1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003 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, 2003 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 1.2 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
69 When you invoke GCC, it normally does preprocessing, compilation,
70 assembly and linking. The ``overall options'' allow you to stop this
71 process at an intermediate stage. For example, the @option{-c} option
72 says not to run the linker. Then the output consists of object files
73 output by the assembler.
75 Other options are passed on to one stage of processing. Some options
76 control the preprocessor and others the compiler itself. Yet other
77 options control the assembler and linker; most of these are not
78 documented here, since you rarely need to use any of them.
80 @cindex C compilation options
81 Most of the command line options that you can use with GCC are useful
82 for C programs; when an option is only useful with another language
83 (usually C++), the explanation says so explicitly. If the description
84 for a particular option does not mention a source language, you can use
85 that option with all supported languages.
87 @cindex C++ compilation options
88 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
89 options for compiling C++ programs.
91 @cindex grouping options
92 @cindex options, grouping
93 The @command{gcc} program accepts options and file names as operands. Many
94 options have multi-letter names; therefore multiple single-letter options
95 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
98 @cindex order of options
99 @cindex options, order
100 You can mix options and other arguments. For the most part, the order
101 you use doesn't matter. Order does matter when you use several options
102 of the same kind; for example, if you specify @option{-L} more than once,
103 the directories are searched in the order specified.
105 Many options have long names starting with @samp{-f} or with
106 @samp{-W}---for example, @option{-fforce-mem},
107 @option{-fstrength-reduce}, @option{-Wformat} and so on. Most of
108 these have both positive and negative forms; the negative form of
109 @option{-ffoo} would be @option{-fno-foo}. This manual documents
110 only one of these two forms, whichever one is not the default.
114 @xref{Option Index}, for an index to GCC's options.
117 * Option Summary:: Brief list of all options, without explanations.
118 * Overall Options:: Controlling the kind of output:
119 an executable, object files, assembler files,
120 or preprocessed source.
121 * Invoking G++:: Compiling C++ programs.
122 * C Dialect Options:: Controlling the variant of C language compiled.
123 * C++ Dialect Options:: Variations on C++.
124 * Objective-C Dialect Options:: Variations on Objective-C.
125 * Language Independent Options:: Controlling how diagnostics should be
127 * Warning Options:: How picky should the compiler be?
128 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
129 * Optimize Options:: How much optimization?
130 * Preprocessor Options:: Controlling header files and macro definitions.
131 Also, getting dependency information for Make.
132 * Assembler Options:: Passing options to the assembler.
133 * Link Options:: Specifying libraries and so on.
134 * Directory Options:: Where to find header files and libraries.
135 Where to find the compiler executable files.
136 * Spec Files:: How to pass switches to sub-processes.
137 * Target Options:: Running a cross-compiler, or an old version of GCC.
138 * Submodel Options:: Specifying minor hardware or convention variations,
139 such as 68010 vs 68020.
140 * Code Gen Options:: Specifying conventions for function calls, data layout
142 * Environment Variables:: Env vars that affect GCC.
143 * Precompiled Headers:: Compiling a header once, and using it many times.
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}.
158 @gccoptlist{-c -S -E -o @var{file} -pipe -pass-exit-codes @gol
159 -x @var{language} -v -### --help --target-help --version}
161 @item C Language Options
162 @xref{C Dialect Options,,Options Controlling C Dialect}.
163 @gccoptlist{-ansi -std=@var{standard} -aux-info @var{filename} @gol
164 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
165 -fhosted -ffreestanding -fms-extensions @gol
166 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
167 -fallow-single-precision -fcond-mismatch @gol
168 -fsigned-bitfields -fsigned-char @gol
169 -funsigned-bitfields -funsigned-char @gol
172 @item C++ Language Options
173 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
174 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
175 -fconserve-space -fno-const-strings @gol
176 -fno-elide-constructors @gol
177 -fno-enforce-eh-specs -fexternal-templates @gol
178 -falt-external-templates @gol
179 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
180 -fno-implicit-templates @gol
181 -fno-implicit-inline-templates @gol
182 -fno-implement-inlines -fms-extensions @gol
183 -fno-nonansi-builtins -fno-operator-names @gol
184 -fno-optional-diags -fpermissive @gol
185 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
186 -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
187 -fno-default-inline -Wabi -Wctor-dtor-privacy @gol
188 -Wnon-virtual-dtor -Wreorder @gol
189 -Weffc++ -Wno-deprecated @gol
190 -Wno-non-template-friend -Wold-style-cast @gol
191 -Woverloaded-virtual -Wno-pmf-conversions @gol
192 -Wsign-promo -Wsynth}
194 @item Objective-C Language Options
195 @xref{Objective-C Dialect Options,,Options Controlling Objective-C Dialect}.
197 -fconstant-string-class=@var{class-name} @gol
198 -fgnu-runtime -fnext-runtime @gol
199 -fno-nil-receivers @gol
200 -fobjc-exceptions @gol
201 -freplace-objc-classes @gol
204 -Wno-protocol -Wselector -Wundeclared-selector}
206 @item Language Independent Options
207 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
208 @gccoptlist{-fmessage-length=@var{n} @gol
209 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}}
211 @item Warning Options
212 @xref{Warning Options,,Options to Request or Suppress Warnings}.
213 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
214 -w -Wextra -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 -Wendif-labels @gol
218 -Werror -Werror-implicit-function-declaration @gol
219 -Wfloat-equal -Wformat -Wformat=2 @gol
220 -Wno-format-extra-args -Wformat-nonliteral @gol
221 -Wformat-security -Wformat-y2k @gol
222 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
223 -Wimport -Wno-import -Winit-self -Winline @gol
224 -Wno-invalid-offsetof -Winvalid-pch @gol
225 -Wlarger-than-@var{len} -Wlong-long @gol
226 -Wmain -Wmissing-braces @gol
227 -Wmissing-format-attribute -Wmissing-noreturn @gol
228 -Wno-multichar -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
239 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
240 -Wmissing-prototypes -Wnested-externs -Wold-style-definition @gol
241 -Wstrict-prototypes -Wtraditional @gol
242 -Wdeclaration-after-statement}
244 @item Debugging Options
245 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
246 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
247 -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
248 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
249 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
250 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
251 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
252 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
253 -feliminate-unused-debug-symbols -fmem-report -fprofile-arcs @gol
254 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
255 -ftest-coverage -ftime-report @gol
256 -g -g@var{level} -gcoff -gdwarf -gdwarf-1 -gdwarf-1+ -gdwarf-2 @gol
257 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
258 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
259 -print-multi-directory -print-multi-lib @gol
260 -print-prog-name=@var{program} -print-search-dirs -Q @gol
263 @item Optimization Options
264 @xref{Optimize Options,,Options that Control Optimization}.
265 @gccoptlist{-falign-functions=@var{n} -falign-jumps=@var{n} @gol
266 -falign-labels=@var{n} -falign-loops=@var{n} @gol
267 -fbranch-probabilities -fprofile-values -fvpt -fbranch-target-load-optimize @gol
268 -fbranch-target-load-optimize2 -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 -fgcse-las -floop-optimize @gol
274 -fcrossjumping -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 -frounding-math -fschedule-insns -fschedule-insns2 @gol
289 -fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
290 -fsched-spec-load-dangerous @gol
291 -fsched-stalled-insns=@var{n} -sched-stalled-insns-dep=@var{n} @gol
292 -fsched2-use-superblocks @gol
293 -fsched2-use-traces -fsignaling-nans @gol
294 -fsingle-precision-constant @gol
295 -fstrength-reduce -fstrict-aliasing -ftracer -fthread-jumps @gol
296 -funroll-all-loops -funroll-loops -fpeel-loops @gol
297 -funswitch-loops -fold-unroll-loops -fold-unroll-all-loops @gol
298 --param @var{name}=@var{value}
299 -O -O0 -O1 -O2 -O3 -Os}
301 @item Preprocessor Options
302 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
303 @gccoptlist{-A@var{question}=@var{answer} @gol
304 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
305 -C -dD -dI -dM -dN @gol
306 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
307 -idirafter @var{dir} @gol
308 -include @var{file} -imacros @var{file} @gol
309 -iprefix @var{file} -iwithprefix @var{dir} @gol
310 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
311 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
312 -P -fworking-directory -remap @gol
313 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
314 -Xpreprocessor @var{option}}
316 @item Assembler Option
317 @xref{Assembler Options,,Passing Options to the Assembler}.
318 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
321 @xref{Link Options,,Options for Linking}.
322 @gccoptlist{@var{object-file-name} -l@var{library} @gol
323 -nostartfiles -nodefaultlibs -nostdlib -pie @gol
324 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
325 -Wl,@var{option} -Xlinker @var{option} @gol
328 @item Directory Options
329 @xref{Directory Options,,Options for Directory Search}.
330 @gccoptlist{-B@var{prefix} -I@var{dir} -I- -L@var{dir} -specs=@var{file}}
333 @c I wrote this xref this way to avoid overfull hbox. -- rms
334 @xref{Target Options}.
335 @gccoptlist{-V @var{version} -b @var{machine}}
337 @item Machine Dependent Options
338 @xref{Submodel Options,,Hardware Models and Configurations}.
340 @emph{M680x0 Options}
341 @gccoptlist{-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
342 -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol
343 -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
344 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
345 -mshared-library-id=n -mid-shared-library -mno-id-shared-library}
347 @emph{M68hc1x Options}
348 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
349 -mauto-incdec -minmax -mlong-calls -mshort @gol
350 -msoft-reg-count=@var{count}}
353 @gccoptlist{-mg -mgnu -munix}
356 @gccoptlist{-mcpu=@var{cpu-type} @gol
357 -mtune=@var{cpu-type} @gol
358 -mcmodel=@var{code-model} @gol
360 -mapp-regs -mbroken-saverestore -mcypress @gol
361 -mfaster-structs -mflat @gol
362 -mfpu -mhard-float -mhard-quad-float @gol
363 -mimpure-text -mlittle-endian -mlive-g0 -mno-app-regs @gol
364 -mno-faster-structs -mno-flat -mno-fpu @gol
365 -mno-impure-text -mno-stack-bias -mno-unaligned-doubles @gol
366 -msoft-float -msoft-quad-float -msparclite -mstack-bias @gol
367 -msupersparc -munaligned-doubles -mv8}
370 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
371 -mapcs-26 -mapcs-32 @gol
372 -mapcs-stack-check -mno-apcs-stack-check @gol
373 -mapcs-float -mno-apcs-float @gol
374 -mapcs-reentrant -mno-apcs-reentrant @gol
375 -msched-prolog -mno-sched-prolog @gol
376 -mlittle-endian -mbig-endian -mwords-little-endian @gol
377 -malignment-traps -mno-alignment-traps @gol
378 -msoft-float -mhard-float -mfpe @gol
379 -mthumb-interwork -mno-thumb-interwork @gol
380 -mcpu=@var{name} -march=@var{name} -mfpe=@var{name} @gol
381 -mstructure-size-boundary=@var{n} @gol
382 -mabort-on-noreturn @gol
383 -mlong-calls -mno-long-calls @gol
384 -msingle-pic-base -mno-single-pic-base @gol
385 -mpic-register=@var{reg} @gol
386 -mnop-fun-dllimport @gol
387 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
388 -mpoke-function-name @gol
390 -mtpcs-frame -mtpcs-leaf-frame @gol
391 -mcaller-super-interworking -mcallee-super-interworking}
393 @emph{MN10200 Options}
396 @emph{MN10300 Options}
397 @gccoptlist{-mmult-bug -mno-mult-bug @gol
398 -mam33 -mno-am33 @gol
399 -mam33-2 -mno-am33-2 @gol
402 @emph{M32R/D Options}
403 @gccoptlist{-m32rx -m32r -mcode-model=@var{model-type} @gol
404 -msdata=@var{sdata-type} -G @var{num}}
407 @gccoptlist{-m88000 -m88100 -m88110 -mbig-pic @gol
408 -mcheck-zero-division -mhandle-large-shift @gol
409 -midentify-revision -mno-check-zero-division @gol
410 -mno-ocs-debug-info -mno-ocs-frame-position @gol
411 -mno-optimize-arg-area -mno-serialize-volatile @gol
412 -mno-underscores -mocs-debug-info @gol
413 -mocs-frame-position -moptimize-arg-area @gol
414 -mserialize-volatile -mshort-data-@var{num} -msvr3 @gol
415 -msvr4 -mtrap-large-shift -muse-div-instruction @gol
416 -mversion-03.00 -mwarn-passed-structs}
418 @emph{RS/6000 and PowerPC Options}
419 @gccoptlist{-mcpu=@var{cpu-type} @gol
420 -mtune=@var{cpu-type} @gol
421 -mpower -mno-power -mpower2 -mno-power2 @gol
422 -mpowerpc -mpowerpc64 -mno-powerpc @gol
423 -maltivec -mno-altivec @gol
424 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
425 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
426 -mnew-mnemonics -mold-mnemonics @gol
427 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
428 -m64 -m32 -mxl-call -mno-xl-call -mpe @gol
429 -malign-power -malign-natural @gol
430 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
431 -mstring -mno-string -mupdate -mno-update @gol
432 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
433 -mstrict-align -mno-strict-align -mrelocatable @gol
434 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
435 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
436 -mdynamic-no-pic @gol
437 -mprioritize-restricted-insns=@var{priority} @gol
438 -msched-costly-dep=@var{dependence_type} @gol
439 -minsert-sched-nops=@var{scheme} @gol
440 -mcall-sysv -mcall-netbsd @gol
441 -maix-struct-return -msvr4-struct-return @gol
442 -mabi=altivec -mabi=no-altivec @gol
443 -mabi=spe -mabi=no-spe @gol
444 -misel=yes -misel=no @gol
445 -mspe=yes -mspe=no @gol
446 -mfloat-gprs=yes -mfloat-gprs=no @gol
447 -mprototype -mno-prototype @gol
448 -msim -mmvme -mads -myellowknife -memb -msdata @gol
449 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
451 @emph{Darwin Options}
452 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
453 -arch_only -bind_at_load -bundle -bundle_loader @gol
454 -client_name -compatibility_version -current_version @gol
455 -dependency-file -dylib_file -dylinker_install_name @gol
456 -dynamic -dynamiclib -exported_symbols_list @gol
457 -filelist -flat_namespace -force_cpusubtype_ALL @gol
458 -force_flat_namespace -headerpad_max_install_names @gol
459 -image_base -init -install_name -keep_private_externs @gol
460 -multi_module -multiply_defined -multiply_defined_unused @gol
461 -noall_load -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
462 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
463 -private_bundle -read_only_relocs -sectalign @gol
464 -sectobjectsymbols -whyload -seg1addr @gol
465 -sectcreate -sectobjectsymbols -sectorder @gol
466 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
467 -segprot -segs_read_only_addr -segs_read_write_addr @gol
468 -single_module -static -sub_library -sub_umbrella @gol
469 -twolevel_namespace -umbrella -undefined @gol
470 -unexported_symbols_list -weak_reference_mismatches @gol
474 @gccoptlist{-mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs @gol
475 -mfull-fp-blocks -mhc-struct-return -min-line-mul @gol
476 -mminimum-fp-blocks -mnohc-struct-return}
479 @gccoptlist{-mabicalls -march=@var{cpu-type} -mtune=@var{cpu=type} @gol
480 -mcpu=@var{cpu-type} -membedded-data -muninit-const-in-rodata @gol
481 -membedded-pic -mfp32 -mfp64 -mfused-madd -mno-fused-madd @gol
482 -mgas -mgp32 -mgp64 -mhard-float -mint64 -mips1 @gol
483 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
484 -mlong64 -mlong32 -mlong-calls -mmemcpy @gol
485 -mmips-as -mmips-tfile -mno-abicalls -mxgot @gol
486 -mno-embedded-data -mno-uninit-const-in-rodata @gol
487 -mno-embedded-pic -mno-long-calls @gol
488 -mno-memcpy -mno-mips-tfile -mno-rnames @gol
489 -mrnames -msoft-float @gol
490 -m4650 -msingle-float -mmad @gol
491 -EL -EB -G @var{num} -nocpp @gol
492 -mabi=32 -mabi=n32 -mabi=64 -mabi=eabi -mabi-fake-default @gol
493 -mfix7000 -mfix-sb1 -mno-fix-sb1 @gol
494 -mno-crt0 -mflush-func=@var{func} -mno-flush-func @gol
495 -mbranch-likely -mno-branch-likely}
497 @emph{i386 and x86-64 Options}
498 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
499 -mfpmath=@var{unit} @gol
500 -masm=@var{dialect} -mno-fancy-math-387 @gol
501 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
502 -mno-wide-multiply -mrtd -malign-double @gol
503 -mpreferred-stack-boundary=@var{num} @gol
504 -mmmx -msse -msse2 -mpni -m3dnow @gol
505 -mthreads -mno-align-stringops -minline-all-stringops @gol
506 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
507 -m96bit-long-double -mregparm=@var{num} -momit-leaf-frame-pointer @gol
508 -mno-red-zone -mno-tls-direct-seg-refs @gol
509 -mcmodel=@var{code-model} @gol
513 @gccoptlist{-march=@var{architecture-type} @gol
514 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
515 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
516 -mjump-in-delay -mlinker-opt -mlong-calls @gol
517 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
518 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
519 -mno-jump-in-delay -mno-long-load-store @gol
520 -mno-portable-runtime -mno-soft-float @gol
521 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
522 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
523 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
524 -nolibdld -static -threads}
526 @emph{Intel 960 Options}
527 @gccoptlist{-m@var{cpu-type} -masm-compat -mclean-linkage @gol
528 -mcode-align -mcomplex-addr -mleaf-procedures @gol
529 -mic-compat -mic2.0-compat -mic3.0-compat @gol
530 -mintel-asm -mno-clean-linkage -mno-code-align @gol
531 -mno-complex-addr -mno-leaf-procedures @gol
532 -mno-old-align -mno-strict-align -mno-tail-call @gol
533 -mnumerics -mold-align -msoft-float -mstrict-align @gol
536 @emph{DEC Alpha Options}
537 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
538 -mieee -mieee-with-inexact -mieee-conformant @gol
539 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
540 -mtrap-precision=@var{mode} -mbuild-constants @gol
541 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
542 -mbwx -mmax -mfix -mcix @gol
543 -mfloat-vax -mfloat-ieee @gol
544 -mexplicit-relocs -msmall-data -mlarge-data @gol
545 -msmall-text -mlarge-text @gol
546 -mmemory-latency=@var{time}}
548 @emph{DEC Alpha/VMS Options}
549 @gccoptlist{-mvms-return-codes}
551 @emph{H8/300 Options}
552 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
555 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
556 -m4-nofpu -m4-single-only -m4-single -m4 @gol
557 -m5-64media -m5-64media-nofpu @gol
558 -m5-32media -m5-32media-nofpu @gol
559 -m5-compact -m5-compact-nofpu @gol
560 -mb -ml -mdalign -mrelax @gol
561 -mbigtable -mfmovd -mhitachi -mnomacsave @gol
562 -mieee -misize -mpadstruct -mspace @gol
563 -mprefergot -musermode}
565 @emph{System V Options}
566 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
569 @gccoptlist{-EB -EL @gol
570 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
571 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
573 @emph{TMS320C3x/C4x Options}
574 @gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
575 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
576 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
577 -mparallel-insns -mparallel-mpy -mpreserve-float}
580 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
581 -mprolog-function -mno-prolog-function -mspace @gol
582 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
583 -mapp-regs -mno-app-regs @gol
584 -mdisable-callt -mno-disable-callt @gol
590 @gccoptlist{-m32032 -m32332 -m32532 -m32081 -m32381 @gol
591 -mmult-add -mnomult-add -msoft-float -mrtd -mnortd @gol
592 -mregparam -mnoregparam -msb -mnosb @gol
593 -mbitfield -mnobitfield -mhimem -mnohimem}
596 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
597 -mcall-prologues -mno-tablejump -mtiny-stack}
600 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
601 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
602 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
603 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
604 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
607 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
608 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
609 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
610 -mno-base-addresses -msingle-exit -mno-single-exit}
613 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
614 -mvolatile-asm-stop -mb-step -mregister-names -mno-sdata @gol
615 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
616 -minline-float-divide-max-throughput @gol
617 -minline-int-divide-min-latency @gol
618 -minline-int-divide-max-throughput -mno-dwarf2-asm @gol
619 -mfixed-range=@var{register-range}}
622 @gccoptlist{-mextmem -mextmemory -monchip -mno-asm-optimize @gol
623 -masm-optimize -mbranch-cost=@var{n} -mcond-exec=@var{n}}
625 @emph{S/390 and zSeries Options}
626 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
627 -mhard-float -msoft-float -mbackchain -mno-backchain @gol
628 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
629 -m64 -m31 -mdebug -mno-debug -mesa -mzarch -mfused-madd -mno-fused-madd}
632 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
633 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
634 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
635 -mstack-align -mdata-align -mconst-align @gol
636 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
637 -melf -maout -melinux -mlinux -sim -sim2}
639 @emph{PDP-11 Options}
640 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
641 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
642 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
643 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
644 -mbranch-expensive -mbranch-cheap @gol
645 -msplit -mno-split -munix-asm -mdec-asm}
647 @emph{Xstormy16 Options}
650 @emph{Xtensa Options}
651 @gccoptlist{-mconst16 -mno-const16 @gol
652 -mfused-madd -mno-fused-madd @gol
653 -mtext-section-literals -mno-text-section-literals @gol
654 -mtarget-align -mno-target-align @gol
655 -mlongcalls -mno-longcalls}
658 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
659 -mhard-float -msoft-float @gol
660 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
661 -mdouble -mno-double @gol
662 -mmedia -mno-media -mmuladd -mno-muladd @gol
663 -mlibrary-pic -macc-4 -macc-8 @gol
664 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
665 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
666 -mvliw-branch -mno-vliw-branch @gol
667 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
668 -mno-nested-cond-exec -mtomcat-stats @gol
671 @item Code Generation Options
672 @xref{Code Gen Options,,Options for Code Generation Conventions}.
673 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
674 -ffixed-@var{reg} -fexceptions @gol
675 -fnon-call-exceptions -funwind-tables @gol
676 -fasynchronous-unwind-tables @gol
677 -finhibit-size-directive -finstrument-functions @gol
678 -fno-common -fno-ident -fno-gnu-linker @gol
679 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
680 -freg-struct-return -fshared-data -fshort-enums @gol
681 -fshort-double -fshort-wchar @gol
682 -fverbose-asm -fpack-struct -fstack-check @gol
683 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
684 -fargument-alias -fargument-noalias @gol
685 -fargument-noalias-global -fleading-underscore @gol
686 -ftls-model=@var{model} @gol
687 -ftrapv -fwrapv -fbounds-check}
691 * Overall Options:: Controlling the kind of output:
692 an executable, object files, assembler files,
693 or preprocessed source.
694 * C Dialect Options:: Controlling the variant of C language compiled.
695 * C++ Dialect Options:: Variations on C++.
696 * Objective-C Dialect Options:: Variations on Objective-C.
697 * Language Independent Options:: Controlling how diagnostics should be
699 * Warning Options:: How picky should the compiler be?
700 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
701 * Optimize Options:: How much optimization?
702 * Preprocessor Options:: Controlling header files and macro definitions.
703 Also, getting dependency information for Make.
704 * Assembler Options:: Passing options to the assembler.
705 * Link Options:: Specifying libraries and so on.
706 * Directory Options:: Where to find header files and libraries.
707 Where to find the compiler executable files.
708 * Spec Files:: How to pass switches to sub-processes.
709 * Target Options:: Running a cross-compiler, or an old version of GCC.
712 @node Overall Options
713 @section Options Controlling the Kind of Output
715 Compilation can involve up to four stages: preprocessing, compilation
716 proper, assembly and linking, always in that order. GCC is capable of
717 preprocessing and compiling several files either into several
718 assembler input files, or into one assembler input file; then each
719 assembler input file produces an object file, and linking combines all
720 the object files (those newly compiled, and those specified as input)
721 into an executable file.
723 @cindex file name suffix
724 For any given input file, the file name suffix determines what kind of
729 C source code which must be preprocessed.
732 C source code which should not be preprocessed.
735 C++ source code which should not be preprocessed.
738 Objective-C source code. Note that you must link with the library
739 @file{libobjc.a} to make an Objective-C program work.
742 Objective-C source code which should not be preprocessed.
745 C or C++ header file to be turned into a precompiled header.
749 @itemx @var{file}.cxx
750 @itemx @var{file}.cpp
751 @itemx @var{file}.CPP
752 @itemx @var{file}.c++
754 C++ source code which must be preprocessed. Note that in @samp{.cxx},
755 the last two letters must both be literally @samp{x}. Likewise,
756 @samp{.C} refers to a literal capital C@.
760 C++ header file to be turned into a precompiled header.
763 @itemx @var{file}.for
764 @itemx @var{file}.FOR
765 Fortran source code which should not be preprocessed.
768 @itemx @var{file}.fpp
769 @itemx @var{file}.FPP
770 Fortran source code which must be preprocessed (with the traditional
774 Fortran source code which must be preprocessed with a RATFOR
775 preprocessor (not included with GCC)@.
777 @xref{Overall Options,,Options Controlling the Kind of Output, g77,
778 Using and Porting GNU Fortran}, for more details of the handling of
781 @c FIXME: Descriptions of Java file types.
788 Ada source code file which contains a library unit declaration (a
789 declaration of a package, subprogram, or generic, or a generic
790 instantiation), or a library unit renaming declaration (a package,
791 generic, or subprogram renaming declaration). Such files are also
794 @itemx @var{file}.adb
795 Ada source code file containing a library unit body (a subprogram or
796 package body). Such files are also called @dfn{bodies}.
798 @c GCC also knows about some suffixes for languages not yet included:
807 Assembler code which must be preprocessed.
810 An object file to be fed straight into linking.
811 Any file name with no recognized suffix is treated this way.
815 You can specify the input language explicitly with the @option{-x} option:
818 @item -x @var{language}
819 Specify explicitly the @var{language} for the following input files
820 (rather than letting the compiler choose a default based on the file
821 name suffix). This option applies to all following input files until
822 the next @option{-x} option. Possible values for @var{language} are:
824 c c-header cpp-output
825 c++ c++-header c++-cpp-output
826 objective-c objective-c-header objc-cpp-output
827 assembler assembler-with-cpp
829 f77 f77-cpp-input ratfor
835 Turn off any specification of a language, so that subsequent files are
836 handled according to their file name suffixes (as they are if @option{-x}
837 has not been used at all).
839 @item -pass-exit-codes
840 @opindex pass-exit-codes
841 Normally the @command{gcc} program will exit with the code of 1 if any
842 phase of the compiler returns a non-success return code. If you specify
843 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
844 numerically highest error produced by any phase that returned an error
848 If you only want some of the stages of compilation, you can use
849 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
850 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
851 @command{gcc} is to stop. Note that some combinations (for example,
852 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
857 Compile or assemble the source files, but do not link. The linking
858 stage simply is not done. The ultimate output is in the form of an
859 object file for each source file.
861 By default, the object file name for a source file is made by replacing
862 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
864 Unrecognized input files, not requiring compilation or assembly, are
869 Stop after the stage of compilation proper; do not assemble. The output
870 is in the form of an assembler code file for each non-assembler input
873 By default, the assembler file name for a source file is made by
874 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
876 Input files that don't require compilation are ignored.
880 Stop after the preprocessing stage; do not run the compiler proper. The
881 output is in the form of preprocessed source code, which is sent to the
884 Input files which don't require preprocessing are ignored.
886 @cindex output file option
889 Place output in file @var{file}. This applies regardless to whatever
890 sort of output is being produced, whether it be an executable file,
891 an object file, an assembler file or preprocessed C code.
893 If you specify @option{-o} when compiling more than one input file, or
894 you are producing an executable file as output, all the source files
895 on the command line will be compiled at once.
897 If @option{-o} is not specified, the default is to put an executable file
898 in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in
899 @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and
900 all preprocessed C source on standard output.
904 Print (on standard error output) the commands executed to run the stages
905 of compilation. Also print the version number of the compiler driver
906 program and of the preprocessor and the compiler proper.
910 Like @option{-v} except the commands are not executed and all command
911 arguments are quoted. This is useful for shell scripts to capture the
912 driver-generated command lines.
916 Use pipes rather than temporary files for communication between the
917 various stages of compilation. This fails to work on some systems where
918 the assembler is unable to read from a pipe; but the GNU assembler has
923 Print (on the standard output) a description of the command line options
924 understood by @command{gcc}. If the @option{-v} option is also specified
925 then @option{--help} will also be passed on to the various processes
926 invoked by @command{gcc}, so that they can display the command line options
927 they accept. If the @option{-Wextra} option is also specified then command
928 line options which have no documentation associated with them will also
933 Print (on the standard output) a description of target specific command
934 line options for each tool.
938 Display the version number and copyrights of the invoked GCC.
942 @section Compiling C++ Programs
944 @cindex suffixes for C++ source
945 @cindex C++ source file suffixes
946 C++ source files conventionally use one of the suffixes @samp{.C},
947 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
948 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
949 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
950 files with these names and compiles them as C++ programs even if you
951 call the compiler the same way as for compiling C programs (usually
952 with the name @command{gcc}).
956 However, C++ programs often require class libraries as well as a
957 compiler that understands the C++ language---and under some
958 circumstances, you might want to compile programs or header files from
959 standard input, or otherwise without a suffix that flags them as C++
960 programs. You might also like to precompile a C header file with a
961 @samp{.h} extension to be used in C++ compilations. @command{g++} is a
962 program that calls GCC with the default language set to C++, and
963 automatically specifies linking against the C++ library. On many
964 systems, @command{g++} is also installed with the name @command{c++}.
966 @cindex invoking @command{g++}
967 When you compile C++ programs, you may specify many of the same
968 command-line options that you use for compiling programs in any
969 language; or command-line options meaningful for C and related
970 languages; or options that are meaningful only for C++ programs.
971 @xref{C Dialect Options,,Options Controlling C Dialect}, for
972 explanations of options for languages related to C@.
973 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
974 explanations of options that are meaningful only for C++ programs.
976 @node C Dialect Options
977 @section Options Controlling C Dialect
978 @cindex dialect options
979 @cindex language dialect options
980 @cindex options, dialect
982 The following options control the dialect of C (or languages derived
983 from C, such as C++ and Objective-C) that the compiler accepts:
990 In C mode, support all ISO C90 programs. In C++ mode,
991 remove GNU extensions that conflict with ISO C++.
993 This turns off certain features of GCC that are incompatible with ISO
994 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
995 such as the @code{asm} and @code{typeof} keywords, and
996 predefined macros such as @code{unix} and @code{vax} that identify the
997 type of system you are using. It also enables the undesirable and
998 rarely used ISO trigraph feature. For the C compiler,
999 it disables recognition of C++ style @samp{//} comments as well as
1000 the @code{inline} keyword.
1002 The alternate keywords @code{__asm__}, @code{__extension__},
1003 @code{__inline__} and @code{__typeof__} continue to work despite
1004 @option{-ansi}. You would not want to use them in an ISO C program, of
1005 course, but it is useful to put them in header files that might be included
1006 in compilations done with @option{-ansi}. Alternate predefined macros
1007 such as @code{__unix__} and @code{__vax__} are also available, with or
1008 without @option{-ansi}.
1010 The @option{-ansi} option does not cause non-ISO programs to be
1011 rejected gratuitously. For that, @option{-pedantic} is required in
1012 addition to @option{-ansi}. @xref{Warning Options}.
1014 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1015 option is used. Some header files may notice this macro and refrain
1016 from declaring certain functions or defining certain macros that the
1017 ISO standard doesn't call for; this is to avoid interfering with any
1018 programs that might use these names for other things.
1020 Functions which would normally be built in but do not have semantics
1021 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1022 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1023 built-in functions provided by GCC}, for details of the functions
1028 Determine the language standard. This option is currently only
1029 supported when compiling C or C++. A value for this option must be
1030 provided; possible values are
1035 ISO C90 (same as @option{-ansi}).
1037 @item iso9899:199409
1038 ISO C90 as modified in amendment 1.
1044 ISO C99. Note that this standard is not yet fully supported; see
1045 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1046 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1049 Default, ISO C90 plus GNU extensions (including some C99 features).
1053 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1054 this will become the default. The name @samp{gnu9x} is deprecated.
1057 The 1998 ISO C++ standard plus amendments.
1060 The same as @option{-std=c++98} plus GNU extensions. This is the
1061 default for C++ code.
1064 Even when this option is not specified, you can still use some of the
1065 features of newer standards in so far as they do not conflict with
1066 previous C standards. For example, you may use @code{__restrict__} even
1067 when @option{-std=c99} is not specified.
1069 The @option{-std} options specifying some version of ISO C have the same
1070 effects as @option{-ansi}, except that features that were not in ISO C90
1071 but are in the specified version (for example, @samp{//} comments and
1072 the @code{inline} keyword in ISO C99) are not disabled.
1074 @xref{Standards,,Language Standards Supported by GCC}, for details of
1075 these standard versions.
1077 @item -aux-info @var{filename}
1079 Output to the given filename prototyped declarations for all functions
1080 declared and/or defined in a translation unit, including those in header
1081 files. This option is silently ignored in any language other than C@.
1083 Besides declarations, the file indicates, in comments, the origin of
1084 each declaration (source file and line), whether the declaration was
1085 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1086 @samp{O} for old, respectively, in the first character after the line
1087 number and the colon), and whether it came from a declaration or a
1088 definition (@samp{C} or @samp{F}, respectively, in the following
1089 character). In the case of function definitions, a K&R-style list of
1090 arguments followed by their declarations is also provided, inside
1091 comments, after the declaration.
1095 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1096 keyword, so that code can use these words as identifiers. You can use
1097 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1098 instead. @option{-ansi} implies @option{-fno-asm}.
1100 In C++, this switch only affects the @code{typeof} keyword, since
1101 @code{asm} and @code{inline} are standard keywords. You may want to
1102 use the @option{-fno-gnu-keywords} flag instead, which has the same
1103 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1104 switch only affects the @code{asm} and @code{typeof} keywords, since
1105 @code{inline} is a standard keyword in ISO C99.
1108 @itemx -fno-builtin-@var{function}
1109 @opindex fno-builtin
1110 @cindex built-in functions
1111 Don't recognize built-in functions that do not begin with
1112 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1113 functions provided by GCC}, for details of the functions affected,
1114 including those which are not built-in functions when @option{-ansi} or
1115 @option{-std} options for strict ISO C conformance are used because they
1116 do not have an ISO standard meaning.
1118 GCC normally generates special code to handle certain built-in functions
1119 more efficiently; for instance, calls to @code{alloca} may become single
1120 instructions that adjust the stack directly, and calls to @code{memcpy}
1121 may become inline copy loops. The resulting code is often both smaller
1122 and faster, but since the function calls no longer appear as such, you
1123 cannot set a breakpoint on those calls, nor can you change the behavior
1124 of the functions by linking with a different library.
1126 With the @option{-fno-builtin-@var{function}} option
1127 only the built-in function @var{function} is
1128 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1129 function is named this is not built-in in this version of GCC, this
1130 option is ignored. There is no corresponding
1131 @option{-fbuiltin-@var{function}} option; if you wish to enable
1132 built-in functions selectively when using @option{-fno-builtin} or
1133 @option{-ffreestanding}, you may define macros such as:
1136 #define abs(n) __builtin_abs ((n))
1137 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1142 @cindex hosted environment
1144 Assert that compilation takes place in a hosted environment. This implies
1145 @option{-fbuiltin}. A hosted environment is one in which the
1146 entire standard library is available, and in which @code{main} has a return
1147 type of @code{int}. Examples are nearly everything except a kernel.
1148 This is equivalent to @option{-fno-freestanding}.
1150 @item -ffreestanding
1151 @opindex ffreestanding
1152 @cindex hosted environment
1154 Assert that compilation takes place in a freestanding environment. This
1155 implies @option{-fno-builtin}. A freestanding environment
1156 is one in which the standard library may not exist, and program startup may
1157 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1158 This is equivalent to @option{-fno-hosted}.
1160 @xref{Standards,,Language Standards Supported by GCC}, for details of
1161 freestanding and hosted environments.
1163 @item -fms-extensions
1164 @opindex fms-extensions
1165 Accept some non-standard constructs used in Microsoft header files.
1169 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1170 options for strict ISO C conformance) implies @option{-trigraphs}.
1172 @item -no-integrated-cpp
1173 @opindex no-integrated-cpp
1174 Performs a compilation in two passes: preprocessing and compiling. This
1175 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1176 @option{-B} option. The user supplied compilation step can then add in
1177 an additional preprocessing step after normal preprocessing but before
1178 compiling. The default is to use the integrated cpp (internal cpp)
1180 The semantics of this option will change if "cc1", "cc1plus", and
1181 "cc1obj" are merged.
1183 @cindex traditional C language
1184 @cindex C language, traditional
1186 @itemx -traditional-cpp
1187 @opindex traditional-cpp
1188 @opindex traditional
1189 Formerly, these options caused GCC to attempt to emulate a pre-standard
1190 C compiler. They are now only supported with the @option{-E} switch.
1191 The preprocessor continues to support a pre-standard mode. See the GNU
1192 CPP manual for details.
1194 @item -fcond-mismatch
1195 @opindex fcond-mismatch
1196 Allow conditional expressions with mismatched types in the second and
1197 third arguments. The value of such an expression is void. This option
1198 is not supported for C++.
