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.\" ======================================================================
.\"
.IX Title "GCC 1"
.TH GCC 1 "gcc-3.1" "2001-03-09" "GNU"
.UC
.SH "NAME"
gcc \- \s-1GNU\s0 project C and \*(C+ compiler
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
gcc [\fB\-c\fR|\fB\-S\fR|\fB\-E\fR] [\fB\-std=\fR\fIstandard\fR]
[\fB\-g\fR] [\fB\-pg\fR] [\fB\-O\fR\fIlevel\fR]
[\fB\-W\fR\fIwarn\fR...] [\fB\-pedantic\fR]
[\fB\-I\fR\fIdir\fR...] [\fB\-L\fR\fIdir\fR...]
[\fB\-D\fR\fImacro\fR[=\fIdefn\fR]...] [\fB\-U\fR\fImacro\fR]
[\fB\-f\fR\fIoption\fR...] [\fB\-m\fR\fImachine-option\fR...]
[\fB\-o\fR \fIoutfile\fR] \fIinfile\fR...
.PP
Only the most useful options are listed here; see below for the
remainder. \fBg++\fR accepts mostly the same options as \fBgcc\fR.
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
When you invoke \s-1GCC\s0, it normally does preprocessing, compilation,
assembly and linking. The ``overall options'' allow you to stop this
process at an intermediate stage. For example, the \fB\-c\fR option
says not to run the linker. Then the output consists of object files
output by the assembler.
.PP
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.
.PP
Most of the command line options that you can use with \s-1GCC\s0 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.
.PP
The \fBgcc\fR program accepts options and file names as operands. Many
options have multi-letter names; therefore multiple single-letter options
may \fInot\fR be grouped: \fB\-dr\fR is very different from \fB\-d\ \-r\fR.
.PP
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 \fB\-L\fR more than once,
the directories are searched in the order specified.
.PP
Many options have long names starting with \fB\-f\fR or with
\&\fB\-W\fR\-\-\-for example, \fB\-fforce-mem\fR,
\&\fB\-fstrength-reduce\fR, \fB\-Wformat\fR and so on. Most of
these have both positive and negative forms; the negative form of
\&\fB\-ffoo\fR would be \fB\-fno-foo\fR. This manual documents
only one of these two forms, whichever one is not the default.
.SH "OPTIONS"
.IX Header "OPTIONS"
.Sh "Option Summary"
.IX Subsection "Option Summary"
Here is a summary of all the options, grouped by type. Explanations are
in the following sections.
.Ip "\fIOverall Options\fR" 4
.IX Item "Overall Options"
\&\fB\-c \-S \-E \-o\fR \fIfile\fR \fB\-pipe \-pass-exit-codes \-x\fR \fIlanguage\fR
\&\fB\-v \-\-target-help \-\-help\fR
.Ip "\fIC Language Options\fR" 4
.IX Item "C Language Options"
\&\fB\-ansi \-std=\fR\fIstandard\fR \fB\-fno-asm \-fno-builtin
\&\-fhosted \-ffreestanding
\&\-trigraphs \-traditional \-traditional-cpp
\&\-fallow-single-precision \-fcond-mismatch
\&\-fsigned-bitfields \-fsigned-char
\&\-funsigned-bitfields \-funsigned-char
\&\-fwritable-strings \-fshort-wchar\fR
.Ip "\fI\*(C+ Language Options\fR" 4
.IX Item " Language Options"
\&\fB\-fno-access-control \-fcheck-new \-fconserve-space
\&\-fdollars-in-identifiers \-fno-elide-constructors
\&\-fno-enforce-eh-specs \-fexternal-templates
\&\-falt-external-templates
\&\-ffor-scope \-fno-for-scope \-fno-gnu-keywords \-fhonor-std
\&\-fhuge-objects \-fno-implicit-templates
\&\-fno-implicit-inline-templates
\&\-fno-implement-inlines \-fms-extensions
\&\-fno-operator-names
\&\-fno-optional-diags \-fpermissive
\&\-frepo \-fno-rtti \-ftemplate-depth-\fR\fIn\fR
\&\fB\-fuse-cxa-atexit \-fvtable-thunks \-nostdinc++
\&\-fno-default-inline \-Wctor-dtor-privacy
\&\-Wnon-virtual-dtor \-Wreorder
\&\-Weffc++ \-Wno-deprecated
\&\-Wno-non-template-friend \-Wold-style-cast
\&\-Woverloaded-virtual \-Wno-pmf-conversions
\&\-Wsign-promo \-Wsynth\fR
.Ip "\fILanguage Independent Options\fR" 4
.IX Item "Language Independent Options"
\&\fB\-fmessage-length=\fR\fIn\fR
\&\fB\-fdiagnostics-show-location=\fR[\fBonce\fR|\fBevery-line\fR]
.Ip "\fIWarning Options\fR" 4
.IX Item "Warning Options"
\&\fB\-fsyntax-only \-pedantic \-pedantic-errors
\&\-w \-W \-Wall \-Waggregate-return
\&\-Wcast-align \-Wcast-qual \-Wchar-subscripts \-Wcomment
\&\-Wconversion \-Wdisabled-optimization \-Werror
\&\-Wfloat-equal \-Wformat \-Wformat=2
\&\-Wformat-nonliteral \-Wformat-security
\&\-Wid-clash-\fR\fIlen\fR \fB\-Wimplicit \-Wimplicit-int
\&\-Wimplicit-function-declaration
\&\-Werror-implicit-function-declaration
\&\-Wimport \-Winline
\&\-Wlarger-than-\fR\fIlen\fR \fB\-Wlong-long
\&\-Wmain \-Wmissing-declarations
\&\-Wmissing-format-attribute \-Wmissing-noreturn
\&\-Wmultichar \-Wno-format-extra-args \-Wno-format-y2k
\&\-Wno-import \-Wpacked \-Wpadded
\&\-Wparentheses \-Wpointer-arith \-Wredundant-decls
\&\-Wreturn-type \-Wsequence-point \-Wshadow
\&\-Wsign-compare \-Wswitch \-Wsystem-headers
\&\-Wtrigraphs \-Wundef \-Wuninitialized
\&\-Wunknown-pragmas \-Wunreachable-code
\&\-Wunused \-Wunused-function \-Wunused-label \-Wunused-parameter
\&\-Wunused-value \-Wunused-variable \-Wwrite-strings\fR
.Ip "\fIC-only Warning Options\fR" 4
.IX Item "C-only Warning Options"
\&\fB\-Wbad-function-cast \-Wmissing-prototypes \-Wnested-externs
\&\-Wstrict-prototypes \-Wtraditional\fR
.Ip "\fIDebugging Options\fR" 4
.IX Item "Debugging Options"
\&\fB\-a \-ax \-d\fR\fIletters\fR \fB\-fdump-unnumbered \-fdump-translation-unit=\fR\fIfile\fR
\&\fB\-fdump-class-layout=\fR\fIfile\fR \fB\-fpretend-float \-fprofile-arcs \-ftest-coverage
\&\-g \-g\fR\fIlevel\fR \fB\-gcoff \-gdwarf \-gdwarf-1 \-gdwarf-1+ \-gdwarf-2
\&\-ggdb \-gstabs \-gstabs+ \-gxcoff \-gxcoff+
\&\-p \-pg \-print-file-name=\fR\fIlibrary\fR \fB\-print-libgcc-file-name
\&\-print-prog-name=\fR\fIprogram\fR \fB\-print-search-dirs \-Q
\&\-save-temps \-time\fR
.Ip "\fIOptimization Options\fR" 4
.IX Item "Optimization Options"
\&\fB\-falign-functions=\fR\fIn\fR \fB\-falign-jumps=\fR\fIn\fR
\&\fB\-falign-labels=\fR\fIn\fR \fB\-falign-loops=\fR\fIn\fR
\&\fB\-fbranch-probabilities \-fcaller-saves
\&\-fcse-follow-jumps \-fcse-skip-blocks \-fdata-sections \-fdce
\&\-fdelayed-branch \-fdelete-null-pointer-checks
\&\-fexpensive-optimizations \-ffast-math \-ffloat-store
\&\-fforce-addr \-fforce-mem \-ffunction-sections \-fgcse
\&\-finline-functions \-finline-limit=\fR\fIn\fR \fB\-fkeep-inline-functions
\&\-fkeep-static-consts \-fmove-all-movables
\&\-fno-default-inline \-fno-defer-pop
\&\-fno-function-cse \-fno-guess-branch-probability
\&\-fno-inline \-fno-math-errno \-fno-peephole
\&\-funsafe-math-optimizations \-fno-trapping-math
\&\-fomit-frame-pointer \-foptimize-register-move
\&\-foptimize-sibling-calls \-freduce-all-givs
\&\-fregmove \-frename-registers
\&\-frerun-cse-after-loop \-frerun-loop-opt
\&\-fschedule-insns \-fschedule-insns2
\&\-fsingle-precision-constant \-fssa
\&\-fstrength-reduce \-fstrict-aliasing \-fthread-jumps \-ftrapv
\&\-funroll-all-loops \-funroll-loops
\&\-\-param\fR \fIname\fR\fB=\fR\fIvalue\fR
\&\fB\-O \-O0 \-O1 \-O2 \-O3 \-Os\fR
.Ip "\fIPreprocessor Options\fR" 4
.IX Item "Preprocessor Options"
\&\fB\-$ \-A\fR\fIquestion\fR\fB=\fR\fIanswer\fR \fB\-A-\fR\fIquestion\fR[\fB=\fR\fIanswer\fR]
\&\fB\-C \-dD \-dI \-dM \-dN
\&\-D\fR\fImacro\fR[\fB=\fR\fIdefn\fR] \fB\-E \-H
\&\-idirafter\fR \fIdir\fR
\&\fB\-include\fR \fIfile\fR \fB\-imacros\fR \fIfile\fR
\&\fB\-iprefix\fR \fIfile\fR \fB\-iwithprefix\fR \fIdir\fR
\&\fB\-iwithprefixbefore\fR \fIdir\fR \fB\-isystem\fR \fIdir\fR \fB\-isystem-c++\fR \fIdir\fR
\&\fB\-M \-MM \-MF \-MG \-MP \-MQ \-MT \-nostdinc \-P \-remap
\&\-trigraphs \-undef \-U\fR\fImacro\fR \fB\-Wp,\fR\fIoption\fR
.Ip "\fIAssembler Option\fR" 4
.IX Item "Assembler Option"
\&\fB\-Wa,\fR\fIoption\fR
.Ip "\fILinker Options\fR" 4
.IX Item "Linker Options"
\&\fB
\&\fR\fIobject-file-name\fR \fB\-l\fR\fIlibrary\fR
\&\fB\-nostartfiles \-nodefaultlibs \-nostdlib
\&\-s \-static \-static-libgcc \-shared \-shared-libgcc \-symbolic
\&\-Wl,\fR\fIoption\fR \fB\-Xlinker\fR \fIoption\fR
\&\fB\-u\fR \fIsymbol\fR
.Ip "\fIDirectory Options\fR" 4
.IX Item "Directory Options"
\&\fB\-B\fR\fIprefix\fR \fB\-I\fR\fIdir\fR \fB\-I- \-L\fR\fIdir\fR \fB\-specs=\fR\fIfile\fR
.Ip "\fITarget Options\fR" 4
.IX Item "Target Options"
\&\fB\-b\fR \fImachine\fR \fB\-V\fR \fIversion\fR
.Ip "\fIMachine Dependent Options\fR" 4
.IX Item "Machine Dependent Options"
\&\fIM680x0 Options\fR
.Sp
\&\fB\-m68000 \-m68020 \-m68020\-40 \-m68020\-60 \-m68030 \-m68040
\&\-m68060 \-mcpu32 \-m5200 \-m68881 \-mbitfield \-mc68000 \-mc68020
\&\-mfpa \-mnobitfield \-mrtd \-mshort \-msoft-float \-mpcrel
\&\-malign-int \-mstrict-align\fR
.Sp
\&\fIM68hc1x Options\fR
.Sp
\&\fB\-m6811 \-m6812 \-m68hc11 \-m68hc12
\&\-mauto-incdec \-mshort \-msoft-reg-count=\fR\fIcount\fR
.Sp
\&\fI\s-1VAX\s0 Options\fR
.Sp
\&\fB\-mg \-mgnu \-munix\fR
.Sp
\&\fI\s-1SPARC\s0 Options\fR
.Sp
\&\fB\-mcpu=\fR\fIcpu type\fR
\&\fB\-mtune=\fR\fIcpu type\fR
\&\fB\-mcmodel=\fR\fIcode model\fR
\&\fB\-m32 \-m64
\&\-mapp-regs \-mbroken-saverestore \-mcypress
\&\-mepilogue \-mfaster-structs \-mflat
\&\-mfpu \-mhard-float \-mhard-quad-float
\&\-mimpure-text \-mlive-g0 \-mno-app-regs
\&\-mno-epilogue \-mno-faster-structs \-mno-flat \-mno-fpu
\&\-mno-impure-text \-mno-stack-bias \-mno-unaligned-doubles
\&\-msoft-float \-msoft-quad-float \-msparclite \-mstack-bias
\&\-msupersparc \-munaligned-doubles \-mv8\fR
.Sp
\&\fIConvex Options\fR
.Sp
\&\fB\-mc1 \-mc2 \-mc32 \-mc34 \-mc38
\&\-margcount \-mnoargcount
\&\-mlong32 \-mlong64
\&\-mvolatile-cache \-mvolatile-nocache\fR
.Sp
\&\fI\s-1AMD29K\s0 Options\fR
.Sp
\&\fB\-m29000 \-m29050 \-mbw \-mnbw \-mdw \-mndw
\&\-mlarge \-mnormal \-msmall
\&\-mkernel-registers \-mno-reuse-arg-regs
\&\-mno-stack-check \-mno-storem-bug
\&\-mreuse-arg-regs \-msoft-float \-mstack-check
\&\-mstorem-bug \-muser-registers\fR
.Sp
\&\fI\s-1ARM\s0 Options\fR
.Sp
\&\fB\-mapcs-frame \-mno-apcs-frame
\&\-mapcs-26 \-mapcs-32
\&\-mapcs-stack-check \-mno-apcs-stack-check
\&\-mapcs-float \-mno-apcs-float
\&\-mapcs-reentrant \-mno-apcs-reentrant
\&\-msched-prolog \-mno-sched-prolog
\&\-mlittle-endian \-mbig-endian \-mwords-little-endian
\&\-malignment-traps \-mno-alignment-traps
\&\-msoft-float \-mhard-float \-mfpe
\&\-mthumb-interwork \-mno-thumb-interwork
\&\-mcpu= \-march= \-mfpe=
\&\-mstructure-size-boundary=
\&\-mbsd \-mxopen \-mno-symrename
\&\-mabort-on-noreturn
\&\-mlong-calls \-mno-long-calls
\&\-mnop-fun-dllimport \-mno-nop-fun-dllimport
\&\-msingle-pic-base \-mno-single-pic-base
\&\-mpic-register=\fR
.Sp
\&\fIThumb Options\fR
.Sp
\&\fB\-mtpcs-frame \-mno-tpcs-frame
\&\-mtpcs-leaf-frame \-mno-tpcs-leaf-frame
\&\-mlittle-endian \-mbig-endian
\&\-mthumb-interwork \-mno-thumb-interwork
\&\-mstructure-size-boundary=
\&\-mnop-fun-dllimport \-mno-nop-fun-dllimport
\&\-mcallee-super-interworking \-mno-callee-super-interworking
\&\-mcaller-super-interworking \-mno-caller-super-interworking
\&\-msingle-pic-base \-mno-single-pic-base
\&\-mpic-register=\fR
.Sp
\&\fI\s-1MN10200\s0 Options\fR
.Sp
\&\fB\-mrelax\fR
.Sp
\&\fI\s-1MN10300\s0 Options\fR
.Sp
\&\fB\-mmult-bug
\&\-mno-mult-bug
\&\-mam33
\&\-mno-am33
\&\-mrelax\fR
.Sp
\&\fIM32R/D Options\fR
.Sp
\&\fB\-mcode-model=\fR\fImodel type\fR \fB\-msdata=\fR\fIsdata type\fR
\&\fB\-G\fR \fInum\fR
.Sp
\&\fIM88K Options\fR
.Sp
\&\fB\-m88000 \-m88100 \-m88110 \-mbig-pic
\&\-mcheck-zero-division \-mhandle-large-shift
\&\-midentify-revision \-mno-check-zero-division
\&\-mno-ocs-debug-info \-mno-ocs-frame-position
\&\-mno-optimize-arg-area \-mno-serialize-volatile
\&\-mno-underscores \-mocs-debug-info
\&\-mocs-frame-position \-moptimize-arg-area
\&\-mserialize-volatile \-mshort-data-\fR\fInum\fR \fB\-msvr3
\&\-msvr4 \-mtrap-large-shift \-muse-div-instruction
\&\-mversion-03.00 \-mwarn-passed-structs\fR
.Sp
\&\fI\s-1RS/6000\s0 and PowerPC Options\fR
.Sp
\&\fB\-mcpu=\fR\fIcpu type\fR
\&\fB\-mtune=\fR\fIcpu type\fR
\&\fB\-mpower \-mno-power \-mpower2 \-mno-power2
\&\-mpowerpc \-mpowerpc64 \-mno-powerpc
\&\-mpowerpc-gpopt \-mno-powerpc-gpopt
\&\-mpowerpc-gfxopt \-mno-powerpc-gfxopt
\&\-mnew-mnemonics \-mold-mnemonics
\&\-mfull-toc \-mminimal-toc \-mno-fop-in-toc \-mno-sum-in-toc
\&\-m64 \-m32 \-mxl-call \-mno-xl-call \-mthreads \-mpe
\&\-msoft-float \-mhard-float \-mmultiple \-mno-multiple
\&\-mstring \-mno-string \-mupdate \-mno-update
\&\-mfused-madd \-mno-fused-madd \-mbit-align \-mno-bit-align
\&\-mstrict-align \-mno-strict-align \-mrelocatable
\&\-mno-relocatable \-mrelocatable-lib \-mno-relocatable-lib
\&\-mtoc \-mno-toc \-mlittle \-mlittle-endian \-mbig \-mbig-endian
\&\-mcall-aix \-mcall-sysv \-mprototype \-mno-prototype
\&\-msim \-mmvme \-mads \-myellowknife \-memb \-msdata
\&\-msdata=\fR\fIopt\fR \fB\-mvxworks \-G\fR \fInum\fR
.Sp
\&\fI\s-1RT\s0 Options\fR
.Sp
\&\fB\-mcall-lib-mul \-mfp-arg-in-fpregs \-mfp-arg-in-gregs
\&\-mfull-fp-blocks \-mhc-struct-return \-min-line-mul
\&\-mminimum-fp-blocks \-mnohc-struct-return\fR
.Sp
\&\fI\s-1MIPS\s0 Options\fR
.Sp
\&\fB\-mabicalls \-mcpu=\fR\fIcpu type\fR
\&\fB\-membedded-data \-muninit-const-in-rodata
\&\-membedded-pic \-mfp32 \-mfp64 \-mgas \-mgp32 \-mgp64
\&\-mgpopt \-mhalf-pic \-mhard-float \-mint64 \-mips1
\&\-mips2 \-mips3 \-mips4 \-mlong64 \-mlong32 \-mlong-calls \-mmemcpy
\&\-mmips-as \-mmips-tfile \-mno-abicalls
\&\-mno-embedded-data \-mno-uninit-const-in-rodata \-mno-embedded-pic
\&\-mno-gpopt \-mno-long-calls
\&\-mno-memcpy \-mno-mips-tfile \-mno-rnames \-mno-stats
\&\-mrnames \-msoft-float
\&\-m4650 \-msingle-float \-mmad
\&\-mstats \-EL \-EB \-G\fR \fInum\fR \fB\-nocpp
\&\-mabi=32 \-mabi=n32 \-mabi=64 \-mabi=eabi
\&\-mfix7000 \-mno-crt0\fR
.Sp
\&\fIi386 Options\fR
.Sp
\&\fB\-mcpu=\fR\fIcpu type\fR \fB\-march=\fR\fIcpu type\fR
\&\fB\-mintel-syntax \-mieee-fp \-mno-fancy-math-387
\&\-mno-fp-ret-in-387 \-msoft-float \-msvr3\-shlib
\&\-mno-wide-multiply \-mrtd \-malign-double
\&\-malign-jumps=\fR\fInum\fR \fB\-malign-loops=\fR\fInum\fR
\&\fB\-malign-functions=\fR\fInum\fR \fB\-mpreferred-stack-boundary=\fR\fInum\fR
\&\fB\-mthreads \-mno-align-stringops \-minline-all-stringops
\&\-mpush-args \-maccumulate-outgoing-args \-m128bit-long-double
\&\-m96bit-long-double \-mregparm=\fR\fInum\fR
.Sp
\&\fI\s-1HPPA\s0 Options\fR
.Sp
\&\fB\-march=\fR\fIarchitecture type\fR
\&\fB\-mbig-switch \-mdisable-fpregs \-mdisable-indexing
\&\-mfast-indirect-calls \-mgas \-mjump-in-delay
\&\-mlong-load-store \-mno-big-switch \-mno-disable-fpregs
\&\-mno-disable-indexing \-mno-fast-indirect-calls \-mno-gas
\&\-mno-jump-in-delay \-mno-long-load-store
\&\-mno-portable-runtime \-mno-soft-float
\&\-mno-space-regs \-msoft-float \-mpa-risc-1\-0
\&\-mpa-risc-1\-1 \-mpa-risc-2\-0 \-mportable-runtime
\&\-mschedule=\fR\fIcpu type\fR \fB\-mspace-regs\fR
.Sp
\&\fIIntel 960 Options\fR
.Sp
\&\fB\-m\fR\fIcpu type\fR \fB\-masm-compat \-mclean-linkage
\&\-mcode-align \-mcomplex-addr \-mleaf-procedures
\&\-mic-compat \-mic2.0\-compat \-mic3.0\-compat
\&\-mintel-asm \-mno-clean-linkage \-mno-code-align
\&\-mno-complex-addr \-mno-leaf-procedures
\&\-mno-old-align \-mno-strict-align \-mno-tail-call
\&\-mnumerics \-mold-align \-msoft-float \-mstrict-align
\&\-mtail-call\fR
.Sp
\&\fI\s-1DEC\s0 Alpha Options\fR
.Sp
\&\fB\-mfp-regs \-mno-fp-regs \-mno-soft-float \-msoft-float
\&\-malpha-as \-mgas
\&\-mieee \-mieee-with-inexact \-mieee-conformant
\&\-mfp-trap-mode=\fR\fImode\fR \fB\-mfp-rounding-mode=\fR\fImode\fR
\&\fB\-mtrap-precision=\fR\fImode\fR \fB\-mbuild-constants
\&\-mcpu=\fR\fIcpu type\fR
\&\fB\-mbwx \-mno-bwx \-mcix \-mno-cix \-mmax \-mno-max
\&\-mmemory-latency=\fR\fItime\fR
.Sp
\&\fIClipper Options\fR
.Sp
\&\fB\-mc300 \-mc400\fR
.Sp
\&\fIH8/300 Options\fR
.Sp
\&\fB\-mrelax \-mh \-ms \-mint32 \-malign-300\fR
.Sp
\&\fI\s-1SH\s0 Options\fR
.Sp
\&\fB\-m1 \-m2 \-m3 \-m3e
\&\-m4\-nofpu \-m4\-single-only \-m4\-single \-m4
\&\-mb \-ml \-mdalign \-mrelax
\&\-mbigtable \-mfmovd \-mhitachi \-mnomacsave
\&\-misize \-mpadstruct \-mspace
\&\-mprefergot
\&\-musermode\fR
.Sp
\&\fISystem V Options\fR
.Sp
\&\fB\-Qy \-Qn \-YP,\fR\fIpaths\fR \fB\-Ym,\fR\fIdir\fR
.Sp
\&\fI\s-1ARC\s0 Options\fR
.Sp
\&\fB\-EB \-EL
\&\-mmangle-cpu \-mcpu=\fR\fIcpu\fR \fB\-mtext=\fR\fItext section\fR
\&\fB\-mdata=\fR\fIdata section\fR \fB\-mrodata=\fR\fIreadonly data section\fR
.Sp
\&\fITMS320C3x/C4x Options\fR
.Sp
\&\fB\-mcpu=\fR\fIcpu\fR \fB\-mbig \-msmall \-mregparm \-mmemparm
\&\-mfast-fix \-mmpyi \-mbk \-mti \-mdp-isr-reload
\&\-mrpts=\fR\fIcount\fR \fB\-mrptb \-mdb \-mloop-unsigned
\&\-mparallel-insns \-mparallel-mpy \-mpreserve-float\fR
.Sp
\&\fIV850 Options\fR
.Sp
\&\fB\-mlong-calls \-mno-long-calls \-mep \-mno-ep
\&\-mprolog-function \-mno-prolog-function \-mspace
\&\-mtda=\fR\fIn\fR \fB\-msda=\fR\fIn\fR \fB\-mzda=\fR\fIn\fR
\&\fB\-mv850 \-mbig-switch\fR
.Sp
\&\fI\s-1NS32K\s0 Options\fR
.Sp
\&\fB\-m32032 \-m32332 \-m32532 \-m32081 \-m32381 \-mmult-add \-mnomult-add
\&\-msoft-float \-mrtd \-mnortd \-mregparam \-mnoregparam \-msb \-mnosb
\&\-mbitfield \-mnobitfield \-mhimem \-mnohimem\fR
.Sp
\&\fI\s-1AVR\s0 Options\fR
.Sp
\&\fB\-mmcu=\fR\fImcu\fR \fB\-msize \-minit-stack=\fR\fIn\fR \fB\-mno-interrupts
\&\-mcall-prologues \-mno-tablejump \-mtiny-stack\fR
.Sp
\&\fIMCore Options\fR
.Sp
\&\fB\-mhardlit \-mno-hardlit \-mdiv \-mno-div \-mrelax-immediates
\&\-mno-relax-immediates \-mwide-bitfields \-mno-wide-bitfields
\&\-m4byte-functions \-mno-4byte-functions \-mcallgraph-data
\&\-mno-callgraph-data \-mslow-bytes \-mno-slow-bytes \-mno-lsim
\&\-mlittle-endian \-mbig-endian \-m210 \-m340 \-mstack-increment\fR
.Sp
\&\fI\s-1IA-64\s0 Options\fR
.Sp
\&\fB\-mbig-endian \-mlittle-endian \-mgnu-as \-mgnu-ld \-mno-pic
\&\-mvolatile-asm-stop \-mb-step \-mregister-names \-mno-sdata
\&\-mconstant-gp \-mauto-pic \-minline-divide-min-latency
\&\-minline-divide-max-throughput \-mno-dwarf2\-asm
\&\-mfixed-range=\fR\fIregister range\fR
.Ip "\fICode Generation Options\fR" 4
.IX Item "Code Generation Options"
\&\fB\-fcall-saved-\fR\fIreg\fR \fB\-fcall-used-\fR\fIreg\fR
\&\fB\-fexceptions \-funwind-tables \-ffixed-\fR\fIreg\fR
\&\fB\-finhibit-size-directive \-finstrument-functions
\&\-fcheck-memory-usage \-fprefix-function-name
\&\-fno-common \-fno-ident \-fno-gnu-linker
\&\-fpcc-struct-return \-fpic \-fPIC
\&\-freg-struct-return \-fshared-data \-fshort-enums
\&\-fshort-double \-fvolatile \-fvolatile-global \-fvolatile-static
\&\-fverbose-asm \-fpack-struct \-fstack-check
\&\-fstack-limit-register=\fR\fIreg\fR \fB\-fstack-limit-symbol=\fR\fIsym\fR
\&\fB\-fargument-alias \-fargument-noalias
\&\-fargument-noalias-global
\&\-fleading-underscore\fR
.Sh "Options Controlling the Kind of Output"
.IX Subsection "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.
.PP
For any given input file, the file name suffix determines what kind of
compilation is done:
.Ip "\fIfile\fR\fB.c\fR" 4
.IX Item "file.c"
C source code which must be preprocessed.
.Ip "\fIfile\fR\fB.i\fR" 4
.IX Item "file.i"
C source code which should not be preprocessed.
.Ip "\fIfile\fR\fB.ii\fR" 4
.IX Item "file.ii"
\&\*(C+ source code which should not be preprocessed.
.Ip "\fIfile\fR\fB.m\fR" 4
.IX Item "file.m"
Objective-C source code. Note that you must link with the library
\&\fIlibobjc.a\fR to make an Objective-C program work.
.Ip "\fIfile\fR\fB.mi\fR" 4
.IX Item "file.mi"
Objective-C source code which should not be preprocessed.
.Ip "\fIfile\fR\fB.h\fR" 4
.IX Item "file.h"
C header file (not to be compiled or linked).
.Ip "\fIfile\fR\fB.cc\fR" 4
.IX Item "file.cc"
.PD 0
.Ip "\fIfile\fR\fB.cp\fR" 4
.IX Item "file.cp"
.Ip "\fIfile\fR\fB.cxx\fR" 4
.IX Item "file.cxx"
.Ip "\fIfile\fR\fB.cpp\fR" 4
.IX Item "file.cpp"
.Ip "\fIfile\fR\fB.c++\fR" 4
.IX Item "file.c++"
.Ip "\fIfile\fR\fB.C\fR" 4
.IX Item "file.C"
.PD
\&\*(C+ source code which must be preprocessed. Note that in \fB.cxx\fR,
the last two letters must both be literally \fBx\fR. Likewise,
\&\fB.C\fR refers to a literal capital C.
.Ip "\fIfile\fR\fB.f\fR" 4
.IX Item "file.f"
.PD 0
.Ip "\fIfile\fR\fB.for\fR" 4
.IX Item "file.for"
.Ip "\fIfile\fR\fB.FOR\fR" 4
.IX Item "file.FOR"
.PD
Fortran source code which should not be preprocessed.
.Ip "\fIfile\fR\fB.F\fR" 4
.IX Item "file.F"
.PD 0
.Ip "\fIfile\fR\fB.fpp\fR" 4
.IX Item "file.fpp"
.Ip "\fIfile\fR\fB.FPP\fR" 4
.IX Item "file.FPP"
.PD
Fortran source code which must be preprocessed (with the traditional
preprocessor).
.Ip "\fIfile\fR\fB.r\fR" 4
.IX Item "file.r"
Fortran source code which must be preprocessed with a \s-1RATFOR\s0
preprocessor (not included with \s-1GCC\s0).
.Ip "\fIfile\fR\fB.ch\fR" 4
.IX Item "file.ch"
.PD 0
.Ip "\fIfile\fR\fB.chi\fR" 4
.IX Item "file.chi"
.PD
\&\s-1CHILL\s0 source code (preprocessed with the traditional preprocessor).
.Ip "\fIfile\fR\fB.s\fR" 4
.IX Item "file.s"
Assembler code.
.Ip "\fIfile\fR\fB.S\fR" 4
.IX Item "file.S"
Assembler code which must be preprocessed.
.Ip "\fIother\fR" 4
.IX Item "other"
An object file to be fed straight into linking.
Any file name with no recognized suffix is treated this way.
.PP
You can specify the input language explicitly with the \fB\-x\fR option:
.Ip "\fB\-x\fR \fIlanguage\fR" 4
.IX Item "-x language"
Specify explicitly the \fIlanguage\fR 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 \fB\-x\fR option. Possible values for \fIlanguage\fR are:
.Sp
.Vb 6
\& c c-header cpp-output
\& c++ c++-cpp-output
\& objective-c objc-cpp-output
\& assembler assembler-with-cpp
\& f77 f77-cpp-input ratfor
\& java chill
.Ve
.Ip "\fB\-x none\fR" 4
.IX 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 \fB\-x\fR
has not been used at all).
.Ip "\fB\-pass-exit-codes\fR" 4
.IX Item "-pass-exit-codes"
Normally the \fBgcc\fR program will exit with the code of 1 if any
phase of the compiler returns a non-success return code. If you specify
\&\fB\-pass-exit-codes\fR, the \fBgcc\fR program will instead return with
numerically highest error produced by any phase that returned an error
indication.
.PP
If you only want some of the stages of compilation, you can use
\&\fB\-x\fR (or filename suffixes) to tell \fBgcc\fR where to start, and
one of the options \fB\-c\fR, \fB\-S\fR, or \fB\-E\fR to say where
\&\fBgcc\fR is to stop. Note that some combinations (for example,
\&\fB\-x cpp-output \-E\fR) instruct \fBgcc\fR to do nothing at all.
.Ip "\fB\-c\fR" 4
.IX Item "-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.
.Sp
By default, the object file name for a source file is made by replacing
the suffix \fB.c\fR, \fB.i\fR, \fB.s\fR, etc., with \fB.o\fR.
.Sp
Unrecognized input files, not requiring compilation or assembly, are
ignored.
.Ip "\fB\-S\fR" 4
.IX Item "-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.
.Sp
By default, the assembler file name for a source file is made by
replacing the suffix \fB.c\fR, \fB.i\fR, etc., with \fB.s\fR.
.Sp
Input files that don't require compilation are ignored.
.Ip "\fB\-E\fR" 4
.IX Item "-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.
.Sp
Input files which don't require preprocessing are ignored.
.Ip "\fB\-o\fR \fIfile\fR" 4
.IX Item "-o file"
Place output in file \fIfile\fR. 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.
.Sp
Since only one output file can be specified, it does not make sense to
use \fB\-o\fR when compiling more than one input file, unless you are
producing an executable file as output.
.Sp
If \fB\-o\fR is not specified, the default is to put an executable file
in \fIa.out\fR, the object file for \fI\fIsource\fI.\fIsuffix\fI\fR in
\&\fI\fIsource\fI.o\fR, its assembler file in \fI\fIsource\fI.s\fR, and
all preprocessed C source on standard output.
.Ip "\fB\-v\fR" 4
.IX Item "-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.
.Ip "\fB\-pipe\fR" 4
.IX Item "-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 \s-1GNU\s0 assembler has
no trouble.
.Ip "\fB\*(--help\fR" 4
.IX Item "help"
Print (on the standard output) a description of the command line options
understood by \fBgcc\fR. If the \fB\-v\fR option is also specified
then \fB\*(--help\fR will also be passed on to the various processes
invoked by \fBgcc\fR, so that they can display the command line options
they accept. If the \fB\-W\fR option is also specified then command
line options which have no documentation associated with them will also
be displayed.
.Ip "\fB\*(--target-help\fR" 4
.IX Item "target-help"
Print (on the standard output) a description of target specific command
line options for each tool.
.Sh "Compiling \*(C+ Programs"
.IX Subsection "Compiling Programs"
\&\*(C+ source files conventionally use one of the suffixes \fB.C\fR,
\&\fB.cc\fR, \fB.cpp\fR, \fB.c++\fR, \fB.cp\fR, or \fB.cxx\fR;
preprocessed \*(C+ files use the suffix \fB.ii\fR. \s-1GCC\s0 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 \fBgcc\fR).
.PP
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.
\&\fBg++\fR is a program that calls \s-1GCC\s0 with the default language
set to \*(C+, and automatically specifies linking against the \*(C+
library. On many systems, \fBg++\fR is also
installed with the name \fBc++\fR.
.PP
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.
.Sh "Options Controlling C Dialect"
.IX Subsection "Options Controlling C Dialect"
The following options control the dialect of C (or languages derived
from C, such as \*(C+ and Objective C) that the compiler accepts:
.Ip "\fB\-ansi\fR" 4
.IX Item "-ansi"
In C mode, support all \s-1ISO\s0 C89 programs. In \*(C+ mode,
remove \s-1GNU\s0 extensions that conflict with \s-1ISO\s0 \*(C+.
.Sp
This turns off certain features of \s-1GCC\s0 that are incompatible with \s-1ISO\s0
C (when compiling C code), or of standard \*(C+ (when compiling \*(C+ code),
such as the \f(CW\*(C`asm\*(C'\fR and \f(CW\*(C`typeof\*(C'\fR keywords, and
predefined macros such as \f(CW\*(C`unix\*(C'\fR and \f(CW\*(C`vax\*(C'\fR that identify the
type of system you are using. It also enables the undesirable and
rarely used \s-1ISO\s0 trigraph feature. For the C compiler,
it disables recognition of \*(C+ style \fB//\fR comments as well as
the \f(CW\*(C`inline\*(C'\fR keyword.
.Sp
The alternate keywords \f(CW\*(C`_\|_asm_\|_\*(C'\fR, \f(CW\*(C`_\|_extension_\|_\*(C'\fR,
\&\f(CW\*(C`_\|_inline_\|_\*(C'\fR and \f(CW\*(C`_\|_typeof_\|_\*(C'\fR continue to work despite
\&\fB\-ansi\fR. You would not want to use them in an \s-1ISO\s0 C program, of
course, but it is useful to put them in header files that might be included
in compilations done with \fB\-ansi\fR. Alternate predefined macros
such as \f(CW\*(C`_\|_unix_\|_\*(C'\fR and \f(CW\*(C`_\|_vax_\|_\*(C'\fR are also available, with or
without \fB\-ansi\fR.
.Sp
The \fB\-ansi\fR option does not cause non-ISO programs to be
rejected gratuitously. For that, \fB\-pedantic\fR is required in
addition to \fB\-ansi\fR.
.Sp
The macro \f(CW\*(C`_\|_STRICT_ANSI_\|_\*(C'\fR is predefined when the \fB\-ansi\fR
option is used. Some header files may notice this macro and refrain
from declaring certain functions or defining certain macros that the
\&\s-1ISO\s0 standard doesn't call for; this is to avoid interfering with any
programs that might use these names for other things.
.Sp
Functions which would normally be builtin but do not have semantics
defined by \s-1ISO\s0 C (such as \f(CW\*(C`alloca\*(C'\fR and \f(CW\*(C`ffs\*(C'\fR) are not builtin
functions with \fB\-ansi\fR is used.
.Ip "\fB\-std=\fR" 4
.IX Item "-std="
Determine the language standard. A value for this option must be provided;
possible values are
.RS 4
.Ip "\fBiso9899:1990\fR" 4
.IX Item "iso9899:1990"
Same as \fB\-ansi\fR
.Ip "\fBiso9899:199409\fR" 4
.IX Item "iso9899:199409"
\&\s-1ISO\s0 C as modified in amend. 1
.Ip "\fBiso9899:1999\fR" 4
.IX Item "iso9899:1999"
\&\s-1ISO\s0 C99. Note that this standard is not yet fully supported; see
<\fBhttp://gcc.gnu.org/c99status.html\fR> for more information.
.Ip "\fBc89\fR" 4
.IX Item "c89"
same as \fB\-std=iso9899:1990\fR
.Ip "\fBc99\fR" 4
.IX Item "c99"
same as \fB\-std=iso9899:1999\fR
.Ip "\fBgnu89\fR" 4
.IX Item "gnu89"
default, iso9899:1990 + gnu extensions
.Ip "\fBgnu99\fR" 4
.IX Item "gnu99"
iso9899:1999 + gnu extensions
.Ip "\fBiso9899:199x\fR" 4
.IX Item "iso9899:199x"
same as \fB\-std=iso9899:1999\fR, deprecated
.Ip "\fBc9x\fR" 4
.IX Item "c9x"
same as \fB\-std=iso9899:1999\fR, deprecated
.Ip "\fBgnu9x\fR" 4
.IX Item "gnu9x"
same as \fB\-std=gnu99\fR, deprecated
.RE
.RS 4
.Sp
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 \f(CW\*(C`_\|_restrict_\|_\*(C'\fR even
when \fB\-std=c99\fR is not specified.
.Sp
The \fB\-std\fR options specifying some version of \s-1ISO\s0 C have the same
effects as \fB\-ansi\fR, except that features that were not in \s-1ISO\s0 C89
but are in the specified version (for example, \fB//\fR comments and
the \f(CW\*(C`inline\*(C'\fR keyword in \s-1ISO\s0 C99) are not disabled.
.RE
.Ip "\fB\-fno-asm\fR" 4
.IX Item "-fno-asm"
Do not recognize \f(CW\*(C`asm\*(C'\fR, \f(CW\*(C`inline\*(C'\fR or \f(CW\*(C`typeof\*(C'\fR as a
keyword, so that code can use these words as identifiers. You can use
the keywords \f(CW\*(C`_\|_asm_\|_\*(C'\fR, \f(CW\*(C`_\|_inline_\|_\*(C'\fR and \f(CW\*(C`_\|_typeof_\|_\*(C'\fR
instead. \fB\-ansi\fR implies \fB\-fno-asm\fR.
.Sp
In \*(C+, this switch only affects the \f(CW\*(C`typeof\*(C'\fR keyword, since
\&\f(CW\*(C`asm\*(C'\fR and \f(CW\*(C`inline\*(C'\fR are standard keywords. You may want to
use the \fB\-fno-gnu-keywords\fR flag instead, which has the same
effect. In C99 mode (\fB\-std=c99\fR or \fB\-std=gnu99\fR), this
switch only affects the \f(CW\*(C`asm\*(C'\fR and \f(CW\*(C`typeof\*(C'\fR keywords, since
\&\f(CW\*(C`inline\*(C'\fR is a standard keyword in \s-1ISO\s0 C99.
.Ip "\fB\-fno-builtin\fR" 4
.IX Item "-fno-builtin"
Don't recognize builtin functions that do not begin with
\&\fB_\|_builtin_\fR as prefix.
.Sp
\&\s-1GCC\s0 normally generates special code to handle certain builtin functions
more efficiently; for instance, calls to \f(CW\*(C`alloca\*(C'\fR may become single
instructions that adjust the stack directly, and calls to \f(CW\*(C`memcpy\*(C'\fR
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.
