1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001 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 Free Software Foundation, Inc.
11 Permission is granted to make and distribute verbatim copies of this
12 manual provided the copyright notice and this permission notice are
13 preserved on all copies.
15 Permission is granted to copy and distribute modified versions of this
16 manual under the conditions for verbatim copying, provided also that the
17 entire resulting derived work is distributed under the terms of a
18 permission notice identical to this one.
20 Permission is granted to copy and distribute translations of this manual
21 into another language, under the above conditions for modified versions,
22 except that this permission notice may be included in translations
23 approved by the Free Software Foundation instead of in the original
26 @c Set file name and title for the man page.
28 @settitle GNU project C and C++ compiler
30 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
31 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
32 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
33 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
34 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
35 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
36 [@option{-o} @var{outfile}] @var{infile}@dots{}
38 Only the most useful options are listed here; see below for the
39 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
42 cpp(1), gcov(1), g77(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
43 and the Info entries for @file{gcc}, @file{cpp}, @file{g77}, @file{as},
44 @file{ld}, @file{binutils} and @file{gdb}.
47 For instructions on reporting bugs, see
48 @w{@uref{http://gcc.gnu.org/bugs.html}}. Use of the @command{gccbug}
49 script to report bugs is recommended.
52 See the Info entry for @file{gcc}, or
53 @w{@uref{http://gcc.gnu.org/thanks.html}}, for contributors to GCC@.
58 @chapter GCC Command Options
59 @cindex GCC command options
60 @cindex command options
61 @cindex options, GCC command
63 @c man begin DESCRIPTION
65 When you invoke GCC, it normally does preprocessing, compilation,
66 assembly and linking. The ``overall options'' allow you to stop this
67 process at an intermediate stage. For example, the @option{-c} option
68 says not to run the linker. Then the output consists of object files
69 output by the assembler.
71 Other options are passed on to one stage of processing. Some options
72 control the preprocessor and others the compiler itself. Yet other
73 options control the assembler and linker; most of these are not
74 documented here, since you rarely need to use any of them.
76 @cindex C compilation options
77 Most of the command line options that you can use with GCC are useful
78 for C programs; when an option is only useful with another language
79 (usually C++), the explanation says so explicitly. If the description
80 for a particular option does not mention a source language, you can use
81 that option with all supported languages.
83 @cindex C++ compilation options
84 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
85 options for compiling C++ programs.
87 @cindex grouping options
88 @cindex options, grouping
89 The @command{gcc} program accepts options and file names as operands. Many
90 options have multi-letter names; therefore multiple single-letter options
91 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
94 @cindex order of options
95 @cindex options, order
96 You can mix options and other arguments. For the most part, the order
97 you use doesn't matter. Order does matter when you use several options
98 of the same kind; for example, if you specify @option{-L} more than once,
99 the directories are searched in the order specified.
101 Many options have long names starting with @samp{-f} or with
102 @samp{-W}---for example, @option{-fforce-mem},
103 @option{-fstrength-reduce}, @option{-Wformat} and so on. Most of
104 these have both positive and negative forms; the negative form of
105 @option{-ffoo} would be @option{-fno-foo}. This manual documents
106 only one of these two forms, whichever one is not the default.
110 @xref{Option Index}, for an index to GCC's options.
113 * Option Summary:: Brief list of all options, without explanations.
114 * Overall Options:: Controlling the kind of output:
115 an executable, object files, assembler files,
116 or preprocessed source.
117 * Invoking G++:: Compiling C++ programs.
118 * C Dialect Options:: Controlling the variant of C language compiled.
119 * C++ Dialect Options:: Variations on C++.
120 * Objective-C Dialect Options:: Variations on Objective-C.
121 * Language Independent Options:: Controlling how diagnostics should be
123 * Warning Options:: How picky should the compiler be?
124 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
125 * Optimize Options:: How much optimization?
126 * Preprocessor Options:: Controlling header files and macro definitions.
127 Also, getting dependency information for Make.
128 * Assembler Options:: Passing options to the assembler.
129 * Link Options:: Specifying libraries and so on.
130 * Directory Options:: Where to find header files and libraries.
131 Where to find the compiler executable files.
132 * Spec Files:: How to pass switches to sub-processes.
133 * Target Options:: Running a cross-compiler, or an old version of GCC.
134 * Submodel Options:: Specifying minor hardware or convention variations,
135 such as 68010 vs 68020.
136 * Code Gen Options:: Specifying conventions for function calls, data layout
138 * Environment Variables:: Env vars that affect GCC.
139 * Running Protoize:: Automatically adding or removing function prototypes.
145 @section Option Summary
147 Here is a summary of all the options, grouped by type. Explanations are
148 in the following sections.
151 @item Overall Options
152 @xref{Overall Options,,Options Controlling the Kind of Output}.
154 -c -S -E -o @var{file} -pipe -pass-exit-codes -x @var{language} @gol
155 -v --target-help --help}
157 @item C Language Options
158 @xref{C Dialect Options,,Options Controlling C Dialect}.
160 -ansi -std=@var{standard} -aux-info @var{filename} @gol
161 -fno-asm -fno-builtin @gol
162 -fhosted -ffreestanding @gol
163 -trigraphs -traditional -traditional-cpp @gol
164 -fallow-single-precision -fcond-mismatch @gol
165 -fsigned-bitfields -fsigned-char @gol
166 -funsigned-bitfields -funsigned-char @gol
167 -fwritable-strings -fshort-wchar}
169 @item C++ Language Options
170 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
172 -fno-access-control -fcheck-new -fconserve-space @gol
173 -fno-const-strings -fdollars-in-identifiers @gol
174 -fno-elide-constructors @gol
175 -fno-enforce-eh-specs -fexternal-templates @gol
176 -falt-external-templates @gol
177 -ffor-scope -fno-for-scope -fno-gnu-keywords -fno-honor-std @gol
178 -fno-implicit-templates @gol
179 -fno-implicit-inline-templates @gol
180 -fno-implement-inlines -fms-extensions @gol
181 -fno-nonansi-builtins -fno-operator-names @gol
182 -fno-optional-diags -fpermissive @gol
183 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
184 -fuse-cxa-atexit -fvtable-gc -fno-weak -nostdinc++ @gol
185 -fno-default-inline -Wctor-dtor-privacy @gol
186 -Wnon-virtual-dtor -Wreorder @gol
187 -Weffc++ -Wno-deprecated @gol
188 -Wno-non-template-friend -Wold-style-cast @gol
189 -Woverloaded-virtual -Wno-pmf-conversions @gol
190 -Wsign-promo -Wsynth}
192 @item Objective-C Language Options
193 @xref{Objective-C Dialect Options,,Options Controlling Objective-C Dialect}.
195 -fconstant-string-class=@var{class-name} @gol
196 -fgnu-runtime -fnext-runtime -gen-decls @gol
197 -Wno-protocol -Wselector}
199 @item Language Independent Options
200 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
202 -fmessage-length=@var{n} @gol
203 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}}
205 @item Warning Options
206 @xref{Warning Options,,Options to Request or Suppress Warnings}.
208 -fsyntax-only -pedantic -pedantic-errors @gol
209 -w -W -Wall -Waggregate-return @gol
210 -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
211 -Wconversion -Wdisabled-optimization -Werror @gol
212 -Wfloat-equal -Wformat -Wformat=2 @gol
213 -Wformat-nonliteral -Wformat-security @gol
214 -Wimplicit -Wimplicit-int @gol
215 -Wimplicit-function-declaration @gol
216 -Werror-implicit-function-declaration @gol
217 -Wimport -Winline @gol
218 -Wlarger-than-@var{len} -Wlong-long @gol
219 -Wmain -Wmissing-braces -Wmissing-declarations @gol
220 -Wmissing-format-attribute -Wmissing-noreturn @gol
221 -Wmultichar -Wno-format-extra-args -Wno-format-y2k @gol
222 -Wno-import -Wpacked -Wpadded @gol
223 -Wparentheses -Wpointer-arith -Wredundant-decls @gol
224 -Wreturn-type -Wsequence-point -Wshadow @gol
225 -Wsign-compare -Wswitch -Wsystem-headers @gol
226 -Wtrigraphs -Wundef -Wuninitialized @gol
227 -Wunknown-pragmas -Wunreachable-code @gol
228 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
229 -Wunused-value -Wunused-variable -Wwrite-strings}
231 @item C-only Warning Options
233 -Wbad-function-cast -Wmissing-prototypes -Wnested-externs @gol
234 -Wstrict-prototypes -Wtraditional}
236 @item Debugging Options
237 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
239 -a -ax -d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
240 -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
241 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
242 -fdump-ast-original@r{[}-@var{n}@r{]} -fdump-ast-optimized@r{[}-@var{n}@r{]} @gol
243 -fdump-ast-inlined@r{[}-@var{n}@r{]} @gol
244 -fmem-report -fpretend-float @gol
245 -fprofile-arcs -ftest-coverage -ftime-report @gol
246 -g -g@var{level} -gcoff -gdwarf -gdwarf-1 -gdwarf-1+ -gdwarf-2 @gol
247 -ggdb -gstabs -gstabs+ -gxcoff -gxcoff+ @gol
248 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
249 -print-multi-directory -print-multi-lib @gol
250 -print-prog-name=@var{program} -print-search-dirs -Q @gol
253 @item Optimization Options
254 @xref{Optimize Options,,Options that Control Optimization}.
256 -falign-functions=@var{n} -falign-jumps=@var{n} @gol
257 -falign-labels=@var{n} -falign-loops=@var{n} @gol
258 -fbranch-probabilities -fcaller-saves @gol
259 -fcse-follow-jumps -fcse-skip-blocks -fdata-sections @gol
260 -fdelayed-branch -fdelete-null-pointer-checks @gol
261 -fexpensive-optimizations -ffast-math -ffloat-store @gol
262 -fforce-addr -fforce-mem -ffunction-sections @gol
263 -fgcse -fgcse-lm -fgcse-sm @gol
264 -finline-functions -finline-limit=@var{n} -fkeep-inline-functions @gol
265 -fkeep-static-consts -fmove-all-movables @gol
266 -fno-default-inline -fno-defer-pop @gol
267 -fno-function-cse -fno-guess-branch-probability @gol
268 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
269 -funsafe-math-optimizations -fno-trapping-math @gol
270 -fomit-frame-pointer -foptimize-register-move @gol
271 -foptimize-sibling-calls -freduce-all-givs @gol
272 -fregmove -frename-registers @gol
273 -frerun-cse-after-loop -frerun-loop-opt @gol
274 -fschedule-insns -fschedule-insns2 @gol
275 -fsingle-precision-constant -fssa -fssa-ccp -fssa-dce @gol
276 -fstrength-reduce -fstrict-aliasing -fthread-jumps -ftrapv @gol
277 -funroll-all-loops -funroll-loops @gol
278 --param @var{name}=@var{value}
279 -O -O0 -O1 -O2 -O3 -Os}
281 @item Preprocessor Options
282 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
284 -$ -A@var{question}=@var{answer} -A-@var{question}@r{[}=@var{answer}@r{]} @gol
285 -C -dD -dI -dM -dN @gol
286 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
287 -idirafter @var{dir} @gol
288 -include @var{file} -imacros @var{file} @gol
289 -iprefix @var{file} -iwithprefix @var{dir} @gol
290 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
291 -M -MM -MF -MG -MP -MQ -MT -nostdinc -P -remap @gol
292 -trigraphs -undef -U@var{macro} -Wp,@var{option}}
294 @item Assembler Option
295 @xref{Assembler Options,,Passing Options to the Assembler}.
300 @xref{Link Options,,Options for Linking}.
302 @var{object-file-name} -l@var{library} @gol
303 -nostartfiles -nodefaultlibs -nostdlib @gol
304 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
305 -Wl,@var{option} -Xlinker @var{option} @gol
308 @item Directory Options
309 @xref{Directory Options,,Options for Directory Search}.
311 -B@var{prefix} -I@var{dir} -I- -L@var{dir} -specs=@var{file}}
314 @c I wrote this xref this way to avoid overfull hbox. -- rms
315 @xref{Target Options}.
317 -b @var{machine} -V @var{version}}
319 @item Machine Dependent Options
320 @xref{Submodel Options,,Hardware Models and Configurations}.
321 @emph{M680x0 Options}
323 -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
324 -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol
325 -mfpa -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
326 -malign-int -mstrict-align}
328 @emph{M68hc1x Options}
330 -m6811 -m6812 -m68hc11 -m68hc12 @gol
331 -mauto-incdec -mshort -msoft-reg-count=@var{count}}
339 -mcpu=@var{cpu-type} @gol
340 -mtune=@var{cpu-type} @gol
341 -mcmodel=@var{code-model} @gol
343 -mapp-regs -mbroken-saverestore -mcypress @gol
344 -mepilogue -mfaster-structs -mflat @gol
345 -mfpu -mhard-float -mhard-quad-float @gol
346 -mimpure-text -mlive-g0 -mno-app-regs @gol
347 -mno-epilogue -mno-faster-structs -mno-flat -mno-fpu @gol
348 -mno-impure-text -mno-stack-bias -mno-unaligned-doubles @gol
349 -msoft-float -msoft-quad-float -msparclite -mstack-bias @gol
350 -msupersparc -munaligned-doubles -mv8}
352 @emph{Convex Options}
354 -mc1 -mc2 -mc32 -mc34 -mc38 @gol
355 -margcount -mnoargcount @gol
356 -mlong32 -mlong64 @gol
357 -mvolatile-cache -mvolatile-nocache}
359 @emph{AMD29K Options}
361 -m29000 -m29050 -mbw -mnbw -mdw -mndw @gol
362 -mlarge -mnormal -msmall @gol
363 -mkernel-registers -mno-reuse-arg-regs @gol
364 -mno-stack-check -mno-storem-bug @gol
365 -mreuse-arg-regs -msoft-float -mstack-check @gol
366 -mstorem-bug -muser-registers}
370 -mapcs-frame -mno-apcs-frame @gol
371 -mapcs-26 -mapcs-32 @gol
372 -mapcs-stack-check -mno-apcs-stack-check @gol
373 -mapcs-float -mno-apcs-float @gol
374 -mapcs-reentrant -mno-apcs-reentrant @gol
375 -msched-prolog -mno-sched-prolog @gol
376 -mlittle-endian -mbig-endian -mwords-little-endian @gol
377 -malignment-traps -mno-alignment-traps @gol
378 -msoft-float -mhard-float -mfpe @gol
379 -mthumb-interwork -mno-thumb-interwork @gol
380 -mcpu=@var{name} -march=@var{name} -mfpe=@var{name} @gol
381 -mstructure-size-boundary=@var{n} @gol
382 -mbsd -mxopen -mno-symrename @gol
383 -mabort-on-noreturn @gol
384 -mlong-calls -mno-long-calls @gol
385 -msingle-pic-base -mno-single-pic-base @gol
386 -mpic-register=@var{reg} @gol
387 -mnop-fun-dllimport @gol
388 -mpoke-function-name @gol
390 -mtpcs-frame -mtpcs-leaf-frame @gol
391 -mcaller-super-interworking -mcallee-super-interworking }
393 @emph{MN10200 Options}
397 @emph{MN10300 Options}
399 -mmult-bug -mno-mult-bug @gol
400 -mam33 -mno-am33 @gol
403 @emph{M32R/D Options}
405 -mcode-model=@var{model-type} -msdata=@var{sdata-type} @gol
410 -m88000 -m88100 -m88110 -mbig-pic @gol
411 -mcheck-zero-division -mhandle-large-shift @gol
412 -midentify-revision -mno-check-zero-division @gol
413 -mno-ocs-debug-info -mno-ocs-frame-position @gol
414 -mno-optimize-arg-area -mno-serialize-volatile @gol
415 -mno-underscores -mocs-debug-info @gol
416 -mocs-frame-position -moptimize-arg-area @gol
417 -mserialize-volatile -mshort-data-@var{num} -msvr3 @gol
418 -msvr4 -mtrap-large-shift -muse-div-instruction @gol
419 -mversion-03.00 -mwarn-passed-structs}
421 @emph{RS/6000 and PowerPC Options}
423 -mcpu=@var{cpu-type} @gol
424 -mtune=@var{cpu-type} @gol
425 -mpower -mno-power -mpower2 -mno-power2 @gol
426 -mpowerpc -mpowerpc64 -mno-powerpc @gol
427 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
428 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
429 -mnew-mnemonics -mold-mnemonics @gol
430 -mfull-toc -mminimal-toc -mno-fop-in-toc -mno-sum-in-toc @gol
431 -m64 -m32 -mxl-call -mno-xl-call -mthreads -mpe @gol
432 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
433 -mstring -mno-string -mupdate -mno-update @gol
434 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
435 -mstrict-align -mno-strict-align -mrelocatable @gol
436 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
437 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
438 -mcall-aix -mcall-sysv -mprototype -mno-prototype @gol
439 -msim -mmvme -mads -myellowknife -memb -msdata @gol
440 -msdata=@var{opt} -mvxworks -G @var{num}}
444 -mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs @gol
445 -mfull-fp-blocks -mhc-struct-return -min-line-mul @gol
446 -mminimum-fp-blocks -mnohc-struct-return}
450 -mabicalls -march=@var{cpu-type} -mtune=@var{cpu=type} @gol
451 -mcpu=@var{cpu-type} -membedded-data -muninit-const-in-rodata @gol
452 -membedded-pic -mfp32 -mfp64 -mgas -mgp32 -mgp64 @gol
453 -mgpopt -mhalf-pic -mhard-float -mint64 -mips1 @gol
454 -mips2 -mips3 -mips4 -mlong64 -mlong32 -mlong-calls -mmemcpy @gol
455 -mmips-as -mmips-tfile -mno-abicalls @gol
456 -mno-embedded-data -mno-uninit-const-in-rodata @gol
457 -mno-embedded-pic -mno-gpopt -mno-long-calls @gol
458 -mno-memcpy -mno-mips-tfile -mno-rnames -mno-stats @gol
459 -mrnames -msoft-float @gol
460 -m4650 -msingle-float -mmad @gol
461 -mstats -EL -EB -G @var{num} -nocpp @gol
462 -mabi=32 -mabi=n32 -mabi=64 -mabi=eabi @gol
467 -mcpu=@var{cpu-type} -march=@var{cpu-type} @gol
468 -mintel-syntax -mieee-fp -mno-fancy-math-387 @gol
469 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
470 -mno-wide-multiply -mrtd -malign-double @gol
471 -mpreferred-stack-boundary=@var{num} @gol
472 -mthreads -mno-align-stringops -minline-all-stringops @gol
473 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
474 -m96bit-long-double -mregparm=@var{num} -momit-leaf-frame-pointer}
478 -march=@var{architecture-type} @gol
479 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
480 -mfast-indirect-calls -mgas -mjump-in-delay @gol
481 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
482 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
483 -mno-jump-in-delay -mno-long-load-store @gol
484 -mno-portable-runtime -mno-soft-float @gol
485 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
486 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
487 -mschedule=@var{cpu-type} -mspace-regs}
489 @emph{Intel 960 Options}
491 -m@var{cpu-type} -masm-compat -mclean-linkage @gol
492 -mcode-align -mcomplex-addr -mleaf-procedures @gol
493 -mic-compat -mic2.0-compat -mic3.0-compat @gol
494 -mintel-asm -mno-clean-linkage -mno-code-align @gol
495 -mno-complex-addr -mno-leaf-procedures @gol
496 -mno-old-align -mno-strict-align -mno-tail-call @gol
497 -mnumerics -mold-align -msoft-float -mstrict-align @gol
500 @emph{DEC Alpha Options}
502 -mfp-regs -mno-fp-regs -mno-soft-float -msoft-float @gol
503 -malpha-as -mgas @gol
504 -mieee -mieee-with-inexact -mieee-conformant @gol
505 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
506 -mtrap-precision=@var{mode} -mbuild-constants @gol
507 -mcpu=@var{cpu-type} @gol
508 -mbwx -mno-bwx -mcix -mno-cix -mmax -mno-max @gol
509 -mmemory-latency=@var{time}}
511 @emph{Clipper Options}
515 @emph{H8/300 Options}
517 -mrelax -mh -ms -mint32 -malign-300}
521 -m1 -m2 -m3 -m3e @gol
522 -m4-nofpu -m4-single-only -m4-single -m4 @gol
523 -mb -ml -mdalign -mrelax @gol
524 -mbigtable -mfmovd -mhitachi -mnomacsave @gol
525 -mieee -misize -mpadstruct -mspace @gol
526 -mprefergot -musermode}
528 @emph{System V Options}
530 -Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
535 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
536 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
538 @emph{TMS320C3x/C4x Options}
540 -mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
541 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
542 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
543 -mparallel-insns -mparallel-mpy -mpreserve-float}
547 -mlong-calls -mno-long-calls -mep -mno-ep @gol
548 -mprolog-function -mno-prolog-function -mspace @gol
549 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
554 -m32032 -m32332 -m32532 -m32081 -m32381 @gol
555 -mmult-add -mnomult-add -msoft-float -mrtd -mnortd @gol
556 -mregparam -mnoregparam -msb -mnosb @gol
557 -mbitfield -mnobitfield -mhimem -mnohimem}
561 -mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
562 -mcall-prologues -mno-tablejump -mtiny-stack}
566 -mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
567 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
568 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
569 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
570 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
574 -mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
575 -mvolatile-asm-stop -mb-step -mregister-names -mno-sdata @gol
576 -mconstant-gp -mauto-pic -minline-divide-min-latency @gol
577 -minline-divide-max-throughput -mno-dwarf2-asm @gol
578 -mfixed-range=@var{register-range}}
580 @item Code Generation Options
581 @xref{Code Gen Options,,Options for Code Generation Conventions}.
583 -fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
584 -ffixed-@var{reg} -fexceptions @gol
585 -fnon-call-exceptions -funwind-tables @gol
586 -finhibit-size-directive -finstrument-functions @gol
587 -fcheck-memory-usage -fprefix-function-name @gol
588 -fno-common -fno-ident -fno-gnu-linker @gol
589 -fpcc-struct-return -fpic -fPIC @gol
590 -freg-struct-return -fshared-data -fshort-enums @gol
591 -fshort-double -fvolatile @gol
592 -fvolatile-global -fvolatile-static @gol
593 -fverbose-asm -fpack-struct -fstack-check @gol
594 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
595 -fargument-alias -fargument-noalias @gol
596 -fargument-noalias-global -fleading-underscore}
600 * Overall Options:: Controlling the kind of output:
601 an executable, object files, assembler files,
602 or preprocessed source.
603 * C Dialect Options:: Controlling the variant of C language compiled.
604 * C++ Dialect Options:: Variations on C++.
605 * Objective-C Dialect Options:: Variations on Objective-C.
606 * Language Independent Options:: Controlling how diagnostics should be
608 * Warning Options:: How picky should the compiler be?
609 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
610 * Optimize Options:: How much optimization?
611 * Preprocessor Options:: Controlling header files and macro definitions.
612 Also, getting dependency information for Make.
613 * Assembler Options:: Passing options to the assembler.
614 * Link Options:: Specifying libraries and so on.
615 * Directory Options:: Where to find header files and libraries.
616 Where to find the compiler executable files.
617 * Spec Files:: How to pass switches to sub-processes.
618 * Target Options:: Running a cross-compiler, or an old version of GCC.
621 @node Overall Options
622 @section Options Controlling the Kind of Output
624 Compilation can involve up to four stages: preprocessing, compilation
625 proper, assembly and linking, always in that order. The first three
626 stages apply to an individual source file, and end by producing an
627 object file; linking combines all the object files (those newly
628 compiled, and those specified as input) into an executable file.
630 @cindex file name suffix
631 For any given input file, the file name suffix determines what kind of
636 C source code which must be preprocessed.
639 C source code which should not be preprocessed.
642 C++ source code which should not be preprocessed.
645 Objective-C source code. Note that you must link with the library
646 @file{libobjc.a} to make an Objective-C program work.
649 Objective-C source code which should not be preprocessed.
652 C header file (not to be compiled or linked).
656 @itemx @var{file}.cxx
657 @itemx @var{file}.cpp
658 @itemx @var{file}.c++
660 C++ source code which must be preprocessed. Note that in @samp{.cxx},
661 the last two letters must both be literally @samp{x}. Likewise,
662 @samp{.C} refers to a literal capital C@.
665 @itemx @var{file}.for
666 @itemx @var{file}.FOR
667 Fortran source code which should not be preprocessed.
670 @itemx @var{file}.fpp
671 @itemx @var{file}.FPP
672 Fortran source code which must be preprocessed (with the traditional
676 Fortran source code which must be preprocessed with a RATFOR
677 preprocessor (not included with GCC)@.
679 @xref{Overall Options,,Options Controlling the Kind of Output, g77,
680 Using and Porting GNU Fortran}, for more details of the handling of
683 @c FIXME: Descriptions of Java file types.
689 @c GCC also knows about some suffixes for languages not yet included:
699 @itemx @var{file}.chi
700 CHILL source code (preprocessed with the traditional preprocessor).
706 Assembler code which must be preprocessed.
709 An object file to be fed straight into linking.
710 Any file name with no recognized suffix is treated this way.
714 You can specify the input language explicitly with the @option{-x} option:
717 @item -x @var{language}
718 Specify explicitly the @var{language} for the following input files
719 (rather than letting the compiler choose a default based on the file
720 name suffix). This option applies to all following input files until
721 the next @option{-x} option. Possible values for @var{language} are:
723 c c-header cpp-output
725 objective-c objc-cpp-output
726 assembler assembler-with-cpp
727 f77 f77-cpp-input ratfor
730 @c Also f77-version, for internal use only.
733 Turn off any specification of a language, so that subsequent files are
734 handled according to their file name suffixes (as they are if @option{-x}
735 has not been used at all).
737 @item -pass-exit-codes
738 @opindex pass-exit-codes
739 Normally the @command{gcc} program will exit with the code of 1 if any
740 phase of the compiler returns a non-success return code. If you specify
741 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
742 numerically highest error produced by any phase that returned an error
746 If you only want some of the stages of compilation, you can use
747 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
748 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
749 @command{gcc} is to stop. Note that some combinations (for example,
750 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
755 Compile or assemble the source files, but do not link. The linking
756 stage simply is not done. The ultimate output is in the form of an
757 object file for each source file.
759 By default, the object file name for a source file is made by replacing
760 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
762 Unrecognized input files, not requiring compilation or assembly, are
767 Stop after the stage of compilation proper; do not assemble. The output
768 is in the form of an assembler code file for each non-assembler input
771 By default, the assembler file name for a source file is made by
772 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
774 Input files that don't require compilation are ignored.
778 Stop after the preprocessing stage; do not run the compiler proper. The
779 output is in the form of preprocessed source code, which is sent to the
782 Input files which don't require preprocessing are ignored.
784 @cindex output file option
787 Place output in file @var{file}. This applies regardless to whatever
788 sort of output is being produced, whether it be an executable file,
789 an object file, an assembler file or preprocessed C code.
791 Since only one output file can be specified, it does not make sense to
792 use @option{-o} when compiling more than one input file, unless you are
793 producing an executable file as output.
795 If @option{-o} is not specified, the default is to put an executable file
796 in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in
797 @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and
798 all preprocessed C source on standard output.
802 Print (on standard error output) the commands executed to run the stages
803 of compilation. Also print the version number of the compiler driver
804 program and of the preprocessor and the compiler proper.
808 Use pipes rather than temporary files for communication between the
809 various stages of compilation. This fails to work on some systems where
810 the assembler is unable to read from a pipe; but the GNU assembler has
815 Print (on the standard output) a description of the command line options
816 understood by @command{gcc}. If the @option{-v} option is also specified
817 then @option{--help} will also be passed on to the various processes
818 invoked by @command{gcc}, so that they can display the command line options
819 they accept. If the @option{-W} option is also specified then command
820 line options which have no documentation associated with them will also
825 Print (on the standard output) a description of target specific command
826 line options for each tool.
830 @section Compiling C++ Programs
832 @cindex suffixes for C++ source
833 @cindex C++ source file suffixes
834 C++ source files conventionally use one of the suffixes @samp{.C},
835 @samp{.cc}, @samp{.cpp}, @samp{.c++}, @samp{.cp}, or @samp{.cxx};
836 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
837 files with these names and compiles them as C++ programs even if you
838 call the compiler the same way as for compiling C programs (usually with
839 the name @command{gcc}).
843 However, C++ programs often require class libraries as well as a
844 compiler that understands the C++ language---and under some
845 circumstances, you might want to compile programs from standard input,
846 or otherwise without a suffix that flags them as C++ programs.
847 @command{g++} is a program that calls GCC with the default language
848 set to C++, and automatically specifies linking against the C++
849 library. On many systems, @command{g++} is also
850 installed with the name @command{c++}.
852 @cindex invoking @command{g++}
853 When you compile C++ programs, you may specify many of the same
854 command-line options that you use for compiling programs in any
855 language; or command-line options meaningful for C and related
856 languages; or options that are meaningful only for C++ programs.
857 @xref{C Dialect Options,,Options Controlling C Dialect}, for
858 explanations of options for languages related to C@.
859 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
860 explanations of options that are meaningful only for C++ programs.
862 @node C Dialect Options
863 @section Options Controlling C Dialect
864 @cindex dialect options
865 @cindex language dialect options
866 @cindex options, dialect
868 The following options control the dialect of C (or languages derived
869 from C, such as C++ and Objective-C) that the compiler accepts:
876 In C mode, support all ISO C89 programs. In C++ mode,
877 remove GNU extensions that conflict with ISO C++.
879 This turns off certain features of GCC that are incompatible with ISO
880 C89 (when compiling C code), or of standard C++ (when compiling C++ code),
881 such as the @code{asm} and @code{typeof} keywords, and
882 predefined macros such as @code{unix} and @code{vax} that identify the
883 type of system you are using. It also enables the undesirable and
884 rarely used ISO trigraph feature. For the C compiler,
885 it disables recognition of C++ style @samp{//} comments as well as
886 the @code{inline} keyword.
888 The alternate keywords @code{__asm__}, @code{__extension__},
889 @code{__inline__} and @code{__typeof__} continue to work despite
890 @option{-ansi}. You would not want to use them in an ISO C program, of
891 course, but it is useful to put them in header files that might be included
892 in compilations done with @option{-ansi}. Alternate predefined macros
893 such as @code{__unix__} and @code{__vax__} are also available, with or
894 without @option{-ansi}.
896 The @option{-ansi} option does not cause non-ISO programs to be
897 rejected gratuitously. For that, @option{-pedantic} is required in
898 addition to @option{-ansi}. @xref{Warning Options}.
900 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
901 option is used. Some header files may notice this macro and refrain
902 from declaring certain functions or defining certain macros that the
903 ISO standard doesn't call for; this is to avoid interfering with any
904 programs that might use these names for other things.
906 Functions which would normally be built in but do not have semantics
907 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
908 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
909 built-in functions provided by GCC}, for details of the functions
914 Determine the language standard. This option is currently only
915 supported when compiling C@. A value for this option must be provided;
921 ISO C89 (same as @option{-ansi}).
924 ISO C89 as modified in amendment 1.
930 ISO C99. Note that this standard is not yet fully supported; see
931 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
932 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
935 Default, ISO C89 plus GNU extensions (including some C99 features).
939 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
940 this will become the default. The name @samp{gnu9x} is deprecated.
944 Even when this option is not specified, you can still use some of the
945 features of newer standards in so far as they do not conflict with
946 previous C standards. For example, you may use @code{__restrict__} even
947 when @option{-std=c99} is not specified.
949 The @option{-std} options specifying some version of ISO C have the same
950 effects as @option{-ansi}, except that features that were not in ISO C89
951 but are in the specified version (for example, @samp{//} comments and
952 the @code{inline} keyword in ISO C99) are not disabled.
954 @xref{Standards,,Language Standards Supported by GCC}, for details of
955 these standard versions.
957 @item -aux-info @var{filename}
959 Output to the given filename prototyped declarations for all functions
960 declared and/or defined in a translation unit, including those in header
961 files. This option is silently ignored in any language other than C@.
963 Besides declarations, the file indicates, in comments, the origin of
964 each declaration (source file and line), whether the declaration was
965 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
966 @samp{O} for old, respectively, in the first character after the line
967 number and the colon), and whether it came from a declaration or a
968 definition (@samp{C} or @samp{F}, respectively, in the following
969 character). In the case of function definitions, a K&R-style list of
970 arguments followed by their declarations is also provided, inside
971 comments, after the declaration.
975 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
976 keyword, so that code can use these words as identifiers. You can use
977 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
978 instead. @option{-ansi} implies @option{-fno-asm}.
980 In C++, this switch only affects the @code{typeof} keyword, since
981 @code{asm} and @code{inline} are standard keywords. You may want to
982 use the @option{-fno-gnu-keywords} flag instead, which has the same
983 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
984 switch only affects the @code{asm} and @code{typeof} keywords, since
985 @code{inline} is a standard keyword in ISO C99.
989 @cindex built-in functions
990 Don't recognize built-in functions that do not begin with
991 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
992 functions provided by GCC}, for details of the functions affected,
993 including those which are not built-in functions when @option{-ansi} or
994 @option{-std} options for strict ISO C conformance are used because they
995 do not have an ISO standard meaning.
997 GCC normally generates special code to handle certain built-in functions
998 more efficiently; for instance, calls to @code{alloca} may become single
999 instructions that adjust the stack directly, and calls to @code{memcpy}
1000 may become inline copy loops. The resulting code is often both smaller
1001 and faster, but since the function calls no longer appear as such, you
1002 cannot set a breakpoint on those calls, nor can you change the behavior
1003 of the functions by linking with a different library.
1005 In C++, @option{-fno-builtin} is always in effect. The @option{-fbuiltin}
1006 option has no effect. Therefore, in C++, the only way to get the
1007 optimization benefits of built-in functions is to call the function
1008 using the @samp{__builtin_} prefix. The GNU C++ Standard Library uses
1009 built-in functions to implement many functions (like
1010 @code{std::strchr}), so that you automatically get efficient code.
1014 @cindex hosted environment
1016 Assert that compilation takes place in a hosted environment. This implies
1017 @option{-fbuiltin}. A hosted environment is one in which the
1018 entire standard library is available, and in which @code{main} has a return
1019 type of @code{int}. Examples are nearly everything except a kernel.
1020 This is equivalent to @option{-fno-freestanding}.
1022 @item -ffreestanding
1023 @opindex ffreestanding
1024 @cindex hosted environment
1026 Assert that compilation takes place in a freestanding environment. This
1027 implies @option{-fno-builtin}. A freestanding environment
1028 is one in which the standard library may not exist, and program startup may
1029 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1030 This is equivalent to @option{-fno-hosted}.
1032 @xref{Standards,,Language Standards Supported by GCC}, for details of
1033 freestanding and hosted environments.
1037 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1038 options for strict ISO C conformance) implies @option{-trigraphs}.
1040 @cindex traditional C language
1041 @cindex C language, traditional
1043 @opindex traditional
1044 Attempt to support some aspects of traditional C compilers.
1049 All @code{extern} declarations take effect globally even if they
1050 are written inside of a function definition. This includes implicit
1051 declarations of functions.
1054 The newer keywords @code{typeof}, @code{inline}, @code{signed}, @code{const}
1055 and @code{volatile} are not recognized. (You can still use the
1056 alternative keywords such as @code{__typeof__}, @code{__inline__}, and
1060 Comparisons between pointers and integers are always allowed.
1063 Integer types @code{unsigned short} and @code{unsigned char} promote
1064 to @code{unsigned int}.
1067 Out-of-range floating point literals are not an error.
1070 Certain constructs which ISO regards as a single invalid preprocessing
1071 number, such as @samp{0xe-0xd}, are treated as expressions instead.
1074 String ``constants'' are not necessarily constant; they are stored in
1075 writable space, and identical looking constants are allocated
1076 separately. (This is the same as the effect of
1077 @option{-fwritable-strings}.)
1079 @cindex @code{longjmp} and automatic variables
1081 All automatic variables not declared @code{register} are preserved by
1082 @code{longjmp}. Ordinarily, GNU C follows ISO C: automatic variables
1083 not declared @code{volatile} may be clobbered.
1088 @cindex escape sequences, traditional
1089 The character escape sequences @samp{\x} and @samp{\a} evaluate as the
1090 literal characters @samp{x} and @samp{a} respectively. Without
1091 @w{@option{-traditional}}, @samp{\x} is a prefix for the hexadecimal
1092 representation of a character, and @samp{\a} produces a bell.
1095 You may wish to use @option{-fno-builtin} as well as @option{-traditional}
1096 if your program uses names that are normally GNU C built-in functions for
1097 other purposes of its own.
1099 You cannot use @option{-traditional} if you include any header files that
1100 rely on ISO C features. Some vendors are starting to ship systems with
1101 ISO C header files and you cannot use @option{-traditional} on such
1102 systems to compile files that include any system headers.
1104 The @option{-traditional} option also enables @option{-traditional-cpp},
1105 which is described next.
1107 @item -traditional-cpp
1108 @opindex traditional-cpp
1109 Attempt to support some aspects of traditional C preprocessors.
1114 Comments convert to nothing at all, rather than to a space. This allows
1115 traditional token concatenation.
1118 In a preprocessing directive, the @samp{#} symbol must appear as the first
1119 character of a line.
1122 Macro arguments are recognized within string constants in a macro
1123 definition (and their values are stringified, though without additional
1124 quote marks, when they appear in such a context). The preprocessor
1125 always considers a string constant to end at a newline.
1128 @cindex detecting @w{@option{-traditional}}
1129 The predefined macro @code{__STDC__} is not defined when you use
1130 @option{-traditional}, but @code{__GNUC__} is (since the GNU extensions
1131 which @code{__GNUC__} indicates are not affected by
1132 @option{-traditional}). If you need to write header files that work
1133 differently depending on whether @option{-traditional} is in use, by
1134 testing both of these predefined macros you can distinguish four
1135 situations: GNU C, traditional GNU C, other ISO C compilers, and other
1136 old C compilers. The predefined macro @code{__STDC_VERSION__} is also
1137 not defined when you use @option{-traditional}. @xref{Standard
1138 Predefined,,Standard Predefined Macros,cpp.info,The C Preprocessor},
1139 for more discussion of these and other predefined macros.
1142 @cindex string constants vs newline
1143 @cindex newline vs string constants
1144 The preprocessor considers a string constant to end at a newline (unless
1145 the newline is escaped with @samp{\}). (Without @w{@option{-traditional}},
1146 string constants can contain the newline character as typed.)
1149 @item -fcond-mismatch
1150 @opindex fcond-mismatch
1151 Allow conditional expressions with mismatched types in the second and
1152 third arguments. The value of such an expression is void. This option
1153 is not supported for C++.
1155 @item -funsigned-char
1156 @opindex funsigned-char
1157 Let the type @code{char} be unsigned, like @code{unsigned char}.
1159 Each kind of machine has a default for what @code{char} should
1160 be. It is either like @code{unsigned char} by default or like
1161 @code{signed char} by default.