1200 @item -funsigned-char
1201 @opindex funsigned-char
1202 Let the type @code{char} be unsigned, like @code{unsigned char}.
1204 Each kind of machine has a default for what @code{char} should
1205 be. It is either like @code{unsigned char} by default or like
1206 @code{signed char} by default.
1208 Ideally, a portable program should always use @code{signed char} or
1209 @code{unsigned char} when it depends on the signedness of an object.
1210 But many programs have been written to use plain @code{char} and
1211 expect it to be signed, or expect it to be unsigned, depending on the
1212 machines they were written for. This option, and its inverse, let you
1213 make such a program work with the opposite default.
1215 The type @code{char} is always a distinct type from each of
1216 @code{signed char} or @code{unsigned char}, even though its behavior
1217 is always just like one of those two.
1220 @opindex fsigned-char
1221 Let the type @code{char} be signed, like @code{signed char}.
1223 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1224 the negative form of @option{-funsigned-char}. Likewise, the option
1225 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1227 @item -fsigned-bitfields
1228 @itemx -funsigned-bitfields
1229 @itemx -fno-signed-bitfields
1230 @itemx -fno-unsigned-bitfields
1231 @opindex fsigned-bitfields
1232 @opindex funsigned-bitfields
1233 @opindex fno-signed-bitfields
1234 @opindex fno-unsigned-bitfields
1235 These options control whether a bit-field is signed or unsigned, when the
1236 declaration does not use either @code{signed} or @code{unsigned}. By
1237 default, such a bit-field is signed, because this is consistent: the
1238 basic integer types such as @code{int} are signed types.
1240 @item -fwritable-strings
1241 @opindex fwritable-strings
1242 Store string constants in the writable data segment and don't uniquize
1243 them. This is for compatibility with old programs which assume they can
1244 write into string constants.
1246 Writing into string constants is a very bad idea; ``constants'' should
1250 @node C++ Dialect Options
1251 @section Options Controlling C++ Dialect
1253 @cindex compiler options, C++
1254 @cindex C++ options, command line
1255 @cindex options, C++
1256 This section describes the command-line options that are only meaningful
1257 for C++ programs; but you can also use most of the GNU compiler options
1258 regardless of what language your program is in. For example, you
1259 might compile a file @code{firstClass.C} like this:
1262 g++ -g -frepo -O -c firstClass.C
1266 In this example, only @option{-frepo} is an option meant
1267 only for C++ programs; you can use the other options with any
1268 language supported by GCC@.
1270 Here is a list of options that are @emph{only} for compiling C++ programs:
1274 @item -fabi-version=@var{n}
1275 @opindex fabi-version
1276 Use version @var{n} of the C++ ABI. Version 1 is the version of the C++
1277 ABI that first appeared in G++ 3.2. Version 0 will always be the
1278 version that conforms most closely to the C++ ABI specification.
1279 Therefore, the ABI obtained using version 0 will change as ABI bugs are
1282 The default is version 1.
1284 @item -fno-access-control
1285 @opindex fno-access-control
1286 Turn off all access checking. This switch is mainly useful for working
1287 around bugs in the access control code.
1291 Check that the pointer returned by @code{operator new} is non-null
1292 before attempting to modify the storage allocated. This check is
1293 normally unnecessary because the C++ standard specifies that
1294 @code{operator new} will only return @code{0} if it is declared
1295 @samp{throw()}, in which case the compiler will always check the
1296 return value even without this option. In all other cases, when
1297 @code{operator new} has a non-empty exception specification, memory
1298 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1299 @samp{new (nothrow)}.
1301 @item -fconserve-space
1302 @opindex fconserve-space
1303 Put uninitialized or runtime-initialized global variables into the
1304 common segment, as C does. This saves space in the executable at the
1305 cost of not diagnosing duplicate definitions. If you compile with this
1306 flag and your program mysteriously crashes after @code{main()} has
1307 completed, you may have an object that is being destroyed twice because
1308 two definitions were merged.
1310 This option is no longer useful on most targets, now that support has
1311 been added for putting variables into BSS without making them common.
1313 @item -fno-const-strings
1314 @opindex fno-const-strings
1315 Give string constants type @code{char *} instead of type @code{const
1316 char *}. By default, G++ uses type @code{const char *} as required by
1317 the standard. Even if you use @option{-fno-const-strings}, you cannot
1318 actually modify the value of a string constant, unless you also use
1319 @option{-fwritable-strings}.
1321 This option might be removed in a future release of G++. For maximum
1322 portability, you should structure your code so that it works with
1323 string constants that have type @code{const char *}.
1325 @item -fno-elide-constructors
1326 @opindex fno-elide-constructors
1327 The C++ standard allows an implementation to omit creating a temporary
1328 which is only used to initialize another object of the same type.
1329 Specifying this option disables that optimization, and forces G++ to
1330 call the copy constructor in all cases.
1332 @item -fno-enforce-eh-specs
1333 @opindex fno-enforce-eh-specs
1334 Don't check for violation of exception specifications at runtime. This
1335 option violates the C++ standard, but may be useful for reducing code
1336 size in production builds, much like defining @samp{NDEBUG}. The compiler
1337 will still optimize based on the exception specifications.
1339 @item -fexternal-templates
1340 @opindex fexternal-templates
1342 Cause @samp{#pragma interface} and @samp{implementation} to apply to
1343 template instantiation; template instances are emitted or not according
1344 to the location of the template definition. @xref{Template
1345 Instantiation}, for more information.
1347 This option is deprecated.
1349 @item -falt-external-templates
1350 @opindex falt-external-templates
1351 Similar to @option{-fexternal-templates}, but template instances are
1352 emitted or not according to the place where they are first instantiated.
1353 @xref{Template Instantiation}, for more information.
1355 This option is deprecated.
1358 @itemx -fno-for-scope
1360 @opindex fno-for-scope
1361 If @option{-ffor-scope} is specified, the scope of variables declared in
1362 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1363 as specified by the C++ standard.
1364 If @option{-fno-for-scope} is specified, the scope of variables declared in
1365 a @i{for-init-statement} extends to the end of the enclosing scope,
1366 as was the case in old versions of G++, and other (traditional)
1367 implementations of C++.
1369 The default if neither flag is given to follow the standard,
1370 but to allow and give a warning for old-style code that would
1371 otherwise be invalid, or have different behavior.
1373 @item -fno-gnu-keywords
1374 @opindex fno-gnu-keywords
1375 Do not recognize @code{typeof} as a keyword, so that code can use this
1376 word as an identifier. You can use the keyword @code{__typeof__} instead.
1377 @option{-ansi} implies @option{-fno-gnu-keywords}.
1379 @item -fno-implicit-templates
1380 @opindex fno-implicit-templates
1381 Never emit code for non-inline templates which are instantiated
1382 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1383 @xref{Template Instantiation}, for more information.
1385 @item -fno-implicit-inline-templates
1386 @opindex fno-implicit-inline-templates
1387 Don't emit code for implicit instantiations of inline templates, either.
1388 The default is to handle inlines differently so that compiles with and
1389 without optimization will need the same set of explicit instantiations.
1391 @item -fno-implement-inlines
1392 @opindex fno-implement-inlines
1393 To save space, do not emit out-of-line copies of inline functions
1394 controlled by @samp{#pragma implementation}. This will cause linker
1395 errors if these functions are not inlined everywhere they are called.
1397 @item -fms-extensions
1398 @opindex fms-extensions
1399 Disable pedantic warnings about constructs used in MFC, such as implicit
1400 int and getting a pointer to member function via non-standard syntax.
1402 @item -fno-nonansi-builtins
1403 @opindex fno-nonansi-builtins
1404 Disable built-in declarations of functions that are not mandated by
1405 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1406 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1408 @item -fno-operator-names
1409 @opindex fno-operator-names
1410 Do not treat the operator name keywords @code{and}, @code{bitand},
1411 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1412 synonyms as keywords.
1414 @item -fno-optional-diags
1415 @opindex fno-optional-diags
1416 Disable diagnostics that the standard says a compiler does not need to
1417 issue. Currently, the only such diagnostic issued by G++ is the one for
1418 a name having multiple meanings within a class.
1421 @opindex fpermissive
1422 Downgrade some diagnostics about nonconformant code from errors to
1423 warnings. Thus, using @option{-fpermissive} will allow some
1424 nonconforming code to compile.
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 Do not use weak symbol support, even if it is provided by the linker.
1464 By default, G++ will use weak symbols if they are available. This
1465 option exists only for testing, and should not be used by end-users;
1466 it will result in inferior code and has no benefits. This option may
1467 be removed in a future release of G++.
1471 Do not search for header files in the standard directories specific to
1472 C++, but do still search the other standard directories. (This option
1473 is used when building the C++ library.)
1476 In addition, these optimization, warning, and code generation options
1477 have meanings only for C++ programs:
1480 @item -fno-default-inline
1481 @opindex fno-default-inline
1482 Do not assume @samp{inline} for functions defined inside a class scope.
1483 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1484 functions will have linkage like inline functions; they just won't be
1487 @item -Wabi @r{(C++ only)}
1489 Warn when G++ generates code that is probably not compatible with the
1490 vendor-neutral C++ ABI. Although an effort has been made to warn about
1491 all such cases, there are probably some cases that are not warned about,
1492 even though G++ is generating incompatible code. There may also be
1493 cases where warnings are emitted even though the code that is generated
1496 You should rewrite your code to avoid these warnings if you are
1497 concerned about the fact that code generated by G++ may not be binary
1498 compatible with code generated by other compilers.
1500 The known incompatibilities at this point include:
1505 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1506 pack data into the same byte as a base class. For example:
1509 struct A @{ virtual void f(); int f1 : 1; @};
1510 struct B : public A @{ int f2 : 1; @};
1514 In this case, G++ will place @code{B::f2} into the same byte
1515 as@code{A::f1}; other compilers will not. You can avoid this problem
1516 by explicitly padding @code{A} so that its size is a multiple of the
1517 byte size on your platform; that will cause G++ and other compilers to
1518 layout @code{B} identically.
1521 Incorrect handling of tail-padding for virtual bases. G++ does not use
1522 tail padding when laying out virtual bases. For example:
1525 struct A @{ virtual void f(); char c1; @};
1526 struct B @{ B(); char c2; @};
1527 struct C : public A, public virtual B @{@};
1531 In this case, G++ will not place @code{B} into the tail-padding for
1532 @code{A}; other compilers will. You can avoid this problem by
1533 explicitly padding @code{A} so that its size is a multiple of its
1534 alignment (ignoring virtual base classes); that will cause G++ and other
1535 compilers to layout @code{C} identically.
1538 Incorrect handling of bit-fields with declared widths greater than that
1539 of their underlying types, when the bit-fields appear in a union. For
1543 union U @{ int i : 4096; @};
1547 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1548 union too small by the number of bits in an @code{int}.
1551 Empty classes can be placed at incorrect offsets. For example:
1561 struct C : public B, public A @{@};
1565 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1566 it should be placed at offset zero. G++ mistakenly believes that the
1567 @code{A} data member of @code{B} is already at offset zero.
1570 Names of template functions whose types involve @code{typename} or
1571 template template parameters can be mangled incorrectly.
1574 template <typename Q>
1575 void f(typename Q::X) @{@}
1577 template <template <typename> class Q>
1578 void f(typename Q<int>::X) @{@}
1582 Instantiations of these templates may be mangled incorrectly.
1586 @item -Wctor-dtor-privacy @r{(C++ only)}
1587 @opindex Wctor-dtor-privacy
1588 Warn when a class seems unusable because all the constructors or
1589 destructors in that class are private, and it has neither friends nor
1590 public static member functions.
1592 @item -Wnon-virtual-dtor @r{(C++ only)}
1593 @opindex Wnon-virtual-dtor
1594 Warn when a class appears to be polymorphic, thereby requiring a virtual
1595 destructor, yet it declares a non-virtual one.
1596 This warning is enabled by @option{-Wall}.
1598 @item -Wreorder @r{(C++ only)}
1600 @cindex reordering, warning
1601 @cindex warning for reordering of member initializers
1602 Warn when the order of member initializers given in the code does not
1603 match the order in which they must be executed. For instance:
1609 A(): j (0), i (1) @{ @}
1613 The compiler will rearrange the member initializers for @samp{i}
1614 and @samp{j} to match the declaration order of the members, emitting
1615 a warning to that effect. This warning is enabled by @option{-Wall}.
1618 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1621 @item -Weffc++ @r{(C++ only)}
1623 Warn about violations of the following style guidelines from Scott Meyers'
1624 @cite{Effective C++} book:
1628 Item 11: Define a copy constructor and an assignment operator for classes
1629 with dynamically allocated memory.
1632 Item 12: Prefer initialization to assignment in constructors.
1635 Item 14: Make destructors virtual in base classes.
1638 Item 15: Have @code{operator=} return a reference to @code{*this}.
1641 Item 23: Don't try to return a reference when you must return an object.
1645 Also warn about violations of the following style guidelines from
1646 Scott Meyers' @cite{More Effective C++} book:
1650 Item 6: Distinguish between prefix and postfix forms of increment and
1651 decrement operators.
1654 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1658 When selecting this option, be aware that the standard library
1659 headers do not obey all of these guidelines; use @samp{grep -v}
1660 to filter out those warnings.
1662 @item -Wno-deprecated @r{(C++ only)}
1663 @opindex Wno-deprecated
1664 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1666 @item -Wno-non-template-friend @r{(C++ only)}
1667 @opindex Wno-non-template-friend
1668 Disable warnings when non-templatized friend functions are declared
1669 within a template. Since the advent of explicit template specification
1670 support in G++, if the name of the friend is an unqualified-id (i.e.,
1671 @samp{friend foo(int)}), the C++ language specification demands that the
1672 friend declare or define an ordinary, nontemplate function. (Section
1673 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1674 could be interpreted as a particular specialization of a templatized
1675 function. Because this non-conforming behavior is no longer the default
1676 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1677 check existing code for potential trouble spots and is on by default.
1678 This new compiler behavior can be turned off with
1679 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1680 but disables the helpful warning.
1682 @item -Wold-style-cast @r{(C++ only)}
1683 @opindex Wold-style-cast
1684 Warn if an old-style (C-style) cast to a non-void type is used within
1685 a C++ program. The new-style casts (@samp{static_cast},
1686 @samp{reinterpret_cast}, and @samp{const_cast}) are less vulnerable to
1687 unintended effects and much easier to search for.
1689 @item -Woverloaded-virtual @r{(C++ only)}
1690 @opindex Woverloaded-virtual
1691 @cindex overloaded virtual fn, warning
1692 @cindex warning for overloaded virtual fn
1693 Warn when a function declaration hides virtual functions from a
1694 base class. For example, in:
1701 struct B: public A @{
1706 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1714 will fail to compile.
1716 @item -Wno-pmf-conversions @r{(C++ only)}
1717 @opindex Wno-pmf-conversions
1718 Disable the diagnostic for converting a bound pointer to member function
1721 @item -Wsign-promo @r{(C++ only)}
1722 @opindex Wsign-promo
1723 Warn when overload resolution chooses a promotion from unsigned or
1724 enumeral type to a signed type, over a conversion to an unsigned type of
1725 the same size. Previous versions of G++ would try to preserve
1726 unsignedness, but the standard mandates the current behavior.
1728 @item -Wsynth @r{(C++ only)}
1730 @cindex warning for synthesized methods
1731 @cindex synthesized methods, warning
1732 Warn when G++'s synthesis behavior does not match that of cfront. For
1738 A& operator = (int);
1748 In this example, G++ will synthesize a default @samp{A& operator =
1749 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1752 @node Objective-C Dialect Options
1753 @section Options Controlling Objective-C Dialect
1755 @cindex compiler options, Objective-C
1756 @cindex Objective-C options, command line
1757 @cindex options, Objective-C
1758 (NOTE: This manual does not describe the Objective-C language itself. See
1759 @w{@uref{http://gcc.gnu.org/readings.html}} for references.)
1761 This section describes the command-line options that are only meaningful
1762 for Objective-C programs, but you can also use most of the GNU compiler
1763 options regardless of what language your program is in. For example,
1764 you might compile a file @code{some_class.m} like this:
1767 gcc -g -fgnu-runtime -O -c some_class.m
1771 In this example, @option{-fgnu-runtime} is an option meant only for
1772 Objective-C programs; you can use the other options with any language
1775 Here is a list of options that are @emph{only} for compiling Objective-C
1779 @item -fconstant-string-class=@var{class-name}
1780 @opindex fconstant-string-class
1781 Use @var{class-name} as the name of the class to instantiate for each
1782 literal string specified with the syntax @code{@@"@dots{}"}. The default
1783 class name is @code{NXConstantString} if the GNU runtime is being used, and
1784 @code{NSConstantString} if the NeXT runtime is being used (see below). The
1785 @option{-fconstant-cfstrings} option, if also present, will override the
1786 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
1787 to be laid out as constant CoreFoundation strings.
1790 @opindex fgnu-runtime
1791 Generate object code compatible with the standard GNU Objective-C
1792 runtime. This is the default for most types of systems.
1794 @item -fnext-runtime
1795 @opindex fnext-runtime
1796 Generate output compatible with the NeXT runtime. This is the default
1797 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1798 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1801 @item -fno-nil-receivers
1802 @opindex -fno-nil-receivers
1803 Assume that all Objective-C message dispatches (e.g.,
1804 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
1805 is not @code{nil}. This allows for more efficient entry points in the runtime to be
1806 used. Currently, this option is only available in conjunction with
1807 the NeXT runtime on Mac OS X 10.3 and later.
1809 @item -fobjc-exceptions
1810 @opindex -fobjc-exceptions
1811 Enable syntactic support for structured exception handling in Objective-C,
1812 similar to what is offered by C++ and Java. Currently, this option is only
1813 available in conjunction with the NeXT runtime on Mac OS X 10.3 and later.
1821 @@catch (AnObjCClass *exc) @{
1828 @@catch (AnotherClass *exc) @{
1831 @@catch (id allOthers) @{
1841 The @code{@@throw} statement may appear anywhere in an Objective-C or
1842 Objective-C++ program; when used inside of a @code{@@catch} block, the
1843 @code{@@throw} may appear without an argument (as shown above), in which case
1844 the object caught by the @code{@@catch} will be rethrown.
1846 Note that only (pointers to) Objective-C objects may be thrown and
1847 caught using this scheme. When an object is thrown, it will be caught
1848 by the nearest @code{@@catch} clause capable of handling objects of that type,
1849 analogously to how @code{catch} blocks work in C++ and Java. A
1850 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
1851 any and all Objective-C exceptions not caught by previous @code{@@catch}
1854 The @code{@@finally} clause, if present, will be executed upon exit from the
1855 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
1856 regardless of whether any exceptions are thrown, caught or rethrown
1857 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
1858 of the @code{finally} clause in Java.
1860 There are several caveats to using the new exception mechanism:
1864 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
1865 idioms provided by the @code{NSException} class, the new
1866 exceptions can only be used on Mac OS X 10.3 (Panther) and later
1867 systems, due to additional functionality needed in the (NeXT) Objective-C
1871 As mentioned above, the new exceptions do not support handling
1872 types other than Objective-C objects. Furthermore, when used from
1873 Objective-C++, the Objective-C exception model does not interoperate with C++
1874 exceptions at this time. This means you cannot @code{@@throw} an exception
1875 from Objective-C and @code{catch} it in C++, or vice versa
1876 (i.e., @code{throw @dots{} @@catch}).
1879 The @option{-fobjc-exceptions} switch also enables the use of synchronization
1880 blocks for thread-safe execution:
1883 @@synchronized (ObjCClass *guard) @{
1888 Upon entering the @code{@@synchronized} block, a thread of execution shall
1889 first check whether a lock has been placed on the corresponding @code{guard}
1890 object by another thread. If it has, the current thread shall wait until
1891 the other thread relinquishes its lock. Once @code{guard} becomes available,
1892 the current thread will place its own lock on it, execute the code contained in
1893 the @code{@@synchronized} block, and finally relinquish the lock (thereby
1894 making @code{guard} available to other threads).
1896 Unlike Java, Objective-C does not allow for entire methods to be marked
1897 @code{@@synchronized}. Note that throwing exceptions out of
1898 @code{@@synchronized} blocks is allowed, and will cause the guarding object
1899 to be unlocked properly.
1901 @item -freplace-objc-classes
1902 @opindex -freplace-objc-classes
1903 Emit a special marker instructing @command{ld(1)} not to statically link in
1904 the resulting object file, and allow @command{dyld(1)} to load it in at
1905 run time instead. This is used in conjunction with the Fix-and-Continue
1906 debugging mode, where the object file in question may be recompiled and
1907 dynamically reloaded in the course of program execution, without the need
1908 to restart the program itself. Currently, Fix-and-Continue functionality
1909 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
1913 @opindex -fzero-link
1914 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
1915 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
1916 compile time) with static class references that get initialized at load time,
1917 which improves run-time performance. Specifying the @option{-fzero-link} flag
1918 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
1919 to be retained. This is useful in Zero-Link debugging mode, since it allows
1920 for individual class implementations to be modified during program execution.
1924 Dump interface declarations for all classes seen in the source file to a
1925 file named @file{@var{sourcename}.decl}.
1928 @opindex Wno-protocol
1929 If a class is declared to implement a protocol, a warning is issued for
1930 every method in the protocol that is not implemented by the class. The
1931 default behavior is to issue a warning for every method not explicitly
1932 implemented in the class, even if a method implementation is inherited
1933 from the superclass. If you use the @code{-Wno-protocol} option, then
1934 methods inherited from the superclass are considered to be implemented,
1935 and no warning is issued for them.
1939 Warn if multiple methods of different types for the same selector are
1940 found during compilation. The check is performed on the list of methods
1941 in the final stage of compilation. Additionally, a check is performed
1942 for each selector appearing in a @code{@@selector(@dots{})}
1943 expression, and a corresponding method for that selector has been found
1944 during compilation. Because these checks scan the method table only at
1945 the end of compilation, these warnings are not produced if the final
1946 stage of compilation is not reached, for example because an error is
1947 found during compilation, or because the @code{-fsyntax-only} option is
1950 @item -Wundeclared-selector
1951 @opindex Wundeclared-selector
1952 Warn if a @code{@@selector(@dots{})} expression referring to an
1953 undeclared selector is found. A selector is considered undeclared if no
1954 method with that name has been declared before the
1955 @code{@@selector(@dots{})} expression, either explicitly in an
1956 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
1957 an @code{@@implementation} section. This option always performs its
1958 checks as soon as a @code{@@selector(@dots{})} expression is found,
1959 while @code{-Wselector} only performs its checks in the final stage of
1960 compilation. This also enforces the coding style convention
1961 that methods and selectors must be declared before being used.
1963 @item -print-objc-runtime-info
1964 @opindex -print-objc-runtime-info
1965 Generate C header describing the largest structure that is passed by
1970 @node Language Independent Options
1971 @section Options to Control Diagnostic Messages Formatting
1972 @cindex options to control diagnostics formatting
1973 @cindex diagnostic messages
1974 @cindex message formatting
1976 Traditionally, diagnostic messages have been formatted irrespective of
1977 the output device's aspect (e.g.@: its width, @dots{}). The options described
1978 below can be used to control the diagnostic messages formatting
1979 algorithm, e.g.@: how many characters per line, how often source location
1980 information should be reported. Right now, only the C++ front end can
1981 honor these options. However it is expected, in the near future, that
1982 the remaining front ends would be able to digest them correctly.
1985 @item -fmessage-length=@var{n}
1986 @opindex fmessage-length
1987 Try to format error messages so that they fit on lines of about @var{n}
1988 characters. The default is 72 characters for @command{g++} and 0 for the rest of
1989 the front ends supported by GCC@. If @var{n} is zero, then no
1990 line-wrapping will be done; each error message will appear on a single
1993 @opindex fdiagnostics-show-location
1994 @item -fdiagnostics-show-location=once
1995 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
1996 reporter to emit @emph{once} source location information; that is, in
1997 case the message is too long to fit on a single physical line and has to
1998 be wrapped, the source location won't be emitted (as prefix) again,
1999 over and over, in subsequent continuation lines. This is the default
2002 @item -fdiagnostics-show-location=every-line
2003 Only meaningful in line-wrapping mode. Instructs the diagnostic
2004 messages reporter to emit the same source location information (as
2005 prefix) for physical lines that result from the process of breaking
2006 a message which is too long to fit on a single line.
2010 @node Warning Options
2011 @section Options to Request or Suppress Warnings
2012 @cindex options to control warnings
2013 @cindex warning messages
2014 @cindex messages, warning
2015 @cindex suppressing warnings
2017 Warnings are diagnostic messages that report constructions which
2018 are not inherently erroneous but which are risky or suggest there
2019 may have been an error.
2021 You can request many specific warnings with options beginning @samp{-W},
2022 for example @option{-Wimplicit} to request warnings on implicit
2023 declarations. Each of these specific warning options also has a
2024 negative form beginning @samp{-Wno-} to turn off warnings;
2025 for example, @option{-Wno-implicit}. This manual lists only one of the
2026 two forms, whichever is not the default.
2028 The following options control the amount and kinds of warnings produced
2029 by GCC; for further, language-specific options also refer to
2030 @ref{C++ Dialect Options} and @ref{Objective-C Dialect Options}.
2033 @cindex syntax checking
2035 @opindex fsyntax-only
2036 Check the code for syntax errors, but don't do anything beyond that.
2040 Issue all the warnings demanded by strict ISO C and ISO C++;
2041 reject all programs that use forbidden extensions, and some other
2042 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2043 version of the ISO C standard specified by any @option{-std} option used.
2045 Valid ISO C and ISO C++ programs should compile properly with or without
2046 this option (though a rare few will require @option{-ansi} or a
2047 @option{-std} option specifying the required version of ISO C)@. However,
2048 without this option, certain GNU extensions and traditional C and C++
2049 features are supported as well. With this option, they are rejected.
2051 @option{-pedantic} does not cause warning messages for use of the
2052 alternate keywords whose names begin and end with @samp{__}. Pedantic
2053 warnings are also disabled in the expression that follows
2054 @code{__extension__}. However, only system header files should use
2055 these escape routes; application programs should avoid them.
2056 @xref{Alternate Keywords}.
2058 Some users try to use @option{-pedantic} to check programs for strict ISO
2059 C conformance. They soon find that it does not do quite what they want:
2060 it finds some non-ISO practices, but not all---only those for which
2061 ISO C @emph{requires} a diagnostic, and some others for which
2062 diagnostics have been added.
2064 A feature to report any failure to conform to ISO C might be useful in
2065 some instances, but would require considerable additional work and would
2066 be quite different from @option{-pedantic}. We don't have plans to
2067 support such a feature in the near future.
2069 Where the standard specified with @option{-std} represents a GNU
2070 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2071 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2072 extended dialect is based. Warnings from @option{-pedantic} are given
2073 where they are required by the base standard. (It would not make sense
2074 for such warnings to be given only for features not in the specified GNU
2075 C dialect, since by definition the GNU dialects of C include all
2076 features the compiler supports with the given option, and there would be
2077 nothing to warn about.)
2079 @item -pedantic-errors
2080 @opindex pedantic-errors
2081 Like @option{-pedantic}, except that errors are produced rather than
2086 Inhibit all warning messages.
2090 Inhibit warning messages about the use of @samp{#import}.
2092 @item -Wchar-subscripts
2093 @opindex Wchar-subscripts
2094 Warn if an array subscript has type @code{char}. This is a common cause
2095 of error, as programmers often forget that this type is signed on some
2100 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2101 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2105 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2106 the arguments supplied have types appropriate to the format string
2107 specified, and that the conversions specified in the format string make
2108 sense. This includes standard functions, and others specified by format
2109 attributes (@pxref{Function Attributes}), in the @code{printf},
2110 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2111 not in the C standard) families.
2113 The formats are checked against the format features supported by GNU
2114 libc version 2.2. These include all ISO C90 and C99 features, as well
2115 as features from the Single Unix Specification and some BSD and GNU
2116 extensions. Other library implementations may not support all these
2117 features; GCC does not support warning about features that go beyond a
2118 particular library's limitations. However, if @option{-pedantic} is used
2119 with @option{-Wformat}, warnings will be given about format features not
2120 in the selected standard version (but not for @code{strfmon} formats,
2121 since those are not in any version of the C standard). @xref{C Dialect
2122 Options,,Options Controlling C Dialect}.
2124 Since @option{-Wformat} also checks for null format arguments for
2125 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2127 @option{-Wformat} is included in @option{-Wall}. For more control over some
2128 aspects of format checking, the options @option{-Wformat-y2k},
2129 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2130 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2131 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2134 @opindex Wformat-y2k
2135 If @option{-Wformat} is specified, also warn about @code{strftime}
2136 formats which may yield only a two-digit year.
2138 @item -Wno-format-extra-args
2139 @opindex Wno-format-extra-args
2140 If @option{-Wformat} is specified, do not warn about excess arguments to a
2141 @code{printf} or @code{scanf} format function. The C standard specifies
2142 that such arguments are ignored.
2144 Where the unused arguments lie between used arguments that are
2145 specified with @samp{$} operand number specifications, normally
2146 warnings are still given, since the implementation could not know what
2147 type to pass to @code{va_arg} to skip the unused arguments. However,
2148 in the case of @code{scanf} formats, this option will suppress the
2149 warning if the unused arguments are all pointers, since the Single
2150 Unix Specification says that such unused arguments are allowed.
2152 @item -Wno-format-zero-length
2153 @opindex Wno-format-zero-length
2154 If @option{-Wformat} is specified, do not warn about zero-length formats.
2155 The C standard specifies that zero-length formats are allowed.
2157 @item -Wformat-nonliteral
2158 @opindex Wformat-nonliteral
2159 If @option{-Wformat} is specified, also warn if the format string is not a
2160 string literal and so cannot be checked, unless the format function
2161 takes its format arguments as a @code{va_list}.
2163 @item -Wformat-security
2164 @opindex Wformat-security
2165 If @option{-Wformat} is specified, also warn about uses of format
2166 functions that represent possible security problems. At present, this
2167 warns about calls to @code{printf} and @code{scanf} functions where the
2168 format string is not a string literal and there are no format arguments,
2169 as in @code{printf (foo);}. This may be a security hole if the format
2170 string came from untrusted input and contains @samp{%n}. (This is
2171 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2172 in future warnings may be added to @option{-Wformat-security} that are not
2173 included in @option{-Wformat-nonliteral}.)
2177 Enable @option{-Wformat} plus format checks not included in
2178 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2179 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2183 Warn about passing a null pointer for arguments marked as
2184 requiring a non-null value by the @code{nonnull} function attribute.
2186 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2187 can be disabled with the @option{-Wno-nonnull} option.
2189 @item -Winit-self @r{(C, C++, and Objective-C only)}
2191 Warn about uninitialized variables which are initialized with themselves.
2192 Note this option can only be used with the @option{-Wuninitialized} option,
2193 which in turn only works with @option{-O1} and above.
2195 For example, GCC will warn about @code{i} being uninitialized in the
2196 following snippet only when @option{-Winit-self} has been specified:
2207 @item -Wimplicit-int
2208 @opindex Wimplicit-int
2209 Warn when a declaration does not specify a type.
2211 @item -Wimplicit-function-declaration
2212 @itemx -Werror-implicit-function-declaration
2213 @opindex Wimplicit-function-declaration
2214 @opindex Werror-implicit-function-declaration
2215 Give a warning (or error) whenever a function is used before being
2220 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2224 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2225 function with external linkage, returning int, taking either zero
2226 arguments, two, or three arguments of appropriate types.
2228 @item -Wmissing-braces
2229 @opindex Wmissing-braces
2230 Warn if an aggregate or union initializer is not fully bracketed. In
2231 the following example, the initializer for @samp{a} is not fully
2232 bracketed, but that for @samp{b} is fully bracketed.
2235 int a[2][2] = @{ 0, 1, 2, 3 @};
2236 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2240 @opindex Wparentheses
2241 Warn if parentheses are omitted in certain contexts, such
2242 as when there is an assignment in a context where a truth value
2243 is expected, or when operators are nested whose precedence people
2244 often get confused about.
2246 Also warn about constructions where there may be confusion to which
2247 @code{if} statement an @code{else} branch belongs. Here is an example of
2262 In C, every @code{else} branch belongs to the innermost possible @code{if}
2263 statement, which in this example is @code{if (b)}. This is often not
2264 what the programmer expected, as illustrated in the above example by
2265 indentation the programmer chose. When there is the potential for this
2266 confusion, GCC will issue a warning when this flag is specified.
2267 To eliminate the warning, add explicit braces around the innermost
2268 @code{if} statement so there is no way the @code{else} could belong to
2269 the enclosing @code{if}. The resulting code would look like this:
2285 @item -Wsequence-point
2286 @opindex Wsequence-point
2287 Warn about code that may have undefined semantics because of violations
2288 of sequence point rules in the C standard.
2290 The C standard defines the order in which expressions in a C program are
2291 evaluated in terms of @dfn{sequence points}, which represent a partial
2292 ordering between the execution of parts of the program: those executed
2293 before the sequence point, and those executed after it. These occur
2294 after the evaluation of a full expression (one which is not part of a
2295 larger expression), after the evaluation of the first operand of a
2296 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2297 function is called (but after the evaluation of its arguments and the
2298 expression denoting the called function), and in certain other places.
2299 Other than as expressed by the sequence point rules, the order of
2300 evaluation of subexpressions of an expression is not specified. All
2301 these rules describe only a partial order rather than a total order,
2302 since, for example, if two functions are called within one expression
2303 with no sequence point between them, the order in which the functions
2304 are called is not specified. However, the standards committee have
2305 ruled that function calls do not overlap.
2307 It is not specified when between sequence points modifications to the
2308 values of objects take effect. Programs whose behavior depends on this
2309 have undefined behavior; the C standard specifies that ``Between the
2310 previous and next sequence point an object shall have its stored value
2311 modified at most once by the evaluation of an expression. Furthermore,
2312 the prior value shall be read only to determine the value to be
2313 stored.''. If a program breaks these rules, the results on any
2314 particular implementation are entirely unpredictable.
2316 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2317 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2318 diagnosed by this option, and it may give an occasional false positive
2319 result, but in general it has been found fairly effective at detecting
2320 this sort of problem in programs.
2322 The present implementation of this option only works for C programs. A
2323 future implementation may also work for C++ programs.
2325 The C standard is worded confusingly, therefore there is some debate
2326 over the precise meaning of the sequence point rules in subtle cases.
2327 Links to discussions of the problem, including proposed formal
2328 definitions, may be found on our readings page, at
2329 @w{@uref{http://gcc.gnu.org/readings.html}}.
2332 @opindex Wreturn-type
2333 Warn whenever a function is defined with a return-type that defaults to
2334 @code{int}. Also warn about any @code{return} statement with no
2335 return-value in a function whose return-type is not @code{void}.
2337 For C++, a function without return type always produces a diagnostic
2338 message, even when @option{-Wno-return-type} is specified. The only
2339 exceptions are @samp{main} and functions defined in system headers.
2343 Warn whenever a @code{switch} statement has an index of enumeral type
2344 and lacks a @code{case} for one or more of the named codes of that
2345 enumeration. (The presence of a @code{default} label prevents this
2346 warning.) @code{case} labels outside the enumeration range also
2347 provoke warnings when this option is used.
2349 @item -Wswitch-default
2350 @opindex Wswitch-switch
2351 Warn whenever a @code{switch} statement does not have a @code{default}
2355 @opindex Wswitch-enum
2356 Warn whenever a @code{switch} statement has an index of enumeral type
2357 and lacks a @code{case} for one or more of the named codes of that
2358 enumeration. @code{case} labels outside the enumeration range also
2359 provoke warnings when this option is used.
2363 Warn if any trigraphs are encountered that might change the meaning of
2364 the program (trigraphs within comments are not warned about).
2366 @item -Wunused-function
2367 @opindex Wunused-function
2368 Warn whenever a static function is declared but not defined or a
2369 non\-inline static function is unused.
2371 @item -Wunused-label
2372 @opindex Wunused-label
2373 Warn whenever a label is declared but not used.
2375 To suppress this warning use the @samp{unused} attribute
2376 (@pxref{Variable Attributes}).
2378 @item -Wunused-parameter
2379 @opindex Wunused-parameter
2380 Warn whenever a function parameter is unused aside from its declaration.
2382 To suppress this warning use the @samp{unused} attribute
2383 (@pxref{Variable Attributes}).
2385 @item -Wunused-variable
2386 @opindex Wunused-variable
2387 Warn whenever a local variable or non-constant static variable is unused
2388 aside from its declaration
2390 To suppress this warning use the @samp{unused} attribute
2391 (@pxref{Variable Attributes}).
2393 @item -Wunused-value
2394 @opindex Wunused-value
2395 Warn whenever a statement computes a result that is explicitly not used.
2397 To suppress this warning cast the expression to @samp{void}.
2401 All the above @option{-Wunused} options combined.
2403 In order to get a warning about an unused function parameter, you must
2404 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2405 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2407 @item -Wuninitialized
2408 @opindex Wuninitialized
2409 Warn if an automatic variable is used without first being initialized or
2410 if a variable may be clobbered by a @code{setjmp} call.
2412 These warnings are possible only in optimizing compilation,
2413 because they require data flow information that is computed only
2414 when optimizing. If you don't specify @option{-O}, you simply won't
2417 If you want to warn about code which uses the uninitialized value of the
2418 variable in its own initializer, use the @option{-Winit-self} option.