.Ip "\fB\-fhosted\fR" 4
.IX Item "-fhosted"
Assert that compilation takes place in a hosted environment. This implies
\&\fB\-fbuiltin\fR. A hosted environment is one in which the
entire standard library is available, and in which \f(CW\*(C`main\*(C'\fR has a return
type of \f(CW\*(C`int\*(C'\fR. Examples are nearly everything except a kernel.
This is equivalent to \fB\-fno-freestanding\fR.
.Ip "\fB\-ffreestanding\fR" 4
.IX Item "-ffreestanding"
Assert that compilation takes place in a freestanding environment. This
implies \fB\-fno-builtin\fR. A freestanding environment
is one in which the standard library may not exist, and program startup may
not necessarily be at \f(CW\*(C`main\*(C'\fR. The most obvious example is an \s-1OS\s0 kernel.
This is equivalent to \fB\-fno-hosted\fR.
.Ip "\fB\-trigraphs\fR" 4
.IX Item "-trigraphs"
Support \s-1ISO\s0 C trigraphs. You don't want to know about this
brain-damage. The \fB\-ansi\fR option (and \fB\-std\fR options for
strict \s-1ISO\s0 C conformance) implies \fB\-trigraphs\fR.
.Ip "\fB\-traditional\fR" 4
.IX Item "-traditional"
Attempt to support some aspects of traditional C compilers.
Specifically:
.RS 4
.Ip "\(bu" 4
All \f(CW\*(C`extern\*(C'\fR declarations take effect globally even if they
are written inside of a function definition. This includes implicit
declarations of functions.
.Ip "\(bu" 4
The newer keywords \f(CW\*(C`typeof\*(C'\fR, \f(CW\*(C`inline\*(C'\fR, \f(CW\*(C`signed\*(C'\fR, \f(CW\*(C`const\*(C'\fR
and \f(CW\*(C`volatile\*(C'\fR are not recognized. (You can still use the
alternative keywords such as \f(CW\*(C`_\|_typeof_\|_\*(C'\fR, \f(CW\*(C`_\|_inline_\|_\*(C'\fR, and
so on.)
.Ip "\(bu" 4
Comparisons between pointers and integers are always allowed.
.Ip "\(bu" 4
Integer types \f(CW\*(C`unsigned short\*(C'\fR and \f(CW\*(C`unsigned char\*(C'\fR promote
to \f(CW\*(C`unsigned int\*(C'\fR.
.Ip "\(bu" 4
Out-of-range floating point literals are not an error.
.Ip "\(bu" 4
Certain constructs which \s-1ISO\s0 regards as a single invalid preprocessing
number, such as \fB0xe-0xd\fR, are treated as expressions instead.
.Ip "\(bu" 4
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
\&\fB\-fwritable-strings\fR.)
.Ip "\(bu" 4
All automatic variables not declared \f(CW\*(C`register\*(C'\fR are preserved by
\&\f(CW\*(C`longjmp\*(C'\fR. Ordinarily, \s-1GNU\s0 C follows \s-1ISO\s0 C: automatic variables
not declared \f(CW\*(C`volatile\*(C'\fR may be clobbered.
.Ip "\(bu" 4
The character escape sequences \fB\ex\fR and \fB\ea\fR evaluate as the
literal characters \fBx\fR and \fBa\fR respectively. Without
\&\fB\-traditional\fR, \fB\ex\fR is a prefix for the hexadecimal
representation of a character, and \fB\ea\fR produces a bell.
.RE
.RS 4
.Sp
You may wish to use \fB\-fno-builtin\fR as well as \fB\-traditional\fR
if your program uses names that are normally \s-1GNU\s0 C builtin functions for
other purposes of its own.
.Sp
You cannot use \fB\-traditional\fR if you include any header files that
rely on \s-1ISO\s0 C features. Some vendors are starting to ship systems with
\&\s-1ISO\s0 C header files and you cannot use \fB\-traditional\fR on such
systems to compile files that include any system headers.
.Sp
The \fB\-traditional\fR option also enables \fB\-traditional-cpp\fR,
which is described next.
.RE
.Ip "\fB\-traditional-cpp\fR" 4
.IX Item "-traditional-cpp"
Attempt to support some aspects of traditional C preprocessors.
Specifically:
.RS 4
.Ip "\(bu" 4
Comments convert to nothing at all, rather than to a space. This allows
traditional token concatenation.
.Ip "\(bu" 4
In a preprocessing directive, the \fB#\fR symbol must appear as the first
character of a line.
.Ip "\(bu" 4
Macro arguments are recognized within string constants in a macro
definition (and their values are stringified, though without additional
quote marks, when they appear in such a context). The preprocessor
always considers a string constant to end at a newline.
.Ip "\(bu" 4
The predefined macro \f(CW\*(C`_\|_STDC_\|_\*(C'\fR is not defined when you use
\&\fB\-traditional\fR, but \f(CW\*(C`_\|_GNUC_\|_\*(C'\fR is (since the \s-1GNU\s0 extensions
which \f(CW\*(C`_\|_GNUC_\|_\*(C'\fR indicates are not affected by
\&\fB\-traditional\fR). If you need to write header files that work
differently depending on whether \fB\-traditional\fR is in use, by
testing both of these predefined macros you can distinguish four
situations: \s-1GNU\s0 C, traditional \s-1GNU\s0 C, other \s-1ISO\s0 C compilers, and other
old C compilers. The predefined macro \f(CW\*(C`_\|_STDC_VERSION_\|_\*(C'\fR is also
not defined when you use \fB\-traditional\fR.
.Ip "\(bu" 4
The preprocessor considers a string constant to end at a newline (unless
the newline is escaped with \fB\e\fR). (Without \fB\-traditional\fR,
string constants can contain the newline character as typed.)
.RE
.RS 4
.RE
.Ip "\fB\-fcond-mismatch\fR" 4
.IX Item "-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+.
.Ip "\fB\-funsigned-char\fR" 4
.IX Item "-funsigned-char"
Let the type \f(CW\*(C`char\*(C'\fR be unsigned, like \f(CW\*(C`unsigned char\*(C'\fR.
.Sp
Each kind of machine has a default for what \f(CW\*(C`char\*(C'\fR should
be. It is either like \f(CW\*(C`unsigned char\*(C'\fR by default or like
\&\f(CW\*(C`signed char\*(C'\fR by default.
.Sp
Ideally, a portable program should always use \f(CW\*(C`signed char\*(C'\fR or
\&\f(CW\*(C`unsigned char\*(C'\fR when it depends on the signedness of an object.
But many programs have been written to use plain \f(CW\*(C`char\*(C'\fR 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.
.Sp
The type \f(CW\*(C`char\*(C'\fR is always a distinct type from each of
\&\f(CW\*(C`signed char\*(C'\fR or \f(CW\*(C`unsigned char\*(C'\fR, even though its behavior
is always just like one of those two.
.Ip "\fB\-fsigned-char\fR" 4
.IX Item "-fsigned-char"
Let the type \f(CW\*(C`char\*(C'\fR be signed, like \f(CW\*(C`signed char\*(C'\fR.
.Sp
Note that this is equivalent to \fB\-fno-unsigned-char\fR, which is
the negative form of \fB\-funsigned-char\fR. Likewise, the option
\&\fB\-fno-signed-char\fR is equivalent to \fB\-funsigned-char\fR.
.Sp
You may wish to use \fB\-fno-builtin\fR as well as \fB\-traditional\fR
if your program uses names that are normally \s-1GNU\s0 C builtin functions for
other purposes of its own.
.Sp
You cannot use \fB\-traditional\fR if you include any header files that
rely on \s-1ISO\s0 C features. Some vendors are starting to ship systems with
\&\s-1ISO\s0 C header files and you cannot use \fB\-traditional\fR on such
systems to compile files that include any system headers.
.Ip "\fB\-fsigned-bitfields\fR" 4
.IX Item "-fsigned-bitfields"
.PD 0
.Ip "\fB\-funsigned-bitfields\fR" 4
.IX Item "-funsigned-bitfields"
.Ip "\fB\-fno-signed-bitfields\fR" 4
.IX Item "-fno-signed-bitfields"
.Ip "\fB\-fno-unsigned-bitfields\fR" 4
.IX Item "-fno-unsigned-bitfields"
.PD
These options control whether a bitfield is signed or unsigned, when the
declaration does not use either \f(CW\*(C`signed\*(C'\fR or \f(CW\*(C`unsigned\*(C'\fR. By
default, such a bitfield is signed, because this is consistent: the
basic integer types such as \f(CW\*(C`int\*(C'\fR are signed types.
.Sp
However, when \fB\-traditional\fR is used, bitfields are all unsigned
no matter what.
.Ip "\fB\-fwritable-strings\fR" 4
.IX Item "-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 \fB\-traditional\fR also has
this effect.
.Sp
Writing into string constants is a very bad idea; ``constants'' should
be constant.
.Ip "\fB\-fallow-single-precision\fR" 4
.IX Item "-fallow-single-precision"
Do not promote single precision math operations to double precision,
even when compiling with \fB\-traditional\fR.
.Sp
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 \fB\-traditional\fR, but want
to use single precision operations when the operands are single
precision, use this option. This option has no effect when compiling
with \s-1ISO\s0 or \s-1GNU\s0 C conventions (the default).
.Ip "\fB\-fshort-wchar\fR" 4
.IX Item "-fshort-wchar"
Override the underlying type for \fBwchar_t\fR to be \fBshort
unsigned int\fR instead of the default for the target. This option is
useful for building programs to run under \s-1WINE\s0.
.Sh "Options Controlling \*(C+ Dialect"
.IX Subsection "Options Controlling Dialect"
This section describes the command-line options that are only meaningful
for \*(C+ programs; but you can also use most of the \s-1GNU\s0 compiler options
regardless of what language your program is in. For example, you
might compile a file \f(CW\*(C`firstClass.C\*(C'\fR like this:
.PP
.Vb 1
\& g++ -g -frepo -O -c firstClass.C
.Ve
In this example, only \fB\-frepo\fR is an option meant
only for \*(C+ programs; you can use the other options with any
language supported by \s-1GCC\s0.
.PP
Here is a list of options that are \fIonly\fR for compiling \*(C+ programs:
.Ip "\fB\-fno-access-control\fR" 4
.IX Item "-fno-access-control"
Turn off all access checking. This switch is mainly useful for working
around bugs in the access control code.
.Ip "\fB\-fcheck-new\fR" 4
.IX Item "-fcheck-new"
Check that the pointer returned by \f(CW\*(C`operator new\*(C'\fR is non-null
before attempting to modify the storage allocated. The current Working
Paper requires that \f(CW\*(C`operator new\*(C'\fR never return a null pointer, so
this check is normally unnecessary.
.Sp
An alternative to using this option is to specify that your
\&\f(CW\*(C`operator new\*(C'\fR does not throw any exceptions; if you declare it
\&\fB\f(BIthrow()\fB\fR, g++ will check the return value. See also \fBnew
(nothrow)\fR.
.Ip "\fB\-fconserve-space\fR" 4
.IX Item "-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 \f(CW\*(C`main()\*(C'\fR has
completed, you may have an object that is being destroyed twice because
two definitions were merged.
.Sp
This option is no longer useful on most targets, now that support has
been added for putting variables into \s-1BSS\s0 without making them common.
.Ip "\fB\-fdollars-in-identifiers\fR" 4
.IX Item "-fdollars-in-identifiers"
Accept \fB$\fR in identifiers. You can also explicitly prohibit use of
\&\fB$\fR with the option \fB\-fno-dollars-in-identifiers\fR. (\s-1GNU\s0 C allows
\&\fB$\fR by default on most target systems, but there are a few exceptions.)
Traditional C allowed the character \fB$\fR to form part of
identifiers. However, \s-1ISO\s0 C and \*(C+ forbid \fB$\fR in identifiers.
.Ip "\fB\-fno-elide-constructors\fR" 4
.IX Item "-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.
.Ip "\fB\-fno-enforce-eh-specs\fR" 4
.IX Item "-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 \fB\s-1NDEBUG\s0\fR. The compiler
will still optimize based on the exception specifications.
.Ip "\fB\-fexternal-templates\fR" 4
.IX Item "-fexternal-templates"
Cause template instantiations to obey \fB#pragma interface\fR and
\&\fBimplementation\fR; template instances are emitted or not according
to the location of the template definition.
.Sp
This option is deprecated.
.Ip "\fB\-falt-external-templates\fR" 4
.IX Item "-falt-external-templates"
Similar to \-fexternal-templates, but template instances are emitted or
not according to the place where they are first instantiated.
.Sp
This option is deprecated.
.Ip "\fB\-ffor-scope\fR" 4
.IX Item "-ffor-scope"
.PD 0
.Ip "\fB\-fno-for-scope\fR" 4
.IX Item "-fno-for-scope"
.PD
If \-ffor-scope is specified, the scope of variables declared in
a \fIfor-init-statement\fR is limited to the \fBfor\fR loop itself,
as specified by the \*(C+ standard.
If \-fno-for-scope is specified, the scope of variables declared in
a \fIfor-init-statement\fR extends to the end of the enclosing scope,
as was the case in old versions of gcc, and other (traditional)
implementations of \*(C+.
.Sp
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.
.Ip "\fB\-fno-gnu-keywords\fR" 4
.IX Item "-fno-gnu-keywords"
Do not recognize \f(CW\*(C`typeof\*(C'\fR as a keyword, so that code can use this
word as an identifier. You can use the keyword \f(CW\*(C`_\|_typeof_\|_\*(C'\fR instead.
\&\fB\-ansi\fR implies \fB\-fno-gnu-keywords\fR.
.Ip "\fB\-fhonor-std\fR" 4
.IX Item "-fhonor-std"
Treat the \f(CW\*(C`namespace std\*(C'\fR as a namespace, instead of ignoring
it. For compatibility with earlier versions of g++, the compiler will,
by default, ignore \f(CW\*(C`namespace\-declarations\*(C'\fR,
\&\f(CW\*(C`using\-declarations\*(C'\fR, \f(CW\*(C`using\-directives\*(C'\fR, and
\&\f(CW\*(C`namespace\-names\*(C'\fR, if they involve \f(CW\*(C`std\*(C'\fR.
.Ip "\fB\-fhuge-objects\fR" 4
.IX Item "-fhuge-objects"
Support virtual function calls for objects that exceed the size
representable by a \fBshort int\fR. Users should not use this flag by
default; if you need to use it, the compiler will tell you so.
.Sp
This flag is not useful when compiling with \-fvtable-thunks.
.Sp
Like all options that change the \s-1ABI\s0, all \*(C+ code, \fIincluding
libgcc\fR must be built with the same setting of this option.
.Ip "\fB\-fno-implicit-templates\fR" 4
.IX Item "-fno-implicit-templates"
Never emit code for non-inline templates which are instantiated
implicitly (i.e. by use); only emit code for explicit instantiations.
.Ip "\fB\-fno-implicit-inline-templates\fR" 4
.IX Item "-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.
.Ip "\fB\-fno-implement-inlines\fR" 4
.IX Item "-fno-implement-inlines"
To save space, do not emit out-of-line copies of inline functions
controlled by \fB#pragma implementation\fR. This will cause linker
errors if these functions are not inlined everywhere they are called.
.Ip "\fB\-fms-extensions\fR" 4
.IX Item "-fms-extensions"
Disable pedantic warnings about constructs used in \s-1MFC\s0, such as implicit
int and getting a pointer to member function via non-standard syntax.
.Ip "\fB\-fno-operator-names\fR" 4
.IX Item "-fno-operator-names"
Do not treat the operator name keywords \f(CW\*(C`and\*(C'\fR, \f(CW\*(C`bitand\*(C'\fR,
\&\f(CW\*(C`bitor\*(C'\fR, \f(CW\*(C`compl\*(C'\fR, \f(CW\*(C`not\*(C'\fR, \f(CW\*(C`or\*(C'\fR and \f(CW\*(C`xor\*(C'\fR as
synonyms as keywords.
.Ip "\fB\-fno-optional-diags\fR" 4
.IX Item "-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.
.Ip "\fB\-fpermissive\fR" 4
.IX Item "-fpermissive"
Downgrade messages about nonconformant code from errors to warnings. By
default, g++ effectively sets \fB\-pedantic-errors\fR without
\&\fB\-pedantic\fR; this option reverses that. This behavior and this
option are superseded by \fB\-pedantic\fR, which works as it does for \s-1GNU\s0 C.
.Ip "\fB\-frepo\fR" 4
.IX Item "-frepo"
Enable automatic template instantiation. This option also implies
\&\fB\-fno-implicit-templates\fR.
.Ip "\fB\-fno-rtti\fR" 4
.IX Item "-fno-rtti"
Disable generation of information about every class with virtual
functions for use by the \*(C+ runtime type identification features
(\fBdynamic_cast\fR and \fBtypeid\fR). 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.
.Ip "\fB\-ftemplate-depth-\fR\fIn\fR" 4
.IX Item "-ftemplate-depth-n"
Set the maximum instantiation depth for template classes to \fIn\fR.
A limit on the template instantiation depth is needed to detect
endless recursions during template class instantiation. \s-1ANSI/ISO\s0 \*(C+
conforming programs must not rely on a maximum depth greater than 17.
.Ip "\fB\-fuse-cxa-atexit\fR" 4
.IX Item "-fuse-cxa-atexit"
Register destructors for objects with static storage duration with the
\&\f(CW\*(C`_\|_cxa_atexit\*(C'\fR function rather than the \f(CW\*(C`atexit\*(C'\fR function.
This option is required for fully standards-compliant handling of static
destructors, but will only work if your C library supports
\&\f(CW\*(C`_\|_cxa_atexit\*(C'\fR.
.Ip "\fB\-fvtable-thunks\fR" 4
.IX Item "-fvtable-thunks"
Use \fBthunks\fR to implement the virtual function dispatch table
(\fBvtable\fR). The traditional (cfront-style) approach to
implementing vtables was to store a pointer to the function and two
offsets for adjusting the \fBthis\fR pointer at the call site. Newer
implementations store a single pointer to a \fBthunk\fR function which
does any necessary adjustment and then calls the target function.
.Sp
This option also enables a heuristic for controlling emission of
vtables; if a class has any non-inline virtual functions, the vtable
will be emitted in the translation unit containing the first one of
those.
.Sp
Like all options that change the \s-1ABI\s0, all \*(C+ code, \fIincluding
libgcc.a\fR must be built with the same setting of this option.
.Ip "\fB\-nostdinc++\fR" 4
.IX Item "-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.)
.PP
In addition, these optimization, warning, and code generation options
have meanings only for \*(C+ programs:
.Ip "\fB\-fno-default-inline\fR" 4
.IX Item "-fno-default-inline"
Do not assume \fBinline\fR for functions defined inside a class scope.
Note that these
functions will have linkage like inline functions; they just won't be
inlined by default.
.Ip "\fB\-Wctor-dtor-privacy (\*(C+ only)\fR" 4
.IX Item "-Wctor-dtor-privacy ( only)"
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.
.Ip "\fB\-Wnon-virtual-dtor (\*(C+ only)\fR" 4
.IX Item "-Wnon-virtual-dtor ( only)"
Warn when a class declares a non-virtual destructor that should probably
be virtual, because it looks like the class will be used polymorphically.
.Ip "\fB\-Wreorder (\*(C+ only)\fR" 4
.IX Item "-Wreorder ( only)"
Warn when the order of member initializers given in the code does not
match the order in which they must be executed. For instance:
.Sp
.Vb 5
\& struct A {
\& int i;
\& int j;
\& A(): j (0), i (1) { }
\& };
.Ve
Here the compiler will warn that the member initializers for \fBi\fR
and \fBj\fR will be rearranged to match the declaration order of the
members.
.PP
The following \fB\-W...\fR options are not affected by \fB\-Wall\fR.
.Ip "\fB\-Weffc++ (\*(C+ only)\fR" 4
.IX Item "-Weffc++ ( only)"
Warn about violations of various style guidelines from Scott Meyers'
\&\fIEffective \*(C+\fR 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 \fBgrep \-v\fR to filter out those warnings.
.Ip "\fB\-Wno-deprecated (\*(C+ only)\fR" 4
.IX Item "-Wno-deprecated ( only)"
Do not warn about usage of deprecated features.
.Ip "\fB\-Wno-non-template-friend (\*(C+ only)\fR" 4
.IX Item "-Wno-non-template-friend ( only)"
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 (ie,
\&\fBfriend foo(int)\fR), 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++, \fB\-Wnon-template-friend\fR 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
\&\fB\-Wno-non-template-friend\fR which keeps the conformant compiler code
but disables the helpful warning.
.Ip "\fB\-Wold-style-cast (\*(C+ only)\fR" 4
.IX Item "-Wold-style-cast ( only)"
Warn if an old-style (C-style) cast is used within a \*(C+ program. The
new-style casts (\fBstatic_cast\fR, \fBreinterpret_cast\fR, and
\&\fBconst_cast\fR) are less vulnerable to unintended effects.
.Ip "\fB\-Woverloaded-virtual (\*(C+ only)\fR" 4
.IX Item "-Woverloaded-virtual ( only)"
Warn when a function declaration hides virtual functions from a
base class. For example, in:
.Sp
.Vb 3
\& struct A {
\& virtual void f();
\& };
.Ve
.Vb 3
\& struct B: public A {
\& void f(int);
\& };
.Ve
the \f(CW\*(C`A\*(C'\fR class version of \f(CW\*(C`f\*(C'\fR is hidden in \f(CW\*(C`B\*(C'\fR, and code
like this:
.Sp
.Vb 2
\& B* b;
\& b->f();
.Ve
will fail to compile.
.Ip "\fB\-Wno-pmf-conversions (\*(C+ only)\fR" 4
.IX Item "-Wno-pmf-conversions ( only)"
Disable the diagnostic for converting a bound pointer to member function
to a plain pointer.
.Ip "\fB\-Wsign-promo (\*(C+ only)\fR" 4
.IX Item "-Wsign-promo ( only)"
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.
.Ip "\fB\-Wsynth (\*(C+ only)\fR" 4
.IX Item "-Wsynth ( only)"
Warn when g++'s synthesis behavior does not match that of cfront. For
instance:
.Sp
.Vb 4
\& struct A {
\& operator int ();
\& A& operator = (int);
\& };
.Ve
.Vb 5
\& main ()
\& {
\& A a,b;
\& a = b;
\& }
.Ve
In this example, g++ will synthesize a default \fBA& operator =
(const A&);\fR, while cfront will use the user-defined \fBoperator =\fR.
.Sh "Options to Control Diagnostic Messages Formatting"
.IX Subsection "Options to Control Diagnostic Messages Formatting"
Traditionally, diagnostic messages have been formatted irrespective of
the output device's aspect (e.g. its width, ...). 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.
.Ip "\fB\-fmessage-length=\fR\fIn\fR" 4
.IX Item "-fmessage-length=n"
Try to format error messages so that they fit on lines of about \fIn\fR
characters. The default is 72 characters for g++ and 0 for the rest of
the front-ends supported by \s-1GCC\s0. If \fIn\fR is zero, then no
line-wrapping will be done; each error message will appear on a single
line.
.Ip "\fB\-fdiagnostics-show-location=once\fR" 4
.IX Item "-fdiagnostics-show-location=once"
Only meaningful in line-wrapping mode. Instructs the diagnostic messages
reporter to emit \fIonce\fR 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
behaviour.
.Ip "\fB\-fdiagnostics-show-location=every-line\fR" 4
.IX 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
a message which is too long to fit on a single line.
.Sh "Options to Request or Suppress Warnings"
.IX Subsection "Options to Request or Suppress 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.
.PP
You can request many specific warnings with options beginning \fB\-W\fR,
for example \fB\-Wimplicit\fR to request warnings on implicit
declarations. Each of these specific warning options also has a
negative form beginning \fB\-Wno-\fR to turn off warnings;
for example, \fB\-Wno-implicit\fR. This manual lists only one of the
two forms, whichever is not the default.
.PP
These options control the amount and kinds of warnings produced by \s-1GCC:\s0
.Ip "\fB\-fsyntax-only\fR" 4
.IX Item "-fsyntax-only"
Check the code for syntax errors, but don't do anything beyond that.
.Ip "\fB\-pedantic\fR" 4
.IX Item "-pedantic"
Issue all the warnings demanded by strict \s-1ISO\s0 C and \s-1ISO\s0 \*(C+;
reject all programs that use forbidden extensions, and some other
programs that do not follow \s-1ISO\s0 C and \s-1ISO\s0 \*(C+. For \s-1ISO\s0 C, follows the
version of the \s-1ISO\s0 C standard specified by any \fB\-std\fR option used.
.Sp
Valid \s-1ISO\s0 C and \s-1ISO\s0 \*(C+ programs should compile properly with or without
this option (though a rare few will require \fB\-ansi\fR or a
\&\fB\-std\fR option specifying the required version of \s-1ISO\s0 C). However,
without this option, certain \s-1GNU\s0 extensions and traditional C and \*(C+
features are supported as well. With this option, they are rejected.
.Sp
\&\fB\-pedantic\fR does not cause warning messages for use of the
alternate keywords whose names begin and end with \fB_\|_\fR. Pedantic
warnings are also disabled in the expression that follows
\&\f(CW\*(C`_\|_extension_\|_\*(C'\fR. However, only system header files should use
these escape routes; application programs should avoid them.
.Sp
Some users try to use \fB\-pedantic\fR to check programs for strict \s-1ISO\s0
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
\&\s-1ISO\s0 C \fIrequires\fR a diagnostic, and some others for which
diagnostics have been added.
.Sp
A feature to report any failure to conform to \s-1ISO\s0 C might be useful in
some instances, but would require considerable additional work and would
be quite different from \fB\-pedantic\fR. We don't have plans to
support such a feature in the near future.
.Ip "\fB\-pedantic-errors\fR" 4
.IX Item "-pedantic-errors"
Like \fB\-pedantic\fR, except that errors are produced rather than
warnings.
.Ip "\fB\-w\fR" 4
.IX Item "-w"
Inhibit all warning messages.
.Ip "\fB\-Wno-import\fR" 4
.IX Item "-Wno-import"
Inhibit warning messages about the use of \fB#import\fR.
.Ip "\fB\-Wchar-subscripts\fR" 4
.IX Item "-Wchar-subscripts"
Warn if an array subscript has type \f(CW\*(C`char\*(C'\fR. This is a common cause
of error, as programmers often forget that this type is signed on some
machines.
.Ip "\fB\-Wcomment\fR" 4
.IX Item "-Wcomment"
Warn whenever a comment-start sequence \fB/*\fR appears in a \fB/*\fR
comment, or whenever a Backslash-Newline appears in a \fB//\fR comment.
.Ip "\fB\-Wformat\fR" 4
.IX Item "-Wformat"
Check calls to \f(CW\*(C`printf\*(C'\fR and \f(CW\*(C`scanf\*(C'\fR, 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, in the \f(CW\*(C`printf\*(C'\fR,
\&\f(CW\*(C`scanf\*(C'\fR, \f(CW\*(C`strftime\*(C'\fR and \f(CW\*(C`strfmon\*(C'\fR (an X/Open extension,
not in the C standard) families.
.Sp
The formats are checked against the format features supported by \s-1GNU\s0
libc version 2.2. These include all \s-1ISO\s0 C89 and C99 features, as well
as features from the Single Unix Specification and some \s-1BSD\s0 and \s-1GNU\s0
extensions. Other library implementations may not support all these
features; \s-1GCC\s0 does not support warning about features that go beyond a
particular library's limitations. However, if \fB\-pedantic\fR is used
with \fB\-Wformat\fR, warnings will be given about format features not
in the selected standard version (but not for \f(CW\*(C`strfmon\*(C'\fR formats,
since those are not in any version of the C standard).
.Sp
\&\fB\-Wformat\fR is included in \fB\-Wall\fR. For more control over some
aspects of format checking, the options \fB\-Wno-format-y2k\fR,
\&\fB\-Wno-format-extra-args\fR, \fB\-Wformat-nonliteral\fR,
\&\fB\-Wformat-security\fR and \fB\-Wformat=2\fR are available, but are
not included in \fB\-Wall\fR.
.Ip "\fB\-Wno-format-y2k\fR" 4
.IX Item "-Wno-format-y2k"
If \fB\-Wformat\fR is specified, do not warn about \f(CW\*(C`strftime\*(C'\fR
formats which may yield only a two-digit year.
.Ip "\fB\-Wno-format-extra-args\fR" 4
.IX Item "-Wno-format-extra-args"
If \fB\-Wformat\fR is specified, do not warn about excess arguments to a
\&\f(CW\*(C`printf\*(C'\fR or \f(CW\*(C`scanf\*(C'\fR format function. The C standard specifies
that such arguments are ignored.
.Ip "\fB\-Wformat-nonliteral\fR" 4
.IX Item "-Wformat-nonliteral"
If \fB\-Wformat\fR 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 \f(CW\*(C`va_list\*(C'\fR.
.Ip "\fB\-Wformat-security\fR" 4
.IX Item "-Wformat-security"
If \fB\-Wformat\fR is specified, also warn about uses of format
functions that represent possible security problems. At present, this
warns about calls to \f(CW\*(C`printf\*(C'\fR and \f(CW\*(C`scanf\*(C'\fR functions where the
format string is not a string literal and there are no format arguments,
as in \f(CW\*(C`printf (foo);\*(C'\fR. This may be a security hole if the format
string came from untrusted input and contains \fB%n\fR. (This is
currently a subset of what \fB\-Wformat-nonliteral\fR warns about, but
in future warnings may be added to \fB\-Wformat-security\fR that are not
included in \fB\-Wformat-nonliteral\fR.)
.Ip "\fB\-Wformat=2\fR" 4
.IX Item "-Wformat=2"
Enable \fB\-Wformat\fR plus format checks not included in
\&\fB\-Wformat\fR. Currently equivalent to \fB\-Wformat
\&\-Wformat-nonliteral \-Wformat-security\fR.
.Ip "\fB\-Wimplicit-int\fR" 4
.IX Item "-Wimplicit-int"
Warn when a declaration does not specify a type.
.Ip "\fB\-Wimplicit-function-declaration\fR" 4
.IX Item "-Wimplicit-function-declaration"
.PD 0
.Ip "\fB\-Werror-implicit-function-declaration\fR" 4
.IX Item "-Werror-implicit-function-declaration"
.PD
Give a warning (or error) whenever a function is used before being
declared.
.Ip "\fB\-Wimplicit\fR" 4
.IX Item "-Wimplicit"
Same as \fB\-Wimplicit-int\fR and \fB\-Wimplicit-function-\fR\fBdeclaration\fR.
.Ip "\fB\-Wmain\fR" 4
.IX Item "-Wmain"
Warn if the type of \fBmain\fR is suspicious. \fBmain\fR should be a
function with external linkage, returning int, taking either zero
arguments, two, or three arguments of appropriate types.
.Ip "\fB\-Wmultichar\fR" 4
.IX Item "-Wmultichar"
Warn if a multicharacter constant (\fB'\s-1FOOF\s0'\fR) is used. Usually they
indicate a typo in the user's code, as they have implementation-defined
values, and should not be used in portable code.
.Ip "\fB\-Wparentheses\fR" 4
.IX Item "-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.
.Sp
Also warn about constructions where there may be confusion to which
\&\f(CW\*(C`if\*(C'\fR statement an \f(CW\*(C`else\*(C'\fR branch belongs. Here is an example of
such a case:
.Sp
.Vb 7
\& {
\& if (a)
\& if (b)
\& foo ();
\& else
\& bar ();
\& }
.Ve
In C, every \f(CW\*(C`else\*(C'\fR branch belongs to the innermost possible \f(CW\*(C`if\*(C'\fR
statement, which in this example is \f(CW\*(C`if (b)\*(C'\fR. 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, \s-1GNU\s0 C will issue a warning when this flag is specified.
To eliminate the warning, add explicit braces around the innermost
\&\f(CW\*(C`if\*(C'\fR statement so there is no way the \f(CW\*(C`else\*(C'\fR could belong to
the enclosing \f(CW\*(C`if\*(C'\fR. The resulting code would look like this:
.Sp
.Vb 9
\& {
\& if (a)
\& {
\& if (b)
\& foo ();
\& else
\& bar ();
\& }
\& }
.Ve
.Ip "\fB\-Wsequence-point\fR" 4
.IX Item "-Wsequence-point"
Warn about code that may have undefined semantics because of violations
of sequence point rules in the C standard.
.Sp
The C standard defines the order in which expressions in a C program are
evaluated in terms of \fIsequence points\fR, 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
\&\f(CW\*(C`&&\*(C'\fR, \f(CW\*(C`||\*(C'\fR, \f(CW\*(C`? :\*(C'\fR or \f(CW\*(C`,\*(C'\fR (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.
.Sp
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.
.Sp
Examples of code with undefined behavior are \f(CW\*(C`a = a++;\*(C'\fR, \f(CW\*(C`a[n]
= b[n++]\*(C'\fR and \f(CW\*(C`a[i++] = i;\*(C'\fR. 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.
.Sp
The present implementation of this option only works for C programs. A
future implementation may also work for \*(C+ programs.
.Sp
There is some controversy over the precise meaning of the sequence point
rules in subtle cases. Alternative formal definitions may be found in
Clive Feather's ``Annex S''
<\fBhttp://wwwold.dkuug.dk/JTC1/SC22/WG14/www/docs/n925.htm\fR> and in
Michael Norrish's thesis
<\fBhttp://www.cl.cam.ac.uk/users/mn200/PhD/thesis-report.ps.gz\fR>.
Other discussions are by Raymond Mak
<\fBhttp://wwwold.dkuug.dk/JTC1/SC22/WG14/www/docs/n926.htm\fR> and
D. Hugh Redelmeier
<\fBhttp://wwwold.dkuug.dk/JTC1/SC22/WG14/www/docs/n927.htm\fR>.
.Ip "\fB\-Wreturn-type\fR" 4
.IX Item "-Wreturn-type"
Warn whenever a function is defined with a return-type that defaults to
\&\f(CW\*(C`int\*(C'\fR. Also warn about any \f(CW\*(C`return\*(C'\fR statement with no
return-value in a function whose return-type is not \f(CW\*(C`void\*(C'\fR.
.Sp
For \*(C+, a function without return type always produces a diagnostic
message, even when \fB\-Wno-return-type\fR is specified. The only
exceptions are \fBmain\fR and functions defined in system headers.
.Ip "\fB\-Wswitch\fR" 4
.IX Item "-Wswitch"
Warn whenever a \f(CW\*(C`switch\*(C'\fR statement has an index of enumeral type
and lacks a \f(CW\*(C`case\*(C'\fR for one or more of the named codes of that
enumeration. (The presence of a \f(CW\*(C`default\*(C'\fR label prevents this
warning.) \f(CW\*(C`case\*(C'\fR labels outside the enumeration range also
provoke warnings when this option is used.
.Ip "\fB\-Wtrigraphs\fR" 4
.IX Item "-Wtrigraphs"
Warn if any trigraphs are encountered that might change the meaning of
the program (trigraphs within comments are not warned about).
.Ip "\fB\-Wunused-function\fR" 4
.IX Item "-Wunused-function"
Warn whenever a static function is declared but not defined or a
non\e-inline static function is unused.
.Ip "\fB\-Wunused-label\fR" 4
.IX Item "-Wunused-label"
Warn whenever a label is declared but not used.
.Sp
To suppress this warning use the \fBunused\fR attribute.
.Ip "\fB\-Wunused-parameter\fR" 4
.IX Item "-Wunused-parameter"
Warn whenever a function parameter is unused aside from its declaration.
.Sp
To suppress this warning use the \fBunused\fR attribute.
.Ip "\fB\-Wunused-variable\fR" 4
.IX Item "-Wunused-variable"
Warn whenever a local variable or non-constant static variable is unused
aside from its declaration
.Sp
To suppress this warning use the \fBunused\fR attribute.
.Ip "\fB\-Wunused-value\fR" 4
.IX Item "-Wunused-value"
Warn whenever a statement computes a result that is explicitly not used.
.Sp
To suppress this warning cast the expression to \fBvoid\fR.
.Ip "\fB\-Wunused\fR" 4
.IX Item "-Wunused"
All all the above \fB\-Wunused\fR options combined.
.Sp
In order to get a warning about an unused function parameter, you must
either specify \fB\-W \-Wunused\fR or separately specify
\&\fB\-Wunused-parameter\fR.
.Ip "\fB\-Wuninitialized\fR" 4
.IX Item "-Wuninitialized"
Warn if an automatic variable is used without first being initialized or
if a variable may be clobbered by a \f(CW\*(C`setjmp\*(C'\fR call.
.Sp
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 \fB\-O\fR, you simply won't
get these warnings.
.Sp
These warnings occur only for variables that are candidates for
register allocation. Therefore, they do not occur for a variable that
is declared \f(CW\*(C`volatile\*(C'\fR, 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.
.Sp
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.
.Sp
These warnings are made optional because \s-1GCC\s0 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:
.Sp
.Vb 12
\& {
\& int x;
\& switch (y)
\& {
\& case 1: x = 1;
\& break;
\& case 2: x = 4;
\& break;
\& case 3: x = 5;
\& }
\& foo (x);
\& }
.Ve
If the value of \f(CW\*(C`y\*(C'\fR is always 1, 2 or 3, then \f(CW\*(C`x\*(C'\fR is
always initialized, but \s-1GCC\s0 doesn't know this. Here is
another common case:
.Sp
.Vb 6
\& {
\& int save_y;
\& if (change_y) save_y = y, y = new_y;
\& ...
\& if (change_y) y = save_y;
\& }
.Ve
This has no bug because \f(CW\*(C`save_y\*(C'\fR is used only if it is set.
.Sp
This option also warns when a non-volatile automatic variable might be
changed by a call to \f(CW\*(C`longjmp\*(C'\fR. These warnings as well are possible
only in optimizing compilation.
.Sp
The compiler sees only the calls to \f(CW\*(C`setjmp\*(C'\fR. It cannot know
where \f(CW\*(C`longjmp\*(C'\fR 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 \f(CW\*(C`longjmp\*(C'\fR cannot
in fact be called at the place which would cause a problem.
.Sp
Some spurious warnings can be avoided if you declare all the functions
you use that never return as \f(CW\*(C`noreturn\*(C'\fR.
.Ip "\fB\-Wreorder (\*(C+ only)\fR" 4
.IX Item "-Wreorder ( only)"
Warn when the order of member initializers given in the code does not
match the order in which they must be executed. For instance:
.Ip "\fB\-Wunknown-pragmas\fR" 4
.IX Item "-Wunknown-pragmas"
Warn when a #pragma directive is encountered which is not understood by
\&\s-1GCC\s0. 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 \fB\-Wall\fR command line option.
.Ip "\fB\-Wall\fR" 4
.IX Item "-Wall"
All of the above \fB\-W\fR 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.
.Ip "\fB\-Wsystem-headers\fR" 4
.IX Item "-Wsystem-headers"
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
\&\s-1GCC\s0 to emit warnings from system headers as if they occurred in user
code. However, note that using \fB\-Wall\fR in conjunction with this
option will \fInot\fR warn about unknown pragmas in system
headers\-\-\-for that, \fB\-Wunknown-pragmas\fR must also be used.
.PP
The following \fB\-W...\fR options are not implied by \fB\-Wall\fR.
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.
.Ip "\fB\-W\fR" 4
.IX Item "-W"
Print extra warning messages for these events:
.RS 4
.Ip "\(bu" 4
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:
.Sp
.Vb 5
\& foo (a)
\& {
\& if (a > 0)
\& return a;
\& }
.Ve
.Ip "\(bu" 4
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 \fBx[i,j]\fR will cause a warning,
but \fBx[(void)i,j]\fR will not.
.Ip "\(bu" 4
An unsigned value is compared against zero with \fB<\fR or \fB<=\fR.
.Ip "\(bu" 4
A comparison like \fBx<=y<=z\fR appears; this is equivalent to
\&\fB(x<=y ? 1 : 0) <= z\fR, which is a different interpretation from
that of ordinary mathematical notation.
.Ip "\(bu" 4
Storage-class specifiers like \f(CW\*(C`static\*(C'\fR are not the first things in
a declaration. According to the C Standard, this usage is obsolescent.
.Ip "\(bu" 4
The return type of a function has a type qualifier such as \f(CW\*(C`const\*(C'\fR.
Such a type qualifier has no effect, since the value returned by a
function is not an lvalue. (But don't warn about the \s-1GNU\s0 extension of
\&\f(CW\*(C`volatile void\*(C'\fR return types. That extension will be warned about
if \fB\-pedantic\fR is specified.)
.Ip "\(bu" 4
If \fB\-Wall\fR or \fB\-Wunused\fR is also specified, warn about unused
arguments.
.Ip "\(bu" 4
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 \fB\-Wno-sign-compare\fR is also specified.)
.Ip "\(bu" 4
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 \f(CW\*(C`x.h\*(C'\fR:
.Sp
.Vb 3
\& struct s { int f, g; };
\& struct t { struct s h; int i; };
\& struct t x = { 1, 2, 3 };
.Ve
.Ip "\(bu" 4
An aggregate has an initializer which does not initialize all members.
For example, the following code would cause such a warning, because
\&\f(CW\*(C`x.h\*(C'\fR would be implicitly initialized to zero:
.Sp
.Vb 2
\& struct s { int f, g, h; };
\& struct s x = { 3, 4 };
.Ve
.RE
.RS 4
.RE
.Ip "\fB\-Wfloat-equal\fR" 4
.IX Item "-Wfloat-equal"
Warn if floating point values are used in equality comparisons.
