@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, @c 2000, 2001, 2002 Free Software Foundation, Inc. @c This is part of the GCC manual. @c For copying conditions, see the file gcc.texi. @ignore @c man begin COPYRIGHT Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being ``GNU General Public License'' and ``Funding Free Software'', the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the gfdl(7) man page. (a) The FSF's Front-Cover Text is: A GNU Manual (b) The FSF's Back-Cover Text is: You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development. @c man end @c Set file name and title for the man page. @setfilename gcc @settitle GNU project C and C++ compiler @c man begin SYNOPSIS gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}] [@option{-g}] [@option{-pg}] [@option{-O}@var{level}] [@option{-W}@var{warn}@dots{}] [@option{-pedantic}] [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}] [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}] [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}] [@option{-o} @var{outfile}] @var{infile}@dots{} Only the most useful options are listed here; see below for the remainder. @samp{g++} accepts mostly the same options as @samp{gcc}. @c APPLE LOCAL begin manual In Apple's version of GCC, both @samp{cc} and @samp{gcc} are actually symbolic links to @samp{gcc3}, while @samp{c++} and @samp{g++} are links to @samp{g++3}. Note that Apple's GCC includes a number of extensions to standard GCC (flagged below with ``APPLE ONLY''), and that not all generic GCC options are available or supported on Darwin / Mac OS 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. @c APPLE LOCAL begin manual @c man end @c man begin SEEALSO gpl(7), gfdl(7), fsf-funding(7), cpp(1), gcov(1), g77(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1) and the Info entries for @file{gcc}, @file{cpp}, @file{g77}, @file{as}, @file{ld}, @file{binutils} and @file{gdb}. @c man end @c man begin BUGS @c APPLE LOCAL begin report bugs to Apple To report bugs to Apple, see @w{@uref{http://developer.apple.com/bugreporter}}. @c APPLE LOCAL end report bugs to Apple @c man end @c man begin AUTHOR See the Info entry for @command{gcc}, or @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}}, for contributors to GCC@. @c man end @end ignore @node Invoking GCC @chapter GCC Command Options @cindex GCC command options @cindex command options @cindex options, GCC command @c man begin DESCRIPTION When you invoke GCC, it normally does preprocessing, compilation, assembly and linking. The ``overall options'' allow you to stop this process at an intermediate stage. For example, the @option{-c} option says not to run the linker. Then the output consists of object files output by the assembler. Other options are passed on to one stage of processing. Some options control the preprocessor and others the compiler itself. Yet other options control the assembler and linker; most of these are not documented here, since you rarely need to use any of them. @cindex C compilation options Most of the command line options that you can use with GCC are useful for C programs; when an option is only useful with another language (usually C++), the explanation says so explicitly. If the description for a particular option does not mention a source language, you can use that option with all supported languages. @cindex C++ compilation options @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special options for compiling C++ programs. @cindex grouping options @cindex options, grouping The @command{gcc} program accepts options and file names as operands. Many options have multi-letter names; therefore multiple single-letter options may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d -r}}. @cindex order of options @cindex options, order You can mix options and other arguments. For the most part, the order you use doesn't matter. Order does matter when you use several options of the same kind; for example, if you specify @option{-L} more than once, the directories are searched in the order specified. Many options have long names starting with @samp{-f} or with @samp{-W}---for example, @option{-fforce-mem}, @option{-fstrength-reduce}, @option{-Wformat} and so on. Most of these have both positive and negative forms; the negative form of @option{-ffoo} would be @option{-fno-foo}. This manual documents only one of these two forms, whichever one is not the default. @c man end @xref{Option Index}, for an index to GCC's options. @menu * Option Summary:: Brief list of all options, without explanations. * Overall Options:: Controlling the kind of output: an executable, object files, assembler files, or preprocessed source. * Invoking G++:: Compiling C++ programs. * C Dialect Options:: Controlling the variant of C language compiled. * C++ Dialect Options:: Variations on C++. * Objective-C Dialect Options:: Variations on Objective-C. * Language Independent Options:: Controlling how diagnostics should be formatted. * Warning Options:: How picky should the compiler be? * Debugging Options:: Symbol tables, measurements, and debugging dumps. * Optimize Options:: How much optimization? * Preprocessor Options:: Controlling header files and macro definitions. Also, getting dependency information for Make. * Assembler Options:: Passing options to the assembler. * Link Options:: Specifying libraries and so on. * Directory Options:: Where to find header files and libraries. Where to find the compiler executable files. * Spec Files:: How to pass switches to sub-processes. * Target Options:: Running a cross-compiler, or an old version of GCC. * Submodel Options:: Specifying minor hardware or convention variations, such as 68010 vs 68020. * Code Gen Options:: Specifying conventions for function calls, data layout and register usage. * Environment Variables:: Env vars that affect GCC. * Running Protoize:: Automatically adding or removing function prototypes. @end menu @c man begin OPTIONS @node Option Summary @section Option Summary Here is a summary of all the options, grouped by type. Explanations are in the following sections. @table @emph @item Overall Options @xref{Overall Options,,Options Controlling the Kind of Output}. @gccoptlist{ -c -S -E -o @var{file} -pipe -pass-exit-codes -x @var{language} @gol @c APPLE LOCAL -ObjC 2001-08-03 sts ** -ObjC (APPLE ONLY) -ObjC++ (APPLE ONLY) @gol @c APPLE LOCAL fat builds -arch @var{arch} (APPLE ONLY) @gol -v -### --target-help --help} @item C Language Options @xref{C Dialect Options,,Options Controlling C Dialect}. @gccoptlist{ -ansi -std=@var{standard} -aux-info @var{filename} @gol @c APPLE LOCAL AltiVec -faltivec (APPLE ONLY) @gol -fno-asm -fno-builtin -fno-builtin-@var{function} @gol -fhosted -ffreestanding @gol -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol -fallow-single-precision -fcond-mismatch @gol @c APPLE LOCAL constant cfstrings -fconstant-cfstrings (APPLE ONLY) @gol -fsigned-bitfields -fsigned-char @gol -funsigned-bitfields -funsigned-char @gol @c APPLE LOCAL begin Pascal Strings 2001-07-05 zll ** -fwritable-strings -fshort-wchar @gol -fpascal-strings (APPLE ONLY) @gol @c APPLE LOCAL end Pascal Strings 2001-07-05 zll ** @c APPLE LOCAL coalescing 2002-04-11 tur ** -fcoalesce (APPLE ONLY) -fweak-coalesced (APPLE ONLY) @gol @c APPLE LOCAL -Wno-#warnings -Wno-#warnings (APPLE ONLY) @gol @c APPLE LOCAL -Wextra-tokens 2001-08-02 sts ** -Wextra-tokens (APPLE ONLY) @gol @c APPLE LOCAL -Wpragma-once 2001-08-01 sts ** -Wpragma-once (APPLE ONLY) @gol @c APPLE LOCAL -Wnewline-eof 2001-08-23 sts ** -Wnewline-eof (APPLE ONLY) @gol @c APPLE LOCAL -Wno-altivec-long-deprecated ilr ** -Wno-altivec-long-deprecated (APPLE ONLY)} @item C++ Language Options @xref{C++ Dialect Options,,Options Controlling C++ Dialect}. @gccoptlist{ -fno-access-control -fcheck-new -fconserve-space @gol -fno-const-strings -fdollars-in-identifiers @gol -fno-elide-constructors @gol -fno-enforce-eh-specs -fexternal-templates @gol -falt-external-templates @gol -ffor-scope -fno-for-scope -fno-gnu-keywords @gol -fno-implicit-templates @gol -fno-implicit-inline-templates @gol -fno-implement-inlines @gol @c APPLE LOCAL -findirect-virtual-calls 2001-10-30 sts ** -findirect-virtual-calls (APPLE ONLY) @gol @c APPLE LOCAL -fapple-kext -fapple-kext (APPLE ONLY) @gol @c APPLE LOCAL coalescing 2002-04-11 tur ** -fcoalesce-templates (APPLE ONLY) @gol -fms-extensions @gol -fno-nonansi-builtins -fno-operator-names @gol -fno-optional-diags -fpermissive @gol -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol -fuse-cxa-atexit -fvtable-gc -fno-weak -nostdinc++ @gol -fno-default-inline -Wctor-dtor-privacy @gol -Wnon-virtual-dtor -Wreorder @gol -Weffc++ -Wno-deprecated @gol -Wno-non-template-friend -Wold-style-cast @gol -Woverloaded-virtual -Wno-pmf-conversions @gol -Wsign-promo -Wsynth} @item Objective-C Language Options @xref{Objective-C Dialect Options,,Options Controlling Objective-C Dialect}. @gccoptlist{ -fconstant-string-class=@var{class-name} @gol -fgnu-runtime -fnext-runtime -gen-decls @gol -Wno-protocol -Wselector} @item Language Independent Options @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}. @gccoptlist{ -fmessage-length=@var{n} @gol -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}} @item Warning Options @xref{Warning Options,,Options to Request or Suppress Warnings}. @gccoptlist{ -fsyntax-only -pedantic -pedantic-errors @gol -w -W -Wall -Waggregate-return @gol -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol -Wconversion -Wno-deprecated-declarations @gol -Wdisabled-optimization -Wdiv-by-zero -Werror @gol -Wfloat-equal -Wformat -Wformat=2 @gol -Wformat-nonliteral -Wformat-security @gol -Wimplicit -Wimplicit-int @gol -Wimplicit-function-declaration @gol -Werror-implicit-function-declaration @gol -Wimport -Winline @gol -Wlarger-than-@var{len} @gol @c APPLE LOCAL long double -Wno-long-double (APPLE ONLY) @gol -Wlong-long @gol -Wmain -Wmissing-braces -Wmissing-declarations @gol -Wmissing-format-attribute -Wmissing-noreturn @gol @c APPLE LOCAL -Wmost -Wmost (APPLE ONLY) @gol -Wmultichar -Wno-format-extra-args -Wno-format-y2k @gol -Wno-import -Wpacked -Wpadded @gol -Wparentheses -Wpointer-arith -Wredundant-decls @gol -Wreturn-type -Wsequence-point -Wshadow @gol -Wsign-compare -Wswitch -Wsystem-headers @gol -Wtrigraphs -Wundef -Wuninitialized @gol -Wunknown-pragmas -Wunreachable-code @gol -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol -Wunused-value -Wunused-variable -Wwrite-strings} @item C-only Warning Options @gccoptlist{ -Wbad-function-cast -Wmissing-prototypes -Wnested-externs @gol -Wstrict-prototypes -Wtraditional} @item Debugging Options @xref{Debugging Options,,Options for Debugging Your Program or GCC}. @gccoptlist{ -d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol -fdump-tree-original@r{[}-@var{n}@r{]} -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol -fmem-report -fpretend-float @gol -fprofile-arcs -ftest-coverage -ftime-report @gol -g -g@var{level} -gcoff -gdwarf -gdwarf-1 -gdwarf-1+ -gdwarf-2 @gol -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol -print-multi-directory -print-multi-lib @gol -print-prog-name=@var{program} -print-search-dirs -Q @gol -save-temps -time} @item Optimization Options @xref{Optimize Options,,Options that Control Optimization}. @gccoptlist{ -falign-functions=@var{n} -falign-jumps=@var{n} @gol -falign-labels=@var{n} -falign-loops=@var{n} @gol -fbranch-probabilities -fcaller-saves -fcprop-registers @gol -fcse-follow-jumps -fcse-skip-blocks -fdata-sections @gol -fdelayed-branch -fdelete-null-pointer-checks @gol -fexpensive-optimizations -ffast-math -ffloat-store @gol -fforce-addr -fforce-mem -ffunction-sections @gol -fgcse -fgcse-lm -fgcse-sm @gol -finline-functions -finline-limit=@var{n} -fkeep-inline-functions @gol -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol -fmove-all-movables -fno-default-inline -fno-defer-pop @gol -fno-function-cse -fno-guess-branch-probability @gol -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol -funsafe-math-optimizations -fno-trapping-math @gol -fomit-frame-pointer -foptimize-register-move @gol -foptimize-sibling-calls -fprefetch-loop-arrays @gol -freduce-all-givs -fregmove -frename-registers @gol -frerun-cse-after-loop -frerun-loop-opt @gol -fschedule-insns -fschedule-insns2 @gol -fsingle-precision-constant -fssa -fssa-ccp -fssa-dce @gol -fstrength-reduce -fstrict-aliasing -fthread-jumps -ftrapv @gol -funroll-all-loops -funroll-loops @gol --param @var{name}=@var{value} -O -O0 -O1 -O2 -O3 -Os} @item Preprocessor Options @xref{Preprocessor Options,,Options Controlling the Preprocessor}. @gccoptlist{ -$ -A@var{question}=@var{answer} -A-@var{question}@r{[}=@var{answer}@r{]} @gol -C -dD -dI -dM -dN @gol -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol -idirafter @var{dir} @gol -include @var{file} -imacros @var{file} @gol -iprefix @var{file} -iwithprefix @var{dir} @gol -iwithprefixbefore @var{dir} -isystem @var{dir} @gol -M -MM -MF -MG -MP -MQ -MT -nostdinc -P -remap @gol @c APPLE LOCAL -dependency-file -dependency-file (APPLE ONLY) @gol @c APPLE LOCAL cpp-precomp -no-cpp-precomp (APPLE ONLY) @gol @c APPLE LOCAL PFE --dump-pch @var{name} (APPLE ONLY) --load-pch @var{name} (APPLE ONLY) @gol -trigraphs -undef -U@var{macro} -Wp,@var{option}} @item Assembler Option @xref{Assembler Options,,Passing Options to the Assembler}. @gccoptlist{ -Wa,@var{option}} @item Linker Options @xref{Link Options,,Options for Linking}. @gccoptlist{ @var{object-file-name} -l@var{library} @gol @c APPLE LOCAL radar 2466994 - -no-c++filt ilr -nostartfiles -nodefaultlibs -nostdlib -no-c++filt (APPLE ONLY) @gol -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol -Wl,@var{option} -Xlinker @var{option} @gol -u @var{symbol}} @item Directory Options @xref{Directory Options,,Options for Directory Search}. @gccoptlist{ -B@var{prefix} -I@var{dir} -I- @gol @c APPLE LOCAL framework headers -F@var{dir} (APPLE ONLY) @gol -L@var{dir} -specs=@var{file}} @item Target Options @c I wrote this xref this way to avoid overfull hbox. -- rms @xref{Target Options}. @gccoptlist{ -b @var{machine} -V @var{version}} @item Machine Dependent Options @xref{Submodel Options,,Hardware Models and Configurations}. @c APPLE LOCAL prune man page @ignore @emph{M680x0 Options} @gccoptlist{ -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol -mfpa -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol -malign-int -mstrict-align} @emph{M68hc1x Options} @gccoptlist{ -m6811 -m6812 -m68hc11 -m68hc12 @gol -mauto-incdec -mshort -msoft-reg-count=@var{count}} @emph{VAX Options} @gccoptlist{ -mg -mgnu -munix} @emph{SPARC Options} @gccoptlist{ -mcpu=@var{cpu-type} @gol -mtune=@var{cpu-type} @gol -mcmodel=@var{code-model} @gol -m32 -m64 @gol -mapp-regs -mbroken-saverestore -mcypress @gol -mfaster-structs -mflat @gol -mfpu -mhard-float -mhard-quad-float @gol -mimpure-text -mlive-g0 -mno-app-regs @gol -mno-faster-structs -mno-flat -mno-fpu @gol -mno-impure-text -mno-stack-bias -mno-unaligned-doubles @gol -msoft-float -msoft-quad-float -msparclite -mstack-bias @gol -msupersparc -munaligned-doubles -mv8} @emph{Convex Options} @gccoptlist{ -mc1 -mc2 -mc32 -mc34 -mc38 @gol -margcount -mnoargcount @gol -mlong32 -mlong64 @gol -mvolatile-cache -mvolatile-nocache} @emph{AMD29K Options} @gccoptlist{ -m29000 -m29050 -mbw -mnbw -mdw -mndw @gol -mlarge -mnormal -msmall @gol -mkernel-registers -mno-reuse-arg-regs @gol -mno-stack-check -mno-storem-bug @gol -mreuse-arg-regs -msoft-float -mstack-check @gol -mstorem-bug -muser-registers} @emph{ARM Options} @gccoptlist{ -mapcs-frame -mno-apcs-frame @gol -mapcs-26 -mapcs-32 @gol -mapcs-stack-check -mno-apcs-stack-check @gol -mapcs-float -mno-apcs-float @gol -mapcs-reentrant -mno-apcs-reentrant @gol -msched-prolog -mno-sched-prolog @gol -mlittle-endian -mbig-endian -mwords-little-endian @gol -malignment-traps -mno-alignment-traps @gol -msoft-float -mhard-float -mfpe @gol -mthumb-interwork -mno-thumb-interwork @gol -mcpu=@var{name} -march=@var{name} -mfpe=@var{name} @gol -mstructure-size-boundary=@var{n} @gol -mbsd -mxopen -mno-symrename @gol -mabort-on-noreturn @gol -mlong-calls -mno-long-calls @gol -msingle-pic-base -mno-single-pic-base @gol -mpic-register=@var{reg} @gol -mnop-fun-dllimport @gol -mpoke-function-name @gol -mthumb -marm @gol -mtpcs-frame -mtpcs-leaf-frame @gol -mcaller-super-interworking -mcallee-super-interworking } @emph{MN10200 Options} @gccoptlist{ -mrelax} @emph{MN10300 Options} @gccoptlist{ -mmult-bug -mno-mult-bug @gol -mam33 -mno-am33 @gol -mno-crt0 -mrelax} @emph{M32R/D Options} @gccoptlist{ -m32rx -m32r -mcode-model=@var{model-type} -msdata=@var{sdata-type} @gol -G @var{num}} @emph{M88K Options} @gccoptlist{ -m88000 -m88100 -m88110 -mbig-pic @gol -mcheck-zero-division -mhandle-large-shift @gol -midentify-revision -mno-check-zero-division @gol -mno-ocs-debug-info -mno-ocs-frame-position @gol -mno-optimize-arg-area -mno-serialize-volatile @gol -mno-underscores -mocs-debug-info @gol -mocs-frame-position -moptimize-arg-area @gol -mserialize-volatile -mshort-data-@var{num} -msvr3 @gol -msvr4 -mtrap-large-shift -muse-div-instruction @gol -mversion-03.00 -mwarn-passed-structs} @c APPLE LOCAL prune man page @end ignore @emph{RS/6000 and PowerPC Options} @gccoptlist{ -mcpu=@var{cpu-type} @gol -mtune=@var{cpu-type} @gol -mpower -mno-power -mpower2 -mno-power2 @gol -mpowerpc -mpowerpc64 -mno-powerpc @gol -maltivec -mno-altivec @gol -mpowerpc-gpopt -mno-powerpc-gpopt @gol -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol -mnew-mnemonics -mold-mnemonics @gol -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol -m64 -m32 -mxl-call -mno-xl-call -mpe @gol @c APPLE LOCAL begin -malign-mac68k -malign-mac68k (APPLE ONLY) @gol -malign-power (APPLE ONLY) @gol -malign-natural (APPLE ONLY) @gol @c APPLE LOCAL end -malign-mac68k -msoft-float -mhard-float -mmultiple -mno-multiple @gol -mstring -mno-string -mupdate -mno-update @gol -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol -mstrict-align -mno-strict-align -mrelocatable @gol -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol @c APPLE LOCAL dynamic-no-pic -mdynamic-no-pic (APPLE ONLY) @gol @c APPLE LOCAL long-branch -mlong-branch (APPLE ONLY) @gol -mcall-aix -mcall-sysv -mcall-netbsd @gol -maix-struct-return -msvr4-struct-return -mabi=altivec -mabi=no-altivec @gol -mprototype -mno-prototype @gol -msim -mmvme -mads -myellowknife -memb -msdata @gol -msdata=@var{opt} -mvxworks -G @var{num} -pthread} @c APPLE LOCAL prune man page @ignore @emph{RT Options} @gccoptlist{ -mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs @gol -mfull-fp-blocks -mhc-struct-return -min-line-mul @gol -mminimum-fp-blocks -mnohc-struct-return} @emph{MIPS Options} @gccoptlist{ -mabicalls -march=@var{cpu-type} -mtune=@var{cpu=type} @gol -mcpu=@var{cpu-type} -membedded-data -muninit-const-in-rodata @gol -membedded-pic -mfp32 -mfp64 -mfused-madd -mno-fused-madd @gol -mgas -mgp32 -mgp64 @gol -mgpopt -mhalf-pic -mhard-float -mint64 -mips1 @gol -mips2 -mips3 -mips4 -mlong64 -mlong32 -mlong-calls -mmemcpy @gol -mmips-as -mmips-tfile -mno-abicalls @gol -mno-embedded-data -mno-uninit-const-in-rodata @gol -mno-embedded-pic -mno-gpopt -mno-long-calls @gol -mno-memcpy -mno-mips-tfile -mno-rnames -mno-stats @gol -mrnames -msoft-float @gol -m4650 -msingle-float -mmad @gol -mstats -EL -EB -G @var{num} -nocpp @gol -mabi=32 -mabi=n32 -mabi=64 -mabi=eabi @gol -mfix7000 -mno-crt0 -mflush-func=@var{func} -mno-flush-func} @c APPLE LOCAL prune man page @end ignore @emph{i386 and x86-64 Options} @gccoptlist{ -mcpu=@var{cpu-type} -march=@var{cpu-type} -mfpmath=@var{unit} @gol -masm=@var{dialect} -mno-fancy-math-387 @gol -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol -mno-wide-multiply -mrtd -malign-double @gol -mpreferred-stack-boundary=@var{num} @gol -mmmx -msse -msse2 -msse-math -m3dnow @gol -mthreads -mno-align-stringops -minline-all-stringops @gol -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol -m96bit-long-double -mregparm=@var{num} -momit-leaf-frame-pointer @gol -mno-red-zone@gol -m32 -m64} @c APPLE LOCAL prune man page @ignore @emph{HPPA Options} @gccoptlist{ -march=@var{architecture-type} @gol -mbig-switch -mdisable-fpregs -mdisable-indexing @gol -mfast-indirect-calls -mgas -mjump-in-delay @gol -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol -mno-jump-in-delay -mno-long-load-store @gol -mno-portable-runtime -mno-soft-float @gol -mno-space-regs -msoft-float -mpa-risc-1-0 @gol -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol -mschedule=@var{cpu-type} -mspace-regs} @emph{Intel 960 Options} @gccoptlist{ -m@var{cpu-type} -masm-compat -mclean-linkage @gol -mcode-align -mcomplex-addr -mleaf-procedures @gol -mic-compat -mic2.0-compat -mic3.0-compat @gol -mintel-asm -mno-clean-linkage -mno-code-align @gol -mno-complex-addr -mno-leaf-procedures @gol -mno-old-align -mno-strict-align -mno-tail-call @gol -mnumerics -mold-align -msoft-float -mstrict-align @gol -mtail-call} @emph{DEC Alpha Options} @gccoptlist{ -mno-fp-regs -msoft-float -malpha-as -mgas @gol -mieee -mieee-with-inexact -mieee-conformant @gol -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol -mtrap-precision=@var{mode} -mbuild-constants @gol -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol -mbwx -mmax -mfix -mcix @gol -mfloat-vax -mfloat-ieee @gol -mexplicit-relocs -msmall-data -mlarge-data @gol -mmemory-latency=@var{time}} @emph{DEC Alpha/VMS Options} @gccoptlist{ -mvms-return-codes} @emph{Clipper Options} @gccoptlist{ -mc300 -mc400} @emph{H8/300 Options} @gccoptlist{ -mrelax -mh -ms -mint32 -malign-300} @emph{SH Options} @gccoptlist{ -m1 -m2 -m3 -m3e @gol -m4-nofpu -m4-single-only -m4-single -m4 @gol -m5-64media -m5-64media-nofpu @gol -m5-32media -m5-32media-nofpu @gol -m5-compact -m5-compact-nofpu @gol -mb -ml -mdalign -mrelax @gol -mbigtable -mfmovd -mhitachi -mnomacsave @gol -mieee -misize -mpadstruct -mspace @gol -mprefergot -musermode} @emph{System V Options} @gccoptlist{ -Qy -Qn -YP,@var{paths} -Ym,@var{dir}} @emph{ARC Options} @gccoptlist{ -EB -EL @gol -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol -mdata=@var{data-section} -mrodata=@var{readonly-data-section}} @emph{TMS320C3x/C4x Options} @gccoptlist{ -mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol -mparallel-insns -mparallel-mpy -mpreserve-float} @emph{V850 Options} @gccoptlist{ -mlong-calls -mno-long-calls -mep -mno-ep @gol -mprolog-function -mno-prolog-function -mspace @gol -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol -mv850 -mbig-switch} @emph{NS32K Options} @gccoptlist{ -m32032 -m32332 -m32532 -m32081 -m32381 @gol -mmult-add -mnomult-add -msoft-float -mrtd -mnortd @gol -mregparam -mnoregparam -msb -mnosb @gol -mbitfield -mnobitfield -mhimem -mnohimem} @emph{AVR Options} @gccoptlist{ -mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol -mcall-prologues -mno-tablejump -mtiny-stack} @emph{MCore Options} @gccoptlist{ -mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment} @emph{MMIX Options} @gccoptlist{ -mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol -mno-base-addresses} @emph{IA-64 Options} @gccoptlist{ -mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol -mvolatile-asm-stop -mb-step -mregister-names -mno-sdata @gol -mconstant-gp -mauto-pic -minline-divide-min-latency @gol -minline-divide-max-throughput -mno-dwarf2-asm @gol -mfixed-range=@var{register-range}} @emph{D30V Options} @gccoptlist{ -mextmem -mextmemory -monchip -mno-asm-optimize -masm-optimize @gol -mbranch-cost=@var{n} -mcond-exec=@var{n}} @emph{S/390 and zSeries Options} @gccoptlist{ -mhard-float -msoft-float -mbackchain -mno-backchain @gol -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol -m64 -m31 -mdebug -mno-debug} @emph{CRIS Options} @gccoptlist{ -mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol -mstack-align -mdata-align -mconst-align @gol -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol -melf -maout -melinux -mlinux -sim -sim2} @emph{PDP-11 Options} @gccoptlist{ -mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol -mint16 -mno-int32 -mfloat32 -mno-float64 @gol -mfloat64 -mno-float32 -mabshi -mno-abshi @gol -mbranch-expensive -mbranch-cheap @gol -msplit -mno-split -munix-asm -mdec-asm} @emph{Xstormy16 Options} @gccoptlist{ -msim} @emph{Xtensa Options} @gccoptlist{ -mbig-endian -mlittle-endian @gol -mdensity -mno-density @gol -mmac16 -mno-mac16 @gol -mmul16 -mno-mul16 @gol -mmul32 -mno-mul32 @gol -mnsa -mno-nsa @gol -mminmax -mno-minmax @gol -msext -mno-sext @gol -mbooleans -mno-booleans @gol -mhard-float -msoft-float @gol -mfused-madd -mno-fused-madd @gol -mserialize-volatile -mno-serialize-volatile @gol -mtext-section-literals -mno-text-section-literals @gol -mtarget-align -mno-target-align @gol -mlongcalls -mno-longcalls} @c APPLE LOCAL prune man page @end ignore @item Code Generation Options @xref{Code Gen Options,,Options for Code Generation Conventions}. @gccoptlist{ -fcall-saved-@var{reg} -fcall-used-@var{reg} @gol -ffixed-@var{reg} -fexceptions @gol -fnon-call-exceptions -funwind-tables @gol -fasynchronous-unwind-tables @gol -finhibit-size-directive -finstrument-functions @gol -fno-common -fno-ident -fno-gnu-linker @gol -fpcc-struct-return -fpic -fPIC @gol -freg-struct-return -fshared-data -fshort-enums @gol -fshort-double -fvolatile @gol -fvolatile-global -fvolatile-static @gol -fverbose-asm -fpack-struct -fstack-check @gol -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol -fargument-alias -fargument-noalias @gol -fargument-noalias-global -fleading-underscore} @end table @menu * Overall Options:: Controlling the kind of output: an executable, object files, assembler files, or preprocessed source. * C Dialect Options:: Controlling the variant of C language compiled. * C++ Dialect Options:: Variations on C++. * Objective-C Dialect Options:: Variations on Objective-C. * Language Independent Options:: Controlling how diagnostics should be formatted. * Warning Options:: How picky should the compiler be? * Debugging Options:: Symbol tables, measurements, and debugging dumps. * Optimize Options:: How much optimization? * Preprocessor Options:: Controlling header files and macro definitions. Also, getting dependency information for Make. * Assembler Options:: Passing options to the assembler. * Link Options:: Specifying libraries and so on. * Directory Options:: Where to find header files and libraries. Where to find the compiler executable files. * Spec Files:: How to pass switches to sub-processes. * Target Options:: Running a cross-compiler, or an old version of GCC. @end menu @node Overall Options @section Options Controlling the Kind of Output Compilation can involve up to four stages: preprocessing, compilation proper, assembly and linking, always in that order. The first three stages apply to an individual source file, and end by producing an object file; linking combines all the object files (those newly compiled, and those specified as input) into an executable file. @cindex file name suffix For any given input file, the file name suffix determines what kind of compilation is done: @table @gcctabopt @item @var{file}.c C source code which must be preprocessed. @item @var{file}.i C source code which should not be preprocessed. @item @var{file}.ii C++ source code which should not be preprocessed. @item @var{file}.m Objective-C source code. Note that you must link with the library @file{libobjc.a} to make an Objective-C program work. @item @var{file}.mi Objective-C source code which should not be preprocessed. @item @var{file}.h C header file (not to be compiled or linked). @item @var{file}.cc @itemx @var{file}.cp @itemx @var{file}.cxx @itemx @var{file}.cpp @itemx @var{file}.c++ @itemx @var{file}.C C++ source code which must be preprocessed. Note that in @samp{.cxx}, the last two letters must both be literally @samp{x}. Likewise, @samp{.C} refers to a literal capital C@. @c APPLE LOCAL begin Objective-C++ @item @var{file}.mm @itemx @var{file}.M Objective-C++ source code which must be preprocessed. (APPLE ONLY) @item @var{file}.mii Objective-C++ source code which should not be preprocessed. (APPLE ONLY) @c APPLE LOCAL end Objective-C++ @item @var{file}.f @itemx @var{file}.for @itemx @var{file}.FOR Fortran source code which should not be preprocessed. @item @var{file}.F @itemx @var{file}.fpp @itemx @var{file}.FPP Fortran source code which must be preprocessed (with the traditional preprocessor). @item @var{file}.r Fortran source code which must be preprocessed with a RATFOR preprocessor (not included with GCC)@. @xref{Overall Options,,Options Controlling the Kind of Output, g77, Using and Porting GNU Fortran}, for more details of the handling of Fortran input files. @c FIXME: Descriptions of Java file types. @c @var{file}.java @c @var{file}.class @c @var{file}.zip @c @var{file}.jar @item @var{file}.ads Ada source code file which contains a library unit declaration (a declaration of a package, subprogram, or generic, or a generic instantiation), or a library unit renaming declaration (a package, generic, or subprogram renaming declaration). Such files are also called @dfn{specs}. @itemx @var{file}.adb Ada source code file containing a library unit body (a subprogram or package body). Such files are also called @dfn{bodies}. @c GCC also knows about some suffixes for languages not yet included: @c Pascal: @c @var{file}.p @c @var{file}.pas @item @var{file}.s @c APPLE LOCAL preprocess .s files Assembler code. Apple's version of GCC runs the preprocessor on these files as well as those ending in @samp{.S}. @item @var{file}.S Assembler code which must be preprocessed. @item @var{other} An object file to be fed straight into linking. Any file name with no recognized suffix is treated this way. @end table @opindex x You can specify the input language explicitly with the @option{-x} option: @table @gcctabopt @item -x @var{language} Specify explicitly the @var{language} for the following input files (rather than letting the compiler choose a default based on the file name suffix). This option applies to all following input files until the next @option{-x} option. Possible values for @var{language} are: @example c c-header cpp-output c++ c++-cpp-output objective-c objc-cpp-output @c APPLE LOCAL Objective-C++ objective-c++ (APPLE ONLY) assembler assembler-with-cpp ada f77 f77-cpp-input ratfor java @end example @item -x none Turn off any specification of a language, so that subsequent files are handled according to their file name suffixes (as they are if @option{-x} has not been used at all). @c APPLE LOCAL begin -ObjC 2001-08-03 sts ** @item -ObjC @item -ObjC++ @opindex ObjC @opindex ObjC++ These are similar in effect to @option{-x objective-c} and @option{-x objective-c++}, but affect only the choice of compiler for files already identified as source files. (APPLE ONLY) @c APPLE LOCAL end -ObjC 2001-08-03 sts ** @c APPLE LOCAL begin fat builds @item -arch @var{arch} Compile for the specified target architecture @var{arch}. The allowable values are @samp{i386} and @samp{ppc}. Multiple options work, and direct the compiler to produce ``fat'' binaries including object code for each architecture specified with @option{-arch}. This option only works if assembler and libraries are available for each architecture specified. (APPLE ONLY) @opindex arch @c APPLE LOCAL end fat builds @item -pass-exit-codes @opindex pass-exit-codes Normally the @command{gcc} program will exit with the code of 1 if any phase of the compiler returns a non-success return code. If you specify @option{-pass-exit-codes}, the @command{gcc} program will instead return with numerically highest error produced by any phase that returned an error indication. @end table If you only want some of the stages of compilation, you can use @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and one of the options @option{-c}, @option{-S}, or @option{-E} to say where @command{gcc} is to stop. Note that some combinations (for example, @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all. @table @gcctabopt @item -c @opindex c Compile or assemble the source files, but do not link. The linking stage simply is not done. The ultimate output is in the form of an object file for each source file. By default, the object file name for a source file is made by replacing the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}. Unrecognized input files, not requiring compilation or assembly, are ignored. @item -S @opindex S Stop after the stage of compilation proper; do not assemble. The output is in the form of an assembler code file for each non-assembler input file specified. By default, the assembler file name for a source file is made by replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}. Input files that don't require compilation are ignored. @item -E @opindex E Stop after the preprocessing stage; do not run the compiler proper. The output is in the form of preprocessed source code, which is sent to the standard output. Input files which don't require preprocessing are ignored. @cindex output file option @item -o @var{file} @opindex o Place output in file @var{file}. This applies regardless to whatever sort of output is being produced, whether it be an executable file, an object file, an assembler file or preprocessed C code. Since only one output file can be specified, it does not make sense to use @option{-o} when compiling more than one input file, unless you are producing an executable file as output. If @option{-o} is not specified, the default is to put an executable file in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and all preprocessed C source on standard output. @item -v @opindex v Print (on standard error output) the commands executed to run the stages of compilation. Also print the version number of the compiler driver program and of the preprocessor and the compiler proper. @item -### @opindex ### Like @option{-v} 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. @item -pipe @opindex pipe Use pipes rather than temporary files for communication between the various stages of compilation. This fails to work on some systems where the assembler is unable to read from a pipe; but the GNU assembler has no trouble. @item --help @opindex help Print (on the standard output) a description of the command line options understood by @command{gcc}. If the @option{-v} option is also specified then @option{--help} will also be passed on to the various processes invoked by @command{gcc}, so that they can display the command line options they accept. If the @option{-W} option is also specified then command line options which have no documentation associated with them will also be displayed. @item --target-help @opindex target-help Print (on the standard output) a description of target specific command line options for each tool. @end table @node Invoking G++ @section Compiling C++ Programs @cindex suffixes for C++ source @cindex C++ source file suffixes C++ source files conventionally use one of the suffixes @samp{.C}, @samp{.cc}, @samp{.cpp}, @samp{.c++}, @samp{.cp}, or @samp{.cxx}; preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes files with these names and compiles them as C++ programs even if you call the compiler the same way as for compiling C programs (usually with the name @command{gcc}). @findex g++ @findex c++ However, C++ programs often require class libraries as well as a compiler that understands the C++ language---and under some circumstances, you might want to compile programs from standard input, or otherwise without a suffix that flags them as C++ programs. @command{g++} is a program that calls GCC with the default language set to C++, and automatically specifies linking against the C++ library. On many systems, @command{g++} is also installed with the name @command{c++}. @cindex invoking @command{g++} When you compile C++ programs, you may specify many of the same command-line options that you use for compiling programs in any language; or command-line options meaningful for C and related languages; or options that are meaningful only for C++ programs. @xref{C Dialect Options,,Options Controlling C Dialect}, for explanations of options for languages related to C@. @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for explanations of options that are meaningful only for C++ programs. @node C Dialect Options @section Options Controlling C Dialect @cindex dialect options @cindex language dialect options @cindex options, dialect The following options control the dialect of C (or languages derived from C, such as C++ and Objective-C) that the compiler accepts: @table @gcctabopt @cindex ANSI support @cindex ISO support @item -ansi @opindex ansi In C mode, support all ISO C89 programs. In C++ mode, remove GNU extensions that conflict with ISO C++. This turns off certain features of GCC that are incompatible with ISO C89 (when compiling C code), or of standard C++ (when compiling C++ code), such as the @code{asm} and @code{typeof} keywords, and predefined macros such as @code{unix} and @code{vax} that identify the type of system you are using. It also enables the undesirable and rarely used ISO trigraph feature. For the C compiler, it disables recognition of C++ style @samp{//} comments as well as the @code{inline} keyword. The alternate keywords @code{__asm__}, @code{__extension__}, @code{__inline__} and @code{__typeof__} continue to work despite @option{-ansi}. You would not want to use them in an ISO C program, of course, but it is useful to put them in header files that might be included in compilations done with @option{-ansi}. Alternate predefined macros such as @code{__unix__} and @code{__vax__} are also available, with or without @option{-ansi}. The @option{-ansi} option does not cause non-ISO programs to be rejected gratuitously. For that, @option{-pedantic} is required in addition to @option{-ansi}. @xref{Warning Options}. The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi} option is used. Some header files may notice this macro and refrain from declaring certain functions or defining certain macros that the ISO standard doesn't call for; this is to avoid interfering with any programs that might use these names for other things. Functions which would normally be built in but do not have semantics defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in functions with @option{-ansi} is used. @xref{Other Builtins,,Other built-in functions provided by GCC}, for details of the functions affected. @item -std= @opindex std Determine the language standard. This option is currently only supported when compiling C@. A value for this option must be provided; possible values are @table @samp @item c89 @itemx iso9899:1990 ISO C89 (same as @option{-ansi}). @item iso9899:199409 ISO C89 as modified in amendment 1. @item c99 @itemx c9x @itemx iso9899:1999 @itemx iso9899:199x ISO C99. Note that this standard is not yet fully supported; see @w{@uref{http://gcc.gnu.org/gcc-3.1/c99status.html}} for more information. The names @samp{c9x} and @samp{iso9899:199x} are deprecated. @item gnu89 Default, ISO C89 plus GNU extensions (including some C99 features). @item gnu99 @item gnu9x ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC, this will become the default. The name @samp{gnu9x} is deprecated. @end table Even when this option is not specified, you can still use some of the features of newer standards in so far as they do not conflict with previous C standards. For example, you may use @code{__restrict__} even when @option{-std=c99} is not specified. The @option{-std} options specifying some version of ISO C have the same effects as @option{-ansi}, except that features that were not in ISO C89 but are in the specified version (for example, @samp{//} comments and the @code{inline} keyword in ISO C99) are not disabled. @xref{Standards,,Language Standards Supported by GCC}, for details of these standard versions. @item -aux-info @var{filename} @opindex aux-info Output to the given filename prototyped declarations for all functions declared and/or defined in a translation unit, including those in header files. This option is silently ignored in any language other than C@. Besides declarations, the file indicates, in comments, the origin of each declaration (source file and line), whether the declaration was implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or @samp{O} for old, respectively, in the first character after the line number and the colon), and whether it came from a declaration or a definition (@samp{C} or @samp{F}, respectively, in the following character). In the case of function definitions, a K&R-style list of arguments followed by their declarations is also provided, inside comments, after the declaration. @c APPLE LOCAL begin AltiVec @item -faltivec Enable the AltiVec language extensions, as defined in Motorola's AltiVec PIM. This includes the recognition of @code{vector} and @code{pixel} as (context-dependent) keywords, the definition of built-in functions such as @code{vec_add}, and other extensions. Note that unlike the option @samp{-maltivec}, the extensions do not require the inclusion of any special header files. (APPLE ONLY) @c APPLE LOCAL end AltiVec @item -fno-asm @opindex fno-asm Do not recognize @code{asm}, @code{inline} or @code{typeof} as a keyword, so that code can use these words as identifiers. You can use the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__} instead. @option{-ansi} implies @option{-fno-asm}. In C++, this switch only affects the @code{typeof} keyword, since @code{asm} and @code{inline} are standard keywords. You may want to use the @option{-fno-gnu-keywords} flag instead, which has the same effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this switch only affects the @code{asm} and @code{typeof} keywords, since @code{inline} is a standard keyword in ISO C99. @item -fno-builtin @itemx -fno-builtin-@var{function} @r{(C and Objective-C only)} @opindex fno-builtin @cindex built-in functions Don't recognize built-in functions that do not begin with @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in functions provided by GCC}, for details of the functions affected, including those which are not built-in functions when @option{-ansi} or @option{-std} options for strict ISO C conformance are used because they do not have an ISO standard meaning. GCC normally generates special code to handle certain built-in functions more efficiently; for instance, calls to @code{alloca} may become single instructions that adjust the stack directly, and calls to @code{memcpy} may become inline copy loops. The resulting code is often both smaller and faster, but since the function calls no longer appear as such, you cannot set a breakpoint on those calls, nor can you change the behavior of the functions by linking with a different library. In C++, @option{-fno-builtin} is always in effect. The @option{-fbuiltin} option has no effect. Therefore, in C++, the only way to get the optimization benefits of built-in functions is to call the function using the @samp{__builtin_} prefix. The GNU C++ Standard Library uses built-in functions to implement many functions (like @code{std::strchr}), so that you automatically get efficient code. With the @option{-fno-builtin-@var{function}} option, not available when compiling C++, only the built-in function @var{function} is disabled. @var{function} must not begin with @samp{__builtin_}. If a function is named this is not built-in in this version of GCC, this option is ignored. There is no corresponding @option{-fbuiltin-@var{function}} option; if you wish to enable built-in functions selectively when using @option{-fno-builtin} or @option{-ffreestanding}, you may define macros such as: @smallexample #define abs(n) __builtin_abs ((n)) #define strcpy(d, s) __builtin_strcpy ((d), (s)) @end smallexample @item -fhosted @opindex fhosted @cindex hosted environment Assert that compilation takes place in a hosted environment. This implies @option{-fbuiltin}. A hosted environment is one in which the entire standard library is available, and in which @code{main} has a return type of @code{int}. Examples are nearly everything except a kernel. This is equivalent to @option{-fno-freestanding}. @item -ffreestanding @opindex ffreestanding @cindex hosted environment Assert that compilation takes place in a freestanding environment. This implies @option{-fno-builtin}. A freestanding environment is one in which the standard library may not exist, and program startup may not necessarily be at @code{main}. The most obvious example is an OS kernel. This is equivalent to @option{-fno-hosted}. @xref{Standards,,Language Standards Supported by GCC}, for details of freestanding and hosted environments. @item -trigraphs @opindex trigraphs Support ISO C trigraphs. The @option{-ansi} option (and @option{-std} options for strict ISO C conformance) implies @option{-trigraphs}. @item -no-integrated-cpp @opindex 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 @option{-B} option. This flag is applicable in both C and C++ modes. We do not guarantee to retain this option in future, and we may change its semantics. @c APPLE LOCAL begin cpp-precomp @item -no-cpp-precomp @opindex no-cpp-precomp By default, Apple's GCC preprocesses C and Objective-C with a special preprocessor called @samp{cpp-precomp} that supports precompiled headers. This preprocessor cannot always handle every construct that GCC supports; use @samp{-no-cpp-precomp} to switch to using GNU cpp instead. (APPLE ONLY) @c APPLE LOCAL end cpp-precomp @c APPLE LOCAL begin PFE @item --dump-pch @var{name} @opindex dump-pch Dump the state of the compiler into a directory named @var{name}, after processing all the other arguments. This is useful for creating precompiled headers. (APPLE ONLY) @item --load-pch @var{name} @opindex load-pch Restore the state of the compiler from the directory @var{name} before processing the other arguments. The net effect is similar to @option{-include}, but it happens much more quickly. (APPLE ONLY) So for instance if the file @file{myprefix.c} #includes various headers that are useful to all files in your program, you can do @example 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 ... @end example @c APPLE LOCAL end PFE @cindex traditional C language @cindex C language, traditional @item -traditional @opindex traditional Attempt to support some aspects of traditional C compilers. Specifically: @itemize @bullet @item All @code{extern} declarations take effect globally even if they are written inside of a function definition. This includes implicit declarations of functions. @item The newer keywords @code{typeof}, @code{inline}, @code{signed}, @code{const} and @code{volatile} are not recognized. (You can still use the alternative keywords such as @code{__typeof__}, @code{__inline__}, and so on.) @item Comparisons between pointers and integers are always allowed. @item Integer types @code{unsigned short} and @code{unsigned char} promote to @code{unsigned int}. @item Out-of-range floating point literals are not an error. @item Certain constructs which ISO regards as a single invalid preprocessing number, such as @samp{0xe-0xd}, are treated as expressions instead. @item String ``constants'' are not necessarily constant; they are stored in writable space, and identical looking constants are allocated separately. (This is the same as the effect of @option{-fwritable-strings}.) @cindex @code{longjmp} and automatic variables @item All automatic variables not declared @code{register} are preserved by @code{longjmp}. Ordinarily, GNU C follows ISO C: automatic variables not declared @code{volatile} may be clobbered. @item @cindex @samp{\x} @cindex @samp{\a} @cindex escape sequences, traditional The character escape sequences @samp{\x} and @samp{\a} evaluate as the literal characters @samp{x} and @samp{a} respectively. Without @w{@option{-traditional}}, @samp{\x} is a prefix for the hexadecimal representation of a character, and @samp{\a} produces a bell. @end itemize This option is deprecated and may be removed. You may wish to use @option{-fno-builtin} as well as @option{-traditional} if your program uses names that are normally GNU C built-in functions for other purposes of its own. You cannot use @option{-traditional} if you include any header files that rely on ISO C features. Some vendors are starting to ship systems with ISO C header files and you cannot use @option{-traditional} on