1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002 Free Software Foundation, Inc.
3 @c This is part of the GCC manual.
4 @c For copying conditions, see the file gcc.texi.
8 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997,
9 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
11 Permission is granted to copy, distribute and/or modify this document
12 under the terms of the GNU Free Documentation License, Version 1.1 or
13 any later version published by the Free Software Foundation; with the
14 Invariant Sections being ``GNU General Public License'' and ``Funding
15 Free Software'', the Front-Cover texts being (a) (see below), and with
16 the Back-Cover Texts being (b) (see below). A copy of the license is
17 included in the gfdl(7) man page.
19 (a) The FSF's Front-Cover Text is:
23 (b) The FSF's Back-Cover Text is:
25 You have freedom to copy and modify this GNU Manual, like GNU
26 software. Copies published by the Free Software Foundation raise
27 funds for GNU development.
29 @c Set file name and title for the man page.
31 @settitle GNU project C and C++ compiler
33 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
34 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
35 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
36 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
37 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
38 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
39 [@option{-o} @var{outfile}] @var{infile}@dots{}
41 Only the most useful options are listed here; see below for the
42 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
45 gpl(7), gfdl(7), fsf-funding(7),
46 cpp(1), gcov(1), g77(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
47 and the Info entries for @file{gcc}, @file{cpp}, @file{g77}, @file{as},
48 @file{ld}, @file{binutils} and @file{gdb}.
51 For instructions on reporting bugs, see
52 @w{@uref{http://gcc.gnu.org/bugs.html}}. Use of the @command{gccbug}
53 script to report bugs is recommended.
56 See the Info entry for @command{gcc}, or
57 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
58 for contributors to GCC@.
63 @chapter GCC Command Options
64 @cindex GCC command options
65 @cindex command options
66 @cindex options, GCC command
68 @c man begin DESCRIPTION
70 When you invoke GCC, it normally does preprocessing, compilation,
71 assembly and linking. The ``overall options'' allow you to stop this
72 process at an intermediate stage. For example, the @option{-c} option
73 says not to run the linker. Then the output consists of object files
74 output by the assembler.
76 Other options are passed on to one stage of processing. Some options
77 control the preprocessor and others the compiler itself. Yet other
78 options control the assembler and linker; most of these are not
79 documented here, since you rarely need to use any of them.
81 @cindex C compilation options
82 Most of the command line options that you can use with GCC are useful
83 for C programs; when an option is only useful with another language
84 (usually C++), the explanation says so explicitly. If the description
85 for a particular option does not mention a source language, you can use
86 that option with all supported languages.
88 @cindex C++ compilation options
89 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
90 options for compiling C++ programs.
92 @cindex grouping options
93 @cindex options, grouping
94 The @command{gcc} program accepts options and file names as operands. Many
95 options have multi-letter names; therefore multiple single-letter options
96 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
99 @cindex order of options
100 @cindex options, order
101 You can mix options and other arguments. For the most part, the order
102 you use doesn't matter. Order does matter when you use several options
103 of the same kind; for example, if you specify @option{-L} more than once,
104 the directories are searched in the order specified.
106 Many options have long names starting with @samp{-f} or with
107 @samp{-W}---for example, @option{-fforce-mem},
108 @option{-fstrength-reduce}, @option{-Wformat} and so on. Most of
109 these have both positive and negative forms; the negative form of
110 @option{-ffoo} would be @option{-fno-foo}. This manual documents
111 only one of these two forms, whichever one is not the default.
115 @xref{Option Index}, for an index to GCC's options.
118 * Option Summary:: Brief list of all options, without explanations.
119 * Overall Options:: Controlling the kind of output:
120 an executable, object files, assembler files,
121 or preprocessed source.
122 * Invoking G++:: Compiling C++ programs.
123 * C Dialect Options:: Controlling the variant of C language compiled.
124 * C++ Dialect Options:: Variations on C++.
125 * Objective-C Dialect Options:: Variations on Objective-C.
126 * Language Independent Options:: Controlling how diagnostics should be
128 * Warning Options:: How picky should the compiler be?
129 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
130 * Optimize Options:: How much optimization?
131 * Preprocessor Options:: Controlling header files and macro definitions.
132 Also, getting dependency information for Make.
133 * Assembler Options:: Passing options to the assembler.
134 * Link Options:: Specifying libraries and so on.
135 * Directory Options:: Where to find header files and libraries.
136 Where to find the compiler executable files.
137 * Spec Files:: How to pass switches to sub-processes.
138 * Target Options:: Running a cross-compiler, or an old version of GCC.
139 * Submodel Options:: Specifying minor hardware or convention variations,
140 such as 68010 vs 68020.
141 * Code Gen Options:: Specifying conventions for function calls, data layout
143 * Environment Variables:: Env vars that affect GCC.
144 * Running Protoize:: Automatically adding or removing function prototypes.
150 @section Option Summary
152 Here is a summary of all the options, grouped by type. Explanations are
153 in the following sections.
156 @item Overall Options
157 @xref{Overall Options,,Options Controlling the Kind of Output}.
159 -c -S -E -o @var{file} -pipe -pass-exit-codes -x @var{language} @gol
160 -v -### --target-help --help}
162 @item C Language Options
163 @xref{C Dialect Options,,Options Controlling C Dialect}.
165 -ansi -std=@var{standard} -aux-info @var{filename} @gol
166 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
167 -fhosted -ffreestanding -fms-extensions @gol
168 -trigraphs -traditional -traditional-cpp @gol
169 -fallow-single-precision -fcond-mismatch @gol
170 -fsigned-bitfields -fsigned-char @gol
171 -funsigned-bitfields -funsigned-char @gol
174 @item C++ Language Options
175 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
177 -fabi-version=@var{n} -fno-access-control -fcheck-new @gol
178 -fconserve-space -fno-const-strings -fdollars-in-identifiers @gol
179 -fno-elide-constructors @gol
180 -fno-enforce-eh-specs -fexternal-templates @gol
181 -falt-external-templates @gol
182 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
183 -fno-implicit-templates @gol
184 -fno-implicit-inline-templates @gol
185 -fno-implement-inlines -fms-extensions @gol
186 -fno-nonansi-builtins -fno-operator-names @gol
187 -fno-optional-diags -fpermissive @gol
188 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
189 -fuse-cxa-atexit -fvtable-gc -fno-weak -nostdinc++ @gol
190 -fno-default-inline -Wabi -Wctor-dtor-privacy @gol
191 -Wnon-virtual-dtor -Wreorder @gol
192 -Weffc++ -Wno-deprecated @gol
193 -Wno-non-template-friend -Wold-style-cast @gol
194 -Woverloaded-virtual -Wno-pmf-conversions @gol
195 -Wsign-promo -Wsynth}
197 @item Objective-C Language Options
198 @xref{Objective-C Dialect Options,,Options Controlling Objective-C Dialect}.
200 -fconstant-string-class=@var{class-name} @gol
201 -fgnu-runtime -fnext-runtime -gen-decls @gol
202 -Wno-protocol -Wselector -Wundeclared-selector}
204 @item Language Independent Options
205 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
207 -fmessage-length=@var{n} @gol
208 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}}
210 @item Warning Options
211 @xref{Warning Options,,Options to Request or Suppress Warnings}.
213 -fsyntax-only -pedantic -pedantic-errors @gol
214 -w -W -Wall -Waggregate-return @gol
215 -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
216 -Wconversion -Wno-deprecated-declarations @gol
217 -Wdisabled-optimization -Wno-div-by-zero -Werror @gol
218 -Wfloat-equal -Wformat -Wformat=2 @gol
219 -Wformat-nonliteral -Wformat-security @gol
220 -Wimplicit -Wimplicit-int @gol
221 -Wimplicit-function-declaration @gol
222 -Werror-implicit-function-declaration @gol
223 -Wimport -Winline -Wno-endif-labels @gol
224 -Wlarger-than-@var{len} -Wlong-long @gol
225 -Wmain -Wmissing-braces -Wmissing-declarations @gol
226 -Wmissing-format-attribute -Wmissing-noreturn @gol
227 -Wno-multichar -Wno-format-extra-args -Wno-format-y2k @gol
228 -Wno-import -Wnonnull -Wpacked -Wpadded @gol
229 -Wparentheses -Wpointer-arith -Wredundant-decls @gol
230 -Wreturn-type -Wsequence-point -Wshadow @gol
231 -Wsign-compare -Wswitch -Wswitch-default -Wswitch-enum @gol
232 -Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized @gol
233 -Wunknown-pragmas -Wunreachable-code @gol
234 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
235 -Wunused-value -Wunused-variable -Wwrite-strings}
237 @item C-only Warning Options
239 -Wbad-function-cast -Wmissing-prototypes -Wnested-externs @gol
240 -Wstrict-prototypes -Wtraditional}
242 @item Debugging Options
243 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
245 -d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
246 -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
247 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
248 -fdump-tree-original@r{[}-@var{n}@r{]} -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
249 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
251 -fprofile-arcs -ftest-coverage -ftime-report @gol
252 -g -g@var{level} -gcoff -gdwarf -gdwarf-1 -gdwarf-1+ -gdwarf-2 @gol
253 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
254 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
255 -print-multi-directory -print-multi-lib @gol
256 -print-prog-name=@var{program} -print-search-dirs -Q @gol
259 @item Optimization Options
260 @xref{Optimize Options,,Options that Control Optimization}.
262 -falign-functions=@var{n} -falign-jumps=@var{n} @gol
263 -falign-labels=@var{n} -falign-loops=@var{n} @gol
264 -fbranch-probabilities -fcaller-saves -fcprop-registers @gol
265 -fcse-follow-jumps -fcse-skip-blocks -fdata-sections @gol
266 -fdelayed-branch -fdelete-null-pointer-checks @gol
267 -fexpensive-optimizations -ffast-math -ffloat-store @gol
268 -fforce-addr -fforce-mem -ffunction-sections @gol
269 -fgcse -fgcse-lm -fgcse-sm -floop-optimize -fcrossjumping @gol
270 -fif-conversion -fif-conversion2 @gol
271 -finline-functions -finline-limit=@var{n} -fkeep-inline-functions @gol
272 -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
273 -fmove-all-movables -fnew-ra -fno-default-inline @gol
275 -fno-function-cse -fno-guess-branch-probability @gol
276 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
277 -funsafe-math-optimizations -ffinite-math-only @gol
278 -fno-trapping-math -fno-zero-initialized-in-bss @gol
279 -fomit-frame-pointer -foptimize-register-move @gol
280 -foptimize-sibling-calls -fprefetch-loop-arrays @gol
281 -freduce-all-givs -fregmove -frename-registers @gol
282 -freorder-blocks -freorder-functions @gol
283 -frerun-cse-after-loop -frerun-loop-opt @gol
284 -fschedule-insns -fschedule-insns2 -fsignaling-nans @gol
285 -fsingle-precision-constant -fssa -fssa-ccp -fssa-dce @gol
286 -fstrength-reduce -fstrict-aliasing -ftracer -fthread-jumps @gol
287 -ftrapv -funroll-all-loops -funroll-loops @gol
288 --param @var{name}=@var{value}
289 -O -O0 -O1 -O2 -O3 -Os}
291 @item Preprocessor Options
292 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
294 -$ -A@var{question}=@var{answer} -A-@var{question}@r{[}=@var{answer}@r{]} @gol
295 -C -dD -dI -dM -dN @gol
296 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
297 -idirafter @var{dir} @gol
298 -include @var{file} -imacros @var{file} @gol
299 -iprefix @var{file} -iwithprefix @var{dir} @gol
300 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
301 -M -MM -MF -MG -MP -MQ -MT -nostdinc -P -remap @gol
302 -trigraphs -undef -U@var{macro} -Wp,@var{option}}
304 @item Assembler Option
305 @xref{Assembler Options,,Passing Options to the Assembler}.
310 @xref{Link Options,,Options for Linking}.
312 @var{object-file-name} -l@var{library} @gol
313 -nostartfiles -nodefaultlibs -nostdlib @gol
314 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
315 -Wl,@var{option} -Xlinker @var{option} @gol
318 @item Directory Options
319 @xref{Directory Options,,Options for Directory Search}.
321 -B@var{prefix} -I@var{dir} -I- -L@var{dir} -specs=@var{file}}
324 @c I wrote this xref this way to avoid overfull hbox. -- rms
325 @xref{Target Options}.
327 -V @var{version} -b @var{machine}}
329 @item Machine Dependent Options
330 @xref{Submodel Options,,Hardware Models and Configurations}.
332 @emph{M680x0 Options}
334 -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
335 -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol
336 -mfpa -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
337 -malign-int -mstrict-align}
339 @emph{M68hc1x Options}
341 -m6811 -m6812 -m68hc11 -m68hc12 @gol
342 -mauto-incdec -minmax -mlong-calls -mshort @gol
343 -msoft-reg-count=@var{count}}
351 -mcpu=@var{cpu-type} @gol
352 -mtune=@var{cpu-type} @gol
353 -mcmodel=@var{code-model} @gol
355 -mapp-regs -mbroken-saverestore -mcypress @gol
356 -mfaster-structs -mflat @gol
357 -mfpu -mhard-float -mhard-quad-float @gol
358 -mimpure-text -mlive-g0 -mno-app-regs @gol
359 -mno-faster-structs -mno-flat -mno-fpu @gol
360 -mno-impure-text -mno-stack-bias -mno-unaligned-doubles @gol
361 -msoft-float -msoft-quad-float -msparclite -mstack-bias @gol
362 -msupersparc -munaligned-doubles -mv8}
364 @emph{Convex Options}
366 -mc1 -mc2 -mc32 -mc34 -mc38 @gol
367 -margcount -mnoargcount @gol
368 -mlong32 -mlong64 @gol
369 -mvolatile-cache -mvolatile-nocache}
371 @emph{AMD29K Options}
373 -m29000 -m29050 -mbw -mnbw -mdw -mndw @gol
374 -mlarge -mnormal -msmall @gol
375 -mkernel-registers -mno-reuse-arg-regs @gol
376 -mno-stack-check -mno-storem-bug @gol
377 -mreuse-arg-regs -msoft-float -mstack-check @gol
378 -mstorem-bug -muser-registers}
382 -mapcs-frame -mno-apcs-frame @gol
383 -mapcs-26 -mapcs-32 @gol
384 -mapcs-stack-check -mno-apcs-stack-check @gol
385 -mapcs-float -mno-apcs-float @gol
386 -mapcs-reentrant -mno-apcs-reentrant @gol
387 -msched-prolog -mno-sched-prolog @gol
388 -mlittle-endian -mbig-endian -mwords-little-endian @gol
389 -malignment-traps -mno-alignment-traps @gol
390 -msoft-float -mhard-float -mfpe @gol
391 -mthumb-interwork -mno-thumb-interwork @gol
392 -mcpu=@var{name} -march=@var{name} -mfpe=@var{name} @gol
393 -mstructure-size-boundary=@var{n} @gol
394 -mbsd -mxopen -mno-symrename @gol
395 -mabort-on-noreturn @gol
396 -mlong-calls -mno-long-calls @gol
397 -msingle-pic-base -mno-single-pic-base @gol
398 -mpic-register=@var{reg} @gol
399 -mnop-fun-dllimport @gol
400 -mpoke-function-name @gol
402 -mtpcs-frame -mtpcs-leaf-frame @gol
403 -mcaller-super-interworking -mcallee-super-interworking }
405 @emph{MN10200 Options}
409 @emph{MN10300 Options}
411 -mmult-bug -mno-mult-bug @gol
412 -mam33 -mno-am33 @gol
415 @emph{M32R/D Options}
417 -m32rx -m32r -mcode-model=@var{model-type} -msdata=@var{sdata-type} @gol
422 -m88000 -m88100 -m88110 -mbig-pic @gol
423 -mcheck-zero-division -mhandle-large-shift @gol
424 -midentify-revision -mno-check-zero-division @gol
425 -mno-ocs-debug-info -mno-ocs-frame-position @gol
426 -mno-optimize-arg-area -mno-serialize-volatile @gol
427 -mno-underscores -mocs-debug-info @gol
428 -mocs-frame-position -moptimize-arg-area @gol
429 -mserialize-volatile -mshort-data-@var{num} -msvr3 @gol
430 -msvr4 -mtrap-large-shift -muse-div-instruction @gol
431 -mversion-03.00 -mwarn-passed-structs}
433 @emph{RS/6000 and PowerPC Options}
435 -mcpu=@var{cpu-type} @gol
436 -mtune=@var{cpu-type} @gol
437 -mpower -mno-power -mpower2 -mno-power2 @gol
438 -mpowerpc -mpowerpc64 -mno-powerpc @gol
439 -maltivec -mno-altivec @gol
440 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
441 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
442 -mnew-mnemonics -mold-mnemonics @gol
443 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
444 -m64 -m32 -mxl-call -mno-xl-call -mpe @gol
445 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
446 -mstring -mno-string -mupdate -mno-update @gol
447 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
448 -mstrict-align -mno-strict-align -mrelocatable @gol
449 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
450 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
451 -mcall-aix -mcall-sysv -mcall-netbsd @gol
452 -maix-struct-return -msvr4-struct-return @gol
453 -mabi=altivec -mabi=no-altivec @gol
454 -mabi=spe -mabi=no-spe @gol
455 -misel=yes -misel=no @gol
456 -mprototype -mno-prototype @gol
457 -msim -mmvme -mads -myellowknife -memb -msdata @gol
458 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
462 -mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs @gol
463 -mfull-fp-blocks -mhc-struct-return -min-line-mul @gol
464 -mminimum-fp-blocks -mnohc-struct-return}
468 -mabicalls -march=@var{cpu-type} -mtune=@var{cpu=type} @gol
469 -mcpu=@var{cpu-type} -membedded-data -muninit-const-in-rodata @gol
470 -membedded-pic -mfp32 -mfp64 -mfused-madd -mno-fused-madd @gol
471 -mgas -mgp32 -mgp64 @gol
472 -mgpopt -mhalf-pic -mhard-float -mint64 -mips1 @gol
473 -mips2 -mips3 -mips4 -mlong64 -mlong32 -mlong-calls -mmemcpy @gol
474 -mmips-as -mmips-tfile -mno-abicalls @gol
475 -mno-embedded-data -mno-uninit-const-in-rodata @gol
476 -mno-embedded-pic -mno-gpopt -mno-long-calls @gol
477 -mno-memcpy -mno-mips-tfile -mno-rnames -mno-stats @gol
478 -mrnames -msoft-float @gol
479 -m4650 -msingle-float -mmad @gol
480 -mstats -EL -EB -G @var{num} -nocpp @gol
481 -mabi=32 -mabi=n32 -mabi=64 -mabi=eabi @gol
482 -mfix7000 -mno-crt0 -mflush-func=@var{func} -mno-flush-func @gol
483 -mbranch-likely -mno-branch-likely}
485 @emph{i386 and x86-64 Options}
487 -mcpu=@var{cpu-type} -march=@var{cpu-type} -mfpmath=@var{unit} @gol
488 -masm=@var{dialect} -mno-fancy-math-387 @gol
489 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
490 -mno-wide-multiply -mrtd -malign-double @gol
491 -mpreferred-stack-boundary=@var{num} @gol
492 -mmmx -msse -msse2 -msse-math -m3dnow @gol
493 -mthreads -mno-align-stringops -minline-all-stringops @gol
494 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
495 -m96bit-long-double -mregparm=@var{num} -momit-leaf-frame-pointer @gol
497 -mcmodel=@var{code-model} @gol
502 -march=@var{architecture-type} @gol
503 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
504 -mfast-indirect-calls -mgas -mjump-in-delay @gol
505 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
506 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
507 -mno-jump-in-delay -mno-long-load-store @gol
508 -mno-portable-runtime -mno-soft-float @gol
509 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
510 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
511 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio}
513 @emph{Intel 960 Options}
515 -m@var{cpu-type} -masm-compat -mclean-linkage @gol
516 -mcode-align -mcomplex-addr -mleaf-procedures @gol
517 -mic-compat -mic2.0-compat -mic3.0-compat @gol
518 -mintel-asm -mno-clean-linkage -mno-code-align @gol
519 -mno-complex-addr -mno-leaf-procedures @gol
520 -mno-old-align -mno-strict-align -mno-tail-call @gol
521 -mnumerics -mold-align -msoft-float -mstrict-align @gol
524 @emph{DEC Alpha Options}
526 -mno-fp-regs -msoft-float -malpha-as -mgas @gol
527 -mieee -mieee-with-inexact -mieee-conformant @gol
528 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
529 -mtrap-precision=@var{mode} -mbuild-constants @gol
530 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
531 -mbwx -mmax -mfix -mcix @gol
532 -mfloat-vax -mfloat-ieee @gol
533 -mexplicit-relocs -msmall-data -mlarge-data @gol
534 -mmemory-latency=@var{time}}
536 @emph{DEC Alpha/VMS Options}
540 @emph{Clipper Options}
544 @emph{H8/300 Options}
546 -mrelax -mh -ms -mint32 -malign-300}
550 -m1 -m2 -m3 -m3e @gol
551 -m4-nofpu -m4-single-only -m4-single -m4 @gol
552 -m5-64media -m5-64media-nofpu @gol
553 -m5-32media -m5-32media-nofpu @gol
554 -m5-compact -m5-compact-nofpu @gol
555 -mb -ml -mdalign -mrelax @gol
556 -mbigtable -mfmovd -mhitachi -mnomacsave @gol
557 -mieee -misize -mpadstruct -mspace @gol
558 -mprefergot -musermode}
560 @emph{System V Options}
562 -Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
567 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
568 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
570 @emph{TMS320C3x/C4x Options}
572 -mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
573 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
574 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
575 -mparallel-insns -mparallel-mpy -mpreserve-float}
579 -mlong-calls -mno-long-calls -mep -mno-ep @gol
580 -mprolog-function -mno-prolog-function -mspace @gol
581 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
582 -mapp-regs -mno-app-regs @gol
583 -mdisable-callt -mno-disable-callt @gol
589 -m32032 -m32332 -m32532 -m32081 -m32381 @gol
590 -mmult-add -mnomult-add -msoft-float -mrtd -mnortd @gol
591 -mregparam -mnoregparam -msb -mnosb @gol
592 -mbitfield -mnobitfield -mhimem -mnohimem}
596 -mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
597 -mcall-prologues -mno-tablejump -mtiny-stack}
601 -mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
602 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
603 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
604 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
605 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
609 -mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
610 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
611 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
612 -mno-base-addresses -msingle-exit -mno-single-exit}
616 -mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
617 -mvolatile-asm-stop -mb-step -mregister-names -mno-sdata @gol
618 -mconstant-gp -mauto-pic -minline-divide-min-latency @gol
619 -minline-divide-max-throughput -mno-dwarf2-asm @gol
620 -mfixed-range=@var{register-range}}
624 -mextmem -mextmemory -monchip -mno-asm-optimize @gol
625 -masm-optimize -mbranch-cost=@var{n} -mcond-exec=@var{n}}
627 @emph{S/390 and zSeries Options}
629 -mhard-float -msoft-float -mbackchain -mno-backchain @gol
630 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
631 -m64 -m31 -mdebug -mno-debug}
635 -mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
636 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
637 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
638 -mstack-align -mdata-align -mconst-align @gol
639 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
640 -melf -maout -melinux -mlinux -sim -sim2}
642 @emph{PDP-11 Options}
644 -mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
645 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
646 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
647 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
648 -mbranch-expensive -mbranch-cheap @gol
649 -msplit -mno-split -munix-asm -mdec-asm}
651 @emph{Xstormy16 Options}
655 @emph{Xtensa Options}
657 -mbig-endian -mlittle-endian @gol
658 -mdensity -mno-density @gol
659 -mmac16 -mno-mac16 @gol
660 -mmul16 -mno-mul16 @gol
661 -mmul32 -mno-mul32 @gol
663 -mminmax -mno-minmax @gol
664 -msext -mno-sext @gol
665 -mbooleans -mno-booleans @gol
666 -mhard-float -msoft-float @gol
667 -mfused-madd -mno-fused-madd @gol
668 -mserialize-volatile -mno-serialize-volatile @gol
669 -mtext-section-literals -mno-text-section-literals @gol
670 -mtarget-align -mno-target-align @gol
671 -mlongcalls -mno-longcalls}
673 @item Code Generation Options
674 @xref{Code Gen Options,,Options for Code Generation Conventions}.
676 -fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
677 -ffixed-@var{reg} -fexceptions @gol
678 -fnon-call-exceptions -funwind-tables @gol
679 -fasynchronous-unwind-tables @gol
680 -finhibit-size-directive -finstrument-functions @gol
681 -fno-common -fno-ident -fno-gnu-linker @gol
682 -fpcc-struct-return -fpic -fPIC @gol
683 -freg-struct-return -fshared-data -fshort-enums @gol
684 -fshort-double -fshort-wchar -fvolatile @gol
685 -fvolatile-global -fvolatile-static @gol
686 -fverbose-asm -fpack-struct -fstack-check @gol
687 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
688 -fargument-alias -fargument-noalias @gol
689 -fargument-noalias-global -fleading-underscore @gol
690 -ftls-model=@var{model}}
694 * Overall Options:: Controlling the kind of output:
695 an executable, object files, assembler files,
696 or preprocessed source.
697 * C Dialect Options:: Controlling the variant of C language compiled.
698 * C++ Dialect Options:: Variations on C++.
699 * Objective-C Dialect Options:: Variations on Objective-C.
700 * Language Independent Options:: Controlling how diagnostics should be
702 * Warning Options:: How picky should the compiler be?
703 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
704 * Optimize Options:: How much optimization?
705 * Preprocessor Options:: Controlling header files and macro definitions.
706 Also, getting dependency information for Make.
707 * Assembler Options:: Passing options to the assembler.
708 * Link Options:: Specifying libraries and so on.
709 * Directory Options:: Where to find header files and libraries.
710 Where to find the compiler executable files.
711 * Spec Files:: How to pass switches to sub-processes.
712 * Target Options:: Running a cross-compiler, or an old version of GCC.
715 @node Overall Options
716 @section Options Controlling the Kind of Output
718 Compilation can involve up to four stages: preprocessing, compilation
719 proper, assembly and linking, always in that order. The first three
720 stages apply to an individual source file, and end by producing an
721 object file; linking combines all the object files (those newly
722 compiled, and those specified as input) into an executable file.
724 @cindex file name suffix
725 For any given input file, the file name suffix determines what kind of
730 C source code which must be preprocessed.
733 C source code which should not be preprocessed.
736 C++ source code which should not be preprocessed.
739 Objective-C source code. Note that you must link with the library
740 @file{libobjc.a} to make an Objective-C program work.
743 Objective-C source code which should not be preprocessed.
746 C header file (not to be compiled or linked).
750 @itemx @var{file}.cxx
751 @itemx @var{file}.cpp
752 @itemx @var{file}.c++
754 C++ source code which must be preprocessed. Note that in @samp{.cxx},
755 the last two letters must both be literally @samp{x}. Likewise,
756 @samp{.C} refers to a literal capital C@.
759 @itemx @var{file}.for
760 @itemx @var{file}.FOR
761 Fortran source code which should not be preprocessed.
764 @itemx @var{file}.fpp
765 @itemx @var{file}.FPP
766 Fortran source code which must be preprocessed (with the traditional
770 Fortran source code which must be preprocessed with a RATFOR
771 preprocessor (not included with GCC)@.
773 @xref{Overall Options,,Options Controlling the Kind of Output, g77,
774 Using and Porting GNU Fortran}, for more details of the handling of
777 @c FIXME: Descriptions of Java file types.
784 Ada source code file which contains a library unit declaration (a
785 declaration of a package, subprogram, or generic, or a generic
786 instantiation), or a library unit renaming declaration (a package,
787 generic, or subprogram renaming declaration). Such files are also
790 @itemx @var{file}.adb
791 Ada source code file containing a library unit body (a subprogram or
792 package body). Such files are also called @dfn{bodies}.
794 @c GCC also knows about some suffixes for languages not yet included:
803 Assembler code which must be preprocessed.
806 An object file to be fed straight into linking.
807 Any file name with no recognized suffix is treated this way.
811 You can specify the input language explicitly with the @option{-x} option:
814 @item -x @var{language}
815 Specify explicitly the @var{language} for the following input files
816 (rather than letting the compiler choose a default based on the file
817 name suffix). This option applies to all following input files until
818 the next @option{-x} option. Possible values for @var{language} are:
820 c c-header cpp-output
822 objective-c objc-cpp-output
823 assembler assembler-with-cpp
825 f77 f77-cpp-input ratfor
831 Turn off any specification of a language, so that subsequent files are
832 handled according to their file name suffixes (as they are if @option{-x}
833 has not been used at all).
835 @item -pass-exit-codes
836 @opindex pass-exit-codes
837 Normally the @command{gcc} program will exit with the code of 1 if any
838 phase of the compiler returns a non-success return code. If you specify
839 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
840 numerically highest error produced by any phase that returned an error
844 If you only want some of the stages of compilation, you can use
845 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
846 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
847 @command{gcc} is to stop. Note that some combinations (for example,
848 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
853 Compile or assemble the source files, but do not link. The linking
854 stage simply is not done. The ultimate output is in the form of an
855 object file for each source file.
857 By default, the object file name for a source file is made by replacing
858 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
860 Unrecognized input files, not requiring compilation or assembly, are
865 Stop after the stage of compilation proper; do not assemble. The output
866 is in the form of an assembler code file for each non-assembler input
869 By default, the assembler file name for a source file is made by
870 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
872 Input files that don't require compilation are ignored.
876 Stop after the preprocessing stage; do not run the compiler proper. The
877 output is in the form of preprocessed source code, which is sent to the
880 Input files which don't require preprocessing are ignored.
882 @cindex output file option
885 Place output in file @var{file}. This applies regardless to whatever
886 sort of output is being produced, whether it be an executable file,
887 an object file, an assembler file or preprocessed C code.
889 Since only one output file can be specified, it does not make sense to
890 use @option{-o} when compiling more than one input file, unless you are
891 producing an executable file as output.
893 If @option{-o} is not specified, the default is to put an executable file
894 in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in
895 @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and
896 all preprocessed C source on standard output.
900 Print (on standard error output) the commands executed to run the stages
901 of compilation. Also print the version number of the compiler driver
902 program and of the preprocessor and the compiler proper.
906 Like @option{-v} except the commands are not executed and all command
907 arguments are quoted. This is useful for shell scripts to capture the
908 driver-generated command lines.
912 Use pipes rather than temporary files for communication between the
913 various stages of compilation. This fails to work on some systems where
914 the assembler is unable to read from a pipe; but the GNU assembler has
919 Print (on the standard output) a description of the command line options
920 understood by @command{gcc}. If the @option{-v} option is also specified
921 then @option{--help} will also be passed on to the various processes
922 invoked by @command{gcc}, so that they can display the command line options
923 they accept. If the @option{-W} option is also specified then command
924 line options which have no documentation associated with them will also
929 Print (on the standard output) a description of target specific command
930 line options for each tool.
934 @section Compiling C++ Programs
936 @cindex suffixes for C++ source
937 @cindex C++ source file suffixes
938 C++ source files conventionally use one of the suffixes @samp{.C},
939 @samp{.cc}, @samp{.cpp}, @samp{.c++}, @samp{.cp}, or @samp{.cxx};
940 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
941 files with these names and compiles them as C++ programs even if you
942 call the compiler the same way as for compiling C programs (usually with
943 the name @command{gcc}).
947 However, C++ programs often require class libraries as well as a
948 compiler that understands the C++ language---and under some
949 circumstances, you might want to compile programs from standard input,
950 or otherwise without a suffix that flags them as C++ programs.
951 @command{g++} is a program that calls GCC with the default language
952 set to C++, and automatically specifies linking against the C++
953 library. On many systems, @command{g++} is also
954 installed with the name @command{c++}.
956 @cindex invoking @command{g++}
957 When you compile C++ programs, you may specify many of the same
958 command-line options that you use for compiling programs in any
959 language; or command-line options meaningful for C and related
960 languages; or options that are meaningful only for C++ programs.
961 @xref{C Dialect Options,,Options Controlling C Dialect}, for
962 explanations of options for languages related to C@.
963 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
964 explanations of options that are meaningful only for C++ programs.
966 @node C Dialect Options
967 @section Options Controlling C Dialect
968 @cindex dialect options
969 @cindex language dialect options
970 @cindex options, dialect
972 The following options control the dialect of C (or languages derived
973 from C, such as C++ and Objective-C) that the compiler accepts:
980 In C mode, support all ISO C90 programs. In C++ mode,
981 remove GNU extensions that conflict with ISO C++.
983 This turns off certain features of GCC that are incompatible with ISO
984 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
985 such as the @code{asm} and @code{typeof} keywords, and
986 predefined macros such as @code{unix} and @code{vax} that identify the
987 type of system you are using. It also enables the undesirable and
988 rarely used ISO trigraph feature. For the C compiler,
989 it disables recognition of C++ style @samp{//} comments as well as
990 the @code{inline} keyword.
992 The alternate keywords @code{__asm__}, @code{__extension__},
993 @code{__inline__} and @code{__typeof__} continue to work despite
994 @option{-ansi}. You would not want to use them in an ISO C program, of
995 course, but it is useful to put them in header files that might be included
996 in compilations done with @option{-ansi}. Alternate predefined macros
997 such as @code{__unix__} and @code{__vax__} are also available, with or
998 without @option{-ansi}.
1000 The @option{-ansi} option does not cause non-ISO programs to be
1001 rejected gratuitously. For that, @option{-pedantic} is required in
1002 addition to @option{-ansi}. @xref{Warning Options}.
1004 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1005 option is used. Some header files may notice this macro and refrain
1006 from declaring certain functions or defining certain macros that the
1007 ISO standard doesn't call for; this is to avoid interfering with any
1008 programs that might use these names for other things.
1010 Functions which would normally be built in but do not have semantics
1011 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1012 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1013 built-in functions provided by GCC}, for details of the functions
1018 Determine the language standard. This option is currently only
1019 supported when compiling C or C++. A value for this option must be
1020 provided; possible values are
1025 ISO C90 (same as @option{-ansi}).
1027 @item iso9899:199409
1028 ISO C90 as modified in amendment 1.
1034 ISO C99. Note that this standard is not yet fully supported; see
1035 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1036 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1039 Default, ISO C90 plus GNU extensions (including some C99 features).
1043 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1044 this will become the default. The name @samp{gnu9x} is deprecated.
1047 The 1998 ISO C++ standard plus amendments.
1050 The same as @option{-std=c++98} plus GNU extensions. This is the
1051 default for C++ code.
1054 Even when this option is not specified, you can still use some of the
1055 features of newer standards in so far as they do not conflict with
1056 previous C standards. For example, you may use @code{__restrict__} even
1057 when @option{-std=c99} is not specified.
1059 The @option{-std} options specifying some version of ISO C have the same
1060 effects as @option{-ansi}, except that features that were not in ISO C90
1061 but are in the specified version (for example, @samp{//} comments and
1062 the @code{inline} keyword in ISO C99) are not disabled.
1064 @xref{Standards,,Language Standards Supported by GCC}, for details of
1065 these standard versions.
1067 @item -aux-info @var{filename}
1069 Output to the given filename prototyped declarations for all functions
1070 declared and/or defined in a translation unit, including those in header
1071 files. This option is silently ignored in any language other than C@.
1073 Besides declarations, the file indicates, in comments, the origin of
1074 each declaration (source file and line), whether the declaration was
1075 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1076 @samp{O} for old, respectively, in the first character after the line
1077 number and the colon), and whether it came from a declaration or a
1078 definition (@samp{C} or @samp{F}, respectively, in the following
1079 character). In the case of function definitions, a K&R-style list of
1080 arguments followed by their declarations is also provided, inside
1081 comments, after the declaration.
1085 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1086 keyword, so that code can use these words as identifiers. You can use
1087 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1088 instead. @option{-ansi} implies @option{-fno-asm}.
1090 In C++, this switch only affects the @code{typeof} keyword, since
1091 @code{asm} and @code{inline} are standard keywords. You may want to
1092 use the @option{-fno-gnu-keywords} flag instead, which has the same
1093 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1094 switch only affects the @code{asm} and @code{typeof} keywords, since
1095 @code{inline} is a standard keyword in ISO C99.
1098 @itemx -fno-builtin-@var{function}
1099 @opindex fno-builtin
1100 @cindex built-in functions
1101 Don't recognize built-in functions that do not begin with
1102 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1103 functions provided by GCC}, for details of the functions affected,
1104 including those which are not built-in functions when @option{-ansi} or
1105 @option{-std} options for strict ISO C conformance are used because they
1106 do not have an ISO standard meaning.
1108 GCC normally generates special code to handle certain built-in functions
1109 more efficiently; for instance, calls to @code{alloca} may become single
1110 instructions that adjust the stack directly, and calls to @code{memcpy}
1111 may become inline copy loops. The resulting code is often both smaller
1112 and faster, but since the function calls no longer appear as such, you
1113 cannot set a breakpoint on those calls, nor can you change the behavior
1114 of the functions by linking with a different library.
1116 With the @option{-fno-builtin-@var{function}} option
1117 only the built-in function @var{function} is
1118 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1119 function is named this is not built-in in this version of GCC, this
1120 option is ignored. There is no corresponding
1121 @option{-fbuiltin-@var{function}} option; if you wish to enable
1122 built-in functions selectively when using @option{-fno-builtin} or
1123 @option{-ffreestanding}, you may define macros such as:
1126 #define abs(n) __builtin_abs ((n))
1127 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1132 @cindex hosted environment
1134 Assert that compilation takes place in a hosted environment. This implies
1135 @option{-fbuiltin}. A hosted environment is one in which the
1136 entire standard library is available, and in which @code{main} has a return
1137 type of @code{int}. Examples are nearly everything except a kernel.
1138 This is equivalent to @option{-fno-freestanding}.
1140 @item -ffreestanding
1141 @opindex ffreestanding
1142 @cindex hosted environment
1144 Assert that compilation takes place in a freestanding environment. This
1145 implies @option{-fno-builtin}. A freestanding environment
1146 is one in which the standard library may not exist, and program startup may
1147 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1148 This is equivalent to @option{-fno-hosted}.
1150 @xref{Standards,,Language Standards Supported by GCC}, for details of
1151 freestanding and hosted environments.
1153 @item -fms-extensions
1154 @opindex fms-extensions
1155 Accept some non-standard constructs used in Microsoft header files.
1159 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1160 options for strict ISO C conformance) implies @option{-trigraphs}.
1162 @cindex traditional C language
1163 @cindex C language, traditional
1165 @itemx -traditional-cpp
1166 @opindex traditional-cpp
1167 @opindex traditional
1168 Formerly, these options caused GCC to attempt to emulate a pre-standard
1169 C compiler. They are now only supported with the @option{-E} switch.
1170 The preprocessor continues to support a pre-standard mode. See the GNU
1171 CPP manual for details.
1173 @item -fcond-mismatch
1174 @opindex fcond-mismatch
1175 Allow conditional expressions with mismatched types in the second and
1176 third arguments. The value of such an expression is void. This option
1177 is not supported for C++.
1179 @item -funsigned-char
1180 @opindex funsigned-char
1181 Let the type @code{char} be unsigned, like @code{unsigned char}.
1183 Each kind of machine has a default for what @code{char} should
1184 be. It is either like @code{unsigned char} by default or like
1185 @code{signed char} by default.
1187 Ideally, a portable program should always use @code{signed char} or
1188 @code{unsigned char} when it depends on the signedness of an object.
1189 But many programs have been written to use plain @code{char} and
1190 expect it to be signed, or expect it to be unsigned, depending on the
1191 machines they were written for. This option, and its inverse, let you
1192 make such a program work with the opposite default.
1194 The type @code{char} is always a distinct type from each of
1195 @code{signed char} or @code{unsigned char}, even though its behavior
1196 is always just like one of those two.
1199 @opindex fsigned-char
1200 Let the type @code{char} be signed, like @code{signed char}.
1202 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1203 the negative form of @option{-funsigned-char}. Likewise, the option
1204 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1206 @item -fsigned-bitfields
1207 @itemx -funsigned-bitfields
1208 @itemx -fno-signed-bitfields
1209 @itemx -fno-unsigned-bitfields
1210 @opindex fsigned-bitfields
1211 @opindex funsigned-bitfields
1212 @opindex fno-signed-bitfields
1213 @opindex fno-unsigned-bitfields
1214 These options control whether a bit-field is signed or unsigned, when the
1215 declaration does not use either @code{signed} or @code{unsigned}. By
1216 default, such a bit-field is signed, because this is consistent: the
1217 basic integer types such as @code{int} are signed types.
1219 @item -fwritable-strings
1220 @opindex fwritable-strings
1221 Store string constants in the writable data segment and don't uniquize
1222 them. This is for compatibility with old programs which assume they can
1223 write into string constants.
1225 Writing into string constants is a very bad idea; ``constants'' should
1229 @node C++ Dialect Options
1230 @section Options Controlling C++ Dialect
1232 @cindex compiler options, C++
1233 @cindex C++ options, command line
1234 @cindex options, C++
1235 This section describes the command-line options that are only meaningful
1236 for C++ programs; but you can also use most of the GNU compiler options
1237 regardless of what language your program is in. For example, you
1238 might compile a file @code{firstClass.C} like this:
1241 g++ -g -frepo -O -c firstClass.C
1245 In this example, only @option{-frepo} is an option meant
1246 only for C++ programs; you can use the other options with any
1247 language supported by GCC@.
