1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002 Free Software Foundation, Inc.
3 @c This is part of the GCC manual.
4 @c For copying conditions, see the file gcc.texi.
8 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997,
9 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
11 Permission is granted to copy, distribute and/or modify this document
12 under the terms of the GNU Free Documentation License, Version 1.1 or
13 any later version published by the Free Software Foundation; with the
14 Invariant Sections being ``GNU General Public License'' and ``Funding
15 Free Software'', the Front-Cover texts being (a) (see below), and with
16 the Back-Cover Texts being (b) (see below). A copy of the license is
17 included in the gfdl(7) man page.
19 (a) The FSF's Front-Cover Text is:
23 (b) The FSF's Back-Cover Text is:
25 You have freedom to copy and modify this GNU Manual, like GNU
26 software. Copies published by the Free Software Foundation raise
27 funds for GNU development.
29 @c Set file name and title for the man page.
31 @settitle GNU project C and C++ compiler
33 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
34 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
35 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
36 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
37 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
38 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
39 [@option{-o} @var{outfile}] @var{infile}@dots{}
41 Only the most useful options are listed here; see below for the
42 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
45 gpl(7), gfdl(7), fsf-funding(7),
46 cpp(1), gcov(1), g77(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
47 and the Info entries for @file{gcc}, @file{cpp}, @file{g77}, @file{as},
48 @file{ld}, @file{binutils} and @file{gdb}.
51 For instructions on reporting bugs, see
52 @w{@uref{http://gcc.gnu.org/bugs.html}}. Use of the @command{gccbug}
53 script to report bugs is recommended.
56 See the Info entry for @command{gcc}, or
57 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
58 for contributors to GCC@.
63 @chapter GCC Command Options
64 @cindex GCC command options
65 @cindex command options
66 @cindex options, GCC command
68 @c man begin DESCRIPTION
70 When you invoke GCC, it normally does preprocessing, compilation,
71 assembly and linking. The ``overall options'' allow you to stop this
72 process at an intermediate stage. For example, the @option{-c} option
73 says not to run the linker. Then the output consists of object files
74 output by the assembler.
76 Other options are passed on to one stage of processing. Some options
77 control the preprocessor and others the compiler itself. Yet other
78 options control the assembler and linker; most of these are not
79 documented here, since you rarely need to use any of them.
81 @cindex C compilation options
82 Most of the command line options that you can use with GCC are useful
83 for C programs; when an option is only useful with another language
84 (usually C++), the explanation says so explicitly. If the description
85 for a particular option does not mention a source language, you can use
86 that option with all supported languages.
88 @cindex C++ compilation options
89 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
90 options for compiling C++ programs.
92 @cindex grouping options
93 @cindex options, grouping
94 The @command{gcc} program accepts options and file names as operands. Many
95 options have multi-letter names; therefore multiple single-letter options
96 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
99 @cindex order of options
100 @cindex options, order
101 You can mix options and other arguments. For the most part, the order
102 you use doesn't matter. Order does matter when you use several options
103 of the same kind; for example, if you specify @option{-L} more than once,
104 the directories are searched in the order specified.
106 Many options have long names starting with @samp{-f} or with
107 @samp{-W}---for example, @option{-fforce-mem},
108 @option{-fstrength-reduce}, @option{-Wformat} and so on. Most of
109 these have both positive and negative forms; the negative form of
110 @option{-ffoo} would be @option{-fno-foo}. This manual documents
111 only one of these two forms, whichever one is not the default.
115 @xref{Option Index}, for an index to GCC's options.
118 * Option Summary:: Brief list of all options, without explanations.
119 * Overall Options:: Controlling the kind of output:
120 an executable, object files, assembler files,
121 or preprocessed source.
122 * Invoking G++:: Compiling C++ programs.
123 * C Dialect Options:: Controlling the variant of C language compiled.
124 * C++ Dialect Options:: Variations on C++.
125 * Objective-C Dialect Options:: Variations on Objective-C.
126 * Language Independent Options:: Controlling how diagnostics should be
128 * Warning Options:: How picky should the compiler be?
129 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
130 * Optimize Options:: How much optimization?
131 * Preprocessor Options:: Controlling header files and macro definitions.
132 Also, getting dependency information for Make.
133 * Assembler Options:: Passing options to the assembler.
134 * Link Options:: Specifying libraries and so on.
135 * Directory Options:: Where to find header files and libraries.
136 Where to find the compiler executable files.
137 * Spec Files:: How to pass switches to sub-processes.
138 * Target Options:: Running a cross-compiler, or an old version of GCC.
139 * Submodel Options:: Specifying minor hardware or convention variations,
140 such as 68010 vs 68020.
141 * Code Gen Options:: Specifying conventions for function calls, data layout
143 * Environment Variables:: Env vars that affect GCC.
144 * Running Protoize:: Automatically adding or removing function prototypes.
150 @section Option Summary
152 Here is a summary of all the options, grouped by type. Explanations are
153 in the following sections.
156 @item Overall Options
157 @xref{Overall Options,,Options Controlling the Kind of Output}.
159 -c -S -E -o @var{file} -pipe -pass-exit-codes -x @var{language} @gol
160 -v -### --help --target-help --version}
162 @item C Language Options
163 @xref{C Dialect Options,,Options Controlling C Dialect}.
165 -ansi -std=@var{standard} -aux-info @var{filename} @gol
166 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
167 -fhosted -ffreestanding -fms-extensions @gol
168 -trigraphs -traditional -traditional-cpp @gol
169 -fallow-single-precision -fcond-mismatch @gol
170 -fsigned-bitfields -fsigned-char @gol
171 -funsigned-bitfields -funsigned-char @gol
174 @item C++ Language Options
175 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
177 -fabi-version=@var{n} -fno-access-control -fcheck-new @gol
178 -fconserve-space -fno-const-strings -fdollars-in-identifiers @gol
179 -fno-elide-constructors @gol
180 -fno-enforce-eh-specs -fexternal-templates @gol
181 -falt-external-templates @gol
182 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
183 -fno-implicit-templates @gol
184 -fno-implicit-inline-templates @gol
185 -fno-implement-inlines -fms-extensions @gol
186 -fno-nonansi-builtins -fno-operator-names @gol
187 -fno-optional-diags -fpermissive @gol
188 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
189 -fuse-cxa-atexit -fvtable-gc -fno-weak -nostdinc++ @gol
190 -fno-default-inline -Wabi -Wctor-dtor-privacy @gol
191 -Wnon-virtual-dtor -Wreorder @gol
192 -Weffc++ -Wno-deprecated @gol
193 -Wno-non-template-friend -Wold-style-cast @gol
194 -Woverloaded-virtual -Wno-pmf-conversions @gol
195 -Wsign-promo -Wsynth}
197 @item Objective-C Language Options
198 @xref{Objective-C Dialect Options,,Options Controlling Objective-C Dialect}.
200 -fconstant-string-class=@var{class-name} @gol
201 -fgnu-runtime -fnext-runtime -gen-decls @gol
202 -Wno-protocol -Wselector -Wundeclared-selector}
204 @item Language Independent Options
205 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
207 -fmessage-length=@var{n} @gol
208 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}}
210 @item Warning Options
211 @xref{Warning Options,,Options to Request or Suppress Warnings}.
213 -fsyntax-only -pedantic -pedantic-errors @gol
214 -w -W -Wall -Waggregate-return @gol
215 -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
216 -Wconversion -Wno-deprecated-declarations @gol
217 -Wdisabled-optimization -Wno-div-by-zero -Werror @gol
218 -Wfloat-equal -Wformat -Wformat=2 @gol
219 -Wformat-nonliteral -Wformat-security @gol
220 -Wimplicit -Wimplicit-int @gol
221 -Wimplicit-function-declaration @gol
222 -Werror-implicit-function-declaration @gol
223 -Wimport -Winline -Wno-endif-labels @gol
224 -Wlarger-than-@var{len} -Wlong-long @gol
225 -Wmain -Wmissing-braces @gol
226 -Wmissing-format-attribute -Wmissing-noreturn @gol
227 -Wno-multichar -Wno-format-extra-args -Wno-format-y2k @gol
228 -Wno-import -Wnonnull -Wpacked -Wpadded @gol
229 -Wparentheses -Wpointer-arith -Wredundant-decls @gol
230 -Wreturn-type -Wsequence-point -Wshadow @gol
231 -Wsign-compare -Wstrict-aliasing @gol
232 -Wswitch -Wswitch-default -Wswitch-enum @gol
233 -Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized @gol
234 -Wunknown-pragmas -Wunreachable-code @gol
235 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
236 -Wunused-value -Wunused-variable -Wwrite-strings}
238 @item C-only Warning Options
240 -Wbad-function-cast -Wmissing-declarations @gol
241 -Wmissing-prototypes -Wnested-externs @gol
242 -Wstrict-prototypes -Wtraditional}
244 @item Debugging Options
245 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
247 -d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
248 -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
249 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
250 -fdump-tree-original@r{[}-@var{n}@r{]} -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
251 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
252 -feliminate-dwarf2-dups -fmem-report @gol
253 -fprofile-arcs -fsched-verbose=@var{n} @gol
254 -ftest-coverage -ftime-report @gol
255 -g -g@var{level} -gcoff -gdwarf -gdwarf-1 -gdwarf-1+ -gdwarf-2 @gol
256 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
257 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
258 -print-multi-directory -print-multi-lib @gol
259 -print-prog-name=@var{program} -print-search-dirs -Q @gol
262 @item Optimization Options
263 @xref{Optimize Options,,Options that Control Optimization}.
265 -falign-functions=@var{n} -falign-jumps=@var{n} @gol
266 -falign-labels=@var{n} -falign-loops=@var{n} @gol
268 -fbranch-probabilities -fcaller-saves -fcprop-registers @gol
269 -fcse-follow-jumps -fcse-skip-blocks -fdata-sections @gol
270 -fdelayed-branch -fdelete-null-pointer-checks @gol
271 -fexpensive-optimizations -ffast-math -ffloat-store @gol
272 -fforce-addr -fforce-mem -ffunction-sections @gol
273 -fgcse -fgcse-lm -fgcse-sm -floop-optimize -fcrossjumping @gol
274 -fif-conversion -fif-conversion2 @gol
275 -finline-functions -finline-limit=@var{n} -fkeep-inline-functions @gol
276 -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
277 -fmove-all-movables -fnew-ra -fno-branch-count-reg @gol
278 -fno-default-inline -fno-defer-pop @gol
279 -fno-function-cse -fno-guess-branch-probability @gol
280 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
281 -funsafe-math-optimizations -ffinite-math-only @gol
282 -fno-trapping-math -fno-zero-initialized-in-bss @gol
283 -fomit-frame-pointer -foptimize-register-move @gol
284 -foptimize-sibling-calls -fprefetch-loop-arrays @gol
285 -freduce-all-givs -fregmove -frename-registers @gol
286 -freorder-blocks -freorder-functions @gol
287 -frerun-cse-after-loop -frerun-loop-opt @gol
288 -fschedule-insns -fschedule-insns2 @gol
289 -fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
290 -fsched-spec-load-dangerous -fsignaling-nans @gol
291 -fsingle-precision-constant -fssa -fssa-ccp -fssa-dce @gol
292 -fstrength-reduce -fstrict-aliasing -ftracer -fthread-jumps @gol
293 -ftrapv -funroll-all-loops -funroll-loops @gol
294 --param @var{name}=@var{value}
295 -O -O0 -O1 -O2 -O3 -Os}
297 @item Preprocessor Options
298 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
300 -$ -A@var{question}=@var{answer} -A-@var{question}@r{[}=@var{answer}@r{]} @gol
301 -C -dD -dI -dM -dN @gol
302 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
303 -idirafter @var{dir} @gol
304 -include @var{file} -imacros @var{file} @gol
305 -iprefix @var{file} -iwithprefix @var{dir} @gol
306 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
307 -M -MM -MF -MG -MP -MQ -MT -nostdinc -P -remap @gol
308 -trigraphs -undef -U@var{macro} -Wp,@var{option}}
310 @item Assembler Option
311 @xref{Assembler Options,,Passing Options to the Assembler}.
316 @xref{Link Options,,Options for Linking}.
318 @var{object-file-name} -l@var{library} @gol
319 -nostartfiles -nodefaultlibs -nostdlib @gol
320 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
321 -Wl,@var{option} -Xlinker @var{option} @gol
324 @item Directory Options
325 @xref{Directory Options,,Options for Directory Search}.
327 -B@var{prefix} -I@var{dir} -I- -L@var{dir} -specs=@var{file}}
330 @c I wrote this xref this way to avoid overfull hbox. -- rms
331 @xref{Target Options}.
333 -V @var{version} -b @var{machine}}
335 @item Machine Dependent Options
336 @xref{Submodel Options,,Hardware Models and Configurations}.
338 @emph{M680x0 Options}
340 -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
341 -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol
342 -mfpa -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
343 -malign-int -mstrict-align}
345 @emph{M68hc1x Options}
347 -m6811 -m6812 -m68hc11 -m68hc12 @gol
348 -mauto-incdec -minmax -mlong-calls -mshort @gol
349 -msoft-reg-count=@var{count}}
357 -mcpu=@var{cpu-type} @gol
358 -mtune=@var{cpu-type} @gol
359 -mcmodel=@var{code-model} @gol
361 -mapp-regs -mbroken-saverestore -mcypress @gol
362 -mfaster-structs -mflat @gol
363 -mfpu -mhard-float -mhard-quad-float @gol
364 -mimpure-text -mlive-g0 -mno-app-regs @gol
365 -mno-faster-structs -mno-flat -mno-fpu @gol
366 -mno-impure-text -mno-stack-bias -mno-unaligned-doubles @gol
367 -msoft-float -msoft-quad-float -msparclite -mstack-bias @gol
368 -msupersparc -munaligned-doubles -mv8}
370 @emph{Convex Options}
372 -mc1 -mc2 -mc32 -mc34 -mc38 @gol
373 -margcount -mnoargcount @gol
374 -mlong32 -mlong64 @gol
375 -mvolatile-cache -mvolatile-nocache}
377 @emph{AMD29K Options}
379 -m29000 -m29050 -mbw -mnbw -mdw -mndw @gol
380 -mlarge -mnormal -msmall @gol
381 -mkernel-registers -mno-reuse-arg-regs @gol
382 -mno-stack-check -mno-storem-bug @gol
383 -mreuse-arg-regs -msoft-float -mstack-check @gol
384 -mstorem-bug -muser-registers}
388 -mapcs-frame -mno-apcs-frame @gol
389 -mapcs-26 -mapcs-32 @gol
390 -mapcs-stack-check -mno-apcs-stack-check @gol
391 -mapcs-float -mno-apcs-float @gol
392 -mapcs-reentrant -mno-apcs-reentrant @gol
393 -msched-prolog -mno-sched-prolog @gol
394 -mlittle-endian -mbig-endian -mwords-little-endian @gol
395 -malignment-traps -mno-alignment-traps @gol
396 -msoft-float -mhard-float -mfpe @gol
397 -mthumb-interwork -mno-thumb-interwork @gol
398 -mcpu=@var{name} -march=@var{name} -mfpe=@var{name} @gol
399 -mstructure-size-boundary=@var{n} @gol
400 -mbsd -mxopen -mno-symrename @gol
401 -mabort-on-noreturn @gol
402 -mlong-calls -mno-long-calls @gol
403 -msingle-pic-base -mno-single-pic-base @gol
404 -mpic-register=@var{reg} @gol
405 -mnop-fun-dllimport @gol
406 -mpoke-function-name @gol
408 -mtpcs-frame -mtpcs-leaf-frame @gol
409 -mcaller-super-interworking -mcallee-super-interworking }
411 @emph{MN10200 Options}
415 @emph{MN10300 Options}
417 -mmult-bug -mno-mult-bug @gol
418 -mam33 -mno-am33 @gol
421 @emph{M32R/D Options}
423 -m32rx -m32r -mcode-model=@var{model-type} -msdata=@var{sdata-type} @gol
428 -m88000 -m88100 -m88110 -mbig-pic @gol
429 -mcheck-zero-division -mhandle-large-shift @gol
430 -midentify-revision -mno-check-zero-division @gol
431 -mno-ocs-debug-info -mno-ocs-frame-position @gol
432 -mno-optimize-arg-area -mno-serialize-volatile @gol
433 -mno-underscores -mocs-debug-info @gol
434 -mocs-frame-position -moptimize-arg-area @gol
435 -mserialize-volatile -mshort-data-@var{num} -msvr3 @gol
436 -msvr4 -mtrap-large-shift -muse-div-instruction @gol
437 -mversion-03.00 -mwarn-passed-structs}
439 @emph{RS/6000 and PowerPC Options}
441 -mcpu=@var{cpu-type} @gol
442 -mtune=@var{cpu-type} @gol
443 -mpower -mno-power -mpower2 -mno-power2 @gol
444 -mpowerpc -mpowerpc64 -mno-powerpc @gol
445 -maltivec -mno-altivec @gol
446 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
447 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
448 -mnew-mnemonics -mold-mnemonics @gol
449 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
450 -m64 -m32 -mxl-call -mno-xl-call -mpe @gol
451 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
452 -mstring -mno-string -mupdate -mno-update @gol
453 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
454 -mstrict-align -mno-strict-align -mrelocatable @gol
455 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
456 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
457 -mcall-aix -mcall-sysv -mcall-netbsd @gol
458 -maix-struct-return -msvr4-struct-return @gol
459 -mabi=altivec -mabi=no-altivec @gol
460 -mabi=spe -mabi=no-spe @gol
461 -misel=yes -misel=no @gol
462 -mprototype -mno-prototype @gol
463 -msim -mmvme -mads -myellowknife -memb -msdata @gol
464 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
468 -mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs @gol
469 -mfull-fp-blocks -mhc-struct-return -min-line-mul @gol
470 -mminimum-fp-blocks -mnohc-struct-return}
474 -mabicalls -march=@var{cpu-type} -mtune=@var{cpu=type} @gol
475 -mcpu=@var{cpu-type} -membedded-data -muninit-const-in-rodata @gol
476 -membedded-pic -mfp32 -mfp64 -mfused-madd -mno-fused-madd @gol
477 -mgas -mgp32 -mgp64 @gol
478 -mgpopt -mhalf-pic -mhard-float -mint64 -mips1 @gol
479 -mips2 -mips3 -mips4 -mlong64 -mlong32 -mlong-calls -mmemcpy @gol
480 -mmips-as -mmips-tfile -mno-abicalls @gol
481 -mno-embedded-data -mno-uninit-const-in-rodata @gol
482 -mno-embedded-pic -mno-gpopt -mno-long-calls @gol
483 -mno-memcpy -mno-mips-tfile -mno-rnames -mno-stats @gol
484 -mrnames -msoft-float @gol
485 -m4650 -msingle-float -mmad @gol
486 -mstats -EL -EB -G @var{num} -nocpp @gol
487 -mabi=32 -mabi=n32 -mabi=64 -mabi=eabi @gol
488 -mfix7000 -mno-crt0 -mflush-func=@var{func} -mno-flush-func @gol
489 -mbranch-likely -mno-branch-likely}
491 @emph{i386 and x86-64 Options}
493 -mcpu=@var{cpu-type} -march=@var{cpu-type} -mfpmath=@var{unit} @gol
494 -masm=@var{dialect} -mno-fancy-math-387 @gol
495 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
496 -mno-wide-multiply -mrtd -malign-double @gol
497 -mpreferred-stack-boundary=@var{num} @gol
498 -mmmx -msse -msse2 -m3dnow @gol
499 -mthreads -mno-align-stringops -minline-all-stringops @gol
500 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
501 -m96bit-long-double -mregparm=@var{num} -momit-leaf-frame-pointer @gol
503 -mcmodel=@var{code-model} @gol
508 -march=@var{architecture-type} @gol
509 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
510 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
511 -mjump-in-delay -mlinker-opt -mlong-calls @gol
512 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
513 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
514 -mno-jump-in-delay -mno-long-load-store @gol
515 -mno-portable-runtime -mno-soft-float @gol
516 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
517 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
518 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio}
520 @emph{Intel 960 Options}
522 -m@var{cpu-type} -masm-compat -mclean-linkage @gol
523 -mcode-align -mcomplex-addr -mleaf-procedures @gol
524 -mic-compat -mic2.0-compat -mic3.0-compat @gol
525 -mintel-asm -mno-clean-linkage -mno-code-align @gol
526 -mno-complex-addr -mno-leaf-procedures @gol
527 -mno-old-align -mno-strict-align -mno-tail-call @gol
528 -mnumerics -mold-align -msoft-float -mstrict-align @gol
531 @emph{DEC Alpha Options}
533 -mno-fp-regs -msoft-float -malpha-as -mgas @gol
534 -mieee -mieee-with-inexact -mieee-conformant @gol
535 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
536 -mtrap-precision=@var{mode} -mbuild-constants @gol
537 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
538 -mbwx -mmax -mfix -mcix @gol
539 -mfloat-vax -mfloat-ieee @gol
540 -mexplicit-relocs -msmall-data -mlarge-data @gol
541 -mmemory-latency=@var{time}}
543 @emph{DEC Alpha/VMS Options}
547 @emph{Clipper Options}
551 @emph{H8/300 Options}
553 -mrelax -mh -ms -mint32 -malign-300}
557 -m1 -m2 -m3 -m3e @gol
558 -m4-nofpu -m4-single-only -m4-single -m4 @gol
559 -m5-64media -m5-64media-nofpu @gol
560 -m5-32media -m5-32media-nofpu @gol
561 -m5-compact -m5-compact-nofpu @gol
562 -mb -ml -mdalign -mrelax @gol
563 -mbigtable -mfmovd -mhitachi -mnomacsave @gol
564 -mieee -misize -mpadstruct -mspace @gol
565 -mprefergot -musermode}
567 @emph{System V Options}
569 -Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
574 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
575 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
577 @emph{TMS320C3x/C4x Options}
579 -mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
580 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
581 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
582 -mparallel-insns -mparallel-mpy -mpreserve-float}
586 -mlong-calls -mno-long-calls -mep -mno-ep @gol
587 -mprolog-function -mno-prolog-function -mspace @gol
588 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
589 -mapp-regs -mno-app-regs @gol
590 -mdisable-callt -mno-disable-callt @gol
596 -m32032 -m32332 -m32532 -m32081 -m32381 @gol
597 -mmult-add -mnomult-add -msoft-float -mrtd -mnortd @gol
598 -mregparam -mnoregparam -msb -mnosb @gol
599 -mbitfield -mnobitfield -mhimem -mnohimem}
603 -mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
604 -mcall-prologues -mno-tablejump -mtiny-stack}
608 -mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
609 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
610 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
611 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
612 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
616 -mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
617 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
618 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
619 -mno-base-addresses -msingle-exit -mno-single-exit}
623 -mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
624 -mvolatile-asm-stop -mb-step -mregister-names -mno-sdata @gol
625 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
626 -minline-float-divide-max-throughput -minline-int-divide-min-latency @gol
627 -minline-int-divide-max-throughput -mno-dwarf2-asm @gol
628 -mfixed-range=@var{register-range}}
632 -mextmem -mextmemory -monchip -mno-asm-optimize @gol
633 -masm-optimize -mbranch-cost=@var{n} -mcond-exec=@var{n}}
635 @emph{S/390 and zSeries Options}
637 -mhard-float -msoft-float -mbackchain -mno-backchain @gol
638 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
639 -m64 -m31 -mdebug -mno-debug}
643 -mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
644 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
645 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
646 -mstack-align -mdata-align -mconst-align @gol
647 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
648 -melf -maout -melinux -mlinux -sim -sim2}
650 @emph{PDP-11 Options}
652 -mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
653 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
654 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
655 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
656 -mbranch-expensive -mbranch-cheap @gol
657 -msplit -mno-split -munix-asm -mdec-asm}
659 @emph{Xstormy16 Options}
663 @emph{Xtensa Options}
665 -mbig-endian -mlittle-endian @gol
666 -mdensity -mno-density @gol
667 -mmac16 -mno-mac16 @gol
668 -mmul16 -mno-mul16 @gol
669 -mmul32 -mno-mul32 @gol
671 -mminmax -mno-minmax @gol
672 -msext -mno-sext @gol
673 -mbooleans -mno-booleans @gol
674 -mhard-float -msoft-float @gol
675 -mfused-madd -mno-fused-madd @gol
676 -mserialize-volatile -mno-serialize-volatile @gol
677 -mtext-section-literals -mno-text-section-literals @gol
678 -mtarget-align -mno-target-align @gol
679 -mlongcalls -mno-longcalls}
681 @item Code Generation Options
682 @xref{Code Gen Options,,Options for Code Generation Conventions}.
684 -fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
685 -ffixed-@var{reg} -fexceptions @gol
686 -fnon-call-exceptions -funwind-tables @gol
687 -fasynchronous-unwind-tables @gol
688 -finhibit-size-directive -finstrument-functions @gol
689 -fno-common -fno-ident -fno-gnu-linker @gol
690 -fpcc-struct-return -fpic -fPIC @gol
691 -freg-struct-return -fshared-data -fshort-enums @gol
692 -fshort-double -fshort-wchar -fvolatile @gol
693 -fvolatile-global -fvolatile-static @gol
694 -fverbose-asm -fpack-struct -fstack-check @gol
695 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
696 -fargument-alias -fargument-noalias @gol
697 -fargument-noalias-global -fleading-underscore @gol
698 -ftls-model=@var{model}}
702 * Overall Options:: Controlling the kind of output:
703 an executable, object files, assembler files,
704 or preprocessed source.
705 * C Dialect Options:: Controlling the variant of C language compiled.
706 * C++ Dialect Options:: Variations on C++.
707 * Objective-C Dialect Options:: Variations on Objective-C.
708 * Language Independent Options:: Controlling how diagnostics should be
710 * Warning Options:: How picky should the compiler be?
711 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
712 * Optimize Options:: How much optimization?
713 * Preprocessor Options:: Controlling header files and macro definitions.
714 Also, getting dependency information for Make.
715 * Assembler Options:: Passing options to the assembler.
716 * Link Options:: Specifying libraries and so on.
717 * Directory Options:: Where to find header files and libraries.
718 Where to find the compiler executable files.
719 * Spec Files:: How to pass switches to sub-processes.
720 * Target Options:: Running a cross-compiler, or an old version of GCC.
723 @node Overall Options
724 @section Options Controlling the Kind of Output
726 Compilation can involve up to four stages: preprocessing, compilation
727 proper, assembly and linking, always in that order. The first three
728 stages apply to an individual source file, and end by producing an
729 object file; linking combines all the object files (those newly
730 compiled, and those specified as input) into an executable file.
732 @cindex file name suffix
733 For any given input file, the file name suffix determines what kind of
738 C source code which must be preprocessed.
741 C source code which should not be preprocessed.
744 C++ source code which should not be preprocessed.
747 Objective-C source code. Note that you must link with the library
748 @file{libobjc.a} to make an Objective-C program work.
751 Objective-C source code which should not be preprocessed.
754 C header file (not to be compiled or linked).
758 @itemx @var{file}.cxx
759 @itemx @var{file}.cpp
760 @itemx @var{file}.c++
762 C++ source code which must be preprocessed. Note that in @samp{.cxx},
763 the last two letters must both be literally @samp{x}. Likewise,
764 @samp{.C} refers to a literal capital C@.
767 @itemx @var{file}.for
768 @itemx @var{file}.FOR
769 Fortran source code which should not be preprocessed.
772 @itemx @var{file}.fpp
773 @itemx @var{file}.FPP
774 Fortran source code which must be preprocessed (with the traditional
778 Fortran source code which must be preprocessed with a RATFOR
779 preprocessor (not included with GCC)@.
781 @xref{Overall Options,,Options Controlling the Kind of Output, g77,
782 Using and Porting GNU Fortran}, for more details of the handling of
785 @c FIXME: Descriptions of Java file types.
792 Ada source code file which contains a library unit declaration (a
793 declaration of a package, subprogram, or generic, or a generic
794 instantiation), or a library unit renaming declaration (a package,
795 generic, or subprogram renaming declaration). Such files are also
798 @itemx @var{file}.adb
799 Ada source code file containing a library unit body (a subprogram or
800 package body). Such files are also called @dfn{bodies}.
802 @c GCC also knows about some suffixes for languages not yet included:
811 Assembler code which must be preprocessed.
814 An object file to be fed straight into linking.
815 Any file name with no recognized suffix is treated this way.
819 You can specify the input language explicitly with the @option{-x} option:
822 @item -x @var{language}
823 Specify explicitly the @var{language} for the following input files
824 (rather than letting the compiler choose a default based on the file
825 name suffix). This option applies to all following input files until
826 the next @option{-x} option. Possible values for @var{language} are:
828 c c-header cpp-output
830 objective-c objc-cpp-output
831 assembler assembler-with-cpp
833 f77 f77-cpp-input ratfor
839 Turn off any specification of a language, so that subsequent files are
840 handled according to their file name suffixes (as they are if @option{-x}
841 has not been used at all).
843 @item -pass-exit-codes
844 @opindex pass-exit-codes
845 Normally the @command{gcc} program will exit with the code of 1 if any
846 phase of the compiler returns a non-success return code. If you specify
847 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
848 numerically highest error produced by any phase that returned an error
852 If you only want some of the stages of compilation, you can use
853 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
854 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
855 @command{gcc} is to stop. Note that some combinations (for example,
856 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
861 Compile or assemble the source files, but do not link. The linking
862 stage simply is not done. The ultimate output is in the form of an
863 object file for each source file.
865 By default, the object file name for a source file is made by replacing
866 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
868 Unrecognized input files, not requiring compilation or assembly, are
873 Stop after the stage of compilation proper; do not assemble. The output
874 is in the form of an assembler code file for each non-assembler input
877 By default, the assembler file name for a source file is made by
878 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
880 Input files that don't require compilation are ignored.
884 Stop after the preprocessing stage; do not run the compiler proper. The
885 output is in the form of preprocessed source code, which is sent to the
888 Input files which don't require preprocessing are ignored.
890 @cindex output file option
893 Place output in file @var{file}. This applies regardless to whatever
894 sort of output is being produced, whether it be an executable file,
895 an object file, an assembler file or preprocessed C code.
897 Since only one output file can be specified, it does not make sense to
898 use @option{-o} when compiling more than one input file, unless you are
899 producing an executable file as output.
901 If @option{-o} is not specified, the default is to put an executable file
902 in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in
903 @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and
904 all preprocessed C source on standard output.
908 Print (on standard error output) the commands executed to run the stages
909 of compilation. Also print the version number of the compiler driver
910 program and of the preprocessor and the compiler proper.
914 Like @option{-v} except the commands are not executed and all command
915 arguments are quoted. This is useful for shell scripts to capture the
916 driver-generated command lines.
920 Use pipes rather than temporary files for communication between the
921 various stages of compilation. This fails to work on some systems where
922 the assembler is unable to read from a pipe; but the GNU assembler has
927 Print (on the standard output) a description of the command line options
928 understood by @command{gcc}. If the @option{-v} option is also specified
929 then @option{--help} will also be passed on to the various processes
930 invoked by @command{gcc}, so that they can display the command line options
931 they accept. If the @option{-W} option is also specified then command
932 line options which have no documentation associated with them will also
937 Print (on the standard output) a description of target specific command
938 line options for each tool.
942 Display the version number and copyrights of the invoked GCC.
946 @section Compiling C++ Programs
948 @cindex suffixes for C++ source
949 @cindex C++ source file suffixes
950 C++ source files conventionally use one of the suffixes @samp{.C},
951 @samp{.cc}, @samp{.cpp}, @samp{.c++}, @samp{.cp}, or @samp{.cxx};
952 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
953 files with these names and compiles them as C++ programs even if you
954 call the compiler the same way as for compiling C programs (usually with
955 the name @command{gcc}).
959 However, C++ programs often require class libraries as well as a
960 compiler that understands the C++ language---and under some
961 circumstances, you might want to compile programs from standard input,
962 or otherwise without a suffix that flags them as C++ programs.
963 @command{g++} is a program that calls GCC with the default language
964 set to C++, and automatically specifies linking against the C++
965 library. On many systems, @command{g++} is also
966 installed with the name @command{c++}.
968 @cindex invoking @command{g++}
969 When you compile C++ programs, you may specify many of the same
970 command-line options that you use for compiling programs in any
971 language; or command-line options meaningful for C and related
972 languages; or options that are meaningful only for C++ programs.
973 @xref{C Dialect Options,,Options Controlling C Dialect}, for
974 explanations of options for languages related to C@.
975 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
976 explanations of options that are meaningful only for C++ programs.
978 @node C Dialect Options
979 @section Options Controlling C Dialect
980 @cindex dialect options
981 @cindex language dialect options
982 @cindex options, dialect
984 The following options control the dialect of C (or languages derived
985 from C, such as C++ and Objective-C) that the compiler accepts:
992 In C mode, support all ISO C90 programs. In C++ mode,
993 remove GNU extensions that conflict with ISO C++.
995 This turns off certain features of GCC that are incompatible with ISO
996 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
997 such as the @code{asm} and @code{typeof} keywords, and
998 predefined macros such as @code{unix} and @code{vax} that identify the
999 type of system you are using. It also enables the undesirable and
1000 rarely used ISO trigraph feature. For the C compiler,
1001 it disables recognition of C++ style @samp{//} comments as well as
1002 the @code{inline} keyword.
1004 The alternate keywords @code{__asm__}, @code{__extension__},
1005 @code{__inline__} and @code{__typeof__} continue to work despite
1006 @option{-ansi}. You would not want to use them in an ISO C program, of
1007 course, but it is useful to put them in header files that might be included
1008 in compilations done with @option{-ansi}. Alternate predefined macros
1009 such as @code{__unix__} and @code{__vax__} are also available, with or
1010 without @option{-ansi}.
1012 The @option{-ansi} option does not cause non-ISO programs to be
1013 rejected gratuitously. For that, @option{-pedantic} is required in
1014 addition to @option{-ansi}. @xref{Warning Options}.
1016 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1017 option is used. Some header files may notice this macro and refrain
1018 from declaring certain functions or defining certain macros that the
1019 ISO standard doesn't call for; this is to avoid interfering with any
1020 programs that might use these names for other things.
1022 Functions which would normally be built in but do not have semantics
1023 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1024 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1025 built-in functions provided by GCC}, for details of the functions
1030 Determine the language standard. This option is currently only
1031 supported when compiling C or C++. A value for this option must be
1032 provided; possible values are
1037 ISO C90 (same as @option{-ansi}).
1039 @item iso9899:199409
1040 ISO C90 as modified in amendment 1.
1046 ISO C99. Note that this standard is not yet fully supported; see
1047 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1048 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1051 Default, ISO C90 plus GNU extensions (including some C99 features).
1055 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1056 this will become the default. The name @samp{gnu9x} is deprecated.
1059 The 1998 ISO C++ standard plus amendments.
1062 The same as @option{-std=c++98} plus GNU extensions. This is the
1063 default for C++ code.
1066 Even when this option is not specified, you can still use some of the
1067 features of newer standards in so far as they do not conflict with
1068 previous C standards. For example, you may use @code{__restrict__} even
1069 when @option{-std=c99} is not specified.
1071 The @option{-std} options specifying some version of ISO C have the same
1072 effects as @option{-ansi}, except that features that were not in ISO C90
1073 but are in the specified version (for example, @samp{//} comments and
1074 the @code{inline} keyword in ISO C99) are not disabled.
1076 @xref{Standards,,Language Standards Supported by GCC}, for details of
1077 these standard versions.
1079 @item -aux-info @var{filename}
1081 Output to the given filename prototyped declarations for all functions
1082 declared and/or defined in a translation unit, including those in header
1083 files. This option is silently ignored in any language other than C@.
1085 Besides declarations, the file indicates, in comments, the origin of
1086 each declaration (source file and line), whether the declaration was
1087 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1088 @samp{O} for old, respectively, in the first character after the line
1089 number and the colon), and whether it came from a declaration or a
1090 definition (@samp{C} or @samp{F}, respectively, in the following
1091 character). In the case of function definitions, a K&R-style list of
1092 arguments followed by their declarations is also provided, inside
1093 comments, after the declaration.
1097 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1098 keyword, so that code can use these words as identifiers. You can use
1099 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1100 instead. @option{-ansi} implies @option{-fno-asm}.
1102 In C++, this switch only affects the @code{typeof} keyword, since
1103 @code{asm} and @code{inline} are standard keywords. You may want to
1104 use the @option{-fno-gnu-keywords} flag instead, which has the same
1105 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1106 switch only affects the @code{asm} and @code{typeof} keywords, since
1107 @code{inline} is a standard keyword in ISO C99.
1110 @itemx -fno-builtin-@var{function}
1111 @opindex fno-builtin
1112 @cindex built-in functions
1113 Don't recognize built-in functions that do not begin with
1114 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1115 functions provided by GCC}, for details of the functions affected,
1116 including those which are not built-in functions when @option{-ansi} or
1117 @option{-std} options for strict ISO C conformance are used because they
1118 do not have an ISO standard meaning.
1120 GCC normally generates special code to handle certain built-in functions
1121 more efficiently; for instance, calls to @code{alloca} may become single
1122 instructions that adjust the stack directly, and calls to @code{memcpy}
1123 may become inline copy loops. The resulting code is often both smaller
1124 and faster, but since the function calls no longer appear as such, you
1125 cannot set a breakpoint on those calls, nor can you change the behavior
1126 of the functions by linking with a different library.
1128 With the @option{-fno-builtin-@var{function}} option
1129 only the built-in function @var{function} is
1130 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1131 function is named this is not built-in in this version of GCC, this
1132 option is ignored. There is no corresponding
1133 @option{-fbuiltin-@var{function}} option; if you wish to enable
1134 built-in functions selectively when using @option{-fno-builtin} or
1135 @option{-ffreestanding}, you may define macros such as:
1138 #define abs(n) __builtin_abs ((n))
1139 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1144 @cindex hosted environment
1146 Assert that compilation takes place in a hosted environment. This implies
1147 @option{-fbuiltin}. A hosted environment is one in which the
1148 entire standard library is available, and in which @code{main} has a return
1149 type of @code{int}. Examples are nearly everything except a kernel.
1150 This is equivalent to @option{-fno-freestanding}.
1152 @item -ffreestanding
1153 @opindex ffreestanding
1154 @cindex hosted environment
1156 Assert that compilation takes place in a freestanding environment. This
1157 implies @option{-fno-builtin}. A freestanding environment
1158 is one in which the standard library may not exist, and program startup may
1159 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1160 This is equivalent to @option{-fno-hosted}.
1162 @xref{Standards,,Language Standards Supported by GCC}, for details of
1163 freestanding and hosted environments.
1165 @item -fms-extensions
1166 @opindex fms-extensions
1167 Accept some non-standard constructs used in Microsoft header files.
1171 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1172 options for strict ISO C conformance) implies @option{-trigraphs}.
1174 @cindex traditional C language
1175 @cindex C language, traditional
1177 @itemx -traditional-cpp
1178 @opindex traditional-cpp
1179 @opindex traditional
1180 Formerly, these options caused GCC to attempt to emulate a pre-standard
1181 C compiler. They are now only supported with the @option{-E} switch.
1182 The preprocessor continues to support a pre-standard mode. See the GNU
1183 CPP manual for details.
1185 @item -fcond-mismatch
1186 @opindex fcond-mismatch
1187 Allow conditional expressions with mismatched types in the second and
1188 third arguments. The value of such an expression is void. This option
1189 is not supported for C++.
1191 @item -funsigned-char
1192 @opindex funsigned-char
1193 Let the type @code{char} be unsigned, like @code{unsigned char}.
1195 Each kind of machine has a default for what @code{char} should
1196 be. It is either like @code{unsigned char} by default or like
1197 @code{signed char} by default.
1199 Ideally, a portable program should always use @code{signed char} or
1200 @code{unsigned char} when it depends on the signedness of an object.
1201 But many programs have been written to use plain @code{char} and
1202 expect it to be signed, or expect it to be unsigned, depending on the
1203 machines they were written for. This option, and its inverse, let you
1204 make such a program work with the opposite default.
1206 The type @code{char} is always a distinct type from each of
1207 @code{signed char} or @code{unsigned char}, even though its behavior
1208 is always just like one of those two.
1211 @opindex fsigned-char
1212 Let the type @code{char} be signed, like @code{signed char}.
1214 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1215 the negative form of @option{-funsigned-char}. Likewise, the option
1216 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1218 @item -fsigned-bitfields
1219 @itemx -funsigned-bitfields
1220 @itemx -fno-signed-bitfields
1221 @itemx -fno-unsigned-bitfields
1222 @opindex fsigned-bitfields
1223 @opindex funsigned-bitfields
1224 @opindex fno-signed-bitfields
1225 @opindex fno-unsigned-bitfields
1226 These options control whether a bit-field is signed or unsigned, when the
1227 declaration does not use either @code{signed} or @code{unsigned}. By
1228 default, such a bit-field is signed, because this is consistent: the
1229 basic integer types such as @code{int} are signed types.
1231 @item -fwritable-strings
1232 @opindex fwritable-strings
1233 Store string constants in the writable data segment and don't uniquize
1234 them. This is for compatibility with old programs which assume they can
1235 write into string constants.
1237 Writing into string constants is a very bad idea; ``constants'' should
1241 @node C++ Dialect Options
1242 @section Options Controlling C++ Dialect
1244 @cindex compiler options, C++
1245 @cindex C++ options, command line
1246 @cindex options, C++
1247 This section describes the command-line options that are only meaningful
1248 for C++ programs; but you can also use most of the GNU compiler options
1249 regardless of what language your program is in. For example, you
1250 might compile a file @code{firstClass.C} like this:
1253 g++ -g -frepo -O -c firstClass.C
1257 In this example, only @option{-frepo} is an option meant
1258 only for C++ programs; you can use the other options with any
1259 language supported by GCC@.
1261 Here is a list of options that are @emph{only} for compiling C++ programs:
1265 @item -fabi-version=@var{n}
1266 @opindex fabi-version
1267 Use version @var{n} of the C++ ABI. Version 1 is the version of the C++
1268 ABI that first appeared in G++ 3.2. Version 0 will always be the
1269 version that conforms most closely to the C++ ABI specification.
1270 Therefore, the ABI obtained using version 0 will change as ABI bugs are
1273 The default is version 1.
1275 @item -fno-access-control
1276 @opindex fno-access-control
1277 Turn off all access checking. This switch is mainly useful for working
1278 around bugs in the access control code.