1163 Ideally, a portable program should always use @code{signed char} or
1164 @code{unsigned char} when it depends on the signedness of an object.
1165 But many programs have been written to use plain @code{char} and
1166 expect it to be signed, or expect it to be unsigned, depending on the
1167 machines they were written for. This option, and its inverse, let you
1168 make such a program work with the opposite default.
1170 The type @code{char} is always a distinct type from each of
1171 @code{signed char} or @code{unsigned char}, even though its behavior
1172 is always just like one of those two.
1175 @opindex fsigned-char
1176 Let the type @code{char} be signed, like @code{signed char}.
1178 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1179 the negative form of @option{-funsigned-char}. Likewise, the option
1180 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1182 @item -fsigned-bitfields
1183 @itemx -funsigned-bitfields
1184 @itemx -fno-signed-bitfields
1185 @itemx -fno-unsigned-bitfields
1186 @opindex fsigned-bitfields
1187 @opindex funsigned-bitfields
1188 @opindex fno-signed-bitfields
1189 @opindex fno-unsigned-bitfields
1190 These options control whether a bit-field is signed or unsigned, when the
1191 declaration does not use either @code{signed} or @code{unsigned}. By
1192 default, such a bit-field is signed, because this is consistent: the
1193 basic integer types such as @code{int} are signed types.
1195 However, when @option{-traditional} is used, bit-fields are all unsigned
1198 @item -fwritable-strings
1199 @opindex fwritable-strings
1200 Store string constants in the writable data segment and don't uniquize
1201 them. This is for compatibility with old programs which assume they can
1202 write into string constants. The option @option{-traditional} also has
1205 Writing into string constants is a very bad idea; ``constants'' should
1208 @item -fallow-single-precision
1209 @opindex fallow-single-precision
1210 Do not promote single precision math operations to double precision,
1211 even when compiling with @option{-traditional}.
1213 Traditional K&R C promotes all floating point operations to double
1214 precision, regardless of the sizes of the operands. On the
1215 architecture for which you are compiling, single precision may be faster
1216 than double precision. If you must use @option{-traditional}, but want
1217 to use single precision operations when the operands are single
1218 precision, use this option. This option has no effect when compiling
1219 with ISO or GNU C conventions (the default).
1222 @opindex fshort-wchar
1223 Override the underlying type for @samp{wchar_t} to be @samp{short
1224 unsigned int} instead of the default for the target. This option is
1225 useful for building programs to run under WINE@.
1228 @node C++ Dialect Options
1229 @section Options Controlling C++ Dialect
1231 @cindex compiler options, C++
1232 @cindex C++ options, command line
1233 @cindex options, C++
1234 This section describes the command-line options that are only meaningful
1235 for C++ programs; but you can also use most of the GNU compiler options
1236 regardless of what language your program is in. For example, you
1237 might compile a file @code{firstClass.C} like this:
1240 g++ -g -frepo -O -c firstClass.C
1244 In this example, only @option{-frepo} is an option meant
1245 only for C++ programs; you can use the other options with any
1246 language supported by GCC@.
1248 Here is a list of options that are @emph{only} for compiling C++ programs:
1251 @item -fno-access-control
1252 @opindex fno-access-control
1253 Turn off all access checking. This switch is mainly useful for working
1254 around bugs in the access control code.
1258 Check that the pointer returned by @code{operator new} is non-null
1259 before attempting to modify the storage allocated. The current Working
1260 Paper requires that @code{operator new} never return a null pointer, so
1261 this check is normally unnecessary.
1263 An alternative to using this option is to specify that your
1264 @code{operator new} does not throw any exceptions; if you declare it
1265 @samp{throw()}, G++ will check the return value. See also @samp{new
1268 @item -fconserve-space
1269 @opindex fconserve-space
1270 Put uninitialized or runtime-initialized global variables into the
1271 common segment, as C does. This saves space in the executable at the
1272 cost of not diagnosing duplicate definitions. If you compile with this
1273 flag and your program mysteriously crashes after @code{main()} has
1274 completed, you may have an object that is being destroyed twice because
1275 two definitions were merged.
1277 This option is no longer useful on most targets, now that support has
1278 been added for putting variables into BSS without making them common.
1280 @item -fno-const-strings
1281 @opindex fno-const-strings
1282 Give string constants type @code{char *} instead of type @code{const
1283 char *}. By default, G++ uses type @code{const char *} as required by
1284 the standard. Even if you use @option{-fno-const-strings}, you cannot
1285 actually modify the value of a string constant, unless you also use
1286 @option{-fwritable-strings}.
1288 This option might be removed in a future release of G++. For maximum
1289 portability, you should structure your code so that it works with
1290 string constants that have type @code{const char *}.
1292 @item -fdollars-in-identifiers
1293 @opindex fdollars-in-identifiers
1294 Accept @samp{$} in identifiers. You can also explicitly prohibit use of
1295 @samp{$} with the option @option{-fno-dollars-in-identifiers}. (GNU C allows
1296 @samp{$} by default on most target systems, but there are a few exceptions.)
1297 Traditional C allowed the character @samp{$} to form part of
1298 identifiers. However, ISO C and C++ forbid @samp{$} in identifiers.
1300 @item -fno-elide-constructors
1301 @opindex fno-elide-constructors
1302 The C++ standard allows an implementation to omit creating a temporary
1303 which is only used to initialize another object of the same type.
1304 Specifying this option disables that optimization, and forces G++ to
1305 call the copy constructor in all cases.
1307 @item -fno-enforce-eh-specs
1308 @opindex fno-enforce-eh-specs
1309 Don't check for violation of exception specifications at runtime. This
1310 option violates the C++ standard, but may be useful for reducing code
1311 size in production builds, much like defining @samp{NDEBUG}. The compiler
1312 will still optimize based on the exception specifications.
1314 @item -fexternal-templates
1315 @opindex fexternal-templates
1316 Cause template instantiations to obey @samp{#pragma interface} and
1317 @samp{implementation}; template instances are emitted or not according
1318 to the location of the template definition. @xref{Template
1319 Instantiation}, for more information.
1321 This option is deprecated.
1323 @item -falt-external-templates
1324 @opindex falt-external-templates
1325 Similar to @option{-fexternal-templates}, but template instances are emitted or
1326 not according to the place where they are first instantiated.
1327 @xref{Template Instantiation}, for more information.
1329 This option is deprecated.
1332 @itemx -fno-for-scope
1334 @opindex fno-for-scope
1335 If @option{-ffor-scope} is specified, the scope of variables declared in
1336 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1337 as specified by the C++ standard.
1338 If @option{-fno-for-scope} is specified, the scope of variables declared in
1339 a @i{for-init-statement} extends to the end of the enclosing scope,
1340 as was the case in old versions of G++, and other (traditional)
1341 implementations of C++.
1343 The default if neither flag is given to follow the standard,
1344 but to allow and give a warning for old-style code that would
1345 otherwise be invalid, or have different behavior.
1347 @item -fno-gnu-keywords
1348 @opindex fno-gnu-keywords
1349 Do not recognize @code{typeof} as a keyword, so that code can use this
1350 word as an identifier. You can use the keyword @code{__typeof__} instead.
1351 @option{-ansi} implies @option{-fno-gnu-keywords}.
1353 @item -fno-honor-std
1354 @opindex fno-honor-std
1355 Ignore @code{namespace std}, instead of treating it as a real namespace.
1356 With this switch, the compiler will ignore
1357 @code{namespace-declarations}, @code{using-declarations},
1358 @code{using-directives}, and @code{namespace-names}, if they involve
1361 This option is only useful if you have manually compiled the C++
1362 run-time library with the same switch. Otherwise, your programs will
1363 not link. The use of this option is not recommended, and the option may
1364 be removed from a future version of G++.
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. This option also implies
1417 @option{-fno-implicit-templates}. @xref{Template Instantiation}, for more
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 -Wctor-dtor-privacy @r{(C++ only)}
1487 @opindex Wctor-dtor-privacy
1488 Warn when a class seems unusable, because all the constructors or
1489 destructors in a class are private and the class has no friends or
1490 public static member functions.
1492 @item -Wnon-virtual-dtor @r{(C++ only)}
1493 @opindex Wnon-virtual-dtor
1494 Warn when a class declares a non-virtual destructor that should probably
1495 be virtual, because it looks like the class will be used polymorphically.
1497 @item -Wreorder @r{(C++ only)}
1499 @cindex reordering, warning
1500 @cindex warning for reordering of member initializers
1501 Warn when the order of member initializers given in the code does not
1502 match the order in which they must be executed. For instance:
1508 A(): j (0), i (1) @{ @}
1512 Here the compiler will warn that the member initializers for @samp{i}
1513 and @samp{j} will be rearranged to match the declaration order of the
1517 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1520 @item -Weffc++ @r{(C++ only)}
1522 Warn about violations of various style guidelines from Scott Meyers'
1523 @cite{Effective C++} books. If you use this option, you should be aware
1524 that the standard library headers do not obey all of these guidelines;
1525 you can use @samp{grep -v} to filter out those warnings.
1527 @item -Wno-deprecated @r{(C++ only)}
1528 @opindex Wno-deprecated
1529 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1531 @item -Wno-non-template-friend @r{(C++ only)}
1532 @opindex Wno-non-template-friend
1533 Disable warnings when non-templatized friend functions are declared
1534 within a template. With the advent of explicit template specification
1535 support in G++, if the name of the friend is an unqualified-id (i.e.,
1536 @samp{friend foo(int)}), the C++ language specification demands that the
1537 friend declare or define an ordinary, nontemplate function. (Section
1538 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1539 could be interpreted as a particular specialization of a templatized
1540 function. Because this non-conforming behavior is no longer the default
1541 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1542 check existing code for potential trouble spots, and is on by default.
1543 This new compiler behavior can be turned off with
1544 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1545 but disables the helpful warning.
1547 @item -Wold-style-cast @r{(C++ only)}
1548 @opindex Wold-style-cast
1549 Warn if an old-style (C-style) cast is used within a C++ program. The
1550 new-style casts (@samp{static_cast}, @samp{reinterpret_cast}, and
1551 @samp{const_cast}) are less vulnerable to unintended effects, and much
1554 @item -Woverloaded-virtual @r{(C++ only)}
1555 @opindex Woverloaded-virtual
1556 @cindex overloaded virtual fn, warning
1557 @cindex warning for overloaded virtual fn
1558 Warn when a function declaration hides virtual functions from a
1559 base class. For example, in:
1566 struct B: public A @{
1571 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1579 will fail to compile.
1581 @item -Wno-pmf-conversions @r{(C++ only)}
1582 @opindex Wno-pmf-conversions
1583 Disable the diagnostic for converting a bound pointer to member function
1586 @item -Wsign-promo @r{(C++ only)}
1587 @opindex Wsign-promo
1588 Warn when overload resolution chooses a promotion from unsigned or
1589 enumeral type to a signed type over a conversion to an unsigned type of
1590 the same size. Previous versions of G++ would try to preserve
1591 unsignedness, but the standard mandates the current behavior.
1593 @item -Wsynth @r{(C++ only)}
1595 @cindex warning for synthesized methods
1596 @cindex synthesized methods, warning
1597 Warn when G++'s synthesis behavior does not match that of cfront. For
1603 A& operator = (int);
1613 In this example, G++ will synthesize a default @samp{A& operator =
1614 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1617 @node Objective-C Dialect Options
1618 @section Options Controlling Objective-C Dialect
1620 @cindex compiler options, Objective-C
1621 @cindex Objective-C options, command line
1622 @cindex options, Objective-C
1623 This section describes the command-line options that are only meaningful
1624 for Objective-C programs; but you can also use most of the GNU compiler
1625 options regardless of what language your program is in. For example,
1626 you might compile a file @code{some_class.m} like this:
1629 gcc -g -fgnu-runtime -O -c some_class.m
1633 In this example, only @option{-fgnu-runtime} is an option meant only for
1634 Objective-C programs; you can use the other options with any language
1637 Here is a list of options that are @emph{only} for compiling Objective-C
1641 @item -fconstant-string-class=@var{class-name}
1642 @opindex fconstant-string-class
1643 Use @var{class-name} as the name of the class to instantiate for each
1644 literal string specified with the syntax @code{@@"@dots{}"}. The default
1645 class name is @code{NXConstantString}.
1648 @opindex fgnu-runtime
1649 Generate object code compatible with the standard GNU Objective-C
1650 runtime. This is the default for most types of systems.
1652 @item -fnext-runtime
1653 @opindex fnext-runtime
1654 Generate output compatible with the NeXT runtime. This is the default
1655 for NeXT-based systems, including Darwin and Mac OS X@.
1659 Dump interface declarations for all classes seen in the source file to a
1660 file named @file{@var{sourcename}.decl}.
1663 @opindex Wno-protocol
1664 Do not warn if methods required by a protocol are not implemented
1665 in the class adopting it.
1669 Warn if a selector has multiple methods of different types defined.
1671 @c not documented because only avail via -Wp
1672 @c @item -print-objc-runtime-info
1676 @node Language Independent Options
1677 @section Options to Control Diagnostic Messages Formatting
1678 @cindex options to control diagnostics formatting
1679 @cindex diagnostic messages
1680 @cindex message formatting
1682 Traditionally, diagnostic messages have been formatted irrespective of
1683 the output device's aspect (e.g.@: its width, @dots{}). The options described
1684 below can be used to control the diagnostic messages formatting
1685 algorithm, e.g.@: how many characters per line, how often source location
1686 information should be reported. Right now, only the C++ front end can
1687 honor these options. However it is expected, in the near future, that
1688 the remaining front ends would be able to digest them correctly.
1691 @item -fmessage-length=@var{n}
1692 @opindex fmessage-length
1693 Try to format error messages so that they fit on lines of about @var{n}
1694 characters. The default is 72 characters for @command{g++} and 0 for the rest of
1695 the front ends supported by GCC@. If @var{n} is zero, then no
1696 line-wrapping will be done; each error message will appear on a single
1699 @opindex fdiagnostics-show-location
1700 @item -fdiagnostics-show-location=once
1701 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
1702 reporter to emit @emph{once} source location information; that is, in
1703 case the message is too long to fit on a single physical line and has to
1704 be wrapped, the source location won't be emitted (as prefix) again,
1705 over and over, in subsequent continuation lines. This is the default
1708 @item -fdiagnostics-show-location=every-line
1709 Only meaningful in line-wrapping mode. Instructs the diagnostic
1710 messages reporter to emit the same source location information (as
1711 prefix) for physical lines that result from the process of breaking a
1712 a message which is too long to fit on a single line.
1716 @node Warning Options
1717 @section Options to Request or Suppress Warnings
1718 @cindex options to control warnings
1719 @cindex warning messages
1720 @cindex messages, warning
1721 @cindex suppressing warnings
1723 Warnings are diagnostic messages that report constructions which
1724 are not inherently erroneous but which are risky or suggest there
1725 may have been an error.
1727 You can request many specific warnings with options beginning @samp{-W},
1728 for example @option{-Wimplicit} to request warnings on implicit
1729 declarations. Each of these specific warning options also has a
1730 negative form beginning @samp{-Wno-} to turn off warnings;
1731 for example, @option{-Wno-implicit}. This manual lists only one of the
1732 two forms, whichever is not the default.
1734 These options control the amount and kinds of warnings produced by GCC:
1737 @cindex syntax checking
1739 @opindex fsyntax-only
1740 Check the code for syntax errors, but don't do anything beyond that.
1744 Issue all the warnings demanded by strict ISO C and ISO C++;
1745 reject all programs that use forbidden extensions, and some other
1746 programs that do not follow ISO C and ISO C++. For ISO C, follows the
1747 version of the ISO C standard specified by any @option{-std} option used.
1749 Valid ISO C and ISO C++ programs should compile properly with or without
1750 this option (though a rare few will require @option{-ansi} or a
1751 @option{-std} option specifying the required version of ISO C)@. However,
1752 without this option, certain GNU extensions and traditional C and C++
1753 features are supported as well. With this option, they are rejected.
1755 @option{-pedantic} does not cause warning messages for use of the
1756 alternate keywords whose names begin and end with @samp{__}. Pedantic
1757 warnings are also disabled in the expression that follows
1758 @code{__extension__}. However, only system header files should use
1759 these escape routes; application programs should avoid them.
1760 @xref{Alternate Keywords}.
1762 Some users try to use @option{-pedantic} to check programs for strict ISO
1763 C conformance. They soon find that it does not do quite what they want:
1764 it finds some non-ISO practices, but not all---only those for which
1765 ISO C @emph{requires} a diagnostic, and some others for which
1766 diagnostics have been added.
1768 A feature to report any failure to conform to ISO C might be useful in
1769 some instances, but would require considerable additional work and would
1770 be quite different from @option{-pedantic}. We don't have plans to
1771 support such a feature in the near future.
1773 Where the standard specified with @option{-std} represents a GNU
1774 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
1775 corresponding @dfn{base standard}, the version of ISO C on which the GNU
1776 extended dialect is based. Warnings from @option{-pedantic} are given
1777 where they are required by the base standard. (It would not make sense
1778 for such warnings to be given only for features not in the specified GNU
1779 C dialect, since by definition the GNU dialects of C include all
1780 features the compiler supports with the given option, and there would be
1781 nothing to warn about.)
1783 @item -pedantic-errors
1784 @opindex pedantic-errors
1785 Like @option{-pedantic}, except that errors are produced rather than
1790 Inhibit all warning messages.
1794 Inhibit warning messages about the use of @samp{#import}.
1796 @item -Wchar-subscripts
1797 @opindex Wchar-subscripts
1798 Warn if an array subscript has type @code{char}. This is a common cause
1799 of error, as programmers often forget that this type is signed on some
1804 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
1805 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
1809 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
1810 the arguments supplied have types appropriate to the format string
1811 specified, and that the conversions specified in the format string make
1812 sense. This includes standard functions, and others specified by format
1813 attributes (@pxref{Function Attributes}), in the @code{printf},
1814 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
1815 not in the C standard) families.
1817 The formats are checked against the format features supported by GNU
1818 libc version 2.2. These include all ISO C89 and C99 features, as well
1819 as features from the Single Unix Specification and some BSD and GNU
1820 extensions. Other library implementations may not support all these
1821 features; GCC does not support warning about features that go beyond a
1822 particular library's limitations. However, if @option{-pedantic} is used
1823 with @option{-Wformat}, warnings will be given about format features not
1824 in the selected standard version (but not for @code{strfmon} formats,
1825 since those are not in any version of the C standard). @xref{C Dialect
1826 Options,,Options Controlling C Dialect}.
1828 @option{-Wformat} is included in @option{-Wall}. For more control over some
1829 aspects of format checking, the options @option{-Wno-format-y2k},
1830 @option{-Wno-format-extra-args}, @option{-Wformat-nonliteral},
1831 @option{-Wformat-security} and @option{-Wformat=2} are available, but are
1832 not included in @option{-Wall}.
1834 @item -Wno-format-y2k
1835 @opindex Wno-format-y2k
1836 If @option{-Wformat} is specified, do not warn about @code{strftime}
1837 formats which may yield only a two-digit year.
1839 @item -Wno-format-extra-args
1840 @opindex Wno-format-extra-args
1841 If @option{-Wformat} is specified, do not warn about excess arguments to a
1842 @code{printf} or @code{scanf} format function. The C standard specifies
1843 that such arguments are ignored.
1845 @item -Wformat-nonliteral
1846 @opindex Wformat-nonliteral
1847 If @option{-Wformat} is specified, also warn if the format string is not a
1848 string literal and so cannot be checked, unless the format function
1849 takes its format arguments as a @code{va_list}.
1851 @item -Wformat-security
1852 @opindex Wformat-security
1853 If @option{-Wformat} is specified, also warn about uses of format
1854 functions that represent possible security problems. At present, this
1855 warns about calls to @code{printf} and @code{scanf} functions where the
1856 format string is not a string literal and there are no format arguments,
1857 as in @code{printf (foo);}. This may be a security hole if the format
1858 string came from untrusted input and contains @samp{%n}. (This is
1859 currently a subset of what @option{-Wformat-nonliteral} warns about, but
1860 in future warnings may be added to @option{-Wformat-security} that are not
1861 included in @option{-Wformat-nonliteral}.)
1865 Enable @option{-Wformat} plus format checks not included in
1866 @option{-Wformat}. Currently equivalent to @samp{-Wformat
1867 -Wformat-nonliteral -Wformat-security}.
1869 @item -Wimplicit-int
1870 @opindex Wimplicit-int
1871 Warn when a declaration does not specify a type.
1873 @item -Wimplicit-function-declaration
1874 @itemx -Werror-implicit-function-declaration
1875 @opindex Wimplicit-function-declaration
1876 @opindex Werror-implicit-function-declaration
1877 Give a warning (or error) whenever a function is used before being
1882 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
1886 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
1887 function with external linkage, returning int, taking either zero
1888 arguments, two, or three arguments of appropriate types.
1890 @item -Wmissing-braces
1891 @opindex Wmissing-braces
1892 Warn if an aggregate or union initializer is not fully bracketed. In
1893 the following example, the initializer for @samp{a} is not fully
1894 bracketed, but that for @samp{b} is fully bracketed.
1897 int a[2][2] = @{ 0, 1, 2, 3 @};
1898 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
1903 Warn if a multicharacter constant (@samp{'FOOF'}) is used. Usually they
1904 indicate a typo in the user's code, as they have implementation-defined
1905 values, and should not be used in portable code.
1908 @opindex Wparentheses
1909 Warn if parentheses are omitted in certain contexts, such
1910 as when there is an assignment in a context where a truth value
1911 is expected, or when operators are nested whose precedence people
1912 often get confused about.
1914 Also warn about constructions where there may be confusion to which
1915 @code{if} statement an @code{else} branch belongs. Here is an example of
1930 In C, every @code{else} branch belongs to the innermost possible @code{if}
1931 statement, which in this example is @code{if (b)}. This is often not
1932 what the programmer expected, as illustrated in the above example by
1933 indentation the programmer chose. When there is the potential for this
1934 confusion, GCC will issue a warning when this flag is specified.
1935 To eliminate the warning, add explicit braces around the innermost
1936 @code{if} statement so there is no way the @code{else} could belong to
1937 the enclosing @code{if}. The resulting code would look like this:
1953 @item -Wsequence-point
1954 @opindex Wsequence-point
1955 Warn about code that may have undefined semantics because of violations
1956 of sequence point rules in the C standard.
1958 The C standard defines the order in which expressions in a C program are
1959 evaluated in terms of @dfn{sequence points}, which represent a partial
1960 ordering between the execution of parts of the program: those executed
1961 before the sequence point, and those executed after it. These occur
1962 after the evaluation of a full expression (one which is not part of a
1963 larger expression), after the evaluation of the first operand of a
1964 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
1965 function is called (but after the evaluation of its arguments and the
1966 expression denoting the called function), and in certain other places.
1967 Other than as expressed by the sequence point rules, the order of
1968 evaluation of subexpressions of an expression is not specified. All
1969 these rules describe only a partial order rather than a total order,
1970 since, for example, if two functions are called within one expression
1971 with no sequence point between them, the order in which the functions
1972 are called is not specified. However, the standards committee have
1973 ruled that function calls do not overlap.
1975 It is not specified when between sequence points modifications to the
1976 values of objects take effect. Programs whose behavior depends on this
1977 have undefined behavior; the C standard specifies that ``Between the
1978 previous and next sequence point an object shall have its stored value
1979 modified at most once by the evaluation of an expression. Furthermore,
1980 the prior value shall be read only to determine the value to be
1981 stored.''. If a program breaks these rules, the results on any
1982 particular implementation are entirely unpredictable.
1984 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
1985 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
1986 diagnosed by this option, and it may give an occasional false positive
1987 result, but in general it has been found fairly effective at detecting
1988 this sort of problem in programs.
1990 The present implementation of this option only works for C programs. A
1991 future implementation may also work for C++ programs.
1993 There is some controversy over the precise meaning of the sequence point
1994 rules in subtle cases. Links to papers with alternative formal definitions
1995 and other related discussions may be found on our readings page
1996 @w{@uref{http://gcc.gnu.org/readings.html}}.
1999 @opindex Wreturn-type
2000 Warn whenever a function is defined with a return-type that defaults to
2001 @code{int}. Also warn about any @code{return} statement with no
2002 return-value in a function whose return-type is not @code{void}.
2004 For C++, a function without return type always produces a diagnostic
2005 message, even when @option{-Wno-return-type} is specified. The only
2006 exceptions are @samp{main} and functions defined in system headers.
2010 Warn whenever a @code{switch} statement has an index of enumeral type
2011 and lacks a @code{case} for one or more of the named codes of that
2012 enumeration. (The presence of a @code{default} label prevents this
2013 warning.) @code{case} labels outside the enumeration range also
2014 provoke warnings when this option is used.
2018 Warn if any trigraphs are encountered that might change the meaning of
2019 the program (trigraphs within comments are not warned about).
2021 @item -Wunused-function
2022 @opindex Wunused-function
2023 Warn whenever a static function is declared but not defined or a
2024 non\-inline static function is unused.
2026 @item -Wunused-label
2027 @opindex Wunused-label
2028 Warn whenever a label is declared but not used.
2030 To suppress this warning use the @samp{unused} attribute
2031 (@pxref{Variable Attributes}).
2033 @item -Wunused-parameter
2034 @opindex Wunused-parameter
2035 Warn whenever a function parameter is unused aside from its declaration.
2037 To suppress this warning use the @samp{unused} attribute
2038 (@pxref{Variable Attributes}).
2040 @item -Wunused-variable
2041 @opindex Wunused-variable
2042 Warn whenever a local variable or non-constant static variable is unused
2043 aside from its declaration
2045 To suppress this warning use the @samp{unused} attribute
2046 (@pxref{Variable Attributes}).
2048 @item -Wunused-value
2049 @opindex Wunused-value
2050 Warn whenever a statement computes a result that is explicitly not used.
2052 To suppress this warning cast the expression to @samp{void}.
2056 All all the above @option{-Wunused} options combined.
2058 In order to get a warning about an unused function parameter, you must
2059 either specify @samp{-W -Wunused} or separately specify
2060 @option{-Wunused-parameter}.
2062 @item -Wuninitialized
2063 @opindex Wuninitialized
2064 Warn if an automatic variable is used without first being initialized or
2065 if a variable may be clobbered by a @code{setjmp} call.
2067 These warnings are possible only in optimizing compilation,
2068 because they require data flow information that is computed only
2069 when optimizing. If you don't specify @option{-O}, you simply won't
2072 These warnings occur only for variables that are candidates for
2073 register allocation. Therefore, they do not occur for a variable that
2074 is declared @code{volatile}, or whose address is taken, or whose size
2075 is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
2076 structures, unions or arrays, even when they are in registers.
2078 Note that there may be no warning about a variable that is used only
2079 to compute a value that itself is never used, because such
2080 computations may be deleted by data flow analysis before the warnings
2083 These warnings are made optional because GCC is not smart
2084 enough to see all the reasons why the code might be correct
2085 despite appearing to have an error. Here is one example of how
2106 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2107 always initialized, but GCC doesn't know this. Here is
2108 another common case:
2113 if (change_y) save_y = y, y = new_y;
2115 if (change_y) y = save_y;
2120 This has no bug because @code{save_y} is used only if it is set.
2122 @cindex @code{longjmp} warnings
2123 This option also warns when a non-volatile automatic variable might be
2124 changed by a call to @code{longjmp}. These warnings as well are possible
2125 only in optimizing compilation.
2127 The compiler sees only the calls to @code{setjmp}. It cannot know
2128 where @code{longjmp} will be called; in fact, a signal handler could
2129 call it at any point in the code. As a result, you may get a warning
2130 even when there is in fact no problem because @code{longjmp} cannot
2131 in fact be called at the place which would cause a problem.
2133 Some spurious warnings can be avoided if you declare all the functions
2134 you use that never return as @code{noreturn}. @xref{Function
2137 @item -Wreorder @r{(C++ only)}
2139 @cindex reordering, warning
2140 @cindex warning for reordering of member initializers
2141 Warn when the order of member initializers given in the code does not
2142 match the order in which they must be executed. For instance:
2144 @item -Wunknown-pragmas
2145 @opindex Wunknown-pragmas
2146 @cindex warning for unknown pragmas
2147 @cindex unknown pragmas, warning
2148 @cindex pragmas, warning of unknown
2149 Warn when a #pragma directive is encountered which is not understood by
2150 GCC@. If this command line option is used, warnings will even be issued
2151 for unknown pragmas in system header files. This is not the case if
2152 the warnings were only enabled by the @option{-Wall} command line option.
2156 All of the above @samp{-W} options combined. This enables all the
2157 warnings about constructions that some users consider questionable, and
2158 that are easy to avoid (or modify to prevent the warning), even in
2159 conjunction with macros.
2161 @item -Wsystem-headers
2162 @opindex Wsystem-headers
2163 @cindex warnings from system headers
2164 @cindex system headers, warnings from
2165 Print warning messages for constructs found in system header files.
2166 Warnings from system headers are normally suppressed, on the assumption
2167 that they usually do not indicate real problems and would only make the
2168 compiler output harder to read. Using this command line option tells
2169 GCC to emit warnings from system headers as if they occurred in user
2170 code. However, note that using @option{-Wall} in conjunction with this
2171 option will @emph{not} warn about unknown pragmas in system
2172 headers---for that, @option{-Wunknown-pragmas} must also be used.
2175 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2176 Some of them warn about constructions that users generally do not
2177 consider questionable, but which occasionally you might wish to check
2178 for; others warn about constructions that are necessary or hard to avoid
2179 in some cases, and there is no simple way to modify the code to suppress
2185 Print extra warning messages for these events:
2189 A function can return either with or without a value. (Falling
2190 off the end of the function body is considered returning without
2191 a value.) For example, this function would evoke such a
2205 An expression-statement or the left-hand side of a comma expression
2206 contains no side effects.
2207 To suppress the warning, cast the unused expression to void.
2208 For example, an expression such as @samp{x[i,j]} will cause a warning,
2209 but @samp{x[(void)i,j]} will not.
2212 An unsigned value is compared against zero with @samp{<} or @samp{<=}.
2215 A comparison like @samp{x<=y<=z} appears; this is equivalent to
2216 @samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from
2217 that of ordinary mathematical notation.
2220 Storage-class specifiers like @code{static} are not the first things in
2221 a declaration. According to the C Standard, this usage is obsolescent.
2224 The return type of a function has a type qualifier such as @code{const}.
2225 Such a type qualifier has no effect, since the value returned by a
2226 function is not an lvalue. (But don't warn about the GNU extension of
2227 @code{volatile void} return types. That extension will be warned about
2228 if @option{-pedantic} is specified.)
2231 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2235 A comparison between signed and unsigned values could produce an
2236 incorrect result when the signed value is converted to unsigned.
2237 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2240 An aggregate has a partly bracketed initializer.
2241 For example, the following code would evoke such a warning,
2242 because braces are missing around the initializer for @code{x.h}:
2245 struct s @{ int f, g; @};
2246 struct t @{ struct s h; int i; @};
2247 struct t x = @{ 1, 2, 3 @};
2251 An aggregate has an initializer which does not initialize all members.
2252 For example, the following code would cause such a warning, because
2253 @code{x.h} would be implicitly initialized to zero:
2256 struct s @{ int f, g, h; @};
2257 struct s x = @{ 3, 4 @};
2262 @opindex Wfloat-equal
2263 Warn if floating point values are used in equality comparisons.
2265 The idea behind this is that sometimes it is convenient (for the
2266 programmer) to consider floating-point values as approximations to
2267 infinitely precise real numbers. If you are doing this, then you need
2268 to compute (by analysing the code, or in some other way) the maximum or
2269 likely maximum error that the computation introduces, and allow for it
2270 when performing comparisons (and when producing output, but that's a
2271 different problem). In particular, instead of testing for equality, you
2272 would check to see whether the two values have ranges that overlap; and
2273 this is done with the relational operators, so equality comparisons are
2276 @item -Wtraditional @r{(C only)}
2277 @opindex Wtraditional
2278 Warn about certain constructs that behave differently in traditional and
2279 ISO C@. Also warn about ISO C constructs that have no traditional C
2280 equivalent, and/or problematic constructs which should be avoided.
2284 Macro parameters that appear within string literals in the macro body.
2285 In traditional C macro replacement takes place within string literals,
2286 but does not in ISO C@.
2289 In traditional C, some preprocessor directives did not exist.
2290 Traditional preprocessors would only consider a line to be a directive
2291 if the @samp{#} appeared in column 1 on the line. Therefore
2292 @option{-Wtraditional} warns about directives that traditional C
2293 understands but would ignore because the @samp{#} does not appear as the
2294 first character on the line. It also suggests you hide directives like
2295 @samp{#pragma} not understood by traditional C by indenting them. Some
2296 traditional implementations would not recognise @samp{#elif}, so it
2297 suggests avoiding it altogether.
2300 A function-like macro that appears without arguments.
2303 The unary plus operator.
2306 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2307 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2308 constants.) Note, these suffixes appear in macros defined in the system
2309 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2310 Use of these macros in user code might normally lead to spurious
2311 warnings, however gcc's integrated preprocessor has enough context to
2312 avoid warning in these cases.
2315 A function declared external in one block and then used after the end of
2319 A @code{switch} statement has an operand of type @code{long}.
2322 A non-@code{static} function declaration follows a @code{static} one.
2323 This construct is not accepted by some traditional C compilers.
2326 The ISO type of an integer constant has a different width or
2327 signedness from its traditional type. This warning is only issued if
2328 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2329 typically represent bit patterns, are not warned about.
2332 Usage of ISO string concatenation is detected.
2335 Initialization of automatic aggregates.
2338 Identifier conflicts with labels. Traditional C lacks a separate
2339 namespace for labels.
2342 Initialization of unions. If the initializer is zero, the warning is
2343 omitted. This is done under the assumption that the zero initializer in
2344 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2345 initializer warnings and relies on default initialization to zero in the
2349 Conversions by prototypes between fixed/floating point values and vice
2350 versa. The absence of these prototypes when compiling with traditional
2351 C would cause serious problems. This is a subset of the possible
2352 conversion warnings, for the full set use @option{-Wconversion}.
2357 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
2361 Warn whenever a local variable shadows another local variable, parameter or
2362 global variable or whenever a built-in function is shadowed.
2364 @item -Wlarger-than-@var{len}
2365 @opindex Wlarger-than
2366 Warn whenever an object of larger than @var{len} bytes is defined.
2368 @item -Wpointer-arith
2369 @opindex Wpointer-arith
2370 Warn about anything that depends on the ``size of'' a function type or
2371 of @code{void}. GNU C assigns these types a size of 1, for
2372 convenience in calculations with @code{void *} pointers and pointers
2375 @item -Wbad-function-cast @r{(C only)}
2376 @opindex Wbad-function-cast
2377 Warn whenever a function call is cast to a non-matching type.
2378 For example, warn if @code{int malloc()} is cast to @code{anything *}.
2382 Warn whenever a pointer is cast so as to remove a type qualifier from
2383 the target type. For example, warn if a @code{const char *} is cast
2384 to an ordinary @code{char *}.
2387 @opindex Wcast-align
2388 Warn whenever a pointer is cast such that the required alignment of the
2389 target is increased. For example, warn if a @code{char *} is cast to
2390 an @code{int *} on machines where integers can only be accessed at
2391 two- or four-byte boundaries.
2393 @item -Wwrite-strings
2394 @opindex Wwrite-strings
2395 When compiling C, give string constants the type @code{const
2396 char[@var{length}]} so that
2397 copying the address of one into a non-@code{const} @code{char *}
2398 pointer will get a warning; when compiling C++, warn about the
2399 deprecated conversion from string constants to @code{char *}.
2400 These warnings will help you find at
2401 compile time code that can try to write into a string constant, but
2402 only if you have been very careful about using @code{const} in
2403 declarations and prototypes. Otherwise, it will just be a nuisance;
2404 this is why we did not make @option{-Wall} request these warnings.
2407 @opindex Wconversion
2408 Warn if a prototype causes a type conversion that is different from what
2409 would happen to the same argument in the absence of a prototype. This
2410 includes conversions of fixed point to floating and vice versa, and
2411 conversions changing the width or signedness of a fixed point argument
2412 except when the same as the default promotion.
2414 Also, warn if a negative integer constant expression is implicitly
2415 converted to an unsigned type. For example, warn about the assignment
2416 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
2417 casts like @code{(unsigned) -1}.
2419 @item -Wsign-compare
2420 @opindex Wsign-compare
2421 @cindex warning for comparison of signed and unsigned values
2422 @cindex comparison of signed and unsigned values, warning
2423 @cindex signed and unsigned values, comparison warning
2424 Warn when a comparison between signed and unsigned values could produce
2425 an incorrect result when the signed value is converted to unsigned.
2426 This warning is also enabled by @option{-W}; to get the other warnings
2427 of @option{-W} without this warning, use @samp{-W -Wno-sign-compare}.
2429 @item -Waggregate-return
2430 @opindex Waggregate-return
2431 Warn if any functions that return structures or unions are defined or
2432 called. (In languages where you can return an array, this also elicits
2435 @item -Wstrict-prototypes @r{(C only)}
2436 @opindex Wstrict-prototypes
2437 Warn if a function is declared or defined without specifying the
2438 argument types. (An old-style function definition is permitted without
2439 a warning if preceded by a declaration which specifies the argument
2442 @item -Wmissing-prototypes @r{(C only)}
2443 @opindex Wmissing-prototypes
2444 Warn if a global function is defined without a previous prototype
2445 declaration. This warning is issued even if the definition itself
2446 provides a prototype. The aim is to detect global functions that fail
2447 to be declared in header files.
2449 @item -Wmissing-declarations
2450 @opindex Wmissing-declarations
2451 Warn if a global function is defined without a previous declaration.
2452 Do so even if the definition itself provides a prototype.
2453 Use this option to detect global functions that are not declared in
2456 @item -Wmissing-noreturn
2457 @opindex Wmissing-noreturn
2458 Warn about functions which might be candidates for attribute @code{noreturn}.
2459 Note these are only possible candidates, not absolute ones. Care should
2460 be taken to manually verify functions actually do not ever return before
2461 adding the @code{noreturn} attribute, otherwise subtle code generation
2462 bugs could be introduced. You will not get a warning for @code{main} in
2463 hosted C environments.
2465 @item -Wmissing-format-attribute
2466 @opindex Wmissing-format-attribute
2468 If @option{-Wformat} is enabled, also warn about functions which might be
2469 candidates for @code{format} attributes. Note these are only possible
2470 candidates, not absolute ones. GCC will guess that @code{format}
2471 attributes might be appropriate for any function that calls a function
2472 like @code{vprintf} or @code{vscanf}, but this might not always be the
2473 case, and some functions for which @code{format} attributes are
2474 appropriate may not be detected. This option has no effect unless
2475 @option{-Wformat} is enabled (possibly by @option{-Wall}).
