond-exec -mearly-cbranchsi @gol |
| -mexpand-adddi -mindexed-loads -mlra -mlra-priority-none @gol |
| -mlra-priority-compact -mlra-priority-noncompact -mmillicode @gol |
| -mmixed-code -mq-class -mRcq -mRcw -msize-level=@var{level} @gol |
| -mtune=@var{cpu} -mmultcost=@var{num} -mcode-density-frame @gol |
| -munalign-prob-threshold=@var{probability} -mmpy-option=@var{multo} @gol |
| -mdiv-rem -mcode-density -mll64 -mfpu=@var{fpu} -mrf16 -mbranch-index} |
| |
| @emph{ARM Options} |
| @gccoptlist{-mapcs-frame -mno-apcs-frame @gol |
| -mabi=@var{name} @gol |
| -mapcs-stack-check -mno-apcs-stack-check @gol |
| -mapcs-reentrant -mno-apcs-reentrant @gol |
| -mgeneral-regs-only @gol |
| -msched-prolog -mno-sched-prolog @gol |
| -mlittle-endian -mbig-endian @gol |
| -mbe8 -mbe32 @gol |
| -mfloat-abi=@var{name} @gol |
| -mfp16-format=@var{name} |
| -mthumb-interwork -mno-thumb-interwork @gol |
| -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol |
| -mtune=@var{name} -mprint-tune-info @gol |
| -mstructure-size-boundary=@var{n} @gol |
| -mabort-on-noreturn @gol |
| -mlong-calls -mno-long-calls @gol |
| -msingle-pic-base -mno-single-pic-base @gol |
| -mpic-register=@var{reg} @gol |
| -mnop-fun-dllimport @gol |
| -mpoke-function-name @gol |
| -mthumb -marm -mflip-thumb @gol |
| -mtpcs-frame -mtpcs-leaf-frame @gol |
| -mcaller-super-interworking -mcallee-super-interworking @gol |
| -mtp=@var{name} -mtls-dialect=@var{dialect} @gol |
| -mword-relocations @gol |
| -mfix-cortex-m3-ldrd @gol |
| -mfix-cortex-a57-aes-1742098 @gol |
| -mfix-cortex-a72-aes-1655431 @gol |
| -munaligned-access @gol |
| -mneon-for-64bits @gol |
| -mslow-flash-data @gol |
| -masm-syntax-unified @gol |
| -mrestrict-it @gol |
| -mverbose-cost-dump @gol |
| -mpure-code @gol |
| -mcmse @gol |
| -mfix-cmse-cve-2021-35465 @gol |
| -mstack-protector-guard=@var{guard} -mstack-protector-guard-offset=@var{offset} @gol |
| -mfdpic} |
| |
| @emph{AVR Options} |
| @gccoptlist{-mmcu=@var{mcu} -mabsdata -maccumulate-args @gol |
| -mbranch-cost=@var{cost} @gol |
| -mcall-prologues -mgas-isr-prologues -mint8 @gol |
| -mdouble=@var{bits} -mlong-double=@var{bits} @gol |
| -mn_flash=@var{size} -mno-interrupts @gol |
| -mmain-is-OS_task -mrelax -mrmw -mstrict-X -mtiny-stack @gol |
| -mfract-convert-truncate @gol |
| -mshort-calls -nodevicelib -nodevicespecs @gol |
| -Waddr-space-convert -Wmisspelled-isr} |
| |
| @emph{Blackfin Options} |
| @gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol |
| -msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol |
| -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol |
| -mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol |
| -mno-id-shared-library -mshared-library-id=@var{n} @gol |
| -mleaf-id-shared-library -mno-leaf-id-shared-library @gol |
| -msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol |
| -mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram @gol |
| -micplb} |
| |
| @emph{C6X Options} |
| @gccoptlist{-mbig-endian -mlittle-endian -march=@var{cpu} @gol |
| -msim -msdata=@var{sdata-type}} |
| |
| @emph{CRIS Options} |
| @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} |
| -mtune=@var{cpu} -mmax-stack-frame=@var{n} @gol |
| -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol |
| -mstack-align -mdata-align -mconst-align @gol |
| -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue @gol |
| -melf -maout -sim -sim2 @gol |
| -mmul-bug-workaround -mno-mul-bug-workaround} |
| |
| @emph{CR16 Options} |
| @gccoptlist{-mmac @gol |
| -mcr16cplus -mcr16c @gol |
| -msim -mint32 -mbit-ops |
| -mdata-model=@var{model}} |
| |
| @emph{C-SKY Options} |
| @gccoptlist{-march=@var{arch} -mcpu=@var{cpu} @gol |
| -mbig-endian -EB -mlittle-endian -EL @gol |
| -mhard-float -msoft-float -mfpu=@var{fpu} -mdouble-float -mfdivdu @gol |
| -mfloat-abi=@var{name} @gol |
| -melrw -mistack -mmp -mcp -mcache -msecurity -mtrust @gol |
| -mdsp -medsp -mvdsp @gol |
| -mdiv -msmart -mhigh-registers -manchor @gol |
| -mpushpop -mmultiple-stld -mconstpool -mstack-size -mccrt @gol |
| -mbranch-cost=@var{n} -mcse-cc -msched-prolog -msim} |
| |
| @emph{Darwin Options} |
| @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol |
| -arch_only -bind_at_load -bundle -bundle_loader @gol |
| -client_name -compatibility_version -current_version @gol |
| -dead_strip @gol |
| -dependency-file -dylib_file -dylinker_install_name @gol |
| -dynamic -dynamiclib -exported_symbols_list @gol |
| -filelist -flat_namespace -force_cpusubtype_ALL @gol |
| -force_flat_namespace -headerpad_max_install_names @gol |
| -iframework @gol |
| -image_base -init -install_name -keep_private_externs @gol |
| -multi_module -multiply_defined -multiply_defined_unused @gol |
| -noall_load -no_dead_strip_inits_and_terms @gol |
| -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol |
| -pagezero_size -prebind -prebind_all_twolevel_modules @gol |
| -private_bundle -read_only_relocs -sectalign @gol |
| -sectobjectsymbols -whyload -seg1addr @gol |
| -sectcreate -sectobjectsymbols -sectorder @gol |
| -segaddr -segs_read_only_addr -segs_read_write_addr @gol |
| -seg_addr_table -seg_addr_table_filename -seglinkedit @gol |
| -segprot -segs_read_only_addr -segs_read_write_addr @gol |
| -single_module -static -sub_library -sub_umbrella @gol |
| -twolevel_namespace -umbrella -undefined @gol |
| -unexported_symbols_list -weak_reference_mismatches @gol |
| -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol |
| -mkernel -mone-byte-bool} |
| |
| @emph{DEC Alpha Options} |
| @gccoptlist{-mno-fp-regs -msoft-float @gol |
| -mieee -mieee-with-inexact -mieee-conformant @gol |
| -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol |
| -mtrap-precision=@var{mode} -mbuild-constants @gol |
| -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol |
| -mbwx -mmax -mfix -mcix @gol |
| -mfloat-vax -mfloat-ieee @gol |
| -mexplicit-relocs -msmall-data -mlarge-data @gol |
| -msmall-text -mlarge-text @gol |
| -mmemory-latency=@var{time}} |
| |
| @emph{eBPF Options} |
| @gccoptlist{-mbig-endian -mlittle-endian -mkernel=@var{version} |
| -mframe-limit=@var{bytes} -mxbpf -mco-re -mno-co-re |
| -mjmpext -mjmp32 -malu32 -mcpu=@var{version}} |
| |
| @emph{FR30 Options} |
| @gccoptlist{-msmall-model -mno-lsim} |
| |
| @emph{FT32 Options} |
| @gccoptlist{-msim -mlra -mnodiv -mft32b -mcompress -mnopm} |
| |
| @emph{FRV Options} |
| @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol |
| -mhard-float -msoft-float @gol |
| -malloc-cc -mfixed-cc -mdword -mno-dword @gol |
| -mdouble -mno-double @gol |
| -mmedia -mno-media -mmuladd -mno-muladd @gol |
| -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol |
| -mlinked-fp -mlong-calls -malign-labels @gol |
| -mlibrary-pic -macc-4 -macc-8 @gol |
| -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol |
| -moptimize-membar -mno-optimize-membar @gol |
| -mscc -mno-scc -mcond-exec -mno-cond-exec @gol |
| -mvliw-branch -mno-vliw-branch @gol |
| -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol |
| -mno-nested-cond-exec -mtomcat-stats @gol |
| -mTLS -mtls @gol |
| -mcpu=@var{cpu}} |
| |
| @emph{GNU/Linux Options} |
| @gccoptlist{-mglibc -muclibc -mmusl -mbionic -mandroid @gol |
| -tno-android-cc -tno-android-ld} |
| |
| @emph{H8/300 Options} |
| @gccoptlist{-mrelax -mh -ms -mn -mexr -mno-exr -mint32 -malign-300} |
| |
| @emph{HPPA Options} |
| @gccoptlist{-march=@var{architecture-type} @gol |
| -mcaller-copies -mdisable-fpregs -mdisable-indexing @gol |
| -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol |
| -mfixed-range=@var{register-range} @gol |
| -mjump-in-delay -mlinker-opt -mlong-calls @gol |
| -mlong-load-store -mno-disable-fpregs @gol |
| -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol |
| -mno-jump-in-delay -mno-long-load-store @gol |
| -mno-portable-runtime -mno-soft-float @gol |
| -mno-space-regs -msoft-float -mpa-risc-1-0 @gol |
| -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol |
| -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol |
| -munix=@var{unix-std} -nolibdld -static -threads} |
| |
| @emph{IA-64 Options} |
| @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol |
| -mvolatile-asm-stop -mregister-names -msdata -mno-sdata @gol |
| -mconstant-gp -mauto-pic -mfused-madd @gol |
| -minline-float-divide-min-latency @gol |
| -minline-float-divide-max-throughput @gol |
| -mno-inline-float-divide @gol |
| -minline-int-divide-min-latency @gol |
| -minline-int-divide-max-throughput @gol |
| -mno-inline-int-divide @gol |
| -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol |
| -mno-inline-sqrt @gol |
| -mdwarf2-asm -mearly-stop-bits @gol |
| -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol |
| -mtune=@var{cpu-type} -milp32 -mlp64 @gol |
| -msched-br-data-spec -msched-ar-data-spec -msched-control-spec @gol |
| -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol |
| -msched-spec-ldc -msched-spec-control-ldc @gol |
| -msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns @gol |
| -msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path @gol |
| -msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost @gol |
| -msched-max-memory-insns-hard-limit -msched-max-memory-insns=@var{max-insns}} |
| |
| @emph{LM32 Options} |
| @gccoptlist{-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled @gol |
| -msign-extend-enabled -muser-enabled} |
| |
| @emph{LoongArch Options} |
| @gccoptlist{-march=@var{cpu-type} -mtune=@var{cpu-type} -mabi=@var{base-abi-type} @gol |
| -mfpu=@var{fpu-type} -msoft-float -msingle-float -mdouble-float @gol |
| -mbranch-cost=@var{n} -mcheck-zero-division -mno-check-zero-division @gol |
| -mcond-move-int -mno-cond-move-int @gol |
| -mcond-move-float -mno-cond-move-float @gol |
| -memcpy -mno-memcpy -mstrict-align -mno-strict-align @gol |
| -mmax-inline-memcpy-size=@var{n} @gol |
| -mcmodel=@var{code-model}} |
| |
| @emph{M32R/D Options} |
| @gccoptlist{-m32r2 -m32rx -m32r @gol |
| -mdebug @gol |
| -malign-loops -mno-align-loops @gol |
| -missue-rate=@var{number} @gol |
| -mbranch-cost=@var{number} @gol |
| -mmodel=@var{code-size-model-type} @gol |
| -msdata=@var{sdata-type} @gol |
| -mno-flush-func -mflush-func=@var{name} @gol |
| -mno-flush-trap -mflush-trap=@var{number} @gol |
| -G @var{num}} |
| |
| @emph{M32C Options} |
| @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}} |
| |
| @emph{M680x0 Options} |
| @gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune} @gol |
| -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol |
| -m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol |
| -mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol |
| -mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol |
| -mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol |
| -malign-int -mstrict-align -msep-data -mno-sep-data @gol |
| -mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol |
| -mxgot -mno-xgot -mlong-jump-table-offsets} |
| |
| @emph{MCore Options} |
| @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol |
| -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol |
| -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol |
| -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol |
| -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment} |
| |
| @emph{MeP Options} |
| @gccoptlist{-mabsdiff -mall-opts -maverage -mbased=@var{n} -mbitops @gol |
| -mc=@var{n} -mclip -mconfig=@var{name} -mcop -mcop32 -mcop64 -mivc2 @gol |
| -mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax @gol |
| -mmult -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf @gol |
| -mtiny=@var{n}} |
| |
| @emph{MicroBlaze Options} |
| @gccoptlist{-msoft-float -mhard-float -msmall-divides -mcpu=@var{cpu} @gol |
| -mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift @gol |
| -mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss @gol |
| -mxl-multiply-high -mxl-float-convert -mxl-float-sqrt @gol |
| -mbig-endian -mlittle-endian -mxl-reorder -mxl-mode-@var{app-model} @gol |
| -mpic-data-is-text-relative} |
| |
| @emph{MIPS Options} |
| @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol |
| -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips32r3 -mips32r5 @gol |
| -mips32r6 -mips64 -mips64r2 -mips64r3 -mips64r5 -mips64r6 @gol |
| -mips16 -mno-mips16 -mflip-mips16 @gol |
| -minterlink-compressed -mno-interlink-compressed @gol |
| -minterlink-mips16 -mno-interlink-mips16 @gol |
| -mabi=@var{abi} -mabicalls -mno-abicalls @gol |
| -mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol |
| -mgp32 -mgp64 -mfp32 -mfpxx -mfp64 -mhard-float -msoft-float @gol |
| -mno-float -msingle-float -mdouble-float @gol |
| -modd-spreg -mno-odd-spreg @gol |
| -mabs=@var{mode} -mnan=@var{encoding} @gol |
| -mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol |
| -mmcu -mmno-mcu @gol |
| -meva -mno-eva @gol |
| -mvirt -mno-virt @gol |
| -mxpa -mno-xpa @gol |
| -mcrc -mno-crc @gol |
| -mginv -mno-ginv @gol |
| -mmicromips -mno-micromips @gol |
| -mmsa -mno-msa @gol |
| -mloongson-mmi -mno-loongson-mmi @gol |
| -mloongson-ext -mno-loongson-ext @gol |
| -mloongson-ext2 -mno-loongson-ext2 @gol |
| -mfpu=@var{fpu-type} @gol |
| -msmartmips -mno-smartmips @gol |
| -mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol |
| -mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol |
| -mlong64 -mlong32 -msym32 -mno-sym32 @gol |
| -G@var{num} -mlocal-sdata -mno-local-sdata @gol |
| -mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol |
| -membedded-data -mno-embedded-data @gol |
| -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol |
| -mcode-readable=@var{setting} @gol |
| -msplit-addresses -mno-split-addresses @gol |
| -mexplicit-relocs -mno-explicit-relocs @gol |
| -mcheck-zero-division -mno-check-zero-division @gol |
| -mdivide-traps -mdivide-breaks @gol |
| -mload-store-pairs -mno-load-store-pairs @gol |
| -munaligned-access -mno-unaligned-access @gol |
| -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol |
| -mmad -mno-mad -mimadd -mno-imadd -mfused-madd -mno-fused-madd -nocpp @gol |
| -mfix-24k -mno-fix-24k @gol |
| -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol |
| -mfix-r5900 -mno-fix-r5900 @gol |
| -mfix-r10000 -mno-fix-r10000 -mfix-rm7000 -mno-fix-rm7000 @gol |
| -mfix-vr4120 -mno-fix-vr4120 @gol |
| -mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 @gol |
| -mflush-func=@var{func} -mno-flush-func @gol |
| -mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol |
| -mcompact-branches=@var{policy} @gol |
| -mfp-exceptions -mno-fp-exceptions @gol |
| -mvr4130-align -mno-vr4130-align -msynci -mno-synci @gol |
| -mlxc1-sxc1 -mno-lxc1-sxc1 -mmadd4 -mno-madd4 @gol |
| -mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address @gol |
| -mframe-header-opt -mno-frame-header-opt} |
| |
| @emph{MMIX Options} |
| @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol |
| -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol |
| -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol |
| -mno-base-addresses -msingle-exit -mno-single-exit} |
| |
| @emph{MN10300 Options} |
| @gccoptlist{-mmult-bug -mno-mult-bug @gol |
| -mno-am33 -mam33 -mam33-2 -mam34 @gol |
| -mtune=@var{cpu-type} @gol |
| -mreturn-pointer-on-d0 @gol |
| -mno-crt0 -mrelax -mliw -msetlb} |
| |
| @emph{Moxie Options} |
| @gccoptlist{-meb -mel -mmul.x -mno-crt0} |
| |
| @emph{MSP430 Options} |
| @gccoptlist{-msim -masm-hex -mmcu= -mcpu= -mlarge -msmall -mrelax @gol |
| -mwarn-mcu @gol |
| -mcode-region= -mdata-region= @gol |
| -msilicon-errata= -msilicon-errata-warn= @gol |
| -mhwmult= -minrt -mtiny-printf -mmax-inline-shift=} |
| |
| @emph{NDS32 Options} |
| @gccoptlist{-mbig-endian -mlittle-endian @gol |
| -mreduced-regs -mfull-regs @gol |
| -mcmov -mno-cmov @gol |
| -mext-perf -mno-ext-perf @gol |
| -mext-perf2 -mno-ext-perf2 @gol |
| -mext-string -mno-ext-string @gol |
| -mv3push -mno-v3push @gol |
| -m16bit -mno-16bit @gol |
| -misr-vector-size=@var{num} @gol |
| -mcache-block-size=@var{num} @gol |
| -march=@var{arch} @gol |
| -mcmodel=@var{code-model} @gol |
| -mctor-dtor -mrelax} |
| |
| @emph{Nios II Options} |
| @gccoptlist{-G @var{num} -mgpopt=@var{option} -mgpopt -mno-gpopt @gol |
| -mgprel-sec=@var{regexp} -mr0rel-sec=@var{regexp} @gol |
| -mel -meb @gol |
| -mno-bypass-cache -mbypass-cache @gol |
| -mno-cache-volatile -mcache-volatile @gol |
| -mno-fast-sw-div -mfast-sw-div @gol |
| -mhw-mul -mno-hw-mul -mhw-mulx -mno-hw-mulx -mno-hw-div -mhw-div @gol |
| -mcustom-@var{insn}=@var{N} -mno-custom-@var{insn} @gol |
| -mcustom-fpu-cfg=@var{name} @gol |
| -mhal -msmallc -msys-crt0=@var{name} -msys-lib=@var{name} @gol |
| -march=@var{arch} -mbmx -mno-bmx -mcdx -mno-cdx} |
| |
| @emph{Nvidia PTX Options} |
| @gccoptlist{-m64 -mmainkernel -moptimize} |
| |
| @emph{OpenRISC Options} |
| @gccoptlist{-mboard=@var{name} -mnewlib -mhard-mul -mhard-div @gol |
| -msoft-mul -msoft-div @gol |
| -msoft-float -mhard-float -mdouble-float -munordered-float @gol |
| -mcmov -mror -mrori -msext -msfimm -mshftimm @gol |
| -mcmodel=@var{code-model}} |
| |
| @emph{PDP-11 Options} |
| @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol |
| -mint32 -mno-int16 -mint16 -mno-int32 @gol |
| -msplit -munix-asm -mdec-asm -mgnu-asm -mlra} |
| |
| @emph{picoChip Options} |
| @gccoptlist{-mae=@var{ae_type} -mvliw-lookahead=@var{N} @gol |
| -msymbol-as-address -mno-inefficient-warnings} |
| |
| @emph{PowerPC Options} |
| See RS/6000 and PowerPC Options. |
| |
| @emph{PRU Options} |
| @gccoptlist{-mmcu=@var{mcu} -minrt -mno-relax -mloop @gol |
| -mabi=@var{variant} @gol} |
| |
| @emph{RISC-V Options} |
| @gccoptlist{-mbranch-cost=@var{N-instruction} @gol |
| -mplt -mno-plt @gol |
| -mabi=@var{ABI-string} @gol |
| -mfdiv -mno-fdiv @gol |
| -mdiv -mno-div @gol |
| -misa-spec=@var{ISA-spec-string} @gol |
| -march=@var{ISA-string} @gol |
| -mtune=@var{processor-string} @gol |
| -mpreferred-stack-boundary=@var{num} @gol |
| -msmall-data-limit=@var{N-bytes} @gol |
| -msave-restore -mno-save-restore @gol |
| -mshorten-memrefs -mno-shorten-memrefs @gol |
| -mstrict-align -mno-strict-align @gol |
| -mcmodel=medlow -mcmodel=medany @gol |
| -mexplicit-relocs -mno-explicit-relocs @gol |
| -mrelax -mno-relax @gol |
| -mriscv-attribute -mmo-riscv-attribute @gol |
| -malign-data=@var{type} @gol |
| -mbig-endian -mlittle-endian @gol |
| -mstack-protector-guard=@var{guard} -mstack-protector-guard-reg=@var{reg} @gol |
| -mstack-protector-guard-offset=@var{offset}} |
| |
| @emph{RL78 Options} |
| @gccoptlist{-msim -mmul=none -mmul=g13 -mmul=g14 -mallregs @gol |
| -mcpu=g10 -mcpu=g13 -mcpu=g14 -mg10 -mg13 -mg14 @gol |
| -m64bit-doubles -m32bit-doubles -msave-mduc-in-interrupts} |
| |
| @emph{RS/6000 and PowerPC Options} |
| @gccoptlist{-mcpu=@var{cpu-type} @gol |
| -mtune=@var{cpu-type} @gol |
| -mcmodel=@var{code-model} @gol |
| -mpowerpc64 @gol |
| -maltivec -mno-altivec @gol |
| -mpowerpc-gpopt -mno-powerpc-gpopt @gol |
| -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol |
| -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd @gol |
| -mfprnd -mno-fprnd @gol |
| -mcmpb -mno-cmpb -mhard-dfp -mno-hard-dfp @gol |
| -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol |
| -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol |
| -malign-power -malign-natural @gol |
| -msoft-float -mhard-float -mmultiple -mno-multiple @gol |
| -mupdate -mno-update @gol |
| -mavoid-indexed-addresses -mno-avoid-indexed-addresses @gol |
| -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol |
| -mstrict-align -mno-strict-align -mrelocatable @gol |
| -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol |
| -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol |
| -mdynamic-no-pic -mswdiv -msingle-pic-base @gol |
| -mprioritize-restricted-insns=@var{priority} @gol |
| -msched-costly-dep=@var{dependence_type} @gol |
| -minsert-sched-nops=@var{scheme} @gol |
| -mcall-aixdesc -mcall-eabi -mcall-freebsd @gol |
| -mcall-linux -mcall-netbsd -mcall-openbsd @gol |
| -mcall-sysv -mcall-sysv-eabi -mcall-sysv-noeabi @gol |
| -mtraceback=@var{traceback_type} @gol |
| -maix-struct-return -msvr4-struct-return @gol |
| -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol |
| -mlongcall -mno-longcall -mpltseq -mno-pltseq @gol |
| -mblock-move-inline-limit=@var{num} @gol |
| -mblock-compare-inline-limit=@var{num} @gol |
| -mblock-compare-inline-loop-limit=@var{num} @gol |
| -mno-block-ops-unaligned-vsx @gol |
| -mstring-compare-inline-limit=@var{num} @gol |
| -misel -mno-isel @gol |
| -mvrsave -mno-vrsave @gol |
| -mmulhw -mno-mulhw @gol |
| -mdlmzb -mno-dlmzb @gol |
| -mprototype -mno-prototype @gol |
| -msim -mmvme -mads -myellowknife -memb -msdata @gol |
| -msdata=@var{opt} -mreadonly-in-sdata -mvxworks -G @var{num} @gol |
| -mrecip -mrecip=@var{opt} -mno-recip -mrecip-precision @gol |
| -mno-recip-precision @gol |
| -mveclibabi=@var{type} -mfriz -mno-friz @gol |
| -mpointers-to-nested-functions -mno-pointers-to-nested-functions @gol |
| -msave-toc-indirect -mno-save-toc-indirect @gol |
| -mpower8-fusion -mno-mpower8-fusion -mpower8-vector -mno-power8-vector @gol |
| -mcrypto -mno-crypto -mhtm -mno-htm @gol |
| -mquad-memory -mno-quad-memory @gol |
| -mquad-memory-atomic -mno-quad-memory-atomic @gol |
| -mcompat-align-parm -mno-compat-align-parm @gol |
| -mfloat128 -mno-float128 -mfloat128-hardware -mno-float128-hardware @gol |
| -mgnu-attribute -mno-gnu-attribute @gol |
| -mstack-protector-guard=@var{guard} -mstack-protector-guard-reg=@var{reg} @gol |
| -mstack-protector-guard-offset=@var{offset} -mprefixed -mno-prefixed @gol |
| -mpcrel -mno-pcrel -mmma -mno-mmma -mrop-protect -mno-rop-protect @gol |
| -mprivileged -mno-privileged} |
| |
| @emph{RX Options} |
| @gccoptlist{-m64bit-doubles -m32bit-doubles -fpu -nofpu@gol |
| -mcpu=@gol |
| -mbig-endian-data -mlittle-endian-data @gol |
| -msmall-data @gol |
| -msim -mno-sim@gol |
| -mas100-syntax -mno-as100-syntax@gol |
| -mrelax@gol |
| -mmax-constant-size=@gol |
| -mint-register=@gol |
| -mpid@gol |
| -mallow-string-insns -mno-allow-string-insns@gol |
| -mjsr@gol |
| -mno-warn-multiple-fast-interrupts@gol |
| -msave-acc-in-interrupts} |
| |
| @emph{S/390 and zSeries Options} |
| @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol |
| -mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol |
| -mlong-double-64 -mlong-double-128 @gol |
| -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol |
| -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol |
| -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol |
| -mhtm -mvx -mzvector @gol |
| -mtpf-trace -mno-tpf-trace -mtpf-trace-skip -mno-tpf-trace-skip @gol |
| -mfused-madd -mno-fused-madd @gol |
| -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard @gol |
| -mhotpatch=@var{halfwords},@var{halfwords}} |
| |
| @emph{Score Options} |
| @gccoptlist{-meb -mel @gol |
| -mnhwloop @gol |
| -muls @gol |
| -mmac @gol |
| -mscore5 -mscore5u -mscore7 -mscore7d} |
| |
| @emph{SH Options} |
| @gccoptlist{-m1 -m2 -m2e @gol |
| -m2a-nofpu -m2a-single-only -m2a-single -m2a @gol |
| -m3 -m3e @gol |
| -m4-nofpu -m4-single-only -m4-single -m4 @gol |
| -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol |
| -mb -ml -mdalign -mrelax @gol |
| -mbigtable -mfmovd -mrenesas -mno-renesas -mnomacsave @gol |
| -mieee -mno-ieee -mbitops -misize -minline-ic_invalidate -mpadstruct @gol |
| -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol |
| -mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol |
| -maccumulate-outgoing-args @gol |
| -matomic-model=@var{atomic-model} @gol |
| -mbranch-cost=@var{num} -mzdcbranch -mno-zdcbranch @gol |
| -mcbranch-force-delay-slot @gol |
| -mfused-madd -mno-fused-madd -mfsca -mno-fsca -mfsrra -mno-fsrra @gol |
| -mpretend-cmove -mtas} |
| |
| @emph{Solaris 2 Options} |
| @gccoptlist{-mclear-hwcap -mno-clear-hwcap -mimpure-text -mno-impure-text @gol |
| -pthreads} |
| |
| @emph{SPARC Options} |
| @gccoptlist{-mcpu=@var{cpu-type} @gol |
| -mtune=@var{cpu-type} @gol |
| -mcmodel=@var{code-model} @gol |
| -mmemory-model=@var{mem-model} @gol |
| -m32 -m64 -mapp-regs -mno-app-regs @gol |
| -mfaster-structs -mno-faster-structs -mflat -mno-flat @gol |
| -mfpu -mno-fpu -mhard-float -msoft-float @gol |
| -mhard-quad-float -msoft-quad-float @gol |
| -mstack-bias -mno-stack-bias @gol |
| -mstd-struct-return -mno-std-struct-return @gol |
| -munaligned-doubles -mno-unaligned-doubles @gol |
| -muser-mode -mno-user-mode @gol |
| -mv8plus -mno-v8plus -mvis -mno-vis @gol |
| -mvis2 -mno-vis2 -mvis3 -mno-vis3 @gol |
| -mvis4 -mno-vis4 -mvis4b -mno-vis4b @gol |
| -mcbcond -mno-cbcond -mfmaf -mno-fmaf -mfsmuld -mno-fsmuld @gol |
| -mpopc -mno-popc -msubxc -mno-subxc @gol |
| -mfix-at697f -mfix-ut699 -mfix-ut700 -mfix-gr712rc @gol |
| -mlra -mno-lra} |
| |
| @emph{System V Options} |
| @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}} |
| |
| @emph{TILE-Gx Options} |
| @gccoptlist{-mcpu=CPU -m32 -m64 -mbig-endian -mlittle-endian @gol |
| -mcmodel=@var{code-model}} |
| |
| @emph{TILEPro Options} |
| @gccoptlist{-mcpu=@var{cpu} -m32} |
| |
| @emph{V850 Options} |
| @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol |
| -mprolog-function -mno-prolog-function -mspace @gol |
| -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol |
| -mapp-regs -mno-app-regs @gol |
| -mdisable-callt -mno-disable-callt @gol |
| -mv850e2v3 -mv850e2 -mv850e1 -mv850es @gol |
| -mv850e -mv850 -mv850e3v5 @gol |
| -mloop @gol |
| -mrelax @gol |
| -mlong-jumps @gol |
| -msoft-float @gol |
| -mhard-float @gol |
| -mgcc-abi @gol |
| -mrh850-abi @gol |
| -mbig-switch} |
| |
| @emph{VAX Options} |
| @gccoptlist{-mg -mgnu -munix -mlra} |
| |
| @emph{Visium Options} |
| @gccoptlist{-mdebug -msim -mfpu -mno-fpu -mhard-float -msoft-float @gol |
| -mcpu=@var{cpu-type} -mtune=@var{cpu-type} -msv-mode -muser-mode} |
| |
| @emph{VMS Options} |
| @gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64 @gol |
| -mpointer-size=@var{size}} |
| |
| @emph{VxWorks Options} |
| @gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol |
| -Xbind-lazy -Xbind-now} |
| |
| @emph{x86 Options} |
| @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol |
| -mtune-ctrl=@var{feature-list} -mdump-tune-features -mno-default @gol |
| -mfpmath=@var{unit} @gol |
| -masm=@var{dialect} -mno-fancy-math-387 @gol |
| -mno-fp-ret-in-387 -m80387 -mhard-float -msoft-float @gol |
| -mno-wide-multiply -mrtd -malign-double @gol |
| -mpreferred-stack-boundary=@var{num} @gol |
| -mincoming-stack-boundary=@var{num} @gol |
| -mcld -mcx16 -msahf -mmovbe -mcrc32 -mmwait @gol |
| -mrecip -mrecip=@var{opt} @gol |
| -mvzeroupper -mprefer-avx128 -mprefer-vector-width=@var{opt} @gol |
| -mmove-max=@var{bits} -mstore-max=@var{bits} @gol |
| -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx @gol |
| -mavx2 -mavx512f -mavx512pf -mavx512er -mavx512cd -mavx512vl @gol |
| -mavx512bw -mavx512dq -mavx512ifma -mavx512vbmi -msha -maes @gol |
| -mpclmul -mfsgsbase -mrdrnd -mf16c -mfma -mpconfig -mwbnoinvd @gol |
| -mptwrite -mprefetchwt1 -mclflushopt -mclwb -mxsavec -mxsaves @gol |
| -msse4a -m3dnow -m3dnowa -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop @gol |
| -madx -mlzcnt -mbmi2 -mfxsr -mxsave -mxsaveopt -mrtm -mhle -mlwp @gol |
| -mmwaitx -mclzero -mpku -mthreads -mgfni -mvaes -mwaitpkg @gol |
| -mshstk -mmanual-endbr -mforce-indirect-call -mavx512vbmi2 -mavx512bf16 -menqcmd @gol |
| -mvpclmulqdq -mavx512bitalg -mmovdiri -mmovdir64b -mavx512vpopcntdq @gol |
| -mavx5124fmaps -mavx512vnni -mavx5124vnniw -mprfchw -mrdpid @gol |
| -mrdseed -msgx -mavx512vp2intersect -mserialize -mtsxldtrk@gol |
| -mamx-tile -mamx-int8 -mamx-bf16 -muintr -mhreset -mavxvnni@gol |
| -mavx512fp16 @gol |
| -mcldemote -mms-bitfields -mno-align-stringops -minline-all-stringops @gol |
| -minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol |
| -mkl -mwidekl @gol |
| -mmemcpy-strategy=@var{strategy} -mmemset-strategy=@var{strategy} @gol |
| -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol |
| -m96bit-long-double -mlong-double-64 -mlong-double-80 -mlong-double-128 @gol |
| -mregparm=@var{num} -msseregparm @gol |
| -mveclibabi=@var{type} -mvect8-ret-in-mem @gol |
| -mpc32 -mpc64 -mpc80 -mstackrealign @gol |
| -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol |
| -mcmodel=@var{code-model} -mabi=@var{name} -maddress-mode=@var{mode} @gol |
| -m32 -m64 -mx32 -m16 -miamcu -mlarge-data-threshold=@var{num} @gol |
| -msse2avx -mfentry -mrecord-mcount -mnop-mcount -m8bit-idiv @gol |
| -minstrument-return=@var{type} -mfentry-name=@var{name} -mfentry-section=@var{name} @gol |
| -mavx256-split-unaligned-load -mavx256-split-unaligned-store @gol |
| -malign-data=@var{type} -mstack-protector-guard=@var{guard} @gol |
| -mstack-protector-guard-reg=@var{reg} @gol |
| -mstack-protector-guard-offset=@var{offset} @gol |
| -mstack-protector-guard-symbol=@var{symbol} @gol |
| -mgeneral-regs-only -mcall-ms2sysv-xlogues -mrelax-cmpxchg-loop @gol |
| -mindirect-branch=@var{choice} -mfunction-return=@var{choice} @gol |
| -mindirect-branch-register -mharden-sls=@var{choice} @gol |
| -mindirect-branch-cs-prefix -mneeded -mno-direct-extern-access} |
| |
| @emph{x86 Windows Options} |
| @gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll @gol |
| -mnop-fun-dllimport -mthread @gol |
| -municode -mwin32 -mwindows -fno-set-stack-executable} |
| |
| @emph{Xstormy16 Options} |
| @gccoptlist{-msim} |
| |
| @emph{Xtensa Options} |
| @gccoptlist{-mconst16 -mno-const16 @gol |
| -mfused-madd -mno-fused-madd @gol |
| -mforce-no-pic @gol |
| -mserialize-volatile -mno-serialize-volatile @gol |
| -mtext-section-literals -mno-text-section-literals @gol |
| -mauto-litpools -mno-auto-litpools @gol |
| -mtarget-align -mno-target-align @gol |
| -mlongcalls -mno-longcalls @gol |
| -mabi=@var{abi-type}} |
| |
| @emph{zSeries Options} |
| See S/390 and zSeries Options. |
| @end table |
| |
| |
| @node Overall Options |
| @section Options Controlling the Kind of Output |
| |
| Compilation can involve up to four stages: preprocessing, compilation |
| proper, assembly and linking, always in that order. GCC is capable of |
| preprocessing and compiling several files either into several |
| assembler input files, or into one assembler input file; then each |
| assembler input file produces an object file, and linking combines all |
| the object files (those newly compiled, and those specified as input) |
| into an executable file. |
| |
| @cindex file name suffix |
| For any given input file, the file name suffix determines what kind of |
| compilation is done: |
| |
| @table @gcctabopt |
| @item @var{file}.c |
| C source code that must be preprocessed. |
| |
| @item @var{file}.i |
| C source code that should not be preprocessed. |
| |
| @item @var{file}.ii |
| C++ source code that should not be preprocessed. |
| |
| @item @var{file}.m |
| Objective-C source code. Note that you must link with the @file{libobjc} |
| library to make an Objective-C program work. |
| |
| @item @var{file}.mi |
| Objective-C source code that should not be preprocessed. |
| |
| @item @var{file}.mm |
| @itemx @var{file}.M |
| Objective-C++ source code. Note that you must link with the @file{libobjc} |
| library to make an Objective-C++ program work. Note that @samp{.M} refers |
| to a literal capital M@. |
| |
| @item @var{file}.mii |
| Objective-C++ source code that should not be preprocessed. |
| |
| @item @var{file}.h |
| C, C++, Objective-C or Objective-C++ header file to be turned into a |
| precompiled header (default), or C, C++ header file to be turned into an |
| Ada spec (via the @option{-fdump-ada-spec} switch). |
| |
| @item @var{file}.cc |
| @itemx @var{file}.cp |
| @itemx @var{file}.cxx |
| @itemx @var{file}.cpp |
| @itemx @var{file}.CPP |
| @itemx @var{file}.c++ |
| @itemx @var{file}.C |
| C++ source code that must be preprocessed. Note that in @samp{.cxx}, |
| the last two letters must both be literally @samp{x}. Likewise, |
| @samp{.C} refers to a literal capital C@. |
| |
| @item @var{file}.mm |
| @itemx @var{file}.M |
| Objective-C++ source code that must be preprocessed. |
| |
| @item @var{file}.mii |
| Objective-C++ source code that should not be preprocessed. |
| |
| @item @var{file}.hh |
| @itemx @var{file}.H |
| @itemx @var{file}.hp |
| @itemx @var{file}.hxx |
| @itemx @var{file}.hpp |
| @itemx @var{file}.HPP |
| @itemx @var{file}.h++ |
| @itemx @var{file}.tcc |
| C++ header file to be turned into a precompiled header or Ada spec. |
| |
| @item @var{file}.f |
| @itemx @var{file}.for |
| @itemx @var{file}.ftn |
| Fixed form Fortran source code that should not be preprocessed. |
| |
| @item @var{file}.F |
| @itemx @var{file}.FOR |
| @itemx @var{file}.fpp |
| @itemx @var{file}.FPP |
| @itemx @var{file}.FTN |
| Fixed form Fortran source code that must be preprocessed (with the traditional |
| preprocessor). |
| |
| @item @var{file}.f90 |
| @itemx @var{file}.f95 |
| @itemx @var{file}.f03 |
| @itemx @var{file}.f08 |
| Free form Fortran source code that should not be preprocessed. |
| |
| @item @var{file}.F90 |
| @itemx @var{file}.F95 |
| @itemx @var{file}.F03 |
| @itemx @var{file}.F08 |
| Free form Fortran source code that must be preprocessed (with the |
| traditional preprocessor). |
| |
| @item @var{file}.go |
| Go source code. |
| |
| @item @var{file}.d |
| D source code. |
| |
| @item @var{file}.di |
| D interface file. |
| |
| @item @var{file}.dd |
| D documentation code (Ddoc). |
| |
| @item @var{file}.ads |
| Ada source code file that contains a library unit declaration (a |
| declaration of a package, subprogram, or generic, or a generic |
| instantiation), or a library unit renaming declaration (a package, |
| generic, or subprogram renaming declaration). Such files are also |
| called @dfn{specs}. |
| |
| @item @var{file}.adb |
| Ada source code file containing a library unit body (a subprogram or |
| package body). Such files are also called @dfn{bodies}. |
| |
| @c GCC also knows about some suffixes for languages not yet included: |
| @c Ratfor: |
| @c @var{file}.r |
| |
| @item @var{file}.s |
| Assembler code. |
| |
| @item @var{file}.S |
| @itemx @var{file}.sx |
| Assembler code that must be preprocessed. |
| |
| @item @var{other} |
| An object file to be fed straight into linking. |
| Any file name with no recognized suffix is treated this way. |
| @end table |
| |
| @opindex x |
| You can specify the input language explicitly with the @option{-x} option: |
| |
| @table @gcctabopt |
| @item -x @var{language} |
| Specify explicitly the @var{language} for the following input files |
| (rather than letting the compiler choose a default based on the file |
| name suffix). This option applies to all following input files until |
| the next @option{-x} option. Possible values for @var{language} are: |
| @smallexample |
| c c-header cpp-output |
| c++ c++-header c++-system-header c++-user-header c++-cpp-output |
| objective-c objective-c-header objective-c-cpp-output |
| objective-c++ objective-c++-header objective-c++-cpp-output |
| assembler assembler-with-cpp |
| ada |
| d |
| f77 f77-cpp-input f95 f95-cpp-input |
| go |
| @end smallexample |
| |
| @item -x none |
| Turn off any specification of a language, so that subsequent files are |
| handled according to their file name suffixes (as they are if @option{-x} |
| has not been used at all). |
| @end table |
| |
| If you only want some of the stages of compilation, you can use |
| @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and |
| one of the options @option{-c}, @option{-S}, or @option{-E} to say where |
| @command{gcc} is to stop. Note that some combinations (for example, |
| @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all. |
| |
| @table @gcctabopt |
| @item -c |
| @opindex c |
| Compile or assemble the source files, but do not link. The linking |
| stage simply is not done. The ultimate output is in the form of an |
| object file for each source file. |
| |
| By default, the object file name for a source file is made by replacing |
| the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}. |
| |
| Unrecognized input files, not requiring compilation or assembly, are |
| ignored. |
| |
| @item -S |
| @opindex S |
| Stop after the stage of compilation proper; do not assemble. The output |
| is in the form of an assembler code file for each non-assembler input |
| file specified. |
| |
| By default, the assembler file name for a source file is made by |
| replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}. |
| |
| Input files that don't require compilation are ignored. |
| |
| @item -E |
| @opindex E |
| Stop after the preprocessing stage; do not run the compiler proper. The |
| output is in the form of preprocessed source code, which is sent to the |
| standard output. |
| |
| Input files that don't require preprocessing are ignored. |
| |
| @cindex output file option |
| @item -o @var{file} |
| @opindex o |
| Place the primary output in file @var{file}. This applies to whatever |
| sort of output is being produced, whether it be an executable file, an |
| object file, an assembler file or preprocessed C code. |
| |
| If @option{-o} is not specified, the default is to put an executable |
| file in @file{a.out}, the object file for |
| @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its |
| assembler file in @file{@var{source}.s}, a precompiled header file in |
| @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on |
| standard output. |
| |
| Though @option{-o} names only the primary output, it also affects the |
| naming of auxiliary and dump outputs. See the examples below. Unless |
| overridden, both auxiliary outputs and dump outputs are placed in the |
| same directory as the primary output. In auxiliary outputs, the suffix |
| of the input file is replaced with that of the auxiliary output file |
| type; in dump outputs, the suffix of the dump file is appended to the |
| input file suffix. In compilation commands, the base name of both |
| auxiliary and dump outputs is that of the primary output; in compile and |
| link commands, the primary output name, minus the executable suffix, is |
| combined with the input file name. If both share the same base name, |
| disregarding the suffix, the result of the combination is that base |
| name, otherwise, they are concatenated, separated by a dash. |
| |
| @smallexample |
| gcc -c foo.c ... |
| @end smallexample |
| |
| will use @file{foo.o} as the primary output, and place aux outputs and |
| dumps next to it, e.g., aux file @file{foo.dwo} for |
| @option{-gsplit-dwarf}, and dump file @file{foo.c.???r.final} for |
| @option{-fdump-rtl-final}. |
| |
| If a non-linker output file is explicitly specified, aux and dump files |
| by default take the same base name: |
| |
| @smallexample |
| gcc -c foo.c -o dir/foobar.o ... |
| @end smallexample |
| |
| will name aux outputs @file{dir/foobar.*} and dump outputs |
| @file{dir/foobar.c.*}. |
| |
| A linker output will instead prefix aux and dump outputs: |
| |
| @smallexample |
| gcc foo.c bar.c -o dir/foobar ... |
| @end smallexample |
| |
| will generally name aux outputs @file{dir/foobar-foo.*} and |
| @file{dir/foobar-bar.*}, and dump outputs @file{dir/foobar-foo.c.*} and |
| @file{dir/foobar-bar.c.*}. |
| |
| The one exception to the above is when the executable shares the base |
| name with the single input: |
| |
| @smallexample |
| gcc foo.c -o dir/foo ... |
| @end smallexample |
| |
| in which case aux outputs are named @file{dir/foo.*} and dump outputs |
| named @file{dir/foo.c.*}. |
| |
| The location and the names of auxiliary and dump outputs can be adjusted |
| by the options @option{-dumpbase}, @option{-dumpbase-ext}, |
| @option{-dumpdir}, @option{-save-temps=cwd}, and |
| @option{-save-temps=obj}. |
| |
| |
| @item -dumpbase @var{dumpbase} |
| @opindex dumpbase |
| This option sets the base name for auxiliary and dump output files. It |
| does not affect the name of the primary output file. Intermediate |
| outputs, when preserved, are not regarded as primary outputs, but as |
| auxiliary outputs: |
| |
| @smallexample |
| gcc -save-temps -S foo.c |
| @end smallexample |
| |
| saves the (no longer) temporary preprocessed file in @file{foo.i}, and |
| then compiles to the (implied) output file @file{foo.s}, whereas: |
| |
| @smallexample |
| gcc -save-temps -dumpbase save-foo -c foo.c |
| @end smallexample |
| |
| preprocesses to in @file{save-foo.i}, compiles to @file{save-foo.s} (now |
| an intermediate, thus auxiliary output), and then assembles to the |
| (implied) output file @file{foo.o}. |
| |
| Absent this option, dump and aux files take their names from the input |
| file, or from the (non-linker) output file, if one is explicitly |
| specified: dump output files (e.g. those requested by @option{-fdump-*} |
| options) with the input name suffix, and aux output files (those |
| requested by other non-dump options, e.g. @code{-save-temps}, |
| @code{-gsplit-dwarf}, @code{-fcallgraph-info}) without it. |
| |
| Similar suffix differentiation of dump and aux outputs can be attained |
| for explicitly-given @option{-dumpbase basename.suf} by also specifying |
| @option{-dumpbase-ext .suf}. |
| |
| If @var{dumpbase} is explicitly specified with any directory component, |
| any @var{dumppfx} specification (e.g. @option{-dumpdir} or |
| @option{-save-temps=*}) is ignored, and instead of appending to it, |
| @var{dumpbase} fully overrides it: |
| |
| @smallexample |
| gcc foo.c -c -o dir/foo.o -dumpbase alt/foo \ |
| -dumpdir pfx- -save-temps=cwd ... |
| @end smallexample |
| |
| creates auxiliary and dump outputs named @file{alt/foo.*}, disregarding |
| @file{dir/} in @option{-o}, the @file{./} prefix implied by |
| @option{-save-temps=cwd}, and @file{pfx-} in @option{-dumpdir}. |
| |
| When @option{-dumpbase} is specified in a command that compiles multiple |
| inputs, or that compiles and then links, it may be combined with |
| @var{dumppfx}, as specified under @option{-dumpdir}. Then, each input |
| file is compiled using the combined @var{dumppfx}, and default values |
| for @var{dumpbase} and @var{auxdropsuf} are computed for each input |
| file: |
| |
| @smallexample |
| gcc foo.c bar.c -c -dumpbase main ... |
| @end smallexample |
| |
| creates @file{foo.o} and @file{bar.o} as primary outputs, and avoids |
| overwriting the auxiliary and dump outputs by using the @var{dumpbase} |
| as a prefix, creating auxiliary and dump outputs named @file{main-foo.*} |
| and @file{main-bar.*}. |
| |
| An empty string specified as @var{dumpbase} avoids the influence of the |
| output basename in the naming of auxiliary and dump outputs during |
| compilation, computing default values : |
| |
| @smallexample |
| gcc -c foo.c -o dir/foobar.o -dumpbase '' ... |
| @end smallexample |
| |
| will name aux outputs @file{dir/foo.*} and dump outputs |
| @file{dir/foo.c.*}. Note how their basenames are taken from the input |
| name, but the directory still defaults to that of the output. |
| |
| The empty-string dumpbase does not prevent the use of the output |
| basename for outputs during linking: |
| |
| @smallexample |
| gcc foo.c bar.c -o dir/foobar -dumpbase '' -flto ... |
| @end smallexample |
| |
| The compilation of the source files will name auxiliary outputs |
| @file{dir/foo.*} and @file{dir/bar.*}, and dump outputs |
| @file{dir/foo.c.*} and @file{dir/bar.c.*}. LTO recompilation during |
| linking will use @file{dir/foobar.} as the prefix for dumps and |
| auxiliary files. |
| |
| |
| @item -dumpbase-ext @var{auxdropsuf} |
| @opindex dumpbase-ext |
| When forming the name of an auxiliary (but not a dump) output file, drop |
| trailing @var{auxdropsuf} from @var{dumpbase} before appending any |
| suffixes. If not specified, this option defaults to the suffix of a |
| default @var{dumpbase}, i.e., the suffix of the input file when |
| @option{-dumpbase} is not present in the command line, or @var{dumpbase} |
| is combined with @var{dumppfx}. |
| |
| @smallexample |
| gcc foo.c -c -o dir/foo.o -dumpbase x-foo.c -dumpbase-ext .c ... |
| @end smallexample |
| |
| creates @file{dir/foo.o} as the main output, and generates auxiliary |
| outputs in @file{dir/x-foo.*}, taking the location of the primary |
| output, and dropping the @file{.c} suffix from the @var{dumpbase}. Dump |
| outputs retain the suffix: @file{dir/x-foo.c.*}. |
| |
| This option is disregarded if it does not match the suffix of a |
| specified @var{dumpbase}, except as an alternative to the executable |
| suffix when appending the linker output base name to @var{dumppfx}, as |
| specified below: |
| |
| @smallexample |
| gcc foo.c bar.c -o main.out -dumpbase-ext .out ... |
| @end smallexample |
| |
| creates @file{main.out} as the primary output, and avoids overwriting |
| the auxiliary and dump outputs by using the executable name minus |
| @var{auxdropsuf} as a prefix, creating auxiliary outputs named |
| @file{main-foo.*} and @file{main-bar.*} and dump outputs named |
| @file{main-foo.c.*} and @file{main-bar.c.*}. |
| |
| |
| @item -dumpdir @var{dumppfx} |
| @opindex dumpdir |
| When forming the name of an auxiliary or dump output file, use |
| @var{dumppfx} as a prefix: |
| |
| @smallexample |
| gcc -dumpdir pfx- -c foo.c ... |
| @end smallexample |
| |
| creates @file{foo.o} as the primary output, and auxiliary outputs named |
| @file{pfx-foo.*}, combining the given @var{dumppfx} with the default |
| @var{dumpbase} derived from the default primary output, derived in turn |
| from the input name. Dump outputs also take the input name suffix: |
| @file{pfx-foo.c.*}. |
| |
| If @var{dumppfx} is to be used as a directory name, it must end with a |
| directory separator: |
| |
| @smallexample |
| gcc -dumpdir dir/ -c foo.c -o obj/bar.o ... |
| @end smallexample |
| |
| creates @file{obj/bar.o} as the primary output, and auxiliary outputs |
| named @file{dir/bar.*}, combining the given @var{dumppfx} with the |
| default @var{dumpbase} derived from the primary output name. Dump |
| outputs also take the input name suffix: @file{dir/bar.c.*}. |
| |
| It defaults to the location of the output file, unless the output |
| file is a special file like @code{/dev/null}. Options |
| @option{-save-temps=cwd} and @option{-save-temps=obj} override this |
| default, just like an explicit @option{-dumpdir} option. In case |
| multiple such options are given, the last one prevails: |
| |
| @smallexample |
| gcc -dumpdir pfx- -c foo.c -save-temps=obj ... |
| @end smallexample |
| |
| outputs @file{foo.o}, with auxiliary outputs named @file{foo.*} because |
| @option{-save-temps=*} overrides the @var{dumppfx} given by the earlier |
| @option{-dumpdir} option. It does not matter that @option{=obj} is the |
| default for @option{-save-temps}, nor that the output directory is |
| implicitly the current directory. Dump outputs are named |
| @file{foo.c.*}. |
| |
| When compiling from multiple input files, if @option{-dumpbase} is |
| specified, @var{dumpbase}, minus a @var{auxdropsuf} suffix, and a dash |
| are appended to (or override, if containing any directory components) an |
| explicit or defaulted @var{dumppfx}, so that each of the multiple |
| compilations gets differently-named aux and dump outputs. |
| |
| @smallexample |
| gcc foo.c bar.c -c -dumpdir dir/pfx- -dumpbase main ... |
| @end smallexample |
| |
| outputs auxiliary dumps to @file{dir/pfx-main-foo.*} and |
| @file{dir/pfx-main-bar.*}, appending @var{dumpbase}- to @var{dumppfx}. |
| Dump outputs retain the input file suffix: @file{dir/pfx-main-foo.c.*} |
| and @file{dir/pfx-main-bar.c.*}, respectively. Contrast with the |
| single-input compilation: |
| |
| @smallexample |
| gcc foo.c -c -dumpdir dir/pfx- -dumpbase main ... |
| @end smallexample |
| |
| that, applying @option{-dumpbase} to a single source, does not compute |
| and append a separate @var{dumpbase} per input file. Its auxiliary and |
| dump outputs go in @file{dir/pfx-main.*}. |
| |
| When compiling and then linking from multiple input files, a defaulted |
| or explicitly specified @var{dumppfx} also undergoes the @var{dumpbase}- |
| transformation above (e.g. the compilation of @file{foo.c} and |
| @file{bar.c} above, but without @option{-c}). If neither |
| @option{-dumpdir} nor @option{-dumpbase} are given, the linker output |
| base name, minus @var{auxdropsuf}, if specified, or the executable |
| suffix otherwise, plus a dash is appended to the default @var{dumppfx} |
| instead. Note, however, that unlike earlier cases of linking: |
| |
| @smallexample |
| gcc foo.c bar.c -dumpdir dir/pfx- -o main ... |
| @end smallexample |
| |
| does not append the output name @file{main} to @var{dumppfx}, because |
| @option{-dumpdir} is explicitly specified. The goal is that the |
| explicitly-specified @var{dumppfx} may contain the specified output name |
| as part of the prefix, if desired; only an explicitly-specified |
| @option{-dumpbase} would be combined with it, in order to avoid simply |
| discarding a meaningful option. |
| |
| When compiling and then linking from a single input file, the linker |
| output base name will only be appended to the default @var{dumppfx} as |
| above if it does not share the base name with the single input file |
| name. This has been covered in single-input linking cases above, but |
| not with an explicit @option{-dumpdir} that inhibits the combination, |
| even if overridden by @option{-save-temps=*}: |
| |
| @smallexample |
| gcc foo.c -dumpdir alt/pfx- -o dir/main.exe -save-temps=cwd ... |
| @end smallexample |
| |
| Auxiliary outputs are named @file{foo.*}, and dump outputs |
| @file{foo.c.*}, in the current working directory as ultimately requested |
| by @option{-save-temps=cwd}. |
| |
| Summing it all up for an intuitive though slightly imprecise data flow: |
| the primary output name is broken into a directory part and a basename |
| part; @var{dumppfx} is set to the former, unless overridden by |
| @option{-dumpdir} or @option{-save-temps=*}, and @var{dumpbase} is set |
| to the latter, unless overriden by @option{-dumpbase}. If there are |
| multiple inputs or linking, this @var{dumpbase} may be combined with |
| @var{dumppfx} and taken from each input file. Auxiliary output names |
| for each input are formed by combining @var{dumppfx}, @var{dumpbase} |
| minus suffix, and the auxiliary output suffix; dump output names are |
| only different in that the suffix from @var{dumpbase} is retained. |
| |
| When it comes to auxiliary and dump outputs created during LTO |
| recompilation, a combination of @var{dumppfx} and @var{dumpbase}, as |
| given or as derived from the linker output name but not from inputs, |
| even in cases in which this combination would not otherwise be used as |
| such, is passed down with a trailing period replacing the compiler-added |
| dash, if any, as a @option{-dumpdir} option to @command{lto-wrapper}; |
| being involved in linking, this program does not normally get any |
| @option{-dumpbase} and @option{-dumpbase-ext}, and it ignores them. |
| |
| When running sub-compilers, @command{lto-wrapper} appends LTO stage |
| names to the received @var{dumppfx}, ensures it contains a directory |
| component so that it overrides any @option{-dumpdir}, and passes that as |
| @option{-dumpbase} to sub-compilers. |
| |
| @item -v |
| @opindex v |
| Print (on standard error output) the commands executed to run the stages |
| of compilation. Also print the version number of the compiler driver |
| program and of the preprocessor and the compiler proper. |
| |
| @item -### |
| @opindex ### |
| Like @option{-v} except the commands are not executed and arguments |
| are quoted unless they contain only alphanumeric characters or @code{./-_}. |
| This is useful for shell scripts to capture the driver-generated command lines. |
| |
| @item --help |
| @opindex help |
| Print (on the standard output) a description of the command-line options |
| understood by @command{gcc}. If the @option{-v} option is also specified |
| then @option{--help} is also passed on to the various processes |
| invoked by @command{gcc}, so that they can display the command-line options |
| they accept. If the @option{-Wextra} option has also been specified |
| (prior to the @option{--help} option), then command-line options that |
| have no documentation associated with them are also displayed. |
| |
| @item --target-help |
| @opindex target-help |
| Print (on the standard output) a description of target-specific command-line |
| options for each tool. For some targets extra target-specific |
| information may also be printed. |
| |
| @item --help=@{@var{class}@r{|[}^@r{]}@var{qualifier}@}@r{[},@dots{}@r{]} |
| Print (on the standard output) a description of the command-line |
| options understood by the compiler that fit into all specified classes |
| and qualifiers. These are the supported classes: |
| |
| @table @asis |
| @item @samp{optimizers} |
| Display all of the optimization options supported by the |
| compiler. |
| |
| @item @samp{warnings} |
| Display all of the options controlling warning messages |
| produced by the compiler. |
| |
| @item @samp{target} |
| Display target-specific options. Unlike the |
| @option{--target-help} option however, target-specific options of the |
| linker and assembler are not displayed. This is because those |
| tools do not currently support the extended @option{--help=} syntax. |
| |
| @item @samp{params} |
| Display the values recognized by the @option{--param} |
| option. |
| |
| @item @var{language} |
| Display the options supported for @var{language}, where |
| @var{language} is the name of one of the languages supported in this |
| version of GCC@. If an option is supported by all languages, one needs |
| to select @samp{common} class. |
| |
| @item @samp{common} |
| Display the options that are common to all languages. |
| @end table |
| |
| These are the supported qualifiers: |
| |
| @table @asis |
| @item @samp{undocumented} |
| Display only those options that are undocumented. |
| |
| @item @samp{joined} |
| Display options taking an argument that appears after an equal |
| sign in the same continuous piece of text, such as: |
| @samp{--help=target}. |
| |
| @item @samp{separate} |
| Display options taking an argument that appears as a separate word |
| following the original option, such as: @samp{-o output-file}. |
| @end table |
| |
| Thus for example to display all the undocumented target-specific |
| switches supported by the compiler, use: |
| |
| @smallexample |
| --help=target,undocumented |
| @end smallexample |
| |
| The sense of a qualifier can be inverted by prefixing it with the |
| @samp{^} character, so for example to display all binary warning |
| options (i.e., ones that are either on or off and that do not take an |
| argument) that have a description, use: |
| |
| @smallexample |
| --help=warnings,^joined,^undocumented |
| @end smallexample |
| |
| The argument to @option{--help=} should not consist solely of inverted |
| qualifiers. |
| |
| Combining several classes is possible, although this usually |
| restricts the output so much that there is nothing to display. One |
| case where it does work, however, is when one of the classes is |
| @var{target}. For example, to display all the target-specific |
| optimization options, use: |
| |
| @smallexample |
| --help=target,optimizers |
| @end smallexample |
| |
| The @option{--help=} option can be repeated on the command line. Each |
| successive use displays its requested class of options, skipping |
| those that have already been displayed. If @option{--help} is also |
| specified anywhere on the command line then this takes precedence |
| over any @option{--help=} option. |
| |
| If the @option{-Q} option appears on the command line before the |
| @option{--help=} option, then the descriptive text displayed by |
| @option{--help=} is changed. Instead of describing the displayed |
| options, an indication is given as to whether the option is enabled, |
| disabled or set to a specific value (assuming that the compiler |
| knows this at the point where the @option{--help=} option is used). |
| |
| Here is a truncated example from the ARM port of @command{gcc}: |
| |
| @smallexample |
| % gcc -Q -mabi=2 --help=target -c |
| The following options are target specific: |
| -mabi= 2 |
| -mabort-on-noreturn [disabled] |
| -mapcs [disabled] |
| @end smallexample |
| |
| The output is sensitive to the effects of previous command-line |
| options, so for example it is possible to find out which optimizations |
| are enabled at @option{-O2} by using: |
| |
| @smallexample |
| -Q -O2 --help=optimizers |
| @end smallexample |
| |
| Alternatively you can discover which binary optimizations are enabled |
| by @option{-O3} by using: |
| |
| @smallexample |
| gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts |
| gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts |
| diff /tmp/O2-opts /tmp/O3-opts | grep enabled |
| @end smallexample |
| |
| @item --version |
| @opindex version |
| Display the version number and copyrights of the invoked GCC@. |
| |
| @item -pass-exit-codes |
| @opindex pass-exit-codes |
| Normally the @command{gcc} program exits with the code of 1 if any |
| phase of the compiler returns a non-success return code. If you specify |
| @option{-pass-exit-codes}, the @command{gcc} program instead returns with |
| the numerically highest error produced by any phase returning an error |
| indication. The C, C++, and Fortran front ends return 4 if an internal |
| compiler error is encountered. |
| |
| @item -pipe |
| @opindex pipe |
| Use pipes rather than temporary files for communication between the |
| various stages of compilation. This fails to work on some systems where |
| the assembler is unable to read from a pipe; but the GNU assembler has |
| no trouble. |
| |
| @item -specs=@var{file} |
| @opindex specs |
| Process @var{file} after the compiler reads in the standard @file{specs} |
| file, in order to override the defaults which the @command{gcc} driver |
| program uses when determining what switches to pass to @command{cc1}, |
| @command{cc1plus}, @command{as}, @command{ld}, etc. More than one |
| @option{-specs=@var{file}} can be specified on the command line, and they |
| are processed in order, from left to right. @xref{Spec Files}, for |
| information about the format of the @var{file}. |
| |
| @item -wrapper |
| @opindex wrapper |
| Invoke all subcommands under a wrapper program. The name of the |
| wrapper program and its parameters are passed as a comma separated |
| list. |
| |
| @smallexample |
| gcc -c t.c -wrapper gdb,--args |
| @end smallexample |
| |
| @noindent |
| This invokes all subprograms of @command{gcc} under |
| @samp{gdb --args}, thus the invocation of @command{cc1} is |
| @samp{gdb --args cc1 @dots{}}. |
| |
| @item -ffile-prefix-map=@var{old}=@var{new} |
| @opindex ffile-prefix-map |
| When compiling files residing in directory @file{@var{old}}, record |
| any references to them in the result of the compilation as if the |
| files resided in directory @file{@var{new}} instead. Specifying this |
| option is equivalent to specifying all the individual |
| @option{-f*-prefix-map} options. This can be used to make reproducible |
| builds that are location independent. See also |
| @option{-fmacro-prefix-map}, @option{-fdebug-prefix-map} and |
| @option{-fprofile-prefix-map}. |
| |
| @item -fplugin=@var{name}.so |
| @opindex fplugin |
| Load the plugin code in file @var{name}.so, assumed to be a |
| shared object to be dlopen'd by the compiler. The base name of |
| the shared object file is used to identify the plugin for the |
| purposes of argument parsing (See |
| @option{-fplugin-arg-@var{name}-@var{key}=@var{value}} below). |
| Each plugin should define the callback functions specified in the |
| Plugins API. |
| |
| @item -fplugin-arg-@var{name}-@var{key}=@var{value} |
| @opindex fplugin-arg |
| Define an argument called @var{key} with a value of @var{value} |
| for the plugin called @var{name}. |
| |
| @item -fdump-ada-spec@r{[}-slim@r{]} |
| @opindex fdump-ada-spec |
| For C and C++ source and include files, generate corresponding Ada specs. |
| @xref{Generating Ada Bindings for C and C++ headers,,, gnat_ugn, |
| GNAT User's Guide}, which provides detailed documentation on this feature. |
| |
| @item -fada-spec-parent=@var{unit} |
| @opindex fada-spec-parent |
| In conjunction with @option{-fdump-ada-spec@r{[}-slim@r{]}} above, generate |
| Ada specs as child units of parent @var{unit}. |
| |
| @item -fdump-go-spec=@var{file} |
| @opindex fdump-go-spec |
| For input files in any language, generate corresponding Go |
| declarations in @var{file}. This generates Go @code{const}, |
| @code{type}, @code{var}, and @code{func} declarations which may be a |
| useful way to start writing a Go interface to code written in some |
| other language. |
| |
| @include @value{srcdir}/../libiberty/at-file.texi |
| @end table |
| |
| @node Invoking G++ |
| @section Compiling C++ Programs |
| |
| @cindex suffixes for C++ source |
| @cindex C++ source file suffixes |
| C++ source files conventionally use one of the suffixes @samp{.C}, |
| @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or |
| @samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp}, |
| @samp{.H}, or (for shared template code) @samp{.tcc}; and |
| preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes |
| files with these names and compiles them as C++ programs even if you |
| call the compiler the same way as for compiling C programs (usually |
| with the name @command{gcc}). |
| |
| @findex g++ |
| @findex c++ |
| However, the use of @command{gcc} does not add the C++ library. |
| @command{g++} is a program that calls GCC and automatically specifies linking |
| against the C++ library. It treats @samp{.c}, |
| @samp{.h} and @samp{.i} files as C++ source files instead of C source |
| files unless @option{-x} is used. This program is also useful when |
| precompiling a C header file with a @samp{.h} extension for use in C++ |
| compilations. On many systems, @command{g++} is also installed with |
| the name @command{c++}. |
| |
| @cindex invoking @command{g++} |
| When you compile C++ programs, you may specify many of the same |
| command-line options that you use for compiling programs in any |
| language; or command-line options meaningful for C and related |
| languages; or options that are meaningful only for C++ programs. |
| @xref{C Dialect Options,,Options Controlling C Dialect}, for |
| explanations of options for languages related to C@. |
| @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for |
| explanations of options that are meaningful only for C++ programs. |
| |
| @node C Dialect Options |
| @section Options Controlling C Dialect |
| @cindex dialect options |
| @cindex language dialect options |
| @cindex options, dialect |
| |
| The following options control the dialect of C (or languages derived |
| from C, such as C++, Objective-C and Objective-C++) that the compiler |
| accepts: |
| |
| @table @gcctabopt |
| @cindex ANSI support |
| @cindex ISO support |
| @item -ansi |
| @opindex ansi |
| In C mode, this is equivalent to @option{-std=c90}. In C++ mode, it is |
| equivalent to @option{-std=c++98}. |
| |
| This turns off certain features of GCC that are incompatible with ISO |
| C90 (when compiling C code), or of standard C++ (when compiling C++ code), |
| such as the @code{asm} and @code{typeof} keywords, and |
| predefined macros such as @code{unix} and @code{vax} that identify the |
| type of system you are using. It also enables the undesirable and |
| rarely used ISO trigraph feature. For the C compiler, |
| it disables recognition of C++ style @samp{//} comments as well as |
| the @code{inline} keyword. |
| |
| The alternate keywords @code{__asm__}, @code{__extension__}, |
| @code{__inline__} and @code{__typeof__} continue to work despite |
| @option{-ansi}. You would not want to use them in an ISO C program, of |
| course, but it is useful to put them in header files that might be included |
| in compilations done with @option{-ansi}. Alternate predefined macros |
| such as @code{__unix__} and @code{__vax__} are also available, with or |
| without @option{-ansi}. |
| |
| The @option{-ansi} option does not cause non-ISO programs to be |
| rejected gratuitously. For that, @option{-Wpedantic} is required in |
| addition to @option{-ansi}. @xref{Warning Options}. |
| |
| The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi} |
| option is used. Some header files may notice this macro and refrain |
| from declaring certain functions or defining certain macros that the |
| ISO standard doesn't call for; this is to avoid interfering with any |
| programs that might use these names for other things. |
| |
| Functions that are normally built in but do not have semantics |
| defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in |
| functions when @option{-ansi} is used. @xref{Other Builtins,,Other |
| built-in functions provided by GCC}, for details of the functions |
| affected. |
| |
| @item -std= |
| @opindex std |
| Determine the language standard. @xref{Standards,,Language Standards |
| Supported by GCC}, for details of these standard versions. This option |
| is currently only supported when compiling C or C++. |
| |
| The compiler can accept several base standards, such as @samp{c90} or |
| @samp{c++98}, and GNU dialects of those standards, such as |
| @samp{gnu90} or @samp{gnu++98}. When a base standard is specified, the |
| compiler accepts all programs following that standard plus those |
| using GNU extensions that do not contradict it. For example, |
| @option{-std=c90} turns off certain features of GCC that are |
| incompatible with ISO C90, such as the @code{asm} and @code{typeof} |
| keywords, but not other GNU extensions that do not have a meaning in |
| ISO C90, such as omitting the middle term of a @code{?:} |
| expression. On the other hand, when a GNU dialect of a standard is |
| specified, all features supported by the compiler are enabled, even when |
| those features change the meaning of the base standard. As a result, some |
| strict-conforming programs may be rejected. The particular standard |
| is used by @option{-Wpedantic} to identify which features are GNU |
| extensions given that version of the standard. For example |
| @option{-std=gnu90 -Wpedantic} warns about C++ style @samp{//} |
| comments, while @option{-std=gnu99 -Wpedantic} does not. |
| |
| A value for this option must be provided; possible values are |
| |
| @table @samp |
| @item c90 |
| @itemx c89 |
| @itemx iso9899:1990 |
| Support all ISO C90 programs (certain GNU extensions that conflict |
| with ISO C90 are disabled). Same as @option{-ansi} for C code. |
| |
| @item iso9899:199409 |
| ISO C90 as modified in amendment 1. |
| |
| @item c99 |
| @itemx c9x |
| @itemx iso9899:1999 |
| @itemx iso9899:199x |
| ISO C99. This standard is substantially completely supported, modulo |
| bugs and floating-point issues |
| (mainly but not entirely relating to optional C99 features from |
| Annexes F and G). See |
| @w{@uref{https://gcc.gnu.org/c99status.html}} for more information. The |
| names @samp{c9x} and @samp{iso9899:199x} are deprecated. |
| |
| @item c11 |
| @itemx c1x |
| @itemx iso9899:2011 |
| ISO C11, the 2011 revision of the ISO C standard. This standard is |
| substantially completely supported, modulo bugs, floating-point issues |
| (mainly but not entirely relating to optional C11 features from |
| Annexes F and G) and the optional Annexes K (Bounds-checking |
| interfaces) and L (Analyzability). The name @samp{c1x} is deprecated. |
| |
| @item c17 |
| @itemx c18 |
| @itemx iso9899:2017 |
| @itemx iso9899:2018 |
| ISO C17, the 2017 revision of the ISO C standard |
| (published in 2018). This standard is |
| same as C11 except for corrections of defects (all of which are also |
| applied with @option{-std=c11}) and a new value of |
| @code{__STDC_VERSION__}, and so is supported to the same extent as C11. |
| |
| @item c2x |
| The next version of the ISO C standard, still under development. The |
| support for this version is experimental and incomplete. |
| |
| @item gnu90 |
| @itemx gnu89 |
| GNU dialect of ISO C90 (including some C99 features). |
| |
| @item gnu99 |
| @itemx gnu9x |
| GNU dialect of ISO C99. The name @samp{gnu9x} is deprecated. |
| |
| @item gnu11 |
| @itemx gnu1x |
| GNU dialect of ISO C11. |
| The name @samp{gnu1x} is deprecated. |
| |
| @item gnu17 |
| @itemx gnu18 |
| GNU dialect of ISO C17. This is the default for C code. |
| |
| @item gnu2x |
| The next version of the ISO C standard, still under development, plus |
| GNU extensions. The support for this version is experimental and |
| incomplete. |
| |
| @item c++98 |
| @itemx c++03 |
| The 1998 ISO C++ standard plus the 2003 technical corrigendum and some |
| additional defect reports. Same as @option{-ansi} for C++ code. |
| |
| @item gnu++98 |
| @itemx gnu++03 |
| GNU dialect of @option{-std=c++98}. |
| |
| @item c++11 |
| @itemx c++0x |
| The 2011 ISO C++ standard plus amendments. |
| The name @samp{c++0x} is deprecated. |
| |
| @item gnu++11 |
| @itemx gnu++0x |
| GNU dialect of @option{-std=c++11}. |
| The name @samp{gnu++0x} is deprecated. |
| |
| @item c++14 |
| @itemx c++1y |
| The 2014 ISO C++ standard plus amendments. |
| The name @samp{c++1y} is deprecated. |
| |
| @item gnu++14 |
| @itemx gnu++1y |
| GNU dialect of @option{-std=c++14}. |
| The name @samp{gnu++1y} is deprecated. |
| |
| @item c++17 |
| @itemx c++1z |
| The 2017 ISO C++ standard plus amendments. |
| The name @samp{c++1z} is deprecated. |
| |
| @item gnu++17 |
| @itemx gnu++1z |
| GNU dialect of @option{-std=c++17}. |
| This is the default for C++ code. |
| The name @samp{gnu++1z} is deprecated. |
| |
| @item c++20 |
| @itemx c++2a |
| The 2020 ISO C++ standard plus amendments. |
| Support is experimental, and could change in incompatible ways in |
| future releases. |
| The name @samp{c++2a} is deprecated. |
| |
| @item gnu++20 |
| @itemx gnu++2a |
| GNU dialect of @option{-std=c++20}. |
| Support is experimental, and could change in incompatible ways in |
| future releases. |
| The name @samp{gnu++2a} is deprecated. |
| |
| @item c++2b |
| @itemx c++23 |
| The next revision of the ISO C++ standard, planned for |
| 2023. Support is highly experimental, and will almost certainly |
| change in incompatible ways in future releases. |
| |
| @item gnu++2b |
| @itemx gnu++23 |
| GNU dialect of @option{-std=c++2b}. Support is highly experimental, |
| and will almost certainly change in incompatible ways in future |
| releases. |
| @end table |
| |
| @item -aux-info @var{filename} |
| @opindex aux-info |
| Output to the given filename prototyped declarations for all functions |
| declared and/or defined in a translation unit, including those in header |
| files. This option is silently ignored in any language other than C@. |
| |
| Besides declarations, the file indicates, in comments, the origin of |
| each declaration (source file and line), whether the declaration was |
| implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or |
| @samp{O} for old, respectively, in the first character after the line |
| number and the colon), and whether it came from a declaration or a |
| definition (@samp{C} or @samp{F}, respectively, in the following |
| character). In the case of function definitions, a K&R-style list of |
| arguments followed by their declarations is also provided, inside |
| comments, after the declaration. |
| |
| @item -fallow-parameterless-variadic-functions |
| @opindex fallow-parameterless-variadic-functions |
| Accept variadic functions without named parameters. |
| |
| Although it is possible to define such a function, this is not very |
| useful as it is not possible to read the arguments. This is only |
| supported for C as this construct is allowed by C++. |
| |
| @item -fno-asm |
| @opindex fno-asm |
| @opindex fasm |
| Do not recognize @code{asm}, @code{inline} or @code{typeof} as a |
| keyword, so that code can use these words as identifiers. You can use |
| the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__} |
| instead. In C, @option{-ansi} implies @option{-fno-asm}. |
| |
| In C++, @code{inline} is a standard keyword and is not affected by |
| this switch. You may want to use the @option{-fno-gnu-keywords} flag |
| instead, which disables @code{typeof} but not @code{asm} and |
| @code{inline}. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), |
| this switch only affects the @code{asm} and @code{typeof} keywords, |
| since @code{inline} is a standard keyword in ISO C99. |
| |
| @item -fno-builtin |
| @itemx -fno-builtin-@var{function} |
| @opindex fno-builtin |
| @opindex fbuiltin |
| @cindex built-in functions |
| Don't recognize built-in functions that do not begin with |
| @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in |
| functions provided by GCC}, for details of the functions affected, |
| including those which are not built-in functions when @option{-ansi} or |
| @option{-std} options for strict ISO C conformance are used because they |
| do not have an ISO standard meaning. |
| |
| GCC normally generates special code to handle certain built-in functions |
| more efficiently; for instance, calls to @code{alloca} may become single |
| instructions which adjust the stack directly, and calls to @code{memcpy} |
| may become inline copy loops. The resulting code is often both smaller |
| and faster, but since the function calls no longer appear as such, you |
| cannot set a breakpoint on those calls, nor can you change the behavior |
| of the functions by linking with a different library. In addition, |
| when a function is recognized as a built-in function, GCC may use |
| information about that function to warn about problems with calls to |
| that function, or to generate more efficient code, even if the |
| resulting code still contains calls to that function. For example, |
| warnings are given with @option{-Wformat} for bad calls to |
| @code{printf} when @code{printf} is built in and @code{strlen} is |
| known not to modify global memory. |
| |
| With the @option{-fno-builtin-@var{function}} option |
| only the built-in function @var{function} is |
| disabled. @var{function} must not begin with @samp{__builtin_}. If a |
| function is named that is not built-in in this version of GCC, this |
| option is ignored. There is no corresponding |
| @option{-fbuiltin-@var{function}} option; if you wish to enable |
| built-in functions selectively when using @option{-fno-builtin} or |
| @option{-ffreestanding}, you may define macros such as: |
| |
| @smallexample |
| #define abs(n) __builtin_abs ((n)) |
| #define strcpy(d, s) __builtin_strcpy ((d), (s)) |
| @end smallexample |
| |
| @item -fcond-mismatch |
| @opindex fcond-mismatch |
| Allow conditional expressions with mismatched types in the second and |
| third arguments. The value of such an expression is void. This option |
| is not supported for C++. |
| |
| @item -ffreestanding |
| @opindex ffreestanding |
| @cindex hosted environment |
| |
| Assert that compilation targets a freestanding environment. This |
| implies @option{-fno-builtin}. A freestanding environment |
| is one in which the standard library may not exist, and program startup may |
| not necessarily be at @code{main}. The most obvious example is an OS kernel. |
| This is equivalent to @option{-fno-hosted}. |
| |
| @xref{Standards,,Language Standards Supported by GCC}, for details of |
| freestanding and hosted environments. |
| |
| @item -fgimple |
| @opindex fgimple |
| |
| Enable parsing of function definitions marked with @code{__GIMPLE}. |
| This is an experimental feature that allows unit testing of GIMPLE |
| passes. |
| |
| @item -fgnu-tm |
| @opindex fgnu-tm |
| When the option @option{-fgnu-tm} is specified, the compiler |
| generates code for the Linux variant of Intel's current Transactional |
| Memory ABI specification document (Revision 1.1, May 6 2009). This is |
| an experimental feature whose interface may change in future versions |
| of GCC, as the official specification changes. Please note that not |
| all architectures are supported for this feature. |
| |
| For more information on GCC's support for transactional memory, |
| @xref{Enabling libitm,,The GNU Transactional Memory Library,libitm,GNU |
| Transactional Memory Library}. |
| |
| Note that the transactional memory feature is not supported with |
| non-call exceptions (@option{-fnon-call-exceptions}). |
| |
| @item -fgnu89-inline |
| @opindex fgnu89-inline |
| The option @option{-fgnu89-inline} tells GCC to use the traditional |
| GNU semantics for @code{inline} functions when in C99 mode. |
| @xref{Inline,,An Inline Function is As Fast As a Macro}. |
| Using this option is roughly equivalent to adding the |
| @code{gnu_inline} function attribute to all inline functions |
| (@pxref{Function Attributes}). |
| |
| The option @option{-fno-gnu89-inline} explicitly tells GCC to use the |
| C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it |
| specifies the default behavior). |
| This option is not supported in @option{-std=c90} or |
| @option{-std=gnu90} mode. |
| |
| The preprocessor macros @code{__GNUC_GNU_INLINE__} and |
| @code{__GNUC_STDC_INLINE__} may be used to check which semantics are |
| in effect for @code{inline} functions. @xref{Common Predefined |
| Macros,,,cpp,The C Preprocessor}. |
| |
| @item -fhosted |
| @opindex fhosted |
| @cindex hosted environment |
| |
| Assert that compilation targets a hosted environment. This implies |
| @option{-fbuiltin}. A hosted environment is one in which the |
| entire standard library is available, and in which @code{main} has a return |
| type of @code{int}. Examples are nearly everything except a kernel. |
| This is equivalent to @option{-fno-freestanding}. |
| |
| @item -flax-vector-conversions |
| @opindex flax-vector-conversions |
| Allow implicit conversions between vectors with differing numbers of |
| elements and/or incompatible element types. This option should not be |
| used for new code. |
| |
| @item -fms-extensions |
| @opindex fms-extensions |
| Accept some non-standard constructs used in Microsoft header files. |
| |
| In C++ code, this allows member names in structures to be similar |
| to previous types declarations. |
| |
| @smallexample |
| typedef int UOW; |
| struct ABC @{ |
| UOW UOW; |
| @}; |
| @end smallexample |
| |
| Some cases of unnamed fields in structures and unions are only |
| accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union |
| fields within structs/unions}, for details. |
| |
| Note that this option is off for all targets except for x86 |
| targets using ms-abi. |
| |
| @item -foffload=disable |
| @itemx -foffload=default |
| @itemx -foffload=@var{target-list} |
| @opindex foffload |
| @cindex Offloading targets |
| @cindex OpenACC offloading targets |
| @cindex OpenMP offloading targets |
| Specify for which OpenMP and OpenACC offload targets code should be generated. |
| The default behavior, equivalent to @option{-foffload=default}, is to generate |
| code for all supported offload targets. The @option{-foffload=disable} form |
| generates code only for the host fallback, while |
| @option{-foffload=@var{target-list}} generates code only for the specified |
| comma-separated list of offload targets. |
| |
| Offload targets are specified in GCC's internal target-triplet format. You can |
| run the compiler with @option{-v} to show the list of configured offload targets |
| under @code{OFFLOAD_TARGET_NAMES}. |
| |
| @item -foffload-options=@var{options} |
| @itemx -foffload-options=@var{target-triplet-list}=@var{options} |
| @opindex foffload-options |
| @cindex Offloading options |
| @cindex OpenACC offloading options |
| @cindex OpenMP offloading options |
| |
| With @option{-foffload-options=@var{options}}, GCC passes the specified |
| @var{options} to the compilers for all enabled offloading targets. You can |
| specify options that apply only to a specific target or targets by using |
| the @option{-foffload-options=@var{target-list}=@var{options}} form. The |
| @var{target-list} is a comma-separated list in the same format as for the |
| @option{-foffload=} option. |
| |
| Typical command lines are |
| |
| @smallexample |
| -foffload-options=-lgfortran -foffload-options=-lm |
| -foffload-options="-lgfortran -lm" -foffload-options=nvptx-none=-latomic |
| -foffload-options=amdgcn-amdhsa=-march=gfx906 -foffload-options=-lm |
| @end smallexample |
| |
| @item -fopenacc |
| @opindex fopenacc |
| @cindex OpenACC accelerator programming |
| Enable handling of OpenACC directives @code{#pragma acc} in C/C++ and |
| @code{!$acc} in Fortran. When @option{-fopenacc} is specified, the |
| compiler generates accelerated code according to the OpenACC Application |
| Programming Interface v2.6 @w{@uref{https://www.openacc.org}}. This option |
| implies @option{-pthread}, and thus is only supported on targets that |
| have support for @option{-pthread}. |
| |
| @item -fopenacc-dim=@var{geom} |
| @opindex fopenacc-dim |
| @cindex OpenACC accelerator programming |
| Specify default compute dimensions for parallel offload regions that do |
| not explicitly specify. The @var{geom} value is a triple of |
| ':'-separated sizes, in order 'gang', 'worker' and, 'vector'. A size |
| can be omitted, to use a target-specific default value. |
| |
| @item -fopenmp |
| @opindex fopenmp |
| @cindex OpenMP parallel |
| Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and |
| @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the |
| compiler generates parallel code according to the OpenMP Application |
| Program Interface v4.5 @w{@uref{https://www.openmp.org}}. This option |
| implies @option{-pthread}, and thus is only supported on targets that |
| have support for @option{-pthread}. @option{-fopenmp} implies |
| @option{-fopenmp-simd}. |
| |
| @item -fopenmp-simd |
| @opindex fopenmp-simd |
| @cindex OpenMP SIMD |
| @cindex SIMD |
| Enable handling of OpenMP's SIMD directives with @code{#pragma omp} |
| in C/C++ and @code{!$omp} in Fortran. Other OpenMP directives |
| are ignored. |
| |
| @item -fpermitted-flt-eval-methods=@var{style} |
| @opindex fpermitted-flt-eval-methods |
| @opindex fpermitted-flt-eval-methods=c11 |
| @opindex fpermitted-flt-eval-methods=ts-18661-3 |
| ISO/IEC TS 18661-3 defines new permissible values for |
| @code{FLT_EVAL_METHOD} that indicate that operations and constants with |
| a semantic type that is an interchange or extended format should be |
| evaluated to the precision and range of that type. These new values are |
| a superset of those permitted under C99/C11, which does not specify the |
| meaning of other positive values of @code{FLT_EVAL_METHOD}. As such, code |
| conforming to C11 may not have been written expecting the possibility of |
| the new values. |
| |
| @option{-fpermitted-flt-eval-methods} specifies whether the compiler |
| should allow only the values of @code{FLT_EVAL_METHOD} specified in C99/C11, |
| or the extended set of values specified in ISO/IEC TS 18661-3. |
| |
| @var{style} is either @code{c11} or @code{ts-18661-3} as appropriate. |
| |
| The default when in a standards compliant mode (@option{-std=c11} or similar) |
| is @option{-fpermitted-flt-eval-methods=c11}. The default when in a GNU |
| dialect (@option{-std=gnu11} or similar) is |
| @option{-fpermitted-flt-eval-methods=ts-18661-3}. |
| |
| @item -fplan9-extensions |
| @opindex fplan9-extensions |
| Accept some non-standard constructs used in Plan 9 code. |
| |
| This enables @option{-fms-extensions}, permits passing pointers to |
| structures with anonymous fields to functions that expect pointers to |
| elements of the type of the field, and permits referring to anonymous |
| fields declared using a typedef. @xref{Unnamed Fields,,Unnamed |
| struct/union fields within structs/unions}, for details. This is only |
| supported for C, not C++. |
| |
| @item -fsigned-bitfields |
| @itemx -funsigned-bitfields |
| @itemx -fno-signed-bitfields |
| @itemx -fno-unsigned-bitfields |
| @opindex fsigned-bitfields |
| @opindex funsigned-bitfields |
| @opindex fno-signed-bitfields |
| @opindex fno-unsigned-bitfields |
| These options control whether a bit-field is signed or unsigned, when the |
| declaration does not use either @code{signed} or @code{unsigned}. By |
| default, such a bit-field is signed, because this is consistent: the |
| basic integer types such as @code{int} are signed types. |
| |
| @item -fsigned-char |
| @opindex fsigned-char |
| Let the type @code{char} be signed, like @code{signed char}. |
| |
| Note that this is equivalent to @option{-fno-unsigned-char}, which is |
| the negative form of @option{-funsigned-char}. Likewise, the option |
| @option{-fno-signed-char} is equivalent to @option{-funsigned-char}. |
| |
| @item -funsigned-char |
| @opindex funsigned-char |
| Let the type @code{char} be unsigned, like @code{unsigned char}. |
| |
| Each kind of machine has a default for what @code{char} should |
| be. It is either like @code{unsigned char} by default or like |
| @code{signed char} by default. |
| |
| Ideally, a portable program should always use @code{signed char} or |
| @code{unsigned char} when it depends on the signedness of an object. |
| But many programs have been written to use plain @code{char} and |
| expect it to be signed, or expect it to be unsigned, depending on the |
| machines they were written for. This option, and its inverse, let you |
| make such a program work with the opposite default. |
| |
| The type @code{char} is always a distinct type from each of |
| @code{signed char} or @code{unsigned char}, even though its behavior |
| is always just like one of those two. |
| |
| @item -fsso-struct=@var{endianness} |
| @opindex fsso-struct |
| Set the default scalar storage order of structures and unions to the |
| specified endianness. The accepted values are @samp{big-endian}, |
| @samp{little-endian} and @samp{native} for the native endianness of |
| the target (the default). This option is not supported for C++. |
| |
| @strong{Warning:} the @option{-fsso-struct} switch causes GCC to generate |
| code that is not binary compatible with code generated without it if the |
| specified endianness is not the native endianness of the target. |
| @end table |
| |
| @node C++ Dialect Options |
| @section Options Controlling C++ Dialect |
| |
| @cindex compiler options, C++ |
| @cindex C++ options, command-line |
| @cindex options, C++ |
| This section describes the command-line options that are only meaningful |
| for C++ programs. You can also use most of the GNU compiler options |
| regardless of what language your program is in. For example, you |
| might compile a file @file{firstClass.C} like this: |
| |
| @smallexample |
| g++ -g -fstrict-enums -O -c firstClass.C |
| @end smallexample |
| |
| @noindent |
| In this example, only @option{-fstrict-enums} is an option meant |
| only for C++ programs; you can use the other options with any |
| language supported by GCC@. |
| |
| Some options for compiling C programs, such as @option{-std}, are also |
| relevant for C++ programs. |
| @xref{C Dialect Options,,Options Controlling C Dialect}. |
| |
| Here is a list of options that are @emph{only} for compiling C++ programs: |
| |
| @table @gcctabopt |
| |
| @item -fabi-version=@var{n} |
| @opindex fabi-version |
| Use version @var{n} of the C++ ABI@. The default is version 0. |
| |
| Version 0 refers to the version conforming most closely to |
| the C++ ABI specification. Therefore, the ABI obtained using version 0 |
| will change in different versions of G++ as ABI bugs are fixed. |
| |
| Version 1 is the version of the C++ ABI that first appeared in G++ 3.2. |
| |
| Version 2 is the version of the C++ ABI that first appeared in G++ |
| 3.4, and was the default through G++ 4.9. |
| |
| Version 3 corrects an error in mangling a constant address as a |
| template argument. |
| |
| Version 4, which first appeared in G++ 4.5, implements a standard |
| mangling for vector types. |
| |
| Version 5, which first appeared in G++ 4.6, corrects the mangling of |
| attribute const/volatile on function pointer types, decltype of a |
| plain decl, and use of a function parameter in the declaration of |
| another parameter. |
| |
| Version 6, which first appeared in G++ 4.7, corrects the promotion |
| behavior of C++11 scoped enums and the mangling of template argument |
| packs, const/static_cast, prefix ++ and --, and a class scope function |
| used as a template argument. |
| |
| Version 7, which first appeared in G++ 4.8, that treats nullptr_t as a |
| builtin type and corrects the mangling of lambdas in default argument |
| scope. |
| |
| Version 8, which first appeared in G++ 4.9, corrects the substitution |
| behavior of function types with function-cv-qualifiers. |
| |
| Version 9, which first appeared in G++ 5.2, corrects the alignment of |
| @code{nullptr_t}. |
| |
| Version 10, which first appeared in G++ 6.1, adds mangling of |
| attributes that affect type identity, such as ia32 calling convention |
| attributes (e.g.@: @samp{stdcall}). |
| |
| Version 11, which first appeared in G++ 7, corrects the mangling of |
| sizeof... expressions and operator names. For multiple entities with |
| the same name within a function, that are declared in different scopes, |
| the mangling now changes starting with the twelfth occurrence. It also |
| implies @option{-fnew-inheriting-ctors}. |
| |
| Version 12, which first appeared in G++ 8, corrects the calling |
| conventions for empty classes on the x86_64 target and for classes |
| with only deleted copy/move constructors. It accidentally changes the |
| calling convention for classes with a deleted copy constructor and a |
| trivial move constructor. |
| |
| Version 13, which first appeared in G++ 8.2, fixes the accidental |
| change in version 12. |
| |
| Version 14, which first appeared in G++ 10, corrects the mangling of |
| the nullptr expression. |
| |
| Version 15, which first appeared in G++ 11, changes the mangling of |
| @code{__alignof__} to be distinct from that of @code{alignof}, and |
| dependent operator names. |
| |
| See also @option{-Wabi}. |
| |
| @item -fabi-compat-version=@var{n} |
| @opindex fabi-compat-version |
| On targets that support strong aliases, G++ |
| works around mangling changes by creating an alias with the correct |
| mangled name when defining a symbol with an incorrect mangled name. |
| This switch specifies which ABI version to use for the alias. |
| |
| With @option{-fabi-version=0} (the default), this defaults to 11 (GCC 7 |
| compatibility). If another ABI version is explicitly selected, this |
| defaults to 0. For compatibility with GCC versions 3.2 through 4.9, |
| use @option{-fabi-compat-version=2}. |
| |
| If this option is not provided but @option{-Wabi=@var{n}} is, that |
| version is used for compatibility aliases. If this option is provided |
| along with @option{-Wabi} (without the version), the version from this |
| option is used for the warning. |
| |
| @item -fno-access-control |
| @opindex fno-access-control |
| @opindex faccess-control |
| Turn off all access checking. This switch is mainly useful for working |
| around bugs in the access control code. |
| |
| @item -faligned-new |
| @opindex faligned-new |
| Enable support for C++17 @code{new} of types that require more |
| alignment than @code{void* ::operator new(std::size_t)} provides. A |
| numeric argument such as @code{-faligned-new=32} can be used to |
| specify how much alignment (in bytes) is provided by that function, |
| but few users will need to override the default of |
| @code{alignof(std::max_align_t)}. |
| |
| This flag is enabled by default for @option{-std=c++17}. |
| |
| @item -fchar8_t |
| @itemx -fno-char8_t |
| @opindex fchar8_t |
| @opindex fno-char8_t |
| Enable support for @code{char8_t} as adopted for C++20. This includes |
| the addition of a new @code{char8_t} fundamental type, changes to the |
| types of UTF-8 string and character literals, new signatures for |
| user-defined literals, associated standard library updates, and new |
| @code{__cpp_char8_t} and @code{__cpp_lib_char8_t} feature test macros. |
| |
| This option enables functions to be overloaded for ordinary and UTF-8 |
| strings: |
| |
| @smallexample |
| int f(const char *); // #1 |
| int f(const char8_t *); // #2 |
| int v1 = f("text"); // Calls #1 |
| int v2 = f(u8"text"); // Calls #2 |
| @end smallexample |
| |
| @noindent |
| and introduces new signatures for user-defined literals: |
| |
| @smallexample |
| int operator""_udl1(char8_t); |
| int v3 = u8'x'_udl1; |
| int operator""_udl2(const char8_t*, std::size_t); |
| int v4 = u8"text"_udl2; |
| template<typename T, T...> int operator""_udl3(); |
| int v5 = u8"text"_udl3; |
| @end smallexample |
| |
| @noindent |
| The change to the types of UTF-8 string and character literals introduces |
| incompatibilities with ISO C++11 and later standards. For example, the |
| following code is well-formed under ISO C++11, but is ill-formed when |
| @option{-fchar8_t} is specified. |
| |
| @smallexample |
| char ca[] = u8"xx"; // error: char-array initialized from wide |
| // string |
| const char *cp = u8"xx";// error: invalid conversion from |
| // `const char8_t*' to `const char*' |
| int f(const char*); |
| auto v = f(u8"xx"); // error: invalid conversion from |
| // `const char8_t*' to `const char*' |
| std::string s@{u8"xx"@}; // error: no matching function for call to |
| // `std::basic_string<char>::basic_string()' |
| using namespace std::literals; |
| s = u8"xx"s; // error: conversion from |
| // `basic_string<char8_t>' to non-scalar |
| // type `basic_string<char>' requested |
| @end smallexample |
| |
| @item -fcheck-new |
| @opindex fcheck-new |
| Check that the pointer returned by @code{operator new} is non-null |
| before attempting to modify the storage allocated. This check is |
| normally unnecessary because the C++ standard specifies that |
| @code{operator new} only returns @code{0} if it is declared |
| @code{throw()}, in which case the compiler always checks the |
| return value even without this option. In all other cases, when |
| @code{operator new} has a non-empty exception specification, memory |
| exhaustion is signalled by throwing @code{std::bad_alloc}. See also |
| @samp{new (nothrow)}. |
| |
| @item -fconcepts |
| @itemx -fconcepts-ts |
| @opindex fconcepts |
| @opindex fconcepts-ts |
| Below @option{-std=c++20}, @option{-fconcepts} enables support for the |
| C++ Extensions for Concepts Technical Specification, ISO 19217 (2015). |
| |
| With @option{-std=c++20} and above, Concepts are part of the language |
| standard, so @option{-fconcepts} defaults to on. But the standard |
| specification of Concepts differs significantly from the TS, so some |
| constructs that were allowed in the TS but didn't make it into the |
| standard can still be enabled by @option{-fconcepts-ts}. |
| |
| @item -fconstexpr-depth=@var{n} |
| @opindex fconstexpr-depth |
| Set the maximum nested evaluation depth for C++11 constexpr functions |
| to @var{n}. A limit is needed to detect endless recursion during |
| constant expression evaluation. The minimum specified by the standard |
| is 512. |
| |
| @item -fconstexpr-cache-depth=@var{n} |
| @opindex fconstexpr-cache-depth |
| Set the maximum level of nested evaluation depth for C++11 constexpr |
| functions that will be cached to @var{n}. This is a heuristic that |
| trades off compilation speed (when the cache avoids repeated |
| calculations) against memory consumption (when the cache grows very |
| large from highly recursive evaluations). The default is 8. Very few |
| users are likely to want to adjust it, but if your code does heavy |
| constexpr calculations you might want to experiment to find which |
| value works best for you. |
| |
| @item -fconstexpr-fp-except |
| @opindex fconstexpr-fp-except |
| Annex F of the C standard specifies that IEC559 floating point |
| exceptions encountered at compile time should not stop compilation. |
| C++ compilers have historically not followed this guidance, instead |
| treating floating point division by zero as non-constant even though |
| it has a well defined value. This flag tells the compiler to give |
| Annex F priority over other rules saying that a particular operation |
| is undefined. |
| |
| @smallexample |
| constexpr float inf = 1./0.; // OK with -fconstexpr-fp-except |
| @end smallexample |
| |
| @item -fconstexpr-loop-limit=@var{n} |
| @opindex fconstexpr-loop-limit |
| Set the maximum number of iterations for a loop in C++14 constexpr functions |
| to @var{n}. A limit is needed to detect infinite loops during |
| constant expression evaluation. The default is 262144 (1<<18). |
| |
| @item -fconstexpr-ops-limit=@var{n} |
| @opindex fconstexpr-ops-limit |
| Set the maximum number of operations during a single constexpr evaluation. |
| Even when number of iterations of a single loop is limited with the above limit, |
| if there are several nested loops and each of them has many iterations but still |
| smaller than the above limit, or if in a body of some loop or even outside |
| of a loop too many expressions need to be evaluated, the resulting constexpr |
| evaluation might take too long. |
| The default is 33554432 (1<<25). |
| |
| @item -fcoroutines |
| @opindex fcoroutines |
| Enable support for the C++ coroutines extension (experimental). |
| |
| @item -fno-elide-constructors |
| @opindex fno-elide-constructors |
| @opindex felide-constructors |
| The C++ standard allows an implementation to omit creating a temporary |
| that is only used to initialize another object of the same type. |
| Specifying this option disables that optimization, and forces G++ to |
| call the copy constructor in all cases. This option also causes G++ |
| to call trivial member functions which otherwise would be expanded inline. |
| |
| In C++17, the compiler is required to omit these temporaries, but this |
| option still affects trivial member functions. |
| |
| @item -fno-enforce-eh-specs |
| @opindex fno-enforce-eh-specs |
| @opindex fenforce-eh-specs |
| Don't generate code to check for violation of exception specifications |
| at run time. This option violates the C++ standard, but may be useful |
| for reducing code size in production builds, much like defining |
| @code{NDEBUG}. This does not give user code permission to throw |
| exceptions in violation of the exception specifications; the compiler |
| still optimizes based on the specifications, so throwing an |
| unexpected exception results in undefined behavior at run time. |
| |
| @item -fextern-tls-init |
| @itemx -fno-extern-tls-init |
| @opindex fextern-tls-init |
| @opindex fno-extern-tls-init |
| The C++11 and OpenMP standards allow @code{thread_local} and |
| @code{threadprivate} variables to have dynamic (runtime) |
| initialization. To support this, any use of such a variable goes |
| through a wrapper function that performs any necessary initialization. |
| When the use and definition of the variable are in the same |
| translation unit, this overhead can be optimized away, but when the |
| use is in a different translation unit there is significant overhead |
| even if the variable doesn't actually need dynamic initialization. If |
| the programmer can be sure that no use of the variable in a |
| non-defining TU needs to trigger dynamic initialization (either |
| because the variable is statically initialized, or a use of the |
| variable in the defining TU will be executed before any uses in |
| another TU), they can avoid this overhead with the |
| @option{-fno-extern-tls-init} option. |
| |
| On targets that support symbol aliases, the default is |
| @option{-fextern-tls-init}. On targets that do not support symbol |
| aliases, the default is @option{-fno-extern-tls-init}. |
| |
| @item -ffold-simple-inlines |
| @itemx -fno-fold-simple-inlines |
| @opindex ffold-simple-inlines |
| @opindex fno-fold-simple-inlines |
| Permit the C++ frontend to fold calls to @code{std::move}, @code{std::forward}, |
| @code{std::addressof} and @code{std::as_const}. In contrast to inlining, this |
| means no debug information will be generated for such calls. Since these |
| functions are rarely interesting to debug, this flag is enabled by default |
| unless @option{-fno-inline} is active. |
| |
| @item -fno-gnu-keywords |
| @opindex fno-gnu-keywords |
| @opindex fgnu-keywords |
| Do not recognize @code{typeof} as a keyword, so that code can use this |
| word as an identifier. You can use the keyword @code{__typeof__} instead. |
| This option is implied by the strict ISO C++ dialects: @option{-ansi}, |
| @option{-std=c++98}, @option{-std=c++11}, etc. |
| |
| @item -fimplicit-constexpr |
| @opindex fimplicit-constexpr |
| Make inline functions implicitly constexpr, if they satisfy the |
| requirements for a constexpr function. This option can be used in |
| C++14 mode or later. This can result in initialization changing from |
| dynamic to static and other optimizations. |
| |
| @item -fno-implicit-templates |
| @opindex fno-implicit-templates |
| @opindex fimplicit-templates |
| Never emit code for non-inline templates that are instantiated |
| implicitly (i.e.@: by use); only emit code for explicit instantiations. |
| If you use this option, you must take care to structure your code to |
| include all the necessary explicit instantiations to avoid getting |
| undefined symbols at link time. |
| @xref{Template Instantiation}, for more information. |
| |
| @item -fno-implicit-inline-templates |
| @opindex fno-implicit-inline-templates |
| @opindex fimplicit-inline-templates |
| Don't emit code for implicit instantiations of inline templates, either. |
| The default is to handle inlines differently so that compiles with and |
| without optimization need the same set of explicit instantiations. |
| |
| @item -fno-implement-inlines |
| @opindex fno-implement-inlines |
| @opindex fimplement-inlines |
| To save space, do not emit out-of-line copies of inline functions |
| controlled by @code{#pragma implementation}. This causes linker |
| errors if these functions are not inlined everywhere they are called. |
| |
| @item -fmodules-ts |
| @itemx -fno-modules-ts |
| @opindex fmodules-ts |
| @opindex fno-modules-ts |
| Enable support for C++20 modules (@pxref{C++ Modules}). The |
| @option{-fno-modules-ts} is usually not needed, as that is the |
| default. Even though this is a C++20 feature, it is not currently |
| implicitly enabled by selecting that standard version. |
| |
| @item -fmodule-header |
| @itemx -fmodule-header=user |
| @itemx -fmodule-header=system |
| @opindex fmodule-header |
| Compile a header file to create an importable header unit. |
| |
| @item -fmodule-implicit-inline |
| @opindex fmodule-implicit-inline |
| Member functions defined in their class definitions are not implicitly |
| inline for modular code. This is different to traditional C++ |
| behavior, for good reasons. However, it may result in a difficulty |
| during code porting. This option makes such function definitions |
| implicitly inline. It does however generate an ABI incompatibility, |
| so you must use it everywhere or nowhere. (Such definitions outside |
| of a named module remain implicitly inline, regardless.) |
| |
| @item -fno-module-lazy |
| @opindex fno-module-lazy |
| @opindex fmodule-lazy |
| Disable lazy module importing and module mapper creation. |
| |
| @item -fmodule-mapper=@r{[}@var{hostname}@r{]}:@var{port}@r{[}?@var{ident}@r{]} |
| @itemx -fmodule-mapper=|@var{program}@r{[}?@var{ident}@r{]} @var{args...} |
| @itemx -fmodule-mapper==@var{socket}@r{[}?@var{ident}@r{]} |
| @itemx -fmodule-mapper=<>@r{[}@var{inout}@r{]}@r{[}?@var{ident}@r{]} |
| @itemx -fmodule-mapper=<@var{in}>@var{out}@r{[}?@var{ident}@r{]} |
| @itemx -fmodule-mapper=@var{file}@r{[}?@var{ident}@r{]} |
| @vindex CXX_MODULE_MAPPER @r{environment variable} |
| @opindex fmodule-mapper |
| An oracle to query for module name to filename mappings. If |
| unspecified the @env{CXX_MODULE_MAPPER} environment variable is used, |
| and if that is unset, an in-process default is provided. |
| |
| @item -fmodule-only |
| @opindex fmodule-only |
| Only emit the Compiled Module Interface, inhibiting any object file. |
| |
| @item -fms-extensions |
| @opindex fms-extensions |
| Disable Wpedantic warnings about constructs used in MFC, such as implicit |
| int and getting a pointer to member function via non-standard syntax. |
| |
| @item -fnew-inheriting-ctors |
| @opindex fnew-inheriting-ctors |
| Enable the P0136 adjustment to the semantics of C++11 constructor |
| inheritance. This is part of C++17 but also considered to be a Defect |
| Report against C++11 and C++14. This flag is enabled by default |
| unless @option{-fabi-version=10} or lower is specified. |
| |
| @item -fnew-ttp-matching |
| @opindex fnew-ttp-matching |
| Enable the P0522 resolution to Core issue 150, template template |
| parameters and default arguments: this allows a template with default |
| template arguments as an argument for a template template parameter |
| with fewer template parameters. This flag is enabled by default for |
| @option{-std=c++17}. |
| |
| @item -fno-nonansi-builtins |
| @opindex fno-nonansi-builtins |
| @opindex fnonansi-builtins |
| Disable built-in declarations of functions that are not mandated by |
| ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit}, |
| @code{index}, @code{bzero}, @code{conjf}, and other related functions. |
| |
| @item -fnothrow-opt |
| @opindex fnothrow-opt |
| Treat a @code{throw()} exception specification as if it were a |
| @code{noexcept} specification to reduce or eliminate the text size |
| overhead relative to a function with no exception specification. If |
| the function has local variables of types with non-trivial |
| destructors, the exception specification actually makes the |
| function smaller because the EH cleanups for those variables can be |
| optimized away. The semantic effect is that an exception thrown out of |
| a function with such an exception specification results in a call |
| to @code{terminate} rather than @code{unexpected}. |
| |
| @item -fno-operator-names |
| @opindex fno-operator-names |
| @opindex foperator-names |
| Do not treat the operator name keywords @code{and}, @code{bitand}, |
| @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as |
| synonyms as keywords. |
| |
| @item -fno-optional-diags |
| @opindex fno-optional-diags |
| @opindex foptional-diags |
| Disable diagnostics that the standard says a compiler does not need to |
| issue. Currently, the only such diagnostic issued by G++ is the one for |
| a name having multiple meanings within a class. |
| |
| @item -fpermissive |
| @opindex fpermissive |
| Downgrade some diagnostics about nonconformant code from errors to |
| warnings. Thus, using @option{-fpermissive} allows some |
| nonconforming code to compile. |
| |
| @item -fno-pretty-templates |
| @opindex fno-pretty-templates |
| @opindex fpretty-templates |
| When an error message refers to a specialization of a function |
| template, the compiler normally prints the signature of the |
| template followed by the template arguments and any typedefs or |
| typenames in the signature (e.g.@: @code{void f(T) [with T = int]} |
| rather than @code{void f(int)}) so that it's clear which template is |
| involved. When an error message refers to a specialization of a class |