1249 Here is a list of options that are @emph{only} for compiling C++ programs:
1253 @item -fabi-version=@var{n}
1254 @opindex fabi-version
1255 Use version @var{n} of the C++ ABI. Version 1 is the version of the C++
1256 ABI that first appeared in G++ 3.2. Version 0 will always be the
1257 version that conforms most closely to the C++ ABI specification.
1258 Therefore, the ABI obtained using version 0 will change as ABI bugs are
1261 The default is version 1.
1263 @item -fno-access-control
1264 @opindex fno-access-control
1265 Turn off all access checking. This switch is mainly useful for working
1266 around bugs in the access control code.
1270 Check that the pointer returned by @code{operator new} is non-null
1271 before attempting to modify the storage allocated. The current Working
1272 Paper requires that @code{operator new} never return a null pointer, so
1273 this check is normally unnecessary.
1275 An alternative to using this option is to specify that your
1276 @code{operator new} does not throw any exceptions; if you declare it
1277 @samp{throw()}, G++ will check the return value. See also @samp{new
1280 @item -fconserve-space
1281 @opindex fconserve-space
1282 Put uninitialized or runtime-initialized global variables into the
1283 common segment, as C does. This saves space in the executable at the
1284 cost of not diagnosing duplicate definitions. If you compile with this
1285 flag and your program mysteriously crashes after @code{main()} has
1286 completed, you may have an object that is being destroyed twice because
1287 two definitions were merged.
1289 This option is no longer useful on most targets, now that support has
1290 been added for putting variables into BSS without making them common.
1292 @item -fno-const-strings
1293 @opindex fno-const-strings
1294 Give string constants type @code{char *} instead of type @code{const
1295 char *}. By default, G++ uses type @code{const char *} as required by
1296 the standard. Even if you use @option{-fno-const-strings}, you cannot
1297 actually modify the value of a string constant, unless you also use
1298 @option{-fwritable-strings}.
1300 This option might be removed in a future release of G++. For maximum
1301 portability, you should structure your code so that it works with
1302 string constants that have type @code{const char *}.
1304 @item -fdollars-in-identifiers
1305 @opindex fdollars-in-identifiers
1306 Accept @samp{$} in identifiers. You can also explicitly prohibit use of
1307 @samp{$} with the option @option{-fno-dollars-in-identifiers}. (GNU C allows
1308 @samp{$} by default on most target systems, but there are a few exceptions.)
1309 Traditional C allowed the character @samp{$} to form part of
1310 identifiers. However, ISO C and C++ forbid @samp{$} in identifiers.
1312 @item -fno-elide-constructors
1313 @opindex fno-elide-constructors
1314 The C++ standard allows an implementation to omit creating a temporary
1315 which is only used to initialize another object of the same type.
1316 Specifying this option disables that optimization, and forces G++ to
1317 call the copy constructor in all cases.
1319 @item -fno-enforce-eh-specs
1320 @opindex fno-enforce-eh-specs
1321 Don't check for violation of exception specifications at runtime. This
1322 option violates the C++ standard, but may be useful for reducing code
1323 size in production builds, much like defining @samp{NDEBUG}. The compiler
1324 will still optimize based on the exception specifications.
1326 @item -fexternal-templates
1327 @opindex fexternal-templates
1329 Cause @samp{#pragma interface} and @samp{implementation} to apply to
1330 template instantiation; template instances are emitted or not according
1331 to the location of the template definition. @xref{Template
1332 Instantiation}, for more information.
1334 This option is deprecated.
1336 @item -falt-external-templates
1337 @opindex falt-external-templates
1338 Similar to @option{-fexternal-templates}, but template instances are
1339 emitted or not according to the place where they are first instantiated.
1340 @xref{Template Instantiation}, for more information.
1342 This option is deprecated.
1345 @itemx -fno-for-scope
1347 @opindex fno-for-scope
1348 If @option{-ffor-scope} is specified, the scope of variables declared in
1349 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1350 as specified by the C++ standard.
1351 If @option{-fno-for-scope} is specified, the scope of variables declared in
1352 a @i{for-init-statement} extends to the end of the enclosing scope,
1353 as was the case in old versions of G++, and other (traditional)
1354 implementations of C++.
1356 The default if neither flag is given to follow the standard,
1357 but to allow and give a warning for old-style code that would
1358 otherwise be invalid, or have different behavior.
1360 @item -fno-gnu-keywords
1361 @opindex fno-gnu-keywords
1362 Do not recognize @code{typeof} as a keyword, so that code can use this
1363 word as an identifier. You can use the keyword @code{__typeof__} instead.
1364 @option{-ansi} implies @option{-fno-gnu-keywords}.
1366 @item -fno-implicit-templates
1367 @opindex fno-implicit-templates
1368 Never emit code for non-inline templates which are instantiated
1369 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1370 @xref{Template Instantiation}, for more information.
1372 @item -fno-implicit-inline-templates
1373 @opindex fno-implicit-inline-templates
1374 Don't emit code for implicit instantiations of inline templates, either.
1375 The default is to handle inlines differently so that compiles with and
1376 without optimization will need the same set of explicit instantiations.
1378 @item -fno-implement-inlines
1379 @opindex fno-implement-inlines
1380 To save space, do not emit out-of-line copies of inline functions
1381 controlled by @samp{#pragma implementation}. This will cause linker
1382 errors if these functions are not inlined everywhere they are called.
1384 @item -fms-extensions
1385 @opindex fms-extensions
1386 Disable pedantic warnings about constructs used in MFC, such as implicit
1387 int and getting a pointer to member function via non-standard syntax.
1389 @item -fno-nonansi-builtins
1390 @opindex fno-nonansi-builtins
1391 Disable built-in declarations of functions that are not mandated by
1392 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1393 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1395 @item -fno-operator-names
1396 @opindex fno-operator-names
1397 Do not treat the operator name keywords @code{and}, @code{bitand},
1398 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1399 synonyms as keywords.
1401 @item -fno-optional-diags
1402 @opindex fno-optional-diags
1403 Disable diagnostics that the standard says a compiler does not need to
1404 issue. Currently, the only such diagnostic issued by G++ is the one for
1405 a name having multiple meanings within a class.
1408 @opindex fpermissive
1409 Downgrade messages about nonconformant code from errors to warnings. By
1410 default, G++ effectively sets @option{-pedantic-errors} without
1411 @option{-pedantic}; this option reverses that. This behavior and this
1412 option are superseded by @option{-pedantic}, which works as it does for GNU C@.
1416 Enable automatic template instantiation at link time. This option also
1417 implies @option{-fno-implicit-templates}. @xref{Template
1418 Instantiation}, for more information.
1422 Disable generation of information about every class with virtual
1423 functions for use by the C++ runtime type identification features
1424 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1425 of the language, you can save some space by using this flag. Note that
1426 exception handling uses the same information, but it will generate it as
1431 Emit statistics about front-end processing at the end of the compilation.
1432 This information is generally only useful to the G++ development team.
1434 @item -ftemplate-depth-@var{n}
1435 @opindex ftemplate-depth
1436 Set the maximum instantiation depth for template classes to @var{n}.
1437 A limit on the template instantiation depth is needed to detect
1438 endless recursions during template class instantiation. ANSI/ISO C++
1439 conforming programs must not rely on a maximum depth greater than 17.
1441 @item -fuse-cxa-atexit
1442 @opindex fuse-cxa-atexit
1443 Register destructors for objects with static storage duration with the
1444 @code{__cxa_atexit} function rather than the @code{atexit} function.
1445 This option is required for fully standards-compliant handling of static
1446 destructors, but will only work if your C library supports
1447 @code{__cxa_atexit}.
1451 Emit special relocations for vtables and virtual function references
1452 so that the linker can identify unused virtual functions and zero out
1453 vtable slots that refer to them. This is most useful with
1454 @option{-ffunction-sections} and @option{-Wl,--gc-sections}, in order to
1455 also discard the functions themselves.
1457 This optimization requires GNU as and GNU ld. Not all systems support
1458 this option. @option{-Wl,--gc-sections} is ignored without @option{-static}.
1462 Do not use weak symbol support, even if it is provided by the linker.
1463 By default, G++ will use weak symbols if they are available. This
1464 option exists only for testing, and should not be used by end-users;
1465 it will result in inferior code and has no benefits. This option may
1466 be removed in a future release of G++.
1470 Do not search for header files in the standard directories specific to
1471 C++, but do still search the other standard directories. (This option
1472 is used when building the C++ library.)
1475 In addition, these optimization, warning, and code generation options
1476 have meanings only for C++ programs:
1479 @item -fno-default-inline
1480 @opindex fno-default-inline
1481 Do not assume @samp{inline} for functions defined inside a class scope.
1482 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1483 functions will have linkage like inline functions; they just won't be
1486 @item -Wabi @r{(C++ only)}
1488 Warn when G++ generates code that is probably not compatible with the
1489 vendor-neutral C++ ABI. Although an effort has been made to warn about
1490 all such cases, there are probably some cases that are not warned about,
1491 even though G++ is generating incompatible code. There may also be
1492 cases where warnings are emitted even though the code that is generated
1495 You should rewrite your code to avoid these warnings if you are
1496 concerned about the fact that code generated by G++ may not be binary
1497 compatible with code generated by other compilers.
1499 The known incompatibilites at this point include:
1504 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1505 pack data into the same byte as a base class. For example:
1508 struct A @{ virtual void f(); int f1 : 1; @};
1509 struct B : public A @{ int f2 : 1; @};
1513 In this case, G++ will place @code{B::f2} into the same byte
1514 as@code{A::f1}; other compilers will not. You can avoid this problem
1515 by explicitly padding @code{A} so that its size is a multiple of the
1516 byte size on your platform; that will cause G++ and other compilers to
1517 layout @code{B} identically.
1520 Incorrect handling of tail-padding for virtual bases. G++ does not use
1521 tail padding when laying out virtual bases. For example:
1524 struct A @{ virtual void f(); char c1; @};
1525 struct B @{ B(); char c2; @};
1526 struct C : public A, public virtual B @{@};
1530 In this case, G++ will not place @code{B} into the tail-padding for
1531 @code{A}; other compilers will. You can avoid this problem by
1532 explicitly padding @code{A} so that its size is a multiple of its
1533 alignment (ignoring virtual base classes); that will cause G++ and other
1534 compilers to layout @code{C} identically.
1537 Incorrect handling of bit-fields with declared widths greater than that
1538 of their underlying types, when the bit-fields appear in a union. For
1542 union U @{ int i : 4096; @};
1546 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1547 union too small by the number of bits in an @code{int}.
1550 Empty classes can be placed at incorrect offsets. For example:
1560 struct C : public B, public A @{@};
1564 G++ will place the @code{A} base class of @code{C} at a non-zero offset;
1565 it should be placed at offset zero. G++ mistakenly believes that the
1566 @code{A} data member of @code{B} is already at offset zero.
1569 Names of template functions whose types involve @code{typename} or
1570 template template parameters can be mangled incorrectly.
1573 template <typename Q>
1574 void f(typename Q::X) @{@}
1576 template <template <typename> class Q>
1577 void f(typename Q<int>::X) @{@}
1581 Instantions of these templates may be mangled incorrectly.
1585 @item -Wctor-dtor-privacy @r{(C++ only)}
1586 @opindex Wctor-dtor-privacy
1587 Warn when a class seems unusable, because all the constructors or
1588 destructors in a class are private and the class has no friends or
1589 public static member functions. This warning is enabled by default.
1591 @item -Wnon-virtual-dtor @r{(C++ only)}
1592 @opindex Wnon-virtual-dtor
1593 Warn when a class declares a non-virtual destructor that should probably
1594 be virtual, because it looks like the class will be used polymorphically.
1595 This warning is enabled by @option{-Wall}.
1597 @item -Wreorder @r{(C++ only)}
1599 @cindex reordering, warning
1600 @cindex warning for reordering of member initializers
1601 Warn when the order of member initializers given in the code does not
1602 match the order in which they must be executed. For instance:
1608 A(): j (0), i (1) @{ @}
1612 Here the compiler will warn that the member initializers for @samp{i}
1613 and @samp{j} will be rearranged to match the declaration order of the
1614 members. This warning is enabled by @option{-Wall}.
1617 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1620 @item -Weffc++ @r{(C++ only)}
1622 Warn about violations of the following style guidelines from Scott Meyers'
1623 @cite{Effective C++} book:
1627 Item 11: Define a copy constructor and an assignment operator for classes
1628 with dynamically allocated memory.
1631 Item 12: Prefer initialization to assignment in constructors.
1634 Item 14: Make destructors virtual in base classes.
1637 Item 15: Have @code{operator=} return a reference to @code{*this}.
1640 Item 23: Don't try to return a reference when you must return an object.
1644 and about violations of the following style guidelines from Scott Meyers'
1645 @cite{More Effective C++} book:
1649 Item 6: Distinguish between prefix and postfix forms of increment and
1650 decrement operators.
1653 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1657 If you use this option, you should be aware that the standard library
1658 headers do not obey all of these guidelines; you can use @samp{grep -v}
1659 to filter out those warnings.
1661 @item -Wno-deprecated @r{(C++ only)}
1662 @opindex Wno-deprecated
1663 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1665 @item -Wno-non-template-friend @r{(C++ only)}
1666 @opindex Wno-non-template-friend
1667 Disable warnings when non-templatized friend functions are declared
1668 within a template. With the advent of explicit template specification
1669 support in G++, if the name of the friend is an unqualified-id (i.e.,
1670 @samp{friend foo(int)}), the C++ language specification demands that the
1671 friend declare or define an ordinary, nontemplate function. (Section
1672 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1673 could be interpreted as a particular specialization of a templatized
1674 function. Because this non-conforming behavior is no longer the default
1675 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1676 check existing code for potential trouble spots, and is on by default.
1677 This new compiler behavior can be turned off with
1678 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1679 but disables the helpful warning.
1681 @item -Wold-style-cast @r{(C++ only)}
1682 @opindex Wold-style-cast
1683 Warn if an old-style (C-style) cast to a non-void type is used within
1684 a C++ program. The new-style casts (@samp{static_cast},
1685 @samp{reinterpret_cast}, and @samp{const_cast}) are less vulnerable to
1686 unintended effects, and much easier to grep for.
1688 @item -Woverloaded-virtual @r{(C++ only)}
1689 @opindex Woverloaded-virtual
1690 @cindex overloaded virtual fn, warning
1691 @cindex warning for overloaded virtual fn
1692 Warn when a function declaration hides virtual functions from a
1693 base class. For example, in:
1700 struct B: public A @{
1705 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1713 will fail to compile.
1715 @item -Wno-pmf-conversions @r{(C++ only)}
1716 @opindex Wno-pmf-conversions
1717 Disable the diagnostic for converting a bound pointer to member function
1720 @item -Wsign-promo @r{(C++ only)}
1721 @opindex Wsign-promo
1722 Warn when overload resolution chooses a promotion from unsigned or
1723 enumeral type to a signed type over a conversion to an unsigned type of
1724 the same size. Previous versions of G++ would try to preserve
1725 unsignedness, but the standard mandates the current behavior.
1727 @item -Wsynth @r{(C++ only)}
1729 @cindex warning for synthesized methods
1730 @cindex synthesized methods, warning
1731 Warn when G++'s synthesis behavior does not match that of cfront. For
1737 A& operator = (int);
1747 In this example, G++ will synthesize a default @samp{A& operator =
1748 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1751 @node Objective-C Dialect Options
1752 @section Options Controlling Objective-C Dialect
1754 @cindex compiler options, Objective-C
1755 @cindex Objective-C options, command line
1756 @cindex options, Objective-C
1757 This section describes the command-line options that are only meaningful
1758 for Objective-C programs; but you can also use most of the GNU compiler
1759 options regardless of what language your program is in. For example,
1760 you might compile a file @code{some_class.m} like this:
1763 gcc -g -fgnu-runtime -O -c some_class.m
1767 In this example, only @option{-fgnu-runtime} is an option meant only for
1768 Objective-C programs; you can use the other options with any language
1771 Here is a list of options that are @emph{only} for compiling Objective-C
1775 @item -fconstant-string-class=@var{class-name}
1776 @opindex fconstant-string-class
1777 Use @var{class-name} as the name of the class to instantiate for each
1778 literal string specified with the syntax @code{@@"@dots{}"}. The default
1779 class name is @code{NXConstantString}.
1782 @opindex fgnu-runtime
1783 Generate object code compatible with the standard GNU Objective-C
1784 runtime. This is the default for most types of systems.
1786 @item -fnext-runtime
1787 @opindex fnext-runtime
1788 Generate output compatible with the NeXT runtime. This is the default
1789 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1790 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1795 Dump interface declarations for all classes seen in the source file to a
1796 file named @file{@var{sourcename}.decl}.
1799 @opindex Wno-protocol
1800 If a class is declared to implement a protocol, a warning is issued for
1801 every method in the protocol that is not implemented by the class. The
1802 default behavior is to issue a warning for every method not explicitly
1803 implemented in the class, even if a method implementation is inherited
1804 from the superclass. If you use the @code{-Wno-protocol} option, then
1805 methods inherited from the superclass are considered to be implemented,
1806 and no warning is issued for them.
1810 Warn if multiple methods of different types for the same selector are
1811 found during compilation. The check is performed on the list of methods
1812 in the final stage of compilation. Additionally, a check is performed
1813 that for each selector appearing in a @code{@@selector(@dots{})}
1814 expression, a corresponding method with that selector has been found
1815 during compilation. Because these checks scan the method table only at
1816 the end of compilation, these warnings are not produced if the final
1817 stage of compilation is not reached, for example because an error is
1818 found during compilation, or because the @code{-fsyntax-only} option is
1821 @item -Wundeclared-selector
1822 @opindex Wundeclared-selector
1823 Warn if a @code{@@selector(@dots{})} expression referring to an
1824 undeclared selector is found. A selector is considered undeclared if no
1825 method with that name has been declared (explicitly, in an
1826 @code{@@interface} or @code{@@protocol} declaration, or implicitly, in
1827 an @code{@@implementation} section) before the
1828 @code{@@selector(@dots{})} expression. This option always performs its
1829 checks as soon as a @code{@@selector(@dots{})} expression is found
1830 (while @code{-Wselector} only performs its checks in the final stage of
1831 compilation), and so additionally enforces the coding style convention
1832 that methods and selectors must be declared before being used.
1834 @c not documented because only avail via -Wp
1835 @c @item -print-objc-runtime-info
1839 @node Language Independent Options
1840 @section Options to Control Diagnostic Messages Formatting
1841 @cindex options to control diagnostics formatting
1842 @cindex diagnostic messages
1843 @cindex message formatting
1845 Traditionally, diagnostic messages have been formatted irrespective of
1846 the output device's aspect (e.g.@: its width, @dots{}). The options described
1847 below can be used to control the diagnostic messages formatting
1848 algorithm, e.g.@: how many characters per line, how often source location
1849 information should be reported. Right now, only the C++ front end can
1850 honor these options. However it is expected, in the near future, that
1851 the remaining front ends would be able to digest them correctly.
1854 @item -fmessage-length=@var{n}
1855 @opindex fmessage-length
1856 Try to format error messages so that they fit on lines of about @var{n}
1857 characters. The default is 72 characters for @command{g++} and 0 for the rest of
1858 the front ends supported by GCC@. If @var{n} is zero, then no
1859 line-wrapping will be done; each error message will appear on a single
1862 @opindex fdiagnostics-show-location
1863 @item -fdiagnostics-show-location=once
1864 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
1865 reporter to emit @emph{once} source location information; that is, in
1866 case the message is too long to fit on a single physical line and has to
1867 be wrapped, the source location won't be emitted (as prefix) again,
1868 over and over, in subsequent continuation lines. This is the default
1871 @item -fdiagnostics-show-location=every-line
1872 Only meaningful in line-wrapping mode. Instructs the diagnostic
1873 messages reporter to emit the same source location information (as
1874 prefix) for physical lines that result from the process of breaking
1875 a message which is too long to fit on a single line.
1879 @node Warning Options
1880 @section Options to Request or Suppress Warnings
1881 @cindex options to control warnings
1882 @cindex warning messages
1883 @cindex messages, warning
1884 @cindex suppressing warnings
1886 Warnings are diagnostic messages that report constructions which
1887 are not inherently erroneous but which are risky or suggest there
1888 may have been an error.
1890 You can request many specific warnings with options beginning @samp{-W},
1891 for example @option{-Wimplicit} to request warnings on implicit
1892 declarations. Each of these specific warning options also has a
1893 negative form beginning @samp{-Wno-} to turn off warnings;
1894 for example, @option{-Wno-implicit}. This manual lists only one of the
1895 two forms, whichever is not the default.
1897 The following options control the amount and kinds of warnings produced
1898 by GCC; for further, language-specific options also refer to
1899 @ref{C++ Dialect Options} and @ref{Objective-C Dialect Options}.
1902 @cindex syntax checking
1904 @opindex fsyntax-only
1905 Check the code for syntax errors, but don't do anything beyond that.
1909 Issue all the warnings demanded by strict ISO C and ISO C++;
1910 reject all programs that use forbidden extensions, and some other
1911 programs that do not follow ISO C and ISO C++. For ISO C, follows the
1912 version of the ISO C standard specified by any @option{-std} option used.
1914 Valid ISO C and ISO C++ programs should compile properly with or without
1915 this option (though a rare few will require @option{-ansi} or a
1916 @option{-std} option specifying the required version of ISO C)@. However,
1917 without this option, certain GNU extensions and traditional C and C++
1918 features are supported as well. With this option, they are rejected.
1920 @option{-pedantic} does not cause warning messages for use of the
1921 alternate keywords whose names begin and end with @samp{__}. Pedantic
1922 warnings are also disabled in the expression that follows
1923 @code{__extension__}. However, only system header files should use
1924 these escape routes; application programs should avoid them.
1925 @xref{Alternate Keywords}.
1927 Some users try to use @option{-pedantic} to check programs for strict ISO
1928 C conformance. They soon find that it does not do quite what they want:
1929 it finds some non-ISO practices, but not all---only those for which
1930 ISO C @emph{requires} a diagnostic, and some others for which
1931 diagnostics have been added.
1933 A feature to report any failure to conform to ISO C might be useful in
1934 some instances, but would require considerable additional work and would
1935 be quite different from @option{-pedantic}. We don't have plans to
1936 support such a feature in the near future.
1938 Where the standard specified with @option{-std} represents a GNU
1939 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
1940 corresponding @dfn{base standard}, the version of ISO C on which the GNU
1941 extended dialect is based. Warnings from @option{-pedantic} are given
1942 where they are required by the base standard. (It would not make sense
1943 for such warnings to be given only for features not in the specified GNU
1944 C dialect, since by definition the GNU dialects of C include all
1945 features the compiler supports with the given option, and there would be
1946 nothing to warn about.)
1948 @item -pedantic-errors
1949 @opindex pedantic-errors
1950 Like @option{-pedantic}, except that errors are produced rather than
1955 Inhibit all warning messages.
1959 Inhibit warning messages about the use of @samp{#import}.
1961 @item -Wchar-subscripts
1962 @opindex Wchar-subscripts
1963 Warn if an array subscript has type @code{char}. This is a common cause
1964 of error, as programmers often forget that this type is signed on some
1969 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
1970 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
1974 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
1975 the arguments supplied have types appropriate to the format string
1976 specified, and that the conversions specified in the format string make
1977 sense. This includes standard functions, and others specified by format
1978 attributes (@pxref{Function Attributes}), in the @code{printf},
1979 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
1980 not in the C standard) families.
1982 The formats are checked against the format features supported by GNU
1983 libc version 2.2. These include all ISO C90 and C99 features, as well
1984 as features from the Single Unix Specification and some BSD and GNU
1985 extensions. Other library implementations may not support all these
1986 features; GCC does not support warning about features that go beyond a
1987 particular library's limitations. However, if @option{-pedantic} is used
1988 with @option{-Wformat}, warnings will be given about format features not
1989 in the selected standard version (but not for @code{strfmon} formats,
1990 since those are not in any version of the C standard). @xref{C Dialect
1991 Options,,Options Controlling C Dialect}.
1993 Since @option{-Wformat} also checks for null format arguments for
1994 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
1996 @option{-Wformat} is included in @option{-Wall}. For more control over some
1997 aspects of format checking, the options @option{-Wno-format-y2k},
1998 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
1999 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2000 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2002 @item -Wno-format-y2k
2003 @opindex Wno-format-y2k
2004 If @option{-Wformat} is specified, do not warn about @code{strftime}
2005 formats which may yield only a two-digit year.
2007 @item -Wno-format-extra-args
2008 @opindex Wno-format-extra-args
2009 If @option{-Wformat} is specified, do not warn about excess arguments to a
2010 @code{printf} or @code{scanf} format function. The C standard specifies
2011 that such arguments are ignored.
2013 Where the unused arguments lie between used arguments that are
2014 specified with @samp{$} operand number specifications, normally
2015 warnings are still given, since the implementation could not know what
2016 type to pass to @code{va_arg} to skip the unused arguments. However,
2017 in the case of @code{scanf} formats, this option will suppress the
2018 warning if the unused arguments are all pointers, since the Single
2019 Unix Specification says that such unused arguments are allowed.
2021 @item -Wno-format-zero-length
2022 @opindex Wno-format-zero-length
2023 If @option{-Wformat} is specified, do not warn about zero-length formats.
2024 The C standard specifies that zero-length formats are allowed.
2026 @item -Wformat-nonliteral
2027 @opindex Wformat-nonliteral
2028 If @option{-Wformat} is specified, also warn if the format string is not a
2029 string literal and so cannot be checked, unless the format function
2030 takes its format arguments as a @code{va_list}.
2032 @item -Wformat-security
2033 @opindex Wformat-security
2034 If @option{-Wformat} is specified, also warn about uses of format
2035 functions that represent possible security problems. At present, this
2036 warns about calls to @code{printf} and @code{scanf} functions where the
2037 format string is not a string literal and there are no format arguments,
2038 as in @code{printf (foo);}. This may be a security hole if the format
2039 string came from untrusted input and contains @samp{%n}. (This is
2040 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2041 in future warnings may be added to @option{-Wformat-security} that are not
2042 included in @option{-Wformat-nonliteral}.)
2046 Enable @option{-Wformat} plus format checks not included in
2047 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2048 -Wformat-nonliteral -Wformat-security}.
2052 Enable warning about passing a null pointer for arguments marked as
2053 requiring a non-null value by the @code{nonnull} function attribute.
2055 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2056 can be disabled with the @option{-Wno-nonnull} option.
2058 @item -Wimplicit-int
2059 @opindex Wimplicit-int
2060 Warn when a declaration does not specify a type.
2062 @item -Wimplicit-function-declaration
2063 @itemx -Werror-implicit-function-declaration
2064 @opindex Wimplicit-function-declaration
2065 @opindex Werror-implicit-function-declaration
2066 Give a warning (or error) whenever a function is used before being
2071 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2075 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2076 function with external linkage, returning int, taking either zero
2077 arguments, two, or three arguments of appropriate types.
2079 @item -Wmissing-braces
2080 @opindex Wmissing-braces
2081 Warn if an aggregate or union initializer is not fully bracketed. In
2082 the following example, the initializer for @samp{a} is not fully
2083 bracketed, but that for @samp{b} is fully bracketed.
2086 int a[2][2] = @{ 0, 1, 2, 3 @};
2087 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2091 @opindex Wparentheses
2092 Warn if parentheses are omitted in certain contexts, such
2093 as when there is an assignment in a context where a truth value
2094 is expected, or when operators are nested whose precedence people
2095 often get confused about.
2097 Also warn about constructions where there may be confusion to which
2098 @code{if} statement an @code{else} branch belongs. Here is an example of
2113 In C, every @code{else} branch belongs to the innermost possible @code{if}
2114 statement, which in this example is @code{if (b)}. This is often not
2115 what the programmer expected, as illustrated in the above example by
2116 indentation the programmer chose. When there is the potential for this
2117 confusion, GCC will issue a warning when this flag is specified.
2118 To eliminate the warning, add explicit braces around the innermost
2119 @code{if} statement so there is no way the @code{else} could belong to
2120 the enclosing @code{if}. The resulting code would look like this:
2136 @item -Wsequence-point
2137 @opindex Wsequence-point
2138 Warn about code that may have undefined semantics because of violations
2139 of sequence point rules in the C standard.
2141 The C standard defines the order in which expressions in a C program are
2142 evaluated in terms of @dfn{sequence points}, which represent a partial
2143 ordering between the execution of parts of the program: those executed
2144 before the sequence point, and those executed after it. These occur
2145 after the evaluation of a full expression (one which is not part of a
2146 larger expression), after the evaluation of the first operand of a
2147 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2148 function is called (but after the evaluation of its arguments and the
2149 expression denoting the called function), and in certain other places.
2150 Other than as expressed by the sequence point rules, the order of
2151 evaluation of subexpressions of an expression is not specified. All
2152 these rules describe only a partial order rather than a total order,
2153 since, for example, if two functions are called within one expression
2154 with no sequence point between them, the order in which the functions
2155 are called is not specified. However, the standards committee have
2156 ruled that function calls do not overlap.
2158 It is not specified when between sequence points modifications to the
2159 values of objects take effect. Programs whose behavior depends on this
2160 have undefined behavior; the C standard specifies that ``Between the
2161 previous and next sequence point an object shall have its stored value
2162 modified at most once by the evaluation of an expression. Furthermore,
2163 the prior value shall be read only to determine the value to be
2164 stored.''. If a program breaks these rules, the results on any
2165 particular implementation are entirely unpredictable.
2167 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2168 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2169 diagnosed by this option, and it may give an occasional false positive
2170 result, but in general it has been found fairly effective at detecting
2171 this sort of problem in programs.
2173 The present implementation of this option only works for C programs. A
2174 future implementation may also work for C++ programs.
2176 The C standard is worded confusingly, therefore there is some debate
2177 over the precise meaning of the sequence point rules in subtle cases.
2178 Links to discussions of the problem, including proposed formal
2179 definitions, may be found on our readings page, at
2180 @w{@uref{http://gcc.gnu.org/readings.html}}.
2183 @opindex Wreturn-type
2184 Warn whenever a function is defined with a return-type that defaults to
2185 @code{int}. Also warn about any @code{return} statement with no
2186 return-value in a function whose return-type is not @code{void}.
2188 For C++, a function without return type always produces a diagnostic
2189 message, even when @option{-Wno-return-type} is specified. The only
2190 exceptions are @samp{main} and functions defined in system headers.
2194 Warn whenever a @code{switch} statement has an index of enumeral type
2195 and lacks a @code{case} for one or more of the named codes of that
2196 enumeration. (The presence of a @code{default} label prevents this
2197 warning.) @code{case} labels outside the enumeration range also
2198 provoke warnings when this option is used.
2200 @item -Wswitch-default
2201 @opindex Wswitch-switch
2202 Warn whenever a @code{switch} statement does not have a @code{default}
2206 @opindex Wswitch-enum
2207 Warn whenever a @code{switch} statement has an index of enumeral type
2208 and lacks a @code{case} for one or more of the named codes of that
2209 enumeration. @code{case} labels outside the enumeration range also
2210 provoke warnings when this option is used.
2214 Warn if any trigraphs are encountered that might change the meaning of
2215 the program (trigraphs within comments are not warned about).
2217 @item -Wunused-function
2218 @opindex Wunused-function
2219 Warn whenever a static function is declared but not defined or a
2220 non\-inline static function is unused.
2222 @item -Wunused-label
2223 @opindex Wunused-label
2224 Warn whenever a label is declared but not used.
2226 To suppress this warning use the @samp{unused} attribute
2227 (@pxref{Variable Attributes}).
2229 @item -Wunused-parameter
2230 @opindex Wunused-parameter
2231 Warn whenever a function parameter is unused aside from its declaration.
2233 To suppress this warning use the @samp{unused} attribute
2234 (@pxref{Variable Attributes}).
2236 @item -Wunused-variable
2237 @opindex Wunused-variable
2238 Warn whenever a local variable or non-constant static variable is unused
2239 aside from its declaration
2241 To suppress this warning use the @samp{unused} attribute
2242 (@pxref{Variable Attributes}).
2244 @item -Wunused-value
2245 @opindex Wunused-value
2246 Warn whenever a statement computes a result that is explicitly not used.
2248 To suppress this warning cast the expression to @samp{void}.
2252 All the above @option{-Wunused} options combined.
2254 In order to get a warning about an unused function parameter, you must
2255 either specify @samp{-W -Wunused} or separately specify
2256 @option{-Wunused-parameter}.
2258 @item -Wuninitialized
2259 @opindex Wuninitialized
2260 Warn if an automatic variable is used without first being initialized or
2261 if a variable may be clobbered by a @code{setjmp} call.
2263 These warnings are possible only in optimizing compilation,
2264 because they require data flow information that is computed only
2265 when optimizing. If you don't specify @option{-O}, you simply won't
2268 These warnings occur only for variables that are candidates for
2269 register allocation. Therefore, they do not occur for a variable that
2270 is declared @code{volatile}, or whose address is taken, or whose size
2271 is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
2272 structures, unions or arrays, even when they are in registers.
2274 Note that there may be no warning about a variable that is used only
2275 to compute a value that itself is never used, because such
2276 computations may be deleted by data flow analysis before the warnings
2279 These warnings are made optional because GCC is not smart
2280 enough to see all the reasons why the code might be correct
2281 despite appearing to have an error. Here is one example of how
2302 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2303 always initialized, but GCC doesn't know this. Here is
2304 another common case:
2309 if (change_y) save_y = y, y = new_y;
2311 if (change_y) y = save_y;
2316 This has no bug because @code{save_y} is used only if it is set.
2318 @cindex @code{longjmp} warnings
2319 This option also warns when a non-volatile automatic variable might be
2320 changed by a call to @code{longjmp}. These warnings as well are possible
2321 only in optimizing compilation.
2323 The compiler sees only the calls to @code{setjmp}. It cannot know
2324 where @code{longjmp} will be called; in fact, a signal handler could
2325 call it at any point in the code. As a result, you may get a warning
2326 even when there is in fact no problem because @code{longjmp} cannot
2327 in fact be called at the place which would cause a problem.
2329 Some spurious warnings can be avoided if you declare all the functions
2330 you use that never return as @code{noreturn}. @xref{Function
2333 @item -Wunknown-pragmas
2334 @opindex Wunknown-pragmas
2335 @cindex warning for unknown pragmas
2336 @cindex unknown pragmas, warning
2337 @cindex pragmas, warning of unknown
2338 Warn when a #pragma directive is encountered which is not understood by
2339 GCC@. If this command line option is used, warnings will even be issued
2340 for unknown pragmas in system header files. This is not the case if
2341 the warnings were only enabled by the @option{-Wall} command line option.
2345 All of the above @samp{-W} options combined. This enables all the
2346 warnings about constructions that some users consider questionable, and
2347 that are easy to avoid (or modify to prevent the warning), even in
2348 conjunction with macros. This also enables some language-specific
2349 warnings described in @ref{C++ Dialect Options} and
2350 @ref{Objective-C Dialect Options}.
2353 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2354 Some of them warn about constructions that users generally do not
2355 consider questionable, but which occasionally you might wish to check
2356 for; others warn about constructions that are necessary or hard to avoid
2357 in some cases, and there is no simple way to modify the code to suppress
2363 Print extra warning messages for these events:
2367 A function can return either with or without a value. (Falling
2368 off the end of the function body is considered returning without
2369 a value.) For example, this function would evoke such a
2383 An expression-statement or the left-hand side of a comma expression
2384 contains no side effects.
2385 To suppress the warning, cast the unused expression to void.
2386 For example, an expression such as @samp{x[i,j]} will cause a warning,
2387 but @samp{x[(void)i,j]} will not.
2390 An unsigned value is compared against zero with @samp{<} or @samp{<=}.
2393 A comparison like @samp{x<=y<=z} appears; this is equivalent to
2394 @samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from
2395 that of ordinary mathematical notation.
2398 Storage-class specifiers like @code{static} are not the first things in
2399 a declaration. According to the C Standard, this usage is obsolescent.
2402 The return type of a function has a type qualifier such as @code{const}.
2403 Such a type qualifier has no effect, since the value returned by a
2404 function is not an lvalue. (But don't warn about the GNU extension of
2405 @code{volatile void} return types. That extension will be warned about
2406 if @option{-pedantic} is specified.)
2409 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2413 A comparison between signed and unsigned values could produce an
2414 incorrect result when the signed value is converted to unsigned.
2415 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2418 An aggregate has a partly bracketed initializer.
2419 For example, the following code would evoke such a warning,
2420 because braces are missing around the initializer for @code{x.h}:
2423 struct s @{ int f, g; @};
2424 struct t @{ struct s h; int i; @};
2425 struct t x = @{ 1, 2, 3 @};
2429 An aggregate has an initializer which does not initialize all members.
2430 For example, the following code would cause such a warning, because
2431 @code{x.h} would be implicitly initialized to zero:
2434 struct s @{ int f, g, h; @};
2435 struct s x = @{ 3, 4 @};
2439 @item -Wno-div-by-zero
2440 @opindex Wno-div-by-zero
2441 @opindex Wdiv-by-zero
2442 Do not warn about compile-time integer division by zero. Floating point
2443 division by zero is not warned about, as it can be a legitimate way of
2444 obtaining infinities and NaNs.
2446 @item -Wsystem-headers
2447 @opindex Wsystem-headers
2448 @cindex warnings from system headers
2449 @cindex system headers, warnings from
2450 Print warning messages for constructs found in system header files.
2451 Warnings from system headers are normally suppressed, on the assumption
2452 that they usually do not indicate real problems and would only make the
2453 compiler output harder to read. Using this command line option tells
2454 GCC to emit warnings from system headers as if they occurred in user
2455 code. However, note that using @option{-Wall} in conjunction with this
2456 option will @emph{not} warn about unknown pragmas in system
2457 headers---for that, @option{-Wunknown-pragmas} must also be used.
2460 @opindex Wfloat-equal
2461 Warn if floating point values are used in equality comparisons.
2463 The idea behind this is that sometimes it is convenient (for the
2464 programmer) to consider floating-point values as approximations to
2465 infinitely precise real numbers. If you are doing this, then you need
2466 to compute (by analysing the code, or in some other way) the maximum or
2467 likely maximum error that the computation introduces, and allow for it
2468 when performing comparisons (and when producing output, but that's a
2469 different problem). In particular, instead of testing for equality, you
2470 would check to see whether the two values have ranges that overlap; and
2471 this is done with the relational operators, so equality comparisons are
2474 @item -Wtraditional @r{(C only)}
2475 @opindex Wtraditional
2476 Warn about certain constructs that behave differently in traditional and
2477 ISO C@. Also warn about ISO C constructs that have no traditional C
2478 equivalent, and/or problematic constructs which should be avoided.
2482 Macro parameters that appear within string literals in the macro body.
2483 In traditional C macro replacement takes place within string literals,
2484 but does not in ISO C@.
2487 In traditional C, some preprocessor directives did not exist.
2488 Traditional preprocessors would only consider a line to be a directive
2489 if the @samp{#} appeared in column 1 on the line. Therefore
2490 @option{-Wtraditional} warns about directives that traditional C
2491 understands but would ignore because the @samp{#} does not appear as the
2492 first character on the line. It also suggests you hide directives like
2493 @samp{#pragma} not understood by traditional C by indenting them. Some
2494 traditional implementations would not recognize @samp{#elif}, so it
2495 suggests avoiding it altogether.
2498 A function-like macro that appears without arguments.
2501 The unary plus operator.
2504 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2505 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2506 constants.) Note, these suffixes appear in macros defined in the system
2507 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2508 Use of these macros in user code might normally lead to spurious
2509 warnings, however gcc's integrated preprocessor has enough context to
2510 avoid warning in these cases.
2513 A function declared external in one block and then used after the end of
2517 A @code{switch} statement has an operand of type @code{long}.
2520 A non-@code{static} function declaration follows a @code{static} one.
2521 This construct is not accepted by some traditional C compilers.
2524 The ISO type of an integer constant has a different width or
2525 signedness from its traditional type. This warning is only issued if
2526 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2527 typically represent bit patterns, are not warned about.
2530 Usage of ISO string concatenation is detected.
2533 Initialization of automatic aggregates.
2536 Identifier conflicts with labels. Traditional C lacks a separate
2537 namespace for labels.
2540 Initialization of unions. If the initializer is zero, the warning is
2541 omitted. This is done under the assumption that the zero initializer in
2542 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2543 initializer warnings and relies on default initialization to zero in the
2547 Conversions by prototypes between fixed/floating point values and vice
2548 versa. The absence of these prototypes when compiling with traditional
2549 C would cause serious problems. This is a subset of the possible
2550 conversion warnings, for the full set use @option{-Wconversion}.
2553 Use of ISO C style function definitions. This warning intentionally is
2554 @emph{not} issued for prototype declarations or variadic functions
2555 because these ISO C features will appear in your code when using
2556 libiberty's traditional C compatibility macros, @code{PARAMS} and
2557 @code{VPARAMS}. This warning is also bypassed for nested functions
2558 because that feature is already a gcc extension and thus not relevant to
2559 traditional C compatibility.
2564 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
2566 @item -Wendif-labels
2567 @opindex Wendif-labels
2568 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
2572 Warn whenever a local variable shadows another local variable, parameter or
2573 global variable or whenever a built-in function is shadowed.