2479 Warn if a structure is given the packed attribute, but the packed
2480 attribute has no effect on the layout or size of the structure.
2481 Such structures may be mis-aligned for little benefit. For
2482 instance, in this code, the variable @code{f.x} in @code{struct bar}
2483 will be misaligned even though @code{struct bar} does not itself
2484 have the packed attribute:
2491 @} __attribute__((packed));
2501 Warn if padding is included in a structure, either to align an element
2502 of the structure or to align the whole structure. Sometimes when this
2503 happens it is possible to rearrange the fields of the structure to
2504 reduce the padding and so make the structure smaller.
2506 @item -Wredundant-decls
2507 @opindex Wredundant-decls
2508 Warn if anything is declared more than once in the same scope, even in
2509 cases where multiple declaration is valid and changes nothing.
2511 @item -Wnested-externs @r{(C only)}
2512 @opindex Wnested-externs
2513 Warn if an @code{extern} declaration is encountered within a function.
2515 @item -Wunreachable-code
2516 @opindex Wunreachable-code
2517 Warn if the compiler detects that code will never be executed.
2519 This option is intended to warn when the compiler detects that at
2520 least a whole line of source code will never be executed, because
2521 some condition is never satisfied or because it is after a
2522 procedure that never returns.
2524 It is possible for this option to produce a warning even though there
2525 are circumstances under which part of the affected line can be executed,
2526 so care should be taken when removing apparently-unreachable code.
2528 For instance, when a function is inlined, a warning may mean that the
2529 line is unreachable in only one inlined copy of the function.
2531 This option is not made part of @option{-Wall} because in a debugging
2532 version of a program there is often substantial code which checks
2533 correct functioning of the program and is, hopefully, unreachable
2534 because the program does work. Another common use of unreachable
2535 code is to provide behaviour which is selectable at compile-time.
2539 Warn if a function can not be inlined and it was declared as inline.
2543 @opindex Wno-long-long
2544 Warn if @samp{long long} type is used. This is default. To inhibit
2545 the warning messages, use @option{-Wno-long-long}. Flags
2546 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
2547 only when @option{-pedantic} flag is used.
2549 @item -Wdisabled-optimization
2550 @opindex Wdisabled-optimization
2551 Warn if a requested optimization pass is disabled. This warning does
2552 not generally indicate that there is anything wrong with your code; it
2553 merely indicates that GCC's optimizers were unable to handle the code
2554 effectively. Often, the problem is that your code is too big or too
2555 complex; GCC will refuse to optimize programs when the optimization
2556 itself is likely to take inordinate amounts of time.
2560 Make all warnings into errors.
2563 @node Debugging Options
2564 @section Options for Debugging Your Program or GCC
2565 @cindex options, debugging
2566 @cindex debugging information options
2568 GCC has various special options that are used for debugging
2569 either your program or GCC:
2574 Produce debugging information in the operating system's native format
2575 (stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging
2578 On most systems that use stabs format, @option{-g} enables use of extra
2579 debugging information that only GDB can use; this extra information
2580 makes debugging work better in GDB but will probably make other debuggers
2582 refuse to read the program. If you want to control for certain whether
2583 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
2584 @option{-gxcoff+}, @option{-gxcoff}, @option{-gdwarf-1+}, or @option{-gdwarf-1}
2587 Unlike most other C compilers, GCC allows you to use @option{-g} with
2588 @option{-O}. The shortcuts taken by optimized code may occasionally
2589 produce surprising results: some variables you declared may not exist
2590 at all; flow of control may briefly move where you did not expect it;
2591 some statements may not be executed because they compute constant
2592 results or their values were already at hand; some statements may
2593 execute in different places because they were moved out of loops.
2595 Nevertheless it proves possible to debug optimized output. This makes
2596 it reasonable to use the optimizer for programs that might have bugs.
2598 The following options are useful when GCC is generated with the
2599 capability for more than one debugging format.
2603 Produce debugging information for use by GDB@. This means to use the
2604 most expressive format available (DWARF 2, stabs, or the native format
2605 if neither of those are supported), including GDB extensions if at all
2610 Produce debugging information in stabs format (if that is supported),
2611 without GDB extensions. This is the format used by DBX on most BSD
2612 systems. On MIPS, Alpha and System V Release 4 systems this option
2613 produces stabs debugging output which is not understood by DBX or SDB@.
2614 On System V Release 4 systems this option requires the GNU assembler.
2618 Produce debugging information in stabs format (if that is supported),
2619 using GNU extensions understood only by the GNU debugger (GDB)@. The
2620 use of these extensions is likely to make other debuggers crash or
2621 refuse to read the program.
2625 Produce debugging information in COFF format (if that is supported).
2626 This is the format used by SDB on most System V systems prior to
2631 Produce debugging information in XCOFF format (if that is supported).
2632 This is the format used by the DBX debugger on IBM RS/6000 systems.
2636 Produce debugging information in XCOFF format (if that is supported),
2637 using GNU extensions understood only by the GNU debugger (GDB)@. The
2638 use of these extensions is likely to make other debuggers crash or
2639 refuse to read the program, and may cause assemblers other than the GNU
2640 assembler (GAS) to fail with an error.
2644 Produce debugging information in DWARF version 1 format (if that is
2645 supported). This is the format used by SDB on most System V Release 4
2650 Produce debugging information in DWARF version 1 format (if that is
2651 supported), using GNU extensions understood only by the GNU debugger
2652 (GDB)@. The use of these extensions is likely to make other debuggers
2653 crash or refuse to read the program.
2657 Produce debugging information in DWARF version 2 format (if that is
2658 supported). This is the format used by DBX on IRIX 6.
2661 @itemx -ggdb@var{level}
2662 @itemx -gstabs@var{level}
2663 @itemx -gcoff@var{level}
2664 @itemx -gxcoff@var{level}
2665 @itemx -gdwarf@var{level}
2666 @itemx -gdwarf-2@var{level}
2667 Request debugging information and also use @var{level} to specify how
2668 much information. The default level is 2.
2670 Level 1 produces minimal information, enough for making backtraces in
2671 parts of the program that you don't plan to debug. This includes
2672 descriptions of functions and external variables, but no information
2673 about local variables and no line numbers.
2675 Level 3 includes extra information, such as all the macro definitions
2676 present in the program. Some debuggers support macro expansion when
2677 you use @option{-g3}.
2682 Generate extra code to write profile information suitable for the
2683 analysis program @code{prof}. You must use this option when compiling
2684 the source files you want data about, and you must also use it when
2687 @cindex @code{gprof}
2690 Generate extra code to write profile information suitable for the
2691 analysis program @code{gprof}. You must use this option when compiling
2692 the source files you want data about, and you must also use it when
2698 Generate extra code to write profile information for basic blocks, which will
2699 record the number of times each basic block is executed, the basic block start
2700 address, and the function name containing the basic block. If @option{-g} is
2701 used, the line number and filename of the start of the basic block will also be
2702 recorded. If not overridden by the machine description, the default action is
2703 to append to the text file @file{bb.out}.
2705 This data could be analyzed by a program like @code{tcov}. Note,
2706 however, that the format of the data is not what @code{tcov} expects.
2707 Eventually GNU @code{gprof} should be extended to process this data.
2711 Makes the compiler print out each function name as it is compiled, and
2712 print some statistics about each pass when it finishes.
2715 @opindex ftime-report
2716 Makes the compiler print some statistics about the time consumed by each
2717 pass when it finishes.
2720 @opindex fmem-report
2721 Makes the compiler print some statistics about permanent memory
2722 allocation when it finishes.
2726 Generate extra code to profile basic blocks. Your executable will
2727 produce output that is a superset of that produced when @option{-a} is
2728 used. Additional output is the source and target address of the basic
2729 blocks where a jump takes place, the number of times a jump is executed,
2730 and (optionally) the complete sequence of basic blocks being executed.
2731 The output is appended to file @file{bb.out}.
2733 You can examine different profiling aspects without recompilation. Your
2734 executable will read a list of function names from file @file{bb.in}.
2735 Profiling starts when a function on the list is entered and stops when
2736 that invocation is exited. To exclude a function from profiling, prefix
2737 its name with @samp{-}. If a function name is not unique, you can
2738 disambiguate it by writing it in the form
2739 @samp{/path/filename.d:functionname}. Your executable will write the
2740 available paths and filenames in file @file{bb.out}.
2742 Several function names have a special meaning:
2745 Write source, target and frequency of jumps to file @file{bb.out}.
2746 @item __bb_hidecall__
2747 Exclude function calls from frequency count.
2748 @item __bb_showret__
2749 Include function returns in frequency count.
2751 Write the sequence of basic blocks executed to file @file{bbtrace.gz}.
2752 The file will be compressed using the program @samp{gzip}, which must
2753 exist in your @env{PATH}. On systems without the @samp{popen}
2754 function, the file will be named @file{bbtrace} and will not be
2755 compressed. @strong{Profiling for even a few seconds on these systems
2756 will produce a very large file.} Note: @code{__bb_hidecall__} and
2757 @code{__bb_showret__} will not affect the sequence written to
2761 Here's a short example using different profiling parameters
2762 in file @file{bb.in}. Assume function @code{foo} consists of basic blocks
2763 1 and 2 and is called twice from block 3 of function @code{main}. After
2764 the calls, block 3 transfers control to block 4 of @code{main}.
2766 With @code{__bb_trace__} and @code{main} contained in file @file{bb.in},
2767 the following sequence of blocks is written to file @file{bbtrace.gz}:
2768 0 3 1 2 1 2 4. The return from block 2 to block 3 is not shown, because
2769 the return is to a point inside the block and not to the top. The
2770 block address 0 always indicates, that control is transferred
2771 to the trace from somewhere outside the observed functions. With
2772 @samp{-foo} added to @file{bb.in}, the blocks of function
2773 @code{foo} are removed from the trace, so only 0 3 4 remains.
2775 With @code{__bb_jumps__} and @code{main} contained in file @file{bb.in},
2776 jump frequencies will be written to file @file{bb.out}. The
2777 frequencies are obtained by constructing a trace of blocks
2778 and incrementing a counter for every neighbouring pair of blocks
2779 in the trace. The trace 0 3 1 2 1 2 4 displays the following
2783 Jump from block 0x0 to block 0x3 executed 1 time(s)
2784 Jump from block 0x3 to block 0x1 executed 1 time(s)
2785 Jump from block 0x1 to block 0x2 executed 2 time(s)
2786 Jump from block 0x2 to block 0x1 executed 1 time(s)
2787 Jump from block 0x2 to block 0x4 executed 1 time(s)
2790 With @code{__bb_hidecall__}, control transfer due to call instructions
2791 is removed from the trace, that is the trace is cut into three parts: 0
2792 3 4, 0 1 2 and 0 1 2. With @code{__bb_showret__}, control transfer due
2793 to return instructions is added to the trace. The trace becomes: 0 3 1
2794 2 3 1 2 3 4. Note, that this trace is not the same, as the sequence
2795 written to @file{bbtrace.gz}. It is solely used for counting jump
2798 @item -fprofile-arcs
2799 @opindex fprofile-arcs
2800 Instrument @dfn{arcs} during compilation. For each function of your
2801 program, GCC creates a program flow graph, then finds a spanning tree
2802 for the graph. Only arcs that are not on the spanning tree have to be
2803 instrumented: the compiler adds code to count the number of times that these
2804 arcs are executed. When an arc is the only exit or only entrance to a
2805 block, the instrumentation code can be added to the block; otherwise, a
2806 new basic block must be created to hold the instrumentation code.
2808 Since not every arc in the program must be instrumented, programs
2809 compiled with this option run faster than programs compiled with
2810 @option{-a}, which adds instrumentation code to every basic block in the
2811 program. The tradeoff: since @code{gcov} does not have
2812 execution counts for all branches, it must start with the execution
2813 counts for the instrumented branches, and then iterate over the program
2814 flow graph until the entire graph has been solved. Hence, @code{gcov}
2815 runs a little more slowly than a program which uses information from
2818 @option{-fprofile-arcs} also makes it possible to estimate branch
2819 probabilities, and to calculate basic block execution counts. In
2820 general, basic block execution counts do not give enough information to
2821 estimate all branch probabilities. When the compiled program exits, it
2822 saves the arc execution counts to a file called
2823 @file{@var{sourcename}.da}. Use the compiler option
2824 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
2825 Control Optimization}) when recompiling, to optimize using estimated
2826 branch probabilities.
2829 @item -ftest-coverage
2830 @opindex ftest-coverage
2831 Create data files for the @code{gcov} code-coverage utility
2832 (@pxref{Gcov,, @code{gcov}: a GCC Test Coverage Program}).
2833 The data file names begin with the name of your source file:
2836 @item @var{sourcename}.bb
2837 A mapping from basic blocks to line numbers, which @code{gcov} uses to
2838 associate basic block execution counts with line numbers.
2840 @item @var{sourcename}.bbg
2841 A list of all arcs in the program flow graph. This allows @code{gcov}
2842 to reconstruct the program flow graph, so that it can compute all basic
2843 block and arc execution counts from the information in the
2844 @code{@var{sourcename}.da} file (this last file is the output from
2845 @option{-fprofile-arcs}).
2848 @item -d@var{letters}
2850 Says to make debugging dumps during compilation at times specified by
2851 @var{letters}. This is used for debugging the compiler. The file names
2852 for most of the dumps are made by appending a pass number and a word to
2853 the source file name (e.g. @file{foo.c.00.rtl} or @file{foo.c.01.sibling}).
2854 Here are the possible letters for use in @var{letters}, and their meanings:
2859 Annotate the assembler output with miscellaneous debugging information.
2862 Dump after computing branch probabilities, to @file{@var{file}.14.bp}.
2865 Dump after block reordering, to @file{@var{file}.28.bbro}.
2868 Dump after instruction combination, to the file @file{@var{file}.16.combine}.
2871 Dump after the first if conversion, to the file @file{@var{file}.17.ce}.
2874 Dump after delayed branch scheduling, to @file{@var{file}.31.dbr}.
2877 Dump all macro definitions, at the end of preprocessing, in addition to
2881 Dump after SSA optimizations, to @file{@var{file}.04.ssa} and
2882 @file{@var{file}.07.ussa}.
2885 Dump after the second if conversion, to @file{@var{file}.26.ce2}.
2888 Dump after life analysis, to @file{@var{file}.15.life}.
2891 Dump after purging @code{ADDRESSOF} codes, to @file{@var{file}.09.addressof}.
2894 Dump after global register allocation, to @file{@var{file}.21.greg}.
2897 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
2901 Dump after post-reload CSE and other optimizations, to @file{@var{file}.22.postreload}.
2904 Dump after GCSE, to @file{@var{file}.10.gcse}.
2907 Dump after sibling call optimizations, to @file{@var{file}.01.sibling}.
2910 Dump after the first jump optimization, to @file{@var{file}.03.jump}.
2913 Dump after conversion from registers to stack, to @file{@var{file}.32.stack}.
2916 Dump after local register allocation, to @file{@var{file}.20.lreg}.
2919 Dump after loop optimization, to @file{@var{file}.11.loop}.
2922 Dump after performing the machine dependent reorganisation pass, to
2923 @file{@var{file}.30.mach}.
2926 Dump after register renumbering, to @file{@var{file}.25.rnreg}.
2929 Dump after the register move pass, to @file{@var{file}.18.regmove}.
2932 Dump after RTL generation, to @file{@var{file}.00.rtl}.
2935 Dump after the second instruction scheduling pass, to
2936 @file{@var{file}.27.sched2}.
2939 Dump after CSE (including the jump optimization that sometimes follows
2940 CSE), to @file{@var{file}.08.cse}.
2943 Dump after the first instruction scheduling pass, to
2944 @file{@var{file}.19.sched}.
2947 Dump after the second CSE pass (including the jump optimization that
2948 sometimes follows CSE), to @file{@var{file}.12.cse2}.
2951 Dump after the second flow pass, to @file{@var{file}.23.flow2}.
2954 Dump after SSA aggressive dead code elimination, to @file{@var{file}.06.ssadce}.
2957 Dump after the peephole pass, to @file{@var{file}.24.peephole2}.
2960 Produce all the dumps listed above.
2963 Print statistics on memory usage, at the end of the run, to
2967 Annotate the assembler output with a comment indicating which
2968 pattern and alternative was used. The length of each instruction is
2972 Dump the RTL in the assembler output as a comment before each instruction.
2973 Also turns on @option{-dp} annotation.
2976 For each of the other indicated dump files (except for
2977 @file{@var{file}.00.rtl}), dump a representation of the control flow graph
2978 suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
2981 Just generate RTL for a function instead of compiling it. Usually used
2985 Dump debugging information during parsing, to standard error.
2988 @item -fdump-unnumbered
2989 @opindex fdump-unnumbered
2990 When doing debugging dumps (see @option{-d} option above), suppress instruction
2991 numbers and line number note output. This makes it more feasible to
2992 use diff on debugging dumps for compiler invocations with different
2993 options, in particular with and without @option{-g}.
2995 @item -fdump-translation-unit @r{(C and C++ only)}
2996 @itemx -fdump-translation-unit-@var{number} @r{(C and C++ only)}
2997 @opindex fdump-translation-unit
2998 Dump a representation of the tree structure for the entire translation
2999 unit to a file. The file name is made by appending @file{.tu} to the
3000 source file name. If the @samp{-@var{number}} form is used, @var{number}
3001 controls the details of the dump as described for the @option{-fdump-tree} options.
3003 @item -fdump-class-hierarchy @r{(C++ only)}
3004 @itemx -fdump-class-hierarchy-@var{number} @r{(C++ only)}
3005 @opindex fdump-class-hierarchy
3006 Dump a representation of each class's hierarchy and virtual function
3007 table layout to a file. The file name is made by appending @file{.class}
3008 to the source file name. If the @samp{-@var{number}} form is used, @var{number}
3009 controls the details of the dump as described for the @option{-fdump-tree}
3012 @item -fdump-ast-@var{switch} @r{(C++ only)}
3013 @itemx -fdump-ast-@var{switch}-@var{number} @r{(C++ only)}
3015 Control the dumping at various stages of processing the abstract syntax
3016 tree to a file. The file name is generated by appending a switch
3017 specific suffix to the source file name. If the @samp{-@var{number}} form is
3018 used, @var{number} is a bit mask which controls the details of the
3019 dump. The following bits are meaningful (these are not set symbolically,
3020 as the primary function of these dumps is for debugging gcc itself):
3024 Print the address of each node. Usually this is not meaningful as it
3025 changes according to the environment and source file.
3027 Inhibit dumping of members of a scope or body of a function, unless they
3028 are reachable by some other path.
3031 The following tree dumps are possible:
3034 Dump before any tree based optimization, to @file{@var{file}.original}.
3036 Dump after all tree based optimization, to @file{@var{file}.optimized}.
3038 Dump after inlining within the body of the function, to
3039 @file{@var{file}.inlined}.
3042 @item -fpretend-float
3043 @opindex fpretend-float
3044 When running a cross-compiler, pretend that the target machine uses the
3045 same floating point format as the host machine. This causes incorrect
3046 output of the actual floating constants, but the actual instruction
3047 sequence will probably be the same as GCC would make when running on
3052 Store the usual ``temporary'' intermediate files permanently; place them
3053 in the current directory and name them based on the source file. Thus,
3054 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
3055 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
3056 preprocessed @file{foo.i} output file even though the compiler now
3057 normally uses an integrated preprocessor.
3061 Report the CPU time taken by each subprocess in the compilation
3062 sequence. For C source files, this is the compiler proper and assembler
3063 (plus the linker if linking is done). The output looks like this:
3070 The first number on each line is the ``user time,'' that is time spent
3071 executing the program itself. The second number is ``system time,''
3072 time spent executing operating system routines on behalf of the program.
3073 Both numbers are in seconds.
3075 @item -print-file-name=@var{library}
3076 @opindex print-file-name
3077 Print the full absolute name of the library file @var{library} that
3078 would be used when linking---and don't do anything else. With this
3079 option, GCC does not compile or link anything; it just prints the
3082 @item -print-multi-directory
3083 @opindex print-multi-directory
3084 Print the directory name corresponding to the multilib selected by any
3085 other switches present in the command line. This directory is supposed
3086 to exist in @env{GCC_EXEC_PREFIX}.
3088 @item -print-multi-lib
3089 @opindex print-multi-lib
3090 Print the mapping from multilib directory names to compiler switches
3091 that enable them. The directory name is separated from the switches by
3092 @samp{;}, and each switch starts with an @samp{@@} instead of the
3093 @samp{-}, without spaces between multiple switches. This is supposed to
3094 ease shell-processing.
3096 @item -print-prog-name=@var{program}
3097 @opindex print-prog-name
3098 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
3100 @item -print-libgcc-file-name
3101 @opindex print-libgcc-file-name
3102 Same as @option{-print-file-name=libgcc.a}.
3104 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
3105 but you do want to link with @file{libgcc.a}. You can do
3108 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
3111 @item -print-search-dirs
3112 @opindex print-search-dirs
3113 Print the name of the configured installation directory and a list of
3114 program and library directories gcc will search---and don't do anything else.
3116 This is useful when gcc prints the error message
3117 @samp{installation problem, cannot exec cpp0: No such file or directory}.
3118 To resolve this you either need to put @file{cpp0} and the other compiler
3119 components where gcc expects to find them, or you can set the environment
3120 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
3121 Don't forget the trailing '/'.
3122 @xref{Environment Variables}.
3125 @opindex dumpmachine
3126 Print the compiler's target machine (for example,
3127 @samp{i686-pc-linux-gnu})---and don't do anything else.
3130 @opindex dumpversion
3131 Print the compiler version (for example, @samp{3.0})---and don't do
3136 Print the compiler's built-in specs---and don't do anything else. (This
3137 is used when GCC itself is being built.) @xref{Spec Files}.
3140 @node Optimize Options
3141 @section Options That Control Optimization
3142 @cindex optimize options
3143 @cindex options, optimization
3145 These options control various sorts of optimizations:
3152 Optimize. Optimizing compilation takes somewhat more time, and a lot
3153 more memory for a large function.
3155 Without @option{-O}, the compiler's goal is to reduce the cost of
3156 compilation and to make debugging produce the expected results.
3157 Statements are independent: if you stop the program with a breakpoint
3158 between statements, you can then assign a new value to any variable or
3159 change the program counter to any other statement in the function and
3160 get exactly the results you would expect from the source code.
3162 Without @option{-O}, the compiler only allocates variables declared
3163 @code{register} in registers. The resulting compiled code is a little
3164 worse than produced by PCC without @option{-O}.
3166 With @option{-O}, the compiler tries to reduce code size and execution
3169 When you specify @option{-O}, the compiler turns on @option{-fthread-jumps}
3170 and @option{-fdefer-pop} on all machines. The compiler turns on
3171 @option{-fdelayed-branch} on machines that have delay slots, and
3172 @option{-fomit-frame-pointer} on machines that can support debugging even
3173 without a frame pointer. On some machines the compiler also turns
3178 Optimize even more. GCC performs nearly all supported optimizations
3179 that do not involve a space-speed tradeoff. The compiler does not
3180 perform loop unrolling or function inlining when you specify @option{-O2}.
3181 As compared to @option{-O}, this option increases both compilation time
3182 and the performance of the generated code.
3184 @option{-O2} turns on all optional optimizations except for loop unrolling,
3185 function inlining, and register renaming. It also turns on the
3186 @option{-fforce-mem} option on all machines and frame pointer elimination
3187 on machines where doing so does not interfere with debugging.
3189 Please note the warning under @option{-fgcse} about
3190 invoking @option{-O2} on programs that use computed gotos.
3194 Optimize yet more. @option{-O3} turns on all optimizations specified by
3195 @option{-O2} and also turns on the @option{-finline-functions} and
3196 @option{-frename-registers} options.
3204 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
3205 do not typically increase code size. It also performs further
3206 optimizations designed to reduce code size.
3208 If you use multiple @option{-O} options, with or without level numbers,
3209 the last such option is the one that is effective.
3212 Options of the form @option{-f@var{flag}} specify machine-independent
3213 flags. Most flags have both positive and negative forms; the negative
3214 form of @option{-ffoo} would be @option{-fno-foo}. In the table below,
3215 only one of the forms is listed---the one which is not the default.
3216 You can figure out the other form by either removing @samp{no-} or
3221 @opindex ffloat-store
3222 Do not store floating point variables in registers, and inhibit other
3223 options that might change whether a floating point value is taken from a
3226 @cindex floating point precision
3227 This option prevents undesirable excess precision on machines such as
3228 the 68000 where the floating registers (of the 68881) keep more
3229 precision than a @code{double} is supposed to have. Similarly for the
3230 x86 architecture. For most programs, the excess precision does only
3231 good, but a few programs rely on the precise definition of IEEE floating
3232 point. Use @option{-ffloat-store} for such programs, after modifying
3233 them to store all pertinent intermediate computations into variables.
3235 @item -fno-default-inline
3236 @opindex fno-default-inline
3237 Do not make member functions inline by default merely because they are
3238 defined inside the class scope (C++ only). Otherwise, when you specify
3239 @w{@option{-O}}, member functions defined inside class scope are compiled
3240 inline by default; i.e., you don't need to add @samp{inline} in front of
3241 the member function name.
3243 @item -fno-defer-pop
3244 @opindex fno-defer-pop
3245 Always pop the arguments to each function call as soon as that function
3246 returns. For machines which must pop arguments after a function call,
3247 the compiler normally lets arguments accumulate on the stack for several
3248 function calls and pops them all at once.
3252 Force memory operands to be copied into registers before doing
3253 arithmetic on them. This produces better code by making all memory
3254 references potential common subexpressions. When they are not common
3255 subexpressions, instruction combination should eliminate the separate
3256 register-load. The @option{-O2} option turns on this option.
3259 @opindex fforce-addr
3260 Force memory address constants to be copied into registers before
3261 doing arithmetic on them. This may produce better code just as
3262 @option{-fforce-mem} may.
3264 @item -fomit-frame-pointer
3265 @opindex fomit-frame-pointer
3266 Don't keep the frame pointer in a register for functions that
3267 don't need one. This avoids the instructions to save, set up and
3268 restore frame pointers; it also makes an extra register available
3269 in many functions. @strong{It also makes debugging impossible on
3273 On some machines, such as the Vax, this flag has no effect, because
3274 the standard calling sequence automatically handles the frame pointer
3275 and nothing is saved by pretending it doesn't exist. The
3276 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
3277 whether a target machine supports this flag. @xref{Registers}.
3280 On some machines, such as the Vax, this flag has no effect, because
3281 the standard calling sequence automatically handles the frame pointer
3282 and nothing is saved by pretending it doesn't exist. The
3283 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
3284 whether a target machine supports this flag. @xref{Registers,,Register
3285 Usage, gcc.info, Using and Porting GCC}.
3288 @item -foptimize-sibling-calls
3289 @opindex foptimize-sibling-calls
3290 Optimize sibling and tail recursive calls.
3294 This option generates traps for signed overflow on addition, subtraction,
3295 multiplication operations.
3299 Don't pay attention to the @code{inline} keyword. Normally this option
3300 is used to keep the compiler from expanding any functions inline.
3301 Note that if you are not optimizing, no functions can be expanded inline.
3303 @item -finline-functions
3304 @opindex finline-functions
3305 Integrate all simple functions into their callers. The compiler
3306 heuristically decides which functions are simple enough to be worth
3307 integrating in this way.
3309 If all calls to a given function are integrated, and the function is
3310 declared @code{static}, then the function is normally not output as
3311 assembler code in its own right.
3313 @item -finline-limit=@var{n}
3314 @opindex finline-limit
3315 By default, gcc limits the size of functions that can be inlined. This flag
3316 allows the control of this limit for functions that are explicitly marked as
3317 inline (ie marked with the inline keyword or defined within the class
3318 definition in c++). @var{n} is the size of functions that can be inlined in
3319 number of pseudo instructions (not counting parameter handling). The default
3320 value of @var{n} is 10000. Increasing this value can result in more inlined code at
3321 the cost of compilation time and memory consumption. Decreasing usually makes
3322 the compilation faster and less code will be inlined (which presumably
3323 means slower programs). This option is particularly useful for programs that
3324 use inlining heavily such as those based on recursive templates with C++.
3326 @emph{Note:} pseudo instruction represents, in this particular context, an
3327 abstract measurement of function's size. In no way, it represents a count
3328 of assembly instructions and as such its exact meaning might change from one
3329 release to an another.
3331 @item -fkeep-inline-functions
3332 @opindex fkeep-inline-functions
3333 Even if all calls to a given function are integrated, and the function
3334 is declared @code{static}, nevertheless output a separate run-time
3335 callable version of the function. This switch does not affect
3336 @code{extern inline} functions.
3338 @item -fkeep-static-consts
3339 @opindex fkeep-static-consts
3340 Emit variables declared @code{static const} when optimization isn't turned
3341 on, even if the variables aren't referenced.
3343 GCC enables this option by default. If you want to force the compiler to
3344 check if the variable was referenced, regardless of whether or not
3345 optimization is turned on, use the @option{-fno-keep-static-consts} option.
3347 @item -fno-function-cse
3348 @opindex fno-function-cse
3349 Do not put function addresses in registers; make each instruction that
3350 calls a constant function contain the function's address explicitly.
3352 This option results in less efficient code, but some strange hacks
3353 that alter the assembler output may be confused by the optimizations
3354 performed when this option is not used.
3358 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations},
3359 and @option{-fno-trapping-math}.
3361 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
3363 This option should never be turned on by any @option{-O} option since
3364 it can result in incorrect output for programs which depend on
3365 an exact implementation of IEEE or ISO rules/specifications for
3368 @item -fno-math-errno
3369 @opindex fno-math-errno
3370 Do not set ERRNO after calling math functions that are executed
3371 with a single instruction, e.g., sqrt. A program that relies on
3372 IEEE exceptions for math error handling may want to use this flag
3373 for speed while maintaining IEEE arithmetic compatibility.
3375 This option should never be turned on by any @option{-O} option since
3376 it can result in incorrect output for programs which depend on
3377 an exact implementation of IEEE or ISO rules/specifications for
3380 The default is @option{-fmath-errno}. The @option{-ffast-math} option
3381 sets @option{-fno-math-errno}.
3383 @item -funsafe-math-optimizations
3384 @opindex funsafe-math-optimizations
3385 Allow optimizations for floating-point arithmetic that (a) assume
3386 that arguments and results are valid and (b) may violate IEEE or
3387 ANSI standards. When used at link-time, it may include libraries
3388 or startup files that change the default FPU control word or other
3389 similar optimizations.
3391 This option should never be turned on by any @option{-O} option since
3392 it can result in incorrect output for programs which depend on
3393 an exact implementation of IEEE or ISO rules/specifications for
3396 The default is @option{-fno-unsafe-math-optimizations}. The
3397 @option{-ffast-math} option sets @option{-funsafe-math-optimizations}.
3399 @item -fno-trapping-math
3400 @opindex fno-trapping-math
3401 Compile code assuming that floating-point operations cannot generate
3402 user-visible traps. Setting this option may allow faster code
3403 if one relies on ``non-stop'' IEEE arithmetic, for example.
3405 This option should never be turned on by any @option{-O} option since
3406 it can result in incorrect output for programs which depend on
3407 an exact implementation of IEEE or ISO rules/specifications for
3410 The default is @option{-ftrapping-math}. The @option{-ffast-math}
3411 option sets @option{-fno-trapping-math}.
3414 @c following causes underfulls.. they don't look great, but we deal.
3416 The following options control specific optimizations. The @option{-O2}
3417 option turns on all of these optimizations except @option{-funroll-loops}
3418 and @option{-funroll-all-loops}. On most machines, the @option{-O} option
3419 turns on the @option{-fthread-jumps} and @option{-fdelayed-branch} options,
3420 but specific machines may handle it differently.
3422 You can use the following flags in the rare cases when ``fine-tuning''
3423 of optimizations to be performed is desired.
3426 @item -fstrength-reduce
3427 @opindex fstrength-reduce
3428 Perform the optimizations of loop strength reduction and
3429 elimination of iteration variables.
3431 @item -fthread-jumps
3432 @opindex fthread-jumps
3433 Perform optimizations where we check to see if a jump branches to a
3434 location where another comparison subsumed by the first is found. If
3435 so, the first branch is redirected to either the destination of the
3436 second branch or a point immediately following it, depending on whether
3437 the condition is known to be true or false.
3439 @item -fcse-follow-jumps
3440 @opindex fcse-follow-jumps
3441 In common subexpression elimination, scan through jump instructions
3442 when the target of the jump is not reached by any other path. For
3443 example, when CSE encounters an @code{if} statement with an
3444 @code{else} clause, CSE will follow the jump when the condition
3447 @item -fcse-skip-blocks
3448 @opindex fcse-skip-blocks
3449 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
3450 follow jumps which conditionally skip over blocks. When CSE
3451 encounters a simple @code{if} statement with no else clause,
3452 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
3453 body of the @code{if}.
3455 @item -frerun-cse-after-loop
3456 @opindex frerun-cse-after-loop
3457 Re-run common subexpression elimination after loop optimizations has been
3460 @item -frerun-loop-opt
3461 @opindex frerun-loop-opt
3462 Run the loop optimizer twice.
3466 Perform a global common subexpression elimination pass.
3467 This pass also performs global constant and copy propagation.
3469 @emph{Note:} When compiling a program using computed gotos, a GCC
3470 extension, you may get better runtime performance if you disable
3471 the global common subexpression elmination pass by adding
3472 @option{-fno-gcse} to the command line.
3476 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
3477 attempt to move loads which are only killed by stores into themselves. This
3478 allows a loop containing a load/store sequence to be changed to a load outside
3479 the loop, and a copy/store within the loop.
3483 When @option{-fgcse-sm} is enabled, A store motion pass is run after global common
3484 subexpression elimination. This pass will attempt to move stores out of loops.
3485 When used in conjunction with @option{-fgcse-lm}, loops containing a load/store sequence
3486 can be changed to a load before the loop and a store after the loop.
3488 @item -fdelete-null-pointer-checks
3489 @opindex fdelete-null-pointer-checks
3490 Use global dataflow analysis to identify and eliminate useless null
3491 pointer checks. Programs which rely on NULL pointer dereferences @emph{not}
3492 halting the program may not work properly with this option. Use
3493 @option{-fno-delete-null-pointer-checks} to disable this optimizing for programs
3494 which depend on that behavior.
3496 @item -fexpensive-optimizations
3497 @opindex fexpensive-optimizations
3498 Perform a number of minor optimizations that are relatively expensive.
3500 @item -foptimize-register-move
3502 @opindex foptimize-register-move
3504 Attempt to reassign register numbers in move instructions and as
3505 operands of other simple instructions in order to maximize the amount of
3506 register tying. This is especially helpful on machines with two-operand
3507 instructions. GCC enables this optimization by default with @option{-O2}
3510 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
3513 @item -fdelayed-branch
3514 @opindex fdelayed-branch
3515 If supported for the target machine, attempt to reorder instructions
3516 to exploit instruction slots available after delayed branch
3519 @item -fschedule-insns
3520 @opindex fschedule-insns
3521 If supported for the target machine, attempt to reorder instructions to
3522 eliminate execution stalls due to required data being unavailable. This
3523 helps machines that have slow floating point or memory load instructions
3524 by allowing other instructions to be issued until the result of the load
3525 or floating point instruction is required.
3527 @item -fschedule-insns2
3528 @opindex fschedule-insns2
3529 Similar to @option{-fschedule-insns}, but requests an additional pass of
3530 instruction scheduling after register allocation has been done. This is
3531 especially useful on machines with a relatively small number of
3532 registers and where memory load instructions take more than one cycle.
3534 @item -ffunction-sections
3535 @itemx -fdata-sections
3536 @opindex ffunction-sections
3537 @opindex fdata-sections
3538 Place each function or data item into its own section in the output
3539 file if the target supports arbitrary sections. The name of the
3540 function or the name of the data item determines the section's name
3543 Use these options on systems where the linker can perform optimizations
3544 to improve locality of reference in the instruction space. HPPA
3545 processors running HP-UX and Sparc processors running Solaris 2 have
3546 linkers with such optimizations. Other systems using the ELF object format
3547 as well as AIX may have these optimizations in the future.
3549 Only use these options when there are significant benefits from doing
3550 so. When you specify these options, the assembler and linker will
3551 create larger object and executable files and will also be slower.
3552 You will not be able to use @code{gprof} on all systems if you
3553 specify this option and you may have problems with debugging if
3554 you specify both this option and @option{-g}.
3556 @item -fcaller-saves
3557 @opindex fcaller-saves
3558 Enable values to be allocated in registers that will be clobbered by
3559 function calls, by emitting extra instructions to save and restore the
3560 registers around such calls. Such allocation is done only when it
3561 seems to result in better code than would otherwise be produced.
3563 This option is always enabled by default on certain machines, usually
3564 those which have no call-preserved registers to use instead.
3566 For all machines, optimization level 2 and higher enables this flag by
3569 @item -funroll-loops
3570 @opindex funroll-loops
3571 Perform the optimization of loop unrolling. This is only done for loops
3572 whose number of iterations can be determined at compile time or run time.
3573 @option{-funroll-loops} implies both @option{-fstrength-reduce} and
3574 @option{-frerun-cse-after-loop}.
3576 @item -funroll-all-loops
3577 @opindex funroll-all-loops
3578 Perform the optimization of loop unrolling. This is done for all loops
3579 and usually makes programs run more slowly. @option{-funroll-all-loops}
3580 implies @option{-fstrength-reduce} as well as @option{-frerun-cse-after-loop}.
3582 @item -fmove-all-movables
3583 @opindex fmove-all-movables
3584 Forces all invariant computations in loops to be moved
3587 @item -freduce-all-givs
3588 @opindex freduce-all-givs
3589 Forces all general-induction variables in loops to be
3592 @emph{Note:} When compiling programs written in Fortran,
3593 @option{-fmove-all-movables} and @option{-freduce-all-givs} are enabled
3594 by default when you use the optimizer.
3596 These options may generate better or worse code; results are highly
3597 dependent on the structure of loops within the source code.
3599 These two options are intended to be removed someday, once
3600 they have helped determine the efficacy of various
3601 approaches to improving loop optimizations.
3603 Please let us (@w{@email{gcc@@gcc.gnu.org}} and @w{@email{fortran@@gnu.org}})
3604 know how use of these options affects
3605 the performance of your production code.
3606 We're very interested in code that runs @emph{slower}
3607 when these options are @emph{enabled}.
3610 @itemx -fno-peephole2
3611 @opindex fno-peephole
3612 @opindex fno-peephole2
3613 Disable any machine-specific peephole optimizations. The difference
3614 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
3615 are implemented in the compiler; some targets use one, some use the
3616 other, a few use both.