such systems to compile files that include any system headers. The @option{-traditional} option also enables @option{-traditional-cpp}. @item -traditional-cpp @opindex traditional-cpp @c APPLE LOCAL cpp-precomp In Apple's version of GCC, this means to use GNU cpp instead of cpp-precomp to preprocess. This meaning of the option is deprecated, and will eventually revert to its standard meaning. @item -fcond-mismatch @opindex fcond-mismatch Allow conditional expressions with mismatched types in the second and third arguments. The value of such an expression is void. This option is not supported for C++. @item -funsigned-char @opindex funsigned-char Let the type @code{char} be unsigned, like @code{unsigned char}. Each kind of machine has a default for what @code{char} should be. It is either like @code{unsigned char} by default or like @code{signed char} by default. Ideally, a portable program should always use @code{signed char} or @code{unsigned char} when it depends on the signedness of an object. But many programs have been written to use plain @code{char} and expect it to be signed, or expect it to be unsigned, depending on the machines they were written for. This option, and its inverse, let you make such a program work with the opposite default. The type @code{char} is always a distinct type from each of @code{signed char} or @code{unsigned char}, even though its behavior is always just like one of those two. @item -fsigned-char @opindex fsigned-char Let the type @code{char} be signed, like @code{signed char}. Note that this is equivalent to @option{-fno-unsigned-char}, which is the negative form of @option{-funsigned-char}. Likewise, the option @option{-fno-signed-char} is equivalent to @option{-funsigned-char}. @item -fsigned-bitfields @itemx -funsigned-bitfields @itemx -fno-signed-bitfields @itemx -fno-unsigned-bitfields @opindex fsigned-bitfields @opindex funsigned-bitfields @opindex fno-signed-bitfields @opindex fno-unsigned-bitfields These options control whether a bit-field is signed or unsigned, when the declaration does not use either @code{signed} or @code{unsigned}. By default, such a bit-field is signed, because this is consistent: the basic integer types such as @code{int} are signed types. However, when @option{-traditional} is used, bit-fields are all unsigned no matter what. @item -fwritable-strings @opindex fwritable-strings Store string constants in the writable data segment and don't uniquize them. This is for compatibility with old programs which assume they can write into string constants. The option @option{-traditional} also has this effect. Writing into string constants is a very bad idea; ``constants'' should be constant. @c APPLE LOCAL begin constant cfstrings @item -fconstant-cfstrings @opindex fconstant-cfstrings Enable the automatic creation of a CoreFoundation-type constant string whenever a special builtin @code{__builtin__CFStringMakeConstantString} is called on a literal string. (APPLE ONLY) @c APPLE LOCAL end constant cfstrings @item -fallow-single-precision @opindex fallow-single-precision Do not promote single precision math operations to double precision, even when compiling with @option{-traditional}. Traditional K&R C promotes all floating point operations to double precision, regardless of the sizes of the operands. On the architecture for which you are compiling, single precision may be faster than double precision. If you must use @option{-traditional}, but want to use single precision operations when the operands are single precision, use this option. This option has no effect when compiling with ISO or GNU C conventions (the default). @item -fshort-wchar @opindex fshort-wchar Override the underlying type for @samp{wchar_t} to be @samp{short unsigned int} instead of the default for the target. This option is useful for building programs to run under WINE@. @c APPLE LOCAL begin Pascal Strings 2001-07-05 zll ** @item -fpascal-strings Allow Pascal-style string literals to be constructed. (APPLE ONLY) @xref{Pascal Strings,,Constructing String Literals with a Pascal-style Length Byte}, for more information on the syntax and semantics of Pascal string literals. @c APPLE LOCAL end Pascal Strings 2001-07-05 zll ** @c APPLE LOCAL begin coalesced 2002-04-11 tur ** @item -fcoalesce @opindex fcoalesce Coalesce duplicated functions and data. The linker will discard all but one, saving space. Enabled by default. (APPLE ONLY) @item -fweak-coalesced @opindex fweak-coalesced Use the new OS X "weak_definitions" section attribute for coalesced items. A single "normal" definition will be chosen by the linker over any number of weakly-coalesced ones. (APPLE ONLY) @c APPLE LOCAL end coalesced 2002-04-11 tur ** @end table @node C++ Dialect Options @section Options Controlling C++ Dialect @cindex compiler options, C++ @cindex C++ options, command line @cindex options, C++ This section describes the command-line options that are only meaningful for C++ programs; but you can also use most of the GNU compiler options regardless of what language your program is in. For example, you might compile a file @code{firstClass.C} like this: @example g++ -g -frepo -O -c firstClass.C @end example @noindent In this example, only @option{-frepo} is an option meant only for C++ programs; you can use the other options with any language supported by GCC@. Here is a list of options that are @emph{only} for compiling C++ programs: @table @gcctabopt @item -fno-access-control @opindex fno-access-control Turn off all access checking. This switch is mainly useful for working around bugs in the access control code. @item -fcheck-new @opindex fcheck-new Check that the pointer returned by @code{operator new} is non-null before attempting to modify the storage allocated. The current Working Paper requires that @code{operator new} never return a null pointer, so this check is normally unnecessary. An alternative to using this option is to specify that your @code{operator new} does not throw any exceptions; if you declare it @samp{throw()}, G++ will check the return value. See also @samp{new (nothrow)}. @item -fconserve-space @opindex fconserve-space Put uninitialized or runtime-initialized global variables into the common segment, as C does. This saves space in the executable at the cost of not diagnosing duplicate definitions. If you compile with this flag and your program mysteriously crashes after @code{main()} has completed, you may have an object that is being destroyed twice because two definitions were merged. This option is no longer useful on most targets, now that support has been added for putting variables into BSS without making them common. @item -fno-const-strings @opindex fno-const-strings Give string constants type @code{char *} instead of type @code{const char *}. By default, G++ uses type @code{const char *} as required by the standard. Even if you use @option{-fno-const-strings}, you cannot actually modify the value of a string constant, unless you also use @option{-fwritable-strings}. This option might be removed in a future release of G++. For maximum portability, you should structure your code so that it works with string constants that have type @code{const char *}. @item -fdollars-in-identifiers @opindex fdollars-in-identifiers Accept @samp{$} in identifiers. You can also explicitly prohibit use of @samp{$} with the option @option{-fno-dollars-in-identifiers}. (GNU C allows @samp{$} by default on most target systems, but there are a few exceptions.) Traditional C allowed the character @samp{$} to form part of identifiers. However, ISO C and C++ forbid @samp{$} in identifiers. @item -fno-elide-constructors @opindex fno-elide-constructors The C++ standard allows an implementation to omit creating a temporary which is only used to initialize another object of the same type. Specifying this option disables that optimization, and forces G++ to call the copy constructor in all cases. @item -fno-enforce-eh-specs @opindex fno-enforce-eh-specs Don't check for violation of exception specifications at runtime. This option violates the C++ standard, but may be useful for reducing code size in production builds, much like defining @samp{NDEBUG}. The compiler will still optimize based on the exception specifications. @item -fexternal-templates @opindex fexternal-templates Cause @samp{#pragma interface} and @samp{implementation} to apply to template instantiation; template instances are emitted or not according to the location of the template definition. @xref{Template Instantiation}, for more information. This option is deprecated. @item -falt-external-templates @opindex falt-external-templates Similar to @option{-fexternal-templates}, but template instances are emitted or not according to the place where they are first instantiated. @xref{Template Instantiation}, for more information. This option is deprecated. @item -ffor-scope @itemx -fno-for-scope @opindex ffor-scope @opindex fno-for-scope If @option{-ffor-scope} is specified, the scope of variables declared in a @i{for-init-statement} is limited to the @samp{for} loop itself, as specified by the C++ standard. If @option{-fno-for-scope} is specified, the scope of variables declared in a @i{for-init-statement} extends to the end of the enclosing scope, as was the case in old versions of G++, and other (traditional) implementations of C++. The default if neither flag is given to follow the standard, but to allow and give a warning for old-style code that would otherwise be invalid, or have different behavior. @item -fno-gnu-keywords @opindex fno-gnu-keywords Do not recognize @code{typeof} as a keyword, so that code can use this word as an identifier. You can use the keyword @code{__typeof__} instead. @option{-ansi} implies @option{-fno-gnu-keywords}. @item -fno-implicit-templates @opindex fno-implicit-templates Never emit code for non-inline templates which are instantiated implicitly (i.e.@: by use); only emit code for explicit instantiations. @xref{Template Instantiation}, for more information. @item -fno-implicit-inline-templates @opindex fno-implicit-inline-templates Don't emit code for implicit instantiations of inline templates, either. The default is to handle inlines differently so that compiles with and without optimization will need the same set of explicit instantiations. @item -fno-implement-inlines @opindex fno-implement-inlines To save space, do not emit out-of-line copies of inline functions controlled by @samp{#pragma implementation}. This will cause linker errors if these functions are not inlined everywhere they are called. @c APPLE LOCAL begin -findirect-virtual-calls 2001-10-30 sts ** @item -findirect-virtual-calls @opindex findirect-virtual-calls Do not make direct calls to virtual functions; instead, always go through the vtable. (APPLE ONLY) @c APPLE LOCAL end -findirect-virtual-calls 2001-10-30 sts ** @c APPLE LOCAL begin -fapple-kext @item -fapple-kext @opindex fapple-kext Alter vtables, destructors, and other implementation details to more closely resemble the GCC 2.95 ABI. This is to make kernel extensions loadable by Darwin kernels built using older compilers, and is required to build any Darwin kernel extension. (APPLE ONLY) @c APPLE LOCAL end -fapple-kext @c APPLE LOCAL begin -fcoalesce-templates 2002-04-11 tur ** @item -fcoalesce-templates @opindex fcoalesce-templates Mark instantiated templates as "coalesced": the linker will discard all but one, thus saving space. (APPLE ONLY) @c APPLE LOCAL end -fcoalesce-templates 2002-04-11 tur ** @item -fms-extensions @opindex fms-extensions Disable pedantic warnings about constructs used in MFC, such as implicit int and getting a pointer to member function via non-standard syntax. @item -fno-nonansi-builtins @opindex fno-nonansi-builtins Disable built-in declarations of functions that are not mandated by ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit}, @code{index}, @code{bzero}, @code{conjf}, and other related functions. @item -fno-operator-names @opindex fno-operator-names Do not treat the operator name keywords @code{and}, @code{bitand}, @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as synonyms as keywords. @item -fno-optional-diags @opindex fno-optional-diags Disable diagnostics that the standard says a compiler does not need to issue. Currently, the only such diagnostic issued by G++ is the one for a name having multiple meanings within a class. @item -fpermissive @opindex fpermissive Downgrade messages about nonconformant code from errors to warnings. By default, G++ effectively sets @option{-pedantic-errors} without @option{-pedantic}; this option reverses that. This behavior and this option are superseded by @option{-pedantic}, which works as it does for GNU C@. @item -frepo @opindex frepo Enable automatic template instantiation at link time. This option also implies @option{-fno-implicit-templates}. @xref{Template Instantiation}, for more information. @item -fno-rtti @opindex fno-rtti Disable generation of information about every class with virtual functions for use by the C++ runtime type identification features (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts of the language, you can save some space by using this flag. Note that exception handling uses the same information, but it will generate it as needed. @item -fstats @opindex fstats Emit statistics about front-end processing at the end of the compilation. This information is generally only useful to the G++ development team. @item -ftemplate-depth-@var{n} @opindex ftemplate-depth Set the maximum instantiation depth for template classes to @var{n}. A limit on the template instantiation depth is needed to detect endless recursions during template class instantiation. ANSI/ISO C++ conforming programs must not rely on a maximum depth greater than 17. @item -fuse-cxa-atexit @opindex fuse-cxa-atexit Register destructors for objects with static storage duration with the @code{__cxa_atexit} function rather than the @code{atexit} function. This option is required for fully standards-compliant handling of static destructors, but will only work if your C library supports @code{__cxa_atexit}. @c APPLE LOCAL manual This option is not supported on Mac OS X. @item -fvtable-gc @opindex fvtable-gc Emit special relocations for vtables and virtual function references so that the linker can identify unused virtual functions and zero out vtable slots that refer to them. This is most useful with @option{-ffunction-sections} and @option{-Wl,--gc-sections}, in order to also discard the functions themselves. This optimization requires GNU as and GNU ld. Not all systems support this option. @option{-Wl,--gc-sections} is ignored without @option{-static}. @item -fno-weak @opindex fno-weak Do not use weak symbol support, even if it is provided by the linker. By default, G++ will use weak symbols if they are available. This option exists only for testing, and should not be used by end-users; it will result in inferior code and has no benefits. This option may be removed in a future release of G++. @item -nostdinc++ @opindex nostdinc++ Do not search for header files in the standard directories specific to C++, but do still search the other standard directories. (This option is used when building the C++ library.) @end table In addition, these optimization, warning, and code generation options have meanings only for C++ programs: @table @gcctabopt @item -fno-default-inline @opindex fno-default-inline Do not assume @samp{inline} for functions defined inside a class scope. @xref{Optimize Options,,Options That Control Optimization}. Note that these functions will have linkage like inline functions; they just won't be inlined by default. @item -Wctor-dtor-privacy @r{(C++ only)} @opindex Wctor-dtor-privacy Warn when a class seems unusable, because all the constructors or destructors in a class are private and the class has no friends or public static member functions. @item -Wnon-virtual-dtor @r{(C++ only)} @opindex Wnon-virtual-dtor Warn when a class declares a non-virtual destructor that should probably be virtual, because it looks like the class will be used polymorphically. @item -Wreorder @r{(C++ only)} @opindex Wreorder @cindex reordering, warning @cindex warning for reordering of member initializers Warn when the order of member initializers given in the code does not match the order in which they must be executed. For instance: @smallexample struct A @{ int i; int j; A(): j (0), i (1) @{ @} @}; @end smallexample Here the compiler will warn that the member initializers for @samp{i} and @samp{j} will be rearranged to match the declaration order of the members. @end table The following @option{-W@dots{}} options are not affected by @option{-Wall}. @table @gcctabopt @item -Weffc++ @r{(C++ only)} @opindex Weffc++ Warn about violations of the following style guidelines from Scott Meyers' @cite{Effective C++} book: @itemize @bullet @item Item 11: Define a copy constructor and an assignment operator for classes with dynamically allocated memory. @item Item 12: Prefer initialization to assignment in constructors. @item Item 14: Make destructors virtual in base classes. @item Item 15: Have @code{operator=} return a reference to @code{*this}. @item Item 23: Don't try to return a reference when you must return an object. @end itemize and about violations of the following style guidelines from Scott Meyers' @cite{More Effective C++} book: @itemize @bullet @item Item 6: Distinguish between prefix and postfix forms of increment and decrement operators. @item Item 7: Never overload @code{&&}, @code{||}, or @code{,}. @end itemize If you use this option, you should be aware that the standard library headers do not obey all of these guidelines; you can use @samp{grep -v} to filter out those warnings. @item -Wno-deprecated @r{(C++ only)} @opindex Wno-deprecated Do not warn about usage of deprecated features. @xref{Deprecated Features}. @item -Wno-non-template-friend @r{(C++ only)} @opindex Wno-non-template-friend Disable warnings when non-templatized friend functions are declared within a template. With the advent of explicit template specification support in G++, if the name of the friend is an unqualified-id (i.e., @samp{friend foo(int)}), the C++ language specification demands that the friend declare or define an ordinary, nontemplate function. (Section 14.5.3). Before G++ implemented explicit specification, unqualified-ids could be interpreted as a particular specialization of a templatized function. Because this non-conforming behavior is no longer the default behavior for G++, @option{-Wnon-template-friend} allows the compiler to check existing code for potential trouble spots, and is on by default. This new compiler behavior can be turned off with @option{-Wno-non-template-friend} which keeps the conformant compiler code but disables the helpful warning. @item -Wold-style-cast @r{(C++ only)} @opindex Wold-style-cast Warn if an old-style (C-style) cast to a non-void type is used within a C++ program. The new-style casts (@samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are less vulnerable to unintended effects, and much easier to grep for. @item -Woverloaded-virtual @r{(C++ only)} @opindex Woverloaded-virtual @cindex overloaded virtual fn, warning @cindex warning for overloaded virtual fn Warn when a function declaration hides virtual functions from a base class. For example, in: @smallexample struct A @{ virtual void f(); @}; struct B: public A @{ void f(int); @}; @end smallexample the @code{A} class version of @code{f} is hidden in @code{B}, and code like this: @smallexample B* b; b->f(); @end smallexample will fail to compile. @item -Wno-pmf-conversions @r{(C++ only)} @opindex Wno-pmf-conversions Disable the diagnostic for converting a bound pointer to member function to a plain pointer. @item -Wsign-promo @r{(C++ only)} @opindex Wsign-promo Warn when overload resolution chooses a promotion from unsigned or enumeral type to a signed type over a conversion to an unsigned type of the same size. Previous versions of G++ would try to preserve unsignedness, but the standard mandates the current behavior. @item -Wsynth @r{(C++ only)} @opindex Wsynth @cindex warning for synthesized methods @cindex synthesized methods, warning Warn when G++'s synthesis behavior does not match that of cfront. For instance: @smallexample struct A @{ operator int (); A& operator = (int); @}; main () @{ A a,b; a = b; @} @end smallexample In this example, G++ will synthesize a default @samp{A& operator = (const A&);}, while cfront will use the user-defined @samp{operator =}. @end table @node Objective-C Dialect Options @section Options Controlling Objective-C Dialect @cindex compiler options, Objective-C @cindex Objective-C options, command line @cindex options, Objective-C This section describes the command-line options that are only meaningful for Objective-C programs; but you can also use most of the GNU compiler options regardless of what language your program is in. For example, you might compile a file @code{some_class.m} like this: @example gcc -g -fgnu-runtime -O -c some_class.m @end example @noindent In this example, only @option{-fgnu-runtime} is an option meant only for Objective-C programs; you can use the other options with any language supported by GCC@. Here is a list of options that are @emph{only} for compiling Objective-C programs: @table @gcctabopt @item -fconstant-string-class=@var{class-name} @opindex fconstant-string-class Use @var{class-name} as the name of the class to instantiate for each literal string specified with the syntax @code{@@"@dots{}"}. The default class name is @code{NXConstantString}. @item -fgnu-runtime @opindex fgnu-runtime Generate object code compatible with the standard GNU Objective-C runtime. This is the default for most types of systems. @item -fnext-runtime @opindex fnext-runtime Generate output compatible with the NeXT runtime. This is the default for NeXT-based systems, including Darwin and Mac OS X@. @item -gen-decls @opindex gen-decls Dump interface declarations for all classes seen in the source file to a file named @file{@var{sourcename}.decl}. @item -Wno-protocol @opindex Wno-protocol Do not warn if methods required by a protocol are not implemented in the class adopting it. @item -Wselector @opindex Wselector Warn if a selector has multiple methods of different types defined. @c not documented because only avail via -Wp @c @item -print-objc-runtime-info @end table @node Language Independent Options @section Options to Control Diagnostic Messages Formatting @cindex options to control diagnostics formatting @cindex diagnostic messages @cindex message formatting Traditionally, diagnostic messages have been formatted irrespective of the output device's aspect (e.g.@: its width, @dots{}). The options described below can be used to control the diagnostic messages formatting algorithm, e.g.@: how many characters per line, how often source location information should be reported. Right now, only the C++ front end can honor these options. However it is expected, in the near future, that the remaining front ends would be able to digest them correctly. @table @gcctabopt @item -fmessage-length=@var{n} @opindex fmessage-length Try to format error messages so that they fit on lines of about @var{n} characters. The default is 72 characters for @command{g++} and 0 for the rest of the front ends supported by GCC@. If @var{n} is zero, then no line-wrapping will be done; each error message will appear on a single line. @opindex fdiagnostics-show-location @item -fdiagnostics-show-location=once Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit @emph{once} source location information; that is, in case the message is too long to fit on a single physical line and has to be wrapped, the source location won't be emitted (as prefix) again, over and over, in subsequent continuation lines. This is the default behavior. @item -fdiagnostics-show-location=every-line Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit the same source location information (as prefix) for physical lines that result from the process of breaking a message which is too long to fit on a single line. @end table @node Warning Options @section Options to Request or Suppress Warnings @cindex options to control warnings @cindex warning messages @cindex messages, warning @cindex suppressing warnings Warnings are diagnostic messages that report constructions which are not inherently erroneous but which are risky or suggest there may have been an error. You can request many specific warnings with options beginning @samp{-W}, for example @option{-Wimplicit} to request warnings on implicit declarations. Each of these specific warning options also has a negative form beginning @samp{-Wno-} to turn off warnings; for example, @option{-Wno-implicit}. This manual lists only one of the two forms, whichever is not the default. The following options control the amount and kinds of warnings produced by GCC; for further, language-specific options also refer to @ref{C++ Dialect Options} and @ref{Objective-C Dialect Options}. @table @gcctabopt @cindex syntax checking @item -fsyntax-only @opindex fsyntax-only Check the code for syntax errors, but don't do anything beyond that. @item -pedantic @opindex pedantic Issue all the warnings demanded by strict ISO C and ISO C++; reject all programs that use forbidden extensions, and some other programs that do not follow ISO C and ISO C++. For ISO C, follows the version of the ISO C standard specified by any @option{-std} option used. Valid ISO C and ISO C++ programs should compile properly with or without this option (though a rare few will require @option{-ansi} or a @option{-std} option specifying the required version of ISO C)@. However, without this option, certain GNU extensions and traditional C and C++ features are supported as well. With this option, they are rejected. @option{-pedantic} does not cause warning messages for use of the alternate keywords whose names begin and end with @samp{__}. Pedantic warnings are also disabled in the expression that follows @code{__extension__}. However, only system header files should use these escape routes; application programs should avoid them. @xref{Alternate Keywords}. Some users try to use @option{-pedantic} to check programs for strict ISO C conformance. They soon find that it does not do quite what they want: it finds some non-ISO practices, but not all---only those for which ISO C @emph{requires} a diagnostic, and some others for which diagnostics have been added. A feature to report any failure to conform to ISO C might be useful in some instances, but would require considerable additional work and would be quite different from @option{-pedantic}. We don't have plans to support such a feature in the near future. Where the standard specified with @option{-std} represents a GNU extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a corresponding @dfn{base standard}, the version of ISO C on which the GNU extended dialect is based. Warnings from @option{-pedantic} are given where they are required by the base standard. (It would not make sense for such warnings to be given only for features not in the specified GNU C dialect, since by definition the GNU dialects of C include all features the compiler supports with the given option, and there would be nothing to warn about.) @item -pedantic-errors @opindex pedantic-errors Like @option{-pedantic}, except that errors are produced rather than warnings. @item -w @opindex w Inhibit all warning messages. @item -Wno-import @opindex Wno-import Inhibit warning messages about the use of @samp{#import}. @c APPLE LOCAL begin -Wno-#warnings @item -Wno-#warnings @opindex Wno-#warnings Inhibit warning messages issued by @samp{#warning}. @c APPLE LOCAL end -Wno-#warnings @c APPLE LOCAL begin -Wpragma-once 2001-08-01 sts ** @item -Wpragma-once @opindex Wpragma-once Warn about the use of @samp{#pragma once}. (APPLE ONLY) @c APPLE LOCAL end -Wpragma-once 2001-08-01 sts ** @c APPLE LOCAL begin -Wextra-tokens 2001-08-02 sts ** @item -Wextra-tokens @opindex Wextra-tokens Warn about extra tokens at the end of prepreprocessor directives. (APPLE ONLY) @c APPLE LOCAL end -Wextra-tokens 2001-08-02 sts ** @c APPLE LOCAL begin -Wnewline-eof 2001-08-23 sts ** @item -Wnewline-eof @opindex Wnewline-eof Warn about files missing a newline at the end of the file. (APPLE ONLY) @c APPLE LOCAL end -Wnewline-eof 2001-08-23 sts ** @c APPLE LOCAL begin -Wno-altivec-long-deprecated ilr ** @item -Wno-altivec-long-deprecated @opindex Wno-altivec-long-deprecated Do not warn about the use of the deprecated 'long' keyword in AltiVec data types. (APPLE ONLY) @c APPLE LOCAL end -Wno-altivec-long-deprecated ilr ** @item -Wchar-subscripts @opindex Wchar-subscripts Warn if an array subscript has type @code{char}. This is a common cause of error, as programmers often forget that this type is signed on some machines. @item -Wcomment @opindex Wcomment Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*} comment, or whenever a Backslash-Newline appears in a @samp{//} comment. @item -Wformat @opindex Wformat Check calls to @code{printf} and @code{scanf}, etc., to make sure that the arguments supplied have types appropriate to the format string specified, and that the conversions specified in the format string make sense. This includes standard functions, and others specified by format attributes (@pxref{Function Attributes}), in the @code{printf}, @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension, not in the C standard) families. The formats are checked against the format features supported by GNU libc version 2.2. These include all ISO C89 and C99 features, as well as features from the Single Unix Specification and some BSD and GNU extensions. Other library implementations may not support all these features; GCC does not support warning about features that go beyond a particular library's limitations. However, if @option{-pedantic} is used with @option{-Wformat}, warnings will be given about format features not in the selected standard version (but not for @code{strfmon} formats, since those are not in any version of the C standard). @xref{C Dialect Options,,Options Controlling C Dialect}. @option{-Wformat} is included in @option{-Wall}. For more control over some aspects of format checking, the options @option{-Wno-format-y2k}, @option{-Wno-format-extra-args}, @option{-Wformat-nonliteral}, @option{-Wformat-security} and @option{-Wformat=2} are available, but are not included in @option{-Wall}. @item -Wno-format-y2k @opindex Wno-format-y2k If @option{-Wformat} is specified, do not warn about @code{strftime} formats which may yield only a two-digit year. @item -Wno-format-extra-args @opindex Wno-format-extra-args If @option{-Wformat} is specified, do not warn about excess arguments to a @code{printf} or @code{scanf} format function. The C standard specifies that such arguments are ignored. Where the unused arguments lie between used arguments that are specified with @samp{$} operand number specifications, normally warnings are still given, since the implementation could not know what type to pass to @code{va_arg} to skip the unused arguments. However, in the case of @code{scanf} formats, this option will suppress the warning if the unused arguments are all pointers, since the Single Unix Specification says that such unused arguments are allowed. @item -Wformat-nonliteral @opindex Wformat-nonliteral If @option{-Wformat} is specified, also warn if the format string is not a string literal and so cannot be checked, unless the format function takes its format arguments as a @code{va_list}. @item -Wformat-security @opindex Wformat-security If @option{-Wformat} is specified, also warn about uses of format functions that represent possible security problems. At present, this warns about calls to @code{printf} and @code{scanf} functions where the format string is not a string literal and there are no format arguments, as in @code{printf (foo);}. This may be a security hole if the format string came from untrusted input and contains @samp{%n}. (This is currently a subset of what @option{-Wformat-nonliteral} warns about, but in future warnings may be added to @option{-Wformat-security} that are not included in @option{-Wformat-nonliteral}.) @item -Wformat=2 @opindex Wformat=2 Enable @option{-Wformat} plus format checks not included in @option{-Wformat}. Currently equivalent to @samp{-Wformat -Wformat-nonliteral -Wformat-security}. @item -Wimplicit-int @opindex Wimplicit-int Warn when a declaration does not specify a type. @item -Wimplicit-function-declaration @itemx -Werror-implicit-function-declaration @opindex Wimplicit-function-declaration @opindex Werror-implicit-function-declaration Give a warning (or error) whenever a function is used before being declared. @item -Wimplicit @opindex Wimplicit Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}. @item -Wmain @opindex Wmain Warn if the type of @samp{main} is suspicious. @samp{main} should be a function with external linkage, returning int, taking either zero arguments, two, or three arguments of appropriate types. @item -Wmissing-braces @opindex Wmissing-braces Warn if an aggregate or union initializer is not fully bracketed. In the following example, the initializer for @samp{a} is not fully bracketed, but that for @samp{b} is fully bracketed. @smallexample int a[2][2] = @{ 0, 1, 2, 3 @}; int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @}; @end smallexample @item -Wparentheses @opindex Wparentheses Warn if parentheses are omitted in certain contexts, such as when there is an assignment in a context where a truth value is expected, or when operators are nested whose precedence people often get confused about. Also warn about constructions where there may be confusion to which @code{if} statement an @code{else} branch belongs. Here is an example of such a case: @smallexample @group @{ if (a) if (b) foo (); else bar (); @} @end group @end smallexample In C, every @code{else} branch belongs to the innermost possible @code{if} statement, which in this example is @code{if (b)}. This is often not what the programmer expected, as illustrated in the above example by indentation the programmer chose. When there is the potential for this confusion, GCC will issue a warning when this flag is specified. To eliminate the warning, add explicit braces around the innermost @code{if} statement so there is no way the @code{else} could belong to the enclosing @code{if}. The resulting code would look like this: @smallexample @group @{ if (a) @{ if (b) foo (); else bar (); @} @} @end group @end smallexample @item -Wsequence-point @opindex Wsequence-point Warn about code that may have undefined semantics because of violations of sequence point rules in the C standard. The C standard defines the order in which expressions in a C program are evaluated in terms of @dfn{sequence points}, which represent a partial ordering between the execution of parts of the program: those executed before the sequence point, and those executed after it. These occur after the evaluation of a full expression (one which is not part of a larger expression), after the evaluation of the first operand of a @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a function is called (but after the evaluation of its arguments and the expression denoting the called function), and in certain other places. Other than as expressed by the sequence point rules, the order of evaluation of subexpressions of an expression is not specified. All these rules describe only a partial order rather than a total order, since, for example, if two functions are called within one expression with no sequence point between them, the order in which the functions are called is not specified. However, the standards committee have ruled that function calls do not overlap. It is not specified when between sequence points modifications to the values of objects take effect. Programs whose behavior depends on this have undefined behavior; the C standard specifies that ``Between the previous and next sequence point an object shall have its stored value modified at most once by the evaluation of an expression. Furthermore, the prior value shall be read only to determine the value to be stored.''. If a program breaks these rules, the results on any particular implementation are entirely unpredictable. Examples of code with undefined behavior are @code{a = a++;}, @code{a[n] = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not diagnosed by this option, and it may give an occasional false positive result, but in general it has been found fairly effective at detecting this sort of problem in programs. The present implementation of this option only works for C programs. A future implementation may also work for C++ programs. The C standard is worded confusingly, therefore there is some debate over the precise meaning of the sequence point rules in subtle cases. Links to discussions of the problem, including proposed formal definitions, may be found on our readings page, at @w{@uref{http://gcc.gnu.org/readings.html}}. @item -Wreturn-type @opindex Wreturn-type Warn whenever a function is defined with a return-type that defaults to @code{int}. Also warn about any @code{return} statement with no return-value in a function whose return-type is not @code{void}. For C++, a function without return type always produces a diagnostic message, even when @option{-Wno-return-type} is specified. The only exceptions are @samp{main} and functions defined in system headers. @item -Wswitch @opindex Wswitch Warn whenever a @code{switch} statement has an index of enumeral type and lacks a @code{case} for one or more of the named codes of that enumeration. (The presence of a @code{default} label prevents this warning.) @code{case} labels outside the enumeration range also provoke warnings when this option is used. @item -Wtrigraphs @opindex Wtrigraphs Warn if any trigraphs are encountered that might change the meaning of the program (trigraphs within comments are not warned about). @item -Wunused-function @opindex Wunused-function Warn whenever a static function is declared but not defined or a non\-inline static function is unused. @item -Wunused-label @opindex Wunused-label Warn whenever a label is declared but not used. To suppress this warning use the @samp{unused} attribute (@pxref{Variable Attributes}). @item -Wunused-parameter @opindex Wunused-parameter Warn whenever a function parameter is unused aside from its declaration. To suppress this warning use the @samp{unused} attribute (@pxref{Variable Attributes}). @item -Wunused-variable @opindex Wunused-variable Warn whenever a local variable or non-constant static variable is unused aside from its declaration To suppress this warning use the @samp{unused} attribute (@pxref{Variable Attributes}). @item -Wunused-value @opindex Wunused-value Warn whenever a statement computes a result that is explicitly not used. To suppress this warning cast the expression to @samp{void}. @item -Wunused @opindex Wunused All all the above @option{-Wunused} options combined. In order to get a warning about an unused function parameter, you must either specify @samp{-W -Wunused} or separately specify @option{-Wunused-parameter}. @item -Wuninitialized @opindex Wuninitialized Warn if an automatic variable is used without first being initialized or if a variable may be clobbered by a @code{setjmp} call. These warnings are possible only in optimizing compilation, because they require data flow information that is computed only when optimizing. If you don't specify @option{-O}, you simply won't get these warnings. These warnings occur only for variables that are candidates for register allocation. Therefore, they do not occur for a variable that is declared @code{volatile}, or whose address is taken, or whose size is other than 1, 2, 4 or 8 bytes. Also, they do not occur for structures, unions or arrays, even when they are in registers. Note that there may be no warning about a variable that is used only to compute a value that itself is never used, because such computations may be deleted by data flow analysis before the warnings are printed. These warnings are made optional because GCC is not smart enough to see all the reasons why the code might be correct despite appearing to have an error. Here is one example of how this can happen: @smallexample @group @{ int x; switch (y) @{ case 1: x = 1; break; case 2: x = 4; break; case 3: x = 5; @} foo (x); @} @end group @end smallexample @noindent If the value of @code{y} is always 1, 2 or 3, then @code{x} is always initialized, but GCC doesn't know this. Here is another common case: @smallexample @{ int save_y; if (change_y) save_y = y, y = new_y; @dots{} if (change_y) y = save_y; @} @end smallexample @noindent This has no bug because @code{save_y} is used only if it is set. @cindex @code{longjmp} warnings This option also warns when a non-volatile automatic variable might be changed by a call to @code{longjmp}. These warnings as well are possible only in optimizing compilation. The compiler sees only the calls to @code{setjmp}. It cannot know where @code{longjmp} will be called; in fact, a signal handler could call it at any point in the code. As a result, you may get a warning even when there is in fact no problem because @code{longjmp} cannot in fact be called at the place which would cause a problem. Some spurious warnings can be avoided if you declare all the functions you use that never return as @code{noreturn}. @xref{Function Attributes}. @item -Wreorder @r{(C++ only)} @opindex Wreorder @cindex reordering, warning @cindex warning for reordering of member initializers Warn when the order of member initializers given in the code does not match the order in which they must be executed. For instance: @item -Wunknown-pragmas @opindex Wunknown-pragmas @cindex warning for unknown pragmas @cindex unknown pragmas, warning @cindex pragmas, warning of unknown Warn when a #pragma directive is encountered which is not understood by GCC@. If this command line option is used, warnings will even be issued for unknown pragmas in system header files. This is not the case if the warnings were only enabled by the @option{-Wall} command line option. @item -Wall @opindex Wall All of the above @samp{-W} options combined. This enables all the warnings about constructions that some users consider questionable, and that are easy to avoid (or modify to prevent the warning), even in conjunction with macros. @c APPLE LOCAL -Wmost @item -Wmost @opindex Wmost This is equivalent to -Wall -Wno-parentheses. (APPLE ONLY) @item -Wdiv-by-zero @opindex Wno-div-by-zero @opindex Wdiv-by-zero Warn about compile-time integer division by zero. This is default. To inhibit the warning messages, use @option{-Wno-div-by-zero}. Floating point division by zero is not warned about, as it can be a legitimate way of obtaining infinities and NaNs. @item -Wmultichar @opindex Wno-multichar @opindex Wmultichar Warn if a multicharacter constant (@samp{'FOOF'}) is used. This is default. To inhibit the warning messages, use @option{-Wno-multichar}. Usually they indicate a typo in the user's code, as they have implementation-defined values, and should not be used in portable code. @item -Wsystem-headers @opindex Wsystem-headers @cindex warnings from system headers @cindex system headers, warnings from Print warning messages for constructs found in system header files. Warnings from system headers are normally suppressed, on the assumption that they usually do not indicate real problems and would only make the compiler output harder to read. Using this command line option tells GCC to emit warnings from system headers as if they occurred in user code. However, note that using @option{-Wall} in conjunction with this option will @emph{not} warn about unknown pragmas in system headers---for that, @option{-Wunknown-pragmas} must also be used. @end table The following @option{-W@dots{}} options are not implied by @option{-Wall}. Some of them warn about constructions that users generally do not consider questionable, but which occasionally you might wish to check for; others warn about constructions that are necessary or hard to avoid in some cases, and there is no simple way to modify the code to suppress the warning. @table @gcctabopt @item -W @opindex W Print extra warning messages for these events: @itemize @bullet @item A function can return either with or without a value. (Falling off the end of the function body is considered returning without a value.) For example, this function would evoke such a warning: @smallexample @group foo (a) @{ if (a > 0) return a; @} @end group @end smallexample @item An expression-statement or the left-hand side of a comma expression contains no side effects. To suppress the warning, cast the unused expression to void. For example, an expression such as @samp{x[i,j]} will cause a warning, but @samp{x[(void)i,j]} will not. @item An unsigned value is compared against zero with @samp{<} or @samp{<=}. @item A comparison like @samp{x<=y<=z} appears; this is equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from that of ordinary mathematical notation. @item Storage-class specifiers like @code{static} are not the first things in a declaration. According to the C Standard, this usage is obsolescent. @item The return type of a function has a type qualifier such as @code{const}. Such a type qualifier has no effect, since the value returned by a function is not an lvalue. (But don't warn about the GNU extension of @code{volatile void} return types. That extension will be warned about if @option{-pedantic} is specified.) @item If @option{-Wall} or @option{-Wunused} is also specified, warn about unused arguments. @item A comparison between signed and unsigned values could produce an incorrect result when the signed value is converted to unsigned. (But don't warn if @option{-Wno-sign-compare} is also specified.) @item An aggregate has a partly bracketed initializer. For example, the following code would evoke such a warning, because braces are missing around the initializer for @code{x.h}: @smallexample struct s @{ int f, g; @}; struct t @{ struct s h; int i; @}; struct t x = @{ 1, 2, 3 @}; @end smallexample @item An aggregate has an initializer which does not initialize all members. For example, the following code would cause such a warning, because @code{x.h} would be implicitly initialized to zero: @smallexample struct s @{ int f, g, h; @}; struct s x = @{ 3, 4 @}; @end smallexample @end itemize @item -Wfloat-equal @opindex Wfloat-equal Warn if floating point values are used in equality comparisons. The idea behind this is that sometimes it is convenient (for the programmer) to consider floating-point values as approximations to infinitely precise real numbers. If you are doing this, then you need to compute (by analysing the code, or in some other way) the maximum or likely maximum error that the computation introduces, and allow for it when performing comparisons (and when producing output, but that's a different problem). In particular, instead of testing for equality, you would check to see whether the two values have ranges that overlap; and this is done with the relational operators, so equality comparisons are probably mistaken. @item -Wtraditional @r{(C only)} @opindex Wtraditional Warn about certain constructs that behave differently in traditional and ISO C@. Also warn about ISO C constructs that have no traditional C equivalent, and/or problematic constructs which should be avoided. @itemize @bullet @item Macro parameters that appear within string literals in the macro body. In traditional C macro replacement takes place within string literals, but does not in ISO C@. @item In traditional C, some preprocessor directives did not exist. Traditional preprocessors would only consider a line to be a directive if the @samp{#} appeared in column 1 on the line. Therefore @option{-Wtraditional} warns about directives that traditional C understands but would ignore because the @samp{#} does not appear as the first character on the line. It also suggests you hide directives like @samp{#pragma} not understood by traditional C by indenting them. Some traditional implementations would not recognize @samp{#elif}, so it suggests avoiding it altogether. @item A function-like macro that appears without arguments. @item The unary plus operator. @item The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point constant suffixes. (Traditional C does support the @samp{L} suffix on integer constants.) Note, these suffixes appear in macros defined in the system headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{}. Use of these macros in user code might normally lead to spurious warnings, however gcc's integrated preprocessor has enough context to avoid warning in these cases. @item A function declared external in one block and then used after the end of the block. @item A @code{switch} statement has an operand of type @code{long}. @item A non-@code{static} function declaration follows a @code{static} one. This construct is not accepted by some traditional C compilers. @item The ISO type of an integer constant has a different width or signedness from its traditional type. This warning is only issued if the base of the constant is ten. I.e.