2575 @item -Wlarger-than-@var{len}
2576 @opindex Wlarger-than
2577 Warn whenever an object of larger than @var{len} bytes is defined.
2579 @item -Wpointer-arith
2580 @opindex Wpointer-arith
2581 Warn about anything that depends on the ``size of'' a function type or
2582 of @code{void}. GNU C assigns these types a size of 1, for
2583 convenience in calculations with @code{void *} pointers and pointers
2586 @item -Wbad-function-cast @r{(C only)}
2587 @opindex Wbad-function-cast
2588 Warn whenever a function call is cast to a non-matching type.
2589 For example, warn if @code{int malloc()} is cast to @code{anything *}.
2593 Warn whenever a pointer is cast so as to remove a type qualifier from
2594 the target type. For example, warn if a @code{const char *} is cast
2595 to an ordinary @code{char *}.
2598 @opindex Wcast-align
2599 Warn whenever a pointer is cast such that the required alignment of the
2600 target is increased. For example, warn if a @code{char *} is cast to
2601 an @code{int *} on machines where integers can only be accessed at
2602 two- or four-byte boundaries.
2604 @item -Wwrite-strings
2605 @opindex Wwrite-strings
2606 When compiling C, give string constants the type @code{const
2607 char[@var{length}]} so that
2608 copying the address of one into a non-@code{const} @code{char *}
2609 pointer will get a warning; when compiling C++, warn about the
2610 deprecated conversion from string constants to @code{char *}.
2611 These warnings will help you find at
2612 compile time code that can try to write into a string constant, but
2613 only if you have been very careful about using @code{const} in
2614 declarations and prototypes. Otherwise, it will just be a nuisance;
2615 this is why we did not make @option{-Wall} request these warnings.
2618 @opindex Wconversion
2619 Warn if a prototype causes a type conversion that is different from what
2620 would happen to the same argument in the absence of a prototype. This
2621 includes conversions of fixed point to floating and vice versa, and
2622 conversions changing the width or signedness of a fixed point argument
2623 except when the same as the default promotion.
2625 Also, warn if a negative integer constant expression is implicitly
2626 converted to an unsigned type. For example, warn about the assignment
2627 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
2628 casts like @code{(unsigned) -1}.
2630 @item -Wsign-compare
2631 @opindex Wsign-compare
2632 @cindex warning for comparison of signed and unsigned values
2633 @cindex comparison of signed and unsigned values, warning
2634 @cindex signed and unsigned values, comparison warning
2635 Warn when a comparison between signed and unsigned values could produce
2636 an incorrect result when the signed value is converted to unsigned.
2637 This warning is also enabled by @option{-W}; to get the other warnings
2638 of @option{-W} without this warning, use @samp{-W -Wno-sign-compare}.
2640 @item -Waggregate-return
2641 @opindex Waggregate-return
2642 Warn if any functions that return structures or unions are defined or
2643 called. (In languages where you can return an array, this also elicits
2646 @item -Wstrict-prototypes @r{(C only)}
2647 @opindex Wstrict-prototypes
2648 Warn if a function is declared or defined without specifying the
2649 argument types. (An old-style function definition is permitted without
2650 a warning if preceded by a declaration which specifies the argument
2653 @item -Wmissing-prototypes @r{(C only)}
2654 @opindex Wmissing-prototypes
2655 Warn if a global function is defined without a previous prototype
2656 declaration. This warning is issued even if the definition itself
2657 provides a prototype. The aim is to detect global functions that fail
2658 to be declared in header files.
2660 @item -Wmissing-declarations
2661 @opindex Wmissing-declarations
2662 Warn if a global function is defined without a previous declaration.
2663 Do so even if the definition itself provides a prototype.
2664 Use this option to detect global functions that are not declared in
2667 @item -Wmissing-noreturn
2668 @opindex Wmissing-noreturn
2669 Warn about functions which might be candidates for attribute @code{noreturn}.
2670 Note these are only possible candidates, not absolute ones. Care should
2671 be taken to manually verify functions actually do not ever return before
2672 adding the @code{noreturn} attribute, otherwise subtle code generation
2673 bugs could be introduced. You will not get a warning for @code{main} in
2674 hosted C environments.
2676 @item -Wmissing-format-attribute
2677 @opindex Wmissing-format-attribute
2679 If @option{-Wformat} is enabled, also warn about functions which might be
2680 candidates for @code{format} attributes. Note these are only possible
2681 candidates, not absolute ones. GCC will guess that @code{format}
2682 attributes might be appropriate for any function that calls a function
2683 like @code{vprintf} or @code{vscanf}, but this might not always be the
2684 case, and some functions for which @code{format} attributes are
2685 appropriate may not be detected. This option has no effect unless
2686 @option{-Wformat} is enabled (possibly by @option{-Wall}).
2688 @item -Wno-multichar
2689 @opindex Wno-multichar
2691 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
2692 Usually they indicate a typo in the user's code, as they have
2693 implementation-defined values, and should not be used in portable code.
2695 @item -Wno-deprecated-declarations
2696 @opindex Wno-deprecated-declarations
2697 Do not warn about uses of functions, variables, and types marked as
2698 deprecated by using the @code{deprecated} attribute.
2699 (@pxref{Function Attributes}, @pxref{Variable Attributes},
2700 @pxref{Type Attributes}.)
2704 Warn if a structure is given the packed attribute, but the packed
2705 attribute has no effect on the layout or size of the structure.
2706 Such structures may be mis-aligned for little benefit. For
2707 instance, in this code, the variable @code{f.x} in @code{struct bar}
2708 will be misaligned even though @code{struct bar} does not itself
2709 have the packed attribute:
2716 @} __attribute__((packed));
2726 Warn if padding is included in a structure, either to align an element
2727 of the structure or to align the whole structure. Sometimes when this
2728 happens it is possible to rearrange the fields of the structure to
2729 reduce the padding and so make the structure smaller.
2731 @item -Wredundant-decls
2732 @opindex Wredundant-decls
2733 Warn if anything is declared more than once in the same scope, even in
2734 cases where multiple declaration is valid and changes nothing.
2736 @item -Wnested-externs @r{(C only)}
2737 @opindex Wnested-externs
2738 Warn if an @code{extern} declaration is encountered within a function.
2740 @item -Wunreachable-code
2741 @opindex Wunreachable-code
2742 Warn if the compiler detects that code will never be executed.
2744 This option is intended to warn when the compiler detects that at
2745 least a whole line of source code will never be executed, because
2746 some condition is never satisfied or because it is after a
2747 procedure that never returns.
2749 It is possible for this option to produce a warning even though there
2750 are circumstances under which part of the affected line can be executed,
2751 so care should be taken when removing apparently-unreachable code.
2753 For instance, when a function is inlined, a warning may mean that the
2754 line is unreachable in only one inlined copy of the function.
2756 This option is not made part of @option{-Wall} because in a debugging
2757 version of a program there is often substantial code which checks
2758 correct functioning of the program and is, hopefully, unreachable
2759 because the program does work. Another common use of unreachable
2760 code is to provide behavior which is selectable at compile-time.
2764 Warn if a function can not be inlined and it was declared as inline.
2768 @opindex Wno-long-long
2769 Warn if @samp{long long} type is used. This is default. To inhibit
2770 the warning messages, use @option{-Wno-long-long}. Flags
2771 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
2772 only when @option{-pedantic} flag is used.
2774 @item -Wdisabled-optimization
2775 @opindex Wdisabled-optimization
2776 Warn if a requested optimization pass is disabled. This warning does
2777 not generally indicate that there is anything wrong with your code; it
2778 merely indicates that GCC's optimizers were unable to handle the code
2779 effectively. Often, the problem is that your code is too big or too
2780 complex; GCC will refuse to optimize programs when the optimization
2781 itself is likely to take inordinate amounts of time.
2785 Make all warnings into errors.
2788 @node Debugging Options
2789 @section Options for Debugging Your Program or GCC
2790 @cindex options, debugging
2791 @cindex debugging information options
2793 GCC has various special options that are used for debugging
2794 either your program or GCC:
2799 Produce debugging information in the operating system's native format
2800 (stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging
2803 On most systems that use stabs format, @option{-g} enables use of extra
2804 debugging information that only GDB can use; this extra information
2805 makes debugging work better in GDB but will probably make other debuggers
2807 refuse to read the program. If you want to control for certain whether
2808 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
2809 @option{-gxcoff+}, @option{-gxcoff}, @option{-gdwarf-1+}, @option{-gdwarf-1},
2810 or @option{-gvms} (see below).
2812 Unlike most other C compilers, GCC allows you to use @option{-g} with
2813 @option{-O}. The shortcuts taken by optimized code may occasionally
2814 produce surprising results: some variables you declared may not exist
2815 at all; flow of control may briefly move where you did not expect it;
2816 some statements may not be executed because they compute constant
2817 results or their values were already at hand; some statements may
2818 execute in different places because they were moved out of loops.
2820 Nevertheless it proves possible to debug optimized output. This makes
2821 it reasonable to use the optimizer for programs that might have bugs.
2823 The following options are useful when GCC is generated with the
2824 capability for more than one debugging format.
2828 Produce debugging information for use by GDB@. This means to use the
2829 most expressive format available (DWARF 2, stabs, or the native format
2830 if neither of those are supported), including GDB extensions if at all
2835 Produce debugging information in stabs format (if that is supported),
2836 without GDB extensions. This is the format used by DBX on most BSD
2837 systems. On MIPS, Alpha and System V Release 4 systems this option
2838 produces stabs debugging output which is not understood by DBX or SDB@.
2839 On System V Release 4 systems this option requires the GNU assembler.
2843 Produce debugging information in stabs format (if that is supported),
2844 using GNU extensions understood only by the GNU debugger (GDB)@. The
2845 use of these extensions is likely to make other debuggers crash or
2846 refuse to read the program.
2850 Produce debugging information in COFF format (if that is supported).
2851 This is the format used by SDB on most System V systems prior to
2856 Produce debugging information in XCOFF format (if that is supported).
2857 This is the format used by the DBX debugger on IBM RS/6000 systems.
2861 Produce debugging information in XCOFF format (if that is supported),
2862 using GNU extensions understood only by the GNU debugger (GDB)@. The
2863 use of these extensions is likely to make other debuggers crash or
2864 refuse to read the program, and may cause assemblers other than the GNU
2865 assembler (GAS) to fail with an error.
2869 Produce debugging information in DWARF version 1 format (if that is
2870 supported). This is the format used by SDB on most System V Release 4
2873 This option is deprecated.
2877 Produce debugging information in DWARF version 1 format (if that is
2878 supported), using GNU extensions understood only by the GNU debugger
2879 (GDB)@. The use of these extensions is likely to make other debuggers
2880 crash or refuse to read the program.
2882 This option is deprecated.
2886 Produce debugging information in DWARF version 2 format (if that is
2887 supported). This is the format used by DBX on IRIX 6.
2891 Produce debugging information in VMS debug format (if that is
2892 supported). This is the format used by DEBUG on VMS systems.
2895 @itemx -ggdb@var{level}
2896 @itemx -gstabs@var{level}
2897 @itemx -gcoff@var{level}
2898 @itemx -gxcoff@var{level}
2899 @itemx -gvms@var{level}
2900 Request debugging information and also use @var{level} to specify how
2901 much information. The default level is 2.
2903 Level 1 produces minimal information, enough for making backtraces in
2904 parts of the program that you don't plan to debug. This includes
2905 descriptions of functions and external variables, but no information
2906 about local variables and no line numbers.
2908 Level 3 includes extra information, such as all the macro definitions
2909 present in the program. Some debuggers support macro expansion when
2910 you use @option{-g3}.
2912 Note that in order to avoid confusion between DWARF1 debug level 2,
2913 and DWARF2, neither @option{-gdwarf} nor @option{-gdwarf-2} accept
2914 a concatenated debug level. Instead use an additional @option{-g@var{level}}
2915 option to change the debug level for DWARF1 or DWARF2.
2920 Generate extra code to write profile information suitable for the
2921 analysis program @code{prof}. You must use this option when compiling
2922 the source files you want data about, and you must also use it when
2925 @cindex @code{gprof}
2928 Generate extra code to write profile information suitable for the
2929 analysis program @code{gprof}. You must use this option when compiling
2930 the source files you want data about, and you must also use it when
2935 Makes the compiler print out each function name as it is compiled, and
2936 print some statistics about each pass when it finishes.
2939 @opindex ftime-report
2940 Makes the compiler print some statistics about the time consumed by each
2941 pass when it finishes.
2944 @opindex fmem-report
2945 Makes the compiler print some statistics about permanent memory
2946 allocation when it finishes.
2948 @item -fprofile-arcs
2949 @opindex fprofile-arcs
2950 Instrument @dfn{arcs} during compilation to generate coverage data or
2951 for profile-directed block ordering. During execution the program
2952 records how many times each branch is executed and how many times it is
2953 taken. When the compiled program exits it saves this data to a file
2954 called @file{@var{auxname}.da} for each source file. @var{auxname} is
2955 generated from the name of the output file, if explicitly specified and
2956 it is not the final executable, otherwise it is the basename of the
2957 source file. In both cases any suffix is removed (e.g. @file{foo.da}
2958 for input file @file{dir/foo.c}, or @file{dir/foo.da} for output file
2959 specified as @option{-o dir/foo.o}).
2961 For profile-directed block ordering, compile the program with
2962 @option{-fprofile-arcs} plus optimization and code generation options,
2963 generate the arc profile information by running the program on a
2964 selected workload, and then compile the program again with the same
2965 optimization and code generation options plus
2966 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
2967 Control Optimization}).
2969 The other use of @option{-fprofile-arcs} is for use with @code{gcov},
2970 when it is used with the @option{-ftest-coverage} option.
2972 With @option{-fprofile-arcs}, for each function of your program GCC
2973 creates a program flow graph, then finds a spanning tree for the graph.
2974 Only arcs that are not on the spanning tree have to be instrumented: the
2975 compiler adds code to count the number of times that these arcs are
2976 executed. When an arc is the only exit or only entrance to a block, the
2977 instrumentation code can be added to the block; otherwise, a new basic
2978 block must be created to hold the instrumentation code.
2981 @item -ftest-coverage
2982 @opindex ftest-coverage
2983 Create data files for the @code{gcov} code-coverage utility
2984 (@pxref{Gcov,, @code{gcov}: a GCC Test Coverage Program}). See
2985 @option{-fprofile-arcs} option above for a description of @var{auxname}.
2988 @item @var{auxname}.bb
2989 A mapping from basic blocks to line numbers, which @code{gcov} uses to
2990 associate basic block execution counts with line numbers.
2992 @item @var{auxname}.bbg
2993 A list of all arcs in the program flow graph. This allows @code{gcov}
2994 to reconstruct the program flow graph, so that it can compute all basic
2995 block and arc execution counts from the information in the
2996 @file{@var{auxname}.da} file.
2999 Use @option{-ftest-coverage} with @option{-fprofile-arcs}; the latter
3000 option adds instrumentation to the program, which then writes
3001 execution counts to another data file:
3004 @item @var{auxname}.da
3005 Runtime arc execution counts, used in conjunction with the arc
3006 information in the file @file{@var{auxname}.bbg}.
3009 Coverage data will map better to the source files if
3010 @option{-ftest-coverage} is used without optimization.
3012 @item -d@var{letters}
3014 Says to make debugging dumps during compilation at times specified by
3015 @var{letters}. This is used for debugging the compiler. The file names
3016 for most of the dumps are made by appending a pass number and a word to
3017 the @var{dumpname}. @var{dumpname} is generated from the name of the
3018 output file, if explicitly specified and it is not an executable,
3019 otherwise it is the basename of the source file. In both cases any
3020 suffix is removed (e.g. @file{foo.00.rtl} or @file{foo.01.sibling}).
3021 Here are the possible letters for use in @var{letters}, and their
3027 Annotate the assembler output with miscellaneous debugging information.
3030 Dump after computing branch probabilities, to @file{@var{file}.15.bp}.
3033 Dump after block reordering, to @file{@var{file}.30.bbro}.
3036 Dump after instruction combination, to the file @file{@var{file}.17.combine}.
3039 Dump after the first if conversion, to the file @file{@var{file}.18.ce}.
3042 Dump after delayed branch scheduling, to @file{@var{file}.32.dbr}.
3045 Dump all macro definitions, at the end of preprocessing, in addition to
3049 Dump after SSA optimizations, to @file{@var{file}.04.ssa} and
3050 @file{@var{file}.07.ussa}.
3053 Dump after the second if conversion, to @file{@var{file}.27.ce2}.
3056 Dump after life analysis, to @file{@var{file}.16.life}.
3059 Dump after purging @code{ADDRESSOF} codes, to @file{@var{file}.10.addressof}.
3062 Dump after global register allocation, to @file{@var{file}.22.greg}.
3065 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
3068 Dump after reg-to-stack conversion, to @file{@var{file}.29.stack}.
3071 Dump after post-reload optimizations, to @file{@var{file}.23.postreload}.
3074 Dump after GCSE, to @file{@var{file}.11.gcse}.
3077 Dump after sibling call optimizations, to @file{@var{file}.01.sibling}.
3080 Dump after the first jump optimization, to @file{@var{file}.03.jump}.
3083 Dump after conversion from registers to stack, to @file{@var{file}.33.stack}.
3086 Dump after local register allocation, to @file{@var{file}.21.lreg}.
3089 Dump after loop optimization, to @file{@var{file}.12.loop}.
3092 Dump after performing the machine dependent reorganisation pass, to
3093 @file{@var{file}.31.mach}.
3096 Dump after register renumbering, to @file{@var{file}.26.rnreg}.
3099 Dump after the register move pass, to @file{@var{file}.19.regmove}.
3102 Dump after RTL generation, to @file{@var{file}.00.rtl}.
3105 Dump after the second scheduling pass, to @file{@var{file}.28.sched2}.
3108 Dump after CSE (including the jump optimization that sometimes follows
3109 CSE), to @file{@var{file}.09.cse}.
3112 Dump after the first scheduling pass, to @file{@var{file}.20.sched}.
3115 Dump after the second CSE pass (including the jump optimization that
3116 sometimes follows CSE), to @file{@var{file}.13.cse2}.
3119 Dump after null pointer ellimination pass ti @file{@var{file}.08.null}.
3122 Dump after the second flow pass, to @file{@var{file}.24.flow2}.
3125 Dump after SSA dead code elimination, to @file{@var{file}.06.ssadce}.
3128 Dump after the peephole pass, to @file{@var{file}.25.peephole2}.
3131 Produce all the dumps listed above.
3134 Print statistics on memory usage, at the end of the run, to
3138 Annotate the assembler output with a comment indicating which
3139 pattern and alternative was used. The length of each instruction is
3143 Dump the RTL in the assembler output as a comment before each instruction.
3144 Also turns on @option{-dp} annotation.
3147 For each of the other indicated dump files (except for
3148 @file{@var{file}.00.rtl}), dump a representation of the control flow graph
3149 suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3152 Just generate RTL for a function instead of compiling it. Usually used
3156 Dump debugging information during parsing, to standard error.
3159 @item -fdump-unnumbered
3160 @opindex fdump-unnumbered
3161 When doing debugging dumps (see @option{-d} option above), suppress instruction
3162 numbers and line number note output. This makes it more feasible to
3163 use diff on debugging dumps for compiler invocations with different
3164 options, in particular with and without @option{-g}.
3166 @item -fdump-translation-unit @r{(C and C++ only)}
3167 @itemx -fdump-translation-unit-@var{options} @r{(C and C++ only)}
3168 @opindex fdump-translation-unit
3169 Dump a representation of the tree structure for the entire translation
3170 unit to a file. The file name is made by appending @file{.tu} to the
3171 source file name. If the @samp{-@var{options}} form is used, @var{options}
3172 controls the details of the dump as described for the
3173 @option{-fdump-tree} options.
3175 @item -fdump-class-hierarchy @r{(C++ only)}
3176 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3177 @opindex fdump-class-hierarchy
3178 Dump a representation of each class's hierarchy and virtual function
3179 table layout to a file. The file name is made by appending @file{.class}
3180 to the source file name. If the @samp{-@var{options}} form is used,
3181 @var{options} controls the details of the dump as described for the
3182 @option{-fdump-tree} options.
3184 @item -fdump-tree-@var{switch} @r{(C++ only)}
3185 @itemx -fdump-tree-@var{switch}-@var{options} @r{(C++ only)}
3187 Control the dumping at various stages of processing the intermediate
3188 language tree to a file. The file name is generated by appending a switch
3189 specific suffix to the source file name. If the @samp{-@var{options}}
3190 form is used, @var{options} is a list of @samp{-} separated options that
3191 control the details of the dump. Not all options are applicable to all
3192 dumps, those which are not meaningful will be ignored. The following
3193 options are available
3197 Print the address of each node. Usually this is not meaningful as it
3198 changes according to the environment and source file. Its primary use
3199 is for tying up a dump file with a debug environment.
3201 Inhibit dumping of members of a scope or body of a function merely
3202 because that scope has been reached. Only dump such items when they
3203 are directly reachable by some other path.
3205 Turn on all options.
3208 The following tree dumps are possible:
3211 Dump before any tree based optimization, to @file{@var{file}.original}.
3213 Dump after all tree based optimization, to @file{@var{file}.optimized}.
3215 Dump after function inlining, to @file{@var{file}.inlined}.
3220 Store the usual ``temporary'' intermediate files permanently; place them
3221 in the current directory and name them based on the source file. Thus,
3222 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
3223 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
3224 preprocessed @file{foo.i} output file even though the compiler now
3225 normally uses an integrated preprocessor.
3229 Report the CPU time taken by each subprocess in the compilation
3230 sequence. For C source files, this is the compiler proper and assembler
3231 (plus the linker if linking is done). The output looks like this:
3238 The first number on each line is the ``user time,'' that is time spent
3239 executing the program itself. The second number is ``system time,''
3240 time spent executing operating system routines on behalf of the program.
3241 Both numbers are in seconds.
3243 @item -print-file-name=@var{library}
3244 @opindex print-file-name
3245 Print the full absolute name of the library file @var{library} that
3246 would be used when linking---and don't do anything else. With this
3247 option, GCC does not compile or link anything; it just prints the
3250 @item -print-multi-directory
3251 @opindex print-multi-directory
3252 Print the directory name corresponding to the multilib selected by any
3253 other switches present in the command line. This directory is supposed
3254 to exist in @env{GCC_EXEC_PREFIX}.
3256 @item -print-multi-lib
3257 @opindex print-multi-lib
3258 Print the mapping from multilib directory names to compiler switches
3259 that enable them. The directory name is separated from the switches by
3260 @samp{;}, and each switch starts with an @samp{@@} instead of the
3261 @samp{-}, without spaces between multiple switches. This is supposed to
3262 ease shell-processing.
3264 @item -print-prog-name=@var{program}
3265 @opindex print-prog-name
3266 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
3268 @item -print-libgcc-file-name
3269 @opindex print-libgcc-file-name
3270 Same as @option{-print-file-name=libgcc.a}.
3272 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
3273 but you do want to link with @file{libgcc.a}. You can do
3276 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
3279 @item -print-search-dirs
3280 @opindex print-search-dirs
3281 Print the name of the configured installation directory and a list of
3282 program and library directories gcc will search---and don't do anything else.
3284 This is useful when gcc prints the error message
3285 @samp{installation problem, cannot exec cpp0: No such file or directory}.
3286 To resolve this you either need to put @file{cpp0} and the other compiler
3287 components where gcc expects to find them, or you can set the environment
3288 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
3289 Don't forget the trailing '/'.
3290 @xref{Environment Variables}.
3293 @opindex dumpmachine
3294 Print the compiler's target machine (for example,
3295 @samp{i686-pc-linux-gnu})---and don't do anything else.
3298 @opindex dumpversion
3299 Print the compiler version (for example, @samp{3.0})---and don't do
3304 Print the compiler's built-in specs---and don't do anything else. (This
3305 is used when GCC itself is being built.) @xref{Spec Files}.
3308 @node Optimize Options
3309 @section Options That Control Optimization
3310 @cindex optimize options
3311 @cindex options, optimization
3313 These options control various sorts of optimizations:
3320 Optimize. Optimizing compilation takes somewhat more time, and a lot
3321 more memory for a large function.
3323 Without @option{-O}, the compiler's goal is to reduce the cost of
3324 compilation and to make debugging produce the expected results.
3325 Statements are independent: if you stop the program with a breakpoint
3326 between statements, you can then assign a new value to any variable or
3327 change the program counter to any other statement in the function and
3328 get exactly the results you would expect from the source code.
3330 With @option{-O}, the compiler tries to reduce code size and execution
3331 time, without performing any optimizations that take a great deal of
3336 Optimize even more. GCC performs nearly all supported optimizations
3337 that do not involve a space-speed tradeoff. The compiler does not
3338 perform loop unrolling or function inlining when you specify @option{-O2}.
3339 As compared to @option{-O}, this option increases both compilation time
3340 and the performance of the generated code.
3342 @option{-O2} turns on all optional optimizations except for loop
3343 unrolling, function inlining, and register renaming. It also turns on
3344 the @option{-fforce-mem} and @option{-fstrict-aliasing} option on all
3345 machines and frame pointer elimination on machines where doing so does
3346 not interfere with debugging.
3348 Please note the warning under @option{-fgcse} about
3349 invoking @option{-O2} on programs that use computed gotos.
3353 Optimize yet more. @option{-O3} turns on all optimizations specified by
3354 @option{-O2} and also turns on the @option{-finline-functions} and
3355 @option{-frename-registers} options.
3363 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
3364 do not typically increase code size. It also performs further
3365 optimizations designed to reduce code size.
3367 If you use multiple @option{-O} options, with or without level numbers,
3368 the last such option is the one that is effective.
3371 Options of the form @option{-f@var{flag}} specify machine-independent
3372 flags. Most flags have both positive and negative forms; the negative
3373 form of @option{-ffoo} would be @option{-fno-foo}. In the table below,
3374 only one of the forms is listed---the one which is not the default.
3375 You can figure out the other form by either removing @samp{no-} or
3380 @opindex ffloat-store
3381 Do not store floating point variables in registers, and inhibit other
3382 options that might change whether a floating point value is taken from a
3385 @cindex floating point precision
3386 This option prevents undesirable excess precision on machines such as
3387 the 68000 where the floating registers (of the 68881) keep more
3388 precision than a @code{double} is supposed to have. Similarly for the
3389 x86 architecture. For most programs, the excess precision does only
3390 good, but a few programs rely on the precise definition of IEEE floating
3391 point. Use @option{-ffloat-store} for such programs, after modifying
3392 them to store all pertinent intermediate computations into variables.
3394 @item -fno-default-inline
3395 @opindex fno-default-inline
3396 Do not make member functions inline by default merely because they are
3397 defined inside the class scope (C++ only). Otherwise, when you specify
3398 @w{@option{-O}}, member functions defined inside class scope are compiled
3399 inline by default; i.e., you don't need to add @samp{inline} in front of
3400 the member function name.
3402 @item -fno-defer-pop
3403 @opindex fno-defer-pop
3404 Always pop the arguments to each function call as soon as that function
3405 returns. For machines which must pop arguments after a function call,
3406 the compiler normally lets arguments accumulate on the stack for several
3407 function calls and pops them all at once.
3411 Force memory operands to be copied into registers before doing
3412 arithmetic on them. This produces better code by making all memory
3413 references potential common subexpressions. When they are not common
3414 subexpressions, instruction combination should eliminate the separate
3415 register-load. The @option{-O2} option turns on this option.
3418 @opindex fforce-addr
3419 Force memory address constants to be copied into registers before
3420 doing arithmetic on them. This may produce better code just as
3421 @option{-fforce-mem} may.
3423 @item -fomit-frame-pointer
3424 @opindex fomit-frame-pointer
3425 Don't keep the frame pointer in a register for functions that
3426 don't need one. This avoids the instructions to save, set up and
3427 restore frame pointers; it also makes an extra register available
3428 in many functions. @strong{It also makes debugging impossible on
3431 On some machines, such as the VAX, this flag has no effect, because
3432 the standard calling sequence automatically handles the frame pointer
3433 and nothing is saved by pretending it doesn't exist. The
3434 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
3435 whether a target machine supports this flag. @xref{Registers,,Register
3436 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
3438 @item -foptimize-sibling-calls
3439 @opindex foptimize-sibling-calls
3440 Optimize sibling and tail recursive calls.
3444 This option generates traps for signed overflow on addition, subtraction,
3445 multiplication operations.
3449 Don't pay attention to the @code{inline} keyword. Normally this option
3450 is used to keep the compiler from expanding any functions inline.
3451 Note that if you are not optimizing, no functions can be expanded inline.
3453 @item -finline-functions
3454 @opindex finline-functions
3455 Integrate all simple functions into their callers. The compiler
3456 heuristically decides which functions are simple enough to be worth
3457 integrating in this way.
3459 If all calls to a given function are integrated, and the function is
3460 declared @code{static}, then the function is normally not output as
3461 assembler code in its own right.
3463 @item -finline-limit=@var{n}
3464 @opindex finline-limit
3465 By default, gcc limits the size of functions that can be inlined. This flag
3466 allows the control of this limit for functions that are explicitly marked as
3467 inline (ie marked with the inline keyword or defined within the class
3468 definition in c++). @var{n} is the size of functions that can be inlined in
3469 number of pseudo instructions (not counting parameter handling). The default
3470 value of @var{n} is 600.
3471 Increasing this value can result in more inlined code at
3472 the cost of compilation time and memory consumption. Decreasing usually makes
3473 the compilation faster and less code will be inlined (which presumably
3474 means slower programs). This option is particularly useful for programs that
3475 use inlining heavily such as those based on recursive templates with C++.
3477 @emph{Note:} pseudo instruction represents, in this particular context, an
3478 abstract measurement of function's size. In no way, it represents a count
3479 of assembly instructions and as such its exact meaning might change from one
3480 release to an another.
3482 @item -fkeep-inline-functions
3483 @opindex fkeep-inline-functions
3484 Even if all calls to a given function are integrated, and the function
3485 is declared @code{static}, nevertheless output a separate run-time
3486 callable version of the function. This switch does not affect
3487 @code{extern inline} functions.
3489 @item -fkeep-static-consts
3490 @opindex fkeep-static-consts
3491 Emit variables declared @code{static const} when optimization isn't turned
3492 on, even if the variables aren't referenced.
3494 GCC enables this option by default. If you want to force the compiler to
3495 check if the variable was referenced, regardless of whether or not
3496 optimization is turned on, use the @option{-fno-keep-static-consts} option.
3498 @item -fmerge-constants
3499 Attempt to merge identical constants (string constants and floating point
3500 constants) accross compilation units.
3502 This option is default for optimized compilation if assembler and linker
3503 support it. Use @option{-fno-merge-constants} to inhibit this behavior.
3505 @item -fmerge-all-constants
3506 Attempt to merge identical constants and identical variables.
3508 This option implies @option{-fmerge-constants}. In addition to
3509 @option{-fmerge-constants} this considers e.g. even constant initialized
3510 arrays or initialized constant variables with integral or floating point
3511 types. Languages like C or C++ require each non-automatic variable to
3512 have distinct location, so using this option will result in non-conforming
3517 Use a graph coloring register allocator. Currently this option is meant
3518 for testing, so we are interested to hear about miscompilations with
3521 @item -fno-function-cse
3522 @opindex fno-function-cse
3523 Do not put function addresses in registers; make each instruction that
3524 calls a constant function contain the function's address explicitly.
3526 This option results in less efficient code, but some strange hacks
3527 that alter the assembler output may be confused by the optimizations
3528 performed when this option is not used.
3532 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
3533 @option{-fno-trapping-math}, @option{-ffinite-math-only} and @*
3534 @option{-fno-signaling-nans}.
3536 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
3538 This option should never be turned on by any @option{-O} option since
3539 it can result in incorrect output for programs which depend on
3540 an exact implementation of IEEE or ISO rules/specifications for
3543 @item -fno-math-errno
3544 @opindex fno-math-errno
3545 Do not set ERRNO after calling math functions that are executed
3546 with a single instruction, e.g., sqrt. A program that relies on
3547 IEEE exceptions for math error handling may want to use this flag
3548 for speed while maintaining IEEE arithmetic compatibility.
3550 This option should never be turned on by any @option{-O} option since
3551 it can result in incorrect output for programs which depend on
3552 an exact implementation of IEEE or ISO rules/specifications for
3555 The default is @option{-fmath-errno}.
3557 @item -funsafe-math-optimizations
3558 @opindex funsafe-math-optimizations
3559 Allow optimizations for floating-point arithmetic that (a) assume
3560 that arguments and results are valid and (b) may violate IEEE or
3561 ANSI standards. When used at link-time, it may include libraries
3562 or startup files that change the default FPU control word or other
3563 similar optimizations.
3565 This option should never be turned on by any @option{-O} option since
3566 it can result in incorrect output for programs which depend on
3567 an exact implementation of IEEE or ISO rules/specifications for
3570 The default is @option{-fno-unsafe-math-optimizations}.
3572 @item -ffinite-math-only
3573 @opindex ffinite-math-only
3574 Allow optimizations for floating-point arithmetic that assume
3575 that arguments and results are not NaNs or +-Infs.
3577 This option should never be turned on by any @option{-O} option since
3578 it can result in incorrect output for programs which depend on
3579 an exact implementation of IEEE or ISO rules/specifications.
3581 The default is @option{-fno-finite-math-only}.
3583 @item -fno-trapping-math
3584 @opindex fno-trapping-math
3585 Compile code assuming that floating-point operations cannot generate
3586 user-visible traps. These traps include division by zero, overflow,
3587 underflow, inexact result and invalid operation. This option implies
3588 @option{-fno-signaling-nans}. Setting this option may allow faster
3589 code if one relies on ``non-stop'' IEEE arithmetic, for example.
3591 This option should never be turned on by any @option{-O} option since
3592 it can result in incorrect output for programs which depend on
3593 an exact implementation of IEEE or ISO rules/specifications for
3596 The default is @option{-ftrapping-math}.
3598 @item -fsignaling-nans
3599 @opindex fsignaling-nans
3600 Compile code assuming that IEEE signaling NaNs may generate user-visible
3601 traps during floating-point operations. Setting this option disables
3602 optimizations that may change the number of exceptions visible with
3603 signaling NaNs. This option implies @option{-ftrapping-math}.
3605 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
3608 The default is @option{-fno-signaling-nans}.
3610 This option is experimental and does not currently guarantee to
3611 disable all GCC optimizations that affect signaling NaN behavior.
3613 @item -fno-zero-initialized-in-bss
3614 @opindex fno-zero-initialized-in-bss
3615 If the target supports a BSS section, GCC by default puts variables that
3616 are initialized to zero into BSS@. This can save space in the resulting
3619 This option turns off this behavior because some programs explicitly
3620 rely on variables going to the data section. E.g., so that the
3621 resulting executable can find the beginning of that section and/or make
3622 assumptions based on that.
3624 The default is @option{-fzero-initialized-in-bss}.
3627 The following options control specific optimizations. The @option{-O2}
3628 option turns on all of these optimizations except @option{-funroll-loops}
3629 and @option{-funroll-all-loops}. On most machines, the @option{-O} option
3630 turns on the @option{-fthread-jumps} and @option{-fdelayed-branch} options,
3631 but specific machines may handle it differently.
3633 You can use the following flags in the rare cases when ``fine-tuning''
3634 of optimizations to be performed is desired.
3636 Not all of the optimizations performed by GCC have @option{-f} options
3640 @item -fstrength-reduce
3641 @opindex fstrength-reduce
3642 Perform the optimizations of loop strength reduction and
3643 elimination of iteration variables.
3645 @item -fthread-jumps
3646 @opindex fthread-jumps
3647 Perform optimizations where we check to see if a jump branches to a
3648 location where another comparison subsumed by the first is found. If
3649 so, the first branch is redirected to either the destination of the
3650 second branch or a point immediately following it, depending on whether
3651 the condition is known to be true or false.
3653 @item -fcse-follow-jumps
3654 @opindex fcse-follow-jumps
3655 In common subexpression elimination, scan through jump instructions
3656 when the target of the jump is not reached by any other path. For
3657 example, when CSE encounters an @code{if} statement with an
3658 @code{else} clause, CSE will follow the jump when the condition
3661 @item -fcse-skip-blocks
3662 @opindex fcse-skip-blocks
3663 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
3664 follow jumps which conditionally skip over blocks. When CSE
3665 encounters a simple @code{if} statement with no else clause,
3666 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
3667 body of the @code{if}.
3669 @item -frerun-cse-after-loop
3670 @opindex frerun-cse-after-loop
3671 Re-run common subexpression elimination after loop optimizations has been
3674 @item -frerun-loop-opt
3675 @opindex frerun-loop-opt
3676 Run the loop optimizer twice.
3680 Perform a global common subexpression elimination pass.
3681 This pass also performs global constant and copy propagation.
3683 @emph{Note:} When compiling a program using computed gotos, a GCC
3684 extension, you may get better runtime performance if you disable
3685 the global common subexpression elmination pass by adding
3686 @option{-fno-gcse} to the command line.
3690 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
3691 attempt to move loads which are only killed by stores into themselves. This
3692 allows a loop containing a load/store sequence to be changed to a load outside
3693 the loop, and a copy/store within the loop.
3697 When @option{-fgcse-sm} is enabled, A store motion pass is run after global common
3698 subexpression elimination. This pass will attempt to move stores out of loops.
3699 When used in conjunction with @option{-fgcse-lm}, loops containing a load/store sequence
3700 can be changed to a load before the loop and a store after the loop.
3702 @item -floop-optimize
3703 @opindex floop-optimize
3704 Perform loop optimizations: move constant expressions out of loops, simplify
3705 exit test conditions and optionally do strength-reduction and loop unrolling as
3708 @item -fcrossjumping
3709 @opindex crossjumping
3710 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
3711 resulting code may or may not perform better than without cross-jumping.
3713 @item -fif-conversion
3714 @opindex if-conversion
3715 Attempt to transform conditional jumps into branch-less equivalents. This
3716 include use of conditional moves, min, max, set flags and abs instructions, and
3717 some tricks doable by standard arithmetics. The use of conditional execution
3718 on chips where it is available is controlled by @code{if-conversion2}.
3720 @item -fif-conversion2
3721 @opindex if-conversion2
3722 Use conditional execution (where available) to transform conditional jumps into
3723 branch-less equivalents.
3725 @item -fdelete-null-pointer-checks
3726 @opindex fdelete-null-pointer-checks
3727 Use global dataflow analysis to identify and eliminate useless checks
3728 for null pointers. The compiler assumes that dereferencing a null
3729 pointer would have halted the program. If a pointer is checked after
3730 it has already been dereferenced, it cannot be null.
3732 In some environments, this assumption is not true, and programs can
3733 safely dereference null pointers. Use
3734 @option{-fno-delete-null-pointer-checks} to disable this optimization
3735 for programs which depend on that behavior.
3737 @item -fexpensive-optimizations
3738 @opindex fexpensive-optimizations
3739 Perform a number of minor optimizations that are relatively expensive.
3741 @item -foptimize-register-move
3743 @opindex foptimize-register-move
3745 Attempt to reassign register numbers in move instructions and as
3746 operands of other simple instructions in order to maximize the amount of
3747 register tying. This is especially helpful on machines with two-operand
3748 instructions. GCC enables this optimization by default with @option{-O2}
3751 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
3754 @item -fdelayed-branch
3755 @opindex fdelayed-branch
3756 If supported for the target machine, attempt to reorder instructions
3757 to exploit instruction slots available after delayed branch
3760 @item -fschedule-insns
3761 @opindex fschedule-insns
3762 If supported for the target machine, attempt to reorder instructions to
3763 eliminate execution stalls due to required data being unavailable. This
3764 helps machines that have slow floating point or memory load instructions
3765 by allowing other instructions to be issued until the result of the load
3766 or floating point instruction is required.
3768 @item -fschedule-insns2
3769 @opindex fschedule-insns2
3770 Similar to @option{-fschedule-insns}, but requests an additional pass of
3771 instruction scheduling after register allocation has been done. This is
3772 especially useful on machines with a relatively small number of
3773 registers and where memory load instructions take more than one cycle.
3775 @item -ffunction-sections
3776 @itemx -fdata-sections
3777 @opindex ffunction-sections
3778 @opindex fdata-sections
3779 Place each function or data item into its own section in the output
3780 file if the target supports arbitrary sections. The name of the
3781 function or the name of the data item determines the section's name
3784 Use these options on systems where the linker can perform optimizations
3785 to improve locality of reference in the instruction space. HPPA
3786 processors running HP-UX and SPARC processors running Solaris 2 have
3787 linkers with such optimizations. Other systems using the ELF object format
3788 as well as AIX may have these optimizations in the future.
3790 Only use these options when there are significant benefits from doing
3791 so. When you specify these options, the assembler and linker will
3792 create larger object and executable files and will also be slower.
3793 You will not be able to use @code{gprof} on all systems if you
3794 specify this option and you may have problems with debugging if
3795 you specify both this option and @option{-g}.
3797 @item -fcaller-saves
3798 @opindex fcaller-saves
3799 Enable values to be allocated in registers that will be clobbered by
3800 function calls, by emitting extra instructions to save and restore the
3801 registers around such calls. Such allocation is done only when it
3802 seems to result in better code than would otherwise be produced.
3804 This option is always enabled by default on certain machines, usually
3805 those which have no call-preserved registers to use instead.
3807 For all machines, optimization level 2 and higher enables this flag by
3812 Perform tail duplication to enlarge superblock size. This transformation
3813 simplifies the control flow of the function allowing other optimizations to do
3816 @item -funroll-loops
3817 @opindex funroll-loops
3818 Unroll loops whose number of iterations can be determined at compile
3819 time or upon entry to the loop. @option{-funroll-loops} implies both
3820 @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
3821 option makes code larger, and may or may not make it run faster.
3823 @item -funroll-all-loops
3824 @opindex funroll-all-loops
3825 Unroll all loops, even if their number of iterations is uncertain when
3826 the loop is entered. This usually makes programs run more slowly.