1282 Check that the pointer returned by @code{operator new} is non-null
1283 before attempting to modify the storage allocated. The current Working
1284 Paper requires that @code{operator new} never return a null pointer, so
1285 this check is normally unnecessary.
1287 An alternative to using this option is to specify that your
1288 @code{operator new} does not throw any exceptions; if you declare it
1289 @samp{throw()}, G++ will check the return value. See also @samp{new
1292 @item -fconserve-space
1293 @opindex fconserve-space
1294 Put uninitialized or runtime-initialized global variables into the
1295 common segment, as C does. This saves space in the executable at the
1296 cost of not diagnosing duplicate definitions. If you compile with this
1297 flag and your program mysteriously crashes after @code{main()} has
1298 completed, you may have an object that is being destroyed twice because
1299 two definitions were merged.
1301 This option is no longer useful on most targets, now that support has
1302 been added for putting variables into BSS without making them common.
1304 @item -fno-const-strings
1305 @opindex fno-const-strings
1306 Give string constants type @code{char *} instead of type @code{const
1307 char *}. By default, G++ uses type @code{const char *} as required by
1308 the standard. Even if you use @option{-fno-const-strings}, you cannot
1309 actually modify the value of a string constant, unless you also use
1310 @option{-fwritable-strings}.
1312 This option might be removed in a future release of G++. For maximum
1313 portability, you should structure your code so that it works with
1314 string constants that have type @code{const char *}.
1316 @item -fdollars-in-identifiers
1317 @opindex fdollars-in-identifiers
1318 Accept @samp{$} in identifiers. You can also explicitly prohibit use of
1319 @samp{$} with the option @option{-fno-dollars-in-identifiers}. (GNU C allows
1320 @samp{$} by default on most target systems, but there are a few exceptions.)
1321 Traditional C allowed the character @samp{$} to form part of
1322 identifiers. However, ISO C and C++ forbid @samp{$} in identifiers.
1324 @item -fno-elide-constructors
1325 @opindex fno-elide-constructors
1326 The C++ standard allows an implementation to omit creating a temporary
1327 which is only used to initialize another object of the same type.
1328 Specifying this option disables that optimization, and forces G++ to
1329 call the copy constructor in all cases.
1331 @item -fno-enforce-eh-specs
1332 @opindex fno-enforce-eh-specs
1333 Don't check for violation of exception specifications at runtime. This
1334 option violates the C++ standard, but may be useful for reducing code
1335 size in production builds, much like defining @samp{NDEBUG}. The compiler
1336 will still optimize based on the exception specifications.
1338 @item -fexternal-templates
1339 @opindex fexternal-templates
1341 Cause @samp{#pragma interface} and @samp{implementation} to apply to
1342 template instantiation; template instances are emitted or not according
1343 to the location of the template definition. @xref{Template
1344 Instantiation}, for more information.
1346 This option is deprecated.
1348 @item -falt-external-templates
1349 @opindex falt-external-templates
1350 Similar to @option{-fexternal-templates}, but template instances are
1351 emitted or not according to the place where they are first instantiated.
1352 @xref{Template Instantiation}, for more information.
1354 This option is deprecated.
1357 @itemx -fno-for-scope
1359 @opindex fno-for-scope
1360 If @option{-ffor-scope} is specified, the scope of variables declared in
1361 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1362 as specified by the C++ standard.
1363 If @option{-fno-for-scope} is specified, the scope of variables declared in
1364 a @i{for-init-statement} extends to the end of the enclosing scope,
1365 as was the case in old versions of G++, and other (traditional)
1366 implementations of C++.
1368 The default if neither flag is given to follow the standard,
1369 but to allow and give a warning for old-style code that would
1370 otherwise be invalid, or have different behavior.
1372 @item -fno-gnu-keywords
1373 @opindex fno-gnu-keywords
1374 Do not recognize @code{typeof} as a keyword, so that code can use this
1375 word as an identifier. You can use the keyword @code{__typeof__} instead.
1376 @option{-ansi} implies @option{-fno-gnu-keywords}.
1378 @item -fno-implicit-templates
1379 @opindex fno-implicit-templates
1380 Never emit code for non-inline templates which are instantiated
1381 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1382 @xref{Template Instantiation}, for more information.
1384 @item -fno-implicit-inline-templates
1385 @opindex fno-implicit-inline-templates
1386 Don't emit code for implicit instantiations of inline templates, either.
1387 The default is to handle inlines differently so that compiles with and
1388 without optimization will need the same set of explicit instantiations.
1390 @item -fno-implement-inlines
1391 @opindex fno-implement-inlines
1392 To save space, do not emit out-of-line copies of inline functions
1393 controlled by @samp{#pragma implementation}. This will cause linker
1394 errors if these functions are not inlined everywhere they are called.
1396 @item -fms-extensions
1397 @opindex fms-extensions
1398 Disable pedantic warnings about constructs used in MFC, such as implicit
1399 int and getting a pointer to member function via non-standard syntax.
1401 @item -fno-nonansi-builtins
1402 @opindex fno-nonansi-builtins
1403 Disable built-in declarations of functions that are not mandated by
1404 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1405 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1407 @item -fno-operator-names
1408 @opindex fno-operator-names
1409 Do not treat the operator name keywords @code{and}, @code{bitand},
1410 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1411 synonyms as keywords.
1413 @item -fno-optional-diags
1414 @opindex fno-optional-diags
1415 Disable diagnostics that the standard says a compiler does not need to
1416 issue. Currently, the only such diagnostic issued by G++ is the one for
1417 a name having multiple meanings within a class.
1420 @opindex fpermissive
1421 Downgrade messages about nonconformant code from errors to warnings. By
1422 default, G++ effectively sets @option{-pedantic-errors} without
1423 @option{-pedantic}; this option reverses that. This behavior and this
1424 option are superseded by @option{-pedantic}, which works as it does for GNU C@.
1428 Enable automatic template instantiation at link time. This option also
1429 implies @option{-fno-implicit-templates}. @xref{Template
1430 Instantiation}, for more information.
1434 Disable generation of information about every class with virtual
1435 functions for use by the C++ runtime type identification features
1436 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1437 of the language, you can save some space by using this flag. Note that
1438 exception handling uses the same information, but it will generate it as
1443 Emit statistics about front-end processing at the end of the compilation.
1444 This information is generally only useful to the G++ development team.
1446 @item -ftemplate-depth-@var{n}
1447 @opindex ftemplate-depth
1448 Set the maximum instantiation depth for template classes to @var{n}.
1449 A limit on the template instantiation depth is needed to detect
1450 endless recursions during template class instantiation. ANSI/ISO C++
1451 conforming programs must not rely on a maximum depth greater than 17.
1453 @item -fuse-cxa-atexit
1454 @opindex fuse-cxa-atexit
1455 Register destructors for objects with static storage duration with the
1456 @code{__cxa_atexit} function rather than the @code{atexit} function.
1457 This option is required for fully standards-compliant handling of static
1458 destructors, but will only work if your C library supports
1459 @code{__cxa_atexit}.
1463 Emit special relocations for vtables and virtual function references
1464 so that the linker can identify unused virtual functions and zero out
1465 vtable slots that refer to them. This is most useful with
1466 @option{-ffunction-sections} and @option{-Wl,--gc-sections}, in order to
1467 also discard the functions themselves.
1469 This optimization requires GNU as and GNU ld. Not all systems support
1470 this option. @option{-Wl,--gc-sections} is ignored without @option{-static}.
1474 Do not use weak symbol support, even if it is provided by the linker.
1475 By default, G++ will use weak symbols if they are available. This
1476 option exists only for testing, and should not be used by end-users;
1477 it will result in inferior code and has no benefits. This option may
1478 be removed in a future release of G++.
1482 Do not search for header files in the standard directories specific to
1483 C++, but do still search the other standard directories. (This option
1484 is used when building the C++ library.)
1487 In addition, these optimization, warning, and code generation options
1488 have meanings only for C++ programs:
1491 @item -fno-default-inline
1492 @opindex fno-default-inline
1493 Do not assume @samp{inline} for functions defined inside a class scope.
1494 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1495 functions will have linkage like inline functions; they just won't be
1498 @item -Wabi @r{(C++ only)}
1500 Warn when G++ generates code that is probably not compatible with the
1501 vendor-neutral C++ ABI. Although an effort has been made to warn about
1502 all such cases, there are probably some cases that are not warned about,
1503 even though G++ is generating incompatible code. There may also be
1504 cases where warnings are emitted even though the code that is generated
1507 You should rewrite your code to avoid these warnings if you are
1508 concerned about the fact that code generated by G++ may not be binary
1509 compatible with code generated by other compilers.
1511 The known incompatibilites at this point include:
1516 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1517 pack data into the same byte as a base class. For example:
1520 struct A @{ virtual void f(); int f1 : 1; @};
1521 struct B : public A @{ int f2 : 1; @};
1525 In this case, G++ will place @code{B::f2} into the same byte
1526 as@code{A::f1}; other compilers will not. You can avoid this problem
1527 by explicitly padding @code{A} so that its size is a multiple of the
1528 byte size on your platform; that will cause G++ and other compilers to
1529 layout @code{B} identically.
1532 Incorrect handling of tail-padding for virtual bases. G++ does not use
1533 tail padding when laying out virtual bases. For example:
1536 struct A @{ virtual void f(); char c1; @};
1537 struct B @{ B(); char c2; @};
1538 struct C : public A, public virtual B @{@};
1542 In this case, G++ will not place @code{B} into the tail-padding for
1543 @code{A}; other compilers will. You can avoid this problem by
1544 explicitly padding @code{A} so that its size is a multiple of its
1545 alignment (ignoring virtual base classes); that will cause G++ and other
1546 compilers to layout @code{C} identically.
1549 Incorrect handling of bit-fields with declared widths greater than that
1550 of their underlying types, when the bit-fields appear in a union. For
1554 union U @{ int i : 4096; @};
1558 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1559 union too small by the number of bits in an @code{int}.
1562 Empty classes can be placed at incorrect offsets. For example:
1572 struct C : public B, public A @{@};
1576 G++ will place the @code{A} base class of @code{C} at a non-zero offset;
1577 it should be placed at offset zero. G++ mistakenly believes that the
1578 @code{A} data member of @code{B} is already at offset zero.
1581 Names of template functions whose types involve @code{typename} or
1582 template template parameters can be mangled incorrectly.
1585 template <typename Q>
1586 void f(typename Q::X) @{@}
1588 template <template <typename> class Q>
1589 void f(typename Q<int>::X) @{@}
1593 Instantions of these templates may be mangled incorrectly.
1597 @item -Wctor-dtor-privacy @r{(C++ only)}
1598 @opindex Wctor-dtor-privacy
1599 Warn when a class seems unusable, because all the constructors or
1600 destructors in a class are private and the class has no friends or
1601 public static member functions. This warning is enabled by default.
1603 @item -Wnon-virtual-dtor @r{(C++ only)}
1604 @opindex Wnon-virtual-dtor
1605 Warn when a class declares a non-virtual destructor that should probably
1606 be virtual, because it looks like the class will be used polymorphically.
1607 This warning is enabled by @option{-Wall}.
1609 @item -Wreorder @r{(C++ only)}
1611 @cindex reordering, warning
1612 @cindex warning for reordering of member initializers
1613 Warn when the order of member initializers given in the code does not
1614 match the order in which they must be executed. For instance:
1620 A(): j (0), i (1) @{ @}
1624 Here the compiler will warn that the member initializers for @samp{i}
1625 and @samp{j} will be rearranged to match the declaration order of the
1626 members. This warning is enabled by @option{-Wall}.
1629 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1632 @item -Weffc++ @r{(C++ only)}
1634 Warn about violations of the following style guidelines from Scott Meyers'
1635 @cite{Effective C++} book:
1639 Item 11: Define a copy constructor and an assignment operator for classes
1640 with dynamically allocated memory.
1643 Item 12: Prefer initialization to assignment in constructors.
1646 Item 14: Make destructors virtual in base classes.
1649 Item 15: Have @code{operator=} return a reference to @code{*this}.
1652 Item 23: Don't try to return a reference when you must return an object.
1656 and about violations of the following style guidelines from Scott Meyers'
1657 @cite{More Effective C++} book:
1661 Item 6: Distinguish between prefix and postfix forms of increment and
1662 decrement operators.
1665 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1669 If you use this option, you should be aware that the standard library
1670 headers do not obey all of these guidelines; you can use @samp{grep -v}
1671 to filter out those warnings.
1673 @item -Wno-deprecated @r{(C++ only)}
1674 @opindex Wno-deprecated
1675 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1677 @item -Wno-non-template-friend @r{(C++ only)}
1678 @opindex Wno-non-template-friend
1679 Disable warnings when non-templatized friend functions are declared
1680 within a template. With the advent of explicit template specification
1681 support in G++, if the name of the friend is an unqualified-id (i.e.,
1682 @samp{friend foo(int)}), the C++ language specification demands that the
1683 friend declare or define an ordinary, nontemplate function. (Section
1684 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1685 could be interpreted as a particular specialization of a templatized
1686 function. Because this non-conforming behavior is no longer the default
1687 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1688 check existing code for potential trouble spots, and is on by default.
1689 This new compiler behavior can be turned off with
1690 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1691 but disables the helpful warning.
1693 @item -Wold-style-cast @r{(C++ only)}
1694 @opindex Wold-style-cast
1695 Warn if an old-style (C-style) cast to a non-void type is used within
1696 a C++ program. The new-style casts (@samp{static_cast},
1697 @samp{reinterpret_cast}, and @samp{const_cast}) are less vulnerable to
1698 unintended effects, and much easier to grep for.
1700 @item -Woverloaded-virtual @r{(C++ only)}
1701 @opindex Woverloaded-virtual
1702 @cindex overloaded virtual fn, warning
1703 @cindex warning for overloaded virtual fn
1704 Warn when a function declaration hides virtual functions from a
1705 base class. For example, in:
1712 struct B: public A @{
1717 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1725 will fail to compile.
1727 @item -Wno-pmf-conversions @r{(C++ only)}
1728 @opindex Wno-pmf-conversions
1729 Disable the diagnostic for converting a bound pointer to member function
1732 @item -Wsign-promo @r{(C++ only)}
1733 @opindex Wsign-promo
1734 Warn when overload resolution chooses a promotion from unsigned or
1735 enumeral type to a signed type over a conversion to an unsigned type of
1736 the same size. Previous versions of G++ would try to preserve
1737 unsignedness, but the standard mandates the current behavior.
1739 @item -Wsynth @r{(C++ only)}
1741 @cindex warning for synthesized methods
1742 @cindex synthesized methods, warning
1743 Warn when G++'s synthesis behavior does not match that of cfront. For
1749 A& operator = (int);
1759 In this example, G++ will synthesize a default @samp{A& operator =
1760 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1763 @node Objective-C Dialect Options
1764 @section Options Controlling Objective-C Dialect
1766 @cindex compiler options, Objective-C
1767 @cindex Objective-C options, command line
1768 @cindex options, Objective-C
1769 This section describes the command-line options that are only meaningful
1770 for Objective-C programs; but you can also use most of the GNU compiler
1771 options regardless of what language your program is in. For example,
1772 you might compile a file @code{some_class.m} like this:
1775 gcc -g -fgnu-runtime -O -c some_class.m
1779 In this example, only @option{-fgnu-runtime} is an option meant only for
1780 Objective-C programs; you can use the other options with any language
1783 Here is a list of options that are @emph{only} for compiling Objective-C
1787 @item -fconstant-string-class=@var{class-name}
1788 @opindex fconstant-string-class
1789 Use @var{class-name} as the name of the class to instantiate for each
1790 literal string specified with the syntax @code{@@"@dots{}"}. The default
1791 class name is @code{NXConstantString}.
1794 @opindex fgnu-runtime
1795 Generate object code compatible with the standard GNU Objective-C
1796 runtime. This is the default for most types of systems.
1798 @item -fnext-runtime
1799 @opindex fnext-runtime
1800 Generate output compatible with the NeXT runtime. This is the default
1801 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1802 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1807 Dump interface declarations for all classes seen in the source file to a
1808 file named @file{@var{sourcename}.decl}.
1811 @opindex Wno-protocol
1812 If a class is declared to implement a protocol, a warning is issued for
1813 every method in the protocol that is not implemented by the class. The
1814 default behavior is to issue a warning for every method not explicitly
1815 implemented in the class, even if a method implementation is inherited
1816 from the superclass. If you use the @code{-Wno-protocol} option, then
1817 methods inherited from the superclass are considered to be implemented,
1818 and no warning is issued for them.
1822 Warn if multiple methods of different types for the same selector are
1823 found during compilation. The check is performed on the list of methods
1824 in the final stage of compilation. Additionally, a check is performed
1825 that for each selector appearing in a @code{@@selector(@dots{})}
1826 expression, a corresponding method with that selector has been found
1827 during compilation. Because these checks scan the method table only at
1828 the end of compilation, these warnings are not produced if the final
1829 stage of compilation is not reached, for example because an error is
1830 found during compilation, or because the @code{-fsyntax-only} option is
1833 @item -Wundeclared-selector
1834 @opindex Wundeclared-selector
1835 Warn if a @code{@@selector(@dots{})} expression referring to an
1836 undeclared selector is found. A selector is considered undeclared if no
1837 method with that name has been declared (explicitly, in an
1838 @code{@@interface} or @code{@@protocol} declaration, or implicitly, in
1839 an @code{@@implementation} section) before the
1840 @code{@@selector(@dots{})} expression. This option always performs its
1841 checks as soon as a @code{@@selector(@dots{})} expression is found
1842 (while @code{-Wselector} only performs its checks in the final stage of
1843 compilation), and so additionally enforces the coding style convention
1844 that methods and selectors must be declared before being used.
1846 @c not documented because only avail via -Wp
1847 @c @item -print-objc-runtime-info
1851 @node Language Independent Options
1852 @section Options to Control Diagnostic Messages Formatting
1853 @cindex options to control diagnostics formatting
1854 @cindex diagnostic messages
1855 @cindex message formatting
1857 Traditionally, diagnostic messages have been formatted irrespective of
1858 the output device's aspect (e.g.@: its width, @dots{}). The options described
1859 below can be used to control the diagnostic messages formatting
1860 algorithm, e.g.@: how many characters per line, how often source location
1861 information should be reported. Right now, only the C++ front end can
1862 honor these options. However it is expected, in the near future, that
1863 the remaining front ends would be able to digest them correctly.
1866 @item -fmessage-length=@var{n}
1867 @opindex fmessage-length
1868 Try to format error messages so that they fit on lines of about @var{n}
1869 characters. The default is 72 characters for @command{g++} and 0 for the rest of
1870 the front ends supported by GCC@. If @var{n} is zero, then no
1871 line-wrapping will be done; each error message will appear on a single
1874 @opindex fdiagnostics-show-location
1875 @item -fdiagnostics-show-location=once
1876 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
1877 reporter to emit @emph{once} source location information; that is, in
1878 case the message is too long to fit on a single physical line and has to
1879 be wrapped, the source location won't be emitted (as prefix) again,
1880 over and over, in subsequent continuation lines. This is the default
1883 @item -fdiagnostics-show-location=every-line
1884 Only meaningful in line-wrapping mode. Instructs the diagnostic
1885 messages reporter to emit the same source location information (as
1886 prefix) for physical lines that result from the process of breaking
1887 a message which is too long to fit on a single line.
1891 @node Warning Options
1892 @section Options to Request or Suppress Warnings
1893 @cindex options to control warnings
1894 @cindex warning messages
1895 @cindex messages, warning
1896 @cindex suppressing warnings
1898 Warnings are diagnostic messages that report constructions which
1899 are not inherently erroneous but which are risky or suggest there
1900 may have been an error.
1902 You can request many specific warnings with options beginning @samp{-W},
1903 for example @option{-Wimplicit} to request warnings on implicit
1904 declarations. Each of these specific warning options also has a
1905 negative form beginning @samp{-Wno-} to turn off warnings;
1906 for example, @option{-Wno-implicit}. This manual lists only one of the
1907 two forms, whichever is not the default.
1909 The following options control the amount and kinds of warnings produced
1910 by GCC; for further, language-specific options also refer to
1911 @ref{C++ Dialect Options} and @ref{Objective-C Dialect Options}.
1914 @cindex syntax checking
1916 @opindex fsyntax-only
1917 Check the code for syntax errors, but don't do anything beyond that.
1921 Issue all the warnings demanded by strict ISO C and ISO C++;
1922 reject all programs that use forbidden extensions, and some other
1923 programs that do not follow ISO C and ISO C++. For ISO C, follows the
1924 version of the ISO C standard specified by any @option{-std} option used.
1926 Valid ISO C and ISO C++ programs should compile properly with or without
1927 this option (though a rare few will require @option{-ansi} or a
1928 @option{-std} option specifying the required version of ISO C)@. However,
1929 without this option, certain GNU extensions and traditional C and C++
1930 features are supported as well. With this option, they are rejected.
1932 @option{-pedantic} does not cause warning messages for use of the
1933 alternate keywords whose names begin and end with @samp{__}. Pedantic
1934 warnings are also disabled in the expression that follows
1935 @code{__extension__}. However, only system header files should use
1936 these escape routes; application programs should avoid them.
1937 @xref{Alternate Keywords}.
1939 Some users try to use @option{-pedantic} to check programs for strict ISO
1940 C conformance. They soon find that it does not do quite what they want:
1941 it finds some non-ISO practices, but not all---only those for which
1942 ISO C @emph{requires} a diagnostic, and some others for which
1943 diagnostics have been added.
1945 A feature to report any failure to conform to ISO C might be useful in
1946 some instances, but would require considerable additional work and would
1947 be quite different from @option{-pedantic}. We don't have plans to
1948 support such a feature in the near future.
1950 Where the standard specified with @option{-std} represents a GNU
1951 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
1952 corresponding @dfn{base standard}, the version of ISO C on which the GNU
1953 extended dialect is based. Warnings from @option{-pedantic} are given
1954 where they are required by the base standard. (It would not make sense
1955 for such warnings to be given only for features not in the specified GNU
1956 C dialect, since by definition the GNU dialects of C include all
1957 features the compiler supports with the given option, and there would be
1958 nothing to warn about.)
1960 @item -pedantic-errors
1961 @opindex pedantic-errors
1962 Like @option{-pedantic}, except that errors are produced rather than
1967 Inhibit all warning messages.
1971 Inhibit warning messages about the use of @samp{#import}.
1973 @item -Wchar-subscripts
1974 @opindex Wchar-subscripts
1975 Warn if an array subscript has type @code{char}. This is a common cause
1976 of error, as programmers often forget that this type is signed on some
1981 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
1982 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
1986 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
1987 the arguments supplied have types appropriate to the format string
1988 specified, and that the conversions specified in the format string make
1989 sense. This includes standard functions, and others specified by format
1990 attributes (@pxref{Function Attributes}), in the @code{printf},
1991 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
1992 not in the C standard) families.
1994 The formats are checked against the format features supported by GNU
1995 libc version 2.2. These include all ISO C90 and C99 features, as well
1996 as features from the Single Unix Specification and some BSD and GNU
1997 extensions. Other library implementations may not support all these
1998 features; GCC does not support warning about features that go beyond a
1999 particular library's limitations. However, if @option{-pedantic} is used
2000 with @option{-Wformat}, warnings will be given about format features not
2001 in the selected standard version (but not for @code{strfmon} formats,
2002 since those are not in any version of the C standard). @xref{C Dialect
2003 Options,,Options Controlling C Dialect}.
2005 Since @option{-Wformat} also checks for null format arguments for
2006 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2008 @option{-Wformat} is included in @option{-Wall}. For more control over some
2009 aspects of format checking, the options @option{-Wno-format-y2k},
2010 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2011 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2012 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2014 @item -Wno-format-y2k
2015 @opindex Wno-format-y2k
2016 If @option{-Wformat} is specified, do not warn about @code{strftime}
2017 formats which may yield only a two-digit year.
2019 @item -Wno-format-extra-args
2020 @opindex Wno-format-extra-args
2021 If @option{-Wformat} is specified, do not warn about excess arguments to a
2022 @code{printf} or @code{scanf} format function. The C standard specifies
2023 that such arguments are ignored.
2025 Where the unused arguments lie between used arguments that are
2026 specified with @samp{$} operand number specifications, normally
2027 warnings are still given, since the implementation could not know what
2028 type to pass to @code{va_arg} to skip the unused arguments. However,
2029 in the case of @code{scanf} formats, this option will suppress the
2030 warning if the unused arguments are all pointers, since the Single
2031 Unix Specification says that such unused arguments are allowed.
2033 @item -Wno-format-zero-length
2034 @opindex Wno-format-zero-length
2035 If @option{-Wformat} is specified, do not warn about zero-length formats.
2036 The C standard specifies that zero-length formats are allowed.
2038 @item -Wformat-nonliteral
2039 @opindex Wformat-nonliteral
2040 If @option{-Wformat} is specified, also warn if the format string is not a
2041 string literal and so cannot be checked, unless the format function
2042 takes its format arguments as a @code{va_list}.
2044 @item -Wformat-security
2045 @opindex Wformat-security
2046 If @option{-Wformat} is specified, also warn about uses of format
2047 functions that represent possible security problems. At present, this
2048 warns about calls to @code{printf} and @code{scanf} functions where the
2049 format string is not a string literal and there are no format arguments,
2050 as in @code{printf (foo);}. This may be a security hole if the format
2051 string came from untrusted input and contains @samp{%n}. (This is
2052 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2053 in future warnings may be added to @option{-Wformat-security} that are not
2054 included in @option{-Wformat-nonliteral}.)
2058 Enable @option{-Wformat} plus format checks not included in
2059 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2060 -Wformat-nonliteral -Wformat-security}.
2064 Enable warning about passing a null pointer for arguments marked as
2065 requiring a non-null value by the @code{nonnull} function attribute.
2067 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2068 can be disabled with the @option{-Wno-nonnull} option.
2070 @item -Wimplicit-int
2071 @opindex Wimplicit-int
2072 Warn when a declaration does not specify a type.
2074 @item -Wimplicit-function-declaration
2075 @itemx -Werror-implicit-function-declaration
2076 @opindex Wimplicit-function-declaration
2077 @opindex Werror-implicit-function-declaration
2078 Give a warning (or error) whenever a function is used before being
2083 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2087 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2088 function with external linkage, returning int, taking either zero
2089 arguments, two, or three arguments of appropriate types.
2091 @item -Wmissing-braces
2092 @opindex Wmissing-braces
2093 Warn if an aggregate or union initializer is not fully bracketed. In
2094 the following example, the initializer for @samp{a} is not fully
2095 bracketed, but that for @samp{b} is fully bracketed.
2098 int a[2][2] = @{ 0, 1, 2, 3 @};
2099 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2103 @opindex Wparentheses
2104 Warn if parentheses are omitted in certain contexts, such
2105 as when there is an assignment in a context where a truth value
2106 is expected, or when operators are nested whose precedence people
2107 often get confused about.
2109 Also warn about constructions where there may be confusion to which
2110 @code{if} statement an @code{else} branch belongs. Here is an example of
2125 In C, every @code{else} branch belongs to the innermost possible @code{if}
2126 statement, which in this example is @code{if (b)}. This is often not
2127 what the programmer expected, as illustrated in the above example by
2128 indentation the programmer chose. When there is the potential for this
2129 confusion, GCC will issue a warning when this flag is specified.
2130 To eliminate the warning, add explicit braces around the innermost
2131 @code{if} statement so there is no way the @code{else} could belong to
2132 the enclosing @code{if}. The resulting code would look like this:
2148 @item -Wsequence-point
2149 @opindex Wsequence-point
2150 Warn about code that may have undefined semantics because of violations
2151 of sequence point rules in the C standard.
2153 The C standard defines the order in which expressions in a C program are
2154 evaluated in terms of @dfn{sequence points}, which represent a partial
2155 ordering between the execution of parts of the program: those executed
2156 before the sequence point, and those executed after it. These occur
2157 after the evaluation of a full expression (one which is not part of a
2158 larger expression), after the evaluation of the first operand of a
2159 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2160 function is called (but after the evaluation of its arguments and the
2161 expression denoting the called function), and in certain other places.
2162 Other than as expressed by the sequence point rules, the order of
2163 evaluation of subexpressions of an expression is not specified. All
2164 these rules describe only a partial order rather than a total order,
2165 since, for example, if two functions are called within one expression
2166 with no sequence point between them, the order in which the functions
2167 are called is not specified. However, the standards committee have
2168 ruled that function calls do not overlap.
2170 It is not specified when between sequence points modifications to the
2171 values of objects take effect. Programs whose behavior depends on this
2172 have undefined behavior; the C standard specifies that ``Between the
2173 previous and next sequence point an object shall have its stored value
2174 modified at most once by the evaluation of an expression. Furthermore,
2175 the prior value shall be read only to determine the value to be
2176 stored.''. If a program breaks these rules, the results on any
2177 particular implementation are entirely unpredictable.
2179 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2180 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2181 diagnosed by this option, and it may give an occasional false positive
2182 result, but in general it has been found fairly effective at detecting
2183 this sort of problem in programs.
2185 The present implementation of this option only works for C programs. A
2186 future implementation may also work for C++ programs.
2188 The C standard is worded confusingly, therefore there is some debate
2189 over the precise meaning of the sequence point rules in subtle cases.
2190 Links to discussions of the problem, including proposed formal
2191 definitions, may be found on our readings page, at
2192 @w{@uref{http://gcc.gnu.org/readings.html}}.
2195 @opindex Wreturn-type
2196 Warn whenever a function is defined with a return-type that defaults to
2197 @code{int}. Also warn about any @code{return} statement with no
2198 return-value in a function whose return-type is not @code{void}.
2200 For C++, a function without return type always produces a diagnostic
2201 message, even when @option{-Wno-return-type} is specified. The only
2202 exceptions are @samp{main} and functions defined in system headers.
2206 Warn whenever a @code{switch} statement has an index of enumeral type
2207 and lacks a @code{case} for one or more of the named codes of that
2208 enumeration. (The presence of a @code{default} label prevents this
2209 warning.) @code{case} labels outside the enumeration range also
2210 provoke warnings when this option is used.
2212 @item -Wswitch-default
2213 @opindex Wswitch-switch
2214 Warn whenever a @code{switch} statement does not have a @code{default}
2218 @opindex Wswitch-enum
2219 Warn whenever a @code{switch} statement has an index of enumeral type
2220 and lacks a @code{case} for one or more of the named codes of that
2221 enumeration. @code{case} labels outside the enumeration range also
2222 provoke warnings when this option is used.
2226 Warn if any trigraphs are encountered that might change the meaning of
2227 the program (trigraphs within comments are not warned about).
2229 @item -Wunused-function
2230 @opindex Wunused-function
2231 Warn whenever a static function is declared but not defined or a
2232 non\-inline static function is unused.
2234 @item -Wunused-label
2235 @opindex Wunused-label
2236 Warn whenever a label is declared but not used.
2238 To suppress this warning use the @samp{unused} attribute
2239 (@pxref{Variable Attributes}).
2241 @item -Wunused-parameter
2242 @opindex Wunused-parameter
2243 Warn whenever a function parameter is unused aside from its declaration.
2245 To suppress this warning use the @samp{unused} attribute
2246 (@pxref{Variable Attributes}).
2248 @item -Wunused-variable
2249 @opindex Wunused-variable
2250 Warn whenever a local variable or non-constant static variable is unused
2251 aside from its declaration
2253 To suppress this warning use the @samp{unused} attribute
2254 (@pxref{Variable Attributes}).
2256 @item -Wunused-value
2257 @opindex Wunused-value
2258 Warn whenever a statement computes a result that is explicitly not used.
2260 To suppress this warning cast the expression to @samp{void}.
2264 All the above @option{-Wunused} options combined.
2266 In order to get a warning about an unused function parameter, you must
2267 either specify @samp{-W -Wunused} or separately specify
2268 @option{-Wunused-parameter}.
2270 @item -Wuninitialized
2271 @opindex Wuninitialized
2272 Warn if an automatic variable is used without first being initialized or
2273 if a variable may be clobbered by a @code{setjmp} call.
2275 These warnings are possible only in optimizing compilation,
2276 because they require data flow information that is computed only
2277 when optimizing. If you don't specify @option{-O}, you simply won't
2280 These warnings occur only for variables that are candidates for
2281 register allocation. Therefore, they do not occur for a variable that
2282 is declared @code{volatile}, or whose address is taken, or whose size
2283 is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
2284 structures, unions or arrays, even when they are in registers.
2286 Note that there may be no warning about a variable that is used only
2287 to compute a value that itself is never used, because such
2288 computations may be deleted by data flow analysis before the warnings
2291 These warnings are made optional because GCC is not smart
2292 enough to see all the reasons why the code might be correct
2293 despite appearing to have an error. Here is one example of how
2314 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2315 always initialized, but GCC doesn't know this. Here is
2316 another common case:
2321 if (change_y) save_y = y, y = new_y;
2323 if (change_y) y = save_y;
2328 This has no bug because @code{save_y} is used only if it is set.
2330 @cindex @code{longjmp} warnings
2331 This option also warns when a non-volatile automatic variable might be
2332 changed by a call to @code{longjmp}. These warnings as well are possible
2333 only in optimizing compilation.
2335 The compiler sees only the calls to @code{setjmp}. It cannot know
2336 where @code{longjmp} will be called; in fact, a signal handler could
2337 call it at any point in the code. As a result, you may get a warning
2338 even when there is in fact no problem because @code{longjmp} cannot
2339 in fact be called at the place which would cause a problem.
2341 Some spurious warnings can be avoided if you declare all the functions
2342 you use that never return as @code{noreturn}. @xref{Function
2345 @item -Wunknown-pragmas
2346 @opindex Wunknown-pragmas
2347 @cindex warning for unknown pragmas
2348 @cindex unknown pragmas, warning
2349 @cindex pragmas, warning of unknown
2350 Warn when a #pragma directive is encountered which is not understood by
2351 GCC@. If this command line option is used, warnings will even be issued
2352 for unknown pragmas in system header files. This is not the case if
2353 the warnings were only enabled by the @option{-Wall} command line option.
2355 @item -Wstrict-aliasing
2356 @opindex Wstrict-aliasing
2357 This option is only active when @option{-fstrict-aliasing} is active.
2358 It warns about code which might break the strict aliasing rules that the
2359 compiler is using for optimization. The warning does not catch all
2360 cases, but does attempt to catch the more common pitfalls. It is
2361 included in @option{-Wall}.
2365 All of the above @samp{-W} options combined. This enables all the
2366 warnings about constructions that some users consider questionable, and
2367 that are easy to avoid (or modify to prevent the warning), even in
2368 conjunction with macros. This also enables some language-specific
2369 warnings described in @ref{C++ Dialect Options} and
2370 @ref{Objective-C Dialect Options}.
2373 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2374 Some of them warn about constructions that users generally do not
2375 consider questionable, but which occasionally you might wish to check
2376 for; others warn about constructions that are necessary or hard to avoid
2377 in some cases, and there is no simple way to modify the code to suppress
2383 Print extra warning messages for these events:
2387 A function can return either with or without a value. (Falling
2388 off the end of the function body is considered returning without
2389 a value.) For example, this function would evoke such a
2403 An expression-statement or the left-hand side of a comma expression
2404 contains no side effects.
2405 To suppress the warning, cast the unused expression to void.
2406 For example, an expression such as @samp{x[i,j]} will cause a warning,
2407 but @samp{x[(void)i,j]} will not.
2410 An unsigned value is compared against zero with @samp{<} or @samp{<=}.
2413 A comparison like @samp{x<=y<=z} appears; this is equivalent to
2414 @samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from
2415 that of ordinary mathematical notation.
2418 Storage-class specifiers like @code{static} are not the first things in
2419 a declaration. According to the C Standard, this usage is obsolescent.
2422 The return type of a function has a type qualifier such as @code{const}.
2423 Such a type qualifier has no effect, since the value returned by a
2424 function is not an lvalue. (But don't warn about the GNU extension of
2425 @code{volatile void} return types. That extension will be warned about
2426 if @option{-pedantic} is specified.)
2429 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2433 A comparison between signed and unsigned values could produce an
2434 incorrect result when the signed value is converted to unsigned.
2435 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2438 An aggregate has a partly bracketed initializer.
2439 For example, the following code would evoke such a warning,
2440 because braces are missing around the initializer for @code{x.h}:
2443 struct s @{ int f, g; @};
2444 struct t @{ struct s h; int i; @};
2445 struct t x = @{ 1, 2, 3 @};
2449 An aggregate has an initializer which does not initialize all members.
2450 For example, the following code would cause such a warning, because
2451 @code{x.h} would be implicitly initialized to zero:
2454 struct s @{ int f, g, h; @};
2455 struct s x = @{ 3, 4 @};
2459 @item -Wno-div-by-zero
2460 @opindex Wno-div-by-zero
2461 @opindex Wdiv-by-zero
2462 Do not warn about compile-time integer division by zero. Floating point
2463 division by zero is not warned about, as it can be a legitimate way of
2464 obtaining infinities and NaNs.
2466 @item -Wsystem-headers
2467 @opindex Wsystem-headers
2468 @cindex warnings from system headers
2469 @cindex system headers, warnings from
2470 Print warning messages for constructs found in system header files.
2471 Warnings from system headers are normally suppressed, on the assumption
2472 that they usually do not indicate real problems and would only make the
2473 compiler output harder to read. Using this command line option tells
2474 GCC to emit warnings from system headers as if they occurred in user
2475 code. However, note that using @option{-Wall} in conjunction with this
2476 option will @emph{not} warn about unknown pragmas in system
2477 headers---for that, @option{-Wunknown-pragmas} must also be used.
2480 @opindex Wfloat-equal
2481 Warn if floating point values are used in equality comparisons.
2483 The idea behind this is that sometimes it is convenient (for the
2484 programmer) to consider floating-point values as approximations to
2485 infinitely precise real numbers. If you are doing this, then you need
2486 to compute (by analysing the code, or in some other way) the maximum or
2487 likely maximum error that the computation introduces, and allow for it
2488 when performing comparisons (and when producing output, but that's a
2489 different problem). In particular, instead of testing for equality, you
2490 would check to see whether the two values have ranges that overlap; and
2491 this is done with the relational operators, so equality comparisons are
2494 @item -Wtraditional @r{(C only)}
2495 @opindex Wtraditional
2496 Warn about certain constructs that behave differently in traditional and
2497 ISO C@. Also warn about ISO C constructs that have no traditional C
2498 equivalent, and/or problematic constructs which should be avoided.
2502 Macro parameters that appear within string literals in the macro body.
2503 In traditional C macro replacement takes place within string literals,
2504 but does not in ISO C@.
2507 In traditional C, some preprocessor directives did not exist.
2508 Traditional preprocessors would only consider a line to be a directive
2509 if the @samp{#} appeared in column 1 on the line. Therefore
2510 @option{-Wtraditional} warns about directives that traditional C
2511 understands but would ignore because the @samp{#} does not appear as the
2512 first character on the line. It also suggests you hide directives like
2513 @samp{#pragma} not understood by traditional C by indenting them. Some
2514 traditional implementations would not recognize @samp{#elif}, so it
2515 suggests avoiding it altogether.
2518 A function-like macro that appears without arguments.
2521 The unary plus operator.
2524 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2525 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2526 constants.) Note, these suffixes appear in macros defined in the system
2527 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2528 Use of these macros in user code might normally lead to spurious
2529 warnings, however gcc's integrated preprocessor has enough context to
2530 avoid warning in these cases.
2533 A function declared external in one block and then used after the end of
2537 A @code{switch} statement has an operand of type @code{long}.
2540 A non-@code{static} function declaration follows a @code{static} one.
2541 This construct is not accepted by some traditional C compilers.
2544 The ISO type of an integer constant has a different width or
2545 signedness from its traditional type. This warning is only issued if
2546 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2547 typically represent bit patterns, are not warned about.
2550 Usage of ISO string concatenation is detected.
2553 Initialization of automatic aggregates.
2556 Identifier conflicts with labels. Traditional C lacks a separate
2557 namespace for labels.
2560 Initialization of unions. If the initializer is zero, the warning is
2561 omitted. This is done under the assumption that the zero initializer in
2562 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2563 initializer warnings and relies on default initialization to zero in the
2567 Conversions by prototypes between fixed/floating point values and vice
2568 versa. The absence of these prototypes when compiling with traditional
2569 C would cause serious problems. This is a subset of the possible
2570 conversion warnings, for the full set use @option{-Wconversion}.
2573 Use of ISO C style function definitions. This warning intentionally is
2574 @emph{not} issued for prototype declarations or variadic functions
2575 because these ISO C features will appear in your code when using
2576 libiberty's traditional C compatibility macros, @code{PARAMS} and
2577 @code{VPARAMS}. This warning is also bypassed for nested functions
2578 because that feature is already a gcc extension and thus not relevant to
2579 traditional C compatibility.
2584 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
2586 @item -Wendif-labels
2587 @opindex Wendif-labels
2588 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
2592 Warn whenever a local variable shadows another local variable, parameter or
2593 global variable or whenever a built-in function is shadowed.
2595 @item -Wlarger-than-@var{len}
2596 @opindex Wlarger-than
2597 Warn whenever an object of larger than @var{len} bytes is defined.
2599 @item -Wpointer-arith
2600 @opindex Wpointer-arith
2601 Warn about anything that depends on the ``size of'' a function type or
2602 of @code{void}. GNU C assigns these types a size of 1, for
2603 convenience in calculations with @code{void *} pointers and pointers
2606 @item -Wbad-function-cast @r{(C only)}
2607 @opindex Wbad-function-cast
2608 Warn whenever a function call is cast to a non-matching type.
2609 For example, warn if @code{int malloc()} is cast to @code{anything *}.
2613 Warn whenever a pointer is cast so as to remove a type qualifier from
2614 the target type. For example, warn if a @code{const char *} is cast
2615 to an ordinary @code{char *}.
2618 @opindex Wcast-align
2619 Warn whenever a pointer is cast such that the required alignment of the
2620 target is increased. For example, warn if a @code{char *} is cast to
2621 an @code{int *} on machines where integers can only be accessed at
2622 two- or four-byte boundaries.
2624 @item -Wwrite-strings
2625 @opindex Wwrite-strings
2626 When compiling C, give string constants the type @code{const
2627 char[@var{length}]} so that
2628 copying the address of one into a non-@code{const} @code{char *}
2629 pointer will get a warning; when compiling C++, warn about the
2630 deprecated conversion from string constants to @code{char *}.