| template, the compiler omits any template arguments that match |
| the default template arguments for that template. If either of these |
| behaviors make it harder to understand the error message rather than |
| easier, you can use @option{-fno-pretty-templates} to disable them. |
| |
| @item -fno-rtti |
| @opindex fno-rtti |
| @opindex frtti |
| Disable generation of information about every class with virtual |
| functions for use by the C++ run-time type identification features |
| (@code{dynamic_cast} and @code{typeid}). If you don't use those parts |
| of the language, you can save some space by using this flag. Note that |
| exception handling uses the same information, but G++ generates it as |
| needed. The @code{dynamic_cast} operator can still be used for casts that |
| do not require run-time type information, i.e.@: casts to @code{void *} or to |
| unambiguous base classes. |
| |
| Mixing code compiled with @option{-frtti} with that compiled with |
| @option{-fno-rtti} may not work. For example, programs may |
| fail to link if a class compiled with @option{-fno-rtti} is used as a base |
| for a class compiled with @option{-frtti}. |
| |
| @item -fsized-deallocation |
| @opindex fsized-deallocation |
| Enable the built-in global declarations |
| @smallexample |
| void operator delete (void *, std::size_t) noexcept; |
| void operator delete[] (void *, std::size_t) noexcept; |
| @end smallexample |
| as introduced in C++14. This is useful for user-defined replacement |
| deallocation functions that, for example, use the size of the object |
| to make deallocation faster. Enabled by default under |
| @option{-std=c++14} and above. The flag @option{-Wsized-deallocation} |
| warns about places that might want to add a definition. |
| |
| @item -fstrict-enums |
| @opindex fstrict-enums |
| Allow the compiler to optimize using the assumption that a value of |
| enumerated type can only be one of the values of the enumeration (as |
| defined in the C++ standard; basically, a value that can be |
| represented in the minimum number of bits needed to represent all the |
| enumerators). This assumption may not be valid if the program uses a |
| cast to convert an arbitrary integer value to the enumerated type. |
| |
| @item -fstrong-eval-order |
| @opindex fstrong-eval-order |
| Evaluate member access, array subscripting, and shift expressions in |
| left-to-right order, and evaluate assignment in right-to-left order, |
| as adopted for C++17. Enabled by default with @option{-std=c++17}. |
| @option{-fstrong-eval-order=some} enables just the ordering of member |
| access and shift expressions, and is the default without |
| @option{-std=c++17}. |
| |
| @item -ftemplate-backtrace-limit=@var{n} |
| @opindex ftemplate-backtrace-limit |
| Set the maximum number of template instantiation notes for a single |
| warning or error to @var{n}. The default value is 10. |
| |
| @item -ftemplate-depth=@var{n} |
| @opindex ftemplate-depth |
| Set the maximum instantiation depth for template classes to @var{n}. |
| A limit on the template instantiation depth is needed to detect |
| endless recursions during template class instantiation. ANSI/ISO C++ |
| conforming programs must not rely on a maximum depth greater than 17 |
| (changed to 1024 in C++11). The default value is 900, as the compiler |
| can run out of stack space before hitting 1024 in some situations. |
| |
| @item -fno-threadsafe-statics |
| @opindex fno-threadsafe-statics |
| @opindex fthreadsafe-statics |
| Do not emit the extra code to use the routines specified in the C++ |
| ABI for thread-safe initialization of local statics. You can use this |
| option to reduce code size slightly in code that doesn't need to be |
| thread-safe. |
| |
| @item -fuse-cxa-atexit |
| @opindex fuse-cxa-atexit |
| Register destructors for objects with static storage duration with the |
| @code{__cxa_atexit} function rather than the @code{atexit} function. |
| This option is required for fully standards-compliant handling of static |
| destructors, but only works if your C library supports |
| @code{__cxa_atexit}. |
| |
| @item -fno-use-cxa-get-exception-ptr |
| @opindex fno-use-cxa-get-exception-ptr |
| @opindex fuse-cxa-get-exception-ptr |
| Don't use the @code{__cxa_get_exception_ptr} runtime routine. This |
| causes @code{std::uncaught_exception} to be incorrect, but is necessary |
| if the runtime routine is not available. |
| |
| @item -fvisibility-inlines-hidden |
| @opindex fvisibility-inlines-hidden |
| This switch declares that the user does not attempt to compare |
| pointers to inline functions or methods where the addresses of the two functions |
| are taken in different shared objects. |
| |
| The effect of this is that GCC may, effectively, mark inline methods with |
| @code{__attribute__ ((visibility ("hidden")))} so that they do not |
| appear in the export table of a DSO and do not require a PLT indirection |
| when used within the DSO@. Enabling this option can have a dramatic effect |
| on load and link times of a DSO as it massively reduces the size of the |
| dynamic export table when the library makes heavy use of templates. |
| |
| The behavior of this switch is not quite the same as marking the |
| methods as hidden directly, because it does not affect static variables |
| local to the function or cause the compiler to deduce that |
| the function is defined in only one shared object. |
| |
| You may mark a method as having a visibility explicitly to negate the |
| effect of the switch for that method. For example, if you do want to |
| compare pointers to a particular inline method, you might mark it as |
| having default visibility. Marking the enclosing class with explicit |
| visibility has no effect. |
| |
| Explicitly instantiated inline methods are unaffected by this option |
| as their linkage might otherwise cross a shared library boundary. |
| @xref{Template Instantiation}. |
| |
| @item -fvisibility-ms-compat |
| @opindex fvisibility-ms-compat |
| This flag attempts to use visibility settings to make GCC's C++ |
| linkage model compatible with that of Microsoft Visual Studio. |
| |
| The flag makes these changes to GCC's linkage model: |
| |
| @enumerate |
| @item |
| It sets the default visibility to @code{hidden}, like |
| @option{-fvisibility=hidden}. |
| |
| @item |
| Types, but not their members, are not hidden by default. |
| |
| @item |
| The One Definition Rule is relaxed for types without explicit |
| visibility specifications that are defined in more than one |
| shared object: those declarations are permitted if they are |
| permitted when this option is not used. |
| @end enumerate |
| |
| In new code it is better to use @option{-fvisibility=hidden} and |
| export those classes that are intended to be externally visible. |
| Unfortunately it is possible for code to rely, perhaps accidentally, |
| on the Visual Studio behavior. |
| |
| Among the consequences of these changes are that static data members |
| of the same type with the same name but defined in different shared |
| objects are different, so changing one does not change the other; |
| and that pointers to function members defined in different shared |
| objects may not compare equal. When this flag is given, it is a |
| violation of the ODR to define types with the same name differently. |
| |
| @item -fno-weak |
| @opindex fno-weak |
| @opindex fweak |
| Do not use weak symbol support, even if it is provided by the linker. |
| By default, G++ uses weak symbols if they are available. This |
| option exists only for testing, and should not be used by end-users; |
| it results in inferior code and has no benefits. This option may |
| be removed in a future release of G++. |
| |
| @item -fext-numeric-literals @r{(C++ and Objective-C++ only)} |
| @opindex fext-numeric-literals |
| @opindex fno-ext-numeric-literals |
| Accept imaginary, fixed-point, or machine-defined |
| literal number suffixes as GNU extensions. |
| When this option is turned off these suffixes are treated |
| as C++11 user-defined literal numeric suffixes. |
| This is on by default for all pre-C++11 dialects and all GNU dialects: |
| @option{-std=c++98}, @option{-std=gnu++98}, @option{-std=gnu++11}, |
| @option{-std=gnu++14}. |
| This option is off by default |
| for ISO C++11 onwards (@option{-std=c++11}, ...). |
| |
| @item -nostdinc++ |
| @opindex nostdinc++ |
| Do not search for header files in the standard directories specific to |
| C++, but do still search the other standard directories. (This option |
| is used when building the C++ library.) |
| |
| @item -flang-info-include-translate |
| @itemx -flang-info-include-translate-not |
| @itemx -flang-info-include-translate=@var{header} |
| @opindex flang-info-include-translate |
| @opindex flang-info-include-translate-not |
| Inform of include translation events. The first will note accepted |
| include translations, the second will note declined include |
| translations. The @var{header} form will inform of include |
| translations relating to that specific header. If @var{header} is of |
| the form @code{"user"} or @code{<system>} it will be resolved to a |
| specific user or system header using the include path. |
| |
| @item -flang-info-module-cmi |
| @itemx -flang-info-module-cmi=@var{module} |
| @opindex flang-info-module-cmi |
| Inform of Compiled Module Interface pathnames. The first will note |
| all read CMI pathnames. The @var{module} form will not reading a |
| specific module's CMI. @var{module} may be a named module or a |
| header-unit (the latter indicated by either being a pathname containing |
| directory separators or enclosed in @code{<>} or @code{""}). |
| |
| @item -stdlib=@var{libstdc++,libc++} |
| @opindex stdlib |
| When G++ is configured to support this option, it allows specification of |
| alternate C++ runtime libraries. Two options are available: @var{libstdc++} |
| (the default, native C++ runtime for G++) and @var{libc++} which is the |
| C++ runtime installed on some operating systems (e.g. Darwin versions from |
| Darwin11 onwards). The option switches G++ to use the headers from the |
| specified library and to emit @code{-lstdc++} or @code{-lc++} respectively, |
| when a C++ runtime is required for linking. |
| @end table |
| |
| In addition, these warning options have meanings only for C++ programs: |
| |
| @table @gcctabopt |
| @item -Wabi-tag @r{(C++ and Objective-C++ only)} |
| @opindex Wabi-tag |
| Warn when a type with an ABI tag is used in a context that does not |
| have that ABI tag. See @ref{C++ Attributes} for more information |
| about ABI tags. |
| |
| @item -Wcomma-subscript @r{(C++ and Objective-C++ only)} |
| @opindex Wcomma-subscript |
| @opindex Wno-comma-subscript |
| Warn about uses of a comma expression within a subscripting expression. |
| This usage was deprecated in C++20 and is going to be removed in C++23. |
| However, a comma expression wrapped in @code{( )} is not deprecated. Example: |
| |
| @smallexample |
| @group |
| void f(int *a, int b, int c) @{ |
| a[b,c]; // deprecated in C++20, invalid in C++23 |
| a[(b,c)]; // OK |
| @} |
| @end group |
| @end smallexample |
| |
| In C++23 it is valid to have comma separated expressions in a subscript |
| when an overloaded subscript operator is found and supports the right |
| number and types of arguments. G++ will accept the formerly valid syntax |
| for code that is not valid in C++23 but used to be valid but deprecated |
| in C++20 with a pedantic warning that can be disabled with |
| @option{-Wno-comma-subscript}. |
| |
| Enabled by default with @option{-std=c++20} unless @option{-Wno-deprecated}, |
| and with @option{-std=c++23} regardless of @option{-Wno-deprecated}. |
| |
| @item -Wctad-maybe-unsupported @r{(C++ and Objective-C++ only)} |
| @opindex Wctad-maybe-unsupported |
| @opindex Wno-ctad-maybe-unsupported |
| Warn when performing class template argument deduction (CTAD) on a type with |
| no explicitly written deduction guides. This warning will point out cases |
| where CTAD succeeded only because the compiler synthesized the implicit |
| deduction guides, which might not be what the programmer intended. Certain |
| style guides allow CTAD only on types that specifically "opt-in"; i.e., on |
| types that are designed to support CTAD. This warning can be suppressed with |
| the following pattern: |
| |
| @smallexample |
| struct allow_ctad_t; // any name works |
| template <typename T> struct S @{ |
| S(T) @{ @} |
| @}; |
| S(allow_ctad_t) -> S<void>; // guide with incomplete parameter type will never be considered |
| @end smallexample |
| |
| @item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)} |
| @opindex Wctor-dtor-privacy |
| @opindex Wno-ctor-dtor-privacy |
| Warn when a class seems unusable because all the constructors or |
| destructors in that class are private, and it has neither friends nor |
| public static member functions. Also warn if there are no non-private |
| methods, and there's at least one private member function that isn't |
| a constructor or destructor. |
| |
| @item -Wdelete-non-virtual-dtor @r{(C++ and Objective-C++ only)} |
| @opindex Wdelete-non-virtual-dtor |
| @opindex Wno-delete-non-virtual-dtor |
| Warn when @code{delete} is used to destroy an instance of a class that |
| has virtual functions and non-virtual destructor. It is unsafe to delete |
| an instance of a derived class through a pointer to a base class if the |
| base class does not have a virtual destructor. This warning is enabled |
| by @option{-Wall}. |
| |
| @item -Wdeprecated-copy @r{(C++ and Objective-C++ only)} |
| @opindex Wdeprecated-copy |
| @opindex Wno-deprecated-copy |
| Warn that the implicit declaration of a copy constructor or copy |
| assignment operator is deprecated if the class has a user-provided |
| copy constructor or copy assignment operator, in C++11 and up. This |
| warning is enabled by @option{-Wextra}. With |
| @option{-Wdeprecated-copy-dtor}, also deprecate if the class has a |
| user-provided destructor. |
| |
| @item -Wno-deprecated-enum-enum-conversion @r{(C++ and Objective-C++ only)} |
| @opindex Wdeprecated-enum-enum-conversion |
| @opindex Wno-deprecated-enum-enum-conversion |
| Disable the warning about the case when the usual arithmetic conversions |
| are applied on operands where one is of enumeration type and the other is |
| of a different enumeration type. This conversion was deprecated in C++20. |
| For example: |
| |
| @smallexample |
| enum E1 @{ e @}; |
| enum E2 @{ f @}; |
| int k = f - e; |
| @end smallexample |
| |
| @option{-Wdeprecated-enum-enum-conversion} is enabled by default with |
| @option{-std=c++20}. In pre-C++20 dialects, this warning can be enabled |
| by @option{-Wenum-conversion}. |
| |
| @item -Wno-deprecated-enum-float-conversion @r{(C++ and Objective-C++ only)} |
| @opindex Wdeprecated-enum-float-conversion |
| @opindex Wno-deprecated-enum-float-conversion |
| Disable the warning about the case when the usual arithmetic conversions |
| are applied on operands where one is of enumeration type and the other is |
| of a floating-point type. This conversion was deprecated in C++20. For |
| example: |
| |
| @smallexample |
| enum E1 @{ e @}; |
| enum E2 @{ f @}; |
| bool b = e <= 3.7; |
| @end smallexample |
| |
| @option{-Wdeprecated-enum-float-conversion} is enabled by default with |
| @option{-std=c++20}. In pre-C++20 dialects, this warning can be enabled |
| by @option{-Wenum-conversion}. |
| |
| @item -Wno-init-list-lifetime @r{(C++ and Objective-C++ only)} |
| @opindex Winit-list-lifetime |
| @opindex Wno-init-list-lifetime |
| Do not warn about uses of @code{std::initializer_list} that are likely |
| to result in dangling pointers. Since the underlying array for an |
| @code{initializer_list} is handled like a normal C++ temporary object, |
| it is easy to inadvertently keep a pointer to the array past the end |
| of the array's lifetime. For example: |
| |
| @itemize @bullet |
| @item |
| If a function returns a temporary @code{initializer_list}, or a local |
| @code{initializer_list} variable, the array's lifetime ends at the end |
| of the return statement, so the value returned has a dangling pointer. |
| |
| @item |
| If a new-expression creates an @code{initializer_list}, the array only |
| lives until the end of the enclosing full-expression, so the |
| @code{initializer_list} in the heap has a dangling pointer. |
| |
| @item |
| When an @code{initializer_list} variable is assigned from a |
| brace-enclosed initializer list, the temporary array created for the |
| right side of the assignment only lives until the end of the |
| full-expression, so at the next statement the @code{initializer_list} |
| variable has a dangling pointer. |
| |
| @smallexample |
| // li's initial underlying array lives as long as li |
| std::initializer_list<int> li = @{ 1,2,3 @}; |
| // assignment changes li to point to a temporary array |
| li = @{ 4, 5 @}; |
| // now the temporary is gone and li has a dangling pointer |
| int i = li.begin()[0] // undefined behavior |
| @end smallexample |
| |
| @item |
| When a list constructor stores the @code{begin} pointer from the |
| @code{initializer_list} argument, this doesn't extend the lifetime of |
| the array, so if a class variable is constructed from a temporary |
| @code{initializer_list}, the pointer is left dangling by the end of |
| the variable declaration statement. |
| |
| @end itemize |
| |
| @item -Winvalid-imported-macros |
| @opindex Winvalid-imported-macros |
| @opindex Wno-invalid-imported-macros |
| Verify all imported macro definitions are valid at the end of |
| compilation. This is not enabled by default, as it requires |
| additional processing to determine. It may be useful when preparing |
| sets of header-units to ensure consistent macros. |
| |
| @item -Wno-literal-suffix @r{(C++ and Objective-C++ only)} |
| @opindex Wliteral-suffix |
| @opindex Wno-literal-suffix |
| Do not warn when a string or character literal is followed by a |
| ud-suffix which does not begin with an underscore. As a conforming |
| extension, GCC treats such suffixes as separate preprocessing tokens |
| in order to maintain backwards compatibility with code that uses |
| formatting macros from @code{<inttypes.h>}. For example: |
| |
| @smallexample |
| #define __STDC_FORMAT_MACROS |
| #include <inttypes.h> |
| #include <stdio.h> |
| |
| int main() @{ |
| int64_t i64 = 123; |
| printf("My int64: %" PRId64"\n", i64); |
| @} |
| @end smallexample |
| |
| In this case, @code{PRId64} is treated as a separate preprocessing token. |
| |
| This option also controls warnings when a user-defined literal |
| operator is declared with a literal suffix identifier that doesn't |
| begin with an underscore. Literal suffix identifiers that don't begin |
| with an underscore are reserved for future standardization. |
| |
| These warnings are enabled by default. |
| |
| @item -Wno-narrowing @r{(C++ and Objective-C++ only)} |
| @opindex Wnarrowing |
| @opindex Wno-narrowing |
| For C++11 and later standards, narrowing conversions are diagnosed by default, |
| as required by the standard. A narrowing conversion from a constant produces |
| an error, and a narrowing conversion from a non-constant produces a warning, |
| but @option{-Wno-narrowing} suppresses the diagnostic. |
| Note that this does not affect the meaning of well-formed code; |
| narrowing conversions are still considered ill-formed in SFINAE contexts. |
| |
| With @option{-Wnarrowing} in C++98, warn when a narrowing |
| conversion prohibited by C++11 occurs within |
| @samp{@{ @}}, e.g. |
| |
| @smallexample |
| int i = @{ 2.2 @}; // error: narrowing from double to int |
| @end smallexample |
| |
| This flag is included in @option{-Wall} and @option{-Wc++11-compat}. |
| |
| @item -Wnoexcept @r{(C++ and Objective-C++ only)} |
| @opindex Wnoexcept |
| @opindex Wno-noexcept |
| Warn when a noexcept-expression evaluates to false because of a call |
| to a function that does not have a non-throwing exception |
| specification (i.e. @code{throw()} or @code{noexcept}) but is known by |
| the compiler to never throw an exception. |
| |
| @item -Wnoexcept-type @r{(C++ and Objective-C++ only)} |
| @opindex Wnoexcept-type |
| @opindex Wno-noexcept-type |
| Warn if the C++17 feature making @code{noexcept} part of a function |
| type changes the mangled name of a symbol relative to C++14. Enabled |
| by @option{-Wabi} and @option{-Wc++17-compat}. |
| |
| As an example: |
| |
| @smallexample |
| template <class T> void f(T t) @{ t(); @}; |
| void g() noexcept; |
| void h() @{ f(g); @} |
| @end smallexample |
| |
| @noindent |
| In C++14, @code{f} calls @code{f<void(*)()>}, but in |
| C++17 it calls @code{f<void(*)()noexcept>}. |
| |
| @item -Wclass-memaccess @r{(C++ and Objective-C++ only)} |
| @opindex Wclass-memaccess |
| @opindex Wno-class-memaccess |
| Warn when the destination of a call to a raw memory function such as |
| @code{memset} or @code{memcpy} is an object of class type, and when writing |
| into such an object might bypass the class non-trivial or deleted constructor |
| or copy assignment, violate const-correctness or encapsulation, or corrupt |
| virtual table pointers. Modifying the representation of such objects may |
| violate invariants maintained by member functions of the class. For example, |
| the call to @code{memset} below is undefined because it modifies a non-trivial |
| class object and is, therefore, diagnosed. The safe way to either initialize |
| or clear the storage of objects of such types is by using the appropriate |
| constructor or assignment operator, if one is available. |
| @smallexample |
| std::string str = "abc"; |
| memset (&str, 0, sizeof str); |
| @end smallexample |
| The @option{-Wclass-memaccess} option is enabled by @option{-Wall}. |
| Explicitly casting the pointer to the class object to @code{void *} or |
| to a type that can be safely accessed by the raw memory function suppresses |
| the warning. |
| |
| @item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)} |
| @opindex Wnon-virtual-dtor |
| @opindex Wno-non-virtual-dtor |
| Warn when a class has virtual functions and an accessible non-virtual |
| destructor itself or in an accessible polymorphic base class, in which |
| case it is possible but unsafe to delete an instance of a derived |
| class through a pointer to the class itself or base class. This |
| warning is automatically enabled if @option{-Weffc++} is specified. |
| |
| @item -Wregister @r{(C++ and Objective-C++ only)} |
| @opindex Wregister |
| @opindex Wno-register |
| Warn on uses of the @code{register} storage class specifier, except |
| when it is part of the GNU @ref{Explicit Register Variables} extension. |
| The use of the @code{register} keyword as storage class specifier has |
| been deprecated in C++11 and removed in C++17. |
| Enabled by default with @option{-std=c++17}. |
| |
| @item -Wreorder @r{(C++ and Objective-C++ only)} |
| @opindex Wreorder |
| @opindex Wno-reorder |
| @cindex reordering, warning |
| @cindex warning for reordering of member initializers |
| Warn when the order of member initializers given in the code does not |
| match the order in which they must be executed. For instance: |
| |
| @smallexample |
| struct A @{ |
| int i; |
| int j; |
| A(): j (0), i (1) @{ @} |
| @}; |
| @end smallexample |
| |
| @noindent |
| The compiler rearranges the member initializers for @code{i} |
| and @code{j} to match the declaration order of the members, emitting |
| a warning to that effect. This warning is enabled by @option{-Wall}. |
| |
| @item -Wno-pessimizing-move @r{(C++ and Objective-C++ only)} |
| @opindex Wpessimizing-move |
| @opindex Wno-pessimizing-move |
| This warning warns when a call to @code{std::move} prevents copy |
| elision. A typical scenario when copy elision can occur is when returning in |
| a function with a class return type, when the expression being returned is the |
| name of a non-volatile automatic object, and is not a function parameter, and |
| has the same type as the function return type. |
| |
| @smallexample |
| struct T @{ |
| @dots{} |
| @}; |
| T fn() |
| @{ |
| T t; |
| @dots{} |
| return std::move (t); |
| @} |
| @end smallexample |
| |
| But in this example, the @code{std::move} call prevents copy elision. |
| |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wno-redundant-move @r{(C++ and Objective-C++ only)} |
| @opindex Wredundant-move |
| @opindex Wno-redundant-move |
| This warning warns about redundant calls to @code{std::move}; that is, when |
| a move operation would have been performed even without the @code{std::move} |
| call. This happens because the compiler is forced to treat the object as if |
| it were an rvalue in certain situations such as returning a local variable, |
| where copy elision isn't applicable. Consider: |
| |
| @smallexample |
| struct T @{ |
| @dots{} |
| @}; |
| T fn(T t) |
| @{ |
| @dots{} |
| return std::move (t); |
| @} |
| @end smallexample |
| |
| Here, the @code{std::move} call is redundant. Because G++ implements Core |
| Issue 1579, another example is: |
| |
| @smallexample |
| struct T @{ // convertible to U |
| @dots{} |
| @}; |
| struct U @{ |
| @dots{} |
| @}; |
| U fn() |
| @{ |
| T t; |
| @dots{} |
| return std::move (t); |
| @} |
| @end smallexample |
| In this example, copy elision isn't applicable because the type of the |
| expression being returned and the function return type differ, yet G++ |
| treats the return value as if it were designated by an rvalue. |
| |
| This warning is enabled by @option{-Wextra}. |
| |
| @item -Wrange-loop-construct @r{(C++ and Objective-C++ only)} |
| @opindex Wrange-loop-construct |
| @opindex Wno-range-loop-construct |
| This warning warns when a C++ range-based for-loop is creating an unnecessary |
| copy. This can happen when the range declaration is not a reference, but |
| probably should be. For example: |
| |
| @smallexample |
| struct S @{ char arr[128]; @}; |
| void fn () @{ |
| S arr[5]; |
| for (const auto x : arr) @{ @dots{} @} |
| @} |
| @end smallexample |
| |
| It does not warn when the type being copied is a trivially-copyable type whose |
| size is less than 64 bytes. |
| |
| This warning also warns when a loop variable in a range-based for-loop is |
| initialized with a value of a different type resulting in a copy. For example: |
| |
| @smallexample |
| void fn() @{ |
| int arr[10]; |
| for (const double &x : arr) @{ @dots{} @} |
| @} |
| @end smallexample |
| |
| In the example above, in every iteration of the loop a temporary value of |
| type @code{double} is created and destroyed, to which the reference |
| @code{const double &} is bound. |
| |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wredundant-tags @r{(C++ and Objective-C++ only)} |
| @opindex Wredundant-tags |
| @opindex Wno-redundant-tags |
| Warn about redundant class-key and enum-key in references to class types |
| and enumerated types in contexts where the key can be eliminated without |
| causing an ambiguity. For example: |
| |
| @smallexample |
| struct foo; |
| struct foo *p; // warn that keyword struct can be eliminated |
| @end smallexample |
| |
| @noindent |
| On the other hand, in this example there is no warning: |
| |
| @smallexample |
| struct foo; |
| void foo (); // "hides" struct foo |
| void bar (struct foo&); // no warning, keyword struct is necessary |
| @end smallexample |
| |
| @item -Wno-subobject-linkage @r{(C++ and Objective-C++ only)} |
| @opindex Wsubobject-linkage |
| @opindex Wno-subobject-linkage |
| Do not warn |
| if a class type has a base or a field whose type uses the anonymous |
| namespace or depends on a type with no linkage. If a type A depends on |
| a type B with no or internal linkage, defining it in multiple |
| translation units would be an ODR violation because the meaning of B |
| is different in each translation unit. If A only appears in a single |
| translation unit, the best way to silence the warning is to give it |
| internal linkage by putting it in an anonymous namespace as well. The |
| compiler doesn't give this warning for types defined in the main .C |
| file, as those are unlikely to have multiple definitions. |
| @option{-Wsubobject-linkage} is enabled by default. |
| |
| @item -Weffc++ @r{(C++ and Objective-C++ only)} |
| @opindex Weffc++ |
| @opindex Wno-effc++ |
| Warn about violations of the following style guidelines from Scott Meyers' |
| @cite{Effective C++} series of books: |
| |
| @itemize @bullet |
| @item |
| Define a copy constructor and an assignment operator for classes |
| with dynamically-allocated memory. |
| |
| @item |
| Prefer initialization to assignment in constructors. |
| |
| @item |
| Have @code{operator=} return a reference to @code{*this}. |
| |
| @item |
| Don't try to return a reference when you must return an object. |
| |
| @item |
| Distinguish between prefix and postfix forms of increment and |
| decrement operators. |
| |
| @item |
| Never overload @code{&&}, @code{||}, or @code{,}. |
| |
| @end itemize |
| |
| This option also enables @option{-Wnon-virtual-dtor}, which is also |
| one of the effective C++ recommendations. However, the check is |
| extended to warn about the lack of virtual destructor in accessible |
| non-polymorphic bases classes too. |
| |
| When selecting this option, be aware that the standard library |
| headers do not obey all of these guidelines; use @samp{grep -v} |
| to filter out those warnings. |
| |
| @item -Wno-exceptions @r{(C++ and Objective-C++ only)} |
| @opindex Wexceptions |
| @opindex Wno-exceptions |
| Disable the warning about the case when an exception handler is shadowed by |
| another handler, which can point out a wrong ordering of exception handlers. |
| |
| @item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)} |
| @opindex Wstrict-null-sentinel |
| @opindex Wno-strict-null-sentinel |
| Warn about the use of an uncasted @code{NULL} as sentinel. When |
| compiling only with GCC this is a valid sentinel, as @code{NULL} is defined |
| to @code{__null}. Although it is a null pointer constant rather than a |
| null pointer, it is guaranteed to be of the same size as a pointer. |
| But this use is not portable across different compilers. |
| |
| @item -Wno-non-template-friend @r{(C++ and Objective-C++ only)} |
| @opindex Wno-non-template-friend |
| @opindex Wnon-template-friend |
| Disable warnings when non-template friend functions are declared |
| within a template. In very old versions of GCC that predate implementation |
| of the ISO standard, declarations such as |
| @samp{friend int foo(int)}, where the name of the friend is an unqualified-id, |
| could be interpreted as a particular specialization of a template |
| function; the warning exists to diagnose compatibility problems, |
| and is enabled by default. |
| |
| @item -Wold-style-cast @r{(C++ and Objective-C++ only)} |
| @opindex Wold-style-cast |
| @opindex Wno-old-style-cast |
| Warn if an old-style (C-style) cast to a non-void type is used within |
| a C++ program. The new-style casts (@code{dynamic_cast}, |
| @code{static_cast}, @code{reinterpret_cast}, and @code{const_cast}) are |
| less vulnerable to unintended effects and much easier to search for. |
| |
| @item -Woverloaded-virtual @r{(C++ and Objective-C++ only)} |
| @opindex Woverloaded-virtual |
| @opindex Wno-overloaded-virtual |
| @cindex overloaded virtual function, warning |
| @cindex warning for overloaded virtual function |
| Warn when a function declaration hides virtual functions from a |
| base class. For example, in: |
| |
| @smallexample |
| struct A @{ |
| virtual void f(); |
| @}; |
| |
| struct B: public A @{ |
| void f(int); |
| @}; |
| @end smallexample |
| |
| the @code{A} class version of @code{f} is hidden in @code{B}, and code |
| like: |
| |
| @smallexample |
| B* b; |
| b->f(); |
| @end smallexample |
| |
| @noindent |
| fails to compile. |
| |
| @item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)} |
| @opindex Wno-pmf-conversions |
| @opindex Wpmf-conversions |
| Disable the diagnostic for converting a bound pointer to member function |
| to a plain pointer. |
| |
| @item -Wsign-promo @r{(C++ and Objective-C++ only)} |
| @opindex Wsign-promo |
| @opindex Wno-sign-promo |
| Warn when overload resolution chooses a promotion from unsigned or |
| enumerated type to a signed type, over a conversion to an unsigned type of |
| the same size. Previous versions of G++ tried to preserve |
| unsignedness, but the standard mandates the current behavior. |
| |
| @item -Wtemplates @r{(C++ and Objective-C++ only)} |
| @opindex Wtemplates |
| @opindex Wno-templates |
| Warn when a primary template declaration is encountered. Some coding |
| rules disallow templates, and this may be used to enforce that rule. |
| The warning is inactive inside a system header file, such as the STL, so |
| one can still use the STL. One may also instantiate or specialize |
| templates. |
| |
| @item -Wmismatched-new-delete @r{(C++ and Objective-C++ only)} |
| @opindex Wmismatched-new-delete |
| @opindex Wno-mismatched-new-delete |
| Warn for mismatches between calls to @code{operator new} or @code{operator |
| delete} and the corresponding call to the allocation or deallocation function. |
| This includes invocations of C++ @code{operator delete} with pointers |
| returned from either mismatched forms of @code{operator new}, or from other |
| functions that allocate objects for which the @code{operator delete} isn't |
| a suitable deallocator, as well as calls to other deallocation functions |
| with pointers returned from @code{operator new} for which the deallocation |
| function isn't suitable. |
| |
| For example, the @code{delete} expression in the function below is diagnosed |
| because it doesn't match the array form of the @code{new} expression |
| the pointer argument was returned from. Similarly, the call to @code{free} |
| is also diagnosed. |
| |
| @smallexample |
| void f () |
| @{ |
| int *a = new int[n]; |
| delete a; // warning: mismatch in array forms of expressions |
| |
| char *p = new char[n]; |
| free (p); // warning: mismatch between new and free |
| @} |
| @end smallexample |
| |
| The related option @option{-Wmismatched-dealloc} diagnoses mismatches |
| involving allocation and deallocation functions other than @code{operator |
| new} and @code{operator delete}. |
| |
| @option{-Wmismatched-new-delete} is included in @option{-Wall}. |
| |
| @item -Wmismatched-tags @r{(C++ and Objective-C++ only)} |
| @opindex Wmismatched-tags |
| @opindex Wno-mismatched-tags |
| Warn for declarations of structs, classes, and class templates and their |
| specializations with a class-key that does not match either the definition |
| or the first declaration if no definition is provided. |
| |
| For example, the declaration of @code{struct Object} in the argument list |
| of @code{draw} triggers the warning. To avoid it, either remove the redundant |
| class-key @code{struct} or replace it with @code{class} to match its definition. |
| @smallexample |
| class Object @{ |
| public: |
| virtual ~Object () = 0; |
| @}; |
| void draw (struct Object*); |
| @end smallexample |
| |
| It is not wrong to declare a class with the class-key @code{struct} as |
| the example above shows. The @option{-Wmismatched-tags} option is intended |
| to help achieve a consistent style of class declarations. In code that is |
| intended to be portable to Windows-based compilers the warning helps prevent |
| unresolved references due to the difference in the mangling of symbols |
| declared with different class-keys. The option can be used either on its |
| own or in conjunction with @option{-Wredundant-tags}. |
| |
| @item -Wmultiple-inheritance @r{(C++ and Objective-C++ only)} |
| @opindex Wmultiple-inheritance |
| @opindex Wno-multiple-inheritance |
| Warn when a class is defined with multiple direct base classes. Some |
| coding rules disallow multiple inheritance, and this may be used to |
| enforce that rule. The warning is inactive inside a system header file, |
| such as the STL, so one can still use the STL. One may also define |
| classes that indirectly use multiple inheritance. |
| |
| @item -Wvirtual-inheritance |
| @opindex Wvirtual-inheritance |
| @opindex Wno-virtual-inheritance |
| Warn when a class is defined with a virtual direct base class. Some |
| coding rules disallow multiple inheritance, and this may be used to |
| enforce that rule. The warning is inactive inside a system header file, |
| such as the STL, so one can still use the STL. One may also define |
| classes that indirectly use virtual inheritance. |
| |
| @item -Wno-virtual-move-assign |
| @opindex Wvirtual-move-assign |
| @opindex Wno-virtual-move-assign |
| Suppress warnings about inheriting from a virtual base with a |
| non-trivial C++11 move assignment operator. This is dangerous because |
| if the virtual base is reachable along more than one path, it is |
| moved multiple times, which can mean both objects end up in the |
| moved-from state. If the move assignment operator is written to avoid |
| moving from a moved-from object, this warning can be disabled. |
| |
| @item -Wnamespaces |
| @opindex Wnamespaces |
| @opindex Wno-namespaces |
| Warn when a namespace definition is opened. Some coding rules disallow |
| namespaces, and this may be used to enforce that rule. The warning is |
| inactive inside a system header file, such as the STL, so one can still |
| use the STL. One may also use using directives and qualified names. |
| |
| @item -Wno-terminate @r{(C++ and Objective-C++ only)} |
| @opindex Wterminate |
| @opindex Wno-terminate |
| Disable the warning about a throw-expression that will immediately |
| result in a call to @code{terminate}. |
| |
| @item -Wno-vexing-parse @r{(C++ and Objective-C++ only)} |
| @opindex Wvexing-parse |
| @opindex Wno-vexing-parse |
| Warn about the most vexing parse syntactic ambiguity. This warns about |
| the cases when a declaration looks like a variable definition, but the |
| C++ language requires it to be interpreted as a function declaration. |
| For instance: |
| |
| @smallexample |
| void f(double a) @{ |
| int i(); // extern int i (void); |
| int n(int(a)); // extern int n (int); |
| @} |
| @end smallexample |
| |
| Another example: |
| |
| @smallexample |
| struct S @{ S(int); @}; |
| void f(double a) @{ |
| S x(int(a)); // extern struct S x (int); |
| S y(int()); // extern struct S y (int (*) (void)); |
| S z(); // extern struct S z (void); |
| @} |
| @end smallexample |
| |
| The warning will suggest options how to deal with such an ambiguity; e.g., |
| it can suggest removing the parentheses or using braces instead. |
| |
| This warning is enabled by default. |
| |
| @item -Wno-class-conversion @r{(C++ and Objective-C++ only)} |
| @opindex Wno-class-conversion |
| @opindex Wclass-conversion |
| Do not warn when a conversion function converts an |
| object to the same type, to a base class of that type, or to void; such |
| a conversion function will never be called. |
| |
| @item -Wvolatile @r{(C++ and Objective-C++ only)} |
| @opindex Wvolatile |
| @opindex Wno-volatile |
| Warn about deprecated uses of the @code{volatile} qualifier. This includes |
| postfix and prefix @code{++} and @code{--} expressions of |
| @code{volatile}-qualified types, using simple assignments where the left |
| operand is a @code{volatile}-qualified non-class type for their value, |
| compound assignments where the left operand is a @code{volatile}-qualified |
| non-class type, @code{volatile}-qualified function return type, |
| @code{volatile}-qualified parameter type, and structured bindings of a |
| @code{volatile}-qualified type. This usage was deprecated in C++20. |
| |
| Enabled by default with @option{-std=c++20}. |
| |
| @item -Wzero-as-null-pointer-constant @r{(C++ and Objective-C++ only)} |
| @opindex Wzero-as-null-pointer-constant |
| @opindex Wno-zero-as-null-pointer-constant |
| Warn when a literal @samp{0} is used as null pointer constant. This can |
| be useful to facilitate the conversion to @code{nullptr} in C++11. |
| |
| @item -Waligned-new |
| @opindex Waligned-new |
| @opindex Wno-aligned-new |
| Warn about a new-expression of a type that requires greater alignment |
| than the @code{alignof(std::max_align_t)} but uses an allocation |
| function without an explicit alignment parameter. This option is |
| enabled by @option{-Wall}. |
| |
| Normally this only warns about global allocation functions, but |
| @option{-Waligned-new=all} also warns about class member allocation |
| functions. |
| |
| @item -Wno-placement-new |
| @itemx -Wplacement-new=@var{n} |
| @opindex Wplacement-new |
| @opindex Wno-placement-new |
| Warn about placement new expressions with undefined behavior, such as |
| constructing an object in a buffer that is smaller than the type of |
| the object. For example, the placement new expression below is diagnosed |
| because it attempts to construct an array of 64 integers in a buffer only |
| 64 bytes large. |
| @smallexample |
| char buf [64]; |
| new (buf) int[64]; |
| @end smallexample |
| This warning is enabled by default. |
| |
| @table @gcctabopt |
| @item -Wplacement-new=1 |
| This is the default warning level of @option{-Wplacement-new}. At this |
| level the warning is not issued for some strictly undefined constructs that |
| GCC allows as extensions for compatibility with legacy code. For example, |
| the following @code{new} expression is not diagnosed at this level even |
| though it has undefined behavior according to the C++ standard because |
| it writes past the end of the one-element array. |
| @smallexample |
| struct S @{ int n, a[1]; @}; |
| S *s = (S *)malloc (sizeof *s + 31 * sizeof s->a[0]); |
| new (s->a)int [32](); |
| @end smallexample |
| |
| @item -Wplacement-new=2 |
| At this level, in addition to diagnosing all the same constructs as at level |
| 1, a diagnostic is also issued for placement new expressions that construct |
| an object in the last member of structure whose type is an array of a single |
| element and whose size is less than the size of the object being constructed. |
| While the previous example would be diagnosed, the following construct makes |
| use of the flexible member array extension to avoid the warning at level 2. |
| @smallexample |
| struct S @{ int n, a[]; @}; |
| S *s = (S *)malloc (sizeof *s + 32 * sizeof s->a[0]); |
| new (s->a)int [32](); |
| @end smallexample |
| |
| @end table |
| |
| @item -Wcatch-value |
| @itemx -Wcatch-value=@var{n} @r{(C++ and Objective-C++ only)} |
| @opindex Wcatch-value |
| @opindex Wno-catch-value |
| Warn about catch handlers that do not catch via reference. |
| With @option{-Wcatch-value=1} (or @option{-Wcatch-value} for short) |
| warn about polymorphic class types that are caught by value. |
| With @option{-Wcatch-value=2} warn about all class types that are caught |
| by value. With @option{-Wcatch-value=3} warn about all types that are |
| not caught by reference. @option{-Wcatch-value} is enabled by @option{-Wall}. |
| |
| @item -Wconditionally-supported @r{(C++ and Objective-C++ only)} |
| @opindex Wconditionally-supported |
| @opindex Wno-conditionally-supported |
| Warn for conditionally-supported (C++11 [intro.defs]) constructs. |
| |
| @item -Wno-delete-incomplete @r{(C++ and Objective-C++ only)} |
| @opindex Wdelete-incomplete |
| @opindex Wno-delete-incomplete |
| Do not warn when deleting a pointer to incomplete type, which may cause |
| undefined behavior at runtime. This warning is enabled by default. |
| |
| @item -Wextra-semi @r{(C++, Objective-C++ only)} |
| @opindex Wextra-semi |
| @opindex Wno-extra-semi |
| Warn about redundant semicolons after in-class function definitions. |
| |
| @item -Wno-inaccessible-base @r{(C++, Objective-C++ only)} |
| @opindex Winaccessible-base |
| @opindex Wno-inaccessible-base |
| This option controls warnings |
| when a base class is inaccessible in a class derived from it due to |
| ambiguity. The warning is enabled by default. |
| Note that the warning for ambiguous virtual |
| bases is enabled by the @option{-Wextra} option. |
| @smallexample |
| @group |
| struct A @{ int a; @}; |
| |
| struct B : A @{ @}; |
| |
| struct C : B, A @{ @}; |
| @end group |
| @end smallexample |
| |
| @item -Wno-inherited-variadic-ctor |
| @opindex Winherited-variadic-ctor |
| @opindex Wno-inherited-variadic-ctor |
| Suppress warnings about use of C++11 inheriting constructors when the |
| base class inherited from has a C variadic constructor; the warning is |
| on by default because the ellipsis is not inherited. |
| |
| @item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)} |
| @opindex Wno-invalid-offsetof |
| @opindex Winvalid-offsetof |
| Suppress warnings from applying the @code{offsetof} macro to a non-POD |
| type. According to the 2014 ISO C++ standard, applying @code{offsetof} |
| to a non-standard-layout type is undefined. In existing C++ implementations, |
| however, @code{offsetof} typically gives meaningful results. |
| This flag is for users who are aware that they are |
| writing nonportable code and who have deliberately chosen to ignore the |
| warning about it. |
| |
| The restrictions on @code{offsetof} may be relaxed in a future version |
| of the C++ standard. |
| |
| @item -Wsized-deallocation @r{(C++ and Objective-C++ only)} |
| @opindex Wsized-deallocation |
| @opindex Wno-sized-deallocation |
| Warn about a definition of an unsized deallocation function |
| @smallexample |
| void operator delete (void *) noexcept; |
| void operator delete[] (void *) noexcept; |
| @end smallexample |
| without a definition of the corresponding sized deallocation function |
| @smallexample |
| void operator delete (void *, std::size_t) noexcept; |
| void operator delete[] (void *, std::size_t) noexcept; |
| @end smallexample |
| or vice versa. Enabled by @option{-Wextra} along with |
| @option{-fsized-deallocation}. |
| |
| @item -Wsuggest-final-types |
| @opindex Wno-suggest-final-types |
| @opindex Wsuggest-final-types |
| Warn about types with virtual methods where code quality would be improved |
| if the type were declared with the C++11 @code{final} specifier, |
| or, if possible, |
| declared in an anonymous namespace. This allows GCC to more aggressively |
| devirtualize the polymorphic calls. This warning is more effective with |
| link-time optimization, |
| where the information about the class hierarchy graph is |
| more complete. |
| |
| @item -Wsuggest-final-methods |
| @opindex Wno-suggest-final-methods |
| @opindex Wsuggest-final-methods |
| Warn about virtual methods where code quality would be improved if the method |
| were declared with the C++11 @code{final} specifier, |
| or, if possible, its type were |
| declared in an anonymous namespace or with the @code{final} specifier. |
| This warning is |
| more effective with link-time optimization, where the information about the |
| class hierarchy graph is more complete. It is recommended to first consider |
| suggestions of @option{-Wsuggest-final-types} and then rebuild with new |
| annotations. |
| |
| @item -Wsuggest-override |
| @opindex Wsuggest-override |
| @opindex Wno-suggest-override |
| Warn about overriding virtual functions that are not marked with the |
| @code{override} keyword. |
| |
| @item -Wuse-after-free |
| @itemx -Wuse-after-free=@var{n} |
| @opindex Wuse-after-free |
| @opindex Wno-use-after-free |
| Warn about uses of pointers to dynamically allocated objects that have |
| been rendered indeterminate by a call to a deallocation function. |
| The warning is enabled at all optimization levels but may yield different |
| results with optimization than without. |
| |
| @table @gcctabopt |
| @item -Wuse-after-free=1 |
| At level 1 the warning attempts to diagnose only unconditional uses |
| of pointers made indeterminate by a deallocation call or a successful |
| call to @code{realloc}, regardless of whether or not the call resulted |
| in an actual reallocatio of memory. This includes double-@code{free} |
| calls as well as uses in arithmetic and relational expressions. Although |
| undefined, uses of indeterminate pointers in equality (or inequality) |
| expressions are not diagnosed at this level. |
| @item -Wuse-after-free=2 |
| At level 2, in addition to unconditional uses, the warning also diagnoses |
| conditional uses of pointers made indeterminate by a deallocation call. |
| As at level 2, uses in equality (or inequality) expressions are not |
| diagnosed. For example, the second call to @code{free} in the following |
| function is diagnosed at this level: |
| @smallexample |
| struct A @{ int refcount; void *data; @}; |
| |
| void release (struct A *p) |
| @{ |
| int refcount = --p->refcount; |
| free (p); |
| if (refcount == 0) |
| free (p->data); // warning: p may be used after free |
| @} |
| @end smallexample |
| @item -Wuse-after-free=3 |
| At level 3, the warning also diagnoses uses of indeterminate pointers in |
| equality expressions. All uses of indeterminate pointers are undefined |
| but equality tests sometimes appear after calls to @code{realloc} as |
| an attempt to determine whether the call resulted in relocating the object |
| to a different address. They are diagnosed at a separate level to aid |
| legacy code gradually transition to safe alternatives. For example, |
| the equality test in the function below is diagnosed at this level: |
| @smallexample |
| void adjust_pointers (int**, int); |
| |
| void grow (int **p, int n) |
| @{ |
| int **q = (int**)realloc (p, n *= 2); |
| if (q == p) |
| return; |
| adjust_pointers ((int**)q, n); |
| @} |
| @end smallexample |
| To avoid the warning at this level, store offsets into allocated memory |
| instead of pointers. This approach obviates needing to adjust the stored |
| pointers after reallocation. |
| @end table |
| |
| @option{-Wuse-after-free=2} is included in @option{-Wall}. |
| |
| @item -Wuseless-cast @r{(C++ and Objective-C++ only)} |
| @opindex Wuseless-cast |
| @opindex Wno-useless-cast |
| Warn when an expression is casted to its own type. |
| |
| @item -Wno-conversion-null @r{(C++ and Objective-C++ only)} |
| @opindex Wconversion-null |
| @opindex Wno-conversion-null |
| Do not warn for conversions between @code{NULL} and non-pointer |
| types. @option{-Wconversion-null} is enabled by default. |
| |
| @end table |
| |
| @node Objective-C and Objective-C++ Dialect Options |
| @section Options Controlling Objective-C and Objective-C++ Dialects |
| |
| @cindex compiler options, Objective-C and Objective-C++ |
| @cindex Objective-C and Objective-C++ options, command-line |
| @cindex options, Objective-C and Objective-C++ |
| (NOTE: This manual does not describe the Objective-C and Objective-C++ |
| languages themselves. @xref{Standards,,Language Standards |
| Supported by GCC}, for references.) |
| |
| This section describes the command-line options that are only meaningful |
| for Objective-C and Objective-C++ programs. You can also use most of |
| the language-independent GNU compiler options. |
| For example, you might compile a file @file{some_class.m} like this: |
| |
| @smallexample |
| gcc -g -fgnu-runtime -O -c some_class.m |
| @end smallexample |
| |
| @noindent |
| In this example, @option{-fgnu-runtime} is an option meant only for |
| Objective-C and Objective-C++ programs; you can use the other options with |
| any language supported by GCC@. |
| |
| Note that since Objective-C is an extension of the C language, Objective-C |
| compilations may also use options specific to the C front-end (e.g., |
| @option{-Wtraditional}). Similarly, Objective-C++ compilations may use |
| C++-specific options (e.g., @option{-Wabi}). |
| |
| Here is a list of options that are @emph{only} for compiling Objective-C |
| and Objective-C++ programs: |
| |
| @table @gcctabopt |
| @item -fconstant-string-class=@var{class-name} |
| @opindex fconstant-string-class |
| Use @var{class-name} as the name of the class to instantiate for each |
| literal string specified with the syntax @code{@@"@dots{}"}. The default |
| class name is @code{NXConstantString} if the GNU runtime is being used, and |
| @code{NSConstantString} if the NeXT runtime is being used (see below). The |
| @option{-fconstant-cfstrings} option, if also present, overrides the |
| @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals |
| to be laid out as constant CoreFoundation strings. |
| |
| @item -fgnu-runtime |
| @opindex fgnu-runtime |
| Generate object code compatible with the standard GNU Objective-C |
| runtime. This is the default for most types of systems. |
| |
| @item -fnext-runtime |
| @opindex fnext-runtime |
| Generate output compatible with the NeXT runtime. This is the default |
| for NeXT-based systems, including Darwin and Mac OS X@. The macro |
| @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is |
| used. |
| |
| @item -fno-nil-receivers |
| @opindex fno-nil-receivers |
| @opindex fnil-receivers |
| Assume that all Objective-C message dispatches (@code{[receiver |
| message:arg]}) in this translation unit ensure that the receiver is |
| not @code{nil}. This allows for more efficient entry points in the |
| runtime to be used. This option is only available in conjunction with |
| the NeXT runtime and ABI version 0 or 1. |
| |
| @item -fobjc-abi-version=@var{n} |
| @opindex fobjc-abi-version |
| Use version @var{n} of the Objective-C ABI for the selected runtime. |
| This option is currently supported only for the NeXT runtime. In that |
| case, Version 0 is the traditional (32-bit) ABI without support for |
| properties and other Objective-C 2.0 additions. Version 1 is the |
| traditional (32-bit) ABI with support for properties and other |
| Objective-C 2.0 additions. Version 2 is the modern (64-bit) ABI. If |
| nothing is specified, the default is Version 0 on 32-bit target |
| machines, and Version 2 on 64-bit target machines. |
| |
| @item -fobjc-call-cxx-cdtors |
| @opindex fobjc-call-cxx-cdtors |
| For each Objective-C class, check if any of its instance variables is a |
| C++ object with a non-trivial default constructor. If so, synthesize a |
| special @code{- (id) .cxx_construct} instance method which runs |
| non-trivial default constructors on any such instance variables, in order, |
| and then return @code{self}. Similarly, check if any instance variable |
| is a C++ object with a non-trivial destructor, and if so, synthesize a |
| special @code{- (void) .cxx_destruct} method which runs |
| all such default destructors, in reverse order. |
| |
| The @code{- (id) .cxx_construct} and @code{- (void) .cxx_destruct} |
| methods thusly generated only operate on instance variables |
| declared in the current Objective-C class, and not those inherited |
| from superclasses. It is the responsibility of the Objective-C |
| runtime to invoke all such methods in an object's inheritance |
| hierarchy. The @code{- (id) .cxx_construct} methods are invoked |
| by the runtime immediately after a new object instance is allocated; |
| the @code{- (void) .cxx_destruct} methods are invoked immediately |
| before the runtime deallocates an object instance. |
| |
| As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has |
| support for invoking the @code{- (id) .cxx_construct} and |
| @code{- (void) .cxx_destruct} methods. |
| |
| @item -fobjc-direct-dispatch |
| @opindex fobjc-direct-dispatch |
| Allow fast jumps to the message dispatcher. On Darwin this is |
| accomplished via the comm page. |
| |
| @item -fobjc-exceptions |
| @opindex fobjc-exceptions |
| Enable syntactic support for structured exception handling in |
| Objective-C, similar to what is offered by C++. This option |
| is required to use the Objective-C keywords @code{@@try}, |
| @code{@@throw}, @code{@@catch}, @code{@@finally} and |
| @code{@@synchronized}. This option is available with both the GNU |
| runtime and the NeXT runtime (but not available in conjunction with |
| the NeXT runtime on Mac OS X 10.2 and earlier). |
| |
| @item -fobjc-gc |
| @opindex fobjc-gc |
| Enable garbage collection (GC) in Objective-C and Objective-C++ |
| programs. This option is only available with the NeXT runtime; the |
| GNU runtime has a different garbage collection implementation that |
| does not require special compiler flags. |
| |
| @item -fobjc-nilcheck |
| @opindex fobjc-nilcheck |
| For the NeXT runtime with version 2 of the ABI, check for a nil |
| receiver in method invocations before doing the actual method call. |
| This is the default and can be disabled using |
| @option{-fno-objc-nilcheck}. Class methods and super calls are never |
| checked for nil in this way no matter what this flag is set to. |
| Currently this flag does nothing when the GNU runtime, or an older |
| version of the NeXT runtime ABI, is used. |
| |
| @item -fobjc-std=objc1 |
| @opindex fobjc-std |
| Conform to the language syntax of Objective-C 1.0, the language |
| recognized by GCC 4.0. This only affects the Objective-C additions to |
| the C/C++ language; it does not affect conformance to C/C++ standards, |
| which is controlled by the separate C/C++ dialect option flags. When |
| this option is used with the Objective-C or Objective-C++ compiler, |
| any Objective-C syntax that is not recognized by GCC 4.0 is rejected. |
| This is useful if you need to make sure that your Objective-C code can |
| be compiled with older versions of GCC@. |
| |
| @item -freplace-objc-classes |
| @opindex freplace-objc-classes |
| Emit a special marker instructing @command{ld(1)} not to statically link in |
| the resulting object file, and allow @command{dyld(1)} to load it in at |
| run time instead. This is used in conjunction with the Fix-and-Continue |
| debugging mode, where the object file in question may be recompiled and |
| dynamically reloaded in the course of program execution, without the need |
| to restart the program itself. Currently, Fix-and-Continue functionality |
| is only available in conjunction with the NeXT runtime on Mac OS X 10.3 |
| and later. |
| |
| @item -fzero-link |
| @opindex fzero-link |
| When compiling for the NeXT runtime, the compiler ordinarily replaces calls |
| to @code{objc_getClass("@dots{}")} (when the name of the class is known at |
| compile time) with static class references that get initialized at load time, |
| which improves run-time performance. Specifying the @option{-fzero-link} flag |
| suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")} |
| to be retained. This is useful in Zero-Link debugging mode, since it allows |
| for individual class implementations to be modified during program execution. |
| The GNU runtime currently always retains calls to @code{objc_get_class("@dots{}")} |
| regardless of command-line options. |
| |
| @item -fno-local-ivars |
| @opindex fno-local-ivars |
| @opindex flocal-ivars |
| By default instance variables in Objective-C can be accessed as if |
| they were local variables from within the methods of the class they're |
| declared in. This can lead to shadowing between instance variables |
| and other variables declared either locally inside a class method or |
| globally with the same name. Specifying the @option{-fno-local-ivars} |
| flag disables this behavior thus avoiding variable shadowing issues. |
| |
| @item -fivar-visibility=@r{[}public@r{|}protected@r{|}private@r{|}package@r{]} |
| @opindex fivar-visibility |
| Set the default instance variable visibility to the specified option |
| so that instance variables declared outside the scope of any access |
| modifier directives default to the specified visibility. |
| |
| @item -gen-decls |
| @opindex gen-decls |
| Dump interface declarations for all classes seen in the source file to a |
| file named @file{@var{sourcename}.decl}. |
| |
| @item -Wassign-intercept @r{(Objective-C and Objective-C++ only)} |
| @opindex Wassign-intercept |
| @opindex Wno-assign-intercept |
| Warn whenever an Objective-C assignment is being intercepted by the |
| garbage collector. |
| |
| @item -Wno-property-assign-default @r{(Objective-C and Objective-C++ only)} |
| @opindex Wproperty-assign-default |
| @opindex Wno-property-assign-default |
| Do not warn if a property for an Objective-C object has no assign |
| semantics specified. |
| |
| @item -Wno-protocol @r{(Objective-C and Objective-C++ only)} |
| @opindex Wno-protocol |
| @opindex Wprotocol |
| If a class is declared to implement a protocol, a warning is issued for |
| every method in the protocol that is not implemented by the class. The |
| default behavior is to issue a warning for every method not explicitly |
| implemented in the class, even if a method implementation is inherited |
| from the superclass. If you use the @option{-Wno-protocol} option, then |
| methods inherited from the superclass are considered to be implemented, |
| and no warning is issued for them. |
| |
| @item -Wobjc-root-class @r{(Objective-C and Objective-C++ only)} |
| @opindex Wobjc-root-class |
| Warn if a class interface lacks a superclass. Most classes will inherit |
| from @code{NSObject} (or @code{Object}) for example. When declaring |
| classes intended to be root classes, the warning can be suppressed by |
| marking their interfaces with @code{__attribute__((objc_root_class))}. |
| |
| @item -Wselector @r{(Objective-C and Objective-C++ only)} |
| @opindex Wselector |
| @opindex Wno-selector |
| Warn if multiple methods of different types for the same selector are |
| found during compilation. The check is performed on the list of methods |
| in the final stage of compilation. Additionally, a check is performed |
| for each selector appearing in a @code{@@selector(@dots{})} |
| expression, and a corresponding method for that selector has been found |
| during compilation. Because these checks scan the method table only at |
| the end of compilation, these warnings are not produced if the final |
| stage of compilation is not reached, for example because an error is |
| found during compilation, or because the @option{-fsyntax-only} option is |
| being used. |
| |
| @item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)} |
| @opindex Wstrict-selector-match |
| @opindex Wno-strict-selector-match |
| Warn if multiple methods with differing argument and/or return types are |
| found for a given selector when attempting to send a message using this |
| selector to a receiver of type @code{id} or @code{Class}. When this flag |
| is off (which is the default behavior), the compiler omits such warnings |
| if any differences found are confined to types that share the same size |
| and alignment. |
| |
| @item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)} |
| @opindex Wundeclared-selector |
| @opindex Wno-undeclared-selector |
| Warn if a @code{@@selector(@dots{})} expression referring to an |
| undeclared selector is found. A selector is considered undeclared if no |
| method with that name has been declared before the |
| @code{@@selector(@dots{})} expression, either explicitly in an |
| @code{@@interface} or @code{@@protocol} declaration, or implicitly in |
| an @code{@@implementation} section. This option always performs its |
| checks as soon as a @code{@@selector(@dots{})} expression is found, |
| while @option{-Wselector} only performs its checks in the final stage of |
| compilation. This also enforces the coding style convention |
| that methods and selectors must be declared before being used. |
| |
| @item -print-objc-runtime-info |
| @opindex print-objc-runtime-info |
| Generate C header describing the largest structure that is passed by |
| value, if any. |
| |
| @end table |
| |
| @node Diagnostic Message Formatting Options |
| @section Options to Control Diagnostic Messages Formatting |
| @cindex options to control diagnostics formatting |
| @cindex diagnostic messages |
| @cindex message formatting |
| |
| Traditionally, diagnostic messages have been formatted irrespective of |
| the output device's aspect (e.g.@: its width, @dots{}). You can use the |
| options described below |
| to control the formatting algorithm for diagnostic messages, |
| e.g.@: how many characters per line, how often source location |
| information should be reported. Note that some language front ends may not |
| honor these options. |
| |
| @table @gcctabopt |
| @item -fmessage-length=@var{n} |
| @opindex fmessage-length |
| Try to format error messages so that they fit on lines of about |
| @var{n} characters. If @var{n} is zero, then no line-wrapping is |
| done; each error message appears on a single line. This is the |
| default for all front ends. |
| |
| Note - this option also affects the display of the @samp{#error} and |
| @samp{#warning} pre-processor directives, and the @samp{deprecated} |
| function/type/variable attribute. It does not however affect the |
| @samp{pragma GCC warning} and @samp{pragma GCC error} pragmas. |
| |
| @item -fdiagnostics-plain-output |
| This option requests that diagnostic output look as plain as possible, which |
| may be useful when running @command{dejagnu} or other utilities that need to |
| parse diagnostics output and prefer that it remain more stable over time. |
| @option{-fdiagnostics-plain-output} is currently equivalent to the following |
| options: |
| @gccoptlist{-fno-diagnostics-show-caret @gol |
| -fno-diagnostics-show-line-numbers @gol |
| -fdiagnostics-color=never @gol |
| -fdiagnostics-urls=never @gol |
| -fdiagnostics-path-format=separate-events} |
| In the future, if GCC changes the default appearance of its diagnostics, the |
| corresponding option to disable the new behavior will be added to this list. |
| |
| @item -fdiagnostics-show-location=once |
| @opindex fdiagnostics-show-location |
| Only meaningful in line-wrapping mode. Instructs the diagnostic messages |
| reporter to emit source location information @emph{once}; that is, in |
| case the message is too long to fit on a single physical line and has to |
| be wrapped, the source location won't be emitted (as prefix) again, |
| over and over, in subsequent continuation lines. This is the default |
| behavior. |
| |
| @item -fdiagnostics-show-location=every-line |
| Only meaningful in line-wrapping mode. Instructs the diagnostic |
| messages reporter to emit the same source location information (as |
| prefix) for physical lines that result from the process of breaking |
| a message which is too long to fit on a single line. |
| |
| @item -fdiagnostics-color[=@var{WHEN}] |
| @itemx -fno-diagnostics-color |
| @opindex fdiagnostics-color |
| @cindex highlight, color |
| @vindex GCC_COLORS @r{environment variable} |
| Use color in diagnostics. @var{WHEN} is @samp{never}, @samp{always}, |
| or @samp{auto}. The default depends on how the compiler has been configured, |
| it can be any of the above @var{WHEN} options or also @samp{never} |
| if @env{GCC_COLORS} environment variable isn't present in the environment, |
| and @samp{auto} otherwise. |
| @samp{auto} makes GCC use color only when the standard error is a terminal, |
| and when not executing in an emacs shell. |
| The forms @option{-fdiagnostics-color} and @option{-fno-diagnostics-color} are |
| aliases for @option{-fdiagnostics-color=always} and |
| @option{-fdiagnostics-color=never}, respectively. |
| |
| The colors are defined by the environment variable @env{GCC_COLORS}. |
| Its value is a colon-separated list of capabilities and Select Graphic |
| Rendition (SGR) substrings. SGR commands are interpreted by the |
| terminal or terminal emulator. (See the section in the documentation |
| of your text terminal for permitted values and their meanings as |
| character attributes.) These substring values are integers in decimal |
| representation and can be concatenated with semicolons. |
| Common values to concatenate include |
| @samp{1} for bold, |
| @samp{4} for underline, |
| @samp{5} for blink, |
| @samp{7} for inverse, |
| @samp{39} for default foreground color, |
| @samp{30} to @samp{37} for foreground colors, |
| @samp{90} to @samp{97} for 16-color mode foreground colors, |
| @samp{38;5;0} to @samp{38;5;255} |
| for 88-color and 256-color modes foreground colors, |
| @samp{49} for default background color, |
| @samp{40} to @samp{47} for background colors, |
| @samp{100} to @samp{107} for 16-color mode background colors, |
| and @samp{48;5;0} to @samp{48;5;255} |
| for 88-color and 256-color modes background colors. |
| |
| The default @env{GCC_COLORS} is |
| @smallexample |
| error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01:\ |
| quote=01:path=01;36:fixit-insert=32:fixit-delete=31:\ |
| diff-filename=01:diff-hunk=32:diff-delete=31:diff-insert=32:\ |
| type-diff=01;32 |
| @end smallexample |
| @noindent |
| where @samp{01;31} is bold red, @samp{01;35} is bold magenta, |
| @samp{01;36} is bold cyan, @samp{32} is green, @samp{34} is blue, |
| @samp{01} is bold, and @samp{31} is red. |
| Setting @env{GCC_COLORS} to the empty string disables colors. |
| Supported capabilities are as follows. |
| |
| @table @code |
| @item error= |
| @vindex error GCC_COLORS @r{capability} |
| SGR substring for error: markers. |
| |
| @item warning= |
| @vindex warning GCC_COLORS @r{capability} |
| SGR substring for warning: markers. |
| |
| @item note= |
| @vindex note GCC_COLORS @r{capability} |
| SGR substring for note: markers. |
| |
| @item path= |
| @vindex path GCC_COLORS @r{capability} |
| SGR substring for colorizing paths of control-flow events as printed |
| via @option{-fdiagnostics-path-format=}, such as the identifiers of |
| individual events and lines indicating interprocedural calls and returns. |
| |
| @item range1= |
| @vindex range1 GCC_COLORS @r{capability} |
| SGR substring for first additional range. |
| |
| @item range2= |
| @vindex range2 GCC_COLORS @r{capability} |
| SGR substring for second additional range. |
| |
| @item locus= |
| @vindex locus GCC_COLORS @r{capability} |
| SGR substring for location information, @samp{file:line} or |
| @samp{file:line:column} etc. |
| |
| @item quote= |
| @vindex quote GCC_COLORS @r{capability} |
| SGR substring for information printed within quotes. |
| |
| @item fixit-insert= |
| @vindex fixit-insert GCC_COLORS @r{capability} |
| SGR substring for fix-it hints suggesting text to |
| be inserted or replaced. |
| |
| @item fixit-delete= |
| @vindex fixit-delete GCC_COLORS @r{capability} |
| SGR substring for fix-it hints suggesting text to |
| be deleted. |
| |
| @item diff-filename= |
| @vindex diff-filename GCC_COLORS @r{capability} |
| SGR substring for filename headers within generated patches. |
| |
| @item diff-hunk= |
| @vindex diff-hunk GCC_COLORS @r{capability} |
| SGR substring for the starts of hunks within generated patches. |
| |
| @item diff-delete= |
| @vindex diff-delete GCC_COLORS @r{capability} |
| SGR substring for deleted lines within generated patches. |
| |
| @item diff-insert= |
| @vindex diff-insert GCC_COLORS @r{capability} |
| SGR substring for inserted lines within generated patches. |
| |
| @item type-diff= |
| @vindex type-diff GCC_COLORS @r{capability} |
| SGR substring for highlighting mismatching types within template |
| arguments in the C++ frontend. |
| @end table |
| |
| @item -fdiagnostics-urls[=@var{WHEN}] |
| @opindex fdiagnostics-urls |
| @cindex urls |
| @vindex GCC_URLS @r{environment variable} |
| @vindex TERM_URLS @r{environment variable} |
| Use escape sequences to embed URLs in diagnostics. For example, when |
| @option{-fdiagnostics-show-option} emits text showing the command-line |
| option controlling a diagnostic, embed a URL for documentation of that |
| option. |
| |
| @var{WHEN} is @samp{never}, @samp{always}, or @samp{auto}. |
| @samp{auto} makes GCC use URL escape sequences only when the standard error |
| is a terminal, and when not executing in an emacs shell or any graphical |
| terminal which is known to be incompatible with this feature, see below. |
| |
| The default depends on how the compiler has been configured. |
| It can be any of the above @var{WHEN} options. |
| |
| GCC can also be configured (via the |
| @option{--with-diagnostics-urls=auto-if-env} configure-time option) |
| so that the default is affected by environment variables. |
| Under such a configuration, GCC defaults to using @samp{auto} |
| if either @env{GCC_URLS} or @env{TERM_URLS} environment variables are |
| present and non-empty in the environment of the compiler, or @samp{never} |
| if neither are. |
| |
| However, even with @option{-fdiagnostics-urls=always} the behavior is |
| dependent on those environment variables: |
| If @env{GCC_URLS} is set to empty or @samp{no}, do not embed URLs in |
| diagnostics. If set to @samp{st}, URLs use ST escape sequences. |
| If set to @samp{bel}, the default, URLs use BEL escape sequences. |
| Any other non-empty value enables the feature. |
| If @env{GCC_URLS} is not set, use @env{TERM_URLS} as a fallback. |
| Note: ST is an ANSI escape sequence, string terminator @samp{ESC \}, |
| BEL is an ASCII character, CTRL-G that usually sounds like a beep. |
| |
| At this time GCC tries to detect also a few terminals that are known to |
| not implement the URL feature, and have bugs or at least had bugs in |
| some versions that are still in use, where the URL escapes are likely |
| to misbehave, i.e. print garbage on the screen. |
| That list is currently xfce4-terminal, certain known to be buggy |
| gnome-terminal versions, the linux console, and mingw. |
| This check can be skipped with the @option{-fdiagnostics-urls=always}. |
| |
| @item -fno-diagnostics-show-option |
| @opindex fno-diagnostics-show-option |
| @opindex fdiagnostics-show-option |
| By default, each diagnostic emitted includes text indicating the |
| command-line option that directly controls the diagnostic (if such an |
| option is known to the diagnostic machinery). Specifying the |
| @option{-fno-diagnostics-show-option} flag suppresses that behavior. |
| |
| @item -fno-diagnostics-show-caret |
| @opindex fno-diagnostics-show-caret |
| @opindex fdiagnostics-show-caret |
| By default, each diagnostic emitted includes the original source line |
| and a caret @samp{^} indicating the column. This option suppresses this |
| information. The source line is truncated to @var{n} characters, if |
| the @option{-fmessage-length=n} option is given. When the output is done |
| to the terminal, the width is limited to the width given by the |
| @env{COLUMNS} environment variable or, if not set, to the terminal width. |
| |
| @item -fno-diagnostics-show-labels |
| @opindex fno-diagnostics-show-labels |
| @opindex fdiagnostics-show-labels |
| By default, when printing source code (via @option{-fdiagnostics-show-caret}), |
| diagnostics can label ranges of source code with pertinent information, such |
| as the types of expressions: |
| |
| @smallexample |
| printf ("foo %s bar", long_i + long_j); |
| ~^ ~~~~~~~~~~~~~~~ |
| | | |
| char * long int |
| @end smallexample |
| |
| This option suppresses the printing of these labels (in the example above, |
| the vertical bars and the ``char *'' and ``long int'' text). |
| |
| @item -fno-diagnostics-show-cwe |
| @opindex fno-diagnostics-show-cwe |
| @opindex fdiagnostics-show-cwe |
| Diagnostic messages can optionally have an associated |
| @url{https://cwe.mitre.org/index.html, CWE} identifier. |
| GCC itself only provides such metadata for some of the @option{-fanalyzer} |
| diagnostics. GCC plugins may also provide diagnostics with such metadata. |
| By default, if this information is present, it will be printed with |
| the diagnostic. This option suppresses the printing of this metadata. |
| |
| @item -fno-diagnostics-show-line-numbers |
| @opindex fno-diagnostics-show-line-numbers |
| @opindex fdiagnostics-show-line-numbers |
| By default, when printing source code (via @option{-fdiagnostics-show-caret}), |
| a left margin is printed, showing line numbers. This option suppresses this |
| left margin. |
| |
| @item -fdiagnostics-minimum-margin-width=@var{width} |
| @opindex fdiagnostics-minimum-margin-width |
| This option controls the minimum width of the left margin printed by |
| @option{-fdiagnostics-show-line-numbers}. It defaults to 6. |
| |
| @item -fdiagnostics-parseable-fixits |
| @opindex fdiagnostics-parseable-fixits |
| Emit fix-it hints in a machine-parseable format, suitable for consumption |
| by IDEs. For each fix-it, a line will be printed after the relevant |
| diagnostic, starting with the string ``fix-it:''. For example: |
| |
| @smallexample |
| fix-it:"test.c":@{45:3-45:21@}:"gtk_widget_show_all" |
| @end smallexample |
| |
| The location is expressed as a half-open range, expressed as a count of |
| bytes, starting at byte 1 for the initial column. In the above example, |
| bytes 3 through 20 of line 45 of ``test.c'' are to be replaced with the |
| given string: |
| |
| @smallexample |
| 00000000011111111112222222222 |
| 12345678901234567890123456789 |
| gtk_widget_showall (dlg); |
| ^^^^^^^^^^^^^^^^^^ |
| gtk_widget_show_all |
| @end smallexample |
| |
| The filename and replacement string escape backslash as ``\\", tab as ``\t'', |
| newline as ``\n'', double quotes as ``\"'', non-printable characters as octal |
| (e.g. vertical tab as ``\013''). |
| |
| An empty replacement string indicates that the given range is to be removed. |
| An empty range (e.g. ``45:3-45:3'') indicates that the string is to |
| be inserted at the given position. |
| |
| @item -fdiagnostics-generate-patch |
| @opindex fdiagnostics-generate-patch |
| Print fix-it hints to stderr in unified diff format, after any diagnostics |
| are printed. For example: |
| |
| @smallexample |
| --- test.c |
| +++ test.c |
| @@ -42,5 +42,5 @@ |
| |
| void show_cb(GtkDialog *dlg) |
| @{ |
| - gtk_widget_showall(dlg); |
| + gtk_widget_show_all(dlg); |
| @} |
| |
| @end smallexample |
| |
| The diff may or may not be colorized, following the same rules |
| as for diagnostics (see @option{-fdiagnostics-color}). |
| |
| @item -fdiagnostics-show-template-tree |
| @opindex fdiagnostics-show-template-tree |
| |
| In the C++ frontend, when printing diagnostics showing mismatching |
| template types, such as: |
| |
| @smallexample |
| could not convert 'std::map<int, std::vector<double> >()' |
| from 'map<[...],vector<double>>' to 'map<[...],vector<float>> |
| @end smallexample |
| |
| the @option{-fdiagnostics-show-template-tree} flag enables printing a |
| tree-like structure showing the common and differing parts of the types, |
| such as: |
| |
| @smallexample |
| map< |
| [...], |
| vector< |
| [double != float]>> |
| @end smallexample |
| |
| The parts that differ are highlighted with color (``double'' and |
| ``float'' in this case). |
| |
| @item -fno-elide-type |
| @opindex fno-elide-type |
| @opindex felide-type |
| By default when the C++ frontend prints diagnostics showing mismatching |
| template types, common parts of the types are printed as ``[...]'' to |
| simplify the error message. For example: |
| |
| @smallexample |
| could not convert 'std::map<int, std::vector<double> >()' |
| from 'map<[...],vector<double>>' to 'map<[...],vector<float>> |
| @end smallexample |
| |
| Specifying the @option{-fno-elide-type} flag suppresses that behavior. |
| This flag also affects the output of the |
| @option{-fdiagnostics-show-template-tree} flag. |
| |
| @item -fdiagnostics-path-format=@var{KIND} |
| @opindex fdiagnostics-path-format |
| Specify how to print paths of control-flow events for diagnostics that |
| have such a path associated with them. |
| |
| @var{KIND} is @samp{none}, @samp{separate-events}, or @samp{inline-events}, |
| the default. |
| |
| @samp{none} means to not print diagnostic paths. |
| |
| @samp{separate-events} means to print a separate ``note'' diagnostic for |
| each event within the diagnostic. For example: |
| |
| @smallexample |
| test.c:29:5: error: passing NULL as argument 1 to 'PyList_Append' which requires a non-NULL parameter |
| test.c:25:10: note: (1) when 'PyList_New' fails, returning NULL |
| test.c:27:3: note: (2) when 'i < count' |
| test.c:29:5: note: (3) when calling 'PyList_Append', passing NULL from (1) as argument 1 |
| @end smallexample |
| |
| @samp{inline-events} means to print the events ``inline'' within the source |
| code. This view attempts to consolidate the events into runs of |
| sufficiently-close events, printing them as labelled ranges within the source. |
| |
| For example, the same events as above might be printed as: |
| |
| @smallexample |
| 'test': events 1-3 |
| | |
| | 25 | list = PyList_New(0); |
| | | ^~~~~~~~~~~~~ |
| | | | |
| | | (1) when 'PyList_New' fails, returning NULL |
| | 26 | |
| | 27 | for (i = 0; i < count; i++) @{ |
| | | ~~~ |
| | | | |
| | | (2) when 'i < count' |
| | 28 | item = PyLong_FromLong(random()); |
| | 29 | PyList_Append(list, item); |
| | | ~~~~~~~~~~~~~~~~~~~~~~~~~ |
| | | | |
| | | (3) when calling 'PyList_Append', passing NULL from (1) as argument 1 |
| | |
| @end smallexample |
| |
| Interprocedural control flow is shown by grouping the events by stack frame, |
| and using indentation to show how stack frames are nested, pushed, and popped. |
| |
| For example: |
| |
| @smallexample |
| 'test': events 1-2 |
| | |
| | 133 | @{ |
| | | ^ |
| | | | |
| | | (1) entering 'test' |
| | 134 | boxed_int *obj = make_boxed_int (i); |
| | | ~~~~~~~~~~~~~~~~~~ |
| | | | |
| | | (2) calling 'make_boxed_int' |
| | |
| +--> 'make_boxed_int': events 3-4 |
| | |
| | 120 | @{ |
| | | ^ |
| | | | |
| | | (3) entering 'make_boxed_int' |
| | 121 | boxed_int *result = (boxed_int *)wrapped_malloc (sizeof (boxed_int)); |
| | | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| | | | |
| | | (4) calling 'wrapped_malloc' |
| | |
| +--> 'wrapped_malloc': events 5-6 |
| | |
| | 7 | @{ |
| | | ^ |
| | | | |
| | | (5) entering 'wrapped_malloc' |
| | 8 | return malloc (size); |
| | | ~~~~~~~~~~~~~ |
| | | | |
| | | (6) calling 'malloc' |
| | |
| <-------------+ |
| | |
| 'test': event 7 |
| | |
| | 138 | free_boxed_int (obj); |
| | | ^~~~~~~~~~~~~~~~~~~~ |
| | | | |
| | | (7) calling 'free_boxed_int' |
| | |
| (etc) |
| @end smallexample |
| |
| @item -fdiagnostics-show-path-depths |
| @opindex fdiagnostics-show-path-depths |
| This option provides additional information when printing control-flow paths |
| associated with a diagnostic. |
| |
| If this is option is provided then the stack depth will be printed for |
| each run of events within @option{-fdiagnostics-path-format=separate-events}. |
| |
| This is intended for use by GCC developers and plugin developers when |
| debugging diagnostics that report interprocedural control flow. |
| |
| @item -fno-show-column |
| @opindex fno-show-column |
| @opindex fshow-column |
| Do not print column numbers in diagnostics. This may be necessary if |
| diagnostics are being scanned by a program that does not understand the |
| column numbers, such as @command{dejagnu}. |
| |
| @item -fdiagnostics-column-unit=@var{UNIT} |
| @opindex fdiagnostics-column-unit |
| Select the units for the column number. This affects traditional diagnostics |
| (in the absence of @option{-fno-show-column}), as well as JSON format |
| diagnostics if requested. |
| |
| The default @var{UNIT}, @samp{display}, considers the number of display |
| columns occupied by each character. This may be larger than the number |
| of bytes required to encode the character, in the case of tab |
| characters, or it may be smaller, in the case of multibyte characters. |
| For example, the character ``GREEK SMALL LETTER PI (U+03C0)'' occupies one |
| display column, and its UTF-8 encoding requires two bytes; the character |
| ``SLIGHTLY SMILING FACE (U+1F642)'' occupies two display columns, and |
| its UTF-8 encoding requires four bytes. |
| |
| Setting @var{UNIT} to @samp{byte} changes the column number to the raw byte |
| count in all cases, as was traditionally output by GCC prior to version 11.1.0. |
| |
| @item -fdiagnostics-column-origin=@var{ORIGIN} |
| @opindex fdiagnostics-column-origin |
| Select the origin for column numbers, i.e. the column number assigned to the |
| first column. The default value of 1 corresponds to traditional GCC |
| behavior and to the GNU style guide. Some utilities may perform better with an |
| origin of 0; any non-negative value may be specified. |
| |
| @item -fdiagnostics-escape-format=@var{FORMAT} |
| @opindex fdiagnostics-escape-format |
| When GCC prints pertinent source lines for a diagnostic it normally attempts |
| to print the source bytes directly. However, some diagnostics relate to encoding |
| issues in the source file, such as malformed UTF-8, or issues with Unicode |
| normalization. These diagnostics are flagged so that GCC will escape bytes |
| that are not printable ASCII when printing their pertinent source lines. |
| |
| This option controls how such bytes should be escaped. |
| |
| The default @var{FORMAT}, @samp{unicode} displays Unicode characters that |
| are not printable ASCII in the form @samp{<U+XXXX>}, and bytes that do not |
| correspond to a Unicode character validly-encoded in UTF-8-encoded will be |
| displayed as hexadecimal in the form @samp{<XX>}. |
| |
| For example, a source line containing the string @samp{before} followed by the |
| Unicode character U+03C0 (``GREEK SMALL LETTER PI'', with UTF-8 encoding |
| 0xCF 0x80) followed by the byte 0xBF (a stray UTF-8 trailing byte), followed by |
| the string @samp{after} will be printed for such a diagnostic as: |
| |
| @smallexample |
| before<U+03C0><BF>after |
| @end smallexample |
| |
| Setting @var{FORMAT} to @samp{bytes} will display all non-printable-ASCII bytes |
| in the form @samp{<XX>}, thus showing the underlying encoding of non-ASCII |
| Unicode characters. For the example above, the following will be printed: |
| |
| @smallexample |
| before<CF><80><BF>after |
| @end smallexample |
| |
| @item -fdiagnostics-format=@var{FORMAT} |
| @opindex fdiagnostics-format |
| Select a different format for printing diagnostics. |
| @var{FORMAT} is @samp{text} or @samp{json}. |
| The default is @samp{text}. |
| |
| The @samp{json} format consists of a top-level JSON array containing JSON |
| objects representing the diagnostics. |
| |
| The JSON is emitted as one line, without formatting; the examples below |
| have been formatted for clarity. |
| |
| Diagnostics can have child diagnostics. For example, this error and note: |
| |
| @smallexample |
| misleading-indentation.c:15:3: warning: this 'if' clause does not |
| guard... [-Wmisleading-indentation] |
| 15 | if (flag) |
| | ^~ |
| misleading-indentation.c:17:5: note: ...this statement, but the latter |
| is misleadingly indented as if it were guarded by the 'if' |
| 17 | y = 2; |
| | ^ |
| @end smallexample |
| |
| @noindent |
| might be printed in JSON form (after formatting) like this: |
| |
| @smallexample |
| [ |
| @{ |
| "kind": "warning", |
| "locations": [ |
| @{ |
| "caret": @{ |
| "display-column": 3, |
| "byte-column": 3, |
| "column": 3, |
| "file": "misleading-indentation.c", |
| "line": 15 |
| @}, |
| "finish": @{ |
| "display-column": 4, |
| "byte-column": 4, |
| "column": 4, |
| "file": "misleading-indentation.c", |
| "line": 15 |
| @} |
| @} |
| ], |
| "message": "this \u2018if\u2019 clause does not guard...", |
| "option": "-Wmisleading-indentation", |
| "option_url": "https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wmisleading-indentation", |
| "children": [ |
| @{ |
| "kind": "note", |
| "locations": [ |
| @{ |
| "caret": @{ |
| "display-column": 5, |
| "byte-column": 5, |
| "column": 5, |
| "file": "misleading-indentation.c", |
| "line": 17 |
| @} |
| @} |
| ], |
| "escape-source": false, |
| "message": "...this statement, but the latter is @dots{}" |
| @} |
| ] |
| "escape-source": false, |
| "column-origin": 1, |
| @} |
| ] |
| @end smallexample |
| |
| @noindent |
| where the @code{note} is a child of the @code{warning}. |
| |
| A diagnostic has a @code{kind}. If this is @code{warning}, then there is |
| an @code{option} key describing the command-line option controlling the |
| warning. |
| |
| A diagnostic can contain zero or more locations. Each location has an |
| optional @code{label} string and up to three positions within it: a |
| @code{caret} position and optional @code{start} and @code{finish} positions. |
| A position is described by a @code{file} name, a @code{line} number, and |
| three numbers indicating a column position: |
| @itemize @bullet |
| |
| @item |
| @code{display-column} counts display columns, accounting for tabs and |
| multibyte characters. |
| |
| @item |
| @code{byte-column} counts raw bytes. |
| |
| @item |
| @code{column} is equal to one of |
| the previous two, as dictated by the @option{-fdiagnostics-column-unit} |
| option. |
| |
| @end itemize |
| All three columns are relative to the origin specified by |
| @option{-fdiagnostics-column-origin}, which is typically equal to 1 but may |
| be set, for instance, to 0 for compatibility with other utilities that |
| number columns from 0. The column origin is recorded in the JSON output in |
| the @code{column-origin} tag. In the remaining examples below, the extra |
| column number outputs have been omitted for brevity. |
| |
| For example, this error: |
| |
| @smallexample |
| bad-binary-ops.c:64:23: error: invalid operands to binary + (have 'S' @{aka |
| 'struct s'@} and 'T' @{aka 'struct t'@}) |
| 64 | return callee_4a () + callee_4b (); |
| | ~~~~~~~~~~~~ ^ ~~~~~~~~~~~~ |
| | | | |
| | | T @{aka struct t@} |
| | S @{aka struct s@} |
| @end smallexample |
| |
| @noindent |
| has three locations. Its primary location is at the ``+'' token at column |
| 23. It has two secondary locations, describing the left and right-hand sides |
| of the expression, which have labels. It might be printed in JSON form as: |
| |
| @smallexample |
| @{ |
| "children": [], |
| "kind": "error", |
| "locations": [ |
| @{ |
| "caret": @{ |
| "column": 23, "file": "bad-binary-ops.c", "line": 64 |
| @} |
| @}, |
| @{ |
| "caret": @{ |
| "column": 10, "file": "bad-binary-ops.c", "line": 64 |
| @}, |
| "finish": @{ |
| "column": 21, "file": "bad-binary-ops.c", "line": 64 |
| @}, |
| "label": "S @{aka struct s@}" |
| @}, |
| @{ |
| "caret": @{ |
| "column": 25, "file": "bad-binary-ops.c", "line": 64 |
| @}, |
| "finish": @{ |
| "column": 36, "file": "bad-binary-ops.c", "line": 64 |
| @}, |
| "label": "T @{aka struct t@}" |
| @} |
| ], |
| "escape-source": false, |
| "message": "invalid operands to binary + @dots{}" |
| @} |
| @end smallexample |
| |
| If a diagnostic contains fix-it hints, it has a @code{fixits} array, |
| consisting of half-open intervals, similar to the output of |
| @option{-fdiagnostics-parseable-fixits}. For example, this diagnostic |
| with a replacement fix-it hint: |
| |
| @smallexample |
| demo.c:8:15: error: 'struct s' has no member named 'colour'; did you |
| mean 'color'? |
| 8 | return ptr->colour; |
| | ^~~~~~ |
| | color |
| @end smallexample |
| |
| @noindent |
| might be printed in JSON form as: |
| |
| @smallexample |
| @{ |
| "children": [], |
| "fixits": [ |
| @{ |
| "next": @{ |
| "column": 21, |
| "file": "demo.c", |
| "line": 8 |
| @}, |
| "start": @{ |
| "column": 15, |
| "file": "demo.c", |
| "line": 8 |
| @}, |
| "string": "color" |
| @} |
| ], |
| "kind": "error", |
| "locations": [ |
| @{ |
| "caret": @{ |
| "column": 15, |
| "file": "demo.c", |
| "line": 8 |
| @}, |
| "finish": @{ |
| "column": 20, |
| "file": "demo.c", |
| "line": 8 |
| @} |
| @} |
| ], |
| "escape-source": false, |
| "message": "\u2018struct s\u2019 has no member named @dots{}" |
| @} |
| @end smallexample |
| |
| @noindent |
| where the fix-it hint suggests replacing the text from @code{start} up |
| to but not including @code{next} with @code{string}'s value. Deletions |
| are expressed via an empty value for @code{string}, insertions by |
| having @code{start} equal @code{next}. |
| |
| If the diagnostic has a path of control-flow events associated with it, |
| it has a @code{path} array of objects representing the events. Each |
| event object has a @code{description} string, a @code{location} object, |
| along with a @code{function} string and a @code{depth} number for |
| representing interprocedural paths. The @code{function} represents the |
| current function at that event, and the @code{depth} represents the |
| stack depth relative to some baseline: the higher, the more frames are |
| within the stack. |
| |
| For example, the intraprocedural example shown for |
| @option{-fdiagnostics-path-format=} might have this JSON for its path: |
| |
| @smallexample |
| "path": [ |
| @{ |
| "depth": 0, |
| "description": "when 'PyList_New' fails, returning NULL", |
| "function": "test", |
| "location": @{ |
| "column": 10, |
| "file": "test.c", |
| "line": 25 |
| @} |
| @}, |
| @{ |
| "depth": 0, |
| "description": "when 'i < count'", |
| "function": "test", |
| "location": @{ |
| "column": 3, |
| "file": "test.c", |
| "line": 27 |
| @} |
| @}, |
| @{ |
| "depth": 0, |
| "description": "when calling 'PyList_Append', passing NULL from (1) as argument 1", |
| "function": "test", |
| "location": @{ |
| "column": 5, |
| "file": "test.c", |
| "line": 29 |
| @} |
| @} |
| ] |
| @end smallexample |
| |
| Diagnostics have a boolean attribute @code{escape-source}, hinting whether |
| non-ASCII bytes should be escaped when printing the pertinent lines of |
| source code (@code{true} for diagnostics involving source encoding issues). |
| |
| @end table |
| |
| @node Warning Options |
| @section Options to Request or Suppress Warnings |
| @cindex options to control warnings |
| @cindex warning messages |
| @cindex messages, warning |
| @cindex suppressing warnings |
| |
| Warnings are diagnostic messages that report constructions that |
| are not inherently erroneous but that are risky or suggest there |
| may have been an error. |
| |
| The following language-independent options do not enable specific |
| warnings but control the kinds of diagnostics produced by GCC@. |
| |
| @table @gcctabopt |
| @cindex syntax checking |
| @item -fsyntax-only |
| @opindex fsyntax-only |
| Check the code for syntax errors, but don't do anything beyond that. |
| |
| @item -fmax-errors=@var{n} |
| @opindex fmax-errors |
| Limits the maximum number of error messages to @var{n}, at which point |
| GCC bails out rather than attempting to continue processing the source |
| code. If @var{n} is 0 (the default), there is no limit on the number |
| of error messages produced. If @option{-Wfatal-errors} is also |
| specified, then @option{-Wfatal-errors} takes precedence over this |
| option. |
| |
| @item -w |
| @opindex w |
| Inhibit all warning messages. |
| |
| @item -Werror |
| @opindex Werror |
| @opindex Wno-error |
| Make all warnings into errors. |
| |
| @item -Werror= |
| @opindex Werror= |
| @opindex Wno-error= |
| Make the specified warning into an error. The specifier for a warning |
| is appended; for example @option{-Werror=switch} turns the warnings |
| controlled by @option{-Wswitch} into errors. This switch takes a |
| negative form, to be used to negate @option{-Werror} for specific |
| warnings; for example @option{-Wno-error=switch} makes |
| @option{-Wswitch} warnings not be errors, even when @option{-Werror} |
| is in effect. |
| |
| The warning message for each controllable warning includes the |
| option that controls the warning. That option can then be used with |
| @option{-Werror=} and @option{-Wno-error=} as described above. |
| (Printing of the option in the warning message can be disabled using the |
| @option{-fno-diagnostics-show-option} flag.) |
| |
| Note that specifying @option{-Werror=}@var{foo} automatically implies |
| @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not |
| imply anything. |
| |
| @item -Wfatal-errors |
| @opindex Wfatal-errors |
| @opindex Wno-fatal-errors |
| This option causes the compiler to abort compilation on the first error |
| occurred rather than trying to keep going and printing further error |
| messages. |
| |
| @end table |
| |
| You can request many specific warnings with options beginning with |
| @samp{-W}, for example @option{-Wimplicit} to request warnings on |
| implicit declarations. Each of these specific warning options also |
| has a negative form beginning @samp{-Wno-} to turn off warnings; for |
| example, @option{-Wno-implicit}. This manual lists only one of the |
| two forms, whichever is not the default. For further |
| language-specific options also refer to @ref{C++ Dialect Options} and |
| @ref{Objective-C and Objective-C++ Dialect Options}. |
| Additional warnings can be produced by enabling the static analyzer; |
| @xref{Static Analyzer Options}. |
| |
| Some options, such as @option{-Wall} and @option{-Wextra}, turn on other |
| options, such as @option{-Wunused}, which may turn on further options, |
| such as @option{-Wunused-value}. The combined effect of positive and |
| negative forms is that more specific options have priority over less |
| specific ones, independently of their position in the command-line. For |
| options of the same specificity, the last one takes effect. Options |
| enabled or disabled via pragmas (@pxref{Diagnostic Pragmas}) take effect |
| as if they appeared at the end of the command-line. |
| |
| When an unrecognized warning option is requested (e.g., |
| @option{-Wunknown-warning}), GCC emits a diagnostic stating |
| that the option is not recognized. However, if the @option{-Wno-} form |
| is used, the behavior is slightly different: no diagnostic is |
| produced for @option{-Wno-unknown-warning} unless other diagnostics |
| are being produced. This allows the use of new @option{-Wno-} options |
| with old compilers, but if something goes wrong, the compiler |
| warns that an unrecognized option is present. |
| |
| The effectiveness of some warnings depends on optimizations also being |
| enabled. For example @option{-Wsuggest-final-types} is more effective |
| with link-time optimization and some instances of other warnings may |
| not be issued at all unless optimization is enabled. While optimization |
| in general improves the efficacy of control and data flow sensitive |
| warnings, in some cases it may also cause false positives. |
| |
| @table @gcctabopt |
| @item -Wpedantic |
| @itemx -pedantic |
| @opindex pedantic |
| @opindex Wpedantic |
| @opindex Wno-pedantic |
| Issue all the warnings demanded by strict ISO C and ISO C++; |
| reject all programs that use forbidden extensions, and some other |
| programs that do not follow ISO C and ISO C++. For ISO C, follows the |
| version of the ISO C standard specified by any @option{-std} option used. |
| |
| Valid ISO C and ISO C++ programs should compile properly with or without |
| this option (though a rare few require @option{-ansi} or a |
| @option{-std} option specifying the required version of ISO C)@. However, |
| without this option, certain GNU extensions and traditional C and C++ |
| features are supported as well. With this option, they are rejected. |
| |
| @option{-Wpedantic} does not cause warning messages for use of the |
| alternate keywords whose names begin and end with @samp{__}. This alternate |
| format can also be used to disable warnings for non-ISO @samp{__intN} types, |
| i.e. @samp{__intN__}. |
| Pedantic warnings are also disabled in the expression that follows |
| @code{__extension__}. However, only system header files should use |
| these escape routes; application programs should avoid them. |
| @xref{Alternate Keywords}. |
| |
| Some users try to use @option{-Wpedantic} to check programs for strict ISO |
| C conformance. They soon find that it does not do quite what they want: |
| it finds some non-ISO practices, but not all---only those for which |
| ISO C @emph{requires} a diagnostic, and some others for which |
| diagnostics have been added. |
| |
| A feature to report any failure to conform to ISO C might be useful in |
| some instances, but would require considerable additional work and would |
| be quite different from @option{-Wpedantic}. We don't have plans to |
| support such a feature in the near future. |
| |
| Where the standard specified with @option{-std} represents a GNU |
| extended dialect of C, such as @samp{gnu90} or @samp{gnu99}, there is a |
| corresponding @dfn{base standard}, the version of ISO C on which the GNU |
| extended dialect is based. Warnings from @option{-Wpedantic} are given |
| where they are required by the base standard. (It does not make sense |
| for such warnings to be given only for features not in the specified GNU |
| C dialect, since by definition the GNU dialects of C include all |
| features the compiler supports with the given option, and there would be |
| nothing to warn about.) |
| |
| @item -pedantic-errors |
| @opindex pedantic-errors |
| Give an error whenever the @dfn{base standard} (see @option{-Wpedantic}) |
| requires a diagnostic, in some cases where there is undefined behavior |
| at compile-time and in some other cases that do not prevent compilation |
| of programs that are valid according to the standard. This is not |
| equivalent to @option{-Werror=pedantic}, since there are errors enabled |
| by this option and not enabled by the latter and vice versa. |
| |
| @item -Wall |
| @opindex Wall |
| @opindex Wno-all |
| This enables all the warnings about constructions that some users |
| consider questionable, and that are easy to avoid (or modify to |
| prevent the warning), even in conjunction with macros. This also |
| enables some language-specific warnings described in @ref{C++ Dialect |
| Options} and @ref{Objective-C and Objective-C++ Dialect Options}. |
| |
| @option{-Wall} turns on the following warning flags: |
| |
| @gccoptlist{-Waddress @gol |
| -Warray-bounds=1 @r{(only with} @option{-O2}@r{)} @gol |
| -Warray-compare @gol |
| -Warray-parameter=2 @r{(C and Objective-C only)} @gol |
| -Wbool-compare @gol |
| -Wbool-operation @gol |
| -Wc++11-compat -Wc++14-compat @gol |
| -Wcatch-value @r{(C++ and Objective-C++ only)} @gol |
| -Wchar-subscripts @gol |
| -Wcomment @gol |
| -Wdangling-pointer=2 @gol |
| -Wduplicate-decl-specifier @r{(C and Objective-C only)} @gol |
| -Wenum-compare @r{(in C/ObjC; this is on by default in C++)} @gol |
| -Wformat @gol |
| -Wformat-overflow @gol |
| -Wformat-truncation @gol |
| -Wint-in-bool-context @gol |
| -Wimplicit @r{(C and Objective-C only)} @gol |
| -Wimplicit-int @r{(C and Objective-C only)} @gol |
| -Wimplicit-function-declaration @r{(C and Objective-C only)} @gol |
| -Winit-self @r{(only for C++)} @gol |
| -Wlogical-not-parentheses @gol |
| -Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol |
| -Wmaybe-uninitialized @gol |
| -Wmemset-elt-size @gol |
| -Wmemset-transposed-args @gol |
| -Wmisleading-indentation @r{(only for C/C++)} @gol |
| -Wmismatched-dealloc @gol |
| -Wmismatched-new-delete @r{(only for C/C++)} @gol |
| -Wmissing-attributes @gol |
| -Wmissing-braces @r{(only for C/ObjC)} @gol |
| -Wmultistatement-macros @gol |
| -Wnarrowing @r{(only for C++)} @gol |
| -Wnonnull @gol |
| -Wnonnull-compare @gol |
| -Wopenmp-simd @gol |
| -Wparentheses @gol |
| -Wpessimizing-move @r{(only for C++)} @gol |
| -Wpointer-sign @gol |
| -Wrange-loop-construct @r{(only for C++)} @gol |
| -Wreorder @gol |
| -Wrestrict @gol |
| -Wreturn-type @gol |
| -Wsequence-point @gol |
| -Wsign-compare @r{(only in C++)} @gol |
| -Wsizeof-array-div @gol |
| -Wsizeof-pointer-div @gol |
| -Wsizeof-pointer-memaccess @gol |
| -Wstrict-aliasing @gol |
| -Wstrict-overflow=1 @gol |
| -Wswitch @gol |
| -Wtautological-compare @gol |
| -Wtrigraphs @gol |
| -Wuninitialized @gol |
| -Wunknown-pragmas @gol |
| -Wunused-function @gol |
| -Wunused-label @gol |
| -Wunused-value @gol |
| -Wunused-variable @gol |
| -Wuse-after-free=3 @gol |
| -Wvla-parameter @r{(C and Objective-C only)} @gol |
| -Wvolatile-register-var @gol |
| -Wzero-length-bounds} |
| |
| Note that some warning flags are not implied by @option{-Wall}. Some of |
| them warn about constructions that users generally do not consider |
| questionable, but which occasionally you might wish to check for; |
| others warn about constructions that are necessary or hard to avoid in |
| some cases, and there is no simple way to modify the code to suppress |
| the warning. Some of them are enabled by @option{-Wextra} but many of |
| them must be enabled individually. |
| |
| @item -Wextra |
| @opindex W |
| @opindex Wextra |
| @opindex Wno-extra |
| This enables some extra warning flags that are not enabled by |
| @option{-Wall}. (This option used to be called @option{-W}. The older |
| name is still supported, but the newer name is more descriptive.) |
| |
| @gccoptlist{-Wclobbered @gol |
| -Wcast-function-type @gol |
| -Wdeprecated-copy @r{(C++ only)} @gol |
| -Wempty-body @gol |
| -Wenum-conversion @r{(C only)} @gol |
| -Wignored-qualifiers @gol |
| -Wimplicit-fallthrough=3 @gol |
| -Wmissing-field-initializers @gol |
| -Wmissing-parameter-type @r{(C only)} @gol |
| -Wold-style-declaration @r{(C only)} @gol |
| -Woverride-init @gol |
| -Wsign-compare @r{(C only)} @gol |
| -Wstring-compare @gol |
| -Wredundant-move @r{(only for C++)} @gol |
| -Wtype-limits @gol |
| -Wuninitialized @gol |
| -Wshift-negative-value @r{(in C++11 to C++17 and in C99 and newer)} @gol |
| -Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol |
| -Wunused-but-set-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)}} |
| |
| |
| The option @option{-Wextra} also prints warning messages for the |
| following cases: |
| |
| @itemize @bullet |
| |
| @item |
| A pointer is compared against integer zero with @code{<}, @code{<=}, |
| @code{>}, or @code{>=}. |
| |
| @item |
| (C++ only) An enumerator and a non-enumerator both appear in a |
| conditional expression. |
| |
| @item |
| (C++ only) Ambiguous virtual bases. |
| |
| @item |
| (C++ only) Subscripting an array that has been declared @code{register}. |
| |
| @item |
| (C++ only) Taking the address of a variable that has been declared |
| @code{register}. |
| |
| @item |
| (C++ only) A base class is not initialized in the copy constructor |
| of a derived class. |
| |
| @end itemize |
| |
| @item -Wabi @r{(C, Objective-C, C++ and Objective-C++ only)} |
| @opindex Wabi |
| @opindex Wno-abi |
| |
| Warn about code affected by ABI changes. This includes code that may |
| not be compatible with the vendor-neutral C++ ABI as well as the psABI |
| for the particular target. |
| |
| Since G++ now defaults to updating the ABI with each major release, |
| normally @option{-Wabi} warns only about C++ ABI compatibility |
| problems if there is a check added later in a release series for an |
| ABI issue discovered since the initial release. @option{-Wabi} warns |
| about more things if an older ABI version is selected (with |
| @option{-fabi-version=@var{n}}). |
| |
| @option{-Wabi} can also be used with an explicit version number to |
| warn about C++ ABI compatibility with a particular @option{-fabi-version} |
| level, e.g.@: @option{-Wabi=2} to warn about changes relative to |
| @option{-fabi-version=2}. |
| |
| If an explicit version number is provided and |
| @option{-fabi-compat-version} is not specified, the version number |
| from this option is used for compatibility aliases. If no explicit |
| version number is provided with this option, but |
| @option{-fabi-compat-version} is specified, that version number is |
| used for C++ ABI warnings. |
| |
| Although an effort has been made to warn about |