3827 @option{-funroll-all-loops} implies the same options as
3828 @option{-funroll-loops},
3830 @item -fprefetch-loop-arrays
3831 @opindex fprefetch-loop-arrays
3832 If supported by the target machine, generate instructions to prefetch
3833 memory to improve the performance of loops that access large arrays.
3835 @item -fmove-all-movables
3836 @opindex fmove-all-movables
3837 Forces all invariant computations in loops to be moved
3840 @item -freduce-all-givs
3841 @opindex freduce-all-givs
3842 Forces all general-induction variables in loops to be
3845 @emph{Note:} When compiling programs written in Fortran,
3846 @option{-fmove-all-movables} and @option{-freduce-all-givs} are enabled
3847 by default when you use the optimizer.
3849 These options may generate better or worse code; results are highly
3850 dependent on the structure of loops within the source code.
3852 These two options are intended to be removed someday, once
3853 they have helped determine the efficacy of various
3854 approaches to improving loop optimizations.
3856 Please let us (@w{@email{gcc@@gcc.gnu.org}} and @w{@email{fortran@@gnu.org}})
3857 know how use of these options affects
3858 the performance of your production code.
3859 We're very interested in code that runs @emph{slower}
3860 when these options are @emph{enabled}.
3863 @itemx -fno-peephole2
3864 @opindex fno-peephole
3865 @opindex fno-peephole2
3866 Disable any machine-specific peephole optimizations. The difference
3867 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
3868 are implemented in the compiler; some targets use one, some use the
3869 other, a few use both.
3871 @item -fbranch-probabilities
3872 @opindex fbranch-probabilities
3873 After running a program compiled with @option{-fprofile-arcs}
3874 (@pxref{Debugging Options,, Options for Debugging Your Program or
3875 @command{gcc}}), you can compile it a second time using
3876 @option{-fbranch-probabilities}, to improve optimizations based on
3877 the number of times each branch was taken. When the program
3878 compiled with @option{-fprofile-arcs} exits it saves arc execution
3879 counts to a file called @file{@var{sourcename}.da} for each source
3880 file The information in this data file is very dependent on the
3881 structure of the generated code, so you must use the same source code
3882 and the same optimization options for both compilations.
3884 With @option{-fbranch-probabilities}, GCC puts a @samp{REG_EXEC_COUNT}
3885 note on the first instruction of each basic block, and a
3886 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
3887 These can be used to improve optimization. Currently, they are only
3888 used in one place: in @file{reorg.c}, instead of guessing which path a
3889 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
3890 exactly determine which path is taken more often.
3892 @item -fno-guess-branch-probability
3893 @opindex fno-guess-branch-probability
3894 Do not guess branch probabilities using a randomized model.
3896 Sometimes gcc will opt to use a randomized model to guess branch
3897 probabilities, when none are available from either profiling feedback
3898 (@option{-fprofile-arcs}) or @samp{__builtin_expect}. This means that
3899 different runs of the compiler on the same program may produce different
3902 In a hard real-time system, people don't want different runs of the
3903 compiler to produce code that has different behavior; minimizing
3904 non-determinism is of paramount import. This switch allows users to
3905 reduce non-determinism, possibly at the expense of inferior
3908 @item -freorder-blocks
3909 @opindex freorder-blocks
3910 Reorder basic blocks in the compiled function in order to reduce number of
3911 taken branches and improve code locality.
3913 @item -freorder-functions
3914 @opindex freorder-functions
3915 Reorder basic blocks in the compiled function in order to reduce number of
3916 taken branches and improve code locality. This is implemented by using special
3917 subsections @code{text.hot} for most frequently executed functions and
3918 @code{text.unlikely} for unlikely executed functions. Reordering is done by
3919 the linker so object file format must support named sections and linker must
3920 place them in resonable way.
3922 Also profile feedback must be available in to make this option effective. See
3923 @option{-fprofile-arcs} for details.
3925 @item -fstrict-aliasing
3926 @opindex fstrict-aliasing
3927 Allows the compiler to assume the strictest aliasing rules applicable to
3928 the language being compiled. For C (and C++), this activates
3929 optimizations based on the type of expressions. In particular, an
3930 object of one type is assumed never to reside at the same address as an
3931 object of a different type, unless the types are almost the same. For
3932 example, an @code{unsigned int} can alias an @code{int}, but not a
3933 @code{void*} or a @code{double}. A character type may alias any other
3936 Pay special attention to code like this:
3949 The practice of reading from a different union member than the one most
3950 recently written to (called ``type-punning'') is common. Even with
3951 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
3952 is accessed through the union type. So, the code above will work as
3953 expected. However, this code might not:
3964 Every language that wishes to perform language-specific alias analysis
3965 should define a function that computes, given an @code{tree}
3966 node, an alias set for the node. Nodes in different alias sets are not
3967 allowed to alias. For an example, see the C front-end function
3968 @code{c_get_alias_set}.
3970 For all machines, optimization level 2 and higher enables this flag by
3973 @item -falign-functions
3974 @itemx -falign-functions=@var{n}
3975 @opindex falign-functions
3976 Align the start of functions to the next power-of-two greater than
3977 @var{n}, skipping up to @var{n} bytes. For instance,
3978 @option{-falign-functions=32} aligns functions to the next 32-byte
3979 boundary, but @option{-falign-functions=24} would align to the next
3980 32-byte boundary only if this can be done by skipping 23 bytes or less.
3982 @option{-fno-align-functions} and @option{-falign-functions=1} are
3983 equivalent and mean that functions will not be aligned.
3985 Some assemblers only support this flag when @var{n} is a power of two;
3986 in that case, it is rounded up.
3988 If @var{n} is not specified, use a machine-dependent default.
3990 @item -falign-labels
3991 @itemx -falign-labels=@var{n}
3992 @opindex falign-labels
3993 Align all branch targets to a power-of-two boundary, skipping up to
3994 @var{n} bytes like @option{-falign-functions}. This option can easily
3995 make code slower, because it must insert dummy operations for when the
3996 branch target is reached in the usual flow of the code.
3998 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
3999 are greater than this value, then their values are used instead.
4001 If @var{n} is not specified, use a machine-dependent default which is
4002 very likely to be @samp{1}, meaning no alignment.
4005 @itemx -falign-loops=@var{n}
4006 @opindex falign-loops
4007 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
4008 like @option{-falign-functions}. The hope is that the loop will be
4009 executed many times, which will make up for any execution of the dummy
4012 If @var{n} is not specified, use a machine-dependent default.
4015 @itemx -falign-jumps=@var{n}
4016 @opindex falign-jumps
4017 Align branch targets to a power-of-two boundary, for branch targets
4018 where the targets can only be reached by jumping, skipping up to @var{n}
4019 bytes like @option{-falign-functions}. In this case, no dummy operations
4022 If @var{n} is not specified, use a machine-dependent default.
4026 Perform optimizations in static single assignment form. Each function's
4027 flow graph is translated into SSA form, optimizations are performed, and
4028 the flow graph is translated back from SSA form. Users should not
4029 specify this option, since it is not yet ready for production use.
4033 Perform Sparse Conditional Constant Propagation in SSA form. Requires
4034 @option{-fssa}. Like @option{-fssa}, this is an experimental feature.
4038 Perform aggressive dead-code elimination in SSA form. Requires @option{-fssa}.
4039 Like @option{-fssa}, this is an experimental feature.
4041 @item -fsingle-precision-constant
4042 @opindex fsingle-precision-constant
4043 Treat floating point constant as single precision constant instead of
4044 implicitly converting it to double precision constant.
4046 @item -frename-registers
4047 @opindex frename-registers
4048 Attempt to avoid false dependencies in scheduled code by making use
4049 of registers left over after register allocation. This optimization
4050 will most benefit processors with lots of registers. It can, however,
4051 make debugging impossible, since variables will no longer stay in
4052 a ``home register''.
4054 @item -fno-cprop-registers
4055 @opindex fno-cprop-registers
4056 After register allocation and post-register allocation instruction splitting,
4057 we perform a copy-propagation pass to try to reduce scheduling dependencies
4058 and occasionally eliminate the copy.
4060 @item --param @var{name}=@var{value}
4062 In some places, GCC uses various constants to control the amount of
4063 optimization that is done. For example, GCC will not inline functions
4064 that contain more that a certain number of instructions. You can
4065 control some of these constants on the command-line using the
4066 @option{--param} option.
4068 In each case, the @var{value} is an integer. The allowable choices for
4069 @var{name} are given in the following table:
4072 @item max-delay-slot-insn-search
4073 The maximum number of instructions to consider when looking for an
4074 instruction to fill a delay slot. If more than this arbitrary number of
4075 instructions is searched, the time savings from filling the delay slot
4076 will be minimal so stop searching. Increasing values mean more
4077 aggressive optimization, making the compile time increase with probably
4078 small improvement in executable run time.
4080 @item max-delay-slot-live-search
4081 When trying to fill delay slots, the maximum number of instructions to
4082 consider when searching for a block with valid live register
4083 information. Increasing this arbitrarily chosen value means more
4084 aggressive optimization, increasing the compile time. This parameter
4085 should be removed when the delay slot code is rewritten to maintain the
4088 @item max-gcse-memory
4089 The approximate maximum amount of memory that will be allocated in
4090 order to perform the global common subexpression elimination
4091 optimization. If more memory than specified is required, the
4092 optimization will not be done.
4094 @item max-gcse-passes
4095 The maximum number of passes of GCSE to run.
4097 @item max-pending-list-length
4098 The maximum number of pending dependencies scheduling will allow
4099 before flushing the current state and starting over. Large functions
4100 with few branches or calls can create excessively large lists which
4101 needlessly consume memory and resources.
4103 @item max-inline-insns
4104 If an function contains more than this many instructions, it
4105 will not be inlined. This option is precisely equivalent to
4106 @option{-finline-limit}.
4108 @item max-unrolled-insns
4109 The maximum number of instructions that a loop should have if that loop
4110 is unrolled, and if the loop is unrolled, it determines how many times
4111 the loop code is unrolled.
4113 @item hot-bb-count-fraction
4114 Select fraction of the maximal count of repetitions of basic block in program
4115 given basic block needs to have to be considered hot.
4117 @item hot-bb-frequency-fraction
4118 Select fraction of the maximal frequency of executions of basic block in
4119 function given basic block needs to have to be considered hot
4121 @item tracer-dynamic-coverage
4122 @itemx tracer-dynamic-coverage-feedback
4124 This value is used to limit superblock formation once given percentage of
4125 executed instructions is covered. This limits unnecesary code size expansion.
4127 The @option{tracer-dynamic-coverage-feedback} is used only when profile
4128 feedback is available. The real profiles (as opposed to statically estimated
4129 ones) are much less balanced allowing the threshold to be larger value.
4131 @item tracer-max-code-growth
4132 Stop tail duplication once code growth has reached given percentage. This is
4133 rather hokey argument, as most of the duplicates will be elliminated later in
4134 cross jumping, so it may be set to much higher values than is the desired code
4137 @item tracer-min-branch-ratio
4139 Stop reverse growth when the reverse probability of best edge is less than this
4140 threshold (in percent).
4142 @item tracer-min-branch-ratio
4143 @itemx tracer-min-branch-ratio-feedback
4145 Stop forward growth if the best edge do have probability lower than this
4148 Similary to @option{tracer-dynamic-coverage} two values are present, one for
4149 compilation for profile feedback and one for compilation without. The value
4150 for compilation with profile feedback needs to be more conservative (higher) in
4151 order to make tracer effective.
4156 @node Preprocessor Options
4157 @section Options Controlling the Preprocessor
4158 @cindex preprocessor options
4159 @cindex options, preprocessor
4161 These options control the C preprocessor, which is run on each C source
4162 file before actual compilation.
4164 If you use the @option{-E} option, nothing is done except preprocessing.
4165 Some of these options make sense only together with @option{-E} because
4166 they cause the preprocessor output to be unsuitable for actual
4170 You can use @option{-Wp,@var{option}} to bypass the compiler driver
4171 and pass @var{option} directly through to the preprocessor. If
4172 @var{option} contains commas, it is split into multiple options at the
4173 commas. However, many options are modified, translated or interpreted
4174 by the compiler driver before being passed to the preprocessor, and
4175 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
4176 interface is undocumented and subject to change, so whenever possible
4177 you should avoid using @option{-Wp} and let the driver handle the
4180 @include cppopts.texi
4182 @node Assembler Options
4183 @section Passing Options to the Assembler
4185 @c prevent bad page break with this line
4186 You can pass options to the assembler.
4189 @item -Wa,@var{option}
4191 Pass @var{option} as an option to the assembler. If @var{option}
4192 contains commas, it is split into multiple options at the commas.
4196 @section Options for Linking
4197 @cindex link options
4198 @cindex options, linking
4200 These options come into play when the compiler links object files into
4201 an executable output file. They are meaningless if the compiler is
4202 not doing a link step.
4206 @item @var{object-file-name}
4207 A file name that does not end in a special recognized suffix is
4208 considered to name an object file or library. (Object files are
4209 distinguished from libraries by the linker according to the file
4210 contents.) If linking is done, these object files are used as input
4219 If any of these options is used, then the linker is not run, and
4220 object file names should not be used as arguments. @xref{Overall
4224 @item -l@var{library}
4225 @itemx -l @var{library}
4227 Search the library named @var{library} when linking. (The second
4228 alternative with the library as a separate argument is only for
4229 POSIX compliance and is not recommended.)
4231 It makes a difference where in the command you write this option; the
4232 linker searches and processes libraries and object files in the order they
4233 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
4234 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
4235 to functions in @samp{z}, those functions may not be loaded.
4237 The linker searches a standard list of directories for the library,
4238 which is actually a file named @file{lib@var{library}.a}. The linker
4239 then uses this file as if it had been specified precisely by name.
4241 The directories searched include several standard system directories
4242 plus any that you specify with @option{-L}.
4244 Normally the files found this way are library files---archive files
4245 whose members are object files. The linker handles an archive file by
4246 scanning through it for members which define symbols that have so far
4247 been referenced but not defined. But if the file that is found is an
4248 ordinary object file, it is linked in the usual fashion. The only
4249 difference between using an @option{-l} option and specifying a file name
4250 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
4251 and searches several directories.
4255 You need this special case of the @option{-l} option in order to
4256 link an Objective-C program.
4259 @opindex nostartfiles
4260 Do not use the standard system startup files when linking.
4261 The standard system libraries are used normally, unless @option{-nostdlib}
4262 or @option{-nodefaultlibs} is used.
4264 @item -nodefaultlibs
4265 @opindex nodefaultlibs
4266 Do not use the standard system libraries when linking.
4267 Only the libraries you specify will be passed to the linker.
4268 The standard startup files are used normally, unless @option{-nostartfiles}
4269 is used. The compiler may generate calls to memcmp, memset, and memcpy
4270 for System V (and ISO C) environments or to bcopy and bzero for
4271 BSD environments. These entries are usually resolved by entries in
4272 libc. These entry points should be supplied through some other
4273 mechanism when this option is specified.
4277 Do not use the standard system startup files or libraries when linking.
4278 No startup files and only the libraries you specify will be passed to
4279 the linker. The compiler may generate calls to memcmp, memset, and memcpy
4280 for System V (and ISO C) environments or to bcopy and bzero for
4281 BSD environments. These entries are usually resolved by entries in
4282 libc. These entry points should be supplied through some other
4283 mechanism when this option is specified.
4285 @cindex @option{-lgcc}, use with @option{-nostdlib}
4286 @cindex @option{-nostdlib} and unresolved references
4287 @cindex unresolved references and @option{-nostdlib}
4288 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
4289 @cindex @option{-nodefaultlibs} and unresolved references
4290 @cindex unresolved references and @option{-nodefaultlibs}
4291 One of the standard libraries bypassed by @option{-nostdlib} and
4292 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
4293 that GCC uses to overcome shortcomings of particular machines, or special
4294 needs for some languages.
4295 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
4296 Collection (GCC) Internals},
4297 for more discussion of @file{libgcc.a}.)
4298 In most cases, you need @file{libgcc.a} even when you want to avoid
4299 other standard libraries. In other words, when you specify @option{-nostdlib}
4300 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
4301 This ensures that you have no unresolved references to internal GCC
4302 library subroutines. (For example, @samp{__main}, used to ensure C++
4303 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
4304 GNU Compiler Collection (GCC) Internals}.)
4308 Remove all symbol table and relocation information from the executable.
4312 On systems that support dynamic linking, this prevents linking with the shared
4313 libraries. On other systems, this option has no effect.
4317 Produce a shared object which can then be linked with other objects to
4318 form an executable. Not all systems support this option. For predictable
4319 results, you must also specify the same set of options that were used to
4320 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
4321 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
4322 needs to build supplementary stub code for constructors to work. On
4323 multi-libbed systems, @samp{gcc -shared} must select the correct support
4324 libraries to link against. Failing to supply the correct flags may lead
4325 to subtle defects. Supplying them in cases where they are not necessary
4328 @item -shared-libgcc
4329 @itemx -static-libgcc
4330 @opindex shared-libgcc
4331 @opindex static-libgcc
4332 On systems that provide @file{libgcc} as a shared library, these options
4333 force the use of either the shared or static version respectively.
4334 If no shared version of @file{libgcc} was built when the compiler was
4335 configured, these options have no effect.
4337 There are several situations in which an application should use the
4338 shared @file{libgcc} instead of the static version. The most common
4339 of these is when the application wishes to throw and catch exceptions
4340 across different shared libraries. In that case, each of the libraries
4341 as well as the application itself should use the shared @file{libgcc}.
4343 Therefore, the G++ and GCJ drivers automatically add
4344 @option{-shared-libgcc} whenever you build a shared library or a main
4345 executable, because C++ and Java programs typically use exceptions, so
4346 this is the right thing to do.
4348 If, instead, you use the GCC driver to create shared libraries, you may
4349 find that they will not always be linked with the shared @file{libgcc}.
4350 If GCC finds, at its configuration time, that you have a GNU linker that
4351 does not support option @option{--eh-frame-hdr}, it will link the shared
4352 version of @file{libgcc} into shared libraries by default. Otherwise,
4353 it will take advantage of the linker and optimize away the linking with
4354 the shared version of @file{libgcc}, linking with the static version of
4355 libgcc by default. This allows exceptions to propagate through such
4356 shared libraries, without incurring relocation costs at library load
4359 However, if a library or main executable is supposed to throw or catch
4360 exceptions, you must link it using the G++ or GCJ driver, as appropriate
4361 for the languages used in the program, or using the option
4362 @option{-shared-libgcc}, such that it is linked with the shared
4367 Bind references to global symbols when building a shared object. Warn
4368 about any unresolved references (unless overridden by the link editor
4369 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
4372 @item -Xlinker @var{option}
4374 Pass @var{option} as an option to the linker. You can use this to
4375 supply system-specific linker options which GCC does not know how to
4378 If you want to pass an option that takes an argument, you must use
4379 @option{-Xlinker} twice, once for the option and once for the argument.
4380 For example, to pass @option{-assert definitions}, you must write
4381 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
4382 @option{-Xlinker "-assert definitions"}, because this passes the entire
4383 string as a single argument, which is not what the linker expects.
4385 @item -Wl,@var{option}
4387 Pass @var{option} as an option to the linker. If @var{option} contains
4388 commas, it is split into multiple options at the commas.
4390 @item -u @var{symbol}
4392 Pretend the symbol @var{symbol} is undefined, to force linking of
4393 library modules to define it. You can use @option{-u} multiple times with
4394 different symbols to force loading of additional library modules.
4397 @node Directory Options
4398 @section Options for Directory Search
4399 @cindex directory options
4400 @cindex options, directory search
4403 These options specify directories to search for header files, for
4404 libraries and for parts of the compiler:
4409 Add the directory @var{dir} to the head of the list of directories to be
4410 searched for header files. This can be used to override a system header
4411 file, substituting your own version, since these directories are
4412 searched before the system header file directories. However, you should
4413 not use this option to add directories that contain vendor-supplied
4414 system header files (use @option{-isystem} for that). If you use more than
4415 one @option{-I} option, the directories are scanned in left-to-right
4416 order; the standard system directories come after.
4418 If a standard system include directory, or a directory specified with
4419 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
4420 option will be ignored. The directory will still be searched but as a
4421 system directory at its normal position in the system include chain.
4422 This is to ensure that GCC's procedure to fix buggy system headers and
4423 the ordering for the include_next directive are not inadvertantly changed.
4424 If you really need to change the search order for system directories,
4425 use the @option{-nostdinc} and/or @option{-isystem} options.
4429 Any directories you specify with @option{-I} options before the @option{-I-}
4430 option are searched only for the case of @samp{#include "@var{file}"};
4431 they are not searched for @samp{#include <@var{file}>}.
4433 If additional directories are specified with @option{-I} options after
4434 the @option{-I-}, these directories are searched for all @samp{#include}
4435 directives. (Ordinarily @emph{all} @option{-I} directories are used
4438 In addition, the @option{-I-} option inhibits the use of the current
4439 directory (where the current input file came from) as the first search
4440 directory for @samp{#include "@var{file}"}. There is no way to
4441 override this effect of @option{-I-}. With @option{-I.} you can specify
4442 searching the directory which was current when the compiler was
4443 invoked. That is not exactly the same as what the preprocessor does
4444 by default, but it is often satisfactory.
4446 @option{-I-} does not inhibit the use of the standard system directories
4447 for header files. Thus, @option{-I-} and @option{-nostdinc} are
4452 Add directory @var{dir} to the list of directories to be searched
4455 @item -B@var{prefix}
4457 This option specifies where to find the executables, libraries,
4458 include files, and data files of the compiler itself.
4460 The compiler driver program runs one or more of the subprograms
4461 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
4462 @var{prefix} as a prefix for each program it tries to run, both with and
4463 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
4465 For each subprogram to be run, the compiler driver first tries the
4466 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
4467 was not specified, the driver tries two standard prefixes, which are
4468 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc-lib/}. If neither of
4469 those results in a file name that is found, the unmodified program
4470 name is searched for using the directories specified in your
4471 @env{PATH} environment variable.
4473 The compiler will check to see if the path provided by the @option{-B}
4474 refers to a directory, and if necessary it will add a directory
4475 separator character at the end of the path.
4477 @option{-B} prefixes that effectively specify directory names also apply
4478 to libraries in the linker, because the compiler translates these
4479 options into @option{-L} options for the linker. They also apply to
4480 includes files in the preprocessor, because the compiler translates these
4481 options into @option{-isystem} options for the preprocessor. In this case,
4482 the compiler appends @samp{include} to the prefix.
4484 The run-time support file @file{libgcc.a} can also be searched for using
4485 the @option{-B} prefix, if needed. If it is not found there, the two
4486 standard prefixes above are tried, and that is all. The file is left
4487 out of the link if it is not found by those means.
4489 Another way to specify a prefix much like the @option{-B} prefix is to use
4490 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
4493 As a special kludge, if the path provided by @option{-B} is
4494 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
4495 9, then it will be replaced by @file{[dir/]include}. This is to help
4496 with boot-strapping the compiler.
4498 @item -specs=@var{file}
4500 Process @var{file} after the compiler reads in the standard @file{specs}
4501 file, in order to override the defaults that the @file{gcc} driver
4502 program uses when determining what switches to pass to @file{cc1},
4503 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
4504 @option{-specs=@var{file}} can be specified on the command line, and they
4505 are processed in order, from left to right.
4511 @section Specifying subprocesses and the switches to pass to them
4513 @command{gcc} is a driver program. It performs its job by invoking a
4514 sequence of other programs to do the work of compiling, assembling and
4515 linking. GCC interprets its command-line parameters and uses these to
4516 deduce which programs it should invoke, and which command-line options
4517 it ought to place on their command lines. This behavior is controlled
4518 by @dfn{spec strings}. In most cases there is one spec string for each
4519 program that GCC can invoke, but a few programs have multiple spec
4520 strings to control their behavior. The spec strings built into GCC can
4521 be overridden by using the @option{-specs=} command-line switch to specify
4524 @dfn{Spec files} are plaintext files that are used to construct spec
4525 strings. They consist of a sequence of directives separated by blank
4526 lines. The type of directive is determined by the first non-whitespace
4527 character on the line and it can be one of the following:
4530 @item %@var{command}
4531 Issues a @var{command} to the spec file processor. The commands that can
4535 @item %include <@var{file}>
4537 Search for @var{file} and insert its text at the current point in the
4540 @item %include_noerr <@var{file}>
4541 @cindex %include_noerr
4542 Just like @samp{%include}, but do not generate an error message if the include
4543 file cannot be found.
4545 @item %rename @var{old_name} @var{new_name}
4547 Rename the spec string @var{old_name} to @var{new_name}.
4551 @item *[@var{spec_name}]:
4552 This tells the compiler to create, override or delete the named spec
4553 string. All lines after this directive up to the next directive or
4554 blank line are considered to be the text for the spec string. If this
4555 results in an empty string then the spec will be deleted. (Or, if the
4556 spec did not exist, then nothing will happened.) Otherwise, if the spec
4557 does not currently exist a new spec will be created. If the spec does
4558 exist then its contents will be overridden by the text of this
4559 directive, unless the first character of that text is the @samp{+}
4560 character, in which case the text will be appended to the spec.
4562 @item [@var{suffix}]:
4563 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
4564 and up to the next directive or blank line are considered to make up the
4565 spec string for the indicated suffix. When the compiler encounters an
4566 input file with the named suffix, it will processes the spec string in
4567 order to work out how to compile that file. For example:
4574 This says that any input file whose name ends in @samp{.ZZ} should be
4575 passed to the program @samp{z-compile}, which should be invoked with the
4576 command-line switch @option{-input} and with the result of performing the
4577 @samp{%i} substitution. (See below.)
4579 As an alternative to providing a spec string, the text that follows a
4580 suffix directive can be one of the following:
4583 @item @@@var{language}
4584 This says that the suffix is an alias for a known @var{language}. This is
4585 similar to using the @option{-x} command-line switch to GCC to specify a
4586 language explicitly. For example:
4593 Says that .ZZ files are, in fact, C++ source files.
4596 This causes an error messages saying:
4599 @var{name} compiler not installed on this system.
4603 GCC already has an extensive list of suffixes built into it.
4604 This directive will add an entry to the end of the list of suffixes, but
4605 since the list is searched from the end backwards, it is effectively
4606 possible to override earlier entries using this technique.
4610 GCC has the following spec strings built into it. Spec files can
4611 override these strings or create their own. Note that individual
4612 targets can also add their own spec strings to this list.
4615 asm Options to pass to the assembler
4616 asm_final Options to pass to the assembler post-processor
4617 cpp Options to pass to the C preprocessor
4618 cc1 Options to pass to the C compiler
4619 cc1plus Options to pass to the C++ compiler
4620 endfile Object files to include at the end of the link
4621 link Options to pass to the linker
4622 lib Libraries to include on the command line to the linker
4623 libgcc Decides which GCC support library to pass to the linker
4624 linker Sets the name of the linker
4625 predefines Defines to be passed to the C preprocessor
4626 signed_char Defines to pass to CPP to say whether @code{char} is signed
4628 startfile Object files to include at the start of the link
4631 Here is a small example of a spec file:
4637 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
4640 This example renames the spec called @samp{lib} to @samp{old_lib} and
4641 then overrides the previous definition of @samp{lib} with a new one.
4642 The new definition adds in some extra command-line options before
4643 including the text of the old definition.
4645 @dfn{Spec strings} are a list of command-line options to be passed to their
4646 corresponding program. In addition, the spec strings can contain
4647 @samp{%}-prefixed sequences to substitute variable text or to
4648 conditionally insert text into the command line. Using these constructs
4649 it is possible to generate quite complex command lines.
4651 Here is a table of all defined @samp{%}-sequences for spec
4652 strings. Note that spaces are not generated automatically around the
4653 results of expanding these sequences. Therefore you can concatenate them
4654 together or combine them with constant text in a single argument.
4658 Substitute one @samp{%} into the program name or argument.
4661 Substitute the name of the input file being processed.
4664 Substitute the basename of the input file being processed.
4665 This is the substring up to (and not including) the last period
4666 and not including the directory.
4669 This is the same as @samp{%b}, but include the file suffix (text after
4673 Marks the argument containing or following the @samp{%d} as a
4674 temporary file name, so that that file will be deleted if GCC exits
4675 successfully. Unlike @samp{%g}, this contributes no text to the
4678 @item %g@var{suffix}
4679 Substitute a file name that has suffix @var{suffix} and is chosen
4680 once per compilation, and mark the argument in the same way as
4681 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
4682 name is now chosen in a way that is hard to predict even when previously
4683 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
4684 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
4685 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
4686 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
4687 was simply substituted with a file name chosen once per compilation,
4688 without regard to any appended suffix (which was therefore treated
4689 just like ordinary text), making such attacks more likely to succeed.
4691 @item %u@var{suffix}
4692 Like @samp{%g}, but generates a new temporary file name even if
4693 @samp{%u@var{suffix}} was already seen.
4695 @item %U@var{suffix}
4696 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
4697 new one if there is no such last file name. In the absence of any
4698 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
4699 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
4700 would involve the generation of two distinct file names, one
4701 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
4702 simply substituted with a file name chosen for the previous @samp{%u},
4703 without regard to any appended suffix.
4705 @item %j@var{SUFFIX}
4706 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
4707 writable, and if save-temps is off; otherwise, substitute the name
4708 of a temporary file, just like @samp{%u}. This temporary file is not
4709 meant for communication between processes, but rather as a junk
4712 @item %.@var{SUFFIX}
4713 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
4714 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
4715 terminated by the next space or %.
4718 Marks the argument containing or following the @samp{%w} as the
4719 designated output file of this compilation. This puts the argument
4720 into the sequence of arguments that @samp{%o} will substitute later.
4723 Substitutes the names of all the output files, with spaces
4724 automatically placed around them. You should write spaces
4725 around the @samp{%o} as well or the results are undefined.
4726 @samp{%o} is for use in the specs for running the linker.
4727 Input files whose names have no recognized suffix are not compiled
4728 at all, but they are included among the output files, so they will
4732 Substitutes the suffix for object files. Note that this is
4733 handled specially when it immediately follows @samp{%g, %u, or %U},
4734 because of the need for those to form complete file names. The
4735 handling is such that @samp{%O} is treated exactly as if it had already
4736 been substituted, except that @samp{%g, %u, and %U} do not currently
4737 support additional @var{suffix} characters following @samp{%O} as they would
4738 following, for example, @samp{.o}.
4741 Substitutes the standard macro predefinitions for the
4742 current target machine. Use this when running @code{cpp}.
4745 Like @samp{%p}, but puts @samp{__} before and after the name of each
4746 predefined macro, except for macros that start with @samp{__} or with
4747 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
4751 Substitute a @option{-iprefix} option made from @env{GCC_EXEC_PREFIX}.
4754 Current argument is the name of a library or startup file of some sort.
4755 Search for that file in a standard list of directories and substitute
4756 the full name found.
4759 Print @var{str} as an error message. @var{str} is terminated by a newline.
4760 Use this when inconsistent options are detected.
4763 Output @samp{-} if the input for the current command is coming from a pipe.
4766 Substitute the contents of spec string @var{name} at this point.
4769 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
4771 @item %x@{@var{option}@}
4772 Accumulate an option for @samp{%X}.
4775 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
4779 Output the accumulated assembler options specified by @option{-Wa}.
4782 Output the accumulated preprocessor options specified by @option{-Wp}.
4785 Substitute the major version number of GCC@.
4786 (For version 2.9.5, this is 2.)
4789 Substitute the minor version number of GCC@.
4790 (For version 2.9.5, this is 9.)
4793 Substitute the patch level number of GCC@.
4794 (For version 2.9.5, this is 5.)
4797 Process the @code{asm} spec. This is used to compute the
4798 switches to be passed to the assembler.
4801 Process the @code{asm_final} spec. This is a spec string for
4802 passing switches to an assembler post-processor, if such a program is
4806 Process the @code{link} spec. This is the spec for computing the
4807 command line passed to the linker. Typically it will make use of the
4808 @samp{%L %G %S %D and %E} sequences.
4811 Dump out a @option{-L} option for each directory that GCC believes might
4812 contain startup files. If the target supports multilibs then the
4813 current multilib directory will be prepended to each of these paths.
4816 Output the multilib directory with directory separators replaced with
4817 @samp{_}. If multilib directories are not set, or the multilib directory is
4818 @file{.} then this option emits nothing.
4821 Process the @code{lib} spec. This is a spec string for deciding which
4822 libraries should be included on the command line to the linker.
4825 Process the @code{libgcc} spec. This is a spec string for deciding
4826 which GCC support library should be included on the command line to the linker.
4829 Process the @code{startfile} spec. This is a spec for deciding which
4830 object files should be the first ones passed to the linker. Typically
4831 this might be a file named @file{crt0.o}.
4834 Process the @code{endfile} spec. This is a spec string that specifies
4835 the last object files that will be passed to the linker.
4838 Process the @code{cpp} spec. This is used to construct the arguments
4839 to be passed to the C preprocessor.
4842 Process the @code{signed_char} spec. This is intended to be used
4843 to tell cpp whether a char is signed. It typically has the definition:
4845 %@{funsigned-char:-D__CHAR_UNSIGNED__@}
4849 Process the @code{cc1} spec. This is used to construct the options to be
4850 passed to the actual C compiler (@samp{cc1}).
4853 Process the @code{cc1plus} spec. This is used to construct the options to be
4854 passed to the actual C++ compiler (@samp{cc1plus}).
4857 Substitute the variable part of a matched option. See below.
4858 Note that each comma in the substituted string is replaced by
4862 Substitutes the @code{-S} switch, if that switch was given to GCC@.
4863 If that switch was not specified, this substitutes nothing. Note that
4864 the leading dash is omitted when specifying this option, and it is
4865 automatically inserted if the substitution is performed. Thus the spec
4866 string @samp{%@{foo@}} would match the command-line option @option{-foo}
4867 and would output the command line option @option{-foo}.
4869 @item %W@{@code{S}@}
4870 Like %@{@code{S}@} but mark last argument supplied within as a file to be
4873 @item %@{@code{S}*@}
4874 Substitutes all the switches specified to GCC whose names start
4875 with @code{-S}, but which also take an argument. This is used for
4876 switches like @option{-o}, @option{-D}, @option{-I}, etc.
4877 GCC considers @option{-o foo} as being
4878 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
4879 text, including the space. Thus two arguments would be generated.
4881 @item %@{^@code{S}*@}
4882 Like %@{@code{S}*@}, but don't put a blank between a switch and its
4883 argument. Thus %@{^o*@} would only generate one argument, not two.
4885 @item %@{@code{S}*&@code{T}*@}
4886 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
4887 (the order of @code{S} and @code{T} in the spec is not significant).
4888 There can be any number of ampersand-separated variables; for each the
4889 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
4891 @item %@{<@code{S}@}
4892 Remove all occurrences of @code{-S} from the command line. Note---this
4893 command is position dependent. @samp{%} commands in the spec string
4894 before this option will see @code{-S}, @samp{%} commands in the spec
4895 string after this option will not.
4897 @item %@{@code{S}*:@code{X}@}
4898 Substitutes @code{X} if one or more switches whose names start with
4899 @code{-S} are specified to GCC@. Note that the tail part of the
4900 @code{-S} option (i.e.@: the part matched by the @samp{*}) will be substituted
4901 for each occurrence of @samp{%*} within @code{X}.
4903 @item %@{@code{S}:@code{X}@}
4904 Substitutes @code{X}, but only if the @samp{-S} switch was given to GCC@.
4906 @item %@{!@code{S}:@code{X}@}
4907 Substitutes @code{X}, but only if the @samp{-S} switch was @emph{not} given to GCC@.
4909 @item %@{|@code{S}:@code{X}@}
4910 Like %@{@code{S}:@code{X}@}, but if no @code{S} switch, substitute @samp{-}.
4912 @item %@{|!@code{S}:@code{X}@}
4913 Like %@{!@code{S}:@code{X}@}, but if there is an @code{S} switch, substitute @samp{-}.
4915 @item %@{.@code{S}:@code{X}@}
4916 Substitutes @code{X}, but only if processing a file with suffix @code{S}.
4918 @item %@{!.@code{S}:@code{X}@}
4919 Substitutes @code{X}, but only if @emph{not} processing a file with suffix @code{S}.
4921 @item %@{@code{S}|@code{P}:@code{X}@}
4922 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@. This may be
4923 combined with @samp{!} and @samp{.} sequences as well, although they
4924 have a stronger binding than the @samp{|}. For example a spec string
4928 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
4931 will output the following command-line options from the following input
4932 command-line options:
4937 -d fred.c -foo -baz -boggle
4938 -d jim.d -bar -baz -boggle
4943 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or
4944 %@{!@code{S}:@code{X}@} construct may contain other nested @samp{%} constructs
4945 or spaces, or even newlines. They are processed as usual, as described
4948 The @option{-O}, @option{-f}, @option{-m}, and @option{-W}
4949 switches are handled specifically in these
4950 constructs. If another value of @option{-O} or the negated form of a @option{-f}, @option{-m}, or
4951 @option{-W} switch is found later in the command line, the earlier switch
4952 value is ignored, except with @{@code{S}*@} where @code{S} is just one
4953 letter, which passes all matching options.
4955 The character @samp{|} at the beginning of the predicate text is used to indicate
4956 that a command should be piped to the following command, but only if @option{-pipe}
4959 It is built into GCC which switches take arguments and which do not.
4960 (You might think it would be useful to generalize this to allow each
4961 compiler's spec to say which switches take arguments. But this cannot
4962 be done in a consistent fashion. GCC cannot even decide which input
4963 files have been specified without knowing which switches take arguments,
4964 and it must know which input files to compile in order to tell which
4967 GCC also knows implicitly that arguments starting in @option{-l} are to be
4968 treated as compiler output files, and passed to the linker in their
4969 proper position among the other output files.
4971 @c man begin OPTIONS
4973 @node Target Options
4974 @section Specifying Target Machine and Compiler Version
4975 @cindex target options
4976 @cindex cross compiling
4977 @cindex specifying machine version
4978 @cindex specifying compiler version and target machine
4979 @cindex compiler version, specifying
4980 @cindex target machine, specifying
4982 The usual way to run GCC is to run the executable called @file{gcc}, or
4983 @file{<machine>-gcc} when cross-compiling, or
4984 @file{<machine>-gcc-<version>} to run a version other than the one that
4985 was installed last. Sometimes this is inconvenient, so GCC provides
4986 options that will switch to another cross-compiler or version.
4989 @item -b @var{machine}
4991 The argument @var{machine} specifies the target machine for compilation.
4993 The value to use for @var{machine} is the same as was specified as the
4994 machine type when configuring GCC as a cross-compiler. For
4995 example, if a cross-compiler was configured with @samp{configure
4996 i386v}, meaning to compile for an 80386 running System V, then you
4997 would specify @option{-b i386v} to run that cross compiler.
4999 @item -V @var{version}
5001 The argument @var{version} specifies which version of GCC to run.
5002 This is useful when multiple versions are installed. For example,
5003 @var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
5006 The @option{-V} and @option{-b} options work by running the
5007 @file{<machine>-gcc-<version>} executable, so there's no real reason to
5008 use them if you can just run that directly.
5010 @node Submodel Options
5011 @section Hardware Models and Configurations
5012 @cindex submodel options
5013 @cindex specifying hardware config
5014 @cindex hardware models and configurations, specifying
5015 @cindex machine dependent options
5017 Earlier we discussed the standard option @option{-b} which chooses among
5018 different installed compilers for completely different target
5019 machines, such as VAX vs.@: 68000 vs.@: 80386.
5021 In addition, each of these target machine types can have its own
5022 special options, starting with @samp{-m}, to choose among various
5023 hardware models or configurations---for example, 68010 vs 68020,
5024 floating coprocessor or none. A single installed version of the
5025 compiler can compile for any model or configuration, according to the
5028 Some configurations of the compiler also support additional special
5029 options, usually for compatibility with other compilers on the same
5032 These options are defined by the macro @code{TARGET_SWITCHES} in the
5033 machine description. The default for the options is also defined by
5034 that macro, which enables you to change the defaults.
5048 * RS/6000 and PowerPC Options::
5051 * i386 and x86-64 Options::
5053 * Intel 960 Options::
5054 * DEC Alpha Options::
5055 * DEC Alpha/VMS Options::
5059 * System V Options::
5060 * TMS320C3x/C4x Options::
5068 * S/390 and zSeries Options::
5072 * Xstormy16 Options::
5076 @node M680x0 Options
5077 @subsection M680x0 Options
5078 @cindex M680x0 options
5080 These are the @samp{-m} options defined for the 68000 series. The default
5081 values for these options depends on which style of 68000 was selected when
5082 the compiler was configured; the defaults for the most common choices are
5090 Generate output for a 68000. This is the default
5091 when the compiler is configured for 68000-based systems.
5093 Use this option for microcontrollers with a 68000 or EC000 core,
5094 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
5100 Generate output for a 68020. This is the default
5101 when the compiler is configured for 68020-based systems.
5105 Generate output containing 68881 instructions for floating point.
5106 This is the default for most 68020 systems unless @option{--nfp} was
5107 specified when the compiler was configured.
5111 Generate output for a 68030. This is the default when the compiler is
5112 configured for 68030-based systems.
5116 Generate output for a 68040. This is the default when the compiler is
5117 configured for 68040-based systems.
5119 This option inhibits the use of 68881/68882 instructions that have to be
5120 emulated by software on the 68040. Use this option if your 68040 does not
5121 have code to emulate those instructions.