.Sp
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.
.Ip "\fB\-Wtraditional (C only)\fR" 4
.IX Item "-Wtraditional (C only)"
Warn about certain constructs that behave differently in traditional and
\&\s-1ISO\s0 C.
.RS 4
.Ip "\(bu" 4
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 \s-1ISO\s0 C.
.Ip "\(bu" 4
In traditional C, some preprocessor directives did not exist.
Traditional preprocessors would only consider a line to be a directive
if the \fB#\fR appeared in column 1 on the line. Therefore
\&\fB\-Wtraditional\fR warns about directives that traditional C
understands but would ignore because the \fB#\fR does not appear as the
first character on the line. It also suggests you hide directives like
\&\fB#pragma\fR not understood by traditional C by indenting them. Some
traditional implementations would not recognise \fB#elif\fR, so it
suggests avoiding it altogether.
.Ip "\(bu" 4
A function-like macro that appears without arguments.
.Ip "\(bu" 4
The unary plus operator.
.Ip "\(bu" 4
The `U' integer constant suffix, or the `F' or `L' floating point
constant suffixes. (Traditonal C does support the `L' suffix on integer
constants.) Note, these suffixes appear in macros defined in the system
headers of most modern systems, e.g. the _MIN/_MAX macros in limits.h.
Use of these macros can lead to spurious warnings as they do not
necessarily reflect whether the code in question is any less portable to
traditional C given that suitable backup definitions are provided.
.Ip "\(bu" 4
A function declared external in one block and then used after the end of
the block.
.Ip "\(bu" 4
A \f(CW\*(C`switch\*(C'\fR statement has an operand of type \f(CW\*(C`long\*(C'\fR.
.Ip "\(bu" 4
A non-\f(CW\*(C`static\*(C'\fR function declaration follows a \f(CW\*(C`static\*(C'\fR one.
This construct is not accepted by some traditional C compilers.
.Ip "\(bu" 4
The \s-1ISO\s0 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.
.Ip "\(bu" 4
Usage of \s-1ISO\s0 string concatenation is detected.
.Ip "\(bu" 4
Initialization of automatic aggregates.
.Ip "\(bu" 4
Identifier conflicts with labels. Traditional C lacks a separate
namespace for labels.
.Ip "\(bu" 4
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. \f(CW\*(C`_\|_STDC_\|_\*(C'\fR to avoid missing
initializer warnings and relies on default initialization to zero in the
traditional C case.
.RE
.RS 4
.RE
.Ip "\fB\-Wundef\fR" 4
.IX Item "-Wundef"
Warn if an undefined identifier is evaluated in an \fB#if\fR directive.
.Ip "\fB\-Wshadow\fR" 4
.IX Item "-Wshadow"
Warn whenever a local variable shadows another local variable.
.Ip "\fB\-Wid-clash-\fR\fIlen\fR" 4
.IX Item "-Wid-clash-len"
Warn whenever two distinct identifiers match in the first \fIlen\fR
characters. This may help you prepare a program that will compile
with certain obsolete, brain-damaged compilers.
.Ip "\fB\-Wlarger-than-\fR\fIlen\fR" 4
.IX Item "-Wlarger-than-len"
Warn whenever an object of larger than \fIlen\fR bytes is defined.
.Ip "\fB\-Wpointer-arith\fR" 4
.IX Item "-Wpointer-arith"
Warn about anything that depends on the ``size of'' a function type or
of \f(CW\*(C`void\*(C'\fR. \s-1GNU\s0 C assigns these types a size of 1, for
convenience in calculations with \f(CW\*(C`void *\*(C'\fR pointers and pointers
to functions.
.Ip "\fB\-Wbad-function-cast (C only)\fR" 4
.IX Item "-Wbad-function-cast (C only)"
Warn whenever a function call is cast to a non-matching type.
For example, warn if \f(CW\*(C`int malloc()\*(C'\fR is cast to \f(CW\*(C`anything *\*(C'\fR.
.Ip "\fB\-Wcast-qual\fR" 4
.IX Item "-Wcast-qual"
Warn whenever a pointer is cast so as to remove a type qualifier from
the target type. For example, warn if a \f(CW\*(C`const char *\*(C'\fR is cast
to an ordinary \f(CW\*(C`char *\*(C'\fR.
.Ip "\fB\-Wcast-align\fR" 4
.IX Item "-Wcast-align"
Warn whenever a pointer is cast such that the required alignment of the
target is increased. For example, warn if a \f(CW\*(C`char *\*(C'\fR is cast to
an \f(CW\*(C`int *\*(C'\fR on machines where integers can only be accessed at
two- or four-byte boundaries.
.Ip "\fB\-Wwrite-strings\fR" 4
.IX Item "-Wwrite-strings"
Give string constants the type \f(CW\*(C`const char[\f(CIlength\f(CW]\*(C'\fR so that
copying the address of one into a non-\f(CW\*(C`const\*(C'\fR \f(CW\*(C`char *\*(C'\fR
pointer will get a warning. 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 \f(CW\*(C`const\*(C'\fR in
declarations and prototypes. Otherwise, it will just be a nuisance;
this is why we did not make \fB\-Wall\fR request these warnings.
.Ip "\fB\-Wconversion\fR" 4
.IX Item "-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.
.Sp
Also, warn if a negative integer constant expression is implicitly
converted to an unsigned type. For example, warn about the assignment
\&\f(CW\*(C`x = \-1\*(C'\fR if \f(CW\*(C`x\*(C'\fR is unsigned. But do not warn about explicit
casts like \f(CW\*(C`(unsigned) \-1\*(C'\fR.
.Ip "\fB\-Wsign-compare\fR" 4
.IX Item "-Wsign-compare"
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 \fB\-W\fR; to get the other warnings
of \fB\-W\fR without this warning, use \fB\-W \-Wno-sign-compare\fR.
.Ip "\fB\-Waggregate-return\fR" 4
.IX Item "-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.)
.Ip "\fB\-Wstrict-prototypes (C only)\fR" 4
.IX Item "-Wstrict-prototypes (C only)"
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.)
.Ip "\fB\-Wmissing-prototypes (C only)\fR" 4
.IX Item "-Wmissing-prototypes (C only)"
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.
.Ip "\fB\-Wmissing-declarations\fR" 4
.IX Item "-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.
.Ip "\fB\-Wmissing-noreturn\fR" 4
.IX Item "-Wmissing-noreturn"
Warn about functions which might be candidates for attribute \f(CW\*(C`noreturn\*(C'\fR.
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 \f(CW\*(C`noreturn\*(C'\fR attribute, otherwise subtle code generation
bugs could be introduced. You will not get a warning for \f(CW\*(C`main\*(C'\fR in
hosted C environments.
.Ip "\fB\-Wmissing-format-attribute\fR" 4
.IX Item "-Wmissing-format-attribute"
If \fB\-Wformat\fR is enabled, also warn about functions which might be
candidates for \f(CW\*(C`format\*(C'\fR attributes. Note these are only possible
candidates, not absolute ones. \s-1GCC\s0 will guess that \f(CW\*(C`format\*(C'\fR
attributes might be appropriate for any function that calls a function
like \f(CW\*(C`vprintf\*(C'\fR or \f(CW\*(C`vscanf\*(C'\fR, but this might not always be the
case, and some functions for which \f(CW\*(C`format\*(C'\fR attributes are
appropriate may not be detected. This option has no effect unless
\&\fB\-Wformat\fR is enabled (possibly by \fB\-Wall\fR).
.Ip "\fB\-Wpacked\fR" 4
.IX Item "-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 \f(CW\*(C`f.x\*(C'\fR in \f(CW\*(C`struct bar\*(C'\fR
will be misaligned even though \f(CW\*(C`struct bar\*(C'\fR does not itself
have the packed attribute:
.Sp
.Vb 8
\& struct foo {
\& int x;
\& char a, b, c, d;
\& } __attribute__((packed));
\& struct bar {
\& char z;
\& struct foo f;
\& };
.Ve
.Ip "\fB\-Wpadded\fR" 4
.IX Item "-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.
.Ip "\fB\-Wredundant-decls\fR" 4
.IX Item "-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.
.Ip "\fB\-Wnested-externs (C only)\fR" 4
.IX Item "-Wnested-externs (C only)"
Warn if an \f(CW\*(C`extern\*(C'\fR declaration is encountered within a function.
.Ip "\fB\-Wunreachable-code\fR" 4
.IX Item "-Wunreachable-code"
Warn if the compiler detects that code will never be executed.
.Sp
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.
.Sp
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.
.Sp
For instance, when a function is inlined, a warning may mean that the
line is unreachable in only one inlined copy of the function.
.Sp
This option is not made part of \fB\-Wall\fR 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 behaviour which is selectable at compile-time.
.Ip "\fB\-Winline\fR" 4
.IX Item "-Winline"
Warn if a function can not be inlined and it was declared as inline.
.Ip "\fB\-Wlong-long\fR" 4
.IX Item "-Wlong-long"
Warn if \fBlong long\fR type is used. This is default. To inhibit
the warning messages, use \fB\-Wno-long-long\fR. Flags
\&\fB\-Wlong-long\fR and \fB\-Wno-long-long\fR are taken into account
only when \fB\-pedantic\fR flag is used.
.Ip "\fB\-Wdisabled-optimization\fR" 4
.IX Item "-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 \s-1GCC\s0's optimizers were unable to handle the code
effectively. Often, the problem is that your code is too big or too
complex; \s-1GCC\s0 will refuse to optimize programs when the optimization
itself is likely to take inordinate amounts of time.
.Ip "\fB\-Werror\fR" 4
.IX Item "-Werror"
Make all warnings into errors.
.Sh "Options for Debugging Your Program or \s-1GCC\s0"
.IX Subsection "Options for Debugging Your Program or GCC"
\&\s-1GCC\s0 has various special options that are used for debugging
either your program or \s-1GCC:\s0
.Ip "\fB\-g\fR" 4
.IX Item "-g"
Produce debugging information in the operating system's native format
(stabs, \s-1COFF\s0, \s-1XCOFF\s0, or \s-1DWARF\s0). \s-1GDB\s0 can work with this debugging
information.
.Sp
On most systems that use stabs format, \fB\-g\fR enables use of extra
debugging information that only \s-1GDB\s0 can use; this extra information
makes debugging work better in \s-1GDB\s0 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 \fB\-gstabs+\fR, \fB\-gstabs\fR,
\&\fB\-gxcoff+\fR, \fB\-gxcoff\fR, \fB\-gdwarf-1+\fR, or \fB\-gdwarf-1\fR
(see below).
.Sp
Unlike most other C compilers, \s-1GCC\s0 allows you to use \fB\-g\fR with
\&\fB\-O\fR. 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.
.Sp
Nevertheless it proves possible to debug optimized output. This makes
it reasonable to use the optimizer for programs that might have bugs.
.Sp
The following options are useful when \s-1GCC\s0 is generated with the
capability for more than one debugging format.
.Ip "\fB\-ggdb\fR" 4
.IX Item "-ggdb"
Produce debugging information for use by \s-1GDB\s0. This means to use the
most expressive format available (\s-1DWARF\s0 2, stabs, or the native format
if neither of those are supported), including \s-1GDB\s0 extensions if at all
possible.
.Ip "\fB\-gstabs\fR" 4
.IX Item "-gstabs"
Produce debugging information in stabs format (if that is supported),
without \s-1GDB\s0 extensions. This is the format used by \s-1DBX\s0 on most \s-1BSD\s0
systems. On \s-1MIPS\s0, Alpha and System V Release 4 systems this option
produces stabs debugging output which is not understood by \s-1DBX\s0 or \s-1SDB\s0.
On System V Release 4 systems this option requires the \s-1GNU\s0 assembler.
.Ip "\fB\-gstabs+\fR" 4
.IX Item "-gstabs+"
Produce debugging information in stabs format (if that is supported),
using \s-1GNU\s0 extensions understood only by the \s-1GNU\s0 debugger (\s-1GDB\s0). The
use of these extensions is likely to make other debuggers crash or
refuse to read the program.
.Ip "\fB\-gcoff\fR" 4
.IX Item "-gcoff"
Produce debugging information in \s-1COFF\s0 format (if that is supported).
This is the format used by \s-1SDB\s0 on most System V systems prior to
System V Release 4.
.Ip "\fB\-gxcoff\fR" 4
.IX Item "-gxcoff"
Produce debugging information in \s-1XCOFF\s0 format (if that is supported).
This is the format used by the \s-1DBX\s0 debugger on \s-1IBM\s0 \s-1RS/6000\s0 systems.
.Ip "\fB\-gxcoff+\fR" 4
.IX Item "-gxcoff+"
Produce debugging information in \s-1XCOFF\s0 format (if that is supported),
using \s-1GNU\s0 extensions understood only by the \s-1GNU\s0 debugger (\s-1GDB\s0). 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 \s-1GNU\s0
assembler (\s-1GAS\s0) to fail with an error.
.Ip "\fB\-gdwarf\fR" 4
.IX Item "-gdwarf"
Produce debugging information in \s-1DWARF\s0 version 1 format (if that is
supported). This is the format used by \s-1SDB\s0 on most System V Release 4
systems.
.Ip "\fB\-gdwarf+\fR" 4
.IX Item "-gdwarf+"
Produce debugging information in \s-1DWARF\s0 version 1 format (if that is
supported), using \s-1GNU\s0 extensions understood only by the \s-1GNU\s0 debugger
(\s-1GDB\s0). The use of these extensions is likely to make other debuggers
crash or refuse to read the program.
.Ip "\fB\-gdwarf-2\fR" 4
.IX Item "-gdwarf-2"
Produce debugging information in \s-1DWARF\s0 version 2 format (if that is
supported). This is the format used by \s-1DBX\s0 on \s-1IRIX\s0 6.
.Ip "\fB\-g\fR\fIlevel\fR" 4
.IX Item "-glevel"
.PD 0
.Ip "\fB\-ggdb\fR\fIlevel\fR" 4
.IX Item "-ggdblevel"
.Ip "\fB\-gstabs\fR\fIlevel\fR" 4
.IX Item "-gstabslevel"
.Ip "\fB\-gcoff\fR\fIlevel\fR" 4
.IX Item "-gcofflevel"
.Ip "\fB\-gxcoff\fR\fIlevel\fR" 4
.IX Item "-gxcofflevel"
.Ip "\fB\-gdwarf\fR\fIlevel\fR" 4
.IX Item "-gdwarflevel"
.Ip "\fB\-gdwarf-2\fR\fIlevel\fR" 4
.IX Item "-gdwarf-2level"
.PD
Request debugging information and also use \fIlevel\fR to specify how
much information. The default level is 2.
.Sp
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.
.Sp
Level 3 includes extra information, such as all the macro definitions
present in the program. Some debuggers support macro expansion when
you use \fB\-g3\fR.
.Ip "\fB\-p\fR" 4
.IX Item "-p"
Generate extra code to write profile information suitable for the
analysis program \f(CW\*(C`prof\*(C'\fR. You must use this option when compiling
the source files you want data about, and you must also use it when
linking.
.Ip "\fB\-pg\fR" 4
.IX Item "-pg"
Generate extra code to write profile information suitable for the
analysis program \f(CW\*(C`gprof\*(C'\fR. You must use this option when compiling
the source files you want data about, and you must also use it when
linking.
.Ip "\fB\-a\fR" 4
.IX Item "-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 \fB\-g\fR 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 \fIbb.out\fR.
.Sp
This data could be analyzed by a program like \f(CW\*(C`tcov\*(C'\fR. Note,
however, that the format of the data is not what \f(CW\*(C`tcov\*(C'\fR expects.
Eventually \s-1GNU\s0 \f(CW\*(C`gprof\*(C'\fR should be extended to process this data.
.Ip "\fB\-Q\fR" 4
.IX Item "-Q"
Makes the compiler print out each function name as it is compiled, and
print some statistics about each pass when it finishes.
.Ip "\fB\-ax\fR" 4
.IX Item "-ax"
Generate extra code to profile basic blocks. Your executable will
produce output that is a superset of that produced when \fB\-a\fR is
used. Additional output is the source and target address of the basic
blocks where a jump takes place, the number of times a jump is executed,
and (optionally) the complete sequence of basic blocks being executed.
The output is appended to file \fIbb.out\fR.
.Sp
You can examine different profiling aspects without recompilation. Your
executable will read a list of function names from file \fIbb.in\fR.
Profiling starts when a function on the list is entered and stops when
that invocation is exited. To exclude a function from profiling, prefix
its name with `\-'. If a function name is not unique, you can
disambiguate it by writing it in the form
\&\fB/path/filename.d:functionname\fR. Your executable will write the
available paths and filenames in file \fIbb.out\fR.
.Sp
Several function names have a special meaning:
.RS 4
.if n .Ip "\f(CW""_\|_bb_jumps_\|_""\fR" 4
.el .Ip "\f(CW_\|_bb_jumps_\|_\fR" 4
.IX Item "__bb_jumps__"
Write source, target and frequency of jumps to file \fIbb.out\fR.
.if n .Ip "\f(CW""_\|_bb_hidecall_\|_""\fR" 4
.el .Ip "\f(CW_\|_bb_hidecall_\|_\fR" 4
.IX Item "__bb_hidecall__"
Exclude function calls from frequency count.
.if n .Ip "\f(CW""_\|_bb_showret_\|_""\fR" 4
.el .Ip "\f(CW_\|_bb_showret_\|_\fR" 4
.IX Item "__bb_showret__"
Include function returns in frequency count.
.if n .Ip "\f(CW""_\|_bb_trace_\|_""\fR" 4
.el .Ip "\f(CW_\|_bb_trace_\|_\fR" 4
.IX Item "__bb_trace__"
Write the sequence of basic blocks executed to file \fIbbtrace.gz\fR.
The file will be compressed using the program \fBgzip\fR, which must
exist in your \fB\s-1PATH\s0\fR. On systems without the \fBpopen\fR
function, the file will be named \fIbbtrace\fR and will not be
compressed. \fBProfiling for even a few seconds on these systems
will produce a very large file.\fR Note: \f(CW\*(C`_\|_bb_hidecall_\|_\*(C'\fR and
\&\f(CW\*(C`_\|_bb_showret_\|_\*(C'\fR will not affect the sequence written to
\&\fIbbtrace.gz\fR.
.RE
.RS 4
.Sp
Here's a short example using different profiling parameters
in file \fIbb.in\fR. Assume function \f(CW\*(C`foo\*(C'\fR consists of basic blocks
1 and 2 and is called twice from block 3 of function \f(CW\*(C`main\*(C'\fR. After
the calls, block 3 transfers control to block 4 of \f(CW\*(C`main\*(C'\fR.
.Sp
With \f(CW\*(C`_\|_bb_trace_\|_\*(C'\fR and \f(CW\*(C`main\*(C'\fR contained in file \fIbb.in\fR,
the following sequence of blocks is written to file \fIbbtrace.gz\fR:
0 3 1 2 1 2 4. The return from block 2 to block 3 is not shown, because
the return is to a point inside the block and not to the top. The
block address 0 always indicates, that control is transferred
to the trace from somewhere outside the observed functions. With
\&\fB\-foo\fR added to \fIbb.in\fR, the blocks of function
\&\f(CW\*(C`foo\*(C'\fR are removed from the trace, so only 0 3 4 remains.
.Sp
With \f(CW\*(C`_\|_bb_jumps_\|_\*(C'\fR and \f(CW\*(C`main\*(C'\fR contained in file \fIbb.in\fR,
jump frequencies will be written to file \fIbb.out\fR. The
frequencies are obtained by constructing a trace of blocks
and incrementing a counter for every neighbouring pair of blocks
in the trace. The trace 0 3 1 2 1 2 4 displays the following
frequencies:
.Sp
.Vb 5
\& Jump from block 0x0 to block 0x3 executed 1 time(s)
\& Jump from block 0x3 to block 0x1 executed 1 time(s)
\& Jump from block 0x1 to block 0x2 executed 2 time(s)
\& Jump from block 0x2 to block 0x1 executed 1 time(s)
\& Jump from block 0x2 to block 0x4 executed 1 time(s)
.Ve
With \f(CW\*(C`_\|_bb_hidecall_\|_\*(C'\fR, control transfer due to call instructions
is removed from the trace, that is the trace is cut into three parts: 0
3 4, 0 1 2 and 0 1 2. With \f(CW\*(C`_\|_bb_showret_\|_\*(C'\fR, control transfer due
to return instructions is added to the trace. The trace becomes: 0 3 1
2 3 1 2 3 4. Note, that this trace is not the same, as the sequence
written to \fIbbtrace.gz\fR. It is solely used for counting jump
frequencies.
.RE
.Ip "\fB\-fprofile-arcs\fR" 4
.IX Item "-fprofile-arcs"
Instrument \fIarcs\fR during compilation. For each function of your
program, \s-1GCC\s0 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.
.Sp
Since not every arc in the program must be instrumented, programs
compiled with this option run faster than programs compiled with
\&\fB\-a\fR, which adds instrumentation code to every basic block in the
program. The tradeoff: since \f(CW\*(C`gcov\*(C'\fR 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, \f(CW\*(C`gcov\*(C'\fR
runs a little more slowly than a program which uses information from
\&\fB\-a\fR.
.Sp
\&\fB\-fprofile-arcs\fR also makes it possible to estimate branch
probabilities, and to calculate basic block execution counts. In
general, basic block execution counts do not give enough information to
estimate all branch probabilities. When the compiled program exits, it
saves the arc execution counts to a file called
\&\fI\fIsourcename\fI.da\fR. Use the compiler option
\&\fB\-fbranch-probabilities\fR when recompiling, to optimize using estimated
branch probabilities.
.Ip "\fB\-ftest-coverage\fR" 4
.IX Item "-ftest-coverage"
Create data files for the \f(CW\*(C`gcov\*(C'\fR code-coverage utility.
The data file names begin with the name of your source file:
.RS 4
.Ip "\fIsourcename\fR\fB.bb\fR" 4
.IX Item "sourcename.bb"
A mapping from basic blocks to line numbers, which \f(CW\*(C`gcov\*(C'\fR uses to
associate basic block execution counts with line numbers.
.Ip "\fIsourcename\fR\fB.bbg\fR" 4
.IX Item "sourcename.bbg"
A list of all arcs in the program flow graph. This allows \f(CW\*(C`gcov\*(C'\fR
to reconstruct the program flow graph, so that it can compute all basic
block and arc execution counts from the information in the
\&\f(CW\*(C`\f(CIsourcename\f(CW.da\*(C'\fR file (this last file is the output from
\&\fB\-fprofile-arcs\fR).
.RE
.RS 4
.RE
.Ip "\fB\-d\fR\fIletters\fR" 4
.IX Item "-dletters"
Says to make debugging dumps during compilation at times specified by
\&\fIletters\fR. 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. \fIfoo.c.00.rtl\fR or \fIfoo.c.01.sibling\fR).
Here are the possible letters for use in \fIletters\fR, and their meanings:
.RS 4
.Ip "\fBA\fR" 4
.IX Item "A"
Annotate the assembler output with miscellaneous debugging information.
.Ip "\fBb\fR" 4
.IX Item "b"
Dump after computing branch probabilities, to \fI\fIfile\fI.11.bp\fR.
.Ip "\fBB\fR" 4
.IX Item "B"
Dump after block reordering, to \fI\fIfile\fI.26.bbro\fR.
.Ip "\fBc\fR" 4
.IX Item "c"
Dump after instruction combination, to the file \fI\fIfile\fI.14.combine\fR.
.Ip "\fBC\fR" 4
.IX Item "C"
Dump after the first if conversion, to the file \fI\fIfile\fI.15.ce\fR.
.Ip "\fBd\fR" 4
.IX Item "d"
Dump after delayed branch scheduling, to \fI\fIfile\fI.29.dbr\fR.
.Ip "\fBD\fR" 4
.IX Item "D"
Dump all macro definitions, at the end of preprocessing, in addition to
normal output.
.Ip "\fBe\fR" 4
.IX Item "e"
Dump after \s-1SSA\s0 optimizations, to \fI\fIfile\fI.05.ssa\fR and
\&\fI\fIfile\fI.06.ussa\fR.
.Ip "\fBE\fR" 4
.IX Item "E"
Dump after the second if conversion, to \fI\fIfile\fI.24.ce2\fR.
.Ip "\fBf\fR" 4
.IX Item "f"
Dump after life analysis, to \fI\fIfile\fI.13.life\fR.
.Ip "\fBF\fR" 4
.IX Item "F"
Dump after purging \f(CW\*(C`ADDRESSOF\*(C'\fR codes, to \fI\fIfile\fI.04.addressof\fR.
.Ip "\fBg\fR" 4
.IX Item "g"
Dump after global register allocation, to \fI\fIfile\fI.19.greg\fR.
.Ip "\fBo\fR" 4
.IX Item "o"
Dump after post-reload \s-1CSE\s0 and other optimizations, to \fI\fIfile\fI.20.postreload\fR.
.Ip "\fBG\fR" 4
.IX Item "G"
Dump after \s-1GCSE\s0, to \fI\fIfile\fI.08.gcse\fR.
.Ip "\fBi\fR" 4
.IX Item "i"
Dump after sibling call optimizations, to \fI\fIfile\fI.01.sibling\fR.
.Ip "\fBj\fR" 4
.IX Item "j"
Dump after the first jump optimization, to \fI\fIfile\fI.02.jump\fR.
.Ip "\fBJ\fR" 4
.IX Item "J"
Dump after the last jump optimization, to \fI\fIfile\fI.27.jump2\fR.
.Ip "\fBk\fR" 4
.IX Item "k"
Dump after conversion from registers to stack, to \fI\fIfile\fI.29.stack\fR.
.Ip "\fBl\fR" 4
.IX Item "l"
Dump after local register allocation, to \fI\fIfile\fI.18.lreg\fR.
.Ip "\fBL\fR" 4
.IX Item "L"
Dump after loop optimization, to \fI\fIfile\fI.09.loop\fR.
.Ip "\fBM\fR" 4
.IX Item "M"
Dump after performing the machine dependent reorganisation pass, to
\&\fI\fIfile\fI.28.mach\fR.
.Ip "\fBn\fR" 4
.IX Item "n"
Dump after register renumbering, to \fI\fIfile\fI.23.rnreg\fR.
.Ip "\fBN\fR" 4
.IX Item "N"
Dump after the register move pass, to \fI\fIfile\fI.16.regmove\fR.
.Ip "\fBr\fR" 4
.IX Item "r"
Dump after \s-1RTL\s0 generation, to \fI\fIfile\fI.00.rtl\fR.
.Ip "\fBR\fR" 4
.IX Item "R"
Dump after the second instruction scheduling pass, to
\&\fI\fIfile\fI.25.sched2\fR.
.Ip "\fBs\fR" 4
.IX Item "s"
Dump after \s-1CSE\s0 (including the jump optimization that sometimes follows
\&\s-1CSE\s0), to \fI\fIfile\fI.03.cse\fR.
.Ip "\fBS\fR" 4
.IX Item "S"
Dump after the first instruction scheduling pass, to
\&\fI\fIfile\fI.17.sched\fR.
.Ip "\fBt\fR" 4
.IX Item "t"
Dump after the second \s-1CSE\s0 pass (including the jump optimization that
sometimes follows \s-1CSE\s0), to \fI\fIfile\fI.10.cse2\fR.
.Ip "\fBw\fR" 4
.IX Item "w"
Dump after the second flow pass, to \fI\fIfile\fI.21.flow2\fR.
.Ip "\fBX\fR" 4
.IX Item "X"
Dump after dead code elimination, to \fI\fIfile\fI.06.dce\fR.
.Ip "\fBz\fR" 4
.IX Item "z"
Dump after the peephole pass, to \fI\fIfile\fI.22.peephole2\fR.
.Ip "\fBa\fR" 4
.IX Item "a"
Produce all the dumps listed above.
.Ip "\fBm\fR" 4
.IX Item "m"
Print statistics on memory usage, at the end of the run, to
standard error.
.Ip "\fBp\fR" 4
.IX Item "p"
Annotate the assembler output with a comment indicating which
pattern and alternative was used. The length of each instruction is
also printed.
.Ip "\fBP\fR" 4
.IX Item "P"
Dump the \s-1RTL\s0 in the assembler output as a comment before each instruction.
Also turns on \fB\-dp\fR annotation.
.Ip "\fBv\fR" 4
.IX Item "v"
For each of the other indicated dump files (except for
\&\fI\fIfile\fI.00.rtl\fR), dump a representation of the control flow graph
suitable for viewing with \s-1VCG\s0 to \fI\fIfile\fI.\fIpass\fI.vcg\fR.
.Ip "\fBx\fR" 4
.IX Item "x"
Just generate \s-1RTL\s0 for a function instead of compiling it. Usually used
with \fBr\fR.
.Ip "\fBy\fR" 4
.IX Item "y"
Dump debugging information during parsing, to standard error.
.RE
.RS 4
.RE
.Ip "\fB\-fdump-unnumbered\fR" 4
.IX Item "-fdump-unnumbered"
When doing debugging dumps (see \-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 \-g.
.Ip "\fB\-fdump-translation-unit=\fR\fIfile\fR \fB(C and \*(C+ only)\fR" 4
.IX Item "-fdump-translation-unit=file (C and only)"
Dump a representation of the tree structure for the entire translation
unit to \fIfile\fR.
.Ip "\fB\-fdump-class_layout=\fR\fIfile\fR \fB(\*(C+ only)\fR" 4
.IX Item "-fdump-class_layout=file ( only)"
.PD 0
.Ip "\fB\-fdump-class_layout (\*(C+ only)\fR" 4
.IX Item "-fdump-class_layout ( only)"
.PD
Dump a representation of each class's heirarchy to \fIfile\fR, or
\&\f(CW\*(C`stderr\*(C'\fR if not specified.
.Ip "\fB\-fpretend-float\fR" 4
.IX Item "-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 \s-1GCC\s0 would make when running on
the target machine.
.Ip "\fB\-save-temps\fR" 4
.IX Item "-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 \fIfoo.c\fR with \fB\-c \-save-temps\fR would produce files
\&\fIfoo.i\fR and \fIfoo.s\fR, as well as \fIfoo.o\fR. This creates a
preprocessed \fIfoo.i\fR output file even though the compiler now
normally uses an integrated preprocessor.
.Ip "\fB\-time\fR" 4
.IX Item "-time"
Report the \s-1CPU\s0 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:
.Sp
.Vb 2
\& # cc1 0.12 0.01
\& # as 0.00 0.01
.Ve
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.
.Ip "\fB\-print-file-name=\fR\fIlibrary\fR" 4
.IX Item "-print-file-name=library"
Print the full absolute name of the library file \fIlibrary\fR that
would be used when linking\-\-\-and don't do anything else. With this
option, \s-1GCC\s0 does not compile or link anything; it just prints the
file name.
.Ip "\fB\-print-prog-name=\fR\fIprogram\fR" 4
.IX Item "-print-prog-name=program"
Like \fB\-print-file-name\fR, but searches for a program such as \fBcpp\fR.
.Ip "\fB\-print-libgcc-file-name\fR" 4
.IX Item "-print-libgcc-file-name"
Same as \fB\-print-file-name=libgcc.a\fR.
.Sp
This is useful when you use \fB\-nostdlib\fR or \fB\-nodefaultlibs\fR
but you do want to link with \fIlibgcc.a\fR. You can do
.Sp
.Vb 1
\& gcc -nostdlib I<files>... `gcc -print-libgcc-file-name`
.Ve
.Ip "\fB\-print-search-dirs\fR" 4
.IX Item "-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.
.Sp
This is useful when gcc prints the error message
\&\fBinstallation problem, cannot exec cpp0: No such file or directory\fR.
To resolve this you either need to put \fIcpp0\fR and the other compiler
components where gcc expects to find them, or you can set the environment
variable \fB\s-1GCC_EXEC_PREFIX\s0\fR to the directory where you installed them.
Don't forget the trailing '/'.
.Sh "Options That Control Optimization"
.IX Subsection "Options That Control Optimization"
These options control various sorts of optimizations:
.Ip "\fB\-O\fR" 4
.IX Item "-O"
.PD 0
.Ip "\fB\-O1\fR" 4
.IX Item "-O1"
.PD
Optimize. Optimizing compilation takes somewhat more time, and a lot
more memory for a large function.
.Sp
Without \fB\-O\fR, 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.
.Sp
Without \fB\-O\fR, the compiler only allocates variables declared
\&\f(CW\*(C`register\*(C'\fR in registers. The resulting compiled code is a little
worse than produced by \s-1PCC\s0 without \fB\-O\fR.
.Sp
With \fB\-O\fR, the compiler tries to reduce code size and execution
time.
.Sp
When you specify \fB\-O\fR, the compiler turns on \fB\-fthread-jumps\fR
and \fB\-fdefer-pop\fR on all machines. The compiler turns on
\&\fB\-fdelayed-branch\fR on machines that have delay slots, and
\&\fB\-fomit-frame-pointer\fR on machines that can support debugging even
without a frame pointer. On some machines the compiler also turns
on other flags.
.Ip "\fB\-O2\fR" 4
.IX Item "-O2"
Optimize even more. \s-1GCC\s0 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 \fB\-O2\fR.
As compared to \fB\-O\fR, this option increases both compilation time
and the performance of the generated code.
.Sp
\&\fB\-O2\fR turns on all optional optimizations except for loop unrolling,
function inlining, and register renaming. It also turns on the
\&\fB\-fforce-mem\fR option on all machines and frame pointer elimination
on machines where doing so does not interfere with debugging.
.Ip "\fB\-O3\fR" 4
.IX Item "-O3"
Optimize yet more. \fB\-O3\fR turns on all optimizations specified by
\&\fB\-O2\fR and also turns on the \fB\-finline-functions\fR and
\&\fB\-frename-registers\fR options.
.Ip "\fB\-O0\fR" 4
.IX Item "-O0"
Do not optimize.
.Ip "\fB\-Os\fR" 4
.IX Item "-Os"
Optimize for size. \fB\-Os\fR enables all \fB\-O2\fR optimizations that
do not typically increase code size. It also performs further
optimizations designed to reduce code size.
.Sp
If you use multiple \fB\-O\fR options, with or without level numbers,
the last such option is the one that is effective.
.PP
Options of the form \fB\-f\fR\fIflag\fR specify machine-independent
flags. Most flags have both positive and negative forms; the negative
form of \fB\-ffoo\fR would be \fB\-fno-foo\fR. 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 \fBno-\fR or
adding it.
.Ip "\fB\-ffloat-store\fR" 4
.IX Item "-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.
.Sp
This option prevents undesirable excess precision on machines such as
the 68000 where the floating registers (of the 68881) keep more
precision than a \f(CW\*(C`double\*(C'\fR 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 \s-1IEEE\s0 floating
point. Use \fB\-ffloat-store\fR for such programs, after modifying
them to store all pertinent intermediate computations into variables.
.Ip "\fB\-fno-default-inline\fR" 4
.IX Item "-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
\&\fB\-O\fR, member functions defined inside class scope are compiled
inline by default; i.e., you don't need to add \fBinline\fR in front of
the member function name.
.Ip "\fB\-fno-defer-pop\fR" 4
.IX Item "-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.
.Ip "\fB\-fforce-mem\fR" 4
.IX Item "-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 \fB\-O2\fR option turns on this option.
.Ip "\fB\-fforce-addr\fR" 4
.IX Item "-fforce-addr"
Force memory address constants to be copied into registers before
doing arithmetic on them. This may produce better code just as
\&\fB\-fforce-mem\fR may.
.Ip "\fB\-fomit-frame-pointer\fR" 4
.IX Item "-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. \fBIt also makes debugging impossible on
some machines.\fR
.Sp
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 \f(CW\*(C`FRAME_POINTER_REQUIRED\*(C'\fR controls
whether a target machine supports this flag.
.Ip "\fB\-foptimize-sibling-calls\fR" 4
.IX Item "-foptimize-sibling-calls"
Optimize sibling and tail recursive calls.
.Ip "\fB\-ftrapv\fR" 4
.IX Item "-ftrapv"
This option generates traps for signed overflow on addition, subtraction,
multiplication operations.
.Ip "\fB\-fno-inline\fR" 4
.IX Item "-fno-inline"
Don't pay attention to the \f(CW\*(C`inline\*(C'\fR 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.
.Ip "\fB\-finline-functions\fR" 4
.IX Item "-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.
.Sp
If all calls to a given function are integrated, and the function is
declared \f(CW\*(C`static\*(C'\fR, then the function is normally not output as
assembler code in its own right.
.Ip "\fB\-finline-limit=\fR\fIn\fR" 4
.IX Item "-finline-limit=n"
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++). \fIn\fR is the size of functions that can be inlined in
number of pseudo instructions (not counting parameter handling). The default
value of n is 10000. 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++.
.Sp
\&\fINote:\fR 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.
.Ip "\fB\-fkeep-inline-functions\fR" 4
.IX Item "-fkeep-inline-functions"
Even if all calls to a given function are integrated, and the function
is declared \f(CW\*(C`static\*(C'\fR, nevertheless output a separate run-time
callable version of the function. This switch does not affect
\&\f(CW\*(C`extern inline\*(C'\fR functions.
.Ip "\fB\-fkeep-static-consts\fR" 4
.IX Item "-fkeep-static-consts"
Emit variables declared \f(CW\*(C`static const\*(C'\fR when optimization isn't turned
on, even if the variables aren't referenced.
.Sp
\&\s-1GCC\s0 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 \fB\-fno-keep-static-consts\fR option.
.Ip "\fB\-fno-function-cse\fR" 4
.IX Item "-fno-function-cse"
Do not put function addresses in registers; make each instruction that
calls a constant function contain the function's address explicitly.
.Sp
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.
.Ip "\fB\-ffast-math\fR" 4
.IX Item "-ffast-math"
Sets \fB\-fno-math-errno\fR, \fB\-funsafe-math-optimizations\fR,
and \fB\-fno-trapping-math\fR.
.Sp
This option causes the preprocessor macro _\|_FAST_MATH_\|_ to be defined.
.Sp
This option causes the preprocessor macro _\|_FAST_MATH_\|_ to be defined.
.Sp
This option should never be turned on by any \fB\-O\fR option since
it can result in incorrect output for programs which depend on
an exact implementation of \s-1IEEE\s0 or \s-1ISO\s0 rules/specifications for
math functions.
.Ip "\fB\-fno-math-errno\fR" 4
.IX Item "-fno-math-errno"
Do not set \s-1ERRNO\s0 after calling math functions that are executed
with a single instruction, e.g., sqrt. A program that relies on
\&\s-1IEEE\s0 exceptions for math error handling may want to use this flag
for speed while maintaining \s-1IEEE\s0 arithmetic compatibility.
.Sp
This option should never be turned on by any \fB\-O\fR option since
it can result in incorrect output for programs which depend on
an exact implementation of \s-1IEEE\s0 or \s-1ISO\s0 rules/specifications for
math functions.
.Sp
The default is \fB\-fmath-errno\fR. The \fB\-ffast-math\fR option
sets \fB\-fno-math-errno\fR.
.Ip "\fB\-funsafe-math-optimizations\fR" 4
.IX Item "-funsafe-math-optimizations"
Allow optimizations for floating-point arithmetic that (a) assume
that arguments and results are valid and (b) may violate \s-1IEEE\s0 or
\&\s-1ANSI\s0 standards.
.Sp
This option should never be turned on by any \fB\-O\fR option since
it can result in incorrect output for programs which depend on
an exact implementation of \s-1IEEE\s0 or \s-1ISO\s0 rules/specifications for
math functions.
.Sp
The default is \fB\-fno-unsafe-math-optimizations\fR. The
\&\fB\-ffast-math\fR option sets \fB\-funsafe-math-optimizations\fR.
.Ip "\fB\-fno-trapping-math\fR" 4
.IX Item "-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'' \s-1IEEE\s0 arithmetic, for example.
.Sp
This option should never be turned on by any \fB\-O\fR option since
it can result in incorrect output for programs which depend on
an exact implementation of \s-1IEEE\s0 or \s-1ISO\s0 rules/specifications for
math functions.
.Sp
The default is \fB\-ftrapping-math\fR. The \fB\-ffast-math\fR
option sets \fB\-fno-trapping-math\fR.
.PP
The following options control specific optimizations. The \fB\-O2\fR
option turns on all of these optimizations except \fB\-funroll-loops\fR
and \fB\-funroll-all-loops\fR. On most machines, the \fB\-O\fR option
turns on the \fB\-fthread-jumps\fR and \fB\-fdelayed-branch\fR options,
but specific machines may handle it differently.
.PP
You can use the following flags in the rare cases when ``fine-tuning''
of optimizations to be performed is desired.
.Ip "\fB\-fstrength-reduce\fR" 4
.IX Item "-fstrength-reduce"
Perform the optimizations of loop strength reduction and
elimination of iteration variables.
.Ip "\fB\-fthread-jumps\fR" 4
.IX Item "-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.
.Ip "\fB\-fcse-follow-jumps\fR" 4
.IX Item "-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 \s-1CSE\s0 encounters an \f(CW\*(C`if\*(C'\fR statement with an
\&\f(CW\*(C`else\*(C'\fR clause, \s-1CSE\s0 will follow the jump when the condition
tested is false.
.Ip "\fB\-fcse-skip-blocks\fR" 4
.IX Item "-fcse-skip-blocks"
This is similar to \fB\-fcse-follow-jumps\fR, but causes \s-1CSE\s0 to
follow jumps which conditionally skip over blocks. When \s-1CSE\s0
encounters a simple \f(CW\*(C`if\*(C'\fR statement with no else clause,
\&\fB\-fcse-skip-blocks\fR causes \s-1CSE\s0 to follow the jump around the
body of the \f(CW\*(C`if\*(C'\fR.