2631 These warnings will help you find at
2632 compile time code that can try to write into a string constant, but
2633 only if you have been very careful about using @code{const} in
2634 declarations and prototypes. Otherwise, it will just be a nuisance;
2635 this is why we did not make @option{-Wall} request these warnings.
2638 @opindex Wconversion
2639 Warn if a prototype causes a type conversion that is different from what
2640 would happen to the same argument in the absence of a prototype. This
2641 includes conversions of fixed point to floating and vice versa, and
2642 conversions changing the width or signedness of a fixed point argument
2643 except when the same as the default promotion.
2645 Also, warn if a negative integer constant expression is implicitly
2646 converted to an unsigned type. For example, warn about the assignment
2647 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
2648 casts like @code{(unsigned) -1}.
2650 @item -Wsign-compare
2651 @opindex Wsign-compare
2652 @cindex warning for comparison of signed and unsigned values
2653 @cindex comparison of signed and unsigned values, warning
2654 @cindex signed and unsigned values, comparison warning
2655 Warn when a comparison between signed and unsigned values could produce
2656 an incorrect result when the signed value is converted to unsigned.
2657 This warning is also enabled by @option{-W}; to get the other warnings
2658 of @option{-W} without this warning, use @samp{-W -Wno-sign-compare}.
2660 @item -Waggregate-return
2661 @opindex Waggregate-return
2662 Warn if any functions that return structures or unions are defined or
2663 called. (In languages where you can return an array, this also elicits
2666 @item -Wstrict-prototypes @r{(C only)}
2667 @opindex Wstrict-prototypes
2668 Warn if a function is declared or defined without specifying the
2669 argument types. (An old-style function definition is permitted without
2670 a warning if preceded by a declaration which specifies the argument
2673 @item -Wmissing-prototypes @r{(C only)}
2674 @opindex Wmissing-prototypes
2675 Warn if a global function is defined without a previous prototype
2676 declaration. This warning is issued even if the definition itself
2677 provides a prototype. The aim is to detect global functions that fail
2678 to be declared in header files.
2680 @item -Wmissing-declarations
2681 @opindex Wmissing-declarations
2682 Warn if a global function is defined without a previous declaration.
2683 Do so even if the definition itself provides a prototype.
2684 Use this option to detect global functions that are not declared in
2687 @item -Wmissing-noreturn
2688 @opindex Wmissing-noreturn
2689 Warn about functions which might be candidates for attribute @code{noreturn}.
2690 Note these are only possible candidates, not absolute ones. Care should
2691 be taken to manually verify functions actually do not ever return before
2692 adding the @code{noreturn} attribute, otherwise subtle code generation
2693 bugs could be introduced. You will not get a warning for @code{main} in
2694 hosted C environments.
2696 @item -Wmissing-format-attribute
2697 @opindex Wmissing-format-attribute
2699 If @option{-Wformat} is enabled, also warn about functions which might be
2700 candidates for @code{format} attributes. Note these are only possible
2701 candidates, not absolute ones. GCC will guess that @code{format}
2702 attributes might be appropriate for any function that calls a function
2703 like @code{vprintf} or @code{vscanf}, but this might not always be the
2704 case, and some functions for which @code{format} attributes are
2705 appropriate may not be detected. This option has no effect unless
2706 @option{-Wformat} is enabled (possibly by @option{-Wall}).
2708 @item -Wno-multichar
2709 @opindex Wno-multichar
2711 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
2712 Usually they indicate a typo in the user's code, as they have
2713 implementation-defined values, and should not be used in portable code.
2715 @item -Wno-deprecated-declarations
2716 @opindex Wno-deprecated-declarations
2717 Do not warn about uses of functions, variables, and types marked as
2718 deprecated by using the @code{deprecated} attribute.
2719 (@pxref{Function Attributes}, @pxref{Variable Attributes},
2720 @pxref{Type Attributes}.)
2724 Warn if a structure is given the packed attribute, but the packed
2725 attribute has no effect on the layout or size of the structure.
2726 Such structures may be mis-aligned for little benefit. For
2727 instance, in this code, the variable @code{f.x} in @code{struct bar}
2728 will be misaligned even though @code{struct bar} does not itself
2729 have the packed attribute:
2736 @} __attribute__((packed));
2746 Warn if padding is included in a structure, either to align an element
2747 of the structure or to align the whole structure. Sometimes when this
2748 happens it is possible to rearrange the fields of the structure to
2749 reduce the padding and so make the structure smaller.
2751 @item -Wredundant-decls
2752 @opindex Wredundant-decls
2753 Warn if anything is declared more than once in the same scope, even in
2754 cases where multiple declaration is valid and changes nothing.
2756 @item -Wnested-externs @r{(C only)}
2757 @opindex Wnested-externs
2758 Warn if an @code{extern} declaration is encountered within a function.
2760 @item -Wunreachable-code
2761 @opindex Wunreachable-code
2762 Warn if the compiler detects that code will never be executed.
2764 This option is intended to warn when the compiler detects that at
2765 least a whole line of source code will never be executed, because
2766 some condition is never satisfied or because it is after a
2767 procedure that never returns.
2769 It is possible for this option to produce a warning even though there
2770 are circumstances under which part of the affected line can be executed,
2771 so care should be taken when removing apparently-unreachable code.
2773 For instance, when a function is inlined, a warning may mean that the
2774 line is unreachable in only one inlined copy of the function.
2776 This option is not made part of @option{-Wall} because in a debugging
2777 version of a program there is often substantial code which checks
2778 correct functioning of the program and is, hopefully, unreachable
2779 because the program does work. Another common use of unreachable
2780 code is to provide behavior which is selectable at compile-time.
2784 Warn if a function can not be inlined and it was declared as inline.
2788 @opindex Wno-long-long
2789 Warn if @samp{long long} type is used. This is default. To inhibit
2790 the warning messages, use @option{-Wno-long-long}. Flags
2791 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
2792 only when @option{-pedantic} flag is used.
2794 @item -Wdisabled-optimization
2795 @opindex Wdisabled-optimization
2796 Warn if a requested optimization pass is disabled. This warning does
2797 not generally indicate that there is anything wrong with your code; it
2798 merely indicates that GCC's optimizers were unable to handle the code
2799 effectively. Often, the problem is that your code is too big or too
2800 complex; GCC will refuse to optimize programs when the optimization
2801 itself is likely to take inordinate amounts of time.
2805 Make all warnings into errors.
2808 @node Debugging Options
2809 @section Options for Debugging Your Program or GCC
2810 @cindex options, debugging
2811 @cindex debugging information options
2813 GCC has various special options that are used for debugging
2814 either your program or GCC:
2819 Produce debugging information in the operating system's native format
2820 (stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging
2823 On most systems that use stabs format, @option{-g} enables use of extra
2824 debugging information that only GDB can use; this extra information
2825 makes debugging work better in GDB but will probably make other debuggers
2827 refuse to read the program. If you want to control for certain whether
2828 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
2829 @option{-gxcoff+}, @option{-gxcoff}, @option{-gdwarf-1+}, @option{-gdwarf-1},
2830 or @option{-gvms} (see below).
2832 Unlike most other C compilers, GCC allows you to use @option{-g} with
2833 @option{-O}. The shortcuts taken by optimized code may occasionally
2834 produce surprising results: some variables you declared may not exist
2835 at all; flow of control may briefly move where you did not expect it;
2836 some statements may not be executed because they compute constant
2837 results or their values were already at hand; some statements may
2838 execute in different places because they were moved out of loops.
2840 Nevertheless it proves possible to debug optimized output. This makes
2841 it reasonable to use the optimizer for programs that might have bugs.
2843 The following options are useful when GCC is generated with the
2844 capability for more than one debugging format.
2848 Produce debugging information for use by GDB@. This means to use the
2849 most expressive format available (DWARF 2, stabs, or the native format
2850 if neither of those are supported), including GDB extensions if at all
2855 Produce debugging information in stabs format (if that is supported),
2856 without GDB extensions. This is the format used by DBX on most BSD
2857 systems. On MIPS, Alpha and System V Release 4 systems this option
2858 produces stabs debugging output which is not understood by DBX or SDB@.
2859 On System V Release 4 systems this option requires the GNU assembler.
2863 Produce debugging information in stabs format (if that is supported),
2864 using GNU extensions understood only by the GNU debugger (GDB)@. The
2865 use of these extensions is likely to make other debuggers crash or
2866 refuse to read the program.
2870 Produce debugging information in COFF format (if that is supported).
2871 This is the format used by SDB on most System V systems prior to
2876 Produce debugging information in XCOFF format (if that is supported).
2877 This is the format used by the DBX debugger on IBM RS/6000 systems.
2881 Produce debugging information in XCOFF format (if that is supported),
2882 using GNU extensions understood only by the GNU debugger (GDB)@. The
2883 use of these extensions is likely to make other debuggers crash or
2884 refuse to read the program, and may cause assemblers other than the GNU
2885 assembler (GAS) to fail with an error.
2889 Produce debugging information in DWARF version 1 format (if that is
2890 supported). This is the format used by SDB on most System V Release 4
2893 This option is deprecated.
2897 Produce debugging information in DWARF version 1 format (if that is
2898 supported), using GNU extensions understood only by the GNU debugger
2899 (GDB)@. The use of these extensions is likely to make other debuggers
2900 crash or refuse to read the program.
2902 This option is deprecated.
2906 Produce debugging information in DWARF version 2 format (if that is
2907 supported). This is the format used by DBX on IRIX 6.
2911 Produce debugging information in VMS debug format (if that is
2912 supported). This is the format used by DEBUG on VMS systems.
2915 @itemx -ggdb@var{level}
2916 @itemx -gstabs@var{level}
2917 @itemx -gcoff@var{level}
2918 @itemx -gxcoff@var{level}
2919 @itemx -gvms@var{level}
2920 Request debugging information and also use @var{level} to specify how
2921 much information. The default level is 2.
2923 Level 1 produces minimal information, enough for making backtraces in
2924 parts of the program that you don't plan to debug. This includes
2925 descriptions of functions and external variables, but no information
2926 about local variables and no line numbers.
2928 Level 3 includes extra information, such as all the macro definitions
2929 present in the program. Some debuggers support macro expansion when
2930 you use @option{-g3}.
2932 Note that in order to avoid confusion between DWARF1 debug level 2,
2933 and DWARF2, neither @option{-gdwarf} nor @option{-gdwarf-2} accept
2934 a concatenated debug level. Instead use an additional @option{-g@var{level}}
2935 option to change the debug level for DWARF1 or DWARF2.
2937 @item -feliminate-dwarf2-dups
2938 @opindex feliminate-dwarf2-dups
2939 Compress DWARF2 debugging information by eliminating duplicated
2940 information about each symbol. This option only makes sense when
2941 generating DWARF2 debugging information with @option{-gdwarf-2}.
2946 Generate extra code to write profile information suitable for the
2947 analysis program @code{prof}. You must use this option when compiling
2948 the source files you want data about, and you must also use it when
2951 @cindex @code{gprof}
2954 Generate extra code to write profile information suitable for the
2955 analysis program @code{gprof}. You must use this option when compiling
2956 the source files you want data about, and you must also use it when
2961 Makes the compiler print out each function name as it is compiled, and
2962 print some statistics about each pass when it finishes.
2965 @opindex ftime-report
2966 Makes the compiler print some statistics about the time consumed by each
2967 pass when it finishes.
2970 @opindex fmem-report
2971 Makes the compiler print some statistics about permanent memory
2972 allocation when it finishes.
2974 @item -fprofile-arcs
2975 @opindex fprofile-arcs
2976 Instrument @dfn{arcs} during compilation to generate coverage data or
2977 for profile-directed block ordering. During execution the program
2978 records how many times each branch is executed and how many times it is
2979 taken. When the compiled program exits it saves this data to a file
2980 called @file{@var{auxname}.da} for each source file. @var{auxname} is
2981 generated from the name of the output file, if explicitly specified and
2982 it is not the final executable, otherwise it is the basename of the
2983 source file. In both cases any suffix is removed (e.g. @file{foo.da}
2984 for input file @file{dir/foo.c}, or @file{dir/foo.da} for output file
2985 specified as @option{-o dir/foo.o}).
2987 For profile-directed block ordering, compile the program with
2988 @option{-fprofile-arcs} plus optimization and code generation options,
2989 generate the arc profile information by running the program on a
2990 selected workload, and then compile the program again with the same
2991 optimization and code generation options plus
2992 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
2993 Control Optimization}).
2995 The other use of @option{-fprofile-arcs} is for use with @code{gcov},
2996 when it is used with the @option{-ftest-coverage} option.
2998 With @option{-fprofile-arcs}, for each function of your program GCC
2999 creates a program flow graph, then finds a spanning tree for the graph.
3000 Only arcs that are not on the spanning tree have to be instrumented: the
3001 compiler adds code to count the number of times that these arcs are
3002 executed. When an arc is the only exit or only entrance to a block, the
3003 instrumentation code can be added to the block; otherwise, a new basic
3004 block must be created to hold the instrumentation code.
3007 @item -ftest-coverage
3008 @opindex ftest-coverage
3009 Create data files for the @code{gcov} code-coverage utility
3010 (@pxref{Gcov,, @code{gcov}: a GCC Test Coverage Program}). See
3011 @option{-fprofile-arcs} option above for a description of @var{auxname}.
3014 @item @var{auxname}.bb
3015 A mapping from basic blocks to line numbers, which @code{gcov} uses to
3016 associate basic block execution counts with line numbers.
3018 @item @var{auxname}.bbg
3019 A list of all arcs in the program flow graph. This allows @code{gcov}
3020 to reconstruct the program flow graph, so that it can compute all basic
3021 block and arc execution counts from the information in the
3022 @file{@var{auxname}.da} file.
3025 Use @option{-ftest-coverage} with @option{-fprofile-arcs}; the latter
3026 option adds instrumentation to the program, which then writes
3027 execution counts to another data file:
3030 @item @var{auxname}.da
3031 Runtime arc execution counts, used in conjunction with the arc
3032 information in the file @file{@var{auxname}.bbg}.
3035 Coverage data will map better to the source files if
3036 @option{-ftest-coverage} is used without optimization.
3038 @item -d@var{letters}
3040 Says to make debugging dumps during compilation at times specified by
3041 @var{letters}. This is used for debugging the compiler. The file names
3042 for most of the dumps are made by appending a pass number and a word to
3043 the @var{dumpname}. @var{dumpname} is generated from the name of the
3044 output file, if explicitly specified and it is not an executable,
3045 otherwise it is the basename of the source file. In both cases any
3046 suffix is removed (e.g. @file{foo.00.rtl} or @file{foo.01.sibling}).
3047 Here are the possible letters for use in @var{letters}, and their
3053 Annotate the assembler output with miscellaneous debugging information.
3056 Dump after computing branch probabilities, to @file{@var{file}.15.bp}.
3059 Dump after block reordering, to @file{@var{file}.30.bbro}.
3062 Dump after instruction combination, to the file @file{@var{file}.17.combine}.
3065 Dump after the first if conversion, to the file @file{@var{file}.18.ce}.
3068 Dump after delayed branch scheduling, to @file{@var{file}.32.dbr}.
3071 Dump all macro definitions, at the end of preprocessing, in addition to
3075 Dump after SSA optimizations, to @file{@var{file}.04.ssa} and
3076 @file{@var{file}.07.ussa}.
3079 Dump after the second if conversion, to @file{@var{file}.27.ce2}.
3082 Dump after life analysis, to @file{@var{file}.16.life}.
3085 Dump after purging @code{ADDRESSOF} codes, to @file{@var{file}.10.addressof}.
3088 Dump after global register allocation, to @file{@var{file}.22.greg}.
3091 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
3094 Dump after reg-to-stack conversion, to @file{@var{file}.29.stack}.
3097 Dump after post-reload optimizations, to @file{@var{file}.23.postreload}.
3100 Dump after GCSE, to @file{@var{file}.11.gcse}.
3103 Dump after sibling call optimizations, to @file{@var{file}.01.sibling}.
3106 Dump after the first jump optimization, to @file{@var{file}.03.jump}.
3109 Dump after conversion from registers to stack, to @file{@var{file}.33.stack}.
3112 Dump after local register allocation, to @file{@var{file}.21.lreg}.
3115 Dump after loop optimization, to @file{@var{file}.12.loop}.
3118 Dump after performing the machine dependent reorganisation pass, to
3119 @file{@var{file}.31.mach}.
3122 Dump after register renumbering, to @file{@var{file}.26.rnreg}.
3125 Dump after the register move pass, to @file{@var{file}.19.regmove}.
3128 Dump after RTL generation, to @file{@var{file}.00.rtl}.
3131 Dump after the second scheduling pass, to @file{@var{file}.28.sched2}.
3134 Dump after CSE (including the jump optimization that sometimes follows
3135 CSE), to @file{@var{file}.09.cse}.
3138 Dump after the first scheduling pass, to @file{@var{file}.20.sched}.
3141 Dump after the second CSE pass (including the jump optimization that
3142 sometimes follows CSE), to @file{@var{file}.13.cse2}.
3145 Dump after null pointer ellimination pass ti @file{@var{file}.08.null}.
3148 Dump after the second flow pass, to @file{@var{file}.24.flow2}.
3151 Dump after SSA dead code elimination, to @file{@var{file}.06.ssadce}.
3154 Dump after the peephole pass, to @file{@var{file}.25.peephole2}.
3157 Produce all the dumps listed above.
3160 Print statistics on memory usage, at the end of the run, to
3164 Annotate the assembler output with a comment indicating which
3165 pattern and alternative was used. The length of each instruction is
3169 Dump the RTL in the assembler output as a comment before each instruction.
3170 Also turns on @option{-dp} annotation.
3173 For each of the other indicated dump files (except for
3174 @file{@var{file}.00.rtl}), dump a representation of the control flow graph
3175 suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3178 Just generate RTL for a function instead of compiling it. Usually used
3182 Dump debugging information during parsing, to standard error.
3185 @item -fdump-unnumbered
3186 @opindex fdump-unnumbered
3187 When doing debugging dumps (see @option{-d} option above), suppress instruction
3188 numbers and line number note output. This makes it more feasible to
3189 use diff on debugging dumps for compiler invocations with different
3190 options, in particular with and without @option{-g}.
3192 @item -fdump-translation-unit @r{(C and C++ only)}
3193 @itemx -fdump-translation-unit-@var{options} @r{(C and C++ only)}
3194 @opindex fdump-translation-unit
3195 Dump a representation of the tree structure for the entire translation
3196 unit to a file. The file name is made by appending @file{.tu} to the
3197 source file name. If the @samp{-@var{options}} form is used, @var{options}
3198 controls the details of the dump as described for the
3199 @option{-fdump-tree} options.
3201 @item -fdump-class-hierarchy @r{(C++ only)}
3202 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3203 @opindex fdump-class-hierarchy
3204 Dump a representation of each class's hierarchy and virtual function
3205 table layout to a file. The file name is made by appending @file{.class}
3206 to the source file name. If the @samp{-@var{options}} form is used,
3207 @var{options} controls the details of the dump as described for the
3208 @option{-fdump-tree} options.
3210 @item -fdump-tree-@var{switch} @r{(C++ only)}
3211 @itemx -fdump-tree-@var{switch}-@var{options} @r{(C++ only)}
3213 Control the dumping at various stages of processing the intermediate
3214 language tree to a file. The file name is generated by appending a switch
3215 specific suffix to the source file name. If the @samp{-@var{options}}
3216 form is used, @var{options} is a list of @samp{-} separated options that
3217 control the details of the dump. Not all options are applicable to all
3218 dumps, those which are not meaningful will be ignored. The following
3219 options are available
3223 Print the address of each node. Usually this is not meaningful as it
3224 changes according to the environment and source file. Its primary use
3225 is for tying up a dump file with a debug environment.
3227 Inhibit dumping of members of a scope or body of a function merely
3228 because that scope has been reached. Only dump such items when they
3229 are directly reachable by some other path.
3231 Turn on all options.
3234 The following tree dumps are possible:
3237 Dump before any tree based optimization, to @file{@var{file}.original}.
3239 Dump after all tree based optimization, to @file{@var{file}.optimized}.
3241 Dump after function inlining, to @file{@var{file}.inlined}.
3244 @item -fsched-verbose=@var{n}
3245 @opindex fsched-verbose
3246 On targets that use instruction scheduling, this option controls the
3247 amount of debugging output the scheduler prints. This information is
3248 written to standard error, unless @option{-dS} or @option{-dR} is
3249 specified, in which case it is output to the usual dump
3250 listing file, @file{.sched} or @file{.sched2} respectively. However
3251 for @var{n} greater than nine, the output is always printed to standard
3254 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
3255 same information as @option{-dRS}. For @var{n} greater than one, it
3256 also output basic block probabilities, detailed ready list information
3257 and unit/insn info. For @var{n} greater than two, it includes RTL
3258 at abort point, control-flow and regions info. And for @var{n} over
3259 four, @option{-fsched-verbose} also includes dependence info.
3263 Store the usual ``temporary'' intermediate files permanently; place them
3264 in the current directory and name them based on the source file. Thus,
3265 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
3266 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
3267 preprocessed @file{foo.i} output file even though the compiler now
3268 normally uses an integrated preprocessor.
3272 Report the CPU time taken by each subprocess in the compilation
3273 sequence. For C source files, this is the compiler proper and assembler
3274 (plus the linker if linking is done). The output looks like this:
3281 The first number on each line is the ``user time,'' that is time spent
3282 executing the program itself. The second number is ``system time,''
3283 time spent executing operating system routines on behalf of the program.
3284 Both numbers are in seconds.
3286 @item -print-file-name=@var{library}
3287 @opindex print-file-name
3288 Print the full absolute name of the library file @var{library} that
3289 would be used when linking---and don't do anything else. With this
3290 option, GCC does not compile or link anything; it just prints the
3293 @item -print-multi-directory
3294 @opindex print-multi-directory
3295 Print the directory name corresponding to the multilib selected by any
3296 other switches present in the command line. This directory is supposed
3297 to exist in @env{GCC_EXEC_PREFIX}.
3299 @item -print-multi-lib
3300 @opindex print-multi-lib
3301 Print the mapping from multilib directory names to compiler switches
3302 that enable them. The directory name is separated from the switches by
3303 @samp{;}, and each switch starts with an @samp{@@} instead of the
3304 @samp{-}, without spaces between multiple switches. This is supposed to
3305 ease shell-processing.
3307 @item -print-prog-name=@var{program}
3308 @opindex print-prog-name
3309 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
3311 @item -print-libgcc-file-name
3312 @opindex print-libgcc-file-name
3313 Same as @option{-print-file-name=libgcc.a}.
3315 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
3316 but you do want to link with @file{libgcc.a}. You can do
3319 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
3322 @item -print-search-dirs
3323 @opindex print-search-dirs
3324 Print the name of the configured installation directory and a list of
3325 program and library directories gcc will search---and don't do anything else.
3327 This is useful when gcc prints the error message
3328 @samp{installation problem, cannot exec cpp0: No such file or directory}.
3329 To resolve this you either need to put @file{cpp0} and the other compiler
3330 components where gcc expects to find them, or you can set the environment
3331 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
3332 Don't forget the trailing '/'.
3333 @xref{Environment Variables}.
3336 @opindex dumpmachine
3337 Print the compiler's target machine (for example,
3338 @samp{i686-pc-linux-gnu})---and don't do anything else.
3341 @opindex dumpversion
3342 Print the compiler version (for example, @samp{3.0})---and don't do
3347 Print the compiler's built-in specs---and don't do anything else. (This
3348 is used when GCC itself is being built.) @xref{Spec Files}.
3351 @node Optimize Options
3352 @section Options That Control Optimization
3353 @cindex optimize options
3354 @cindex options, optimization
3356 These options control various sorts of optimizations:
3363 Optimize. Optimizing compilation takes somewhat more time, and a lot
3364 more memory for a large function.
3366 Without @option{-O}, the compiler's goal is to reduce the cost of
3367 compilation and to make debugging produce the expected results.
3368 Statements are independent: if you stop the program with a breakpoint
3369 between statements, you can then assign a new value to any variable or
3370 change the program counter to any other statement in the function and
3371 get exactly the results you would expect from the source code.
3373 With @option{-O}, the compiler tries to reduce code size and execution
3374 time, without performing any optimizations that take a great deal of
3379 Optimize even more. GCC performs nearly all supported optimizations
3380 that do not involve a space-speed tradeoff. The compiler does not
3381 perform loop unrolling or function inlining when you specify @option{-O2}.
3382 As compared to @option{-O}, this option increases both compilation time
3383 and the performance of the generated code.
3385 @option{-O2} turns on all optional optimizations except for loop
3386 unrolling, function inlining, and register renaming. It also turns on
3387 the @option{-fforce-mem} and @option{-fstrict-aliasing} option on all
3388 machines and frame pointer elimination on machines where doing so does
3389 not interfere with debugging.
3391 Please note the warning under @option{-fgcse} about
3392 invoking @option{-O2} on programs that use computed gotos.
3396 Optimize yet more. @option{-O3} turns on all optimizations specified by
3397 @option{-O2} and also turns on the @option{-finline-functions} and
3398 @option{-frename-registers} options.
3406 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
3407 do not typically increase code size. It also performs further
3408 optimizations designed to reduce code size.
3410 If you use multiple @option{-O} options, with or without level numbers,
3411 the last such option is the one that is effective.
3414 Options of the form @option{-f@var{flag}} specify machine-independent
3415 flags. Most flags have both positive and negative forms; the negative
3416 form of @option{-ffoo} would be @option{-fno-foo}. In the table below,
3417 only one of the forms is listed---the one which is not the default.
3418 You can figure out the other form by either removing @samp{no-} or
3423 @opindex ffloat-store
3424 Do not store floating point variables in registers, and inhibit other
3425 options that might change whether a floating point value is taken from a
3428 @cindex floating point precision
3429 This option prevents undesirable excess precision on machines such as
3430 the 68000 where the floating registers (of the 68881) keep more
3431 precision than a @code{double} is supposed to have. Similarly for the
3432 x86 architecture. For most programs, the excess precision does only
3433 good, but a few programs rely on the precise definition of IEEE floating
3434 point. Use @option{-ffloat-store} for such programs, after modifying
3435 them to store all pertinent intermediate computations into variables.
3437 @item -fno-default-inline
3438 @opindex fno-default-inline
3439 Do not make member functions inline by default merely because they are
3440 defined inside the class scope (C++ only). Otherwise, when you specify
3441 @w{@option{-O}}, member functions defined inside class scope are compiled
3442 inline by default; i.e., you don't need to add @samp{inline} in front of
3443 the member function name.
3445 @item -fno-defer-pop
3446 @opindex fno-defer-pop
3447 Always pop the arguments to each function call as soon as that function
3448 returns. For machines which must pop arguments after a function call,
3449 the compiler normally lets arguments accumulate on the stack for several
3450 function calls and pops them all at once.
3454 Force memory operands to be copied into registers before doing
3455 arithmetic on them. This produces better code by making all memory
3456 references potential common subexpressions. When they are not common
3457 subexpressions, instruction combination should eliminate the separate
3458 register-load. The @option{-O2} option turns on this option.
3461 @opindex fforce-addr
3462 Force memory address constants to be copied into registers before
3463 doing arithmetic on them. This may produce better code just as
3464 @option{-fforce-mem} may.
3466 @item -fomit-frame-pointer
3467 @opindex fomit-frame-pointer
3468 Don't keep the frame pointer in a register for functions that
3469 don't need one. This avoids the instructions to save, set up and
3470 restore frame pointers; it also makes an extra register available
3471 in many functions. @strong{It also makes debugging impossible on
3474 On some machines, such as the VAX, this flag has no effect, because
3475 the standard calling sequence automatically handles the frame pointer
3476 and nothing is saved by pretending it doesn't exist. The
3477 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
3478 whether a target machine supports this flag. @xref{Registers,,Register
3479 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
3481 @item -foptimize-sibling-calls
3482 @opindex foptimize-sibling-calls
3483 Optimize sibling and tail recursive calls.
3487 This option generates traps for signed overflow on addition, subtraction,
3488 multiplication operations.
3492 Don't pay attention to the @code{inline} keyword. Normally this option
3493 is used to keep the compiler from expanding any functions inline.
3494 Note that if you are not optimizing, no functions can be expanded inline.
3496 @item -finline-functions
3497 @opindex finline-functions
3498 Integrate all simple functions into their callers. The compiler
3499 heuristically decides which functions are simple enough to be worth
3500 integrating in this way.
3502 If all calls to a given function are integrated, and the function is
3503 declared @code{static}, then the function is normally not output as
3504 assembler code in its own right.
3506 @item -finline-limit=@var{n}
3507 @opindex finline-limit
3508 By default, gcc limits the size of functions that can be inlined. This flag
3509 allows the control of this limit for functions that are explicitly marked as
3510 inline (ie marked with the inline keyword or defined within the class
3511 definition in c++). @var{n} is the size of functions that can be inlined in
3512 number of pseudo instructions (not counting parameter handling). The default
3513 value of @var{n} is 600.
3514 Increasing this value can result in more inlined code at
3515 the cost of compilation time and memory consumption. Decreasing usually makes
3516 the compilation faster and less code will be inlined (which presumably
3517 means slower programs). This option is particularly useful for programs that
3518 use inlining heavily such as those based on recursive templates with C++.
3520 @emph{Note:} pseudo instruction represents, in this particular context, an
3521 abstract measurement of function's size. In no way, it represents a count
3522 of assembly instructions and as such its exact meaning might change from one
3523 release to an another.
3525 @item -fkeep-inline-functions
3526 @opindex fkeep-inline-functions
3527 Even if all calls to a given function are integrated, and the function
3528 is declared @code{static}, nevertheless output a separate run-time
3529 callable version of the function. This switch does not affect
3530 @code{extern inline} functions.
3532 @item -fkeep-static-consts
3533 @opindex fkeep-static-consts
3534 Emit variables declared @code{static const} when optimization isn't turned
3535 on, even if the variables aren't referenced.
3537 GCC enables this option by default. If you want to force the compiler to
3538 check if the variable was referenced, regardless of whether or not
3539 optimization is turned on, use the @option{-fno-keep-static-consts} option.
3541 @item -fmerge-constants
3542 Attempt to merge identical constants (string constants and floating point
3543 constants) accross compilation units.
3545 This option is default for optimized compilation if assembler and linker
3546 support it. Use @option{-fno-merge-constants} to inhibit this behavior.
3548 @item -fmerge-all-constants
3549 Attempt to merge identical constants and identical variables.
3551 This option implies @option{-fmerge-constants}. In addition to
3552 @option{-fmerge-constants} this considers e.g. even constant initialized
3553 arrays or initialized constant variables with integral or floating point
3554 types. Languages like C or C++ require each non-automatic variable to
3555 have distinct location, so using this option will result in non-conforming
3560 Use a graph coloring register allocator. Currently this option is meant
3561 for testing, so we are interested to hear about miscompilations with
3564 @item -fno-branch-count-reg
3565 @opindex fno-branch-count-reg
3566 Do not use ``decrement and branch'' instructions on a count register,
3567 but instead generate a sequence of instructions that decrement a
3568 register, compare it against zero, then branch based upon the result.
3569 This option is only meaningful on architectures that support such
3570 instructions, which include x86, PowerPC, IA-64 and S/390.
3572 @item -fno-function-cse
3573 @opindex fno-function-cse
3574 Do not put function addresses in registers; make each instruction that
3575 calls a constant function contain the function's address explicitly.
3577 This option results in less efficient code, but some strange hacks
3578 that alter the assembler output may be confused by the optimizations
3579 performed when this option is not used.
3583 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
3584 @option{-fno-trapping-math}, @option{-ffinite-math-only} and @*
3585 @option{-fno-signaling-nans}.
3587 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
3589 This option should never be turned on by any @option{-O} option since
3590 it can result in incorrect output for programs which depend on
3591 an exact implementation of IEEE or ISO rules/specifications for
3594 @item -fno-math-errno
3595 @opindex fno-math-errno
3596 Do not set ERRNO after calling math functions that are executed
3597 with a single instruction, e.g., sqrt. A program that relies on
3598 IEEE exceptions for math error handling may want to use this flag
3599 for speed while maintaining IEEE arithmetic compatibility.
3601 This option should never be turned on by any @option{-O} option since
3602 it can result in incorrect output for programs which depend on
3603 an exact implementation of IEEE or ISO rules/specifications for
3606 The default is @option{-fmath-errno}.
3608 @item -funsafe-math-optimizations
3609 @opindex funsafe-math-optimizations
3610 Allow optimizations for floating-point arithmetic that (a) assume
3611 that arguments and results are valid and (b) may violate IEEE or
3612 ANSI standards. When used at link-time, it may include libraries
3613 or startup files that change the default FPU control word or other
3614 similar optimizations.
3616 This option should never be turned on by any @option{-O} option since
3617 it can result in incorrect output for programs which depend on
3618 an exact implementation of IEEE or ISO rules/specifications for
3621 The default is @option{-fno-unsafe-math-optimizations}.
3623 @item -ffinite-math-only
3624 @opindex ffinite-math-only
3625 Allow optimizations for floating-point arithmetic that assume
3626 that arguments and results are not NaNs or +-Infs.
3628 This option should never be turned on by any @option{-O} option since
3629 it can result in incorrect output for programs which depend on
3630 an exact implementation of IEEE or ISO rules/specifications.
3632 The default is @option{-fno-finite-math-only}.
3634 @item -fno-trapping-math
3635 @opindex fno-trapping-math
3636 Compile code assuming that floating-point operations cannot generate
3637 user-visible traps. These traps include division by zero, overflow,
3638 underflow, inexact result and invalid operation. This option implies
3639 @option{-fno-signaling-nans}. Setting this option may allow faster
3640 code if one relies on ``non-stop'' IEEE arithmetic, for example.
3642 This option should never be turned on by any @option{-O} option since
3643 it can result in incorrect output for programs which depend on
3644 an exact implementation of IEEE or ISO rules/specifications for
3647 The default is @option{-ftrapping-math}.
3649 @item -fsignaling-nans
3650 @opindex fsignaling-nans
3651 Compile code assuming that IEEE signaling NaNs may generate user-visible
3652 traps during floating-point operations. Setting this option disables
3653 optimizations that may change the number of exceptions visible with
3654 signaling NaNs. This option implies @option{-ftrapping-math}.
3656 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
3659 The default is @option{-fno-signaling-nans}.
3661 This option is experimental and does not currently guarantee to
3662 disable all GCC optimizations that affect signaling NaN behavior.
3664 @item -fno-zero-initialized-in-bss
3665 @opindex fno-zero-initialized-in-bss
3666 If the target supports a BSS section, GCC by default puts variables that
3667 are initialized to zero into BSS@. This can save space in the resulting
3670 This option turns off this behavior because some programs explicitly
3671 rely on variables going to the data section. E.g., so that the
3672 resulting executable can find the beginning of that section and/or make
3673 assumptions based on that.
3675 The default is @option{-fzero-initialized-in-bss}.
3677 @item -fbounds-check
3678 @opindex fbounds-check
3679 For front-ends that support it, generate additional code to check that
3680 indices used to access arrays are within the declared range. This is
3681 currenly only supported by the Java and Fortran 77 front-ends, where
3682 this option defaults to true and false respectively.
3686 The following options control specific optimizations. The @option{-O2}
3687 option turns on all of these optimizations except @option{-funroll-loops}
3688 and @option{-funroll-all-loops}. On most machines, the @option{-O} option
3689 turns on the @option{-fthread-jumps} and @option{-fdelayed-branch} options,
3690 but specific machines may handle it differently.
3692 You can use the following flags in the rare cases when ``fine-tuning''
3693 of optimizations to be performed is desired.
3695 Not all of the optimizations performed by GCC have @option{-f} options
3699 @item -fstrength-reduce
3700 @opindex fstrength-reduce
3701 Perform the optimizations of loop strength reduction and
3702 elimination of iteration variables.
3704 @item -fthread-jumps
3705 @opindex fthread-jumps
3706 Perform optimizations where we check to see if a jump branches to a
3707 location where another comparison subsumed by the first is found. If
3708 so, the first branch is redirected to either the destination of the
3709 second branch or a point immediately following it, depending on whether
3710 the condition is known to be true or false.
3712 @item -fcse-follow-jumps
3713 @opindex fcse-follow-jumps
3714 In common subexpression elimination, scan through jump instructions
3715 when the target of the jump is not reached by any other path. For
3716 example, when CSE encounters an @code{if} statement with an
3717 @code{else} clause, CSE will follow the jump when the condition
3720 @item -fcse-skip-blocks
3721 @opindex fcse-skip-blocks
3722 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
3723 follow jumps which conditionally skip over blocks. When CSE
3724 encounters a simple @code{if} statement with no else clause,
3725 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
3726 body of the @code{if}.
3728 @item -frerun-cse-after-loop
3729 @opindex frerun-cse-after-loop
3730 Re-run common subexpression elimination after loop optimizations has been
3733 @item -frerun-loop-opt
3734 @opindex frerun-loop-opt
3735 Run the loop optimizer twice.
3739 Perform a global common subexpression elimination pass.
3740 This pass also performs global constant and copy propagation.
3742 @emph{Note:} When compiling a program using computed gotos, a GCC
3743 extension, you may get better runtime performance if you disable
3744 the global common subexpression elmination pass by adding
3745 @option{-fno-gcse} to the command line.
3749 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
3750 attempt to move loads which are only killed by stores into themselves. This
3751 allows a loop containing a load/store sequence to be changed to a load outside
3752 the loop, and a copy/store within the loop.
3756 When @option{-fgcse-sm} is enabled, A store motion pass is run after global common
3757 subexpression elimination. This pass will attempt to move stores out of loops.
3758 When used in conjunction with @option{-fgcse-lm}, loops containing a load/store sequence
3759 can be changed to a load before the loop and a store after the loop.
3761 @item -floop-optimize
3762 @opindex floop-optimize
3763 Perform loop optimizations: move constant expressions out of loops, simplify
3764 exit test conditions and optionally do strength-reduction and loop unrolling as
3767 @item -fcrossjumping
3768 @opindex crossjumping
3769 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
3770 resulting code may or may not perform better than without cross-jumping.
3772 @item -fif-conversion
3773 @opindex if-conversion
3774 Attempt to transform conditional jumps into branch-less equivalents. This
3775 include use of conditional moves, min, max, set flags and abs instructions, and
3776 some tricks doable by standard arithmetics. The use of conditional execution
3777 on chips where it is available is controlled by @code{if-conversion2}.
3779 @item -fif-conversion2
3780 @opindex if-conversion2
3781 Use conditional execution (where available) to transform conditional jumps into
3782 branch-less equivalents.
3784 @item -fdelete-null-pointer-checks
3785 @opindex fdelete-null-pointer-checks
3786 Use global dataflow analysis to identify and eliminate useless checks
3787 for null pointers. The compiler assumes that dereferencing a null
3788 pointer would have halted the program. If a pointer is checked after
3789 it has already been dereferenced, it cannot be null.
3791 In some environments, this assumption is not true, and programs can
3792 safely dereference null pointers. Use
3793 @option{-fno-delete-null-pointer-checks} to disable this optimization
3794 for programs which depend on that behavior.
3796 @item -fexpensive-optimizations
3797 @opindex fexpensive-optimizations
3798 Perform a number of minor optimizations that are relatively expensive.
3800 @item -foptimize-register-move
3802 @opindex foptimize-register-move
3804 Attempt to reassign register numbers in move instructions and as
3805 operands of other simple instructions in order to maximize the amount of
3806 register tying. This is especially helpful on machines with two-operand
3807 instructions. GCC enables this optimization by default with @option{-O2}
3810 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
3813 @item -fdelayed-branch
3814 @opindex fdelayed-branch
3815 If supported for the target machine, attempt to reorder instructions
3816 to exploit instruction slots available after delayed branch
3819 @item -fschedule-insns
3820 @opindex fschedule-insns
3821 If supported for the target machine, attempt to reorder instructions to
3822 eliminate execution stalls due to required data being unavailable. This
3823 helps machines that have slow floating point or memory load instructions
3824 by allowing other instructions to be issued until the result of the load
3825 or floating point instruction is required.
3827 @item -fschedule-insns2
3828 @opindex fschedule-insns2
3829 Similar to @option{-fschedule-insns}, but requests an additional pass of
3830 instruction scheduling after register allocation has been done. This is
3831 especially useful on machines with a relatively small number of
3832 registers and where memory load instructions take more than one cycle.
3834 @item -fno-sched-interblock
3835 @opindex fno-sched-interblock
3836 Don't schedule instructions across basic blocks. This is normally
3837 enabled by default when scheduling before register allocation, i.e.@:
3838 with @option{-fschedule-insns} or at @option{-O2} or higher.
3840 @item -fno-sched-spec
3841 @opindex fno-sched-spec
3842 Don't allow speculative motion of non-load instructions. This is normally
3843 enabled by default when scheduling before register allocation, i.e.@:
3844 with @option{-fschedule-insns} or at @option{-O2} or higher.
3846 @item -fsched-spec-load
3847 @opindex fsched-spec-load
3848 Allow speculative motion of some load instructions. This only makes
3849 sense when scheduling before register allocation, i.e.@: with
3850 @option{-fschedule-insns} or at @option{-O2} or higher.
3852 @item -fsched-spec-load-dangerous
3853 @opindex fsched-spec-load-dangerous
3854 Allow speculative motion of more load instructions. This only makes
3855 sense when scheduling before register allocation, i.e.@: with
3856 @option{-fschedule-insns} or at @option{-O2} or higher.
3858 @item -ffunction-sections
3859 @itemx -fdata-sections
3860 @opindex ffunction-sections
3861 @opindex fdata-sections
3862 Place each function or data item into its own section in the output
3863 file if the target supports arbitrary sections. The name of the
3864 function or the name of the data item determines the section's name
3867 Use these options on systems where the linker can perform optimizations
3868 to improve locality of reference in the instruction space. HPPA
3869 processors running HP-UX and SPARC processors running Solaris 2 have
3870 linkers with such optimizations. Other systems using the ELF object format
3871 as well as AIX may have these optimizations in the future.
3873 Only use these options when there are significant benefits from doing
3874 so. When you specify these options, the assembler and linker will
3875 create larger object and executable files and will also be slower.
3876 You will not be able to use @code{gprof} on all systems if you
3877 specify this option and you may have problems with debugging if
3878 you specify both this option and @option{-g}.