2420 These warnings occur only for variables that are candidates for
2421 register allocation. Therefore, they do not occur for a variable that
2422 is declared @code{volatile}, or whose address is taken, or whose size
2423 is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
2424 structures, unions or arrays, even when they are in registers.
2426 Note that there may be no warning about a variable that is used only
2427 to compute a value that itself is never used, because such
2428 computations may be deleted by data flow analysis before the warnings
2431 These warnings are made optional because GCC is not smart
2432 enough to see all the reasons why the code might be correct
2433 despite appearing to have an error. Here is one example of how
2454 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2455 always initialized, but GCC doesn't know this. Here is
2456 another common case:
2461 if (change_y) save_y = y, y = new_y;
2463 if (change_y) y = save_y;
2468 This has no bug because @code{save_y} is used only if it is set.
2470 @cindex @code{longjmp} warnings
2471 This option also warns when a non-volatile automatic variable might be
2472 changed by a call to @code{longjmp}. These warnings as well are possible
2473 only in optimizing compilation.
2475 The compiler sees only the calls to @code{setjmp}. It cannot know
2476 where @code{longjmp} will be called; in fact, a signal handler could
2477 call it at any point in the code. As a result, you may get a warning
2478 even when there is in fact no problem because @code{longjmp} cannot
2479 in fact be called at the place which would cause a problem.
2481 Some spurious warnings can be avoided if you declare all the functions
2482 you use that never return as @code{noreturn}. @xref{Function
2485 @item -Wunknown-pragmas
2486 @opindex Wunknown-pragmas
2487 @cindex warning for unknown pragmas
2488 @cindex unknown pragmas, warning
2489 @cindex pragmas, warning of unknown
2490 Warn when a #pragma directive is encountered which is not understood by
2491 GCC@. If this command line option is used, warnings will even be issued
2492 for unknown pragmas in system header files. This is not the case if
2493 the warnings were only enabled by the @option{-Wall} command line option.
2495 @item -Wstrict-aliasing
2496 @opindex Wstrict-aliasing
2497 This option is only active when @option{-fstrict-aliasing} is active.
2498 It warns about code which might break the strict aliasing rules that the
2499 compiler is using for optimization. The warning does not catch all
2500 cases, but does attempt to catch the more common pitfalls. It is
2501 included in @option{-Wall}.
2505 All of the above @samp{-W} options combined. This enables all the
2506 warnings about constructions that some users consider questionable, and
2507 that are easy to avoid (or modify to prevent the warning), even in
2508 conjunction with macros. This also enables some language-specific
2509 warnings described in @ref{C++ Dialect Options} and
2510 @ref{Objective-C Dialect Options}.
2513 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2514 Some of them warn about constructions that users generally do not
2515 consider questionable, but which occasionally you might wish to check
2516 for; others warn about constructions that are necessary or hard to avoid
2517 in some cases, and there is no simple way to modify the code to suppress
2524 (This option used to be called @option{-W}. The older name is still
2525 supported, but the newer name is more descriptive.) Print extra warning
2526 messages for these events:
2530 A function can return either with or without a value. (Falling
2531 off the end of the function body is considered returning without
2532 a value.) For example, this function would evoke such a
2546 An expression-statement or the left-hand side of a comma expression
2547 contains no side effects.
2548 To suppress the warning, cast the unused expression to void.
2549 For example, an expression such as @samp{x[i,j]} will cause a warning,
2550 but @samp{x[(void)i,j]} will not.
2553 An unsigned value is compared against zero with @samp{<} or @samp{>=}.
2556 A comparison like @samp{x<=y<=z} appears; this is equivalent to
2557 @samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from
2558 that of ordinary mathematical notation.
2561 Storage-class specifiers like @code{static} are not the first things in
2562 a declaration. According to the C Standard, this usage is obsolescent.
2565 The return type of a function has a type qualifier such as @code{const}.
2566 Such a type qualifier has no effect, since the value returned by a
2567 function is not an lvalue. (But don't warn about the GNU extension of
2568 @code{volatile void} return types. That extension will be warned about
2569 if @option{-pedantic} is specified.)
2572 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2576 A comparison between signed and unsigned values could produce an
2577 incorrect result when the signed value is converted to unsigned.
2578 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2581 An aggregate has an initializer which does not initialize all members.
2582 For example, the following code would cause such a warning, because
2583 @code{x.h} would be implicitly initialized to zero:
2586 struct s @{ int f, g, h; @};
2587 struct s x = @{ 3, 4 @};
2591 A function parameter is declared without a type specifier in K&R-style
2599 An empty body occurs in an @samp{if} or @samp{else} statement.
2602 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2603 @samp{>}, or @samp{>=}.
2606 A variable might be changed by @samp{longjmp} or @samp{vfork}.
2609 Any of several floating-point events that often indicate errors, such as
2610 overflow, underflow, loss of precision, etc.
2612 @item @r{(C++ only)}
2613 An enumerator and a non-enumerator both appear in a conditional expression.
2615 @item @r{(C++ only)}
2616 A non-static reference or non-static @samp{const} member appears in a
2617 class without constructors.
2619 @item @r{(C++ only)}
2620 Ambiguous virtual bases.
2622 @item @r{(C++ only)}
2623 Subscripting an array which has been declared @samp{register}.
2625 @item @r{(C++ only)}
2626 Taking the address of a variable which has been declared @samp{register}.
2628 @item @r{(C++ only)}
2629 A base class is not initialized in a derived class' copy constructor.
2632 @item -Wno-div-by-zero
2633 @opindex Wno-div-by-zero
2634 @opindex Wdiv-by-zero
2635 Do not warn about compile-time integer division by zero. Floating point
2636 division by zero is not warned about, as it can be a legitimate way of
2637 obtaining infinities and NaNs.
2639 @item -Wsystem-headers
2640 @opindex Wsystem-headers
2641 @cindex warnings from system headers
2642 @cindex system headers, warnings from
2643 Print warning messages for constructs found in system header files.
2644 Warnings from system headers are normally suppressed, on the assumption
2645 that they usually do not indicate real problems and would only make the
2646 compiler output harder to read. Using this command line option tells
2647 GCC to emit warnings from system headers as if they occurred in user
2648 code. However, note that using @option{-Wall} in conjunction with this
2649 option will @emph{not} warn about unknown pragmas in system
2650 headers---for that, @option{-Wunknown-pragmas} must also be used.
2653 @opindex Wfloat-equal
2654 Warn if floating point values are used in equality comparisons.
2656 The idea behind this is that sometimes it is convenient (for the
2657 programmer) to consider floating-point values as approximations to
2658 infinitely precise real numbers. If you are doing this, then you need
2659 to compute (by analyzing the code, or in some other way) the maximum or
2660 likely maximum error that the computation introduces, and allow for it
2661 when performing comparisons (and when producing output, but that's a
2662 different problem). In particular, instead of testing for equality, you
2663 would check to see whether the two values have ranges that overlap; and
2664 this is done with the relational operators, so equality comparisons are
2667 @item -Wtraditional @r{(C only)}
2668 @opindex Wtraditional
2669 Warn about certain constructs that behave differently in traditional and
2670 ISO C@. Also warn about ISO C constructs that have no traditional C
2671 equivalent, and/or problematic constructs which should be avoided.
2675 Macro parameters that appear within string literals in the macro body.
2676 In traditional C macro replacement takes place within string literals,
2677 but does not in ISO C@.
2680 In traditional C, some preprocessor directives did not exist.
2681 Traditional preprocessors would only consider a line to be a directive
2682 if the @samp{#} appeared in column 1 on the line. Therefore
2683 @option{-Wtraditional} warns about directives that traditional C
2684 understands but would ignore because the @samp{#} does not appear as the
2685 first character on the line. It also suggests you hide directives like
2686 @samp{#pragma} not understood by traditional C by indenting them. Some
2687 traditional implementations would not recognize @samp{#elif}, so it
2688 suggests avoiding it altogether.
2691 A function-like macro that appears without arguments.
2694 The unary plus operator.
2697 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2698 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2699 constants.) Note, these suffixes appear in macros defined in the system
2700 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2701 Use of these macros in user code might normally lead to spurious
2702 warnings, however gcc's integrated preprocessor has enough context to
2703 avoid warning in these cases.
2706 A function declared external in one block and then used after the end of
2710 A @code{switch} statement has an operand of type @code{long}.
2713 A non-@code{static} function declaration follows a @code{static} one.
2714 This construct is not accepted by some traditional C compilers.
2717 The ISO type of an integer constant has a different width or
2718 signedness from its traditional type. This warning is only issued if
2719 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2720 typically represent bit patterns, are not warned about.
2723 Usage of ISO string concatenation is detected.
2726 Initialization of automatic aggregates.
2729 Identifier conflicts with labels. Traditional C lacks a separate
2730 namespace for labels.
2733 Initialization of unions. If the initializer is zero, the warning is
2734 omitted. This is done under the assumption that the zero initializer in
2735 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2736 initializer warnings and relies on default initialization to zero in the
2740 Conversions by prototypes between fixed/floating point values and vice
2741 versa. The absence of these prototypes when compiling with traditional
2742 C would cause serious problems. This is a subset of the possible
2743 conversion warnings, for the full set use @option{-Wconversion}.
2746 Use of ISO C style function definitions. This warning intentionally is
2747 @emph{not} issued for prototype declarations or variadic functions
2748 because these ISO C features will appear in your code when using
2749 libiberty's traditional C compatibility macros, @code{PARAMS} and
2750 @code{VPARAMS}. This warning is also bypassed for nested functions
2751 because that feature is already a gcc extension and thus not relevant to
2752 traditional C compatibility.
2755 @item -Wdeclaration-after-statement @r{(C only)}
2756 @opindex Wdeclaration-after-statement
2757 Warn when a declaration is found after a statement in a block. This
2758 construct, known from C++, was introduced with ISO C99 and is by default
2759 allowed in GCC@. It is not supported by ISO C90 and was not supported by
2760 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
2764 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
2766 @item -Wendif-labels
2767 @opindex Wendif-labels
2768 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
2772 Warn whenever a local variable shadows another local variable, parameter or
2773 global variable or whenever a built-in function is shadowed.
2775 @item -Wlarger-than-@var{len}
2776 @opindex Wlarger-than
2777 Warn whenever an object of larger than @var{len} bytes is defined.
2779 @item -Wpointer-arith
2780 @opindex Wpointer-arith
2781 Warn about anything that depends on the ``size of'' a function type or
2782 of @code{void}. GNU C assigns these types a size of 1, for
2783 convenience in calculations with @code{void *} pointers and pointers
2786 @item -Wbad-function-cast @r{(C only)}
2787 @opindex Wbad-function-cast
2788 Warn whenever a function call is cast to a non-matching type.
2789 For example, warn if @code{int malloc()} is cast to @code{anything *}.
2793 Warn whenever a pointer is cast so as to remove a type qualifier from
2794 the target type. For example, warn if a @code{const char *} is cast
2795 to an ordinary @code{char *}.
2798 @opindex Wcast-align
2799 Warn whenever a pointer is cast such that the required alignment of the
2800 target is increased. For example, warn if a @code{char *} is cast to
2801 an @code{int *} on machines where integers can only be accessed at
2802 two- or four-byte boundaries.
2804 @item -Wwrite-strings
2805 @opindex Wwrite-strings
2806 When compiling C, give string constants the type @code{const
2807 char[@var{length}]} so that
2808 copying the address of one into a non-@code{const} @code{char *}
2809 pointer will get a warning; when compiling C++, warn about the
2810 deprecated conversion from string constants to @code{char *}.
2811 These warnings will help you find at
2812 compile time code that can try to write into a string constant, but
2813 only if you have been very careful about using @code{const} in
2814 declarations and prototypes. Otherwise, it will just be a nuisance;
2815 this is why we did not make @option{-Wall} request these warnings.
2818 @opindex Wconversion
2819 Warn if a prototype causes a type conversion that is different from what
2820 would happen to the same argument in the absence of a prototype. This
2821 includes conversions of fixed point to floating and vice versa, and
2822 conversions changing the width or signedness of a fixed point argument
2823 except when the same as the default promotion.
2825 Also, warn if a negative integer constant expression is implicitly
2826 converted to an unsigned type. For example, warn about the assignment
2827 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
2828 casts like @code{(unsigned) -1}.
2830 @item -Wsign-compare
2831 @opindex Wsign-compare
2832 @cindex warning for comparison of signed and unsigned values
2833 @cindex comparison of signed and unsigned values, warning
2834 @cindex signed and unsigned values, comparison warning
2835 Warn when a comparison between signed and unsigned values could produce
2836 an incorrect result when the signed value is converted to unsigned.
2837 This warning is also enabled by @option{-Wextra}; to get the other warnings
2838 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
2840 @item -Waggregate-return
2841 @opindex Waggregate-return
2842 Warn if any functions that return structures or unions are defined or
2843 called. (In languages where you can return an array, this also elicits
2846 @item -Wstrict-prototypes @r{(C only)}
2847 @opindex Wstrict-prototypes
2848 Warn if a function is declared or defined without specifying the
2849 argument types. (An old-style function definition is permitted without
2850 a warning if preceded by a declaration which specifies the argument
2853 @item -Wold-style-definition @r{(C only)}
2854 @opindex Wold-style-definition
2855 Warn if an old-style function definition is used. A warning is given
2856 even if there is a previous prototype.
2858 @item -Wmissing-prototypes @r{(C only)}
2859 @opindex Wmissing-prototypes
2860 Warn if a global function is defined without a previous prototype
2861 declaration. This warning is issued even if the definition itself
2862 provides a prototype. The aim is to detect global functions that fail
2863 to be declared in header files.
2865 @item -Wmissing-declarations @r{(C only)}
2866 @opindex Wmissing-declarations
2867 Warn if a global function is defined without a previous declaration.
2868 Do so even if the definition itself provides a prototype.
2869 Use this option to detect global functions that are not declared in
2872 @item -Wmissing-noreturn
2873 @opindex Wmissing-noreturn
2874 Warn about functions which might be candidates for attribute @code{noreturn}.
2875 Note these are only possible candidates, not absolute ones. Care should
2876 be taken to manually verify functions actually do not ever return before
2877 adding the @code{noreturn} attribute, otherwise subtle code generation
2878 bugs could be introduced. You will not get a warning for @code{main} in
2879 hosted C environments.
2881 @item -Wmissing-format-attribute
2882 @opindex Wmissing-format-attribute
2884 If @option{-Wformat} is enabled, also warn about functions which might be
2885 candidates for @code{format} attributes. Note these are only possible
2886 candidates, not absolute ones. GCC will guess that @code{format}
2887 attributes might be appropriate for any function that calls a function
2888 like @code{vprintf} or @code{vscanf}, but this might not always be the
2889 case, and some functions for which @code{format} attributes are
2890 appropriate may not be detected. This option has no effect unless
2891 @option{-Wformat} is enabled (possibly by @option{-Wall}).
2893 @item -Wno-multichar
2894 @opindex Wno-multichar
2896 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
2897 Usually they indicate a typo in the user's code, as they have
2898 implementation-defined values, and should not be used in portable code.
2900 @item -Wno-deprecated-declarations
2901 @opindex Wno-deprecated-declarations
2902 Do not warn about uses of functions, variables, and types marked as
2903 deprecated by using the @code{deprecated} attribute.
2904 (@pxref{Function Attributes}, @pxref{Variable Attributes},
2905 @pxref{Type Attributes}.)
2909 Warn if a structure is given the packed attribute, but the packed
2910 attribute has no effect on the layout or size of the structure.
2911 Such structures may be mis-aligned for little benefit. For
2912 instance, in this code, the variable @code{f.x} in @code{struct bar}
2913 will be misaligned even though @code{struct bar} does not itself
2914 have the packed attribute:
2921 @} __attribute__((packed));
2931 Warn if padding is included in a structure, either to align an element
2932 of the structure or to align the whole structure. Sometimes when this
2933 happens it is possible to rearrange the fields of the structure to
2934 reduce the padding and so make the structure smaller.
2936 @item -Wredundant-decls
2937 @opindex Wredundant-decls
2938 Warn if anything is declared more than once in the same scope, even in
2939 cases where multiple declaration is valid and changes nothing.
2941 @item -Wnested-externs @r{(C only)}
2942 @opindex Wnested-externs
2943 Warn if an @code{extern} declaration is encountered within a function.
2945 @item -Wunreachable-code
2946 @opindex Wunreachable-code
2947 Warn if the compiler detects that code will never be executed.
2949 This option is intended to warn when the compiler detects that at
2950 least a whole line of source code will never be executed, because
2951 some condition is never satisfied or because it is after a
2952 procedure that never returns.
2954 It is possible for this option to produce a warning even though there
2955 are circumstances under which part of the affected line can be executed,
2956 so care should be taken when removing apparently-unreachable code.
2958 For instance, when a function is inlined, a warning may mean that the
2959 line is unreachable in only one inlined copy of the function.
2961 This option is not made part of @option{-Wall} because in a debugging
2962 version of a program there is often substantial code which checks
2963 correct functioning of the program and is, hopefully, unreachable
2964 because the program does work. Another common use of unreachable
2965 code is to provide behavior which is selectable at compile-time.
2969 Warn if a function can not be inlined and it was declared as inline.
2970 Even with this option, the compiler will not warn about failures to
2971 inline functions declared in system headers.
2973 The compiler uses a variety of heuristics to determine whether or not
2974 to inline a function. For example, the compiler takes into account
2975 the size of the function being inlined and the the amount of inlining
2976 that has already been done in the current function. Therefore,
2977 seemingly insignificant changes in the source program can cause the
2978 warnings produced by @option{-Winline} to appear or disappear.
2980 @item -Wno-invalid-offsetof @r{(C++ only)}
2981 @opindex Wno-invalid-offsetof
2982 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
2983 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
2984 to a non-POD type is undefined. In existing C++ implementations,
2985 however, @samp{offsetof} typically gives meaningful results even when
2986 applied to certain kinds of non-POD types. (Such as a simple
2987 @samp{struct} that fails to be a POD type only by virtue of having a
2988 constructor.) This flag is for users who are aware that they are
2989 writing nonportable code and who have deliberately chosen to ignore the
2992 The restrictions on @samp{offsetof} may be relaxed in a future version
2993 of the C++ standard.
2996 @opindex Winvalid-pch
2997 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
2998 the search path but can't be used.
3002 @opindex Wno-long-long
3003 Warn if @samp{long long} type is used. This is default. To inhibit
3004 the warning messages, use @option{-Wno-long-long}. Flags
3005 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
3006 only when @option{-pedantic} flag is used.
3008 @item -Wdisabled-optimization
3009 @opindex Wdisabled-optimization
3010 Warn if a requested optimization pass is disabled. This warning does
3011 not generally indicate that there is anything wrong with your code; it
3012 merely indicates that GCC's optimizers were unable to handle the code
3013 effectively. Often, the problem is that your code is too big or too
3014 complex; GCC will refuse to optimize programs when the optimization
3015 itself is likely to take inordinate amounts of time.
3019 Make all warnings into errors.
3022 @node Debugging Options
3023 @section Options for Debugging Your Program or GCC
3024 @cindex options, debugging
3025 @cindex debugging information options
3027 GCC has various special options that are used for debugging
3028 either your program or GCC:
3033 Produce debugging information in the operating system's native format
3034 (stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging
3037 On most systems that use stabs format, @option{-g} enables use of extra
3038 debugging information that only GDB can use; this extra information
3039 makes debugging work better in GDB but will probably make other debuggers
3041 refuse to read the program. If you want to control for certain whether
3042 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
3043 @option{-gxcoff+}, @option{-gxcoff}, @option{-gdwarf-1+}, @option{-gdwarf-1},
3044 or @option{-gvms} (see below).
3046 Unlike most other C compilers, GCC allows you to use @option{-g} with
3047 @option{-O}. The shortcuts taken by optimized code may occasionally
3048 produce surprising results: some variables you declared may not exist
3049 at all; flow of control may briefly move where you did not expect it;
3050 some statements may not be executed because they compute constant
3051 results or their values were already at hand; some statements may
3052 execute in different places because they were moved out of loops.
3054 Nevertheless it proves possible to debug optimized output. This makes
3055 it reasonable to use the optimizer for programs that might have bugs.
3057 The following options are useful when GCC is generated with the
3058 capability for more than one debugging format.
3062 Produce debugging information for use by GDB@. This means to use the
3063 most expressive format available (DWARF 2, stabs, or the native format
3064 if neither of those are supported), including GDB extensions if at all
3069 Produce debugging information in stabs format (if that is supported),
3070 without GDB extensions. This is the format used by DBX on most BSD
3071 systems. On MIPS, Alpha and System V Release 4 systems this option
3072 produces stabs debugging output which is not understood by DBX or SDB@.
3073 On System V Release 4 systems this option requires the GNU assembler.
3075 @item -feliminate-unused-debug-symbols
3076 @opindex feliminate-unused-debug-symbols
3077 Produce debugging information in stabs format (if that is supported),
3078 for only symbols that are actually used.
3082 Produce debugging information in stabs format (if that is supported),
3083 using GNU extensions understood only by the GNU debugger (GDB)@. The
3084 use of these extensions is likely to make other debuggers crash or
3085 refuse to read the program.
3089 Produce debugging information in COFF format (if that is supported).
3090 This is the format used by SDB on most System V systems prior to
3095 Produce debugging information in XCOFF format (if that is supported).
3096 This is the format used by the DBX debugger on IBM RS/6000 systems.
3100 Produce debugging information in XCOFF format (if that is supported),
3101 using GNU extensions understood only by the GNU debugger (GDB)@. The
3102 use of these extensions is likely to make other debuggers crash or
3103 refuse to read the program, and may cause assemblers other than the GNU
3104 assembler (GAS) to fail with an error.
3108 Produce debugging information in DWARF version 1 format (if that is
3109 supported). This is the format used by SDB on most System V Release 4
3112 This option is deprecated.
3116 Produce debugging information in DWARF version 1 format (if that is
3117 supported), using GNU extensions understood only by the GNU debugger
3118 (GDB)@. The use of these extensions is likely to make other debuggers
3119 crash or refuse to read the program.
3121 This option is deprecated.
3125 Produce debugging information in DWARF version 2 format (if that is
3126 supported). This is the format used by DBX on IRIX 6.
3130 Produce debugging information in VMS debug format (if that is
3131 supported). This is the format used by DEBUG on VMS systems.
3134 @itemx -ggdb@var{level}
3135 @itemx -gstabs@var{level}
3136 @itemx -gcoff@var{level}
3137 @itemx -gxcoff@var{level}
3138 @itemx -gvms@var{level}
3139 Request debugging information and also use @var{level} to specify how
3140 much information. The default level is 2.
3142 Level 1 produces minimal information, enough for making backtraces in
3143 parts of the program that you don't plan to debug. This includes
3144 descriptions of functions and external variables, but no information
3145 about local variables and no line numbers.
3147 Level 3 includes extra information, such as all the macro definitions
3148 present in the program. Some debuggers support macro expansion when
3149 you use @option{-g3}.
3151 Note that in order to avoid confusion between DWARF1 debug level 2,
3152 and DWARF2, neither @option{-gdwarf} nor @option{-gdwarf-2} accept
3153 a concatenated debug level. Instead use an additional @option{-g@var{level}}
3154 option to change the debug level for DWARF1 or DWARF2.
3156 @item -feliminate-dwarf2-dups
3157 @opindex feliminate-dwarf2-dups
3158 Compress DWARF2 debugging information by eliminating duplicated
3159 information about each symbol. This option only makes sense when
3160 generating DWARF2 debugging information with @option{-gdwarf-2}.
3162 @cindex @command{prof}
3165 Generate extra code to write profile information suitable for the
3166 analysis program @command{prof}. You must use this option when compiling
3167 the source files you want data about, and you must also use it when
3170 @cindex @command{gprof}
3173 Generate extra code to write profile information suitable for the
3174 analysis program @command{gprof}. You must use this option when compiling
3175 the source files you want data about, and you must also use it when
3180 Makes the compiler print out each function name as it is compiled, and
3181 print some statistics about each pass when it finishes.
3184 @opindex ftime-report
3185 Makes the compiler print some statistics about the time consumed by each
3186 pass when it finishes.
3189 @opindex fmem-report
3190 Makes the compiler print some statistics about permanent memory
3191 allocation when it finishes.
3193 @item -fprofile-arcs
3194 @opindex fprofile-arcs
3195 Add code so that program flow @dfn{arcs} are instrumented. During
3196 execution the program records how many times each branch and call is
3197 executed and how many times it is taken or returns. When the compiled
3198 program exits it saves this data to a file called
3199 @file{@var{auxname}.gcda} for each source file. The data may be used for
3200 profile-directed optimizations (@option{-fbranch-probabilities}), or for
3201 test coverage analysis (@option{-ftest-coverage}). Each object file's
3202 @var{auxname} is generated from the name of the output file, if
3203 explicitly specified and it is not the final executable, otherwise it is
3204 the basename of the source file. In both cases any suffix is removed
3205 (e.g. @file{foo.gcda} for input file @file{dir/foo.c}, or
3206 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
3211 Compile the source files with @option{-fprofile-arcs} plus optimization
3212 and code generation options. For test coverage analysis, use the
3213 additional @option{-ftest-coverage} option. You do not need to profile
3214 every source file in a program.
3217 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
3218 (the latter implies the former).
3221 Run the program on a representative workload to generate the arc profile
3222 information. This may be repeated any number of times. You can run
3223 concurrent instances of your program, and provided that the file system
3224 supports locking, the data files will be correctly updated. Also
3225 @code{fork} calls are detected and correctly handled (double counting
3229 For profile-directed optimizations, compile the source files again with
3230 the same optimization and code generation options plus
3231 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
3232 Control Optimization}).
3235 For test coverage analysis, use @command{gcov} to produce human readable
3236 information from the @file{.gcno} and @file{.gcda} files. Refer to the
3237 @command{gcov} documentation for further information.
3241 With @option{-fprofile-arcs}, for each function of your program GCC
3242 creates a program flow graph, then finds a spanning tree for the graph.
3243 Only arcs that are not on the spanning tree have to be instrumented: the
3244 compiler adds code to count the number of times that these arcs are
3245 executed. When an arc is the only exit or only entrance to a block, the
3246 instrumentation code can be added to the block; otherwise, a new basic
3247 block must be created to hold the instrumentation code.
3250 @item -ftest-coverage
3251 @opindex ftest-coverage
3252 Produce a notes file that the @command{gcov} code-coverage utility
3253 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
3254 show program coverage. Each source file's note file is called
3255 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
3256 above for a description of @var{auxname} and instructions on how to
3257 generate test coverage data. Coverage data will match the source files
3258 more closely, if you do not optimize.
3260 @item -d@var{letters}
3262 Says to make debugging dumps during compilation at times specified by
3263 @var{letters}. This is used for debugging the compiler. The file names
3264 for most of the dumps are made by appending a pass number and a word to
3265 the @var{dumpname}. @var{dumpname} is generated from the name of the
3266 output file, if explicitly specified and it is not an executable,
3267 otherwise it is the basename of the source file. In both cases any
3268 suffix is removed (e.g. @file{foo.01.rtl} or @file{foo.02.sibling}).
3269 Here are the possible letters for use in @var{letters}, and their
3275 Annotate the assembler output with miscellaneous debugging information.
3278 Dump after computing branch probabilities, to @file{@var{file}.12.bp}.
3281 Dump after block reordering, to @file{@var{file}.30.bbro}.
3284 Dump after instruction combination, to the file @file{@var{file}.20.combine}.
3287 Dump after the first if conversion, to the file @file{@var{file}.14.ce1}.
3288 Also dump after the second if conversion, to the file @file{@var{file}.21.ce2}.
3291 Dump after branch target load optimization, to to @file{@var{file}.32.btl}.
3292 Also dump after delayed branch scheduling, to @file{@var{file}.36.dbr}.
3295 Dump all macro definitions, at the end of preprocessing, in addition to
3299 Dump after the second if conversion, to @file{@var{file}.31.ce3}.
3302 Dump after control and data flow analysis, to @file{@var{file}.11.cfg}.
3303 Also dump after life analysis, to @file{@var{file}.19.life}.
3306 Dump after purging @code{ADDRESSOF} codes, to @file{@var{file}.07.addressof}.
3309 Dump after global register allocation, to @file{@var{file}.25.greg}.
3312 Dump after GCSE, to @file{@var{file}.08.gcse}.
3313 Also dump after jump bypassing and control flow optimizations, to
3314 @file{@var{file}.10.bypass}.
3317 Dump after finalization of EH handling code, to @file{@var{file}.03.eh}.
3320 Dump after sibling call optimizations, to @file{@var{file}.02.sibling}.
3323 Dump after the first jump optimization, to @file{@var{file}.04.jump}.
3326 Dump after conversion from registers to stack, to @file{@var{file}.34.stack}.
3329 Dump after local register allocation, to @file{@var{file}.24.lreg}.
3332 Dump after loop optimization passes, to @file{@var{file}.09.loop} and
3333 @file{@var{file}.16.loop2}.
3336 Dump after performing the machine dependent reorganization pass, to
3337 @file{@var{file}.35.mach}.
3340 Dump after register renumbering, to @file{@var{file}.29.rnreg}.
3343 Dump after the register move pass, to @file{@var{file}.22.regmove}.
3346 Dump after post-reload optimizations, to @file{@var{file}.26.postreload}.
3349 Dump after RTL generation, to @file{@var{file}.01.rtl}.
3352 Dump after the second scheduling pass, to @file{@var{file}.33.sched2}.
3355 Dump after CSE (including the jump optimization that sometimes follows
3356 CSE), to @file{@var{file}.06.cse}.
3359 Dump after the first scheduling pass, to @file{@var{file}.23.sched}.
3362 Dump after the second CSE pass (including the jump optimization that
3363 sometimes follows CSE), to @file{@var{file}.18.cse2}.
3366 Dump after running tracer, to @file{@var{file}.15.tracer}.
3369 Dump after null pointer elimination pass to @file{@var{file}.05.null}.
3372 Dump callgraph and unit-at-a-time optimization @file{@var{file}.00.unit}.
3375 Dump after the second flow pass, to @file{@var{file}.27.flow2}.
3378 Dump after the peephole pass, to @file{@var{file}.28.peephole2}.
3381 Produce all the dumps listed above.
3384 Produce a core dump whenever an error occurs.
3387 Print statistics on memory usage, at the end of the run, to
3391 Annotate the assembler output with a comment indicating which
3392 pattern and alternative was used. The length of each instruction is
3396 Dump the RTL in the assembler output as a comment before each instruction.
3397 Also turns on @option{-dp} annotation.
3400 For each of the other indicated dump files (except for
3401 @file{@var{file}.01.rtl}), dump a representation of the control flow graph
3402 suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3405 Just generate RTL for a function instead of compiling it. Usually used
3409 Dump debugging information during parsing, to standard error.
3412 @item -fdump-unnumbered
3413 @opindex fdump-unnumbered
3414 When doing debugging dumps (see @option{-d} option above), suppress instruction
3415 numbers and line number note output. This makes it more feasible to
3416 use diff on debugging dumps for compiler invocations with different
3417 options, in particular with and without @option{-g}.
3419 @item -fdump-translation-unit @r{(C and C++ only)}
3420 @itemx -fdump-translation-unit-@var{options} @r{(C and C++ only)}
3421 @opindex fdump-translation-unit
3422 Dump a representation of the tree structure for the entire translation
3423 unit to a file. The file name is made by appending @file{.tu} to the
3424 source file name. If the @samp{-@var{options}} form is used, @var{options}
3425 controls the details of the dump as described for the
3426 @option{-fdump-tree} options.
3428 @item -fdump-class-hierarchy @r{(C++ only)}
3429 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3430 @opindex fdump-class-hierarchy
3431 Dump a representation of each class's hierarchy and virtual function
3432 table layout to a file. The file name is made by appending @file{.class}
3433 to the source file name. If the @samp{-@var{options}} form is used,
3434 @var{options} controls the details of the dump as described for the
3435 @option{-fdump-tree} options.
3437 @item -fdump-tree-@var{switch} @r{(C++ only)}
3438 @itemx -fdump-tree-@var{switch}-@var{options} @r{(C++ only)}
3440 Control the dumping at various stages of processing the intermediate
3441 language tree to a file. The file name is generated by appending a switch
3442 specific suffix to the source file name. If the @samp{-@var{options}}
3443 form is used, @var{options} is a list of @samp{-} separated options that
3444 control the details of the dump. Not all options are applicable to all
3445 dumps, those which are not meaningful will be ignored. The following
3446 options are available
3450 Print the address of each node. Usually this is not meaningful as it
3451 changes according to the environment and source file. Its primary use
3452 is for tying up a dump file with a debug environment.
3454 Inhibit dumping of members of a scope or body of a function merely
3455 because that scope has been reached. Only dump such items when they
3456 are directly reachable by some other path.
3458 Turn on all options.
3461 The following tree dumps are possible:
3464 Dump before any tree based optimization, to @file{@var{file}.original}.
3466 Dump after all tree based optimization, to @file{@var{file}.optimized}.
3468 Dump after function inlining, to @file{@var{file}.inlined}.
3471 @item -frandom-seed=@var{string}
3472 @opindex frandom-string
3473 This option provides a seed that GCC uses when it would otherwise use
3474 random numbers. It is used to generate certain symbol names
3475 that have to be different in every compiled file. It is also used to
3476 place unique stamps in coverage data files and the object files that
3477 produce them. You can use the @option{-frandom-seed} option to produce
3478 reproducibly identical object files.
3480 The @var{string} should be different for every file you compile.
3482 @item -fsched-verbose=@var{n}
3483 @opindex fsched-verbose
3484 On targets that use instruction scheduling, this option controls the
3485 amount of debugging output the scheduler prints. This information is
3486 written to standard error, unless @option{-dS} or @option{-dR} is
3487 specified, in which case it is output to the usual dump
3488 listing file, @file{.sched} or @file{.sched2} respectively. However
3489 for @var{n} greater than nine, the output is always printed to standard
3492 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
3493 same information as @option{-dRS}. For @var{n} greater than one, it
3494 also output basic block probabilities, detailed ready list information
3495 and unit/insn info. For @var{n} greater than two, it includes RTL
3496 at abort point, control-flow and regions info. And for @var{n} over
3497 four, @option{-fsched-verbose} also includes dependence info.
3501 Store the usual ``temporary'' intermediate files permanently; place them
3502 in the current directory and name them based on the source file. Thus,
3503 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
3504 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
3505 preprocessed @file{foo.i} output file even though the compiler now
3506 normally uses an integrated preprocessor.
3510 Report the CPU time taken by each subprocess in the compilation
3511 sequence. For C source files, this is the compiler proper and assembler
3512 (plus the linker if linking is done). The output looks like this:
3519 The first number on each line is the ``user time,'' that is time spent
3520 executing the program itself. The second number is ``system time,''
3521 time spent executing operating system routines on behalf of the program.
3522 Both numbers are in seconds.
3524 @item -print-file-name=@var{library}
3525 @opindex print-file-name
3526 Print the full absolute name of the library file @var{library} that
3527 would be used when linking---and don't do anything else. With this
3528 option, GCC does not compile or link anything; it just prints the
3531 @item -print-multi-directory
3532 @opindex print-multi-directory
3533 Print the directory name corresponding to the multilib selected by any
3534 other switches present in the command line. This directory is supposed
3535 to exist in @env{GCC_EXEC_PREFIX}.
3537 @item -print-multi-lib
3538 @opindex print-multi-lib
3539 Print the mapping from multilib directory names to compiler switches
3540 that enable them. The directory name is separated from the switches by
3541 @samp{;}, and each switch starts with an @samp{@@} instead of the
3542 @samp{-}, without spaces between multiple switches. This is supposed to
3543 ease shell-processing.
3545 @item -print-prog-name=@var{program}
3546 @opindex print-prog-name
3547 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
3549 @item -print-libgcc-file-name
3550 @opindex print-libgcc-file-name
3551 Same as @option{-print-file-name=libgcc.a}.
3553 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
3554 but you do want to link with @file{libgcc.a}. You can do
3557 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
3560 @item -print-search-dirs
3561 @opindex print-search-dirs
3562 Print the name of the configured installation directory and a list of
3563 program and library directories gcc will search---and don't do anything else.
3565 This is useful when gcc prints the error message
3566 @samp{installation problem, cannot exec cpp0: No such file or directory}.
3567 To resolve this you either need to put @file{cpp0} and the other compiler
3568 components where gcc expects to find them, or you can set the environment
3569 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
3570 Don't forget the trailing '/'.
3571 @xref{Environment Variables}.
3574 @opindex dumpmachine
3575 Print the compiler's target machine (for example,
3576 @samp{i686-pc-linux-gnu})---and don't do anything else.
3579 @opindex dumpversion
3580 Print the compiler version (for example, @samp{3.0})---and don't do
3585 Print the compiler's built-in specs---and don't do anything else. (This
3586 is used when GCC itself is being built.) @xref{Spec Files}.
3588 @item -feliminate-unused-debug-types
3589 @opindex feliminate-unused-debug-types
3590 Normally, when producing DWARF2 output, GCC will emit debugging
3591 information for all types declared in a compilation
3592 unit, regardless of whether or not they are actually used
3593 in that compilation unit. Sometimes this is useful, such as
3594 if, in the debugger, you want to cast a value to a type that is
3595 not actually used in your program (but is declared). More often,
3596 however, this results in a significant amount of wasted space.