@: hexadecimal or octal values, which typically represent bit patterns, are not warned about. @item Usage of ISO string concatenation is detected. @item Initialization of automatic aggregates. @item Identifier conflicts with labels. Traditional C lacks a separate namespace for labels. @item Initialization of unions. If the initializer is zero, the warning is omitted. This is done under the assumption that the zero initializer in user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing initializer warnings and relies on default initialization to zero in the traditional C case. @item Conversions by prototypes between fixed/floating point values and vice versa. The absence of these prototypes when compiling with traditional C would cause serious problems. This is a subset of the possible conversion warnings, for the full set use @option{-Wconversion}. @end itemize @item -Wundef @opindex Wundef Warn if an undefined identifier is evaluated in an @samp{#if} directive. @item -Wshadow @opindex Wshadow Warn whenever a local variable shadows another local variable, parameter or global variable or whenever a built-in function is shadowed. @item -Wlarger-than-@var{len} @opindex Wlarger-than Warn whenever an object of larger than @var{len} bytes is defined. @item -Wpointer-arith @opindex Wpointer-arith Warn about anything that depends on the ``size of'' a function type or of @code{void}. GNU C assigns these types a size of 1, for convenience in calculations with @code{void *} pointers and pointers to functions. @item -Wbad-function-cast @r{(C only)} @opindex Wbad-function-cast Warn whenever a function call is cast to a non-matching type. For example, warn if @code{int malloc()} is cast to @code{anything *}. @item -Wcast-qual @opindex Wcast-qual Warn whenever a pointer is cast so as to remove a type qualifier from the target type. For example, warn if a @code{const char *} is cast to an ordinary @code{char *}. @item -Wcast-align @opindex Wcast-align Warn whenever a pointer is cast such that the required alignment of the target is increased. For example, warn if a @code{char *} is cast to an @code{int *} on machines where integers can only be accessed at two- or four-byte boundaries. @item -Wwrite-strings @opindex Wwrite-strings When compiling C, give string constants the type @code{const char[@var{length}]} so that copying the address of one into a non-@code{const} @code{char *} pointer will get a warning; when compiling C++, warn about the deprecated conversion from string constants to @code{char *}. These warnings will help you find at compile time code that can try to write into a string constant, but only if you have been very careful about using @code{const} in declarations and prototypes. Otherwise, it will just be a nuisance; this is why we did not make @option{-Wall} request these warnings. @item -Wconversion @opindex Wconversion Warn if a prototype causes a type conversion that is different from what would happen to the same argument in the absence of a prototype. This includes conversions of fixed point to floating and vice versa, and conversions changing the width or signedness of a fixed point argument except when the same as the default promotion. Also, warn if a negative integer constant expression is implicitly converted to an unsigned type. For example, warn about the assignment @code{x = -1} if @code{x} is unsigned. But do not warn about explicit casts like @code{(unsigned) -1}. @item -Wsign-compare @opindex Wsign-compare @cindex warning for comparison of signed and unsigned values @cindex comparison of signed and unsigned values, warning @cindex signed and unsigned values, comparison warning Warn when a comparison between signed and unsigned values could produce an incorrect result when the signed value is converted to unsigned. This warning is also enabled by @option{-W}; to get the other warnings of @option{-W} without this warning, use @samp{-W -Wno-sign-compare}. @item -Waggregate-return @opindex Waggregate-return Warn if any functions that return structures or unions are defined or called. (In languages where you can return an array, this also elicits a warning.) @item -Wstrict-prototypes @r{(C only)} @opindex Wstrict-prototypes Warn if a function is declared or defined without specifying the argument types. (An old-style function definition is permitted without a warning if preceded by a declaration which specifies the argument types.) @item -Wmissing-prototypes @r{(C only)} @opindex Wmissing-prototypes Warn if a global function is defined without a previous prototype declaration. This warning is issued even if the definition itself provides a prototype. The aim is to detect global functions that fail to be declared in header files. @item -Wmissing-declarations @opindex Wmissing-declarations Warn if a global function is defined without a previous declaration. Do so even if the definition itself provides a prototype. Use this option to detect global functions that are not declared in header files. @item -Wmissing-noreturn @opindex Wmissing-noreturn Warn about functions which might be candidates for attribute @code{noreturn}. Note these are only possible candidates, not absolute ones. Care should be taken to manually verify functions actually do not ever return before adding the @code{noreturn} attribute, otherwise subtle code generation bugs could be introduced. You will not get a warning for @code{main} in hosted C environments. @item -Wmissing-format-attribute @opindex Wmissing-format-attribute @opindex Wformat If @option{-Wformat} is enabled, also warn about functions which might be candidates for @code{format} attributes. Note these are only possible candidates, not absolute ones. GCC will guess that @code{format} attributes might be appropriate for any function that calls a function like @code{vprintf} or @code{vscanf}, but this might not always be the case, and some functions for which @code{format} attributes are appropriate may not be detected. This option has no effect unless @option{-Wformat} is enabled (possibly by @option{-Wall}). @item -Wno-deprecated-declarations @opindex Wno-deprecated-declarations Do not warn about uses of functions, variables, and types marked as deprecated by using the @code{deprecated} attribute. (@pxref{Function Attributes}, @pxref{Variable Attributes}, @pxref{Type Attributes}.) @item -Wpacked @opindex Wpacked Warn if a structure is given the packed attribute, but the packed attribute has no effect on the layout or size of the structure. Such structures may be mis-aligned for little benefit. For instance, in this code, the variable @code{f.x} in @code{struct bar} will be misaligned even though @code{struct bar} does not itself have the packed attribute: @smallexample @group struct foo @{ int x; char a, b, c, d; @} __attribute__((packed)); struct bar @{ char z; struct foo f; @}; @end group @end smallexample @item -Wpadded @opindex Wpadded Warn if padding is included in a structure, either to align an element of the structure or to align the whole structure. Sometimes when this happens it is possible to rearrange the fields of the structure to reduce the padding and so make the structure smaller. @item -Wredundant-decls @opindex Wredundant-decls Warn if anything is declared more than once in the same scope, even in cases where multiple declaration is valid and changes nothing. @item -Wnested-externs @r{(C only)} @opindex Wnested-externs Warn if an @code{extern} declaration is encountered within a function. @item -Wunreachable-code @opindex Wunreachable-code Warn if the compiler detects that code will never be executed. This option is intended to warn when the compiler detects that at least a whole line of source code will never be executed, because some condition is never satisfied or because it is after a procedure that never returns. It is possible for this option to produce a warning even though there are circumstances under which part of the affected line can be executed, so care should be taken when removing apparently-unreachable code. For instance, when a function is inlined, a warning may mean that the line is unreachable in only one inlined copy of the function. This option is not made part of @option{-Wall} because in a debugging version of a program there is often substantial code which checks correct functioning of the program and is, hopefully, unreachable because the program does work. Another common use of unreachable code is to provide behavior which is selectable at compile-time. @item -Winline @opindex Winline Warn if a function can not be inlined and it was declared as inline. @c APPLE LOCAL begin long double @item -Wno-long-double @opindex Wno-long-double Inhibit warning if the @samp{long double} type is used. (APPLE ONLY) @c APPLE LOCAL end long double @item -Wlong-long @opindex Wlong-long @opindex Wno-long-long Warn if @samp{long long} type is used. This is default. To inhibit the warning messages, use @option{-Wno-long-long}. Flags @option{-Wlong-long} and @option{-Wno-long-long} are taken into account only when @option{-pedantic} flag is used. @item -Wdisabled-optimization @opindex Wdisabled-optimization Warn if a requested optimization pass is disabled. This warning does not generally indicate that there is anything wrong with your code; it merely indicates that GCC's optimizers were unable to handle the code effectively. Often, the problem is that your code is too big or too complex; GCC will refuse to optimize programs when the optimization itself is likely to take inordinate amounts of time. @item -Werror @opindex Werror Make all warnings into errors. @end table @node Debugging Options @section Options for Debugging Your Program or GCC @cindex options, debugging @cindex debugging information options GCC has various special options that are used for debugging either your program or GCC: @table @gcctabopt @item -g @opindex g Produce debugging information in the operating system's native format (stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging information. On most systems that use stabs format, @option{-g} enables use of extra debugging information that only GDB can use; this extra information makes debugging work better in GDB but will probably make other debuggers crash or refuse to read the program. If you want to control for certain whether @c APPLE LOCAL prune man page to generate the extra information, use @option{-gstabs+} or @option{-gstabs} (see below). Unlike most other C compilers, GCC allows you to use @option{-g} with @option{-O}. The shortcuts taken by optimized code may occasionally produce surprising results: some variables you declared may not exist at all; flow of control may briefly move where you did not expect it; some statements may not be executed because they compute constant results or their values were already at hand; some statements may execute in different places because they were moved out of loops. Nevertheless it proves possible to debug optimized output. This makes it reasonable to use the optimizer for programs that might have bugs. The following options are useful when GCC is generated with the capability for more than one debugging format. @item -ggdb @opindex ggdb Produce debugging information for use by GDB@. This means to use the most expressive format available (DWARF 2, stabs, or the native format if neither of those are supported), including GDB extensions if at all possible. @item -gstabs @opindex gstabs Produce debugging information in stabs format (if that is supported), without GDB extensions. This is the format used by DBX on most BSD systems. On MIPS, Alpha and System V Release 4 systems this option produces stabs debugging output which is not understood by DBX or SDB@. On System V Release 4 systems this option requires the GNU assembler. @item -gstabs+ @opindex gstabs+ Produce debugging information in stabs format (if that is supported), using GNU extensions understood only by the GNU debugger (GDB)@. The use of these extensions is likely to make other debuggers crash or refuse to read the program. @c APPLE LOCAL prune man page (Other debug formats, such as @option{-gcoff}, are not supported in Darwin or Mac OS X.) @ignore @item -gcoff @opindex gcoff Produce debugging information in COFF format (if that is supported). This is the format used by SDB on most System V systems prior to System V Release 4. @item -gxcoff @opindex gxcoff Produce debugging information in XCOFF format (if that is supported). This is the format used by the DBX debugger on IBM RS/6000 systems. @item -gxcoff+ @opindex gxcoff+ Produce debugging information in XCOFF format (if that is supported), using GNU extensions understood only by the GNU debugger (GDB)@. The use of these extensions is likely to make other debuggers crash or refuse to read the program, and may cause assemblers other than the GNU assembler (GAS) to fail with an error. @item -gdwarf @opindex gdwarf Produce debugging information in DWARF version 1 format (if that is supported). This is the format used by SDB on most System V Release 4 systems. @item -gdwarf+ @opindex gdwarf+ Produce debugging information in DWARF version 1 format (if that is supported), using GNU extensions understood only by the GNU debugger (GDB)@. The use of these extensions is likely to make other debuggers crash or refuse to read the program. @item -gdwarf-2 @opindex gdwarf-2 Produce debugging information in DWARF version 2 format (if that is supported). This is the format used by DBX on IRIX 6. @item -gvms @opindex gvms Produce debugging information in VMS debug format (if that is supported). This is the format used by DEBUG on VMS systems. @c APPLE LOCAL prune man page @end ignore @item -g@var{level} @itemx -ggdb@var{level} @itemx -gstabs@var{level} @c APPLE LOCAL prune man page @ignore @itemx -gcoff@var{level} @itemx -gxcoff@var{level} @itemx -gdwarf@var{level} @itemx -gdwarf-2@var{level} @itemx -gvms@var{level} @c APPLE LOCAL prune man page @end ignore Request debugging information and also use @var{level} to specify how much information. The default level is 2. Level 1 produces minimal information, enough for making backtraces in parts of the program that you don't plan to debug. This includes descriptions of functions and external variables, but no information about local variables and no line numbers. Level 3 includes extra information, such as all the macro definitions present in the program. Some debuggers support macro expansion when you use @option{-g3}. @cindex @code{prof} @item -p @opindex p Generate extra code to write profile information suitable for the analysis program @code{prof}. You must use this option when compiling the source files you want data about, and you must also use it when linking. @cindex @code{gprof} @item -pg @opindex pg Generate extra code to write profile information suitable for the analysis program @code{gprof}. You must use this option when compiling the source files you want data about, and you must also use it when linking. @cindex @code{tcov} @item -a @opindex a Generate extra code to write profile information for basic blocks, which will record the number of times each basic block is executed, the basic block start address, and the function name containing the basic block. If @option{-g} is used, the line number and filename of the start of the basic block will also be recorded. If not overridden by the machine description, the default action is to append to the text file @file{bb.out}. This data could be analyzed by a program like @code{tcov}. Note, however, that the format of the data is not what @code{tcov} expects. Eventually GNU @code{gprof} should be extended to process this data. @item -Q @opindex Q Makes the compiler print out each function name as it is compiled, and print some statistics about each pass when it finishes. @item -ftime-report @opindex ftime-report Makes the compiler print some statistics about the time consumed by each pass when it finishes. @item -fmem-report @opindex fmem-report Makes the compiler print some statistics about permanent memory allocation when it finishes. @item -fprofile-arcs @opindex fprofile-arcs Instrument @dfn{arcs} during compilation to generate coverage data or for profile-directed block ordering. During execution the program records how many times each branch is executed and how many times it is taken. When the compiled program exits it saves this data to a file called @file{@var{sourcename}.da} for each source file. For profile-directed block ordering, compile the program with @option{-fprofile-arcs} plus optimization and code generation options, generate the arc profile information by running the program on a selected workload, and then compile the program again with the same optimization and code generation options plus @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that Control Optimization}). The other use of @option{-fprofile-arcs} is for use with @code{gcov}, when it is used with the @option{-ftest-coverage} option. GCC supports two methods of determining code coverage: the options that support @code{gcov}, and options @option{-a} and @option{-ax}, which write information to text files. The options that support @code{gcov} do not need to instrument every arc in the program, so a program compiled with them runs faster than a program compiled with @option{-a}, which adds instrumentation code to every basic block in the program. The tradeoff: since @code{gcov} does not have execution counts for all branches, it must start with the execution counts for the instrumented branches, and then iterate over the program flow graph until the entire graph has been solved. Hence, @code{gcov} runs a little more slowly than a program which uses information from @option{-a} and @option{-ax}. With @option{-fprofile-arcs}, for each function of your program GCC creates a program flow graph, then finds a spanning tree for the graph. Only arcs that are not on the spanning tree have to be instrumented: the compiler adds code to count the number of times that these arcs are executed. When an arc is the only exit or only entrance to a block, the instrumentation code can be added to the block; otherwise, a new basic block must be created to hold the instrumentation code. This option makes it possible to estimate branch probabilities and to calculate basic block execution counts. In general, basic block execution counts as provided by @option{-a} do not give enough information to estimate all branch probabilities. @need 2000 @item -ftest-coverage @opindex ftest-coverage Create data files for the @code{gcov} code-coverage utility (@pxref{Gcov,, @code{gcov}: a GCC Test Coverage Program}). The data file names begin with the name of your source file: @table @gcctabopt @item @var{sourcename}.bb A mapping from basic blocks to line numbers, which @code{gcov} uses to associate basic block execution counts with line numbers. @item @var{sourcename}.bbg A list of all arcs in the program flow graph. This allows @code{gcov} to reconstruct the program flow graph, so that it can compute all basic block and arc execution counts from the information in the @code{@var{sourcename}.da} file. @end table Use @option{-ftest-coverage} with @option{-fprofile-arcs}; the latter option adds instrumentation to the program, which then writes execution counts to another data file: @table @gcctabopt @item @var{sourcename}.da Runtime arc execution counts, used in conjunction with the arc information in the file @code{@var{sourcename}.bbg}. @end table Coverage data will map better to the source files if @option{-ftest-coverage} is used without optimization. @item -d@var{letters} @opindex d Says to make debugging dumps during compilation at times specified by @var{letters}. This is used for debugging the compiler. The file names for most of the dumps are made by appending a pass number and a word to the source file name (e.g. @file{foo.c.00.rtl} or @file{foo.c.01.sibling}). Here are the possible letters for use in @var{letters}, and their meanings: @table @samp @item A @opindex dA Annotate the assembler output with miscellaneous debugging information. @item b @opindex db Dump after computing branch probabilities, to @file{@var{file}.14.bp}. @item B @opindex dB Dump after block reordering, to @file{@var{file}.29.bbro}. @item c @opindex dc Dump after instruction combination, to the file @file{@var{file}.16.combine}. @item C @opindex dC Dump after the first if conversion, to the file @file{@var{file}.17.ce}. @item d @opindex dd Dump after delayed branch scheduling, to @file{@var{file}.31.dbr}. @item D @opindex dD Dump all macro definitions, at the end of preprocessing, in addition to normal output. @item e @opindex de Dump after SSA optimizations, to @file{@var{file}.04.ssa} and @file{@var{file}.07.ussa}. @item E @opindex dE Dump after the second if conversion, to @file{@var{file}.26.ce2}. @item f @opindex df Dump after life analysis, to @file{@var{file}.15.life}. @item F @opindex dF Dump after purging @code{ADDRESSOF} codes, to @file{@var{file}.09.addressof}. @item g @opindex dg Dump after global register allocation, to @file{@var{file}.21.greg}. @item h @opindex dh Dump after finalization of EH handling code, to @file{@var{file}.02.eh}. @item k @opindex dk Dump after reg-to-stack conversion, to @file{@var{file}.28.stack}. @item o @opindex do Dump after post-reload optimizations, to @file{@var{file}.22.postreload}. @item G @opindex dG Dump after GCSE, to @file{@var{file}.10.gcse}. @item i @opindex di Dump after sibling call optimizations, to @file{@var{file}.01.sibling}. @item j @opindex dj Dump after the first jump optimization, to @file{@var{file}.03.jump}. @item k @opindex dk Dump after conversion from registers to stack, to @file{@var{file}.32.stack}. @item l @opindex dl Dump after local register allocation, to @file{@var{file}.20.lreg}. @item L @opindex dL Dump after loop optimization, to @file{@var{file}.11.loop}. @item M @opindex dM Dump after performing the machine dependent reorganisation pass, to @file{@var{file}.30.mach}. @item n @opindex dn Dump after register renumbering, to @file{@var{file}.25.rnreg}. @item N @opindex dN Dump after the register move pass, to @file{@var{file}.18.regmove}. @item r @opindex dr Dump after RTL generation, to @file{@var{file}.00.rtl}. @item R @opindex dR Dump after the second scheduling pass, to @file{@var{file}.27.sched2}. @item s @opindex ds Dump after CSE (including the jump optimization that sometimes follows CSE), to @file{@var{file}.08.cse}. @item S @opindex dS Dump after the first scheduling pass, to @file{@var{file}.19.sched}. @item t @opindex dt Dump after the second CSE pass (including the jump optimization that sometimes follows CSE), to @file{@var{file}.12.cse2}. @item w @opindex dw Dump after the second flow pass, to @file{@var{file}.23.flow2}. @item X @opindex dX Dump after SSA dead code elimination, to @file{@var{file}.06.ssadce}. @item z @opindex dz Dump after the peephole pass, to @file{@var{file}.24.peephole2}. @item a @opindex da Produce all the dumps listed above. @item m @opindex dm Print statistics on memory usage, at the end of the run, to standard error. @item p @opindex dp Annotate the assembler output with a comment indicating which pattern and alternative was used. The length of each instruction is also printed. @item P @opindex dP Dump the RTL in the assembler output as a comment before each instruction. Also turns on @option{-dp} annotation. @item v @opindex dv For each of the other indicated dump files (except for @file{@var{file}.00.rtl}), dump a representation of the control flow graph suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}. @item x @opindex dx Just generate RTL for a function instead of compiling it. Usually used with @samp{r}. @item y @opindex dy Dump debugging information during parsing, to standard error. @end table @item -fdump-unnumbered @opindex fdump-unnumbered When doing debugging dumps (see @option{-d} option above), suppress instruction numbers and line number note output. This makes it more feasible to use diff on debugging dumps for compiler invocations with different options, in particular with and without @option{-g}. @item -fdump-translation-unit @r{(C and C++ only)} @itemx -fdump-translation-unit-@var{options} @r{(C and C++ only)} @opindex fdump-translation-unit Dump a representation of the tree structure for the entire translation unit to a file. The file name is made by appending @file{.tu} to the source file name. If the @samp{-@var{options}} form is used, @var{options} controls the details of the dump as described for the @option{-fdump-tree} options. @item -fdump-class-hierarchy @r{(C++ only)} @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)} @opindex fdump-class-hierarchy Dump a representation of each class's hierarchy and virtual function table layout to a file. The file name is made by appending @file{.class} to the source file name. If the @samp{-@var{options}} form is used, @var{options} controls the details of the dump as described for the @option{-fdump-tree} options. @item -fdump-tree-@var{switch} @r{(C++ only)} @itemx -fdump-tree-@var{switch}-@var{options} @r{(C++ only)} @opindex fdump-tree Control the dumping at various stages of processing the intermediate language tree to a file. The file name is generated by appending a switch specific suffix to the source file name. If the @samp{-@var{options}} form is used, @var{options} is a list of @samp{-} separated options that control the details of the dump. Not all options are applicable to all dumps, those which are not meaningful will be ignored. The following options are available @table @samp @item address Print the address of each node. Usually this is not meaningful as it changes according to the environment and source file. Its primary use is for tying up a dump file with a debug environment. @item slim Inhibit dumping of members of a scope or body of a function merely because that scope has been reached. Only dump such items when they are directly reachable by some other path. @item all Turn on all options. @end table The following tree dumps are possible: @table @samp @item original Dump before any tree based optimization, to @file{@var{file}.original}. @item optimized Dump after all tree based optimization, to @file{@var{file}.optimized}. @item inlined Dump after function inlining, to @file{@var{file}.inlined}. @end table @item -fpretend-float @opindex fpretend-float When running a cross-compiler, pretend that the target machine uses the same floating point format as the host machine. This causes incorrect output of the actual floating constants, but the actual instruction sequence will probably be the same as GCC would make when running on the target machine. @item -save-temps @opindex save-temps Store the usual ``temporary'' intermediate files permanently; place them in the current directory and name them based on the source file. Thus, compiling @file{foo.c} with @samp{-c -save-temps} would produce files @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a preprocessed @file{foo.i} output file even though the compiler now normally uses an integrated preprocessor. @item -time @opindex time Report the CPU time taken by each subprocess in the compilation sequence. For C source files, this is the compiler proper and assembler (plus the linker if linking is done). The output looks like this: @smallexample # cc1 0.12 0.01 # as 0.00 0.01 @end smallexample The first number on each line is the ``user time,'' that is time spent executing the program itself. The second number is ``system time,'' time spent executing operating system routines on behalf of the program. Both numbers are in seconds. @item -print-file-name=@var{library} @opindex print-file-name Print the full absolute name of the library file @var{library} that would be used when linking---and don't do anything else. With this option, GCC does not compile or link anything; it just prints the file name. @item -print-multi-directory @opindex print-multi-directory Print the directory name corresponding to the multilib selected by any other switches present in the command line. This directory is supposed to exist in @env{GCC_EXEC_PREFIX}. @item -print-multi-lib @opindex print-multi-lib Print the mapping from multilib directory names to compiler switches that enable them. The directory name is separated from the switches by @samp{;}, and each switch starts with an @samp{@@} instead of the @samp{-}, without spaces between multiple switches. This is supposed to ease shell-processing. @item -print-prog-name=@var{program} @opindex print-prog-name Like @option{-print-file-name}, but searches for a program such as @samp{cpp}. @item -print-libgcc-file-name @opindex print-libgcc-file-name Same as @option{-print-file-name=libgcc.a}. This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs} but you do want to link with @file{libgcc.a}. You can do @example gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name` @end example @item -print-search-dirs @opindex print-search-dirs Print the name of the configured installation directory and a list of program and library directories gcc will search---and don't do anything else. This is useful when gcc prints the error message @samp{installation problem, cannot exec cpp0: No such file or directory}. To resolve this you either need to put @file{cpp0} and the other compiler components where gcc expects to find them, or you can set the environment variable @env{GCC_EXEC_PREFIX} to the directory where you installed them. Don't forget the trailing '/'. @xref{Environment Variables}. @item -dumpmachine @opindex dumpmachine Print the compiler's target machine (for example, @samp{i686-pc-linux-gnu})---and don't do anything else. @item -dumpversion @opindex dumpversion Print the compiler version (for example, @samp{3.0})---and don't do anything else. @item -dumpspecs @opindex dumpspecs Print the compiler's built-in specs---and don't do anything else. (This is used when GCC itself is being built.) @xref{Spec Files}. @end table @node Optimize Options @section Options That Control Optimization @cindex optimize options @cindex options, optimization These options control various sorts of optimizations: @table @gcctabopt @item -O @itemx -O1 @opindex O @opindex O1 Optimize. Optimizing compilation takes somewhat more time, and a lot more memory for a large function. Without @option{-O}, the compiler's goal is to reduce the cost of compilation and to make debugging produce the expected results. Statements are independent: if you stop the program with a breakpoint between statements, you can then assign a new value to any variable or change the program counter to any other statement in the function and get exactly the results you would expect from the source code. With @option{-O}, the compiler tries to reduce code size and execution time, without performing any optimizations that take a great deal of compilation time. When you specify @option{-O}, the compiler turns on @option{-fthread-jumps} and @option{-fdefer-pop} on all machines. The compiler turns on @option{-fdelayed-branch} on machines that have delay slots, and @option{-fomit-frame-pointer} on machines that can support debugging even without a frame pointer. On some machines the compiler also turns on other flags. @c APPLE LOCAL begin optimization In Apple's version of GCC, @option{-fstrict-aliasing}, @option{-freorder-blocks}, and @option{-fsched-interblock} are disabled by default when optimizing. @c APPLE LOCAL end optimization @item -O2 @opindex O2 Optimize even more. GCC performs nearly all supported optimizations that do not involve a space-speed tradeoff. The compiler does not perform loop unrolling or function inlining when you specify @option{-O2}. As compared to @option{-O}, this option increases both compilation time and the performance of the generated code. @option{-O2} turns on all optional optimizations except for loop unrolling, function inlining, and register renaming. It also turns on the @option{-fforce-mem} option on all machines and frame pointer elimination on machines where doing so does not interfere with debugging. Please note the warning under @option{-fgcse} about invoking @option{-O2} on programs that use computed gotos. @item -O3 @opindex O3 Optimize yet more. @option{-O3} turns on all optimizations specified by @option{-O2} and also turns on the @option{-finline-functions} and @option{-frename-registers} options. @item -O0 @opindex O0 Do not optimize. @item -Os @opindex Os Optimize for size. @option{-Os} enables all @option{-O2} optimizations that do not typically increase code size. It also performs further optimizations designed to reduce code size. If you use multiple @option{-O} options, with or without level numbers, the last such option is the one that is effective. @end table Options of the form @option{-f@var{flag}} specify machine-independent flags. Most flags have both positive and negative forms; the negative form of @option{-ffoo} would be @option{-fno-foo}. In the table below, only one of the forms is listed---the one which is not the default. You can figure out the other form by either removing @samp{no-} or adding it. @table @gcctabopt @item -ffloat-store @opindex ffloat-store Do not store floating point variables in registers, and inhibit other options that might change whether a floating point value is taken from a register or memory. @cindex floating point precision This option prevents undesirable excess precision on machines such as the 68000 where the floating registers (of the 68881) keep more precision than a @code{double} is supposed to have. Similarly for the x86 architecture. For most programs, the excess precision does only good, but a few programs rely on the precise definition of IEEE floating point. Use @option{-ffloat-store} for such programs, after modifying them to store all pertinent intermediate computations into variables. @item -fno-default-inline @opindex fno-default-inline Do not make member functions inline by default merely because they are defined inside the class scope (C++ only). Otherwise, when you specify @w{@option{-O}}, member functions defined inside class scope are compiled inline by default; i.e., you don't need to add @samp{inline} in front of the member function name. @item -fno-defer-pop @opindex fno-defer-pop Always pop the arguments to each function call as soon as that function returns. For machines which must pop arguments after a function call, the compiler normally lets arguments accumulate on the stack for several function calls and pops them all at once. @item -fforce-mem @opindex fforce-mem Force memory operands to be copied into registers before doing arithmetic on them. This produces better code by making all memory references potential common subexpressions. When they are not common subexpressions, instruction combination should eliminate the separate register-load. The @option{-O2} option turns on this option. @item -fforce-addr @opindex fforce-addr Force memory address constants to be copied into registers before doing arithmetic on them. This may produce better code just as @option{-fforce-mem} may. @item -fomit-frame-pointer @opindex fomit-frame-pointer Don't keep the frame pointer in a register for functions that don't need one. This avoids the instructions to save, set up and restore frame pointers; it also makes an extra register available in many functions. @strong{It also makes debugging impossible on some machines.} On some machines, such as the VAX, this flag has no effect, because the standard calling sequence automatically handles the frame pointer and nothing is saved by pretending it doesn't exist. The machine-description macro @code{FRAME_POINTER_REQUIRED} controls whether a target machine supports this flag. @xref{Registers,,Register Usage, gccint, GNU Compiler Collection (GCC) Internals}. @item -foptimize-sibling-calls @opindex foptimize-sibling-calls Optimize sibling and tail recursive calls. @item -ftrapv @opindex ftrapv This option generates traps for signed overflow on addition, subtraction, multiplication operations. @item -fno-inline @opindex fno-inline Don't pay attention to the @code{inline} keyword. Normally this option is used to keep the compiler from expanding any functions inline. Note that if you are not optimizing, no functions can be expanded inline. @item -finline-functions @opindex finline-functions Integrate all simple functions into their callers. The compiler heuristically decides which functions are simple enough to be worth integrating in this way. If all calls to a given function are integrated, and the function is declared @code{static}, then the function is normally not output as assembler code in its own right. @item -finline-limit=@var{n} @opindex finline-limit By default, gcc limits the size of functions that can be inlined. This flag allows the control of this limit for functions that are explicitly marked as inline (ie marked with the inline keyword or defined within the class definition in c++). @var{n} is the size of functions that can be inlined in number of pseudo instructions (not counting parameter handling). The default value of @var{n} is 600. Increasing this value can result in more inlined code at the cost of compilation time and memory consumption. Decreasing usually makes the compilation faster and less code will be inlined (which presumably means slower programs). This option is particularly useful for programs that use inlining heavily such as those based on recursive templates with C++. @emph{Note:} pseudo instruction represents, in this particular context, an abstract measurement of function's size. In no way, it represents a count of assembly instructions and as such its exact meaning might change from one release to an another. @item -fkeep-inline-functions @opindex fkeep-inline-functions Even if all calls to a given function are integrated, and the function is declared @code{static}, nevertheless output a separate run-time callable version of the function. This switch does not affect @code{extern inline} functions. @item -fkeep-static-consts @opindex fkeep-static-consts Emit variables declared @code{static const} when optimization isn't turned on, even if the variables aren't referenced. GCC enables this option by default. If you want to force the compiler to check if the variable was referenced, regardless of whether or not optimization is turned on, use the @option{-fno-keep-static-consts} option. @item -fmerge-constants Attempt to merge identical constants (string constants and floating point constants) accross compilation units. This option is default for optimized compilation if assembler and linker support it. Use @option{-fno-merge-constants} to inhibit this behavior. @item -fmerge-all-constants Attempt to merge identical constants and identical variables. This option implies @option{-fmerge-constants}. In addition to @option{-fmerge-constants} this considers e.g. even constant initialized arrays or initialized constant variables with integral or floating point types. Languages like C or C++ require each non-automatic variable to have distinct location, so using this option will result in non-conforming behavior. @item -fno-function-cse @opindex fno-function-cse Do not put function addresses in registers; make each instruction that calls a constant function contain the function's address explicitly. This option results in less efficient code, but some strange hacks that alter the assembler output may be confused by the optimizations performed when this option is not used. @item -ffast-math @opindex ffast-math Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, and @* @option{-fno-trapping-math}. This option causes the preprocessor macro @code{__FAST_MATH__} to be defined. This option should never be turned on by any @option{-O} option since it can result in incorrect output for programs which depend on an exact implementation of IEEE or ISO rules/specifications for math functions. @item -fno-math-errno @opindex fno-math-errno Do not set ERRNO after calling math functions that are executed with a single instruction, e.g., sqrt. A program that relies on IEEE exceptions for math error handling may want to use this flag for speed while maintaining IEEE arithmetic compatibility. This option should never be turned on by any @option{-O} option since it can result in incorrect output for programs which depend on an exact implementation of IEEE or ISO rules/specifications for math functions. The default is @option{-fmath-errno}. @item -funsafe-math-optimizations @opindex funsafe-math-optimizations Allow optimizations for floating-point arithmetic that (a) assume that arguments and results are valid and (b) may violate IEEE or ANSI standards. When used at link-time, it may include libraries or startup files that change the default FPU control word or other similar optimizations. This option should never be turned on by any @option{-O} option since it can result in incorrect output for programs which depend on an exact implementation of IEEE or ISO rules/specifications for math functions. The default is @option{-fno-unsafe-math-optimizations}. @item -fno-trapping-math @opindex fno-trapping-math Compile code assuming that floating-point operations cannot generate user-visible traps. Setting this option may allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example. This option should never be turned on by any @option{-O} option since it can result in incorrect output for programs which depend on an exact implementation of IEEE or ISO rules/specifications for math functions. The default is @option{-ftrapping-math}. @end table The following options control specific optimizations. The @option{-O2} option turns on all of these optimizations except @option{-funroll-loops} and @option{-funroll-all-loops}. On most machines, the @option{-O} option turns on the @option{-fthread-jumps} and @option{-fdelayed-branch} options, but specific machines may handle it differently. You can use the following flags in the rare cases when ``fine-tuning'' of optimizations to be performed is desired. Not all of the optimizations performed by GCC have @option{-f} options to control them. @table @gcctabopt @item -fstrength-reduce @opindex fstrength-reduce Perform the optimizations of loop strength reduction and elimination of iteration variables. @item -fthread-jumps @opindex fthread-jumps Perform optimizations where we check to see if a jump branches to a location where another comparison subsumed by the first is found. If so, the first branch is redirected to either the destination of the second branch or a point immediately following it, depending on whether the condition is known to be true or false. @item -fcse-follow-jumps @opindex fcse-follow-jumps In common subexpression elimination, scan through jump instructions when the target of the jump is not reached by any other path. For example, when CSE encounters an @code{if} statement with an @code{else} clause, CSE will follow the jump when the condition tested is false. @item -fcse-skip-blocks @opindex fcse-skip-blocks This is similar to @option{-fcse-follow-jumps}, but causes CSE to follow jumps which conditionally skip over blocks. When CSE encounters a simple @code{if} statement with no else clause, @option{-fcse-skip-blocks} causes CSE to follow the jump around the body of the @code{if}. @item -frerun-cse-after-loop @opindex frerun-cse-after-loop Re-run common subexpression elimination after loop optimizations has been performed. @item -frerun-loop-opt @opindex frerun-loop-opt Run the loop optimizer twice. @item -fgcse @opindex fgcse Perform a global common subexpression elimination pass. This pass also performs global constant and copy propagation. @emph{Note:} When compiling a program using computed gotos, a GCC extension, you may get better runtime performance if you disable the global common subexpression elmination pass by adding @option{-fno-gcse} to the command line. @item -fgcse-lm @opindex fgcse-lm When @option{-fgcse-lm} is enabled, global common subexpression elimination will attempt to move loads which are only killed by stores into themselves. This allows a loop containing a load/store sequence to be changed to a load outside the loop, and a copy/store within the loop. @item -fgcse-sm @opindex fgcse-sm When @option{-fgcse-sm} is enabled, A store motion pass is run after global common subexpression elimination. This pass will attempt to move stores out of loops. When used in conjunction with @option{-fgcse-lm}, loops containing a load/store sequence can be changed to a load before the loop and a store after the loop. @item -fdelete-null-pointer-checks @opindex fdelete-null-pointer-checks Use global dataflow analysis to identify and eliminate useless checks for null pointers. The compiler assumes that dereferencing a null pointer would have halted the program. If a pointer is checked after it has already been dereferenced, it cannot be null. In some environments, this assumption is not true, and programs can safely dereference null pointers. Use @option{-fno-delete-null-pointer-checks} to disable this optimization for programs which depend on that behavior. @item -fexpensive-optimizations @opindex fexpensive-optimizations Perform a number of minor optimizations that are relatively expensive. @item -foptimize-register-move @itemx -fregmove @opindex foptimize-register-move @opindex fregmove Attempt to reassign register numbers in move instructions and as operands of other simple instructions in order to maximize the amount of register tying. This is especially helpful on machines with two-operand instructions. GCC enables this optimization by default with @option{-O2} or higher. Note @option{-fregmove} and @option{-foptimize-register-move} are the same optimization. @item -fdelayed-branch @opindex fdelayed-branch If supported for the target machine, attempt to reorder instructions to exploit instruction slots available after delayed branch instructions. @item -fschedule-insns @opindex fschedule-insns If supported for the target machine, attempt to reorder instructions to eliminate execution stalls due to required data being unavailable. This helps machines that have slow floating point or memory load instructions by allowing other instructions to be issued until the result of the load or floating point instruction is required. @item -fschedule-insns2 @opindex fschedule-insns2 Similar to @option{-fschedule-insns}, but requests an additional pass of instruction scheduling after register allocation has been done. This is especially useful on machines with a relatively small number of registers and where memory load instructions take more than one cycle. @item -ffunction-sections @itemx -fdata-sections @opindex ffunction-sections @opindex fdata-sections Place each function or data item into its own section in the output file if the target supports arbitrary sections. The name of the function or the name of the data item determines the section's name in the output file. Use these options on systems where the linker can perform optimizations to improve locality of reference in the instruction space. HPPA processors running HP-UX and Sparc processors running Solaris 2 have linkers with such optimizations. Other systems using the ELF object format as well as AIX may have these optimizations in the future. Only use these options when there are significant benefits from doing so. When you specify these options, the assembler and linker will create larger object and executable files and will also be slower. You will not be able to use @code{gprof} on all systems