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@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
@c 2000, 2001 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 COPYRIGHT
Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997,
1998, 1999, 2000, 2001 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 1.1 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{-pedantic}]
[@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{infile}@dots{}
Only the most useful options are listed here; see below for the
remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
@c man end
@c man begin SEEALSO
gpl(7), gfdl(7), fsf-funding(7),
cpp(1), gcov(1), g77(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
and the Info entries for @file{gcc}, @file{cpp}, @file{g77}, @file{as},
@file{ld}, @file{binutils} and @file{gdb}.
@c man end
@c man begin BUGS
For instructions on reporting bugs, see
@w{@uref{http://gcc.gnu.org/bugs.html}}. Use of the @command{gccbug}
script to report bugs is recommended.
@c man end
@c man begin AUTHOR
See the Info entry for @file{gcc}, or
@w{@uref{http://gcc.gnu.org/thanks.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.
Other options are passed on to one stage 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 C++ compilation options
@xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
options for 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{-dr} is very different from @w{@samp{-d
-r}}.
@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.
Many options have long names starting with @samp{-f} or with
@samp{-W}---for example, @option{-fforce-mem},
@option{-fstrength-reduce}, @option{-Wformat} and so on. Most of
these have both positive and negative forms; the negative form of
@option{-ffoo} would be @option{-fno-foo}. This manual documents
only one of these two forms, whichever one is not the default.
@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 Dialect Options:: Variations on Objective-C.
* Language Independent Options:: Controlling how diagnostics should be
formatted.
* Warning Options:: How picky should the compiler be?
* Debugging Options:: Symbol tables, measurements, and debugging dumps.
* Optimize Options:: How much optimization?
* 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.
* Spec Files:: How to pass switches to sub-processes.
* Target Options:: Running a cross-compiler, or an old version of GCC.
* Submodel Options:: Specifying minor hardware or convention variations,
such as 68010 vs 68020.
* Code Gen Options:: Specifying conventions for function calls, data layout
and register usage.
* Environment Variables:: Env vars that affect GCC.
* Running Protoize:: Automatically adding or removing function prototypes.
@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} -pipe -pass-exit-codes -x @var{language} @gol
-v --target-help --help}
@item C Language Options
@xref{C Dialect Options,,Options Controlling C Dialect}.
@gccoptlist{
-ansi -std=@var{standard} -aux-info @var{filename} @gol
-fno-asm -fno-builtin -fno-builtin-@var{function} @gol
-fhosted -ffreestanding @gol
-trigraphs -traditional -traditional-cpp @gol
-fallow-single-precision -fcond-mismatch @gol
-fsigned-bitfields -fsigned-char @gol
-funsigned-bitfields -funsigned-char @gol
-fwritable-strings -fshort-wchar}
@item C++ Language Options
@xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
@gccoptlist{
-fno-access-control -fcheck-new -fconserve-space @gol
-fno-const-strings -fdollars-in-identifiers @gol
-fno-elide-constructors @gol
-fno-enforce-eh-specs -fexternal-templates @gol
-falt-external-templates @gol
-ffor-scope -fno-for-scope -fno-gnu-keywords @gol
-fno-implicit-templates @gol
-fno-implicit-inline-templates @gol
-fno-implement-inlines -fms-extensions @gol
-fno-nonansi-builtins -fno-operator-names @gol
-fno-optional-diags -fpermissive @gol
-frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
-fuse-cxa-atexit -fvtable-gc -fno-weak -nostdinc++ @gol
-fno-default-inline -Wctor-dtor-privacy @gol
-Wnon-virtual-dtor -Wreorder @gol
-Weffc++ -Wno-deprecated @gol
-Wno-non-template-friend -Wold-style-cast @gol
-Woverloaded-virtual -Wno-pmf-conversions @gol
-Wsign-promo -Wsynth}
@item Objective-C Language Options
@xref{Objective-C Dialect Options,,Options Controlling Objective-C Dialect}.
@gccoptlist{
-fconstant-string-class=@var{class-name} @gol
-fgnu-runtime -fnext-runtime -gen-decls @gol
-Wno-protocol -Wselector}
@item Language Independent Options
@xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
@gccoptlist{
-fmessage-length=@var{n} @gol
-fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}}
@item Warning Options
@xref{Warning Options,,Options to Request or Suppress Warnings}.
@gccoptlist{
-fsyntax-only -pedantic -pedantic-errors @gol
-w -W -Wall -Waggregate-return @gol
-Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
-Wconversion -Wdisabled-optimization -Wdiv-by-zero -Werror @gol
-Wfloat-equal -Wformat -Wformat=2 @gol
-Wformat-nonliteral -Wformat-security @gol
-Wimplicit -Wimplicit-int @gol
-Wimplicit-function-declaration @gol
-Werror-implicit-function-declaration @gol
-Wimport -Winline @gol
-Wlarger-than-@var{len} -Wlong-long @gol
-Wmain -Wmissing-braces -Wmissing-declarations @gol
-Wmissing-format-attribute -Wmissing-noreturn @gol
-Wmultichar -Wno-format-extra-args -Wno-format-y2k @gol
-Wno-import -Wpacked -Wpadded @gol
-Wparentheses -Wpointer-arith -Wredundant-decls @gol
-Wreturn-type -Wsequence-point -Wshadow @gol
-Wsign-compare -Wswitch -Wsystem-headers @gol
-Wtrigraphs -Wundef -Wuninitialized @gol
-Wunknown-pragmas -Wunreachable-code @gol
-Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
-Wunused-value -Wunused-variable -Wwrite-strings}
@item C-only Warning Options
@gccoptlist{
-Wbad-function-cast -Wmissing-prototypes -Wnested-externs @gol
-Wstrict-prototypes -Wtraditional}
@item Debugging Options
@xref{Debugging Options,,Options for Debugging Your Program or GCC}.
@gccoptlist{
-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
-fdump-unnumbered
-fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
-fdump-tree-original@r{[}-@var{n}@r{]} -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
-fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
-fmem-report -fpretend-float @gol
-fprofile-arcs -ftest-coverage -ftime-report @gol
-g -g@var{level} -gcoff -gdwarf -gdwarf-1 -gdwarf-1+ -gdwarf-2 @gol
-ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
-p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
-print-multi-directory -print-multi-lib @gol
-print-prog-name=@var{program} -print-search-dirs -Q @gol
-save-temps -time}
@item Optimization Options
@xref{Optimize Options,,Options that Control Optimization}.
@gccoptlist{
-falign-functions=@var{n} -falign-jumps=@var{n} @gol
-falign-labels=@var{n} -falign-loops=@var{n} @gol
-fbranch-probabilities -fcaller-saves -fcprop-registers @gol
-fcse-follow-jumps -fcse-skip-blocks -fdata-sections @gol
-fdelayed-branch -fdelete-null-pointer-checks @gol
-fexpensive-optimizations -ffast-math -ffloat-store @gol
-fforce-addr -fforce-mem -ffunction-sections @gol
-fgcse -fgcse-lm -fgcse-sm @gol
-finline-functions -finline-limit=@var{n} -fkeep-inline-functions @gol
-fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
-fmove-all-movables -fno-default-inline -fno-defer-pop @gol
-fno-function-cse -fno-guess-branch-probability @gol
-fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
-funsafe-math-optimizations -fno-trapping-math @gol
-fomit-frame-pointer -foptimize-register-move @gol
-foptimize-sibling-calls -fprefetch-loop-arrays -freduce-all-givs @gol
-fregmove -frename-registers @gol
-frerun-cse-after-loop -frerun-loop-opt @gol
-fschedule-insns -fschedule-insns2 @gol
-fsingle-precision-constant -fssa -fssa-ccp -fssa-dce @gol
-fstrength-reduce -fstrict-aliasing -fthread-jumps -ftrapv @gol
-funroll-all-loops -funroll-loops @gol
--param @var{name}=@var{value}
-O -O0 -O1 -O2 -O3 -Os}
@item Preprocessor Options
@xref{Preprocessor Options,,Options Controlling the Preprocessor}.
@gccoptlist{
-$ -A@var{question}=@var{answer} -A-@var{question}@r{[}=@var{answer}@r{]} @gol
-C -dD -dI -dM -dN @gol
-D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
-idirafter @var{dir} @gol
-include @var{file} -imacros @var{file} @gol
-iprefix @var{file} -iwithprefix @var{dir} @gol
-iwithprefixbefore @var{dir} -isystem @var{dir} @gol
-M -MM -MF -MG -MP -MQ -MT -nostdinc -P -remap @gol
-trigraphs -undef -U@var{macro} -Wp,@var{option}}
@item Assembler Option
@xref{Assembler Options,,Passing Options to the Assembler}.
@gccoptlist{
-Wa,@var{option}}
@item Linker Options
@xref{Link Options,,Options for Linking}.
@gccoptlist{
@var{object-file-name} -l@var{library} @gol
-nostartfiles -nodefaultlibs -nostdlib @gol
-s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
-Wl,@var{option} -Xlinker @var{option} @gol
-u @var{symbol}}
@item Directory Options
@xref{Directory Options,,Options for Directory Search}.
@gccoptlist{
-B@var{prefix} -I@var{dir} -I- -L@var{dir} -specs=@var{file}}
@item Target Options
@c I wrote this xref this way to avoid overfull hbox. -- rms
@xref{Target Options}.
@gccoptlist{
-b @var{machine} -V @var{version}}
@item Machine Dependent Options
@xref{Submodel Options,,Hardware Models and Configurations}.
@emph{M680x0 Options}
@gccoptlist{
-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
-m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol
-mfpa -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
-malign-int -mstrict-align}
@emph{M68hc1x Options}
@gccoptlist{
-m6811 -m6812 -m68hc11 -m68hc12 @gol
-mauto-incdec -mshort -msoft-reg-count=@var{count}}
@emph{VAX Options}
@gccoptlist{
-mg -mgnu -munix}
@emph{SPARC Options}
@gccoptlist{
-mcpu=@var{cpu-type} @gol
-mtune=@var{cpu-type} @gol
-mcmodel=@var{code-model} @gol
-m32 -m64 @gol
-mapp-regs -mbroken-saverestore -mcypress @gol
-mepilogue -mfaster-structs -mflat @gol
-mfpu -mhard-float -mhard-quad-float @gol
-mimpure-text -mlive-g0 -mno-app-regs @gol
-mno-epilogue -mno-faster-structs -mno-flat -mno-fpu @gol
-mno-impure-text -mno-stack-bias -mno-unaligned-doubles @gol
-msoft-float -msoft-quad-float -msparclite -mstack-bias @gol
-msupersparc -munaligned-doubles -mv8}
@emph{Convex Options}
@gccoptlist{
-mc1 -mc2 -mc32 -mc34 -mc38 @gol
-margcount -mnoargcount @gol
-mlong32 -mlong64 @gol
-mvolatile-cache -mvolatile-nocache}
@emph{AMD29K Options}
@gccoptlist{
-m29000 -m29050 -mbw -mnbw -mdw -mndw @gol
-mlarge -mnormal -msmall @gol
-mkernel-registers -mno-reuse-arg-regs @gol
-mno-stack-check -mno-storem-bug @gol
-mreuse-arg-regs -msoft-float -mstack-check @gol
-mstorem-bug -muser-registers}
@emph{ARM Options}
@gccoptlist{
-mapcs-frame -mno-apcs-frame @gol
-mapcs-26 -mapcs-32 @gol
-mapcs-stack-check -mno-apcs-stack-check @gol
-mapcs-float -mno-apcs-float @gol
-mapcs-reentrant -mno-apcs-reentrant @gol
-msched-prolog -mno-sched-prolog @gol
-mlittle-endian -mbig-endian -mwords-little-endian @gol
-malignment-traps -mno-alignment-traps @gol
-msoft-float -mhard-float -mfpe @gol
-mthumb-interwork -mno-thumb-interwork @gol
-mcpu=@var{name} -march=@var{name} -mfpe=@var{name} @gol
-mstructure-size-boundary=@var{n} @gol
-mbsd -mxopen -mno-symrename @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 @gol
-mtpcs-frame -mtpcs-leaf-frame @gol
-mcaller-super-interworking -mcallee-super-interworking }
@emph{MN10200 Options}
@gccoptlist{
-mrelax}
@emph{MN10300 Options}
@gccoptlist{
-mmult-bug -mno-mult-bug @gol
-mam33 -mno-am33 @gol
-mno-crt0 -mrelax}
@emph{M32R/D Options}
@gccoptlist{
-m32rx -m32r -mcode-model=@var{model-type} -msdata=@var{sdata-type} @gol
-G @var{num}}
@emph{M88K Options}
@gccoptlist{
-m88000 -m88100 -m88110 -mbig-pic @gol
-mcheck-zero-division -mhandle-large-shift @gol
-midentify-revision -mno-check-zero-division @gol
-mno-ocs-debug-info -mno-ocs-frame-position @gol
-mno-optimize-arg-area -mno-serialize-volatile @gol
-mno-underscores -mocs-debug-info @gol
-mocs-frame-position -moptimize-arg-area @gol
-mserialize-volatile -mshort-data-@var{num} -msvr3 @gol
-msvr4 -mtrap-large-shift -muse-div-instruction @gol
-mversion-03.00 -mwarn-passed-structs}
@emph{RS/6000 and PowerPC Options}
@gccoptlist{
-mcpu=@var{cpu-type} @gol
-mtune=@var{cpu-type} @gol
-mpower -mno-power -mpower2 -mno-power2 @gol
-mpowerpc -mpowerpc64 -mno-powerpc @gol
-maltivec -mno-altivec @gol
-mpowerpc-gpopt -mno-powerpc-gpopt @gol
-mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
-mnew-mnemonics -mold-mnemonics @gol
-mfull-toc -mminimal-toc -mno-fop-in-toc -mno-sum-in-toc @gol
-m64 -m32 -mxl-call -mno-xl-call -mthreads -mpe @gol
-msoft-float -mhard-float -mmultiple -mno-multiple @gol
-mstring -mno-string -mupdate -mno-update @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
-mcall-aix -mcall-sysv -mcall-netbsd @gol
-maix-struct-return -msvr4-struct-return
-mabi=altivec @gol
-mprototype -mno-prototype @gol
-msim -mmvme -mads -myellowknife -memb -msdata @gol
-msdata=@var{opt} -mvxworks -G @var{num}}
@emph{RT Options}
@gccoptlist{
-mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs @gol
-mfull-fp-blocks -mhc-struct-return -min-line-mul @gol
-mminimum-fp-blocks -mnohc-struct-return}
@emph{MIPS Options}
@gccoptlist{
-mabicalls -march=@var{cpu-type} -mtune=@var{cpu=type} @gol
-mcpu=@var{cpu-type} -membedded-data -muninit-const-in-rodata @gol
-membedded-pic -mfp32 -mfp64 -mfused-madd -mno-fused-madd @gol
-mgas -mgp32 -mgp64 @gol
-mgpopt -mhalf-pic -mhard-float -mint64 -mips1 @gol
-mips2 -mips3 -mips4 -mlong64 -mlong32 -mlong-calls -mmemcpy @gol
-mmips-as -mmips-tfile -mno-abicalls @gol
-mno-embedded-data -mno-uninit-const-in-rodata @gol
-mno-embedded-pic -mno-gpopt -mno-long-calls @gol
-mno-memcpy -mno-mips-tfile -mno-rnames -mno-stats @gol
-mrnames -msoft-float @gol
-m4650 -msingle-float -mmad @gol
-mstats -EL -EB -G @var{num} -nocpp @gol
-mabi=32 -mabi=n32 -mabi=64 -mabi=eabi @gol
-mfix7000 -mno-crt0 -mflush-func=@var{func} -mno-flush-func}
@emph{i386 and x86-64 Options}
@gccoptlist{
-mcpu=@var{cpu-type} -march=@var{cpu-type} -mfpmath=@var{unit} @gol
-masm=@var{dialect} -mno-fancy-math-387 @gol
-mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
-mno-wide-multiply -mrtd -malign-double @gol
-mpreferred-stack-boundary=@var{num} @gol
-mmmx -msse -msse2 -msse-math -m3dnow @gol
-mthreads -mno-align-stringops -minline-all-stringops @gol
-mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
-m96bit-long-double -mregparm=@var{num} -momit-leaf-frame-pointer @gol
-mno-red-zone@gol
-m32 -m64}
@emph{HPPA Options}
@gccoptlist{
-march=@var{architecture-type} @gol
-mbig-switch -mdisable-fpregs -mdisable-indexing @gol
-mfast-indirect-calls -mgas -mjump-in-delay @gol
-mlong-load-store -mno-big-switch -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}
@emph{Intel 960 Options}
@gccoptlist{
-m@var{cpu-type} -masm-compat -mclean-linkage @gol
-mcode-align -mcomplex-addr -mleaf-procedures @gol
-mic-compat -mic2.0-compat -mic3.0-compat @gol
-mintel-asm -mno-clean-linkage -mno-code-align @gol
-mno-complex-addr -mno-leaf-procedures @gol
-mno-old-align -mno-strict-align -mno-tail-call @gol
-mnumerics -mold-align -msoft-float -mstrict-align @gol
-mtail-call}
@emph{DEC Alpha Options}
@gccoptlist{
-mfp-regs -mno-fp-regs -mno-soft-float -msoft-float @gol
-malpha-as -mgas @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} @gol
-mbwx -mno-bwx -mcix -mno-cix -mmax -mno-max @gol
-mmemory-latency=@var{time}}
@emph{DEC Alpha/VMS Options}
@gccoptlist{
-mvms-return-codes}
@emph{Clipper Options}
@gccoptlist{
-mc300 -mc400}
@emph{H8/300 Options}
@gccoptlist{
-mrelax -mh -ms -mint32 -malign-300}
@emph{SH Options}
@gccoptlist{
-m1 -m2 -m3 -m3e @gol
-m4-nofpu -m4-single-only -m4-single -m4 @gol
-mb -ml -mdalign -mrelax @gol
-mbigtable -mfmovd -mhitachi -mnomacsave @gol
-mieee -misize -mpadstruct -mspace @gol
-mprefergot -musermode}
@emph{System V Options}
@gccoptlist{
-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
@emph{ARC Options}
@gccoptlist{
-EB -EL @gol
-mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
-mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
@emph{TMS320C3x/C4x Options}
@gccoptlist{
-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
-mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
-mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
-mparallel-insns -mparallel-mpy -mpreserve-float}
@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
-mv850 -mbig-switch}
@emph{NS32K Options}
@gccoptlist{
-m32032 -m32332 -m32532 -m32081 -m32381 @gol
-mmult-add -mnomult-add -msoft-float -mrtd -mnortd @gol
-mregparam -mnoregparam -msb -mnosb @gol
-mbitfield -mnobitfield -mhimem -mnohimem}
@emph{AVR Options}
@gccoptlist{
-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
-mcall-prologues -mno-tablejump -mtiny-stack}
@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{MMIX Options}
@gccoptlist{
-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
-mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
-melf}
@emph{IA-64 Options}
@gccoptlist{
-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
-mvolatile-asm-stop -mb-step -mregister-names -mno-sdata @gol
-mconstant-gp -mauto-pic -minline-divide-min-latency @gol
-minline-divide-max-throughput -mno-dwarf2-asm @gol
-mfixed-range=@var{register-range}}
@emph{S/390 and zSeries Options}
@gccoptlist{
-mhard-float -msoft-float -mbackchain -mno-backchain @gol
-msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
-m64 -m31 -mdebug -mno-debug}
@emph{CRIS Options}
@gccoptlist{
-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
-mmax-stack-frame=@var{n} -melinux-stacksize=@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 -mno-gotplt @gol
-melf -maout -melinux -mlinux -sim -sim2}
@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 -funwind-tables -fasynchronous-unwind-tables @gol
-finhibit-size-directive -finstrument-functions @gol
-fno-common -fno-ident -fno-gnu-linker @gol
-fpcc-struct-return -fpic -fPIC @gol
-freg-struct-return -fshared-data -fshort-enums @gol
-fshort-double -fvolatile @gol
-fvolatile-global -fvolatile-static @gol
-fverbose-asm -fpack-struct -fstack-check @gol
-fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
-fargument-alias -fargument-noalias @gol
-fargument-noalias-global -fleading-underscore}
@end table
@menu
* Overall Options:: Controlling the kind of output:
an executable, object files, assembler files,
or preprocessed source.
* C Dialect Options:: Controlling the variant of C language compiled.
* C++ Dialect Options:: Variations on C++.
* Objective-C Dialect Options:: Variations on Objective-C.
* Language Independent Options:: Controlling how diagnostics should be
formatted.
* Warning Options:: How picky should the compiler be?
* Debugging Options:: Symbol tables, measurements, and debugging dumps.
* Optimize Options:: How much optimization?
* 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.
* Spec Files:: How to pass switches to sub-processes.
* Target Options:: Running a cross-compiler, or an old version of GCC.
@end menu
@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. The first three
stages apply to an individual source file, and end by producing an
object file; 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 which must be preprocessed.
@item @var{file}.i
C source code which should not be preprocessed.
@item @var{file}.ii
C++ source code which should not be preprocessed.
@item @var{file}.m
Objective-C source code. Note that you must link with the library
@file{libobjc.a} to make an Objective-C program work.
@item @var{file}.mi
Objective-C source code which should not be preprocessed.
@item @var{file}.h
C header file (not to be compiled or linked).
@item @var{file}.cc
@itemx @var{file}.cp
@itemx @var{file}.cxx
@itemx @var{file}.cpp
@itemx @var{file}.c++
@itemx @var{file}.C
C++ source code which 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}.f
@itemx @var{file}.for
@itemx @var{file}.FOR
Fortran source code which should not be preprocessed.
@item @var{file}.F
@itemx @var{file}.fpp
@itemx @var{file}.FPP
Fortran source code which must be preprocessed (with the traditional
preprocessor).
@item @var{file}.r
Fortran source code which must be preprocessed with a RATFOR
preprocessor (not included with GCC)@.
@xref{Overall Options,,Options Controlling the Kind of Output, g77,
Using and Porting GNU Fortran}, for more details of the handling of
Fortran input files.
@c FIXME: Descriptions of Java file types.
@c @var{file}.java
@c @var{file}.class
@c @var{file}.zip
@c @var{file}.jar
@item @var{file}.ads
Ada source code file which 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}.
@itemx @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 Pascal:
@c @var{file}.p
@c @var{file}.pas
@item @var{file}.ch
@itemx @var{file}.chi
CHILL source code (preprocessed with the traditional preprocessor).
@item @var{file}.s
Assembler code.
@item @var{file}.S
Assembler code which 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:
@example
c c-header cpp-output
c++ c++-cpp-output
objective-c objc-cpp-output
assembler assembler-with-cpp
ada
chill
f77 f77-cpp-input ratfor
java
@end example
@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).
@item -pass-exit-codes
@opindex pass-exit-codes
Normally the @command{gcc} program will exit 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 will instead return with
numerically highest error produced by any phase that returned an error
indication.
@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 which don't require preprocessing are ignored.
@cindex output file option
@item -o @var{file}
@opindex o
Place output in file @var{file}. This applies regardless to whatever
sort of output is being produced, whether it be an executable file,
an object file, an assembler file or preprocessed C code.
Since only one output file can be specified, it does not make sense to
use @option{-o} when compiling more than one input file, unless you are
producing an executable file as output.
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}, and
all preprocessed C source on standard output.
@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 -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 --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} will also be passed on to the various processes
invoked by @command{gcc}, so that they can display the command line options
they accept. If the @option{-W} option is also specified then command
line options which have no documentation associated with them will also
be displayed.
@item --target-help
@opindex target-help
Print (on the standard output) a description of target specific command
line options for each tool.
@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{.c++}, @samp{.cp}, or @samp{.cxx};
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, C++ programs often require class libraries as well as a
compiler that understands the C++ language---and under some
circumstances, you might want to compile programs from standard input,
or otherwise without a suffix that flags them as C++ programs.
@command{g++} is a program that calls GCC with the default language
set to C++, and automatically specifies linking against the C++
library. 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++ and Objective-C) that the compiler accepts:
@table @gcctabopt
@cindex ANSI support
@cindex ISO support
@item -ansi
@opindex ansi
In C mode, support all ISO C89 programs. In C++ mode,
remove GNU extensions that conflict with ISO C++.
This turns off certain features of GCC that are incompatible with ISO
C89 (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{-pedantic} 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 which would normally be built in but do not have semantics
defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
functions with @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. This option is currently only
supported when compiling C@. A value for this option must be provided;
possible values are
@table @samp
@item c89
@itemx iso9899:1990
ISO C89 (same as @option{-ansi}).
@item iso9899:199409
ISO C89 as modified in amendment 1.
@item c99
@itemx c9x
@itemx iso9899:1999
@itemx iso9899:199x
ISO C99. Note that this standard is not yet fully supported; see
@w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
names @samp{c9x} and @samp{iso9899:199x} are deprecated.
@item gnu89
Default, ISO C89 plus GNU extensions (including some C99 features).
@item gnu99
@item gnu9x
ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
this will become the default. The name @samp{gnu9x} is deprecated.
@end table
Even when this option is not specified, you can still use some of the
features of newer standards in so far as they do not conflict with
previous C standards. For example, you may use @code{__restrict__} even
when @option{-std=c99} is not specified.
The @option{-std} options specifying some version of ISO C have the same
effects as @option{-ansi}, except that features that were not in ISO C89
but are in the specified version (for example, @samp{//} comments and
the @code{inline} keyword in ISO C99) are not disabled.
@xref{Standards,,Language Standards Supported by GCC}, for details of
these standard versions.
@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 -fno-asm
@opindex fno-asm
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. @option{-ansi} implies @option{-fno-asm}.
In C++, this switch only affects the @code{typeof} keyword, since
@code{asm} and @code{inline} are standard keywords. You may want to
use the @option{-fno-gnu-keywords} flag instead, which has the same
effect. 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} @r{(C and Objective-C only)}
@opindex fno-builtin
@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 that 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 C++, @option{-fno-builtin} is always in effect. The @option{-fbuiltin}
option has no effect. Therefore, in C++, the only way to get the
optimization benefits of built-in functions is to call the function
using the @samp{__builtin_} prefix. The GNU C++ Standard Library uses
built-in functions to implement many functions (like
@code{std::strchr}), so that you automatically get efficient code.
With the @option{-fno-builtin-@var{function}} option, not available
when compiling C++, only the built-in function @var{function} is
disabled. @var{function} must not begin with @samp{__builtin_}. If a
function is named this 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 -fhosted
@opindex fhosted
@cindex hosted environment
Assert that compilation takes place in 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 -ffreestanding
@opindex ffreestanding
@cindex hosted environment
Assert that compilation takes place in 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 -trigraphs
@opindex trigraphs
Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
options for strict ISO C conformance) implies @option{-trigraphs}.
@cindex traditional C language
@cindex C language, traditional
@item -traditional
@opindex traditional
Attempt to support some aspects of traditional C compilers.
Specifically:
@itemize @bullet
@item
All @code{extern} declarations take effect globally even if they
are written inside of a function definition. This includes implicit
declarations of functions.
@item
The newer keywords @code{typeof}, @code{inline}, @code{signed}, @code{const}
and @code{volatile} are not recognized. (You can still use the
alternative keywords such as @code{__typeof__}, @code{__inline__}, and
so on.)
@item
Comparisons between pointers and integers are always allowed.
@item
Integer types @code{unsigned short} and @code{unsigned char} promote
to @code{unsigned int}.
@item
Out-of-range floating point literals are not an error.
@item
Certain constructs which ISO regards as a single invalid preprocessing
number, such as @samp{0xe-0xd}, are treated as expressions instead.
@item
String ``constants'' are not necessarily constant; they are stored in
writable space, and identical looking constants are allocated
separately. (This is the same as the effect of
@option{-fwritable-strings}.)
@cindex @code{longjmp} and automatic variables
@item
All automatic variables not declared @code{register} are preserved by
@code{longjmp}. Ordinarily, GNU C follows ISO C: automatic variables
not declared @code{volatile} may be clobbered.
@item
@cindex @samp{\x}
@cindex @samp{\a}
@cindex escape sequences, traditional
The character escape sequences @samp{\x} and @samp{\a} evaluate as the
literal characters @samp{x} and @samp{a} respectively. Without
@w{@option{-traditional}}, @samp{\x} is a prefix for the hexadecimal
representation of a character, and @samp{\a} produces a bell.
@end itemize
This option is deprecated and may be removed.
You may wish to use @option{-fno-builtin} as well as @option{-traditional}
if your program uses names that are normally GNU C built-in functions for
other purposes of its own.
You cannot use @option{-traditional} if you include any header files that
rely on ISO C features. Some vendors are starting to ship systems with
ISO C header files and you cannot use @option{-traditional} on such
systems to compile files that include any system headers.
The @option{-traditional} option also enables @option{-traditional-cpp}.
@item -traditional-cpp
@opindex traditional-cpp
Attempt to support some aspects of traditional C preprocessors.
See the GNU CPP manual for details.
@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 -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 -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 -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.
However, when @option{-traditional} is used, bit-fields are all unsigned
no matter what.
@item -fwritable-strings
@opindex fwritable-strings
Store string constants in the writable data segment and don't uniquize
them. This is for compatibility with old programs which assume they can
write into string constants. The option @option{-traditional} also has
this effect.
Writing into string constants is a very bad idea; ``constants'' should
be constant.
@item -fallow-single-precision
@opindex fallow-single-precision
Do not promote single precision math operations to double precision,
even when compiling with @option{-traditional}.
Traditional K&R C promotes all floating point operations to double
precision, regardless of the sizes of the operands. On the
architecture for which you are compiling, single precision may be faster
than double precision. If you must use @option{-traditional}, but want
to use single precision operations when the operands are single
precision, use this option. This option has no effect when compiling
with ISO or GNU C conventions (the default).
@item -fshort-wchar
@opindex fshort-wchar
Override the underlying type for @samp{wchar_t} to be @samp{short
unsigned int} instead of the default for the target. This option is
useful for building programs to run under WINE@.
@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; but 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 @code{firstClass.C} like this:
@example
g++ -g -frepo -O -c firstClass.C
@end example
@noindent
In this example, only @option{-frepo} is an option meant
only for C++ programs; you can use the other options with any
language supported by GCC@.
Here is a list of options that are @emph{only} for compiling C++ programs:
@table @gcctabopt
@item -fno-access-control
@opindex fno-access-control
Turn off all access checking. This switch is mainly useful for working
around bugs in the access control code.
@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. The current Working
Paper requires that @code{operator new} never return a null pointer, so
this check is normally unnecessary.
An alternative to using this option is to specify that your
@code{operator new} does not throw any exceptions; if you declare it
@samp{throw()}, G++ will check the return value. See also @samp{new
(nothrow)}.
@item -fconserve-space
@opindex fconserve-space
Put uninitialized or runtime-initialized global variables into the
common segment, as C does. This saves space in the executable at the
cost of not diagnosing duplicate definitions. If you compile with this
flag and your program mysteriously crashes after @code{main()} has
completed, you may have an object that is being destroyed twice because
two definitions were merged.
This option is no longer useful on most targets, now that support has
been added for putting variables into BSS without making them common.
@item -fno-const-strings
@opindex fno-const-strings
Give string constants type @code{char *} instead of type @code{const
char *}. By default, G++ uses type @code{const char *} as required by
the standard. Even if you use @option{-fno-const-strings}, you cannot
actually modify the value of a string constant, unless you also use
@option{-fwritable-strings}.
This option might be removed in a future release of G++. For maximum
portability, you should structure your code so that it works with
string constants that have type @code{const char *}.
@item -fdollars-in-identifiers
@opindex fdollars-in-identifiers
Accept @samp{$} in identifiers. You can also explicitly prohibit use of
@samp{$} with the option @option{-fno-dollars-in-identifiers}. (GNU C allows
@samp{$} by default on most target systems, but there are a few exceptions.)
Traditional C allowed the character @samp{$} to form part of
identifiers. However, ISO C and C++ forbid @samp{$} in identifiers.
@item -fno-elide-constructors
@opindex fno-elide-constructors
The C++ standard allows an implementation to omit creating a temporary
which 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.
@item -fno-enforce-eh-specs
@opindex fno-enforce-eh-specs
Don't check for violation of exception specifications at runtime. This
option violates the C++ standard, but may be useful for reducing code
size in production builds, much like defining @samp{NDEBUG}. The compiler
will still optimize based on the exception specifications.
@item -fexternal-templates
@opindex fexternal-templates
Cause @samp{#pragma interface} and @samp{implementation} to apply to
template instantiation; template instances are emitted or not according
to the location of the template definition. @xref{Template
Instantiation}, for more information.
This option is deprecated.
@item -falt-external-templates
@opindex falt-external-templates
Similar to @option{-fexternal-templates}, but template instances are
emitted or not according to the place where they are first instantiated.
@xref{Template Instantiation}, for more information.
This option is deprecated.
@item -ffor-scope
@itemx -fno-for-scope
@opindex ffor-scope
@opindex fno-for-scope
If @option{-ffor-scope} is specified, the scope of variables declared in
a @i{for-init-statement} is limited to the @samp{for} loop itself,
as specified by the C++ standard.
If @option{-fno-for-scope} is specified, the scope of variables declared in
a @i{for-init-statement} extends to the end of the enclosing scope,
as was the case in old versions of G++, and other (traditional)
implementations of C++.
The default if neither flag is given to follow the standard,
but to allow and give a warning for old-style code that would
otherwise be invalid, or have different behavior.
@item -fno-gnu-keywords
@opindex fno-gnu-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.
@option{-ansi} implies @option{-fno-gnu-keywords}.
@item -fno-implicit-templates
@opindex fno-implicit-templates
Never emit code for non-inline templates which are instantiated
implicitly (i.e.@: by use); only emit code for explicit instantiations.
@xref{Template Instantiation}, for more information.
@item -fno-implicit-inline-templates
@opindex fno-implicit-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 will need the same set of explicit instantiations.
@item -fno-implement-inlines
@opindex fno-implement-inlines
To save space, do not emit out-of-line copies of inline functions
controlled by @samp{#pragma implementation}. This will cause linker
errors if these functions are not inlined everywhere they are called.
@item -fms-extensions
@opindex fms-extensions
Disable pedantic warnings about constructs used in MFC, such as implicit
int and getting a pointer to member function via non-standard syntax.
@item -fno-nonansi-builtins
@opindex fno-nonansi-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 -fno-operator-names
@opindex fno-operator-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
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 messages about nonconformant code from errors to warnings. By
default, G++ effectively sets @option{-pedantic-errors} without
@option{-pedantic}; this option reverses that. This behavior and this
option are superseded by @option{-pedantic}, which works as it does for GNU C@.
@item -frepo
@opindex frepo
Enable automatic template instantiation at link time. This option also
implies @option{-fno-implicit-templates}. @xref{Template
Instantiation}, for more information.
@item -fno-rtti
@opindex fno-rtti
Disable generation of information about every class with virtual
functions for use by the C++ runtime type identification features
(@samp{dynamic_cast} and @samp{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 it will generate it as
needed.
@item -fstats
@opindex fstats
Emit statistics about front-end processing at the end of the compilation.
This information is generally only useful to the G++ development team.
@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.
@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 will only work if your C library supports
@code{__cxa_atexit}.
@item -fvtable-gc
@opindex fvtable-gc
Emit special relocations for vtables and virtual function references
so that the linker can identify unused virtual functions and zero out
vtable slots that refer to them. This is most useful with
@option{-ffunction-sections} and @option{-Wl,--gc-sections}, in order to
also discard the functions themselves.
