path: root/man-pages/gcc3.1

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.\" ======================================================================
.\"
.IX Title "GCC 1"
.TH GCC 1 "gcc-3.1" "2002-06-19" "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.
.PP
In Apple's version of \s-1GCC\s0, both \fBcc\fR and \fBgcc\fR are actually
symbolic links to \fBgcc3\fR, while \fBc++\fR and \fBg++\fR are links
to \fBg++3\fR.
.PP
Note that Apple's \s-1GCC\s0 includes a number of extensions to standard \s-1GCC\s0
(flagged below with ``\s-1APPLE\s0 \s-1ONLY\s0''), and that not all generic \s-1GCC\s0
options are available or supported on Darwin / Mac \s-1OS\s0 X.  In particular,
Apple does not currently support the compilation of Fortran, Ada, or
Java, although there are third parties who have made these work.
.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\-ObjC (\s-1APPLE\s0 \s-1ONLY\s0) \-ObjC++ (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-arch\fR \fIarch\fR \fB(\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-v  \-###  \-\-target-help  \-\-help\fR
.Ip "\fIC Language Options\fR" 4
.IX Item "C Language Options"
\&\fB\-ansi  \-std=\fR\fIstandard\fR  \fB\-aux-info\fR \fIfilename\fR 
\&\fB\-faltivec (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-fno-asm  \-fno-builtin \-fno-builtin-\fR\fIfunction\fR 
\&\fB\-fhosted  \-ffreestanding 
\&\-trigraphs  \-no-integrated-cpp  \-traditional  \-traditional-cpp 
\&\-fallow-single-precision  \-fcond-mismatch 
\&\-fconstant-cfstrings (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-fsigned-bitfields  \-fsigned-char 
\&\-funsigned-bitfields  \-funsigned-char 
\&\-fwritable-strings  \-fshort-wchar 
\&\-fpascal-strings (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-fcoalesce (\s-1APPLE\s0 \s-1ONLY\s0) \-fweak-coalesced (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-Wno-#warnings (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-Wextra-tokens (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-Wpragma-once (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-Wnewline-eof (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-Wno-altivec-long-deprecated (\s-1APPLE\s0 \s-1ONLY\s0)\fR
.Ip "\fI\*(C+ Language Options\fR" 4
.IX Item " Language Options"
\&\fB\-fno-access-control  \-fcheck-new  \-fconserve-space 
\&\-fno-const-strings  \-fdollars-in-identifiers 
\&\-fno-elide-constructors 
\&\-fno-enforce-eh-specs  \-fexternal-templates 
\&\-falt-external-templates 
\&\-ffor-scope  \-fno-for-scope  \-fno-gnu-keywords 
\&\-fno-implicit-templates 
\&\-fno-implicit-inline-templates 
\&\-fno-implement-inlines 
\&\-findirect-virtual-calls (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-fapple-kext (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-fcoalesce-templates (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-fms-extensions 
\&\-fno-nonansi-builtins  \-fno-operator-names 
\&\-fno-optional-diags  \-fpermissive 
\&\-frepo  \-fno-rtti  \-fstats  \-ftemplate-depth-\fR\fIn\fR 
\&\fB\-fuse-cxa-atexit  \-fvtable-gc  \-fno-weak  \-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 "\fIObjective-C Language Options\fR" 4
.IX Item "Objective-C Language Options"
\&\fB\-fconstant-string-class=\fR\fIclass-name\fR 
\&\fB\-fgnu-runtime  \-fnext-runtime  \-gen-decls 
\&\-Wno-protocol  \-Wselector\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  \-Wno-deprecated-declarations 
\&\-Wdisabled-optimization  \-Wdiv-by-zero  \-Werror 
\&\-Wfloat-equal  \-Wformat  \-Wformat=2 
\&\-Wformat-nonliteral  \-Wformat-security 
\&\-Wimplicit  \-Wimplicit-int  
\&\-Wimplicit-function-declaration 
\&\-Werror-implicit-function-declaration 
\&\-Wimport  \-Winline 
\&\-Wlarger-than-\fR\fIlen\fR 
\&\fB\-Wno-long-double (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-Wlong-long 
\&\-Wmain  \-Wmissing-braces  \-Wmissing-declarations 
\&\-Wmissing-format-attribute  \-Wmissing-noreturn 
\&\-Wmost (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-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\-d\fR\fIletters\fR  \fB\-dumpspecs  \-dumpmachine  \-dumpversion 
\&\-fdump-unnumbered \-fdump-translation-unit\fR[\fB-\fR\fIn\fR] 
\&\fB\-fdump-class-hierarchy\fR[\fB-\fR\fIn\fR] 
\&\fB\-fdump-tree-original\fR[\fB-\fR\fIn\fR] \fB\-fdump-tree-optimized\fR[\fB-\fR\fIn\fR] 
\&\fB\-fdump-tree-inlined\fR[\fB-\fR\fIn\fR] 
\&\fB\-fmem-report  \-fpretend-float 
\&\-fprofile-arcs  \-ftest-coverage  \-ftime-report 
\&\-g  \-g\fR\fIlevel\fR  \fB\-gcoff  \-gdwarf  \-gdwarf-1  \-gdwarf-1+  \-gdwarf-2 
\&\-ggdb  \-gstabs  \-gstabs+  \-gvms  \-gxcoff  \-gxcoff+ 
\&\-p  \-pg  \-print-file-name=\fR\fIlibrary\fR  \fB\-print-libgcc-file-name 
\&\-print-multi-directory  \-print-multi-lib 
\&\-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 \-fcprop-registers 
\&\-fcse-follow-jumps  \-fcse-skip-blocks  \-fdata-sections 
\&\-fdelayed-branch  \-fdelete-null-pointer-checks 
\&\-fexpensive-optimizations  \-ffast-math  \-ffloat-store 
\&\-fforce-addr  \-fforce-mem  \-ffunction-sections 
\&\-fgcse  \-fgcse-lm  \-fgcse-sm 
\&\-finline-functions  \-finline-limit=\fR\fIn\fR  \fB\-fkeep-inline-functions 
\&\-fkeep-static-consts  \-fmerge-constants  \-fmerge-all-constants 
\&\-fmove-all-movables  \-fno-default-inline  \-fno-defer-pop 
\&\-fno-function-cse  \-fno-guess-branch-probability 
\&\-fno-inline  \-fno-math-errno  \-fno-peephole  \-fno-peephole2 
\&\-funsafe-math-optimizations \-fno-trapping-math 
\&\-fomit-frame-pointer  \-foptimize-register-move 
\&\-foptimize-sibling-calls  \-fprefetch-loop-arrays 
\&\-freduce-all-givs \-fregmove  \-frename-registers 
\&\-frerun-cse-after-loop  \-frerun-loop-opt 
\&\-fschedule-insns  \-fschedule-insns2 
\&\-fsingle-precision-constant  \-fssa \-fssa-ccp \-fssa-dce 
\&\-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\-M  \-MM  \-MF  \-MG  \-MP  \-MQ  \-MT  \-nostdinc  \-P  \-remap 
\&\-dependency-file (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-\-dump-pch\fR \fIname\fR \fB(\s-1APPLE\s0 \s-1ONLY\s0) \-\-load-pch\fR \fIname\fR \fB(\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-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  \-no-c++filt (\s-1APPLE\s0 \s-1ONLY\s0)  
\&\-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- 
\&\-F\fR\fIdir\fR \fB(\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-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"
\&\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 
\&\-maltivec \-mno-altivec 
\&\-mpowerpc-gpopt  \-mno-powerpc-gpopt 
\&\-mpowerpc-gfxopt  \-mno-powerpc-gfxopt 
\&\-mnew-mnemonics  \-mold-mnemonics 
\&\-mfull-toc   \-mminimal-toc  \-mno-fp-in-toc  \-mno-sum-in-toc 
\&\-m64  \-m32  \-mxl-call  \-mno-xl-call  \-mpe 
\&\-malign-mac68k (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-malign-power (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-malign-natural (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-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 
\&\-mdynamic-no-pic (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-mlong-branch (\s-1APPLE\s0 \s-1ONLY\s0) 
\&\-mcall-aix \-mcall-sysv \-mcall-netbsd 
\&\-maix-struct-return \-msvr4\-struct-return
\&\-mabi=altivec \-mabi=no-altivec 
\&\-mprototype  \-mno-prototype 
\&\-msim  \-mmvme  \-mads  \-myellowknife  \-memb \-msdata 
\&\-msdata=\fR\fIopt\fR  \fB\-mvxworks \-G\fR \fInum\fR \fB\-pthread\fR
.Sp
\&\fIi386 and x86\-64 Options\fR
.Sp
\&\fB\-mcpu=\fR\fIcpu-type\fR  \fB\-march=\fR\fIcpu-type\fR \fB\-mfpmath=\fR\fIunit\fR 
\&\fB\-masm=\fR\fIdialect\fR  \fB\-mno-fancy-math-387 
\&\-mno-fp-ret-in-387  \-msoft-float  \-msvr3\-shlib 
\&\-mno-wide-multiply  \-mrtd  \-malign-double 
\&\-mpreferred-stack-boundary=\fR\fInum\fR 
\&\fB\-mmmx  \-msse \-msse2 \-msse-math \-m3dnow 
\&\-mthreads  \-mno-align-stringops  \-minline-all-stringops 
\&\-mpush-args  \-maccumulate-outgoing-args  \-m128bit-long-double 
\&\-m96bit-long-double  \-mregparm=\fR\fInum\fR  \fB\-momit-leaf-frame-pointer 
\&\-mno-red-zone
\&\-m32 \-m64\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\-ffixed-\fR\fIreg\fR \fB\-fexceptions 
\&\-fnon-call-exceptions  \-funwind-tables 
\&\-fasynchronous-unwind-tables 
\&\-finhibit-size-directive  \-finstrument-functions 
\&\-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.mm\fR" 4
.IX Item "file.mm"
.PD 0
.Ip "\fIfile\fR\fB.M\fR" 4
.IX Item "file.M"
.PD
Objective-\*(C+ source code which must be preprocessed.  (\s-1APPLE\s0 \s-1ONLY\s0)
.Ip "\fIfile\fR\fB.mii\fR" 4
.IX Item "file.mii"
Objective-\*(C+ source code which should not be preprocessed.  (\s-1APPLE\s0 \s-1ONLY\s0)
.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.ads\fR" 4
.IX Item "file.ads"
Ada source code file which contains a library unit declaration (a
declaration of a package, subprogram, or generic, or a generic
instantiation), or a library unit renaming declaration (a package,
generic, or subprogram renaming declaration).  Such files are also
called \fIspecs\fR.
.Ip "\fIfile\fR\fB.adb\fR" 4
.IX Item "file.adb"
Ada source code file containing a library unit body (a subprogram or
package body).  Such files are also called \fIbodies\fR.
.Ip "\fIfile\fR\fB.s\fR" 4
.IX Item "file.s"
Assembler code.  Apple's version of \s-1GCC\s0 runs the preprocessor
on these files as well as those ending in \fB.S\fR.
.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 8
\&        c  c-header  cpp-output
\&        c++  c++-cpp-output
\&        objective-c  objc-cpp-output
\&        objective-c++ (APPLE ONLY)
\&        assembler  assembler-with-cpp
\&        ada
\&        f77  f77-cpp-input  ratfor
\&        java
.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\-ObjC\fR" 4
.IX Item "-ObjC"
.PD 0
.Ip "\fB\-ObjC++\fR" 4
.IX Item "-ObjC++"
.PD
These are similar in effect to \fB\-x objective-c\fR and \fB\-x
objective-c++\fR, but affect only the choice of compiler for files already
identified as source files. (\s-1APPLE\s0 \s-1ONLY\s0)
.Ip "\fB\-arch\fR \fIarch\fR" 4
.IX Item "-arch arch"
Compile for the specified target architecture \fIarch\fR.  The allowable
values are \fBi386\fR and \fBppc\fR.  Multiple options work, and
direct the compiler to produce ``fat'' binaries including object code
for each architecture specified with \fB\-arch\fR.  This option only
works if assembler and libraries are available for each architecture
specified. (\s-1APPLE\s0 \s-1ONLY\s0)
.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\-###\fR" 4
.IX Item "-###"
Like \fB\-v\fR except the commands are not executed and all command
arguments are quoted.  This is useful for shell scripts to capture the
driver-generated command lines.
.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
C89 (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 built in 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 built-in
functions with \fB\-ansi\fR is used.  