.Ip "\fB\-frerun-cse-after-loop\fR" 4
.IX Item "-frerun-cse-after-loop"
Re-run common subexpression elimination after loop optimizations has been
performed.
.Ip "\fB\-frerun-loop-opt\fR" 4
.IX Item "-frerun-loop-opt"
Run the loop optimizer twice.
.Ip "\fB\-fgcse\fR" 4
.IX Item "-fgcse"
Perform a global common subexpression elimination pass.
This pass also performs global constant and copy propagation.
.Ip "\fB\-fdelete-null-pointer-checks\fR" 4
.IX Item "-fdelete-null-pointer-checks"
Use global dataflow analysis to identify and eliminate useless null
pointer checks. Programs which rely on \s-1NULL\s0 pointer dereferences \fInot\fR
halting the program may not work properly with this option. Use
\&\-fno-delete-null-pointer-checks to disable this optimizing for programs
which depend on that behavior.
.Ip "\fB\-fexpensive-optimizations\fR" 4
.IX Item "-fexpensive-optimizations"
Perform a number of minor optimizations that are relatively expensive.
.Ip "\fB\-foptimize-register-move\fR" 4
.IX Item "-foptimize-register-move"
.PD 0
.Ip "\fB\-fregmove\fR" 4
.IX Item "-fregmove"
.PD
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. \s-1GCC\s0 enables this optimization by default with \fB\-O2\fR
or higher.
.Sp
Note \fB\-fregmove\fR and \fB\-foptimize-register-move\fR are the same
optimization.
.Ip "\fB\-fdelayed-branch\fR" 4
.IX Item "-fdelayed-branch"
If supported for the target machine, attempt to reorder instructions
to exploit instruction slots available after delayed branch
instructions.
.Ip "\fB\-fschedule-insns\fR" 4
.IX Item "-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.
.Ip "\fB\-fschedule-insns2\fR" 4
.IX Item "-fschedule-insns2"
Similar to \fB\-fschedule-insns\fR, 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.
.Ip "\fB\-ffunction-sections\fR" 4
.IX Item "-ffunction-sections"
.PD 0
.Ip "\fB\-fdata-sections\fR" 4
.IX Item "-fdata-sections"
.PD
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.
.Sp
Use these options on systems where the linker can perform optimizations
to improve locality of reference in the instruction space. \s-1HPPA\s0
processors running \s-1HP-UX\s0 and Sparc processors running Solaris 2 have
linkers with such optimizations. Other systems using the \s-1ELF\s0 object format
as well as \s-1AIX\s0 may have these optimizations in the future.
.Sp
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 \f(CW\*(C`gprof\*(C'\fR on all systems if you
specify this option and you may have problems with debugging if
you specify both this option and \fB\-g\fR.
.Ip "\fB\-fcaller-saves\fR" 4
.IX Item "-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.
.Sp
This option is always enabled by default on certain machines, usually
those which have no call-preserved registers to use instead.
.Sp
For all machines, optimization level 2 and higher enables this flag by
default.
.Ip "\fB\-funroll-loops\fR" 4
.IX Item "-funroll-loops"
Perform the optimization of loop unrolling. This is only done for loops
whose number of iterations can be determined at compile time or run time.
\&\fB\-funroll-loops\fR implies both \fB\-fstrength-reduce\fR and
\&\fB\-frerun-cse-after-loop\fR.
.Ip "\fB\-funroll-all-loops\fR" 4
.IX Item "-funroll-all-loops"
Perform the optimization of loop unrolling. This is done for all loops
and usually makes programs run more slowly. \fB\-funroll-all-loops\fR
implies \fB\-fstrength-reduce\fR as well as \fB\-frerun-cse-after-loop\fR.
.Ip "\fB\-fmove-all-movables\fR" 4
.IX Item "-fmove-all-movables"
Forces all invariant computations in loops to be moved
outside the loop.
.Ip "\fB\-freduce-all-givs\fR" 4
.IX Item "-freduce-all-givs"
Forces all general-induction variables in loops to be
strength-reduced.
.Sp
\&\fINote:\fR When compiling programs written in Fortran,
\&\fB\-fmove-all-movables\fR and \fB\-freduce-all-givs\fR are enabled
by default when you use the optimizer.
.Sp
These options may generate better or worse code; results are highly
dependent on the structure of loops within the source code.
.Sp
These two options are intended to be removed someday, once
they have helped determine the efficacy of various
approaches to improving loop optimizations.
.Sp
Please let us (<\fBgcc@gcc.gnu.org\fR> and <\fBfortran@gnu.org\fR>)
know how use of these options affects
the performance of your production code.
We're very interested in code that runs \fIslower\fR
when these options are \fIenabled\fR.
.Ip "\fB\-fno-peephole\fR" 4
.IX Item "-fno-peephole"
Disable any machine-specific peephole optimizations.
.Ip "\fB\-fbranch-probabilities\fR" 4
.IX Item "-fbranch-probabilities"
After running a program compiled with \fB\-fprofile-arcs\fR, you can compile it a second time using
\&\fB\-fbranch-probabilities\fR, to improve optimizations based on
guessing the path a branch might take.
.Ip "\fB\-fno-guess-branch-probability\fR" 4
.IX Item "-fno-guess-branch-probability"
Sometimes gcc will opt to guess branch probabilities when none are
available from either profile directed feedback (\fB\-fprofile-arcs\fR)
or \fB_\|_builtin_expect\fR. 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.
.Ip "\fB\-fstrict-aliasing\fR" 4
.IX Item "-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 \f(CW\*(C`unsigned int\*(C'\fR can alias an \f(CW\*(C`int\*(C'\fR, but not a
\&\f(CW\*(C`void*\*(C'\fR or a \f(CW\*(C`double\*(C'\fR. A character type may alias any other
type.
.Sp
Pay special attention to code like this:
.Sp
.Vb 4
\& union a_union {
\& int i;
\& double d;
\& };
.Ve
.Vb 5
\& int f() {
\& a_union t;
\& t.d = 3.0;
\& return t.i;
\& }
.Ve
The practice of reading from a different union member than the one most
recently written to (called ``type-punning'') is common. Even with
\&\fB\-fstrict-aliasing\fR, 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:
.Sp
.Vb 7
\& int f() {
\& a_union t;
\& int* ip;
\& t.d = 3.0;
\& ip = &t.i;
\& return *ip;
\& }
.Ve
.Ip "\fB\-falign-functions\fR" 4
.IX Item "-falign-functions"
.PD 0
.Ip "\fB\-falign-functions=\fR\fIn\fR" 4
.IX Item "-falign-functions=n"
.PD
Align the start of functions to the next power-of-two greater than
\&\fIn\fR, skipping up to \fIn\fR bytes. For instance,
\&\fB\-falign-functions=32\fR aligns functions to the next 32\-byte
boundary, but \fB\-falign-functions=24\fR would align to the next
32\-byte boundary only if this can be done by skipping 23 bytes or less.
.Sp
\&\fB\-fno-align-functions\fR and \fB\-falign-functions=1\fR are
equivalent and mean that functions will not be aligned.
.Sp
Some assemblers only support this flag when \fIn\fR is a power of two;
in that case, it is rounded up.
.Sp
If \fIn\fR is not specified, use a machine-dependent default.
.Ip "\fB\-falign-labels\fR" 4
.IX Item "-falign-labels"
.PD 0
.Ip "\fB\-falign-labels=\fR\fIn\fR" 4
.IX Item "-falign-labels=n"
.PD
Align all branch targets to a power-of-two boundary, skipping up to
\&\fIn\fR bytes like \fB\-falign-functions\fR. 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.
.Sp
If \fB\-falign-loops\fR or \fB\-falign-jumps\fR are applicable and
are greater than this value, then their values are used instead.
.Sp
If \fIn\fR is not specified, use a machine-dependent default which is
very likely to be \fB1\fR, meaning no alignment.
.Ip "\fB\-falign-loops\fR" 4
.IX Item "-falign-loops"
.PD 0
.Ip "\fB\-falign-loops=\fR\fIn\fR" 4
.IX Item "-falign-loops=n"
.PD
Align loops to a power-of-two boundary, skipping up to \fIn\fR bytes
like \fB\-falign-functions\fR. The hope is that the loop will be
executed many times, which will make up for any execution of the dummy
operations.
.Sp
If \fIn\fR is not specified, use a machine-dependent default.
.Ip "\fB\-falign-jumps\fR" 4
.IX Item "-falign-jumps"
.PD 0
.Ip "\fB\-falign-jumps=\fR\fIn\fR" 4
.IX Item "-falign-jumps=n"
.PD
Align branch targets to a power-of-two boundary, for branch targets
where the targets can only be reached by jumping, skipping up to \fIn\fR
bytes like \fB\-falign-functions\fR. In this case, no dummy operations
need be executed.
.Sp
If \fIn\fR is not specified, use a machine-dependent default.
.Ip "\fB\-fssa\fR" 4
.IX Item "-fssa"
Perform optimizations in static single assignment form. Each function's
flow graph is translated into \s-1SSA\s0 form, optimizations are performed, and
the flow graph is translated back from \s-1SSA\s0 form. User's should not
specify this option, since it is not yet ready for production use.
.Ip "\fB\-fdce\fR" 4
.IX Item "-fdce"
Perform dead-code elimination in \s-1SSA\s0 form. Requires \fB\-fssa\fR. Like
\&\fB\-fssa\fR, this is an experimental feature.
.Ip "\fB\-fsingle-precision-constant\fR" 4
.IX Item "-fsingle-precision-constant"
Treat floating point constant as single precision constant instead of
implicitly converting it to double precision constant.
.Ip "\fB\-frename-registers\fR" 4
.IX Item "-frename-registers"
Attempt to avoid false dependancies 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''.
.Ip "\fB\*(--param\fR \fIname\fR\fB=\fR\fIvalue\fR" 4
.IX Item "param name=value"
In some places, \s-1GCC\s0 uses various constants to control the amount of
optimization that is done. For example, \s-1GCC\s0 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
\&\fB\*(--param\fR option.
.Sp
In each case, the \fIvalue\fR is a integer. The allowable choices for
\&\fIname\fR are given in the following table:
.RS 4
.Ip "\fBmax-inline-insns\fR" 4
.IX Item "max-inline-insns"
If an function contains more than this many instructions, it
will not be inlined. This option is precisely equivalent to
\&\fB\-finline-limit\fR.
.RE
.RS 4
.RE
.Sh "Options Controlling the Preprocessor"
.IX Subsection "Options Controlling the Preprocessor"
These options control the C preprocessor, which is run on each C source
file before actual compilation.
.PP
If you use the \fB\-E\fR option, nothing is done except preprocessing.
Some of these options make sense only together with \fB\-E\fR because
they cause the preprocessor output to be unsuitable for actual
compilation.
.Ip "\fB\-include\fR \fIfile\fR" 4
.IX Item "-include file"
Process \fIfile\fR as input before processing the regular input file.
In effect, the contents of \fIfile\fR are compiled first. Any \fB\-D\fR
and \fB\-U\fR options on the command line are always processed before
\&\fB\-include\fR \fIfile\fR, regardless of the order in which they are
written. All the \fB\-include\fR and \fB\-imacros\fR options are
processed in the order in which they are written.
.Ip "\fB\-imacros\fR \fIfile\fR" 4
.IX Item "-imacros file"
Process \fIfile\fR as input, discarding the resulting output, before
processing the regular input file. Because the output generated from
\&\fIfile\fR is discarded, the only effect of \fB\-imacros\fR \fIfile\fR
is to make the macros defined in \fIfile\fR available for use in the
main input. All the \fB\-include\fR and \fB\-imacros\fR options are
processed in the order in which they are written.
.Ip "\fB\-idirafter\fR \fIdir\fR" 4
.IX Item "-idirafter dir"
Add the directory \fIdir\fR 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
\&\fB\-I\fR adds to).
.Ip "\fB\-iprefix\fR \fIprefix\fR" 4
.IX Item "-iprefix prefix"
Specify \fIprefix\fR as the prefix for subsequent \fB\-iwithprefix\fR
options.
.Ip "\fB\-iwithprefix\fR \fIdir\fR" 4
.IX Item "-iwithprefix dir"
Add a directory to the second include path. The directory's name is
made by concatenating \fIprefix\fR and \fIdir\fR, where \fIprefix\fR was
specified previously with \fB\-iprefix\fR. If you have not specified a
prefix yet, the directory containing the installed passes of the
compiler is used as the default.
.Ip "\fB\-iwithprefixbefore\fR \fIdir\fR" 4
.IX Item "-iwithprefixbefore dir"
Add a directory to the main include path. The directory's name is made
by concatenating \fIprefix\fR and \fIdir\fR, as in the case of
\&\fB\-iwithprefix\fR.
.Ip "\fB\-isystem\fR \fIdir\fR" 4
.IX Item "-isystem dir"
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.
.Ip "\fB\-nostdinc\fR" 4
.IX Item "-nostdinc"
Do not search the standard system directories for header files. Only
the directories you have specified with \fB\-I\fR options (and the
current directory, if appropriate) are searched.
.Sp
By using both \fB\-nostdinc\fR and \fB\-I-\fR, you can limit the include-file
search path to only those directories you specify explicitly.
.Ip "\fB\-remap\fR" 4
.IX Item "-remap"
When searching for a header file in a directory, remap file names if a
file named \fIheader.gcc\fR exists in that directory. This can be used
to work around limitations of file systems with file name restrictions.
The \fIheader.gcc\fR 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.
.Ip "\fB\-undef\fR" 4
.IX Item "-undef"
Do not predefine any nonstandard macros. (Including architecture flags).
.Ip "\fB\-E\fR" 4
.IX Item "-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.
.Ip "\fB\-C\fR" 4
.IX Item "-C"
Tell the preprocessor not to discard comments. Used with the
\&\fB\-E\fR option.
.Ip "\fB\-P\fR" 4
.IX Item "-P"
Tell the preprocessor not to generate \fB#line\fR directives.
Used with the \fB\-E\fR option.
.Ip "\fB\-M\fR" 4
.IX Item "-M"
Instead of outputting the result of preprocessing, output a rule
suitable for \f(CW\*(C`make\*(C'\fR describing the dependencies of the main source
file. The preprocessor outputs one \f(CW\*(C`make\*(C'\fR 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 \fB\e\fR\-newline.
.Sp
\&\fB\-M\fR implies \fB\-E\fR.
.Ip "\fB\-MM\fR" 4
.IX Item "-MM"
Like \fB\-M\fR, but mention only the files included with \fB#include
"\fR\fIfile\fR\fB"\fR. System header files included with \fB#include
<\fR\fIfile\fR\fB>\fR are omitted.
.Ip "\fB\-MD\fR" 4
.IX Item "-MD"
Like \fB\-M\fR but the dependency information is written to a file
rather than stdout. \f(CW\*(C`gcc\*(C'\fR will use the same file name and
directory as the object file, but with the suffix \*(L".d\*(R" instead.
.Sp
This is in addition to compiling the main file as specified \-\-\-
\&\fB\-MD\fR does not inhibit ordinary compilation the way \fB\-M\fR does,
unless you also specify \fB\-MG\fR.
.Sp
With Mach, you can use the utility \f(CW\*(C`md\*(C'\fR to merge multiple
dependency files into a single dependency file suitable for using with
the \fBmake\fR command.
.Ip "\fB\-MMD\fR" 4
.IX Item "-MMD"
Like \fB\-MD\fR except mention only user header files, not system
\&\-header files.
.Ip "\fB\-MF\fR \fIfile\fR" 4
.IX Item "-MF file"
When used with \fB\-M\fR or \fB\-MM\fR, specifies a file to write the
dependencies to. This allows the preprocessor to write the preprocessed
file to stdout normally. If no \fB\-MF\fR switch is given, \s-1CPP\s0 sends
the rules to stdout and suppresses normal preprocessed output.
.Sp
Another way to specify output of a \f(CW\*(C`make\*(C'\fR rule is by setting
the environment variable \fB\s-1DEPENDENCIES_OUTPUT\s0\fR.
.Ip "\fB\-MG\fR" 4
.IX Item "-MG"
When used with \fB\-M\fR or \fB\-MM\fR, \fB\-MG\fR 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.
.Sp
This feature is used in automatic updating of makefiles.
.Ip "\fB\-MP\fR" 4
.IX Item "-MP"
This option instructs \s-1CPP\s0 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 \f(CW\*(C`make\*(C'\fR gives if you remove header
files without updating the \f(CW\*(C`Makefile\*(C'\fR to match.
.Sp
This is typical output:\-
.Sp
.Vb 1
\& /tmp/test.o: /tmp/test.c /tmp/test.h
.Ve
.Vb 1
\& /tmp/test.h:
.Ve
.Ip "\fB\-MQ\fR \fItarget\fR" 4
.IX Item "-MQ target"
.PD 0
.Ip "\fB\-MT\fR \fItarget\fR" 4
.IX Item "-MT target"
.PD
By default \s-1CPP\s0 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 \fB\-MT\fR you can specify a
target yourself, overriding the default one.
.Sp
If you want multiple targets, you can specify them as a single argument
to \fB\-MT\fR, or use multiple \fB\-MT\fR options.
.Sp
The targets you specify are output in the order they appear on the
command line. \fB\-MQ\fR is identical to \fB\-MT\fR, except that the
target name is quoted for Make, but with \fB\-MT\fR it isn't. For
example, \-MT '$(objpfx)foo.o' gives
.Sp
.Vb 1
\& $(objpfx)foo.o: /tmp/foo.c
.Ve
but \-MQ '$(objpfx)foo.o' gives
.Sp
.Vb 1
\& $$(objpfx)foo.o: /tmp/foo.c
.Ve
The default target is automatically quoted, as if it were given with
\&\fB\-MQ\fR.
.Ip "\fB\-H\fR" 4
.IX Item "-H"
Print the name of each header file used, in addition to other normal
activities.
.Ip "\fB\-A\fR\fIquestion\fR\fB(\fR\fIanswer\fR\fB)\fR" 4
.IX Item "-Aquestion(answer)"
Assert the answer \fIanswer\fR for \fIquestion\fR, in case it is tested
with a preprocessing conditional such as \fB#if
#\fR\fIquestion\fR\fB(\fR\fIanswer\fR\fB)\fR. \fB\-A-\fR disables the standard
assertions that normally describe the target machine.
.Ip "\fB\-D\fR\fImacro\fR" 4
.IX Item "-Dmacro"
Define macro \fImacro\fR with the string \fB1\fR as its definition.
.Ip "\fB\-D\fR\fImacro\fR\fB=\fR\fIdefn\fR" 4
.IX Item "-Dmacro=defn"
Define macro \fImacro\fR as \fIdefn\fR. All instances of \fB\-D\fR on
the command line are processed before any \fB\-U\fR options.
.Sp
Any \fB\-D\fR and \fB\-U\fR options on the command line are processed in
order, and always before \fB\-imacros\fR \fIfile\fR, regardless of the
order in which they are written.
.Ip "\fB\-U\fR\fImacro\fR" 4
.IX Item "-Umacro"
Undefine macro \fImacro\fR. \fB\-U\fR options are evaluated after all
\&\fB\-D\fR options, but before any \fB\-include\fR and \fB\-imacros\fR
options.
.Sp
Any \fB\-D\fR and \fB\-U\fR options on the command line are processed in
order, and always before \fB\-imacros\fR \fIfile\fR, regardless of the
order in which they are written.
.Ip "\fB\-dM\fR" 4
.IX Item "-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 \fB\-E\fR
option.
.Ip "\fB\-dD\fR" 4
.IX Item "-dD"
Tell the preprocessing to pass all macro definitions into the output, in
their proper sequence in the rest of the output.
.Ip "\fB\-dN\fR" 4
.IX Item "-dN"
Like \fB\-dD\fR except that the macro arguments and contents are omitted.
Only \fB#define\fR \fIname\fR is included in the output.
.Ip "\fB\-dI\fR" 4
.IX Item "-dI"
Output \fB#include\fR directives in addition to the result of
preprocessing.
.Ip "\fB\-trigraphs\fR" 4
.IX Item "-trigraphs"
Process \s-1ISO\s0 standard trigraph sequences. These are three-character
sequences, all starting with \fB??\fR, that are defined by \s-1ISO\s0 C to
stand for single characters. For example, \fB??/\fR stands for
\&\fB\e\fR, so \fB'??/n'\fR is a character constant for a newline. By
default, \s-1GCC\s0 ignores trigraphs, but in standard-conforming modes it
converts them. See the \fB\-std\fR and \fB\-ansi\fR options.
.Sp
The nine trigraph sequences are
.RS 4
.Ip "\fB??(\fR" 4
.IX Item "??("
-> \fB[\fR
.Ip "\fB??)\fR" 4
.IX Item "??)"
-> \fB]\fR
.Ip "\fB??<\fR" 4
.IX Item "??<"
-> \fB{\fR
.Ip "\fB??>\fR" 4
.IX Item "??>"
-> \fB}\fR
.Ip "\fB??=\fR" 4
.IX Item "??="
-> \fB#\fR
.Ip "\fB??/\fR" 4
.IX Item "??/"
-> \fB\e\fR
.Ip "\fB??'\fR" 4
.IX Item "??'"
-> \fB^\fR
.Ip "\fB??!\fR" 4
.IX Item "??!"
-> \fB|\fR
.Ip "\fB??-\fR" 4
.IX Item "??-"
-> \fB~\fR
.RE
.RS 4
.Sp
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.
.RE
.Ip "\fB\-Wp,\fR\fIoption\fR" 4
.IX Item "-Wp,option"
Pass \fIoption\fR as an option to the preprocessor. If \fIoption\fR
contains commas, it is split into multiple options at the commas.
.Sh "Passing Options to the Assembler"
.IX Subsection "Passing Options to the Assembler"
You can pass options to the assembler.
.Ip "\fB\-Wa,\fR\fIoption\fR" 4
.IX Item "-Wa,option"
Pass \fIoption\fR as an option to the assembler. If \fIoption\fR
contains commas, it is split into multiple options at the commas.
.Sh "Options for Linking"
.IX Subsection "Options for 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.
.Ip "\fIobject-file-name\fR" 4
.IX Item "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.
.Ip "\fB\-c\fR" 4
.IX Item "-c"
.PD 0
.Ip "\fB\-S\fR" 4
.IX Item "-S"
.Ip "\fB\-E\fR" 4
.IX Item "-E"
.PD
If any of these options is used, then the linker is not run, and
object file names should not be used as arguments.
.Ip "\fB\-l\fR\fIlibrary\fR" 4
.IX Item "-llibrary"
Search the library named \fIlibrary\fR when linking.
.Sp
It makes a difference where in the command you write this option; the
linker searches processes libraries and object files in the order they
are specified. Thus, \fBfoo.o \-lz bar.o\fR searches library \fBz\fR
after file \fIfoo.o\fR but before \fIbar.o\fR. If \fIbar.o\fR refers
to functions in \fBz\fR, those functions may not be loaded.
.Sp
The linker searches a standard list of directories for the library,
which is actually a file named \fIlib\fIlibrary\fI.a\fR. The linker
then uses this file as if it had been specified precisely by name.
.Sp
The directories searched include several standard system directories
plus any that you specify with \fB\-L\fR.
.Sp
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 \fB\-l\fR option and specifying a file name
is that \fB\-l\fR surrounds \fIlibrary\fR with \fBlib\fR and \fB.a\fR
and searches several directories.
.Ip "\fB\-lobjc\fR" 4
.IX Item "-lobjc"
You need this special case of the \fB\-l\fR option in order to
link an Objective C program.
.Ip "\fB\-nostartfiles\fR" 4
.IX Item "-nostartfiles"
Do not use the standard system startup files when linking.
The standard system libraries are used normally, unless \fB\-nostdlib\fR
or \fB\-nodefaultlibs\fR is used.
.Ip "\fB\-nodefaultlibs\fR" 4
.IX Item "-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 \fB\-nostartfiles\fR
is used. The compiler may generate calls to memcmp, memset, and memcpy
for System V (and \s-1ISO\s0 C) environments or to bcopy and bzero for
\&\s-1BSD\s0 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.
.Ip "\fB\-nostdlib\fR" 4
.IX Item "-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 \s-1ISO\s0 C) environments or to bcopy and bzero for
\&\s-1BSD\s0 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.
.Sp
One of the standard libraries bypassed by \fB\-nostdlib\fR and
\&\fB\-nodefaultlibs\fR is \fIlibgcc.a\fR, a library of internal subroutines
that \s-1GCC\s0 uses to overcome shortcomings of particular machines, or special
needs for some languages.
.Sp
In most cases, you need \fIlibgcc.a\fR even when you want to avoid
other standard libraries. In other words, when you specify \fB\-nostdlib\fR
or \fB\-nodefaultlibs\fR you should usually specify \fB\-lgcc\fR as well.
This ensures that you have no unresolved references to internal \s-1GCC\s0
library subroutines. (For example, \fB_\|_main\fR, used to ensure \*(C+
constructors will be called.)
.Ip "\fB\-s\fR" 4
.IX Item "-s"
Remove all symbol table and relocation information from the executable.
.Ip "\fB\-static\fR" 4
.IX Item "-static"
On systems that support dynamic linking, this prevents linking with the shared
libraries. On other systems, this option has no effect.
.Ip "\fB\-shared\fR" 4
.IX Item "-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 (\fB\-fpic\fR, \fB\-fPIC\fR, or model suboptions)
when you specify this option.[1]
.Ip "\fB\-shared-libgcc\fR" 4
.IX Item "-shared-libgcc"
.PD 0
.Ip "\fB\-static-libgcc\fR" 4
.IX Item "-static-libgcc"
.PD
On systems that provide \fIlibgcc\fR as a shared library, these options
force the use of either the shared or static version respectively.
If no shared version of \fIlibgcc\fR was built when the compiler was
configured, these options have no effect.
.Sp
There are several situations in which an application should use the
shared \fIlibgcc\fR 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 \fIlibgcc\fR.
.Sp
Therefore, whenever you specify the \fB\-shared\fR option, the \s-1GCC\s0
driver automatically adds \fB\-shared-libgcc\fR, unless you explicitly
specify \fB\-static-libgcc\fR. The G++ driver automatically adds
\&\fB\-shared-libgcc\fR 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.)
.Sp
However, when linking a main executable written in C, you must
explicitly say \fB\-shared-libgcc\fR if you want to use the shared
\&\fIlibgcc\fR.
.Ip "\fB\-symbolic\fR" 4
.IX Item "-symbolic"
Bind references to global symbols when building a shared object. Warn
about any unresolved references (unless overridden by the link editor
option \fB\-Xlinker \-z \-Xlinker defs\fR). Only a few systems support
this option.
.Ip "\fB\-Xlinker\fR \fIoption\fR" 4
.IX Item "-Xlinker option"
Pass \fIoption\fR as an option to the linker. You can use this to
supply system-specific linker options which \s-1GCC\s0 does not know how to
recognize.
.Sp
If you want to pass an option that takes an argument, you must use
\&\fB\-Xlinker\fR twice, once for the option and once for the argument.
For example, to pass \fB\-assert definitions\fR, you must write
\&\fB\-Xlinker \-assert \-Xlinker definitions\fR. It does not work to write
\&\fB\-Xlinker \*(L"\-assert definitions\*(R"\fR, because this passes the entire
string as a single argument, which is not what the linker expects.
.Ip "\fB\-Wl,\fR\fIoption\fR" 4
.IX Item "-Wl,option"
Pass \fIoption\fR as an option to the linker. If \fIoption\fR contains
commas, it is split into multiple options at the commas.
.Ip "\fB\-u\fR \fIsymbol\fR" 4
.IX Item "-u symbol"
Pretend the symbol \fIsymbol\fR is undefined, to force linking of
library modules to define it. You can use \fB\-u\fR multiple times with
different symbols to force loading of additional library modules.
.Sh "Options for Directory Search"
.IX Subsection "Options for Directory Search"
These options specify directories to search for header files, for
libraries and for parts of the compiler:
.Ip "\fB\-I\fR\fIdir\fR" 4
.IX Item "-Idir"
Add the directory \fIdir\fR 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 \fB\-isystem\fR for that). If you use more than
one \fB\-I\fR option, the directories are scanned in left-to-right
order; the standard system directories come after.
.Ip "\fB\-I-\fR" 4
.IX Item "-I-"
Any directories you specify with \fB\-I\fR options before the \fB\-I-\fR
option are searched only for the case of \fB#include "\fR\fIfile\fR\fB"\fR;
they are not searched for \fB#include <\fR\fIfile\fR\fB>\fR.
.Sp
If additional directories are specified with \fB\-I\fR options after
the \fB\-I-\fR, these directories are searched for all \fB#include\fR
directives. (Ordinarily \fIall\fR \fB\-I\fR directories are used
this way.)
.Sp
In addition, the \fB\-I-\fR option inhibits the use of the current
directory (where the current input file came from) as the first search
directory for \fB#include "\fR\fIfile\fR\fB"\fR. There is no way to
override this effect of \fB\-I-\fR. With \fB\-I.\fR 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.
.Sp
\&\fB\-I-\fR does not inhibit the use of the standard system directories
for header files. Thus, \fB\-I-\fR and \fB\-nostdinc\fR are
independent.
.Ip "\fB\-L\fR\fIdir\fR" 4
.IX Item "-Ldir"
Add directory \fIdir\fR to the list of directories to be searched
for \fB\-l\fR.
.Ip "\fB\-B\fR\fIprefix\fR" 4
.IX Item "-Bprefix"
This option specifies where to find the executables, libraries,
include files, and data files of the compiler itself.
.Sp
The compiler driver program runs one or more of the subprograms
\&\fIcpp\fR, \fIcc1\fR, \fIas\fR and \fIld\fR. It tries
\&\fIprefix\fR as a prefix for each program it tries to run, both with and
without \fImachine\fR\fB/\fR\fIversion\fR\fB/\fR.
.Sp
For each subprogram to be run, the compiler driver first tries the
\&\fB\-B\fR prefix, if any. If that name is not found, or if \fB\-B\fR
was not specified, the driver tries two standard prefixes, which are
\&\fI/usr/lib/gcc/\fR and \fI/usr/local/lib/gcc-lib/\fR. 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
\&\fB\s-1PATH\s0\fR environment variable.
.Sp
\&\fB\-B\fR prefixes that effectively specify directory names also apply
to libraries in the linker, because the compiler translates these
options into \fB\-L\fR options for the linker. They also apply to
includes files in the preprocessor, because the compiler translates these
options into \fB\-isystem\fR options for the preprocessor. In this case,
the compiler appends \fBinclude\fR to the prefix.
.Sp
The run-time support file \fIlibgcc.a\fR can also be searched for using
the \fB\-B\fR 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.
.Sp
Another way to specify a prefix much like the \fB\-B\fR prefix is to use
the environment variable \fB\s-1GCC_EXEC_PREFIX\s0\fR.
.Ip "\fB\-specs=\fR\fIfile\fR" 4
.IX Item "-specs=file"
Process \fIfile\fR after the compiler reads in the standard \fIspecs\fR
file, in order to override the defaults that the \fIgcc\fR driver
program uses when determining what switches to pass to \fIcc1\fR,
\&\fIcc1plus\fR, \fIas\fR, \fIld\fR, etc. More than one
\&\fB\-specs=\fR\fIfile\fR can be specified on the command line, and they
are processed in order, from left to right.
.Sh "Specifying Target Machine and Compiler Version"
.IX Subsection "Specifying Target Machine and Compiler Version"
By default, \s-1GCC\s0 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 \s-1GCC\s0, for different target machines, can be
installed side by side. Then you specify which one to use with the
\&\fB\-b\fR option.
.PP
In addition, older and newer versions of \s-1GCC\s0 can be installed side
by side. One of them (probably the newest) will be the default, but
you may sometimes wish to use another.
.Ip "\fB\-b\fR \fImachine\fR" 4
.IX Item "-b machine"
The argument \fImachine\fR specifies the target machine for compilation.
This is useful when you have installed \s-1GCC\s0 as a cross-compiler.
.Sp
The value to use for \fImachine\fR is the same as was specified as the
machine type when configuring \s-1GCC\s0 as a cross-compiler. For
example, if a cross-compiler was configured with \fBconfigure
i386v\fR, meaning to compile for an 80386 running System V, then you
would specify \fB\-b i386v\fR to run that cross compiler.
.Sp
When you do not specify \fB\-b\fR, it normally means to compile for
the same type of machine that you are using.
.Ip "\fB\-V\fR \fIversion\fR" 4
.IX Item "-V version"
The argument \fIversion\fR specifies which version of \s-1GCC\s0 to run.
This is useful when multiple versions are installed. For example,
\&\fIversion\fR might be \fB2.0\fR, meaning to run \s-1GCC\s0 version 2.0.
.Sp
The default version, when you do not specify \fB\-V\fR, is the last
version of \s-1GCC\s0 that you installed.
.PP
The \fB\-b\fR and \fB\-V\fR options actually work by controlling part of
the file name used for the executable files and libraries used for
compilation. A given version of \s-1GCC\s0, for a given target machine, is
normally kept in the directory \fI/usr/local/lib/gcc-lib/\fImachine\fI/\fIversion\fI\fR.
.PP
Thus, sites can customize the effect of \fB\-b\fR or \fB\-V\fR either by
changing the names of these directories or adding alternate names (or
symbolic links). If in directory \fI/usr/local/lib/gcc-lib/\fR the
file \fI80386\fR is a link to the file \fIi386v\fR, then \fB\-b
80386\fR becomes an alias for \fB\-b i386v\fR.
.PP
In one respect, the \fB\-b\fR or \fB\-V\fR do not completely change
to a different compiler: the top-level driver program \fBgcc\fR
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, \fB\-V 3.0\fR with a driver program from \s-1GCC\s0
version 3.0.1), use of \fB\-V\fR may not work; for example, using
\&\fB\-V 2.95.2\fR will not work with a driver program from \s-1GCC\s0 3.0.
.PP
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.
.PP
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.
.PP
For example, if the driver for version 2.0 is installed as \fBogcc\fR
and that for version 2.1 is installed as \fBgcc\fR, then the command
\&\fBgcc\fR will use version 2.1 by default, while \fBogcc\fR will use
2.0 by default. However, you can choose either version with either
command with the \fB\-V\fR option.
.Sh "Hardware Models and Configurations"
.IX Subsection "Hardware Models and Configurations"
Earlier we discussed the standard option \fB\-b\fR which chooses among
different installed compilers for completely different target
machines, such as Vax vs. 68000 vs. 80386.
.PP
In addition, each of these target machine types can have its own
special options, starting with \fB\-m\fR, 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.
.PP
Some configurations of the compiler also support additional special
options, usually for compatibility with other compilers on the same
platform.
.PP
.I "M680x0 Options"
.IX Subsection "M680x0 Options"
.PP
These are the \fB\-m\fR 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.
.Ip "\fB\-m68000\fR" 4
.IX Item "-m68000"
.PD 0
.Ip "\fB\-mc68000\fR" 4
.IX Item "-mc68000"
.PD
Generate output for a 68000. This is the default
when the compiler is configured for 68000\-based systems.
.Sp
Use this option for microcontrollers with a 68000 or \s-1EC000\s0 core,
including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
.Ip "\fB\-m68020\fR" 4
.IX Item "-m68020"
.PD 0
.Ip "\fB\-mc68020\fR" 4
.IX Item "-mc68020"
.PD
Generate output for a 68020. This is the default
when the compiler is configured for 68020\-based systems.
.Ip "\fB\-m68881\fR" 4
.IX Item "-m68881"
Generate output containing 68881 instructions for floating point.
This is the default for most 68020 systems unless \fB\-nfp\fR was
specified when the compiler was configured.
.Ip "\fB\-m68030\fR" 4
.IX Item "-m68030"
Generate output for a 68030. This is the default when the compiler is
configured for 68030\-based systems.
.Ip "\fB\-m68040\fR" 4
.IX Item "-m68040"
Generate output for a 68040. This is the default when the compiler is
configured for 68040\-based systems.
.Sp
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.
.Ip "\fB\-m68060\fR" 4
.IX Item "-m68060"
Generate output for a 68060. This is the default when the compiler is
configured for 68060\-based systems.
.Sp
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.
.Ip "\fB\-mcpu32\fR" 4
.IX Item "-mcpu32"
Generate output for a \s-1CPU32\s0. This is the default
when the compiler is configured for CPU32\-based systems.
.Sp
Use this option for microcontrollers with a
\&\s-1CPU32\s0 or \s-1CPU32+\s0 core, including the 68330, 68331, 68332, 68333, 68334,
68336, 68340, 68341, 68349 and 68360.
.Ip "\fB\-m5200\fR" 4
.IX Item "-m5200"
Generate output for a 520X \*(L"coldfire\*(R" family cpu. This is the default
when the compiler is configured for 520X-based systems.
.Sp
Use this option for microcontroller with a 5200 core, including
the \s-1MCF5202\s0, \s-1MCF5203\s0, \s-1MCF5204\s0 and \s-1MCF5202\s0.
.Ip "\fB\-m68020\-40\fR" 4
.IX Item "-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.
.Ip "\fB\-m68020\-60\fR" 4
.IX Item "-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.
.Ip "\fB\-mfpa\fR" 4
.IX Item "-mfpa"
Generate output containing Sun \s-1FPA\s0 instructions for floating point.
.Ip "\fB\-msoft-float\fR" 4
.IX Item "-msoft-float"
Generate output containing library calls for floating point.
\&\fBWarning:\fR 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 \fBm68k-*\-aout\fR and
\&\fBm68k-*\-coff\fR do provide software floating point support.
.Ip "\fB\-mshort\fR" 4
.IX Item "-mshort"
Consider type \f(CW\*(C`int\*(C'\fR to be 16 bits wide, like \f(CW\*(C`short int\*(C'\fR.
.Ip "\fB\-mnobitfield\fR" 4
.IX Item "-mnobitfield"
Do not use the bit-field instructions. The \fB\-m68000\fR, \fB\-mcpu32\fR
and \fB\-m5200\fR options imply \fB\-mnobitfield\fR.
.Ip "\fB\-mbitfield\fR" 4
.IX Item "-mbitfield"
Do use the bit-field instructions. The \fB\-m68020\fR option implies
\&\fB\-mbitfield\fR. This is the default if you use a configuration
designed for a 68020.
.Ip "\fB\-mrtd\fR" 4
.IX Item "-mrtd"
Use a different function-calling convention, in which functions
that take a fixed number of arguments return with the \f(CW\*(C`rtd\*(C'\fR
instruction, which pops their arguments while returning. This
saves one instruction in the caller since there is no need to pop
the arguments there.
.Sp
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.
.Sp
Also, you must provide function prototypes for all functions that
take variable numbers of arguments (including \f(CW\*(C`printf\*(C'\fR);
otherwise incorrect code will be generated for calls to those
functions.
.Sp
In addition, seriously incorrect code will result if you call a
function with too many arguments. (Normally, extra arguments are
harmlessly ignored.)
.Sp
The \f(CW\*(C`rtd\*(C'\fR instruction is supported by the 68010, 68020, 68030,
68040, 68060 and \s-1CPU32\s0 processors, but not by the 68000 or 5200.
.Ip "\fB\-malign-int\fR" 4
.IX Item "-malign-int"
.PD 0
.Ip "\fB\-mno-align-int\fR" 4
.IX Item "-mno-align-int"
.PD
Control whether \s-1GCC\s0 aligns \f(CW\*(C`int\*(C'\fR, \f(CW\*(C`long\*(C'\fR, \f(CW\*(C`long long\*(C'\fR,
\&\f(CW\*(C`float\*(C'\fR, \f(CW\*(C`double\*(C'\fR, and \f(CW\*(C`long double\*(C'\fR variables on a 32\-bit
boundary (\fB\-malign-int\fR) or a 16\-bit boundary (\fB\-mno-align-int\fR).
Aligning variables on 32\-bit boundaries produces code that runs somewhat
faster on processors with 32\-bit busses at the expense of more memory.
.Sp
\&\fBWarning:\fR if you use the \fB\-malign-int\fR switch, \s-1GCC\s0 will
align structures containing the above types differently than
most published application binary interface specifications for the m68k.
.Ip "\fB\-mpcrel\fR" 4
.IX Item "-mpcrel"
Use the pc-relative addressing mode of the 68000 directly, instead of
using a global offset table. At present, this option implies \-fpic,
allowing at most a 16\-bit offset for pc-relative addressing. \-fPIC is
not presently supported with \-mpcrel, though this could be supported for
68020 and higher processors.
.Ip "\fB\-mno-strict-align\fR" 4
.IX Item "-mno-strict-align"
.PD 0
.Ip "\fB\-mstrict-align\fR" 4
.IX Item "-mstrict-align"
.PD
Do not (do) assume that unaligned memory references will be handled by
the system.
.PP
.I "M68hc1x Options"
.IX Subsection "M68hc1x Options"
.PP
These are the \fB\-m\fR 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.
.Ip "\fB\-m6811\fR" 4
.IX Item "-m6811"
.PD 0
.Ip "\fB\-m68hc11\fR" 4
.IX Item "-m68hc11"
.PD
Generate output for a 68HC11. This is the default
when the compiler is configured for 68HC11\-based systems.
.Ip "\fB\-m6812\fR" 4
.IX Item "-m6812"
.PD 0
.Ip "\fB\-m68hc12\fR" 4
.IX Item "-m68hc12"
.PD
Generate output for a 68HC12. This is the default
when the compiler is configured for 68HC12\-based systems.