3880 @item -fcaller-saves
3881 @opindex fcaller-saves
3882 Enable values to be allocated in registers that will be clobbered by
3883 function calls, by emitting extra instructions to save and restore the
3884 registers around such calls. Such allocation is done only when it
3885 seems to result in better code than would otherwise be produced.
3887 This option is always enabled by default on certain machines, usually
3888 those which have no call-preserved registers to use instead.
3890 For all machines, optimization level 2 and higher enables this flag by
3895 Perform tail duplication to enlarge superblock size. This transformation
3896 simplifies the control flow of the function allowing other optimizations to do
3899 @item -funroll-loops
3900 @opindex funroll-loops
3901 Unroll loops whose number of iterations can be determined at compile
3902 time or upon entry to the loop. @option{-funroll-loops} implies both
3903 @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
3904 option makes code larger, and may or may not make it run faster.
3906 @item -funroll-all-loops
3907 @opindex funroll-all-loops
3908 Unroll all loops, even if their number of iterations is uncertain when
3909 the loop is entered. This usually makes programs run more slowly.
3910 @option{-funroll-all-loops} implies the same options as
3911 @option{-funroll-loops},
3913 @item -fprefetch-loop-arrays
3914 @opindex fprefetch-loop-arrays
3915 If supported by the target machine, generate instructions to prefetch
3916 memory to improve the performance of loops that access large arrays.
3918 @item -fmove-all-movables
3919 @opindex fmove-all-movables
3920 Forces all invariant computations in loops to be moved
3923 @item -freduce-all-givs
3924 @opindex freduce-all-givs
3925 Forces all general-induction variables in loops to be
3928 @emph{Note:} When compiling programs written in Fortran,
3929 @option{-fmove-all-movables} and @option{-freduce-all-givs} are enabled
3930 by default when you use the optimizer.
3932 These options may generate better or worse code; results are highly
3933 dependent on the structure of loops within the source code.
3935 These two options are intended to be removed someday, once
3936 they have helped determine the efficacy of various
3937 approaches to improving loop optimizations.
3939 Please let us (@w{@email{gcc@@gcc.gnu.org}} and @w{@email{fortran@@gnu.org}})
3940 know how use of these options affects
3941 the performance of your production code.
3942 We're very interested in code that runs @emph{slower}
3943 when these options are @emph{enabled}.
3946 @itemx -fno-peephole2
3947 @opindex fno-peephole
3948 @opindex fno-peephole2
3949 Disable any machine-specific peephole optimizations. The difference
3950 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
3951 are implemented in the compiler; some targets use one, some use the
3952 other, a few use both.
3954 @item -fbranch-probabilities
3955 @opindex fbranch-probabilities
3956 After running a program compiled with @option{-fprofile-arcs}
3957 (@pxref{Debugging Options,, Options for Debugging Your Program or
3958 @command{gcc}}), you can compile it a second time using
3959 @option{-fbranch-probabilities}, to improve optimizations based on
3960 the number of times each branch was taken. When the program
3961 compiled with @option{-fprofile-arcs} exits it saves arc execution
3962 counts to a file called @file{@var{sourcename}.da} for each source
3963 file The information in this data file is very dependent on the
3964 structure of the generated code, so you must use the same source code
3965 and the same optimization options for both compilations.
3967 With @option{-fbranch-probabilities}, GCC puts a @samp{REG_EXEC_COUNT}
3968 note on the first instruction of each basic block, and a
3969 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
3970 These can be used to improve optimization. Currently, they are only
3971 used in one place: in @file{reorg.c}, instead of guessing which path a
3972 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
3973 exactly determine which path is taken more often.
3975 @item -fno-guess-branch-probability
3976 @opindex fno-guess-branch-probability
3977 Do not guess branch probabilities using a randomized model.
3979 Sometimes gcc will opt to use a randomized model to guess branch
3980 probabilities, when none are available from either profiling feedback
3981 (@option{-fprofile-arcs}) or @samp{__builtin_expect}. This means that
3982 different runs of the compiler on the same program may produce different
3985 In a hard real-time system, people don't want different runs of the
3986 compiler to produce code that has different behavior; minimizing
3987 non-determinism is of paramount import. This switch allows users to
3988 reduce non-determinism, possibly at the expense of inferior
3991 @item -freorder-blocks
3992 @opindex freorder-blocks
3993 Reorder basic blocks in the compiled function in order to reduce number of
3994 taken branches and improve code locality.
3996 @item -freorder-functions
3997 @opindex freorder-functions
3998 Reorder basic blocks in the compiled function in order to reduce number of
3999 taken branches and improve code locality. This is implemented by using special
4000 subsections @code{text.hot} for most frequently executed functions and
4001 @code{text.unlikely} for unlikely executed functions. Reordering is done by
4002 the linker so object file format must support named sections and linker must
4003 place them in resonable way.
4005 Also profile feedback must be available in to make this option effective. See
4006 @option{-fprofile-arcs} for details.
4008 @item -fstrict-aliasing
4009 @opindex fstrict-aliasing
4010 Allows the compiler to assume the strictest aliasing rules applicable to
4011 the language being compiled. For C (and C++), this activates
4012 optimizations based on the type of expressions. In particular, an
4013 object of one type is assumed never to reside at the same address as an
4014 object of a different type, unless the types are almost the same. For
4015 example, an @code{unsigned int} can alias an @code{int}, but not a
4016 @code{void*} or a @code{double}. A character type may alias any other
4019 Pay special attention to code like this:
4032 The practice of reading from a different union member than the one most
4033 recently written to (called ``type-punning'') is common. Even with
4034 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
4035 is accessed through the union type. So, the code above will work as
4036 expected. However, this code might not:
4047 Every language that wishes to perform language-specific alias analysis
4048 should define a function that computes, given an @code{tree}
4049 node, an alias set for the node. Nodes in different alias sets are not
4050 allowed to alias. For an example, see the C front-end function
4051 @code{c_get_alias_set}.
4053 For all machines, optimization level 2 and higher enables this flag by
4056 @item -falign-functions
4057 @itemx -falign-functions=@var{n}
4058 @opindex falign-functions
4059 Align the start of functions to the next power-of-two greater than
4060 @var{n}, skipping up to @var{n} bytes. For instance,
4061 @option{-falign-functions=32} aligns functions to the next 32-byte
4062 boundary, but @option{-falign-functions=24} would align to the next
4063 32-byte boundary only if this can be done by skipping 23 bytes or less.
4065 @option{-fno-align-functions} and @option{-falign-functions=1} are
4066 equivalent and mean that functions will not be aligned.
4068 Some assemblers only support this flag when @var{n} is a power of two;
4069 in that case, it is rounded up.
4071 If @var{n} is not specified, use a machine-dependent default.
4073 @item -falign-labels
4074 @itemx -falign-labels=@var{n}
4075 @opindex falign-labels
4076 Align all branch targets to a power-of-two boundary, skipping up to
4077 @var{n} bytes like @option{-falign-functions}. This option can easily
4078 make code slower, because it must insert dummy operations for when the
4079 branch target is reached in the usual flow of the code.
4081 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
4082 are greater than this value, then their values are used instead.
4084 If @var{n} is not specified, use a machine-dependent default which is
4085 very likely to be @samp{1}, meaning no alignment.
4088 @itemx -falign-loops=@var{n}
4089 @opindex falign-loops
4090 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
4091 like @option{-falign-functions}. The hope is that the loop will be
4092 executed many times, which will make up for any execution of the dummy
4095 If @var{n} is not specified, use a machine-dependent default.
4098 @itemx -falign-jumps=@var{n}
4099 @opindex falign-jumps
4100 Align branch targets to a power-of-two boundary, for branch targets
4101 where the targets can only be reached by jumping, skipping up to @var{n}
4102 bytes like @option{-falign-functions}. In this case, no dummy operations
4105 If @var{n} is not specified, use a machine-dependent default.
4109 Perform optimizations in static single assignment form. Each function's
4110 flow graph is translated into SSA form, optimizations are performed, and
4111 the flow graph is translated back from SSA form. Users should not
4112 specify this option, since it is not yet ready for production use.
4116 Perform Sparse Conditional Constant Propagation in SSA form. Requires
4117 @option{-fssa}. Like @option{-fssa}, this is an experimental feature.
4121 Perform aggressive dead-code elimination in SSA form. Requires @option{-fssa}.
4122 Like @option{-fssa}, this is an experimental feature.
4124 @item -fsingle-precision-constant
4125 @opindex fsingle-precision-constant
4126 Treat floating point constant as single precision constant instead of
4127 implicitly converting it to double precision constant.
4129 @item -frename-registers
4130 @opindex frename-registers
4131 Attempt to avoid false dependencies in scheduled code by making use
4132 of registers left over after register allocation. This optimization
4133 will most benefit processors with lots of registers. It can, however,
4134 make debugging impossible, since variables will no longer stay in
4135 a ``home register''.
4137 @item -fno-cprop-registers
4138 @opindex fno-cprop-registers
4139 After register allocation and post-register allocation instruction splitting,
4140 we perform a copy-propagation pass to try to reduce scheduling dependencies
4141 and occasionally eliminate the copy.
4143 @item --param @var{name}=@var{value}
4145 In some places, GCC uses various constants to control the amount of
4146 optimization that is done. For example, GCC will not inline functions
4147 that contain more that a certain number of instructions. You can
4148 control some of these constants on the command-line using the
4149 @option{--param} option.
4151 In each case, the @var{value} is an integer. The allowable choices for
4152 @var{name} are given in the following table:
4155 @item max-delay-slot-insn-search
4156 The maximum number of instructions to consider when looking for an
4157 instruction to fill a delay slot. If more than this arbitrary number of
4158 instructions is searched, the time savings from filling the delay slot
4159 will be minimal so stop searching. Increasing values mean more
4160 aggressive optimization, making the compile time increase with probably
4161 small improvement in executable run time.
4163 @item max-delay-slot-live-search
4164 When trying to fill delay slots, the maximum number of instructions to
4165 consider when searching for a block with valid live register
4166 information. Increasing this arbitrarily chosen value means more
4167 aggressive optimization, increasing the compile time. This parameter
4168 should be removed when the delay slot code is rewritten to maintain the
4171 @item max-gcse-memory
4172 The approximate maximum amount of memory that will be allocated in
4173 order to perform the global common subexpression elimination
4174 optimization. If more memory than specified is required, the
4175 optimization will not be done.
4177 @item max-gcse-passes
4178 The maximum number of passes of GCSE to run.
4180 @item max-pending-list-length
4181 The maximum number of pending dependencies scheduling will allow
4182 before flushing the current state and starting over. Large functions
4183 with few branches or calls can create excessively large lists which
4184 needlessly consume memory and resources.
4186 @item max-inline-insns
4187 If an function contains more than this many instructions, it
4188 will not be inlined. This option is precisely equivalent to
4189 @option{-finline-limit}.
4191 @item max-unrolled-insns
4192 The maximum number of instructions that a loop should have if that loop
4193 is unrolled, and if the loop is unrolled, it determines how many times
4194 the loop code is unrolled.
4196 @item hot-bb-count-fraction
4197 Select fraction of the maximal count of repetitions of basic block in program
4198 given basic block needs to have to be considered hot.
4200 @item hot-bb-frequency-fraction
4201 Select fraction of the maximal frequency of executions of basic block in
4202 function given basic block needs to have to be considered hot
4204 @item tracer-dynamic-coverage
4205 @itemx tracer-dynamic-coverage-feedback
4207 This value is used to limit superblock formation once given percentage of
4208 executed instructions is covered. This limits unnecesary code size expansion.
4210 The @option{tracer-dynamic-coverage-feedback} is used only when profile
4211 feedback is available. The real profiles (as opposed to statically estimated
4212 ones) are much less balanced allowing the threshold to be larger value.
4214 @item tracer-max-code-growth
4215 Stop tail duplication once code growth has reached given percentage. This is
4216 rather hokey argument, as most of the duplicates will be elliminated later in
4217 cross jumping, so it may be set to much higher values than is the desired code
4220 @item tracer-min-branch-ratio
4222 Stop reverse growth when the reverse probability of best edge is less than this
4223 threshold (in percent).
4225 @item tracer-min-branch-ratio
4226 @itemx tracer-min-branch-ratio-feedback
4228 Stop forward growth if the best edge do have probability lower than this
4231 Similary to @option{tracer-dynamic-coverage} two values are present, one for
4232 compilation for profile feedback and one for compilation without. The value
4233 for compilation with profile feedback needs to be more conservative (higher) in
4234 order to make tracer effective.
4236 @item ggc-min-expand
4238 GCC uses a garbage collector to manage its own memory allocation. This
4239 parameter specifies the minimum percentage by which the garbage
4240 collector's heap should be allowed to expand between collections.
4241 Tuning this may improve compilation speed; it has no effect on code
4244 The default is 30%. Setting this parameter to zero causes a full
4245 collection to occur at every opportunity. This is extremely slow, but
4246 can be useful for debugging.
4248 @item ggc-min-heapsize
4250 Minimum size of the garbage collector's heap before it begins bothering
4251 to collect garbage. The first collection occurs after the heap expands
4252 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
4253 tuning this may improve compilation speed, and has no effect on code
4256 The default is 4096 (four megabytes). Setting this parameter very large
4257 effectively disables garbage collection.
4262 @node Preprocessor Options
4263 @section Options Controlling the Preprocessor
4264 @cindex preprocessor options
4265 @cindex options, preprocessor
4267 These options control the C preprocessor, which is run on each C source
4268 file before actual compilation.
4270 If you use the @option{-E} option, nothing is done except preprocessing.
4271 Some of these options make sense only together with @option{-E} because
4272 they cause the preprocessor output to be unsuitable for actual
4276 You can use @option{-Wp,@var{option}} to bypass the compiler driver
4277 and pass @var{option} directly through to the preprocessor. If
4278 @var{option} contains commas, it is split into multiple options at the
4279 commas. However, many options are modified, translated or interpreted
4280 by the compiler driver before being passed to the preprocessor, and
4281 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
4282 interface is undocumented and subject to change, so whenever possible
4283 you should avoid using @option{-Wp} and let the driver handle the
4286 @include cppopts.texi
4288 @node Assembler Options
4289 @section Passing Options to the Assembler
4291 @c prevent bad page break with this line
4292 You can pass options to the assembler.
4295 @item -Wa,@var{option}
4297 Pass @var{option} as an option to the assembler. If @var{option}
4298 contains commas, it is split into multiple options at the commas.
4302 @section Options for Linking
4303 @cindex link options
4304 @cindex options, linking
4306 These options come into play when the compiler links object files into
4307 an executable output file. They are meaningless if the compiler is
4308 not doing a link step.
4312 @item @var{object-file-name}
4313 A file name that does not end in a special recognized suffix is
4314 considered to name an object file or library. (Object files are
4315 distinguished from libraries by the linker according to the file
4316 contents.) If linking is done, these object files are used as input
4325 If any of these options is used, then the linker is not run, and
4326 object file names should not be used as arguments. @xref{Overall
4330 @item -l@var{library}
4331 @itemx -l @var{library}
4333 Search the library named @var{library} when linking. (The second
4334 alternative with the library as a separate argument is only for
4335 POSIX compliance and is not recommended.)
4337 It makes a difference where in the command you write this option; the
4338 linker searches and processes libraries and object files in the order they
4339 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
4340 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
4341 to functions in @samp{z}, those functions may not be loaded.
4343 The linker searches a standard list of directories for the library,
4344 which is actually a file named @file{lib@var{library}.a}. The linker
4345 then uses this file as if it had been specified precisely by name.
4347 The directories searched include several standard system directories
4348 plus any that you specify with @option{-L}.
4350 Normally the files found this way are library files---archive files
4351 whose members are object files. The linker handles an archive file by
4352 scanning through it for members which define symbols that have so far
4353 been referenced but not defined. But if the file that is found is an
4354 ordinary object file, it is linked in the usual fashion. The only
4355 difference between using an @option{-l} option and specifying a file name
4356 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
4357 and searches several directories.
4361 You need this special case of the @option{-l} option in order to
4362 link an Objective-C program.
4365 @opindex nostartfiles
4366 Do not use the standard system startup files when linking.
4367 The standard system libraries are used normally, unless @option{-nostdlib}
4368 or @option{-nodefaultlibs} is used.
4370 @item -nodefaultlibs
4371 @opindex nodefaultlibs
4372 Do not use the standard system libraries when linking.
4373 Only the libraries you specify will be passed to the linker.
4374 The standard startup files are used normally, unless @option{-nostartfiles}
4375 is used. The compiler may generate calls to memcmp, memset, and memcpy
4376 for System V (and ISO C) environments or to bcopy and bzero for
4377 BSD environments. These entries are usually resolved by entries in
4378 libc. These entry points should be supplied through some other
4379 mechanism when this option is specified.
4383 Do not use the standard system startup files or libraries when linking.
4384 No startup files and only the libraries you specify will be passed to
4385 the linker. The compiler may generate calls to memcmp, memset, and memcpy
4386 for System V (and ISO C) environments or to bcopy and bzero for
4387 BSD environments. These entries are usually resolved by entries in
4388 libc. These entry points should be supplied through some other
4389 mechanism when this option is specified.
4391 @cindex @option{-lgcc}, use with @option{-nostdlib}
4392 @cindex @option{-nostdlib} and unresolved references
4393 @cindex unresolved references and @option{-nostdlib}
4394 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
4395 @cindex @option{-nodefaultlibs} and unresolved references
4396 @cindex unresolved references and @option{-nodefaultlibs}
4397 One of the standard libraries bypassed by @option{-nostdlib} and
4398 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
4399 that GCC uses to overcome shortcomings of particular machines, or special
4400 needs for some languages.
4401 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
4402 Collection (GCC) Internals},
4403 for more discussion of @file{libgcc.a}.)
4404 In most cases, you need @file{libgcc.a} even when you want to avoid
4405 other standard libraries. In other words, when you specify @option{-nostdlib}
4406 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
4407 This ensures that you have no unresolved references to internal GCC
4408 library subroutines. (For example, @samp{__main}, used to ensure C++
4409 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
4410 GNU Compiler Collection (GCC) Internals}.)
4414 Remove all symbol table and relocation information from the executable.
4418 On systems that support dynamic linking, this prevents linking with the shared
4419 libraries. On other systems, this option has no effect.
4423 Produce a shared object which can then be linked with other objects to
4424 form an executable. Not all systems support this option. For predictable
4425 results, you must also specify the same set of options that were used to
4426 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
4427 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
4428 needs to build supplementary stub code for constructors to work. On
4429 multi-libbed systems, @samp{gcc -shared} must select the correct support
4430 libraries to link against. Failing to supply the correct flags may lead
4431 to subtle defects. Supplying them in cases where they are not necessary
4434 @item -shared-libgcc
4435 @itemx -static-libgcc
4436 @opindex shared-libgcc
4437 @opindex static-libgcc
4438 On systems that provide @file{libgcc} as a shared library, these options
4439 force the use of either the shared or static version respectively.
4440 If no shared version of @file{libgcc} was built when the compiler was
4441 configured, these options have no effect.
4443 There are several situations in which an application should use the
4444 shared @file{libgcc} instead of the static version. The most common
4445 of these is when the application wishes to throw and catch exceptions
4446 across different shared libraries. In that case, each of the libraries
4447 as well as the application itself should use the shared @file{libgcc}.
4449 Therefore, the G++ and GCJ drivers automatically add
4450 @option{-shared-libgcc} whenever you build a shared library or a main
4451 executable, because C++ and Java programs typically use exceptions, so
4452 this is the right thing to do.
4454 If, instead, you use the GCC driver to create shared libraries, you may
4455 find that they will not always be linked with the shared @file{libgcc}.
4456 If GCC finds, at its configuration time, that you have a GNU linker that
4457 does not support option @option{--eh-frame-hdr}, it will link the shared
4458 version of @file{libgcc} into shared libraries by default. Otherwise,
4459 it will take advantage of the linker and optimize away the linking with
4460 the shared version of @file{libgcc}, linking with the static version of
4461 libgcc by default. This allows exceptions to propagate through such
4462 shared libraries, without incurring relocation costs at library load
4465 However, if a library or main executable is supposed to throw or catch
4466 exceptions, you must link it using the G++ or GCJ driver, as appropriate
4467 for the languages used in the program, or using the option
4468 @option{-shared-libgcc}, such that it is linked with the shared
4473 Bind references to global symbols when building a shared object. Warn
4474 about any unresolved references (unless overridden by the link editor
4475 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
4478 @item -Xlinker @var{option}
4480 Pass @var{option} as an option to the linker. You can use this to
4481 supply system-specific linker options which GCC does not know how to
4484 If you want to pass an option that takes an argument, you must use
4485 @option{-Xlinker} twice, once for the option and once for the argument.
4486 For example, to pass @option{-assert definitions}, you must write
4487 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
4488 @option{-Xlinker "-assert definitions"}, because this passes the entire
4489 string as a single argument, which is not what the linker expects.
4491 @item -Wl,@var{option}
4493 Pass @var{option} as an option to the linker. If @var{option} contains
4494 commas, it is split into multiple options at the commas.
4496 @item -u @var{symbol}
4498 Pretend the symbol @var{symbol} is undefined, to force linking of
4499 library modules to define it. You can use @option{-u} multiple times with
4500 different symbols to force loading of additional library modules.
4503 @node Directory Options
4504 @section Options for Directory Search
4505 @cindex directory options
4506 @cindex options, directory search
4509 These options specify directories to search for header files, for
4510 libraries and for parts of the compiler:
4515 Add the directory @var{dir} to the head of the list of directories to be
4516 searched for header files. This can be used to override a system header
4517 file, substituting your own version, since these directories are
4518 searched before the system header file directories. However, you should
4519 not use this option to add directories that contain vendor-supplied
4520 system header files (use @option{-isystem} for that). If you use more than
4521 one @option{-I} option, the directories are scanned in left-to-right
4522 order; the standard system directories come after.
4524 If a standard system include directory, or a directory specified with
4525 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
4526 option will be ignored. The directory will still be searched but as a
4527 system directory at its normal position in the system include chain.
4528 This is to ensure that GCC's procedure to fix buggy system headers and
4529 the ordering for the include_next directive are not inadvertantly changed.
4530 If you really need to change the search order for system directories,
4531 use the @option{-nostdinc} and/or @option{-isystem} options.
4535 Any directories you specify with @option{-I} options before the @option{-I-}
4536 option are searched only for the case of @samp{#include "@var{file}"};
4537 they are not searched for @samp{#include <@var{file}>}.
4539 If additional directories are specified with @option{-I} options after
4540 the @option{-I-}, these directories are searched for all @samp{#include}
4541 directives. (Ordinarily @emph{all} @option{-I} directories are used
4544 In addition, the @option{-I-} option inhibits the use of the current
4545 directory (where the current input file came from) as the first search
4546 directory for @samp{#include "@var{file}"}. There is no way to
4547 override this effect of @option{-I-}. With @option{-I.} you can specify
4548 searching the directory which was current when the compiler was
4549 invoked. That is not exactly the same as what the preprocessor does
4550 by default, but it is often satisfactory.
4552 @option{-I-} does not inhibit the use of the standard system directories
4553 for header files. Thus, @option{-I-} and @option{-nostdinc} are
4558 Add directory @var{dir} to the list of directories to be searched
4561 @item -B@var{prefix}
4563 This option specifies where to find the executables, libraries,
4564 include files, and data files of the compiler itself.
4566 The compiler driver program runs one or more of the subprograms
4567 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
4568 @var{prefix} as a prefix for each program it tries to run, both with and
4569 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
4571 For each subprogram to be run, the compiler driver first tries the
4572 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
4573 was not specified, the driver tries two standard prefixes, which are
4574 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc-lib/}. If neither of
4575 those results in a file name that is found, the unmodified program
4576 name is searched for using the directories specified in your
4577 @env{PATH} environment variable.
4579 The compiler will check to see if the path provided by the @option{-B}
4580 refers to a directory, and if necessary it will add a directory
4581 separator character at the end of the path.
4583 @option{-B} prefixes that effectively specify directory names also apply
4584 to libraries in the linker, because the compiler translates these
4585 options into @option{-L} options for the linker. They also apply to
4586 includes files in the preprocessor, because the compiler translates these
4587 options into @option{-isystem} options for the preprocessor. In this case,
4588 the compiler appends @samp{include} to the prefix.
4590 The run-time support file @file{libgcc.a} can also be searched for using
4591 the @option{-B} prefix, if needed. If it is not found there, the two
4592 standard prefixes above are tried, and that is all. The file is left
4593 out of the link if it is not found by those means.
4595 Another way to specify a prefix much like the @option{-B} prefix is to use
4596 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
4599 As a special kludge, if the path provided by @option{-B} is
4600 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
4601 9, then it will be replaced by @file{[dir/]include}. This is to help
4602 with boot-strapping the compiler.
4604 @item -specs=@var{file}
4606 Process @var{file} after the compiler reads in the standard @file{specs}
4607 file, in order to override the defaults that the @file{gcc} driver
4608 program uses when determining what switches to pass to @file{cc1},
4609 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
4610 @option{-specs=@var{file}} can be specified on the command line, and they
4611 are processed in order, from left to right.
4617 @section Specifying subprocesses and the switches to pass to them
4619 @command{gcc} is a driver program. It performs its job by invoking a
4620 sequence of other programs to do the work of compiling, assembling and
4621 linking. GCC interprets its command-line parameters and uses these to
4622 deduce which programs it should invoke, and which command-line options
4623 it ought to place on their command lines. This behavior is controlled
4624 by @dfn{spec strings}. In most cases there is one spec string for each
4625 program that GCC can invoke, but a few programs have multiple spec
4626 strings to control their behavior. The spec strings built into GCC can
4627 be overridden by using the @option{-specs=} command-line switch to specify
4630 @dfn{Spec files} are plaintext files that are used to construct spec
4631 strings. They consist of a sequence of directives separated by blank
4632 lines. The type of directive is determined by the first non-whitespace
4633 character on the line and it can be one of the following:
4636 @item %@var{command}
4637 Issues a @var{command} to the spec file processor. The commands that can
4641 @item %include <@var{file}>
4643 Search for @var{file} and insert its text at the current point in the
4646 @item %include_noerr <@var{file}>
4647 @cindex %include_noerr
4648 Just like @samp{%include}, but do not generate an error message if the include
4649 file cannot be found.
4651 @item %rename @var{old_name} @var{new_name}
4653 Rename the spec string @var{old_name} to @var{new_name}.
4657 @item *[@var{spec_name}]:
4658 This tells the compiler to create, override or delete the named spec
4659 string. All lines after this directive up to the next directive or
4660 blank line are considered to be the text for the spec string. If this
4661 results in an empty string then the spec will be deleted. (Or, if the
4662 spec did not exist, then nothing will happened.) Otherwise, if the spec
4663 does not currently exist a new spec will be created. If the spec does
4664 exist then its contents will be overridden by the text of this
4665 directive, unless the first character of that text is the @samp{+}
4666 character, in which case the text will be appended to the spec.
4668 @item [@var{suffix}]:
4669 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
4670 and up to the next directive or blank line are considered to make up the
4671 spec string for the indicated suffix. When the compiler encounters an
4672 input file with the named suffix, it will processes the spec string in
4673 order to work out how to compile that file. For example:
4680 This says that any input file whose name ends in @samp{.ZZ} should be
4681 passed to the program @samp{z-compile}, which should be invoked with the
4682 command-line switch @option{-input} and with the result of performing the
4683 @samp{%i} substitution. (See below.)
4685 As an alternative to providing a spec string, the text that follows a
4686 suffix directive can be one of the following:
4689 @item @@@var{language}
4690 This says that the suffix is an alias for a known @var{language}. This is
4691 similar to using the @option{-x} command-line switch to GCC to specify a
4692 language explicitly. For example:
4699 Says that .ZZ files are, in fact, C++ source files.
4702 This causes an error messages saying:
4705 @var{name} compiler not installed on this system.
4709 GCC already has an extensive list of suffixes built into it.
4710 This directive will add an entry to the end of the list of suffixes, but
4711 since the list is searched from the end backwards, it is effectively
4712 possible to override earlier entries using this technique.
4716 GCC has the following spec strings built into it. Spec files can
4717 override these strings or create their own. Note that individual
4718 targets can also add their own spec strings to this list.
4721 asm Options to pass to the assembler
4722 asm_final Options to pass to the assembler post-processor
4723 cpp Options to pass to the C preprocessor
4724 cc1 Options to pass to the C compiler
4725 cc1plus Options to pass to the C++ compiler
4726 endfile Object files to include at the end of the link
4727 link Options to pass to the linker
4728 lib Libraries to include on the command line to the linker
4729 libgcc Decides which GCC support library to pass to the linker
4730 linker Sets the name of the linker
4731 predefines Defines to be passed to the C preprocessor
4732 signed_char Defines to pass to CPP to say whether @code{char} is signed
4734 startfile Object files to include at the start of the link
4737 Here is a small example of a spec file:
4743 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
4746 This example renames the spec called @samp{lib} to @samp{old_lib} and
4747 then overrides the previous definition of @samp{lib} with a new one.
4748 The new definition adds in some extra command-line options before
4749 including the text of the old definition.
4751 @dfn{Spec strings} are a list of command-line options to be passed to their
4752 corresponding program. In addition, the spec strings can contain
4753 @samp{%}-prefixed sequences to substitute variable text or to
4754 conditionally insert text into the command line. Using these constructs
4755 it is possible to generate quite complex command lines.
4757 Here is a table of all defined @samp{%}-sequences for spec
4758 strings. Note that spaces are not generated automatically around the
4759 results of expanding these sequences. Therefore you can concatenate them
4760 together or combine them with constant text in a single argument.
4764 Substitute one @samp{%} into the program name or argument.
4767 Substitute the name of the input file being processed.
4770 Substitute the basename of the input file being processed.
4771 This is the substring up to (and not including) the last period
4772 and not including the directory.
4775 This is the same as @samp{%b}, but include the file suffix (text after
4779 Marks the argument containing or following the @samp{%d} as a
4780 temporary file name, so that that file will be deleted if GCC exits
4781 successfully. Unlike @samp{%g}, this contributes no text to the
4784 @item %g@var{suffix}
4785 Substitute a file name that has suffix @var{suffix} and is chosen
4786 once per compilation, and mark the argument in the same way as
4787 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
4788 name is now chosen in a way that is hard to predict even when previously
4789 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
4790 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
4791 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
4792 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
4793 was simply substituted with a file name chosen once per compilation,
4794 without regard to any appended suffix (which was therefore treated
4795 just like ordinary text), making such attacks more likely to succeed.
4797 @item %u@var{suffix}
4798 Like @samp{%g}, but generates a new temporary file name even if
4799 @samp{%u@var{suffix}} was already seen.
4801 @item %U@var{suffix}
4802 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
4803 new one if there is no such last file name. In the absence of any
4804 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
4805 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
4806 would involve the generation of two distinct file names, one
4807 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
4808 simply substituted with a file name chosen for the previous @samp{%u},
4809 without regard to any appended suffix.
4811 @item %j@var{SUFFIX}
4812 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
4813 writable, and if save-temps is off; otherwise, substitute the name
4814 of a temporary file, just like @samp{%u}. This temporary file is not
4815 meant for communication between processes, but rather as a junk
4818 @item %.@var{SUFFIX}
4819 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
4820 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
4821 terminated by the next space or %.
4824 Marks the argument containing or following the @samp{%w} as the
4825 designated output file of this compilation. This puts the argument
4826 into the sequence of arguments that @samp{%o} will substitute later.
4829 Substitutes the names of all the output files, with spaces
4830 automatically placed around them. You should write spaces
4831 around the @samp{%o} as well or the results are undefined.
4832 @samp{%o} is for use in the specs for running the linker.
4833 Input files whose names have no recognized suffix are not compiled
4834 at all, but they are included among the output files, so they will
4838 Substitutes the suffix for object files. Note that this is
4839 handled specially when it immediately follows @samp{%g, %u, or %U},
4840 because of the need for those to form complete file names. The
4841 handling is such that @samp{%O} is treated exactly as if it had already
4842 been substituted, except that @samp{%g, %u, and %U} do not currently
4843 support additional @var{suffix} characters following @samp{%O} as they would
4844 following, for example, @samp{.o}.
4847 Substitutes the standard macro predefinitions for the
4848 current target machine. Use this when running @code{cpp}.
4851 Like @samp{%p}, but puts @samp{__} before and after the name of each
4852 predefined macro, except for macros that start with @samp{__} or with
4853 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
4857 Substitute a @option{-iprefix} option made from @env{GCC_EXEC_PREFIX}.
4860 Current argument is the name of a library or startup file of some sort.
4861 Search for that file in a standard list of directories and substitute
4862 the full name found.
4865 Print @var{str} as an error message. @var{str} is terminated by a newline.
4866 Use this when inconsistent options are detected.
4869 Output @samp{-} if the input for the current command is coming from a pipe.
4872 Substitute the contents of spec string @var{name} at this point.
4875 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
4877 @item %x@{@var{option}@}
4878 Accumulate an option for @samp{%X}.
4881 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
4885 Output the accumulated assembler options specified by @option{-Wa}.
4888 Output the accumulated preprocessor options specified by @option{-Wp}.
4891 Substitute the major version number of GCC@.
4892 (For version 2.9.5, this is 2.)
4895 Substitute the minor version number of GCC@.
4896 (For version 2.9.5, this is 9.)
4899 Substitute the patch level number of GCC@.
4900 (For version 2.9.5, this is 5.)
4903 Process the @code{asm} spec. This is used to compute the
4904 switches to be passed to the assembler.
4907 Process the @code{asm_final} spec. This is a spec string for
4908 passing switches to an assembler post-processor, if such a program is
4912 Process the @code{link} spec. This is the spec for computing the
4913 command line passed to the linker. Typically it will make use of the
4914 @samp{%L %G %S %D and %E} sequences.
4917 Dump out a @option{-L} option for each directory that GCC believes might
4918 contain startup files. If the target supports multilibs then the
4919 current multilib directory will be prepended to each of these paths.
4922 Output the multilib directory with directory separators replaced with
4923 @samp{_}. If multilib directories are not set, or the multilib directory is
4924 @file{.} then this option emits nothing.
4927 Process the @code{lib} spec. This is a spec string for deciding which
4928 libraries should be included on the command line to the linker.
4931 Process the @code{libgcc} spec. This is a spec string for deciding
4932 which GCC support library should be included on the command line to the linker.
4935 Process the @code{startfile} spec. This is a spec for deciding which
4936 object files should be the first ones passed to the linker. Typically
4937 this might be a file named @file{crt0.o}.
4940 Process the @code{endfile} spec. This is a spec string that specifies
4941 the last object files that will be passed to the linker.
4944 Process the @code{cpp} spec. This is used to construct the arguments
4945 to be passed to the C preprocessor.
4948 Process the @code{signed_char} spec. This is intended to be used
4949 to tell cpp whether a char is signed. It typically has the definition:
4951 %@{funsigned-char:-D__CHAR_UNSIGNED__@}
4955 Process the @code{cc1} spec. This is used to construct the options to be
4956 passed to the actual C compiler (@samp{cc1}).
4959 Process the @code{cc1plus} spec. This is used to construct the options to be
4960 passed to the actual C++ compiler (@samp{cc1plus}).
4963 Substitute the variable part of a matched option. See below.
4964 Note that each comma in the substituted string is replaced by
4968 Substitutes the @code{-S} switch, if that switch was given to GCC@.
4969 If that switch was not specified, this substitutes nothing. Note that
4970 the leading dash is omitted when specifying this option, and it is
4971 automatically inserted if the substitution is performed. Thus the spec
4972 string @samp{%@{foo@}} would match the command-line option @option{-foo}
4973 and would output the command line option @option{-foo}.
4975 @item %W@{@code{S}@}
4976 Like %@{@code{S}@} but mark last argument supplied within as a file to be
4979 @item %@{@code{S}*@}
4980 Substitutes all the switches specified to GCC whose names start
4981 with @code{-S}, but which also take an argument. This is used for
4982 switches like @option{-o}, @option{-D}, @option{-I}, etc.
4983 GCC considers @option{-o foo} as being
4984 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
4985 text, including the space. Thus two arguments would be generated.
4987 @item %@{^@code{S}*@}
4988 Like %@{@code{S}*@}, but don't put a blank between a switch and its
4989 argument. Thus %@{^o*@} would only generate one argument, not two.
4991 @item %@{@code{S}*&@code{T}*@}
4992 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
4993 (the order of @code{S} and @code{T} in the spec is not significant).
4994 There can be any number of ampersand-separated variables; for each the
4995 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
4997 @item %@{<@code{S}@}
4998 Remove all occurrences of @code{-S} from the command line. Note---this
4999 command is position dependent. @samp{%} commands in the spec string
5000 before this option will see @code{-S}, @samp{%} commands in the spec
5001 string after this option will not.
5003 @item %@{@code{S}*:@code{X}@}
5004 Substitutes @code{X} if one or more switches whose names start with
5005 @code{-S} are specified to GCC@. Note that the tail part of the
5006 @code{-S} option (i.e.@: the part matched by the @samp{*}) will be substituted
5007 for each occurrence of @samp{%*} within @code{X}.
5009 @item %@{@code{S}:@code{X}@}
5010 Substitutes @code{X}, but only if the @samp{-S} switch was given to GCC@.
5012 @item %@{!@code{S}:@code{X}@}
5013 Substitutes @code{X}, but only if the @samp{-S} switch was @emph{not} given to GCC@.
5015 @item %@{|@code{S}:@code{X}@}
5016 Like %@{@code{S}:@code{X}@}, but if no @code{S} switch, substitute @samp{-}.
5018 @item %@{|!@code{S}:@code{X}@}
5019 Like %@{!@code{S}:@code{X}@}, but if there is an @code{S} switch, substitute @samp{-}.
5021 @item %@{.@code{S}:@code{X}@}
5022 Substitutes @code{X}, but only if processing a file with suffix @code{S}.
5024 @item %@{!.@code{S}:@code{X}@}
5025 Substitutes @code{X}, but only if @emph{not} processing a file with suffix @code{S}.
5027 @item %@{@code{S}|@code{P}:@code{X}@}
5028 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@. This may be
5029 combined with @samp{!} and @samp{.} sequences as well, although they
5030 have a stronger binding than the @samp{|}. For example a spec string
5034 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
5037 will output the following command-line options from the following input
5038 command-line options:
5043 -d fred.c -foo -baz -boggle
5044 -d jim.d -bar -baz -boggle
5049 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or
5050 %@{!@code{S}:@code{X}@} construct may contain other nested @samp{%} constructs
5051 or spaces, or even newlines. They are processed as usual, as described
5054 The @option{-O}, @option{-f}, @option{-m}, and @option{-W}
5055 switches are handled specifically in these
5056 constructs. If another value of @option{-O} or the negated form of a @option{-f}, @option{-m}, or
5057 @option{-W} switch is found later in the command line, the earlier switch
5058 value is ignored, except with @{@code{S}*@} where @code{S} is just one
5059 letter, which passes all matching options.
5061 The character @samp{|} at the beginning of the predicate text is used to indicate
5062 that a command should be piped to the following command, but only if @option{-pipe}
5065 It is built into GCC which switches take arguments and which do not.
5066 (You might think it would be useful to generalize this to allow each
5067 compiler's spec to say which switches take arguments. But this cannot
5068 be done in a consistent fashion. GCC cannot even decide which input
5069 files have been specified without knowing which switches take arguments,
5070 and it must know which input files to compile in order to tell which
5073 GCC also knows implicitly that arguments starting in @option{-l} are to be
5074 treated as compiler output files, and passed to the linker in their
5075 proper position among the other output files.
5077 @c man begin OPTIONS
5079 @node Target Options
5080 @section Specifying Target Machine and Compiler Version
5081 @cindex target options
5082 @cindex cross compiling
5083 @cindex specifying machine version
5084 @cindex specifying compiler version and target machine
5085 @cindex compiler version, specifying
5086 @cindex target machine, specifying
5088 The usual way to run GCC is to run the executable called @file{gcc}, or
5089 @file{<machine>-gcc} when cross-compiling, or
5090 @file{<machine>-gcc-<version>} to run a version other than the one that
5091 was installed last. Sometimes this is inconvenient, so GCC provides
5092 options that will switch to another cross-compiler or version.
5095 @item -b @var{machine}
5097 The argument @var{machine} specifies the target machine for compilation.
5099 The value to use for @var{machine} is the same as was specified as the
5100 machine type when configuring GCC as a cross-compiler. For
5101 example, if a cross-compiler was configured with @samp{configure
5102 i386v}, meaning to compile for an 80386 running System V, then you
5103 would specify @option{-b i386v} to run that cross compiler.
5105 @item -V @var{version}
5107 The argument @var{version} specifies which version of GCC to run.
5108 This is useful when multiple versions are installed. For example,
5109 @var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
5112 The @option{-V} and @option{-b} options work by running the
5113 @file{<machine>-gcc-<version>} executable, so there's no real reason to
5114 use them if you can just run that directly.
5116 @node Submodel Options
5117 @section Hardware Models and Configurations
5118 @cindex submodel options
5119 @cindex specifying hardware config
5120 @cindex hardware models and configurations, specifying
5121 @cindex machine dependent options
5123 Earlier we discussed the standard option @option{-b} which chooses among
5124 different installed compilers for completely different target
5125 machines, such as VAX vs.@: 68000 vs.@: 80386.
5127 In addition, each of these target machine types can have its own
5128 special options, starting with @samp{-m}, to choose among various
5129 hardware models or configurations---for example, 68010 vs 68020,
5130 floating coprocessor or none. A single installed version of the
5131 compiler can compile for any model or configuration, according to the
5134 Some configurations of the compiler also support additional special
5135 options, usually for compatibility with other compilers on the same
5138 These options are defined by the macro @code{TARGET_SWITCHES} in the
5139 machine description. The default for the options is also defined by
5140 that macro, which enables you to change the defaults.
5154 * RS/6000 and PowerPC Options::
5157 * i386 and x86-64 Options::
5159 * Intel 960 Options::
5160 * DEC Alpha Options::
5161 * DEC Alpha/VMS Options::
5165 * System V Options::
5166 * TMS320C3x/C4x Options::
5174 * S/390 and zSeries Options::
5178 * Xstormy16 Options::
5182 @node M680x0 Options
5183 @subsection M680x0 Options
5184 @cindex M680x0 options
5186 These are the @samp{-m} options defined for the 68000 series. The default
5187 values for these options depends on which style of 68000 was selected when
5188 the compiler was configured; the defaults for the most common choices are
5196 Generate output for a 68000. This is the default
5197 when the compiler is configured for 68000-based systems.