5125 Generate output for a 68060. This is the default when the compiler is
5126 configured for 68060-based systems.
5128 This option inhibits the use of 68020 and 68881/68882 instructions that
5129 have to be emulated by software on the 68060. Use this option if your 68060
5130 does not have code to emulate those instructions.
5134 Generate output for a CPU32. This is the default
5135 when the compiler is configured for CPU32-based systems.
5137 Use this option for microcontrollers with a
5138 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
5139 68336, 68340, 68341, 68349 and 68360.
5143 Generate output for a 520X ``coldfire'' family cpu. This is the default
5144 when the compiler is configured for 520X-based systems.
5146 Use this option for microcontroller with a 5200 core, including
5147 the MCF5202, MCF5203, MCF5204 and MCF5202.
5152 Generate output for a 68040, without using any of the new instructions.
5153 This results in code which can run relatively efficiently on either a
5154 68020/68881 or a 68030 or a 68040. The generated code does use the
5155 68881 instructions that are emulated on the 68040.
5159 Generate output for a 68060, without using any of the new instructions.
5160 This results in code which can run relatively efficiently on either a
5161 68020/68881 or a 68030 or a 68040. The generated code does use the
5162 68881 instructions that are emulated on the 68060.
5166 Generate output containing Sun FPA instructions for floating point.
5169 @opindex msoft-float
5170 Generate output containing library calls for floating point.
5171 @strong{Warning:} the requisite libraries are not available for all m68k
5172 targets. Normally the facilities of the machine's usual C compiler are
5173 used, but this can't be done directly in cross-compilation. You must
5174 make your own arrangements to provide suitable library functions for
5175 cross-compilation. The embedded targets @samp{m68k-*-aout} and
5176 @samp{m68k-*-coff} do provide software floating point support.
5180 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5183 @opindex mnobitfield
5184 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
5185 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
5189 Do use the bit-field instructions. The @option{-m68020} option implies
5190 @option{-mbitfield}. This is the default if you use a configuration
5191 designed for a 68020.
5195 Use a different function-calling convention, in which functions
5196 that take a fixed number of arguments return with the @code{rtd}
5197 instruction, which pops their arguments while returning. This
5198 saves one instruction in the caller since there is no need to pop
5199 the arguments there.
5201 This calling convention is incompatible with the one normally
5202 used on Unix, so you cannot use it if you need to call libraries
5203 compiled with the Unix compiler.
5205 Also, you must provide function prototypes for all functions that
5206 take variable numbers of arguments (including @code{printf});
5207 otherwise incorrect code will be generated for calls to those
5210 In addition, seriously incorrect code will result if you call a
5211 function with too many arguments. (Normally, extra arguments are
5212 harmlessly ignored.)
5214 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
5215 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
5218 @itemx -mno-align-int
5220 @opindex mno-align-int
5221 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
5222 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
5223 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
5224 Aligning variables on 32-bit boundaries produces code that runs somewhat
5225 faster on processors with 32-bit busses at the expense of more memory.
5227 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
5228 align structures containing the above types differently than
5229 most published application binary interface specifications for the m68k.
5233 Use the pc-relative addressing mode of the 68000 directly, instead of
5234 using a global offset table. At present, this option implies @option{-fpic},
5235 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
5236 not presently supported with @option{-mpcrel}, though this could be supported for
5237 68020 and higher processors.
5239 @item -mno-strict-align
5240 @itemx -mstrict-align
5241 @opindex mno-strict-align
5242 @opindex mstrict-align
5243 Do not (do) assume that unaligned memory references will be handled by
5248 @node M68hc1x Options
5249 @subsection M68hc1x Options
5250 @cindex M68hc1x options
5252 These are the @samp{-m} options defined for the 68hc11 and 68hc12
5253 microcontrollers. The default values for these options depends on
5254 which style of microcontroller was selected when the compiler was configured;
5255 the defaults for the most common choices are given below.
5262 Generate output for a 68HC11. This is the default
5263 when the compiler is configured for 68HC11-based systems.
5269 Generate output for a 68HC12. This is the default
5270 when the compiler is configured for 68HC12-based systems.
5273 @opindex mauto-incdec
5274 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
5281 Enable the use of 68HC12 min and max instructions.
5284 @itemx -mno-long-calls
5285 @opindex mlong-calls
5286 @opindex mno-long-calls
5287 Treat all calls as being far away (near). If calls are assumed to be
5288 far away, the compiler will use the @code{call} instruction to
5289 call a function and the @code{rtc} instruction for returning.
5293 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5295 @item -msoft-reg-count=@var{count}
5296 @opindex msoft-reg-count
5297 Specify the number of pseudo-soft registers which are used for the
5298 code generation. The maximum number is 32. Using more pseudo-soft
5299 register may or may not result in better code depending on the program.
5300 The default is 4 for 68HC11 and 2 for 68HC12.
5305 @subsection VAX Options
5308 These @samp{-m} options are defined for the VAX:
5313 Do not output certain jump instructions (@code{aobleq} and so on)
5314 that the Unix assembler for the VAX cannot handle across long
5319 Do output those jump instructions, on the assumption that you
5320 will assemble with the GNU assembler.
5324 Output code for g-format floating point numbers instead of d-format.
5328 @subsection SPARC Options
5329 @cindex SPARC options
5331 These @samp{-m} switches are supported on the SPARC:
5336 @opindex mno-app-regs
5338 Specify @option{-mapp-regs} to generate output using the global registers
5339 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
5342 To be fully SVR4 ABI compliant at the cost of some performance loss,
5343 specify @option{-mno-app-regs}. You should compile libraries and system
5344 software with this option.
5349 @opindex mhard-float
5350 Generate output containing floating point instructions. This is the
5356 @opindex msoft-float
5357 Generate output containing library calls for floating point.
5358 @strong{Warning:} the requisite libraries are not available for all SPARC
5359 targets. Normally the facilities of the machine's usual C compiler are
5360 used, but this cannot be done directly in cross-compilation. You must make
5361 your own arrangements to provide suitable library functions for
5362 cross-compilation. The embedded targets @samp{sparc-*-aout} and
5363 @samp{sparclite-*-*} do provide software floating point support.
5365 @option{-msoft-float} changes the calling convention in the output file;
5366 therefore, it is only useful if you compile @emph{all} of a program with
5367 this option. In particular, you need to compile @file{libgcc.a}, the
5368 library that comes with GCC, with @option{-msoft-float} in order for
5371 @item -mhard-quad-float
5372 @opindex mhard-quad-float
5373 Generate output containing quad-word (long double) floating point
5376 @item -msoft-quad-float
5377 @opindex msoft-quad-float
5378 Generate output containing library calls for quad-word (long double)
5379 floating point instructions. The functions called are those specified
5380 in the SPARC ABI@. This is the default.
5382 As of this writing, there are no sparc implementations that have hardware
5383 support for the quad-word floating point instructions. They all invoke
5384 a trap handler for one of these instructions, and then the trap handler
5385 emulates the effect of the instruction. Because of the trap handler overhead,
5386 this is much slower than calling the ABI library routines. Thus the
5387 @option{-msoft-quad-float} option is the default.
5393 With @option{-mflat}, the compiler does not generate save/restore instructions
5394 and will use a ``flat'' or single register window calling convention.
5395 This model uses %i7 as the frame pointer and is compatible with the normal
5396 register window model. Code from either may be intermixed.
5397 The local registers and the input registers (0--5) are still treated as
5398 ``call saved'' registers and will be saved on the stack as necessary.
5400 With @option{-mno-flat} (the default), the compiler emits save/restore
5401 instructions (except for leaf functions) and is the normal mode of operation.
5403 @item -mno-unaligned-doubles
5404 @itemx -munaligned-doubles
5405 @opindex mno-unaligned-doubles
5406 @opindex munaligned-doubles
5407 Assume that doubles have 8 byte alignment. This is the default.
5409 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
5410 alignment only if they are contained in another type, or if they have an
5411 absolute address. Otherwise, it assumes they have 4 byte alignment.
5412 Specifying this option avoids some rare compatibility problems with code
5413 generated by other compilers. It is not the default because it results
5414 in a performance loss, especially for floating point code.
5416 @item -mno-faster-structs
5417 @itemx -mfaster-structs
5418 @opindex mno-faster-structs
5419 @opindex mfaster-structs
5420 With @option{-mfaster-structs}, the compiler assumes that structures
5421 should have 8 byte alignment. This enables the use of pairs of
5422 @code{ldd} and @code{std} instructions for copies in structure
5423 assignment, in place of twice as many @code{ld} and @code{st} pairs.
5424 However, the use of this changed alignment directly violates the SPARC
5425 ABI@. Thus, it's intended only for use on targets where the developer
5426 acknowledges that their resulting code will not be directly in line with
5427 the rules of the ABI@.
5433 These two options select variations on the SPARC architecture.
5435 By default (unless specifically configured for the Fujitsu SPARClite),
5436 GCC generates code for the v7 variant of the SPARC architecture.
5438 @option{-mv8} will give you SPARC v8 code. The only difference from v7
5439 code is that the compiler emits the integer multiply and integer
5440 divide instructions which exist in SPARC v8 but not in SPARC v7.
5442 @option{-msparclite} will give you SPARClite code. This adds the integer
5443 multiply, integer divide step and scan (@code{ffs}) instructions which
5444 exist in SPARClite but not in SPARC v7.
5446 These options are deprecated and will be deleted in a future GCC release.
5447 They have been replaced with @option{-mcpu=xxx}.
5452 @opindex msupersparc
5453 These two options select the processor for which the code is optimized.
5455 With @option{-mcypress} (the default), the compiler optimizes code for the
5456 Cypress CY7C602 chip, as used in the SPARCStation/SPARCServer 3xx series.
5457 This is also appropriate for the older SPARCStation 1, 2, IPX etc.
5459 With @option{-msupersparc} the compiler optimizes code for the SuperSPARC cpu, as
5460 used in the SPARCStation 10, 1000 and 2000 series. This flag also enables use
5461 of the full SPARC v8 instruction set.
5463 These options are deprecated and will be deleted in a future GCC release.
5464 They have been replaced with @option{-mcpu=xxx}.
5466 @item -mcpu=@var{cpu_type}
5468 Set the instruction set, register set, and instruction scheduling parameters
5469 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
5470 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
5471 @samp{hypersparc}, @samp{sparclite86x}, @samp{f930}, @samp{f934},
5472 @samp{sparclet}, @samp{tsc701}, @samp{v9}, and @samp{ultrasparc}.
5474 Default instruction scheduling parameters are used for values that select
5475 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
5476 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
5478 Here is a list of each supported architecture and their supported
5483 v8: supersparc, hypersparc
5484 sparclite: f930, f934, sparclite86x
5489 @item -mtune=@var{cpu_type}
5491 Set the instruction scheduling parameters for machine type
5492 @var{cpu_type}, but do not set the instruction set or register set that the
5493 option @option{-mcpu=@var{cpu_type}} would.
5495 The same values for @option{-mcpu=@var{cpu_type}} can be used for
5496 @option{-mtune=@var{cpu_type}}, but the only useful values are those
5497 that select a particular cpu implementation. Those are @samp{cypress},
5498 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
5499 @samp{sparclite86x}, @samp{tsc701}, and @samp{ultrasparc}.
5503 These @samp{-m} switches are supported in addition to the above
5504 on the SPARCLET processor.
5507 @item -mlittle-endian
5508 @opindex mlittle-endian
5509 Generate code for a processor running in little-endian mode.
5513 Treat register @code{%g0} as a normal register.
5514 GCC will continue to clobber it as necessary but will not assume
5515 it always reads as 0.
5517 @item -mbroken-saverestore
5518 @opindex mbroken-saverestore
5519 Generate code that does not use non-trivial forms of the @code{save} and
5520 @code{restore} instructions. Early versions of the SPARCLET processor do
5521 not correctly handle @code{save} and @code{restore} instructions used with
5522 arguments. They correctly handle them used without arguments. A @code{save}
5523 instruction used without arguments increments the current window pointer
5524 but does not allocate a new stack frame. It is assumed that the window
5525 overflow trap handler will properly handle this case as will interrupt
5529 These @samp{-m} switches are supported in addition to the above
5530 on SPARC V9 processors in 64-bit environments.
5533 @item -mlittle-endian
5534 @opindex mlittle-endian
5535 Generate code for a processor running in little-endian mode.
5541 Generate code for a 32-bit or 64-bit environment.
5542 The 32-bit environment sets int, long and pointer to 32 bits.
5543 The 64-bit environment sets int to 32 bits and long and pointer
5546 @item -mcmodel=medlow
5547 @opindex mcmodel=medlow
5548 Generate code for the Medium/Low code model: the program must be linked
5549 in the low 32 bits of the address space. Pointers are 64 bits.
5550 Programs can be statically or dynamically linked.
5552 @item -mcmodel=medmid
5553 @opindex mcmodel=medmid
5554 Generate code for the Medium/Middle code model: the program must be linked
5555 in the low 44 bits of the address space, the text segment must be less than
5556 2G bytes, and data segment must be within 2G of the text segment.
5557 Pointers are 64 bits.
5559 @item -mcmodel=medany
5560 @opindex mcmodel=medany
5561 Generate code for the Medium/Anywhere code model: the program may be linked
5562 anywhere in the address space, the text segment must be less than
5563 2G bytes, and data segment must be within 2G of the text segment.
5564 Pointers are 64 bits.
5566 @item -mcmodel=embmedany
5567 @opindex mcmodel=embmedany
5568 Generate code for the Medium/Anywhere code model for embedded systems:
5569 assume a 32-bit text and a 32-bit data segment, both starting anywhere
5570 (determined at link time). Register %g4 points to the base of the
5571 data segment. Pointers are still 64 bits.
5572 Programs are statically linked, PIC is not supported.
5575 @itemx -mno-stack-bias
5576 @opindex mstack-bias
5577 @opindex mno-stack-bias
5578 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
5579 frame pointer if present, are offset by @minus{}2047 which must be added back
5580 when making stack frame references.
5581 Otherwise, assume no such offset is present.
5584 @node Convex Options
5585 @subsection Convex Options
5586 @cindex Convex options
5588 These @samp{-m} options are defined for Convex:
5593 Generate output for C1. The code will run on any Convex machine.
5594 The preprocessor symbol @code{__convex__c1__} is defined.
5598 Generate output for C2. Uses instructions not available on C1.
5599 Scheduling and other optimizations are chosen for max performance on C2.
5600 The preprocessor symbol @code{__convex_c2__} is defined.
5604 Generate output for C32xx. Uses instructions not available on C1.
5605 Scheduling and other optimizations are chosen for max performance on C32.
5606 The preprocessor symbol @code{__convex_c32__} is defined.
5610 Generate output for C34xx. Uses instructions not available on C1.
5611 Scheduling and other optimizations are chosen for max performance on C34.
5612 The preprocessor symbol @code{__convex_c34__} is defined.
5616 Generate output for C38xx. Uses instructions not available on C1.
5617 Scheduling and other optimizations are chosen for max performance on C38.
5618 The preprocessor symbol @code{__convex_c38__} is defined.
5622 Generate code which puts an argument count in the word preceding each
5623 argument list. This is compatible with regular CC, and a few programs
5624 may need the argument count word. GDB and other source-level debuggers
5625 do not need it; this info is in the symbol table.
5628 @opindex mnoargcount
5629 Omit the argument count word. This is the default.
5631 @item -mvolatile-cache
5632 @opindex mvolatile-cache
5633 Allow volatile references to be cached. This is the default.
5635 @item -mvolatile-nocache
5636 @opindex mvolatile-nocache
5637 Volatile references bypass the data cache, going all the way to memory.
5638 This is only needed for multi-processor code that does not use standard
5639 synchronization instructions. Making non-volatile references to volatile
5640 locations will not necessarily work.
5644 Type long is 32 bits, the same as type int. This is the default.
5648 Type long is 64 bits, the same as type long long. This option is useless,
5649 because no library support exists for it.
5652 @node AMD29K Options
5653 @subsection AMD29K Options
5654 @cindex AMD29K options
5656 These @samp{-m} options are defined for the AMD Am29000:
5661 @cindex DW bit (29k)
5662 Generate code that assumes the @code{DW} bit is set, i.e., that byte and
5663 halfword operations are directly supported by the hardware. This is the
5668 Generate code that assumes the @code{DW} bit is not set.
5672 @cindex byte writes (29k)
5673 Generate code that assumes the system supports byte and halfword write
5674 operations. This is the default.
5678 Generate code that assumes the systems does not support byte and
5679 halfword write operations. @option{-mnbw} implies @option{-mndw}.
5683 @cindex memory model (29k)
5684 Use a small memory model that assumes that all function addresses are
5685 either within a single 256 KB segment or at an absolute address of less
5686 than 256k. This allows the @code{call} instruction to be used instead
5687 of a @code{const}, @code{consth}, @code{calli} sequence.
5691 Use the normal memory model: Generate @code{call} instructions only when
5692 calling functions in the same file and @code{calli} instructions
5693 otherwise. This works if each file occupies less than 256 KB but allows
5694 the entire executable to be larger than 256 KB@. This is the default.
5698 Always use @code{calli} instructions. Specify this option if you expect
5699 a single file to compile into more than 256 KB of code.
5703 @cindex processor selection (29k)
5704 Generate code for the Am29050.
5708 Generate code for the Am29000. This is the default.
5710 @item -mkernel-registers
5711 @opindex mkernel-registers
5712 @cindex kernel and user registers (29k)
5713 Generate references to registers @code{gr64-gr95} instead of to
5714 registers @code{gr96-gr127}. This option can be used when compiling
5715 kernel code that wants a set of global registers disjoint from that used
5718 Note that when this option is used, register names in @samp{-f} flags
5719 must use the normal, user-mode, names.
5721 @item -muser-registers
5722 @opindex muser-registers
5723 Use the normal set of global registers, @code{gr96-gr127}. This is the
5727 @itemx -mno-stack-check
5728 @opindex mstack-check
5729 @opindex mno-stack-check
5730 @cindex stack checks (29k)
5731 Insert (or do not insert) a call to @code{__msp_check} after each stack
5732 adjustment. This is often used for kernel code.
5735 @itemx -mno-storem-bug
5736 @opindex mstorem-bug
5737 @opindex mno-storem-bug
5738 @cindex storem bug (29k)
5739 @option{-mstorem-bug} handles 29k processors which cannot handle the
5740 separation of a mtsrim insn and a storem instruction (most 29000 chips
5741 to date, but not the 29050).
5743 @item -mno-reuse-arg-regs
5744 @itemx -mreuse-arg-regs
5745 @opindex mno-reuse-arg-regs
5746 @opindex mreuse-arg-regs
5747 @option{-mno-reuse-arg-regs} tells the compiler to only use incoming argument
5748 registers for copying out arguments. This helps detect calling a function
5749 with fewer arguments than it was declared with.
5751 @item -mno-impure-text
5752 @itemx -mimpure-text
5753 @opindex mno-impure-text
5754 @opindex mimpure-text
5755 @option{-mimpure-text}, used in addition to @option{-shared}, tells the compiler to
5756 not pass @option{-assert pure-text} to the linker when linking a shared object.
5759 @opindex msoft-float
5760 Generate output containing library calls for floating point.
5761 @strong{Warning:} the requisite libraries are not part of GCC@.
5762 Normally the facilities of the machine's usual C compiler are used, but
5763 this can't be done directly in cross-compilation. You must make your
5764 own arrangements to provide suitable library functions for
5769 Do not generate multm or multmu instructions. This is useful for some embedded
5770 systems which do not have trap handlers for these instructions.
5774 @subsection ARM Options
5777 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
5782 @opindex mapcs-frame
5783 Generate a stack frame that is compliant with the ARM Procedure Call
5784 Standard for all functions, even if this is not strictly necessary for
5785 correct execution of the code. Specifying @option{-fomit-frame-pointer}
5786 with this option will cause the stack frames not to be generated for
5787 leaf functions. The default is @option{-mno-apcs-frame}.
5791 This is a synonym for @option{-mapcs-frame}.
5795 Generate code for a processor running with a 26-bit program counter,
5796 and conforming to the function calling standards for the APCS 26-bit
5797 option. This option replaces the @option{-m2} and @option{-m3} options
5798 of previous releases of the compiler.
5802 Generate code for a processor running with a 32-bit program counter,
5803 and conforming to the function calling standards for the APCS 32-bit
5804 option. This option replaces the @option{-m6} option of previous releases
5808 @c not currently implemented
5809 @item -mapcs-stack-check
5810 @opindex mapcs-stack-check
5811 Generate code to check the amount of stack space available upon entry to
5812 every function (that actually uses some stack space). If there is
5813 insufficient space available then either the function
5814 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
5815 called, depending upon the amount of stack space required. The run time
5816 system is required to provide these functions. The default is
5817 @option{-mno-apcs-stack-check}, since this produces smaller code.
5819 @c not currently implemented
5821 @opindex mapcs-float
5822 Pass floating point arguments using the float point registers. This is
5823 one of the variants of the APCS@. This option is recommended if the
5824 target hardware has a floating point unit or if a lot of floating point
5825 arithmetic is going to be performed by the code. The default is
5826 @option{-mno-apcs-float}, since integer only code is slightly increased in
5827 size if @option{-mapcs-float} is used.
5829 @c not currently implemented
5830 @item -mapcs-reentrant
5831 @opindex mapcs-reentrant
5832 Generate reentrant, position independent code. The default is
5833 @option{-mno-apcs-reentrant}.
5836 @item -mthumb-interwork
5837 @opindex mthumb-interwork
5838 Generate code which supports calling between the ARM and Thumb
5839 instruction sets. Without this option the two instruction sets cannot
5840 be reliably used inside one program. The default is
5841 @option{-mno-thumb-interwork}, since slightly larger code is generated
5842 when @option{-mthumb-interwork} is specified.
5844 @item -mno-sched-prolog
5845 @opindex mno-sched-prolog
5846 Prevent the reordering of instructions in the function prolog, or the
5847 merging of those instruction with the instructions in the function's
5848 body. This means that all functions will start with a recognizable set
5849 of instructions (or in fact one of a choice from a small set of
5850 different function prologues), and this information can be used to
5851 locate the start if functions inside an executable piece of code. The
5852 default is @option{-msched-prolog}.
5855 @opindex mhard-float
5856 Generate output containing floating point instructions. This is the
5860 @opindex msoft-float
5861 Generate output containing library calls for floating point.
5862 @strong{Warning:} the requisite libraries are not available for all ARM
5863 targets. Normally the facilities of the machine's usual C compiler are
5864 used, but this cannot be done directly in cross-compilation. You must make
5865 your own arrangements to provide suitable library functions for
5868 @option{-msoft-float} changes the calling convention in the output file;
5869 therefore, it is only useful if you compile @emph{all} of a program with
5870 this option. In particular, you need to compile @file{libgcc.a}, the
5871 library that comes with GCC, with @option{-msoft-float} in order for
5874 @item -mlittle-endian
5875 @opindex mlittle-endian
5876 Generate code for a processor running in little-endian mode. This is
5877 the default for all standard configurations.
5880 @opindex mbig-endian
5881 Generate code for a processor running in big-endian mode; the default is
5882 to compile code for a little-endian processor.
5884 @item -mwords-little-endian
5885 @opindex mwords-little-endian
5886 This option only applies when generating code for big-endian processors.
5887 Generate code for a little-endian word order but a big-endian byte
5888 order. That is, a byte order of the form @samp{32107654}. Note: this
5889 option should only be used if you require compatibility with code for
5890 big-endian ARM processors generated by versions of the compiler prior to
5893 @item -malignment-traps
5894 @opindex malignment-traps
5895 Generate code that will not trap if the MMU has alignment traps enabled.
5896 On ARM architectures prior to ARMv4, there were no instructions to
5897 access half-word objects stored in memory. However, when reading from
5898 memory a feature of the ARM architecture allows a word load to be used,
5899 even if the address is unaligned, and the processor core will rotate the
5900 data as it is being loaded. This option tells the compiler that such
5901 misaligned accesses will cause a MMU trap and that it should instead
5902 synthesize the access as a series of byte accesses. The compiler can
5903 still use word accesses to load half-word data if it knows that the
5904 address is aligned to a word boundary.
5906 This option is ignored when compiling for ARM architecture 4 or later,
5907 since these processors have instructions to directly access half-word
5910 @item -mno-alignment-traps
5911 @opindex mno-alignment-traps
5912 Generate code that assumes that the MMU will not trap unaligned
5913 accesses. This produces better code when the target instruction set
5914 does not have half-word memory operations (i.e.@: implementations prior to
5917 Note that you cannot use this option to access unaligned word objects,
5918 since the processor will only fetch one 32-bit aligned object from
5921 The default setting for most targets is @option{-mno-alignment-traps}, since
5922 this produces better code when there are no half-word memory
5923 instructions available.
5925 @item -mshort-load-bytes
5926 @itemx -mno-short-load-words
5927 @opindex mshort-load-bytes
5928 @opindex mno-short-load-words
5929 These are deprecated aliases for @option{-malignment-traps}.
5931 @item -mno-short-load-bytes
5932 @itemx -mshort-load-words
5933 @opindex mno-short-load-bytes
5934 @opindex mshort-load-words
5935 This are deprecated aliases for @option{-mno-alignment-traps}.
5939 This option only applies to RISC iX@. Emulate the native BSD-mode
5940 compiler. This is the default if @option{-ansi} is not specified.
5944 This option only applies to RISC iX@. Emulate the native X/Open-mode
5947 @item -mno-symrename
5948 @opindex mno-symrename
5949 This option only applies to RISC iX@. Do not run the assembler
5950 post-processor, @samp{symrename}, after code has been assembled.
5951 Normally it is necessary to modify some of the standard symbols in
5952 preparation for linking with the RISC iX C library; this option
5953 suppresses this pass. The post-processor is never run when the
5954 compiler is built for cross-compilation.
5956 @item -mcpu=@var{name}
5958 This specifies the name of the target ARM processor. GCC uses this name
5959 to determine what kind of instructions it can emit when generating
5960 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
5961 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
5962 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
5963 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
5964 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
5965 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm8},
5966 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
5967 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
5968 @samp{arm920t}, @samp{arm940t}, @samp{arm9tdmi}, @samp{arm10tdmi},
5969 @samp{arm1020t}, @samp{xscale}.
5971 @itemx -mtune=@var{name}
5973 This option is very similar to the @option{-mcpu=} option, except that
5974 instead of specifying the actual target processor type, and hence
5975 restricting which instructions can be used, it specifies that GCC should
5976 tune the performance of the code as if the target were of the type
5977 specified in this option, but still choosing the instructions that it
5978 will generate based on the cpu specified by a @option{-mcpu=} option.
5979 For some ARM implementations better performance can be obtained by using
5982 @item -march=@var{name}
5984 This specifies the name of the target ARM architecture. GCC uses this
5985 name to determine what kind of instructions it can emit when generating
5986 assembly code. This option can be used in conjunction with or instead
5987 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
5988 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
5989 @samp{armv5}, @samp{armv5t}, @samp{armv5te}.
5991 @item -mfpe=@var{number}
5992 @itemx -mfp=@var{number}
5995 This specifies the version of the floating point emulation available on
5996 the target. Permissible values are 2 and 3. @option{-mfp=} is a synonym
5997 for @option{-mfpe=}, for compatibility with older versions of GCC@.
5999 @item -mstructure-size-boundary=@var{n}
6000 @opindex mstructure-size-boundary
6001 The size of all structures and unions will be rounded up to a multiple
6002 of the number of bits set by this option. Permissible values are 8 and
6003 32. The default value varies for different toolchains. For the COFF
6004 targeted toolchain the default value is 8. Specifying the larger number
6005 can produce faster, more efficient code, but can also increase the size
6006 of the program. The two values are potentially incompatible. Code
6007 compiled with one value cannot necessarily expect to work with code or
6008 libraries compiled with the other value, if they exchange information
6009 using structures or unions.
6011 @item -mabort-on-noreturn
6012 @opindex mabort-on-noreturn
6013 Generate a call to the function @code{abort} at the end of a
6014 @code{noreturn} function. It will be executed if the function tries to
6018 @itemx -mno-long-calls
6019 @opindex mlong-calls
6020 @opindex mno-long-calls
6021 Tells the compiler to perform function calls by first loading the
6022 address of the function into a register and then performing a subroutine
6023 call on this register. This switch is needed if the target function
6024 will lie outside of the 64 megabyte addressing range of the offset based
6025 version of subroutine call instruction.
6027 Even if this switch is enabled, not all function calls will be turned
6028 into long calls. The heuristic is that static functions, functions
6029 which have the @samp{short-call} attribute, functions that are inside
6030 the scope of a @samp{#pragma no_long_calls} directive and functions whose
6031 definitions have already been compiled within the current compilation
6032 unit, will not be turned into long calls. The exception to this rule is
6033 that weak function definitions, functions with the @samp{long-call}
6034 attribute or the @samp{section} attribute, and functions that are within
6035 the scope of a @samp{#pragma long_calls} directive, will always be
6036 turned into long calls.
6038 This feature is not enabled by default. Specifying
6039 @option{-mno-long-calls} will restore the default behavior, as will
6040 placing the function calls within the scope of a @samp{#pragma
6041 long_calls_off} directive. Note these switches have no effect on how
6042 the compiler generates code to handle function calls via function
6045 @item -mnop-fun-dllimport
6046 @opindex mnop-fun-dllimport
6047 Disable support for the @code{dllimport} attribute.
6049 @item -msingle-pic-base
6050 @opindex msingle-pic-base
6051 Treat the register used for PIC addressing as read-only, rather than
6052 loading it in the prologue for each function. The run-time system is
6053 responsible for initializing this register with an appropriate value
6054 before execution begins.
6056 @item -mpic-register=@var{reg}
6057 @opindex mpic-register
6058 Specify the register to be used for PIC addressing. The default is R10
6059 unless stack-checking is enabled, when R9 is used.
6061 @item -mpoke-function-name
6062 @opindex mpoke-function-name
6063 Write the name of each function into the text section, directly
6064 preceding the function prologue. The generated code is similar to this:
6068 .ascii "arm_poke_function_name", 0
6071 .word 0xff000000 + (t1 - t0)
6072 arm_poke_function_name
6074 stmfd sp!, @{fp, ip, lr, pc@}
6078 When performing a stack backtrace, code can inspect the value of
6079 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
6080 location @code{pc - 12} and the top 8 bits are set, then we know that
6081 there is a function name embedded immediately preceding this location
6082 and has length @code{((pc[-3]) & 0xff000000)}.
6086 Generate code for the 16-bit Thumb instruction set. The default is to
6087 use the 32-bit ARM instruction set.
6090 @opindex mtpcs-frame
6091 Generate a stack frame that is compliant with the Thumb Procedure Call
6092 Standard for all non-leaf functions. (A leaf function is one that does
6093 not call any other functions.) The default is @option{-mno-tpcs-frame}.
6095 @item -mtpcs-leaf-frame
6096 @opindex mtpcs-leaf-frame
6097 Generate a stack frame that is compliant with the Thumb Procedure Call
6098 Standard for all leaf functions. (A leaf function is one that does
6099 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
6101 @item -mcallee-super-interworking
6102 @opindex mcallee-super-interworking
6103 Gives all externally visible functions in the file being compiled an ARM
6104 instruction set header which switches to Thumb mode before executing the
6105 rest of the function. This allows these functions to be called from
6106 non-interworking code.
6108 @item -mcaller-super-interworking
6109 @opindex mcaller-super-interworking
6110 Allows calls via function pointers (including virtual functions) to
6111 execute correctly regardless of whether the target code has been
6112 compiled for interworking or not. There is a small overhead in the cost
6113 of executing a function pointer if this option is enabled.
6117 @node MN10200 Options
6118 @subsection MN10200 Options
6119 @cindex MN10200 options
6120 These @option{-m} options are defined for Matsushita MN10200 architectures:
6125 Indicate to the linker that it should perform a relaxation optimization pass
6126 to shorten branches, calls and absolute memory addresses. This option only
6127 has an effect when used on the command line for the final link step.
6129 This option makes symbolic debugging impossible.
6132 @node MN10300 Options
6133 @subsection MN10300 Options
6134 @cindex MN10300 options
6135 These @option{-m} options are defined for Matsushita MN10300 architectures:
6140 Generate code to avoid bugs in the multiply instructions for the MN10300
6141 processors. This is the default.
6144 @opindex mno-mult-bug
6145 Do not generate code to avoid bugs in the multiply instructions for the
6150 Generate code which uses features specific to the AM33 processor.
6154 Do not generate code which uses features specific to the AM33 processor. This
6159 Do not link in the C run-time initialization object file.
6163 Indicate to the linker that it should perform a relaxation optimization pass
6164 to shorten branches, calls and absolute memory addresses. This option only
6165 has an effect when used on the command line for the final link step.
6167 This option makes symbolic debugging impossible.
6171 @node M32R/D Options
6172 @subsection M32R/D Options
6173 @cindex M32R/D options
6175 These @option{-m} options are defined for Mitsubishi M32R/D architectures:
6180 Generate code for the M32R/X@.
6184 Generate code for the M32R@. This is the default.
6186 @item -mcode-model=small
6187 @opindex mcode-model=small
6188 Assume all objects live in the lower 16MB of memory (so that their addresses
6189 can be loaded with the @code{ld24} instruction), and assume all subroutines
6190 are reachable with the @code{bl} instruction.
6191 This is the default.
6193 The addressability of a particular object can be set with the
6194 @code{model} attribute.
6196 @item -mcode-model=medium
6197 @opindex mcode-model=medium
6198 Assume objects may be anywhere in the 32-bit address space (the compiler
6199 will generate @code{seth/add3} instructions to load their addresses), and
6200 assume all subroutines are reachable with the @code{bl} instruction.
6202 @item -mcode-model=large
6203 @opindex mcode-model=large
6204 Assume objects may be anywhere in the 32-bit address space (the compiler
6205 will generate @code{seth/add3} instructions to load their addresses), and
6206 assume subroutines may not be reachable with the @code{bl} instruction
6207 (the compiler will generate the much slower @code{seth/add3/jl}
6208 instruction sequence).
6211 @opindex msdata=none
6212 Disable use of the small data area. Variables will be put into
6213 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
6214 @code{section} attribute has been specified).
6215 This is the default.
6217 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
6218 Objects may be explicitly put in the small data area with the
6219 @code{section} attribute using one of these sections.
6222 @opindex msdata=sdata
6223 Put small global and static data in the small data area, but do not
6224 generate special code to reference them.
6228 Put small global and static data in the small data area, and generate
6229 special instructions to reference them.
6233 @cindex smaller data references
6234 Put global and static objects less than or equal to @var{num} bytes
6235 into the small data or bss sections instead of the normal data or bss
6236 sections. The default value of @var{num} is 8.
6237 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
6238 for this option to have any effect.
6240 All modules should be compiled with the same @option{-G @var{num}} value.
6241 Compiling with different values of @var{num} may or may not work; if it
6242 doesn't the linker will give an error message---incorrect code will not be
6248 @subsection M88K Options
6249 @cindex M88k options
6251 These @samp{-m} options are defined for Motorola 88k architectures:
6256 Generate code that works well on both the m88100 and the
6261 Generate code that works best for the m88100, but that also
6266 Generate code that works best for the m88110, and may not run
6271 Obsolete option to be removed from the next revision.
6274 @item -midentify-revision
6275 @opindex midentify-revision
6276 @cindex identifying source, compiler (88k)
6277 Include an @code{ident} directive in the assembler output recording the
6278 source file name, compiler name and version, timestamp, and compilation
6281 @item -mno-underscores
6282 @opindex mno-underscores
6283 @cindex underscores, avoiding (88k)
6284 In assembler output, emit symbol names without adding an underscore
6285 character at the beginning of each name. The default is to use an
6286 underscore as prefix on each name.
6288 @item -mocs-debug-info
6289 @itemx -mno-ocs-debug-info
6290 @opindex mocs-debug-info
6291 @opindex mno-ocs-debug-info
6293 @cindex debugging, 88k OCS
6294 Include (or omit) additional debugging information (about registers used
6295 in each stack frame) as specified in the 88open Object Compatibility
6296 Standard, ``OCS''@. This extra information allows debugging of code that
6297 has had the frame pointer eliminated. The default for DG/UX, SVr4, and
6298 Delta 88 SVr3.2 is to include this information; other 88k configurations
6299 omit this information by default.
6301 @item -mocs-frame-position
6302 @opindex mocs-frame-position
6303 @cindex register positions in frame (88k)
6304 When emitting COFF debugging information for automatic variables and
6305 parameters stored on the stack, use the offset from the canonical frame
6306 address, which is the stack pointer (register 31) on entry to the
6307 function. The DG/UX, SVr4, Delta88 SVr3.2, and BCS configurations use
6308 @option{-mocs-frame-position}; other 88k configurations have the default
6309 @option{-mno-ocs-frame-position}.
6311 @item -mno-ocs-frame-position
6312 @opindex mno-ocs-frame-position
6313 @cindex register positions in frame (88k)
6314 When emitting COFF debugging information for automatic variables and
6315 parameters stored on the stack, use the offset from the frame pointer
6316 register (register 30). When this option is in effect, the frame
6317 pointer is not eliminated when debugging information is selected by the
6320 @item -moptimize-arg-area
6321 @opindex moptimize-arg-area
6322 @cindex arguments in frame (88k)
6323 Save space by reorganizing the stack frame. This option generates code
6324 that does not agree with the 88open specifications, but uses less
6327 @itemx -mno-optimize-arg-area
6328 @opindex mno-optimize-arg-area
6329 Do not reorganize the stack frame to save space. This is the default.
6330 The generated conforms to the specification, but uses more memory.
6332 @item -mshort-data-@var{num}
6333 @opindex mshort-data
6334 @cindex smaller data references (88k)
6335 @cindex r0-relative references (88k)
6336 Generate smaller data references by making them relative to @code{r0},
6337 which allows loading a value using a single instruction (rather than the
6338 usual two). You control which data references are affected by
6339 specifying @var{num} with this option. For example, if you specify
6340 @option{-mshort-data-512}, then the data references affected are those
6341 involving displacements of less than 512 bytes.
6342 @option{-mshort-data-@var{num}} is not effective for @var{num} greater
6345 @item -mserialize-volatile
6346 @opindex mserialize-volatile
6347 @itemx -mno-serialize-volatile
6348 @opindex mno-serialize-volatile
6349 @cindex sequential consistency on 88k
6350 Do, or don't, generate code to guarantee sequential consistency
6351 of volatile memory references. By default, consistency is
6354 The order of memory references made by the MC88110 processor does
6355 not always match the order of the instructions requesting those
6356 references. In particular, a load instruction may execute before
6357 a preceding store instruction. Such reordering violates
6358 sequential consistency of volatile memory references, when there
6359 are multiple processors. When consistency must be guaranteed,
6360 GCC generates special instructions, as needed, to force
6361 execution in the proper order.
6363 The MC88100 processor does not reorder memory references and so
6364 always provides sequential consistency. However, by default, GCC
6365 generates the special instructions to guarantee consistency
6366 even when you use @option{-m88100}, so that the code may be run on an
6367 MC88110 processor. If you intend to run your code only on the
6368 MC88100 processor, you may use @option{-mno-serialize-volatile}.
6370 The extra code generated to guarantee consistency may affect the
6371 performance of your application. If you know that you can safely
6372 forgo this guarantee, you may use @option{-mno-serialize-volatile}.
6378 @cindex assembler syntax, 88k
6380 Turn on (@option{-msvr4}) or off (@option{-msvr3}) compiler extensions
6381 related to System V release 4 (SVr4). This controls the following:
6385 Which variant of the assembler syntax to emit.
6387 @option{-msvr4} makes the C preprocessor recognize @samp{#pragma weak}
6388 that is used on System V release 4.
6390 @option{-msvr4} makes GCC issue additional declaration directives used in
6394 @option{-msvr4} is the default for the m88k-motorola-sysv4 and
6395 m88k-dg-dgux m88k configurations. @option{-msvr3} is the default for all
6396 other m88k configurations.
6398 @item -mversion-03.00
6399 @opindex mversion-03.00
6400 This option is obsolete, and is ignored.
6401 @c ??? which asm syntax better for GAS? option there too?
6403 @item -mno-check-zero-division
6404 @itemx -mcheck-zero-division
6405 @opindex mno-check-zero-division
6406 @opindex mcheck-zero-division
6407 @cindex zero division on 88k
6408 Do, or don't, generate code to guarantee that integer division by
6409 zero will be detected. By default, detection is guaranteed.
6411 Some models of the MC88100 processor fail to trap upon integer
6412 division by zero under certain conditions. By default, when
6413 compiling code that might be run on such a processor, GCC
6414 generates code that explicitly checks for zero-valued divisors
6415 and traps with exception number 503 when one is detected. Use of
6416 @option{-mno-check-zero-division} suppresses such checking for code
6417 generated to run on an MC88100 processor.
6419 GCC assumes that the MC88110 processor correctly detects all instances
6420 of integer division by zero. When @option{-m88110} is specified, no
6421 explicit checks for zero-valued divisors are generated, and both
6422 @option{-mcheck-zero-division} and @option{-mno-check-zero-division} are
6425 @item -muse-div-instruction
6426 @opindex muse-div-instruction
6427 @cindex divide instruction, 88k
6428 Use the div instruction for signed integer division on the
6429 MC88100 processor. By default, the div instruction is not used.
6431 On the MC88100 processor the signed integer division instruction
6432 div) traps to the operating system on a negative operand. The
6433 operating system transparently completes the operation, but at a
6434 large cost in execution time. By default, when compiling code
6435 that might be run on an MC88100 processor, GCC emulates signed
6436 integer division using the unsigned integer division instruction
6437 divu), thereby avoiding the large penalty of a trap to the
6438 operating system. Such emulation has its own, smaller, execution
6439 cost in both time and space. To the extent that your code's
6440 important signed integer division operations are performed on two
6441 nonnegative operands, it may be desirable to use the div
6442 instruction directly.