| all such cases, there are probably some cases that are not warned about, |
| even though G++ is generating incompatible code. There may also be |
| cases where warnings are emitted even though the code that is generated |
| is compatible. |
| |
| You should rewrite your code to avoid these warnings if you are |
| concerned about the fact that code generated by G++ may not be binary |
| compatible with code generated by other compilers. |
| |
| Known incompatibilities in @option{-fabi-version=2} (which was the |
| default from GCC 3.4 to 4.9) include: |
| |
| @itemize @bullet |
| |
| @item |
| A template with a non-type template parameter of reference type was |
| mangled incorrectly: |
| @smallexample |
| extern int N; |
| template <int &> struct S @{@}; |
| void n (S<N>) @{2@} |
| @end smallexample |
| |
| This was fixed in @option{-fabi-version=3}. |
| |
| @item |
| SIMD vector types declared using @code{__attribute ((vector_size))} were |
| mangled in a non-standard way that does not allow for overloading of |
| functions taking vectors of different sizes. |
| |
| The mangling was changed in @option{-fabi-version=4}. |
| |
| @item |
| @code{__attribute ((const))} and @code{noreturn} were mangled as type |
| qualifiers, and @code{decltype} of a plain declaration was folded away. |
| |
| These mangling issues were fixed in @option{-fabi-version=5}. |
| |
| @item |
| Scoped enumerators passed as arguments to a variadic function are |
| promoted like unscoped enumerators, causing @code{va_arg} to complain. |
| On most targets this does not actually affect the parameter passing |
| ABI, as there is no way to pass an argument smaller than @code{int}. |
| |
| Also, the ABI changed the mangling of template argument packs, |
| @code{const_cast}, @code{static_cast}, prefix increment/decrement, and |
| a class scope function used as a template argument. |
| |
| These issues were corrected in @option{-fabi-version=6}. |
| |
| @item |
| Lambdas in default argument scope were mangled incorrectly, and the |
| ABI changed the mangling of @code{nullptr_t}. |
| |
| These issues were corrected in @option{-fabi-version=7}. |
| |
| @item |
| When mangling a function type with function-cv-qualifiers, the |
| un-qualified function type was incorrectly treated as a substitution |
| candidate. |
| |
| This was fixed in @option{-fabi-version=8}, the default for GCC 5.1. |
| |
| @item |
| @code{decltype(nullptr)} incorrectly had an alignment of 1, leading to |
| unaligned accesses. Note that this did not affect the ABI of a |
| function with a @code{nullptr_t} parameter, as parameters have a |
| minimum alignment. |
| |
| This was fixed in @option{-fabi-version=9}, the default for GCC 5.2. |
| |
| @item |
| Target-specific attributes that affect the identity of a type, such as |
| ia32 calling conventions on a function type (stdcall, regparm, etc.), |
| did not affect the mangled name, leading to name collisions when |
| function pointers were used as template arguments. |
| |
| This was fixed in @option{-fabi-version=10}, the default for GCC 6.1. |
| |
| @end itemize |
| |
| This option also enables warnings about psABI-related changes. |
| The known psABI changes at this point include: |
| |
| @itemize @bullet |
| |
| @item |
| For SysV/x86-64, unions with @code{long double} members are |
| passed in memory as specified in psABI. Prior to GCC 4.4, this was not |
| the case. For example: |
| |
| @smallexample |
| union U @{ |
| long double ld; |
| int i; |
| @}; |
| @end smallexample |
| |
| @noindent |
| @code{union U} is now always passed in memory. |
| |
| @end itemize |
| |
| @item -Wchar-subscripts |
| @opindex Wchar-subscripts |
| @opindex Wno-char-subscripts |
| Warn if an array subscript has type @code{char}. This is a common cause |
| of error, as programmers often forget that this type is signed on some |
| machines. |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wno-coverage-mismatch |
| @opindex Wno-coverage-mismatch |
| @opindex Wcoverage-mismatch |
| Warn if feedback profiles do not match when using the |
| @option{-fprofile-use} option. |
| If a source file is changed between compiling with @option{-fprofile-generate} |
| and with @option{-fprofile-use}, the files with the profile feedback can fail |
| to match the source file and GCC cannot use the profile feedback |
| information. By default, this warning is enabled and is treated as an |
| error. @option{-Wno-coverage-mismatch} can be used to disable the |
| warning or @option{-Wno-error=coverage-mismatch} can be used to |
| disable the error. Disabling the error for this warning can result in |
| poorly optimized code and is useful only in the |
| case of very minor changes such as bug fixes to an existing code-base. |
| Completely disabling the warning is not recommended. |
| |
| @item -Wno-coverage-invalid-line-number |
| @opindex Wno-coverage-invalid-line-number |
| @opindex Wcoverage-invalid-line-number |
| Warn in case a function ends earlier than it begins due |
| to an invalid linenum macros. The warning is emitted only |
| with @option{--coverage} enabled. |
| |
| By default, this warning is enabled and is treated as an |
| error. @option{-Wno-coverage-invalid-line-number} can be used to disable the |
| warning or @option{-Wno-error=coverage-invalid-line-number} can be used to |
| disable the error. |
| |
| @item -Wno-cpp @r{(C, Objective-C, C++, Objective-C++ and Fortran only)} |
| @opindex Wno-cpp |
| @opindex Wcpp |
| Suppress warning messages emitted by @code{#warning} directives. |
| |
| @item -Wdouble-promotion @r{(C, C++, Objective-C and Objective-C++ only)} |
| @opindex Wdouble-promotion |
| @opindex Wno-double-promotion |
| Give a warning when a value of type @code{float} is implicitly |
| promoted to @code{double}. CPUs with a 32-bit ``single-precision'' |
| floating-point unit implement @code{float} in hardware, but emulate |
| @code{double} in software. On such a machine, doing computations |
| using @code{double} values is much more expensive because of the |
| overhead required for software emulation. |
| |
| It is easy to accidentally do computations with @code{double} because |
| floating-point literals are implicitly of type @code{double}. For |
| example, in: |
| @smallexample |
| @group |
| float area(float radius) |
| @{ |
| return 3.14159 * radius * radius; |
| @} |
| @end group |
| @end smallexample |
| the compiler performs the entire computation with @code{double} |
| because the floating-point literal is a @code{double}. |
| |
| @item -Wduplicate-decl-specifier @r{(C and Objective-C only)} |
| @opindex Wduplicate-decl-specifier |
| @opindex Wno-duplicate-decl-specifier |
| Warn if a declaration has duplicate @code{const}, @code{volatile}, |
| @code{restrict} or @code{_Atomic} specifier. This warning is enabled by |
| @option{-Wall}. |
| |
| @item -Wformat |
| @itemx -Wformat=@var{n} |
| @opindex Wformat |
| @opindex Wno-format |
| @opindex ffreestanding |
| @opindex fno-builtin |
| @opindex Wformat= |
| Check calls to @code{printf} and @code{scanf}, etc., to make sure that |
| the arguments supplied have types appropriate to the format string |
| specified, and that the conversions specified in the format string make |
| sense. This includes standard functions, and others specified by format |
| attributes (@pxref{Function Attributes}), in the @code{printf}, |
| @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension, |
| not in the C standard) families (or other target-specific families). |
| Which functions are checked without format attributes having been |
| specified depends on the standard version selected, and such checks of |
| functions without the attribute specified are disabled by |
| @option{-ffreestanding} or @option{-fno-builtin}. |
| |
| The formats are checked against the format features supported by GNU |
| libc version 2.2. These include all ISO C90 and C99 features, as well |
| as features from the Single Unix Specification and some BSD and GNU |
| extensions. Other library implementations may not support all these |
| features; GCC does not support warning about features that go beyond a |
| particular library's limitations. However, if @option{-Wpedantic} is used |
| with @option{-Wformat}, warnings are given about format features not |
| in the selected standard version (but not for @code{strfmon} formats, |
| since those are not in any version of the C standard). @xref{C Dialect |
| Options,,Options Controlling C Dialect}. |
| |
| @table @gcctabopt |
| @item -Wformat=1 |
| @itemx -Wformat |
| @opindex Wformat |
| @opindex Wformat=1 |
| Option @option{-Wformat} is equivalent to @option{-Wformat=1}, and |
| @option{-Wno-format} is equivalent to @option{-Wformat=0}. Since |
| @option{-Wformat} also checks for null format arguments for several |
| functions, @option{-Wformat} also implies @option{-Wnonnull}. Some |
| aspects of this level of format checking can be disabled by the |
| options: @option{-Wno-format-contains-nul}, |
| @option{-Wno-format-extra-args}, and @option{-Wno-format-zero-length}. |
| @option{-Wformat} is enabled by @option{-Wall}. |
| |
| @item -Wformat=2 |
| @opindex Wformat=2 |
| Enable @option{-Wformat} plus additional format checks. Currently |
| equivalent to @option{-Wformat -Wformat-nonliteral -Wformat-security |
| -Wformat-y2k}. |
| @end table |
| |
| @item -Wno-format-contains-nul |
| @opindex Wno-format-contains-nul |
| @opindex Wformat-contains-nul |
| If @option{-Wformat} is specified, do not warn about format strings that |
| contain NUL bytes. |
| |
| @item -Wno-format-extra-args |
| @opindex Wno-format-extra-args |
| @opindex Wformat-extra-args |
| If @option{-Wformat} is specified, do not warn about excess arguments to a |
| @code{printf} or @code{scanf} format function. The C standard specifies |
| that such arguments are ignored. |
| |
| Where the unused arguments lie between used arguments that are |
| specified with @samp{$} operand number specifications, normally |
| warnings are still given, since the implementation could not know what |
| type to pass to @code{va_arg} to skip the unused arguments. However, |
| in the case of @code{scanf} formats, this option suppresses the |
| warning if the unused arguments are all pointers, since the Single |
| Unix Specification says that such unused arguments are allowed. |
| |
| @item -Wformat-overflow |
| @itemx -Wformat-overflow=@var{level} |
| @opindex Wformat-overflow |
| @opindex Wno-format-overflow |
| Warn about calls to formatted input/output functions such as @code{sprintf} |
| and @code{vsprintf} that might overflow the destination buffer. When the |
| exact number of bytes written by a format directive cannot be determined |
| at compile-time it is estimated based on heuristics that depend on the |
| @var{level} argument and on optimization. While enabling optimization |
| will in most cases improve the accuracy of the warning, it may also |
| result in false positives. |
| |
| @table @gcctabopt |
| @item -Wformat-overflow |
| @itemx -Wformat-overflow=1 |
| @opindex Wformat-overflow |
| @opindex Wno-format-overflow |
| Level @var{1} of @option{-Wformat-overflow} enabled by @option{-Wformat} |
| employs a conservative approach that warns only about calls that most |
| likely overflow the buffer. At this level, numeric arguments to format |
| directives with unknown values are assumed to have the value of one, and |
| strings of unknown length to be empty. Numeric arguments that are known |
| to be bounded to a subrange of their type, or string arguments whose output |
| is bounded either by their directive's precision or by a finite set of |
| string literals, are assumed to take on the value within the range that |
| results in the most bytes on output. For example, the call to @code{sprintf} |
| below is diagnosed because even with both @var{a} and @var{b} equal to zero, |
| the terminating NUL character (@code{'\0'}) appended by the function |
| to the destination buffer will be written past its end. Increasing |
| the size of the buffer by a single byte is sufficient to avoid the |
| warning, though it may not be sufficient to avoid the overflow. |
| |
| @smallexample |
| void f (int a, int b) |
| @{ |
| char buf [13]; |
| sprintf (buf, "a = %i, b = %i\n", a, b); |
| @} |
| @end smallexample |
| |
| @item -Wformat-overflow=2 |
| Level @var{2} warns also about calls that might overflow the destination |
| buffer given an argument of sufficient length or magnitude. At level |
| @var{2}, unknown numeric arguments are assumed to have the minimum |
| representable value for signed types with a precision greater than 1, and |
| the maximum representable value otherwise. Unknown string arguments whose |
| length cannot be assumed to be bounded either by the directive's precision, |
| or by a finite set of string literals they may evaluate to, or the character |
| array they may point to, are assumed to be 1 character long. |
| |
| At level @var{2}, the call in the example above is again diagnosed, but |
| this time because with @var{a} equal to a 32-bit @code{INT_MIN} the first |
| @code{%i} directive will write some of its digits beyond the end of |
| the destination buffer. To make the call safe regardless of the values |
| of the two variables, the size of the destination buffer must be increased |
| to at least 34 bytes. GCC includes the minimum size of the buffer in |
| an informational note following the warning. |
| |
| An alternative to increasing the size of the destination buffer is to |
| constrain the range of formatted values. The maximum length of string |
| arguments can be bounded by specifying the precision in the format |
| directive. When numeric arguments of format directives can be assumed |
| to be bounded by less than the precision of their type, choosing |
| an appropriate length modifier to the format specifier will reduce |
| the required buffer size. For example, if @var{a} and @var{b} in the |
| example above can be assumed to be within the precision of |
| the @code{short int} type then using either the @code{%hi} format |
| directive or casting the argument to @code{short} reduces the maximum |
| required size of the buffer to 24 bytes. |
| |
| @smallexample |
| void f (int a, int b) |
| @{ |
| char buf [23]; |
| sprintf (buf, "a = %hi, b = %i\n", a, (short)b); |
| @} |
| @end smallexample |
| @end table |
| |
| @item -Wno-format-zero-length |
| @opindex Wno-format-zero-length |
| @opindex Wformat-zero-length |
| If @option{-Wformat} is specified, do not warn about zero-length formats. |
| The C standard specifies that zero-length formats are allowed. |
| |
| @item -Wformat-nonliteral |
| @opindex Wformat-nonliteral |
| @opindex Wno-format-nonliteral |
| If @option{-Wformat} is specified, also warn if the format string is not a |
| string literal and so cannot be checked, unless the format function |
| takes its format arguments as a @code{va_list}. |
| |
| @item -Wformat-security |
| @opindex Wformat-security |
| @opindex Wno-format-security |
| If @option{-Wformat} is specified, also warn about uses of format |
| functions that represent possible security problems. At present, this |
| warns about calls to @code{printf} and @code{scanf} functions where the |
| format string is not a string literal and there are no format arguments, |
| as in @code{printf (foo);}. This may be a security hole if the format |
| string came from untrusted input and contains @samp{%n}. (This is |
| currently a subset of what @option{-Wformat-nonliteral} warns about, but |
| in future warnings may be added to @option{-Wformat-security} that are not |
| included in @option{-Wformat-nonliteral}.) |
| |
| @item -Wformat-signedness |
| @opindex Wformat-signedness |
| @opindex Wno-format-signedness |
| If @option{-Wformat} is specified, also warn if the format string |
| requires an unsigned argument and the argument is signed and vice versa. |
| |
| @item -Wformat-truncation |
| @itemx -Wformat-truncation=@var{level} |
| @opindex Wformat-truncation |
| @opindex Wno-format-truncation |
| Warn about calls to formatted input/output functions such as @code{snprintf} |
| and @code{vsnprintf} that might result in output truncation. When the exact |
| number of bytes written by a format directive cannot be determined at |
| compile-time it is estimated based on heuristics that depend on |
| the @var{level} argument and on optimization. While enabling optimization |
| will in most cases improve the accuracy of the warning, it may also result |
| in false positives. Except as noted otherwise, the option uses the same |
| logic @option{-Wformat-overflow}. |
| |
| @table @gcctabopt |
| @item -Wformat-truncation |
| @itemx -Wformat-truncation=1 |
| @opindex Wformat-truncation |
| @opindex Wno-format-truncation |
| Level @var{1} of @option{-Wformat-truncation} enabled by @option{-Wformat} |
| employs a conservative approach that warns only about calls to bounded |
| functions whose return value is unused and that will most likely result |
| in output truncation. |
| |
| @item -Wformat-truncation=2 |
| Level @var{2} warns also about calls to bounded functions whose return |
| value is used and that might result in truncation given an argument of |
| sufficient length or magnitude. |
| @end table |
| |
| @item -Wformat-y2k |
| @opindex Wformat-y2k |
| @opindex Wno-format-y2k |
| If @option{-Wformat} is specified, also warn about @code{strftime} |
| formats that may yield only a two-digit year. |
| |
| @item -Wnonnull |
| @opindex Wnonnull |
| @opindex Wno-nonnull |
| Warn about passing a null pointer for arguments marked as |
| requiring a non-null value by the @code{nonnull} function attribute. |
| |
| @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It |
| can be disabled with the @option{-Wno-nonnull} option. |
| |
| @item -Wnonnull-compare |
| @opindex Wnonnull-compare |
| @opindex Wno-nonnull-compare |
| Warn when comparing an argument marked with the @code{nonnull} |
| function attribute against null inside the function. |
| |
| @option{-Wnonnull-compare} is included in @option{-Wall}. It |
| can be disabled with the @option{-Wno-nonnull-compare} option. |
| |
| @item -Wnull-dereference |
| @opindex Wnull-dereference |
| @opindex Wno-null-dereference |
| Warn if the compiler detects paths that trigger erroneous or |
| undefined behavior due to dereferencing a null pointer. This option |
| is only active when @option{-fdelete-null-pointer-checks} is active, |
| which is enabled by optimizations in most targets. The precision of |
| the warnings depends on the optimization options used. |
| |
| @item -Winfinite-recursion |
| @opindex Winfinite-recursion |
| @opindex Wno-infinite-recursion |
| Warn about infinitely recursive calls. The warning is effective at all |
| optimization levels but requires optimization in order to detect infinite |
| recursion in calls between two or more functions. |
| @option{-Winfinite-recursion} is included in @option{-Wall}. |
| |
| @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)} |
| @opindex Winit-self |
| @opindex Wno-init-self |
| Warn about uninitialized variables that are initialized with themselves. |
| Note this option can only be used with the @option{-Wuninitialized} option. |
| |
| For example, GCC warns about @code{i} being uninitialized in the |
| following snippet only when @option{-Winit-self} has been specified: |
| @smallexample |
| @group |
| int f() |
| @{ |
| int i = i; |
| return i; |
| @} |
| @end group |
| @end smallexample |
| |
| This warning is enabled by @option{-Wall} in C++. |
| |
| @item -Wno-implicit-int @r{(C and Objective-C only)} |
| @opindex Wimplicit-int |
| @opindex Wno-implicit-int |
| This option controls warnings when a declaration does not specify a type. |
| This warning is enabled by default in C99 and later dialects of C, |
| and also by @option{-Wall}. |
| |
| @item -Wno-implicit-function-declaration @r{(C and Objective-C only)} |
| @opindex Wimplicit-function-declaration |
| @opindex Wno-implicit-function-declaration |
| This option controls warnings when a function is used before being declared. |
| This warning is enabled by default in C99 and later dialects of C, |
| and also by @option{-Wall}. |
| The warning is made into an error by @option{-pedantic-errors}. |
| |
| @item -Wimplicit @r{(C and Objective-C only)} |
| @opindex Wimplicit |
| @opindex Wno-implicit |
| Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}. |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wimplicit-fallthrough |
| @opindex Wimplicit-fallthrough |
| @opindex Wno-implicit-fallthrough |
| @option{-Wimplicit-fallthrough} is the same as @option{-Wimplicit-fallthrough=3} |
| and @option{-Wno-implicit-fallthrough} is the same as |
| @option{-Wimplicit-fallthrough=0}. |
| |
| @item -Wimplicit-fallthrough=@var{n} |
| @opindex Wimplicit-fallthrough= |
| Warn when a switch case falls through. For example: |
| |
| @smallexample |
| @group |
| switch (cond) |
| @{ |
| case 1: |
| a = 1; |
| break; |
| case 2: |
| a = 2; |
| case 3: |
| a = 3; |
| break; |
| @} |
| @end group |
| @end smallexample |
| |
| This warning does not warn when the last statement of a case cannot |
| fall through, e.g. when there is a return statement or a call to function |
| declared with the noreturn attribute. @option{-Wimplicit-fallthrough=} |
| also takes into account control flow statements, such as ifs, and only |
| warns when appropriate. E.g.@: |
| |
| @smallexample |
| @group |
| switch (cond) |
| @{ |
| case 1: |
| if (i > 3) @{ |
| bar (5); |
| break; |
| @} else if (i < 1) @{ |
| bar (0); |
| @} else |
| return; |
| default: |
| @dots{} |
| @} |
| @end group |
| @end smallexample |
| |
| Since there are occasions where a switch case fall through is desirable, |
| GCC provides an attribute, @code{__attribute__ ((fallthrough))}, that is |
| to be used along with a null statement to suppress this warning that |
| would normally occur: |
| |
| @smallexample |
| @group |
| switch (cond) |
| @{ |
| case 1: |
| bar (0); |
| __attribute__ ((fallthrough)); |
| default: |
| @dots{} |
| @} |
| @end group |
| @end smallexample |
| |
| C++17 provides a standard way to suppress the @option{-Wimplicit-fallthrough} |
| warning using @code{[[fallthrough]];} instead of the GNU attribute. In C++11 |
| or C++14 users can use @code{[[gnu::fallthrough]];}, which is a GNU extension. |
| Instead of these attributes, it is also possible to add a fallthrough comment |
| to silence the warning. The whole body of the C or C++ style comment should |
| match the given regular expressions listed below. The option argument @var{n} |
| specifies what kind of comments are accepted: |
| |
| @itemize @bullet |
| |
| @item @option{-Wimplicit-fallthrough=0} disables the warning altogether. |
| |
| @item @option{-Wimplicit-fallthrough=1} matches @code{.*} regular |
| expression, any comment is used as fallthrough comment. |
| |
| @item @option{-Wimplicit-fallthrough=2} case insensitively matches |
| @code{.*falls?[ \t-]*thr(ough|u).*} regular expression. |
| |
| @item @option{-Wimplicit-fallthrough=3} case sensitively matches one of the |
| following regular expressions: |
| |
| @itemize @bullet |
| |
| @item @code{-fallthrough} |
| |
| @item @code{@@fallthrough@@} |
| |
| @item @code{lint -fallthrough[ \t]*} |
| |
| @item @code{[ \t.!]*(ELSE,? |INTENTIONAL(LY)? )?@*FALL(S | |-)?THR(OUGH|U)[ \t.!]*(-[^\n\r]*)?} |
| |
| @item @code{[ \t.!]*(Else,? |Intentional(ly)? )?@*Fall((s | |-)[Tt]|t)hr(ough|u)[ \t.!]*(-[^\n\r]*)?} |
| |
| @item @code{[ \t.!]*([Ee]lse,? |[Ii]ntentional(ly)? )?@*fall(s | |-)?thr(ough|u)[ \t.!]*(-[^\n\r]*)?} |
| |
| @end itemize |
| |
| @item @option{-Wimplicit-fallthrough=4} case sensitively matches one of the |
| following regular expressions: |
| |
| @itemize @bullet |
| |
| @item @code{-fallthrough} |
| |
| @item @code{@@fallthrough@@} |
| |
| @item @code{lint -fallthrough[ \t]*} |
| |
| @item @code{[ \t]*FALLTHR(OUGH|U)[ \t]*} |
| |
| @end itemize |
| |
| @item @option{-Wimplicit-fallthrough=5} doesn't recognize any comments as |
| fallthrough comments, only attributes disable the warning. |
| |
| @end itemize |
| |
| The comment needs to be followed after optional whitespace and other comments |
| by @code{case} or @code{default} keywords or by a user label that precedes some |
| @code{case} or @code{default} label. |
| |
| @smallexample |
| @group |
| switch (cond) |
| @{ |
| case 1: |
| bar (0); |
| /* FALLTHRU */ |
| default: |
| @dots{} |
| @} |
| @end group |
| @end smallexample |
| |
| The @option{-Wimplicit-fallthrough=3} warning is enabled by @option{-Wextra}. |
| |
| @item -Wno-if-not-aligned @r{(C, C++, Objective-C and Objective-C++ only)} |
| @opindex Wif-not-aligned |
| @opindex Wno-if-not-aligned |
| Control if warnings triggered by the @code{warn_if_not_aligned} attribute |
| should be issued. These warnings are enabled by default. |
| |
| @item -Wignored-qualifiers @r{(C and C++ only)} |
| @opindex Wignored-qualifiers |
| @opindex Wno-ignored-qualifiers |
| Warn if the return type of a function has a type qualifier |
| such as @code{const}. For ISO C such a type qualifier has no effect, |
| since the value returned by a function is not an lvalue. |
| For C++, the warning is only emitted for scalar types or @code{void}. |
| ISO C prohibits qualified @code{void} return types on function |
| definitions, so such return types always receive a warning |
| even without this option. |
| |
| This warning is also enabled by @option{-Wextra}. |
| |
| @item -Wno-ignored-attributes @r{(C and C++ only)} |
| @opindex Wignored-attributes |
| @opindex Wno-ignored-attributes |
| This option controls warnings when an attribute is ignored. |
| This is different from the |
| @option{-Wattributes} option in that it warns whenever the compiler decides |
| to drop an attribute, not that the attribute is either unknown, used in a |
| wrong place, etc. This warning is enabled by default. |
| |
| @item -Wmain |
| @opindex Wmain |
| @opindex Wno-main |
| Warn if the type of @code{main} is suspicious. @code{main} should be |
| a function with external linkage, returning int, taking either zero |
| arguments, two, or three arguments of appropriate types. This warning |
| is enabled by default in C++ and is enabled by either @option{-Wall} |
| or @option{-Wpedantic}. |
| |
| @item -Wmisleading-indentation @r{(C and C++ only)} |
| @opindex Wmisleading-indentation |
| @opindex Wno-misleading-indentation |
| Warn when the indentation of the code does not reflect the block structure. |
| Specifically, a warning is issued for @code{if}, @code{else}, @code{while}, and |
| @code{for} clauses with a guarded statement that does not use braces, |
| followed by an unguarded statement with the same indentation. |
| |
| In the following example, the call to ``bar'' is misleadingly indented as |
| if it were guarded by the ``if'' conditional. |
| |
| @smallexample |
| if (some_condition ()) |
| foo (); |
| bar (); /* Gotcha: this is not guarded by the "if". */ |
| @end smallexample |
| |
| In the case of mixed tabs and spaces, the warning uses the |
| @option{-ftabstop=} option to determine if the statements line up |
| (defaulting to 8). |
| |
| The warning is not issued for code involving multiline preprocessor logic |
| such as the following example. |
| |
| @smallexample |
| if (flagA) |
| foo (0); |
| #if SOME_CONDITION_THAT_DOES_NOT_HOLD |
| if (flagB) |
| #endif |
| foo (1); |
| @end smallexample |
| |
| The warning is not issued after a @code{#line} directive, since this |
| typically indicates autogenerated code, and no assumptions can be made |
| about the layout of the file that the directive references. |
| |
| This warning is enabled by @option{-Wall} in C and C++. |
| |
| @item -Wmissing-attributes |
| @opindex Wmissing-attributes |
| @opindex Wno-missing-attributes |
| Warn when a declaration of a function is missing one or more attributes |
| that a related function is declared with and whose absence may adversely |
| affect the correctness or efficiency of generated code. For example, |
| the warning is issued for declarations of aliases that use attributes |
| to specify less restrictive requirements than those of their targets. |
| This typically represents a potential optimization opportunity. |
| By contrast, the @option{-Wattribute-alias=2} option controls warnings |
| issued when the alias is more restrictive than the target, which could |
| lead to incorrect code generation. |
| Attributes considered include @code{alloc_align}, @code{alloc_size}, |
| @code{cold}, @code{const}, @code{hot}, @code{leaf}, @code{malloc}, |
| @code{nonnull}, @code{noreturn}, @code{nothrow}, @code{pure}, |
| @code{returns_nonnull}, and @code{returns_twice}. |
| |
| In C++, the warning is issued when an explicit specialization of a primary |
| template declared with attribute @code{alloc_align}, @code{alloc_size}, |
| @code{assume_aligned}, @code{format}, @code{format_arg}, @code{malloc}, |
| or @code{nonnull} is declared without it. Attributes @code{deprecated}, |
| @code{error}, and @code{warning} suppress the warning. |
| (@pxref{Function Attributes}). |
| |
| You can use the @code{copy} attribute to apply the same |
| set of attributes to a declaration as that on another declaration without |
| explicitly enumerating the attributes. This attribute can be applied |
| to declarations of functions (@pxref{Common Function Attributes}), |
| variables (@pxref{Common Variable Attributes}), or types |
| (@pxref{Common Type Attributes}). |
| |
| @option{-Wmissing-attributes} is enabled by @option{-Wall}. |
| |
| For example, since the declaration of the primary function template |
| below makes use of both attribute @code{malloc} and @code{alloc_size} |
| the declaration of the explicit specialization of the template is |
| diagnosed because it is missing one of the attributes. |
| |
| @smallexample |
| template <class T> |
| T* __attribute__ ((malloc, alloc_size (1))) |
| allocate (size_t); |
| |
| template <> |
| void* __attribute__ ((malloc)) // missing alloc_size |
| allocate<void> (size_t); |
| @end smallexample |
| |
| @item -Wmissing-braces |
| @opindex Wmissing-braces |
| @opindex Wno-missing-braces |
| Warn if an aggregate or union initializer is not fully bracketed. In |
| the following example, the initializer for @code{a} is not fully |
| bracketed, but that for @code{b} is fully bracketed. |
| |
| @smallexample |
| int a[2][2] = @{ 0, 1, 2, 3 @}; |
| int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @}; |
| @end smallexample |
| |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wmissing-include-dirs @r{(C, C++, Objective-C, Objective-C++ and Fortran only)} |
| @opindex Wmissing-include-dirs |
| @opindex Wno-missing-include-dirs |
| Warn if a user-supplied include directory does not exist. This opions is disabled |
| by default for C, C++, Objective-C and Objective-C++. For Fortran, it is partially |
| enabled by default by warning for -I and -J, only. |
| |
| @item -Wno-missing-profile |
| @opindex Wmissing-profile |
| @opindex Wno-missing-profile |
| This option controls warnings if feedback profiles are missing when using the |
| @option{-fprofile-use} option. |
| This option diagnoses those cases where a new function or a new file is added |
| between compiling with @option{-fprofile-generate} and with |
| @option{-fprofile-use}, without regenerating the profiles. |
| In these cases, the profile feedback data files do not contain any |
| profile feedback information for |
| the newly added function or file respectively. Also, in the case when profile |
| count data (.gcda) files are removed, GCC cannot use any profile feedback |
| information. In all these cases, warnings are issued to inform you that a |
| profile generation step is due. |
| Ignoring the warning can result in poorly optimized code. |
| @option{-Wno-missing-profile} can be used to |
| disable the warning, but this is not recommended and should be done only |
| when non-existent profile data is justified. |
| |
| @item -Wmismatched-dealloc |
| @opindex Wmismatched-dealloc |
| @opindex Wno-mismatched-dealloc |
| |
| Warn for calls to deallocation functions with pointer arguments returned |
| from from allocations functions for which the former isn't a suitable |
| deallocator. A pair of functions can be associated as matching allocators |
| and deallocators by use of attribute @code{malloc}. Unless disabled by |
| the @option{-fno-builtin} option the standard functions @code{calloc}, |
| @code{malloc}, @code{realloc}, and @code{free}, as well as the corresponding |
| forms of C++ @code{operator new} and @code{operator delete} are implicitly |
| associated as matching allocators and deallocators. In the following |
| example @code{mydealloc} is the deallocator for pointers returned from |
| @code{myalloc}. |
| |
| @smallexample |
| void mydealloc (void*); |
| |
| __attribute__ ((malloc (mydealloc, 1))) void* |
| myalloc (size_t); |
| |
| void f (void) |
| @{ |
| void *p = myalloc (32); |
| // @dots{}use p@dots{} |
| free (p); // warning: not a matching deallocator for myalloc |
| mydealloc (p); // ok |
| @} |
| @end smallexample |
| |
| In C++, the related option @option{-Wmismatched-new-delete} diagnoses |
| mismatches involving either @code{operator new} or @code{operator delete}. |
| |
| Option @option{-Wmismatched-dealloc} is included in @option{-Wall}. |
| |
| @item -Wmultistatement-macros |
| @opindex Wmultistatement-macros |
| @opindex Wno-multistatement-macros |
| Warn about unsafe multiple statement macros that appear to be guarded |
| by a clause such as @code{if}, @code{else}, @code{for}, @code{switch}, or |
| @code{while}, in which only the first statement is actually guarded after |
| the macro is expanded. |
| |
| For example: |
| |
| @smallexample |
| #define DOIT x++; y++ |
| if (c) |
| DOIT; |
| @end smallexample |
| |
| will increment @code{y} unconditionally, not just when @code{c} holds. |
| The can usually be fixed by wrapping the macro in a do-while loop: |
| @smallexample |
| #define DOIT do @{ x++; y++; @} while (0) |
| if (c) |
| DOIT; |
| @end smallexample |
| |
| This warning is enabled by @option{-Wall} in C and C++. |
| |
| @item -Wparentheses |
| @opindex Wparentheses |
| @opindex Wno-parentheses |
| Warn if parentheses are omitted in certain contexts, such |
| as when there is an assignment in a context where a truth value |
| is expected, or when operators are nested whose precedence people |
| often get confused about. |
| |
| Also warn if a comparison like @code{x<=y<=z} appears; this is |
| equivalent to @code{(x<=y ? 1 : 0) <= z}, which is a different |
| interpretation from that of ordinary mathematical notation. |
| |
| Also warn for dangerous uses of the GNU extension to |
| @code{?:} with omitted middle operand. When the condition |
| in the @code{?}: operator is a boolean expression, the omitted value is |
| always 1. Often programmers expect it to be a value computed |
| inside the conditional expression instead. |
| |
| For C++ this also warns for some cases of unnecessary parentheses in |
| declarations, which can indicate an attempt at a function call instead |
| of a declaration: |
| @smallexample |
| @{ |
| // Declares a local variable called mymutex. |
| std::unique_lock<std::mutex> (mymutex); |
| // User meant std::unique_lock<std::mutex> lock (mymutex); |
| @} |
| @end smallexample |
| |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wsequence-point |
| @opindex Wsequence-point |
| @opindex Wno-sequence-point |
| Warn about code that may have undefined semantics because of violations |
| of sequence point rules in the C and C++ standards. |
| |
| The C and C++ standards define the order in which expressions in a C/C++ |
| program are evaluated in terms of @dfn{sequence points}, which represent |
| a partial ordering between the execution of parts of the program: those |
| executed before the sequence point, and those executed after it. These |
| occur after the evaluation of a full expression (one which is not part |
| of a larger expression), after the evaluation of the first operand of a |
| @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a |
| function is called (but after the evaluation of its arguments and the |
| expression denoting the called function), and in certain other places. |
| Other than as expressed by the sequence point rules, the order of |
| evaluation of subexpressions of an expression is not specified. All |
| these rules describe only a partial order rather than a total order, |
| since, for example, if two functions are called within one expression |
| with no sequence point between them, the order in which the functions |
| are called is not specified. However, the standards committee have |
| ruled that function calls do not overlap. |
| |
| It is not specified when between sequence points modifications to the |
| values of objects take effect. Programs whose behavior depends on this |
| have undefined behavior; the C and C++ standards specify that ``Between |
| the previous and next sequence point an object shall have its stored |
| value modified at most once by the evaluation of an expression. |
| Furthermore, the prior value shall be read only to determine the value |
| to be stored.''. If a program breaks these rules, the results on any |
| particular implementation are entirely unpredictable. |
| |
| Examples of code with undefined behavior are @code{a = a++;}, @code{a[n] |
| = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not |
| diagnosed by this option, and it may give an occasional false positive |
| result, but in general it has been found fairly effective at detecting |
| this sort of problem in programs. |
| |
| The C++17 standard will define the order of evaluation of operands in |
| more cases: in particular it requires that the right-hand side of an |
| assignment be evaluated before the left-hand side, so the above |
| examples are no longer undefined. But this option will still warn |
| about them, to help people avoid writing code that is undefined in C |
| and earlier revisions of C++. |
| |
| The standard is worded confusingly, therefore there is some debate |
| over the precise meaning of the sequence point rules in subtle cases. |
| Links to discussions of the problem, including proposed formal |
| definitions, may be found on the GCC readings page, at |
| @uref{https://gcc.gnu.org/@/readings.html}. |
| |
| This warning is enabled by @option{-Wall} for C and C++. |
| |
| @item -Wno-return-local-addr |
| @opindex Wno-return-local-addr |
| @opindex Wreturn-local-addr |
| Do not warn about returning a pointer (or in C++, a reference) to a |
| variable that goes out of scope after the function returns. |
| |
| @item -Wreturn-type |
| @opindex Wreturn-type |
| @opindex Wno-return-type |
| Warn whenever a function is defined with a return type that defaults |
| to @code{int}. Also warn about any @code{return} statement with no |
| return value in a function whose return type is not @code{void} |
| (falling off the end of the function body is considered returning |
| without a value). |
| |
| For C only, warn about a @code{return} statement with an expression in a |
| function whose return type is @code{void}, unless the expression type is |
| also @code{void}. As a GNU extension, the latter case is accepted |
| without a warning unless @option{-Wpedantic} is used. Attempting |
| to use the return value of a non-@code{void} function other than @code{main} |
| that flows off the end by reaching the closing curly brace that terminates |
| the function is undefined. |
| |
| Unlike in C, in C++, flowing off the end of a non-@code{void} function other |
| than @code{main} results in undefined behavior even when the value of |
| the function is not used. |
| |
| This warning is enabled by default in C++ and by @option{-Wall} otherwise. |
| |
| @item -Wno-shift-count-negative |
| @opindex Wshift-count-negative |
| @opindex Wno-shift-count-negative |
| Controls warnings if a shift count is negative. |
| This warning is enabled by default. |
| |
| @item -Wno-shift-count-overflow |
| @opindex Wshift-count-overflow |
| @opindex Wno-shift-count-overflow |
| Controls warnings if a shift count is greater than or equal to the bit width |
| of the type. This warning is enabled by default. |
| |
| @item -Wshift-negative-value |
| @opindex Wshift-negative-value |
| @opindex Wno-shift-negative-value |
| Warn if left shifting a negative value. This warning is enabled by |
| @option{-Wextra} in C99 (and newer) and C++11 to C++17 modes. |
| |
| @item -Wno-shift-overflow |
| @itemx -Wshift-overflow=@var{n} |
| @opindex Wshift-overflow |
| @opindex Wno-shift-overflow |
| These options control warnings about left shift overflows. |
| |
| @table @gcctabopt |
| @item -Wshift-overflow=1 |
| This is the warning level of @option{-Wshift-overflow} and is enabled |
| by default in C99 and C++11 modes (and newer). This warning level does |
| not warn about left-shifting 1 into the sign bit. (However, in C, such |
| an overflow is still rejected in contexts where an integer constant expression |
| is required.) No warning is emitted in C++20 mode (and newer), as signed left |
| shifts always wrap. |
| |
| @item -Wshift-overflow=2 |
| This warning level also warns about left-shifting 1 into the sign bit, |
| unless C++14 mode (or newer) is active. |
| @end table |
| |
| @item -Wswitch |
| @opindex Wswitch |
| @opindex Wno-switch |
| Warn whenever a @code{switch} statement has an index of enumerated type |
| and lacks a @code{case} for one or more of the named codes of that |
| enumeration. (The presence of a @code{default} label prevents this |
| warning.) @code{case} labels outside the enumeration range also |
| provoke warnings when this option is used (even if there is a |
| @code{default} label). |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wswitch-default |
| @opindex Wswitch-default |
| @opindex Wno-switch-default |
| Warn whenever a @code{switch} statement does not have a @code{default} |
| case. |
| |
| @item -Wswitch-enum |
| @opindex Wswitch-enum |
| @opindex Wno-switch-enum |
| Warn whenever a @code{switch} statement has an index of enumerated type |
| and lacks a @code{case} for one or more of the named codes of that |
| enumeration. @code{case} labels outside the enumeration range also |
| provoke warnings when this option is used. The only difference |
| between @option{-Wswitch} and this option is that this option gives a |
| warning about an omitted enumeration code even if there is a |
| @code{default} label. |
| |
| @item -Wno-switch-bool |
| @opindex Wswitch-bool |
| @opindex Wno-switch-bool |
| Do not warn when a @code{switch} statement has an index of boolean type |
| and the case values are outside the range of a boolean type. |
| It is possible to suppress this warning by casting the controlling |
| expression to a type other than @code{bool}. For example: |
| @smallexample |
| @group |
| switch ((int) (a == 4)) |
| @{ |
| @dots{} |
| @} |
| @end group |
| @end smallexample |
| This warning is enabled by default for C and C++ programs. |
| |
| @item -Wno-switch-outside-range |
| @opindex Wswitch-outside-range |
| @opindex Wno-switch-outside-range |
| This option controls warnings when a @code{switch} case has a value |
| that is outside of its |
| respective type range. This warning is enabled by default for |
| C and C++ programs. |
| |
| @item -Wno-switch-unreachable |
| @opindex Wswitch-unreachable |
| @opindex Wno-switch-unreachable |
| Do not warn when a @code{switch} statement contains statements between the |
| controlling expression and the first case label, which will never be |
| executed. For example: |
| @smallexample |
| @group |
| switch (cond) |
| @{ |
| i = 15; |
| @dots{} |
| case 5: |
| @dots{} |
| @} |
| @end group |
| @end smallexample |
| @option{-Wswitch-unreachable} does not warn if the statement between the |
| controlling expression and the first case label is just a declaration: |
| @smallexample |
| @group |
| switch (cond) |
| @{ |
| int i; |
| @dots{} |
| case 5: |
| i = 5; |
| @dots{} |
| @} |
| @end group |
| @end smallexample |
| This warning is enabled by default for C and C++ programs. |
| |
| @item -Wsync-nand @r{(C and C++ only)} |
| @opindex Wsync-nand |
| @opindex Wno-sync-nand |
| Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch} |
| built-in functions are used. These functions changed semantics in GCC 4.4. |
| |
| @item -Wtrivial-auto-var-init |
| @opindex Wtrivial-auto-var-init |
| @opindex Wno-trivial-auto-var-init |
| Warn when @code{-ftrivial-auto-var-init} cannot initialize the automatic |
| variable. A common situation is an automatic variable that is declared |
| between the controlling expression and the first case label of a @code{switch} |
| statement. |
| |
| @item -Wunused-but-set-parameter |
| @opindex Wunused-but-set-parameter |
| @opindex Wno-unused-but-set-parameter |
| Warn whenever a function parameter is assigned to, but otherwise unused |
| (aside from its declaration). |
| |
| To suppress this warning use the @code{unused} attribute |
| (@pxref{Variable Attributes}). |
| |
| This warning is also enabled by @option{-Wunused} together with |
| @option{-Wextra}. |
| |
| @item -Wunused-but-set-variable |
| @opindex Wunused-but-set-variable |
| @opindex Wno-unused-but-set-variable |
| Warn whenever a local variable is assigned to, but otherwise unused |
| (aside from its declaration). |
| This warning is enabled by @option{-Wall}. |
| |
| To suppress this warning use the @code{unused} attribute |
| (@pxref{Variable Attributes}). |
| |
| This warning is also enabled by @option{-Wunused}, which is enabled |
| by @option{-Wall}. |
| |
| @item -Wunused-function |
| @opindex Wunused-function |
| @opindex Wno-unused-function |
| Warn whenever a static function is declared but not defined or a |
| non-inline static function is unused. |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wunused-label |
| @opindex Wunused-label |
| @opindex Wno-unused-label |
| Warn whenever a label is declared but not used. |
| This warning is enabled by @option{-Wall}. |
| |
| To suppress this warning use the @code{unused} attribute |
| (@pxref{Variable Attributes}). |
| |
| @item -Wunused-local-typedefs @r{(C, Objective-C, C++ and Objective-C++ only)} |
| @opindex Wunused-local-typedefs |
| @opindex Wno-unused-local-typedefs |
| Warn when a typedef locally defined in a function is not used. |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wunused-parameter |
| @opindex Wunused-parameter |
| @opindex Wno-unused-parameter |
| Warn whenever a function parameter is unused aside from its declaration. |
| |
| To suppress this warning use the @code{unused} attribute |
| (@pxref{Variable Attributes}). |
| |
| @item -Wno-unused-result |
| @opindex Wunused-result |
| @opindex Wno-unused-result |
| Do not warn if a caller of a function marked with attribute |
| @code{warn_unused_result} (@pxref{Function Attributes}) does not use |
| its return value. The default is @option{-Wunused-result}. |
| |
| @item -Wunused-variable |
| @opindex Wunused-variable |
| @opindex Wno-unused-variable |
| Warn whenever a local or static variable is unused aside from its |
| declaration. This option implies @option{-Wunused-const-variable=1} for C, |
| but not for C++. This warning is enabled by @option{-Wall}. |
| |
| To suppress this warning use the @code{unused} attribute |
| (@pxref{Variable Attributes}). |
| |
| @item -Wunused-const-variable |
| @itemx -Wunused-const-variable=@var{n} |
| @opindex Wunused-const-variable |
| @opindex Wno-unused-const-variable |
| Warn whenever a constant static variable is unused aside from its declaration. |
| @option{-Wunused-const-variable=1} is enabled by @option{-Wunused-variable} |
| for C, but not for C++. In C this declares variable storage, but in C++ this |
| is not an error since const variables take the place of @code{#define}s. |
| |
| To suppress this warning use the @code{unused} attribute |
| (@pxref{Variable Attributes}). |
| |
| @table @gcctabopt |
| @item -Wunused-const-variable=1 |
| This is the warning level that is enabled by @option{-Wunused-variable} for |
| C. It warns only about unused static const variables defined in the main |
| compilation unit, but not about static const variables declared in any |
| header included. |
| |
| @item -Wunused-const-variable=2 |
| This warning level also warns for unused constant static variables in |
| headers (excluding system headers). This is the warning level of |
| @option{-Wunused-const-variable} and must be explicitly requested since |
| in C++ this isn't an error and in C it might be harder to clean up all |
| headers included. |
| @end table |
| |
| @item -Wunused-value |
| @opindex Wunused-value |
| @opindex Wno-unused-value |
| Warn whenever a statement computes a result that is explicitly not |
| used. To suppress this warning cast the unused expression to |
| @code{void}. This includes an expression-statement or the left-hand |
| side of a comma expression that contains no side effects. For example, |
| an expression such as @code{x[i,j]} causes a warning, while |
| @code{x[(void)i,j]} does not. |
| |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wunused |
| @opindex Wunused |
| @opindex Wno-unused |
| All the above @option{-Wunused} options combined. |
| |
| In order to get a warning about an unused function parameter, you must |
| either specify @option{-Wextra -Wunused} (note that @option{-Wall} implies |
| @option{-Wunused}), or separately specify @option{-Wunused-parameter}. |
| |
| @item -Wuninitialized |
| @opindex Wuninitialized |
| @opindex Wno-uninitialized |
| Warn if an object with automatic or allocated storage duration is used |
| without having been initialized. In C++, also warn if a non-static |
| reference or non-static @code{const} member appears in a class without |
| constructors. |
| |
| In addition, passing a pointer (or in C++, a reference) to an uninitialized |
| object to a @code{const}-qualified argument of a built-in function known to |
| read the object is also diagnosed by this warning. |
| (@option{-Wmaybe-uninitialized} is issued for ordinary functions.) |
| |
| If you want to warn about code that uses the uninitialized value of the |
| variable in its own initializer, use the @option{-Winit-self} option. |
| |
| These warnings occur for individual uninitialized elements of |
| structure, union or array variables as well as for variables that are |
| uninitialized as a whole. They do not occur for variables or elements |
| declared @code{volatile}. Because these warnings depend on |
| optimization, the exact variables or elements for which there are |
| warnings depend on the precise optimization options and version of GCC |
| used. |
| |
| Note that there may be no warning about a variable that is used only |
| to compute a value that itself is never used, because such |
| computations may be deleted by data flow analysis before the warnings |
| are printed. |
| |
| In C++, this warning also warns about using uninitialized objects in |
| member-initializer-lists. For example, GCC warns about @code{b} being |
| uninitialized in the following snippet: |
| |
| @smallexample |
| struct A @{ |
| int a; |
| int b; |
| A() : a(b) @{ @} |
| @}; |
| @end smallexample |
| |
| @item -Wno-invalid-memory-model |
| @opindex Winvalid-memory-model |
| @opindex Wno-invalid-memory-model |
| This option controls warnings |
| for invocations of @ref{__atomic Builtins}, @ref{__sync Builtins}, |
| and the C11 atomic generic functions with a memory consistency argument |
| that is either invalid for the operation or outside the range of values |
| of the @code{memory_order} enumeration. For example, since the |
| @code{__atomic_store} and @code{__atomic_store_n} built-ins are only |
| defined for the relaxed, release, and sequentially consistent memory |
| orders the following code is diagnosed: |
| |
| @smallexample |
| void store (int *i) |
| @{ |
| __atomic_store_n (i, 0, memory_order_consume); |
| @} |
| @end smallexample |
| |
| @option{-Winvalid-memory-model} is enabled by default. |
| |
| @item -Wmaybe-uninitialized |
| @opindex Wmaybe-uninitialized |
| @opindex Wno-maybe-uninitialized |
| For an object with automatic or allocated storage duration, if there exists |
| a path from the function entry to a use of the object that is initialized, |
| but there exist some other paths for which the object is not initialized, |
| the compiler emits a warning if it cannot prove the uninitialized paths |
| are not executed at run time. |
| |
| In addition, passing a pointer (or in C++, a reference) to an uninitialized |
| object to a @code{const}-qualified function argument is also diagnosed by |
| this warning. (@option{-Wuninitialized} is issued for built-in functions |
| known to read the object.) Annotating the function with attribute |
| @code{access (none)} indicates that the argument isn't used to access |
| the object and avoids the warning (@pxref{Common Function Attributes}). |
| |
| These warnings are only possible in optimizing compilation, because otherwise |
| GCC does not keep track of the state of variables. |
| |
| These warnings are made optional because GCC may not be able to determine when |
| the code is correct in spite of appearing to have an error. Here is one |
| example of how this can happen: |
| |
| @smallexample |
| @group |
| @{ |
| int x; |
| switch (y) |
| @{ |
| case 1: x = 1; |
| break; |
| case 2: x = 4; |
| break; |
| case 3: x = 5; |
| @} |
| foo (x); |
| @} |
| @end group |
| @end smallexample |
| |
| @noindent |
| If the value of @code{y} is always 1, 2 or 3, then @code{x} is |
| always initialized, but GCC doesn't know this. To suppress the |
| warning, you need to provide a default case with assert(0) or |
| similar code. |
| |
| @cindex @code{longjmp} warnings |
| This option also warns when a non-volatile automatic variable might be |
| changed by a call to @code{longjmp}. |
| The compiler sees only the calls to @code{setjmp}. It cannot know |
| where @code{longjmp} will be called; in fact, a signal handler could |
| call it at any point in the code. As a result, you may get a warning |
| even when there is in fact no problem because @code{longjmp} cannot |
| in fact be called at the place that would cause a problem. |
| |
| Some spurious warnings can be avoided if you declare all the functions |
| you use that never return as @code{noreturn}. @xref{Function |
| Attributes}. |
| |
| This warning is enabled by @option{-Wall} or @option{-Wextra}. |
| |
| @item -Wunknown-pragmas |
| @opindex Wunknown-pragmas |
| @opindex Wno-unknown-pragmas |
| @cindex warning for unknown pragmas |
| @cindex unknown pragmas, warning |
| @cindex pragmas, warning of unknown |
| Warn when a @code{#pragma} directive is encountered that is not understood by |
| GCC@. If this command-line option is used, warnings are even issued |
| for unknown pragmas in system header files. This is not the case if |
| the warnings are only enabled by the @option{-Wall} command-line option. |
| |
| @item -Wno-pragmas |
| @opindex Wno-pragmas |
| @opindex Wpragmas |
| Do not warn about misuses of pragmas, such as incorrect parameters, |
| invalid syntax, or conflicts between pragmas. See also |
| @option{-Wunknown-pragmas}. |
| |
| @item -Wno-prio-ctor-dtor |
| @opindex Wno-prio-ctor-dtor |
| @opindex Wprio-ctor-dtor |
| Do not warn if a priority from 0 to 100 is used for constructor or destructor. |
| The use of constructor and destructor attributes allow you to assign a |
| priority to the constructor/destructor to control its order of execution |
| before @code{main} is called or after it returns. The priority values must be |
| greater than 100 as the compiler reserves priority values between 0--100 for |
| the implementation. |
| |
| @item -Wstrict-aliasing |
| @opindex Wstrict-aliasing |
| @opindex Wno-strict-aliasing |
| This option is only active when @option{-fstrict-aliasing} is active. |
| It warns about code that might break the strict aliasing rules that the |
| compiler is using for optimization. The warning does not catch all |
| cases, but does attempt to catch the more common pitfalls. It is |
| included in @option{-Wall}. |
| It is equivalent to @option{-Wstrict-aliasing=3} |
| |
| @item -Wstrict-aliasing=n |
| @opindex Wstrict-aliasing=n |
| This option is only active when @option{-fstrict-aliasing} is active. |
| It warns about code that might break the strict aliasing rules that the |
| compiler is using for optimization. |
| Higher levels correspond to higher accuracy (fewer false positives). |
| Higher levels also correspond to more effort, similar to the way @option{-O} |
| works. |
| @option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=3}. |
| |
| Level 1: Most aggressive, quick, least accurate. |
| Possibly useful when higher levels |
| do not warn but @option{-fstrict-aliasing} still breaks the code, as it has very few |
| false negatives. However, it has many false positives. |
| Warns for all pointer conversions between possibly incompatible types, |
| even if never dereferenced. Runs in the front end only. |
| |
| Level 2: Aggressive, quick, not too precise. |
| May still have many false positives (not as many as level 1 though), |
| and few false negatives (but possibly more than level 1). |
| Unlike level 1, it only warns when an address is taken. Warns about |
| incomplete types. Runs in the front end only. |
| |
| Level 3 (default for @option{-Wstrict-aliasing}): |
| Should have very few false positives and few false |
| negatives. Slightly slower than levels 1 or 2 when optimization is enabled. |
| Takes care of the common pun+dereference pattern in the front end: |
| @code{*(int*)&some_float}. |
| If optimization is enabled, it also runs in the back end, where it deals |
| with multiple statement cases using flow-sensitive points-to information. |
| Only warns when the converted pointer is dereferenced. |
| Does not warn about incomplete types. |
| |
| @item -Wstrict-overflow |
| @itemx -Wstrict-overflow=@var{n} |
| @opindex Wstrict-overflow |
| @opindex Wno-strict-overflow |
| This option is only active when signed overflow is undefined. |
| It warns about cases where the compiler optimizes based on the |
| assumption that signed overflow does not occur. Note that it does not |
| warn about all cases where the code might overflow: it only warns |
| about cases where the compiler implements some optimization. Thus |
| this warning depends on the optimization level. |
| |
| An optimization that assumes that signed overflow does not occur is |
| perfectly safe if the values of the variables involved are such that |
| overflow never does, in fact, occur. Therefore this warning can |
| easily give a false positive: a warning about code that is not |
| actually a problem. To help focus on important issues, several |
| warning levels are defined. No warnings are issued for the use of |
| undefined signed overflow when estimating how many iterations a loop |
| requires, in particular when determining whether a loop will be |
| executed at all. |
| |
| @table @gcctabopt |
| @item -Wstrict-overflow=1 |
| Warn about cases that are both questionable and easy to avoid. For |
| example the compiler simplifies |
| @code{x + 1 > x} to @code{1}. This level of |
| @option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels |
| are not, and must be explicitly requested. |
| |
| @item -Wstrict-overflow=2 |
| Also warn about other cases where a comparison is simplified to a |
| constant. For example: @code{abs (x) >= 0}. This can only be |
| simplified when signed integer overflow is undefined, because |
| @code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than |
| zero. @option{-Wstrict-overflow} (with no level) is the same as |
| @option{-Wstrict-overflow=2}. |
| |
| @item -Wstrict-overflow=3 |
| Also warn about other cases where a comparison is simplified. For |
| example: @code{x + 1 > 1} is simplified to @code{x > 0}. |
| |
| @item -Wstrict-overflow=4 |
| Also warn about other simplifications not covered by the above cases. |
| For example: @code{(x * 10) / 5} is simplified to @code{x * 2}. |
| |
| @item -Wstrict-overflow=5 |
| Also warn about cases where the compiler reduces the magnitude of a |
| constant involved in a comparison. For example: @code{x + 2 > y} is |
| simplified to @code{x + 1 >= y}. This is reported only at the |
| highest warning level because this simplification applies to many |
| comparisons, so this warning level gives a very large number of |
| false positives. |
| @end table |
| |
| @item -Wstring-compare |
| @opindex Wstring-compare |
| @opindex Wno-string-compare |
| Warn for calls to @code{strcmp} and @code{strncmp} whose result is |
| determined to be either zero or non-zero in tests for such equality |
| owing to the length of one argument being greater than the size of |
| the array the other argument is stored in (or the bound in the case |
| of @code{strncmp}). Such calls could be mistakes. For example, |
| the call to @code{strcmp} below is diagnosed because its result is |
| necessarily non-zero irrespective of the contents of the array @code{a}. |
| |
| @smallexample |
| extern char a[4]; |
| void f (char *d) |
| @{ |
| strcpy (d, "string"); |
| @dots{} |
| if (0 == strcmp (a, d)) // cannot be true |
| puts ("a and d are the same"); |
| @} |
| @end smallexample |
| |
| @option{-Wstring-compare} is enabled by @option{-Wextra}. |
| |
| @item -Wno-stringop-overflow |
| @item -Wstringop-overflow |
| @itemx -Wstringop-overflow=@var{type} |
| @opindex Wstringop-overflow |
| @opindex Wno-stringop-overflow |
| Warn for calls to string manipulation functions such as @code{memcpy} and |
| @code{strcpy} that are determined to overflow the destination buffer. The |
| optional argument is one greater than the type of Object Size Checking to |
| perform to determine the size of the destination. @xref{Object Size Checking}. |
| The argument is meaningful only for functions that operate on character arrays |
| but not for raw memory functions like @code{memcpy} which always make use |
| of Object Size type-0. The option also warns for calls that specify a size |
| in excess of the largest possible object or at most @code{SIZE_MAX / 2} bytes. |
| The option produces the best results with optimization enabled but can detect |
| a small subset of simple buffer overflows even without optimization in |
| calls to the GCC built-in functions like @code{__builtin_memcpy} that |
| correspond to the standard functions. In any case, the option warns about |
| just a subset of buffer overflows detected by the corresponding overflow |
| checking built-ins. For example, the option issues a warning for |
| the @code{strcpy} call below because it copies at least 5 characters |
| (the string @code{"blue"} including the terminating NUL) into the buffer |
| of size 4. |
| |
| @smallexample |
| enum Color @{ blue, purple, yellow @}; |
| const char* f (enum Color clr) |
| @{ |
| static char buf [4]; |
| const char *str; |
| switch (clr) |
| @{ |
| case blue: str = "blue"; break; |
| case purple: str = "purple"; break; |
| case yellow: str = "yellow"; break; |
| @} |
| |
| return strcpy (buf, str); // warning here |
| @} |
| @end smallexample |
| |
| Option @option{-Wstringop-overflow=2} is enabled by default. |
| |
| @table @gcctabopt |
| @item -Wstringop-overflow |
| @itemx -Wstringop-overflow=1 |
| @opindex Wstringop-overflow |
| @opindex Wno-stringop-overflow |
| The @option{-Wstringop-overflow=1} option uses type-zero Object Size Checking |
| to determine the sizes of destination objects. At this setting the option |
| does not warn for writes past the end of subobjects of larger objects accessed |
| by pointers unless the size of the largest surrounding object is known. When |
| the destination may be one of several objects it is assumed to be the largest |
| one of them. On Linux systems, when optimization is enabled at this setting |
| the option warns for the same code as when the @code{_FORTIFY_SOURCE} macro |
| is defined to a non-zero value. |
| |
| @item -Wstringop-overflow=2 |
| The @option{-Wstringop-overflow=2} option uses type-one Object Size Checking |
| to determine the sizes of destination objects. At this setting the option |
| warns about overflows when writing to members of the largest complete |
| objects whose exact size is known. However, it does not warn for excessive |
| writes to the same members of unknown objects referenced by pointers since |
| they may point to arrays containing unknown numbers of elements. This is |
| the default setting of the option. |
| |
| @item -Wstringop-overflow=3 |
| The @option{-Wstringop-overflow=3} option uses type-two Object Size Checking |
| to determine the sizes of destination objects. At this setting the option |
| warns about overflowing the smallest object or data member. This is the |
| most restrictive setting of the option that may result in warnings for safe |
| code. |
| |
| @item -Wstringop-overflow=4 |
| The @option{-Wstringop-overflow=4} option uses type-three Object Size Checking |
| to determine the sizes of destination objects. At this setting the option |
| warns about overflowing any data members, and when the destination is |
| one of several objects it uses the size of the largest of them to decide |
| whether to issue a warning. Similarly to @option{-Wstringop-overflow=3} this |
| setting of the option may result in warnings for benign code. |
| @end table |
| |
| @item -Wno-stringop-overread |
| @opindex Wstringop-overread |
| @opindex Wno-stringop-overread |
| Warn for calls to string manipulation functions such as @code{memchr}, or |
| @code{strcpy} that are determined to read past the end of the source |
| sequence. |
| |
| Option @option{-Wstringop-overread} is enabled by default. |
| |
| @item -Wno-stringop-truncation |
| @opindex Wstringop-truncation |
| @opindex Wno-stringop-truncation |
| Do not warn for calls to bounded string manipulation functions |
| such as @code{strncat}, |
| @code{strncpy}, and @code{stpncpy} that may either truncate the copied string |
| or leave the destination unchanged. |
| |
| In the following example, the call to @code{strncat} specifies a bound that |
| is less than the length of the source string. As a result, the copy of |
| the source will be truncated and so the call is diagnosed. To avoid the |
| warning use @code{bufsize - strlen (buf) - 1)} as the bound. |
| |
| @smallexample |
| void append (char *buf, size_t bufsize) |
| @{ |
| strncat (buf, ".txt", 3); |
| @} |
| @end smallexample |
| |
| As another example, the following call to @code{strncpy} results in copying |
| to @code{d} just the characters preceding the terminating NUL, without |
| appending the NUL to the end. Assuming the result of @code{strncpy} is |
| necessarily a NUL-terminated string is a common mistake, and so the call |
| is diagnosed. To avoid the warning when the result is not expected to be |
| NUL-terminated, call @code{memcpy} instead. |
| |
| @smallexample |
| void copy (char *d, const char *s) |
| @{ |
| strncpy (d, s, strlen (s)); |
| @} |
| @end smallexample |
| |
| In the following example, the call to @code{strncpy} specifies the size |
| of the destination buffer as the bound. If the length of the source |
| string is equal to or greater than this size the result of the copy will |
| not be NUL-terminated. Therefore, the call is also diagnosed. To avoid |
| the warning, specify @code{sizeof buf - 1} as the bound and set the last |
| element of the buffer to @code{NUL}. |
| |
| @smallexample |
| void copy (const char *s) |
| @{ |
| char buf[80]; |
| strncpy (buf, s, sizeof buf); |
| @dots{} |
| @} |
| @end smallexample |
| |
| In situations where a character array is intended to store a sequence |
| of bytes with no terminating @code{NUL} such an array may be annotated |
| with attribute @code{nonstring} to avoid this warning. Such arrays, |
| however, are not suitable arguments to functions that expect |
| @code{NUL}-terminated strings. To help detect accidental misuses of |
| such arrays GCC issues warnings unless it can prove that the use is |
| safe. @xref{Common Variable Attributes}. |
| |
| @item -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{|}cold@r{|}malloc@r{]} |
| @opindex Wsuggest-attribute= |
| @opindex Wno-suggest-attribute= |
| Warn for cases where adding an attribute may be beneficial. The |
| attributes currently supported are listed below. |
| |
| @table @gcctabopt |
| @item -Wsuggest-attribute=pure |
| @itemx -Wsuggest-attribute=const |
| @itemx -Wsuggest-attribute=noreturn |
| @itemx -Wmissing-noreturn |
| @itemx -Wsuggest-attribute=malloc |
| @opindex Wsuggest-attribute=pure |
| @opindex Wno-suggest-attribute=pure |
| @opindex Wsuggest-attribute=const |
| @opindex Wno-suggest-attribute=const |
| @opindex Wsuggest-attribute=noreturn |
| @opindex Wno-suggest-attribute=noreturn |
| @opindex Wmissing-noreturn |
| @opindex Wno-missing-noreturn |
| @opindex Wsuggest-attribute=malloc |
| @opindex Wno-suggest-attribute=malloc |
| |
| Warn about functions that might be candidates for attributes |
| @code{pure}, @code{const} or @code{noreturn} or @code{malloc}. The compiler |
| only warns for functions visible in other compilation units or (in the case of |
| @code{pure} and @code{const}) if it cannot prove that the function returns |
| normally. A function returns normally if it doesn't contain an infinite loop or |
| return abnormally by throwing, calling @code{abort} or trapping. This analysis |
| requires option @option{-fipa-pure-const}, which is enabled by default at |
| @option{-O} and higher. Higher optimization levels improve the accuracy |
| of the analysis. |
| |
| @item -Wsuggest-attribute=format |
| @itemx -Wmissing-format-attribute |
| @opindex Wsuggest-attribute=format |
| @opindex Wmissing-format-attribute |
| @opindex Wno-suggest-attribute=format |
| @opindex Wno-missing-format-attribute |
| @opindex Wformat |
| @opindex Wno-format |
| |
| Warn about function pointers that might be candidates for @code{format} |
| attributes. Note these are only possible candidates, not absolute ones. |
| GCC guesses that function pointers with @code{format} attributes that |
| are used in assignment, initialization, parameter passing or return |
| statements should have a corresponding @code{format} attribute in the |
| resulting type. I.e.@: the left-hand side of the assignment or |
| initialization, the type of the parameter variable, or the return type |
| of the containing function respectively should also have a @code{format} |
| attribute to avoid the warning. |
| |
| GCC also warns about function definitions that might be |
| candidates for @code{format} attributes. Again, these are only |
| possible candidates. GCC guesses that @code{format} attributes |
| might be appropriate for any function that calls a function like |
| @code{vprintf} or @code{vscanf}, but this might not always be the |
| case, and some functions for which @code{format} attributes are |
| appropriate may not be detected. |
| |
| @item -Wsuggest-attribute=cold |
| @opindex Wsuggest-attribute=cold |
| @opindex Wno-suggest-attribute=cold |
| |
| Warn about functions that might be candidates for @code{cold} attribute. This |
| is based on static detection and generally only warns about functions which |
| always leads to a call to another @code{cold} function such as wrappers of |
| C++ @code{throw} or fatal error reporting functions leading to @code{abort}. |
| @end table |
| |
| @item -Walloc-zero |
| @opindex Wno-alloc-zero |
| @opindex Walloc-zero |
| Warn about calls to allocation functions decorated with attribute |
| @code{alloc_size} that specify zero bytes, including those to the built-in |
| forms of the functions @code{aligned_alloc}, @code{alloca}, @code{calloc}, |
| @code{malloc}, and @code{realloc}. Because the behavior of these functions |
| when called with a zero size differs among implementations (and in the case |
| of @code{realloc} has been deprecated) relying on it may result in subtle |
| portability bugs and should be avoided. |
| |
| @item -Walloc-size-larger-than=@var{byte-size} |
| @opindex Walloc-size-larger-than= |
| @opindex Wno-alloc-size-larger-than |
| Warn about calls to functions decorated with attribute @code{alloc_size} |
| that attempt to allocate objects larger than the specified number of bytes, |
| or where the result of the size computation in an integer type with infinite |
| precision would exceed the value of @samp{PTRDIFF_MAX} on the target. |
| @option{-Walloc-size-larger-than=}@samp{PTRDIFF_MAX} is enabled by default. |
| Warnings controlled by the option can be disabled either by specifying |
| @var{byte-size} of @samp{SIZE_MAX} or more or by |
| @option{-Wno-alloc-size-larger-than}. |
| @xref{Function Attributes}. |
| |
| @item -Wno-alloc-size-larger-than |
| @opindex Wno-alloc-size-larger-than |
| Disable @option{-Walloc-size-larger-than=} warnings. The option is |
| equivalent to @option{-Walloc-size-larger-than=}@samp{SIZE_MAX} or |
| larger. |
| |
| @item -Walloca |
| @opindex Wno-alloca |
| @opindex Walloca |
| This option warns on all uses of @code{alloca} in the source. |
| |
| @item -Walloca-larger-than=@var{byte-size} |
| @opindex Walloca-larger-than= |
| @opindex Wno-alloca-larger-than |
| This option warns on calls to @code{alloca} with an integer argument whose |
| value is either zero, or that is not bounded by a controlling predicate |
| that limits its value to at most @var{byte-size}. It also warns for calls |
| to @code{alloca} where the bound value is unknown. Arguments of non-integer |
| types are considered unbounded even if they appear to be constrained to |
| the expected range. |
| |
| For example, a bounded case of @code{alloca} could be: |
| |
| @smallexample |
| void func (size_t n) |
| @{ |
| void *p; |
| if (n <= 1000) |
| p = alloca (n); |
| else |
| p = malloc (n); |
| f (p); |
| @} |
| @end smallexample |
| |
| In the above example, passing @code{-Walloca-larger-than=1000} would not |
| issue a warning because the call to @code{alloca} is known to be at most |
| 1000 bytes. However, if @code{-Walloca-larger-than=500} were passed, |
| the compiler would emit a warning. |
| |
| Unbounded uses, on the other hand, are uses of @code{alloca} with no |
| controlling predicate constraining its integer argument. For example: |
| |
| @smallexample |
| void func () |
| @{ |
| void *p = alloca (n); |
| f (p); |
| @} |
| @end smallexample |
| |
| If @code{-Walloca-larger-than=500} were passed, the above would trigger |
| a warning, but this time because of the lack of bounds checking. |
| |
| Note, that even seemingly correct code involving signed integers could |
| cause a warning: |
| |
| @smallexample |
| void func (signed int n) |
| @{ |
| if (n < 500) |
| @{ |
| p = alloca (n); |
| f (p); |
| @} |
| @} |
| @end smallexample |
| |
| In the above example, @var{n} could be negative, causing a larger than |
| expected argument to be implicitly cast into the @code{alloca} call. |
| |
| This option also warns when @code{alloca} is used in a loop. |
| |
| @option{-Walloca-larger-than=}@samp{PTRDIFF_MAX} is enabled by default |
| but is usually only effective when @option{-ftree-vrp} is active (default |
| for @option{-O2} and above). |
| |
| See also @option{-Wvla-larger-than=}@samp{byte-size}. |
| |
| @item -Wno-alloca-larger-than |
| @opindex Wno-alloca-larger-than |
| Disable @option{-Walloca-larger-than=} warnings. The option is |
| equivalent to @option{-Walloca-larger-than=}@samp{SIZE_MAX} or larger. |
| |
| @item -Warith-conversion |
| @opindex Warith-conversion |
| @opindex Wno-arith-conversion |
| Do warn about implicit conversions from arithmetic operations even |
| when conversion of the operands to the same type cannot change their |
| values. This affects warnings from @option{-Wconversion}, |
| @option{-Wfloat-conversion}, and @option{-Wsign-conversion}. |
| |
| @smallexample |
| @group |
| void f (char c, int i) |
| @{ |
| c = c + i; // warns with @option{-Wconversion} |
| c = c + 1; // only warns with @option{-Warith-conversion} |
| @} |
| @end group |
| @end smallexample |
| |
| @item -Warray-bounds |
| @itemx -Warray-bounds=@var{n} |
| @opindex Wno-array-bounds |
| @opindex Warray-bounds |
| Warn about out of bounds subscripts or offsets into arrays. This warning |
| is enabled by @option{-Wall}. It is more effective when @option{-ftree-vrp} |
| is active (the default for @option{-O2} and above) but a subset of instances |
| are issued even without optimization. |
| |
| @table @gcctabopt |
| @item -Warray-bounds=1 |
| This is the default warning level of @option{-Warray-bounds} and is enabled |
| by @option{-Wall}; higher levels are not, and must be explicitly requested. |
| |
| @item -Warray-bounds=2 |
| This warning level also warns about out of bounds accesses to trailing |
| struct members of one-element array types (@pxref{Zero Length}) and about |
| the intermediate results of pointer arithmetic that may yield out of bounds |
| values. This warning level may give a larger number of false positives and |
| is deactivated by default. |
| @end table |
| |
| @item -Warray-compare |
| @opindex Warray-compare |
| @opindex Wno-array-compare |
| Warn about equality and relational comparisons between two operands of array |
| type. This comparison was deprecated in C++20. For example: |
| |
| @smallexample |
| int arr1[5]; |
| int arr2[5]; |
| bool same = arr1 == arr2; |
| @end smallexample |
| |
| @option{-Warray-compare} is enabled by @option{-Wall}. |
| |
| @item -Warray-parameter |
| @itemx -Warray-parameter=@var{n} |
| @opindex Wno-array-parameter |
| Warn about redeclarations of functions involving arguments of array or |
| pointer types of inconsistent kinds or forms, and enable the detection |
| of out-of-bounds accesses to such parameters by warnings such as |
| @option{-Warray-bounds}. |
| |
| If the first function declaration uses the array form the bound specified |
| in the array is assumed to be the minimum number of elements expected to |
| be provided in calls to the function and the maximum number of elements |
| accessed by it. Failing to provide arguments of sufficient size or accessing |
| more than the maximum number of elements may be diagnosed by warnings such |
| as @option{-Warray-bounds}. At level 1 the warning diagnoses inconsistencies |
| involving array parameters declared using the @code{T[static N]} form. |
| |
| For example, the warning triggers for the following redeclarations because |
| the first one allows an array of any size to be passed to @code{f} while |
| the second one with the keyword @code{static} specifies that the array |
| argument must have at least four elements. |
| |
| @smallexample |
| void f (int[static 4]); |
| void f (int[]); // warning (inconsistent array form) |
| |
| void g (void) |
| @{ |
| int *p = (int *)malloc (4); |
| f (p); // warning (array too small) |
| @dots{} |
| @} |
| @end smallexample |
| |
| At level 2 the warning also triggers for redeclarations involving any other |
| inconsistency in array or pointer argument forms denoting array sizes. |
| Pointers and arrays of unspecified bound are considered equivalent and do |
| not trigger a warning. |
| |
| @smallexample |
| void g (int*); |
| void g (int[]); // no warning |
| void g (int[8]); // warning (inconsistent array bound) |
| @end smallexample |
| |
| @option{-Warray-parameter=2} is included in @option{-Wall}. The |
| @option{-Wvla-parameter} option triggers warnings for similar inconsistencies |
| involving Variable Length Array arguments. |
| |
| @item -Wattribute-alias=@var{n} |
| @itemx -Wno-attribute-alias |
| @opindex Wattribute-alias |
| @opindex Wno-attribute-alias |
| Warn about declarations using the @code{alias} and similar attributes whose |
| target is incompatible with the type of the alias. |
| @xref{Function Attributes,,Declaring Attributes of Functions}. |
| |
| @table @gcctabopt |
| @item -Wattribute-alias=1 |
| The default warning level of the @option{-Wattribute-alias} option diagnoses |
| incompatibilities between the type of the alias declaration and that of its |
| target. Such incompatibilities are typically indicative of bugs. |
| |
| @item -Wattribute-alias=2 |
| |
| At this level @option{-Wattribute-alias} also diagnoses cases where |
| the attributes of the alias declaration are more restrictive than the |
| attributes applied to its target. These mismatches can potentially |
| result in incorrect code generation. In other cases they may be |
| benign and could be resolved simply by adding the missing attribute to |
| the target. For comparison, see the @option{-Wmissing-attributes} |
| option, which controls diagnostics when the alias declaration is less |
| restrictive than the target, rather than more restrictive. |
| |
| Attributes considered include @code{alloc_align}, @code{alloc_size}, |
| @code{cold}, @code{const}, @code{hot}, @code{leaf}, @code{malloc}, |
| @code{nonnull}, @code{noreturn}, @code{nothrow}, @code{pure}, |
| @code{returns_nonnull}, and @code{returns_twice}. |
| @end table |
| |
| @option{-Wattribute-alias} is equivalent to @option{-Wattribute-alias=1}. |
| This is the default. You can disable these warnings with either |
| @option{-Wno-attribute-alias} or @option{-Wattribute-alias=0}. |
| |
| @item -Wbidi-chars=@r{[}none@r{|}unpaired@r{|}any@r{|}ucn@r{]} |
| @opindex Wbidi-chars= |
| @opindex Wbidi-chars |
| @opindex Wno-bidi-chars |
| Warn about possibly misleading UTF-8 bidirectional control characters in |
| comments, string literals, character constants, and identifiers. Such |
| characters can change left-to-right writing direction into right-to-left |
| (and vice versa), which can cause confusion between the logical order and |
| visual order. This may be dangerous; for instance, it may seem that a piece |
| of code is not commented out, whereas it in fact is. |
| |
| There are three levels of warning supported by GCC@. The default is |
| @option{-Wbidi-chars=unpaired}, which warns about improperly terminated |
| bidi contexts. @option{-Wbidi-chars=none} turns the warning off. |
| @option{-Wbidi-chars=any} warns about any use of bidirectional control |
| characters. |
| |
| By default, this warning does not warn about UCNs. It is, however, possible |
| to turn on such checking by using @option{-Wbidi-chars=unpaired,ucn} or |
| @option{-Wbidi-chars=any,ucn}. Using @option{-Wbidi-chars=ucn} is valid, |
| and is equivalent to @option{-Wbidi-chars=unpaired,ucn}, if no previous |
| @option{-Wbidi-chars=any} was specified. |
| |
| @item -Wbool-compare |
| @opindex Wno-bool-compare |
| @opindex Wbool-compare |
| Warn about boolean expression compared with an integer value different from |
| @code{true}/@code{false}. For instance, the following comparison is |
| always false: |
| @smallexample |
| int n = 5; |
| @dots{} |
| if ((n > 1) == 2) @{ @dots{} @} |
| @end smallexample |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wbool-operation |
| @opindex Wno-bool-operation |
| @opindex Wbool-operation |
| Warn about suspicious operations on expressions of a boolean type. For |
| instance, bitwise negation of a boolean is very likely a bug in the program. |
| For C, this warning also warns about incrementing or decrementing a boolean, |
| which rarely makes sense. (In C++, decrementing a boolean is always invalid. |
| Incrementing a boolean is invalid in C++17, and deprecated otherwise.) |
| |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wduplicated-branches |
| @opindex Wno-duplicated-branches |
| @opindex Wduplicated-branches |
| Warn when an if-else has identical branches. This warning detects cases like |
| @smallexample |
| if (p != NULL) |
| return 0; |
| else |
| return 0; |
| @end smallexample |
| It doesn't warn when both branches contain just a null statement. This warning |
| also warn for conditional operators: |
| @smallexample |
| int i = x ? *p : *p; |
| @end smallexample |
| |
| @item -Wduplicated-cond |
| @opindex Wno-duplicated-cond |
| @opindex Wduplicated-cond |
| Warn about duplicated conditions in an if-else-if chain. For instance, |
| warn for the following code: |
| @smallexample |
| if (p->q != NULL) @{ @dots{} @} |
| else if (p->q != NULL) @{ @dots{} @} |
| @end smallexample |
| |
| @item -Wframe-address |
| @opindex Wno-frame-address |
| @opindex Wframe-address |
| Warn when the @samp{__builtin_frame_address} or @samp{__builtin_return_address} |
| is called with an argument greater than 0. Such calls may return indeterminate |
| values or crash the program. The warning is included in @option{-Wall}. |
| |
| @item -Wno-discarded-qualifiers @r{(C and Objective-C only)} |
| @opindex Wno-discarded-qualifiers |
| @opindex Wdiscarded-qualifiers |
| Do not warn if type qualifiers on pointers are being discarded. |
| Typically, the compiler warns if a @code{const char *} variable is |
| passed to a function that takes a @code{char *} parameter. This option |
| can be used to suppress such a warning. |
| |
| @item -Wno-discarded-array-qualifiers @r{(C and Objective-C only)} |
| @opindex Wno-discarded-array-qualifiers |
| @opindex Wdiscarded-array-qualifiers |
| Do not warn if type qualifiers on arrays which are pointer targets |
| are being discarded. Typically, the compiler warns if a |
| @code{const int (*)[]} variable is passed to a function that |
| takes a @code{int (*)[]} parameter. This option can be used to |
| suppress such a warning. |
| |
| @item -Wno-incompatible-pointer-types @r{(C and Objective-C only)} |
| @opindex Wno-incompatible-pointer-types |
| @opindex Wincompatible-pointer-types |
| Do not warn when there is a conversion between pointers that have incompatible |
| types. This warning is for cases not covered by @option{-Wno-pointer-sign}, |
| which warns for pointer argument passing or assignment with different |
| signedness. |
| |
| @item -Wno-int-conversion @r{(C and Objective-C only)} |
| @opindex Wno-int-conversion |
| @opindex Wint-conversion |
| Do not warn about incompatible integer to pointer and pointer to integer |
| conversions. This warning is about implicit conversions; for explicit |
| conversions the warnings @option{-Wno-int-to-pointer-cast} and |
| @option{-Wno-pointer-to-int-cast} may be used. |
| |
| @item -Wzero-length-bounds |
| @opindex Wzero-length-bounds |
| @opindex Wzero-length-bounds |
| Warn about accesses to elements of zero-length array members that might |
| overlap other members of the same object. Declaring interior zero-length |
| arrays is discouraged because accesses to them are undefined. See |
| @xref{Zero Length}. |
| |
| For example, the first two stores in function @code{bad} are diagnosed |
| because the array elements overlap the subsequent members @code{b} and |
| @code{c}. The third store is diagnosed by @option{-Warray-bounds} |
| because it is beyond the bounds of the enclosing object. |
| |
| @smallexample |
| struct X @{ int a[0]; int b, c; @}; |
| struct X x; |
| |
| void bad (void) |
| @{ |
| x.a[0] = 0; // -Wzero-length-bounds |
| x.a[1] = 1; // -Wzero-length-bounds |
| x.a[2] = 2; // -Warray-bounds |
| @} |
| @end smallexample |
| |
| Option @option{-Wzero-length-bounds} is enabled by @option{-Warray-bounds}. |
| |
| @item -Wno-div-by-zero |
| @opindex Wno-div-by-zero |
| @opindex Wdiv-by-zero |
| Do not warn about compile-time integer division by zero. Floating-point |
| division by zero is not warned about, as it can be a legitimate way of |
| obtaining infinities and NaNs. |
| |
| @item -Wsystem-headers |
| @opindex Wsystem-headers |
| @opindex Wno-system-headers |
| @cindex warnings from system headers |
| @cindex system headers, warnings from |
| Print warning messages for constructs found in system header files. |
| Warnings from system headers are normally suppressed, on the assumption |
| that they usually do not indicate real problems and would only make the |
| compiler output harder to read. Using this command-line option tells |
| GCC to emit warnings from system headers as if they occurred in user |
| code. However, note that using @option{-Wall} in conjunction with this |
| option does @emph{not} warn about unknown pragmas in system |
| headers---for that, @option{-Wunknown-pragmas} must also be used. |
| |
| @item -Wtautological-compare |
| @opindex Wtautological-compare |
| @opindex Wno-tautological-compare |
| Warn if a self-comparison always evaluates to true or false. This |
| warning detects various mistakes such as: |
| @smallexample |
| int i = 1; |
| @dots{} |
| if (i > i) @{ @dots{} @} |
| @end smallexample |
| |
| This warning also warns about bitwise comparisons that always evaluate |
| to true or false, for instance: |
| @smallexample |
| if ((a & 16) == 10) @{ @dots{} @} |
| @end smallexample |
| will always be false. |
| |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wtrampolines |
| @opindex Wtrampolines |
| @opindex Wno-trampolines |
| Warn about trampolines generated for pointers to nested functions. |
| A trampoline is a small piece of data or code that is created at run |
| time on the stack when the address of a nested function is taken, and is |
| used to call the nested function indirectly. For some targets, it is |
| made up of data only and thus requires no special treatment. But, for |
| most targets, it is made up of code and thus requires the stack to be |
| made executable in order for the program to work properly. |
| |
| @item -Wfloat-equal |
| @opindex Wfloat-equal |
| @opindex Wno-float-equal |
| Warn if floating-point values are used in equality comparisons. |
| |
| The idea behind this is that sometimes it is convenient (for the |
| programmer) to consider floating-point values as approximations to |
| infinitely precise real numbers. If you are doing this, then you need |
| to compute (by analyzing the code, or in some other way) the maximum or |
| likely maximum error that the computation introduces, and allow for it |
| when performing comparisons (and when producing output, but that's a |
| different problem). In particular, instead of testing for equality, you |
| should check to see whether the two values have ranges that overlap; and |
| this is done with the relational operators, so equality comparisons are |
| probably mistaken. |
| |
| @item -Wtraditional @r{(C and Objective-C only)} |
| @opindex Wtraditional |
| @opindex Wno-traditional |
| Warn about certain constructs that behave differently in traditional and |
| ISO C@. Also warn about ISO C constructs that have no traditional C |
| equivalent, and/or problematic constructs that should be avoided. |
| |
| @itemize @bullet |
| @item |
| Macro parameters that appear within string literals in the macro body. |
| In traditional C macro replacement takes place within string literals, |
| but in ISO C it does not. |
| |
| @item |
| In traditional C, some preprocessor directives did not exist. |
| Traditional preprocessors only considered a line to be a directive |
| if the @samp{#} appeared in column 1 on the line. Therefore |
| @option{-Wtraditional} warns about directives that traditional C |
| understands but ignores because the @samp{#} does not appear as the |
| first character on the line. It also suggests you hide directives like |
| @code{#pragma} not understood by traditional C by indenting them. Some |
| traditional implementations do not recognize @code{#elif}, so this option |
| suggests avoiding it altogether. |
| |
| @item |
| A function-like macro that appears without arguments. |
| |
| @item |
| The unary plus operator. |
| |
| @item |
| The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating-point |
| constant suffixes. (Traditional C does support the @samp{L} suffix on integer |
| constants.) Note, these suffixes appear in macros defined in the system |
| headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}. |
| Use of these macros in user code might normally lead to spurious |
| warnings, however GCC's integrated preprocessor has enough context to |
| avoid warning in these cases. |
| |
| @item |
| A function declared external in one block and then used after the end of |
| the block. |
| |
| @item |
| A @code{switch} statement has an operand of type @code{long}. |
| |
| @item |
| A non-@code{static} function declaration follows a @code{static} one. |
| This construct is not accepted by some traditional C compilers. |
| |
| @item |
| The ISO type of an integer constant has a different width or |
| signedness from its traditional type. This warning is only issued if |
| the base of the constant is ten. I.e.@: hexadecimal or octal values, which |
| typically represent bit patterns, are not warned about. |
| |
| @item |
| Usage of ISO string concatenation is detected. |
| |
| @item |
| Initialization of automatic aggregates. |
| |
| @item |
| Identifier conflicts with labels. Traditional C lacks a separate |
| namespace for labels. |
| |
| @item |
| Initialization of unions. If the initializer is zero, the warning is |
| omitted. This is done under the assumption that the zero initializer in |
| user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing |
| initializer warnings and relies on default initialization to zero in the |
| traditional C case. |
| |
| @item |
| Conversions by prototypes between fixed/floating-point values and vice |
| versa. The absence of these prototypes when compiling with traditional |
| C causes serious problems. This is a subset of the possible |
| conversion warnings; for the full set use @option{-Wtraditional-conversion}. |
| |
| @item |
| Use of ISO C style function definitions. This warning intentionally is |
| @emph{not} issued for prototype declarations or variadic functions |
| because these ISO C features appear in your code when using |
| libiberty's traditional C compatibility macros, @code{PARAMS} and |
| @code{VPARAMS}. This warning is also bypassed for nested functions |
| because that feature is already a GCC extension and thus not relevant to |
| traditional C compatibility. |
| @end itemize |
| |
| @item -Wtraditional-conversion @r{(C and Objective-C only)} |
| @opindex Wtraditional-conversion |
| @opindex Wno-traditional-conversion |
| Warn if a prototype causes a type conversion that is different from what |
| would happen to the same argument in the absence of a prototype. This |
| includes conversions of fixed point to floating and vice versa, and |
| conversions changing the width or signedness of a fixed-point argument |
| except when the same as the default promotion. |
| |
| @item -Wdeclaration-after-statement @r{(C and Objective-C only)} |
| @opindex Wdeclaration-after-statement |
| @opindex Wno-declaration-after-statement |
| Warn when a declaration is found after a statement in a block. This |
| construct, known from C++, was introduced with ISO C99 and is by default |
| allowed in GCC@. It is not supported by ISO C90. @xref{Mixed Labels and Declarations}. |
| |
| @item -Wshadow |
| @opindex Wshadow |
| @opindex Wno-shadow |
| Warn whenever a local variable or type declaration shadows another |
| variable, parameter, type, class member (in C++), or instance variable |
| (in Objective-C) or whenever a built-in function is shadowed. Note |
| that in C++, the compiler warns if a local variable shadows an |
| explicit typedef, but not if it shadows a struct/class/enum. |
| If this warning is enabled, it includes also all instances of |
| local shadowing. This means that @option{-Wno-shadow=local} |
| and @option{-Wno-shadow=compatible-local} are ignored when |
| @option{-Wshadow} is used. |
| Same as @option{-Wshadow=global}. |
| |
| @item -Wno-shadow-ivar @r{(Objective-C only)} |
| @opindex Wno-shadow-ivar |
| @opindex Wshadow-ivar |
| Do not warn whenever a local variable shadows an instance variable in an |
| Objective-C method. |
| |
| @item -Wshadow=global |
| @opindex Wshadow=global |
| Warn for any shadowing. |
| Same as @option{-Wshadow}. |
| |
| @item -Wshadow=local |
| @opindex Wshadow=local |
| Warn when a local variable shadows another local variable or parameter. |
| |
| @item -Wshadow=compatible-local |
| @opindex Wshadow=compatible-local |
| Warn when a local variable shadows another local variable or parameter |
| whose type is compatible with that of the shadowing variable. In C++, |
| type compatibility here means the type of the shadowing variable can be |
| converted to that of the shadowed variable. The creation of this flag |
| (in addition to @option{-Wshadow=local}) is based on the idea that when |
| a local variable shadows another one of incompatible type, it is most |
| likely intentional, not a bug or typo, as shown in the following example: |
| |
| @smallexample |
| @group |
| for (SomeIterator i = SomeObj.begin(); i != SomeObj.end(); ++i) |
| @{ |
| for (int i = 0; i < N; ++i) |
| @{ |
| ... |
| @} |
| ... |
| @} |
| @end group |
| @end smallexample |
| |
| Since the two variable @code{i} in the example above have incompatible types, |
| enabling only @option{-Wshadow=compatible-local} does not emit a warning. |
| Because their types are incompatible, if a programmer accidentally uses one |
| in place of the other, type checking is expected to catch that and emit an |
| error or warning. Use of this flag instead of @option{-Wshadow=local} can |
| possibly reduce the number of warnings triggered by intentional shadowing. |
| Note that this also means that shadowing @code{const char *i} by |
| @code{char *i} does not emit a warning. |
| |
| This warning is also enabled by @option{-Wshadow=local}. |
| |
| @item -Wlarger-than=@var{byte-size} |
| @opindex Wlarger-than= |
| @opindex Wlarger-than-@var{byte-size} |
| Warn whenever an object is defined whose size exceeds @var{byte-size}. |
| @option{-Wlarger-than=}@samp{PTRDIFF_MAX} is enabled by default. |
| Warnings controlled by the option can be disabled either by specifying |
| @var{byte-size} of @samp{SIZE_MAX} or more or by @option{-Wno-larger-than}. |
| |
| Also warn for calls to bounded functions such as @code{memchr} or |
| @code{strnlen} that specify a bound greater than the largest possible |
| object, which is @samp{PTRDIFF_MAX} bytes by default. These warnings |
| can only be disabled by @option{-Wno-larger-than}. |
| |
| @item -Wno-larger-than |
| @opindex Wno-larger-than |
| Disable @option{-Wlarger-than=} warnings. The option is equivalent |
| to @option{-Wlarger-than=}@samp{SIZE_MAX} or larger. |
| |
| @item -Wframe-larger-than=@var{byte-size} |
| @opindex Wframe-larger-than= |
| @opindex Wno-frame-larger-than |
| Warn if the size of a function frame exceeds @var{byte-size}. |
| The computation done to determine the stack frame size is approximate |
| and not conservative. |
| The actual requirements may be somewhat greater than @var{byte-size} |
| even if you do not get a warning. In addition, any space allocated |
| via @code{alloca}, variable-length arrays, or related constructs |
| is not included by the compiler when determining |
| whether or not to issue a warning. |
| @option{-Wframe-larger-than=}@samp{PTRDIFF_MAX} is enabled by default. |
| Warnings controlled by the option can be disabled either by specifying |
| @var{byte-size} of @samp{SIZE_MAX} or more or by |
| @option{-Wno-frame-larger-than}. |
| |
| @item -Wno-frame-larger-than |
| @opindex Wno-frame-larger-than |
| Disable @option{-Wframe-larger-than=} warnings. The option is equivalent |
| to @option{-Wframe-larger-than=}@samp{SIZE_MAX} or larger. |
| |
| @item -Wfree-nonheap-object |
| @opindex Wfree-nonheap-object |
| @opindex Wno-free-nonheap-object |
| Warn when attempting to deallocate an object that was either not allocated |
| on the heap, or by using a pointer that was not returned from a prior call |
| to the corresponding allocation function. For example, because the call |
| to @code{stpcpy} returns a pointer to the terminating nul character and |
| not to the beginning of the object, the call to @code{free} below is |
| diagnosed. |
| |
| @smallexample |
| void f (char *p) |
| @{ |
| p = stpcpy (p, "abc"); |
| // ... |
| free (p); // warning |
| @} |
| @end smallexample |
| |
| @option{-Wfree-nonheap-object} is included in @option{-Wall}. |
| |
| @item -Wstack-usage=@var{byte-size} |
| @opindex Wstack-usage |
| @opindex Wno-stack-usage |
| Warn if the stack usage of a function might exceed @var{byte-size}. |
| The computation done to determine the stack usage is conservative. |
| Any space allocated via @code{alloca}, variable-length arrays, or related |
| constructs is included by the compiler when determining whether or not to |
| issue a warning. |
| |
| The message is in keeping with the output of @option{-fstack-usage}. |
| |
| @itemize |
| @item |
| If the stack usage is fully static but exceeds the specified amount, it's: |
| |
| @smallexample |
| warning: stack usage is 1120 bytes |
| @end smallexample |
| @item |
| If the stack usage is (partly) dynamic but bounded, it's: |
| |
| @smallexample |
| warning: stack usage might be 1648 bytes |
| @end smallexample |
| @item |
| If the stack usage is (partly) dynamic and not bounded, it's: |
| |
| @smallexample |
| warning: stack usage might be unbounded |
| @end smallexample |
| @end itemize |
| |
| @option{-Wstack-usage=}@samp{PTRDIFF_MAX} is enabled by default. |
| Warnings controlled by the option can be disabled either by specifying |
| @var{byte-size} of @samp{SIZE_MAX} or more or by |
| @option{-Wno-stack-usage}. |
| |
| @item -Wno-stack-usage |
| @opindex Wno-stack-usage |
| Disable @option{-Wstack-usage=} warnings. The option is equivalent |
| to @option{-Wstack-usage=}@samp{SIZE_MAX} or larger. |
| |
| @item -Wunsafe-loop-optimizations |
| @opindex Wunsafe-loop-optimizations |
| @opindex Wno-unsafe-loop-optimizations |
| Warn if the loop cannot be optimized because the compiler cannot |
| assume anything on the bounds of the loop indices. With |
| @option{-funsafe-loop-optimizations} warn if the compiler makes |
| such assumptions. |
| |
| @item -Wno-pedantic-ms-format @r{(MinGW targets only)} |
| @opindex Wno-pedantic-ms-format |
| @opindex Wpedantic-ms-format |
| When used in combination with @option{-Wformat} |
| and @option{-pedantic} without GNU extensions, this option |
| disables the warnings about non-ISO @code{printf} / @code{scanf} format |
| width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets, |
| which depend on the MS runtime. |
| |
| @item -Wpointer-arith |
| @opindex Wpointer-arith |
| @opindex Wno-pointer-arith |
| Warn about anything that depends on the ``size of'' a function type or |
| of @code{void}. GNU C assigns these types a size of 1, for |
| convenience in calculations with @code{void *} pointers and pointers |
| to functions. In C++, warn also when an arithmetic operation involves |
| @code{NULL}. This warning is also enabled by @option{-Wpedantic}. |
| |
| @item -Wno-pointer-compare |
| @opindex Wpointer-compare |
| @opindex Wno-pointer-compare |
| Do not warn if a pointer is compared with a zero character constant. |
| This usually |
| means that the pointer was meant to be dereferenced. For example: |
| |
| @smallexample |
| const char *p = foo (); |
| if (p == '\0') |
| return 42; |
| @end smallexample |
| |
| Note that the code above is invalid in C++11. |
| |
| This warning is enabled by default. |
| |
| @item -Wtsan |
| @opindex Wtsan |
| @opindex Wno-tsan |
| Warn about unsupported features in ThreadSanitizer. |
| |
| ThreadSanitizer does not support @code{std::atomic_thread_fence} and |
| can report false positives. |
| |
| This warning is enabled by default. |
| |
| @item -Wtype-limits |
| @opindex Wtype-limits |
| @opindex Wno-type-limits |
| Warn if a comparison is always true or always false due to the limited |
| range of the data type, but do not warn for constant expressions. For |
| example, warn if an unsigned variable is compared against zero with |
| @code{<} or @code{>=}. This warning is also enabled by |
| @option{-Wextra}. |
| |
| @item -Wabsolute-value @r{(C and Objective-C only)} |
| @opindex Wabsolute-value |
| @opindex Wno-absolute-value |
| Warn for calls to standard functions that compute the absolute value |
| of an argument when a more appropriate standard function is available. |
| For example, calling @code{abs(3.14)} triggers the warning because the |
| appropriate function to call to compute the absolute value of a double |
| argument is @code{fabs}. The option also triggers warnings when the |
| argument in a call to such a function has an unsigned type. This |
| warning can be suppressed with an explicit type cast and it is also |
| enabled by @option{-Wextra}. |
| |
| @include cppwarnopts.texi |
| |
| @item -Wbad-function-cast @r{(C and Objective-C only)} |
| @opindex Wbad-function-cast |
| @opindex Wno-bad-function-cast |
| Warn when a function call is cast to a non-matching type. |
| For example, warn if a call to a function returning an integer type |
| is cast to a pointer type. |
| |
| @item -Wc90-c99-compat @r{(C and Objective-C only)} |
| @opindex Wc90-c99-compat |
| @opindex Wno-c90-c99-compat |
| Warn about features not present in ISO C90, but present in ISO C99. |
| For instance, warn about use of variable length arrays, @code{long long} |
| type, @code{bool} type, compound literals, designated initializers, and so |
| on. This option is independent of the standards mode. Warnings are disabled |
| in the expression that follows @code{__extension__}. |
| |
| @item -Wc99-c11-compat @r{(C and Objective-C only)} |
| @opindex Wc99-c11-compat |
| @opindex Wno-c99-c11-compat |
| Warn about features not present in ISO C99, but present in ISO C11. |
| For instance, warn about use of anonymous structures and unions, |
| @code{_Atomic} type qualifier, @code{_Thread_local} storage-class specifier, |
| @code{_Alignas} specifier, @code{Alignof} operator, @code{_Generic} keyword, |
| and so on. This option is independent of the standards mode. Warnings are |
| disabled in the expression that follows @code{__extension__}. |
| |
| @item -Wc11-c2x-compat @r{(C and Objective-C only)} |
| @opindex Wc11-c2x-compat |
| @opindex Wno-c11-c2x-compat |
| Warn about features not present in ISO C11, but present in ISO C2X. |
| For instance, warn about omitting the string in @code{_Static_assert}, |
| use of @samp{[[]]} syntax for attributes, use of decimal |
| floating-point types, and so on. This option is independent of the |
| standards mode. Warnings are disabled in the expression that follows |
| @code{__extension__}. |
| |
| @item -Wc++-compat @r{(C and Objective-C only)} |
| @opindex Wc++-compat |
| @opindex Wno-c++-compat |
| Warn about ISO C constructs that are outside of the common subset of |
| ISO C and ISO C++, e.g.@: request for implicit conversion from |
| @code{void *} to a pointer to non-@code{void} type. |
| |
| @item -Wc++11-compat @r{(C++ and Objective-C++ only)} |
| @opindex Wc++11-compat |
| @opindex Wno-c++11-compat |
| Warn about C++ constructs whose meaning differs between ISO C++ 1998 |
| and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are keywords |
| in ISO C++ 2011. This warning turns on @option{-Wnarrowing} and is |
| enabled by @option{-Wall}. |
| |
| @item -Wc++14-compat @r{(C++ and Objective-C++ only)} |
| @opindex Wc++14-compat |
| @opindex Wno-c++14-compat |
| Warn about C++ constructs whose meaning differs between ISO C++ 2011 |
| and ISO C++ 2014. This warning is enabled by @option{-Wall}. |
| |
| @item -Wc++17-compat @r{(C++ and Objective-C++ only)} |
| @opindex Wc++17-compat |
| @opindex Wno-c++17-compat |
| Warn about C++ constructs whose meaning differs between ISO C++ 2014 |