5199 Use this option for microcontrollers with a 68000 or EC000 core,
5200 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
5206 Generate output for a 68020. This is the default
5207 when the compiler is configured for 68020-based systems.
5211 Generate output containing 68881 instructions for floating point.
5212 This is the default for most 68020 systems unless @option{--nfp} was
5213 specified when the compiler was configured.
5217 Generate output for a 68030. This is the default when the compiler is
5218 configured for 68030-based systems.
5222 Generate output for a 68040. This is the default when the compiler is
5223 configured for 68040-based systems.
5225 This option inhibits the use of 68881/68882 instructions that have to be
5226 emulated by software on the 68040. Use this option if your 68040 does not
5227 have code to emulate those instructions.
5231 Generate output for a 68060. This is the default when the compiler is
5232 configured for 68060-based systems.
5234 This option inhibits the use of 68020 and 68881/68882 instructions that
5235 have to be emulated by software on the 68060. Use this option if your 68060
5236 does not have code to emulate those instructions.
5240 Generate output for a CPU32. This is the default
5241 when the compiler is configured for CPU32-based systems.
5243 Use this option for microcontrollers with a
5244 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
5245 68336, 68340, 68341, 68349 and 68360.
5249 Generate output for a 520X ``coldfire'' family cpu. This is the default
5250 when the compiler is configured for 520X-based systems.
5252 Use this option for microcontroller with a 5200 core, including
5253 the MCF5202, MCF5203, MCF5204 and MCF5202.
5258 Generate output for a 68040, without using any of the new instructions.
5259 This results in code which can run relatively efficiently on either a
5260 68020/68881 or a 68030 or a 68040. The generated code does use the
5261 68881 instructions that are emulated on the 68040.
5265 Generate output for a 68060, without using any of the new instructions.
5266 This results in code which can run relatively efficiently on either a
5267 68020/68881 or a 68030 or a 68040. The generated code does use the
5268 68881 instructions that are emulated on the 68060.
5272 Generate output containing Sun FPA instructions for floating point.
5275 @opindex msoft-float
5276 Generate output containing library calls for floating point.
5277 @strong{Warning:} the requisite libraries are not available for all m68k
5278 targets. Normally the facilities of the machine's usual C compiler are
5279 used, but this can't be done directly in cross-compilation. You must
5280 make your own arrangements to provide suitable library functions for
5281 cross-compilation. The embedded targets @samp{m68k-*-aout} and
5282 @samp{m68k-*-coff} do provide software floating point support.
5286 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5289 @opindex mnobitfield
5290 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
5291 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
5295 Do use the bit-field instructions. The @option{-m68020} option implies
5296 @option{-mbitfield}. This is the default if you use a configuration
5297 designed for a 68020.
5301 Use a different function-calling convention, in which functions
5302 that take a fixed number of arguments return with the @code{rtd}
5303 instruction, which pops their arguments while returning. This
5304 saves one instruction in the caller since there is no need to pop
5305 the arguments there.
5307 This calling convention is incompatible with the one normally
5308 used on Unix, so you cannot use it if you need to call libraries
5309 compiled with the Unix compiler.
5311 Also, you must provide function prototypes for all functions that
5312 take variable numbers of arguments (including @code{printf});
5313 otherwise incorrect code will be generated for calls to those
5316 In addition, seriously incorrect code will result if you call a
5317 function with too many arguments. (Normally, extra arguments are
5318 harmlessly ignored.)
5320 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
5321 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
5324 @itemx -mno-align-int
5326 @opindex mno-align-int
5327 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
5328 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
5329 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
5330 Aligning variables on 32-bit boundaries produces code that runs somewhat
5331 faster on processors with 32-bit busses at the expense of more memory.
5333 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
5334 align structures containing the above types differently than
5335 most published application binary interface specifications for the m68k.
5339 Use the pc-relative addressing mode of the 68000 directly, instead of
5340 using a global offset table. At present, this option implies @option{-fpic},
5341 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
5342 not presently supported with @option{-mpcrel}, though this could be supported for
5343 68020 and higher processors.
5345 @item -mno-strict-align
5346 @itemx -mstrict-align
5347 @opindex mno-strict-align
5348 @opindex mstrict-align
5349 Do not (do) assume that unaligned memory references will be handled by
5354 @node M68hc1x Options
5355 @subsection M68hc1x Options
5356 @cindex M68hc1x options
5358 These are the @samp{-m} options defined for the 68hc11 and 68hc12
5359 microcontrollers. The default values for these options depends on
5360 which style of microcontroller was selected when the compiler was configured;
5361 the defaults for the most common choices are given below.
5368 Generate output for a 68HC11. This is the default
5369 when the compiler is configured for 68HC11-based systems.
5375 Generate output for a 68HC12. This is the default
5376 when the compiler is configured for 68HC12-based systems.
5379 @opindex mauto-incdec
5380 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
5387 Enable the use of 68HC12 min and max instructions.
5390 @itemx -mno-long-calls
5391 @opindex mlong-calls
5392 @opindex mno-long-calls
5393 Treat all calls as being far away (near). If calls are assumed to be
5394 far away, the compiler will use the @code{call} instruction to
5395 call a function and the @code{rtc} instruction for returning.
5399 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5401 @item -msoft-reg-count=@var{count}
5402 @opindex msoft-reg-count
5403 Specify the number of pseudo-soft registers which are used for the
5404 code generation. The maximum number is 32. Using more pseudo-soft
5405 register may or may not result in better code depending on the program.
5406 The default is 4 for 68HC11 and 2 for 68HC12.
5411 @subsection VAX Options
5414 These @samp{-m} options are defined for the VAX:
5419 Do not output certain jump instructions (@code{aobleq} and so on)
5420 that the Unix assembler for the VAX cannot handle across long
5425 Do output those jump instructions, on the assumption that you
5426 will assemble with the GNU assembler.
5430 Output code for g-format floating point numbers instead of d-format.
5434 @subsection SPARC Options
5435 @cindex SPARC options
5437 These @samp{-m} switches are supported on the SPARC:
5442 @opindex mno-app-regs
5444 Specify @option{-mapp-regs} to generate output using the global registers
5445 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
5448 To be fully SVR4 ABI compliant at the cost of some performance loss,
5449 specify @option{-mno-app-regs}. You should compile libraries and system
5450 software with this option.
5455 @opindex mhard-float
5456 Generate output containing floating point instructions. This is the
5462 @opindex msoft-float
5463 Generate output containing library calls for floating point.
5464 @strong{Warning:} the requisite libraries are not available for all SPARC
5465 targets. Normally the facilities of the machine's usual C compiler are
5466 used, but this cannot be done directly in cross-compilation. You must make
5467 your own arrangements to provide suitable library functions for
5468 cross-compilation. The embedded targets @samp{sparc-*-aout} and
5469 @samp{sparclite-*-*} do provide software floating point support.
5471 @option{-msoft-float} changes the calling convention in the output file;
5472 therefore, it is only useful if you compile @emph{all} of a program with
5473 this option. In particular, you need to compile @file{libgcc.a}, the
5474 library that comes with GCC, with @option{-msoft-float} in order for
5477 @item -mhard-quad-float
5478 @opindex mhard-quad-float
5479 Generate output containing quad-word (long double) floating point
5482 @item -msoft-quad-float
5483 @opindex msoft-quad-float
5484 Generate output containing library calls for quad-word (long double)
5485 floating point instructions. The functions called are those specified
5486 in the SPARC ABI@. This is the default.
5488 As of this writing, there are no sparc implementations that have hardware
5489 support for the quad-word floating point instructions. They all invoke
5490 a trap handler for one of these instructions, and then the trap handler
5491 emulates the effect of the instruction. Because of the trap handler overhead,
5492 this is much slower than calling the ABI library routines. Thus the
5493 @option{-msoft-quad-float} option is the default.
5499 With @option{-mflat}, the compiler does not generate save/restore instructions
5500 and will use a ``flat'' or single register window calling convention.
5501 This model uses %i7 as the frame pointer and is compatible with the normal
5502 register window model. Code from either may be intermixed.
5503 The local registers and the input registers (0--5) are still treated as
5504 ``call saved'' registers and will be saved on the stack as necessary.
5506 With @option{-mno-flat} (the default), the compiler emits save/restore
5507 instructions (except for leaf functions) and is the normal mode of operation.
5509 @item -mno-unaligned-doubles
5510 @itemx -munaligned-doubles
5511 @opindex mno-unaligned-doubles
5512 @opindex munaligned-doubles
5513 Assume that doubles have 8 byte alignment. This is the default.
5515 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
5516 alignment only if they are contained in another type, or if they have an
5517 absolute address. Otherwise, it assumes they have 4 byte alignment.
5518 Specifying this option avoids some rare compatibility problems with code
5519 generated by other compilers. It is not the default because it results
5520 in a performance loss, especially for floating point code.
5522 @item -mno-faster-structs
5523 @itemx -mfaster-structs
5524 @opindex mno-faster-structs
5525 @opindex mfaster-structs
5526 With @option{-mfaster-structs}, the compiler assumes that structures
5527 should have 8 byte alignment. This enables the use of pairs of
5528 @code{ldd} and @code{std} instructions for copies in structure
5529 assignment, in place of twice as many @code{ld} and @code{st} pairs.
5530 However, the use of this changed alignment directly violates the SPARC
5531 ABI@. Thus, it's intended only for use on targets where the developer
5532 acknowledges that their resulting code will not be directly in line with
5533 the rules of the ABI@.
5539 These two options select variations on the SPARC architecture.
5541 By default (unless specifically configured for the Fujitsu SPARClite),
5542 GCC generates code for the v7 variant of the SPARC architecture.
5544 @option{-mv8} will give you SPARC v8 code. The only difference from v7
5545 code is that the compiler emits the integer multiply and integer
5546 divide instructions which exist in SPARC v8 but not in SPARC v7.
5548 @option{-msparclite} will give you SPARClite code. This adds the integer
5549 multiply, integer divide step and scan (@code{ffs}) instructions which
5550 exist in SPARClite but not in SPARC v7.
5552 These options are deprecated and will be deleted in a future GCC release.
5553 They have been replaced with @option{-mcpu=xxx}.
5558 @opindex msupersparc
5559 These two options select the processor for which the code is optimized.
5561 With @option{-mcypress} (the default), the compiler optimizes code for the
5562 Cypress CY7C602 chip, as used in the SPARCStation/SPARCServer 3xx series.
5563 This is also appropriate for the older SPARCStation 1, 2, IPX etc.
5565 With @option{-msupersparc} the compiler optimizes code for the SuperSPARC cpu, as
5566 used in the SPARCStation 10, 1000 and 2000 series. This flag also enables use
5567 of the full SPARC v8 instruction set.
5569 These options are deprecated and will be deleted in a future GCC release.
5570 They have been replaced with @option{-mcpu=xxx}.
5572 @item -mcpu=@var{cpu_type}
5574 Set the instruction set, register set, and instruction scheduling parameters
5575 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
5576 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
5577 @samp{hypersparc}, @samp{sparclite86x}, @samp{f930}, @samp{f934},
5578 @samp{sparclet}, @samp{tsc701}, @samp{v9}, and @samp{ultrasparc}.
5580 Default instruction scheduling parameters are used for values that select
5581 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
5582 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
5584 Here is a list of each supported architecture and their supported
5589 v8: supersparc, hypersparc
5590 sparclite: f930, f934, sparclite86x
5595 @item -mtune=@var{cpu_type}
5597 Set the instruction scheduling parameters for machine type
5598 @var{cpu_type}, but do not set the instruction set or register set that the
5599 option @option{-mcpu=@var{cpu_type}} would.
5601 The same values for @option{-mcpu=@var{cpu_type}} can be used for
5602 @option{-mtune=@var{cpu_type}}, but the only useful values are those
5603 that select a particular cpu implementation. Those are @samp{cypress},
5604 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
5605 @samp{sparclite86x}, @samp{tsc701}, and @samp{ultrasparc}.
5609 These @samp{-m} switches are supported in addition to the above
5610 on the SPARCLET processor.
5613 @item -mlittle-endian
5614 @opindex mlittle-endian
5615 Generate code for a processor running in little-endian mode.
5619 Treat register @code{%g0} as a normal register.
5620 GCC will continue to clobber it as necessary but will not assume
5621 it always reads as 0.
5623 @item -mbroken-saverestore
5624 @opindex mbroken-saverestore
5625 Generate code that does not use non-trivial forms of the @code{save} and
5626 @code{restore} instructions. Early versions of the SPARCLET processor do
5627 not correctly handle @code{save} and @code{restore} instructions used with
5628 arguments. They correctly handle them used without arguments. A @code{save}
5629 instruction used without arguments increments the current window pointer
5630 but does not allocate a new stack frame. It is assumed that the window
5631 overflow trap handler will properly handle this case as will interrupt
5635 These @samp{-m} switches are supported in addition to the above
5636 on SPARC V9 processors in 64-bit environments.
5639 @item -mlittle-endian
5640 @opindex mlittle-endian
5641 Generate code for a processor running in little-endian mode.
5647 Generate code for a 32-bit or 64-bit environment.
5648 The 32-bit environment sets int, long and pointer to 32 bits.
5649 The 64-bit environment sets int to 32 bits and long and pointer
5652 @item -mcmodel=medlow
5653 @opindex mcmodel=medlow
5654 Generate code for the Medium/Low code model: the program must be linked
5655 in the low 32 bits of the address space. Pointers are 64 bits.
5656 Programs can be statically or dynamically linked.
5658 @item -mcmodel=medmid
5659 @opindex mcmodel=medmid
5660 Generate code for the Medium/Middle code model: the program must be linked
5661 in the low 44 bits of the address space, the text segment must be less than
5662 2G bytes, and data segment must be within 2G of the text segment.
5663 Pointers are 64 bits.
5665 @item -mcmodel=medany
5666 @opindex mcmodel=medany
5667 Generate code for the Medium/Anywhere code model: the program may be linked
5668 anywhere in the address space, the text segment must be less than
5669 2G bytes, and data segment must be within 2G of the text segment.
5670 Pointers are 64 bits.
5672 @item -mcmodel=embmedany
5673 @opindex mcmodel=embmedany
5674 Generate code for the Medium/Anywhere code model for embedded systems:
5675 assume a 32-bit text and a 32-bit data segment, both starting anywhere
5676 (determined at link time). Register %g4 points to the base of the
5677 data segment. Pointers are still 64 bits.
5678 Programs are statically linked, PIC is not supported.
5681 @itemx -mno-stack-bias
5682 @opindex mstack-bias
5683 @opindex mno-stack-bias
5684 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
5685 frame pointer if present, are offset by @minus{}2047 which must be added back
5686 when making stack frame references.
5687 Otherwise, assume no such offset is present.
5690 @node Convex Options
5691 @subsection Convex Options
5692 @cindex Convex options
5694 These @samp{-m} options are defined for Convex:
5699 Generate output for C1. The code will run on any Convex machine.
5700 The preprocessor symbol @code{__convex__c1__} is defined.
5704 Generate output for C2. Uses instructions not available on C1.
5705 Scheduling and other optimizations are chosen for max performance on C2.
5706 The preprocessor symbol @code{__convex_c2__} is defined.
5710 Generate output for C32xx. Uses instructions not available on C1.
5711 Scheduling and other optimizations are chosen for max performance on C32.
5712 The preprocessor symbol @code{__convex_c32__} is defined.
5716 Generate output for C34xx. Uses instructions not available on C1.
5717 Scheduling and other optimizations are chosen for max performance on C34.
5718 The preprocessor symbol @code{__convex_c34__} is defined.
5722 Generate output for C38xx. Uses instructions not available on C1.
5723 Scheduling and other optimizations are chosen for max performance on C38.
5724 The preprocessor symbol @code{__convex_c38__} is defined.
5728 Generate code which puts an argument count in the word preceding each
5729 argument list. This is compatible with regular CC, and a few programs
5730 may need the argument count word. GDB and other source-level debuggers
5731 do not need it; this info is in the symbol table.
5734 @opindex mnoargcount
5735 Omit the argument count word. This is the default.
5737 @item -mvolatile-cache
5738 @opindex mvolatile-cache
5739 Allow volatile references to be cached. This is the default.
5741 @item -mvolatile-nocache
5742 @opindex mvolatile-nocache
5743 Volatile references bypass the data cache, going all the way to memory.
5744 This is only needed for multi-processor code that does not use standard
5745 synchronization instructions. Making non-volatile references to volatile
5746 locations will not necessarily work.
5750 Type long is 32 bits, the same as type int. This is the default.
5754 Type long is 64 bits, the same as type long long. This option is useless,
5755 because no library support exists for it.
5758 @node AMD29K Options
5759 @subsection AMD29K Options
5760 @cindex AMD29K options
5762 These @samp{-m} options are defined for the AMD Am29000:
5767 @cindex DW bit (29k)
5768 Generate code that assumes the @code{DW} bit is set, i.e., that byte and
5769 halfword operations are directly supported by the hardware. This is the
5774 Generate code that assumes the @code{DW} bit is not set.
5778 @cindex byte writes (29k)
5779 Generate code that assumes the system supports byte and halfword write
5780 operations. This is the default.
5784 Generate code that assumes the systems does not support byte and
5785 halfword write operations. @option{-mnbw} implies @option{-mndw}.
5789 @cindex memory model (29k)
5790 Use a small memory model that assumes that all function addresses are
5791 either within a single 256 KB segment or at an absolute address of less
5792 than 256k. This allows the @code{call} instruction to be used instead
5793 of a @code{const}, @code{consth}, @code{calli} sequence.
5797 Use the normal memory model: Generate @code{call} instructions only when
5798 calling functions in the same file and @code{calli} instructions
5799 otherwise. This works if each file occupies less than 256 KB but allows
5800 the entire executable to be larger than 256 KB@. This is the default.
5804 Always use @code{calli} instructions. Specify this option if you expect
5805 a single file to compile into more than 256 KB of code.
5809 @cindex processor selection (29k)
5810 Generate code for the Am29050.
5814 Generate code for the Am29000. This is the default.
5816 @item -mkernel-registers
5817 @opindex mkernel-registers
5818 @cindex kernel and user registers (29k)
5819 Generate references to registers @code{gr64-gr95} instead of to
5820 registers @code{gr96-gr127}. This option can be used when compiling
5821 kernel code that wants a set of global registers disjoint from that used
5824 Note that when this option is used, register names in @samp{-f} flags
5825 must use the normal, user-mode, names.
5827 @item -muser-registers
5828 @opindex muser-registers
5829 Use the normal set of global registers, @code{gr96-gr127}. This is the
5833 @itemx -mno-stack-check
5834 @opindex mstack-check
5835 @opindex mno-stack-check
5836 @cindex stack checks (29k)
5837 Insert (or do not insert) a call to @code{__msp_check} after each stack
5838 adjustment. This is often used for kernel code.
5841 @itemx -mno-storem-bug
5842 @opindex mstorem-bug
5843 @opindex mno-storem-bug
5844 @cindex storem bug (29k)
5845 @option{-mstorem-bug} handles 29k processors which cannot handle the
5846 separation of a mtsrim insn and a storem instruction (most 29000 chips
5847 to date, but not the 29050).
5849 @item -mno-reuse-arg-regs
5850 @itemx -mreuse-arg-regs
5851 @opindex mno-reuse-arg-regs
5852 @opindex mreuse-arg-regs
5853 @option{-mno-reuse-arg-regs} tells the compiler to only use incoming argument
5854 registers for copying out arguments. This helps detect calling a function
5855 with fewer arguments than it was declared with.
5857 @item -mno-impure-text
5858 @itemx -mimpure-text
5859 @opindex mno-impure-text
5860 @opindex mimpure-text
5861 @option{-mimpure-text}, used in addition to @option{-shared}, tells the compiler to
5862 not pass @option{-assert pure-text} to the linker when linking a shared object.
5865 @opindex msoft-float
5866 Generate output containing library calls for floating point.
5867 @strong{Warning:} the requisite libraries are not part of GCC@.
5868 Normally the facilities of the machine's usual C compiler are used, but
5869 this can't be done directly in cross-compilation. You must make your
5870 own arrangements to provide suitable library functions for
5875 Do not generate multm or multmu instructions. This is useful for some embedded
5876 systems which do not have trap handlers for these instructions.
5880 @subsection ARM Options
5883 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
5888 @opindex mapcs-frame
5889 Generate a stack frame that is compliant with the ARM Procedure Call
5890 Standard for all functions, even if this is not strictly necessary for
5891 correct execution of the code. Specifying @option{-fomit-frame-pointer}
5892 with this option will cause the stack frames not to be generated for
5893 leaf functions. The default is @option{-mno-apcs-frame}.
5897 This is a synonym for @option{-mapcs-frame}.
5901 Generate code for a processor running with a 26-bit program counter,
5902 and conforming to the function calling standards for the APCS 26-bit
5903 option. This option replaces the @option{-m2} and @option{-m3} options
5904 of previous releases of the compiler.
5908 Generate code for a processor running with a 32-bit program counter,
5909 and conforming to the function calling standards for the APCS 32-bit
5910 option. This option replaces the @option{-m6} option of previous releases
5914 @c not currently implemented
5915 @item -mapcs-stack-check
5916 @opindex mapcs-stack-check
5917 Generate code to check the amount of stack space available upon entry to
5918 every function (that actually uses some stack space). If there is
5919 insufficient space available then either the function
5920 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
5921 called, depending upon the amount of stack space required. The run time
5922 system is required to provide these functions. The default is
5923 @option{-mno-apcs-stack-check}, since this produces smaller code.
5925 @c not currently implemented
5927 @opindex mapcs-float
5928 Pass floating point arguments using the float point registers. This is
5929 one of the variants of the APCS@. This option is recommended if the
5930 target hardware has a floating point unit or if a lot of floating point
5931 arithmetic is going to be performed by the code. The default is
5932 @option{-mno-apcs-float}, since integer only code is slightly increased in
5933 size if @option{-mapcs-float} is used.
5935 @c not currently implemented
5936 @item -mapcs-reentrant
5937 @opindex mapcs-reentrant
5938 Generate reentrant, position independent code. The default is
5939 @option{-mno-apcs-reentrant}.
5942 @item -mthumb-interwork
5943 @opindex mthumb-interwork
5944 Generate code which supports calling between the ARM and Thumb
5945 instruction sets. Without this option the two instruction sets cannot
5946 be reliably used inside one program. The default is
5947 @option{-mno-thumb-interwork}, since slightly larger code is generated
5948 when @option{-mthumb-interwork} is specified.
5950 @item -mno-sched-prolog
5951 @opindex mno-sched-prolog
5952 Prevent the reordering of instructions in the function prolog, or the
5953 merging of those instruction with the instructions in the function's
5954 body. This means that all functions will start with a recognizable set
5955 of instructions (or in fact one of a choice from a small set of
5956 different function prologues), and this information can be used to
5957 locate the start if functions inside an executable piece of code. The
5958 default is @option{-msched-prolog}.
5961 @opindex mhard-float
5962 Generate output containing floating point instructions. This is the
5966 @opindex msoft-float
5967 Generate output containing library calls for floating point.
5968 @strong{Warning:} the requisite libraries are not available for all ARM
5969 targets. Normally the facilities of the machine's usual C compiler are
5970 used, but this cannot be done directly in cross-compilation. You must make
5971 your own arrangements to provide suitable library functions for
5974 @option{-msoft-float} changes the calling convention in the output file;
5975 therefore, it is only useful if you compile @emph{all} of a program with
5976 this option. In particular, you need to compile @file{libgcc.a}, the
5977 library that comes with GCC, with @option{-msoft-float} in order for
5980 @item -mlittle-endian
5981 @opindex mlittle-endian
5982 Generate code for a processor running in little-endian mode. This is
5983 the default for all standard configurations.
5986 @opindex mbig-endian
5987 Generate code for a processor running in big-endian mode; the default is
5988 to compile code for a little-endian processor.
5990 @item -mwords-little-endian
5991 @opindex mwords-little-endian
5992 This option only applies when generating code for big-endian processors.
5993 Generate code for a little-endian word order but a big-endian byte
5994 order. That is, a byte order of the form @samp{32107654}. Note: this
5995 option should only be used if you require compatibility with code for
5996 big-endian ARM processors generated by versions of the compiler prior to
5999 @item -malignment-traps
6000 @opindex malignment-traps
6001 Generate code that will not trap if the MMU has alignment traps enabled.
6002 On ARM architectures prior to ARMv4, there were no instructions to
6003 access half-word objects stored in memory. However, when reading from
6004 memory a feature of the ARM architecture allows a word load to be used,
6005 even if the address is unaligned, and the processor core will rotate the
6006 data as it is being loaded. This option tells the compiler that such
6007 misaligned accesses will cause a MMU trap and that it should instead
6008 synthesize the access as a series of byte accesses. The compiler can
6009 still use word accesses to load half-word data if it knows that the
6010 address is aligned to a word boundary.
6012 This option is ignored when compiling for ARM architecture 4 or later,
6013 since these processors have instructions to directly access half-word
6016 @item -mno-alignment-traps
6017 @opindex mno-alignment-traps
6018 Generate code that assumes that the MMU will not trap unaligned
6019 accesses. This produces better code when the target instruction set
6020 does not have half-word memory operations (i.e.@: implementations prior to
6023 Note that you cannot use this option to access unaligned word objects,
6024 since the processor will only fetch one 32-bit aligned object from
6027 The default setting for most targets is @option{-mno-alignment-traps}, since
6028 this produces better code when there are no half-word memory
6029 instructions available.
6031 @item -mshort-load-bytes
6032 @itemx -mno-short-load-words
6033 @opindex mshort-load-bytes
6034 @opindex mno-short-load-words
6035 These are deprecated aliases for @option{-malignment-traps}.
6037 @item -mno-short-load-bytes
6038 @itemx -mshort-load-words
6039 @opindex mno-short-load-bytes
6040 @opindex mshort-load-words
6041 This are deprecated aliases for @option{-mno-alignment-traps}.
6045 This option only applies to RISC iX@. Emulate the native BSD-mode
6046 compiler. This is the default if @option{-ansi} is not specified.
6050 This option only applies to RISC iX@. Emulate the native X/Open-mode
6053 @item -mno-symrename
6054 @opindex mno-symrename
6055 This option only applies to RISC iX@. Do not run the assembler
6056 post-processor, @samp{symrename}, after code has been assembled.
6057 Normally it is necessary to modify some of the standard symbols in
6058 preparation for linking with the RISC iX C library; this option
6059 suppresses this pass. The post-processor is never run when the
6060 compiler is built for cross-compilation.
6062 @item -mcpu=@var{name}
6064 This specifies the name of the target ARM processor. GCC uses this name
6065 to determine what kind of instructions it can emit when generating
6066 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
6067 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
6068 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
6069 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
6070 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
6071 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm8},
6072 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
6073 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
6074 @samp{arm920t}, @samp{arm940t}, @samp{arm9tdmi}, @samp{arm10tdmi},
6075 @samp{arm1020t}, @samp{xscale}.
6077 @itemx -mtune=@var{name}
6079 This option is very similar to the @option{-mcpu=} option, except that
6080 instead of specifying the actual target processor type, and hence
6081 restricting which instructions can be used, it specifies that GCC should
6082 tune the performance of the code as if the target were of the type
6083 specified in this option, but still choosing the instructions that it
6084 will generate based on the cpu specified by a @option{-mcpu=} option.
6085 For some ARM implementations better performance can be obtained by using
6088 @item -march=@var{name}
6090 This specifies the name of the target ARM architecture. GCC uses this
6091 name to determine what kind of instructions it can emit when generating
6092 assembly code. This option can be used in conjunction with or instead
6093 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
6094 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
6095 @samp{armv5}, @samp{armv5t}, @samp{armv5te}.
6097 @item -mfpe=@var{number}
6098 @itemx -mfp=@var{number}
6101 This specifies the version of the floating point emulation available on
6102 the target. Permissible values are 2 and 3. @option{-mfp=} is a synonym
6103 for @option{-mfpe=}, for compatibility with older versions of GCC@.
6105 @item -mstructure-size-boundary=@var{n}
6106 @opindex mstructure-size-boundary
6107 The size of all structures and unions will be rounded up to a multiple
6108 of the number of bits set by this option. Permissible values are 8 and
6109 32. The default value varies for different toolchains. For the COFF
6110 targeted toolchain the default value is 8. Specifying the larger number
6111 can produce faster, more efficient code, but can also increase the size
6112 of the program. The two values are potentially incompatible. Code
6113 compiled with one value cannot necessarily expect to work with code or
6114 libraries compiled with the other value, if they exchange information
6115 using structures or unions.
6117 @item -mabort-on-noreturn
6118 @opindex mabort-on-noreturn
6119 Generate a call to the function @code{abort} at the end of a
6120 @code{noreturn} function. It will be executed if the function tries to
6124 @itemx -mno-long-calls
6125 @opindex mlong-calls
6126 @opindex mno-long-calls
6127 Tells the compiler to perform function calls by first loading the
6128 address of the function into a register and then performing a subroutine
6129 call on this register. This switch is needed if the target function
6130 will lie outside of the 64 megabyte addressing range of the offset based
6131 version of subroutine call instruction.
6133 Even if this switch is enabled, not all function calls will be turned
6134 into long calls. The heuristic is that static functions, functions
6135 which have the @samp{short-call} attribute, functions that are inside
6136 the scope of a @samp{#pragma no_long_calls} directive and functions whose
6137 definitions have already been compiled within the current compilation
6138 unit, will not be turned into long calls. The exception to this rule is
6139 that weak function definitions, functions with the @samp{long-call}
6140 attribute or the @samp{section} attribute, and functions that are within
6141 the scope of a @samp{#pragma long_calls} directive, will always be
6142 turned into long calls.
6144 This feature is not enabled by default. Specifying
6145 @option{-mno-long-calls} will restore the default behavior, as will
6146 placing the function calls within the scope of a @samp{#pragma
6147 long_calls_off} directive. Note these switches have no effect on how
6148 the compiler generates code to handle function calls via function
6151 @item -mnop-fun-dllimport
6152 @opindex mnop-fun-dllimport
6153 Disable support for the @code{dllimport} attribute.
6155 @item -msingle-pic-base
6156 @opindex msingle-pic-base
6157 Treat the register used for PIC addressing as read-only, rather than
6158 loading it in the prologue for each function. The run-time system is
6159 responsible for initializing this register with an appropriate value
6160 before execution begins.
6162 @item -mpic-register=@var{reg}
6163 @opindex mpic-register
6164 Specify the register to be used for PIC addressing. The default is R10
6165 unless stack-checking is enabled, when R9 is used.
6167 @item -mpoke-function-name
6168 @opindex mpoke-function-name
6169 Write the name of each function into the text section, directly
6170 preceding the function prologue. The generated code is similar to this:
6174 .ascii "arm_poke_function_name", 0
6177 .word 0xff000000 + (t1 - t0)
6178 arm_poke_function_name
6180 stmfd sp!, @{fp, ip, lr, pc@}
6184 When performing a stack backtrace, code can inspect the value of
6185 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
6186 location @code{pc - 12} and the top 8 bits are set, then we know that
6187 there is a function name embedded immediately preceding this location
6188 and has length @code{((pc[-3]) & 0xff000000)}.
6192 Generate code for the 16-bit Thumb instruction set. The default is to
6193 use the 32-bit ARM instruction set.
6196 @opindex mtpcs-frame
6197 Generate a stack frame that is compliant with the Thumb Procedure Call
6198 Standard for all non-leaf functions. (A leaf function is one that does
6199 not call any other functions.) The default is @option{-mno-tpcs-frame}.
6201 @item -mtpcs-leaf-frame
6202 @opindex mtpcs-leaf-frame
6203 Generate a stack frame that is compliant with the Thumb Procedure Call
6204 Standard for all leaf functions. (A leaf function is one that does
6205 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
6207 @item -mcallee-super-interworking
6208 @opindex mcallee-super-interworking
6209 Gives all externally visible functions in the file being compiled an ARM
6210 instruction set header which switches to Thumb mode before executing the
6211 rest of the function. This allows these functions to be called from
6212 non-interworking code.
6214 @item -mcaller-super-interworking
6215 @opindex mcaller-super-interworking
6216 Allows calls via function pointers (including virtual functions) to
6217 execute correctly regardless of whether the target code has been
6218 compiled for interworking or not. There is a small overhead in the cost
6219 of executing a function pointer if this option is enabled.
6223 @node MN10200 Options
6224 @subsection MN10200 Options
6225 @cindex MN10200 options
6226 These @option{-m} options are defined for Matsushita MN10200 architectures:
6231 Indicate to the linker that it should perform a relaxation optimization pass
6232 to shorten branches, calls and absolute memory addresses. This option only
6233 has an effect when used on the command line for the final link step.
6235 This option makes symbolic debugging impossible.
6238 @node MN10300 Options
6239 @subsection MN10300 Options
6240 @cindex MN10300 options
6241 These @option{-m} options are defined for Matsushita MN10300 architectures:
6246 Generate code to avoid bugs in the multiply instructions for the MN10300
6247 processors. This is the default.
6250 @opindex mno-mult-bug
6251 Do not generate code to avoid bugs in the multiply instructions for the
6256 Generate code which uses features specific to the AM33 processor.
6260 Do not generate code which uses features specific to the AM33 processor. This
6265 Do not link in the C run-time initialization object file.
6269 Indicate to the linker that it should perform a relaxation optimization pass
6270 to shorten branches, calls and absolute memory addresses. This option only
6271 has an effect when used on the command line for the final link step.
6273 This option makes symbolic debugging impossible.
6277 @node M32R/D Options
6278 @subsection M32R/D Options
6279 @cindex M32R/D options
6281 These @option{-m} options are defined for Mitsubishi M32R/D architectures:
6286 Generate code for the M32R/X@.
6290 Generate code for the M32R@. This is the default.
6292 @item -mcode-model=small
6293 @opindex mcode-model=small
6294 Assume all objects live in the lower 16MB of memory (so that their addresses
6295 can be loaded with the @code{ld24} instruction), and assume all subroutines
6296 are reachable with the @code{bl} instruction.
6297 This is the default.
6299 The addressability of a particular object can be set with the
6300 @code{model} attribute.
6302 @item -mcode-model=medium
6303 @opindex mcode-model=medium
6304 Assume objects may be anywhere in the 32-bit address space (the compiler
6305 will generate @code{seth/add3} instructions to load their addresses), and
6306 assume all subroutines are reachable with the @code{bl} instruction.
6308 @item -mcode-model=large
6309 @opindex mcode-model=large
6310 Assume objects may be anywhere in the 32-bit address space (the compiler
6311 will generate @code{seth/add3} instructions to load their addresses), and
6312 assume subroutines may not be reachable with the @code{bl} instruction
6313 (the compiler will generate the much slower @code{seth/add3/jl}
6314 instruction sequence).
6317 @opindex msdata=none
6318 Disable use of the small data area. Variables will be put into
6319 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
6320 @code{section} attribute has been specified).
6321 This is the default.
6323 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
6324 Objects may be explicitly put in the small data area with the
6325 @code{section} attribute using one of these sections.
6328 @opindex msdata=sdata
6329 Put small global and static data in the small data area, but do not
6330 generate special code to reference them.
6334 Put small global and static data in the small data area, and generate
6335 special instructions to reference them.
6339 @cindex smaller data references
6340 Put global and static objects less than or equal to @var{num} bytes
6341 into the small data or bss sections instead of the normal data or bss
6342 sections. The default value of @var{num} is 8.
6343 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
6344 for this option to have any effect.
6346 All modules should be compiled with the same @option{-G @var{num}} value.
6347 Compiling with different values of @var{num} may or may not work; if it
6348 doesn't the linker will give an error message---incorrect code will not be
6354 @subsection M88K Options
6355 @cindex M88k options
6357 These @samp{-m} options are defined for Motorola 88k architectures:
6362 Generate code that works well on both the m88100 and the
6367 Generate code that works best for the m88100, but that also
6372 Generate code that works best for the m88110, and may not run
6377 Obsolete option to be removed from the next revision.
6380 @item -midentify-revision
6381 @opindex midentify-revision
6382 @cindex identifying source, compiler (88k)
6383 Include an @code{ident} directive in the assembler output recording the
6384 source file name, compiler name and version, timestamp, and compilation
6387 @item -mno-underscores
6388 @opindex mno-underscores
6389 @cindex underscores, avoiding (88k)
6390 In assembler output, emit symbol names without adding an underscore
6391 character at the beginning of each name. The default is to use an
6392 underscore as prefix on each name.
6394 @item -mocs-debug-info
6395 @itemx -mno-ocs-debug-info
6396 @opindex mocs-debug-info
6397 @opindex mno-ocs-debug-info
6399 @cindex debugging, 88k OCS
6400 Include (or omit) additional debugging information (about registers used
6401 in each stack frame) as specified in the 88open Object Compatibility
6402 Standard, ``OCS''@. This extra information allows debugging of code that
6403 has had the frame pointer eliminated. The default for DG/UX, SVr4, and
6404 Delta 88 SVr3.2 is to include this information; other 88k configurations
6405 omit this information by default.
6407 @item -mocs-frame-position
6408 @opindex mocs-frame-position
6409 @cindex register positions in frame (88k)
6410 When emitting COFF debugging information for automatic variables and
6411 parameters stored on the stack, use the offset from the canonical frame
6412 address, which is the stack pointer (register 31) on entry to the
6413 function. The DG/UX, SVr4, Delta88 SVr3.2, and BCS configurations use
6414 @option{-mocs-frame-position}; other 88k configurations have the default
6415 @option{-mno-ocs-frame-position}.
6417 @item -mno-ocs-frame-position
6418 @opindex mno-ocs-frame-position
6419 @cindex register positions in frame (88k)
6420 When emitting COFF debugging information for automatic variables and
6421 parameters stored on the stack, use the offset from the frame pointer
6422 register (register 30). When this option is in effect, the frame
6423 pointer is not eliminated when debugging information is selected by the
6426 @item -moptimize-arg-area
6427 @opindex moptimize-arg-area
6428 @cindex arguments in frame (88k)
6429 Save space by reorganizing the stack frame. This option generates code
6430 that does not agree with the 88open specifications, but uses less
6433 @itemx -mno-optimize-arg-area
6434 @opindex mno-optimize-arg-area
6435 Do not reorganize the stack frame to save space. This is the default.
6436 The generated conforms to the specification, but uses more memory.
6438 @item -mshort-data-@var{num}
6439 @opindex mshort-data
6440 @cindex smaller data references (88k)
6441 @cindex r0-relative references (88k)
6442 Generate smaller data references by making them relative to @code{r0},
6443 which allows loading a value using a single instruction (rather than the
6444 usual two). You control which data references are affected by
6445 specifying @var{num} with this option. For example, if you specify
6446 @option{-mshort-data-512}, then the data references affected are those
6447 involving displacements of less than 512 bytes.
6448 @option{-mshort-data-@var{num}} is not effective for @var{num} greater
6451 @item -mserialize-volatile
6452 @opindex mserialize-volatile
6453 @itemx -mno-serialize-volatile
6454 @opindex mno-serialize-volatile
6455 @cindex sequential consistency on 88k
6456 Do, or don't, generate code to guarantee sequential consistency
6457 of volatile memory references. By default, consistency is
6460 The order of memory references made by the MC88110 processor does
6461 not always match the order of the instructions requesting those
6462 references. In particular, a load instruction may execute before
6463 a preceding store instruction. Such reordering violates
6464 sequential consistency of volatile memory references, when there
6465 are multiple processors. When consistency must be guaranteed,
6466 GCC generates special instructions, as needed, to force
6467 execution in the proper order.
6469 The MC88100 processor does not reorder memory references and so
6470 always provides sequential consistency. However, by default, GCC
6471 generates the special instructions to guarantee consistency
6472 even when you use @option{-m88100}, so that the code may be run on an
6473 MC88110 processor. If you intend to run your code only on the
6474 MC88100 processor, you may use @option{-mno-serialize-volatile}.
6476 The extra code generated to guarantee consistency may affect the
6477 performance of your application. If you know that you can safely
6478 forgo this guarantee, you may use @option{-mno-serialize-volatile}.
6484 @cindex assembler syntax, 88k
6486 Turn on (@option{-msvr4}) or off (@option{-msvr3}) compiler extensions
6487 related to System V release 4 (SVr4). This controls the following:
6491 Which variant of the assembler syntax to emit.
6493 @option{-msvr4} makes the C preprocessor recognize @samp{#pragma weak}
6494 that is used on System V release 4.
6496 @option{-msvr4} makes GCC issue additional declaration directives used in
6500 @option{-msvr4} is the default for the m88k-motorola-sysv4 and
6501 m88k-dg-dgux m88k configurations. @option{-msvr3} is the default for all
6502 other m88k configurations.
6504 @item -mversion-03.00
6505 @opindex mversion-03.00
6506 This option is obsolete, and is ignored.
6507 @c ??? which asm syntax better for GAS? option there too?
6509 @item -mno-check-zero-division
6510 @itemx -mcheck-zero-division
6511 @opindex mno-check-zero-division
6512 @opindex mcheck-zero-division
6513 @cindex zero division on 88k
6514 Do, or don't, generate code to guarantee that integer division by
6515 zero will be detected. By default, detection is guaranteed.
6517 Some models of the MC88100 processor fail to trap upon integer
6518 division by zero under certain conditions. By default, when
6519 compiling code that might be run on such a processor, GCC
6520 generates code that explicitly checks for zero-valued divisors
6521 and traps with exception number 503 when one is detected. Use of
6522 @option{-mno-check-zero-division} suppresses such checking for code
6523 generated to run on an MC88100 processor.
6525 GCC assumes that the MC88110 processor correctly detects all instances
6526 of integer division by zero. When @option{-m88110} is specified, no
6527 explicit checks for zero-valued divisors are generated, and both
6528 @option{-mcheck-zero-division} and @option{-mno-check-zero-division} are
6531 @item -muse-div-instruction
6532 @opindex muse-div-instruction
6533 @cindex divide instruction, 88k
6534 Use the div instruction for signed integer division on the
6535 MC88100 processor. By default, the div instruction is not used.
6537 On the MC88100 processor the signed integer division instruction
6538 div) traps to the operating system on a negative operand. The
6539 operating system transparently completes the operation, but at a
6540 large cost in execution time. By default, when compiling code
6541 that might be run on an MC88100 processor, GCC emulates signed
6542 integer division using the unsigned integer division instruction
6543 divu), thereby avoiding the large penalty of a trap to the
6544 operating system. Such emulation has its own, smaller, execution
6545 cost in both time and space. To the extent that your code's
6546 important signed integer division operations are performed on two
6547 nonnegative operands, it may be desirable to use the div
6548 instruction directly.