This optimization requires GNU as and GNU ld. Not all systems support
this option. @option{-Wl,--gc-sections} is ignored without @option{-static}.
@item -fno-weak
@opindex fno-weak
Do not use weak symbol support, even if it is provided by the linker.
By default, G++ will use weak symbols if they are available. This
option exists only for testing, and should not be used by end-users;
it will result in inferior code and has no benefits. This option may
be removed in a future release of G++.
@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.)
@end table
In addition, these optimization, warning, and code generation options
have meanings only for C++ programs:
@table @gcctabopt
@item -fno-default-inline
@opindex fno-default-inline
Do not assume @samp{inline} for functions defined inside a class scope.
@xref{Optimize Options,,Options That Control Optimization}. Note that these
functions will have linkage like inline functions; they just won't be
inlined by default.
@item -Wctor-dtor-privacy @r{(C++ only)}
@opindex Wctor-dtor-privacy
Warn when a class seems unusable, because all the constructors or
destructors in a class are private and the class has no friends or
public static member functions.
@item -Wnon-virtual-dtor @r{(C++ only)}
@opindex Wnon-virtual-dtor
Warn when a class declares a non-virtual destructor that should probably
be virtual, because it looks like the class will be used polymorphically.
@item -Wreorder @r{(C++ only)}
@opindex Wreorder
@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
Here the compiler will warn that the member initializers for @samp{i}
and @samp{j} will be rearranged to match the declaration order of the
members.
@end table
The following @option{-W@dots{}} options are not affected by @option{-Wall}.
@table @gcctabopt
@item -Weffc++ @r{(C++ only)}
@opindex Weffc++
Warn about violations of various style guidelines from Scott Meyers'
@cite{Effective C++} books. If you use this option, you should be aware
that the standard library headers do not obey all of these guidelines;
you can use @samp{grep -v} to filter out those warnings.
@item -Wno-deprecated @r{(C++ only)}
@opindex Wno-deprecated
Do not warn about usage of deprecated features. @xref{Deprecated Features}.
@item -Wno-non-template-friend @r{(C++ only)}
@opindex Wno-non-template-friend
Disable warnings when non-templatized friend functions are declared
within a template. With the advent of explicit template specification
support in G++, if the name of the friend is an unqualified-id (i.e.,
@samp{friend foo(int)}), the C++ language specification demands that the
friend declare or define an ordinary, nontemplate function. (Section
14.5.3). Before G++ implemented explicit specification, unqualified-ids
could be interpreted as a particular specialization of a templatized
function. Because this non-conforming behavior is no longer the default
behavior for G++, @option{-Wnon-template-friend} allows the compiler to
check existing code for potential trouble spots, and is on by default.
This new compiler behavior can be turned off with
@option{-Wno-non-template-friend} which keeps the conformant compiler code
but disables the helpful warning.
@item -Wold-style-cast @r{(C++ only)}
@opindex Wold-style-cast
Warn if an old-style (C-style) cast is used within a C++ program. The
new-style casts (@samp{static_cast}, @samp{reinterpret_cast}, and
@samp{const_cast}) are less vulnerable to unintended effects, and much
easier to grep for.
@item -Woverloaded-virtual @r{(C++ only)}
@opindex Woverloaded-virtual
@cindex overloaded virtual fn, warning
@cindex warning for overloaded virtual fn
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 this:
@smallexample
B* b;
b->f();
@end smallexample
will fail to compile.
@item -Wno-pmf-conversions @r{(C++ only)}
@opindex Wno-pmf-conversions
Disable the diagnostic for converting a bound pointer to member function
to a plain pointer.
@item -Wsign-promo @r{(C++ only)}
@opindex Wsign-promo
Warn when overload resolution chooses a promotion from unsigned or
enumeral type to a signed type over a conversion to an unsigned type of
the same size. Previous versions of G++ would try to preserve
unsignedness, but the standard mandates the current behavior.
@item -Wsynth @r{(C++ only)}
@opindex Wsynth
@cindex warning for synthesized methods
@cindex synthesized methods, warning
Warn when G++'s synthesis behavior does not match that of cfront. For
instance:
@smallexample
struct A @{
operator int ();
A& operator = (int);
@};
main ()
@{
A a,b;
a = b;
@}
@end smallexample
In this example, G++ will synthesize a default @samp{A& operator =
(const A&);}, while cfront will use the user-defined @samp{operator =}.
@end table
@node Objective-C Dialect Options
@section Options Controlling Objective-C Dialect
@cindex compiler options, Objective-C
@cindex Objective-C options, command line
@cindex options, Objective-C
This section describes the command-line options that are only meaningful
for Objective-C programs; but 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 @code{some_class.m} like this:
@example
gcc -g -fgnu-runtime -O -c some_class.m
@end example
@noindent
In this example, only @option{-fgnu-runtime} is an option meant only for
Objective-C programs; you can use the other options with any language
supported by GCC@.
Here is a list of options that are @emph{only} for compiling 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}.
@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@.
@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 -Wno-protocol
@opindex Wno-protocol
Do not warn if methods required by a protocol are not implemented
in the class adopting it.
@item -Wselector
@opindex Wselector
Warn if a selector has multiple methods of different types defined.
@c not documented because only avail via -Wp
@c @item -print-objc-runtime-info
@end table
@node Language Independent 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{}). The options described
below can be used to control the diagnostic messages formatting
algorithm, e.g.@: how many characters per line, how often source location
information should be reported. Right now, only the C++ front end can
honor these options. However it is expected, in the near future, that
the remaining front ends would be able to digest them correctly.
@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. The default is 72 characters for @command{g++} and 0 for the rest of
the front ends supported by GCC@. If @var{n} is zero, then no
line-wrapping will be done; each error message will appear on a single
line.
@opindex fdiagnostics-show-location
@item -fdiagnostics-show-location=once
Only meaningful in line-wrapping mode. Instructs the diagnostic messages
reporter to emit @emph{once} source location information; 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.
@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 which
are not inherently erroneous but which are risky or suggest there
may have been an error.
You can request many specific warnings with options beginning @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.
These options control the amount and kinds of warnings 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 -pedantic
@opindex 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 will 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{-pedantic} does not cause warning messages for use of the
alternate keywords whose names begin and end with @samp{__}. 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{-pedantic} 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{-pedantic}. 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{gnu89} 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{-pedantic} are given
where they are required by the base standard. (It would 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
Like @option{-pedantic}, except that errors are produced rather than
warnings.
@item -w
@opindex w
Inhibit all warning messages.
@item -Wno-import
@opindex Wno-import
Inhibit warning messages about the use of @samp{#import}.
@item -Wchar-subscripts
@opindex Wchar-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.
@item -Wcomment
@opindex Wcomment
Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
@item -Wformat
@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.
The formats are checked against the format features supported by GNU
libc version 2.2. These include all ISO C89 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{-pedantic} is used
with @option{-Wformat}, warnings will be 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}.
@option{-Wformat} is included in @option{-Wall}. For more control over some
aspects of format checking, the options @option{-Wno-format-y2k},
@option{-Wno-format-extra-args}, @option{-Wformat-nonliteral},
@option{-Wformat-security} and @option{-Wformat=2} are available, but are
not included in @option{-Wall}.
@item -Wno-format-y2k
@opindex Wno-format-y2k
If @option{-Wformat} is specified, do not warn about @code{strftime}
formats which may yield only a two-digit year.
@item -Wno-format-extra-args
@opindex Wno-format-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 will suppress the
warning if the unused arguments are all pointers, since the Single
Unix Specification says that such unused arguments are allowed.
@item -Wformat-nonliteral
@opindex Wformat-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
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=2
@opindex Wformat=2
Enable @option{-Wformat} plus format checks not included in
@option{-Wformat}. Currently equivalent to @samp{-Wformat
-Wformat-nonliteral -Wformat-security}.
@item -Wimplicit-int
@opindex Wimplicit-int
Warn when a declaration does not specify a type.
@item -Wimplicit-function-declaration
@itemx -Werror-implicit-function-declaration
@opindex Wimplicit-function-declaration
@opindex Werror-implicit-function-declaration
Give a warning (or error) whenever a function is used before being
declared.
@item -Wimplicit
@opindex Wimplicit
Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
@item -Wmain
@opindex Wmain
Warn if the type of @samp{main} is suspicious. @samp{main} should be a
function with external linkage, returning int, taking either zero
arguments, two, or three arguments of appropriate types.
@item -Wmissing-braces
@opindex Wmissing-braces
Warn if an aggregate or union initializer is not fully bracketed. In
the following example, the initializer for @samp{a} is not fully
bracketed, but that for @samp{b} is fully bracketed.
@smallexample
int a[2][2] = @{ 0, 1, 2, 3 @};
int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
@end smallexample
@item -Wparentheses
@opindex Wparentheses
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 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, 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 will issue 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} could belong to
the enclosing @code{if}. The resulting code would look like this:
@smallexample
@group
@{
if (a)
@{
if (b)
foo ();
else
bar ();
@}
@}
@end group
@end smallexample
@item -Wsequence-point
@opindex Wsequence-point
Warn about code that may have undefined semantics because of violations
of sequence point rules in the C standard.
The C standard defines the order in which expressions in a 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 standard specifies 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 present implementation of this option only works for C programs. A
future implementation may also work for C++ programs.
The C 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 our readings page, at
@w{@uref{http://gcc.gnu.org/readings.html}}.
@item -Wreturn-type
@opindex Wreturn-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}.
For C++, a function without return type always produces a diagnostic
message, even when @option{-Wno-return-type} is specified. The only
exceptions are @samp{main} and functions defined in system headers.
@item -Wswitch
@opindex Wswitch
Warn whenever a @code{switch} statement has an index of enumeral 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.
@item -Wtrigraphs
@opindex Wtrigraphs
Warn if any trigraphs are encountered that might change the meaning of
the program (trigraphs within comments are not warned about).
@item -Wunused-function
@opindex Wunused-function
Warn whenever a static function is declared but not defined or a
non\-inline static function is unused.
@item -Wunused-label
@opindex Wunused-label
Warn whenever a label is declared but not used.
To suppress this warning use the @samp{unused} attribute
(@pxref{Variable Attributes}).
@item -Wunused-parameter
@opindex Wunused-parameter
Warn whenever a function parameter is unused aside from its declaration.
To suppress this warning use the @samp{unused} attribute
(@pxref{Variable Attributes}).
@item -Wunused-variable
@opindex Wunused-variable
Warn whenever a local variable or non-constant static variable is unused
aside from its declaration
To suppress this warning use the @samp{unused} attribute
(@pxref{Variable Attributes}).
@item -Wunused-value
@opindex Wunused-value
Warn whenever a statement computes a result that is explicitly not used.
To suppress this warning cast the expression to @samp{void}.
@item -Wunused
@opindex Wunused
All all the above @option{-Wunused} options combined.
In order to get a warning about an unused function parameter, you must
either specify @samp{-W -Wunused} or separately specify
@option{-Wunused-parameter}.
@item -Wuninitialized
@opindex Wuninitialized
Warn if an automatic variable is used without first being initialized or
if a variable may be clobbered by a @code{setjmp} call.
These warnings are possible only in optimizing compilation,
because they require data flow information that is computed only
when optimizing. If you don't specify @option{-O}, you simply won't
get these warnings.
These warnings occur only for variables that are candidates for
register allocation. Therefore, they do not occur for a variable that
is declared @code{volatile}, or whose address is taken, or whose size
is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
structures, unions or arrays, even when they are in registers.
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.
These warnings are made optional because GCC is not smart
enough to see all the reasons why the code might be correct
despite 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. Here is
another common case:
@smallexample
@{
int save_y;
if (change_y) save_y = y, y = new_y;
@dots{}
if (change_y) y = save_y;
@}
@end smallexample
@noindent
This has no bug because @code{save_y} is used only if it is set.
@cindex @code{longjmp} warnings
This option also warns when a non-volatile automatic variable might be
changed by a call to @code{longjmp}. These warnings as well are possible
only in optimizing compilation.
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 which 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}.
@item -Wreorder @r{(C++ only)}
@opindex Wreorder
@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:
@item -Wunknown-pragmas
@opindex Wunknown-pragmas
@cindex warning for unknown pragmas
@cindex unknown pragmas, warning
@cindex pragmas, warning of unknown
Warn when a #pragma directive is encountered which is not understood by
GCC@. If this command line option is used, warnings will even be issued
for unknown pragmas in system header files. This is not the case if
the warnings were only enabled by the @option{-Wall} command line option.
@item -Wall
@opindex Wall
All of the above @samp{-W} options combined. 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.
@item -Wdiv-by-zero
@opindex Wno-div-by-zero
@opindex Wdiv-by-zero
Warn about compile-time integer division by zero. This is default. To
inhibit the warning messages, use @option{-Wno-div-by-zero}. Floating
point division by zero is not warned about, as it can be a legitimate
way of obtaining infinities and NaNs.
@item -Wmultichar
@opindex Wno-multichar
@opindex Wmultichar
Warn if a multicharacter constant (@samp{'FOOF'}) is used. This is
default. To inhibit the warning messages, use @option{-Wno-multichar}.
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 -Wsystem-headers
@opindex Wsystem-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 will @emph{not} warn about unknown pragmas in system
headers---for that, @option{-Wunknown-pragmas} must also be used.
@end table
The following @option{-W@dots{}} options 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.
@table @gcctabopt
@item -W
@opindex W
Print extra warning messages for these events:
@itemize @bullet
@item
A function can return either with or without a value. (Falling
off the end of the function body is considered returning without
a value.) For example, this function would evoke such a
warning:
@smallexample
@group
foo (a)
@{
if (a > 0)
return a;
@}
@end group
@end smallexample
@item
An expression-statement or the left-hand side of a comma expression
contains no side effects.
To suppress the warning, cast the unused expression to void.
For example, an expression such as @samp{x[i,j]} will cause a warning,
but @samp{x[(void)i,j]} will not.
@item
An unsigned value is compared against zero with @samp{<} or @samp{<=}.
@item
A comparison like @samp{x<=y<=z} appears; this is equivalent to
@samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from
that of ordinary mathematical notation.
@item
Storage-class specifiers like @code{static} are not the first things in
a declaration. According to the C Standard, this usage is obsolescent.
@item
The return type of a function has a type qualifier such as @code{const}.
Such a type qualifier has no effect, since the value returned by a
function is not an lvalue. (But don't warn about the GNU extension of
@code{volatile void} return types. That extension will be warned about
if @option{-pedantic} is specified.)
@item
If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
arguments.
@item
A comparison between signed and unsigned values could produce an
incorrect result when the signed value is converted to unsigned.
(But don't warn if @option{-Wno-sign-compare} is also specified.)
@item
An aggregate has a partly bracketed initializer.
For example, the following code would evoke such a warning,
because braces are missing around the initializer for @code{x.h}:
@smallexample
struct s @{ int f, g; @};
struct t @{ struct s h; int i; @};
struct t x = @{ 1, 2, 3 @};
@end smallexample
@item
An aggregate has an initializer which does not initialize all members.
For example, the following code would cause such a warning, because
@code{x.h} would be implicitly initialized to zero:
@smallexample
struct s @{ int f, g, h; @};
struct s x = @{ 3, 4 @};
@end smallexample
@end itemize
@item -Wfloat-equal
@opindex Wfloat-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 analysing 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
would 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 only)}
@opindex Wtraditional
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 which 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 does not in ISO C@.
@item
In traditional C, some preprocessor directives did not exist.
Traditional preprocessors would only consider 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 would ignore because the @samp{#} does not appear as the
first character on the line. It also suggests you hide directives like
@samp{#pragma} not understood by traditional C by indenting them. Some
traditional implementations would not recognize @samp{#elif}, so it
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 would cause serious problems. This is a subset of the possible
conversion warnings, for the full set use @option{-Wconversion}.
@end itemize
@item -Wundef
@opindex Wundef
Warn if an undefined identifier is evaluated in an @samp{#if} directive.
@item -Wshadow
@opindex Wshadow
Warn whenever a local variable shadows another local variable, parameter or
global variable or whenever a built-in function is shadowed.
@item -Wlarger-than-@var{len}
@opindex Wlarger-than
Warn whenever an object of larger than @var{len} bytes is defined.
@item -Wpointer-arith
@opindex Wpointer-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.
@item -Wbad-function-cast @r{(C only)}
@opindex Wbad-function-cast
Warn whenever a function call is cast to a non-matching type.
For example, warn if @code{int malloc()} is cast to @code{anything *}.
@item -Wcast-qual
@opindex Wcast-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 *}.
@item -Wcast-align
@opindex Wcast-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 -Wwrite-strings
@opindex Wwrite-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 will get a warning; when compiling C++, warn about the
deprecated conversion from string constants to @code{char *}.
These warnings will 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 will just be a nuisance;
this is why we did not make @option{-Wall} request these warnings.
@item -Wconversion
@opindex Wconversion
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.
Also, warn if a negative integer constant expression is implicitly
converted to an unsigned type. For example, warn about the assignment
@code{x = -1} if @code{x} is unsigned. But do not warn about explicit
casts like @code{(unsigned) -1}.
@item -Wsign-compare
@opindex Wsign-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.
This warning is also enabled by @option{-W}; to get the other warnings
of @option{-W} without this warning, use @samp{-W -Wno-sign-compare}.
@item -Waggregate-return
@opindex Waggregate-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 -Wstrict-prototypes @r{(C only)}
@opindex Wstrict-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 which specifies the argument
types.)
@item -Wmissing-prototypes @r{(C only)}
@opindex Wmissing-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. The aim is to detect global functions that fail
to be declared in header files.
@item -Wmissing-declarations
@opindex Wmissing-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.
@item -Wmissing-noreturn
@opindex Wmissing-noreturn
Warn about functions which might be candidates for attribute @code{noreturn}.
Note these are only possible candidates, not absolute ones. Care should
be taken to manually verify functions actually do not ever return before
adding the @code{noreturn} attribute, otherwise subtle code generation
bugs could be introduced. You will not get a warning for @code{main} in
hosted C environments.
@item -Wmissing-format-attribute
@opindex Wmissing-format-attribute
@opindex Wformat
If @option{-Wformat} is enabled, also warn about functions which might be
candidates for @code{format} attributes. Note these are only possible
candidates, not absolute ones. GCC will guess 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. This option has no effect unless
@option{-Wformat} is enabled (possibly by @option{-Wall}).
@item -Wpacked
@opindex Wpacked
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}
will be 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 -Wpadded
@opindex Wpadded
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
Warn if anything is declared more than once in the same scope, even in
cases where multiple declaration is valid and changes nothing.
@item -Wnested-externs @r{(C only)}
@opindex Wnested-externs
Warn if an @code{extern} declaration is encountered within a function.
@item -Wunreachable-code
@opindex Wunreachable-code
Warn if the compiler detects that code will never be executed.
This option is intended to warn when the compiler detects that at
least a whole line of source code will never be executed, because
some condition is never satisfied or because it is after a
procedure that never returns.
It is possible for this option to produce a warning even though there
are circumstances under which part of the affected line can be executed,
so care should be taken when removing apparently-unreachable code.
For instance, when a function is inlined, a warning may mean that the
line is unreachable in only one inlined copy of the function.
This option is not made part of @option{-Wall} because in a debugging
version of a program there is often substantial code which checks
correct functioning of the program and is, hopefully, unreachable
because the program does work. Another common use of unreachable
code is to provide behavior which is selectable at compile-time.
@item -Winline
@opindex Winline
Warn if a function can not be inlined and it was declared as inline.
@item -Wlong-long
@opindex Wlong-long
@opindex Wno-long-long
Warn if @samp{long long} type is used. This is default. To inhibit
the warning messages, use @option{-Wno-long-long}. Flags
@option{-Wlong-long} and @option{-Wno-long-long} are taken into account
only when @option{-pedantic} flag is used.
@item -Wdisabled-optimization
@opindex Wdisabled-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 were unable to handle the code
effectively. Often, the problem is that your code is too big or too
complex; GCC will refuse to optimize programs when the optimization
itself is likely to take inordinate amounts of time.
@item -Werror
@opindex Werror
Make all warnings into errors.
@end table
@node Debugging Options
@section Options for Debugging Your Program or GCC
@cindex options, debugging
@cindex debugging information options
GCC has various special options that are used for debugging
either your program or GCC:
@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 will probably make 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}, @option{-gdwarf-1+}, @option{-gdwarf-1},
or @option{-gvms} (see below).
Unlike most other C compilers, GCC allows you to use @option{-g} with
@option{-O}. The shortcuts taken by optimized code may occasionally
produce surprising results: 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 were already at hand; some statements may
execute in different places because they were moved out of loops.
Nevertheless it proves possible to debug optimized output. This makes
it reasonable to use the optimizer for programs that might have bugs.
The following options are useful when GCC is generated with the
capability for more than one debugging format.
@item -ggdb
@opindex ggdb
Produce debugging information for use by GDB@. This means to use the
most expressive format available (DWARF 2, stabs, or the native format
if neither of those are supported), including GDB extensions if at all
possible.
@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 which is not understood by DBX or SDB@.
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 -gcoff
@opindex gcoff
Produce debugging information in COFF format (if that is supported).
This is the format used by SDB on most System V systems prior to
System V Release 4.
@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 -gdwarf
@opindex gdwarf
Produce debugging information in DWARF version 1 format (if that is
supported). This is the format used by SDB on most System V Release 4
systems.
@item -gdwarf+
@opindex gdwarf+
Produce debugging information in DWARF version 1 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 -gdwarf-2
@opindex gdwarf-2
Produce debugging information in DWARF version 2 format (if that is
supported). This is the format used by DBX on IRIX 6.
@item -gvms
@opindex gvms
Produce debugging information in VMS debug format (if that is
supported). This is the format used by DEBUG on VMS systems.
@item -g@var{level}
@itemx -ggdb@var{level}
@itemx -gstabs@var{level}
@itemx -gcoff@var{level}
@itemx -gxcoff@var{level}
@itemx -gdwarf@var{level}
@itemx -gdwarf-2@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 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, but no information
about local variables and no line numbers.
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}.
@cindex @code{prof}
@item -p
@opindex p
Generate extra code to write profile information suitable for the
analysis program @code{prof}. You must use this option when compiling
the source files you want data about, and you must also use it when
linking.
@cindex @code{gprof}
@item -pg
@opindex pg
Generate extra code to write profile information suitable for the
analysis program @code{gprof}. You must use this option when compiling
the source files you want data about, and you must also use it when
linking.
@cindex @code{tcov}
@item -a
@opindex a
Generate extra code to write profile information for basic blocks, which will
record the number of times each basic block is executed, the basic block start
address, and the function name containing the basic block. If @option{-g} is
used, the line number and filename of the start of the basic block will also be
recorded. If not overridden by the machine description, the default action is
to append to the text file @file{bb.out}.
This data could be analyzed by a program like @code{tcov}. Note,
however, that the format of the data is not what @code{tcov} expects.
Eventually GNU @code{gprof} should be extended to process this data.
@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 -fmem-report
@opindex fmem-report
Makes the compiler print some statistics about permanent memory
allocation when it finishes.
@item -fprofile-arcs
@opindex fprofile-arcs
Instrument @dfn{arcs} during compilation to generate coverage data
or for profile-directed block ordering. During execution the program
records how many times each branch is executed and how many times it is
taken. When the compiled program exits it saves this data to a file
called @file{@var{sourcename}.da} for each source file.
For profile-directed block ordering, compile the program with
@option{-fprofile-arcs} plus optimization and code generation options,
generate the arc profile information by running the program on a
selected workload, and then compile the program again with the same
optimization and code generation options plus
@option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
Control Optimization}).
The other use of @option{-fprofile-arcs} is for use with @code{gcov},
when it is used with the @option{-ftest-coverage} option. GCC
supports two methods of determining code coverage: the options that
support @code{gcov}, and options @option{-a} and @option{-ax}, which
write information to text files. The options that support @code{gcov}
do not need to instrument every arc in the program, so a program compiled
with them runs faster than a program compiled with @option{-a}, which
adds instrumentation code to every basic block in the program. The
tradeoff: since @code{gcov} does not have execution counts for all
branches, it must start with the execution counts for the instrumented
branches, and then iterate over the program flow graph until the entire
graph has been solved. Hence, @code{gcov} runs a little more slowly than
a program which uses information from @option{-a} and @option{-ax}.
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.
This option makes it possible to estimate branch probabilities and to
calculate basic block execution counts. In general, basic block
execution counts as provided by @option{-a} do not give enough
information to estimate all branch probabilities.
@need 2000
@item -ftest-coverage
@opindex ftest-coverage
Create data files for the @code{gcov} code-coverage utility
(@pxref{Gcov,, @code{gcov}: a GCC Test Coverage Program}).
The data file names begin with the name of your source file:
@table @gcctabopt
@item @var{sourcename}.bb
A mapping from basic blocks to line numbers, which @code{gcov} uses to
associate basic block execution counts with line numbers.
@item @var{sourcename}.bbg
A list of all arcs in the program flow graph. This allows @code{gcov}
to reconstruct the program flow graph, so that it can compute all basic
block and arc execution counts from the information in the
@code{@var{sourcename}.da} file.
@end table
Use @option{-ftest-coverage} with @option{-fprofile-arcs}; the latter
option adds instrumentation to the program, which then writes
execution counts to another data file:
@table @gcctabopt
@item @var{sourcename}.da
Runtime arc execution counts, used in conjunction with the arc
information in the file @code{@var{sourcename}.bbg}.
@end table
Coverage data will map better to the source files if
@option{-ftest-coverage} is used without optimization.
@item -d@var{letters}
@opindex d
Says to make debugging dumps during compilation at times specified by
@var{letters}. This is used for debugging the compiler. The file names
for most of the dumps are made by appending a pass number and a word to
the source file name (e.g. @file{foo.c.00.rtl} or @file{foo.c.01.sibling}).
Here are the possible letters for use in @var{letters}, and their meanings:
@table @samp
@item A
@opindex dA
Annotate the assembler output with miscellaneous debugging information.
@item b
@opindex db
Dump after computing branch probabilities, to @file{@var{file}.14.bp}.
@item B
@opindex dB
Dump after block reordering, to @file{@var{file}.28.bbro}.
@item c
@opindex dc
Dump after instruction combination, to the file @file{@var{file}.16.combine}.
@item C
@opindex dC
Dump after the first if conversion, to the file @file{@var{file}.17.ce}.
@item d
@opindex dd
Dump after delayed branch scheduling, to @file{@var{file}.31.dbr}.
@item D
@opindex dD
Dump all macro definitions, at the end of preprocessing, in addition to
normal output.
@item e
@opindex de
Dump after SSA optimizations, to @file{@var{file}.04.ssa} and
@file{@var{file}.07.ussa}.
@item E
@opindex dE
Dump after the second if conversion, to @file{@var{file}.26.ce2}.
@item f
@opindex df
Dump after life analysis, to @file{@var{file}.15.life}.
@item F
@opindex dF
Dump after purging @code{ADDRESSOF} codes, to @file{@var{file}.09.addressof}.
@item g
@opindex dg
Dump after global register allocation, to @file{@var{file}.21.greg}.
@item h
@opindex dh
Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
@item o
@opindex do
Dump after post-reload optimizations, to @file{@var{file}.22.postreload}.
@item G
@opindex dG
Dump after GCSE, to @file{@var{file}.10.gcse}.
@item i
@opindex di
Dump after sibling call optimizations, to @file{@var{file}.01.sibling}.
@item j
@opindex dj
Dump after the first jump optimization, to @file{@var{file}.03.jump}.
@item k
@opindex dk
Dump after conversion from registers to stack, to @file{@var{file}.32.stack}.
@item l
@opindex dl
Dump after local register allocation, to @file{@var{file}.20.lreg}.
@item L
@opindex dL
Dump after loop optimization, to @file{@var{file}.11.loop}.
@item M
@opindex dM
Dump after performing the machine dependent reorganisation pass, to
@file{@var{file}.30.mach}.
@item n
@opindex dn
Dump after register renumbering, to @file{@var{file}.25.rnreg}.
@item N
@opindex dN
Dump after the register move pass, to @file{@var{file}.18.regmove}.
@item r
@opindex dr
Dump after RTL generation, to @file{@var{file}.00.rtl}.
@item R
@opindex dR
Dump after the second scheduling pass, to @file{@var{file}.27.sched2}.
@item s
@opindex ds
Dump after CSE (including the jump optimization that sometimes follows
CSE), to @file{@var{file}.08.cse}.
@item S
@opindex dS
Dump after the first scheduling pass, to @file{@var{file}.19.sched}.
@item t
@opindex dt
Dump after the second CSE pass (including the jump optimization that
sometimes follows CSE), to @file{@var{file}.12.cse2}.
@item w
@opindex dw
Dump after the second flow pass, to @file{@var{file}.23.flow2}.
@item X
@opindex dX
Dump after SSA dead code elimination, to @file{@var{file}.06.ssadce}.
@item z
@opindex dz
Dump after the peephole pass, to @file{@var{file}.24.peephole2}.
@item a
@opindex da
Produce all the dumps listed above.
@item m
@opindex dm
Print statistics on memory usage, at the end of the run, to
standard error.
@item p
@opindex dp
Annotate the assembler output with a comment indicating which
pattern and alternative was used. The length of each instruction is
also printed.
@item P
@opindex dP
Dump the RTL in the assembler output as a comment before each instruction.
Also turns on @option{-dp} annotation.
@item v
@opindex dv
For each of the other indicated dump files (except for
@file{@var{file}.00.rtl}), dump a representation of the control flow graph
suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
@item x
@opindex dx
Just generate RTL for a function instead of compiling it. Usually used
with @samp{r}.
@item y
@opindex dy
Dump debugging information during parsing, to standard error.
@end table
@item -fdump-unnumbered
@opindex fdump-unnumbered
When doing debugging dumps (see @option{-d} option above), suppress instruction
numbers and line number note 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-class-hierarchy @r{(C++ only)}
@itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
@opindex fdump-class-hierarchy
Dump a representation of each class's hierarchy and virtual function
table layout to a file. The file name is made by appending @file{.class}
to the source file name. If the @samp{-@var{options}} form is used,
@var{options} controls the details of the dump as described for the
@option{-fdump-tree} options.
@item -fdump-tree-@var{switch} @r{(C++ only)}
@itemx -fdump-tree-@var{switch}-@var{options} @r{(C++ only)}
@opindex fdump-tree
Control the dumping at various stages of processing the intermediate
language tree to a file. The file name is generated by appending a switch
specific suffix to the source file name. If the @samp{-@var{options}}
form is used, @var{options} is a list of @samp{-} separated options that
control the details of the dump. Not all options are applicable to all
dumps, those which are not meaningful will be 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 slim
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.
@item all
Turn on all options.
@end table
The following tree dumps are possible:
@table @samp
@item original
Dump before any tree based optimization, to @file{@var{file}.original}.
@item optimized
Dump after all tree based optimization, to @file{@var{file}.optimized}.
@item inlined
Dump after function inlining, to @file{@var{file}.inlined}.
@end table
@item -fpretend-float
@opindex fpretend-float
When running a cross-compiler, pretend that the target machine uses the
same floating point format as the host machine. This causes incorrect
output of the actual floating constants, but the actual instruction
sequence will probably be the same as GCC would make when running on
the target machine.
@item -save-temps
@opindex save-temps
Store the usual ``temporary'' intermediate files permanently; place them
in the current directory and name them based on the source file. Thus,
compiling @file{foo.c} with @samp{-c -save-temps} would produce files
@file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
preprocessed @file{foo.i} output file even though the compiler now
normally uses an integrated preprocessor.
@item -time
@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). 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.
@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-prog-name=@var{program}
@opindex print-prog-name
Like @option{-print-file-name}, but searches for a program such as @samp{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
@example
gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
@end example
@item -print-search-dirs
@opindex print-search-dirs
Print the name of the configured installation directory and a list of
program and library directories gcc will search---and don't do anything else.
This is useful when 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 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 '/'.
@xref{Environment Variables}.
@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, @samp{3.0})---and don't do
anything else.
@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 Optimize Options
@section Options That Control Optimization
@cindex optimize options
@cindex options, optimization
These options control various sorts of optimizations:
@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.
Without @option{-O}, 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 would expect from the source code.
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.
@item -O2
@opindex O2
Optimize even more. GCC performs nearly all supported optimizations
that do not involve a space-speed tradeoff. The compiler does not
perform loop unrolling or function inlining when you specify @option{-O2}.
As compared to @option{-O}, this option increases both compilation time
and the performance of the generated code.
@option{-O2} turns on all optional optimizations except for loop unrolling,
function inlining, and register renaming. It also turns on the
@option{-fforce-mem} option on all machines and frame pointer elimination
on machines where doing so does not interfere with debugging.
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 @option{-finline-functions} and
@option{-frename-registers} options.
@item -O0
@opindex O0
Do not optimize.
@item -Os
@opindex Os
Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
do not typically increase code size. It also performs further
optimizations designed to reduce code size.
If you use multiple @option{-O} options, with or without level numbers,
the last such option is the one that is effective.
@end table
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} would be @option{-fno-foo}. In the table below,
only one of the forms is listed---the one which is not the default.
You can figure out the other form by either removing @samp{no-} or
adding it.
@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 -fno-default-inline
@opindex fno-default-inline
Do not make member functions inline by default merely because they are
defined inside the class scope (C++ only). Otherwise, when you specify
@w{@option{-O}}, member functions defined inside class scope are compiled
inline by default; i.e., you don't need to add @samp{inline} in front of
the member function name.
@item -fno-defer-pop
@opindex fno-defer-pop
Always pop the arguments to each function call as soon as that function
returns. For machines which must pop arguments after a function call,
the compiler normally lets arguments accumulate on the stack for several
function calls and pops them all at once.
@item -fforce-mem
@opindex fforce-mem
Force memory operands to be copied into registers before doing
arithmetic on them. This produces better code by making all memory
references potential common subexpressions. When they are not common
subexpressions, instruction combination should eliminate the separate
register-load. The @option{-O2} option turns on this option.
@item -fforce-addr
@opindex fforce-addr
Force memory address constants to be copied into registers before
doing arithmetic on them. This may produce better code just as
@option{-fforce-mem} may.
@item -fomit-frame-pointer
@opindex fomit-frame-pointer
Don't keep the frame pointer in a register for functions that
don't need one. This avoids the instructions to save, set up and
restore frame pointers; it also makes an extra register available
in many functions. @strong{It also makes debugging impossible on
some machines.}
On some machines, such as the VAX, this flag has no effect, because
the standard calling sequence automatically handles the frame pointer
and nothing is saved by pretending it doesn't exist. The
machine-description macro @code{FRAME_POINTER_REQUIRED} controls
whether a target machine supports this flag. @xref{Registers,,Register
Usage, gccint, GNU Compiler Collection (GCC) Internals}.
@item -foptimize-sibling-calls
@opindex foptimize-sibling-calls
Optimize sibling and tail recursive calls.
@item -ftrapv
@opindex ftrapv
This option generates traps for signed overflow on addition, subtraction,
multiplication operations.
@item -fno-inline
@opindex fno-inline
Don't pay attention to the @code{inline} keyword. Normally this option
is used to keep the compiler from expanding any functions inline.
Note that if you are not optimizing, no functions can be expanded inline.
@item -finline-functions
@opindex finline-functions
Integrate all simple functions into their callers. The compiler
heuristically decides which functions are simple enough to be 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.