| and ISO C++ 2017. This warning is enabled by @option{-Wall}. |
| |
| @item -Wc++20-compat @r{(C++ and Objective-C++ only)} |
| @opindex Wc++20-compat |
| @opindex Wno-c++20-compat |
| Warn about C++ constructs whose meaning differs between ISO C++ 2017 |
| and ISO C++ 2020. This warning is enabled by @option{-Wall}. |
| |
| @item -Wno-c++11-extensions @r{(C++ and Objective-C++ only)} |
| @opindex Wc++11-extensions |
| @opindex Wno-c++11-extensions |
| Do not warn about C++11 constructs in code being compiled using |
| an older C++ standard. Even without this option, some C++11 constructs |
| will only be diagnosed if @option{-Wpedantic} is used. |
| |
| @item -Wno-c++14-extensions @r{(C++ and Objective-C++ only)} |
| @opindex Wc++14-extensions |
| @opindex Wno-c++14-extensions |
| Do not warn about C++14 constructs in code being compiled using |
| an older C++ standard. Even without this option, some C++14 constructs |
| will only be diagnosed if @option{-Wpedantic} is used. |
| |
| @item -Wno-c++17-extensions @r{(C++ and Objective-C++ only)} |
| @opindex Wc++17-extensions |
| @opindex Wno-c++17-extensions |
| Do not warn about C++17 constructs in code being compiled using |
| an older C++ standard. Even without this option, some C++17 constructs |
| will only be diagnosed if @option{-Wpedantic} is used. |
| |
| @item -Wno-c++20-extensions @r{(C++ and Objective-C++ only)} |
| @opindex Wc++20-extensions |
| @opindex Wno-c++20-extensions |
| Do not warn about C++20 constructs in code being compiled using |
| an older C++ standard. Even without this option, some C++20 constructs |
| will only be diagnosed if @option{-Wpedantic} is used. |
| |
| @item -Wno-c++23-extensions @r{(C++ and Objective-C++ only)} |
| @opindex Wc++23-extensions |
| @opindex Wno-c++23-extensions |
| Do not warn about C++23 constructs in code being compiled using |
| an older C++ standard. Even without this option, some C++23 constructs |
| will only be diagnosed if @option{-Wpedantic} is used. |
| |
| @item -Wcast-qual |
| @opindex Wcast-qual |
| @opindex Wno-cast-qual |
| Warn whenever a pointer is cast so as to remove a type qualifier from |
| the target type. For example, warn if a @code{const char *} is cast |
| to an ordinary @code{char *}. |
| |
| Also warn when making a cast that introduces a type qualifier in an |
| unsafe way. For example, casting @code{char **} to @code{const char **} |
| is unsafe, as in this example: |
| |
| @smallexample |
| /* p is char ** value. */ |
| const char **q = (const char **) p; |
| /* Assignment of readonly string to const char * is OK. */ |
| *q = "string"; |
| /* Now char** pointer points to read-only memory. */ |
| **p = 'b'; |
| @end smallexample |
| |
| @item -Wcast-align |
| @opindex Wcast-align |
| @opindex Wno-cast-align |
| Warn whenever a pointer is cast such that the required alignment of the |
| target is increased. For example, warn if a @code{char *} is cast to |
| an @code{int *} on machines where integers can only be accessed at |
| two- or four-byte boundaries. |
| |
| @item -Wcast-align=strict |
| @opindex Wcast-align=strict |
| Warn whenever a pointer is cast such that the required alignment of the |
| target is increased. For example, warn if a @code{char *} is cast to |
| an @code{int *} regardless of the target machine. |
| |
| @item -Wcast-function-type |
| @opindex Wcast-function-type |
| @opindex Wno-cast-function-type |
| Warn when a function pointer is cast to an incompatible function pointer. |
| In a cast involving function types with a variable argument list only |
| the types of initial arguments that are provided are considered. |
| Any parameter of pointer-type matches any other pointer-type. Any benign |
| differences in integral types are ignored, like @code{int} vs.@: @code{long} |
| on ILP32 targets. Likewise type qualifiers are ignored. The function |
| type @code{void (*) (void)} is special and matches everything, which can |
| be used to suppress this warning. |
| In a cast involving pointer to member types this warning warns whenever |
| the type cast is changing the pointer to member type. |
| This warning is enabled by @option{-Wextra}. |
| |
| @item -Wwrite-strings |
| @opindex Wwrite-strings |
| @opindex Wno-write-strings |
| When compiling C, give string constants the type @code{const |
| char[@var{length}]} so that copying the address of one into a |
| non-@code{const} @code{char *} pointer produces a warning. These |
| warnings help you find at compile time code that can try to write |
| into a string constant, but only if you have been very careful about |
| using @code{const} in declarations and prototypes. Otherwise, it is |
| just a nuisance. This is why we did not make @option{-Wall} request |
| these warnings. |
| |
| When compiling C++, warn about the deprecated conversion from string |
| literals to @code{char *}. This warning is enabled by default for C++ |
| programs. |
| |
| @item -Wclobbered |
| @opindex Wclobbered |
| @opindex Wno-clobbered |
| Warn for variables that might be changed by @code{longjmp} or |
| @code{vfork}. This warning is also enabled by @option{-Wextra}. |
| |
| @item -Wconversion |
| @opindex Wconversion |
| @opindex Wno-conversion |
| Warn for implicit conversions that may alter a value. This includes |
| conversions between real and integer, like @code{abs (x)} when |
| @code{x} is @code{double}; conversions between signed and unsigned, |
| like @code{unsigned ui = -1}; and conversions to smaller types, like |
| @code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs |
| ((int) x)} and @code{ui = (unsigned) -1}, or if the value is not |
| changed by the conversion like in @code{abs (2.0)}. Warnings about |
| conversions between signed and unsigned integers can be disabled by |
| using @option{-Wno-sign-conversion}. |
| |
| For C++, also warn for confusing overload resolution for user-defined |
| conversions; and conversions that never use a type conversion |
| operator: conversions to @code{void}, the same type, a base class or a |
| reference to them. Warnings about conversions between signed and |
| unsigned integers are disabled by default in C++ unless |
| @option{-Wsign-conversion} is explicitly enabled. |
| |
| Warnings about conversion from arithmetic on a small type back to that |
| type are only given with @option{-Warith-conversion}. |
| |
| @item -Wdangling-else |
| @opindex Wdangling-else |
| @opindex Wno-dangling-else |
| Warn about constructions where there may be confusion to which |
| @code{if} statement an @code{else} branch belongs. Here is an example of |
| such a case: |
| |
| @smallexample |
| @group |
| @{ |
| if (a) |
| if (b) |
| foo (); |
| else |
| bar (); |
| @} |
| @end group |
| @end smallexample |
| |
| In C/C++, every @code{else} branch belongs to the innermost possible |
| @code{if} statement, which in this example is @code{if (b)}. This is |
| often not what the programmer expected, as illustrated in the above |
| example by indentation the programmer chose. When there is the |
| potential for this confusion, GCC issues a warning when this flag |
| is specified. To eliminate the warning, add explicit braces around |
| the innermost @code{if} statement so there is no way the @code{else} |
| can belong to the enclosing @code{if}. The resulting code |
| looks like this: |
| |
| @smallexample |
| @group |
| @{ |
| if (a) |
| @{ |
| if (b) |
| foo (); |
| else |
| bar (); |
| @} |
| @} |
| @end group |
| @end smallexample |
| |
| This warning is enabled by @option{-Wparentheses}. |
| |
| @item -Wdangling-pointer |
| @itemx -Wdangling-pointer=@var{n} |
| @opindex Wdangling-pointer |
| @opindex Wno-dangling-pointer |
| Warn about uses of pointers (or C++ references) to objects with automatic |
| storage duration after their lifetime has ended. This includes local |
| variables declared in nested blocks, compound literals and other unnamed |
| temporary objects. In addition, warn about storing the address of such |
| objects in escaped pointers. The warning is enabled at all optimization |
| levels but may yield different results with optimization than without. |
| |
| @table @gcctabopt |
| @item -Wdangling-pointer=1 |
| At level 1 the warning diagnoses only unconditional uses of dangling pointers. |
| For example |
| @smallexample |
| int f (int c1, int c2, x) |
| @{ |
| char *p = strchr ((char[])@{ c1, c2 @}, c3); |
| return p ? *p : 'x'; // warning: dangling pointer to a compound literal |
| @} |
| @end smallexample |
| In the following function the store of the address of the local variable |
| @code{x} in the escaped pointer @code{*p} also triggers the warning. |
| @smallexample |
| void g (int **p) |
| @{ |
| int x = 7; |
| *p = &x; // warning: storing the address of a local variable in *p |
| @} |
| @end smallexample |
| |
| @item -Wdangling-pointer=2 |
| At level 2, in addition to unconditional uses the warning also diagnoses |
| conditional uses of dangling pointers. |
| |
| For example, because the array @var{a} in the following function is out of |
| scope when the pointer @var{s} that was set to point is used, the warning |
| triggers at this level. |
| |
| @smallexample |
| void f (char *s) |
| @{ |
| if (!s) |
| @{ |
| char a[12] = "tmpname"; |
| s = a; |
| @} |
| strcat (s, ".tmp"); // warning: dangling pointer to a may be used |
| ... |
| @} |
| @end smallexample |
| @end table |
| |
| @option{-Wdangling-pointer=2} is included in @option{-Wall}. |
| |
| @item -Wdate-time |
| @opindex Wdate-time |
| @opindex Wno-date-time |
| Warn when macros @code{__TIME__}, @code{__DATE__} or @code{__TIMESTAMP__} |
| are encountered as they might prevent bit-wise-identical reproducible |
| compilations. |
| |
| @item -Wempty-body |
| @opindex Wempty-body |
| @opindex Wno-empty-body |
| Warn if an empty body occurs in an @code{if}, @code{else} or @code{do |
| while} statement. This warning is also enabled by @option{-Wextra}. |
| |
| @item -Wno-endif-labels |
| @opindex Wendif-labels |
| @opindex Wno-endif-labels |
| Do not warn about stray tokens after @code{#else} and @code{#endif}. |
| |
| @item -Wenum-compare |
| @opindex Wenum-compare |
| @opindex Wno-enum-compare |
| Warn about a comparison between values of different enumerated types. |
| In C++ enumerated type mismatches in conditional expressions are also |
| diagnosed and the warning is enabled by default. In C this warning is |
| enabled by @option{-Wall}. |
| |
| @item -Wenum-conversion |
| @opindex Wenum-conversion |
| @opindex Wno-enum-conversion |
| Warn when a value of enumerated type is implicitly converted to a |
| different enumerated type. This warning is enabled by @option{-Wextra} |
| in C@. |
| |
| @item -Wjump-misses-init @r{(C, Objective-C only)} |
| @opindex Wjump-misses-init |
| @opindex Wno-jump-misses-init |
| Warn if a @code{goto} statement or a @code{switch} statement jumps |
| forward across the initialization of a variable, or jumps backward to a |
| label after the variable has been initialized. This only warns about |
| variables that are initialized when they are declared. This warning is |
| only supported for C and Objective-C; in C++ this sort of branch is an |
| error in any case. |
| |
| @option{-Wjump-misses-init} is included in @option{-Wc++-compat}. It |
| can be disabled with the @option{-Wno-jump-misses-init} option. |
| |
| @item -Wsign-compare |
| @opindex Wsign-compare |
| @opindex Wno-sign-compare |
| @cindex warning for comparison of signed and unsigned values |
| @cindex comparison of signed and unsigned values, warning |
| @cindex signed and unsigned values, comparison warning |
| Warn when a comparison between signed and unsigned values could produce |
| an incorrect result when the signed value is converted to unsigned. |
| In C++, this warning is also enabled by @option{-Wall}. In C, it is |
| also enabled by @option{-Wextra}. |
| |
| @item -Wsign-conversion |
| @opindex Wsign-conversion |
| @opindex Wno-sign-conversion |
| Warn for implicit conversions that may change the sign of an integer |
| value, like assigning a signed integer expression to an unsigned |
| integer variable. An explicit cast silences the warning. In C, this |
| option is enabled also by @option{-Wconversion}. |
| |
| @item -Wfloat-conversion |
| @opindex Wfloat-conversion |
| @opindex Wno-float-conversion |
| Warn for implicit conversions that reduce the precision of a real value. |
| This includes conversions from real to integer, and from higher precision |
| real to lower precision real values. This option is also enabled by |
| @option{-Wconversion}. |
| |
| @item -Wno-scalar-storage-order |
| @opindex Wno-scalar-storage-order |
| @opindex Wscalar-storage-order |
| Do not warn on suspicious constructs involving reverse scalar storage order. |
| |
| @item -Wsizeof-array-div |
| @opindex Wsizeof-array-div |
| @opindex Wno-sizeof-array-div |
| Warn about divisions of two sizeof operators when the first one is applied |
| to an array and the divisor does not equal the size of the array element. |
| In such a case, the computation will not yield the number of elements in the |
| array, which is likely what the user intended. This warning warns e.g. about |
| @smallexample |
| int fn () |
| @{ |
| int arr[10]; |
| return sizeof (arr) / sizeof (short); |
| @} |
| @end smallexample |
| |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wsizeof-pointer-div |
| @opindex Wsizeof-pointer-div |
| @opindex Wno-sizeof-pointer-div |
| Warn for suspicious divisions of two sizeof expressions that divide |
| the pointer size by the element size, which is the usual way to compute |
| the array size but won't work out correctly with pointers. This warning |
| warns e.g.@: about @code{sizeof (ptr) / sizeof (ptr[0])} if @code{ptr} is |
| not an array, but a pointer. This warning is enabled by @option{-Wall}. |
| |
| @item -Wsizeof-pointer-memaccess |
| @opindex Wsizeof-pointer-memaccess |
| @opindex Wno-sizeof-pointer-memaccess |
| Warn for suspicious length parameters to certain string and memory built-in |
| functions if the argument uses @code{sizeof}. This warning triggers for |
| example for @code{memset (ptr, 0, sizeof (ptr));} if @code{ptr} is not |
| an array, but a pointer, and suggests a possible fix, or about |
| @code{memcpy (&foo, ptr, sizeof (&foo));}. @option{-Wsizeof-pointer-memaccess} |
| also warns about calls to bounded string copy functions like @code{strncat} |
| or @code{strncpy} that specify as the bound a @code{sizeof} expression of |
| the source array. For example, in the following function the call to |
| @code{strncat} specifies the size of the source string as the bound. That |
| is almost certainly a mistake and so the call is diagnosed. |
| @smallexample |
| void make_file (const char *name) |
| @{ |
| char path[PATH_MAX]; |
| strncpy (path, name, sizeof path - 1); |
| strncat (path, ".text", sizeof ".text"); |
| @dots{} |
| @} |
| @end smallexample |
| |
| The @option{-Wsizeof-pointer-memaccess} option is enabled by @option{-Wall}. |
| |
| @item -Wno-sizeof-array-argument |
| @opindex Wsizeof-array-argument |
| @opindex Wno-sizeof-array-argument |
| Do not warn when the @code{sizeof} operator is applied to a parameter that is |
| declared as an array in a function definition. This warning is enabled by |
| default for C and C++ programs. |
| |
| @item -Wmemset-elt-size |
| @opindex Wmemset-elt-size |
| @opindex Wno-memset-elt-size |
| Warn for suspicious calls to the @code{memset} built-in function, if the |
| first argument references an array, and the third argument is a number |
| equal to the number of elements, but not equal to the size of the array |
| in memory. This indicates that the user has omitted a multiplication by |
| the element size. This warning is enabled by @option{-Wall}. |
| |
| @item -Wmemset-transposed-args |
| @opindex Wmemset-transposed-args |
| @opindex Wno-memset-transposed-args |
| Warn for suspicious calls to the @code{memset} built-in function where |
| the second argument is not zero and the third argument is zero. For |
| example, the call @code{memset (buf, sizeof buf, 0)} is diagnosed because |
| @code{memset (buf, 0, sizeof buf)} was meant instead. The diagnostic |
| is only emitted if the third argument is a literal zero. Otherwise, if |
| it is an expression that is folded to zero, or a cast of zero to some |
| type, it is far less likely that the arguments have been mistakenly |
| transposed and no warning is emitted. This warning is enabled |
| by @option{-Wall}. |
| |
| @item -Waddress |
| @opindex Waddress |
| @opindex Wno-address |
| Warn about suspicious uses of address expressions. These include comparing |
| the address of a function or a declared object to the null pointer constant |
| such as in |
| @smallexample |
| void f (void); |
| void g (void) |
| @{ |
| if (!func) // warning: expression evaluates to false |
| abort (); |
| @} |
| @end smallexample |
| comparisons of a pointer to a string literal, such as in |
| @smallexample |
| void f (const char *x) |
| @{ |
| if (x == "abc") // warning: expression evaluates to false |
| puts ("equal"); |
| @} |
| @end smallexample |
| and tests of the results of pointer addition or subtraction for equality |
| to null, such as in |
| @smallexample |
| void f (const int *p, int i) |
| @{ |
| return p + i == NULL; |
| @} |
| @end smallexample |
| Such uses typically indicate a programmer error: the address of most |
| functions and objects necessarily evaluates to true (the exception are |
| weak symbols), so their use in a conditional might indicate missing |
| parentheses in a function call or a missing dereference in an array |
| expression. The subset of the warning for object pointers can be |
| suppressed by casting the pointer operand to an integer type such |
| as @code{inptr_t} or @code{uinptr_t}. |
| Comparisons against string literals result in unspecified behavior |
| and are not portable, and suggest the intent was to call @code{strcmp}. |
| The warning is suppressed if the suspicious expression is the result |
| of macro expansion. |
| @option{-Waddress} warning is enabled by @option{-Wall}. |
| |
| @item -Wno-address-of-packed-member |
| @opindex Waddress-of-packed-member |
| @opindex Wno-address-of-packed-member |
| Do not warn when the address of packed member of struct or union is taken, |
| which usually results in an unaligned pointer value. This is |
| enabled by default. |
| |
| @item -Wlogical-op |
| @opindex Wlogical-op |
| @opindex Wno-logical-op |
| Warn about suspicious uses of logical operators in expressions. |
| This includes using logical operators in contexts where a |
| bit-wise operator is likely to be expected. Also warns when |
| the operands of a logical operator are the same: |
| @smallexample |
| extern int a; |
| if (a < 0 && a < 0) @{ @dots{} @} |
| @end smallexample |
| |
| @item -Wlogical-not-parentheses |
| @opindex Wlogical-not-parentheses |
| @opindex Wno-logical-not-parentheses |
| Warn about logical not used on the left hand side operand of a comparison. |
| This option does not warn if the right operand is considered to be a boolean |
| expression. Its purpose is to detect suspicious code like the following: |
| @smallexample |
| int a; |
| @dots{} |
| if (!a > 1) @{ @dots{} @} |
| @end smallexample |
| |
| It is possible to suppress the warning by wrapping the LHS into |
| parentheses: |
| @smallexample |
| if ((!a) > 1) @{ @dots{} @} |
| @end smallexample |
| |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Waggregate-return |
| @opindex Waggregate-return |
| @opindex Wno-aggregate-return |
| Warn if any functions that return structures or unions are defined or |
| called. (In languages where you can return an array, this also elicits |
| a warning.) |
| |
| @item -Wno-aggressive-loop-optimizations |
| @opindex Wno-aggressive-loop-optimizations |
| @opindex Waggressive-loop-optimizations |
| Warn if in a loop with constant number of iterations the compiler detects |
| undefined behavior in some statement during one or more of the iterations. |
| |
| @item -Wno-attributes |
| @opindex Wno-attributes |
| @opindex Wattributes |
| Do not warn if an unexpected @code{__attribute__} is used, such as |
| unrecognized attributes, function attributes applied to variables, |
| etc. This does not stop errors for incorrect use of supported |
| attributes. |
| |
| Additionally, using @option{-Wno-attributes=}, it is possible to suppress |
| warnings about unknown scoped attributes (in C++11 and C2X). For example, |
| @option{-Wno-attributes=vendor::attr} disables warning about the following |
| declaration: |
| |
| @smallexample |
| [[vendor::attr]] void f(); |
| @end smallexample |
| |
| It is also possible to disable warning about all attributes in a namespace |
| using @option{-Wno-attributes=vendor::} which prevents warning about both |
| of these declarations: |
| |
| @smallexample |
| [[vendor::safe]] void f(); |
| [[vendor::unsafe]] void f2(); |
| @end smallexample |
| |
| Note that @option{-Wno-attributes=} does not imply @option{-Wno-attributes}. |
| |
| @item -Wno-builtin-declaration-mismatch |
| @opindex Wno-builtin-declaration-mismatch |
| @opindex Wbuiltin-declaration-mismatch |
| Warn if a built-in function is declared with an incompatible signature |
| or as a non-function, or when a built-in function declared with a type |
| that does not include a prototype is called with arguments whose promoted |
| types do not match those expected by the function. When @option{-Wextra} |
| is specified, also warn when a built-in function that takes arguments is |
| declared without a prototype. The @option{-Wbuiltin-declaration-mismatch} |
| warning is enabled by default. To avoid the warning include the appropriate |
| header to bring the prototypes of built-in functions into scope. |
| |
| For example, the call to @code{memset} below is diagnosed by the warning |
| because the function expects a value of type @code{size_t} as its argument |
| but the type of @code{32} is @code{int}. With @option{-Wextra}, |
| the declaration of the function is diagnosed as well. |
| @smallexample |
| extern void* memset (); |
| void f (void *d) |
| @{ |
| memset (d, '\0', 32); |
| @} |
| @end smallexample |
| |
| @item -Wno-builtin-macro-redefined |
| @opindex Wno-builtin-macro-redefined |
| @opindex Wbuiltin-macro-redefined |
| Do not warn if certain built-in macros are redefined. This suppresses |
| warnings for redefinition of @code{__TIMESTAMP__}, @code{__TIME__}, |
| @code{__DATE__}, @code{__FILE__}, and @code{__BASE_FILE__}. |
| |
| @item -Wstrict-prototypes @r{(C and Objective-C only)} |
| @opindex Wstrict-prototypes |
| @opindex Wno-strict-prototypes |
| Warn if a function is declared or defined without specifying the |
| argument types. (An old-style function definition is permitted without |
| a warning if preceded by a declaration that specifies the argument |
| types.) |
| |
| @item -Wold-style-declaration @r{(C and Objective-C only)} |
| @opindex Wold-style-declaration |
| @opindex Wno-old-style-declaration |
| Warn for obsolescent usages, according to the C Standard, in a |
| declaration. For example, warn if storage-class specifiers like |
| @code{static} are not the first things in a declaration. This warning |
| is also enabled by @option{-Wextra}. |
| |
| @item -Wold-style-definition @r{(C and Objective-C only)} |
| @opindex Wold-style-definition |
| @opindex Wno-old-style-definition |
| Warn if an old-style function definition is used. A warning is given |
| even if there is a previous prototype. A definition using @samp{()} |
| is not considered an old-style definition in C2X mode, because it is |
| equivalent to @samp{(void)} in that case, but is considered an |
| old-style definition for older standards. |
| |
| @item -Wmissing-parameter-type @r{(C and Objective-C only)} |
| @opindex Wmissing-parameter-type |
| @opindex Wno-missing-parameter-type |
| A function parameter is declared without a type specifier in K&R-style |
| functions: |
| |
| @smallexample |
| void foo(bar) @{ @} |
| @end smallexample |
| |
| This warning is also enabled by @option{-Wextra}. |
| |
| @item -Wmissing-prototypes @r{(C and Objective-C only)} |
| @opindex Wmissing-prototypes |
| @opindex Wno-missing-prototypes |
| Warn if a global function is defined without a previous prototype |
| declaration. This warning is issued even if the definition itself |
| provides a prototype. Use this option to detect global functions |
| that do not have a matching prototype declaration in a header file. |
| This option is not valid for C++ because all function declarations |
| provide prototypes and a non-matching declaration declares an |
| overload rather than conflict with an earlier declaration. |
| Use @option{-Wmissing-declarations} to detect missing declarations in C++. |
| |
| @item -Wmissing-declarations |
| @opindex Wmissing-declarations |
| @opindex Wno-missing-declarations |
| Warn if a global function is defined without a previous declaration. |
| Do so even if the definition itself provides a prototype. |
| Use this option to detect global functions that are not declared in |
| header files. In C, no warnings are issued for functions with previous |
| non-prototype declarations; use @option{-Wmissing-prototypes} to detect |
| missing prototypes. In C++, no warnings are issued for function templates, |
| or for inline functions, or for functions in anonymous namespaces. |
| |
| @item -Wmissing-field-initializers |
| @opindex Wmissing-field-initializers |
| @opindex Wno-missing-field-initializers |
| @opindex W |
| @opindex Wextra |
| @opindex Wno-extra |
| Warn if a structure's initializer has some fields missing. For |
| example, the following code causes such a warning, because |
| @code{x.h} is implicitly zero: |
| |
| @smallexample |
| struct s @{ int f, g, h; @}; |
| struct s x = @{ 3, 4 @}; |
| @end smallexample |
| |
| This option does not warn about designated initializers, so the following |
| modification does not trigger a warning: |
| |
| @smallexample |
| struct s @{ int f, g, h; @}; |
| struct s x = @{ .f = 3, .g = 4 @}; |
| @end smallexample |
| |
| In C this option does not warn about the universal zero initializer |
| @samp{@{ 0 @}}: |
| |
| @smallexample |
| struct s @{ int f, g, h; @}; |
| struct s x = @{ 0 @}; |
| @end smallexample |
| |
| Likewise, in C++ this option does not warn about the empty @{ @} |
| initializer, for example: |
| |
| @smallexample |
| struct s @{ int f, g, h; @}; |
| s x = @{ @}; |
| @end smallexample |
| |
| This warning is included in @option{-Wextra}. To get other @option{-Wextra} |
| warnings without this one, use @option{-Wextra -Wno-missing-field-initializers}. |
| |
| @item -Wno-missing-requires |
| @opindex Wmissing-requires |
| @opindex Wno-missing-requires |
| |
| By default, the compiler warns about a concept-id appearing as a C++20 simple-requirement: |
| |
| @smallexample |
| bool satisfied = requires @{ C<T> @}; |
| @end smallexample |
| |
| Here @samp{satisfied} will be true if @samp{C<T>} is a valid |
| expression, which it is for all T. Presumably the user meant to write |
| |
| @smallexample |
| bool satisfied = requires @{ requires C<T> @}; |
| @end smallexample |
| |
| so @samp{satisfied} is only true if concept @samp{C} is satisfied for |
| type @samp{T}. |
| |
| This warning can be disabled with @option{-Wno-missing-requires}. |
| |
| @item -Wno-missing-template-keyword |
| @opindex Wmissing-template-keyword |
| @opindex Wno-missing-template-keyword |
| |
| The member access tokens ., -> and :: must be followed by the @code{template} |
| keyword if the parent object is dependent and the member being named is a |
| template. |
| |
| @smallexample |
| template <class X> |
| void DoStuff (X x) |
| @{ |
| x.template DoSomeOtherStuff<X>(); // Good. |
| x.DoMoreStuff<X>(); // Warning, x is dependent. |
| @} |
| @end smallexample |
| |
| In rare cases it is possible to get false positives. To silence this, wrap |
| the expression in parentheses. For example, the following is treated as a |
| template, even where m and N are integers: |
| |
| @smallexample |
| void NotATemplate (my_class t) |
| @{ |
| int N = 5; |
| |
| bool test = t.m < N > (0); // Treated as a template. |
| test = (t.m < N) > (0); // Same meaning, but not treated as a template. |
| @} |
| @end smallexample |
| |
| This warning can be disabled with @option{-Wno-missing-template-keyword}. |
| |
| @item -Wno-multichar |
| @opindex Wno-multichar |
| @opindex Wmultichar |
| Do not warn if a multicharacter constant (@samp{'FOOF'}) is used. |
| Usually they indicate a typo in the user's code, as they have |
| implementation-defined values, and should not be used in portable code. |
| |
| @item -Wnormalized=@r{[}none@r{|}id@r{|}nfc@r{|}nfkc@r{]} |
| @opindex Wnormalized= |
| @opindex Wnormalized |
| @opindex Wno-normalized |
| @cindex NFC |
| @cindex NFKC |
| @cindex character set, input normalization |
| In ISO C and ISO C++, two identifiers are different if they are |
| different sequences of characters. However, sometimes when characters |
| outside the basic ASCII character set are used, you can have two |
| different character sequences that look the same. To avoid confusion, |
| the ISO 10646 standard sets out some @dfn{normalization rules} which |
| when applied ensure that two sequences that look the same are turned into |
| the same sequence. GCC can warn you if you are using identifiers that |
| have not been normalized; this option controls that warning. |
| |
| There are four levels of warning supported by GCC@. The default is |
| @option{-Wnormalized=nfc}, which warns about any identifier that is |
| not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the |
| recommended form for most uses. It is equivalent to |
| @option{-Wnormalized}. |
| |
| Unfortunately, there are some characters allowed in identifiers by |
| ISO C and ISO C++ that, when turned into NFC, are not allowed in |
| identifiers. That is, there's no way to use these symbols in portable |
| ISO C or C++ and have all your identifiers in NFC@. |
| @option{-Wnormalized=id} suppresses the warning for these characters. |
| It is hoped that future versions of the standards involved will correct |
| this, which is why this option is not the default. |
| |
| You can switch the warning off for all characters by writing |
| @option{-Wnormalized=none} or @option{-Wno-normalized}. You should |
| only do this if you are using some other normalization scheme (like |
| ``D''), because otherwise you can easily create bugs that are |
| literally impossible to see. |
| |
| Some characters in ISO 10646 have distinct meanings but look identical |
| in some fonts or display methodologies, especially once formatting has |
| been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL |
| LETTER N'', displays just like a regular @code{n} that has been |
| placed in a superscript. ISO 10646 defines the @dfn{NFKC} |
| normalization scheme to convert all these into a standard form as |
| well, and GCC warns if your code is not in NFKC if you use |
| @option{-Wnormalized=nfkc}. This warning is comparable to warning |
| about every identifier that contains the letter O because it might be |
| confused with the digit 0, and so is not the default, but may be |
| useful as a local coding convention if the programming environment |
| cannot be fixed to display these characters distinctly. |
| |
| @item -Wno-attribute-warning |
| @opindex Wno-attribute-warning |
| @opindex Wattribute-warning |
| Do not warn about usage of functions (@pxref{Function Attributes}) |
| declared with @code{warning} attribute. By default, this warning is |
| enabled. @option{-Wno-attribute-warning} can be used to disable the |
| warning or @option{-Wno-error=attribute-warning} can be used to |
| disable the error when compiled with @option{-Werror} flag. |
| |
| @item -Wno-deprecated |
| @opindex Wno-deprecated |
| @opindex Wdeprecated |
| Do not warn about usage of deprecated features. @xref{Deprecated Features}. |
| |
| @item -Wno-deprecated-declarations |
| @opindex Wno-deprecated-declarations |
| @opindex Wdeprecated-declarations |
| Do not warn about uses of functions (@pxref{Function Attributes}), |
| variables (@pxref{Variable Attributes}), and types (@pxref{Type |
| Attributes}) marked as deprecated by using the @code{deprecated} |
| attribute. |
| |
| @item -Wno-overflow |
| @opindex Wno-overflow |
| @opindex Woverflow |
| Do not warn about compile-time overflow in constant expressions. |
| |
| @item -Wno-odr |
| @opindex Wno-odr |
| @opindex Wodr |
| Warn about One Definition Rule violations during link-time optimization. |
| Enabled by default. |
| |
| @item -Wopenacc-parallelism |
| @opindex Wopenacc-parallelism |
| @opindex Wno-openacc-parallelism |
| @cindex OpenACC accelerator programming |
| Warn about potentially suboptimal choices related to OpenACC parallelism. |
| |
| @item -Wopenmp-simd |
| @opindex Wopenmp-simd |
| @opindex Wno-openmp-simd |
| Warn if the vectorizer cost model overrides the OpenMP |
| simd directive set by user. The @option{-fsimd-cost-model=unlimited} |
| option can be used to relax the cost model. |
| |
| @item -Woverride-init @r{(C and Objective-C only)} |
| @opindex Woverride-init |
| @opindex Wno-override-init |
| @opindex W |
| @opindex Wextra |
| @opindex Wno-extra |
| Warn if an initialized field without side effects is overridden when |
| using designated initializers (@pxref{Designated Inits, , Designated |
| Initializers}). |
| |
| This warning is included in @option{-Wextra}. To get other |
| @option{-Wextra} warnings without this one, use @option{-Wextra |
| -Wno-override-init}. |
| |
| @item -Wno-override-init-side-effects @r{(C and Objective-C only)} |
| @opindex Woverride-init-side-effects |
| @opindex Wno-override-init-side-effects |
| Do not warn if an initialized field with side effects is overridden when |
| using designated initializers (@pxref{Designated Inits, , Designated |
| Initializers}). This warning is enabled by default. |
| |
| @item -Wpacked |
| @opindex Wpacked |
| @opindex Wno-packed |
| Warn if a structure is given the packed attribute, but the packed |
| attribute has no effect on the layout or size of the structure. |
| Such structures may be mis-aligned for little benefit. For |
| instance, in this code, the variable @code{f.x} in @code{struct bar} |
| is misaligned even though @code{struct bar} does not itself |
| have the packed attribute: |
| |
| @smallexample |
| @group |
| struct foo @{ |
| int x; |
| char a, b, c, d; |
| @} __attribute__((packed)); |
| struct bar @{ |
| char z; |
| struct foo f; |
| @}; |
| @end group |
| @end smallexample |
| |
| @item -Wnopacked-bitfield-compat |
| @opindex Wpacked-bitfield-compat |
| @opindex Wno-packed-bitfield-compat |
| The 4.1, 4.2 and 4.3 series of GCC ignore the @code{packed} attribute |
| on bit-fields of type @code{char}. This was fixed in GCC 4.4 but |
| the change can lead to differences in the structure layout. GCC |
| informs you when the offset of such a field has changed in GCC 4.4. |
| For example there is no longer a 4-bit padding between field @code{a} |
| and @code{b} in this structure: |
| |
| @smallexample |
| struct foo |
| @{ |
| char a:4; |
| char b:8; |
| @} __attribute__ ((packed)); |
| @end smallexample |
| |
| This warning is enabled by default. Use |
| @option{-Wno-packed-bitfield-compat} to disable this warning. |
| |
| @item -Wpacked-not-aligned @r{(C, C++, Objective-C and Objective-C++ only)} |
| @opindex Wpacked-not-aligned |
| @opindex Wno-packed-not-aligned |
| Warn if a structure field with explicitly specified alignment in a |
| packed struct or union is misaligned. For example, a warning will |
| be issued on @code{struct S}, like, @code{warning: alignment 1 of |
| 'struct S' is less than 8}, in this code: |
| |
| @smallexample |
| @group |
| struct __attribute__ ((aligned (8))) S8 @{ char a[8]; @}; |
| struct __attribute__ ((packed)) S @{ |
| struct S8 s8; |
| @}; |
| @end group |
| @end smallexample |
| |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wpadded |
| @opindex Wpadded |
| @opindex Wno-padded |
| Warn if padding is included in a structure, either to align an element |
| of the structure or to align the whole structure. Sometimes when this |
| happens it is possible to rearrange the fields of the structure to |
| reduce the padding and so make the structure smaller. |
| |
| @item -Wredundant-decls |
| @opindex Wredundant-decls |
| @opindex Wno-redundant-decls |
| Warn if anything is declared more than once in the same scope, even in |
| cases where multiple declaration is valid and changes nothing. |
| |
| @item -Wrestrict |
| @opindex Wrestrict |
| @opindex Wno-restrict |
| Warn when an object referenced by a @code{restrict}-qualified parameter |
| (or, in C++, a @code{__restrict}-qualified parameter) is aliased by another |
| argument, or when copies between such objects overlap. For example, |
| the call to the @code{strcpy} function below attempts to truncate the string |
| by replacing its initial characters with the last four. However, because |
| the call writes the terminating NUL into @code{a[4]}, the copies overlap and |
| the call is diagnosed. |
| |
| @smallexample |
| void foo (void) |
| @{ |
| char a[] = "abcd1234"; |
| strcpy (a, a + 4); |
| @dots{} |
| @} |
| @end smallexample |
| The @option{-Wrestrict} option detects some instances of simple overlap |
| even without optimization but works best at @option{-O2} and above. It |
| is included in @option{-Wall}. |
| |
| @item -Wnested-externs @r{(C and Objective-C only)} |
| @opindex Wnested-externs |
| @opindex Wno-nested-externs |
| Warn if an @code{extern} declaration is encountered within a function. |
| |
| @item -Winline |
| @opindex Winline |
| @opindex Wno-inline |
| Warn if a function that is declared as inline cannot be inlined. |
| Even with this option, the compiler does not warn about failures to |
| inline functions declared in system headers. |
| |
| The compiler uses a variety of heuristics to determine whether or not |
| to inline a function. For example, the compiler takes into account |
| the size of the function being inlined and the amount of inlining |
| that has already been done in the current function. Therefore, |
| seemingly insignificant changes in the source program can cause the |
| warnings produced by @option{-Winline} to appear or disappear. |
| |
| @item -Winterference-size |
| @opindex Winterference-size |
| Warn about use of C++17 @code{std::hardware_destructive_interference_size} |
| without specifying its value with @option{--param destructive-interference-size}. |
| Also warn about questionable values for that option. |
| |
| This variable is intended to be used for controlling class layout, to |
| avoid false sharing in concurrent code: |
| |
| @smallexample |
| struct independent_fields @{ |
| alignas(std::hardware_destructive_interference_size) std::atomic<int> one; |
| alignas(std::hardware_destructive_interference_size) std::atomic<int> two; |
| @}; |
| @end smallexample |
| |
| Here @samp{one} and @samp{two} are intended to be far enough apart |
| that stores to one won't require accesses to the other to reload the |
| cache line. |
| |
| By default, @option{--param destructive-interference-size} and |
| @option{--param constructive-interference-size} are set based on the |
| current @option{-mtune} option, typically to the L1 cache line size |
| for the particular target CPU, sometimes to a range if tuning for a |
| generic target. So all translation units that depend on ABI |
| compatibility for the use of these variables must be compiled with |
| the same @option{-mtune} (or @option{-mcpu}). |
| |
| If ABI stability is important, such as if the use is in a header for a |
| library, you should probably not use the hardware interference size |
| variables at all. Alternatively, you can force a particular value |
| with @option{--param}. |
| |
| If you are confident that your use of the variable does not affect ABI |
| outside a single build of your project, you can turn off the warning |
| with @option{-Wno-interference-size}. |
| |
| @item -Wint-in-bool-context |
| @opindex Wint-in-bool-context |
| @opindex Wno-int-in-bool-context |
| Warn for suspicious use of integer values where boolean values are expected, |
| such as conditional expressions (?:) using non-boolean integer constants in |
| boolean context, like @code{if (a <= b ? 2 : 3)}. Or left shifting of signed |
| integers in boolean context, like @code{for (a = 0; 1 << a; a++);}. Likewise |
| for all kinds of multiplications regardless of the data type. |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wno-int-to-pointer-cast |
| @opindex Wno-int-to-pointer-cast |
| @opindex Wint-to-pointer-cast |
| Suppress warnings from casts to pointer type of an integer of a |
| different size. In C++, casting to a pointer type of smaller size is |
| an error. @option{Wint-to-pointer-cast} is enabled by default. |
| |
| |
| @item -Wno-pointer-to-int-cast @r{(C and Objective-C only)} |
| @opindex Wno-pointer-to-int-cast |
| @opindex Wpointer-to-int-cast |
| Suppress warnings from casts from a pointer to an integer type of a |
| different size. |
| |
| @item -Winvalid-pch |
| @opindex Winvalid-pch |
| @opindex Wno-invalid-pch |
| Warn if a precompiled header (@pxref{Precompiled Headers}) is found in |
| the search path but cannot be used. |
| |
| @item -Wlong-long |
| @opindex Wlong-long |
| @opindex Wno-long-long |
| Warn if @code{long long} type is used. This is enabled by either |
| @option{-Wpedantic} or @option{-Wtraditional} in ISO C90 and C++98 |
| modes. To inhibit the warning messages, use @option{-Wno-long-long}. |
| |
| @item -Wvariadic-macros |
| @opindex Wvariadic-macros |
| @opindex Wno-variadic-macros |
| Warn if variadic macros are used in ISO C90 mode, or if the GNU |
| alternate syntax is used in ISO C99 mode. This is enabled by either |
| @option{-Wpedantic} or @option{-Wtraditional}. To inhibit the warning |
| messages, use @option{-Wno-variadic-macros}. |
| |
| @item -Wno-varargs |
| @opindex Wvarargs |
| @opindex Wno-varargs |
| Do not warn upon questionable usage of the macros used to handle variable |
| arguments like @code{va_start}. These warnings are enabled by default. |
| |
| @item -Wvector-operation-performance |
| @opindex Wvector-operation-performance |
| @opindex Wno-vector-operation-performance |
| Warn if vector operation is not implemented via SIMD capabilities of the |
| architecture. Mainly useful for the performance tuning. |
| Vector operation can be implemented @code{piecewise}, which means that the |
| scalar operation is performed on every vector element; |
| @code{in parallel}, which means that the vector operation is implemented |
| using scalars of wider type, which normally is more performance efficient; |
| and @code{as a single scalar}, which means that vector fits into a |
| scalar type. |
| |
| @item -Wvla |
| @opindex Wvla |
| @opindex Wno-vla |
| Warn if a variable-length array is used in the code. |
| @option{-Wno-vla} prevents the @option{-Wpedantic} warning of |
| the variable-length array. |
| |
| @item -Wvla-larger-than=@var{byte-size} |
| @opindex Wvla-larger-than= |
| @opindex Wno-vla-larger-than |
| If this option is used, the compiler warns for declarations of |
| variable-length arrays whose size is either unbounded, or bounded |
| by an argument that allows the array size to exceed @var{byte-size} |
| bytes. This is similar to how @option{-Walloca-larger-than=}@var{byte-size} |
| works, but with variable-length arrays. |
| |
| Note that GCC may optimize small variable-length arrays of a known |
| value into plain arrays, so this warning may not get triggered for |
| such arrays. |
| |
| @option{-Wvla-larger-than=}@samp{PTRDIFF_MAX} is enabled by default but |
| is typically only effective when @option{-ftree-vrp} is active (default |
| for @option{-O2} and above). |
| |
| See also @option{-Walloca-larger-than=@var{byte-size}}. |
| |
| @item -Wno-vla-larger-than |
| @opindex Wno-vla-larger-than |
| Disable @option{-Wvla-larger-than=} warnings. The option is equivalent |
| to @option{-Wvla-larger-than=}@samp{SIZE_MAX} or larger. |
| |
| @item -Wvla-parameter |
| @opindex Wno-vla-parameter |
| Warn about redeclarations of functions involving arguments of Variable |
| Length Array types of inconsistent kinds or forms, and enable the detection |
| of out-of-bounds accesses to such parameters by warnings such as |
| @option{-Warray-bounds}. |
| |
| If the first function declaration uses the VLA form the bound specified |
| in the array is assumed to be the minimum number of elements expected to |
| be provided in calls to the function and the maximum number of elements |
| accessed by it. Failing to provide arguments of sufficient size or |
| accessing more than the maximum number of elements may be diagnosed. |
| |
| For example, the warning triggers for the following redeclarations because |
| the first one allows an array of any size to be passed to @code{f} while |
| the second one specifies that the array argument must have at least @code{n} |
| elements. In addition, calling @code{f} with the associated VLA bound |
| parameter in excess of the actual VLA bound triggers a warning as well. |
| |
| @smallexample |
| void f (int n, int[n]); |
| void f (int, int[]); // warning: argument 2 previously declared as a VLA |
| |
| void g (int n) |
| @{ |
| if (n > 4) |
| return; |
| int a[n]; |
| f (sizeof a, a); // warning: access to a by f may be out of bounds |
| @dots{} |
| @} |
| |
| @end smallexample |
| |
| @option{-Wvla-parameter} is included in @option{-Wall}. The |
| @option{-Warray-parameter} option triggers warnings for similar problems |
| involving ordinary array arguments. |
| |
| @item -Wvolatile-register-var |
| @opindex Wvolatile-register-var |
| @opindex Wno-volatile-register-var |
| Warn if a register variable is declared volatile. The volatile |
| modifier does not inhibit all optimizations that may eliminate reads |
| and/or writes to register variables. This warning is enabled by |
| @option{-Wall}. |
| |
| @item -Wdisabled-optimization |
| @opindex Wdisabled-optimization |
| @opindex Wno-disabled-optimization |
| Warn if a requested optimization pass is disabled. This warning does |
| not generally indicate that there is anything wrong with your code; it |
| merely indicates that GCC's optimizers are unable to handle the code |
| effectively. Often, the problem is that your code is too big or too |
| complex; GCC refuses to optimize programs when the optimization |
| itself is likely to take inordinate amounts of time. |
| |
| @item -Wpointer-sign @r{(C and Objective-C only)} |
| @opindex Wpointer-sign |
| @opindex Wno-pointer-sign |
| Warn for pointer argument passing or assignment with different signedness. |
| This option is only supported for C and Objective-C@. It is implied by |
| @option{-Wall} and by @option{-Wpedantic}, which can be disabled with |
| @option{-Wno-pointer-sign}. |
| |
| @item -Wstack-protector |
| @opindex Wstack-protector |
| @opindex Wno-stack-protector |
| This option is only active when @option{-fstack-protector} is active. It |
| warns about functions that are not protected against stack smashing. |
| |
| @item -Woverlength-strings |
| @opindex Woverlength-strings |
| @opindex Wno-overlength-strings |
| Warn about string constants that are longer than the ``minimum |
| maximum'' length specified in the C standard. Modern compilers |
| generally allow string constants that are much longer than the |
| standard's minimum limit, but very portable programs should avoid |
| using longer strings. |
| |
| The limit applies @emph{after} string constant concatenation, and does |
| not count the trailing NUL@. In C90, the limit was 509 characters; in |
| C99, it was raised to 4095. C++98 does not specify a normative |
| minimum maximum, so we do not diagnose overlength strings in C++@. |
| |
| This option is implied by @option{-Wpedantic}, and can be disabled with |
| @option{-Wno-overlength-strings}. |
| |
| @item -Wunsuffixed-float-constants @r{(C and Objective-C only)} |
| @opindex Wunsuffixed-float-constants |
| @opindex Wno-unsuffixed-float-constants |
| |
| Issue a warning for any floating constant that does not have |
| a suffix. When used together with @option{-Wsystem-headers} it |
| warns about such constants in system header files. This can be useful |
| when preparing code to use with the @code{FLOAT_CONST_DECIMAL64} pragma |
| from the decimal floating-point extension to C99. |
| |
| @item -Wno-lto-type-mismatch |
| @opindex Wlto-type-mismatch |
| @opindex Wno-lto-type-mismatch |
| |
| During the link-time optimization, do not warn about type mismatches in |
| global declarations from different compilation units. |
| Requires @option{-flto} to be enabled. Enabled by default. |
| |
| @item -Wno-designated-init @r{(C and Objective-C only)} |
| @opindex Wdesignated-init |
| @opindex Wno-designated-init |
| Suppress warnings when a positional initializer is used to initialize |
| a structure that has been marked with the @code{designated_init} |
| attribute. |
| |
| @end table |
| |
| @node Static Analyzer Options |
| @section Options That Control Static Analysis |
| |
| @table @gcctabopt |
| @item -fanalyzer |
| @opindex analyzer |
| @opindex fanalyzer |
| @opindex fno-analyzer |
| This option enables an static analysis of program flow which looks |
| for ``interesting'' interprocedural paths through the |
| code, and issues warnings for problems found on them. |
| |
| This analysis is much more expensive than other GCC warnings. |
| |
| Enabling this option effectively enables the following warnings: |
| |
| @gccoptlist{ @gol |
| -Wanalyzer-double-fclose @gol |
| -Wanalyzer-double-free @gol |
| -Wanalyzer-exposure-through-output-file @gol |
| -Wanalyzer-file-leak @gol |
| -Wanalyzer-free-of-non-heap @gol |
| -Wanalyzer-malloc-leak @gol |
| -Wanalyzer-mismatching-deallocation @gol |
| -Wanalyzer-null-argument @gol |
| -Wanalyzer-null-dereference @gol |
| -Wanalyzer-possible-null-argument @gol |
| -Wanalyzer-possible-null-dereference @gol |
| -Wanalyzer-shift-count-negative @gol |
| -Wanalyzer-shift-count-overflow @gol |
| -Wanalyzer-stale-setjmp-buffer @gol |
| -Wanalyzer-unsafe-call-within-signal-handler @gol |
| -Wanalyzer-use-after-free @gol |
| -Wanalyzer-use-of-pointer-in-stale-stack-frame @gol |
| -Wanalyzer-use-of-uninitialized-value @gol |
| -Wanalyzer-write-to-const @gol |
| -Wanalyzer-write-to-string-literal @gol |
| } |
| @ignore |
| -Wanalyzer-tainted-allocation-size @gol |
| -Wanalyzer-tainted-array-index @gol |
| -Wanalyzer-tainted-divisor @gol |
| -Wanalyzer-tainted-offset @gol |
| -Wanalyzer-tainted-size @gol |
| @end ignore |
| |
| This option is only available if GCC was configured with analyzer |
| support enabled. |
| |
| @item -Wanalyzer-too-complex |
| @opindex Wanalyzer-too-complex |
| @opindex Wno-analyzer-too-complex |
| If @option{-fanalyzer} is enabled, the analyzer uses various heuristics |
| to attempt to explore the control flow and data flow in the program, |
| but these can be defeated by sufficiently complicated code. |
| |
| By default, the analysis silently stops if the code is too |
| complicated for the analyzer to fully explore and it reaches an internal |
| limit. The @option{-Wanalyzer-too-complex} option warns if this occurs. |
| |
| @item -Wno-analyzer-double-fclose |
| @opindex Wanalyzer-double-fclose |
| @opindex Wno-analyzer-double-fclose |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-double-fclose} to disable it. |
| |
| This diagnostic warns for paths through the code in which a @code{FILE *} |
| can have @code{fclose} called on it more than once. |
| |
| @item -Wno-analyzer-double-free |
| @opindex Wanalyzer-double-free |
| @opindex Wno-analyzer-double-free |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-double-free} to disable it. |
| |
| This diagnostic warns for paths through the code in which a pointer |
| can have a deallocator called on it more than once, either @code{free}, |
| or a deallocator referenced by attribute @code{malloc}. |
| |
| @item -Wno-analyzer-exposure-through-output-file |
| @opindex Wanalyzer-exposure-through-output-file |
| @opindex Wno-analyzer-exposure-through-output-file |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-exposure-through-output-file} |
| to disable it. |
| |
| This diagnostic warns for paths through the code in which a |
| security-sensitive value is written to an output file |
| (such as writing a password to a log file). |
| |
| @item -Wno-analyzer-file-leak |
| @opindex Wanalyzer-file-leak |
| @opindex Wno-analyzer-file-leak |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-file-leak} |
| to disable it. |
| |
| This diagnostic warns for paths through the code in which a |
| @code{<stdio.h>} @code{FILE *} stream object is leaked. |
| |
| @item -Wno-analyzer-free-of-non-heap |
| @opindex Wanalyzer-free-of-non-heap |
| @opindex Wno-analyzer-free-of-non-heap |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-free-of-non-heap} |
| to disable it. |
| |
| This diagnostic warns for paths through the code in which @code{free} |
| is called on a non-heap pointer (e.g. an on-stack buffer, or a global). |
| |
| @item -Wno-analyzer-malloc-leak |
| @opindex Wanalyzer-malloc-leak |
| @opindex Wno-analyzer-malloc-leak |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-malloc-leak} |
| to disable it. |
| |
| This diagnostic warns for paths through the code in which a |
| pointer allocated via an allocator is leaked: either @code{malloc}, |
| or a function marked with attribute @code{malloc}. |
| |
| @item -Wno-analyzer-mismatching-deallocation |
| @opindex Wanalyzer-mismatching-deallocation |
| @opindex Wno-analyzer-mismatching-deallocation |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-mismatching-deallocation} |
| to disable it. |
| |
| This diagnostic warns for paths through the code in which the |
| wrong deallocation function is called on a pointer value, based on |
| which function was used to allocate the pointer value. The diagnostic |
| will warn about mismatches between @code{free}, scalar @code{delete} |
| and vector @code{delete[]}, and those marked as allocator/deallocator |
| pairs using attribute @code{malloc}. |
| |
| @item -Wno-analyzer-possible-null-argument |
| @opindex Wanalyzer-possible-null-argument |
| @opindex Wno-analyzer-possible-null-argument |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-possible-null-argument} to disable it. |
| |
| This diagnostic warns for paths through the code in which a |
| possibly-NULL value is passed to a function argument marked |
| with @code{__attribute__((nonnull))} as requiring a non-NULL |
| value. |
| |
| @item -Wno-analyzer-possible-null-dereference |
| @opindex Wanalyzer-possible-null-dereference |
| @opindex Wno-analyzer-possible-null-dereference |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-possible-null-dereference} to disable it. |
| |
| This diagnostic warns for paths through the code in which a |
| possibly-NULL value is dereferenced. |
| |
| @item -Wno-analyzer-null-argument |
| @opindex Wanalyzer-null-argument |
| @opindex Wno-analyzer-null-argument |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-null-argument} to disable it. |
| |
| This diagnostic warns for paths through the code in which a |
| value known to be NULL is passed to a function argument marked |
| with @code{__attribute__((nonnull))} as requiring a non-NULL |
| value. |
| |
| @item -Wno-analyzer-null-dereference |
| @opindex Wanalyzer-null-dereference |
| @opindex Wno-analyzer-null-dereference |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-null-dereference} to disable it. |
| |
| This diagnostic warns for paths through the code in which a |
| value known to be NULL is dereferenced. |
| |
| @item -Wno-analyzer-shift-count-negative |
| @opindex Wanalyzer-shift-count-negative |
| @opindex Wno-analyzer-shift-count-negative |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-shift-count-negative} to disable it. |
| |
| This diagnostic warns for paths through the code in which a |
| shift is attempted with a negative count. It is analogous to |
| the @option{-Wshift-count-negative} diagnostic implemented in |
| the C/C++ front ends, but is implemented based on analyzing |
| interprocedural paths, rather than merely parsing the syntax tree. |
| However, the analyzer does not prioritize detection of such paths, so |
| false negatives are more likely relative to other warnings. |
| |
| @item -Wno-analyzer-shift-count-overflow |
| @opindex Wanalyzer-shift-count-overflow |
| @opindex Wno-analyzer-shift-count-overflow |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-shift-count-overflow} to disable it. |
| |
| This diagnostic warns for paths through the code in which a |
| shift is attempted with a count greater than or equal to the |
| precision of the operand's type. It is analogous to |
| the @option{-Wshift-count-overflow} diagnostic implemented in |
| the C/C++ front ends, but is implemented based on analyzing |
| interprocedural paths, rather than merely parsing the syntax tree. |
| However, the analyzer does not prioritize detection of such paths, so |
| false negatives are more likely relative to other warnings. |
| |
| @item -Wno-analyzer-stale-setjmp-buffer |
| @opindex Wanalyzer-stale-setjmp-buffer |
| @opindex Wno-analyzer-stale-setjmp-buffer |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-stale-setjmp-buffer} to disable it. |
| |
| This diagnostic warns for paths through the code in which |
| @code{longjmp} is called to rewind to a @code{jmp_buf} relating |
| to a @code{setjmp} call in a function that has returned. |
| |
| When @code{setjmp} is called on a @code{jmp_buf} to record a rewind |
| location, it records the stack frame. The stack frame becomes invalid |
| when the function containing the @code{setjmp} call returns. Attempting |
| to rewind to it via @code{longjmp} would reference a stack frame that |
| no longer exists, and likely lead to a crash (or worse). |
| |
| @item -Wno-analyzer-tainted-allocation-size |
| @opindex Wanalyzer-tainted-allocation-size |
| @opindex Wno-analyzer-tainted-allocation-size |
| This warning requires both @option{-fanalyzer} and |
| @option{-fanalyzer-checker=taint} to enable it; |
| use @option{-Wno-analyzer-tainted-allocation-size} to disable it. |
| |
| This diagnostic warns for paths through the code in which a value |
| that could be under an attacker's control is used as the size |
| of an allocation without being sanitized, so that an attacker could |
| inject an excessively large allocation and potentially cause a denial |
| of service attack. |
| |
| See @url{https://cwe.mitre.org/data/definitions/789.html, CWE-789: Memory Allocation with Excessive Size Value}. |
| |
| @item -Wno-analyzer-tainted-array-index |
| @opindex Wanalyzer-tainted-array-index |
| @opindex Wno-analyzer-tainted-array-index |
| This warning requires both @option{-fanalyzer} and |
| @option{-fanalyzer-checker=taint} to enable it; |
| use @option{-Wno-analyzer-tainted-array-index} to disable it. |
| |
| This diagnostic warns for paths through the code in which a value |
| that could be under an attacker's control is used as the index |
| of an array access without being sanitized, so that an attacker |
| could inject an out-of-bounds access. |
| |
| See @url{https://cwe.mitre.org/data/definitions/129.html, CWE-129: Improper Validation of Array Index}. |
| |
| @item -Wno-analyzer-tainted-divisor |
| @opindex Wanalyzer-tainted-divisor |
| @opindex Wno-analyzer-tainted-divisor |
| This warning requires both @option{-fanalyzer} and |
| @option{-fanalyzer-checker=taint} to enable it; |
| use @option{-Wno-analyzer-tainted-divisor} to disable it. |
| |
| This diagnostic warns for paths through the code in which a value |
| that could be under an attacker's control is used as the divisor |
| in a division or modulus operation without being sanitized, so that |
| an attacker could inject a division-by-zero. |
| |
| @item -Wno-analyzer-tainted-offset |
| @opindex Wanalyzer-tainted-offset |
| @opindex Wno-analyzer-tainted-offset |
| This warning requires both @option{-fanalyzer} and |
| @option{-fanalyzer-checker=taint} to enable it; |
| use @option{-Wno-analyzer-tainted-offset} to disable it. |
| |
| This diagnostic warns for paths through the code in which a value |
| that could be under an attacker's control is used as a pointer offset |
| without being sanitized, so that an attacker could inject an out-of-bounds |
| access. |
| |
| See @url{https://cwe.mitre.org/data/definitions/823.html, CWE-823: Use of Out-of-range Pointer Offset}. |
| |
| @item -Wno-analyzer-tainted-size |
| @opindex Wanalyzer-tainted-size |
| @opindex Wno-analyzer-tainted-size |
| This warning requires both @option{-fanalyzer} and |
| @option{-fanalyzer-checker=taint} to enable it; |
| use @option{-Wno-analyzer-tainted-size} to disable it. |
| |
| This diagnostic warns for paths through the code in which a value |
| that could be under an attacker's control is used as the size of |
| an operation such as @code{memset} without being sanitized, so that an |
| attacker could inject an out-of-bounds access. |
| |
| @item -Wno-analyzer-unsafe-call-within-signal-handler |
| @opindex Wanalyzer-unsafe-call-within-signal-handler |
| @opindex Wno-analyzer-unsafe-call-within-signal-handler |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-unsafe-call-within-signal-handler} to disable it. |
| |
| This diagnostic warns for paths through the code in which a |
| function known to be async-signal-unsafe (such as @code{fprintf}) is |
| called from a signal handler. |
| |
| @item -Wno-analyzer-use-after-free |
| @opindex Wanalyzer-use-after-free |
| @opindex Wno-analyzer-use-after-free |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-use-after-free} to disable it. |
| |
| This diagnostic warns for paths through the code in which a |
| pointer is used after a deallocator is called on it: either @code{free}, |
| or a deallocator referenced by attribute @code{malloc}. |
| |
| @item -Wno-analyzer-use-of-pointer-in-stale-stack-frame |
| @opindex Wanalyzer-use-of-pointer-in-stale-stack-frame |
| @opindex Wno-analyzer-use-of-pointer-in-stale-stack-frame |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-use-of-pointer-in-stale-stack-frame} |
| to disable it. |
| |
| This diagnostic warns for paths through the code in which a pointer |
| is dereferenced that points to a variable in a stale stack frame. |
| |
| @item -Wno-analyzer-write-to-const |
| @opindex Wanalyzer-write-to-const |
| @opindex Wno-analyzer-write-to-const |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-write-to-const} |
| to disable it. |
| |
| This diagnostic warns for paths through the code in which the analyzer |
| detects an attempt to write through a pointer to a @code{const} object. |
| However, the analyzer does not prioritize detection of such paths, so |
| false negatives are more likely relative to other warnings. |
| |
| @item -Wno-analyzer-write-to-string-literal |
| @opindex Wanalyzer-write-to-string-literal |
| @opindex Wno-analyzer-write-to-string-literal |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-write-to-string-literal} |
| to disable it. |
| |
| This diagnostic warns for paths through the code in which the analyzer |
| detects an attempt to write through a pointer to a string literal. |
| However, the analyzer does not prioritize detection of such paths, so |
| false negatives are more likely relative to other warnings. |
| |
| @item -Wno-analyzer-use-of-uninitialized-value |
| @opindex Wanalyzer-use-of-uninitialized-value |
| @opindex Wno-analyzer-use-of-uninitialized-value |
| This warning requires @option{-fanalyzer}, which enables it; use |
| @option{-Wno-analyzer-use-of-uninitialized-value} to disable it. |
| |
| This diagnostic warns for paths through the code in which an uninitialized |
| value is used. |
| |
| @end table |
| |
| Pertinent parameters for controlling the exploration are: |
| @option{--param analyzer-bb-explosion-factor=@var{value}}, |
| @option{--param analyzer-max-enodes-per-program-point=@var{value}}, |
| @option{--param analyzer-max-recursion-depth=@var{value}}, and |
| @option{--param analyzer-min-snodes-for-call-summary=@var{value}}. |
| |
| The following options control the analyzer. |
| |
| @table @gcctabopt |
| |
| @item -fanalyzer-call-summaries |
| @opindex fanalyzer-call-summaries |
| @opindex fno-analyzer-call-summaries |
| Simplify interprocedural analysis by computing the effect of certain calls, |
| rather than exploring all paths through the function from callsite to each |
| possible return. |
| |
| If enabled, call summaries are only used for functions with more than one |
| call site, and that are sufficiently complicated (as per |
| @option{--param analyzer-min-snodes-for-call-summary=@var{value}}). |
| |
| @item -fanalyzer-checker=@var{name} |
| @opindex fanalyzer-checker |
| Restrict the analyzer to run just the named checker, and enable it. |
| |
| Some checkers are disabled by default (even with @option{-fanalyzer}), |
| such as the @code{taint} checker that implements |
| @option{-Wanalyzer-tainted-array-index}, and this option is required |
| to enable them. |
| |
| @emph{Note:} currently, @option{-fanalyzer-checker=taint} disables the |
| following warnings from @option{-fanalyzer}: |
| |
| @gccoptlist{ @gol |
| -Wanalyzer-double-fclose @gol |
| -Wanalyzer-double-free @gol |
| -Wanalyzer-exposure-through-output-file @gol |
| -Wanalyzer-file-leak @gol |
| -Wanalyzer-free-of-non-heap @gol |
| -Wanalyzer-malloc-leak @gol |
| -Wanalyzer-mismatching-deallocation @gol |
| -Wanalyzer-null-argument @gol |
| -Wanalyzer-null-dereference @gol |
| -Wanalyzer-possible-null-argument @gol |
| -Wanalyzer-possible-null-dereference @gol |
| -Wanalyzer-unsafe-call-within-signal-handler @gol |
| -Wanalyzer-use-after-free @gol |
| } |
| |
| @item -fno-analyzer-feasibility |
| @opindex fanalyzer-feasibility |
| @opindex fno-analyzer-feasibility |
| This option is intended for analyzer developers. |
| |
| By default the analyzer verifies that there is a feasible control flow path |
| for each diagnostic it emits: that the conditions that hold are not mutually |
| exclusive. Diagnostics for which no feasible path can be found are rejected. |
| This filtering can be suppressed with @option{-fno-analyzer-feasibility}, for |
| debugging issues in this code. |
| |
| @item -fanalyzer-fine-grained |
| @opindex fanalyzer-fine-grained |
| @opindex fno-analyzer-fine-grained |
| This option is intended for analyzer developers. |
| |
| Internally the analyzer builds an ``exploded graph'' that combines |
| control flow graphs with data flow information. |
| |
| By default, an edge in this graph can contain the effects of a run |
| of multiple statements within a basic block. With |
| @option{-fanalyzer-fine-grained}, each statement gets its own edge. |
| |
| @item -fanalyzer-show-duplicate-count |
| @opindex fanalyzer-show-duplicate-count |
| @opindex fno-analyzer-show-duplicate-count |
| This option is intended for analyzer developers: if multiple diagnostics |
| have been detected as being duplicates of each other, it emits a note when |
| reporting the best diagnostic, giving the number of additional diagnostics |
| that were suppressed by the deduplication logic. |
| |
| @item -fno-analyzer-state-merge |
| @opindex fanalyzer-state-merge |
| @opindex fno-analyzer-state-merge |
| This option is intended for analyzer developers. |
| |
| By default the analyzer attempts to simplify analysis by merging |
| sufficiently similar states at each program point as it builds its |
| ``exploded graph''. With @option{-fno-analyzer-state-merge} this |
| merging can be suppressed, for debugging state-handling issues. |
| |
| @item -fno-analyzer-state-purge |
| @opindex fanalyzer-state-purge |
| @opindex fno-analyzer-state-purge |
| This option is intended for analyzer developers. |
| |
| By default the analyzer attempts to simplify analysis by purging |
| aspects of state at a program point that appear to no longer be relevant |
| e.g. the values of locals that aren't accessed later in the function |
| and which aren't relevant to leak analysis. |
| |
| With @option{-fno-analyzer-state-purge} this purging of state can |
| be suppressed, for debugging state-handling issues. |
| |
| @item -fanalyzer-transitivity |
| @opindex fanalyzer-transitivity |
| @opindex fno-analyzer-transitivity |
| This option enables transitivity of constraints within the analyzer. |
| |
| @item -fanalyzer-verbose-edges |
| This option is intended for analyzer developers. It enables more |
| verbose, lower-level detail in the descriptions of control flow |
| within diagnostic paths. |
| |
| @item -fanalyzer-verbose-state-changes |
| This option is intended for analyzer developers. It enables more |
| verbose, lower-level detail in the descriptions of events relating |
| to state machines within diagnostic paths. |
| |
| @item -fanalyzer-verbosity=@var{level} |
| This option controls the complexity of the control flow paths that are |
| emitted for analyzer diagnostics. |
| |
| The @var{level} can be one of: |
| |
| @table @samp |
| @item 0 |
| At this level, interprocedural call and return events are displayed, |
| along with the most pertinent state-change events relating to |
| a diagnostic. For example, for a double-@code{free} diagnostic, |
| both calls to @code{free} will be shown. |
| |
| @item 1 |
| As per the previous level, but also show events for the entry |
| to each function. |
| |
| @item 2 |
| As per the previous level, but also show events relating to |
| control flow that are significant to triggering the issue |
| (e.g. ``true path taken'' at a conditional). |
| |
| This level is the default. |
| |
| @item 3 |
| As per the previous level, but show all control flow events, not |
| just significant ones. |
| |
| @item 4 |
| This level is intended for analyzer developers; it adds various |
| other events intended for debugging the analyzer. |
| |
| @end table |
| |
| @item -fdump-analyzer |
| @opindex fdump-analyzer |
| Dump internal details about what the analyzer is doing to |
| @file{@var{file}.analyzer.txt}. |
| This option is overridden by @option{-fdump-analyzer-stderr}. |
| |
| @item -fdump-analyzer-stderr |
| @opindex fdump-analyzer-stderr |
| Dump internal details about what the analyzer is doing to stderr. |
| This option overrides @option{-fdump-analyzer}. |
| |
| @item -fdump-analyzer-callgraph |
| @opindex fdump-analyzer-callgraph |
| Dump a representation of the call graph suitable for viewing with |
| GraphViz to @file{@var{file}.callgraph.dot}. |
| |
| @item -fdump-analyzer-exploded-graph |
| @opindex fdump-analyzer-exploded-graph |
| Dump a representation of the ``exploded graph'' suitable for viewing with |
| GraphViz to @file{@var{file}.eg.dot}. |
| Nodes are color-coded based on state-machine states to emphasize |
| state changes. |
| |
| @item -fdump-analyzer-exploded-nodes |
| @opindex dump-analyzer-exploded-nodes |
| Emit diagnostics showing where nodes in the ``exploded graph'' are |
| in relation to the program source. |
| |
| @item -fdump-analyzer-exploded-nodes-2 |
| @opindex dump-analyzer-exploded-nodes-2 |
| Dump a textual representation of the ``exploded graph'' to |
| @file{@var{file}.eg.txt}. |
| |
| @item -fdump-analyzer-exploded-nodes-3 |
| @opindex dump-analyzer-exploded-nodes-3 |
| Dump a textual representation of the ``exploded graph'' to |
| one dump file per node, to @file{@var{file}.eg-@var{id}.txt}. |
| This is typically a large number of dump files. |
| |
| @item -fdump-analyzer-exploded-paths |
| @opindex fdump-analyzer-exploded-paths |
| Dump a textual representation of the ``exploded path'' for each |
| diagnostic to @file{@var{file}.@var{idx}.@var{kind}.epath.txt}. |
| |
| @item -fdump-analyzer-feasibility |
| @opindex dump-analyzer-feasibility |
| Dump internal details about the analyzer's search for feasible paths. |
| The details are written in a form suitable for viewing with GraphViz |
| to filenames of the form @file{@var{file}.*.fg.dot} and |
| @file{@var{file}.*.tg.dot}. |
| |
| @item -fdump-analyzer-json |
| @opindex fdump-analyzer-json |
| Dump a compressed JSON representation of analyzer internals to |
| @file{@var{file}.analyzer.json.gz}. The precise format is subject |
| to change. |
| |
| @item -fdump-analyzer-state-purge |
| @opindex fdump-analyzer-state-purge |
| As per @option{-fdump-analyzer-supergraph}, dump a representation of the |
| ``supergraph'' suitable for viewing with GraphViz, but annotate the |
| graph with information on what state will be purged at each node. |
| The graph is written to @file{@var{file}.state-purge.dot}. |
| |
| @item -fdump-analyzer-supergraph |
| @opindex fdump-analyzer-supergraph |
| Dump representations of the ``supergraph'' suitable for viewing with |
| GraphViz to @file{@var{file}.supergraph.dot} and to |
| @file{@var{file}.supergraph-eg.dot}. These show all of the |
| control flow graphs in the program, with interprocedural edges for |
| calls and returns. The second dump contains annotations showing nodes |
| in the ``exploded graph'' and diagnostics associated with them. |
| |
| @item -fdump-analyzer-untracked |
| @opindex fdump-analyzer-untracked |
| Emit custom warnings with internal details intended for analyzer developers. |
| |
| @end table |
| |
| @node Debugging Options |
| @section Options for Debugging Your Program |
| @cindex options, debugging |
| @cindex debugging information options |
| |
| To tell GCC to emit extra information for use by a debugger, in almost |
| all cases you need only to add @option{-g} to your other options. Some debug |
| formats can co-exist (like DWARF with CTF) when each of them is enabled |
| explicitly by adding the respective command line option to your other options. |
| |
| GCC allows you to use @option{-g} with |
| @option{-O}. The shortcuts taken by optimized code may occasionally |
| be surprising: some variables you declared may not exist |
| at all; flow of control may briefly move where you did not expect it; |
| some statements may not be executed because they compute constant |
| results or their values are already at hand; some statements may |
| execute in different places because they have been moved out of loops. |
| Nevertheless it is possible to debug optimized output. This makes |
| it reasonable to use the optimizer for programs that might have bugs. |
| |
| If you are not using some other optimization option, consider |
| using @option{-Og} (@pxref{Optimize Options}) with @option{-g}. |
| With no @option{-O} option at all, some compiler passes that collect |
| information useful for debugging do not run at all, so that |
| @option{-Og} may result in a better debugging experience. |
| |
| @table @gcctabopt |
| @item -g |
| @opindex g |
| Produce debugging information in the operating system's native format |
| (stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging |
| information. |
| |
| On most systems that use stabs format, @option{-g} enables use of extra |
| debugging information that only GDB can use; this extra information |
| makes debugging work better in GDB but probably makes other debuggers |
| crash or |
| refuse to read the program. If you want to control for certain whether |
| to generate the extra information, use @option{-gstabs+}, @option{-gstabs}, |
| @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below). |
| |
| @item -ggdb |
| @opindex ggdb |
| Produce debugging information for use by GDB@. This means to use the |
| most expressive format available (DWARF, stabs, or the native format |
| if neither of those are supported), including GDB extensions if at all |
| possible. |
| |
| @item -gdwarf |
| @itemx -gdwarf-@var{version} |
| @opindex gdwarf |
| Produce debugging information in DWARF format (if that is supported). |
| The value of @var{version} may be either 2, 3, 4 or 5; the default |
| version for most targets is 5 (with the exception of VxWorks, TPF and |
| Darwin/Mac OS X, which default to version 2, and AIX, which defaults |
| to version 4). |
| |
| Note that with DWARF Version 2, some ports require and always |
| use some non-conflicting DWARF 3 extensions in the unwind tables. |
| |
| Version 4 may require GDB 7.0 and @option{-fvar-tracking-assignments} |
| for maximum benefit. Version 5 requires GDB 8.0 or higher. |
| |
| GCC no longer supports DWARF Version 1, which is substantially |
| different than Version 2 and later. For historical reasons, some |
| other DWARF-related options such as |
| @option{-fno-dwarf2-cfi-asm}) retain a reference to DWARF Version 2 |
| in their names, but apply to all currently-supported versions of DWARF. |
| |
| @item -gbtf |
| @opindex gbtf |
| Request BTF debug information. BTF is the default debugging format for the |
| eBPF target. On other targets, like x86, BTF debug information can be |
| generated along with DWARF debug information when both of the debug formats are |
| enabled explicitly via their respective command line options. |
| |
| @item -gctf |
| @itemx -gctf@var{level} |
| @opindex gctf |
| Request CTF debug information and use level to specify how much CTF debug |
| information should be produced. If @option{-gctf} is specified |
| without a value for level, the default level of CTF debug information is 2. |
| |
| CTF debug information can be generated along with DWARF debug information when |
| both of the debug formats are enabled explicitly via their respective command |
| line options. |
| |
| Level 0 produces no CTF debug information at all. Thus, @option{-gctf0} |
| negates @option{-gctf}. |
| |
| Level 1 produces CTF information for tracebacks only. This includes callsite |
| information, but does not include type information. |
| |
| Level 2 produces type information for entities (functions, data objects etc.) |
| at file-scope or global-scope only. |
| |
| @item -gstabs |
| @opindex gstabs |
| Produce debugging information in stabs format (if that is supported), |
| without GDB extensions. This is the format used by DBX on most BSD |
| systems. On MIPS, Alpha and System V Release 4 systems this option |
| produces stabs debugging output that is not understood by DBX@. |
| On System V Release 4 systems this option requires the GNU assembler. |
| |
| @item -gstabs+ |
| @opindex gstabs+ |
| Produce debugging information in stabs format (if that is supported), |
| using GNU extensions understood only by the GNU debugger (GDB)@. The |
| use of these extensions is likely to make other debuggers crash or |
| refuse to read the program. |
| |
| @item -gxcoff |
| @opindex gxcoff |
| Produce debugging information in XCOFF format (if that is supported). |
| This is the format used by the DBX debugger on IBM RS/6000 systems. |
| |
| @item -gxcoff+ |
| @opindex gxcoff+ |
| Produce debugging information in XCOFF format (if that is supported), |
| using GNU extensions understood only by the GNU debugger (GDB)@. The |
| use of these extensions is likely to make other debuggers crash or |
| refuse to read the program, and may cause assemblers other than the GNU |
| assembler (GAS) to fail with an error. |
| |
| @item -gvms |
| @opindex gvms |
| Produce debugging information in Alpha/VMS debug format (if that is |
| supported). This is the format used by DEBUG on Alpha/VMS systems. |
| |
| @item -g@var{level} |
| @itemx -ggdb@var{level} |
| @itemx -gstabs@var{level} |
| @itemx -gxcoff@var{level} |
| @itemx -gvms@var{level} |
| Request debugging information and also use @var{level} to specify how |
| much information. The default level is 2. |
| |
| Level 0 produces no debug information at all. Thus, @option{-g0} negates |
| @option{-g}. |
| |
| Level 1 produces minimal information, enough for making backtraces in |
| parts of the program that you don't plan to debug. This includes |
| descriptions of functions and external variables, and line number |
| tables, but no information about local variables. |
| |
| Level 3 includes extra information, such as all the macro definitions |
| present in the program. Some debuggers support macro expansion when |
| you use @option{-g3}. |
| |
| If you use multiple @option{-g} options, with or without level numbers, |
| the last such option is the one that is effective. |
| |
| @option{-gdwarf} does not accept a concatenated debug level, to avoid |
| confusion with @option{-gdwarf-@var{level}}. |
| Instead use an additional @option{-g@var{level}} option to change the |
| debug level for DWARF. |
| |
| @item -fno-eliminate-unused-debug-symbols |
| @opindex feliminate-unused-debug-symbols |
| @opindex fno-eliminate-unused-debug-symbols |
| By default, no debug information is produced for symbols that are not actually |
| used. Use this option if you want debug information for all symbols. |
| |
| @item -femit-class-debug-always |
| @opindex femit-class-debug-always |
| Instead of emitting debugging information for a C++ class in only one |
| object file, emit it in all object files using the class. This option |
| should be used only with debuggers that are unable to handle the way GCC |
| normally emits debugging information for classes because using this |
| option increases the size of debugging information by as much as a |
| factor of two. |
| |
| @item -fno-merge-debug-strings |
| @opindex fmerge-debug-strings |
| @opindex fno-merge-debug-strings |
| Direct the linker to not merge together strings in the debugging |
| information that are identical in different object files. Merging is |
| not supported by all assemblers or linkers. Merging decreases the size |
| of the debug information in the output file at the cost of increasing |
| link processing time. Merging is enabled by default. |
| |
| @item -fdebug-prefix-map=@var{old}=@var{new} |
| @opindex fdebug-prefix-map |
| When compiling files residing in directory @file{@var{old}}, record |
| debugging information describing them as if the files resided in |
| directory @file{@var{new}} instead. This can be used to replace a |
| build-time path with an install-time path in the debug info. It can |
| also be used to change an absolute path to a relative path by using |
| @file{.} for @var{new}. This can give more reproducible builds, which |
| are location independent, but may require an extra command to tell GDB |
| where to find the source files. See also @option{-ffile-prefix-map}. |
| |
| @item -fvar-tracking |
| @opindex fvar-tracking |
| Run variable tracking pass. It computes where variables are stored at each |
| position in code. Better debugging information is then generated |
| (if the debugging information format supports this information). |
| |
| It is enabled by default when compiling with optimization (@option{-Os}, |
| @option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and |
| the debug info format supports it. |
| |
| @item -fvar-tracking-assignments |
| @opindex fvar-tracking-assignments |
| @opindex fno-var-tracking-assignments |
| Annotate assignments to user variables early in the compilation and |
| attempt to carry the annotations over throughout the compilation all the |
| way to the end, in an attempt to improve debug information while |
| optimizing. Use of @option{-gdwarf-4} is recommended along with it. |
| |
| It can be enabled even if var-tracking is disabled, in which case |
| annotations are created and maintained, but discarded at the end. |
| By default, this flag is enabled together with @option{-fvar-tracking}, |
| except when selective scheduling is enabled. |
| |
| @item -gsplit-dwarf |
| @opindex gsplit-dwarf |
| If DWARF debugging information is enabled, separate as much debugging |
| information as possible into a separate output file with the extension |
| @file{.dwo}. This option allows the build system to avoid linking files with |
| debug information. To be useful, this option requires a debugger capable of |
| reading @file{.dwo} files. |
| |
| @item -gdwarf32 |
| @itemx -gdwarf64 |
| @opindex gdwarf32 |
| @opindex gdwarf64 |
| If DWARF debugging information is enabled, the @option{-gdwarf32} selects |
| the 32-bit DWARF format and the @option{-gdwarf64} selects the 64-bit |
| DWARF format. The default is target specific, on most targets it is |
| @option{-gdwarf32} though. The 32-bit DWARF format is smaller, but |
| can't support more than 2GiB of debug information in any of the DWARF |
| debug information sections. The 64-bit DWARF format allows larger debug |
| information and might not be well supported by all consumers yet. |
| |
| @item -gdescribe-dies |
| @opindex gdescribe-dies |
| Add description attributes to some DWARF DIEs that have no name attribute, |
| such as artificial variables, external references and call site |
| parameter DIEs. |
| |
| @item -gpubnames |
| @opindex gpubnames |
| Generate DWARF @code{.debug_pubnames} and @code{.debug_pubtypes} sections. |
| |
| @item -ggnu-pubnames |
| @opindex ggnu-pubnames |
| Generate @code{.debug_pubnames} and @code{.debug_pubtypes} sections in a format |
| suitable for conversion into a GDB@ index. This option is only useful |
| with a linker that can produce GDB@ index version 7. |
| |
| @item -fdebug-types-section |
| @opindex fdebug-types-section |
| @opindex fno-debug-types-section |
| When using DWARF Version 4 or higher, type DIEs can be put into |
| their own @code{.debug_types} section instead of making them part of the |
| @code{.debug_info} section. It is more efficient to put them in a separate |
| comdat section since the linker can then remove duplicates. |
| But not all DWARF consumers support @code{.debug_types} sections yet |
| and on some objects @code{.debug_types} produces larger instead of smaller |
| debugging information. |
| |
| @item -grecord-gcc-switches |
| @itemx -gno-record-gcc-switches |
| @opindex grecord-gcc-switches |
| @opindex gno-record-gcc-switches |
| This switch causes the command-line options used to invoke the |
| compiler that may affect code generation to be appended to the |
| DW_AT_producer attribute in DWARF debugging information. The options |
| are concatenated with spaces separating them from each other and from |
| the compiler version. |
| It is enabled by default. |
| See also @option{-frecord-gcc-switches} for another |
| way of storing compiler options into the object file. |
| |
| @item -gstrict-dwarf |
| @opindex gstrict-dwarf |
| Disallow using extensions of later DWARF standard version than selected |
| with @option{-gdwarf-@var{version}}. On most targets using non-conflicting |
| DWARF extensions from later standard versions is allowed. |
| |
| @item -gno-strict-dwarf |
| @opindex gno-strict-dwarf |
| Allow using extensions of later DWARF standard version than selected with |
| @option{-gdwarf-@var{version}}. |
| |
| @item -gas-loc-support |
| @opindex gas-loc-support |
| Inform the compiler that the assembler supports @code{.loc} directives. |
| It may then use them for the assembler to generate DWARF2+ line number |
| tables. |
| |
| This is generally desirable, because assembler-generated line-number |
| tables are a lot more compact than those the compiler can generate |
| itself. |
| |
| This option will be enabled by default if, at GCC configure time, the |
| assembler was found to support such directives. |
| |
| @item -gno-as-loc-support |
| @opindex gno-as-loc-support |
| Force GCC to generate DWARF2+ line number tables internally, if DWARF2+ |
| line number tables are to be generated. |
| |
| @item -gas-locview-support |
| @opindex gas-locview-support |
| Inform the compiler that the assembler supports @code{view} assignment |
| and reset assertion checking in @code{.loc} directives. |
| |
| This option will be enabled by default if, at GCC configure time, the |
| assembler was found to support them. |
| |
| @item -gno-as-locview-support |
| Force GCC to assign view numbers internally, if |
| @option{-gvariable-location-views} are explicitly requested. |
| |
| @item -gcolumn-info |
| @itemx -gno-column-info |
| @opindex gcolumn-info |
| @opindex gno-column-info |
| Emit location column information into DWARF debugging information, rather |
| than just file and line. |
| This option is enabled by default. |
| |
| @item -gstatement-frontiers |
| @itemx -gno-statement-frontiers |
| @opindex gstatement-frontiers |
| @opindex gno-statement-frontiers |
| This option causes GCC to create markers in the internal representation |
| at the beginning of statements, and to keep them roughly in place |
| throughout compilation, using them to guide the output of @code{is_stmt} |
| markers in the line number table. This is enabled by default when |
| compiling with optimization (@option{-Os}, @option{-O1}, @option{-O2}, |
| @dots{}), and outputting DWARF 2 debug information at the normal level. |
| |
| @item -gvariable-location-views |
| @itemx -gvariable-location-views=incompat5 |
| @itemx -gno-variable-location-views |
| @opindex gvariable-location-views |
| @opindex gvariable-location-views=incompat5 |
| @opindex gno-variable-location-views |
| Augment variable location lists with progressive view numbers implied |
| from the line number table. This enables debug information consumers to |
| inspect state at certain points of the program, even if no instructions |
| associated with the corresponding source locations are present at that |
| point. If the assembler lacks support for view numbers in line number |
| tables, this will cause the compiler to emit the line number table, |
| which generally makes them somewhat less compact. The augmented line |
| number tables and location lists are fully backward-compatible, so they |
| can be consumed by debug information consumers that are not aware of |
| these augmentations, but they won't derive any benefit from them either. |
| |
| This is enabled by default when outputting DWARF 2 debug information at |
| the normal level, as long as there is assembler support, |
| @option{-fvar-tracking-assignments} is enabled and |
| @option{-gstrict-dwarf} is not. When assembler support is not |
| available, this may still be enabled, but it will force GCC to output |
| internal line number tables, and if |
| @option{-ginternal-reset-location-views} is not enabled, that will most |
| certainly lead to silently mismatching location views. |
| |
| There is a proposed representation for view numbers that is not backward |
| compatible with the location list format introduced in DWARF 5, that can |
| be enabled with @option{-gvariable-location-views=incompat5}. This |
| option may be removed in the future, is only provided as a reference |
| implementation of the proposed representation. Debug information |
| consumers are not expected to support this extended format, and they |
| would be rendered unable to decode location lists using it. |
| |
| @item -ginternal-reset-location-views |
| @itemx -gno-internal-reset-location-views |
| @opindex ginternal-reset-location-views |
| @opindex gno-internal-reset-location-views |
| Attempt to determine location views that can be omitted from location |
| view lists. This requires the compiler to have very accurate insn |
| length estimates, which isn't always the case, and it may cause |
| incorrect view lists to be generated silently when using an assembler |
| that does not support location view lists. The GNU assembler will flag |
| any such error as a @code{view number mismatch}. This is only enabled |
| on ports that define a reliable estimation function. |
| |
| @item -ginline-points |
| @itemx -gno-inline-points |
| @opindex ginline-points |
| @opindex gno-inline-points |
| Generate extended debug information for inlined functions. Location |
| view tracking markers are inserted at inlined entry points, so that |
| address and view numbers can be computed and output in debug |
| information. This can be enabled independently of location views, in |
| which case the view numbers won't be output, but it can only be enabled |
| along with statement frontiers, and it is only enabled by default if |
| location views are enabled. |
| |
| @item -gz@r{[}=@var{type}@r{]} |
| @opindex gz |
| Produce compressed debug sections in DWARF format, if that is supported. |
| If @var{type} is not given, the default type depends on the capabilities |
| of the assembler and linker used. @var{type} may be one of |
| @samp{none} (don't compress debug sections), @samp{zlib} (use zlib |
| compression in ELF gABI format), or @samp{zlib-gnu} (use zlib |
| compression in traditional GNU format). If the linker doesn't support |
| writing compressed debug sections, the option is rejected. Otherwise, |
| if the assembler does not support them, @option{-gz} is silently ignored |
| when producing object files. |
| |
| @item -femit-struct-debug-baseonly |
| @opindex femit-struct-debug-baseonly |
| Emit debug information for struct-like types |
| only when the base name of the compilation source file |
| matches the base name of file in which the struct is defined. |
| |
| This option substantially reduces the size of debugging information, |
| but at significant potential loss in type information to the debugger. |
| See @option{-femit-struct-debug-reduced} for a less aggressive option. |
| See @option{-femit-struct-debug-detailed} for more detailed control. |
| |
| This option works only with DWARF debug output. |
| |
| @item -femit-struct-debug-reduced |
| @opindex femit-struct-debug-reduced |
| Emit debug information for struct-like types |
| only when the base name of the compilation source file |
| matches the base name of file in which the type is defined, |
| unless the struct is a template or defined in a system header. |
| |
| This option significantly reduces the size of debugging information, |
| with some potential loss in type information to the debugger. |
| See @option{-femit-struct-debug-baseonly} for a more aggressive option. |
| See @option{-femit-struct-debug-detailed} for more detailed control. |
| |
| This option works only with DWARF debug output. |
| |
| @item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} |
| @opindex femit-struct-debug-detailed |
| Specify the struct-like types |
| for which the compiler generates debug information. |
| The intent is to reduce duplicate struct debug information |
| between different object files within the same program. |
| |
| This option is a detailed version of |
| @option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly}, |
| which serves for most needs. |
| |
| A specification has the syntax@* |
| [@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none}) |
| |
| The optional first word limits the specification to |
| structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}). |
| A struct type is used directly when it is the type of a variable, member. |
| Indirect uses arise through pointers to structs. |
| That is, when use of an incomplete struct is valid, the use is indirect. |
| An example is |
| @samp{struct one direct; struct two * indirect;}. |
| |
| The optional second word limits the specification to |
| ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}). |
| Generic structs are a bit complicated to explain. |
| For C++, these are non-explicit specializations of template classes, |
| or non-template classes within the above. |
| Other programming languages have generics, |
| but @option{-femit-struct-debug-detailed} does not yet implement them. |
| |
| The third word specifies the source files for those |
| structs for which the compiler should emit debug information. |
| The values @samp{none} and @samp{any} have the normal meaning. |
| The value @samp{base} means that |
| the base of name of the file in which the type declaration appears |
| must match the base of the name of the main compilation file. |
| In practice, this means that when compiling @file{foo.c}, debug information |
| is generated for types declared in that file and @file{foo.h}, |
| but not other header files. |
| The value @samp{sys} means those types satisfying @samp{base} |
| or declared in system or compiler headers. |
| |
| You may need to experiment to determine the best settings for your application. |
| |
| The default is @option{-femit-struct-debug-detailed=all}. |
| |
| This option works only with DWARF debug output. |
| |
| @item -fno-dwarf2-cfi-asm |
| @opindex fdwarf2-cfi-asm |
| @opindex fno-dwarf2-cfi-asm |
| Emit DWARF unwind info as compiler generated @code{.eh_frame} section |
| instead of using GAS @code{.cfi_*} directives. |
| |
| @item -fno-eliminate-unused-debug-types |
| @opindex feliminate-unused-debug-types |
| @opindex fno-eliminate-unused-debug-types |
| Normally, when producing DWARF output, GCC avoids producing debug symbol |
| output for types that are nowhere used in the source file being compiled. |
| Sometimes it is useful to have GCC emit debugging |
| information for all types declared in a compilation |
| unit, regardless of whether or not they are actually used |
| in that compilation unit, for example |
| if, in the debugger, you want to cast a value to a type that is |
| not actually used in your program (but is declared). More often, |
| however, this results in a significant amount of wasted space. |
| @end table |
| |
| @node Optimize Options |
| @section Options That Control Optimization |
| @cindex optimize options |
| @cindex options, optimization |
| |
| These options control various sorts of optimizations. |
| |
| Without any optimization option, the compiler's goal is to reduce the |
| cost of compilation and to make debugging produce the expected |
| results. Statements are independent: if you stop the program with a |
| breakpoint between statements, you can then assign a new value to any |
| variable or change the program counter to any other statement in the |
| function and get exactly the results you expect from the source |
| code. |
| |
| Turning on optimization flags makes the compiler attempt to improve |
| the performance and/or code size at the expense of compilation time |
| and possibly the ability to debug the program. |
| |
| The compiler performs optimization based on the knowledge it has of the |
| program. Compiling multiple files at once to a single output file mode allows |
| the compiler to use information gained from all of the files when compiling |
| each of them. |
| |
| Not all optimizations are controlled directly by a flag. Only |
| optimizations that have a flag are listed in this section. |
| |
| Most optimizations are completely disabled at @option{-O0} or if an |
| @option{-O} level is not set on the command line, even if individual |
| optimization flags are specified. Similarly, @option{-Og} suppresses |
| many optimization passes. |
| |
| Depending on the target and how GCC was configured, a slightly different |
| set of optimizations may be enabled at each @option{-O} level than |
| those listed here. You can invoke GCC with @option{-Q --help=optimizers} |
| to find out the exact set of optimizations that are enabled at each level. |
| @xref{Overall Options}, for examples. |
| |
| @table @gcctabopt |
| @item -O |
| @itemx -O1 |
| @opindex O |
| @opindex O1 |
| Optimize. Optimizing compilation takes somewhat more time, and a lot |
| more memory for a large function. |
| |
| With @option{-O}, the compiler tries to reduce code size and execution |
| time, without performing any optimizations that take a great deal of |
| compilation time. |
| |
| @c Note that in addition to the default_options_table list in opts.cc, |
| @c several optimization flags default to true but control optimization |
| @c passes that are explicitly disabled at -O0. |
| |
| @option{-O} turns on the following optimization flags: |
| |
| @c Please keep the following list alphabetized. |
| @gccoptlist{-fauto-inc-dec @gol |
| -fbranch-count-reg @gol |
| -fcombine-stack-adjustments @gol |
| -fcompare-elim @gol |
| -fcprop-registers @gol |
| -fdce @gol |
| -fdefer-pop @gol |
| -fdelayed-branch @gol |
| -fdse @gol |
| -fforward-propagate @gol |
| -fguess-branch-probability @gol |
| -fif-conversion @gol |
| -fif-conversion2 @gol |
| -finline-functions-called-once @gol |
| -fipa-modref @gol |
| -fipa-profile @gol |
| -fipa-pure-const @gol |
| -fipa-reference @gol |
| -fipa-reference-addressable @gol |
| -fmerge-constants @gol |
| -fmove-loop-invariants @gol |
| -fmove-loop-stores@gol |
| -fomit-frame-pointer @gol |
| -freorder-blocks @gol |
| -fshrink-wrap @gol |
| -fshrink-wrap-separate @gol |
| -fsplit-wide-types @gol |
| -fssa-backprop @gol |
| -fssa-phiopt @gol |
| -ftree-bit-ccp @gol |
| -ftree-ccp @gol |
| -ftree-ch @gol |
| -ftree-coalesce-vars @gol |
| -ftree-copy-prop @gol |
| -ftree-dce @gol |
| -ftree-dominator-opts @gol |
| -ftree-dse @gol |
| -ftree-forwprop @gol |
| -ftree-fre @gol |
| -ftree-phiprop @gol |
| -ftree-pta @gol |
| -ftree-scev-cprop @gol |
| -ftree-sink @gol |
| -ftree-slsr @gol |
| -ftree-sra @gol |
| -ftree-ter @gol |
| -funit-at-a-time} |
| |
| @item -O2 |
| @opindex O2 |
| Optimize even more. GCC performs nearly all supported optimizations |
| that do not involve a space-speed tradeoff. |
| As compared to @option{-O}, this option increases both compilation time |
| and the performance of the generated code. |
| |
| @option{-O2} turns on all optimization flags specified by @option{-O1}. It |
| also turns on the following optimization flags: |
| |
| @c Please keep the following list alphabetized! |
| @gccoptlist{-falign-functions -falign-jumps @gol |
| -falign-labels -falign-loops @gol |
| -fcaller-saves @gol |
| -fcode-hoisting @gol |
| -fcrossjumping @gol |
| -fcse-follow-jumps -fcse-skip-blocks @gol |
| -fdelete-null-pointer-checks @gol |
| -fdevirtualize -fdevirtualize-speculatively @gol |
| -fexpensive-optimizations @gol |
| -ffinite-loops @gol |
| -fgcse -fgcse-lm @gol |
| -fhoist-adjacent-loads @gol |
| -finline-functions @gol |
| -finline-small-functions @gol |
| -findirect-inlining @gol |
| -fipa-bit-cp -fipa-cp -fipa-icf @gol |
| -fipa-ra -fipa-sra -fipa-vrp @gol |
| -fisolate-erroneous-paths-dereference @gol |
| -flra-remat @gol |
| -foptimize-sibling-calls @gol |
| -foptimize-strlen @gol |
| -fpartial-inlining @gol |
| -fpeephole2 @gol |
| -freorder-blocks-algorithm=stc @gol |
| -freorder-blocks-and-partition -freorder-functions @gol |
| -frerun-cse-after-loop @gol |
| -fschedule-insns -fschedule-insns2 @gol |
| -fsched-interblock -fsched-spec @gol |
| -fstore-merging @gol |
| -fstrict-aliasing @gol |
| -fthread-jumps @gol |
| -ftree-builtin-call-dce @gol |
| -ftree-loop-vectorize @gol |
| -ftree-pre @gol |
| -ftree-slp-vectorize @gol |
| -ftree-switch-conversion -ftree-tail-merge @gol |
| -ftree-vrp @gol |
| -fvect-cost-model=very-cheap} |
| |
| Please note the warning under @option{-fgcse} about |
| invoking @option{-O2} on programs that use computed gotos. |
| |
| @item -O3 |
| @opindex O3 |
| Optimize yet more. @option{-O3} turns on all optimizations specified |
| by @option{-O2} and also turns on the following optimization flags: |
| |
| @c Please keep the following list alphabetized! |
| @gccoptlist{-fgcse-after-reload @gol |
| -fipa-cp-clone |
| -floop-interchange @gol |
| -floop-unroll-and-jam @gol |
| -fpeel-loops @gol |
| -fpredictive-commoning @gol |
| -fsplit-loops @gol |
| -fsplit-paths @gol |
| -ftree-loop-distribution @gol |
| -ftree-partial-pre @gol |
| -funswitch-loops @gol |
| -fvect-cost-model=dynamic @gol |
| -fversion-loops-for-strides} |
| |
| @item -O0 |
| @opindex O0 |
| Reduce compilation time and make debugging produce the expected |
| results. This is the default. |
| |
| @item -Os |
| @opindex Os |
| Optimize for size. @option{-Os} enables all @option{-O2} optimizations |
| except those that often increase code size: |
| |
| @gccoptlist{-falign-functions -falign-jumps @gol |
| -falign-labels -falign-loops @gol |
| -fprefetch-loop-arrays -freorder-blocks-algorithm=stc} |
| |
| It also enables @option{-finline-functions}, causes the compiler to tune for |
| code size rather than execution speed, and performs further optimizations |
| designed to reduce code size. |
| |
| @item -Ofast |
| @opindex Ofast |
| Disregard strict standards compliance. @option{-Ofast} enables all |
| @option{-O3} optimizations. It also enables optimizations that are not |
| valid for all standard-compliant programs. |
| It turns on @option{-ffast-math}, @option{-fallow-store-data-races} |
| and the Fortran-specific @option{-fstack-arrays}, unless |
| @option{-fmax-stack-var-size} is specified, and @option{-fno-protect-parens}. |
| It turns off @option{-fsemantic-interposition}. |
| |
| @item -Og |
| @opindex Og |
| Optimize debugging experience. @option{-Og} should be the optimization |
| level of choice for the standard edit-compile-debug cycle, offering |
| a reasonable level of optimization while maintaining fast compilation |
| and a good debugging experience. It is a better choice than @option{-O0} |
| for producing debuggable code because some compiler passes |
| that collect debug information are disabled at @option{-O0}. |
| |
| Like @option{-O0}, @option{-Og} completely disables a number of |
| optimization passes so that individual options controlling them have |
| no effect. Otherwise @option{-Og} enables all @option{-O1} |
| optimization flags except for those that may interfere with debugging: |
| |
| @gccoptlist{-fbranch-count-reg -fdelayed-branch @gol |
| -fdse -fif-conversion -fif-conversion2 @gol |
| -finline-functions-called-once @gol |
| -fmove-loop-invariants -fmove-loop-stores -fssa-phiopt @gol |
| -ftree-bit-ccp -ftree-dse -ftree-pta -ftree-sra} |
| |
| @item -Oz |
| @opindex Oz |
| Optimize aggressively for size rather than speed. This may increase |
| the number of instructions executed if those instructions require |
| fewer bytes to encode. @option{-Oz} behaves similarly to @option{-Os} |
| including enabling most @option{-O2} optimizations. |
| |
| @end table |
| |
| If you use multiple @option{-O} options, with or without level numbers, |
| the last such option is the one that is effective. |
| |
| Options of the form @option{-f@var{flag}} specify machine-independent |
| flags. Most flags have both positive and negative forms; the negative |
| form of @option{-ffoo} is @option{-fno-foo}. In the table |
| below, only one of the forms is listed---the one you typically |
| use. You can figure out the other form by either removing @samp{no-} |
| or adding it. |
| |
| The following options control specific optimizations. They are either |
| activated by @option{-O} options or are related to ones that are. You |
| can use the following flags in the rare cases when ``fine-tuning'' of |
| optimizations to be performed is desired. |
| |
| @table @gcctabopt |
| @item -fno-defer-pop |
| @opindex fno-defer-pop |
| @opindex fdefer-pop |
| For machines that must pop arguments after a function call, always pop |
| the arguments as soon as each function returns. |
| At levels @option{-O1} and higher, @option{-fdefer-pop} is the default; |
| this allows the compiler to let arguments accumulate on the stack for several |
| function calls and pop them all at once. |
| |
| @item -fforward-propagate |
| @opindex fforward-propagate |
| Perform a forward propagation pass on RTL@. The pass tries to combine two |
| instructions and checks if the result can be simplified. If loop unrolling |
| is active, two passes are performed and the second is scheduled after |
| loop unrolling. |
| |
| This option is enabled by default at optimization levels @option{-O1}, |