6444 On the MC88110 processor the div instruction (also known as the
6445 divs instruction) processes negative operands without trapping to
6446 the operating system. When @option{-m88110} is specified,
6447 @option{-muse-div-instruction} is ignored, and the div instruction is used
6448 for signed integer division.
6450 Note that the result of dividing @code{INT_MIN} by @minus{}1 is undefined. In
6451 particular, the behavior of such a division with and without
6452 @option{-muse-div-instruction} may differ.
6454 @item -mtrap-large-shift
6455 @itemx -mhandle-large-shift
6456 @opindex mtrap-large-shift
6457 @opindex mhandle-large-shift
6458 @cindex bit shift overflow (88k)
6459 @cindex large bit shifts (88k)
6460 Include code to detect bit-shifts of more than 31 bits; respectively,
6461 trap such shifts or emit code to handle them properly. By default GCC
6462 makes no special provision for large bit shifts.
6464 @item -mwarn-passed-structs
6465 @opindex mwarn-passed-structs
6466 @cindex structure passing (88k)
6467 Warn when a function passes a struct as an argument or result.
6468 Structure-passing conventions have changed during the evolution of the C
6469 language, and are often the source of portability problems. By default,
6470 GCC issues no such warning.
6473 @c break page here to avoid unsightly interparagraph stretch.
6477 @node RS/6000 and PowerPC Options
6478 @subsection IBM RS/6000 and PowerPC Options
6479 @cindex RS/6000 and PowerPC Options
6480 @cindex IBM RS/6000 and PowerPC Options
6482 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
6490 @itemx -mpowerpc-gpopt
6491 @itemx -mno-powerpc-gpopt
6492 @itemx -mpowerpc-gfxopt
6493 @itemx -mno-powerpc-gfxopt
6495 @itemx -mno-powerpc64
6501 @opindex mno-powerpc
6502 @opindex mpowerpc-gpopt
6503 @opindex mno-powerpc-gpopt
6504 @opindex mpowerpc-gfxopt
6505 @opindex mno-powerpc-gfxopt
6507 @opindex mno-powerpc64
6508 GCC supports two related instruction set architectures for the
6509 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
6510 instructions supported by the @samp{rios} chip set used in the original
6511 RS/6000 systems and the @dfn{PowerPC} instruction set is the
6512 architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
6513 the IBM 4xx microprocessors.
6515 Neither architecture is a subset of the other. However there is a
6516 large common subset of instructions supported by both. An MQ
6517 register is included in processors supporting the POWER architecture.
6519 You use these options to specify which instructions are available on the
6520 processor you are using. The default value of these options is
6521 determined when configuring GCC@. Specifying the
6522 @option{-mcpu=@var{cpu_type}} overrides the specification of these
6523 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
6524 rather than the options listed above.
6526 The @option{-mpower} option allows GCC to generate instructions that
6527 are found only in the POWER architecture and to use the MQ register.
6528 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
6529 to generate instructions that are present in the POWER2 architecture but
6530 not the original POWER architecture.
6532 The @option{-mpowerpc} option allows GCC to generate instructions that
6533 are found only in the 32-bit subset of the PowerPC architecture.
6534 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
6535 GCC to use the optional PowerPC architecture instructions in the
6536 General Purpose group, including floating-point square root. Specifying
6537 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
6538 use the optional PowerPC architecture instructions in the Graphics
6539 group, including floating-point select.
6541 The @option{-mpowerpc64} option allows GCC to generate the additional
6542 64-bit instructions that are found in the full PowerPC64 architecture
6543 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
6544 @option{-mno-powerpc64}.
6546 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
6547 will use only the instructions in the common subset of both
6548 architectures plus some special AIX common-mode calls, and will not use
6549 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
6550 permits GCC to use any instruction from either architecture and to
6551 allow use of the MQ register; specify this for the Motorola MPC601.
6553 @item -mnew-mnemonics
6554 @itemx -mold-mnemonics
6555 @opindex mnew-mnemonics
6556 @opindex mold-mnemonics
6557 Select which mnemonics to use in the generated assembler code. With
6558 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
6559 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
6560 assembler mnemonics defined for the POWER architecture. Instructions
6561 defined in only one architecture have only one mnemonic; GCC uses that
6562 mnemonic irrespective of which of these options is specified.
6564 GCC defaults to the mnemonics appropriate for the architecture in
6565 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
6566 value of these option. Unless you are building a cross-compiler, you
6567 should normally not specify either @option{-mnew-mnemonics} or
6568 @option{-mold-mnemonics}, but should instead accept the default.
6570 @item -mcpu=@var{cpu_type}
6572 Set architecture type, register usage, choice of mnemonics, and
6573 instruction scheduling parameters for machine type @var{cpu_type}.
6574 Supported values for @var{cpu_type} are @samp{rios}, @samp{rios1},
6575 @samp{rsc}, @samp{rios2}, @samp{rs64a}, @samp{601}, @samp{602},
6576 @samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620},
6577 @samp{630}, @samp{740}, @samp{7400}, @samp{7450}, @samp{750},
6578 @samp{power}, @samp{power2}, @samp{powerpc}, @samp{403}, @samp{505},
6579 @samp{801}, @samp{821}, @samp{823}, and @samp{860} and @samp{common}.
6581 @option{-mcpu=common} selects a completely generic processor. Code
6582 generated under this option will run on any POWER or PowerPC processor.
6583 GCC will use only the instructions in the common subset of both
6584 architectures, and will not use the MQ register. GCC assumes a generic
6585 processor model for scheduling purposes.
6587 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
6588 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
6589 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
6590 types, with an appropriate, generic processor model assumed for
6591 scheduling purposes.
6593 The other options specify a specific processor. Code generated under
6594 those options will run best on that processor, and may not run at all on
6597 The @option{-mcpu} options automatically enable or disable other
6598 @option{-m} options as follows:
6602 @option{-mno-power}, @option{-mno-powerc}
6609 @option{-mpower}, @option{-mno-powerpc}, @option{-mno-new-mnemonics}
6624 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}
6627 @option{-mpower}, @option{-mpowerpc}, @option{-mnew-mnemonics}
6632 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}, @option{-msoft-float}
6635 @item -mtune=@var{cpu_type}
6637 Set the instruction scheduling parameters for machine type
6638 @var{cpu_type}, but do not set the architecture type, register usage, or
6639 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
6640 values for @var{cpu_type} are used for @option{-mtune} as for
6641 @option{-mcpu}. If both are specified, the code generated will use the
6642 architecture, registers, and mnemonics set by @option{-mcpu}, but the
6643 scheduling parameters set by @option{-mtune}.
6648 @opindex mno-altivec
6649 These switches enable or disable the use of built-in functions that
6650 allow access to the AltiVec instruction set. You may also need to set
6651 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
6656 Extend the current ABI with SPE ABI extensions. This does not change
6657 the default ABI, instead it adds the SPE ABI extensions to the current
6661 @opindex mabi=no-spe
6662 Disable Booke SPE ABI extensions for the current ABI.
6664 @item -misel=@var{yes/no}
6667 This switch enables or disables the generation of ISEL instructions.
6670 @itemx -mno-fp-in-toc
6671 @itemx -mno-sum-in-toc
6672 @itemx -mminimal-toc
6674 @opindex mno-fp-in-toc
6675 @opindex mno-sum-in-toc
6676 @opindex mminimal-toc
6677 Modify generation of the TOC (Table Of Contents), which is created for
6678 every executable file. The @option{-mfull-toc} option is selected by
6679 default. In that case, GCC will allocate at least one TOC entry for
6680 each unique non-automatic variable reference in your program. GCC
6681 will also place floating-point constants in the TOC@. However, only
6682 16,384 entries are available in the TOC@.
6684 If you receive a linker error message that saying you have overflowed
6685 the available TOC space, you can reduce the amount of TOC space used
6686 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
6687 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
6688 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
6689 generate code to calculate the sum of an address and a constant at
6690 run-time instead of putting that sum into the TOC@. You may specify one
6691 or both of these options. Each causes GCC to produce very slightly
6692 slower and larger code at the expense of conserving TOC space.
6694 If you still run out of space in the TOC even when you specify both of
6695 these options, specify @option{-mminimal-toc} instead. This option causes
6696 GCC to make only one TOC entry for every file. When you specify this
6697 option, GCC will produce code that is slower and larger but which
6698 uses extremely little TOC space. You may wish to use this option
6699 only on files that contain less frequently executed code.
6705 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
6706 @code{long} type, and the infrastructure needed to support them.
6707 Specifying @option{-maix64} implies @option{-mpowerpc64} and
6708 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
6709 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
6714 @opindex mno-xl-call
6715 On AIX, pass floating-point arguments to prototyped functions beyond the
6716 register save area (RSA) on the stack in addition to argument FPRs. The
6717 AIX calling convention was extended but not initially documented to
6718 handle an obscure K&R C case of calling a function that takes the
6719 address of its arguments with fewer arguments than declared. AIX XL
6720 compilers access floating point arguments which do not fit in the
6721 RSA from the stack when a subroutine is compiled without
6722 optimization. Because always storing floating-point arguments on the
6723 stack is inefficient and rarely needed, this option is not enabled by
6724 default and only is necessary when calling subroutines compiled by AIX
6725 XL compilers without optimization.
6729 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
6730 application written to use message passing with special startup code to
6731 enable the application to run. The system must have PE installed in the
6732 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
6733 must be overridden with the @option{-specs=} option to specify the
6734 appropriate directory location. The Parallel Environment does not
6735 support threads, so the @option{-mpe} option and the @option{-pthread}
6736 option are incompatible.
6740 @opindex msoft-float
6741 @opindex mhard-float
6742 Generate code that does not use (uses) the floating-point register set.
6743 Software floating point emulation is provided if you use the
6744 @option{-msoft-float} option, and pass the option to GCC when linking.
6747 @itemx -mno-multiple
6749 @opindex mno-multiple
6750 Generate code that uses (does not use) the load multiple word
6751 instructions and the store multiple word instructions. These
6752 instructions are generated by default on POWER systems, and not
6753 generated on PowerPC systems. Do not use @option{-mmultiple} on little
6754 endian PowerPC systems, since those instructions do not work when the
6755 processor is in little endian mode. The exceptions are PPC740 and
6756 PPC750 which permit the instructions usage in little endian mode.
6762 Generate code that uses (does not use) the load string instructions
6763 and the store string word instructions to save multiple registers and
6764 do small block moves. These instructions are generated by default on
6765 POWER systems, and not generated on PowerPC systems. Do not use
6766 @option{-mstring} on little endian PowerPC systems, since those
6767 instructions do not work when the processor is in little endian mode.
6768 The exceptions are PPC740 and PPC750 which permit the instructions
6769 usage in little endian mode.
6775 Generate code that uses (does not use) the load or store instructions
6776 that update the base register to the address of the calculated memory
6777 location. These instructions are generated by default. If you use
6778 @option{-mno-update}, there is a small window between the time that the
6779 stack pointer is updated and the address of the previous frame is
6780 stored, which means code that walks the stack frame across interrupts or
6781 signals may get corrupted data.
6784 @itemx -mno-fused-madd
6785 @opindex mfused-madd
6786 @opindex mno-fused-madd
6787 Generate code that uses (does not use) the floating point multiply and
6788 accumulate instructions. These instructions are generated by default if
6789 hardware floating is used.
6791 @item -mno-bit-align
6793 @opindex mno-bit-align
6795 On System V.4 and embedded PowerPC systems do not (do) force structures
6796 and unions that contain bit-fields to be aligned to the base type of the
6799 For example, by default a structure containing nothing but 8
6800 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
6801 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
6802 the structure would be aligned to a 1 byte boundary and be one byte in
6805 @item -mno-strict-align
6806 @itemx -mstrict-align
6807 @opindex mno-strict-align
6808 @opindex mstrict-align
6809 On System V.4 and embedded PowerPC systems do not (do) assume that
6810 unaligned memory references will be handled by the system.
6813 @itemx -mno-relocatable
6814 @opindex mrelocatable
6815 @opindex mno-relocatable
6816 On embedded PowerPC systems generate code that allows (does not allow)
6817 the program to be relocated to a different address at runtime. If you
6818 use @option{-mrelocatable} on any module, all objects linked together must
6819 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
6821 @item -mrelocatable-lib
6822 @itemx -mno-relocatable-lib
6823 @opindex mrelocatable-lib
6824 @opindex mno-relocatable-lib
6825 On embedded PowerPC systems generate code that allows (does not allow)
6826 the program to be relocated to a different address at runtime. Modules
6827 compiled with @option{-mrelocatable-lib} can be linked with either modules
6828 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
6829 with modules compiled with the @option{-mrelocatable} options.
6835 On System V.4 and embedded PowerPC systems do not (do) assume that
6836 register 2 contains a pointer to a global area pointing to the addresses
6837 used in the program.
6840 @itemx -mlittle-endian
6842 @opindex mlittle-endian
6843 On System V.4 and embedded PowerPC systems compile code for the
6844 processor in little endian mode. The @option{-mlittle-endian} option is
6845 the same as @option{-mlittle}.
6850 @opindex mbig-endian
6851 On System V.4 and embedded PowerPC systems compile code for the
6852 processor in big endian mode. The @option{-mbig-endian} option is
6853 the same as @option{-mbig}.
6857 On System V.4 and embedded PowerPC systems compile code using calling
6858 conventions that adheres to the March 1995 draft of the System V
6859 Application Binary Interface, PowerPC processor supplement. This is the
6860 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
6862 @item -mcall-sysv-eabi
6863 @opindex mcall-sysv-eabi
6864 Specify both @option{-mcall-sysv} and @option{-meabi} options.
6866 @item -mcall-sysv-noeabi
6867 @opindex mcall-sysv-noeabi
6868 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
6872 On System V.4 and embedded PowerPC systems compile code using calling
6873 conventions that are similar to those used on AIX@. This is the
6874 default if you configured GCC using @samp{powerpc-*-eabiaix}.
6876 @item -mcall-solaris
6877 @opindex mcall-solaris
6878 On System V.4 and embedded PowerPC systems compile code for the Solaris
6882 @opindex mcall-linux
6883 On System V.4 and embedded PowerPC systems compile code for the
6884 Linux-based GNU system.
6888 On System V.4 and embedded PowerPC systems compile code for the
6889 Hurd-based GNU system.
6892 @opindex mcall-netbsd
6893 On System V.4 and embedded PowerPC systems compile code for the
6894 NetBSD operating system.
6896 @item -maix-struct-return
6897 @opindex maix-struct-return
6898 Return all structures in memory (as specified by the AIX ABI)@.
6900 @item -msvr4-struct-return
6901 @opindex msvr4-struct-return
6902 Return structures smaller than 8 bytes in registers (as specified by the
6906 @opindex mabi=altivec
6907 Extend the current ABI with AltiVec ABI extensions. This does not
6908 change the default ABI, instead it adds the AltiVec ABI extensions to
6911 @item -mabi=no-altivec
6912 @opindex mabi=no-altivec
6913 Disable AltiVec ABI extensions for the current ABI.
6916 @itemx -mno-prototype
6918 @opindex mno-prototype
6919 On System V.4 and embedded PowerPC systems assume that all calls to
6920 variable argument functions are properly prototyped. Otherwise, the
6921 compiler must insert an instruction before every non prototyped call to
6922 set or clear bit 6 of the condition code register (@var{CR}) to
6923 indicate whether floating point values were passed in the floating point
6924 registers in case the function takes a variable arguments. With
6925 @option{-mprototype}, only calls to prototyped variable argument functions
6926 will set or clear the bit.
6930 On embedded PowerPC systems, assume that the startup module is called
6931 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
6932 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
6937 On embedded PowerPC systems, assume that the startup module is called
6938 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
6943 On embedded PowerPC systems, assume that the startup module is called
6944 @file{crt0.o} and the standard C libraries are @file{libads.a} and
6948 @opindex myellowknife
6949 On embedded PowerPC systems, assume that the startup module is called
6950 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
6955 On System V.4 and embedded PowerPC systems, specify that you are
6956 compiling for a VxWorks system.
6960 Specify that you are compiling for the WindISS simulation environment.
6964 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
6965 header to indicate that @samp{eabi} extended relocations are used.
6971 On System V.4 and embedded PowerPC systems do (do not) adhere to the
6972 Embedded Applications Binary Interface (eabi) which is a set of
6973 modifications to the System V.4 specifications. Selecting @option{-meabi}
6974 means that the stack is aligned to an 8 byte boundary, a function
6975 @code{__eabi} is called to from @code{main} to set up the eabi
6976 environment, and the @option{-msdata} option can use both @code{r2} and
6977 @code{r13} to point to two separate small data areas. Selecting
6978 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
6979 do not call an initialization function from @code{main}, and the
6980 @option{-msdata} option will only use @code{r13} to point to a single
6981 small data area. The @option{-meabi} option is on by default if you
6982 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
6985 @opindex msdata=eabi
6986 On System V.4 and embedded PowerPC systems, put small initialized
6987 @code{const} global and static data in the @samp{.sdata2} section, which
6988 is pointed to by register @code{r2}. Put small initialized
6989 non-@code{const} global and static data in the @samp{.sdata} section,
6990 which is pointed to by register @code{r13}. Put small uninitialized
6991 global and static data in the @samp{.sbss} section, which is adjacent to
6992 the @samp{.sdata} section. The @option{-msdata=eabi} option is
6993 incompatible with the @option{-mrelocatable} option. The
6994 @option{-msdata=eabi} option also sets the @option{-memb} option.
6997 @opindex msdata=sysv
6998 On System V.4 and embedded PowerPC systems, put small global and static
6999 data in the @samp{.sdata} section, which is pointed to by register
7000 @code{r13}. Put small uninitialized global and static data in the
7001 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
7002 The @option{-msdata=sysv} option is incompatible with the
7003 @option{-mrelocatable} option.
7005 @item -msdata=default
7007 @opindex msdata=default
7009 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
7010 compile code the same as @option{-msdata=eabi}, otherwise compile code the
7011 same as @option{-msdata=sysv}.
7014 @opindex msdata-data
7015 On System V.4 and embedded PowerPC systems, put small global and static
7016 data in the @samp{.sdata} section. Put small uninitialized global and
7017 static data in the @samp{.sbss} section. Do not use register @code{r13}
7018 to address small data however. This is the default behavior unless
7019 other @option{-msdata} options are used.
7023 @opindex msdata=none
7025 On embedded PowerPC systems, put all initialized global and static data
7026 in the @samp{.data} section, and all uninitialized data in the
7027 @samp{.bss} section.
7031 @cindex smaller data references (PowerPC)
7032 @cindex .sdata/.sdata2 references (PowerPC)
7033 On embedded PowerPC systems, put global and static items less than or
7034 equal to @var{num} bytes into the small data or bss sections instead of
7035 the normal data or bss section. By default, @var{num} is 8. The
7036 @option{-G @var{num}} switch is also passed to the linker.
7037 All modules should be compiled with the same @option{-G @var{num}} value.
7040 @itemx -mno-regnames
7042 @opindex mno-regnames
7043 On System V.4 and embedded PowerPC systems do (do not) emit register
7044 names in the assembly language output using symbolic forms.
7047 @itemx -mno-longcall
7049 @opindex mno-longcall
7050 Default to making all function calls via pointers, so that functions
7051 which reside further than 64 megabytes (67,108,864 bytes) from the
7052 current location can be called. This setting can be overridden by the
7053 @code{shortcall} function attribute, or by @code{#pragma longcall(0)}.
7055 Some linkers are capable of detecting out-of-range calls and generating
7056 glue code on the fly. On these systems, long calls are unnecessary and
7057 generate slower code. As of this writing, the AIX linker can do this,
7058 as can the GNU linker for PowerPC/64. It is planned to add this feature
7059 to the GNU linker for 32-bit PowerPC systems as well.
7061 In the future, we may cause GCC to ignore all longcall specifications
7062 when the linker is known to generate glue.
7066 Adds support for multithreading with the @dfn{pthreads} library.
7067 This option sets flags for both the preprocessor and linker.
7072 @subsection IBM RT Options
7074 @cindex IBM RT options
7076 These @samp{-m} options are defined for the IBM RT PC:
7080 @opindex min-line-mul
7081 Use an in-line code sequence for integer multiplies. This is the
7084 @item -mcall-lib-mul
7085 @opindex mcall-lib-mul
7086 Call @code{lmul$$} for integer multiples.
7088 @item -mfull-fp-blocks
7089 @opindex mfull-fp-blocks
7090 Generate full-size floating point data blocks, including the minimum
7091 amount of scratch space recommended by IBM@. This is the default.
7093 @item -mminimum-fp-blocks
7094 @opindex mminimum-fp-blocks
7095 Do not include extra scratch space in floating point data blocks. This
7096 results in smaller code, but slower execution, since scratch space must
7097 be allocated dynamically.
7099 @cindex @file{stdarg.h} and RT PC
7100 @item -mfp-arg-in-fpregs
7101 @opindex mfp-arg-in-fpregs
7102 Use a calling sequence incompatible with the IBM calling convention in
7103 which floating point arguments are passed in floating point registers.
7104 Note that @code{stdarg.h} will not work with floating point operands
7105 if this option is specified.
7107 @item -mfp-arg-in-gregs
7108 @opindex mfp-arg-in-gregs
7109 Use the normal calling convention for floating point arguments. This is
7112 @item -mhc-struct-return
7113 @opindex mhc-struct-return
7114 Return structures of more than one word in memory, rather than in a
7115 register. This provides compatibility with the MetaWare HighC (hc)
7116 compiler. Use the option @option{-fpcc-struct-return} for compatibility
7117 with the Portable C Compiler (pcc).
7119 @item -mnohc-struct-return
7120 @opindex mnohc-struct-return
7121 Return some structures of more than one word in registers, when
7122 convenient. This is the default. For compatibility with the
7123 IBM-supplied compilers, use the option @option{-fpcc-struct-return} or the
7124 option @option{-mhc-struct-return}.
7128 @subsection MIPS Options
7129 @cindex MIPS options
7131 These @samp{-m} options are defined for the MIPS family of computers:
7135 @item -march=@var{arch}
7137 Generate code that will run on @var{arch}, which can be the name of a
7138 generic MIPS ISA, or the name of a particular processor. The ISA names
7139 are: @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4}, @samp{mips32}
7140 and @samp{mips64}. The processor names are: @samp{r2000},
7141 @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{vr4100}, @samp{vr4300},
7142 @samp{r4400}, @samp{r4600}, @samp{r4650}, @samp{vr5000}, @samp{r6000},
7143 @samp{r8000}, @samp{4kc}, @samp{4kp}, @samp{5kc}, @samp{20kc},
7144 @samp{orion}, and @samp{sb1}. The special value @samp{from-abi} selects the
7145 most compatible architecture for the selected ABI (that is,
7146 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
7148 In processor names, a final @samp{000} can be abbreviated as @samp{k}
7149 (for example, @samp{-march=r2k}). Prefixes are optional, and
7150 @samp{vr} may be written @samp{r}.
7152 GCC defines two macros based on the value of this option. The first
7153 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
7154 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
7155 where @var{foo} is the capitialized value of @samp{_MIPS_ARCH}@.
7156 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
7157 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
7159 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
7160 above. In other words, it will have the full prefix and will not
7161 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
7162 the macro names the resolved architecture (either @samp{"mips1"} or
7163 @samp{"mips3"}). It names the default architecture when no
7164 @option{-march} option is given.
7166 @item -mtune=@var{arch}
7168 Optimize for @var{arch}. Among other things, this option controls
7169 the way instructions are scheduled, and the perceived cost of arithmetic
7170 operations. The list of @var{arch} values is the same as for
7173 When this option is not used, GCC will optimize for the processor
7174 specified by @option{-march}. By using @option{-march} and
7175 @option{-mtune} together, it is possible to generate code that will
7176 run on a family of processors, but optimize the code for one
7177 particular member of that family.
7179 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
7180 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
7181 @samp{-march} ones described above.
7185 Equivalent to @samp{-march=mips1}.
7189 Equivalent to @samp{-march=mips2}.
7193 Equivalent to @samp{-march=mips3}.
7197 Equivalent to @samp{-march=mips4}.
7201 Equivalent to @samp{-march=mips32}.
7205 Equivalent to @samp{-march=mips64}.
7208 @itemx -mno-fused-madd
7209 @opindex mfused-madd
7210 @opindex mno-fused-madd
7211 Generate code that uses (does not use) the floating point multiply and
7212 accumulate instructions, when they are available. These instructions
7213 are generated by default if they are available, but this may be
7214 undesirable if the extra precision causes problems or on certain chips
7215 in the mode where denormals are rounded to zero where denormals
7216 generated by multiply and accumulate instructions cause exceptions
7221 Assume that floating point registers are 32 bits wide.
7225 Assume that floating point registers are 64 bits wide.
7229 Assume that general purpose registers are 32 bits wide.
7233 Assume that general purpose registers are 64 bits wide.
7237 Force int and long types to be 64 bits wide. See @option{-mlong32} for an
7238 explanation of the default, and the width of pointers.
7242 Force long types to be 64 bits wide. See @option{-mlong32} for an
7243 explanation of the default, and the width of pointers.
7247 Force long, int, and pointer types to be 32 bits wide.
7249 The default size of ints, longs and pointers depends on the ABI@. All
7250 the supported ABIs use 32-bit ints. The n64 ABI uses 64-bit longs, as
7251 does the 64-bit Cygnus EABI; the others use 32-bit longs. Pointers
7252 are the same size as longs, or the same size as integer registers,
7253 whichever is smaller.
7267 Generate code for the given ABI@.
7269 Note that there are two embedded ABIs: @option{-mabi=eabi}
7270 selects the one defined by Cygnus while @option{-meabi=meabi}
7271 selects the one defined by MIPS@. Both these ABIs have
7272 32-bit and 64-bit variants. Normally, GCC will generate
7273 64-bit code when you select a 64-bit architecture, but you
7274 can use @option{-mgp32} to get 32-bit code instead.
7278 Generate code for the MIPS assembler, and invoke @file{mips-tfile} to
7279 add normal debug information. This is the default for all
7280 platforms except for the OSF/1 reference platform, using the OSF/rose
7281 object format. If the either of the @option{-gstabs} or @option{-gstabs+}
7282 switches are used, the @file{mips-tfile} program will encapsulate the
7283 stabs within MIPS ECOFF@.
7287 Generate code for the GNU assembler. This is the default on the OSF/1
7288 reference platform, using the OSF/rose object format. Also, this is
7289 the default if the configure option @option{--with-gnu-as} is used.
7291 @item -msplit-addresses
7292 @itemx -mno-split-addresses
7293 @opindex msplit-addresses
7294 @opindex mno-split-addresses
7295 Generate code to load the high and low parts of address constants separately.
7296 This allows GCC to optimize away redundant loads of the high order
7297 bits of addresses. This optimization requires GNU as and GNU ld.
7298 This optimization is enabled by default for some embedded targets where
7299 GNU as and GNU ld are standard.
7305 The @option{-mrnames} switch says to output code using the MIPS software
7306 names for the registers, instead of the hardware names (ie, @var{a0}
7307 instead of @var{$4}). The only known assembler that supports this option
7308 is the Algorithmics assembler.
7314 The @option{-mgpopt} switch says to write all of the data declarations
7315 before the instructions in the text section, this allows the MIPS
7316 assembler to generate one word memory references instead of using two
7317 words for short global or static data items. This is on by default if
7318 optimization is selected.
7324 For each non-inline function processed, the @option{-mstats} switch
7325 causes the compiler to emit one line to the standard error file to
7326 print statistics about the program (number of registers saved, stack
7333 The @option{-mmemcpy} switch makes all block moves call the appropriate
7334 string function (@samp{memcpy} or @samp{bcopy}) instead of possibly
7335 generating inline code.
7338 @itemx -mno-mips-tfile
7339 @opindex mmips-tfile
7340 @opindex mno-mips-tfile
7341 The @option{-mno-mips-tfile} switch causes the compiler not
7342 postprocess the object file with the @file{mips-tfile} program,
7343 after the MIPS assembler has generated it to add debug support. If
7344 @file{mips-tfile} is not run, then no local variables will be
7345 available to the debugger. In addition, @file{stage2} and
7346 @file{stage3} objects will have the temporary file names passed to the
7347 assembler embedded in the object file, which means the objects will
7348 not compare the same. The @option{-mno-mips-tfile} switch should only
7349 be used when there are bugs in the @file{mips-tfile} program that
7350 prevents compilation.
7353 @opindex msoft-float
7354 Generate output containing library calls for floating point.
7355 @strong{Warning:} the requisite libraries are not part of GCC@.
7356 Normally the facilities of the machine's usual C compiler are used, but
7357 this can't be done directly in cross-compilation. You must make your
7358 own arrangements to provide suitable library functions for
7362 @opindex mhard-float
7363 Generate output containing floating point instructions. This is the
7364 default if you use the unmodified sources.
7367 @itemx -mno-abicalls
7369 @opindex mno-abicalls
7370 Emit (or do not emit) the pseudo operations @samp{.abicalls},
7371 @samp{.cpload}, and @samp{.cprestore} that some System V.4 ports use for
7372 position independent code.
7375 @itemx -mno-long-calls
7376 @opindex mlong-calls
7377 @opindex mno-long-calls
7378 Do all calls with the @samp{JALR} instruction, which requires
7379 loading up a function's address into a register before the call.
7380 You need to use this switch, if you call outside of the current
7381 512 megabyte segment to functions that are not through pointers.
7384 @itemx -mno-half-pic
7386 @opindex mno-half-pic
7387 Put pointers to extern references into the data section and load them
7388 up, rather than put the references in the text section.
7390 @item -membedded-pic
7391 @itemx -mno-embedded-pic
7392 @opindex membedded-pic
7393 @opindex mno-embedded-pic
7394 Generate PIC code suitable for some embedded systems. All calls are
7395 made using PC relative address, and all data is addressed using the $gp
7396 register. No more than 65536 bytes of global data may be used. This
7397 requires GNU as and GNU ld which do most of the work. This currently
7398 only works on targets which use ECOFF; it does not work with ELF@.
7400 @item -membedded-data
7401 @itemx -mno-embedded-data
7402 @opindex membedded-data
7403 @opindex mno-embedded-data
7404 Allocate variables to the read-only data section first if possible, then
7405 next in the small data section if possible, otherwise in data. This gives
7406 slightly slower code than the default, but reduces the amount of RAM required
7407 when executing, and thus may be preferred for some embedded systems.
7409 @item -muninit-const-in-rodata
7410 @itemx -mno-uninit-const-in-rodata
7411 @opindex muninit-const-in-rodata
7412 @opindex mno-uninit-const-in-rodata
7413 When used together with @option{-membedded-data}, it will always store uninitialized
7414 const variables in the read-only data section.
7416 @item -msingle-float
7417 @itemx -mdouble-float
7418 @opindex msingle-float
7419 @opindex mdouble-float
7420 The @option{-msingle-float} switch tells gcc to assume that the floating
7421 point coprocessor only supports single precision operations, as on the
7422 @samp{r4650} chip. The @option{-mdouble-float} switch permits gcc to use
7423 double precision operations. This is the default.
7429 Permit use of the @samp{mad}, @samp{madu} and @samp{mul} instructions,
7430 as on the @samp{r4650} chip.
7434 Turns on @option{-msingle-float}, @option{-mmad}, and, at least for now,
7435 @option{-mcpu=r4650}.
7441 Enable 16-bit instructions.
7445 Use the entry and exit pseudo ops. This option can only be used with
7450 Compile code for the processor in little endian mode.
7451 The requisite libraries are assumed to exist.
7455 Compile code for the processor in big endian mode.
7456 The requisite libraries are assumed to exist.
7460 @cindex smaller data references (MIPS)
7461 @cindex gp-relative references (MIPS)
7462 Put global and static items less than or equal to @var{num} bytes into
7463 the small data or bss sections instead of the normal data or bss
7464 section. This allows the assembler to emit one word memory reference
7465 instructions based on the global pointer (@var{gp} or @var{$28}),
7466 instead of the normal two words used. By default, @var{num} is 8 when
7467 the MIPS assembler is used, and 0 when the GNU assembler is used. The
7468 @option{-G @var{num}} switch is also passed to the assembler and linker.
7469 All modules should be compiled with the same @option{-G @var{num}}
7474 Tell the MIPS assembler to not run its preprocessor over user
7475 assembler files (with a @samp{.s} suffix) when assembling them.
7479 Pass an option to gas which will cause nops to be inserted if
7480 the read of the destination register of an mfhi or mflo instruction
7481 occurs in the following two instructions.
7485 Do not include the default crt0.
7487 @item -mflush-func=@var{func}
7488 @itemx -mno-flush-func
7489 @opindex mflush-func
7490 Specifies the function to call to flush the I and D caches, or to not
7491 call any such function. If called, the function must take the same
7492 arguments as the common @code{_flush_func()}, that is, the address of the
7493 memory range for which the cache is being flushed, the size of the
7494 memory range, and the number 3 (to flush both caches). The default
7495 depends on the target gcc was configured for, but commonly is either
7496 @samp{_flush_func} or @samp{__cpu_flush}.
7498 @item -mbranch-likely
7499 @itemx -mno-branch-likely
7500 @opindex mbranch-likely
7501 @opindex mno-branch-likely
7502 Enable or disable use of Branch Likely instructions, regardless of the
7503 default for the selected architecture. By default, Branch Likely
7504 instructions may be generated if they are supported by the selected
7505 architecture. An exception is for the MIPS32 and MIPS64 architectures
7506 and processors which implement those architectures; for those, Branch
7507 Likely instructions will not be generated by default because the MIPS32
7508 and MIPS64 architectures specifically deprecate their use.
7511 @node i386 and x86-64 Options
7512 @subsection Intel 386 and AMD x86-64 Options
7513 @cindex i386 Options
7514 @cindex x86-64 Options
7515 @cindex Intel 386 Options
7516 @cindex AMD x86-64 Options
7518 These @samp{-m} options are defined for the i386 and x86-64 family of
7522 @item -mcpu=@var{cpu-type}
7524 Tune to @var{cpu-type} everything applicable about the generated code, except
7525 for the ABI and the set of available instructions. The choices for
7526 @var{cpu-type} are @samp{i386}, @samp{i486}, @samp{i586}, @samp{i686},
7527 @samp{pentium}, @samp{pentium-mmx}, @samp{pentiumpro}, @samp{pentium2},
7528 @samp{pentium3}, @samp{pentium4}, @samp{k6}, @samp{k6-2}, @samp{k6-3},
7529 @samp{athlon}, @samp{athlon-tbird}, @samp{athlon-4}, @samp{athlon-xp},
7530 @samp{athlon-mp}, @samp{winchip-c6}, @samp{winchip2} and @samp{c3}.
7532 While picking a specific @var{cpu-type} will schedule things appropriately
7533 for that particular chip, the compiler will not generate any code that
7534 does not run on the i386 without the @option{-march=@var{cpu-type}} option
7535 being used. @samp{i586} is equivalent to @samp{pentium} and @samp{i686}
7536 is equivalent to @samp{pentiumpro}. @samp{k6} and @samp{athlon} are the
7537 AMD chips as opposed to the Intel ones.
7539 @item -march=@var{cpu-type}
7541 Generate instructions for the machine type @var{cpu-type}. The choices
7542 for @var{cpu-type} are the same as for @option{-mcpu}. Moreover,
7543 specifying @option{-march=@var{cpu-type}} implies @option{-mcpu=@var{cpu-type}}.
7552 @opindex mpentiumpro
7553 These options are synonyms for @option{-mcpu=i386}, @option{-mcpu=i486},
7554 @option{-mcpu=pentium}, and @option{-mcpu=pentiumpro} respectively.
7555 These synonyms are deprecated.
7557 @item -mfpmath=@var{unit}
7559 generate floating point arithmetics for selected unit @var{unit}. the choices
7564 Use the standard 387 floating point coprocessor present majority of chips and
7565 emulated otherwise. Code compiled with this option will run almost everywhere.
7566 The temporary results are computed in 80bit precesion instead of precision
7567 specified by the type resulting in slightly different results compared to most
7568 of other chips. See @option{-ffloat-store} for more detailed description.
7570 This is the default choice for i386 compiler.
7573 Use scalar floating point instructions present in the SSE instruction set.
7574 This instruction set is supported by Pentium3 and newer chips, in the AMD line
7575 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
7576 instruction set supports only single precision arithmetics, thus the double and
7577 extended precision arithmetics is still done using 387. Later version, present
7578 only in Pentium4 and the future AMD x86-64 chips supports double precision
7581 For i387 you need to use @option{-march=@var{cpu-type}}, @option{-msse} or
7582 @option{-msse2} switches to enable SSE extensions and make this option
7583 effective. For x86-64 compiler, these extensions are enabled by default.
7585 The resulting code should be considerably faster in majority of cases and avoid
7586 the numerical instability problems of 387 code, but may break some existing
7587 code that expects temporaries to be 80bit.
7589 This is the default choice for x86-64 compiler.
7592 Attempt to utilize both instruction sets at once. This effectivly double the
7593 amount of available registers and on chips with separate execution units for
7594 387 and SSE the execution resources too. Use this option with care, as it is
7595 still experimental, because gcc register allocator does not model separate
7596 functional units well resulting in instable performance.
7599 @item -masm=@var{dialect}
7600 @opindex masm=@var{dialect}
7601 Output asm instructions using selected @var{dialect}. Supported choices are
7602 @samp{intel} or @samp{att} (the default one).
7607 @opindex mno-ieee-fp
7608 Control whether or not the compiler uses IEEE floating point
7609 comparisons. These handle correctly the case where the result of a
7610 comparison is unordered.
7613 @opindex msoft-float
7614 Generate output containing library calls for floating point.
7615 @strong{Warning:} the requisite libraries are not part of GCC@.
7616 Normally the facilities of the machine's usual C compiler are used, but
7617 this can't be done directly in cross-compilation. You must make your
7618 own arrangements to provide suitable library functions for
7621 On machines where a function returns floating point results in the 80387
7622 register stack, some floating point opcodes may be emitted even if
7623 @option{-msoft-float} is used.
7625 @item -mno-fp-ret-in-387
7626 @opindex mno-fp-ret-in-387
7627 Do not use the FPU registers for return values of functions.
7629 The usual calling convention has functions return values of types
7630 @code{float} and @code{double} in an FPU register, even if there
7631 is no FPU@. The idea is that the operating system should emulate
7634 The option @option{-mno-fp-ret-in-387} causes such values to be returned
7635 in ordinary CPU registers instead.
7637 @item -mno-fancy-math-387
7638 @opindex mno-fancy-math-387
7639 Some 387 emulators do not support the @code{sin}, @code{cos} and
7640 @code{sqrt} instructions for the 387. Specify this option to avoid
7641 generating those instructions. This option is the default on FreeBSD,
7642 OpenBSD and NetBSD@. This option is overridden when @option{-march}
7643 indicates that the target cpu will always have an FPU and so the
7644 instruction will not need emulation. As of revision 2.6.1, these
7645 instructions are not generated unless you also use the
7646 @option{-funsafe-math-optimizations} switch.
7648 @item -malign-double
7649 @itemx -mno-align-double
7650 @opindex malign-double
7651 @opindex mno-align-double
7652 Control whether GCC aligns @code{double}, @code{long double}, and
7653 @code{long long} variables on a two word boundary or a one word
7654 boundary. Aligning @code{double} variables on a two word boundary will
7655 produce code that runs somewhat faster on a @samp{Pentium} at the
7656 expense of more memory.
7658 @strong{Warning:} if you use the @samp{-malign-double} switch,
7659 structures containing the above types will be aligned differently than
7660 the published application binary interface specifications for the 386.
7662 @item -m128bit-long-double
7663 @opindex m128bit-long-double
7664 Control the size of @code{long double} type. i386 application binary interface
7665 specify the size to be 12 bytes, while modern architectures (Pentium and newer)
7666 prefer @code{long double} aligned to 8 or 16 byte boundary. This is
7667 impossible to reach with 12 byte long doubles in the array accesses.
7669 @strong{Warning:} if you use the @option{-m128bit-long-double} switch, the
7670 structures and arrays containing @code{long double} will change their size as
7671 well as function calling convention for function taking @code{long double}
7674 @item -m96bit-long-double
7675 @opindex m96bit-long-double
7676 Set the size of @code{long double} to 96 bits as required by the i386
7677 application binary interface. This is the default.
7680 @itemx -mno-svr3-shlib
7681 @opindex msvr3-shlib
7682 @opindex mno-svr3-shlib
7683 Control whether GCC places uninitialized local variables into the
7684 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
7685 into @code{bss}. These options are meaningful only on System V Release 3.
7689 Use a different function-calling convention, in which functions that
7690 take a fixed number of arguments return with the @code{ret} @var{num}
7691 instruction, which pops their arguments while returning. This saves one
7692 instruction in the caller since there is no need to pop the arguments
7695 You can specify that an individual function is called with this calling
7696 sequence with the function attribute @samp{stdcall}. You can also
7697 override the @option{-mrtd} option by using the function attribute
7698 @samp{cdecl}. @xref{Function Attributes}.
7700 @strong{Warning:} this calling convention is incompatible with the one
7701 normally used on Unix, so you cannot use it if you need to call
7702 libraries compiled with the Unix compiler.