3618 @item -fbranch-probabilities
3619 @opindex fbranch-probabilities
3620 After running a program compiled with @option{-fprofile-arcs}
3621 (@pxref{Debugging Options,, Options for Debugging Your Program or
3622 @command{gcc}}), you can compile it a second time using
3623 @option{-fbranch-probabilities}, to improve optimizations based on
3624 guessing the path a branch might take.
3627 With @option{-fbranch-probabilities}, GCC puts a @samp{REG_EXEC_COUNT}
3628 note on the first instruction of each basic block, and a
3629 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
3630 These can be used to improve optimization. Currently, they are only
3631 used in one place: in @file{reorg.c}, instead of guessing which path a
3632 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
3633 exactly determine which path is taken more often.
3636 @item -fno-guess-branch-probability
3637 @opindex fno-guess-branch-probability
3638 Sometimes gcc will opt to guess branch probabilities when none are
3639 available from either profile directed feedback (@option{-fprofile-arcs})
3640 or @samp{__builtin_expect}. In a hard real-time system, people don't
3641 want different runs of the compiler to produce code that has different
3642 behavior; minimizing non-determinism is of paramount import. This
3643 switch allows users to reduce non-determinism, possibly at the expense
3644 of inferior optimization.
3646 @item -fstrict-aliasing
3647 @opindex fstrict-aliasing
3648 Allows the compiler to assume the strictest aliasing rules applicable to
3649 the language being compiled. For C (and C++), this activates
3650 optimizations based on the type of expressions. In particular, an
3651 object of one type is assumed never to reside at the same address as an
3652 object of a different type, unless the types are almost the same. For
3653 example, an @code{unsigned int} can alias an @code{int}, but not a
3654 @code{void*} or a @code{double}. A character type may alias any other
3657 Pay special attention to code like this:
3670 The practice of reading from a different union member than the one most
3671 recently written to (called ``type-punning'') is common. Even with
3672 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
3673 is accessed through the union type. So, the code above will work as
3674 expected. However, this code might not:
3686 Every language that wishes to perform language-specific alias analysis
3687 should define a function that computes, given an @code{tree}
3688 node, an alias set for the node. Nodes in different alias sets are not
3689 allowed to alias. For an example, see the C front-end function
3690 @code{c_get_alias_set}.
3693 @item -falign-functions
3694 @itemx -falign-functions=@var{n}
3695 @opindex falign-functions
3696 Align the start of functions to the next power-of-two greater than
3697 @var{n}, skipping up to @var{n} bytes. For instance,
3698 @option{-falign-functions=32} aligns functions to the next 32-byte
3699 boundary, but @option{-falign-functions=24} would align to the next
3700 32-byte boundary only if this can be done by skipping 23 bytes or less.
3702 @option{-fno-align-functions} and @option{-falign-functions=1} are
3703 equivalent and mean that functions will not be aligned.
3705 Some assemblers only support this flag when @var{n} is a power of two;
3706 in that case, it is rounded up.
3708 If @var{n} is not specified, use a machine-dependent default.
3710 @item -falign-labels
3711 @itemx -falign-labels=@var{n}
3712 @opindex falign-labels
3713 Align all branch targets to a power-of-two boundary, skipping up to
3714 @var{n} bytes like @option{-falign-functions}. This option can easily
3715 make code slower, because it must insert dummy operations for when the
3716 branch target is reached in the usual flow of the code.
3718 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
3719 are greater than this value, then their values are used instead.
3721 If @var{n} is not specified, use a machine-dependent default which is
3722 very likely to be @samp{1}, meaning no alignment.
3725 @itemx -falign-loops=@var{n}
3726 @opindex falign-loops
3727 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
3728 like @option{-falign-functions}. The hope is that the loop will be
3729 executed many times, which will make up for any execution of the dummy
3732 If @var{n} is not specified, use a machine-dependent default.
3735 @itemx -falign-jumps=@var{n}
3736 @opindex falign-jumps
3737 Align branch targets to a power-of-two boundary, for branch targets
3738 where the targets can only be reached by jumping, skipping up to @var{n}
3739 bytes like @option{-falign-functions}. In this case, no dummy operations
3742 If @var{n} is not specified, use a machine-dependent default.
3746 Perform optimizations in static single assignment form. Each function's
3747 flow graph is translated into SSA form, optimizations are performed, and
3748 the flow graph is translated back from SSA form. Users should not
3749 specify this option, since it is not yet ready for production use.
3753 Perform Sparse Conditional Constant Propagation in SSA form. Requires
3754 @option{-fssa}. Like @option{-fssa}, this is an experimental feature.
3758 Perform aggressive dead-code elimination in SSA form. Requires @option{-fssa}.
3759 Like @option{-fssa}, this is an experimental feature.
3761 @item -fsingle-precision-constant
3762 @opindex fsingle-precision-constant
3763 Treat floating point constant as single precision constant instead of
3764 implicitly converting it to double precision constant.
3766 @item -frename-registers
3767 @opindex frename-registers
3768 Attempt to avoid false dependencies in scheduled code by making use
3769 of registers left over after register allocation. This optimization
3770 will most benefit processors with lots of registers. It can, however,
3771 make debugging impossible, since variables will no longer stay in
3772 a ``home register''.
3774 @item --param @var{name}=@var{value}
3776 In some places, GCC uses various constants to control the amount of
3777 optimization that is done. For example, GCC will not inline functions
3778 that contain more that a certain number of instructions. You can
3779 control some of these constants on the command-line using the
3780 @option{--param} option.
3782 In each case, the @var{value} is a integer. The allowable choices for
3783 @var{name} are given in the following table:
3786 @item max-delay-slot-insn-search
3787 The maximum number of instructions to consider when looking for an
3788 instruction to fill a delay slot. If more than this arbitrary number of
3789 instructions is searched, the time savings from filling the delay slot
3790 will be minimal so stop searching. Increasing values mean more
3791 aggressive optimization, making the compile time increase with probably
3792 small improvement in executable run time.
3794 @item max-delay-slot-live-search
3795 When trying to fill delay slots, the maximum number of instructions to
3796 consider when searching for a block with valid live register
3797 information. Increasing this arbitrarily chosen value means more
3798 aggressive optimization, increasing the compile time. This parameter
3799 should be removed when the delay slot code is rewritten to maintain the
3802 @item max-gcse-memory
3803 The approximate maximum amount of memory that will be allocated in
3804 order to perform the global common subexpression elimination
3805 optimization. If more memory than specified is required, the
3806 optimization will not be done.
3808 @item max-gcse-passes
3809 The maximum number of passes of GCSE to run.
3811 @item max-inline-insns
3812 If an function contains more than this many instructions, it
3813 will not be inlined. This option is precisely equivalent to
3814 @option{-finline-limit}.
3819 @node Preprocessor Options
3820 @section Options Controlling the Preprocessor
3821 @cindex preprocessor options
3822 @cindex options, preprocessor
3824 These options control the C preprocessor, which is run on each C source
3825 file before actual compilation.
3827 If you use the @option{-E} option, nothing is done except preprocessing.
3828 Some of these options make sense only together with @option{-E} because
3829 they cause the preprocessor output to be unsuitable for actual
3833 @item -include @var{file}
3835 Process @var{file} as input before processing the regular input file.
3836 In effect, the contents of @var{file} are compiled first. Any @option{-D}
3837 and @option{-U} options on the command line are always processed before
3838 @option{-include @var{file}}, regardless of the order in which they are
3839 written. All the @option{-include} and @option{-imacros} options are
3840 processed in the order in which they are written.
3842 @item -imacros @var{file}
3844 Process @var{file} as input, discarding the resulting output, before
3845 processing the regular input file. Because the output generated from
3846 @var{file} is discarded, the only effect of @option{-imacros @var{file}}
3847 is to make the macros defined in @var{file} available for use in the
3848 main input. All the @option{-include} and @option{-imacros} options are
3849 processed in the order in which they are written.
3851 @item -idirafter @var{dir}
3853 @cindex second include path
3854 Add the directory @var{dir} to the second include path. The directories
3855 on the second include path are searched when a header file is not found
3856 in any of the directories in the main include path (the one that
3857 @option{-I} adds to).
3859 @item -iprefix @var{prefix}
3861 Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix}
3864 @item -iwithprefix @var{dir}
3865 @opindex iwithprefix
3866 Add a directory to the second include path. The directory's name is
3867 made by concatenating @var{prefix} and @var{dir}, where @var{prefix} was
3868 specified previously with @option{-iprefix}. If you have not specified a
3869 prefix yet, the directory containing the installed passes of the
3870 compiler is used as the default.
3872 @item -iwithprefixbefore @var{dir}
3873 @opindex iwithprefixbefore
3874 Add a directory to the main include path. The directory's name is made
3875 by concatenating @var{prefix} and @var{dir}, as in the case of
3876 @option{-iwithprefix}.
3878 @item -isystem @var{dir}
3880 Add a directory to the beginning of the second include path, marking it
3881 as a system directory, so that it gets the same special treatment as
3882 is applied to the standard system directories.
3886 Do not search the standard system directories for header files. Only
3887 the directories you have specified with @option{-I} options (and the
3888 current directory, if appropriate) are searched. @xref{Directory
3889 Options}, for information on @option{-I}.
3891 By using both @option{-nostdinc} and @option{-I-}, you can limit the include-file
3892 search path to only those directories you specify explicitly.
3896 When searching for a header file in a directory, remap file names if a
3897 file named @file{header.gcc} exists in that directory. This can be used
3898 to work around limitations of file systems with file name restrictions.
3899 The @file{header.gcc} file should contain a series of lines with two
3900 tokens on each line: the first token is the name to map, and the second
3901 token is the actual name to use.
3905 Do not predefine any nonstandard macros. (Including architecture flags).
3909 Run only the C preprocessor. Preprocess all the C source files
3910 specified and output the results to standard output or to the
3911 specified output file.
3915 Tell the preprocessor not to discard comments. Used with the
3920 Tell the preprocessor not to generate @samp{#line} directives.
3921 Used with the @option{-E} option.
3924 @cindex dependencies, make
3927 Instead of outputting the result of preprocessing, output a rule
3928 suitable for @code{make} describing the dependencies of the main source
3929 file. The preprocessor outputs one @code{make} rule containing the
3930 object file name for that source file, a colon, and the names of all the
3931 included files. Unless overridden explicitly, the object file name
3932 consists of the basename of the source file with any suffix replaced with
3933 object file suffix. If there are many included files then the
3934 rule is split into several lines using @samp{\}-newline.
3936 @option{-M} implies @option{-E}.
3940 Like @option{-M}, but mention only the files included with @samp{#include
3941 "@var{file}"}. System header files included with @samp{#include
3942 <@var{file}>} are omitted.
3946 Like @option{-M} but the dependency information is written to a file
3947 rather than stdout. @code{gcc} will use the same file name and
3948 directory as the object file, but with the suffix @file{.d} instead.
3950 This is in addition to compiling the main file as specified---@option{-MD}
3951 does not inhibit ordinary compilation the way @option{-M} does,
3952 unless you also specify @option{-MG}.
3954 With Mach, you can use the utility @code{md} to merge multiple
3955 dependency files into a single dependency file suitable for using with
3956 the @samp{make} command.
3960 Like @option{-MD} except mention only user header files, not system
3963 @item -MF @var{file}
3965 When used with @option{-M} or @option{-MM}, specifies a file to write the
3966 dependencies to. This allows the preprocessor to write the preprocessed
3967 file to stdout normally. If no @option{-MF} switch is given, CPP sends
3968 the rules to stdout and suppresses normal preprocessed output.
3970 Another way to specify output of a @code{make} rule is by setting
3971 the environment variable @env{DEPENDENCIES_OUTPUT} (@pxref{Environment
3976 When used with @option{-M} or @option{-MM}, @option{-MG} says to treat missing
3977 header files as generated files and assume they live in the same
3978 directory as the source file. It suppresses preprocessed output, as a
3979 missing header file is ordinarily an error.
3981 This feature is used in automatic updating of makefiles.
3985 This option instructs CPP to add a phony target for each dependency
3986 other than the main file, causing each to depend on nothing. These
3987 dummy rules work around errors @code{make} gives if you remove header
3988 files without updating the @code{Makefile} to match.
3990 This is typical output:-
3993 /tmp/test.o: /tmp/test.c /tmp/test.h
3998 @item -MQ @var{target}
3999 @item -MT @var{target}
4002 By default CPP uses the main file name, including any path, and appends
4003 the object suffix, normally ``.o'', to it to obtain the name of the
4004 target for dependency generation. With @option{-MT} you can specify a
4005 target yourself, overriding the default one.
4007 If you want multiple targets, you can specify them as a single argument
4008 to @option{-MT}, or use multiple @option{-MT} options.
4010 The targets you specify are output in the order they appear on the
4011 command line. @option{-MQ} is identical to @option{-MT}, except that the
4012 target name is quoted for Make, but with @option{-MT} it isn't. For
4013 example, @option{-MT '$(objpfx)foo.o'} gives
4016 $(objpfx)foo.o: /tmp/foo.c
4019 but @option{-MQ '$(objpfx)foo.o'} gives
4022 $$(objpfx)foo.o: /tmp/foo.c
4025 The default target is automatically quoted, as if it were given with
4030 Print the name of each header file used, in addition to other normal
4033 @item -A@var{question}(@var{answer})
4035 Assert the answer @var{answer} for @var{question}, in case it is tested
4036 with a preprocessing conditional such as @samp{#if
4037 #@var{question}(@var{answer})}. @option{-A-} disables the standard
4038 assertions that normally describe the target machine.
4042 Define macro @var{macro} with the string @samp{1} as its definition.
4044 @item -D@var{macro}=@var{defn}
4045 Define macro @var{macro} as @var{defn}. All instances of @option{-D} on
4046 the command line are processed before any @option{-U} options.
4048 Any @option{-D} and @option{-U} options on the command line are processed in
4049 order, and always before @option{-imacros @var{file}}, regardless of the
4050 order in which they are written.
4054 Undefine macro @var{macro}. @option{-U} options are evaluated after all
4055 @option{-D} options, but before any @option{-include} and @option{-imacros}
4058 Any @option{-D} and @option{-U} options on the command line are processed in
4059 order, and always before @option{-imacros @var{file}}, regardless of the
4060 order in which they are written.
4064 Tell the preprocessor to output only a list of the macro definitions
4065 that are in effect at the end of preprocessing. Used with the @option{-E}
4070 Tell the preprocessing to pass all macro definitions into the output, in
4071 their proper sequence in the rest of the output.
4075 Like @option{-dD} except that the macro arguments and contents are omitted.
4076 Only @samp{#define @var{name}} is included in the output.
4080 Output @samp{#include} directives in addition to the result of
4083 @item -fpreprocessed
4084 @opindex fpreprocessed
4085 Indicate to the preprocessor that the input file has already been
4086 preprocessed. This suppresses things like macro expansion, trigraph
4087 conversion, escaped newline splicing, and processing of most directives.
4088 The preprocessor still recognizes and removes comments, so that you can
4089 pass a file preprocessed with @option{-C} to the compiler without
4090 problems. In this mode the integrated preprocessor is little more than
4091 a tokenizer for the front ends.
4093 @option{-fpreprocessed} is implicit if the input file has one of the
4094 extensions @samp{i}, @samp{ii} or @samp{mi}. These are the extensions
4095 that GCC uses for preprocessed files created by @option{-save-temps}.
4099 Process ISO standard trigraph sequences. These are three-character
4100 sequences, all starting with @samp{??}, that are defined by ISO C to
4101 stand for single characters. For example, @samp{??/} stands for
4102 @samp{\}, so @samp{'??/n'} is a character constant for a newline. By
4103 default, GCC ignores trigraphs, but in standard-conforming modes it
4104 converts them. See the @option{-std} and @option{-ansi} options.
4106 The nine trigraph sequences are
4109 @expansion{} @samp{[}
4112 @expansion{} @samp{]}
4115 @expansion{} @samp{@{}
4118 @expansion{} @samp{@}}
4121 @expansion{} @samp{#}
4124 @expansion{} @samp{\}
4127 @expansion{} @samp{^}
4130 @expansion{} @samp{|}
4133 @expansion{} @samp{~}
4137 Trigraph support is not popular, so many compilers do not implement it
4138 properly. Portable code should not rely on trigraphs being either
4139 converted or ignored.
4141 @item -Wp,@var{option}
4143 Pass @var{option} as an option to the preprocessor. If @var{option}
4144 contains commas, it is split into multiple options at the commas.
4147 @node Assembler Options
4148 @section Passing Options to the Assembler
4150 @c prevent bad page break with this line
4151 You can pass options to the assembler.
4154 @item -Wa,@var{option}
4156 Pass @var{option} as an option to the assembler. If @var{option}
4157 contains commas, it is split into multiple options at the commas.
4161 @section Options for Linking
4162 @cindex link options
4163 @cindex options, linking
4165 These options come into play when the compiler links object files into
4166 an executable output file. They are meaningless if the compiler is
4167 not doing a link step.
4171 @item @var{object-file-name}
4172 A file name that does not end in a special recognized suffix is
4173 considered to name an object file or library. (Object files are
4174 distinguished from libraries by the linker according to the file
4175 contents.) If linking is done, these object files are used as input
4184 If any of these options is used, then the linker is not run, and
4185 object file names should not be used as arguments. @xref{Overall
4189 @item -l@var{library}
4190 @itemx -l @var{library}
4192 Search the library named @var{library} when linking. (The second
4193 alternative with the library as a separate argument is only for
4194 POSIX compliance and is not recommended.)
4196 It makes a difference where in the command you write this option; the
4197 linker searches and processes libraries and object files in the order they
4198 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
4199 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
4200 to functions in @samp{z}, those functions may not be loaded.
4202 The linker searches a standard list of directories for the library,
4203 which is actually a file named @file{lib@var{library}.a}. The linker
4204 then uses this file as if it had been specified precisely by name.
4206 The directories searched include several standard system directories
4207 plus any that you specify with @option{-L}.
4209 Normally the files found this way are library files---archive files
4210 whose members are object files. The linker handles an archive file by
4211 scanning through it for members which define symbols that have so far
4212 been referenced but not defined. But if the file that is found is an
4213 ordinary object file, it is linked in the usual fashion. The only
4214 difference between using an @option{-l} option and specifying a file name
4215 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
4216 and searches several directories.
4220 You need this special case of the @option{-l} option in order to
4221 link an Objective-C program.
4224 @opindex nostartfiles
4225 Do not use the standard system startup files when linking.
4226 The standard system libraries are used normally, unless @option{-nostdlib}
4227 or @option{-nodefaultlibs} is used.
4229 @item -nodefaultlibs
4230 @opindex nodefaultlibs
4231 Do not use the standard system libraries when linking.
4232 Only the libraries you specify will be passed to the linker.
4233 The standard startup files are used normally, unless @option{-nostartfiles}
4234 is used. The compiler may generate calls to memcmp, memset, and memcpy
4235 for System V (and ISO C) environments or to bcopy and bzero for
4236 BSD environments. These entries are usually resolved by entries in
4237 libc. These entry points should be supplied through some other
4238 mechanism when this option is specified.
4242 Do not use the standard system startup files or libraries when linking.
4243 No startup files and only the libraries you specify will be passed to
4244 the linker. The compiler may generate calls to memcmp, memset, and memcpy
4245 for System V (and ISO C) environments or to bcopy and bzero for
4246 BSD environments. These entries are usually resolved by entries in
4247 libc. These entry points should be supplied through some other
4248 mechanism when this option is specified.
4250 @cindex @option{-lgcc}, use with @option{-nostdlib}
4251 @cindex @option{-nostdlib} and unresolved references
4252 @cindex unresolved references and @option{-nostdlib}
4253 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
4254 @cindex @option{-nodefaultlibs} and unresolved references
4255 @cindex unresolved references and @option{-nodefaultlibs}
4256 One of the standard libraries bypassed by @option{-nostdlib} and
4257 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
4258 that GCC uses to overcome shortcomings of particular machines, or special
4259 needs for some languages.
4261 (@xref{Interface,,Interfacing to GCC Output}, for more discussion of
4265 (@xref{Interface,,Interfacing to GCC Output,gcc.info,Porting GCC},
4266 for more discussion of @file{libgcc.a}.)
4268 In most cases, you need @file{libgcc.a} even when you want to avoid
4269 other standard libraries. In other words, when you specify @option{-nostdlib}
4270 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
4271 This ensures that you have no unresolved references to internal GCC
4272 library subroutines. (For example, @samp{__main}, used to ensure C++
4273 constructors will be called; @pxref{Collect2,,@command{collect2}}.)
4277 Remove all symbol table and relocation information from the executable.
4281 On systems that support dynamic linking, this prevents linking with the shared
4282 libraries. On other systems, this option has no effect.
4286 Produce a shared object which can then be linked with other objects to
4287 form an executable. Not all systems support this option. For predictable
4288 results, you must also specify the same set of options that were used to
4289 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
4290 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
4291 needs to build supplementary stub code for constructors to work. On
4292 multi-libbed systems, @samp{gcc -shared} must select the correct support
4293 libraries to link against. Failing to supply the correct flags may lead
4294 to subtle defects. Supplying them in cases where they are not necessary
4297 @item -shared-libgcc
4298 @itemx -static-libgcc
4299 @opindex shared-libgcc
4300 @opindex static-libgcc
4301 On systems that provide @file{libgcc} as a shared library, these options
4302 force the use of either the shared or static version respectively.
4303 If no shared version of @file{libgcc} was built when the compiler was
4304 configured, these options have no effect.
4306 There are several situations in which an application should use the
4307 shared @file{libgcc} instead of the static version. The most common
4308 of these is when the application wishes to throw and catch exceptions
4309 across different shared libraries. In that case, each of the libraries
4310 as well as the application itself should use the shared @file{libgcc}.
4312 Therefore, whenever you specify the @option{-shared} option, the GCC
4313 driver automatically adds @option{-shared-libgcc}, unless you explicitly
4314 specify @option{-static-libgcc}. The G++ driver automatically adds
4315 @option{-shared-libgcc} when you build a main executable as well because
4316 for C++ programs that is typically the right thing to do.
4317 (Exception-handling will not work reliably otherwise.)
4319 However, when linking a main executable written in C, you must
4320 explicitly say @option{-shared-libgcc} if you want to use the shared
4325 Bind references to global symbols when building a shared object. Warn
4326 about any unresolved references (unless overridden by the link editor
4327 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
4330 @item -Xlinker @var{option}
4332 Pass @var{option} as an option to the linker. You can use this to
4333 supply system-specific linker options which GCC does not know how to
4336 If you want to pass an option that takes an argument, you must use
4337 @option{-Xlinker} twice, once for the option and once for the argument.
4338 For example, to pass @option{-assert definitions}, you must write
4339 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
4340 @option{-Xlinker "-assert definitions"}, because this passes the entire
4341 string as a single argument, which is not what the linker expects.
4343 @item -Wl,@var{option}
4345 Pass @var{option} as an option to the linker. If @var{option} contains
4346 commas, it is split into multiple options at the commas.
4348 @item -u @var{symbol}
4350 Pretend the symbol @var{symbol} is undefined, to force linking of
4351 library modules to define it. You can use @option{-u} multiple times with
4352 different symbols to force loading of additional library modules.
4355 @node Directory Options
4356 @section Options for Directory Search
4357 @cindex directory options
4358 @cindex options, directory search
4361 These options specify directories to search for header files, for
4362 libraries and for parts of the compiler:
4367 Add the directory @var{dir} to the head of the list of directories to be
4368 searched for header files. This can be used to override a system header
4369 file, substituting your own version, since these directories are
4370 searched before the system header file directories. However, you should
4371 not use this option to add directories that contain vendor-supplied
4372 system header files (use @option{-isystem} for that). If you use more than
4373 one @option{-I} option, the directories are scanned in left-to-right
4374 order; the standard system directories come after.
4376 If a standard system include directory, or a directory specified with
4377 @option{-isystem}, is also specified with @option{-I}, it will be
4378 searched only in the position requested by @option{-I}. Also, it will
4379 not be considered a system include directory. If that directory really
4380 does contain system headers, there is a good chance that they will
4381 break. For instance, if GCC's installation procedure edited the headers
4382 in @file{/usr/include} to fix bugs, @samp{-I/usr/include} will cause the
4383 original, buggy headers to be found instead of the corrected ones. GCC
4384 will issue a warning when a system include directory is hidden in this
4389 Any directories you specify with @option{-I} options before the @option{-I-}
4390 option are searched only for the case of @samp{#include "@var{file}"};
4391 they are not searched for @samp{#include <@var{file}>}.
4393 If additional directories are specified with @option{-I} options after
4394 the @option{-I-}, these directories are searched for all @samp{#include}
4395 directives. (Ordinarily @emph{all} @option{-I} directories are used
4398 In addition, the @option{-I-} option inhibits the use of the current
4399 directory (where the current input file came from) as the first search
4400 directory for @samp{#include "@var{file}"}. There is no way to
4401 override this effect of @option{-I-}. With @option{-I.} you can specify
4402 searching the directory which was current when the compiler was
4403 invoked. That is not exactly the same as what the preprocessor does
4404 by default, but it is often satisfactory.
4406 @option{-I-} does not inhibit the use of the standard system directories
4407 for header files. Thus, @option{-I-} and @option{-nostdinc} are
4412 Add directory @var{dir} to the list of directories to be searched
4415 @item -B@var{prefix}
4417 This option specifies where to find the executables, libraries,
4418 include files, and data files of the compiler itself.
4420 The compiler driver program runs one or more of the subprograms
4421 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
4422 @var{prefix} as a prefix for each program it tries to run, both with and
4423 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
4425 For each subprogram to be run, the compiler driver first tries the
4426 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
4427 was not specified, the driver tries two standard prefixes, which are
4428 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc-lib/}. If neither of
4429 those results in a file name that is found, the unmodified program
4430 name is searched for using the directories specified in your
4431 @env{PATH} environment variable.
4433 The compiler will check to see if the path provided by the @option{-B}
4434 refers to a directory, and if necessary it will add a directory
4435 separator character at the end of the path.
4437 @option{-B} prefixes that effectively specify directory names also apply
4438 to libraries in the linker, because the compiler translates these
4439 options into @option{-L} options for the linker. They also apply to
4440 includes files in the preprocessor, because the compiler translates these
4441 options into @option{-isystem} options for the preprocessor. In this case,
4442 the compiler appends @samp{include} to the prefix.
4444 The run-time support file @file{libgcc.a} can also be searched for using
4445 the @option{-B} prefix, if needed. If it is not found there, the two
4446 standard prefixes above are tried, and that is all. The file is left
4447 out of the link if it is not found by those means.
4449 Another way to specify a prefix much like the @option{-B} prefix is to use
4450 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
4453 As a special kludge, if the path provided by @option{-B} is
4454 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
4455 9, then it will be replaced by @file{[dir/]include}. This is to help
4456 with boot-strapping the compiler.
4458 @item -specs=@var{file}
4460 Process @var{file} after the compiler reads in the standard @file{specs}
4461 file, in order to override the defaults that the @file{gcc} driver
4462 program uses when determining what switches to pass to @file{cc1},
4463 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
4464 @option{-specs=@var{file}} can be specified on the command line, and they
4465 are processed in order, from left to right.
4471 @section Specifying subprocesses and the switches to pass to them
4473 @command{gcc} is a driver program. It performs its job by invoking a
4474 sequence of other programs to do the work of compiling, assembling and
4475 linking. GCC interprets its command-line parameters and uses these to
4476 deduce which programs it should invoke, and which command-line options
4477 it ought to place on their command lines. This behaviour is controlled
4478 by @dfn{spec strings}. In most cases there is one spec string for each
4479 program that GCC can invoke, but a few programs have multiple spec
4480 strings to control their behaviour. The spec strings built into GCC can
4481 be overridden by using the @option{-specs=} command-line switch to specify
4484 @dfn{Spec files} are plaintext files that are used to construct spec
4485 strings. They consist of a sequence of directives separated by blank
4486 lines. The type of directive is determined by the first non-whitespace
4487 character on the line and it can be one of the following:
4490 @item %@var{command}
4491 Issues a @var{command} to the spec file processor. The commands that can
4495 @item %include <@var{file}>
4497 Search for @var{file} and insert its text at the current point in the
4500 @item %include_noerr <@var{file}>
4501 @cindex %include_noerr
4502 Just like @samp{%include}, but do not generate an error message if the include
4503 file cannot be found.
4505 @item %rename @var{old_name} @var{new_name}
4507 Rename the spec string @var{old_name} to @var{new_name}.
4511 @item *[@var{spec_name}]:
4512 This tells the compiler to create, override or delete the named spec
4513 string. All lines after this directive up to the next directive or
4514 blank line are considered to be the text for the spec string. If this
4515 results in an empty string then the spec will be deleted. (Or, if the
4516 spec did not exist, then nothing will happened.) Otherwise, if the spec
4517 does not currently exist a new spec will be created. If the spec does
4518 exist then its contents will be overridden by the text of this
4519 directive, unless the first character of that text is the @samp{+}
4520 character, in which case the text will be appended to the spec.
4522 @item [@var{suffix}]:
4523 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
4524 and up to the next directive or blank line are considered to make up the
4525 spec string for the indicated suffix. When the compiler encounters an
4526 input file with the named suffix, it will processes the spec string in
4527 order to work out how to compile that file. For example:
4534 This says that any input file whose name ends in @samp{.ZZ} should be
4535 passed to the program @samp{z-compile}, which should be invoked with the
4536 command-line switch @option{-input} and with the result of performing the
4537 @samp{%i} substitution. (See below.)
4539 As an alternative to providing a spec string, the text that follows a
4540 suffix directive can be one of the following:
4543 @item @@@var{language}
4544 This says that the suffix is an alias for a known @var{language}. This is
4545 similar to using the @option{-x} command-line switch to GCC to specify a
4546 language explicitly. For example:
4553 Says that .ZZ files are, in fact, C++ source files.
4556 This causes an error messages saying:
4559 @var{name} compiler not installed on this system.
4563 GCC already has an extensive list of suffixes built into it.
4564 This directive will add an entry to the end of the list of suffixes, but
4565 since the list is searched from the end backwards, it is effectively
4566 possible to override earlier entries using this technique.
4570 GCC has the following spec strings built into it. Spec files can
4571 override these strings or create their own. Note that individual
4572 targets can also add their own spec strings to this list.
4575 asm Options to pass to the assembler
4576 asm_final Options to pass to the assembler post-processor
4577 cpp Options to pass to the C preprocessor
4578 cc1 Options to pass to the C compiler
4579 cc1plus Options to pass to the C++ compiler
4580 endfile Object files to include at the end of the link
4581 link Options to pass to the linker
4582 lib Libraries to include on the command line to the linker
4583 libgcc Decides which GCC support library to pass to the linker
4584 linker Sets the name of the linker
4585 predefines Defines to be passed to the C preprocessor
4586 signed_char Defines to pass to CPP to say whether @code{char} is signed
4588 startfile Object files to include at the start of the link
4591 Here is a small example of a spec file:
4597 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
4600 This example renames the spec called @samp{lib} to @samp{old_lib} and
4601 then overrides the previous definition of @samp{lib} with a new one.
4602 The new definition adds in some extra command-line options before
4603 including the text of the old definition.
4605 @dfn{Spec strings} are a list of command-line options to be passed to their
4606 corresponding program. In addition, the spec strings can contain
4607 @samp{%}-prefixed sequences to substitute variable text or to
4608 conditionally insert text into the command line. Using these constructs
4609 it is possible to generate quite complex command lines.
4611 Here is a table of all defined @samp{%}-sequences for spec
4612 strings. Note that spaces are not generated automatically around the
4613 results of expanding these sequences. Therefore you can concatenate them
4614 together or combine them with constant text in a single argument.
4618 Substitute one @samp{%} into the program name or argument.
4621 Substitute the name of the input file being processed.
4624 Substitute the basename of the input file being processed.
4625 This is the substring up to (and not including) the last period
4626 and not including the directory.
4629 This is the same as @samp{%b}, but include the file suffix (text after
4633 Marks the argument containing or following the @samp{%d} as a
4634 temporary file name, so that that file will be deleted if GCC exits
4635 successfully. Unlike @samp{%g}, this contributes no text to the
4638 @item %g@var{suffix}
4639 Substitute a file name that has suffix @var{suffix} and is chosen
4640 once per compilation, and mark the argument in the same way as
4641 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
4642 name is now chosen in a way that is hard to predict even when previously
4643 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
4644 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
4645 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
4646 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
4647 was simply substituted with a file name chosen once per compilation,
4648 without regard to any appended suffix (which was therefore treated
4649 just like ordinary text), making such attacks more likely to succeed.
4651 @item %u@var{suffix}
4652 Like @samp{%g}, but generates a new temporary file name even if
4653 @samp{%u@var{suffix}} was already seen.
4655 @item %U@var{suffix}
4656 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
4657 new one if there is no such last file name. In the absence of any
4658 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
4659 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
4660 would involve the generation of two distinct file names, one
4661 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
4662 simply substituted with a file name chosen for the previous @samp{%u},
4663 without regard to any appended suffix.
4665 @item %j@var{SUFFIX}
4666 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
4667 writable, and if save-temps is off; otherwise, substitute the name
4668 of a temporary file, just like @samp{%u}. This temporary file is not
4669 meant for communication between processes, but rather as a junk
4672 @item %.@var{SUFFIX}
4673 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
4674 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
4675 terminated by the next space or %.
4678 Marks the argument containing or following the @samp{%w} as the
4679 designated output file of this compilation. This puts the argument
4680 into the sequence of arguments that @samp{%o} will substitute later.
4683 Substitutes the names of all the output files, with spaces
4684 automatically placed around them. You should write spaces
4685 around the @samp{%o} as well or the results are undefined.
4686 @samp{%o} is for use in the specs for running the linker.
4687 Input files whose names have no recognized suffix are not compiled
4688 at all, but they are included among the output files, so they will
4692 Substitutes the suffix for object files. Note that this is
4693 handled specially when it immediately follows @samp{%g, %u, or %U},
4694 because of the need for those to form complete file names. The
4695 handling is such that @samp{%O} is treated exactly as if it had already
4696 been substituted, except that @samp{%g, %u, and %U} do not currently
4697 support additional @var{suffix} characters following @samp{%O} as they would
4698 following, for example, @samp{.o}.
4701 Substitutes the standard macro predefinitions for the
4702 current target machine. Use this when running @code{cpp}.
4705 Like @samp{%p}, but puts @samp{__} before and after the name of each
4706 predefined macro, except for macros that start with @samp{__} or with
4707 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
4711 Substitute a @option{-iprefix} option made from @env{GCC_EXEC_PREFIX}.
4714 Current argument is the name of a library or startup file of some sort.
4715 Search for that file in a standard list of directories and substitute
4716 the full name found.
4719 Print @var{str} as an error message. @var{str} is terminated by a newline.
4720 Use this when inconsistent options are detected.
4723 Output @samp{-} if the input for the current command is coming from a pipe.
4726 Substitute the contents of spec string @var{name} at this point.
4729 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
4731 @item %x@{@var{option}@}
4732 Accumulate an option for @samp{%X}.
4735 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
4739 Output the accumulated assembler options specified by @option{-Wa}.
4742 Output the accumulated preprocessor options specified by @option{-Wp}.
4745 Substitute the major version number of GCC@.
4746 (For version 2.9.5, this is 2.)
4749 Substitute the minor version number of GCC@.
4750 (For version 2.9.5, this is 9.)
4753 Substitute the patch level number of GCC@.
4754 (For version 2.9.5, this is 5.)
4757 Process the @code{asm} spec. This is used to compute the
4758 switches to be passed to the assembler.
4761 Process the @code{asm_final} spec. This is a spec string for
4762 passing switches to an assembler post-processor, if such a program is
4766 Process the @code{link} spec. This is the spec for computing the
4767 command line passed to the linker. Typically it will make use of the
4768 @samp{%L %G %S %D and %E} sequences.
4771 Dump out a @option{-L} option for each directory that GCC believes might
4772 contain startup files. If the target supports multilibs then the
4773 current multilib directory will be prepended to each of these paths.
4776 Output the multilib directory with directory separators replaced with
4777 @samp{_}. If multilib directories are not set, or the multilib directory is
4778 @file{.} then this option emits nothing.
4781 Process the @code{lib} spec. This is a spec string for deciding which
4782 libraries should be included on the command line to the linker.
4785 Process the @code{libgcc} spec. This is a spec string for deciding
4786 which GCC support library should be included on the command line to the linker.
4789 Process the @code{startfile} spec. This is a spec for deciding which
4790 object files should be the first ones passed to the linker. Typically
4791 this might be a file named @file{crt0.o}.
4794 Process the @code{endfile} spec. This is a spec string that specifies
4795 the last object files that will be passed to the linker.
4798 Process the @code{cpp} spec. This is used to construct the arguments
4799 to be passed to the C preprocessor.
4802 Process the @code{signed_char} spec. This is intended to be used
4803 to tell cpp whether a char is signed. It typically has the definition:
4805 %@{funsigned-char:-D__CHAR_UNSIGNED__@}
4809 Process the @code{cc1} spec. This is used to construct the options to be
4810 passed to the actual C compiler (@samp{cc1}).
4813 Process the @code{cc1plus} spec. This is used to construct the options to be
4814 passed to the actual C++ compiler (@samp{cc1plus}).
4817 Substitute the variable part of a matched option. See below.
4818 Note that each comma in the substituted string is replaced by
4822 Substitutes the @code{-S} switch, if that switch was given to GCC@.
4823 If that switch was not specified, this substitutes nothing. Note that
4824 the leading dash is omitted when specifying this option, and it is
4825 automatically inserted if the substitution is performed. Thus the spec
4826 string @samp{%@{foo@}} would match the command-line option @option{-foo}
4827 and would output the command line option @option{-foo}.
4829 @item %W@{@code{S}@}
4830 Like %@{@code{S}@} but mark last argument supplied within as a file to be
4833 @item %@{@code{S}*@}
4834 Substitutes all the switches specified to GCC whose names start
4835 with @code{-S}, but which also take an argument. This is used for
4836 switches like @option{-o}, @option{-D}, @option{-I}, etc.
4837 GCC considers @option{-o foo} as being
4838 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
4839 text, including the space. Thus two arguments would be generated.
4841 @item %@{^@code{S}*@}
4842 Like %@{@code{S}*@}, but don't put a blank between a switch and its
4843 argument. Thus %@{^o*@} would only generate one argument, not two.
4845 @item %@{@code{S}*&@code{T}*@}
4846 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
4847 (the order of @code{S} and @code{T} in the spec is not significant).
4848 There can be any number of ampersand-separated variables; for each the
4849 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
4851 @item %@{<@code{S}@}
4852 Remove all occurrences of @code{-S} from the command line. Note---this
4853 command is position dependent. @samp{%} commands in the spec string
4854 before this option will see @code{-S}, @samp{%} commands in the spec
4855 string after this option will not.