3597 With this option, GCC will avoid producing debug symbol output
3598 for types that are nowhere used in the source file being compiled.
3601 @node Optimize Options
3602 @section Options That Control Optimization
3603 @cindex optimize options
3604 @cindex options, optimization
3606 These options control various sorts of optimizations.
3608 Without any optimization option, the compiler's goal is to reduce the
3609 cost of compilation and to make debugging produce the expected
3610 results. Statements are independent: if you stop the program with a
3611 breakpoint between statements, you can then assign a new value to any
3612 variable or change the program counter to any other statement in the
3613 function and get exactly the results you would expect from the source
3616 Turning on optimization flags makes the compiler attempt to improve
3617 the performance and/or code size at the expense of compilation time
3618 and possibly the ability to debug the program.
3620 The compiler performs optimisation based on the knowledge it has of
3621 the program. Using the @option{-funit-at-a-time} flag will allow the
3622 compiler to consider information gained from later functions in the
3623 file when compiling a function. Compiling multiple files at once to a
3624 single output file (and using @option{-funit-at-a-time}) will allow
3625 the compiler to use information gained from all of the files when
3626 compiling each of them.
3628 Not all optimizations are controlled directly by a flag. Only
3629 optimizations that have a flag are listed.
3636 Optimize. Optimizing compilation takes somewhat more time, and a lot
3637 more memory for a large function.
3639 With @option{-O}, the compiler tries to reduce code size and execution
3640 time, without performing any optimizations that take a great deal of
3643 @option{-O} turns on the following optimization flags:
3644 @gccoptlist{-fdefer-pop @gol
3645 -fmerge-constants @gol
3647 -floop-optimize @gol
3649 -fif-conversion @gol
3650 -fif-conversion2 @gol
3651 -fdelayed-branch @gol
3652 -fguess-branch-probability @gol
3655 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
3656 where doing so does not interfere with debugging.
3660 Optimize even more. GCC performs nearly all supported optimizations
3661 that do not involve a space-speed tradeoff. The compiler does not
3662 perform loop unrolling or function inlining when you specify @option{-O2}.
3663 As compared to @option{-O}, this option increases both compilation time
3664 and the performance of the generated code.
3666 @option{-O2} turns on all optimization flags specified by @option{-O}. It
3667 also turns on the following optimization flags:
3668 @gccoptlist{-fforce-mem @gol
3669 -foptimize-sibling-calls @gol
3670 -fstrength-reduce @gol
3671 -fcse-follow-jumps -fcse-skip-blocks @gol
3672 -frerun-cse-after-loop -frerun-loop-opt @gol
3673 -fgcse -fgcse-lm -fgcse-sm -fgcse-las @gol
3674 -fdelete-null-pointer-checks @gol
3675 -fexpensive-optimizations @gol
3677 -fschedule-insns -fschedule-insns2 @gol
3678 -fsched-interblock -fsched-spec @gol
3681 -freorder-blocks -freorder-functions @gol
3682 -fstrict-aliasing @gol
3683 -funit-at-a-time -fweb @gol
3684 -falign-functions -falign-jumps @gol
3685 -falign-loops -falign-labels}
3687 Please note the warning under @option{-fgcse} about
3688 invoking @option{-O2} on programs that use computed gotos.
3692 Optimize yet more. @option{-O3} turns on all optimizations specified by
3693 @option{-O2} and also turns on the @option{-finline-functions},
3694 @option{-fweb} and @option{-frename-registers} options.
3698 Do not optimize. This is the default.
3702 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
3703 do not typically increase code size. It also performs further
3704 optimizations designed to reduce code size.
3706 @option{-Os} disables the following optimization flags:
3707 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
3708 -falign-labels -freorder-blocks -fprefetch-loop-arrays}
3710 If you use multiple @option{-O} options, with or without level numbers,
3711 the last such option is the one that is effective.
3714 Options of the form @option{-f@var{flag}} specify machine-independent
3715 flags. Most flags have both positive and negative forms; the negative
3716 form of @option{-ffoo} would be @option{-fno-foo}. In the table
3717 below, only one of the forms is listed---the one you typically will
3718 use. You can figure out the other form by either removing @samp{no-}
3721 The following options control specific optimizations. They are either
3722 activated by @option{-O} options or are related to ones that are. You
3723 can use the following flags in the rare cases when ``fine-tuning'' of
3724 optimizations to be performed is desired.
3727 @item -fno-default-inline
3728 @opindex fno-default-inline
3729 Do not make member functions inline by default merely because they are
3730 defined inside the class scope (C++ only). Otherwise, when you specify
3731 @w{@option{-O}}, member functions defined inside class scope are compiled
3732 inline by default; i.e., you don't need to add @samp{inline} in front of
3733 the member function name.
3735 @item -fno-defer-pop
3736 @opindex fno-defer-pop
3737 Always pop the arguments to each function call as soon as that function
3738 returns. For machines which must pop arguments after a function call,
3739 the compiler normally lets arguments accumulate on the stack for several
3740 function calls and pops them all at once.
3742 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3746 Force memory operands to be copied into registers before doing
3747 arithmetic on them. This produces better code by making all memory
3748 references potential common subexpressions. When they are not common
3749 subexpressions, instruction combination should eliminate the separate
3752 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3755 @opindex fforce-addr
3756 Force memory address constants to be copied into registers before
3757 doing arithmetic on them. This may produce better code just as
3758 @option{-fforce-mem} may.
3760 @item -fomit-frame-pointer
3761 @opindex fomit-frame-pointer
3762 Don't keep the frame pointer in a register for functions that
3763 don't need one. This avoids the instructions to save, set up and
3764 restore frame pointers; it also makes an extra register available
3765 in many functions. @strong{It also makes debugging impossible on
3768 On some machines, such as the VAX, this flag has no effect, because
3769 the standard calling sequence automatically handles the frame pointer
3770 and nothing is saved by pretending it doesn't exist. The
3771 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
3772 whether a target machine supports this flag. @xref{Registers,,Register
3773 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
3775 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3777 @item -foptimize-sibling-calls
3778 @opindex foptimize-sibling-calls
3779 Optimize sibling and tail recursive calls.
3781 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3785 Don't pay attention to the @code{inline} keyword. Normally this option
3786 is used to keep the compiler from expanding any functions inline.
3787 Note that if you are not optimizing, no functions can be expanded inline.
3789 @item -finline-functions
3790 @opindex finline-functions
3791 Integrate all simple functions into their callers. The compiler
3792 heuristically decides which functions are simple enough to be worth
3793 integrating in this way.
3795 If all calls to a given function are integrated, and the function is
3796 declared @code{static}, then the function is normally not output as
3797 assembler code in its own right.
3799 Enabled at level @option{-O3}.
3801 @item -finline-limit=@var{n}
3802 @opindex finline-limit
3803 By default, gcc limits the size of functions that can be inlined. This flag
3804 allows the control of this limit for functions that are explicitly marked as
3805 inline (i.e., marked with the inline keyword or defined within the class
3806 definition in c++). @var{n} is the size of functions that can be inlined in
3807 number of pseudo instructions (not counting parameter handling). The default
3808 value of @var{n} is 600.
3809 Increasing this value can result in more inlined code at
3810 the cost of compilation time and memory consumption. Decreasing usually makes
3811 the compilation faster and less code will be inlined (which presumably
3812 means slower programs). This option is particularly useful for programs that
3813 use inlining heavily such as those based on recursive templates with C++.
3815 Inlining is actually controlled by a number of parameters, which may be
3816 specified individually by using @option{--param @var{name}=@var{value}}.
3817 The @option{-finline-limit=@var{n}} option sets some of these parameters
3821 @item max-inline-insns-single
3822 is set to @var{n}/2.
3823 @item max-inline-insns-auto
3824 is set to @var{n}/2.
3825 @item min-inline-insns
3826 is set to 130 or @var{n}/4, whichever is smaller.
3827 @item max-inline-insns-rtl
3831 See below for a documentation of the individual
3832 parameters controlling inlining.
3834 @emph{Note:} pseudo instruction represents, in this particular context, an
3835 abstract measurement of function's size. In no way, it represents a count
3836 of assembly instructions and as such its exact meaning might change from one
3837 release to an another.
3839 @item -fkeep-inline-functions
3840 @opindex fkeep-inline-functions
3841 Even if all calls to a given function are integrated, and the function
3842 is declared @code{static}, nevertheless output a separate run-time
3843 callable version of the function. This switch does not affect
3844 @code{extern inline} functions.
3846 @item -fkeep-static-consts
3847 @opindex fkeep-static-consts
3848 Emit variables declared @code{static const} when optimization isn't turned
3849 on, even if the variables aren't referenced.
3851 GCC enables this option by default. If you want to force the compiler to
3852 check if the variable was referenced, regardless of whether or not
3853 optimization is turned on, use the @option{-fno-keep-static-consts} option.
3855 @item -fmerge-constants
3856 Attempt to merge identical constants (string constants and floating point
3857 constants) across compilation units.
3859 This option is the default for optimized compilation if the assembler and
3860 linker support it. Use @option{-fno-merge-constants} to inhibit this
3863 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3865 @item -fmerge-all-constants
3866 Attempt to merge identical constants and identical variables.
3868 This option implies @option{-fmerge-constants}. In addition to
3869 @option{-fmerge-constants} this considers e.g. even constant initialized
3870 arrays or initialized constant variables with integral or floating point
3871 types. Languages like C or C++ require each non-automatic variable to
3872 have distinct location, so using this option will result in non-conforming
3877 Use a graph coloring register allocator. Currently this option is meant
3878 for testing, so we are interested to hear about miscompilations with
3881 @item -fno-branch-count-reg
3882 @opindex fno-branch-count-reg
3883 Do not use ``decrement and branch'' instructions on a count register,
3884 but instead generate a sequence of instructions that decrement a
3885 register, compare it against zero, then branch based upon the result.
3886 This option is only meaningful on architectures that support such
3887 instructions, which include x86, PowerPC, IA-64 and S/390.
3889 The default is @option{-fbranch-count-reg}, enabled when
3890 @option{-fstrength-reduce} is enabled.
3892 @item -fno-function-cse
3893 @opindex fno-function-cse
3894 Do not put function addresses in registers; make each instruction that
3895 calls a constant function contain the function's address explicitly.
3897 This option results in less efficient code, but some strange hacks
3898 that alter the assembler output may be confused by the optimizations
3899 performed when this option is not used.
3901 The default is @option{-ffunction-cse}
3903 @item -fno-zero-initialized-in-bss
3904 @opindex fno-zero-initialized-in-bss
3905 If the target supports a BSS section, GCC by default puts variables that
3906 are initialized to zero into BSS@. This can save space in the resulting
3909 This option turns off this behavior because some programs explicitly
3910 rely on variables going to the data section. E.g., so that the
3911 resulting executable can find the beginning of that section and/or make
3912 assumptions based on that.
3914 The default is @option{-fzero-initialized-in-bss}.
3916 @item -fstrength-reduce
3917 @opindex fstrength-reduce
3918 Perform the optimizations of loop strength reduction and
3919 elimination of iteration variables.
3921 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3923 @item -fthread-jumps
3924 @opindex fthread-jumps
3925 Perform optimizations where we check to see if a jump branches to a
3926 location where another comparison subsumed by the first is found. If
3927 so, the first branch is redirected to either the destination of the
3928 second branch or a point immediately following it, depending on whether
3929 the condition is known to be true or false.
3931 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3933 @item -fcse-follow-jumps
3934 @opindex fcse-follow-jumps
3935 In common subexpression elimination, scan through jump instructions
3936 when the target of the jump is not reached by any other path. For
3937 example, when CSE encounters an @code{if} statement with an
3938 @code{else} clause, CSE will follow the jump when the condition
3941 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3943 @item -fcse-skip-blocks
3944 @opindex fcse-skip-blocks
3945 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
3946 follow jumps which conditionally skip over blocks. When CSE
3947 encounters a simple @code{if} statement with no else clause,
3948 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
3949 body of the @code{if}.
3951 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3953 @item -frerun-cse-after-loop
3954 @opindex frerun-cse-after-loop
3955 Re-run common subexpression elimination after loop optimizations has been
3958 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3960 @item -frerun-loop-opt
3961 @opindex frerun-loop-opt
3962 Run the loop optimizer twice.
3964 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3968 Perform a global common subexpression elimination pass.
3969 This pass also performs global constant and copy propagation.
3971 @emph{Note:} When compiling a program using computed gotos, a GCC
3972 extension, you may get better runtime performance if you disable
3973 the global common subexpression elimination pass by adding
3974 @option{-fno-gcse} to the command line.
3976 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3980 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
3981 attempt to move loads which are only killed by stores into themselves. This
3982 allows a loop containing a load/store sequence to be changed to a load outside
3983 the loop, and a copy/store within the loop.
3985 Enabled by default when gcse is enabled.
3989 When @option{-fgcse-sm} is enabled, a store motion pass is run after
3990 global common subexpression elimination. This pass will attempt to move
3991 stores out of loops. When used in conjunction with @option{-fgcse-lm},
3992 loops containing a load/store sequence can be changed to a load before
3993 the loop and a store after the loop.
3995 Enabled by default when gcse is enabled.
3999 When @option{-fgcse-las} is enabled, the global common subexpression
4000 elimination pass eliminates redundant loads that come after stores to the
4001 same memory location (both partial and full redundancies).
4003 Enabled by default when gcse is enabled.
4005 @item -floop-optimize
4006 @opindex floop-optimize
4007 Perform loop optimizations: move constant expressions out of loops, simplify
4008 exit test conditions and optionally do strength-reduction and loop unrolling as
4011 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4013 @item -fcrossjumping
4014 @opindex crossjumping
4015 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
4016 resulting code may or may not perform better than without cross-jumping.
4018 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4020 @item -fif-conversion
4021 @opindex if-conversion
4022 Attempt to transform conditional jumps into branch-less equivalents. This
4023 include use of conditional moves, min, max, set flags and abs instructions, and
4024 some tricks doable by standard arithmetics. The use of conditional execution
4025 on chips where it is available is controlled by @code{if-conversion2}.
4027 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4029 @item -fif-conversion2
4030 @opindex if-conversion2
4031 Use conditional execution (where available) to transform conditional jumps into
4032 branch-less equivalents.
4034 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4036 @item -fdelete-null-pointer-checks
4037 @opindex fdelete-null-pointer-checks
4038 Use global dataflow analysis to identify and eliminate useless checks
4039 for null pointers. The compiler assumes that dereferencing a null
4040 pointer would have halted the program. If a pointer is checked after
4041 it has already been dereferenced, it cannot be null.
4043 In some environments, this assumption is not true, and programs can
4044 safely dereference null pointers. Use
4045 @option{-fno-delete-null-pointer-checks} to disable this optimization
4046 for programs which depend on that behavior.
4048 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4050 @item -fexpensive-optimizations
4051 @opindex fexpensive-optimizations
4052 Perform a number of minor optimizations that are relatively expensive.
4054 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4056 @item -foptimize-register-move
4058 @opindex foptimize-register-move
4060 Attempt to reassign register numbers in move instructions and as
4061 operands of other simple instructions in order to maximize the amount of
4062 register tying. This is especially helpful on machines with two-operand
4065 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
4068 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4070 @item -fdelayed-branch
4071 @opindex fdelayed-branch
4072 If supported for the target machine, attempt to reorder instructions
4073 to exploit instruction slots available after delayed branch
4076 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4078 @item -fschedule-insns
4079 @opindex fschedule-insns
4080 If supported for the target machine, attempt to reorder instructions to
4081 eliminate execution stalls due to required data being unavailable. This
4082 helps machines that have slow floating point or memory load instructions
4083 by allowing other instructions to be issued until the result of the load
4084 or floating point instruction is required.
4086 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4088 @item -fschedule-insns2
4089 @opindex fschedule-insns2
4090 Similar to @option{-fschedule-insns}, but requests an additional pass of
4091 instruction scheduling after register allocation has been done. This is
4092 especially useful on machines with a relatively small number of
4093 registers and where memory load instructions take more than one cycle.
4095 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4097 @item -fno-sched-interblock
4098 @opindex fno-sched-interblock
4099 Don't schedule instructions across basic blocks. This is normally
4100 enabled by default when scheduling before register allocation, i.e.@:
4101 with @option{-fschedule-insns} or at @option{-O2} or higher.
4103 @item -fno-sched-spec
4104 @opindex fno-sched-spec
4105 Don't allow speculative motion of non-load instructions. This is normally
4106 enabled by default when scheduling before register allocation, i.e.@:
4107 with @option{-fschedule-insns} or at @option{-O2} or higher.
4109 @item -fsched-spec-load
4110 @opindex fsched-spec-load
4111 Allow speculative motion of some load instructions. This only makes
4112 sense when scheduling before register allocation, i.e.@: with
4113 @option{-fschedule-insns} or at @option{-O2} or higher.
4115 @item -fsched-spec-load-dangerous
4116 @opindex fsched-spec-load-dangerous
4117 Allow speculative motion of more load instructions. This only makes
4118 sense when scheduling before register allocation, i.e.@: with
4119 @option{-fschedule-insns} or at @option{-O2} or higher.
4121 @item -fsched-stalled-insns=@var{n}
4122 @opindex fsched-stalled-insns
4123 Define how many insns (if any) can be moved prematurely from the queue
4124 of stalled insns into the ready list, during the second scheduling pass.
4126 @item -fsched-stalled-insns-dep=@var{n}
4127 @opindex fsched-stalled-insns-dep
4128 Define how many insn groups (cycles) will be examined for a dependency
4129 on a stalled insn that is candidate for premature removal from the queue
4130 of stalled insns. Has an effect only during the second scheduling pass,
4131 and only if @option{-fsched-stalled-insns} is used and its value is not zero.
4133 @item -fsched2-use-superblocks
4134 @opindex fsched2-use-superblocks
4135 When scheduling after register allocation, do use superblock scheduling
4136 algorithm. Superblock scheduling allows motion across basic block boundaries
4137 resulting on faster schedules. This option is experimental, as not all machine
4138 descriptions used by GCC model the CPU closely enough to avoid unreliable
4139 results from the algorithm.
4141 This only makes sense when scheduling after register allocation, i.e.@: with
4142 @option{-fschedule-insns2} or at @option{-O2} or higher.
4144 @item -fsched2-use-traces
4145 @opindex fsched2-use-traces
4146 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
4147 allocation and additionally perform code duplication in order to increase the
4148 size of superblocks using tracer pass. See @option{-ftracer} for details on
4151 This mode should produce faster but significantly longer programs. Also
4152 without @code{-fbranch-probabilities} the traces constructed may not match the
4153 reality and hurt the performance. This only makes
4154 sense when scheduling after register allocation, i.e.@: with
4155 @option{-fschedule-insns2} or at @option{-O2} or higher.
4157 @item -fcaller-saves
4158 @opindex fcaller-saves
4159 Enable values to be allocated in registers that will be clobbered by
4160 function calls, by emitting extra instructions to save and restore the
4161 registers around such calls. Such allocation is done only when it
4162 seems to result in better code than would otherwise be produced.
4164 This option is always enabled by default on certain machines, usually
4165 those which have no call-preserved registers to use instead.
4167 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4169 @item -fmove-all-movables
4170 @opindex fmove-all-movables
4171 Forces all invariant computations in loops to be moved
4174 @item -freduce-all-givs
4175 @opindex freduce-all-givs
4176 Forces all general-induction variables in loops to be
4179 @emph{Note:} When compiling programs written in Fortran,
4180 @option{-fmove-all-movables} and @option{-freduce-all-givs} are enabled
4181 by default when you use the optimizer.
4183 These options may generate better or worse code; results are highly
4184 dependent on the structure of loops within the source code.
4186 These two options are intended to be removed someday, once
4187 they have helped determine the efficacy of various
4188 approaches to improving loop optimizations.
4190 Please let us (@w{@email{gcc@@gcc.gnu.org}} and @w{@email{fortran@@gnu.org}})
4191 know how use of these options affects
4192 the performance of your production code.
4193 We're very interested in code that runs @emph{slower}
4194 when these options are @emph{enabled}.
4197 @itemx -fno-peephole2
4198 @opindex fno-peephole
4199 @opindex fno-peephole2
4200 Disable any machine-specific peephole optimizations. The difference
4201 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
4202 are implemented in the compiler; some targets use one, some use the
4203 other, a few use both.
4205 @option{-fpeephole} is enabled by default.
4206 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4208 @item -fno-guess-branch-probability
4209 @opindex fno-guess-branch-probability
4210 Do not guess branch probabilities using a randomized model.
4212 Sometimes gcc will opt to use a randomized model to guess branch
4213 probabilities, when none are available from either profiling feedback
4214 (@option{-fprofile-arcs}) or @samp{__builtin_expect}. This means that
4215 different runs of the compiler on the same program may produce different
4218 In a hard real-time system, people don't want different runs of the
4219 compiler to produce code that has different behavior; minimizing
4220 non-determinism is of paramount import. This switch allows users to
4221 reduce non-determinism, possibly at the expense of inferior
4224 The default is @option{-fguess-branch-probability} at levels
4225 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4227 @item -freorder-blocks
4228 @opindex freorder-blocks
4229 Reorder basic blocks in the compiled function in order to reduce number of
4230 taken branches and improve code locality.
4232 Enabled at levels @option{-O2}, @option{-O3}.
4234 @item -freorder-functions
4235 @opindex freorder-functions
4236 Reorder basic blocks in the compiled function in order to reduce number of
4237 taken branches and improve code locality. This is implemented by using special
4238 subsections @code{text.hot} for most frequently executed functions and
4239 @code{text.unlikely} for unlikely executed functions. Reordering is done by
4240 the linker so object file format must support named sections and linker must
4241 place them in a reasonable way.
4243 Also profile feedback must be available in to make this option effective. See
4244 @option{-fprofile-arcs} for details.
4246 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4248 @item -fstrict-aliasing
4249 @opindex fstrict-aliasing
4250 Allows the compiler to assume the strictest aliasing rules applicable to
4251 the language being compiled. For C (and C++), this activates
4252 optimizations based on the type of expressions. In particular, an
4253 object of one type is assumed never to reside at the same address as an
4254 object of a different type, unless the types are almost the same. For
4255 example, an @code{unsigned int} can alias an @code{int}, but not a
4256 @code{void*} or a @code{double}. A character type may alias any other
4259 Pay special attention to code like this:
4272 The practice of reading from a different union member than the one most
4273 recently written to (called ``type-punning'') is common. Even with
4274 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
4275 is accessed through the union type. So, the code above will work as
4276 expected. However, this code might not:
4287 Every language that wishes to perform language-specific alias analysis
4288 should define a function that computes, given an @code{tree}
4289 node, an alias set for the node. Nodes in different alias sets are not
4290 allowed to alias. For an example, see the C front-end function
4291 @code{c_get_alias_set}.
4293 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4295 @item -falign-functions
4296 @itemx -falign-functions=@var{n}
4297 @opindex falign-functions
4298 Align the start of functions to the next power-of-two greater than
4299 @var{n}, skipping up to @var{n} bytes. For instance,
4300 @option{-falign-functions=32} aligns functions to the next 32-byte
4301 boundary, but @option{-falign-functions=24} would align to the next
4302 32-byte boundary only if this can be done by skipping 23 bytes or less.
4304 @option{-fno-align-functions} and @option{-falign-functions=1} are
4305 equivalent and mean that functions will not be aligned.
4307 Some assemblers only support this flag when @var{n} is a power of two;
4308 in that case, it is rounded up.
4310 If @var{n} is not specified or is zero, use a machine-dependent default.
4312 Enabled at levels @option{-O2}, @option{-O3}.
4314 @item -falign-labels
4315 @itemx -falign-labels=@var{n}
4316 @opindex falign-labels
4317 Align all branch targets to a power-of-two boundary, skipping up to
4318 @var{n} bytes like @option{-falign-functions}. This option can easily
4319 make code slower, because it must insert dummy operations for when the
4320 branch target is reached in the usual flow of the code.
4322 @option{-fno-align-labels} and @option{-falign-labels=1} are
4323 equivalent and mean that labels will not be aligned.
4325 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
4326 are greater than this value, then their values are used instead.
4328 If @var{n} is not specified or is zero, use a machine-dependent default
4329 which is very likely to be @samp{1}, meaning no alignment.
4331 Enabled at levels @option{-O2}, @option{-O3}.
4334 @itemx -falign-loops=@var{n}
4335 @opindex falign-loops
4336 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
4337 like @option{-falign-functions}. The hope is that the loop will be
4338 executed many times, which will make up for any execution of the dummy
4341 @option{-fno-align-loops} and @option{-falign-loops=1} are
4342 equivalent and mean that loops will not be aligned.
4344 If @var{n} is not specified or is zero, use a machine-dependent default.
4346 Enabled at levels @option{-O2}, @option{-O3}.
4349 @itemx -falign-jumps=@var{n}
4350 @opindex falign-jumps
4351 Align branch targets to a power-of-two boundary, for branch targets
4352 where the targets can only be reached by jumping, skipping up to @var{n}
4353 bytes like @option{-falign-functions}. In this case, no dummy operations
4356 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
4357 equivalent and mean that loops will not be aligned.
4359 If @var{n} is not specified or is zero, use a machine-dependent default.
4361 Enabled at levels @option{-O2}, @option{-O3}.
4363 @item -frename-registers
4364 @opindex frename-registers
4365 Attempt to avoid false dependencies in scheduled code by making use
4366 of registers left over after register allocation. This optimization
4367 will most benefit processors with lots of registers. It can, however,
4368 make debugging impossible, since variables will no longer stay in
4369 a ``home register''.
4373 Constructs webs as commonly used for register allocation purposes and assign
4374 each web individual pseudo register. This allows our register allocation pass
4375 to operate on pseudos directly, but also strengthens several other optimization
4376 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
4377 however, make debugging impossible, since variables will no longer stay in a
4380 Enabled at levels @option{-O3}.
4382 @item -fno-cprop-registers
4383 @opindex fno-cprop-registers
4384 After register allocation and post-register allocation instruction splitting,
4385 we perform a copy-propagation pass to try to reduce scheduling dependencies
4386 and occasionally eliminate the copy.
4388 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4392 The following options control compiler behavior regarding floating
4393 point arithmetic. These options trade off between speed and
4394 correctness. All must be specifically enabled.
4398 @opindex ffloat-store
4399 Do not store floating point variables in registers, and inhibit other
4400 options that might change whether a floating point value is taken from a
4403 @cindex floating point precision
4404 This option prevents undesirable excess precision on machines such as
4405 the 68000 where the floating registers (of the 68881) keep more
4406 precision than a @code{double} is supposed to have. Similarly for the
4407 x86 architecture. For most programs, the excess precision does only
4408 good, but a few programs rely on the precise definition of IEEE floating
4409 point. Use @option{-ffloat-store} for such programs, after modifying
4410 them to store all pertinent intermediate computations into variables.
4414 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
4415 @option{-fno-trapping-math}, @option{-ffinite-math-only},
4416 @option{-fno-rounding-math} and @option{-fno-signaling-nans}.
4418 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
4420 This option should never be turned on by any @option{-O} option since
4421 it can result in incorrect output for programs which depend on
4422 an exact implementation of IEEE or ISO rules/specifications for
4425 @item -fno-math-errno
4426 @opindex fno-math-errno
4427 Do not set ERRNO after calling math functions that are executed
4428 with a single instruction, e.g., sqrt. A program that relies on
4429 IEEE exceptions for math error handling may want to use this flag
4430 for speed while maintaining IEEE arithmetic compatibility.
4432 This option should never be turned on by any @option{-O} option since
4433 it can result in incorrect output for programs which depend on
4434 an exact implementation of IEEE or ISO rules/specifications for
4437 The default is @option{-fmath-errno}.
4439 @item -funsafe-math-optimizations
4440 @opindex funsafe-math-optimizations
4441 Allow optimizations for floating-point arithmetic that (a) assume
4442 that arguments and results are valid and (b) may violate IEEE or
4443 ANSI standards. When used at link-time, it may include libraries
4444 or startup files that change the default FPU control word or other
4445 similar optimizations.
4447 This option should never be turned on by any @option{-O} option since
4448 it can result in incorrect output for programs which depend on
4449 an exact implementation of IEEE or ISO rules/specifications for
4452 The default is @option{-fno-unsafe-math-optimizations}.
4454 @item -ffinite-math-only
4455 @opindex ffinite-math-only
4456 Allow optimizations for floating-point arithmetic that assume
4457 that arguments and results are not NaNs or +-Infs.
4459 This option should never be turned on by any @option{-O} option since
4460 it can result in incorrect output for programs which depend on
4461 an exact implementation of IEEE or ISO rules/specifications.
4463 The default is @option{-fno-finite-math-only}.
4465 @item -fno-trapping-math
4466 @opindex fno-trapping-math
4467 Compile code assuming that floating-point operations cannot generate
4468 user-visible traps. These traps include division by zero, overflow,
4469 underflow, inexact result and invalid operation. This option implies
4470 @option{-fno-signaling-nans}. Setting this option may allow faster
4471 code if one relies on ``non-stop'' IEEE arithmetic, for example.
4473 This option should never be turned on by any @option{-O} option since
4474 it can result in incorrect output for programs which depend on
4475 an exact implementation of IEEE or ISO rules/specifications for
4478 The default is @option{-ftrapping-math}.
4480 @item -frounding-math
4481 @opindex frounding-math
4482 Disable transformations and optimizations that assume default floating
4483 point rounding behavior. This is round-to-zero for all floating point
4484 to integer conversions, and round-to-nearest for all other arithmetic
4485 truncations. This option should be specified for programs that change
4486 the FP rounding mode dynamically, or that may be executed with a
4487 non-default rounding mode. This option disables constant folding of
4488 floating point expressions at compile-time (which may be affected by
4489 rounding mode) and arithmetic transformations that are unsafe in the
4490 presence of sign-dependent rounding modes.
4492 The default is @option{-fno-rounding-math}.
4494 This option is experimental and does not currently guarantee to
4495 disable all GCC optimizations that are affected by rounding mode.
4496 Future versions of gcc may provide finer control of this setting
4497 using C99's @code{FENV_ACCESS} pragma. This command line option
4498 will be used to specify the default state for @code{FENV_ACCESS}.
4500 @item -fsignaling-nans
4501 @opindex fsignaling-nans
4502 Compile code assuming that IEEE signaling NaNs may generate user-visible
4503 traps during floating-point operations. Setting this option disables
4504 optimizations that may change the number of exceptions visible with
4505 signaling NaNs. This option implies @option{-ftrapping-math}.
4507 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
4510 The default is @option{-fno-signaling-nans}.
4512 This option is experimental and does not currently guarantee to
4513 disable all GCC optimizations that affect signaling NaN behavior.
4515 @item -fsingle-precision-constant
4516 @opindex fsingle-precision-constant
4517 Treat floating point constant as single precision constant instead of
4518 implicitly converting it to double precision constant.
4523 The following options control optimizations that may improve
4524 performance, but are not enabled by any @option{-O} options. This
4525 section includes experimental options that may produce broken code.
4528 @item -fbranch-probabilities
4529 @opindex fbranch-probabilities
4530 After running a program compiled with @option{-fprofile-arcs}
4531 (@pxref{Debugging Options,, Options for Debugging Your Program or
4532 @command{gcc}}), you can compile it a second time using
4533 @option{-fbranch-probabilities}, to improve optimizations based on
4534 the number of times each branch was taken. When the program
4535 compiled with @option{-fprofile-arcs} exits it saves arc execution
4536 counts to a file called @file{@var{sourcename}.gcda} for each source
4537 file The information in this data file is very dependent on the
4538 structure of the generated code, so you must use the same source code
4539 and the same optimization options for both compilations.
4541 With @option{-fbranch-probabilities}, GCC puts a
4542 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
4543 These can be used to improve optimization. Currently, they are only
4544 used in one place: in @file{reorg.c}, instead of guessing which path a
4545 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
4546 exactly determine which path is taken more often.
4548 @item -fprofile-values
4549 @opindex fprofile-values
4550 If combined with @option{-fprofile-arcs}, it adds code so that some
4551 data about values of expressions in the program is gathered.
4553 With @option{-fbranch-probabilities}, it reads back the data gathered
4554 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
4555 notes to instructions for their later usage in optimizations.
4559 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
4560 a code to gather information about values of expressions.
4562 With @option{-fbranch-probabilities}, it reads back the data gathered
4563 and actually performs the optimizations based on them.
4564 Currently the optimizations include specialization of division operation
4565 using the knowledge about the value of the denominator.
4569 Use a graph coloring register allocator. Currently this option is meant
4570 for testing, so we are interested to hear about miscompilations with
4575 Perform tail duplication to enlarge superblock size. This transformation
4576 simplifies the control flow of the function allowing other optimizations to do
4579 @item -funit-at-a-time
4580 @opindex funit-at-a-time
4581 Parse the whole compilation unit before starting to produce code.
4582 This allows some extra optimizations to take place but consumes more
4585 @item -funroll-loops
4586 @opindex funroll-loops
4587 Unroll loops whose number of iterations can be determined at compile time or
4588 upon entry to the loop. @option{-funroll-loops} implies
4589 @option{-frerun-cse-after-loop}. It also turns on complete loop peeling
4590 (i.e. complete removal of loops with small constant number of iterations).
4591 This option makes code larger, and may or may not make it run faster.
4593 @item -funroll-all-loops
4594 @opindex funroll-all-loops
4595 Unroll all loops, even if their number of iterations is uncertain when
4596 the loop is entered. This usually makes programs run more slowly.
4597 @option{-funroll-all-loops} implies the same options as
4598 @option{-funroll-loops}.
4601 @opindex fpeel-loops
4602 Peels the loops for that there is enough information that they do not
4603 roll much (from profile feedback). It also turns on complete loop peeling
4604 (i.e. complete removal of loops with small constant number of iterations).
4606 @item -funswitch-loops
4607 @opindex funswitch-loops
4608 Move branches with loop invariant conditions out of the loop, with duplicates
4609 of the loop on both branches (modified according to result of the condition).
4611 @item -fold-unroll-loops
4612 @opindex fold-unroll-loops
4613 Unroll loops whose number of iterations can be determined at compile
4614 time or upon entry to the loop, using the old loop unroller whose loop
4615 recognition is based on notes from frontend. @option{-fold-unroll-loops} implies
4616 both @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
4617 option makes code larger, and may or may not make it run faster.
4619 @item -fold-unroll-all-loops
4620 @opindex fold-unroll-all-loops
4621 Unroll all loops, even if their number of iterations is uncertain when
4622 the loop is entered. This is done using the old loop unroller whose loop
4623 recognition is based on notes from frontend. This usually makes programs run more slowly.
4624 @option{-fold-unroll-all-loops} implies the same options as
4625 @option{-fold-unroll-loops}.
4627 @item -funswitch-loops
4628 @opindex funswitch-loops
4629 Move branches with loop invariant conditions out of the loop, with duplicates
4630 of the loop on both branches (modified according to result of the condition).
4632 @item -funswitch-loops
4633 @opindex funswitch-loops
4634 Move branches with loop invariant conditions out of the loop, with duplicates
4635 of the loop on both branches (modified according to result of the condition).
4637 @item -fprefetch-loop-arrays
4638 @opindex fprefetch-loop-arrays
4639 If supported by the target machine, generate instructions to prefetch
4640 memory to improve the performance of loops that access large arrays.
4642 Disabled at level @option{-Os}.
4644 @item -ffunction-sections
4645 @itemx -fdata-sections
4646 @opindex ffunction-sections
4647 @opindex fdata-sections
4648 Place each function or data item into its own section in the output
4649 file if the target supports arbitrary sections. The name of the
4650 function or the name of the data item determines the section's name
4653 Use these options on systems where the linker can perform optimizations
4654 to improve locality of reference in the instruction space. Most systems
4655 using the ELF object format and SPARC processors running Solaris 2 have
4656 linkers with such optimizations. AIX may have these optimizations in
4659 Only use these options when there are significant benefits from doing
4660 so. When you specify these options, the assembler and linker will
4661 create larger object and executable files and will also be slower.
4662 You will not be able to use @code{gprof} on all systems if you
4663 specify this option and you may have problems with debugging if
4664 you specify both this option and @option{-g}.
4666 @item -fbranch-target-load-optimize
4667 @opindex fbranch-target-load-optimize
4668 Perform branch target register load optimization before prologue / epilogue
4670 The use of target registers can typically be exposed only during reload,
4671 thus hoisting loads out of loops and doing inter-block scheduling needs
4672 a separate optimization pass.
4674 @item -fbranch-target-load-optimize2
4675 @opindex fbranch-target-load-optimize2
4676 Perform branch target register load optimization after prologue / epilogue
4679 @item --param @var{name}=@var{value}
4681 In some places, GCC uses various constants to control the amount of
4682 optimization that is done. For example, GCC will not inline functions
4683 that contain more that a certain number of instructions. You can
4684 control some of these constants on the command-line using the
4685 @option{--param} option.
4687 In each case, the @var{value} is an integer. The allowable choices for
4688 @var{name} are given in the following table:
4691 @item max-crossjump-edges
4692 The maximum number of incoming edges to consider for crossjumping.
4693 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
4694 the number of edges incoming to each block. Increasing values mean
4695 more aggressive optimization, making the compile time increase with
4696 probably small improvement in executable size.
4698 @item max-delay-slot-insn-search
4699 The maximum number of instructions to consider when looking for an
4700 instruction to fill a delay slot. If more than this arbitrary number of
4701 instructions is searched, the time savings from filling the delay slot
4702 will be minimal so stop searching. Increasing values mean more
4703 aggressive optimization, making the compile time increase with probably
4704 small improvement in executable run time.