.Ip "\fB\-std=\fR" 4
.IX Item "-std="
Determine the language standard.  This option is currently only
supported when compiling C.  A value for this option must be provided;
possible values are
.RS 4
.Ip "\fBc89\fR" 4
.IX Item "c89"
.PD 0
.Ip "\fBiso9899:1990\fR" 4
.IX Item "iso9899:1990"
.PD
\&\s-1ISO\s0 C89 (same as \fB\-ansi\fR).
.Ip "\fBiso9899:199409\fR" 4
.IX Item "iso9899:199409"
\&\s-1ISO\s0 C89 as modified in amendment 1.
.Ip "\fBc99\fR" 4
.IX Item "c99"
.PD 0
.Ip "\fBc9x\fR" 4
.IX Item "c9x"
.Ip "\fBiso9899:1999\fR" 4
.IX Item "iso9899:1999"
.Ip "\fBiso9899:199x\fR" 4
.IX Item "iso9899:199x"
.PD
\&\s-1ISO\s0 C99.  Note that this standard is not yet fully supported; see
<\fBhttp://gcc.gnu.org/gcc-3.1/c99status.html\fR> for more information.  The
names \fBc9x\fR and \fBiso9899:199x\fR are deprecated.
.Ip "\fBgnu89\fR" 4
.IX Item "gnu89"
Default, \s-1ISO\s0 C89 plus \s-1GNU\s0 extensions (including some C99 features).
.Ip "\fBgnu99\fR" 4
.IX Item "gnu99"
.PD 0
.Ip "\fBgnu9x\fR" 4
.IX Item "gnu9x"
.PD
\&\s-1ISO\s0 C99 plus \s-1GNU\s0 extensions.  When \s-1ISO\s0 C99 is fully implemented in \s-1GCC\s0,
this will become the default.  The name \fBgnu9x\fR is 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\-aux-info\fR \fIfilename\fR" 4
.IX Item "-aux-info filename"
Output to the given filename prototyped declarations for all functions
declared and/or defined in a translation unit, including those in header
files.  This option is silently ignored in any language other than C.
.Sp
Besides declarations, the file indicates, in comments, the origin of
each declaration (source file and line), whether the declaration was
implicit, prototyped or unprototyped (\fBI\fR, \fBN\fR for new or
\&\fBO\fR for old, respectively, in the first character after the line
number and the colon), and whether it came from a declaration or a
definition (\fBC\fR or \fBF\fR, respectively, in the following
character).  In the case of function definitions, a K&R-style list of
arguments followed by their declarations is also provided, inside
comments, after the declaration.
.Ip "\fB\-faltivec\fR" 4
.IX Item "-faltivec"
Enable the AltiVec language extensions, as defined in Motorola's AltiVec
\&\s-1PIM\s0.  This includes the recognition of \f(CW\*(C`vector\*(C'\fR and \f(CW\*(C`pixel\*(C'\fR as
(context-dependent) keywords, the definition of built-in functions such
as \f(CW\*(C`vec_add\*(C'\fR, and other extensions.  Note that unlike the option
\&\fB\-maltivec\fR, the extensions do not require the inclusion of any
special header files. (\s-1APPLE\s0 \s-1ONLY\s0)
.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"
.PD 0
.Ip "\fB\-fno-builtin-\fR\fIfunction\fR\fB \fR(C and Objective-C only)" 4
.IX Item "-fno-builtin-function (C and Objective-C only)"
.PD
Don't recognize built-in functions that do not begin with
\&\fB_\|_builtin_\fR as prefix.  
.Sp
\&\s-1GCC\s0 normally generates special code to handle certain built-in 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.
.Sp
In \*(C+, \fB\-fno-builtin\fR is always in effect.  The \fB\-fbuiltin\fR
option has no effect.  Therefore, in \*(C+, the only way to get the
optimization benefits of built-in functions is to call the function
using the \fB_\|_builtin_\fR prefix.  The \s-1GNU\s0 \*(C+ Standard Library uses
built-in functions to implement many functions (like
\&\f(CW\*(C`std::strchr\*(C'\fR), so that you automatically get efficient code.
.Sp
With the \fB\-fno-builtin-\fR\fIfunction\fR option, not available
when compiling \*(C+, only the built-in function \fIfunction\fR is
disabled.  \fIfunction\fR must not begin with \fB_\|_builtin_\fR.  If a
function is named this is not built-in in this version of \s-1GCC\s0, this
option is ignored.  There is no corresponding
\&\fB\-fbuiltin-\fR\fIfunction\fR option; if you wish to enable
built-in functions selectively when using \fB\-fno-builtin\fR or
\&\fB\-ffreestanding\fR, you may define macros such as:
.Sp
.Vb 2
\&        #define abs(n)          __builtin_abs ((n))
\&        #define strcpy(d, s)    __builtin_strcpy ((d), (s))
.Ve
.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.  The \fB\-ansi\fR option (and \fB\-std\fR
options for strict \s-1ISO\s0 C conformance) implies \fB\-trigraphs\fR.
.Ip "\fB\-no-integrated-cpp\fR" 4
.IX Item "-no-integrated-cpp"
Invoke the external cpp during compilation.  The default is to use the
integrated cpp (internal cpp).  This option also allows a
user-supplied cpp via the \fB\-B\fR option.  This flag is applicable
in both C and \*(C+ modes.
.Sp
We do not guarantee to retain this option in future, and we may change
its semantics.
.Ip "\fB\*(--dump-pch\fR \fIname\fR" 4
.IX Item "dump-pch name"
Dump the state of the compiler into a directory named \fIname\fR, after
processing all the other arguments.  This is useful for creating
precompiled headers.  (\s-1APPLE\s0 \s-1ONLY\s0)
.Ip "\fB\*(--load-pch\fR \fIname\fR" 4
.IX Item "load-pch name"
Restore the state of the compiler from the directory \fIname\fR before
processing the other arguments.  The net effect is similar to
\&\fB\-include\fR, but it happens much more quickly.  (\s-1APPLE\s0 \s-1ONLY\s0)
.Sp
So for instance if the file \fImyprefix.c\fR #includes various
headers that are useful to all files in your program, you can do
.Sp
.Vb 5
\&        gcc --dump-pch foo -c myprefix.c
\&        gcc --load-pch foo myfile1.c
\&        gcc --load-pch foo myfile2.c
\&        gcc --load-pch foo myfile2.c
\&        ...
.Ve
.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
This option is deprecated and may be removed.
.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 built-in 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.
.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.
.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 bit-field 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 bit-field 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, bit-fields 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\-fconstant-cfstrings\fR" 4
.IX Item "-fconstant-cfstrings"
Enable the automatic creation of a CoreFoundation-type constant string
whenever a special builtin \f(CW\*(C`_\|_builtin_\|_CFStringMakeConstantString\*(C'\fR
is called on a literal string.  (\s-1APPLE\s0 \s-1ONLY\s0)
.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.
.Ip "\fB\-fpascal-strings\fR" 4
.IX Item "-fpascal-strings"
Allow Pascal-style string literals to be constructed.  (\s-1APPLE\s0 \s-1ONLY\s0)
.Ip "\fB\-fcoalesce\fR" 4
.IX Item "-fcoalesce"
Coalesce duplicated functions and data. The linker will discard all
but one, saving space.  Enabled by default. (\s-1APPLE\s0 \s-1ONLY\s0)
.Ip "\fB\-fweak-coalesced\fR" 4
.IX Item "-fweak-coalesced"
Use the new \s-1OS\s0 X \*(L"weak_definitions\*(R" section attribute for coalesced items.
A single \*(L"normal\*(R" definition will be chosen by the linker over any number
of weakly-coalesced ones.  (\s-1APPLE\s0 \s-1ONLY\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\-fno-const-strings\fR" 4
.IX Item "-fno-const-strings"
Give string constants type \f(CW\*(C`char *\*(C'\fR instead of type \f(CW\*(C`const
char *\*(C'\fR.  By default, G++ uses type \f(CW\*(C`const char *\*(C'\fR as required by
the standard.  Even if you use \fB\-fno-const-strings\fR, you cannot
actually modify the value of a string constant, unless you also use
\&\fB\-fwritable-strings\fR.
.Sp
This option might be removed in a future release of G++.  For maximum
portability, you should structure your code so that it works with
string constants that have type \f(CW\*(C`const char *\*(C'\fR.
.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 \fB#pragma interface\fR and \fBimplementation\fR to apply to
template instantiation; 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 \fB\-fexternal-templates\fR, 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 \fB\-ffor-scope\fR 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 \fB\-fno-for-scope\fR 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 G++, 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\-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\-findirect-virtual-calls\fR" 4
.IX Item "-findirect-virtual-calls"
Do not make direct calls to virtual functions; instead, always
go through the vtable. (\s-1APPLE\s0 \s-1ONLY\s0)
.Ip "\fB\-fapple-kext\fR" 4
.IX Item "-fapple-kext"
Alter vtables, destructors, and other implementation details to more
closely resemble the \s-1GCC\s0 2.95 \s-1ABI\s0.  This is to make kernel extensions
loadable by Darwin kernels built using older compilers, and is required
to build any Darwin kernel extension.  (\s-1APPLE\s0 \s-1ONLY\s0)
.Ip "\fB\-fcoalesce-templates\fR" 4
.IX Item "-fcoalesce-templates"
Mark instantiated templates as \*(L"coalesced\*(R": the linker will discard
all but one, thus saving space. (\s-1APPLE\s0 \s-1ONLY\s0)
.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-nonansi-builtins\fR" 4
.IX Item "-fno-nonansi-builtins"
Disable built-in declarations of functions that are not mandated by
\&\s-1ANSI/ISO\s0 C.  These include \f(CW\*(C`ffs\*(C'\fR, \f(CW\*(C`alloca\*(C'\fR, \f(CW\*(C`_exit\*(C'\fR,
\&\f(CW\*(C`index\*(C'\fR, \f(CW\*(C`bzero\*(C'\fR, \f(CW\*(C`conjf\*(C'\fR, and other related functions.
.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 at link time.  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\-fstats\fR" 4
.IX Item "-fstats"
Emit statistics about front-end processing at the end of the compilation.
This information is generally only useful to the G++ development team.
.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.
This option is not supported on Mac \s-1OS\s0 X.
.Ip "\fB\-fvtable-gc\fR" 4
.IX Item "-fvtable-gc"
Emit special relocations for vtables and virtual function references
so that the linker can identify unused virtual functions and zero out
vtable slots that refer to them.  This is most useful with
\&\fB\-ffunction-sections\fR and \fB\-Wl,\-\-gc-sections\fR, in order to
also discard the functions themselves.
.Sp
This optimization requires \s-1GNU\s0 as and \s-1GNU\s0 ld.  Not all systems support
this option.  \fB\-Wl,\-\-gc-sections\fR is ignored without \fB\-static\fR.
.Ip "\fB\-fno-weak\fR" 4
.IX Item "-fno-weak"
Do not use weak symbol support, even if it is provided by the linker.
By default, G++ will use weak symbols if they are available.  This
option exists only for testing, and should not be used by end-users;
it will result in inferior code and has no benefits.  This option may
be removed in a future release of G++.
.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\fR (\*(C+ only)" 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\fR (\*(C+ only)" 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\fR (\*(C+ only)" 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++\fR (\*(C+ only)" 4
.IX Item "-Weffc++ ( only)"
Warn about violations of the following style guidelines from Scott Meyers'
\&\fIEffective \*(C+\fR book:
.RS 4
.Ip "\(bu" 4
Item 11:  Define a copy constructor and an assignment operator for classes
with dynamically allocated memory.
.Ip "\(bu" 4
Item 12:  Prefer initialization to assignment in constructors.
.Ip "\(bu" 4
Item 14:  Make destructors virtual in base classes.
.Ip "\(bu" 4
Item 15:  Have \f(CW\*(C`operator=\*(C'\fR return a reference to \f(CW\*(C`*this\*(C'\fR.
.Ip "\(bu" 4
Item 23:  Don't try to return a reference when you must return an object.
.RE
.RS 4
.Sp
and about violations of the following style guidelines from Scott Meyers'
\&\fIMore Effective \*(C+\fR book:
.RS 4
.RE
.Ip "\(bu" 4
Item 6:  Distinguish between prefix and postfix forms of increment and
decrement operators.
.Ip "\(bu" 4
Item 7:  Never overload \f(CW\*(C`&&\*(C'\fR, \f(CW\*(C`||\*(C'\fR, or \f(CW\*(C`,\*(C'\fR.
.RE
.RS 4
.Sp
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.
.RE
.Ip "\fB\-Wno-deprecated\fR (\*(C+ only)" 4
.IX Item "-Wno-deprecated ( only)"
Do not warn about usage of deprecated features.  