@item -finline-limit=@var{n}
@opindex finline-limit
By default, gcc limits the size of functions that can be inlined. This flag
allows the control of this limit for functions that are explicitly marked as
inline (ie marked with the inline keyword or defined within the class
definition in c++). @var{n} is the size of functions that can be inlined in
number of pseudo instructions (not counting parameter handling). The default
value of @var{n} is 600.
Increasing this value can result in more inlined code at
the cost of compilation time and memory consumption. Decreasing usually makes
the compilation faster and less code will be inlined (which presumably
means slower programs). This option is particularly useful for programs that
use inlining heavily such as those based on recursive templates with C++.
@emph{Note:} pseudo instruction represents, in this particular context, an
abstract measurement of function's size. In no way, it represents a count
of assembly instructions and as such its exact meaning might change from one
release to an another.
@item -fkeep-inline-functions
@opindex fkeep-inline-functions
Even if all calls to a given function are integrated, and the function
is declared @code{static}, nevertheless output a separate run-time
callable version of the function. This switch does not affect
@code{extern inline} functions.
@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 the variable was referenced, regardless of whether or not
optimization is turned on, use the @option{-fno-keep-static-consts} option.
@item -fmerge-constants
Attempt to merge identical constants (string constants and floating point
constants) accross compilation units.
This option is default for optimized compilation if assembler and linker
support it. Use @option{-fno-merge-constants} to inhibit this behavior.
@item -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 non-automatic variable to
have distinct location, so using this option will result in non-conforming
behavior.
@item -fno-function-cse
@opindex fno-function-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.
@item -ffast-math
@opindex ffast-math
Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, and @*
@option{-fno-trapping-math}.
This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
This option should never be turned on by any @option{-O} option since
it can result in incorrect output for programs which depend on
an exact implementation of IEEE or ISO rules/specifications for
math functions.
@item -fno-math-errno
@opindex fno-math-errno
Do not set ERRNO after calling math functions that are executed
with a single instruction, e.g., 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 should never be turned on by any @option{-O} option since
it can result in incorrect output for programs which depend on
an exact implementation of IEEE or ISO rules/specifications for
math functions.
The default is @option{-fmath-errno}.
@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 should never be turned on by any @option{-O} option since
it can result in incorrect output for programs which depend on
an exact implementation of IEEE or ISO rules/specifications for
math functions.
The default is @option{-fno-unsafe-math-optimizations}.
@item -fno-trapping-math
@opindex fno-trapping-math
Compile code assuming that floating-point operations cannot generate
user-visible traps. 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 which depend on
an exact implementation of IEEE or ISO rules/specifications for
math functions.
The default is @option{-ftrapping-math}.
@end table
The following options control specific optimizations. The @option{-O2}
option turns on all of these optimizations except @option{-funroll-loops}
and @option{-funroll-all-loops}. On most machines, the @option{-O} option
turns on the @option{-fthread-jumps} and @option{-fdelayed-branch} options,
but specific machines may handle it differently.
You can use the following flags in the rare cases when ``fine-tuning''
of optimizations to be performed is desired.
Not all of the optimizations performed by GCC have @option{-f} options
to control them.
@table @gcctabopt
@item -fstrength-reduce
@opindex fstrength-reduce
Perform the optimizations of loop strength reduction and
elimination of iteration variables.
@item -fthread-jumps
@opindex fthread-jumps
Perform optimizations where we 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.
@item -fcse-follow-jumps
@opindex fcse-follow-jumps
In common subexpression elimination, 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 will follow the jump when the condition
tested is false.
@item -fcse-skip-blocks
@opindex fcse-skip-blocks
This is similar to @option{-fcse-follow-jumps}, but causes CSE to
follow jumps which 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}.
@item -frerun-cse-after-loop
@opindex frerun-cse-after-loop
Re-run common subexpression elimination after loop optimizations has been
performed.
@item -frerun-loop-opt
@opindex frerun-loop-opt
Run the loop optimizer twice.
@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 runtime performance if you disable
the global common subexpression elmination pass by adding
@option{-fno-gcse} to the command line.
@item -fgcse-lm
@opindex fgcse-lm
When @option{-fgcse-lm} is enabled, global common subexpression elimination will
attempt to move loads which 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.
@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 will attempt 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.
@item -fdelete-null-pointer-checks
@opindex fdelete-null-pointer-checks
Use global dataflow analysis to identify and eliminate useless checks
for null pointers. The compiler assumes that dereferencing a null
pointer would have halted the program. If a pointer is checked after
it has already been dereferenced, it cannot be null.
In some environments, this assumption is not true, and programs can
safely dereference null pointers. Use
@option{-fno-delete-null-pointer-checks} to disable this optimization
for programs which depend on that behavior.
@item -fexpensive-optimizations
@opindex fexpensive-optimizations
Perform a number of minor optimizations that are relatively expensive.
@item -foptimize-register-move
@itemx -fregmove
@opindex foptimize-register-move
@opindex fregmove
Attempt to reassign register numbers in move instructions and as
operands of other simple instructions in order to maximize the amount of
register tying. This is especially helpful on machines with two-operand
instructions. GCC enables this optimization by default with @option{-O2}
or higher.
Note @option{-fregmove} and @option{-foptimize-register-move} are the same
optimization.
@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.
@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.
@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.
@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. HPPA
processors running HP-UX and Sparc processors running Solaris 2 have
linkers with such optimizations. Other systems using the ELF object format
as well as AIX may have these optimizations in the future.
Only use these options when there are significant benefits from doing
so. When you specify these options, the assembler and linker will
create larger object and executable files and will also be slower.
You will not be able to use @code{gprof} on all systems if you
specify this option and you may have problems with debugging if
you specify both this option and @option{-g}.
@item -fcaller-saves
@opindex fcaller-saves
Enable values to be allocated in registers that will be 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 than would otherwise be produced.
This option is always enabled by default on certain machines, usually
those which have no call-preserved registers to use instead.
For all machines, optimization level 2 and higher enables this flag by
default.
@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 both
@option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
option makes code larger, and may or may not make it run faster.
@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 -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.
@item -fmove-all-movables
@opindex fmove-all-movables
Forces all invariant computations in loops to be moved
outside the loop.
@item -freduce-all-givs
@opindex freduce-all-givs
Forces all general-induction variables in loops to be
strength-reduced.
@emph{Note:} When compiling programs written in Fortran,
@option{-fmove-all-movables} and @option{-freduce-all-givs} are enabled
by default when you use the optimizer.
These options may generate better or worse code; results are highly
dependent on the structure of loops within the source code.
These two options are intended to be removed someday, once
they have helped determine the efficacy of various
approaches to improving loop optimizations.
Please let us (@w{@email{gcc@@gcc.gnu.org}} and @w{@email{fortran@@gnu.org}})
know how use of these options affects
the performance of your production code.
We're very interested in code that runs @emph{slower}
when these options are @emph{enabled}.
@item -fno-peephole
@itemx -fno-peephole2
@opindex fno-peephole
@opindex fno-peephole2
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.
@item -fbranch-probabilities
@opindex fbranch-probabilities
After running a program compiled with @option{-fprofile-arcs}
(@pxref{Debugging Options,, Options for Debugging Your Program or
@command{gcc}}), 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 the program
compiled with @option{-fprofile-arcs} exits it saves arc execution
counts to a file called @file{@var{sourcename}.da} 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.
With @option{-fbranch-probabilities}, GCC puts a @samp{REG_EXEC_COUNT}
note on the first instruction of each basic block, and 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.c}, instead of guessing which path a
branch is mostly to take, the @samp{REG_BR_PROB} values are used to
exactly determine which path is taken more often.
@item -fno-guess-branch-probability
@opindex fno-guess-branch-probability
Do not guess branch probabilities using a randomized model.
Sometimes gcc will opt to use a randomized model to guess branch
probabilities, when none are available from either profiling feedback
(@option{-fprofile-arcs}) or @samp{__builtin_expect}. This means that
different runs of the compiler on the same program may produce different
object code.
In a hard real-time system, people don't want different runs of the
compiler to produce code that has different behavior; minimizing
non-determinism is of paramount import. This switch allows users to
reduce non-determinism, possibly at the expense of inferior
optimization.
@item -fstrict-aliasing
@opindex fstrict-aliasing
Allows 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.
Pay special attention to code like this:
@example
union a_union @{
int i;
double d;
@};
int f() @{
a_union t;
t.d = 3.0;
return t.i;
@}
@end example
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 will work as
expected. However, this code might not:
@example
int f() @{
a_union t;
int* ip;
t.d = 3.0;
ip = &t.i;
return *ip;
@}
@end example
Every language that wishes to perform language-specific alias analysis
should define a function that computes, given an @code{tree}
node, an alias set for the node. Nodes in different alias sets are not
allowed to alias. For an example, see the C front-end function
@code{c_get_alias_set}.
@item -falign-functions
@itemx -falign-functions=@var{n}
@opindex falign-functions
Align the start of functions to the next power-of-two greater than
@var{n}, skipping up to @var{n} bytes. For instance,
@option{-falign-functions=32} aligns functions to the next 32-byte
boundary, but @option{-falign-functions=24} would align to the next
32-byte boundary only if this can be done by skipping 23 bytes or less.
@option{-fno-align-functions} and @option{-falign-functions=1} are
equivalent and mean that functions will not be aligned.
Some assemblers only support this flag when @var{n} is a power of two;
in that case, it is rounded up.
If @var{n} is not specified, use a machine-dependent default.
@item -falign-labels
@itemx -falign-labels=@var{n}
@opindex falign-labels
Align all branch targets to a power-of-two boundary, skipping up to
@var{n} bytes like @option{-falign-functions}. This option can easily
make code slower, because it must insert dummy operations for when the
branch target is reached in the usual flow of the code.
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, use a machine-dependent default which is
very likely to be @samp{1}, meaning no alignment.
@item -falign-loops
@itemx -falign-loops=@var{n}
@opindex falign-loops
Align loops to a power-of-two boundary, skipping up to @var{n} bytes
like @option{-falign-functions}. The hope is that the loop will be
executed many times, which will make up for any execution of the dummy
operations.
If @var{n} is not specified, use a machine-dependent default.
@item -falign-jumps
@itemx -falign-jumps=@var{n}
@opindex falign-jumps
Align branch targets to a power-of-two boundary, for branch targets
where the targets can only be reached by jumping, skipping up to @var{n}
bytes like @option{-falign-functions}. In this case, no dummy operations
need be executed.
If @var{n} is not specified, use a machine-dependent default.
@item -fssa
@opindex fssa
Perform optimizations in static single assignment form. Each function's
flow graph is translated into SSA form, optimizations are performed, and
the flow graph is translated back from SSA form. Users should not
specify this option, since it is not yet ready for production use.
@item -fssa-ccp
@opindex fssa-ccp
Perform Sparse Conditional Constant Propagation in SSA form. Requires
@option{-fssa}. Like @option{-fssa}, this is an experimental feature.
@item -fssa-dce
@opindex fssa-dce
Perform aggressive dead-code elimination in SSA form. Requires @option{-fssa}.
Like @option{-fssa}, this is an experimental feature.
@item -fsingle-precision-constant
@opindex fsingle-precision-constant
Treat floating point constant as single precision constant instead of
implicitly converting it to double precision constant.
@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
will most benefit processors with lots of registers. It can, however,
make debugging impossible, since variables will no longer stay in
a ``home register''.
@item -fno-cprop-registers
@opindex fno-cprop-registers
After register allocation and post-register allocation instruction splitting,
we perform a copy-propagation pass to try to reduce scheduling dependencies
and occasionally eliminate the copy.
@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 will not inline functions
that contain more that a certain number of instructions. You can
control some of these constants on the command-line using the
@option{--param} option.
In each case, the @var{value} is an integer. The allowable choices for
@var{name} are given in the following table:
@table @gcctabopt
@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 is searched, the time savings from filling the delay slot
will be minimal so stop searching. Increasing values mean more
aggressive optimization, making the compile time increase with probably
small improvement in executable run 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 compile 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 that will be allocated in
order to perform the global common subexpression elimination
optimization. If more memory than specified is required, the
optimization will not be done.
@item max-gcse-passes
The maximum number of passes of GCSE to run.
@item max-pending-list-length
The maximum number of pending dependencies scheduling will allow
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-inline-insns
If an function contains more than this many instructions, it
will not be inlined. This option is precisely equivalent to
@option{-finline-limit}.
@end table
@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.
@table @gcctabopt
@item -include @var{file}
@opindex include
Process @var{file} as input before processing the regular input file.
In effect, the contents of @var{file} are compiled first. Any @option{-D}
and @option{-U} options on the command line are always processed before
@option{-include @var{file}}, regardless of the order in which they are
written. All the @option{-include} and @option{-imacros} options are
processed in the order in which they are written.
@item -imacros @var{file}
@opindex imacros
Process @var{file} as input, discarding the resulting output, before
processing the regular input file. Because the output generated from
@var{file} is discarded, the only effect of @option{-imacros @var{file}}
is to make the macros defined in @var{file} available for use in the
main input. All the @option{-include} and @option{-imacros} options are
processed in the order in which they are written.
@item -idirafter @var{dir}
@opindex idirafter
@cindex second include path
Add the directory @var{dir} to the second include path. The directories
on the second include path are searched when a header file is not found
in any of the directories in the main include path (the one that
@option{-I} adds to).
@item -iprefix @var{prefix}
@opindex iprefix
Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix}
options.
@item -iwithprefix @var{dir}
@opindex iwithprefix
Add a directory to the second include path. The directory's name is
made by concatenating @var{prefix} and @var{dir}, where @var{prefix} was
specified previously with @option{-iprefix}. If you have not specified a
prefix yet, the directory containing the installed passes of the
compiler is used as the default.
@item -iwithprefixbefore @var{dir}
@opindex iwithprefixbefore
Add a directory to the main include path. The directory's name is made
by concatenating @var{prefix} and @var{dir}, as in the case of
@option{-iwithprefix}.
@item -isystem @var{dir}
@opindex isystem
Add a directory to the beginning of the second include path, marking it
as a system directory, so that it gets the same special treatment as
is applied to the standard system directories.
@item -nostdinc
@opindex nostdinc
Do not search the standard system directories for header files. Only
the directories you have specified with @option{-I} options (and the
current directory, if appropriate) are searched. @xref{Directory
Options}, for information on @option{-I}.
By using both @option{-nostdinc} and @option{-I-}, you can limit the include-file
search path to only those directories you specify explicitly.
@item -remap
@opindex remap
When searching for a header file in a directory, remap file names if a
file named @file{header.gcc} exists in that directory. This can be used
to work around limitations of file systems with file name restrictions.
The @file{header.gcc} file should contain a series of lines with two
tokens on each line: the first token is the name to map, and the second
token is the actual name to use.
@item -undef
@opindex undef
Do not predefine any nonstandard macros. (Including architecture flags).
@item -E
@opindex E
Run only the C preprocessor. Preprocess all the C source files
specified and output the results to standard output or to the
specified output file.
@item -C
@opindex C
Tell the preprocessor not to discard comments. Used with the
@option{-E} option.
@item -P
@opindex P
Tell the preprocessor not to generate @samp{#line} directives.
Used with the @option{-E} option.
@cindex make
@cindex dependencies, make
@item -M
@opindex M
Instead of outputting the result of preprocessing, output a rule
suitable for @code{make} describing the dependencies of the main source
file. The preprocessor outputs one @code{make} rule containing the
object file name for that source file, a colon, and the names of all the
included files. Unless overridden explicitly, the object file name
consists of the basename of the source file with any suffix replaced with
object file suffix. If there are many included files then the
rule is split into several lines using @samp{\}-newline.
@option{-M} implies @option{-E}.
@item -MM
@opindex MM
Like @option{-M}, but mention only the files included with @samp{#include
"@var{file}"}. System header files included with @samp{#include
<@var{file}>} are omitted.
@item -MD
@opindex MD
Like @option{-M} but the dependency information is written to a file
rather than stdout. @code{gcc} will use the same file name and
directory as the object file, but with the suffix @file{.d} instead.
This is in addition to compiling the main file as specified---@option{-MD}
does not inhibit ordinary compilation the way @option{-M} does,
unless you also specify @option{-MG}.
With Mach, you can use the utility @code{md} to merge multiple
dependency files into a single dependency file suitable for using with
the @samp{make} command.
@item -MMD
@opindex MMD
Like @option{-MD} except mention only user header files, not system
-header files.
@item -MF @var{file}
@opindex MF
When used with @option{-M} or @option{-MM}, specifies a file to write the
dependencies to. This allows the preprocessor to write the preprocessed
file to stdout normally. If no @option{-MF} switch is given, CPP sends
the rules to stdout and suppresses normal preprocessed output.
Another way to specify output of a @code{make} rule is by setting
the environment variable @env{DEPENDENCIES_OUTPUT} (@pxref{Environment
Variables}).
@item -MG
@opindex MG
When used with @option{-M} or @option{-MM}, @option{-MG} says to treat missing
header files as generated files and assume they live in the same
directory as the source file. It suppresses preprocessed output, as a
missing header file is ordinarily an error.
This feature is used in automatic updating of makefiles.
@item -MP
@opindex MP
This option instructs CPP to add a phony target for each dependency
other than the main file, causing each to depend on nothing. These
dummy rules work around errors @code{make} gives if you remove header
files without updating the @code{Makefile} to match.
This is typical output:-
@smallexample
/tmp/test.o: /tmp/test.c /tmp/test.h
/tmp/test.h:
@end smallexample
@item -MQ @var{target}
@item -MT @var{target}
@opindex MQ
@opindex MT
By default CPP uses the main file name, including any path, and appends
the object suffix, normally ``.o'', to it to obtain the name of the
target for dependency generation. With @option{-MT} you can specify a
target yourself, overriding the default one.
If you want multiple targets, you can specify them as a single argument
to @option{-MT}, or use multiple @option{-MT} options.
The targets you specify are output in the order they appear on the
command line. @option{-MQ} is identical to @option{-MT}, except that the
target name is quoted for Make, but with @option{-MT} it isn't. For
example, @option{-MT '$(objpfx)foo.o'} gives
@smallexample
$(objpfx)foo.o: /tmp/foo.c
@end smallexample
but @option{-MQ '$(objpfx)foo.o'} gives
@smallexample
$$(objpfx)foo.o: /tmp/foo.c
@end smallexample
The default target is automatically quoted, as if it were given with
@option{-MQ}.
@item -H
@opindex H
Print the name of each header file used, in addition to other normal
activities.
@item -A@var{question}(@var{answer})
@opindex A
Assert the answer @var{answer} for @var{question}, in case it is tested
with a preprocessing conditional such as @samp{#if
#@var{question}(@var{answer})}. @option{-A-} disables the standard
assertions that normally describe the target machine.
@item -D@var{macro}
@opindex D
Define macro @var{macro} with the string @samp{1} as its definition.
@item -D@var{macro}=@var{defn}
Define macro @var{macro} as @var{defn}. All instances of @option{-D} on
the command line are processed before any @option{-U} options.
Any @option{-D} and @option{-U} options on the command line are processed in
order, and always before @option{-imacros @var{file}}, regardless of the
order in which they are written.
@item -U@var{macro}
@opindex U
Undefine macro @var{macro}. @option{-U} options are evaluated after all
@option{-D} options, but before any @option{-include} and @option{-imacros}
options.
Any @option{-D} and @option{-U} options on the command line are processed in
order, and always before @option{-imacros @var{file}}, regardless of the
order in which they are written.
@item -dM
@opindex dM
Tell the preprocessor to output only a list of the macro definitions
that are in effect at the end of preprocessing. Used with the @option{-E}
option.
@item -dD
@opindex dD
Tell the preprocessing to pass all macro definitions into the output, in
their proper sequence in the rest of the output.
@item -dN
@opindex dN
Like @option{-dD} except that the macro arguments and contents are omitted.
Only @samp{#define @var{name}} is included in the output.
@item -dI
@opindex dI
Output @samp{#include} directives in addition to the result of
preprocessing.
@item -fpreprocessed
@opindex fpreprocessed
Indicate to the preprocessor that the input file has already been
preprocessed. This suppresses things like macro expansion, trigraph
conversion, escaped newline splicing, and processing of most directives.
The preprocessor still recognizes and removes comments, so that you can
pass a file preprocessed with @option{-C} to the compiler without
problems. In this mode the integrated preprocessor is little more than
a tokenizer for the front ends.
@option{-fpreprocessed} is implicit if the input file has one of the
extensions @samp{i}, @samp{ii} or @samp{mi}. These are the extensions
that GCC uses for preprocessed files created by @option{-save-temps}.
@item -trigraphs
@opindex trigraphs
Process ISO standard trigraph sequences. These are three-character
sequences, all starting with @samp{??}, that are defined by ISO C to
stand for single characters. For example, @samp{??/} stands for
@samp{\}, so @samp{'??/n'} is a character constant for a newline. By
default, GCC ignores trigraphs, but in standard-conforming modes it
converts them. See the @option{-std} and @option{-ansi} options.
The nine trigraph sequences are
@table @samp
@item ??(
@expansion{} @samp{[}
@item ??)
@expansion{} @samp{]}
@item ??<
@expansion{} @samp{@{}
@item ??>
@expansion{} @samp{@}}
@item ??=
@expansion{} @samp{#}
@item ??/
@expansion{} @samp{\}
@item ??'
@expansion{} @samp{^}
@item ??!
@expansion{} @samp{|}
@item ??-
@expansion{} @samp{~}
@end table
Trigraph support is not popular, so many compilers do not implement it
properly. Portable code should not rely on trigraphs being either
converted or ignored.
@item -Wp,@var{option}
@opindex Wp
Pass @var{option} as an option to the preprocessor. If @var{option}
contains commas, it is split into multiple options at the commas.
@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.
@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}.
@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.)
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.
The linker searches a standard list of directories for the library,
which is actually a file named @file{lib@var{library}.a}. The linker
then uses this file as if it had been specified precisely by name.
The directories searched include several standard system directories
plus any that you specify with @option{-L}.
Normally the files found this way are library files---archive files
whose members are object files. The linker handles an archive file by
scanning through it for members which define symbols that have so far
been referenced but not defined. But if the file that is found is an
ordinary object file, it is linked in the usual fashion. The only
difference between using an @option{-l} option and specifying a file name
is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
and searches several directories.
@item -lobjc
@opindex lobjc
You need this special case of the @option{-l} option in order to
link an 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}
or @option{-nodefaultlibs} is used.
@item -nodefaultlibs
@opindex nodefaultlibs
Do not use the standard system libraries when linking.
Only the libraries you specify will be passed to the linker.
The standard startup files are used normally, unless @option{-nostartfiles}
is used. The compiler may generate calls to memcmp, memset, and memcpy
for System V (and ISO C) environments or to bcopy and bzero for
BSD environments. 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 -nostdlib
@opindex nostdlib
Do not use the standard system startup files or libraries when linking.
No startup files and only the libraries you specify will be passed to
the linker. The compiler may generate calls to memcmp, memset, and memcpy
for System V (and ISO C) environments or to bcopy and bzero for
BSD environments. 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
that 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. (For example, @samp{__main}, used to ensure C++
constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
GNU Compiler Collection (GCC) Internals}.)
@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 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 that were used to
generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
when you specify this 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, whenever you specify the @option{-shared} option, the GCC
driver automatically adds @option{-shared-libgcc}, unless you explicitly
specify @option{-static-libgcc}. The G++ driver automatically adds
@option{-shared-libgcc} when you build a main executable as well because
for C++ programs that is typically the right thing to do.
(Exception-handling will not work reliably otherwise.)
However, when linking a main executable written in C, you must
explicitly say @option{-shared-libgcc} if you want to use the shared
@file{libgcc}.
@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 @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
this option.
@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 which GCC does not know how to
recognize.
If you want to pass an option that takes an 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
@samp{-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.
@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.
@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.
@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
@item -I@var{dir}
@opindex I
Add the directory @var{dir} to the head of the list of directories to be
searched for header files. This can be used to override a system header
file, substituting your own version, since these directories are
searched before the system header file directories. However, you should
not use this option to add directories that contain vendor-supplied
system header files (use @option{-isystem} for that). If you use more than
one @option{-I} option, the directories are scanned in left-to-right
order; the standard system directories come after.
If a standard system include directory, or a directory specified with
@option{-isystem}, is also specified with @option{-I}, it will be
searched only in the position requested by @option{-I}. Also, it will
not be considered a system include directory. If that directory really
does contain system headers, there is a good chance that they will
break. For instance, if GCC's installation procedure edited the headers
in @file{/usr/include} to fix bugs, @samp{-I/usr/include} will cause the
original, buggy headers to be found instead of the corrected ones. GCC
will issue a warning when a system include directory is hidden in this
way.
@item -I-
@opindex I-
Any directories you specify with @option{-I} options before the @option{-I-}
option are searched only for the case of @samp{#include "@var{file}"};
they are not searched for @samp{#include <@var{file}>}.
If additional directories are specified with @option{-I} options after
the @option{-I-}, these directories are searched for all @samp{#include}
directives. (Ordinarily @emph{all} @option{-I} directories are used
this way.)
In addition, the @option{-I-} option inhibits the use of the current
directory (where the current input file came from) as the first search
directory for @samp{#include "@var{file}"}. There is no way to
override this effect of @option{-I-}. With @option{-I.} you can specify
searching the directory which was current when the compiler was
invoked. That is not exactly the same as what the preprocessor does
by default, but it is often satisfactory.
@option{-I-} does not inhibit the use of the standard system directories
for header files. Thus, @option{-I-} and @option{-nostdinc} are
independent.
@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
@file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
@var{prefix} as a prefix for each program it tries to run, both with and
without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
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}
was not specified, the driver tries two standard prefixes, which are
@file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc-lib/}. 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 will check to see if the path provided by the @option{-B}
refers to a directory, and if necessary it will add 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
includes 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 run-time 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 will be replaced by @file{[dir/]include}. This is to help
with boot-strapping the compiler.
@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 that the @file{gcc} driver
program uses when determining what switches to pass to @file{cc1},
@file{cc1plus}, @file{as}, @file{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.
@end table
@c man end
@node Spec Files
@section Specifying subprocesses and the switches to pass to them
@cindex Spec Files
@command{gcc} is a driver program. It performs its job by invoking a
sequence of other programs to do the work of compiling, assembling and
linking. GCC interprets its command-line parameters and uses these to
deduce which programs it should invoke, and which command-line options
it ought to place on their command lines. This behavior is controlled
by @dfn{spec strings}. In most cases there is one spec string for each
program that GCC can invoke, but a few programs have multiple spec
strings to control their behavior. The spec strings built into GCC can
be overridden by using the @option{-specs=} command-line switch to specify
a spec file.
@dfn{Spec files} are plaintext files that are used to construct spec
strings. They consist of a sequence of directives separated by blank
lines. The type of directive is determined by the first non-whitespace
character on the line and it can be one of the following:
@table @code
@item %@var{command}
Issues a @var{command} to the spec file processor. The commands that can
appear here are:
@table @code
@item %include <@var{file}>
@cindex %include
Search for @var{file} and insert its text at the current point in the
specs file.
@item %include_noerr <@var{file}>
@cindex %include_noerr
Just like @samp{%include}, but do not generate an error message if the include
file cannot be found.
@item %rename @var{old_name} @var{new_name}
@cindex %rename
Rename the spec string @var{old_name} to @var{new_name}.
@end table
@item *[@var{spec_name}]:
This tells the compiler to create, override or delete the named spec
string. All lines after this directive up to the next directive or
blank line are considered to be the text for the spec string. If this
results in an empty string then the spec will be deleted. (Or, if the
spec did not exist, then nothing will happened.) Otherwise, if the spec
does not currently exist a new spec will be created. If the spec does
exist then its contents will be overridden by the text of this
directive, unless the first character of that text is the @samp{+}
character, in which case the text will be appended to the spec.
@item [@var{suffix}]:
Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
and up to the next directive or blank line are considered to make up the
spec string for the indicated suffix. When the compiler encounters an
input file with the named suffix, it will processes the spec string in
order to work out how to compile that file. For example:
@smallexample
.ZZ:
z-compile -input %i
@end smallexample
This says that any input file whose name ends in @samp{.ZZ} should be
passed to the program @samp{z-compile}, which should be invoked with the
command-line switch @option{-input} and with the result of performing the
@samp{%i} substitution. (See below.)
As an alternative to providing a spec string, the text that follows a
suffix directive can be one of the following:
@table @code
@item @@@var{language}
This says that the suffix is an alias for a known @var{language}. This is
similar to using the @option{-x} command-line switch to GCC to specify a
language explicitly. For example:
@smallexample
.ZZ:
@@c++
@end smallexample
Says that .ZZ files are, in fact, C++ source files.
@item #@var{name}
This causes an error messages saying:
@smallexample
@var{name} compiler not installed on this system.
@end smallexample
@end table
GCC already has an extensive list of suffixes built into it.
This directive will add an entry to the end of the list of suffixes, but
since the list is searched from the end backwards, it is effectively
possible to override earlier entries using this technique.
@end table
GCC has the following spec strings built into it. Spec files can
override these strings or create their own. Note that individual
targets can also add their own spec strings to this list.
@smallexample
asm Options to pass to the assembler
asm_final Options to pass to the assembler post-processor
cpp Options to pass to the C preprocessor
cc1 Options to pass to the C compiler
cc1plus Options to pass to the C++ compiler
endfile Object files to include at the end of the link
link Options to pass to the linker
lib Libraries to include on the command line to the linker
libgcc Decides which GCC support library to pass to the linker
linker Sets the name of the linker
predefines Defines to be passed to the C preprocessor
signed_char Defines to pass to CPP to say whether @code{char} is signed
by default
startfile Object files to include at the start of the link
@end smallexample
Here is a small example of a spec file:
@smallexample
%rename lib old_lib
*lib:
--start-group -lgcc -lc -leval1 --end-group %(old_lib)
@end smallexample
This example renames the spec called @samp{lib} to @samp{old_lib} and
then overrides the previous definition of @samp{lib} with a new one.
The new definition adds in some extra command-line options before
including the text of the old definition.
@dfn{Spec strings} are a list of command-line options to be passed to their
corresponding program. In addition, the spec strings can contain
@samp{%}-prefixed sequences to substitute variable text or to
conditionally insert text into the command line. Using these constructs
it is possible to generate quite complex command lines.
Here is a table of all defined @samp{%}-sequences for spec
strings. Note that spaces are not generated automatically around the
results of expanding these sequences. Therefore you can concatenate them
together or combine them with constant text in a single argument.
@table @code
@item %%
Substitute one @samp{%} into the program name or argument.
@item %i
Substitute the name of the input file being processed.
@item %b
Substitute the basename of the input file being processed.
This is the substring up to (and not including) the last period
and not including the directory.
@item %B
This is the same as @samp{%b}, but include the file suffix (text after
the last period).
@item %d
Marks the argument containing or following the @samp{%d} as a
temporary file name, so that that file will be deleted if GCC exits
successfully. Unlike @samp{%g}, this contributes no text to the
argument.
@item %g@var{suffix}
Substitute a file name that has suffix @var{suffix} and is chosen
once per compilation, and mark the argument in the same way as
@samp{%d}. To reduce exposure to denial-of-service attacks, the file
name is now chosen in a way that is hard to predict even when previously
chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
was simply substituted with a file name chosen once per compilation,
without regard to any appended suffix (which was therefore treated
just like ordinary text), making such attacks more likely to succeed.
@item %u@var{suffix}
Like @samp{%g}, but generates a new temporary file name even if
@samp{%u@var{suffix}} was already seen.
@item %U@var{suffix}
Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
new one if there is no such last file name. In the absence of any
@samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
would involve the generation of two distinct file names, one
for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
simply substituted with a file name chosen for the previous @samp{%u},
without regard to any appended suffix.
@item %j@var{SUFFIX}
Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
writable, and if save-temps is off; otherwise, substitute the name
of a temporary file, just like @samp{%u}. This temporary file is not
meant for communication between processes, but rather as a junk
disposal mechanism.
@item %.@var{SUFFIX}
Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
when it is subsequently output with @samp{%*}. @var{SUFFIX} is
terminated by the next space or %.
@item %w
Marks the argument containing or following the @samp{%w} as the
designated output file of this compilation. This puts the argument
into the sequence of arguments that @samp{%o} will substitute later.
@item %o
Substitutes the names of all the output files, with spaces
automatically placed around them. You should write spaces
around the @samp{%o} as well or the results are undefined.
@samp{%o} is for use in the specs for running the linker.
Input files whose names have no recognized suffix are not compiled
at all, but they are included among the output files, so they will
be linked.
@item %O
Substitutes the suffix for object files. Note that this is
handled specially when it immediately follows @samp{%g, %u, or %U},
because of the need for those to form complete file names. The
handling is such that @samp{%O} is treated exactly as if it had already
been substituted, except that @samp{%g, %u, and %U} do not currently
support additional @var{suffix} characters following @samp{%O} as they would
following, for example, @samp{.o}.
@item %p
Substitutes the standard macro predefinitions for the
current target machine. Use this when running @code{cpp}.
@item %P
Like @samp{%p}, but puts @samp{__} before and after the name of each
predefined macro, except for macros that start with @samp{__} or with
@samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
C@.
@item %I
Substitute a @option{-iprefix} option made from @env{GCC_EXEC_PREFIX}.
@item %s
Current argument is the name of a library or startup file of some sort.
Search for that file in a standard list of directories and substitute
the full name found.
@item %e@var{str}
Print @var{str} as an error message. @var{str} is terminated by a newline.
Use this when inconsistent options are detected.
@item %|
Output @samp{-} if the input for the current command is coming from a pipe.
@item %(@var{name})
Substitute the contents of spec string @var{name} at this point.
@item %[@var{name}]
Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
@item %x@{@var{option}@}
Accumulate an option for @samp{%X}.
@item %X
Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
spec string.
@item %Y
Output the accumulated assembler options specified by @option{-Wa}.
@item %Z
Output the accumulated preprocessor options specified by @option{-Wp}.
@item %v1
Substitute the major version number of GCC@.
(For version 2.9.5, this is 2.)
@item %v2
Substitute the minor version number of GCC@.
(For version 2.9.5, this is 9.)
@item %v3
Substitute the patch level number of GCC@.
(For version 2.9.5, this is 5.)
@item %a
Process the @code{asm} spec. This is used to compute the
switches to be passed to the assembler.
@item %A
Process the @code{asm_final} spec. This is a spec string for
passing switches to an assembler post-processor, if such a program is
needed.
@item %l
Process the @code{link} spec. This is the spec for computing the
command line passed to the linker. Typically it will make use of the
@samp{%L %G %S %D and %E} sequences.
@item %D
Dump out a @option{-L} option for each directory that GCC believes might
contain startup files. If the target supports multilibs then the
current multilib directory will be prepended to each of these paths.
@item %M
Output the multilib directory with directory separators replaced with
@samp{_}. If multilib directories are not set, or the multilib directory is
@file{.} then this option emits nothing.
@item %L
Process the @code{lib} spec. This is a spec string for deciding which
libraries should be included on the command line to the linker.
@item %G
Process the @code{libgcc} spec. This is a spec string for deciding
which GCC support library should be included on the command line to the linker.
@item %S
Process the @code{startfile} spec. This is a spec for deciding which
object files should be the first ones passed to the linker. Typically
this might be a file named @file{crt0.o}.
@item %E
Process the @code{endfile} spec. This is a spec string that specifies
the last object files that will be passed to the linker.