.Ip "\fB\-mauto-incdec\fR" 4
.IX Item "-mauto-incdec"
Enable the use of 68HC12 pre and post auto-increment and auto-decrement
addressing modes.
.Ip "\fB\-mshort\fR" 4
.IX Item "-mshort"
Consider type \f(CW\*(C`int\*(C'\fR to be 16 bits wide, like \f(CW\*(C`short int\*(C'\fR.
.Ip "\fB\-msoft-reg-count=\fR\fIcount\fR" 4
.IX Item "-msoft-reg-count=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.
.PP
.I "\s-1VAX\s0 Options"
.IX Subsection "VAX Options"
.PP
These \fB\-m\fR options are defined for the Vax:
.Ip "\fB\-munix\fR" 4
.IX Item "-munix"
Do not output certain jump instructions (\f(CW\*(C`aobleq\*(C'\fR and so on)
that the Unix assembler for the Vax cannot handle across long
ranges.
.Ip "\fB\-mgnu\fR" 4
.IX Item "-mgnu"
Do output those jump instructions, on the assumption that you
will assemble with the \s-1GNU\s0 assembler.
.Ip "\fB\-mg\fR" 4
.IX Item "-mg"
Output code for g-format floating point numbers instead of d-format.
.PP
.I "\s-1SPARC\s0 Options"
.IX Subsection "SPARC Options"
.PP
These \fB\-m\fR switches are supported on the \s-1SPARC:\s0
.Ip "\fB\-mno-app-regs\fR" 4
.IX Item "-mno-app-regs"
.PD 0
.Ip "\fB\-mapp-regs\fR" 4
.IX Item "-mapp-regs"
.PD
Specify \fB\-mapp-regs\fR to generate output using the global registers
2 through 4, which the \s-1SPARC\s0 \s-1SVR4\s0 \s-1ABI\s0 reserves for applications. This
is the default.
.Sp
To be fully \s-1SVR4\s0 \s-1ABI\s0 compliant at the cost of some performance loss,
specify \fB\-mno-app-regs\fR. You should compile libraries and system
software with this option.
.Ip "\fB\-mfpu\fR" 4
.IX Item "-mfpu"
.PD 0
.Ip "\fB\-mhard-float\fR" 4
.IX Item "-mhard-float"
.PD
Generate output containing floating point instructions. This is the
default.
.Ip "\fB\-mno-fpu\fR" 4
.IX Item "-mno-fpu"
.PD 0
.Ip "\fB\-msoft-float\fR" 4
.IX Item "-msoft-float"
.PD
Generate output containing library calls for floating point.
\&\fBWarning:\fR the requisite libraries are not available for all \s-1SPARC\s0
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 \fBsparc-*\-aout\fR and
\&\fBsparclite-*\-*\fR do provide software floating point support.
.Sp
\&\fB\-msoft-float\fR changes the calling convention in the output file;
therefore, it is only useful if you compile \fIall\fR of a program with
this option. In particular, you need to compile \fIlibgcc.a\fR, the
library that comes with \s-1GCC\s0, with \fB\-msoft-float\fR in order for
this to work.
.Ip "\fB\-mhard-quad-float\fR" 4
.IX Item "-mhard-quad-float"
Generate output containing quad-word (long double) floating point
instructions.
.Ip "\fB\-msoft-quad-float\fR" 4
.IX Item "-msoft-quad-float"
Generate output containing library calls for quad-word (long double)
floating point instructions. The functions called are those specified
in the \s-1SPARC\s0 \s-1ABI\s0. This is the default.
.Sp
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 \s-1ABI\s0 library routines. Thus the
\&\fB\-msoft-quad-float\fR option is the default.
.Ip "\fB\-mno-epilogue\fR" 4
.IX Item "-mno-epilogue"
.PD 0
.Ip "\fB\-mepilogue\fR" 4
.IX Item "-mepilogue"
.PD
With \fB\-mepilogue\fR (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.
.Sp
With \fB\-mno-epilogue\fR, the compiler tries to emit exit code inline
at every function exit.
.Ip "\fB\-mno-flat\fR" 4
.IX Item "-mno-flat"
.PD 0
.Ip "\fB\-mflat\fR" 4
.IX Item "-mflat"
.PD
With \fB\-mflat\fR, the compiler does not generate save/restore instructions
and will use a \*(L"flat\*(R" or single register window calling convention.
This model uses \f(CW%i7\fR 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
\&\*(L"call saved\*(R" registers and will be saved on the stack as necessary.
.Sp
With \fB\-mno-flat\fR (the default), the compiler emits save/restore
instructions (except for leaf functions) and is the normal mode of operation.
.Ip "\fB\-mno-unaligned-doubles\fR" 4
.IX Item "-mno-unaligned-doubles"
.PD 0
.Ip "\fB\-munaligned-doubles\fR" 4
.IX Item "-munaligned-doubles"
.PD
Assume that doubles have 8 byte alignment. This is the default.
.Sp
With \fB\-munaligned-doubles\fR, \s-1GCC\s0 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.
.Ip "\fB\-mno-faster-structs\fR" 4
.IX Item "-mno-faster-structs"
.PD 0
.Ip "\fB\-mfaster-structs\fR" 4
.IX Item "-mfaster-structs"
.PD
With \fB\-mfaster-structs\fR, the compiler assumes that structures
should have 8 byte alignment. This enables the use of pairs of
\&\f(CW\*(C`ldd\*(C'\fR and \f(CW\*(C`std\*(C'\fR instructions for copies in structure
assignment, in place of twice as many \f(CW\*(C`ld\*(C'\fR and \f(CW\*(C`st\*(C'\fR pairs.
However, the use of this changed alignment directly violates the Sparc
\&\s-1ABI\s0. 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 \s-1ABI\s0.
.Ip "\fB\-mv8\fR" 4
.IX Item "-mv8"
.PD 0
.Ip "\fB\-msparclite\fR" 4
.IX Item "-msparclite"
.PD
These two options select variations on the \s-1SPARC\s0 architecture.
.Sp
By default (unless specifically configured for the Fujitsu SPARClite),
\&\s-1GCC\s0 generates code for the v7 variant of the \s-1SPARC\s0 architecture.
.Sp
\&\fB\-mv8\fR will give you \s-1SPARC\s0 v8 code. The only difference from v7
code is that the compiler emits the integer multiply and integer
divide instructions which exist in \s-1SPARC\s0 v8 but not in \s-1SPARC\s0 v7.
.Sp
\&\fB\-msparclite\fR will give you SPARClite code. This adds the integer
multiply, integer divide step and scan (\f(CW\*(C`ffs\*(C'\fR) instructions which
exist in SPARClite but not in \s-1SPARC\s0 v7.
.Sp
These options are deprecated and will be deleted in a future \s-1GCC\s0 release.
They have been replaced with \fB\-mcpu=xxx\fR.
.Ip "\fB\-mcypress\fR" 4
.IX Item "-mcypress"
.PD 0
.Ip "\fB\-msupersparc\fR" 4
.IX Item "-msupersparc"
.PD
These two options select the processor for which the code is optimised.
.Sp
With \fB\-mcypress\fR (the default), the compiler optimizes code for the
Cypress \s-1CY7C602\s0 chip, as used in the SparcStation/SparcServer 3xx series.
This is also appropriate for the older SparcStation 1, 2, \s-1IPX\s0 etc.
.Sp
With \fB\-msupersparc\fR 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 \s-1SPARC\s0 v8 instruction set.
.Sp
These options are deprecated and will be deleted in a future \s-1GCC\s0 release.
They have been replaced with \fB\-mcpu=xxx\fR.
.Ip "\fB\-mcpu=\fR\fIcpu_type\fR" 4
.IX Item "-mcpu=cpu_type"
Set the instruction set, register set, and instruction scheduling parameters
for machine type \fIcpu_type\fR. Supported values for \fIcpu_type\fR are
\&\fBv7\fR, \fBcypress\fR, \fBv8\fR, \fBsupersparc\fR, \fBsparclite\fR,
\&\fBhypersparc\fR, \fBsparclite86x\fR, \fBf930\fR, \fBf934\fR,
\&\fBsparclet\fR, \fBtsc701\fR, \fBv9\fR, and \fBultrasparc\fR.
.Sp
Default instruction scheduling parameters are used for values that select
an architecture and not an implementation. These are \fBv7\fR, \fBv8\fR,
\&\fBsparclite\fR, \fBsparclet\fR, \fBv9\fR.
.Sp
Here is a list of each supported architecture and their supported
implementations.
.Sp
.Vb 5
\& v7: cypress
\& v8: supersparc, hypersparc
\& sparclite: f930, f934, sparclite86x
\& sparclet: tsc701
\& v9: ultrasparc
.Ve
.Ip "\fB\-mtune=\fR\fIcpu_type\fR" 4
.IX Item "-mtune=cpu_type"
Set the instruction scheduling parameters for machine type
\&\fIcpu_type\fR, but do not set the instruction set or register set that the
option \fB\-mcpu=\fR\fIcpu_type\fR would.
.Sp
The same values for \fB\-mcpu=\fR\fIcpu_type\fR are used for
\&\fB\-mtune=\fR\fIcpu_type\fR, though the only useful values are those that
select a particular cpu implementation: \fBcypress\fR, \fBsupersparc\fR,
\&\fBhypersparc\fR, \fBf930\fR, \fBf934\fR, \fBsparclite86x\fR,
\&\fBtsc701\fR, \fBultrasparc\fR.
.PP
These \fB\-m\fR switches are supported in addition to the above
on the \s-1SPARCLET\s0 processor.
.Ip "\fB\-mlittle-endian\fR" 4
.IX Item "-mlittle-endian"
Generate code for a processor running in little-endian mode.
.Ip "\fB\-mlive-g0\fR" 4
.IX Item "-mlive-g0"
Treat register \f(CW\*(C`%g0\*(C'\fR as a normal register.
\&\s-1GCC\s0 will continue to clobber it as necessary but will not assume
it always reads as 0.
.Ip "\fB\-mbroken-saverestore\fR" 4
.IX Item "-mbroken-saverestore"
Generate code that does not use non-trivial forms of the \f(CW\*(C`save\*(C'\fR and
\&\f(CW\*(C`restore\*(C'\fR instructions. Early versions of the \s-1SPARCLET\s0 processor do
not correctly handle \f(CW\*(C`save\*(C'\fR and \f(CW\*(C`restore\*(C'\fR instructions used with
arguments. They correctly handle them used without arguments. A \f(CW\*(C`save\*(C'\fR
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.
.PP
These \fB\-m\fR switches are supported in addition to the above
on \s-1SPARC\s0 V9 processors in 64 bit environments.
.Ip "\fB\-mlittle-endian\fR" 4
.IX Item "-mlittle-endian"
Generate code for a processor running in little-endian mode.
.Ip "\fB\-m32\fR" 4
.IX Item "-m32"
.PD 0
.Ip "\fB\-m64\fR" 4
.IX Item "-m64"
.PD
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.
.Ip "\fB\-mcmodel=medlow\fR" 4
.IX Item "-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.
.Ip "\fB\-mcmodel=medmid\fR" 4
.IX Item "-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.
.Ip "\fB\-mcmodel=medany\fR" 4
.IX Item "-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.
.Ip "\fB\-mcmodel=embmedany\fR" 4
.IX Item "-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 \f(CW%g4\fR points to the base of the
data segment. Pointers still 64 bits.
Programs are statically linked, \s-1PIC\s0 is not supported.
.Ip "\fB\-mstack-bias\fR" 4
.IX Item "-mstack-bias"
.PD 0
.Ip "\fB\-mno-stack-bias\fR" 4
.IX Item "-mno-stack-bias"
.PD
With \fB\-mstack-bias\fR, \s-1GCC\s0 assumes that the stack pointer, and
frame pointer if present, are offset by \-2047 which must be added back
when making stack frame references.
Otherwise, assume no such offset is present.
.PP
.I "Convex Options"
.IX Subsection "Convex Options"
.PP
These \fB\-m\fR options are defined for Convex:
.Ip "\fB\-mc1\fR" 4
.IX Item "-mc1"
Generate output for C1. The code will run on any Convex machine.
The preprocessor symbol \f(CW\*(C`_\|_convex_\|_c1_\|_\*(C'\fR is defined.
.Ip "\fB\-mc2\fR" 4
.IX Item "-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 \f(CW\*(C`_\|_convex_c2_\|_\*(C'\fR is defined.
.Ip "\fB\-mc32\fR" 4
.IX Item "-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 \f(CW\*(C`_\|_convex_c32_\|_\*(C'\fR is defined.
.Ip "\fB\-mc34\fR" 4
.IX Item "-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 \f(CW\*(C`_\|_convex_c34_\|_\*(C'\fR is defined.
.Ip "\fB\-mc38\fR" 4
.IX Item "-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 \f(CW\*(C`_\|_convex_c38_\|_\*(C'\fR is defined.
.Ip "\fB\-margcount\fR" 4
.IX Item "-margcount"
Generate code which puts an argument count in the word preceding each
argument list. This is compatible with regular \s-1CC\s0, and a few programs
may need the argument count word. \s-1GDB\s0 and other source-level debuggers
do not need it; this info is in the symbol table.
.Ip "\fB\-mnoargcount\fR" 4
.IX Item "-mnoargcount"
Omit the argument count word. This is the default.
.Ip "\fB\-mvolatile-cache\fR" 4
.IX Item "-mvolatile-cache"
Allow volatile references to be cached. This is the default.
.Ip "\fB\-mvolatile-nocache\fR" 4
.IX Item "-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.
.Ip "\fB\-mlong32\fR" 4
.IX Item "-mlong32"
Type long is 32 bits, the same as type int. This is the default.
.Ip "\fB\-mlong64\fR" 4
.IX Item "-mlong64"
Type long is 64 bits, the same as type long long. This option is useless,
because no library support exists for it.
.PP
.I "\s-1AMD29K\s0 Options"
.IX Subsection "AMD29K Options"
.PP
These \fB\-m\fR options are defined for the \s-1AMD\s0 Am29000:
.Ip "\fB\-mdw\fR" 4
.IX Item "-mdw"
Generate code that assumes the \f(CW\*(C`DW\*(C'\fR bit is set, i.e., that byte and
halfword operations are directly supported by the hardware. This is the
default.
.Ip "\fB\-mndw\fR" 4
.IX Item "-mndw"
Generate code that assumes the \f(CW\*(C`DW\*(C'\fR bit is not set.
.Ip "\fB\-mbw\fR" 4
.IX Item "-mbw"
Generate code that assumes the system supports byte and halfword write
operations. This is the default.
.Ip "\fB\-mnbw\fR" 4
.IX Item "-mnbw"
Generate code that assumes the systems does not support byte and
halfword write operations. \fB\-mnbw\fR implies \fB\-mndw\fR.
.Ip "\fB\-msmall\fR" 4
.IX Item "-msmall"
Use a small memory model that assumes that all function addresses are
either within a single 256 \s-1KB\s0 segment or at an absolute address of less
than 256k. This allows the \f(CW\*(C`call\*(C'\fR instruction to be used instead
of a \f(CW\*(C`const\*(C'\fR, \f(CW\*(C`consth\*(C'\fR, \f(CW\*(C`calli\*(C'\fR sequence.
.Ip "\fB\-mnormal\fR" 4
.IX Item "-mnormal"
Use the normal memory model: Generate \f(CW\*(C`call\*(C'\fR instructions only when
calling functions in the same file and \f(CW\*(C`calli\*(C'\fR instructions
otherwise. This works if each file occupies less than 256 \s-1KB\s0 but allows
the entire executable to be larger than 256 \s-1KB\s0. This is the default.
.Ip "\fB\-mlarge\fR" 4
.IX Item "-mlarge"
Always use \f(CW\*(C`calli\*(C'\fR instructions. Specify this option if you expect
a single file to compile into more than 256 \s-1KB\s0 of code.
.Ip "\fB\-m29050\fR" 4
.IX Item "-m29050"
Generate code for the Am29050.
.Ip "\fB\-m29000\fR" 4
.IX Item "-m29000"
Generate code for the Am29000. This is the default.
.Ip "\fB\-mkernel-registers\fR" 4
.IX Item "-mkernel-registers"
Generate references to registers \f(CW\*(C`gr64\-gr95\*(C'\fR instead of to
registers \f(CW\*(C`gr96\-gr127\*(C'\fR. This option can be used when compiling
kernel code that wants a set of global registers disjoint from that used
by user-mode code.
.Sp
Note that when this option is used, register names in \fB\-f\fR flags
must use the normal, user-mode, names.
.Ip "\fB\-muser-registers\fR" 4
.IX Item "-muser-registers"
Use the normal set of global registers, \f(CW\*(C`gr96\-gr127\*(C'\fR. This is the
default.
.Ip "\fB\-mstack-check\fR" 4
.IX Item "-mstack-check"
.PD 0
.Ip "\fB\-mno-stack-check\fR" 4
.IX Item "-mno-stack-check"
.PD
Insert (or do not insert) a call to \f(CW\*(C`_\|_msp_check\*(C'\fR after each stack
adjustment. This is often used for kernel code.
.Ip "\fB\-mstorem-bug\fR" 4
.IX Item "-mstorem-bug"
.PD 0
.Ip "\fB\-mno-storem-bug\fR" 4
.IX Item "-mno-storem-bug"
.PD
\&\fB\-mstorem-bug\fR 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).
.Ip "\fB\-mno-reuse-arg-regs\fR" 4
.IX Item "-mno-reuse-arg-regs"
.PD 0
.Ip "\fB\-mreuse-arg-regs\fR" 4
.IX Item "-mreuse-arg-regs"
.PD
\&\fB\-mno-reuse-arg-regs\fR 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.
.Ip "\fB\-mno-impure-text\fR" 4
.IX Item "-mno-impure-text"
.PD 0
.Ip "\fB\-mimpure-text\fR" 4
.IX Item "-mimpure-text"
.PD
\&\fB\-mimpure-text\fR, used in addition to \fB\-shared\fR, tells the compiler to
not pass \fB\-assert pure-text\fR to the linker when linking a shared object.
.Ip "\fB\-msoft-float\fR" 4
.IX Item "-msoft-float"
Generate output containing library calls for floating point.
\&\fBWarning:\fR the requisite libraries are not part of \s-1GCC\s0.
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.
.Ip "\fB\-mno-multm\fR" 4
.IX Item "-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.
.PP
.I "\s-1ARM\s0 Options"
.IX Subsection "ARM Options"
.PP
These \fB\-m\fR options are defined for Advanced \s-1RISC\s0 Machines (\s-1ARM\s0)
architectures:
.Ip "\fB\-mapcs-frame\fR" 4
.IX Item "-mapcs-frame"
Generate a stack frame that is compliant with the \s-1ARM\s0 Procedure Call
Standard for all functions, even if this is not strictly necessary for
correct execution of the code. Specifying \fB\-fomit-frame-pointer\fR
with this option will cause the stack frames not to be generated for
leaf functions. The default is \fB\-mno-apcs-frame\fR.
.Ip "\fB\-mapcs\fR" 4
.IX Item "-mapcs"
This is a synonym for \fB\-mapcs-frame\fR.
.Ip "\fB\-mapcs-26\fR" 4
.IX Item "-mapcs-26"
Generate code for a processor running with a 26\-bit program counter,
and conforming to the function calling standards for the \s-1APCS\s0 26\-bit
option. This option replaces the \fB\-m2\fR and \fB\-m3\fR options
of previous releases of the compiler.
.Ip "\fB\-mapcs-32\fR" 4
.IX Item "-mapcs-32"
Generate code for a processor running with a 32\-bit program counter,
and conforming to the function calling standards for the \s-1APCS\s0 32\-bit
option. This option replaces the \fB\-m6\fR option of previous releases
of the compiler.
.Ip "\fB\-mapcs-stack-check\fR" 4
.IX Item "-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
\&\fB_\|_rt_stkovf_split_small\fR or \fB_\|_rt_stkovf_split_big\fR will be
called, depending upon the amount of stack space required. The run time
system is required to provide these functions. The default is
\&\fB\-mno-apcs-stack-check\fR, since this produces smaller code.
.Ip "\fB\-mapcs-float\fR" 4
.IX Item "-mapcs-float"
Pass floating point arguments using the float point registers. This is
one of the variants of the \s-1APCS\s0. 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
\&\fB\-mno-apcs-float\fR, since integer only code is slightly increased in
size if \fB\-mapcs-float\fR is used.
.Ip "\fB\-mapcs-reentrant\fR" 4
.IX Item "-mapcs-reentrant"
Generate reentrant, position independent code. This is the equivalent
to specifying the \fB\-fpic\fR option. The default is
\&\fB\-mno-apcs-reentrant\fR.
.Ip "\fB\-mthumb-interwork\fR" 4
.IX Item "-mthumb-interwork"
Generate code which supports calling between the \s-1ARM\s0 and \s-1THUMB\s0
instruction sets. Without this option the two instruction sets cannot
be reliably used inside one program. The default is
\&\fB\-mno-thumb-interwork\fR, since slightly larger code is generated
when \fB\-mthumb-interwork\fR is specified.
.Ip "\fB\-mno-sched-prolog\fR" 4
.IX Item "-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 \fB\-msched-prolog\fR.
.Ip "\fB\-mhard-float\fR" 4
.IX Item "-mhard-float"
Generate output containing floating point instructions. This is the
default.
.Ip "\fB\-msoft-float\fR" 4
.IX Item "-msoft-float"
Generate output containing library calls for floating point.
\&\fBWarning:\fR the requisite libraries are not available for all \s-1ARM\s0
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.
.Sp
\&\fB\-msoft-float\fR changes the calling convention in the output file;
therefore, it is only useful if you compile \fIall\fR of a program with
this option. In particular, you need to compile \fIlibgcc.a\fR, the
library that comes with \s-1GCC\s0, with \fB\-msoft-float\fR in order for
this to work.
.Ip "\fB\-mlittle-endian\fR" 4
.IX Item "-mlittle-endian"
Generate code for a processor running in little-endian mode. This is
the default for all standard configurations.
.Ip "\fB\-mbig-endian\fR" 4
.IX Item "-mbig-endian"
Generate code for a processor running in big-endian mode; the default is
to compile code for a little-endian processor.
.Ip "\fB\-mwords-little-endian\fR" 4
.IX Item "-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 \fB32107654\fR. Note: this
option should only be used if you require compatibility with code for
big-endian \s-1ARM\s0 processors generated by versions of the compiler prior to
2.8.
.Ip "\fB\-malignment-traps\fR" 4
.IX Item "-malignment-traps"
Generate code that will not trap if the \s-1MMU\s0 has alignment traps enabled.
On \s-1ARM\s0 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 \s-1ARM\s0 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 \s-1MMU\s0 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.
.Sp
This option is ignored when compiling for \s-1ARM\s0 architecture 4 or later,
since these processors have instructions to directly access half-word
objects in memory.
.Ip "\fB\-mno-alignment-traps\fR" 4
.IX Item "-mno-alignment-traps"
Generate code that assumes that the \s-1MMU\s0 will not trap unaligned
accesses. This produces better code when the target instruction set
does not have half-word memory operations (implementations prior to
ARMv4).
.Sp
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.
.Sp
The default setting for most targets is \-mno-alignment-traps, since
this produces better code when there are no half-word memory
instructions available.
.Ip "\fB\-mshort-load-bytes\fR" 4
.IX Item "-mshort-load-bytes"
This is a deprecated alias for \fB\-malignment-traps\fR.
.Ip "\fB\-mno-short-load-bytes\fR" 4
.IX Item "-mno-short-load-bytes"
This is a deprecated alias for \fB\-mno-alignment-traps\fR.
.Ip "\fB\-mshort-load-words\fR" 4
.IX Item "-mshort-load-words"
This is a deprecated alias for \fB\-mno-alignment-traps\fR.
.Ip "\fB\-mno-short-load-words\fR" 4
.IX Item "-mno-short-load-words"
This is a deprecated alias for \fB\-malignment-traps\fR.
.Ip "\fB\-mbsd\fR" 4
.IX Item "-mbsd"
This option only applies to \s-1RISC\s0 iX. Emulate the native BSD-mode
compiler. This is the default if \fB\-ansi\fR is not specified.
.Ip "\fB\-mxopen\fR" 4
.IX Item "-mxopen"
This option only applies to \s-1RISC\s0 iX. Emulate the native X/Open-mode
compiler.
.Ip "\fB\-mno-symrename\fR" 4
.IX Item "-mno-symrename"
This option only applies to \s-1RISC\s0 iX. Do not run the assembler
post-processor, \fBsymrename\fR, after code has been assembled.
Normally it is necessary to modify some of the standard symbols in
preparation for linking with the \s-1RISC\s0 iX C library; this option
suppresses this pass. The post-processor is never run when the
compiler is built for cross-compilation.
.Ip "\fB\-mcpu=<name>\fR" 4
.IX Item "-mcpu=<name>"
This specifies the name of the target \s-1ARM\s0 processor. \s-1GCC\s0 uses this name
to determine what kind of instructions it can use when generating
assembly code. Permissible names are: arm2, arm250, arm3, arm6, arm60,
arm600, arm610, arm620, arm7, arm7m, arm7d, arm7dm, arm7di, arm7dmi,
arm70, arm700, arm700i, arm710, arm710c, arm7100, arm7500, arm7500fe,
arm7tdmi, arm8, strongarm, strongarm110, strongarm1100, arm8, arm810,
arm9, arm920, arm920t, arm9tdmi.
.Ip "\fB\-mtune=<name>\fR" 4
.IX Item "-mtune=<name>"
This option is very similar to the \fB\-mcpu=\fR option, except that
instead of specifying the actual target processor type, and hence
restricting which instructions can be used, it specifies that \s-1GCC\s0 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 \fB\-mcpu=\fR option.
For some arm implementations better performance can be obtained by using
this option.
.Ip "\fB\-march=<name>\fR" 4
.IX Item "-march=<name>"
This specifies the name of the target \s-1ARM\s0 architecture. \s-1GCC\s0 uses this
name to determine what kind of instructions it can use when generating
assembly code. This option can be used in conjunction with or instead
of the \fB\-mcpu=\fR option. Permissible names are: armv2, armv2a,
armv3, armv3m, armv4, armv4t, armv5.
.Ip "\fB\-mfpe=<number>\fR" 4
.IX Item "-mfpe=<number>"
.PD 0
.Ip "\fB\-mfp=<number>\fR" 4
.IX Item "-mfp=<number>"
.PD
This specifies the version of the floating point emulation available on
the target. Permissible values are 2 and 3. \fB\-mfp=\fR is a synonym
for \fB\-mfpe=\fR to support older versions of \s-1GCC\s0.
.Ip "\fB\-mstructure-size-boundary=<n>\fR" 4
.IX Item "-mstructure-size-boundary=<n>"
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 \s-1COFF\s0
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. Programmers are encouraged to use the 32
value as future versions of the toolchain may default to this value.
.Ip "\fB\-mabort-on-noreturn\fR" 4
.IX Item "-mabort-on-noreturn"
Generate a call to the function abort at the end of a noreturn function.
It will be executed if the function tries to return.
.Ip "\fB\-mlong-calls\fR" 4
.IX Item "-mlong-calls"
.PD 0
.Ip "\fB\-mno-long-calls\fR" 4
.IX Item "-mno-long-calls"
.PD
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.
.Sp
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 \fBshort-call\fR attribute, functions that are inside
the scope of a \fB#pragma no_long_calls\fR 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 \fBlong-call\fR
attribute or the \fBsection\fR attribute, and functions that are within
the scope of a \fB#pragma long_calls\fR directive, will always be
turned into long calls.
.Sp
This feature is not enabled by default. Specifying
\&\fB\*(--no-long-calls\fR will restore the default behaviour, as will
placing the function calls within the scope of a \fB#pragma
long_calls_off\fR directive. Note these switches have no effect on how
the compiler generates code to handle function calls via function
pointers.
.Ip "\fB\-mnop-fun-dllimport\fR" 4
.IX Item "-mnop-fun-dllimport"
Disable the support for the \fIdllimport\fR attribute.
.Ip "\fB\-msingle-pic-base\fR" 4
.IX Item "-msingle-pic-base"
Treat the register used for \s-1PIC\s0 addressing as read-only, rather than
loading it in the prologue for each function. The run-time system is
responsible for initialising this register with an appropriate value
before execution begins.
.Ip "\fB\-mpic-register=<reg>\fR" 4
.IX Item "-mpic-register=<reg>"
Specify the register to be used for \s-1PIC\s0 addressing. The default is R10
unless stack-checking is enabled, when R9 is used.
.PP
.I "Thumb Options"
.IX Subsection "Thumb Options"
.Ip "\fB\-mthumb-interwork\fR" 4
.IX Item "-mthumb-interwork"
Generate code which supports calling between the \s-1THUMB\s0 and \s-1ARM\s0
instruction sets. Without this option the two instruction sets cannot
be reliably used inside one program. The default is
\&\fB\-mno-thumb-interwork\fR, since slightly smaller code is generated
with this option.
.Ip "\fB\-mtpcs-frame\fR" 4
.IX Item "-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 \fB\-mno-apcs-frame\fR.
.Ip "\fB\-mtpcs-leaf-frame\fR" 4
.IX Item "-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 \fB\-mno-apcs-leaf-frame\fR.
.Ip "\fB\-mlittle-endian\fR" 4
.IX Item "-mlittle-endian"
Generate code for a processor running in little-endian mode. This is
the default for all standard configurations.
.Ip "\fB\-mbig-endian\fR" 4
.IX Item "-mbig-endian"
Generate code for a processor running in big-endian mode.
.Ip "\fB\-mstructure-size-boundary=<n>\fR" 4
.IX Item "-mstructure-size-boundary=<n>"
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 \s-1COFF\s0
targeted toolchain the default value is 8. Specifying the larger number
can produced 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. Programmers are encouraged to use the 32
value as future versions of the toolchain may default to this value.
.Ip "\fB\-mnop-fun-dllimport\fR" 4
.IX Item "-mnop-fun-dllimport"
Disable the support for the \fIdllimport\fR attribute.
.Ip "\fB\-mcallee-super-interworking\fR" 4
.IX Item "-mcallee-super-interworking"
Gives all externally visible functions in the file being compiled an \s-1ARM\s0
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.
.Ip "\fB\-mcaller-super-interworking\fR" 4
.IX Item "-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.
.Ip "\fB\-msingle-pic-base\fR" 4
.IX Item "-msingle-pic-base"
Treat the register used for \s-1PIC\s0 addressing as read-only, rather than
loading it in the prologue for each function. The run-time system is
responsible for initialising this register with an appropriate value
before execution begins.
.Ip "\fB\-mpic-register=<reg>\fR" 4
.IX Item "-mpic-register=<reg>"
Specify the register to be used for \s-1PIC\s0 addressing. The default is R10.
.PP
.I "\s-1MN10200\s0 Options"
.IX Subsection "MN10200 Options"
.PP
These \fB\-m\fR options are defined for Matsushita \s-1MN10200\s0 architectures:
.Ip "\fB\-mrelax\fR" 4
.IX Item "-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.
.Sp
This option makes symbolic debugging impossible.
.PP
.I "\s-1MN10300\s0 Options"
.IX Subsection "MN10300 Options"
.PP
These \fB\-m\fR options are defined for Matsushita \s-1MN10300\s0 architectures:
.Ip "\fB\-mmult-bug\fR" 4
.IX Item "-mmult-bug"
Generate code to avoid bugs in the multiply instructions for the \s-1MN10300\s0
processors. This is the default.
.Ip "\fB\-mno-mult-bug\fR" 4
.IX Item "-mno-mult-bug"
Do not generate code to avoid bugs in the multiply instructions for the
\&\s-1MN10300\s0 processors.
.Ip "\fB\-mam33\fR" 4
.IX Item "-mam33"
Generate code which uses features specific to the \s-1AM33\s0 processor.
.Ip "\fB\-mno-am33\fR" 4
.IX Item "-mno-am33"
Do not generate code which uses features specific to the \s-1AM33\s0 processor. This
is the default.
.Ip "\fB\-mrelax\fR" 4
.IX Item "-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.
.Sp
This option makes symbolic debugging impossible.
.PP
.I "M32R/D Options"
.IX Subsection "M32R/D Options"
.PP
These \fB\-m\fR options are defined for Mitsubishi M32R/D architectures:
.Ip "\fB\-mcode-model=small\fR" 4
.IX Item "-mcode-model=small"
Assume all objects live in the lower 16MB of memory (so that their addresses
can be loaded with the \f(CW\*(C`ld24\*(C'\fR instruction), and assume all subroutines
are reachable with the \f(CW\*(C`bl\*(C'\fR instruction.
This is the default.
.Sp
The addressability of a particular object can be set with the
\&\f(CW\*(C`model\*(C'\fR attribute.
.Ip "\fB\-mcode-model=medium\fR" 4
.IX Item "-mcode-model=medium"
Assume objects may be anywhere in the 32 bit address space (the compiler
will generate \f(CW\*(C`seth/add3\*(C'\fR instructions to load their addresses), and
assume all subroutines are reachable with the \f(CW\*(C`bl\*(C'\fR instruction.
.Ip "\fB\-mcode-model=large\fR" 4
.IX Item "-mcode-model=large"
Assume objects may be anywhere in the 32 bit address space (the compiler
will generate \f(CW\*(C`seth/add3\*(C'\fR instructions to load their addresses), and
assume subroutines may not be reachable with the \f(CW\*(C`bl\*(C'\fR instruction
(the compiler will generate the much slower \f(CW\*(C`seth/add3/jl\*(C'\fR
instruction sequence).
.Ip "\fB\-msdata=none\fR" 4
.IX Item "-msdata=none"
Disable use of the small data area. Variables will be put into
one of \fB.data\fR, \fBbss\fR, or \fB.rodata\fR (unless the
\&\f(CW\*(C`section\*(C'\fR attribute has been specified).
This is the default.
.Sp
The small data area consists of sections \fB.sdata\fR and \fB.sbss\fR.
Objects may be explicitly put in the small data area with the
\&\f(CW\*(C`section\*(C'\fR attribute using one of these sections.
.Ip "\fB\-msdata=sdata\fR" 4
.IX Item "-msdata=sdata"
Put small global and static data in the small data area, but do not
generate special code to reference them.
.Ip "\fB\-msdata=use\fR" 4
.IX Item "-msdata=use"
Put small global and static data in the small data area, and generate
special instructions to reference them.
.Ip "\fB\-G\fR \fInum\fR" 4
.IX Item "-G num"
Put global and static objects less than or equal to \fInum\fR bytes
into the small data or bss sections instead of the normal data or bss
sections. The default value of \fInum\fR is 8.
The \fB\-msdata\fR option must be set to one of \fBsdata\fR or \fBuse\fR
for this option to have any effect.
.Sp
All modules should be compiled with the same \fB\-G\fR \fInum\fR value.
Compiling with different values of \fInum\fR may or may not work; if it
doesn't the linker will give an error message \- incorrect code will not be
generated.
.PP
.I "M88K Options"
.IX Subsection "M88K Options"
.PP
These \fB\-m\fR options are defined for Motorola 88k architectures:
.Ip "\fB\-m88000\fR" 4
.IX Item "-m88000"
Generate code that works well on both the m88100 and the
m88110.
.Ip "\fB\-m88100\fR" 4
.IX Item "-m88100"
Generate code that works best for the m88100, but that also
runs on the m88110.
.Ip "\fB\-m88110\fR" 4
.IX Item "-m88110"
Generate code that works best for the m88110, and may not run
on the m88100.
.Ip "\fB\-mbig-pic\fR" 4
.IX Item "-mbig-pic"
Obsolete option to be removed from the next revision.
Use \fB\-fPIC\fR.
.Ip "\fB\-midentify-revision\fR" 4
.IX Item "-midentify-revision"
Include an \f(CW\*(C`ident\*(C'\fR directive in the assembler output recording the
source file name, compiler name and version, timestamp, and compilation
flags used.
.Ip "\fB\-mno-underscores\fR" 4
.IX Item "-mno-underscores"
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.
.Ip "\fB\-mocs-debug-info\fR" 4
.IX Item "-mocs-debug-info"
.PD 0
.Ip "\fB\-mno-ocs-debug-info\fR" 4
.IX Item "-mno-ocs-debug-info"
.PD
Include (or omit) additional debugging information (about registers used
in each stack frame) as specified in the 88open Object Compatibility
Standard, ``\s-1OCS\s0''. This extra information allows debugging of code that
has had the frame pointer eliminated. The default for \s-1DG/UX\s0, SVr4, and
Delta 88 SVr3.2 is to include this information; other 88k configurations
omit this information by default.
.Ip "\fB\-mocs-frame-position\fR" 4
.IX Item "-mocs-frame-position"
When emitting \s-1COFF\s0 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 \s-1DG/UX\s0, SVr4, Delta88 SVr3.2, and \s-1BCS\s0 configurations use
\&\fB\-mocs-frame-position\fR; other 88k configurations have the default
\&\fB\-mno-ocs-frame-position\fR.
.Ip "\fB\-mno-ocs-frame-position\fR" 4
.IX Item "-mno-ocs-frame-position"
When emitting \s-1COFF\s0 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.
.Ip "\fB\-moptimize-arg-area\fR" 4
.IX Item "-moptimize-arg-area"
.PD 0
.Ip "\fB\-mno-optimize-arg-area\fR" 4
.IX Item "-mno-optimize-arg-area"
.PD
Control how function arguments are stored in stack frames.
\&\fB\-moptimize-arg-area\fR saves space by optimizing them, but this
conflicts with the 88open specifications. The opposite alternative,
\&\fB\-mno-optimize-arg-area\fR, agrees with 88open standards. By default
\&\s-1GCC\s0 does not optimize the argument area.
.Ip "\fB\-mshort-data-\fR\fInum\fR" 4
.IX Item "-mshort-data-num"
Generate smaller data references by making them relative to \f(CW\*(C`r0\*(C'\fR,
which allows loading a value using a single instruction (rather than the
usual two). You control which data references are affected by
specifying \fInum\fR with this option. For example, if you specify
\&\fB\-mshort-data-512\fR, then the data references affected are those
involving displacements of less than 512 bytes.
\&\fB\-mshort-data-\fR\fInum\fR is not effective for \fInum\fR greater
than 64k.
.Ip "\fB\-mserialize-volatile\fR" 4
.IX Item "-mserialize-volatile"
.PD 0
.Ip "\fB\-mno-serialize-volatile\fR" 4
.IX Item "-mno-serialize-volatile"
.PD
Do, or don't, generate code to guarantee sequential consistency
of volatile memory references. By default, consistency is
guaranteed.
.Sp
The order of memory references made by the \s-1MC88110\s0 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,
\&\s-1GNU\s0 C generates special instructions, as needed, to force
execution in the proper order.
.Sp
The \s-1MC88100\s0 processor does not reorder memory references and so
always provides sequential consistency. However, by default, \s-1GNU\s0
C generates the special instructions to guarantee consistency
even when you use \fB\-m88100\fR, so that the code may be run on an
\&\s-1MC88110\s0 processor. If you intend to run your code only on the
\&\s-1MC88100\s0 processor, you may use \fB\-mno-serialize-volatile\fR.
.Sp
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 \fB\-mno-serialize-volatile\fR.
.Ip "\fB\-msvr4\fR" 4
.IX Item "-msvr4"
.PD 0
.Ip "\fB\-msvr3\fR" 4
.IX Item "-msvr3"
.PD
Turn on (\fB\-msvr4\fR) or off (\fB\-msvr3\fR) compiler extensions
related to System V release 4 (SVr4). This controls the following:
.RS 4
.Ip "1." 4
Which variant of the assembler syntax to emit.
.Ip "2." 4
\&\fB\-msvr4\fR makes the C preprocessor recognize \fB#pragma weak\fR
that is used on System V release 4.
.Ip "3." 4
\&\fB\-msvr4\fR makes \s-1GCC\s0 issue additional declaration directives used in
SVr4.
.RE
.RS 4
.Sp
\&\fB\-msvr4\fR is the default for the m88k-motorola-sysv4 and
m88k-dg-dgux m88k configurations. \fB\-msvr3\fR is the default for all
other m88k configurations.
.RE
.Ip "\fB\-mversion-03.00\fR" 4
.IX Item "-mversion-03.00"
This option is obsolete, and is ignored.
.Ip "\fB\-mno-check-zero-division\fR" 4
.IX Item "-mno-check-zero-division"
.PD 0
.Ip "\fB\-mcheck-zero-division\fR" 4
.IX Item "-mcheck-zero-division"
.PD
Do, or don't, generate code to guarantee that integer division by
zero will be detected. By default, detection is guaranteed.
.Sp
Some models of the \s-1MC88100\s0 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, \s-1GNU\s0 C
generates code that explicitly checks for zero-valued divisors
and traps with exception number 503 when one is detected. Use of
mno-check-zero-division suppresses such checking for code
generated to run on an \s-1MC88100\s0 processor.
.Sp
\&\s-1GNU\s0 C assumes that the \s-1MC88110\s0 processor correctly detects all
instances of integer division by zero. When \fB\-m88110\fR is
specified, both \fB\-mcheck-zero-division\fR and
\&\fB\-mno-check-zero-division\fR are ignored, and no explicit checks for
zero-valued divisors are generated.
.Ip "\fB\-muse-div-instruction\fR" 4
.IX Item "-muse-div-instruction"
Use the div instruction for signed integer division on the
\&\s-1MC88100\s0 processor. By default, the div instruction is not used.