6550 On the MC88110 processor the div instruction (also known as the
6551 divs instruction) processes negative operands without trapping to
6552 the operating system. When @option{-m88110} is specified,
6553 @option{-muse-div-instruction} is ignored, and the div instruction is used
6554 for signed integer division.
6556 Note that the result of dividing @code{INT_MIN} by @minus{}1 is undefined. In
6557 particular, the behavior of such a division with and without
6558 @option{-muse-div-instruction} may differ.
6560 @item -mtrap-large-shift
6561 @itemx -mhandle-large-shift
6562 @opindex mtrap-large-shift
6563 @opindex mhandle-large-shift
6564 @cindex bit shift overflow (88k)
6565 @cindex large bit shifts (88k)
6566 Include code to detect bit-shifts of more than 31 bits; respectively,
6567 trap such shifts or emit code to handle them properly. By default GCC
6568 makes no special provision for large bit shifts.
6570 @item -mwarn-passed-structs
6571 @opindex mwarn-passed-structs
6572 @cindex structure passing (88k)
6573 Warn when a function passes a struct as an argument or result.
6574 Structure-passing conventions have changed during the evolution of the C
6575 language, and are often the source of portability problems. By default,
6576 GCC issues no such warning.
6579 @c break page here to avoid unsightly interparagraph stretch.
6583 @node RS/6000 and PowerPC Options
6584 @subsection IBM RS/6000 and PowerPC Options
6585 @cindex RS/6000 and PowerPC Options
6586 @cindex IBM RS/6000 and PowerPC Options
6588 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
6596 @itemx -mpowerpc-gpopt
6597 @itemx -mno-powerpc-gpopt
6598 @itemx -mpowerpc-gfxopt
6599 @itemx -mno-powerpc-gfxopt
6601 @itemx -mno-powerpc64
6607 @opindex mno-powerpc
6608 @opindex mpowerpc-gpopt
6609 @opindex mno-powerpc-gpopt
6610 @opindex mpowerpc-gfxopt
6611 @opindex mno-powerpc-gfxopt
6613 @opindex mno-powerpc64
6614 GCC supports two related instruction set architectures for the
6615 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
6616 instructions supported by the @samp{rios} chip set used in the original
6617 RS/6000 systems and the @dfn{PowerPC} instruction set is the
6618 architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
6619 the IBM 4xx microprocessors.
6621 Neither architecture is a subset of the other. However there is a
6622 large common subset of instructions supported by both. An MQ
6623 register is included in processors supporting the POWER architecture.
6625 You use these options to specify which instructions are available on the
6626 processor you are using. The default value of these options is
6627 determined when configuring GCC@. Specifying the
6628 @option{-mcpu=@var{cpu_type}} overrides the specification of these
6629 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
6630 rather than the options listed above.
6632 The @option{-mpower} option allows GCC to generate instructions that
6633 are found only in the POWER architecture and to use the MQ register.
6634 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
6635 to generate instructions that are present in the POWER2 architecture but
6636 not the original POWER architecture.
6638 The @option{-mpowerpc} option allows GCC to generate instructions that
6639 are found only in the 32-bit subset of the PowerPC architecture.
6640 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
6641 GCC to use the optional PowerPC architecture instructions in the
6642 General Purpose group, including floating-point square root. Specifying
6643 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
6644 use the optional PowerPC architecture instructions in the Graphics
6645 group, including floating-point select.
6647 The @option{-mpowerpc64} option allows GCC to generate the additional
6648 64-bit instructions that are found in the full PowerPC64 architecture
6649 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
6650 @option{-mno-powerpc64}.
6652 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
6653 will use only the instructions in the common subset of both
6654 architectures plus some special AIX common-mode calls, and will not use
6655 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
6656 permits GCC to use any instruction from either architecture and to
6657 allow use of the MQ register; specify this for the Motorola MPC601.
6659 @item -mnew-mnemonics
6660 @itemx -mold-mnemonics
6661 @opindex mnew-mnemonics
6662 @opindex mold-mnemonics
6663 Select which mnemonics to use in the generated assembler code. With
6664 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
6665 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
6666 assembler mnemonics defined for the POWER architecture. Instructions
6667 defined in only one architecture have only one mnemonic; GCC uses that
6668 mnemonic irrespective of which of these options is specified.
6670 GCC defaults to the mnemonics appropriate for the architecture in
6671 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
6672 value of these option. Unless you are building a cross-compiler, you
6673 should normally not specify either @option{-mnew-mnemonics} or
6674 @option{-mold-mnemonics}, but should instead accept the default.
6676 @item -mcpu=@var{cpu_type}
6678 Set architecture type, register usage, choice of mnemonics, and
6679 instruction scheduling parameters for machine type @var{cpu_type}.
6680 Supported values for @var{cpu_type} are @samp{rios}, @samp{rios1},
6681 @samp{rsc}, @samp{rios2}, @samp{rs64a}, @samp{601}, @samp{602},
6682 @samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620},
6683 @samp{630}, @samp{740}, @samp{7400}, @samp{7450}, @samp{750},
6684 @samp{power}, @samp{power2}, @samp{powerpc}, @samp{403}, @samp{505},
6685 @samp{801}, @samp{821}, @samp{823}, and @samp{860} and @samp{common}.
6687 @option{-mcpu=common} selects a completely generic processor. Code
6688 generated under this option will run on any POWER or PowerPC processor.
6689 GCC will use only the instructions in the common subset of both
6690 architectures, and will not use the MQ register. GCC assumes a generic
6691 processor model for scheduling purposes.
6693 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
6694 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
6695 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
6696 types, with an appropriate, generic processor model assumed for
6697 scheduling purposes.
6699 The other options specify a specific processor. Code generated under
6700 those options will run best on that processor, and may not run at all on
6703 The @option{-mcpu} options automatically enable or disable other
6704 @option{-m} options as follows:
6708 @option{-mno-power}, @option{-mno-powerc}
6715 @option{-mpower}, @option{-mno-powerpc}, @option{-mno-new-mnemonics}
6730 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}
6733 @option{-mpower}, @option{-mpowerpc}, @option{-mnew-mnemonics}
6738 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}, @option{-msoft-float}
6741 @item -mtune=@var{cpu_type}
6743 Set the instruction scheduling parameters for machine type
6744 @var{cpu_type}, but do not set the architecture type, register usage, or
6745 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
6746 values for @var{cpu_type} are used for @option{-mtune} as for
6747 @option{-mcpu}. If both are specified, the code generated will use the
6748 architecture, registers, and mnemonics set by @option{-mcpu}, but the
6749 scheduling parameters set by @option{-mtune}.
6754 @opindex mno-altivec
6755 These switches enable or disable the use of built-in functions that
6756 allow access to the AltiVec instruction set. You may also need to set
6757 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
6762 Extend the current ABI with SPE ABI extensions. This does not change
6763 the default ABI, instead it adds the SPE ABI extensions to the current
6767 @opindex mabi=no-spe
6768 Disable Booke SPE ABI extensions for the current ABI.
6770 @item -misel=@var{yes/no}
6773 This switch enables or disables the generation of ISEL instructions.
6776 @itemx -mno-fp-in-toc
6777 @itemx -mno-sum-in-toc
6778 @itemx -mminimal-toc
6780 @opindex mno-fp-in-toc
6781 @opindex mno-sum-in-toc
6782 @opindex mminimal-toc
6783 Modify generation of the TOC (Table Of Contents), which is created for
6784 every executable file. The @option{-mfull-toc} option is selected by
6785 default. In that case, GCC will allocate at least one TOC entry for
6786 each unique non-automatic variable reference in your program. GCC
6787 will also place floating-point constants in the TOC@. However, only
6788 16,384 entries are available in the TOC@.
6790 If you receive a linker error message that saying you have overflowed
6791 the available TOC space, you can reduce the amount of TOC space used
6792 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
6793 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
6794 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
6795 generate code to calculate the sum of an address and a constant at
6796 run-time instead of putting that sum into the TOC@. You may specify one
6797 or both of these options. Each causes GCC to produce very slightly
6798 slower and larger code at the expense of conserving TOC space.
6800 If you still run out of space in the TOC even when you specify both of
6801 these options, specify @option{-mminimal-toc} instead. This option causes
6802 GCC to make only one TOC entry for every file. When you specify this
6803 option, GCC will produce code that is slower and larger but which
6804 uses extremely little TOC space. You may wish to use this option
6805 only on files that contain less frequently executed code.
6811 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
6812 @code{long} type, and the infrastructure needed to support them.
6813 Specifying @option{-maix64} implies @option{-mpowerpc64} and
6814 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
6815 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
6820 @opindex mno-xl-call
6821 On AIX, pass floating-point arguments to prototyped functions beyond the
6822 register save area (RSA) on the stack in addition to argument FPRs. The
6823 AIX calling convention was extended but not initially documented to
6824 handle an obscure K&R C case of calling a function that takes the
6825 address of its arguments with fewer arguments than declared. AIX XL
6826 compilers access floating point arguments which do not fit in the
6827 RSA from the stack when a subroutine is compiled without
6828 optimization. Because always storing floating-point arguments on the
6829 stack is inefficient and rarely needed, this option is not enabled by
6830 default and only is necessary when calling subroutines compiled by AIX
6831 XL compilers without optimization.
6835 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
6836 application written to use message passing with special startup code to
6837 enable the application to run. The system must have PE installed in the
6838 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
6839 must be overridden with the @option{-specs=} option to specify the
6840 appropriate directory location. The Parallel Environment does not
6841 support threads, so the @option{-mpe} option and the @option{-pthread}
6842 option are incompatible.
6846 @opindex msoft-float
6847 @opindex mhard-float
6848 Generate code that does not use (uses) the floating-point register set.
6849 Software floating point emulation is provided if you use the
6850 @option{-msoft-float} option, and pass the option to GCC when linking.
6853 @itemx -mno-multiple
6855 @opindex mno-multiple
6856 Generate code that uses (does not use) the load multiple word
6857 instructions and the store multiple word instructions. These
6858 instructions are generated by default on POWER systems, and not
6859 generated on PowerPC systems. Do not use @option{-mmultiple} on little
6860 endian PowerPC systems, since those instructions do not work when the
6861 processor is in little endian mode. The exceptions are PPC740 and
6862 PPC750 which permit the instructions usage in little endian mode.
6868 Generate code that uses (does not use) the load string instructions
6869 and the store string word instructions to save multiple registers and
6870 do small block moves. These instructions are generated by default on
6871 POWER systems, and not generated on PowerPC systems. Do not use
6872 @option{-mstring} on little endian PowerPC systems, since those
6873 instructions do not work when the processor is in little endian mode.
6874 The exceptions are PPC740 and PPC750 which permit the instructions
6875 usage in little endian mode.
6881 Generate code that uses (does not use) the load or store instructions
6882 that update the base register to the address of the calculated memory
6883 location. These instructions are generated by default. If you use
6884 @option{-mno-update}, there is a small window between the time that the
6885 stack pointer is updated and the address of the previous frame is
6886 stored, which means code that walks the stack frame across interrupts or
6887 signals may get corrupted data.
6890 @itemx -mno-fused-madd
6891 @opindex mfused-madd
6892 @opindex mno-fused-madd
6893 Generate code that uses (does not use) the floating point multiply and
6894 accumulate instructions. These instructions are generated by default if
6895 hardware floating is used.
6897 @item -mno-bit-align
6899 @opindex mno-bit-align
6901 On System V.4 and embedded PowerPC systems do not (do) force structures
6902 and unions that contain bit-fields to be aligned to the base type of the
6905 For example, by default a structure containing nothing but 8
6906 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
6907 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
6908 the structure would be aligned to a 1 byte boundary and be one byte in
6911 @item -mno-strict-align
6912 @itemx -mstrict-align
6913 @opindex mno-strict-align
6914 @opindex mstrict-align
6915 On System V.4 and embedded PowerPC systems do not (do) assume that
6916 unaligned memory references will be handled by the system.
6919 @itemx -mno-relocatable
6920 @opindex mrelocatable
6921 @opindex mno-relocatable
6922 On embedded PowerPC systems generate code that allows (does not allow)
6923 the program to be relocated to a different address at runtime. If you
6924 use @option{-mrelocatable} on any module, all objects linked together must
6925 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
6927 @item -mrelocatable-lib
6928 @itemx -mno-relocatable-lib
6929 @opindex mrelocatable-lib
6930 @opindex mno-relocatable-lib
6931 On embedded PowerPC systems generate code that allows (does not allow)
6932 the program to be relocated to a different address at runtime. Modules
6933 compiled with @option{-mrelocatable-lib} can be linked with either modules
6934 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
6935 with modules compiled with the @option{-mrelocatable} options.
6941 On System V.4 and embedded PowerPC systems do not (do) assume that
6942 register 2 contains a pointer to a global area pointing to the addresses
6943 used in the program.
6946 @itemx -mlittle-endian
6948 @opindex mlittle-endian
6949 On System V.4 and embedded PowerPC systems compile code for the
6950 processor in little endian mode. The @option{-mlittle-endian} option is
6951 the same as @option{-mlittle}.
6956 @opindex mbig-endian
6957 On System V.4 and embedded PowerPC systems compile code for the
6958 processor in big endian mode. The @option{-mbig-endian} option is
6959 the same as @option{-mbig}.
6963 On System V.4 and embedded PowerPC systems compile code using calling
6964 conventions that adheres to the March 1995 draft of the System V
6965 Application Binary Interface, PowerPC processor supplement. This is the
6966 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
6968 @item -mcall-sysv-eabi
6969 @opindex mcall-sysv-eabi
6970 Specify both @option{-mcall-sysv} and @option{-meabi} options.
6972 @item -mcall-sysv-noeabi
6973 @opindex mcall-sysv-noeabi
6974 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
6978 On System V.4 and embedded PowerPC systems compile code using calling
6979 conventions that are similar to those used on AIX@. This is the
6980 default if you configured GCC using @samp{powerpc-*-eabiaix}.
6982 @item -mcall-solaris
6983 @opindex mcall-solaris
6984 On System V.4 and embedded PowerPC systems compile code for the Solaris
6988 @opindex mcall-linux
6989 On System V.4 and embedded PowerPC systems compile code for the
6990 Linux-based GNU system.
6994 On System V.4 and embedded PowerPC systems compile code for the
6995 Hurd-based GNU system.
6998 @opindex mcall-netbsd
6999 On System V.4 and embedded PowerPC systems compile code for the
7000 NetBSD operating system.
7002 @item -maix-struct-return
7003 @opindex maix-struct-return
7004 Return all structures in memory (as specified by the AIX ABI)@.
7006 @item -msvr4-struct-return
7007 @opindex msvr4-struct-return
7008 Return structures smaller than 8 bytes in registers (as specified by the
7012 @opindex mabi=altivec
7013 Extend the current ABI with AltiVec ABI extensions. This does not
7014 change the default ABI, instead it adds the AltiVec ABI extensions to
7017 @item -mabi=no-altivec
7018 @opindex mabi=no-altivec
7019 Disable AltiVec ABI extensions for the current ABI.
7022 @itemx -mno-prototype
7024 @opindex mno-prototype
7025 On System V.4 and embedded PowerPC systems assume that all calls to
7026 variable argument functions are properly prototyped. Otherwise, the
7027 compiler must insert an instruction before every non prototyped call to
7028 set or clear bit 6 of the condition code register (@var{CR}) to
7029 indicate whether floating point values were passed in the floating point
7030 registers in case the function takes a variable arguments. With
7031 @option{-mprototype}, only calls to prototyped variable argument functions
7032 will set or clear the bit.
7036 On embedded PowerPC systems, assume that the startup module is called
7037 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
7038 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
7043 On embedded PowerPC systems, assume that the startup module is called
7044 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
7049 On embedded PowerPC systems, assume that the startup module is called
7050 @file{crt0.o} and the standard C libraries are @file{libads.a} and
7054 @opindex myellowknife
7055 On embedded PowerPC systems, assume that the startup module is called
7056 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
7061 On System V.4 and embedded PowerPC systems, specify that you are
7062 compiling for a VxWorks system.
7066 Specify that you are compiling for the WindISS simulation environment.
7070 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
7071 header to indicate that @samp{eabi} extended relocations are used.
7077 On System V.4 and embedded PowerPC systems do (do not) adhere to the
7078 Embedded Applications Binary Interface (eabi) which is a set of
7079 modifications to the System V.4 specifications. Selecting @option{-meabi}
7080 means that the stack is aligned to an 8 byte boundary, a function
7081 @code{__eabi} is called to from @code{main} to set up the eabi
7082 environment, and the @option{-msdata} option can use both @code{r2} and
7083 @code{r13} to point to two separate small data areas. Selecting
7084 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
7085 do not call an initialization function from @code{main}, and the
7086 @option{-msdata} option will only use @code{r13} to point to a single
7087 small data area. The @option{-meabi} option is on by default if you
7088 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
7091 @opindex msdata=eabi
7092 On System V.4 and embedded PowerPC systems, put small initialized
7093 @code{const} global and static data in the @samp{.sdata2} section, which
7094 is pointed to by register @code{r2}. Put small initialized
7095 non-@code{const} global and static data in the @samp{.sdata} section,
7096 which is pointed to by register @code{r13}. Put small uninitialized
7097 global and static data in the @samp{.sbss} section, which is adjacent to
7098 the @samp{.sdata} section. The @option{-msdata=eabi} option is
7099 incompatible with the @option{-mrelocatable} option. The
7100 @option{-msdata=eabi} option also sets the @option{-memb} option.
7103 @opindex msdata=sysv
7104 On System V.4 and embedded PowerPC systems, put small global and static
7105 data in the @samp{.sdata} section, which is pointed to by register
7106 @code{r13}. Put small uninitialized global and static data in the
7107 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
7108 The @option{-msdata=sysv} option is incompatible with the
7109 @option{-mrelocatable} option.
7111 @item -msdata=default
7113 @opindex msdata=default
7115 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
7116 compile code the same as @option{-msdata=eabi}, otherwise compile code the
7117 same as @option{-msdata=sysv}.
7120 @opindex msdata-data
7121 On System V.4 and embedded PowerPC systems, put small global and static
7122 data in the @samp{.sdata} section. Put small uninitialized global and
7123 static data in the @samp{.sbss} section. Do not use register @code{r13}
7124 to address small data however. This is the default behavior unless
7125 other @option{-msdata} options are used.
7129 @opindex msdata=none
7131 On embedded PowerPC systems, put all initialized global and static data
7132 in the @samp{.data} section, and all uninitialized data in the
7133 @samp{.bss} section.
7137 @cindex smaller data references (PowerPC)
7138 @cindex .sdata/.sdata2 references (PowerPC)
7139 On embedded PowerPC systems, put global and static items less than or
7140 equal to @var{num} bytes into the small data or bss sections instead of
7141 the normal data or bss section. By default, @var{num} is 8. The
7142 @option{-G @var{num}} switch is also passed to the linker.
7143 All modules should be compiled with the same @option{-G @var{num}} value.
7146 @itemx -mno-regnames
7148 @opindex mno-regnames
7149 On System V.4 and embedded PowerPC systems do (do not) emit register
7150 names in the assembly language output using symbolic forms.
7153 @itemx -mno-longcall
7155 @opindex mno-longcall
7156 Default to making all function calls via pointers, so that functions
7157 which reside further than 64 megabytes (67,108,864 bytes) from the
7158 current location can be called. This setting can be overridden by the
7159 @code{shortcall} function attribute, or by @code{#pragma longcall(0)}.
7161 Some linkers are capable of detecting out-of-range calls and generating
7162 glue code on the fly. On these systems, long calls are unnecessary and
7163 generate slower code. As of this writing, the AIX linker can do this,
7164 as can the GNU linker for PowerPC/64. It is planned to add this feature
7165 to the GNU linker for 32-bit PowerPC systems as well.
7167 In the future, we may cause GCC to ignore all longcall specifications
7168 when the linker is known to generate glue.
7172 Adds support for multithreading with the @dfn{pthreads} library.
7173 This option sets flags for both the preprocessor and linker.
7178 @subsection IBM RT Options
7180 @cindex IBM RT options
7182 These @samp{-m} options are defined for the IBM RT PC:
7186 @opindex min-line-mul
7187 Use an in-line code sequence for integer multiplies. This is the
7190 @item -mcall-lib-mul
7191 @opindex mcall-lib-mul
7192 Call @code{lmul$$} for integer multiples.
7194 @item -mfull-fp-blocks
7195 @opindex mfull-fp-blocks
7196 Generate full-size floating point data blocks, including the minimum
7197 amount of scratch space recommended by IBM@. This is the default.
7199 @item -mminimum-fp-blocks
7200 @opindex mminimum-fp-blocks
7201 Do not include extra scratch space in floating point data blocks. This
7202 results in smaller code, but slower execution, since scratch space must
7203 be allocated dynamically.
7205 @cindex @file{stdarg.h} and RT PC
7206 @item -mfp-arg-in-fpregs
7207 @opindex mfp-arg-in-fpregs
7208 Use a calling sequence incompatible with the IBM calling convention in
7209 which floating point arguments are passed in floating point registers.
7210 Note that @code{stdarg.h} will not work with floating point operands
7211 if this option is specified.
7213 @item -mfp-arg-in-gregs
7214 @opindex mfp-arg-in-gregs
7215 Use the normal calling convention for floating point arguments. This is
7218 @item -mhc-struct-return
7219 @opindex mhc-struct-return
7220 Return structures of more than one word in memory, rather than in a
7221 register. This provides compatibility with the MetaWare HighC (hc)
7222 compiler. Use the option @option{-fpcc-struct-return} for compatibility
7223 with the Portable C Compiler (pcc).
7225 @item -mnohc-struct-return
7226 @opindex mnohc-struct-return
7227 Return some structures of more than one word in registers, when
7228 convenient. This is the default. For compatibility with the
7229 IBM-supplied compilers, use the option @option{-fpcc-struct-return} or the
7230 option @option{-mhc-struct-return}.
7234 @subsection MIPS Options
7235 @cindex MIPS options
7237 These @samp{-m} options are defined for the MIPS family of computers:
7241 @item -march=@var{arch}
7243 Generate code that will run on @var{arch}, which can be the name of a
7244 generic MIPS ISA, or the name of a particular processor. The ISA names
7245 are: @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4}, @samp{mips32}
7246 and @samp{mips64}. The processor names are: @samp{r2000},
7247 @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{vr4100}, @samp{vr4300},
7248 @samp{r4400}, @samp{r4600}, @samp{r4650}, @samp{vr5000}, @samp{r6000},
7249 @samp{r8000}, @samp{4kc}, @samp{4kp}, @samp{5kc}, @samp{20kc},
7250 @samp{orion}, and @samp{sb1}. The special value @samp{from-abi} selects the
7251 most compatible architecture for the selected ABI (that is,
7252 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
7254 In processor names, a final @samp{000} can be abbreviated as @samp{k}
7255 (for example, @samp{-march=r2k}). Prefixes are optional, and
7256 @samp{vr} may be written @samp{r}.
7258 GCC defines two macros based on the value of this option. The first
7259 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
7260 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
7261 where @var{foo} is the capitialized value of @samp{_MIPS_ARCH}@.
7262 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
7263 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
7265 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
7266 above. In other words, it will have the full prefix and will not
7267 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
7268 the macro names the resolved architecture (either @samp{"mips1"} or
7269 @samp{"mips3"}). It names the default architecture when no
7270 @option{-march} option is given.
7272 @item -mtune=@var{arch}
7274 Optimize for @var{arch}. Among other things, this option controls
7275 the way instructions are scheduled, and the perceived cost of arithmetic
7276 operations. The list of @var{arch} values is the same as for
7279 When this option is not used, GCC will optimize for the processor
7280 specified by @option{-march}. By using @option{-march} and
7281 @option{-mtune} together, it is possible to generate code that will
7282 run on a family of processors, but optimize the code for one
7283 particular member of that family.
7285 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
7286 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
7287 @samp{-march} ones described above.
7291 Equivalent to @samp{-march=mips1}.
7295 Equivalent to @samp{-march=mips2}.
7299 Equivalent to @samp{-march=mips3}.
7303 Equivalent to @samp{-march=mips4}.
7307 Equivalent to @samp{-march=mips32}.
7311 Equivalent to @samp{-march=mips64}.
7314 @itemx -mno-fused-madd
7315 @opindex mfused-madd
7316 @opindex mno-fused-madd
7317 Generate code that uses (does not use) the floating point multiply and
7318 accumulate instructions, when they are available. These instructions
7319 are generated by default if they are available, but this may be
7320 undesirable if the extra precision causes problems or on certain chips
7321 in the mode where denormals are rounded to zero where denormals
7322 generated by multiply and accumulate instructions cause exceptions
7327 Assume that floating point registers are 32 bits wide.
7331 Assume that floating point registers are 64 bits wide.
7335 Assume that general purpose registers are 32 bits wide.
7339 Assume that general purpose registers are 64 bits wide.
7343 Force int and long types to be 64 bits wide. See @option{-mlong32} for an
7344 explanation of the default, and the width of pointers.
7348 Force long types to be 64 bits wide. See @option{-mlong32} for an
7349 explanation of the default, and the width of pointers.
7353 Force long, int, and pointer types to be 32 bits wide.
7355 The default size of ints, longs and pointers depends on the ABI@. All
7356 the supported ABIs use 32-bit ints. The n64 ABI uses 64-bit longs, as
7357 does the 64-bit Cygnus EABI; the others use 32-bit longs. Pointers
7358 are the same size as longs, or the same size as integer registers,
7359 whichever is smaller.
7373 Generate code for the given ABI@.
7375 Note that there are two embedded ABIs: @option{-mabi=eabi}
7376 selects the one defined by Cygnus while @option{-meabi=meabi}
7377 selects the one defined by MIPS@. Both these ABIs have
7378 32-bit and 64-bit variants. Normally, GCC will generate
7379 64-bit code when you select a 64-bit architecture, but you
7380 can use @option{-mgp32} to get 32-bit code instead.
7384 Generate code for the MIPS assembler, and invoke @file{mips-tfile} to
7385 add normal debug information. This is the default for all
7386 platforms except for the OSF/1 reference platform, using the OSF/rose
7387 object format. If the either of the @option{-gstabs} or @option{-gstabs+}
7388 switches are used, the @file{mips-tfile} program will encapsulate the
7389 stabs within MIPS ECOFF@.
7393 Generate code for the GNU assembler. This is the default on the OSF/1
7394 reference platform, using the OSF/rose object format. Also, this is
7395 the default if the configure option @option{--with-gnu-as} is used.
7397 @item -msplit-addresses
7398 @itemx -mno-split-addresses
7399 @opindex msplit-addresses
7400 @opindex mno-split-addresses
7401 Generate code to load the high and low parts of address constants separately.
7402 This allows GCC to optimize away redundant loads of the high order
7403 bits of addresses. This optimization requires GNU as and GNU ld.
7404 This optimization is enabled by default for some embedded targets where
7405 GNU as and GNU ld are standard.
7411 The @option{-mrnames} switch says to output code using the MIPS software
7412 names for the registers, instead of the hardware names (ie, @var{a0}
7413 instead of @var{$4}). The only known assembler that supports this option
7414 is the Algorithmics assembler.
7420 The @option{-mgpopt} switch says to write all of the data declarations
7421 before the instructions in the text section, this allows the MIPS
7422 assembler to generate one word memory references instead of using two
7423 words for short global or static data items. This is on by default if
7424 optimization is selected.
7430 For each non-inline function processed, the @option{-mstats} switch
7431 causes the compiler to emit one line to the standard error file to
7432 print statistics about the program (number of registers saved, stack
7439 The @option{-mmemcpy} switch makes all block moves call the appropriate
7440 string function (@samp{memcpy} or @samp{bcopy}) instead of possibly
7441 generating inline code.
7444 @itemx -mno-mips-tfile
7445 @opindex mmips-tfile
7446 @opindex mno-mips-tfile
7447 The @option{-mno-mips-tfile} switch causes the compiler not
7448 postprocess the object file with the @file{mips-tfile} program,
7449 after the MIPS assembler has generated it to add debug support. If
7450 @file{mips-tfile} is not run, then no local variables will be
7451 available to the debugger. In addition, @file{stage2} and
7452 @file{stage3} objects will have the temporary file names passed to the
7453 assembler embedded in the object file, which means the objects will
7454 not compare the same. The @option{-mno-mips-tfile} switch should only
7455 be used when there are bugs in the @file{mips-tfile} program that
7456 prevents compilation.
7459 @opindex msoft-float
7460 Generate output containing library calls for floating point.
7461 @strong{Warning:} the requisite libraries are not part of GCC@.
7462 Normally the facilities of the machine's usual C compiler are used, but
7463 this can't be done directly in cross-compilation. You must make your
7464 own arrangements to provide suitable library functions for
7468 @opindex mhard-float
7469 Generate output containing floating point instructions. This is the
7470 default if you use the unmodified sources.
7473 @itemx -mno-abicalls
7475 @opindex mno-abicalls
7476 Emit (or do not emit) the pseudo operations @samp{.abicalls},
7477 @samp{.cpload}, and @samp{.cprestore} that some System V.4 ports use for
7478 position independent code.
7481 @itemx -mno-long-calls
7482 @opindex mlong-calls
7483 @opindex mno-long-calls
7484 Do all calls with the @samp{JALR} instruction, which requires
7485 loading up a function's address into a register before the call.
7486 You need to use this switch, if you call outside of the current
7487 512 megabyte segment to functions that are not through pointers.
7490 @itemx -mno-half-pic
7492 @opindex mno-half-pic
7493 Put pointers to extern references into the data section and load them
7494 up, rather than put the references in the text section.
7496 @item -membedded-pic
7497 @itemx -mno-embedded-pic
7498 @opindex membedded-pic
7499 @opindex mno-embedded-pic
7500 Generate PIC code suitable for some embedded systems. All calls are
7501 made using PC relative address, and all data is addressed using the $gp
7502 register. No more than 65536 bytes of global data may be used. This
7503 requires GNU as and GNU ld which do most of the work. This currently
7504 only works on targets which use ECOFF; it does not work with ELF@.
7506 @item -membedded-data
7507 @itemx -mno-embedded-data
7508 @opindex membedded-data
7509 @opindex mno-embedded-data
7510 Allocate variables to the read-only data section first if possible, then
7511 next in the small data section if possible, otherwise in data. This gives
7512 slightly slower code than the default, but reduces the amount of RAM required
7513 when executing, and thus may be preferred for some embedded systems.
7515 @item -muninit-const-in-rodata
7516 @itemx -mno-uninit-const-in-rodata
7517 @opindex muninit-const-in-rodata
7518 @opindex mno-uninit-const-in-rodata
7519 When used together with @option{-membedded-data}, it will always store uninitialized
7520 const variables in the read-only data section.
7522 @item -msingle-float
7523 @itemx -mdouble-float
7524 @opindex msingle-float
7525 @opindex mdouble-float
7526 The @option{-msingle-float} switch tells gcc to assume that the floating
7527 point coprocessor only supports single precision operations, as on the
7528 @samp{r4650} chip. The @option{-mdouble-float} switch permits gcc to use
7529 double precision operations. This is the default.
7535 Permit use of the @samp{mad}, @samp{madu} and @samp{mul} instructions,
7536 as on the @samp{r4650} chip.
7540 Turns on @option{-msingle-float}, @option{-mmad}, and, at least for now,
7541 @option{-mcpu=r4650}.
7547 Enable 16-bit instructions.
7551 Use the entry and exit pseudo ops. This option can only be used with
7556 Compile code for the processor in little endian mode.
7557 The requisite libraries are assumed to exist.
7561 Compile code for the processor in big endian mode.
7562 The requisite libraries are assumed to exist.
7566 @cindex smaller data references (MIPS)
7567 @cindex gp-relative references (MIPS)
7568 Put global and static items less than or equal to @var{num} bytes into
7569 the small data or bss sections instead of the normal data or bss
7570 section. This allows the assembler to emit one word memory reference
7571 instructions based on the global pointer (@var{gp} or @var{$28}),
7572 instead of the normal two words used. By default, @var{num} is 8 when
7573 the MIPS assembler is used, and 0 when the GNU assembler is used. The
7574 @option{-G @var{num}} switch is also passed to the assembler and linker.
7575 All modules should be compiled with the same @option{-G @var{num}}
7580 Tell the MIPS assembler to not run its preprocessor over user
7581 assembler files (with a @samp{.s} suffix) when assembling them.
7585 Pass an option to gas which will cause nops to be inserted if
7586 the read of the destination register of an mfhi or mflo instruction
7587 occurs in the following two instructions.
7591 Do not include the default crt0.
7593 @item -mflush-func=@var{func}
7594 @itemx -mno-flush-func
7595 @opindex mflush-func
7596 Specifies the function to call to flush the I and D caches, or to not
7597 call any such function. If called, the function must take the same
7598 arguments as the common @code{_flush_func()}, that is, the address of the
7599 memory range for which the cache is being flushed, the size of the
7600 memory range, and the number 3 (to flush both caches). The default
7601 depends on the target gcc was configured for, but commonly is either
7602 @samp{_flush_func} or @samp{__cpu_flush}.
7604 @item -mbranch-likely
7605 @itemx -mno-branch-likely
7606 @opindex mbranch-likely
7607 @opindex mno-branch-likely
7608 Enable or disable use of Branch Likely instructions, regardless of the
7609 default for the selected architecture. By default, Branch Likely
7610 instructions may be generated if they are supported by the selected
7611 architecture. An exception is for the MIPS32 and MIPS64 architectures
7612 and processors which implement those architectures; for those, Branch
7613 Likely instructions will not be generated by default because the MIPS32
7614 and MIPS64 architectures specifically deprecate their use.
7617 @node i386 and x86-64 Options
7618 @subsection Intel 386 and AMD x86-64 Options
7619 @cindex i386 Options
7620 @cindex x86-64 Options
7621 @cindex Intel 386 Options
7622 @cindex AMD x86-64 Options
7624 These @samp{-m} options are defined for the i386 and x86-64 family of
7628 @item -mcpu=@var{cpu-type}
7630 Tune to @var{cpu-type} everything applicable about the generated code, except
7631 for the ABI and the set of available instructions. The choices for
7632 @var{cpu-type} are @samp{i386}, @samp{i486}, @samp{i586}, @samp{i686},
7633 @samp{pentium}, @samp{pentium-mmx}, @samp{pentiumpro}, @samp{pentium2},
7634 @samp{pentium3}, @samp{pentium4}, @samp{k6}, @samp{k6-2}, @samp{k6-3},
7635 @samp{athlon}, @samp{athlon-tbird}, @samp{athlon-4}, @samp{athlon-xp},
7636 @samp{athlon-mp}, @samp{winchip-c6}, @samp{winchip2} and @samp{c3}.
7638 While picking a specific @var{cpu-type} will schedule things appropriately
7639 for that particular chip, the compiler will not generate any code that
7640 does not run on the i386 without the @option{-march=@var{cpu-type}} option
7641 being used. @samp{i586} is equivalent to @samp{pentium} and @samp{i686}
7642 is equivalent to @samp{pentiumpro}. @samp{k6} and @samp{athlon} are the
7643 AMD chips as opposed to the Intel ones.
7645 @item -march=@var{cpu-type}
7647 Generate instructions for the machine type @var{cpu-type}. The choices
7648 for @var{cpu-type} are the same as for @option{-mcpu}. Moreover,
7649 specifying @option{-march=@var{cpu-type}} implies @option{-mcpu=@var{cpu-type}}.
7658 @opindex mpentiumpro
7659 These options are synonyms for @option{-mcpu=i386}, @option{-mcpu=i486},
7660 @option{-mcpu=pentium}, and @option{-mcpu=pentiumpro} respectively.
7661 These synonyms are deprecated.
7663 @item -mfpmath=@var{unit}
7665 generate floating point arithmetics for selected unit @var{unit}. the choices
7670 Use the standard 387 floating point coprocessor present majority of chips and
7671 emulated otherwise. Code compiled with this option will run almost everywhere.
7672 The temporary results are computed in 80bit precesion instead of precision
7673 specified by the type resulting in slightly different results compared to most
7674 of other chips. See @option{-ffloat-store} for more detailed description.
7676 This is the default choice for i386 compiler.
7679 Use scalar floating point instructions present in the SSE instruction set.
7680 This instruction set is supported by Pentium3 and newer chips, in the AMD line
7681 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
7682 instruction set supports only single precision arithmetics, thus the double and
7683 extended precision arithmetics is still done using 387. Later version, present
7684 only in Pentium4 and the future AMD x86-64 chips supports double precision
7687 For i387 you need to use @option{-march=@var{cpu-type}}, @option{-msse} or
7688 @option{-msse2} switches to enable SSE extensions and make this option
7689 effective. For x86-64 compiler, these extensions are enabled by default.
7691 The resulting code should be considerably faster in majority of cases and avoid
7692 the numerical instability problems of 387 code, but may break some existing
7693 code that expects temporaries to be 80bit.
7695 This is the default choice for x86-64 compiler.
7698 Attempt to utilize both instruction sets at once. This effectivly double the
7699 amount of available registers and on chips with separate execution units for
7700 387 and SSE the execution resources too. Use this option with care, as it is
7701 still experimental, because gcc register allocator does not model separate
7702 functional units well resulting in instable performance.
7705 @item -masm=@var{dialect}
7706 @opindex masm=@var{dialect}
7707 Output asm instructions using selected @var{dialect}. Supported choices are
7708 @samp{intel} or @samp{att} (the default one).
7713 @opindex mno-ieee-fp
7714 Control whether or not the compiler uses IEEE floating point
7715 comparisons. These handle correctly the case where the result of a
7716 comparison is unordered.
7719 @opindex msoft-float
7720 Generate output containing library calls for floating point.
7721 @strong{Warning:} the requisite libraries are not part of GCC@.
7722 Normally the facilities of the machine's usual C compiler are used, but
7723 this can't be done directly in cross-compilation. You must make your
7724 own arrangements to provide suitable library functions for
7727 On machines where a function returns floating point results in the 80387
7728 register stack, some floating point opcodes may be emitted even if
7729 @option{-msoft-float} is used.
7731 @item -mno-fp-ret-in-387
7732 @opindex mno-fp-ret-in-387
7733 Do not use the FPU registers for return values of functions.
7735 The usual calling convention has functions return values of types
7736 @code{float} and @code{double} in an FPU register, even if there
7737 is no FPU@. The idea is that the operating system should emulate
7740 The option @option{-mno-fp-ret-in-387} causes such values to be returned
7741 in ordinary CPU registers instead.
7743 @item -mno-fancy-math-387
7744 @opindex mno-fancy-math-387
7745 Some 387 emulators do not support the @code{sin}, @code{cos} and
7746 @code{sqrt} instructions for the 387. Specify this option to avoid
7747 generating those instructions. This option is the default on FreeBSD,
7748 OpenBSD and NetBSD@. This option is overridden when @option{-march}
7749 indicates that the target cpu will always have an FPU and so the
7750 instruction will not need emulation. As of revision 2.6.1, these
7751 instructions are not generated unless you also use the
7752 @option{-funsafe-math-optimizations} switch.
7754 @item -malign-double
7755 @itemx -mno-align-double
7756 @opindex malign-double
7757 @opindex mno-align-double
7758 Control whether GCC aligns @code{double}, @code{long double}, and
7759 @code{long long} variables on a two word boundary or a one word
7760 boundary. Aligning @code{double} variables on a two word boundary will
7761 produce code that runs somewhat faster on a @samp{Pentium} at the
7762 expense of more memory.
7764 @strong{Warning:} if you use the @samp{-malign-double} switch,
7765 structures containing the above types will be aligned differently than
7766 the published application binary interface specifications for the 386.
7768 @item -m128bit-long-double
7769 @opindex m128bit-long-double
7770 Control the size of @code{long double} type. i386 application binary interface
7771 specify the size to be 12 bytes, while modern architectures (Pentium and newer)
7772 prefer @code{long double} aligned to 8 or 16 byte boundary. This is
7773 impossible to reach with 12 byte long doubles in the array accesses.
7775 @strong{Warning:} if you use the @option{-m128bit-long-double} switch, the
7776 structures and arrays containing @code{long double} will change their size as
7777 well as function calling convention for function taking @code{long double}
7780 @item -m96bit-long-double
7781 @opindex m96bit-long-double
7782 Set the size of @code{long double} to 96 bits as required by the i386
7783 application binary interface. This is the default.
7786 @itemx -mno-svr3-shlib
7787 @opindex msvr3-shlib
7788 @opindex mno-svr3-shlib
7789 Control whether GCC places uninitialized local variables into the
7790 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
7791 into @code{bss}. These options are meaningful only on System V Release 3.
7795 Use a different function-calling convention, in which functions that
7796 take a fixed number of arguments return with the @code{ret} @var{num}
7797 instruction, which pops their arguments while returning. This saves one
7798 instruction in the caller since there is no need to pop the arguments
7801 You can specify that an individual function is called with this calling
7802 sequence with the function attribute @samp{stdcall}. You can also
7803 override the @option{-mrtd} option by using the function attribute
7804 @samp{cdecl}. @xref{Function Attributes}.
7806 @strong{Warning:} this calling convention is incompatible with the one
7807 normally used on Unix, so you cannot use it if you need to call
7808 libraries compiled with the Unix compiler.
7810 Also, you must provide function prototypes for all functions that
7811 take variable numbers of arguments (including @code{printf});
7812 otherwise incorrect code will be generated for calls to those
7815 In addition, seriously incorrect code will result if you call a
7816 function with too many arguments. (Normally, extra arguments are
7817 harmlessly ignored.)
7819 @item -mregparm=@var{num}
7821 Control how many registers are used to pass integer arguments. By
7822 default, no registers are used to pass arguments, and at most 3
7823 registers can be used. You can control this behavior for a specific
7824 function by using the function attribute @samp{regparm}.
7825 @xref{Function Attributes}.
7827 @strong{Warning:} if you use this switch, and
7828 @var{num} is nonzero, then you must build all modules with the same
7829 value, including any libraries. This includes the system libraries and
7832 @item -mpreferred-stack-boundary=@var{num}
7833 @opindex mpreferred-stack-boundary
7834 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
7835 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
7836 the default is 4 (16 bytes or 128 bits), except when optimizing for code
7837 size (@option{-Os}), in which case the default is the minimum correct
7838 alignment (4 bytes for x86, and 8 bytes for x86-64).