@item %C
Process the @code{cpp} spec. This is used to construct the arguments
to be passed to the C preprocessor.
@item %c
Process the @code{signed_char} spec. This is intended to be used
to tell cpp whether a char is signed. It typically has the definition:
@smallexample
%@{funsigned-char:-D__CHAR_UNSIGNED__@}
@end smallexample
@item %1
Process the @code{cc1} spec. This is used to construct the options to be
passed to the actual C compiler (@samp{cc1}).
@item %2
Process the @code{cc1plus} spec. This is used to construct the options to be
passed to the actual C++ compiler (@samp{cc1plus}).
@item %*
Substitute the variable part of a matched option. See below.
Note that each comma in the substituted string is replaced by
a single space.
@item %@{@code{S}@}
Substitutes the @code{-S} switch, if that switch was given to GCC@.
If that switch was not specified, this substitutes nothing. Note that
the leading dash is omitted when specifying this option, and it is
automatically inserted if the substitution is performed. Thus the spec
string @samp{%@{foo@}} would match the command-line option @option{-foo}
and would output the command line option @option{-foo}.
@item %W@{@code{S}@}
Like %@{@code{S}@} but mark last argument supplied within as a file to be
deleted on failure.
@item %@{@code{S}*@}
Substitutes all the switches specified to GCC whose names start
with @code{-S}, but which also take an argument. This is used for
switches like @option{-o}, @option{-D}, @option{-I}, etc.
GCC considers @option{-o foo} as being
one switch whose names starts with @samp{o}. %@{o*@} would substitute this
text, including the space. Thus two arguments would be generated.
@item %@{^@code{S}*@}
Like %@{@code{S}*@}, but don't put a blank between a switch and its
argument. Thus %@{^o*@} would only generate one argument, not two.
@item %@{@code{S}*&@code{T}*@}
Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
(the order of @code{S} and @code{T} in the spec is not significant).
There can be any number of ampersand-separated variables; for each the
wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
@item %@{<@code{S}@}
Remove all occurrences of @code{-S} from the command line. Note---this
command is position dependent. @samp{%} commands in the spec string
before this option will see @code{-S}, @samp{%} commands in the spec
string after this option will not.
@item %@{@code{S}*:@code{X}@}
Substitutes @code{X} if one or more switches whose names start with
@code{-S} are specified to GCC@. Note that the tail part of the
@code{-S} option (i.e.@: the part matched by the @samp{*}) will be substituted
for each occurrence of @samp{%*} within @code{X}.
@item %@{@code{S}:@code{X}@}
Substitutes @code{X}, but only if the @samp{-S} switch was given to GCC@.
@item %@{!@code{S}:@code{X}@}
Substitutes @code{X}, but only if the @samp{-S} switch was @emph{not} given to GCC@.
@item %@{|@code{S}:@code{X}@}
Like %@{@code{S}:@code{X}@}, but if no @code{S} switch, substitute @samp{-}.
@item %@{|!@code{S}:@code{X}@}
Like %@{!@code{S}:@code{X}@}, but if there is an @code{S} switch, substitute @samp{-}.
@item %@{.@code{S}:@code{X}@}
Substitutes @code{X}, but only if processing a file with suffix @code{S}.
@item %@{!.@code{S}:@code{X}@}
Substitutes @code{X}, but only if @emph{not} processing a file with suffix @code{S}.
@item %@{@code{S}|@code{P}:@code{X}@}
Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@. This may be
combined with @samp{!} and @samp{.} sequences as well, although they
have a stronger binding than the @samp{|}. For example a spec string
like this:
@smallexample
%@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
@end smallexample
will output the following command-line options from the following input
command-line options:
@smallexample
fred.c -foo -baz
jim.d -bar -boggle
-d fred.c -foo -baz -boggle
-d jim.d -bar -baz -boggle
@end smallexample
@end table
The conditional text @code{X} in a %@{@code{S}:@code{X}@} or
%@{!@code{S}:@code{X}@} construct may contain other nested @samp{%} constructs
or spaces, or even newlines. They are processed as usual, as described
above.
The @option{-O}, @option{-f}, @option{-m}, and @option{-W}
switches are handled specifically in these
constructs. If another value of @option{-O} or the negated form of a @option{-f}, @option{-m}, or
@option{-W} switch is found later in the command line, the earlier switch
value is ignored, except with @{@code{S}*@} where @code{S} is just one
letter, which passes all matching options.
The character @samp{|} at the beginning of the predicate text is used to indicate
that a command should be piped to the following command, but only if @option{-pipe}
is specified.
It is built into GCC which switches take arguments and which do not.
(You might think it would be useful to generalize this to allow each
compiler's spec to say which switches take arguments. But this cannot
be done in a consistent fashion. GCC cannot even decide which input
files have been specified without knowing which switches take arguments,
and it must know which input files to compile in order to tell which
compilers to run).
GCC also knows implicitly that arguments starting in @option{-l} are to be
treated as compiler output files, and passed to the linker in their
proper position among the other output files.
@c man begin OPTIONS
@node Target Options
@section Specifying Target Machine and Compiler Version
@cindex target options
@cindex cross compiling
@cindex specifying machine version
@cindex specifying compiler version and target machine
@cindex compiler version, specifying
@cindex target machine, specifying
By default, GCC compiles code for the same type of machine that you
are using. However, it can also be installed as a cross-compiler, to
compile for some other type of machine. In fact, several different
configurations of GCC, for different target machines, can be
installed side by side. Then you specify which one to use with the
@option{-b} option.
In addition, older and newer versions of GCC can be installed side
by side. One of them (probably the newest) will be the default, but
you may sometimes wish to use another.
@table @gcctabopt
@item -b @var{machine}
@opindex b
The argument @var{machine} specifies the target machine for compilation.
This is useful when you have installed GCC as a cross-compiler.
The value to use for @var{machine} is the same as was specified as the
machine type when configuring GCC as a cross-compiler. For
example, if a cross-compiler was configured with @samp{configure
i386v}, meaning to compile for an 80386 running System V, then you
would specify @option{-b i386v} to run that cross compiler.
When you do not specify @option{-b}, it normally means to compile for
the same type of machine that you are using.
@item -V @var{version}
@opindex V
The argument @var{version} specifies which version of GCC to run.
This is useful when multiple versions are installed. For example,
@var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
The default version, when you do not specify @option{-V}, is the last
version of GCC that you installed.
@end table
The @option{-b} and @option{-V} options actually work by controlling part of
the file name used for the executable files and libraries used for
compilation. A given version of GCC, for a given target machine, is
normally kept in the directory @file{/usr/local/lib/gcc-lib/@var{machine}/@var{version}}.
Thus, sites can customize the effect of @option{-b} or @option{-V} either by
changing the names of these directories or adding alternate names (or
symbolic links). If in directory @file{/usr/local/lib/gcc-lib/} the
file @file{80386} is a link to the file @file{i386v}, then @option{-b
80386} becomes an alias for @option{-b i386v}.
In one respect, the @option{-b} or @option{-V} do not completely change
to a different compiler: the top-level driver program @command{gcc}
that you originally invoked continues to run and invoke the other
executables (preprocessor, compiler per se, assembler and linker)
that do the real work. However, since no real work is done in the
driver program, it usually does not matter that the driver program
in use is not the one for the specified target. It is common for the
interface to the other executables to change incompatibly between
compiler versions, so unless the version specified is very close to that
of the driver (for example, @option{-V 3.0} with a driver program from GCC
version 3.0.1), use of @option{-V} may not work; for example, using
@option{-V 2.95.2} will not work with a driver program from GCC 3.0.
The only way that the driver program depends on the target machine is
in the parsing and handling of special machine-specific options.
However, this is controlled by a file which is found, along with the
other executables, in the directory for the specified version and
target machine. As a result, a single installed driver program adapts
to any specified target machine, and sufficiently similar compiler
versions.
The driver program executable does control one significant thing,
however: the default version and target machine. Therefore, you can
install different instances of the driver program, compiled for
different targets or versions, under different names.
For example, if the driver for version 2.0 is installed as @command{ogcc}
and that for version 2.1 is installed as @command{gcc}, then the command
@command{gcc} will use version 2.1 by default, while @command{ogcc} will use
2.0 by default. However, you can choose either version with either
command with the @option{-V} option.
@node Submodel Options
@section Hardware Models and Configurations
@cindex submodel options
@cindex specifying hardware config
@cindex hardware models and configurations, specifying
@cindex machine dependent options
Earlier we discussed the standard option @option{-b} which chooses among
different installed compilers for completely different target
machines, such as VAX vs.@: 68000 vs.@: 80386.
In addition, each of these target machine types can have its own
special options, starting with @samp{-m}, to choose among various
hardware models or configurations---for example, 68010 vs 68020,
floating coprocessor or none. A single installed version of the
compiler can compile for any model or configuration, according to the
options specified.
Some configurations of the compiler also support additional special
options, usually for compatibility with other compilers on the same
platform.
These options are defined by the macro @code{TARGET_SWITCHES} in the
machine description. The default for the options is also defined by
that macro, which enables you to change the defaults.
@menu
* M680x0 Options::
* M68hc1x Options::
* VAX Options::
* SPARC Options::
* Convex Options::
* AMD29K Options::
* ARM Options::
* MN10200 Options::
* MN10300 Options::
* M32R/D Options::
* M88K Options::
* RS/6000 and PowerPC Options::
* RT Options::
* MIPS Options::
* i386 and x86-64 Options::
* HPPA Options::
* Intel 960 Options::
* DEC Alpha Options::
* DEC Alpha/VMS Options::
* Clipper Options::
* H8/300 Options::
* SH Options::
* System V Options::
* TMS320C3x/C4x Options::
* V850 Options::
* ARC Options::
* NS32K Options::
* AVR Options::
* MCore Options::
* IA-64 Options::
* D30V Options::
* S/390 and zSeries Options::
* CRIS Options::
* MMIX Options::
@end menu
@node M680x0 Options
@subsection M680x0 Options
@cindex M680x0 options
These are the @samp{-m} options defined for the 68000 series. The default
values for these options depends on which style of 68000 was selected when
the compiler was configured; the defaults for the most common choices are
given below.
@table @gcctabopt
@item -m68000
@itemx -mc68000
@opindex m68000
@opindex mc68000
Generate output for a 68000. This is the default
when the compiler is configured for 68000-based systems.
Use this option for microcontrollers with a 68000 or EC000 core,
including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
@item -m68020
@itemx -mc68020
@opindex m68020
@opindex mc68020
Generate output for a 68020. This is the default
when the compiler is configured for 68020-based systems.
@item -m68881
@opindex m68881
Generate output containing 68881 instructions for floating point.
This is the default for most 68020 systems unless @option{--nfp} was
specified when the compiler was configured.
@item -m68030
@opindex m68030
Generate output for a 68030. This is the default when the compiler is
configured for 68030-based systems.
@item -m68040
@opindex m68040
Generate output for a 68040. This is the default when the compiler is
configured for 68040-based systems.
This option inhibits the use of 68881/68882 instructions that have to be
emulated by software on the 68040. Use this option if your 68040 does not
have code to emulate those instructions.
@item -m68060
@opindex m68060
Generate output for a 68060. This is the default when the compiler is
configured for 68060-based systems.
This option inhibits the use of 68020 and 68881/68882 instructions that
have to be emulated by software on the 68060. Use this option if your 68060
does not have code to emulate those instructions.
@item -mcpu32
@opindex mcpu32
Generate output for a CPU32. This is the default
when the compiler is configured for CPU32-based systems.
Use this option for microcontrollers with a
CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
68336, 68340, 68341, 68349 and 68360.
@item -m5200
@opindex m5200
Generate output for a 520X ``coldfire'' family cpu. This is the default
when the compiler is configured for 520X-based systems.
Use this option for microcontroller with a 5200 core, including
the MCF5202, MCF5203, MCF5204 and MCF5202.
@item -m68020-40
@opindex m68020-40
Generate output for a 68040, without using any of the new instructions.
This results in code which can run relatively efficiently on either a
68020/68881 or a 68030 or a 68040. The generated code does use the
68881 instructions that are emulated on the 68040.
@item -m68020-60
@opindex m68020-60
Generate output for a 68060, without using any of the new instructions.
This results in code which can run relatively efficiently on either a
68020/68881 or a 68030 or a 68040. The generated code does use the
68881 instructions that are emulated on the 68060.
@item -mfpa
@opindex mfpa
Generate output containing Sun FPA instructions for floating point.
@item -msoft-float
@opindex msoft-float
Generate output containing library calls for floating point.
@strong{Warning:} the requisite libraries are not available for all m68k
targets. Normally the facilities of the machine's usual C compiler are
used, but this can't be done directly in cross-compilation. You must
make your own arrangements to provide suitable library functions for
cross-compilation. The embedded targets @samp{m68k-*-aout} and
@samp{m68k-*-coff} do provide software floating point support.
@item -mshort
@opindex mshort
Consider type @code{int} to be 16 bits wide, like @code{short int}.
@item -mnobitfield
@opindex mnobitfield
Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
and @option{-m5200} options imply @w{@option{-mnobitfield}}.
@item -mbitfield
@opindex mbitfield
Do use the bit-field instructions. The @option{-m68020} option implies
@option{-mbitfield}. This is the default if you use a configuration
designed for a 68020.
@item -mrtd
@opindex mrtd
Use a different function-calling convention, in which functions
that take a fixed number of arguments return with the @code{rtd}
instruction, which pops their arguments while returning. This
saves one instruction in the caller since there is no need to pop
the arguments there.
This calling convention is incompatible with the one normally
used on Unix, so you cannot use it if you need to call libraries
compiled with the Unix compiler.
Also, you must provide function prototypes for all functions that
take variable numbers of arguments (including @code{printf});
otherwise incorrect code will be generated for calls to those
functions.
In addition, seriously incorrect code will result if you call a
function with too many arguments. (Normally, extra arguments are
harmlessly ignored.)
The @code{rtd} instruction is supported by the 68010, 68020, 68030,
68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
@item -malign-int
@itemx -mno-align-int
@opindex malign-int
@opindex mno-align-int
Control whether GCC aligns @code{int}, @code{long}, @code{long long},
@code{float}, @code{double}, and @code{long double} variables on a 32-bit
boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
Aligning variables on 32-bit boundaries produces code that runs somewhat
faster on processors with 32-bit busses at the expense of more memory.
@strong{Warning:} if you use the @option{-malign-int} switch, GCC will
align structures containing the above types differently than
most published application binary interface specifications for the m68k.
@item -mpcrel
@opindex mpcrel
Use the pc-relative addressing mode of the 68000 directly, instead of
using a global offset table. At present, this option implies @option{-fpic},
allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
not presently supported with @option{-mpcrel}, though this could be supported for
68020 and higher processors.
@item -mno-strict-align
@itemx -mstrict-align
@opindex mno-strict-align
@opindex mstrict-align
Do not (do) assume that unaligned memory references will be handled by
the system.
@end table
@node M68hc1x Options
@subsection M68hc1x Options
@cindex M68hc1x options
These are the @samp{-m} options defined for the 68hc11 and 68hc12
microcontrollers. The default values for these options depends on
which style of microcontroller was selected when the compiler was configured;
the defaults for the most common choices are given below.
@table @gcctabopt
@item -m6811
@itemx -m68hc11
@opindex m6811
@opindex m68hc11
Generate output for a 68HC11. This is the default
when the compiler is configured for 68HC11-based systems.
@item -m6812
@itemx -m68hc12
@opindex m6812
@opindex m68hc12
Generate output for a 68HC12. This is the default
when the compiler is configured for 68HC12-based systems.
@item -mauto-incdec
@opindex mauto-incdec
Enable the use of 68HC12 pre and post auto-increment and auto-decrement
addressing modes.
@item -mshort
@opindex mshort
Consider type @code{int} to be 16 bits wide, like @code{short int}.
@item -msoft-reg-count=@var{count}
@opindex msoft-reg-count
Specify the number of pseudo-soft registers which are used for the
code generation. The maximum number is 32. Using more pseudo-soft
register may or may not result in better code depending on the program.
The default is 4 for 68HC11 and 2 for 68HC12.
@end table
@node VAX Options
@subsection VAX Options
@cindex VAX options
These @samp{-m} options are defined for the VAX:
@table @gcctabopt
@item -munix
@opindex munix
Do not output certain jump instructions (@code{aobleq} and so on)
that the Unix assembler for the VAX cannot handle across long
ranges.
@item -mgnu
@opindex mgnu
Do output those jump instructions, on the assumption that you
will assemble with the GNU assembler.
@item -mg
@opindex mg
Output code for g-format floating point numbers instead of d-format.
@end table
@node SPARC Options
@subsection SPARC Options
@cindex SPARC options
These @samp{-m} switches are supported on the SPARC:
@table @gcctabopt
@item -mno-app-regs
@itemx -mapp-regs
@opindex mno-app-regs
@opindex mapp-regs
Specify @option{-mapp-regs} to generate output using the global registers
2 through 4, which the SPARC SVR4 ABI reserves for applications. This
is the default.
To be fully SVR4 ABI compliant at the cost of some performance loss,
specify @option{-mno-app-regs}. You should compile libraries and system
software with this option.
@item -mfpu
@itemx -mhard-float
@opindex mfpu
@opindex mhard-float
Generate output containing floating point instructions. This is the
default.
@item -mno-fpu
@itemx -msoft-float
@opindex mno-fpu
@opindex msoft-float
Generate output containing library calls for floating point.
@strong{Warning:} the requisite libraries are not available for all SPARC
targets. Normally the facilities of the machine's usual C compiler are
used, but this cannot be done directly in cross-compilation. You must make
your own arrangements to provide suitable library functions for
cross-compilation. The embedded targets @samp{sparc-*-aout} and
@samp{sparclite-*-*} do provide software floating point support.
@option{-msoft-float} changes the calling convention in the output file;
therefore, it is only useful if you compile @emph{all} of a program with
this option. In particular, you need to compile @file{libgcc.a}, the
library that comes with GCC, with @option{-msoft-float} in order for
this to work.
@item -mhard-quad-float
@opindex mhard-quad-float
Generate output containing quad-word (long double) floating point
instructions.
@item -msoft-quad-float
@opindex msoft-quad-float
Generate output containing library calls for quad-word (long double)
floating point instructions. The functions called are those specified
in the SPARC ABI@. This is the default.
As of this writing, there are no sparc implementations that have hardware
support for the quad-word floating point instructions. They all invoke
a trap handler for one of these instructions, and then the trap handler
emulates the effect of the instruction. Because of the trap handler overhead,
this is much slower than calling the ABI library routines. Thus the
@option{-msoft-quad-float} option is the default.
@item -mno-epilogue
@itemx -mepilogue
@opindex mno-epilogue
@opindex mepilogue
With @option{-mepilogue} (the default), the compiler always emits code for
function exit at the end of each function. Any function exit in
the middle of the function (such as a return statement in C) will
generate a jump to the exit code at the end of the function.
With @option{-mno-epilogue}, the compiler tries to emit exit code inline
at every function exit.
@item -mno-flat
@itemx -mflat
@opindex mno-flat
@opindex mflat
With @option{-mflat}, the compiler does not generate save/restore instructions
and will use a ``flat'' or single register window calling convention.
This model uses %i7 as the frame pointer and is compatible with the normal
register window model. Code from either may be intermixed.
The local registers and the input registers (0--5) are still treated as
``call saved'' registers and will be saved on the stack as necessary.
With @option{-mno-flat} (the default), the compiler emits save/restore
instructions (except for leaf functions) and is the normal mode of operation.
@item -mno-unaligned-doubles
@itemx -munaligned-doubles
@opindex mno-unaligned-doubles
@opindex munaligned-doubles
Assume that doubles have 8 byte alignment. This is the default.
With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
alignment only if they are contained in another type, or if they have an
absolute address. Otherwise, it assumes they have 4 byte alignment.
Specifying this option avoids some rare compatibility problems with code
generated by other compilers. It is not the default because it results
in a performance loss, especially for floating point code.
@item -mno-faster-structs
@itemx -mfaster-structs
@opindex mno-faster-structs
@opindex mfaster-structs
With @option{-mfaster-structs}, the compiler assumes that structures
should have 8 byte alignment. This enables the use of pairs of
@code{ldd} and @code{std} instructions for copies in structure
assignment, in place of twice as many @code{ld} and @code{st} pairs.
However, the use of this changed alignment directly violates the Sparc
ABI@. Thus, it's intended only for use on targets where the developer
acknowledges that their resulting code will not be directly in line with
the rules of the ABI@.
@item -mv8
@itemx -msparclite
@opindex mv8
@opindex msparclite
These two options select variations on the SPARC architecture.
By default (unless specifically configured for the Fujitsu SPARClite),
GCC generates code for the v7 variant of the SPARC architecture.
@option{-mv8} will give you SPARC v8 code. The only difference from v7
code is that the compiler emits the integer multiply and integer
divide instructions which exist in SPARC v8 but not in SPARC v7.
@option{-msparclite} will give you SPARClite code. This adds the integer
multiply, integer divide step and scan (@code{ffs}) instructions which
exist in SPARClite but not in SPARC v7.
These options are deprecated and will be deleted in a future GCC release.
They have been replaced with @option{-mcpu=xxx}.
@item -mcypress
@itemx -msupersparc
@opindex mcypress
@opindex msupersparc
These two options select the processor for which the code is optimized.
With @option{-mcypress} (the default), the compiler optimizes code for the
Cypress CY7C602 chip, as used in the SparcStation/SparcServer 3xx series.
This is also appropriate for the older SparcStation 1, 2, IPX etc.
With @option{-msupersparc} the compiler optimizes code for the SuperSparc cpu, as
used in the SparcStation 10, 1000 and 2000 series. This flag also enables use
of the full SPARC v8 instruction set.
These options are deprecated and will be deleted in a future GCC release.
They have been replaced with @option{-mcpu=xxx}.
@item -mcpu=@var{cpu_type}
@opindex mcpu
Set the instruction set, register set, and instruction scheduling parameters
for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
@samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
@samp{hypersparc}, @samp{sparclite86x}, @samp{f930}, @samp{f934},
@samp{sparclet}, @samp{tsc701}, @samp{v9}, and @samp{ultrasparc}.
Default instruction scheduling parameters are used for values that select
an architecture and not an implementation. These are @samp{v7}, @samp{v8},
@samp{sparclite}, @samp{sparclet}, @samp{v9}.
Here is a list of each supported architecture and their supported
implementations.
@smallexample
v7: cypress
v8: supersparc, hypersparc
sparclite: f930, f934, sparclite86x
sparclet: tsc701
v9: ultrasparc
@end smallexample
@item -mtune=@var{cpu_type}
@opindex mtune
Set the instruction scheduling parameters for machine type
@var{cpu_type}, but do not set the instruction set or register set that the
option @option{-mcpu=@var{cpu_type}} would.
The same values for @option{-mcpu=@var{cpu_type}} can be used for
@option{-mtune=@var{cpu_type}}, but the only useful values are those
that select a particular cpu implementation. Those are @samp{cypress},
@samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
@samp{sparclite86x}, @samp{tsc701}, and @samp{ultrasparc}.
@end table
These @samp{-m} switches are supported in addition to the above
on the SPARCLET processor.
@table @gcctabopt
@item -mlittle-endian
@opindex mlittle-endian
Generate code for a processor running in little-endian mode.
@item -mlive-g0
@opindex mlive-g0
Treat register @code{%g0} as a normal register.
GCC will continue to clobber it as necessary but will not assume
it always reads as 0.
@item -mbroken-saverestore
@opindex mbroken-saverestore
Generate code that does not use non-trivial forms of the @code{save} and
@code{restore} instructions. Early versions of the SPARCLET processor do
not correctly handle @code{save} and @code{restore} instructions used with
arguments. They correctly handle them used without arguments. A @code{save}
instruction used without arguments increments the current window pointer
but does not allocate a new stack frame. It is assumed that the window
overflow trap handler will properly handle this case as will interrupt
handlers.
@end table
These @samp{-m} switches are supported in addition to the above
on SPARC V9 processors in 64-bit environments.
@table @gcctabopt
@item -mlittle-endian
@opindex mlittle-endian
Generate code for a processor running in little-endian mode.
@item -m32
@itemx -m64
@opindex m32
@opindex m64
Generate code for a 32-bit or 64-bit environment.
The 32-bit environment sets int, long and pointer to 32 bits.
The 64-bit environment sets int to 32 bits and long and pointer
to 64 bits.
@item -mcmodel=medlow
@opindex mcmodel=medlow
Generate code for the Medium/Low code model: the program must be linked
in the low 32 bits of the address space. Pointers are 64 bits.
Programs can be statically or dynamically linked.
@item -mcmodel=medmid
@opindex mcmodel=medmid
Generate code for the Medium/Middle code model: the program must be linked
in the low 44 bits of the address space, the text segment must be less than
2G bytes, and data segment must be within 2G of the text segment.
Pointers are 64 bits.
@item -mcmodel=medany
@opindex mcmodel=medany
Generate code for the Medium/Anywhere code model: the program may be linked
anywhere in the address space, the text segment must be less than
2G bytes, and data segment must be within 2G of the text segment.
Pointers are 64 bits.
@item -mcmodel=embmedany
@opindex mcmodel=embmedany
Generate code for the Medium/Anywhere code model for embedded systems:
assume a 32-bit text and a 32-bit data segment, both starting anywhere
(determined at link time). Register %g4 points to the base of the
data segment. Pointers are still 64 bits.
Programs are statically linked, PIC is not supported.
@item -mstack-bias
@itemx -mno-stack-bias
@opindex mstack-bias
@opindex mno-stack-bias
With @option{-mstack-bias}, GCC assumes that the stack pointer, and
frame pointer if present, are offset by @minus{}2047 which must be added back
when making stack frame references.
Otherwise, assume no such offset is present.
@end table
@node Convex Options
@subsection Convex Options
@cindex Convex options
These @samp{-m} options are defined for Convex:
@table @gcctabopt
@item -mc1
@opindex mc1
Generate output for C1. The code will run on any Convex machine.
The preprocessor symbol @code{__convex__c1__} is defined.
@item -mc2
@opindex mc2
Generate output for C2. Uses instructions not available on C1.
Scheduling and other optimizations are chosen for max performance on C2.
The preprocessor symbol @code{__convex_c2__} is defined.
@item -mc32
@opindex mc32
Generate output for C32xx. Uses instructions not available on C1.
Scheduling and other optimizations are chosen for max performance on C32.
The preprocessor symbol @code{__convex_c32__} is defined.
@item -mc34
@opindex mc34
Generate output for C34xx. Uses instructions not available on C1.
Scheduling and other optimizations are chosen for max performance on C34.
The preprocessor symbol @code{__convex_c34__} is defined.
@item -mc38
@opindex mc38
Generate output for C38xx. Uses instructions not available on C1.
Scheduling and other optimizations are chosen for max performance on C38.
The preprocessor symbol @code{__convex_c38__} is defined.
@item -margcount
@opindex margcount
Generate code which puts an argument count in the word preceding each
argument list. This is compatible with regular CC, and a few programs
may need the argument count word. GDB and other source-level debuggers
do not need it; this info is in the symbol table.
@item -mnoargcount
@opindex mnoargcount
Omit the argument count word. This is the default.
@item -mvolatile-cache
@opindex mvolatile-cache
Allow volatile references to be cached. This is the default.
@item -mvolatile-nocache
@opindex mvolatile-nocache
Volatile references bypass the data cache, going all the way to memory.
This is only needed for multi-processor code that does not use standard
synchronization instructions. Making non-volatile references to volatile
locations will not necessarily work.
@item -mlong32
@opindex mlong32
Type long is 32 bits, the same as type int. This is the default.
@item -mlong64
@opindex mlong64
Type long is 64 bits, the same as type long long. This option is useless,
because no library support exists for it.
@end table
@node AMD29K Options
@subsection AMD29K Options
@cindex AMD29K options
These @samp{-m} options are defined for the AMD Am29000:
@table @gcctabopt
@item -mdw
@opindex mdw
@cindex DW bit (29k)
Generate code that assumes the @code{DW} bit is set, i.e., that byte and
halfword operations are directly supported by the hardware. This is the
default.
@item -mndw
@opindex mndw
Generate code that assumes the @code{DW} bit is not set.
@item -mbw
@opindex mbw
@cindex byte writes (29k)
Generate code that assumes the system supports byte and halfword write
operations. This is the default.
@item -mnbw
@opindex mnbw
Generate code that assumes the systems does not support byte and
halfword write operations. @option{-mnbw} implies @option{-mndw}.
@item -msmall
@opindex msmall
@cindex memory model (29k)
Use a small memory model that assumes that all function addresses are
either within a single 256 KB segment or at an absolute address of less
than 256k. This allows the @code{call} instruction to be used instead
of a @code{const}, @code{consth}, @code{calli} sequence.
@item -mnormal
@opindex mnormal
Use the normal memory model: Generate @code{call} instructions only when
calling functions in the same file and @code{calli} instructions
otherwise. This works if each file occupies less than 256 KB but allows
the entire executable to be larger than 256 KB@. This is the default.
@item -mlarge
@opindex mlarge
Always use @code{calli} instructions. Specify this option if you expect
a single file to compile into more than 256 KB of code.
@item -m29050
@opindex m29050
@cindex processor selection (29k)
Generate code for the Am29050.
@item -m29000
@opindex m29000
Generate code for the Am29000. This is the default.
@item -mkernel-registers
@opindex mkernel-registers
@cindex kernel and user registers (29k)
Generate references to registers @code{gr64-gr95} instead of to
registers @code{gr96-gr127}. This option can be used when compiling
kernel code that wants a set of global registers disjoint from that used
by user-mode code.
Note that when this option is used, register names in @samp{-f} flags
must use the normal, user-mode, names.
@item -muser-registers
@opindex muser-registers
Use the normal set of global registers, @code{gr96-gr127}. This is the
default.
@item -mstack-check
@itemx -mno-stack-check
@opindex mstack-check
@opindex mno-stack-check
@cindex stack checks (29k)
Insert (or do not insert) a call to @code{__msp_check} after each stack
adjustment. This is often used for kernel code.
@item -mstorem-bug
@itemx -mno-storem-bug
@opindex mstorem-bug
@opindex mno-storem-bug
@cindex storem bug (29k)
@option{-mstorem-bug} handles 29k processors which cannot handle the
separation of a mtsrim insn and a storem instruction (most 29000 chips
to date, but not the 29050).
@item -mno-reuse-arg-regs
@itemx -mreuse-arg-regs
@opindex mno-reuse-arg-regs
@opindex mreuse-arg-regs
@option{-mno-reuse-arg-regs} tells the compiler to only use incoming argument
registers for copying out arguments. This helps detect calling a function
with fewer arguments than it was declared with.
@item -mno-impure-text
@itemx -mimpure-text
@opindex mno-impure-text
@opindex mimpure-text
@option{-mimpure-text}, used in addition to @option{-shared}, tells the compiler to
not pass @option{-assert pure-text} to the linker when linking a shared object.
@item -msoft-float
@opindex msoft-float
Generate output containing library calls for floating point.
@strong{Warning:} the requisite libraries are not part of GCC@.
Normally the facilities of the machine's usual C compiler are used, but
this can't be done directly in cross-compilation. You must make your
own arrangements to provide suitable library functions for
cross-compilation.
@item -mno-multm
@opindex mno-multm
Do not generate multm or multmu instructions. This is useful for some embedded
systems which do not have trap handlers for these instructions.
@end table
@node ARM Options
@subsection ARM Options
@cindex ARM options
These @samp{-m} options are defined for Advanced RISC Machines (ARM)
architectures:
@table @gcctabopt
@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 will cause the stack frames not to be generated for
leaf functions. The default is @option{-mno-apcs-frame}.
@item -mapcs
@opindex mapcs
This is a synonym for @option{-mapcs-frame}.
@item -mapcs-26
@opindex mapcs-26
Generate code for a processor running with a 26-bit program counter,
and conforming to the function calling standards for the APCS 26-bit
option. This option replaces the @option{-m2} and @option{-m3} options
of previous releases of the compiler.
@item -mapcs-32
@opindex mapcs-32
Generate code for a processor running with a 32-bit program counter,
and conforming to the function calling standards for the APCS 32-bit
option. This option replaces the @option{-m6} option of previous releases
of the compiler.
@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
@samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
called, depending upon the amount of stack space required. The run time
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-float
@opindex mapcs-float
Pass floating point arguments using the float point registers. This is
one of the variants of the APCS@. This option is recommended if the
target hardware has a floating point unit or if a lot of floating point
arithmetic is going to be performed by the code. The default is
@option{-mno-apcs-float}, since integer only code is slightly increased in
size if @option{-mapcs-float} is used.
@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 which supports calling between the ARM and Thumb
instruction sets. Without this option 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.
@item -mno-sched-prolog
@opindex mno-sched-prolog
Prevent the reordering of instructions in the function prolog, or the
merging of those instruction with the instructions in the function's
body. This means that all functions will 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 if functions inside an executable piece of code. The
default is @option{-msched-prolog}.
@item -mhard-float
@opindex mhard-float
Generate output containing floating point instructions. This is the
default.
@item -msoft-float
@opindex msoft-float
Generate output containing library calls for floating point.
@strong{Warning:} the requisite libraries are not available for all ARM
targets. Normally the facilities of the machine's usual C compiler are
used, but this cannot be done directly in cross-compilation. You must make
your own arrangements to provide suitable library functions for
cross-compilation.
@option{-msoft-float} changes the calling convention in the output file;
therefore, it is only useful if you compile @emph{all} of a program with
this option. In particular, you need to compile @file{libgcc.a}, the
library that comes with GCC, with @option{-msoft-float} in order for
this to work.
@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 -mwords-little-endian
@opindex mwords-little-endian
This option only applies when generating code for big-endian processors.
Generate code for a little-endian word order but a big-endian byte
order. That is, a byte order of the form @samp{32107654}. Note: this
option should only be used if you require compatibility with code for
big-endian ARM processors generated by versions of the compiler prior to
2.8.
@item -malignment-traps
@opindex malignment-traps
Generate code that will not trap if the MMU has alignment traps enabled.
On ARM architectures prior to ARMv4, there were no instructions to
access half-word objects stored in memory. However, when reading from
memory a feature of the ARM architecture allows a word load to be used,
even if the address is unaligned, and the processor core will rotate the
data as it is being loaded. This option tells the compiler that such
misaligned accesses will cause a MMU trap and that it should instead
synthesise the access as a series of byte accesses. The compiler can
still use word accesses to load half-word data if it knows that the
address is aligned to a word boundary.
This option is ignored when compiling for ARM architecture 4 or later,
since these processors have instructions to directly access half-word
objects in memory.
@item -mno-alignment-traps
@opindex mno-alignment-traps
Generate code that assumes that the MMU will not trap unaligned
accesses. This produces better code when the target instruction set
does not have half-word memory operations (i.e.@: implementations prior to
ARMv4).
Note that you cannot use this option to access unaligned word objects,
since the processor will only fetch one 32-bit aligned object from
memory.
The default setting for most targets is @option{-mno-alignment-traps}, since
this produces better code when there are no half-word memory
instructions available.
@item -mshort-load-bytes
@itemx -mno-short-load-words
@opindex mshort-load-bytes
@opindex mno-short-load-words
These are deprecated aliases for @option{-malignment-traps}.
@item -mno-short-load-bytes
@itemx -mshort-load-words
@opindex mno-short-load-bytes
@opindex mshort-load-words
This are deprecated aliases for @option{-mno-alignment-traps}.