.Sp
On the \s-1MC88100\s0 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 \s-1MC88100\s0 processor, \s-1GNU\s0 C 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.
.Sp
On the \s-1MC88110\s0 processor the div instruction (also known as the
divs instruction) processes negative operands without trapping to
the operating system. When \fB\-m88110\fR is specified,
\&\fB\-muse-div-instruction\fR is ignored, and the div instruction is used
for signed integer division.
.Sp
Note that the result of dividing \s-1INT_MIN\s0 by \-1 is undefined. In
particular, the behavior of such a division with and without
\&\fB\-muse-div-instruction\fR may differ.
.Ip "\fB\-mtrap-large-shift\fR" 4
.IX Item "-mtrap-large-shift"
.PD 0
.Ip "\fB\-mhandle-large-shift\fR" 4
.IX Item "-mhandle-large-shift"
.PD
Include code to detect bit-shifts of more than 31 bits; respectively,
trap such shifts or emit code to handle them properly. By default \s-1GCC\s0
makes no special provision for large bit shifts.
.Ip "\fB\-mwarn-passed-structs\fR" 4
.IX Item "-mwarn-passed-structs"
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,
\&\s-1GCC\s0 issues no such warning.
.PP
.I "\s-1IBM\s0 \s-1RS/6000\s0 and PowerPC Options"
.IX Subsection "IBM RS/6000 and PowerPC Options"
.PP
These \fB\-m\fR options are defined for the \s-1IBM\s0 \s-1RS/6000\s0 and PowerPC:
.Ip "\fB\-mpower\fR" 4
.IX Item "-mpower"
.PD 0
.Ip "\fB\-mno-power\fR" 4
.IX Item "-mno-power"
.Ip "\fB\-mpower2\fR" 4
.IX Item "-mpower2"
.Ip "\fB\-mno-power2\fR" 4
.IX Item "-mno-power2"
.Ip "\fB\-mpowerpc\fR" 4
.IX Item "-mpowerpc"
.Ip "\fB\-mno-powerpc\fR" 4
.IX Item "-mno-powerpc"
.Ip "\fB\-mpowerpc-gpopt\fR" 4
.IX Item "-mpowerpc-gpopt"
.Ip "\fB\-mno-powerpc-gpopt\fR" 4
.IX Item "-mno-powerpc-gpopt"
.Ip "\fB\-mpowerpc-gfxopt\fR" 4
.IX Item "-mpowerpc-gfxopt"
.Ip "\fB\-mno-powerpc-gfxopt\fR" 4
.IX Item "-mno-powerpc-gfxopt"
.Ip "\fB\-mpowerpc64\fR" 4
.IX Item "-mpowerpc64"
.Ip "\fB\-mno-powerpc64\fR" 4
.IX Item "-mno-powerpc64"
.PD
\&\s-1GCC\s0 supports two related instruction set architectures for the
\&\s-1RS/6000\s0 and PowerPC. The \fI\s-1POWER\s0\fR instruction set are those
instructions supported by the \fBrios\fR chip set used in the original
\&\s-1RS/6000\s0 systems and the \fIPowerPC\fR instruction set is the
architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
the \s-1IBM\s0 4xx microprocessors.
.Sp
Neither architecture is a subset of the other. However there is a
large common subset of instructions supported by both. An \s-1MQ\s0
register is included in processors supporting the \s-1POWER\s0 architecture.
.Sp
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 \s-1GCC\s0. Specifying the
\&\fB\-mcpu=\fR\fIcpu_type\fR overrides the specification of these
options. We recommend you use the \fB\-mcpu=\fR\fIcpu_type\fR option
rather than the options listed above.
.Sp
The \fB\-mpower\fR option allows \s-1GCC\s0 to generate instructions that
are found only in the \s-1POWER\s0 architecture and to use the \s-1MQ\s0 register.
Specifying \fB\-mpower2\fR implies \fB\-power\fR and also allows \s-1GCC\s0
to generate instructions that are present in the \s-1POWER2\s0 architecture but
not the original \s-1POWER\s0 architecture.
.Sp
The \fB\-mpowerpc\fR option allows \s-1GCC\s0 to generate instructions that
are found only in the 32\-bit subset of the PowerPC architecture.
Specifying \fB\-mpowerpc-gpopt\fR implies \fB\-mpowerpc\fR and also allows
\&\s-1GCC\s0 to use the optional PowerPC architecture instructions in the
General Purpose group, including floating-point square root. Specifying
\&\fB\-mpowerpc-gfxopt\fR implies \fB\-mpowerpc\fR and also allows \s-1GCC\s0 to
use the optional PowerPC architecture instructions in the Graphics
group, including floating-point select.
.Sp
The \fB\-mpowerpc64\fR option allows \s-1GCC\s0 to generate the additional
64\-bit instructions that are found in the full PowerPC64 architecture
and to treat GPRs as 64\-bit, doubleword quantities. \s-1GCC\s0 defaults to
\&\fB\-mno-powerpc64\fR.
.Sp
If you specify both \fB\-mno-power\fR and \fB\-mno-powerpc\fR, \s-1GCC\s0
will use only the instructions in the common subset of both
architectures plus some special \s-1AIX\s0 common-mode calls, and will not use
the \s-1MQ\s0 register. Specifying both \fB\-mpower\fR and \fB\-mpowerpc\fR
permits \s-1GCC\s0 to use any instruction from either architecture and to
allow use of the \s-1MQ\s0 register; specify this for the Motorola \s-1MPC601\s0.
.Ip "\fB\-mnew-mnemonics\fR" 4
.IX Item "-mnew-mnemonics"
.PD 0
.Ip "\fB\-mold-mnemonics\fR" 4
.IX Item "-mold-mnemonics"
.PD
Select which mnemonics to use in the generated assembler code.
\&\fB\-mnew-mnemonics\fR requests output that uses the assembler mnemonics
defined for the PowerPC architecture, while \fB\-mold-mnemonics\fR
requests the assembler mnemonics defined for the \s-1POWER\s0 architecture.
Instructions defined in only one architecture have only one mnemonic;
\&\s-1GCC\s0 uses that mnemonic irrespective of which of these options is
specified.
.Sp
\&\s-1GCC\s0 defaults to the mnemonics appropriate for the architecture in
use. Specifying \fB\-mcpu=\fR\fIcpu_type\fR sometimes overrides the
value of these option. Unless you are building a cross-compiler, you
should normally not specify either \fB\-mnew-mnemonics\fR or
\&\fB\-mold-mnemonics\fR, but should instead accept the default.
.Ip "\fB\-mcpu=\fR\fIcpu_type\fR" 4
.IX Item "-mcpu=cpu_type"
Set architecture type, register usage, choice of mnemonics, and
instruction scheduling parameters for machine type \fIcpu_type\fR.
Supported values for \fIcpu_type\fR are \fBrios\fR, \fBrios1\fR,
\&\fBrsc\fR, \fBrios2\fR, \fBrs64a\fR, \fB601\fR, \fB602\fR,
\&\fB603\fR, \fB603e\fR, \fB604\fR, \fB604e\fR, \fB620\fR,
\&\fB630\fR, \fB740\fR, \fB750\fR, \fBpower\fR, \fBpower2\fR,
\&\fBpowerpc\fR, \fB403\fR, \fB505\fR, \fB801\fR, \fB821\fR,
\&\fB823\fR, and \fB860\fR and \fBcommon\fR. \fB\-mcpu=power\fR,
\&\fB\-mcpu=power2\fR, \fB\-mcpu=powerpc\fR, and \fB\-mcpu=powerpc64\fR
specify generic \s-1POWER\s0, \s-1POWER2\s0, pure 32\-bit PowerPC (i.e., not \s-1MPC601\s0),
and 64\-bit PowerPC architecture machine types, with an appropriate,
generic processor model assumed for scheduling purposes.
.Sp
Specifying any of the following options:
\&\fB\-mcpu=rios1\fR, \fB\-mcpu=rios2\fR, \fB\-mcpu=rsc\fR,
\&\fB\-mcpu=power\fR, or \fB\-mcpu=power2\fR
enables the \fB\-mpower\fR option and disables the \fB\-mpowerpc\fR option;
\&\fB\-mcpu=601\fR enables both the \fB\-mpower\fR and \fB\-mpowerpc\fR options.
All of \fB\-mcpu=rs64a\fR, \fB\-mcpu=602\fR, \fB\-mcpu=603\fR,
\&\fB\-mcpu=603e\fR, \fB\-mcpu=604\fR, \fB\-mcpu=620\fR, \fB\-mcpu=630\fR,
\&\fB\-mcpu=740\fR, and \fB\-mcpu=750\fR
enable the \fB\-mpowerpc\fR option and disable the \fB\-mpower\fR option.
Exactly similarly, all of \fB\-mcpu=403\fR,
\&\fB\-mcpu=505\fR, \fB\-mcpu=821\fR, \fB\-mcpu=860\fR and \fB\-mcpu=powerpc\fR
enable the \fB\-mpowerpc\fR option and disable the \fB\-mpower\fR option.
\&\fB\-mcpu=common\fR disables both the
\&\fB\-mpower\fR and \fB\-mpowerpc\fR options.
.Sp
\&\s-1AIX\s0 versions 4 or greater selects \fB\-mcpu=common\fR by default, so
that code will operate on all members of the \s-1RS/6000\s0 \s-1POWER\s0 and PowerPC
families. In that case, \s-1GCC\s0 will use only the instructions in the
common subset of both architectures plus some special \s-1AIX\s0 common-mode
calls, and will not use the \s-1MQ\s0 register. \s-1GCC\s0 assumes a generic
processor model for scheduling purposes.
.Sp
Specifying any of the options \fB\-mcpu=rios1\fR, \fB\-mcpu=rios2\fR,
\&\fB\-mcpu=rsc\fR, \fB\-mcpu=power\fR, or \fB\-mcpu=power2\fR also
disables the \fBnew-mnemonics\fR option. Specifying \fB\-mcpu=601\fR,
\&\fB\-mcpu=602\fR, \fB\-mcpu=603\fR, \fB\-mcpu=603e\fR, \fB\-mcpu=604\fR,
\&\fB\-mcpu=620\fR, \fB\-mcpu=630\fR, \fB\-mcpu=403\fR, \fB\-mcpu=505\fR,
\&\fB\-mcpu=821\fR, \fB\-mcpu=860\fR or \fB\-mcpu=powerpc\fR also enables
the \fBnew-mnemonics\fR option.
.Sp
Specifying \fB\-mcpu=403\fR, \fB\-mcpu=821\fR, or \fB\-mcpu=860\fR also
enables the \fB\-msoft-float\fR option.
.Ip "\fB\-mtune=\fR\fIcpu_type\fR" 4
.IX Item "-mtune=cpu_type"
Set the instruction scheduling parameters for machine type
\&\fIcpu_type\fR, but do not set the architecture type, register usage,
choice of mnemonics like \fB\-mcpu=\fR\fIcpu_type\fR would. The same
values for \fIcpu_type\fR are used for \fB\-mtune=\fR\fIcpu_type\fR as
for \fB\-mcpu=\fR\fIcpu_type\fR. The \fB\-mtune=\fR\fIcpu_type\fR
option overrides the \fB\-mcpu=\fR\fIcpu_type\fR option in terms of
instruction scheduling parameters.
.Ip "\fB\-mfull-toc\fR" 4
.IX Item "-mfull-toc"
.PD 0
.Ip "\fB\-mno-fp-in-toc\fR" 4
.IX Item "-mno-fp-in-toc"
.Ip "\fB\-mno-sum-in-toc\fR" 4
.IX Item "-mno-sum-in-toc"
.Ip "\fB\-mminimal-toc\fR" 4
.IX Item "-mminimal-toc"
.PD
Modify generation of the \s-1TOC\s0 (Table Of Contents), which is created for
every executable file. The \fB\-mfull-toc\fR option is selected by
default. In that case, \s-1GCC\s0 will allocate at least one \s-1TOC\s0 entry for
each unique non-automatic variable reference in your program. \s-1GCC\s0
will also place floating-point constants in the \s-1TOC\s0. However, only
16,384 entries are available in the \s-1TOC\s0.
.Sp
If you receive a linker error message that saying you have overflowed
the available \s-1TOC\s0 space, you can reduce the amount of \s-1TOC\s0 space used
with the \fB\-mno-fp-in-toc\fR and \fB\-mno-sum-in-toc\fR options.
\&\fB\-mno-fp-in-toc\fR prevents \s-1GCC\s0 from putting floating-point
constants in the \s-1TOC\s0 and \fB\-mno-sum-in-toc\fR forces \s-1GCC\s0 to
generate code to calculate the sum of an address and a constant at
run-time instead of putting that sum into the \s-1TOC\s0. You may specify one
or both of these options. Each causes \s-1GCC\s0 to produce very slightly
slower and larger code at the expense of conserving \s-1TOC\s0 space.
.Sp
If you still run out of space in the \s-1TOC\s0 even when you specify both of
these options, specify \fB\-mminimal-toc\fR instead. This option causes
\&\s-1GCC\s0 to make only one \s-1TOC\s0 entry for every file. When you specify this
option, \s-1GCC\s0 will produce code that is slower and larger but which
uses extremely little \s-1TOC\s0 space. You may wish to use this option
only on files that contain less frequently executed code.
.Ip "\fB\-maix64\fR" 4
.IX Item "-maix64"
.PD 0
.Ip "\fB\-maix32\fR" 4
.IX Item "-maix32"
.PD
Enable 64\-bit \s-1AIX\s0 \s-1ABI\s0 and calling convention: 64\-bit pointers, 64\-bit
\&\f(CW\*(C`long\*(C'\fR type, and the infrastructure needed to support them.
Specifying \fB\-maix64\fR implies \fB\-mpowerpc64\fR and
\&\fB\-mpowerpc\fR, while \fB\-maix32\fR disables the 64\-bit \s-1ABI\s0 and
implies \fB\-mno-powerpc64\fR. \s-1GCC\s0 defaults to \fB\-maix32\fR.
.Ip "\fB\-mxl-call\fR" 4
.IX Item "-mxl-call"
.PD 0
.Ip "\fB\-mno-xl-call\fR" 4
.IX Item "-mno-xl-call"
.PD
On \s-1AIX\s0, pass floating-point arguments to prototyped functions beyond the
register save area (\s-1RSA\s0) on the stack in addition to argument FPRs. The
\&\s-1AIX\s0 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. \s-1AIX\s0 \s-1XL\s0
compilers access floating point arguments which do not fit in the
\&\s-1RSA\s0 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 \s-1AIX\s0
\&\s-1XL\s0 compilers without optimization.
.Ip "\fB\-mthreads\fR" 4
.IX Item "-mthreads"
Support \fI\s-1AIX\s0 Threads\fR. Link an application written to use
\&\fIpthreads\fR with special libraries and startup code to enable the
application to run.
.Ip "\fB\-mpe\fR" 4
.IX Item "-mpe"
Support \fI\s-1IBM\s0 \s-1RS/6000\s0 \s-1SP\s0\fR \fIParallel Environment\fR (\s-1PE\s0). Link an
application written to use message passing with special startup code to
enable the application to run. The system must have \s-1PE\s0 installed in the
standard location (\fI/usr/lpp/ppe.poe/\fR), or the \fIspecs\fR file
must be overridden with the \fB\-specs=\fR option to specify the
appropriate directory location. The Parallel Environment does not
support threads, so the \fB\-mpe\fR option and the \fB\-mthreads\fR
option are incompatible.
.Ip "\fB\-msoft-float\fR" 4
.IX Item "-msoft-float"
.PD 0
.Ip "\fB\-mhard-float\fR" 4
.IX Item "-mhard-float"
.PD
Generate code that does not use (uses) the floating-point register set.
Software floating point emulation is provided if you use the
\&\fB\-msoft-float\fR option, and pass the option to \s-1GCC\s0 when linking.
.Ip "\fB\-mmultiple\fR" 4
.IX Item "-mmultiple"
.PD 0
.Ip "\fB\-mno-multiple\fR" 4
.IX Item "-mno-multiple"
.PD
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 \s-1POWER\s0 systems, and not
generated on PowerPC systems. Do not use \fB\-mmultiple\fR on little
endian PowerPC systems, since those instructions do not work when the
processor is in little endian mode. The exceptions are \s-1PPC740\s0 and
\&\s-1PPC750\s0 which permit the instructions usage in little endian mode.
.Ip "\fB\-mstring\fR" 4
.IX Item "-mstring"
.PD 0
.Ip "\fB\-mno-string\fR" 4
.IX Item "-mno-string"
.PD
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
\&\s-1POWER\s0 systems, and not generated on PowerPC systems. Do not use
\&\fB\-mstring\fR on little endian PowerPC systems, since those
instructions do not work when the processor is in little endian mode.
The exceptions are \s-1PPC740\s0 and \s-1PPC750\s0 which permit the instructions
usage in little endian mode.
.Ip "\fB\-mupdate\fR" 4
.IX Item "-mupdate"
.PD 0
.Ip "\fB\-mno-update\fR" 4
.IX Item "-mno-update"
.PD
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
\&\fB\-mno-update\fR, 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.
.Ip "\fB\-mfused-madd\fR" 4
.IX Item "-mfused-madd"
.PD 0
.Ip "\fB\-mno-fused-madd\fR" 4
.IX Item "-mno-fused-madd"
.PD
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.
.Ip "\fB\-mno-bit-align\fR" 4
.IX Item "-mno-bit-align"
.PD 0
.Ip "\fB\-mbit-align\fR" 4
.IX Item "-mbit-align"
.PD
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.
.Sp
For example, by default a structure containing nothing but 8
\&\f(CW\*(C`unsigned\*(C'\fR bitfields of length 1 would be aligned to a 4 byte
boundary and have a size of 4 bytes. By using \fB\-mno-bit-align\fR,
the structure would be aligned to a 1 byte boundary and be one byte in
size.
.Ip "\fB\-mno-strict-align\fR" 4
.IX Item "-mno-strict-align"
.PD 0
.Ip "\fB\-mstrict-align\fR" 4
.IX Item "-mstrict-align"
.PD
On System V.4 and embedded PowerPC systems do not (do) assume that
unaligned memory references will be handled by the system.
.Ip "\fB\-mrelocatable\fR" 4
.IX Item "-mrelocatable"
.PD 0
.Ip "\fB\-mno-relocatable\fR" 4
.IX Item "-mno-relocatable"
.PD
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 \fB\-mrelocatable\fR on any module, all objects linked together must
be compiled with \fB\-mrelocatable\fR or \fB\-mrelocatable-lib\fR.
.Ip "\fB\-mrelocatable-lib\fR" 4
.IX Item "-mrelocatable-lib"
.PD 0
.Ip "\fB\-mno-relocatable-lib\fR" 4
.IX Item "-mno-relocatable-lib"
.PD
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 \fB\-mrelocatable-lib\fR can be linked with either modules
compiled without \fB\-mrelocatable\fR and \fB\-mrelocatable-lib\fR or
with modules compiled with the \fB\-mrelocatable\fR options.
.Ip "\fB\-mno-toc\fR" 4
.IX Item "-mno-toc"
.PD 0
.Ip "\fB\-mtoc\fR" 4
.IX Item "-mtoc"
.PD
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.
.Ip "\fB\-mlittle\fR" 4
.IX Item "-mlittle"
.PD 0
.Ip "\fB\-mlittle-endian\fR" 4
.IX Item "-mlittle-endian"
.PD
On System V.4 and embedded PowerPC systems compile code for the
processor in little endian mode. The \fB\-mlittle-endian\fR option is
the same as \fB\-mlittle\fR.
.Ip "\fB\-mbig\fR" 4
.IX Item "-mbig"
.PD 0
.Ip "\fB\-mbig-endian\fR" 4
.IX Item "-mbig-endian"
.PD
On System V.4 and embedded PowerPC systems compile code for the
processor in big endian mode. The \fB\-mbig-endian\fR option is
the same as \fB\-mbig\fR.
.Ip "\fB\-mcall-sysv\fR" 4
.IX Item "-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 \s-1GCC\s0 using \fBpowerpc-*\-eabiaix\fR.
.Ip "\fB\-mcall-sysv-eabi\fR" 4
.IX Item "-mcall-sysv-eabi"
Specify both \fB\-mcall-sysv\fR and \fB\-meabi\fR options.
.Ip "\fB\-mcall-sysv-noeabi\fR" 4
.IX Item "-mcall-sysv-noeabi"
Specify both \fB\-mcall-sysv\fR and \fB\-mno-eabi\fR options.
.Ip "\fB\-mcall-aix\fR" 4
.IX Item "-mcall-aix"
On System V.4 and embedded PowerPC systems compile code using calling
conventions that are similar to those used on \s-1AIX\s0. This is the
default if you configured \s-1GCC\s0 using \fBpowerpc-*\-eabiaix\fR.
.Ip "\fB\-mcall-solaris\fR" 4
.IX Item "-mcall-solaris"
On System V.4 and embedded PowerPC systems compile code for the Solaris
operating system.
.Ip "\fB\-mcall-linux\fR" 4
.IX Item "-mcall-linux"
On System V.4 and embedded PowerPC systems compile code for the
Linux-based \s-1GNU\s0 system.
.Ip "\fB\-mprototype\fR" 4
.IX Item "-mprototype"
.PD 0
.Ip "\fB\-mno-prototype\fR" 4
.IX Item "-mno-prototype"
.PD
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 (\fI\s-1CR\s0\fR) to
indicate whether floating point values were passed in the floating point
registers in case the function takes a variable arguments. With
\&\fB\-mprototype\fR, only calls to prototyped variable argument functions
will set or clear the bit.
.Ip "\fB\-msim\fR" 4
.IX Item "-msim"
On embedded PowerPC systems, assume that the startup module is called
\&\fIsim-crt0.o\fR and that the standard C libraries are \fIlibsim.a\fR and
\&\fIlibc.a\fR. This is the default for \fBpowerpc-*\-eabisim\fR.
configurations.
.Ip "\fB\-mmvme\fR" 4
.IX Item "-mmvme"
On embedded PowerPC systems, assume that the startup module is called
\&\fIcrt0.o\fR and the standard C libraries are \fIlibmvme.a\fR and
\&\fIlibc.a\fR.
.Ip "\fB\-mads\fR" 4
.IX Item "-mads"
On embedded PowerPC systems, assume that the startup module is called
\&\fIcrt0.o\fR and the standard C libraries are \fIlibads.a\fR and
\&\fIlibc.a\fR.
.Ip "\fB\-myellowknife\fR" 4
.IX Item "-myellowknife"
On embedded PowerPC systems, assume that the startup module is called
\&\fIcrt0.o\fR and the standard C libraries are \fIlibyk.a\fR and
\&\fIlibc.a\fR.
.Ip "\fB\-mvxworks\fR" 4
.IX Item "-mvxworks"
On System V.4 and embedded PowerPC systems, specify that you are
compiling for a VxWorks system.
.Ip "\fB\-memb\fR" 4
.IX Item "-memb"
On embedded PowerPC systems, set the \fI\s-1PPC_EMB\s0\fR bit in the \s-1ELF\s0 flags
header to indicate that \fBeabi\fR extended relocations are used.
.Ip "\fB\-meabi\fR" 4
.IX Item "-meabi"
.PD 0
.Ip "\fB\-mno-eabi\fR" 4
.IX Item "-mno-eabi"
.PD
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 \fB\-meabi\fR
means that the stack is aligned to an 8 byte boundary, a function
\&\f(CW\*(C`_\|_eabi\*(C'\fR is called to from \f(CW\*(C`main\*(C'\fR to set up the eabi
environment, and the \fB\-msdata\fR option can use both \f(CW\*(C`r2\*(C'\fR and
\&\f(CW\*(C`r13\*(C'\fR to point to two separate small data areas. Selecting
\&\fB\-mno-eabi\fR means that the stack is aligned to a 16 byte boundary,
do not call an initialization function from \f(CW\*(C`main\*(C'\fR, and the
\&\fB\-msdata\fR option will only use \f(CW\*(C`r13\*(C'\fR to point to a single
small data area. The \fB\-meabi\fR option is on by default if you
configured \s-1GCC\s0 using one of the \fBpowerpc*\-*\-eabi*\fR options.
.Ip "\fB\-msdata=eabi\fR" 4
.IX Item "-msdata=eabi"
On System V.4 and embedded PowerPC systems, put small initialized
\&\f(CW\*(C`const\*(C'\fR global and static data in the \fB.sdata2\fR section, which
is pointed to by register \f(CW\*(C`r2\*(C'\fR. Put small initialized
non-\f(CW\*(C`const\*(C'\fR global and static data in the \fB.sdata\fR section,
which is pointed to by register \f(CW\*(C`r13\*(C'\fR. Put small uninitialized
global and static data in the \fB.sbss\fR section, which is adjacent to
the \fB.sdata\fR section. The \fB\-msdata=eabi\fR option is
incompatible with the \fB\-mrelocatable\fR option. The
\&\fB\-msdata=eabi\fR option also sets the \fB\-memb\fR option.
.Ip "\fB\-msdata=sysv\fR" 4
.IX Item "-msdata=sysv"
On System V.4 and embedded PowerPC systems, put small global and static
data in the \fB.sdata\fR section, which is pointed to by register
\&\f(CW\*(C`r13\*(C'\fR. Put small uninitialized global and static data in the
\&\fB.sbss\fR section, which is adjacent to the \fB.sdata\fR section.
The \fB\-msdata=sysv\fR option is incompatible with the
\&\fB\-mrelocatable\fR option.
.Ip "\fB\-msdata=default\fR" 4
.IX Item "-msdata=default"
.PD 0
.Ip "\fB\-msdata\fR" 4
.IX Item "-msdata"
.PD
On System V.4 and embedded PowerPC systems, if \fB\-meabi\fR is used,
compile code the same as \fB\-msdata=eabi\fR, otherwise compile code the
same as \fB\-msdata=sysv\fR.
.Ip "\fB\-msdata-data\fR" 4
.IX Item "-msdata-data"
On System V.4 and embedded PowerPC systems, put small global and static
data in the \fB.sdata\fR section. Put small uninitialized global and
static data in the \fB.sbss\fR section. Do not use register \f(CW\*(C`r13\*(C'\fR
to address small data however. This is the default behavior unless
other \fB\-msdata\fR options are used.
.Ip "\fB\-msdata=none\fR" 4
.IX Item "-msdata=none"
.PD 0
.Ip "\fB\-mno-sdata\fR" 4
.IX Item "-mno-sdata"
.PD
On embedded PowerPC systems, put all initialized global and static data
in the \fB.data\fR section, and all uninitialized data in the
\&\fB.bss\fR section.
.Ip "\fB\-G\fR \fInum\fR" 4
.IX Item "-G num"
On embedded PowerPC systems, put global and static items less than or
equal to \fInum\fR bytes into the small data or bss sections instead of
the normal data or bss section. By default, \fInum\fR is 8. The
\&\fB\-G\fR \fInum\fR switch is also passed to the linker.
All modules should be compiled with the same \fB\-G\fR \fInum\fR value.
.Ip "\fB\-mregnames\fR" 4
.IX Item "-mregnames"
.PD 0
.Ip "\fB\-mno-regnames\fR" 4
.IX Item "-mno-regnames"
.PD
On System V.4 and embedded PowerPC systems do (do not) emit register
names in the assembly language output using symbolic forms.
.PP
.I "\s-1IBM\s0 \s-1RT\s0 Options"
.IX Subsection "IBM RT Options"
.PP
These \fB\-m\fR options are defined for the \s-1IBM\s0 \s-1RT\s0 \s-1PC:\s0
.Ip "\fB\-min-line-mul\fR" 4
.IX Item "-min-line-mul"
Use an in-line code sequence for integer multiplies. This is the
default.
.Ip "\fB\-mcall-lib-mul\fR" 4
.IX Item "-mcall-lib-mul"
Call \f(CW\*(C`lmul$$\*(C'\fR for integer multiples.
.Ip "\fB\-mfull-fp-blocks\fR" 4
.IX Item "-mfull-fp-blocks"
Generate full-size floating point data blocks, including the minimum
amount of scratch space recommended by \s-1IBM\s0. This is the default.
.Ip "\fB\-mminimum-fp-blocks\fR" 4
.IX Item "-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.
.Ip "\fB\-mfp-arg-in-fpregs\fR" 4
.IX Item "-mfp-arg-in-fpregs"
Use a calling sequence incompatible with the \s-1IBM\s0 calling convention in
which floating point arguments are passed in floating point registers.
Note that \f(CW\*(C`varargs.h\*(C'\fR and \f(CW\*(C`stdargs.h\*(C'\fR will not work with
floating point operands if this option is specified.
.Ip "\fB\-mfp-arg-in-gregs\fR" 4
.IX Item "-mfp-arg-in-gregs"
Use the normal calling convention for floating point arguments. This is
the default.
.Ip "\fB\-mhc-struct-return\fR" 4
.IX Item "-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 \fB\-fpcc-struct-return\fR for compatibility
with the Portable C Compiler (pcc).
.Ip "\fB\-mnohc-struct-return\fR" 4
.IX Item "-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 \fB\-fpcc-struct-return\fR or the
option \fB\-mhc-struct-return\fR.
.PP
.I "\s-1MIPS\s0 Options"
.IX Subsection "MIPS Options"
.PP
These \fB\-m\fR options are defined for the \s-1MIPS\s0 family of computers:
.Ip "\fB\-mcpu=\fR\fIcpu type\fR" 4
.IX Item "-mcpu=cpu type"
Assume the defaults for the machine type \fIcpu type\fR when scheduling
instructions. The choices for \fIcpu type\fR are \fBr2000\fR, \fBr3000\fR,
\&\fBr3900\fR, \fBr4000\fR, \fBr4100\fR, \fBr4300\fR, \fBr4400\fR,
\&\fBr4600\fR, \fBr4650\fR, \fBr5000\fR, \fBr6000\fR, \fBr8000\fR,
and \fBorion\fR. Additionally, the \fBr2000\fR, \fBr3000\fR,
\&\fBr4000\fR, \fBr5000\fR, and \fBr6000\fR can be abbreviated as
\&\fBr2k\fR (or \fBr2K\fR), \fBr3k\fR, etc. While picking a specific
\&\fIcpu type\fR will schedule things appropriately for that particular
chip, the compiler will not generate any code that does not meet level 1
of the \s-1MIPS\s0 \s-1ISA\s0 (instruction set architecture) without a \fB\-mipsX\fR
or \fB\-mabi\fR switch being used.
.Ip "\fB\-mips1\fR" 4
.IX Item "-mips1"
Issue instructions from level 1 of the \s-1MIPS\s0 \s-1ISA\s0. This is the default.
\&\fBr3000\fR is the default \fIcpu type\fR at this \s-1ISA\s0 level.
.Ip "\fB\-mips2\fR" 4
.IX Item "-mips2"
Issue instructions from level 2 of the \s-1MIPS\s0 \s-1ISA\s0 (branch likely, square
root instructions). \fBr6000\fR is the default \fIcpu type\fR at this
\&\s-1ISA\s0 level.
.Ip "\fB\-mips3\fR" 4
.IX Item "-mips3"
Issue instructions from level 3 of the \s-1MIPS\s0 \s-1ISA\s0 (64 bit instructions).
\&\fBr4000\fR is the default \fIcpu type\fR at this \s-1ISA\s0 level.
.Ip "\fB\-mips4\fR" 4
.IX Item "-mips4"
Issue instructions from level 4 of the \s-1MIPS\s0 \s-1ISA\s0 (conditional move,
prefetch, enhanced \s-1FPU\s0 instructions). \fBr8000\fR is the default
\&\fIcpu type\fR at this \s-1ISA\s0 level.
.Ip "\fB\-mfp32\fR" 4
.IX Item "-mfp32"
Assume that 32 32\-bit floating point registers are available. This is
the default.
.Ip "\fB\-mfp64\fR" 4
.IX Item "-mfp64"
Assume that 32 64\-bit floating point registers are available. This is
the default when the \fB\-mips3\fR option is used.
.Ip "\fB\-mgp32\fR" 4
.IX Item "-mgp32"
Assume that 32 32\-bit general purpose registers are available. This is
the default.
.Ip "\fB\-mgp64\fR" 4
.IX Item "-mgp64"
Assume that 32 64\-bit general purpose registers are available. This is
the default when the \fB\-mips3\fR option is used.
.Ip "\fB\-mint64\fR" 4
.IX Item "-mint64"
Force int and long types to be 64 bits wide. See \fB\-mlong32\fR for an
explanation of the default, and the width of pointers.
.Ip "\fB\-mlong64\fR" 4
.IX Item "-mlong64"
Force long types to be 64 bits wide. See \fB\-mlong32\fR for an
explanation of the default, and the width of pointers.
.Ip "\fB\-mlong32\fR" 4
.IX Item "-mlong32"
Force long, int, and pointer types to be 32 bits wide.
.Sp
If none of \fB\-mlong32\fR, \fB\-mlong64\fR, or \fB\-mint64\fR are set,
the size of ints, longs, and pointers depends on the \s-1ABI\s0 and \s-1ISA\s0 chosen.
For \fB\-mabi=32\fR, and \fB\-mabi=n32\fR, ints and longs are 32 bits
wide. For \fB\-mabi=64\fR, ints are 32 bits, and longs are 64 bits wide.
For \fB\-mabi=eabi\fR and either \fB\-mips1\fR or \fB\-mips2\fR, ints
and longs are 32 bits wide. For \fB\-mabi=eabi\fR 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 \s-1ISA\s0).
.Ip "\fB\-mabi=32\fR" 4
.IX Item "-mabi=32"
.PD 0
.Ip "\fB\-mabi=o64\fR" 4
.IX Item "-mabi=o64"
.Ip "\fB\-mabi=n32\fR" 4
.IX Item "-mabi=n32"
.Ip "\fB\-mabi=64\fR" 4
.IX Item "-mabi=64"
.Ip "\fB\-mabi=eabi\fR" 4
.IX Item "-mabi=eabi"
.PD
Generate code for the indicated \s-1ABI\s0. The default instruction level is
\&\fB\-mips1\fR for \fB32\fR, \fB\-mips3\fR for \fBn32\fR, and
\&\fB\-mips4\fR otherwise. Conversely, with \fB\-mips1\fR or
\&\fB\-mips2\fR, the default \s-1ABI\s0 is \fB32\fR; otherwise, the default \s-1ABI\s0
is \fB64\fR.
.Ip "\fB\-mmips-as\fR" 4
.IX Item "-mmips-as"
Generate code for the \s-1MIPS\s0 assembler, and invoke \fImips-tfile\fR to
add normal debug information. This is the default for all
platforms except for the \s-1OSF/1\s0 reference platform, using the OSF/rose
object format. If the either of the \fB\-gstabs\fR or \fB\-gstabs+\fR
switches are used, the \fImips-tfile\fR program will encapsulate the
stabs within \s-1MIPS\s0 \s-1ECOFF\s0.
.Ip "\fB\-mgas\fR" 4
.IX Item "-mgas"
Generate code for the \s-1GNU\s0 assembler. This is the default on the \s-1OSF/1\s0
reference platform, using the OSF/rose object format. Also, this is
the default if the configure option \fB\*(--with-gnu-as\fR is used.
.Ip "\fB\-msplit-addresses\fR" 4
.IX Item "-msplit-addresses"
.PD 0
.Ip "\fB\-mno-split-addresses\fR" 4
.IX Item "-mno-split-addresses"
.PD
Generate code to load the high and low parts of address constants separately.
This allows \f(CW\*(C`gcc\*(C'\fR to optimize away redundant loads of the high order
bits of addresses. This optimization requires \s-1GNU\s0 as and \s-1GNU\s0 ld.
This optimization is enabled by default for some embedded targets where
\&\s-1GNU\s0 as and \s-1GNU\s0 ld are standard.
.Ip "\fB\-mrnames\fR" 4
.IX Item "-mrnames"
.PD 0
.Ip "\fB\-mno-rnames\fR" 4
.IX Item "-mno-rnames"
.PD
The \fB\-mrnames\fR switch says to output code using the \s-1MIPS\s0 software
names for the registers, instead of the hardware names (ie, \fIa0\fR
instead of \fI$4\fR). The only known assembler that supports this option
is the Algorithmics assembler.
.Ip "\fB\-mgpopt\fR" 4
.IX Item "-mgpopt"
.PD 0
.Ip "\fB\-mno-gpopt\fR" 4
.IX Item "-mno-gpopt"
.PD
The \fB\-mgpopt\fR switch says to write all of the data declarations
before the instructions in the text section, this allows the \s-1MIPS\s0
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.
.Ip "\fB\-mstats\fR" 4
.IX Item "-mstats"
.PD 0
.Ip "\fB\-mno-stats\fR" 4
.IX Item "-mno-stats"
.PD
For each non-inline function processed, the \fB\-mstats\fR 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.).
.Ip "\fB\-mmemcpy\fR" 4
.IX Item "-mmemcpy"
.PD 0
.Ip "\fB\-mno-memcpy\fR" 4
.IX Item "-mno-memcpy"
.PD
The \fB\-mmemcpy\fR switch makes all block moves call the appropriate
string function (\fBmemcpy\fR or \fBbcopy\fR) instead of possibly
generating inline code.
.Ip "\fB\-mmips-tfile\fR" 4
.IX Item "-mmips-tfile"
.PD 0
.Ip "\fB\-mno-mips-tfile\fR" 4
.IX Item "-mno-mips-tfile"
.PD
The \fB\-mno-mips-tfile\fR switch causes the compiler not
postprocess the object file with the \fImips-tfile\fR program,
after the \s-1MIPS\s0 assembler has generated it to add debug support. If
\&\fImips-tfile\fR is not run, then no local variables will be
available to the debugger. In addition, \fIstage2\fR and
\&\fIstage3\fR 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 \fB\-mno-mips-tfile\fR switch should only
be used when there are bugs in the \fImips-tfile\fR program that
prevents compilation.
.Ip "\fB\-msoft-float\fR" 4
.IX Item "-msoft-float"
Generate output containing library calls for floating point.
\&\fBWarning:\fR the requisite libraries are not part of \s-1GCC\s0.
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.
.Ip "\fB\-mhard-float\fR" 4
.IX Item "-mhard-float"
Generate output containing floating point instructions. This is the
default if you use the unmodified sources.
.Ip "\fB\-mabicalls\fR" 4
.IX Item "-mabicalls"
.PD 0
.Ip "\fB\-mno-abicalls\fR" 4
.IX Item "-mno-abicalls"
.PD
Emit (or do not emit) the pseudo operations \fB.abicalls\fR,
\&\fB.cpload\fR, and \fB.cprestore\fR that some System V.4 ports use for
position independent code.
.Ip "\fB\-mlong-calls\fR" 4
.IX Item "-mlong-calls"
.PD 0
.Ip "\fB\-mno-long-calls\fR" 4
.IX Item "-mno-long-calls"
.PD
Do all calls with the \fB\s-1JALR\s0\fR 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.
.Ip "\fB\-mhalf-pic\fR" 4
.IX Item "-mhalf-pic"
.PD 0
.Ip "\fB\-mno-half-pic\fR" 4
.IX Item "-mno-half-pic"
.PD
Put pointers to extern references into the data section and load them
up, rather than put the references in the text section.
.Ip "\fB\-membedded-pic\fR" 4
.IX Item "-membedded-pic"
.PD 0
.Ip "\fB\-mno-embedded-pic\fR" 4
.IX Item "-mno-embedded-pic"
.PD
Generate \s-1PIC\s0 code suitable for some embedded systems. All calls are
made using \s-1PC\s0 relative address, and all data is addressed using the \f(CW$gp\fR
register. No more than 65536 bytes of global data may be used. This
requires \s-1GNU\s0 as and \s-1GNU\s0 ld which do most of the work. This currently
only works on targets which use \s-1ECOFF\s0; it does not work with \s-1ELF\s0.
.Ip "\fB\-membedded-data\fR" 4
.IX Item "-membedded-data"
.PD 0
.Ip "\fB\-mno-embedded-data\fR" 4
.IX Item "-mno-embedded-data"
.PD
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 \s-1RAM\s0 required
when executing, and thus may be preferred for some embedded systems.
.Ip "\fB\-muninit-const-in-rodata\fR" 4
.IX Item "-muninit-const-in-rodata"
.PD 0
.Ip "\fB\-mno-uninit-const-in-rodata\fR" 4
.IX Item "-mno-uninit-const-in-rodata"
.PD
When used together with \-membedded-data, it will always store uninitialized
const variables in the read-only data section.
.Ip "\fB\-msingle-float\fR" 4
.IX Item "-msingle-float"
.PD 0
.Ip "\fB\-mdouble-float\fR" 4
.IX Item "-mdouble-float"
.PD
The \fB\-msingle-float\fR switch tells gcc to assume that the floating
point coprocessor only supports single precision operations, as on the
\&\fBr4650\fR chip. The \fB\-mdouble-float\fR switch permits gcc to use
double precision operations. This is the default.
.Ip "\fB\-mmad\fR" 4
.IX Item "-mmad"
.PD 0
.Ip "\fB\-mno-mad\fR" 4
.IX Item "-mno-mad"
.PD
Permit use of the \fBmad\fR, \fBmadu\fR and \fBmul\fR instructions,
as on the \fBr4650\fR chip.
.Ip "\fB\-m4650\fR" 4
.IX Item "-m4650"
Turns on \fB\-msingle-float\fR, \fB\-mmad\fR, and, at least for now,
\&\fB\-mcpu=r4650\fR.
.Ip "\fB\-mips16\fR" 4
.IX Item "-mips16"
.PD 0
.Ip "\fB\-mno-mips16\fR" 4
.IX Item "-mno-mips16"
.PD
Enable 16\-bit instructions.