if you specify this option and you may have problems with debugging if you specify both this option and @option{-g}. @item -fcaller-saves @opindex fcaller-saves Enable values to be allocated in registers that will be clobbered by function calls, by emitting extra instructions to save and restore the registers around such calls. Such allocation is done only when it seems to result in better code than would otherwise be produced. This option is always enabled by default on certain machines, usually those which have no call-preserved registers to use instead. For all machines, optimization level 2 and higher enables this flag by default. @item -funroll-loops @opindex funroll-loops Unroll loops whose number of iterations can be determined at compile time or upon entry to the loop. @option{-funroll-loops} implies both @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This option makes code larger, and may or may not make it run faster. @item -funroll-all-loops @opindex funroll-all-loops Unroll all loops, even if their number of iterations is uncertain when the loop is entered. This usually makes programs run more slowly. @option{-funroll-all-loops} implies the same options as @option{-funroll-loops}, @item -fprefetch-loop-arrays @opindex fprefetch-loop-arrays If supported by the target machine, generate instructions to prefetch memory to improve the performance of loops that access large arrays. @item -fmove-all-movables @opindex fmove-all-movables Forces all invariant computations in loops to be moved outside the loop. @item -freduce-all-givs @opindex freduce-all-givs Forces all general-induction variables in loops to be strength-reduced. @emph{Note:} When compiling programs written in Fortran, @option{-fmove-all-movables} and @option{-freduce-all-givs} are enabled by default when you use the optimizer. These options may generate better or worse code; results are highly dependent on the structure of loops within the source code. These two options are intended to be removed someday, once they have helped determine the efficacy of various approaches to improving loop optimizations. Please let us (@w{@email{gcc@@gcc.gnu.org}} and @w{@email{fortran@@gnu.org}}) know how use of these options affects the performance of your production code. We're very interested in code that runs @emph{slower} when these options are @emph{enabled}. @item -fno-peephole @itemx -fno-peephole2 @opindex fno-peephole @opindex fno-peephole2 Disable any machine-specific peephole optimizations. The difference between @option{-fno-peephole} and @option{-fno-peephole2} is in how they are implemented in the compiler; some targets use one, some use the other, a few use both. @item -fbranch-probabilities @opindex fbranch-probabilities After running a program compiled with @option{-fprofile-arcs} (@pxref{Debugging Options,, Options for Debugging Your Program or @command{gcc}}), you can compile it a second time using @option{-fbranch-probabilities}, to improve optimizations based on the number of times each branch was taken. When the program compiled with @option{-fprofile-arcs} exits it saves arc execution counts to a file called @file{@var{sourcename}.da} for each source file The information in this data file is very dependent on the structure of the generated code, so you must use the same source code and the same optimization options for both compilations. With @option{-fbranch-probabilities}, GCC puts a @samp{REG_EXEC_COUNT} note on the first instruction of each basic block, and a @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}. These can be used to improve optimization. Currently, they are only used in one place: in @file{reorg.c}, instead of guessing which path a branch is mostly to take, the @samp{REG_BR_PROB} values are used to exactly determine which path is taken more often. @item -fno-guess-branch-probability @opindex fno-guess-branch-probability Do not guess branch probabilities using a randomized model. Sometimes gcc will opt to use a randomized model to guess branch probabilities, when none are available from either profiling feedback (@option{-fprofile-arcs}) or @samp{__builtin_expect}. This means that different runs of the compiler on the same program may produce different object code. In a hard real-time system, people don't want different runs of the compiler to produce code that has different behavior; minimizing non-determinism is of paramount import. This switch allows users to reduce non-determinism, possibly at the expense of inferior optimization. @item -fstrict-aliasing @opindex fstrict-aliasing Allows the compiler to assume the strictest aliasing rules applicable to the language being compiled. For C (and C++), this activates optimizations based on the type of expressions. In particular, an object of one type is assumed never to reside at the same address as an object of a different type, unless the types are almost the same. For example, an @code{unsigned int} can alias an @code{int}, but not a @code{void*} or a @code{double}. A character type may alias any other type. Pay special attention to code like this: @example union a_union @{ int i; double d; @}; int f() @{ a_union t; t.d = 3.0; return t.i; @} @end example The practice of reading from a different union member than the one most recently written to (called ``type-punning'') is common. Even with @option{-fstrict-aliasing}, type-punning is allowed, provided the memory is accessed through the union type. So, the code above will work as expected. However, this code might not: @example int f() @{ a_union t; int* ip; t.d = 3.0; ip = &t.i; return *ip; @} @end example Every language that wishes to perform language-specific alias analysis should define a function that computes, given an @code{tree} node, an alias set for the node. Nodes in different alias sets are not allowed to alias. For an example, see the C front-end function @code{c_get_alias_set}. @item -falign-functions @itemx -falign-functions=@var{n} @opindex falign-functions Align the start of functions to the next power-of-two greater than @var{n}, skipping up to @var{n} bytes. For instance, @option{-falign-functions=32} aligns functions to the next 32-byte boundary, but @option{-falign-functions=24} would align to the next 32-byte boundary only if this can be done by skipping 23 bytes or less. @option{-fno-align-functions} and @option{-falign-functions=1} are equivalent and mean that functions will not be aligned. Some assemblers only support this flag when @var{n} is a power of two; in that case, it is rounded up. If @var{n} is not specified, use a machine-dependent default. @item -falign-labels @itemx -falign-labels=@var{n} @opindex falign-labels Align all branch targets to a power-of-two boundary, skipping up to @var{n} bytes like @option{-falign-functions}. This option can easily make code slower, because it must insert dummy operations for when the branch target is reached in the usual flow of the code. If @option{-falign-loops} or @option{-falign-jumps} are applicable and are greater than this value, then their values are used instead. If @var{n} is not specified, use a machine-dependent default which is very likely to be @samp{1}, meaning no alignment. @c APPLE LOCAL manual This option does not work on Mac OS X. @item -falign-loops @itemx -falign-loops=@var{n} @opindex falign-loops Align loops to a power-of-two boundary, skipping up to @var{n} bytes like @option{-falign-functions}. The hope is that the loop will be executed many times, which will make up for any execution of the dummy operations. If @var{n} is not specified, use a machine-dependent default. @c APPLE LOCAL manual This option does not work on Mac OS X. @item -falign-jumps @itemx -falign-jumps=@var{n} @opindex falign-jumps Align branch targets to a power-of-two boundary, for branch targets where the targets can only be reached by jumping, skipping up to @var{n} bytes like @option{-falign-functions}. In this case, no dummy operations need be executed. If @var{n} is not specified, use a machine-dependent default. @c APPLE LOCAL manual This option does not work on Mac OS X. @item -fssa @opindex fssa Perform optimizations in static single assignment form. Each function's flow graph is translated into SSA form, optimizations are performed, and the flow graph is translated back from SSA form. Users should not specify this option, since it is not yet ready for production use. @item -fssa-ccp @opindex fssa-ccp Perform Sparse Conditional Constant Propagation in SSA form. Requires @option{-fssa}. Like @option{-fssa}, this is an experimental feature. @item -fssa-dce @opindex fssa-dce Perform aggressive dead-code elimination in SSA form. Requires @option{-fssa}. Like @option{-fssa}, this is an experimental feature. @item -fsingle-precision-constant @opindex fsingle-precision-constant Treat floating point constant as single precision constant instead of implicitly converting it to double precision constant. @item -frename-registers @opindex frename-registers Attempt to avoid false dependencies in scheduled code by making use of registers left over after register allocation. This optimization will most benefit processors with lots of registers. It can, however, make debugging impossible, since variables will no longer stay in a ``home register''. @item -fno-cprop-registers @opindex fno-cprop-registers After register allocation and post-register allocation instruction splitting, we perform a copy-propagation pass to try to reduce scheduling dependencies and occasionally eliminate the copy. @item --param @var{name}=@var{value} @opindex param In some places, GCC uses various constants to control the amount of optimization that is done. For example, GCC will not inline functions that contain more that a certain number of instructions. You can control some of these constants on the command-line using the @option{--param} option. In each case, the @var{value} is an integer. The allowable choices for @var{name} are given in the following table: @table @gcctabopt @item max-delay-slot-insn-search The maximum number of instructions to consider when looking for an instruction to fill a delay slot. If more than this arbitrary number of instructions is searched, the time savings from filling the delay slot will be minimal so stop searching. Increasing values mean more aggressive optimization, making the compile time increase with probably small improvement in executable run time. @item max-delay-slot-live-search When trying to fill delay slots, the maximum number of instructions to consider when searching for a block with valid live register information. Increasing this arbitrarily chosen value means more aggressive optimization, increasing the compile time. This parameter should be removed when the delay slot code is rewritten to maintain the control-flow graph. @item max-gcse-memory The approximate maximum amount of memory that will be allocated in order to perform the global common subexpression elimination optimization. If more memory than specified is required, the optimization will not be done. @item max-gcse-passes The maximum number of passes of GCSE to run. @item max-pending-list-length The maximum number of pending dependencies scheduling will allow before flushing the current state and starting over. Large functions with few branches or calls can create excessively large lists which needlessly consume memory and resources. @item max-inline-insns If an function contains more than this many instructions, it will not be inlined. This option is precisely equivalent to @option{-finline-limit}. @end table @end table @node Preprocessor Options @section Options Controlling the Preprocessor @cindex preprocessor options @cindex options, preprocessor These options control the C preprocessor, which is run on each C source file before actual compilation. If you use the @option{-E} option, nothing is done except preprocessing. Some of these options make sense only together with @option{-E} because they cause the preprocessor output to be unsuitable for actual compilation. @opindex Wp You can use @option{-Wp,@var{option}} to bypass the compiler driver and pass @var{option} directly through to the preprocessor. If @var{option} contains commas, it is split into multiple options at the commas. However, many options are modified, translated or interpreted by the compiler driver before being passed to the preprocessor, and @option{-Wp} forcibly bypasses this phase. The preprocessor's direct interface is undocumented and subject to change, so whenever possible you should avoid using @option{-Wp} and let the driver handle the options instead. @include cppopts.texi @node Assembler Options @section Passing Options to the Assembler @c prevent bad page break with this line You can pass options to the assembler. @table @gcctabopt @item -Wa,@var{option} @opindex Wa Pass @var{option} as an option to the assembler. If @var{option} contains commas, it is split into multiple options at the commas. @end table @node Link Options @section Options for Linking @cindex link options @cindex options, linking These options come into play when the compiler links object files into an executable output file. They are meaningless if the compiler is not doing a link step. @c APPLE LOCAL begin linker flags In addition to the options listed below, Apple's GCC also accepts and passes nearly all of the options defined by the linker @samp{ld} and by the library tool @samp{libtool}. Common options include @samp{-framework}, @samp{-dynamic}, @samp{-bundle}, @samp{-flat_namespace}, and so forth. See the ld and libtool man pages for further details. @c APPLE LOCAL end linker flags @table @gcctabopt @cindex file names @item @var{object-file-name} A file name that does not end in a special recognized suffix is considered to name an object file or library. (Object files are distinguished from libraries by the linker according to the file contents.) If linking is done, these object files are used as input to the linker. @item -c @itemx -S @itemx -E @opindex c @opindex S @opindex E If any of these options is used, then the linker is not run, and object file names should not be used as arguments. @xref{Overall Options}. @cindex Libraries @item -l@var{library} @itemx -l @var{library} @opindex l Search the library named @var{library} when linking. (The second alternative with the library as a separate argument is only for POSIX compliance and is not recommended.) It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z} after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers to functions in @samp{z}, those functions may not be loaded. The linker searches a standard list of directories for the library, which is actually a file named @file{lib@var{library}.a}. The linker then uses this file as if it had been specified precisely by name. The directories searched include several standard system directories plus any that you specify with @option{-L}. Normally the files found this way are library files---archive files whose members are object files. The linker handles an archive file by scanning through it for members which define symbols that have so far been referenced but not defined. But if the file that is found is an ordinary object file, it is linked in the usual fashion. The only difference between using an @option{-l} option and specifying a file name is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a} and searches several directories. @item -lobjc @opindex lobjc You need this special case of the @option{-l} option in order to link an Objective-C program. @item -nostartfiles @opindex nostartfiles Do not use the standard system startup files when linking. The standard system libraries are used normally, unless @option{-nostdlib} or @option{-nodefaultlibs} is used. @item -nodefaultlibs @opindex nodefaultlibs Do not use the standard system libraries when linking. Only the libraries you specify will be passed to the linker. The standard startup files are used normally, unless @option{-nostartfiles} is used. The compiler may generate calls to memcmp, memset, and memcpy for System V (and ISO C) environments or to bcopy and bzero for BSD environments. These entries are usually resolved by entries in libc. These entry points should be supplied through some other mechanism when this option is specified. @item -nostdlib @opindex nostdlib Do not use the standard system startup files or libraries when linking. No startup files and only the libraries you specify will be passed to the linker. The compiler may generate calls to memcmp, memset, and memcpy for System V (and ISO C) environments or to bcopy and bzero for BSD environments. These entries are usually resolved by entries in libc. These entry points should be supplied through some other mechanism when this option is specified. @c APPLE LOCAL begin radar 2466994 - -no-c++filt ilr @item -no-c++filt By default all linker diagnostic output is piped through c++filt. This option suppresses that behavior. (APPLE ONLY) @c APPLE LOCAL end radar 2466994 - -no-c++filt ilr @cindex @option{-lgcc}, use with @option{-nostdlib} @cindex @option{-nostdlib} and unresolved references @cindex unresolved references and @option{-nostdlib} @cindex @option{-lgcc}, use with @option{-nodefaultlibs} @cindex @option{-nodefaultlibs} and unresolved references @cindex unresolved references and @option{-nodefaultlibs} One of the standard libraries bypassed by @option{-nostdlib} and @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines that GCC uses to overcome shortcomings of particular machines, or special needs for some languages. (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler Collection (GCC) Internals}, for more discussion of @file{libgcc.a}.) In most cases, you need @file{libgcc.a} even when you want to avoid other standard libraries. In other words, when you specify @option{-nostdlib} or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well. This ensures that you have no unresolved references to internal GCC library subroutines. (For example, @samp{__main}, used to ensure C++ constructors will be called; @pxref{Collect2,,@code{collect2}, gccint, GNU Compiler Collection (GCC) Internals}.) @item -s @opindex s Remove all symbol table and relocation information from the executable. @item -static @opindex static On systems that support dynamic linking, this prevents linking with the shared libraries. On other systems, this option has no effect. @c APPLE LOCAL manual This option will not work on Mac OS X unless all of your libraries (including @file{libgcc.a}) have also been compiled with @option{-static}. @item -shared @opindex shared Produce a shared object which can then be linked with other objects to form an executable. Not all systems support this option. For predictable results, you must also specify the same set of options that were used to generate code (@option{-fpic}, @option{-fPIC}, or model suboptions) when you specify this option.@footnote{On some systems, @samp{gcc -shared} needs to build supplementary stub code for constructors to work. On multi-libbed systems, @samp{gcc -shared} must select the correct support libraries to link against. Failing to supply the correct flags may lead to subtle defects. Supplying them in cases where they are not necessary is innocuous.} @c APPLE LOCAL manual This option is not supported on Mac OS X. @item -shared-libgcc @itemx -static-libgcc @opindex shared-libgcc @opindex static-libgcc On systems that provide @file{libgcc} as a shared library, these options force the use of either the shared or static version respectively. If no shared version of @file{libgcc} was built when the compiler was configured, these options have no effect. There are several situations in which an application should use the shared @file{libgcc} instead of the static version. The most common of these is when the application wishes to throw and catch exceptions across different shared libraries. In that case, each of the libraries as well as the application itself should use the shared @file{libgcc}. Therefore, the G++ and GCJ drivers automatically add @option{-shared-libgcc} 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. If, instead, you use the GCC driver to create shared libraries, you may find that they will not always be linked with the shared @file{libgcc}. If GCC finds, at its configuration time, that you have a GNU linker that does not support option @option{--eh-frame-hdr}, it will link the shared version of @file{libgcc} into shared libraries by default. Otherwise, it will take advantage of the linker and optimize away the linking with the shared version of @file{libgcc}, linking with the static version of libgcc by default. This allows exceptions to propagate through such shared libraries, without incurring relocation costs at library load time. However, if a library or main executable is supposed to throw or catch exceptions, you must link it using the G++ or GCJ driver, as appropriate for the languages used in the program, or using the option @option{-shared-libgcc}, such that it is linked with the shared @file{libgcc}. @item -symbolic @opindex symbolic Bind references to global symbols when building a shared object. Warn about any unresolved references (unless overridden by the link editor option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support this option. @item -Xlinker @var{option} @opindex Xlinker Pass @var{option} as an option to the linker. You can use this to supply system-specific linker options which GCC does not know how to recognize. If you want to pass an option that takes an argument, you must use @option{-Xlinker} twice, once for the option and once for the argument. For example, to pass @option{-assert definitions}, you must write @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write @option{-Xlinker "-assert definitions"}, because this passes the entire string as a single argument, which is not what the linker expects. @item -Wl,@var{option} @opindex Wl Pass @var{option} as an option to the linker. If @var{option} contains commas, it is split into multiple options at the commas. @item -u @var{symbol} @opindex u Pretend the symbol @var{symbol} is undefined, to force linking of library modules to define it. You can use @option{-u} multiple times with different symbols to force loading of additional library modules. @end table @node Directory Options @section Options for Directory Search @cindex directory options @cindex options, directory search @cindex search path These options specify directories to search for header files, for libraries and for parts of the compiler: @table @gcctabopt @item -I@var{dir} @opindex I Add the directory @var{dir} to the head of the list of directories to be searched for header files. This can be used to override a system header file, substituting your own version, since these directories are searched before the system header file directories. However, you should not use this option to add directories that contain vendor-supplied system header files (use @option{-isystem} for that). If you use more than one @option{-I} option, the directories are scanned in left-to-right order; the standard system directories come after. If a standard system include directory, or a directory specified with @option{-isystem}, is also specified with @option{-I}, it will be searched only in the position requested by @option{-I}. Also, it will not be considered a system include directory. If that directory really does contain system headers, there is a good chance that they will break. For instance, if GCC's installation procedure edited the headers in @file{/usr/include} to fix bugs, @samp{-I/usr/include} will cause the original, buggy headers to be found instead of the corrected ones. GCC will issue a warning when a system include directory is hidden in this way. @item -I- @opindex I- Any directories you specify with @option{-I} options before the @option{-I-} option are searched only for the case of @samp{#include "@var{file}"}; they are not searched for @samp{#include <@var{file}>}. If additional directories are specified with @option{-I} options after the @option{-I-}, these directories are searched for all @samp{#include} directives. (Ordinarily @emph{all} @option{-I} directories are used this way.) In addition, the @option{-I-} option inhibits the use of the current directory (where the current input file came from) as the first search directory for @samp{#include "@var{file}"}. There is no way to override this effect of @option{-I-}. With @option{-I.} you can specify searching the directory which was current when the compiler was invoked. That is not exactly the same as what the preprocessor does by default, but it is often satisfactory. @option{-I-} does not inhibit the use of the standard system directories for header files. Thus, @option{-I-} and @option{-nostdinc} are independent. @item -L@var{dir} @opindex L Add directory @var{dir} to the list of directories to be searched for @option{-l}. @c APPLE LOCAL begin framework headers @item -F@var{dir} @opindex F In Apple's version of GCC only, add the directory @var{dir} to the head of the list of directories to be searched for frameworks. The framework search algorithm is, for an inclusion of @samp{}, to look for files named @file{@var{path}/Fmwk.framework/Headers/Header.h} or @file{@var{path}/Fmwk.framework/PrivateHeaders/Header.h} where @var{path} includes @file{/System/Library/Frameworks/} @file{/Library/Frameworks/}, and @file{/Local/Library/Frameworks/}, plus any additional paths specified by @option{-F}. All the @option{-F} options are also passed to the linker. @c APPLE LOCAL end framework headers @item -B@var{prefix} @opindex B This option specifies where to find the executables, libraries, include files, and data files of the compiler itself. The compiler driver program runs one or more of the subprograms @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries @var{prefix} as a prefix for each program it tries to run, both with and without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}). For each subprogram to be run, the compiler driver first tries the @option{-B} prefix, if any. If that name is not found, or if @option{-B} was not specified, the driver tries two standard prefixes, which are @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc-lib/}. If neither of those results in a file name that is found, the unmodified program name is searched for using the directories specified in your @env{PATH} environment variable. The compiler will check to see if the path provided by the @option{-B} refers to a directory, and if necessary it will add a directory separator character at the end of the path. @option{-B} prefixes that effectively specify directory names also apply to libraries in the linker, because the compiler translates these options into @option{-L} options for the linker. They also apply to includes files in the preprocessor, because the compiler translates these options into @option{-isystem} options for the preprocessor. In this case, the compiler appends @samp{include} to the prefix. The run-time support file @file{libgcc.a} can also be searched for using the @option{-B} prefix, if needed. If it is not found there, the two standard prefixes above are tried, and that is all. The file is left out of the link if it is not found by those means. Another way to specify a prefix much like the @option{-B} prefix is to use the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment Variables}. As a special kludge, if the path provided by @option{-B} is @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to 9, then it will be replaced by @file{[dir/]include}. This is to help with boot-strapping the compiler. @item -specs=@var{file} @opindex specs Process @var{file} after the compiler reads in the standard @file{specs} file, in order to override the defaults that the @file{gcc} driver program uses when determining what switches to pass to @file{cc1}, @file{cc1plus}, @file{as}, @file{ld}, etc. More than one @option{-specs=@var{file}} can be specified on the command line, and they are processed in order, from left to right. @end table @c man end @node Spec Files @section Specifying subprocesses and the switches to pass to them @cindex Spec Files @command{gcc} is a driver program. It performs its job by invoking a sequence of other programs to do the work of compiling, assembling and linking. GCC interprets its command-line parameters and uses these to deduce which programs it should invoke, and which command-line options it ought to place on their command lines. This behavior is controlled by @dfn{spec strings}. In most cases there is one spec string for each program that GCC can invoke, but a few programs have multiple spec strings to control their behavior. The spec strings built into GCC can be overridden by using the @option{-specs=} command-line switch to specify a spec file. @dfn{Spec files} are plaintext files that are used to construct spec strings. They consist of a sequence of directives separated by blank lines. The type of directive is determined by the first non-whitespace character on the line and it can be one of the following: @table @code @item %@var{command} Issues a @var{command} to the spec file processor. The commands that can appear here are: @table @code @item %include <@var{file}> @cindex %include Search for @var{file} and insert its text at the current point in the specs file. @item %include_noerr <@var{file}> @cindex %include_noerr Just like @samp{%include}, but do not generate an error message if the include file cannot be found. @item %rename @var{old_name} @var{new_name} @cindex %rename Rename the spec string @var{old_name} to @var{new_name}. @end table @item *[@var{spec_name}]: This tells the compiler to create, override or delete the named spec string. All lines after this directive up to the next directive or blank line are considered to be the text for the spec string. If this results in an empty string then the spec will be deleted. (Or, if the spec did not exist, then nothing will happened.) Otherwise, if the spec does not currently exist a new spec will be created. If the spec does exist then its contents will be overridden by the text of this directive, unless the first character of that text is the @samp{+} character, in which case the text will be appended to the spec. @item [@var{suffix}]: Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive and up to the next directive or blank line are considered to make up the spec string for the indicated suffix. When the compiler encounters an input file with the named suffix, it will processes the spec string in order to work out how to compile that file. For example: @smallexample .ZZ: z-compile -input %i @end smallexample This says that any input file whose name ends in @samp{.ZZ} should be passed to the program @samp{z-compile}, which should be invoked with the command-line switch @option{-input} and with the result of performing the @samp{%i} substitution. (See below.) As an alternative to providing a spec string, the text that follows a suffix directive can be one of the following: @table @code @item @@@var{language} This says that the suffix is an alias for a known @var{language}. This is similar to using the @option{-x} command-line switch to GCC to specify a language explicitly. For example: @smallexample .ZZ: @@c++ @end smallexample Says that .ZZ files are, in fact, C++ source files. @item #@var{name} This causes an error messages saying: @smallexample @var{name} compiler not installed on this system. @end smallexample @end table GCC already has an extensive list of suffixes built into it. This directive will add an entry to the end of the list of suffixes, but since the list is searched from the end backwards, it is effectively possible to override earlier entries using this technique. @end table GCC has the following spec strings built into it. Spec files can override these strings or create their own. Note that individual targets can also add their own spec strings to this list. @smallexample asm Options to pass to the assembler asm_final Options to pass to the assembler post-processor cpp Options to pass to the C preprocessor cc1 Options to pass to the C compiler cc1plus Options to pass to the C++ compiler endfile Object files to include at the end of the link link Options to pass to the linker lib Libraries to include on the command line to the linker libgcc Decides which GCC support library to pass to the linker linker Sets the name of the linker predefines Defines to be passed to the C preprocessor signed_char Defines to pass to CPP to say whether @code{char} is signed by default startfile Object files to include at the start of the link @end smallexample Here is a small example of a spec file: @smallexample %rename lib old_lib *lib: --start-group -lgcc -lc -leval1 --end-group %(old_lib) @end smallexample This example renames the spec called @samp{lib} to @samp{old_lib} and then overrides the previous definition of @samp{lib} with a new one. The new definition adds in some extra command-line options before including the text of the old definition. @dfn{Spec strings} are a list of command-line options to be passed to their corresponding program. In addition, the spec strings can contain @samp{%}-prefixed sequences to substitute variable text or to conditionally insert text into the command line. Using these constructs it is possible to generate quite complex command lines. Here is a table of all defined @samp{%}-sequences for spec strings. Note that spaces are not generated automatically around the results of expanding these sequences. Therefore you can concatenate them together or combine them with constant text in a single argument. @table @code @item %% Substitute one @samp{%} into the program name or argument. @item %i Substitute the name of the input file being processed. @item %b Substitute the basename of the input file being processed. This is the substring up to (and not including) the last period and not including the directory. @item %B This is the same as @samp{%b}, but include the file suffix (text after the last period). @item %d Marks the argument containing or following the @samp{%d} as a temporary file name, so that that file will be deleted if GCC exits successfully. Unlike @samp{%g}, this contributes no text to the argument. @item %g@var{suffix} Substitute a file name that has suffix @var{suffix} and is chosen once per compilation, and mark the argument in the same way as @samp{%d}. To reduce exposure to denial-of-service attacks, the file name is now chosen in a way that is hard to predict even when previously chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s} might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g} was simply substituted with a file name chosen once per compilation, without regard to any appended suffix (which was therefore treated just like ordinary text), making such attacks more likely to succeed. @item %u@var{suffix} Like @samp{%g}, but generates a new temporary file name even if @samp{%u@var{suffix}} was already seen. @item %U@var{suffix} Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a new one if there is no such last file name. In the absence of any @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s} would involve the generation of two distinct file names, one for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was simply substituted with a file name chosen for the previous @samp{%u}, without regard to any appended suffix. @item %j@var{SUFFIX} Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is writable, and if save-temps is off; otherwise, substitute the name of a temporary file, just like @samp{%u}. This temporary file is not meant for communication between processes, but rather as a junk disposal mechanism. @item %.@var{SUFFIX} Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args when it is subsequently output with @samp{%*}. @var{SUFFIX} is terminated by the next space or %. @item %w Marks the argument containing or following the @samp{%w} as the designated output file of this compilation. This puts the argument into the sequence of arguments that @samp{%o} will substitute later. @item %o Substitutes the names of all the output files, with spaces automatically placed around them. You should write spaces around the @samp{%o} as well or the results are undefined. @samp{%o} is for use in the specs for running the linker. Input files whose names have no recognized suffix are not compiled at all, but they are included among the output files, so they will be linked. @item %O Substitutes the suffix for object files. Note that this is handled specially when it immediately follows @samp{%g, %u, or %U}, because of the need for those to form complete file names. The handling is such that @samp{%O} is treated exactly as if it had already been substituted, except that @samp{%g, %u, and %U} do not currently support additional @var{suffix} characters following @samp{%O} as they would following, for example, @samp{.o}. @item %p Substitutes the standard macro predefinitions for the current target machine. Use this when running @code{cpp}. @item %P Like @samp{%p}, but puts @samp{__} before and after the name of each predefined macro, except for macros that start with @samp{__} or with @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO C@. @item %I Substitute a @option{-iprefix} option made from @env{GCC_EXEC_PREFIX}. @item %s Current argument is the name of a library or startup file of some sort. Search for that file in a standard list of directories and substitute the full name found. @item %e@var{str} Print @var{str} as an error message. @var{str} is terminated by a newline. Use this when inconsistent options are detected. @item %| Output @samp{-} if the input for the current command is coming from a pipe. @item %(@var{name}) Substitute the contents of spec string @var{name} at this point. @item %[@var{name}] Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments. @item %x@{@var{option}@} Accumulate an option for @samp{%X}. @item %X Output the accumulated linker options specified by @option{-Wl} or a @samp{%x} spec string. @item %Y Output the accumulated assembler options specified by @option{-Wa}. @item %Z Output the accumulated preprocessor options specified by @option{-Wp}. @item %v1 Substitute the major version number of GCC@. (For version 2.9.5, this is 2.) @item %v2 Substitute the minor version number of GCC@. (For version 2.9.5, this is 9.) @item %v3 Substitute the patch level number of GCC@. (For version 2.9.5, this is 5.) @item %a Process the @code{asm} spec. This is used to compute the switches to be passed to the assembler. @item %A Process the @code{asm_final} spec. This is a spec string for passing switches to an assembler post-processor, if such a program is needed. @item %l Process the @code{link} spec. This is the spec for computing the command line passed to the linker. Typically it will make use of the @samp{%L %G %S %D and %E} sequences. @item %D Dump out a @option{-L} option for each directory that GCC believes might contain startup files. If the target supports multilibs then the current multilib directory will be prepended to each of these paths. @item %M Output the multilib directory with directory separators replaced with @samp{_}. If multilib directories are not set, or the multilib directory is @file{.} then this option emits nothing. @item %L Process the @code{lib} spec. This is a spec string for deciding which libraries should be included on the command line to the linker. @item %G Process the @code{libgcc} spec. This is a spec string for deciding which GCC support library should be included on the command line to the linker. @item %S Process the @code{startfile} spec. This is a spec for deciding which object files should be the first ones passed to the linker. Typically this might be a file named @file{crt0.o}. @item %E Process the @code{endfile} spec. This is a spec string that specifies the last object files that will be passed to the linker. @item %C Process the @code{cpp} spec. This is used to construct the arguments to be passed to the C preprocessor. @item %c Process the @code{signed_char} spec. This is intended to be used to tell cpp whether a char is signed. It typically has the definition: @smallexample %@{funsigned-char:-D__CHAR_UNSIGNED__@} @end smallexample @item %1 Process the @code{cc1} spec. This is used to construct the options to be passed to the actual C compiler (@samp{cc1}). @item %2 Process the @code{cc1plus} spec. This is used to construct the options to be passed to the actual C++ compiler (@samp{cc1plus}). @item %* Substitute the variable part of a matched option. See below. Note that each comma in the substituted string is replaced by a single space. @item %@{@code{S}@} Substitutes the @code{-S} switch, if that switch was given to GCC@. If that switch was not specified, this substitutes nothing. Note that the leading dash is omitted when specifying this option, and it is automatically inserted if the substitution is performed. Thus the spec string @samp{%@{foo@}} would match the command-line option @option{-foo} and would output the command line option @option{-foo}. @item %W@{@code{S}@} Like %@{@code{S}@} but mark last argument supplied within as a file to be deleted on failure. @item %@{@code{S}*@} Substitutes all the switches specified to GCC whose names start with @code{-S}, but which also take an argument. This is used for switches like @option{-o}, @option{-D}, @option{-I}, etc. GCC considers @option{-o foo} as being one switch whose names starts with @samp{o}. %@{o*@} would substitute this text, including the space. Thus two arguments would be generated. @item %@{^@code{S}*@} Like %@{@code{S}*@}, but don't put a blank between a switch and its argument. Thus %@{^o*@} would only generate one argument, not two. @item %@{@code{S}*&@code{T}*@} Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options (the order of @code{S} and @code{T} in the spec is not significant). There can be any number of ampersand-separated variables; for each the wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}. @item %@{<@code{S}@} Remove all occurrences of @code{-S} from the command line. Note---this command is position dependent. @samp{%} commands in the spec string before this option will see @code{-S}, @samp{%} commands in the spec string after this option will not. @item %@{@code{S}*:@code{X}@} Substitutes @code{X} if one or more switches whose names start with @code{-S} are specified to GCC@. Note that the tail part of the @code{-S} option (i.e.@: the part matched by the @samp{*}) will be substituted for each occurrence of @samp{%*} within @code{X}. @item %@{@code{S}:@code{X}@} Substitutes @code{X}, but only if the @samp{-S} switch was given to GCC@. @item %@{!@code{S}:@code{X}@} Substitutes @code{X}, but only if the @samp{-S} switch was @emph{not} given to GCC@. @item %@{|@code{S}:@code{X}@} Like %@{@code{S}:@code{X}@}, but if no @code{S} switch, substitute @samp{-}. @item %@{|!@code{S}:@code{X}@} Like %@{!@code{S}:@code{X}@}, but if there is an @code{S} switch, substitute @samp{-}. @item %@{.@code{S}:@code{X}@} Substitutes @code{X}, but only if processing a file with suffix @code{S}. @item %@{!.@code{S}:@code{X}@} Substitutes @code{X}, but only if @emph{not} processing a file with suffix @code{S}. @item %@{@code{S}|@code{P}:@code{X}@} Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@. This may be combined with @samp{!} and @samp{.} sequences as well, although they have a stronger binding than the @samp{|}. For example a spec string like this: @smallexample %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@} @end smallexample will output the following command-line options from the following input command-line options: @smallexample fred.c -foo -baz jim.d -bar -boggle -d fred.c -foo -baz -boggle -d jim.d -bar -baz -boggle @end smallexample @end table The conditional text @code{X} in a %@{@code{S}:@code{X}@} or %@{!@code{S}:@code{X}@} construct may contain other nested @samp{%} constructs or spaces, or even newlines. They are processed as usual, as described above. The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are handled specifically in these constructs. If another value of @option{-O} or the negated form of a @option{-f}, @option{-m}, or @option{-W} switch is found later in the command line, the earlier switch value is ignored, except with @{@code{S}*@} where @code{S} is just one letter, which passes all matching options. The character @samp{|} at the beginning of the predicate text is used to indicate that a command should be piped to the following command, but only if @option{-pipe} is specified. It is built into GCC which switches take arguments and which do not. (You might think it would be useful to generalize this to allow each compiler's spec to say which switches take arguments. But this cannot be done in a consistent fashion. GCC cannot even decide which input files have been specified without knowing which switches take arguments, and it must know which input files to compile in order to tell which compilers to run). GCC also knows implicitly that arguments starting in @option{-l} are to be treated as compiler output files, and passed to the linker in their proper position among the other output files. @c man begin OPTIONS @node Target Options @section Specifying Target Machine and Compiler Version @cindex target options @cindex cross compiling @cindex specifying machine version @cindex specifying compiler version and target machine @cindex compiler version, specifying @cindex target machine, specifying By default, GCC compiles code for the same type of machine that you are using. However, it can also be installed as a cross-compiler, to compile for some other type of machine. In fact, several different configurations of GCC, for different target machines, can be installed side by side. Then you specify which one to use with the @option{-b} option. In addition, older and newer versions of GCC can be installed side by side. One of them (probably the newest) will be the default, but you may sometimes wish to use another. @table @gcctabopt @item -b @var{machine} @opindex b The argument @var{machine} specifies the target machine for compilation. This is useful when you have installed GCC as a cross-compiler. The value to use for @var{machine} is the same as was specified as the machine type when configuring GCC as a cross-compiler. For example, if a cross-compiler was configured with @samp{configure i386v}, meaning to compile for an 80386 running System V, then you would specify @option{-b i386v} to run that cross compiler. When you do not specify @option{-b}, it normally means to compile for the same type of machine that you are using. @item -V @var{version} @opindex V The argument @var{version} specifies which version of GCC to run. This is useful when multiple versions are installed. For example, @var{version} might be @samp{2.0}, meaning to run GCC version 2.0. The default version, when you do not specify @option{-V}, is the last version of GCC that you installed. @end table The @option{-b} and @option{-V} options actually work by controlling part of the file name used for the executable files and libraries used for compilation. A given version of GCC, for a given target machine, is normally kept in the directory @file{/usr/local/lib/gcc-lib/@var{machine}/@var{version}}. Thus, sites can customize the effect of @option{-b} or @option{-V} either by changing the names of these directories or adding alternate names (or symbolic links). If in directory @file{/usr/local/lib/gcc-lib/} the file @file{80386} is a link to the file @file{i386v}, then @option{-b 80386} becomes an alias for @option{-b i386v}. In one respect, the @option{-b} or @option{-V} do not completely change to a different compiler: the top-level driver program @command{gcc} that you originally invoked continues to run and invoke the other executables (preprocessor, compiler per se, assembler and linker) that do the real work. However, since no real work is done in the driver program, it usually does not matter that the driver program in use is not the one for the specified target. It is common for the interface to the other executables to change incompatibly between compiler versions, so unless the version specified is very close to that of the driver (for example, @option{-V 3.0} with a driver program from GCC version 3.0.1), use of @option{-V} may not work; for example, using @option{-V 2.95.2} will not work with a driver program from GCC 3.0. The only way that the driver program depends on the target machine is in the parsing and handling of special machine-specific options. However, this is controlled by a file which is found, along with the other executables, in the directory for the specified version and target machine. As a result, a single installed driver program adapts to any specified target machine, and sufficiently similar compiler versions. The driver program executable does control one significant thing, however: the default version and target machine. Therefore, you can install different instances of the driver program, compiled for different targets or versions, under different names. For example, if the driver for version 2.0 is installed as @command{ogcc} and that for version 2.1 is installed as @command{gcc}, then the command @command{gcc} will use version 2.1 by default, while @command{ogcc} will use 2.0 by default. However, you can choose either version with either command with the @option{-V} option. @node Submodel Options @section Hardware Models and Configurations @cindex submodel options @cindex specifying hardware config @cindex hardware models and configurations, specifying @cindex machine dependent options Earlier we discussed the standard option @option{-b} which chooses among different installed compilers for completely different target machines, such as VAX vs.