.Ip "\fB\-Wno-non-template-friend\fR (\*(C+ only)" 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 (i.e.,
\&\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\fR (\*(C+ only)" 4
.IX Item "-Wold-style-cast ( only)"
Warn if an old-style (C-style) cast to a non-void type 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, and much easier to grep for.
.Ip "\fB\-Woverloaded-virtual\fR (\*(C+ only)" 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\fR (\*(C+ only)" 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\fR (\*(C+ only)" 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\fR (\*(C+ only)" 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 Controlling Objective-C Dialect"
.IX Subsection "Options Controlling Objective-C Dialect"
This section describes the command-line options that are only meaningful
for Objective-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`some_class.m\*(C'\fR like this:
.PP
.Vb 1
\&        gcc -g -fgnu-runtime -O -c some_class.m
.Ve
In this example, only \fB\-fgnu-runtime\fR is an option meant only for
Objective-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 Objective-C
programs:
.Ip "\fB\-fconstant-string-class=\fR\fIclass-name\fR" 4
.IX Item "-fconstant-string-class=class-name"
Use \fIclass-name\fR as the name of the class to instantiate for each
literal string specified with the syntax \f(CW\*(C`@"..."\*(C'\fR.  The default
class name is \f(CW\*(C`NXConstantString\*(C'\fR.
.Ip "\fB\-fgnu-runtime\fR" 4
.IX Item "-fgnu-runtime"
Generate object code compatible with the standard \s-1GNU\s0 Objective-C
runtime.  This is the default for most types of systems.
.Ip "\fB\-fnext-runtime\fR" 4
.IX Item "-fnext-runtime"
Generate output compatible with the NeXT runtime.  This is the default
for NeXT-based systems, including Darwin and Mac \s-1OS\s0 X.
.Ip "\fB\-gen-decls\fR" 4
.IX Item "-gen-decls"
Dump interface declarations for all classes seen in the source file to a
file named \fI\fIsourcename\fI.decl\fR.
.Ip "\fB\-Wno-protocol\fR" 4
.IX Item "-Wno-protocol"
Do not warn if methods required by a protocol are not implemented
in the class adopting it.
.Ip "\fB\-Wselector\fR" 4
.IX Item "-Wselector"
Warn if a selector has multiple methods of different types defined.
.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 \fBg++\fR 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
behavior.
.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 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
The following options control the amount and kinds of warnings produced
by \s-1GCC\s0; for further, language-specific options also refer to
\&\f(CW@ref\fR{\*(C+ Dialect Options} and \f(CW@ref\fR{Objective-C Dialect Options}.
.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.
.Sp
Where the standard specified with \fB\-std\fR represents a \s-1GNU\s0
extended dialect of C, such as \fBgnu89\fR or \fBgnu99\fR, there is a
corresponding \fIbase standard\fR, the version of \s-1ISO\s0 C on which the \s-1GNU\s0
extended dialect is based.  Warnings from \fB\-pedantic\fR are given
where they are required by the base standard.  (It would not make sense
for such warnings to be given only for features not in the specified \s-1GNU\s0
C dialect, since by definition the \s-1GNU\s0 dialects of C include all
features the compiler supports with the given option, and there would be
nothing to warn about.)
.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\-Wno-#warnings\fR" 4
.IX Item "-Wno-#warnings"
Inhibit warning messages issued by \fB#warning\fR.
.Ip "\fB\-Wpragma-once\fR" 4
.IX Item "-Wpragma-once"
Warn about the use of \fB#pragma once\fR.  (\s-1APPLE\s0 \s-1ONLY\s0)
.Ip "\fB\-Wextra-tokens\fR" 4
.IX Item "-Wextra-tokens"
Warn about extra tokens at the end of prepreprocessor directives.  (\s-1APPLE\s0 \s-1ONLY\s0)
.Ip "\fB\-Wnewline-eof\fR" 4
.IX Item "-Wnewline-eof"
Warn about files missing a newline at the end of the file.  (\s-1APPLE\s0 \s-1ONLY\s0)
.Ip "\fB\-Wno-altivec-long-deprecated\fR" 4
.IX Item "-Wno-altivec-long-deprecated"
Do not warn about the use of the deprecated 'long' keyword in
AltiVec data types.  (\s-1APPLE\s0 \s-1ONLY\s0)
.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.
.Sp
Where the unused arguments lie between used arguments that are
specified with \fB$\fR operand number specifications, normally
warnings are still given, since the implementation could not know what
type to pass to \f(CW\*(C`va_arg\*(C'\fR to skip the unused arguments.  However,
in the case of \f(CW\*(C`scanf\*(C'\fR formats, this option will suppress the
warning if the unused arguments are all pointers, since the Single
Unix Specification says that such unused arguments are allowed.
.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-declaration\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\-Wmissing-braces\fR" 4
.IX Item "-Wmissing-braces"
Warn if an aggregate or union initializer is not fully bracketed.  In
the following example, the initializer for \fBa\fR is not fully
bracketed, but that for \fBb\fR is fully bracketed.
.Sp
.Vb 2
\&        int a[2][2] = { 0, 1, 2, 3 };
\&        int b[2][2] = { { 0, 1 }, { 2, 3 } };
.Ve
.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-1GCC\s0 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
The C standard is worded confusingly, therefore there is some debate
over the precise meaning of the sequence point rules in subtle cases.
Links to discussions of the problem, including proposed formal
definitions, may be found on our readings page, at
<\fBhttp://gcc.gnu.org/readings.html\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\fR (\*(C+ only)" 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\-Wmost\fR" 4
.IX Item "-Wmost"
This is equivalent to \-Wall \-Wno-parentheses. (\s-1APPLE\s0 \s-1ONLY\s0)
.Ip "\fB\-Wdiv-by-zero\fR" 4
.IX Item "-Wdiv-by-zero"
Warn about compile-time integer division by zero.  This is default.  To
inhibit the warning messages, use \fB\-Wno-div-by-zero\fR.  Floating
point division by zero is not warned about, as it can be a legitimate
way of obtaining infinities and NaNs.
.Ip "\fB\-Wmultichar\fR" 4
.IX Item "-Wmultichar"
Warn if a multicharacter constant (\fB'\s-1FOOF\s0'\fR) is used.  This is
default.  To inhibit the warning messages, use \fB\-Wno-multichar\fR.
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\-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\fR (C only)" 4
.IX Item "-Wtraditional (C only)"
Warn about certain constructs that behave differently in traditional and
\&\s-1ISO\s0 C.  Also warn about \s-1ISO\s0 C constructs that have no traditional C
equivalent, and/or problematic constructs which should be avoided.
.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 recognize \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 \fBU\fR integer constant suffix, or the \fBF\fR or \fBL\fR floating point
constant suffixes.  (Traditional C does support the \fBL\fR suffix on integer
constants.)  Note, these suffixes appear in macros defined in the system
headers of most modern systems, e.g. the \fB_MIN\fR/\fB_MAX\fR macros in \f(CW\*(C`<limits.h>\*(C'\fR.
Use of these macros in user code might normally lead to spurious
warnings, however gcc's integrated preprocessor has enough context to
avoid warning in these cases.
.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.
.Ip "\(bu" 4
Conversions by prototypes between fixed/floating point values and vice
versa.  The absence of these prototypes when compiling with traditional
C would cause serious problems.  This is a subset of the possible
conversion warnings, for the full set use \fB\-Wconversion\fR.
.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, parameter or
global variable or whenever a built-in function is shadowed.
.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\fR (C only)" 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"
When compiling C, 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; when compiling \*(C+, warn about the
deprecated conversion from string constants to \f(CW\*(C`char *\*(C'\fR.
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\fR (C only)" 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\fR (C only)" 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\-Wno-deprecated-declarations\fR" 4
.IX Item "-Wno-deprecated-declarations"
Do not warn about uses of functions, variables, and types marked as
deprecated by using the \f(CW\*(C`deprecated\*(C'\fR attribute.
(@pxref{Function Attributes}, \f(CW@pxref\fR{Variable Attributes},
\&\f(CW@pxref\fR{Type Attributes}.)
.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\fR (C only)" 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 behavior 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\-Wno-long-double\fR" 4
.IX Item "-Wno-long-double"
Inhibit warning if the \fBlong double\fR type is used. (\s-1APPLE\s0 \s-1ONLY\s0)
.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 or \fB\-gstabs\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.
.Sp
(Other debug formats, such as \fB\-gcoff\fR, are not supported in
Darwin or Mac \s-1OS\s0 X.)
.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"
.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\-ftime-report\fR" 4
.IX Item "-ftime-report"
Makes the compiler print some statistics about the time consumed by each
pass when it finishes.
.Ip "\fB\-fmem-report\fR" 4
.IX Item "-fmem-report"
Makes the compiler print some statistics about permanent memory
allocation when it finishes.
.Ip "\fB\-fprofile-arcs\fR" 4
.IX Item "-fprofile-arcs"
Instrument \fIarcs\fR during compilation to generate coverage data
or for profile-directed block ordering.  During execution the program
records how many times each branch is executed and how many times it is
taken.  When the compiled program exits it saves this data to a file
called \fI\fIsourcename\fI.da\fR for each source file.
.Sp
For profile-directed block ordering, compile the program with
\&\fB\-fprofile-arcs\fR plus optimization and code generation options,
generate the arc profile information by running the program on a
selected workload, and then compile the program again with the same
optimization and code generation options plus
\&\fB\-fbranch-probabilities\fR.
.Sp
The other use of \fB\-fprofile-arcs\fR is for use with \f(CW\*(C`gcov\*(C'\fR,
when it is used with the \fB\-ftest-coverage\fR option.  \s-1GCC\s0
supports two methods of determining code coverage: the options that
support \f(CW\*(C`gcov\*(C'\fR, and options \fB\-a\fR and \fB\-ax\fR, which
write information to text files.  The options that support \f(CW\*(C`gcov\*(C'\fR
do not need to instrument every arc in the program, so a program compiled
with them runs faster than a program 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 and \fB\-ax\fR.
.Sp
With \fB\-fprofile-arcs\fR, 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
This option makes it possible to estimate branch probabilities and to
calculate basic block execution counts.  In general, basic block
execution counts as provided by \fB\-a\fR do not give enough
information to estimate all 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.
.RE
.RS 4
.Sp
Use \fB\-ftest-coverage\fR with \fB\-fprofile-arcs\fR; the latter
option adds instrumentation to the program, which then writes
execution counts to another data file:
.RS 4
.RE
.Ip "\fIsourcename\fR\fB.da\fR" 4
.IX Item "sourcename.da"
Runtime arc execution counts, used in conjunction with the arc
information in the file \f(CW\*(C`\f(CIsourcename\f(CW.bbg\*(C'\fR.
.RE
.RS 4
.Sp
Coverage data will map better to the source files if
\&\fB\-ftest-coverage\fR is used without optimization.
.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.14.bp\fR.
.Ip "\fBB\fR" 4
.IX Item "B"
Dump after block reordering, to \fI\fIfile\fI.29.bbro\fR.
.Ip "\fBc\fR" 4
.IX Item "c"
Dump after instruction combination, to the file \fI\fIfile\fI.16.combine\fR.
.Ip "\fBC\fR" 4
.IX Item "C"
Dump after the first if conversion, to the file \fI\fIfile\fI.17.ce\fR.
.Ip "\fBd\fR" 4
.IX Item "d"
Dump after delayed branch scheduling, to \fI\fIfile\fI.31.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.04.ssa\fR and
\&\fI\fIfile\fI.07.ussa\fR.
.Ip "\fBE\fR" 4
.IX Item "E"
Dump after the second if conversion, to \fI\fIfile\fI.26.ce2\fR.
.Ip "\fBf\fR" 4
.IX Item "f"
Dump after life analysis, to \fI\fIfile\fI.15.life\fR.
.Ip "\fBF\fR" 4
.IX Item "F"
Dump after purging \f(CW\*(C`ADDRESSOF\*(C'\fR codes, to \fI\fIfile\fI.09.addressof\fR.
.Ip "\fBg\fR" 4
.IX Item "g"
Dump after global register allocation, to \fI\fIfile\fI.21.greg\fR.
.Ip "\fBh\fR" 4
.IX Item "h"
Dump after finalization of \s-1EH\s0 handling code, to \fI\fIfile\fI.02.eh\fR.
.Ip "\fBk\fR" 4
.IX Item "k"
Dump after reg-to-stack conversion, to \fI\fIfile\fI.28.stack\fR.
.Ip "\fBo\fR" 4
.IX Item "o"
Dump after post-reload optimizations, to \fI\fIfile\fI.22.postreload\fR.