4706 @item max-delay-slot-live-search
4707 When trying to fill delay slots, the maximum number of instructions to
4708 consider when searching for a block with valid live register
4709 information. Increasing this arbitrarily chosen value means more
4710 aggressive optimization, increasing the compile time. This parameter
4711 should be removed when the delay slot code is rewritten to maintain the
4714 @item max-gcse-memory
4715 The approximate maximum amount of memory that will be allocated in
4716 order to perform the global common subexpression elimination
4717 optimization. If more memory than specified is required, the
4718 optimization will not be done.
4720 @item max-gcse-passes
4721 The maximum number of passes of GCSE to run.
4723 @item max-pending-list-length
4724 The maximum number of pending dependencies scheduling will allow
4725 before flushing the current state and starting over. Large functions
4726 with few branches or calls can create excessively large lists which
4727 needlessly consume memory and resources.
4729 @item max-inline-insns-single
4730 Several parameters control the tree inliner used in gcc.
4731 This number sets the maximum number of instructions (counted in gcc's
4732 internal representation) in a single function that the tree inliner
4733 will consider for inlining. This only affects functions declared
4734 inline and methods implemented in a class declaration (C++).
4735 The default value is 500.
4737 @item max-inline-insns-auto
4738 When you use @option{-finline-functions} (included in @option{-O3}),
4739 a lot of functions that would otherwise not be considered for inlining
4740 by the compiler will be investigated. To those functions, a different
4741 (more restrictive) limit compared to functions declared inline can
4743 The default value is 150.
4745 @item large-function-insns
4746 The limit specifying really large functions. For functions greater than this
4747 limit inlining is constrained by @option{--param large-function-growth}.
4748 This parameter is useful primarily to avoid extreme compilation time caused by non-linear
4749 algorithms used by the backend.
4750 This parameter is ignored when @option{-funit-at-a-time} is not used.
4751 The default value is 30000.
4753 @item large-function-growth
4754 Specifies maximal growth of large functtion caused by inlining in percents.
4755 This parameter is ignored when @option{-funit-at-a-time} is not used.
4756 The default value is 200.
4758 @item inline-unit-growth
4759 Specifies maximal overall growth of the compilation unit caused by inlining.
4760 This parameter is ignored when @option{-funit-at-a-time} is not used.
4761 The default value is 150.
4763 @item max-inline-insns-rtl
4764 For languages that use the RTL inliner (this happens at a later stage
4765 than tree inlining), you can set the maximum allowable size (counted
4766 in RTL instructions) for the RTL inliner with this parameter.
4767 The default value is 600.
4769 @item max-unrolled-insns
4770 The maximum number of instructions that a loop should have if that loop
4771 is unrolled, and if the loop is unrolled, it determines how many times
4772 the loop code is unrolled.
4774 @item max-average-unrolled-insns
4775 The maximum number of instructions biased by probabilities of their execution
4776 that a loop should have if that loop is unrolled, and if the loop is unrolled,
4777 it determines how many times the loop code is unrolled.
4779 @item max-unroll-times
4780 The maximum number of unrollings of a single loop.
4782 @item max-peeled-insns
4783 The maximum number of instructions that a loop should have if that loop
4784 is peeled, and if the loop is peeled, it determines how many times
4785 the loop code is peeled.
4787 @item max-peel-times
4788 The maximum number of peelings of a single loop.
4790 @item max-completely-peeled-insns
4791 The maximum number of insns of a completely peeled loop.
4793 @item max-completely-peel-times
4794 The maximum number of iterations of a loop to be suitable for complete peeling.
4796 @item max-unswitch-insns
4797 The maximum number of insns of an unswitched loop.
4799 @item max-unswitch-level
4800 The maximum number of branches unswitched in a single loop.
4802 @item hot-bb-count-fraction
4803 Select fraction of the maximal count of repetitions of basic block in program
4804 given basic block needs to have to be considered hot.
4806 @item hot-bb-frequency-fraction
4807 Select fraction of the maximal frequency of executions of basic block in
4808 function given basic block needs to have to be considered hot
4810 @item tracer-dynamic-coverage
4811 @itemx tracer-dynamic-coverage-feedback
4813 This value is used to limit superblock formation once the given percentage of
4814 executed instructions is covered. This limits unnecessary code size
4817 The @option{tracer-dynamic-coverage-feedback} is used only when profile
4818 feedback is available. The real profiles (as opposed to statically estimated
4819 ones) are much less balanced allowing the threshold to be larger value.
4821 @item tracer-max-code-growth
4822 Stop tail duplication once code growth has reached given percentage. This is
4823 rather hokey argument, as most of the duplicates will be eliminated later in
4824 cross jumping, so it may be set to much higher values than is the desired code
4827 @item tracer-min-branch-ratio
4829 Stop reverse growth when the reverse probability of best edge is less than this
4830 threshold (in percent).
4832 @item tracer-min-branch-ratio
4833 @itemx tracer-min-branch-ratio-feedback
4835 Stop forward growth if the best edge do have probability lower than this
4838 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
4839 compilation for profile feedback and one for compilation without. The value
4840 for compilation with profile feedback needs to be more conservative (higher) in
4841 order to make tracer effective.
4843 @item max-cse-path-length
4845 Maximum number of basic blocks on path that cse considers.
4847 @item ggc-min-expand
4849 GCC uses a garbage collector to manage its own memory allocation. This
4850 parameter specifies the minimum percentage by which the garbage
4851 collector's heap should be allowed to expand between collections.
4852 Tuning this may improve compilation speed; it has no effect on code
4855 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
4856 RAM >= 1GB. If @code{getrlimit} is available, the notion of "RAM" is
4857 the smallest of actual RAM, RLIMIT_RSS, RLIMIT_DATA and RLIMIT_AS. If
4858 GCC is not able to calculate RAM on a particular platform, the lower
4859 bound of 30% is used. Setting this parameter and
4860 @option{ggc-min-heapsize} to zero causes a full collection to occur at
4861 every opportunity. This is extremely slow, but can be useful for
4864 @item ggc-min-heapsize
4866 Minimum size of the garbage collector's heap before it begins bothering
4867 to collect garbage. The first collection occurs after the heap expands
4868 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
4869 tuning this may improve compilation speed, and has no effect on code
4872 The default is RAM/8, with a lower bound of 4096 (four megabytes) and an
4873 upper bound of 131072 (128 megabytes). If @code{getrlimit} is
4874 available, the notion of "RAM" is the smallest of actual RAM,
4875 RLIMIT_RSS, RLIMIT_DATA and RLIMIT_AS. If GCC is not able to calculate
4876 RAM on a particular platform, the lower bound is used. Setting this
4877 parameter very large effectively disables garbage collection. Setting
4878 this parameter and @option{ggc-min-expand} to zero causes a full
4879 collection to occur at every opportunity.
4881 @item reorder-blocks-duplicate
4882 @itemx reorder-blocks-duplicate-feedback
4884 Used by basic block reordering pass to decide whether to use unconditional
4885 branch or duplicate the code on its destination. Code is duplicated when its
4886 estimated size is smaller than this value multiplied by the estimated size of
4887 unconditional jump in the hot spots of the program.
4889 The @option{reorder-block-duplicate-feedback} is used only when profile
4890 feedback is available and may be set to higher values than
4891 @option{reorder-block-duplicate} since information about the hot spots is more
4896 @node Preprocessor Options
4897 @section Options Controlling the Preprocessor
4898 @cindex preprocessor options
4899 @cindex options, preprocessor
4901 These options control the C preprocessor, which is run on each C source
4902 file before actual compilation.
4904 If you use the @option{-E} option, nothing is done except preprocessing.
4905 Some of these options make sense only together with @option{-E} because
4906 they cause the preprocessor output to be unsuitable for actual
4911 You can use @option{-Wp,@var{option}} to bypass the compiler driver
4912 and pass @var{option} directly through to the preprocessor. If
4913 @var{option} contains commas, it is split into multiple options at the
4914 commas. However, many options are modified, translated or interpreted
4915 by the compiler driver before being passed to the preprocessor, and
4916 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
4917 interface is undocumented and subject to change, so whenever possible
4918 you should avoid using @option{-Wp} and let the driver handle the
4921 @item -Xpreprocessor @var{option}
4922 @opindex preprocessor
4923 Pass @var{option} as an option to the preprocessor. You can use this to
4924 supply system-specific preprocessor options which GCC does not know how to
4927 If you want to pass an option that takes an argument, you must use
4928 @option{-Xpreprocessor} twice, once for the option and once for the argument.
4931 @include cppopts.texi
4933 @node Assembler Options
4934 @section Passing Options to the Assembler
4936 @c prevent bad page break with this line
4937 You can pass options to the assembler.
4940 @item -Wa,@var{option}
4942 Pass @var{option} as an option to the assembler. If @var{option}
4943 contains commas, it is split into multiple options at the commas.
4945 @item -Xassembler @var{option}
4947 Pass @var{option} as an option to the assembler. You can use this to
4948 supply system-specific assembler options which GCC does not know how to
4951 If you want to pass an option that takes an argument, you must use
4952 @option{-Xassembler} twice, once for the option and once for the argument.
4957 @section Options for Linking
4958 @cindex link options
4959 @cindex options, linking
4961 These options come into play when the compiler links object files into
4962 an executable output file. They are meaningless if the compiler is
4963 not doing a link step.
4967 @item @var{object-file-name}
4968 A file name that does not end in a special recognized suffix is
4969 considered to name an object file or library. (Object files are
4970 distinguished from libraries by the linker according to the file
4971 contents.) If linking is done, these object files are used as input
4980 If any of these options is used, then the linker is not run, and
4981 object file names should not be used as arguments. @xref{Overall
4985 @item -l@var{library}
4986 @itemx -l @var{library}
4988 Search the library named @var{library} when linking. (The second
4989 alternative with the library as a separate argument is only for
4990 POSIX compliance and is not recommended.)
4992 It makes a difference where in the command you write this option; the
4993 linker searches and processes libraries and object files in the order they
4994 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
4995 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
4996 to functions in @samp{z}, those functions may not be loaded.
4998 The linker searches a standard list of directories for the library,
4999 which is actually a file named @file{lib@var{library}.a}. The linker
5000 then uses this file as if it had been specified precisely by name.
5002 The directories searched include several standard system directories
5003 plus any that you specify with @option{-L}.
5005 Normally the files found this way are library files---archive files
5006 whose members are object files. The linker handles an archive file by
5007 scanning through it for members which define symbols that have so far
5008 been referenced but not defined. But if the file that is found is an
5009 ordinary object file, it is linked in the usual fashion. The only
5010 difference between using an @option{-l} option and specifying a file name
5011 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
5012 and searches several directories.
5016 You need this special case of the @option{-l} option in order to
5017 link an Objective-C program.
5020 @opindex nostartfiles
5021 Do not use the standard system startup files when linking.
5022 The standard system libraries are used normally, unless @option{-nostdlib}
5023 or @option{-nodefaultlibs} is used.
5025 @item -nodefaultlibs
5026 @opindex nodefaultlibs
5027 Do not use the standard system libraries when linking.
5028 Only the libraries you specify will be passed to the linker.
5029 The standard startup files are used normally, unless @option{-nostartfiles}
5030 is used. The compiler may generate calls to memcmp, memset, and memcpy
5031 for System V (and ISO C) environments or to bcopy and bzero for
5032 BSD environments. These entries are usually resolved by entries in
5033 libc. These entry points should be supplied through some other
5034 mechanism when this option is specified.
5038 Do not use the standard system startup files or libraries when linking.
5039 No startup files and only the libraries you specify will be passed to
5040 the linker. The compiler may generate calls to memcmp, memset, and memcpy
5041 for System V (and ISO C) environments or to bcopy and bzero for
5042 BSD environments. These entries are usually resolved by entries in
5043 libc. These entry points should be supplied through some other
5044 mechanism when this option is specified.
5046 @cindex @option{-lgcc}, use with @option{-nostdlib}
5047 @cindex @option{-nostdlib} and unresolved references
5048 @cindex unresolved references and @option{-nostdlib}
5049 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
5050 @cindex @option{-nodefaultlibs} and unresolved references
5051 @cindex unresolved references and @option{-nodefaultlibs}
5052 One of the standard libraries bypassed by @option{-nostdlib} and
5053 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
5054 that GCC uses to overcome shortcomings of particular machines, or special
5055 needs for some languages.
5056 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
5057 Collection (GCC) Internals},
5058 for more discussion of @file{libgcc.a}.)
5059 In most cases, you need @file{libgcc.a} even when you want to avoid
5060 other standard libraries. In other words, when you specify @option{-nostdlib}
5061 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
5062 This ensures that you have no unresolved references to internal GCC
5063 library subroutines. (For example, @samp{__main}, used to ensure C++
5064 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
5065 GNU Compiler Collection (GCC) Internals}.)
5069 Produce a position independent executable on targets which support it.
5070 For predictable results, you must also specify the same set of options
5071 that were used to generate code (@option{-fpie}, @option{-fPIE},
5072 or model suboptions) when you specify this option.
5076 Remove all symbol table and relocation information from the executable.
5080 On systems that support dynamic linking, this prevents linking with the shared
5081 libraries. On other systems, this option has no effect.
5085 Produce a shared object which can then be linked with other objects to
5086 form an executable. Not all systems support this option. For predictable
5087 results, you must also specify the same set of options that were used to
5088 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
5089 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
5090 needs to build supplementary stub code for constructors to work. On
5091 multi-libbed systems, @samp{gcc -shared} must select the correct support
5092 libraries to link against. Failing to supply the correct flags may lead
5093 to subtle defects. Supplying them in cases where they are not necessary
5096 @item -shared-libgcc
5097 @itemx -static-libgcc
5098 @opindex shared-libgcc
5099 @opindex static-libgcc
5100 On systems that provide @file{libgcc} as a shared library, these options
5101 force the use of either the shared or static version respectively.
5102 If no shared version of @file{libgcc} was built when the compiler was
5103 configured, these options have no effect.
5105 There are several situations in which an application should use the
5106 shared @file{libgcc} instead of the static version. The most common
5107 of these is when the application wishes to throw and catch exceptions
5108 across different shared libraries. In that case, each of the libraries
5109 as well as the application itself should use the shared @file{libgcc}.
5111 Therefore, the G++ and GCJ drivers automatically add
5112 @option{-shared-libgcc} whenever you build a shared library or a main
5113 executable, because C++ and Java programs typically use exceptions, so
5114 this is the right thing to do.
5116 If, instead, you use the GCC driver to create shared libraries, you may
5117 find that they will not always be linked with the shared @file{libgcc}.
5118 If GCC finds, at its configuration time, that you have a GNU linker that
5119 does not support option @option{--eh-frame-hdr}, it will link the shared
5120 version of @file{libgcc} into shared libraries by default. Otherwise,
5121 it will take advantage of the linker and optimize away the linking with
5122 the shared version of @file{libgcc}, linking with the static version of
5123 libgcc by default. This allows exceptions to propagate through such
5124 shared libraries, without incurring relocation costs at library load
5127 However, if a library or main executable is supposed to throw or catch
5128 exceptions, you must link it using the G++ or GCJ driver, as appropriate
5129 for the languages used in the program, or using the option
5130 @option{-shared-libgcc}, such that it is linked with the shared
5135 Bind references to global symbols when building a shared object. Warn
5136 about any unresolved references (unless overridden by the link editor
5137 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
5140 @item -Xlinker @var{option}
5142 Pass @var{option} as an option to the linker. You can use this to
5143 supply system-specific linker options which GCC does not know how to
5146 If you want to pass an option that takes an argument, you must use
5147 @option{-Xlinker} twice, once for the option and once for the argument.
5148 For example, to pass @option{-assert definitions}, you must write
5149 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
5150 @option{-Xlinker "-assert definitions"}, because this passes the entire
5151 string as a single argument, which is not what the linker expects.
5153 @item -Wl,@var{option}
5155 Pass @var{option} as an option to the linker. If @var{option} contains
5156 commas, it is split into multiple options at the commas.
5158 @item -u @var{symbol}
5160 Pretend the symbol @var{symbol} is undefined, to force linking of
5161 library modules to define it. You can use @option{-u} multiple times with
5162 different symbols to force loading of additional library modules.
5165 @node Directory Options
5166 @section Options for Directory Search
5167 @cindex directory options
5168 @cindex options, directory search
5171 These options specify directories to search for header files, for
5172 libraries and for parts of the compiler:
5177 Add the directory @var{dir} to the head of the list of directories to be
5178 searched for header files. This can be used to override a system header
5179 file, substituting your own version, since these directories are
5180 searched before the system header file directories. However, you should
5181 not use this option to add directories that contain vendor-supplied
5182 system header files (use @option{-isystem} for that). If you use more than
5183 one @option{-I} option, the directories are scanned in left-to-right
5184 order; the standard system directories come after.
5186 If a standard system include directory, or a directory specified with
5187 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
5188 option will be ignored. The directory will still be searched but as a
5189 system directory at its normal position in the system include chain.
5190 This is to ensure that GCC's procedure to fix buggy system headers and
5191 the ordering for the include_next directive are not inadvertently changed.
5192 If you really need to change the search order for system directories,
5193 use the @option{-nostdinc} and/or @option{-isystem} options.
5197 Any directories you specify with @option{-I} options before the @option{-I-}
5198 option are searched only for the case of @samp{#include "@var{file}"};
5199 they are not searched for @samp{#include <@var{file}>}.
5201 If additional directories are specified with @option{-I} options after
5202 the @option{-I-}, these directories are searched for all @samp{#include}
5203 directives. (Ordinarily @emph{all} @option{-I} directories are used
5206 In addition, the @option{-I-} option inhibits the use of the current
5207 directory (where the current input file came from) as the first search
5208 directory for @samp{#include "@var{file}"}. There is no way to
5209 override this effect of @option{-I-}. With @option{-I.} you can specify
5210 searching the directory which was current when the compiler was
5211 invoked. That is not exactly the same as what the preprocessor does
5212 by default, but it is often satisfactory.
5214 @option{-I-} does not inhibit the use of the standard system directories
5215 for header files. Thus, @option{-I-} and @option{-nostdinc} are
5220 Add directory @var{dir} to the list of directories to be searched
5223 @item -B@var{prefix}
5225 This option specifies where to find the executables, libraries,
5226 include files, and data files of the compiler itself.
5228 The compiler driver program runs one or more of the subprograms
5229 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
5230 @var{prefix} as a prefix for each program it tries to run, both with and
5231 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
5233 For each subprogram to be run, the compiler driver first tries the
5234 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
5235 was not specified, the driver tries two standard prefixes, which are
5236 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
5237 those results in a file name that is found, the unmodified program
5238 name is searched for using the directories specified in your
5239 @env{PATH} environment variable.
5241 The compiler will check to see if the path provided by the @option{-B}
5242 refers to a directory, and if necessary it will add a directory
5243 separator character at the end of the path.
5245 @option{-B} prefixes that effectively specify directory names also apply
5246 to libraries in the linker, because the compiler translates these
5247 options into @option{-L} options for the linker. They also apply to
5248 includes files in the preprocessor, because the compiler translates these
5249 options into @option{-isystem} options for the preprocessor. In this case,
5250 the compiler appends @samp{include} to the prefix.
5252 The run-time support file @file{libgcc.a} can also be searched for using
5253 the @option{-B} prefix, if needed. If it is not found there, the two
5254 standard prefixes above are tried, and that is all. The file is left
5255 out of the link if it is not found by those means.
5257 Another way to specify a prefix much like the @option{-B} prefix is to use
5258 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
5261 As a special kludge, if the path provided by @option{-B} is
5262 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
5263 9, then it will be replaced by @file{[dir/]include}. This is to help
5264 with boot-strapping the compiler.
5266 @item -specs=@var{file}
5268 Process @var{file} after the compiler reads in the standard @file{specs}
5269 file, in order to override the defaults that the @file{gcc} driver
5270 program uses when determining what switches to pass to @file{cc1},
5271 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
5272 @option{-specs=@var{file}} can be specified on the command line, and they
5273 are processed in order, from left to right.
5279 @section Specifying subprocesses and the switches to pass to them
5282 @command{gcc} is a driver program. It performs its job by invoking a
5283 sequence of other programs to do the work of compiling, assembling and
5284 linking. GCC interprets its command-line parameters and uses these to
5285 deduce which programs it should invoke, and which command-line options
5286 it ought to place on their command lines. This behavior is controlled
5287 by @dfn{spec strings}. In most cases there is one spec string for each
5288 program that GCC can invoke, but a few programs have multiple spec
5289 strings to control their behavior. The spec strings built into GCC can
5290 be overridden by using the @option{-specs=} command-line switch to specify
5293 @dfn{Spec files} are plaintext files that are used to construct spec
5294 strings. They consist of a sequence of directives separated by blank
5295 lines. The type of directive is determined by the first non-whitespace
5296 character on the line and it can be one of the following:
5299 @item %@var{command}
5300 Issues a @var{command} to the spec file processor. The commands that can
5304 @item %include <@var{file}>
5306 Search for @var{file} and insert its text at the current point in the
5309 @item %include_noerr <@var{file}>
5310 @cindex %include_noerr
5311 Just like @samp{%include}, but do not generate an error message if the include
5312 file cannot be found.
5314 @item %rename @var{old_name} @var{new_name}
5316 Rename the spec string @var{old_name} to @var{new_name}.
5320 @item *[@var{spec_name}]:
5321 This tells the compiler to create, override or delete the named spec
5322 string. All lines after this directive up to the next directive or
5323 blank line are considered to be the text for the spec string. If this
5324 results in an empty string then the spec will be deleted. (Or, if the
5325 spec did not exist, then nothing will happened.) Otherwise, if the spec
5326 does not currently exist a new spec will be created. If the spec does
5327 exist then its contents will be overridden by the text of this
5328 directive, unless the first character of that text is the @samp{+}
5329 character, in which case the text will be appended to the spec.
5331 @item [@var{suffix}]:
5332 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
5333 and up to the next directive or blank line are considered to make up the
5334 spec string for the indicated suffix. When the compiler encounters an
5335 input file with the named suffix, it will processes the spec string in
5336 order to work out how to compile that file. For example:
5343 This says that any input file whose name ends in @samp{.ZZ} should be
5344 passed to the program @samp{z-compile}, which should be invoked with the
5345 command-line switch @option{-input} and with the result of performing the
5346 @samp{%i} substitution. (See below.)
5348 As an alternative to providing a spec string, the text that follows a
5349 suffix directive can be one of the following:
5352 @item @@@var{language}
5353 This says that the suffix is an alias for a known @var{language}. This is
5354 similar to using the @option{-x} command-line switch to GCC to specify a
5355 language explicitly. For example:
5362 Says that .ZZ files are, in fact, C++ source files.
5365 This causes an error messages saying:
5368 @var{name} compiler not installed on this system.
5372 GCC already has an extensive list of suffixes built into it.
5373 This directive will add an entry to the end of the list of suffixes, but
5374 since the list is searched from the end backwards, it is effectively
5375 possible to override earlier entries using this technique.
5379 GCC has the following spec strings built into it. Spec files can
5380 override these strings or create their own. Note that individual
5381 targets can also add their own spec strings to this list.
5384 asm Options to pass to the assembler
5385 asm_final Options to pass to the assembler post-processor
5386 cpp Options to pass to the C preprocessor
5387 cc1 Options to pass to the C compiler
5388 cc1plus Options to pass to the C++ compiler
5389 endfile Object files to include at the end of the link
5390 link Options to pass to the linker
5391 lib Libraries to include on the command line to the linker
5392 libgcc Decides which GCC support library to pass to the linker
5393 linker Sets the name of the linker
5394 predefines Defines to be passed to the C preprocessor
5395 signed_char Defines to pass to CPP to say whether @code{char} is signed
5397 startfile Object files to include at the start of the link
5400 Here is a small example of a spec file:
5406 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
5409 This example renames the spec called @samp{lib} to @samp{old_lib} and
5410 then overrides the previous definition of @samp{lib} with a new one.
5411 The new definition adds in some extra command-line options before
5412 including the text of the old definition.
5414 @dfn{Spec strings} are a list of command-line options to be passed to their
5415 corresponding program. In addition, the spec strings can contain
5416 @samp{%}-prefixed sequences to substitute variable text or to
5417 conditionally insert text into the command line. Using these constructs
5418 it is possible to generate quite complex command lines.
5420 Here is a table of all defined @samp{%}-sequences for spec
5421 strings. Note that spaces are not generated automatically around the
5422 results of expanding these sequences. Therefore you can concatenate them
5423 together or combine them with constant text in a single argument.
5427 Substitute one @samp{%} into the program name or argument.
5430 Substitute the name of the input file being processed.
5433 Substitute the basename of the input file being processed.
5434 This is the substring up to (and not including) the last period
5435 and not including the directory.
5438 This is the same as @samp{%b}, but include the file suffix (text after
5442 Marks the argument containing or following the @samp{%d} as a
5443 temporary file name, so that that file will be deleted if GCC exits
5444 successfully. Unlike @samp{%g}, this contributes no text to the
5447 @item %g@var{suffix}
5448 Substitute a file name that has suffix @var{suffix} and is chosen
5449 once per compilation, and mark the argument in the same way as
5450 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
5451 name is now chosen in a way that is hard to predict even when previously
5452 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
5453 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
5454 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
5455 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
5456 was simply substituted with a file name chosen once per compilation,
5457 without regard to any appended suffix (which was therefore treated
5458 just like ordinary text), making such attacks more likely to succeed.
5460 @item %u@var{suffix}
5461 Like @samp{%g}, but generates a new temporary file name even if
5462 @samp{%u@var{suffix}} was already seen.
5464 @item %U@var{suffix}
5465 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
5466 new one if there is no such last file name. In the absence of any
5467 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
5468 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
5469 would involve the generation of two distinct file names, one
5470 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
5471 simply substituted with a file name chosen for the previous @samp{%u},
5472 without regard to any appended suffix.
5474 @item %j@var{suffix}
5475 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
5476 writable, and if save-temps is off; otherwise, substitute the name
5477 of a temporary file, just like @samp{%u}. This temporary file is not
5478 meant for communication between processes, but rather as a junk
5481 @item %|@var{suffix}
5482 @itemx %m@var{suffix}
5483 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
5484 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
5485 all. These are the two most common ways to instruct a program that it
5486 should read from standard input or write to standard output. If you
5487 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
5488 construct: see for example @file{f/lang-specs.h}.
5490 @item %.@var{SUFFIX}
5491 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
5492 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
5493 terminated by the next space or %.
5496 Marks the argument containing or following the @samp{%w} as the
5497 designated output file of this compilation. This puts the argument
5498 into the sequence of arguments that @samp{%o} will substitute later.
5501 Substitutes the names of all the output files, with spaces
5502 automatically placed around them. You should write spaces
5503 around the @samp{%o} as well or the results are undefined.
5504 @samp{%o} is for use in the specs for running the linker.
5505 Input files whose names have no recognized suffix are not compiled
5506 at all, but they are included among the output files, so they will
5510 Substitutes the suffix for object files. Note that this is
5511 handled specially when it immediately follows @samp{%g, %u, or %U},
5512 because of the need for those to form complete file names. The
5513 handling is such that @samp{%O} is treated exactly as if it had already
5514 been substituted, except that @samp{%g, %u, and %U} do not currently
5515 support additional @var{suffix} characters following @samp{%O} as they would
5516 following, for example, @samp{.o}.
5519 Substitutes the standard macro predefinitions for the
5520 current target machine. Use this when running @code{cpp}.
5523 Like @samp{%p}, but puts @samp{__} before and after the name of each
5524 predefined macro, except for macros that start with @samp{__} or with
5525 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
5529 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
5530 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), and
5531 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
5535 Current argument is the name of a library or startup file of some sort.
5536 Search for that file in a standard list of directories and substitute
5537 the full name found.
5540 Print @var{str} as an error message. @var{str} is terminated by a newline.
5541 Use this when inconsistent options are detected.
5544 Substitute the contents of spec string @var{name} at this point.
5547 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
5549 @item %x@{@var{option}@}
5550 Accumulate an option for @samp{%X}.
5553 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
5557 Output the accumulated assembler options specified by @option{-Wa}.
5560 Output the accumulated preprocessor options specified by @option{-Wp}.
5563 Process the @code{asm} spec. This is used to compute the
5564 switches to be passed to the assembler.
5567 Process the @code{asm_final} spec. This is a spec string for
5568 passing switches to an assembler post-processor, if such a program is
5572 Process the @code{link} spec. This is the spec for computing the
5573 command line passed to the linker. Typically it will make use of the
5574 @samp{%L %G %S %D and %E} sequences.
5577 Dump out a @option{-L} option for each directory that GCC believes might
5578 contain startup files. If the target supports multilibs then the
5579 current multilib directory will be prepended to each of these paths.
5582 Output the multilib directory with directory separators replaced with
5583 @samp{_}. If multilib directories are not set, or the multilib directory is
5584 @file{.} then this option emits nothing.
5587 Process the @code{lib} spec. This is a spec string for deciding which
5588 libraries should be included on the command line to the linker.
5591 Process the @code{libgcc} spec. This is a spec string for deciding
5592 which GCC support library should be included on the command line to the linker.
5595 Process the @code{startfile} spec. This is a spec for deciding which
5596 object files should be the first ones passed to the linker. Typically
5597 this might be a file named @file{crt0.o}.
5600 Process the @code{endfile} spec. This is a spec string that specifies
5601 the last object files that will be passed to the linker.
5604 Process the @code{cpp} spec. This is used to construct the arguments
5605 to be passed to the C preprocessor.
5608 Process the @code{signed_char} spec. This is intended to be used
5609 to tell cpp whether a char is signed. It typically has the definition:
5611 %@{funsigned-char:-D__CHAR_UNSIGNED__@}
5615 Process the @code{cc1} spec. This is used to construct the options to be
5616 passed to the actual C compiler (@samp{cc1}).
5619 Process the @code{cc1plus} spec. This is used to construct the options to be
5620 passed to the actual C++ compiler (@samp{cc1plus}).
5623 Substitute the variable part of a matched option. See below.
5624 Note that each comma in the substituted string is replaced by
5628 Remove all occurrences of @code{-S} from the command line. Note---this
5629 command is position dependent. @samp{%} commands in the spec string
5630 before this one will see @code{-S}, @samp{%} commands in the spec string
5631 after this one will not.
5633 @item %:@var{function}(@var{args})
5634 Call the named function @var{function}, passing it @var{args}.
5635 @var{args} is first processed as a nested spec string, then split
5636 into an argument vector in the usual fashion. The function returns
5637 a string which is processed as if it had appeared literally as part
5638 of the current spec.
5640 The following built-in spec functions are provided:
5643 @item @code{if-exists}
5644 The @code{if-exists} spec function takes one argument, an absolute
5645 pathname to a file. If the file exists, @code{if-exists} returns the
5646 pathname. Here is a small example of its usage:
5650 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
5653 @item @code{if-exists-else}
5654 The @code{if-exists-else} spec function is similar to the @code{if-exists}
5655 spec function, except that it takes two arguments. The first argument is
5656 an absolute pathname to a file. If the file exists, @code{if-exists-else}
5657 returns the pathname. If it does not exist, it returns the second argument.
5658 This way, @code{if-exists-else} can be used to select one file or another,
5659 based on the existence of the first. Here is a small example of its usage:
5663 crt0%O%s %:if-exists(crti%O%s) \
5664 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
5669 Substitutes the @code{-S} switch, if that switch was given to GCC@.
5670 If that switch was not specified, this substitutes nothing. Note that
5671 the leading dash is omitted when specifying this option, and it is
5672 automatically inserted if the substitution is performed. Thus the spec
5673 string @samp{%@{foo@}} would match the command-line option @option{-foo}
5674 and would output the command line option @option{-foo}.
5676 @item %W@{@code{S}@}
5677 Like %@{@code{S}@} but mark last argument supplied within as a file to be
5680 @item %@{@code{S}*@}
5681 Substitutes all the switches specified to GCC whose names start
5682 with @code{-S}, but which also take an argument. This is used for
5683 switches like @option{-o}, @option{-D}, @option{-I}, etc.
5684 GCC considers @option{-o foo} as being
5685 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
5686 text, including the space. Thus two arguments would be generated.
5688 @item %@{@code{S}*&@code{T}*@}
5689 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
5690 (the order of @code{S} and @code{T} in the spec is not significant).
5691 There can be any number of ampersand-separated variables; for each the
5692 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
5694 @item %@{@code{S}:@code{X}@}
5695 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
5697 @item %@{!@code{S}:@code{X}@}
5698 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
5700 @item %@{@code{S}*:@code{X}@}
5701 Substitutes @code{X} if one or more switches whose names start with
5702 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
5703 once, no matter how many such switches appeared. However, if @code{%*}
5704 appears somewhere in @code{X}, then @code{X} will be substituted once
5705 for each matching switch, with the @code{%*} replaced by the part of
5706 that switch that matched the @code{*}.
5708 @item %@{.@code{S}:@code{X}@}
5709 Substitutes @code{X}, if processing a file with suffix @code{S}.
5711 @item %@{!.@code{S}:@code{X}@}
5712 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
5714 @item %@{@code{S}|@code{P}:@code{X}@}
5715 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
5716 This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
5717 although they have a stronger binding than the @samp{|}. If @code{%*}
5718 appears in @code{X}, all of the alternatives must be starred, and only
5719 the first matching alternative is substituted.
5721 For example, a spec string like this:
5724 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
5727 will output the following command-line options from the following input
5728 command-line options:
5733 -d fred.c -foo -baz -boggle
5734 -d jim.d -bar -baz -boggle
5737 @item %@{S:X; T:Y; :D@}
5739 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
5740 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
5741 be as many clauses as you need. This may be combined with @code{.},
5742 @code{!}, @code{|}, and @code{*} as needed.
5747 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
5748 construct may contain other nested @samp{%} constructs or spaces, or
5749 even newlines. They are processed as usual, as described above.
5750 Trailing white space in @code{X} is ignored. White space may also
5751 appear anywhere on the left side of the colon in these constructs,
5752 except between @code{.} or @code{*} and the corresponding word.
5754 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
5755 handled specifically in these constructs. If another value of
5756 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
5757 @option{-W} switch is found later in the command line, the earlier
5758 switch value is ignored, except with @{@code{S}*@} where @code{S} is
5759 just one letter, which passes all matching options.
5761 The character @samp{|} at the beginning of the predicate text is used to
5762 indicate that a command should be piped to the following command, but
5763 only if @option{-pipe} is specified.
5765 It is built into GCC which switches take arguments and which do not.
5766 (You might think it would be useful to generalize this to allow each
5767 compiler's spec to say which switches take arguments. But this cannot
5768 be done in a consistent fashion. GCC cannot even decide which input
5769 files have been specified without knowing which switches take arguments,
5770 and it must know which input files to compile in order to tell which
5773 GCC also knows implicitly that arguments starting in @option{-l} are to be
5774 treated as compiler output files, and passed to the linker in their
5775 proper position among the other output files.
5777 @c man begin OPTIONS
5779 @node Target Options
5780 @section Specifying Target Machine and Compiler Version
5781 @cindex target options
5782 @cindex cross compiling
5783 @cindex specifying machine version
5784 @cindex specifying compiler version and target machine
5785 @cindex compiler version, specifying
5786 @cindex target machine, specifying
5788 The usual way to run GCC is to run the executable called @file{gcc}, or
5789 @file{<machine>-gcc} when cross-compiling, or
5790 @file{<machine>-gcc-<version>} to run a version other than the one that
5791 was installed last. Sometimes this is inconvenient, so GCC provides
5792 options that will switch to another cross-compiler or version.
5795 @item -b @var{machine}
5797 The argument @var{machine} specifies the target machine for compilation.
5799 The value to use for @var{machine} is the same as was specified as the
5800 machine type when configuring GCC as a cross-compiler. For
5801 example, if a cross-compiler was configured with @samp{configure
5802 i386v}, meaning to compile for an 80386 running System V, then you
5803 would specify @option{-b i386v} to run that cross compiler.
5805 @item -V @var{version}
5807 The argument @var{version} specifies which version of GCC to run.
5808 This is useful when multiple versions are installed. For example,
5809 @var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
5812 The @option{-V} and @option{-b} options work by running the
5813 @file{<machine>-gcc-<version>} executable, so there's no real reason to
5814 use them if you can just run that directly.
5816 @node Submodel Options
5817 @section Hardware Models and Configurations
5818 @cindex submodel options
5819 @cindex specifying hardware config
5820 @cindex hardware models and configurations, specifying
5821 @cindex machine dependent options
5823 Earlier we discussed the standard option @option{-b} which chooses among
5824 different installed compilers for completely different target
5825 machines, such as VAX vs.@: 68000 vs.@: 80386.
5827 In addition, each of these target machine types can have its own
5828 special options, starting with @samp{-m}, to choose among various
5829 hardware models or configurations---for example, 68010 vs 68020,
5830 floating coprocessor or none. A single installed version of the
5831 compiler can compile for any model or configuration, according to the
5834 Some configurations of the compiler also support additional special
5835 options, usually for compatibility with other compilers on the same
5838 These options are defined by the macro @code{TARGET_SWITCHES} in the
5839 machine description. The default for the options is also defined by
5840 that macro, which enables you to change the defaults.