.Ip "\fB\-mentry\fR" 4
.IX Item "-mentry"
Use the entry and exit pseudo ops. This option can only be used with
\&\fB\-mips16\fR.
.Ip "\fB\-EL\fR" 4
.IX Item "-EL"
Compile code for the processor in little endian mode.
The requisite libraries are assumed to exist.
.Ip "\fB\-EB\fR" 4
.IX Item "-EB"
Compile code for the processor in big endian mode.
The requisite libraries are assumed to exist.
.Ip "\fB\-G\fR \fInum\fR" 4
.IX Item "-G num"
Put global and static items less than or equal to \fInum\fR 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 (\fIgp\fR or \fI$28\fR),
instead of the normal two words used. By default, \fInum\fR is 8 when
the \s-1MIPS\s0 assembler is used, and 0 when the \s-1GNU\s0 assembler is used. The
\&\fB\-G\fR \fInum\fR switch is also passed to the assembler and linker.
All modules should be compiled with the same \fB\-G\fR \fInum\fR
value.
.Ip "\fB\-nocpp\fR" 4
.IX Item "-nocpp"
Tell the \s-1MIPS\s0 assembler to not run its preprocessor over user
assembler files (with a \fB.s\fR suffix) when assembling them.
.Ip "\fB\-mfix7000\fR" 4
.IX Item "-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.
.Ip "\fB\-no-crt0\fR" 4
.IX Item "-no-crt0"
Do not include the default crt0.
.PP
.I "Intel 386 Options"
.IX Subsection "Intel 386 Options"
.PP
These \fB\-m\fR options are defined for the i386 family of computers:
.Ip "\fB\-mcpu=\fR\fIcpu type\fR" 4
.IX Item "-mcpu=cpu type"
Assume the defaults for the machine type \fIcpu type\fR when scheduling
instructions. The choices for \fIcpu type\fR are \fBi386\fR,
\&\fBi486\fR, \fBi586\fR, \fBi686\fR, \fBpentium\fR,
\&\fBpentiumpro\fR, \fBpentium4\fR, \fBk6\fR, and \fBathlon\fR
.Sp
While picking a specific \fIcpu type\fR will schedule things appropriately
for that particular chip, the compiler will not generate any code that
does not run on the i386 without the \fB\-march=\fR\fIcpu type\fR option
being used. \fBi586\fR is equivalent to \fBpentium\fR and \fBi686\fR
is equivalent to \fBpentiumpro\fR. \fBk6\fR and \fBathlon\fR are the
\&\s-1AMD\s0 chips as opposed to the Intel ones.
.Ip "\fB\-march=\fR\fIcpu type\fR" 4
.IX Item "-march=cpu type"
Generate instructions for the machine type \fIcpu type\fR. The choices
for \fIcpu type\fR are the same as for \fB\-mcpu\fR. Moreover,
specifying \fB\-march=\fR\fIcpu type\fR implies \fB\-mcpu=\fR\fIcpu type\fR.
.Ip "\fB\-m386\fR" 4
.IX Item "-m386"
.PD 0
.Ip "\fB\-m486\fR" 4
.IX Item "-m486"
.Ip "\fB\-mpentium\fR" 4
.IX Item "-mpentium"
.Ip "\fB\-mpentiumpro\fR" 4
.IX Item "-mpentiumpro"
.PD
Synonyms for \-mcpu=i386, \-mcpu=i486, \-mcpu=pentium, and \-mcpu=pentiumpro
respectively. These synonyms are deprecated.
.Ip "\fB\-mintel-syntax\fR" 4
.IX Item "-mintel-syntax"
Emit assembly using Intel syntax opcodes instead of \s-1AT&T\s0 syntax.
.Ip "\fB\-mieee-fp\fR" 4
.IX Item "-mieee-fp"
.PD 0
.Ip "\fB\-mno-ieee-fp\fR" 4
.IX Item "-mno-ieee-fp"
.PD
Control whether or not the compiler uses \s-1IEEE\s0 floating point
comparisons. These handle correctly the case where the result of a
comparison is unordered.
.Ip "\fB\-msoft-float\fR" 4
.IX Item "-msoft-float"
Generate output containing library calls for floating point.
\&\fBWarning:\fR the requisite libraries are not part of \s-1GCC\s0.
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.
.Sp
On machines where a function returns floating point results in the 80387
register stack, some floating point opcodes may be emitted even if
\&\fB\-msoft-float\fR is used.
.Ip "\fB\-mno-fp-ret-in-387\fR" 4
.IX Item "-mno-fp-ret-in-387"
Do not use the \s-1FPU\s0 registers for return values of functions.
.Sp
The usual calling convention has functions return values of types
\&\f(CW\*(C`float\*(C'\fR and \f(CW\*(C`double\*(C'\fR in an \s-1FPU\s0 register, even if there
is no \s-1FPU\s0. The idea is that the operating system should emulate
an \s-1FPU\s0.
.Sp
The option \fB\-mno-fp-ret-in-387\fR causes such values to be returned
in ordinary \s-1CPU\s0 registers instead.
.Ip "\fB\-mno-fancy-math-387\fR" 4
.IX Item "-mno-fancy-math-387"
Some 387 emulators do not support the \f(CW\*(C`sin\*(C'\fR, \f(CW\*(C`cos\*(C'\fR and
\&\f(CW\*(C`sqrt\*(C'\fR 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 \fB\-funsafe-math-optimizations\fR switch.
.Ip "\fB\-malign-double\fR" 4
.IX Item "-malign-double"
.PD 0
.Ip "\fB\-mno-align-double\fR" 4
.IX Item "-mno-align-double"
.PD
Control whether \s-1GCC\s0 aligns \f(CW\*(C`double\*(C'\fR, \f(CW\*(C`long double\*(C'\fR, and
\&\f(CW\*(C`long long\*(C'\fR variables on a two word boundary or a one word
boundary. Aligning \f(CW\*(C`double\*(C'\fR variables on a two word boundary will
produce code that runs somewhat faster on a \fBPentium\fR at the
expense of more memory.
.Ip "\fB\-m128bit-long-double\fR" 4
.IX Item "-m128bit-long-double"
.PD 0
.Ip "\fB\-m128bit-long-double\fR" 4
.IX Item "-m128bit-long-double"
.PD
Control the size of \f(CW\*(C`long double\*(C'\fR type. i386 application binary interface
specify the size to be 12 bytes, while modern architectures (Pentium and newer)
preffer \f(CW\*(C`long double\*(C'\fR aligned to 8 or 16 byte boundary. This is
impossible to reach with 12 byte long doubles in the array accesses.
.Sp
\&\fBWarning:\fR if you use the \fB\-m128bit-long-double\fR switch, the
structures and arrays containing \f(CW\*(C`long double\*(C'\fR will change their size as
well as function calling convention for function taking \f(CW\*(C`long double\*(C'\fR
will be modified.
.Ip "\fB\-m96bit-long-double\fR" 4
.IX Item "-m96bit-long-double"
.PD 0
.Ip "\fB\-m96bit-long-double\fR" 4
.IX Item "-m96bit-long-double"
.PD
Set the size of \f(CW\*(C`long double\*(C'\fR to 96 bits as required by the i386
application binary interface. This is the default.
.Ip "\fB\-msvr3\-shlib\fR" 4
.IX Item "-msvr3-shlib"
.PD 0
.Ip "\fB\-mno-svr3\-shlib\fR" 4
.IX Item "-mno-svr3-shlib"
.PD
Control whether \s-1GCC\s0 places uninitialized locals into \f(CW\*(C`bss\*(C'\fR or
\&\f(CW\*(C`data\*(C'\fR. \fB\-msvr3\-shlib\fR places these locals into \f(CW\*(C`bss\*(C'\fR.
These options are meaningful only on System V Release 3.
.Ip "\fB\-mno-wide-multiply\fR" 4
.IX Item "-mno-wide-multiply"
.PD 0
.Ip "\fB\-mwide-multiply\fR" 4
.IX Item "-mwide-multiply"
.PD
Control whether \s-1GCC\s0 uses the \f(CW\*(C`mul\*(C'\fR and \f(CW\*(C`imul\*(C'\fR that produce
64 bit results in \f(CW\*(C`eax:edx\*(C'\fR from 32 bit operands to do \f(CW\*(C`long
long\*(C'\fR multiplies and 32\-bit division by constants.
.Ip "\fB\-mrtd\fR" 4
.IX Item "-mrtd"
Use a different function-calling convention, in which functions that
take a fixed number of arguments return with the \f(CW\*(C`ret\*(C'\fR \fInum\fR
instruction, which pops their arguments while returning. This saves one
instruction in the caller since there is no need to pop the arguments
there.
.Sp
You can specify that an individual function is called with this calling
sequence with the function attribute \fBstdcall\fR. You can also
override the \fB\-mrtd\fR option by using the function attribute
\&\fBcdecl\fR.
.Sp
\&\fBWarning:\fR 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.
.Sp
Also, you must provide function prototypes for all functions that
take variable numbers of arguments (including \f(CW\*(C`printf\*(C'\fR);
otherwise incorrect code will be generated for calls to those
functions.
.Sp
In addition, seriously incorrect code will result if you call a
function with too many arguments. (Normally, extra arguments are
harmlessly ignored.)
.Ip "\fB\-mregparm=\fR\fInum\fR" 4
.IX Item "-mregparm=num"
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 \fBregparm\fR.
.Sp
\&\fBWarning:\fR if you use this switch, and
\&\fInum\fR is nonzero, then you must build all modules with the same
value, including any libraries. This includes the system libraries and
startup modules.
.Ip "\fB\-malign-loops=\fR\fInum\fR" 4
.IX Item "-malign-loops=num"
Align loops to a 2 raised to a \fInum\fR byte boundary. If
\&\fB\-malign-loops\fR is not specified, the default is 2 unless
gas 2.8 (or later) is being used in which case the default is
to align the loop on a 16 byte boundary if it is less than 8
bytes away.
.Ip "\fB\-malign-jumps=\fR\fInum\fR" 4
.IX Item "-malign-jumps=num"
Align instructions that are only jumped to to a 2 raised to a \fInum\fR
byte boundary. If \fB\-malign-jumps\fR is not specified, the default is
2 if optimizing for a 386, and 4 if optimizing for a 486 unless
gas 2.8 (or later) is being used in which case the default is
to align the instruction on a 16 byte boundary if it is less
than 8 bytes away.
.Ip "\fB\-malign-functions=\fR\fInum\fR" 4
.IX Item "-malign-functions=num"
Align the start of functions to a 2 raised to \fInum\fR byte boundary.
If \fB\-malign-functions\fR is not specified, the default is 2 if optimizing
for a 386, and 4 if optimizing for a 486.
.Ip "\fB\-mpreferred-stack-boundary=\fR\fInum\fR" 4
.IX Item "-mpreferred-stack-boundary=num"
Attempt to keep the stack boundary aligned to a 2 raised to \fInum\fR
byte boundary. If \fB\-mpreferred-stack-boundary\fR is not specified,
the default is 4 (16 bytes or 128 bits).
.Sp
The stack is required to be aligned on a 4 byte boundary. On Pentium
and PentiumPro, \f(CW\*(C`double\*(C'\fR and \f(CW\*(C`long double\*(C'\fR values should be
aligned to an 8 byte boundary (see \fB\-malign-double\fR) or suffer
significant run time performance penalties. On Pentium \s-1III\s0, the
Streaming \s-1SIMD\s0 Extension (\s-1SSE\s0) data type \f(CW\*(C`_\|_m128\*(C'\fR suffers similar
penalties if it is not 16 byte aligned.
.Sp
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.
.Sp
This extra alignment does consume extra stack space. Code that is sensitive
to stack space usage, such as embedded systems and operating system kernels,
may want to reduce the preferred alignment to
\&\fB\-mpreferred-stack-boundary=2\fR.
.Ip "\fB\-mpush-args\fR" 4
.IX Item "-mpush-args"
Use \s-1PUSH\s0 operations to store outgoing parameters. This method is shorter
and usually equally fast as method using \s-1SUB/MOV\s0 operations and is enabled
by default. In some cases disabling it may improve performance because of
improved scheduling and reduced dependencies.
.Ip "\fB\-maccumulate-outgoing-args\fR" 4
.IX Item "-maccumulate-outgoing-args"
If enabled, the maximum amount of space required for outgoing arguments will be
computed in the function prologue. This in 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 \-mno-push-args.
.Ip "\fB\-mthreads\fR" 4
.IX Item "-mthreads"
Support thread-safe exception handling on \fBMingw32\fR. Code that relies
on thread-safe exception handling must compile and link all code with the
\&\fB\-mthreads\fR option. When compiling, \fB\-mthreads\fR defines
\&\fB\-D_MT\fR; when linking, it links in a special thread helper library
\&\fB\-lmingwthrd\fR which cleans up per thread exception handling data.
.Ip "\fB\-mno-align-stringops\fR" 4
.IX Item "-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.
.Ip "\fB\-minline-all-stringops\fR" 4
.IX Item "-minline-all-stringops"
By default \s-1GCC\s0 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.
.PP
.I "\s-1HPPA\s0 Options"
.IX Subsection "HPPA Options"
.PP
These \fB\-m\fR options are defined for the \s-1HPPA\s0 family of computers:
.Ip "\fB\-march=\fR\fIarchitecture type\fR" 4
.IX Item "-march=architecture type"
Generate code for the specified architecture. The choices for
\&\fIarchitecture type\fR are \fB1.0\fR for \s-1PA\s0 1.0, \fB1.1\fR for \s-1PA\s0
1.1, and \fB2.0\fR for \s-1PA\s0 2.0 processors. Refer to
\&\fI/usr/lib/sched.models\fR on an \s-1HP-UX\s0 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.
.Sp
\&\s-1PA\s0 2.0 support currently requires gas snapshot 19990413 or later. The
next release of binutils (current is 2.9.1) will probably contain \s-1PA\s0 2.0
support.
.Ip "\fB\-mpa-risc-1\-0\fR" 4
.IX Item "-mpa-risc-1-0"
.PD 0
.Ip "\fB\-mpa-risc-1\-1\fR" 4
.IX Item "-mpa-risc-1-1"
.Ip "\fB\-mpa-risc-2\-0\fR" 4
.IX Item "-mpa-risc-2-0"
.PD
Synonyms for \-march=1.0, \-march=1.1, and \-march=2.0 respectively.
.Ip "\fB\-mbig-switch\fR" 4
.IX Item "-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.
.Ip "\fB\-mjump-in-delay\fR" 4
.IX Item "-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.
.Ip "\fB\-mdisable-fpregs\fR" 4
.IX Item "-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.
.Ip "\fB\-mdisable-indexing\fR" 4
.IX Item "-mdisable-indexing"
Prevent the compiler from using indexing address modes. This avoids some
rather obscure problems when compiling \s-1MIG\s0 generated code under \s-1MACH\s0.
.Ip "\fB\-mno-space-regs\fR" 4
.IX Item "-mno-space-regs"
Generate code that assumes the target has no space registers. This allows
\&\s-1GCC\s0 to generate faster indirect calls and use unscaled index address modes.
.Sp
Such code is suitable for level 0 \s-1PA\s0 systems and kernels.
.Ip "\fB\-mfast-indirect-calls\fR" 4
.IX Item "-mfast-indirect-calls"
Generate code that assumes calls never cross space boundaries. This
allows \s-1GCC\s0 to emit code which performs faster indirect calls.
.Sp
This option will not work in the presence of shared libraries or nested
functions.
.Ip "\fB\-mlong-load-store\fR" 4
.IX Item "-mlong-load-store"
Generate 3\-instruction load and store sequences as sometimes required by
the \s-1HP-UX\s0 10 linker. This is equivalent to the \fB+k\fR option to
the \s-1HP\s0 compilers.
.Ip "\fB\-mportable-runtime\fR" 4
.IX Item "-mportable-runtime"
Use the portable calling conventions proposed by \s-1HP\s0 for \s-1ELF\s0 systems.
.Ip "\fB\-mgas\fR" 4
.IX Item "-mgas"
Enable the use of assembler directives only \s-1GAS\s0 understands.
.Ip "\fB\-mschedule=\fR\fIcpu type\fR" 4
.IX Item "-mschedule=cpu type"
Schedule code according to the constraints for the machine type
\&\fIcpu type\fR. The choices for \fIcpu type\fR are \fB700\fR
\&\fB7100\fR, \fB7100LC\fR, \fB7200\fR, and \fB8000\fR. Refer to
\&\fI/usr/lib/sched.models\fR on an \s-1HP-UX\s0 system to determine the
proper scheduling option for your machine.
.Ip "\fB\-mlinker-opt\fR" 4
.IX Item "-mlinker-opt"
Enable the optimization pass in the \s-1HPUX\s0 linker. Note this makes symbolic
debugging impossible. It also triggers a bug in the \s-1HPUX\s0 8 and \s-1HPUX\s0 9 linkers
in which they give bogus error messages when linking some programs.
.Ip "\fB\-msoft-float\fR" 4
.IX Item "-msoft-float"
Generate output containing library calls for floating point.
\&\fBWarning:\fR the requisite libraries are not available for all \s-1HPPA\s0
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 \fBhppa1.1\-*\-pro\fR
does provide software floating point support.
.Sp
\&\fB\-msoft-float\fR changes the calling convention in the output file;
therefore, it is only useful if you compile \fIall\fR of a program with
this option. In particular, you need to compile \fIlibgcc.a\fR, the
library that comes with \s-1GCC\s0, with \fB\-msoft-float\fR in order for
this to work.
.PP
.I "Intel 960 Options"
.IX Subsection "Intel 960 Options"
.PP
These \fB\-m\fR options are defined for the Intel 960 implementations:
.Ip "\fB\-m\fR\fIcpu type\fR" 4
.IX Item "-mcpu type"
Assume the defaults for the machine type \fIcpu type\fR for some of
the other options, including instruction scheduling, floating point
support, and addressing modes. The choices for \fIcpu type\fR are
\&\fBka\fR, \fBkb\fR, \fBmc\fR, \fBca\fR, \fBcf\fR,
\&\fBsa\fR, and \fBsb\fR.
The default is
\&\fBkb\fR.
.Ip "\fB\-mnumerics\fR" 4
.IX Item "-mnumerics"
.PD 0
.Ip "\fB\-msoft-float\fR" 4
.IX Item "-msoft-float"
.PD
The \fB\-mnumerics\fR option indicates that the processor does support
floating-point instructions. The \fB\-msoft-float\fR option indicates
that floating-point support should not be assumed.
.Ip "\fB\-mleaf-procedures\fR" 4
.IX Item "-mleaf-procedures"
.PD 0
.Ip "\fB\-mno-leaf-procedures\fR" 4
.IX Item "-mno-leaf-procedures"
.PD
Do (or do not) attempt to alter leaf procedures to be callable with the
\&\f(CW\*(C`bal\*(C'\fR instruction as well as \f(CW\*(C`call\*(C'\fR. This will result in more
efficient code for explicit calls when the \f(CW\*(C`bal\*(C'\fR 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.
.Ip "\fB\-mtail-call\fR" 4
.IX Item "-mtail-call"
.PD 0
.Ip "\fB\-mno-tail-call\fR" 4
.IX Item "-mno-tail-call"
.PD
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
\&\fB\-mno-tail-call\fR.
.Ip "\fB\-mcomplex-addr\fR" 4
.IX Item "-mcomplex-addr"
.PD 0
.Ip "\fB\-mno-complex-addr\fR" 4
.IX Item "-mno-complex-addr"
.PD
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 \fB\-mcomplex-addr\fR for all processors except
the \s-1CB\s0 and \s-1CC\s0.
.Ip "\fB\-mcode-align\fR" 4
.IX Item "-mcode-align"
.PD 0
.Ip "\fB\-mno-code-align\fR" 4
.IX Item "-mno-code-align"
.PD
Align code to 8\-byte boundaries for faster fetching (or don't bother).
Currently turned on by default for C-series implementations only.
.Ip "\fB\-mic-compat\fR" 4
.IX Item "-mic-compat"
.PD 0
.Ip "\fB\-mic2.0\-compat\fR" 4
.IX Item "-mic2.0-compat"
.Ip "\fB\-mic3.0\-compat\fR" 4
.IX Item "-mic3.0-compat"
.PD
Enable compatibility with iC960 v2.0 or v3.0.
.Ip "\fB\-masm-compat\fR" 4
.IX Item "-masm-compat"
.PD 0
.Ip "\fB\-mintel-asm\fR" 4
.IX Item "-mintel-asm"
.PD
Enable compatibility with the iC960 assembler.
.Ip "\fB\-mstrict-align\fR" 4
.IX Item "-mstrict-align"
.PD 0
.Ip "\fB\-mno-strict-align\fR" 4
.IX Item "-mno-strict-align"
.PD
Do not permit (do permit) unaligned accesses.
.Ip "\fB\-mold-align\fR" 4
.IX Item "-mold-align"
Enable structure-alignment compatibility with Intel's gcc release version
1.3 (based on gcc 1.37). This option implies \fB\-mstrict-align\fR.
.Ip "\fB\-mlong-double-64\fR" 4
.IX Item "-mlong-double-64"
Implement type \fBlong double\fR as 64\-bit floating point numbers.
Without the option \fBlong double\fR is implemented by 80\-bit
floating point numbers. The only reason we have it because there is
no 128\-bit \fBlong double\fR support in \fBfp-bit.c\fR yet. So it
is only useful for people using soft-float targets. Otherwise, we
should recommend against use of it.
.PP
.I "\s-1DEC\s0 Alpha Options"
.IX Subsection "DEC Alpha Options"
.PP
These \fB\-m\fR options are defined for the \s-1DEC\s0 Alpha implementations:
.Ip "\fB\-mno-soft-float\fR" 4
.IX Item "-mno-soft-float"
.PD 0
.Ip "\fB\-msoft-float\fR" 4
.IX Item "-msoft-float"
.PD
Use (do not use) the hardware floating-point instructions for
floating-point operations. When \fB\-msoft-float\fR is specified,
functions in \fIlibgcc1.c\fR 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.
.Sp
Note that Alpha implementations without floating-point operations are
required to have floating-point registers.
.Ip "\fB\-mfp-reg\fR" 4
.IX Item "-mfp-reg"
.PD 0
.Ip "\fB\-mno-fp-regs\fR" 4
.IX Item "-mno-fp-regs"
.PD
Generate code that uses (does not use) the floating-point register set.
\&\fB\-mno-fp-regs\fR implies \fB\-msoft-float\fR. 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 \f(CW$0\fR instead of \f(CW$f0\fR. This is a non-standard calling sequence, so any
function with a floating-point argument or return value called by code
compiled with \fB\-mno-fp-regs\fR must also be compiled with that
option.
.Sp
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.
.Ip "\fB\-mieee\fR" 4
.IX Item "-mieee"
The Alpha architecture implements floating-point hardware optimized for
maximum performance. It is mostly compliant with the \s-1IEEE\s0 floating
point standard. However, for full compliance, software assistance is
required. This option generates code fully \s-1IEEE\s0 compliant code
\&\fIexcept\fR that the \fIinexact flag\fR is not maintained (see below).
If this option is turned on, the \s-1CPP\s0 macro \f(CW\*(C`_IEEE_FP\*(C'\fR is defined
during compilation. The option is a shorthand for: \fB\-D_IEEE_FP
\&\-mfp-trap-mode=su \-mtrap-precision=i \-mieee-conformant\fR. The resulting
code is less efficient but is able to correctly support denormalized
numbers and exceptional \s-1IEEE\s0 values such as not-a-number and plus/minus
infinity. Other Alpha compilers call this option
\&\fB\-ieee_with_no_inexact\fR.
.Ip "\fB\-mieee-with-inexact\fR" 4
.IX Item "-mieee-with-inexact"
This is like \fB\-mieee\fR except the generated code also maintains the
\&\s-1IEEE\s0 \fIinexact flag\fR. Turning on this option causes the generated
code to implement fully-compliant \s-1IEEE\s0 math. The option is a shorthand
for \fB\-D_IEEE_FP \-D_IEEE_FP_INEXACT\fR plus the three following:
\&\fB\-mieee-conformant\fR,
\&\fB\-mfp-trap-mode=sui\fR,
and \fB\-mtrap-precision=i\fR.
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 \fIinexact flag\fR, you should
normally not specify this option. Other Alpha compilers call this
option \fB\-ieee_with_inexact\fR.
.Ip "\fB\-mfp-trap-mode=\fR\fItrap mode\fR" 4
.IX Item "-mfp-trap-mode=trap mode"
This option controls what floating-point related traps are enabled.
Other Alpha compilers call this option \fB\-fptm\fR \fItrap mode\fR.
The trap mode can be set to one of four values:
.RS 4
.Ip "\fBn\fR" 4
.IX 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).
.Ip "\fBu\fR" 4
.IX Item "u"
In addition to the traps enabled by \fBn\fR, underflow traps are enabled
as well.
.Ip "\fBsu\fR" 4
.IX Item "su"
Like \fBsu\fR, but the instructions are marked to be safe for software
completion (see Alpha architecture manual for details).
.Ip "\fBsui\fR" 4
.IX Item "sui"
Like \fBsu\fR, but inexact traps are enabled as well.
.RE
.RS 4
.RE
.Ip "\fB\-mfp-rounding-mode=\fR\fIrounding mode\fR" 4
.IX Item "-mfp-rounding-mode=rounding mode"
Selects the \s-1IEEE\s0 rounding mode. Other Alpha compilers call this option
\&\fB\-fprm\fR \fIrounding mode\fR. The \fIrounding mode\fR can be one
of:
.RS 4
.Ip "\fBn\fR" 4
.IX Item "n"
Normal \s-1IEEE\s0 rounding mode. Floating point numbers are rounded towards
the nearest machine number or towards the even machine number in case
of a tie.
.Ip "\fBm\fR" 4
.IX Item "m"
Round towards minus infinity.
.Ip "\fBc\fR" 4
.IX Item "c"
Chopped rounding mode. Floating point numbers are rounded towards zero.
.Ip "\fBd\fR" 4
.IX Item "d"
Dynamic rounding mode. A field in the floating point control register
(\fIfpcr\fR, 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
\&\fIfpcr\fR, \fBd\fR corresponds to round towards plus infinity.
.RE
.RS 4
.RE
.Ip "\fB\-mtrap-precision=\fR\fItrap precision\fR" 4
.IX Item "-mtrap-precision=trap 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.
\&\s-1GCC\s0 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:
.RS 4
.Ip "\fBp\fR" 4
.IX Item "p"
Program precision. This option is the default and means a trap handler
can only identify which program caused a floating point exception.
.Ip "\fBf\fR" 4
.IX Item "f"
Function precision. The trap handler can determine the function that
caused a floating point exception.
.Ip "\fBi\fR" 4
.IX Item "i"
Instruction precision. The trap handler can determine the exact
instruction that caused a floating point exception.
.RE
.RS 4
.Sp
Other Alpha compilers provide the equivalent options called
\&\fB\-scope_safe\fR and \fB\-resumption_safe\fR.
.RE
.Ip "\fB\-mieee-conformant\fR" 4
.IX Item "-mieee-conformant"
This option marks the generated code as \s-1IEEE\s0 conformant. You must not
use this option unless you also specify \fB\-mtrap-precision=i\fR and either
\&\fB\-mfp-trap-mode=su\fR or \fB\-mfp-trap-mode=sui\fR. Its only effect
is to emit the line \fB.eflag 48\fR in the function prologue of the
generated assembly file. Under \s-1DEC\s0 Unix, this has the effect that
IEEE-conformant math library routines will be linked in.
.Ip "\fB\-mbuild-constants\fR" 4
.IX Item "-mbuild-constants"
Normally \s-1GCC\s0 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.
.Sp
Use this option to require \s-1GCC\s0 to construct \fIall\fR integer constants
using code, even if it takes more instructions (the maximum is six).
.Sp
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.
.Ip "\fB\-malpha-as\fR" 4
.IX Item "-malpha-as"
.PD 0
.Ip "\fB\-mgas\fR" 4
.IX Item "-mgas"
.PD
Select whether to generate code to be assembled by the vendor-supplied
assembler (\fB\-malpha-as\fR) or by the \s-1GNU\s0 assembler \fB\-mgas\fR.
.Ip "\fB\-mbwx\fR" 4
.IX Item "-mbwx"
.PD 0
.Ip "\fB\-mno-bwx\fR" 4
.IX Item "-mno-bwx"
.Ip "\fB\-mcix\fR" 4
.IX Item "-mcix"
.Ip "\fB\-mno-cix\fR" 4
.IX Item "-mno-cix"
.Ip "\fB\-mmax\fR" 4
.IX Item "-mmax"
.Ip "\fB\-mno-max\fR" 4
.IX Item "-mno-max"
.PD
Indicate whether \s-1GCC\s0 should generate code to use the optional \s-1BWX\s0,
\&\s-1CIX\s0, and \s-1MAX\s0 instruction sets. The default is to use the instruction sets
supported by the \s-1CPU\s0 type specified via \fB\-mcpu=\fR option or that
of the \s-1CPU\s0 on which \s-1GCC\s0 was built if none was specified.
.Ip "\fB\-mcpu=\fR\fIcpu_type\fR" 4
.IX Item "-mcpu=cpu_type"
Set the instruction set, register set, and instruction scheduling
parameters for machine type \fIcpu_type\fR. You can specify either the
\&\fB\s-1EV\s0\fR style name or the corresponding chip number. \s-1GCC\s0
supports scheduling parameters for the \s-1EV4\s0 and \s-1EV5\s0 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,
\&\s-1GCC\s0 will default to the processor on which the compiler was built.
.Sp
Supported values for \fIcpu_type\fR are
.RS 4
.Ip "\fBev4\fR" 4
.IX Item "ev4"
.PD 0
.Ip "\fB21064\fR" 4
.IX Item "21064"
.PD
Schedules as an \s-1EV4\s0 and has no instruction set extensions.
.Ip "\fBev5\fR" 4
.IX Item "ev5"
.PD 0
.Ip "\fB21164\fR" 4
.IX Item "21164"
.PD
Schedules as an \s-1EV5\s0 and has no instruction set extensions.
.Ip "\fBev56\fR" 4
.IX Item "ev56"
.PD 0
.Ip "\fB21164a\fR" 4
.IX Item "21164a"
.PD
Schedules as an \s-1EV5\s0 and supports the \s-1BWX\s0 extension.
.Ip "\fBpca56\fR" 4
.IX Item "pca56"
.PD 0
.Ip "\fB21164pc\fR" 4
.IX Item "21164pc"
.Ip "\fB21164PC\fR" 4
.IX Item "21164PC"
.PD
Schedules as an \s-1EV5\s0 and supports the \s-1BWX\s0 and \s-1MAX\s0 extensions.
.Ip "\fBev6\fR" 4
.IX Item "ev6"
.PD 0
.Ip "\fB21264\fR" 4
.IX Item "21264"
.PD
Schedules as an \s-1EV5\s0 (until Digital releases the scheduling parameters
for the \s-1EV6\s0) and supports the \s-1BWX\s0, \s-1CIX\s0, and \s-1MAX\s0 extensions.
.RE
.RS 4
.RE
.Ip "\fB\-mmemory-latency=\fR\fItime\fR" 4
.IX Item "-mmemory-latency=time"
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.
.Sp
Valid options for \fItime\fR are
.RS 4
.Ip "\fInumber\fR" 4
.IX Item "number"
A decimal number representing clock cycles.
.Ip "\fBL1\fR" 4
.IX Item "L1"
.PD 0
.Ip "\fBL2\fR" 4
.IX Item "L2"
.Ip "\fBL3\fR" 4
.IX Item "L3"
.Ip "\fBmain\fR" 4
.IX Item "main"
.PD
The compiler contains estimates of the number of clock cycles for
``typical'' \s-1EV4\s0 & \s-1EV5\s0 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 \s-1EV5\s0.
.RE
.RS 4
.RE
.PP
.I "Clipper Options"
.IX Subsection "Clipper Options"
.PP
These \fB\-m\fR options are defined for the Clipper implementations:
.Ip "\fB\-mc300\fR" 4
.IX Item "-mc300"
Produce code for a C300 Clipper processor. This is the default.
.Ip "\fB\-mc400\fR" 4
.IX Item "-mc400"
Produce code for a C400 Clipper processor i.e. use floating point
registers f8..f15.
.PP
.I "H8/300 Options"
.IX Subsection "H8/300 Options"
.PP
These \fB\-m\fR options are defined for the H8/300 implementations:
.Ip "\fB\-mrelax\fR" 4
.IX Item "-mrelax"
Shorten some address references at link time, when possible; uses the
linker option \fB\-relax\fR.
.Ip "\fB\-mh\fR" 4
.IX Item "-mh"
Generate code for the H8/300H.
.Ip "\fB\-ms\fR" 4
.IX Item "-ms"
Generate code for the H8/S.
.Ip "\fB\-ms2600\fR" 4
.IX Item "-ms2600"
Generate code for the H8/S2600. This switch must be used with \-ms.
.Ip "\fB\-mint32\fR" 4
.IX Item "-mint32"
Make \f(CW\*(C`int\*(C'\fR data 32 bits by default.
.Ip "\fB\-malign-300\fR" 4
.IX Item "-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.
\&\fB\-malign-300\fR causes them to be aligned on 2 byte boundaries.
This option has no effect on the H8/300.
.PP
.I "\s-1SH\s0 Options"
.IX Subsection "SH Options"
.PP
These \fB\-m\fR options are defined for the \s-1SH\s0 implementations:
.Ip "\fB\-m1\fR" 4
.IX Item "-m1"
Generate code for the \s-1SH1\s0.
.Ip "\fB\-m2\fR" 4
.IX Item "-m2"
Generate code for the \s-1SH2\s0.
.Ip "\fB\-m3\fR" 4
.IX Item "-m3"
Generate code for the \s-1SH3\s0.
.Ip "\fB\-m3e\fR" 4
.IX Item "-m3e"
Generate code for the SH3e.
.Ip "\fB\-m4\-nofpu\fR" 4
.IX Item "-m4-nofpu"
Generate code for the \s-1SH4\s0 without a floating-point unit.
.Ip "\fB\-m4\-single-only\fR" 4
.IX Item "-m4-single-only"
Generate code for the \s-1SH4\s0 with a floating-point unit that only
supports single-precision arithmentic.
.Ip "\fB\-m4\-single\fR" 4
.IX Item "-m4-single"
Generate code for the \s-1SH4\s0 assuming the floating-point unit is in
single-precision mode by default.
.Ip "\fB\-m4\fR" 4
.IX Item "-m4"
Generate code for the \s-1SH4\s0.
.Ip "\fB\-mb\fR" 4
.IX Item "-mb"
Compile code for the processor in big endian mode.
.Ip "\fB\-ml\fR" 4
.IX Item "-ml"
Compile code for the processor in little endian mode.
.Ip "\fB\-mdalign\fR" 4
.IX Item "-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 \-mdalign.
.Ip "\fB\-mrelax\fR" 4
.IX Item "-mrelax"
Shorten some address references at link time, when possible; uses the
linker option \fB\-relax\fR.
.Ip "\fB\-mbigtable\fR" 4
.IX Item "-mbigtable"
Use 32\-bit offsets in \f(CW\*(C`switch\*(C'\fR tables. The default is to use
16\-bit offsets.
.Ip "\fB\-mfmovd\fR" 4
.IX Item "-mfmovd"
Enable the use of the instruction \f(CW\*(C`fmovd\*(C'\fR.
.Ip "\fB\-mhitachi\fR" 4
.IX Item "-mhitachi"
Comply with the calling conventions defined by Hitachi.
.Ip "\fB\-mnomacsave\fR" 4
.IX Item "-mnomacsave"
Mark the \f(CW\*(C`MAC\*(C'\fR register as call-clobbered, even if
\&\fB\-mhitachi\fR is given.
.Ip "\fB\-misize\fR" 4
.IX Item "-misize"
Dump instruction size and location in the assembly code.
.Ip "\fB\-mpadstruct\fR" 4
.IX Item "-mpadstruct"
This option is deprecated. It pads structures to multiple of 4 bytes,
which is incompatible with the \s-1SH\s0 \s-1ABI\s0.
.Ip "\fB\-mspace\fR" 4
.IX Item "-mspace"
Optimize for space instead of speed. Implied by \fB\-Os\fR.
.Ip "\fB\-mprefergot\fR" 4
.IX Item "-mprefergot"
When generating position-independent code, emit function calls using
the Global Offset Table instead of the Procedure Linkage Table.
.Ip "\fB\-musermode\fR" 4
.IX Item "-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 \f(CW\*(C`sh\-*\-linux*\*(C'\fR.
.PP
.I "Options for System V"
.IX Subsection "Options for System V"
.PP
These additional options are available on System V Release 4 for
compatibility with other compilers on those systems:
.Ip "\fB\-G\fR" 4
.IX Item "-G"
Create a shared object.
It is recommended that \fB\-symbolic\fR or \fB\-shared\fR be used instead.
.Ip "\fB\-Qy\fR" 4
.IX Item "-Qy"
Identify the versions of each tool used by the compiler, in a
\&\f(CW\*(C`.ident\*(C'\fR assembler directive in the output.
.Ip "\fB\-Qn\fR" 4
.IX Item "-Qn"
Refrain from adding \f(CW\*(C`.ident\*(C'\fR directives to the output file (this is
the default).
.Ip "\fB\-YP,\fR\fIdirs\fR" 4
.IX Item "-YP,dirs"
Search the directories \fIdirs\fR, and no others, for libraries
specified with \fB\-l\fR.
.Ip "\fB\-Ym,\fR\fIdir\fR" 4
.IX Item "-Ym,dir"
Look in the directory \fIdir\fR to find the M4 preprocessor.
The assembler uses this option.
.PP
.I "TMS320C3x/C4x Options"
.IX Subsection "TMS320C3x/C4x Options"
.PP
These \fB\-m\fR options are defined for TMS320C3x/C4x implementations:
.Ip "\fB\-mcpu=\fR\fIcpu_type\fR" 4
.IX Item "-mcpu=cpu_type"
Set the instruction set, register set, and instruction scheduling
parameters for machine type \fIcpu_type\fR. Supported values for
\&\fIcpu_type\fR are \fBc30\fR, \fBc31\fR, \fBc32\fR, \fBc40\fR, and
\&\fBc44\fR. The default is \fBc40\fR to generate code for the
\&\s-1TMS320C40\s0.
.Ip "\fB\-mbig-memory\fR" 4
.IX Item "-mbig-memory"
.PD 0
.Ip "\fB\-mbig\fR" 4
.IX Item "-mbig"
.Ip "\fB\-msmall-memory\fR" 4
.IX Item "-msmall-memory"
.Ip "\fB\-msmall\fR" 4
.IX Item "-msmall"
.PD
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 (\s-1DP\s0) 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 \s-1DP\s0 register for every direct
memory access.
.Ip "\fB\-mbk\fR" 4
.IX Item "-mbk"
.PD 0
.Ip "\fB\-mno-bk\fR" 4
.IX Item "-mno-bk"
.PD
Allow (disallow) allocation of general integer operands into the block
count register \s-1BK\s0.
.Ip "\fB\-mdb\fR" 4
.IX Item "-mdb"
.PD 0
.Ip "\fB\-mno-db\fR" 4
.IX Item "-mno-db"
.PD
Enable (disable) generation of code using decrement and branch,
\&\fIDBcond\fR\|(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 2^23 + 1 (but who iterates loops more than
2^23 times on the C3x?). Note that \s-1GCC\s0 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 \s-1RPTB\s0 instruction cannot be utilised.
.Ip "\fB\-mdp-isr-reload\fR" 4
.IX Item "-mdp-isr-reload"
.PD 0
.Ip "\fB\-mparanoid\fR" 4
.IX Item "-mparanoid"
.PD
Force the \s-1DP\s0 register to be saved on entry to an interrupt service
routine (\s-1ISR\s0), reloaded to point to the data section, and restored on
exit from the \s-1ISR\s0. This should not be required unless someone has
violated the small memory model by modifying the \s-1DP\s0 register, say within
an object library.
.Ip "\fB\-mmpyi\fR" 4
.IX Item "-mmpyi"
.PD 0
.Ip "\fB\-mno-mpyi\fR" 4
.IX Item "-mno-mpyi"
.PD
For the C3x use the 24\-bit \s-1MPYI\s0 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 \-mmpyi option is not specified for the C3x,
then squaring operations are performed inline instead of a library call.
.Ip "\fB\-mfast-fix\fR" 4
.IX Item "-mfast-fix"
.PD 0
.Ip "\fB\-mno-fast-fix\fR" 4
.IX Item "-mno-fast-fix"
.PD
The C3x/C4x \s-1FIX\s0 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.
.Ip "\fB\-mrptb\fR" 4
.IX Item "-mrptb"
.PD 0
.Ip "\fB\-mno-rptb\fR" 4
.IX Item "-mno-rptb"
.PD
Enable (disable) generation of repeat block sequences using the \s-1RPTB\s0
instruction for zero overhead looping. The \s-1RPTB\s0 construct is only used
for innermost loops that do not call functions or jump across the loop
boundaries. There is no advantage having nested \s-1RPTB\s0 loops due to the
overhead required to save and restore the \s-1RC\s0, \s-1RS\s0, and \s-1RE\s0 registers.
This is enabled by default with \-O2.