| @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -ffp-contract=@var{style} |
| @opindex ffp-contract |
| @option{-ffp-contract=off} disables floating-point expression contraction. |
| @option{-ffp-contract=fast} enables floating-point expression contraction |
| such as forming of fused multiply-add operations if the target has |
| native support for them. |
| @option{-ffp-contract=on} enables floating-point expression contraction |
| if allowed by the language standard. This is currently not implemented |
| and treated equal to @option{-ffp-contract=off}. |
| |
| The default is @option{-ffp-contract=fast}. |
| |
| @item -fomit-frame-pointer |
| @opindex fomit-frame-pointer |
| Omit the frame pointer in functions that don't need one. This avoids the |
| instructions to save, set up and restore the frame pointer; on many targets |
| it also makes an extra register available. |
| |
| On some targets this flag has no effect because the standard calling sequence |
| always uses a frame pointer, so it cannot be omitted. |
| |
| Note that @option{-fno-omit-frame-pointer} doesn't guarantee the frame pointer |
| is used in all functions. Several targets always omit the frame pointer in |
| leaf functions. |
| |
| Enabled by default at @option{-O1} and higher. |
| |
| @item -foptimize-sibling-calls |
| @opindex foptimize-sibling-calls |
| Optimize sibling and tail recursive calls. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -foptimize-strlen |
| @opindex foptimize-strlen |
| Optimize various standard C string functions (e.g.@: @code{strlen}, |
| @code{strchr} or @code{strcpy}) and |
| their @code{_FORTIFY_SOURCE} counterparts into faster alternatives. |
| |
| Enabled at levels @option{-O2}, @option{-O3}. |
| |
| @item -fno-inline |
| @opindex fno-inline |
| @opindex finline |
| Do not expand any functions inline apart from those marked with |
| the @code{always_inline} attribute. This is the default when not |
| optimizing. |
| |
| Single functions can be exempted from inlining by marking them |
| with the @code{noinline} attribute. |
| |
| @item -finline-small-functions |
| @opindex finline-small-functions |
| Integrate functions into their callers when their body is smaller than expected |
| function call code (so overall size of program gets smaller). The compiler |
| heuristically decides which functions are simple enough to be worth integrating |
| in this way. This inlining applies to all functions, even those not declared |
| inline. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -findirect-inlining |
| @opindex findirect-inlining |
| Inline also indirect calls that are discovered to be known at compile |
| time thanks to previous inlining. This option has any effect only |
| when inlining itself is turned on by the @option{-finline-functions} |
| or @option{-finline-small-functions} options. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -finline-functions |
| @opindex finline-functions |
| Consider all functions for inlining, even if they are not declared inline. |
| The compiler heuristically decides which functions are worth integrating |
| in this way. |
| |
| If all calls to a given function are integrated, and the function is |
| declared @code{static}, then the function is normally not output as |
| assembler code in its own right. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. Also enabled |
| by @option{-fprofile-use} and @option{-fauto-profile}. |
| |
| @item -finline-functions-called-once |
| @opindex finline-functions-called-once |
| Consider all @code{static} functions called once for inlining into their |
| caller even if they are not marked @code{inline}. If a call to a given |
| function is integrated, then the function is not output as assembler code |
| in its own right. |
| |
| Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}, |
| but not @option{-Og}. |
| |
| @item -fearly-inlining |
| @opindex fearly-inlining |
| Inline functions marked by @code{always_inline} and functions whose body seems |
| smaller than the function call overhead early before doing |
| @option{-fprofile-generate} instrumentation and real inlining pass. Doing so |
| makes profiling significantly cheaper and usually inlining faster on programs |
| having large chains of nested wrapper functions. |
| |
| Enabled by default. |
| |
| @item -fipa-sra |
| @opindex fipa-sra |
| Perform interprocedural scalar replacement of aggregates, removal of |
| unused parameters and replacement of parameters passed by reference |
| by parameters passed by value. |
| |
| Enabled at levels @option{-O2}, @option{-O3} and @option{-Os}. |
| |
| @item -finline-limit=@var{n} |
| @opindex finline-limit |
| By default, GCC limits the size of functions that can be inlined. This flag |
| allows coarse control of this limit. @var{n} is the size of functions that |
| can be inlined in number of pseudo instructions. |
| |
| Inlining is actually controlled by a number of parameters, which may be |
| specified individually by using @option{--param @var{name}=@var{value}}. |
| The @option{-finline-limit=@var{n}} option sets some of these parameters |
| as follows: |
| |
| @table @gcctabopt |
| @item max-inline-insns-single |
| is set to @var{n}/2. |
| @item max-inline-insns-auto |
| is set to @var{n}/2. |
| @end table |
| |
| See below for a documentation of the individual |
| parameters controlling inlining and for the defaults of these parameters. |
| |
| @emph{Note:} there may be no value to @option{-finline-limit} that results |
| in default behavior. |
| |
| @emph{Note:} pseudo instruction represents, in this particular context, an |
| abstract measurement of function's size. In no way does it represent a count |
| of assembly instructions and as such its exact meaning might change from one |
| release to an another. |
| |
| @item -fno-keep-inline-dllexport |
| @opindex fno-keep-inline-dllexport |
| @opindex fkeep-inline-dllexport |
| This is a more fine-grained version of @option{-fkeep-inline-functions}, |
| which applies only to functions that are declared using the @code{dllexport} |
| attribute or declspec. @xref{Function Attributes,,Declaring Attributes of |
| Functions}. |
| |
| @item -fkeep-inline-functions |
| @opindex fkeep-inline-functions |
| In C, emit @code{static} functions that are declared @code{inline} |
| into the object file, even if the function has been inlined into all |
| of its callers. This switch does not affect functions using the |
| @code{extern inline} extension in GNU C90@. In C++, emit any and all |
| inline functions into the object file. |
| |
| @item -fkeep-static-functions |
| @opindex fkeep-static-functions |
| Emit @code{static} functions into the object file, even if the function |
| is never used. |
| |
| @item -fkeep-static-consts |
| @opindex fkeep-static-consts |
| Emit variables declared @code{static const} when optimization isn't turned |
| on, even if the variables aren't referenced. |
| |
| GCC enables this option by default. If you want to force the compiler to |
| check if a variable is referenced, regardless of whether or not |
| optimization is turned on, use the @option{-fno-keep-static-consts} option. |
| |
| @item -fmerge-constants |
| @opindex fmerge-constants |
| Attempt to merge identical constants (string constants and floating-point |
| constants) across compilation units. |
| |
| This option is the default for optimized compilation if the assembler and |
| linker support it. Use @option{-fno-merge-constants} to inhibit this |
| behavior. |
| |
| Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fmerge-all-constants |
| @opindex fmerge-all-constants |
| Attempt to merge identical constants and identical variables. |
| |
| This option implies @option{-fmerge-constants}. In addition to |
| @option{-fmerge-constants} this considers e.g.@: even constant initialized |
| arrays or initialized constant variables with integral or floating-point |
| types. Languages like C or C++ require each variable, including multiple |
| instances of the same variable in recursive calls, to have distinct locations, |
| so using this option results in non-conforming |
| behavior. |
| |
| @item -fmodulo-sched |
| @opindex fmodulo-sched |
| Perform swing modulo scheduling immediately before the first scheduling |
| pass. This pass looks at innermost loops and reorders their |
| instructions by overlapping different iterations. |
| |
| @item -fmodulo-sched-allow-regmoves |
| @opindex fmodulo-sched-allow-regmoves |
| Perform more aggressive SMS-based modulo scheduling with register moves |
| allowed. By setting this flag certain anti-dependences edges are |
| deleted, which triggers the generation of reg-moves based on the |
| life-range analysis. This option is effective only with |
| @option{-fmodulo-sched} enabled. |
| |
| @item -fno-branch-count-reg |
| @opindex fno-branch-count-reg |
| @opindex fbranch-count-reg |
| Disable the optimization pass that scans for opportunities to use |
| ``decrement and branch'' instructions on a count register instead of |
| instruction sequences that decrement a register, compare it against zero, and |
| then branch based upon the result. This option is only meaningful on |
| architectures that support such instructions, which include x86, PowerPC, |
| IA-64 and S/390. Note that the @option{-fno-branch-count-reg} option |
| doesn't remove the decrement and branch instructions from the generated |
| instruction stream introduced by other optimization passes. |
| |
| The default is @option{-fbranch-count-reg} at @option{-O1} and higher, |
| except for @option{-Og}. |
| |
| @item -fno-function-cse |
| @opindex fno-function-cse |
| @opindex ffunction-cse |
| Do not put function addresses in registers; make each instruction that |
| calls a constant function contain the function's address explicitly. |
| |
| This option results in less efficient code, but some strange hacks |
| that alter the assembler output may be confused by the optimizations |
| performed when this option is not used. |
| |
| The default is @option{-ffunction-cse} |
| |
| @item -fno-zero-initialized-in-bss |
| @opindex fno-zero-initialized-in-bss |
| @opindex fzero-initialized-in-bss |
| If the target supports a BSS section, GCC by default puts variables that |
| are initialized to zero into BSS@. This can save space in the resulting |
| code. |
| |
| This option turns off this behavior because some programs explicitly |
| rely on variables going to the data section---e.g., so that the |
| resulting executable can find the beginning of that section and/or make |
| assumptions based on that. |
| |
| The default is @option{-fzero-initialized-in-bss}. |
| |
| @item -fthread-jumps |
| @opindex fthread-jumps |
| Perform optimizations that check to see if a jump branches to a |
| location where another comparison subsumed by the first is found. If |
| so, the first branch is redirected to either the destination of the |
| second branch or a point immediately following it, depending on whether |
| the condition is known to be true or false. |
| |
| Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fsplit-wide-types |
| @opindex fsplit-wide-types |
| When using a type that occupies multiple registers, such as @code{long |
| long} on a 32-bit system, split the registers apart and allocate them |
| independently. This normally generates better code for those types, |
| but may make debugging more difficult. |
| |
| Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, |
| @option{-Os}. |
| |
| @item -fsplit-wide-types-early |
| @opindex fsplit-wide-types-early |
| Fully split wide types early, instead of very late. |
| This option has no effect unless @option{-fsplit-wide-types} is turned on. |
| |
| This is the default on some targets. |
| |
| @item -fcse-follow-jumps |
| @opindex fcse-follow-jumps |
| In common subexpression elimination (CSE), scan through jump instructions |
| when the target of the jump is not reached by any other path. For |
| example, when CSE encounters an @code{if} statement with an |
| @code{else} clause, CSE follows the jump when the condition |
| tested is false. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fcse-skip-blocks |
| @opindex fcse-skip-blocks |
| This is similar to @option{-fcse-follow-jumps}, but causes CSE to |
| follow jumps that conditionally skip over blocks. When CSE |
| encounters a simple @code{if} statement with no else clause, |
| @option{-fcse-skip-blocks} causes CSE to follow the jump around the |
| body of the @code{if}. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -frerun-cse-after-loop |
| @opindex frerun-cse-after-loop |
| Re-run common subexpression elimination after loop optimizations are |
| performed. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fgcse |
| @opindex fgcse |
| Perform a global common subexpression elimination pass. |
| This pass also performs global constant and copy propagation. |
| |
| @emph{Note:} When compiling a program using computed gotos, a GCC |
| extension, you may get better run-time performance if you disable |
| the global common subexpression elimination pass by adding |
| @option{-fno-gcse} to the command line. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fgcse-lm |
| @opindex fgcse-lm |
| When @option{-fgcse-lm} is enabled, global common subexpression elimination |
| attempts to move loads that are only killed by stores into themselves. This |
| allows a loop containing a load/store sequence to be changed to a load outside |
| the loop, and a copy/store within the loop. |
| |
| Enabled by default when @option{-fgcse} is enabled. |
| |
| @item -fgcse-sm |
| @opindex fgcse-sm |
| When @option{-fgcse-sm} is enabled, a store motion pass is run after |
| global common subexpression elimination. This pass attempts to move |
| stores out of loops. When used in conjunction with @option{-fgcse-lm}, |
| loops containing a load/store sequence can be changed to a load before |
| the loop and a store after the loop. |
| |
| Not enabled at any optimization level. |
| |
| @item -fgcse-las |
| @opindex fgcse-las |
| When @option{-fgcse-las} is enabled, the global common subexpression |
| elimination pass eliminates redundant loads that come after stores to the |
| same memory location (both partial and full redundancies). |
| |
| Not enabled at any optimization level. |
| |
| @item -fgcse-after-reload |
| @opindex fgcse-after-reload |
| When @option{-fgcse-after-reload} is enabled, a redundant load elimination |
| pass is performed after reload. The purpose of this pass is to clean up |
| redundant spilling. |
| |
| Enabled by @option{-O3}, @option{-fprofile-use} and @option{-fauto-profile}. |
| |
| @item -faggressive-loop-optimizations |
| @opindex faggressive-loop-optimizations |
| This option tells the loop optimizer to use language constraints to |
| derive bounds for the number of iterations of a loop. This assumes that |
| loop code does not invoke undefined behavior by for example causing signed |
| integer overflows or out-of-bound array accesses. The bounds for the |
| number of iterations of a loop are used to guide loop unrolling and peeling |
| and loop exit test optimizations. |
| This option is enabled by default. |
| |
| @item -funconstrained-commons |
| @opindex funconstrained-commons |
| This option tells the compiler that variables declared in common blocks |
| (e.g.@: Fortran) may later be overridden with longer trailing arrays. This |
| prevents certain optimizations that depend on knowing the array bounds. |
| |
| @item -fcrossjumping |
| @opindex fcrossjumping |
| Perform cross-jumping transformation. |
| This transformation unifies equivalent code and saves code size. The |
| resulting code may or may not perform better than without cross-jumping. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fauto-inc-dec |
| @opindex fauto-inc-dec |
| Combine increments or decrements of addresses with memory accesses. |
| This pass is always skipped on architectures that do not have |
| instructions to support this. Enabled by default at @option{-O1} and |
| higher on architectures that support this. |
| |
| @item -fdce |
| @opindex fdce |
| Perform dead code elimination (DCE) on RTL@. |
| Enabled by default at @option{-O1} and higher. |
| |
| @item -fdse |
| @opindex fdse |
| Perform dead store elimination (DSE) on RTL@. |
| Enabled by default at @option{-O1} and higher. |
| |
| @item -fif-conversion |
| @opindex fif-conversion |
| Attempt to transform conditional jumps into branch-less equivalents. This |
| includes use of conditional moves, min, max, set flags and abs instructions, and |
| some tricks doable by standard arithmetics. The use of conditional execution |
| on chips where it is available is controlled by @option{-fif-conversion2}. |
| |
| Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}, but |
| not with @option{-Og}. |
| |
| @item -fif-conversion2 |
| @opindex fif-conversion2 |
| Use conditional execution (where available) to transform conditional jumps into |
| branch-less equivalents. |
| |
| Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}, but |
| not with @option{-Og}. |
| |
| @item -fdeclone-ctor-dtor |
| @opindex fdeclone-ctor-dtor |
| The C++ ABI requires multiple entry points for constructors and |
| destructors: one for a base subobject, one for a complete object, and |
| one for a virtual destructor that calls operator delete afterwards. |
| For a hierarchy with virtual bases, the base and complete variants are |
| clones, which means two copies of the function. With this option, the |
| base and complete variants are changed to be thunks that call a common |
| implementation. |
| |
| Enabled by @option{-Os}. |
| |
| @item -fdelete-null-pointer-checks |
| @opindex fdelete-null-pointer-checks |
| Assume that programs cannot safely dereference null pointers, and that |
| no code or data element resides at address zero. |
| This option enables simple constant |
| folding optimizations at all optimization levels. In addition, other |
| optimization passes in GCC use this flag to control global dataflow |
| analyses that eliminate useless checks for null pointers; these assume |
| that a memory access to address zero always results in a trap, so |
| that if a pointer is checked after it has already been dereferenced, |
| it cannot be null. |
| |
| Note however that in some environments this assumption is not true. |
| Use @option{-fno-delete-null-pointer-checks} to disable this optimization |
| for programs that depend on that behavior. |
| |
| This option is enabled by default on most targets. On Nios II ELF, it |
| defaults to off. On AVR, CR16, and MSP430, this option is completely disabled. |
| |
| Passes that use the dataflow information |
| are enabled independently at different optimization levels. |
| |
| @item -fdevirtualize |
| @opindex fdevirtualize |
| Attempt to convert calls to virtual functions to direct calls. This |
| is done both within a procedure and interprocedurally as part of |
| indirect inlining (@option{-findirect-inlining}) and interprocedural constant |
| propagation (@option{-fipa-cp}). |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fdevirtualize-speculatively |
| @opindex fdevirtualize-speculatively |
| Attempt to convert calls to virtual functions to speculative direct calls. |
| Based on the analysis of the type inheritance graph, determine for a given call |
| the set of likely targets. If the set is small, preferably of size 1, change |
| the call into a conditional deciding between direct and indirect calls. The |
| speculative calls enable more optimizations, such as inlining. When they seem |
| useless after further optimization, they are converted back into original form. |
| |
| @item -fdevirtualize-at-ltrans |
| @opindex fdevirtualize-at-ltrans |
| Stream extra information needed for aggressive devirtualization when running |
| the link-time optimizer in local transformation mode. |
| This option enables more devirtualization but |
| significantly increases the size of streamed data. For this reason it is |
| disabled by default. |
| |
| @item -fexpensive-optimizations |
| @opindex fexpensive-optimizations |
| Perform a number of minor optimizations that are relatively expensive. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -free |
| @opindex free |
| Attempt to remove redundant extension instructions. This is especially |
| helpful for the x86-64 architecture, which implicitly zero-extends in 64-bit |
| registers after writing to their lower 32-bit half. |
| |
| Enabled for Alpha, AArch64 and x86 at levels @option{-O2}, |
| @option{-O3}, @option{-Os}. |
| |
| @item -fno-lifetime-dse |
| @opindex fno-lifetime-dse |
| @opindex flifetime-dse |
| In C++ the value of an object is only affected by changes within its |
| lifetime: when the constructor begins, the object has an indeterminate |
| value, and any changes during the lifetime of the object are dead when |
| the object is destroyed. Normally dead store elimination will take |
| advantage of this; if your code relies on the value of the object |
| storage persisting beyond the lifetime of the object, you can use this |
| flag to disable this optimization. To preserve stores before the |
| constructor starts (e.g.@: because your operator new clears the object |
| storage) but still treat the object as dead after the destructor, you |
| can use @option{-flifetime-dse=1}. The default behavior can be |
| explicitly selected with @option{-flifetime-dse=2}. |
| @option{-flifetime-dse=0} is equivalent to @option{-fno-lifetime-dse}. |
| |
| @item -flive-range-shrinkage |
| @opindex flive-range-shrinkage |
| Attempt to decrease register pressure through register live range |
| shrinkage. This is helpful for fast processors with small or moderate |
| size register sets. |
| |
| @item -fira-algorithm=@var{algorithm} |
| @opindex fira-algorithm |
| Use the specified coloring algorithm for the integrated register |
| allocator. The @var{algorithm} argument can be @samp{priority}, which |
| specifies Chow's priority coloring, or @samp{CB}, which specifies |
| Chaitin-Briggs coloring. Chaitin-Briggs coloring is not implemented |
| for all architectures, but for those targets that do support it, it is |
| the default because it generates better code. |
| |
| @item -fira-region=@var{region} |
| @opindex fira-region |
| Use specified regions for the integrated register allocator. The |
| @var{region} argument should be one of the following: |
| |
| @table @samp |
| |
| @item all |
| Use all loops as register allocation regions. |
| This can give the best results for machines with a small and/or |
| irregular register set. |
| |
| @item mixed |
| Use all loops except for loops with small register pressure |
| as the regions. This value usually gives |
| the best results in most cases and for most architectures, |
| and is enabled by default when compiling with optimization for speed |
| (@option{-O}, @option{-O2}, @dots{}). |
| |
| @item one |
| Use all functions as a single region. |
| This typically results in the smallest code size, and is enabled by default for |
| @option{-Os} or @option{-O0}. |
| |
| @end table |
| |
| @item -fira-hoist-pressure |
| @opindex fira-hoist-pressure |
| Use IRA to evaluate register pressure in the code hoisting pass for |
| decisions to hoist expressions. This option usually results in smaller |
| code, but it can slow the compiler down. |
| |
| This option is enabled at level @option{-Os} for all targets. |
| |
| @item -fira-loop-pressure |
| @opindex fira-loop-pressure |
| Use IRA to evaluate register pressure in loops for decisions to move |
| loop invariants. This option usually results in generation |
| of faster and smaller code on machines with large register files (>= 32 |
| registers), but it can slow the compiler down. |
| |
| This option is enabled at level @option{-O3} for some targets. |
| |
| @item -fno-ira-share-save-slots |
| @opindex fno-ira-share-save-slots |
| @opindex fira-share-save-slots |
| Disable sharing of stack slots used for saving call-used hard |
| registers living through a call. Each hard register gets a |
| separate stack slot, and as a result function stack frames are |
| larger. |
| |
| @item -fno-ira-share-spill-slots |
| @opindex fno-ira-share-spill-slots |
| @opindex fira-share-spill-slots |
| Disable sharing of stack slots allocated for pseudo-registers. Each |
| pseudo-register that does not get a hard register gets a separate |
| stack slot, and as a result function stack frames are larger. |
| |
| @item -flra-remat |
| @opindex flra-remat |
| Enable CFG-sensitive rematerialization in LRA. Instead of loading |
| values of spilled pseudos, LRA tries to rematerialize (recalculate) |
| values if it is profitable. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fdelayed-branch |
| @opindex fdelayed-branch |
| If supported for the target machine, attempt to reorder instructions |
| to exploit instruction slots available after delayed branch |
| instructions. |
| |
| Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}, |
| but not at @option{-Og}. |
| |
| @item -fschedule-insns |
| @opindex fschedule-insns |
| If supported for the target machine, attempt to reorder instructions to |
| eliminate execution stalls due to required data being unavailable. This |
| helps machines that have slow floating point or memory load instructions |
| by allowing other instructions to be issued until the result of the load |
| or floating-point instruction is required. |
| |
| Enabled at levels @option{-O2}, @option{-O3}. |
| |
| @item -fschedule-insns2 |
| @opindex fschedule-insns2 |
| Similar to @option{-fschedule-insns}, but requests an additional pass of |
| instruction scheduling after register allocation has been done. This is |
| especially useful on machines with a relatively small number of |
| registers and where memory load instructions take more than one cycle. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fno-sched-interblock |
| @opindex fno-sched-interblock |
| @opindex fsched-interblock |
| Disable instruction scheduling across basic blocks, which |
| is normally enabled when scheduling before register allocation, i.e.@: |
| with @option{-fschedule-insns} or at @option{-O2} or higher. |
| |
| @item -fno-sched-spec |
| @opindex fno-sched-spec |
| @opindex fsched-spec |
| Disable speculative motion of non-load instructions, which |
| is normally enabled when scheduling before register allocation, i.e.@: |
| with @option{-fschedule-insns} or at @option{-O2} or higher. |
| |
| @item -fsched-pressure |
| @opindex fsched-pressure |
| Enable register pressure sensitive insn scheduling before register |
| allocation. This only makes sense when scheduling before register |
| allocation is enabled, i.e.@: with @option{-fschedule-insns} or at |
| @option{-O2} or higher. Usage of this option can improve the |
| generated code and decrease its size by preventing register pressure |
| increase above the number of available hard registers and subsequent |
| spills in register allocation. |
| |
| @item -fsched-spec-load |
| @opindex fsched-spec-load |
| Allow speculative motion of some load instructions. This only makes |
| sense when scheduling before register allocation, i.e.@: with |
| @option{-fschedule-insns} or at @option{-O2} or higher. |
| |
| @item -fsched-spec-load-dangerous |
| @opindex fsched-spec-load-dangerous |
| Allow speculative motion of more load instructions. This only makes |
| sense when scheduling before register allocation, i.e.@: with |
| @option{-fschedule-insns} or at @option{-O2} or higher. |
| |
| @item -fsched-stalled-insns |
| @itemx -fsched-stalled-insns=@var{n} |
| @opindex fsched-stalled-insns |
| Define how many insns (if any) can be moved prematurely from the queue |
| of stalled insns into the ready list during the second scheduling pass. |
| @option{-fno-sched-stalled-insns} means that no insns are moved |
| prematurely, @option{-fsched-stalled-insns=0} means there is no limit |
| on how many queued insns can be moved prematurely. |
| @option{-fsched-stalled-insns} without a value is equivalent to |
| @option{-fsched-stalled-insns=1}. |
| |
| @item -fsched-stalled-insns-dep |
| @itemx -fsched-stalled-insns-dep=@var{n} |
| @opindex fsched-stalled-insns-dep |
| Define how many insn groups (cycles) are examined for a dependency |
| on a stalled insn that is a candidate for premature removal from the queue |
| of stalled insns. This has an effect only during the second scheduling pass, |
| and only if @option{-fsched-stalled-insns} is used. |
| @option{-fno-sched-stalled-insns-dep} is equivalent to |
| @option{-fsched-stalled-insns-dep=0}. |
| @option{-fsched-stalled-insns-dep} without a value is equivalent to |
| @option{-fsched-stalled-insns-dep=1}. |
| |
| @item -fsched2-use-superblocks |
| @opindex fsched2-use-superblocks |
| When scheduling after register allocation, use superblock scheduling. |
| This allows motion across basic block boundaries, |
| resulting in faster schedules. This option is experimental, as not all machine |
| descriptions used by GCC model the CPU closely enough to avoid unreliable |
| results from the algorithm. |
| |
| This only makes sense when scheduling after register allocation, i.e.@: with |
| @option{-fschedule-insns2} or at @option{-O2} or higher. |
| |
| @item -fsched-group-heuristic |
| @opindex fsched-group-heuristic |
| Enable the group heuristic in the scheduler. This heuristic favors |
| the instruction that belongs to a schedule group. This is enabled |
| by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns} |
| or @option{-fschedule-insns2} or at @option{-O2} or higher. |
| |
| @item -fsched-critical-path-heuristic |
| @opindex fsched-critical-path-heuristic |
| Enable the critical-path heuristic in the scheduler. This heuristic favors |
| instructions on the critical path. This is enabled by default when |
| scheduling is enabled, i.e.@: with @option{-fschedule-insns} |
| or @option{-fschedule-insns2} or at @option{-O2} or higher. |
| |
| @item -fsched-spec-insn-heuristic |
| @opindex fsched-spec-insn-heuristic |
| Enable the speculative instruction heuristic in the scheduler. This |
| heuristic favors speculative instructions with greater dependency weakness. |
| This is enabled by default when scheduling is enabled, i.e.@: |
| with @option{-fschedule-insns} or @option{-fschedule-insns2} |
| or at @option{-O2} or higher. |
| |
| @item -fsched-rank-heuristic |
| @opindex fsched-rank-heuristic |
| Enable the rank heuristic in the scheduler. This heuristic favors |
| the instruction belonging to a basic block with greater size or frequency. |
| This is enabled by default when scheduling is enabled, i.e.@: |
| with @option{-fschedule-insns} or @option{-fschedule-insns2} or |
| at @option{-O2} or higher. |
| |
| @item -fsched-last-insn-heuristic |
| @opindex fsched-last-insn-heuristic |
| Enable the last-instruction heuristic in the scheduler. This heuristic |
| favors the instruction that is less dependent on the last instruction |
| scheduled. This is enabled by default when scheduling is enabled, |
| i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or |
| at @option{-O2} or higher. |
| |
| @item -fsched-dep-count-heuristic |
| @opindex fsched-dep-count-heuristic |
| Enable the dependent-count heuristic in the scheduler. This heuristic |
| favors the instruction that has more instructions depending on it. |
| This is enabled by default when scheduling is enabled, i.e.@: |
| with @option{-fschedule-insns} or @option{-fschedule-insns2} or |
| at @option{-O2} or higher. |
| |
| @item -freschedule-modulo-scheduled-loops |
| @opindex freschedule-modulo-scheduled-loops |
| Modulo scheduling is performed before traditional scheduling. If a loop |
| is modulo scheduled, later scheduling passes may change its schedule. |
| Use this option to control that behavior. |
| |
| @item -fselective-scheduling |
| @opindex fselective-scheduling |
| Schedule instructions using selective scheduling algorithm. Selective |
| scheduling runs instead of the first scheduler pass. |
| |
| @item -fselective-scheduling2 |
| @opindex fselective-scheduling2 |
| Schedule instructions using selective scheduling algorithm. Selective |
| scheduling runs instead of the second scheduler pass. |
| |
| @item -fsel-sched-pipelining |
| @opindex fsel-sched-pipelining |
| Enable software pipelining of innermost loops during selective scheduling. |
| This option has no effect unless one of @option{-fselective-scheduling} or |
| @option{-fselective-scheduling2} is turned on. |
| |
| @item -fsel-sched-pipelining-outer-loops |
| @opindex fsel-sched-pipelining-outer-loops |
| When pipelining loops during selective scheduling, also pipeline outer loops. |
| This option has no effect unless @option{-fsel-sched-pipelining} is turned on. |
| |
| @item -fsemantic-interposition |
| @opindex fsemantic-interposition |
| Some object formats, like ELF, allow interposing of symbols by the |
| dynamic linker. |
| This means that for symbols exported from the DSO, the compiler cannot perform |
| interprocedural propagation, inlining and other optimizations in anticipation |
| that the function or variable in question may change. While this feature is |
| useful, for example, to rewrite memory allocation functions by a debugging |
| implementation, it is expensive in the terms of code quality. |
| With @option{-fno-semantic-interposition} the compiler assumes that |
| if interposition happens for functions the overwriting function will have |
| precisely the same semantics (and side effects). |
| Similarly if interposition happens |
| for variables, the constructor of the variable will be the same. The flag |
| has no effect for functions explicitly declared inline |
| (where it is never allowed for interposition to change semantics) |
| and for symbols explicitly declared weak. |
| |
| @item -fshrink-wrap |
| @opindex fshrink-wrap |
| Emit function prologues only before parts of the function that need it, |
| rather than at the top of the function. This flag is enabled by default at |
| @option{-O} and higher. |
| |
| @item -fshrink-wrap-separate |
| @opindex fshrink-wrap-separate |
| Shrink-wrap separate parts of the prologue and epilogue separately, so that |
| those parts are only executed when needed. |
| This option is on by default, but has no effect unless @option{-fshrink-wrap} |
| is also turned on and the target supports this. |
| |
| @item -fcaller-saves |
| @opindex fcaller-saves |
| Enable allocation of values to registers that are clobbered by |
| function calls, by emitting extra instructions to save and restore the |
| registers around such calls. Such allocation is done only when it |
| seems to result in better code. |
| |
| This option is always enabled by default on certain machines, usually |
| those which have no call-preserved registers to use instead. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fcombine-stack-adjustments |
| @opindex fcombine-stack-adjustments |
| Tracks stack adjustments (pushes and pops) and stack memory references |
| and then tries to find ways to combine them. |
| |
| Enabled by default at @option{-O1} and higher. |
| |
| @item -fipa-ra |
| @opindex fipa-ra |
| Use caller save registers for allocation if those registers are not used by |
| any called function. In that case it is not necessary to save and restore |
| them around calls. This is only possible if called functions are part of |
| same compilation unit as current function and they are compiled before it. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, however the option |
| is disabled if generated code will be instrumented for profiling |
| (@option{-p}, or @option{-pg}) or if callee's register usage cannot be known |
| exactly (this happens on targets that do not expose prologues |
| and epilogues in RTL). |
| |
| @item -fconserve-stack |
| @opindex fconserve-stack |
| Attempt to minimize stack usage. The compiler attempts to use less |
| stack space, even if that makes the program slower. This option |
| implies setting the @option{large-stack-frame} parameter to 100 |
| and the @option{large-stack-frame-growth} parameter to 400. |
| |
| @item -ftree-reassoc |
| @opindex ftree-reassoc |
| Perform reassociation on trees. This flag is enabled by default |
| at @option{-O1} and higher. |
| |
| @item -fcode-hoisting |
| @opindex fcode-hoisting |
| Perform code hoisting. Code hoisting tries to move the |
| evaluation of expressions executed on all paths to the function exit |
| as early as possible. This is especially useful as a code size |
| optimization, but it often helps for code speed as well. |
| This flag is enabled by default at @option{-O2} and higher. |
| |
| @item -ftree-pre |
| @opindex ftree-pre |
| Perform partial redundancy elimination (PRE) on trees. This flag is |
| enabled by default at @option{-O2} and @option{-O3}. |
| |
| @item -ftree-partial-pre |
| @opindex ftree-partial-pre |
| Make partial redundancy elimination (PRE) more aggressive. This flag is |
| enabled by default at @option{-O3}. |
| |
| @item -ftree-forwprop |
| @opindex ftree-forwprop |
| Perform forward propagation on trees. This flag is enabled by default |
| at @option{-O1} and higher. |
| |
| @item -ftree-fre |
| @opindex ftree-fre |
| Perform full redundancy elimination (FRE) on trees. The difference |
| between FRE and PRE is that FRE only considers expressions |
| that are computed on all paths leading to the redundant computation. |
| This analysis is faster than PRE, though it exposes fewer redundancies. |
| This flag is enabled by default at @option{-O1} and higher. |
| |
| @item -ftree-phiprop |
| @opindex ftree-phiprop |
| Perform hoisting of loads from conditional pointers on trees. This |
| pass is enabled by default at @option{-O1} and higher. |
| |
| @item -fhoist-adjacent-loads |
| @opindex fhoist-adjacent-loads |
| Speculatively hoist loads from both branches of an if-then-else if the |
| loads are from adjacent locations in the same structure and the target |
| architecture has a conditional move instruction. This flag is enabled |
| by default at @option{-O2} and higher. |
| |
| @item -ftree-copy-prop |
| @opindex ftree-copy-prop |
| Perform copy propagation on trees. This pass eliminates unnecessary |
| copy operations. This flag is enabled by default at @option{-O1} and |
| higher. |
| |
| @item -fipa-pure-const |
| @opindex fipa-pure-const |
| Discover which functions are pure or constant. |
| Enabled by default at @option{-O1} and higher. |
| |
| @item -fipa-reference |
| @opindex fipa-reference |
| Discover which static variables do not escape the |
| compilation unit. |
| Enabled by default at @option{-O1} and higher. |
| |
| @item -fipa-reference-addressable |
| @opindex fipa-reference-addressable |
| Discover read-only, write-only and non-addressable static variables. |
| Enabled by default at @option{-O1} and higher. |
| |
| @item -fipa-stack-alignment |
| @opindex fipa-stack-alignment |
| Reduce stack alignment on call sites if possible. |
| Enabled by default. |
| |
| @item -fipa-pta |
| @opindex fipa-pta |
| Perform interprocedural pointer analysis and interprocedural modification |
| and reference analysis. This option can cause excessive memory and |
| compile-time usage on large compilation units. It is not enabled by |
| default at any optimization level. |
| |
| @item -fipa-profile |
| @opindex fipa-profile |
| Perform interprocedural profile propagation. The functions called only from |
| cold functions are marked as cold. Also functions executed once (such as |
| @code{cold}, @code{noreturn}, static constructors or destructors) are |
| identified. Cold functions and loop less parts of functions executed once are |
| then optimized for size. |
| Enabled by default at @option{-O1} and higher. |
| |
| @item -fipa-modref |
| @opindex fipa-modref |
| Perform interprocedural mod/ref analysis. This optimization analyzes the side |
| effects of functions (memory locations that are modified or referenced) and |
| enables better optimization across the function call boundary. This flag is |
| enabled by default at @option{-O1} and higher. |
| |
| @item -fipa-cp |
| @opindex fipa-cp |
| Perform interprocedural constant propagation. |
| This optimization analyzes the program to determine when values passed |
| to functions are constants and then optimizes accordingly. |
| This optimization can substantially increase performance |
| if the application has constants passed to functions. |
| This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}. |
| It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. |
| |
| @item -fipa-cp-clone |
| @opindex fipa-cp-clone |
| Perform function cloning to make interprocedural constant propagation stronger. |
| When enabled, interprocedural constant propagation performs function cloning |
| when externally visible function can be called with constant arguments. |
| Because this optimization can create multiple copies of functions, |
| it may significantly increase code size |
| (see @option{--param ipa-cp-unit-growth=@var{value}}). |
| This flag is enabled by default at @option{-O3}. |
| It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. |
| |
| @item -fipa-bit-cp |
| @opindex fipa-bit-cp |
| When enabled, perform interprocedural bitwise constant |
| propagation. This flag is enabled by default at @option{-O2} and |
| by @option{-fprofile-use} and @option{-fauto-profile}. |
| It requires that @option{-fipa-cp} is enabled. |
| |
| @item -fipa-vrp |
| @opindex fipa-vrp |
| When enabled, perform interprocedural propagation of value |
| ranges. This flag is enabled by default at @option{-O2}. It requires |
| that @option{-fipa-cp} is enabled. |
| |
| @item -fipa-icf |
| @opindex fipa-icf |
| Perform Identical Code Folding for functions and read-only variables. |
| The optimization reduces code size and may disturb unwind stacks by replacing |
| a function by equivalent one with a different name. The optimization works |
| more effectively with link-time optimization enabled. |
| |
| Although the behavior is similar to the Gold Linker's ICF optimization, GCC ICF |
| works on different levels and thus the optimizations are not same - there are |
| equivalences that are found only by GCC and equivalences found only by Gold. |
| |
| This flag is enabled by default at @option{-O2} and @option{-Os}. |
| |
| @item -flive-patching=@var{level} |
| @opindex flive-patching |
| Control GCC's optimizations to produce output suitable for live-patching. |
| |
| If the compiler's optimization uses a function's body or information extracted |
| from its body to optimize/change another function, the latter is called an |
| impacted function of the former. If a function is patched, its impacted |
| functions should be patched too. |
| |
| The impacted functions are determined by the compiler's interprocedural |
| optimizations. For example, a caller is impacted when inlining a function |
| into its caller, |
| cloning a function and changing its caller to call this new clone, |
| or extracting a function's pureness/constness information to optimize |
| its direct or indirect callers, etc. |
| |
| Usually, the more IPA optimizations enabled, the larger the number of |
| impacted functions for each function. In order to control the number of |
| impacted functions and more easily compute the list of impacted function, |
| IPA optimizations can be partially enabled at two different levels. |
| |
| The @var{level} argument should be one of the following: |
| |
| @table @samp |
| |
| @item inline-clone |
| |
| Only enable inlining and cloning optimizations, which includes inlining, |
| cloning, interprocedural scalar replacement of aggregates and partial inlining. |
| As a result, when patching a function, all its callers and its clones' |
| callers are impacted, therefore need to be patched as well. |
| |
| @option{-flive-patching=inline-clone} disables the following optimization flags: |
| @gccoptlist{-fwhole-program -fipa-pta -fipa-reference -fipa-ra @gol |
| -fipa-icf -fipa-icf-functions -fipa-icf-variables @gol |
| -fipa-bit-cp -fipa-vrp -fipa-pure-const -fipa-reference-addressable @gol |
| -fipa-stack-alignment -fipa-modref} |
| |
| @item inline-only-static |
| |
| Only enable inlining of static functions. |
| As a result, when patching a static function, all its callers are impacted |
| and so need to be patched as well. |
| |
| In addition to all the flags that @option{-flive-patching=inline-clone} |
| disables, |
| @option{-flive-patching=inline-only-static} disables the following additional |
| optimization flags: |
| @gccoptlist{-fipa-cp-clone -fipa-sra -fpartial-inlining -fipa-cp} |
| |
| @end table |
| |
| When @option{-flive-patching} is specified without any value, the default value |
| is @var{inline-clone}. |
| |
| This flag is disabled by default. |
| |
| Note that @option{-flive-patching} is not supported with link-time optimization |
| (@option{-flto}). |
| |
| @item -fisolate-erroneous-paths-dereference |
| @opindex fisolate-erroneous-paths-dereference |
| Detect paths that trigger erroneous or undefined behavior due to |
| dereferencing a null pointer. Isolate those paths from the main control |
| flow and turn the statement with erroneous or undefined behavior into a trap. |
| This flag is enabled by default at @option{-O2} and higher and depends on |
| @option{-fdelete-null-pointer-checks} also being enabled. |
| |
| @item -fisolate-erroneous-paths-attribute |
| @opindex fisolate-erroneous-paths-attribute |
| Detect paths that trigger erroneous or undefined behavior due to a null value |
| being used in a way forbidden by a @code{returns_nonnull} or @code{nonnull} |
| attribute. Isolate those paths from the main control flow and turn the |
| statement with erroneous or undefined behavior into a trap. This is not |
| currently enabled, but may be enabled by @option{-O2} in the future. |
| |
| @item -ftree-sink |
| @opindex ftree-sink |
| Perform forward store motion on trees. This flag is |
| enabled by default at @option{-O1} and higher. |
| |
| @item -ftree-bit-ccp |
| @opindex ftree-bit-ccp |
| Perform sparse conditional bit constant propagation on trees and propagate |
| pointer alignment information. |
| This pass only operates on local scalar variables and is enabled by default |
| at @option{-O1} and higher, except for @option{-Og}. |
| It requires that @option{-ftree-ccp} is enabled. |
| |
| @item -ftree-ccp |
| @opindex ftree-ccp |
| Perform sparse conditional constant propagation (CCP) on trees. This |
| pass only operates on local scalar variables and is enabled by default |
| at @option{-O1} and higher. |
| |
| @item -fssa-backprop |
| @opindex fssa-backprop |
| Propagate information about uses of a value up the definition chain |
| in order to simplify the definitions. For example, this pass strips |
| sign operations if the sign of a value never matters. The flag is |
| enabled by default at @option{-O1} and higher. |
| |
| @item -fssa-phiopt |
| @opindex fssa-phiopt |
| Perform pattern matching on SSA PHI nodes to optimize conditional |
| code. This pass is enabled by default at @option{-O1} and higher, |
| except for @option{-Og}. |
| |
| @item -ftree-switch-conversion |
| @opindex ftree-switch-conversion |
| Perform conversion of simple initializations in a switch to |
| initializations from a scalar array. This flag is enabled by default |
| at @option{-O2} and higher. |
| |
| @item -ftree-tail-merge |
| @opindex ftree-tail-merge |
| Look for identical code sequences. When found, replace one with a jump to the |
| other. This optimization is known as tail merging or cross jumping. This flag |
| is enabled by default at @option{-O2} and higher. The compilation time |
| in this pass can |
| be limited using @option{max-tail-merge-comparisons} parameter and |
| @option{max-tail-merge-iterations} parameter. |
| |
| @item -ftree-dce |
| @opindex ftree-dce |
| Perform dead code elimination (DCE) on trees. This flag is enabled by |
| default at @option{-O1} and higher. |
| |
| @item -ftree-builtin-call-dce |
| @opindex ftree-builtin-call-dce |
| Perform conditional dead code elimination (DCE) for calls to built-in functions |
| that may set @code{errno} but are otherwise free of side effects. This flag is |
| enabled by default at @option{-O2} and higher if @option{-Os} is not also |
| specified. |
| |
| @item -ffinite-loops |
| @opindex ffinite-loops |
| @opindex fno-finite-loops |
| Assume that a loop with an exit will eventually take the exit and not loop |
| indefinitely. This allows the compiler to remove loops that otherwise have |
| no side-effects, not considering eventual endless looping as such. |
| |
| This option is enabled by default at @option{-O2} for C++ with -std=c++11 |
| or higher. |
| |
| @item -ftree-dominator-opts |
| @opindex ftree-dominator-opts |
| Perform a variety of simple scalar cleanups (constant/copy |
| propagation, redundancy elimination, range propagation and expression |
| simplification) based on a dominator tree traversal. This also |
| performs jump threading (to reduce jumps to jumps). This flag is |
| enabled by default at @option{-O1} and higher. |
| |
| @item -ftree-dse |
| @opindex ftree-dse |
| Perform dead store elimination (DSE) on trees. A dead store is a store into |
| a memory location that is later overwritten by another store without |
| any intervening loads. In this case the earlier store can be deleted. This |
| flag is enabled by default at @option{-O1} and higher. |
| |
| @item -ftree-ch |
| @opindex ftree-ch |
| Perform loop header copying on trees. This is beneficial since it increases |
| effectiveness of code motion optimizations. It also saves one jump. This flag |
| is enabled by default at @option{-O1} and higher. It is not enabled |
| for @option{-Os}, since it usually increases code size. |
| |
| @item -ftree-loop-optimize |
| @opindex ftree-loop-optimize |
| Perform loop optimizations on trees. This flag is enabled by default |
| at @option{-O1} and higher. |
| |
| @item -ftree-loop-linear |
| @itemx -floop-strip-mine |
| @itemx -floop-block |
| @opindex ftree-loop-linear |
| @opindex floop-strip-mine |
| @opindex floop-block |
| Perform loop nest optimizations. Same as |
| @option{-floop-nest-optimize}. To use this code transformation, GCC has |
| to be configured with @option{--with-isl} to enable the Graphite loop |
| transformation infrastructure. |
| |
| @item -fgraphite-identity |
| @opindex fgraphite-identity |
| Enable the identity transformation for graphite. For every SCoP we generate |
| the polyhedral representation and transform it back to gimple. Using |
| @option{-fgraphite-identity} we can check the costs or benefits of the |
| GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations |
| are also performed by the code generator isl, like index splitting and |
| dead code elimination in loops. |
| |
| @item -floop-nest-optimize |
| @opindex floop-nest-optimize |
| Enable the isl based loop nest optimizer. This is a generic loop nest |
| optimizer based on the Pluto optimization algorithms. It calculates a loop |
| structure optimized for data-locality and parallelism. This option |
| is experimental. |
| |
| @item -floop-parallelize-all |
| @opindex floop-parallelize-all |
| Use the Graphite data dependence analysis to identify loops that can |
| be parallelized. Parallelize all the loops that can be analyzed to |
| not contain loop carried dependences without checking that it is |
| profitable to parallelize the loops. |
| |
| @item -ftree-coalesce-vars |
| @opindex ftree-coalesce-vars |
| While transforming the program out of the SSA representation, attempt to |
| reduce copying by coalescing versions of different user-defined |
| variables, instead of just compiler temporaries. This may severely |
| limit the ability to debug an optimized program compiled with |
| @option{-fno-var-tracking-assignments}. In the negated form, this flag |
| prevents SSA coalescing of user variables. This option is enabled by |
| default if optimization is enabled, and it does very little otherwise. |
| |
| @item -ftree-loop-if-convert |
| @opindex ftree-loop-if-convert |
| Attempt to transform conditional jumps in the innermost loops to |
| branch-less equivalents. The intent is to remove control-flow from |
| the innermost loops in order to improve the ability of the |
| vectorization pass to handle these loops. This is enabled by default |
| if vectorization is enabled. |
| |
| @item -ftree-loop-distribution |
| @opindex ftree-loop-distribution |
| Perform loop distribution. This flag can improve cache performance on |
| big loop bodies and allow further loop optimizations, like |
| parallelization or vectorization, to take place. For example, the loop |
| @smallexample |
| DO I = 1, N |
| A(I) = B(I) + C |
| D(I) = E(I) * F |
| ENDDO |
| @end smallexample |
| is transformed to |
| @smallexample |
| DO I = 1, N |
| A(I) = B(I) + C |
| ENDDO |
| DO I = 1, N |
| D(I) = E(I) * F |
| ENDDO |
| @end smallexample |
| This flag is enabled by default at @option{-O3}. |
| It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. |
| |
| @item -ftree-loop-distribute-patterns |
| @opindex ftree-loop-distribute-patterns |
| Perform loop distribution of patterns that can be code generated with |
| calls to a library. This flag is enabled by default at @option{-O2} and |
| higher, and by @option{-fprofile-use} and @option{-fauto-profile}. |
| |
| This pass distributes the initialization loops and generates a call to |
| memset zero. For example, the loop |
| @smallexample |
| DO I = 1, N |
| A(I) = 0 |
| B(I) = A(I) + I |
| ENDDO |
| @end smallexample |
| is transformed to |
| @smallexample |
| DO I = 1, N |
| A(I) = 0 |
| ENDDO |
| DO I = 1, N |
| B(I) = A(I) + I |
| ENDDO |
| @end smallexample |
| and the initialization loop is transformed into a call to memset zero. |
| This flag is enabled by default at @option{-O3}. |
| It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. |
| |
| @item -floop-interchange |
| @opindex floop-interchange |
| Perform loop interchange outside of graphite. This flag can improve cache |
| performance on loop nest and allow further loop optimizations, like |
| vectorization, to take place. For example, the loop |
| @smallexample |
| for (int i = 0; i < N; i++) |
| for (int j = 0; j < N; j++) |
| for (int k = 0; k < N; k++) |
| c[i][j] = c[i][j] + a[i][k]*b[k][j]; |
| @end smallexample |
| is transformed to |
| @smallexample |
| for (int i = 0; i < N; i++) |
| for (int k = 0; k < N; k++) |
| for (int j = 0; j < N; j++) |
| c[i][j] = c[i][j] + a[i][k]*b[k][j]; |
| @end smallexample |
| This flag is enabled by default at @option{-O3}. |
| It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. |
| |
| @item -floop-unroll-and-jam |
| @opindex floop-unroll-and-jam |
| Apply unroll and jam transformations on feasible loops. In a loop |
| nest this unrolls the outer loop by some factor and fuses the resulting |
| multiple inner loops. This flag is enabled by default at @option{-O3}. |
| It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. |
| |
| @item -ftree-loop-im |
| @opindex ftree-loop-im |
| Perform loop invariant motion on trees. This pass moves only invariants that |
| are hard to handle at RTL level (function calls, operations that expand to |
| nontrivial sequences of insns). With @option{-funswitch-loops} it also moves |
| operands of conditions that are invariant out of the loop, so that we can use |
| just trivial invariantness analysis in loop unswitching. The pass also includes |
| store motion. |
| |
| @item -ftree-loop-ivcanon |
| @opindex ftree-loop-ivcanon |
| Create a canonical counter for number of iterations in loops for which |
| determining number of iterations requires complicated analysis. Later |
| optimizations then may determine the number easily. Useful especially |
| in connection with unrolling. |
| |
| @item -ftree-scev-cprop |
| @opindex ftree-scev-cprop |
| Perform final value replacement. If a variable is modified in a loop |
| in such a way that its value when exiting the loop can be determined using |
| only its initial value and the number of loop iterations, replace uses of |
| the final value by such a computation, provided it is sufficiently cheap. |
| This reduces data dependencies and may allow further simplifications. |
| Enabled by default at @option{-O1} and higher. |
| |
| @item -fivopts |
| @opindex fivopts |
| Perform induction variable optimizations (strength reduction, induction |
| variable merging and induction variable elimination) on trees. |
| |
| @item -ftree-parallelize-loops=n |
| @opindex ftree-parallelize-loops |
| Parallelize loops, i.e., split their iteration space to run in n threads. |
| This is only possible for loops whose iterations are independent |
| and can be arbitrarily reordered. The optimization is only |
| profitable on multiprocessor machines, for loops that are CPU-intensive, |
| rather than constrained e.g.@: by memory bandwidth. This option |
| implies @option{-pthread}, and thus is only supported on targets |
| that have support for @option{-pthread}. |
| |
| @item -ftree-pta |
| @opindex ftree-pta |
| Perform function-local points-to analysis on trees. This flag is |
| enabled by default at @option{-O1} and higher, except for @option{-Og}. |
| |
| @item -ftree-sra |
| @opindex ftree-sra |
| Perform scalar replacement of aggregates. This pass replaces structure |
| references with scalars to prevent committing structures to memory too |
| early. This flag is enabled by default at @option{-O1} and higher, |
| except for @option{-Og}. |
| |
| @item -fstore-merging |
| @opindex fstore-merging |
| Perform merging of narrow stores to consecutive memory addresses. This pass |
| merges contiguous stores of immediate values narrower than a word into fewer |
| wider stores to reduce the number of instructions. This is enabled by default |
| at @option{-O2} and higher as well as @option{-Os}. |
| |
| @item -ftree-ter |
| @opindex ftree-ter |
| Perform temporary expression replacement during the SSA->normal phase. Single |
| use/single def temporaries are replaced at their use location with their |
| defining expression. This results in non-GIMPLE code, but gives the expanders |
| much more complex trees to work on resulting in better RTL generation. This is |
| enabled by default at @option{-O1} and higher. |
| |
| @item -ftree-slsr |
| @opindex ftree-slsr |
| Perform straight-line strength reduction on trees. This recognizes related |
| expressions involving multiplications and replaces them by less expensive |
| calculations when possible. This is enabled by default at @option{-O1} and |
| higher. |
| |
| @item -ftree-vectorize |
| @opindex ftree-vectorize |
| Perform vectorization on trees. This flag enables @option{-ftree-loop-vectorize} |
| and @option{-ftree-slp-vectorize} if not explicitly specified. |
| |
| @item -ftree-loop-vectorize |
| @opindex ftree-loop-vectorize |
| Perform loop vectorization on trees. This flag is enabled by default at |
| @option{-O2} and by @option{-ftree-vectorize}, @option{-fprofile-use}, |
| and @option{-fauto-profile}. |
| |
| @item -ftree-slp-vectorize |
| @opindex ftree-slp-vectorize |
| Perform basic block vectorization on trees. This flag is enabled by default at |
| @option{-O2} and by @option{-ftree-vectorize}, @option{-fprofile-use}, |
| and @option{-fauto-profile}. |
| |
| @item -ftrivial-auto-var-init=@var{choice} |
| @opindex ftrivial-auto-var-init |
| Initialize automatic variables with either a pattern or with zeroes to increase |
| the security and predictability of a program by preventing uninitialized memory |
| disclosure and use. |
| GCC still considers an automatic variable that doesn't have an explicit |
| initializer as uninitialized, @option{-Wuninitialized} and |
| @option{-Wanalyzer-use-of-uninitialized-value} will still report |
| warning messages on such automatic variables. |
| With this option, GCC will also initialize any padding of automatic variables |
| that have structure or union types to zeroes. |
| However, the current implementation cannot initialize automatic variables that |
| are declared between the controlling expression and the first case of a |
| @code{switch} statement. Using @option{-Wtrivial-auto-var-init} to report all |
| such cases. |
| |
| The three values of @var{choice} are: |
| |
| @itemize @bullet |
| @item |
| @samp{uninitialized} doesn't initialize any automatic variables. |
| This is C and C++'s default. |
| |
| @item |
| @samp{pattern} Initialize automatic variables with values which will likely |
| transform logic bugs into crashes down the line, are easily recognized in a |
| crash dump and without being values that programmers can rely on for useful |
| program semantics. |
| The current value is byte-repeatable pattern with byte "0xFE". |
| The values used for pattern initialization might be changed in the future. |
| |
| @item |
| @samp{zero} Initialize automatic variables with zeroes. |
| @end itemize |
| |
| The default is @samp{uninitialized}. |
| |
| You can control this behavior for a specific variable by using the variable |
| attribute @code{uninitialized} (@pxref{Variable Attributes}). |
| |
| @item -fvect-cost-model=@var{model} |
| @opindex fvect-cost-model |
| Alter the cost model used for vectorization. The @var{model} argument |
| should be one of @samp{unlimited}, @samp{dynamic}, @samp{cheap} or |
| @samp{very-cheap}. |
| With the @samp{unlimited} model the vectorized code-path is assumed |
| to be profitable while with the @samp{dynamic} model a runtime check |
| guards the vectorized code-path to enable it only for iteration |
| counts that will likely execute faster than when executing the original |
| scalar loop. The @samp{cheap} model disables vectorization of |
| loops where doing so would be cost prohibitive for example due to |
| required runtime checks for data dependence or alignment but otherwise |
| is equal to the @samp{dynamic} model. The @samp{very-cheap} model only |
| allows vectorization if the vector code would entirely replace the |
| scalar code that is being vectorized. For example, if each iteration |
| of a vectorized loop would only be able to handle exactly four iterations |
| of the scalar loop, the @samp{very-cheap} model would only allow |
| vectorization if the scalar iteration count is known to be a multiple |
| of four. |
| |
| The default cost model depends on other optimization flags and is |
| either @samp{dynamic} or @samp{cheap}. |
| |
| @item -fsimd-cost-model=@var{model} |
| @opindex fsimd-cost-model |
| Alter the cost model used for vectorization of loops marked with the OpenMP |
| simd directive. The @var{model} argument should be one of |
| @samp{unlimited}, @samp{dynamic}, @samp{cheap}. All values of @var{model} |
| have the same meaning as described in @option{-fvect-cost-model} and by |
| default a cost model defined with @option{-fvect-cost-model} is used. |
| |
| @item -ftree-vrp |
| @opindex ftree-vrp |
| Perform Value Range Propagation on trees. This is similar to the |
| constant propagation pass, but instead of values, ranges of values are |
| propagated. This allows the optimizers to remove unnecessary range |
| checks like array bound checks and null pointer checks. This is |
| enabled by default at @option{-O2} and higher. Null pointer check |
| elimination is only done if @option{-fdelete-null-pointer-checks} is |
| enabled. |
| |
| @item -fsplit-paths |
| @opindex fsplit-paths |
| Split paths leading to loop backedges. This can improve dead code |
| elimination and common subexpression elimination. This is enabled by |
| default at @option{-O3} and above. |
| |
| @item -fsplit-ivs-in-unroller |
| @opindex fsplit-ivs-in-unroller |
| Enables expression of values of induction variables in later iterations |
| of the unrolled loop using the value in the first iteration. This breaks |
| long dependency chains, thus improving efficiency of the scheduling passes. |
| |
| A combination of @option{-fweb} and CSE is often sufficient to obtain the |
| same effect. However, that is not reliable in cases where the loop body |
| is more complicated than a single basic block. It also does not work at all |
| on some architectures due to restrictions in the CSE pass. |
| |
| This optimization is enabled by default. |
| |
| @item -fvariable-expansion-in-unroller |
| @opindex fvariable-expansion-in-unroller |
| With this option, the compiler creates multiple copies of some |
| local variables when unrolling a loop, which can result in superior code. |
| |
| This optimization is enabled by default for PowerPC targets, but disabled |
| by default otherwise. |
| |
| @item -fpartial-inlining |
| @opindex fpartial-inlining |
| Inline parts of functions. This option has any effect only |
| when inlining itself is turned on by the @option{-finline-functions} |
| or @option{-finline-small-functions} options. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fpredictive-commoning |
| @opindex fpredictive-commoning |
| Perform predictive commoning optimization, i.e., reusing computations |
| (especially memory loads and stores) performed in previous |
| iterations of loops. |
| |
| This option is enabled at level @option{-O3}. |
| It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. |
| |
| @item -fprefetch-loop-arrays |
| @opindex fprefetch-loop-arrays |
| If supported by the target machine, generate instructions to prefetch |
| memory to improve the performance of loops that access large arrays. |
| |
| This option may generate better or worse code; results are highly |
| dependent on the structure of loops within the source code. |
| |
| Disabled at level @option{-Os}. |
| |
| @item -fno-printf-return-value |
| @opindex fno-printf-return-value |
| @opindex fprintf-return-value |
| Do not substitute constants for known return value of formatted output |
| functions such as @code{sprintf}, @code{snprintf}, @code{vsprintf}, and |
| @code{vsnprintf} (but not @code{printf} of @code{fprintf}). This |
| transformation allows GCC to optimize or even eliminate branches based |
| on the known return value of these functions called with arguments that |
| are either constant, or whose values are known to be in a range that |
| makes determining the exact return value possible. For example, when |
| @option{-fprintf-return-value} is in effect, both the branch and the |
| body of the @code{if} statement (but not the call to @code{snprint}) |
| can be optimized away when @code{i} is a 32-bit or smaller integer |
| because the return value is guaranteed to be at most 8. |
| |
| @smallexample |
| char buf[9]; |
| if (snprintf (buf, "%08x", i) >= sizeof buf) |
| @dots{} |
| @end smallexample |
| |
| The @option{-fprintf-return-value} option relies on other optimizations |
| and yields best results with @option{-O2} and above. It works in tandem |
| with the @option{-Wformat-overflow} and @option{-Wformat-truncation} |
| options. The @option{-fprintf-return-value} option is enabled by default. |
| |
| @item -fno-peephole |
| @itemx -fno-peephole2 |
| @opindex fno-peephole |
| @opindex fpeephole |
| @opindex fno-peephole2 |
| @opindex fpeephole2 |
| Disable any machine-specific peephole optimizations. The difference |
| between @option{-fno-peephole} and @option{-fno-peephole2} is in how they |
| are implemented in the compiler; some targets use one, some use the |
| other, a few use both. |
| |
| @option{-fpeephole} is enabled by default. |
| @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fno-guess-branch-probability |
| @opindex fno-guess-branch-probability |
| @opindex fguess-branch-probability |
| Do not guess branch probabilities using heuristics. |
| |
| GCC uses heuristics to guess branch probabilities if they are |
| not provided by profiling feedback (@option{-fprofile-arcs}). These |
| heuristics are based on the control flow graph. If some branch probabilities |
| are specified by @code{__builtin_expect}, then the heuristics are |
| used to guess branch probabilities for the rest of the control flow graph, |
| taking the @code{__builtin_expect} info into account. The interactions |
| between the heuristics and @code{__builtin_expect} can be complex, and in |
| some cases, it may be useful to disable the heuristics so that the effects |
| of @code{__builtin_expect} are easier to understand. |
| |
| It is also possible to specify expected probability of the expression |
| with @code{__builtin_expect_with_probability} built-in function. |
| |
| The default is @option{-fguess-branch-probability} at levels |
| @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -freorder-blocks |
| @opindex freorder-blocks |
| Reorder basic blocks in the compiled function in order to reduce number of |
| taken branches and improve code locality. |
| |
| Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -freorder-blocks-algorithm=@var{algorithm} |
| @opindex freorder-blocks-algorithm |
| Use the specified algorithm for basic block reordering. The |
| @var{algorithm} argument can be @samp{simple}, which does not increase |
| code size (except sometimes due to secondary effects like alignment), |
| or @samp{stc}, the ``software trace cache'' algorithm, which tries to |
| put all often executed code together, minimizing the number of branches |
| executed by making extra copies of code. |
| |
| The default is @samp{simple} at levels @option{-O1}, @option{-Os}, and |
| @samp{stc} at levels @option{-O2}, @option{-O3}. |
| |
| @item -freorder-blocks-and-partition |
| @opindex freorder-blocks-and-partition |
| In addition to reordering basic blocks in the compiled function, in order |
| to reduce number of taken branches, partitions hot and cold basic blocks |
| into separate sections of the assembly and @file{.o} files, to improve |
| paging and cache locality performance. |
| |
| This optimization is automatically turned off in the presence of |
| exception handling or unwind tables (on targets using setjump/longjump or target specific scheme), for linkonce sections, for functions with a user-defined |
| section attribute and on any architecture that does not support named |
| sections. When @option{-fsplit-stack} is used this option is not |
| enabled by default (to avoid linker errors), but may be enabled |
| explicitly (if using a working linker). |
| |
| Enabled for x86 at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -freorder-functions |
| @opindex freorder-functions |
| Reorder functions in the object file in order to |
| improve code locality. This is implemented by using special |
| subsections @code{.text.hot} for most frequently executed functions and |
| @code{.text.unlikely} for unlikely executed functions. Reordering is done by |
| the linker so object file format must support named sections and linker must |
| place them in a reasonable way. |
| |
| This option isn't effective unless you either provide profile feedback |
| (see @option{-fprofile-arcs} for details) or manually annotate functions with |
| @code{hot} or @code{cold} attributes (@pxref{Common Function Attributes}). |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fstrict-aliasing |
| @opindex fstrict-aliasing |
| Allow the compiler to assume the strictest aliasing rules applicable to |
| the language being compiled. For C (and C++), this activates |
| optimizations based on the type of expressions. In particular, an |
| object of one type is assumed never to reside at the same address as an |
| object of a different type, unless the types are almost the same. For |
| example, an @code{unsigned int} can alias an @code{int}, but not a |
| @code{void*} or a @code{double}. A character type may alias any other |
| type. |
| |
| @anchor{Type-punning}Pay special attention to code like this: |
| @smallexample |
| union a_union @{ |
| int i; |
| double d; |
| @}; |
| |
| int f() @{ |
| union a_union t; |
| t.d = 3.0; |
| return t.i; |
| @} |
| @end smallexample |
| The practice of reading from a different union member than the one most |
| recently written to (called ``type-punning'') is common. Even with |
| @option{-fstrict-aliasing}, type-punning is allowed, provided the memory |
| is accessed through the union type. So, the code above works as |
| expected. @xref{Structures unions enumerations and bit-fields |
| implementation}. However, this code might not: |
| @smallexample |
| int f() @{ |
| union a_union t; |
| int* ip; |
| t.d = 3.0; |
| ip = &t.i; |
| return *ip; |
| @} |
| @end smallexample |
| |
| Similarly, access by taking the address, casting the resulting pointer |
| and dereferencing the result has undefined behavior, even if the cast |
| uses a union type, e.g.: |
| @smallexample |
| int f() @{ |
| double d = 3.0; |
| return ((union a_union *) &d)->i; |
| @} |
| @end smallexample |
| |
| The @option{-fstrict-aliasing} option is enabled at levels |
| @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fipa-strict-aliasing |
| @opindex fipa-strict-aliasing |
| Controls whether rules of @option{-fstrict-aliasing} are applied across |
| function boundaries. Note that if multiple functions gets inlined into a |
| single function the memory accesses are no longer considered to be crossing a |
| function boundary. |
| |
| The @option{-fipa-strict-aliasing} option is enabled by default and is |
| effective only in combination with @option{-fstrict-aliasing}. |
| |
| @item -falign-functions |
| @itemx -falign-functions=@var{n} |
| @itemx -falign-functions=@var{n}:@var{m} |
| @itemx -falign-functions=@var{n}:@var{m}:@var{n2} |
| @itemx -falign-functions=@var{n}:@var{m}:@var{n2}:@var{m2} |
| @opindex falign-functions |
| Align the start of functions to the next power-of-two greater than or |
| equal to @var{n}, skipping up to @var{m}-1 bytes. This ensures that at |
| least the first @var{m} bytes of the function can be fetched by the CPU |
| without crossing an @var{n}-byte alignment boundary. |
| |
| If @var{m} is not specified, it defaults to @var{n}. |
| |
| Examples: @option{-falign-functions=32} aligns functions to the next |
| 32-byte boundary, @option{-falign-functions=24} aligns to the next |
| 32-byte boundary only if this can be done by skipping 23 bytes or less, |
| @option{-falign-functions=32:7} aligns to the next |
| 32-byte boundary only if this can be done by skipping 6 bytes or less. |
| |
| The second pair of @var{n2}:@var{m2} values allows you to specify |
| a secondary alignment: @option{-falign-functions=64:7:32:3} aligns to |
| the next 64-byte boundary if this can be done by skipping 6 bytes or less, |
| otherwise aligns to the next 32-byte boundary if this can be done |
| by skipping 2 bytes or less. |
| If @var{m2} is not specified, it defaults to @var{n2}. |
| |
| Some assemblers only support this flag when @var{n} is a power of two; |
| in that case, it is rounded up. |
| |
| @option{-fno-align-functions} and @option{-falign-functions=1} are |
| equivalent and mean that functions are not aligned. |
| |
| If @var{n} is not specified or is zero, use a machine-dependent default. |
| The maximum allowed @var{n} option value is 65536. |
| |
| Enabled at levels @option{-O2}, @option{-O3}. |
| |
| @item -flimit-function-alignment |
| If this option is enabled, the compiler tries to avoid unnecessarily |
| overaligning functions. It attempts to instruct the assembler to align |
| by the amount specified by @option{-falign-functions}, but not to |
| skip more bytes than the size of the function. |
| |
| @item -falign-labels |
| @itemx -falign-labels=@var{n} |
| @itemx -falign-labels=@var{n}:@var{m} |
| @itemx -falign-labels=@var{n}:@var{m}:@var{n2} |
| @itemx -falign-labels=@var{n}:@var{m}:@var{n2}:@var{m2} |
| @opindex falign-labels |
| Align all branch targets to a power-of-two boundary. |
| |
| Parameters of this option are analogous to the @option{-falign-functions} option. |
| @option{-fno-align-labels} and @option{-falign-labels=1} are |
| equivalent and mean that labels are not aligned. |
| |
| If @option{-falign-loops} or @option{-falign-jumps} are applicable and |
| are greater than this value, then their values are used instead. |
| |
| If @var{n} is not specified or is zero, use a machine-dependent default |
| which is very likely to be @samp{1}, meaning no alignment. |
| The maximum allowed @var{n} option value is 65536. |
| |
| Enabled at levels @option{-O2}, @option{-O3}. |
| |
| @item -falign-loops |
| @itemx -falign-loops=@var{n} |
| @itemx -falign-loops=@var{n}:@var{m} |
| @itemx -falign-loops=@var{n}:@var{m}:@var{n2} |
| @itemx -falign-loops=@var{n}:@var{m}:@var{n2}:@var{m2} |
| @opindex falign-loops |
| Align loops to a power-of-two boundary. If the loops are executed |
| many times, this makes up for any execution of the dummy padding |
| instructions. |
| |
| If @option{-falign-labels} is greater than this value, then its value |
| is used instead. |
| |
| Parameters of this option are analogous to the @option{-falign-functions} option. |
| @option{-fno-align-loops} and @option{-falign-loops=1} are |
| equivalent and mean that loops are not aligned. |
| The maximum allowed @var{n} option value is 65536. |
| |
| If @var{n} is not specified or is zero, use a machine-dependent default. |
| |
| Enabled at levels @option{-O2}, @option{-O3}. |
| |
| @item -falign-jumps |
| @itemx -falign-jumps=@var{n} |
| @itemx -falign-jumps=@var{n}:@var{m} |
| @itemx -falign-jumps=@var{n}:@var{m}:@var{n2} |
| @itemx -falign-jumps=@var{n}:@var{m}:@var{n2}:@var{m2} |
| @opindex falign-jumps |
| Align branch targets to a power-of-two boundary, for branch targets |
| where the targets can only be reached by jumping. In this case, |
| no dummy operations need be executed. |
| |
| If @option{-falign-labels} is greater than this value, then its value |
| is used instead. |
| |
| Parameters of this option are analogous to the @option{-falign-functions} option. |
| @option{-fno-align-jumps} and @option{-falign-jumps=1} are |
| equivalent and mean that loops are not aligned. |
| |
| If @var{n} is not specified or is zero, use a machine-dependent default. |
| The maximum allowed @var{n} option value is 65536. |
| |
| Enabled at levels @option{-O2}, @option{-O3}. |
| |
| @item -fno-allocation-dce |
| @opindex fno-allocation-dce |
| Do not remove unused C++ allocations in dead code elimination. |
| |
| @item -fallow-store-data-races |
| @opindex fallow-store-data-races |
| Allow the compiler to perform optimizations that may introduce new data races |
| on stores, without proving that the variable cannot be concurrently accessed |
| by other threads. Does not affect optimization of local data. It is safe to |
| use this option if it is known that global data will not be accessed by |
| multiple threads. |
| |
| Examples of optimizations enabled by @option{-fallow-store-data-races} include |
| hoisting or if-conversions that may cause a value that was already in memory |
| to be re-written with that same value. Such re-writing is safe in a single |
| threaded context but may be unsafe in a multi-threaded context. Note that on |
| some processors, if-conversions may be required in order to enable |
| vectorization. |
| |
| Enabled at level @option{-Ofast}. |
| |
| @item -funit-at-a-time |
| @opindex funit-at-a-time |
| This option is left for compatibility reasons. @option{-funit-at-a-time} |
| has no effect, while @option{-fno-unit-at-a-time} implies |
| @option{-fno-toplevel-reorder} and @option{-fno-section-anchors}. |
| |
| Enabled by default. |
| |
| @item -fno-toplevel-reorder |
| @opindex fno-toplevel-reorder |
| @opindex ftoplevel-reorder |
| Do not reorder top-level functions, variables, and @code{asm} |
| statements. Output them in the same order that they appear in the |
| input file. When this option is used, unreferenced static variables |
| are not removed. This option is intended to support existing code |
| that relies on a particular ordering. For new code, it is better to |
| use attributes when possible. |
| |
| @option{-ftoplevel-reorder} is the default at @option{-O1} and higher, and |
| also at @option{-O0} if @option{-fsection-anchors} is explicitly requested. |
| Additionally @option{-fno-toplevel-reorder} implies |
| @option{-fno-section-anchors}. |
| |
| @item -fweb |
| @opindex fweb |
| Constructs webs as commonly used for register allocation purposes and assign |
| each web individual pseudo register. This allows the register allocation pass |
| to operate on pseudos directly, but also strengthens several other optimization |
| passes, such as CSE, loop optimizer and trivial dead code remover. It can, |
| however, make debugging impossible, since variables no longer stay in a |
| ``home register''. |
| |
| Enabled by default with @option{-funroll-loops}. |
| |
| @item -fwhole-program |
| @opindex fwhole-program |
| Assume that the current compilation unit represents the whole program being |
| compiled. All public functions and variables with the exception of @code{main} |
| and those merged by attribute @code{externally_visible} become static functions |
| and in effect are optimized more aggressively by interprocedural optimizers. |
| |
| This option should not be used in combination with @option{-flto}. |
| Instead relying on a linker plugin should provide safer and more precise |
| information. |
| |
| @item -flto[=@var{n}] |
| @opindex flto |
| This option runs the standard link-time optimizer. When invoked |
| with source code, it generates GIMPLE (one of GCC's internal |
| representations) and writes it to special ELF sections in the object |
| file. When the object files are linked together, all the function |
| bodies are read from these ELF sections and instantiated as if they |
| had been part of the same translation unit. |
| |
| To use the link-time optimizer, @option{-flto} and optimization |
| options should be specified at compile time and during the final link. |
| It is recommended that you compile all the files participating in the |
| same link with the same options and also specify those options at |
| link time. |
| For example: |
| |
| @smallexample |
| gcc -c -O2 -flto foo.c |
| gcc -c -O2 -flto bar.c |
| gcc -o myprog -flto -O2 foo.o bar.o |
| @end smallexample |
| |
| The first two invocations to GCC save a bytecode representation |
| of GIMPLE into special ELF sections inside @file{foo.o} and |
| @file{bar.o}. The final invocation reads the GIMPLE bytecode from |
| @file{foo.o} and @file{bar.o}, merges the two files into a single |
| internal image, and compiles the result as usual. Since both |
| @file{foo.o} and @file{bar.o} are merged into a single image, this |
| causes all the interprocedural analyses and optimizations in GCC to |
| work across the two files as if they were a single one. This means, |
| for example, that the inliner is able to inline functions in |
| @file{bar.o} into functions in @file{foo.o} and vice-versa. |
| |
| Another (simpler) way to enable link-time optimization is: |
| |
| @smallexample |
| gcc -o myprog -flto -O2 foo.c bar.c |
| @end smallexample |
| |
| The above generates bytecode for @file{foo.c} and @file{bar.c}, |
| merges them together into a single GIMPLE representation and optimizes |
| them as usual to produce @file{myprog}. |
| |
| The important thing to keep in mind is that to enable link-time |
| optimizations you need to use the GCC driver to perform the link step. |
| GCC automatically performs link-time optimization if any of the |
| objects involved were compiled with the @option{-flto} command-line option. |
| You can always override |
| the automatic decision to do link-time optimization |
| by passing @option{-fno-lto} to the link command. |
| |
| To make whole program optimization effective, it is necessary to make |
| certain whole program assumptions. The compiler needs to know |
| what functions and variables can be accessed by libraries and runtime |
| outside of the link-time optimized unit. When supported by the linker, |
| the linker plugin (see @option{-fuse-linker-plugin}) passes information |
| to the compiler about used and externally visible symbols. When |
| the linker plugin is not available, @option{-fwhole-program} should be |
| used to allow the compiler to make these assumptions, which leads |
| to more aggressive optimization decisions. |
| |
| When a file is compiled with @option{-flto} without |
| @option{-fuse-linker-plugin}, the generated object file is larger than |
| a regular object file because it contains GIMPLE bytecodes and the usual |
| final code (see @option{-ffat-lto-objects}). This means that |
| object files with LTO information can be linked as normal object |
| files; if @option{-fno-lto} is passed to the linker, no |
| interprocedural optimizations are applied. Note that when |
| @option{-fno-fat-lto-objects} is enabled the compile stage is faster |
| but you cannot perform a regular, non-LTO link on them. |
| |
| When producing the final binary, GCC only |
| applies link-time optimizations to those files that contain bytecode. |
| Therefore, you can mix and match object files and libraries with |
| GIMPLE bytecodes and final object code. GCC automatically selects |
| which files to optimize in LTO mode and which files to link without |
| further processing. |
| |
| Generally, options specified at link time override those |
| specified at compile time, although in some cases GCC attempts to infer |
| link-time options from the settings used to compile the input files. |
| |
| If you do not specify an optimization level option @option{-O} at |
| link time, then GCC uses the highest optimization level |
| used when compiling the object files. Note that it is generally |
| ineffective to specify an optimization level option only at link time and |
| not at compile time, for two reasons. First, compiling without |
| optimization suppresses compiler passes that gather information |
| needed for effective optimization at link time. Second, some early |
| optimization passes can be performed only at compile time and |
| not at link time. |
| |
| There are some code generation flags preserved by GCC when |
| generating bytecodes, as they need to be used during the final link. |
| Currently, the following options and their settings are taken from |
| the first object file that explicitly specifies them: |
| @option{-fcommon}, @option{-fexceptions}, @option{-fnon-call-exceptions}, |
| @option{-fgnu-tm} and all the @option{-m} target flags. |
| |
| The following options @option{-fPIC}, @option{-fpic}, @option{-fpie} and |
| @option{-fPIE} are combined based on the following scheme: |
| |
| @smallexample |
| @option{-fPIC} + @option{-fpic} = @option{-fpic} |
| @option{-fPIC} + @option{-fno-pic} = @option{-fno-pic} |
| @option{-fpic/-fPIC} + (no option) = (no option) |
| @option{-fPIC} + @option{-fPIE} = @option{-fPIE} |
| @option{-fpic} + @option{-fPIE} = @option{-fpie} |
| @option{-fPIC/-fpic} + @option{-fpie} = @option{-fpie} |
| @end smallexample |
| |
| Certain ABI-changing flags are required to match in all compilation units, |
| and trying to override this at link time with a conflicting value |
| is ignored. This includes options such as @option{-freg-struct-return} |
| and @option{-fpcc-struct-return}. |
| |
| Other options such as @option{-ffp-contract}, @option{-fno-strict-overflow}, |
| @option{-fwrapv}, @option{-fno-trapv} or @option{-fno-strict-aliasing} |
| are passed through to the link stage and merged conservatively for |
| conflicting translation units. Specifically |
| @option{-fno-strict-overflow}, @option{-fwrapv} and @option{-fno-trapv} take |
| precedence; and for example @option{-ffp-contract=off} takes precedence |
| over @option{-ffp-contract=fast}. You can override them at link time. |
| |
| Diagnostic options such as @option{-Wstringop-overflow} are passed |
| through to the link stage and their setting matches that of the |
| compile-step at function granularity. Note that this matters only |
| for diagnostics emitted during optimization. Note that code |
| transforms such as inlining can lead to warnings being enabled |
| or disabled for regions if code not consistent with the setting |
| at compile time. |
| |
| When you need to pass options to the assembler via @option{-Wa} or |
| @option{-Xassembler} make sure to either compile such translation |
| units with @option{-fno-lto} or consistently use the same assembler |
| options on all translation units. You can alternatively also |
| specify assembler options at LTO link time. |
| |
| To enable debug info generation you need to supply @option{-g} at |
| compile time. If any of the input files at link time were built |
| with debug info generation enabled the link will enable debug info |
| generation as well. Any elaborate debug info settings |
| like the dwarf level @option{-gdwarf-5} need to be explicitly repeated |
| at the linker command line and mixing different settings in different |
| translation units is discouraged. |
| |
| If LTO encounters objects with C linkage declared with incompatible |
| types in separate translation units to be linked together (undefined |
| behavior according to ISO C99 6.2.7), a non-fatal diagnostic may be |
| issued. The behavior is still undefined at run time. Similar |
| diagnostics may be raised for other languages. |
| |
| Another feature of LTO is that it is possible to apply interprocedural |
| optimizations on files written in different languages: |
| |
| @smallexample |
| gcc -c -flto foo.c |
| g++ -c -flto bar.cc |
| gfortran -c -flto baz.f90 |
| g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran |
| @end smallexample |
| |
| Notice that the final link is done with @command{g++} to get the C++ |
| runtime libraries and @option{-lgfortran} is added to get the Fortran |
| runtime libraries. In general, when mixing languages in LTO mode, you |
| should use the same link command options as when mixing languages in a |
| regular (non-LTO) compilation. |
| |
| If object files containing GIMPLE bytecode are stored in a library archive, say |
| @file{libfoo.a}, it is possible to extract and use them in an LTO link if you |
| are using a linker with plugin support. To create static libraries suitable |
| for LTO, use @command{gcc-ar} and @command{gcc-ranlib} instead of @command{ar} |
| and @command{ranlib}; |
| to show the symbols of object files with GIMPLE bytecode, use |
| @command{gcc-nm}. Those commands require that @command{ar}, @command{ranlib} |
| and @command{nm} have been compiled with plugin support. At link time, use the |
| flag @option{-fuse-linker-plugin} to ensure that the library participates in |
| the LTO optimization process: |
| |
| @smallexample |
| gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo |
| @end smallexample |
| |
| With the linker plugin enabled, the linker extracts the needed |
| GIMPLE files from @file{libfoo.a} and passes them on to the running GCC |
| to make them part of the aggregated GIMPLE image to be optimized. |
| |
| If you are not using a linker with plugin support and/or do not |
| enable the linker plugin, then the objects inside @file{libfoo.a} |
| are extracted and linked as usual, but they do not participate |
| in the LTO optimization process. In order to make a static library suitable |
| for both LTO optimization and usual linkage, compile its object files with |
| @option{-flto} @option{-ffat-lto-objects}. |
| |
| Link-time optimizations do not require the presence of the whole program to |
| operate. If the program does not require any symbols to be exported, it is |
| possible to combine @option{-flto} and @option{-fwhole-program} to allow |
| the interprocedural optimizers to use more aggressive assumptions which may |
| lead to improved optimization opportunities. |
| Use of @option{-fwhole-program} is not needed when linker plugin is |
| active (see @option{-fuse-linker-plugin}). |
| |
| The current implementation of LTO makes no |
| attempt to generate bytecode that is portable between different |
| types of hosts. The bytecode files are versioned and there is a |
| strict version check, so bytecode files generated in one version of |
| GCC do not work with an older or newer version of GCC. |
| |
| Link-time optimization does not work well with generation of debugging |
| information on systems other than those using a combination of ELF and |
| DWARF. |
| |
| If you specify the optional @var{n}, the optimization and code |
| generation done at link time is executed in parallel using @var{n} |
| parallel jobs by utilizing an installed @command{make} program. The |
| environment variable @env{MAKE} may be used to override the program |
| used. |
| |
| You can also specify @option{-flto=jobserver} to use GNU make's |
| job server mode to determine the number of parallel jobs. This |
| is useful when the Makefile calling GCC is already executing in parallel. |
| You must prepend a @samp{+} to the command recipe in the parent Makefile |
| for this to work. This option likely only works if @env{MAKE} is |
| GNU make. Even without the option value, GCC tries to automatically |
| detect a running GNU make's job server. |
| |
| Use @option{-flto=auto} to use GNU make's job server, if available, |
| or otherwise fall back to autodetection of the number of CPU threads |
| present in your system. |
| |
| @item -flto-partition=@var{alg} |
| @opindex flto-partition |
| Specify the partitioning algorithm used by the link-time optimizer. |
| The value is either @samp{1to1} to specify a partitioning mirroring |
| the original source files or @samp{balanced} to specify partitioning |
| into equally sized chunks (whenever possible) or @samp{max} to create |
| new partition for every symbol where possible. Specifying @samp{none} |
| as an algorithm disables partitioning and streaming completely. |
| The default value is @samp{balanced}. While @samp{1to1} can be used |
| as an workaround for various code ordering issues, the @samp{max} |
| partitioning is intended for internal testing only. |
| The value @samp{one} specifies that exactly one partition should be |
| used while the value @samp{none} bypasses partitioning and executes |
| the link-time optimization step directly from the WPA phase. |
| |
| @item -flto-compression-level=@var{n} |
| @opindex flto-compression-level |
| This option specifies the level of compression used for intermediate |
| language written to LTO object files, and is only meaningful in |
| conjunction with LTO mode (@option{-flto}). GCC currently supports two |
| LTO compression algorithms. For zstd, valid values are 0 (no compression) |
| to 19 (maximum compression), while zlib supports values from 0 to 9. |
| Values outside this range are clamped to either minimum or maximum |
| of the supported values. If the option is not given, |
| a default balanced compression setting is used. |
| |
| @item -fuse-linker-plugin |
| @opindex fuse-linker-plugin |
| Enables the use of a linker plugin during link-time optimization. This |
| option relies on plugin support in the linker, which is available in gold |
| or in GNU ld 2.21 or newer. |
| |
| This option enables the extraction of object files with GIMPLE bytecode out |
| of library archives. This improves the quality of optimization by exposing |
| more code to the link-time optimizer. This information specifies what |
| symbols can be accessed externally (by non-LTO object or during dynamic |
| linking). Resulting code quality improvements on binaries (and shared |
| libraries that use hidden visibility) are similar to @option{-fwhole-program}. |
| See @option{-flto} for a description of the effect of this flag and how to |
| use it. |
| |
| This option is enabled by default when LTO support in GCC is enabled |
| and GCC was configured for use with |
| a linker supporting plugins (GNU ld 2.21 or newer or gold). |
| |
| @item -ffat-lto-objects |
| @opindex ffat-lto-objects |
| Fat LTO objects are object files that contain both the intermediate language |
| and the object code. This makes them usable for both LTO linking and normal |
| linking. This option is effective only when compiling with @option{-flto} |
| and is ignored at link time. |
| |
| @option{-fno-fat-lto-objects} improves compilation time over plain LTO, but |
| requires the complete toolchain to be aware of LTO. It requires a linker with |
| linker plugin support for basic functionality. Additionally, |
| @command{nm}, @command{ar} and @command{ranlib} |
| need to support linker plugins to allow a full-featured build environment |
| (capable of building static libraries etc). GCC provides the @command{gcc-ar}, |
| @command{gcc-nm}, @command{gcc-ranlib} wrappers to pass the right options |
| to these tools. With non fat LTO makefiles need to be modified to use them. |
| |
| Note that modern binutils provide plugin auto-load mechanism. |
| Installing the linker plugin into @file{$libdir/bfd-plugins} has the same |
| effect as usage of the command wrappers (@command{gcc-ar}, @command{gcc-nm} and |
| @command{gcc-ranlib}). |
| |
| The default is @option{-fno-fat-lto-objects} on targets with linker plugin |
| support. |
| |
| @item -fcompare-elim |
| @opindex fcompare-elim |
| After register allocation and post-register allocation instruction splitting, |
| identify arithmetic instructions that compute processor flags similar to a |
| comparison operation based on that arithmetic. If possible, eliminate the |
| explicit comparison operation. |
| |
| This pass only applies to certain targets that cannot explicitly represent |
| the comparison operation before register allocation is complete. |
| |
| Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fcprop-registers |
| @opindex fcprop-registers |
| After register allocation and post-register allocation instruction splitting, |
| perform a copy-propagation pass to try to reduce scheduling dependencies |
| and occasionally eliminate the copy. |
| |
| Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fprofile-correction |
| @opindex fprofile-correction |
| Profiles collected using an instrumented binary for multi-threaded programs may |
| be inconsistent due to missed counter updates. When this option is specified, |
| GCC uses heuristics to correct or smooth out such inconsistencies. By |
| default, GCC emits an error message when an inconsistent profile is detected. |
| |
| This option is enabled by @option{-fauto-profile}. |
| |
| @item -fprofile-partial-training |
| @opindex fprofile-partial-training |
| With @code{-fprofile-use} all portions of programs not executed during train |
| run are optimized agressively for size rather than speed. In some cases it is |
| not practical to train all possible hot paths in the program. (For |
| example, program may contain functions specific for a given hardware and |
| trianing may not cover all hardware configurations program is run on.) With |
| @code{-fprofile-partial-training} profile feedback will be ignored for all |
| functions not executed during the train run leading them to be optimized as if |
| they were compiled without profile feedback. This leads to better performance |
| when train run is not representative but also leads to significantly bigger |
| code. |
| |
| @item -fprofile-use |
| @itemx -fprofile-use=@var{path} |
| @opindex fprofile-use |
| Enable profile feedback-directed optimizations, |
| and the following optimizations, many of which |
| are generally profitable only with profile feedback available: |
| |
| @gccoptlist{-fbranch-probabilities -fprofile-values @gol |
| -funroll-loops -fpeel-loops -ftracer -fvpt @gol |
| -finline-functions -fipa-cp -fipa-cp-clone -fipa-bit-cp @gol |
| -fpredictive-commoning -fsplit-loops -funswitch-loops @gol |
| -fgcse-after-reload -ftree-loop-vectorize -ftree-slp-vectorize @gol |
| -fvect-cost-model=dynamic -ftree-loop-distribute-patterns @gol |
| -fprofile-reorder-functions} |
| |
| Before you can use this option, you must first generate profiling information. |
| @xref{Instrumentation Options}, for information about the |
| @option{-fprofile-generate} option. |
| |
| By default, GCC emits an error message if the feedback profiles do not |
| match the source code. This error can be turned into a warning by using |
| @option{-Wno-error=coverage-mismatch}. Note this may result in poorly |
| optimized code. Additionally, by default, GCC also emits a warning message if |
| the feedback profiles do not exist (see @option{-Wmissing-profile}). |
| |
| If @var{path} is specified, GCC looks at the @var{path} to find |
| the profile feedback data files. See @option{-fprofile-dir}. |
| |
| @item -fauto-profile |
| @itemx -fauto-profile=@var{path} |
| @opindex fauto-profile |
| Enable sampling-based feedback-directed optimizations, |
| and the following optimizations, |
| many of which are generally profitable only with profile feedback available: |
| |
| @gccoptlist{-fbranch-probabilities -fprofile-values @gol |
| -funroll-loops -fpeel-loops -ftracer -fvpt @gol |
| -finline-functions -fipa-cp -fipa-cp-clone -fipa-bit-cp @gol |
| -fpredictive-commoning -fsplit-loops -funswitch-loops @gol |
| -fgcse-after-reload -ftree-loop-vectorize -ftree-slp-vectorize @gol |
| -fvect-cost-model=dynamic -ftree-loop-distribute-patterns @gol |
| -fprofile-correction} |
| |
| @var{path} is the name of a file containing AutoFDO profile information. |
| If omitted, it defaults to @file{fbdata.afdo} in the current directory. |
| |
| Producing an AutoFDO profile data file requires running your program |
| with the @command{perf} utility on a supported GNU/Linux target system. |
| For more information, see @uref{https://perf.wiki.kernel.org/}. |
| |
| E.g. |
| @smallexample |
| perf record -e br_inst_retired:near_taken -b -o perf.data \ |
| -- your_program |
| @end smallexample |
| |
| Then use the @command{create_gcov} tool to convert the raw profile data |
| to a format that can be used by GCC.@ You must also supply the |
| unstripped binary for your program to this tool. |
| See @uref{https://github.com/google/autofdo}. |
| |
| E.g. |
| @smallexample |
| create_gcov --binary=your_program.unstripped --profile=perf.data \ |
| --gcov=profile.afdo |
| @end smallexample |
| @end table |
| |
| The following options control compiler behavior regarding floating-point |
| arithmetic. These options trade off between speed and |
| correctness. All must be specifically enabled. |
| |
| @table @gcctabopt |
| @item -ffloat-store |
| @opindex ffloat-store |
| Do not store floating-point variables in registers, and inhibit other |
| options that might change whether a floating-point value is taken from a |
| register or memory. |
| |
| @cindex floating-point precision |
| This option prevents undesirable excess precision on machines such as |
| the 68000 where the floating registers (of the 68881) keep more |
| precision than a @code{double} is supposed to have. Similarly for the |
| x86 architecture. For most programs, the excess precision does only |
| good, but a few programs rely on the precise definition of IEEE floating |
| point. Use @option{-ffloat-store} for such programs, after modifying |
| them to store all pertinent intermediate computations into variables. |
| |
| @item -fexcess-precision=@var{style} |
| @opindex fexcess-precision |
| This option allows further control over excess precision on machines |
| where floating-point operations occur in a format with more precision or |
| range than the IEEE standard and interchange floating-point types. By |
| default, @option{-fexcess-precision=fast} is in effect; this means that |
| operations may be carried out in a wider precision than the types specified |
| in the source if that would result in faster code, and it is unpredictable |
| when rounding to the types specified in the source code takes place. |
| When compiling C, if @option{-fexcess-precision=standard} is specified then |
| excess precision follows the rules specified in ISO C99; in particular, |
| both casts and assignments cause values to be rounded to their |
| semantic types (whereas @option{-ffloat-store} only affects |
| assignments). This option is enabled by default for C if a strict |
| conformance option such as @option{-std=c99} is used. |
| @option{-ffast-math} enables @option{-fexcess-precision=fast} by default |
| regardless of whether a strict conformance option is used. |
| |
| @opindex mfpmath |
| @option{-fexcess-precision=standard} is not implemented for languages |
| other than C. On the x86, it has no effect if @option{-mfpmath=sse} |
| or @option{-mfpmath=sse+387} is specified; in the former case, IEEE |
| semantics apply without excess precision, and in the latter, rounding |
| is unpredictable. |
| |
| @item -ffast-math |
| @opindex ffast-math |
| Sets the options @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, |
| @option{-ffinite-math-only}, @option{-fno-rounding-math}, |
| @option{-fno-signaling-nans}, @option{-fcx-limited-range} and |
| @option{-fexcess-precision=fast}. |
| |
| This option causes the preprocessor macro @code{__FAST_MATH__} to be defined. |
| |
| This option is not turned on by any @option{-O} option besides |
| @option{-Ofast} since it can result in incorrect output for programs |
| that depend on an exact implementation of IEEE or ISO rules/specifications |
| for math functions. It may, however, yield faster code for programs |
| that do not require the guarantees of these specifications. |
| |
| @item -fno-math-errno |
| @opindex fno-math-errno |
| @opindex fmath-errno |
| Do not set @code{errno} after calling math functions that are executed |
| with a single instruction, e.g., @code{sqrt}. A program that relies on |
| IEEE exceptions for math error handling may want to use this flag |
| for speed while maintaining IEEE arithmetic compatibility. |
| |
| This option is not turned on by any @option{-O} option since |
| it can result in incorrect output for programs that depend on |
| an exact implementation of IEEE or ISO rules/specifications for |
| math functions. It may, however, yield faster code for programs |
| that do not require the guarantees of these specifications. |
| |
| The default is @option{-fmath-errno}. |
| |
| On Darwin systems, the math library never sets @code{errno}. There is |
| therefore no reason for the compiler to consider the possibility that |
| it might, and @option{-fno-math-errno} is the default. |
| |
| @item -funsafe-math-optimizations |
| @opindex funsafe-math-optimizations |
| |
| Allow optimizations for floating-point arithmetic that (a) assume |
| that arguments and results are valid and (b) may violate IEEE or |
| ANSI standards. When used at link time, it may include libraries |
| or startup files that change the default FPU control word or other |
| similar optimizations. |
| |
| This option is not turned on by any @option{-O} option since |
| it can result in incorrect output for programs that depend on |
| an exact implementation of IEEE or ISO rules/specifications for |
| math functions. It may, however, yield faster code for programs |
| that do not require the guarantees of these specifications. |
| Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math}, |
| @option{-fassociative-math} and @option{-freciprocal-math}. |
| |
| The default is @option{-fno-unsafe-math-optimizations}. |
| |
| @item -fassociative-math |
| @opindex fassociative-math |
| |
| Allow re-association of operands in series of floating-point operations. |
| This violates the ISO C and C++ language standard by possibly changing |
| computation result. NOTE: re-ordering may change the sign of zero as |