.Ip "\fBG\fR" 4
.IX Item "G"
Dump after \s-1GCSE\s0, to \fI\fIfile\fI.10.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.03.jump\fR.
.Ip "\fBk\fR" 4
.IX Item "k"
Dump after conversion from registers to stack, to \fI\fIfile\fI.32.stack\fR.
.Ip "\fBl\fR" 4
.IX Item "l"
Dump after local register allocation, to \fI\fIfile\fI.20.lreg\fR.
.Ip "\fBL\fR" 4
.IX Item "L"
Dump after loop optimization, to \fI\fIfile\fI.11.loop\fR.
.Ip "\fBM\fR" 4
.IX Item "M"
Dump after performing the machine dependent reorganisation pass, to
\&\fI\fIfile\fI.30.mach\fR.
.Ip "\fBn\fR" 4
.IX Item "n"
Dump after register renumbering, to \fI\fIfile\fI.25.rnreg\fR.
.Ip "\fBN\fR" 4
.IX Item "N"
Dump after the register move pass, to \fI\fIfile\fI.18.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 scheduling pass, to \fI\fIfile\fI.27.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.08.cse\fR.
.Ip "\fBS\fR" 4
.IX Item "S"
Dump after the first scheduling pass, to \fI\fIfile\fI.19.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.12.cse2\fR.
.Ip "\fBw\fR" 4
.IX Item "w"
Dump after the second flow pass, to \fI\fIfile\fI.23.flow2\fR.
.Ip "\fBX\fR" 4
.IX Item "X"
Dump after \s-1SSA\s0 dead code elimination, to \fI\fIfile\fI.06.ssadce\fR.
.Ip "\fBz\fR" 4
.IX Item "z"
Dump after the peephole pass, to \fI\fIfile\fI.24.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 \fB\-d\fR 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 \fB\-g\fR.
.Ip "\fB\-fdump-translation-unit\fR (C and \*(C+ only)" 4
.IX Item "-fdump-translation-unit (C and  only)"
.PD 0
.Ip "\fB\-fdump-translation-unit-\fR\fIoptions\fR\fB \fR(C and \*(C+ only)" 4
.IX Item "-fdump-translation-unit-options (C and  only)"
.PD
Dump a representation of the tree structure for the entire translation
unit to a file.  The file name is made by appending \fI.tu\fR to the
source file name.  If the \fB-\fR\fIoptions\fR form is used, \fIoptions\fR
controls the details of the dump as described for the
\&\fB\-fdump-tree\fR options.
.Ip "\fB\-fdump-class-hierarchy\fR (\*(C+ only)" 4
.IX Item "-fdump-class-hierarchy ( only)"
.PD 0
.Ip "\fB\-fdump-class-hierarchy-\fR\fIoptions\fR\fB \fR(\*(C+ only)" 4
.IX Item "-fdump-class-hierarchy-options ( only)"
.PD
Dump a representation of each class's hierarchy and virtual function
table layout to a file.  The file name is made by appending \fI.class\fR
to the source file name.  If the \fB-\fR\fIoptions\fR form is used,
\&\fIoptions\fR controls the details of the dump as described for the
\&\fB\-fdump-tree\fR options.
.Ip "\fB\-fdump-tree-\fR\fIswitch\fR\fB \fR(\*(C+ only)" 4
.IX Item "-fdump-tree-switch ( only)"
.PD 0
.Ip "\fB\-fdump-tree-\fR\fIswitch\fR\fB-\fR\fIoptions\fR\fB \fR(\*(C+ only)" 4
.IX Item "-fdump-tree-switch-options ( only)"
.PD
Control the dumping at various stages of processing the intermediate
language tree to a file.  The file name is generated by appending a switch
specific suffix to the source file name.  If the \fB-\fR\fIoptions\fR
form is used, \fIoptions\fR is a list of \fB-\fR separated options that
control the details of the dump. Not all options are applicable to all
dumps, those which are not meaningful will be ignored. The following
options are available
.RS 4
.Ip "\fBaddress\fR" 4
.IX Item "address"
Print the address of each node.  Usually this is not meaningful as it
changes according to the environment and source file. Its primary use
is for tying up a dump file with a debug environment.
.Ip "\fBslim\fR" 4
.IX Item "slim"
Inhibit dumping of members of a scope or body of a function merely
because that scope has been reached. Only dump such items when they
are directly reachable by some other path.
.Ip "\fBall\fR" 4
.IX Item "all"
Turn on all options.
.RE
.RS 4
.Sp
The following tree dumps are possible:
.RS 4
.RE
.Ip "\fBoriginal\fR" 4
.IX Item "original"
Dump before any tree based optimization, to \fI\fIfile\fI.original\fR.
.Ip "\fBoptimized\fR" 4
.IX Item "optimized"
Dump after all tree based optimization, to \fI\fIfile\fI.optimized\fR.
.Ip "\fBinlined\fR" 4
.IX Item "inlined"
Dump after function inlining, to \fI\fIfile\fI.inlined\fR.
.RE
.RS 4
.RE
.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-multi-directory\fR" 4
.IX Item "-print-multi-directory"
Print the directory name corresponding to the multilib selected by any
other switches present in the command line.  This directory is supposed
to exist in \fB\s-1GCC_EXEC_PREFIX\s0\fR.
.Ip "\fB\-print-multi-lib\fR" 4
.IX Item "-print-multi-lib"
Print the mapping from multilib directory names to compiler switches
that enable them.  The directory name is separated from the switches by
\&\fB;\fR, and each switch starts with an \fB@} instead of the
\&\f(CB@samp\fB{-\fR, without spaces between multiple switches.  This is supposed to
ease shell-processing.
.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 <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 '/'.
.Ip "\fB\-dumpmachine\fR" 4
.IX Item "-dumpmachine"
Print the compiler's target machine (for example,
\&\fBi686\-pc-linux-gnu\fR)\-\-\-and don't do anything else.
.Ip "\fB\-dumpversion\fR" 4
.IX Item "-dumpversion"
Print the compiler version (for example, \fB3.0\fR)\-\-\-and don't do
anything else.
.Ip "\fB\-dumpspecs\fR" 4
.IX Item "-dumpspecs"
Print the compiler's built-in specs\-\-\-and don't do anything else.  (This
is used when \s-1GCC\s0 itself is being built.)  
.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
With \fB\-O\fR, the compiler tries to reduce code size and execution
time, without performing any optimizations that take a great deal of
compilation 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.
.Sp
In Apple's version of \s-1GCC\s0, \fB\-fstrict-aliasing\fR,
\&\fB\-freorder-blocks\fR, and \fB\-fsched-interblock\fR
are disabled by default when optimizing.
.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.
.Sp
Please note the warning under \fB\-fgcse\fR about
invoking \fB\-O2\fR on programs that use computed gotos.
.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 \s-1VAX\s0, 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 \fIn\fR is 600.
Increasing this value can result in more inlined code at
the cost of compilation time and memory consumption.  Decreasing usually makes
the compilation faster and less code will be inlined (which presumably
means slower programs).  This option is particularly useful for programs that
use inlining heavily such as those based on recursive templates with \*(C+.
.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\-fmerge-constants\fR" 4
.IX Item "-fmerge-constants"
Attempt to merge identical constants (string constants and floating point
constants) accross compilation units.
.Sp
This option is default for optimized compilation if assembler and linker
support it.  Use \fB\-fno-merge-constants\fR to inhibit this behavior.
.Ip "\fB\-fmerge-all-constants\fR" 4
.IX Item "-fmerge-all-constants"
Attempt to merge identical constants and identical variables.
.Sp
This option implies \fB\-fmerge-constants\fR.  In addition to
\&\fB\-fmerge-constants\fR this considers e.g. even constant initialized
arrays or initialized constant variables with integral or floating point
types.  Languages like C or \*(C+ require each non-automatic variable to
have distinct location, so using this option will result in non-conforming
behavior.
.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 \f(CW\*(C`_\|_FAST_MATH_\|_\*(C'\fR 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.
.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.  When used at link-time, it may include libraries
or startup files that change the default \s-1FPU\s0 control word or other
similar optimizations.
.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.
.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.
.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.
.PP
Not all of the optimizations performed by \s-1GCC\s0 have \fB\-f\fR options
to control them.
.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.
.Sp
\&\fINote:\fR When compiling a program using computed gotos, a \s-1GCC\s0
extension, you may get better runtime performance if you disable
the global common subexpression elmination pass by adding
\&\fB\-fno-gcse\fR to the command line.
.Ip "\fB\-fgcse-lm\fR" 4
.IX Item "-fgcse-lm"
When \fB\-fgcse-lm\fR is enabled, global common subexpression elimination will
attempt to move loads which are only killed by stores into themselves.  This
allows a loop containing a load/store sequence to be changed to a load outside
the loop, and a copy/store within the loop.
.Ip "\fB\-fgcse-sm\fR" 4
.IX Item "-fgcse-sm"
When \fB\-fgcse-sm\fR is enabled, A store motion pass is run after global common
subexpression elimination.  This pass will attempt to move stores out of loops.
When used in conjunction with \fB\-fgcse-lm\fR, loops containing a load/store sequence
can be changed to a load before the loop and a store after the loop.
.Ip "\fB\-fdelete-null-pointer-checks\fR" 4
.IX Item "-fdelete-null-pointer-checks"
Use global dataflow analysis to identify and eliminate useless checks
for null pointers.  The compiler assumes that dereferencing a null
pointer would have halted the program.  If a pointer is checked after
it has already been dereferenced, it cannot be null.
.Sp
In some environments, this assumption is not true, and programs can
safely dereference null pointers.  Use
\&\fB\-fno-delete-null-pointer-checks\fR to disable this optimization
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"
Unroll loops whose number of iterations can be determined at compile
time or upon entry to the loop.  \fB\-funroll-loops\fR implies both
\&\fB\-fstrength-reduce\fR and \fB\-frerun-cse-after-loop\fR.  This
option makes code larger, and may or may not make it run faster.
.Ip "\fB\-funroll-all-loops\fR" 4
.IX Item "-funroll-all-loops"
Unroll all loops, even if their number of iterations is uncertain when
the loop is entered.  This usually makes programs run more slowly.
\&\fB\-funroll-all-loops\fR implies the same options as
\&\fB\-funroll-loops\fR,
.Ip "\fB\-fprefetch-loop-arrays\fR" 4
.IX Item "-fprefetch-loop-arrays"
If supported by the target machine, generate instructions to prefetch
memory to improve the performance of loops that access large arrays.
.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"
.PD 0
.Ip "\fB\-fno-peephole2\fR" 4
.IX Item "-fno-peephole2"
.PD
Disable any machine-specific peephole optimizations.  The difference
between \fB\-fno-peephole\fR and \fB\-fno-peephole2\fR is in how they
are implemented in the compiler; some targets use one, some use the
other, a few use both.
.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
the number of times each branch was taken.  When the program
compiled with \fB\-fprofile-arcs\fR exits it saves arc execution
counts to a file called \fI\fIsourcename\fI.da\fR for each source
file  The information in this data file is very dependent on the
structure of the generated code, so you must use the same source code
and the same optimization options for both compilations.
.Sp
With \fB\-fbranch-probabilities\fR, \s-1GCC\s0 puts a \fB\s-1REG_EXEC_COUNT\s0\fR
note on the first instruction of each basic block, and a
\&\fB\s-1REG_BR_PROB\s0\fR note on each \fB\s-1JUMP_INSN\s0\fR and \fB\s-1CALL_INSN\s0\fR.
These can be used to improve optimization.  Currently, they are only
used in one place: in \fIreorg.c\fR, instead of guessing which path a
branch is mostly to take, the \fB\s-1REG_BR_PROB\s0\fR values are used to
exactly determine which path is taken more often.
.Ip "\fB\-fno-guess-branch-probability\fR" 4
.IX Item "-fno-guess-branch-probability"
Do not guess branch probabilities using a randomized model.
.Sp
Sometimes gcc will opt to use a randomized model to guess branch
probabilities, when none are available from either profiling feedback
(\fB\-fprofile-arcs\fR) or \fB_\|_builtin_expect\fR.  This means that
different runs of the compiler on the same program may produce different
object code.
.Sp
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
Every language that wishes to perform language-specific alias analysis
should define a function that computes, given an \f(CW\*(C`tree\*(C'\fR
node, an alias set for the node.  Nodes in different alias sets are not
allowed to alias.  For an example, see the C front-end function
\&\f(CW\*(C`c_get_alias_set\*(C'\fR.
.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.
.Sp
This option does not work on Mac \s-1OS\s0 X.
.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.
.Sp
This option does not work on Mac \s-1OS\s0 X.
.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.
.Sp
This option does not work on Mac \s-1OS\s0 X.