@item -mbsd
@opindex mbsd
This option only applies to RISC iX@. Emulate the native BSD-mode
compiler. This is the default if @option{-ansi} is not specified.
@item -mxopen
@opindex mxopen
This option only applies to RISC iX@. Emulate the native X/Open-mode
compiler.
@item -mno-symrename
@opindex mno-symrename
This option only applies to RISC iX@. Do not run the assembler
post-processor, @samp{symrename}, after code has been assembled.
Normally it is necessary to modify some of the standard symbols in
preparation for linking with the RISC iX C library; this option
suppresses this pass. The post-processor is never run when the
compiler is built for cross-compilation.
@item -mcpu=@var{name}
@opindex mcpu
This specifies the name of the target ARM processor. GCC uses this name
to determine what kind of instructions it can emit when generating
assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
@samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
@samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
@samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
@samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
@samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm8},
@samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
@samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
@samp{arm920t}, @samp{arm940t}, @samp{arm9tdmi}, @samp{arm10tdmi},
@samp{arm1020t}, @samp{xscale}.
@itemx -mtune=@var{name}
@opindex mtune
This option is very similar to the @option{-mcpu=} option, except that
instead of specifying the actual target processor type, and hence
restricting which instructions can be used, it specifies that GCC should
tune the performance of the code as if the target were of the type
specified in this option, but still choosing the instructions that it
will generate based on the cpu specified by a @option{-mcpu=} option.
For some ARM implementations better performance can be obtained by using
this option.
@item -march=@var{name}
@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{armv2},
@samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
@samp{armv5}, @samp{armv5t}, @samp{armv5te}.
@item -mfpe=@var{number}
@itemx -mfp=@var{number}
@opindex mfpe
@opindex mfp
This specifies the version of the floating point emulation available on
the target. Permissible values are 2 and 3. @option{-mfp=} is a synonym
for @option{-mfpe=}, for compatibility with older versions of GCC@.
@item -mstructure-size-boundary=@var{n}
@opindex mstructure-size-boundary
The size of all structures and unions will be rounded up to a multiple
of the number of bits set by this option. Permissible values are 8 and
32. The default value varies for different toolchains. For the COFF
targeted toolchain the default value is 8. Specifying the larger number
can produce faster, more efficient code, but can also increase the size
of the program. The two values are potentially incompatible. Code
compiled with one value cannot necessarily expect to work with code or
libraries compiled with the other value, if they exchange information
using structures or unions.
@item -mabort-on-noreturn
@opindex mabort-on-noreturn
Generate a call to the function @code{abort} at the end of a
@code{noreturn} function. It will be executed if the function tries to
return.
@item -mlong-calls
@itemx -mno-long-calls
@opindex mlong-calls
@opindex mno-long-calls
Tells the compiler to perform function calls by first loading the
address of the function into a register and then performing a subroutine
call on this register. This switch is needed if the target function
will lie outside of the 64 megabyte addressing range of the offset based
version of subroutine call instruction.
Even if this switch is enabled, not all function calls will be turned
into long calls. The heuristic is that static functions, functions
which have the @samp{short-call} attribute, functions that are inside
the scope of a @samp{#pragma no_long_calls} directive and functions whose
definitions have already been compiled within the current compilation
unit, will not be turned into long calls. The exception to this rule is
that weak function definitions, functions with the @samp{long-call}
attribute or the @samp{section} attribute, and functions that are within
the scope of a @samp{#pragma long_calls} directive, will always be
turned into long calls.
This feature is not enabled by default. Specifying
@option{-mno-long-calls} will restore the default behavior, as will
placing the function calls within the scope of a @samp{#pragma
long_calls_off} directive. Note these switches have no effect on how
the compiler generates code to handle function calls via function
pointers.
@item -mnop-fun-dllimport
@opindex mnop-fun-dllimport
Disable support for the @code{dllimport} attribute.
@item -msingle-pic-base
@opindex msingle-pic-base
Treat the register used for PIC addressing as read-only, rather than
loading it in the prologue for each function. The run-time system is
responsible for initializing this register with an appropriate value
before execution begins.
@item -mpic-register=@var{reg}
@opindex mpic-register
Specify the register to be used for PIC addressing. The default is R10
unless stack-checking is enabled, when R9 is used.
@item -mpoke-function-name
@opindex mpoke-function-name
Write the name of each function into the text section, directly
preceding the function prologue. The generated code is similar to this:
@smallexample
t0
.ascii "arm_poke_function_name", 0
.align
t1
.word 0xff000000 + (t1 - t0)
arm_poke_function_name
mov ip, sp
stmfd sp!, @{fp, ip, lr, pc@}
sub fp, ip, #4
@end smallexample
When performing a stack backtrace, code can inspect the value of
@code{pc} stored at @code{fp + 0}. If the trace function then looks at
location @code{pc - 12} and the top 8 bits are set, then we know that
there is a function name embedded immediately preceding this location
and has length @code{((pc[-3]) & 0xff000000)}.
@item -mthumb
@opindex mthumb
Generate code for the 16-bit Thumb instruction set. The default is to
use the 32-bit ARM instruction set.
@item -mtpcs-frame
@opindex mtpcs-frame
Generate a stack frame that is compliant with the Thumb Procedure Call
Standard for all non-leaf functions. (A leaf function is one that does
not call any other functions.) The default is @option{-mno-tpcs-frame}.
@item -mtpcs-leaf-frame
@opindex mtpcs-leaf-frame
Generate a stack frame that is compliant with the Thumb Procedure Call
Standard for all leaf functions. (A leaf function is one that does
not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
@item -mcallee-super-interworking
@opindex mcallee-super-interworking
Gives all externally visible functions in the file being compiled an ARM
instruction set header which switches to Thumb mode before executing the
rest of the function. This allows these functions to be called from
non-interworking code.
@item -mcaller-super-interworking
@opindex mcaller-super-interworking
Allows calls via function pointers (including virtual functions) to
execute correctly regardless of whether the target code has been
compiled for interworking or not. There is a small overhead in the cost
of executing a function pointer if this option is enabled.
@end table
@node MN10200 Options
@subsection MN10200 Options
@cindex MN10200 options
These @option{-m} options are defined for Matsushita MN10200 architectures:
@table @gcctabopt
@item -mrelax
@opindex mrelax
Indicate to the linker that it should perform a relaxation optimization pass
to shorten branches, calls and absolute memory addresses. This option only
has an effect when used on the command line for the final link step.
This option makes symbolic debugging impossible.
@end table
@node MN10300 Options
@subsection MN10300 Options
@cindex MN10300 options
These @option{-m} options are defined for Matsushita MN10300 architectures:
@table @gcctabopt
@item -mmult-bug
@opindex mmult-bug
Generate code to avoid bugs in the multiply instructions for the MN10300
processors. This is the default.
@item -mno-mult-bug
@opindex mno-mult-bug
Do not generate code to avoid bugs in the multiply instructions for the
MN10300 processors.
@item -mam33
@opindex mam33
Generate code which uses features specific to the AM33 processor.
@item -mno-am33
@opindex mno-am33
Do not generate code which uses features specific to the AM33 processor. This
is the default.
@item -mno-crt0
@opindex mno-crt0
Do not link in the C run-time initialization object file.
@item -mrelax
@opindex mrelax
Indicate to the linker that it should perform a relaxation optimization pass
to shorten branches, calls and absolute memory addresses. This option only
has an effect when used on the command line for the final link step.
This option makes symbolic debugging impossible.
@end table
@node M32R/D Options
@subsection M32R/D Options
@cindex M32R/D options
These @option{-m} options are defined for Mitsubishi M32R/D architectures:
@table @gcctabopt
@item -m32rx
@opindex m32rx
Generate code for the M32R/X@.
@item -m32r
@opindex m32r
Generate code for the M32R@. This is the default.
@item -mcode-model=small
@opindex mcode-model=small
Assume all objects live in the lower 16MB of memory (so that their addresses
can be loaded with the @code{ld24} instruction), and assume all subroutines
are reachable with the @code{bl} instruction.
This is the default.
The addressability of a particular object can be set with the
@code{model} attribute.
@item -mcode-model=medium
@opindex mcode-model=medium
Assume objects may be anywhere in the 32-bit address space (the compiler
will generate @code{seth/add3} instructions to load their addresses), and
assume all subroutines are reachable with the @code{bl} instruction.
@item -mcode-model=large
@opindex mcode-model=large
Assume objects may be anywhere in the 32-bit address space (the compiler
will generate @code{seth/add3} instructions to load their addresses), and
assume subroutines may not be reachable with the @code{bl} instruction
(the compiler will generate the much slower @code{seth/add3/jl}
instruction sequence).
@item -msdata=none
@opindex msdata=none
Disable use of the small data area. Variables will be put into
one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
@code{section} attribute has been specified).
This is the default.
The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
Objects may be explicitly put in the small data area with the
@code{section} attribute using one of these sections.
@item -msdata=sdata
@opindex msdata=sdata
Put small global and static data in the small data area, but do not
generate special code to reference them.
@item -msdata=use
@opindex msdata=use
Put small global and static data in the small data area, and generate
special instructions to reference them.
@item -G @var{num}
@opindex G
@cindex smaller data references
Put global and static objects less than or equal to @var{num} bytes
into the small data or bss sections instead of the normal data or bss
sections. The default value of @var{num} is 8.
The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
for this option to have any effect.
All modules should be compiled with the same @option{-G @var{num}} value.
Compiling with different values of @var{num} may or may not work; if it
doesn't the linker will give an error message---incorrect code will not be
generated.
@end table
@node M88K Options
@subsection M88K Options
@cindex M88k options
These @samp{-m} options are defined for Motorola 88k architectures:
@table @gcctabopt
@item -m88000
@opindex m88000
Generate code that works well on both the m88100 and the
m88110.
@item -m88100
@opindex m88100
Generate code that works best for the m88100, but that also
runs on the m88110.
@item -m88110
@opindex m88110
Generate code that works best for the m88110, and may not run
on the m88100.
@item -mbig-pic
@opindex mbig-pic
Obsolete option to be removed from the next revision.
Use @option{-fPIC}.
@item -midentify-revision
@opindex midentify-revision
@cindex identifying source, compiler (88k)
Include an @code{ident} directive in the assembler output recording the
source file name, compiler name and version, timestamp, and compilation
flags used.
@item -mno-underscores
@opindex mno-underscores
@cindex underscores, avoiding (88k)
In assembler output, emit symbol names without adding an underscore
character at the beginning of each name. The default is to use an
underscore as prefix on each name.
@item -mocs-debug-info
@itemx -mno-ocs-debug-info
@opindex mocs-debug-info
@opindex mno-ocs-debug-info
@cindex OCS (88k)
@cindex debugging, 88k OCS
Include (or omit) additional debugging information (about registers used
in each stack frame) as specified in the 88open Object Compatibility
Standard, ``OCS''@. This extra information allows debugging of code that
has had the frame pointer eliminated. The default for DG/UX, SVr4, and
Delta 88 SVr3.2 is to include this information; other 88k configurations
omit this information by default.
@item -mocs-frame-position
@opindex mocs-frame-position
@cindex register positions in frame (88k)
When emitting COFF debugging information for automatic variables and
parameters stored on the stack, use the offset from the canonical frame
address, which is the stack pointer (register 31) on entry to the
function. The DG/UX, SVr4, Delta88 SVr3.2, and BCS configurations use
@option{-mocs-frame-position}; other 88k configurations have the default
@option{-mno-ocs-frame-position}.
@item -mno-ocs-frame-position
@opindex mno-ocs-frame-position
@cindex register positions in frame (88k)
When emitting COFF debugging information for automatic variables and
parameters stored on the stack, use the offset from the frame pointer
register (register 30). When this option is in effect, the frame
pointer is not eliminated when debugging information is selected by the
-g switch.
@item -moptimize-arg-area
@opindex moptimize-arg-area
@cindex arguments in frame (88k)
Save space by reorganizing the stack frame. This option generates code
that does not agree with the 88open specifications, but uses less
memory.
@itemx -mno-optimize-arg-area
@opindex mno-optimize-arg-area
Do not reorganize the stack frame to save space. This is the default.
The generated conforms to the specification, but uses more memory.
@item -mshort-data-@var{num}
@opindex mshort-data
@cindex smaller data references (88k)
@cindex r0-relative references (88k)
Generate smaller data references by making them relative to @code{r0},
which allows loading a value using a single instruction (rather than the
usual two). You control which data references are affected by
specifying @var{num} with this option. For example, if you specify
@option{-mshort-data-512}, then the data references affected are those
involving displacements of less than 512 bytes.
@option{-mshort-data-@var{num}} is not effective for @var{num} greater
than 64k.
@item -mserialize-volatile
@opindex mserialize-volatile
@itemx -mno-serialize-volatile
@opindex mno-serialize-volatile
@cindex sequential consistency on 88k
Do, or don't, generate code to guarantee sequential consistency
of volatile memory references. By default, consistency is
guaranteed.
The order of memory references made by the MC88110 processor does
not always match the order of the instructions requesting those
references. In particular, a load instruction may execute before
a preceding store instruction. Such reordering violates
sequential consistency of volatile memory references, when there
are multiple processors. When consistency must be guaranteed,
GCC generates special instructions, as needed, to force
execution in the proper order.
The MC88100 processor does not reorder memory references and so
always provides sequential consistency. However, by default, GCC
generates the special instructions to guarantee consistency
even when you use @option{-m88100}, so that the code may be run on an
MC88110 processor. If you intend to run your code only on the
MC88100 processor, you may use @option{-mno-serialize-volatile}.
The extra code generated to guarantee consistency may affect the
performance of your application. If you know that you can safely
forgo this guarantee, you may use @option{-mno-serialize-volatile}.
@item -msvr4
@itemx -msvr3
@opindex msvr4
@opindex msvr3
@cindex assembler syntax, 88k
@cindex SVr4
Turn on (@option{-msvr4}) or off (@option{-msvr3}) compiler extensions
related to System V release 4 (SVr4). This controls the following:
@enumerate
@item
Which variant of the assembler syntax to emit.
@item
@option{-msvr4} makes the C preprocessor recognize @samp{#pragma weak}
that is used on System V release 4.
@item
@option{-msvr4} makes GCC issue additional declaration directives used in
SVr4.
@end enumerate
@option{-msvr4} is the default for the m88k-motorola-sysv4 and
m88k-dg-dgux m88k configurations. @option{-msvr3} is the default for all
other m88k configurations.
@item -mversion-03.00
@opindex mversion-03.00
This option is obsolete, and is ignored.
@c ??? which asm syntax better for GAS? option there too?
@item -mno-check-zero-division
@itemx -mcheck-zero-division
@opindex mno-check-zero-division
@opindex mcheck-zero-division
@cindex zero division on 88k
Do, or don't, generate code to guarantee that integer division by
zero will be detected. By default, detection is guaranteed.
Some models of the MC88100 processor fail to trap upon integer
division by zero under certain conditions. By default, when
compiling code that might be run on such a processor, GCC
generates code that explicitly checks for zero-valued divisors
and traps with exception number 503 when one is detected. Use of
@option{-mno-check-zero-division} suppresses such checking for code
generated to run on an MC88100 processor.
GCC assumes that the MC88110 processor correctly detects all instances
of integer division by zero. When @option{-m88110} is specified, no
explicit checks for zero-valued divisors are generated, and both
@option{-mcheck-zero-division} and @option{-mno-check-zero-division} are
ignored.
@item -muse-div-instruction
@opindex muse-div-instruction
@cindex divide instruction, 88k
Use the div instruction for signed integer division on the
MC88100 processor. By default, the div instruction is not used.
On the MC88100 processor the signed integer division instruction
div) traps to the operating system on a negative operand. The
operating system transparently completes the operation, but at a
large cost in execution time. By default, when compiling code
that might be run on an MC88100 processor, GCC emulates signed
integer division using the unsigned integer division instruction
divu), thereby avoiding the large penalty of a trap to the
operating system. Such emulation has its own, smaller, execution
cost in both time and space. To the extent that your code's
important signed integer division operations are performed on two
nonnegative operands, it may be desirable to use the div
instruction directly.
On the MC88110 processor the div instruction (also known as the
divs instruction) processes negative operands without trapping to
the operating system. When @option{-m88110} is specified,
@option{-muse-div-instruction} is ignored, and the div instruction is used
for signed integer division.
Note that the result of dividing @code{INT_MIN} by @minus{}1 is undefined. In
particular, the behavior of such a division with and without
@option{-muse-div-instruction} may differ.
@item -mtrap-large-shift
@itemx -mhandle-large-shift
@opindex mtrap-large-shift
@opindex mhandle-large-shift
@cindex bit shift overflow (88k)
@cindex large bit shifts (88k)
Include code to detect bit-shifts of more than 31 bits; respectively,
trap such shifts or emit code to handle them properly. By default GCC
makes no special provision for large bit shifts.
@item -mwarn-passed-structs
@opindex mwarn-passed-structs
@cindex structure passing (88k)
Warn when a function passes a struct as an argument or result.
Structure-passing conventions have changed during the evolution of the C
language, and are often the source of portability problems. By default,
GCC issues no such warning.
@end table
@c break page here to avoid unsightly interparagraph stretch.
@c -zw, 2001-8-17
@page
@node RS/6000 and PowerPC Options
@subsection IBM RS/6000 and PowerPC Options
@cindex RS/6000 and PowerPC Options
@cindex IBM RS/6000 and PowerPC Options
These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
@table @gcctabopt
@item -mpower
@itemx -mno-power
@itemx -mpower2
@itemx -mno-power2
@itemx -mpowerpc
@itemx -mno-powerpc
@itemx -mpowerpc-gpopt
@itemx -mno-powerpc-gpopt
@itemx -mpowerpc-gfxopt
@itemx -mno-powerpc-gfxopt
@itemx -mpowerpc64
@itemx -mno-powerpc64
@opindex mpower
@opindex mno-power
@opindex mpower2
@opindex mno-power2
@opindex mpowerpc
@opindex mno-powerpc
@opindex mpowerpc-gpopt
@opindex mno-powerpc-gpopt
@opindex mpowerpc-gfxopt
@opindex mno-powerpc-gfxopt
@opindex mpowerpc64
@opindex mno-powerpc64
GCC supports two related instruction set architectures for the
RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
instructions supported by the @samp{rios} chip set used in the original
RS/6000 systems and the @dfn{PowerPC} instruction set is the
architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
the IBM 4xx microprocessors.
Neither architecture is a subset of the other. However there is a
large common subset of instructions supported by both. An MQ
register is included in processors supporting the POWER architecture.
You use these options to specify which instructions are available on the
processor you are using. The default value of these options is
determined when configuring GCC@. Specifying the
@option{-mcpu=@var{cpu_type}} overrides the specification of these
options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
rather than the options listed above.
The @option{-mpower} option allows GCC to generate instructions that
are found only in the POWER architecture and to use the MQ register.
Specifying @option{-mpower2} implies @option{-power} and also allows GCC
to generate instructions that are present in the POWER2 architecture but
not the original POWER architecture.
The @option{-mpowerpc} option allows GCC to generate instructions that
are found only in the 32-bit subset of the PowerPC architecture.
Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
GCC to use the optional PowerPC architecture instructions in the
General Purpose group, including floating-point square root. Specifying
@option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
use the optional PowerPC architecture instructions in the Graphics
group, including floating-point select.
The @option{-mpowerpc64} option allows GCC to generate the additional
64-bit instructions that are found in the full PowerPC64 architecture
and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
@option{-mno-powerpc64}.
If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
will use only the instructions in the common subset of both
architectures plus some special AIX common-mode calls, and will not use
the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
permits GCC to use any instruction from either architecture and to
allow use of the MQ register; specify this for the Motorola MPC601.
@item -mnew-mnemonics
@itemx -mold-mnemonics
@opindex mnew-mnemonics
@opindex mold-mnemonics
Select which mnemonics to use in the generated assembler code. With
@option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
the PowerPC architecture. With @option{-mold-mnemonics} it uses the
assembler mnemonics defined for the POWER architecture. Instructions
defined in only one architecture have only one mnemonic; GCC uses that
mnemonic irrespective of which of these options is specified.
GCC defaults to the mnemonics appropriate for the architecture in
use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
value of these option. Unless you are building a cross-compiler, you
should normally not specify either @option{-mnew-mnemonics} or
@option{-mold-mnemonics}, but should instead accept the default.
@item -mcpu=@var{cpu_type}
@opindex mcpu
Set architecture type, register usage, choice of mnemonics, and
instruction scheduling parameters for machine type @var{cpu_type}.
Supported values for @var{cpu_type} are @samp{rios}, @samp{rios1},
@samp{rsc}, @samp{rios2}, @samp{rs64a}, @samp{601}, @samp{602},
@samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620},
@samp{630}, @samp{740}, @samp{7400}, @samp{7450}, @samp{750},
@samp{power}, @samp{power2}, @samp{powerpc}, @samp{403}, @samp{505},
@samp{801}, @samp{821}, @samp{823}, and @samp{860} and @samp{common}.
@option{-mcpu=common} selects a completely generic processor. Code
generated under this option will run on any POWER or PowerPC processor.
GCC will use only the instructions in the common subset of both
architectures, and will not use the MQ register. GCC assumes a generic
processor model for scheduling purposes.
@option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
@option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
types, with an appropriate, generic processor model assumed for
scheduling purposes.
The other options specify a specific processor. Code generated under
those options will run best on that processor, and may not run at all on
others.
The @option{-mcpu} options automatically enable or disable other
@option{-m} options as follows:
@table @samp
@item common
@option{-mno-power}, @option{-mno-powerc}
@item power
@itemx power2
@itemx rios1
@itemx rios2
@itemx rsc
@option{-mpower}, @option{-mno-powerpc}, @option{-mno-new-mnemonics}
@item powerpc
@itemx rs64a
@itemx 602
@itemx 603
@itemx 603e
@itemx 604
@itemx 620
@itemx 630
@itemx 740
@itemx 7400
@itemx 7450
@itemx 750
@itemx 505
@option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}
@item 601
@option{-mpower}, @option{-mpowerpc}, @option{-mnew-mnemonics}
@item 403
@itemx 821
@itemx 860
@option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}, @option{-msoft-float}
@end table
@item -mtune=@var{cpu_type}
@opindex mtune
Set the instruction scheduling parameters for machine type
@var{cpu_type}, but do not set the architecture type, register usage, or
choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
values for @var{cpu_type} are used for @option{-mtune} as for
@option{-mcpu}. If both are specified, the code generated will use the
architecture, registers, and mnemonics set by @option{-mcpu}, but the
scheduling parameters set by @option{-mtune}.
@item -maltivec
@itemx -mno-altivec
@opindex maltivec
@opindex mno-altivec
These switches enable or disable the use of built-in functions that
allow access to the AltiVec instruction set. You may also need to set
@option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
enhancements.
@item -mfull-toc
@itemx -mno-fp-in-toc
@itemx -mno-sum-in-toc
@itemx -mminimal-toc
@opindex mfull-toc
@opindex mno-fp-in-toc
@opindex mno-sum-in-toc
@opindex mminimal-toc
Modify generation of the TOC (Table Of Contents), which is created for
every executable file. The @option{-mfull-toc} option is selected by
default. In that case, GCC will allocate at least one TOC entry for
each unique non-automatic variable reference in your program. GCC
will also place floating-point constants in the TOC@. However, only
16,384 entries are available in the TOC@.
If you receive a linker error message that saying you have overflowed
the available TOC space, you can reduce the amount of TOC space used
with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
@option{-mno-fp-in-toc} prevents GCC from putting floating-point
constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
generate code to calculate the sum of an address and a constant at
run-time instead of putting that sum into the TOC@. You may specify one
or both of these options. Each causes GCC to produce very slightly
slower and larger code at the expense of conserving TOC space.
If you still run out of space in the TOC even when you specify both of
these options, specify @option{-mminimal-toc} instead. This option causes
GCC to make only one TOC entry for every file. When you specify this
option, GCC will produce code that is slower and larger but which
uses extremely little TOC space. You may wish to use this option
only on files that contain less frequently executed code.
@item -maix64
@itemx -maix32
@opindex maix64
@opindex maix32
Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
@code{long} type, and the infrastructure needed to support them.
Specifying @option{-maix64} implies @option{-mpowerpc64} and
@option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
@item -mxl-call
@itemx -mno-xl-call
@opindex mxl-call
@opindex mno-xl-call
On AIX, pass floating-point arguments to prototyped functions beyond the
register save area (RSA) on the stack in addition to argument FPRs. The
AIX calling convention was extended but not initially documented to
handle an obscure K&R C case of calling a function that takes the
address of its arguments with fewer arguments than declared. AIX XL
compilers access floating point arguments which do not fit in the
RSA from the stack when a subroutine is compiled without
optimization. Because always storing floating-point arguments on the
stack is inefficient and rarely needed, this option is not enabled by
default and only is necessary when calling subroutines compiled by AIX
XL compilers without optimization.
@item -mthreads
@opindex mthreads
Support @dfn{AIX Threads}. Link an application written to use
@dfn{pthreads} with special libraries and startup code to enable the
application to run.
@item -mpe
@opindex mpe
Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
application written to use message passing with special startup code to
enable the application to run. The system must have PE installed in the
standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
must be overridden with the @option{-specs=} option to specify the
appropriate directory location. The Parallel Environment does not
support threads, so the @option{-mpe} option and the @option{-mthreads}
option are incompatible.
@item -msoft-float
@itemx -mhard-float
@opindex msoft-float
@opindex mhard-float
Generate code that does not use (uses) the floating-point register set.
Software floating point emulation is provided if you use the
@option{-msoft-float} option, and pass the option to GCC when linking.
@item -mmultiple
@itemx -mno-multiple
@opindex mmultiple
@opindex mno-multiple
Generate code that uses (does not use) the load multiple word
instructions and the store multiple word instructions. These
instructions are generated by default on POWER systems, and not
generated on PowerPC systems. Do not use @option{-mmultiple} on little
endian PowerPC systems, since those instructions do not work when the
processor is in little endian mode. The exceptions are PPC740 and
PPC750 which permit the instructions usage in little endian mode.
@item -mstring
@itemx -mno-string
@opindex mstring
@opindex mno-string
Generate code that uses (does not use) the load string instructions
and the store string word instructions to save multiple registers and
do small block moves. These instructions are generated by default on
POWER systems, and not generated on PowerPC systems. Do not use
@option{-mstring} on little endian PowerPC systems, since those
instructions do not work when the processor is in little endian mode.
The exceptions are PPC740 and PPC750 which permit the instructions
usage in little endian mode.
@item -mupdate
@itemx -mno-update
@opindex mupdate
@opindex mno-update
Generate code that uses (does not use) the load or store instructions
that update the base register to the address of the calculated memory
location. These instructions are generated by default. If you use
@option{-mno-update}, there is a small window between the time that the
stack pointer is updated and the address of the previous frame is
stored, which means code that walks the stack frame across interrupts or
signals may get corrupted data.
@item -mfused-madd
@itemx -mno-fused-madd
@opindex mfused-madd
@opindex mno-fused-madd
Generate code that uses (does not use) the floating point multiply and
accumulate instructions. These instructions are generated by default if
hardware floating is used.
@item -mno-bit-align
@itemx -mbit-align
@opindex mno-bit-align
@opindex mbit-align
On System V.4 and embedded PowerPC systems do not (do) force structures
and unions that contain bit-fields to be aligned to the base type of the
bit-field.
For example, by default a structure containing nothing but 8
@code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
the structure would be aligned to a 1 byte boundary and be one byte in
size.
@item -mno-strict-align
@itemx -mstrict-align
@opindex mno-strict-align
@opindex mstrict-align
On System V.4 and embedded PowerPC systems do not (do) assume that
unaligned memory references will be handled by the system.
@item -mrelocatable
@itemx -mno-relocatable
@opindex mrelocatable
@opindex mno-relocatable
On embedded PowerPC systems generate code that allows (does not allow)
the program to be relocated to a different address at runtime. If you
use @option{-mrelocatable} on any module, all objects linked together must
be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
@item -mrelocatable-lib
@itemx -mno-relocatable-lib
@opindex mrelocatable-lib
@opindex mno-relocatable-lib
On embedded PowerPC systems generate code that allows (does not allow)
the program to be relocated to a different address at runtime. Modules
compiled with @option{-mrelocatable-lib} can be linked with either modules
compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
with modules compiled with the @option{-mrelocatable} options.
@item -mno-toc
@itemx -mtoc
@opindex mno-toc
@opindex mtoc
On System V.4 and embedded PowerPC systems do not (do) assume that
register 2 contains a pointer to a global area pointing to the addresses
used in the program.
@item -mlittle
@itemx -mlittle-endian
@opindex mlittle
@opindex mlittle-endian
On System V.4 and embedded PowerPC systems compile code for the
processor in little endian mode. The @option{-mlittle-endian} option is
the same as @option{-mlittle}.
@item -mbig
@itemx -mbig-endian
@opindex mbig
@opindex mbig-endian
On System V.4 and embedded PowerPC systems compile code for the
processor in big endian mode. The @option{-mbig-endian} option is
the same as @option{-mbig}.
@item -mcall-sysv
@opindex mcall-sysv
On System V.4 and embedded PowerPC systems compile code using calling
conventions that adheres to the March 1995 draft of the System V
Application Binary Interface, PowerPC processor supplement. This is the
default unless you configured GCC using @samp{powerpc-*-eabiaix}.
@item -mcall-sysv-eabi
@opindex mcall-sysv-eabi
Specify both @option{-mcall-sysv} and @option{-meabi} options.
@item -mcall-sysv-noeabi
@opindex mcall-sysv-noeabi
Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
@item -mcall-aix
@opindex mcall-aix
On System V.4 and embedded PowerPC systems compile code using calling
conventions that are similar to those used on AIX@. This is the
default if you configured GCC using @samp{powerpc-*-eabiaix}.
@item -mcall-solaris
@opindex mcall-solaris
On System V.4 and embedded PowerPC systems compile code for the Solaris
operating system.
@item -mcall-linux
@opindex mcall-linux
On System V.4 and embedded PowerPC systems compile code for the
Linux-based GNU system.
@item -mcall-netbsd
@opindex mcall-netbsd
On System V.4 and embedded PowerPC systems compile code for the
NetBSD operating system.
@item -maix-struct-return
@opindex maix-struct-return
Return all structures in memory (as specified by the AIX ABI)@.
@item -msvr4-struct-return
@opindex msvr4-struct-return
Return structures smaller than 8 bytes in registers (as specified by the
SVR4 ABI)@.
@item -mabi=altivec
@opindex mabi=altivec
Extend the current ABI with AltiVec ABI extensions. This does not
change the default ABI, instead it adds the AltiVec ABI extensions to
the current ABI@.
@item -mprototype
@itemx -mno-prototype
@opindex mprototype
@opindex mno-prototype
On System V.4 and embedded PowerPC systems assume that all calls to
variable argument functions are properly prototyped. Otherwise, the
compiler must insert an instruction before every non prototyped call to
set or clear bit 6 of the condition code register (@var{CR}) to
indicate whether floating point values were passed in the floating point
registers in case the function takes a variable arguments. With
@option{-mprototype}, only calls to prototyped variable argument functions
will set or clear the bit.
@item -msim
@opindex msim
On embedded PowerPC systems, assume that the startup module is called
@file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
@file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
configurations.
@item -mmvme
@opindex mmvme
On embedded PowerPC systems, assume that the startup module is called
@file{crt0.o} and the standard C libraries are @file{libmvme.a} and
@file{libc.a}.
@item -mads
@opindex mads
On embedded PowerPC systems, assume that the startup module is called
@file{crt0.o} and the standard C libraries are @file{libads.a} and
@file{libc.a}.
@item -myellowknife
@opindex myellowknife
On embedded PowerPC systems, assume that the startup module is called
@file{crt0.o} and the standard C libraries are @file{libyk.a} and
@file{libc.a}.
@item -mvxworks
@opindex mvxworks
On System V.4 and embedded PowerPC systems, specify that you are
compiling for a VxWorks system.
@item -memb
@opindex memb
On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
header to indicate that @samp{eabi} extended relocations are used.
@item -meabi
@itemx -mno-eabi
@opindex meabi
@opindex mno-eabi
On System V.4 and embedded PowerPC systems do (do not) adhere to the
Embedded Applications Binary Interface (eabi) which is a set of
modifications to the System V.4 specifications. Selecting @option{-meabi}
means that the stack is aligned to an 8 byte boundary, a function
@code{__eabi} is called to from @code{main} to set up the eabi
environment, and the @option{-msdata} option can use both @code{r2} and
@code{r13} to point to two separate small data areas. Selecting
@option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
do not call an initialization function from @code{main}, and the
@option{-msdata} option will only use @code{r13} to point to a single
small data area. The @option{-meabi} option is on by default if you
configured GCC using one of the @samp{powerpc*-*-eabi*} options.
@item -msdata=eabi
@opindex msdata=eabi
On System V.4 and embedded PowerPC systems, put small initialized
@code{const} global and static data in the @samp{.sdata2} section, which
is pointed to by register @code{r2}. Put small initialized
non-@code{const} global and static data in the @samp{.sdata} section,
which is pointed to by register @code{r13}. Put small uninitialized
global and static data in the @samp{.sbss} section, which is adjacent to
the @samp{.sdata} section. The @option{-msdata=eabi} option is
incompatible with the @option{-mrelocatable} option. The
@option{-msdata=eabi} option also sets the @option{-memb} option.
@item -msdata=sysv
@opindex msdata=sysv
On System V.4 and embedded PowerPC systems, put small global and static
data in the @samp{.sdata} section, which is pointed to by register
@code{r13}. Put small uninitialized global and static data in the
@samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
The @option{-msdata=sysv} option is incompatible with the
@option{-mrelocatable} option.
@item -msdata=default
@itemx -msdata
@opindex msdata=default
@opindex msdata
On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
compile code the same as @option{-msdata=eabi}, otherwise compile code the
same as @option{-msdata=sysv}.
@item -msdata-data
@opindex msdata-data
On System V.4 and embedded PowerPC systems, put small global and static
data in the @samp{.sdata} section. Put small uninitialized global and
static data in the @samp{.sbss} section. Do not use register @code{r13}
to address small data however. This is the default behavior unless
other @option{-msdata} options are used.
@item -msdata=none
@itemx -mno-sdata
@opindex msdata=none
@opindex mno-sdata
On embedded PowerPC systems, put all initialized global and static data
in the @samp{.data} section, and all uninitialized data in the
@samp{.bss} section.
@item -G @var{num}
@opindex G
@cindex smaller data references (PowerPC)
@cindex .sdata/.sdata2 references (PowerPC)
On embedded PowerPC systems, put global and static items less than or
equal to @var{num} bytes into the small data or bss sections instead of
the normal data or bss section. By default, @var{num} is 8. The
@option{-G @var{num}} switch is also passed to the linker.
All modules should be compiled with the same @option{-G @var{num}} value.
@item -mregnames
@itemx -mno-regnames
@opindex mregnames
@opindex mno-regnames
On System V.4 and embedded PowerPC systems do (do not) emit register
names in the assembly language output using symbolic forms.
@end table
@node RT Options
@subsection IBM RT Options
@cindex RT options
@cindex IBM RT options
These @samp{-m} options are defined for the IBM RT PC:
@table @gcctabopt
@item -min-line-mul
@opindex min-line-mul
Use an in-line code sequence for integer multiplies. This is the
default.