@: 68000 vs.@: 80386. In addition, each of these target machine types can have its own special options, starting with @samp{-m}, to choose among various hardware models or configurations---for example, 68010 vs 68020, floating coprocessor or none. A single installed version of the compiler can compile for any model or configuration, according to the options specified. Some configurations of the compiler also support additional special options, usually for compatibility with other compilers on the same platform. These options are defined by the macro @code{TARGET_SWITCHES} in the machine description. The default for the options is also defined by that macro, which enables you to change the defaults. @menu @c APPLE LOCAL prune man page @ignore * M680x0 Options:: * M68hc1x Options:: * VAX Options:: * SPARC Options:: * Convex Options:: * AMD29K Options:: * ARM Options:: * MN10200 Options:: * MN10300 Options:: * M32R/D Options:: * M88K Options:: @c APPLE LOCAL prune man page @end ignore * RS/6000 and PowerPC Options:: @c APPLE LOCAL prune man page @ignore * RT Options:: * MIPS Options:: @c APPLE LOCAL prune man page @end ignore * i386 and x86-64 Options:: @c APPLE LOCAL prune man page @ignore * HPPA Options:: * Intel 960 Options:: * DEC Alpha Options:: * DEC Alpha/VMS Options:: * Clipper Options:: * H8/300 Options:: * SH Options:: * System V Options:: * TMS320C3x/C4x Options:: * V850 Options:: * ARC Options:: * NS32K Options:: * AVR Options:: * MCore Options:: * IA-64 Options:: * D30V Options:: * S/390 and zSeries Options:: * CRIS Options:: * MMIX Options:: * PDP-11 Options:: * Xstormy16 Options:: * Xtensa Options:: @c APPLE LOCAL prune man page @end ignore @end menu @c APPLE LOCAL prune man page @ignore @node M680x0 Options @subsection M680x0 Options @cindex M680x0 options These are the @samp{-m} options defined for the 68000 series. The default values for these options depends on which style of 68000 was selected when the compiler was configured; the defaults for the most common choices are given below. @table @gcctabopt @item -m68000 @itemx -mc68000 @opindex m68000 @opindex mc68000 Generate output for a 68000. This is the default when the compiler is configured for 68000-based systems. Use this option for microcontrollers with a 68000 or EC000 core, including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356. @item -m68020 @itemx -mc68020 @opindex m68020 @opindex mc68020 Generate output for a 68020. This is the default when the compiler is configured for 68020-based systems. @item -m68881 @opindex m68881 Generate output containing 68881 instructions for floating point. This is the default for most 68020 systems unless @option{--nfp} was specified when the compiler was configured. @item -m68030 @opindex m68030 Generate output for a 68030. This is the default when the compiler is configured for 68030-based systems. @item -m68040 @opindex m68040 Generate output for a 68040. This is the default when the compiler is configured for 68040-based systems. This option inhibits the use of 68881/68882 instructions that have to be emulated by software on the 68040. Use this option if your 68040 does not have code to emulate those instructions. @item -m68060 @opindex m68060 Generate output for a 68060. This is the default when the compiler is configured for 68060-based systems. This option inhibits the use of 68020 and 68881/68882 instructions that have to be emulated by software on the 68060. Use this option if your 68060 does not have code to emulate those instructions. @item -mcpu32 @opindex mcpu32 Generate output for a CPU32. This is the default when the compiler is configured for CPU32-based systems. Use this option for microcontrollers with a CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334, 68336, 68340, 68341, 68349 and 68360. @item -m5200 @opindex m5200 Generate output for a 520X ``coldfire'' family cpu. This is the default when the compiler is configured for 520X-based systems. Use this option for microcontroller with a 5200 core, including the MCF5202, MCF5203, MCF5204 and MCF5202. @item -m68020-40 @opindex m68020-40 Generate output for a 68040, without using any of the new instructions. This results in code which can run relatively efficiently on either a 68020/68881 or a 68030 or a 68040. The generated code does use the 68881 instructions that are emulated on the 68040. @item -m68020-60 @opindex m68020-60 Generate output for a 68060, without using any of the new instructions. This results in code which can run relatively efficiently on either a 68020/68881 or a 68030 or a 68040. The generated code does use the 68881 instructions that are emulated on the 68060. @item -mfpa @opindex mfpa Generate output containing Sun FPA instructions for floating point. @item -msoft-float @opindex msoft-float Generate output containing library calls for floating point. @strong{Warning:} the requisite libraries are not available for all m68k targets. Normally the facilities of the machine's usual C compiler are used, but this can't be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. The embedded targets @samp{m68k-*-aout} and @samp{m68k-*-coff} do provide software floating point support. @item -mshort @opindex mshort Consider type @code{int} to be 16 bits wide, like @code{short int}. @item -mnobitfield @opindex mnobitfield Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32} and @option{-m5200} options imply @w{@option{-mnobitfield}}. @item -mbitfield @opindex mbitfield Do use the bit-field instructions. The @option{-m68020} option implies @option{-mbitfield}. This is the default if you use a configuration designed for a 68020. @item -mrtd @opindex mrtd Use a different function-calling convention, in which functions that take a fixed number of arguments return with the @code{rtd} instruction, which pops their arguments while returning. This saves one instruction in the caller since there is no need to pop the arguments there. This calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler. Also, you must provide function prototypes for all functions that take variable numbers of arguments (including @code{printf}); otherwise incorrect code will be generated for calls to those functions. In addition, seriously incorrect code will result if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.) The @code{rtd} instruction is supported by the 68010, 68020, 68030, 68040, 68060 and CPU32 processors, but not by the 68000 or 5200. @item -malign-int @itemx -mno-align-int @opindex malign-int @opindex mno-align-int Control whether GCC aligns @code{int}, @code{long}, @code{long long}, @code{float}, @code{double}, and @code{long double} variables on a 32-bit boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}). Aligning variables on 32-bit boundaries produces code that runs somewhat faster on processors with 32-bit busses at the expense of more memory. @strong{Warning:} if you use the @option{-malign-int} switch, GCC will align structures containing the above types differently than most published application binary interface specifications for the m68k. @item -mpcrel @opindex mpcrel Use the pc-relative addressing mode of the 68000 directly, instead of using a global offset table. At present, this option implies @option{-fpic}, allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is not presently supported with @option{-mpcrel}, though this could be supported for 68020 and higher processors. @item -mno-strict-align @itemx -mstrict-align @opindex mno-strict-align @opindex mstrict-align Do not (do) assume that unaligned memory references will be handled by the system. @end table @node M68hc1x Options @subsection M68hc1x Options @cindex M68hc1x options These are the @samp{-m} options defined for the 68hc11 and 68hc12 microcontrollers. The default values for these options depends on which style of microcontroller was selected when the compiler was configured; the defaults for the most common choices are given below. @table @gcctabopt @item -m6811 @itemx -m68hc11 @opindex m6811 @opindex m68hc11 Generate output for a 68HC11. This is the default when the compiler is configured for 68HC11-based systems. @item -m6812 @itemx -m68hc12 @opindex m6812 @opindex m68hc12 Generate output for a 68HC12. This is the default when the compiler is configured for 68HC12-based systems. @item -mauto-incdec @opindex mauto-incdec Enable the use of 68HC12 pre and post auto-increment and auto-decrement addressing modes. @item -mshort @opindex mshort Consider type @code{int} to be 16 bits wide, like @code{short int}. @item -msoft-reg-count=@var{count} @opindex msoft-reg-count Specify the number of pseudo-soft registers which are used for the code generation. The maximum number is 32. Using more pseudo-soft register may or may not result in better code depending on the program. The default is 4 for 68HC11 and 2 for 68HC12. @end table @node VAX Options @subsection VAX Options @cindex VAX options These @samp{-m} options are defined for the VAX: @table @gcctabopt @item -munix @opindex munix Do not output certain jump instructions (@code{aobleq} and so on) that the Unix assembler for the VAX cannot handle across long ranges. @item -mgnu @opindex mgnu Do output those jump instructions, on the assumption that you will assemble with the GNU assembler. @item -mg @opindex mg Output code for g-format floating point numbers instead of d-format. @end table @node SPARC Options @subsection SPARC Options @cindex SPARC options These @samp{-m} switches are supported on the SPARC: @table @gcctabopt @item -mno-app-regs @itemx -mapp-regs @opindex mno-app-regs @opindex mapp-regs Specify @option{-mapp-regs} to generate output using the global registers 2 through 4, which the SPARC SVR4 ABI reserves for applications. This is the default. To be fully SVR4 ABI compliant at the cost of some performance loss, specify @option{-mno-app-regs}. You should compile libraries and system software with this option. @item -mfpu @itemx -mhard-float @opindex mfpu @opindex mhard-float Generate output containing floating point instructions. This is the default. @item -mno-fpu @itemx -msoft-float @opindex mno-fpu @opindex msoft-float Generate output containing library calls for floating point. @strong{Warning:} the requisite libraries are not available for all SPARC targets. Normally the facilities of the machine's usual C compiler are used, but this cannot be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. The embedded targets @samp{sparc-*-aout} and @samp{sparclite-*-*} do provide software floating point support. @option{-msoft-float} changes the calling convention in the output file; therefore, it is only useful if you compile @emph{all} of a program with this option. In particular, you need to compile @file{libgcc.a}, the library that comes with GCC, with @option{-msoft-float} in order for this to work. @item -mhard-quad-float @opindex mhard-quad-float Generate output containing quad-word (long double) floating point instructions. @item -msoft-quad-float @opindex msoft-quad-float Generate output containing library calls for quad-word (long double) floating point instructions. The functions called are those specified in the SPARC ABI@. This is the default. As of this writing, there are no sparc implementations that have hardware support for the quad-word floating point instructions. They all invoke a trap handler for one of these instructions, and then the trap handler emulates the effect of the instruction. Because of the trap handler overhead, this is much slower than calling the ABI library routines. Thus the @option{-msoft-quad-float} option is the default. @item -mno-flat @itemx -mflat @opindex mno-flat @opindex mflat With @option{-mflat}, the compiler does not generate save/restore instructions and will use a ``flat'' or single register window calling convention. This model uses %i7 as the frame pointer and is compatible with the normal register window model. Code from either may be intermixed. The local registers and the input registers (0--5) are still treated as ``call saved'' registers and will be saved on the stack as necessary. With @option{-mno-flat} (the default), the compiler emits save/restore instructions (except for leaf functions) and is the normal mode of operation. @item -mno-unaligned-doubles @itemx -munaligned-doubles @opindex mno-unaligned-doubles @opindex munaligned-doubles Assume that doubles have 8 byte alignment. This is the default. With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte alignment only if they are contained in another type, or if they have an absolute address. Otherwise, it assumes they have 4 byte alignment. Specifying this option avoids some rare compatibility problems with code generated by other compilers. It is not the default because it results in a performance loss, especially for floating point code. @item -mno-faster-structs @itemx -mfaster-structs @opindex mno-faster-structs @opindex mfaster-structs With @option{-mfaster-structs}, the compiler assumes that structures should have 8 byte alignment. This enables the use of pairs of @code{ldd} and @code{std} instructions for copies in structure assignment, in place of twice as many @code{ld} and @code{st} pairs. However, the use of this changed alignment directly violates the Sparc ABI@. Thus, it's intended only for use on targets where the developer acknowledges that their resulting code will not be directly in line with the rules of the ABI@. @item -mv8 @itemx -msparclite @opindex mv8 @opindex msparclite These two options select variations on the SPARC architecture. By default (unless specifically configured for the Fujitsu SPARClite), GCC generates code for the v7 variant of the SPARC architecture. @option{-mv8} will give you SPARC v8 code. The only difference from v7 code is that the compiler emits the integer multiply and integer divide instructions which exist in SPARC v8 but not in SPARC v7. @option{-msparclite} will give you SPARClite code. This adds the integer multiply, integer divide step and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC v7. These options are deprecated and will be deleted in a future GCC release. They have been replaced with @option{-mcpu=xxx}. @item -mcypress @itemx -msupersparc @opindex mcypress @opindex msupersparc These two options select the processor for which the code is optimized. With @option{-mcypress} (the default), the compiler optimizes code for the Cypress CY7C602 chip, as used in the SparcStation/SparcServer 3xx series. This is also appropriate for the older SparcStation 1, 2, IPX etc. With @option{-msupersparc} the compiler optimizes code for the SuperSparc cpu, as used in the SparcStation 10, 1000 and 2000 series. This flag also enables use of the full SPARC v8 instruction set. These options are deprecated and will be deleted in a future GCC release. They have been replaced with @option{-mcpu=xxx}. @item -mcpu=@var{cpu_type} @opindex mcpu Set the instruction set, register set, and instruction scheduling parameters for machine type @var{cpu_type}. Supported values for @var{cpu_type} are @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite}, @samp{hypersparc}, @samp{sparclite86x}, @samp{f930}, @samp{f934}, @samp{sparclet}, @samp{tsc701}, @samp{v9}, and @samp{ultrasparc}. Default instruction scheduling parameters are used for values that select an architecture and not an implementation. These are @samp{v7}, @samp{v8}, @samp{sparclite}, @samp{sparclet}, @samp{v9}. Here is a list of each supported architecture and their supported implementations. @smallexample v7: cypress v8: supersparc, hypersparc sparclite: f930, f934, sparclite86x sparclet: tsc701 v9: ultrasparc @end smallexample @item -mtune=@var{cpu_type} @opindex mtune Set the instruction scheduling parameters for machine type @var{cpu_type}, but do not set the instruction set or register set that the option @option{-mcpu=@var{cpu_type}} would. The same values for @option{-mcpu=@var{cpu_type}} can be used for @option{-mtune=@var{cpu_type}}, but the only useful values are those that select a particular cpu implementation. Those are @samp{cypress}, @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934}, @samp{sparclite86x}, @samp{tsc701}, and @samp{ultrasparc}. @end table These @samp{-m} switches are supported in addition to the above on the SPARCLET processor. @table @gcctabopt @item -mlittle-endian @opindex mlittle-endian Generate code for a processor running in little-endian mode. @item -mlive-g0 @opindex mlive-g0 Treat register @code{%g0} as a normal register. GCC will continue to clobber it as necessary but will not assume it always reads as 0. @item -mbroken-saverestore @opindex mbroken-saverestore Generate code that does not use non-trivial forms of the @code{save} and @code{restore} instructions. Early versions of the SPARCLET processor do not correctly handle @code{save} and @code{restore} instructions used with arguments. They correctly handle them used without arguments. A @code{save} instruction used without arguments increments the current window pointer but does not allocate a new stack frame. It is assumed that the window overflow trap handler will properly handle this case as will interrupt handlers. @end table These @samp{-m} switches are supported in addition to the above on SPARC V9 processors in 64-bit environments. @table @gcctabopt @item -mlittle-endian @opindex mlittle-endian Generate code for a processor running in little-endian mode. @item -m32 @itemx -m64 @opindex m32 @opindex m64 Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets int, long and pointer to 32 bits. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits. @item -mcmodel=medlow @opindex mcmodel=medlow Generate code for the Medium/Low code model: the program must be linked in the low 32 bits of the address space. Pointers are 64 bits. Programs can be statically or dynamically linked. @item -mcmodel=medmid @opindex mcmodel=medmid Generate code for the Medium/Middle code model: the program must be linked in the low 44 bits of the address space, the text segment must be less than 2G bytes, and data segment must be within 2G of the text segment. Pointers are 64 bits. @item -mcmodel=medany @opindex mcmodel=medany Generate code for the Medium/Anywhere code model: the program may be linked anywhere in the address space, the text segment must be less than 2G bytes, and data segment must be within 2G of the text segment. Pointers are 64 bits. @item -mcmodel=embmedany @opindex mcmodel=embmedany Generate code for the Medium/Anywhere code model for embedded systems: assume a 32-bit text and a 32-bit data segment, both starting anywhere (determined at link time). Register %g4 points to the base of the data segment. Pointers are still 64 bits. Programs are statically linked, PIC is not supported. @item -mstack-bias @itemx -mno-stack-bias @opindex mstack-bias @opindex mno-stack-bias With @option{-mstack-bias}, GCC assumes that the stack pointer, and frame pointer if present, are offset by @minus{}2047 which must be added back when making stack frame references. Otherwise, assume no such offset is present. @end table @node Convex Options @subsection Convex Options @cindex Convex options These @samp{-m} options are defined for Convex: @table @gcctabopt @item -mc1 @opindex mc1 Generate output for C1. The code will run on any Convex machine. The preprocessor symbol @code{__convex__c1__} is defined. @item -mc2 @opindex mc2 Generate output for C2. Uses instructions not available on C1. Scheduling and other optimizations are chosen for max performance on C2. The preprocessor symbol @code{__convex_c2__} is defined. @item -mc32 @opindex mc32 Generate output for C32xx. Uses instructions not available on C1. Scheduling and other optimizations are chosen for max performance on C32. The preprocessor symbol @code{__convex_c32__} is defined. @item -mc34 @opindex mc34 Generate output for C34xx. Uses instructions not available on C1. Scheduling and other optimizations are chosen for max performance on C34. The preprocessor symbol @code{__convex_c34__} is defined. @item -mc38 @opindex mc38 Generate output for C38xx. Uses instructions not available on C1. Scheduling and other optimizations are chosen for max performance on C38. The preprocessor symbol @code{__convex_c38__} is defined. @item -margcount @opindex margcount Generate code which puts an argument count in the word preceding each argument list. This is compatible with regular CC, and a few programs may need the argument count word. GDB and other source-level debuggers do not need it; this info is in the symbol table. @item -mnoargcount @opindex mnoargcount Omit the argument count word. This is the default. @item -mvolatile-cache @opindex mvolatile-cache Allow volatile references to be cached. This is the default. @item -mvolatile-nocache @opindex mvolatile-nocache Volatile references bypass the data cache, going all the way to memory. This is only needed for multi-processor code that does not use standard synchronization instructions. Making non-volatile references to volatile locations will not necessarily work. @item -mlong32 @opindex mlong32 Type long is 32 bits, the same as type int. This is the default. @item -mlong64 @opindex mlong64 Type long is 64 bits, the same as type long long. This option is useless, because no library support exists for it. @end table @node AMD29K Options @subsection AMD29K Options @cindex AMD29K options These @samp{-m} options are defined for the AMD Am29000: @table @gcctabopt @item -mdw @opindex mdw @cindex DW bit (29k) Generate code that assumes the @code{DW} bit is set, i.e., that byte and halfword operations are directly supported by the hardware. This is the default. @item -mndw @opindex mndw Generate code that assumes the @code{DW} bit is not set. @item -mbw @opindex mbw @cindex byte writes (29k) Generate code that assumes the system supports byte and halfword write operations. This is the default. @item -mnbw @opindex mnbw Generate code that assumes the systems does not support byte and halfword write operations. @option{-mnbw} implies @option{-mndw}. @item -msmall @opindex msmall @cindex memory model (29k) Use a small memory model that assumes that all function addresses are either within a single 256 KB segment or at an absolute address of less than 256k. This allows the @code{call} instruction to be used instead of a @code{const}, @code{consth}, @code{calli} sequence. @item -mnormal @opindex mnormal Use the normal memory model: Generate @code{call} instructions only when calling functions in the same file and @code{calli} instructions otherwise. This works if each file occupies less than 256 KB but allows the entire executable to be larger than 256 KB@. This is the default. @item -mlarge @opindex mlarge Always use @code{calli} instructions. Specify this option if you expect a single file to compile into more than 256 KB of code. @item -m29050 @opindex m29050 @cindex processor selection (29k) Generate code for the Am29050. @item -m29000 @opindex m29000 Generate code for the Am29000. This is the default. @item -mkernel-registers @opindex mkernel-registers @cindex kernel and user registers (29k) Generate references to registers @code{gr64-gr95} instead of to registers @code{gr96-gr127}. This option can be used when compiling kernel code that wants a set of global registers disjoint from that used by user-mode code. Note that when this option is used, register names in @samp{-f} flags must use the normal, user-mode, names. @item -muser-registers @opindex muser-registers Use the normal set of global registers, @code{gr96-gr127}. This is the default. @item -mstack-check @itemx -mno-stack-check @opindex mstack-check @opindex mno-stack-check @cindex stack checks (29k) Insert (or do not insert) a call to @code{__msp_check} after each stack adjustment. This is often used for kernel code. @item -mstorem-bug @itemx -mno-storem-bug @opindex mstorem-bug @opindex mno-storem-bug @cindex storem bug (29k) @option{-mstorem-bug} handles 29k processors which cannot handle the separation of a mtsrim insn and a storem instruction (most 29000 chips to date, but not the 29050). @item -mno-reuse-arg-regs @itemx -mreuse-arg-regs @opindex mno-reuse-arg-regs @opindex mreuse-arg-regs @option{-mno-reuse-arg-regs} tells the compiler to only use incoming argument registers for copying out arguments. This helps detect calling a function with fewer arguments than it was declared with. @item -mno-impure-text @itemx -mimpure-text @opindex mno-impure-text @opindex mimpure-text @option{-mimpure-text}, used in addition to @option{-shared}, tells the compiler to not pass @option{-assert pure-text} to the linker when linking a shared object. @item -msoft-float @opindex msoft-float Generate output containing library calls for floating point. @strong{Warning:} the requisite libraries are not part of GCC@. Normally the facilities of the machine's usual C compiler are used, but this can't be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. @item -mno-multm @opindex mno-multm Do not generate multm or multmu instructions. This is useful for some embedded systems which do not have trap handlers for these instructions. @end table @node ARM Options @subsection ARM Options @cindex ARM options These @samp{-m} options are defined for Advanced RISC Machines (ARM) architectures: @table @gcctabopt @item -mapcs-frame @opindex mapcs-frame Generate a stack frame that is compliant with the ARM Procedure Call Standard for all functions, even if this is not strictly necessary for correct execution of the code. Specifying @option{-fomit-frame-pointer} with this option will cause the stack frames not to be generated for leaf functions. The default is @option{-mno-apcs-frame}. @item -mapcs @opindex mapcs This is a synonym for @option{-mapcs-frame}. @item -mapcs-26 @opindex mapcs-26 Generate code for a processor running with a 26-bit program counter, and conforming to the function calling standards for the APCS 26-bit option. This option replaces the @option{-m2} and @option{-m3} options of previous releases of the compiler. @item -mapcs-32 @opindex mapcs-32 Generate code for a processor running with a 32-bit program counter, and conforming to the function calling standards for the APCS 32-bit option. This option replaces the @option{-m6} option of previous releases of the compiler. @c APPLE LOCAL prune man page @c @ignore @c not currently implemented @item -mapcs-stack-check @opindex mapcs-stack-check Generate code to check the amount of stack space available upon entry to every function (that actually uses some stack space). If there is insufficient space available then either the function @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be called, depending upon the amount of stack space required. The run time system is required to provide these functions. The default is @option{-mno-apcs-stack-check}, since this produces smaller code. @c not currently implemented @item -mapcs-float @opindex mapcs-float Pass floating point arguments using the float point registers. This is one of the variants of the APCS@. This option is recommended if the target hardware has a floating point unit or if a lot of floating point arithmetic is going to be performed by the code. The default is @option{-mno-apcs-float}, since integer only code is slightly increased in size if @option{-mapcs-float} is used. @c not currently implemented @item -mapcs-reentrant @opindex mapcs-reentrant Generate reentrant, position independent code. The default is @option{-mno-apcs-reentrant}. @c APPLE LOCAL prune man page @c @end ignore @item -mthumb-interwork @opindex mthumb-interwork Generate code which supports calling between the ARM and Thumb instruction sets. Without this option the two instruction sets cannot be reliably used inside one program. The default is @option{-mno-thumb-interwork}, since slightly larger code is generated when @option{-mthumb-interwork} is specified. @item -mno-sched-prolog @opindex mno-sched-prolog Prevent the reordering of instructions in the function prolog, or the merging of those instruction with the instructions in the function's body. This means that all functions will start with a recognizable set of instructions (or in fact one of a choice from a small set of different function prologues), and this information can be used to locate the start if functions inside an executable piece of code. The default is @option{-msched-prolog}. @item -mhard-float @opindex mhard-float Generate output containing floating point instructions. This is the default. @item -msoft-float @opindex msoft-float Generate output containing library calls for floating point. @strong{Warning:} the requisite libraries are not available for all ARM targets. Normally the facilities of the machine's usual C compiler are used, but this cannot be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. @option{-msoft-float} changes the calling convention in the output file; therefore, it is only useful if you compile @emph{all} of a program with this option. In particular, you need to compile @file{libgcc.a}, the library that comes with GCC, with @option{-msoft-float} in order for this to work. @item -mlittle-endian @opindex mlittle-endian Generate code for a processor running in little-endian mode. This is the default for all standard configurations. @item -mbig-endian @opindex mbig-endian Generate code for a processor running in big-endian mode; the default is to compile code for a little-endian processor. @item -mwords-little-endian @opindex mwords-little-endian This option only applies when generating code for big-endian processors. Generate code for a little-endian word order but a big-endian byte order. That is, a byte order of the form @samp{32107654}. Note: this option should only be used if you require compatibility with code for big-endian ARM processors generated by versions of the compiler prior to 2.8. @item -malignment-traps @opindex malignment-traps Generate code that will not trap if the MMU has alignment traps enabled. On ARM architectures prior to ARMv4, there were no instructions to access half-word objects stored in memory. However, when reading from memory a feature of the ARM architecture allows a word load to be used, even if the address is unaligned, and the processor core will rotate the data as it is being loaded. This option tells the compiler that such misaligned accesses will cause a MMU trap and that it should instead synthesise the access as a series of byte accesses. The compiler can still use word accesses to load half-word data if it knows that the address is aligned to a word boundary. This option is ignored when compiling for ARM architecture 4 or later, since these processors have instructions to directly access half-word objects in memory. @item -mno-alignment-traps @opindex mno-alignment-traps Generate code that assumes that the MMU will not trap unaligned accesses. This produces better code when the target instruction set does not have half-word memory operations (i.e.@: implementations prior to ARMv4). Note that you cannot use this option to access unaligned word objects, since the processor will only fetch one 32-bit aligned object from memory. The default setting for most targets is @option{-mno-alignment-traps}, since this produces better code when there are no half-word memory instructions available. @item -mshort-load-bytes @itemx -mno-short-load-words @opindex mshort-load-bytes @opindex mno-short-load-words These are deprecated aliases for @option{-malignment-traps}. @item -mno-short-load-bytes @itemx -mshort-load-words @opindex mno-short-load-bytes @opindex mshort-load-words This are deprecated aliases for @option{-mno-alignment-traps}. @item -mbsd @opindex mbsd This option only applies to RISC iX@. Emulate the native BSD-mode compiler. This is the default if @option{-ansi} is not specified. @item -mxopen @opindex mxopen This option only applies to RISC iX@. Emulate the native X/Open-mode compiler. @item -mno-symrename @opindex mno-symrename This option only applies to RISC iX@. Do not run the assembler post-processor, @samp{symrename}, after code has been assembled. Normally it is necessary to modify some of the standard symbols in preparation for linking with the RISC iX C library; this option suppresses this pass. The post-processor is never run when the compiler is built for cross-compilation. @item -mcpu=@var{name} @opindex mcpu This specifies the name of the target ARM processor. GCC uses this name to determine what kind of instructions it can emit when generating assembly code. Permissible names are: @samp{arm2}, @samp{arm250}, @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610}, @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm}, @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700}, @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100}, @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm8}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100}, @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920}, @samp{arm920t}, @samp{arm940t}, @samp{arm9tdmi}, @samp{arm10tdmi}, @samp{arm1020t}, @samp{xscale}. @itemx -mtune=@var{name} @opindex mtune This option is very similar to the @option{-mcpu=} option, except that instead of specifying the actual target processor type, and hence restricting which instructions can be used, it specifies that GCC should tune the performance of the code as if the target were of the type specified in this option, but still choosing the instructions that it will generate based on the cpu specified by a @option{-mcpu=} option. For some ARM implementations better performance can be obtained by using this option. @item -march=@var{name} @opindex march This specifies the name of the target ARM architecture. GCC uses this name to determine what kind of instructions it can emit when generating assembly code. This option can be used in conjunction with or instead of the @option{-mcpu=} option. Permissible names are: @samp{armv2}, @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t}, @samp{armv5}, @samp{armv5t}, @samp{armv5te}. @item -mfpe=@var{number} @itemx -mfp=@var{number} @opindex mfpe @opindex mfp This specifies the version of the floating point emulation available on the target. Permissible values are 2 and 3. @option{-mfp=} is a synonym for @option{-mfpe=}, for compatibility with older versions of GCC@. @item -mstructure-size-boundary=@var{n} @opindex mstructure-size-boundary The size of all structures and unions will be rounded up to a multiple of the number of bits set by this option. Permissible values are 8 and 32. The default value varies for different toolchains. For the COFF targeted toolchain the default value is 8. Specifying the larger number can produce faster, more efficient code, but can also increase the size of the program. The two values are potentially incompatible. Code compiled with one value cannot necessarily expect to work with code or libraries compiled with the other value, if they exchange information using structures or unions. @item -mabort-on-noreturn @opindex mabort-on-noreturn Generate a call to the function @code{abort} at the end of a @code{noreturn} function. It will be executed if the function tries to return. @item -mlong-calls @itemx -mno-long-calls @opindex mlong-calls @opindex mno-long-calls Tells the compiler to perform function calls by first loading the address of the function into a register and then performing a subroutine call on this register. This switch is needed if the target function will lie outside of the 64 megabyte addressing range of the offset based version of subroutine call instruction. Even if this switch is enabled, not all function calls will be turned into long calls. The heuristic is that static functions, functions which have the @samp{short-call} attribute, functions that are inside the scope of a @samp{#pragma no_long_calls} directive and functions whose definitions have already been compiled within the current compilation unit, will not be turned into long calls. The exception to this rule is that weak function definitions, functions with the @samp{long-call} attribute or the @samp{section} attribute, and functions that are within the scope of a @samp{#pragma long_calls} directive, will always be turned into long calls. This feature is not enabled by default. Specifying @option{-mno-long-calls} will restore the default behavior, as will placing the function calls within the scope of a @samp{#pragma long_calls_off} directive. Note these switches have no effect on how the compiler generates code to handle function calls via function pointers. @item -mnop-fun-dllimport @opindex mnop-fun-dllimport Disable support for the @code{dllimport} attribute. @item -msingle-pic-base @opindex msingle-pic-base Treat the register used for PIC addressing as read-only, rather than loading it in the prologue for each function. The run-time system is responsible for initializing this register with an appropriate value before execution begins. @item -mpic-register=@var{reg} @opindex mpic-register Specify the register to be used for PIC addressing. The default is R10 unless stack-checking is enabled, when R9 is used. @item -mpoke-function-name @opindex mpoke-function-name Write the name of each function into the text section, directly preceding the function prologue. The generated code is similar to this: @smallexample t0 .ascii "arm_poke_function_name", 0 .align t1 .word 0xff000000 + (t1 - t0) arm_poke_function_name mov ip, sp stmfd sp!, @{fp, ip, lr, pc@} sub fp, ip, #4 @end smallexample When performing a stack backtrace, code can inspect the value of @code{pc} stored at @code{fp + 0}. If the trace function then looks at location @code{pc - 12} and the top 8 bits are set, then we know that there is a function name embedded immediately preceding this location and has length @code{((pc[-3]) & 0xff000000)}. @item -mthumb @opindex mthumb Generate code for the 16-bit Thumb instruction set. The default is to use the 32-bit ARM instruction set. @item -mtpcs-frame @opindex mtpcs-frame Generate a stack frame that is compliant with the Thumb Procedure Call Standard for all non-leaf functions. (A leaf function is one that does not call any other functions.) The default is @option{-mno-tpcs-frame}. @item -mtpcs-leaf-frame @opindex mtpcs-leaf-frame Generate a stack frame that is compliant with the Thumb Procedure Call Standard for all leaf functions. (A leaf function is one that does not call any other functions.) The default is @option{-mno-apcs-leaf-frame}. @item -mcallee-super-interworking @opindex mcallee-super-interworking Gives all externally visible functions in the file being compiled an ARM instruction set header which switches to Thumb mode before executing the rest of the function. This allows these functions to be called from non-interworking code. @item -mcaller-super-interworking @opindex mcaller-super-interworking Allows calls via function pointers (including virtual functions) to execute correctly regardless of whether the target code has been compiled for interworking or not. There is a small overhead in the cost of executing a function pointer if this option is enabled. @end table @node MN10200 Options @subsection MN10200 Options @cindex MN10200 options These @option{-m} options are defined for Matsushita MN10200 architectures: @table @gcctabopt @item -mrelax @opindex mrelax Indicate to the linker that it should perform a relaxation optimization pass to shorten branches, calls and absolute memory addresses. This option only has an effect when used on the command line for the final link step. This option makes symbolic debugging impossible. @end table @node MN10300 Options @subsection MN10300 Options @cindex MN10300 options These @option{-m} options are defined for Matsushita MN10300 architectures: @table @gcctabopt @item -mmult-bug @opindex mmult-bug Generate code to avoid bugs in the multiply instructions for the MN10300 processors. This is the default. @item -mno-mult-bug @opindex mno-mult-bug Do not generate code to avoid bugs in the multiply instructions for the MN10300 processors. @item -mam33 @opindex mam33 Generate code which uses features specific to the AM33 processor. @item -mno-am33 @opindex mno-am33 Do not generate code which uses features specific to the AM33 processor. This is the default. @item -mno-crt0 @opindex mno-crt0 Do not link in the C run-time initialization object file. @item -mrelax @opindex mrelax Indicate to the linker that it should perform a relaxation optimization pass to shorten branches, calls and absolute memory addresses. This option only has an effect when used on the command line for the final link step. This option makes symbolic debugging impossible. @end table @node M32R/D Options @subsection M32R/D Options @cindex M32R/D options These @option{-m} options are defined for Mitsubishi M32R/D architectures: @table @gcctabopt @item -m32rx @opindex m32rx Generate code for the M32R/X@. @item -m32r @opindex m32r Generate code for the M32R@. This is the default. @item -mcode-model=small @opindex mcode-model=small Assume all objects live in the lower 16MB of memory (so that their addresses can be loaded with the @code{ld24} instruction), and assume all subroutines are reachable with the @code{bl} instruction. This is the default. The addressability of a particular object can be set with the @code{model} attribute. @item -mcode-model=medium @opindex mcode-model=medium Assume objects may be anywhere in the 32-bit address space (the compiler will generate @code{seth/add3} instructions to load their addresses), and assume all subroutines are reachable with the @code{bl} instruction. @item -mcode-model=large @opindex mcode-model=large Assume objects may be anywhere in the 32-bit address space (the compiler will generate @code{seth/add3} instructions to load their addresses), and assume subroutines may not be reachable with the @code{bl} instruction (the compiler will generate the much slower @code{seth/add3/jl} instruction sequence). @item -msdata=none @opindex msdata=none Disable use of the small data area. Variables will be put into one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the @code{section} attribute has been specified). This is the default. The small data area consists of sections @samp{.sdata} and @samp{.sbss}. Objects may be explicitly put in the small data area with the @code{section} attribute using one of these sections. @item -msdata=sdata @opindex msdata=sdata Put small global and static data in the small data area, but do not generate special code to reference them. @item -msdata=use @opindex msdata=use Put small global and static data in the small data area, and generate special instructions to reference them. @item -G @var{num} @opindex G @cindex smaller data references Put global and static objects less than or equal to @var{num} bytes into the small data or bss sections instead of the normal data or bss sections. The default value of @var{num} is 8. The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use} for this option to have any effect. All modules should be compiled with the same @option{-G @var{num}} value. Compiling with different values of @var{num} may or may not work; if it doesn't the linker will give an error message---incorrect code will not be generated. @end table @node M88K Options @subsection M88K Options @cindex M88k options These @samp{-m} options are defined for Motorola 88k architectures: @table @gcctabopt @item -m88000 @opindex m88000 Generate code that works well on both the m88100 and the m88110. @item -m88100 @opindex m88100 Generate code that works best for the m88100, but that also runs on the m88110. @item -m88110 @opindex m88110 Generate code that works best for the m88110, and may not run on the m88100. @item -mbig-pic @opindex mbig-pic Obsolete option to be removed from the next revision. Use @option{-fPIC}. @item -midentify-revision @opindex midentify-revision @cindex identifying source, compiler (88k) Include an @code{ident} directive in the assembler output recording the source file name, compiler name and version, timestamp, and compilation flags used. @item -mno-underscores @opindex mno-underscores @cindex underscores, avoiding (88k) In assembler output, emit symbol names without adding an underscore character at the beginning of each name. The default is to use an underscore as prefix on each name. @item -mocs-debug-info @itemx -mno-ocs-debug-info @opindex mocs-debug-info @opindex mno-ocs-debug-info @cindex OCS (88k) @cindex debugging, 88k OCS Include (or omit) additional debugging information (about registers used in each stack frame) as specified in the 88open Object Compatibility Standard, ``OCS''@. This extra information allows debugging of code that has had the frame pointer eliminated. The default for DG/UX, SVr4, and Delta 88 SVr3.2 is to include this information; other 88k configurations omit this information by default. @item -mocs-frame-position @opindex mocs-frame-position @cindex register positions in frame (88k) When emitting COFF debugging information for automatic variables and parameters stored on the stack, use the offset from the canonical frame address, which is the stack pointer (register 31) on entry to the function. The DG/UX, SVr4, Delta88 SVr3.2, and BCS configurations use @option{-mocs-frame-position}; other 88k configurations have the default @option{-mno-ocs-frame-position}. @item -mno-ocs-frame-position @opindex mno-ocs-frame-position @cindex register positions in frame (88k) When emitting COFF debugging information for automatic variables and parameters stored on the stack, use the offset from the frame pointer register (register 30). When this option is in effect, the frame pointer is not eliminated when debugging information is selected by the -g switch. @item -moptimize-arg-area @opindex moptimize-arg-area @cindex arguments in frame (88k) Save space by reorganizing the stack frame. This option generates code that does not agree with the 88open specifications, but uses less memory. @itemx -mno-optimize-arg-area @opindex mno-optimize-arg-area Do not reorganize the stack frame to save space. This is the default. The generated conforms to the specification, but uses more memory. @item -mshort-data-@var{num} @opindex mshort-data @cindex smaller data references (88k) @cindex r0-relative references (88k) Generate smaller data references by making them relative to @code{r0}, which allows loading a value using a single instruction (rather than the usual two). You control which data references are affected by specifying @var{num} with this option. For example, if you specify @option{-mshort-data-512}, then the data references affected are those involving displacements of less than 512 bytes. @option{-mshort-data-@var{num}} is not effective for @var{num} greater than 64k. @item -mserialize-volatile @opindex mserialize-volatile @itemx -mno-serialize-volatile @opindex mno-serialize-volatile @cindex sequential consistency on 88k Do, or don't, generate code to guarantee sequential consistency of volatile memory references. By default, consistency is guaranteed. The order of memory references made by the MC88110 processor does not always match the order of the instructions requesting those references. In particular, a load instruction may execute before a preceding store instruction. Such reordering violates sequential consistency of volatile memory references, when there are multiple processors. When consistency must be guaranteed, GCC generates special instructions, as needed, to force execution in the proper order. The MC88100 processor does not reorder memory references and so always provides sequential consistency. However, by default, GCC generates the special instructions to guarantee consistency even when you use @option{-m88100}, so that the code may be run on an MC88110 processor. If you intend to run your code only on the MC88100 processor, you may use @option{-mno-serialize-volatile}. The extra code generated to guarantee consistency may affect the performance of your application. If you know that you can safely forgo this guarantee, you may use @option{-mno-serialize-volatile}. @item -msvr4 @itemx -msvr3 @opindex msvr4 @opindex msvr3 @cindex assembler syntax, 88k @cindex SVr4 Turn on (@option{-msvr4}) or off (@option{-msvr3}) compiler extensions related to System V release 4 (SVr4). This controls the following: @enumerate @item Which variant of the assembler syntax to emit. @item @option{-msvr4} makes the C preprocessor recognize @samp{#pragma weak} that is used on System V release 4. @item @option{-msvr4} makes GCC issue additional declaration directives used in SVr4. @end enumerate @option{-msvr4} is the default for the m88k-motorola-sysv4 and m88k-dg-dgux m88k configurations. @option{-msvr3} is the default for all other m88k configurations. @item -mversion-03.00 @opindex mversion-03.00 This option is obsolete, and is ignored. @c ??? which asm syntax better for GAS? option there too? @item -mno-check-zero-division @itemx -mcheck-zero-division @opindex mno-check-zero-division @opindex mcheck-zero-division @cindex zero division on 88k Do, or don't, generate code to guarantee that integer division by zero will be detected. By default, detection is guaranteed. Some models of the MC88100 processor fail to trap upon integer division by zero under certain conditions. By default, when compiling code that might be run on such a processor, GCC generates code that explicitly checks for zero-valued divisors and traps with exception number 503 when one is detected. Use of @option{-mno-check-zero-division} suppresses such checking for code generated to run on an MC88100 processor. GCC assumes that the MC88110 processor correctly detects all instances of integer division by zero. When @option{-m88110} is specified, no explicit checks for zero-valued divisors are generated, and both @option{-mcheck-zero-division} and @option{-mno-check-zero-division} are ignored. @item -muse-div-instruction @opindex muse-div-instruction @cindex divide instruction, 88k Use the div instruction for signed integer division on the MC88100 processor. By default, the div instruction is not used. On the MC88100 processor the signed integer division instruction div) traps to the operating system on a negative operand. The operating system transparently completes the operation, but at a large cost in execution time. By default, when compiling code that might be run on an MC88100 processor, GCC emulates signed integer division using the unsigned integer division instruction divu), thereby avoiding the large penalty of a trap to the operating system. Such emulation has its own, smaller, execution cost in both time and space. To the extent that your code's important signed integer division operations are performed on two nonnegative operands, it may be desirable to use the div instruction directly. On the MC88110 processor the div instruction (also known as the divs instruction) processes negative operands without trapping to the operating system. When @option{-m88110} is specified, @option{-muse-div-instruction} is ignored, and the div instruction is used for signed integer division. Note that the result of dividing @code{INT_MIN} by @minus{}1 is undefined. In particular, the behavior of such a division with and without @option{-muse-div-instruction} may differ. @item -mtrap-large-shift @itemx -mhandle-large-shift @opindex mtrap-large-shift @opindex mhandle-large-shift @cindex bit shift overflow (88k) @cindex large bit shifts (88k) Include code to detect bit-shifts of more than 31 bits; respectively, trap such shifts or emit code to handle them properly. By default GCC makes no special provision for large bit shifts. @item -mwarn-passed-structs @opindex mwarn-passed-structs @cindex structure passing (88k) Warn when a function passes a struct as an argument or result. Structure-passing conventions have changed during the evolution of the C language, and are often the source of portability problems. By default, GCC issues no such warning. @end table @c break page here to avoid unsightly interparagraph stretch. @c -zw, 2001-8-17 @page @c APPLE LOCAL prune man page @end ignore @node RS/6000 and PowerPC Options @subsection IBM RS/6000 and PowerPC Options @cindex RS/6000 and PowerPC Options @cindex IBM RS/6000 and PowerPC Options These @samp{-m} options are defined for the IBM RS/6000 and PowerPC: @table @gcctabopt @item -mpower @itemx -mno-power @itemx -mpower2 @itemx -mno-power2 @itemx -mpowerpc @itemx -mno-powerpc @itemx -mpowerpc-gpopt @itemx -mno-powerpc-gpopt @itemx -mpowerpc-gfxopt @itemx -mno-powerpc-gfxopt @itemx -mpowerpc64 @itemx -mno-powerpc64 @opindex mpower @opindex mno-power @opindex mpower2 @opindex mno-power2 @opindex mpowerpc @opindex mno-powerpc @opindex mpowerpc-gpopt @opindex mno-powerpc-gpopt @opindex mpowerpc-gfxopt @opindex mno-powerpc-gfxopt @opindex mpowerpc64 @opindex mno-powerpc64 GCC supports two related instruction set architectures for the RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those instructions supported by the @samp{rios} chip set used in the original RS/6000 systems and the @dfn{PowerPC} instruction set is the architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and the IBM 4xx microprocessors. Neither architecture is a subset of the other. However there is a large common subset of instructions supported by both. An MQ register is included in processors supporting the POWER architecture. You use these options to specify which instructions are available on the processor you are using. The default value of these options is determined when configuring GCC@. Specifying the @option{-mcpu=@var{cpu_type}} overrides the specification of these options. We recommend you use the @option{-mcpu=@var{cpu_type}} option rather than the options listed above. The @option{-mpower} option allows GCC to generate instructions that are found only in the POWER architecture and to use the MQ register. Specifying @option{-mpower2} implies @option{-power} and also allows GCC to generate instructions that are present in the POWER2 architecture but not the original POWER architecture. The @option{-mpowerpc} option allows GCC to generate instructions that are found only in the 32-bit subset of the PowerPC architecture. Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows GCC to use the optional PowerPC architecture instructions in the General Purpose group, including floating-point square root. Specifying @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to use the optional PowerPC architecture instructions in the Graphics group, including floating-point select. The @option{-mpowerpc64} option allows GCC to generate the additional 64-bit instructions that are found in the full PowerPC64 architecture and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to @option{-mno-powerpc64}. If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC will use only the instructions in the common subset of both architectures plus some special AIX common-mode calls, and will not use the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc} permits GCC to use any instruction from either architecture and to allow use of the MQ register; specify this for the Motorola MPC601. @item -mnew-mnemonics @itemx -mold-mnemonics @opindex mnew-mnemonics @opindex mold-mnemonics Select which mnemonics to use in the generated assembler code. With @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for the PowerPC architecture. With @option{-mold-mnemonics} it uses the assembler mnemonics defined for the POWER architecture. Instructions defined in only one architecture have only one mnemonic; GCC uses that mnemonic irrespective of which of these options is specified. GCC defaults to the mnemonics appropriate for the architecture in use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the value of these option. Unless you are building a cross-compiler, you should normally not specify either @option{-mnew-mnemonics} or @option{-mold-mnemonics}, but should instead accept the default. @item -mcpu=@var{cpu_type} @opindex mcpu Set architecture type, register usage, choice of mnemonics, and instruction scheduling parameters for machine type @var{cpu_type}. Supported values for @var{cpu_type} are @samp{rios}, @samp{rios1}, @samp{rsc}, @samp{rios2}, @samp{rs64a}, @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400}, @samp{7450}, @samp{750}, @samp{power}, @samp{power2}, @samp{powerpc}, @samp{403}, @samp{505}, @samp{801}, @samp{821}, @samp{823}, and @samp{860} and @samp{common}. @option{-mcpu=common} selects a completely generic processor. Code generated under this option will run on any POWER or PowerPC processor. GCC will use only the instructions in the common subset of both architectures, and will not use the MQ register. GCC assumes a generic processor model for scheduling purposes. @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine types, with an appropriate, generic processor model assumed for scheduling purposes. The other options specify a specific processor. Code generated under those options will run best on that processor, and may not run at all on others. The @option{-mcpu} options automatically enable or disable other @option{-m} options as follows: @table @samp @item common @option{-mno-power}, @option{-mno-powerc} @item power @itemx power2 @itemx rios1 @itemx rios2 @itemx rsc @option{-mpower}, @option{-mno-powerpc}, @option{-mno-new-mnemonics} @item powerpc @itemx rs64a @itemx 602 @itemx 603 @itemx 603e @itemx 604 @itemx 620 @itemx 630 @itemx 740 @itemx 7400 @itemx 7450 @itemx 750 @itemx 505 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics} @item 601 @option{-mpower}, @option{-mpowerpc}, @option{-mnew-mnemonics} @item 403 @itemx 821 @itemx 860 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}, @option{-msoft-float} @end table @item -mtune=@var{cpu_type} @opindex mtune Set the instruction scheduling parameters for machine type @var{cpu_type}, but do not set the architecture type, register usage, or choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same values for @var{cpu_type} are used for @option{-mtune} as for @option{-mcpu}. If both are specified, the code generated will use the architecture, registers, and mnemonics set by @option{-mcpu}, but the scheduling parameters set by @option{-mtune}. @item -maltivec @itemx -mno-altivec @opindex maltivec @opindex mno-altivec These switches enable or disable the use of built-in functions that allow access to the AltiVec instruction set. You may also need to set @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI enhancements. @c APPLE LOCAL manual This option is not supported on Mac OS X; use @option{-faltivec} instead. @item -mfull-toc @itemx -mno-fp-in-toc @itemx -mno-sum-in-toc @itemx -mminimal-toc @opindex mfull-toc @opindex mno-fp-in-toc @opindex mno-sum-in-toc @opindex mminimal-toc Modify generation of the TOC (Table Of Contents), which is created for every executable file. The @option{-mfull-toc} option is selected by default. In that case, GCC will allocate at least one TOC entry for each unique non-automatic variable reference in your program. GCC will also place floating-point constants in the TOC@. However, only 16,384 entries are available in the TOC@. If you receive a linker error message that saying you have overflowed the available TOC space, you can reduce the amount of TOC space used with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options. @option{-mno-fp-in-toc} prevents GCC from putting floating-point constants in the TOC and @option{-mno-sum-in-toc} forces GCC to generate code to calculate the sum of an address and a constant at run-time instead of putting that sum into the TOC@. You may specify one or both of these options. Each causes GCC to produce very slightly slower and larger code at the expense of conserving TOC space. If you still run out of space in the TOC even when you specify both of these options, specify @option{-mminimal-toc} instead. This option causes GCC to make only one TOC entry for every file. When you specify this option, GCC will produce code that is slower and larger but which uses extremely little TOC space. You may wish to use this option only on files that contain less frequently executed code. @item -maix64 @itemx -maix32 @opindex maix64 @opindex maix32 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit @code{long} type, and the infrastructure needed to support them. Specifying @option{-maix64} implies @option{-mpowerpc64} and @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}. @item -mxl-call @itemx -mno-xl-call @opindex mxl-call @opindex mno-xl-call On AIX, pass floating-point arguments to prototyped functions beyond the register save area (RSA) on the stack in addition to argument FPRs. The AIX calling convention was extended but not initially documented to handle an obscure K&R C case of calling a function that takes the address of its arguments with fewer arguments than declared. AIX XL compilers access floating point arguments which do not fit in the RSA from the stack when a subroutine is compiled without optimization. Because always storing floating-point arguments on the stack is inefficient and rarely needed, this option is not enabled by default and only is necessary when calling subroutines compiled by AIX XL compilers without optimization. @item -mpe @opindex mpe Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an application written to use message passing with special startup code to enable the application to run. The system must have PE installed in the standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file must be overridden with the @option{-specs=} option to specify the appropriate directory location. The Parallel Environment does not support threads, so the @option{-mpe} option and the @option{-pthread} option are incompatible. @c APPLE LOCAL begin -malign-mac68k 2002-2-19 ff @item -malign-mac68k @itemx -malign-power @itemx -malign-natural The option @option{-malign-mac68k} causes structure fields to be aligned on 2-byte boundaries, in order to be compatible with m68k compiler output. The option @option{-malign-power} is the standard alignment mode for the PowerPC. The option @option{-malign-natural} is an extension of PowerPC alignment that aligns larger data types such as doubles on their natural boundaries. (APPLE ONLY) @c APPLE LOCAL end -malign-mac68k 2002-2-19 ff @item -msoft-float @itemx -mhard-float @opindex msoft-float @opindex mhard-float Generate code that does not use (uses) the floating-point register set. Software floating point emulation is provided if you use the @option{-msoft-float} option, and pass the option to GCC when linking. @item -mmultiple @itemx -mno-multiple @opindex mmultiple @opindex mno-multiple Generate code that uses (does not use) the load multiple word instructions and the store multiple word instructions. These instructions are generated by default on POWER systems, and not generated on PowerPC systems. Do not use @option{-mmultiple} on little endian PowerPC systems, since those instructions do not work when the processor is in little endian mode. The exceptions are PPC740 and PPC750 which permit the instructions usage in little endian mode. @item -mstring @itemx -mno-string @opindex mstring @opindex mno-string Generate code that uses (does not use) the load string instructions and the store string word instructions to save multiple registers and do small block moves. These instructions are generated by default on POWER systems, and not generated on PowerPC systems. Do not use @option{-mstring} on little endian PowerPC systems, since those instructions do not work when the processor is in little endian mode. The exceptions are PPC740 and PPC750 which permit the instructions usage in little endian mode. @item -mupdate @itemx -mno-update @opindex mupdate @opindex mno-update Generate code that uses (does not use) the load or store instructions that update the base register to the address of the calculated memory location. These instructions are generated by default. If you use @option{-mno-update}, there is a small window between the time that the stack pointer is updated and the address of the previous frame is stored, which means code that walks the stack frame across interrupts or signals may get corrupted data. @item -mfused-madd @itemx -mno-fused-madd @opindex mfused-madd @opindex mno-fused-madd Generate code that uses (does not use) the floating point multiply and accumulate instructions. These instructions are generated by default if hardware floating is used. @item -mno-bit-align @itemx -mbit-align @opindex mno-bit-align @opindex mbit-align On System V.4 and embedded PowerPC systems do not (do) force structures and unions that contain bit-fields to be aligned to the base type of the bit-field. For example, by default a structure containing nothing but 8 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte boundary and have a size of 4 bytes. By using @option{-mno-bit-align}, the structure would be aligned to a 1 byte boundary and be one byte in size. @item -mno-strict-align @itemx -mstrict-align @opindex mno-strict-align @opindex mstrict-align On System V.4 and embedded PowerPC systems do not (do) assume that unaligned memory references will be handled by the system. @item -mrelocatable @itemx -mno-relocatable @opindex mrelocatable @opindex mno-relocatable On embedded PowerPC systems generate code that allows (does not allow) the program to be relocated to a different address at runtime. If you use @option{-mrelocatable} on any module, all objects linked together must be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}. @item -mrelocatable-lib @itemx -mno-relocatable-lib @opindex mrelocatable-lib @opindex mno-relocatable-lib On embedded PowerPC systems generate code that allows (does not allow) the program to be relocated to a different address at runtime. Modules compiled with @option{-mrelocatable-lib} can be linked with either modules compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or with modules compiled with the @option{-mrelocatable} options. @item -mno-toc @itemx -mtoc @opindex mno-toc @opindex mtoc On System V.4 and embedded PowerPC systems do not (do) assume that register 2 contains a pointer to a global area pointing to the addresses used in the program. @item -mlittle @itemx -mlittle-endian @opindex mlittle @opindex mlittle-endian On System V.4 and embedded PowerPC systems compile code for the processor in little endian mode. The @option{-mlittle-endian} option is the same as @option{-mlittle}. @item -mbig @itemx -mbig-endian @opindex mbig @opindex mbig-endian On System V.4 and embedded PowerPC systems compile code for the processor in big endian mode. The @option{-mbig-endian} option is the same as @option{-mbig}. @c APPLE LOCAL begin dynamic-no-pic @item -mdynamic-no-pic @opindex mdynamic-no-pic On Darwin and Mac OS 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. (APPLE ONLY) @c APPLE LOCAL end dynamic-no-pic @c APPLE LOCAL begin long-branch @item -mlong-branch @opindex mlong-branch On Darwin and Mac OS 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. (APPLE ONLY) @c APPLE LOCAL end long-branch @item -mcall-sysv @opindex mcall-sysv On System V.4 and embedded PowerPC systems compile code using calling conventions that adheres to the March 1995 draft of the System V Application Binary Interface, PowerPC processor supplement. This is the default unless you configured GCC using @samp{powerpc-*-eabiaix}. @item -mcall-sysv-eabi @opindex mcall-sysv-eabi Specify both @option{-mcall-sysv} and @option{-meabi} options. @item -mcall-sysv-noeabi @opindex mcall-sysv-noeabi Specify both @option{-mcall-sysv} and @option{-mno-eabi} options. @item -mcall-aix @opindex mcall-aix On System V.4 and embedded PowerPC systems compile code using calling conventions that are similar to those used on AIX@. This is the default if you configured GCC using @samp{powerpc-*-eabiaix}. @item -mcall-solaris @opindex mcall-solaris On System V.4 and embedded PowerPC systems compile code for the Solaris operating system. @item -mcall-linux @opindex mcall-linux On System V.4 and embedded PowerPC systems compile code for the Linux-based GNU system. @item -mcall-gnu @opindex mcall-gnu On System V.4 and embedded PowerPC systems compile code for the Hurd-based GNU system. @item -mcall-netbsd @opindex mcall-netbsd On System V.4 and embedded PowerPC systems compile code for the NetBSD operating system. @item -maix-struct-return @opindex maix-struct-return Return all structures in memory (as specified by the AIX ABI)@. @item -msvr4-struct-return @opindex msvr4-struct-return Return structures smaller than 8 bytes in registers (as specified by the SVR4 ABI)@. @item -mabi=altivec @opindex mabi=altivec Extend the current ABI with AltiVec ABI extensions. This does not change the default ABI, instead it adds the AltiVec ABI extensions to the current ABI@. @c APPLE LOCAL manual This option is effectively permanently enabled on Mac OS X. @item -mabi=no-altivec @opindex mabi=no-altivec Disable AltiVec ABI extensions for the current ABI. @c APPLE LOCAL manual This option will not work on Mac OS X. @item -mprototype @itemx -mno-prototype @opindex mprototype @opindex mno-prototype On System V.4 and embedded PowerPC systems assume that all calls to variable argument functions are properly prototyped. Otherwise, the compiler must insert an instruction before every non prototyped call to set or clear bit 6 of the condition code register (@var{CR}) to indicate whether floating point values were passed in the floating point registers in case the function takes a variable arguments. With @option{-mprototype}, only calls to prototyped variable argument functions will set or clear the bit. @item -msim @opindex msim On embedded PowerPC systems, assume that the startup module is called @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}. configurations. @item -mmvme @opindex mmvme On embedded PowerPC systems, assume that the startup module is called @file{crt0.o} and the standard C libraries are @file{libmvme.a} and @file{libc.a}. @item -mads @opindex mads On embedded PowerPC systems, assume that the startup module is called @file{crt0.o} and the standard C libraries are @file{libads.a} and @file{libc.a}. @item -myellowknife @opindex myellowknife On embedded PowerPC systems, assume that the startup module is called @file{crt0.o} and the standard C libraries are @file{libyk.a} and @file{libc.a}. @item -mvxworks @opindex mvxworks On System V.4 and embedded PowerPC systems, specify that you are compiling for a VxWorks system. @item -memb @opindex memb On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags header to indicate that @samp{eabi} extended relocations are used. @item -meabi @itemx -mno-eabi @opindex meabi @opindex mno-eabi On System V.4 and embedded PowerPC systems do (do not) adhere to the Embedded Applications Binary Interface (eabi) which is a set of modifications to the System V.4 specifications. Selecting @option{-meabi} means that the stack is aligned to an 8 byte boundary, a function @code{__eabi} is called to from @code{main} to set up the eabi environment, and the @option{-msdata} option can use both @code{r2} and @code{r13} to point to two separate small data areas. Selecting @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary, do not call an initialization function from @code{main}, and the @option{-msdata} option will only use @code{r13} to point to a single small data area. The @option{-meabi} option is on by default if you configured GCC using one of the @samp{powerpc*-*-eabi*} options. @item -msdata=eabi @opindex msdata=eabi On System V.4 and embedded PowerPC systems, put small initialized @code{const} global and static data in the @samp{.sdata2} section, which is pointed to by register @code{r2}. Put small initialized non-@code{const} global and static data in the @samp{.sdata} section, which is pointed to by register @code{r13}. Put small uninitialized global and static data in the @samp{.sbss} section, which is adjacent to the @samp{.sdata} section. The @option{-msdata=eabi} option is incompatible with the @option{-mrelocatable} option. The @option{-msdata=eabi} option also sets the @option{-memb} option. @item -msdata=sysv @opindex msdata=sysv On System V.4 and embedded PowerPC systems, put small global and static data in the @samp{.sdata} section, which is pointed to by register @code{r13}. Put small uninitialized global and static data in the @samp{.sbss} section, which is adjacent to the @samp{.sdata} section. The @option{-msdata=sysv} option is incompatible with the @option{-mrelocatable} option. @item -msdata=default @itemx -msdata @opindex msdata=default @opindex msdata On System V.4 and embedded PowerPC systems, if @option{-meabi} is used, compile code the same as @option{-msdata=eabi}, otherwise compile code the same as @option{-msdata=sysv}. @item -msdata-data @opindex msdata-data On System V.4 and embedded PowerPC systems, put small global and static data in the @samp{.sdata} section. Put small uninitialized global and static data in the @samp{.sbss} section. Do not use register @code{r13} to address small data however. This is the default behavior unless other @option{-msdata} options are used. @item -msdata=none @itemx -mno-sdata @opindex msdata=none @opindex mno-sdata On embedded PowerPC systems, put all initialized global and static data in the @samp{.data} section, and all uninitialized data in the @samp{.bss} section. @item -G @var{num} @opindex G @cindex smaller data references (PowerPC) @cindex .sdata/.sdata2 references (PowerPC) On embedded PowerPC systems, put global and static items less than or equal to @var{num} bytes into the small data or bss sections instead of the normal data or bss section. By default, @var{num} is 8. The @option{-G @var{num}} switch is also passed to the linker. All modules should be compiled with the same @option{-G @var{num}} value. @item -mregnames @itemx -mno-regnames @opindex mregnames @opindex mno-regnames On System V.4 and embedded PowerPC systems do (do not) emit register names in the assembly language output using symbolic forms. @item -pthread @opindex pthread Adds support for multithreading with the @dfn{pthreads} library. This option sets flags for both the preprocessor and linker. @end table @c APPLE LOCAL prune man page @ignore @node RT Options @subsection IBM RT Options @cindex RT options @cindex IBM RT options These @samp{-m} options are defined for the IBM RT PC: @table @gcctabopt @item -min-line-mul @opindex min-line-mul Use an in-line code sequence for integer multiplies. This is the default. @item -mcall-lib-mul @opindex mcall-lib-mul Call @code{lmul$$} for integer multiples. @item -mfull-fp-blocks @opindex mfull-fp-blocks Generate full-size floating point data blocks, including the minimum amount of scratch space recommended by IBM@. This is the default. @item -mminimum-fp-blocks @opindex mminimum-fp-blocks Do not include extra scratch space in floating point data blocks. This results in smaller code, but slower execution, since scratch space must be allocated dynamically. @cindex @file{varargs.h} and RT PC @cindex @file{stdarg.h} and RT PC @item -mfp-arg-in-fpregs @opindex mfp-arg-in-fpregs Use a calling sequence incompatible with the IBM calling convention in which floating point arguments are passed in floating point registers. Note that @code{varargs.h} and @code{stdarg.h} will not work with floating point operands if this option is specified. @item -mfp-arg-in-gregs @opindex mfp-arg-in-gregs Use the normal calling convention for floating point arguments. This is the default. @item -mhc-struct-return @opindex mhc-struct-return Return structures of more than one word in memory, rather than in a register. This provides compatibility with the MetaWare HighC (hc) compiler. Use the option @option{-fpcc-struct-return} for compatibility with the Portable C Compiler (pcc). @item -mnohc-struct-return @opindex mnohc-struct-return Return some structures of more than one word in registers, when convenient. This is the default. For compatibility with the IBM-supplied compilers, use the option @option{-fpcc-struct-return} or the option @option{-mhc-struct-return}. @end table @node MIPS Options @subsection MIPS Options @cindex MIPS options These @samp{-m} options are defined for the MIPS family of computers: @table @gcctabopt @item -march=@var{cpu-type} @opindex march Assume the defaults for the machine type @var{cpu-type} when generating instructions. The choices for @var{cpu-type} are @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4100}, @samp{r4300}, @samp{r4400}, @samp{r4600}, @samp{r4650}, @samp{r5000}, @samp{r6000}, @samp{r8000}, and @samp{orion}. Additionally, the @samp{r2000}, @samp{r3000}, @samp{r4000}, @samp{r5000}, and @samp{r6000} can be abbreviated as @samp{r2k} (or @samp{r2K}), @samp{r3k}, etc. @item -mtune=@var{cpu-type} @opindex mtune Assume the defaults for the machine type @var{cpu-type} when scheduling instructions. The choices for @var{cpu-type} are @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4100}, @samp{r4300}, @samp{r4400}, @samp{r4600}, @samp{r4650}, @samp{r5000}, @samp{r6000}, @samp{r8000}, and @samp{orion}. Additionally, the @samp{r2000}, @samp{r3000}, @samp{r4000}, @samp{r5000}, and @samp{r6000} can be abbreviated as @samp{r2k} (or @samp{r2K}), @samp{r3k}, etc. While picking a specific @var{cpu-type} will schedule things appropriately for that particular chip, the compiler will not generate any code that does not meet level 1 of the MIPS ISA (instruction set architecture) without a @option{-mipsX} or @option{-mabi} switch being used. @item -mcpu=@var{cpu-type} @opindex mcpu This is identical to specifying both @option{-march} and @option{-mtune}. @item -mips1 @opindex mips1 Issue instructions from level 1 of the MIPS ISA@. This is the default. @samp{r3000} is the default @var{cpu-type} at this ISA level. @item -mips2 @opindex mips2 Issue instructions from level 2 of the MIPS ISA (branch likely, square root instructions). @samp{r6000} is the default @var{cpu-type} at this ISA level. @item -mips3 @opindex mips3 Issue instructions from level 3 of the MIPS ISA (64-bit instructions). @samp{r4000} is the default @var{cpu-type} at this ISA level. @item -mips4 @opindex mips4 Issue instructions from level 4 of the MIPS ISA (conditional move, prefetch, enhanced FPU instructions). @samp{r8000} is the default @var{cpu-type} at this ISA level. @item -mfp32 @opindex mfp32 Assume that 32 32-bit floating point registers are available. This is the default. @item -mfp64 @opindex mfp64 Assume that 32 64-bit floating point registers are available. This is the default when the @option{-mips3} option is used. @item -mfused-madd @itemx -mno-fused-madd @opindex mfused-madd @opindex mno-fused-madd Generate code that uses (does not use) the floating point multiply and accumulate instructions, when they are available. These instructions are generated by default if they are available, but this may be undesirable if the extra precision causes problems or on certain chips in the mode where denormals are rounded to zero where denormals generated by multiply and accumulate instructions cause exceptions anyway. @item -mgp32 @opindex mgp32 Assume that 32 32-bit general purpose registers are available. This is the default. @item -mgp64 @opindex mgp64 Assume that 32 64-bit general purpose registers are available. This is the default when the @option{-mips3} option is used. @item -mint64 @opindex mint64 Force int and long types to be 64 bits wide. See @option{-mlong32} for an explanation of the default, and the width of pointers. @item -mlong64 @opindex mlong64 Force long types to be 64 bits wide. See @option{-mlong32} for an explanation of the default, and the width of pointers. @item -mlong32 @opindex mlong32 Force long, int, and pointer types to be 32 bits wide. If none of @option{-mlong32}, @option{-mlong64}, or @option{-mint64} are set, the size of ints, longs, and pointers depends on the ABI and ISA chosen. For @option{-mabi=32}, and @option{-mabi=n32}, ints and longs are 32 bits wide. For @option{-mabi=64}, ints are 32 bits, and longs are 64 bits wide. For @option{-mabi=eabi} and either @option{-mips1} or @option{-mips2}, ints and longs are 32 bits wide. For @option{-mabi=eabi} and higher ISAs, ints are 32 bits, and longs are 64 bits wide. The width of pointer types is the smaller of the width of longs or the width of general purpose registers (which in turn depends on the ISA)@. @item -mabi=32 @itemx -mabi=o64 @itemx -mabi=n32 @itemx -mabi=64 @itemx -mabi=eabi @opindex mabi=32 @opindex mabi=o64 @opindex mabi=n32 @opindex mabi=64 @opindex mabi=eabi Generate code for the indicated ABI@. The default instruction level is @option{-mips1} for @samp{32}, @option{-mips3} for @samp{n32}, and @option{-mips4} otherwise. Conversely, with @option{-mips1} or @option{-mips2}, the default ABI is @samp{32}; otherwise, the default ABI is @samp{64}. @item -mmips-as @opindex mmips-as Generate code for the MIPS assembler, and invoke @file{mips-tfile} to add normal debug information. This is the default for all platforms except for the OSF/1 reference platform, using the OSF/rose object format. If the either of the @option{-gstabs} or @option{-gstabs+} switches are used, the @file{mips-tfile} program will encapsulate the stabs within MIPS ECOFF@. @item -mgas @opindex mgas Generate code for the GNU assembler. This is the default on the OSF/1 reference platform, using the OSF/rose object format. Also, this is the default if the configure option @option{--with-gnu-as} is used. @item -msplit-addresses @itemx -mno-split-addresses @opindex msplit-addresses @opindex mno-split-addresses Generate code to load the high and low parts of address constants separately. This allows GCC to optimize away redundant loads of the high order bits of addresses. This optimization requires GNU as and GNU ld. This optimization is enabled by default for some embedded targets where GNU as and GNU ld are standard. @item -mrnames @itemx -mno-rnames @opindex mrnames @opindex mno-rnames The @option{-mrnames} switch says to output code using the MIPS software names for the registers, instead of the hardware names (ie, @var{a0} instead of @var{$4}). The only known assembler that supports this option is the Algorithmics assembler. @item -mgpopt @itemx -mno-gpopt @opindex mgpopt @opindex mno-gpopt The @option{-mgpopt} switch says to write all of the data declarations before the instructions in the text section, this allows the MIPS assembler to generate one word memory references instead of using two words for short global or static data items. This is on by default if optimization is selected. @item -mstats @itemx -mno-stats @opindex mstats @opindex mno-stats For each non-inline function processed, the @option{-mstats} switch causes the compiler to emit one line to the standard error file to print statistics about the program (number of registers saved, stack size, etc.). @item -mmemcpy @itemx -mno-memcpy @opindex mmemcpy @opindex mno-memcpy The @option{-mmemcpy} switch makes all block moves call the appropriate string function (@samp{memcpy} or @samp{bcopy}) instead of possibly generating inline code. @item -mmips-tfile @itemx -mno-mips-tfile @opindex mmips-tfile @opindex mno-mips-tfile The @option{-mno-mips-tfile} switch causes the compiler not postprocess the object file with the @file{mips-tfile} program, after the MIPS assembler has generated it to add debug support. If @file{mips-tfile} is not run, then no local variables will be available to the debugger. In addition, @file{stage2} and @file{stage3} objects will have the temporary file names passed to the assembler embedded in the object file, which means the objects will not compare the same. The @option{-mno-mips-tfile} switch should only be used when there are bugs in the @file{mips-tfile} program that prevents compilation. @item -msoft-float @opindex msoft-float Generate output containing library calls for floating point. @strong{Warning:} the requisite libraries are not part of GCC@. Normally the facilities of the machine's usual C compiler are used, but this can't be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. @item -mhard-float @opindex mhard-float Generate output containing floating point instructions. This is the default if you use the unmodified sources. @item -mabicalls @itemx -mno-abicalls @opindex mabicalls @opindex mno-abicalls Emit (or do not emit) the pseudo operations @samp{.abicalls}, @samp{.cpload}, and @samp{.cprestore} that some System V.4 ports use for position independent code. @item -mlong-calls @itemx -mno-long-calls @opindex mlong-calls @opindex mno-long-calls Do all calls with the @samp{JALR} instruction, which requires loading up a function's address into a register before the call. You need to use this switch, if you call outside of the current 512 megabyte segment to functions that are not through pointers. @item -mhalf-pic @itemx -mno-half-pic @opindex mhalf-pic @opindex mno-half-pic Put pointers to extern references into the data section and load them up, rather than put the references in the text section. @item -membedded-pic @itemx -mno-embedded-pic @opindex membedded-pic @opindex mno-embedded-pic Generate PIC code suitable for some embedded systems. All calls are made using PC relative address, and all data is addressed using the $gp register. No more than 65536 bytes of global data may be used. This requires GNU as and GNU ld which do most of the work. This currently only works on targets which use ECOFF; it does not work with ELF@. @item -membedded-data @itemx -mno-embedded-data @opindex membedded-data @opindex mno-embedded-data Allocate variables to the read-only data section first if possible, then next in the small data section if possible, otherwise in data. This gives slightly slower code than the default, but reduces the amount of RAM required when executing, and thus may be preferred for some embedded systems. @item -muninit-const-in-rodata @itemx -mno-uninit-const-in-rodata @opindex muninit-const-in-rodata @opindex mno-uninit-const-in-rodata When used together with @option{-membedded-data}, it will always store uninitialized const variables in the read-only data section. @item -msingle-float @itemx -mdouble-float @opindex msingle-float @opindex mdouble-float The @option{-msingle-float} switch tells gcc to assume that the floating point coprocessor only supports single precision operations, as on the @samp{r4650} chip. The @option{-mdouble-float} switch permits gcc to use double precision operations. This is the default. @item -mmad @itemx -mno-mad @opindex mmad @opindex mno-mad Permit use of the @samp{mad}, @samp{madu} and @samp{mul} instructions, as on the @samp{r4650} chip. @item -m4650 @opindex m4650 Turns on @option{-msingle-float}, @option{-mmad}, and, at least for now, @option{-mcpu=r4650}. @item -mips16 @itemx -mno-mips16 @opindex mips16 @opindex mno-mips16 Enable 16-bit instructions. @item -mentry @opindex mentry Use the entry and exit pseudo ops. This option can only be used with @option{-mips16}. @item -EL @opindex EL Compile code for the processor in little endian mode. The requisite libraries are assumed to exist. @item -EB @opindex EB Compile code for the processor in big endian mode. The requisite libraries are assumed to exist. @item -G @var{num} @opindex G @cindex smaller data references (MIPS) @cindex gp-relative references (MIPS) Put global and static items less than or equal to @var{num} bytes into the small data or bss sections instead of the normal data or bss section. This allows the assembler to emit one word memory reference instructions based on the global pointer (@var{gp} or @var{$28}), instead of the normal two words used. By default, @var{num} is 8 when the MIPS assembler is used, and 0 when the GNU assembler is used. The @option{-G @var{num}} switch is also passed to the assembler and linker. All modules should be compiled with the same @option{-G @var{num}} value. @item -nocpp @opindex nocpp Tell the MIPS assembler to not run its preprocessor over user assembler files (with a @samp{.s} suffix) when assembling them. @item -mfix7000 @opindex mfix7000 Pass an option to gas which will cause nops to be inserted if the read of the destination register of an mfhi or mflo instruction occurs in the following two instructions. @item -no-crt0 @opindex no-crt0 Do not include the default crt0. @item -mflush-func=@var{func} @itemx -mno-flush-func @opindex mflush-func Specifies the function to call to flush the I and D caches, or to not call any such function. If called, the function must take the same arguments as the common @code{_flush_func()}, that is, the address of the memory range for which the cache is being flushed, the size of the memory range, and the number 3 (to flush both caches). The default depends on the target gcc was configured for, but commonly is either @samp{_flush_func} or @samp{__cpu_flush}. @end table These options are defined by the macro @code{TARGET_SWITCHES} in the machine description. The default for the options is also defined by that macro, which enables you to change the defaults. @c APPLE LOCAL prune man page @end ignore @node i386 and x86-64 Options @subsection Intel 386 and AMD x86-64 Options @cindex i386 Options @cindex x86-64 Options @cindex Intel 386 Options @cindex AMD x86-64 Options These @samp{-m} options are defined for the i386 and x86-64 family of computers: @table @gcctabopt @item -mcpu=@var{cpu-type} @opindex mcpu Tune to @var{cpu-type} everything applicable about the generated code, except for the ABI and the set of available instructions. The choices for @var{cpu-type} are @samp{i386}, @samp{i486}, @samp{i586}, @samp{i686}, @samp{pentium}, @samp{pentium-mmx}, @samp{pentiumpro}, @samp{pentium2}, @samp{pentium3}, @samp{pentium4}, @samp{k6}, @samp{k6-2}, @samp{k6-3}, @samp{athlon}, @samp{athlon-tbird}, @samp{athlon-4}, @samp{athlon-xp} and @samp{athlon-mp}. While picking a specific @var{cpu-type} will schedule things appropriately for that particular chip, the compiler will not generate any code that does not run on the i386 without the @option{-march=@var{cpu-type}} option being used. @samp{i586} is equivalent to @samp{pentium} and @samp{i686} is equivalent to @samp{pentiumpro}. @samp{k6} and @samp{athlon} are the AMD chips as opposed to the Intel ones. @item -march=@var{cpu-type} @opindex march Generate instructions for the machine type @var{cpu-type}. The choices for @var{cpu-type} are the same as for @option{-mcpu}. Moreover, specifying @option{-march=@var{cpu-type}} implies @option{-mcpu=@var{cpu-type}}. @item -m386 @itemx -m486 @itemx -mpentium @itemx -mpentiumpro @opindex m386 @opindex m486 @opindex mpentium @opindex mpentiumpro These options are synonyms for @option{-mcpu=i386}, @option{-mcpu=i486}, @option{-mcpu=pentium}, and @option{-mcpu=pentiumpro} respectively. These synonyms are deprecated. @item -mfpmath=@var{unit} @opindex march generate floating point arithmetics for selected unit @var{unit}. the choices for @var{unit} are: @table @samp @item 387 Use the standard 387 floating point coprocessor present majority of chips and emulated otherwise. Code compiled with this option will run almost everywhere. The temporary results are computed in 80bit precesion instead of precision specified by the type resulting in slightly different results compared to most of other chips. See @option{-ffloat-store} for more detailed description. This is the default choice for i386 compiler. @item sse Use scalar floating point instructions present in the SSE instruction set. This instruction set is supported by Pentium3 and newer chips, in the AMD line by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE instruction set supports only single precision arithmetics, thus the double and extended precision arithmetics is still done using 387. Later version, present only in Pentium4 and the future AMD x86-64 chips supports double precision arithmetics too. For i387 you need to use @option{-march=@var{cpu-type}}, @option{-msse} or @option{-msse2} switches to enable SSE extensions and make this option effective. For x86-64 compiler, these extensions are enabled by default. The resulting code should be considerably faster in majority of cases and avoid the numerical instability problems of 387 code, but may break some existing code that expects temporaries to be 80bit. This is the default choice for x86-64 compiler. @item sse,387 Attempt to utilize both instruction sets at once. This effectivly double the amount of available registers and on chips with separate execution units for 387 and SSE the execution resources too. Use this option with care, as it is still experimental, because gcc register allocator does not model separate functional units well resulting in instable performance. @end table @item -masm=@var{dialect} @opindex masm=@var{dialect} Output asm instructions using selected @var{dialect}. Supported choices are @samp{intel} or @samp{att} (the default one). @item -mieee-fp @itemx -mno-ieee-fp @opindex mieee-fp @opindex mno-ieee-fp Control whether or not the compiler uses IEEE floating point comparisons. These handle correctly the case where the result of a comparison is unordered. @item -msoft-float @opindex msoft-float Generate output containing library calls for floating point. @strong{Warning:} the requisite libraries are not part of GCC@. Normally the facilities of the machine's usual C compiler are used, but this can't be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. On machines where a function returns floating point results in the 80387 register stack, some floating point opcodes may be emitted even if @option{-msoft-float} is used. @item -mno-fp-ret-in-387 @opindex mno-fp-ret-in-387 Do not use the FPU registers for return values of functions. The usual calling convention has functions return values of types @code{float} and @code{double} in an FPU register, even if there is no FPU@. The idea is that the operating system should emulate an FPU@. The option @option{-mno-fp-ret-in-387} causes such values to be returned in ordinary CPU registers instead. @item -mno-fancy-math-387 @opindex mno-fancy-math-387 Some 387 emulators do not support the @code{sin}, @code{cos} and @code{sqrt} instructions for the 387. Specify this option to avoid generating those instructions. This option is the default on FreeBSD, OpenBSD and NetBSD@. This option is overridden when @option{-march} indicates that the target cpu will always have an FPU and so the instruction will not need emulation. As of revision 2.6.1, these instructions are not generated unless you also use the @option{-funsafe-math-optimizations} switch. @item -malign-double @itemx -mno-align-double @opindex malign-double @opindex mno-align-double Control whether GCC aligns @code{double}, @code{long double}, and @code{long long} variables on a two word boundary or a one word boundary. Aligning @code{double} variables on a two word boundary will produce code that runs somewhat faster on a @samp{Pentium} at the expense of more memory. @item -m128bit-long-double @opindex m128bit-long-double Control the size of @code{long double} type. i386 application binary interface specify the size to be 12 bytes, while modern architectures (Pentium and newer) prefer @code{long double} aligned to 8 or 16 byte boundary. This is impossible to reach with 12 byte long doubles in the array accesses. @strong{Warning:} if you use the @option{-m128bit-long-double} switch, the structures and arrays containing @code{long double} will change their size as well as function calling convention for function taking @code{long double} will be modified. @item -m96bit-long-double @opindex m96bit-long-double Set the size of @code{long double} to 96 bits as required by the i386 application binary interface. This is the default. @item -msvr3-shlib @itemx -mno-svr3-shlib @opindex msvr3-shlib @opindex mno-svr3-shlib Control whether GCC places uninitialized local variables into the @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them into @code{bss}. These options are meaningful only on System V Release 3. @item -mrtd @opindex mrtd Use a different function-calling convention, in which functions that take a fixed number of arguments return with the @code{ret} @var{num} instruction, which pops their arguments while returning. This saves one instruction in the caller since there is no need to pop the arguments there. You can specify that an individual function is called with this calling sequence with the function attribute @samp{stdcall}. You can also override the @option{-mrtd} option by using the function attribute @samp{cdecl}. @xref{Function Attributes}. @strong{Warning:} this calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler. Also, you must provide function prototypes for all functions that take variable numbers of arguments (including @code{printf}); otherwise incorrect code will be generated for calls to those functions. In addition, seriously incorrect code will result if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.) @item -mregparm=@var{num} @opindex mregparm Control how many registers are used to pass integer arguments. By default, no registers are used to pass arguments, and at most 3 registers can be used. You can control this behavior for a specific function by using the function attribute @samp{regparm}. @xref{Function Attributes}. @strong{Warning:} if you use this switch, and @var{num} is nonzero, then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules. @item -mpreferred-stack-boundary=@var{num} @opindex mpreferred-stack-boundary Attempt to keep the stack boundary aligned to a 2 raised to @var{num} byte boundary. If @option{-mpreferred-stack-boundary} is not specified, the default is 4 (16 bytes or 128 bits), except when optimizing for code size (@option{-Os}), in which case the default is the minimum correct alignment (4 bytes for x86, and 8 bytes for x86-64). On Pentium and PentiumPro, @code{double} and @code{long double} values should be aligned to an 8 byte boundary (see @option{-malign-double}) or suffer significant run time performance penalties. On Pentium III, the Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar penalties if it is not 16 byte aligned. To ensure proper alignment of this values on the stack, the stack boundary must be as aligned as that required by any value stored on the stack. Further, every function must be generated such that it keeps the stack aligned. Thus calling a function compiled with a higher preferred stack boundary from a function compiled with a lower preferred stack boundary will most likely misalign the stack. It is recommended that libraries that use callbacks always use the default setting. This extra alignment does consume extra stack space, and generally increases code size. Code that is sensitive to stack space usage, such as embedded systems and operating system kernels, may want to reduce the preferred alignment to @option{-mpreferred-stack-boundary=2}. @item -mmmx @itemx -mno-mmx @item -msse @itemx -mno-sse @item -msse2 @itemx -mno-sse2 @item -m3dnow @itemx -mno-3dnow @opindex mmmx @opindex mno-mmx @opindex msse @opindex mno-sse @opindex m3dnow @opindex mno-3dnow These switches enable or disable the use of built-in functions that allow direct access to the MMX, SSE and 3Dnow extensions of the instruction set. @xref{X86 Built-in Functions}, for details of the functions enabled and disabled by these switches. @item -mpush-args @itemx -mno-push-args @opindex mpush-args @opindex mno-push-args Use PUSH operations to store outgoing parameters. This method is shorter and usually equally fast as method using SUB/MOV operations and is enabled by default. In some cases disabling it may improve performance because of improved scheduling and reduced dependencies. @item -maccumulate-outgoing-args @opindex maccumulate-outgoing-args If enabled, the maximum amount of space required for outgoing arguments will be computed in the function prologue. This is faster on most modern CPUs because of reduced dependencies, improved scheduling and reduced stack usage when preferred stack boundary is not equal to 2. The drawback is a notable increase in code size. This switch implies @option{-mno-push-args}. @item -mthreads @opindex mthreads Support thread-safe exception handling on @samp{Mingw32}. Code that relies on thread-safe exception handling must compile and link all code with the @option{-mthreads} option. When compiling, @option{-mthreads} defines @option{-D_MT}; when linking, it links in a special thread helper library @option{-lmingwthrd} which cleans up per thread exception handling data. @item -mno-align-stringops @opindex mno-align-stringops Do not align destination of inlined string operations. This switch reduces code size and improves performance in case the destination is already aligned, but gcc don't know about it. @item -minline-all-stringops @opindex minline-all-stringops By default GCC inlines string operations only when destination is known to be aligned at least to 4 byte boundary. This enables more inlining, increase code size, but may improve performance of code that depends on fast memcpy, strlen and memset for short lengths. @item -momit-leaf-frame-pointer @opindex momit-leaf-frame-pointer Don't keep the frame pointer in a register for leaf functions. This avoids the instructions to save, set up and restore frame pointers and makes an extra register available in leaf functions. The option @option{-fomit-frame-pointer} removes the frame pointer for all functions which might make debugging harder. @end table These @samp{-m} switches are supported in addition to the above on AMD x86-64 processors in 64-bit environments. @table @gcctabopt @item -m32 @itemx -m64 @opindex m32 @opindex m64 Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets int, long and pointer to 32 bits and generates code that runs on any i386 system. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits and generates code for AMD's x86-64 architecture. @item -mno-red-zone @opindex no-red-zone Do not use a so called red zone for x86-64 code. The red zone is mandated by the x86-64 ABI, it is a 128-byte area beyond the location of the stack pointer that will not be modified by signal or interrupt handlers and therefore can be used for temporary data without adjusting the stack pointer. The flag @option{-mno-red-zone} disables this red zone. @end table @c APPLE LOCAL prune man page @ignore @node HPPA Options @subsection HPPA Options @cindex HPPA Options These @samp{-m} options are defined for the HPPA family of computers: @table @gcctabopt @item -march=@var{architecture-type} @opindex march Generate code for the specified architecture. The choices for @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA 1.1, and @samp{2.0} for PA 2.0 processors. Refer to @file{/usr/lib/sched.models} on an HP-UX system to determine the proper architecture option for your machine. Code compiled for lower numbered architectures will run on higher numbered architectures, but not the other way around. PA 2.0 support currently requires gas snapshot 19990413 or later. The next release of binutils (current is 2.9.1) will probably contain PA 2.0 support. @item -mpa-risc-1-0 @itemx -mpa-risc-1-1 @itemx -mpa-risc-2-0 @opindex mpa-risc-1-0 @opindex mpa-risc-1-1 @opindex mpa-risc-2-0 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively. @item -mbig-switch @opindex mbig-switch Generate code suitable for big switch tables. Use this option only if the assembler/linker complain about out of range branches within a switch table. @item -mjump-in-delay @opindex mjump-in-delay Fill delay slots of function calls with unconditional jump instructions by modifying the return pointer for the function call to be the target of the conditional jump. @item -mdisable-fpregs @opindex mdisable-fpregs Prevent floating point registers from being used in any manner. This is necessary for compiling kernels which perform lazy context switching of floating point registers. If you use this option and attempt to perform floating point operations, the compiler will abort. @item -mdisable-indexing @opindex mdisable-indexing Prevent the compiler from using indexing address modes. This avoids some rather obscure problems when compiling MIG generated code under MACH@. @item -mno-space-regs @opindex mno-space-regs Generate code that assumes the target has no space registers. This allows GCC to generate faster indirect calls and use unscaled index address modes. Such code is suitable for level 0 PA systems and kernels. @item -mfast-indirect-calls @opindex mfast-indirect-calls Generate code that assumes calls never cross space boundaries. This allows GCC to emit code which performs faster indirect calls. This option will not work in the presence of shared libraries or nested functions. @item -mlong-load-store @opindex mlong-load-store Generate 3-instruction load and store sequences as sometimes required by the HP-UX 10 linker. This is equivalent to the @samp{+k} option to the HP compilers. @item -mportable-runtime @opindex mportable-runtime Use the portable calling conventions proposed by HP for ELF systems. @item -mgas @opindex mgas Enable the use of assembler directives only GAS understands. @item -mschedule=@var{cpu-type} @opindex mschedule Schedule code according to the constraints for the machine type @var{cpu-type}. The choices for @var{cpu-type} are @samp{700} @samp{7100}, @samp{7100LC}, @samp{7200}, and @samp{8000}. Refer to @file{/usr/lib/sched.models} on an HP-UX system to determine the proper scheduling option for your machine. @item -mlinker-opt @opindex mlinker-opt Enable the optimization pass in the HPUX linker. Note this makes symbolic debugging impossible. It also triggers a bug in the HPUX 8 and HPUX 9 linkers in which they give bogus error messages when linking some programs. @item -msoft-float @opindex msoft-float Generate output containing library calls for floating point. @strong{Warning:} the requisite libraries are not available for all HPPA targets. Normally the facilities of the machine's usual C compiler are used, but this cannot be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. The embedded target @samp{hppa1.1-*-pro} does provide software floating point support. @option{-msoft-float} changes the calling convention in the output file; therefore, it is only useful if you compile @emph{all} of a program with this option. In particular, you need to compile @file{libgcc.a}, the library that comes with GCC, with @option{-msoft-float} in order for this to work. @end table @node Intel 960 Options @subsection Intel 960 Options These @samp{-m} options are defined for the Intel 960 implementations: @table @gcctabopt @item -m@var{cpu-type} @opindex mka @opindex mkb @opindex mmc @opindex mca @opindex mcf @opindex msa @opindex msb Assume the defaults for the machine type @var{cpu-type} for some of the other options, including instruction scheduling, floating point support, and addressing modes. The choices for @var{cpu-type} are @samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf}, @samp{sa}, and @samp{sb}. The default is @samp{kb}. @item -mnumerics @itemx -msoft-float @opindex mnumerics @opindex msoft-float The @option{-mnumerics} option indicates that the processor does support floating-point instructions. The @option{-msoft-float} option indicates that floating-point support should not be assumed. @item -mleaf-procedures @itemx -mno-leaf-procedures @opindex mleaf-procedures @opindex mno-leaf-procedures Do (or do not) attempt to alter leaf procedures to be callable with the @code{bal} instruction as well as @code{call}. This will result in more efficient code for explicit calls when the @code{bal} instruction can be substituted by the assembler or linker, but less efficient code in other cases, such as calls via function pointers, or using a linker that doesn't support this optimization. @item -mtail-call @itemx -mno-tail-call @opindex mtail-call @opindex mno-tail-call Do (or do not) make additional attempts (beyond those of the machine-independent portions of the compiler) to optimize tail-recursive calls into branches. You may not want to do this because the detection of cases where this is not valid is not totally complete. The default is @option{-mno-tail-call}. @item -mcomplex-addr @itemx -mno-complex-addr @opindex mcomplex-addr @opindex mno-complex-addr Assume (or do not assume) that the use of a complex addressing mode is a win on this implementation of the i960. Complex addressing modes may not be worthwhile on the K-series, but they definitely are on the C-series. The default is currently @option{-mcomplex-addr} for all processors except the CB and CC@. @item -mcode-align @itemx -mno-code-align @opindex mcode-align @opindex mno-code-align Align code to 8-byte boundaries for faster fetching (or don't bother). Currently turned on by default for C-series implementations only. @c APPLE LOCAL prune man page @c @ignore @item -mclean-linkage @itemx -mno-clean-linkage @opindex mclean-linkage @opindex mno-clean-linkage These options are not fully implemented. @c APPLE LOCAL prune man page @c @end ignore @item -mic-compat @itemx -mic2.0-compat @itemx -mic3.0-compat @opindex mic-compat @opindex mic2.0-compat @opindex mic3.0-compat Enable compatibility with iC960 v2.0 or v3.0. @item -masm-compat @itemx -mintel-asm @opindex masm-compat @opindex mintel-asm Enable compatibility with the iC960 assembler. @item -mstrict-align @itemx -mno-strict-align @opindex mstrict-align @opindex mno-strict-align Do not permit (do permit) unaligned accesses. @item -mold-align @opindex mold-align Enable structure-alignment compatibility with Intel's gcc release version 1.3 (based on gcc 1.37). This option implies @option{-mstrict-align}. @item -mlong-double-64 @opindex mlong-double-64 Implement type @samp{long double} as 64-bit floating point numbers. Without the option @samp{long double} is implemented by 80-bit floating point numbers. The only reason we have it because there is no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it is only useful for people using soft-float targets. Otherwise, we should recommend against use of it. @end table @node DEC Alpha Options @subsection DEC Alpha Options These @samp{-m} options are defined for the DEC Alpha implementations: @table @gcctabopt @item -mno-soft-float @itemx -msoft-float @opindex mno-soft-float @opindex msoft-float Use (do not use) the hardware floating-point instructions for floating-point operations. When @option{-msoft-float} is specified, functions in @file{libgcc.a} will be used to perform floating-point operations. Unless they are replaced by routines that emulate the floating-point operations, or compiled in such a way as to call such emulations routines, these routines will issue floating-point operations. If you are compiling for an Alpha without floating-point operations, you must ensure that the library is built so as not to call them. Note that Alpha implementations without floating-point operations are required to have floating-point registers. @item -mfp-reg @itemx -mno-fp-regs @opindex mfp-reg @opindex mno-fp-regs Generate code that uses (does not use) the floating-point register set. @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point register set is not used, floating point operands are passed in integer registers as if they were integers and floating-point results are passed in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence, so any function with a floating-point argument or return value called by code compiled with @option{-mno-fp-regs} must also be compiled with that option. A typical use of this option is building a kernel that does not use, and hence need not save and restore, any floating-point registers. @item -mieee @opindex mieee The Alpha architecture implements floating-point hardware optimized for maximum performance. It is mostly compliant with the IEEE floating point standard. However, for full compliance, software assistance is required. This option generates code fully IEEE compliant code @emph{except} that the @var{inexact-flag} is not maintained (see below). If this option is turned on, the preprocessor macro @code{_IEEE_FP} is defined during compilation. The resulting code is less efficient but is able to correctly support denormalized numbers and exceptional IEEE values such as not-a-number and plus/minus infinity. Other Alpha compilers call this option @option{-ieee_with_no_inexact}. @item -mieee-with-inexact @opindex mieee-with-inexact This is like @option{-mieee} except the generated code also maintains the IEEE @var{inexact-flag}. Turning on this option causes the generated code to implement fully-compliant IEEE math. In addition to @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor macro. On some Alpha implementations the resulting code may execute significantly slower than the code generated by default. Since there is very little code that depends on the @var{inexact-flag}, you should normally not specify this option. Other Alpha compilers call this option @option{-ieee_with_inexact}. @item -mfp-trap-mode=@var{trap-mode} @opindex mfp-trap-mode This option controls what floating-point related traps are enabled. Other Alpha compilers call this option @option{-fptm @var{trap-mode}}. The trap mode can be set to one of four values: @table @samp @item n This is the default (normal) setting. The only traps that are enabled are the ones that cannot be disabled in software (e.g., division by zero trap). @item u In addition to the traps enabled by @samp{n}, underflow traps are enabled as well. @item su Like @samp{su}, but the instructions are marked to be safe for software completion (see Alpha architecture manual for details). @item sui Like @samp{su}, but inexact traps are enabled as well. @end table @item -mfp-rounding-mode=@var{rounding-mode} @opindex mfp-rounding-mode Selects the IEEE rounding mode. Other Alpha compilers call this option @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one of: @table @samp @item n Normal IEEE rounding mode. Floating point numbers are rounded towards the nearest machine number or towards the even machine number in case of a tie. @item m Round towards minus infinity. @item c Chopped rounding mode. Floating point numbers are rounded towards zero. @item d Dynamic rounding mode. A field in the floating point control register (@var{fpcr}, see Alpha architecture reference manual) controls the rounding mode in effect. The C library initializes this register for rounding towards plus infinity. Thus, unless your program modifies the @var{fpcr}, @samp{d} corresponds to round towards plus infinity. @end table @item -mtrap-precision=@var{trap-precision} @opindex mtrap-precision In the Alpha architecture, floating point traps are imprecise. This means without software assistance it is impossible to recover from a floating trap and program execution normally needs to be terminated. GCC can generate code that can assist operating system trap handlers in determining the exact location that caused a floating point trap. Depending on the requirements of an application, different levels of precisions can be selected: @table @samp @item p Program precision. This option is the default and means a trap handler can only identify which program caused a floating point exception. @item f Function precision. The trap handler can determine the function that caused a floating point exception. @item i Instruction precision. The trap handler can determine the exact instruction that caused a floating point exception. @end table Other Alpha compilers provide the equivalent options called @option{-scope_safe} and @option{-resumption_safe}. @item -mieee-conformant @opindex mieee-conformant This option marks the generated code as IEEE conformant. You must not use this option unless you also specify @option{-mtrap-precision=i} and either @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect is to emit the line @samp{.eflag 48} in the function prologue of the generated assembly file. Under DEC Unix, this has the effect that IEEE-conformant math library routines will be linked in. @item -mbuild-constants @opindex mbuild-constants Normally GCC examines a 32- or 64-bit integer constant to see if it can construct it from smaller constants in two or three instructions. If it cannot, it will output the constant as a literal and generate code to load it from the data segment at runtime. Use this option to require GCC to construct @emph{all} integer constants using code, even if it takes more instructions (the maximum is six). You would typically use this option to build a shared library dynamic loader. Itself a shared library, it must relocate itself in memory before it can find the variables and constants in its own data segment. @item -malpha-as @itemx -mgas @opindex malpha-as @opindex mgas Select whether to generate code to be assembled by the vendor-supplied assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}. @item -mbwx @itemx -mno-bwx @itemx -mcix @itemx -mno-cix @itemx -mfix @itemx -mno-fix @itemx -mmax @itemx -mno-max @opindex mbwx @opindex mno-bwx @opindex mcix @opindex mno-cix @opindex mfix @opindex mno-fix @opindex mmax @opindex mno-max Indicate whether GCC should generate code to use the optional BWX, CIX, FIX and MAX instruction sets. The default is to use the instruction sets supported by the CPU type specified via @option{-mcpu=} option or that of the CPU on which GCC was built if none was specified. @item -mfloat-vax @itemx -mfloat-ieee @opindex mfloat-vax @opindex mfloat-ieee Generate code that uses (does not use) VAX F and G floating point arithmetic instead of IEEE single and double precision. @item -mexplicit-relocs @itemx -mno-explicit-relocs @opindex mexplicit-relocs @opindex mno-explicit-relocs Older Alpha assemblers provided no way to generate symbol relocations except via assembler macros. Use of these macros does not allow optimial instruction scheduling. GNU binutils as of version 2.12 supports a new syntax that allows the compiler to explicitly mark which relocations should apply to which instructions. This option is mostly useful for debugging, as GCC detects the capabilities of the assembler when it is built and sets the default accordingly. @item -msmall-data @itemx -mlarge-data @opindex msmall-data @opindex mlarge-data When @option{-mexplicit-relocs} is in effect, static data is accessed via @dfn{gp-relative} relocations. When @option{-msmall-data} is used, objects 8 bytes long or smaller are placed in a @dfn{small data area} (the @code{.sdata} and @code{.sbss} sections) and are accessed via 16-bit relocations off of the @code{$gp} register. This limits the size of the small data area to 64KB, but allows the variables to be directly accessed via a single instruction. The default is @option{-mlarge-data}. With this option the data area is limited to just below 2GB. Programs that require more than 2GB of data must use @code{malloc} or @code{mmap} to allocate the data in the heap instead of in the program's data segment. When generating code for shared libraries, @option{-fpic} implies @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}. @item -mcpu=@var{cpu_type} @opindex mcpu Set the instruction set and instruction scheduling parameters for machine type @var{cpu_type}. You can specify either the @samp{EV} style name or the corresponding chip number. GCC supports scheduling parameters for the EV4, EV5 and EV6 family of processors and will choose the default values for the instruction set from the processor you specify. If you do not specify a processor type, GCC will default to the processor on which the compiler was built. Supported values for @var{cpu_type} are @table @samp @item ev4 @item ev45 @itemx 21064 Schedules as an EV4 and has no instruction set extensions. @item ev5 @itemx 21164 Schedules as an EV5 and has no instruction set extensions. @item ev56 @itemx 21164a Schedules as an EV5 and supports the BWX extension. @item pca56 @itemx 21164pc @itemx 21164PC Schedules as an EV5 and supports the BWX and MAX extensions. @item ev6 @itemx 21264 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions. @item ev67 @item 21264a Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions. @end table @item -mtune=@var{cpu_type} @opindex mtune Set only the instruction scheduling parameters for machine type @var{cpu_type}. The instruction set is not changed. @item -mmemory-latency=@var{time} @opindex mmemory-latency Sets the latency the scheduler should assume for typical memory references as seen by the application. This number is highly dependent on the memory access patterns used by the application and the size of the external cache on the machine. Valid options for @var{time} are @table @samp @item @var{number} A decimal number representing clock cycles. @item L1 @itemx L2 @itemx L3 @itemx main The compiler contains estimates of the number of clock cycles for ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches (also called Dcache, Scache, and Bcache), as well as to main memory. Note that L3 is only valid for EV5. @end table @end table @node DEC Alpha/VMS Options @subsection DEC Alpha/VMS Options These @samp{-m} options are defined for the DEC Alpha/VMS implementations: @table @gcctabopt @item -mvms-return-codes @opindex mvms-return-codes Return VMS condition codes from main. The default is to return POSIX style condition (e.g.@ error) codes. @end table @node Clipper Options @subsection Clipper Options These @samp{-m} options are defined for the Clipper implementations: @table @gcctabopt @item -mc300 @opindex mc300 Produce code for a C300 Clipper processor. This is the default. @item -mc400 @opindex mc400 Produce code for a C400 Clipper processor, i.e.@: use floating point registers f8--f15. @end table @node H8/300 Options @subsection H8/300 Options These @samp{-m} options are defined for the H8/300 implementations: @table @gcctabopt @item -mrelax @opindex mrelax Shorten some address references at link time, when possible; uses the linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300, ld.info, Using ld}, for a fuller description. @item -mh @opindex mh Generate code for the H8/300H@. @item -ms @opindex ms Generate code for the H8/S@. @item -ms2600 @opindex ms2600 Generate code for the H8/S2600. This switch must be used with @option{-ms}. @item -mint32 @opindex mint32 Make @code{int} data 32 bits by default. @item -malign-300 @opindex malign-300 On the H8/300H and H8/S, use the same alignment rules as for the H8/300. The default for the H8/300H and H8/S is to align longs and floats on 4 byte boundaries. @option{-malign-300} causes them to be aligned on 2 byte boundaries. This option has no effect on the H8/300. @end table @node SH Options @subsection SH Options These @samp{-m} options are defined for the SH implementations: @table @gcctabopt @item -m1 @opindex m1 Generate code for the SH1. @item -m2 @opindex m2 Generate code for the SH2. @item -m3 @opindex m3 Generate code for the SH3. @item -m3e @opindex m3e Generate code for the SH3e. @item -m4-nofpu @opindex m4-nofpu Generate code for the SH4 without a floating-point unit. @item -m4-single-only @opindex m4-single-only Generate code for the SH4 with a floating-point unit that only supports single-precision arithmetic. @item -m4-single @opindex m4-single Generate code for the SH4 assuming the floating-point unit is in single-precision mode by default. @item -m4 @opindex m4 Generate code for the SH4. @item -mb @opindex mb Compile code for the processor in big endian mode. @item -ml @opindex ml Compile code for the processor in little endian mode. @item -mdalign @opindex mdalign Align doubles at 64-bit boundaries. Note that this changes the calling conventions, and thus some functions from the standard C library will not work unless you recompile it first with @option{-mdalign}. @item -mrelax @opindex mrelax Shorten some address references at link time, when possible; uses the linker option @option{-relax}. @item -mbigtable @opindex mbigtable Use 32-bit offsets in @code{switch} tables. The default is to use 16-bit offsets. @item -mfmovd @opindex mfmovd Enable the use of the instruction @code{fmovd}. @item -mhitachi @opindex mhitachi Comply with the calling conventions defined by Hitachi. @item -mnomacsave @opindex mnomacsave Mark the @code{MAC} register as call-clobbered, even if @option{-mhitachi} is given. @item -mieee @opindex mieee Increase IEEE-compliance of floating-point code. @item -misize @opindex misize Dump instruction size and location in the assembly code. @item -mpadstruct @opindex mpadstruct This option is deprecated. It pads structures to multiple of 4 bytes, which is incompatible with the SH ABI@. @item -mspace @opindex mspace Optimize for space instead of speed. Implied by @option{-Os}. @item -mprefergot @opindex mprefergot When generating position-independent code, emit function calls using the Global Offset Table instead of the Procedure Linkage Table. @item -musermode @opindex musermode Generate a library function call to invalidate instruction cache entries, after fixing up a trampoline. This library function call doesn't assume it can write to the whole memory address space. This is the default when the target is @code{sh-*-linux*}. @end table @node System V Options @subsection Options for System V These additional options are available on System V Release 4 for compatibility with other compilers on those systems: @table @gcctabopt @item -G @opindex G Create a shared object. It is recommended that @option{-symbolic} or @option{-shared} be used instead. @item -Qy @opindex Qy Identify the versions of each tool used by the compiler, in a @code{.ident} assembler directive in the output. @item -Qn @opindex Qn Refrain from adding @code{.ident} directives to the output file (this is the default). @item -YP,@var{dirs} @opindex YP Search the directories @var{dirs}, and no others, for libraries specified with @option{-l}. @item -Ym,@var{dir} @opindex Ym Look in the directory @var{dir} to find the M4 preprocessor. The assembler uses this option. @c This is supposed to go with a -Yd for predefined M4 macro files, but @c the generic assembler that comes with Solaris takes just -Ym. @end table @node TMS320C3x/C4x Options @subsection TMS320C3x/C4x Options @cindex TMS320C3x/C4x Options These @samp{-m} options are defined for TMS320C3x/C4x implementations: @table @gcctabopt @item -mcpu=@var{cpu_type} @opindex mcpu Set the instruction set, register set, and instruction scheduling parameters for machine type @var{cpu_type}. Supported values for @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and @samp{c44}. The default is @samp{c40} to generate code for the TMS320C40. @item -mbig-memory @item -mbig @itemx -msmall-memory @itemx -msmall @opindex mbig-memory @opindex mbig @opindex msmall-memory @opindex msmall Generates code for the big or small memory model. The small memory model assumed that all data fits into one 64K word page. At run-time the data page (DP) register must be set to point to the 64K page containing the .bss and .data program sections. The big memory model is the default and requires reloading of the DP register for every direct memory access. @item -mbk @itemx -mno-bk @opindex mbk @opindex mno-bk Allow (disallow) allocation of general integer operands into the block count register BK@. @item -mdb @itemx -mno-db @opindex mdb @opindex mno-db Enable (disable) generation of code using decrement and branch, DBcond(D), instructions. This is enabled by default for the C4x. To be on the safe side, this is disabled for the C3x, since the maximum @c APPLE LOCAL work around a makeinfo complaint iteration count on the C3x is @math{2^23 + 1} (but who iterates loops more than @math{2^23} times on the C3x?). Note that GCC will try to reverse a loop so that it can utilise the decrement and branch instruction, but will give up if there is more than one memory reference in the loop. Thus a loop where the loop counter is decremented can generate slightly more efficient code, in cases where the RPTB instruction cannot be utilised. @item -mdp-isr-reload @itemx -mparanoid @opindex mdp-isr-reload @opindex mparanoid Force the DP register to be saved on entry to an interrupt service routine (ISR), reloaded to point to the data section, and restored on exit from the ISR@. This should not be required unless someone has violated the small memory model by modifying the DP register, say within an object library. @item -mmpyi @itemx -mno-mpyi @opindex mmpyi @opindex mno-mpyi For the C3x use the 24-bit MPYI instruction for integer multiplies instead of a library call to guarantee 32-bit results. Note that if one of the operands is a constant, then the multiplication will be performed using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x, then squaring operations are performed inline instead of a library call. @item -mfast-fix @itemx -mno-fast-fix @opindex mfast-fix @opindex mno-fast-fix The C3x/C4x FIX instruction to convert a floating point value to an integer value chooses the nearest integer less than or equal to the floating point value rather than to the nearest integer. Thus if the floating point number is negative, the result will be incorrectly truncated an additional code is necessary to detect and correct this case. This option can be used to disable generation of the additional code required to correct the result. @item -mrptb @itemx -mno-rptb @opindex mrptb @opindex mno-rptb Enable (disable) generation of repeat block sequences using the RPTB instruction for zero overhead looping. The RPTB construct is only used for innermost loops that do not call functions or jump across the loop boundaries. There is no advantage having nested RPTB loops due to the overhead required to save and restore the RC, RS, and RE registers. This is enabled by default with @option{-O2}. @item -mrpts=@var{count} @itemx -mno-rpts @opindex mrpts @opindex mno-rpts Enable (disable) the use of the single instruction repeat instruction RPTS@. If a repeat block contains a single instruction, and the loop count can be guaranteed to be less than the value @var{count}, GCC will emit a RPTS instruction instead of a RPTB@. If no value is specified, then a RPTS will be emitted even if the loop count cannot be determined at compile time. Note that the repeated instruction following RPTS does not have to be reloaded from memory each iteration, thus freeing up the CPU buses for operands. However, since interrupts are blocked by this instruction, it is disabled by default. @item -mloop-unsigned @itemx -mno-loop-unsigned @opindex mloop-unsigned @opindex mno-loop-unsigned The maximum iteration count when using RPTS and RPTB (and DB on the C40) @c APPLE LOCAL work around a makeinfo complaint is @math{2^31 + 1} since these instructions test if the iteration count is negative to terminate the loop. If the iteration count is unsigned @c APPLE LOCAL work around a makeinfo complaint there is a possibility than the @math{2^31 + 1} maximum iteration count may be exceeded. This switch allows an unsigned iteration count. @item -mti @opindex mti Try to emit an assembler syntax that the TI assembler (asm30) is happy with. This also enforces compatibility with the API employed by the TI C3x C compiler. For example, long doubles are passed as structures rather than in floating point registers. @item -mregparm @itemx -mmemparm @opindex mregparm @opindex mmemparm Generate code that uses registers (stack) for passing arguments to functions. By default, arguments are passed in registers where possible rather than by pushing arguments on to the stack. @item -mparallel-insns @itemx -mno-parallel-insns @opindex mparallel-insns @opindex mno-parallel-insns Allow the generation of parallel instructions. This is enabled by default with @option{-O2}. @item -mparallel-mpy @itemx -mno-parallel-mpy @opindex mparallel-mpy @opindex mno-parallel-mpy Allow the generation of MPY||ADD and MPY||SUB parallel instructions, provided @option{-mparallel-insns} is also specified. These instructions have tight register constraints which can pessimize the code generation of large functions. @end table @node V850 Options @subsection V850 Options @cindex V850 Options These @samp{-m} options are defined for V850 implementations: @table @gcctabopt @item -mlong-calls @itemx -mno-long-calls @opindex mlong-calls @opindex mno-long-calls Treat all calls as being far away (near). If calls are assumed to be far away, the compiler will always load the functions address up into a register, and call indirect through the pointer. @item -mno-ep @itemx -mep @opindex mno-ep @opindex mep Do not optimize (do optimize) basic blocks that use the same index pointer 4 or more times to copy pointer into the @code{ep} register, and use the shorter @code{sld} and @code{sst} instructions. The @option{-mep} option is on by default if you optimize. @item -mno-prolog-function @itemx -mprolog-function @opindex mno-prolog-function @opindex mprolog-function Do not use (do use) external functions to save and restore registers at the prolog and epilog of a function. The external functions are slower, but use less code space if more than one function saves the same number of registers. The @option{-mprolog-function} option is on by default if you optimize. @item -mspace @opindex mspace Try to make the code as small as possible. At present, this just turns on the @option{-mep} and @option{-mprolog-function} options. @item -mtda=@var{n} @opindex mtda Put static or global variables whose size is @var{n} bytes or less into the tiny data area that register @code{ep} points to. The tiny data area can hold up to 256 bytes in total (128 bytes for byte references). @item -msda=@var{n} @opindex msda Put static or global variables whose size is @var{n} bytes or less into the small data area that register @code{gp} points to. The small data area can hold up to 64 kilobytes. @item -mzda=@var{n} @opindex mzda Put static or global variables whose size is @var{n} bytes or less into the first 32 kilobytes of memory. @item -mv850 @opindex mv850 Specify that the target processor is the V850. @item -mbig-switch @opindex mbig-switch Generate code suitable for big switch tables. Use this option only if the assembler/linker complain about out of range branches within a switch table. @end table @node ARC Options @subsection ARC Options @cindex ARC Options These options are defined for ARC implementations: @table @gcctabopt @item -EL @opindex EL Compile code for little endian mode. This is the default. @item -EB @opindex EB Compile code for big endian mode. @item -mmangle-cpu @opindex mmangle-cpu Prepend the name of the cpu to all public symbol names. In multiple-processor systems, there are many ARC variants with different instruction and register set characteristics. This flag prevents code compiled for one cpu to be linked with code compiled for another. No facility exists for handling variants that are ``almost identical''. This is an all or nothing option. @item -mcpu=@var{cpu} @opindex mcpu Compile code for ARC variant @var{cpu}. Which variants are supported depend on the configuration. All variants support @option{-mcpu=base}, this is the default. @item -mtext=@var{text-section} @itemx -mdata=@var{data-section} @itemx -mrodata=@var{readonly-data-section} @opindex mtext @opindex mdata @opindex mrodata Put functions, data, and readonly data in @var{text-section}, @var{data-section}, and @var{readonly-data-section} respectively by default. This can be overridden with the @code{section} attribute. @xref{Variable Attributes}. @end table @node NS32K Options @subsection NS32K Options @cindex NS32K options These are the @samp{-m} options defined for the 32000 series. The default values for these options depends on which style of 32000 was selected when the compiler was configured; the defaults for the most common choices are given below. @table @gcctabopt @item -m32032 @itemx -m32032 @opindex m32032 @opindex m32032 Generate output for a 32032. This is the default when the compiler is configured for 32032 and 32016 based systems. @item -m32332 @itemx -m32332 @opindex m32332 @opindex m32332 Generate output for a 32332. This is the default when the compiler is configured for 32332-based systems. @item -m32532 @itemx -m32532 @opindex m32532 @opindex m32532 Generate output for a 32532. This is the default when the compiler is configured for 32532-based systems. @item -m32081 @opindex m32081 Generate output containing 32081 instructions for floating point. This is the default for all systems. @item -m32381 @opindex m32381 Generate output containing 32381 instructions for floating point. This also implies @option{-m32081}. The 32381 is only compatible with the 32332 and 32532 cpus. This is the default for the pc532-netbsd configuration. @item -mmulti-add @opindex mmulti-add Try and generate multiply-add floating point instructions @code{polyF} and @code{dotF}. This option is only available if the @option{-m32381} option is in effect. Using these instructions requires changes to register allocation which generally has a negative impact on performance. This option should only be enabled when compiling code particularly likely to make heavy use of multiply-add instructions. @item -mnomulti-add @opindex mnomulti-add Do not try and generate multiply-add floating point instructions @code{polyF} and @code{dotF}. This is the default on all platforms. @item -msoft-float @opindex msoft-float Generate output containing library calls for floating point. @strong{Warning:} the requisite libraries may not be available. @item -mnobitfield @opindex mnobitfield Do not use the bit-field instructions. On some machines it is faster to use shifting and masking operations. This is the default for the pc532. @item -mbitfield @opindex mbitfield Do use the bit-field instructions. This is the default for all platforms except the pc532. @item -mrtd @opindex mrtd Use a different function-calling convention, in which functions that take a fixed number of arguments return pop their arguments on return with the @code{ret} instruction. This calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler. Also, you must provide function prototypes for all functions that take variable numbers of arguments (including @code{printf}); otherwise incorrect code will be generated for calls to those functions. In addition, seriously incorrect code will result if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.) This option takes its name from the 680x0 @code{rtd} instruction. @item -mregparam @opindex mregparam Use a different function-calling convention where the first two arguments are passed in registers. This calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler. @item -mnoregparam @opindex mnoregparam Do not pass any arguments in registers. This is the default for all targets. @item -msb @opindex msb It is OK to use the sb as an index register which is always loaded with zero. This is the default for the pc532-netbsd target. @item -mnosb @opindex mnosb The sb register is not available for use or has not been initialized to zero by the run time system. This is the default for all targets except the pc532-netbsd. It is also implied whenever @option{-mhimem} or @option{-fpic} is set. @item -mhimem @opindex mhimem Many ns32000 series addressing modes use displacements of up to 512MB@. If an address is above 512MB then displacements from zero can not be used. This option causes code to be generated which can be loaded above 512MB@. This may be useful for operating systems or ROM code. @item -mnohimem @opindex mnohimem Assume code will be loaded in the first 512MB of virtual address space. This is the default for all platforms. @end table @node AVR Options @subsection AVR Options @cindex AVR Options These options are defined for AVR implementations: @table @gcctabopt @item -mmcu=@var{mcu} @opindex mmcu Specify ATMEL AVR instruction set or MCU type. Instruction set avr1 is for the minimal AVR core, not supported by the C compiler, only for assembler programs (MCU types: at90s1200, attiny10, attiny11, attiny12, attiny15, attiny28). Instruction set avr2 (default) is for the classic AVR core with up to 8K program memory space (MCU types: at90s2313, at90s2323, attiny22, at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515, at90c8534, at90s8535). Instruction set avr3 is for the classic AVR core with up to 128K program memory space (MCU types: atmega103, atmega603, at43usb320, at76c711). Instruction set avr4 is for the enhanced AVR core with up to 8K program memory space (MCU types: atmega8, atmega83, atmega85). Instruction set avr5 is for the enhanced AVR core with up to 128K program memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323, atmega64, atmega128, at43usb355, at94k). @item -msize @opindex msize Output instruction sizes to the asm file. @item -minit-stack=@var{N} @opindex minit-stack Specify the initial stack address, which may be a symbol or numeric value, @samp{__stack} is the default. @item -mno-interrupts @opindex mno-interrupts Generated code is not compatible with hardware interrupts. Code size will be smaller. @item -mcall-prologues @opindex mcall-prologues Functions prologues/epilogues expanded as call to appropriate subroutines. Code size will be smaller. @item -mno-tablejump @opindex mno-tablejump Do not generate tablejump insns which sometimes increase code size. @item -mtiny-stack @opindex mtiny-stack Change only the low 8 bits of the stack pointer. @end table @node MCore Options @subsection MCore Options @cindex MCore options These are the @samp{-m} options defined for the Motorola M*Core processors. @table @gcctabopt @item -mhardlit @itemx -mhardlit @itemx -mno-hardlit @opindex mhardlit @opindex mhardlit @opindex mno-hardlit Inline constants into the code stream if it can be done in two instructions or less. @item -mdiv @itemx -mdiv @itemx -mno-div @opindex mdiv @opindex mdiv @opindex mno-div Use the divide instruction. (Enabled by default). @item -mrelax-immediate @itemx -mrelax-immediate @itemx -mno-relax-immediate @opindex mrelax-immediate @opindex mrelax-immediate @opindex mno-relax-immediate Allow arbitrary sized immediates in bit operations. @item -mwide-bitfields @itemx -mwide-bitfields @itemx -mno-wide-bitfields @opindex mwide-bitfields @opindex mwide-bitfields @opindex mno-wide-bitfields Always treat bit-fields as int-sized. @item -m4byte-functions @itemx -m4byte-functions @itemx -mno-4byte-functions @opindex m4byte-functions @opindex m4byte-functions @opindex mno-4byte-functions Force all functions to be aligned to a four byte boundary. @item -mcallgraph-data @itemx -mcallgraph-data @itemx -mno-callgraph-data @opindex mcallgraph-data @opindex mcallgraph-data @opindex mno-callgraph-data Emit callgraph information. @item -mslow-bytes @itemx -mslow-bytes @itemx -mno-slow-bytes @opindex mslow-bytes @opindex mslow-bytes @opindex mno-slow-bytes Prefer word access when reading byte quantities. @item -mlittle-endian @itemx -mlittle-endian @itemx -mbig-endian @opindex mlittle-endian @opindex mlittle-endian @opindex mbig-endian Generate code for a little endian target. @item -m210 @itemx -m210 @itemx -m340 @opindex m210 @opindex m210 @opindex m340 Generate code for the 210 processor. @end table @node IA-64 Options @subsection IA-64 Options @cindex IA-64 Options These are the @samp{-m} options defined for the Intel IA-64 architecture. @table @gcctabopt @item -mbig-endian @opindex mbig-endian Generate code for a big endian target. This is the default for HPUX@. @item -mlittle-endian @opindex mlittle-endian Generate code for a little endian target. This is the default for AIX5 and Linux. @item -mgnu-as @itemx -mno-gnu-as @opindex mgnu-as @opindex mno-gnu-as Generate (or don't) code for the GNU assembler. This is the default. @c Also, this is the default if the configure option @option{--with-gnu-as} @c is used. @item -mgnu-ld @itemx -mno-gnu-ld @opindex mgnu-ld @opindex