4857 @item %@{@code{S}*:@code{X}@}
4858 Substitutes @code{X} if one or more switches whose names start with
4859 @code{-S} are specified to GCC@. Note that the tail part of the
4860 @code{-S} option (i.e.@: the part matched by the @samp{*}) will be substituted
4861 for each occurrence of @samp{%*} within @code{X}.
4863 @item %@{@code{S}:@code{X}@}
4864 Substitutes @code{X}, but only if the @samp{-S} switch was given to GCC@.
4866 @item %@{!@code{S}:@code{X}@}
4867 Substitutes @code{X}, but only if the @samp{-S} switch was @emph{not} given to GCC@.
4869 @item %@{|@code{S}:@code{X}@}
4870 Like %@{@code{S}:@code{X}@}, but if no @code{S} switch, substitute @samp{-}.
4872 @item %@{|!@code{S}:@code{X}@}
4873 Like %@{!@code{S}:@code{X}@}, but if there is an @code{S} switch, substitute @samp{-}.
4875 @item %@{.@code{S}:@code{X}@}
4876 Substitutes @code{X}, but only if processing a file with suffix @code{S}.
4878 @item %@{!.@code{S}:@code{X}@}
4879 Substitutes @code{X}, but only if @emph{not} processing a file with suffix @code{S}.
4881 @item %@{@code{S}|@code{P}:@code{X}@}
4882 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@. This may be
4883 combined with @samp{!} and @samp{.} sequences as well, although they
4884 have a stronger binding than the @samp{|}. For example a spec string
4888 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
4891 will output the following command-line options from the following input
4892 command-line options:
4897 -d fred.c -foo -baz -boggle
4898 -d jim.d -bar -baz -boggle
4903 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or
4904 %@{!@code{S}:@code{X}@} construct may contain other nested @samp{%} constructs
4905 or spaces, or even newlines. They are processed as usual, as described
4908 The @option{-O}, @option{-f}, @option{-m}, and @option{-W}
4909 switches are handled specifically in these
4910 constructs. If another value of @option{-O} or the negated form of a @option{-f}, @option{-m}, or
4911 @option{-W} switch is found later in the command line, the earlier switch
4912 value is ignored, except with @{@code{S}*@} where @code{S} is just one
4913 letter, which passes all matching options.
4915 The character @samp{|} at the beginning of the predicate text is used to indicate
4916 that a command should be piped to the following command, but only if @option{-pipe}
4919 It is built into GCC which switches take arguments and which do not.
4920 (You might think it would be useful to generalize this to allow each
4921 compiler's spec to say which switches take arguments. But this cannot
4922 be done in a consistent fashion. GCC cannot even decide which input
4923 files have been specified without knowing which switches take arguments,
4924 and it must know which input files to compile in order to tell which
4927 GCC also knows implicitly that arguments starting in @option{-l} are to be
4928 treated as compiler output files, and passed to the linker in their
4929 proper position among the other output files.
4931 @c man begin OPTIONS
4933 @node Target Options
4934 @section Specifying Target Machine and Compiler Version
4935 @cindex target options
4936 @cindex cross compiling
4937 @cindex specifying machine version
4938 @cindex specifying compiler version and target machine
4939 @cindex compiler version, specifying
4940 @cindex target machine, specifying
4942 By default, GCC compiles code for the same type of machine that you
4943 are using. However, it can also be installed as a cross-compiler, to
4944 compile for some other type of machine. In fact, several different
4945 configurations of GCC, for different target machines, can be
4946 installed side by side. Then you specify which one to use with the
4949 In addition, older and newer versions of GCC can be installed side
4950 by side. One of them (probably the newest) will be the default, but
4951 you may sometimes wish to use another.
4954 @item -b @var{machine}
4956 The argument @var{machine} specifies the target machine for compilation.
4957 This is useful when you have installed GCC as a cross-compiler.
4959 The value to use for @var{machine} is the same as was specified as the
4960 machine type when configuring GCC as a cross-compiler. For
4961 example, if a cross-compiler was configured with @samp{configure
4962 i386v}, meaning to compile for an 80386 running System V, then you
4963 would specify @option{-b i386v} to run that cross compiler.
4965 When you do not specify @option{-b}, it normally means to compile for
4966 the same type of machine that you are using.
4968 @item -V @var{version}
4970 The argument @var{version} specifies which version of GCC to run.
4971 This is useful when multiple versions are installed. For example,
4972 @var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
4974 The default version, when you do not specify @option{-V}, is the last
4975 version of GCC that you installed.
4978 The @option{-b} and @option{-V} options actually work by controlling part of
4979 the file name used for the executable files and libraries used for
4980 compilation. A given version of GCC, for a given target machine, is
4981 normally kept in the directory @file{/usr/local/lib/gcc-lib/@var{machine}/@var{version}}.
4983 Thus, sites can customize the effect of @option{-b} or @option{-V} either by
4984 changing the names of these directories or adding alternate names (or
4985 symbolic links). If in directory @file{/usr/local/lib/gcc-lib/} the
4986 file @file{80386} is a link to the file @file{i386v}, then @option{-b
4987 80386} becomes an alias for @option{-b i386v}.
4989 In one respect, the @option{-b} or @option{-V} do not completely change
4990 to a different compiler: the top-level driver program @command{gcc}
4991 that you originally invoked continues to run and invoke the other
4992 executables (preprocessor, compiler per se, assembler and linker)
4993 that do the real work. However, since no real work is done in the
4994 driver program, it usually does not matter that the driver program
4995 in use is not the one for the specified target. It is common for the
4996 interface to the other executables to change incompatibly between
4997 compiler versions, so unless the version specified is very close to that
4998 of the driver (for example, @option{-V 3.0} with a driver program from GCC
4999 version 3.0.1), use of @option{-V} may not work; for example, using
5000 @option{-V 2.95.2} will not work with a driver program from GCC 3.0.
5002 The only way that the driver program depends on the target machine is
5003 in the parsing and handling of special machine-specific options.
5004 However, this is controlled by a file which is found, along with the
5005 other executables, in the directory for the specified version and
5006 target machine. As a result, a single installed driver program adapts
5007 to any specified target machine, and sufficiently similar compiler
5010 The driver program executable does control one significant thing,
5011 however: the default version and target machine. Therefore, you can
5012 install different instances of the driver program, compiled for
5013 different targets or versions, under different names.
5015 For example, if the driver for version 2.0 is installed as @command{ogcc}
5016 and that for version 2.1 is installed as @command{gcc}, then the command
5017 @command{gcc} will use version 2.1 by default, while @command{ogcc} will use
5018 2.0 by default. However, you can choose either version with either
5019 command with the @option{-V} option.
5021 @node Submodel Options
5022 @section Hardware Models and Configurations
5023 @cindex submodel options
5024 @cindex specifying hardware config
5025 @cindex hardware models and configurations, specifying
5026 @cindex machine dependent options
5028 Earlier we discussed the standard option @option{-b} which chooses among
5029 different installed compilers for completely different target
5030 machines, such as Vax vs.@: 68000 vs.@: 80386.
5032 In addition, each of these target machine types can have its own
5033 special options, starting with @samp{-m}, to choose among various
5034 hardware models or configurations---for example, 68010 vs 68020,
5035 floating coprocessor or none. A single installed version of the
5036 compiler can compile for any model or configuration, according to the
5039 Some configurations of the compiler also support additional special
5040 options, usually for compatibility with other compilers on the same
5044 These options are defined by the macro @code{TARGET_SWITCHES} in the
5045 machine description. The default for the options is also defined by
5046 that macro, which enables you to change the defaults.
5061 * RS/6000 and PowerPC Options::
5066 * Intel 960 Options::
5067 * DEC Alpha Options::
5071 * System V Options::
5072 * TMS320C3x/C4x Options::
5082 @node M680x0 Options
5083 @subsection M680x0 Options
5084 @cindex M680x0 options
5086 These are the @samp{-m} options defined for the 68000 series. The default
5087 values for these options depends on which style of 68000 was selected when
5088 the compiler was configured; the defaults for the most common choices are
5096 Generate output for a 68000. This is the default
5097 when the compiler is configured for 68000-based systems.
5099 Use this option for microcontrollers with a 68000 or EC000 core,
5100 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
5106 Generate output for a 68020. This is the default
5107 when the compiler is configured for 68020-based systems.
5111 Generate output containing 68881 instructions for floating point.
5112 This is the default for most 68020 systems unless @option{--nfp} was
5113 specified when the compiler was configured.
5117 Generate output for a 68030. This is the default when the compiler is
5118 configured for 68030-based systems.
5122 Generate output for a 68040. This is the default when the compiler is
5123 configured for 68040-based systems.
5125 This option inhibits the use of 68881/68882 instructions that have to be
5126 emulated by software on the 68040. Use this option if your 68040 does not
5127 have code to emulate those instructions.
5131 Generate output for a 68060. This is the default when the compiler is
5132 configured for 68060-based systems.
5134 This option inhibits the use of 68020 and 68881/68882 instructions that
5135 have to be emulated by software on the 68060. Use this option if your 68060
5136 does not have code to emulate those instructions.
5140 Generate output for a CPU32. This is the default
5141 when the compiler is configured for CPU32-based systems.
5143 Use this option for microcontrollers with a
5144 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
5145 68336, 68340, 68341, 68349 and 68360.
5149 Generate output for a 520X ``coldfire'' family cpu. This is the default
5150 when the compiler is configured for 520X-based systems.
5152 Use this option for microcontroller with a 5200 core, including
5153 the MCF5202, MCF5203, MCF5204 and MCF5202.
5158 Generate output for a 68040, without using any of the new instructions.
5159 This results in code which can run relatively efficiently on either a
5160 68020/68881 or a 68030 or a 68040. The generated code does use the
5161 68881 instructions that are emulated on the 68040.
5165 Generate output for a 68060, without using any of the new instructions.
5166 This results in code which can run relatively efficiently on either a
5167 68020/68881 or a 68030 or a 68040. The generated code does use the
5168 68881 instructions that are emulated on the 68060.
5172 Generate output containing Sun FPA instructions for floating point.
5175 @opindex msoft-float
5176 Generate output containing library calls for floating point.
5177 @strong{Warning:} the requisite libraries are not available for all m68k
5178 targets. Normally the facilities of the machine's usual C compiler are
5179 used, but this can't be done directly in cross-compilation. You must
5180 make your own arrangements to provide suitable library functions for
5181 cross-compilation. The embedded targets @samp{m68k-*-aout} and
5182 @samp{m68k-*-coff} do provide software floating point support.
5186 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5189 @opindex mnobitfield
5190 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
5191 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
5195 Do use the bit-field instructions. The @option{-m68020} option implies
5196 @option{-mbitfield}. This is the default if you use a configuration
5197 designed for a 68020.
5201 Use a different function-calling convention, in which functions
5202 that take a fixed number of arguments return with the @code{rtd}
5203 instruction, which pops their arguments while returning. This
5204 saves one instruction in the caller since there is no need to pop
5205 the arguments there.
5207 This calling convention is incompatible with the one normally
5208 used on Unix, so you cannot use it if you need to call libraries
5209 compiled with the Unix compiler.
5211 Also, you must provide function prototypes for all functions that
5212 take variable numbers of arguments (including @code{printf});
5213 otherwise incorrect code will be generated for calls to those
5216 In addition, seriously incorrect code will result if you call a
5217 function with too many arguments. (Normally, extra arguments are
5218 harmlessly ignored.)
5220 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
5221 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
5224 @itemx -mno-align-int
5226 @opindex mno-align-int
5227 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
5228 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
5229 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
5230 Aligning variables on 32-bit boundaries produces code that runs somewhat
5231 faster on processors with 32-bit busses at the expense of more memory.
5233 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
5234 align structures containing the above types differently than
5235 most published application binary interface specifications for the m68k.
5239 Use the pc-relative addressing mode of the 68000 directly, instead of
5240 using a global offset table. At present, this option implies @option{-fpic},
5241 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
5242 not presently supported with @option{-mpcrel}, though this could be supported for
5243 68020 and higher processors.
5245 @item -mno-strict-align
5246 @itemx -mstrict-align
5247 @opindex mno-strict-align
5248 @opindex mstrict-align
5249 Do not (do) assume that unaligned memory references will be handled by
5254 @node M68hc1x Options
5255 @subsection M68hc1x Options
5256 @cindex M68hc1x options
5258 These are the @samp{-m} options defined for the 68hc11 and 68hc12
5259 microcontrollers. The default values for these options depends on
5260 which style of microcontroller was selected when the compiler was configured;
5261 the defaults for the most common choices are given below.
5268 Generate output for a 68HC11. This is the default
5269 when the compiler is configured for 68HC11-based systems.
5275 Generate output for a 68HC12. This is the default
5276 when the compiler is configured for 68HC12-based systems.
5279 @opindex mauto-incdec
5280 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
5285 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5287 @item -msoft-reg-count=@var{count}
5288 @opindex msoft-reg-count
5289 Specify the number of pseudo-soft registers which are used for the
5290 code generation. The maximum number is 32. Using more pseudo-soft
5291 register may or may not result in better code depending on the program.
5292 The default is 4 for 68HC11 and 2 for 68HC12.
5297 @subsection VAX Options
5300 These @samp{-m} options are defined for the Vax:
5305 Do not output certain jump instructions (@code{aobleq} and so on)
5306 that the Unix assembler for the Vax cannot handle across long
5311 Do output those jump instructions, on the assumption that you
5312 will assemble with the GNU assembler.
5316 Output code for g-format floating point numbers instead of d-format.
5320 @subsection SPARC Options
5321 @cindex SPARC options
5323 These @samp{-m} switches are supported on the SPARC:
5328 @opindex mno-app-regs
5330 Specify @option{-mapp-regs} to generate output using the global registers
5331 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
5334 To be fully SVR4 ABI compliant at the cost of some performance loss,
5335 specify @option{-mno-app-regs}. You should compile libraries and system
5336 software with this option.
5341 @opindex mhard-float
5342 Generate output containing floating point instructions. This is the
5348 @opindex msoft-float
5349 Generate output containing library calls for floating point.
5350 @strong{Warning:} the requisite libraries are not available for all SPARC
5351 targets. Normally the facilities of the machine's usual C compiler are
5352 used, but this cannot be done directly in cross-compilation. You must make
5353 your own arrangements to provide suitable library functions for
5354 cross-compilation. The embedded targets @samp{sparc-*-aout} and
5355 @samp{sparclite-*-*} do provide software floating point support.
5357 @option{-msoft-float} changes the calling convention in the output file;
5358 therefore, it is only useful if you compile @emph{all} of a program with
5359 this option. In particular, you need to compile @file{libgcc.a}, the
5360 library that comes with GCC, with @option{-msoft-float} in order for
5363 @item -mhard-quad-float
5364 @opindex mhard-quad-float
5365 Generate output containing quad-word (long double) floating point
5368 @item -msoft-quad-float
5369 @opindex msoft-quad-float
5370 Generate output containing library calls for quad-word (long double)
5371 floating point instructions. The functions called are those specified
5372 in the SPARC ABI@. This is the default.
5374 As of this writing, there are no sparc implementations that have hardware
5375 support for the quad-word floating point instructions. They all invoke
5376 a trap handler for one of these instructions, and then the trap handler
5377 emulates the effect of the instruction. Because of the trap handler overhead,
5378 this is much slower than calling the ABI library routines. Thus the
5379 @option{-msoft-quad-float} option is the default.
5383 @opindex mno-epilogue
5385 With @option{-mepilogue} (the default), the compiler always emits code for
5386 function exit at the end of each function. Any function exit in
5387 the middle of the function (such as a return statement in C) will
5388 generate a jump to the exit code at the end of the function.
5390 With @option{-mno-epilogue}, the compiler tries to emit exit code inline
5391 at every function exit.
5397 With @option{-mflat}, the compiler does not generate save/restore instructions
5398 and will use a ``flat'' or single register window calling convention.
5399 This model uses %i7 as the frame pointer and is compatible with the normal
5400 register window model. Code from either may be intermixed.
5401 The local registers and the input registers (0--5) are still treated as
5402 ``call saved'' registers and will be saved on the stack as necessary.
5404 With @option{-mno-flat} (the default), the compiler emits save/restore
5405 instructions (except for leaf functions) and is the normal mode of operation.
5407 @item -mno-unaligned-doubles
5408 @itemx -munaligned-doubles
5409 @opindex mno-unaligned-doubles
5410 @opindex munaligned-doubles
5411 Assume that doubles have 8 byte alignment. This is the default.
5413 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
5414 alignment only if they are contained in another type, or if they have an
5415 absolute address. Otherwise, it assumes they have 4 byte alignment.
5416 Specifying this option avoids some rare compatibility problems with code
5417 generated by other compilers. It is not the default because it results
5418 in a performance loss, especially for floating point code.
5420 @item -mno-faster-structs
5421 @itemx -mfaster-structs
5422 @opindex mno-faster-structs
5423 @opindex mfaster-structs
5424 With @option{-mfaster-structs}, the compiler assumes that structures
5425 should have 8 byte alignment. This enables the use of pairs of
5426 @code{ldd} and @code{std} instructions for copies in structure
5427 assignment, in place of twice as many @code{ld} and @code{st} pairs.
5428 However, the use of this changed alignment directly violates the Sparc
5429 ABI@. Thus, it's intended only for use on targets where the developer
5430 acknowledges that their resulting code will not be directly in line with
5431 the rules of the ABI@.
5437 These two options select variations on the SPARC architecture.
5439 By default (unless specifically configured for the Fujitsu SPARClite),
5440 GCC generates code for the v7 variant of the SPARC architecture.
5442 @option{-mv8} will give you SPARC v8 code. The only difference from v7
5443 code is that the compiler emits the integer multiply and integer
5444 divide instructions which exist in SPARC v8 but not in SPARC v7.
5446 @option{-msparclite} will give you SPARClite code. This adds the integer
5447 multiply, integer divide step and scan (@code{ffs}) instructions which
5448 exist in SPARClite but not in SPARC v7.
5450 These options are deprecated and will be deleted in a future GCC release.
5451 They have been replaced with @option{-mcpu=xxx}.
5456 @opindex msupersparc
5457 These two options select the processor for which the code is optimised.
5459 With @option{-mcypress} (the default), the compiler optimizes code for the
5460 Cypress CY7C602 chip, as used in the SparcStation/SparcServer 3xx series.
5461 This is also appropriate for the older SparcStation 1, 2, IPX etc.
5463 With @option{-msupersparc} the compiler optimizes code for the SuperSparc cpu, as
5464 used in the SparcStation 10, 1000 and 2000 series. This flag also enables use
5465 of the full SPARC v8 instruction set.
5467 These options are deprecated and will be deleted in a future GCC release.
5468 They have been replaced with @option{-mcpu=xxx}.
5470 @item -mcpu=@var{cpu_type}
5472 Set the instruction set, register set, and instruction scheduling parameters
5473 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
5474 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
5475 @samp{hypersparc}, @samp{sparclite86x}, @samp{f930}, @samp{f934},
5476 @samp{sparclet}, @samp{tsc701}, @samp{v9}, and @samp{ultrasparc}.
5478 Default instruction scheduling parameters are used for values that select
5479 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
5480 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
5482 Here is a list of each supported architecture and their supported
5487 v8: supersparc, hypersparc
5488 sparclite: f930, f934, sparclite86x
5493 @item -mtune=@var{cpu_type}
5495 Set the instruction scheduling parameters for machine type
5496 @var{cpu_type}, but do not set the instruction set or register set that the
5497 option @option{-mcpu=@var{cpu_type}} would.
5499 The same values for @option{-mcpu=@var{cpu_type}} are used for
5500 @option{-mtune=@var{cpu_type}}, though the only useful values are those that
5501 select a particular cpu implementation: @samp{cypress}, @samp{supersparc},
5502 @samp{hypersparc}, @samp{f930}, @samp{f934}, @samp{sparclite86x},
5503 @samp{tsc701}, @samp{ultrasparc}.
5507 These @samp{-m} switches are supported in addition to the above
5508 on the SPARCLET processor.
5511 @item -mlittle-endian
5512 @opindex mlittle-endian
5513 Generate code for a processor running in little-endian mode.
5517 Treat register @code{%g0} as a normal register.
5518 GCC will continue to clobber it as necessary but will not assume
5519 it always reads as 0.
5521 @item -mbroken-saverestore
5522 @opindex mbroken-saverestore
5523 Generate code that does not use non-trivial forms of the @code{save} and
5524 @code{restore} instructions. Early versions of the SPARCLET processor do
5525 not correctly handle @code{save} and @code{restore} instructions used with
5526 arguments. They correctly handle them used without arguments. A @code{save}
5527 instruction used without arguments increments the current window pointer
5528 but does not allocate a new stack frame. It is assumed that the window
5529 overflow trap handler will properly handle this case as will interrupt
5533 These @samp{-m} switches are supported in addition to the above
5534 on SPARC V9 processors in 64-bit environments.
5537 @item -mlittle-endian
5538 @opindex mlittle-endian
5539 Generate code for a processor running in little-endian mode.
5545 Generate code for a 32-bit or 64-bit environment.
5546 The 32-bit environment sets int, long and pointer to 32 bits.
5547 The 64-bit environment sets int to 32 bits and long and pointer
5550 @item -mcmodel=medlow
5551 @opindex mcmodel=medlow
5552 Generate code for the Medium/Low code model: the program must be linked
5553 in the low 32 bits of the address space. Pointers are 64 bits.
5554 Programs can be statically or dynamically linked.
5556 @item -mcmodel=medmid
5557 @opindex mcmodel=medmid
5558 Generate code for the Medium/Middle code model: the program must be linked
5559 in the low 44 bits of the address space, the text segment must be less than
5560 2G bytes, and data segment must be within 2G of the text segment.
5561 Pointers are 64 bits.
5563 @item -mcmodel=medany
5564 @opindex mcmodel=medany
5565 Generate code for the Medium/Anywhere code model: the program may be linked
5566 anywhere in the address space, the text segment must be less than
5567 2G bytes, and data segment must be within 2G of the text segment.
5568 Pointers are 64 bits.
5570 @item -mcmodel=embmedany
5571 @opindex mcmodel=embmedany
5572 Generate code for the Medium/Anywhere code model for embedded systems:
5573 assume a 32-bit text and a 32-bit data segment, both starting anywhere
5574 (determined at link time). Register %g4 points to the base of the
5575 data segment. Pointers are still 64 bits.
5576 Programs are statically linked, PIC is not supported.
5579 @itemx -mno-stack-bias
5580 @opindex mstack-bias
5581 @opindex mno-stack-bias
5582 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
5583 frame pointer if present, are offset by @minus{}2047 which must be added back
5584 when making stack frame references.
5585 Otherwise, assume no such offset is present.
5588 @node Convex Options
5589 @subsection Convex Options
5590 @cindex Convex options
5592 These @samp{-m} options are defined for Convex:
5597 Generate output for C1. The code will run on any Convex machine.
5598 The preprocessor symbol @code{__convex__c1__} is defined.
5602 Generate output for C2. Uses instructions not available on C1.
5603 Scheduling and other optimizations are chosen for max performance on C2.
5604 The preprocessor symbol @code{__convex_c2__} is defined.
5608 Generate output for C32xx. Uses instructions not available on C1.
5609 Scheduling and other optimizations are chosen for max performance on C32.
5610 The preprocessor symbol @code{__convex_c32__} is defined.
5614 Generate output for C34xx. Uses instructions not available on C1.
5615 Scheduling and other optimizations are chosen for max performance on C34.
5616 The preprocessor symbol @code{__convex_c34__} is defined.
5620 Generate output for C38xx. Uses instructions not available on C1.
5621 Scheduling and other optimizations are chosen for max performance on C38.
5622 The preprocessor symbol @code{__convex_c38__} is defined.
5626 Generate code which puts an argument count in the word preceding each
5627 argument list. This is compatible with regular CC, and a few programs
5628 may need the argument count word. GDB and other source-level debuggers
5629 do not need it; this info is in the symbol table.
5632 @opindex mnoargcount
5633 Omit the argument count word. This is the default.
5635 @item -mvolatile-cache
5636 @opindex mvolatile-cache
5637 Allow volatile references to be cached. This is the default.
5639 @item -mvolatile-nocache
5640 @opindex mvolatile-nocache
5641 Volatile references bypass the data cache, going all the way to memory.
5642 This is only needed for multi-processor code that does not use standard
5643 synchronization instructions. Making non-volatile references to volatile
5644 locations will not necessarily work.
5648 Type long is 32 bits, the same as type int. This is the default.
5652 Type long is 64 bits, the same as type long long. This option is useless,
5653 because no library support exists for it.
5656 @node AMD29K Options
5657 @subsection AMD29K Options
5658 @cindex AMD29K options
5660 These @samp{-m} options are defined for the AMD Am29000:
5665 @cindex DW bit (29k)
5666 Generate code that assumes the @code{DW} bit is set, i.e., that byte and
5667 halfword operations are directly supported by the hardware. This is the
5672 Generate code that assumes the @code{DW} bit is not set.
5676 @cindex byte writes (29k)
5677 Generate code that assumes the system supports byte and halfword write
5678 operations. This is the default.
5682 Generate code that assumes the systems does not support byte and
5683 halfword write operations. @option{-mnbw} implies @option{-mndw}.
5687 @cindex memory model (29k)
5688 Use a small memory model that assumes that all function addresses are
5689 either within a single 256 KB segment or at an absolute address of less
5690 than 256k. This allows the @code{call} instruction to be used instead
5691 of a @code{const}, @code{consth}, @code{calli} sequence.
5695 Use the normal memory model: Generate @code{call} instructions only when
5696 calling functions in the same file and @code{calli} instructions
5697 otherwise. This works if each file occupies less than 256 KB but allows
5698 the entire executable to be larger than 256 KB@. This is the default.
5702 Always use @code{calli} instructions. Specify this option if you expect
5703 a single file to compile into more than 256 KB of code.
5707 @cindex processor selection (29k)
5708 Generate code for the Am29050.
5712 Generate code for the Am29000. This is the default.
5714 @item -mkernel-registers
5715 @opindex mkernel-registers
5716 @cindex kernel and user registers (29k)
5717 Generate references to registers @code{gr64-gr95} instead of to
5718 registers @code{gr96-gr127}. This option can be used when compiling
5719 kernel code that wants a set of global registers disjoint from that used
5722 Note that when this option is used, register names in @samp{-f} flags
5723 must use the normal, user-mode, names.
5725 @item -muser-registers
5726 @opindex muser-registers
5727 Use the normal set of global registers, @code{gr96-gr127}. This is the
5731 @itemx -mno-stack-check
5732 @opindex mstack-check
5733 @opindex mno-stack-check
5734 @cindex stack checks (29k)
5735 Insert (or do not insert) a call to @code{__msp_check} after each stack
5736 adjustment. This is often used for kernel code.
5739 @itemx -mno-storem-bug
5740 @opindex mstorem-bug
5741 @opindex mno-storem-bug
5742 @cindex storem bug (29k)
5743 @option{-mstorem-bug} handles 29k processors which cannot handle the
5744 separation of a mtsrim insn and a storem instruction (most 29000 chips
5745 to date, but not the 29050).
5747 @item -mno-reuse-arg-regs
5748 @itemx -mreuse-arg-regs
5749 @opindex mno-reuse-arg-regs
5750 @opindex mreuse-arg-regs
5751 @option{-mno-reuse-arg-regs} tells the compiler to only use incoming argument
5752 registers for copying out arguments. This helps detect calling a function
5753 with fewer arguments than it was declared with.
5755 @item -mno-impure-text
5756 @itemx -mimpure-text
5757 @opindex mno-impure-text
5758 @opindex mimpure-text
5759 @option{-mimpure-text}, used in addition to @option{-shared}, tells the compiler to
5760 not pass @option{-assert pure-text} to the linker when linking a shared object.
5763 @opindex msoft-float
5764 Generate output containing library calls for floating point.
5765 @strong{Warning:} the requisite libraries are not part of GCC@.
5766 Normally the facilities of the machine's usual C compiler are used, but
5767 this can't be done directly in cross-compilation. You must make your
5768 own arrangements to provide suitable library functions for
5773 Do not generate multm or multmu instructions. This is useful for some embedded
5774 systems which do not have trap handlers for these instructions.
5778 @subsection ARM Options
5781 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
5786 @opindex mapcs-frame
5787 Generate a stack frame that is compliant with the ARM Procedure Call
5788 Standard for all functions, even if this is not strictly necessary for
5789 correct execution of the code. Specifying @option{-fomit-frame-pointer}
5790 with this option will cause the stack frames not to be generated for
5791 leaf functions. The default is @option{-mno-apcs-frame}.
5795 This is a synonym for @option{-mapcs-frame}.
5799 Generate code for a processor running with a 26-bit program counter,
5800 and conforming to the function calling standards for the APCS 26-bit
5801 option. This option replaces the @option{-m2} and @option{-m3} options
5802 of previous releases of the compiler.
5806 Generate code for a processor running with a 32-bit program counter,
5807 and conforming to the function calling standards for the APCS 32-bit
5808 option. This option replaces the @option{-m6} option of previous releases
5812 @c not currently implemented
5813 @item -mapcs-stack-check
5814 @opindex mapcs-stack-check
5815 Generate code to check the amount of stack space available upon entry to
5816 every function (that actually uses some stack space). If there is
5817 insufficient space available then either the function
5818 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
5819 called, depending upon the amount of stack space required. The run time
5820 system is required to provide these functions. The default is
5821 @option{-mno-apcs-stack-check}, since this produces smaller code.
5823 @c not currently implemented
5825 @opindex mapcs-float
5826 Pass floating point arguments using the float point registers. This is
5827 one of the variants of the APCS@. This option is recommended if the
5828 target hardware has a floating point unit or if a lot of floating point
5829 arithmetic is going to be performed by the code. The default is
5830 @option{-mno-apcs-float}, since integer only code is slightly increased in
5831 size if @option{-mapcs-float} is used.
5833 @c not currently implemented
5834 @item -mapcs-reentrant
5835 @opindex mapcs-reentrant
5836 Generate reentrant, position independent code. The default is
5837 @option{-mno-apcs-reentrant}.
5840 @item -mthumb-interwork
5841 @opindex mthumb-interwork
5842 Generate code which supports calling between the ARM and Thumb
5843 instruction sets. Without this option the two instruction sets cannot
5844 be reliably used inside one program. The default is
5845 @option{-mno-thumb-interwork}, since slightly larger code is generated
5846 when @option{-mthumb-interwork} is specified.
5848 @item -mno-sched-prolog
5849 @opindex mno-sched-prolog
5850 Prevent the reordering of instructions in the function prolog, or the
5851 merging of those instruction with the instructions in the function's
5852 body. This means that all functions will start with a recognizable set
5853 of instructions (or in fact one of a choice from a small set of
5854 different function prologues), and this information can be used to
5855 locate the start if functions inside an executable piece of code. The
5856 default is @option{-msched-prolog}.
5859 @opindex mhard-float
5860 Generate output containing floating point instructions. This is the
5864 @opindex msoft-float
5865 Generate output containing library calls for floating point.
5866 @strong{Warning:} the requisite libraries are not available for all ARM
5867 targets. Normally the facilities of the machine's usual C compiler are
5868 used, but this cannot be done directly in cross-compilation. You must make
5869 your own arrangements to provide suitable library functions for
5872 @option{-msoft-float} changes the calling convention in the output file;
5873 therefore, it is only useful if you compile @emph{all} of a program with
5874 this option. In particular, you need to compile @file{libgcc.a}, the
5875 library that comes with GCC, with @option{-msoft-float} in order for
5878 @item -mlittle-endian
5879 @opindex mlittle-endian
5880 Generate code for a processor running in little-endian mode. This is
5881 the default for all standard configurations.
5884 @opindex mbig-endian
5885 Generate code for a processor running in big-endian mode; the default is
5886 to compile code for a little-endian processor.
5888 @item -mwords-little-endian
5889 @opindex mwords-little-endian
5890 This option only applies when generating code for big-endian processors.
5891 Generate code for a little-endian word order but a big-endian byte
5892 order. That is, a byte order of the form @samp{32107654}. Note: this
5893 option should only be used if you require compatibility with code for
5894 big-endian ARM processors generated by versions of the compiler prior to
5897 @item -malignment-traps
5898 @opindex malignment-traps
5899 Generate code that will not trap if the MMU has alignment traps enabled.
5900 On ARM architectures prior to ARMv4, there were no instructions to
5901 access half-word objects stored in memory. However, when reading from
5902 memory a feature of the ARM architecture allows a word load to be used,
5903 even if the address is unaligned, and the processor core will rotate the
5904 data as it is being loaded. This option tells the compiler that such
5905 misaligned accesses will cause a MMU trap and that it should instead
5906 synthesise the access as a series of byte accesses. The compiler can
5907 still use word accesses to load half-word data if it knows that the
5908 address is aligned to a word boundary.
5910 This option is ignored when compiling for ARM architecture 4 or later,
5911 since these processors have instructions to directly access half-word
5914 @item -mno-alignment-traps
5915 @opindex mno-alignment-traps
5916 Generate code that assumes that the MMU will not trap unaligned
5917 accesses. This produces better code when the target instruction set
5918 does not have half-word memory operations (i.e.@: implementations prior to
5921 Note that you cannot use this option to access unaligned word objects,
5922 since the processor will only fetch one 32-bit aligned object from
5925 The default setting for most targets is @option{-mno-alignment-traps}, since
5926 this produces better code when there are no half-word memory
5927 instructions available.
5929 @item -mshort-load-bytes
5930 @itemx -mno-short-load-words
5931 @opindex mshort-load-bytes
5932 @opindex mno-short-load-words
5933 These are deprecated aliases for @option{-malignment-traps}.
5935 @item -mno-short-load-bytes
5936 @itemx -mshort-load-words
5937 @opindex mno-short-load-bytes
5938 @opindex mshort-load-words
5939 This are deprecated aliases for @option{-mno-alignment-traps}.
5943 This option only applies to RISC iX@. Emulate the native BSD-mode
5944 compiler. This is the default if @option{-ansi} is not specified.
5948 This option only applies to RISC iX@. Emulate the native X/Open-mode
5951 @item -mno-symrename
5952 @opindex mno-symrename
5953 This option only applies to RISC iX@. Do not run the assembler
5954 post-processor, @samp{symrename}, after code has been assembled.
5955 Normally it is necessary to modify some of the standard symbols in
5956 preparation for linking with the RISC iX C library; this option
5957 suppresses this pass. The post-processor is never run when the
5958 compiler is built for cross-compilation.
5960 @item -mcpu=@var{name}
5962 This specifies the name of the target ARM processor. GCC uses this name
5963 to determine what kind of instructions it can emit when generating
5964 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
5965 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
5966 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
5967 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
5968 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
5969 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm8},
5970 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
5971 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
5972 @samp{arm920t}, @samp{arm940t}, @samp{arm9tdmi}, @samp{arm10tdmi},
5973 @samp{arm1020t}, @samp{xscale}.
5975 @itemx -mtune=@var{name}
5977 This option is very similar to the @option{-mcpu=} option, except that
5978 instead of specifying the actual target processor type, and hence
5979 restricting which instructions can be used, it specifies that GCC should
5980 tune the performance of the code as if the target were of the type
5981 specified in this option, but still choosing the instructions that it
5982 will generate based on the cpu specified by a @option{-mcpu=} option.
5983 For some ARM implementations better performance can be obtained by using
5986 @item -march=@var{name}
5988 This specifies the name of the target ARM architecture. GCC uses this
5989 name to determine what kind of instructions it can emit when generating
5990 assembly code. This option can be used in conjunction with or instead
5991 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
5992 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
5993 @samp{armv5}, @samp{armv5t}, @samp{armv5te}.
5995 @item -mfpe=@var{number}
5996 @itemx -mfp=@var{number}
5999 This specifies the version of the floating point emulation available on
6000 the target. Permissible values are 2 and 3. @option{-mfp=} is a synonym
6001 for @option{-mfpe=}, for compatibility with older versions of GCC@.
6003 @item -mstructure-size-boundary=@var{n}
6004 @opindex mstructure-size-boundary
6005 The size of all structures and unions will be rounded up to a multiple
6006 of the number of bits set by this option. Permissible values are 8 and
6007 32. The default value varies for different toolchains. For the COFF
6008 targeted toolchain the default value is 8. Specifying the larger number
6009 can produce faster, more efficient code, but can also increase the size
6010 of the program. The two values are potentially incompatible. Code
6011 compiled with one value cannot necessarily expect to work with code or
6012 libraries compiled with the other value, if they exchange information
6013 using structures or unions.
6015 @item -mabort-on-noreturn
6016 @opindex mabort-on-noreturn
6017 Generate a call to the function @code{abort} at the end of a
6018 @code{noreturn} function. It will be executed if the function tries to
6022 @itemx -mno-long-calls
6023 @opindex mlong-calls
6024 @opindex mno-long-calls
6025 Tells the compiler to perform function calls by first loading the
6026 address of the function into a register and then performing a subroutine
6027 call on this register. This switch is needed if the target function
6028 will lie outside of the 64 megabyte addressing range of the offset based
6029 version of subroutine call instruction.
6031 Even if this switch is enabled, not all function calls will be turned
6032 into long calls. The heuristic is that static functions, functions
6033 which have the @samp{short-call} attribute, functions that are inside
6034 the scope of a @samp{#pragma no_long_calls} directive and functions whose
6035 definitions have already been compiled within the current compilation
6036 unit, will not be turned into long calls. The exception to this rule is
6037 that weak function definitions, functions with the @samp{long-call}
6038 attribute or the @samp{section} attribute, and functions that are within
6039 the scope of a @samp{#pragma long_calls} directive, will always be
6040 turned into long calls.
6042 This feature is not enabled by default. Specifying
6043 @option{-mno-long-calls} will restore the default behaviour, as will
6044 placing the function calls within the scope of a @samp{#pragma
6045 long_calls_off} directive. Note these switches have no effect on how
6046 the compiler generates code to handle function calls via function
6049 @item -mnop-fun-dllimport
6050 @opindex mnop-fun-dllimport
6051 Disable support for the @code{dllimport} attribute.
6053 @item -msingle-pic-base
6054 @opindex msingle-pic-base
6055 Treat the register used for PIC addressing as read-only, rather than
6056 loading it in the prologue for each function. The run-time system is
6057 responsible for initialising this register with an appropriate value
6058 before execution begins.
6060 @item -mpic-register=@var{reg}
6061 @opindex mpic-register
6062 Specify the register to be used for PIC addressing. The default is R10
6063 unless stack-checking is enabled, when R9 is used.
6065 @item -mpoke-function-name
6066 @opindex mpoke-function-name
6067 Write the name of each function into the text section, directly
6068 preceding the function prologue. The generated code is similar to this:
6072 .ascii "arm_poke_function_name", 0
6075 .word 0xff000000 + (t1 - t0)
6076 arm_poke_function_name
6078 stmfd sp!, @{fp, ip, lr, pc@}
6082 When performing a stack backtrace, code can inspect the value of
6083 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
6084 location @code{pc - 12} and the top 8 bits are set, then we know that
6085 there is a function name embedded immediately preceding this location
6086 and has length @code{((pc[-3]) & 0xff000000)}.