| well as ignore NaNs and inhibit or create underflow or overflow (and |
| thus cannot be used on code that relies on rounding behavior like |
| @code{(x + 2**52) - 2**52}. May also reorder floating-point comparisons |
| and thus may not be used when ordered comparisons are required. |
| This option requires that both @option{-fno-signed-zeros} and |
| @option{-fno-trapping-math} be in effect. Moreover, it doesn't make |
| much sense with @option{-frounding-math}. For Fortran the option |
| is automatically enabled when both @option{-fno-signed-zeros} and |
| @option{-fno-trapping-math} are in effect. |
| |
| The default is @option{-fno-associative-math}. |
| |
| @item -freciprocal-math |
| @opindex freciprocal-math |
| |
| Allow the reciprocal of a value to be used instead of dividing by |
| the value if this enables optimizations. For example @code{x / y} |
| can be replaced with @code{x * (1/y)}, which is useful if @code{(1/y)} |
| is subject to common subexpression elimination. Note that this loses |
| precision and increases the number of flops operating on the value. |
| |
| The default is @option{-fno-reciprocal-math}. |
| |
| @item -ffinite-math-only |
| @opindex ffinite-math-only |
| Allow optimizations for floating-point arithmetic that assume |
| that arguments and results are not NaNs or +-Infs. |
| |
| This option is not turned on by any @option{-O} option since |
| it can result in incorrect output for programs that depend on |
| an exact implementation of IEEE or ISO rules/specifications for |
| math functions. It may, however, yield faster code for programs |
| that do not require the guarantees of these specifications. |
| |
| The default is @option{-fno-finite-math-only}. |
| |
| @item -fno-signed-zeros |
| @opindex fno-signed-zeros |
| @opindex fsigned-zeros |
| Allow optimizations for floating-point arithmetic that ignore the |
| signedness of zero. IEEE arithmetic specifies the behavior of |
| distinct +0.0 and @minus{}0.0 values, which then prohibits simplification |
| of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}). |
| This option implies that the sign of a zero result isn't significant. |
| |
| The default is @option{-fsigned-zeros}. |
| |
| @item -fno-trapping-math |
| @opindex fno-trapping-math |
| @opindex ftrapping-math |
| Compile code assuming that floating-point operations cannot generate |
| user-visible traps. These traps include division by zero, overflow, |
| underflow, inexact result and invalid operation. This option requires |
| that @option{-fno-signaling-nans} be in effect. Setting this option may |
| allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example. |
| |
| This option should never be turned on by any @option{-O} option since |
| it can result in incorrect output for programs that depend on |
| an exact implementation of IEEE or ISO rules/specifications for |
| math functions. |
| |
| The default is @option{-ftrapping-math}. |
| |
| @item -frounding-math |
| @opindex frounding-math |
| Disable transformations and optimizations that assume default floating-point |
| rounding behavior. This is round-to-zero for all floating point |
| to integer conversions, and round-to-nearest for all other arithmetic |
| truncations. This option should be specified for programs that change |
| the FP rounding mode dynamically, or that may be executed with a |
| non-default rounding mode. This option disables constant folding of |
| floating-point expressions at compile time (which may be affected by |
| rounding mode) and arithmetic transformations that are unsafe in the |
| presence of sign-dependent rounding modes. |
| |
| The default is @option{-fno-rounding-math}. |
| |
| This option is experimental and does not currently guarantee to |
| disable all GCC optimizations that are affected by rounding mode. |
| Future versions of GCC may provide finer control of this setting |
| using C99's @code{FENV_ACCESS} pragma. This command-line option |
| will be used to specify the default state for @code{FENV_ACCESS}. |
| |
| @item -fsignaling-nans |
| @opindex fsignaling-nans |
| Compile code assuming that IEEE signaling NaNs may generate user-visible |
| traps during floating-point operations. Setting this option disables |
| optimizations that may change the number of exceptions visible with |
| signaling NaNs. This option implies @option{-ftrapping-math}. |
| |
| This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to |
| be defined. |
| |
| The default is @option{-fno-signaling-nans}. |
| |
| This option is experimental and does not currently guarantee to |
| disable all GCC optimizations that affect signaling NaN behavior. |
| |
| @item -fno-fp-int-builtin-inexact |
| @opindex fno-fp-int-builtin-inexact |
| @opindex ffp-int-builtin-inexact |
| Do not allow the built-in functions @code{ceil}, @code{floor}, |
| @code{round} and @code{trunc}, and their @code{float} and @code{long |
| double} variants, to generate code that raises the ``inexact'' |
| floating-point exception for noninteger arguments. ISO C99 and C11 |
| allow these functions to raise the ``inexact'' exception, but ISO/IEC |
| TS 18661-1:2014, the C bindings to IEEE 754-2008, as integrated into |
| ISO C2X, does not allow these functions to do so. |
| |
| The default is @option{-ffp-int-builtin-inexact}, allowing the |
| exception to be raised, unless C2X or a later C standard is selected. |
| This option does nothing unless @option{-ftrapping-math} is in effect. |
| |
| Even if @option{-fno-fp-int-builtin-inexact} is used, if the functions |
| generate a call to a library function then the ``inexact'' exception |
| may be raised if the library implementation does not follow TS 18661. |
| |
| @item -fsingle-precision-constant |
| @opindex fsingle-precision-constant |
| Treat floating-point constants as single precision instead of |
| implicitly converting them to double-precision constants. |
| |
| @item -fcx-limited-range |
| @opindex fcx-limited-range |
| When enabled, this option states that a range reduction step is not |
| needed when performing complex division. Also, there is no checking |
| whether the result of a complex multiplication or division is @code{NaN |
| + I*NaN}, with an attempt to rescue the situation in that case. The |
| default is @option{-fno-cx-limited-range}, but is enabled by |
| @option{-ffast-math}. |
| |
| This option controls the default setting of the ISO C99 |
| @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to |
| all languages. |
| |
| @item -fcx-fortran-rules |
| @opindex fcx-fortran-rules |
| Complex multiplication and division follow Fortran rules. Range |
| reduction is done as part of complex division, but there is no checking |
| whether the result of a complex multiplication or division is @code{NaN |
| + I*NaN}, with an attempt to rescue the situation in that case. |
| |
| The default is @option{-fno-cx-fortran-rules}. |
| |
| @end table |
| |
| The following options control optimizations that may improve |
| performance, but are not enabled by any @option{-O} options. This |
| section includes experimental options that may produce broken code. |
| |
| @table @gcctabopt |
| @item -fbranch-probabilities |
| @opindex fbranch-probabilities |
| After running a program compiled with @option{-fprofile-arcs} |
| (@pxref{Instrumentation Options}), |
| you can compile it a second time using |
| @option{-fbranch-probabilities}, to improve optimizations based on |
| the number of times each branch was taken. When a program |
| compiled with @option{-fprofile-arcs} exits, it saves arc execution |
| counts to a file called @file{@var{sourcename}.gcda} for each source |
| file. The information in this data file is very dependent on the |
| structure of the generated code, so you must use the same source code |
| and the same optimization options for both compilations. |
| See details about the file naming in @option{-fprofile-arcs}. |
| |
| With @option{-fbranch-probabilities}, GCC puts a |
| @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}. |
| These can be used to improve optimization. Currently, they are only |
| used in one place: in @file{reorg.cc}, instead of guessing which path a |
| branch is most likely to take, the @samp{REG_BR_PROB} values are used to |
| exactly determine which path is taken more often. |
| |
| Enabled by @option{-fprofile-use} and @option{-fauto-profile}. |
| |
| @item -fprofile-values |
| @opindex fprofile-values |
| If combined with @option{-fprofile-arcs}, it adds code so that some |
| data about values of expressions in the program is gathered. |
| |
| With @option{-fbranch-probabilities}, it reads back the data gathered |
| from profiling values of expressions for usage in optimizations. |
| |
| Enabled by @option{-fprofile-generate}, @option{-fprofile-use}, and |
| @option{-fauto-profile}. |
| |
| @item -fprofile-reorder-functions |
| @opindex fprofile-reorder-functions |
| Function reordering based on profile instrumentation collects |
| first time of execution of a function and orders these functions |
| in ascending order. |
| |
| Enabled with @option{-fprofile-use}. |
| |
| @item -fvpt |
| @opindex fvpt |
| If combined with @option{-fprofile-arcs}, this option instructs the compiler |
| to add code to gather information about values of expressions. |
| |
| With @option{-fbranch-probabilities}, it reads back the data gathered |
| and actually performs the optimizations based on them. |
| Currently the optimizations include specialization of division operations |
| using the knowledge about the value of the denominator. |
| |
| Enabled with @option{-fprofile-use} and @option{-fauto-profile}. |
| |
| @item -frename-registers |
| @opindex frename-registers |
| Attempt to avoid false dependencies in scheduled code by making use |
| of registers left over after register allocation. This optimization |
| most benefits processors with lots of registers. Depending on the |
| debug information format adopted by the target, however, it can |
| make debugging impossible, since variables no longer stay in |
| a ``home register''. |
| |
| Enabled by default with @option{-funroll-loops}. |
| |
| @item -fschedule-fusion |
| @opindex fschedule-fusion |
| Performs a target dependent pass over the instruction stream to schedule |
| instructions of same type together because target machine can execute them |
| more efficiently if they are adjacent to each other in the instruction flow. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -ftracer |
| @opindex ftracer |
| Perform tail duplication to enlarge superblock size. This transformation |
| simplifies the control flow of the function allowing other optimizations to do |
| a better job. |
| |
| Enabled by @option{-fprofile-use} and @option{-fauto-profile}. |
| |
| @item -funroll-loops |
| @opindex funroll-loops |
| Unroll loops whose number of iterations can be determined at compile time or |
| upon entry to the loop. @option{-funroll-loops} implies |
| @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}. |
| It also turns on complete loop peeling (i.e.@: complete removal of loops with |
| a small constant number of iterations). This option makes code larger, and may |
| or may not make it run faster. |
| |
| Enabled by @option{-fprofile-use} and @option{-fauto-profile}. |
| |
| @item -funroll-all-loops |
| @opindex funroll-all-loops |
| Unroll all loops, even if their number of iterations is uncertain when |
| the loop is entered. This usually makes programs run more slowly. |
| @option{-funroll-all-loops} implies the same options as |
| @option{-funroll-loops}. |
| |
| @item -fpeel-loops |
| @opindex fpeel-loops |
| Peels loops for which there is enough information that they do not |
| roll much (from profile feedback or static analysis). It also turns on |
| complete loop peeling (i.e.@: complete removal of loops with small constant |
| number of iterations). |
| |
| Enabled by @option{-O3}, @option{-fprofile-use}, and @option{-fauto-profile}. |
| |
| @item -fmove-loop-invariants |
| @opindex fmove-loop-invariants |
| Enables the loop invariant motion pass in the RTL loop optimizer. Enabled |
| at level @option{-O1} and higher, except for @option{-Og}. |
| |
| @item -fmove-loop-stores |
| @opindex fmove-loop-stores |
| Enables the loop store motion pass in the GIMPLE loop optimizer. This |
| moves invariant stores to after the end of the loop in exchange for |
| carrying the stored value in a register across the iteration. |
| Note for this option to have an effect @option{-ftree-loop-im} has to |
| be enabled as well. Enabled at level @option{-O1} and higher, except |
| for @option{-Og}. |
| |
| @item -fsplit-loops |
| @opindex fsplit-loops |
| Split a loop into two if it contains a condition that's always true |
| for one side of the iteration space and false for the other. |
| |
| Enabled by @option{-fprofile-use} and @option{-fauto-profile}. |
| |
| @item -funswitch-loops |
| @opindex funswitch-loops |
| Move branches with loop invariant conditions out of the loop, with duplicates |
| of the loop on both branches (modified according to result of the condition). |
| |
| Enabled by @option{-fprofile-use} and @option{-fauto-profile}. |
| |
| @item -fversion-loops-for-strides |
| @opindex fversion-loops-for-strides |
| If a loop iterates over an array with a variable stride, create another |
| version of the loop that assumes the stride is always one. For example: |
| |
| @smallexample |
| for (int i = 0; i < n; ++i) |
| x[i * stride] = @dots{}; |
| @end smallexample |
| |
| becomes: |
| |
| @smallexample |
| if (stride == 1) |
| for (int i = 0; i < n; ++i) |
| x[i] = @dots{}; |
| else |
| for (int i = 0; i < n; ++i) |
| x[i * stride] = @dots{}; |
| @end smallexample |
| |
| This is particularly useful for assumed-shape arrays in Fortran where |
| (for example) it allows better vectorization assuming contiguous accesses. |
| This flag is enabled by default at @option{-O3}. |
| It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. |
| |
| @item -ffunction-sections |
| @itemx -fdata-sections |
| @opindex ffunction-sections |
| @opindex fdata-sections |
| Place each function or data item into its own section in the output |
| file if the target supports arbitrary sections. The name of the |
| function or the name of the data item determines the section's name |
| in the output file. |
| |
| Use these options on systems where the linker can perform optimizations to |
| improve locality of reference in the instruction space. Most systems using the |
| ELF object format have linkers with such optimizations. On AIX, the linker |
| rearranges sections (CSECTs) based on the call graph. The performance impact |
| varies. |
| |
| Together with a linker garbage collection (linker @option{--gc-sections} |
| option) these options may lead to smaller statically-linked executables (after |
| stripping). |
| |
| On ELF/DWARF systems these options do not degenerate the quality of the debug |
| information. There could be issues with other object files/debug info formats. |
| |
| Only use these options when there are significant benefits from doing so. When |
| you specify these options, the assembler and linker create larger object and |
| executable files and are also slower. These options affect code generation. |
| They prevent optimizations by the compiler and assembler using relative |
| locations inside a translation unit since the locations are unknown until |
| link time. An example of such an optimization is relaxing calls to short call |
| instructions. |
| |
| @item -fstdarg-opt |
| @opindex fstdarg-opt |
| Optimize the prologue of variadic argument functions with respect to usage of |
| those arguments. |
| |
| @item -fsection-anchors |
| @opindex fsection-anchors |
| Try to reduce the number of symbolic address calculations by using |
| shared ``anchor'' symbols to address nearby objects. This transformation |
| can help to reduce the number of GOT entries and GOT accesses on some |
| targets. |
| |
| For example, the implementation of the following function @code{foo}: |
| |
| @smallexample |
| static int a, b, c; |
| int foo (void) @{ return a + b + c; @} |
| @end smallexample |
| |
| @noindent |
| usually calculates the addresses of all three variables, but if you |
| compile it with @option{-fsection-anchors}, it accesses the variables |
| from a common anchor point instead. The effect is similar to the |
| following pseudocode (which isn't valid C): |
| |
| @smallexample |
| int foo (void) |
| @{ |
| register int *xr = &x; |
| return xr[&a - &x] + xr[&b - &x] + xr[&c - &x]; |
| @} |
| @end smallexample |
| |
| Not all targets support this option. |
| |
| @item -fzero-call-used-regs=@var{choice} |
| @opindex fzero-call-used-regs |
| Zero call-used registers at function return to increase program |
| security by either mitigating Return-Oriented Programming (ROP) |
| attacks or preventing information leakage through registers. |
| |
| The possible values of @var{choice} are the same as for the |
| @code{zero_call_used_regs} attribute (@pxref{Function Attributes}). |
| The default is @samp{skip}. |
| |
| You can control this behavior for a specific function by using the function |
| attribute @code{zero_call_used_regs} (@pxref{Function Attributes}). |
| |
| @item --param @var{name}=@var{value} |
| @opindex param |
| In some places, GCC uses various constants to control the amount of |
| optimization that is done. For example, GCC does not inline functions |
| that contain more than a certain number of instructions. You can |
| control some of these constants on the command line using the |
| @option{--param} option. |
| |
| The names of specific parameters, and the meaning of the values, are |
| tied to the internals of the compiler, and are subject to change |
| without notice in future releases. |
| |
| In order to get minimal, maximal and default value of a parameter, |
| one can use @option{--help=param -Q} options. |
| |
| In each case, the @var{value} is an integer. The following choices |
| of @var{name} are recognized for all targets: |
| |
| @table @gcctabopt |
| @item predictable-branch-outcome |
| When branch is predicted to be taken with probability lower than this threshold |
| (in percent), then it is considered well predictable. |
| |
| @item max-rtl-if-conversion-insns |
| RTL if-conversion tries to remove conditional branches around a block and |
| replace them with conditionally executed instructions. This parameter |
| gives the maximum number of instructions in a block which should be |
| considered for if-conversion. The compiler will |
| also use other heuristics to decide whether if-conversion is likely to be |
| profitable. |
| |
| @item max-rtl-if-conversion-predictable-cost |
| RTL if-conversion will try to remove conditional branches around a block |
| and replace them with conditionally executed instructions. These parameters |
| give the maximum permissible cost for the sequence that would be generated |
| by if-conversion depending on whether the branch is statically determined |
| to be predictable or not. The units for this parameter are the same as |
| those for the GCC internal seq_cost metric. The compiler will try to |
| provide a reasonable default for this parameter using the BRANCH_COST |
| target macro. |
| |
| @item max-crossjump-edges |
| The maximum number of incoming edges to consider for cross-jumping. |
| The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in |
| the number of edges incoming to each block. Increasing values mean |
| more aggressive optimization, making the compilation time increase with |
| probably small improvement in executable size. |
| |
| @item min-crossjump-insns |
| The minimum number of instructions that must be matched at the end |
| of two blocks before cross-jumping is performed on them. This |
| value is ignored in the case where all instructions in the block being |
| cross-jumped from are matched. |
| |
| @item max-grow-copy-bb-insns |
| The maximum code size expansion factor when copying basic blocks |
| instead of jumping. The expansion is relative to a jump instruction. |
| |
| @item max-goto-duplication-insns |
| The maximum number of instructions to duplicate to a block that jumps |
| to a computed goto. To avoid @math{O(N^2)} behavior in a number of |
| passes, GCC factors computed gotos early in the compilation process, |
| and unfactors them as late as possible. Only computed jumps at the |
| end of a basic blocks with no more than max-goto-duplication-insns are |
| unfactored. |
| |
| @item max-delay-slot-insn-search |
| The maximum number of instructions to consider when looking for an |
| instruction to fill a delay slot. If more than this arbitrary number of |
| instructions are searched, the time savings from filling the delay slot |
| are minimal, so stop searching. Increasing values mean more |
| aggressive optimization, making the compilation time increase with probably |
| small improvement in execution time. |
| |
| @item max-delay-slot-live-search |
| When trying to fill delay slots, the maximum number of instructions to |
| consider when searching for a block with valid live register |
| information. Increasing this arbitrarily chosen value means more |
| aggressive optimization, increasing the compilation time. This parameter |
| should be removed when the delay slot code is rewritten to maintain the |
| control-flow graph. |
| |
| @item max-gcse-memory |
| The approximate maximum amount of memory in @code{kB} that can be allocated in |
| order to perform the global common subexpression elimination |
| optimization. If more memory than specified is required, the |
| optimization is not done. |
| |
| @item max-gcse-insertion-ratio |
| If the ratio of expression insertions to deletions is larger than this value |
| for any expression, then RTL PRE inserts or removes the expression and thus |
| leaves partially redundant computations in the instruction stream. |
| |
| @item max-pending-list-length |
| The maximum number of pending dependencies scheduling allows |
| before flushing the current state and starting over. Large functions |
| with few branches or calls can create excessively large lists which |
| needlessly consume memory and resources. |
| |
| @item max-modulo-backtrack-attempts |
| The maximum number of backtrack attempts the scheduler should make |
| when modulo scheduling a loop. Larger values can exponentially increase |
| compilation time. |
| |
| @item max-inline-functions-called-once-loop-depth |
| Maximal loop depth of a call considered by inline heuristics that tries to |
| inline all functions called once. |
| |
| @item max-inline-functions-called-once-insns |
| Maximal estimated size of functions produced while inlining functions called |
| once. |
| |
| @item max-inline-insns-single |
| Several parameters control the tree inliner used in GCC@. This number sets the |
| maximum number of instructions (counted in GCC's internal representation) in a |
| single function that the tree inliner considers for inlining. This only |
| affects functions declared inline and methods implemented in a class |
| declaration (C++). |
| |
| |
| @item max-inline-insns-auto |
| When you use @option{-finline-functions} (included in @option{-O3}), |
| a lot of functions that would otherwise not be considered for inlining |
| by the compiler are investigated. To those functions, a different |
| (more restrictive) limit compared to functions declared inline can |
| be applied (@option{--param max-inline-insns-auto}). |
| |
| @item max-inline-insns-small |
| This is bound applied to calls which are considered relevant with |
| @option{-finline-small-functions}. |
| |
| @item max-inline-insns-size |
| This is bound applied to calls which are optimized for size. Small growth |
| may be desirable to anticipate optimization oppurtunities exposed by inlining. |
| |
| @item uninlined-function-insns |
| Number of instructions accounted by inliner for function overhead such as |
| function prologue and epilogue. |
| |
| @item uninlined-function-time |
| Extra time accounted by inliner for function overhead such as time needed to |
| execute function prologue and epilogue. |
| |
| @item inline-heuristics-hint-percent |
| The scale (in percents) applied to @option{inline-insns-single}, |
| @option{inline-insns-single-O2}, @option{inline-insns-auto} |
| when inline heuristics hints that inlining is |
| very profitable (will enable later optimizations). |
| |
| @item uninlined-thunk-insns |
| @item uninlined-thunk-time |
| Same as @option{--param uninlined-function-insns} and |
| @option{--param uninlined-function-time} but applied to function thunks. |
| |
| @item inline-min-speedup |
| When estimated performance improvement of caller + callee runtime exceeds this |
| threshold (in percent), the function can be inlined regardless of the limit on |
| @option{--param max-inline-insns-single} and @option{--param |
| max-inline-insns-auto}. |
| |
| @item large-function-insns |
| The limit specifying really large functions. For functions larger than this |
| limit after inlining, inlining is constrained by |
| @option{--param large-function-growth}. This parameter is useful primarily |
| to avoid extreme compilation time caused by non-linear algorithms used by the |
| back end. |
| |
| @item large-function-growth |
| Specifies maximal growth of large function caused by inlining in percents. |
| For example, parameter value 100 limits large function growth to 2.0 times |
| the original size. |
| |
| @item large-unit-insns |
| The limit specifying large translation unit. Growth caused by inlining of |
| units larger than this limit is limited by @option{--param inline-unit-growth}. |
| For small units this might be too tight. |
| For example, consider a unit consisting of function A |
| that is inline and B that just calls A three times. If B is small relative to |
| A, the growth of unit is 300\% and yet such inlining is very sane. For very |
| large units consisting of small inlineable functions, however, the overall unit |
| growth limit is needed to avoid exponential explosion of code size. Thus for |
| smaller units, the size is increased to @option{--param large-unit-insns} |
| before applying @option{--param inline-unit-growth}. |
| |
| @item lazy-modules |
| Maximum number of concurrently open C++ module files when lazy loading. |
| |
| @item inline-unit-growth |
| Specifies maximal overall growth of the compilation unit caused by inlining. |
| For example, parameter value 20 limits unit growth to 1.2 times the original |
| size. Cold functions (either marked cold via an attribute or by profile |
| feedback) are not accounted into the unit size. |
| |
| @item ipa-cp-unit-growth |
| Specifies maximal overall growth of the compilation unit caused by |
| interprocedural constant propagation. For example, parameter value 10 limits |
| unit growth to 1.1 times the original size. |
| |
| @item ipa-cp-large-unit-insns |
| The size of translation unit that IPA-CP pass considers large. |
| |
| @item large-stack-frame |
| The limit specifying large stack frames. While inlining the algorithm is trying |
| to not grow past this limit too much. |
| |
| @item large-stack-frame-growth |
| Specifies maximal growth of large stack frames caused by inlining in percents. |
| For example, parameter value 1000 limits large stack frame growth to 11 times |
| the original size. |
| |
| @item max-inline-insns-recursive |
| @itemx max-inline-insns-recursive-auto |
| Specifies the maximum number of instructions an out-of-line copy of a |
| self-recursive inline |
| function can grow into by performing recursive inlining. |
| |
| @option{--param max-inline-insns-recursive} applies to functions |
| declared inline. |
| For functions not declared inline, recursive inlining |
| happens only when @option{-finline-functions} (included in @option{-O3}) is |
| enabled; @option{--param max-inline-insns-recursive-auto} applies instead. |
| |
| @item max-inline-recursive-depth |
| @itemx max-inline-recursive-depth-auto |
| Specifies the maximum recursion depth used for recursive inlining. |
| |
| @option{--param max-inline-recursive-depth} applies to functions |
| declared inline. For functions not declared inline, recursive inlining |
| happens only when @option{-finline-functions} (included in @option{-O3}) is |
| enabled; @option{--param max-inline-recursive-depth-auto} applies instead. |
| |
| @item min-inline-recursive-probability |
| Recursive inlining is profitable only for function having deep recursion |
| in average and can hurt for function having little recursion depth by |
| increasing the prologue size or complexity of function body to other |
| optimizers. |
| |
| When profile feedback is available (see @option{-fprofile-generate}) the actual |
| recursion depth can be guessed from the probability that function recurses |
| via a given call expression. This parameter limits inlining only to call |
| expressions whose probability exceeds the given threshold (in percents). |
| |
| @item early-inlining-insns |
| Specify growth that the early inliner can make. In effect it increases |
| the amount of inlining for code having a large abstraction penalty. |
| |
| @item max-early-inliner-iterations |
| Limit of iterations of the early inliner. This basically bounds |
| the number of nested indirect calls the early inliner can resolve. |
| Deeper chains are still handled by late inlining. |
| |
| @item comdat-sharing-probability |
| Probability (in percent) that C++ inline function with comdat visibility |
| are shared across multiple compilation units. |
| |
| @item modref-max-bases |
| @item modref-max-refs |
| @item modref-max-accesses |
| Specifies the maximal number of base pointers, references and accesses stored |
| for a single function by mod/ref analysis. |
| |
| @item modref-max-tests |
| Specifies the maxmal number of tests alias oracle can perform to disambiguate |
| memory locations using the mod/ref information. This parameter ought to be |
| bigger than @option{--param modref-max-bases} and @option{--param |
| modref-max-refs}. |
| |
| @item modref-max-depth |
| Specifies the maximum depth of DFS walk used by modref escape analysis. |
| Setting to 0 disables the analysis completely. |
| |
| @item modref-max-escape-points |
| Specifies the maximum number of escape points tracked by modref per SSA-name. |
| |
| @item modref-max-adjustments |
| Specifies the maximum number the access range is enlarged during modref dataflow |
| analysis. |
| |
| @item profile-func-internal-id |
| A parameter to control whether to use function internal id in profile |
| database lookup. If the value is 0, the compiler uses an id that |
| is based on function assembler name and filename, which makes old profile |
| data more tolerant to source changes such as function reordering etc. |
| |
| @item min-vect-loop-bound |
| The minimum number of iterations under which loops are not vectorized |
| when @option{-ftree-vectorize} is used. The number of iterations after |
| vectorization needs to be greater than the value specified by this option |
| to allow vectorization. |
| |
| @item gcse-cost-distance-ratio |
| Scaling factor in calculation of maximum distance an expression |
| can be moved by GCSE optimizations. This is currently supported only in the |
| code hoisting pass. The bigger the ratio, the more aggressive code hoisting |
| is with simple expressions, i.e., the expressions that have cost |
| less than @option{gcse-unrestricted-cost}. Specifying 0 disables |
| hoisting of simple expressions. |
| |
| @item gcse-unrestricted-cost |
| Cost, roughly measured as the cost of a single typical machine |
| instruction, at which GCSE optimizations do not constrain |
| the distance an expression can travel. This is currently |
| supported only in the code hoisting pass. The lesser the cost, |
| the more aggressive code hoisting is. Specifying 0 |
| allows all expressions to travel unrestricted distances. |
| |
| @item max-hoist-depth |
| The depth of search in the dominator tree for expressions to hoist. |
| This is used to avoid quadratic behavior in hoisting algorithm. |
| The value of 0 does not limit on the search, but may slow down compilation |
| of huge functions. |
| |
| @item max-tail-merge-comparisons |
| The maximum amount of similar bbs to compare a bb with. This is used to |
| avoid quadratic behavior in tree tail merging. |
| |
| @item max-tail-merge-iterations |
| The maximum amount of iterations of the pass over the function. This is used to |
| limit compilation time in tree tail merging. |
| |
| @item store-merging-allow-unaligned |
| Allow the store merging pass to introduce unaligned stores if it is legal to |
| do so. |
| |
| @item max-stores-to-merge |
| The maximum number of stores to attempt to merge into wider stores in the store |
| merging pass. |
| |
| @item max-store-chains-to-track |
| The maximum number of store chains to track at the same time in the attempt |
| to merge them into wider stores in the store merging pass. |
| |
| @item max-stores-to-track |
| The maximum number of stores to track at the same time in the attemt to |
| to merge them into wider stores in the store merging pass. |
| |
| @item max-unrolled-insns |
| The maximum number of instructions that a loop may have to be unrolled. |
| If a loop is unrolled, this parameter also determines how many times |
| the loop code is unrolled. |
| |
| @item max-average-unrolled-insns |
| The maximum number of instructions biased by probabilities of their execution |
| that a loop may have to be unrolled. If a loop is unrolled, |
| this parameter also determines how many times the loop code is unrolled. |
| |
| @item max-unroll-times |
| The maximum number of unrollings of a single loop. |
| |
| @item max-peeled-insns |
| The maximum number of instructions that a loop may have to be peeled. |
| If a loop is peeled, this parameter also determines how many times |
| the loop code is peeled. |
| |
| @item max-peel-times |
| The maximum number of peelings of a single loop. |
| |
| @item max-peel-branches |
| The maximum number of branches on the hot path through the peeled sequence. |
| |
| @item max-completely-peeled-insns |
| The maximum number of insns of a completely peeled loop. |
| |
| @item max-completely-peel-times |
| The maximum number of iterations of a loop to be suitable for complete peeling. |
| |
| @item max-completely-peel-loop-nest-depth |
| The maximum depth of a loop nest suitable for complete peeling. |
| |
| @item max-unswitch-insns |
| The maximum number of insns of an unswitched loop. |
| |
| @item max-unswitch-level |
| The maximum number of branches unswitched in a single loop. |
| |
| @item lim-expensive |
| The minimum cost of an expensive expression in the loop invariant motion. |
| |
| @item min-loop-cond-split-prob |
| When FDO profile information is available, @option{min-loop-cond-split-prob} |
| specifies minimum threshold for probability of semi-invariant condition |
| statement to trigger loop split. |
| |
| @item iv-consider-all-candidates-bound |
| Bound on number of candidates for induction variables, below which |
| all candidates are considered for each use in induction variable |
| optimizations. If there are more candidates than this, |
| only the most relevant ones are considered to avoid quadratic time complexity. |
| |
| @item iv-max-considered-uses |
| The induction variable optimizations give up on loops that contain more |
| induction variable uses. |
| |
| @item iv-always-prune-cand-set-bound |
| If the number of candidates in the set is smaller than this value, |
| always try to remove unnecessary ivs from the set |
| when adding a new one. |
| |
| @item avg-loop-niter |
| Average number of iterations of a loop. |
| |
| @item dse-max-object-size |
| Maximum size (in bytes) of objects tracked bytewise by dead store elimination. |
| Larger values may result in larger compilation times. |
| |
| @item dse-max-alias-queries-per-store |
| Maximum number of queries into the alias oracle per store. |
| Larger values result in larger compilation times and may result in more |
| removed dead stores. |
| |
| @item scev-max-expr-size |
| Bound on size of expressions used in the scalar evolutions analyzer. |
| Large expressions slow the analyzer. |
| |
| @item scev-max-expr-complexity |
| Bound on the complexity of the expressions in the scalar evolutions analyzer. |
| Complex expressions slow the analyzer. |
| |
| @item max-tree-if-conversion-phi-args |
| Maximum number of arguments in a PHI supported by TREE if conversion |
| unless the loop is marked with simd pragma. |
| |
| @item vect-max-version-for-alignment-checks |
| The maximum number of run-time checks that can be performed when |
| doing loop versioning for alignment in the vectorizer. |
| |
| @item vect-max-version-for-alias-checks |
| The maximum number of run-time checks that can be performed when |
| doing loop versioning for alias in the vectorizer. |
| |
| @item vect-max-peeling-for-alignment |
| The maximum number of loop peels to enhance access alignment |
| for vectorizer. Value -1 means no limit. |
| |
| @item max-iterations-to-track |
| The maximum number of iterations of a loop the brute-force algorithm |
| for analysis of the number of iterations of the loop tries to evaluate. |
| |
| @item hot-bb-count-fraction |
| The denominator n of fraction 1/n of the maximal execution count of a |
| basic block in the entire program that a basic block needs to at least |
| have in order to be considered hot. The default is 10000, which means |
| that a basic block is considered hot if its execution count is greater |
| than 1/10000 of the maximal execution count. 0 means that it is never |
| considered hot. Used in non-LTO mode. |
| |
| @item hot-bb-count-ws-permille |
| The number of most executed permilles, ranging from 0 to 1000, of the |
| profiled execution of the entire program to which the execution count |
| of a basic block must be part of in order to be considered hot. The |
| default is 990, which means that a basic block is considered hot if |
| its execution count contributes to the upper 990 permilles, or 99.0%, |
| of the profiled execution of the entire program. 0 means that it is |
| never considered hot. Used in LTO mode. |
| |
| @item hot-bb-frequency-fraction |
| The denominator n of fraction 1/n of the execution frequency of the |
| entry block of a function that a basic block of this function needs |
| to at least have in order to be considered hot. The default is 1000, |
| which means that a basic block is considered hot in a function if it |
| is executed more frequently than 1/1000 of the frequency of the entry |
| block of the function. 0 means that it is never considered hot. |
| |
| @item unlikely-bb-count-fraction |
| The denominator n of fraction 1/n of the number of profiled runs of |
| the entire program below which the execution count of a basic block |
| must be in order for the basic block to be considered unlikely executed. |
| The default is 20, which means that a basic block is considered unlikely |
| executed if it is executed in fewer than 1/20, or 5%, of the runs of |
| the program. 0 means that it is always considered unlikely executed. |
| |
| @item max-predicted-iterations |
| The maximum number of loop iterations we predict statically. This is useful |
| in cases where a function contains a single loop with known bound and |
| another loop with unknown bound. |
| The known number of iterations is predicted correctly, while |
| the unknown number of iterations average to roughly 10. This means that the |
| loop without bounds appears artificially cold relative to the other one. |
| |
| @item builtin-expect-probability |
| Control the probability of the expression having the specified value. This |
| parameter takes a percentage (i.e.@: 0 ... 100) as input. |
| |
| @item builtin-string-cmp-inline-length |
| The maximum length of a constant string for a builtin string cmp call |
| eligible for inlining. |
| |
| @item align-threshold |
| |
| Select fraction of the maximal frequency of executions of a basic block in |
| a function to align the basic block. |
| |
| @item align-loop-iterations |
| |
| A loop expected to iterate at least the selected number of iterations is |
| aligned. |
| |
| @item tracer-dynamic-coverage |
| @itemx tracer-dynamic-coverage-feedback |
| |
| This value is used to limit superblock formation once the given percentage of |
| executed instructions is covered. This limits unnecessary code size |
| expansion. |
| |
| The @option{tracer-dynamic-coverage-feedback} parameter |
| is used only when profile |
| feedback is available. The real profiles (as opposed to statically estimated |
| ones) are much less balanced allowing the threshold to be larger value. |
| |
| @item tracer-max-code-growth |
| Stop tail duplication once code growth has reached given percentage. This is |
| a rather artificial limit, as most of the duplicates are eliminated later in |
| cross jumping, so it may be set to much higher values than is the desired code |
| growth. |
| |
| @item tracer-min-branch-ratio |
| |
| Stop reverse growth when the reverse probability of best edge is less than this |
| threshold (in percent). |
| |
| @item tracer-min-branch-probability |
| @itemx tracer-min-branch-probability-feedback |
| |
| Stop forward growth if the best edge has probability lower than this |
| threshold. |
| |
| Similarly to @option{tracer-dynamic-coverage} two parameters are |
| provided. @option{tracer-min-branch-probability-feedback} is used for |
| compilation with profile feedback and @option{tracer-min-branch-probability} |
| compilation without. The value for compilation with profile feedback |
| needs to be more conservative (higher) in order to make tracer |
| effective. |
| |
| @item stack-clash-protection-guard-size |
| Specify the size of the operating system provided stack guard as |
| 2 raised to @var{num} bytes. Higher values may reduce the |
| number of explicit probes, but a value larger than the operating system |
| provided guard will leave code vulnerable to stack clash style attacks. |
| |
| @item stack-clash-protection-probe-interval |
| Stack clash protection involves probing stack space as it is allocated. This |
| param controls the maximum distance between probes into the stack as 2 raised |
| to @var{num} bytes. Higher values may reduce the number of explicit probes, but a value |
| larger than the operating system provided guard will leave code vulnerable to |
| stack clash style attacks. |
| |
| @item max-cse-path-length |
| |
| The maximum number of basic blocks on path that CSE considers. |
| |
| @item max-cse-insns |
| The maximum number of instructions CSE processes before flushing. |
| |
| @item ggc-min-expand |
| |
| GCC uses a garbage collector to manage its own memory allocation. This |
| parameter specifies the minimum percentage by which the garbage |
| collector's heap should be allowed to expand between collections. |
| Tuning this may improve compilation speed; it has no effect on code |
| generation. |
| |
| The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when |
| RAM >= 1GB@. If @code{getrlimit} is available, the notion of ``RAM'' is |
| the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If |
| GCC is not able to calculate RAM on a particular platform, the lower |
| bound of 30% is used. Setting this parameter and |
| @option{ggc-min-heapsize} to zero causes a full collection to occur at |
| every opportunity. This is extremely slow, but can be useful for |
| debugging. |
| |
| @item ggc-min-heapsize |
| |
| Minimum size of the garbage collector's heap before it begins bothering |
| to collect garbage. The first collection occurs after the heap expands |
| by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again, |
| tuning this may improve compilation speed, and has no effect on code |
| generation. |
| |
| The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that |
| tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but |
| with a lower bound of 4096 (four megabytes) and an upper bound of |
| 131072 (128 megabytes). If GCC is not able to calculate RAM on a |
| particular platform, the lower bound is used. Setting this parameter |
| very large effectively disables garbage collection. Setting this |
| parameter and @option{ggc-min-expand} to zero causes a full collection |
| to occur at every opportunity. |
| |
| @item max-reload-search-insns |
| The maximum number of instruction reload should look backward for equivalent |
| register. Increasing values mean more aggressive optimization, making the |
| compilation time increase with probably slightly better performance. |
| |
| @item max-cselib-memory-locations |
| The maximum number of memory locations cselib should take into account. |
| Increasing values mean more aggressive optimization, making the compilation time |
| increase with probably slightly better performance. |
| |
| @item max-sched-ready-insns |
| The maximum number of instructions ready to be issued the scheduler should |
| consider at any given time during the first scheduling pass. Increasing |
| values mean more thorough searches, making the compilation time increase |
| with probably little benefit. |
| |
| @item max-sched-region-blocks |
| The maximum number of blocks in a region to be considered for |
| interblock scheduling. |
| |
| @item max-pipeline-region-blocks |
| The maximum number of blocks in a region to be considered for |
| pipelining in the selective scheduler. |
| |
| @item max-sched-region-insns |
| The maximum number of insns in a region to be considered for |
| interblock scheduling. |
| |
| @item max-pipeline-region-insns |
| The maximum number of insns in a region to be considered for |
| pipelining in the selective scheduler. |
| |
| @item min-spec-prob |
| The minimum probability (in percents) of reaching a source block |
| for interblock speculative scheduling. |
| |
| @item max-sched-extend-regions-iters |
| The maximum number of iterations through CFG to extend regions. |
| A value of 0 disables region extensions. |
| |
| @item max-sched-insn-conflict-delay |
| The maximum conflict delay for an insn to be considered for speculative motion. |
| |
| @item sched-spec-prob-cutoff |
| The minimal probability of speculation success (in percents), so that |
| speculative insns are scheduled. |
| |
| @item sched-state-edge-prob-cutoff |
| The minimum probability an edge must have for the scheduler to save its |
| state across it. |
| |
| @item sched-mem-true-dep-cost |
| Minimal distance (in CPU cycles) between store and load targeting same |
| memory locations. |
| |
| @item selsched-max-lookahead |
| The maximum size of the lookahead window of selective scheduling. It is a |
| depth of search for available instructions. |
| |
| @item selsched-max-sched-times |
| The maximum number of times that an instruction is scheduled during |
| selective scheduling. This is the limit on the number of iterations |
| through which the instruction may be pipelined. |
| |
| @item selsched-insns-to-rename |
| The maximum number of best instructions in the ready list that are considered |
| for renaming in the selective scheduler. |
| |
| @item sms-min-sc |
| The minimum value of stage count that swing modulo scheduler |
| generates. |
| |
| @item max-last-value-rtl |
| The maximum size measured as number of RTLs that can be recorded in an expression |
| in combiner for a pseudo register as last known value of that register. |
| |
| @item max-combine-insns |
| The maximum number of instructions the RTL combiner tries to combine. |
| |
| @item integer-share-limit |
| Small integer constants can use a shared data structure, reducing the |
| compiler's memory usage and increasing its speed. This sets the maximum |
| value of a shared integer constant. |
| |
| @item ssp-buffer-size |
| The minimum size of buffers (i.e.@: arrays) that receive stack smashing |
| protection when @option{-fstack-protector} is used. |
| |
| @item min-size-for-stack-sharing |
| The minimum size of variables taking part in stack slot sharing when not |
| optimizing. |
| |
| @item max-jump-thread-duplication-stmts |
| Maximum number of statements allowed in a block that needs to be |
| duplicated when threading jumps. |
| |
| @item max-fields-for-field-sensitive |
| Maximum number of fields in a structure treated in |
| a field sensitive manner during pointer analysis. |
| |
| @item prefetch-latency |
| Estimate on average number of instructions that are executed before |
| prefetch finishes. The distance prefetched ahead is proportional |
| to this constant. Increasing this number may also lead to less |
| streams being prefetched (see @option{simultaneous-prefetches}). |
| |
| @item simultaneous-prefetches |
| Maximum number of prefetches that can run at the same time. |
| |
| @item l1-cache-line-size |
| The size of cache line in L1 data cache, in bytes. |
| |
| @item l1-cache-size |
| The size of L1 data cache, in kilobytes. |
| |
| @item l2-cache-size |
| The size of L2 data cache, in kilobytes. |
| |
| @item prefetch-dynamic-strides |
| Whether the loop array prefetch pass should issue software prefetch hints |
| for strides that are non-constant. In some cases this may be |
| beneficial, though the fact the stride is non-constant may make it |
| hard to predict when there is clear benefit to issuing these hints. |
| |
| Set to 1 if the prefetch hints should be issued for non-constant |
| strides. Set to 0 if prefetch hints should be issued only for strides that |
| are known to be constant and below @option{prefetch-minimum-stride}. |
| |
| @item prefetch-minimum-stride |
| Minimum constant stride, in bytes, to start using prefetch hints for. If |
| the stride is less than this threshold, prefetch hints will not be issued. |
| |
| This setting is useful for processors that have hardware prefetchers, in |
| which case there may be conflicts between the hardware prefetchers and |
| the software prefetchers. If the hardware prefetchers have a maximum |
| stride they can handle, it should be used here to improve the use of |
| software prefetchers. |
| |
| A value of -1 means we don't have a threshold and therefore |
| prefetch hints can be issued for any constant stride. |
| |
| This setting is only useful for strides that are known and constant. |
| |
| @item destructive-interference-size |
| @item constructive-interference-size |
| The values for the C++17 variables |
| @code{std::hardware_destructive_interference_size} and |
| @code{std::hardware_constructive_interference_size}. The destructive |
| interference size is the minimum recommended offset between two |
| independent concurrently-accessed objects; the constructive |
| interference size is the maximum recommended size of contiguous memory |
| accessed together. Typically both will be the size of an L1 cache |
| line for the target, in bytes. For a generic target covering a range of L1 |
| cache line sizes, typically the constructive interference size will be |
| the small end of the range and the destructive size will be the large |
| end. |
| |
| The destructive interference size is intended to be used for layout, |
| and thus has ABI impact. The default value is not expected to be |
| stable, and on some targets varies with @option{-mtune}, so use of |
| this variable in a context where ABI stability is important, such as |
| the public interface of a library, is strongly discouraged; if it is |
| used in that context, users can stabilize the value using this |
| option. |
| |
| The constructive interference size is less sensitive, as it is |
| typically only used in a @samp{static_assert} to make sure that a type |
| fits within a cache line. |
| |
| See also @option{-Winterference-size}. |
| |
| @item loop-interchange-max-num-stmts |
| The maximum number of stmts in a loop to be interchanged. |
| |
| @item loop-interchange-stride-ratio |
| The minimum ratio between stride of two loops for interchange to be profitable. |
| |
| @item min-insn-to-prefetch-ratio |
| The minimum ratio between the number of instructions and the |
| number of prefetches to enable prefetching in a loop. |
| |
| @item prefetch-min-insn-to-mem-ratio |
| The minimum ratio between the number of instructions and the |
| number of memory references to enable prefetching in a loop. |
| |
| @item use-canonical-types |
| Whether the compiler should use the ``canonical'' type system. |
| Should always be 1, which uses a more efficient internal |
| mechanism for comparing types in C++ and Objective-C++. However, if |
| bugs in the canonical type system are causing compilation failures, |
| set this value to 0 to disable canonical types. |
| |
| @item switch-conversion-max-branch-ratio |
| Switch initialization conversion refuses to create arrays that are |
| bigger than @option{switch-conversion-max-branch-ratio} times the number of |
| branches in the switch. |
| |
| @item max-partial-antic-length |
| Maximum length of the partial antic set computed during the tree |
| partial redundancy elimination optimization (@option{-ftree-pre}) when |
| optimizing at @option{-O3} and above. For some sorts of source code |
| the enhanced partial redundancy elimination optimization can run away, |
| consuming all of the memory available on the host machine. This |
| parameter sets a limit on the length of the sets that are computed, |
| which prevents the runaway behavior. Setting a value of 0 for |
| this parameter allows an unlimited set length. |
| |
| @item rpo-vn-max-loop-depth |
| Maximum loop depth that is value-numbered optimistically. |
| When the limit hits the innermost |
| @var{rpo-vn-max-loop-depth} loops and the outermost loop in the |
| loop nest are value-numbered optimistically and the remaining ones not. |
| |
| @item sccvn-max-alias-queries-per-access |
| Maximum number of alias-oracle queries we perform when looking for |
| redundancies for loads and stores. If this limit is hit the search |
| is aborted and the load or store is not considered redundant. The |
| number of queries is algorithmically limited to the number of |
| stores on all paths from the load to the function entry. |
| |
| @item ira-max-loops-num |
| IRA uses regional register allocation by default. If a function |
| contains more loops than the number given by this parameter, only at most |
| the given number of the most frequently-executed loops form regions |
| for regional register allocation. |
| |
| @item ira-max-conflict-table-size |
| Although IRA uses a sophisticated algorithm to compress the conflict |
| table, the table can still require excessive amounts of memory for |
| huge functions. If the conflict table for a function could be more |
| than the size in MB given by this parameter, the register allocator |
| instead uses a faster, simpler, and lower-quality |
| algorithm that does not require building a pseudo-register conflict table. |
| |
| @item ira-loop-reserved-regs |
| IRA can be used to evaluate more accurate register pressure in loops |
| for decisions to move loop invariants (see @option{-O3}). The number |
| of available registers reserved for some other purposes is given |
| by this parameter. Default of the parameter |
| is the best found from numerous experiments. |
| |
| @item ira-consider-dup-in-all-alts |
| Make IRA to consider matching constraint (duplicated operand number) |
| heavily in all available alternatives for preferred register class. |
| If it is set as zero, it means IRA only respects the matching |
| constraint when it's in the only available alternative with an |
| appropriate register class. Otherwise, it means IRA will check all |
| available alternatives for preferred register class even if it has |
| found some choice with an appropriate register class and respect the |
| found qualified matching constraint. |
| |
| @item lra-inheritance-ebb-probability-cutoff |
| LRA tries to reuse values reloaded in registers in subsequent insns. |
| This optimization is called inheritance. EBB is used as a region to |
| do this optimization. The parameter defines a minimal fall-through |
| edge probability in percentage used to add BB to inheritance EBB in |
| LRA. The default value was chosen |
| from numerous runs of SPEC2000 on x86-64. |
| |
| @item loop-invariant-max-bbs-in-loop |
| Loop invariant motion can be very expensive, both in compilation time and |
| in amount of needed compile-time memory, with very large loops. Loops |
| with more basic blocks than this parameter won't have loop invariant |
| motion optimization performed on them. |
| |
| @item loop-max-datarefs-for-datadeps |
| Building data dependencies is expensive for very large loops. This |
| parameter limits the number of data references in loops that are |
| considered for data dependence analysis. These large loops are no |
| handled by the optimizations using loop data dependencies. |
| |
| @item max-vartrack-size |
| Sets a maximum number of hash table slots to use during variable |
| tracking dataflow analysis of any function. If this limit is exceeded |
| with variable tracking at assignments enabled, analysis for that |
| function is retried without it, after removing all debug insns from |
| the function. If the limit is exceeded even without debug insns, var |
| tracking analysis is completely disabled for the function. Setting |
| the parameter to zero makes it unlimited. |
| |
| @item max-vartrack-expr-depth |
| Sets a maximum number of recursion levels when attempting to map |
| variable names or debug temporaries to value expressions. This trades |
| compilation time for more complete debug information. If this is set too |
| low, value expressions that are available and could be represented in |
| debug information may end up not being used; setting this higher may |
| enable the compiler to find more complex debug expressions, but compile |
| time and memory use may grow. |
| |
| @item max-debug-marker-count |
| Sets a threshold on the number of debug markers (e.g.@: begin stmt |
| markers) to avoid complexity explosion at inlining or expanding to RTL. |
| If a function has more such gimple stmts than the set limit, such stmts |
| will be dropped from the inlined copy of a function, and from its RTL |
| expansion. |
| |
| @item min-nondebug-insn-uid |
| Use uids starting at this parameter for nondebug insns. The range below |
| the parameter is reserved exclusively for debug insns created by |
| @option{-fvar-tracking-assignments}, but debug insns may get |
| (non-overlapping) uids above it if the reserved range is exhausted. |
| |
| @item ipa-sra-ptr-growth-factor |
| IPA-SRA replaces a pointer to an aggregate with one or more new |
| parameters only when their cumulative size is less or equal to |
| @option{ipa-sra-ptr-growth-factor} times the size of the original |
| pointer parameter. |
| |
| @item ipa-sra-max-replacements |
| Maximum pieces of an aggregate that IPA-SRA tracks. As a |
| consequence, it is also the maximum number of replacements of a formal |
| parameter. |
| |
| @item sra-max-scalarization-size-Ospeed |
| @itemx sra-max-scalarization-size-Osize |
| The two Scalar Reduction of Aggregates passes (SRA and IPA-SRA) aim to |
| replace scalar parts of aggregates with uses of independent scalar |
| variables. These parameters control the maximum size, in storage units, |
| of aggregate which is considered for replacement when compiling for |
| speed |
| (@option{sra-max-scalarization-size-Ospeed}) or size |
| (@option{sra-max-scalarization-size-Osize}) respectively. |
| |
| @item sra-max-propagations |
| The maximum number of artificial accesses that Scalar Replacement of |
| Aggregates (SRA) will track, per one local variable, in order to |
| facilitate copy propagation. |
| |
| @item tm-max-aggregate-size |
| When making copies of thread-local variables in a transaction, this |
| parameter specifies the size in bytes after which variables are |
| saved with the logging functions as opposed to save/restore code |
| sequence pairs. This option only applies when using |
| @option{-fgnu-tm}. |
| |
| @item graphite-max-nb-scop-params |
| To avoid exponential effects in the Graphite loop transforms, the |
| number of parameters in a Static Control Part (SCoP) is bounded. |
| A value of zero can be used to lift |
| the bound. A variable whose value is unknown at compilation time and |
| defined outside a SCoP is a parameter of the SCoP. |
| |
| @item loop-block-tile-size |
| Loop blocking or strip mining transforms, enabled with |
| @option{-floop-block} or @option{-floop-strip-mine}, strip mine each |
| loop in the loop nest by a given number of iterations. The strip |
| length can be changed using the @option{loop-block-tile-size} |
| parameter. |
| |
| @item ipa-jump-function-lookups |
| Specifies number of statements visited during jump function offset discovery. |
| |
| @item ipa-cp-value-list-size |
| IPA-CP attempts to track all possible values and types passed to a function's |
| parameter in order to propagate them and perform devirtualization. |
| @option{ipa-cp-value-list-size} is the maximum number of values and types it |
| stores per one formal parameter of a function. |
| |
| @item ipa-cp-eval-threshold |
| IPA-CP calculates its own score of cloning profitability heuristics |
| and performs those cloning opportunities with scores that exceed |
| @option{ipa-cp-eval-threshold}. |
| |
| @item ipa-cp-max-recursive-depth |
| Maximum depth of recursive cloning for self-recursive function. |
| |
| @item ipa-cp-min-recursive-probability |
| Recursive cloning only when the probability of call being executed exceeds |
| the parameter. |
| |
| @item ipa-cp-profile-count-base |
| When using @option{-fprofile-use} option, IPA-CP will consider the measured |
| execution count of a call graph edge at this percentage position in their |
| histogram as the basis for its heuristics calculation. |
| |
| @item ipa-cp-recursive-freq-factor |
| The number of times interprocedural copy propagation expects recursive |
| functions to call themselves. |
| |
| @item ipa-cp-recursion-penalty |
| Percentage penalty the recursive functions will receive when they |
| are evaluated for cloning. |
| |
| @item ipa-cp-single-call-penalty |
| Percentage penalty functions containing a single call to another |
| function will receive when they are evaluated for cloning. |
| |
| @item ipa-max-agg-items |
| IPA-CP is also capable to propagate a number of scalar values passed |
| in an aggregate. @option{ipa-max-agg-items} controls the maximum |
| number of such values per one parameter. |
| |
| @item ipa-cp-loop-hint-bonus |
| When IPA-CP determines that a cloning candidate would make the number |
| of iterations of a loop known, it adds a bonus of |
| @option{ipa-cp-loop-hint-bonus} to the profitability score of |
| the candidate. |
| |
| @item ipa-max-loop-predicates |
| The maximum number of different predicates IPA will use to describe when |
| loops in a function have known properties. |
| |
| @item ipa-max-aa-steps |
| During its analysis of function bodies, IPA-CP employs alias analysis |
| in order to track values pointed to by function parameters. In order |
| not spend too much time analyzing huge functions, it gives up and |
| consider all memory clobbered after examining |
| @option{ipa-max-aa-steps} statements modifying memory. |
| |
| @item ipa-max-switch-predicate-bounds |
| Maximal number of boundary endpoints of case ranges of switch statement. |
| For switch exceeding this limit, IPA-CP will not construct cloning cost |
| predicate, which is used to estimate cloning benefit, for default case |
| of the switch statement. |
| |
| @item ipa-max-param-expr-ops |
| IPA-CP will analyze conditional statement that references some function |
| parameter to estimate benefit for cloning upon certain constant value. |
| But if number of operations in a parameter expression exceeds |
| @option{ipa-max-param-expr-ops}, the expression is treated as complicated |
| one, and is not handled by IPA analysis. |
| |
| @item lto-partitions |
| Specify desired number of partitions produced during WHOPR compilation. |
| The number of partitions should exceed the number of CPUs used for compilation. |
| |
| @item lto-min-partition |
| Size of minimal partition for WHOPR (in estimated instructions). |
| This prevents expenses of splitting very small programs into too many |
| partitions. |
| |
| @item lto-max-partition |
| Size of max partition for WHOPR (in estimated instructions). |
| to provide an upper bound for individual size of partition. |
| Meant to be used only with balanced partitioning. |
| |
| @item lto-max-streaming-parallelism |
| Maximal number of parallel processes used for LTO streaming. |
| |
| @item cxx-max-namespaces-for-diagnostic-help |
| The maximum number of namespaces to consult for suggestions when C++ |
| name lookup fails for an identifier. |
| |
| @item sink-frequency-threshold |
| The maximum relative execution frequency (in percents) of the target block |
| relative to a statement's original block to allow statement sinking of a |
| statement. Larger numbers result in more aggressive statement sinking. |
| A small positive adjustment is applied for |
| statements with memory operands as those are even more profitable so sink. |
| |
| @item max-stores-to-sink |
| The maximum number of conditional store pairs that can be sunk. Set to 0 |
| if either vectorization (@option{-ftree-vectorize}) or if-conversion |
| (@option{-ftree-loop-if-convert}) is disabled. |
| |
| @item case-values-threshold |
| The smallest number of different values for which it is best to use a |
| jump-table instead of a tree of conditional branches. If the value is |
| 0, use the default for the machine. |
| |
| @item jump-table-max-growth-ratio-for-size |
| The maximum code size growth ratio when expanding |
| into a jump table (in percent). The parameter is used when |
| optimizing for size. |
| |
| @item jump-table-max-growth-ratio-for-speed |
| The maximum code size growth ratio when expanding |
| into a jump table (in percent). The parameter is used when |
| optimizing for speed. |
| |
| @item tree-reassoc-width |
| Set the maximum number of instructions executed in parallel in |
| reassociated tree. This parameter overrides target dependent |
| heuristics used by default if has non zero value. |
| |
| @item sched-pressure-algorithm |
| Choose between the two available implementations of |
| @option{-fsched-pressure}. Algorithm 1 is the original implementation |
| and is the more likely to prevent instructions from being reordered. |
| Algorithm 2 was designed to be a compromise between the relatively |
| conservative approach taken by algorithm 1 and the rather aggressive |
| approach taken by the default scheduler. It relies more heavily on |
| having a regular register file and accurate register pressure classes. |
| See @file{haifa-sched.cc} in the GCC sources for more details. |
| |
| The default choice depends on the target. |
| |
| @item max-slsr-cand-scan |
| Set the maximum number of existing candidates that are considered when |
| seeking a basis for a new straight-line strength reduction candidate. |
| |
| @item asan-globals |
| Enable buffer overflow detection for global objects. This kind |
| of protection is enabled by default if you are using |
| @option{-fsanitize=address} option. |
| To disable global objects protection use @option{--param asan-globals=0}. |
| |
| @item asan-stack |
| Enable buffer overflow detection for stack objects. This kind of |
| protection is enabled by default when using @option{-fsanitize=address}. |
| To disable stack protection use @option{--param asan-stack=0} option. |
| |
| @item asan-instrument-reads |
| Enable buffer overflow detection for memory reads. This kind of |
| protection is enabled by default when using @option{-fsanitize=address}. |
| To disable memory reads protection use |
| @option{--param asan-instrument-reads=0}. |
| |
| @item asan-instrument-writes |
| Enable buffer overflow detection for memory writes. This kind of |
| protection is enabled by default when using @option{-fsanitize=address}. |
| To disable memory writes protection use |
| @option{--param asan-instrument-writes=0} option. |
| |
| @item asan-memintrin |
| Enable detection for built-in functions. This kind of protection |
| is enabled by default when using @option{-fsanitize=address}. |
| To disable built-in functions protection use |
| @option{--param asan-memintrin=0}. |
| |
| @item asan-use-after-return |
| Enable detection of use-after-return. This kind of protection |
| is enabled by default when using the @option{-fsanitize=address} option. |
| To disable it use @option{--param asan-use-after-return=0}. |
| |
| Note: By default the check is disabled at run time. To enable it, |
| add @code{detect_stack_use_after_return=1} to the environment variable |
| @env{ASAN_OPTIONS}. |
| |
| @item asan-instrumentation-with-call-threshold |
| If number of memory accesses in function being instrumented |
| is greater or equal to this number, use callbacks instead of inline checks. |
| E.g. to disable inline code use |
| @option{--param asan-instrumentation-with-call-threshold=0}. |
| |
| @item hwasan-instrument-stack |
| Enable hwasan instrumentation of statically sized stack-allocated variables. |
| This kind of instrumentation is enabled by default when using |
| @option{-fsanitize=hwaddress} and disabled by default when using |
| @option{-fsanitize=kernel-hwaddress}. |
| To disable stack instrumentation use |
| @option{--param hwasan-instrument-stack=0}, and to enable it use |
| @option{--param hwasan-instrument-stack=1}. |
| |
| @item hwasan-random-frame-tag |
| When using stack instrumentation, decide tags for stack variables using a |
| deterministic sequence beginning at a random tag for each frame. With this |
| parameter unset tags are chosen using the same sequence but beginning from 1. |
| This is enabled by default for @option{-fsanitize=hwaddress} and unavailable |
| for @option{-fsanitize=kernel-hwaddress}. |
| To disable it use @option{--param hwasan-random-frame-tag=0}. |
| |
| @item hwasan-instrument-allocas |
| Enable hwasan instrumentation of dynamically sized stack-allocated variables. |
| This kind of instrumentation is enabled by default when using |
| @option{-fsanitize=hwaddress} and disabled by default when using |
| @option{-fsanitize=kernel-hwaddress}. |
| To disable instrumentation of such variables use |
| @option{--param hwasan-instrument-allocas=0}, and to enable it use |
| @option{--param hwasan-instrument-allocas=1}. |
| |
| @item hwasan-instrument-reads |
| Enable hwasan checks on memory reads. Instrumentation of reads is enabled by |
| default for both @option{-fsanitize=hwaddress} and |
| @option{-fsanitize=kernel-hwaddress}. |
| To disable checking memory reads use |
| @option{--param hwasan-instrument-reads=0}. |
| |
| @item hwasan-instrument-writes |
| Enable hwasan checks on memory writes. Instrumentation of writes is enabled by |
| default for both @option{-fsanitize=hwaddress} and |
| @option{-fsanitize=kernel-hwaddress}. |
| To disable checking memory writes use |
| @option{--param hwasan-instrument-writes=0}. |
| |
| @item hwasan-instrument-mem-intrinsics |
| Enable hwasan instrumentation of builtin functions. Instrumentation of these |
| builtin functions is enabled by default for both @option{-fsanitize=hwaddress} |
| and @option{-fsanitize=kernel-hwaddress}. |
| To disable instrumentation of builtin functions use |
| @option{--param hwasan-instrument-mem-intrinsics=0}. |
| |
| @item use-after-scope-direct-emission-threshold |
| If the size of a local variable in bytes is smaller or equal to this |
| number, directly poison (or unpoison) shadow memory instead of using |
| run-time callbacks. |
| |
| @item tsan-distinguish-volatile |
| Emit special instrumentation for accesses to volatiles. |
| |
| @item tsan-instrument-func-entry-exit |
| Emit instrumentation calls to __tsan_func_entry() and __tsan_func_exit(). |
| |
| @item max-fsm-thread-path-insns |
| Maximum number of instructions to copy when duplicating blocks on a |
| finite state automaton jump thread path. |
| |
| @item max-fsm-thread-length |
| Maximum number of basic blocks on a jump thread path. |
| |
| @item threader-debug |
| threader-debug=[none|all] Enables verbose dumping of the threader solver. |
| |
| @item parloops-chunk-size |
| Chunk size of omp schedule for loops parallelized by parloops. |
| |
| @item parloops-schedule |
| Schedule type of omp schedule for loops parallelized by parloops (static, |
| dynamic, guided, auto, runtime). |
| |
| @item parloops-min-per-thread |
| The minimum number of iterations per thread of an innermost parallelized |
| loop for which the parallelized variant is preferred over the single threaded |
| one. Note that for a parallelized loop nest the |
| minimum number of iterations of the outermost loop per thread is two. |
| |
| @item max-ssa-name-query-depth |
| Maximum depth of recursion when querying properties of SSA names in things |
| like fold routines. One level of recursion corresponds to following a |
| use-def chain. |
| |
| @item max-speculative-devirt-maydefs |
| The maximum number of may-defs we analyze when looking for a must-def |
| specifying the dynamic type of an object that invokes a virtual call |
| we may be able to devirtualize speculatively. |
| |
| @item max-vrp-switch-assertions |
| The maximum number of assertions to add along the default edge of a switch |
| statement during VRP. |
| |
| @item evrp-sparse-threshold |
| Maximum number of basic blocks before EVRP uses a sparse cache. |
| |
| @item evrp-mode |
| Specifies the mode Early VRP should operate in. |
| |
| @item vrp1-mode |
| Specifies the mode VRP pass 1 should operate in. |
| |
| @item vrp2-mode |
| Specifies the mode VRP pass 2 should operate in. |
| |
| @item ranger-debug |
| Specifies the type of debug output to be issued for ranges. |
| |
| @item evrp-switch-limit |
| Specifies the maximum number of switch cases before EVRP ignores a switch. |
| |
| @item unroll-jam-min-percent |
| The minimum percentage of memory references that must be optimized |
| away for the unroll-and-jam transformation to be considered profitable. |
| |
| @item unroll-jam-max-unroll |
| The maximum number of times the outer loop should be unrolled by |
| the unroll-and-jam transformation. |
| |
| @item max-rtl-if-conversion-unpredictable-cost |
| Maximum permissible cost for the sequence that would be generated |
| by the RTL if-conversion pass for a branch that is considered unpredictable. |
| |
| @item max-variable-expansions-in-unroller |
| If @option{-fvariable-expansion-in-unroller} is used, the maximum number |
| of times that an individual variable will be expanded during loop unrolling. |
| |
| @item partial-inlining-entry-probability |
| Maximum probability of the entry BB of split region |
| (in percent relative to entry BB of the function) |
| to make partial inlining happen. |
| |
| @item max-tracked-strlens |
| Maximum number of strings for which strlen optimization pass will |
| track string lengths. |
| |
| @item gcse-after-reload-partial-fraction |
| The threshold ratio for performing partial redundancy |
| elimination after reload. |
| |
| @item gcse-after-reload-critical-fraction |
| The threshold ratio of critical edges execution count that |
| permit performing redundancy elimination after reload. |
| |
| @item max-loop-header-insns |
| The maximum number of insns in loop header duplicated |
| by the copy loop headers pass. |
| |
| @item vect-epilogues-nomask |
| Enable loop epilogue vectorization using smaller vector size. |
| |
| @item vect-partial-vector-usage |
| Controls when the loop vectorizer considers using partial vector loads |
| and stores as an alternative to falling back to scalar code. 0 stops |
| the vectorizer from ever using partial vector loads and stores. 1 allows |
| partial vector loads and stores if vectorization removes the need for the |
| code to iterate. 2 allows partial vector loads and stores in all loops. |
| The parameter only has an effect on targets that support partial |
| vector loads and stores. |
| |
| @item vect-inner-loop-cost-factor |
| The maximum factor which the loop vectorizer applies to the cost of statements |
| in an inner loop relative to the loop being vectorized. The factor applied |
| is the maximum of the estimated number of iterations of the inner loop and |
| this parameter. The default value of this parameter is 50. |
| |
| @item vect-induction-float |
| Enable loop vectorization of floating point inductions. |
| |
| @item avoid-fma-max-bits |
| Maximum number of bits for which we avoid creating FMAs. |
| |
| @item sms-loop-average-count-threshold |
| A threshold on the average loop count considered by the swing modulo scheduler. |
| |
| @item sms-dfa-history |
| The number of cycles the swing modulo scheduler considers when checking |
| conflicts using DFA. |
| |
| @item graphite-allow-codegen-errors |
| Whether codegen errors should be ICEs when @option{-fchecking}. |
| |
| @item sms-max-ii-factor |
| A factor for tuning the upper bound that swing modulo scheduler |
| uses for scheduling a loop. |
| |
| @item lra-max-considered-reload-pseudos |
| The max number of reload pseudos which are considered during |
| spilling a non-reload pseudo. |
| |
| @item max-pow-sqrt-depth |
| Maximum depth of sqrt chains to use when synthesizing exponentiation |
| by a real constant. |
| |
| @item max-dse-active-local-stores |
| Maximum number of active local stores in RTL dead store elimination. |
| |
| @item asan-instrument-allocas |
| Enable asan allocas/VLAs protection. |
| |
| @item max-iterations-computation-cost |
| Bound on the cost of an expression to compute the number of iterations. |
| |
| @item max-isl-operations |
| Maximum number of isl operations, 0 means unlimited. |
| |
| @item graphite-max-arrays-per-scop |
| Maximum number of arrays per scop. |
| |
| @item max-vartrack-reverse-op-size |
| Max. size of loc list for which reverse ops should be added. |
| |
| @item fsm-scale-path-stmts |
| Scale factor to apply to the number of statements in a threading path |
| when comparing to the number of (scaled) blocks. |
| |
| @item uninit-control-dep-attempts |
| Maximum number of nested calls to search for control dependencies |
| during uninitialized variable analysis. |
| |
| @item fsm-scale-path-blocks |
| Scale factor to apply to the number of blocks in a threading path |
| when comparing to the number of (scaled) statements. |
| |
| @item sched-autopref-queue-depth |
| Hardware autoprefetcher scheduler model control flag. |
| Number of lookahead cycles the model looks into; at ' |
| ' only enable instruction sorting heuristic. |
| |
| @item loop-versioning-max-inner-insns |
| The maximum number of instructions that an inner loop can have |
| before the loop versioning pass considers it too big to copy. |
| |
| @item loop-versioning-max-outer-insns |
| The maximum number of instructions that an outer loop can have |
| before the loop versioning pass considers it too big to copy, |
| discounting any instructions in inner loops that directly benefit |
| from versioning. |
| |
| @item ssa-name-def-chain-limit |
| The maximum number of SSA_NAME assignments to follow in determining |
| a property of a variable such as its value. This limits the number |
| of iterations or recursive calls GCC performs when optimizing certain |
| statements or when determining their validity prior to issuing |
| diagnostics. |
| |
| @item store-merging-max-size |
| Maximum size of a single store merging region in bytes. |
| |
| @item hash-table-verification-limit |
| The number of elements for which hash table verification is done |
| for each searched element. |
| |
| @item max-find-base-term-values |
| Maximum number of VALUEs handled during a single find_base_term call. |
| |
| @item analyzer-max-enodes-per-program-point |
| The maximum number of exploded nodes per program point within |
| the analyzer, before terminating analysis of that point. |
| |
| @item analyzer-max-constraints |
| The maximum number of constraints per state. |
| |
| @item analyzer-min-snodes-for-call-summary |
| The minimum number of supernodes within a function for the |
| analyzer to consider summarizing its effects at call sites. |
| |
| @item analyzer-max-enodes-for-full-dump |
| The maximum depth of exploded nodes that should appear in a dot dump |
| before switching to a less verbose format. |
| |
| @item analyzer-max-recursion-depth |
| The maximum number of times a callsite can appear in a call stack |
| within the analyzer, before terminating analysis of a call that would |
| recurse deeper. |
| |
| @item analyzer-max-svalue-depth |
| The maximum depth of a symbolic value, before approximating |
| the value as unknown. |
| |
| @item analyzer-max-infeasible-edges |
| The maximum number of infeasible edges to reject before declaring |
| a diagnostic as infeasible. |
| |
| @item gimple-fe-computed-hot-bb-threshold |
| The number of executions of a basic block which is considered hot. |
| The parameter is used only in GIMPLE FE. |
| |
| @item analyzer-bb-explosion-factor |
| The maximum number of 'after supernode' exploded nodes within the analyzer |
| per supernode, before terminating analysis. |
| |
| @item ranger-logical-depth |
| Maximum depth of logical expression evaluation ranger will look through |
| when evaluating outgoing edge ranges. |
| |
| @item relation-block-limit |
| Maximum number of relations the oracle will register in a basic block. |
| |
| @item min-pagesize |
| Minimum page size for warning purposes. |
| |
| @item openacc-kernels |
| Specify mode of OpenACC `kernels' constructs handling. |
| With @option{--param=openacc-kernels=decompose}, OpenACC `kernels' |
| constructs are decomposed into parts, a sequence of compute |
| constructs, each then handled individually. |
| This is work in progress. |
| With @option{--param=openacc-kernels=parloops}, OpenACC `kernels' |
| constructs are handled by the @samp{parloops} pass, en bloc. |
| This is the current default. |
| |
| @item openacc-privatization |
| Specify mode of OpenACC privatization diagnostics for |
| @option{-fopt-info-omp-note} and applicable |
| @option{-fdump-tree-*-details}. |
| With @option{--param=openacc-privatization=quiet}, don't diagnose. |
| This is the current default. |
| With @option{--param=openacc-privatization=noisy}, do diagnose. |
| |
| @end table |
| |
| The following choices of @var{name} are available on AArch64 targets: |
| |
| @table @gcctabopt |
| @item aarch64-sve-compare-costs |
| When vectorizing for SVE, consider using ``unpacked'' vectors for |
| smaller elements and use the cost model to pick the cheapest approach. |
| Also use the cost model to choose between SVE and Advanced SIMD vectorization. |
| |
| Using unpacked vectors includes storing smaller elements in larger |
| containers and accessing elements with extending loads and truncating |
| stores. |
| |
| @item aarch64-float-recp-precision |
| The number of Newton iterations for calculating the reciprocal for float type. |
| The precision of division is proportional to this param when division |
| approximation is enabled. The default value is 1. |
| |
| @item aarch64-double-recp-precision |
| The number of Newton iterations for calculating the reciprocal for double type. |
| The precision of division is propotional to this param when division |
| approximation is enabled. The default value is 2. |
| |
| @item aarch64-autovec-preference |
| Force an ISA selection strategy for auto-vectorization. Accepts values from |
| 0 to 4, inclusive. |
| @table @samp |
| @item 0 |
| Use the default heuristics. |
| @item 1 |
| Use only Advanced SIMD for auto-vectorization. |
| @item 2 |
| Use only SVE for auto-vectorization. |
| @item 3 |
| Use both Advanced SIMD and SVE. Prefer Advanced SIMD when the costs are |
| deemed equal. |
| @item 4 |
| Use both Advanced SIMD and SVE. Prefer SVE when the costs are deemed equal. |
| @end table |
| The default value is 0. |
| |
| @item aarch64-loop-vect-issue-rate-niters |
| The tuning for some AArch64 CPUs tries to take both latencies and issue |
| rates into account when deciding whether a loop should be vectorized |
| using SVE, vectorized using Advanced SIMD, or not vectorized at all. |
| If this parameter is set to @var{n}, GCC will not use this heuristic |
| for loops that are known to execute in fewer than @var{n} Advanced |
| SIMD iterations. |
| |
| @item aarch64-vect-unroll-limit |
| The vectorizer will use available tuning information to determine whether it |
| would be beneficial to unroll the main vectorized loop and by how much. This |
| parameter set's the upper bound of how much the vectorizer will unroll the main |
| loop. The default value is four. |
| |
| @end table |
| |
| The following choices of @var{name} are available on i386 and x86_64 targets: |
| |
| @table @gcctabopt |
| @item x86-stlf-window-ninsns |
| Instructions number above which STFL stall penalty can be compensated. |
| |
| @end table |
| |
| @end table |
| |
| @node Instrumentation Options |
| @section Program Instrumentation Options |
| @cindex instrumentation options |
| @cindex program instrumentation options |
| @cindex run-time error checking options |
| @cindex profiling options |
| @cindex options, program instrumentation |
| @cindex options, run-time error checking |
| @cindex options, profiling |
| |
| GCC supports a number of command-line options that control adding |
| run-time instrumentation to the code it normally generates. |
| For example, one purpose of instrumentation is collect profiling |
| statistics for use in finding program hot spots, code coverage |
| analysis, or profile-guided optimizations. |
| Another class of program instrumentation is adding run-time checking |
| to detect programming errors like invalid pointer |
| dereferences or out-of-bounds array accesses, as well as deliberately |
| hostile attacks such as stack smashing or C++ vtable hijacking. |
| There is also a general hook which can be used to implement other |
| forms of tracing or function-level instrumentation for debug or |
| program analysis purposes. |
| |
| @table @gcctabopt |
| @cindex @command{prof} |
| @cindex @command{gprof} |
| @item -p |
| @itemx -pg |
| @opindex p |
| @opindex pg |
| Generate extra code to write profile information suitable for the |
| analysis program @command{prof} (for @option{-p}) or @command{gprof} |
| (for @option{-pg}). You must use this option when compiling |
| the source files you want data about, and you must also use it when |
| linking. |
| |
| You can use the function attribute @code{no_instrument_function} to |
| suppress profiling of individual functions when compiling with these options. |
| @xref{Common Function Attributes}. |
| |
| @item -fprofile-arcs |
| @opindex fprofile-arcs |
| Add code so that program flow @dfn{arcs} are instrumented. During |
| execution the program records how many times each branch and call is |
| executed and how many times it is taken or returns. On targets that support |
| constructors with priority support, profiling properly handles constructors, |
| destructors and C++ constructors (and destructors) of classes which are used |
| as a type of a global variable. |
| |
| When the compiled |
| program exits it saves this data to a file called |
| @file{@var{auxname}.gcda} for each source file. The data may be used for |
| profile-directed optimizations (@option{-fbranch-probabilities}), or for |
| test coverage analysis (@option{-ftest-coverage}). Each object file's |
| @var{auxname} is generated from the name of the output file, if |
| explicitly specified and it is not the final executable, otherwise it is |
| the basename of the source file. In both cases any suffix is removed |
| (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or |
| @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}). |
| |
| Note that if a command line directly links source files, the corresponding |
| @var{.gcda} files will be prefixed with the unsuffixed name of the output file. |
| E.g. @code{gcc a.c b.c -o binary} would generate @file{binary-a.gcda} and |
| @file{binary-b.gcda} files. |
| |
| @xref{Cross-profiling}. |
| |
| @cindex @command{gcov} |
| @item --coverage |
| @opindex coverage |
| |
| This option is used to compile and link code instrumented for coverage |
| analysis. The option is a synonym for @option{-fprofile-arcs} |
| @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when |
| linking). See the documentation for those options for more details. |
| |
| @itemize |
| |
| @item |
| Compile the source files with @option{-fprofile-arcs} plus optimization |
| and code generation options. For test coverage analysis, use the |
| additional @option{-ftest-coverage} option. You do not need to profile |
| every source file in a program. |
| |
| @item |
| Compile the source files additionally with @option{-fprofile-abs-path} |
| to create absolute path names in the @file{.gcno} files. This allows |
| @command{gcov} to find the correct sources in projects where compilations |
| occur with different working directories. |
| |
| @item |
| Link your object files with @option{-lgcov} or @option{-fprofile-arcs} |
| (the latter implies the former). |
| |
| @item |
| Run the program on a representative workload to generate the arc profile |
| information. This may be repeated any number of times. You can run |
| concurrent instances of your program, and provided that the file system |
| supports locking, the data files will be correctly updated. Unless |
| a strict ISO C dialect option is in effect, @code{fork} calls are |
| detected and correctly handled without double counting. |
| |
| Moreover, an object file can be recompiled multiple times |
| and the corresponding @file{.gcda} file merges as long as |
| the source file and the compiler options are unchanged. |
| |
| @item |
| For profile-directed optimizations, compile the source files again with |
| the same optimization and code generation options plus |
| @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that |
| Control Optimization}). |
| |
| @item |
| For test coverage analysis, use @command{gcov} to produce human readable |
| information from the @file{.gcno} and @file{.gcda} files. Refer to the |
| @command{gcov} documentation for further information. |
| |
| @end itemize |
| |
| With @option{-fprofile-arcs}, for each function of your program GCC |
| creates a program flow graph, then finds a spanning tree for the graph. |
| Only arcs that are not on the spanning tree have to be instrumented: the |
| compiler adds code to count the number of times that these arcs are |
| executed. When an arc is the only exit or only entrance to a block, the |
| instrumentation code can be added to the block; otherwise, a new basic |
| block must be created to hold the instrumentation code. |
| |
| @need 2000 |
| @item -ftest-coverage |
| @opindex ftest-coverage |
| Produce a notes file that the @command{gcov} code-coverage utility |
| (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to |
| show program coverage. Each source file's note file is called |
| @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option |
| above for a description of @var{auxname} and instructions on how to |
| generate test coverage data. Coverage data matches the source files |
| more closely if you do not optimize. |
| |
| @item -fprofile-abs-path |
| @opindex fprofile-abs-path |
| Automatically convert relative source file names to absolute path names |
| in the @file{.gcno} files. This allows @command{gcov} to find the correct |
| sources in projects where compilations occur with different working |
| directories. |
| |
| @item -fprofile-dir=@var{path} |
| @opindex fprofile-dir |
| |
| Set the directory to search for the profile data files in to @var{path}. |
| This option affects only the profile data generated by |
| @option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs} |
| and used by @option{-fprofile-use} and @option{-fbranch-probabilities} |
| and its related options. Both absolute and relative paths can be used. |
| By default, GCC uses the current directory as @var{path}, thus the |
| profile data file appears in the same directory as the object file. |
| In order to prevent the file name clashing, if the object file name is |
| not an absolute path, we mangle the absolute path of the |
| @file{@var{sourcename}.gcda} file and use it as the file name of a |
| @file{.gcda} file. See details about the file naming in @option{-fprofile-arcs}. |
| See similar option @option{-fprofile-note}. |
| |
| When an executable is run in a massive parallel environment, it is recommended |
| to save profile to different folders. That can be done with variables |
| in @var{path} that are exported during run-time: |
| |
| @table @gcctabopt |
| |
| @item %p |
| process ID. |
| |
| @item %q@{VAR@} |
| value of environment variable @var{VAR} |
| |
| @end table |
| |
| @item -fprofile-generate |
| @itemx -fprofile-generate=@var{path} |
| @opindex fprofile-generate |
| |
| Enable options usually used for instrumenting application to produce |
| profile useful for later recompilation with profile feedback based |
| optimization. You must use @option{-fprofile-generate} both when |
| compiling and when linking your program. |
| |
| The following options are enabled: |
| @option{-fprofile-arcs}, @option{-fprofile-values}, |
| @option{-finline-functions}, and @option{-fipa-bit-cp}. |
| |
| If @var{path} is specified, GCC looks at the @var{path} to find |
| the profile feedback data files. See @option{-fprofile-dir}. |
| |
| To optimize the program based on the collected profile information, use |
| @option{-fprofile-use}. @xref{Optimize Options}, for more information. |
| |
| @item -fprofile-info-section |
| @itemx -fprofile-info-section=@var{name} |
| @opindex fprofile-info-section |
| |
| Register the profile information in the specified section instead of using a |
| constructor/destructor. The section name is @var{name} if it is specified, |
| otherwise the section name defaults to @code{.gcov_info}. A pointer to the |
| profile information generated by @option{-fprofile-arcs} is placed in the |
| specified section for each translation unit. This option disables the profile |
| information registration through a constructor and it disables the profile |
| information processing through a destructor. This option is not intended to be |
| used in hosted environments such as GNU/Linux. It targets free-standing |
| environments (for example embedded systems) with limited resources which do not |
| support constructors/destructors or the C library file I/O. |
| |
| The linker could collect the input sections in a continuous memory block and |
| define start and end symbols. A GNU linker script example which defines a |
| linker output section follows: |
| |
| @smallexample |
| .gcov_info : |
| @{ |
| PROVIDE (__gcov_info_start = .); |
| KEEP (*(.gcov_info)) |
| PROVIDE (__gcov_info_end = .); |
| @} |
| @end smallexample |
| |
| The program could dump the profiling information registered in this linker set |
| for example like this: |
| |
| @smallexample |
| #include <gcov.h> |
| #include <stdio.h> |
| #include <stdlib.h> |
| |
| extern const struct gcov_info *__gcov_info_start[]; |
| extern const struct gcov_info *__gcov_info_end[]; |
| |
| static void |
| filename (const char *f, void *arg) |
| @{ |
| puts (f); |
| @} |
| |
| static void |
| dump (const void *d, unsigned n, void *arg) |
| @{ |
| const unsigned char *c = d; |
| |
| for (unsigned i = 0; i < n; ++i) |
| printf ("%02x", c[i]); |
| @} |
| |
| static void * |
| allocate (unsigned length, void *arg) |
| @{ |
| return malloc (length); |
| @} |
| |
| static void |
| dump_gcov_info (void) |
| @{ |
| const struct gcov_info **info = __gcov_info_start; |
| const struct gcov_info **end = __gcov_info_end; |
| |
| /* Obfuscate variable to prevent compiler optimizations. */ |
| __asm__ ("" : "+r" (info)); |
| |
| while (info != end) |
| @{ |
| void *arg = NULL; |
| __gcov_info_to_gcda (*info, filename, dump, allocate, arg); |
| putchar ('\n'); |
| ++info; |
| @} |
| @} |
| |
| int |
| main() |
| @{ |
| dump_gcov_info(); |
| return 0; |
| @} |
| @end smallexample |
| |
| @item -fprofile-note=@var{path} |
| @opindex fprofile-note |
| |
| If @var{path} is specified, GCC saves @file{.gcno} file into @var{path} |
| location. If you combine the option with multiple source files, |
| the @file{.gcno} file will be overwritten. |
| |
| @item -fprofile-prefix-path=@var{path} |
| @opindex fprofile-prefix-path |
| |
| This option can be used in combination with |
| @option{profile-generate=}@var{profile_dir} and |
| @option{profile-use=}@var{profile_dir} to inform GCC where is the base |
| directory of built source tree. By default @var{profile_dir} will contain |
| files with mangled absolute paths of all object files in the built project. |
| This is not desirable when directory used to build the instrumented binary |
| differs from the directory used to build the binary optimized with profile |
| feedback because the profile data will not be found during the optimized build. |
| In such setups @option{-fprofile-prefix-path=}@var{path} with @var{path} |
| pointing to the base directory of the build can be used to strip the irrelevant |
| part of the path and keep all file names relative to the main build directory. |
| |
| @item -fprofile-prefix-map=@var{old}=@var{new} |
| @opindex fprofile-prefix-map |
| When compiling files residing in directory @file{@var{old}}, record |
| profiling information (with @option{--coverage}) |
| describing them as if the files resided in |
| directory @file{@var{new}} instead. |
| See also @option{-ffile-prefix-map}. |
| |
| @item -fprofile-update=@var{method} |
| @opindex fprofile-update |
| |
| Alter the update method for an application instrumented for profile |
| feedback based optimization. The @var{method} argument should be one of |
| @samp{single}, @samp{atomic} or @samp{prefer-atomic}. |
| The first one is useful for single-threaded applications, |
| while the second one prevents profile corruption by emitting thread-safe code. |
| |
| @strong{Warning:} When an application does not properly join all threads |
| (or creates an detached thread), a profile file can be still corrupted. |
| |
| Using @samp{prefer-atomic} would be transformed either to @samp{atomic}, |
| when supported by a target, or to @samp{single} otherwise. The GCC driver |
| automatically selects @samp{prefer-atomic} when @option{-pthread} |
| is present in the command line. |
| |
| @item -fprofile-filter-files=@var{regex} |
| @opindex fprofile-filter-files |
| |
| Instrument only functions from files whose name matches |
| any of the regular expressions (separated by semi-colons). |
| |
| For example, @option{-fprofile-filter-files=main\.c;module.*\.c} will instrument |
| only @file{main.c} and all C files starting with 'module'. |
| |
| @item -fprofile-exclude-files=@var{regex} |
| @opindex fprofile-exclude-files |
| |
| Instrument only functions from files whose name does not match |
| any of the regular expressions (separated by semi-colons). |
| |
| For example, @option{-fprofile-exclude-files=/usr/.*} will prevent instrumentation |
| of all files that are located in the @file{/usr/} folder. |
| |
| @item -fprofile-reproducible=@r{[}multithreaded@r{|}parallel-runs@r{|}serial@r{]} |
| @opindex fprofile-reproducible |
| Control level of reproducibility of profile gathered by |
| @code{-fprofile-generate}. This makes it possible to rebuild program |
| with same outcome which is useful, for example, for distribution |
| packages. |
| |
| With @option{-fprofile-reproducible=serial} the profile gathered by |
| @option{-fprofile-generate} is reproducible provided the trained program |
| behaves the same at each invocation of the train run, it is not |
| multi-threaded and profile data streaming is always done in the same |
| order. Note that profile streaming happens at the end of program run but |
| also before @code{fork} function is invoked. |
| |
| Note that it is quite common that execution counts of some part of |
| programs depends, for example, on length of temporary file names or |
| memory space randomization (that may affect hash-table collision rate). |
| Such non-reproducible part of programs may be annotated by |
| @code{no_instrument_function} function attribute. @command{gcov-dump} with |
| @option{-l} can be used to dump gathered data and verify that they are |
| indeed reproducible. |
| |
| With @option{-fprofile-reproducible=parallel-runs} collected profile |
| stays reproducible regardless the order of streaming of the data into |
| gcda files. This setting makes it possible to run multiple instances of |
| instrumented program in parallel (such as with @code{make -j}). This |
| reduces quality of gathered data, in particular of indirect call |
| profiling. |
| |
| @item -fsanitize=address |
| @opindex fsanitize=address |
| Enable AddressSanitizer, a fast memory error detector. |
| Memory access instructions are instrumented to detect |
| out-of-bounds and use-after-free bugs. |
| The option enables @option{-fsanitize-address-use-after-scope}. |
| See @uref{https://github.com/google/sanitizers/wiki/AddressSanitizer} for |
| more details. The run-time behavior can be influenced using the |
| @env{ASAN_OPTIONS} environment variable. When set to @code{help=1}, |
| the available options are shown at startup of the instrumented program. See |
| @url{https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time-flags} |
| for a list of supported options. |
| The option cannot be combined with @option{-fsanitize=thread} or |
| @option{-fsanitize=hwaddress}. Note that the only target |
| @option{-fsanitize=hwaddress} is currently supported on is AArch64. |
| |
| @item -fsanitize=kernel-address |
| @opindex fsanitize=kernel-address |
| Enable AddressSanitizer for Linux kernel. |
| See @uref{https://github.com/google/kasan} for more details. |
| |
| @item -fsanitize=hwaddress |
| @opindex fsanitize=hwaddress |
| Enable Hardware-assisted AddressSanitizer, which uses a hardware ability to |
| ignore the top byte of a pointer to allow the detection of memory errors with |
| a low memory overhead. |
| Memory access instructions are instrumented to detect out-of-bounds and |
| use-after-free bugs. |
| The option enables @option{-fsanitize-address-use-after-scope}. |
| See |
| @uref{https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html} |
| for more details. The run-time behavior can be influenced using the |
| @env{HWASAN_OPTIONS} environment variable. When set to @code{help=1}, |
| the available options are shown at startup of the instrumented program. |
| The option cannot be combined with @option{-fsanitize=thread} or |
| @option{-fsanitize=address}, and is currently only available on AArch64. |
| |
| @item -fsanitize=kernel-hwaddress |
| @opindex fsanitize=kernel-hwaddress |
| Enable Hardware-assisted AddressSanitizer for compilation of the Linux kernel. |
| Similar to @option{-fsanitize=kernel-address} but using an alternate |
| instrumentation method, and similar to @option{-fsanitize=hwaddress} but with |
| instrumentation differences necessary for compiling the Linux kernel. |
| These differences are to avoid hwasan library initialization calls and to |
| account for the stack pointer having a different value in its top byte. |
| |
| @emph{Note:} This option has different defaults to the @option{-fsanitize=hwaddress}. |
| Instrumenting the stack and alloca calls are not on by default but are still |
| possible by specifying the command-line options |
| @option{--param hwasan-instrument-stack=1} and |
| @option{--param hwasan-instrument-allocas=1} respectively. Using a random frame |
| tag is not implemented for kernel instrumentation. |
| |
| @item -fsanitize=pointer-compare |
| @opindex fsanitize=pointer-compare |
| Instrument comparison operation (<, <=, >, >=) with pointer operands. |
| The option must be combined with either @option{-fsanitize=kernel-address} or |
| @option{-fsanitize=address} |
| The option cannot be combined with @option{-fsanitize=thread}. |
| Note: By default the check is disabled at run time. To enable it, |
| add @code{detect_invalid_pointer_pairs=2} to the environment variable |
| @env{ASAN_OPTIONS}. Using @code{detect_invalid_pointer_pairs=1} detects |
| invalid operation only when both pointers are non-null. |
| |
| @item -fsanitize=pointer-subtract |
| @opindex fsanitize=pointer-subtract |
| Instrument subtraction with pointer operands. |
| The option must be combined with either @option{-fsanitize=kernel-address} or |
| @option{-fsanitize=address} |
| The option cannot be combined with @option{-fsanitize=thread}. |
| Note: By default the check is disabled at run time. To enable it, |
| add @code{detect_invalid_pointer_pairs=2} to the environment variable |
| @env{ASAN_OPTIONS}. Using @code{detect_invalid_pointer_pairs=1} detects |
| invalid operation only when both pointers are non-null. |
| |
| @item -fsanitize=shadow-call-stack |
| @opindex fsanitize=shadow-call-stack |
| Enable ShadowCallStack, a security enhancement mechanism used to protect |
| programs against return address overwrites (e.g. stack buffer overflows.) |
| It works by saving a function's return address to a separately allocated |
| shadow call stack in the function prologue and restoring the return address |
| from the shadow call stack in the function epilogue. Instrumentation only |
| occurs in functions that need to save the return address to the stack. |
| |
| Currently it only supports the aarch64 platform. It is specifically |
| designed for linux kernels that enable the CONFIG_SHADOW_CALL_STACK option. |
| For the user space programs, runtime support is not currently provided |
| in libc and libgcc. Users who want to use this feature in user space need |
| to provide their own support for the runtime. It should be noted that |
| this may cause the ABI rules to be broken. |
| |
| On aarch64, the instrumentation makes use of the platform register @code{x18}. |
| This generally means that any code that may run on the same thread as code |
| compiled with ShadowCallStack must be compiled with the flag |
| @option{-ffixed-x18}, otherwise functions compiled without |
| @option{-ffixed-x18} might clobber @code{x18} and so corrupt the shadow |
| stack pointer. |
| |
| Also, because there is no userspace runtime support, code compiled with |
| ShadowCallStack cannot use exception handling. Use @option{-fno-exceptions} |
| to turn off exceptions. |
| |
| See @uref{https://clang.llvm.org/docs/ShadowCallStack.html} for more |
| details. |
| |
| @item -fsanitize=thread |
| @opindex fsanitize=thread |
| Enable ThreadSanitizer, a fast data race detector. |
| Memory access instructions are instrumented to detect |
| data race bugs. See @uref{https://github.com/google/sanitizers/wiki#threadsanitizer} for more |
| details. The run-time behavior can be influenced using the @env{TSAN_OPTIONS} |
| environment variable; see |
| @url{https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags} for a list of |
| supported options. |
| The option cannot be combined with @option{-fsanitize=address}, |
| @option{-fsanitize=leak}. |
| |
| Note that sanitized atomic builtins cannot throw exceptions when |
| operating on invalid memory addresses with non-call exceptions |