.Ip "\fB\-mrpts=\fR\fIcount\fR" 4
.IX Item "-mrpts=count"
.PD 0
.Ip "\fB\-mno-rpts\fR" 4
.IX Item "-mno-rpts"
.PD
Enable (disable) the use of the single instruction repeat instruction
\&\s-1RPTS\s0. If a repeat block contains a single instruction, and the loop
count can be guaranteed to be less than the value \fIcount\fR, \s-1GCC\s0 will
emit a \s-1RPTS\s0 instruction instead of a \s-1RPTB\s0. If no value is specified,
then a \s-1RPTS\s0 will be emitted even if the loop count cannot be determined
at compile time. Note that the repeated instruction following \s-1RPTS\s0 does
not have to be reloaded from memory each iteration, thus freeing up the
\&\s-1CPU\s0 buses for operands. However, since interrupts are blocked by this
instruction, it is disabled by default.
.Ip "\fB\-mloop-unsigned\fR" 4
.IX Item "-mloop-unsigned"
.PD 0
.Ip "\fB\-mno-loop-unsigned\fR" 4
.IX Item "-mno-loop-unsigned"
.PD
The maximum iteration count when using \s-1RPTS\s0 and \s-1RPTB\s0 (and \s-1DB\s0 on the C40)
is 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 2^31 + 1 maximum iteration count may be
exceeded. This switch allows an unsigned iteration count.
.Ip "\fB\-mti\fR" 4
.IX Item "-mti"
Try to emit an assembler syntax that the \s-1TI\s0 assembler (asm30) is happy
with. This also enforces compatibility with the \s-1API\s0 employed by the \s-1TI\s0
C3x C compiler. For example, long doubles are passed as structures
rather than in floating point registers.
.Ip "\fB\-mregparm\fR" 4
.IX Item "-mregparm"
.PD 0
.Ip "\fB\-mmemparm\fR" 4
.IX Item "-mmemparm"
.PD
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.
.Ip "\fB\-mparallel-insns\fR" 4
.IX Item "-mparallel-insns"
.PD 0
.Ip "\fB\-mno-parallel-insns\fR" 4
.IX Item "-mno-parallel-insns"
.PD
Allow the generation of parallel instructions. This is enabled by
default with \-O2.
.Ip "\fB\-mparallel-mpy\fR" 4
.IX Item "-mparallel-mpy"
.PD 0
.Ip "\fB\-mno-parallel-mpy\fR" 4
.IX Item "-mno-parallel-mpy"
.PD
Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
provided \-mparallel-insns is also specified. These instructions have
tight register constraints which can pessimize the code generation
of large functions.
.PP
.I "V850 Options"
.IX Subsection "V850 Options"
.PP
These \fB\-m\fR options are defined for V850 implementations:
.Ip "\fB\-mlong-calls\fR" 4
.IX Item "-mlong-calls"
.PD 0
.Ip "\fB\-mno-long-calls\fR" 4
.IX Item "-mno-long-calls"
.PD
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.
.Ip "\fB\-mno-ep\fR" 4
.IX Item "-mno-ep"
.PD 0
.Ip "\fB\-mep\fR" 4
.IX Item "-mep"
.PD
Do not optimize (do optimize) basic blocks that use the same index
pointer 4 or more times to copy pointer into the \f(CW\*(C`ep\*(C'\fR register, and
use the shorter \f(CW\*(C`sld\*(C'\fR and \f(CW\*(C`sst\*(C'\fR instructions. The \fB\-mep\fR
option is on by default if you optimize.
.Ip "\fB\-mno-prolog-function\fR" 4
.IX Item "-mno-prolog-function"
.PD 0
.Ip "\fB\-mprolog-function\fR" 4
.IX Item "-mprolog-function"
.PD
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 \fB\-mprolog-function\fR option is on by default if
you optimize.
.Ip "\fB\-mspace\fR" 4
.IX Item "-mspace"
Try to make the code as small as possible. At present, this just turns
on the \fB\-mep\fR and \fB\-mprolog-function\fR options.
.Ip "\fB\-mtda=\fR\fIn\fR" 4
.IX Item "-mtda=n"
Put static or global variables whose size is \fIn\fR bytes or less into
the tiny data area that register \f(CW\*(C`ep\*(C'\fR points to. The tiny data
area can hold up to 256 bytes in total (128 bytes for byte references).
.Ip "\fB\-msda=\fR\fIn\fR" 4
.IX Item "-msda=n"
Put static or global variables whose size is \fIn\fR bytes or less into
the small data area that register \f(CW\*(C`gp\*(C'\fR points to. The small data
area can hold up to 64 kilobytes.
.Ip "\fB\-mzda=\fR\fIn\fR" 4
.IX Item "-mzda=n"
Put static or global variables whose size is \fIn\fR bytes or less into
the first 32 kilobytes of memory.
.Ip "\fB\-mv850\fR" 4
.IX Item "-mv850"
Specify that the target processor is the V850.
.Ip "\fB\-mbig-switch\fR" 4
.IX Item "-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.
.PP
.I "\s-1ARC\s0 Options"
.IX Subsection "ARC Options"
.PP
These options are defined for \s-1ARC\s0 implementations:
.Ip "\fB\-EL\fR" 4
.IX Item "-EL"
Compile code for little endian mode. This is the default.
.Ip "\fB\-EB\fR" 4
.IX Item "-EB"
Compile code for big endian mode.
.Ip "\fB\-mmangle-cpu\fR" 4
.IX Item "-mmangle-cpu"
Prepend the name of the cpu to all public symbol names.
In multiple-processor systems, there are many \s-1ARC\s0 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 \*(L"almost identical\*(R".
This is an all or nothing option.
.Ip "\fB\-mcpu=\fR\fIcpu\fR" 4
.IX Item "-mcpu=cpu"
Compile code for \s-1ARC\s0 variant \fIcpu\fR.
Which variants are supported depend on the configuration.
All variants support \fB\-mcpu=base\fR, this is the default.
.Ip "\fB\-mtext=\fR\fItext section\fR" 4
.IX Item "-mtext=text section"
.PD 0
.Ip "\fB\-mdata=\fR\fIdata section\fR" 4
.IX Item "-mdata=data section"
.Ip "\fB\-mrodata=\fR\fIreadonly data section\fR" 4
.IX Item "-mrodata=readonly data section"
.PD
Put functions, data, and readonly data in \fItext section\fR,
\&\fIdata section\fR, and \fIreadonly data section\fR respectively
by default. This can be overridden with the \f(CW\*(C`section\*(C'\fR attribute.
.PP
.I "\s-1NS32K\s0 Options"
.IX Subsection "NS32K Options"
.PP
These are the \fB\-m\fR 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.
.Ip "\fB\-m32032\fR" 4
.IX Item "-m32032"
.PD 0
.Ip "\fB\-m32032\fR" 4
.IX Item "-m32032"
.PD
Generate output for a 32032. This is the default
when the compiler is configured for 32032 and 32016 based systems.
.Ip "\fB\-m32332\fR" 4
.IX Item "-m32332"
.PD 0
.Ip "\fB\-m32332\fR" 4
.IX Item "-m32332"
.PD
Generate output for a 32332. This is the default
when the compiler is configured for 32332\-based systems.
.Ip "\fB\-m32532\fR" 4
.IX Item "-m32532"
.PD 0
.Ip "\fB\-m32532\fR" 4
.IX Item "-m32532"
.PD
Generate output for a 32532. This is the default
when the compiler is configured for 32532\-based systems.
.Ip "\fB\-m32081\fR" 4
.IX Item "-m32081"
Generate output containing 32081 instructions for floating point.
This is the default for all systems.
.Ip "\fB\-m32381\fR" 4
.IX Item "-m32381"
Generate output containing 32381 instructions for floating point. This
also implies \fB\-m32081\fR. The 32381 is only compatible with the 32332
and 32532 cpus. This is the default for the pc532\-netbsd configuration.
.Ip "\fB\-mmulti-add\fR" 4
.IX Item "-mmulti-add"
Try and generate multiply-add floating point instructions \f(CW\*(C`polyF\*(C'\fR
and \f(CW\*(C`dotF\*(C'\fR. This option is only available if the \fB\-m32381\fR
option is in effect. Using these instructions requires changes to 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.
.Ip "\fB\-mnomulti-add\fR" 4
.IX Item "-mnomulti-add"
Do not try and generate multiply-add floating point instructions
\&\f(CW\*(C`polyF\*(C'\fR and \f(CW\*(C`dotF\*(C'\fR. This is the default on all platforms.
.Ip "\fB\-msoft-float\fR" 4
.IX Item "-msoft-float"
Generate output containing library calls for floating point.
\&\fBWarning:\fR the requisite libraries may not be available.
.Ip "\fB\-mnobitfield\fR" 4
.IX Item "-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.
.Ip "\fB\-mbitfield\fR" 4
.IX Item "-mbitfield"
Do use the bit-field instructions. This is the default for all platforms
except the pc532.
.Ip "\fB\-mrtd\fR" 4
.IX Item "-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 \f(CW\*(C`ret\*(C'\fR instruction.
.Sp
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.
.Sp
Also, you must provide function prototypes for all functions that
take variable numbers of arguments (including \f(CW\*(C`printf\*(C'\fR);
otherwise incorrect code will be generated for calls to those
functions.
.Sp
In addition, seriously incorrect code will result if you call a
function with too many arguments. (Normally, extra arguments are
harmlessly ignored.)
.Sp
This option takes its name from the 680x0 \f(CW\*(C`rtd\*(C'\fR instruction.
.Ip "\fB\-mregparam\fR" 4
.IX Item "-mregparam"
Use a different function-calling convention where the first two arguments
are passed in registers.
.Sp
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.
.Ip "\fB\-mnoregparam\fR" 4
.IX Item "-mnoregparam"
Do not pass any arguments in registers. This is the default for all
targets.
.Ip "\fB\-msb\fR" 4
.IX Item "-msb"
It is \s-1OK\s0 to use the sb as an index register which is always loaded with
zero. This is the default for the pc532\-netbsd target.
.Ip "\fB\-mnosb\fR" 4
.IX Item "-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 \fB\-mhimem\fR or
\&\fB\-fpic\fR is set.
.Ip "\fB\-mhimem\fR" 4
.IX Item "-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 \s-1ROM\s0 code.
.Ip "\fB\-mnohimem\fR" 4
.IX Item "-mnohimem"
Assume code will be loaded in the first 512MB of virtual address space.
This is the default for all platforms.
.PP
.I "\s-1AVR\s0 Options"
.IX Subsection "AVR Options"
.PP
These options are defined for \s-1AVR\s0 implementations:
.Ip "\fB\-mmcu=\fR\fImcu\fR" 4
.IX Item "-mmcu=mcu"
Specify \s-1ATMEL\s0 \s-1AVR\s0 instruction set or \s-1MCU\s0 type.
.Sp
Instruction set avr1 is for the minimal \s-1AVR\s0 core, not supported by the C
compiler, only for assembler programs (\s-1MCU\s0 types: at90s1200, attiny10,
attiny11, attiny12, attiny15, attiny28).
.Sp
Instruction set avr2 (default) is for the classic \s-1AVR\s0 core with up to
8K program memory space (\s-1MCU\s0 types: at90s2313, at90s2323, attiny22,
at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
at90c8534, at90s8535).
.Sp
Instruction set avr3 is for the classic \s-1AVR\s0 core with up to 128K program
memory space (\s-1MCU\s0 types: atmega103, atmega603).
.Sp
Instruction set avr4 is for the enhanced \s-1AVR\s0 core with up to 8K program
memory space (\s-1MCU\s0 types: atmega83, atmega85).
.Sp
Instruction set avr5 is for the enhanced \s-1AVR\s0 core with up to 128K program
memory space (\s-1MCU\s0 types: atmega161, atmega163, atmega32, at94k).
.Ip "\fB\-msize\fR" 4
.IX Item "-msize"
Output instruction sizes to the asm file.
.Ip "\fB\-minit-stack=\fR\fIN\fR" 4
.IX Item "-minit-stack=N"
Specify the initial stack address, which may be a symbol or numeric value,
_\|_stack is the default.
.Ip "\fB\-mno-interrupts\fR" 4
.IX Item "-mno-interrupts"
Generated code is not compatible with hardware interrupts.
Code size will be smaller.
.Ip "\fB\-mcall-prologues\fR" 4
.IX Item "-mcall-prologues"
Functions prologues/epilogues expanded as call to appropriate
subroutines. Code size will be smaller.
.Ip "\fB\-mno-tablejump\fR" 4
.IX Item "-mno-tablejump"
Do not generate tablejump insns which sometimes increase code size.
.Ip "\fB\-mtiny-stack\fR" 4
.IX Item "-mtiny-stack"
Change only the low 8 bits of the stack pointer.
.PP
.I "MCore Options"
.IX Subsection "MCore Options"
.PP
These are the \fB\-m\fR options defined for the Motorola M*Core
processors.
.Ip "\fB\-mhardlit\fR" 4
.IX Item "-mhardlit"
.PD 0
.Ip "\fB\-mhardlit\fR" 4
.IX Item "-mhardlit"
.Ip "\fB\-mno-hardlit\fR" 4
.IX Item "-mno-hardlit"
.PD
Inline constants into the code stream if it can be done in two
instructions or less.
.Ip "\fB\-mdiv\fR" 4
.IX Item "-mdiv"
.PD 0
.Ip "\fB\-mdiv\fR" 4
.IX Item "-mdiv"
.Ip "\fB\-mno-div\fR" 4
.IX Item "-mno-div"
.PD
Use the divide instruction. (Enabled by default).
.Ip "\fB\-mrelax-immediate\fR" 4
.IX Item "-mrelax-immediate"
.PD 0
.Ip "\fB\-mrelax-immediate\fR" 4
.IX Item "-mrelax-immediate"
.Ip "\fB\-mno-relax-immediate\fR" 4
.IX Item "-mno-relax-immediate"
.PD
Allow arbitrary sized immediates in bit operations.
.Ip "\fB\-mwide-bitfields\fR" 4
.IX Item "-mwide-bitfields"
.PD 0
.Ip "\fB\-mwide-bitfields\fR" 4
.IX Item "-mwide-bitfields"
.Ip "\fB\-mno-wide-bitfields\fR" 4
.IX Item "-mno-wide-bitfields"
.PD
Always treat bitfields as int-sized.
.Ip "\fB\-m4byte-functions\fR" 4
.IX Item "-m4byte-functions"
.PD 0
.Ip "\fB\-m4byte-functions\fR" 4
.IX Item "-m4byte-functions"
.Ip "\fB\-mno-4byte-functions\fR" 4
.IX Item "-mno-4byte-functions"
.PD
Force all functions to be aligned to a four byte boundary.
.Ip "\fB\-mcallgraph-data\fR" 4
.IX Item "-mcallgraph-data"
.PD 0
.Ip "\fB\-mcallgraph-data\fR" 4
.IX Item "-mcallgraph-data"
.Ip "\fB\-mno-callgraph-data\fR" 4
.IX Item "-mno-callgraph-data"
.PD
Emit callgraph information.
.Ip "\fB\-mslow-bytes\fR" 4
.IX Item "-mslow-bytes"
.PD 0
.Ip "\fB\-mslow-bytes\fR" 4
.IX Item "-mslow-bytes"
.Ip "\fB\-mno-slow-bytes\fR" 4
.IX Item "-mno-slow-bytes"
.PD
Prefer word access when reading byte quantities.
.Ip "\fB\-mlittle-endian\fR" 4
.IX Item "-mlittle-endian"
.PD 0
.Ip "\fB\-mlittle-endian\fR" 4
.IX Item "-mlittle-endian"
.Ip "\fB\-mbig-endian\fR" 4
.IX Item "-mbig-endian"
.PD
Generate code for a little endian target.
.Ip "\fB\-m210\fR" 4
.IX Item "-m210"
.PD 0
.Ip "\fB\-m210\fR" 4
.IX Item "-m210"
.Ip "\fB\-m340\fR" 4
.IX Item "-m340"
.PD
Generate code for the 210 processor.
.PP
.I "\s-1IA-64\s0 Options"
.IX Subsection "IA-64 Options"
.PP
These are the \fB\-m\fR options defined for the Intel \s-1IA-64\s0 architecture.
.Ip "\fB\-mbig-endian\fR" 4
.IX Item "-mbig-endian"
Generate code for a big endian target. This is the default for \s-1HPUX\s0.
.Ip "\fB\-mlittle-endian\fR" 4
.IX Item "-mlittle-endian"
Generate code for a little endian target. This is the default for \s-1AIX5\s0
and Linux.
.Ip "\fB\-mgnu-as\fR" 4
.IX Item "-mgnu-as"
.PD 0
.Ip "\fB\-mno-gnu-as\fR" 4
.IX Item "-mno-gnu-as"
.PD
Generate (or don't) code for the \s-1GNU\s0 assembler. This is the default.
.Ip "\fB\-mgnu-ld\fR" 4
.IX Item "-mgnu-ld"
.PD 0
.Ip "\fB\-mno-gnu-ld\fR" 4
.IX Item "-mno-gnu-ld"
.PD
Generate (or don't) code for the \s-1GNU\s0 linker. This is the default.
.Ip "\fB\-mno-pic\fR" 4
.IX Item "-mno-pic"
Generate code that does not use a global pointer register. The result
is not position independent code, and violates the \s-1IA-64\s0 \s-1ABI\s0.
.Ip "\fB\-mvolatile-asm-stop\fR" 4
.IX Item "-mvolatile-asm-stop"
.PD 0
.Ip "\fB\-mno-volatile-asm-stop\fR" 4
.IX Item "-mno-volatile-asm-stop"
.PD
Generate (or don't) a stop bit immediately before and after volatile asm
statements.
.Ip "\fB\-mb-step\fR" 4
.IX Item "-mb-step"
Generate code that works around Itanium B step errata.
.Ip "\fB\-mregister-names\fR" 4
.IX Item "-mregister-names"
.PD 0
.Ip "\fB\-mno-register-names\fR" 4
.IX Item "-mno-register-names"
.PD
Generate (or don't) \fBin\fR, \fBloc\fR, and \fBout\fR register names for
the stacked registers. This may make assembler output more readable.
.Ip "\fB\-mno-sdata\fR" 4
.IX Item "-mno-sdata"
.PD 0
.Ip "\fB\-msdata\fR" 4
.IX Item "-msdata"
.PD
Disable (or enable) optimizations that use the small data section. This may
be useful for working around optimizer bugs.
.Ip "\fB\-mconstant-gp\fR" 4
.IX Item "-mconstant-gp"
Generate code that uses a single constant global pointer value. This is
useful when compiling kernel code.
.Ip "\fB\-mauto-pic\fR" 4
.IX Item "-mauto-pic"
Generate code that is self-relocatable. This implies \fB\-mconstant-gp\fR.
This is useful when compiling firmware code.
.Ip "\fB\-minline-divide-min-latency\fR" 4
.IX Item "-minline-divide-min-latency"
Generate code for inline divides using the minimum latency algorithm.
.Ip "\fB\-minline-divide-max-throughput\fR" 4
.IX Item "-minline-divide-max-throughput"
Generate code for inline divides using the maximum throughput algorithm.
.Ip "\fB\-mno-dwarf2\-asm\fR" 4
.IX Item "-mno-dwarf2-asm"
.PD 0
.Ip "\fB\-mdwarf2\-asm\fR" 4
.IX Item "-mdwarf2-asm"
.PD
Don't (or do) generate assembler code for the \s-1DWARF2\s0 line number debugging
info. This may be useful when not using the \s-1GNU\s0 assembler.
.Ip "\fB\-mfixed-range=\fR\fIregister range\fR" 4
.IX Item "-mfixed-range=register 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.
.PP
.I "D30V Options"
.IX Subsection "D30V Options"
.PP
These \fB\-m\fR options are defined for D30V implementations:
.Ip "\fB\-mextmem\fR" 4
.IX Item "-mextmem"
Link the \fB.text\fR, \fB.data\fR, \fB.bss\fR, \fB.strings\fR,
\&\fB.rodata\fR, \fB.rodata1\fR, \fB.data1\fR sections into external
memory, which starts at location \f(CW\*(C`0x80000000\*(C'\fR.
.Ip "\fB\-mextmemory\fR" 4
.IX Item "-mextmemory"
Same as the \fB\-mextmem\fR switch.
.Ip "\fB\-monchip\fR" 4
.IX Item "-monchip"
Link the \fB.text\fR section into onchip text memory, which starts at
location \f(CW\*(C`0x0\*(C'\fR. Also link \fB.data\fR, \fB.bss\fR,
\&\fB.strings\fR, \fB.rodata\fR, \fB.rodata1\fR, \fB.data1\fR sections
into onchip data memory, which starts at location \f(CW\*(C`0x20000000\*(C'\fR.
.Ip "\fB\-mno-asm-optimize\fR" 4
.IX Item "-mno-asm-optimize"
.PD 0
.Ip "\fB\-masm-optimize\fR" 4
.IX Item "-masm-optimize"
.PD
Disable (enable) passing \fB\-O\fR to the assembler when optimizing.
The assembler uses the \fB\-O\fR option to automatically parallelize
adjacent short instructions where possible.
.Ip "\fB\-mbranch-cost=\fR\fIn\fR" 4
.IX Item "-mbranch-cost=n"
Increase the internal costs of branches to \fIn\fR. Higher costs means
that the compiler will issue more instructions to avoid doing a branch.
The default is 2.
.Ip "\fB\-mcond-exec=\fR\fIn\fR" 4
.IX Item "-mcond-exec=n"
Specify the maximum number of conditionally executed instructions that
replace a branch. The default is 4.
.Sh "Options for Code Generation Conventions"
.IX Subsection "Options for Code Generation Conventions"
These machine-independent options control the interface conventions
used in code generation.
.PP
Most of them have both positive and negative forms; the negative form
of \fB\-ffoo\fR would be \fB\-fno-foo\fR. 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 \fBno-\fR or adding
it.
.Ip "\fB\-fexceptions\fR" 4
.IX Item "-fexceptions"
Enable exception handling. Generates extra code needed to propagate
exceptions. For some targets, this implies \s-1GNU\s0 \s-1CC\s0 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, \s-1GNU\s0 \s-1CC\s0 will enable it by default for languages like
\&\*(C+ which normally require exception handling, and disable itfor
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.
.Ip "\fB\-funwind-tables\fR" 4
.IX Item "-funwind-tables"
Similar to \fB\-fexceptions\fR, 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.
.Ip "\fB\-fpcc-struct-return\fR" 4
.IX Item "-fpcc-struct-return"
Return ``short'' \f(CW\*(C`struct\*(C'\fR and \f(CW\*(C`union\*(C'\fR 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.
.Sp
The precise convention for returning structures in memory depends
on the target configuration macros.
.Sp
Short structures and unions are those whose size and alignment match
that of some integer type.
.Ip "\fB\-freg-struct-return\fR" 4
.IX Item "-freg-struct-return"
Use the convention that \f(CW\*(C`struct\*(C'\fR and \f(CW\*(C`union\*(C'\fR values are
returned in registers when possible. This is more efficient for small
structures than \fB\-fpcc-struct-return\fR.
.Sp
If you specify neither \fB\-fpcc-struct-return\fR nor its contrary
\&\fB\-freg-struct-return\fR, \s-1GCC\s0 defaults to whichever convention is
standard for the target. If there is no standard convention, \s-1GCC\s0
defaults to \fB\-fpcc-struct-return\fR, except on targets where \s-1GCC\s0
is the principal compiler. In those cases, we can choose the standard,
and we chose the more efficient register return alternative.
.Ip "\fB\-fshort-enums\fR" 4
.IX Item "-fshort-enums"
Allocate to an \f(CW\*(C`enum\*(C'\fR type only as many bytes as it needs for the
declared range of possible values. Specifically, the \f(CW\*(C`enum\*(C'\fR type
will be equivalent to the smallest integer type which has enough room.
.Ip "\fB\-fshort-double\fR" 4
.IX Item "-fshort-double"
Use the same size for \f(CW\*(C`double\*(C'\fR as for \f(CW\*(C`float\*(C'\fR.
.Ip "\fB\-fshared-data\fR" 4
.IX Item "-fshared-data"
Requests that the data and non-\f(CW\*(C`const\*(C'\fR 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.
.Ip "\fB\-fno-common\fR" 4
.IX Item "-fno-common"
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 \f(CW\*(C`extern\*(C'\fR) 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.
.Ip "\fB\-fno-ident\fR" 4
.IX Item "-fno-ident"
Ignore the \fB#ident\fR directive.
.Ip "\fB\-fno-gnu-linker\fR" 4
.IX Item "-fno-gnu-linker"
Do not output global initializations (such as \*(C+ constructors and
destructors) in the form used by the \s-1GNU\s0 linker (on systems where the \s-1GNU\s0
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
\&\fBcollect2\fR program to make sure the system linker includes
constructors and destructors. (\fBcollect2\fR is included in the \s-1GCC\s0
distribution.) For systems which \fImust\fR use \fBcollect2\fR, the
compiler driver \fBgcc\fR is configured to do this automatically.
.Ip "\fB\-finhibit-size-directive\fR" 4
.IX Item "-finhibit-size-directive"
Don't output a \f(CW\*(C`.size\*(C'\fR 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 \fIcrtstuff.c\fR; you should not need to use it
for anything else.
.Ip "\fB\-fverbose-asm\fR" 4
.IX Item "-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).
.Sp
\&\fB\-fno-verbose-asm\fR, the default, causes the
extra information to be omitted and is useful when comparing two assembler
files.
.Ip "\fB\-fvolatile\fR" 4
.IX Item "-fvolatile"
Consider all memory references through pointers to be volatile.
.Ip "\fB\-fvolatile-global\fR" 4
.IX Item "-fvolatile-global"
Consider all memory references to extern and global data items to
be volatile. \s-1GCC\s0 does not consider static data items to be volatile
because of this switch.
.Ip "\fB\-fvolatile-static\fR" 4
.IX Item "-fvolatile-static"
Consider all memory references to static data to be volatile.
.Ip "\fB\-fpic\fR" 4
.IX Item "-fpic"
Generate position-independent code (\s-1PIC\s0) suitable for use in a shared
library, if supported for the target machine. Such code accesses all
constant addresses through a global offset table (\s-1GOT\s0). The dynamic
loader resolves the \s-1GOT\s0 entries when the program starts (the dynamic
loader is not part of \s-1GCC\s0; it is part of the operating system). If
the \s-1GOT\s0 size for the linked executable exceeds a machine-specific
maximum size, you get an error message from the linker indicating that
\&\fB\-fpic\fR does not work; in that case, recompile with \fB\-fPIC\fR
instead. (These maximums are 16k on the m88k, 8k on the Sparc, and 32k
on the m68k and \s-1RS/6000\s0. The 386 has no such limit.)
.Sp
Position-independent code requires special support, and therefore works
only on certain machines. For the 386, \s-1GCC\s0 supports \s-1PIC\s0 for System V
but not for the Sun 386i. Code generated for the \s-1IBM\s0 \s-1RS/6000\s0 is always
position-independent.
.Ip "\fB\-fPIC\fR" 4
.IX Item "-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.
.Sp
Position-independent code requires special support, and therefore works
only on certain machines.
.Ip "\fB\-ffixed-\fR\fIreg\fR" 4
.IX Item "-ffixed-reg"
Treat the register named \fIreg\fR 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).
.Sp
\&\fIreg\fR must be the name of a register. The register names accepted
are machine-specific and are defined in the \f(CW\*(C`REGISTER_NAMES\*(C'\fR
macro in the machine description macro file.
.Sp
This flag does not have a negative form, because it specifies a
three-way choice.
.Ip "\fB\-fcall-used-\fR\fIreg\fR" 4
.IX Item "-fcall-used-reg"
Treat the register named \fIreg\fR 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 \fIreg\fR.
.Sp
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.
.Sp
This flag does not have a negative form, because it specifies a
three-way choice.
.Ip "\fB\-fcall-saved-\fR\fIreg\fR" 4
.IX Item "-fcall-saved-reg"
Treat the register named \fIreg\fR 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 \fIreg\fR if they use it.
.Sp
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.
.Sp
A different sort of disaster will result from the use of this flag for
a register in which function values may be returned.
.Sp
This flag does not have a negative form, because it specifies a
three-way choice.
.Ip "\fB\-fpack-struct\fR" 4
.IX Item "-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.
.Ip "\fB\-fcheck-memory-usage\fR" 4
.IX Item "-fcheck-memory-usage"
Generate extra code to check each memory access. \s-1GCC\s0 will generate
code that is suitable for a detector of bad memory accesses such as
\&\fIChecker\fR.
.Sp
Normally, you should compile all, or none, of your code with this option.
.Sp
If you do mix code compiled with and without this option,
you must ensure that all code that has side effects
and that is called by code compiled with this option
is, itself, compiled with this option.
If you do not, you might get erroneous messages from the detector.
.Sp
If you use functions from a library that have side-effects (such as
\&\f(CW\*(C`read\*(C'\fR), you might not be able to recompile the library and
specify this option. In that case, you can enable the
\&\fB\-fprefix-function-name\fR option, which requests \s-1GCC\s0 to encapsulate
your code and make other functions look as if they were compiled with
\&\fB\-fcheck-memory-usage\fR. This is done by calling ``stubs'',
which are provided by the detector. If you cannot find or build
stubs for every function you call, you might have to specify
\&\fB\-fcheck-memory-usage\fR without \fB\-fprefix-function-name\fR.
.Sp
If you specify this option, you can not use the \f(CW\*(C`asm\*(C'\fR or
\&\f(CW\*(C`_\|_asm_\|_\*(C'\fR keywords in functions with memory checking enabled. \s-1GNU\s0
\&\s-1CC\s0 cannot understand what the \f(CW\*(C`asm\*(C'\fR statement may do, and therefore
cannot generate the appropriate code, so it will reject it. However, if
you specify the function attribute \f(CW\*(C`no_check_memory_usage\*(C'\fR, \s-1GNU\s0 \s-1CC\s0 will disable memory checking within a
function; you may use \f(CW\*(C`asm\*(C'\fR statements inside such functions. You
may have an inline expansion of a non-checked function within a checked
function; in that case \s-1GNU\s0 \s-1CC\s0 will not generate checks for the inlined
function's memory accesses.
.Sp
If you move your \f(CW\*(C`asm\*(C'\fR statements to non-checked inline functions
and they do access memory, you can add calls to the support code in your
inline function, to indicate any reads, writes, or copies being done.
These calls would be similar to those done in the stubs described above.
.Ip "\fB\-fprefix-function-name\fR" 4
.IX Item "-fprefix-function-name"
Request \s-1GCC\s0 to add a prefix to the symbols generated for function names.
\&\s-1GCC\s0 adds a prefix to the names of functions defined as well as
functions called. Code compiled with this option and code compiled
without the option can't be linked together, unless stubs are used.
.Sp
If you compile the following code with \fB\-fprefix-function-name\fR
.Sp
.Vb 6
\& extern void bar (int);
\& void
\& foo (int a)
\& {
\& return bar (a + 5);
\& }
.Ve
\&\s-1GCC\s0 will compile the code as if it was written:
.Sp
.Vb 6
\& extern void prefix_bar (int);
\& void
\& prefix_foo (int a)
\& {
\& return prefix_bar (a + 5);
\& }
.Ve
This option is designed to be used with \fB\-fcheck-memory-usage\fR.
.Ip "\fB\-finstrument-functions\fR" 4
.IX Item "-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,
\&\f(CW\*(C`_\|_builtin_return_address\*(C'\fR does not work beyond the current
function, so the call site information may not be available to the
profiling functions otherwise.)
.Sp
.Vb 2
\& void __cyg_profile_func_enter (void *this_fn, void *call_site);
\& void __cyg_profile_func_exit (void *this_fn, void *call_site);
.Ve
The first argument is the address of the start of the current function,
which may be looked up exactly in the symbol table.
.Sp
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 \fBextern inline\fR 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.)
.Sp
A function may be given the attribute \f(CW\*(C`no_instrument_function\*(C'\fR, 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).
.Ip "\fB\-fstack-check\fR" 4
.IX Item "-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.
.Sp
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.
.Ip "\fB\-fstack-limit-register=\fR\fIreg\fR" 4
.IX Item "-fstack-limit-register=reg"
.PD 0
.Ip "\fB\-fstack-limit-symbol=\fR\fIsym\fR" 4
.IX Item "-fstack-limit-symbol=sym"
.Ip "\fB\-fno-stack-limit\fR" 4
.IX Item "-fno-stack-limit"
.PD
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.
.Sp
For instance, if the stack starts at address \fB0x80000000\fR and grows
downwards you can use the flags
\&\fB\-fstack-limit-symbol=_\|_stack_limit\fR
\&\fB\-Wl,\-\-defsym,_\|_stack_limit=0x7ffe0000\fR which will enforce a stack
limit of 128K.
.Ip "\fB\-fargument-alias\fR" 4
.IX Item "-fargument-alias"
.PD 0
.Ip "\fB\-fargument-noalias\fR" 4
.IX Item "-fargument-noalias"
.Ip "\fB\-fargument-noalias-global\fR" 4
.IX Item "-fargument-noalias-global"
.PD
Specify the possible relationships among parameters and between
parameters and global data.
.Sp
\&\fB\-fargument-alias\fR specifies that arguments (parameters) may
alias each other and may alias global storage.
\&\fB\-fargument-noalias\fR specifies that arguments do not alias
each other, but may alias global storage.
\&\fB\-fargument-noalias-global\fR specifies that arguments do not
alias each other and do not alias global storage.
.Sp
Each language will automatically use whatever option is required by
the language standard. You should not need to use these options yourself.
.Ip "\fB\-fleading-underscore\fR" 4
.IX Item "-fleading-underscore"
This option and its counterpart, \-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.
.Sp
Be warned that you should know what you are doing when invoking this
option, and that not all targets provide complete support for it.
.SH "ENVIRONMENT"
.IX Header "ENVIRONMENT"
This section describes several environment variables that affect how \s-1GCC\s0
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.
.PP
Note that you can also specify places to search using options such as
\&\fB\-B\fR, \fB\-I\fR and \fB\-L\fR. These
take precedence over places specified using environment variables, which
in turn take precedence over those specified by the configuration of \s-1GCC\s0.
.Ip "\fB\s-1LANG\s0\fR" 4
.IX Item "LANG"
.PD 0
.Ip "\fB\s-1LC_CTYPE\s0\fR" 4
.IX Item "LC_CTYPE"
.Ip "\fB\s-1LC_MESSAGES\s0\fR" 4
.IX Item "LC_MESSAGES"
.Ip "\fB\s-1LC_ALL\s0\fR" 4
.IX Item "LC_ALL"
.PD
These environment variables control the way that \s-1GCC\s0 uses
localization information that allow \s-1GCC\s0 to work with different
national conventions. \s-1GCC\s0 inspects the locale categories
\&\fB\s-1LC_CTYPE\s0\fR and \fB\s-1LC_MESSAGES\s0\fR 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 \fBen_UK\fR for English in the United
Kingdom.
.Sp
The \fB\s-1LC_CTYPE\s0\fR environment variable specifies character
classification. \s-1GCC\s0 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.
.Sp
The \fB\s-1LC_MESSAGES\s0\fR environment variable specifies the language to
use in diagnostic messages.
.Sp
If the \fB\s-1LC_ALL\s0\fR environment variable is set, it overrides the value
of \fB\s-1LC_CTYPE\s0\fR and \fB\s-1LC_MESSAGES\s0\fR; otherwise, \fB\s-1LC_CTYPE\s0\fR
and \fB\s-1LC_MESSAGES\s0\fR default to the value of the \fB\s-1LANG\s0\fR
environment variable. If none of these variables are set, \s-1GCC\s0
defaults to traditional C English behavior.
.Ip "\fB\s-1TMPDIR\s0\fR" 4
.IX Item "TMPDIR"
If \fB\s-1TMPDIR\s0\fR is set, it specifies the directory to use for temporary
files. \s-1GCC\s0 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.
.Ip "\fB\s-1GCC_EXEC_PREFIX\s0\fR" 4
.IX Item "GCC_EXEC_PREFIX"
If \fB\s-1GCC_EXEC_PREFIX\s0\fR 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.
.Sp
If \fB\s-1GCC_EXEC_PREFIX\s0\fR is not set, \s-1GNU\s0 \s-1CC\s0 will attempt to figure out
an appropriate prefix to use based on the pathname it was invoked with.
.Sp
If \s-1GCC\s0 cannot find the subprogram using the specified prefix, it
tries looking in the usual places for the subprogram.
.Sp
The default value of \fB\s-1GCC_EXEC_PREFIX\s0\fR is
\&\fI\fIprefix\fI/lib/gcc-lib/\fR where \fIprefix\fR is the value
of \f(CW\*(C`prefix\*(C'\fR when you ran the \fIconfigure\fR script.
.Sp
Other prefixes specified with \fB\-B\fR take precedence over this prefix.
.Sp
This prefix is also used for finding files such as \fIcrt0.o\fR that are
used for linking.
.Sp
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 \fB/usr/local/lib/gcc-lib\fR
(more precisely, with the value of \fB\s-1GCC_INCLUDE_DIR\s0\fR), \s-1GCC\s0 tries
replacing that beginning with the specified prefix to produce an
alternate directory name. Thus, with \fB\-Bfoo/\fR, \s-1GCC\s0 will search
\&\fIfoo/bar\fR where it would normally search \fI/usr/local/lib/bar\fR.
These alternate directories are searched first; the standard directories
come next.
.Ip "\fB\s-1COMPILER_PATH\s0\fR" 4
.IX Item "COMPILER_PATH"
The value of \fB\s-1COMPILER_PATH\s0\fR is a colon-separated list of
directories, much like \fB\s-1PATH\s0\fR. \s-1GCC\s0 tries the directories thus
specified when searching for subprograms, if it can't find the
subprograms using \fB\s-1GCC_EXEC_PREFIX\s0\fR.
.Ip "\fB\s-1LIBRARY_PATH\s0\fR" 4
.IX Item "LIBRARY_PATH"
The value of \fB\s-1LIBRARY_PATH\s0\fR is a colon-separated list of
directories, much like \fB\s-1PATH\s0\fR. When configured as a native compiler,
\&\s-1GCC\s0 tries the directories thus specified when searching for special
linker files, if it can't find them using \fB\s-1GCC_EXEC_PREFIX\s0\fR. Linking
using \s-1GCC\s0 also uses these directories when searching for ordinary
libraries for the \fB\-l\fR option (but directories specified with
\&\fB\-L\fR come first).
.Ip "\fBC_INCLUDE_PATH\fR" 4
.IX Item "C_INCLUDE_PATH"
.PD 0
.Ip "\fB\s-1CPLUS_INCLUDE_PATH\s0\fR" 4
.IX Item "CPLUS_INCLUDE_PATH"
.Ip "\fB\s-1OBJC_INCLUDE_PATH\s0\fR" 4
.IX Item "OBJC_INCLUDE_PATH"
.PD
These environment variables pertain to particular languages. Each
variable's value is a colon-separated list of directories, much like
\&\fB\s-1PATH\s0\fR. When \s-1GCC\s0 searches for header files, it tries the
directories listed in the variable for the language you are using, after
the directories specified with \fB\-I\fR but before the standard header
file directories.
.Ip "\fB\s-1DEPENDENCIES_OUTPUT\s0\fR" 4
.IX Item "DEPENDENCIES_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 \fB\-M\fR option, but it goes to a separate file, and is
in addition to the usual results of compilation.
.Sp
The value of \fB\s-1DEPENDENCIES_OUTPUT\s0\fR 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
\&\fIfile\fR\fB \fR\fItarget\fR, in which case the rules are written to
file \fIfile\fR using \fItarget\fR as the target name.
.Ip "\fB\s-1LANG\s0\fR" 4
.IX Item "LANG"
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 \fB\s-1LANG\s0\fR are recognized:
.RS 4
.Ip "\fBC-JIS\fR" 4
.IX Item "C-JIS"
Recognize \s-1JIS\s0 characters.
.Ip "\fBC-SJIS\fR" 4
.IX Item "C-SJIS"
Recognize \s-1SJIS\s0 characters.
.Ip "\fBC-EUCJP\fR" 4
.IX Item "C-EUCJP"
Recognize \s-1EUCJP\s0 characters.
.RE
.RS 4
.Sp
If \fB\s-1LANG\s0\fR 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.
.RE
.SH "BUGS"
.IX Header "BUGS"
For instructions on reporting bugs, see
<\fBhttp://gcc.gnu.org/bugs.html\fR>. Use of the \fBgccbug\fR
script to report bugs is recommended.
.SH "FOOTNOTES"
.IX Header "FOOTNOTES"
.Ip "1." 4
On some systems, \fBgcc \-shared\fR
needs to build supplementary stub code for constructors to work. On
multi-libbed systems, \fBgcc \-shared\fR 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.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIcpp\fR\|(1), \fIgcov\fR\|(1), \fIg77\fR\|(1), \fIas\fR\|(1), \fIld\fR\|(1), \fIgdb\fR\|(1), \fIadb\fR\|(1), \fIdbx\fR\|(1), \fIsdb\fR\|(1)
and the Info entries for \fIgcc\fR, \fIcpp\fR, \fIg77\fR, \fIas\fR,
\&\fIld\fR, \fIbinutils\fR and \fIgdb\fR.
.SH "AUTHOR"
.IX Header "AUTHOR"
See the Info entry for \fIgcc\fR, or
<\fBhttp://gcc.gnu.org/thanks.html\fR>, for contributors to \s-1GCC\s0.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (c) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997,
1998, 1999, 2000, 2001 Free Software Foundation, Inc.
.PP
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
.PP
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided also that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.
.PP
Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be included in translations
approved by the Free Software Foundation instead of in the original
English.