mno-gnu-ld Generate (or don't) code for the GNU linker. This is the default. @c Also, this is the default if the configure option @option{--with-gnu-ld} @c is used. @item -mno-pic @opindex mno-pic Generate code that does not use a global pointer register. The result is not position independent code, and violates the IA-64 ABI@. @item -mvolatile-asm-stop @itemx -mno-volatile-asm-stop @opindex mvolatile-asm-stop @opindex mno-volatile-asm-stop Generate (or don't) a stop bit immediately before and after volatile asm statements. @item -mb-step @opindex mb-step Generate code that works around Itanium B step errata. @item -mregister-names @itemx -mno-register-names @opindex mregister-names @opindex mno-register-names Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for the stacked registers. This may make assembler output more readable. @item -mno-sdata @itemx -msdata @opindex mno-sdata @opindex msdata Disable (or enable) optimizations that use the small data section. This may be useful for working around optimizer bugs. @item -mconstant-gp @opindex mconstant-gp Generate code that uses a single constant global pointer value. This is useful when compiling kernel code. @item -mauto-pic @opindex mauto-pic Generate code that is self-relocatable. This implies @option{-mconstant-gp}. This is useful when compiling firmware code. @item -minline-divide-min-latency @opindex minline-divide-min-latency Generate code for inline divides using the minimum latency algorithm. @item -minline-divide-max-throughput @opindex minline-divide-max-throughput Generate code for inline divides using the maximum throughput algorithm. @item -mno-dwarf2-asm @itemx -mdwarf2-asm @opindex mno-dwarf2-asm @opindex mdwarf2-asm Don't (or do) generate assembler code for the DWARF2 line number debugging info. This may be useful when not using the GNU assembler. @item -mfixed-range=@var{register-range} @opindex mfixed-range Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator can not use. This is useful when compiling kernel code. A register range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma. @end table @node D30V Options @subsection D30V Options @cindex D30V Options These @samp{-m} options are defined for D30V implementations: @table @gcctabopt @item -mextmem @opindex mextmem Link the @samp{.text}, @samp{.data}, @samp{.bss}, @samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into external memory, which starts at location @code{0x80000000}. @item -mextmemory @opindex mextmemory Same as the @option{-mextmem} switch. @item -monchip @opindex monchip Link the @samp{.text} section into onchip text memory, which starts at location @code{0x0}. Also link @samp{.data}, @samp{.bss}, @samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into onchip data memory, which starts at location @code{0x20000000}. @item -mno-asm-optimize @itemx -masm-optimize @opindex mno-asm-optimize @opindex masm-optimize Disable (enable) passing @option{-O} to the assembler when optimizing. The assembler uses the @option{-O} option to automatically parallelize adjacent short instructions where possible. @item -mbranch-cost=@var{n} @opindex mbranch-cost Increase the internal costs of branches to @var{n}. Higher costs means that the compiler will issue more instructions to avoid doing a branch. The default is 2. @item -mcond-exec=@var{n} @opindex mcond-exec Specify the maximum number of conditionally executed instructions that replace a branch. The default is 4. @end table @node S/390 and zSeries Options @subsection S/390 and zSeries Options @cindex S/390 and zSeries Options These are the @samp{-m} options defined for the S/390 and zSeries architecture. @table @gcctabopt @item -mhard-float @itemx -msoft-float @opindex mhard-float @opindex msoft-float Use (do not use) the hardware floating-point instructions and registers for floating-point operations. When @option{-msoft-float} is specified, functions in @file{libgcc.a} will be used to perform floating-point operations. When @option{-mhard-float} is specified, the compiler generates IEEE floating-point instructions. This is the default. @item -mbackchain @itemx -mno-backchain @opindex mbackchain @opindex mno-backchain Generate (or do not generate) code which maintains an explicit backchain within the stack frame that points to the caller's frame. This is currently needed to allow debugging. The default is to generate the backchain. @item -msmall-exec @itemx -mno-small-exec @opindex msmall-exec @opindex mno-small-exec Generate (or do not generate) code using the @code{bras} instruction to do subroutine calls. This only works reliably if the total executable size does not exceed 64k. The default is to use the @code{basr} instruction instead, which does not have this limitation. @item -m64 @itemx -m31 @opindex m64 @opindex m31 When @option{-m31} is specified, generate code compliant to the Linux for S/390 ABI@. When @option{-m64} is specified, generate code compliant to the Linux for zSeries ABI@. This allows GCC in particular to generate 64-bit instructions. For the @samp{s390} targets, the default is @option{-m31}, while the @samp{s390x} targets default to @option{-m64}. @item -mmvcle @itemx -mno-mvcle @opindex mmvcle @opindex mno-mvcle Generate (or do not generate) code using the @code{mvcle} instruction to perform block moves. When @option{-mno-mvcle} is specifed, use a @code{mvc} loop instead. This is the default. @item -mdebug @itemx -mno-debug @opindex mdebug @opindex mno-debug Print (or do not print) additional debug information when compiling. The default is to not print debug information. @end table @node CRIS Options @subsection CRIS Options @cindex CRIS Options These options are defined specifically for the CRIS ports. @table @gcctabopt @item -march=@var{architecture-type} @itemx -mcpu=@var{architecture-type} @opindex march @opindex mcpu Generate code for the specified architecture. The choices for @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX. Default is @samp{v0} except for cris-axis-linux-gnu, where the default is @samp{v10}. @item -mtune=@var{architecture-type} @opindex mtune Tune to @var{architecture-type} everything applicable about the generated code, except for the ABI and the set of available instructions. The choices for @var{architecture-type} are the same as for @option{-march=@var{architecture-type}}. @item -mmax-stack-frame=@var{n} @opindex mmax-stack-frame Warn when the stack frame of a function exceeds @var{n} bytes. @item -melinux-stacksize=@var{n} @opindex melinux-stacksize Only available with the @samp{cris-axis-aout} target. Arranges for indications in the program to the kernel loader that the stack of the program should be set to @var{n} bytes. @item -metrax4 @itemx -metrax100 @opindex metrax4 @opindex metrax100 The options @option{-metrax4} and @option{-metrax100} are synonyms for @option{-march=v3} and @option{-march=v8} respectively. @item -mpdebug @opindex mpdebug Enable CRIS-specific verbose debug-related information in the assembly code. This option also has the effect to turn off the @samp{#NO_APP} formatted-code indicator to the assembler at the beginning of the assembly file. @item -mcc-init @opindex mcc-init Do not use condition-code results from previous instruction; always emit compare and test instructions before use of condition codes. @item -mno-side-effects @opindex mno-side-effects Do not emit instructions with side-effects in addressing modes other than post-increment. @item -mstack-align @itemx -mno-stack-align @itemx -mdata-align @itemx -mno-data-align @itemx -mconst-align @itemx -mno-const-align @opindex mstack-align @opindex mno-stack-align @opindex mdata-align @opindex mno-data-align @opindex mconst-align @opindex mno-const-align These options (no-options) arranges (eliminate arrangements) for the stack-frame, individual data and constants to be aligned for the maximum single data access size for the chosen CPU model. The default is to arrange for 32-bit alignment. ABI details such as structure layout are not affected by these options. @item -m32-bit @itemx -m16-bit @itemx -m8-bit @opindex m32-bit @opindex m16-bit @opindex m8-bit Similar to the stack- data- and const-align options above, these options arrange for stack-frame, writable data and constants to all be 32-bit, 16-bit or 8-bit aligned. The default is 32-bit alignment. @item -mno-prologue-epilogue @itemx -mprologue-epilogue @opindex mno-prologue-epilogue @opindex mprologue-epilogue With @option{-mno-prologue-epilogue}, the normal function prologue and epilogue that sets up the stack-frame are omitted and no return instructions or return sequences are generated in the code. Use this option only together with visual inspection of the compiled code: no warnings or errors are generated when call-saved registers must be saved, or storage for local variable needs to be allocated. @item -mno-gotplt @itemx -mgotplt @opindex mno-gotplt @opindex mgotplt With @option{-fpic} and @option{-fPIC}, don't generate (do generate) instruction sequences that load addresses for functions from the PLT part of the GOT rather than (traditional on other architectures) calls to the PLT. The default is @option{-mgotplt}. @item -maout @opindex maout Legacy no-op option only recognized with the cris-axis-aout target. @item -melf @opindex melf Legacy no-op option only recognized with the cris-axis-elf and cris-axis-linux-gnu targets. @item -melinux @opindex melinux Only recognized with the cris-axis-aout target, where it selects a GNU/linux-like multilib, include files and instruction set for @option{-march=v8}. @item -mlinux @opindex mlinux Legacy no-op option only recognized with the cris-axis-linux-gnu target. @item -sim @opindex sim This option, recognized for the cris-axis-aout and cris-axis-elf arranges to link with input-output functions from a simulator library. Code, initialized data and zero-initialized data are allocated consecutively. @item -sim2 @opindex sim2 Like @option{-sim}, but pass linker options to locate initialized data at 0x40000000 and zero-initialized data at 0x80000000. @end table @node MMIX Options @subsection MMIX Options @cindex MMIX Options These options are defined for the MMIX: @table @gcctabopt @item -mlibfuncs @itemx -mno-libfuncs @opindex mlibfuncs @opindex mno-libfuncs Specify that intrinsic library functions are being compiled, passing all values in registers, no matter the size. @item -mepsilon @itemx -mno-epsilon @opindex mepsilon @opindex mno-epsilon Generate floating-point comparison instructions that compare with respect to the @code{rE} epsilon register. @item -mabi=mmixware @itemx -mabi=gnu @opindex mabi-mmixware @opindex mabi=gnu Generate code that passes function parameters and return values that (in the called function) are seen as registers @code{$0} and up, as opposed to the GNU ABI which uses global registers @code{$231} and up. @item -mzero-extend @itemx -mno-zero-extend @opindex mzero-extend @opindex mno-zero-extend When reading data from memory in sizes shorter than 64 bits, use (do not use) zero-extending load instructions by default, rather than sign-extending ones. @item -mknuthdiv @itemx -mno-knuthdiv @opindex mknuthdiv @opindex mno-knuthdiv Make the result of a division yielding a remainder have the same sign as the divisor. With the default, @option{-mno-knuthdiv}, the sign of the remainder follows the sign of the dividend. Both methods are arithmetically valid, the latter being almost exclusively used. @item -mtoplevel-symbols @itemx -mno-toplevel-symbols @opindex mtoplevel-symbols @opindex mno-toplevel-symbols Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly code can be used with the @code{PREFIX} assembly directive. @item -melf @opindex melf Generate an executable in the ELF format, rather than the default @samp{mmo} format used by the @command{mmix} simulator. @item -mbranch-predict @itemx -mno-branch-predict @opindex mbranch-predict @opindex mno-branch-predict Use (do not use) the probable-branch instructions, when static branch prediction indicates a probable branch. @item -mbase-addresses @itemx -mno-base-addresses @opindex mbase-addresses @opindex mno-base-addresses Generate (do not generate) code that uses @emph{base addresses}. Using a base address automatically generates a request (handled by the assembler and the linker) for a constant to be set up in a global register. The register is used for one or more base address requests within the range 0 to 255 from the value held in the register. The generally leads to short and fast code, but the number of different data items that can be addressed is limited. This means that a program that uses lots of static data may require @option{-mno-base-addresses}. @end table @node PDP-11 Options @subsection PDP-11 Options @cindex PDP-11 Options These options are defined for the PDP-11: @table @gcctabopt @item -mfpu @opindex mfpu Use hardware FPP floating point. This is the default. (FIS floating point on the PDP-11/40 is not supported.) @item -msoft-float @opindex msoft-float Do not use hardware floating point. @item -mac0 @opindex mac0 Return floating-point results in ac0 (fr0 in Unix assembler syntax). @item -mno-ac0 @opindex mno-ac0 Return floating-point results in memory. This is the default. @item -m40 @opindex m40 Generate code for a PDP-11/40. @item -m45 @opindex m45 Generate code for a PDP-11/45. This is the default. @item -m10 @opindex m10 Generate code for a PDP-11/10. @item -mbcopy-builtin @opindex bcopy-builtin Use inline @code{movstrhi} patterns for copying memory. This is the default. @item -mbcopy @opindex mbcopy Do not use inline @code{movstrhi} patterns for copying memory. @item -mint16 @itemx -mno-int32 @opindex mint16 @opindex mno-int32 Use 16-bit @code{int}. This is the default. @item -mint32 @itemx -mno-int16 @opindex mint32 @opindex mno-int16 Use 32-bit @code{int}. @item -mfloat64 @itemx -mno-float32 @opindex mfloat64 @opindex mno-float32 Use 64-bit @code{float}. This is the default. @item -mfloat32 @item -mno-float64 @opindex mfloat32 @opindex mno-float64 Use 32-bit @code{float}. @item -mabshi @opindex mabshi Use @code{abshi2} pattern. This is the default. @item -mno-abshi @opindex mno-abshi Do not use @code{abshi2} pattern. @item -mbranch-expensive @opindex mbranch-expensive Pretend that branches are expensive. This is for experimenting with code generation only. @item -mbranch-cheap @opindex mbranch-cheap Do not pretend that branches are expensive. This is the default. @item -msplit @opindex msplit Generate code for a system with split I&D. @item -mno-split @opindex mno-split Generate code for a system without split I&D. This is the default. @item -munix-asm @opindex munix-asm Use Unix assembler syntax. This is the default when configured for @samp{pdp11-*-bsd}. @item -mdec-asm @opindex mdec-asm Use DEC assembler syntax. This is the default when configured for any PDP-11 target other than @samp{pdp11-*-bsd}. @end table @node Xstormy16 Options @subsection Xstormy16 Options @cindex Xstormy16 Options These options are defined for Xstormy16: @table @gcctabopt @item -msim @opindex msim Choose startup files and linker script suitable for the simulator. @end table @node Xtensa Options @subsection Xtensa Options @cindex Xtensa Options The Xtensa architecture is designed to support many different configurations. The compiler's default options can be set to match a particular Xtensa configuration by copying a configuration file into the GCC sources when building GCC@. The options below may be used to override the default options. @table @gcctabopt @item -mbig-endian @itemx -mlittle-endian @opindex mbig-endian @opindex mlittle-endian Specify big-endian or little-endian byte ordering for the target Xtensa processor. @item -mdensity @itemx -mno-density @opindex mdensity @opindex mno-density Enable or disable use of the optional Xtensa code density instructions. @item -mmac16 @itemx -mno-mac16 @opindex mmac16 @opindex mno-mac16 Enable or disable use of the Xtensa MAC16 option. When enabled, GCC will generate MAC16 instructions from standard C code, with the limitation that it will use neither the MR register file nor any instruction that operates on the MR registers. When this option is disabled, GCC will translate 16-bit multiply/accumulate operations to a combination of core instructions and library calls, depending on whether any other multiplier options are enabled. @item -mmul16 @itemx -mno-mul16 @opindex mmul16 @opindex mno-mul16 Enable or disable use of the 16-bit integer multiplier option. When enabled, the compiler will generate 16-bit multiply instructions for multiplications of 16 bits or smaller in standard C code. When this option is disabled, the compiler will either use 32-bit multiply or MAC16 instructions if they are available or generate library calls to perform the multiply operations using shifts and adds. @item -mmul32 @itemx -mno-mul32 @opindex mmul32 @opindex mno-mul32 Enable or disable use of the 32-bit integer multiplier option. When enabled, the compiler will generate 32-bit multiply instructions for multiplications of 32 bits or smaller in standard C code. When this option is disabled, the compiler will generate library calls to perform the multiply operations using either shifts and adds or 16-bit multiply instructions if they are available. @item -mnsa @itemx -mno-nsa @opindex mnsa @opindex mno-nsa Enable or disable use of the optional normalization shift amount (@code{NSA}) instructions to implement the built-in @code{ffs} function. @item -mminmax @itemx -mno-minmax @opindex mminmax @opindex mno-minmax Enable or disable use of the optional minimum and maximum value instructions. @item -msext @itemx -mno-sext @opindex msext @opindex mno-sext Enable or disable use of the optional sign extend (@code{SEXT}) instruction. @item -mbooleans @itemx -mno-booleans @opindex mbooleans @opindex mno-booleans Enable or disable support for the boolean register file used by Xtensa coprocessors. This is not typically useful by itself but may be required for other options that make use of the boolean registers (e.g., the floating-point option). @item -mhard-float @itemx -msoft-float @opindex mhard-float @opindex msoft-float Enable or disable use of the floating-point option. When enabled, GCC generates floating-point instructions for 32-bit @code{float} operations. When this option is disabled, GCC generates library calls to emulate 32-bit floating-point operations using integer instructions. Regardless of this option, 64-bit @code{double} operations are always emulated with calls to library functions. @item -mfused-madd @itemx -mno-fused-madd @opindex mfused-madd @opindex mno-fused-madd Enable or disable use of fused multiply/add and multiply/subtract instructions in the floating-point option. This has no effect if the floating-point option is not also enabled. Disabling fused multiply/add and multiply/subtract instructions forces the compiler to use separate instructions for the multiply and add/subtract operations. This may be desirable in some cases where strict IEEE 754-compliant results are required: the fused multiply add/subtract instructions do not round the intermediate result, thereby producing results with @emph{more} bits of precision than specified by the IEEE standard. Disabling fused multiply add/subtract instructions also ensures that the program output is not sensitive to the compiler's ability to combine multiply and add/subtract operations. @item -mserialize-volatile @itemx -mno-serialize-volatile @opindex mserialize-volatile @opindex mno-serialize-volatile When this option is enabled, GCC inserts @code{MEMW} instructions before @code{volatile} memory references to guarantee sequential consistency. The default is @option{-mserialize-volatile}. Use @option{-mno-serialize-volatile} to omit the @code{MEMW} instructions. @item -mtext-section-literals @itemx -mno-text-section-literals @opindex mtext-section-literals @opindex mno-text-section-literals Control the treatment of literal pools. The default is @option{-mno-text-section-literals}, which places literals in a separate section in the output file. This allows the literal pool to be placed in a data RAM/ROM, and it also allows the linker to combine literal pools from separate object files to remove redundant literals and improve code size. With @option{-mtext-section-literals}, the literals are interspersed in the text section in order to keep them as close as possible to their references. This may be necessary for large assembly files. @item -mtarget-align @itemx -mno-target-align @opindex mtarget-align @opindex mno-target-align When this option is enabled, GCC instructs the assembler to automatically align instructions to reduce branch penalties at the expense of some code density. The assembler attempts to widen density instructions to align branch targets and the instructions following call instructions. If there are not enough preceding safe density instructions to align a target, no widening will be performed. The default is @option{-mtarget-align}. These options do not affect the treatment of auto-aligned instructions like @code{LOOP}, which the assembler will always align, either by widening density instructions or by inserting no-op instructions. @item -mlongcalls @itemx -mno-longcalls @opindex mlongcalls @opindex mno-longcalls When this option is enabled, GCC instructs the assembler to translate direct calls to indirect calls unless it can determine that the target of a direct call is in the range allowed by the call instruction. This translation typically occurs for calls to functions in other source files. Specifically, the assembler translates a direct @code{CALL} instruction into an @code{L32R} followed by a @code{CALLX} instruction. The default is @option{-mno-longcalls}. This option should be used in programs where the call target can potentially be out of range. This option is implemented in the assembler, not the compiler, so the assembly code generated by GCC will still show direct call instructions---look at the disassembled object code to see the actual instructions. Note that the assembler will use an indirect call for every cross-file call, not just those that really will be out of range. @end table @c APPLE LOCAL prune man page @end ignore @node Code Gen Options @section Options for Code Generation Conventions @cindex code generation conventions @cindex options, code generation @cindex run-time options These machine-independent options control the interface conventions used in code generation. Most of them have both positive and negative forms; the negative form of @option{-ffoo} would be @option{-fno-foo}. In the table below, only one of the forms is listed---the one which is not the default. You can figure out the other form by either removing @samp{no-} or adding it. @table @gcctabopt @item -fexceptions @opindex fexceptions Enable exception handling. Generates extra code needed to propagate exceptions. For some targets, this implies GCC will generate frame unwind information for all functions, which can produce significant data size overhead, although it does not affect execution. If you do not specify this option, GCC will enable it by default for languages like C++ which normally require exception handling, and disable it for languages like C that do not normally require it. However, you may need to enable this option when compiling C code that needs to interoperate properly with exception handlers written in C++. You may also wish to disable this option if you are compiling older C++ programs that don't use exception handling. @item -fnon-call-exceptions @opindex fnon-call-exceptions Generate code that allows trapping instructions to throw exceptions. Note that this requires platform-specific runtime support that does not exist everywhere. Moreover, it only allows @emph{trapping} instructions to throw exceptions, i.e.@: memory references or floating point instructions. It does not allow exceptions to be thrown from arbitrary signal handlers such as @code{SIGALRM}. @item -funwind-tables @opindex funwind-tables Similar to @option{-fexceptions}, except that it will just generate any needed static data, but will not affect the generated code in any other way. You will normally not enable this option; instead, a language processor that needs this handling would enable it on your behalf. @item -fasynchronous-unwind-tables @opindex funwind-tables Generate unwind table in dwarf2 format, if supported by target machine. The table is exact at each instruction boundary, so it can be used for stack unwinding from asynchronous events (such as debugger or garbage collector). @item -fpcc-struct-return @opindex fpcc-struct-return Return ``short'' @code{struct} and @code{union} values in memory like longer ones, rather than in registers. This convention is less efficient, but it has the advantage of allowing intercallability between GCC-compiled files and files compiled with other compilers. The precise convention for returning structures in memory depends on the target configuration macros. Short structures and unions are those whose size and alignment match that of some integer type. @item -freg-struct-return @opindex freg-struct-return Return @code{struct} and @code{union} values in registers when possible. This is more efficient for small structures than @option{-fpcc-struct-return}. If you specify neither @option{-fpcc-struct-return} nor @option{-freg-struct-return}, GCC defaults to whichever convention is standard for the target. If there is no standard convention, GCC defaults to @option{-fpcc-struct-return}, except on targets where GCC is the principal compiler. In those cases, we can choose the standard, and we chose the more efficient register return alternative. @item -fshort-enums @opindex fshort-enums Allocate to an @code{enum} type only as many bytes as it needs for the declared range of possible values. Specifically, the @code{enum} type will be equivalent to the smallest integer type which has enough room. @item -fshort-double @opindex fshort-double Use the same size for @code{double} as for @code{float}. @item -fshared-data @opindex fshared-data Requests that the data and non-@code{const} variables of this compilation be shared data rather than private data. The distinction makes sense only on certain operating systems, where shared data is shared between processes running the same program, while private data exists in one copy per process. @item -fno-common @opindex fno-common In C, allocate even uninitialized global variables in the data section of the object file, rather than generating them as common blocks. This has the effect that if the same variable is declared (without @code{extern}) in two different compilations, you will get an error when you link them. The only reason this might be useful is if you wish to verify that the program will work on other systems which always work this way. @item -fno-ident @opindex fno-ident Ignore the @samp{#ident} directive. @item -fno-gnu-linker @opindex fno-gnu-linker Do not output global initializations (such as C++ constructors and destructors) in the form used by the GNU linker (on systems where the GNU linker is the standard method of handling them). Use this option when you want to use a non-GNU linker, which also requires using the @command{collect2} program to make sure the system linker includes constructors and destructors. (@command{collect2} is included in the GCC distribution.) For systems which @emph{must} use @command{collect2}, the compiler driver @command{gcc} is configured to do this automatically. @item -finhibit-size-directive @opindex finhibit-size-directive Don't output a @code{.size} assembler directive, or anything else that would cause trouble if the function is split in the middle, and the two halves are placed at locations far apart in memory. This option is used when compiling @file{crtstuff.c}; you should not need to use it for anything else. @item -fverbose-asm @opindex fverbose-asm Put extra commentary information in the generated assembly code to make it more readable. This option is generally only of use to those who actually need to read the generated assembly code (perhaps while debugging the compiler itself). @option{-fno-verbose-asm}, the default, causes the extra information to be omitted and is useful when comparing two assembler files. @item -fvolatile @opindex fvolatile Consider all memory references through pointers to be volatile. @item -fvolatile-global @opindex fvolatile-global Consider all memory references to extern and global data items to be volatile. GCC does not consider static data items to be volatile because of this switch. @item -fvolatile-static @opindex fvolatile-static Consider all memory references to static data to be volatile. @item -fpic @opindex fpic @cindex global offset table @cindex PIC Generate position-independent code (PIC) suitable for use in a shared library, if supported for the target machine. Such code accesses all constant addresses through a global offset table (GOT)@. The dynamic loader resolves the GOT entries when the program starts (the dynamic loader is not part of GCC; it is part of the operating system). If the GOT size for the linked executable exceeds a machine-specific maximum size, you get an error message from the linker indicating that @option{-fpic} does not work; in that case, recompile with @option{-fPIC} instead. (These maximums are 16k on the m88k, 8k on the Sparc, and 32k on the m68k and RS/6000. The 386 has no such limit.) Position-independent code requires special support, and therefore works only on certain machines. For the 386, GCC supports PIC for System V but not for the Sun 386i. Code generated for the IBM RS/6000 is always position-independent. @c APPLE LOCAL manual @option{-fpic} is not supported on Mac OS X. @item -fPIC @opindex fPIC If supported for the target machine, emit position-independent code, suitable for dynamic linking and avoiding any limit on the size of the global offset table. This option makes a difference on the m68k, m88k, and the Sparc. Position-independent code requires special support, and therefore works only on certain machines. @c APPLE LOCAL manual @option{-fPIC} is the default on Darwin and Mac OS X. @item -ffixed-@var{reg} @opindex ffixed Treat the register named @var{reg} as a fixed register; generated code should never refer to it (except perhaps as a stack pointer, frame pointer or in some other fixed role). @var{reg} must be the name of a register. The register names accepted are machine-specific and are defined in the @code{REGISTER_NAMES} macro in the machine description macro file. This flag does not have a negative form, because it specifies a three-way choice. @item -fcall-used-@var{reg} @opindex fcall-used Treat the register named @var{reg} as an allocable register that is clobbered by function calls. It may be allocated for temporaries or variables that do not live across a call. Functions compiled this way will not save and restore the register @var{reg}. It is an error to used this flag with the frame pointer or stack pointer. Use of this flag for other registers that have fixed pervasive roles in the machine's execution model will produce disastrous results. This flag does not have a negative form, because it specifies a three-way choice. @item -fcall-saved-@var{reg} @opindex fcall-saved Treat the register named @var{reg} as an allocable register saved by functions. It may be allocated even for temporaries or variables that live across a call. Functions compiled this way will save and restore the register @var{reg} if they use it. It is an error to used this flag with the frame pointer or stack pointer. Use of this flag for other registers that have fixed pervasive roles in the machine's execution model will produce disastrous results. A different sort of disaster will result from the use of this flag for a register in which function values may be returned. This flag does not have a negative form, because it specifies a three-way choice. @item -fpack-struct @opindex fpack-struct Pack all structure members together without holes. Usually you would not want to use this option, since it makes the code suboptimal, and the offsets of structure members won't agree with system libraries. @item -finstrument-functions @opindex finstrument-functions Generate instrumentation calls for entry and exit to functions. Just after function entry and just before function exit, the following profiling functions will be called with the address of the current function and its call site. (On some platforms, @code{__builtin_return_address} does not work beyond the current function, so the call site information may not be available to the profiling functions otherwise.) @example void __cyg_profile_func_enter (void *this_fn, void *call_site); void __cyg_profile_func_exit (void *this_fn, void *call_site); @end example The first argument is the address of the start of the current function, which may be looked up exactly in the symbol table. This instrumentation is also done for functions expanded inline in other functions. The profiling calls will indicate where, conceptually, the inline function is entered and exited. This means that addressable versions of such functions must be available. If all your uses of a function are expanded inline, this may mean an additional expansion of code size. If you use @samp{extern inline} in your C code, an addressable version of such functions must be provided. (This is normally the case anyways, but if you get lucky and the optimizer always expands the functions inline, you might have gotten away without providing static copies.) A function may be given the attribute @code{no_instrument_function}, in which case this instrumentation will not be done. This can be used, for example, for the profiling functions listed above, high-priority interrupt routines, and any functions from which the profiling functions cannot safely be called (perhaps signal handlers, if the profiling routines generate output or allocate memory). @item -fstack-check @opindex fstack-check Generate code to verify that you do not go beyond the boundary of the stack. You should specify this flag if you are running in an environment with multiple threads, but only rarely need to specify it in a single-threaded environment since stack overflow is automatically detected on nearly all systems if there is only one stack. Note that this switch does not actually cause checking to be done; the operating system must do that. The switch causes generation of code to ensure that the operating system sees the stack being extended. @item -fstack-limit-register=@var{reg} @itemx -fstack-limit-symbol=@var{sym} @itemx -fno-stack-limit @opindex fstack-limit-register @opindex fstack-limit-symbol @opindex fno-stack-limit Generate code to ensure that the stack does not grow beyond a certain value, either the value of a register or the address of a symbol. If the stack would grow beyond the value, a signal is raised. For most targets, the signal is raised before the stack overruns the boundary, so it is possible to catch the signal without taking special precautions. For instance, if the stack starts at absolute address @samp{0x80000000} and grows downwards, you can use the flags @option{-fstack-limit-symbol=__stack_limit} and @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit of 128KB@. Note that this may only work with the GNU linker. @cindex aliasing of parameters @cindex parameters, aliased @item -fargument-alias @itemx -fargument-noalias @itemx -fargument-noalias-global @opindex fargument-alias @opindex fargument-noalias @opindex fargument-noalias-global Specify the possible relationships among parameters and between parameters and global data. @option{-fargument-alias} specifies that arguments (parameters) may alias each other and may alias global storage.@* @option{-fargument-noalias} specifies that arguments do not alias each other, but may alias global storage.@* @option{-fargument-noalias-global} specifies that arguments do not alias each other and do not alias global storage. Each language will automatically use whatever option is required by the language standard. You should not need to use these options yourself. @item -fleading-underscore @opindex fleading-underscore This option and its counterpart, @option{-fno-leading-underscore}, forcibly change the way C symbols are represented in the object file. One use is to help link with legacy assembly code. Be warned that you should know what you are doing when invoking this option, and that not all targets provide complete support for it. @end table @c man end @node Environment Variables @section Environment Variables Affecting GCC @cindex environment variables @c man begin ENVIRONMENT This section describes several environment variables that affect how GCC operates. Some of them work by specifying directories or prefixes to use when searching for various kinds of files. Some are used to specify other aspects of the compilation environment. Note that you can also specify places to search using options such as @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These take precedence over places specified using environment variables, which in turn take precedence over those specified by the configuration of GCC@. @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint, GNU Compiler Collection (GCC) Internals}. @table @env @item LANG @itemx LC_CTYPE @c @itemx LC_COLLATE @itemx LC_MESSAGES @c @itemx LC_MONETARY @c @itemx LC_NUMERIC @c @itemx LC_TIME @itemx LC_ALL @findex LANG @findex LC_CTYPE @c @findex LC_COLLATE @findex LC_MESSAGES @c @findex LC_MONETARY @c @findex LC_NUMERIC @c @findex LC_TIME @findex LC_ALL @cindex locale These environment variables control the way that GCC uses localization information that allow GCC to work with different national conventions. GCC inspects the locale categories @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do so. These locale categories can be set to any value supported by your installation. A typical value is @samp{en_UK} for English in the United Kingdom. The @env{LC_CTYPE} environment variable specifies character classification. GCC uses it to determine the character boundaries in a string; this is needed for some multibyte encodings that contain quote and escape characters that would otherwise be interpreted as a string end or escape. The @env{LC_MESSAGES} environment variable specifies the language to use in diagnostic messages. If the @env{LC_ALL} environment variable is set, it overrides the value of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE} and @env{LC_MESSAGES} default to the value of the @env{LANG} environment variable. If none of these variables are set, GCC defaults to traditional C English behavior. @item TMPDIR @findex TMPDIR If @env{TMPDIR} is set, it specifies the directory to use for temporary files. GCC uses temporary files to hold the output of one stage of compilation which is to be used as input to the next stage: for example, the output of the preprocessor, which is the input to the compiler proper. @item GCC_EXEC_PREFIX @findex GCC_EXEC_PREFIX If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the names of the subprograms executed by the compiler. No slash is added when this prefix is combined with the name of a subprogram, but you can specify a prefix that ends with a slash if you wish. If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out an appropriate prefix to use based on the pathname it was invoked with. If GCC cannot find the subprogram using the specified prefix, it tries looking in the usual places for the subprogram. The default value of @env{GCC_EXEC_PREFIX} is @file{@var{prefix}/lib/gcc-lib/} where @var{prefix} is the value of @code{prefix} when you ran the @file{configure} script. Other prefixes specified with @option{-B} take precedence over this prefix. This prefix is also used for finding files such as @file{crt0.o} that are used for linking. In addition, the prefix is used in an unusual way in finding the directories to search for header files. For each of the standard directories whose name normally begins with @samp{/usr/local/lib/gcc-lib} (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries replacing that beginning with the specified prefix to produce an alternate directory name. Thus, with @option{-Bfoo/}, GCC will search @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}. These alternate directories are searched first; the standard directories come next. @item COMPILER_PATH @findex COMPILER_PATH The value of @env{COMPILER_PATH} is a colon-separated list of directories, much like @env{PATH}. GCC tries the directories thus specified when searching for subprograms, if it can't find the subprograms using @env{GCC_EXEC_PREFIX}. @item LIBRARY_PATH @findex LIBRARY_PATH The value of @env{LIBRARY_PATH} is a colon-separated list of directories, much like @env{PATH}. When configured as a native compiler, GCC tries the directories thus specified when searching for special linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking using GCC also uses these directories when searching for ordinary libraries for the @option{-l} option (but directories specified with @option{-L} come first). @item LANG @findex LANG @cindex locale definition This variable is used to pass locale information to the compiler. One way in which this information is used is to determine the character set to be used when character literals, string literals and comments are parsed in C and C++. When the compiler is configured to allow multibyte characters, the following values for @env{LANG} are recognized: @table @samp @item C-JIS Recognize JIS characters. @item C-SJIS Recognize SJIS characters. @item C-EUCJP Recognize EUCJP characters. @end table If @env{LANG} is not defined, or if it has some other value, then the compiler will use mblen and mbtowc as defined by the default locale to recognize and translate multibyte characters. @end table @noindent Some additional environments variables affect the behavior of the preprocessor. @include cppenv.texi @c man end @node Running Protoize @section Running Protoize The program @code{protoize} is an optional part of GCC@. You can use it to add prototypes to a program, thus converting the program to ISO C in one respect. The companion program @code{unprotoize} does the reverse: it removes argument types from any prototypes that are found. When you run these programs, you must specify a set of source files as command line arguments. The conversion programs start out by compiling these files to see what functions they define. The information gathered about a file @var{foo} is saved in a file named @file{@var{foo}.X}. After scanning comes actual conversion. The specified files are all eligible to be converted; any files they include (whether sources or just headers) are eligible as well. But not all the eligible files are converted. By default, @code{protoize} and @code{unprotoize} convert only source and header files in the current directory. You can specify additional directories whose files should be converted with the @option{-d @var{directory}} option. You can also specify particular files to exclude with the @option{-x @var{file}} option. A file is converted if it is eligible, its directory name matches one of the specified directory names, and its name within the directory has not been excluded. Basic conversion with @code{protoize} consists of rewriting most function definitions and function declarations to specify the types of the arguments. The only ones not rewritten are those for varargs functions. @code{protoize} optionally inserts prototype declarations at the beginning of the source file, to make them available for any calls that precede the function's definition. Or it can insert prototype declarations with block scope in the blocks where undeclared functions are called. Basic conversion with @code{unprotoize} consists of rewriting most function declarations to remove any argument types, and rewriting function definitions to the old-style pre-ISO form. Both conversion programs print a warning for any function declaration or definition that they can't convert. You can suppress these warnings with @option{-q}. The output from @code{protoize} or @code{unprotoize} replaces the original source file. The original file is renamed to a name ending with @samp{.save} (for DOS, the saved filename ends in @samp{.sav} without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav} for DOS) file already exists, then the source file is simply discarded. @code{protoize} and @code{unprotoize} both depend on GCC itself to scan the program and collect information about the functions it uses. So neither of these programs will work until GCC is installed. Here is a table of the options you can use with @code{protoize} and @code{unprotoize}. Each option works with both programs unless otherwise stated. @table @code @item -B @var{directory} Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the usual directory (normally @file{/usr/local/lib}). This file contains prototype information about standard system functions. This option applies only to @code{protoize}. @item -c @var{compilation-options} Use @var{compilation-options} as the options when running @code{gcc} to produce the @samp{.X} files. The special option @option{-aux-info} is always passed in addition, to tell @code{gcc} to write a @samp{.X} file. Note that the compilation options must be given as a single argument to @code{protoize} or @code{unprotoize}. If you want to specify several @code{gcc} options, you must quote the entire set of compilation options to make them a single word in the shell. There are certain @code{gcc} arguments that you cannot use, because they would produce the wrong kind of output. These include @option{-g}, @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in the @var{compilation-options}, they are ignored. @item -C Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file systems) instead of @samp{.c}. This is convenient if you are converting a C program to C++. This option applies only to @code{protoize}. @item -g Add explicit global declarations. This means inserting explicit declarations at the beginning of each source file for each function that is called in the file and was not declared. These declarations precede the first function definition that contains a call to an undeclared function. This option applies only to @code{protoize}. @item -i @var{string} Indent old-style parameter declarations with the string @var{string}. This option applies only to @code{protoize}. @code{unprotoize} converts prototyped function definitions to old-style function definitions, where the arguments are declared between the argument list and the initial @samp{@{}. By default, @code{unprotoize} uses five spaces as the indentation. If you want to indent with just one space instead, use @option{-i " "}. @item -k Keep the @samp{.X} files. Normally, they are deleted after conversion is finished. @item -l Add explicit local declarations. @code{protoize} with @option{-l} inserts a prototype declaration for each function in each block which calls the function without any declaration. This option applies only to @code{protoize}. @item -n Make no real changes. This mode just prints information about the conversions that would have been done without @option{-n}. @item -N Make no @samp{.save} files. The original files are simply deleted. Use this option with caution. @item -p @var{program} Use the program @var{program} as the compiler. Normally, the name @file{gcc} is used. @item -q Work quietly. Most warnings are suppressed. @item -v Print the version number, just like @option{-v} for @code{gcc}. @end table If you need special compiler options to compile one of your program's source files, then you should generate that file's @samp{.X} file specially, by running @code{gcc} on that source file with the appropriate options and the option @option{-aux-info}. Then run @code{protoize} on the entire set of files. @code{protoize} will use the existing @samp{.X} file because it is newer than the source file. For example: @example gcc -Dfoo=bar file1.c -aux-info file1.X protoize *.c @end example @noindent You need to include the special files along with the rest in the @code{protoize} command, even though their @samp{.X} files already exist, because otherwise they won't get converted. @xref{Protoize Caveats}, for more information on how to use @code{protoize} successfully.