| (@option{-fnon-call-exceptions}). |
| |
| @item -fsanitize=leak |
| @opindex fsanitize=leak |
| Enable LeakSanitizer, a memory leak detector. |
| This option only matters for linking of executables and |
| the executable is linked against a library that overrides @code{malloc} |
| and other allocator functions. See |
| @uref{https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer} for more |
| details. The run-time behavior can be influenced using the |
| @env{LSAN_OPTIONS} environment variable. |
| The option cannot be combined with @option{-fsanitize=thread}. |
| |
| @item -fsanitize=undefined |
| @opindex fsanitize=undefined |
| Enable UndefinedBehaviorSanitizer, a fast undefined behavior detector. |
| Various computations are instrumented to detect undefined behavior |
| at runtime. See @uref{https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html} for more details. The run-time behavior can be influenced using the |
| @env{UBSAN_OPTIONS} environment variable. Current suboptions are: |
| |
| @table @gcctabopt |
| |
| @item -fsanitize=shift |
| @opindex fsanitize=shift |
| This option enables checking that the result of a shift operation is |
| not undefined. Note that what exactly is considered undefined differs |
| slightly between C and C++, as well as between ISO C90 and C99, etc. |
| This option has two suboptions, @option{-fsanitize=shift-base} and |
| @option{-fsanitize=shift-exponent}. |
| |
| @item -fsanitize=shift-exponent |
| @opindex fsanitize=shift-exponent |
| This option enables checking that the second argument of a shift operation |
| is not negative and is smaller than the precision of the promoted first |
| argument. |
| |
| @item -fsanitize=shift-base |
| @opindex fsanitize=shift-base |
| If the second argument of a shift operation is within range, check that the |
| result of a shift operation is not undefined. Note that what exactly is |
| considered undefined differs slightly between C and C++, as well as between |
| ISO C90 and C99, etc. |
| |
| @item -fsanitize=integer-divide-by-zero |
| @opindex fsanitize=integer-divide-by-zero |
| Detect integer division by zero. |
| |
| @item -fsanitize=unreachable |
| @opindex fsanitize=unreachable |
| With this option, the compiler turns the @code{__builtin_unreachable} |
| call into a diagnostics message call instead. When reaching the |
| @code{__builtin_unreachable} call, the behavior is undefined. |
| |
| @item -fsanitize=vla-bound |
| @opindex fsanitize=vla-bound |
| This option instructs the compiler to check that the size of a variable |
| length array is positive. |
| |
| @item -fsanitize=null |
| @opindex fsanitize=null |
| This option enables pointer checking. Particularly, the application |
| built with this option turned on will issue an error message when it |
| tries to dereference a NULL pointer, or if a reference (possibly an |
| rvalue reference) is bound to a NULL pointer, or if a method is invoked |
| on an object pointed by a NULL pointer. |
| |
| @item -fsanitize=return |
| @opindex fsanitize=return |
| This option enables return statement checking. Programs |
| built with this option turned on will issue an error message |
| when the end of a non-void function is reached without actually |
| returning a value. This option works in C++ only. |
| |
| @item -fsanitize=signed-integer-overflow |
| @opindex fsanitize=signed-integer-overflow |
| This option enables signed integer overflow checking. We check that |
| the result of @code{+}, @code{*}, and both unary and binary @code{-} |
| does not overflow in the signed arithmetics. This also detects |
| @code{INT_MIN / -1} signed division. Note, integer promotion |
| rules must be taken into account. That is, the following is not an |
| overflow: |
| @smallexample |
| signed char a = SCHAR_MAX; |
| a++; |
| @end smallexample |
| |
| @item -fsanitize=bounds |
| @opindex fsanitize=bounds |
| This option enables instrumentation of array bounds. Various out of bounds |
| accesses are detected. Flexible array members, flexible array member-like |
| arrays, and initializers of variables with static storage are not instrumented. |
| |
| @item -fsanitize=bounds-strict |
| @opindex fsanitize=bounds-strict |
| This option enables strict instrumentation of array bounds. Most out of bounds |
| accesses are detected, including flexible array members and flexible array |
| member-like arrays. Initializers of variables with static storage are not |
| instrumented. |
| |
| @item -fsanitize=alignment |
| @opindex fsanitize=alignment |
| |
| This option enables checking of alignment of pointers when they are |
| dereferenced, or when a reference is bound to insufficiently aligned target, |
| or when a method or constructor is invoked on insufficiently aligned object. |
| |
| @item -fsanitize=object-size |
| @opindex fsanitize=object-size |
| This option enables instrumentation of memory references using the |
| @code{__builtin_object_size} function. Various out of bounds pointer |
| accesses are detected. |
| |
| @item -fsanitize=float-divide-by-zero |
| @opindex fsanitize=float-divide-by-zero |
| Detect floating-point division by zero. Unlike other similar options, |
| @option{-fsanitize=float-divide-by-zero} is not enabled by |
| @option{-fsanitize=undefined}, since floating-point division by zero can |
| be a legitimate way of obtaining infinities and NaNs. |
| |
| @item -fsanitize=float-cast-overflow |
| @opindex fsanitize=float-cast-overflow |
| This option enables floating-point type to integer conversion checking. |
| We check that the result of the conversion does not overflow. |
| Unlike other similar options, @option{-fsanitize=float-cast-overflow} is |
| not enabled by @option{-fsanitize=undefined}. |
| This option does not work well with @code{FE_INVALID} exceptions enabled. |
| |
| @item -fsanitize=nonnull-attribute |
| @opindex fsanitize=nonnull-attribute |
| |
| This option enables instrumentation of calls, checking whether null values |
| are not passed to arguments marked as requiring a non-null value by the |
| @code{nonnull} function attribute. |
| |
| @item -fsanitize=returns-nonnull-attribute |
| @opindex fsanitize=returns-nonnull-attribute |
| |
| This option enables instrumentation of return statements in functions |
| marked with @code{returns_nonnull} function attribute, to detect returning |
| of null values from such functions. |
| |
| @item -fsanitize=bool |
| @opindex fsanitize=bool |
| |
| This option enables instrumentation of loads from bool. If a value other |
| than 0/1 is loaded, a run-time error is issued. |
| |
| @item -fsanitize=enum |
| @opindex fsanitize=enum |
| |
| This option enables instrumentation of loads from an enum type. If |
| a value outside the range of values for the enum type is loaded, |
| a run-time error is issued. |
| |
| @item -fsanitize=vptr |
| @opindex fsanitize=vptr |
| |
| This option enables instrumentation of C++ member function calls, member |
| accesses and some conversions between pointers to base and derived classes, |
| to verify the referenced object has the correct dynamic type. |
| |
| @item -fsanitize=pointer-overflow |
| @opindex fsanitize=pointer-overflow |
| |
| This option enables instrumentation of pointer arithmetics. If the pointer |
| arithmetics overflows, a run-time error is issued. |
| |
| @item -fsanitize=builtin |
| @opindex fsanitize=builtin |
| |
| This option enables instrumentation of arguments to selected builtin |
| functions. If an invalid value is passed to such arguments, a run-time |
| error is issued. E.g.@ passing 0 as the argument to @code{__builtin_ctz} |
| or @code{__builtin_clz} invokes undefined behavior and is diagnosed |
| by this option. |
| |
| @end table |
| |
| While @option{-ftrapv} causes traps for signed overflows to be emitted, |
| @option{-fsanitize=undefined} gives a diagnostic message. |
| This currently works only for the C family of languages. |
| |
| @item -fno-sanitize=all |
| @opindex fno-sanitize=all |
| |
| This option disables all previously enabled sanitizers. |
| @option{-fsanitize=all} is not allowed, as some sanitizers cannot be used |
| together. |
| |
| @item -fasan-shadow-offset=@var{number} |
| @opindex fasan-shadow-offset |
| This option forces GCC to use custom shadow offset in AddressSanitizer checks. |
| It is useful for experimenting with different shadow memory layouts in |
| Kernel AddressSanitizer. |
| |
| @item -fsanitize-sections=@var{s1},@var{s2},... |
| @opindex fsanitize-sections |
| Sanitize global variables in selected user-defined sections. @var{si} may |
| contain wildcards. |
| |
| @item -fsanitize-recover@r{[}=@var{opts}@r{]} |
| @opindex fsanitize-recover |
| @opindex fno-sanitize-recover |
| @option{-fsanitize-recover=} controls error recovery mode for sanitizers |
| mentioned in comma-separated list of @var{opts}. Enabling this option |
| for a sanitizer component causes it to attempt to continue |
| running the program as if no error happened. This means multiple |
| runtime errors can be reported in a single program run, and the exit |
| code of the program may indicate success even when errors |
| have been reported. The @option{-fno-sanitize-recover=} option |
| can be used to alter |
| this behavior: only the first detected error is reported |
| and program then exits with a non-zero exit code. |
| |
| Currently this feature only works for @option{-fsanitize=undefined} (and its suboptions |
| except for @option{-fsanitize=unreachable} and @option{-fsanitize=return}), |
| @option{-fsanitize=float-cast-overflow}, @option{-fsanitize=float-divide-by-zero}, |
| @option{-fsanitize=bounds-strict}, |
| @option{-fsanitize=kernel-address} and @option{-fsanitize=address}. |
| For these sanitizers error recovery is turned on by default, |
| except @option{-fsanitize=address}, for which this feature is experimental. |
| @option{-fsanitize-recover=all} and @option{-fno-sanitize-recover=all} is also |
| accepted, the former enables recovery for all sanitizers that support it, |
| the latter disables recovery for all sanitizers that support it. |
| |
| Even if a recovery mode is turned on the compiler side, it needs to be also |
| enabled on the runtime library side, otherwise the failures are still fatal. |
| The runtime library defaults to @code{halt_on_error=0} for |
| ThreadSanitizer and UndefinedBehaviorSanitizer, while default value for |
| AddressSanitizer is @code{halt_on_error=1}. This can be overridden through |
| setting the @code{halt_on_error} flag in the corresponding environment variable. |
| |
| Syntax without an explicit @var{opts} parameter is deprecated. It is |
| equivalent to specifying an @var{opts} list of: |
| |
| @smallexample |
| undefined,float-cast-overflow,float-divide-by-zero,bounds-strict |
| @end smallexample |
| |
| @item -fsanitize-address-use-after-scope |
| @opindex fsanitize-address-use-after-scope |
| Enable sanitization of local variables to detect use-after-scope bugs. |
| The option sets @option{-fstack-reuse} to @samp{none}. |
| |
| @item -fsanitize-undefined-trap-on-error |
| @opindex fsanitize-undefined-trap-on-error |
| The @option{-fsanitize-undefined-trap-on-error} option instructs the compiler to |
| report undefined behavior using @code{__builtin_trap} rather than |
| a @code{libubsan} library routine. The advantage of this is that the |
| @code{libubsan} library is not needed and is not linked in, so this |
| is usable even in freestanding environments. |
| |
| @item -fsanitize-coverage=trace-pc |
| @opindex fsanitize-coverage=trace-pc |
| Enable coverage-guided fuzzing code instrumentation. |
| Inserts a call to @code{__sanitizer_cov_trace_pc} into every basic block. |
| |
| @item -fsanitize-coverage=trace-cmp |
| @opindex fsanitize-coverage=trace-cmp |
| Enable dataflow guided fuzzing code instrumentation. |
| Inserts a call to @code{__sanitizer_cov_trace_cmp1}, |
| @code{__sanitizer_cov_trace_cmp2}, @code{__sanitizer_cov_trace_cmp4} or |
| @code{__sanitizer_cov_trace_cmp8} for integral comparison with both operands |
| variable or @code{__sanitizer_cov_trace_const_cmp1}, |
| @code{__sanitizer_cov_trace_const_cmp2}, |
| @code{__sanitizer_cov_trace_const_cmp4} or |
| @code{__sanitizer_cov_trace_const_cmp8} for integral comparison with one |
| operand constant, @code{__sanitizer_cov_trace_cmpf} or |
| @code{__sanitizer_cov_trace_cmpd} for float or double comparisons and |
| @code{__sanitizer_cov_trace_switch} for switch statements. |
| |
| @item -fcf-protection=@r{[}full@r{|}branch@r{|}return@r{|}none@r{|}check@r{]} |
| @opindex fcf-protection |
| Enable code instrumentation of control-flow transfers to increase |
| program security by checking that target addresses of control-flow |
| transfer instructions (such as indirect function call, function return, |
| indirect jump) are valid. This prevents diverting the flow of control |
| to an unexpected target. This is intended to protect against such |
| threats as Return-oriented Programming (ROP), and similarly |
| call/jmp-oriented programming (COP/JOP). |
| |
| The value @code{branch} tells the compiler to implement checking of |
| validity of control-flow transfer at the point of indirect branch |
| instructions, i.e.@: call/jmp instructions. The value @code{return} |
| implements checking of validity at the point of returning from a |
| function. The value @code{full} is an alias for specifying both |
| @code{branch} and @code{return}. The value @code{none} turns off |
| instrumentation. |
| |
| The value @code{check} is used for the final link with link-time |
| optimization (LTO). An error is issued if LTO object files are |
| compiled with different @option{-fcf-protection} values. The |
| value @code{check} is ignored at the compile time. |
| |
| The macro @code{__CET__} is defined when @option{-fcf-protection} is |
| used. The first bit of @code{__CET__} is set to 1 for the value |
| @code{branch} and the second bit of @code{__CET__} is set to 1 for |
| the @code{return}. |
| |
| You can also use the @code{nocf_check} attribute to identify |
| which functions and calls should be skipped from instrumentation |
| (@pxref{Function Attributes}). |
| |
| Currently the x86 GNU/Linux target provides an implementation based |
| on Intel Control-flow Enforcement Technology (CET) which works for |
| i686 processor or newer. |
| |
| @item -fharden-compares |
| @opindex fharden-compares |
| For every logical test that survives gimple optimizations and is |
| @emph{not} the condition in a conditional branch (for example, |
| conditions tested for conditional moves, or to store in boolean |
| variables), emit extra code to compute and verify the reversed |
| condition, and to call @code{__builtin_trap} if the results do not |
| match. Use with @samp{-fharden-conditional-branches} to cover all |
| conditionals. |
| |
| @item -fharden-conditional-branches |
| @opindex fharden-conditional-branches |
| For every non-vectorized conditional branch that survives gimple |
| optimizations, emit extra code to compute and verify the reversed |
| condition, and to call @code{__builtin_trap} if the result is |
| unexpected. Use with @samp{-fharden-compares} to cover all |
| conditionals. |
| |
| @item -fstack-protector |
| @opindex fstack-protector |
| Emit extra code to check for buffer overflows, such as stack smashing |
| attacks. This is done by adding a guard variable to functions with |
| vulnerable objects. This includes functions that call @code{alloca}, and |
| functions with buffers larger than or equal to 8 bytes. The guards are |
| initialized when a function is entered and then checked when the function |
| exits. If a guard check fails, an error message is printed and the program |
| exits. Only variables that are actually allocated on the stack are |
| considered, optimized away variables or variables allocated in registers |
| don't count. |
| |
| @item -fstack-protector-all |
| @opindex fstack-protector-all |
| Like @option{-fstack-protector} except that all functions are protected. |
| |
| @item -fstack-protector-strong |
| @opindex fstack-protector-strong |
| Like @option{-fstack-protector} but includes additional functions to |
| be protected --- those that have local array definitions, or have |
| references to local frame addresses. Only variables that are actually |
| allocated on the stack are considered, optimized away variables or variables |
| allocated in registers don't count. |
| |
| @item -fstack-protector-explicit |
| @opindex fstack-protector-explicit |
| Like @option{-fstack-protector} but only protects those functions which |
| have the @code{stack_protect} attribute. |
| |
| @item -fstack-check |
| @opindex fstack-check |
| Generate code to verify that you do not go beyond the boundary of the |
| stack. You should specify this flag if you are running in an |
| environment with multiple threads, but you only rarely need to specify it in |
| a single-threaded environment since stack overflow is automatically |
| detected on nearly all systems if there is only one stack. |
| |
| Note that this switch does not actually cause checking to be done; the |
| operating system or the language runtime must do that. The switch causes |
| generation of code to ensure that they see the stack being extended. |
| |
| You can additionally specify a string parameter: @samp{no} means no |
| checking, @samp{generic} means force the use of old-style checking, |
| @samp{specific} means use the best checking method and is equivalent |
| to bare @option{-fstack-check}. |
| |
| Old-style checking is a generic mechanism that requires no specific |
| target support in the compiler but comes with the following drawbacks: |
| |
| @enumerate |
| @item |
| Modified allocation strategy for large objects: they are always |
| allocated dynamically if their size exceeds a fixed threshold. Note this |
| may change the semantics of some code. |
| |
| @item |
| Fixed limit on the size of the static frame of functions: when it is |
| topped by a particular function, stack checking is not reliable and |
| a warning is issued by the compiler. |
| |
| @item |
| Inefficiency: because of both the modified allocation strategy and the |
| generic implementation, code performance is hampered. |
| @end enumerate |
| |
| Note that old-style stack checking is also the fallback method for |
| @samp{specific} if no target support has been added in the compiler. |
| |
| @samp{-fstack-check=} is designed for Ada's needs to detect infinite recursion |
| and stack overflows. @samp{specific} is an excellent choice when compiling |
| Ada code. It is not generally sufficient to protect against stack-clash |
| attacks. To protect against those you want @samp{-fstack-clash-protection}. |
| |
| @item -fstack-clash-protection |
| @opindex fstack-clash-protection |
| Generate code to prevent stack clash style attacks. When this option is |
| enabled, the compiler will only allocate one page of stack space at a time |
| and each page is accessed immediately after allocation. Thus, it prevents |
| allocations from jumping over any stack guard page provided by the |
| operating system. |
| |
| Most targets do not fully support stack clash protection. However, on |
| those targets @option{-fstack-clash-protection} will protect dynamic stack |
| allocations. @option{-fstack-clash-protection} may also provide limited |
| protection for static stack allocations if the target supports |
| @option{-fstack-check=specific}. |
| |
| @item -fstack-limit-register=@var{reg} |
| @itemx -fstack-limit-symbol=@var{sym} |
| @itemx -fno-stack-limit |
| @opindex fstack-limit-register |
| @opindex fstack-limit-symbol |
| @opindex fno-stack-limit |
| Generate code to ensure that the stack does not grow beyond a certain value, |
| either the value of a register or the address of a symbol. If a larger |
| stack is required, a signal is raised at run time. For most targets, |
| the signal is raised before the stack overruns the boundary, so |
| it is possible to catch the signal without taking special precautions. |
| |
| For instance, if the stack starts at absolute address @samp{0x80000000} |
| and grows downwards, you can use the flags |
| @option{-fstack-limit-symbol=__stack_limit} and |
| @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit |
| of 128KB@. Note that this may only work with the GNU linker. |
| |
| You can locally override stack limit checking by using the |
| @code{no_stack_limit} function attribute (@pxref{Function Attributes}). |
| |
| @item -fsplit-stack |
| @opindex fsplit-stack |
| Generate code to automatically split the stack before it overflows. |
| The resulting program has a discontiguous stack which can only |
| overflow if the program is unable to allocate any more memory. This |
| is most useful when running threaded programs, as it is no longer |
| necessary to calculate a good stack size to use for each thread. This |
| is currently only implemented for the x86 targets running |
| GNU/Linux. |
| |
| When code compiled with @option{-fsplit-stack} calls code compiled |
| without @option{-fsplit-stack}, there may not be much stack space |
| available for the latter code to run. If compiling all code, |
| including library code, with @option{-fsplit-stack} is not an option, |
| then the linker can fix up these calls so that the code compiled |
| without @option{-fsplit-stack} always has a large stack. Support for |
| this is implemented in the gold linker in GNU binutils release 2.21 |
| and later. |
| |
| @item -fvtable-verify=@r{[}std@r{|}preinit@r{|}none@r{]} |
| @opindex fvtable-verify |
| This option is only available when compiling C++ code. |
| It turns on (or off, if using @option{-fvtable-verify=none}) the security |
| feature that verifies at run time, for every virtual call, that |
| the vtable pointer through which the call is made is valid for the type of |
| the object, and has not been corrupted or overwritten. If an invalid vtable |
| pointer is detected at run time, an error is reported and execution of the |
| program is immediately halted. |
| |
| This option causes run-time data structures to be built at program startup, |
| which are used for verifying the vtable pointers. |
| The options @samp{std} and @samp{preinit} |
| control the timing of when these data structures are built. In both cases the |
| data structures are built before execution reaches @code{main}. Using |
| @option{-fvtable-verify=std} causes the data structures to be built after |
| shared libraries have been loaded and initialized. |
| @option{-fvtable-verify=preinit} causes them to be built before shared |
| libraries have been loaded and initialized. |
| |
| If this option appears multiple times in the command line with different |
| values specified, @samp{none} takes highest priority over both @samp{std} and |
| @samp{preinit}; @samp{preinit} takes priority over @samp{std}. |
| |
| @item -fvtv-debug |
| @opindex fvtv-debug |
| When used in conjunction with @option{-fvtable-verify=std} or |
| @option{-fvtable-verify=preinit}, causes debug versions of the |
| runtime functions for the vtable verification feature to be called. |
| This flag also causes the compiler to log information about which |
| vtable pointers it finds for each class. |
| This information is written to a file named @file{vtv_set_ptr_data.log} |
| in the directory named by the environment variable @env{VTV_LOGS_DIR} |
| if that is defined or the current working directory otherwise. |
| |
| Note: This feature @emph{appends} data to the log file. If you want a fresh log |
| file, be sure to delete any existing one. |
| |
| @item -fvtv-counts |
| @opindex fvtv-counts |
| This is a debugging flag. When used in conjunction with |
| @option{-fvtable-verify=std} or @option{-fvtable-verify=preinit}, this |
| causes the compiler to keep track of the total number of virtual calls |
| it encounters and the number of verifications it inserts. It also |
| counts the number of calls to certain run-time library functions |
| that it inserts and logs this information for each compilation unit. |
| The compiler writes this information to a file named |
| @file{vtv_count_data.log} in the directory named by the environment |
| variable @env{VTV_LOGS_DIR} if that is defined or the current working |
| directory otherwise. It also counts the size of the vtable pointer sets |
| for each class, and writes this information to @file{vtv_class_set_sizes.log} |
| in the same directory. |
| |
| Note: This feature @emph{appends} data to the log files. To get fresh log |
| files, be sure to delete any existing ones. |
| |
| @item -finstrument-functions |
| @opindex finstrument-functions |
| Generate instrumentation calls for entry and exit to functions. Just |
| after function entry and just before function exit, the following |
| profiling functions are called with the address of the current |
| function and its call site. (On some platforms, |
| @code{__builtin_return_address} does not work beyond the current |
| function, so the call site information may not be available to the |
| profiling functions otherwise.) |
| |
| @smallexample |
| void __cyg_profile_func_enter (void *this_fn, |
| void *call_site); |
| void __cyg_profile_func_exit (void *this_fn, |
| void *call_site); |
| @end smallexample |
| |
| The first argument is the address of the start of the current function, |
| which may be looked up exactly in the symbol table. |
| |
| This instrumentation is also done for functions expanded inline in other |
| functions. The profiling calls indicate where, conceptually, the |
| inline function is entered and exited. This means that addressable |
| versions of such functions must be available. If all your uses of a |
| function are expanded inline, this may mean an additional expansion of |
| code size. If you use @code{extern inline} in your C code, an |
| addressable version of such functions must be provided. (This is |
| normally the case anyway, but if you get lucky and the optimizer always |
| expands the functions inline, you might have gotten away without |
| providing static copies.) |
| |
| A function may be given the attribute @code{no_instrument_function}, in |
| which case this instrumentation is not done. This can be used, for |
| example, for the profiling functions listed above, high-priority |
| interrupt routines, and any functions from which the profiling functions |
| cannot safely be called (perhaps signal handlers, if the profiling |
| routines generate output or allocate memory). |
| @xref{Common Function Attributes}. |
| |
| @item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} |
| @opindex finstrument-functions-exclude-file-list |
| |
| Set the list of functions that are excluded from instrumentation (see |
| the description of @option{-finstrument-functions}). If the file that |
| contains a function definition matches with one of @var{file}, then |
| that function is not instrumented. The match is done on substrings: |
| if the @var{file} parameter is a substring of the file name, it is |
| considered to be a match. |
| |
| For example: |
| |
| @smallexample |
| -finstrument-functions-exclude-file-list=/bits/stl,include/sys |
| @end smallexample |
| |
| @noindent |
| excludes any inline function defined in files whose pathnames |
| contain @file{/bits/stl} or @file{include/sys}. |
| |
| If, for some reason, you want to include letter @samp{,} in one of |
| @var{sym}, write @samp{\,}. For example, |
| @option{-finstrument-functions-exclude-file-list='\,\,tmp'} |
| (note the single quote surrounding the option). |
| |
| @item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} |
| @opindex finstrument-functions-exclude-function-list |
| |
| This is similar to @option{-finstrument-functions-exclude-file-list}, |
| but this option sets the list of function names to be excluded from |
| instrumentation. The function name to be matched is its user-visible |
| name, such as @code{vector<int> blah(const vector<int> &)}, not the |
| internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The |
| match is done on substrings: if the @var{sym} parameter is a substring |
| of the function name, it is considered to be a match. For C99 and C++ |
| extended identifiers, the function name must be given in UTF-8, not |
| using universal character names. |
| |
| @item -fpatchable-function-entry=@var{N}[,@var{M}] |
| @opindex fpatchable-function-entry |
| Generate @var{N} NOPs right at the beginning |
| of each function, with the function entry point before the @var{M}th NOP. |
| If @var{M} is omitted, it defaults to @code{0} so the |
| function entry points to the address just at the first NOP. |
| The NOP instructions reserve extra space which can be used to patch in |
| any desired instrumentation at run time, provided that the code segment |
| is writable. The amount of space is controllable indirectly via |
| the number of NOPs; the NOP instruction used corresponds to the instruction |
| emitted by the internal GCC back-end interface @code{gen_nop}. This behavior |
| is target-specific and may also depend on the architecture variant and/or |
| other compilation options. |
| |
| For run-time identification, the starting addresses of these areas, |
| which correspond to their respective function entries minus @var{M}, |
| are additionally collected in the @code{__patchable_function_entries} |
| section of the resulting binary. |
| |
| Note that the value of @code{__attribute__ ((patchable_function_entry |
| (N,M)))} takes precedence over command-line option |
| @option{-fpatchable-function-entry=N,M}. This can be used to increase |
| the area size or to remove it completely on a single function. |
| If @code{N=0}, no pad location is recorded. |
| |
| The NOP instructions are inserted at---and maybe before, depending on |
| @var{M}---the function entry address, even before the prologue. |
| |
| The maximum value of @var{N} and @var{M} is 65535. |
| @end table |
| |
| |
| @node Preprocessor Options |
| @section Options Controlling the Preprocessor |
| @cindex preprocessor options |
| @cindex options, preprocessor |
| |
| These options control the C preprocessor, which is run on each C source |
| file before actual compilation. |
| |
| If you use the @option{-E} option, nothing is done except preprocessing. |
| Some of these options make sense only together with @option{-E} because |
| they cause the preprocessor output to be unsuitable for actual |
| compilation. |
| |
| In addition to the options listed here, there are a number of options |
| to control search paths for include files documented in |
| @ref{Directory Options}. |
| Options to control preprocessor diagnostics are listed in |
| @ref{Warning Options}. |
| |
| @table @gcctabopt |
| @include cppopts.texi |
| |
| @item -Wp,@var{option} |
| @opindex Wp |
| You can use @option{-Wp,@var{option}} to bypass the compiler driver |
| and pass @var{option} directly through to the preprocessor. If |
| @var{option} contains commas, it is split into multiple options at the |
| commas. However, many options are modified, translated or interpreted |
| by the compiler driver before being passed to the preprocessor, and |
| @option{-Wp} forcibly bypasses this phase. The preprocessor's direct |
| interface is undocumented and subject to change, so whenever possible |
| you should avoid using @option{-Wp} and let the driver handle the |
| options instead. |
| |
| @item -Xpreprocessor @var{option} |
| @opindex Xpreprocessor |
| Pass @var{option} as an option to the preprocessor. You can use this to |
| supply system-specific preprocessor options that GCC does not |
| recognize. |
| |
| If you want to pass an option that takes an argument, you must use |
| @option{-Xpreprocessor} twice, once for the option and once for the argument. |
| |
| @item -no-integrated-cpp |
| @opindex no-integrated-cpp |
| Perform preprocessing as a separate pass before compilation. |
| By default, GCC performs preprocessing as an integrated part of |
| input tokenization and parsing. |
| If this option is provided, the appropriate language front end |
| (@command{cc1}, @command{cc1plus}, or @command{cc1obj} for C, C++, |
| and Objective-C, respectively) is instead invoked twice, |
| once for preprocessing only and once for actual compilation |
| of the preprocessed input. |
| This option may be useful in conjunction with the @option{-B} or |
| @option{-wrapper} options to specify an alternate preprocessor or |
| perform additional processing of the program source between |
| normal preprocessing and compilation. |
| |
| @item -flarge-source-files |
| @opindex flarge-source-files |
| Adjust GCC to expect large source files, at the expense of slower |
| compilation and higher memory usage. |
| |
| Specifically, GCC normally tracks both column numbers and line numbers |
| within source files and it normally prints both of these numbers in |
| diagnostics. However, once it has processed a certain number of source |
| lines, it stops tracking column numbers and only tracks line numbers. |
| This means that diagnostics for later lines do not include column numbers. |
| It also means that options like @option{-Wmisleading-indentation} cease to work |
| at that point, although the compiler prints a note if this happens. |
| Passing @option{-flarge-source-files} significantly increases the number |
| of source lines that GCC can process before it stops tracking columns. |
| |
| @end table |
| |
| @node Assembler Options |
| @section Passing Options to the Assembler |
| |
| @c prevent bad page break with this line |
| You can pass options to the assembler. |
| |
| @table @gcctabopt |
| @item -Wa,@var{option} |
| @opindex Wa |
| Pass @var{option} as an option to the assembler. If @var{option} |
| contains commas, it is split into multiple options at the commas. |
| |
| @item -Xassembler @var{option} |
| @opindex Xassembler |
| Pass @var{option} as an option to the assembler. You can use this to |
| supply system-specific assembler options that GCC does not |
| recognize. |
| |
| If you want to pass an option that takes an argument, you must use |
| @option{-Xassembler} twice, once for the option and once for the argument. |
| |
| @end table |
| |
| @node Link Options |
| @section Options for Linking |
| @cindex link options |
| @cindex options, linking |
| |
| These options come into play when the compiler links object files into |
| an executable output file. They are meaningless if the compiler is |
| not doing a link step. |
| |
| @table @gcctabopt |
| @cindex file names |
| @item @var{object-file-name} |
| A file name that does not end in a special recognized suffix is |
| considered to name an object file or library. (Object files are |
| distinguished from libraries by the linker according to the file |
| contents.) If linking is done, these object files are used as input |
| to the linker. |
| |
| @item -c |
| @itemx -S |
| @itemx -E |
| @opindex c |
| @opindex S |
| @opindex E |
| If any of these options is used, then the linker is not run, and |
| object file names should not be used as arguments. @xref{Overall |
| Options}. |
| |
| @item -flinker-output=@var{type} |
| @opindex flinker-output |
| This option controls code generation of the link-time optimizer. By |
| default the linker output is automatically determined by the linker |
| plugin. For debugging the compiler and if incremental linking with a |
| non-LTO object file is desired, it may be useful to control the type |
| manually. |
| |
| If @var{type} is @samp{exec}, code generation produces a static |
| binary. In this case @option{-fpic} and @option{-fpie} are both |
| disabled. |
| |
| If @var{type} is @samp{dyn}, code generation produces a shared |
| library. In this case @option{-fpic} or @option{-fPIC} is preserved, |
| but not enabled automatically. This allows to build shared libraries |
| without position-independent code on architectures where this is |
| possible, i.e.@: on x86. |
| |
| If @var{type} is @samp{pie}, code generation produces an @option{-fpie} |
| executable. This results in similar optimizations as @samp{exec} |
| except that @option{-fpie} is not disabled if specified at compilation |
| time. |
| |
| If @var{type} is @samp{rel}, the compiler assumes that incremental linking is |
| done. The sections containing intermediate code for link-time optimization are |
| merged, pre-optimized, and output to the resulting object file. In addition, if |
| @option{-ffat-lto-objects} is specified, binary code is produced for future |
| non-LTO linking. The object file produced by incremental linking is smaller |
| than a static library produced from the same object files. At link time the |
| result of incremental linking also loads faster than a static |
| library assuming that the majority of objects in the library are used. |
| |
| Finally @samp{nolto-rel} configures the compiler for incremental linking where |
| code generation is forced, a final binary is produced, and the intermediate |
| code for later link-time optimization is stripped. When multiple object files |
| are linked together the resulting code is better optimized than with |
| link-time optimizations disabled (for example, cross-module inlining |
| happens), but most of benefits of whole program optimizations are lost. |
| |
| During the incremental link (by @option{-r}) the linker plugin defaults to |
| @option{rel}. With current interfaces to GNU Binutils it is however not |
| possible to incrementally link LTO objects and non-LTO objects into a single |
| mixed object file. If any of object files in incremental link cannot |
| be used for link-time optimization, the linker plugin issues a warning and |
| uses @samp{nolto-rel}. To maintain whole program optimization, it is |
| recommended to link such objects into static library instead. Alternatively it |
| is possible to use H.J. Lu's binutils with support for mixed objects. |
| |
| @item -fuse-ld=bfd |
| @opindex fuse-ld=bfd |
| Use the @command{bfd} linker instead of the default linker. |
| |
| @item -fuse-ld=gold |
| @opindex fuse-ld=gold |
| Use the @command{gold} linker instead of the default linker. |
| |
| @item -fuse-ld=lld |
| @opindex fuse-ld=lld |
| Use the LLVM @command{lld} linker instead of the default linker. |
| |
| @item -fuse-ld=mold |
| @opindex fuse-ld=mold |
| Use the Modern Linker (@command{mold}) instead of the default linker. |
| |
| @cindex Libraries |
| @item -l@var{library} |
| @itemx -l @var{library} |
| @opindex l |
| Search the library named @var{library} when linking. (The second |
| alternative with the library as a separate argument is only for |
| POSIX compliance and is not recommended.) |
| |
| The @option{-l} option is passed directly to the linker by GCC. Refer |
| to your linker documentation for exact details. The general |
| description below applies to the GNU linker. |
| |
| The linker searches a standard list of directories for the library. |
| The directories searched include several standard system directories |
| plus any that you specify with @option{-L}. |
| |
| Static libraries are archives of object files, and have file names |
| like @file{lib@var{library}.a}. Some targets also support shared |
| libraries, which typically have names like @file{lib@var{library}.so}. |
| If both static and shared libraries are found, the linker gives |
| preference to linking with the shared library unless the |
| @option{-static} option is used. |
| |
| It makes a difference where in the command you write this option; the |
| linker searches and processes libraries and object files in the order they |
| are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z} |
| after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers |
| to functions in @samp{z}, those functions may not be loaded. |
| |
| @item -lobjc |
| @opindex lobjc |
| You need this special case of the @option{-l} option in order to |
| link an Objective-C or Objective-C++ program. |
| |
| @item -nostartfiles |
| @opindex nostartfiles |
| Do not use the standard system startup files when linking. |
| The standard system libraries are used normally, unless @option{-nostdlib}, |
| @option{-nolibc}, or @option{-nodefaultlibs} is used. |
| |
| @item -nodefaultlibs |
| @opindex nodefaultlibs |
| Do not use the standard system libraries when linking. |
| Only the libraries you specify are passed to the linker, and options |
| specifying linkage of the system libraries, such as @option{-static-libgcc} |
| or @option{-shared-libgcc}, are ignored. |
| The standard startup files are used normally, unless @option{-nostartfiles} |
| is used. |
| |
| The compiler may generate calls to @code{memcmp}, |
| @code{memset}, @code{memcpy} and @code{memmove}. |
| These entries are usually resolved by entries in |
| libc. These entry points should be supplied through some other |
| mechanism when this option is specified. |
| |
| @item -nolibc |
| @opindex nolibc |
| Do not use the C library or system libraries tightly coupled with it when |
| linking. Still link with the startup files, @file{libgcc} or toolchain |
| provided language support libraries such as @file{libgnat}, @file{libgfortran} |
| or @file{libstdc++} unless options preventing their inclusion are used as |
| well. This typically removes @option{-lc} from the link command line, as well |
| as system libraries that normally go with it and become meaningless when |
| absence of a C library is assumed, for example @option{-lpthread} or |
| @option{-lm} in some configurations. This is intended for bare-board |
| targets when there is indeed no C library available. |
| |
| @item -nostdlib |
| @opindex nostdlib |
| Do not use the standard system startup files or libraries when linking. |
| No startup files and only the libraries you specify are passed to |
| the linker, and options specifying linkage of the system libraries, such as |
| @option{-static-libgcc} or @option{-shared-libgcc}, are ignored. |
| |
| The compiler may generate calls to @code{memcmp}, @code{memset}, |
| @code{memcpy} and @code{memmove}. |
| These entries are usually resolved by entries in |
| libc. These entry points should be supplied through some other |
| mechanism when this option is specified. |
| |
| @cindex @option{-lgcc}, use with @option{-nostdlib} |
| @cindex @option{-nostdlib} and unresolved references |
| @cindex unresolved references and @option{-nostdlib} |
| @cindex @option{-lgcc}, use with @option{-nodefaultlibs} |
| @cindex @option{-nodefaultlibs} and unresolved references |
| @cindex unresolved references and @option{-nodefaultlibs} |
| One of the standard libraries bypassed by @option{-nostdlib} and |
| @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines |
| which GCC uses to overcome shortcomings of particular machines, or special |
| needs for some languages. |
| (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler |
| Collection (GCC) Internals}, |
| for more discussion of @file{libgcc.a}.) |
| In most cases, you need @file{libgcc.a} even when you want to avoid |
| other standard libraries. In other words, when you specify @option{-nostdlib} |
| or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well. |
| This ensures that you have no unresolved references to internal GCC |
| library subroutines. |
| (An example of such an internal subroutine is @code{__main}, used to ensure C++ |
| constructors are called; @pxref{Collect2,,@code{collect2}, gccint, |
| GNU Compiler Collection (GCC) Internals}.) |
| |
| @item -e @var{entry} |
| @itemx --entry=@var{entry} |
| @opindex e |
| @opindex entry |
| |
| Specify that the program entry point is @var{entry}. The argument is |
| interpreted by the linker; the GNU linker accepts either a symbol name |
| or an address. |
| |
| @item -pie |
| @opindex pie |
| Produce a dynamically linked position independent executable on targets |
| that support it. For predictable results, you must also specify the same |
| set of options used for compilation (@option{-fpie}, @option{-fPIE}, |
| or model suboptions) when you specify this linker option. |
| |
| @item -no-pie |
| @opindex no-pie |
| Don't produce a dynamically linked position independent executable. |
| |
| @item -static-pie |
| @opindex static-pie |
| Produce a static position independent executable on targets that support |
| it. A static position independent executable is similar to a static |
| executable, but can be loaded at any address without a dynamic linker. |
| For predictable results, you must also specify the same set of options |
| used for compilation (@option{-fpie}, @option{-fPIE}, or model |
| suboptions) when you specify this linker option. |
| |
| @item -pthread |
| @opindex pthread |
| Link with the POSIX threads library. This option is supported on |
| GNU/Linux targets, most other Unix derivatives, and also on |
| x86 Cygwin and MinGW targets. On some targets this option also sets |
| flags for the preprocessor, so it should be used consistently for both |
| compilation and linking. |
| |
| @item -r |
| @opindex r |
| Produce a relocatable object as output. This is also known as partial |
| linking. |
| |
| @item -rdynamic |
| @opindex rdynamic |
| Pass the flag @option{-export-dynamic} to the ELF linker, on targets |
| that support it. This instructs the linker to add all symbols, not |
| only used ones, to the dynamic symbol table. This option is needed |
| for some uses of @code{dlopen} or to allow obtaining backtraces |
| from within a program. |
| |
| @item -s |
| @opindex s |
| Remove all symbol table and relocation information from the executable. |
| |
| @item -static |
| @opindex static |
| On systems that support dynamic linking, this overrides @option{-pie} |
| and prevents linking with the shared libraries. On other systems, this |
| option has no effect. |
| |
| @item -shared |
| @opindex shared |
| Produce a shared object which can then be linked with other objects to |
| form an executable. Not all systems support this option. For predictable |
| results, you must also specify the same set of options used for compilation |
| (@option{-fpic}, @option{-fPIC}, or model suboptions) when |
| you specify this linker option.@footnote{On some systems, @samp{gcc -shared} |
| needs to build supplementary stub code for constructors to work. On |
| multi-libbed systems, @samp{gcc -shared} must select the correct support |
| libraries to link against. Failing to supply the correct flags may lead |
| to subtle defects. Supplying them in cases where they are not necessary |
| is innocuous.} |
| |
| @item -shared-libgcc |
| @itemx -static-libgcc |
| @opindex shared-libgcc |
| @opindex static-libgcc |
| On systems that provide @file{libgcc} as a shared library, these options |
| force the use of either the shared or static version, respectively. |
| If no shared version of @file{libgcc} was built when the compiler was |
| configured, these options have no effect. |
| |
| There are several situations in which an application should use the |
| shared @file{libgcc} instead of the static version. The most common |
| of these is when the application wishes to throw and catch exceptions |
| across different shared libraries. In that case, each of the libraries |
| as well as the application itself should use the shared @file{libgcc}. |
| |
| Therefore, the G++ driver automatically adds @option{-shared-libgcc} |
| whenever you build a shared library or a main executable, because C++ |
| programs typically use exceptions, so this is the right thing to do. |
| |
| If, instead, you use the GCC driver to create shared libraries, you may |
| find that they are not always linked with the shared @file{libgcc}. |
| If GCC finds, at its configuration time, that you have a non-GNU linker |
| or a GNU linker that does not support option @option{--eh-frame-hdr}, |
| it links the shared version of @file{libgcc} into shared libraries |
| by default. Otherwise, it takes advantage of the linker and optimizes |
| away the linking with the shared version of @file{libgcc}, linking with |
| the static version of libgcc by default. This allows exceptions to |
| propagate through such shared libraries, without incurring relocation |
| costs at library load time. |
| |
| However, if a library or main executable is supposed to throw or catch |
| exceptions, you must link it using the G++ driver, or using the option |
| @option{-shared-libgcc}, such that it is linked with the shared |
| @file{libgcc}. |
| |
| @item -static-libasan |
| @opindex static-libasan |
| When the @option{-fsanitize=address} option is used to link a program, |
| the GCC driver automatically links against @option{libasan}. If |
| @file{libasan} is available as a shared library, and the @option{-static} |
| option is not used, then this links against the shared version of |
| @file{libasan}. The @option{-static-libasan} option directs the GCC |
| driver to link @file{libasan} statically, without necessarily linking |
| other libraries statically. |
| |
| @item -static-libtsan |
| @opindex static-libtsan |
| When the @option{-fsanitize=thread} option is used to link a program, |
| the GCC driver automatically links against @option{libtsan}. If |
| @file{libtsan} is available as a shared library, and the @option{-static} |
| option is not used, then this links against the shared version of |
| @file{libtsan}. The @option{-static-libtsan} option directs the GCC |
| driver to link @file{libtsan} statically, without necessarily linking |
| other libraries statically. |
| |
| @item -static-liblsan |
| @opindex static-liblsan |
| When the @option{-fsanitize=leak} option is used to link a program, |
| the GCC driver automatically links against @option{liblsan}. If |
| @file{liblsan} is available as a shared library, and the @option{-static} |
| option is not used, then this links against the shared version of |
| @file{liblsan}. The @option{-static-liblsan} option directs the GCC |
| driver to link @file{liblsan} statically, without necessarily linking |
| other libraries statically. |
| |
| @item -static-libubsan |
| @opindex static-libubsan |
| When the @option{-fsanitize=undefined} option is used to link a program, |
| the GCC driver automatically links against @option{libubsan}. If |
| @file{libubsan} is available as a shared library, and the @option{-static} |
| option is not used, then this links against the shared version of |
| @file{libubsan}. The @option{-static-libubsan} option directs the GCC |
| driver to link @file{libubsan} statically, without necessarily linking |
| other libraries statically. |
| |
| @item -static-libstdc++ |
| @opindex static-libstdc++ |
| When the @command{g++} program is used to link a C++ program, it |
| normally automatically links against @option{libstdc++}. If |
| @file{libstdc++} is available as a shared library, and the |
| @option{-static} option is not used, then this links against the |
| shared version of @file{libstdc++}. That is normally fine. However, it |
| is sometimes useful to freeze the version of @file{libstdc++} used by |
| the program without going all the way to a fully static link. The |
| @option{-static-libstdc++} option directs the @command{g++} driver to |
| link @file{libstdc++} statically, without necessarily linking other |
| libraries statically. |
| |
| @item -symbolic |
| @opindex symbolic |
| Bind references to global symbols when building a shared object. Warn |
| about any unresolved references (unless overridden by the link editor |
| option @option{-Xlinker -z -Xlinker defs}). Only a few systems support |
| this option. |
| |
| @item -T @var{script} |
| @opindex T |
| @cindex linker script |
| Use @var{script} as the linker script. This option is supported by most |
| systems using the GNU linker. On some targets, such as bare-board |
| targets without an operating system, the @option{-T} option may be required |
| when linking to avoid references to undefined symbols. |
| |
| @item -Xlinker @var{option} |
| @opindex Xlinker |
| Pass @var{option} as an option to the linker. You can use this to |
| supply system-specific linker options that GCC does not recognize. |
| |
| If you want to pass an option that takes a separate argument, you must use |
| @option{-Xlinker} twice, once for the option and once for the argument. |
| For example, to pass @option{-assert definitions}, you must write |
| @option{-Xlinker -assert -Xlinker definitions}. It does not work to write |
| @option{-Xlinker "-assert definitions"}, because this passes the entire |
| string as a single argument, which is not what the linker expects. |
| |
| When using the GNU linker, it is usually more convenient to pass |
| arguments to linker options using the @option{@var{option}=@var{value}} |
| syntax than as separate arguments. For example, you can specify |
| @option{-Xlinker -Map=output.map} rather than |
| @option{-Xlinker -Map -Xlinker output.map}. Other linkers may not support |
| this syntax for command-line options. |
| |
| @item -Wl,@var{option} |
| @opindex Wl |
| Pass @var{option} as an option to the linker. If @var{option} contains |
| commas, it is split into multiple options at the commas. You can use this |
| syntax to pass an argument to the option. |
| For example, @option{-Wl,-Map,output.map} passes @option{-Map output.map} to the |
| linker. When using the GNU linker, you can also get the same effect with |
| @option{-Wl,-Map=output.map}. |
| |
| @item -u @var{symbol} |
| @opindex u |
| Pretend the symbol @var{symbol} is undefined, to force linking of |
| library modules to define it. You can use @option{-u} multiple times with |
| different symbols to force loading of additional library modules. |
| |
| @item -z @var{keyword} |
| @opindex z |
| @option{-z} is passed directly on to the linker along with the keyword |
| @var{keyword}. See the section in the documentation of your linker for |
| permitted values and their meanings. |
| @end table |
| |
| @node Directory Options |
| @section Options for Directory Search |
| @cindex directory options |
| @cindex options, directory search |
| @cindex search path |
| |
| These options specify directories to search for header files, for |
| libraries and for parts of the compiler: |
| |
| @table @gcctabopt |
| @include cppdiropts.texi |
| |
| @item -iplugindir=@var{dir} |
| @opindex iplugindir= |
| Set the directory to search for plugins that are passed |
| by @option{-fplugin=@var{name}} instead of |
| @option{-fplugin=@var{path}/@var{name}.so}. This option is not meant |
| to be used by the user, but only passed by the driver. |
| |
| @item -L@var{dir} |
| @opindex L |
| Add directory @var{dir} to the list of directories to be searched |
| for @option{-l}. |
| |
| @item -B@var{prefix} |
| @opindex B |
| This option specifies where to find the executables, libraries, |
| include files, and data files of the compiler itself. |
| |
| The compiler driver program runs one or more of the subprograms |
| @command{cpp}, @command{cc1}, @command{as} and @command{ld}. It tries |
| @var{prefix} as a prefix for each program it tries to run, both with and |
| without @samp{@var{machine}/@var{version}/} for the corresponding target |
| machine and compiler version. |
| |
| For each subprogram to be run, the compiler driver first tries the |
| @option{-B} prefix, if any. If that name is not found, or if @option{-B} |
| is not specified, the driver tries two standard prefixes, |
| @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of |
| those results in a file name that is found, the unmodified program |
| name is searched for using the directories specified in your |
| @env{PATH} environment variable. |
| |
| The compiler checks to see if the path provided by @option{-B} |
| refers to a directory, and if necessary it adds a directory |
| separator character at the end of the path. |
| |
| @option{-B} prefixes that effectively specify directory names also apply |
| to libraries in the linker, because the compiler translates these |
| options into @option{-L} options for the linker. They also apply to |
| include files in the preprocessor, because the compiler translates these |
| options into @option{-isystem} options for the preprocessor. In this case, |
| the compiler appends @samp{include} to the prefix. |
| |
| The runtime support file @file{libgcc.a} can also be searched for using |
| the @option{-B} prefix, if needed. If it is not found there, the two |
| standard prefixes above are tried, and that is all. The file is left |
| out of the link if it is not found by those means. |
| |
| Another way to specify a prefix much like the @option{-B} prefix is to use |
| the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment |
| Variables}. |
| |
| As a special kludge, if the path provided by @option{-B} is |
| @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to |
| 9, then it is replaced by @file{[dir/]include}. This is to help |
| with boot-strapping the compiler. |
| |
| @item -no-canonical-prefixes |
| @opindex no-canonical-prefixes |
| Do not expand any symbolic links, resolve references to @samp{/../} |
| or @samp{/./}, or make the path absolute when generating a relative |
| prefix. |
| |
| @item --sysroot=@var{dir} |
| @opindex sysroot |
| Use @var{dir} as the logical root directory for headers and libraries. |
| For example, if the compiler normally searches for headers in |
| @file{/usr/include} and libraries in @file{/usr/lib}, it instead |
| searches @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}. |
| |
| If you use both this option and the @option{-isysroot} option, then |
| the @option{--sysroot} option applies to libraries, but the |
| @option{-isysroot} option applies to header files. |
| |
| The GNU linker (beginning with version 2.16) has the necessary support |
| for this option. If your linker does not support this option, the |
| header file aspect of @option{--sysroot} still works, but the |
| library aspect does not. |
| |
| @item --no-sysroot-suffix |
| @opindex no-sysroot-suffix |
| For some targets, a suffix is added to the root directory specified |
| with @option{--sysroot}, depending on the other options used, so that |
| headers may for example be found in |
| @file{@var{dir}/@var{suffix}/usr/include} instead of |
| @file{@var{dir}/usr/include}. This option disables the addition of |
| such a suffix. |
| |
| @end table |
| |
| @node Code Gen Options |
| @section Options for Code Generation Conventions |
| @cindex code generation conventions |
| @cindex options, code generation |
| @cindex run-time options |
| |
| These machine-independent options control the interface conventions |
| used in code generation. |
| |
| Most of them have both positive and negative forms; the negative form |
| of @option{-ffoo} is @option{-fno-foo}. In the table below, only |
| one of the forms is listed---the one that is not the default. You |
| can figure out the other form by either removing @samp{no-} or adding |
| it. |
| |
| @table @gcctabopt |
| @item -fstack-reuse=@var{reuse-level} |
| @opindex fstack_reuse |
| This option controls stack space reuse for user declared local/auto variables |
| and compiler generated temporaries. @var{reuse_level} can be @samp{all}, |
| @samp{named_vars}, or @samp{none}. @samp{all} enables stack reuse for all |
| local variables and temporaries, @samp{named_vars} enables the reuse only for |
| user defined local variables with names, and @samp{none} disables stack reuse |
| completely. The default value is @samp{all}. The option is needed when the |
| program extends the lifetime of a scoped local variable or a compiler generated |
| temporary beyond the end point defined by the language. When a lifetime of |
| a variable ends, and if the variable lives in memory, the optimizing compiler |
| has the freedom to reuse its stack space with other temporaries or scoped |
| local variables whose live range does not overlap with it. Legacy code extending |
| local lifetime is likely to break with the stack reuse optimization. |
| |
| For example, |
| |
| @smallexample |
| int *p; |
| @{ |
| int local1; |
| |
| p = &local1; |
| local1 = 10; |
| .... |
| @} |
| @{ |
| int local2; |
| local2 = 20; |
| ... |
| @} |
| |
| if (*p == 10) // out of scope use of local1 |
| @{ |
| |
| @} |
| @end smallexample |
| |
| Another example: |
| @smallexample |
| |
| struct A |
| @{ |
| A(int k) : i(k), j(k) @{ @} |
| int i; |
| int j; |
| @}; |
| |
| A *ap; |
| |
| void foo(const A& ar) |
| @{ |
| ap = &ar; |
| @} |
| |
| void bar() |
| @{ |
| foo(A(10)); // temp object's lifetime ends when foo returns |
| |
| @{ |
| A a(20); |
| .... |
| @} |
| ap->i+= 10; // ap references out of scope temp whose space |
| // is reused with a. What is the value of ap->i? |
| @} |
| |
| @end smallexample |
| |
| The lifetime of a compiler generated temporary is well defined by the C++ |
| standard. When a lifetime of a temporary ends, and if the temporary lives |
| in memory, the optimizing compiler has the freedom to reuse its stack |
| space with other temporaries or scoped local variables whose live range |
| does not overlap with it. However some of the legacy code relies on |
| the behavior of older compilers in which temporaries' stack space is |
| not reused, the aggressive stack reuse can lead to runtime errors. This |
| option is used to control the temporary stack reuse optimization. |
| |
| @item -ftrapv |
| @opindex ftrapv |
| This option generates traps for signed overflow on addition, subtraction, |
| multiplication operations. |
| The options @option{-ftrapv} and @option{-fwrapv} override each other, so using |
| @option{-ftrapv} @option{-fwrapv} on the command-line results in |
| @option{-fwrapv} being effective. Note that only active options override, so |
| using @option{-ftrapv} @option{-fwrapv} @option{-fno-wrapv} on the command-line |
| results in @option{-ftrapv} being effective. |
| |
| @item -fwrapv |
| @opindex fwrapv |
| This option instructs the compiler to assume that signed arithmetic |
| overflow of addition, subtraction and multiplication wraps around |
| using twos-complement representation. This flag enables some optimizations |
| and disables others. |
| The options @option{-ftrapv} and @option{-fwrapv} override each other, so using |
| @option{-ftrapv} @option{-fwrapv} on the command-line results in |
| @option{-fwrapv} being effective. Note that only active options override, so |
| using @option{-ftrapv} @option{-fwrapv} @option{-fno-wrapv} on the command-line |
| results in @option{-ftrapv} being effective. |
| |
| @item -fwrapv-pointer |
| @opindex fwrapv-pointer |
| This option instructs the compiler to assume that pointer arithmetic |
| overflow on addition and subtraction wraps around using twos-complement |
| representation. This flag disables some optimizations which assume |
| pointer overflow is invalid. |
| |
| @item -fstrict-overflow |
| @opindex fstrict-overflow |
| This option implies @option{-fno-wrapv} @option{-fno-wrapv-pointer} and when |
| negated implies @option{-fwrapv} @option{-fwrapv-pointer}. |
| |
| @item -fexceptions |
| @opindex fexceptions |
| Enable exception handling. Generates extra code needed to propagate |
| exceptions. For some targets, this implies GCC generates frame |
| unwind information for all functions, which can produce significant data |
| size overhead, although it does not affect execution. If you do not |
| specify this option, GCC enables it by default for languages like |
| C++ that normally require exception handling, and disables it for |
| languages like C that do not normally require it. However, you may need |
| to enable this option when compiling C code that needs to interoperate |
| properly with exception handlers written in C++. You may also wish to |
| disable this option if you are compiling older C++ programs that don't |
| use exception handling. |
| |
| @item -fnon-call-exceptions |
| @opindex fnon-call-exceptions |
| Generate code that allows trapping instructions to throw exceptions. |
| Note that this requires platform-specific runtime support that does |
| not exist everywhere. Moreover, it only allows @emph{trapping} |
| instructions to throw exceptions, i.e.@: memory references or floating-point |
| instructions. It does not allow exceptions to be thrown from |
| arbitrary signal handlers such as @code{SIGALRM}. This enables |
| @option{-fexceptions}. |
| |
| @item -fdelete-dead-exceptions |
| @opindex fdelete-dead-exceptions |
| Consider that instructions that may throw exceptions but don't otherwise |
| contribute to the execution of the program can be optimized away. |
| This does not affect calls to functions except those with the |
| @code{pure} or @code{const} attributes. |
| This option is enabled by default for the Ada and C++ compilers, as permitted by |
| the language specifications. |
| Optimization passes that cause dead exceptions to be removed are enabled independently at different optimization levels. |
| |
| @item -funwind-tables |
| @opindex funwind-tables |
| Similar to @option{-fexceptions}, except that it just generates any needed |
| static data, but does not affect the generated code in any other way. |
| You normally do not need to enable this option; instead, a language processor |
| that needs this handling enables it on your behalf. |
| |
| @item -fasynchronous-unwind-tables |
| @opindex fasynchronous-unwind-tables |
| Generate unwind table in DWARF format, if supported by target machine. The |
| table is exact at each instruction boundary, so it can be used for stack |
| unwinding from asynchronous events (such as debugger or garbage collector). |
| |
| @item -fno-gnu-unique |
| @opindex fno-gnu-unique |
| @opindex fgnu-unique |
| On systems with recent GNU assembler and C library, the C++ compiler |
| uses the @code{STB_GNU_UNIQUE} binding to make sure that definitions |
| of template static data members and static local variables in inline |
| functions are unique even in the presence of @code{RTLD_LOCAL}; this |
| is necessary to avoid problems with a library used by two different |
| @code{RTLD_LOCAL} plugins depending on a definition in one of them and |
| therefore disagreeing with the other one about the binding of the |
| symbol. But this causes @code{dlclose} to be ignored for affected |
| DSOs; if your program relies on reinitialization of a DSO via |
| @code{dlclose} and @code{dlopen}, you can use |
| @option{-fno-gnu-unique}. |
| |
| @item -fpcc-struct-return |
| @opindex fpcc-struct-return |
| Return ``short'' @code{struct} and @code{union} values in memory like |
| longer ones, rather than in registers. This convention is less |
| efficient, but it has the advantage of allowing intercallability between |
| GCC-compiled files and files compiled with other compilers, particularly |
| the Portable C Compiler (pcc). |
| |
| The precise convention for returning structures in memory depends |
| on the target configuration macros. |
| |
| Short structures and unions are those whose size and alignment match |
| that of some integer type. |
| |
| @strong{Warning:} code compiled with the @option{-fpcc-struct-return} |
| switch is not binary compatible with code compiled with the |
| @option{-freg-struct-return} switch. |
| Use it to conform to a non-default application binary interface. |
| |
| @item -freg-struct-return |
| @opindex freg-struct-return |
| Return @code{struct} and @code{union} values in registers when possible. |
| This is more efficient for small structures than |
| @option{-fpcc-struct-return}. |
| |
| If you specify neither @option{-fpcc-struct-return} nor |
| @option{-freg-struct-return}, GCC defaults to whichever convention is |
| standard for the target. If there is no standard convention, GCC |
| defaults to @option{-fpcc-struct-return}, except on targets where GCC is |
| the principal compiler. In those cases, we can choose the standard, and |
| we chose the more efficient register return alternative. |
| |
| @strong{Warning:} code compiled with the @option{-freg-struct-return} |
| switch is not binary compatible with code compiled with the |
| @option{-fpcc-struct-return} switch. |
| Use it to conform to a non-default application binary interface. |
| |
| @item -fshort-enums |
| @opindex fshort-enums |
| Allocate to an @code{enum} type only as many bytes as it needs for the |
| declared range of possible values. Specifically, the @code{enum} type |
| is equivalent to the smallest integer type that has enough room. |
| |
| @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate |
| code that is not binary compatible with code generated without that switch. |
| Use it to conform to a non-default application binary interface. |
| |
| @item -fshort-wchar |
| @opindex fshort-wchar |
| Override the underlying type for @code{wchar_t} to be @code{short |
| unsigned int} instead of the default for the target. This option is |
| useful for building programs to run under WINE@. |
| |
| @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate |
| code that is not binary compatible with code generated without that switch. |
| Use it to conform to a non-default application binary interface. |
| |
| @item -fcommon |
| @opindex fcommon |
| @opindex fno-common |
| @cindex tentative definitions |
| In C code, this option controls the placement of global variables |
| defined without an initializer, known as @dfn{tentative definitions} |
| in the C standard. Tentative definitions are distinct from declarations |
| of a variable with the @code{extern} keyword, which do not allocate storage. |
| |
| The default is @option{-fno-common}, which specifies that the compiler places |
| uninitialized global variables in the BSS section of the object file. |
| This inhibits the merging of tentative definitions by the linker so you get a |
| multiple-definition error if the same variable is accidentally defined in more |
| than one compilation unit. |
| |
| The @option{-fcommon} places uninitialized global variables in a common block. |
| This allows the linker to resolve all tentative definitions of the same variable |
| in different compilation units to the same object, or to a non-tentative |
| definition. This behavior is inconsistent with C++, and on many targets implies |
| a speed and code size penalty on global variable references. It is mainly |
| useful to enable legacy code to link without errors. |
| |
| @item -fno-ident |
| @opindex fno-ident |
| @opindex fident |
| Ignore the @code{#ident} directive. |
| |
| @item -finhibit-size-directive |
| @opindex finhibit-size-directive |
| Don't output a @code{.size} assembler directive, or anything else that |
| would cause trouble if the function is split in the middle, and the |
| two halves are placed at locations far apart in memory. This option is |
| used when compiling @file{crtstuff.c}; you should not need to use it |
| for anything else. |
| |
| @item -fverbose-asm |
| @opindex fverbose-asm |
| Put extra commentary information in the generated assembly code to |
| make it more readable. This option is generally only of use to those |
| who actually need to read the generated assembly code (perhaps while |
| debugging the compiler itself). |
| |
| @option{-fno-verbose-asm}, the default, causes the |
| extra information to be omitted and is useful when comparing two assembler |
| files. |
| |
| The added comments include: |
| |
| @itemize @bullet |
| |
| @item |
| information on the compiler version and command-line options, |
| |
| @item |
| the source code lines associated with the assembly instructions, |
| in the form FILENAME:LINENUMBER:CONTENT OF LINE, |
| |
| @item |
| hints on which high-level expressions correspond to |
| the various assembly instruction operands. |
| |
| @end itemize |
| |
| For example, given this C source file: |
| |
| @smallexample |
| int test (int n) |
| @{ |
| int i; |
| int total = 0; |
| |
| for (i = 0; i < n; i++) |
| total += i * i; |
| |
| return total; |
| @} |
| @end smallexample |
| |
| compiling to (x86_64) assembly via @option{-S} and emitting the result |
| direct to stdout via @option{-o} @option{-} |
| |
| @smallexample |
| gcc -S test.c -fverbose-asm -Os -o - |
| @end smallexample |
| |
| gives output similar to this: |
| |
| @smallexample |
| .file "test.c" |
| # GNU C11 (GCC) version 7.0.0 20160809 (experimental) (x86_64-pc-linux-gnu) |
| [...snip...] |
| # options passed: |
| [...snip...] |
| |
| .text |
| .globl test |
| .type test, @@function |
| test: |
| .LFB0: |
| .cfi_startproc |
| # test.c:4: int total = 0; |
| xorl %eax, %eax # <retval> |
| # test.c:6: for (i = 0; i < n; i++) |
| xorl %edx, %edx # i |
| .L2: |
| # test.c:6: for (i = 0; i < n; i++) |
| cmpl %edi, %edx # n, i |
| jge .L5 #, |
| # test.c:7: total += i * i; |
| movl %edx, %ecx # i, tmp92 |
| imull %edx, %ecx # i, tmp92 |
| # test.c:6: for (i = 0; i < n; i++) |
| incl %edx # i |
| # test.c:7: total += i * i; |
| addl %ecx, %eax # tmp92, <retval> |
| jmp .L2 # |
| .L5: |
| # test.c:10: @} |
| ret |
| .cfi_endproc |
| .LFE0: |
| .size test, .-test |
| .ident "GCC: (GNU) 7.0.0 20160809 (experimental)" |
| .section .note.GNU-stack,"",@@progbits |
| @end smallexample |
| |
| The comments are intended for humans rather than machines and hence the |
| precise format of the comments is subject to change. |
| |
| @item -frecord-gcc-switches |
| @opindex frecord-gcc-switches |
| This switch causes the command line used to invoke the |
| compiler to be recorded into the object file that is being created. |
| This switch is only implemented on some targets and the exact format |
| of the recording is target and binary file format dependent, but it |
| usually takes the form of a section containing ASCII text. This |
| switch is related to the @option{-fverbose-asm} switch, but that |
| switch only records information in the assembler output file as |
| comments, so it never reaches the object file. |
| See also @option{-grecord-gcc-switches} for another |
| way of storing compiler options into the object file. |
| |
| @item -fpic |
| @opindex fpic |
| @cindex global offset table |
| @cindex PIC |
| Generate position-independent code (PIC) suitable for use in a shared |
| library, if supported for the target machine. Such code accesses all |
| constant addresses through a global offset table (GOT)@. The dynamic |
| loader resolves the GOT entries when the program starts (the dynamic |
| loader is not part of GCC; it is part of the operating system). If |
| the GOT size for the linked executable exceeds a machine-specific |
| maximum size, you get an error message from the linker indicating that |
| @option{-fpic} does not work; in that case, recompile with @option{-fPIC} |
| instead. (These maximums are 8k on the SPARC, 28k on AArch64 and 32k |
| on the m68k and RS/6000. The x86 has no such limit.) |
| |
| Position-independent code requires special support, and therefore works |
| only on certain machines. For the x86, GCC supports PIC for System V |
| but not for the Sun 386i. Code generated for the IBM RS/6000 is always |
| position-independent. |
| |
| When this flag is set, the macros @code{__pic__} and @code{__PIC__} |
| are defined to 1. |
| |
| @item -fPIC |
| @opindex fPIC |
| If supported for the target machine, emit position-independent code, |
| suitable for dynamic linking and avoiding any limit on the size of the |
| global offset table. This option makes a difference on AArch64, m68k, |
| PowerPC and SPARC@. |
| |
| Position-independent code requires special support, and therefore works |
| only on certain machines. |
| |
| When this flag is set, the macros @code{__pic__} and @code{__PIC__} |
| are defined to 2. |
| |
| @item -fpie |
| @itemx -fPIE |
| @opindex fpie |
| @opindex fPIE |
| These options are similar to @option{-fpic} and @option{-fPIC}, but the |
| generated position-independent code can be only linked into executables. |
| Usually these options are used to compile code that will be linked using |
| the @option{-pie} GCC option. |
| |
| @option{-fpie} and @option{-fPIE} both define the macros |
| @code{__pie__} and @code{__PIE__}. The macros have the value 1 |
| for @option{-fpie} and 2 for @option{-fPIE}. |
| |
| @item -fno-plt |
| @opindex fno-plt |
| @opindex fplt |
| Do not use the PLT for external function calls in position-independent code. |
| Instead, load the callee address at call sites from the GOT and branch to it. |
| This leads to more efficient code by eliminating PLT stubs and exposing |
| GOT loads to optimizations. On architectures such as 32-bit x86 where |
| PLT stubs expect the GOT pointer in a specific register, this gives more |
| register allocation freedom to the compiler. |
| Lazy binding requires use of the PLT; |
| with @option{-fno-plt} all external symbols are resolved at load time. |
| |
| Alternatively, the function attribute @code{noplt} can be used to avoid calls |
| through the PLT for specific external functions. |
| |
| In position-dependent code, a few targets also convert calls to |
| functions that are marked to not use the PLT to use the GOT instead. |
| |
| @item -fno-jump-tables |
| @opindex fno-jump-tables |
| @opindex fjump-tables |
| Do not use jump tables for switch statements even where it would be |
| more efficient than other code generation strategies. This option is |
| of use in conjunction with @option{-fpic} or @option{-fPIC} for |
| building code that forms part of a dynamic linker and cannot |
| reference the address of a jump table. On some targets, jump tables |
| do not require a GOT and this option is not needed. |
| |
| @item -fno-bit-tests |
| @opindex fno-bit-tests |
| @opindex fbit-tests |
| Do not use bit tests for switch statements even where it would be |
| more efficient than other code generation strategies. |
| |
| @item -ffixed-@var{reg} |
| @opindex ffixed |
| Treat the register named @var{reg} as a fixed register; generated code |
| should never refer to it (except perhaps as a stack pointer, frame |
| pointer or in some other fixed role). |
| |
| @var{reg} must be the name of a register. The register names accepted |
| are machine-specific and are defined in the @code{REGISTER_NAMES} |
| macro in the machine description macro file. |
| |
| This flag does not have a negative form, because it specifies a |
| three-way choice. |
| |
| @item -fcall-used-@var{reg} |
| @opindex fcall-used |
| Treat the register named @var{reg} as an allocable register that is |
| clobbered by function calls. It may be allocated for temporaries or |
| variables that do not live across a call. Functions compiled this way |
| do not save and restore the register @var{reg}. |
| |
| It is an error to use this flag with the frame pointer or stack pointer. |
| Use of this flag for other registers that have fixed pervasive roles in |
| the machine's execution model produces disastrous results. |
| |
| This flag does not have a negative form, because it specifies a |
| three-way choice. |
| |
| @item -fcall-saved-@var{reg} |
| @opindex fcall-saved |
| Treat the register named @var{reg} as an allocable register saved by |
| functions. It may be allocated even for temporaries or variables that |
| live across a call. Functions compiled this way save and restore |
| the register @var{reg} if they use it. |
| |
| It is an error to use this flag with the frame pointer or stack pointer. |
| Use of this flag for other registers that have fixed pervasive roles in |
| the machine's execution model produces disastrous results. |
| |
| A different sort of disaster results from the use of this flag for |
| a register in which function values may be returned. |
| |
| This flag does not have a negative form, because it specifies a |
| three-way choice. |
| |
| @item -fpack-struct[=@var{n}] |
| @opindex fpack-struct |
| Without a value specified, pack all structure members together without |
| holes. When a value is specified (which must be a small power of two), pack |
| structure members according to this value, representing the maximum |
| alignment (that is, objects with default alignment requirements larger than |
| this are output potentially unaligned at the next fitting location. |
| |
| @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate |
| code that is not binary compatible with code generated without that switch. |
| Additionally, it makes the code suboptimal. |
| Use it to conform to a non-default application binary interface. |
| |
| @item -fleading-underscore |
| @opindex fleading-underscore |
| This option and its counterpart, @option{-fno-leading-underscore}, forcibly |
| change the way C symbols are represented in the object file. One use |
| is to help link with legacy assembly code. |
| |
| @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to |
| generate code that is not binary compatible with code generated without that |
| switch. Use it to conform to a non-default application binary interface. |
| Not all targets provide complete support for this switch. |
| |
| @item -ftls-model=@var{model} |
| @opindex ftls-model |
| Alter the thread-local storage model to be used (@pxref{Thread-Local}). |
| The @var{model} argument should be one of @samp{global-dynamic}, |
| @samp{local-dynamic}, @samp{initial-exec} or @samp{local-exec}. |
| Note that the choice is subject to optimization: the compiler may use |
| a more efficient model for symbols not visible outside of the translation |
| unit, or if @option{-fpic} is not given on the command line. |
| |
| The default without @option{-fpic} is @samp{initial-exec}; with |
| @option{-fpic} the default is @samp{global-dynamic}. |
| |
| @item -ftrampolines |
| @opindex ftrampolines |
| For targets that normally need trampolines for nested functions, always |
| generate them instead of using descriptors. Otherwise, for targets that |
| do not need them, like for example HP-PA or IA-64, do nothing. |
| |
| A trampoline is a small piece of code that is created at run time on the |
| stack when the address of a nested function is taken, and is used to call |
| the nested function indirectly. Therefore, it requires the stack to be |
| made executable in order for the program to work properly. |
| |
| @option{-fno-trampolines} is enabled by default on a language by language |
| basis to let the compiler avoid generating them, if it computes that this |
| is safe, and replace them with descriptors. Descriptors are made up of data |
| only, but the generated code must be prepared to deal with them. As of this |
| writing, @option{-fno-trampolines} is enabled by default only for Ada. |
| |
| Moreover, code compiled with @option{-ftrampolines} and code compiled with |
| @option{-fno-trampolines} are not binary compatible if nested functions are |
| present. This option must therefore be used on a program-wide basis and be |
| manipulated with extreme care. |
| |
| For languages other than Ada, the @code{-ftrampolines} and |
| @code{-fno-trampolines} options currently have no effect, and |
| trampolines are always generated on platforms that need them |
| for nested functions. |
| |
| @item -fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]} |
| @opindex fvisibility |
| Set the default ELF image symbol visibility to the specified option---all |
| symbols are marked with this unless overridden within the code. |
| Using this feature can very substantially improve linking and |
| load times of shared object libraries, produce more optimized |
| code, provide near-perfect API export and prevent symbol clashes. |
| It is @strong{strongly} recommended that you use this in any shared objects |
| you distribute. |
| |
| Despite the nomenclature, @samp{default} always means public; i.e., |
| available to be linked against from outside the shared object. |
| @samp{protected} and @samp{internal} are pretty useless in real-world |
| usage so the only other commonly used option is @samp{hidden}. |
| The default if @option{-fvisibility} isn't specified is |
| @samp{default}, i.e., make every symbol public. |
| |
| A good explanation of the benefits offered by ensuring ELF |
| symbols have the correct visibility is given by ``How To Write |
| Shared Libraries'' by Ulrich Drepper (which can be found at |
| @w{@uref{https://www.akkadia.org/drepper/}})---however a superior |
| solution made possible by this option to marking things hidden when |
| the default is public is to make the default hidden and mark things |
| public. This is the norm with DLLs on Windows and with @option{-fvisibility=hidden} |
| and @code{__attribute__ ((visibility("default")))} instead of |
| @code{__declspec(dllexport)} you get almost identical semantics with |
| identical syntax. This is a great boon to those working with |
| cross-platform projects. |
| |
| For those adding visibility support to existing code, you may find |
| @code{#pragma GCC visibility} of use. This works by you enclosing |
| the declarations you wish to set visibility for with (for example) |
| @code{#pragma GCC visibility push(hidden)} and |
| @code{#pragma GCC visibility pop}. |
| Bear in mind that symbol visibility should be viewed @strong{as |
| part of the API interface contract} and thus all new code should |
| always specify visibility when it is not the default; i.e., declarations |
| only for use within the local DSO should @strong{always} be marked explicitly |
| as hidden as so to avoid PLT indirection overheads---making this |
| abundantly clear also aids readability and self-documentation of the code. |
| Note that due to ISO C++ specification requirements, @code{operator new} and |
| @code{operator delete} must always be of default visibility. |
| |
| Be aware that headers from outside your project, in particular system |
| headers and headers from any other library you use, may not be |
| expecting to be compiled with visibility other than the default. You |
| may need to explicitly say @code{#pragma GCC visibility push(default)} |
| before including any such headers. |
| |
| @code{extern} declarations are not affected by @option{-fvisibility}, so |
| a lot of code can be recompiled with @option{-fvisibility=hidden} with |
| no modifications. However, this means that calls to @code{extern} |
| functions with no explicit visibility use the PLT, so it is more |
| effective to use @code{__attribute ((visibility))} and/or |
| @code{#pragma GCC visibility} to tell the compiler which @code{extern} |
| declarations should be treated as hidden. |
| |
| Note that @option{-fvisibility} does affect C++ vague linkage |
| entities. This means that, for instance, an exception class that is |
| be thrown between DSOs must be explicitly marked with default |
| visibility so that the @samp{type_info} nodes are unified between |
| the DSOs. |
| |
| An overview of these techniques, their benefits and how to use them |
| is at @uref{https://gcc.gnu.org/@/wiki/@/Visibility}. |
| |
| @item -fstrict-volatile-bitfields |
| @opindex fstrict-volatile-bitfields |
| This option should be used if accesses to volatile bit-fields (or other |
| structure fields, although the compiler usually honors those types |
| anyway) should use a single access of the width of the |
| field's type, aligned to a natural alignment if possible. For |
| example, targets with memory-mapped peripheral registers might require |
| all such accesses to be 16 bits wide; with this flag you can |
| declare all peripheral bit-fields as @code{unsigned short} (assuming short |
| is 16 bits on these targets) to force GCC to use 16-bit accesses |
| instead of, perhaps, a more efficient 32-bit access. |
| |
| If this option is disabled, the compiler uses the most efficient |
| instruction. In the previous example, that might be a 32-bit load |
| instruction, even though that accesses bytes that do not contain |
| any portion of the bit-field, or memory-mapped registers unrelated to |
| the one being updated. |
| |
| In some cases, such as when the @code{packed} attribute is applied to a |
| structure field, it may not be possible to access the field with a single |
| read or write that is correctly aligned for the target machine. In this |
| case GCC falls back to generating multiple accesses rather than code that |
| will fault or truncate the result at run time. |
| |
| Note: Due to restrictions of the C/C++11 memory model, write accesses are |
| not allowed to touch non bit-field members. It is therefore recommended |
| to define all bits of the field's type as bit-field members. |
| |
| The default value of this option is determined by the application binary |
| interface for the target processor. |
| |
| @item -fsync-libcalls |
| @opindex fsync-libcalls |
| This option controls whether any out-of-line instance of the @code{__sync} |
| family of functions may be used to implement the C++11 @code{__atomic} |
| family of functions. |
| |
| The default value of this option is enabled, thus the only useful form |
| of the option is @option{-fno-sync-libcalls}. This option is used in |
| the implementation of the @file{libatomic} runtime library. |
| |
| @end table |
| |
| @node Developer Options |
| @section GCC Developer Options |
| @cindex developer options |
| @cindex debugging GCC |
| @cindex debug dump options |
| @cindex dump options |
| @cindex compilation statistics |
| |
| This section describes command-line options that are primarily of |
| interest to GCC developers, including options to support compiler |
| testing and investigation of compiler bugs and compile-time |
| performance problems. This includes options that produce debug dumps |
| at various points in the compilation; that print statistics such as |
| memory use and execution time; and that print information about GCC's |
| configuration, such as where it searches for libraries. You should |
| rarely need to use any of these options for ordinary compilation and |
| linking tasks. |
| |
| Many developer options that cause GCC to dump output to a file take an |
| optional @samp{=@var{filename}} suffix. You can specify @samp{stdout} |
| or @samp{-} to dump to standard output, and @samp{stderr} for standard |
| error. |
| |
| If @samp{=@var{filename}} is omitted, a default dump file name is |
| constructed by concatenating the base dump file name, a pass number, |
| phase letter, and pass name. The base dump file name is the name of |
| output file produced by the compiler if explicitly specified and not |
| an executable; otherwise it is the source file name. |
| The pass number is determined by the order passes are registered with |
| the compiler's pass manager. |
| This is generally the same as the order of execution, but passes |
| registered by plugins, target-specific passes, or passes that are |
| otherwise registered late are numbered higher than the pass named |
| @samp{final}, even if they are executed earlier. The phase letter is |
| one of @samp{i} (inter-procedural analysis), @samp{l} |
| (language-specific), @samp{r} (RTL), or @samp{t} (tree). |
| The files are created in the directory of the output file. |
| |
| @table @gcctabopt |
| |
| @item -fcallgraph-info |
| @itemx -fcallgraph-info=@var{MARKERS} |
| @opindex fcallgraph-info |
| Makes the compiler output callgraph information for the program, on a |
| per-object-file basis. The information is generated in the common VCG |
| format. It can be decorated with additional, per-node and/or per-edge |
| information, if a list of comma-separated markers is additionally |
| specified. When the @code{su} marker is specified, the callgraph is |
| decorated with stack usage information; it is equivalent to |
| @option{-fstack-usage}. When the @code{da} marker is specified, the |
| callgraph is decorated with information about dynamically allocated |
| objects. |
| |
| When compiling with @option{-flto}, no callgraph information is output |
| along with the object file. At LTO link time, @option{-fcallgraph-info} |
| may generate multiple callgraph information files next to intermediate |
| LTO output files. |
| |
| @item -d@var{letters} |
| @itemx -fdump-rtl-@var{pass} |
| @itemx -fdump-rtl-@var{pass}=@var{filename} |
| @opindex d |
| @opindex fdump-rtl-@var{pass} |
| Says to make debugging dumps during compilation at times specified by |
| @var{letters}. This is used for debugging the RTL-based passes of the |
| compiler. |
| |
| Some @option{-d@var{letters}} switches have different meaning when |
| @option{-E} is used for preprocessing. @xref{Preprocessor Options}, |
| for information about preprocessor-specific dump options. |
| |
| Debug dumps can be enabled with a @option{-fdump-rtl} switch or some |
| @option{-d} option @var{letters}. Here are the possible |
| letters for use in @var{pass} and @var{letters}, and their meanings: |
| |
| @table @gcctabopt |
| |
| @item -fdump-rtl-alignments |
| @opindex fdump-rtl-alignments |
| Dump after branch alignments have been computed. |
| |
| @item -fdump-rtl-asmcons |
| @opindex fdump-rtl-asmcons |
| Dump after fixing rtl statements that have unsatisfied in/out constraints. |
| |
| @item -fdump-rtl-auto_inc_dec |
| @opindex fdump-rtl-auto_inc_dec |
| Dump after auto-inc-dec discovery. This pass is only run on |
| architectures that have auto inc or auto dec instructions. |
| |
| @item -fdump-rtl-barriers |
| @opindex fdump-rtl-barriers |
| Dump after cleaning up the barrier instructions. |
| |
| @item -fdump-rtl-bbpart |
| @opindex fdump-rtl-bbpart |
| Dump after partitioning hot and cold basic blocks. |
| |
| @item -fdump-rtl-bbro |
| @opindex fdump-rtl-bbro |
| Dump after block reordering. |
| |
| @item -fdump-rtl-btl1 |
| @itemx -fdump-rtl-btl2 |
| @opindex fdump-rtl-btl2 |
| @opindex fdump-rtl-btl2 |
| @option{-fdump-rtl-btl1} and @option{-fdump-rtl-btl2} enable dumping |
| after the two branch |
| target load optimization passes. |
| |
| @item -fdump-rtl-bypass |
| @opindex fdump-rtl-bypass |
| Dump after jump bypassing and control flow optimizations. |
| |
| @item -fdump-rtl-combine |
| @opindex fdump-rtl-combine |
| Dump after the RTL instruction combination pass. |
| |
| @item -fdump-rtl-compgotos |
| @opindex fdump-rtl-compgotos |
| Dump after duplicating the computed gotos. |
| |
| @item -fdump-rtl-ce1 |
| @itemx -fdump-rtl-ce2 |
| @itemx -fdump-rtl-ce3 |
| @opindex fdump-rtl-ce1 |
| @opindex fdump-rtl-ce2 |
| @opindex fdump-rtl-ce3 |
| @option{-fdump-rtl-ce1}, @option{-fdump-rtl-ce2}, and |
| @option{-fdump-rtl-ce3} enable dumping after the three |
| if conversion passes. |
| |
| @item -fdump-rtl-cprop_hardreg |
| @opindex fdump-rtl-cprop_hardreg |
| Dump after hard register copy propagation. |
| |
| @item -fdump-rtl-csa |
| @opindex fdump-rtl-csa |
| Dump after combining stack adjustments. |
| |
| @item -fdump-rtl-cse1 |
| @itemx -fdump-rtl-cse2 |
| @opindex fdump-rtl-cse1 |
| @opindex fdump-rtl-cse2 |
| @option{-fdump-rtl-cse1} and @option{-fdump-rtl-cse2} enable dumping after |
| the two common subexpression elimination passes. |
| |
| @item -fdump-rtl-dce |
| @opindex fdump-rtl-dce |
| Dump after the standalone dead code elimination passes. |
| |
| @item -fdump-rtl-dbr |
| @opindex fdump-rtl-dbr |
| Dump after delayed branch scheduling. |
| |
| @item -fdump-rtl-dce1 |
| @itemx -fdump-rtl-dce2 |
| @opindex fdump-rtl-dce1 |
| @opindex fdump-rtl-dce2 |
| @option{-fdump-rtl-dce1} and @option{-fdump-rtl-dce2} enable dumping after |
| the two dead store elimination passes. |
| |
| @item -fdump-rtl-eh |
| @opindex fdump-rtl-eh |
| Dump after finalization of EH handling code. |
| |
| @item -fdump-rtl-eh_ranges |
| @opindex fdump-rtl-eh_ranges |
| Dump after conversion of EH handling range regions. |
| |
| @item -fdump-rtl-expand |
| @opindex fdump-rtl-expand |
| Dump after RTL generation. |
| |
| @item -fdump-rtl-fwprop1 |
| @itemx -fdump-rtl-fwprop2 |
| @opindex fdump-rtl-fwprop1 |
| @opindex fdump-rtl-fwprop2 |
| @option{-fdump-rtl-fwprop1} and @option{-fdump-rtl-fwprop2} enable |
| dumping after the two forward propagation passes. |
| |
| @item -fdump-rtl-gcse1 |
| @itemx -fdump-rtl-gcse2 |
| @opindex fdump-rtl-gcse1 |
| @opindex fdump-rtl-gcse2 |
| @option{-fdump-rtl-gcse1} and @option{-fdump-rtl-gcse2} enable dumping |
| after global common subexpression elimination. |
| |
| @item -fdump-rtl-init-regs |
| @opindex fdump-rtl-init-regs |
| Dump after the initialization of the registers. |
| |
| @item -fdump-rtl-initvals |
| @opindex fdump-rtl-initvals |
| Dump after the computation of the initial value sets. |
| |
| @item -fdump-rtl-into_cfglayout |
| @opindex fdump-rtl-into_cfglayout |
| Dump after converting to cfglayout mode. |
| |
| @item -fdump-rtl-ira |
| @opindex fdump-rtl-ira |
| Dump after iterated register allocation. |
| |
| @item -fdump-rtl-jump |
| @opindex fdump-rtl-jump |
| Dump after the second jump optimization. |
| |
| @item -fdump-rtl-loop2 |
| @opindex fdump-rtl-loop2 |
| @option{-fdump-rtl-loop2} enables dumping after the rtl |
| loop optimization passes. |
| |
| @item -fdump-rtl-mach |
| @opindex fdump-rtl-mach |
| Dump after performing the machine dependent reorganization pass, if that |
| pass exists. |
| |
| @item -fdump-rtl-mode_sw |
| @opindex fdump-rtl-mode_sw |
| Dump after removing redundant mode switches. |
| |
| @item -fdump-rtl-rnreg |
| @opindex fdump-rtl-rnreg |
| Dump after register renumbering. |
| |
| @item -fdump-rtl-outof_cfglayout |
| @opindex fdump-rtl-outof_cfglayout |
| Dump after converting from cfglayout mode. |
| |
| @item -fdump-rtl-peephole2 |
| @opindex fdump-rtl-peephole2 |
| Dump after the peephole pass. |
| |
| @item -fdump-rtl-postreload |
| @opindex fdump-rtl-postreload |
| Dump after post-reload optimizations. |
| |
| @item -fdump-rtl-pro_and_epilogue |
| @opindex fdump-rtl-pro_and_epilogue |
| Dump after generating the function prologues and epilogues. |
| |
| @item -fdump-rtl-sched1 |
| @itemx -fdump-rtl-sched2 |
| @opindex fdump-rtl-sched1 |
| @opindex fdump-rtl-sched2 |
| @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2} enable dumping |
| after the basic block scheduling passes. |
| |
| @item -fdump-rtl-ree |
| @opindex fdump-rtl-ree |
| Dump after sign/zero extension elimination. |
| |
| @item -fdump-rtl-seqabstr |
| @opindex fdump-rtl-seqabstr |
| Dump after common sequence discovery. |
| |
| @item -fdump-rtl-shorten |
| @opindex fdump-rtl-shorten |
| Dump after shortening branches. |
| |
| @item -fdump-rtl-sibling |
| @opindex fdump-rtl-sibling |
| Dump after sibling call optimizations. |
| |
| @item -fdump-rtl-split1 |
| @itemx -fdump-rtl-split2 |
| @itemx -fdump-rtl-split3 |
| @itemx -fdump-rtl-split4 |
| @itemx -fdump-rtl-split5 |
| @opindex fdump-rtl-split1 |
| @opindex fdump-rtl-split2 |
| @opindex fdump-rtl-split3 |
| @opindex fdump-rtl-split4 |
| @opindex fdump-rtl-split5 |
| These options enable dumping after five rounds of |
| instruction splitting. |
| |
| @item -fdump-rtl-sms |
| @opindex fdump-rtl-sms |
| Dump after modulo scheduling. This pass is only run on some |
| architectures. |
| |
| @item -fdump-rtl-stack |
| @opindex fdump-rtl-stack |
| Dump after conversion from GCC's ``flat register file'' registers to the |
| x87's stack-like registers. This pass is only run on x86 variants. |
| |
| @item -fdump-rtl-subreg1 |
| @itemx -fdump-rtl-subreg2 |
| @opindex fdump-rtl-subreg1 |
| @opindex fdump-rtl-subreg2 |
| @option{-fdump-rtl-subreg1} and @option{-fdump-rtl-subreg2} enable dumping after |
| the two subreg expansion passes. |
| |
| @item -fdump-rtl-unshare |
| @opindex fdump-rtl-unshare |
| Dump after all rtl has been unshared. |
| |
| @item -fdump-rtl-vartrack |
| @opindex fdump-rtl-vartrack |
| Dump after variable tracking. |
| |
| @item -fdump-rtl-vregs |
| @opindex fdump-rtl-vregs |
| Dump after converting virtual registers to hard registers. |
| |
| @item -fdump-rtl-web |
| @opindex fdump-rtl-web |
| Dump after live range splitting. |
| |
| @item -fdump-rtl-regclass |
| @itemx -fdump-rtl-subregs_of_mode_init |
| @itemx -fdump-rtl-subregs_of_mode_finish |
| @itemx -fdump-rtl-dfinit |
| @itemx -fdump-rtl-dfinish |
| @opindex fdump-rtl-regclass |
| @opindex fdump-rtl-subregs_of_mode_init |
| @opindex fdump-rtl-subregs_of_mode_finish |
| @opindex fdump-rtl-dfinit |
| @opindex fdump-rtl-dfinish |
| These dumps are defined but always produce empty files. |
| |
| @item -da |
| @itemx -fdump-rtl-all |
| @opindex da |
| @opindex fdump-rtl-all |
| Produce all the dumps listed above. |
| |
| @item -dA |
| @opindex dA |
| Annotate the assembler output with miscellaneous debugging information. |
| |
| @item -dD |
| @opindex dD |
| Dump all macro definitions, at the end of preprocessing, in addition to |
| normal output. |
| |
| @item -dH |
| @opindex dH |
| Produce a core dump whenever an error occurs. |
| |
| @item -dp |
| @opindex dp |
| Annotate the assembler output with a comment indicating which |
| pattern and alternative is used. The length and cost of each instruction are |
| also printed. |
| |
| @item -dP |
| @opindex dP |
| Dump the RTL in the assembler output as a comment before each instruction. |
| Also turns on @option{-dp} annotation. |
| |
| @item -dx |
| @opindex dx |
| Just generate RTL for a function instead of compiling it. Usually used |
| with @option{-fdump-rtl-expand}. |
| @end table |
| |
| @item -fdump-debug |
| @opindex fdump-debug |
| Dump debugging information generated during the debug |
| generation phase. |
| |
| @item -fdump-earlydebug |
| @opindex fdump-earlydebug |
| Dump debugging information generated during the early debug |
| generation phase. |
| |
| @item -fdump-noaddr |
| @opindex fdump-noaddr |
| When doing debugging dumps, suppress address output. This makes it more |
| feasible to use diff on debugging dumps for compiler invocations with |
| different compiler binaries and/or different |
| text / bss / data / heap / stack / dso start locations. |
| |
| @item -freport-bug |
| @opindex freport-bug |
| Collect and dump debug information into a temporary file if an |
| internal compiler error (ICE) occurs. |
| |
| @item -fdump-unnumbered |
| @opindex fdump-unnumbered |
| When doing debugging dumps, suppress instruction numbers and address output. |
| This makes it more feasible to use diff on debugging dumps for compiler |
| invocations with different options, in particular with and without |
| @option{-g}. |
| |
| @item -fdump-unnumbered-links |
| @opindex fdump-unnumbered-links |
| When doing debugging dumps (see @option{-d} option above), suppress |
| instruction numbers for the links to the previous and next instructions |
| in a sequence. |
| |
| @item -fdump-ipa-@var{switch} |
| @itemx -fdump-ipa-@var{switch}-@var{options} |
| @opindex fdump-ipa |
| Control the dumping at various stages of inter-procedural analysis |
| language tree to a file. The file name is generated by appending a |
| switch specific suffix to the source file name, and the file is created |
| in the same directory as the output file. The following dumps are |
| possible: |
| |
| @table @samp |
| @item all |
| Enables all inter-procedural analysis dumps. |
| |
| @item cgraph |
| Dumps information about call-graph optimization, unused function removal, |
| and inlining decisions. |
| |
| @item inline |
| Dump after function inlining. |
| |
| @end table |
| |
| Additionally, the options @option{-optimized}, @option{-missed}, |
| @option{-note}, and @option{-all} can be provided, with the same meaning |
| as for @option{-fopt-info}, defaulting to @option{-optimized}. |
| |
| For example, @option{-fdump-ipa-inline-optimized-missed} will emit |
| information on callsites that were inlined, along with callsites |
| that were not inlined. |
| |
| By default, the dump will contain messages about successful |
| optimizations (equivalent to @option{-optimized}) together with |
| low-level details about the analysis. |
| |
| @item -fdump-lang |
| @opindex fdump-lang |
| Dump language-specific information. The file name is made by appending |
| @file{.lang} to the source file name. |
| |
| @item -fdump-lang-all |
| @itemx -fdump-lang-@var{switch} |
| @itemx -fdump-lang-@var{switch}-@var{options} |
| @itemx -fdump-lang-@var{switch}-@var{options}=@var{filename} |
| @opindex fdump-lang-all |
| @opindex fdump-lang |
| Control the dumping of language-specific information. The @var{options} |
| and @var{filename} portions behave as described in the |
| @option{-fdump-tree} option. The following @var{switch} values are |
| accepted: |
| |
| @table @samp |
| @item all |
| |
| Enable all language-specific dumps. |
| |
| @item class |
| Dump class hierarchy information. Virtual table information is emitted |
| unless '@option{slim}' is specified. This option is applicable to C++ only. |
| |
| @item module |
| Dump module information. Options @option{lineno} (locations), |
| @option{graph} (reachability), @option{blocks} (clusters), |
| @option{uid} (serialization), @option{alias} (mergeable), |
| @option{asmname} (Elrond), @option{eh} (mapper) & @option{vops} |
| (macros) may provide additional information. This option is |
| applicable to C++ only. |
| |
| @item raw |
| Dump the raw internal tree data. This option is applicable to C++ only. |
| |
| @end table |
| |
| @item -fdump-passes |
| @opindex fdump-passes |
| Print on @file{stderr} the list of optimization passes that are turned |
| on and off by the current command-line options. |
| |
| @item -fdump-statistics-@var{option} |
| @opindex fdump-statistics |
| Enable and control dumping of pass statistics in a separate file. The |
| file name is generated by appending a suffix ending in |
| @samp{.statistics} to the source file name, and the file is created in |
| the same directory as the output file. If the @samp{-@var{option}} |
| form is used, @samp{-stats} causes counters to be summed over the |
| whole compilation unit while @samp{-details} dumps every event as |
| the passes generate them. The default with no option is to sum |
| counters for each function compiled. |
| |
| @item -fdump-tree-all |
| @itemx -fdump-tree-@var{switch} |
| @itemx -fdump-tree-@var{switch}-@var{options} |
| @itemx -fdump-tree-@var{switch}-@var{options}=@var{filename} |
| @opindex fdump-tree-all |
| @opindex fdump-tree |
| Control the dumping at various stages of processing the intermediate |
| language tree to a file. If the @samp{-@var{options}} |
| form is used, @var{options} is a list of @samp{-} separated options |
| which control the details of the dump. Not all options are applicable |
| to all dumps; those that are not meaningful are ignored. The |
| following options are available |
| |
| @table @samp |
| @item address |
| Print the address of each node. Usually this is not meaningful as it |
| changes according to the environment and source file. Its primary use |
| is for tying up a dump file with a debug environment. |
| @item asmname |
| If @code{DECL_ASSEMBLER_NAME} has been set for a given decl, use that |
| in the dump instead of @code{DECL_NAME}. Its primary use is ease of |
| use working backward from mangled names in the assembly file. |
| @item slim |
| When dumping front-end intermediate representations, inhibit dumping |
| of members of a scope or body of a function merely because that scope |
| has been reached. Only dump such items when they are directly reachable |
| by some other path. |
| |
| When dumping pretty-printed trees, this option inhibits dumping the |
| bodies of control structures. |
| |
| When dumping RTL, print the RTL in slim (condensed) form instead of |
| the default LISP-like representation. |
| @item raw |
| Print a raw representation of the tree. By default, trees are |
| pretty-printed into a C-like representation. |
| @item details |
| Enable more detailed dumps (not honored by every dump option). Also |
| include information from the optimization passes. |
| @item stats |