5852 * RS/6000 and PowerPC Options::
5856 * i386 and x86-64 Options::
5858 * Intel 960 Options::
5859 * DEC Alpha Options::
5860 * DEC Alpha/VMS Options::
5863 * System V Options::
5864 * TMS320C3x/C4x Options::
5872 * S/390 and zSeries Options::
5876 * Xstormy16 Options::
5881 @node M680x0 Options
5882 @subsection M680x0 Options
5883 @cindex M680x0 options
5885 These are the @samp{-m} options defined for the 68000 series. The default
5886 values for these options depends on which style of 68000 was selected when
5887 the compiler was configured; the defaults for the most common choices are
5895 Generate output for a 68000. This is the default
5896 when the compiler is configured for 68000-based systems.
5898 Use this option for microcontrollers with a 68000 or EC000 core,
5899 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
5905 Generate output for a 68020. This is the default
5906 when the compiler is configured for 68020-based systems.
5910 Generate output containing 68881 instructions for floating point.
5911 This is the default for most 68020 systems unless @option{--nfp} was
5912 specified when the compiler was configured.
5916 Generate output for a 68030. This is the default when the compiler is
5917 configured for 68030-based systems.
5921 Generate output for a 68040. This is the default when the compiler is
5922 configured for 68040-based systems.
5924 This option inhibits the use of 68881/68882 instructions that have to be
5925 emulated by software on the 68040. Use this option if your 68040 does not
5926 have code to emulate those instructions.
5930 Generate output for a 68060. This is the default when the compiler is
5931 configured for 68060-based systems.
5933 This option inhibits the use of 68020 and 68881/68882 instructions that
5934 have to be emulated by software on the 68060. Use this option if your 68060
5935 does not have code to emulate those instructions.
5939 Generate output for a CPU32. This is the default
5940 when the compiler is configured for CPU32-based systems.
5942 Use this option for microcontrollers with a
5943 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
5944 68336, 68340, 68341, 68349 and 68360.
5948 Generate output for a 520X ``coldfire'' family cpu. This is the default
5949 when the compiler is configured for 520X-based systems.
5951 Use this option for microcontroller with a 5200 core, including
5952 the MCF5202, MCF5203, MCF5204 and MCF5202.
5957 Generate output for a 68040, without using any of the new instructions.
5958 This results in code which can run relatively efficiently on either a
5959 68020/68881 or a 68030 or a 68040. The generated code does use the
5960 68881 instructions that are emulated on the 68040.
5964 Generate output for a 68060, without using any of the new instructions.
5965 This results in code which can run relatively efficiently on either a
5966 68020/68881 or a 68030 or a 68040. The generated code does use the
5967 68881 instructions that are emulated on the 68060.
5970 @opindex msoft-float
5971 Generate output containing library calls for floating point.
5972 @strong{Warning:} the requisite libraries are not available for all m68k
5973 targets. Normally the facilities of the machine's usual C compiler are
5974 used, but this can't be done directly in cross-compilation. You must
5975 make your own arrangements to provide suitable library functions for
5976 cross-compilation. The embedded targets @samp{m68k-*-aout} and
5977 @samp{m68k-*-coff} do provide software floating point support.
5981 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5984 @opindex mnobitfield
5985 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
5986 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
5990 Do use the bit-field instructions. The @option{-m68020} option implies
5991 @option{-mbitfield}. This is the default if you use a configuration
5992 designed for a 68020.
5996 Use a different function-calling convention, in which functions
5997 that take a fixed number of arguments return with the @code{rtd}
5998 instruction, which pops their arguments while returning. This
5999 saves one instruction in the caller since there is no need to pop
6000 the arguments there.
6002 This calling convention is incompatible with the one normally
6003 used on Unix, so you cannot use it if you need to call libraries
6004 compiled with the Unix compiler.
6006 Also, you must provide function prototypes for all functions that
6007 take variable numbers of arguments (including @code{printf});
6008 otherwise incorrect code will be generated for calls to those
6011 In addition, seriously incorrect code will result if you call a
6012 function with too many arguments. (Normally, extra arguments are
6013 harmlessly ignored.)
6015 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
6016 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
6019 @itemx -mno-align-int
6021 @opindex mno-align-int
6022 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
6023 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
6024 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
6025 Aligning variables on 32-bit boundaries produces code that runs somewhat
6026 faster on processors with 32-bit busses at the expense of more memory.
6028 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
6029 align structures containing the above types differently than
6030 most published application binary interface specifications for the m68k.
6034 Use the pc-relative addressing mode of the 68000 directly, instead of
6035 using a global offset table. At present, this option implies @option{-fpic},
6036 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
6037 not presently supported with @option{-mpcrel}, though this could be supported for
6038 68020 and higher processors.
6040 @item -mno-strict-align
6041 @itemx -mstrict-align
6042 @opindex mno-strict-align
6043 @opindex mstrict-align
6044 Do not (do) assume that unaligned memory references will be handled by
6048 Generate code that allows the data segment to be located in a different
6049 area of memory from the text segment. This allows for execute in place in
6050 an environment without virtual memory management. This option implies -fPIC.
6053 Generate code that assumes that the data segment follows the text segment.
6054 This is the default.
6056 @item -mid-shared-library
6057 Generate code that supports shared libraries via the library ID method.
6058 This allows for execute in place and shared libraries in an environment
6059 without virtual memory management. This option implies -fPIC.
6061 @item -mno-id-shared-library
6062 Generate code that doesn't assume ID based shared libraries are being used.
6063 This is the default.
6065 @item -mshared-library-id=n
6066 Specified the identification number of the ID based shared library being
6067 compiled. Specifying a value of 0 will generate more compact code, specifying
6068 other values will force the allocation of that number to the current
6069 library but is no more space or time efficient than omitting this option.
6073 @node M68hc1x Options
6074 @subsection M68hc1x Options
6075 @cindex M68hc1x options
6077 These are the @samp{-m} options defined for the 68hc11 and 68hc12
6078 microcontrollers. The default values for these options depends on
6079 which style of microcontroller was selected when the compiler was configured;
6080 the defaults for the most common choices are given below.
6087 Generate output for a 68HC11. This is the default
6088 when the compiler is configured for 68HC11-based systems.
6094 Generate output for a 68HC12. This is the default
6095 when the compiler is configured for 68HC12-based systems.
6101 Generate output for a 68HCS12.
6104 @opindex mauto-incdec
6105 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
6112 Enable the use of 68HC12 min and max instructions.
6115 @itemx -mno-long-calls
6116 @opindex mlong-calls
6117 @opindex mno-long-calls
6118 Treat all calls as being far away (near). If calls are assumed to be
6119 far away, the compiler will use the @code{call} instruction to
6120 call a function and the @code{rtc} instruction for returning.
6124 Consider type @code{int} to be 16 bits wide, like @code{short int}.
6126 @item -msoft-reg-count=@var{count}
6127 @opindex msoft-reg-count
6128 Specify the number of pseudo-soft registers which are used for the
6129 code generation. The maximum number is 32. Using more pseudo-soft
6130 register may or may not result in better code depending on the program.
6131 The default is 4 for 68HC11 and 2 for 68HC12.
6136 @subsection VAX Options
6139 These @samp{-m} options are defined for the VAX:
6144 Do not output certain jump instructions (@code{aobleq} and so on)
6145 that the Unix assembler for the VAX cannot handle across long
6150 Do output those jump instructions, on the assumption that you
6151 will assemble with the GNU assembler.
6155 Output code for g-format floating point numbers instead of d-format.
6159 @subsection SPARC Options
6160 @cindex SPARC options
6162 These @samp{-m} switches are supported on the SPARC:
6167 @opindex mno-app-regs
6169 Specify @option{-mapp-regs} to generate output using the global registers
6170 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
6173 To be fully SVR4 ABI compliant at the cost of some performance loss,
6174 specify @option{-mno-app-regs}. You should compile libraries and system
6175 software with this option.
6180 @opindex mhard-float
6181 Generate output containing floating point instructions. This is the
6187 @opindex msoft-float
6188 Generate output containing library calls for floating point.
6189 @strong{Warning:} the requisite libraries are not available for all SPARC
6190 targets. Normally the facilities of the machine's usual C compiler are
6191 used, but this cannot be done directly in cross-compilation. You must make
6192 your own arrangements to provide suitable library functions for
6193 cross-compilation. The embedded targets @samp{sparc-*-aout} and
6194 @samp{sparclite-*-*} do provide software floating point support.
6196 @option{-msoft-float} changes the calling convention in the output file;
6197 therefore, it is only useful if you compile @emph{all} of a program with
6198 this option. In particular, you need to compile @file{libgcc.a}, the
6199 library that comes with GCC, with @option{-msoft-float} in order for
6202 @item -mhard-quad-float
6203 @opindex mhard-quad-float
6204 Generate output containing quad-word (long double) floating point
6207 @item -msoft-quad-float
6208 @opindex msoft-quad-float
6209 Generate output containing library calls for quad-word (long double)
6210 floating point instructions. The functions called are those specified
6211 in the SPARC ABI@. This is the default.
6213 As of this writing, there are no sparc implementations that have hardware
6214 support for the quad-word floating point instructions. They all invoke
6215 a trap handler for one of these instructions, and then the trap handler
6216 emulates the effect of the instruction. Because of the trap handler overhead,
6217 this is much slower than calling the ABI library routines. Thus the
6218 @option{-msoft-quad-float} option is the default.
6224 With @option{-mflat}, the compiler does not generate save/restore instructions
6225 and will use a ``flat'' or single register window calling convention.
6226 This model uses %i7 as the frame pointer and is compatible with the normal
6227 register window model. Code from either may be intermixed.
6228 The local registers and the input registers (0--5) are still treated as
6229 ``call saved'' registers and will be saved on the stack as necessary.
6231 With @option{-mno-flat} (the default), the compiler emits save/restore
6232 instructions (except for leaf functions) and is the normal mode of operation.
6234 @item -mno-unaligned-doubles
6235 @itemx -munaligned-doubles
6236 @opindex mno-unaligned-doubles
6237 @opindex munaligned-doubles
6238 Assume that doubles have 8 byte alignment. This is the default.
6240 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
6241 alignment only if they are contained in another type, or if they have an
6242 absolute address. Otherwise, it assumes they have 4 byte alignment.
6243 Specifying this option avoids some rare compatibility problems with code
6244 generated by other compilers. It is not the default because it results
6245 in a performance loss, especially for floating point code.
6247 @item -mno-faster-structs
6248 @itemx -mfaster-structs
6249 @opindex mno-faster-structs
6250 @opindex mfaster-structs
6251 With @option{-mfaster-structs}, the compiler assumes that structures
6252 should have 8 byte alignment. This enables the use of pairs of
6253 @code{ldd} and @code{std} instructions for copies in structure
6254 assignment, in place of twice as many @code{ld} and @code{st} pairs.
6255 However, the use of this changed alignment directly violates the SPARC
6256 ABI@. Thus, it's intended only for use on targets where the developer
6257 acknowledges that their resulting code will not be directly in line with
6258 the rules of the ABI@.
6261 @opindex mimpure-text
6262 @option{-mimpure-text}, used in addition to @option{-shared}, tells
6263 the compiler to not pass @option{-z text} to the linker when linking a
6264 shared object. Using this option, you can link position-dependent
6265 code into a shared object.
6267 @option{-mimpure-text} suppresses the ``relocations remain against
6268 allocatable but non-writable sections'' linker error message.
6269 However, the necessary relocations will trigger copy-on-write, and the
6270 shared object is not actually shared across processes. Instead of
6271 using @option{-mimpure-text}, you should compile all source code with
6272 @option{-fpic} or @option{-fPIC}.
6274 This option is only available on SunOS and Solaris.
6280 These two options select variations on the SPARC architecture.
6282 By default (unless specifically configured for the Fujitsu SPARClite),
6283 GCC generates code for the v7 variant of the SPARC architecture.
6285 @option{-mv8} will give you SPARC v8 code. The only difference from v7
6286 code is that the compiler emits the integer multiply and integer
6287 divide instructions which exist in SPARC v8 but not in SPARC v7.
6289 @option{-msparclite} will give you SPARClite code. This adds the integer
6290 multiply, integer divide step and scan (@code{ffs}) instructions which
6291 exist in SPARClite but not in SPARC v7.
6293 These options are deprecated and will be deleted in a future GCC release.
6294 They have been replaced with @option{-mcpu=xxx}.
6299 @opindex msupersparc
6300 These two options select the processor for which the code is optimized.
6302 With @option{-mcypress} (the default), the compiler optimizes code for the
6303 Cypress CY7C602 chip, as used in the SPARCStation/SPARCServer 3xx series.
6304 This is also appropriate for the older SPARCStation 1, 2, IPX etc.
6306 With @option{-msupersparc} the compiler optimizes code for the SuperSPARC cpu, as
6307 used in the SPARCStation 10, 1000 and 2000 series. This flag also enables use
6308 of the full SPARC v8 instruction set.
6310 These options are deprecated and will be deleted in a future GCC release.
6311 They have been replaced with @option{-mcpu=xxx}.
6313 @item -mcpu=@var{cpu_type}
6315 Set the instruction set, register set, and instruction scheduling parameters
6316 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
6317 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
6318 @samp{hypersparc}, @samp{sparclite86x}, @samp{f930}, @samp{f934},
6319 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, and
6322 Default instruction scheduling parameters are used for values that select
6323 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
6324 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
6326 Here is a list of each supported architecture and their supported
6331 v8: supersparc, hypersparc
6332 sparclite: f930, f934, sparclite86x
6334 v9: ultrasparc, ultrasparc3
6337 @item -mtune=@var{cpu_type}
6339 Set the instruction scheduling parameters for machine type
6340 @var{cpu_type}, but do not set the instruction set or register set that the
6341 option @option{-mcpu=@var{cpu_type}} would.
6343 The same values for @option{-mcpu=@var{cpu_type}} can be used for
6344 @option{-mtune=@var{cpu_type}}, but the only useful values are those
6345 that select a particular cpu implementation. Those are @samp{cypress},
6346 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
6347 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, and
6352 These @samp{-m} switches are supported in addition to the above
6353 on the SPARCLET processor.
6356 @item -mlittle-endian
6357 @opindex mlittle-endian
6358 Generate code for a processor running in little-endian mode.
6362 Treat register @code{%g0} as a normal register.
6363 GCC will continue to clobber it as necessary but will not assume
6364 it always reads as 0.
6366 @item -mbroken-saverestore
6367 @opindex mbroken-saverestore
6368 Generate code that does not use non-trivial forms of the @code{save} and
6369 @code{restore} instructions. Early versions of the SPARCLET processor do
6370 not correctly handle @code{save} and @code{restore} instructions used with
6371 arguments. They correctly handle them used without arguments. A @code{save}
6372 instruction used without arguments increments the current window pointer
6373 but does not allocate a new stack frame. It is assumed that the window
6374 overflow trap handler will properly handle this case as will interrupt
6378 These @samp{-m} switches are supported in addition to the above
6379 on SPARC V9 processors in 64-bit environments.
6382 @item -mlittle-endian
6383 @opindex mlittle-endian
6384 Generate code for a processor running in little-endian mode. It is only
6385 available for a few configurations and most notably not on Solaris.
6391 Generate code for a 32-bit or 64-bit environment.
6392 The 32-bit environment sets int, long and pointer to 32 bits.
6393 The 64-bit environment sets int to 32 bits and long and pointer
6396 @item -mcmodel=medlow
6397 @opindex mcmodel=medlow
6398 Generate code for the Medium/Low code model: the program must be linked
6399 in the low 32 bits of the address space. Pointers are 64 bits.
6400 Programs can be statically or dynamically linked.
6402 @item -mcmodel=medmid
6403 @opindex mcmodel=medmid
6404 Generate code for the Medium/Middle code model: the program must be linked
6405 in the low 44 bits of the address space, the text segment must be less than
6406 2G bytes, and data segment must be within 2G of the text segment.
6407 Pointers are 64 bits.
6409 @item -mcmodel=medany
6410 @opindex mcmodel=medany
6411 Generate code for the Medium/Anywhere code model: the program may be linked
6412 anywhere in the address space, the text segment must be less than
6413 2G bytes, and data segment must be within 2G of the text segment.
6414 Pointers are 64 bits.
6416 @item -mcmodel=embmedany
6417 @opindex mcmodel=embmedany
6418 Generate code for the Medium/Anywhere code model for embedded systems:
6419 assume a 32-bit text and a 32-bit data segment, both starting anywhere
6420 (determined at link time). Register %g4 points to the base of the
6421 data segment. Pointers are still 64 bits.
6422 Programs are statically linked, PIC is not supported.
6425 @itemx -mno-stack-bias
6426 @opindex mstack-bias
6427 @opindex mno-stack-bias
6428 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
6429 frame pointer if present, are offset by @minus{}2047 which must be added back
6430 when making stack frame references.
6431 Otherwise, assume no such offset is present.
6435 @subsection ARM Options
6438 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
6443 @opindex mapcs-frame
6444 Generate a stack frame that is compliant with the ARM Procedure Call
6445 Standard for all functions, even if this is not strictly necessary for
6446 correct execution of the code. Specifying @option{-fomit-frame-pointer}
6447 with this option will cause the stack frames not to be generated for
6448 leaf functions. The default is @option{-mno-apcs-frame}.
6452 This is a synonym for @option{-mapcs-frame}.
6456 Generate code for a processor running with a 26-bit program counter,
6457 and conforming to the function calling standards for the APCS 26-bit
6458 option. This option replaces the @option{-m2} and @option{-m3} options
6459 of previous releases of the compiler.
6463 Generate code for a processor running with a 32-bit program counter,
6464 and conforming to the function calling standards for the APCS 32-bit
6465 option. This option replaces the @option{-m6} option of previous releases
6469 @c not currently implemented
6470 @item -mapcs-stack-check
6471 @opindex mapcs-stack-check
6472 Generate code to check the amount of stack space available upon entry to
6473 every function (that actually uses some stack space). If there is
6474 insufficient space available then either the function
6475 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
6476 called, depending upon the amount of stack space required. The run time
6477 system is required to provide these functions. The default is
6478 @option{-mno-apcs-stack-check}, since this produces smaller code.
6480 @c not currently implemented
6482 @opindex mapcs-float
6483 Pass floating point arguments using the float point registers. This is
6484 one of the variants of the APCS@. This option is recommended if the
6485 target hardware has a floating point unit or if a lot of floating point
6486 arithmetic is going to be performed by the code. The default is
6487 @option{-mno-apcs-float}, since integer only code is slightly increased in
6488 size if @option{-mapcs-float} is used.
6490 @c not currently implemented
6491 @item -mapcs-reentrant
6492 @opindex mapcs-reentrant
6493 Generate reentrant, position independent code. The default is
6494 @option{-mno-apcs-reentrant}.
6497 @item -mthumb-interwork
6498 @opindex mthumb-interwork
6499 Generate code which supports calling between the ARM and Thumb
6500 instruction sets. Without this option the two instruction sets cannot
6501 be reliably used inside one program. The default is
6502 @option{-mno-thumb-interwork}, since slightly larger code is generated
6503 when @option{-mthumb-interwork} is specified.
6505 @item -mno-sched-prolog
6506 @opindex mno-sched-prolog
6507 Prevent the reordering of instructions in the function prolog, or the
6508 merging of those instruction with the instructions in the function's
6509 body. This means that all functions will start with a recognizable set
6510 of instructions (or in fact one of a choice from a small set of
6511 different function prologues), and this information can be used to
6512 locate the start if functions inside an executable piece of code. The
6513 default is @option{-msched-prolog}.
6516 @opindex mhard-float
6517 Generate output containing floating point instructions. This is the
6521 @opindex msoft-float
6522 Generate output containing library calls for floating point.
6523 @strong{Warning:} the requisite libraries are not available for all ARM
6524 targets. Normally the facilities of the machine's usual C compiler are
6525 used, but this cannot be done directly in cross-compilation. You must make
6526 your own arrangements to provide suitable library functions for
6529 @option{-msoft-float} changes the calling convention in the output file;
6530 therefore, it is only useful if you compile @emph{all} of a program with
6531 this option. In particular, you need to compile @file{libgcc.a}, the
6532 library that comes with GCC, with @option{-msoft-float} in order for
6535 @item -mlittle-endian
6536 @opindex mlittle-endian
6537 Generate code for a processor running in little-endian mode. This is
6538 the default for all standard configurations.
6541 @opindex mbig-endian
6542 Generate code for a processor running in big-endian mode; the default is
6543 to compile code for a little-endian processor.
6545 @item -mwords-little-endian
6546 @opindex mwords-little-endian
6547 This option only applies when generating code for big-endian processors.
6548 Generate code for a little-endian word order but a big-endian byte
6549 order. That is, a byte order of the form @samp{32107654}. Note: this
6550 option should only be used if you require compatibility with code for
6551 big-endian ARM processors generated by versions of the compiler prior to
6554 @item -malignment-traps
6555 @opindex malignment-traps
6556 Generate code that will not trap if the MMU has alignment traps enabled.
6557 On ARM architectures prior to ARMv4, there were no instructions to
6558 access half-word objects stored in memory. However, when reading from
6559 memory a feature of the ARM architecture allows a word load to be used,
6560 even if the address is unaligned, and the processor core will rotate the
6561 data as it is being loaded. This option tells the compiler that such
6562 misaligned accesses will cause a MMU trap and that it should instead
6563 synthesize the access as a series of byte accesses. The compiler can
6564 still use word accesses to load half-word data if it knows that the
6565 address is aligned to a word boundary.
6567 This option is ignored when compiling for ARM architecture 4 or later,
6568 since these processors have instructions to directly access half-word
6571 @item -mno-alignment-traps
6572 @opindex mno-alignment-traps
6573 Generate code that assumes that the MMU will not trap unaligned
6574 accesses. This produces better code when the target instruction set
6575 does not have half-word memory operations (i.e.@: implementations prior to
6578 Note that you cannot use this option to access unaligned word objects,
6579 since the processor will only fetch one 32-bit aligned object from
6582 The default setting for most targets is @option{-mno-alignment-traps}, since
6583 this produces better code when there are no half-word memory
6584 instructions available.
6586 @item -mshort-load-bytes
6587 @itemx -mno-short-load-words
6588 @opindex mshort-load-bytes
6589 @opindex mno-short-load-words
6590 These are deprecated aliases for @option{-malignment-traps}.
6592 @item -mno-short-load-bytes
6593 @itemx -mshort-load-words
6594 @opindex mno-short-load-bytes
6595 @opindex mshort-load-words
6596 This are deprecated aliases for @option{-mno-alignment-traps}.
6598 @item -mcpu=@var{name}
6600 This specifies the name of the target ARM processor. GCC uses this name
6601 to determine what kind of instructions it can emit when generating
6602 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
6603 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
6604 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
6605 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
6606 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
6607 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm8},
6608 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
6609 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
6610 @samp{arm920t}, @samp{arm926ejs}, @samp{arm940t}, @samp{arm9tdmi},
6611 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ejs},
6612 @samp{arm1136js}, @samp{arm1136jfs} ,@samp{xscale}, @samp{iwmmxt},
6615 @itemx -mtune=@var{name}
6617 This option is very similar to the @option{-mcpu=} option, except that
6618 instead of specifying the actual target processor type, and hence
6619 restricting which instructions can be used, it specifies that GCC should
6620 tune the performance of the code as if the target were of the type
6621 specified in this option, but still choosing the instructions that it
6622 will generate based on the cpu specified by a @option{-mcpu=} option.
6623 For some ARM implementations better performance can be obtained by using
6626 @item -march=@var{name}
6628 This specifies the name of the target ARM architecture. GCC uses this
6629 name to determine what kind of instructions it can emit when generating
6630 assembly code. This option can be used in conjunction with or instead
6631 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
6632 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
6633 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6j},
6634 @samp{iwmmxt}, @samp{ep9312}.
6636 @item -mfpe=@var{number}
6637 @itemx -mfp=@var{number}
6640 This specifies the version of the floating point emulation available on
6641 the target. Permissible values are 2 and 3. @option{-mfp=} is a synonym
6642 for @option{-mfpe=}, for compatibility with older versions of GCC@.
6644 @item -mstructure-size-boundary=@var{n}
6645 @opindex mstructure-size-boundary
6646 The size of all structures and unions will be rounded up to a multiple
6647 of the number of bits set by this option. Permissible values are 8 and
6648 32. The default value varies for different toolchains. For the COFF
6649 targeted toolchain the default value is 8. Specifying the larger number
6650 can produce faster, more efficient code, but can also increase the size
6651 of the program. The two values are potentially incompatible. Code
6652 compiled with one value cannot necessarily expect to work with code or
6653 libraries compiled with the other value, if they exchange information
6654 using structures or unions.
6656 @item -mabort-on-noreturn
6657 @opindex mabort-on-noreturn
6658 Generate a call to the function @code{abort} at the end of a
6659 @code{noreturn} function. It will be executed if the function tries to
6663 @itemx -mno-long-calls
6664 @opindex mlong-calls
6665 @opindex mno-long-calls
6666 Tells the compiler to perform function calls by first loading the
6667 address of the function into a register and then performing a subroutine
6668 call on this register. This switch is needed if the target function
6669 will lie outside of the 64 megabyte addressing range of the offset based
6670 version of subroutine call instruction.
6672 Even if this switch is enabled, not all function calls will be turned
6673 into long calls. The heuristic is that static functions, functions
6674 which have the @samp{short-call} attribute, functions that are inside
6675 the scope of a @samp{#pragma no_long_calls} directive and functions whose
6676 definitions have already been compiled within the current compilation
6677 unit, will not be turned into long calls. The exception to this rule is
6678 that weak function definitions, functions with the @samp{long-call}
6679 attribute or the @samp{section} attribute, and functions that are within
6680 the scope of a @samp{#pragma long_calls} directive, will always be
6681 turned into long calls.
6683 This feature is not enabled by default. Specifying
6684 @option{-mno-long-calls} will restore the default behavior, as will
6685 placing the function calls within the scope of a @samp{#pragma
6686 long_calls_off} directive. Note these switches have no effect on how
6687 the compiler generates code to handle function calls via function
6690 @item -mnop-fun-dllimport
6691 @opindex mnop-fun-dllimport
6692 Disable support for the @code{dllimport} attribute.
6694 @item -msingle-pic-base
6695 @opindex msingle-pic-base
6696 Treat the register used for PIC addressing as read-only, rather than
6697 loading it in the prologue for each function. The run-time system is
6698 responsible for initializing this register with an appropriate value
6699 before execution begins.
6701 @item -mpic-register=@var{reg}
6702 @opindex mpic-register
6703 Specify the register to be used for PIC addressing. The default is R10
6704 unless stack-checking is enabled, when R9 is used.
6706 @item -mcirrus-fix-invalid-insns
6707 @opindex mcirrus-fix-invalid-insns
6708 @opindex mno-cirrus-fix-invalid-insns
6709 Insert NOPs into the instruction stream to in order to work around
6710 problems with invalid Maverick instruction combinations. This option
6711 is only valid if the @option{-mcpu=ep9312} option has been used to
6712 enable generation of instructions for the Cirrus Maverick floating
6713 point co-processor. This option is not enabled by default, since the
6714 problem is only present in older Maverick implementations. The default
6715 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
6718 @item -mpoke-function-name
6719 @opindex mpoke-function-name
6720 Write the name of each function into the text section, directly
6721 preceding the function prologue. The generated code is similar to this:
6725 .ascii "arm_poke_function_name", 0
6728 .word 0xff000000 + (t1 - t0)
6729 arm_poke_function_name
6731 stmfd sp!, @{fp, ip, lr, pc@}
6735 When performing a stack backtrace, code can inspect the value of
6736 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
6737 location @code{pc - 12} and the top 8 bits are set, then we know that
6738 there is a function name embedded immediately preceding this location
6739 and has length @code{((pc[-3]) & 0xff000000)}.
6743 Generate code for the 16-bit Thumb instruction set. The default is to
6744 use the 32-bit ARM instruction set.
6747 @opindex mtpcs-frame
6748 Generate a stack frame that is compliant with the Thumb Procedure Call
6749 Standard for all non-leaf functions. (A leaf function is one that does
6750 not call any other functions.) The default is @option{-mno-tpcs-frame}.
6752 @item -mtpcs-leaf-frame
6753 @opindex mtpcs-leaf-frame
6754 Generate a stack frame that is compliant with the Thumb Procedure Call
6755 Standard for all leaf functions. (A leaf function is one that does
6756 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
6758 @item -mcallee-super-interworking
6759 @opindex mcallee-super-interworking
6760 Gives all externally visible functions in the file being compiled an ARM
6761 instruction set header which switches to Thumb mode before executing the
6762 rest of the function. This allows these functions to be called from
6763 non-interworking code.
6765 @item -mcaller-super-interworking
6766 @opindex mcaller-super-interworking
6767 Allows calls via function pointers (including virtual functions) to
6768 execute correctly regardless of whether the target code has been
6769 compiled for interworking or not. There is a small overhead in the cost
6770 of executing a function pointer if this option is enabled.
6774 @node MN10200 Options
6775 @subsection MN10200 Options
6776 @cindex MN10200 options
6778 These @option{-m} options are defined for Matsushita MN10200 architectures:
6783 Indicate to the linker that it should perform a relaxation optimization pass
6784 to shorten branches, calls and absolute memory addresses. This option only
6785 has an effect when used on the command line for the final link step.
6787 This option makes symbolic debugging impossible.
6790 @node MN10300 Options
6791 @subsection MN10300 Options
6792 @cindex MN10300 options
6794 These @option{-m} options are defined for Matsushita MN10300 architectures:
6799 Generate code to avoid bugs in the multiply instructions for the MN10300
6800 processors. This is the default.
6803 @opindex mno-mult-bug
6804 Do not generate code to avoid bugs in the multiply instructions for the
6809 Generate code which uses features specific to the AM33 processor.
6813 Do not generate code which uses features specific to the AM33 processor. This
6818 Do not link in the C run-time initialization object file.
6822 Indicate to the linker that it should perform a relaxation optimization pass
6823 to shorten branches, calls and absolute memory addresses. This option only
6824 has an effect when used on the command line for the final link step.
6826 This option makes symbolic debugging impossible.
6830 @node M32R/D Options
6831 @subsection M32R/D Options
6832 @cindex M32R/D options
6834 These @option{-m} options are defined for Mitsubishi M32R/D architectures:
6839 Generate code for the M32R/X@.
6843 Generate code for the M32R@. This is the default.
6845 @item -mcode-model=small
6846 @opindex mcode-model=small
6847 Assume all objects live in the lower 16MB of memory (so that their addresses
6848 can be loaded with the @code{ld24} instruction), and assume all subroutines
6849 are reachable with the @code{bl} instruction.
6850 This is the default.
6852 The addressability of a particular object can be set with the
6853 @code{model} attribute.
6855 @item -mcode-model=medium
6856 @opindex mcode-model=medium
6857 Assume objects may be anywhere in the 32-bit address space (the compiler
6858 will generate @code{seth/add3} instructions to load their addresses), and
6859 assume all subroutines are reachable with the @code{bl} instruction.
6861 @item -mcode-model=large
6862 @opindex mcode-model=large
6863 Assume objects may be anywhere in the 32-bit address space (the compiler
6864 will generate @code{seth/add3} instructions to load their addresses), and
6865 assume subroutines may not be reachable with the @code{bl} instruction
6866 (the compiler will generate the much slower @code{seth/add3/jl}
6867 instruction sequence).
6870 @opindex msdata=none
6871 Disable use of the small data area. Variables will be put into
6872 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
6873 @code{section} attribute has been specified).
6874 This is the default.
6876 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
6877 Objects may be explicitly put in the small data area with the
6878 @code{section} attribute using one of these sections.
6881 @opindex msdata=sdata
6882 Put small global and static data in the small data area, but do not
6883 generate special code to reference them.
6887 Put small global and static data in the small data area, and generate
6888 special instructions to reference them.
6892 @cindex smaller data references
6893 Put global and static objects less than or equal to @var{num} bytes
6894 into the small data or bss sections instead of the normal data or bss
6895 sections. The default value of @var{num} is 8.
6896 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
6897 for this option to have any effect.
6899 All modules should be compiled with the same @option{-G @var{num}} value.
6900 Compiling with different values of @var{num} may or may not work; if it
6901 doesn't the linker will give an error message---incorrect code will not be
6907 @subsection M88K Options
6908 @cindex M88k options
6910 These @samp{-m} options are defined for Motorola 88k architectures:
6915 Generate code that works well on both the m88100 and the
6920 Generate code that works best for the m88100, but that also
6925 Generate code that works best for the m88110, and may not run
6930 Obsolete option to be removed from the next revision.
6933 @item -midentify-revision
6934 @opindex midentify-revision
6935 @cindex identifying source, compiler (88k)
6936 Include an @code{ident} directive in the assembler output recording the
6937 source file name, compiler name and version, timestamp, and compilation
6940 @item -mno-underscores
6941 @opindex mno-underscores
6942 @cindex underscores, avoiding (88k)
6943 In assembler output, emit symbol names without adding an underscore
6944 character at the beginning of each name. The default is to use an
6945 underscore as prefix on each name.
6947 @item -mocs-debug-info
6948 @itemx -mno-ocs-debug-info
6949 @opindex mocs-debug-info
6950 @opindex mno-ocs-debug-info
6952 @cindex debugging, 88k OCS
6953 Include (or omit) additional debugging information (about registers used
6954 in each stack frame) as specified in the 88open Object Compatibility
6955 Standard, ``OCS''@. This extra information allows debugging of code that
6956 has had the frame pointer eliminated. The default for SVr4 and Delta 88
6957 SVr3.2 is to include this information; other 88k configurations omit this
6958 information by default.
6960 @item -mocs-frame-position
6961 @opindex mocs-frame-position
6962 @cindex register positions in frame (88k)
6963 When emitting COFF debugging information for automatic variables and
6964 parameters stored on the stack, use the offset from the canonical frame
6965 address, which is the stack pointer (register 31) on entry to the
6966 function. The SVr4 and Delta88 SVr3.2, and BCS configurations use
6967 @option{-mocs-frame-position}; other 88k configurations have the default
6968 @option{-mno-ocs-frame-position}.
6970 @item -mno-ocs-frame-position
6971 @opindex mno-ocs-frame-position
6972 @cindex register positions in frame (88k)
6973 When emitting COFF debugging information for automatic variables and
6974 parameters stored on the stack, use the offset from the frame pointer
6975 register (register 30). When this option is in effect, the frame
6976 pointer is not eliminated when debugging information is selected by the
6979 @item -moptimize-arg-area
6980 @opindex moptimize-arg-area
6981 @cindex arguments in frame (88k)
6982 Save space by reorganizing the stack frame. This option generates code
6983 that does not agree with the 88open specifications, but uses less
6986 @itemx -mno-optimize-arg-area
6987 @opindex mno-optimize-arg-area
6988 Do not reorganize the stack frame to save space. This is the default.
6989 The generated conforms to the specification, but uses more memory.
6991 @item -mshort-data-@var{num}
6992 @opindex mshort-data
6993 @cindex smaller data references (88k)
6994 @cindex r0-relative references (88k)
6995 Generate smaller data references by making them relative to @code{r0},
6996 which allows loading a value using a single instruction (rather than the
6997 usual two). You control which data references are affected by
6998 specifying @var{num} with this option. For example, if you specify
6999 @option{-mshort-data-512}, then the data references affected are those
7000 involving displacements of less than 512 bytes.
7001 @option{-mshort-data-@var{num}} is not effective for @var{num} greater
7004 @item -mserialize-volatile
7005 @opindex mserialize-volatile
7006 @itemx -mno-serialize-volatile
7007 @opindex mno-serialize-volatile
7008 @cindex sequential consistency on 88k
7009 Do, or don't, generate code to guarantee sequential consistency
7010 of volatile memory references. By default, consistency is
7013 The order of memory references made by the MC88110 processor does
7014 not always match the order of the instructions requesting those
7015 references. In particular, a load instruction may execute before
7016 a preceding store instruction. Such reordering violates
7017 sequential consistency of volatile memory references, when there
7018 are multiple processors. When consistency must be guaranteed,
7019 GCC generates special instructions, as needed, to force
7020 execution in the proper order.
7022 The MC88100 processor does not reorder memory references and so
7023 always provides sequential consistency. However, by default, GCC
7024 generates the special instructions to guarantee consistency
7025 even when you use @option{-m88100}, so that the code may be run on an
7026 MC88110 processor. If you intend to run your code only on the
7027 MC88100 processor, you may use @option{-mno-serialize-volatile}.
7029 The extra code generated to guarantee consistency may affect the
7030 performance of your application. If you know that you can safely
7031 forgo this guarantee, you may use @option{-mno-serialize-volatile}.
7037 @cindex assembler syntax, 88k
7039 Turn on (@option{-msvr4}) or off (@option{-msvr3}) compiler extensions
7040 related to System V release 4 (SVr4). This controls the following:
7044 Which variant of the assembler syntax to emit.
7046 @option{-msvr4} makes the C preprocessor recognize @samp{#pragma weak}
7047 that is used on System V release 4.
7049 @option{-msvr4} makes GCC issue additional declaration directives used in
7053 @option{-msvr4} is the default for the m88k-motorola-sysv4 configuration.
7054 @option{-msvr3} is the default for all other m88k configurations.
7056 @item -mversion-03.00
7057 @opindex mversion-03.00
7058 This option is obsolete, and is ignored.
7059 @c ??? which asm syntax better for GAS? option there too?