6090 Generate code for the 16-bit Thumb instruction set. The default is to
6091 use the 32-bit ARM instruction set.
6094 @opindex mtpcs-frame
6095 Generate a stack frame that is compliant with the Thumb Procedure Call
6096 Standard for all non-leaf functions. (A leaf function is one that does
6097 not call any other functions.) The default is @option{-mno-tpcs-frame}.
6099 @item -mtpcs-leaf-frame
6100 @opindex mtpcs-leaf-frame
6101 Generate a stack frame that is compliant with the Thumb Procedure Call
6102 Standard for all leaf functions. (A leaf function is one that does
6103 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
6105 @item -mcallee-super-interworking
6106 @opindex mcallee-super-interworking
6107 Gives all externally visible functions in the file being compiled an ARM
6108 instruction set header which switches to Thumb mode before executing the
6109 rest of the function. This allows these functions to be called from
6110 non-interworking code.
6112 @item -mcaller-super-interworking
6113 @opindex mcaller-super-interworking
6114 Allows calls via function pointers (including virtual functions) to
6115 execute correctly regardless of whether the target code has been
6116 compiled for interworking or not. There is a small overhead in the cost
6117 of executing a function pointer if this option is enabled.
6121 @node MN10200 Options
6122 @subsection MN10200 Options
6123 @cindex MN10200 options
6124 These @option{-m} options are defined for Matsushita MN10200 architectures:
6129 Indicate to the linker that it should perform a relaxation optimization pass
6130 to shorten branches, calls and absolute memory addresses. This option only
6131 has an effect when used on the command line for the final link step.
6133 This option makes symbolic debugging impossible.
6136 @node MN10300 Options
6137 @subsection MN10300 Options
6138 @cindex MN10300 options
6139 These @option{-m} options are defined for Matsushita MN10300 architectures:
6144 Generate code to avoid bugs in the multiply instructions for the MN10300
6145 processors. This is the default.
6148 @opindex mno-mult-bug
6149 Do not generate code to avoid bugs in the multiply instructions for the
6154 Generate code which uses features specific to the AM33 processor.
6158 Do not generate code which uses features specific to the AM33 processor. This
6163 Do not link in the C run-time initialization object file.
6167 Indicate to the linker that it should perform a relaxation optimization pass
6168 to shorten branches, calls and absolute memory addresses. This option only
6169 has an effect when used on the command line for the final link step.
6171 This option makes symbolic debugging impossible.
6175 @node M32R/D Options
6176 @subsection M32R/D Options
6177 @cindex M32R/D options
6179 These @option{-m} options are defined for Mitsubishi M32R/D architectures:
6182 @item -mcode-model=small
6183 @opindex mcode-model=small
6184 Assume all objects live in the lower 16MB of memory (so that their addresses
6185 can be loaded with the @code{ld24} instruction), and assume all subroutines
6186 are reachable with the @code{bl} instruction.
6187 This is the default.
6189 The addressability of a particular object can be set with the
6190 @code{model} attribute.
6192 @item -mcode-model=medium
6193 @opindex mcode-model=medium
6194 Assume objects may be anywhere in the 32-bit address space (the compiler
6195 will generate @code{seth/add3} instructions to load their addresses), and
6196 assume all subroutines are reachable with the @code{bl} instruction.
6198 @item -mcode-model=large
6199 @opindex mcode-model=large
6200 Assume objects may be anywhere in the 32-bit address space (the compiler
6201 will generate @code{seth/add3} instructions to load their addresses), and
6202 assume subroutines may not be reachable with the @code{bl} instruction
6203 (the compiler will generate the much slower @code{seth/add3/jl}
6204 instruction sequence).
6207 @opindex msdata=none
6208 Disable use of the small data area. Variables will be put into
6209 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
6210 @code{section} attribute has been specified).
6211 This is the default.
6213 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
6214 Objects may be explicitly put in the small data area with the
6215 @code{section} attribute using one of these sections.
6218 @opindex msdata=sdata
6219 Put small global and static data in the small data area, but do not
6220 generate special code to reference them.
6224 Put small global and static data in the small data area, and generate
6225 special instructions to reference them.
6229 @cindex smaller data references
6230 Put global and static objects less than or equal to @var{num} bytes
6231 into the small data or bss sections instead of the normal data or bss
6232 sections. The default value of @var{num} is 8.
6233 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
6234 for this option to have any effect.
6236 All modules should be compiled with the same @option{-G @var{num}} value.
6237 Compiling with different values of @var{num} may or may not work; if it
6238 doesn't the linker will give an error message---incorrect code will not be
6244 @subsection M88K Options
6245 @cindex M88k options
6247 These @samp{-m} options are defined for Motorola 88k architectures:
6252 Generate code that works well on both the m88100 and the
6257 Generate code that works best for the m88100, but that also
6262 Generate code that works best for the m88110, and may not run
6267 Obsolete option to be removed from the next revision.
6270 @item -midentify-revision
6271 @opindex midentify-revision
6272 @cindex identifying source, compiler (88k)
6273 Include an @code{ident} directive in the assembler output recording the
6274 source file name, compiler name and version, timestamp, and compilation
6277 @item -mno-underscores
6278 @opindex mno-underscores
6279 @cindex underscores, avoiding (88k)
6280 In assembler output, emit symbol names without adding an underscore
6281 character at the beginning of each name. The default is to use an
6282 underscore as prefix on each name.
6284 @item -mocs-debug-info
6285 @itemx -mno-ocs-debug-info
6286 @opindex mocs-debug-info
6287 @opindex mno-ocs-debug-info
6289 @cindex debugging, 88k OCS
6290 Include (or omit) additional debugging information (about registers used
6291 in each stack frame) as specified in the 88open Object Compatibility
6292 Standard, ``OCS''@. This extra information allows debugging of code that
6293 has had the frame pointer eliminated. The default for DG/UX, SVr4, and
6294 Delta 88 SVr3.2 is to include this information; other 88k configurations
6295 omit this information by default.
6297 @item -mocs-frame-position
6298 @opindex mocs-frame-position
6299 @cindex register positions in frame (88k)
6300 When emitting COFF debugging information for automatic variables and
6301 parameters stored on the stack, use the offset from the canonical frame
6302 address, which is the stack pointer (register 31) on entry to the
6303 function. The DG/UX, SVr4, Delta88 SVr3.2, and BCS configurations use
6304 @option{-mocs-frame-position}; other 88k configurations have the default
6305 @option{-mno-ocs-frame-position}.
6307 @item -mno-ocs-frame-position
6308 @opindex mno-ocs-frame-position
6309 @cindex register positions in frame (88k)
6310 When emitting COFF debugging information for automatic variables and
6311 parameters stored on the stack, use the offset from the frame pointer
6312 register (register 30). When this option is in effect, the frame
6313 pointer is not eliminated when debugging information is selected by the
6316 @item -moptimize-arg-area
6317 @itemx -mno-optimize-arg-area
6318 @opindex moptimize-arg-area
6319 @opindex mno-optimize-arg-area
6320 @cindex arguments in frame (88k)
6321 Control how function arguments are stored in stack frames.
6322 @option{-moptimize-arg-area} saves space by optimizing them, but this
6323 conflicts with the 88open specifications. The opposite alternative,
6324 @option{-mno-optimize-arg-area}, agrees with 88open standards. By default
6325 GCC does not optimize the argument area.
6327 @item -mshort-data-@var{num}
6328 @opindex mshort-data
6329 @cindex smaller data references (88k)
6330 @cindex r0-relative references (88k)
6331 Generate smaller data references by making them relative to @code{r0},
6332 which allows loading a value using a single instruction (rather than the
6333 usual two). You control which data references are affected by
6334 specifying @var{num} with this option. For example, if you specify
6335 @option{-mshort-data-512}, then the data references affected are those
6336 involving displacements of less than 512 bytes.
6337 @option{-mshort-data-@var{num}} is not effective for @var{num} greater
6340 @item -mserialize-volatile
6341 @opindex mserialize-volatile
6342 @itemx -mno-serialize-volatile
6343 @opindex mno-serialize-volatile
6344 @cindex sequential consistency on 88k
6345 Do, or don't, generate code to guarantee sequential consistency
6346 of volatile memory references. By default, consistency is
6349 The order of memory references made by the MC88110 processor does
6350 not always match the order of the instructions requesting those
6351 references. In particular, a load instruction may execute before
6352 a preceding store instruction. Such reordering violates
6353 sequential consistency of volatile memory references, when there
6354 are multiple processors. When consistency must be guaranteed,
6355 GCC generates special instructions, as needed, to force
6356 execution in the proper order.
6358 The MC88100 processor does not reorder memory references and so
6359 always provides sequential consistency. However, by default, GCC
6360 generates the special instructions to guarantee consistency
6361 even when you use @option{-m88100}, so that the code may be run on an
6362 MC88110 processor. If you intend to run your code only on the
6363 MC88100 processor, you may use @option{-mno-serialize-volatile}.
6365 The extra code generated to guarantee consistency may affect the
6366 performance of your application. If you know that you can safely
6367 forgo this guarantee, you may use @option{-mno-serialize-volatile}.
6373 @cindex assembler syntax, 88k
6375 Turn on (@option{-msvr4}) or off (@option{-msvr3}) compiler extensions
6376 related to System V release 4 (SVr4). This controls the following:
6380 Which variant of the assembler syntax to emit.
6382 @option{-msvr4} makes the C preprocessor recognize @samp{#pragma weak}
6383 that is used on System V release 4.
6385 @option{-msvr4} makes GCC issue additional declaration directives used in
6389 @option{-msvr4} is the default for the m88k-motorola-sysv4 and
6390 m88k-dg-dgux m88k configurations. @option{-msvr3} is the default for all
6391 other m88k configurations.
6393 @item -mversion-03.00
6394 @opindex mversion-03.00
6395 This option is obsolete, and is ignored.
6396 @c ??? which asm syntax better for GAS? option there too?
6398 @item -mno-check-zero-division
6399 @itemx -mcheck-zero-division
6400 @opindex mno-check-zero-division
6401 @opindex mcheck-zero-division
6402 @cindex zero division on 88k
6403 Do, or don't, generate code to guarantee that integer division by
6404 zero will be detected. By default, detection is guaranteed.
6406 Some models of the MC88100 processor fail to trap upon integer
6407 division by zero under certain conditions. By default, when
6408 compiling code that might be run on such a processor, GCC
6409 generates code that explicitly checks for zero-valued divisors
6410 and traps with exception number 503 when one is detected. Use of
6411 mno-check-zero-division suppresses such checking for code
6412 generated to run on an MC88100 processor.
6414 GCC assumes that the MC88110 processor correctly detects all
6415 instances of integer division by zero. When @option{-m88110} is
6416 specified, both @option{-mcheck-zero-division} and
6417 @option{-mno-check-zero-division} are ignored, and no explicit checks for
6418 zero-valued divisors are generated.
6420 @item -muse-div-instruction
6421 @opindex muse-div-instruction
6422 @cindex divide instruction, 88k
6423 Use the div instruction for signed integer division on the
6424 MC88100 processor. By default, the div instruction is not used.
6426 On the MC88100 processor the signed integer division instruction
6427 div) traps to the operating system on a negative operand. The
6428 operating system transparently completes the operation, but at a
6429 large cost in execution time. By default, when compiling code
6430 that might be run on an MC88100 processor, GCC emulates signed
6431 integer division using the unsigned integer division instruction
6432 divu), thereby avoiding the large penalty of a trap to the
6433 operating system. Such emulation has its own, smaller, execution
6434 cost in both time and space. To the extent that your code's
6435 important signed integer division operations are performed on two
6436 nonnegative operands, it may be desirable to use the div
6437 instruction directly.
6439 On the MC88110 processor the div instruction (also known as the
6440 divs instruction) processes negative operands without trapping to
6441 the operating system. When @option{-m88110} is specified,
6442 @option{-muse-div-instruction} is ignored, and the div instruction is used
6443 for signed integer division.
6445 Note that the result of dividing @code{INT_MIN} by @minus{}1 is undefined. In
6446 particular, the behavior of such a division with and without
6447 @option{-muse-div-instruction} may differ.
6449 @item -mtrap-large-shift
6450 @itemx -mhandle-large-shift
6451 @opindex mtrap-large-shift
6452 @opindex mhandle-large-shift
6453 @cindex bit shift overflow (88k)
6454 @cindex large bit shifts (88k)
6455 Include code to detect bit-shifts of more than 31 bits; respectively,
6456 trap such shifts or emit code to handle them properly. By default GCC
6457 makes no special provision for large bit shifts.
6459 @item -mwarn-passed-structs
6460 @opindex mwarn-passed-structs
6461 @cindex structure passing (88k)
6462 Warn when a function passes a struct as an argument or result.
6463 Structure-passing conventions have changed during the evolution of the C
6464 language, and are often the source of portability problems. By default,
6465 GCC issues no such warning.
6468 @node RS/6000 and PowerPC Options
6469 @subsection IBM RS/6000 and PowerPC Options
6470 @cindex RS/6000 and PowerPC Options
6471 @cindex IBM RS/6000 and PowerPC Options
6473 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
6481 @itemx -mpowerpc-gpopt
6482 @itemx -mno-powerpc-gpopt
6483 @itemx -mpowerpc-gfxopt
6484 @itemx -mno-powerpc-gfxopt
6486 @itemx -mno-powerpc64
6492 @opindex mno-powerpc
6493 @opindex mpowerpc-gpopt
6494 @opindex mno-powerpc-gpopt
6495 @opindex mpowerpc-gfxopt
6496 @opindex mno-powerpc-gfxopt
6498 @opindex mno-powerpc64
6499 GCC supports two related instruction set architectures for the
6500 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
6501 instructions supported by the @samp{rios} chip set used in the original
6502 RS/6000 systems and the @dfn{PowerPC} instruction set is the
6503 architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
6504 the IBM 4xx microprocessors.
6506 Neither architecture is a subset of the other. However there is a
6507 large common subset of instructions supported by both. An MQ
6508 register is included in processors supporting the POWER architecture.
6510 You use these options to specify which instructions are available on the
6511 processor you are using. The default value of these options is
6512 determined when configuring GCC@. Specifying the
6513 @option{-mcpu=@var{cpu_type}} overrides the specification of these
6514 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
6515 rather than the options listed above.
6517 The @option{-mpower} option allows GCC to generate instructions that
6518 are found only in the POWER architecture and to use the MQ register.
6519 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
6520 to generate instructions that are present in the POWER2 architecture but
6521 not the original POWER architecture.
6523 The @option{-mpowerpc} option allows GCC to generate instructions that
6524 are found only in the 32-bit subset of the PowerPC architecture.
6525 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
6526 GCC to use the optional PowerPC architecture instructions in the
6527 General Purpose group, including floating-point square root. Specifying
6528 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
6529 use the optional PowerPC architecture instructions in the Graphics
6530 group, including floating-point select.
6532 The @option{-mpowerpc64} option allows GCC to generate the additional
6533 64-bit instructions that are found in the full PowerPC64 architecture
6534 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
6535 @option{-mno-powerpc64}.
6537 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
6538 will use only the instructions in the common subset of both
6539 architectures plus some special AIX common-mode calls, and will not use
6540 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
6541 permits GCC to use any instruction from either architecture and to
6542 allow use of the MQ register; specify this for the Motorola MPC601.
6544 @item -mnew-mnemonics
6545 @itemx -mold-mnemonics
6546 @opindex mnew-mnemonics
6547 @opindex mold-mnemonics
6548 Select which mnemonics to use in the generated assembler code.
6549 @option{-mnew-mnemonics} requests output that uses the assembler mnemonics
6550 defined for the PowerPC architecture, while @option{-mold-mnemonics}
6551 requests the assembler mnemonics defined for the POWER architecture.
6552 Instructions defined in only one architecture have only one mnemonic;
6553 GCC uses that mnemonic irrespective of which of these options is
6556 GCC defaults to the mnemonics appropriate for the architecture in
6557 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
6558 value of these option. Unless you are building a cross-compiler, you
6559 should normally not specify either @option{-mnew-mnemonics} or
6560 @option{-mold-mnemonics}, but should instead accept the default.
6562 @item -mcpu=@var{cpu_type}
6564 Set architecture type, register usage, choice of mnemonics, and
6565 instruction scheduling parameters for machine type @var{cpu_type}.
6566 Supported values for @var{cpu_type} are @samp{rios}, @samp{rios1},
6567 @samp{rsc}, @samp{rios2}, @samp{rs64a}, @samp{601}, @samp{602},
6568 @samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620},
6569 @samp{630}, @samp{740}, @samp{750}, @samp{power}, @samp{power2},
6570 @samp{powerpc}, @samp{403}, @samp{505}, @samp{801}, @samp{821},
6571 @samp{823}, and @samp{860} and @samp{common}. @option{-mcpu=power},
6572 @option{-mcpu=power2}, @option{-mcpu=powerpc}, and @option{-mcpu=powerpc64}
6573 specify generic POWER, POWER2, pure 32-bit PowerPC (i.e., not MPC601),
6574 and 64-bit PowerPC architecture machine types, with an appropriate,
6575 generic processor model assumed for scheduling purposes.
6577 Specifying any of the following options:
6578 @option{-mcpu=rios1}, @option{-mcpu=rios2}, @option{-mcpu=rsc},
6579 @option{-mcpu=power}, or @option{-mcpu=power2}
6580 enables the @option{-mpower} option and disables the @option{-mpowerpc} option;
6581 @option{-mcpu=601} enables both the @option{-mpower} and @option{-mpowerpc} options.
6582 All of @option{-mcpu=rs64a}, @option{-mcpu=602}, @option{-mcpu=603},
6583 @option{-mcpu=603e}, @option{-mcpu=604}, @option{-mcpu=620}, @option{-mcpu=630},
6584 @option{-mcpu=740}, and @option{-mcpu=750}
6585 enable the @option{-mpowerpc} option and disable the @option{-mpower} option.
6586 Exactly similarly, all of @option{-mcpu=403},
6587 @option{-mcpu=505}, @option{-mcpu=821}, @option{-mcpu=860} and @option{-mcpu=powerpc}
6588 enable the @option{-mpowerpc} option and disable the @option{-mpower} option.
6589 @option{-mcpu=common} disables both the
6590 @option{-mpower} and @option{-mpowerpc} options.
6592 AIX versions 4 or greater selects @option{-mcpu=common} by default, so
6593 that code will operate on all members of the RS/6000 POWER and PowerPC
6594 families. In that case, GCC will use only the instructions in the
6595 common subset of both architectures plus some special AIX common-mode
6596 calls, and will not use the MQ register. GCC assumes a generic
6597 processor model for scheduling purposes.
6599 Specifying any of the options @option{-mcpu=rios1}, @option{-mcpu=rios2},
6600 @option{-mcpu=rsc}, @option{-mcpu=power}, or @option{-mcpu=power2} also
6601 disables the @samp{new-mnemonics} option. Specifying @option{-mcpu=601},
6602 @option{-mcpu=602}, @option{-mcpu=603}, @option{-mcpu=603e}, @option{-mcpu=604},
6603 @option{-mcpu=620}, @option{-mcpu=630}, @option{-mcpu=403}, @option{-mcpu=505},
6604 @option{-mcpu=821}, @option{-mcpu=860} or @option{-mcpu=powerpc} also enables
6605 the @samp{new-mnemonics} option.
6607 Specifying @option{-mcpu=403}, @option{-mcpu=821}, or @option{-mcpu=860} also
6608 enables the @option{-msoft-float} option.
6610 @item -mtune=@var{cpu_type}
6612 Set the instruction scheduling parameters for machine type
6613 @var{cpu_type}, but do not set the architecture type, register usage,
6614 choice of mnemonics like @option{-mcpu=@var{cpu_type}} would. The same
6615 values for @var{cpu_type} are used for @option{-mtune=@var{cpu_type}} as
6616 for @option{-mcpu=@var{cpu_type}}. The @option{-mtune=@var{cpu_type}}
6617 option overrides the @option{-mcpu=@var{cpu_type}} option in terms of
6618 instruction scheduling parameters.
6621 @itemx -mno-fp-in-toc
6622 @itemx -mno-sum-in-toc
6623 @itemx -mminimal-toc
6625 @opindex mno-fp-in-toc
6626 @opindex mno-sum-in-toc
6627 @opindex mminimal-toc
6628 Modify generation of the TOC (Table Of Contents), which is created for
6629 every executable file. The @option{-mfull-toc} option is selected by
6630 default. In that case, GCC will allocate at least one TOC entry for
6631 each unique non-automatic variable reference in your program. GCC
6632 will also place floating-point constants in the TOC@. However, only
6633 16,384 entries are available in the TOC@.
6635 If you receive a linker error message that saying you have overflowed
6636 the available TOC space, you can reduce the amount of TOC space used
6637 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
6638 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
6639 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
6640 generate code to calculate the sum of an address and a constant at
6641 run-time instead of putting that sum into the TOC@. You may specify one
6642 or both of these options. Each causes GCC to produce very slightly
6643 slower and larger code at the expense of conserving TOC space.
6645 If you still run out of space in the TOC even when you specify both of
6646 these options, specify @option{-mminimal-toc} instead. This option causes
6647 GCC to make only one TOC entry for every file. When you specify this
6648 option, GCC will produce code that is slower and larger but which
6649 uses extremely little TOC space. You may wish to use this option
6650 only on files that contain less frequently executed code.
6656 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
6657 @code{long} type, and the infrastructure needed to support them.
6658 Specifying @option{-maix64} implies @option{-mpowerpc64} and
6659 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
6660 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
6665 @opindex mno-xl-call
6666 On AIX, pass floating-point arguments to prototyped functions beyond the
6667 register save area (RSA) on the stack in addition to argument FPRs. The
6668 AIX calling convention was extended but not initially documented to
6669 handle an obscure K&R C case of calling a function that takes the
6670 address of its arguments with fewer arguments than declared. AIX XL
6671 compilers access floating point arguments which do not fit in the
6672 RSA from the stack when a subroutine is compiled without
6673 optimization. Because always storing floating-point arguments on the
6674 stack is inefficient and rarely needed, this option is not enabled by
6675 default and only is necessary when calling subroutines compiled by AIX
6676 XL compilers without optimization.
6680 Support @dfn{AIX Threads}. Link an application written to use
6681 @dfn{pthreads} with special libraries and startup code to enable the
6686 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
6687 application written to use message passing with special startup code to
6688 enable the application to run. The system must have PE installed in the
6689 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
6690 must be overridden with the @option{-specs=} option to specify the
6691 appropriate directory location. The Parallel Environment does not
6692 support threads, so the @option{-mpe} option and the @option{-mthreads}
6693 option are incompatible.
6697 @opindex msoft-float
6698 @opindex mhard-float
6699 Generate code that does not use (uses) the floating-point register set.
6700 Software floating point emulation is provided if you use the
6701 @option{-msoft-float} option, and pass the option to GCC when linking.
6704 @itemx -mno-multiple
6706 @opindex mno-multiple
6707 Generate code that uses (does not use) the load multiple word
6708 instructions and the store multiple word instructions. These
6709 instructions are generated by default on POWER systems, and not
6710 generated on PowerPC systems. Do not use @option{-mmultiple} on little
6711 endian PowerPC systems, since those instructions do not work when the
6712 processor is in little endian mode. The exceptions are PPC740 and
6713 PPC750 which permit the instructions usage in little endian mode.
6719 Generate code that uses (does not use) the load string instructions
6720 and the store string word instructions to save multiple registers and
6721 do small block moves. These instructions are generated by default on
6722 POWER systems, and not generated on PowerPC systems. Do not use
6723 @option{-mstring} on little endian PowerPC systems, since those
6724 instructions do not work when the processor is in little endian mode.
6725 The exceptions are PPC740 and PPC750 which permit the instructions
6726 usage in little endian mode.
6732 Generate code that uses (does not use) the load or store instructions
6733 that update the base register to the address of the calculated memory
6734 location. These instructions are generated by default. If you use
6735 @option{-mno-update}, there is a small window between the time that the
6736 stack pointer is updated and the address of the previous frame is
6737 stored, which means code that walks the stack frame across interrupts or
6738 signals may get corrupted data.
6741 @itemx -mno-fused-madd
6742 @opindex mfused-madd
6743 @opindex mno-fused-madd
6744 Generate code that uses (does not use) the floating point multiply and
6745 accumulate instructions. These instructions are generated by default if
6746 hardware floating is used.
6748 @item -mno-bit-align
6750 @opindex mno-bit-align
6752 On System V.4 and embedded PowerPC systems do not (do) force structures
6753 and unions that contain bit-fields to be aligned to the base type of the
6756 For example, by default a structure containing nothing but 8
6757 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
6758 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
6759 the structure would be aligned to a 1 byte boundary and be one byte in
6762 @item -mno-strict-align
6763 @itemx -mstrict-align
6764 @opindex mno-strict-align
6765 @opindex mstrict-align
6766 On System V.4 and embedded PowerPC systems do not (do) assume that
6767 unaligned memory references will be handled by the system.
6770 @itemx -mno-relocatable
6771 @opindex mrelocatable
6772 @opindex mno-relocatable
6773 On embedded PowerPC systems generate code that allows (does not allow)
6774 the program to be relocated to a different address at runtime. If you
6775 use @option{-mrelocatable} on any module, all objects linked together must
6776 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
6778 @item -mrelocatable-lib
6779 @itemx -mno-relocatable-lib
6780 @opindex mrelocatable-lib
6781 @opindex mno-relocatable-lib
6782 On embedded PowerPC systems generate code that allows (does not allow)
6783 the program to be relocated to a different address at runtime. Modules
6784 compiled with @option{-mrelocatable-lib} can be linked with either modules
6785 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
6786 with modules compiled with the @option{-mrelocatable} options.
6792 On System V.4 and embedded PowerPC systems do not (do) assume that
6793 register 2 contains a pointer to a global area pointing to the addresses
6794 used in the program.
6797 @itemx -mlittle-endian
6799 @opindex mlittle-endian
6800 On System V.4 and embedded PowerPC systems compile code for the
6801 processor in little endian mode. The @option{-mlittle-endian} option is
6802 the same as @option{-mlittle}.
6807 @opindex mbig-endian
6808 On System V.4 and embedded PowerPC systems compile code for the
6809 processor in big endian mode. The @option{-mbig-endian} option is
6810 the same as @option{-mbig}.
6814 On System V.4 and embedded PowerPC systems compile code using calling
6815 conventions that adheres to the March 1995 draft of the System V
6816 Application Binary Interface, PowerPC processor supplement. This is the
6817 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
6819 @item -mcall-sysv-eabi
6820 @opindex mcall-sysv-eabi
6821 Specify both @option{-mcall-sysv} and @option{-meabi} options.
6823 @item -mcall-sysv-noeabi
6824 @opindex mcall-sysv-noeabi
6825 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
6829 On System V.4 and embedded PowerPC systems compile code using calling
6830 conventions that are similar to those used on AIX@. This is the
6831 default if you configured GCC using @samp{powerpc-*-eabiaix}.
6833 @item -mcall-solaris
6834 @opindex mcall-solaris
6835 On System V.4 and embedded PowerPC systems compile code for the Solaris
6839 @opindex mcall-linux
6840 On System V.4 and embedded PowerPC systems compile code for the
6841 Linux-based GNU system.
6844 @itemx -mno-prototype
6846 @opindex mno-prototype
6847 On System V.4 and embedded PowerPC systems assume that all calls to
6848 variable argument functions are properly prototyped. Otherwise, the
6849 compiler must insert an instruction before every non prototyped call to
6850 set or clear bit 6 of the condition code register (@var{CR}) to
6851 indicate whether floating point values were passed in the floating point
6852 registers in case the function takes a variable arguments. With
6853 @option{-mprototype}, only calls to prototyped variable argument functions
6854 will set or clear the bit.
6858 On embedded PowerPC systems, assume that the startup module is called
6859 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
6860 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
6865 On embedded PowerPC systems, assume that the startup module is called
6866 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
6871 On embedded PowerPC systems, assume that the startup module is called
6872 @file{crt0.o} and the standard C libraries are @file{libads.a} and
6876 @opindex myellowknife
6877 On embedded PowerPC systems, assume that the startup module is called
6878 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
6883 On System V.4 and embedded PowerPC systems, specify that you are
6884 compiling for a VxWorks system.
6888 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
6889 header to indicate that @samp{eabi} extended relocations are used.
6895 On System V.4 and embedded PowerPC systems do (do not) adhere to the
6896 Embedded Applications Binary Interface (eabi) which is a set of
6897 modifications to the System V.4 specifications. Selecting @option{-meabi}
6898 means that the stack is aligned to an 8 byte boundary, a function
6899 @code{__eabi} is called to from @code{main} to set up the eabi
6900 environment, and the @option{-msdata} option can use both @code{r2} and
6901 @code{r13} to point to two separate small data areas. Selecting
6902 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
6903 do not call an initialization function from @code{main}, and the
6904 @option{-msdata} option will only use @code{r13} to point to a single
6905 small data area. The @option{-meabi} option is on by default if you
6906 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
6909 @opindex msdata=eabi
6910 On System V.4 and embedded PowerPC systems, put small initialized
6911 @code{const} global and static data in the @samp{.sdata2} section, which
6912 is pointed to by register @code{r2}. Put small initialized
6913 non-@code{const} global and static data in the @samp{.sdata} section,
6914 which is pointed to by register @code{r13}. Put small uninitialized
6915 global and static data in the @samp{.sbss} section, which is adjacent to
6916 the @samp{.sdata} section. The @option{-msdata=eabi} option is
6917 incompatible with the @option{-mrelocatable} option. The
6918 @option{-msdata=eabi} option also sets the @option{-memb} option.
6921 @opindex msdata=sysv
6922 On System V.4 and embedded PowerPC systems, put small global and static
6923 data in the @samp{.sdata} section, which is pointed to by register
6924 @code{r13}. Put small uninitialized global and static data in the
6925 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
6926 The @option{-msdata=sysv} option is incompatible with the
6927 @option{-mrelocatable} option.
6929 @item -msdata=default
6931 @opindex msdata=default
6933 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
6934 compile code the same as @option{-msdata=eabi}, otherwise compile code the
6935 same as @option{-msdata=sysv}.
6938 @opindex msdata-data
6939 On System V.4 and embedded PowerPC systems, put small global and static
6940 data in the @samp{.sdata} section. Put small uninitialized global and
6941 static data in the @samp{.sbss} section. Do not use register @code{r13}
6942 to address small data however. This is the default behavior unless
6943 other @option{-msdata} options are used.
6947 @opindex msdata=none
6949 On embedded PowerPC systems, put all initialized global and static data
6950 in the @samp{.data} section, and all uninitialized data in the
6951 @samp{.bss} section.
6955 @cindex smaller data references (PowerPC)
6956 @cindex .sdata/.sdata2 references (PowerPC)
6957 On embedded PowerPC systems, put global and static items less than or
6958 equal to @var{num} bytes into the small data or bss sections instead of
6959 the normal data or bss section. By default, @var{num} is 8. The
6960 @option{-G @var{num}} switch is also passed to the linker.
6961 All modules should be compiled with the same @option{-G @var{num}} value.
6964 @itemx -mno-regnames
6966 @opindex mno-regnames
6967 On System V.4 and embedded PowerPC systems do (do not) emit register
6968 names in the assembly language output using symbolic forms.
6973 @subsection IBM RT Options
6975 @cindex IBM RT options
6977 These @samp{-m} options are defined for the IBM RT PC:
6981 @opindex min-line-mul
6982 Use an in-line code sequence for integer multiplies. This is the
6985 @item -mcall-lib-mul
6986 @opindex mcall-lib-mul
6987 Call @code{lmul$$} for integer multiples.
6989 @item -mfull-fp-blocks
6990 @opindex mfull-fp-blocks
6991 Generate full-size floating point data blocks, including the minimum
6992 amount of scratch space recommended by IBM@. This is the default.
6994 @item -mminimum-fp-blocks
6995 @opindex mminimum-fp-blocks
6996 Do not include extra scratch space in floating point data blocks. This
6997 results in smaller code, but slower execution, since scratch space must
6998 be allocated dynamically.
7000 @cindex @file{varargs.h} and RT PC
7001 @cindex @file{stdarg.h} and RT PC
7002 @item -mfp-arg-in-fpregs
7003 @opindex mfp-arg-in-fpregs
7004 Use a calling sequence incompatible with the IBM calling convention in
7005 which floating point arguments are passed in floating point registers.
7006 Note that @code{varargs.h} and @code{stdarg.h} will not work with
7007 floating point operands if this option is specified.
7009 @item -mfp-arg-in-gregs
7010 @opindex mfp-arg-in-gregs
7011 Use the normal calling convention for floating point arguments. This is
7014 @item -mhc-struct-return
7015 @opindex mhc-struct-return
7016 Return structures of more than one word in memory, rather than in a
7017 register. This provides compatibility with the MetaWare HighC (hc)
7018 compiler. Use the option @option{-fpcc-struct-return} for compatibility
7019 with the Portable C Compiler (pcc).
7021 @item -mnohc-struct-return
7022 @opindex mnohc-struct-return
7023 Return some structures of more than one word in registers, when
7024 convenient. This is the default. For compatibility with the
7025 IBM-supplied compilers, use the option @option{-fpcc-struct-return} or the
7026 option @option{-mhc-struct-return}.
7030 @subsection MIPS Options
7031 @cindex MIPS options
7033 These @samp{-m} options are defined for the MIPS family of computers:
7037 @item -march=@var{cpu-type}
7039 Assume the defaults for the machine type @var{cpu-type} when generating
7040 instructions. The choices for @var{cpu-type} are @samp{r2000}, @samp{r3000},
7041 @samp{r3900}, @samp{r4000}, @samp{r4100}, @samp{r4300}, @samp{r4400},
7042 @samp{r4600}, @samp{r4650}, @samp{r5000}, @samp{r6000}, @samp{r8000},
7043 and @samp{orion}. Additionally, the @samp{r2000}, @samp{r3000},
7044 @samp{r4000}, @samp{r5000}, and @samp{r6000} can be abbreviated as
7045 @samp{r2k} (or @samp{r2K}), @samp{r3k}, etc.
7047 @item -mtune=@var{cpu-type}
7049 Assume the defaults for the machine type @var{cpu-type} when scheduling
7050 instructions. The choices for @var{cpu-type} are @samp{r2000}, @samp{r3000},
7051 @samp{r3900}, @samp{r4000}, @samp{r4100}, @samp{r4300}, @samp{r4400},
7052 @samp{r4600}, @samp{r4650}, @samp{r5000}, @samp{r6000}, @samp{r8000},
7053 and @samp{orion}. Additionally, the @samp{r2000}, @samp{r3000},
7054 @samp{r4000}, @samp{r5000}, and @samp{r6000} can be abbreviated as
7055 @samp{r2k} (or @samp{r2K}), @samp{r3k}, etc. While picking a specific
7056 @var{cpu-type} will schedule things appropriately for that particular
7057 chip, the compiler will not generate any code that does not meet level 1
7058 of the MIPS ISA (instruction set architecture) without a @option{-mipsX}
7059 or @option{-mabi} switch being used.
7061 @item -mcpu=@var{cpu-type}
7063 This is identical to specifying both @option{-march} and @option{-mtune}.
7067 Issue instructions from level 1 of the MIPS ISA@. This is the default.
7068 @samp{r3000} is the default @var{cpu-type} at this ISA level.
7072 Issue instructions from level 2 of the MIPS ISA (branch likely, square
7073 root instructions). @samp{r6000} is the default @var{cpu-type} at this
7078 Issue instructions from level 3 of the MIPS ISA (64-bit instructions).
7079 @samp{r4000} is the default @var{cpu-type} at this ISA level.
7083 Issue instructions from level 4 of the MIPS ISA (conditional move,
7084 prefetch, enhanced FPU instructions). @samp{r8000} is the default
7085 @var{cpu-type} at this ISA level.
7089 Assume that 32 32-bit floating point registers are available. This is
7094 Assume that 32 64-bit floating point registers are available. This is
7095 the default when the @option{-mips3} option is used.
7099 Assume that 32 32-bit general purpose registers are available. This is
7104 Assume that 32 64-bit general purpose registers are available. This is
7105 the default when the @option{-mips3} option is used.
7109 Force int and long types to be 64 bits wide. See @option{-mlong32} for an
7110 explanation of the default, and the width of pointers.
7114 Force long types to be 64 bits wide. See @option{-mlong32} for an
7115 explanation of the default, and the width of pointers.
7119 Force long, int, and pointer types to be 32 bits wide.
7121 If none of @option{-mlong32}, @option{-mlong64}, or @option{-mint64} are set,
7122 the size of ints, longs, and pointers depends on the ABI and ISA chosen.
7123 For @option{-mabi=32}, and @option{-mabi=n32}, ints and longs are 32 bits
7124 wide. For @option{-mabi=64}, ints are 32 bits, and longs are 64 bits wide.
7125 For @option{-mabi=eabi} and either @option{-mips1} or @option{-mips2}, ints
7126 and longs are 32 bits wide. For @option{-mabi=eabi} and higher ISAs, ints
7127 are 32 bits, and longs are 64 bits wide. The width of pointer types is
7128 the smaller of the width of longs or the width of general purpose
7129 registers (which in turn depends on the ISA)@.
7141 Generate code for the indicated ABI@. The default instruction level is
7142 @option{-mips1} for @samp{32}, @option{-mips3} for @samp{n32}, and
7143 @option{-mips4} otherwise. Conversely, with @option{-mips1} or
7144 @option{-mips2}, the default ABI is @samp{32}; otherwise, the default ABI
7149 Generate code for the MIPS assembler, and invoke @file{mips-tfile} to
7150 add normal debug information. This is the default for all
7151 platforms except for the OSF/1 reference platform, using the OSF/rose
7152 object format. If the either of the @option{-gstabs} or @option{-gstabs+}
7153 switches are used, the @file{mips-tfile} program will encapsulate the
7154 stabs within MIPS ECOFF@.
7158 Generate code for the GNU assembler. This is the default on the OSF/1
7159 reference platform, using the OSF/rose object format. Also, this is
7160 the default if the configure option @option{--with-gnu-as} is used.
7162 @item -msplit-addresses
7163 @itemx -mno-split-addresses
7164 @opindex msplit-addresses
7165 @opindex mno-split-addresses
7166 Generate code to load the high and low parts of address constants separately.
7167 This allows GCC to optimize away redundant loads of the high order
7168 bits of addresses. This optimization requires GNU as and GNU ld.
7169 This optimization is enabled by default for some embedded targets where
7170 GNU as and GNU ld are standard.
7176 The @option{-mrnames} switch says to output code using the MIPS software
7177 names for the registers, instead of the hardware names (ie, @var{a0}
7178 instead of @var{$4}). The only known assembler that supports this option
7179 is the Algorithmics assembler.