7840 On Pentium and PentiumPro, @code{double} and @code{long double} values
7841 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
7842 suffer significant run time performance penalties. On Pentium III, the
7843 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
7844 penalties if it is not 16 byte aligned.
7846 To ensure proper alignment of this values on the stack, the stack boundary
7847 must be as aligned as that required by any value stored on the stack.
7848 Further, every function must be generated such that it keeps the stack
7849 aligned. Thus calling a function compiled with a higher preferred
7850 stack boundary from a function compiled with a lower preferred stack
7851 boundary will most likely misalign the stack. It is recommended that
7852 libraries that use callbacks always use the default setting.
7854 This extra alignment does consume extra stack space, and generally
7855 increases code size. Code that is sensitive to stack space usage, such
7856 as embedded systems and operating system kernels, may want to reduce the
7857 preferred alignment to @option{-mpreferred-stack-boundary=2}.
7873 These switches enable or disable the use of built-in functions that allow
7874 direct access to the MMX, SSE and 3Dnow extensions of the instruction set.
7876 @xref{X86 Built-in Functions}, for details of the functions enabled
7877 and disabled by these switches.
7879 To have SSE/SSE2 instructions generated automatically from floating-point
7880 code, see @option{-mfpmath=sse}.
7883 @itemx -mno-push-args
7885 @opindex mno-push-args
7886 Use PUSH operations to store outgoing parameters. This method is shorter
7887 and usually equally fast as method using SUB/MOV operations and is enabled
7888 by default. In some cases disabling it may improve performance because of
7889 improved scheduling and reduced dependencies.
7891 @item -maccumulate-outgoing-args
7892 @opindex maccumulate-outgoing-args
7893 If enabled, the maximum amount of space required for outgoing arguments will be
7894 computed in the function prologue. This is faster on most modern CPUs
7895 because of reduced dependencies, improved scheduling and reduced stack usage
7896 when preferred stack boundary is not equal to 2. The drawback is a notable
7897 increase in code size. This switch implies @option{-mno-push-args}.
7901 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
7902 on thread-safe exception handling must compile and link all code with the
7903 @option{-mthreads} option. When compiling, @option{-mthreads} defines
7904 @option{-D_MT}; when linking, it links in a special thread helper library
7905 @option{-lmingwthrd} which cleans up per thread exception handling data.
7907 @item -mno-align-stringops
7908 @opindex mno-align-stringops
7909 Do not align destination of inlined string operations. This switch reduces
7910 code size and improves performance in case the destination is already aligned,
7911 but gcc don't know about it.
7913 @item -minline-all-stringops
7914 @opindex minline-all-stringops
7915 By default GCC inlines string operations only when destination is known to be
7916 aligned at least to 4 byte boundary. This enables more inlining, increase code
7917 size, but may improve performance of code that depends on fast memcpy, strlen
7918 and memset for short lengths.
7920 @item -momit-leaf-frame-pointer
7921 @opindex momit-leaf-frame-pointer
7922 Don't keep the frame pointer in a register for leaf functions. This
7923 avoids the instructions to save, set up and restore frame pointers and
7924 makes an extra register available in leaf functions. The option
7925 @option{-fomit-frame-pointer} removes the frame pointer for all functions
7926 which might make debugging harder.
7929 These @samp{-m} switches are supported in addition to the above
7930 on AMD x86-64 processors in 64-bit environments.
7937 Generate code for a 32-bit or 64-bit environment.
7938 The 32-bit environment sets int, long and pointer to 32 bits and
7939 generates code that runs on any i386 system.
7940 The 64-bit environment sets int to 32 bits and long and pointer
7941 to 64 bits and generates code for AMD's x86-64 architecture.
7944 @opindex no-red-zone
7945 Do not use a so called red zone for x86-64 code. The red zone is mandated
7946 by the x86-64 ABI, it is a 128-byte area beyond the location of the
7947 stack pointer that will not be modified by signal or interrupt handlers
7948 and therefore can be used for temporary data without adjusting the stack
7949 pointer. The flag @option{-mno-red-zone} disables this red zone.
7951 @item -mcmodel=small
7952 @opindex mcmodel=small
7953 Generate code for the small code model: the program and its symbols must
7954 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
7955 Programs can be statically or dynamically linked. This is the default
7958 @item -mcmodel=kernel
7959 @opindex mcmodel=kernel
7960 Generate code for the kernel code model. The kernel runs in the
7961 negative 2 GB of the address space.
7962 This model has to be used for Linux kernel code.
7964 @item -mcmodel=medium
7965 @opindex mcmodel=medium
7966 Generate code for the medium model: The program is linked in the lower 2
7967 GB of the address space but symbols can be located anywhere in the
7968 address space. Programs can be statically or dynamically linked, but
7969 building of shared libraries are not supported with the medium model.
7971 @item -mcmodel=large
7972 @opindex mcmodel=large
7973 Generate code for the large model: This model makes no assumptions
7974 about addresses and sizes of sections. Currently GCC does not implement
7979 @subsection HPPA Options
7980 @cindex HPPA Options
7982 These @samp{-m} options are defined for the HPPA family of computers:
7985 @item -march=@var{architecture-type}
7987 Generate code for the specified architecture. The choices for
7988 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
7989 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
7990 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
7991 architecture option for your machine. Code compiled for lower numbered
7992 architectures will run on higher numbered architectures, but not the
7995 PA 2.0 support currently requires gas snapshot 19990413 or later. The
7996 next release of binutils (current is 2.9.1) will probably contain PA 2.0
8000 @itemx -mpa-risc-1-1
8001 @itemx -mpa-risc-2-0
8002 @opindex mpa-risc-1-0
8003 @opindex mpa-risc-1-1
8004 @opindex mpa-risc-2-0
8005 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8008 @opindex mbig-switch
8009 Generate code suitable for big switch tables. Use this option only if
8010 the assembler/linker complain about out of range branches within a switch
8013 @item -mjump-in-delay
8014 @opindex mjump-in-delay
8015 Fill delay slots of function calls with unconditional jump instructions
8016 by modifying the return pointer for the function call to be the target
8017 of the conditional jump.
8019 @item -mdisable-fpregs
8020 @opindex mdisable-fpregs
8021 Prevent floating point registers from being used in any manner. This is
8022 necessary for compiling kernels which perform lazy context switching of
8023 floating point registers. If you use this option and attempt to perform
8024 floating point operations, the compiler will abort.
8026 @item -mdisable-indexing
8027 @opindex mdisable-indexing
8028 Prevent the compiler from using indexing address modes. This avoids some
8029 rather obscure problems when compiling MIG generated code under MACH@.
8031 @item -mno-space-regs
8032 @opindex mno-space-regs
8033 Generate code that assumes the target has no space registers. This allows
8034 GCC to generate faster indirect calls and use unscaled index address modes.
8036 Such code is suitable for level 0 PA systems and kernels.
8038 @item -mfast-indirect-calls
8039 @opindex mfast-indirect-calls
8040 Generate code that assumes calls never cross space boundaries. This
8041 allows GCC to emit code which performs faster indirect calls.
8043 This option will not work in the presence of shared libraries or nested
8046 @item -mlong-load-store
8047 @opindex mlong-load-store
8048 Generate 3-instruction load and store sequences as sometimes required by
8049 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8052 @item -mportable-runtime
8053 @opindex mportable-runtime
8054 Use the portable calling conventions proposed by HP for ELF systems.
8058 Enable the use of assembler directives only GAS understands.
8060 @item -mschedule=@var{cpu-type}
8062 Schedule code according to the constraints for the machine type
8063 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8064 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
8065 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
8066 proper scheduling option for your machine. The default scheduling is
8070 @opindex mlinker-opt
8071 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
8072 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
8073 linkers in which they give bogus error messages when linking some programs.
8076 @opindex msoft-float
8077 Generate output containing library calls for floating point.
8078 @strong{Warning:} the requisite libraries are not available for all HPPA
8079 targets. Normally the facilities of the machine's usual C compiler are
8080 used, but this cannot be done directly in cross-compilation. You must make
8081 your own arrangements to provide suitable library functions for
8082 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8083 does provide software floating point support.
8085 @option{-msoft-float} changes the calling convention in the output file;
8086 therefore, it is only useful if you compile @emph{all} of a program with
8087 this option. In particular, you need to compile @file{libgcc.a}, the
8088 library that comes with GCC, with @option{-msoft-float} in order for
8093 Generate the predefine, @code{_SIO}, for server IO. The default is
8094 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
8095 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO. These
8096 options are available under HP-UX and HI-UX.
8100 Use GNU ld specific options. This passes @option{-shared} to ld when
8101 building a shared library. It is the default when GCC is configured,
8102 explicitly or implicitly, with the GNU linker. This option does not
8103 have any affect on which ld is called, it only changes what parameters
8104 are passed to that ld. The ld that is called is determined by the
8105 @option{--with-ld} configure option, gcc's program search path, and
8106 finally by the user's @env{PATH}. The linker used by GCC can be printed
8107 using @samp{which `gcc -print-prog-name=ld`}.
8111 Use HP ld specific options. This passes @option{-b} to ld when building
8112 a shared library and passes @option{+Accept TypeMismatch} to ld on all
8113 links. It is the default when GCC is configured, explicitly or
8114 implicitly, with the HP linker. This option does not have any affect on
8115 which ld is called, it only changes what parameters are passed to that
8116 ld. The ld that is called is determined by the @option{--with-ld}
8117 configure option, gcc's program search path, and finally by the user's
8118 @env{PATH}. The linker used by GCC can be printed using @samp{which
8119 `gcc -print-prog-name=ld`}.
8122 @opindex mno-long-calls
8123 Generate code that uses long call sequences. This ensures that a call
8124 is always able to reach linker generated stubs. The default is to generate
8125 long calls only when the distance from the call site to the beginning
8126 of the function or translation unit, as the case may be, exceeds a
8127 predefined limit set by the branch type being used. The limits for
8128 normal calls are 7,600,000 and 240,000 bytes, respectively for the
8129 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
8132 Distances are measured from the beginning of functions when using the
8133 @option{-ffunction-sections} option, or when using the @option{-mgas}
8134 and @option{-mno-portable-runtime} options together under HP-UX with
8137 It is normally not desirable to use this option as it will degrade
8138 performance. However, it may be useful in large applications,
8139 particularly when partial linking is used to build the application.
8141 The types of long calls used depends on the capabilities of the
8142 assembler and linker, and the type of code being generated. The
8143 impact on systems that support long absolute calls, and long pic
8144 symbol-difference or pc-relative calls should be relatively small.
8145 However, an indirect call is used on 32-bit ELF systems in pic code
8146 and it is quite long.
8150 @node Intel 960 Options
8151 @subsection Intel 960 Options
8153 These @samp{-m} options are defined for the Intel 960 implementations:
8156 @item -m@var{cpu-type}
8164 Assume the defaults for the machine type @var{cpu-type} for some of
8165 the other options, including instruction scheduling, floating point
8166 support, and addressing modes. The choices for @var{cpu-type} are
8167 @samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf},
8168 @samp{sa}, and @samp{sb}.
8175 @opindex msoft-float
8176 The @option{-mnumerics} option indicates that the processor does support
8177 floating-point instructions. The @option{-msoft-float} option indicates
8178 that floating-point support should not be assumed.
8180 @item -mleaf-procedures
8181 @itemx -mno-leaf-procedures
8182 @opindex mleaf-procedures
8183 @opindex mno-leaf-procedures
8184 Do (or do not) attempt to alter leaf procedures to be callable with the
8185 @code{bal} instruction as well as @code{call}. This will result in more
8186 efficient code for explicit calls when the @code{bal} instruction can be
8187 substituted by the assembler or linker, but less efficient code in other
8188 cases, such as calls via function pointers, or using a linker that doesn't
8189 support this optimization.
8192 @itemx -mno-tail-call
8194 @opindex mno-tail-call
8195 Do (or do not) make additional attempts (beyond those of the
8196 machine-independent portions of the compiler) to optimize tail-recursive
8197 calls into branches. You may not want to do this because the detection of
8198 cases where this is not valid is not totally complete. The default is
8199 @option{-mno-tail-call}.
8201 @item -mcomplex-addr
8202 @itemx -mno-complex-addr
8203 @opindex mcomplex-addr
8204 @opindex mno-complex-addr
8205 Assume (or do not assume) that the use of a complex addressing mode is a
8206 win on this implementation of the i960. Complex addressing modes may not
8207 be worthwhile on the K-series, but they definitely are on the C-series.
8208 The default is currently @option{-mcomplex-addr} for all processors except
8212 @itemx -mno-code-align
8213 @opindex mcode-align
8214 @opindex mno-code-align
8215 Align code to 8-byte boundaries for faster fetching (or don't bother).
8216 Currently turned on by default for C-series implementations only.
8219 @item -mclean-linkage
8220 @itemx -mno-clean-linkage
8221 @opindex mclean-linkage
8222 @opindex mno-clean-linkage
8223 These options are not fully implemented.
8227 @itemx -mic2.0-compat
8228 @itemx -mic3.0-compat
8230 @opindex mic2.0-compat
8231 @opindex mic3.0-compat
8232 Enable compatibility with iC960 v2.0 or v3.0.
8236 @opindex masm-compat
8238 Enable compatibility with the iC960 assembler.
8240 @item -mstrict-align
8241 @itemx -mno-strict-align
8242 @opindex mstrict-align
8243 @opindex mno-strict-align
8244 Do not permit (do permit) unaligned accesses.
8248 Enable structure-alignment compatibility with Intel's gcc release version
8249 1.3 (based on gcc 1.37). This option implies @option{-mstrict-align}.
8251 @item -mlong-double-64
8252 @opindex mlong-double-64
8253 Implement type @samp{long double} as 64-bit floating point numbers.
8254 Without the option @samp{long double} is implemented by 80-bit
8255 floating point numbers. The only reason we have it because there is
8256 no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it
8257 is only useful for people using soft-float targets. Otherwise, we
8258 should recommend against use of it.
8262 @node DEC Alpha Options
8263 @subsection DEC Alpha Options
8265 These @samp{-m} options are defined for the DEC Alpha implementations:
8268 @item -mno-soft-float
8270 @opindex mno-soft-float
8271 @opindex msoft-float
8272 Use (do not use) the hardware floating-point instructions for
8273 floating-point operations. When @option{-msoft-float} is specified,
8274 functions in @file{libgcc.a} will be used to perform floating-point
8275 operations. Unless they are replaced by routines that emulate the
8276 floating-point operations, or compiled in such a way as to call such
8277 emulations routines, these routines will issue floating-point
8278 operations. If you are compiling for an Alpha without floating-point
8279 operations, you must ensure that the library is built so as not to call
8282 Note that Alpha implementations without floating-point operations are
8283 required to have floating-point registers.
8288 @opindex mno-fp-regs
8289 Generate code that uses (does not use) the floating-point register set.
8290 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
8291 register set is not used, floating point operands are passed in integer
8292 registers as if they were integers and floating-point results are passed
8293 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
8294 so any function with a floating-point argument or return value called by code
8295 compiled with @option{-mno-fp-regs} must also be compiled with that
8298 A typical use of this option is building a kernel that does not use,
8299 and hence need not save and restore, any floating-point registers.
8303 The Alpha architecture implements floating-point hardware optimized for
8304 maximum performance. It is mostly compliant with the IEEE floating
8305 point standard. However, for full compliance, software assistance is
8306 required. This option generates code fully IEEE compliant code
8307 @emph{except} that the @var{inexact-flag} is not maintained (see below).
8308 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
8309 defined during compilation. The resulting code is less efficient but is
8310 able to correctly support denormalized numbers and exceptional IEEE
8311 values such as not-a-number and plus/minus infinity. Other Alpha
8312 compilers call this option @option{-ieee_with_no_inexact}.
8314 @item -mieee-with-inexact
8315 @opindex mieee-with-inexact
8316 This is like @option{-mieee} except the generated code also maintains
8317 the IEEE @var{inexact-flag}. Turning on this option causes the
8318 generated code to implement fully-compliant IEEE math. In addition to
8319 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
8320 macro. On some Alpha implementations the resulting code may execute
8321 significantly slower than the code generated by default. Since there is
8322 very little code that depends on the @var{inexact-flag}, you should
8323 normally not specify this option. Other Alpha compilers call this
8324 option @option{-ieee_with_inexact}.
8326 @item -mfp-trap-mode=@var{trap-mode}
8327 @opindex mfp-trap-mode
8328 This option controls what floating-point related traps are enabled.
8329 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
8330 The trap mode can be set to one of four values:
8334 This is the default (normal) setting. The only traps that are enabled
8335 are the ones that cannot be disabled in software (e.g., division by zero
8339 In addition to the traps enabled by @samp{n}, underflow traps are enabled
8343 Like @samp{su}, but the instructions are marked to be safe for software
8344 completion (see Alpha architecture manual for details).
8347 Like @samp{su}, but inexact traps are enabled as well.
8350 @item -mfp-rounding-mode=@var{rounding-mode}
8351 @opindex mfp-rounding-mode
8352 Selects the IEEE rounding mode. Other Alpha compilers call this option
8353 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
8358 Normal IEEE rounding mode. Floating point numbers are rounded towards
8359 the nearest machine number or towards the even machine number in case
8363 Round towards minus infinity.
8366 Chopped rounding mode. Floating point numbers are rounded towards zero.
8369 Dynamic rounding mode. A field in the floating point control register
8370 (@var{fpcr}, see Alpha architecture reference manual) controls the
8371 rounding mode in effect. The C library initializes this register for
8372 rounding towards plus infinity. Thus, unless your program modifies the
8373 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
8376 @item -mtrap-precision=@var{trap-precision}
8377 @opindex mtrap-precision
8378 In the Alpha architecture, floating point traps are imprecise. This
8379 means without software assistance it is impossible to recover from a
8380 floating trap and program execution normally needs to be terminated.
8381 GCC can generate code that can assist operating system trap handlers
8382 in determining the exact location that caused a floating point trap.
8383 Depending on the requirements of an application, different levels of
8384 precisions can be selected:
8388 Program precision. This option is the default and means a trap handler
8389 can only identify which program caused a floating point exception.
8392 Function precision. The trap handler can determine the function that
8393 caused a floating point exception.
8396 Instruction precision. The trap handler can determine the exact
8397 instruction that caused a floating point exception.
8400 Other Alpha compilers provide the equivalent options called
8401 @option{-scope_safe} and @option{-resumption_safe}.
8403 @item -mieee-conformant
8404 @opindex mieee-conformant
8405 This option marks the generated code as IEEE conformant. You must not
8406 use this option unless you also specify @option{-mtrap-precision=i} and either
8407 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
8408 is to emit the line @samp{.eflag 48} in the function prologue of the
8409 generated assembly file. Under DEC Unix, this has the effect that
8410 IEEE-conformant math library routines will be linked in.
8412 @item -mbuild-constants
8413 @opindex mbuild-constants
8414 Normally GCC examines a 32- or 64-bit integer constant to
8415 see if it can construct it from smaller constants in two or three
8416 instructions. If it cannot, it will output the constant as a literal and
8417 generate code to load it from the data segment at runtime.
8419 Use this option to require GCC to construct @emph{all} integer constants
8420 using code, even if it takes more instructions (the maximum is six).
8422 You would typically use this option to build a shared library dynamic
8423 loader. Itself a shared library, it must relocate itself in memory
8424 before it can find the variables and constants in its own data segment.
8430 Select whether to generate code to be assembled by the vendor-supplied
8431 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
8449 Indicate whether GCC should generate code to use the optional BWX,
8450 CIX, FIX and MAX instruction sets. The default is to use the instruction
8451 sets supported by the CPU type specified via @option{-mcpu=} option or that
8452 of the CPU on which GCC was built if none was specified.
8457 @opindex mfloat-ieee
8458 Generate code that uses (does not use) VAX F and G floating point
8459 arithmetic instead of IEEE single and double precision.
8461 @item -mexplicit-relocs
8462 @itemx -mno-explicit-relocs
8463 @opindex mexplicit-relocs
8464 @opindex mno-explicit-relocs
8465 Older Alpha assemblers provided no way to generate symbol relocations
8466 except via assembler macros. Use of these macros does not allow
8467 optimial instruction scheduling. GNU binutils as of version 2.12
8468 supports a new syntax that allows the compiler to explicitly mark
8469 which relocations should apply to which instructions. This option
8470 is mostly useful for debugging, as GCC detects the capabilities of
8471 the assembler when it is built and sets the default accordingly.
8475 @opindex msmall-data
8476 @opindex mlarge-data
8477 When @option{-mexplicit-relocs} is in effect, static data is
8478 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
8479 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
8480 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
8481 16-bit relocations off of the @code{$gp} register. This limits the
8482 size of the small data area to 64KB, but allows the variables to be
8483 directly accessed via a single instruction.
8485 The default is @option{-mlarge-data}. With this option the data area
8486 is limited to just below 2GB. Programs that require more than 2GB of
8487 data must use @code{malloc} or @code{mmap} to allocate the data in the
8488 heap instead of in the program's data segment.
8490 When generating code for shared libraries, @option{-fpic} implies
8491 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
8493 @item -mcpu=@var{cpu_type}
8495 Set the instruction set and instruction scheduling parameters for
8496 machine type @var{cpu_type}. You can specify either the @samp{EV}
8497 style name or the corresponding chip number. GCC supports scheduling
8498 parameters for the EV4, EV5 and EV6 family of processors and will
8499 choose the default values for the instruction set from the processor
8500 you specify. If you do not specify a processor type, GCC will default
8501 to the processor on which the compiler was built.
8503 Supported values for @var{cpu_type} are
8509 Schedules as an EV4 and has no instruction set extensions.
8513 Schedules as an EV5 and has no instruction set extensions.
8517 Schedules as an EV5 and supports the BWX extension.
8522 Schedules as an EV5 and supports the BWX and MAX extensions.
8526 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
8530 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
8533 @item -mtune=@var{cpu_type}
8535 Set only the instruction scheduling parameters for machine type
8536 @var{cpu_type}. The instruction set is not changed.
8538 @item -mmemory-latency=@var{time}
8539 @opindex mmemory-latency
8540 Sets the latency the scheduler should assume for typical memory
8541 references as seen by the application. This number is highly
8542 dependent on the memory access patterns used by the application
8543 and the size of the external cache on the machine.
8545 Valid options for @var{time} are
8549 A decimal number representing clock cycles.
8555 The compiler contains estimates of the number of clock cycles for
8556 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
8557 (also called Dcache, Scache, and Bcache), as well as to main memory.
8558 Note that L3 is only valid for EV5.
8563 @node DEC Alpha/VMS Options
8564 @subsection DEC Alpha/VMS Options
8566 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
8569 @item -mvms-return-codes
8570 @opindex mvms-return-codes
8571 Return VMS condition codes from main. The default is to return POSIX
8572 style condition (e.g.@ error) codes.
8575 @node Clipper Options
8576 @subsection Clipper Options
8578 These @samp{-m} options are defined for the Clipper implementations:
8583 Produce code for a C300 Clipper processor. This is the default.
8587 Produce code for a C400 Clipper processor, i.e.@: use floating point
8591 @node H8/300 Options
8592 @subsection H8/300 Options
8594 These @samp{-m} options are defined for the H8/300 implementations:
8599 Shorten some address references at link time, when possible; uses the
8600 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
8601 ld.info, Using ld}, for a fuller description.
8605 Generate code for the H8/300H@.
8609 Generate code for the H8S@.
8613 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
8617 Make @code{int} data 32 bits by default.
8621 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
8622 The default for the H8/300H and H8S is to align longs and floats on 4
8624 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
8625 This option has no effect on the H8/300.
8629 @subsection SH Options
8631 These @samp{-m} options are defined for the SH implementations:
8636 Generate code for the SH1.
8640 Generate code for the SH2.
8644 Generate code for the SH3.
8648 Generate code for the SH3e.
8652 Generate code for the SH4 without a floating-point unit.
8654 @item -m4-single-only
8655 @opindex m4-single-only
8656 Generate code for the SH4 with a floating-point unit that only
8657 supports single-precision arithmetic.
8661 Generate code for the SH4 assuming the floating-point unit is in
8662 single-precision mode by default.
8666 Generate code for the SH4.
8670 Compile code for the processor in big endian mode.
8674 Compile code for the processor in little endian mode.
8678 Align doubles at 64-bit boundaries. Note that this changes the calling
8679 conventions, and thus some functions from the standard C library will
8680 not work unless you recompile it first with @option{-mdalign}.
8684 Shorten some address references at link time, when possible; uses the
8685 linker option @option{-relax}.
8689 Use 32-bit offsets in @code{switch} tables. The default is to use
8694 Enable the use of the instruction @code{fmovd}.
8698 Comply with the calling conventions defined by Hitachi.
8702 Mark the @code{MAC} register as call-clobbered, even if
8703 @option{-mhitachi} is given.
8707 Increase IEEE-compliance of floating-point code.
8711 Dump instruction size and location in the assembly code.
8715 This option is deprecated. It pads structures to multiple of 4 bytes,
8716 which is incompatible with the SH ABI@.
8720 Optimize for space instead of speed. Implied by @option{-Os}.
8724 When generating position-independent code, emit function calls using
8725 the Global Offset Table instead of the Procedure Linkage Table.
8729 Generate a library function call to invalidate instruction cache
8730 entries, after fixing up a trampoline. This library function call
8731 doesn't assume it can write to the whole memory address space. This
8732 is the default when the target is @code{sh-*-linux*}.
8735 @node System V Options
8736 @subsection Options for System V
8738 These additional options are available on System V Release 4 for
8739 compatibility with other compilers on those systems:
8744 Create a shared object.
8745 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
8749 Identify the versions of each tool used by the compiler, in a
8750 @code{.ident} assembler directive in the output.
8754 Refrain from adding @code{.ident} directives to the output file (this is
8757 @item -YP,@var{dirs}
8759 Search the directories @var{dirs}, and no others, for libraries
8760 specified with @option{-l}.
8764 Look in the directory @var{dir} to find the M4 preprocessor.
8765 The assembler uses this option.
8766 @c This is supposed to go with a -Yd for predefined M4 macro files, but
8767 @c the generic assembler that comes with Solaris takes just -Ym.
8770 @node TMS320C3x/C4x Options
8771 @subsection TMS320C3x/C4x Options
8772 @cindex TMS320C3x/C4x Options
8774 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
8778 @item -mcpu=@var{cpu_type}
8780 Set the instruction set, register set, and instruction scheduling
8781 parameters for machine type @var{cpu_type}. Supported values for
8782 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
8783 @samp{c44}. The default is @samp{c40} to generate code for the
8788 @itemx -msmall-memory
8790 @opindex mbig-memory
8792 @opindex msmall-memory
8794 Generates code for the big or small memory model. The small memory
8795 model assumed that all data fits into one 64K word page. At run-time
8796 the data page (DP) register must be set to point to the 64K page
8797 containing the .bss and .data program sections. The big memory model is
8798 the default and requires reloading of the DP register for every direct
8805 Allow (disallow) allocation of general integer operands into the block
8812 Enable (disable) generation of code using decrement and branch,
8813 DBcond(D), instructions. This is enabled by default for the C4x. To be
8814 on the safe side, this is disabled for the C3x, since the maximum
8815 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
8816 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
8817 that it can utilize the decrement and branch instruction, but will give
8818 up if there is more than one memory reference in the loop. Thus a loop
8819 where the loop counter is decremented can generate slightly more
8820 efficient code, in cases where the RPTB instruction cannot be utilized.
8822 @item -mdp-isr-reload
8824 @opindex mdp-isr-reload
8826 Force the DP register to be saved on entry to an interrupt service
8827 routine (ISR), reloaded to point to the data section, and restored on
8828 exit from the ISR@. This should not be required unless someone has
8829 violated the small memory model by modifying the DP register, say within
8836 For the C3x use the 24-bit MPYI instruction for integer multiplies
8837 instead of a library call to guarantee 32-bit results. Note that if one
8838 of the operands is a constant, then the multiplication will be performed
8839 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
8840 then squaring operations are performed inline instead of a library call.
8843 @itemx -mno-fast-fix
8845 @opindex mno-fast-fix
8846 The C3x/C4x FIX instruction to convert a floating point value to an
8847 integer value chooses the nearest integer less than or equal to the
8848 floating point value rather than to the nearest integer. Thus if the
8849 floating point number is negative, the result will be incorrectly
8850 truncated an additional code is necessary to detect and correct this
8851 case. This option can be used to disable generation of the additional
8852 code required to correct the result.
8858 Enable (disable) generation of repeat block sequences using the RPTB
8859 instruction for zero overhead looping. The RPTB construct is only used
8860 for innermost loops that do not call functions or jump across the loop
8861 boundaries. There is no advantage having nested RPTB loops due to the
8862 overhead required to save and restore the RC, RS, and RE registers.
8863 This is enabled by default with @option{-O2}.
8865 @item -mrpts=@var{count}
8869 Enable (disable) the use of the single instruction repeat instruction
8870 RPTS@. If a repeat block contains a single instruction, and the loop
8871 count can be guaranteed to be less than the value @var{count}, GCC will
8872 emit a RPTS instruction instead of a RPTB@. If no value is specified,
8873 then a RPTS will be emitted even if the loop count cannot be determined
8874 at compile time. Note that the repeated instruction following RPTS does
8875 not have to be reloaded from memory each iteration, thus freeing up the
8876 CPU buses for operands. However, since interrupts are blocked by this
8877 instruction, it is disabled by default.
8879 @item -mloop-unsigned
8880 @itemx -mno-loop-unsigned
8881 @opindex mloop-unsigned
8882 @opindex mno-loop-unsigned
8883 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
8884 is @math{2^{31} + 1} since these instructions test if the iteration count is
8885 negative to terminate the loop. If the iteration count is unsigned
8886 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
8887 exceeded. This switch allows an unsigned iteration count.
8891 Try to emit an assembler syntax that the TI assembler (asm30) is happy
8892 with. This also enforces compatibility with the API employed by the TI
8893 C3x C compiler. For example, long doubles are passed as structures
8894 rather than in floating point registers.
8900 Generate code that uses registers (stack) for passing arguments to functions.
8901 By default, arguments are passed in registers where possible rather
8902 than by pushing arguments on to the stack.
8904 @item -mparallel-insns
8905 @itemx -mno-parallel-insns
8906 @opindex mparallel-insns
8907 @opindex mno-parallel-insns
8908 Allow the generation of parallel instructions. This is enabled by
8909 default with @option{-O2}.
8911 @item -mparallel-mpy
8912 @itemx -mno-parallel-mpy
8913 @opindex mparallel-mpy
8914 @opindex mno-parallel-mpy
8915 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
8916 provided @option{-mparallel-insns} is also specified. These instructions have
8917 tight register constraints which can pessimize the code generation
8923 @subsection V850 Options
8924 @cindex V850 Options
8926 These @samp{-m} options are defined for V850 implementations:
8930 @itemx -mno-long-calls
8931 @opindex mlong-calls
8932 @opindex mno-long-calls
8933 Treat all calls as being far away (near). If calls are assumed to be
8934 far away, the compiler will always load the functions address up into a
8935 register, and call indirect through the pointer.
8941 Do not optimize (do optimize) basic blocks that use the same index
8942 pointer 4 or more times to copy pointer into the @code{ep} register, and
8943 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
8944 option is on by default if you optimize.
8946 @item -mno-prolog-function
8947 @itemx -mprolog-function
8948 @opindex mno-prolog-function
8949 @opindex mprolog-function
8950 Do not use (do use) external functions to save and restore registers at
8951 the prolog and epilog of a function. The external functions are slower,
8952 but use less code space if more than one function saves the same number
8953 of registers. The @option{-mprolog-function} option is on by default if
8958 Try to make the code as small as possible. At present, this just turns
8959 on the @option{-mep} and @option{-mprolog-function} options.
8963 Put static or global variables whose size is @var{n} bytes or less into
8964 the tiny data area that register @code{ep} points to. The tiny data
8965 area can hold up to 256 bytes in total (128 bytes for byte references).
8969 Put static or global variables whose size is @var{n} bytes or less into
8970 the small data area that register @code{gp} points to. The small data
8971 area can hold up to 64 kilobytes.
8975 Put static or global variables whose size is @var{n} bytes or less into
8976 the first 32 kilobytes of memory.
8980 Specify that the target processor is the V850.
8983 @opindex mbig-switch
8984 Generate code suitable for big switch tables. Use this option only if
8985 the assembler/linker complain about out of range branches within a switch
8990 This option will cause r2 and r5 to be used in the code generated by
8991 the compiler. This setting is the default.
8994 @opindex -mno-app-regs
8995 This option will cause r2 and r5 to be treated as fixed registers.
8999 Specify that the target processor is the V850E. The preprocessor
9000 constant @samp{__v850e__} will be defined if this option is used.
9002 If neither @option{-mv850} nor @option{-mv850e} are defined
9003 then a default target processor will be chosen and the relevant
9004 @samp{__v850*__} preprocessor constant will be defined.
9006 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
9007 defined, regardless of which processor variant is the target.
9009 @item -mdisable-callt
9010 @opindex -mdisable-callt
9011 This option will suppress generation of the CALLT instruction for the
9012 v850e flavors of the v850 architecture. The default is
9013 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
9018 @subsection ARC Options
9021 These options are defined for ARC implementations:
9026 Compile code for little endian mode. This is the default.
9030 Compile code for big endian mode.
9033 @opindex mmangle-cpu
9034 Prepend the name of the cpu to all public symbol names.
9035 In multiple-processor systems, there are many ARC variants with different
9036 instruction and register set characteristics. This flag prevents code
9037 compiled for one cpu to be linked with code compiled for another.
9038 No facility exists for handling variants that are ``almost identical''.
9039 This is an all or nothing option.
9041 @item -mcpu=@var{cpu}
9043 Compile code for ARC variant @var{cpu}.
9044 Which variants are supported depend on the configuration.
9045 All variants support @option{-mcpu=base}, this is the default.
9047 @item -mtext=@var{text-section}
9048 @itemx -mdata=@var{data-section}
9049 @itemx -mrodata=@var{readonly-data-section}
9053 Put functions, data, and readonly data in @var{text-section},
9054 @var{data-section}, and @var{readonly-data-section} respectively
9055 by default. This can be overridden with the @code{section} attribute.
9056 @xref{Variable Attributes}.
9061 @subsection NS32K Options
9062 @cindex NS32K options
9064 These are the @samp{-m} options defined for the 32000 series. The default
9065 values for these options depends on which style of 32000 was selected when
9066 the compiler was configured; the defaults for the most common choices are
9074 Generate output for a 32032. This is the default
9075 when the compiler is configured for 32032 and 32016 based systems.
9081 Generate output for a 32332. This is the default
9082 when the compiler is configured for 32332-based systems.
9088 Generate output for a 32532. This is the default
9089 when the compiler is configured for 32532-based systems.
9093 Generate output containing 32081 instructions for floating point.
9094 This is the default for all systems.
9098 Generate output containing 32381 instructions for floating point. This
9099 also implies @option{-m32081}. The 32381 is only compatible with the 32332
9100 and 32532 cpus. This is the default for the pc532-netbsd configuration.
9104 Try and generate multiply-add floating point instructions @code{polyF}
9105 and @code{dotF}. This option is only available if the @option{-m32381}
9106 option is in effect. Using these instructions requires changes to
9107 register allocation which generally has a negative impact on
9108 performance. This option should only be enabled when compiling code
9109 particularly likely to make heavy use of multiply-add instructions.
9112 @opindex mnomulti-add
9113 Do not try and generate multiply-add floating point instructions
9114 @code{polyF} and @code{dotF}. This is the default on all platforms.
9117 @opindex msoft-float
9118 Generate output containing library calls for floating point.
9119 @strong{Warning:} the requisite libraries may not be available.
9121 @item -mieee-compare
9122 @itemx -mno-ieee-compare
9123 @opindex mieee-compare
9124 @opindex mno-ieee-compare
9125 Control whether or not the compiler uses IEEE floating point
9126 comparisons. These handle correctly the case where the result of a
9127 comparison is unordered.
9128 @strong{Warning:} the requisite kernel support may not be available.
9131 @opindex mnobitfield
9132 Do not use the bit-field instructions. On some machines it is faster to
9133 use shifting and masking operations. This is the default for the pc532.
9137 Do use the bit-field instructions. This is the default for all platforms
9142 Use a different function-calling convention, in which functions
9143 that take a fixed number of arguments return pop their
9144 arguments on return with the @code{ret} instruction.
9146 This calling convention is incompatible with the one normally
9147 used on Unix, so you cannot use it if you need to call libraries
9148 compiled with the Unix compiler.
9150 Also, you must provide function prototypes for all functions that
9151 take variable numbers of arguments (including @code{printf});
9152 otherwise incorrect code will be generated for calls to those
9155 In addition, seriously incorrect code will result if you call a
9156 function with too many arguments. (Normally, extra arguments are
9157 harmlessly ignored.)
9159 This option takes its name from the 680x0 @code{rtd} instruction.
9164 Use a different function-calling convention where the first two arguments
9165 are passed in registers.
9167 This calling convention is incompatible with the one normally
9168 used on Unix, so you cannot use it if you need to call libraries
9169 compiled with the Unix compiler.
9172 @opindex mnoregparam
9173 Do not pass any arguments in registers. This is the default for all
9178 It is OK to use the sb as an index register which is always loaded with
9179 zero. This is the default for the pc532-netbsd target.
9183 The sb register is not available for use or has not been initialized to
9184 zero by the run time system. This is the default for all targets except
9185 the pc532-netbsd. It is also implied whenever @option{-mhimem} or
9186 @option{-fpic} is set.
9190 Many ns32000 series addressing modes use displacements of up to 512MB@.
9191 If an address is above 512MB then displacements from zero can not be used.
9192 This option causes code to be generated which can be loaded above 512MB@.
9193 This may be useful for operating systems or ROM code.
9197 Assume code will be loaded in the first 512MB of virtual address space.
9198 This is the default for all platforms.
9204 @subsection AVR Options
9207 These options are defined for AVR implementations:
9210 @item -mmcu=@var{mcu}
9212 Specify ATMEL AVR instruction set or MCU type.
9214 Instruction set avr1 is for the minimal AVR core, not supported by the C
9215 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
9216 attiny11, attiny12, attiny15, attiny28).
9218 Instruction set avr2 (default) is for the classic AVR core with up to
9219 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
9220 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
9221 at90c8534, at90s8535).
9223 Instruction set avr3 is for the classic AVR core with up to 128K program
9224 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
9226 Instruction set avr4 is for the enhanced AVR core with up to 8K program
9227 memory space (MCU types: atmega8, atmega83, atmega85).
9229 Instruction set avr5 is for the enhanced AVR core with up to 128K program
9230 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
9231 atmega64, atmega128, at43usb355, at94k).
9235 Output instruction sizes to the asm file.
9237 @item -minit-stack=@var{N}
9238 @opindex minit-stack
9239 Specify the initial stack address, which may be a symbol or numeric value,
9240 @samp{__stack} is the default.
9242 @item -mno-interrupts
9243 @opindex mno-interrupts
9244 Generated code is not compatible with hardware interrupts.
9245 Code size will be smaller.
9247 @item -mcall-prologues
9248 @opindex mcall-prologues
9249 Functions prologues/epilogues expanded as call to appropriate
9250 subroutines. Code size will be smaller.
9252 @item -mno-tablejump
9253 @opindex mno-tablejump
9254 Do not generate tablejump insns which sometimes increase code size.
9257 @opindex mtiny-stack
9258 Change only the low 8 bits of the stack pointer.
9262 @subsection MCore Options
9263 @cindex MCore options
9265 These are the @samp{-m} options defined for the Motorola M*Core
9275 @opindex mno-hardlit
9276 Inline constants into the code stream if it can be done in two
9277 instructions or less.
9285 Use the divide instruction. (Enabled by default).
9287 @item -mrelax-immediate
9288 @itemx -mrelax-immediate
9289 @itemx -mno-relax-immediate
9290 @opindex mrelax-immediate
9291 @opindex mrelax-immediate
9292 @opindex mno-relax-immediate
9293 Allow arbitrary sized immediates in bit operations.
9295 @item -mwide-bitfields
9296 @itemx -mwide-bitfields
9297 @itemx -mno-wide-bitfields
9298 @opindex mwide-bitfields
9299 @opindex mwide-bitfields
9300 @opindex mno-wide-bitfields
9301 Always treat bit-fields as int-sized.
9303 @item -m4byte-functions
9304 @itemx -m4byte-functions
9305 @itemx -mno-4byte-functions
9306 @opindex m4byte-functions
9307 @opindex m4byte-functions
9308 @opindex mno-4byte-functions
9309 Force all functions to be aligned to a four byte boundary.
9311 @item -mcallgraph-data
9312 @itemx -mcallgraph-data
9313 @itemx -mno-callgraph-data
9314 @opindex mcallgraph-data
9315 @opindex mcallgraph-data
9316 @opindex mno-callgraph-data
9317 Emit callgraph information.
9321 @itemx -mno-slow-bytes
9322 @opindex mslow-bytes
9323 @opindex mslow-bytes
9324 @opindex mno-slow-bytes
9325 Prefer word access when reading byte quantities.
9327 @item -mlittle-endian
9328 @itemx -mlittle-endian
9330 @opindex mlittle-endian
9331 @opindex mlittle-endian
9332 @opindex mbig-endian
9333 Generate code for a little endian target.
9341 Generate code for the 210 processor.
9345 @subsection IA-64 Options
9346 @cindex IA-64 Options
9348 These are the @samp{-m} options defined for the Intel IA-64 architecture.
9352 @opindex mbig-endian
9353 Generate code for a big endian target. This is the default for HP-UX@.
9355 @item -mlittle-endian
9356 @opindex mlittle-endian
9357 Generate code for a little endian target. This is the default for AIX5
9364 Generate (or don't) code for the GNU assembler. This is the default.
9365 @c Also, this is the default if the configure option @option{--with-gnu-as}
9372 Generate (or don't) code for the GNU linker. This is the default.
9373 @c Also, this is the default if the configure option @option{--with-gnu-ld}
9378 Generate code that does not use a global pointer register. The result
9379 is not position independent code, and violates the IA-64 ABI@.