7061 @item -mno-check-zero-division
7062 @itemx -mcheck-zero-division
7063 @opindex mno-check-zero-division
7064 @opindex mcheck-zero-division
7065 @cindex zero division on 88k
7066 Do, or don't, generate code to guarantee that integer division by
7067 zero will be detected. By default, detection is guaranteed.
7069 Some models of the MC88100 processor fail to trap upon integer
7070 division by zero under certain conditions. By default, when
7071 compiling code that might be run on such a processor, GCC
7072 generates code that explicitly checks for zero-valued divisors
7073 and traps with exception number 503 when one is detected. Use of
7074 @option{-mno-check-zero-division} suppresses such checking for code
7075 generated to run on an MC88100 processor.
7077 GCC assumes that the MC88110 processor correctly detects all instances
7078 of integer division by zero. When @option{-m88110} is specified, no
7079 explicit checks for zero-valued divisors are generated, and both
7080 @option{-mcheck-zero-division} and @option{-mno-check-zero-division} are
7083 @item -muse-div-instruction
7084 @opindex muse-div-instruction
7085 @cindex divide instruction, 88k
7086 Use the div instruction for signed integer division on the
7087 MC88100 processor. By default, the div instruction is not used.
7089 On the MC88100 processor the signed integer division instruction
7090 div) traps to the operating system on a negative operand. The
7091 operating system transparently completes the operation, but at a
7092 large cost in execution time. By default, when compiling code
7093 that might be run on an MC88100 processor, GCC emulates signed
7094 integer division using the unsigned integer division instruction
7095 divu), thereby avoiding the large penalty of a trap to the
7096 operating system. Such emulation has its own, smaller, execution
7097 cost in both time and space. To the extent that your code's
7098 important signed integer division operations are performed on two
7099 nonnegative operands, it may be desirable to use the div
7100 instruction directly.
7102 On the MC88110 processor the div instruction (also known as the
7103 divs instruction) processes negative operands without trapping to
7104 the operating system. When @option{-m88110} is specified,
7105 @option{-muse-div-instruction} is ignored, and the div instruction is used
7106 for signed integer division.
7108 Note that the result of dividing @code{INT_MIN} by @minus{}1 is undefined. In
7109 particular, the behavior of such a division with and without
7110 @option{-muse-div-instruction} may differ.
7112 @item -mtrap-large-shift
7113 @itemx -mhandle-large-shift
7114 @opindex mtrap-large-shift
7115 @opindex mhandle-large-shift
7116 @cindex bit shift overflow (88k)
7117 @cindex large bit shifts (88k)
7118 Include code to detect bit-shifts of more than 31 bits; respectively,
7119 trap such shifts or emit code to handle them properly. By default GCC
7120 makes no special provision for large bit shifts.
7122 @item -mwarn-passed-structs
7123 @opindex mwarn-passed-structs
7124 @cindex structure passing (88k)
7125 Warn when a function passes a struct as an argument or result.
7126 Structure-passing conventions have changed during the evolution of the C
7127 language, and are often the source of portability problems. By default,
7128 GCC issues no such warning.
7131 @c break page here to avoid unsightly interparagraph stretch.
7135 @node RS/6000 and PowerPC Options
7136 @subsection IBM RS/6000 and PowerPC Options
7137 @cindex RS/6000 and PowerPC Options
7138 @cindex IBM RS/6000 and PowerPC Options
7140 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
7148 @itemx -mpowerpc-gpopt
7149 @itemx -mno-powerpc-gpopt
7150 @itemx -mpowerpc-gfxopt
7151 @itemx -mno-powerpc-gfxopt
7153 @itemx -mno-powerpc64
7159 @opindex mno-powerpc
7160 @opindex mpowerpc-gpopt
7161 @opindex mno-powerpc-gpopt
7162 @opindex mpowerpc-gfxopt
7163 @opindex mno-powerpc-gfxopt
7165 @opindex mno-powerpc64
7166 GCC supports two related instruction set architectures for the
7167 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
7168 instructions supported by the @samp{rios} chip set used in the original
7169 RS/6000 systems and the @dfn{PowerPC} instruction set is the
7170 architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
7171 the IBM 4xx microprocessors.
7173 Neither architecture is a subset of the other. However there is a
7174 large common subset of instructions supported by both. An MQ
7175 register is included in processors supporting the POWER architecture.
7177 You use these options to specify which instructions are available on the
7178 processor you are using. The default value of these options is
7179 determined when configuring GCC@. Specifying the
7180 @option{-mcpu=@var{cpu_type}} overrides the specification of these
7181 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
7182 rather than the options listed above.
7184 The @option{-mpower} option allows GCC to generate instructions that
7185 are found only in the POWER architecture and to use the MQ register.
7186 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
7187 to generate instructions that are present in the POWER2 architecture but
7188 not the original POWER architecture.
7190 The @option{-mpowerpc} option allows GCC to generate instructions that
7191 are found only in the 32-bit subset of the PowerPC architecture.
7192 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
7193 GCC to use the optional PowerPC architecture instructions in the
7194 General Purpose group, including floating-point square root. Specifying
7195 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
7196 use the optional PowerPC architecture instructions in the Graphics
7197 group, including floating-point select.
7199 The @option{-mpowerpc64} option allows GCC to generate the additional
7200 64-bit instructions that are found in the full PowerPC64 architecture
7201 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
7202 @option{-mno-powerpc64}.
7204 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
7205 will use only the instructions in the common subset of both
7206 architectures plus some special AIX common-mode calls, and will not use
7207 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
7208 permits GCC to use any instruction from either architecture and to
7209 allow use of the MQ register; specify this for the Motorola MPC601.
7211 @item -mnew-mnemonics
7212 @itemx -mold-mnemonics
7213 @opindex mnew-mnemonics
7214 @opindex mold-mnemonics
7215 Select which mnemonics to use in the generated assembler code. With
7216 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
7217 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
7218 assembler mnemonics defined for the POWER architecture. Instructions
7219 defined in only one architecture have only one mnemonic; GCC uses that
7220 mnemonic irrespective of which of these options is specified.
7222 GCC defaults to the mnemonics appropriate for the architecture in
7223 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
7224 value of these option. Unless you are building a cross-compiler, you
7225 should normally not specify either @option{-mnew-mnemonics} or
7226 @option{-mold-mnemonics}, but should instead accept the default.
7228 @item -mcpu=@var{cpu_type}
7230 Set architecture type, register usage, choice of mnemonics, and
7231 instruction scheduling parameters for machine type @var{cpu_type}.
7232 Supported values for @var{cpu_type} are @samp{rios}, @samp{rios1},
7233 @samp{rsc}, @samp{rios2}, @samp{rs64a}, @samp{601}, @samp{602},
7234 @samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620},
7235 @samp{630}, @samp{740}, @samp{7400}, @samp{7450}, @samp{G4},
7236 @samp{750}, @samp{G3}, @samp{power}, @samp{power2}, @samp{powerpc},
7237 @samp{403}, @samp{505}, @samp{801}, @samp{821}, @samp{823}, @samp{860},
7238 @samp{970}, @samp{G5} and @samp{common}.
7240 @option{-mcpu=common} selects a completely generic processor. Code
7241 generated under this option will run on any POWER or PowerPC processor.
7242 GCC will use only the instructions in the common subset of both
7243 architectures, and will not use the MQ register. GCC assumes a generic
7244 processor model for scheduling purposes.
7246 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
7247 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
7248 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
7249 types, with an appropriate, generic processor model assumed for
7250 scheduling purposes.
7252 The other options specify a specific processor. Code generated under
7253 those options will run best on that processor, and may not run at all on
7256 The @option{-mcpu} options automatically enable or disable other
7257 @option{-m} options as follows:
7261 @option{-mno-power}, @option{-mno-powerpc}
7268 @option{-mpower}, @option{-mno-powerpc}, @option{-mno-new-mnemonics}
7287 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}
7290 @option{-mpower}, @option{-mpowerpc}, @option{-mnew-mnemonics}
7295 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}, @option{-msoft-float}
7298 @item -mtune=@var{cpu_type}
7300 Set the instruction scheduling parameters for machine type
7301 @var{cpu_type}, but do not set the architecture type, register usage, or
7302 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
7303 values for @var{cpu_type} are used for @option{-mtune} as for
7304 @option{-mcpu}. If both are specified, the code generated will use the
7305 architecture, registers, and mnemonics set by @option{-mcpu}, but the
7306 scheduling parameters set by @option{-mtune}.
7311 @opindex mno-altivec
7312 These switches enable or disable the use of built-in functions that
7313 allow access to the AltiVec instruction set. You may also need to set
7314 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
7319 Extend the current ABI with SPE ABI extensions. This does not change
7320 the default ABI, instead it adds the SPE ABI extensions to the current
7324 @opindex mabi=no-spe
7325 Disable Booke SPE ABI extensions for the current ABI.
7327 @item -misel=@var{yes/no}
7330 This switch enables or disables the generation of ISEL instructions.
7332 @item -mspe=@var{yes/no}
7335 This switch enables or disables the generation of SPE simd
7338 @item -mfloat-gprs=@var{yes/no}
7340 @opindex mfloat-gprs
7341 This switch enables or disables the generation of floating point
7342 operations on the general purpose registers for architectures that
7343 support it. This option is currently only available on the MPC8540.
7346 @itemx -mno-fp-in-toc
7347 @itemx -mno-sum-in-toc
7348 @itemx -mminimal-toc
7350 @opindex mno-fp-in-toc
7351 @opindex mno-sum-in-toc
7352 @opindex mminimal-toc
7353 Modify generation of the TOC (Table Of Contents), which is created for
7354 every executable file. The @option{-mfull-toc} option is selected by
7355 default. In that case, GCC will allocate at least one TOC entry for
7356 each unique non-automatic variable reference in your program. GCC
7357 will also place floating-point constants in the TOC@. However, only
7358 16,384 entries are available in the TOC@.
7360 If you receive a linker error message that saying you have overflowed
7361 the available TOC space, you can reduce the amount of TOC space used
7362 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
7363 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
7364 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
7365 generate code to calculate the sum of an address and a constant at
7366 run-time instead of putting that sum into the TOC@. You may specify one
7367 or both of these options. Each causes GCC to produce very slightly
7368 slower and larger code at the expense of conserving TOC space.
7370 If you still run out of space in the TOC even when you specify both of
7371 these options, specify @option{-mminimal-toc} instead. This option causes
7372 GCC to make only one TOC entry for every file. When you specify this
7373 option, GCC will produce code that is slower and larger but which
7374 uses extremely little TOC space. You may wish to use this option
7375 only on files that contain less frequently executed code.
7381 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
7382 @code{long} type, and the infrastructure needed to support them.
7383 Specifying @option{-maix64} implies @option{-mpowerpc64} and
7384 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
7385 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
7390 @opindex mno-xl-call
7391 On AIX, pass floating-point arguments to prototyped functions beyond the
7392 register save area (RSA) on the stack in addition to argument FPRs. The
7393 AIX calling convention was extended but not initially documented to
7394 handle an obscure K&R C case of calling a function that takes the
7395 address of its arguments with fewer arguments than declared. AIX XL
7396 compilers access floating point arguments which do not fit in the
7397 RSA from the stack when a subroutine is compiled without
7398 optimization. Because always storing floating-point arguments on the
7399 stack is inefficient and rarely needed, this option is not enabled by
7400 default and only is necessary when calling subroutines compiled by AIX
7401 XL compilers without optimization.
7405 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
7406 application written to use message passing with special startup code to
7407 enable the application to run. The system must have PE installed in the
7408 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
7409 must be overridden with the @option{-specs=} option to specify the
7410 appropriate directory location. The Parallel Environment does not
7411 support threads, so the @option{-mpe} option and the @option{-pthread}
7412 option are incompatible.
7414 @item -malign-natural
7415 @itemx -malign-power
7416 @opindex malign-natural
7417 @opindex malign-power
7418 On AIX, Darwin, and 64-bit PowerPC Linux, the option
7419 @option{-malign-natural} overrides the ABI-defined alignment of larger
7420 types, such as floating-point doubles, on their natural size-based boundary.
7421 The option @option{-malign-power} instructs GCC to follow the ABI-specified
7422 alignment rules. GCC defaults to the standard alignment defined in the ABI.
7426 @opindex msoft-float
7427 @opindex mhard-float
7428 Generate code that does not use (uses) the floating-point register set.
7429 Software floating point emulation is provided if you use the
7430 @option{-msoft-float} option, and pass the option to GCC when linking.
7433 @itemx -mno-multiple
7435 @opindex mno-multiple
7436 Generate code that uses (does not use) the load multiple word
7437 instructions and the store multiple word instructions. These
7438 instructions are generated by default on POWER systems, and not
7439 generated on PowerPC systems. Do not use @option{-mmultiple} on little
7440 endian PowerPC systems, since those instructions do not work when the
7441 processor is in little endian mode. The exceptions are PPC740 and
7442 PPC750 which permit the instructions usage in little endian mode.
7448 Generate code that uses (does not use) the load string instructions
7449 and the store string word instructions to save multiple registers and
7450 do small block moves. These instructions are generated by default on
7451 POWER systems, and not generated on PowerPC systems. Do not use
7452 @option{-mstring} on little endian PowerPC systems, since those
7453 instructions do not work when the processor is in little endian mode.
7454 The exceptions are PPC740 and PPC750 which permit the instructions
7455 usage in little endian mode.
7461 Generate code that uses (does not use) the load or store instructions
7462 that update the base register to the address of the calculated memory
7463 location. These instructions are generated by default. If you use
7464 @option{-mno-update}, there is a small window between the time that the
7465 stack pointer is updated and the address of the previous frame is
7466 stored, which means code that walks the stack frame across interrupts or
7467 signals may get corrupted data.
7470 @itemx -mno-fused-madd
7471 @opindex mfused-madd
7472 @opindex mno-fused-madd
7473 Generate code that uses (does not use) the floating point multiply and
7474 accumulate instructions. These instructions are generated by default if
7475 hardware floating is used.
7477 @item -mno-bit-align
7479 @opindex mno-bit-align
7481 On System V.4 and embedded PowerPC systems do not (do) force structures
7482 and unions that contain bit-fields to be aligned to the base type of the
7485 For example, by default a structure containing nothing but 8
7486 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
7487 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
7488 the structure would be aligned to a 1 byte boundary and be one byte in
7491 @item -mno-strict-align
7492 @itemx -mstrict-align
7493 @opindex mno-strict-align
7494 @opindex mstrict-align
7495 On System V.4 and embedded PowerPC systems do not (do) assume that
7496 unaligned memory references will be handled by the system.
7499 @itemx -mno-relocatable
7500 @opindex mrelocatable
7501 @opindex mno-relocatable
7502 On embedded PowerPC systems generate code that allows (does not allow)
7503 the program to be relocated to a different address at runtime. If you
7504 use @option{-mrelocatable} on any module, all objects linked together must
7505 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
7507 @item -mrelocatable-lib
7508 @itemx -mno-relocatable-lib
7509 @opindex mrelocatable-lib
7510 @opindex mno-relocatable-lib
7511 On embedded PowerPC systems generate code that allows (does not allow)
7512 the program to be relocated to a different address at runtime. Modules
7513 compiled with @option{-mrelocatable-lib} can be linked with either modules
7514 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
7515 with modules compiled with the @option{-mrelocatable} options.
7521 On System V.4 and embedded PowerPC systems do not (do) assume that
7522 register 2 contains a pointer to a global area pointing to the addresses
7523 used in the program.
7526 @itemx -mlittle-endian
7528 @opindex mlittle-endian
7529 On System V.4 and embedded PowerPC systems compile code for the
7530 processor in little endian mode. The @option{-mlittle-endian} option is
7531 the same as @option{-mlittle}.
7536 @opindex mbig-endian
7537 On System V.4 and embedded PowerPC systems compile code for the
7538 processor in big endian mode. The @option{-mbig-endian} option is
7539 the same as @option{-mbig}.
7541 @item -mdynamic-no-pic
7542 @opindex mdynamic-no-pic
7543 On Darwin and Mac OS X systems, compile code so that it is not
7544 relocatable, but that its external references are relocatable. The
7545 resulting code is suitable for applications, but not shared
7548 @item -mprioritize-restricted-insns=@var{priority}
7549 @opindex mprioritize-restricted-insns
7550 This option controls the priority that is assigned to
7551 dispatch-slot restricted instructions during the second scheduling
7552 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
7553 @var{no/highest/second-highest} priority to dispatch slot restricted
7556 @item -msched-costly-dep=@var{dependence_type}
7557 @opindex msched-costly-dep
7558 This option controls which dependences are considered costly
7559 by the target during instruction scheduling. The argument
7560 @var{dependence_type} takes one of the following values:
7561 @var{no}: no dependence is costly,
7562 @var{all}: all dependences are costly,
7563 @var{true_store_to_load}: a true dependence from store to load is costly,
7564 @var{store_to_load}: any dependence from store to load is costly,
7565 @var{number}: any dependence which latency >= @var{number} is costly.
7567 @item -minsert-sched-nops=@var{scheme}
7568 @opindex minsert-sched-nops
7569 This option controls which nop insertion scheme will be used during
7570 the second scheduling pass. The argument @var{scheme} takes one of the
7572 @var{no}: Don't insert nops.
7573 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
7574 according to the scheduler's grouping.
7575 @var{regroup_exact}: Insert nops to force costly dependent insns into
7576 separate groups. Insert exactly as many nops as needed to force an insn
7577 to a new group, according to the estimatied processor grouping.
7578 @var{number}: Insert nops to force costly dependent insns into
7579 separate groups. Insert @var{number} nops to force an insn to a new group.
7583 On System V.4 and embedded PowerPC systems compile code using calling
7584 conventions that adheres to the March 1995 draft of the System V
7585 Application Binary Interface, PowerPC processor supplement. This is the
7586 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
7588 @item -mcall-sysv-eabi
7589 @opindex mcall-sysv-eabi
7590 Specify both @option{-mcall-sysv} and @option{-meabi} options.
7592 @item -mcall-sysv-noeabi
7593 @opindex mcall-sysv-noeabi
7594 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
7596 @item -mcall-solaris
7597 @opindex mcall-solaris
7598 On System V.4 and embedded PowerPC systems compile code for the Solaris
7602 @opindex mcall-linux
7603 On System V.4 and embedded PowerPC systems compile code for the
7604 Linux-based GNU system.
7608 On System V.4 and embedded PowerPC systems compile code for the
7609 Hurd-based GNU system.
7612 @opindex mcall-netbsd
7613 On System V.4 and embedded PowerPC systems compile code for the
7614 NetBSD operating system.
7616 @item -maix-struct-return
7617 @opindex maix-struct-return
7618 Return all structures in memory (as specified by the AIX ABI)@.
7620 @item -msvr4-struct-return
7621 @opindex msvr4-struct-return
7622 Return structures smaller than 8 bytes in registers (as specified by the
7626 @opindex mabi=altivec
7627 Extend the current ABI with AltiVec ABI extensions. This does not
7628 change the default ABI, instead it adds the AltiVec ABI extensions to
7631 @item -mabi=no-altivec
7632 @opindex mabi=no-altivec
7633 Disable AltiVec ABI extensions for the current ABI.
7636 @itemx -mno-prototype
7638 @opindex mno-prototype
7639 On System V.4 and embedded PowerPC systems assume that all calls to
7640 variable argument functions are properly prototyped. Otherwise, the
7641 compiler must insert an instruction before every non prototyped call to
7642 set or clear bit 6 of the condition code register (@var{CR}) to
7643 indicate whether floating point values were passed in the floating point
7644 registers in case the function takes a variable arguments. With
7645 @option{-mprototype}, only calls to prototyped variable argument functions
7646 will set or clear the bit.
7650 On embedded PowerPC systems, assume that the startup module is called
7651 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
7652 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
7657 On embedded PowerPC systems, assume that the startup module is called
7658 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
7663 On embedded PowerPC systems, assume that the startup module is called
7664 @file{crt0.o} and the standard C libraries are @file{libads.a} and
7668 @opindex myellowknife
7669 On embedded PowerPC systems, assume that the startup module is called
7670 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
7675 On System V.4 and embedded PowerPC systems, specify that you are
7676 compiling for a VxWorks system.
7680 Specify that you are compiling for the WindISS simulation environment.
7684 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
7685 header to indicate that @samp{eabi} extended relocations are used.
7691 On System V.4 and embedded PowerPC systems do (do not) adhere to the
7692 Embedded Applications Binary Interface (eabi) which is a set of
7693 modifications to the System V.4 specifications. Selecting @option{-meabi}
7694 means that the stack is aligned to an 8 byte boundary, a function
7695 @code{__eabi} is called to from @code{main} to set up the eabi
7696 environment, and the @option{-msdata} option can use both @code{r2} and
7697 @code{r13} to point to two separate small data areas. Selecting
7698 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
7699 do not call an initialization function from @code{main}, and the
7700 @option{-msdata} option will only use @code{r13} to point to a single
7701 small data area. The @option{-meabi} option is on by default if you
7702 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
7705 @opindex msdata=eabi
7706 On System V.4 and embedded PowerPC systems, put small initialized
7707 @code{const} global and static data in the @samp{.sdata2} section, which
7708 is pointed to by register @code{r2}. Put small initialized
7709 non-@code{const} global and static data in the @samp{.sdata} section,
7710 which is pointed to by register @code{r13}. Put small uninitialized
7711 global and static data in the @samp{.sbss} section, which is adjacent to
7712 the @samp{.sdata} section. The @option{-msdata=eabi} option is
7713 incompatible with the @option{-mrelocatable} option. The
7714 @option{-msdata=eabi} option also sets the @option{-memb} option.
7717 @opindex msdata=sysv
7718 On System V.4 and embedded PowerPC systems, put small global and static
7719 data in the @samp{.sdata} section, which is pointed to by register
7720 @code{r13}. Put small uninitialized global and static data in the
7721 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
7722 The @option{-msdata=sysv} option is incompatible with the
7723 @option{-mrelocatable} option.
7725 @item -msdata=default
7727 @opindex msdata=default
7729 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
7730 compile code the same as @option{-msdata=eabi}, otherwise compile code the
7731 same as @option{-msdata=sysv}.
7734 @opindex msdata-data
7735 On System V.4 and embedded PowerPC systems, put small global and static
7736 data in the @samp{.sdata} section. Put small uninitialized global and
7737 static data in the @samp{.sbss} section. Do not use register @code{r13}
7738 to address small data however. This is the default behavior unless
7739 other @option{-msdata} options are used.
7743 @opindex msdata=none
7745 On embedded PowerPC systems, put all initialized global and static data
7746 in the @samp{.data} section, and all uninitialized data in the
7747 @samp{.bss} section.
7751 @cindex smaller data references (PowerPC)
7752 @cindex .sdata/.sdata2 references (PowerPC)
7753 On embedded PowerPC systems, put global and static items less than or
7754 equal to @var{num} bytes into the small data or bss sections instead of
7755 the normal data or bss section. By default, @var{num} is 8. The
7756 @option{-G @var{num}} switch is also passed to the linker.
7757 All modules should be compiled with the same @option{-G @var{num}} value.
7760 @itemx -mno-regnames
7762 @opindex mno-regnames
7763 On System V.4 and embedded PowerPC systems do (do not) emit register
7764 names in the assembly language output using symbolic forms.
7767 @itemx -mno-longcall
7769 @opindex mno-longcall
7770 Default to making all function calls via pointers, so that functions
7771 which reside further than 64 megabytes (67,108,864 bytes) from the
7772 current location can be called. This setting can be overridden by the
7773 @code{shortcall} function attribute, or by @code{#pragma longcall(0)}.
7775 Some linkers are capable of detecting out-of-range calls and generating
7776 glue code on the fly. On these systems, long calls are unnecessary and
7777 generate slower code. As of this writing, the AIX linker can do this,
7778 as can the GNU linker for PowerPC/64. It is planned to add this feature
7779 to the GNU linker for 32-bit PowerPC systems as well.
7781 In the future, we may cause GCC to ignore all longcall specifications
7782 when the linker is known to generate glue.
7786 Adds support for multithreading with the @dfn{pthreads} library.
7787 This option sets flags for both the preprocessor and linker.
7791 @node Darwin Options
7792 @subsection Darwin Options
7793 @cindex Darwin options
7795 These options are defined for all architectures running the Darwin operating
7796 system. They are useful for compatibility with other Mac OS compilers.
7801 Loads all members of static archive libraries.
7802 See man ld(1) for more information.
7804 @item -arch_errors_fatal
7805 @opindex arch_errors_fatal
7806 Cause the errors having to do with files that have the wrong architecture
7810 @opindex bind_at_load
7811 Causes the output file to be marked such that the dynamic linker will
7812 bind all undefined references when the file is loaded or launched.
7816 Produce a Mach-o bundle format file.
7817 See man ld(1) for more information.
7819 @item -bundle_loader @var{executable}
7820 @opindex bundle_loader
7821 This specifies the @var{executable} that will be loading the build
7822 output file being linked. See man ld(1) for more information.
7824 @item -allowable_client @var{client_name}
7828 @item -compatibility_version
7829 @item -current_version
7830 @item -dependency-file
7832 @item -dylinker_install_name
7835 @item -exported_symbols_list
7837 @item -flat_namespace
7838 @item -force_cpusubtype_ALL
7839 @item -force_flat_namespace
7840 @item -headerpad_max_install_names
7844 @item -keep_private_externs
7846 @item -multiply_defined
7847 @item -multiply_defined_unused
7849 @item -nofixprebinding
7852 @item -noseglinkedit
7853 @item -pagezero_size
7855 @item -prebind_all_twolevel_modules
7856 @item -private_bundle
7857 @item -read_only_relocs
7859 @item -sectobjectsymbols
7863 @item -sectobjectsymbols
7865 @item -seg_addr_table
7866 @item -seg_addr_table_filename
7869 @item -segs_read_only_addr
7870 @item -segs_read_write_addr
7871 @item -single_module
7875 @item -twolevel_namespace
7878 @item -unexported_symbols_list
7879 @item -weak_reference_mismatches
7882 @opindex allowable_client
7884 @opindex client_name
7885 @opindex compatibility_version
7886 @opindex current_version
7887 @opindex dependency-file
7889 @opindex dylinker_install_name
7892 @opindex exported_symbols_list
7894 @opindex flat_namespace
7895 @opindex force_cpusubtype_ALL
7896 @opindex force_flat_namespace
7897 @opindex headerpad_max_install_names
7900 @opindex install_name
7901 @opindex keep_private_externs
7902 @opindex multi_module
7903 @opindex multiply_defined
7904 @opindex multiply_defined_unused
7906 @opindex nofixprebinding
7907 @opindex nomultidefs
7909 @opindex noseglinkedit
7910 @opindex pagezero_size
7912 @opindex prebind_all_twolevel_modules
7913 @opindex private_bundle
7914 @opindex read_only_relocs
7916 @opindex sectobjectsymbols
7920 @opindex sectobjectsymbols
7922 @opindex seg_addr_table
7923 @opindex seg_addr_table_filename
7924 @opindex seglinkedit
7926 @opindex segs_read_only_addr
7927 @opindex segs_read_write_addr
7928 @opindex single_module
7930 @opindex sub_library
7931 @opindex sub_umbrella
7932 @opindex twolevel_namespace
7935 @opindex unexported_symbols_list
7936 @opindex weak_reference_mismatches
7937 @opindex whatsloaded
7939 This options are available for Darwin linker. Darwin linker man page
7940 describes them in detail.
7945 @subsection IBM RT Options
7947 @cindex IBM RT options
7949 These @samp{-m} options are defined for the IBM RT PC:
7953 @opindex min-line-mul
7954 Use an in-line code sequence for integer multiplies. This is the
7957 @item -mcall-lib-mul
7958 @opindex mcall-lib-mul
7959 Call @code{lmul$$} for integer multiples.
7961 @item -mfull-fp-blocks
7962 @opindex mfull-fp-blocks
7963 Generate full-size floating point data blocks, including the minimum
7964 amount of scratch space recommended by IBM@. This is the default.
7966 @item -mminimum-fp-blocks
7967 @opindex mminimum-fp-blocks
7968 Do not include extra scratch space in floating point data blocks. This
7969 results in smaller code, but slower execution, since scratch space must
7970 be allocated dynamically.
7972 @cindex @file{stdarg.h} and RT PC
7973 @item -mfp-arg-in-fpregs
7974 @opindex mfp-arg-in-fpregs
7975 Use a calling sequence incompatible with the IBM calling convention in
7976 which floating point arguments are passed in floating point registers.
7977 Note that @code{stdarg.h} will not work with floating point operands
7978 if this option is specified.
7980 @item -mfp-arg-in-gregs
7981 @opindex mfp-arg-in-gregs
7982 Use the normal calling convention for floating point arguments. This is
7985 @item -mhc-struct-return
7986 @opindex mhc-struct-return
7987 Return structures of more than one word in memory, rather than in a
7988 register. This provides compatibility with the MetaWare HighC (hc)
7989 compiler. Use the option @option{-fpcc-struct-return} for compatibility
7990 with the Portable C Compiler (pcc).
7992 @item -mnohc-struct-return
7993 @opindex mnohc-struct-return
7994 Return some structures of more than one word in registers, when
7995 convenient. This is the default. For compatibility with the
7996 IBM-supplied compilers, use the option @option{-fpcc-struct-return} or the
7997 option @option{-mhc-struct-return}.
8001 @subsection MIPS Options
8002 @cindex MIPS options
8004 These @samp{-m} options are defined for the MIPS family of computers:
8008 @item -march=@var{arch}
8010 Generate code that will run on @var{arch}, which can be the name of a
8011 generic MIPS ISA, or the name of a particular processor.
8013 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
8014 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
8015 The processor names are:
8016 @samp{4kc}, @samp{4kp}, @samp{5kc}, @samp{20kc},
8018 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
8019 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000}, @samp{rm7000},
8023 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4300},
8024 @samp{vr5000}, @samp{vr5400} and @samp{vr5500}.
8025 The special value @samp{from-abi} selects the
8026 most compatible architecture for the selected ABI (that is,
8027 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
8029 In processor names, a final @samp{000} can be abbreviated as @samp{k}
8030 (for example, @samp{-march=r2k}). Prefixes are optional, and
8031 @samp{vr} may be written @samp{r}.
8033 GCC defines two macros based on the value of this option. The first
8034 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
8035 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
8036 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
8037 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
8038 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
8040 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
8041 above. In other words, it will have the full prefix and will not
8042 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
8043 the macro names the resolved architecture (either @samp{"mips1"} or
8044 @samp{"mips3"}). It names the default architecture when no
8045 @option{-march} option is given.
8047 @item -mtune=@var{arch}
8049 Optimize for @var{arch}. Among other things, this option controls
8050 the way instructions are scheduled, and the perceived cost of arithmetic
8051 operations. The list of @var{arch} values is the same as for
8054 When this option is not used, GCC will optimize for the processor
8055 specified by @option{-march}. By using @option{-march} and
8056 @option{-mtune} together, it is possible to generate code that will
8057 run on a family of processors, but optimize the code for one
8058 particular member of that family.
8060 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
8061 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
8062 @samp{-march} ones described above.
8066 Equivalent to @samp{-march=mips1}.
8070 Equivalent to @samp{-march=mips2}.
8074 Equivalent to @samp{-march=mips3}.
8078 Equivalent to @samp{-march=mips4}.
8082 Equivalent to @samp{-march=mips32}.
8086 Equivalent to @samp{-march=mips32r2}.
8090 Equivalent to @samp{-march=mips64}.
8093 @itemx -mno-fused-madd
8094 @opindex mfused-madd
8095 @opindex mno-fused-madd
8096 Generate code that uses (does not use) the floating point multiply and
8097 accumulate instructions, when they are available. These instructions
8098 are generated by default if they are available, but this may be
8099 undesirable if the extra precision causes problems or on certain chips
8100 in the mode where denormals are rounded to zero where denormals
8101 generated by multiply and accumulate instructions cause exceptions
8106 Assume that floating point registers are 32 bits wide.
8110 Assume that floating point registers are 64 bits wide.
8114 Assume that general purpose registers are 32 bits wide.
8118 Assume that general purpose registers are 64 bits wide.
8122 Force int and long types to be 64 bits wide. See @option{-mlong32} for an
8123 explanation of the default, and the width of pointers.
8127 Force long types to be 64 bits wide. See @option{-mlong32} for an
8128 explanation of the default, and the width of pointers.
8132 Force long, int, and pointer types to be 32 bits wide.
8134 The default size of ints, longs and pointers depends on the ABI@. All
8135 the supported ABIs use 32-bit ints. The n64 ABI uses 64-bit longs, as
8136 does the 64-bit Cygnus EABI; the others use 32-bit longs. Pointers
8137 are the same size as longs, or the same size as integer registers,
8138 whichever is smaller.
8152 Generate code for the given ABI@.
8154 Note that there are two embedded ABIs: @option{-mabi=eabi}
8155 selects the one defined by Cygnus while @option{-meabi=meabi}
8156 selects the one defined by MIPS@. Both these ABIs have
8157 32-bit and 64-bit variants. Normally, GCC will generate
8158 64-bit code when you select a 64-bit architecture, but you
8159 can use @option{-mgp32} to get 32-bit code instead.
8161 @item -mabi-fake-default
8162 @opindex mabi-fake-default
8163 You don't want to know what this option does. No, really. I mean
8164 it. Move on to the next option.
8166 What? You're still here? Oh, well@enddots{} Ok, here's the deal. GCC
8167 wants the default set of options to get the root of the multilib tree,
8168 and the shared library SONAMEs without any multilib-indicating
8169 suffixes. This is not convenience for @samp{mips64-linux-gnu}, since
8170 we want to default to the N32 ABI, while still being binary-compatible
8171 with @samp{mips-linux-gnu} if you stick to the O32 ABI@. Being
8172 binary-compatible means shared libraries should have the same SONAMEs,
8173 and libraries should live in the same location. Having O32 libraries
8174 in a sub-directory named say @file{o32} is not acceptable.
8176 So we trick GCC into believing that O32 is the default ABI, except
8177 that we override the default with some internal command-line
8178 processing magic. Problem is, if we stopped at that, and you then
8179 created a multilib-aware package that used the output of @command{gcc
8180 -print-multi-lib} to decide which multilibs to build, and how, and
8181 you'd find yourself in an awkward situation when you found out that
8182 some of the options listed ended up mapping to the same multilib, and
8183 none of your libraries was actually built for the multilib that
8184 @option{-print-multi-lib} claims to be the default. So we added this
8185 option that disables the default switcher, falling back to GCC's
8186 original notion of the default library. Confused yet?
8188 For short: don't ever use this option, unless you find it in the list
8189 of additional options to be used when building for multilibs, in the
8190 output of @option{gcc -print-multi-lib}.
8194 Generate code for the MIPS assembler, and invoke @file{mips-tfile} to
8195 add normal debug information. This is the default for all
8196 platforms except for the OSF/1 reference platform, using the OSF/rose
8197 object format. If the either of the @option{-gstabs} or @option{-gstabs+}
8198 switches are used, the @file{mips-tfile} program will encapsulate the
8199 stabs within MIPS ECOFF@.
8203 Generate code for the GNU assembler. This is the default on the OSF/1
8204 reference platform, using the OSF/rose object format. Also, this is
8205 the default if the configure option @option{--with-gnu-as} is used.
8207 @item -msplit-addresses
8208 @itemx -mno-split-addresses
8209 @opindex msplit-addresses
8210 @opindex mno-split-addresses
8211 Generate code to load the high and low parts of address constants separately.
8212 This allows GCC to optimize away redundant loads of the high order
8213 bits of addresses. This optimization requires GNU as and GNU ld.
8214 This optimization is enabled by default for some embedded targets where
8215 GNU as and GNU ld are standard.
8221 The @option{-mrnames} switch says to output code using the MIPS software
8222 names for the registers, instead of the hardware names (ie, @var{a0}
8223 instead of @var{$4}). The only known assembler that supports this option
8224 is the Algorithmics assembler.
8230 The @option{-mmemcpy} switch makes all block moves call the appropriate
8231 string function (@samp{memcpy} or @samp{bcopy}) instead of possibly
8232 generating inline code.
8235 @itemx -mno-mips-tfile
8236 @opindex mmips-tfile
8237 @opindex mno-mips-tfile
8238 The @option{-mno-mips-tfile} switch causes the compiler not
8239 postprocess the object file with the @file{mips-tfile} program,
8240 after the MIPS assembler has generated it to add debug support. If
8241 @file{mips-tfile} is not run, then no local variables will be
8242 available to the debugger. In addition, @file{stage2} and
8243 @file{stage3} objects will have the temporary file names passed to the
8244 assembler embedded in the object file, which means the objects will
8245 not compare the same. The @option{-mno-mips-tfile} switch should only
8246 be used when there are bugs in the @file{mips-tfile} program that
8247 prevents compilation.
8250 @opindex msoft-float
8251 Generate output containing library calls for floating point.
8252 @strong{Warning:} the requisite libraries are not part of GCC@.
8253 Normally the facilities of the machine's usual C compiler are used, but
8254 this can't be done directly in cross-compilation. You must make your
8255 own arrangements to provide suitable library functions for
8259 @opindex mhard-float
8260 Generate output containing floating point instructions. This is the
8261 default if you use the unmodified sources.
8264 @itemx -mno-abicalls
8266 @opindex mno-abicalls
8267 Emit (or do not emit) the pseudo operations @samp{.abicalls},
8268 @samp{.cpload}, and @samp{.cprestore} that some System V.4 ports use for
8269 position independent code.