.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.  Users should not
specify this option, since it is not yet ready for production use.
.Ip "\fB\-fssa-ccp\fR" 4
.IX Item "-fssa-ccp"
Perform Sparse Conditional Constant Propagation in \s-1SSA\s0 form.  Requires
\&\fB\-fssa\fR.  Like \fB\-fssa\fR, this is an experimental feature.
.Ip "\fB\-fssa-dce\fR" 4
.IX Item "-fssa-dce"
Perform aggressive 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 dependencies in scheduled code by making use
of registers left over after register allocation.  This optimization
will most benefit processors with lots of registers.  It can, however,
make debugging impossible, since variables will no longer stay in
a ``home register''.
.Ip "\fB\-fno-cprop-registers\fR" 4
.IX Item "-fno-cprop-registers"
After register allocation and post-register allocation instruction splitting,
we perform a copy-propagation pass to try to reduce scheduling dependencies
and occasionally eliminate the copy.
.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 an integer.  The allowable choices for
\&\fIname\fR are given in the following table:
.RS 4
.Ip "\fBmax-delay-slot-insn-search\fR" 4
.IX Item "max-delay-slot-insn-search"
The maximum number of instructions to consider when looking for an
instruction to fill a delay slot.  If more than this arbitrary number of
instructions is searched, the time savings from filling the delay slot
will be minimal so stop searching.  Increasing values mean more
aggressive optimization, making the compile time increase with probably
small improvement in executable run time.
.Ip "\fBmax-delay-slot-live-search\fR" 4
.IX Item "max-delay-slot-live-search"
When trying to fill delay slots, the maximum number of instructions to
consider when searching for a block with valid live register
information.  Increasing this arbitrarily chosen value means more
aggressive optimization, increasing the compile time.  This parameter
should be removed when the delay slot code is rewritten to maintain the
control-flow graph.
.Ip "\fBmax-gcse-memory\fR" 4
.IX Item "max-gcse-memory"
The approximate maximum amount of memory that will be allocated in
order to perform the global common subexpression elimination
optimization.  If more memory than specified is required, the
optimization will not be done.
.Ip "\fBmax-gcse-passes\fR" 4
.IX Item "max-gcse-passes"
The maximum number of passes of \s-1GCSE\s0 to run.
.Ip "\fBmax-pending-list-length\fR" 4
.IX Item "max-pending-list-length"
The maximum number of pending dependencies scheduling will allow
before flushing the current state and starting over.  Large functions
with few branches or calls can create excessively large lists which
needlessly consume memory and resources.
.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.
.PP
You can use \fB\-Wp,\fR\fIoption\fR to bypass the compiler driver
and pass \fIoption\fR directly through to the preprocessor.  If
\&\fIoption\fR contains commas, it is split into multiple options at the
commas.  However, many options are modified, translated or interpreted
by the compiler driver before being passed to the preprocessor, and
\&\fB\-Wp\fR forcibly bypasses this phase.  The preprocessor's direct
interface is undocumented and subject to change, so whenever possible
you should avoid using \fB\-Wp\fR and let the driver handle the
options instead.
.Ip "\fB\-D\fR \fIname\fR" 4
.IX Item "-D name"
Predefine \fIname\fR as a macro, with definition \f(CW\*(C`1\*(C'\fR.
.Ip "\fB\-D\fR \fIname\fR\fB=\fR\fIdefinition\fR" 4
.IX Item "-D name=definition"
Predefine \fIname\fR as a macro, with definition \fIdefinition\fR.
There are no restrictions on the contents of \fIdefinition\fR, but if
you are invoking the preprocessor from a shell or shell-like program you
may need to use the shell's quoting syntax to protect characters such as
spaces that have a meaning in the shell syntax.
.Sp
If you wish to define a function-like macro on the command line, write
its argument list with surrounding parentheses before the equals sign
(if any).  Parentheses are meaningful to most shells, so you will need
to quote the option.  With \fBsh\fR and \fBcsh\fR,
\&\fB\-D'\fR\fIname\fR\fB(\fR\fIargs...\fR\fB)=\fR\fIdefinition\fR\fB'\fR works.
.Sp
\&\fB\-D\fR and \fB\-U\fR options are processed in the order they
are given on the command line.  All \fB\-imacros\fR \fIfile\fR and
\&\fB\-include\fR \fIfile\fR options are processed after all
\&\fB\-D\fR and \fB\-U\fR options.
.Ip "\fB\-U\fR \fIname\fR" 4
.IX Item "-U name"
Cancel any previous definition of \fIname\fR, either built in or
provided with a \fB\-D\fR option.
.Ip "\fB\-undef\fR" 4
.IX Item "-undef"
Do not predefine any system-specific macros.  The common predefined
macros remain defined.
.Ip "\fB\-I\fR \fIdir\fR" 4
.IX Item "-I dir"
Add the directory \fIdir\fR to the list of directories to be searched
for header files.
Directories named by \fB\-I\fR are searched before the standard
system include directories.
.Sp
It is dangerous to specify a standard system include directory in an
\&\fB\-I\fR option.  This defeats the special treatment of system
headers
\&.  It can also defeat the repairs to buggy system headers which \s-1GCC\s0
makes when it is installed.
.Ip "\fB\-o\fR \fIfile\fR" 4
.IX Item "-o file"
Write output to \fIfile\fR.  This is the same as specifying \fIfile\fR
as the second non-option argument to \fBcpp\fR.  \fBgcc\fR has a
different interpretation of a second non-option argument, so you must
use \fB\-o\fR to specify the output file.
.Ip "\fB\-Wall\fR" 4
.IX Item "-Wall"
Turns on all optional warnings which are desirable for normal code.  At
present this is \fB\-Wcomment\fR and \fB\-Wtrigraphs\fR.  Note that
many of the preprocessor's warnings are on by default and have no
options to control them.
.Ip "\fB\-Wcomment\fR" 4
.IX Item "-Wcomment"
.PD 0
.Ip "\fB\-Wcomments\fR" 4
.IX Item "-Wcomments"
.PD
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.
(Both forms have the same effect.)
.Ip "\fB\-Wtrigraphs\fR" 4
.IX Item "-Wtrigraphs"
Warn if any trigraphs are encountered.  This option used to take effect
only if \fB\-trigraphs\fR was also specified, but now works
independently.  Warnings are not given for trigraphs within comments, as
they do not affect the meaning of the program.
.Ip "\fB\-Wtraditional\fR" 4
.IX Item "-Wtraditional"
Warn about certain constructs that behave differently in traditional and
\&\s-1ISO\s0 C.  Also warn about \s-1ISO\s0 C constructs that have no traditional C
equivalent, and problematic constructs which should be avoided.
.Ip "\fB\-Wimport\fR" 4
.IX Item "-Wimport"
Warn the first time \fB#import\fR is used.
.Ip "\fB\-Wundef\fR" 4
.IX Item "-Wundef"
Warn whenever an identifier which is not a macro is encountered in an
\&\fB#if\fR directive, outside of \fBdefined\fR.  Such identifiers are
replaced with zero.
.Ip "\fB\-Werror\fR" 4
.IX Item "-Werror"
Make all warnings into hard errors.  Source code which triggers warnings
will be rejected.
.Ip "\fB\-Wsystem-headers\fR" 4
.IX Item "-Wsystem-headers"
Issue warnings for code in system headers.  These are normally unhelpful
in finding bugs in your own code, therefore suppressed.  If you are
responsible for the system library, you may want to see them.
.Ip "\fB\-w\fR" 4
.IX Item "-w"
Suppress all warnings, including those which \s-1GNU\s0 \s-1CPP\s0 issues by default.
.Ip "\fB\-pedantic\fR" 4
.IX Item "-pedantic"
Issue all the mandatory diagnostics listed in the C standard.  Some of
them are left out by default, since they trigger frequently on harmless
code.
.Ip "\fB\-pedantic-errors\fR" 4
.IX Item "-pedantic-errors"
Issue all the mandatory diagnostics, and make all mandatory diagnostics
into errors.  This includes mandatory diagnostics that \s-1GCC\s0 issues
without \fB\-pedantic\fR but treats as warnings.
.Ip "\fB\-M\fR" 4
.IX Item "-M"
Instead of outputting the result of preprocessing, output a rule
suitable for \fBmake\fR describing the dependencies of the main
source file.  The preprocessor outputs one \fBmake\fR rule containing
the object file name for that source file, a colon, and the names of all
the included files, including those coming from \fB\-include\fR or
\&\fB\-imacros\fR command line options.
.Sp
Unless specified explicitly (with \fB\-MT\fR or \fB\-MQ\fR), 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.
The rule has no commands.
.Sp
This option does not suppress the preprocessor's debug output, such as
\&\fB\-dM\fR.  To avoid mixing such debug output with the dependency
rules you should explicitly specify the dependency output file with
\&\fB\-MF\fR, or use an environment variable like
\&\fB\s-1DEPENDENCIES_OUTPUT\s0\fR.  Debug output
will still be sent to the regular output stream as normal.
.Sp
Passing \fB\-M\fR to the driver implies \fB\-E\fR.
.Ip "\fB\-MM\fR" 4
.IX Item "-MM"
Like \fB\-M\fR but do not mention header files that are found in
system header directories, nor header files that are included,
directly or indirectly, from such a header.
.Sp
This implies that the choice of angle brackets or double quotes in an
\&\fB#include\fR directive does not in itself determine whether that
header will appear in \fB\-MM\fR dependency output.  This is a
slight change in semantics from \s-1GCC\s0 versions 3.0 and earlier.
.Ip "\fB\-MF\fR \fIfile\fR" 4
.IX Item "-MF file"
@anchor{\-MF}
When used with \fB\-M\fR or \fB\-MM\fR, specifies a
file to write the dependencies to.  If no \fB\-MF\fR switch is given
the preprocessor sends the rules to the same place it would have sent
preprocessed output.
.Sp
When used with the driver options \fB\-MD\fR or \fB\-MMD\fR,
\&\fB\-MF\fR overrides the default dependency output file.
.Ip "\fB\-dependency-file\fR" 4
.IX Item "-dependency-file"
Like \fB\-MF\fR. (\s-1APPLE\s0 \s-1ONLY\s0)
.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 \fBmake\fR gives if you remove header
files without updating the \fIMakefile\fR to match.
.Sp
This is typical output:
.Sp
.Vb 1
\&        test.o: test.c test.h
.Ve
.Vb 1
\&        test.h:
.Ve
.Ip "\fB\-MT\fR \fItarget\fR" 4
.IX Item "-MT target"
Change the target of the rule emitted by dependency generation.  By
default \s-1CPP\s0 takes the name of the main input file, including any path,
deletes any file suffix such as \fB.c\fR, and appends the platform's
usual object suffix.  The result is the target.
.Sp
An \fB\-MT\fR option will set the target to be exactly the string you
specify.  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
For example, \fB\-MT\ '$(objpfx)foo.o'\fR might give
.Sp
.Vb 1
\&        $(objpfx)foo.o: foo.c
.Ve
.Ip "\fB\-MQ\fR \fItarget\fR" 4
.IX Item "-MQ target"
Same as \fB\-MT\fR, but it quotes any characters which are special to
Make.  \fB\-MQ\ '$(objpfx)foo.o'\fR gives
.Sp
.Vb 1
\&        $$(objpfx)foo.o: foo.c
.Ve
The default target is automatically quoted, as if it were given with
\&\fB\-MQ\fR.
.Ip "\fB\-MD\fR" 4
.IX Item "-MD"
\&\fB\-MD\fR is equivalent to \fB\-M \-MF\fR \fIfile\fR, except that
\&\fB\-E\fR is not implied.  The driver determines \fIfile\fR based on
whether an \fB\-o\fR option is given.  If it is, the driver uses its
argument but with a suffix of \fI.d\fR, otherwise it take the
basename of the input file and applies a \fI.d\fR suffix.
.Sp
If \fB\-MD\fR is used in conjunction with \fB\-E\fR, any
\&\fB\-o\fR switch is understood to specify the dependency output file
(but \f(CW@pxref\fR{\-MF}), but if used without \fB\-E\fR, each \fB\-o\fR
is understood to specify a target object file.
.Sp
Since \fB\-E\fR is not implied, \fB\-MD\fR can be used to generate
a dependency output file as a side-effect of the compilation process.
.Ip "\fB\-MMD\fR" 4
.IX Item "-MMD"
Like \fB\-MD\fR except mention only user header files, not system
\&\-header files.