@item -mcall-lib-mul
@opindex mcall-lib-mul
Call @code{lmul$$} for integer multiples.
@item -mfull-fp-blocks
@opindex mfull-fp-blocks
Generate full-size floating point data blocks, including the minimum
amount of scratch space recommended by IBM@. This is the default.
@item -mminimum-fp-blocks
@opindex mminimum-fp-blocks
Do not include extra scratch space in floating point data blocks. This
results in smaller code, but slower execution, since scratch space must
be allocated dynamically.
@cindex @file{varargs.h} and RT PC
@cindex @file{stdarg.h} and RT PC
@item -mfp-arg-in-fpregs
@opindex mfp-arg-in-fpregs
Use a calling sequence incompatible with the IBM calling convention in
which floating point arguments are passed in floating point registers.
Note that @code{varargs.h} and @code{stdarg.h} will not work with
floating point operands if this option is specified.
@item -mfp-arg-in-gregs
@opindex mfp-arg-in-gregs
Use the normal calling convention for floating point arguments. This is
the default.
@item -mhc-struct-return
@opindex mhc-struct-return
Return structures of more than one word in memory, rather than in a
register. This provides compatibility with the MetaWare HighC (hc)
compiler. Use the option @option{-fpcc-struct-return} for compatibility
with the Portable C Compiler (pcc).
@item -mnohc-struct-return
@opindex mnohc-struct-return
Return some structures of more than one word in registers, when
convenient. This is the default. For compatibility with the
IBM-supplied compilers, use the option @option{-fpcc-struct-return} or the
option @option{-mhc-struct-return}.
@end table
@node MIPS Options
@subsection MIPS Options
@cindex MIPS options
These @samp{-m} options are defined for the MIPS family of computers:
@table @gcctabopt
@item -march=@var{cpu-type}
@opindex march
Assume the defaults for the machine type @var{cpu-type} when generating
instructions. The choices for @var{cpu-type} are @samp{r2000}, @samp{r3000},
@samp{r3900}, @samp{r4000}, @samp{r4100}, @samp{r4300}, @samp{r4400},
@samp{r4600}, @samp{r4650}, @samp{r5000}, @samp{r6000}, @samp{r8000},
and @samp{orion}. Additionally, the @samp{r2000}, @samp{r3000},
@samp{r4000}, @samp{r5000}, and @samp{r6000} can be abbreviated as
@samp{r2k} (or @samp{r2K}), @samp{r3k}, etc.
@item -mtune=@var{cpu-type}
@opindex mtune
Assume the defaults for the machine type @var{cpu-type} when scheduling
instructions. The choices for @var{cpu-type} are @samp{r2000}, @samp{r3000},
@samp{r3900}, @samp{r4000}, @samp{r4100}, @samp{r4300}, @samp{r4400},
@samp{r4600}, @samp{r4650}, @samp{r5000}, @samp{r6000}, @samp{r8000},
and @samp{orion}. Additionally, the @samp{r2000}, @samp{r3000},
@samp{r4000}, @samp{r5000}, and @samp{r6000} can be abbreviated as
@samp{r2k} (or @samp{r2K}), @samp{r3k}, etc. While picking a specific
@var{cpu-type} will schedule things appropriately for that particular
chip, the compiler will not generate any code that does not meet level 1
of the MIPS ISA (instruction set architecture) without a @option{-mipsX}
or @option{-mabi} switch being used.
@item -mcpu=@var{cpu-type}
@opindex mcpu
This is identical to specifying both @option{-march} and @option{-mtune}.
@item -mips1
@opindex mips1
Issue instructions from level 1 of the MIPS ISA@. This is the default.
@samp{r3000} is the default @var{cpu-type} at this ISA level.
@item -mips2
@opindex mips2
Issue instructions from level 2 of the MIPS ISA (branch likely, square
root instructions). @samp{r6000} is the default @var{cpu-type} at this
ISA level.
@item -mips3
@opindex mips3
Issue instructions from level 3 of the MIPS ISA (64-bit instructions).
@samp{r4000} is the default @var{cpu-type} at this ISA level.
@item -mips4
@opindex mips4
Issue instructions from level 4 of the MIPS ISA (conditional move,
prefetch, enhanced FPU instructions). @samp{r8000} is the default
@var{cpu-type} at this ISA level.
@item -mfp32
@opindex mfp32
Assume that 32 32-bit floating point registers are available. This is
the default.
@item -mfp64
@opindex mfp64
Assume that 32 64-bit floating point registers are available. This is
the default when the @option{-mips3} option is used.
@item -mfused-madd
@itemx -mno-fused-madd
@opindex mfused-madd
@opindex mno-fused-madd
Generate code that uses (does not use) the floating point multiply and
accumulate instructions, when they are available. These instructions
are generated by default if they are available, but this may be
undesirable if the extra precision causes problems or on certain chips
in the mode where denormals are rounded to zero where denormals
generated by multiply and accumulate instructions cause exceptions
anyway.
@item -mgp32
@opindex mgp32
Assume that 32 32-bit general purpose registers are available. This is
the default.
@item -mgp64
@opindex mgp64
Assume that 32 64-bit general purpose registers are available. This is
the default when the @option{-mips3} option is used.
@item -mint64
@opindex mint64
Force int and long types to be 64 bits wide. See @option{-mlong32} for an
explanation of the default, and the width of pointers.
@item -mlong64
@opindex mlong64
Force long types to be 64 bits wide. See @option{-mlong32} for an
explanation of the default, and the width of pointers.
@item -mlong32
@opindex mlong32
Force long, int, and pointer types to be 32 bits wide.
If none of @option{-mlong32}, @option{-mlong64}, or @option{-mint64} are set,
the size of ints, longs, and pointers depends on the ABI and ISA chosen.
For @option{-mabi=32}, and @option{-mabi=n32}, ints and longs are 32 bits
wide. For @option{-mabi=64}, ints are 32 bits, and longs are 64 bits wide.
For @option{-mabi=eabi} and either @option{-mips1} or @option{-mips2}, ints
and longs are 32 bits wide. For @option{-mabi=eabi} and higher ISAs, ints
are 32 bits, and longs are 64 bits wide. The width of pointer types is
the smaller of the width of longs or the width of general purpose
registers (which in turn depends on the ISA)@.
@item -mabi=32
@itemx -mabi=o64
@itemx -mabi=n32
@itemx -mabi=64
@itemx -mabi=eabi
@opindex mabi=32
@opindex mabi=o64
@opindex mabi=n32
@opindex mabi=64
@opindex mabi=eabi
Generate code for the indicated ABI@. The default instruction level is
@option{-mips1} for @samp{32}, @option{-mips3} for @samp{n32}, and
@option{-mips4} otherwise. Conversely, with @option{-mips1} or
@option{-mips2}, the default ABI is @samp{32}; otherwise, the default ABI
is @samp{64}.
@item -mmips-as
@opindex mmips-as
Generate code for the MIPS assembler, and invoke @file{mips-tfile} to
add normal debug information. This is the default for all
platforms except for the OSF/1 reference platform, using the OSF/rose
object format. If the either of the @option{-gstabs} or @option{-gstabs+}
switches are used, the @file{mips-tfile} program will encapsulate the
stabs within MIPS ECOFF@.
@item -mgas
@opindex mgas
Generate code for the GNU assembler. This is the default on the OSF/1
reference platform, using the OSF/rose object format. Also, this is
the default if the configure option @option{--with-gnu-as} is used.
@item -msplit-addresses
@itemx -mno-split-addresses
@opindex msplit-addresses
@opindex mno-split-addresses
Generate code to load the high and low parts of address constants separately.
This allows GCC to optimize away redundant loads of the high order
bits of addresses. This optimization requires GNU as and GNU ld.
This optimization is enabled by default for some embedded targets where
GNU as and GNU ld are standard.
@item -mrnames
@itemx -mno-rnames
@opindex mrnames
@opindex mno-rnames
The @option{-mrnames} switch says to output code using the MIPS software
names for the registers, instead of the hardware names (ie, @var{a0}
instead of @var{$4}). The only known assembler that supports this option
is the Algorithmics assembler.
@item -mgpopt
@itemx -mno-gpopt
@opindex mgpopt
@opindex mno-gpopt
The @option{-mgpopt} switch says to write all of the data declarations
before the instructions in the text section, this allows the MIPS
assembler to generate one word memory references instead of using two
words for short global or static data items. This is on by default if
optimization is selected.
@item -mstats
@itemx -mno-stats
@opindex mstats
@opindex mno-stats
For each non-inline function processed, the @option{-mstats} switch
causes the compiler to emit one line to the standard error file to
print statistics about the program (number of registers saved, stack
size, etc.).
@item -mmemcpy
@itemx -mno-memcpy
@opindex mmemcpy
@opindex mno-memcpy
The @option{-mmemcpy} switch makes all block moves call the appropriate
string function (@samp{memcpy} or @samp{bcopy}) instead of possibly
generating inline code.
@item -mmips-tfile
@itemx -mno-mips-tfile
@opindex mmips-tfile
@opindex mno-mips-tfile
The @option{-mno-mips-tfile} switch causes the compiler not
postprocess the object file with the @file{mips-tfile} program,
after the MIPS assembler has generated it to add debug support. If
@file{mips-tfile} is not run, then no local variables will be
available to the debugger. In addition, @file{stage2} and
@file{stage3} objects will have the temporary file names passed to the
assembler embedded in the object file, which means the objects will
not compare the same. The @option{-mno-mips-tfile} switch should only
be used when there are bugs in the @file{mips-tfile} program that
prevents compilation.
@item -msoft-float
@opindex msoft-float
Generate output containing library calls for floating point.
@strong{Warning:} the requisite libraries are not part of GCC@.
Normally the facilities of the machine's usual C compiler are used, but
this can't be done directly in cross-compilation. You must make your
own arrangements to provide suitable library functions for
cross-compilation.
@item -mhard-float
@opindex mhard-float
Generate output containing floating point instructions. This is the
default if you use the unmodified sources.
@item -mabicalls
@itemx -mno-abicalls
@opindex mabicalls
@opindex mno-abicalls
Emit (or do not emit) the pseudo operations @samp{.abicalls},
@samp{.cpload}, and @samp{.cprestore} that some System V.4 ports use for
position independent code.
@item -mlong-calls
@itemx -mno-long-calls
@opindex mlong-calls
@opindex mno-long-calls
Do all calls with the @samp{JALR} instruction, which requires
loading up a function's address into a register before the call.
You need to use this switch, if you call outside of the current
512 megabyte segment to functions that are not through pointers.
@item -mhalf-pic
@itemx -mno-half-pic
@opindex mhalf-pic
@opindex mno-half-pic
Put pointers to extern references into the data section and load them
up, rather than put the references in the text section.
@item -membedded-pic
@itemx -mno-embedded-pic
@opindex membedded-pic
@opindex mno-embedded-pic
Generate PIC code suitable for some embedded systems. All calls are
made using PC relative address, and all data is addressed using the $gp
register. No more than 65536 bytes of global data may be used. This
requires GNU as and GNU ld which do most of the work. This currently
only works on targets which use ECOFF; it does not work with ELF@.
@item -membedded-data
@itemx -mno-embedded-data
@opindex membedded-data
@opindex mno-embedded-data
Allocate variables to the read-only data section first if possible, then
next in the small data section if possible, otherwise in data. This gives
slightly slower code than the default, but reduces the amount of RAM required
when executing, and thus may be preferred for some embedded systems.
@item -muninit-const-in-rodata
@itemx -mno-uninit-const-in-rodata
@opindex muninit-const-in-rodata
@opindex mno-uninit-const-in-rodata
When used together with @option{-membedded-data}, it will always store uninitialized
const variables in the read-only data section.
@item -msingle-float
@itemx -mdouble-float
@opindex msingle-float
@opindex mdouble-float
The @option{-msingle-float} switch tells gcc to assume that the floating
point coprocessor only supports single precision operations, as on the
@samp{r4650} chip. The @option{-mdouble-float} switch permits gcc to use
double precision operations. This is the default.
@item -mmad
@itemx -mno-mad
@opindex mmad
@opindex mno-mad
Permit use of the @samp{mad}, @samp{madu} and @samp{mul} instructions,
as on the @samp{r4650} chip.
@item -m4650
@opindex m4650
Turns on @option{-msingle-float}, @option{-mmad}, and, at least for now,
@option{-mcpu=r4650}.
@item -mips16
@itemx -mno-mips16
@opindex mips16
@opindex mno-mips16
Enable 16-bit instructions.
@item -mentry
@opindex mentry
Use the entry and exit pseudo ops. This option can only be used with
@option{-mips16}.
@item -EL
@opindex EL
Compile code for the processor in little endian mode.
The requisite libraries are assumed to exist.
@item -EB
@opindex EB
Compile code for the processor in big endian mode.
The requisite libraries are assumed to exist.
@item -G @var{num}
@opindex G
@cindex smaller data references (MIPS)
@cindex gp-relative references (MIPS)
Put global and static items less than or equal to @var{num} bytes into
the small data or bss sections instead of the normal data or bss
section. This allows the assembler to emit one word memory reference
instructions based on the global pointer (@var{gp} or @var{$28}),
instead of the normal two words used. By default, @var{num} is 8 when
the MIPS assembler is used, and 0 when the GNU assembler is used. The
@option{-G @var{num}} switch is also passed to the assembler and linker.
All modules should be compiled with the same @option{-G @var{num}}
value.
@item -nocpp
@opindex nocpp
Tell the MIPS assembler to not run its preprocessor over user
assembler files (with a @samp{.s} suffix) when assembling them.
@item -mfix7000
@opindex mfix7000
Pass an option to gas which will cause nops to be inserted if
the read of the destination register of an mfhi or mflo instruction
occurs in the following two instructions.
@item -no-crt0
@opindex no-crt0
Do not include the default crt0.
@item -mflush-func=@var{func}
@itemx -mno-flush-func
@opindex mflush-func
Specifies the function to call to flush the I and D caches, or to not
call any such function. If called, the function must take the same
arguments as the common @code{_flush_func()}, that is, the address of the
memory range for which the cache is being flushed, the size of the
memory range, and the number 3 (to flush both caches). The default
depends on the target gcc was configured for, but commonly is either
@samp{_flush_func} or @samp{__cpu_flush}.
@end table
These options are defined by the macro
@code{TARGET_SWITCHES} in the machine description. The default for the
options is also defined by that macro, which enables you to change the
defaults.
@node i386 and x86-64 Options
@subsection Intel 386 and AMD x86-64 Options
@cindex i386 Options
@cindex x86-64 Options
@cindex Intel 386 Options
@cindex AMD x86-64 Options
These @samp{-m} options are defined for the i386 and x86-64 family of
computers:
@table @gcctabopt
@item -mcpu=@var{cpu-type}
@opindex mcpu
Tune to @var{cpu-type} everything applicable about the generated code, except
for the ABI and the set of available instructions. The choices for
@var{cpu-type} are @samp{i386}, @samp{i486}, @samp{i586}, @samp{i686},
@samp{pentium}, @samp{pentium-mmx}, @samp{pentiumpro}, @samp{pentium2},
@samp{pentium3}, @samp{pentium4}, @samp{k6}, @samp{k6-2}, @samp{k6-3},
@samp{athlon}, @samp{athlon-tbird}, @samp{athlon-4}, @samp{athlon-xp}
and @samp{athlon-mp}.
While picking a specific @var{cpu-type} will schedule things appropriately
for that particular chip, the compiler will not generate any code that
does not run on the i386 without the @option{-march=@var{cpu-type}} option
being used. @samp{i586} is equivalent to @samp{pentium} and @samp{i686}
is equivalent to @samp{pentiumpro}. @samp{k6} and @samp{athlon} are the
AMD chips as opposed to the Intel ones.
@item -march=@var{cpu-type}
@opindex march
Generate instructions for the machine type @var{cpu-type}. The choices
for @var{cpu-type} are the same as for @option{-mcpu}. Moreover,
specifying @option{-march=@var{cpu-type}} implies @option{-mcpu=@var{cpu-type}}.
@item -m386
@itemx -m486
@itemx -mpentium
@itemx -mpentiumpro
@opindex m386
@opindex m486
@opindex mpentium
@opindex mpentiumpro
These options are synonyms for @option{-mcpu=i386}, @option{-mcpu=i486},
@option{-mcpu=pentium}, and @option{-mcpu=pentiumpro} respectively.
These synonyms are deprecated.
@item -mfpmath=@var{unit}
@opindex march
generate floating point arithmetics for selected unit @var{unit}. the choices
for @var{unit} are:
@table @samp
@item 387
Use the standard 387 floating point coprocessor present majority of chips and
emulated otherwise. Code compiled with this option will run almost everywhere.
The temporary results are computed in 80bit precesion instead of precision
specified by the type resulting in slightly different results compared to most
of other chips. See @option{-ffloat-store} for more detailed description.
This is the default choice for i386 compiler.
@item sse
Use scalar floating point instructions present in the SSE instruction set.
This instruction set is supported by Pentium3 and newer chips, in the AMD line
by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
instruction set supports only single precision arithmetics, thus the double and
extended precision arithmetics is still done using 387. Later version, present
only in Pentium4 and the future AMD x86-64 chips supports double precision
arithmetics too.
For i387 you need to use @option{-march=@var{cpu-type}}, @option{-msse} or
@option{-msse2} switches to enable SSE extensions and make this option
effective. For x86-64 compiler, these extensions are enabled by default.
The resulting code should be considerably faster in majority of cases and avoid
the numerical instability problems of 387 code, but may break some existing
code that expects temporaries to be 80bit.
This is the default choice for x86-64 compiler.
@item sse,387
Attempt to utilize both instruction sets at once. This effectivly double the
amount of available registers and on chips with separate execution units for
387 and SSE the execution resources too. Use this option with care, as it is
still experimental, because gcc register allocator does not model separate
functional units well resulting in instable performance.
@end table
@item -masm=@var{dialect}
@opindex masm=@var{dialect}
Output asm instructions using selected @var{dialect}. Supported choices are
@samp{intel} or @samp{att} (the default one).
@item -mieee-fp
@itemx -mno-ieee-fp
@opindex mieee-fp
@opindex mno-ieee-fp
Control whether or not the compiler uses IEEE floating point
comparisons. These handle correctly the case where the result of a
comparison is unordered.
@item -msoft-float
@opindex msoft-float
Generate output containing library calls for floating point.
@strong{Warning:} the requisite libraries are not part of GCC@.
Normally the facilities of the machine's usual C compiler are used, but
this can't be done directly in cross-compilation. You must make your
own arrangements to provide suitable library functions for
cross-compilation.
On machines where a function returns floating point results in the 80387
register stack, some floating point opcodes may be emitted even if
@option{-msoft-float} is used.
@item -mno-fp-ret-in-387
@opindex mno-fp-ret-in-387
Do not use the FPU registers for return values of functions.
The usual calling convention has functions return values of types
@code{float} and @code{double} in an FPU register, even if there
is no FPU@. The idea is that the operating system should emulate
an FPU@.
The option @option{-mno-fp-ret-in-387} causes such values to be returned
in ordinary CPU registers instead.
@item -mno-fancy-math-387
@opindex mno-fancy-math-387
Some 387 emulators do not support the @code{sin}, @code{cos} and
@code{sqrt} instructions for the 387. Specify this option to avoid
generating those instructions. This option is the default on FreeBSD@.
As of revision 2.6.1, these instructions are not generated unless you
also use the @option{-funsafe-math-optimizations} switch.
@item -malign-double
@itemx -mno-align-double
@opindex malign-double
@opindex mno-align-double
Control whether GCC aligns @code{double}, @code{long double}, and
@code{long long} variables on a two word boundary or a one word
boundary. Aligning @code{double} variables on a two word boundary will
produce code that runs somewhat faster on a @samp{Pentium} at the
expense of more memory.
@item -m128bit-long-double
@opindex m128bit-long-double
Control the size of @code{long double} type. i386 application binary interface
specify the size to be 12 bytes, while modern architectures (Pentium and newer)
prefer @code{long double} aligned to 8 or 16 byte boundary. This is
impossible to reach with 12 byte long doubles in the array accesses.
@strong{Warning:} if you use the @option{-m128bit-long-double} switch, the
structures and arrays containing @code{long double} will change their size as
well as function calling convention for function taking @code{long double}
will be modified.
@item -m96bit-long-double
@opindex m96bit-long-double
Set the size of @code{long double} to 96 bits as required by the i386
application binary interface. This is the default.
@item -msvr3-shlib
@itemx -mno-svr3-shlib
@opindex msvr3-shlib
@opindex mno-svr3-shlib
Control whether GCC places uninitialized local variables into the
@code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
into @code{bss}. These options are meaningful only on System V Release 3.
@item -mrtd
@opindex mrtd
Use a different function-calling convention, in which functions that
take a fixed number of arguments return with the @code{ret} @var{num}
instruction, which pops their arguments while returning. This saves one
instruction in the caller since there is no need to pop the arguments
there.
You can specify that an individual function is called with this calling
sequence with the function attribute @samp{stdcall}. You can also
override the @option{-mrtd} option by using the function attribute
@samp{cdecl}. @xref{Function Attributes}.
@strong{Warning:} this calling convention is incompatible with the one
normally used on Unix, so you cannot use it if you need to call
libraries compiled with the Unix compiler.
Also, you must provide function prototypes for all functions that
take variable numbers of arguments (including @code{printf});
otherwise incorrect code will be generated for calls to those
functions.
In addition, seriously incorrect code will result if you call a
function with too many arguments. (Normally, extra arguments are
harmlessly ignored.)
@item -mregparm=@var{num}
@opindex mregparm
Control how many registers are used to pass integer arguments. By
default, no registers are used to pass arguments, and at most 3
registers can be used. You can control this behavior for a specific
function by using the function attribute @samp{regparm}.
@xref{Function Attributes}.
@strong{Warning:} if you use this switch, and
@var{num} is nonzero, then you must build all modules with the same
value, including any libraries. This includes the system libraries and
startup modules.
@item -mpreferred-stack-boundary=@var{num}
@opindex mpreferred-stack-boundary
Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
the default is 4 (16 bytes or 128 bits), except when optimizing for code
size (@option{-Os}), in which case the default is the minimum correct
alignment (4 bytes for x86, and 8 bytes for x86-64).
On Pentium and PentiumPro, @code{double} and @code{long double} values
should be aligned to an 8 byte boundary (see @option{-malign-double}) or
suffer significant run time performance penalties. On Pentium III, the
Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
penalties if it is not 16 byte aligned.
To ensure proper alignment of this values on the stack, the stack boundary
must be as aligned as that required by any value stored on the stack.
Further, every function must be generated such that it keeps the stack
aligned. Thus calling a function compiled with a higher preferred
stack boundary from a function compiled with a lower preferred stack
boundary will most likely misalign the stack. It is recommended that
libraries that use callbacks always use the default setting.
This extra alignment does consume extra stack space, and generally
increases code size. Code that is sensitive to stack space usage, such
as embedded systems and operating system kernels, may want to reduce the
preferred alignment to @option{-mpreferred-stack-boundary=2}.
@item -mmmx
@itemx -mno-mmx
@item -msse
@itemx -mno-sse
@item -msse2
@itemx -mno-sse2
@item -m3dnow
@itemx -mno-3dnow
@opindex mmmx
@opindex mno-mmx
@opindex msse
@opindex mno-sse
@opindex m3dnow
@opindex mno-3dnow
These switches enable or disable the use of built-in functions that allow
direct access to the MMX, SSE and 3Dnow extensions of the instruction set.
The following machine modes are available for use with MMX built-in functions
(@pxref{Vector Extensions}): @code{V2SI} for a vector of two 32 bit integers,
@code{V4HI} for a vector of four 16 bit integers, and @code{V8QI} for a
vector of eight 8 bit integers. Some of the built-in functions operate on
MMX registers as a whole 64 bit entity, these use @code{DI} as their mode.
If 3Dnow extensions are enabled, @code{V2SF} is used as a mode for a vector
of two 32 bit floating point values.
If SSE extensions are enabled, @code{V4SF} is used for a vector of four 32 bit
floating point values. Some instructions use a vector of four 32 bit
integers, these use @code{V4SI}. Finally, some instructions operate on an
entire vector register, interpreting it as a 128 bit integer, these use mode
@code{TI}.
The following built-in functions are made available by @option{-mmmx}:
@table @code
@item v8qi __builtin_ia32_paddb (v8qi, v8qi)
Generates the @code{paddb} machine instruction.
@item v4hi __builtin_ia32_paddw (v4hi, v4hi)
Generates the @code{paddw} machine instruction.
@item v2si __builtin_ia32_paddd (v2si, v2si)
Generates the @code{paddd} machine instruction.
@item v8qi __builtin_ia32_psubb (v8qi, v8qi)
Generates the @code{psubb} machine instruction.
@item v4hi __builtin_ia32_psubw (v4hi, v4hi)
Generates the @code{psubw} machine instruction.
@item v2si __builtin_ia32_psubd (v2si, v2si)
Generates the @code{psubd} machine instruction.
@item v8qi __builtin_ia32_paddsb (v8qi, v8qi)
Generates the @code{paddsb} machine instruction.
@item v4hi __builtin_ia32_paddsw (v4hi, v4hi)
Generates the @code{paddsw} machine instruction.
@item v8qi __builtin_ia32_psubsb (v8qi, v8qi)
Generates the @code{psubsb} machine instruction.
@item v4hi __builtin_ia32_psubsw (v4hi, v4hi)
Generates the @code{psubsw} machine instruction.
@item v8qi __builtin_ia32_paddusb (v8qi, v8qi)
Generates the @code{paddusb} machine instruction.
@item v4hi __builtin_ia32_paddusw (v4hi, v4hi)
Generates the @code{paddusw} machine instruction.
@item v8qi __builtin_ia32_psubusb (v8qi, v8qi)
Generates the @code{psubusb} machine instruction.
@item v4hi __builtin_ia32_psubusw (v4hi, v4hi)
Generates the @code{psubusw} machine instruction.
@item v4hi __builtin_ia32_pmullw (v4hi, v4hi)
Generates the @code{pmullw} machine instruction.
@item v4hi __builtin_ia32_pmulhw (v4hi, v4hi)
Generates the @code{pmulhw} machine instruction.
@item di __builtin_ia32_pand (di, di)
Generates the @code{pand} machine instruction.
@item di __builtin_ia32_pandn (di,di)
Generates the @code{pandn} machine instruction.
@item di __builtin_ia32_por (di, di)
Generates the @code{por} machine instruction.
@item di __builtin_ia32_pxor (di, di)
Generates the @code{pxor} machine instruction.
@item v8qi __builtin_ia32_pcmpeqb (v8qi, v8qi)
Generates the @code{pcmpeqb} machine instruction.
@item v4hi __builtin_ia32_pcmpeqw (v4hi, v4hi)
Generates the @code{pcmpeqw} machine instruction.
@item v2si __builtin_ia32_pcmpeqd (v2si, v2si)
Generates the @code{pcmpeqd} machine instruction.
@item v8qi __builtin_ia32_pcmpgtb (v8qi, v8qi)
Generates the @code{pcmpgtb} machine instruction.
@item v4hi __builtin_ia32_pcmpgtw (v4hi, v4hi)
Generates the @code{pcmpgtw} machine instruction.
@item v2si __builtin_ia32_pcmpgtd (v2si, v2si)
Generates the @code{pcmpgtd} machine instruction.
@item v8qi __builtin_ia32_punpckhbw (v8qi, v8qi)
Generates the @code{punpckhbw} machine instruction.
@item v4hi __builtin_ia32_punpckhwd (v4hi, v4hi)
Generates the @code{punpckhwd} machine instruction.
@item v2si __builtin_ia32_punpckhdq (v2si, v2si)
Generates the @code{punpckhdq} machine instruction.
@item v8qi __builtin_ia32_punpcklbw (v8qi, v8qi)
Generates the @code{punpcklbw} machine instruction.
@item v4hi __builtin_ia32_punpcklwd (v4hi, v4hi)
Generates the @code{punpcklwd} machine instruction.
@item v2si __builtin_ia32_punpckldq (v2si, v2si)
Generates the @code{punpckldq} machine instruction.
@item v8qi __builtin_ia32_packsswb (v4hi, v4hi)
Generates the @code{packsswb} machine instruction.
@item v4hi __builtin_ia32_packssdw (v2si, v2si)
Generates the @code{packssdw} machine instruction.
@item v8qi __builtin_ia32_packuswb (v4hi, v4hi)
Generates the @code{packuswb} machine instruction.
@end table
The following built-in functions are made available either with @option{-msse}, or
with a combination of @option{-m3dnow} and @option{-march=athlon}.
@table @code
@item v4hi __builtin_ia32_pmulhuw (v4hi, v4hi)
Generates the @code{pmulhuw} machine instruction.
@item v8qi __builtin_ia32_pavgb (v8qi, v8qi)
Generates the @code{pavgb} machine instruction.
@item v4hi __builtin_ia32_pavgw (v4hi, v4hi)
Generates the @code{pavgw} machine instruction.
@item v4hi __builtin_ia32_psadbw (v8qi, v8qi)
Generates the @code{psadbw} machine instruction.
@item v8qi __builtin_ia32_pmaxub (v8qi, v8qi)
Generates the @code{pmaxub} machine instruction.
@item v4hi __builtin_ia32_pmaxsw (v4hi, v4hi)
Generates the @code{pmaxsw} machine instruction.
@item v8qi __builtin_ia32_pminub (v8qi, v8qi)
Generates the @code{pminub} machine instruction.
@item v4hi __builtin_ia32_pminsw (v4hi, v4hi)
Generates the @code{pminsw} machine instruction.
@item int __builtin_ia32_pextrw (v4hi, int)
Generates the @code{pextrw} machine instruction.
@item v4hi __builtin_ia32_pinsrw (v4hi, int, int)
Generates the @code{pinsrw} machine instruction.
@item int __builtin_ia32_pmovmskb (v8qi)
Generates the @code{pmovmskb} machine instruction.
@item void __builtin_ia32_maskmovq (v8qi, v8qi, char *)
Generates the @code{maskmovq} machine instruction.
@item void __builtin_ia32_movntq (di *, di)
Generates the @code{movntq} machine instruction.
@item void __builtin_ia32_sfence (void)
Generates the @code{sfence} machine instruction.
@item void __builtin_ia32_prefetch (char *, int selector)
Generates a prefetch machine instruction, depending on the value of
selector. If @code{selector} is 0, it generates @code{prefetchnta}; for
a value of 1, it generates @code{prefetcht0}; for a value of 2, it generates
@code{prefetcht1}; and for a value of 3 it generates @code{prefetcht2}.
@end table
The following built-in functions are available when @option{-msse} is used.
@table @code
@item int __builtin_ia32_comieq (v4sf, v4sf)
Generates the @code{comiss} machine instruction and performs an equality
comparison. The return value is the truth value of that comparison.
@item int __builtin_ia32_comineq (v4sf, v4sf)
Generates the @code{comiss} machine instruction and performs an inequality
comparison. The return value is the truth value of that comparison.
@item int __builtin_ia32_comilt (v4sf, v4sf)
Generates the @code{comiss} machine instruction and performs a ``less than''
comparison. The return value is the truth value of that comparison.
@item int __builtin_ia32_comile (v4sf, v4sf)
Generates the @code{comiss} machine instruction and performs a ``less or
equal'' comparison. The return value is the truth value of that comparison.
@item int __builtin_ia32_comigt (v4sf, v4sf)
Generates the @code{comiss} machine instruction and performs a ``greater than''
comparison. The return value is the truth value of that comparison.
@item int __builtin_ia32_comige (v4sf, v4sf)
Generates the @code{comiss} machine instruction and performs a ``greater or
equal'' comparison. The return value is the truth value of that comparison.
@item int __builtin_ia32_ucomieq (v4sf, v4sf)
Generates the @code{ucomiss} machine instruction and performs an equality
comparison. The return value is the truth value of that comparison.
@item int __builtin_ia32_ucomineq (v4sf, v4sf)
Generates the @code{ucomiss} machine instruction and performs an inequality
comparison. The return value is the truth value of that comparison.
@item int __builtin_ia32_ucomilt (v4sf, v4sf)
Generates the @code{ucomiss} machine instruction and performs a ``less than''
comparison. The return value is the truth value of that comparison.
@item int __builtin_ia32_ucomile (v4sf, v4sf)
Generates the @code{ucomiss} machine instruction and performs a ``less or
equal'' comparison. The return value is the truth value of that comparison.
@item int __builtin_ia32_ucomigt (v4sf, v4sf)
Generates the @code{ucomiss} machine instruction and performs a ``greater than''
comparison. The return value is the truth value of that comparison.
@item int __builtin_ia32_ucomige (v4sf, v4sf)
Generates the @code{ucomiss} machine instruction and performs a ``greater or
equal'' comparison. The return value is the truth value of that comparison.
@item v4sf __builtin_ia32_addps (v4sf, v4sf)
Generates the @code{addps} machine instruction.
@item v4sf __builtin_ia32_addss (v4sf, v4sf)
Generates the @code{addss} machine instruction.
@item v4sf __builtin_ia32_subps (v4sf, v4sf)
Generates the @code{subps} machine instruction.
@item v4sf __builtin_ia32_subss (v4sf, v4sf)
Generates the @code{subss} machine instruction.
@item v4sf __builtin_ia32_mulps (v4sf, v4sf)
Generates the @code{mulps} machine instruction.
@item v4sf __builtin_ia32_mulss (v4sf, v4sf)
Generates the @code{mulss} machine instruction.
@item v4sf __builtin_ia32_divps (v4sf, v4sf)
Generates the @code{divps} machine instruction.
@item v4sf __builtin_ia32_divss (v4sf, v4sf)
Generates the @code{divss} machine instruction.
@item v4si __builtin_ia32_cmpeqps (v4sf, v4sf)
Generates the @code{cmpeqps} machine instruction.
@item v4si __builtin_ia32_cmplts (v4sf, v4sf)
Generates the @code{cmpltps} machine instruction.
@item v4si __builtin_ia32_cmpleps (v4sf, v4sf)
Generates the @code{cmpleps} machine instruction.
@item v4si __builtin_ia32_cmpgtps (v4sf, v4sf)
Generates the @code{cmpgtps} machine instruction.
@item v4si __builtin_ia32_cmpgeps (v4sf, v4sf)
Generates the @code{cmpgeps} machine instruction.
@item v4si __builtin_ia32_cmpunordps (v4sf, v4sf)
Generates the @code{cmpunodps} machine instruction.
@item v4si __builtin_ia32_cmpneqps (v4sf, v4sf)
Generates the @code{cmpeqps} machine instruction.
@item v4si __builtin_ia32_cmpnltps (v4sf, v4sf)
Generates the @code{cmpltps} machine instruction.
@item v4si __builtin_ia32_cmpnleps (v4sf, v4sf)
Generates the @code{cmpleps} machine instruction.
@item v4si __builtin_ia32_cmpngtps (v4sf, v4sf)
Generates the @code{cmpgtps} machine instruction.
@item v4si __builtin_ia32_cmpngeps (v4sf, v4sf)
Generates the @code{cmpgeps} machine instruction.
@item v4si __builtin_ia32_cmpordps (v4sf, v4sf)
Generates the @code{cmpunodps} machine instruction.
@item v4si __builtin_ia32_cmpeqss (v4sf, v4sf)
Generates the @code{cmpeqss} machine instruction.
@item v4si __builtin_ia32_cmpltss (v4sf, v4sf)
Generates the @code{cmpltss} machine instruction.