9381 @item -mvolatile-asm-stop
9382 @itemx -mno-volatile-asm-stop
9383 @opindex mvolatile-asm-stop
9384 @opindex mno-volatile-asm-stop
9385 Generate (or don't) a stop bit immediately before and after volatile asm
9390 Generate code that works around Itanium B step errata.
9392 @item -mregister-names
9393 @itemx -mno-register-names
9394 @opindex mregister-names
9395 @opindex mno-register-names
9396 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
9397 the stacked registers. This may make assembler output more readable.
9403 Disable (or enable) optimizations that use the small data section. This may
9404 be useful for working around optimizer bugs.
9407 @opindex mconstant-gp
9408 Generate code that uses a single constant global pointer value. This is
9409 useful when compiling kernel code.
9413 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
9414 This is useful when compiling firmware code.
9416 @item -minline-float-divide-min-latency
9417 @opindex minline-float-divide-min-latency
9418 Generate code for inline divides of floating point values
9419 using the minimum latency algorithm.
9421 @item -minline-float-divide-max-throughput
9422 @opindex minline-float-divide-max-throughput
9423 Generate code for inline divides of floating point values
9424 using the maximum throughput algorithm.
9426 @item -minline-int-divide-min-latency
9427 @opindex minline-int-divide-min-latency
9428 Generate code for inline divides of integer values
9429 using the minimum latency algorithm.
9431 @item -minline-int-divide-max-throughput
9432 @opindex minline-int-divide-max-throughput
9433 Generate code for inline divides of integer values
9434 using the maximum throughput algorithm.
9436 @item -mno-dwarf2-asm
9438 @opindex mno-dwarf2-asm
9439 @opindex mdwarf2-asm
9440 Don't (or do) generate assembler code for the DWARF2 line number debugging
9441 info. This may be useful when not using the GNU assembler.
9443 @item -mfixed-range=@var{register-range}
9444 @opindex mfixed-range
9445 Generate code treating the given register range as fixed registers.
9446 A fixed register is one that the register allocator can not use. This is
9447 useful when compiling kernel code. A register range is specified as
9448 two registers separated by a dash. Multiple register ranges can be
9449 specified separated by a comma.
9453 @subsection D30V Options
9454 @cindex D30V Options
9456 These @samp{-m} options are defined for D30V implementations:
9461 Link the @samp{.text}, @samp{.data}, @samp{.bss}, @samp{.strings},
9462 @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into external
9463 memory, which starts at location @code{0x80000000}.
9467 Same as the @option{-mextmem} switch.
9471 Link the @samp{.text} section into onchip text memory, which starts at
9472 location @code{0x0}. Also link @samp{.data}, @samp{.bss},
9473 @samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections
9474 into onchip data memory, which starts at location @code{0x20000000}.
9476 @item -mno-asm-optimize
9477 @itemx -masm-optimize
9478 @opindex mno-asm-optimize
9479 @opindex masm-optimize
9480 Disable (enable) passing @option{-O} to the assembler when optimizing.
9481 The assembler uses the @option{-O} option to automatically parallelize
9482 adjacent short instructions where possible.
9484 @item -mbranch-cost=@var{n}
9485 @opindex mbranch-cost
9486 Increase the internal costs of branches to @var{n}. Higher costs means
9487 that the compiler will issue more instructions to avoid doing a branch.
9490 @item -mcond-exec=@var{n}
9492 Specify the maximum number of conditionally executed instructions that
9493 replace a branch. The default is 4.
9496 @node S/390 and zSeries Options
9497 @subsection S/390 and zSeries Options
9498 @cindex S/390 and zSeries Options
9500 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
9505 @opindex mhard-float
9506 @opindex msoft-float
9507 Use (do not use) the hardware floating-point instructions and registers
9508 for floating-point operations. When @option{-msoft-float} is specified,
9509 functions in @file{libgcc.a} will be used to perform floating-point
9510 operations. When @option{-mhard-float} is specified, the compiler
9511 generates IEEE floating-point instructions. This is the default.
9514 @itemx -mno-backchain
9516 @opindex mno-backchain
9517 Generate (or do not generate) code which maintains an explicit
9518 backchain within the stack frame that points to the caller's frame.
9519 This is currently needed to allow debugging. The default is to
9520 generate the backchain.
9523 @itemx -mno-small-exec
9524 @opindex msmall-exec
9525 @opindex mno-small-exec
9526 Generate (or do not generate) code using the @code{bras} instruction
9527 to do subroutine calls.
9528 This only works reliably if the total executable size does not
9529 exceed 64k. The default is to use the @code{basr} instruction instead,
9530 which does not have this limitation.
9536 When @option{-m31} is specified, generate code compliant to the
9537 Linux for S/390 ABI@. When @option{-m64} is specified, generate
9538 code compliant to the Linux for zSeries ABI@. This allows GCC in
9539 particular to generate 64-bit instructions. For the @samp{s390}
9540 targets, the default is @option{-m31}, while the @samp{s390x}
9541 targets default to @option{-m64}.
9547 Generate (or do not generate) code using the @code{mvcle} instruction
9548 to perform block moves. When @option{-mno-mvcle} is specifed,
9549 use a @code{mvc} loop instead. This is the default.
9555 Print (or do not print) additional debug information when compiling.
9556 The default is to not print debug information.
9561 @subsection CRIS Options
9562 @cindex CRIS Options
9564 These options are defined specifically for the CRIS ports.
9567 @item -march=@var{architecture-type}
9568 @itemx -mcpu=@var{architecture-type}
9571 Generate code for the specified architecture. The choices for
9572 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
9573 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX.
9574 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
9577 @item -mtune=@var{architecture-type}
9579 Tune to @var{architecture-type} everything applicable about the generated
9580 code, except for the ABI and the set of available instructions. The
9581 choices for @var{architecture-type} are the same as for
9582 @option{-march=@var{architecture-type}}.
9584 @item -mmax-stack-frame=@var{n}
9585 @opindex mmax-stack-frame
9586 Warn when the stack frame of a function exceeds @var{n} bytes.
9588 @item -melinux-stacksize=@var{n}
9589 @opindex melinux-stacksize
9590 Only available with the @samp{cris-axis-aout} target. Arranges for
9591 indications in the program to the kernel loader that the stack of the
9592 program should be set to @var{n} bytes.
9598 The options @option{-metrax4} and @option{-metrax100} are synonyms for
9599 @option{-march=v3} and @option{-march=v8} respectively.
9603 Enable CRIS-specific verbose debug-related information in the assembly
9604 code. This option also has the effect to turn off the @samp{#NO_APP}
9605 formatted-code indicator to the assembler at the beginning of the
9610 Do not use condition-code results from previous instruction; always emit
9611 compare and test instructions before use of condition codes.
9613 @item -mno-side-effects
9614 @opindex mno-side-effects
9615 Do not emit instructions with side-effects in addressing modes other than
9619 @itemx -mno-stack-align
9621 @itemx -mno-data-align
9622 @itemx -mconst-align
9623 @itemx -mno-const-align
9624 @opindex mstack-align
9625 @opindex mno-stack-align
9626 @opindex mdata-align
9627 @opindex mno-data-align
9628 @opindex mconst-align
9629 @opindex mno-const-align
9630 These options (no-options) arranges (eliminate arrangements) for the
9631 stack-frame, individual data and constants to be aligned for the maximum
9632 single data access size for the chosen CPU model. The default is to
9633 arrange for 32-bit alignment. ABI details such as structure layout are
9634 not affected by these options.
9642 Similar to the stack- data- and const-align options above, these options
9643 arrange for stack-frame, writable data and constants to all be 32-bit,
9644 16-bit or 8-bit aligned. The default is 32-bit alignment.
9646 @item -mno-prologue-epilogue
9647 @itemx -mprologue-epilogue
9648 @opindex mno-prologue-epilogue
9649 @opindex mprologue-epilogue
9650 With @option{-mno-prologue-epilogue}, the normal function prologue and
9651 epilogue that sets up the stack-frame are omitted and no return
9652 instructions or return sequences are generated in the code. Use this
9653 option only together with visual inspection of the compiled code: no
9654 warnings or errors are generated when call-saved registers must be saved,
9655 or storage for local variable needs to be allocated.
9661 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
9662 instruction sequences that load addresses for functions from the PLT part
9663 of the GOT rather than (traditional on other architectures) calls to the
9664 PLT. The default is @option{-mgotplt}.
9668 Legacy no-op option only recognized with the cris-axis-aout target.
9672 Legacy no-op option only recognized with the cris-axis-elf and
9673 cris-axis-linux-gnu targets.
9677 Only recognized with the cris-axis-aout target, where it selects a
9678 GNU/linux-like multilib, include files and instruction set for
9683 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
9687 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
9688 to link with input-output functions from a simulator library. Code,
9689 initialized data and zero-initialized data are allocated consecutively.
9693 Like @option{-sim}, but pass linker options to locate initialized data at
9694 0x40000000 and zero-initialized data at 0x80000000.
9698 @subsection MMIX Options
9699 @cindex MMIX Options
9701 These options are defined for the MMIX:
9705 @itemx -mno-libfuncs
9707 @opindex mno-libfuncs
9708 Specify that intrinsic library functions are being compiled, passing all
9709 values in registers, no matter the size.
9714 @opindex mno-epsilon
9715 Generate floating-point comparison instructions that compare with respect
9716 to the @code{rE} epsilon register.
9718 @item -mabi=mmixware
9720 @opindex mabi-mmixware
9722 Generate code that passes function parameters and return values that (in
9723 the called function) are seen as registers @code{$0} and up, as opposed to
9724 the GNU ABI which uses global registers @code{$231} and up.
9727 @itemx -mno-zero-extend
9728 @opindex mzero-extend
9729 @opindex mno-zero-extend
9730 When reading data from memory in sizes shorter than 64 bits, use (do not
9731 use) zero-extending load instructions by default, rather than
9732 sign-extending ones.
9735 @itemx -mno-knuthdiv
9737 @opindex mno-knuthdiv
9738 Make the result of a division yielding a remainder have the same sign as
9739 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
9740 remainder follows the sign of the dividend. Both methods are
9741 arithmetically valid, the latter being almost exclusively used.
9743 @item -mtoplevel-symbols
9744 @itemx -mno-toplevel-symbols
9745 @opindex mtoplevel-symbols
9746 @opindex mno-toplevel-symbols
9747 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
9748 code can be used with the @code{PREFIX} assembly directive.
9752 Generate an executable in the ELF format, rather than the default
9753 @samp{mmo} format used by the @command{mmix} simulator.
9755 @item -mbranch-predict
9756 @itemx -mno-branch-predict
9757 @opindex mbranch-predict
9758 @opindex mno-branch-predict
9759 Use (do not use) the probable-branch instructions, when static branch
9760 prediction indicates a probable branch.
9762 @item -mbase-addresses
9763 @itemx -mno-base-addresses
9764 @opindex mbase-addresses
9765 @opindex mno-base-addresses
9766 Generate (do not generate) code that uses @emph{base addresses}. Using a
9767 base address automatically generates a request (handled by the assembler
9768 and the linker) for a constant to be set up in a global register. The
9769 register is used for one or more base address requests within the range 0
9770 to 255 from the value held in the register. The generally leads to short
9771 and fast code, but the number of different data items that can be
9772 addressed is limited. This means that a program that uses lots of static
9773 data may require @option{-mno-base-addresses}.
9776 @itemx -mno-single-exit
9777 @opindex msingle-exit
9778 @opindex mno-single-exit
9779 Force (do not force) generated code to have a single exit point in each
9783 @node PDP-11 Options
9784 @subsection PDP-11 Options
9785 @cindex PDP-11 Options
9787 These options are defined for the PDP-11:
9792 Use hardware FPP floating point. This is the default. (FIS floating
9793 point on the PDP-11/40 is not supported.)
9796 @opindex msoft-float
9797 Do not use hardware floating point.
9801 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
9805 Return floating-point results in memory. This is the default.
9809 Generate code for a PDP-11/40.
9813 Generate code for a PDP-11/45. This is the default.
9817 Generate code for a PDP-11/10.
9819 @item -mbcopy-builtin
9820 @opindex bcopy-builtin
9821 Use inline @code{movstrhi} patterns for copying memory. This is the
9826 Do not use inline @code{movstrhi} patterns for copying memory.
9832 Use 16-bit @code{int}. This is the default.
9838 Use 32-bit @code{int}.
9843 @opindex mno-float32
9844 Use 64-bit @code{float}. This is the default.
9849 @opindex mno-float64
9850 Use 32-bit @code{float}.
9854 Use @code{abshi2} pattern. This is the default.
9858 Do not use @code{abshi2} pattern.
9860 @item -mbranch-expensive
9861 @opindex mbranch-expensive
9862 Pretend that branches are expensive. This is for experimenting with
9863 code generation only.
9865 @item -mbranch-cheap
9866 @opindex mbranch-cheap
9867 Do not pretend that branches are expensive. This is the default.
9871 Generate code for a system with split I&D.
9875 Generate code for a system without split I&D. This is the default.
9879 Use Unix assembler syntax. This is the default when configured for
9884 Use DEC assembler syntax. This is the default when configured for any
9885 PDP-11 target other than @samp{pdp11-*-bsd}.
9888 @node Xstormy16 Options
9889 @subsection Xstormy16 Options
9890 @cindex Xstormy16 Options
9892 These options are defined for Xstormy16:
9897 Choose startup files and linker script suitable for the simulator.
9900 @node Xtensa Options
9901 @subsection Xtensa Options
9902 @cindex Xtensa Options
9904 The Xtensa architecture is designed to support many different
9905 configurations. The compiler's default options can be set to match a
9906 particular Xtensa configuration by copying a configuration file into the
9907 GCC sources when building GCC@. The options below may be used to
9908 override the default options.
9912 @itemx -mlittle-endian
9913 @opindex mbig-endian
9914 @opindex mlittle-endian
9915 Specify big-endian or little-endian byte ordering for the target Xtensa
9921 @opindex mno-density
9922 Enable or disable use of the optional Xtensa code density instructions.
9928 Enable or disable use of the Xtensa MAC16 option. When enabled, GCC
9929 will generate MAC16 instructions from standard C code, with the
9930 limitation that it will use neither the MR register file nor any
9931 instruction that operates on the MR registers. When this option is
9932 disabled, GCC will translate 16-bit multiply/accumulate operations to a
9933 combination of core instructions and library calls, depending on whether
9934 any other multiplier options are enabled.
9940 Enable or disable use of the 16-bit integer multiplier option. When
9941 enabled, the compiler will generate 16-bit multiply instructions for
9942 multiplications of 16 bits or smaller in standard C code. When this
9943 option is disabled, the compiler will either use 32-bit multiply or
9944 MAC16 instructions if they are available or generate library calls to
9945 perform the multiply operations using shifts and adds.
9951 Enable or disable use of the 32-bit integer multiplier option. When
9952 enabled, the compiler will generate 32-bit multiply instructions for
9953 multiplications of 32 bits or smaller in standard C code. When this
9954 option is disabled, the compiler will generate library calls to perform
9955 the multiply operations using either shifts and adds or 16-bit multiply
9956 instructions if they are available.
9962 Enable or disable use of the optional normalization shift amount
9963 (@code{NSA}) instructions to implement the built-in @code{ffs} function.
9969 Enable or disable use of the optional minimum and maximum value
9976 Enable or disable use of the optional sign extend (@code{SEXT})
9980 @itemx -mno-booleans
9982 @opindex mno-booleans
9983 Enable or disable support for the boolean register file used by Xtensa
9984 coprocessors. This is not typically useful by itself but may be
9985 required for other options that make use of the boolean registers (e.g.,
9986 the floating-point option).
9990 @opindex mhard-float
9991 @opindex msoft-float
9992 Enable or disable use of the floating-point option. When enabled, GCC
9993 generates floating-point instructions for 32-bit @code{float}
9994 operations. When this option is disabled, GCC generates library calls
9995 to emulate 32-bit floating-point operations using integer instructions.
9996 Regardless of this option, 64-bit @code{double} operations are always
9997 emulated with calls to library functions.
10000 @itemx -mno-fused-madd
10001 @opindex mfused-madd
10002 @opindex mno-fused-madd
10003 Enable or disable use of fused multiply/add and multiply/subtract
10004 instructions in the floating-point option. This has no effect if the
10005 floating-point option is not also enabled. Disabling fused multiply/add
10006 and multiply/subtract instructions forces the compiler to use separate
10007 instructions for the multiply and add/subtract operations. This may be
10008 desirable in some cases where strict IEEE 754-compliant results are
10009 required: the fused multiply add/subtract instructions do not round the
10010 intermediate result, thereby producing results with @emph{more} bits of
10011 precision than specified by the IEEE standard. Disabling fused multiply
10012 add/subtract instructions also ensures that the program output is not
10013 sensitive to the compiler's ability to combine multiply and add/subtract
10016 @item -mserialize-volatile
10017 @itemx -mno-serialize-volatile
10018 @opindex mserialize-volatile
10019 @opindex mno-serialize-volatile
10020 When this option is enabled, GCC inserts @code{MEMW} instructions before
10021 @code{volatile} memory references to guarantee sequential consistency.
10022 The default is @option{-mserialize-volatile}. Use
10023 @option{-mno-serialize-volatile} to omit the @code{MEMW} instructions.
10025 @item -mtext-section-literals
10026 @itemx -mno-text-section-literals
10027 @opindex mtext-section-literals
10028 @opindex mno-text-section-literals
10029 Control the treatment of literal pools. The default is
10030 @option{-mno-text-section-literals}, which places literals in a separate
10031 section in the output file. This allows the literal pool to be placed
10032 in a data RAM/ROM, and it also allows the linker to combine literal
10033 pools from separate object files to remove redundant literals and
10034 improve code size. With @option{-mtext-section-literals}, the literals
10035 are interspersed in the text section in order to keep them as close as
10036 possible to their references. This may be necessary for large assembly
10039 @item -mtarget-align
10040 @itemx -mno-target-align
10041 @opindex mtarget-align
10042 @opindex mno-target-align
10043 When this option is enabled, GCC instructs the assembler to
10044 automatically align instructions to reduce branch penalties at the
10045 expense of some code density. The assembler attempts to widen density
10046 instructions to align branch targets and the instructions following call
10047 instructions. If there are not enough preceding safe density
10048 instructions to align a target, no widening will be performed. The
10049 default is @option{-mtarget-align}. These options do not affect the
10050 treatment of auto-aligned instructions like @code{LOOP}, which the
10051 assembler will always align, either by widening density instructions or
10052 by inserting no-op instructions.
10055 @itemx -mno-longcalls
10056 @opindex mlongcalls
10057 @opindex mno-longcalls
10058 When this option is enabled, GCC instructs the assembler to translate
10059 direct calls to indirect calls unless it can determine that the target
10060 of a direct call is in the range allowed by the call instruction. This
10061 translation typically occurs for calls to functions in other source
10062 files. Specifically, the assembler translates a direct @code{CALL}
10063 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
10064 The default is @option{-mno-longcalls}. This option should be used in
10065 programs where the call target can potentially be out of range. This
10066 option is implemented in the assembler, not the compiler, so the
10067 assembly code generated by GCC will still show direct call
10068 instructions---look at the disassembled object code to see the actual
10069 instructions. Note that the assembler will use an indirect call for
10070 every cross-file call, not just those that really will be out of range.
10073 @node Code Gen Options
10074 @section Options for Code Generation Conventions
10075 @cindex code generation conventions
10076 @cindex options, code generation
10077 @cindex run-time options
10079 These machine-independent options control the interface conventions
10080 used in code generation.
10082 Most of them have both positive and negative forms; the negative form
10083 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
10084 one of the forms is listed---the one which is not the default. You
10085 can figure out the other form by either removing @samp{no-} or adding
10090 @opindex fexceptions
10091 Enable exception handling. Generates extra code needed to propagate
10092 exceptions. For some targets, this implies GCC will generate frame
10093 unwind information for all functions, which can produce significant data
10094 size overhead, although it does not affect execution. If you do not
10095 specify this option, GCC will enable it by default for languages like
10096 C++ which normally require exception handling, and disable it for
10097 languages like C that do not normally require it. However, you may need
10098 to enable this option when compiling C code that needs to interoperate
10099 properly with exception handlers written in C++. You may also wish to
10100 disable this option if you are compiling older C++ programs that don't
10101 use exception handling.
10103 @item -fnon-call-exceptions
10104 @opindex fnon-call-exceptions
10105 Generate code that allows trapping instructions to throw exceptions.
10106 Note that this requires platform-specific runtime support that does
10107 not exist everywhere. Moreover, it only allows @emph{trapping}
10108 instructions to throw exceptions, i.e.@: memory references or floating
10109 point instructions. It does not allow exceptions to be thrown from
10110 arbitrary signal handlers such as @code{SIGALRM}.
10112 @item -funwind-tables
10113 @opindex funwind-tables
10114 Similar to @option{-fexceptions}, except that it will just generate any needed
10115 static data, but will not affect the generated code in any other way.
10116 You will normally not enable this option; instead, a language processor
10117 that needs this handling would enable it on your behalf.
10119 @item -fasynchronous-unwind-tables
10120 @opindex funwind-tables
10121 Generate unwind table in dwarf2 format, if supported by target machine. The
10122 table is exact at each instruction boundary, so it can be used for stack
10123 unwinding from asynchronous events (such as debugger or garbage collector).
10125 @item -fpcc-struct-return
10126 @opindex fpcc-struct-return
10127 Return ``short'' @code{struct} and @code{union} values in memory like
10128 longer ones, rather than in registers. This convention is less
10129 efficient, but it has the advantage of allowing intercallability between
10130 GCC-compiled files and files compiled with other compilers, particularly
10131 the Portable C Compiler (pcc).
10133 The precise convention for returning structures in memory depends
10134 on the target configuration macros.
10136 Short structures and unions are those whose size and alignment match
10137 that of some integer type.
10139 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
10140 switch is not binary compatible with code compiled with the
10141 @option{-freg-struct-return} switch.
10142 Use it to conform to a non-default application binary interface.
10144 @item -freg-struct-return
10145 @opindex freg-struct-return
10146 Return @code{struct} and @code{union} values in registers when possible.
10147 This is more efficient for small structures than
10148 @option{-fpcc-struct-return}.
10150 If you specify neither @option{-fpcc-struct-return} nor
10151 @option{-freg-struct-return}, GCC defaults to whichever convention is
10152 standard for the target. If there is no standard convention, GCC
10153 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
10154 the principal compiler. In those cases, we can choose the standard, and
10155 we chose the more efficient register return alternative.
10157 @strong{Warning:} code compiled with the @option{-freg-struct-return}
10158 switch is not binary compatible with code compiled with the
10159 @option{-fpcc-struct-return} switch.
10160 Use it to conform to a non-default application binary interface.
10162 @item -fshort-enums
10163 @opindex fshort-enums
10164 Allocate to an @code{enum} type only as many bytes as it needs for the
10165 declared range of possible values. Specifically, the @code{enum} type
10166 will be equivalent to the smallest integer type which has enough room.
10168 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
10169 code that is not binary compatible with code generated without that switch.
10170 Use it to conform to a non-default application binary interface.
10172 @item -fshort-double
10173 @opindex fshort-double
10174 Use the same size for @code{double} as for @code{float}.
10176 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
10177 code that is not binary compatible with code generated without that switch.
10178 Use it to conform to a non-default application binary interface.
10180 @item -fshort-wchar
10181 @opindex fshort-wchar
10182 Override the underlying type for @samp{wchar_t} to be @samp{short
10183 unsigned int} instead of the default for the target. This option is
10184 useful for building programs to run under WINE@.
10186 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
10187 code that is not binary compatible with code generated without that switch.
10188 Use it to conform to a non-default application binary interface.
10190 @item -fshared-data
10191 @opindex fshared-data
10192 Requests that the data and non-@code{const} variables of this
10193 compilation be shared data rather than private data. The distinction
10194 makes sense only on certain operating systems, where shared data is
10195 shared between processes running the same program, while private data
10196 exists in one copy per process.
10199 @opindex fno-common
10200 In C, allocate even uninitialized global variables in the data section of the
10201 object file, rather than generating them as common blocks. This has the
10202 effect that if the same variable is declared (without @code{extern}) in
10203 two different compilations, you will get an error when you link them.
10204 The only reason this might be useful is if you wish to verify that the
10205 program will work on other systems which always work this way.
10209 Ignore the @samp{#ident} directive.
10211 @item -fno-gnu-linker
10212 @opindex fno-gnu-linker
10213 Do not output global initializations (such as C++ constructors and
10214 destructors) in the form used by the GNU linker (on systems where the GNU
10215 linker is the standard method of handling them). Use this option when
10216 you want to use a non-GNU linker, which also requires using the
10217 @command{collect2} program to make sure the system linker includes
10218 constructors and destructors. (@command{collect2} is included in the GCC
10219 distribution.) For systems which @emph{must} use @command{collect2}, the
10220 compiler driver @command{gcc} is configured to do this automatically.
10222 @item -finhibit-size-directive
10223 @opindex finhibit-size-directive
10224 Don't output a @code{.size} assembler directive, or anything else that
10225 would cause trouble if the function is split in the middle, and the
10226 two halves are placed at locations far apart in memory. This option is
10227 used when compiling @file{crtstuff.c}; you should not need to use it
10230 @item -fverbose-asm
10231 @opindex fverbose-asm
10232 Put extra commentary information in the generated assembly code to
10233 make it more readable. This option is generally only of use to those
10234 who actually need to read the generated assembly code (perhaps while
10235 debugging the compiler itself).
10237 @option{-fno-verbose-asm}, the default, causes the
10238 extra information to be omitted and is useful when comparing two assembler
10243 Consider all memory references through pointers to be volatile.
10245 @item -fvolatile-global
10246 @opindex fvolatile-global
10247 Consider all memory references to extern and global data items to
10248 be volatile. GCC does not consider static data items to be volatile
10249 because of this switch.
10251 @item -fvolatile-static
10252 @opindex fvolatile-static
10253 Consider all memory references to static data to be volatile.
10257 @cindex global offset table
10259 Generate position-independent code (PIC) suitable for use in a shared
10260 library, if supported for the target machine. Such code accesses all
10261 constant addresses through a global offset table (GOT)@. The dynamic
10262 loader resolves the GOT entries when the program starts (the dynamic
10263 loader is not part of GCC; it is part of the operating system). If
10264 the GOT size for the linked executable exceeds a machine-specific
10265 maximum size, you get an error message from the linker indicating that
10266 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
10267 instead. (These maximums are 16k on the m88k, 8k on the SPARC, and 32k
10268 on the m68k and RS/6000. The 386 has no such limit.)
10270 Position-independent code requires special support, and therefore works
10271 only on certain machines. For the 386, GCC supports PIC for System V
10272 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
10273 position-independent.
10277 If supported for the target machine, emit position-independent code,
10278 suitable for dynamic linking and avoiding any limit on the size of the
10279 global offset table. This option makes a difference on the m68k, m88k,
10282 Position-independent code requires special support, and therefore works
10283 only on certain machines.
10285 @item -ffixed-@var{reg}
10287 Treat the register named @var{reg} as a fixed register; generated code
10288 should never refer to it (except perhaps as a stack pointer, frame
10289 pointer or in some other fixed role).
10291 @var{reg} must be the name of a register. The register names accepted
10292 are machine-specific and are defined in the @code{REGISTER_NAMES}
10293 macro in the machine description macro file.
10295 This flag does not have a negative form, because it specifies a
10298 @item -fcall-used-@var{reg}
10299 @opindex fcall-used
10300 Treat the register named @var{reg} as an allocable register that is
10301 clobbered by function calls. It may be allocated for temporaries or
10302 variables that do not live across a call. Functions compiled this way
10303 will not save and restore the register @var{reg}.
10305 It is an error to used this flag with the frame pointer or stack pointer.
10306 Use of this flag for other registers that have fixed pervasive roles in
10307 the machine's execution model will produce disastrous results.
10309 This flag does not have a negative form, because it specifies a
10312 @item -fcall-saved-@var{reg}
10313 @opindex fcall-saved
10314 Treat the register named @var{reg} as an allocable register saved by
10315 functions. It may be allocated even for temporaries or variables that
10316 live across a call. Functions compiled this way will save and restore
10317 the register @var{reg} if they use it.
10319 It is an error to used this flag with the frame pointer or stack pointer.
10320 Use of this flag for other registers that have fixed pervasive roles in
10321 the machine's execution model will produce disastrous results.
10323 A different sort of disaster will result from the use of this flag for
10324 a register in which function values may be returned.
10326 This flag does not have a negative form, because it specifies a
10329 @item -fpack-struct
10330 @opindex fpack-struct
10331 Pack all structure members together without holes.
10333 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
10334 code that is not binary compatible with code generated without that switch.
10335 Additionally, it makes the code suboptimial.
10336 Use it to conform to a non-default application binary interface.
10338 @item -finstrument-functions
10339 @opindex finstrument-functions
10340 Generate instrumentation calls for entry and exit to functions. Just
10341 after function entry and just before function exit, the following
10342 profiling functions will be called with the address of the current
10343 function and its call site. (On some platforms,
10344 @code{__builtin_return_address} does not work beyond the current
10345 function, so the call site information may not be available to the
10346 profiling functions otherwise.)
10349 void __cyg_profile_func_enter (void *this_fn,
10351 void __cyg_profile_func_exit (void *this_fn,
10355 The first argument is the address of the start of the current function,
10356 which may be looked up exactly in the symbol table.
10358 This instrumentation is also done for functions expanded inline in other
10359 functions. The profiling calls will indicate where, conceptually, the
10360 inline function is entered and exited. This means that addressable
10361 versions of such functions must be available. If all your uses of a
10362 function are expanded inline, this may mean an additional expansion of
10363 code size. If you use @samp{extern inline} in your C code, an
10364 addressable version of such functions must be provided. (This is
10365 normally the case anyways, but if you get lucky and the optimizer always
10366 expands the functions inline, you might have gotten away without
10367 providing static copies.)
10369 A function may be given the attribute @code{no_instrument_function}, in
10370 which case this instrumentation will not be done. This can be used, for
10371 example, for the profiling functions listed above, high-priority
10372 interrupt routines, and any functions from which the profiling functions
10373 cannot safely be called (perhaps signal handlers, if the profiling
10374 routines generate output or allocate memory).
10376 @item -fstack-check
10377 @opindex fstack-check
10378 Generate code to verify that you do not go beyond the boundary of the
10379 stack. You should specify this flag if you are running in an
10380 environment with multiple threads, but only rarely need to specify it in
10381 a single-threaded environment since stack overflow is automatically
10382 detected on nearly all systems if there is only one stack.
10384 Note that this switch does not actually cause checking to be done; the
10385 operating system must do that. The switch causes generation of code
10386 to ensure that the operating system sees the stack being extended.
10388 @item -fstack-limit-register=@var{reg}
10389 @itemx -fstack-limit-symbol=@var{sym}
10390 @itemx -fno-stack-limit
10391 @opindex fstack-limit-register
10392 @opindex fstack-limit-symbol
10393 @opindex fno-stack-limit
10394 Generate code to ensure that the stack does not grow beyond a certain value,
10395 either the value of a register or the address of a symbol. If the stack
10396 would grow beyond the value, a signal is raised. For most targets,
10397 the signal is raised before the stack overruns the boundary, so
10398 it is possible to catch the signal without taking special precautions.
10400 For instance, if the stack starts at absolute address @samp{0x80000000}
10401 and grows downwards, you can use the flags
10402 @option{-fstack-limit-symbol=__stack_limit} and
10403 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
10404 of 128KB@. Note that this may only work with the GNU linker.
10406 @cindex aliasing of parameters
10407 @cindex parameters, aliased
10408 @item -fargument-alias
10409 @itemx -fargument-noalias
10410 @itemx -fargument-noalias-global
10411 @opindex fargument-alias
10412 @opindex fargument-noalias
10413 @opindex fargument-noalias-global
10414 Specify the possible relationships among parameters and between
10415 parameters and global data.
10417 @option{-fargument-alias} specifies that arguments (parameters) may
10418 alias each other and may alias global storage.@*
10419 @option{-fargument-noalias} specifies that arguments do not alias
10420 each other, but may alias global storage.@*
10421 @option{-fargument-noalias-global} specifies that arguments do not
10422 alias each other and do not alias global storage.
10424 Each language will automatically use whatever option is required by
10425 the language standard. You should not need to use these options yourself.
10427 @item -fleading-underscore
10428 @opindex fleading-underscore
10429 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
10430 change the way C symbols are represented in the object file. One use
10431 is to help link with legacy assembly code.
10433 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
10434 generate code that is not binary compatible with code generated without that
10435 switch. Use it to conform to a non-default application binary interface.
10436 Not all targets provide complete support for this switch.
10438 @item -ftls-model=@var{model}
10439 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
10440 The @var{model} argument should be one of @code{global-dynamic},
10441 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
10443 The default without @option{-fpic} is @code{initial-exec}; with
10444 @option{-fpic} the default is @code{global-dynamic}.
10449 @node Environment Variables
10450 @section Environment Variables Affecting GCC
10451 @cindex environment variables
10453 @c man begin ENVIRONMENT
10455 This section describes several environment variables that affect how GCC
10456 operates. Some of them work by specifying directories or prefixes to use
10457 when searching for various kinds of files. Some are used to specify other
10458 aspects of the compilation environment.
10460 Note that you can also specify places to search using options such as
10461 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
10462 take precedence over places specified using environment variables, which
10463 in turn take precedence over those specified by the configuration of GCC@.
10464 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
10465 GNU Compiler Collection (GCC) Internals}.
10470 @c @itemx LC_COLLATE
10472 @c @itemx LC_MONETARY
10473 @c @itemx LC_NUMERIC
10478 @c @findex LC_COLLATE
10479 @findex LC_MESSAGES
10480 @c @findex LC_MONETARY
10481 @c @findex LC_NUMERIC
10485 These environment variables control the way that GCC uses
10486 localization information that allow GCC to work with different
10487 national conventions. GCC inspects the locale categories
10488 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
10489 so. These locale categories can be set to any value supported by your
10490 installation. A typical value is @samp{en_UK} for English in the United
10493 The @env{LC_CTYPE} environment variable specifies character
10494 classification. GCC uses it to determine the character boundaries in
10495 a string; this is needed for some multibyte encodings that contain quote
10496 and escape characters that would otherwise be interpreted as a string
10499 The @env{LC_MESSAGES} environment variable specifies the language to
10500 use in diagnostic messages.
10502 If the @env{LC_ALL} environment variable is set, it overrides the value
10503 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
10504 and @env{LC_MESSAGES} default to the value of the @env{LANG}
10505 environment variable. If none of these variables are set, GCC
10506 defaults to traditional C English behavior.
10510 If @env{TMPDIR} is set, it specifies the directory to use for temporary
10511 files. GCC uses temporary files to hold the output of one stage of
10512 compilation which is to be used as input to the next stage: for example,
10513 the output of the preprocessor, which is the input to the compiler
10516 @item GCC_EXEC_PREFIX
10517 @findex GCC_EXEC_PREFIX
10518 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
10519 names of the subprograms executed by the compiler. No slash is added
10520 when this prefix is combined with the name of a subprogram, but you can
10521 specify a prefix that ends with a slash if you wish.
10523 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
10524 an appropriate prefix to use based on the pathname it was invoked with.
10526 If GCC cannot find the subprogram using the specified prefix, it
10527 tries looking in the usual places for the subprogram.
10529 The default value of @env{GCC_EXEC_PREFIX} is
10530 @file{@var{prefix}/lib/gcc-lib/} where @var{prefix} is the value
10531 of @code{prefix} when you ran the @file{configure} script.
10533 Other prefixes specified with @option{-B} take precedence over this prefix.
10535 This prefix is also used for finding files such as @file{crt0.o} that are
10538 In addition, the prefix is used in an unusual way in finding the
10539 directories to search for header files. For each of the standard
10540 directories whose name normally begins with @samp{/usr/local/lib/gcc-lib}
10541 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
10542 replacing that beginning with the specified prefix to produce an
10543 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
10544 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
10545 These alternate directories are searched first; the standard directories
10548 @item COMPILER_PATH
10549 @findex COMPILER_PATH
10550 The value of @env{COMPILER_PATH} is a colon-separated list of
10551 directories, much like @env{PATH}. GCC tries the directories thus
10552 specified when searching for subprograms, if it can't find the
10553 subprograms using @env{GCC_EXEC_PREFIX}.
10556 @findex LIBRARY_PATH
10557 The value of @env{LIBRARY_PATH} is a colon-separated list of
10558 directories, much like @env{PATH}. When configured as a native compiler,
10559 GCC tries the directories thus specified when searching for special
10560 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
10561 using GCC also uses these directories when searching for ordinary
10562 libraries for the @option{-l} option (but directories specified with
10563 @option{-L} come first).
10567 @cindex locale definition
10568 This variable is used to pass locale information to the compiler. One way in
10569 which this information is used is to determine the character set to be used
10570 when character literals, string literals and comments are parsed in C and C++.
10571 When the compiler is configured to allow multibyte characters,
10572 the following values for @env{LANG} are recognized:
10576 Recognize JIS characters.
10578 Recognize SJIS characters.
10580 Recognize EUCJP characters.
10583 If @env{LANG} is not defined, or if it has some other value, then the
10584 compiler will use mblen and mbtowc as defined by the default locale to
10585 recognize and translate multibyte characters.
10589 Some additional environments variables affect the behavior of the
10592 @include cppenv.texi
10596 @node Running Protoize
10597 @section Running Protoize
10599 The program @code{protoize} is an optional part of GCC@. You can use
10600 it to add prototypes to a program, thus converting the program to ISO
10601 C in one respect. The companion program @code{unprotoize} does the
10602 reverse: it removes argument types from any prototypes that are found.
10604 When you run these programs, you must specify a set of source files as
10605 command line arguments. The conversion programs start out by compiling
10606 these files to see what functions they define. The information gathered
10607 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
10609 After scanning comes actual conversion. The specified files are all
10610 eligible to be converted; any files they include (whether sources or
10611 just headers) are eligible as well.
10613 But not all the eligible files are converted. By default,
10614 @code{protoize} and @code{unprotoize} convert only source and header
10615 files in the current directory. You can specify additional directories
10616 whose files should be converted with the @option{-d @var{directory}}
10617 option. You can also specify particular files to exclude with the
10618 @option{-x @var{file}} option. A file is converted if it is eligible, its
10619 directory name matches one of the specified directory names, and its
10620 name within the directory has not been excluded.
10622 Basic conversion with @code{protoize} consists of rewriting most
10623 function definitions and function declarations to specify the types of
10624 the arguments. The only ones not rewritten are those for varargs
10627 @code{protoize} optionally inserts prototype declarations at the
10628 beginning of the source file, to make them available for any calls that
10629 precede the function's definition. Or it can insert prototype
10630 declarations with block scope in the blocks where undeclared functions
10633 Basic conversion with @code{unprotoize} consists of rewriting most
10634 function declarations to remove any argument types, and rewriting
10635 function definitions to the old-style pre-ISO form.
10637 Both conversion programs print a warning for any function declaration or
10638 definition that they can't convert. You can suppress these warnings
10641 The output from @code{protoize} or @code{unprotoize} replaces the
10642 original source file. The original file is renamed to a name ending
10643 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
10644 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
10645 for DOS) file already exists, then the source file is simply discarded.
10647 @code{protoize} and @code{unprotoize} both depend on GCC itself to
10648 scan the program and collect information about the functions it uses.
10649 So neither of these programs will work until GCC is installed.
10651 Here is a table of the options you can use with @code{protoize} and
10652 @code{unprotoize}. Each option works with both programs unless
10656 @item -B @var{directory}
10657 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
10658 usual directory (normally @file{/usr/local/lib}). This file contains
10659 prototype information about standard system functions. This option
10660 applies only to @code{protoize}.
10662 @item -c @var{compilation-options}
10663 Use @var{compilation-options} as the options when running @code{gcc} to
10664 produce the @samp{.X} files. The special option @option{-aux-info} is
10665 always passed in addition, to tell @code{gcc} to write a @samp{.X} file.
10667 Note that the compilation options must be given as a single argument to
10668 @code{protoize} or @code{unprotoize}. If you want to specify several
10669 @code{gcc} options, you must quote the entire set of compilation options
10670 to make them a single word in the shell.
10672 There are certain @code{gcc} arguments that you cannot use, because they
10673 would produce the wrong kind of output. These include @option{-g},
10674 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
10675 the @var{compilation-options}, they are ignored.
10678 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
10679 systems) instead of @samp{.c}. This is convenient if you are converting
10680 a C program to C++. This option applies only to @code{protoize}.
10683 Add explicit global declarations. This means inserting explicit
10684 declarations at the beginning of each source file for each function
10685 that is called in the file and was not declared. These declarations
10686 precede the first function definition that contains a call to an
10687 undeclared function. This option applies only to @code{protoize}.
10689 @item -i @var{string}
10690 Indent old-style parameter declarations with the string @var{string}.
10691 This option applies only to @code{protoize}.
10693 @code{unprotoize} converts prototyped function definitions to old-style
10694 function definitions, where the arguments are declared between the
10695 argument list and the initial @samp{@{}. By default, @code{unprotoize}
10696 uses five spaces as the indentation. If you want to indent with just
10697 one space instead, use @option{-i " "}.
10700 Keep the @samp{.X} files. Normally, they are deleted after conversion
10704 Add explicit local declarations. @code{protoize} with @option{-l} inserts
10705 a prototype declaration for each function in each block which calls the
10706 function without any declaration. This option applies only to
10710 Make no real changes. This mode just prints information about the conversions
10711 that would have been done without @option{-n}.
10714 Make no @samp{.save} files. The original files are simply deleted.
10715 Use this option with caution.
10717 @item -p @var{program}
10718 Use the program @var{program} as the compiler. Normally, the name
10719 @file{gcc} is used.
10722 Work quietly. Most warnings are suppressed.
10725 Print the version number, just like @option{-v} for @code{gcc}.
10728 If you need special compiler options to compile one of your program's
10729 source files, then you should generate that file's @samp{.X} file
10730 specially, by running @code{gcc} on that source file with the
10731 appropriate options and the option @option{-aux-info}. Then run
10732 @code{protoize} on the entire set of files. @code{protoize} will use
10733 the existing @samp{.X} file because it is newer than the source file.
10737 gcc -Dfoo=bar file1.c -aux-info file1.X
10742 You need to include the special files along with the rest in the
10743 @code{protoize} command, even though their @samp{.X} files already
10744 exist, because otherwise they won't get converted.
10746 @xref{Protoize Caveats}, for more information on how to use
10747 @code{protoize} successfully.