| Enable dumping various statistics about the pass (not honored by every dump |
| option). |
| @item blocks |
| Enable showing basic block boundaries (disabled in raw dumps). |
| @item graph |
| For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}), |
| dump a representation of the control flow graph suitable for viewing with |
| GraphViz to @file{@var{file}.@var{passid}.@var{pass}.dot}. Each function in |
| the file is pretty-printed as a subgraph, so that GraphViz can render them |
| all in a single plot. |
| |
| This option currently only works for RTL dumps, and the RTL is always |
| dumped in slim form. |
| @item vops |
| Enable showing virtual operands for every statement. |
| @item lineno |
| Enable showing line numbers for statements. |
| @item uid |
| Enable showing the unique ID (@code{DECL_UID}) for each variable. |
| @item verbose |
| Enable showing the tree dump for each statement. |
| @item eh |
| Enable showing the EH region number holding each statement. |
| @item scev |
| Enable showing scalar evolution analysis details. |
| @item optimized |
| Enable showing optimization information (only available in certain |
| passes). |
| @item missed |
| Enable showing missed optimization information (only available in certain |
| passes). |
| @item note |
| Enable other detailed optimization information (only available in |
| certain passes). |
| @item all |
| Turn on all options, except @option{raw}, @option{slim}, @option{verbose} |
| and @option{lineno}. |
| @item optall |
| Turn on all optimization options, i.e., @option{optimized}, |
| @option{missed}, and @option{note}. |
| @end table |
| |
| To determine what tree dumps are available or find the dump for a pass |
| of interest follow the steps below. |
| |
| @enumerate |
| @item |
| Invoke GCC with @option{-fdump-passes} and in the @file{stderr} output |
| look for a code that corresponds to the pass you are interested in. |
| For example, the codes @code{tree-evrp}, @code{tree-vrp1}, and |
| @code{tree-vrp2} correspond to the three Value Range Propagation passes. |
| The number at the end distinguishes distinct invocations of the same pass. |
| @item |
| To enable the creation of the dump file, append the pass code to |
| the @option{-fdump-} option prefix and invoke GCC with it. For example, |
| to enable the dump from the Early Value Range Propagation pass, invoke |
| GCC with the @option{-fdump-tree-evrp} option. Optionally, you may |
| specify the name of the dump file. If you don't specify one, GCC |
| creates as described below. |
| @item |
| Find the pass dump in a file whose name is composed of three components |
| separated by a period: the name of the source file GCC was invoked to |
| compile, a numeric suffix indicating the pass number followed by the |
| letter @samp{t} for tree passes (and the letter @samp{r} for RTL passes), |
| and finally the pass code. For example, the Early VRP pass dump might |
| be in a file named @file{myfile.c.038t.evrp} in the current working |
| directory. Note that the numeric codes are not stable and may change |
| from one version of GCC to another. |
| @end enumerate |
| |
| @item -fopt-info |
| @itemx -fopt-info-@var{options} |
| @itemx -fopt-info-@var{options}=@var{filename} |
| @opindex fopt-info |
| Controls optimization dumps from various optimization passes. If the |
| @samp{-@var{options}} form is used, @var{options} is a list of |
| @samp{-} separated option keywords to select the dump details and |
| optimizations. |
| |
| The @var{options} can be divided into three groups: |
| @enumerate |
| @item |
| options describing what kinds of messages should be emitted, |
| @item |
| options describing the verbosity of the dump, and |
| @item |
| options describing which optimizations should be included. |
| @end enumerate |
| The options from each group can be freely mixed as they are |
| non-overlapping. However, in case of any conflicts, |
| the later options override the earlier options on the command |
| line. |
| |
| The following options control which kinds of messages should be emitted: |
| |
| @table @samp |
| @item optimized |
| Print information when an optimization is successfully applied. It is |
| up to a pass to decide which information is relevant. For example, the |
| vectorizer passes print the source location of loops which are |
| successfully vectorized. |
| @item missed |
| Print information about missed optimizations. Individual passes |
| control which information to include in the output. |
| @item note |
| Print verbose information about optimizations, such as certain |
| transformations, more detailed messages about decisions etc. |
| @item all |
| Print detailed optimization information. This includes |
| @samp{optimized}, @samp{missed}, and @samp{note}. |
| @end table |
| |
| The following option controls the dump verbosity: |
| |
| @table @samp |
| @item internals |
| By default, only ``high-level'' messages are emitted. This option enables |
| additional, more detailed, messages, which are likely to only be of interest |
| to GCC developers. |
| @end table |
| |
| One or more of the following option keywords can be used to describe a |
| group of optimizations: |
| |
| @table @samp |
| @item ipa |
| Enable dumps from all interprocedural optimizations. |
| @item loop |
| Enable dumps from all loop optimizations. |
| @item inline |
| Enable dumps from all inlining optimizations. |
| @item omp |
| Enable dumps from all OMP (Offloading and Multi Processing) optimizations. |
| @item vec |
| Enable dumps from all vectorization optimizations. |
| @item optall |
| Enable dumps from all optimizations. This is a superset of |
| the optimization groups listed above. |
| @end table |
| |
| If @var{options} is |
| omitted, it defaults to @samp{optimized-optall}, which means to dump messages |
| about successful optimizations from all the passes, omitting messages |
| that are treated as ``internals''. |
| |
| If the @var{filename} is provided, then the dumps from all the |
| applicable optimizations are concatenated into the @var{filename}. |
| Otherwise the dump is output onto @file{stderr}. Though multiple |
| @option{-fopt-info} options are accepted, only one of them can include |
| a @var{filename}. If other filenames are provided then all but the |
| first such option are ignored. |
| |
| Note that the output @var{filename} is overwritten |
| in case of multiple translation units. If a combined output from |
| multiple translation units is desired, @file{stderr} should be used |
| instead. |
| |
| In the following example, the optimization info is output to |
| @file{stderr}: |
| |
| @smallexample |
| gcc -O3 -fopt-info |
| @end smallexample |
| |
| This example: |
| @smallexample |
| gcc -O3 -fopt-info-missed=missed.all |
| @end smallexample |
| |
| @noindent |
| outputs missed optimization report from all the passes into |
| @file{missed.all}, and this one: |
| |
| @smallexample |
| gcc -O2 -ftree-vectorize -fopt-info-vec-missed |
| @end smallexample |
| |
| @noindent |
| prints information about missed optimization opportunities from |
| vectorization passes on @file{stderr}. |
| Note that @option{-fopt-info-vec-missed} is equivalent to |
| @option{-fopt-info-missed-vec}. The order of the optimization group |
| names and message types listed after @option{-fopt-info} does not matter. |
| |
| As another example, |
| @smallexample |
| gcc -O3 -fopt-info-inline-optimized-missed=inline.txt |
| @end smallexample |
| |
| @noindent |
| outputs information about missed optimizations as well as |
| optimized locations from all the inlining passes into |
| @file{inline.txt}. |
| |
| Finally, consider: |
| |
| @smallexample |
| gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt |
| @end smallexample |
| |
| @noindent |
| Here the two output filenames @file{vec.miss} and @file{loop.opt} are |
| in conflict since only one output file is allowed. In this case, only |
| the first option takes effect and the subsequent options are |
| ignored. Thus only @file{vec.miss} is produced which contains |
| dumps from the vectorizer about missed opportunities. |
| |
| @item -fsave-optimization-record |
| @opindex fsave-optimization-record |
| Write a SRCFILE.opt-record.json.gz file detailing what optimizations |
| were performed, for those optimizations that support @option{-fopt-info}. |
| |
| This option is experimental and the format of the data within the |
| compressed JSON file is subject to change. |
| |
| It is roughly equivalent to a machine-readable version of |
| @option{-fopt-info-all}, as a collection of messages with source file, |
| line number and column number, with the following additional data for |
| each message: |
| |
| @itemize @bullet |
| |
| @item |
| the execution count of the code being optimized, along with metadata about |
| whether this was from actual profile data, or just an estimate, allowing |
| consumers to prioritize messages by code hotness, |
| |
| @item |
| the function name of the code being optimized, where applicable, |
| |
| @item |
| the ``inlining chain'' for the code being optimized, so that when |
| a function is inlined into several different places (which might |
| themselves be inlined), the reader can distinguish between the copies, |
| |
| @item |
| objects identifying those parts of the message that refer to expressions, |
| statements or symbol-table nodes, which of these categories they are, and, |
| when available, their source code location, |
| |
| @item |
| the GCC pass that emitted the message, and |
| |
| @item |
| the location in GCC's own code from which the message was emitted |
| |
| @end itemize |
| |
| Additionally, some messages are logically nested within other |
| messages, reflecting implementation details of the optimization |
| passes. |
| |
| @item -fsched-verbose=@var{n} |
| @opindex fsched-verbose |
| On targets that use instruction scheduling, this option controls the |
| amount of debugging output the scheduler prints to the dump files. |
| |
| For @var{n} greater than zero, @option{-fsched-verbose} outputs the |
| same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}. |
| For @var{n} greater than one, it also output basic block probabilities, |
| detailed ready list information and unit/insn info. For @var{n} greater |
| than two, it includes RTL at abort point, control-flow and regions info. |
| And for @var{n} over four, @option{-fsched-verbose} also includes |
| dependence info. |
| |
| |
| |
| @item -fenable-@var{kind}-@var{pass} |
| @itemx -fdisable-@var{kind}-@var{pass}=@var{range-list} |
| @opindex fdisable- |
| @opindex fenable- |
| |
| This is a set of options that are used to explicitly disable/enable |
| optimization passes. These options are intended for use for debugging GCC. |
| Compiler users should use regular options for enabling/disabling |
| passes instead. |
| |
| @table @gcctabopt |
| |
| @item -fdisable-ipa-@var{pass} |
| Disable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is |
| statically invoked in the compiler multiple times, the pass name should be |
| appended with a sequential number starting from 1. |
| |
| @item -fdisable-rtl-@var{pass} |
| @itemx -fdisable-rtl-@var{pass}=@var{range-list} |
| Disable RTL pass @var{pass}. @var{pass} is the pass name. If the same pass is |
| statically invoked in the compiler multiple times, the pass name should be |
| appended with a sequential number starting from 1. @var{range-list} is a |
| comma-separated list of function ranges or assembler names. Each range is a number |
| pair separated by a colon. The range is inclusive in both ends. If the range |
| is trivial, the number pair can be simplified as a single number. If the |
| function's call graph node's @var{uid} falls within one of the specified ranges, |
| the @var{pass} is disabled for that function. The @var{uid} is shown in the |
| function header of a dump file, and the pass names can be dumped by using |
| option @option{-fdump-passes}. |
| |
| @item -fdisable-tree-@var{pass} |
| @itemx -fdisable-tree-@var{pass}=@var{range-list} |
| Disable tree pass @var{pass}. See @option{-fdisable-rtl} for the description of |
| option arguments. |
| |
| @item -fenable-ipa-@var{pass} |
| Enable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is |
| statically invoked in the compiler multiple times, the pass name should be |
| appended with a sequential number starting from 1. |
| |
| @item -fenable-rtl-@var{pass} |
| @itemx -fenable-rtl-@var{pass}=@var{range-list} |
| Enable RTL pass @var{pass}. See @option{-fdisable-rtl} for option argument |
| description and examples. |
| |
| @item -fenable-tree-@var{pass} |
| @itemx -fenable-tree-@var{pass}=@var{range-list} |
| Enable tree pass @var{pass}. See @option{-fdisable-rtl} for the description |
| of option arguments. |
| |
| @end table |
| |
| Here are some examples showing uses of these options. |
| |
| @smallexample |
| |
| # disable ccp1 for all functions |
| -fdisable-tree-ccp1 |
| # disable complete unroll for function whose cgraph node uid is 1 |
| -fenable-tree-cunroll=1 |
| # disable gcse2 for functions at the following ranges [1,1], |
| # [300,400], and [400,1000] |
| # disable gcse2 for functions foo and foo2 |
| -fdisable-rtl-gcse2=foo,foo2 |
| # disable early inlining |
| -fdisable-tree-einline |
| # disable ipa inlining |
| -fdisable-ipa-inline |
| # enable tree full unroll |
| -fenable-tree-unroll |
| |
| @end smallexample |
| |
| @item -fchecking |
| @itemx -fchecking=@var{n} |
| @opindex fchecking |
| @opindex fno-checking |
| Enable internal consistency checking. The default depends on |
| the compiler configuration. @option{-fchecking=2} enables further |
| internal consistency checking that might affect code generation. |
| |
| @item -frandom-seed=@var{string} |
| @opindex frandom-seed |
| This option provides a seed that GCC uses in place of |
| random numbers in generating certain symbol names |
| that have to be different in every compiled file. It is also used to |
| place unique stamps in coverage data files and the object files that |
| produce them. You can use the @option{-frandom-seed} option to produce |
| reproducibly identical object files. |
| |
| The @var{string} can either be a number (decimal, octal or hex) or an |
| arbitrary string (in which case it's converted to a number by |
| computing CRC32). |
| |
| The @var{string} should be different for every file you compile. |
| |
| @item -save-temps |
| @opindex save-temps |
| Store the usual ``temporary'' intermediate files permanently; name them |
| as auxiliary output files, as specified described under |
| @option{-dumpbase} and @option{-dumpdir}. |
| |
| When used in combination with the @option{-x} command-line option, |
| @option{-save-temps} is sensible enough to avoid overwriting an |
| input source file with the same extension as an intermediate file. |
| The corresponding intermediate file may be obtained by renaming the |
| source file before using @option{-save-temps}. |
| |
| @item -save-temps=cwd |
| @opindex save-temps=cwd |
| Equivalent to @option{-save-temps -dumpdir ./}. |
| |
| @item -save-temps=obj |
| @opindex save-temps=obj |
| Equivalent to @option{-save-temps -dumpdir @file{outdir/}}, where |
| @file{outdir/} is the directory of the output file specified after the |
| @option{-o} option, including any directory separators. If the |
| @option{-o} option is not used, the @option{-save-temps=obj} switch |
| behaves like @option{-save-temps=cwd}. |
| |
| @item -time@r{[}=@var{file}@r{]} |
| @opindex time |
| Report the CPU time taken by each subprocess in the compilation |
| sequence. For C source files, this is the compiler proper and assembler |
| (plus the linker if linking is done). |
| |
| Without the specification of an output file, the output looks like this: |
| |
| @smallexample |
| # cc1 0.12 0.01 |
| # as 0.00 0.01 |
| @end smallexample |
| |
| The first number on each line is the ``user time'', that is time spent |
| executing the program itself. The second number is ``system time'', |
| time spent executing operating system routines on behalf of the program. |
| Both numbers are in seconds. |
| |
| With the specification of an output file, the output is appended to the |
| named file, and it looks like this: |
| |
| @smallexample |
| 0.12 0.01 cc1 @var{options} |
| 0.00 0.01 as @var{options} |
| @end smallexample |
| |
| The ``user time'' and the ``system time'' are moved before the program |
| name, and the options passed to the program are displayed, so that one |
| can later tell what file was being compiled, and with which options. |
| |
| @item -fdump-final-insns@r{[}=@var{file}@r{]} |
| @opindex fdump-final-insns |
| Dump the final internal representation (RTL) to @var{file}. If the |
| optional argument is omitted (or if @var{file} is @code{.}), the name |
| of the dump file is determined by appending @code{.gkd} to the |
| dump base name, see @option{-dumpbase}. |
| |
| @item -fcompare-debug@r{[}=@var{opts}@r{]} |
| @opindex fcompare-debug |
| @opindex fno-compare-debug |
| If no error occurs during compilation, run the compiler a second time, |
| adding @var{opts} and @option{-fcompare-debug-second} to the arguments |
| passed to the second compilation. Dump the final internal |
| representation in both compilations, and print an error if they differ. |
| |
| If the equal sign is omitted, the default @option{-gtoggle} is used. |
| |
| The environment variable @env{GCC_COMPARE_DEBUG}, if defined, non-empty |
| and nonzero, implicitly enables @option{-fcompare-debug}. If |
| @env{GCC_COMPARE_DEBUG} is defined to a string starting with a dash, |
| then it is used for @var{opts}, otherwise the default @option{-gtoggle} |
| is used. |
| |
| @option{-fcompare-debug=}, with the equal sign but without @var{opts}, |
| is equivalent to @option{-fno-compare-debug}, which disables the dumping |
| of the final representation and the second compilation, preventing even |
| @env{GCC_COMPARE_DEBUG} from taking effect. |
| |
| To verify full coverage during @option{-fcompare-debug} testing, set |
| @env{GCC_COMPARE_DEBUG} to say @option{-fcompare-debug-not-overridden}, |
| which GCC rejects as an invalid option in any actual compilation |
| (rather than preprocessing, assembly or linking). To get just a |
| warning, setting @env{GCC_COMPARE_DEBUG} to @samp{-w%n-fcompare-debug |
| not overridden} will do. |
| |
| @item -fcompare-debug-second |
| @opindex fcompare-debug-second |
| This option is implicitly passed to the compiler for the second |
| compilation requested by @option{-fcompare-debug}, along with options to |
| silence warnings, and omitting other options that would cause the compiler |
| to produce output to files or to standard output as a side effect. Dump |
| files and preserved temporary files are renamed so as to contain the |
| @code{.gk} additional extension during the second compilation, to avoid |
| overwriting those generated by the first. |
| |
| When this option is passed to the compiler driver, it causes the |
| @emph{first} compilation to be skipped, which makes it useful for little |
| other than debugging the compiler proper. |
| |
| @item -gtoggle |
| @opindex gtoggle |
| Turn off generation of debug info, if leaving out this option |
| generates it, or turn it on at level 2 otherwise. The position of this |
| argument in the command line does not matter; it takes effect after all |
| other options are processed, and it does so only once, no matter how |
| many times it is given. This is mainly intended to be used with |
| @option{-fcompare-debug}. |
| |
| @item -fvar-tracking-assignments-toggle |
| @opindex fvar-tracking-assignments-toggle |
| @opindex fno-var-tracking-assignments-toggle |
| Toggle @option{-fvar-tracking-assignments}, in the same way that |
| @option{-gtoggle} toggles @option{-g}. |
| |
| @item -Q |
| @opindex Q |
| Makes the compiler print out each function name as it is compiled, and |
| print some statistics about each pass when it finishes. |
| |
| @item -ftime-report |
| @opindex ftime-report |
| Makes the compiler print some statistics about the time consumed by each |
| pass when it finishes. |
| |
| @item -ftime-report-details |
| @opindex ftime-report-details |
| Record the time consumed by infrastructure parts separately for each pass. |
| |
| @item -fira-verbose=@var{n} |
| @opindex fira-verbose |
| Control the verbosity of the dump file for the integrated register allocator. |
| The default value is 5. If the value @var{n} is greater or equal to 10, |
| the dump output is sent to stderr using the same format as @var{n} minus 10. |
| |
| @item -flto-report |
| @opindex flto-report |
| Prints a report with internal details on the workings of the link-time |
| optimizer. The contents of this report vary from version to version. |
| It is meant to be useful to GCC developers when processing object |
| files in LTO mode (via @option{-flto}). |
| |
| Disabled by default. |
| |
| @item -flto-report-wpa |
| @opindex flto-report-wpa |
| Like @option{-flto-report}, but only print for the WPA phase of link-time |
| optimization. |
| |
| @item -fmem-report |
| @opindex fmem-report |
| Makes the compiler print some statistics about permanent memory |
| allocation when it finishes. |
| |
| @item -fmem-report-wpa |
| @opindex fmem-report-wpa |
| Makes the compiler print some statistics about permanent memory |
| allocation for the WPA phase only. |
| |
| @item -fpre-ipa-mem-report |
| @opindex fpre-ipa-mem-report |
| @item -fpost-ipa-mem-report |
| @opindex fpost-ipa-mem-report |
| Makes the compiler print some statistics about permanent memory |
| allocation before or after interprocedural optimization. |
| |
| @item -fprofile-report |
| @opindex fprofile-report |
| Makes the compiler print some statistics about consistency of the |
| (estimated) profile and effect of individual passes. |
| |
| @item -fstack-usage |
| @opindex fstack-usage |
| Makes the compiler output stack usage information for the program, on a |
| per-function basis. The filename for the dump is made by appending |
| @file{.su} to the @var{auxname}. @var{auxname} is generated from the name of |
| the output file, if explicitly specified and it is not an executable, |
| otherwise it is the basename of the source file. An entry is made up |
| of three fields: |
| |
| @itemize |
| @item |
| The name of the function. |
| @item |
| A number of bytes. |
| @item |
| One or more qualifiers: @code{static}, @code{dynamic}, @code{bounded}. |
| @end itemize |
| |
| The qualifier @code{static} means that the function manipulates the stack |
| statically: a fixed number of bytes are allocated for the frame on function |
| entry and released on function exit; no stack adjustments are otherwise made |
| in the function. The second field is this fixed number of bytes. |
| |
| The qualifier @code{dynamic} means that the function manipulates the stack |
| dynamically: in addition to the static allocation described above, stack |
| adjustments are made in the body of the function, for example to push/pop |
| arguments around function calls. If the qualifier @code{bounded} is also |
| present, the amount of these adjustments is bounded at compile time and |
| the second field is an upper bound of the total amount of stack used by |
| the function. If it is not present, the amount of these adjustments is |
| not bounded at compile time and the second field only represents the |
| bounded part. |
| |
| @item -fstats |
| @opindex fstats |
| Emit statistics about front-end processing at the end of the compilation. |
| This option is supported only by the C++ front end, and |
| the information is generally only useful to the G++ development team. |
| |
| @item -fdbg-cnt-list |
| @opindex fdbg-cnt-list |
| Print the name and the counter upper bound for all debug counters. |
| |
| |
| @item -fdbg-cnt=@var{counter-value-list} |
| @opindex fdbg-cnt |
| Set the internal debug counter lower and upper bound. @var{counter-value-list} |
| is a comma-separated list of @var{name}:@var{lower_bound1}-@var{upper_bound1} |
| [:@var{lower_bound2}-@var{upper_bound2}...] tuples which sets |
| the name of the counter and list of closed intervals. |
| The @var{lower_bound} is optional and is zero |
| initialized if not set. |
| For example, with @option{-fdbg-cnt=dce:2-4:10-11,tail_call:10}, |
| @code{dbg_cnt(dce)} returns true only for second, third, fourth, tenth and |
| eleventh invocation. |
| For @code{dbg_cnt(tail_call)} true is returned for first 10 invocations. |
| |
| @item -print-file-name=@var{library} |
| @opindex print-file-name |
| Print the full absolute name of the library file @var{library} that |
| would be used when linking---and don't do anything else. With this |
| option, GCC does not compile or link anything; it just prints the |
| file name. |
| |
| @item -print-multi-directory |
| @opindex print-multi-directory |
| Print the directory name corresponding to the multilib selected by any |
| other switches present in the command line. This directory is supposed |
| to exist in @env{GCC_EXEC_PREFIX}. |
| |
| @item -print-multi-lib |
| @opindex print-multi-lib |
| Print the mapping from multilib directory names to compiler switches |
| that enable them. The directory name is separated from the switches by |
| @samp{;}, and each switch starts with an @samp{@@} instead of the |
| @samp{-}, without spaces between multiple switches. This is supposed to |
| ease shell processing. |
| |
| @item -print-multi-os-directory |
| @opindex print-multi-os-directory |
| Print the path to OS libraries for the selected |
| multilib, relative to some @file{lib} subdirectory. If OS libraries are |
| present in the @file{lib} subdirectory and no multilibs are used, this is |
| usually just @file{.}, if OS libraries are present in @file{lib@var{suffix}} |
| sibling directories this prints e.g.@: @file{../lib64}, @file{../lib} or |
| @file{../lib32}, or if OS libraries are present in @file{lib/@var{subdir}} |
| subdirectories it prints e.g.@: @file{amd64}, @file{sparcv9} or @file{ev6}. |
| |
| @item -print-multiarch |
| @opindex print-multiarch |
| Print the path to OS libraries for the selected multiarch, |
| relative to some @file{lib} subdirectory. |
| |
| @item -print-prog-name=@var{program} |
| @opindex print-prog-name |
| Like @option{-print-file-name}, but searches for a program such as @command{cpp}. |
| |
| @item -print-libgcc-file-name |
| @opindex print-libgcc-file-name |
| Same as @option{-print-file-name=libgcc.a}. |
| |
| This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs} |
| but you do want to link with @file{libgcc.a}. You can do: |
| |
| @smallexample |
| gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name` |
| @end smallexample |
| |
| @item -print-search-dirs |
| @opindex print-search-dirs |
| Print the name of the configured installation directory and a list of |
| program and library directories @command{gcc} searches---and don't do anything else. |
| |
| This is useful when @command{gcc} prints the error message |
| @samp{installation problem, cannot exec cpp0: No such file or directory}. |
| To resolve this you either need to put @file{cpp0} and the other compiler |
| components where @command{gcc} expects to find them, or you can set the environment |
| variable @env{GCC_EXEC_PREFIX} to the directory where you installed them. |
| Don't forget the trailing @samp{/}. |
| @xref{Environment Variables}. |
| |
| @item -print-sysroot |
| @opindex print-sysroot |
| Print the target sysroot directory that is used during |
| compilation. This is the target sysroot specified either at configure |
| time or using the @option{--sysroot} option, possibly with an extra |
| suffix that depends on compilation options. If no target sysroot is |
| specified, the option prints nothing. |
| |
| @item -print-sysroot-headers-suffix |
| @opindex print-sysroot-headers-suffix |
| Print the suffix added to the target sysroot when searching for |
| headers, or give an error if the compiler is not configured with such |
| a suffix---and don't do anything else. |
| |
| @item -dumpmachine |
| @opindex dumpmachine |
| Print the compiler's target machine (for example, |
| @samp{i686-pc-linux-gnu})---and don't do anything else. |
| |
| @item -dumpversion |
| @opindex dumpversion |
| Print the compiler version (for example, @code{3.0}, @code{6.3.0} or @code{7})---and don't do |
| anything else. This is the compiler version used in filesystem paths and |
| specs. Depending on how the compiler has been configured it can be just |
| a single number (major version), two numbers separated by a dot (major and |
| minor version) or three numbers separated by dots (major, minor and patchlevel |
| version). |
| |
| @item -dumpfullversion |
| @opindex dumpfullversion |
| Print the full compiler version---and don't do anything else. The output is |
| always three numbers separated by dots, major, minor and patchlevel version. |
| |
| @item -dumpspecs |
| @opindex dumpspecs |
| Print the compiler's built-in specs---and don't do anything else. (This |
| is used when GCC itself is being built.) @xref{Spec Files}. |
| @end table |
| |
| @node Submodel Options |
| @section Machine-Dependent Options |
| @cindex submodel options |
| @cindex specifying hardware config |
| @cindex hardware models and configurations, specifying |
| @cindex target-dependent options |
| @cindex machine-dependent options |
| |
| Each target machine supported by GCC can have its own options---for |
| example, to allow you to compile for a particular processor variant or |
| ABI, or to control optimizations specific to that machine. By |
| convention, the names of machine-specific options start with |
| @samp{-m}. |
| |
| Some configurations of the compiler also support additional target-specific |
| options, usually for compatibility with other compilers on the same |
| platform. |
| |
| @c This list is ordered alphanumerically by subsection name. |
| @c It should be the same order and spelling as these options are listed |
| @c in Machine Dependent Options |
| |
| @menu |
| * AArch64 Options:: |
| * Adapteva Epiphany Options:: |
| * AMD GCN Options:: |
| * ARC Options:: |
| * ARM Options:: |
| * AVR Options:: |
| * Blackfin Options:: |
| * C6X Options:: |
| * CRIS Options:: |
| * CR16 Options:: |
| * C-SKY Options:: |
| * Darwin Options:: |
| * DEC Alpha Options:: |
| * eBPF Options:: |
| * FR30 Options:: |
| * FT32 Options:: |
| * FRV Options:: |
| * GNU/Linux Options:: |
| * H8/300 Options:: |
| * HPPA Options:: |
| * IA-64 Options:: |
| * LM32 Options:: |
| * LoongArch Options:: |
| * M32C Options:: |
| * M32R/D Options:: |
| * M680x0 Options:: |
| * MCore Options:: |
| * MeP Options:: |
| * MicroBlaze Options:: |
| * MIPS Options:: |
| * MMIX Options:: |
| * MN10300 Options:: |
| * Moxie Options:: |
| * MSP430 Options:: |
| * NDS32 Options:: |
| * Nios II Options:: |
| * Nvidia PTX Options:: |
| * OpenRISC Options:: |
| * PDP-11 Options:: |
| * picoChip Options:: |
| * PowerPC Options:: |
| * PRU Options:: |
| * RISC-V Options:: |
| * RL78 Options:: |
| * RS/6000 and PowerPC Options:: |
| * RX Options:: |
| * S/390 and zSeries Options:: |
| * Score Options:: |
| * SH Options:: |
| * Solaris 2 Options:: |
| * SPARC Options:: |
| * System V Options:: |
| * TILE-Gx Options:: |
| * TILEPro Options:: |
| * V850 Options:: |
| * VAX Options:: |
| * Visium Options:: |
| * VMS Options:: |
| * VxWorks Options:: |
| * x86 Options:: |
| * x86 Windows Options:: |
| * Xstormy16 Options:: |
| * Xtensa Options:: |
| * zSeries Options:: |
| @end menu |
| |
| @node AArch64 Options |
| @subsection AArch64 Options |
| @cindex AArch64 Options |
| |
| These options are defined for AArch64 implementations: |
| |
| @table @gcctabopt |
| |
| @item -mabi=@var{name} |
| @opindex mabi |
| Generate code for the specified data model. Permissible values |
| are @samp{ilp32} for SysV-like data model where int, long int and pointers |
| are 32 bits, and @samp{lp64} for SysV-like data model where int is 32 bits, |
| but long int and pointers are 64 bits. |
| |
| The default depends on the specific target configuration. Note that |
| the LP64 and ILP32 ABIs are not link-compatible; you must compile your |
| entire program with the same ABI, and link with a compatible set of libraries. |
| |
| @item -mbig-endian |
| @opindex mbig-endian |
| Generate big-endian code. This is the default when GCC is configured for an |
| @samp{aarch64_be-*-*} target. |
| |
| @item -mgeneral-regs-only |
| @opindex mgeneral-regs-only |
| Generate code which uses only the general-purpose registers. This will prevent |
| the compiler from using floating-point and Advanced SIMD registers but will not |
| impose any restrictions on the assembler. |
| |
| @item -mlittle-endian |
| @opindex mlittle-endian |
| Generate little-endian code. This is the default when GCC is configured for an |
| @samp{aarch64-*-*} but not an @samp{aarch64_be-*-*} target. |
| |
| @item -mcmodel=tiny |
| @opindex mcmodel=tiny |
| Generate code for the tiny code model. The program and its statically defined |
| symbols must be within 1MB of each other. Programs can be statically or |
| dynamically linked. |
| |
| @item -mcmodel=small |
| @opindex mcmodel=small |
| Generate code for the small code model. The program and its statically defined |
| symbols must be within 4GB of each other. Programs can be statically or |
| dynamically linked. This is the default code model. |
| |
| @item -mcmodel=large |
| @opindex mcmodel=large |
| Generate code for the large code model. This makes no assumptions about |
| addresses and sizes of sections. Programs can be statically linked only. The |
| @option{-mcmodel=large} option is incompatible with @option{-mabi=ilp32}, |
| @option{-fpic} and @option{-fPIC}. |
| |
| @item -mstrict-align |
| @itemx -mno-strict-align |
| @opindex mstrict-align |
| @opindex mno-strict-align |
| Avoid or allow generating memory accesses that may not be aligned on a natural |
| object boundary as described in the architecture specification. |
| |
| @item -momit-leaf-frame-pointer |
| @itemx -mno-omit-leaf-frame-pointer |
| @opindex momit-leaf-frame-pointer |
| @opindex mno-omit-leaf-frame-pointer |
| Omit or keep the frame pointer in leaf functions. The former behavior is the |
| default. |
| |
| @item -mstack-protector-guard=@var{guard} |
| @itemx -mstack-protector-guard-reg=@var{reg} |
| @itemx -mstack-protector-guard-offset=@var{offset} |
| @opindex mstack-protector-guard |
| @opindex mstack-protector-guard-reg |
| @opindex mstack-protector-guard-offset |
| Generate stack protection code using canary at @var{guard}. Supported |
| locations are @samp{global} for a global canary or @samp{sysreg} for a |
| canary in an appropriate system register. |
| |
| With the latter choice the options |
| @option{-mstack-protector-guard-reg=@var{reg}} and |
| @option{-mstack-protector-guard-offset=@var{offset}} furthermore specify |
| which system register to use as base register for reading the canary, |
| and from what offset from that base register. There is no default |
| register or offset as this is entirely for use within the Linux |
| kernel. |
| |
| @item -mtls-dialect=desc |
| @opindex mtls-dialect=desc |
| Use TLS descriptors as the thread-local storage mechanism for dynamic accesses |
| of TLS variables. This is the default. |
| |
| @item -mtls-dialect=traditional |
| @opindex mtls-dialect=traditional |
| Use traditional TLS as the thread-local storage mechanism for dynamic accesses |
| of TLS variables. |
| |
| @item -mtls-size=@var{size} |
| @opindex mtls-size |
| Specify bit size of immediate TLS offsets. Valid values are 12, 24, 32, 48. |
| This option requires binutils 2.26 or newer. |
| |
| @item -mfix-cortex-a53-835769 |
| @itemx -mno-fix-cortex-a53-835769 |
| @opindex mfix-cortex-a53-835769 |
| @opindex mno-fix-cortex-a53-835769 |
| Enable or disable the workaround for the ARM Cortex-A53 erratum number 835769. |
| This involves inserting a NOP instruction between memory instructions and |
| 64-bit integer multiply-accumulate instructions. |
| |
| @item -mfix-cortex-a53-843419 |
| @itemx -mno-fix-cortex-a53-843419 |
| @opindex mfix-cortex-a53-843419 |
| @opindex mno-fix-cortex-a53-843419 |
| Enable or disable the workaround for the ARM Cortex-A53 erratum number 843419. |
| This erratum workaround is made at link time and this will only pass the |
| corresponding flag to the linker. |
| |
| @item -mlow-precision-recip-sqrt |
| @itemx -mno-low-precision-recip-sqrt |
| @opindex mlow-precision-recip-sqrt |
| @opindex mno-low-precision-recip-sqrt |
| Enable or disable the reciprocal square root approximation. |
| This option only has an effect if @option{-ffast-math} or |
| @option{-funsafe-math-optimizations} is used as well. Enabling this reduces |
| precision of reciprocal square root results to about 16 bits for |
| single precision and to 32 bits for double precision. |
| |
| @item -mlow-precision-sqrt |
| @itemx -mno-low-precision-sqrt |
| @opindex mlow-precision-sqrt |
| @opindex mno-low-precision-sqrt |
| Enable or disable the square root approximation. |
| This option only has an effect if @option{-ffast-math} or |
| @option{-funsafe-math-optimizations} is used as well. Enabling this reduces |
| precision of square root results to about 16 bits for |
| single precision and to 32 bits for double precision. |
| If enabled, it implies @option{-mlow-precision-recip-sqrt}. |
| |
| @item -mlow-precision-div |
| @itemx -mno-low-precision-div |
| @opindex mlow-precision-div |
| @opindex mno-low-precision-div |
| Enable or disable the division approximation. |
| This option only has an effect if @option{-ffast-math} or |
| @option{-funsafe-math-optimizations} is used as well. Enabling this reduces |
| precision of division results to about 16 bits for |
| single precision and to 32 bits for double precision. |
| |
| @item -mtrack-speculation |
| @itemx -mno-track-speculation |
| Enable or disable generation of additional code to track speculative |
| execution through conditional branches. The tracking state can then |
| be used by the compiler when expanding calls to |
| @code{__builtin_speculation_safe_copy} to permit a more efficient code |
| sequence to be generated. |
| |
| @item -moutline-atomics |
| @itemx -mno-outline-atomics |
| Enable or disable calls to out-of-line helpers to implement atomic operations. |
| These helpers will, at runtime, determine if the LSE instructions from |
| ARMv8.1-A can be used; if not, they will use the load/store-exclusive |
| instructions that are present in the base ARMv8.0 ISA. |
| |
| This option is only applicable when compiling for the base ARMv8.0 |
| instruction set. If using a later revision, e.g. @option{-march=armv8.1-a} |
| or @option{-march=armv8-a+lse}, the ARMv8.1-Atomics instructions will be |
| used directly. The same applies when using @option{-mcpu=} when the |
| selected cpu supports the @samp{lse} feature. |
| This option is on by default. |
| |
| @item -march=@var{name} |
| @opindex march |
| Specify the name of the target architecture and, optionally, one or |
| more feature modifiers. This option has the form |
| @option{-march=@var{arch}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}. |
| |
| The table below summarizes the permissible values for @var{arch} |
| and the features that they enable by default: |
| |
| @multitable @columnfractions 0.20 0.20 0.60 |
| @headitem @var{arch} value @tab Architecture @tab Includes by default |
| @item @samp{armv8-a} @tab Armv8-A @tab @samp{+fp}, @samp{+simd} |
| @item @samp{armv8.1-a} @tab Armv8.1-A @tab @samp{armv8-a}, @samp{+crc}, @samp{+lse}, @samp{+rdma} |
| @item @samp{armv8.2-a} @tab Armv8.2-A @tab @samp{armv8.1-a} |
| @item @samp{armv8.3-a} @tab Armv8.3-A @tab @samp{armv8.2-a}, @samp{+pauth} |
| @item @samp{armv8.4-a} @tab Armv8.4-A @tab @samp{armv8.3-a}, @samp{+flagm}, @samp{+fp16fml}, @samp{+dotprod} |
| @item @samp{armv8.5-a} @tab Armv8.5-A @tab @samp{armv8.4-a}, @samp{+sb}, @samp{+ssbs}, @samp{+predres} |
| @item @samp{armv8.6-a} @tab Armv8.6-A @tab @samp{armv8.5-a}, @samp{+bf16}, @samp{+i8mm} |
| @item @samp{armv8.7-a} @tab Armv8.7-A @tab @samp{armv8.6-a}, @samp{+ls64} |
| @item @samp{armv8.8-a} @tab Armv8.8-a @tab @samp{armv8.7-a}, @samp{+mops} |
| @item @samp{armv9-a} @tab Armv9-A @tab @samp{armv8.5-a}, @samp{+sve}, @samp{+sve2} |
| @item @samp{armv8-r} @tab Armv8-R @tab @samp{armv8-r} |
| @end multitable |
| |
| The value @samp{native} is available on native AArch64 GNU/Linux and |
| causes the compiler to pick the architecture of the host system. This |
| option has no effect if the compiler is unable to recognize the |
| architecture of the host system, |
| |
| The permissible values for @var{feature} are listed in the sub-section |
| on @ref{aarch64-feature-modifiers,,@option{-march} and @option{-mcpu} |
| Feature Modifiers}. Where conflicting feature modifiers are |
| specified, the right-most feature is used. |
| |
| GCC uses @var{name} to determine what kind of instructions it can emit |
| when generating assembly code. If @option{-march} is specified |
| without either of @option{-mtune} or @option{-mcpu} also being |
| specified, the code is tuned to perform well across a range of target |
| processors implementing the target architecture. |
| |
| @item -mtune=@var{name} |
| @opindex mtune |
| Specify the name of the target processor for which GCC should tune the |
| performance of the code. Permissible values for this option are: |
| @samp{generic}, @samp{cortex-a35}, @samp{cortex-a53}, @samp{cortex-a55}, |
| @samp{cortex-a57}, @samp{cortex-a72}, @samp{cortex-a73}, @samp{cortex-a75}, |
| @samp{cortex-a76}, @samp{cortex-a76ae}, @samp{cortex-a77}, |
| @samp{cortex-a65}, @samp{cortex-a65ae}, @samp{cortex-a34}, |
| @samp{cortex-a78}, @samp{cortex-a78ae}, @samp{cortex-a78c}, |
| @samp{ares}, @samp{exynos-m1}, @samp{emag}, @samp{falkor}, |
| @samp{neoverse-512tvb}, @samp{neoverse-e1}, @samp{neoverse-n1}, |
| @samp{neoverse-n2}, @samp{neoverse-v1}, @samp{qdf24xx}, |
| @samp{saphira}, @samp{phecda}, @samp{xgene1}, @samp{vulcan}, |
| @samp{octeontx}, @samp{octeontx81}, @samp{octeontx83}, |
| @samp{octeontx2}, @samp{octeontx2t98}, @samp{octeontx2t96} |
| @samp{octeontx2t93}, @samp{octeontx2f95}, @samp{octeontx2f95n}, |
| @samp{octeontx2f95mm}, |
| @samp{a64fx}, |
| @samp{thunderx}, @samp{thunderxt88}, |
| @samp{thunderxt88p1}, @samp{thunderxt81}, @samp{tsv110}, |
| @samp{thunderxt83}, @samp{thunderx2t99}, @samp{thunderx3t110}, @samp{zeus}, |
| @samp{cortex-a57.cortex-a53}, @samp{cortex-a72.cortex-a53}, |
| @samp{cortex-a73.cortex-a35}, @samp{cortex-a73.cortex-a53}, |
| @samp{cortex-a75.cortex-a55}, @samp{cortex-a76.cortex-a55}, |
| @samp{cortex-r82}, @samp{cortex-x1}, @samp{cortex-x2}, |
| @samp{cortex-a510}, @samp{cortex-a710}, @samp{ampere1}, @samp{native}. |
| |
| The values @samp{cortex-a57.cortex-a53}, @samp{cortex-a72.cortex-a53}, |
| @samp{cortex-a73.cortex-a35}, @samp{cortex-a73.cortex-a53}, |
| @samp{cortex-a75.cortex-a55}, @samp{cortex-a76.cortex-a55} specify that GCC |
| should tune for a big.LITTLE system. |
| |
| The value @samp{neoverse-512tvb} specifies that GCC should tune |
| for Neoverse cores that (a) implement SVE and (b) have a total vector |
| bandwidth of 512 bits per cycle. In other words, the option tells GCC to |
| tune for Neoverse cores that can execute 4 128-bit Advanced SIMD arithmetic |
| instructions a cycle and that can execute an equivalent number of SVE |
| arithmetic instructions per cycle (2 for 256-bit SVE, 4 for 128-bit SVE). |
| This is more general than tuning for a specific core like Neoverse V1 |
| but is more specific than the default tuning described below. |
| |
| Additionally on native AArch64 GNU/Linux systems the value |
| @samp{native} tunes performance to the host system. This option has no effect |
| if the compiler is unable to recognize the processor of the host system. |
| |
| Where none of @option{-mtune=}, @option{-mcpu=} or @option{-march=} |
| are specified, the code is tuned to perform well across a range |
| of target processors. |
| |
| This option cannot be suffixed by feature modifiers. |
| |
| @item -mcpu=@var{name} |
| @opindex mcpu |
| Specify the name of the target processor, optionally suffixed by one |
| or more feature modifiers. This option has the form |
| @option{-mcpu=@var{cpu}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}, where |
| the permissible values for @var{cpu} are the same as those available |
| for @option{-mtune}. The permissible values for @var{feature} are |
| documented in the sub-section on |
| @ref{aarch64-feature-modifiers,,@option{-march} and @option{-mcpu} |
| Feature Modifiers}. Where conflicting feature modifiers are |
| specified, the right-most feature is used. |
| |
| GCC uses @var{name} to determine what kind of instructions it can emit when |
| generating assembly code (as if by @option{-march}) and to determine |
| the target processor for which to tune for performance (as if |
| by @option{-mtune}). Where this option is used in conjunction |
| with @option{-march} or @option{-mtune}, those options take precedence |
| over the appropriate part of this option. |
| |
| @option{-mcpu=neoverse-512tvb} is special in that it does not refer |
| to a specific core, but instead refers to all Neoverse cores that |
| (a) implement SVE and (b) have a total vector bandwidth of 512 bits |
| a cycle. Unless overridden by @option{-march}, |
| @option{-mcpu=neoverse-512tvb} generates code that can run on a |
| Neoverse V1 core, since Neoverse V1 is the first Neoverse core with |
| these properties. Unless overridden by @option{-mtune}, |
| @option{-mcpu=neoverse-512tvb} tunes code in the same way as for |
| @option{-mtune=neoverse-512tvb}. |
| |
| @item -moverride=@var{string} |
| @opindex moverride |
| Override tuning decisions made by the back-end in response to a |
| @option{-mtune=} switch. The syntax, semantics, and accepted values |
| for @var{string} in this option are not guaranteed to be consistent |
| across releases. |
| |
| This option is only intended to be useful when developing GCC. |
| |
| @item -mverbose-cost-dump |
| @opindex mverbose-cost-dump |
| Enable verbose cost model dumping in the debug dump files. This option is |
| provided for use in debugging the compiler. |
| |
| @item -mpc-relative-literal-loads |
| @itemx -mno-pc-relative-literal-loads |
| @opindex mpc-relative-literal-loads |
| @opindex mno-pc-relative-literal-loads |
| Enable or disable PC-relative literal loads. With this option literal pools are |
| accessed using a single instruction and emitted after each function. This |
| limits the maximum size of functions to 1MB. This is enabled by default for |
| @option{-mcmodel=tiny}. |
| |
| @item -msign-return-address=@var{scope} |
| @opindex msign-return-address |
| Select the function scope on which return address signing will be applied. |
| Permissible values are @samp{none}, which disables return address signing, |
| @samp{non-leaf}, which enables pointer signing for functions which are not leaf |
| functions, and @samp{all}, which enables pointer signing for all functions. The |
| default value is @samp{none}. This option has been deprecated by |
| -mbranch-protection. |
| |
| @item -mbranch-protection=@var{none}|@var{standard}|@var{pac-ret}[+@var{leaf}+@var{b-key}]|@var{bti} |
| @opindex mbranch-protection |
| Select the branch protection features to use. |
| @samp{none} is the default and turns off all types of branch protection. |
| @samp{standard} turns on all types of branch protection features. If a feature |
| has additional tuning options, then @samp{standard} sets it to its standard |
| level. |
| @samp{pac-ret[+@var{leaf}]} turns on return address signing to its standard |
| level: signing functions that save the return address to memory (non-leaf |
| functions will practically always do this) using the a-key. The optional |
| argument @samp{leaf} can be used to extend the signing to include leaf |
| functions. The optional argument @samp{b-key} can be used to sign the functions |
| with the B-key instead of the A-key. |
| @samp{bti} turns on branch target identification mechanism. |
| |
| @item -mharden-sls=@var{opts} |
| @opindex mharden-sls |
| Enable compiler hardening against straight line speculation (SLS). |
| @var{opts} is a comma-separated list of the following options: |
| @table @samp |
| @item retbr |
| @item blr |
| @end table |
| In addition, @samp{-mharden-sls=all} enables all SLS hardening while |
| @samp{-mharden-sls=none} disables all SLS hardening. |
| |
| @item -msve-vector-bits=@var{bits} |
| @opindex msve-vector-bits |
| Specify the number of bits in an SVE vector register. This option only has |
| an effect when SVE is enabled. |
| |
| GCC supports two forms of SVE code generation: ``vector-length |
| agnostic'' output that works with any size of vector register and |
| ``vector-length specific'' output that allows GCC to make assumptions |
| about the vector length when it is useful for optimization reasons. |
| The possible values of @samp{bits} are: @samp{scalable}, @samp{128}, |
| @samp{256}, @samp{512}, @samp{1024} and @samp{2048}. |
| Specifying @samp{scalable} selects vector-length agnostic |
| output. At present @samp{-msve-vector-bits=128} also generates vector-length |
| agnostic output for big-endian targets. All other values generate |
| vector-length specific code. The behavior of these values may change |
| in future releases and no value except @samp{scalable} should be |
| relied on for producing code that is portable across different |
| hardware SVE vector lengths. |
| |
| The default is @samp{-msve-vector-bits=scalable}, which produces |
| vector-length agnostic code. |
| @end table |
| |
| @subsubsection @option{-march} and @option{-mcpu} Feature Modifiers |
| @anchor{aarch64-feature-modifiers} |
| @cindex @option{-march} feature modifiers |
| @cindex @option{-mcpu} feature modifiers |
| Feature modifiers used with @option{-march} and @option{-mcpu} can be any of |
| the following and their inverses @option{no@var{feature}}: |
| |
| @table @samp |
| @item crc |
| Enable CRC extension. This is on by default for |
| @option{-march=armv8.1-a}. |
| @item crypto |
| Enable Crypto extension. This also enables Advanced SIMD and floating-point |
| instructions. |
| @item fp |
| Enable floating-point instructions. This is on by default for all possible |
| values for options @option{-march} and @option{-mcpu}. |
| @item simd |
| Enable Advanced SIMD instructions. This also enables floating-point |
| instructions. This is on by default for all possible values for options |
| @option{-march} and @option{-mcpu}. |
| @item sve |
| Enable Scalable Vector Extension instructions. This also enables Advanced |
| SIMD and floating-point instructions. |
| @item lse |
| Enable Large System Extension instructions. This is on by default for |
| @option{-march=armv8.1-a}. |
| @item rdma |
| Enable Round Double Multiply Accumulate instructions. This is on by default |
| for @option{-march=armv8.1-a}. |
| @item fp16 |
| Enable FP16 extension. This also enables floating-point instructions. |
| @item fp16fml |
| Enable FP16 fmla extension. This also enables FP16 extensions and |
| floating-point instructions. This option is enabled by default for @option{-march=armv8.4-a}. Use of this option with architectures prior to Armv8.2-A is not supported. |
| |
| @item rcpc |
| Enable the RcPc extension. This does not change code generation from GCC, |
| but is passed on to the assembler, enabling inline asm statements to use |
| instructions from the RcPc extension. |
| @item dotprod |
| Enable the Dot Product extension. This also enables Advanced SIMD instructions. |
| @item aes |
| Enable the Armv8-a aes and pmull crypto extension. This also enables Advanced |
| SIMD instructions. |
| @item sha2 |
| Enable the Armv8-a sha2 crypto extension. This also enables Advanced SIMD instructions. |
| @item sha3 |
| Enable the sha512 and sha3 crypto extension. This also enables Advanced SIMD |
| instructions. Use of this option with architectures prior to Armv8.2-A is not supported. |
| @item sm4 |
| Enable the sm3 and sm4 crypto extension. This also enables Advanced SIMD instructions. |
| Use of this option with architectures prior to Armv8.2-A is not supported. |
| @item profile |
| Enable the Statistical Profiling extension. This option is only to enable the |
| extension at the assembler level and does not affect code generation. |
| @item rng |
| Enable the Armv8.5-a Random Number instructions. This option is only to |
| enable the extension at the assembler level and does not affect code |
| generation. |
| @item memtag |
| Enable the Armv8.5-a Memory Tagging Extensions. |
| Use of this option with architectures prior to Armv8.5-A is not supported. |
| @item sb |
| Enable the Armv8-a Speculation Barrier instruction. This option is only to |
| enable the extension at the assembler level and does not affect code |
| generation. This option is enabled by default for @option{-march=armv8.5-a}. |
| @item ssbs |
| Enable the Armv8-a Speculative Store Bypass Safe instruction. This option |
| is only to enable the extension at the assembler level and does not affect code |
| generation. This option is enabled by default for @option{-march=armv8.5-a}. |
| @item predres |
| Enable the Armv8-a Execution and Data Prediction Restriction instructions. |
| This option is only to enable the extension at the assembler level and does |
| not affect code generation. This option is enabled by default for |
| @option{-march=armv8.5-a}. |
| @item sve2 |
| Enable the Armv8-a Scalable Vector Extension 2. This also enables SVE |
| instructions. |
| @item sve2-bitperm |
| Enable SVE2 bitperm instructions. This also enables SVE2 instructions. |
| @item sve2-sm4 |
| Enable SVE2 sm4 instructions. This also enables SVE2 instructions. |
| @item sve2-aes |
| Enable SVE2 aes instructions. This also enables SVE2 instructions. |
| @item sve2-sha3 |
| Enable SVE2 sha3 instructions. This also enables SVE2 instructions. |
| @item tme |
| Enable the Transactional Memory Extension. |
| @item i8mm |
| Enable 8-bit Integer Matrix Multiply instructions. This also enables |
| Advanced SIMD and floating-point instructions. This option is enabled by |
| default for @option{-march=armv8.6-a}. Use of this option with architectures |
| prior to Armv8.2-A is not supported. |
| @item f32mm |
| Enable 32-bit Floating point Matrix Multiply instructions. This also enables |
| SVE instructions. Use of this option with architectures prior to Armv8.2-A is |
| not supported. |
| @item f64mm |
| Enable 64-bit Floating point Matrix Multiply instructions. This also enables |
| SVE instructions. Use of this option with architectures prior to Armv8.2-A is |
| not supported. |
| @item bf16 |
| Enable brain half-precision floating-point instructions. This also enables |
| Advanced SIMD and floating-point instructions. This option is enabled by |
| default for @option{-march=armv8.6-a}. Use of this option with architectures |
| prior to Armv8.2-A is not supported. |
| @item ls64 |
| Enable the 64-byte atomic load and store instructions for accelerators. |
| This option is enabled by default for @option{-march=armv8.7-a}. |
| @item mops |
| Enable the instructions to accelerate memory operations like @code{memcpy}, |
| @code{memmove}, @code{memset}. This option is enabled by default for |
| @option{-march=armv8.8-a} |
| @item flagm |
| Enable the Flag Manipulation instructions Extension. |
| @item pauth |
| Enable the Pointer Authentication Extension. |
| |
| @end table |
| |
| Feature @option{crypto} implies @option{aes}, @option{sha2}, and @option{simd}, |
| which implies @option{fp}. |
| Conversely, @option{nofp} implies @option{nosimd}, which implies |
| @option{nocrypto}, @option{noaes} and @option{nosha2}. |
| |
| @node Adapteva Epiphany Options |
| @subsection Adapteva Epiphany Options |
| |
| These @samp{-m} options are defined for Adapteva Epiphany: |
| |
| @table @gcctabopt |
| @item -mhalf-reg-file |
| @opindex mhalf-reg-file |
| Don't allocate any register in the range @code{r32}@dots{}@code{r63}. |
| That allows code to run on hardware variants that lack these registers. |
| |
| @item -mprefer-short-insn-regs |
| @opindex mprefer-short-insn-regs |
| Preferentially allocate registers that allow short instruction generation. |
| This can result in increased instruction count, so this may either reduce or |
| increase overall code size. |
| |
| @item -mbranch-cost=@var{num} |
| @opindex mbranch-cost |
| Set the cost of branches to roughly @var{num} ``simple'' instructions. |
| This cost is only a heuristic and is not guaranteed to produce |
| consistent results across releases. |
| |
| @item -mcmove |
| @opindex mcmove |
| Enable the generation of conditional moves. |
| |
| @item -mnops=@var{num} |
| @opindex mnops |
| Emit @var{num} NOPs before every other generated instruction. |
| |
| @item -mno-soft-cmpsf |
| @opindex mno-soft-cmpsf |
| @opindex msoft-cmpsf |
| For single-precision floating-point comparisons, emit an @code{fsub} instruction |
| and test the flags. This is faster than a software comparison, but can |
| get incorrect results in the presence of NaNs, or when two different small |
| numbers are compared such that their difference is calculated as zero. |
| The default is @option{-msoft-cmpsf}, which uses slower, but IEEE-compliant, |
| software comparisons. |
| |
| @item -mstack-offset=@var{num} |
| @opindex mstack-offset |
| Set the offset between the top of the stack and the stack pointer. |
| E.g., a value of 8 means that the eight bytes in the range @code{sp+0@dots{}sp+7} |
| can be used by leaf functions without stack allocation. |
| Values other than @samp{8} or @samp{16} are untested and unlikely to work. |
| Note also that this option changes the ABI; compiling a program with a |
| different stack offset than the libraries have been compiled with |
| generally does not work. |
| This option can be useful if you want to evaluate if a different stack |
| offset would give you better code, but to actually use a different stack |
| offset to build working programs, it is recommended to configure the |
| toolchain with the appropriate @option{--with-stack-offset=@var{num}} option. |
| |
| @item -mno-round-nearest |
| @opindex mno-round-nearest |
| @opindex mround-nearest |
| Make the scheduler assume that the rounding mode has been set to |
| truncating. The default is @option{-mround-nearest}. |
| |
| @item -mlong-calls |
| @opindex mlong-calls |
| If not otherwise specified by an attribute, assume all calls might be beyond |
| the offset range of the @code{b} / @code{bl} instructions, and therefore load the |
| function address into a register before performing a (otherwise direct) call. |
| This is the default. |
| |
| @item -mshort-calls |
| @opindex short-calls |
| If not otherwise specified by an attribute, assume all direct calls are |
| in the range of the @code{b} / @code{bl} instructions, so use these instructions |
| for direct calls. The default is @option{-mlong-calls}. |
| |
| @item -msmall16 |
| @opindex msmall16 |
| Assume addresses can be loaded as 16-bit unsigned values. This does not |
| apply to function addresses for which @option{-mlong-calls} semantics |
| are in effect. |
| |
| @item -mfp-mode=@var{mode} |
| @opindex mfp-mode |
| Set the prevailing mode of the floating-point unit. |
| This determines the floating-point mode that is provided and expected |
| at function call and return time. Making this mode match the mode you |
| predominantly need at function start can make your programs smaller and |
| faster by avoiding unnecessary mode switches. |
| |
| @var{mode} can be set to one the following values: |
| |
| @table @samp |
| @item caller |
| Any mode at function entry is valid, and retained or restored when |
| the function returns, and when it calls other functions. |
| This mode is useful for compiling libraries or other compilation units |
| you might want to incorporate into different programs with different |
| prevailing FPU modes, and the convenience of being able to use a single |
| object file outweighs the size and speed overhead for any extra |
| mode switching that might be needed, compared with what would be needed |
| with a more specific choice of prevailing FPU mode. |
| |
| @item truncate |
| This is the mode used for floating-point calculations with |
| truncating (i.e.@: round towards zero) rounding mode. That includes |
| conversion from floating point to integer. |
| |
| @item round-nearest |
| This is the mode used for floating-point calculations with |
| round-to-nearest-or-even rounding mode. |
| |
| @item int |
| This is the mode used to perform integer calculations in the FPU, e.g.@: |
| integer multiply, or integer multiply-and-accumulate. |
| @end table |
| |
| The default is @option{-mfp-mode=caller} |
| |
| @item -mno-split-lohi |
| @itemx -mno-postinc |
| @itemx -mno-postmodify |
| @opindex mno-split-lohi |
| @opindex msplit-lohi |
| @opindex mno-postinc |
| @opindex mpostinc |
| @opindex mno-postmodify |
| @opindex mpostmodify |
| Code generation tweaks that disable, respectively, splitting of 32-bit |
| loads, generation of post-increment addresses, and generation of |
| post-modify addresses. The defaults are @option{msplit-lohi}, |
| @option{-mpost-inc}, and @option{-mpost-modify}. |
| |
| @item -mnovect-double |
| @opindex mno-vect-double |
| @opindex mvect-double |
| Change the preferred SIMD mode to SImode. The default is |
| @option{-mvect-double}, which uses DImode as preferred SIMD mode. |
| |
| @item -max-vect-align=@var{num} |
| @opindex max-vect-align |
| The maximum alignment for SIMD vector mode types. |
| @var{num} may be 4 or 8. The default is 8. |
| Note that this is an ABI change, even though many library function |
| interfaces are unaffected if they don't use SIMD vector modes |
| in places that affect size and/or alignment of relevant types. |
| |
| @item -msplit-vecmove-early |
| @opindex msplit-vecmove-early |
| Split vector moves into single word moves before reload. In theory this |
| can give better register allocation, but so far the reverse seems to be |
| generally the case. |
| |
| @item -m1reg-@var{reg} |
| @opindex m1reg- |
| Specify a register to hold the constant @minus{}1, which makes loading small negative |
| constants and certain bitmasks faster. |
| Allowable values for @var{reg} are @samp{r43} and @samp{r63}, |
| which specify use of that register as a fixed register, |
| and @samp{none}, which means that no register is used for this |
| purpose. The default is @option{-m1reg-none}. |
| |
| @end table |
| |
| @node AMD GCN Options |
| @subsection AMD GCN Options |
| @cindex AMD GCN Options |
| |
| These options are defined specifically for the AMD GCN port. |
| |
| @table @gcctabopt |
| |
| @item -march=@var{gpu} |
| @opindex march |
| @itemx -mtune=@var{gpu} |
| @opindex mtune |
| Set architecture type or tuning for @var{gpu}. Supported values for @var{gpu} |
| are |
| |
| @table @samp |
| @opindex fiji |
| @item fiji |
| Compile for GCN3 Fiji devices (gfx803). |
| |
| @item gfx900 |
| Compile for GCN5 Vega 10 devices (gfx900). |
| |
| @item gfx906 |
| Compile for GCN5 Vega 20 devices (gfx906). |
| |
| @end table |
| |
| @item -msram-ecc=on |
| @itemx -msram-ecc=off |
| @itemx -msram-ecc=any |
| @opindex msram-ecc |
| Compile binaries suitable for devices with the SRAM-ECC feature enabled, |
| disabled, or either mode. This feature can be enabled per-process on some |
| devices. The compiled code must match the device mode. The default is |
| @samp{any}, for devices that support it. |
| |
| @item -mstack-size=@var{bytes} |
| @opindex mstack-size |
| Specify how many @var{bytes} of stack space will be requested for each GPU |
| thread (wave-front). Beware that there may be many threads and limited memory |
| available. The size of the stack allocation may also have an impact on |
| run-time performance. The default is 32KB when using OpenACC or OpenMP, and |
| 1MB otherwise. |
| |
| @item -mxnack |
| @opindex mxnack |
| Compile binaries suitable for devices with the XNACK feature enabled. Some |
| devices always require XNACK and some allow the user to configure XNACK. The |
| compiled code must match the device mode. The default is @samp{-mno-xnack}. |
| At present this option is a placeholder for support that is not yet |
| implemented. |
| |
| @end table |
| |
| @node ARC Options |
| @subsection ARC Options |
| @cindex ARC options |
| |
| The following options control the architecture variant for which code |
| is being compiled: |
| |
| @c architecture variants |
| @table @gcctabopt |
| |
| @item -mbarrel-shifter |
| @opindex mbarrel-shifter |
| Generate instructions supported by barrel shifter. This is the default |
| unless @option{-mcpu=ARC601} or @samp{-mcpu=ARCEM} is in effect. |
| |
| @item -mjli-always |
| @opindex mjli-always |
| Force to call a function using jli_s instruction. This option is |
| valid only for ARCv2 architecture. |
| |
| @item -mcpu=@var{cpu} |
| @opindex mcpu |
| Set architecture type, register usage, and instruction scheduling |
| parameters for @var{cpu}. There are also shortcut alias options |
| available for backward compatibility and convenience. Supported |
| values for @var{cpu} are |
| |
| @table @samp |
| @opindex mA6 |
| @opindex mARC600 |
| @item arc600 |
| Compile for ARC600. Aliases: @option{-mA6}, @option{-mARC600}. |
| |
| @item arc601 |
| @opindex mARC601 |
| Compile for ARC601. Alias: @option{-mARC601}. |
| |
| @item arc700 |
| @opindex mA7 |
| @opindex mARC700 |
| Compile for ARC700. Aliases: @option{-mA7}, @option{-mARC700}. |
| This is the default when configured with @option{--with-cpu=arc700}@. |
| |
| @item arcem |
| Compile for ARC EM. |
| |
| @item archs |
| Compile for ARC HS. |
| |
| @item em |
| Compile for ARC EM CPU with no hardware extensions. |
| |
| @item em4 |
| Compile for ARC EM4 CPU. |
| |
| @item em4_dmips |
| Compile for ARC EM4 DMIPS CPU. |
| |
| @item em4_fpus |
| Compile for ARC EM4 DMIPS CPU with the single-precision floating-point |
| extension. |
| |
| @item em4_fpuda |
| Compile for ARC EM4 DMIPS CPU with single-precision floating-point and |
| double assist instructions. |
| |
| @item hs |
| Compile for ARC HS CPU with no hardware extensions except the atomic |
| instructions. |
| |
| @item hs34 |
| Compile for ARC HS34 CPU. |
| |
| @item hs38 |
| Compile for ARC HS38 CPU. |
| |
| @item hs38_linux |
| Compile for ARC HS38 CPU with all hardware extensions on. |
| |
| @item arc600_norm |
| Compile for ARC 600 CPU with @code{norm} instructions enabled. |
| |
| @item arc600_mul32x16 |
| Compile for ARC 600 CPU with @code{norm} and 32x16-bit multiply |
| instructions enabled. |
| |
| @item arc600_mul64 |
| Compile for ARC 600 CPU with @code{norm} and @code{mul64}-family |
| instructions enabled. |
| |
| @item arc601_norm |
| Compile for ARC 601 CPU with @code{norm} instructions enabled. |
| |
| @item arc601_mul32x16 |
| Compile for ARC 601 CPU with @code{norm} and 32x16-bit multiply |
| instructions enabled. |
| |
| @item arc601_mul64 |
| Compile for ARC 601 CPU with @code{norm} and @code{mul64}-family |
| instructions enabled. |
| |
| @item nps400 |
| Compile for ARC 700 on NPS400 chip. |
| |
| @item em_mini |
| Compile for ARC EM minimalist configuration featuring reduced register |
| set. |
| |
| @end table |
| |
| @item -mdpfp |
| @opindex mdpfp |
| @itemx -mdpfp-compact |
| @opindex mdpfp-compact |
| Generate double-precision FPX instructions, tuned for the compact |
| implementation. |
| |
| @item -mdpfp-fast |
| @opindex mdpfp-fast |
| Generate double-precision FPX instructions, tuned for the fast |
| implementation. |
| |
| @item -mno-dpfp-lrsr |
| @opindex mno-dpfp-lrsr |
| Disable @code{lr} and @code{sr} instructions from using FPX extension |
| aux registers. |
| |
| @item -mea |
| @opindex mea |
| Generate extended arithmetic instructions. Currently only |
| @code{divaw}, @code{adds}, @code{subs}, and @code{sat16} are |
| supported. Only valid for @option{-mcpu=ARC700}. |
| |
| @item -mno-mpy |
| @opindex mno-mpy |
| @opindex mmpy |
| Do not generate @code{mpy}-family instructions for ARC700. This option is |
| deprecated. |
| |
| @item -mmul32x16 |
| @opindex mmul32x16 |
| Generate 32x16-bit multiply and multiply-accumulate instructions. |
| |
| @item -mmul64 |
| @opindex mmul64 |
| Generate @code{mul64} and @code{mulu64} instructions. |
| Only valid for @option{-mcpu=ARC600}. |
| |
| @item -mnorm |
| @opindex mnorm |
| Generate @code{norm} instructions. This is the default if @option{-mcpu=ARC700} |
| is in effect. |
| |
| @item -mspfp |
| @opindex mspfp |
| @itemx -mspfp-compact |
| @opindex mspfp-compact |
| Generate single-precision FPX instructions, tuned for the compact |
| implementation. |
| |
| @item -mspfp-fast |
| @opindex mspfp-fast |
| Generate single-precision FPX instructions, tuned for the fast |
| implementation. |
| |
| @item -msimd |
| @opindex msimd |
| Enable generation of ARC SIMD instructions via target-specific |
| builtins. Only valid for @option{-mcpu=ARC700}. |
| |
| @item -msoft-float |
| @opindex msoft-float |
| This option ignored; it is provided for compatibility purposes only. |
| Software floating-point code is emitted by default, and this default |
| can overridden by FPX options; @option{-mspfp}, @option{-mspfp-compact}, or |
| @option{-mspfp-fast} for single precision, and @option{-mdpfp}, |
| @option{-mdpfp-compact}, or @option{-mdpfp-fast} for double precision. |
| |
| @item -mswap |
| @opindex mswap |
| Generate @code{swap} instructions. |
| |
| @item -matomic |
| @opindex matomic |
| This enables use of the locked load/store conditional extension to implement |
| atomic memory built-in functions. Not available for ARC 6xx or ARC |
| EM cores. |
| |
| @item -mdiv-rem |
| @opindex mdiv-rem |
| Enable @code{div} and @code{rem} instructions for ARCv2 cores. |
| |
| @item -mcode-density |
| @opindex mcode-density |
| Enable code density instructions for ARC EM. |
| This option is on by default for ARC HS. |
| |
| @item -mll64 |
| @opindex mll64 |
| Enable double load/store operations for ARC HS cores. |
| |
| @item -mtp-regno=@var{regno} |
| @opindex mtp-regno |
| Specify thread pointer register number. |
| |
| @item -mmpy-option=@var{multo} |
| @opindex mmpy-option |
| Compile ARCv2 code with a multiplier design option. You can specify |
| the option using either a string or numeric value for @var{multo}. |
| @samp{wlh1} is the default value. The recognized values are: |
| |
| @table @samp |
| @item 0 |
| @itemx none |
| No multiplier available. |
| |
| @item 1 |
| @itemx w |
| 16x16 multiplier, fully pipelined. |
| The following instructions are enabled: @code{mpyw} and @code{mpyuw}. |
| |
| @item 2 |
| @itemx wlh1 |
| 32x32 multiplier, fully |
| pipelined (1 stage). The following instructions are additionally |
| enabled: @code{mpy}, @code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}. |
| |
| @item 3 |
| @itemx wlh2 |
| 32x32 multiplier, fully pipelined |
| (2 stages). The following instructions are additionally enabled: @code{mpy}, |
| @code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}. |
| |
| @item 4 |
| @itemx wlh3 |
| Two 16x16 multipliers, blocking, |
| sequential. The following instructions are additionally enabled: @code{mpy}, |
| @code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}. |
| |
| @item 5 |
| @itemx wlh4 |
| One 16x16 multiplier, blocking, |
| sequential. The following instructions are additionally enabled: @code{mpy}, |
| @code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}. |
| |
| @item 6 |
| @itemx wlh5 |
| One 32x4 multiplier, blocking, |
| sequential. The following instructions are additionally enabled: @code{mpy}, |
| @code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}. |
| |
| @item 7 |
| @itemx plus_dmpy |
| ARC HS SIMD support. |
| |
| @item 8 |
| @itemx plus_macd |
| ARC HS SIMD support. |
| |
| @item 9 |
| @itemx plus_qmacw |
| ARC HS SIMD support. |
| |
| @end table |
| |
| This option is only available for ARCv2 cores@. |
| |
| @item -mfpu=@var{fpu} |
| @opindex mfpu |
| Enables support for specific floating-point hardware extensions for ARCv2 |
| cores. Supported values for @var{fpu} are: |
| |
| @table @samp |
| |
| @item fpus |
| Enables support for single-precision floating-point hardware |
| extensions@. |
| |
| @item fpud |
| Enables support for double-precision floating-point hardware |
| extensions. The single-precision floating-point extension is also |
| enabled. Not available for ARC EM@. |
| |
| @item fpuda |
| Enables support for double-precision floating-point hardware |
| extensions using double-precision assist instructions. The single-precision |
| floating-point extension is also enabled. This option is |
| only available for ARC EM@. |
| |
| @item fpuda_div |
| Enables support for double-precision floating-point hardware |
| extensions using double-precision assist instructions. |
| The single-precision floating-point, square-root, and divide |
| extensions are also enabled. This option is |
| only available for ARC EM@. |
| |
| @item fpuda_fma |
| Enables support for double-precision floating-point hardware |
| extensions using double-precision assist instructions. |
| The single-precision floating-point and fused multiply and add |
| hardware extensions are also enabled. This option is |
| only available for ARC EM@. |
| |
| @item fpuda_all |
| Enables support for double-precision floating-point hardware |
| extensions using double-precision assist instructions. |
| All single-precision floating-point hardware extensions are also |
| enabled. This option is only available for ARC EM@. |
| |
| @item fpus_div |
| Enables support for single-precision floating-point, square-root and divide |
| hardware extensions@. |
| |
| @item fpud_div |
| Enables support for double-precision floating-point, square-root and divide |
| hardware extensions. This option |
| includes option @samp{fpus_div}. Not available for ARC EM@. |
| |
| @item fpus_fma |
| Enables support for single-precision floating-point and |
| fused multiply and add hardware extensions@. |
| |
| @item fpud_fma |
| Enables support for double-precision floating-point and |
| fused multiply and add hardware extensions. This option |
| includes option @samp{fpus_fma}. Not available for ARC EM@. |
| |
| @item fpus_all |
| Enables support for all single-precision floating-point hardware |
| extensions@. |
| |
| @item fpud_all |
| Enables support for all single- and double-precision floating-point |
| hardware extensions. Not available for ARC EM@. |
| |
| @end table |
| |
| @item -mirq-ctrl-saved=@var{register-range}, @var{blink}, @var{lp_count} |
| @opindex mirq-ctrl-saved |
| Specifies general-purposes registers that the processor automatically |
| saves/restores on interrupt entry and exit. @var{register-range} is |
| specified as two registers separated by a dash. The register range |
| always starts with @code{r0}, the upper limit is @code{fp} register. |
| @var{blink} and @var{lp_count} are optional. This option is only |
| valid for ARC EM and ARC HS cores. |
| |
| @item -mrgf-banked-regs=@var{number} |
| @opindex mrgf-banked-regs |
| Specifies the number of registers replicated in second register bank |
| on entry to fast interrupt. Fast interrupts are interrupts with the |
| highest priority level P0. These interrupts save only PC and STATUS32 |
| registers to avoid memory transactions during interrupt entry and exit |
| sequences. Use this option when you are using fast interrupts in an |
| ARC V2 family processor. Permitted values are 4, 8, 16, and 32. |
| |
| @item -mlpc-width=@var{width} |
| @opindex mlpc-width |
| Specify the width of the @code{lp_count} register. Valid values for |
| @var{width} are 8, 16, 20, 24, 28 and 32 bits. The default width is |
| fixed to 32 bits. If the width is less than 32, the compiler does not |
| attempt to transform loops in your program to use the zero-delay loop |
| mechanism unless it is known that the @code{lp_count} register can |
| hold the required loop-counter value. Depending on the width |
| specified, the compiler and run-time library might continue to use the |
| loop mechanism for various needs. This option defines macro |
| @code{__ARC_LPC_WIDTH__} with the value of @var{width}. |
| |
| @item -mrf16 |
| @opindex mrf16 |
| This option instructs the compiler to generate code for a 16-entry |
| register file. This option defines the @code{__ARC_RF16__} |
| preprocessor macro. |
| |
| @item -mbranch-index |
| @opindex mbranch-index |
| Enable use of @code{bi} or @code{bih} instructions to implement jump |
| tables. |
| |
| @end table |
| |
| The following options are passed through to the assembler, and also |
| define preprocessor macro symbols. |
| |
| @c Flags used by the assembler, but for which we define preprocessor |
| @c macro symbols as well. |
| @table @gcctabopt |
| @item -mdsp-packa |
| @opindex mdsp-packa |
| Passed down to the assembler to enable the DSP Pack A extensions. |
| Also sets the preprocessor symbol @code{__Xdsp_packa}. This option is |
| deprecated. |
| |
| @item -mdvbf |
| @opindex mdvbf |
| Passed down to the assembler to enable the dual Viterbi butterfly |
| extension. Also sets the preprocessor symbol @code{__Xdvbf}. This |
| option is deprecated. |
| |
| @c ARC700 4.10 extension instruction |
| @item -mlock |
| @opindex mlock |
| Passed down to the assembler to enable the locked load/store |
| conditional extension. Also sets the preprocessor symbol |
| @code{__Xlock}. |
| |
| @item -mmac-d16 |
| @opindex mmac-d16 |
| Passed down to the assembler. Also sets the preprocessor symbol |
| @code{__Xxmac_d16}. This option is deprecated. |
| |
| @item -mmac-24 |
| @opindex mmac-24 |
| Passed down to the assembler. Also sets the preprocessor symbol |
| @code{__Xxmac_24}. This option is deprecated. |
| |
| @c ARC700 4.10 extension instruction |
| @item -mrtsc |
| @opindex mrtsc |
| Passed down to the assembler to enable the 64-bit time-stamp counter |
| extension instruction. Also sets the preprocessor symbol |
| @code{__Xrtsc}. This option is deprecated. |
| |
| @c ARC700 4.10 extension instruction |
| @item -mswape |
| @opindex mswape |
| Passed down to the assembler to enable the swap byte ordering |
| extension instruction. Also sets the preprocessor symbol |
| @code{__Xswape}. |
| |
| @item -mtelephony |
| @opindex mtelephony |
| Passed down to the assembler to enable dual- and single-operand |
| instructions for telephony. Also sets the preprocessor symbol |
| @code{__Xtelephony}. This option is deprecated. |
| |
| @item -mxy |
| @opindex mxy |
| Passed down to the assembler to enable the XY memory extension. Also |
| sets the preprocessor symbol @code{__Xxy}. |
| |
| @end table |
| |
| The following options control how the assembly code is annotated: |
| |
| @c Assembly annotation options |
| @table @gcctabopt |
| @item -misize |
| @opindex misize |
| Annotate assembler instructions with estimated addresses. |
| |
| @item -mannotate-align |
| @opindex mannotate-align |
| Explain what alignment considerations lead to the decision to make an |
| instruction short or long. |
| |
| @end table |
| |
| The following options are passed through to the linker: |
| |
| @c options passed through to the linker |
| @table @gcctabopt |
| @item -marclinux |
| @opindex marclinux |
| Passed through to the linker, to specify use of the @code{arclinux} emulation. |
| This option is enabled by default in tool chains built for |
| @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} targets |
| when profiling is not requested. |
| |
| @item -marclinux_prof |
| @opindex marclinux_prof |
| Passed through to the linker, to specify use of the |
| @code{arclinux_prof} emulation. This option is enabled by default in |
| tool chains built for @w{@code{arc-linux-uclibc}} and |
| @w{@code{arceb-linux-uclibc}} targets when profiling is requested. |
| |
| @end table |
| |
| The following options control the semantics of generated code: |
| |
| @c semantically relevant code generation options |
| @table @gcctabopt |
| @item -mlong-calls |
| @opindex mlong-calls |
| Generate calls as register indirect calls, thus providing access |
| to the full 32-bit address range. |
| |
| @item -mmedium-calls |
| @opindex mmedium-calls |
| Don't use less than 25-bit addressing range for calls, which is the |
| offset available for an unconditional branch-and-link |
| instruction. Conditional execution of function calls is suppressed, to |
| allow use of the 25-bit range, rather than the 21-bit range with |
| conditional branch-and-link. This is the default for tool chains built |
| for @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} targets. |
| |
| @item -G @var{num} |
| @opindex G |
| Put definitions of externally-visible data in a small data section if |
| that data is no bigger than @var{num} bytes. The default value of |
| @var{num} is 4 for any ARC configuration, or 8 when we have double |
| load/store operations. |
| |
| @item -mno-sdata |
| @opindex mno-sdata |
| @opindex msdata |
| Do not generate sdata references. This is the default for tool chains |
| built for @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} |
| targets. |
| |
| @item -mvolatile-cache |
| @opindex mvolatile-cache |
| Use ordinarily cached memory accesses for volatile references. This is the |
| default. |
| |
| @item -mno-volatile-cache |
| @opindex mno-volatile-cache |
| @opindex mvolatile-cache |
| Enable cache bypass for volatile references. |
| |
| @end table |
| |
| The following options fine tune code generation: |
| @c code generation tuning options |
| @table @gcctabopt |
| @item -malign-call |
| @opindex malign-call |
| Does nothing. Preserved for backward compatibility. |
| |
| @item -mauto-modify-reg |
| @opindex mauto-modify-reg |
| Enable the use of pre/post modify with register displacement. |
| |
| @item -mbbit-peephole |
| @opindex mbbit-peephole |
| Enable bbit peephole2. |
| |
| @item -mno-brcc |
| @opindex mno-brcc |
| This option disables a target-specific pass in @file{arc_reorg} to |
| generate compare-and-branch (@code{br@var{cc}}) instructions. |
| It has no effect on |
| generation of these instructions driven by the combiner pass. |
| |
| @item -mcase-vector-pcrel |
| @opindex mcase-vector-pcrel |
| Use PC-relative switch case tables to enable case table shortening. |
| This is the default for @option{-Os}. |
| |
| @item -mcompact-casesi |
| @opindex mcompact-casesi |
| Enable compact @code{casesi} pattern. This is the default for @option{-Os}, |
| and only available for ARCv1 cores. This option is deprecated. |
| |
| @item -mno-cond-exec |
| @opindex mno-cond-exec |
| Disable the ARCompact-specific pass to generate conditional |
| execution instructions. |
| |
| Due to delay slot scheduling and interactions between operand numbers, |
| literal sizes, instruction lengths, and the support for conditional execution, |
| the target-independent pass to generate conditional execution is often lacking, |
| so the ARC port has kept a special pass around that tries to find more |
| conditional execution generation opportunities after register allocation, |
| branch shortening, and delay slot scheduling have been done. This pass |
| generally, but not always, improves performance and code size, at the cost of |
| extra compilation time, which is why there is an option to switch it off. |
| If you have a problem with call instructions exceeding their allowable |
| offset range because they are conditionalized, you should consider using |
| @option{-mmedium-calls} instead. |
| |
| @item -mearly-cbranchsi |
| @opindex mearly-cbranchsi |
| Enable pre-reload use of the @code{cbranchsi} pattern. |
| |
| @item -mexpand-adddi |
| @opindex mexpand-adddi |
| Expand @code{adddi3} and @code{subdi3} at RTL generation time into |
| @code{add.f}, @code{adc} etc. This option is deprecated. |
| |
| @item -mindexed-loads |
| @opindex mindexed-loads |
| Enable the use of indexed loads. This can be problematic because some |
| optimizers then assume that indexed stores exist, which is not |
| the case. |
| |
| @item -mlra |
| @opindex mlra |
| Enable Local Register Allocation. This is still experimental for ARC, |
| so by default the compiler uses standard reload |
| (i.e.@: @option{-mno-lra}). |
| |
| @item -mlra-priority-none |
| @opindex mlra-priority-none |
| Don't indicate any priority for target registers. |
| |
| @item -mlra-priority-compact |
| @opindex mlra-priority-compact |
| Indicate target register priority for r0..r3 / r12..r15. |
| |
| @item -mlra-priority-noncompact |
| @opindex mlra-priority-noncompact |
| Reduce target register priority for r0..r3 / r12..r15. |
| |
| @item -mmillicode |
| @opindex mmillicode |
| When optimizing for size (using @option{-Os}), prologues and epilogues |
| that have to save or restore a large number of registers are often |
| shortened by using call to a special function in libgcc; this is |
| referred to as a @emph{millicode} call. As these calls can pose |
| performance issues, and/or cause linking issues when linking in a |
| nonstandard way, this option is provided to turn on or off millicode |
| call generation. |
| |
| @item -mcode-density-frame |
| @opindex mcode-density-frame |
| This option enable the compiler to emit @code{enter} and @code{leave} |
| instructions. These instructions are only valid for CPUs with |
| code-density feature. |
| |
| @item -mmixed-code |
| @opindex mmixed-code |
| Does nothing. Preserved for backward compatibility. |
| |
| @item -mq-class |
| @opindex mq-class |
| Ths option is deprecated. Enable @samp{q} instruction alternatives. |
| This is the default for @option{-Os}. |
| |
| @item -mRcq |
| @opindex mRcq |
| Enable @samp{Rcq} constraint handling. |
| Most short code generation depends on this. |
| This is the default. |
| |
| @item -mRcw |
| @opindex mRcw |
| Enable @samp{Rcw} constraint handling. |
| Most ccfsm condexec mostly depends on this. |
| This is the default. |
| |
| @item -msize-level=@var{level} |
| @opindex msize-level |
| Fine-tune size optimization with regards to instruction lengths and alignment. |
| The recognized values for @var{level} are: |
| @table @samp |
| @item 0 |
| No size optimization. This level is deprecated and treated like @samp{1}. |
| |
| @item 1 |
| Short instructions are used opportunistically. |
| |
| @item 2 |
| In addition, alignment of loops and of code after barriers are dropped. |
| |
| @item 3 |
| In addition, optional data alignment is dropped, and the option @option{Os} is enabled. |
| |
| @end table |
| |
| This defaults to @samp{3} when @option{-Os} is in effect. Otherwise, |
| the behavior when this is not set is equivalent to level @samp{1}. |
| |
| @item -mtune=@var{cpu} |
| @opindex mtune |
| Set instruction scheduling parameters for @var{cpu}, overriding any implied |
| by @option{-mcpu=}. |
| |
| Supported values for @var{cpu} are |
| |
| @table @samp |
| @item ARC600 |
| Tune for ARC600 CPU. |
| |
| @item ARC601 |
| Tune for ARC601 CPU. |
| |
| @item ARC700 |
| Tune for ARC700 CPU with standard multiplier block. |
| |
| @item ARC700-xmac |
| Tune for ARC700 CPU with XMAC block. |
| |
| @item ARC725D |
| Tune for ARC725D CPU. |
| |
| @item ARC750D |
| Tune for ARC750D CPU. |
| |
| @end table |
| |
| @item -mmultcost=@var{num} |
| @opindex mmultcost |
| Cost to assume for a multiply instruction, with @samp{4} being equal to a |
| normal instruction. |
| |
| @item -munalign-prob-threshold=@var{probability} |
| @opindex munalign-prob-threshold |
| Does nothing. Preserved for backward compatibility. |
| |
| @end table |
| |
| The following options are maintained for backward compatibility, but |
| are now deprecated and will be removed in a future release: |
| |
| @c Deprecated options |
| @table @gcctabopt |
| |
| @item -margonaut |
| @opindex margonaut |
| Obsolete FPX. |
| |
| @item -mbig-endian |
| @opindex mbig-endian |
| @itemx -EB |
| @opindex EB |
| Compile code for big-endian targets. Use of these options is now |
| deprecated. Big-endian code is supported by configuring GCC to build |
| @w{@code{arceb-elf32}} and @w{@code{arceb-linux-uclibc}} targets, |
| for which big endian is the default. |
| |
| @item -mlittle-endian |
| @opindex mlittle-endian |
| @itemx -EL |
| @opindex EL |
| Compile code for little-endian targets. Use of these options is now |
| deprecated. Little-endian code is supported by configuring GCC to build |
| @w{@code{arc-elf32}} and @w{@code{arc-linux-uclibc}} targets, |
| for which little endian is the default. |
| |
| @item -mbarrel_shifter |
| @opindex mbarrel_shifter |
| Replaced by @option{-mbarrel-shifter}. |
| |
| @item -mdpfp_compact |
| @opindex mdpfp_compact |
| Replaced by @option{-mdpfp-compact}. |
| |
| @item -mdpfp_fast |
| @opindex mdpfp_fast |
| Replaced by @option{-mdpfp-fast}. |
| |
| @item -mdsp_packa |
| @opindex mdsp_packa |
| Replaced by @option{-mdsp-packa}. |
| |
| @item -mEA |
| @opindex mEA |
| Replaced by @option{-mea}. |
| |
| @item -mmac_24 |
| @opindex mmac_24 |
| Replaced by @option{-mmac-24}. |
| |
| @item -mmac_d16 |
| @opindex mmac_d16 |
| Replaced by @option{-mmac-d16}. |
| |
| @item -mspfp_compact |
| @opindex mspfp_compact |
| Replaced by @option{-mspfp-compact}. |
| |
| @item -mspfp_fast |
| @opindex mspfp_fast |
| Replaced by @option{-mspfp-fast}. |
| |
| @item -mtune=@var{cpu} |
| @opindex mtune |
| Values @samp{arc600}, @samp{arc601}, @samp{arc700} and |
| @samp{arc700-xmac} for @var{cpu} are replaced by @samp{ARC600}, |
| @samp{ARC601}, @samp{ARC700} and @samp{ARC700-xmac} respectively. |
| |
| @item -multcost=@var{num} |
| @opindex multcost |
| Replaced by @option{-mmultcost}. |
| |
| @end table |
| |
| @node ARM Options |
| @subsection ARM Options |
| @cindex ARM options |
| |
| These @samp{-m} options are defined for the ARM port: |
| |
| @table @gcctabopt |
| @item -mabi=@var{name} |
| @opindex mabi |
| Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu}, |
| @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}. |
| |
| @item -mapcs-frame |
| @opindex mapcs-frame |
| Generate a stack frame that is compliant with the ARM Procedure Call |
| Standard for all functions, even if this is not strictly necessary for |
| correct execution of the code. Specifying @option{-fomit-frame-pointer} |
| with this option causes the stack frames not to be generated for |
| leaf functions. The default is @option{-mno-apcs-frame}. |
| This option is deprecated. |
| |
| @item -mapcs |
| @opindex mapcs |
| This is a synonym for @option{-mapcs-frame} and is deprecated. |
| |
| @ignore |
| @c not currently implemented |
| @item -mapcs-stack-check |
| @opindex mapcs-stack-check |
| Generate code to check the amount of stack space available upon entry to |
| every function (that actually uses some stack space). If there is |
| insufficient space available then either the function |
| @code{__rt_stkovf_split_small} or @code{__rt_stkovf_split_big} is |
| called, depending upon the amount of stack space required. The runtime |
| system is required to provide these functions. The default is |
| @option{-mno-apcs-stack-check}, since this produces smaller code. |
| |
| @c not currently implemented |
| @item -mapcs-reentrant |
| @opindex mapcs-reentrant |
| Generate reentrant, position-independent code. The default is |
| @option{-mno-apcs-reentrant}. |
| @end ignore |
| |
| @item -mthumb-interwork |
| @opindex mthumb-interwork |
| Generate code that supports calling between the ARM and Thumb |
| instruction sets. Without this option, on pre-v5 architectures, the |
| two instruction sets cannot be reliably used inside one program. The |
| default is @option{-mno-thumb-interwork}, since slightly larger code |
| is generated when @option{-mthumb-interwork} is specified. In AAPCS |
| configurations this option is meaningless. |
| |
| @item -mno-sched-prolog |
| @opindex mno-sched-prolog |
| @opindex msched-prolog |
| Prevent the reordering of instructions in the function prologue, or the |
| merging of those instruction with the instructions in the function's |
| body. This means that all functions start with a recognizable set |
| of instructions (or in fact one of a choice from a small set of |
| different function prologues), and this information can be used to |
| locate the start of functions inside an executable piece of code. The |
| default is @option{-msched-prolog}. |
| |
| @item -mfloat-abi=@var{name} |
| @opindex mfloat-abi |
| Specifies which floating-point ABI to use. Permissible values |
| are: @samp{soft}, @samp{softfp} and @samp{hard}. |
| |
| Specifying @samp{soft} causes GCC to generate output containing |
| library calls for floating-point operations. |
| @samp{softfp} allows the generation of code using hardware floating-point |
| instructions, but still uses the soft-float calling conventions. |
| @samp{hard} allows generation of floating-point instructions |
| and uses FPU-specific calling conventions. |
| |
| The default depends on the specific target configuration. Note that |
| the hard-float and soft-float ABIs are not link-compatible; you must |
| compile your entire program with the same ABI, and link with a |
| compatible set of libraries. |
| |
| @item -mgeneral-regs-only |
| @opindex mgeneral-regs-only |
| Generate code which uses only the general-purpose registers. This will prevent |
| the compiler from using floating-point and Advanced SIMD registers but will not |
| impose any restrictions on the assembler. |
| |
| @item -mlittle-endian |
| @opindex mlittle-endian |
| Generate code for a processor running in little-endian mode. This is |
| the default for all standard configurations. |
| |
| @item -mbig-endian |
| @opindex mbig-endian |
| Generate code for a processor running in big-endian mode; the default is |
| to compile code for a little-endian processor. |
| |
| @item -mbe8 |
| @itemx -mbe32 |
| @opindex mbe8 |
| When linking a big-endian image select between BE8 and BE32 formats. |
| The option has no effect for little-endian images and is ignored. The |
| default is dependent on the selected target architecture. For ARMv6 |
| and later architectures the default is BE8, for older architectures |
| the default is BE32. BE32 format has been deprecated by ARM. |
| |
| @item -march=@var{name}@r{[}+extension@dots{}@r{]} |
| @opindex march |
| This specifies the name of the target ARM architecture. GCC uses this |
| name to determine what kind of instructions it can emit when generating |
| assembly code. This option can be used in conjunction with or instead |
| of the @option{-mcpu=} option. |
| |
| Permissible names are: |
| @samp{armv4t}, |
| @samp{armv5t}, @samp{armv5te}, |
| @samp{armv6}, @samp{armv6j}, @samp{armv6k}, @samp{armv6kz}, @samp{armv6t2}, |
| @samp{armv6z}, @samp{armv6zk}, |
| @samp{armv7}, @samp{armv7-a}, @samp{armv7ve}, |
| @samp{armv8-a}, @samp{armv8.1-a}, @samp{armv8.2-a}, @samp{armv8.3-a}, |
| @samp{armv8.4-a}, |
| @samp{armv8.5-a}, |
| @samp{armv8.6-a}, |
| @samp{armv9-a}, |
| @samp{armv7-r}, |
| @samp{armv8-r}, |
| @samp{armv6-m}, @samp{armv6s-m}, |
| @samp{armv7-m}, @samp{armv7e-m}, |
| @samp{armv8-m.base}, @samp{armv8-m.main}, |
| @samp{armv8.1-m.main}, |
| @samp{armv9-a}, |
| @samp{iwmmxt} and @samp{iwmmxt2}. |
| |
| Additionally, the following architectures, which lack support for the |
| Thumb execution state, are recognized but support is deprecated: @samp{armv4}. |
| |
| Many of the architectures support extensions. These can be added by |
| appending @samp{+@var{extension}} to the architecture name. Extension |
| options are processed in order and capabilities accumulate. An extension |
| will also enable any necessary base extensions |
| upon which it depends. For example, the @samp{+crypto} extension |
| will always enable the @samp{+simd} extension. The exception to the |
| additive construction is for extensions that are prefixed with |
| @samp{+no@dots{}}: these extensions disable the specified option and |
| any other extensions that may depend on the presence of that |
| extension. |
| |
| For example, @samp{-march=armv7-a+simd+nofp+vfpv4} is equivalent to |
| writing @samp{-march=armv7-a+vfpv4} since the @samp{+simd} option is |
| entirely disabled by the @samp{+nofp} option that follows it. |
| |
| Most extension names are generically named, but have an effect that is |
| dependent upon the architecture to which it is applied. For example, |
| the @samp{+simd} option can be applied to both @samp{armv7-a} and |
| @samp{armv8-a} architectures, but will enable the original ARMv7-A |
| Advanced SIMD (Neon) extensions for @samp{armv7-a} and the ARMv8-A |
| variant for @samp{armv8-a}. |
| |
| The table below lists the supported extensions for each architecture. |
| Architectures not mentioned do not support any extensions. |
| |
| @table @samp |
| @item armv5te |
| @itemx armv6 |
| @itemx armv6j |
| @itemx armv6k |
| @itemx armv6kz |
| @itemx armv6t2 |
| @itemx armv6z |
| @itemx armv6zk |
| @table @samp |
| @item +fp |
| The VFPv2 floating-point instructions. The extension @samp{+vfpv2} can be |
| used as an alias for this extension. |
| |
| @item +nofp |
| Disable the floating-point instructions. |
| @end table |
| |
| @item armv7 |
| The common subset of the ARMv7-A, ARMv7-R and ARMv7-M architectures. |
| @table @samp |
| @item +fp |
| The VFPv3 floating-point instructions, with 16 double-precision |
| registers. The extension @samp{+vfpv3-d16} can be used as an alias |
| for this extension. Note that floating-point is not supported by the |
| base ARMv7-M architecture, but is compatible with both the ARMv7-A and |
| ARMv7-R architectures. |
| |
| @item +nofp |
| Disable the floating-point instructions. |
| @end table |
| |
| @item armv7-a |
| @table @samp |
| @item +mp |
| The multiprocessing extension. |
| |
| @item +sec |
| The security extension. |
| |
| @item +fp |
| The VFPv3 floating-point instructions, with 16 double-precision |
| registers. The extension @samp{+vfpv3-d16} can be used as an alias |
| for this extension. |
| |
| @item +simd |
| The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions. |
| The extensions @samp{+neon} and @samp{+neon-vfpv3} can be used as aliases |
| for this extension. |
| |
| @item +vfpv3 |
| The VFPv3 floating-point instructions, with 32 double-precision |
| registers. |
| |
| @item +vfpv3-d16-fp16 |
| The VFPv3 floating-point instructions, with 16 double-precision |
| registers and the half-precision floating-point conversion operations. |
| |
| @item +vfpv3-fp16 |
| The VFPv3 floating-point instructions, with 32 double-precision |
| registers and the half-precision floating-point conversion operations. |
| |
| @item +vfpv4-d16 |
| The VFPv4 floating-point instructions, with 16 double-precision |
| registers. |
| |
| @item +vfpv4 |
| The VFPv4 floating-point instructions, with 32 double-precision |
| registers. |
| |
| @item +neon-fp16 |
| The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions, with |
| the half-precision floating-point conversion operations. |
| |
| @item +neon-vfpv4 |
| The Advanced SIMD (Neon) v2 and the VFPv4 floating-point instructions. |
| |
| @item +nosimd |
| Disable the Advanced SIMD instructions (does not disable floating point). |
| |
| @item +nofp |
| Disable the floating-point and Advanced SIMD instructions. |
| @end table |
| |
| @item armv7ve |
| The extended version of the ARMv7-A architecture with support for |
| virtualization. |
| @table @samp |
| @item +fp |
| The VFPv4 floating-point instructions, with 16 double-precision registers. |
| The extension @samp{+vfpv4-d16} can be used as an alias for this extension. |
| |
| @item +simd |
| The Advanced SIMD (Neon) v2 and the VFPv4 floating-point instructions. The |
| extension @samp{+neon-vfpv4} can be used as an alias for this extension. |
| |
| @item +vfpv3-d16 |
| The VFPv3 floating-point instructions, with 16 double-precision |
| registers. |
| |
| @item +vfpv3 |
| The VFPv3 floating-point instructions, with 32 double-precision |
| registers. |
| |
| @item +vfpv3-d16-fp16 |
| The VFPv3 floating-point instructions, with 16 double-precision |
| registers and the half-precision floating-point conversion operations. |
| |
| @item +vfpv3-fp16 |
| The VFPv3 floating-point instructions, with 32 double-precision |
| registers and the half-precision floating-point conversion operations. |
| |
| @item +vfpv4-d16 |
| The VFPv4 floating-point instructions, with 16 double-precision |
| registers. |
| |
| @item +vfpv4 |
| The VFPv4 floating-point instructions, with 32 double-precision |
| registers. |
| |
| @item +neon |
| The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions. |
| The extension @samp{+neon-vfpv3} can be used as an alias for this extension. |
| |
| @item +neon-fp16 |
| The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions, with |
| the half-precision floating-point conversion operations. |
| |
| @item +nosimd |
| Disable the Advanced SIMD instructions (does not disable floating point). |
| |
| @item +nofp |
| Disable the floating-point and Advanced SIMD instructions. |
| @end table |
| |
| @item armv8-a |
| @table @samp |
| @item +crc |
| The Cyclic Redundancy Check (CRC) instructions. |
| @item +simd |
| The ARMv8-A Advanced SIMD and floating-point instructions. |
| @item +crypto |
| The cryptographic instructions. |
| @item +nocrypto |
| Disable the cryptographic instructions. |
| @item +nofp |
| Disable the floating-point, Advanced SIMD and cryptographic instructions. |
| @item +sb |
| Speculation Barrier Instruction. |
| @item +predres |
| Execution and Data Prediction Restriction Instructions. |
| @end table |
| |
| @item armv8.1-a |
| @table @samp |
| @item +simd |
| The ARMv8.1-A Advanced SIMD and floating-point instructions. |
| |
| @item +crypto |
| The cryptographic instructions. This also enables the Advanced SIMD and |
| floating-point instructions. |
| |
| @item +nocrypto |
| Disable the cryptographic instructions. |
| |
| @item +nofp |
| Disable the floating-point, Advanced SIMD and cryptographic instructions. |
| |
| @item +sb |
| Speculation Barrier Instruction. |
| |
| @item +predres |
| Execution and Data Prediction Restriction Instructions. |
| @end table |
| |
| @item armv8.2-a |
| @itemx armv8.3-a |
| @table @samp |
| @item +fp16 |
| The half-precision floating-point data processing instructions. |
| This also enables the Advanced SIMD and floating-point instructions. |
| |
| @item +fp16fml |
| The half-precision floating-point fmla extension. This also enables |
| the half-precision floating-point extension and Advanced SIMD and |
| floating-point instructions. |
| |
| @item +simd |
| The ARMv8.1-A Advanced SIMD and floating-point instructions. |
| |
| @item +crypto |
| The cryptographic instructions. This also enables the Advanced SIMD and |
| floating-point instructions. |
| |
| @item +dotprod |
| Enable the Dot Product extension. This also enables Advanced SIMD instructions. |
| |
| @item +nocrypto |
| Disable the cryptographic extension. |
| |
| @item +nofp |
| Disable the floating-point, Advanced SIMD and cryptographic instructions. |
| |
| @item +sb |
| Speculation Barrier Instruction. |
| |
| @item +predres |
| Execution and Data Prediction Restriction Instructions. |
| |
| @item +i8mm |
| 8-bit Integer Matrix Multiply instructions. |
| This also enables Advanced SIMD and floating-point instructions. |
| |
| @item +bf16 |
| Brain half-precision floating-point instructions. |
| This also enables Advanced SIMD and floating-point instructions. |
| @end table |
| |
| @item armv8.4-a |
| @table @samp |
| @item +fp16 |
| The half-precision floating-point data processing instructions. |
| This also enables the Advanced SIMD and floating-point instructions as well |
| as the Dot Product extension and the half-precision floating-point fmla |
| extension. |
| |
| @item +simd |
| The ARMv8.3-A Advanced SIMD and floating-point instructions as well as the |
| Dot Product extension. |
| |
| @item +crypto |
| The cryptographic instructions. This also enables the Advanced SIMD and |
| floating-point instructions as well as the Dot Product extension. |
| |
| @item +nocrypto |
| Disable the cryptographic extension. |
| |
| @item +nofp |
| Disable the floating-point, Advanced SIMD and cryptographic instructions. |
| |
| @item +sb |
| Speculation Barrier Instruction. |
| |
| @item +predres |
| Execution and Data Prediction Restriction Instructions. |
| |
| @item +i8mm |
| 8-bit Integer Matrix Multiply instructions. |
| This also enables Advanced SIMD and floating-point instructions. |
| |
| @item +bf16 |
| Brain half-precision floating-point instructions. |
| This also enables Advanced SIMD and floating-point instructions. |
| @end table |
| |
| @item armv8.5-a |
| @table @samp |
| @item +fp16 |
| The half-precision floating-point data processing instructions. |
| This also enables the Advanced SIMD and floating-point instructions as well |
| as the Dot Product extension and the half-precision floating-point fmla |
| extension. |
| |
| @item +simd |
| The ARMv8.3-A Advanced SIMD and floating-point instructions as well as the |
| Dot Product extension. |
| |
| @item +crypto |
| The cryptographic instructions. This also enables the Advanced SIMD and |
| floating-point instructions as well as the Dot Product extension. |
| |
| @item +nocrypto |
| Disable the cryptographic extension. |
| |
| @item +nofp |
| Disable the floating-point, Advanced SIMD and cryptographic instructions. |
| |
| @item +i8mm |
| 8-bit Integer Matrix Multiply instructions. |
| This also enables Advanced SIMD and floating-point instructions. |
| |
| @item +bf16 |
| Brain half-precision floating-point instructions. |
| This also enables Advanced SIMD and floating-point instructions. |
| @end table |
| |
| @item armv8.6-a |
| @table @samp |
| @item +fp16 |
| The half-precision floating-point data processing instructions. |
| This also enables the Advanced SIMD and floating-point instructions as well |
| as the Dot Product extension and the half-precision floating-point fmla |
| extension. |
| |
| @item +simd |
| The ARMv8.3-A Advanced SIMD and floating-point instructions as well as the |
| Dot Product extension. |
| |
| @item +crypto |
| The cryptographic instructions. This also enables the Advanced SIMD and |
| floating-point instructions as well as the Dot Product extension. |
| |
| @item +nocrypto |
| Disable the cryptographic extension. |
| |
| @item +nofp |
| Disable the floating-point, Advanced SIMD and cryptographic instructions. |
| |
| @item +i8mm |
| 8-bit Integer Matrix Multiply instructions. |
| This also enables Advanced SIMD and floating-point instructions. |
| |
| @item +bf16 |
| Brain half-precision floating-point instructions. |
| This also enables Advanced SIMD and floating-point instructions. |
| @end table |
| |
| @item armv7-r |
| @table @samp |
| @item +fp.sp |
| The single-precision VFPv3 floating-point instructions. The extension |
| @samp{+vfpv3xd} can be used as an alias for this extension. |
| |
| @item +fp |
| The VFPv3 floating-point instructions with 16 double-precision registers. |
| The extension +vfpv3-d16 can be used as an alias for this extension. |
| |
| @item +vfpv3xd-d16-fp16 |
| The single-precision VFPv3 floating-point instructions with 16 double-precision |
| registers and the half-precision floating-point conversion operations. |
| |
| @item +vfpv3-d16-fp16 |
| The VFPv3 floating-point instructions with 16 double-precision |
| registers and the half-precision floating-point conversion operations. |
| |