.Ip "\fB\-x c\fR" 4
.IX Item "-x c"
.PD 0
.Ip "\fB\-x c++\fR" 4
.IX Item "-x c++"
.Ip "\fB\-x objective-c\fR" 4
.IX Item "-x objective-c"
.Ip "\fB\-x objective-c++\fR" 4
.IX Item "-x objective-c++"
.Ip "\fB\-x assembler-with-cpp\fR" 4
.IX Item "-x assembler-with-cpp"
.PD
Specify the source language: C, \*(C+, Objective-C, Objective-\*(C+, or assembly.  This has
nothing to do with standards conformance or extensions; it merely
selects which base syntax to expect.  If you give none of these options,
cpp will deduce the language from the extension of the source file:
\&\fB.c\fR, \fB.cc\fR, \fB.m\fR, \fB.mm\fR, or \fB.S\fR.  Some other common
extensions for \*(C+ and assembly are also recognized.  If cpp does not
recognize the extension, it will treat the file as C; this is the most
generic mode.
.Sp
\&\fBNote:\fR Previous versions of cpp accepted a \fB\-lang\fR option
which selected both the language and the standards conformance level.
This option has been removed, because it conflicts with the \fB\-l\fR
option.
.Ip "\fB\-std=\fR\fIstandard\fR" 4
.IX Item "-std=standard"
.PD 0
.Ip "\fB\-ansi\fR" 4
.IX Item "-ansi"
.PD
Specify the standard to which the code should conform.  Currently cpp
only knows about the standards for C; other language standards will be
added in the future.
.Sp
\&\fIstandard\fR
may be one of:
.RS 4
.if n .Ip "\f(CW""""iso9899:1990""""\fR" 4
.el .Ip "\f(CWiso9899:1990\fR" 4
.IX Item "iso9899:1990"
.PD 0
.if n .Ip "\f(CW""""c89""""\fR" 4
.el .Ip "\f(CWc89\fR" 4
.IX Item "c89"
.PD
The \s-1ISO\s0 C standard from 1990.  \fBc89\fR is the customary shorthand for
this version of the standard.
.Sp
The \fB\-ansi\fR option is equivalent to \fB\-std=c89\fR.
.if n .Ip "\f(CW""""iso9899:199409""""\fR" 4
.el .Ip "\f(CWiso9899:199409\fR" 4
.IX Item "iso9899:199409"
The 1990 C standard, as amended in 1994.
.if n .Ip "\f(CW""""iso9899:1999""""\fR" 4
.el .Ip "\f(CWiso9899:1999\fR" 4
.IX Item "iso9899:1999"
.PD 0
.if n .Ip "\f(CW""""c99""""\fR" 4
.el .Ip "\f(CWc99\fR" 4
.IX Item "c99"
.if n .Ip "\f(CW""""iso9899:199x""""\fR" 4
.el .Ip "\f(CWiso9899:199x\fR" 4
.IX Item "iso9899:199x"
.if n .Ip "\f(CW""""c9x""""\fR" 4
.el .Ip "\f(CWc9x\fR" 4
.IX Item "c9x"
.PD
The revised \s-1ISO\s0 C standard, published in December 1999.  Before
publication, this was known as C9X.
.if n .Ip "\f(CW""""gnu89""""\fR" 4
.el .Ip "\f(CWgnu89\fR" 4
.IX Item "gnu89"
The 1990 C standard plus \s-1GNU\s0 extensions.  This is the default.
.if n .Ip "\f(CW""""gnu99""""\fR" 4
.el .Ip "\f(CWgnu99\fR" 4
.IX Item "gnu99"
.PD 0
.if n .Ip "\f(CW""""gnu9x""""\fR" 4
.el .Ip "\f(CWgnu9x\fR" 4
.IX Item "gnu9x"
.PD
The 1999 C standard plus \s-1GNU\s0 extensions.
.RE
.RS 4
.RE
.Ip "\fB\-I-\fR" 4
.IX Item "-I-"
Split the include path.  Any directories specified with \fB\-I\fR
options before \fB\-I-\fR are searched only for headers requested with
\&\f(CW\*(C`#include\ "\f(CIfile\f(CW"\*(C'\fR; they are not searched for
\&\f(CW\*(C`#include\ <\f(CIfile\f(CW>\*(C'\fR.  If additional directories are
specified with \fB\-I\fR options after the \fB\-I-\fR, those
directories are searched for all \fB#include\fR directives.
.Sp
In addition, \fB\-I-\fR inhibits the use of the directory of the current
file directory as the first search directory for \f(CW\*(C`#include\ "\f(CIfile\f(CW"\*(C'\fR.
.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 directory of the current file, if appropriate) are searched.
.Ip "\fB\-nostdinc++\fR" 4
.IX Item "-nostdinc++"
Do not search for header files in the \*(C+\-specific standard directories,
but do still search the other standard directories.  (This option is
used when building the \*(C+ library.)
.Ip "\fB\-include\fR \fIfile\fR" 4
.IX Item "-include file"
Process \fIfile\fR as if \f(CW\*(C`#include "file"\*(C'\fR appeared as the first
line of the primary source file.  However, the first directory searched
for \fIfile\fR is the preprocessor's working directory \fIinstead of\fR
the directory containing the main source file.  If not found there, it
is searched for in the remainder of the \f(CW\*(C`#include "..."\*(C'\fR search
chain as normal.
.Sp
If multiple \fB\-include\fR options are given, the files are included
in the order they appear on the command line.
.Ip "\fB\-imacros\fR \fIfile\fR" 4
.IX Item "-imacros file"
Exactly like \fB\-include\fR, except that any output produced by
scanning \fIfile\fR is thrown away.  Macros it defines remain defined.
This allows you to acquire all the macros from a header without also
processing its declarations.
.Sp
All files specified by \fB\-imacros\fR are processed before all files
specified by \fB\-include\fR.
.Ip "\fB\-idirafter\fR \fIdir\fR" 4
.IX Item "-idirafter dir"
Search \fIdir\fR for header files, but do it \fIafter\fR all
directories specified with \fB\-I\fR and the standard system directories
have been exhausted.  \fIdir\fR is treated as a system include directory.
.Ip "\fB\-iprefix\fR \fIprefix\fR" 4
.IX Item "-iprefix prefix"
Specify \fIprefix\fR as the prefix for subsequent \fB\-iwithprefix\fR
options.  If the prefix represents a directory, you should include the
final \fB/\fR.
.Ip "\fB\-iwithprefix\fR \fIdir\fR" 4
.IX Item "-iwithprefix dir"
.PD 0
.Ip "\fB\-iwithprefixbefore\fR \fIdir\fR" 4
.IX Item "-iwithprefixbefore dir"
.PD
Append \fIdir\fR to the prefix specified previously with
\&\fB\-iprefix\fR, and add the resulting directory to the include search
path.  \fB\-iwithprefixbefore\fR puts it in the same place \fB\-I\fR
would; \fB\-iwithprefix\fR puts it where \fB\-idirafter\fR would.
.Sp
Use of these options is discouraged.
.Ip "\fB\-isystem\fR \fIdir\fR" 4
.IX Item "-isystem dir"
Search \fIdir\fR for header files, after all directories specified by
\&\fB\-I\fR but before the standard system directories.  Mark it
as a system directory, so that it gets the same special treatment as
is applied to the standard system directories.
.Ip "\fB\-fpreprocessed\fR" 4
.IX Item "-fpreprocessed"
Indicate to the preprocessor that the input file has already been
preprocessed.  This suppresses things like macro expansion, trigraph
conversion, escaped newline splicing, and processing of most directives.
The preprocessor still recognizes and removes comments, so that you can
pass a file preprocessed with \fB\-C\fR to the compiler without
problems.  In this mode the integrated preprocessor is little more than
a tokenizer for the front ends.
.Sp
\&\fB\-fpreprocessed\fR is implicit if the input file has one of the
extensions \fB.i\fR, \fB.ii\fR or \fB.mi\fR.  These are the
extensions that \s-1GCC\s0 uses for preprocessed files created by
\&\fB\-save-temps\fR.
.Ip "\fB\-ftabstop=\fR\fIwidth\fR" 4
.IX Item "-ftabstop=width"
Set the distance between tab stops.  This helps the preprocessor report
correct column numbers in warnings or errors, even if tabs appear on the
line.  If the value is less than 1 or greater than 100, the option is
ignored.  The default is 8.
.Ip "\fB\-fno-show-column\fR" 4
.IX Item "-fno-show-column"
Do not print column numbers in diagnostics.  This may be necessary if
diagnostics are being scanned by a program that does not understand the
column numbers, such as \fBdejagnu\fR.
.Ip "\fB\-A\fR \fIpredicate\fR\fB=\fR\fIanswer\fR" 4
.IX Item "-A predicate=answer"
Make an assertion with the predicate \fIpredicate\fR and answer
\&\fIanswer\fR.  This form is preferred to the older form \fB\-A\fR
\&\fIpredicate\fR\fB(\fR\fIanswer\fR\fB)\fR, which is still supported, because
it does not use shell special characters.
.Ip "\fB\-A -\fR\fIpredicate\fR\fB=\fR\fIanswer\fR" 4
.IX Item "-A -predicate=answer"
Cancel an assertion with the predicate \fIpredicate\fR and answer
\&\fIanswer\fR.
.Ip "\fB\-A-\fR" 4
.IX Item "-A-"
Cancel all predefined assertions and all assertions preceding it on
the command line.  Also, undefine all predefined macros and all
macros preceding it on the command line.  (This is a historical wart and
may change in the future.)
.Ip "\fB\-dCHARS\fR" 4
.IX Item "-dCHARS"
\&\fI\s-1CHARS\s0\fR is a sequence of one or more of the following characters,
and must not be preceded by a space.  Other characters are interpreted
by the compiler proper, or reserved for future versions of \s-1GCC\s0, and so
are silently ignored.  If you specify characters whose behavior
conflicts, the result is undefined.
.RS 4
.Ip "\fBM\fR" 4
.IX Item "M"
Instead of the normal output, generate a list of \fB#define\fR
directives for all the macros defined during the execution of the
preprocessor, including predefined macros.  This gives you a way of
finding out what is predefined in your version of the preprocessor.
Assuming you have no file \fIfoo.h\fR, the command
.Sp
.Vb 1
\&        touch foo.h; cpp -dM foo.h
.Ve
will show all the predefined macros.
.Ip "\fBD\fR" 4
.IX Item "D"
Like \fBM\fR except in two respects: it does \fInot\fR include the
predefined macros, and it outputs \fIboth\fR the \fB#define\fR
directives and the result of preprocessing.  Both kinds of output go to
the standard output file.
.Ip "\fBN\fR" 4
.IX Item "N"
Like \fBD\fR, but emit only the macro names, not their expansions.
.Ip "\fBI\fR" 4
.IX Item "I"
Output \fB#include\fR directives in addition to the result of
preprocessing.
.RE
.RS 4
.RE
.Ip "\fB\-P\fR" 4
.IX Item "-P"
Inhibit generation of linemarkers in the output from the preprocessor.
This might be useful when running the preprocessor on something that is
not C code, and will be sent to a program which might be confused by the
linemarkers.
.Ip "\fB\-C\fR" 4
.IX Item "-C"
Do not discard comments.  All comments are passed through to the output
file, except for comments in processed directives, which are deleted
along with the directive.
.Sp
You should be prepared for side effects when using \fB\-C\fR; it
causes the preprocessor to treat comments as tokens in their own right.
For example, comments appearing at the start of what would be a
directive line have the effect of turning that line into an ordinary
source line, since the first token on the line is no longer a \fB#\fR.
.Ip "\fB\-gcc\fR" 4
.IX Item "-gcc"
Define the macros _\|_GNUC_\|_, _\|_GNUC_MINOR_\|_ and
_\|_GNUC_PATCHLEVEL_\|_.  These are defined automatically when you use
\&\fBgcc \-E\fR; you can turn them off in that case with
\&\fB\-no-gcc\fR.
.Ip "\fB\-traditional\fR" 4
.IX Item "-traditional"
Try to imitate the behavior of old-fashioned C, as opposed to \s-1ISO\s0
C.
.Ip "\fB\-trigraphs\fR" 4
.IX Item "-trigraphs"
Process 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 trigraphs and their replacements are
.Sp
.Vb 2
\&        Trigraph:       ??(  ??)  ??<  ??>  ??=  ??/  ??'  ??!  ??-
\&        Replacement:      [    ]    {    }    #    \e    ^    |    ~
.Ve
.Ip "\fB\-remap\fR" 4
.IX Item "-remap"
Enable special code to work around file systems which only permit very
short file names, such as \s-1MS-DOS\s0.