7704 Also, you must provide function prototypes for all functions that
7705 take variable numbers of arguments (including @code{printf});
7706 otherwise incorrect code will be generated for calls to those
7709 In addition, seriously incorrect code will result if you call a
7710 function with too many arguments. (Normally, extra arguments are
7711 harmlessly ignored.)
7713 @item -mregparm=@var{num}
7715 Control how many registers are used to pass integer arguments. By
7716 default, no registers are used to pass arguments, and at most 3
7717 registers can be used. You can control this behavior for a specific
7718 function by using the function attribute @samp{regparm}.
7719 @xref{Function Attributes}.
7721 @strong{Warning:} if you use this switch, and
7722 @var{num} is nonzero, then you must build all modules with the same
7723 value, including any libraries. This includes the system libraries and
7726 @item -mpreferred-stack-boundary=@var{num}
7727 @opindex mpreferred-stack-boundary
7728 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
7729 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
7730 the default is 4 (16 bytes or 128 bits), except when optimizing for code
7731 size (@option{-Os}), in which case the default is the minimum correct
7732 alignment (4 bytes for x86, and 8 bytes for x86-64).
7734 On Pentium and PentiumPro, @code{double} and @code{long double} values
7735 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
7736 suffer significant run time performance penalties. On Pentium III, the
7737 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
7738 penalties if it is not 16 byte aligned.
7740 To ensure proper alignment of this values on the stack, the stack boundary
7741 must be as aligned as that required by any value stored on the stack.
7742 Further, every function must be generated such that it keeps the stack
7743 aligned. Thus calling a function compiled with a higher preferred
7744 stack boundary from a function compiled with a lower preferred stack
7745 boundary will most likely misalign the stack. It is recommended that
7746 libraries that use callbacks always use the default setting.
7748 This extra alignment does consume extra stack space, and generally
7749 increases code size. Code that is sensitive to stack space usage, such
7750 as embedded systems and operating system kernels, may want to reduce the
7751 preferred alignment to @option{-mpreferred-stack-boundary=2}.
7767 These switches enable or disable the use of built-in functions that allow
7768 direct access to the MMX, SSE and 3Dnow extensions of the instruction set.
7770 @xref{X86 Built-in Functions}, for details of the functions enabled
7771 and disabled by these switches.
7774 @itemx -mno-push-args
7776 @opindex mno-push-args
7777 Use PUSH operations to store outgoing parameters. This method is shorter
7778 and usually equally fast as method using SUB/MOV operations and is enabled
7779 by default. In some cases disabling it may improve performance because of
7780 improved scheduling and reduced dependencies.
7782 @item -maccumulate-outgoing-args
7783 @opindex maccumulate-outgoing-args
7784 If enabled, the maximum amount of space required for outgoing arguments will be
7785 computed in the function prologue. This is faster on most modern CPUs
7786 because of reduced dependencies, improved scheduling and reduced stack usage
7787 when preferred stack boundary is not equal to 2. The drawback is a notable
7788 increase in code size. This switch implies @option{-mno-push-args}.
7792 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
7793 on thread-safe exception handling must compile and link all code with the
7794 @option{-mthreads} option. When compiling, @option{-mthreads} defines
7795 @option{-D_MT}; when linking, it links in a special thread helper library
7796 @option{-lmingwthrd} which cleans up per thread exception handling data.
7798 @item -mno-align-stringops
7799 @opindex mno-align-stringops
7800 Do not align destination of inlined string operations. This switch reduces
7801 code size and improves performance in case the destination is already aligned,
7802 but gcc don't know about it.
7804 @item -minline-all-stringops
7805 @opindex minline-all-stringops
7806 By default GCC inlines string operations only when destination is known to be
7807 aligned at least to 4 byte boundary. This enables more inlining, increase code
7808 size, but may improve performance of code that depends on fast memcpy, strlen
7809 and memset for short lengths.
7811 @item -momit-leaf-frame-pointer
7812 @opindex momit-leaf-frame-pointer
7813 Don't keep the frame pointer in a register for leaf functions. This
7814 avoids the instructions to save, set up and restore frame pointers and
7815 makes an extra register available in leaf functions. The option
7816 @option{-fomit-frame-pointer} removes the frame pointer for all functions
7817 which might make debugging harder.
7820 These @samp{-m} switches are supported in addition to the above
7821 on AMD x86-64 processors in 64-bit environments.
7828 Generate code for a 32-bit or 64-bit environment.
7829 The 32-bit environment sets int, long and pointer to 32 bits and
7830 generates code that runs on any i386 system.
7831 The 64-bit environment sets int to 32 bits and long and pointer
7832 to 64 bits and generates code for AMD's x86-64 architecture.
7835 @opindex no-red-zone
7836 Do not use a so called red zone for x86-64 code. The red zone is mandated
7837 by the x86-64 ABI, it is a 128-byte area beyond the location of the
7838 stack pointer that will not be modified by signal or interrupt handlers
7839 and therefore can be used for temporary data without adjusting the stack
7840 pointer. The flag @option{-mno-red-zone} disables this red zone.
7842 @item -mcmodel=small
7843 @opindex mcmodel=small
7844 Generate code for the small code model: the program and its symbols must
7845 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
7846 Programs can be statically or dynamically linked. This is the default
7849 @item -mcmodel=kernel
7850 @opindex mcmodel=kernel
7851 Generate code for the kernel code model. The kernel runs in the
7852 negative 2 GB of the address space.
7853 This model has to be used for Linux kernel code.
7855 @item -mcmodel=medium
7856 @opindex mcmodel=medium
7857 Generate code for the medium model: The program is linked in the lower 2
7858 GB of the address space but symbols can be located anywhere in the
7859 address space. Programs can be statically or dynamically linked, but
7860 building of shared libraries are not supported with the medium model.
7862 @item -mcmodel=large
7863 @opindex mcmodel=large
7864 Generate code for the large model: This model makes no assumptions
7865 about addresses and sizes of sections. Currently GCC does not implement
7870 @subsection HPPA Options
7871 @cindex HPPA Options
7873 These @samp{-m} options are defined for the HPPA family of computers:
7876 @item -march=@var{architecture-type}
7878 Generate code for the specified architecture. The choices for
7879 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
7880 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
7881 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
7882 architecture option for your machine. Code compiled for lower numbered
7883 architectures will run on higher numbered architectures, but not the
7886 PA 2.0 support currently requires gas snapshot 19990413 or later. The
7887 next release of binutils (current is 2.9.1) will probably contain PA 2.0
7891 @itemx -mpa-risc-1-1
7892 @itemx -mpa-risc-2-0
7893 @opindex mpa-risc-1-0
7894 @opindex mpa-risc-1-1
7895 @opindex mpa-risc-2-0
7896 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
7899 @opindex mbig-switch
7900 Generate code suitable for big switch tables. Use this option only if
7901 the assembler/linker complain about out of range branches within a switch
7904 @item -mjump-in-delay
7905 @opindex mjump-in-delay
7906 Fill delay slots of function calls with unconditional jump instructions
7907 by modifying the return pointer for the function call to be the target
7908 of the conditional jump.
7910 @item -mdisable-fpregs
7911 @opindex mdisable-fpregs
7912 Prevent floating point registers from being used in any manner. This is
7913 necessary for compiling kernels which perform lazy context switching of
7914 floating point registers. If you use this option and attempt to perform
7915 floating point operations, the compiler will abort.
7917 @item -mdisable-indexing
7918 @opindex mdisable-indexing
7919 Prevent the compiler from using indexing address modes. This avoids some
7920 rather obscure problems when compiling MIG generated code under MACH@.
7922 @item -mno-space-regs
7923 @opindex mno-space-regs
7924 Generate code that assumes the target has no space registers. This allows
7925 GCC to generate faster indirect calls and use unscaled index address modes.
7927 Such code is suitable for level 0 PA systems and kernels.
7929 @item -mfast-indirect-calls
7930 @opindex mfast-indirect-calls
7931 Generate code that assumes calls never cross space boundaries. This
7932 allows GCC to emit code which performs faster indirect calls.
7934 This option will not work in the presence of shared libraries or nested
7937 @item -mlong-load-store
7938 @opindex mlong-load-store
7939 Generate 3-instruction load and store sequences as sometimes required by
7940 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
7943 @item -mportable-runtime
7944 @opindex mportable-runtime
7945 Use the portable calling conventions proposed by HP for ELF systems.
7949 Enable the use of assembler directives only GAS understands.
7951 @item -mschedule=@var{cpu-type}
7953 Schedule code according to the constraints for the machine type
7954 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
7955 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
7956 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
7957 proper scheduling option for your machine. The default scheduling is
7961 @opindex mlinker-opt
7962 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
7963 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
7964 linkers in which they give bogus error messages when linking some programs.
7967 @opindex msoft-float
7968 Generate output containing library calls for floating point.
7969 @strong{Warning:} the requisite libraries are not available for all HPPA
7970 targets. Normally the facilities of the machine's usual C compiler are
7971 used, but this cannot be done directly in cross-compilation. You must make
7972 your own arrangements to provide suitable library functions for
7973 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
7974 does provide software floating point support.
7976 @option{-msoft-float} changes the calling convention in the output file;
7977 therefore, it is only useful if you compile @emph{all} of a program with
7978 this option. In particular, you need to compile @file{libgcc.a}, the
7979 library that comes with GCC, with @option{-msoft-float} in order for
7984 Generate the predefine, @code{_SIO}, for server IO. The default is
7985 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
7986 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO. These
7987 options are available under HP-UX and HI-UX.
7990 @node Intel 960 Options
7991 @subsection Intel 960 Options
7993 These @samp{-m} options are defined for the Intel 960 implementations:
7996 @item -m@var{cpu-type}
8004 Assume the defaults for the machine type @var{cpu-type} for some of
8005 the other options, including instruction scheduling, floating point
8006 support, and addressing modes. The choices for @var{cpu-type} are
8007 @samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf},
8008 @samp{sa}, and @samp{sb}.
8015 @opindex msoft-float
8016 The @option{-mnumerics} option indicates that the processor does support
8017 floating-point instructions. The @option{-msoft-float} option indicates
8018 that floating-point support should not be assumed.
8020 @item -mleaf-procedures
8021 @itemx -mno-leaf-procedures
8022 @opindex mleaf-procedures
8023 @opindex mno-leaf-procedures
8024 Do (or do not) attempt to alter leaf procedures to be callable with the
8025 @code{bal} instruction as well as @code{call}. This will result in more
8026 efficient code for explicit calls when the @code{bal} instruction can be
8027 substituted by the assembler or linker, but less efficient code in other
8028 cases, such as calls via function pointers, or using a linker that doesn't
8029 support this optimization.
8032 @itemx -mno-tail-call
8034 @opindex mno-tail-call
8035 Do (or do not) make additional attempts (beyond those of the
8036 machine-independent portions of the compiler) to optimize tail-recursive
8037 calls into branches. You may not want to do this because the detection of
8038 cases where this is not valid is not totally complete. The default is
8039 @option{-mno-tail-call}.
8041 @item -mcomplex-addr
8042 @itemx -mno-complex-addr
8043 @opindex mcomplex-addr
8044 @opindex mno-complex-addr
8045 Assume (or do not assume) that the use of a complex addressing mode is a
8046 win on this implementation of the i960. Complex addressing modes may not
8047 be worthwhile on the K-series, but they definitely are on the C-series.
8048 The default is currently @option{-mcomplex-addr} for all processors except
8052 @itemx -mno-code-align
8053 @opindex mcode-align
8054 @opindex mno-code-align
8055 Align code to 8-byte boundaries for faster fetching (or don't bother).
8056 Currently turned on by default for C-series implementations only.
8059 @item -mclean-linkage
8060 @itemx -mno-clean-linkage
8061 @opindex mclean-linkage
8062 @opindex mno-clean-linkage
8063 These options are not fully implemented.
8067 @itemx -mic2.0-compat
8068 @itemx -mic3.0-compat
8070 @opindex mic2.0-compat
8071 @opindex mic3.0-compat
8072 Enable compatibility with iC960 v2.0 or v3.0.
8076 @opindex masm-compat
8078 Enable compatibility with the iC960 assembler.
8080 @item -mstrict-align
8081 @itemx -mno-strict-align
8082 @opindex mstrict-align
8083 @opindex mno-strict-align
8084 Do not permit (do permit) unaligned accesses.
8088 Enable structure-alignment compatibility with Intel's gcc release version
8089 1.3 (based on gcc 1.37). This option implies @option{-mstrict-align}.
8091 @item -mlong-double-64
8092 @opindex mlong-double-64
8093 Implement type @samp{long double} as 64-bit floating point numbers.
8094 Without the option @samp{long double} is implemented by 80-bit
8095 floating point numbers. The only reason we have it because there is
8096 no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it
8097 is only useful for people using soft-float targets. Otherwise, we
8098 should recommend against use of it.
8102 @node DEC Alpha Options
8103 @subsection DEC Alpha Options
8105 These @samp{-m} options are defined for the DEC Alpha implementations:
8108 @item -mno-soft-float
8110 @opindex mno-soft-float
8111 @opindex msoft-float
8112 Use (do not use) the hardware floating-point instructions for
8113 floating-point operations. When @option{-msoft-float} is specified,
8114 functions in @file{libgcc.a} will be used to perform floating-point
8115 operations. Unless they are replaced by routines that emulate the
8116 floating-point operations, or compiled in such a way as to call such
8117 emulations routines, these routines will issue floating-point
8118 operations. If you are compiling for an Alpha without floating-point
8119 operations, you must ensure that the library is built so as not to call
8122 Note that Alpha implementations without floating-point operations are
8123 required to have floating-point registers.
8128 @opindex mno-fp-regs
8129 Generate code that uses (does not use) the floating-point register set.
8130 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
8131 register set is not used, floating point operands are passed in integer
8132 registers as if they were integers and floating-point results are passed
8133 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
8134 so any function with a floating-point argument or return value called by code
8135 compiled with @option{-mno-fp-regs} must also be compiled with that
8138 A typical use of this option is building a kernel that does not use,
8139 and hence need not save and restore, any floating-point registers.
8143 The Alpha architecture implements floating-point hardware optimized for
8144 maximum performance. It is mostly compliant with the IEEE floating
8145 point standard. However, for full compliance, software assistance is
8146 required. This option generates code fully IEEE compliant code
8147 @emph{except} that the @var{inexact-flag} is not maintained (see below).
8148 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
8149 defined during compilation. The resulting code is less efficient but is
8150 able to correctly support denormalized numbers and exceptional IEEE
8151 values such as not-a-number and plus/minus infinity. Other Alpha
8152 compilers call this option @option{-ieee_with_no_inexact}.
8154 @item -mieee-with-inexact
8155 @opindex mieee-with-inexact
8156 This is like @option{-mieee} except the generated code also maintains
8157 the IEEE @var{inexact-flag}. Turning on this option causes the
8158 generated code to implement fully-compliant IEEE math. In addition to
8159 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
8160 macro. On some Alpha implementations the resulting code may execute
8161 significantly slower than the code generated by default. Since there is
8162 very little code that depends on the @var{inexact-flag}, you should
8163 normally not specify this option. Other Alpha compilers call this
8164 option @option{-ieee_with_inexact}.
8166 @item -mfp-trap-mode=@var{trap-mode}
8167 @opindex mfp-trap-mode
8168 This option controls what floating-point related traps are enabled.
8169 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
8170 The trap mode can be set to one of four values:
8174 This is the default (normal) setting. The only traps that are enabled
8175 are the ones that cannot be disabled in software (e.g., division by zero
8179 In addition to the traps enabled by @samp{n}, underflow traps are enabled
8183 Like @samp{su}, but the instructions are marked to be safe for software
8184 completion (see Alpha architecture manual for details).
8187 Like @samp{su}, but inexact traps are enabled as well.
8190 @item -mfp-rounding-mode=@var{rounding-mode}
8191 @opindex mfp-rounding-mode
8192 Selects the IEEE rounding mode. Other Alpha compilers call this option
8193 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
8198 Normal IEEE rounding mode. Floating point numbers are rounded towards
8199 the nearest machine number or towards the even machine number in case
8203 Round towards minus infinity.
8206 Chopped rounding mode. Floating point numbers are rounded towards zero.
8209 Dynamic rounding mode. A field in the floating point control register
8210 (@var{fpcr}, see Alpha architecture reference manual) controls the
8211 rounding mode in effect. The C library initializes this register for
8212 rounding towards plus infinity. Thus, unless your program modifies the
8213 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
8216 @item -mtrap-precision=@var{trap-precision}
8217 @opindex mtrap-precision
8218 In the Alpha architecture, floating point traps are imprecise. This
8219 means without software assistance it is impossible to recover from a
8220 floating trap and program execution normally needs to be terminated.
8221 GCC can generate code that can assist operating system trap handlers
8222 in determining the exact location that caused a floating point trap.
8223 Depending on the requirements of an application, different levels of
8224 precisions can be selected:
8228 Program precision. This option is the default and means a trap handler
8229 can only identify which program caused a floating point exception.
8232 Function precision. The trap handler can determine the function that
8233 caused a floating point exception.
8236 Instruction precision. The trap handler can determine the exact
8237 instruction that caused a floating point exception.
8240 Other Alpha compilers provide the equivalent options called
8241 @option{-scope_safe} and @option{-resumption_safe}.
8243 @item -mieee-conformant
8244 @opindex mieee-conformant
8245 This option marks the generated code as IEEE conformant. You must not
8246 use this option unless you also specify @option{-mtrap-precision=i} and either
8247 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
8248 is to emit the line @samp{.eflag 48} in the function prologue of the
8249 generated assembly file. Under DEC Unix, this has the effect that
8250 IEEE-conformant math library routines will be linked in.
8252 @item -mbuild-constants
8253 @opindex mbuild-constants
8254 Normally GCC examines a 32- or 64-bit integer constant to
8255 see if it can construct it from smaller constants in two or three
8256 instructions. If it cannot, it will output the constant as a literal and
8257 generate code to load it from the data segment at runtime.
8259 Use this option to require GCC to construct @emph{all} integer constants
8260 using code, even if it takes more instructions (the maximum is six).
8262 You would typically use this option to build a shared library dynamic
8263 loader. Itself a shared library, it must relocate itself in memory
8264 before it can find the variables and constants in its own data segment.
8270 Select whether to generate code to be assembled by the vendor-supplied
8271 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
8289 Indicate whether GCC should generate code to use the optional BWX,
8290 CIX, FIX and MAX instruction sets. The default is to use the instruction
8291 sets supported by the CPU type specified via @option{-mcpu=} option or that
8292 of the CPU on which GCC was built if none was specified.
8297 @opindex mfloat-ieee
8298 Generate code that uses (does not use) VAX F and G floating point
8299 arithmetic instead of IEEE single and double precision.
8301 @item -mexplicit-relocs
8302 @itemx -mno-explicit-relocs
8303 @opindex mexplicit-relocs
8304 @opindex mno-explicit-relocs
8305 Older Alpha assemblers provided no way to generate symbol relocations
8306 except via assembler macros. Use of these macros does not allow
8307 optimial instruction scheduling. GNU binutils as of version 2.12
8308 supports a new syntax that allows the compiler to explicitly mark
8309 which relocations should apply to which instructions. This option
8310 is mostly useful for debugging, as GCC detects the capabilities of
8311 the assembler when it is built and sets the default accordingly.
8315 @opindex msmall-data
8316 @opindex mlarge-data
8317 When @option{-mexplicit-relocs} is in effect, static data is
8318 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
8319 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
8320 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
8321 16-bit relocations off of the @code{$gp} register. This limits the
8322 size of the small data area to 64KB, but allows the variables to be
8323 directly accessed via a single instruction.
8325 The default is @option{-mlarge-data}. With this option the data area
8326 is limited to just below 2GB. Programs that require more than 2GB of
8327 data must use @code{malloc} or @code{mmap} to allocate the data in the
8328 heap instead of in the program's data segment.
8330 When generating code for shared libraries, @option{-fpic} implies
8331 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
8333 @item -mcpu=@var{cpu_type}
8335 Set the instruction set and instruction scheduling parameters for
8336 machine type @var{cpu_type}. You can specify either the @samp{EV}
8337 style name or the corresponding chip number. GCC supports scheduling
8338 parameters for the EV4, EV5 and EV6 family of processors and will
8339 choose the default values for the instruction set from the processor
8340 you specify. If you do not specify a processor type, GCC will default
8341 to the processor on which the compiler was built.
8343 Supported values for @var{cpu_type} are
8349 Schedules as an EV4 and has no instruction set extensions.
8353 Schedules as an EV5 and has no instruction set extensions.
8357 Schedules as an EV5 and supports the BWX extension.
8362 Schedules as an EV5 and supports the BWX and MAX extensions.
8366 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
8370 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
8373 @item -mtune=@var{cpu_type}
8375 Set only the instruction scheduling parameters for machine type
8376 @var{cpu_type}. The instruction set is not changed.
8378 @item -mmemory-latency=@var{time}
8379 @opindex mmemory-latency
8380 Sets the latency the scheduler should assume for typical memory
8381 references as seen by the application. This number is highly
8382 dependent on the memory access patterns used by the application
8383 and the size of the external cache on the machine.
8385 Valid options for @var{time} are
8389 A decimal number representing clock cycles.
8395 The compiler contains estimates of the number of clock cycles for
8396 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
8397 (also called Dcache, Scache, and Bcache), as well as to main memory.
8398 Note that L3 is only valid for EV5.
8403 @node DEC Alpha/VMS Options
8404 @subsection DEC Alpha/VMS Options
8406 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
8409 @item -mvms-return-codes
8410 @opindex mvms-return-codes
8411 Return VMS condition codes from main. The default is to return POSIX
8412 style condition (e.g.@ error) codes.
8415 @node Clipper Options
8416 @subsection Clipper Options
8418 These @samp{-m} options are defined for the Clipper implementations:
8423 Produce code for a C300 Clipper processor. This is the default.
8427 Produce code for a C400 Clipper processor, i.e.@: use floating point
8431 @node H8/300 Options
8432 @subsection H8/300 Options
8434 These @samp{-m} options are defined for the H8/300 implementations:
8439 Shorten some address references at link time, when possible; uses the
8440 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
8441 ld.info, Using ld}, for a fuller description.
8445 Generate code for the H8/300H@.
8449 Generate code for the H8S@.
8453 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
8457 Make @code{int} data 32 bits by default.
8461 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
8462 The default for the H8/300H and H8S is to align longs and floats on 4
8464 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
8465 This option has no effect on the H8/300.
8469 @subsection SH Options
8471 These @samp{-m} options are defined for the SH implementations:
8476 Generate code for the SH1.
8480 Generate code for the SH2.
8484 Generate code for the SH3.
8488 Generate code for the SH3e.
8492 Generate code for the SH4 without a floating-point unit.
8494 @item -m4-single-only
8495 @opindex m4-single-only
8496 Generate code for the SH4 with a floating-point unit that only
8497 supports single-precision arithmetic.
8501 Generate code for the SH4 assuming the floating-point unit is in
8502 single-precision mode by default.
8506 Generate code for the SH4.
8510 Compile code for the processor in big endian mode.
8514 Compile code for the processor in little endian mode.
8518 Align doubles at 64-bit boundaries. Note that this changes the calling
8519 conventions, and thus some functions from the standard C library will
8520 not work unless you recompile it first with @option{-mdalign}.
8524 Shorten some address references at link time, when possible; uses the
8525 linker option @option{-relax}.
8529 Use 32-bit offsets in @code{switch} tables. The default is to use
8534 Enable the use of the instruction @code{fmovd}.
8538 Comply with the calling conventions defined by Hitachi.
8542 Mark the @code{MAC} register as call-clobbered, even if
8543 @option{-mhitachi} is given.
8547 Increase IEEE-compliance of floating-point code.
8551 Dump instruction size and location in the assembly code.
8555 This option is deprecated. It pads structures to multiple of 4 bytes,
8556 which is incompatible with the SH ABI@.
8560 Optimize for space instead of speed. Implied by @option{-Os}.
8564 When generating position-independent code, emit function calls using
8565 the Global Offset Table instead of the Procedure Linkage Table.
8569 Generate a library function call to invalidate instruction cache
8570 entries, after fixing up a trampoline. This library function call
8571 doesn't assume it can write to the whole memory address space. This
8572 is the default when the target is @code{sh-*-linux*}.
8575 @node System V Options
8576 @subsection Options for System V
8578 These additional options are available on System V Release 4 for
8579 compatibility with other compilers on those systems:
8584 Create a shared object.
8585 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
8589 Identify the versions of each tool used by the compiler, in a
8590 @code{.ident} assembler directive in the output.
8594 Refrain from adding @code{.ident} directives to the output file (this is
8597 @item -YP,@var{dirs}
8599 Search the directories @var{dirs}, and no others, for libraries
8600 specified with @option{-l}.
8604 Look in the directory @var{dir} to find the M4 preprocessor.
8605 The assembler uses this option.
8606 @c This is supposed to go with a -Yd for predefined M4 macro files, but
8607 @c the generic assembler that comes with Solaris takes just -Ym.
8610 @node TMS320C3x/C4x Options
8611 @subsection TMS320C3x/C4x Options
8612 @cindex TMS320C3x/C4x Options
8614 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
8618 @item -mcpu=@var{cpu_type}
8620 Set the instruction set, register set, and instruction scheduling
8621 parameters for machine type @var{cpu_type}. Supported values for
8622 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
8623 @samp{c44}. The default is @samp{c40} to generate code for the
8628 @itemx -msmall-memory
8630 @opindex mbig-memory
8632 @opindex msmall-memory
8634 Generates code for the big or small memory model. The small memory
8635 model assumed that all data fits into one 64K word page. At run-time
8636 the data page (DP) register must be set to point to the 64K page
8637 containing the .bss and .data program sections. The big memory model is
8638 the default and requires reloading of the DP register for every direct
8645 Allow (disallow) allocation of general integer operands into the block
8652 Enable (disable) generation of code using decrement and branch,
8653 DBcond(D), instructions. This is enabled by default for the C4x. To be
8654 on the safe side, this is disabled for the C3x, since the maximum
8655 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
8656 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
8657 that it can utilize the decrement and branch instruction, but will give
8658 up if there is more than one memory reference in the loop. Thus a loop
8659 where the loop counter is decremented can generate slightly more
8660 efficient code, in cases where the RPTB instruction cannot be utilized.
8662 @item -mdp-isr-reload
8664 @opindex mdp-isr-reload
8666 Force the DP register to be saved on entry to an interrupt service
8667 routine (ISR), reloaded to point to the data section, and restored on
8668 exit from the ISR@. This should not be required unless someone has
8669 violated the small memory model by modifying the DP register, say within
8676 For the C3x use the 24-bit MPYI instruction for integer multiplies
8677 instead of a library call to guarantee 32-bit results. Note that if one
8678 of the operands is a constant, then the multiplication will be performed
8679 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
8680 then squaring operations are performed inline instead of a library call.
8683 @itemx -mno-fast-fix
8685 @opindex mno-fast-fix
8686 The C3x/C4x FIX instruction to convert a floating point value to an
8687 integer value chooses the nearest integer less than or equal to the
8688 floating point value rather than to the nearest integer. Thus if the
8689 floating point number is negative, the result will be incorrectly
8690 truncated an additional code is necessary to detect and correct this
8691 case. This option can be used to disable generation of the additional
8692 code required to correct the result.
8698 Enable (disable) generation of repeat block sequences using the RPTB
8699 instruction for zero overhead looping. The RPTB construct is only used
8700 for innermost loops that do not call functions or jump across the loop
8701 boundaries. There is no advantage having nested RPTB loops due to the
8702 overhead required to save and restore the RC, RS, and RE registers.
8703 This is enabled by default with @option{-O2}.
8705 @item -mrpts=@var{count}
8709 Enable (disable) the use of the single instruction repeat instruction
8710 RPTS@. If a repeat block contains a single instruction, and the loop
8711 count can be guaranteed to be less than the value @var{count}, GCC will
8712 emit a RPTS instruction instead of a RPTB@. If no value is specified,
8713 then a RPTS will be emitted even if the loop count cannot be determined
8714 at compile time. Note that the repeated instruction following RPTS does
8715 not have to be reloaded from memory each iteration, thus freeing up the
8716 CPU buses for operands. However, since interrupts are blocked by this
8717 instruction, it is disabled by default.
8719 @item -mloop-unsigned
8720 @itemx -mno-loop-unsigned
8721 @opindex mloop-unsigned
8722 @opindex mno-loop-unsigned
8723 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
8724 is @math{2^{31} + 1} since these instructions test if the iteration count is
8725 negative to terminate the loop. If the iteration count is unsigned
8726 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
8727 exceeded. This switch allows an unsigned iteration count.
8731 Try to emit an assembler syntax that the TI assembler (asm30) is happy
8732 with. This also enforces compatibility with the API employed by the TI
8733 C3x C compiler. For example, long doubles are passed as structures
8734 rather than in floating point registers.
8740 Generate code that uses registers (stack) for passing arguments to functions.
8741 By default, arguments are passed in registers where possible rather
8742 than by pushing arguments on to the stack.
8744 @item -mparallel-insns
8745 @itemx -mno-parallel-insns
8746 @opindex mparallel-insns
8747 @opindex mno-parallel-insns
8748 Allow the generation of parallel instructions. This is enabled by
8749 default with @option{-O2}.
8751 @item -mparallel-mpy
8752 @itemx -mno-parallel-mpy
8753 @opindex mparallel-mpy
8754 @opindex mno-parallel-mpy
8755 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
8756 provided @option{-mparallel-insns} is also specified. These instructions have
8757 tight register constraints which can pessimize the code generation
8763 @subsection V850 Options
8764 @cindex V850 Options
8766 These @samp{-m} options are defined for V850 implementations:
8770 @itemx -mno-long-calls
8771 @opindex mlong-calls
8772 @opindex mno-long-calls
8773 Treat all calls as being far away (near). If calls are assumed to be
8774 far away, the compiler will always load the functions address up into a
8775 register, and call indirect through the pointer.
8781 Do not optimize (do optimize) basic blocks that use the same index
8782 pointer 4 or more times to copy pointer into the @code{ep} register, and
8783 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
8784 option is on by default if you optimize.
8786 @item -mno-prolog-function
8787 @itemx -mprolog-function
8788 @opindex mno-prolog-function
8789 @opindex mprolog-function
8790 Do not use (do use) external functions to save and restore registers at
8791 the prolog and epilog of a function. The external functions are slower,
8792 but use less code space if more than one function saves the same number
8793 of registers. The @option{-mprolog-function} option is on by default if
8798 Try to make the code as small as possible. At present, this just turns
8799 on the @option{-mep} and @option{-mprolog-function} options.
8803 Put static or global variables whose size is @var{n} bytes or less into
8804 the tiny data area that register @code{ep} points to. The tiny data
8805 area can hold up to 256 bytes in total (128 bytes for byte references).
8809 Put static or global variables whose size is @var{n} bytes or less into
8810 the small data area that register @code{gp} points to. The small data
8811 area can hold up to 64 kilobytes.
8815 Put static or global variables whose size is @var{n} bytes or less into
8816 the first 32 kilobytes of memory.
8820 Specify that the target processor is the V850.
8823 @opindex mbig-switch
8824 Generate code suitable for big switch tables. Use this option only if
8825 the assembler/linker complain about out of range branches within a switch
8830 This option will cause r2 and r5 to be used in the code generated by
8831 the compiler. This setting is the default.
8834 @opindex -mno-app-regs
8835 This option will cause r2 and r5 to be treated as fixed registers.
8839 Specify that the target processor is the V850E. The preprocessor
8840 constant @samp{__v850e__} will be defined if this option is used.
8842 If neither @option{-mv850} nor @option{-mv850e} are defined
8843 then a default target processor will be chosen and the relevant
8844 @samp{__v850*__} preprocessor constant will be defined.
8846 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
8847 defined, regardless of which processor variant is the target.
8849 @item -mdisable-callt
8850 @opindex -mdisable-callt
8851 This option will suppress generation of the CALLT instruction for the
8852 v850e flavors of the v850 architecture. The default is
8853 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
8858 @subsection ARC Options
8861 These options are defined for ARC implementations:
8866 Compile code for little endian mode. This is the default.
8870 Compile code for big endian mode.
8873 @opindex mmangle-cpu
8874 Prepend the name of the cpu to all public symbol names.
8875 In multiple-processor systems, there are many ARC variants with different
8876 instruction and register set characteristics. This flag prevents code
8877 compiled for one cpu to be linked with code compiled for another.
8878 No facility exists for handling variants that are ``almost identical''.
8879 This is an all or nothing option.
8881 @item -mcpu=@var{cpu}
8883 Compile code for ARC variant @var{cpu}.
8884 Which variants are supported depend on the configuration.
8885 All variants support @option{-mcpu=base}, this is the default.
8887 @item -mtext=@var{text-section}
8888 @itemx -mdata=@var{data-section}
8889 @itemx -mrodata=@var{readonly-data-section}
8893 Put functions, data, and readonly data in @var{text-section},
8894 @var{data-section}, and @var{readonly-data-section} respectively
8895 by default. This can be overridden with the @code{section} attribute.
8896 @xref{Variable Attributes}.
8901 @subsection NS32K Options
8902 @cindex NS32K options
8904 These are the @samp{-m} options defined for the 32000 series. The default
8905 values for these options depends on which style of 32000 was selected when
8906 the compiler was configured; the defaults for the most common choices are
8914 Generate output for a 32032. This is the default
8915 when the compiler is configured for 32032 and 32016 based systems.
8921 Generate output for a 32332. This is the default
8922 when the compiler is configured for 32332-based systems.
8928 Generate output for a 32532. This is the default
8929 when the compiler is configured for 32532-based systems.
8933 Generate output containing 32081 instructions for floating point.
8934 This is the default for all systems.
8938 Generate output containing 32381 instructions for floating point. This
8939 also implies @option{-m32081}. The 32381 is only compatible with the 32332
8940 and 32532 cpus. This is the default for the pc532-netbsd configuration.
8944 Try and generate multiply-add floating point instructions @code{polyF}
8945 and @code{dotF}. This option is only available if the @option{-m32381}
8946 option is in effect. Using these instructions requires changes to
8947 register allocation which generally has a negative impact on
8948 performance. This option should only be enabled when compiling code
8949 particularly likely to make heavy use of multiply-add instructions.
8952 @opindex mnomulti-add
8953 Do not try and generate multiply-add floating point instructions
8954 @code{polyF} and @code{dotF}. This is the default on all platforms.
8957 @opindex msoft-float
8958 Generate output containing library calls for floating point.
8959 @strong{Warning:} the requisite libraries may not be available.
8961 @item -mieee-compare
8962 @itemx -mno-ieee-compare
8963 @opindex mieee-compare
8964 @opindex mno-ieee-compare
8965 Control whether or not the compiler uses IEEE floating point
8966 comparisons. These handle correctly the case where the result of a
8967 comparison is unordered.
8968 @strong{Warning:} the requisite kernel support may not be available.
8971 @opindex mnobitfield
8972 Do not use the bit-field instructions. On some machines it is faster to
8973 use shifting and masking operations. This is the default for the pc532.
8977 Do use the bit-field instructions. This is the default for all platforms
8982 Use a different function-calling convention, in which functions
8983 that take a fixed number of arguments return pop their
8984 arguments on return with the @code{ret} instruction.
8986 This calling convention is incompatible with the one normally
8987 used on Unix, so you cannot use it if you need to call libraries
8988 compiled with the Unix compiler.
8990 Also, you must provide function prototypes for all functions that
8991 take variable numbers of arguments (including @code{printf});
8992 otherwise incorrect code will be generated for calls to those
8995 In addition, seriously incorrect code will result if you call a
8996 function with too many arguments. (Normally, extra arguments are
8997 harmlessly ignored.)
8999 This option takes its name from the 680x0 @code{rtd} instruction.
9004 Use a different function-calling convention where the first two arguments
9005 are passed in registers.
9007 This calling convention is incompatible with the one normally
9008 used on Unix, so you cannot use it if you need to call libraries
9009 compiled with the Unix compiler.
9012 @opindex mnoregparam
9013 Do not pass any arguments in registers. This is the default for all
9018 It is OK to use the sb as an index register which is always loaded with
9019 zero. This is the default for the pc532-netbsd target.
9023 The sb register is not available for use or has not been initialized to
9024 zero by the run time system. This is the default for all targets except
9025 the pc532-netbsd. It is also implied whenever @option{-mhimem} or
9026 @option{-fpic} is set.
9030 Many ns32000 series addressing modes use displacements of up to 512MB@.
9031 If an address is above 512MB then displacements from zero can not be used.
9032 This option causes code to be generated which can be loaded above 512MB@.
9033 This may be useful for operating systems or ROM code.
9037 Assume code will be loaded in the first 512MB of virtual address space.
9038 This is the default for all platforms.
9044 @subsection AVR Options
9047 These options are defined for AVR implementations:
9050 @item -mmcu=@var{mcu}
9052 Specify ATMEL AVR instruction set or MCU type.
9054 Instruction set avr1 is for the minimal AVR core, not supported by the C
9055 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
9056 attiny11, attiny12, attiny15, attiny28).
9058 Instruction set avr2 (default) is for the classic AVR core with up to
9059 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
9060 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
9061 at90c8534, at90s8535).
9063 Instruction set avr3 is for the classic AVR core with up to 128K program
9064 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
9066 Instruction set avr4 is for the enhanced AVR core with up to 8K program
9067 memory space (MCU types: atmega8, atmega83, atmega85).
9069 Instruction set avr5 is for the enhanced AVR core with up to 128K program
9070 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
9071 atmega64, atmega128, at43usb355, at94k).
9075 Output instruction sizes to the asm file.
9077 @item -minit-stack=@var{N}
9078 @opindex minit-stack
9079 Specify the initial stack address, which may be a symbol or numeric value,
9080 @samp{__stack} is the default.
9082 @item -mno-interrupts
9083 @opindex mno-interrupts
9084 Generated code is not compatible with hardware interrupts.
9085 Code size will be smaller.
9087 @item -mcall-prologues
9088 @opindex mcall-prologues
9089 Functions prologues/epilogues expanded as call to appropriate
9090 subroutines. Code size will be smaller.
9092 @item -mno-tablejump
9093 @opindex mno-tablejump
9094 Do not generate tablejump insns which sometimes increase code size.
9097 @opindex mtiny-stack
9098 Change only the low 8 bits of the stack pointer.
9102 @subsection MCore Options
9103 @cindex MCore options
9105 These are the @samp{-m} options defined for the Motorola M*Core
9115 @opindex mno-hardlit
9116 Inline constants into the code stream if it can be done in two
9117 instructions or less.
9125 Use the divide instruction. (Enabled by default).
9127 @item -mrelax-immediate
9128 @itemx -mrelax-immediate
9129 @itemx -mno-relax-immediate
9130 @opindex mrelax-immediate
9131 @opindex mrelax-immediate
9132 @opindex mno-relax-immediate
9133 Allow arbitrary sized immediates in bit operations.
9135 @item -mwide-bitfields
9136 @itemx -mwide-bitfields
9137 @itemx -mno-wide-bitfields
9138 @opindex mwide-bitfields
9139 @opindex mwide-bitfields
9140 @opindex mno-wide-bitfields
9141 Always treat bit-fields as int-sized.
9143 @item -m4byte-functions
9144 @itemx -m4byte-functions
9145 @itemx -mno-4byte-functions
9146 @opindex m4byte-functions
9147 @opindex m4byte-functions
9148 @opindex mno-4byte-functions
9149 Force all functions to be aligned to a four byte boundary.
9151 @item -mcallgraph-data
9152 @itemx -mcallgraph-data
9153 @itemx -mno-callgraph-data
9154 @opindex mcallgraph-data
9155 @opindex mcallgraph-data
9156 @opindex mno-callgraph-data
9157 Emit callgraph information.
9161 @itemx -mno-slow-bytes
9162 @opindex mslow-bytes
9163 @opindex mslow-bytes
9164 @opindex mno-slow-bytes
9165 Prefer word access when reading byte quantities.
9167 @item -mlittle-endian
9168 @itemx -mlittle-endian
9170 @opindex mlittle-endian
9171 @opindex mlittle-endian
9172 @opindex mbig-endian
9173 Generate code for a little endian target.
9181 Generate code for the 210 processor.
9185 @subsection IA-64 Options
9186 @cindex IA-64 Options
9188 These are the @samp{-m} options defined for the Intel IA-64 architecture.
9192 @opindex mbig-endian
9193 Generate code for a big endian target. This is the default for HP-UX@.
9195 @item -mlittle-endian
9196 @opindex mlittle-endian
9197 Generate code for a little endian target. This is the default for AIX5
9204 Generate (or don't) code for the GNU assembler. This is the default.
9205 @c Also, this is the default if the configure option @option{--with-gnu-as}
9212 Generate (or don't) code for the GNU linker. This is the default.
9213 @c Also, this is the default if the configure option @option{--with-gnu-ld}
9218 Generate code that does not use a global pointer register. The result
9219 is not position independent code, and violates the IA-64 ABI@.
9221 @item -mvolatile-asm-stop
9222 @itemx -mno-volatile-asm-stop
9223 @opindex mvolatile-asm-stop
9224 @opindex mno-volatile-asm-stop
9225 Generate (or don't) a stop bit immediately before and after volatile asm
9230 Generate code that works around Itanium B step errata.
9232 @item -mregister-names
9233 @itemx -mno-register-names
9234 @opindex mregister-names
9235 @opindex mno-register-names
9236 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
9237 the stacked registers. This may make assembler output more readable.