7185 The @option{-mgpopt} switch says to write all of the data declarations
7186 before the instructions in the text section, this allows the MIPS
7187 assembler to generate one word memory references instead of using two
7188 words for short global or static data items. This is on by default if
7189 optimization is selected.
7195 For each non-inline function processed, the @option{-mstats} switch
7196 causes the compiler to emit one line to the standard error file to
7197 print statistics about the program (number of registers saved, stack
7204 The @option{-mmemcpy} switch makes all block moves call the appropriate
7205 string function (@samp{memcpy} or @samp{bcopy}) instead of possibly
7206 generating inline code.
7209 @itemx -mno-mips-tfile
7210 @opindex mmips-tfile
7211 @opindex mno-mips-tfile
7212 The @option{-mno-mips-tfile} switch causes the compiler not
7213 postprocess the object file with the @file{mips-tfile} program,
7214 after the MIPS assembler has generated it to add debug support. If
7215 @file{mips-tfile} is not run, then no local variables will be
7216 available to the debugger. In addition, @file{stage2} and
7217 @file{stage3} objects will have the temporary file names passed to the
7218 assembler embedded in the object file, which means the objects will
7219 not compare the same. The @option{-mno-mips-tfile} switch should only
7220 be used when there are bugs in the @file{mips-tfile} program that
7221 prevents compilation.
7224 @opindex msoft-float
7225 Generate output containing library calls for floating point.
7226 @strong{Warning:} the requisite libraries are not part of GCC@.
7227 Normally the facilities of the machine's usual C compiler are used, but
7228 this can't be done directly in cross-compilation. You must make your
7229 own arrangements to provide suitable library functions for
7233 @opindex mhard-float
7234 Generate output containing floating point instructions. This is the
7235 default if you use the unmodified sources.
7238 @itemx -mno-abicalls
7240 @opindex mno-abicalls
7241 Emit (or do not emit) the pseudo operations @samp{.abicalls},
7242 @samp{.cpload}, and @samp{.cprestore} that some System V.4 ports use for
7243 position independent code.
7246 @itemx -mno-long-calls
7247 @opindex mlong-calls
7248 @opindex mno-long-calls
7249 Do all calls with the @samp{JALR} instruction, which requires
7250 loading up a function's address into a register before the call.
7251 You need to use this switch, if you call outside of the current
7252 512 megabyte segment to functions that are not through pointers.
7255 @itemx -mno-half-pic
7257 @opindex mno-half-pic
7258 Put pointers to extern references into the data section and load them
7259 up, rather than put the references in the text section.
7261 @item -membedded-pic
7262 @itemx -mno-embedded-pic
7263 @opindex membedded-pic
7264 @opindex mno-embedded-pic
7265 Generate PIC code suitable for some embedded systems. All calls are
7266 made using PC relative address, and all data is addressed using the $gp
7267 register. No more than 65536 bytes of global data may be used. This
7268 requires GNU as and GNU ld which do most of the work. This currently
7269 only works on targets which use ECOFF; it does not work with ELF@.
7271 @item -membedded-data
7272 @itemx -mno-embedded-data
7273 @opindex membedded-data
7274 @opindex mno-embedded-data
7275 Allocate variables to the read-only data section first if possible, then
7276 next in the small data section if possible, otherwise in data. This gives
7277 slightly slower code than the default, but reduces the amount of RAM required
7278 when executing, and thus may be preferred for some embedded systems.
7280 @item -muninit-const-in-rodata
7281 @itemx -mno-uninit-const-in-rodata
7282 @opindex muninit-const-in-rodata
7283 @opindex mno-uninit-const-in-rodata
7284 When used together with @option{-membedded-data}, it will always store uninitialized
7285 const variables in the read-only data section.
7287 @item -msingle-float
7288 @itemx -mdouble-float
7289 @opindex msingle-float
7290 @opindex mdouble-float
7291 The @option{-msingle-float} switch tells gcc to assume that the floating
7292 point coprocessor only supports single precision operations, as on the
7293 @samp{r4650} chip. The @option{-mdouble-float} switch permits gcc to use
7294 double precision operations. This is the default.
7300 Permit use of the @samp{mad}, @samp{madu} and @samp{mul} instructions,
7301 as on the @samp{r4650} chip.
7305 Turns on @option{-msingle-float}, @option{-mmad}, and, at least for now,
7306 @option{-mcpu=r4650}.
7312 Enable 16-bit instructions.
7316 Use the entry and exit pseudo ops. This option can only be used with
7321 Compile code for the processor in little endian mode.
7322 The requisite libraries are assumed to exist.
7326 Compile code for the processor in big endian mode.
7327 The requisite libraries are assumed to exist.
7331 @cindex smaller data references (MIPS)
7332 @cindex gp-relative references (MIPS)
7333 Put global and static items less than or equal to @var{num} bytes into
7334 the small data or bss sections instead of the normal data or bss
7335 section. This allows the assembler to emit one word memory reference
7336 instructions based on the global pointer (@var{gp} or @var{$28}),
7337 instead of the normal two words used. By default, @var{num} is 8 when
7338 the MIPS assembler is used, and 0 when the GNU assembler is used. The
7339 @option{-G @var{num}} switch is also passed to the assembler and linker.
7340 All modules should be compiled with the same @option{-G @var{num}}
7345 Tell the MIPS assembler to not run its preprocessor over user
7346 assembler files (with a @samp{.s} suffix) when assembling them.
7350 Pass an option to gas which will cause nops to be inserted if
7351 the read of the destination register of an mfhi or mflo instruction
7352 occurs in the following two instructions.
7356 Do not include the default crt0.
7360 These options are defined by the macro
7361 @code{TARGET_SWITCHES} in the machine description. The default for the
7362 options is also defined by that macro, which enables you to change the
7367 @subsection Intel 386 Options
7368 @cindex i386 Options
7369 @cindex Intel 386 Options
7371 These @samp{-m} options are defined for the i386 family of computers:
7374 @item -mcpu=@var{cpu-type}
7376 Assume the defaults for the machine type @var{cpu-type} when scheduling
7377 instructions. The choices for @var{cpu-type} are @samp{i386},
7378 @samp{i486}, @samp{i586}, @samp{i686}, @samp{pentium},
7379 @samp{pentiumpro}, @samp{pentium4}, @samp{k6}, and @samp{athlon}
7381 While picking a specific @var{cpu-type} will schedule things appropriately
7382 for that particular chip, the compiler will not generate any code that
7383 does not run on the i386 without the @option{-march=@var{cpu-type}} option
7384 being used. @samp{i586} is equivalent to @samp{pentium} and @samp{i686}
7385 is equivalent to @samp{pentiumpro}. @samp{k6} and @samp{athlon} are the
7386 AMD chips as opposed to the Intel ones.
7388 @item -march=@var{cpu-type}
7390 Generate instructions for the machine type @var{cpu-type}. The choices
7391 for @var{cpu-type} are the same as for @option{-mcpu}. Moreover,
7392 specifying @option{-march=@var{cpu-type}} implies @option{-mcpu=@var{cpu-type}}.
7401 @opindex mpentiumpro
7402 Synonyms for @option{-mcpu=i386}, @option{-mcpu=i486}, @option{-mcpu=pentium}, and @option{-mcpu=pentiumpro}
7403 respectively. These synonyms are deprecated.
7405 @item -mintel-syntax
7406 @opindex mintel-syntax
7407 Emit assembly using Intel syntax opcodes instead of AT&T syntax.
7412 @opindex mno-ieee-fp
7413 Control whether or not the compiler uses IEEE floating point
7414 comparisons. These handle correctly the case where the result of a
7415 comparison is unordered.
7418 @opindex msoft-float
7419 Generate output containing library calls for floating point.
7420 @strong{Warning:} the requisite libraries are not part of GCC@.
7421 Normally the facilities of the machine's usual C compiler are used, but
7422 this can't be done directly in cross-compilation. You must make your
7423 own arrangements to provide suitable library functions for
7426 On machines where a function returns floating point results in the 80387
7427 register stack, some floating point opcodes may be emitted even if
7428 @option{-msoft-float} is used.
7430 @item -mno-fp-ret-in-387
7431 @opindex mno-fp-ret-in-387
7432 Do not use the FPU registers for return values of functions.
7434 The usual calling convention has functions return values of types
7435 @code{float} and @code{double} in an FPU register, even if there
7436 is no FPU@. The idea is that the operating system should emulate
7439 The option @option{-mno-fp-ret-in-387} causes such values to be returned
7440 in ordinary CPU registers instead.
7442 @item -mno-fancy-math-387
7443 @opindex mno-fancy-math-387
7444 Some 387 emulators do not support the @code{sin}, @code{cos} and
7445 @code{sqrt} instructions for the 387. Specify this option to avoid
7446 generating those instructions. This option is the default on FreeBSD@.
7447 As of revision 2.6.1, these instructions are not generated unless you
7448 also use the @option{-funsafe-math-optimizations} switch.
7450 @item -malign-double
7451 @itemx -mno-align-double
7452 @opindex malign-double
7453 @opindex mno-align-double
7454 Control whether GCC aligns @code{double}, @code{long double}, and
7455 @code{long long} variables on a two word boundary or a one word
7456 boundary. Aligning @code{double} variables on a two word boundary will
7457 produce code that runs somewhat faster on a @samp{Pentium} at the
7458 expense of more memory.
7460 @item -m128bit-long-double
7461 @itemx -m128bit-long-double
7462 @opindex m128bit-long-double
7463 @opindex m128bit-long-double
7464 Control the size of @code{long double} type. i386 application binary interface
7465 specify the size to be 12 bytes, while modern architectures (Pentium and newer)
7466 prefer @code{long double} aligned to 8 or 16 byte boundary. This is
7467 impossible to reach with 12 byte long doubles in the array accesses.
7469 @strong{Warning:} if you use the @option{-m128bit-long-double} switch, the
7470 structures and arrays containing @code{long double} will change their size as
7471 well as function calling convention for function taking @code{long double}
7474 @item -m96bit-long-double
7475 @itemx -m96bit-long-double
7476 @opindex m96bit-long-double
7477 @opindex m96bit-long-double
7478 Set the size of @code{long double} to 96 bits as required by the i386
7479 application binary interface. This is the default.
7482 @itemx -mno-svr3-shlib
7483 @opindex msvr3-shlib
7484 @opindex mno-svr3-shlib
7485 Control whether GCC places uninitialized locals into @code{bss} or
7486 @code{data}. @option{-msvr3-shlib} places these locals into @code{bss}.
7487 These options are meaningful only on System V Release 3.
7489 @item -mno-wide-multiply
7490 @itemx -mwide-multiply
7491 @opindex mno-wide-multiply
7492 @opindex mwide-multiply
7493 Control whether GCC uses the @code{mul} and @code{imul} that produce
7494 64-bit results in @code{eax:edx} from 32-bit operands to do @code{long
7495 long} multiplies and 32-bit division by constants.
7499 Use a different function-calling convention, in which functions that
7500 take a fixed number of arguments return with the @code{ret} @var{num}
7501 instruction, which pops their arguments while returning. This saves one
7502 instruction in the caller since there is no need to pop the arguments
7505 You can specify that an individual function is called with this calling
7506 sequence with the function attribute @samp{stdcall}. You can also
7507 override the @option{-mrtd} option by using the function attribute
7508 @samp{cdecl}. @xref{Function Attributes}.
7510 @strong{Warning:} this calling convention is incompatible with the one
7511 normally used on Unix, so you cannot use it if you need to call
7512 libraries compiled with the Unix compiler.
7514 Also, you must provide function prototypes for all functions that
7515 take variable numbers of arguments (including @code{printf});
7516 otherwise incorrect code will be generated for calls to those
7519 In addition, seriously incorrect code will result if you call a
7520 function with too many arguments. (Normally, extra arguments are
7521 harmlessly ignored.)
7523 @item -mregparm=@var{num}
7525 Control how many registers are used to pass integer arguments. By
7526 default, no registers are used to pass arguments, and at most 3
7527 registers can be used. You can control this behavior for a specific
7528 function by using the function attribute @samp{regparm}.
7529 @xref{Function Attributes}.
7531 @strong{Warning:} if you use this switch, and
7532 @var{num} is nonzero, then you must build all modules with the same
7533 value, including any libraries. This includes the system libraries and
7536 @item -mpreferred-stack-boundary=@var{num}
7537 @opindex mpreferred-stack-boundary
7538 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
7539 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
7540 the default is 4 (16 bytes or 128 bits).
7542 The stack is required to be aligned on a 4 byte boundary. On Pentium
7543 and PentiumPro, @code{double} and @code{long double} values should be
7544 aligned to an 8 byte boundary (see @option{-malign-double}) or suffer
7545 significant run time performance penalties. On Pentium III, the
7546 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
7547 penalties if it is not 16 byte aligned.
7549 To ensure proper alignment of this values on the stack, the stack boundary
7550 must be as aligned as that required by any value stored on the stack.
7551 Further, every function must be generated such that it keeps the stack
7552 aligned. Thus calling a function compiled with a higher preferred
7553 stack boundary from a function compiled with a lower preferred stack
7554 boundary will most likely misalign the stack. It is recommended that
7555 libraries that use callbacks always use the default setting.
7557 This extra alignment does consume extra stack space. Code that is sensitive
7558 to stack space usage, such as embedded systems and operating system kernels,
7559 may want to reduce the preferred alignment to
7560 @option{-mpreferred-stack-boundary=2}.
7564 Use PUSH operations to store outgoing parameters. This method is shorter
7565 and usually equally fast as method using SUB/MOV operations and is enabled
7566 by default. In some cases disabling it may improve performance because of
7567 improved scheduling and reduced dependencies.
7569 @item -maccumulate-outgoing-args
7570 @opindex maccumulate-outgoing-args
7571 If enabled, the maximum amount of space required for outgoing arguments will be
7572 computed in the function prologue. This in faster on most modern CPUs
7573 because of reduced dependencies, improved scheduling and reduced stack usage
7574 when preferred stack boundary is not equal to 2. The drawback is a notable
7575 increase in code size. This switch implies @option{-mno-push-args}.
7579 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
7580 on thread-safe exception handling must compile and link all code with the
7581 @option{-mthreads} option. When compiling, @option{-mthreads} defines
7582 @option{-D_MT}; when linking, it links in a special thread helper library
7583 @option{-lmingwthrd} which cleans up per thread exception handling data.
7585 @item -mno-align-stringops
7586 @opindex mno-align-stringops
7587 Do not align destination of inlined string operations. This switch reduces
7588 code size and improves performance in case the destination is already aligned,
7589 but gcc don't know about it.
7591 @item -minline-all-stringops
7592 @opindex minline-all-stringops
7593 By default GCC inlines string operations only when destination is known to be
7594 aligned at least to 4 byte boundary. This enables more inlining, increase code
7595 size, but may improve performance of code that depends on fast memcpy, strlen
7596 and memset for short lengths.
7598 @item -momit-leaf-frame-pointer
7599 @opindex momit-leaf-frame-pointer
7600 Don't keep the frame pointer in a register for leaf functions. This
7601 avoids the instructions to save, set up and restore frame pointers and
7602 makes an extra register available in leaf functions. The option
7603 @option{-fomit-frame-pointer} removes the frame pointer for all functions
7604 which might make debugging harder.
7608 @subsection HPPA Options
7609 @cindex HPPA Options
7611 These @samp{-m} options are defined for the HPPA family of computers:
7614 @item -march=@var{architecture-type}
7616 Generate code for the specified architecture. The choices for
7617 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
7618 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
7619 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
7620 architecture option for your machine. Code compiled for lower numbered
7621 architectures will run on higher numbered architectures, but not the
7624 PA 2.0 support currently requires gas snapshot 19990413 or later. The
7625 next release of binutils (current is 2.9.1) will probably contain PA 2.0
7629 @itemx -mpa-risc-1-1
7630 @itemx -mpa-risc-2-0
7631 @opindex mpa-risc-1-0
7632 @opindex mpa-risc-1-1
7633 @opindex mpa-risc-2-0
7634 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
7637 @opindex mbig-switch
7638 Generate code suitable for big switch tables. Use this option only if
7639 the assembler/linker complain about out of range branches within a switch
7642 @item -mjump-in-delay
7643 @opindex mjump-in-delay
7644 Fill delay slots of function calls with unconditional jump instructions
7645 by modifying the return pointer for the function call to be the target
7646 of the conditional jump.
7648 @item -mdisable-fpregs
7649 @opindex mdisable-fpregs
7650 Prevent floating point registers from being used in any manner. This is
7651 necessary for compiling kernels which perform lazy context switching of
7652 floating point registers. If you use this option and attempt to perform
7653 floating point operations, the compiler will abort.
7655 @item -mdisable-indexing
7656 @opindex mdisable-indexing
7657 Prevent the compiler from using indexing address modes. This avoids some
7658 rather obscure problems when compiling MIG generated code under MACH@.
7660 @item -mno-space-regs
7661 @opindex mno-space-regs
7662 Generate code that assumes the target has no space registers. This allows
7663 GCC to generate faster indirect calls and use unscaled index address modes.
7665 Such code is suitable for level 0 PA systems and kernels.
7667 @item -mfast-indirect-calls
7668 @opindex mfast-indirect-calls
7669 Generate code that assumes calls never cross space boundaries. This
7670 allows GCC to emit code which performs faster indirect calls.
7672 This option will not work in the presence of shared libraries or nested
7675 @item -mlong-load-store
7676 @opindex mlong-load-store
7677 Generate 3-instruction load and store sequences as sometimes required by
7678 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
7681 @item -mportable-runtime
7682 @opindex mportable-runtime
7683 Use the portable calling conventions proposed by HP for ELF systems.
7687 Enable the use of assembler directives only GAS understands.
7689 @item -mschedule=@var{cpu-type}
7691 Schedule code according to the constraints for the machine type
7692 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
7693 @samp{7100}, @samp{7100LC}, @samp{7200}, and @samp{8000}. Refer to
7694 @file{/usr/lib/sched.models} on an HP-UX system to determine the
7695 proper scheduling option for your machine.
7698 @opindex mlinker-opt
7699 Enable the optimization pass in the HPUX linker. Note this makes symbolic
7700 debugging impossible. It also triggers a bug in the HPUX 8 and HPUX 9 linkers
7701 in which they give bogus error messages when linking some programs.
7704 @opindex msoft-float
7705 Generate output containing library calls for floating point.
7706 @strong{Warning:} the requisite libraries are not available for all HPPA
7707 targets. Normally the facilities of the machine's usual C compiler are
7708 used, but this cannot be done directly in cross-compilation. You must make
7709 your own arrangements to provide suitable library functions for
7710 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
7711 does provide software floating point support.
7713 @option{-msoft-float} changes the calling convention in the output file;
7714 therefore, it is only useful if you compile @emph{all} of a program with
7715 this option. In particular, you need to compile @file{libgcc.a}, the
7716 library that comes with GCC, with @option{-msoft-float} in order for
7720 @node Intel 960 Options
7721 @subsection Intel 960 Options
7723 These @samp{-m} options are defined for the Intel 960 implementations:
7726 @item -m@var{cpu-type}
7734 Assume the defaults for the machine type @var{cpu-type} for some of
7735 the other options, including instruction scheduling, floating point
7736 support, and addressing modes. The choices for @var{cpu-type} are
7737 @samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf},
7738 @samp{sa}, and @samp{sb}.
7745 @opindex msoft-float
7746 The @option{-mnumerics} option indicates that the processor does support
7747 floating-point instructions. The @option{-msoft-float} option indicates
7748 that floating-point support should not be assumed.
7750 @item -mleaf-procedures
7751 @itemx -mno-leaf-procedures
7752 @opindex mleaf-procedures
7753 @opindex mno-leaf-procedures
7754 Do (or do not) attempt to alter leaf procedures to be callable with the
7755 @code{bal} instruction as well as @code{call}. This will result in more
7756 efficient code for explicit calls when the @code{bal} instruction can be
7757 substituted by the assembler or linker, but less efficient code in other
7758 cases, such as calls via function pointers, or using a linker that doesn't
7759 support this optimization.
7762 @itemx -mno-tail-call
7764 @opindex mno-tail-call
7765 Do (or do not) make additional attempts (beyond those of the
7766 machine-independent portions of the compiler) to optimize tail-recursive
7767 calls into branches. You may not want to do this because the detection of
7768 cases where this is not valid is not totally complete. The default is
7769 @option{-mno-tail-call}.
7771 @item -mcomplex-addr
7772 @itemx -mno-complex-addr
7773 @opindex mcomplex-addr
7774 @opindex mno-complex-addr
7775 Assume (or do not assume) that the use of a complex addressing mode is a
7776 win on this implementation of the i960. Complex addressing modes may not
7777 be worthwhile on the K-series, but they definitely are on the C-series.
7778 The default is currently @option{-mcomplex-addr} for all processors except
7782 @itemx -mno-code-align
7783 @opindex mcode-align
7784 @opindex mno-code-align
7785 Align code to 8-byte boundaries for faster fetching (or don't bother).
7786 Currently turned on by default for C-series implementations only.
7789 @item -mclean-linkage
7790 @itemx -mno-clean-linkage
7791 @opindex mclean-linkage
7792 @opindex mno-clean-linkage
7793 These options are not fully implemented.
7797 @itemx -mic2.0-compat
7798 @itemx -mic3.0-compat
7800 @opindex mic2.0-compat
7801 @opindex mic3.0-compat
7802 Enable compatibility with iC960 v2.0 or v3.0.
7806 @opindex masm-compat
7808 Enable compatibility with the iC960 assembler.
7810 @item -mstrict-align
7811 @itemx -mno-strict-align
7812 @opindex mstrict-align
7813 @opindex mno-strict-align
7814 Do not permit (do permit) unaligned accesses.
7818 Enable structure-alignment compatibility with Intel's gcc release version
7819 1.3 (based on gcc 1.37). This option implies @option{-mstrict-align}.
7821 @item -mlong-double-64
7822 @opindex mlong-double-64
7823 Implement type @samp{long double} as 64-bit floating point numbers.
7824 Without the option @samp{long double} is implemented by 80-bit
7825 floating point numbers. The only reason we have it because there is
7826 no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it
7827 is only useful for people using soft-float targets. Otherwise, we
7828 should recommend against use of it.
7832 @node DEC Alpha Options
7833 @subsection DEC Alpha Options
7835 These @samp{-m} options are defined for the DEC Alpha implementations:
7838 @item -mno-soft-float
7840 @opindex mno-soft-float
7841 @opindex msoft-float
7842 Use (do not use) the hardware floating-point instructions for
7843 floating-point operations. When @option{-msoft-float} is specified,
7844 functions in @file{libgcc.a} will be used to perform floating-point
7845 operations. Unless they are replaced by routines that emulate the
7846 floating-point operations, or compiled in such a way as to call such
7847 emulations routines, these routines will issue floating-point
7848 operations. If you are compiling for an Alpha without floating-point
7849 operations, you must ensure that the library is built so as not to call
7852 Note that Alpha implementations without floating-point operations are
7853 required to have floating-point registers.
7858 @opindex mno-fp-regs
7859 Generate code that uses (does not use) the floating-point register set.
7860 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
7861 register set is not used, floating point operands are passed in integer
7862 registers as if they were integers and floating-point results are passed
7863 in $0 instead of $f0. This is a non-standard calling sequence, so any
7864 function with a floating-point argument or return value called by code
7865 compiled with @option{-mno-fp-regs} must also be compiled with that
7868 A typical use of this option is building a kernel that does not use,
7869 and hence need not save and restore, any floating-point registers.
7873 The Alpha architecture implements floating-point hardware optimized for
7874 maximum performance. It is mostly compliant with the IEEE floating
7875 point standard. However, for full compliance, software assistance is
7876 required. This option generates code fully IEEE compliant code
7877 @emph{except} that the @var{inexact-flag} is not maintained (see below).
7878 If this option is turned on, the CPP macro @code{_IEEE_FP} is defined
7879 during compilation. The option is a shorthand for: @option{-D_IEEE_FP
7880 -mfp-trap-mode=su -mtrap-precision=i -mieee-conformant}. The resulting
7881 code is less efficient but is able to correctly support denormalized
7882 numbers and exceptional IEEE values such as not-a-number and plus/minus
7883 infinity. Other Alpha compilers call this option
7884 @option{-ieee_with_no_inexact}.
7886 @item -mieee-with-inexact
7887 @opindex mieee-with-inexact
7888 @c overfull hbox here --bob 22 jul96
7889 @c original text between ignore ... end ignore
7891 This is like @option{-mieee} except the generated code also maintains the
7892 IEEE @var{inexact-flag}. Turning on this option causes the generated
7893 code to implement fully-compliant IEEE math. The option is a shorthand
7894 for @option{-D_IEEE_FP -D_IEEE_FP_INEXACT} plus @option{-mieee-conformant},
7895 @option{-mfp-trap-mode=sui}, and @option{-mtrap-precision=i}. On some Alpha
7896 implementations the resulting code may execute significantly slower than
7897 the code generated by default. Since there is very little code that
7898 depends on the @var{inexact-flag}, you should normally not specify this
7899 option. Other Alpha compilers call this option
7900 @option{-ieee_with_inexact}.
7902 @c changed paragraph
7903 This is like @option{-mieee} except the generated code also maintains the
7904 IEEE @var{inexact-flag}. Turning on this option causes the generated
7905 code to implement fully-compliant IEEE math. The option is a shorthand
7906 for @option{-D_IEEE_FP -D_IEEE_FP_INEXACT} plus the three following:
7907 @option{-mieee-conformant},
7908 @option{-mfp-trap-mode=sui},
7909 and @option{-mtrap-precision=i}.
7910 On some Alpha implementations the resulting code may execute
7911 significantly slower than the code generated by default. Since there
7912 is very little code that depends on the @var{inexact-flag}, you should
7913 normally not specify this option. Other Alpha compilers call this
7914 option @option{-ieee_with_inexact}.
7915 @c end changes to prevent overfull hboxes
7917 @item -mfp-trap-mode=@var{trap-mode}
7918 @opindex mfp-trap-mode
7919 This option controls what floating-point related traps are enabled.
7920 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
7921 The trap mode can be set to one of four values:
7925 This is the default (normal) setting. The only traps that are enabled
7926 are the ones that cannot be disabled in software (e.g., division by zero
7930 In addition to the traps enabled by @samp{n}, underflow traps are enabled
7934 Like @samp{su}, but the instructions are marked to be safe for software
7935 completion (see Alpha architecture manual for details).
7938 Like @samp{su}, but inexact traps are enabled as well.
7941 @item -mfp-rounding-mode=@var{rounding-mode}
7942 @opindex mfp-rounding-mode
7943 Selects the IEEE rounding mode. Other Alpha compilers call this option
7944 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
7949 Normal IEEE rounding mode. Floating point numbers are rounded towards
7950 the nearest machine number or towards the even machine number in case
7954 Round towards minus infinity.
7957 Chopped rounding mode. Floating point numbers are rounded towards zero.
7960 Dynamic rounding mode. A field in the floating point control register
7961 (@var{fpcr}, see Alpha architecture reference manual) controls the
7962 rounding mode in effect. The C library initializes this register for
7963 rounding towards plus infinity. Thus, unless your program modifies the
7964 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
7967 @item -mtrap-precision=@var{trap-precision}
7968 @opindex mtrap-precision
7969 In the Alpha architecture, floating point traps are imprecise. This
7970 means without software assistance it is impossible to recover from a
7971 floating trap and program execution normally needs to be terminated.
7972 GCC can generate code that can assist operating system trap handlers
7973 in determining the exact location that caused a floating point trap.
7974 Depending on the requirements of an application, different levels of
7975 precisions can be selected:
7979 Program precision. This option is the default and means a trap handler
7980 can only identify which program caused a floating point exception.
7983 Function precision. The trap handler can determine the function that
7984 caused a floating point exception.
7987 Instruction precision. The trap handler can determine the exact
7988 instruction that caused a floating point exception.
7991 Other Alpha compilers provide the equivalent options called
7992 @option{-scope_safe} and @option{-resumption_safe}.
7994 @item -mieee-conformant
7995 @opindex mieee-conformant
7996 This option marks the generated code as IEEE conformant. You must not
7997 use this option unless you also specify @option{-mtrap-precision=i} and either
7998 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
7999 is to emit the line @samp{.eflag 48} in the function prologue of the
8000 generated assembly file. Under DEC Unix, this has the effect that
8001 IEEE-conformant math library routines will be linked in.
8003 @item -mbuild-constants
8004 @opindex mbuild-constants
8005 Normally GCC examines a 32- or 64-bit integer constant to
8006 see if it can construct it from smaller constants in two or three
8007 instructions. If it cannot, it will output the constant as a literal and
8008 generate code to load it from the data segment at runtime.
8010 Use this option to require GCC to construct @emph{all} integer constants
8011 using code, even if it takes more instructions (the maximum is six).
8013 You would typically use this option to build a shared library dynamic
8014 loader. Itself a shared library, it must relocate itself in memory
8015 before it can find the variables and constants in its own data segment.
8021 Select whether to generate code to be assembled by the vendor-supplied
8022 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
8036 Indicate whether GCC should generate code to use the optional BWX,
8037 CIX, and MAX instruction sets. The default is to use the instruction sets
8038 supported by the CPU type specified via @option{-mcpu=} option or that
8039 of the CPU on which GCC was built if none was specified.
8041 @item -mcpu=@var{cpu_type}
8043 Set the instruction set, register set, and instruction scheduling
8044 parameters for machine type @var{cpu_type}. You can specify either the
8045 @samp{EV} style name or the corresponding chip number. GCC
8046 supports scheduling parameters for the EV4 and EV5 family of processors
8047 and will choose the default values for the instruction set from
8048 the processor you specify. If you do not specify a processor type,
8049 GCC will default to the processor on which the compiler was built.
8051 Supported values for @var{cpu_type} are
8056 Schedules as an EV4 and has no instruction set extensions.
8060 Schedules as an EV5 and has no instruction set extensions.
8064 Schedules as an EV5 and supports the BWX extension.
8069 Schedules as an EV5 and supports the BWX and MAX extensions.
8073 Schedules as an EV5 (until Digital releases the scheduling parameters
8074 for the EV6) and supports the BWX, CIX, and MAX extensions.
8077 @item -mmemory-latency=@var{time}
8078 @opindex mmemory-latency
8079 Sets the latency the scheduler should assume for typical memory
8080 references as seen by the application. This number is highly
8081 dependent on the memory access patterns used by the application
8082 and the size of the external cache on the machine.
8084 Valid options for @var{time} are
8088 A decimal number representing clock cycles.
8094 The compiler contains estimates of the number of clock cycles for
8095 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
8096 (also called Dcache, Scache, and Bcache), as well as to main memory.
8097 Note that L3 is only valid for EV5.
8102 @node Clipper Options
8103 @subsection Clipper Options
8105 These @samp{-m} options are defined for the Clipper implementations:
8110 Produce code for a C300 Clipper processor. This is the default.
8114 Produce code for a C400 Clipper processor i.e.@: use floating point
8118 @node H8/300 Options
8119 @subsection H8/300 Options
8121 These @samp{-m} options are defined for the H8/300 implementations:
8126 Shorten some address references at link time, when possible; uses the
8127 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
8128 ld.info, Using ld}, for a fuller description.
8132 Generate code for the H8/300H@.
8136 Generate code for the H8/S@.
8140 Generate code for the H8/S2600. This switch must be used with @option{-ms}.
8144 Make @code{int} data 32 bits by default.
8148 On the H8/300H and H8/S, use the same alignment rules as for the H8/300.
8149 The default for the H8/300H and H8/S is to align longs and floats on 4
8151 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
8152 This option has no effect on the H8/300.
8156 @subsection SH Options
8158 These @samp{-m} options are defined for the SH implementations:
8163 Generate code for the SH1.
8167 Generate code for the SH2.
8171 Generate code for the SH3.
8175 Generate code for the SH3e.
8179 Generate code for the SH4 without a floating-point unit.
8181 @item -m4-single-only
8182 @opindex m4-single-only
8183 Generate code for the SH4 with a floating-point unit that only
8184 supports single-precision arithmetic.
8188 Generate code for the SH4 assuming the floating-point unit is in
8189 single-precision mode by default.
8193 Generate code for the SH4.
8197 Compile code for the processor in big endian mode.
8201 Compile code for the processor in little endian mode.
8205 Align doubles at 64-bit boundaries. Note that this changes the calling
8206 conventions, and thus some functions from the standard C library will
8207 not work unless you recompile it first with @option{-mdalign}.
8211 Shorten some address references at link time, when possible; uses the
8212 linker option @option{-relax}.
8216 Use 32-bit offsets in @code{switch} tables. The default is to use
8221 Enable the use of the instruction @code{fmovd}.
8225 Comply with the calling conventions defined by Hitachi.
8229 Mark the @code{MAC} register as call-clobbered, even if
8230 @option{-mhitachi} is given.
8234 Increase IEEE-compliance of floating-point code.
8238 Dump instruction size and location in the assembly code.
8242 This option is deprecated. It pads structures to multiple of 4 bytes,
8243 which is incompatible with the SH ABI@.
8247 Optimize for space instead of speed. Implied by @option{-Os}.
8251 When generating position-independent code, emit function calls using
8252 the Global Offset Table instead of the Procedure Linkage Table.
8256 Generate a library function call to invalidate instruction cache
8257 entries, after fixing up a trampoline. This library function call
8258 doesn't assume it can write to the whole memory address space. This
8259 is the default when the target is @code{sh-*-linux*}.
8262 @node System V Options
8263 @subsection Options for System V
8265 These additional options are available on System V Release 4 for
8266 compatibility with other compilers on those systems:
8271 Create a shared object.
8272 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
8276 Identify the versions of each tool used by the compiler, in a
8277 @code{.ident} assembler directive in the output.
8281 Refrain from adding @code{.ident} directives to the output file (this is
8284 @item -YP,@var{dirs}
8286 Search the directories @var{dirs}, and no others, for libraries
8287 specified with @option{-l}.
8291 Look in the directory @var{dir} to find the M4 preprocessor.
8292 The assembler uses this option.
8293 @c This is supposed to go with a -Yd for predefined M4 macro files, but
8294 @c the generic assembler that comes with Solaris takes just -Ym.
8297 @node TMS320C3x/C4x Options
8298 @subsection TMS320C3x/C4x Options
8299 @cindex TMS320C3x/C4x Options
8301 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
8305 @item -mcpu=@var{cpu_type}
8307 Set the instruction set, register set, and instruction scheduling
8308 parameters for machine type @var{cpu_type}. Supported values for
8309 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
8310 @samp{c44}. The default is @samp{c40} to generate code for the
8315 @itemx -msmall-memory
8317 @opindex mbig-memory
8319 @opindex msmall-memory
8321 Generates code for the big or small memory model. The small memory
8322 model assumed that all data fits into one 64K word page. At run-time
8323 the data page (DP) register must be set to point to the 64K page
8324 containing the .bss and .data program sections. The big memory model is
8325 the default and requires reloading of the DP register for every direct
8332 Allow (disallow) allocation of general integer operands into the block
8339 Enable (disable) generation of code using decrement and branch,
8340 DBcond(D), instructions. This is enabled by default for the C4x. To be
8341 on the safe side, this is disabled for the C3x, since the maximum
8342 iteration count on the C3x is @math{2^23 + 1} (but who iterates loops more than
8343 @math{2^23} times on the C3x?). Note that GCC will try to reverse a loop so
8344 that it can utilise the decrement and branch instruction, but will give
8345 up if there is more than one memory reference in the loop. Thus a loop
8346 where the loop counter is decremented can generate slightly more
8347 efficient code, in cases where the RPTB instruction cannot be utilised.
8349 @item -mdp-isr-reload
8351 @opindex mdp-isr-reload
8353 Force the DP register to be saved on entry to an interrupt service
8354 routine (ISR), reloaded to point to the data section, and restored on
8355 exit from the ISR@. This should not be required unless someone has
8356 violated the small memory model by modifying the DP register, say within
8363 For the C3x use the 24-bit MPYI instruction for integer multiplies
8364 instead of a library call to guarantee 32-bit results. Note that if one
8365 of the operands is a constant, then the multiplication will be performed
8366 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
8367 then squaring operations are performed inline instead of a library call.
8370 @itemx -mno-fast-fix
8372 @opindex mno-fast-fix
8373 The C3x/C4x FIX instruction to convert a floating point value to an
8374 integer value chooses the nearest integer less than or equal to the
8375 floating point value rather than to the nearest integer. Thus if the
8376 floating point number is negative, the result will be incorrectly
8377 truncated an additional code is necessary to detect and correct this
8378 case. This option can be used to disable generation of the additional
8379 code required to correct the result.
8385 Enable (disable) generation of repeat block sequences using the RPTB
8386 instruction for zero overhead looping. The RPTB construct is only used
8387 for innermost loops that do not call functions or jump across the loop
8388 boundaries. There is no advantage having nested RPTB loops due to the
8389 overhead required to save and restore the RC, RS, and RE registers.
8390 This is enabled by default with @option{-O2}.
8392 @item -mrpts=@var{count}
8396 Enable (disable) the use of the single instruction repeat instruction
8397 RPTS@. If a repeat block contains a single instruction, and the loop
8398 count can be guaranteed to be less than the value @var{count}, GCC will
8399 emit a RPTS instruction instead of a RPTB@. If no value is specified,
8400 then a RPTS will be emitted even if the loop count cannot be determined
8401 at compile time. Note that the repeated instruction following RPTS does
8402 not have to be reloaded from memory each iteration, thus freeing up the
8403 CPU buses for operands. However, since interrupts are blocked by this
8404 instruction, it is disabled by default.
8406 @item -mloop-unsigned
8407 @itemx -mno-loop-unsigned
8408 @opindex mloop-unsigned
8409 @opindex mno-loop-unsigned
8410 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
8411 is @math{2^31 + 1} since these instructions test if the iteration count is
8412 negative to terminate the loop. If the iteration count is unsigned
8413 there is a possibility than the @math{2^31 + 1} maximum iteration count may be
8414 exceeded. This switch allows an unsigned iteration count.
8418 Try to emit an assembler syntax that the TI assembler (asm30) is happy
8419 with. This also enforces compatibility with the API employed by the TI
8420 C3x C compiler. For example, long doubles are passed as structures
8421 rather than in floating point registers.
8427 Generate code that uses registers (stack) for passing arguments to functions.
8428 By default, arguments are passed in registers where possible rather
8429 than by pushing arguments on to the stack.
8431 @item -mparallel-insns
8432 @itemx -mno-parallel-insns
8433 @opindex mparallel-insns
8434 @opindex mno-parallel-insns
8435 Allow the generation of parallel instructions. This is enabled by
8436 default with @option{-O2}.