@item v4si __builtin_ia32_cmpless (v4sf, v4sf)
Generates the @code{cmpless} machine instruction.
@item v4si __builtin_ia32_cmpgtss (v4sf, v4sf)
Generates the @code{cmpgtss} machine instruction.
@item v4si __builtin_ia32_cmpgess (v4sf, v4sf)
Generates the @code{cmpgess} machine instruction.
@item v4si __builtin_ia32_cmpunordss (v4sf, v4sf)
Generates the @code{cmpunodss} machine instruction.
@item v4si __builtin_ia32_cmpneqss (v4sf, v4sf)
Generates the @code{cmpeqss} machine instruction.
@item v4si __builtin_ia32_cmpnlts (v4sf, v4sf)
Generates the @code{cmpltss} machine instruction.
@item v4si __builtin_ia32_cmpnless (v4sf, v4sf)
Generates the @code{cmpless} machine instruction.
@item v4si __builtin_ia32_cmpngtss (v4sf, v4sf)
Generates the @code{cmpgtss} machine instruction.
@item v4si __builtin_ia32_cmpngess (v4sf, v4sf)
Generates the @code{cmpgess} machine instruction.
@item v4si __builtin_ia32_cmpordss (v4sf, v4sf)
Generates the @code{cmpunodss} machine instruction.
@item v4sf __builtin_ia32_maxps (v4sf, v4sf)
Generates the @code{maxps} machine instruction.
@item v4sf __builtin_ia32_maxsss (v4sf, v4sf)
Generates the @code{maxss} machine instruction.
@item v4sf __builtin_ia32_minps (v4sf, v4sf)
Generates the @code{minps} machine instruction.
@item v4sf __builtin_ia32_minsss (v4sf, v4sf)
Generates the @code{minss} machine instruction.
@item ti __builtin_ia32_andps (ti, ti)
Generates the @code{andps} machine instruction.
@item ti __builtin_ia32_andnps (ti, ti)
Generates the @code{andnps} machine instruction.
@item ti __builtin_ia32_orps (ti, ti)
Generates the @code{orps} machine instruction.
@item ti __builtin_ia32_xorps (ti, ti)
Generates the @code{xorps} machine instruction.
@item v4sf __builtin_ia32_movps (v4sf, v4sf)
Generates the @code{movps} machine instruction.
@item v4sf __builtin_ia32_movhlps (v4sf, v4sf)
Generates the @code{movhlps} machine instruction.
@item v4sf __builtin_ia32_movlhps (v4sf, v4sf)
Generates the @code{movlhps} machine instruction.
@item v4sf __builtin_ia32_unpckhps (v4sf, v4sf)
Generates the @code{unpckhps} machine instruction.
@item v4sf __builtin_ia32_unpcklps (v4sf, v4sf)
Generates the @code{unpcklps} machine instruction.
@item v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si)
Generates the @code{cvtpi2ps} machine instruction.
@item v2si __builtin_ia32_cvtps2pi (v4sf)
Generates the @code{cvtps2pi} machine instruction.
@item v4sf __builtin_ia32_cvtsi2ss (v4sf, int)
Generates the @code{cvtsi2ss} machine instruction.
@item int __builtin_ia32_cvtss2si (v4sf)
Generates the @code{cvtsi2ss} machine instruction.
@item v2si __builtin_ia32_cvttps2pi (v4sf)
Generates the @code{cvttps2pi} machine instruction.
@item int __builtin_ia32_cvttss2si (v4sf)
Generates the @code{cvttsi2ss} machine instruction.
@item v4sf __builtin_ia32_rcpps (v4sf)
Generates the @code{rcpps} machine instruction.
@item v4sf __builtin_ia32_rsqrtps (v4sf)
Generates the @code{rsqrtps} machine instruction.
@item v4sf __builtin_ia32_sqrtps (v4sf)
Generates the @code{sqrtps} machine instruction.
@item v4sf __builtin_ia32_rcpss (v4sf)
Generates the @code{rcpss} machine instruction.
@item v4sf __builtin_ia32_rsqrtss (v4sf)
Generates the @code{rsqrtss} machine instruction.
@item v4sf __builtin_ia32_sqrtss (v4sf)
Generates the @code{sqrtss} machine instruction.
@item v4sf __builtin_ia32_shufps (v4sf, v4sf, int)
Generates the @code{shufps} machine instruction.
@item v4sf __builtin_ia32_loadaps (float *)
Generates the @code{movaps} machine instruction as a load from memory.
@item void __builtin_ia32_storeaps (float *, v4sf)
Generates the @code{movaps} machine instruction as a store to memory.
@item v4sf __builtin_ia32_loadups (float *)
Generates the @code{movups} machine instruction as a load from memory.
@item void __builtin_ia32_storeups (float *, v4sf)
Generates the @code{movups} machine instruction as a store to memory.
@item v4sf __builtin_ia32_loadsss (float *)
Generates the @code{movss} machine instruction as a load from memory.
@item void __builtin_ia32_storess (float *, v4sf)
Generates the @code{movss} machine instruction as a store to memory.
@item v4sf __builtin_ia32_loadhps (v4sf, v2si *)
Generates the @code{movhps} machine instruction as a load from memory.
@item v4sf __builtin_ia32_loadlps (v4sf, v2si *)
Generates the @code{movlps} machine instruction as a load from memory
@item void __builtin_ia32_storehps (v4sf, v2si *)
Generates the @code{movhps} machine instruction as a store to memory.
@item void __builtin_ia32_storelps (v4sf, v2si *)
Generates the @code{movlps} machine instruction as a store to memory.
@item void __builtin_ia32_movntps (float *, v4sf)
Generates the @code{movntps} machine instruction.
@item int __builtin_ia32_movmskps (v4sf)
Generates the @code{movntps} machine instruction.
@item void __builtin_ia32_storeps1 (float *, v4sf)
Generates the @code{movaps} machine instruction as a store to memory.
Before storing, the value is modified with a @code{shufps} instruction
so that the lowest of the four floating point elements is replicated
across the entire vector that is stored.
@item void __builtin_ia32_storerps (float *, v4sf)
Generates the @code{movaps} machine instruction as a store to memory.
Before storing, the value is modified with a @code{shufps} instruction
so that the order of the four floating point elements in the vector is
reversed.
@item v4sf __builtin_ia32_loadps1 (float *)
Generates a @code{movss} machine instruction to load a floating point
value from memory, and a @code{shufps} instruction to replicate the
loaded value across all four elements of the result vector.
@item v4sf __builtin_ia32_loadrps (float *)
Generates a @code{movaps} machine instruction to load a vector from
memory, and a @code{shufps} instruction to reverse the order of the
four floating point elements in the result vector.
@item v4sf __builtin_ia32_setps (float, float, float, float)
Constructs a vector from four single floating point values. The return
value is equal to the value that would result from storing the four
arguments into consecutive memory locations and then executing a
@code{movaps} to load the vector from memory.
@item v4sf __builtin_ia32_setps1 (float)
Constructs a vector from a single floating point value by replicating
it across all four elements of the result vector.
@end table
@item -mpush-args
@itemx -mno-push-args
@opindex mpush-args
@opindex mno-push-args
Use PUSH operations to store outgoing parameters. This method is shorter
and usually equally fast as method using SUB/MOV operations and is enabled
by default. In some cases disabling it may improve performance because of
improved scheduling and reduced dependencies.
@item -maccumulate-outgoing-args
@opindex maccumulate-outgoing-args
If enabled, the maximum amount of space required for outgoing arguments will be
computed in the function prologue. This is faster on most modern CPUs
because of reduced dependencies, improved scheduling and reduced stack usage
when preferred stack boundary is not equal to 2. The drawback is a notable
increase in code size. This switch implies @option{-mno-push-args}.
@item -mthreads
@opindex mthreads
Support thread-safe exception handling on @samp{Mingw32}. Code that relies
on thread-safe exception handling must compile and link all code with the
@option{-mthreads} option. When compiling, @option{-mthreads} defines
@option{-D_MT}; when linking, it links in a special thread helper library
@option{-lmingwthrd} which cleans up per thread exception handling data.
@item -mno-align-stringops
@opindex mno-align-stringops
Do not align destination of inlined string operations. This switch reduces
code size and improves performance in case the destination is already aligned,
but gcc don't know about it.
@item -minline-all-stringops
@opindex minline-all-stringops
By default GCC inlines string operations only when destination is known to be
aligned at least to 4 byte boundary. This enables more inlining, increase code
size, but may improve performance of code that depends on fast memcpy, strlen
and memset for short lengths.
@item -momit-leaf-frame-pointer
@opindex momit-leaf-frame-pointer
Don't keep the frame pointer in a register for leaf functions. This
avoids the instructions to save, set up and restore frame pointers and
makes an extra register available in leaf functions. The option
@option{-fomit-frame-pointer} removes the frame pointer for all functions
which might make debugging harder.
@end table
These @samp{-m} switches are supported in addition to the above
on AMD x86-64 processors in 64-bit environments.
@table @gcctabopt
@item -m32
@itemx -m64
@opindex m32
@opindex m64
Generate code for a 32-bit or 64-bit environment.
The 32-bit environment sets int, long and pointer to 32 bits and
generates code that runs on any i386 system.
The 64-bit environment sets int to 32 bits and long and pointer
to 64 bits and generates code for AMD's x86-64 architecture.
@item -mno-red-zone
@opindex no-red-zone
Do not use a so called red zone for x86-64 code. The red zone is mandated
by the x86-64 ABI, it is a 128-byte area beyond the location of the
stack pointer that will not be modified by signal or interrupt handlers
and therefore can be used for temporary data without adjusting the stack
pointer. The flag @option{-mno-red-zone} disables this red zone.
@end table
@node HPPA Options
@subsection HPPA Options
@cindex HPPA Options
These @samp{-m} options are defined for the HPPA family of computers:
@table @gcctabopt
@item -march=@var{architecture-type}
@opindex march
Generate code for the specified architecture. The choices for
@var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
1.1, and @samp{2.0} for PA 2.0 processors. Refer to
@file{/usr/lib/sched.models} on an HP-UX system to determine the proper
architecture option for your machine. Code compiled for lower numbered
architectures will run on higher numbered architectures, but not the
other way around.
PA 2.0 support currently requires gas snapshot 19990413 or later. The
next release of binutils (current is 2.9.1) will probably contain PA 2.0
support.
@item -mpa-risc-1-0
@itemx -mpa-risc-1-1
@itemx -mpa-risc-2-0
@opindex mpa-risc-1-0
@opindex mpa-risc-1-1
@opindex mpa-risc-2-0
Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
@item -mbig-switch
@opindex mbig-switch
Generate code suitable for big switch tables. Use this option only if
the assembler/linker complain about out of range branches within a switch
table.
@item -mjump-in-delay
@opindex mjump-in-delay
Fill delay slots of function calls with unconditional jump instructions
by modifying the return pointer for the function call to be the target
of the conditional jump.
@item -mdisable-fpregs
@opindex mdisable-fpregs
Prevent floating point registers from being used in any manner. This is
necessary for compiling kernels which perform lazy context switching of
floating point registers. If you use this option and attempt to perform
floating point operations, the compiler will abort.
@item -mdisable-indexing
@opindex mdisable-indexing
Prevent the compiler from using indexing address modes. This avoids some
rather obscure problems when compiling MIG generated code under MACH@.
@item -mno-space-regs
@opindex mno-space-regs
Generate code that assumes the target has no space registers. This allows
GCC to generate faster indirect calls and use unscaled index address modes.
Such code is suitable for level 0 PA systems and kernels.
@item -mfast-indirect-calls
@opindex mfast-indirect-calls
Generate code that assumes calls never cross space boundaries. This
allows GCC to emit code which performs faster indirect calls.
This option will not work in the presence of shared libraries or nested
functions.
@item -mlong-load-store
@opindex mlong-load-store
Generate 3-instruction load and store sequences as sometimes required by
the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
the HP compilers.
@item -mportable-runtime
@opindex mportable-runtime
Use the portable calling conventions proposed by HP for ELF systems.
@item -mgas
@opindex mgas
Enable the use of assembler directives only GAS understands.
@item -mschedule=@var{cpu-type}
@opindex mschedule
Schedule code according to the constraints for the machine type
@var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
@samp{7100}, @samp{7100LC}, @samp{7200}, and @samp{8000}. Refer to
@file{/usr/lib/sched.models} on an HP-UX system to determine the
proper scheduling option for your machine.
@item -mlinker-opt
@opindex mlinker-opt
Enable the optimization pass in the HPUX linker. Note this makes symbolic
debugging impossible. It also triggers a bug in the HPUX 8 and HPUX 9 linkers
in which they give bogus error messages when linking some programs.
@item -msoft-float
@opindex msoft-float
Generate output containing library calls for floating point.
@strong{Warning:} the requisite libraries are not available for all HPPA
targets. Normally the facilities of the machine's usual C compiler are
used, but this cannot be done directly in cross-compilation. You must make
your own arrangements to provide suitable library functions for
cross-compilation. The embedded target @samp{hppa1.1-*-pro}
does provide software floating point support.
@option{-msoft-float} changes the calling convention in the output file;
therefore, it is only useful if you compile @emph{all} of a program with
this option. In particular, you need to compile @file{libgcc.a}, the
library that comes with GCC, with @option{-msoft-float} in order for
this to work.
@end table
@node Intel 960 Options
@subsection Intel 960 Options
These @samp{-m} options are defined for the Intel 960 implementations:
@table @gcctabopt
@item -m@var{cpu-type}
@opindex mka
@opindex mkb
@opindex mmc
@opindex mca
@opindex mcf
@opindex msa
@opindex msb
Assume the defaults for the machine type @var{cpu-type} for some of
the other options, including instruction scheduling, floating point
support, and addressing modes. The choices for @var{cpu-type} are
@samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf},
@samp{sa}, and @samp{sb}.
The default is
@samp{kb}.
@item -mnumerics
@itemx -msoft-float
@opindex mnumerics
@opindex msoft-float
The @option{-mnumerics} option indicates that the processor does support
floating-point instructions. The @option{-msoft-float} option indicates
that floating-point support should not be assumed.
@item -mleaf-procedures
@itemx -mno-leaf-procedures
@opindex mleaf-procedures
@opindex mno-leaf-procedures
Do (or do not) attempt to alter leaf procedures to be callable with the
@code{bal} instruction as well as @code{call}. This will result in more
efficient code for explicit calls when the @code{bal} instruction can be
substituted by the assembler or linker, but less efficient code in other
cases, such as calls via function pointers, or using a linker that doesn't
support this optimization.
@item -mtail-call
@itemx -mno-tail-call
@opindex mtail-call
@opindex mno-tail-call
Do (or do not) make additional attempts (beyond those of the
machine-independent portions of the compiler) to optimize tail-recursive
calls into branches. You may not want to do this because the detection of
cases where this is not valid is not totally complete. The default is
@option{-mno-tail-call}.
@item -mcomplex-addr
@itemx -mno-complex-addr
@opindex mcomplex-addr
@opindex mno-complex-addr
Assume (or do not assume) that the use of a complex addressing mode is a
win on this implementation of the i960. Complex addressing modes may not
be worthwhile on the K-series, but they definitely are on the C-series.
The default is currently @option{-mcomplex-addr} for all processors except
the CB and CC@.
@item -mcode-align
@itemx -mno-code-align
@opindex mcode-align
@opindex mno-code-align
Align code to 8-byte boundaries for faster fetching (or don't bother).
Currently turned on by default for C-series implementations only.
@ignore
@item -mclean-linkage
@itemx -mno-clean-linkage
@opindex mclean-linkage
@opindex mno-clean-linkage
These options are not fully implemented.
@end ignore
@item -mic-compat
@itemx -mic2.0-compat
@itemx -mic3.0-compat
@opindex mic-compat
@opindex mic2.0-compat
@opindex mic3.0-compat
Enable compatibility with iC960 v2.0 or v3.0.
@item -masm-compat
@itemx -mintel-asm
@opindex masm-compat
@opindex mintel-asm
Enable compatibility with the iC960 assembler.
@item -mstrict-align
@itemx -mno-strict-align
@opindex mstrict-align
@opindex mno-strict-align
Do not permit (do permit) unaligned accesses.
@item -mold-align
@opindex mold-align
Enable structure-alignment compatibility with Intel's gcc release version
1.3 (based on gcc 1.37). This option implies @option{-mstrict-align}.
@item -mlong-double-64
@opindex mlong-double-64
Implement type @samp{long double} as 64-bit floating point numbers.
Without the option @samp{long double} is implemented by 80-bit
floating point numbers. The only reason we have it because there is
no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it
is only useful for people using soft-float targets. Otherwise, we
should recommend against use of it.
@end table
@node DEC Alpha Options
@subsection DEC Alpha Options
These @samp{-m} options are defined for the DEC Alpha implementations:
@table @gcctabopt
@item -mno-soft-float
@itemx -msoft-float
@opindex mno-soft-float
@opindex msoft-float
Use (do not use) the hardware floating-point instructions for
floating-point operations. When @option{-msoft-float} is specified,
functions in @file{libgcc.a} will be used to perform floating-point
operations. Unless they are replaced by routines that emulate the
floating-point operations, or compiled in such a way as to call such
emulations routines, these routines will issue floating-point
operations. If you are compiling for an Alpha without floating-point
operations, you must ensure that the library is built so as not to call
them.
Note that Alpha implementations without floating-point operations are
required to have floating-point registers.
@item -mfp-reg
@itemx -mno-fp-regs
@opindex mfp-reg
@opindex mno-fp-regs
Generate code that uses (does not use) the floating-point register set.
@option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
register set is not used, floating point operands are passed in integer
registers as if they were integers and floating-point results are passed
in $0 instead of $f0. This is a non-standard calling sequence, so any
function with a floating-point argument or return value called by code
compiled with @option{-mno-fp-regs} must also be compiled with that
option.
A typical use of this option is building a kernel that does not use,
and hence need not save and restore, any floating-point registers.
@item -mieee
@opindex mieee
The Alpha architecture implements floating-point hardware optimized for
maximum performance. It is mostly compliant with the IEEE floating
point standard. However, for full compliance, software assistance is
required. This option generates code fully IEEE compliant code
@emph{except} that the @var{inexact-flag} is not maintained (see below).
If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
defined during compilation. The resulting code is less efficient but is
able to correctly support denormalized numbers and exceptional IEEE
values such as not-a-number and plus/minus infinity. Other Alpha
compilers call this option @option{-ieee_with_no_inexact}.
@item -mieee-with-inexact
@opindex mieee-with-inexact
This is like @option{-mieee} except the generated code also maintains
the IEEE @var{inexact-flag}. Turning on this option causes the
generated code to implement fully-compliant IEEE math. In addition to
@code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
macro. On some Alpha implementations the resulting code may execute
significantly slower than the code generated by default. Since there is
very little code that depends on the @var{inexact-flag}, you should
normally not specify this option. Other Alpha compilers call this
option @option{-ieee_with_inexact}.
@item -mfp-trap-mode=@var{trap-mode}
@opindex mfp-trap-mode
This option controls what floating-point related traps are enabled.
Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
The trap mode can be set to one of four values:
@table @samp
@item n
This is the default (normal) setting. The only traps that are enabled
are the ones that cannot be disabled in software (e.g., division by zero
trap).
@item u
In addition to the traps enabled by @samp{n}, underflow traps are enabled
as well.
@item su
Like @samp{su}, but the instructions are marked to be safe for software
completion (see Alpha architecture manual for details).
@item sui
Like @samp{su}, but inexact traps are enabled as well.
@end table
@item -mfp-rounding-mode=@var{rounding-mode}
@opindex mfp-rounding-mode
Selects the IEEE rounding mode. Other Alpha compilers call this option
@option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
of:
@table @samp
@item n
Normal IEEE rounding mode. Floating point numbers are rounded towards
the nearest machine number or towards the even machine number in case
of a tie.
@item m
Round towards minus infinity.
@item c
Chopped rounding mode. Floating point numbers are rounded towards zero.
@item d
Dynamic rounding mode. A field in the floating point control register
(@var{fpcr}, see Alpha architecture reference manual) controls the
rounding mode in effect. The C library initializes this register for
rounding towards plus infinity. Thus, unless your program modifies the
@var{fpcr}, @samp{d} corresponds to round towards plus infinity.
@end table
@item -mtrap-precision=@var{trap-precision}
@opindex mtrap-precision
In the Alpha architecture, floating point traps are imprecise. This
means without software assistance it is impossible to recover from a
floating trap and program execution normally needs to be terminated.
GCC can generate code that can assist operating system trap handlers
in determining the exact location that caused a floating point trap.
Depending on the requirements of an application, different levels of
precisions can be selected:
@table @samp
@item p
Program precision. This option is the default and means a trap handler
can only identify which program caused a floating point exception.
@item f
Function precision. The trap handler can determine the function that
caused a floating point exception.
@item i
Instruction precision. The trap handler can determine the exact
instruction that caused a floating point exception.
@end table
Other Alpha compilers provide the equivalent options called
@option{-scope_safe} and @option{-resumption_safe}.
@item -mieee-conformant
@opindex mieee-conformant
This option marks the generated code as IEEE conformant. You must not
use this option unless you also specify @option{-mtrap-precision=i} and either
@option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
is to emit the line @samp{.eflag 48} in the function prologue of the
generated assembly file. Under DEC Unix, this has the effect that
IEEE-conformant math library routines will be linked in.
@item -mbuild-constants
@opindex mbuild-constants
Normally GCC examines a 32- or 64-bit integer constant to
see if it can construct it from smaller constants in two or three
instructions. If it cannot, it will output the constant as a literal and
generate code to load it from the data segment at runtime.
Use this option to require GCC to construct @emph{all} integer constants
using code, even if it takes more instructions (the maximum is six).
You would typically use this option to build a shared library dynamic
loader. Itself a shared library, it must relocate itself in memory
before it can find the variables and constants in its own data segment.
@item -malpha-as
@itemx -mgas
@opindex malpha-as
@opindex mgas
Select whether to generate code to be assembled by the vendor-supplied
assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
@item -mbwx
@itemx -mno-bwx
@itemx -mcix
@itemx -mno-cix
@itemx -mmax
@itemx -mno-max
@opindex mbwx
@opindex mno-bwx
@opindex mcix
@opindex mno-cix
@opindex mmax
@opindex mno-max
Indicate whether GCC should generate code to use the optional BWX,
CIX, and MAX instruction sets. The default is to use the instruction sets
supported by the CPU type specified via @option{-mcpu=} option or that
of the CPU on which GCC was built if none was specified.
@item -mcpu=@var{cpu_type}
@opindex mcpu
Set the instruction set, register set, and instruction scheduling
parameters for machine type @var{cpu_type}. You can specify either the
@samp{EV} style name or the corresponding chip number. GCC
supports scheduling parameters for the EV4 and EV5 family of processors
and will choose the default values for the instruction set from
the processor you specify. If you do not specify a processor type,
GCC will default to the processor on which the compiler was built.
Supported values for @var{cpu_type} are
@table @samp
@item ev4
@itemx 21064
Schedules as an EV4 and has no instruction set extensions.
@item ev5
@itemx 21164
Schedules as an EV5 and has no instruction set extensions.
@item ev56
@itemx 21164a
Schedules as an EV5 and supports the BWX extension.
@item pca56
@itemx 21164pc
@itemx 21164PC
Schedules as an EV5 and supports the BWX and MAX extensions.
@item ev6
@itemx 21264
Schedules as an EV5 (until Digital releases the scheduling parameters
for the EV6) and supports the BWX, CIX, and MAX extensions.
@end table
@item -mmemory-latency=@var{time}
@opindex mmemory-latency
Sets the latency the scheduler should assume for typical memory
references as seen by the application. This number is highly
dependent on the memory access patterns used by the application
and the size of the external cache on the machine.
Valid options for @var{time} are
@table @samp
@item @var{number}
A decimal number representing clock cycles.
@item L1
@itemx L2
@itemx L3
@itemx main
The compiler contains estimates of the number of clock cycles for
``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
(also called Dcache, Scache, and Bcache), as well as to main memory.
Note that L3 is only valid for EV5.
@end table
@end table
@node DEC Alpha/VMS Options
@subsection DEC Alpha/VMS Options
These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
@table @gcctabopt
@item -mvms-return-codes
@opindex mvms-return-codes
Return VMS condition codes from main. The default is to return POSIX
style condition (e.g.@ error) codes.
@end table
@node Clipper Options
@subsection Clipper Options
These @samp{-m} options are defined for the Clipper implementations:
@table @gcctabopt
@item -mc300
@opindex mc300
Produce code for a C300 Clipper processor. This is the default.
@item -mc400
@opindex mc400
Produce code for a C400 Clipper processor, i.e.@: use floating point
registers f8--f15.
@end table
@node H8/300 Options
@subsection H8/300 Options
These @samp{-m} options are defined for the H8/300 implementations:
@table @gcctabopt
@item -mrelax
@opindex mrelax
Shorten some address references at link time, when possible; uses the
linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
ld.info, Using ld}, for a fuller description.
@item -mh
@opindex mh
Generate code for the H8/300H@.
@item -ms
@opindex ms
Generate code for the H8/S@.
@item -ms2600
@opindex ms2600
Generate code for the H8/S2600. This switch must be used with @option{-ms}.
@item -mint32
@opindex mint32
Make @code{int} data 32 bits by default.
@item -malign-300
@opindex malign-300
On the H8/300H and H8/S, use the same alignment rules as for the H8/300.
The default for the H8/300H and H8/S is to align longs and floats on 4
byte boundaries.
@option{-malign-300} causes them to be aligned on 2 byte boundaries.
This option has no effect on the H8/300.
@end table
@node SH Options
@subsection SH Options
These @samp{-m} options are defined for the SH implementations:
@table @gcctabopt
@item -m1
@opindex m1
Generate code for the SH1.
@item -m2
@opindex m2
Generate code for the SH2.
@item -m3
@opindex m3
Generate code for the SH3.
@item -m3e
@opindex m3e
Generate code for the SH3e.
@item -m4-nofpu
@opindex m4-nofpu
Generate code for the SH4 without a floating-point unit.
@item -m4-single-only
@opindex m4-single-only
Generate code for the SH4 with a floating-point unit that only
supports single-precision arithmetic.
@item -m4-single
@opindex m4-single
Generate code for the SH4 assuming the floating-point unit is in
single-precision mode by default.
@item -m4
@opindex m4
Generate code for the SH4.
@item -mb
@opindex mb
Compile code for the processor in big endian mode.
@item -ml
@opindex ml
Compile code for the processor in little endian mode.
@item -mdalign
@opindex mdalign
Align doubles at 64-bit boundaries. Note that this changes the calling
conventions, and thus some functions from the standard C library will
not work unless you recompile it first with @option{-mdalign}.
@item -mrelax
@opindex mrelax
Shorten some address references at link time, when possible; uses the
linker option @option{-relax}.
@item -mbigtable
@opindex mbigtable
Use 32-bit offsets in @code{switch} tables. The default is to use
16-bit offsets.
@item -mfmovd
@opindex mfmovd
Enable the use of the instruction @code{fmovd}.
@item -mhitachi
@opindex mhitachi
Comply with the calling conventions defined by Hitachi.
@item -mnomacsave
@opindex mnomacsave
Mark the @code{MAC} register as call-clobbered, even if
@option{-mhitachi} is given.
@item -mieee
@opindex mieee
Increase IEEE-compliance of floating-point code.
@item -misize
@opindex misize
Dump instruction size and location in the assembly code.
@item -mpadstruct
@opindex mpadstruct
This option is deprecated. It pads structures to multiple of 4 bytes,
which is incompatible with the SH ABI@.
@item -mspace
@opindex mspace
Optimize for space instead of speed. Implied by @option{-Os}.
@item -mprefergot
@opindex mprefergot
When generating position-independent code, emit function calls using
the Global Offset Table instead of the Procedure Linkage Table.
@item -musermode
@opindex musermode
Generate a library function call to invalidate instruction cache
entries, after fixing up a trampoline. This library function call
doesn't assume it can write to the whole memory address space. This
is the default when the target is @code{sh-*-linux*}.
@end table
@node System V Options
@subsection Options for System V
These additional options are available on System V Release 4 for
compatibility with other compilers on those systems:
@table @gcctabopt
@item -G
@opindex G
Create a shared object.
It is recommended that @option{-symbolic} or @option{-shared} be used instead.
@item -Qy
@opindex Qy
Identify the versions of each tool used by the compiler, in a
@code{.ident} assembler directive in the output.
@item -Qn
@opindex Qn
Refrain from adding @code{.ident} directives to the output file (this is
the default).
@item -YP,@var{dirs}
@opindex YP
Search the directories @var{dirs}, and no others, for libraries
specified with @option{-l}.
@item -Ym,@var{dir}
@opindex Ym
Look in the directory @var{dir} to find the M4 preprocessor.
The assembler uses this option.
@c This is supposed to go with a -Yd for predefined M4 macro files, but
@c the generic assembler that comes with Solaris takes just -Ym.
@end table
@node TMS320C3x/C4x Options
@subsection TMS320C3x/C4x Options
@cindex TMS320C3x/C4x Options
These @samp{-m} options are defined for TMS320C3x/C4x implementations:
@table @gcctabopt
@item -mcpu=@var{cpu_type}
@opindex mcpu
Set the instruction set, register set, and instruction scheduling
parameters for machine type @var{cpu_type}. Supported values for
@var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
@samp{c44}. The default is @samp{c40} to generate code for the
TMS320C40.
@item -mbig-memory
@item -mbig
@itemx -msmall-memory
@itemx -msmall
@opindex mbig-memory
@opindex mbig
@opindex msmall-memory
@opindex msmall
Generates code for the big or small memory model. The small memory
model assumed that all data fits into one 64K word page. At run-time
the data page (DP) register must be set to point to the 64K page
containing the .bss and .data program sections. The big memory model is
the default and requires reloading of the DP register for every direct
memory access.
@item -mbk
@itemx -mno-bk
@opindex mbk
@opindex mno-bk
Allow (disallow) allocation of general integer operands into the block
count register BK@.
@item -mdb
@itemx -mno-db
@opindex mdb
@opindex mno-db
Enable (disable) generation of code using decrement and branch,
DBcond(D), instructions. This is enabled by default for the C4x. To be
on the safe side, this is disabled for the C3x, since the maximum
iteration count on the C3x is @math{2^23 + 1} (but who iterates loops more than
@math{2^23} times on the C3x?). Note that GCC will try to reverse a loop so
that it can utilise the decrement and branch instruction, but will give
up if there is more than one memory reference in the loop. Thus a loop
where the loop counter is decremented can generate slightly more
efficient code, in cases where the RPTB instruction cannot be utilised.
@item -mdp-isr-reload
@itemx -mparanoid
@opindex mdp-isr-reload
@opindex mparanoid
Force the DP register to be saved on entry to an interrupt service
routine (ISR), reloaded to point to the data section, and restored on
exit from the ISR@. This should not be required unless someone has
violated the small memory model by modifying the DP register, say within
an object library.
@item -mmpyi
@itemx -mno-mpyi
@opindex mmpyi
@opindex mno-mpyi
For the C3x use the 24-bit MPYI instruction for integer multiplies
instead of a library call to guarantee 32-bit results. Note that if one
of the operands is a constant, then the multiplication will be performed
using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
then squaring operations are performed inline instead of a library call.
@item -mfast-fix
@itemx -mno-fast-fix
@opindex mfast-fix
@opindex mno-fast-fix
The C3x/C4x FIX instruction to convert a floating point value to an
integer value chooses the nearest integer less than or equal to the
floating point value rather than to the nearest integer. Thus if the
floating point number is negative, the result will be incorrectly
truncated an additional code is necessary to detect and correct this
case. This option can be used to disable generation of the additional
code required to correct the result.
@item -mrptb
@itemx -mno-rptb
@opindex mrptb
@opindex mno-rptb
Enable (disable) generation of repeat block sequences using the RPTB
instruction for zero overhead looping. The RPTB construct is only used
for innermost loops that do not call functions or jump across the loop
boundaries. There is no advantage having nested RPTB loops due to the
overhead required to save and restore the RC, RS, and RE registers.
This is enabled by default with @option{-O2}.
@item -mrpts=@var{count}
@itemx -mno-rpts
@opindex mrpts
@opindex mno-rpts
Enable (disable) the use of the single instruction repeat instruction
RPTS@. If a repeat block contains a single instruction, and the loop
count can be guaranteed to be less than the value @var{count}, GCC will
emit a RPTS instruction instead of a RPTB@. If no value is specified,
then a RPTS will be emitted even if the loop count cannot be determined
at compile time. Note that the repeated instruction following RPTS does
not have to be reloaded from memory each iteration, thus freeing up the
CPU buses for operands. However, since interrupts are blocked by this
instruction, it is disabled by default.
@item -mloop-unsigned
@itemx -mno-loop-unsigned
@opindex mloop-unsigned
@opindex mno-loop-unsigned
The maximum iteration count when using RPTS and RPTB (and DB on the C40)
is @math{2^31 + 1} since these instructions test if the iteration count is
negative to terminate the loop. If the iteration count is unsigned
there is a possibility than the @math{2^31 + 1} maximum iteration count may be
exceeded. This switch allows an unsigned iteration count.
@item -mti
@opindex mti
Try to emit an assembler syntax that the TI assembler (asm30) is happy
with. This also enforces compatibility with the API employed by the TI
C3x C compiler. For example, long doubles are passed as structures
rather than in floating point registers.
@item -mregparm
@itemx -mmemparm
@opindex mregparm
@opindex mmemparm
Generate code that uses registers (stack) for passing arguments to functions.
By default, arguments are passed in registers where possible rather
than by pushing arguments on to the stack.
@item -mparallel-insns
@itemx -mno-parallel-insns
@opindex mparallel-insns
@opindex mno-parallel-insns
Allow the generation of parallel instructions. This is enabled by
default with @option{-O2}.
@item -mparallel-mpy
@itemx -mno-parallel-mpy
@opindex mparallel-mpy
@opindex mno-parallel-mpy
Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
provided @option{-mparallel-insns} is also specified. These instructions have
tight register constraints which can pessimize the code generation
of large functions.
@end table
@node V850 Options
@subsection V850 Options
@cindex V850 Options
These @samp{-m} options are defined for V850 implementations:
@table @gcctabopt
@item -mlong-calls
@itemx -mno-long-calls
@opindex mlong-calls
@opindex mno-long-calls
Treat all calls as being far away (near). If calls are assumed to be
far away, the compiler will always load the functions address up into a
register, and call indirect through the pointer.
@item -mno-ep
@itemx -mep
@opindex mno-ep
@opindex mep
Do not optimize (do optimize) basic blocks that use the same index
pointer 4 or more times to copy pointer into the @code{ep} register, and
use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
option is on by default if you optimize.
@item -mno-prolog-function
@itemx -mprolog-function
@opindex mno-prolog-function
@opindex mprolog-function
Do not use (do use) external functions to save and restore registers at
the prolog and epilog of a function. The external functions are slower,
but use less code space if more than one function saves the same number
of registers. The @option{-mprolog-function} option is on by default if
you optimize.
@item -mspace
@opindex mspace
Try to make the code as small as possible. At present, this just turns
on the @option{-mep} and @option{-mprolog-function} options.
@item -mtda=@var{n}
@opindex mtda
Put static or global variables whose size is @var{n} bytes or less into
the tiny data area that register @code{ep} points to. The tiny data
area can hold up to 256 bytes in total (128 bytes for byte references).