.Ip "\fB\-$\fR" 4
.IX Item "-$"
Forbid the use of \fB$\fR in identifiers.  The C standard allows
implementations to define extra characters that can appear in
identifiers.  By default \s-1GNU\s0 \s-1CPP\s0 permits \fB$\fR, a common extension.
.Ip "\fB\-h\fR" 4
.IX Item "-h"
.PD 0
.Ip "\fB\*(--help\fR" 4
.IX Item "help"
.Ip "\fB\*(--target-help\fR" 4
.IX Item "target-help"
.PD
Print text describing all the command line options instead of
preprocessing anything.
.Ip "\fB\-v\fR" 4
.IX Item "-v"
Verbose mode.  Print out \s-1GNU\s0 \s-1CPP\s0's version number at the beginning of
execution, and report the final form of the include path.
.Ip "\fB\-H\fR" 4
.IX Item "-H"
Print the name of each header file used, in addition to other normal
activities.  Each name is indented to show how deep in the
\&\fB#include\fR stack it is.
.Ip "\fB\-version\fR" 4
.IX Item "-version"
.PD 0
.Ip "\fB\*(--version\fR" 4
.IX Item "version"
.PD
Print out \s-1GNU\s0 \s-1CPP\s0's version number.  With one dash, proceed to
preprocess as normal.  With two dashes, exit immediately.
.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.
.PP
In addition to the options listed below, Apple's \s-1GCC\s0 also accepts and
passes nearly all of the options defined by the linker \fBld\fR and by
the library tool \fBlibtool\fR.  Common options include
\&\fB\-framework\fR, \fB\-dynamic\fR, \fB\-bundle\fR,
\&\fB\-flat_namespace\fR, and so forth.  See the ld and libtool man pages
for further details.
.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"
.PD 0
.Ip "\fB\-l\fR \fIlibrary\fR" 4
.IX Item "-l library"
.PD
Search the library named \fIlibrary\fR when linking.  (The second
alternative with the library as a separate argument is only for
\&\s-1POSIX\s0 compliance and is not recommended.)
.Sp
It makes a difference where in the command you write this option; the
linker searches and processes libraries and object files in the order they
are specified.  Thus, \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.
.Ip "\fB\-no-c++filt\fR" 4
.IX Item "-no-c++filt"
By default all linker diagnostic output is piped through c++filt.
This option suppresses that behavior. (\s-1APPLE\s0 \s-1ONLY\s0)
.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.
.Sp
This option will not work on Mac \s-1OS\s0 X unless all of your libraries
(including \fIlibgcc.a\fR) have also been compiled with
\&\fB\-static\fR.
.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]
.Sp
This option is not supported on Mac \s-1OS\s0 X.
.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, the G++ and \s-1GCJ\s0 drivers automatically add
\&\fB\-shared-libgcc\fR whenever you build a shared library or a main
executable, because \*(C+ and Java programs typically use exceptions, so
this is the right thing to do.
.Sp
If, instead, you use the \s-1GCC\s0 driver to create shared libraries, you may
find that they will not always be linked with the shared \fIlibgcc\fR.
If \s-1GCC\s0 finds, at its configuration time, that you have a \s-1GNU\s0 linker that
does not support option \fB\*(--eh-frame-hdr\fR, it will link the shared
version of \fIlibgcc\fR into shared libraries by default.  Otherwise,
it will take advantage of the linker and optimize away the linking with
the shared version of \fIlibgcc\fR, linking with the static version of
libgcc by default.  This allows exceptions to propagate through such
shared libraries, without incurring relocation costs at library load
time.
.Sp
However, if a library or main executable is supposed to throw or catch
exceptions, you must link it using the G++ or \s-1GCJ\s0 driver, as appropriate
for the languages used in the program, or using the option
\&\fB\-shared-libgcc\fR, such that it is linked with 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.
.Sp
If a standard system include directory, or a directory specified with
\&\fB\-isystem\fR, is also specified with \fB\-I\fR, it will be
searched only in the position requested by \fB\-I\fR.  Also, it will
not be considered a system include directory.  If that directory really
does contain system headers, there is a good chance that they will
break.  For instance, if \s-1GCC\s0's installation procedure edited the headers
in \fI/usr/include\fR to fix bugs, \fB\-I/usr/include\fR will cause the
original, buggy headers to be found instead of the corrected ones.  \s-1GCC\s0
will issue a warning when a system include directory is hidden in this
way.
.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\-F\fR\fIdir\fR" 4
.IX Item "-Fdir"
In Apple's version of \s-1GCC\s0 only, add the directory \fIdir\fR to the head
of the list of directories to be searched for frameworks.
.Sp
The framework search algorithm is, for an inclusion of
\&\fB<Fmwk/Header.h>\fR, to look for files named
\&\fI\fIpath\fI/Fmwk.framework/Headers/Header.h\fR or
\&\fI\fIpath\fI/Fmwk.framework/PrivateHeaders/Header.h\fR where
\&\fIpath\fR includes \fI/System/Library/Frameworks/\fR
\&\fI/Library/Frameworks/\fR, and \fI/Local/Library/Frameworks/\fR, plus
any additional paths specified by \fB\-F\fR.
.Sp
All the \fB\-F\fR options are also passed to the linker.
.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
The compiler will check to see if the path provided by the \fB\-B\fR
refers to a directory, and if necessary it will add a directory
separator character at the end of the path.
.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.  
.Sp
As a special kludge, if the path provided by \fB\-B\fR is
\&\fI[dir/]stage\fIN\fI/\fR, where \fIN\fR is a number in the range 0 to
9, then it will be replaced by \fI[dir/]include\fR.  This is to help
with boot-strapping the compiler.
.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 \s-1VAX\s0 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
These options are defined by the macro \f(CW\*(C`TARGET_SWITCHES\*(C'\fR in the
machine description.  The default for the options is also defined by
that macro, which enables you to change the defaults.
.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.  With
\&\fB\-mnew-mnemonics\fR, \s-1GCC\s0 uses the assembler mnemonics defined for
the PowerPC architecture.  With \fB\-mold-mnemonics\fR it uses 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, \fB7400\fR, \fB7450\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.
.Sp
\&\fB\-mcpu=common\fR selects a completely generic processor.  Code
generated under this option will run on any \s-1POWER\s0 or PowerPC processor.
\&\s-1GCC\s0 will use only the instructions in the common subset of both
architectures, and will not use the \s-1MQ\s0 register.  \s-1GCC\s0 assumes a generic
processor model for scheduling purposes.
.Sp
\&\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
The other options specify a specific processor.  Code generated under
those options will run best on that processor, and may not run at all on
others.
.Sp
The \fB\-mcpu\fR options automatically enable or disable other
\&\fB\-m\fR options as follows:
.RS 4
.Ip "\fBcommon\fR" 4
.IX Item "common"
\&\fB\-mno-power\fR, \fB\-mno-powerc\fR
.Ip "\fBpower\fR" 4
.IX Item "power"
.PD 0
.Ip "\fBpower2\fR" 4
.IX Item "power2"
.Ip "\fBrios1\fR" 4
.IX Item "rios1"
.Ip "\fBrios2\fR" 4
.IX Item "rios2"
.Ip "\fBrsc\fR" 4
.IX Item "rsc"
.PD
\&\fB\-mpower\fR, \fB\-mno-powerpc\fR, \fB\-mno-new-mnemonics\fR
.Ip "\fBpowerpc\fR" 4
.IX Item "powerpc"
.PD 0
.Ip "\fBrs64a\fR" 4
.IX Item "rs64a"
.Ip "\fB602\fR" 4
.IX Item "602"
.Ip "\fB603\fR" 4
.IX Item "603"
.Ip "\fB603e\fR" 4
.IX Item "603e"
.Ip "\fB604\fR" 4
.IX Item "604"
.Ip "\fB620\fR" 4
.IX Item "620"
.Ip "\fB630\fR" 4
.IX Item "630"
.Ip "\fB740\fR" 4
.IX Item "740"
.Ip "\fB7400\fR" 4
.IX Item "7400"
.Ip "\fB7450\fR" 4
.IX Item "7450"
.Ip "\fB750\fR" 4
.IX Item "750"
.Ip "\fB505\fR" 4
.IX Item "505"
.PD
\&\fB\-mno-power\fR, \fB\-mpowerpc\fR, \fB\-mnew-mnemonics\fR
.Ip "\fB601\fR" 4
.IX Item "601"
\&\fB\-mpower\fR, \fB\-mpowerpc\fR, \fB\-mnew-mnemonics\fR
.Ip "\fB403\fR" 4
.IX Item "403"
.PD 0
.Ip "\fB821\fR" 4
.IX Item "821"
.Ip "\fB860\fR" 4
.IX Item "860"
.PD
\&\fB\-mno-power\fR, \fB\-mpowerpc\fR, \fB\-mnew-mnemonics\fR, \fB\-msoft-float\fR
.RE
.RS 4
.RE
.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, or
choice of mnemonics, as \fB\-mcpu=\fR\fIcpu_type\fR would.  The same
values for \fIcpu_type\fR are used for \fB\-mtune\fR as for
\&\fB\-mcpu\fR.  If both are specified, the code generated will use the
architecture, registers, and mnemonics set by \fB\-mcpu\fR, but the
scheduling parameters set by \fB\-mtune\fR.
.Ip "\fB\-maltivec\fR" 4
.IX Item "-maltivec"
.PD 0
.Ip "\fB\-mno-altivec\fR" 4
.IX Item "-mno-altivec"
.PD
These switches enable or disable the use of built-in functions that
allow access to the AltiVec instruction set.  You may also need to set
\&\fB\-mabi=altivec\fR to adjust the current \s-1ABI\s0 with AltiVec \s-1ABI\s0
enhancements.
.Sp
This option is not supported on Mac \s-1OS\s0 X; use \fB\-faltivec\fR instead.
.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\-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\-pthread\fR
option are incompatible.
.Ip "\fB\-malign-mac68k\fR" 4
.IX Item "-malign-mac68k"
.PD 0
.Ip "\fB\-malign-power\fR" 4
.IX Item "-malign-power"
.Ip "\fB\-malign-natural\fR" 4
.IX Item "-malign-natural"
.PD
The option \fB\-malign-mac68k\fR causes structure fields to be aligned
on 2\-byte boundaries, in order to be compatible with m68k compiler
output.  The option \fB\-malign-power\fR is the standard alignment
mode for the PowerPC.  The option \fB\-malign-natural\fR is an
extension of PowerPC alignment that aligns larger data types such as
doubles on their natural boundaries.  (\s-1APPLE\s0 \s-1ONLY\s0)
.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 bit-fields 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\-mdynamic-no-pic\fR" 4
.IX Item "-mdynamic-no-pic"
On Darwin and Mac \s-1OS\s0 X systems, compile code so that it is not
relocatable, but that its external references are relocatable.  The
resulting code is suitable for applications, but not shared
libraries. (\s-1APPLE\s0 \s-1ONLY\s0)
.Ip "\fB\-mlong-branch\fR" 4
.IX Item "-mlong-branch"
On Darwin and Mac \s-1OS\s0 X systems, compile calls to use a 32\-bit
destination address.  This is to support kernel extensions, which may
load anywhere within the kernel address space.  (\s-1APPLE\s0 \s-1ONLY\s0)
.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\-mcall-gnu\fR" 4
.IX Item "-mcall-gnu"
On System V.4 and embedded PowerPC systems compile code for the
Hurd-based \s-1GNU\s0 system.
.Ip "\fB\-mcall-netbsd\fR" 4
.IX Item "-mcall-netbsd"
On System V.4 and embedded PowerPC systems compile code for the
NetBSD operating system.
.Ip "\fB\-maix-struct-return\fR" 4
.IX Item "-maix-struct-return"
Return all structures in memory (as specified by the \s-1AIX\s0 \s-1ABI\s0).
.Ip "\fB\-msvr4\-struct-return\fR" 4
.IX Item "-msvr4-struct-return"
Return structures smaller than 8 bytes in registers (as specified by the
\&\s-1SVR4\s0 \s-1ABI\s0).
.Ip "\fB\-mabi=altivec\fR" 4
.IX Item "-mabi=altivec"
Extend the current \s-1ABI\s0 with AltiVec \s-1ABI\s0 extensions.  This does not
change the default \s-1ABI\s0, instead it adds the AltiVec \s-1ABI\s0 extensions to
the current \s-1ABI\s0.
.Sp
This option is effectively permanently enabled on Mac \s-1OS\s0 X.
.Ip "\fB\-mabi=no-altivec\fR" 4
.IX Item "-mabi=no-altivec"
Disable AltiVec \s-1ABI\s0 extensions for the current \s-1ABI\s0.
.Sp
This option will not work on Mac \s-1OS\s0 X.