8438 @item -mparallel-mpy
8439 @itemx -mno-parallel-mpy
8440 @opindex mparallel-mpy
8441 @opindex mno-parallel-mpy
8442 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
8443 provided @option{-mparallel-insns} is also specified. These instructions have
8444 tight register constraints which can pessimize the code generation
8450 @subsection V850 Options
8451 @cindex V850 Options
8453 These @samp{-m} options are defined for V850 implementations:
8457 @itemx -mno-long-calls
8458 @opindex mlong-calls
8459 @opindex mno-long-calls
8460 Treat all calls as being far away (near). If calls are assumed to be
8461 far away, the compiler will always load the functions address up into a
8462 register, and call indirect through the pointer.
8468 Do not optimize (do optimize) basic blocks that use the same index
8469 pointer 4 or more times to copy pointer into the @code{ep} register, and
8470 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
8471 option is on by default if you optimize.
8473 @item -mno-prolog-function
8474 @itemx -mprolog-function
8475 @opindex mno-prolog-function
8476 @opindex mprolog-function
8477 Do not use (do use) external functions to save and restore registers at
8478 the prolog and epilog of a function. The external functions are slower,
8479 but use less code space if more than one function saves the same number
8480 of registers. The @option{-mprolog-function} option is on by default if
8485 Try to make the code as small as possible. At present, this just turns
8486 on the @option{-mep} and @option{-mprolog-function} options.
8490 Put static or global variables whose size is @var{n} bytes or less into
8491 the tiny data area that register @code{ep} points to. The tiny data
8492 area can hold up to 256 bytes in total (128 bytes for byte references).
8496 Put static or global variables whose size is @var{n} bytes or less into
8497 the small data area that register @code{gp} points to. The small data
8498 area can hold up to 64 kilobytes.
8502 Put static or global variables whose size is @var{n} bytes or less into
8503 the first 32 kilobytes of memory.
8507 Specify that the target processor is the V850.
8510 @opindex mbig-switch
8511 Generate code suitable for big switch tables. Use this option only if
8512 the assembler/linker complain about out of range branches within a switch
8517 @subsection ARC Options
8520 These options are defined for ARC implementations:
8525 Compile code for little endian mode. This is the default.
8529 Compile code for big endian mode.
8532 @opindex mmangle-cpu
8533 Prepend the name of the cpu to all public symbol names.
8534 In multiple-processor systems, there are many ARC variants with different
8535 instruction and register set characteristics. This flag prevents code
8536 compiled for one cpu to be linked with code compiled for another.
8537 No facility exists for handling variants that are ``almost identical''.
8538 This is an all or nothing option.
8540 @item -mcpu=@var{cpu}
8542 Compile code for ARC variant @var{cpu}.
8543 Which variants are supported depend on the configuration.
8544 All variants support @option{-mcpu=base}, this is the default.
8546 @item -mtext=@var{text-section}
8547 @itemx -mdata=@var{data-section}
8548 @itemx -mrodata=@var{readonly-data-section}
8552 Put functions, data, and readonly data in @var{text-section},
8553 @var{data-section}, and @var{readonly-data-section} respectively
8554 by default. This can be overridden with the @code{section} attribute.
8555 @xref{Variable Attributes}.
8560 @subsection NS32K Options
8561 @cindex NS32K options
8563 These are the @samp{-m} options defined for the 32000 series. The default
8564 values for these options depends on which style of 32000 was selected when
8565 the compiler was configured; the defaults for the most common choices are
8573 Generate output for a 32032. This is the default
8574 when the compiler is configured for 32032 and 32016 based systems.
8580 Generate output for a 32332. This is the default
8581 when the compiler is configured for 32332-based systems.
8587 Generate output for a 32532. This is the default
8588 when the compiler is configured for 32532-based systems.
8592 Generate output containing 32081 instructions for floating point.
8593 This is the default for all systems.
8597 Generate output containing 32381 instructions for floating point. This
8598 also implies @option{-m32081}. The 32381 is only compatible with the 32332
8599 and 32532 cpus. This is the default for the pc532-netbsd configuration.
8603 Try and generate multiply-add floating point instructions @code{polyF}
8604 and @code{dotF}. This option is only available if the @option{-m32381}
8605 option is in effect. Using these instructions requires changes to to
8606 register allocation which generally has a negative impact on
8607 performance. This option should only be enabled when compiling code
8608 particularly likely to make heavy use of multiply-add instructions.
8611 @opindex mnomulti-add
8612 Do not try and generate multiply-add floating point instructions
8613 @code{polyF} and @code{dotF}. This is the default on all platforms.
8616 @opindex msoft-float
8617 Generate output containing library calls for floating point.
8618 @strong{Warning:} the requisite libraries may not be available.
8621 @opindex mnobitfield
8622 Do not use the bit-field instructions. On some machines it is faster to
8623 use shifting and masking operations. This is the default for the pc532.
8627 Do use the bit-field instructions. This is the default for all platforms
8632 Use a different function-calling convention, in which functions
8633 that take a fixed number of arguments return pop their
8634 arguments on return with the @code{ret} instruction.
8636 This calling convention is incompatible with the one normally
8637 used on Unix, so you cannot use it if you need to call libraries
8638 compiled with the Unix compiler.
8640 Also, you must provide function prototypes for all functions that
8641 take variable numbers of arguments (including @code{printf});
8642 otherwise incorrect code will be generated for calls to those
8645 In addition, seriously incorrect code will result if you call a
8646 function with too many arguments. (Normally, extra arguments are
8647 harmlessly ignored.)
8649 This option takes its name from the 680x0 @code{rtd} instruction.
8654 Use a different function-calling convention where the first two arguments
8655 are passed in registers.
8657 This calling convention is incompatible with the one normally
8658 used on Unix, so you cannot use it if you need to call libraries
8659 compiled with the Unix compiler.
8662 @opindex mnoregparam
8663 Do not pass any arguments in registers. This is the default for all
8668 It is OK to use the sb as an index register which is always loaded with
8669 zero. This is the default for the pc532-netbsd target.
8673 The sb register is not available for use or has not been initialized to
8674 zero by the run time system. This is the default for all targets except
8675 the pc532-netbsd. It is also implied whenever @option{-mhimem} or
8676 @option{-fpic} is set.
8680 Many ns32000 series addressing modes use displacements of up to 512MB@.
8681 If an address is above 512MB then displacements from zero can not be used.
8682 This option causes code to be generated which can be loaded above 512MB@.
8683 This may be useful for operating systems or ROM code.
8687 Assume code will be loaded in the first 512MB of virtual address space.
8688 This is the default for all platforms.
8694 @subsection AVR Options
8697 These options are defined for AVR implementations:
8700 @item -mmcu=@var{mcu}
8702 Specify ATMEL AVR instruction set or MCU type.
8704 Instruction set avr1 is for the minimal AVR core, not supported by the C
8705 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
8706 attiny11, attiny12, attiny15, attiny28).
8708 Instruction set avr2 (default) is for the classic AVR core with up to
8709 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
8710 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
8711 at90c8534, at90s8535).
8713 Instruction set avr3 is for the classic AVR core with up to 128K program
8714 memory space (MCU types: atmega103, atmega603).
8716 Instruction set avr4 is for the enhanced AVR core with up to 8K program
8717 memory space (MCU types: atmega83, atmega85).
8719 Instruction set avr5 is for the enhanced AVR core with up to 128K program
8720 memory space (MCU types: atmega161, atmega163, atmega32, at94k).
8724 Output instruction sizes to the asm file.
8726 @item -minit-stack=@var{N}
8727 @opindex minit-stack
8728 Specify the initial stack address, which may be a symbol or numeric value,
8729 @samp{__stack} is the default.
8731 @item -mno-interrupts
8732 @opindex mno-interrupts
8733 Generated code is not compatible with hardware interrupts.
8734 Code size will be smaller.
8736 @item -mcall-prologues
8737 @opindex mcall-prologues
8738 Functions prologues/epilogues expanded as call to appropriate
8739 subroutines. Code size will be smaller.
8741 @item -mno-tablejump
8742 @opindex mno-tablejump
8743 Do not generate tablejump insns which sometimes increase code size.
8746 @opindex mtiny-stack
8747 Change only the low 8 bits of the stack pointer.
8751 @subsection MCore Options
8752 @cindex MCore options
8754 These are the @samp{-m} options defined for the Motorola M*Core
8764 @opindex mno-hardlit
8765 Inline constants into the code stream if it can be done in two
8766 instructions or less.
8774 Use the divide instruction. (Enabled by default).
8776 @item -mrelax-immediate
8777 @itemx -mrelax-immediate
8778 @itemx -mno-relax-immediate
8779 @opindex mrelax-immediate
8780 @opindex mrelax-immediate
8781 @opindex mno-relax-immediate
8782 Allow arbitrary sized immediates in bit operations.
8784 @item -mwide-bitfields
8785 @itemx -mwide-bitfields
8786 @itemx -mno-wide-bitfields
8787 @opindex mwide-bitfields
8788 @opindex mwide-bitfields
8789 @opindex mno-wide-bitfields
8790 Always treat bit-fields as int-sized.
8792 @item -m4byte-functions
8793 @itemx -m4byte-functions
8794 @itemx -mno-4byte-functions
8795 @opindex m4byte-functions
8796 @opindex m4byte-functions
8797 @opindex mno-4byte-functions
8798 Force all functions to be aligned to a four byte boundary.
8800 @item -mcallgraph-data
8801 @itemx -mcallgraph-data
8802 @itemx -mno-callgraph-data
8803 @opindex mcallgraph-data
8804 @opindex mcallgraph-data
8805 @opindex mno-callgraph-data
8806 Emit callgraph information.
8810 @itemx -mno-slow-bytes
8811 @opindex mslow-bytes
8812 @opindex mslow-bytes
8813 @opindex mno-slow-bytes
8814 Prefer word access when reading byte quantities.
8816 @item -mlittle-endian
8817 @itemx -mlittle-endian
8819 @opindex mlittle-endian
8820 @opindex mlittle-endian
8821 @opindex mbig-endian
8822 Generate code for a little endian target.
8830 Generate code for the 210 processor.
8834 @subsection IA-64 Options
8835 @cindex IA-64 Options
8837 These are the @samp{-m} options defined for the Intel IA-64 architecture.
8841 @opindex mbig-endian
8842 Generate code for a big endian target. This is the default for HPUX@.
8844 @item -mlittle-endian
8845 @opindex mlittle-endian
8846 Generate code for a little endian target. This is the default for AIX5
8853 Generate (or don't) code for the GNU assembler. This is the default.
8854 @c Also, this is the default if the configure option @option{--with-gnu-as}
8861 Generate (or don't) code for the GNU linker. This is the default.
8862 @c Also, this is the default if the configure option @option{--with-gnu-ld}
8867 Generate code that does not use a global pointer register. The result
8868 is not position independent code, and violates the IA-64 ABI@.
8870 @item -mvolatile-asm-stop
8871 @itemx -mno-volatile-asm-stop
8872 @opindex mvolatile-asm-stop
8873 @opindex mno-volatile-asm-stop
8874 Generate (or don't) a stop bit immediately before and after volatile asm
8879 Generate code that works around Itanium B step errata.
8881 @item -mregister-names
8882 @itemx -mno-register-names
8883 @opindex mregister-names
8884 @opindex mno-register-names
8885 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
8886 the stacked registers. This may make assembler output more readable.
8892 Disable (or enable) optimizations that use the small data section. This may
8893 be useful for working around optimizer bugs.
8896 @opindex mconstant-gp
8897 Generate code that uses a single constant global pointer value. This is
8898 useful when compiling kernel code.
8902 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
8903 This is useful when compiling firmware code.
8905 @item -minline-divide-min-latency
8906 @opindex minline-divide-min-latency
8907 Generate code for inline divides using the minimum latency algorithm.
8909 @item -minline-divide-max-throughput
8910 @opindex minline-divide-max-throughput
8911 Generate code for inline divides using the maximum throughput algorithm.
8913 @item -mno-dwarf2-asm
8915 @opindex mno-dwarf2-asm
8916 @opindex mdwarf2-asm
8917 Don't (or do) generate assembler code for the DWARF2 line number debugging
8918 info. This may be useful when not using the GNU assembler.
8920 @item -mfixed-range=@var{register-range}
8921 @opindex mfixed-range
8922 Generate code treating the given register range as fixed registers.
8923 A fixed register is one that the register allocator can not use. This is
8924 useful when compiling kernel code. A register range is specified as
8925 two registers separated by a dash. Multiple register ranges can be
8926 specified separated by a comma.
8930 @subsection D30V Options
8931 @cindex D30V Options
8933 These @samp{-m} options are defined for D30V implementations:
8938 Link the @samp{.text}, @samp{.data}, @samp{.bss}, @samp{.strings},
8939 @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into external
8940 memory, which starts at location @code{0x80000000}.
8944 Same as the @option{-mextmem} switch.
8948 Link the @samp{.text} section into onchip text memory, which starts at
8949 location @code{0x0}. Also link @samp{.data}, @samp{.bss},
8950 @samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections
8951 into onchip data memory, which starts at location @code{0x20000000}.
8953 @item -mno-asm-optimize
8954 @itemx -masm-optimize
8955 @opindex mno-asm-optimize
8956 @opindex masm-optimize
8957 Disable (enable) passing @option{-O} to the assembler when optimizing.
8958 The assembler uses the @option{-O} option to automatically parallelize
8959 adjacent short instructions where possible.
8961 @item -mbranch-cost=@var{n}
8962 @opindex mbranch-cost
8963 Increase the internal costs of branches to @var{n}. Higher costs means
8964 that the compiler will issue more instructions to avoid doing a branch.
8967 @item -mcond-exec=@var{n}
8969 Specify the maximum number of conditionally executed instructions that
8970 replace a branch. The default is 4.
8973 @node Code Gen Options
8974 @section Options for Code Generation Conventions
8975 @cindex code generation conventions
8976 @cindex options, code generation
8977 @cindex run-time options
8979 These machine-independent options control the interface conventions
8980 used in code generation.
8982 Most of them have both positive and negative forms; the negative form
8983 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
8984 one of the forms is listed---the one which is not the default. You
8985 can figure out the other form by either removing @samp{no-} or adding
8990 @opindex fexceptions
8991 Enable exception handling. Generates extra code needed to propagate
8992 exceptions. For some targets, this implies GCC will generate frame
8993 unwind information for all functions, which can produce significant data
8994 size overhead, although it does not affect execution. If you do not
8995 specify this option, GCC will enable it by default for languages like
8996 C++ which normally require exception handling, and disable it for
8997 languages like C that do not normally require it. However, you may need
8998 to enable this option when compiling C code that needs to interoperate
8999 properly with exception handlers written in C++. You may also wish to
9000 disable this option if you are compiling older C++ programs that don't
9001 use exception handling.
9003 @item -fnon-call-exceptions
9004 @opindex fnon-call-exceptions
9005 Generate code that allows trapping instructions to throw exceptions.
9006 Note that this requires platform-specific runtime support that does
9007 not exist everywhere. Moreover, it only allows @emph{trapping}
9008 instructions to throw exceptions, i.e.@: memory references or floating
9009 point instructions. It does not allow exceptions to be thrown from
9010 arbitrary signal handlers such as @code{SIGALRM}.
9012 @item -funwind-tables
9013 @opindex funwind-tables
9014 Similar to @option{-fexceptions}, except that it will just generate any needed
9015 static data, but will not affect the generated code in any other way.
9016 You will normally not enable this option; instead, a language processor
9017 that needs this handling would enable it on your behalf.
9019 @item -fpcc-struct-return
9020 @opindex fpcc-struct-return
9021 Return ``short'' @code{struct} and @code{union} values in memory like
9022 longer ones, rather than in registers. This convention is less
9023 efficient, but it has the advantage of allowing intercallability between
9024 GCC-compiled files and files compiled with other compilers.
9026 The precise convention for returning structures in memory depends
9027 on the target configuration macros.
9029 Short structures and unions are those whose size and alignment match
9030 that of some integer type.
9032 @item -freg-struct-return
9033 @opindex freg-struct-return
9034 Use the convention that @code{struct} and @code{union} values are
9035 returned in registers when possible. This is more efficient for small
9036 structures than @option{-fpcc-struct-return}.
9038 If you specify neither @option{-fpcc-struct-return} nor its contrary
9039 @option{-freg-struct-return}, GCC defaults to whichever convention is
9040 standard for the target. If there is no standard convention, GCC
9041 defaults to @option{-fpcc-struct-return}, except on targets where GCC
9042 is the principal compiler. In those cases, we can choose the standard,
9043 and we chose the more efficient register return alternative.
9046 @opindex fshort-enums
9047 Allocate to an @code{enum} type only as many bytes as it needs for the
9048 declared range of possible values. Specifically, the @code{enum} type
9049 will be equivalent to the smallest integer type which has enough room.
9051 @item -fshort-double
9052 @opindex fshort-double
9053 Use the same size for @code{double} as for @code{float}.
9056 @opindex fshared-data
9057 Requests that the data and non-@code{const} variables of this
9058 compilation be shared data rather than private data. The distinction
9059 makes sense only on certain operating systems, where shared data is
9060 shared between processes running the same program, while private data
9061 exists in one copy per process.
9065 In C, allocate even uninitialized global variables in the data section of the
9066 object file, rather than generating them as common blocks. This has the
9067 effect that if the same variable is declared (without @code{extern}) in
9068 two different compilations, you will get an error when you link them.
9069 The only reason this might be useful is if you wish to verify that the
9070 program will work on other systems which always work this way.
9074 Ignore the @samp{#ident} directive.
9076 @item -fno-gnu-linker
9077 @opindex fno-gnu-linker
9078 Do not output global initializations (such as C++ constructors and
9079 destructors) in the form used by the GNU linker (on systems where the GNU
9080 linker is the standard method of handling them). Use this option when
9081 you want to use a non-GNU linker, which also requires using the
9082 @command{collect2} program to make sure the system linker includes
9083 constructors and destructors. (@command{collect2} is included in the GCC
9084 distribution.) For systems which @emph{must} use @command{collect2}, the
9085 compiler driver @command{gcc} is configured to do this automatically.
9087 @item -finhibit-size-directive
9088 @opindex finhibit-size-directive
9089 Don't output a @code{.size} assembler directive, or anything else that
9090 would cause trouble if the function is split in the middle, and the
9091 two halves are placed at locations far apart in memory. This option is
9092 used when compiling @file{crtstuff.c}; you should not need to use it
9096 @opindex fverbose-asm
9097 Put extra commentary information in the generated assembly code to
9098 make it more readable. This option is generally only of use to those
9099 who actually need to read the generated assembly code (perhaps while
9100 debugging the compiler itself).
9102 @option{-fno-verbose-asm}, the default, causes the
9103 extra information to be omitted and is useful when comparing two assembler
9108 Consider all memory references through pointers to be volatile.
9110 @item -fvolatile-global
9111 @opindex fvolatile-global
9112 Consider all memory references to extern and global data items to
9113 be volatile. GCC does not consider static data items to be volatile
9114 because of this switch.
9116 @item -fvolatile-static
9117 @opindex fvolatile-static
9118 Consider all memory references to static data to be volatile.
9122 @cindex global offset table
9124 Generate position-independent code (PIC) suitable for use in a shared
9125 library, if supported for the target machine. Such code accesses all
9126 constant addresses through a global offset table (GOT)@. The dynamic
9127 loader resolves the GOT entries when the program starts (the dynamic
9128 loader is not part of GCC; it is part of the operating system). If
9129 the GOT size for the linked executable exceeds a machine-specific
9130 maximum size, you get an error message from the linker indicating that
9131 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
9132 instead. (These maximums are 16k on the m88k, 8k on the Sparc, and 32k
9133 on the m68k and RS/6000. The 386 has no such limit.)
9135 Position-independent code requires special support, and therefore works
9136 only on certain machines. For the 386, GCC supports PIC for System V
9137 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
9138 position-independent.
9142 If supported for the target machine, emit position-independent code,
9143 suitable for dynamic linking and avoiding any limit on the size of the
9144 global offset table. This option makes a difference on the m68k, m88k,
9147 Position-independent code requires special support, and therefore works
9148 only on certain machines.
9150 @item -ffixed-@var{reg}
9152 Treat the register named @var{reg} as a fixed register; generated code
9153 should never refer to it (except perhaps as a stack pointer, frame
9154 pointer or in some other fixed role).
9156 @var{reg} must be the name of a register. The register names accepted
9157 are machine-specific and are defined in the @code{REGISTER_NAMES}
9158 macro in the machine description macro file.
9160 This flag does not have a negative form, because it specifies a
9163 @item -fcall-used-@var{reg}
9165 Treat the register named @var{reg} as an allocable register that is
9166 clobbered by function calls. It may be allocated for temporaries or
9167 variables that do not live across a call. Functions compiled this way
9168 will not save and restore the register @var{reg}.
9170 It is an error to used this flag with the frame pointer or stack pointer.
9171 Use of this flag for other registers that have fixed pervasive roles in
9172 the machine's execution model will produce disastrous results.
9174 This flag does not have a negative form, because it specifies a
9177 @item -fcall-saved-@var{reg}
9178 @opindex fcall-saved
9179 Treat the register named @var{reg} as an allocable register saved by
9180 functions. It may be allocated even for temporaries or variables that
9181 live across a call. Functions compiled this way will save and restore
9182 the register @var{reg} if they use it.
9184 It is an error to used this flag with the frame pointer or stack pointer.
9185 Use of this flag for other registers that have fixed pervasive roles in
9186 the machine's execution model will produce disastrous results.
9188 A different sort of disaster will result from the use of this flag for
9189 a register in which function values may be returned.
9191 This flag does not have a negative form, because it specifies a
9195 @opindex fpack-struct
9196 Pack all structure members together without holes. Usually you would
9197 not want to use this option, since it makes the code suboptimal, and
9198 the offsets of structure members won't agree with system libraries.
9200 @item -fcheck-memory-usage
9201 @opindex fcheck-memory-usage
9202 Generate extra code to check each memory access. GCC will generate
9203 code that is suitable for a detector of bad memory accesses such as
9206 Normally, you should compile all, or none, of your code with this option.
9208 If you do mix code compiled with and without this option,
9209 you must ensure that all code that has side effects
9210 and that is called by code compiled with this option
9211 is, itself, compiled with this option.
9212 If you do not, you might get erroneous messages from the detector.
9214 If you use functions from a library that have side-effects (such as
9215 @code{read}), you might not be able to recompile the library and
9216 specify this option. In that case, you can enable the
9217 @option{-fprefix-function-name} option, which requests GCC to encapsulate
9218 your code and make other functions look as if they were compiled with
9219 @option{-fcheck-memory-usage}. This is done by calling ``stubs'',
9220 which are provided by the detector. If you cannot find or build
9221 stubs for every function you call, you might have to specify
9222 @option{-fcheck-memory-usage} without @option{-fprefix-function-name}.
9224 If you specify this option, you can not use the @code{asm} or
9225 @code{__asm__} keywords in functions with memory checking enabled. GCC
9226 cannot understand what the @code{asm} statement may do, and therefore
9227 cannot generate the appropriate code, so it will reject it. However, if
9228 you specify the function attribute @code{no_check_memory_usage}
9229 (@pxref{Function Attributes}), GCC will disable memory checking within a
9230 function; you may use @code{asm} statements inside such functions. You
9231 may have an inline expansion of a non-checked function within a checked
9232 function; in that case GCC will not generate checks for the inlined
9233 function's memory accesses.
9235 If you move your @code{asm} statements to non-checked inline functions
9236 and they do access memory, you can add calls to the support code in your
9237 inline function, to indicate any reads, writes, or copies being done.
9238 These calls would be similar to those done in the stubs described above.
9240 @item -fprefix-function-name
9241 @opindex fprefix-function-name
9242 Request GCC to add a prefix to the symbols generated for function names.
9243 GCC adds a prefix to the names of functions defined as well as
9244 functions called. Code compiled with this option and code compiled
9245 without the option can't be linked together, unless stubs are used.
9247 If you compile the following code with @option{-fprefix-function-name}
9249 extern void bar (int);
9258 GCC will compile the code as if it was written:
9260 extern void prefix_bar (int);
9264 return prefix_bar (a + 5);
9267 This option is designed to be used with @option{-fcheck-memory-usage}.
9269 @item -finstrument-functions
9270 @opindex finstrument-functions
9271 Generate instrumentation calls for entry and exit to functions. Just
9272 after function entry and just before function exit, the following
9273 profiling functions will be called with the address of the current
9274 function and its call site. (On some platforms,
9275 @code{__builtin_return_address} does not work beyond the current
9276 function, so the call site information may not be available to the
9277 profiling functions otherwise.)
9280 void __cyg_profile_func_enter (void *this_fn,
9282 void __cyg_profile_func_exit (void *this_fn,
9286 The first argument is the address of the start of the current function,
9287 which may be looked up exactly in the symbol table.
9289 This instrumentation is also done for functions expanded inline in other
9290 functions. The profiling calls will indicate where, conceptually, the
9291 inline function is entered and exited. This means that addressable
9292 versions of such functions must be available. If all your uses of a
9293 function are expanded inline, this may mean an additional expansion of
9294 code size. If you use @samp{extern inline} in your C code, an
9295 addressable version of such functions must be provided. (This is
9296 normally the case anyways, but if you get lucky and the optimizer always
9297 expands the functions inline, you might have gotten away without
9298 providing static copies.)
9300 A function may be given the attribute @code{no_instrument_function}, in
9301 which case this instrumentation will not be done. This can be used, for
9302 example, for the profiling functions listed above, high-priority
9303 interrupt routines, and any functions from which the profiling functions
9304 cannot safely be called (perhaps signal handlers, if the profiling
9305 routines generate output or allocate memory).
9308 @opindex fstack-check
9309 Generate code to verify that you do not go beyond the boundary of the
9310 stack. You should specify this flag if you are running in an
9311 environment with multiple threads, but only rarely need to specify it in
9312 a single-threaded environment since stack overflow is automatically
9313 detected on nearly all systems if there is only one stack.
9315 Note that this switch does not actually cause checking to be done; the
9316 operating system must do that. The switch causes generation of code
9317 to ensure that the operating system sees the stack being extended.
9319 @item -fstack-limit-register=@var{reg}
9320 @itemx -fstack-limit-symbol=@var{sym}
9321 @itemx -fno-stack-limit
9322 @opindex fstack-limit-register
9323 @opindex fstack-limit-symbol
9324 @opindex fno-stack-limit
9325 Generate code to ensure that the stack does not grow beyond a certain value,
9326 either the value of a register or the address of a symbol. If the stack
9327 would grow beyond the value, a signal is raised. For most targets,
9328 the signal is raised before the stack overruns the boundary, so
9329 it is possible to catch the signal without taking special precautions.
9331 For instance, if the stack starts at address @samp{0x80000000} and grows
9332 downwards you can use the flags
9333 @samp{-fstack-limit-symbol=__stack_limit
9334 -Wl,--defsym,__stack_limit=0x7ffe0000} which will enforce a stack
9337 @cindex aliasing of parameters
9338 @cindex parameters, aliased
9339 @item -fargument-alias
9340 @itemx -fargument-noalias
9341 @itemx -fargument-noalias-global
9342 @opindex fargument-alias
9343 @opindex fargument-noalias
9344 @opindex fargument-noalias-global
9345 Specify the possible relationships among parameters and between
9346 parameters and global data.
9348 @option{-fargument-alias} specifies that arguments (parameters) may
9349 alias each other and may alias global storage.
9350 @option{-fargument-noalias} specifies that arguments do not alias
9351 each other, but may alias global storage.
9352 @option{-fargument-noalias-global} specifies that arguments do not
9353 alias each other and do not alias global storage.
9355 Each language will automatically use whatever option is required by
9356 the language standard. You should not need to use these options yourself.
9358 @item -fleading-underscore
9359 @opindex fleading-underscore
9360 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
9361 change the way C symbols are represented in the object file. One use
9362 is to help link with legacy assembly code.
9364 Be warned that you should know what you are doing when invoking this
9365 option, and that not all targets provide complete support for it.
9370 @node Environment Variables
9371 @section Environment Variables Affecting GCC
9372 @cindex environment variables
9374 @c man begin ENVIRONMENT
9376 This section describes several environment variables that affect how GCC
9377 operates. Some of them work by specifying directories or prefixes to use
9378 when searching for various kinds of files. Some are used to specify other
9379 aspects of the compilation environment.
9382 Note that you can also specify places to search using options such as
9383 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
9384 take precedence over places specified using environment variables, which
9385 in turn take precedence over those specified by the configuration of GCC@.
9389 Note that you can also specify places to search using options such as
9390 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
9391 take precedence over places specified using environment variables, which
9392 in turn take precedence over those specified by the configuration of GCC@.
9399 @c @itemx LC_COLLATE
9401 @c @itemx LC_MONETARY
9402 @c @itemx LC_NUMERIC
9407 @c @findex LC_COLLATE
9409 @c @findex LC_MONETARY
9410 @c @findex LC_NUMERIC
9414 These environment variables control the way that GCC uses
9415 localization information that allow GCC to work with different
9416 national conventions. GCC inspects the locale categories
9417 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
9418 so. These locale categories can be set to any value supported by your
9419 installation. A typical value is @samp{en_UK} for English in the United
9422 The @env{LC_CTYPE} environment variable specifies character
9423 classification. GCC uses it to determine the character boundaries in
9424 a string; this is needed for some multibyte encodings that contain quote
9425 and escape characters that would otherwise be interpreted as a string
9428 The @env{LC_MESSAGES} environment variable specifies the language to
9429 use in diagnostic messages.
9431 If the @env{LC_ALL} environment variable is set, it overrides the value
9432 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
9433 and @env{LC_MESSAGES} default to the value of the @env{LANG}
9434 environment variable. If none of these variables are set, GCC
9435 defaults to traditional C English behavior.
9439 If @env{TMPDIR} is set, it specifies the directory to use for temporary
9440 files. GCC uses temporary files to hold the output of one stage of
9441 compilation which is to be used as input to the next stage: for example,
9442 the output of the preprocessor, which is the input to the compiler
9445 @item GCC_EXEC_PREFIX
9446 @findex GCC_EXEC_PREFIX
9447 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
9448 names of the subprograms executed by the compiler. No slash is added
9449 when this prefix is combined with the name of a subprogram, but you can
9450 specify a prefix that ends with a slash if you wish.
9452 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
9453 an appropriate prefix to use based on the pathname it was invoked with.
9455 If GCC cannot find the subprogram using the specified prefix, it
9456 tries looking in the usual places for the subprogram.
9458 The default value of @env{GCC_EXEC_PREFIX} is
9459 @file{@var{prefix}/lib/gcc-lib/} where @var{prefix} is the value
9460 of @code{prefix} when you ran the @file{configure} script.
9462 Other prefixes specified with @option{-B} take precedence over this prefix.
9464 This prefix is also used for finding files such as @file{crt0.o} that are
9467 In addition, the prefix is used in an unusual way in finding the
9468 directories to search for header files. For each of the standard
9469 directories whose name normally begins with @samp{/usr/local/lib/gcc-lib}
9470 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
9471 replacing that beginning with the specified prefix to produce an
9472 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
9473 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
9474 These alternate directories are searched first; the standard directories
9478 @findex COMPILER_PATH
9479 The value of @env{COMPILER_PATH} is a colon-separated list of
9480 directories, much like @env{PATH}. GCC tries the directories thus
9481 specified when searching for subprograms, if it can't find the
9482 subprograms using @env{GCC_EXEC_PREFIX}.
9485 @findex LIBRARY_PATH
9486 The value of @env{LIBRARY_PATH} is a colon-separated list of
9487 directories, much like @env{PATH}. When configured as a native compiler,
9488 GCC tries the directories thus specified when searching for special
9489 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
9490 using GCC also uses these directories when searching for ordinary
9491 libraries for the @option{-l} option (but directories specified with
9492 @option{-L} come first).
9494 @item C_INCLUDE_PATH
9495 @itemx CPLUS_INCLUDE_PATH
9496 @itemx OBJC_INCLUDE_PATH
9497 @findex C_INCLUDE_PATH
9498 @findex CPLUS_INCLUDE_PATH
9499 @findex OBJC_INCLUDE_PATH
9500 @c @itemx OBJCPLUS_INCLUDE_PATH
9501 These environment variables pertain to particular languages. Each
9502 variable's value is a colon-separated list of directories, much like
9503 @env{PATH}. When GCC searches for header files, it tries the
9504 directories listed in the variable for the language you are using, after
9505 the directories specified with @option{-I} but before the standard header
9508 @item DEPENDENCIES_OUTPUT
9509 @findex DEPENDENCIES_OUTPUT
9510 @cindex dependencies for make as output
9511 If this variable is set, its value specifies how to output dependencies
9512 for Make based on the header files processed by the compiler. This
9513 output looks much like the output from the @option{-M} option
9514 (@pxref{Preprocessor Options}), but it goes to a separate file, and is
9515 in addition to the usual results of compilation.
9517 The value of @env{DEPENDENCIES_OUTPUT} can be just a file name, in
9518 which case the Make rules are written to that file, guessing the target
9519 name from the source file name. Or the value can have the form
9520 @samp{@var{file} @var{target}}, in which case the rules are written to
9521 file @var{file} using @var{target} as the target name.
9525 @cindex locale definition
9526 This variable is used to pass locale information to the compiler. One way in
9527 which this information is used is to determine the character set to be used
9528 when character literals, string literals and comments are parsed in C and C++.
9529 When the compiler is configured to allow multibyte characters,
9530 the following values for @env{LANG} are recognized:
9534 Recognize JIS characters.
9536 Recognize SJIS characters.
9538 Recognize EUCJP characters.
9541 If @env{LANG} is not defined, or if it has some other value, then the
9542 compiler will use mblen and mbtowc as defined by the default locale to
9543 recognize and translate multibyte characters.
9548 @node Running Protoize
9549 @section Running Protoize
9551 The program @code{protoize} is an optional part of GCC@. You can use
9552 it to add prototypes to a program, thus converting the program to ISO
9553 C in one respect. The companion program @code{unprotoize} does the
9554 reverse: it removes argument types from any prototypes that are found.
9556 When you run these programs, you must specify a set of source files as
9557 command line arguments. The conversion programs start out by compiling
9558 these files to see what functions they define. The information gathered
9559 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
9561 After scanning comes actual conversion. The specified files are all
9562 eligible to be converted; any files they include (whether sources or
9563 just headers) are eligible as well.
9565 But not all the eligible files are converted. By default,
9566 @code{protoize} and @code{unprotoize} convert only source and header
9567 files in the current directory. You can specify additional directories
9568 whose files should be converted with the @option{-d @var{directory}}
9569 option. You can also specify particular files to exclude with the
9570 @option{-x @var{file}} option. A file is converted if it is eligible, its
9571 directory name matches one of the specified directory names, and its
9572 name within the directory has not been excluded.
9574 Basic conversion with @code{protoize} consists of rewriting most
9575 function definitions and function declarations to specify the types of
9576 the arguments. The only ones not rewritten are those for varargs
9579 @code{protoize} optionally inserts prototype declarations at the
9580 beginning of the source file, to make them available for any calls that
9581 precede the function's definition. Or it can insert prototype
9582 declarations with block scope in the blocks where undeclared functions
9585 Basic conversion with @code{unprotoize} consists of rewriting most
9586 function declarations to remove any argument types, and rewriting
9587 function definitions to the old-style pre-ISO form.
9589 Both conversion programs print a warning for any function declaration or
9590 definition that they can't convert. You can suppress these warnings
9593 The output from @code{protoize} or @code{unprotoize} replaces the
9594 original source file. The original file is renamed to a name ending
9595 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
9596 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
9597 for DOS) file already exists, then the source file is simply discarded.
9599 @code{protoize} and @code{unprotoize} both depend on GCC itself to
9600 scan the program and collect information about the functions it uses.
9601 So neither of these programs will work until GCC is installed.
9603 Here is a table of the options you can use with @code{protoize} and
9604 @code{unprotoize}. Each option works with both programs unless
9608 @item -B @var{directory}
9609 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
9610 usual directory (normally @file{/usr/local/lib}). This file contains
9611 prototype information about standard system functions. This option
9612 applies only to @code{protoize}.
9614 @item -c @var{compilation-options}
9615 Use @var{compilation-options} as the options when running @code{gcc} to
9616 produce the @samp{.X} files. The special option @option{-aux-info} is
9617 always passed in addition, to tell @code{gcc} to write a @samp{.X} file.
9619 Note that the compilation options must be given as a single argument to
9620 @code{protoize} or @code{unprotoize}. If you want to specify several
9621 @code{gcc} options, you must quote the entire set of compilation options
9622 to make them a single word in the shell.
9624 There are certain @code{gcc} arguments that you cannot use, because they
9625 would produce the wrong kind of output. These include @option{-g},
9626 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
9627 the @var{compilation-options}, they are ignored.
9630 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
9631 systems) instead of @samp{.c}. This is convenient if you are converting
9632 a C program to C++. This option applies only to @code{protoize}.
9635 Add explicit global declarations. This means inserting explicit
9636 declarations at the beginning of each source file for each function
9637 that is called in the file and was not declared. These declarations
9638 precede the first function definition that contains a call to an
9639 undeclared function. This option applies only to @code{protoize}.
9641 @item -i @var{string}
9642 Indent old-style parameter declarations with the string @var{string}.
9643 This option applies only to @code{protoize}.
9645 @code{unprotoize} converts prototyped function definitions to old-style
9646 function definitions, where the arguments are declared between the
9647 argument list and the initial @samp{@{}. By default, @code{unprotoize}
9648 uses five spaces as the indentation. If you want to indent with just
9649 one space instead, use @option{-i " "}.
9652 Keep the @samp{.X} files. Normally, they are deleted after conversion
9656 Add explicit local declarations. @code{protoize} with @option{-l} inserts
9657 a prototype declaration for each function in each block which calls the
9658 function without any declaration. This option applies only to
9662 Make no real changes. This mode just prints information about the conversions
9663 that would have been done without @option{-n}.
9666 Make no @samp{.save} files. The original files are simply deleted.
9667 Use this option with caution.
9669 @item -p @var{program}
9670 Use the program @var{program} as the compiler. Normally, the name
9674 Work quietly. Most warnings are suppressed.
9677 Print the version number, just like @option{-v} for @code{gcc}.
9680 If you need special compiler options to compile one of your program's
9681 source files, then you should generate that file's @samp{.X} file
9682 specially, by running @code{gcc} on that source file with the
9683 appropriate options and the option @option{-aux-info}. Then run
9684 @code{protoize} on the entire set of files. @code{protoize} will use
9685 the existing @samp{.X} file because it is newer than the source file.
9689 gcc -Dfoo=bar file1.c -aux-info file1.X
9694 You need to include the special files along with the rest in the
9695 @code{protoize} command, even though their @samp{.X} files already
9696 exist, because otherwise they won't get converted.
9698 @xref{Protoize Caveats}, for more information on how to use
9699 @code{protoize} successfully.