@item -msda=@var{n}
@opindex msda
Put static or global variables whose size is @var{n} bytes or less into
the small data area that register @code{gp} points to. The small data
area can hold up to 64 kilobytes.
@item -mzda=@var{n}
@opindex mzda
Put static or global variables whose size is @var{n} bytes or less into
the first 32 kilobytes of memory.
@item -mv850
@opindex mv850
Specify that the target processor is the V850.
@item -mbig-switch
@opindex mbig-switch
Generate code suitable for big switch tables. Use this option only if
the assembler/linker complain about out of range branches within a switch
table.
@end table
@node ARC Options
@subsection ARC Options
@cindex ARC Options
These options are defined for ARC implementations:
@table @gcctabopt
@item -EL
@opindex EL
Compile code for little endian mode. This is the default.
@item -EB
@opindex EB
Compile code for big endian mode.
@item -mmangle-cpu
@opindex mmangle-cpu
Prepend the name of the cpu to all public symbol names.
In multiple-processor systems, there are many ARC variants with different
instruction and register set characteristics. This flag prevents code
compiled for one cpu to be linked with code compiled for another.
No facility exists for handling variants that are ``almost identical''.
This is an all or nothing option.
@item -mcpu=@var{cpu}
@opindex mcpu
Compile code for ARC variant @var{cpu}.
Which variants are supported depend on the configuration.
All variants support @option{-mcpu=base}, this is the default.
@item -mtext=@var{text-section}
@itemx -mdata=@var{data-section}
@itemx -mrodata=@var{readonly-data-section}
@opindex mtext
@opindex mdata
@opindex mrodata
Put functions, data, and readonly data in @var{text-section},
@var{data-section}, and @var{readonly-data-section} respectively
by default. This can be overridden with the @code{section} attribute.
@xref{Variable Attributes}.
@end table
@node NS32K Options
@subsection NS32K Options
@cindex NS32K options
These are the @samp{-m} options defined for the 32000 series. The default
values for these options depends on which style of 32000 was selected when
the compiler was configured; the defaults for the most common choices are
given below.
@table @gcctabopt
@item -m32032
@itemx -m32032
@opindex m32032
@opindex m32032
Generate output for a 32032. This is the default
when the compiler is configured for 32032 and 32016 based systems.
@item -m32332
@itemx -m32332
@opindex m32332
@opindex m32332
Generate output for a 32332. This is the default
when the compiler is configured for 32332-based systems.
@item -m32532
@itemx -m32532
@opindex m32532
@opindex m32532
Generate output for a 32532. This is the default
when the compiler is configured for 32532-based systems.
@item -m32081
@opindex m32081
Generate output containing 32081 instructions for floating point.
This is the default for all systems.
@item -m32381
@opindex m32381
Generate output containing 32381 instructions for floating point. This
also implies @option{-m32081}. The 32381 is only compatible with the 32332
and 32532 cpus. This is the default for the pc532-netbsd configuration.
@item -mmulti-add
@opindex mmulti-add
Try and generate multiply-add floating point instructions @code{polyF}
and @code{dotF}. This option is only available if the @option{-m32381}
option is in effect. Using these instructions requires changes to
register allocation which generally has a negative impact on
performance. This option should only be enabled when compiling code
particularly likely to make heavy use of multiply-add instructions.
@item -mnomulti-add
@opindex mnomulti-add
Do not try and generate multiply-add floating point instructions
@code{polyF} and @code{dotF}. This is the default on all platforms.
@item -msoft-float
@opindex msoft-float
Generate output containing library calls for floating point.
@strong{Warning:} the requisite libraries may not be available.
@item -mnobitfield
@opindex mnobitfield
Do not use the bit-field instructions. On some machines it is faster to
use shifting and masking operations. This is the default for the pc532.
@item -mbitfield
@opindex mbitfield
Do use the bit-field instructions. This is the default for all platforms
except the pc532.
@item -mrtd
@opindex mrtd
Use a different function-calling convention, in which functions
that take a fixed number of arguments return pop their
arguments on return with the @code{ret} instruction.
This calling convention is incompatible with the one normally
used on Unix, so you cannot use it if you need to call libraries
compiled with the Unix compiler.
Also, you must provide function prototypes for all functions that
take variable numbers of arguments (including @code{printf});
otherwise incorrect code will be generated for calls to those
functions.
In addition, seriously incorrect code will result if you call a
function with too many arguments. (Normally, extra arguments are
harmlessly ignored.)
This option takes its name from the 680x0 @code{rtd} instruction.
@item -mregparam
@opindex mregparam
Use a different function-calling convention where the first two arguments
are passed in registers.
This calling convention is incompatible with the one normally
used on Unix, so you cannot use it if you need to call libraries
compiled with the Unix compiler.
@item -mnoregparam
@opindex mnoregparam
Do not pass any arguments in registers. This is the default for all
targets.
@item -msb
@opindex msb
It is OK to use the sb as an index register which is always loaded with
zero. This is the default for the pc532-netbsd target.
@item -mnosb
@opindex mnosb
The sb register is not available for use or has not been initialized to
zero by the run time system. This is the default for all targets except
the pc532-netbsd. It is also implied whenever @option{-mhimem} or
@option{-fpic} is set.
@item -mhimem
@opindex mhimem
Many ns32000 series addressing modes use displacements of up to 512MB@.
If an address is above 512MB then displacements from zero can not be used.
This option causes code to be generated which can be loaded above 512MB@.
This may be useful for operating systems or ROM code.
@item -mnohimem
@opindex mnohimem
Assume code will be loaded in the first 512MB of virtual address space.
This is the default for all platforms.
@end table
@node AVR Options
@subsection AVR Options
@cindex AVR Options
These options are defined for AVR implementations:
@table @gcctabopt
@item -mmcu=@var{mcu}
@opindex mmcu
Specify ATMEL AVR instruction set or MCU type.
Instruction set avr1 is for the minimal AVR core, not supported by the C
compiler, only for assembler programs (MCU types: at90s1200, attiny10,
attiny11, attiny12, attiny15, attiny28).
Instruction set avr2 (default) is for the classic AVR core with up to
8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
at90c8534, at90s8535).
Instruction set avr3 is for the classic AVR core with up to 128K program
memory space (MCU types: atmega103, atmega603).
Instruction set avr4 is for the enhanced AVR core with up to 8K program
memory space (MCU types: atmega83, atmega85).
Instruction set avr5 is for the enhanced AVR core with up to 128K program
memory space (MCU types: atmega161, atmega163, atmega32, at94k).
@item -msize
@opindex msize
Output instruction sizes to the asm file.
@item -minit-stack=@var{N}
@opindex minit-stack
Specify the initial stack address, which may be a symbol or numeric value,
@samp{__stack} is the default.
@item -mno-interrupts
@opindex mno-interrupts
Generated code is not compatible with hardware interrupts.
Code size will be smaller.
@item -mcall-prologues
@opindex mcall-prologues
Functions prologues/epilogues expanded as call to appropriate
subroutines. Code size will be smaller.
@item -mno-tablejump
@opindex mno-tablejump
Do not generate tablejump insns which sometimes increase code size.
@item -mtiny-stack
@opindex mtiny-stack
Change only the low 8 bits of the stack pointer.
@end table
@node MCore Options
@subsection MCore Options
@cindex MCore options
These are the @samp{-m} options defined for the Motorola M*Core
processors.
@table @gcctabopt
@item -mhardlit
@itemx -mhardlit
@itemx -mno-hardlit
@opindex mhardlit
@opindex mhardlit
@opindex mno-hardlit
Inline constants into the code stream if it can be done in two
instructions or less.
@item -mdiv
@itemx -mdiv
@itemx -mno-div
@opindex mdiv
@opindex mdiv
@opindex mno-div
Use the divide instruction. (Enabled by default).
@item -mrelax-immediate
@itemx -mrelax-immediate
@itemx -mno-relax-immediate
@opindex mrelax-immediate
@opindex mrelax-immediate
@opindex mno-relax-immediate
Allow arbitrary sized immediates in bit operations.
@item -mwide-bitfields
@itemx -mwide-bitfields
@itemx -mno-wide-bitfields
@opindex mwide-bitfields
@opindex mwide-bitfields
@opindex mno-wide-bitfields
Always treat bit-fields as int-sized.
@item -m4byte-functions
@itemx -m4byte-functions
@itemx -mno-4byte-functions
@opindex m4byte-functions
@opindex m4byte-functions
@opindex mno-4byte-functions
Force all functions to be aligned to a four byte boundary.
@item -mcallgraph-data
@itemx -mcallgraph-data
@itemx -mno-callgraph-data
@opindex mcallgraph-data
@opindex mcallgraph-data
@opindex mno-callgraph-data
Emit callgraph information.
@item -mslow-bytes
@itemx -mslow-bytes
@itemx -mno-slow-bytes
@opindex mslow-bytes
@opindex mslow-bytes
@opindex mno-slow-bytes
Prefer word access when reading byte quantities.
@item -mlittle-endian
@itemx -mlittle-endian
@itemx -mbig-endian
@opindex mlittle-endian
@opindex mlittle-endian
@opindex mbig-endian
Generate code for a little endian target.
@item -m210
@itemx -m210
@itemx -m340
@opindex m210
@opindex m210
@opindex m340
Generate code for the 210 processor.
@end table
@node IA-64 Options
@subsection IA-64 Options
@cindex IA-64 Options
These are the @samp{-m} options defined for the Intel IA-64 architecture.
@table @gcctabopt
@item -mbig-endian
@opindex mbig-endian
Generate code for a big endian target. This is the default for HPUX@.
@item -mlittle-endian
@opindex mlittle-endian
Generate code for a little endian target. This is the default for AIX5
and Linux.
@item -mgnu-as
@itemx -mno-gnu-as
@opindex mgnu-as
@opindex mno-gnu-as
Generate (or don't) code for the GNU assembler. This is the default.
@c Also, this is the default if the configure option @option{--with-gnu-as}
@c is used.
@item -mgnu-ld
@itemx -mno-gnu-ld
@opindex mgnu-ld
@opindex mno-gnu-ld
Generate (or don't) code for the GNU linker. This is the default.
@c Also, this is the default if the configure option @option{--with-gnu-ld}
@c is used.
@item -mno-pic
@opindex mno-pic
Generate code that does not use a global pointer register. The result
is not position independent code, and violates the IA-64 ABI@.
@item -mvolatile-asm-stop
@itemx -mno-volatile-asm-stop
@opindex mvolatile-asm-stop
@opindex mno-volatile-asm-stop
Generate (or don't) a stop bit immediately before and after volatile asm
statements.
@item -mb-step
@opindex mb-step
Generate code that works around Itanium B step errata.
@item -mregister-names
@itemx -mno-register-names
@opindex mregister-names
@opindex mno-register-names
Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
the stacked registers. This may make assembler output more readable.
@item -mno-sdata
@itemx -msdata
@opindex mno-sdata
@opindex msdata
Disable (or enable) optimizations that use the small data section. This may
be useful for working around optimizer bugs.
@item -mconstant-gp
@opindex mconstant-gp
Generate code that uses a single constant global pointer value. This is
useful when compiling kernel code.
@item -mauto-pic
@opindex mauto-pic
Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
This is useful when compiling firmware code.
@item -minline-divide-min-latency
@opindex minline-divide-min-latency
Generate code for inline divides using the minimum latency algorithm.
@item -minline-divide-max-throughput
@opindex minline-divide-max-throughput
Generate code for inline divides using the maximum throughput algorithm.
@item -mno-dwarf2-asm
@itemx -mdwarf2-asm
@opindex mno-dwarf2-asm
@opindex mdwarf2-asm
Don't (or do) generate assembler code for the DWARF2 line number debugging
info. This may be useful when not using the GNU assembler.
@item -mfixed-range=@var{register-range}
@opindex mfixed-range
Generate code treating the given register range as fixed registers.
A fixed register is one that the register allocator can not use. This is
useful when compiling kernel code. A register range is specified as
two registers separated by a dash. Multiple register ranges can be
specified separated by a comma.
@end table
@node D30V Options
@subsection D30V Options
@cindex D30V Options
These @samp{-m} options are defined for D30V implementations:
@table @gcctabopt
@item -mextmem
@opindex mextmem
Link the @samp{.text}, @samp{.data}, @samp{.bss}, @samp{.strings},
@samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into external
memory, which starts at location @code{0x80000000}.
@item -mextmemory
@opindex mextmemory
Same as the @option{-mextmem} switch.
@item -monchip
@opindex monchip
Link the @samp{.text} section into onchip text memory, which starts at
location @code{0x0}. Also link @samp{.data}, @samp{.bss},
@samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections
into onchip data memory, which starts at location @code{0x20000000}.
@item -mno-asm-optimize
@itemx -masm-optimize
@opindex mno-asm-optimize
@opindex masm-optimize
Disable (enable) passing @option{-O} to the assembler when optimizing.
The assembler uses the @option{-O} option to automatically parallelize
adjacent short instructions where possible.
@item -mbranch-cost=@var{n}
@opindex mbranch-cost
Increase the internal costs of branches to @var{n}. Higher costs means
that the compiler will issue more instructions to avoid doing a branch.
The default is 2.
@item -mcond-exec=@var{n}
@opindex mcond-exec
Specify the maximum number of conditionally executed instructions that
replace a branch. The default is 4.
@end table
@node S/390 and zSeries Options
@subsection S/390 and zSeries Options
@cindex S/390 and zSeries Options
These are the @samp{-m} options defined for the S/390 and zSeries architecture.
@table @gcctabopt
@item -mhard-float
@itemx -msoft-float
@opindex mhard-float
@opindex msoft-float
Use (do not use) the hardware floating-point instructions and registers
for floating-point operations. When @option{-msoft-float} is specified,
functions in @file{libgcc.a} will be used to perform floating-point
operations. When @option{-mhard-float} is specified, the compiler
generates IEEE floating-point instructions. This is the default.
@item -mbackchain
@itemx -mno-backchain
@opindex mbackchain
@opindex mno-backchain
Generate (or do not generate) code which maintains an explicit
backchain within the stack frame that points to the caller's frame.
This is currently needed to allow debugging. The default is to
generate the backchain.
@item -msmall-exec
@itemx -mno-small-exec
@opindex msmall-exec
@opindex mno-small-exec
Generate (or do not generate) code using the @code{bras} instruction
to do subroutine calls.
This only works reliably if the total executable size does not
exceed 64k. The default is to use the @code{basr} instruction instead,
which does not have this limitation.
@item -m64
@itemx -m31
@opindex m64
@opindex m31
When @option{-m31} is specified, generate code compliant to the
Linux for S/390 ABI@. When @option{-m64} is specified, generate
code compliant to the Linux for zSeries ABI@. This allows GCC in
particular to generate 64-bit instructions. For the @samp{s390}
targets, the default is @option{-m31}, while the @samp{s390x}
targets default to @option{-m64}.
@item -mmvcle
@itemx -mno-mvcle
@opindex mmvcle
@opindex mno-mvcle
Generate (or do not generate) code using the @code{mvcle} instruction
to perform block moves. When @option{-mno-mvcle} is specifed,
use a @code{mvc} loop instead. This is the default.
@item -mdebug
@itemx -mno-debug
@opindex mdebug
@opindex mno-debug
Print (or do not print) additional debug information when compiling.
The default is to not print debug information.
@end table
@node CRIS Options
@subsection CRIS Options
@cindex CRIS Options
These options are defined specifically for the CRIS ports.
@table @gcctabopt
@item -march=@var{architecture-type}
@itemx -mcpu=@var{architecture-type}
@opindex march
@opindex mcpu
Generate code for the specified architecture. The choices for
@var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX.
Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
@samp{v10}.
@item -mtune=@var{architecture-type}
@opindex mtune
Tune to @var{architecture-type} everything applicable about the generated
code, except for the ABI and the set of available instructions. The
choices for @var{architecture-type} are the same as for
@option{-march=@var{architecture-type}}.
@item -mmax-stack-frame=@var{n}
@opindex mmax-stack-frame
Warn when the stack frame of a function exceeds @var{n} bytes.
@item -melinux-stacksize=@var{n}
@opindex melinux-stacksize
Only available with the @samp{cris-axis-aout} target. Arranges for
indications in the program to the kernel loader that the stack of the
program should be set to @var{n} bytes.
@item -metrax4
@itemx -metrax100
@opindex metrax4
@opindex metrax100
The options @option{-metrax4} and @option{-metrax100} are synonyms for
@option{-march=v3} and @option{-march=v8} respectively.
@item -mpdebug
@opindex mpdebug
Enable CRIS-specific verbose debug-related information in the assembly
code. This option also has the effect to turn off the @samp{#NO_APP}
formatted-code indicator to the assembler at the beginning of the
assembly file.
@item -mcc-init
@opindex mcc-init
Do not use condition-code results from previous instruction; always emit
compare and test instructions before use of condition codes.
@item -mno-side-effects
@opindex mno-side-effects
Do not emit instructions with side-effects in addressing modes other than
post-increment.
@item -mstack-align
@itemx -mno-stack-align
@itemx -mdata-align
@itemx -mno-data-align
@itemx -mconst-align
@itemx -mno-const-align
@opindex mstack-align
@opindex mno-stack-align
@opindex mdata-align
@opindex mno-data-align
@opindex mconst-align
@opindex mno-const-align
These options (no-options) arranges (eliminate arrangements) for the
stack-frame, individual data and constants to be aligned for the maximum
single data access size for the chosen CPU model. The default is to
arrange for 32-bit alignment. ABI details such as structure layout are
not affected by these options.
@item -m32-bit
@itemx -m16-bit
@itemx -m8-bit
@opindex m32-bit
@opindex m16-bit
@opindex m8-bit
Similar to the stack- data- and const-align options above, these options
arrange for stack-frame, writable data and constants to all be 32-bit,
16-bit or 8-bit aligned. The default is 32-bit alignment.
@item -mno-prologue-epilogue
@itemx -mprologue-epilogue
@opindex mno-prologue-epilogue
@opindex mprologue-epilogue
With @option{-mno-prologue-epilogue}, the normal function prologue and
epilogue that sets up the stack-frame are omitted and no return
instructions or return sequences are generated in the code. Use this
option only together with visual inspection of the compiled code: no
warnings or errors are generated when call-saved registers must be saved,
or storage for local variable needs to be allocated.
@item -mno-gotplt
@itemx -mgotplt
@opindex mno-gotplt
@opindex mgotplt
With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
instruction sequences that load addresses for functions from the PLT part
of the GOT rather than (traditional on other architectures) calls to the
PLT. The default is @option{-mgotplt}.
@item -maout
@opindex maout
Legacy no-op option only recognized with the cris-axis-aout target.
@item -melf
@opindex melf
Legacy no-op option only recognized with the cris-axis-elf and
cris-axis-linux-gnu targets.
@item -melinux
@opindex melinux
Only recognized with the cris-axis-aout target, where it selects a
GNU/linux-like multilib, include files and instruction set for
@option{-march=v8}.
@item -mlinux
@opindex mlinux
Legacy no-op option only recognized with the cris-axis-linux-gnu target.
@item -sim
@opindex sim
This option, recognized for the cris-axis-aout and cris-axis-elf arranges
to link with input-output functions from a simulator library. Code,
initialized data and zero-initialized data are allocated consecutively.
@item -sim2
@opindex sim2
Like @option{-sim}, but pass linker options to locate initialized data at
0x40000000 and zero-initialized data at 0x80000000.
@end table
@node MMIX Options
@subsection MMIX Options
@cindex MMIX Options
These options are defined for the MMIX:
@table @code
@item -mlibfuncs
@itemx -mno-libfuncs
Specify that intrinsic library functions are being compiled, passing all
values in registers, no matter the size.
@item -mepsilon
@itemx -mno-epsilon
Generate floating-point comparison instructions that compare with respect
to the @code{rE} epsilon register.
@item -mabi=mmixware
@itemx -mabi=gnu
Generate code that passes function parameters and return values that (in
the called function) are seen as registers @code{$0} and up, as opposed to
the GNU ABI which uses global registers @code{$231} and up.
@item -mzero-extend
@item -mno-zero-extend
When reading data from memory in sizes shorter than 64 bits, use (do not
use) zero-extending load instructions by default, rather than
sign-extending ones.
@item -mknuthdiv
@itemx -mno-knuthdiv
Make the result of a division yielding a remainder have the same sign as
the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
remainder follows the sign of the dividend. Both methods are
arithmetically valid, the latter being almost exclusively used.
@item -mtoplevel-symbols
@itemx -mno-toplevel-symbols
Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
code can be used with the @code{PREFIX} assembly directive.
@item -melf
Generate an executable in the ELF format, rather than the default
@samp{mmo} format used by the @command{mmix} simulator.
@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} would be @option{-fno-foo}. In the table below, only
one of the forms is listed---the one which is not the default. You
can figure out the other form by either removing @samp{no-} or adding
it.
@table @gcctabopt
@item -fexceptions
@opindex fexceptions
Enable exception handling. Generates extra code needed to propagate
exceptions. For some targets, this implies GCC will generate 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 will enable it by default for languages like
C++ which normally require exception handling, and disable 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}.
@item -funwind-tables
@opindex funwind-tables
Similar to @option{-fexceptions}, except that it will just generate any needed
static data, but will not affect the generated code in any other way.
You will normally not enable this option; instead, a language processor
that needs this handling would enable it on your behalf.
@item -fasynchronous-unwind-tables
@opindex funwind-tables
Generate unwind table in dwarf2 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 -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.
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.
@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.
@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
will be equivalent to the smallest integer type which has enough room.
@item -fshort-double
@opindex fshort-double
Use the same size for @code{double} as for @code{float}.
@item -fshared-data
@opindex fshared-data
Requests that the data and non-@code{const} variables of this
compilation be shared data rather than private data. The distinction
makes sense only on certain operating systems, where shared data is
shared between processes running the same program, while private data
exists in one copy per process.
@item -fno-common
@opindex fno-common
In C, allocate even uninitialized global variables in the data section of the
object file, rather than generating them as common blocks. This has the
effect that if the same variable is declared (without @code{extern}) in
two different compilations, you will get an error when you link them.
The only reason this might be useful is if you wish to verify that the
program will work on other systems which always work this way.
@item -fno-ident
@opindex fno-ident
Ignore the @samp{#ident} directive.
@item -fno-gnu-linker
@opindex fno-gnu-linker
Do not output global initializations (such as C++ constructors and
destructors) in the form used by the GNU linker (on systems where the GNU
linker is the standard method of handling them). Use this option when
you want to use a non-GNU linker, which also requires using the
@command{collect2} program to make sure the system linker includes
constructors and destructors. (@command{collect2} is included in the GCC
distribution.) For systems which @emph{must} use @command{collect2}, the
compiler driver @command{gcc} is configured to do this automatically.
@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.
@item -fvolatile
@opindex fvolatile
Consider all memory references through pointers to be volatile.
@item -fvolatile-global
@opindex fvolatile-global
Consider all memory references to extern and global data items to
be volatile. GCC does not consider static data items to be volatile
because of this switch.
@item -fvolatile-static
@opindex fvolatile-static
Consider all memory references to static data to be volatile.
@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 16k on the m88k, 8k on the Sparc, and 32k
on the m68k and RS/6000. The 386 has no such limit.)
Position-independent code requires special support, and therefore works
only on certain machines. For the 386, GCC supports PIC for System V
but not for the Sun 386i. Code generated for the IBM RS/6000 is always
position-independent.
@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 the m68k, m88k,
and the Sparc.
Position-independent code requires special support, and therefore works
only on certain machines.
@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
will not save and restore the register @var{reg}.
It is an error to used 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 will produce 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 will save and restore
the register @var{reg} if they use it.
It is an error to used 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 will produce disastrous results.
A different sort of disaster will result 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
@opindex fpack-struct
Pack all structure members together without holes. Usually you would
not want to use this option, since it makes the code suboptimal, and
the offsets of structure members won't agree with system libraries.
@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 will be 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.)
@example
void __cyg_profile_func_enter (void *this_fn,
void *call_site);
void __cyg_profile_func_exit (void *this_fn,
void *call_site);
@end example
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 will 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 @samp{extern inline} in your C code, an
addressable version of such functions must be provided. (This is
normally the case anyways, 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 will not be 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).
@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 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 must do that. The switch causes generation of code
to ensure that the operating system sees the stack being extended.
@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 the stack
would grow beyond the value, a signal is raised. 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.
@cindex aliasing of parameters
@cindex parameters, aliased
@item -fargument-alias
@itemx -fargument-noalias
@itemx -fargument-noalias-global
@opindex fargument-alias
@opindex fargument-noalias
@opindex fargument-noalias-global
Specify the possible relationships among parameters and between
parameters and global data.
@option{-fargument-alias} specifies that arguments (parameters) may
alias each other and may alias global storage.@*
@option{-fargument-noalias} specifies that arguments do not alias
each other, but may alias global storage.@*
@option{-fargument-noalias-global} specifies that arguments do not
alias each other and do not alias global storage.
Each language will automatically use whatever option is required by
the language standard. You should not need to use these options yourself.
@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.
Be warned that you should know what you are doing when invoking this
option, and that not all targets provide complete support for it.
@end table
@c man end
@node Environment Variables
@section Environment Variables Affecting GCC
@cindex environment variables
@c man begin ENVIRONMENT
This section describes several environment variables that affect how GCC
operates. Some of them work by specifying directories or prefixes to use
when searching for various kinds of files. Some are used to specify other
aspects of the compilation environment.
Note that you can also specify places to search using options such as
@option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
take precedence over places specified using environment variables, which
in turn take precedence over those specified by the configuration of GCC@.
@xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
GNU Compiler Collection (GCC) Internals}.
@table @env
@item LANG
@itemx LC_CTYPE
@c @itemx LC_COLLATE
@itemx LC_MESSAGES
@c @itemx LC_MONETARY
@c @itemx LC_NUMERIC
@c @itemx LC_TIME
@itemx LC_ALL
@findex LANG
@findex LC_CTYPE
@c @findex LC_COLLATE
@findex LC_MESSAGES
@c @findex LC_MONETARY
@c @findex LC_NUMERIC
@c @findex LC_TIME
@findex LC_ALL
@cindex locale
These environment variables control the way that GCC uses
localization information that allow GCC to work with different
national conventions. GCC inspects the locale categories
@env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
so. These locale categories can be set to any value supported by your
installation. A typical value is @samp{en_UK} for English in the United
Kingdom.
The @env{LC_CTYPE} environment variable specifies character
classification. GCC uses it to determine the character boundaries in
a string; this is needed for some multibyte encodings that contain quote
and escape characters that would otherwise be interpreted as a string
end or escape.
The @env{LC_MESSAGES} environment variable specifies the language to
use in diagnostic messages.
If the @env{LC_ALL} environment variable is set, it overrides the value
of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
and @env{LC_MESSAGES} default to the value of the @env{LANG}
environment variable. If none of these variables are set, GCC
defaults to traditional C English behavior.
@item TMPDIR
@findex TMPDIR
If @env{TMPDIR} is set, it specifies the directory to use for temporary
files. GCC uses temporary files to hold the output of one stage of
compilation which is to be used as input to the next stage: for example,
the output of the preprocessor, which is the input to the compiler
proper.
@item GCC_EXEC_PREFIX
@findex GCC_EXEC_PREFIX
If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
names of the subprograms executed by the compiler. No slash is added
when this prefix is combined with the name of a subprogram, but you can
specify a prefix that ends with a slash if you wish.
If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
an appropriate prefix to use based on the pathname it was invoked with.
If GCC cannot find the subprogram using the specified prefix, it
tries looking in the usual places for the subprogram.
The default value of @env{GCC_EXEC_PREFIX} is
@file{@var{prefix}/lib/gcc-lib/} where @var{prefix} is the value
of @code{prefix} when you ran the @file{configure} script.
Other prefixes specified with @option{-B} take precedence over this prefix.
This prefix is also used for finding files such as @file{crt0.o} that are
used for linking.
In addition, the prefix is used in an unusual way in finding the
directories to search for header files. For each of the standard
directories whose name normally begins with @samp{/usr/local/lib/gcc-lib}
(more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
replacing that beginning with the specified prefix to produce an
alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
@file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
These alternate directories are searched first; the standard directories
come next.
@item COMPILER_PATH
@findex COMPILER_PATH
The value of @env{COMPILER_PATH} is a colon-separated list of
directories, much like @env{PATH}. GCC tries the directories thus
specified when searching for subprograms, if it can't find the
subprograms using @env{GCC_EXEC_PREFIX}.
@item LIBRARY_PATH
@findex LIBRARY_PATH
The value of @env{LIBRARY_PATH} is a colon-separated list of
directories, much like @env{PATH}. When configured as a native compiler,
GCC tries the directories thus specified when searching for special
linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
using GCC also uses these directories when searching for ordinary
libraries for the @option{-l} option (but directories specified with
@option{-L} come first).
@item C_INCLUDE_PATH
@itemx CPLUS_INCLUDE_PATH
@itemx OBJC_INCLUDE_PATH
@findex C_INCLUDE_PATH
@findex CPLUS_INCLUDE_PATH
@findex OBJC_INCLUDE_PATH
@c @itemx OBJCPLUS_INCLUDE_PATH
These environment variables pertain to particular languages. Each
variable's value is a colon-separated list of directories, much like
@env{PATH}. When GCC searches for header files, it tries the
directories listed in the variable for the language you are using, after
the directories specified with @option{-I} but before the standard header
file directories.
@item DEPENDENCIES_OUTPUT
@findex DEPENDENCIES_OUTPUT
@cindex dependencies for make as output
If this variable is set, its value specifies how to output dependencies
for Make based on the header files processed by the compiler. This
output looks much like the output from the @option{-M} option
(@pxref{Preprocessor Options}), but it goes to a separate file, and is
in addition to the usual results of compilation.
The value of @env{DEPENDENCIES_OUTPUT} can be just a file name, in
which case the Make rules are written to that file, guessing the target
name from the source file name. Or the value can have the form
@samp{@var{file} @var{target}}, in which case the rules are written to
file @var{file} using @var{target} as the target name.
@item LANG
@findex LANG
@cindex locale definition
This variable is used to pass locale information to the compiler. One way in
which this information is used is to determine the character set to be used
when character literals, string literals and comments are parsed in C and C++.
When the compiler is configured to allow multibyte characters,
the following values for @env{LANG} are recognized:
@table @samp
@item C-JIS
Recognize JIS characters.
@item C-SJIS
Recognize SJIS characters.
@item C-EUCJP
Recognize EUCJP characters.
@end table
If @env{LANG} is not defined, or if it has some other value, then the
compiler will use mblen and mbtowc as defined by the default locale to
recognize and translate multibyte characters.
@end table
@c man end
@node Running Protoize
@section Running Protoize
The program @code{protoize} is an optional part of GCC@. You can use
it to add prototypes to a program, thus converting the program to ISO
C in one respect. The companion program @code{unprotoize} does the
reverse: it removes argument types from any prototypes that are found.
When you run these programs, you must specify a set of source files as
command line arguments. The conversion programs start out by compiling
these files to see what functions they define. The information gathered
about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
After scanning comes actual conversion. The specified files are all
eligible to be converted; any files they include (whether sources or
just headers) are eligible as well.
But not all the eligible files are converted. By default,
@code{protoize} and @code{unprotoize} convert only source and header
files in the current directory. You can specify additional directories
whose files should be converted with the @option{-d @var{directory}}
option. You can also specify particular files to exclude with the
@option{-x @var{file}} option. A file is converted if it is eligible, its
directory name matches one of the specified directory names, and its
name within the directory has not been excluded.
Basic conversion with @code{protoize} consists of rewriting most
function definitions and function declarations to specify the types of
the arguments. The only ones not rewritten are those for varargs
functions.
@code{protoize} optionally inserts prototype declarations at the
beginning of the source file, to make them available for any calls that
precede the function's definition. Or it can insert prototype
declarations with block scope in the blocks where undeclared functions
are called.
Basic conversion with @code{unprotoize} consists of rewriting most
function declarations to remove any argument types, and rewriting
function definitions to the old-style pre-ISO form.
Both conversion programs print a warning for any function declaration or
definition that they can't convert. You can suppress these warnings
with @option{-q}.
The output from @code{protoize} or @code{unprotoize} replaces the
original source file. The original file is renamed to a name ending
with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
for DOS) file already exists, then the source file is simply discarded.
@code{protoize} and @code{unprotoize} both depend on GCC itself to
scan the program and collect information about the functions it uses.
So neither of these programs will work until GCC is installed.
Here is a table of the options you can use with @code{protoize} and
@code{unprotoize}. Each option works with both programs unless
otherwise stated.
@table @code
@item -B @var{directory}
Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
usual directory (normally @file{/usr/local/lib}). This file contains
prototype information about standard system functions. This option
applies only to @code{protoize}.
@item -c @var{compilation-options}
Use @var{compilation-options} as the options when running @code{gcc} to
produce the @samp{.X} files. The special option @option{-aux-info} is
always passed in addition, to tell @code{gcc} to write a @samp{.X} file.
Note that the compilation options must be given as a single argument to
@code{protoize} or @code{unprotoize}. If you want to specify several
@code{gcc} options, you must quote the entire set of compilation options
to make them a single word in the shell.
There are certain @code{gcc} arguments that you cannot use, because they
would produce the wrong kind of output. These include @option{-g},
@option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
the @var{compilation-options}, they are ignored.
@item -C
Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
systems) instead of @samp{.c}. This is convenient if you are converting
a C program to C++. This option applies only to @code{protoize}.
@item -g
Add explicit global declarations. This means inserting explicit
declarations at the beginning of each source file for each function
that is called in the file and was not declared. These declarations
precede the first function definition that contains a call to an
undeclared function. This option applies only to @code{protoize}.
@item -i @var{string}
Indent old-style parameter declarations with the string @var{string}.
This option applies only to @code{protoize}.
@code{unprotoize} converts prototyped function definitions to old-style
function definitions, where the arguments are declared between the
argument list and the initial @samp{@{}. By default, @code{unprotoize}
uses five spaces as the indentation. If you want to indent with just
one space instead, use @option{-i " "}.
@item -k
Keep the @samp{.X} files. Normally, they are deleted after conversion
is finished.
@item -l
Add explicit local declarations. @code{protoize} with @option{-l} inserts
a prototype declaration for each function in each block which calls the
function without any declaration. This option applies only to
@code{protoize}.
@item -n
Make no real changes. This mode just prints information about the conversions
that would have been done without @option{-n}.
@item -N
Make no @samp{.save} files. The original files are simply deleted.
Use this option with caution.
@item -p @var{program}
Use the program @var{program} as the compiler. Normally, the name
@file{gcc} is used.
@item -q
Work quietly. Most warnings are suppressed.
@item -v
Print the version number, just like @option{-v} for @code{gcc}.
@end table
If you need special compiler options to compile one of your program's
source files, then you should generate that file's @samp{.X} file
specially, by running @code{gcc} on that source file with the
appropriate options and the option @option{-aux-info}. Then run
@code{protoize} on the entire set of files. @code{protoize} will use
the existing @samp{.X} file because it is newer than the source file.
For example:
@example
gcc -Dfoo=bar file1.c -aux-info file1.X
protoize *.c
@end example
@noindent
You need to include the special files along with the rest in the
@code{protoize} command, even though their @samp{.X} files already
exist, because otherwise they won't get converted.
@xref{Protoize Caveats}, for more information on how to use
@code{protoize} successfully.