.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.
.Ip "\fB\-pthread\fR" 4
.IX Item "-pthread"
Adds support for multithreading with the \fIpthreads\fR library.
This option sets flags for both the preprocessor and linker.
.PP
.I "Intel 386 and \s-1AMD\s0 x86\-64 Options"
.IX Subsection "Intel 386 and AMD x86-64 Options"
.PP
These \fB\-m\fR options are defined for the i386 and x86\-64 family of
computers:
.Ip "\fB\-mcpu=\fR\fIcpu-type\fR" 4
.IX Item "-mcpu=cpu-type"
Tune to \fIcpu-type\fR everything applicable about the generated code, except
for the \s-1ABI\s0 and the set of available instructions.  The choices for
\&\fIcpu-type\fR are \fBi386\fR, \fBi486\fR, \fBi586\fR, \fBi686\fR,
\&\fBpentium\fR, \fBpentium-mmx\fR, \fBpentiumpro\fR, \fBpentium2\fR,
\&\fBpentium3\fR, \fBpentium4\fR, \fBk6\fR, \fBk6\-2\fR, \fBk6\-3\fR,
\&\fBathlon\fR, \fBathlon-tbird\fR, \fBathlon-4\fR, \fBathlon-xp\fR
and \fBathlon-mp\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
These options are synonyms for \fB\-mcpu=i386\fR, \fB\-mcpu=i486\fR,
\&\fB\-mcpu=pentium\fR, and \fB\-mcpu=pentiumpro\fR respectively.
These synonyms are deprecated.
.Ip "\fB\-mfpmath=\fR\fIunit\fR" 4
.IX Item "-mfpmath=unit"
generate floating point arithmetics for selected unit \fIunit\fR.  the choices
for \fIunit\fR are:
.RS 4
.Ip "\fB387\fR" 4
.IX Item "387"
Use the standard 387 floating point coprocessor present majority of chips and
emulated otherwise.  Code compiled with this option will run almost everywhere.
The temporary results are computed in 80bit precesion instead of precision
specified by the type resulting in slightly different results compared to most
of other chips. See \fB\-ffloat-store\fR for more detailed description.
.Sp
This is the default choice for i386 compiler.
.Ip "\fBsse\fR" 4
.IX Item "sse"
Use scalar floating point instructions present in the \s-1SSE\s0 instruction set.
This instruction set is supported by Pentium3 and newer chips, in the \s-1AMD\s0 line
by Athlon-4, Athlon-xp and Athlon-mp chips.  The earlier version of \s-1SSE\s0
instruction set supports only single precision arithmetics, thus the double and
extended precision arithmetics is still done using 387.  Later version, present
only in Pentium4 and the future \s-1AMD\s0 x86\-64 chips supports double precision
arithmetics too.
.Sp
For i387 you need to use \fB\-march=\fR\fIcpu-type\fR, \fB\-msse\fR or
\&\fB\-msse2\fR switches to enable \s-1SSE\s0 extensions and make this option
effective.  For x86\-64 compiler, these extensions are enabled by default.
.Sp
The resulting code should be considerably faster in majority of cases and avoid
the numerical instability problems of 387 code, but may break some existing
code that expects temporaries to be 80bit.
.Sp
This is the default choice for x86\-64 compiler.
.Ip "\fBsse,387\fR" 4
.IX Item "sse,387"
Attempt to utilize both instruction sets at once.  This effectivly double the
amount of available registers and on chips with separate execution units for
387 and \s-1SSE\s0 the execution resources too.  Use this option with care, as it is
still experimental, because gcc register allocator does not model separate
functional units well resulting in instable performance.
.RE
.RS 4
.RE
.Ip "\fB\-masm=\fR\fIdialect\fR" 4
.IX Item "-masm=dialect"
Output asm instructions using selected \fIdialect\fR. Supported choices are
\&\fBintel\fR or \fBatt\fR (the default one).
.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,
OpenBSD and NetBSD.  This option is overridden when \fB\-march\fR
indicates that the target cpu will always have an \s-1FPU\s0 and so the
instruction will not need emulation.  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"
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)
prefer \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"
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 local variables into the
\&\f(CW\*(C`bss\*(C'\fR or \f(CW\*(C`data\*(C'\fR segments.  \fB\-msvr3\-shlib\fR places them
into \f(CW\*(C`bss\*(C'\fR.  These options are meaningful only on System V Release 3.
.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\-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), except when optimizing for code
size (\fB\-Os\fR), in which case the default is the minimum correct
alignment (4 bytes for x86, and 8 bytes for x86\-64).
.Sp
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, and generally
increases code size.  Code that is sensitive to stack space usage, such
as embedded systems and operating system kernels, may want to reduce the
preferred alignment to \fB\-mpreferred-stack-boundary=2\fR.
.Ip "\fB\-mmmx\fR" 4
.IX Item "-mmmx"
.PD 0
.Ip "\fB\-mno-mmx\fR" 4
.IX Item "-mno-mmx"
.Ip "\fB\-msse\fR" 4
.IX Item "-msse"
.Ip "\fB\-mno-sse\fR" 4
.IX Item "-mno-sse"
.Ip "\fB\-msse2\fR" 4
.IX Item "-msse2"
.Ip "\fB\-mno-sse2\fR" 4
.IX Item "-mno-sse2"
.Ip "\fB\-m3dnow\fR" 4
.IX Item "-m3dnow"
.Ip "\fB\-mno-3dnow\fR" 4
.IX Item "-mno-3dnow"
.PD
These switches enable or disable the use of built-in functions that allow
direct access to the \s-1MMX\s0, \s-1SSE\s0 and 3Dnow extensions of the instruction set.
.Ip "\fB\-mpush-args\fR" 4
.IX Item "-mpush-args"
.PD 0
.Ip "\fB\-mno-push-args\fR" 4
.IX Item "-mno-push-args"
.PD
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 is faster on most modern CPUs
because of reduced dependencies, improved scheduling and reduced stack usage
when preferred stack boundary is not equal to 2.  The drawback is a notable
increase in code size.  This switch implies \fB\-mno-push-args\fR.
.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.
.Ip "\fB\-momit-leaf-frame-pointer\fR" 4
.IX Item "-momit-leaf-frame-pointer"
Don't keep the frame pointer in a register for leaf functions.  This
avoids the instructions to save, set up and restore frame pointers and
makes an extra register available in leaf functions.  The option
\&\fB\-fomit-frame-pointer\fR removes the frame pointer for all functions
which might make debugging harder.
.PP
These \fB\-m\fR switches are supported in addition to the above
on \s-1AMD\s0 x86\-64 processors in 64\-bit environments.
.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 and
generates code that runs on any i386 system.
The 64\-bit environment sets int to 32 bits and long and pointer
to 64 bits and generates code for \s-1AMD\s0's x86\-64 architecture.
.Ip "\fB\-mno-red-zone\fR" 4
.IX Item "-mno-red-zone"
Do not use a so called red zone for x86\-64 code.  The red zone is mandated
by the x86\-64 \s-1ABI\s0, it is a 128\-byte area beyond the location of the
stack pointer that will not be modified by signal or interrupt handlers
and therefore can be used for temporary data without adjusting the stack
pointer.  The flag \fB\-mno-red-zone\fR disables this red zone.
.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-1GCC\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-1GCC\s0 will enable it by default for languages like
\&\*(C+ which normally require exception handling, and disable it for
languages like C that do not normally require it.  However, you may need
to enable this option when compiling C code that needs to interoperate
properly with exception handlers written in \*(C+.  You may also wish to
disable this option if you are compiling older \*(C+ programs that don't
use exception handling.
.Ip "\fB\-fnon-call-exceptions\fR" 4
.IX Item "-fnon-call-exceptions"
Generate code that allows trapping instructions to throw exceptions.
Note that this requires platform-specific runtime support that does
not exist everywhere.  Moreover, it only allows \fItrapping\fR
instructions to throw exceptions, i.e. memory references or floating
point instructions.  It does not allow exceptions to be thrown from
arbitrary signal handlers such as \f(CW\*(C`SIGALRM\*(C'\fR.
.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\-fasynchronous-unwind-tables\fR" 4
.IX Item "-fasynchronous-unwind-tables"
Generate unwind table in dwarf2 format, if supported by target machine.  The
table is exact at each instruction boundary, so it can be used for stack
unwinding from asynchronous events (such as debugger or garbage collector).
.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"
Return \f(CW\*(C`struct\*(C'\fR and \f(CW\*(C`union\*(C'\fR values 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
\&\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"
In C, allocate even uninitialized global variables in the data section of the
object file, rather than generating them as common blocks.  This has the
effect that if the same variable is declared (without \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.
.Sp
\&\fB\-fpic\fR is not supported on Mac \s-1OS\s0 X.
.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.
.Sp
\&\fB\-fPIC\fR is the default on Darwin and Mac \s-1OS\s0 X.
.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\-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 4
\&        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 absolute address \fB0x80000000\fR
and grows downwards, you can use the flags
\&\fB\-fstack-limit-symbol=_\|_stack_limit\fR and
\&\fB\-Wl,\-\-defsym,_\|_stack_limit=0x7ffe0000\fR to enforce a stack limit
of 128KB.  Note that this may only work with the \s-1GNU\s0 linker.
.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, \fB\-fno-leading-underscore\fR, 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-1GCC\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 "\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
.PP
Some additional environments variables affect the behavior of the
preprocessor.
.Ip "\fB\s-1CPATH\s0\fR" 4
.IX Item "CPATH"
.PD 0
.Ip "\fBC_INCLUDE_PATH\fR" 4
.IX Item "C_INCLUDE_PATH"
.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
Each variable's value is a list of directories separated by a special
character, much like \fB\s-1PATH\s0\fR, in which to look for header files.
The special character, \f(CW\*(C`PATH_SEPARATOR\*(C'\fR, is target-dependent and
determined at \s-1GCC\s0 build time.  For Windows-based targets it is a
semicolon, and for almost all other targets it is a colon.
.Sp
\&\fB\s-1CPATH\s0\fR specifies a list of directories to be searched as if
specified with \fB\-I\fR, but after any paths given with \fB\-I\fR
options on the command line.  The environment variable is used
regardless of which language is being preprocessed.
.Sp
The remaining environment variables apply only when preprocessing the
particular language indicated.  Each specifies a list of directories
to be searched as if specified with \fB\-isystem\fR, but after any
paths given with \fB\-isystem\fR options on the command line.
.Ip "\fB\s-1DEPENDENCIES_OUTPUT\s0\fR" 4
.IX Item "DEPENDENCIES_OUTPUT"
@anchor{\s-1DEPENDENCIES_OUTPUT\s0}
If this variable is set, its value specifies how to output
dependencies for Make based on the non-system header files processed
by the compiler.  System header files are ignored in the dependency
output.
.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.
.Sp
In other words, this environment variable is equivalent to combining
the options \fB\-MM\fR and \fB\-MF\fR,
with an optional \fB\-MT\fR switch too.
.Ip "\fB\s-1SUNPRO_DEPENDENCIES\s0\fR" 4
.IX Item "SUNPRO_DEPENDENCIES"
This variable is the same as the environment variable
\&\fB\s-1DEPENDENCIES_OUTPUT\s0\fR, except that
system header files are not ignored, so it implies \fB\-M\fR rather
than \fB\-MM\fR.
.SH "BUGS"
.IX Header "BUGS"
To report bugs to Apple, see
<\fBhttp://developer.apple.com/bugreporter\fR>.
.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"
\&\fIgpl\fR\|(7), \fIgfdl\fR\|(7), \fIfsf-funding\fR\|(7),
\&\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 \fBgcc\fR, or
<\fBhttp://gcc.gnu.org/onlinedocs/gcc/Contributors.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, 2002 Free Software Foundation, Inc.
.PP
Permission is granted to copy, distribute and/or modify this document
under the terms of the \s-1GNU\s0 Free Documentation License, Version 1.1 or
any later version published by the Free Software Foundation; with the
Invariant Sections being ``\s-1GNU\s0 General Public License'' and ``Funding
Free Software'', the Front-Cover texts being (a) (see below), and with
the Back-Cover Texts being (b) (see below).  A copy of the license is
included in the \fIgfdl\fR\|(7) man page.
.PP
(a) The \s-1FSF\s0's Front-Cover Text is:
.PP
.Vb 1
\&     A GNU Manual
.Ve
(b) The \s-1FSF\s0's Back-Cover Text is:
.PP
.Vb 3
\&     You have freedom to copy and modify this GNU Manual, like GNU
\&     software.  Copies published by the Free Software Foundation raise
\&     funds for GNU development.
.Ve