9243 Disable (or enable) optimizations that use the small data section. This may
9244 be useful for working around optimizer bugs.
9247 @opindex mconstant-gp
9248 Generate code that uses a single constant global pointer value. This is
9249 useful when compiling kernel code.
9253 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
9254 This is useful when compiling firmware code.
9256 @item -minline-divide-min-latency
9257 @opindex minline-divide-min-latency
9258 Generate code for inline divides using the minimum latency algorithm.
9260 @item -minline-divide-max-throughput
9261 @opindex minline-divide-max-throughput
9262 Generate code for inline divides using the maximum throughput algorithm.
9264 @item -mno-dwarf2-asm
9266 @opindex mno-dwarf2-asm
9267 @opindex mdwarf2-asm
9268 Don't (or do) generate assembler code for the DWARF2 line number debugging
9269 info. This may be useful when not using the GNU assembler.
9271 @item -mfixed-range=@var{register-range}
9272 @opindex mfixed-range
9273 Generate code treating the given register range as fixed registers.
9274 A fixed register is one that the register allocator can not use. This is
9275 useful when compiling kernel code. A register range is specified as
9276 two registers separated by a dash. Multiple register ranges can be
9277 specified separated by a comma.
9281 @subsection D30V Options
9282 @cindex D30V Options
9284 These @samp{-m} options are defined for D30V implementations:
9289 Link the @samp{.text}, @samp{.data}, @samp{.bss}, @samp{.strings},
9290 @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into external
9291 memory, which starts at location @code{0x80000000}.
9295 Same as the @option{-mextmem} switch.
9299 Link the @samp{.text} section into onchip text memory, which starts at
9300 location @code{0x0}. Also link @samp{.data}, @samp{.bss},
9301 @samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections
9302 into onchip data memory, which starts at location @code{0x20000000}.
9304 @item -mno-asm-optimize
9305 @itemx -masm-optimize
9306 @opindex mno-asm-optimize
9307 @opindex masm-optimize
9308 Disable (enable) passing @option{-O} to the assembler when optimizing.
9309 The assembler uses the @option{-O} option to automatically parallelize
9310 adjacent short instructions where possible.
9312 @item -mbranch-cost=@var{n}
9313 @opindex mbranch-cost
9314 Increase the internal costs of branches to @var{n}. Higher costs means
9315 that the compiler will issue more instructions to avoid doing a branch.
9318 @item -mcond-exec=@var{n}
9320 Specify the maximum number of conditionally executed instructions that
9321 replace a branch. The default is 4.
9324 @node S/390 and zSeries Options
9325 @subsection S/390 and zSeries Options
9326 @cindex S/390 and zSeries Options
9328 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
9333 @opindex mhard-float
9334 @opindex msoft-float
9335 Use (do not use) the hardware floating-point instructions and registers
9336 for floating-point operations. When @option{-msoft-float} is specified,
9337 functions in @file{libgcc.a} will be used to perform floating-point
9338 operations. When @option{-mhard-float} is specified, the compiler
9339 generates IEEE floating-point instructions. This is the default.
9342 @itemx -mno-backchain
9344 @opindex mno-backchain
9345 Generate (or do not generate) code which maintains an explicit
9346 backchain within the stack frame that points to the caller's frame.
9347 This is currently needed to allow debugging. The default is to
9348 generate the backchain.
9351 @itemx -mno-small-exec
9352 @opindex msmall-exec
9353 @opindex mno-small-exec
9354 Generate (or do not generate) code using the @code{bras} instruction
9355 to do subroutine calls.
9356 This only works reliably if the total executable size does not
9357 exceed 64k. The default is to use the @code{basr} instruction instead,
9358 which does not have this limitation.
9364 When @option{-m31} is specified, generate code compliant to the
9365 Linux for S/390 ABI@. When @option{-m64} is specified, generate
9366 code compliant to the Linux for zSeries ABI@. This allows GCC in
9367 particular to generate 64-bit instructions. For the @samp{s390}
9368 targets, the default is @option{-m31}, while the @samp{s390x}
9369 targets default to @option{-m64}.
9375 Generate (or do not generate) code using the @code{mvcle} instruction
9376 to perform block moves. When @option{-mno-mvcle} is specifed,
9377 use a @code{mvc} loop instead. This is the default.
9383 Print (or do not print) additional debug information when compiling.
9384 The default is to not print debug information.
9389 @subsection CRIS Options
9390 @cindex CRIS Options
9392 These options are defined specifically for the CRIS ports.
9395 @item -march=@var{architecture-type}
9396 @itemx -mcpu=@var{architecture-type}
9399 Generate code for the specified architecture. The choices for
9400 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
9401 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX.
9402 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
9405 @item -mtune=@var{architecture-type}
9407 Tune to @var{architecture-type} everything applicable about the generated
9408 code, except for the ABI and the set of available instructions. The
9409 choices for @var{architecture-type} are the same as for
9410 @option{-march=@var{architecture-type}}.
9412 @item -mmax-stack-frame=@var{n}
9413 @opindex mmax-stack-frame
9414 Warn when the stack frame of a function exceeds @var{n} bytes.
9416 @item -melinux-stacksize=@var{n}
9417 @opindex melinux-stacksize
9418 Only available with the @samp{cris-axis-aout} target. Arranges for
9419 indications in the program to the kernel loader that the stack of the
9420 program should be set to @var{n} bytes.
9426 The options @option{-metrax4} and @option{-metrax100} are synonyms for
9427 @option{-march=v3} and @option{-march=v8} respectively.
9431 Enable CRIS-specific verbose debug-related information in the assembly
9432 code. This option also has the effect to turn off the @samp{#NO_APP}
9433 formatted-code indicator to the assembler at the beginning of the
9438 Do not use condition-code results from previous instruction; always emit
9439 compare and test instructions before use of condition codes.
9441 @item -mno-side-effects
9442 @opindex mno-side-effects
9443 Do not emit instructions with side-effects in addressing modes other than
9447 @itemx -mno-stack-align
9449 @itemx -mno-data-align
9450 @itemx -mconst-align
9451 @itemx -mno-const-align
9452 @opindex mstack-align
9453 @opindex mno-stack-align
9454 @opindex mdata-align
9455 @opindex mno-data-align
9456 @opindex mconst-align
9457 @opindex mno-const-align
9458 These options (no-options) arranges (eliminate arrangements) for the
9459 stack-frame, individual data and constants to be aligned for the maximum
9460 single data access size for the chosen CPU model. The default is to
9461 arrange for 32-bit alignment. ABI details such as structure layout are
9462 not affected by these options.
9470 Similar to the stack- data- and const-align options above, these options
9471 arrange for stack-frame, writable data and constants to all be 32-bit,
9472 16-bit or 8-bit aligned. The default is 32-bit alignment.
9474 @item -mno-prologue-epilogue
9475 @itemx -mprologue-epilogue
9476 @opindex mno-prologue-epilogue
9477 @opindex mprologue-epilogue
9478 With @option{-mno-prologue-epilogue}, the normal function prologue and
9479 epilogue that sets up the stack-frame are omitted and no return
9480 instructions or return sequences are generated in the code. Use this
9481 option only together with visual inspection of the compiled code: no
9482 warnings or errors are generated when call-saved registers must be saved,
9483 or storage for local variable needs to be allocated.
9489 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
9490 instruction sequences that load addresses for functions from the PLT part
9491 of the GOT rather than (traditional on other architectures) calls to the
9492 PLT. The default is @option{-mgotplt}.
9496 Legacy no-op option only recognized with the cris-axis-aout target.
9500 Legacy no-op option only recognized with the cris-axis-elf and
9501 cris-axis-linux-gnu targets.
9505 Only recognized with the cris-axis-aout target, where it selects a
9506 GNU/linux-like multilib, include files and instruction set for
9511 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
9515 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
9516 to link with input-output functions from a simulator library. Code,
9517 initialized data and zero-initialized data are allocated consecutively.
9521 Like @option{-sim}, but pass linker options to locate initialized data at
9522 0x40000000 and zero-initialized data at 0x80000000.
9526 @subsection MMIX Options
9527 @cindex MMIX Options
9529 These options are defined for the MMIX:
9533 @itemx -mno-libfuncs
9535 @opindex mno-libfuncs
9536 Specify that intrinsic library functions are being compiled, passing all
9537 values in registers, no matter the size.
9542 @opindex mno-epsilon
9543 Generate floating-point comparison instructions that compare with respect
9544 to the @code{rE} epsilon register.
9546 @item -mabi=mmixware
9548 @opindex mabi-mmixware
9550 Generate code that passes function parameters and return values that (in
9551 the called function) are seen as registers @code{$0} and up, as opposed to
9552 the GNU ABI which uses global registers @code{$231} and up.
9555 @itemx -mno-zero-extend
9556 @opindex mzero-extend
9557 @opindex mno-zero-extend
9558 When reading data from memory in sizes shorter than 64 bits, use (do not
9559 use) zero-extending load instructions by default, rather than
9560 sign-extending ones.
9563 @itemx -mno-knuthdiv
9565 @opindex mno-knuthdiv
9566 Make the result of a division yielding a remainder have the same sign as
9567 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
9568 remainder follows the sign of the dividend. Both methods are
9569 arithmetically valid, the latter being almost exclusively used.
9571 @item -mtoplevel-symbols
9572 @itemx -mno-toplevel-symbols
9573 @opindex mtoplevel-symbols
9574 @opindex mno-toplevel-symbols
9575 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
9576 code can be used with the @code{PREFIX} assembly directive.
9580 Generate an executable in the ELF format, rather than the default
9581 @samp{mmo} format used by the @command{mmix} simulator.
9583 @item -mbranch-predict
9584 @itemx -mno-branch-predict
9585 @opindex mbranch-predict
9586 @opindex mno-branch-predict
9587 Use (do not use) the probable-branch instructions, when static branch
9588 prediction indicates a probable branch.
9590 @item -mbase-addresses
9591 @itemx -mno-base-addresses
9592 @opindex mbase-addresses
9593 @opindex mno-base-addresses
9594 Generate (do not generate) code that uses @emph{base addresses}. Using a
9595 base address automatically generates a request (handled by the assembler
9596 and the linker) for a constant to be set up in a global register. The
9597 register is used for one or more base address requests within the range 0
9598 to 255 from the value held in the register. The generally leads to short
9599 and fast code, but the number of different data items that can be
9600 addressed is limited. This means that a program that uses lots of static
9601 data may require @option{-mno-base-addresses}.
9604 @itemx -mno-single-exit
9605 @opindex msingle-exit
9606 @opindex mno-single-exit
9607 Force (do not force) generated code to have a single exit point in each
9611 @node PDP-11 Options
9612 @subsection PDP-11 Options
9613 @cindex PDP-11 Options
9615 These options are defined for the PDP-11:
9620 Use hardware FPP floating point. This is the default. (FIS floating
9621 point on the PDP-11/40 is not supported.)
9624 @opindex msoft-float
9625 Do not use hardware floating point.
9629 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
9633 Return floating-point results in memory. This is the default.
9637 Generate code for a PDP-11/40.
9641 Generate code for a PDP-11/45. This is the default.
9645 Generate code for a PDP-11/10.
9647 @item -mbcopy-builtin
9648 @opindex bcopy-builtin
9649 Use inline @code{movstrhi} patterns for copying memory. This is the
9654 Do not use inline @code{movstrhi} patterns for copying memory.
9660 Use 16-bit @code{int}. This is the default.
9666 Use 32-bit @code{int}.
9671 @opindex mno-float32
9672 Use 64-bit @code{float}. This is the default.
9677 @opindex mno-float64
9678 Use 32-bit @code{float}.
9682 Use @code{abshi2} pattern. This is the default.
9686 Do not use @code{abshi2} pattern.
9688 @item -mbranch-expensive
9689 @opindex mbranch-expensive
9690 Pretend that branches are expensive. This is for experimenting with
9691 code generation only.
9693 @item -mbranch-cheap
9694 @opindex mbranch-cheap
9695 Do not pretend that branches are expensive. This is the default.
9699 Generate code for a system with split I&D.
9703 Generate code for a system without split I&D. This is the default.
9707 Use Unix assembler syntax. This is the default when configured for
9712 Use DEC assembler syntax. This is the default when configured for any
9713 PDP-11 target other than @samp{pdp11-*-bsd}.
9716 @node Xstormy16 Options
9717 @subsection Xstormy16 Options
9718 @cindex Xstormy16 Options
9720 These options are defined for Xstormy16:
9725 Choose startup files and linker script suitable for the simulator.
9728 @node Xtensa Options
9729 @subsection Xtensa Options
9730 @cindex Xtensa Options
9732 The Xtensa architecture is designed to support many different
9733 configurations. The compiler's default options can be set to match a
9734 particular Xtensa configuration by copying a configuration file into the
9735 GCC sources when building GCC@. The options below may be used to
9736 override the default options.
9740 @itemx -mlittle-endian
9741 @opindex mbig-endian
9742 @opindex mlittle-endian
9743 Specify big-endian or little-endian byte ordering for the target Xtensa
9749 @opindex mno-density
9750 Enable or disable use of the optional Xtensa code density instructions.
9756 Enable or disable use of the Xtensa MAC16 option. When enabled, GCC
9757 will generate MAC16 instructions from standard C code, with the
9758 limitation that it will use neither the MR register file nor any
9759 instruction that operates on the MR registers. When this option is
9760 disabled, GCC will translate 16-bit multiply/accumulate operations to a
9761 combination of core instructions and library calls, depending on whether
9762 any other multiplier options are enabled.
9768 Enable or disable use of the 16-bit integer multiplier option. When
9769 enabled, the compiler will generate 16-bit multiply instructions for
9770 multiplications of 16 bits or smaller in standard C code. When this
9771 option is disabled, the compiler will either use 32-bit multiply or
9772 MAC16 instructions if they are available or generate library calls to
9773 perform the multiply operations using shifts and adds.
9779 Enable or disable use of the 32-bit integer multiplier option. When
9780 enabled, the compiler will generate 32-bit multiply instructions for
9781 multiplications of 32 bits or smaller in standard C code. When this
9782 option is disabled, the compiler will generate library calls to perform
9783 the multiply operations using either shifts and adds or 16-bit multiply
9784 instructions if they are available.
9790 Enable or disable use of the optional normalization shift amount
9791 (@code{NSA}) instructions to implement the built-in @code{ffs} function.
9797 Enable or disable use of the optional minimum and maximum value
9804 Enable or disable use of the optional sign extend (@code{SEXT})
9808 @itemx -mno-booleans
9810 @opindex mno-booleans
9811 Enable or disable support for the boolean register file used by Xtensa
9812 coprocessors. This is not typically useful by itself but may be
9813 required for other options that make use of the boolean registers (e.g.,
9814 the floating-point option).
9818 @opindex mhard-float
9819 @opindex msoft-float
9820 Enable or disable use of the floating-point option. When enabled, GCC
9821 generates floating-point instructions for 32-bit @code{float}
9822 operations. When this option is disabled, GCC generates library calls
9823 to emulate 32-bit floating-point operations using integer instructions.
9824 Regardless of this option, 64-bit @code{double} operations are always
9825 emulated with calls to library functions.
9828 @itemx -mno-fused-madd
9829 @opindex mfused-madd
9830 @opindex mno-fused-madd
9831 Enable or disable use of fused multiply/add and multiply/subtract
9832 instructions in the floating-point option. This has no effect if the
9833 floating-point option is not also enabled. Disabling fused multiply/add
9834 and multiply/subtract instructions forces the compiler to use separate
9835 instructions for the multiply and add/subtract operations. This may be
9836 desirable in some cases where strict IEEE 754-compliant results are
9837 required: the fused multiply add/subtract instructions do not round the
9838 intermediate result, thereby producing results with @emph{more} bits of
9839 precision than specified by the IEEE standard. Disabling fused multiply
9840 add/subtract instructions also ensures that the program output is not
9841 sensitive to the compiler's ability to combine multiply and add/subtract
9844 @item -mserialize-volatile
9845 @itemx -mno-serialize-volatile
9846 @opindex mserialize-volatile
9847 @opindex mno-serialize-volatile
9848 When this option is enabled, GCC inserts @code{MEMW} instructions before
9849 @code{volatile} memory references to guarantee sequential consistency.
9850 The default is @option{-mserialize-volatile}. Use
9851 @option{-mno-serialize-volatile} to omit the @code{MEMW} instructions.
9853 @item -mtext-section-literals
9854 @itemx -mno-text-section-literals
9855 @opindex mtext-section-literals
9856 @opindex mno-text-section-literals
9857 Control the treatment of literal pools. The default is
9858 @option{-mno-text-section-literals}, which places literals in a separate
9859 section in the output file. This allows the literal pool to be placed
9860 in a data RAM/ROM, and it also allows the linker to combine literal
9861 pools from separate object files to remove redundant literals and
9862 improve code size. With @option{-mtext-section-literals}, the literals
9863 are interspersed in the text section in order to keep them as close as
9864 possible to their references. This may be necessary for large assembly
9867 @item -mtarget-align
9868 @itemx -mno-target-align
9869 @opindex mtarget-align
9870 @opindex mno-target-align
9871 When this option is enabled, GCC instructs the assembler to
9872 automatically align instructions to reduce branch penalties at the
9873 expense of some code density. The assembler attempts to widen density
9874 instructions to align branch targets and the instructions following call
9875 instructions. If there are not enough preceding safe density
9876 instructions to align a target, no widening will be performed. The
9877 default is @option{-mtarget-align}. These options do not affect the
9878 treatment of auto-aligned instructions like @code{LOOP}, which the
9879 assembler will always align, either by widening density instructions or
9880 by inserting no-op instructions.
9883 @itemx -mno-longcalls
9885 @opindex mno-longcalls
9886 When this option is enabled, GCC instructs the assembler to translate
9887 direct calls to indirect calls unless it can determine that the target
9888 of a direct call is in the range allowed by the call instruction. This
9889 translation typically occurs for calls to functions in other source
9890 files. Specifically, the assembler translates a direct @code{CALL}
9891 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
9892 The default is @option{-mno-longcalls}. This option should be used in
9893 programs where the call target can potentially be out of range. This
9894 option is implemented in the assembler, not the compiler, so the
9895 assembly code generated by GCC will still show direct call
9896 instructions---look at the disassembled object code to see the actual
9897 instructions. Note that the assembler will use an indirect call for
9898 every cross-file call, not just those that really will be out of range.
9901 @node Code Gen Options
9902 @section Options for Code Generation Conventions
9903 @cindex code generation conventions
9904 @cindex options, code generation
9905 @cindex run-time options
9907 These machine-independent options control the interface conventions
9908 used in code generation.
9910 Most of them have both positive and negative forms; the negative form
9911 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
9912 one of the forms is listed---the one which is not the default. You
9913 can figure out the other form by either removing @samp{no-} or adding
9918 @opindex fexceptions
9919 Enable exception handling. Generates extra code needed to propagate
9920 exceptions. For some targets, this implies GCC will generate frame
9921 unwind information for all functions, which can produce significant data
9922 size overhead, although it does not affect execution. If you do not
9923 specify this option, GCC will enable it by default for languages like
9924 C++ which normally require exception handling, and disable it for
9925 languages like C that do not normally require it. However, you may need
9926 to enable this option when compiling C code that needs to interoperate
9927 properly with exception handlers written in C++. You may also wish to
9928 disable this option if you are compiling older C++ programs that don't
9929 use exception handling.
9931 @item -fnon-call-exceptions
9932 @opindex fnon-call-exceptions
9933 Generate code that allows trapping instructions to throw exceptions.
9934 Note that this requires platform-specific runtime support that does
9935 not exist everywhere. Moreover, it only allows @emph{trapping}
9936 instructions to throw exceptions, i.e.@: memory references or floating
9937 point instructions. It does not allow exceptions to be thrown from
9938 arbitrary signal handlers such as @code{SIGALRM}.
9940 @item -funwind-tables
9941 @opindex funwind-tables
9942 Similar to @option{-fexceptions}, except that it will just generate any needed
9943 static data, but will not affect the generated code in any other way.
9944 You will normally not enable this option; instead, a language processor
9945 that needs this handling would enable it on your behalf.
9947 @item -fasynchronous-unwind-tables
9948 @opindex funwind-tables
9949 Generate unwind table in dwarf2 format, if supported by target machine. The
9950 table is exact at each instruction boundary, so it can be used for stack
9951 unwinding from asynchronous events (such as debugger or garbage collector).
9953 @item -fpcc-struct-return
9954 @opindex fpcc-struct-return
9955 Return ``short'' @code{struct} and @code{union} values in memory like
9956 longer ones, rather than in registers. This convention is less
9957 efficient, but it has the advantage of allowing intercallability between
9958 GCC-compiled files and files compiled with other compilers, particularly
9959 the Portable C Compiler (pcc).
9961 The precise convention for returning structures in memory depends
9962 on the target configuration macros.
9964 Short structures and unions are those whose size and alignment match
9965 that of some integer type.
9967 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
9968 switch is not binary compatible with code compiled with the
9969 @option{-freg-struct-return} switch.
9970 Use it to conform to a non-default application binary interface.
9972 @item -freg-struct-return
9973 @opindex freg-struct-return
9974 Return @code{struct} and @code{union} values in registers when possible.
9975 This is more efficient for small structures than
9976 @option{-fpcc-struct-return}.
9978 If you specify neither @option{-fpcc-struct-return} nor
9979 @option{-freg-struct-return}, GCC defaults to whichever convention is
9980 standard for the target. If there is no standard convention, GCC
9981 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
9982 the principal compiler. In those cases, we can choose the standard, and
9983 we chose the more efficient register return alternative.
9985 @strong{Warning:} code compiled with the @option{-freg-struct-return}
9986 switch is not binary compatible with code compiled with the
9987 @option{-fpcc-struct-return} switch.
9988 Use it to conform to a non-default application binary interface.
9991 @opindex fshort-enums
9992 Allocate to an @code{enum} type only as many bytes as it needs for the
9993 declared range of possible values. Specifically, the @code{enum} type
9994 will be equivalent to the smallest integer type which has enough room.
9996 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
9997 code that is not binary compatible with code generated without that switch.
9998 Use it to conform to a non-default application binary interface.
10000 @item -fshort-double
10001 @opindex fshort-double
10002 Use the same size for @code{double} as for @code{float}.
10004 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
10005 code that is not binary compatible with code generated without that switch.
10006 Use it to conform to a non-default application binary interface.
10008 @item -fshort-wchar
10009 @opindex fshort-wchar
10010 Override the underlying type for @samp{wchar_t} to be @samp{short
10011 unsigned int} instead of the default for the target. This option is
10012 useful for building programs to run under WINE@.
10014 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
10015 code that is not binary compatible with code generated without that switch.
10016 Use it to conform to a non-default application binary interface.
10018 @item -fshared-data
10019 @opindex fshared-data
10020 Requests that the data and non-@code{const} variables of this
10021 compilation be shared data rather than private data. The distinction
10022 makes sense only on certain operating systems, where shared data is
10023 shared between processes running the same program, while private data
10024 exists in one copy per process.
10027 @opindex fno-common
10028 In C, allocate even uninitialized global variables in the data section of the
10029 object file, rather than generating them as common blocks. This has the
10030 effect that if the same variable is declared (without @code{extern}) in
10031 two different compilations, you will get an error when you link them.
10032 The only reason this might be useful is if you wish to verify that the
10033 program will work on other systems which always work this way.
10037 Ignore the @samp{#ident} directive.
10039 @item -fno-gnu-linker
10040 @opindex fno-gnu-linker
10041 Do not output global initializations (such as C++ constructors and
10042 destructors) in the form used by the GNU linker (on systems where the GNU
10043 linker is the standard method of handling them). Use this option when
10044 you want to use a non-GNU linker, which also requires using the
10045 @command{collect2} program to make sure the system linker includes
10046 constructors and destructors. (@command{collect2} is included in the GCC
10047 distribution.) For systems which @emph{must} use @command{collect2}, the
10048 compiler driver @command{gcc} is configured to do this automatically.
10050 @item -finhibit-size-directive
10051 @opindex finhibit-size-directive
10052 Don't output a @code{.size} assembler directive, or anything else that
10053 would cause trouble if the function is split in the middle, and the
10054 two halves are placed at locations far apart in memory. This option is
10055 used when compiling @file{crtstuff.c}; you should not need to use it
10058 @item -fverbose-asm
10059 @opindex fverbose-asm
10060 Put extra commentary information in the generated assembly code to
10061 make it more readable. This option is generally only of use to those
10062 who actually need to read the generated assembly code (perhaps while
10063 debugging the compiler itself).
10065 @option{-fno-verbose-asm}, the default, causes the
10066 extra information to be omitted and is useful when comparing two assembler
10071 Consider all memory references through pointers to be volatile.
10073 @item -fvolatile-global
10074 @opindex fvolatile-global
10075 Consider all memory references to extern and global data items to
10076 be volatile. GCC does not consider static data items to be volatile
10077 because of this switch.
10079 @item -fvolatile-static
10080 @opindex fvolatile-static
10081 Consider all memory references to static data to be volatile.
10085 @cindex global offset table
10087 Generate position-independent code (PIC) suitable for use in a shared
10088 library, if supported for the target machine. Such code accesses all
10089 constant addresses through a global offset table (GOT)@. The dynamic
10090 loader resolves the GOT entries when the program starts (the dynamic
10091 loader is not part of GCC; it is part of the operating system). If
10092 the GOT size for the linked executable exceeds a machine-specific
10093 maximum size, you get an error message from the linker indicating that
10094 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
10095 instead. (These maximums are 16k on the m88k, 8k on the SPARC, and 32k
10096 on the m68k and RS/6000. The 386 has no such limit.)
10098 Position-independent code requires special support, and therefore works
10099 only on certain machines. For the 386, GCC supports PIC for System V
10100 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
10101 position-independent.
10105 If supported for the target machine, emit position-independent code,
10106 suitable for dynamic linking and avoiding any limit on the size of the
10107 global offset table. This option makes a difference on the m68k, m88k,
10110 Position-independent code requires special support, and therefore works
10111 only on certain machines.
10113 @item -ffixed-@var{reg}
10115 Treat the register named @var{reg} as a fixed register; generated code
10116 should never refer to it (except perhaps as a stack pointer, frame
10117 pointer or in some other fixed role).
10119 @var{reg} must be the name of a register. The register names accepted
10120 are machine-specific and are defined in the @code{REGISTER_NAMES}
10121 macro in the machine description macro file.
10123 This flag does not have a negative form, because it specifies a
10126 @item -fcall-used-@var{reg}
10127 @opindex fcall-used
10128 Treat the register named @var{reg} as an allocable register that is
10129 clobbered by function calls. It may be allocated for temporaries or
10130 variables that do not live across a call. Functions compiled this way
10131 will not save and restore the register @var{reg}.
10133 It is an error to used this flag with the frame pointer or stack pointer.
10134 Use of this flag for other registers that have fixed pervasive roles in
10135 the machine's execution model will produce disastrous results.
10137 This flag does not have a negative form, because it specifies a
10140 @item -fcall-saved-@var{reg}
10141 @opindex fcall-saved
10142 Treat the register named @var{reg} as an allocable register saved by
10143 functions. It may be allocated even for temporaries or variables that
10144 live across a call. Functions compiled this way will save and restore
10145 the register @var{reg} if they use it.
10147 It is an error to used this flag with the frame pointer or stack pointer.
10148 Use of this flag for other registers that have fixed pervasive roles in
10149 the machine's execution model will produce disastrous results.
10151 A different sort of disaster will result from the use of this flag for
10152 a register in which function values may be returned.
10154 This flag does not have a negative form, because it specifies a
10157 @item -fpack-struct
10158 @opindex fpack-struct
10159 Pack all structure members together without holes.
10161 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
10162 code that is not binary compatible with code generated without that switch.
10163 Additionally, it makes the code suboptimial.
10164 Use it to conform to a non-default application binary interface.
10166 @item -finstrument-functions
10167 @opindex finstrument-functions
10168 Generate instrumentation calls for entry and exit to functions. Just
10169 after function entry and just before function exit, the following
10170 profiling functions will be called with the address of the current
10171 function and its call site. (On some platforms,
10172 @code{__builtin_return_address} does not work beyond the current
10173 function, so the call site information may not be available to the
10174 profiling functions otherwise.)
10177 void __cyg_profile_func_enter (void *this_fn,
10179 void __cyg_profile_func_exit (void *this_fn,
10183 The first argument is the address of the start of the current function,
10184 which may be looked up exactly in the symbol table.
10186 This instrumentation is also done for functions expanded inline in other
10187 functions. The profiling calls will indicate where, conceptually, the
10188 inline function is entered and exited. This means that addressable
10189 versions of such functions must be available. If all your uses of a
10190 function are expanded inline, this may mean an additional expansion of
10191 code size. If you use @samp{extern inline} in your C code, an
10192 addressable version of such functions must be provided. (This is
10193 normally the case anyways, but if you get lucky and the optimizer always
10194 expands the functions inline, you might have gotten away without
10195 providing static copies.)
10197 A function may be given the attribute @code{no_instrument_function}, in
10198 which case this instrumentation will not be done. This can be used, for
10199 example, for the profiling functions listed above, high-priority
10200 interrupt routines, and any functions from which the profiling functions
10201 cannot safely be called (perhaps signal handlers, if the profiling
10202 routines generate output or allocate memory).
10204 @item -fstack-check
10205 @opindex fstack-check
10206 Generate code to verify that you do not go beyond the boundary of the
10207 stack. You should specify this flag if you are running in an
10208 environment with multiple threads, but only rarely need to specify it in
10209 a single-threaded environment since stack overflow is automatically
10210 detected on nearly all systems if there is only one stack.
10212 Note that this switch does not actually cause checking to be done; the
10213 operating system must do that. The switch causes generation of code
10214 to ensure that the operating system sees the stack being extended.
10216 @item -fstack-limit-register=@var{reg}
10217 @itemx -fstack-limit-symbol=@var{sym}
10218 @itemx -fno-stack-limit
10219 @opindex fstack-limit-register
10220 @opindex fstack-limit-symbol
10221 @opindex fno-stack-limit
10222 Generate code to ensure that the stack does not grow beyond a certain value,
10223 either the value of a register or the address of a symbol. If the stack
10224 would grow beyond the value, a signal is raised. For most targets,
10225 the signal is raised before the stack overruns the boundary, so
10226 it is possible to catch the signal without taking special precautions.
10228 For instance, if the stack starts at absolute address @samp{0x80000000}
10229 and grows downwards, you can use the flags
10230 @option{-fstack-limit-symbol=__stack_limit} and
10231 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
10232 of 128KB@. Note that this may only work with the GNU linker.
10234 @cindex aliasing of parameters
10235 @cindex parameters, aliased
10236 @item -fargument-alias
10237 @itemx -fargument-noalias
10238 @itemx -fargument-noalias-global
10239 @opindex fargument-alias
10240 @opindex fargument-noalias
10241 @opindex fargument-noalias-global
10242 Specify the possible relationships among parameters and between
10243 parameters and global data.
10245 @option{-fargument-alias} specifies that arguments (parameters) may
10246 alias each other and may alias global storage.@*
10247 @option{-fargument-noalias} specifies that arguments do not alias
10248 each other, but may alias global storage.@*
10249 @option{-fargument-noalias-global} specifies that arguments do not
10250 alias each other and do not alias global storage.
10252 Each language will automatically use whatever option is required by
10253 the language standard. You should not need to use these options yourself.
10255 @item -fleading-underscore
10256 @opindex fleading-underscore
10257 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
10258 change the way C symbols are represented in the object file. One use
10259 is to help link with legacy assembly code.
10261 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
10262 generate code that is not binary compatible with code generated without that
10263 switch. Use it to conform to a non-default application binary interface.
10264 Not all targets provide complete support for this switch.
10266 @item -ftls-model=@var{model}
10267 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
10268 The @var{model} argument should be one of @code{global-dynamic},
10269 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
10271 The default without @option{-fpic} is @code{initial-exec}; with
10272 @option{-fpic} the default is @code{global-dynamic}.
10277 @node Environment Variables
10278 @section Environment Variables Affecting GCC
10279 @cindex environment variables
10281 @c man begin ENVIRONMENT
10283 This section describes several environment variables that affect how GCC
10284 operates. Some of them work by specifying directories or prefixes to use
10285 when searching for various kinds of files. Some are used to specify other
10286 aspects of the compilation environment.
10288 Note that you can also specify places to search using options such as
10289 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
10290 take precedence over places specified using environment variables, which
10291 in turn take precedence over those specified by the configuration of GCC@.
10292 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
10293 GNU Compiler Collection (GCC) Internals}.
10298 @c @itemx LC_COLLATE
10300 @c @itemx LC_MONETARY
10301 @c @itemx LC_NUMERIC
10306 @c @findex LC_COLLATE
10307 @findex LC_MESSAGES
10308 @c @findex LC_MONETARY
10309 @c @findex LC_NUMERIC
10313 These environment variables control the way that GCC uses
10314 localization information that allow GCC to work with different
10315 national conventions. GCC inspects the locale categories
10316 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
10317 so. These locale categories can be set to any value supported by your
10318 installation. A typical value is @samp{en_UK} for English in the United
10321 The @env{LC_CTYPE} environment variable specifies character
10322 classification. GCC uses it to determine the character boundaries in
10323 a string; this is needed for some multibyte encodings that contain quote
10324 and escape characters that would otherwise be interpreted as a string
10327 The @env{LC_MESSAGES} environment variable specifies the language to
10328 use in diagnostic messages.
10330 If the @env{LC_ALL} environment variable is set, it overrides the value
10331 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
10332 and @env{LC_MESSAGES} default to the value of the @env{LANG}
10333 environment variable. If none of these variables are set, GCC
10334 defaults to traditional C English behavior.
10338 If @env{TMPDIR} is set, it specifies the directory to use for temporary
10339 files. GCC uses temporary files to hold the output of one stage of
10340 compilation which is to be used as input to the next stage: for example,
10341 the output of the preprocessor, which is the input to the compiler
10344 @item GCC_EXEC_PREFIX
10345 @findex GCC_EXEC_PREFIX
10346 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
10347 names of the subprograms executed by the compiler. No slash is added
10348 when this prefix is combined with the name of a subprogram, but you can
10349 specify a prefix that ends with a slash if you wish.
10351 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
10352 an appropriate prefix to use based on the pathname it was invoked with.
10354 If GCC cannot find the subprogram using the specified prefix, it
10355 tries looking in the usual places for the subprogram.
10357 The default value of @env{GCC_EXEC_PREFIX} is
10358 @file{@var{prefix}/lib/gcc-lib/} where @var{prefix} is the value
10359 of @code{prefix} when you ran the @file{configure} script.
10361 Other prefixes specified with @option{-B} take precedence over this prefix.
10363 This prefix is also used for finding files such as @file{crt0.o} that are
10366 In addition, the prefix is used in an unusual way in finding the
10367 directories to search for header files. For each of the standard
10368 directories whose name normally begins with @samp{/usr/local/lib/gcc-lib}
10369 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
10370 replacing that beginning with the specified prefix to produce an
10371 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
10372 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
10373 These alternate directories are searched first; the standard directories
10376 @item COMPILER_PATH
10377 @findex COMPILER_PATH
10378 The value of @env{COMPILER_PATH} is a colon-separated list of
10379 directories, much like @env{PATH}. GCC tries the directories thus
10380 specified when searching for subprograms, if it can't find the
10381 subprograms using @env{GCC_EXEC_PREFIX}.
10384 @findex LIBRARY_PATH
10385 The value of @env{LIBRARY_PATH} is a colon-separated list of
10386 directories, much like @env{PATH}. When configured as a native compiler,
10387 GCC tries the directories thus specified when searching for special
10388 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
10389 using GCC also uses these directories when searching for ordinary
10390 libraries for the @option{-l} option (but directories specified with
10391 @option{-L} come first).
10395 @cindex locale definition
10396 This variable is used to pass locale information to the compiler. One way in
10397 which this information is used is to determine the character set to be used
10398 when character literals, string literals and comments are parsed in C and C++.
10399 When the compiler is configured to allow multibyte characters,
10400 the following values for @env{LANG} are recognized:
10404 Recognize JIS characters.
10406 Recognize SJIS characters.
10408 Recognize EUCJP characters.
10411 If @env{LANG} is not defined, or if it has some other value, then the
10412 compiler will use mblen and mbtowc as defined by the default locale to
10413 recognize and translate multibyte characters.
10417 Some additional environments variables affect the behavior of the
10420 @include cppenv.texi
10424 @node Running Protoize
10425 @section Running Protoize
10427 The program @code{protoize} is an optional part of GCC@. You can use
10428 it to add prototypes to a program, thus converting the program to ISO
10429 C in one respect. The companion program @code{unprotoize} does the
10430 reverse: it removes argument types from any prototypes that are found.
10432 When you run these programs, you must specify a set of source files as
10433 command line arguments. The conversion programs start out by compiling
10434 these files to see what functions they define. The information gathered
10435 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
10437 After scanning comes actual conversion. The specified files are all
10438 eligible to be converted; any files they include (whether sources or
10439 just headers) are eligible as well.
10441 But not all the eligible files are converted. By default,
10442 @code{protoize} and @code{unprotoize} convert only source and header
10443 files in the current directory. You can specify additional directories
10444 whose files should be converted with the @option{-d @var{directory}}
10445 option. You can also specify particular files to exclude with the
10446 @option{-x @var{file}} option. A file is converted if it is eligible, its
10447 directory name matches one of the specified directory names, and its
10448 name within the directory has not been excluded.
10450 Basic conversion with @code{protoize} consists of rewriting most
10451 function definitions and function declarations to specify the types of
10452 the arguments. The only ones not rewritten are those for varargs
10455 @code{protoize} optionally inserts prototype declarations at the
10456 beginning of the source file, to make them available for any calls that
10457 precede the function's definition. Or it can insert prototype
10458 declarations with block scope in the blocks where undeclared functions
10461 Basic conversion with @code{unprotoize} consists of rewriting most
10462 function declarations to remove any argument types, and rewriting
10463 function definitions to the old-style pre-ISO form.
10465 Both conversion programs print a warning for any function declaration or
10466 definition that they can't convert. You can suppress these warnings
10469 The output from @code{protoize} or @code{unprotoize} replaces the
10470 original source file. The original file is renamed to a name ending
10471 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
10472 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
10473 for DOS) file already exists, then the source file is simply discarded.
10475 @code{protoize} and @code{unprotoize} both depend on GCC itself to
10476 scan the program and collect information about the functions it uses.
10477 So neither of these programs will work until GCC is installed.
10479 Here is a table of the options you can use with @code{protoize} and
10480 @code{unprotoize}. Each option works with both programs unless
10484 @item -B @var{directory}
10485 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
10486 usual directory (normally @file{/usr/local/lib}). This file contains
10487 prototype information about standard system functions. This option
10488 applies only to @code{protoize}.
10490 @item -c @var{compilation-options}
10491 Use @var{compilation-options} as the options when running @code{gcc} to
10492 produce the @samp{.X} files. The special option @option{-aux-info} is
10493 always passed in addition, to tell @code{gcc} to write a @samp{.X} file.
10495 Note that the compilation options must be given as a single argument to
10496 @code{protoize} or @code{unprotoize}. If you want to specify several
10497 @code{gcc} options, you must quote the entire set of compilation options
10498 to make them a single word in the shell.
10500 There are certain @code{gcc} arguments that you cannot use, because they
10501 would produce the wrong kind of output. These include @option{-g},
10502 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
10503 the @var{compilation-options}, they are ignored.
10506 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
10507 systems) instead of @samp{.c}. This is convenient if you are converting
10508 a C program to C++. This option applies only to @code{protoize}.
10511 Add explicit global declarations. This means inserting explicit
10512 declarations at the beginning of each source file for each function
10513 that is called in the file and was not declared. These declarations
10514 precede the first function definition that contains a call to an
10515 undeclared function. This option applies only to @code{protoize}.
10517 @item -i @var{string}
10518 Indent old-style parameter declarations with the string @var{string}.
10519 This option applies only to @code{protoize}.
10521 @code{unprotoize} converts prototyped function definitions to old-style
10522 function definitions, where the arguments are declared between the
10523 argument list and the initial @samp{@{}. By default, @code{unprotoize}
10524 uses five spaces as the indentation. If you want to indent with just
10525 one space instead, use @option{-i " "}.
10528 Keep the @samp{.X} files. Normally, they are deleted after conversion
10532 Add explicit local declarations. @code{protoize} with @option{-l} inserts
10533 a prototype declaration for each function in each block which calls the
10534 function without any declaration. This option applies only to
10538 Make no real changes. This mode just prints information about the conversions
10539 that would have been done without @option{-n}.
10542 Make no @samp{.save} files. The original files are simply deleted.
10543 Use this option with caution.
10545 @item -p @var{program}
10546 Use the program @var{program} as the compiler. Normally, the name
10547 @file{gcc} is used.
10550 Work quietly. Most warnings are suppressed.
10553 Print the version number, just like @option{-v} for @code{gcc}.
10556 If you need special compiler options to compile one of your program's
10557 source files, then you should generate that file's @samp{.X} file
10558 specially, by running @code{gcc} on that source file with the
10559 appropriate options and the option @option{-aux-info}. Then run
10560 @code{protoize} on the entire set of files. @code{protoize} will use
10561 the existing @samp{.X} file because it is newer than the source file.
10565 gcc -Dfoo=bar file1.c -aux-info file1.X
10570 You need to include the special files along with the rest in the
10571 @code{protoize} command, even though their @samp{.X} files already
10572 exist, because otherwise they won't get converted.
10574 @xref{Protoize Caveats}, for more information on how to use
10575 @code{protoize} successfully.