8275 Lift (or do not lift) the usual restrictions on the size of the global
8278 GCC normally uses a single instruction to load values from the GOT.
8279 While this is relatively efficient, it will only work if the GOT
8280 is smaller than about 64k. Anything larger will cause the linker
8281 to report an error such as:
8283 @cindex relocation truncated to fit (MIPS)
8285 relocation truncated to fit: R_MIPS_GOT16 foobar
8288 If this happens, you should recompile your code with @option{-mxgot}.
8289 It should then work with very large GOTs, although it will also be
8290 less efficient, since it will take three instructions to fetch the
8291 value of a global symbol.
8293 Note that some linkers can create multiple GOTs. If you have such a
8294 linker, you should only need to use @option{-mxgot} when a single object
8295 file accesses more than 64k's worth of GOT entries. Very few do.
8297 These options have no effect unless GCC is generating position
8301 @itemx -mno-long-calls
8302 @opindex mlong-calls
8303 @opindex mno-long-calls
8304 Do all calls with the @samp{JALR} instruction, which requires
8305 loading up a function's address into a register before the call.
8306 You need to use this switch, if you call outside of the current
8307 512 megabyte segment to functions that are not through pointers.
8309 @item -membedded-pic
8310 @itemx -mno-embedded-pic
8311 @opindex membedded-pic
8312 @opindex mno-embedded-pic
8313 Generate PIC code suitable for some embedded systems. All calls are
8314 made using PC relative address, and all data is addressed using the $gp
8315 register. No more than 65536 bytes of global data may be used. This
8316 requires GNU as and GNU ld which do most of the work. This currently
8317 only works on targets which use ECOFF; it does not work with ELF@.
8319 @item -membedded-data
8320 @itemx -mno-embedded-data
8321 @opindex membedded-data
8322 @opindex mno-embedded-data
8323 Allocate variables to the read-only data section first if possible, then
8324 next in the small data section if possible, otherwise in data. This gives
8325 slightly slower code than the default, but reduces the amount of RAM required
8326 when executing, and thus may be preferred for some embedded systems.
8328 @item -muninit-const-in-rodata
8329 @itemx -mno-uninit-const-in-rodata
8330 @opindex muninit-const-in-rodata
8331 @opindex mno-uninit-const-in-rodata
8332 When used together with @option{-membedded-data}, it will always store uninitialized
8333 const variables in the read-only data section.
8335 @item -msingle-float
8336 @itemx -mdouble-float
8337 @opindex msingle-float
8338 @opindex mdouble-float
8339 The @option{-msingle-float} switch tells gcc to assume that the floating
8340 point coprocessor only supports single precision operations, as on the
8341 @samp{r4650} chip. The @option{-mdouble-float} switch permits gcc to use
8342 double precision operations. This is the default.
8348 Permit use of the @samp{mad}, @samp{madu} and @samp{mul} instructions,
8349 as on the @samp{r4650} chip.
8353 Turns on @option{-msingle-float}, @option{-mmad}, and, at least for now,
8354 @option{-mcpu=r4650}.
8360 Enable 16-bit instructions.
8364 Compile code for the processor in little endian mode.
8365 The requisite libraries are assumed to exist.
8369 Compile code for the processor in big endian mode.
8370 The requisite libraries are assumed to exist.
8374 @cindex smaller data references (MIPS)
8375 @cindex gp-relative references (MIPS)
8376 Put global and static items less than or equal to @var{num} bytes into
8377 the small data or bss sections instead of the normal data or bss
8378 section. This allows the assembler to emit one word memory reference
8379 instructions based on the global pointer (@var{gp} or @var{$28}),
8380 instead of the normal two words used. By default, @var{num} is 8 when
8381 the MIPS assembler is used, and 0 when the GNU assembler is used. The
8382 @option{-G @var{num}} switch is also passed to the assembler and linker.
8383 All modules should be compiled with the same @option{-G @var{num}}
8388 Tell the MIPS assembler to not run its preprocessor over user
8389 assembler files (with a @samp{.s} suffix) when assembling them.
8393 Pass an option to gas which will cause nops to be inserted if
8394 the read of the destination register of an mfhi or mflo instruction
8395 occurs in the following two instructions.
8400 Work around certain SB-1 CPU core errata.
8401 (This flag currently works around the SB-1 revision 2
8402 ``F1'' and ``F2'' floating point errata.)
8406 Do not include the default crt0.
8408 @item -mflush-func=@var{func}
8409 @itemx -mno-flush-func
8410 @opindex mflush-func
8411 Specifies the function to call to flush the I and D caches, or to not
8412 call any such function. If called, the function must take the same
8413 arguments as the common @code{_flush_func()}, that is, the address of the
8414 memory range for which the cache is being flushed, the size of the
8415 memory range, and the number 3 (to flush both caches). The default
8416 depends on the target gcc was configured for, but commonly is either
8417 @samp{_flush_func} or @samp{__cpu_flush}.
8419 @item -mbranch-likely
8420 @itemx -mno-branch-likely
8421 @opindex mbranch-likely
8422 @opindex mno-branch-likely
8423 Enable or disable use of Branch Likely instructions, regardless of the
8424 default for the selected architecture. By default, Branch Likely
8425 instructions may be generated if they are supported by the selected
8426 architecture. An exception is for the MIPS32 and MIPS64 architectures
8427 and processors which implement those architectures; for those, Branch
8428 Likely instructions will not be generated by default because the MIPS32
8429 and MIPS64 architectures specifically deprecate their use.
8432 @node i386 and x86-64 Options
8433 @subsection Intel 386 and AMD x86-64 Options
8434 @cindex i386 Options
8435 @cindex x86-64 Options
8436 @cindex Intel 386 Options
8437 @cindex AMD x86-64 Options
8439 These @samp{-m} options are defined for the i386 and x86-64 family of
8443 @item -mtune=@var{cpu-type}
8445 Tune to @var{cpu-type} everything applicable about the generated code, except
8446 for the ABI and the set of available instructions. The choices for
8447 @var{cpu-type} are @samp{i386}, @samp{i486}, @samp{i586}, @samp{i686},
8448 @samp{pentium}, @samp{pentium-mmx}, @samp{pentiumpro}, @samp{pentium2},
8449 @samp{pentium3}, @samp{pentium4}, @samp{k6}, @samp{k6-2}, @samp{k6-3},
8450 @samp{athlon}, @samp{athlon-tbird}, @samp{athlon-4}, @samp{athlon-xp},
8451 @samp{athlon-mp}, @samp{winchip-c6}, @samp{winchip2}, @samp{k8}, @samp{c3}
8454 While picking a specific @var{cpu-type} will schedule things appropriately
8455 for that particular chip, the compiler will not generate any code that
8456 does not run on the i386 without the @option{-march=@var{cpu-type}} option
8457 being used. @samp{i586} is equivalent to @samp{pentium} and @samp{i686}
8458 is equivalent to @samp{pentiumpro}. @samp{k6} and @samp{athlon} are the
8459 AMD chips as opposed to the Intel ones.
8461 @item -march=@var{cpu-type}
8463 Generate instructions for the machine type @var{cpu-type}. The choices
8464 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
8465 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
8467 @item -mcpu=@var{cpu-type}
8469 A deprecated synonym for @option{-mtune}.
8478 @opindex mpentiumpro
8479 These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
8480 @option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
8481 These synonyms are deprecated.
8483 @item -mfpmath=@var{unit}
8485 generate floating point arithmetics for selected unit @var{unit}. the choices
8490 Use the standard 387 floating point coprocessor present majority of chips and
8491 emulated otherwise. Code compiled with this option will run almost everywhere.
8492 The temporary results are computed in 80bit precision instead of precision
8493 specified by the type resulting in slightly different results compared to most
8494 of other chips. See @option{-ffloat-store} for more detailed description.
8496 This is the default choice for i386 compiler.
8499 Use scalar floating point instructions present in the SSE instruction set.
8500 This instruction set is supported by Pentium3 and newer chips, in the AMD line
8501 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
8502 instruction set supports only single precision arithmetics, thus the double and
8503 extended precision arithmetics is still done using 387. Later version, present
8504 only in Pentium4 and the future AMD x86-64 chips supports double precision
8507 For i387 you need to use @option{-march=@var{cpu-type}}, @option{-msse} or
8508 @option{-msse2} switches to enable SSE extensions and make this option
8509 effective. For x86-64 compiler, these extensions are enabled by default.
8511 The resulting code should be considerably faster in majority of cases and avoid
8512 the numerical instability problems of 387 code, but may break some existing
8513 code that expects temporaries to be 80bit.
8515 This is the default choice for x86-64 compiler.
8518 Use all SSE extensions enabled by @option{-msse2} as well as the new
8519 SSE extensions in Prescott New Instructions. @option{-mpni} also
8520 enables 2 builtin functions, @code{__builtin_ia32_monitor} and
8521 @code{__builtin_ia32_mwait}, for new instructions @code{monitor} and
8525 Attempt to utilize both instruction sets at once. This effectively double the
8526 amount of available registers and on chips with separate execution units for
8527 387 and SSE the execution resources too. Use this option with care, as it is
8528 still experimental, because gcc register allocator does not model separate
8529 functional units well resulting in instable performance.
8532 @item -masm=@var{dialect}
8533 @opindex masm=@var{dialect}
8534 Output asm instructions using selected @var{dialect}. Supported choices are
8535 @samp{intel} or @samp{att} (the default one).
8540 @opindex mno-ieee-fp
8541 Control whether or not the compiler uses IEEE floating point
8542 comparisons. These handle correctly the case where the result of a
8543 comparison is unordered.
8546 @opindex msoft-float
8547 Generate output containing library calls for floating point.
8548 @strong{Warning:} the requisite libraries are not part of GCC@.
8549 Normally the facilities of the machine's usual C compiler are used, but
8550 this can't be done directly in cross-compilation. You must make your
8551 own arrangements to provide suitable library functions for
8554 On machines where a function returns floating point results in the 80387
8555 register stack, some floating point opcodes may be emitted even if
8556 @option{-msoft-float} is used.
8558 @item -mno-fp-ret-in-387
8559 @opindex mno-fp-ret-in-387
8560 Do not use the FPU registers for return values of functions.
8562 The usual calling convention has functions return values of types
8563 @code{float} and @code{double} in an FPU register, even if there
8564 is no FPU@. The idea is that the operating system should emulate
8567 The option @option{-mno-fp-ret-in-387} causes such values to be returned
8568 in ordinary CPU registers instead.
8570 @item -mno-fancy-math-387
8571 @opindex mno-fancy-math-387
8572 Some 387 emulators do not support the @code{sin}, @code{cos} and
8573 @code{sqrt} instructions for the 387. Specify this option to avoid
8574 generating those instructions. This option is the default on FreeBSD,
8575 OpenBSD and NetBSD@. This option is overridden when @option{-march}
8576 indicates that the target cpu will always have an FPU and so the
8577 instruction will not need emulation. As of revision 2.6.1, these
8578 instructions are not generated unless you also use the
8579 @option{-funsafe-math-optimizations} switch.
8581 @item -malign-double
8582 @itemx -mno-align-double
8583 @opindex malign-double
8584 @opindex mno-align-double
8585 Control whether GCC aligns @code{double}, @code{long double}, and
8586 @code{long long} variables on a two word boundary or a one word
8587 boundary. Aligning @code{double} variables on a two word boundary will
8588 produce code that runs somewhat faster on a @samp{Pentium} at the
8589 expense of more memory.
8591 @strong{Warning:} if you use the @option{-malign-double} switch,
8592 structures containing the above types will be aligned differently than
8593 the published application binary interface specifications for the 386
8594 and will not be binary compatible with structures in code compiled
8595 without that switch.
8597 @item -m96bit-long-double
8598 @item -m128bit-long-double
8599 @opindex m96bit-long-double
8600 @opindex m128bit-long-double
8601 These switches control the size of @code{long double} type. The i386
8602 application binary interface specifies the size to be 96 bits,
8603 so @option{-m96bit-long-double} is the default in 32 bit mode.
8605 Modern architectures (Pentium and newer) would prefer @code{long double}
8606 to be aligned to an 8 or 16 byte boundary. In arrays or structures
8607 conforming to the ABI, this would not be possible. So specifying a
8608 @option{-m128bit-long-double} will align @code{long double}
8609 to a 16 byte boundary by padding the @code{long double} with an additional
8612 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
8613 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
8615 Notice that neither of these options enable any extra precision over the x87
8616 standard of 80 bits for a @code{long double}.
8618 @strong{Warning:} if you override the default value for your target ABI, the
8619 structures and arrays containing @code{long double} will change their size as
8620 well as function calling convention for function taking @code{long double}
8621 will be modified. Hence they will not be binary compatible with arrays or
8622 structures in code compiled without that switch.
8626 @itemx -mno-svr3-shlib
8627 @opindex msvr3-shlib
8628 @opindex mno-svr3-shlib
8629 Control whether GCC places uninitialized local variables into the
8630 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
8631 into @code{bss}. These options are meaningful only on System V Release 3.
8635 Use a different function-calling convention, in which functions that
8636 take a fixed number of arguments return with the @code{ret} @var{num}
8637 instruction, which pops their arguments while returning. This saves one
8638 instruction in the caller since there is no need to pop the arguments
8641 You can specify that an individual function is called with this calling
8642 sequence with the function attribute @samp{stdcall}. You can also
8643 override the @option{-mrtd} option by using the function attribute
8644 @samp{cdecl}. @xref{Function Attributes}.
8646 @strong{Warning:} this calling convention is incompatible with the one
8647 normally used on Unix, so you cannot use it if you need to call
8648 libraries compiled with the Unix compiler.
8650 Also, you must provide function prototypes for all functions that
8651 take variable numbers of arguments (including @code{printf});
8652 otherwise incorrect code will be generated for calls to those
8655 In addition, seriously incorrect code will result if you call a
8656 function with too many arguments. (Normally, extra arguments are
8657 harmlessly ignored.)
8659 @item -mregparm=@var{num}
8661 Control how many registers are used to pass integer arguments. By
8662 default, no registers are used to pass arguments, and at most 3
8663 registers can be used. You can control this behavior for a specific
8664 function by using the function attribute @samp{regparm}.
8665 @xref{Function Attributes}.
8667 @strong{Warning:} if you use this switch, and
8668 @var{num} is nonzero, then you must build all modules with the same
8669 value, including any libraries. This includes the system libraries and
8672 @item -mpreferred-stack-boundary=@var{num}
8673 @opindex mpreferred-stack-boundary
8674 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
8675 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
8676 the default is 4 (16 bytes or 128 bits), except when optimizing for code
8677 size (@option{-Os}), in which case the default is the minimum correct
8678 alignment (4 bytes for x86, and 8 bytes for x86-64).
8680 On Pentium and PentiumPro, @code{double} and @code{long double} values
8681 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
8682 suffer significant run time performance penalties. On Pentium III, the
8683 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
8684 penalties if it is not 16 byte aligned.
8686 To ensure proper alignment of this values on the stack, the stack boundary
8687 must be as aligned as that required by any value stored on the stack.
8688 Further, every function must be generated such that it keeps the stack
8689 aligned. Thus calling a function compiled with a higher preferred
8690 stack boundary from a function compiled with a lower preferred stack
8691 boundary will most likely misalign the stack. It is recommended that
8692 libraries that use callbacks always use the default setting.
8694 This extra alignment does consume extra stack space, and generally
8695 increases code size. Code that is sensitive to stack space usage, such
8696 as embedded systems and operating system kernels, may want to reduce the
8697 preferred alignment to @option{-mpreferred-stack-boundary=2}.
8715 These switches enable or disable the use of built-in functions that allow
8716 direct access to the MMX, SSE and 3Dnow extensions of the instruction set.
8718 @xref{X86 Built-in Functions}, for details of the functions enabled
8719 and disabled by these switches.
8721 To have SSE/SSE2 instructions generated automatically from floating-point
8722 code, see @option{-mfpmath=sse}.
8725 @itemx -mno-push-args
8727 @opindex mno-push-args
8728 Use PUSH operations to store outgoing parameters. This method is shorter
8729 and usually equally fast as method using SUB/MOV operations and is enabled
8730 by default. In some cases disabling it may improve performance because of
8731 improved scheduling and reduced dependencies.
8733 @item -maccumulate-outgoing-args
8734 @opindex maccumulate-outgoing-args
8735 If enabled, the maximum amount of space required for outgoing arguments will be
8736 computed in the function prologue. This is faster on most modern CPUs
8737 because of reduced dependencies, improved scheduling and reduced stack usage
8738 when preferred stack boundary is not equal to 2. The drawback is a notable
8739 increase in code size. This switch implies @option{-mno-push-args}.
8743 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
8744 on thread-safe exception handling must compile and link all code with the
8745 @option{-mthreads} option. When compiling, @option{-mthreads} defines
8746 @option{-D_MT}; when linking, it links in a special thread helper library
8747 @option{-lmingwthrd} which cleans up per thread exception handling data.
8749 @item -mno-align-stringops
8750 @opindex mno-align-stringops
8751 Do not align destination of inlined string operations. This switch reduces
8752 code size and improves performance in case the destination is already aligned,
8753 but gcc don't know about it.
8755 @item -minline-all-stringops
8756 @opindex minline-all-stringops
8757 By default GCC inlines string operations only when destination is known to be
8758 aligned at least to 4 byte boundary. This enables more inlining, increase code
8759 size, but may improve performance of code that depends on fast memcpy, strlen
8760 and memset for short lengths.
8762 @item -momit-leaf-frame-pointer
8763 @opindex momit-leaf-frame-pointer
8764 Don't keep the frame pointer in a register for leaf functions. This
8765 avoids the instructions to save, set up and restore frame pointers and
8766 makes an extra register available in leaf functions. The option
8767 @option{-fomit-frame-pointer} removes the frame pointer for all functions
8768 which might make debugging harder.
8770 @item -mtls-direct-seg-refs
8771 @itemx -mno-tls-direct-seg-refs
8772 @opindex mtls-direct-seg-refs
8773 Controls whether TLS variables may be accessed with offsets from the
8774 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
8775 or whether the thread base pointer must be added. Whether or not this
8776 is legal depends on the operating system, and whether it maps the
8777 segment to cover the entire TLS area.
8779 For systems that use GNU libc, the default is on.
8782 These @samp{-m} switches are supported in addition to the above
8783 on AMD x86-64 processors in 64-bit environments.
8790 Generate code for a 32-bit or 64-bit environment.
8791 The 32-bit environment sets int, long and pointer to 32 bits and
8792 generates code that runs on any i386 system.
8793 The 64-bit environment sets int to 32 bits and long and pointer
8794 to 64 bits and generates code for AMD's x86-64 architecture.
8797 @opindex no-red-zone
8798 Do not use a so called red zone for x86-64 code. The red zone is mandated
8799 by the x86-64 ABI, it is a 128-byte area beyond the location of the
8800 stack pointer that will not be modified by signal or interrupt handlers
8801 and therefore can be used for temporary data without adjusting the stack
8802 pointer. The flag @option{-mno-red-zone} disables this red zone.
8804 @item -mcmodel=small
8805 @opindex mcmodel=small
8806 Generate code for the small code model: the program and its symbols must
8807 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
8808 Programs can be statically or dynamically linked. This is the default
8811 @item -mcmodel=kernel
8812 @opindex mcmodel=kernel
8813 Generate code for the kernel code model. The kernel runs in the
8814 negative 2 GB of the address space.
8815 This model has to be used for Linux kernel code.
8817 @item -mcmodel=medium
8818 @opindex mcmodel=medium
8819 Generate code for the medium model: The program is linked in the lower 2
8820 GB of the address space but symbols can be located anywhere in the
8821 address space. Programs can be statically or dynamically linked, but
8822 building of shared libraries are not supported with the medium model.
8824 @item -mcmodel=large
8825 @opindex mcmodel=large
8826 Generate code for the large model: This model makes no assumptions
8827 about addresses and sizes of sections. Currently GCC does not implement
8832 @subsection HPPA Options
8833 @cindex HPPA Options
8835 These @samp{-m} options are defined for the HPPA family of computers:
8838 @item -march=@var{architecture-type}
8840 Generate code for the specified architecture. The choices for
8841 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8842 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8843 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8844 architecture option for your machine. Code compiled for lower numbered
8845 architectures will run on higher numbered architectures, but not the
8848 PA 2.0 support currently requires gas snapshot 19990413 or later. The
8849 next release of binutils (current is 2.9.1) will probably contain PA 2.0
8853 @itemx -mpa-risc-1-1
8854 @itemx -mpa-risc-2-0
8855 @opindex mpa-risc-1-0
8856 @opindex mpa-risc-1-1
8857 @opindex mpa-risc-2-0
8858 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8861 @opindex mbig-switch
8862 Generate code suitable for big switch tables. Use this option only if
8863 the assembler/linker complain about out of range branches within a switch
8866 @item -mjump-in-delay
8867 @opindex mjump-in-delay
8868 Fill delay slots of function calls with unconditional jump instructions
8869 by modifying the return pointer for the function call to be the target
8870 of the conditional jump.
8872 @item -mdisable-fpregs
8873 @opindex mdisable-fpregs
8874 Prevent floating point registers from being used in any manner. This is
8875 necessary for compiling kernels which perform lazy context switching of
8876 floating point registers. If you use this option and attempt to perform
8877 floating point operations, the compiler will abort.
8879 @item -mdisable-indexing
8880 @opindex mdisable-indexing
8881 Prevent the compiler from using indexing address modes. This avoids some
8882 rather obscure problems when compiling MIG generated code under MACH@.
8884 @item -mno-space-regs
8885 @opindex mno-space-regs
8886 Generate code that assumes the target has no space registers. This allows
8887 GCC to generate faster indirect calls and use unscaled index address modes.
8889 Such code is suitable for level 0 PA systems and kernels.
8891 @item -mfast-indirect-calls
8892 @opindex mfast-indirect-calls
8893 Generate code that assumes calls never cross space boundaries. This
8894 allows GCC to emit code which performs faster indirect calls.
8896 This option will not work in the presence of shared libraries or nested
8899 @item -mlong-load-store
8900 @opindex mlong-load-store
8901 Generate 3-instruction load and store sequences as sometimes required by
8902 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8905 @item -mportable-runtime
8906 @opindex mportable-runtime
8907 Use the portable calling conventions proposed by HP for ELF systems.
8911 Enable the use of assembler directives only GAS understands.
8913 @item -mschedule=@var{cpu-type}
8915 Schedule code according to the constraints for the machine type
8916 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8917 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
8918 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
8919 proper scheduling option for your machine. The default scheduling is
8923 @opindex mlinker-opt
8924 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
8925 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
8926 linkers in which they give bogus error messages when linking some programs.
8929 @opindex msoft-float
8930 Generate output containing library calls for floating point.
8931 @strong{Warning:} the requisite libraries are not available for all HPPA
8932 targets. Normally the facilities of the machine's usual C compiler are
8933 used, but this cannot be done directly in cross-compilation. You must make
8934 your own arrangements to provide suitable library functions for
8935 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8936 does provide software floating point support.
8938 @option{-msoft-float} changes the calling convention in the output file;
8939 therefore, it is only useful if you compile @emph{all} of a program with
8940 this option. In particular, you need to compile @file{libgcc.a}, the
8941 library that comes with GCC, with @option{-msoft-float} in order for
8946 Generate the predefine, @code{_SIO}, for server IO. The default is
8947 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
8948 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO. These
8949 options are available under HP-UX and HI-UX.
8953 Use GNU ld specific options. This passes @option{-shared} to ld when
8954 building a shared library. It is the default when GCC is configured,
8955 explicitly or implicitly, with the GNU linker. This option does not
8956 have any affect on which ld is called, it only changes what parameters
8957 are passed to that ld. The ld that is called is determined by the
8958 @option{--with-ld} configure option, gcc's program search path, and
8959 finally by the user's @env{PATH}. The linker used by GCC can be printed
8960 using @samp{which `gcc -print-prog-name=ld`}.
8964 Use HP ld specific options. This passes @option{-b} to ld when building
8965 a shared library and passes @option{+Accept TypeMismatch} to ld on all
8966 links. It is the default when GCC is configured, explicitly or
8967 implicitly, with the HP linker. This option does not have any affect on
8968 which ld is called, it only changes what parameters are passed to that
8969 ld. The ld that is called is determined by the @option{--with-ld}
8970 configure option, gcc's program search path, and finally by the user's
8971 @env{PATH}. The linker used by GCC can be printed using @samp{which
8972 `gcc -print-prog-name=ld`}.
8975 @opindex mno-long-calls
8976 Generate code that uses long call sequences. This ensures that a call
8977 is always able to reach linker generated stubs. The default is to generate
8978 long calls only when the distance from the call site to the beginning
8979 of the function or translation unit, as the case may be, exceeds a
8980 predefined limit set by the branch type being used. The limits for
8981 normal calls are 7,600,000 and 240,000 bytes, respectively for the
8982 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
8985 Distances are measured from the beginning of functions when using the
8986 @option{-ffunction-sections} option, or when using the @option{-mgas}
8987 and @option{-mno-portable-runtime} options together under HP-UX with
8990 It is normally not desirable to use this option as it will degrade
8991 performance. However, it may be useful in large applications,
8992 particularly when partial linking is used to build the application.
8994 The types of long calls used depends on the capabilities of the
8995 assembler and linker, and the type of code being generated. The
8996 impact on systems that support long absolute calls, and long pic
8997 symbol-difference or pc-relative calls should be relatively small.
8998 However, an indirect call is used on 32-bit ELF systems in pic code
8999 and it is quite long.
9003 Suppress the generation of link options to search libdld.sl when the
9004 @option{-static} option is specified on HP-UX 10 and later.
9008 The HP-UX implementation of setlocale in libc has a dependency on
9009 libdld.sl. There isn't an archive version of libdld.sl. Thus,
9010 when the @option{-static} option is specified, special link options
9011 are needed to resolve this dependency.
9013 On HP-UX 10 and later, the GCC driver adds the necessary options to
9014 link with libdld.sl when the @option{-static} option is specified.
9015 This causes the resulting binary to be dynamic. On the 64-bit port,
9016 the linkers generate dynamic binaries by default in any case. The
9017 @option{-nolibdld} option can be used to prevent the GCC driver from
9018 adding these link options.
9022 Add support for multithreading with the @dfn{dce thread} library
9023 under HP-UX. This option sets flags for both the preprocessor and
9027 @node Intel 960 Options
9028 @subsection Intel 960 Options
9030 These @samp{-m} options are defined for the Intel 960 implementations:
9033 @item -m@var{cpu-type}
9041 Assume the defaults for the machine type @var{cpu-type} for some of
9042 the other options, including instruction scheduling, floating point
9043 support, and addressing modes. The choices for @var{cpu-type} are
9044 @samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf},
9045 @samp{sa}, and @samp{sb}.
9052 @opindex msoft-float
9053 The @option{-mnumerics} option indicates that the processor does support
9054 floating-point instructions. The @option{-msoft-float} option indicates
9055 that floating-point support should not be assumed.
9057 @item -mleaf-procedures
9058 @itemx -mno-leaf-procedures
9059 @opindex mleaf-procedures
9060 @opindex mno-leaf-procedures
9061 Do (or do not) attempt to alter leaf procedures to be callable with the
9062 @code{bal} instruction as well as @code{call}. This will result in more
9063 efficient code for explicit calls when the @code{bal} instruction can be
9064 substituted by the assembler or linker, but less efficient code in other
9065 cases, such as calls via function pointers, or using a linker that doesn't
9066 support this optimization.
9069 @itemx -mno-tail-call
9071 @opindex mno-tail-call
9072 Do (or do not) make additional attempts (beyond those of the
9073 machine-independent portions of the compiler) to optimize tail-recursive
9074 calls into branches. You may not want to do this because the detection of
9075 cases where this is not valid is not totally complete. The default is
9076 @option{-mno-tail-call}.
9078 @item -mcomplex-addr
9079 @itemx -mno-complex-addr
9080 @opindex mcomplex-addr
9081 @opindex mno-complex-addr
9082 Assume (or do not assume) that the use of a complex addressing mode is a
9083 win on this implementation of the i960. Complex addressing modes may not
9084 be worthwhile on the K-series, but they definitely are on the C-series.
9085 The default is currently @option{-mcomplex-addr} for all processors except
9089 @itemx -mno-code-align
9090 @opindex mcode-align
9091 @opindex mno-code-align
9092 Align code to 8-byte boundaries for faster fetching (or don't bother).
9093 Currently turned on by default for C-series implementations only.
9096 @item -mclean-linkage
9097 @itemx -mno-clean-linkage
9098 @opindex mclean-linkage
9099 @opindex mno-clean-linkage
9100 These options are not fully implemented.
9104 @itemx -mic2.0-compat
9105 @itemx -mic3.0-compat
9107 @opindex mic2.0-compat
9108 @opindex mic3.0-compat
9109 Enable compatibility with iC960 v2.0 or v3.0.
9113 @opindex masm-compat
9115 Enable compatibility with the iC960 assembler.
9117 @item -mstrict-align
9118 @itemx -mno-strict-align
9119 @opindex mstrict-align
9120 @opindex mno-strict-align
9121 Do not permit (do permit) unaligned accesses.
9125 Enable structure-alignment compatibility with Intel's gcc release version
9126 1.3 (based on gcc 1.37). This option implies @option{-mstrict-align}.
9128 @item -mlong-double-64
9129 @opindex mlong-double-64
9130 Implement type @samp{long double} as 64-bit floating point numbers.
9131 Without the option @samp{long double} is implemented by 80-bit
9132 floating point numbers. The only reason we have it because there is
9133 no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it
9134 is only useful for people using soft-float targets. Otherwise, we
9135 should recommend against use of it.
9139 @node DEC Alpha Options
9140 @subsection DEC Alpha Options
9142 These @samp{-m} options are defined for the DEC Alpha implementations:
9145 @item -mno-soft-float
9147 @opindex mno-soft-float
9148 @opindex msoft-float
9149 Use (do not use) the hardware floating-point instructions for
9150 floating-point operations. When @option{-msoft-float} is specified,
9151 functions in @file{libgcc.a} will be used to perform floating-point
9152 operations. Unless they are replaced by routines that emulate the
9153 floating-point operations, or compiled in such a way as to call such
9154 emulations routines, these routines will issue floating-point
9155 operations. If you are compiling for an Alpha without floating-point
9156 operations, you must ensure that the library is built so as not to call
9159 Note that Alpha implementations without floating-point operations are
9160 required to have floating-point registers.
9165 @opindex mno-fp-regs
9166 Generate code that uses (does not use) the floating-point register set.
9167 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
9168 register set is not used, floating point operands are passed in integer
9169 registers as if they were integers and floating-point results are passed
9170 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
9171 so any function with a floating-point argument or return value called by code
9172 compiled with @option{-mno-fp-regs} must also be compiled with that
9175 A typical use of this option is building a kernel that does not use,
9176 and hence need not save and restore, any floating-point registers.
9180 The Alpha architecture implements floating-point hardware optimized for
9181 maximum performance. It is mostly compliant with the IEEE floating
9182 point standard. However, for full compliance, software assistance is
9183 required. This option generates code fully IEEE compliant code
9184 @emph{except} that the @var{inexact-flag} is not maintained (see below).
9185 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
9186 defined during compilation. The resulting code is less efficient but is
9187 able to correctly support denormalized numbers and exceptional IEEE
9188 values such as not-a-number and plus/minus infinity. Other Alpha
9189 compilers call this option @option{-ieee_with_no_inexact}.
9191 @item -mieee-with-inexact
9192 @opindex mieee-with-inexact
9193 This is like @option{-mieee} except the generated code also maintains
9194 the IEEE @var{inexact-flag}. Turning on this option causes the
9195 generated code to implement fully-compliant IEEE math. In addition to
9196 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
9197 macro. On some Alpha implementations the resulting code may execute
9198 significantly slower than the code generated by default. Since there is
9199 very little code that depends on the @var{inexact-flag}, you should
9200 normally not specify this option. Other Alpha compilers call this
9201 option @option{-ieee_with_inexact}.
9203 @item -mfp-trap-mode=@var{trap-mode}
9204 @opindex mfp-trap-mode
9205 This option controls what floating-point related traps are enabled.
9206 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
9207 The trap mode can be set to one of four values:
9211 This is the default (normal) setting. The only traps that are enabled
9212 are the ones that cannot be disabled in software (e.g., division by zero
9216 In addition to the traps enabled by @samp{n}, underflow traps are enabled
9220 Like @samp{su}, but the instructions are marked to be safe for software
9221 completion (see Alpha architecture manual for details).
9224 Like @samp{su}, but inexact traps are enabled as well.
9227 @item -mfp-rounding-mode=@var{rounding-mode}
9228 @opindex mfp-rounding-mode
9229 Selects the IEEE rounding mode. Other Alpha compilers call this option
9230 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
9235 Normal IEEE rounding mode. Floating point numbers are rounded towards
9236 the nearest machine number or towards the even machine number in case
9240 Round towards minus infinity.
9243 Chopped rounding mode. Floating point numbers are rounded towards zero.
9246 Dynamic rounding mode. A field in the floating point control register
9247 (@var{fpcr}, see Alpha architecture reference manual) controls the
9248 rounding mode in effect. The C library initializes this register for
9249 rounding towards plus infinity. Thus, unless your program modifies the
9250 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
9253 @item -mtrap-precision=@var{trap-precision}
9254 @opindex mtrap-precision
9255 In the Alpha architecture, floating point traps are imprecise. This
9256 means without software assistance it is impossible to recover from a
9257 floating trap and program execution normally needs to be terminated.
9258 GCC can generate code that can assist operating system trap handlers
9259 in determining the exact location that caused a floating point trap.
9260 Depending on the requirements of an application, different levels of
9261 precisions can be selected:
9265 Program precision. This option is the default and means a trap handler
9266 can only identify which program caused a floating point exception.
9269 Function precision. The trap handler can determine the function that
9270 caused a floating point exception.
9273 Instruction precision. The trap handler can determine the exact
9274 instruction that caused a floating point exception.
9277 Other Alpha compilers provide the equivalent options called
9278 @option{-scope_safe} and @option{-resumption_safe}.
9280 @item -mieee-conformant
9281 @opindex mieee-conformant
9282 This option marks the generated code as IEEE conformant. You must not
9283 use this option unless you also specify @option{-mtrap-precision=i} and either
9284 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
9285 is to emit the line @samp{.eflag 48} in the function prologue of the
9286 generated assembly file. Under DEC Unix, this has the effect that
9287 IEEE-conformant math library routines will be linked in.
9289 @item -mbuild-constants
9290 @opindex mbuild-constants
9291 Normally GCC examines a 32- or 64-bit integer constant to
9292 see if it can construct it from smaller constants in two or three
9293 instructions. If it cannot, it will output the constant as a literal and
9294 generate code to load it from the data segment at runtime.
9296 Use this option to require GCC to construct @emph{all} integer constants
9297 using code, even if it takes more instructions (the maximum is six).
9299 You would typically use this option to build a shared library dynamic
9300 loader. Itself a shared library, it must relocate itself in memory
9301 before it can find the variables and constants in its own data segment.
9307 Select whether to generate code to be assembled by the vendor-supplied
9308 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
9326 Indicate whether GCC should generate code to use the optional BWX,
9327 CIX, FIX and MAX instruction sets. The default is to use the instruction
9328 sets supported by the CPU type specified via @option{-mcpu=} option or that
9329 of the CPU on which GCC was built if none was specified.
9334 @opindex mfloat-ieee
9335 Generate code that uses (does not use) VAX F and G floating point
9336 arithmetic instead of IEEE single and double precision.
9338 @item -mexplicit-relocs
9339 @itemx -mno-explicit-relocs
9340 @opindex mexplicit-relocs
9341 @opindex mno-explicit-relocs
9342 Older Alpha assemblers provided no way to generate symbol relocations
9343 except via assembler macros. Use of these macros does not allow
9344 optimal instruction scheduling. GNU binutils as of version 2.12
9345 supports a new syntax that allows the compiler to explicitly mark
9346 which relocations should apply to which instructions. This option
9347 is mostly useful for debugging, as GCC detects the capabilities of
9348 the assembler when it is built and sets the default accordingly.
9352 @opindex msmall-data
9353 @opindex mlarge-data
9354 When @option{-mexplicit-relocs} is in effect, static data is
9355 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
9356 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
9357 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
9358 16-bit relocations off of the @code{$gp} register. This limits the
9359 size of the small data area to 64KB, but allows the variables to be
9360 directly accessed via a single instruction.
9362 The default is @option{-mlarge-data}. With this option the data area
9363 is limited to just below 2GB. Programs that require more than 2GB of
9364 data must use @code{malloc} or @code{mmap} to allocate the data in the
9365 heap instead of in the program's data segment.
9367 When generating code for shared libraries, @option{-fpic} implies
9368 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
9372 @opindex msmall-text
9373 @opindex mlarge-text
9374 When @option{-msmall-text} is used, the compiler assumes that the
9375 code of the entire program (or shared library) fits in 4MB, and is
9376 thus reachable with a branch instruction. When @option{-msmall-data}
9377 is used, the compiler can assume that all local symbols share the
9378 same @code{$gp} value, and thus reduce the number of instructions
9379 required for a function call from 4 to 1.
9381 The default is @option{-mlarge-text}.
9383 @item -mcpu=@var{cpu_type}
9385 Set the instruction set and instruction scheduling parameters for
9386 machine type @var{cpu_type}. You can specify either the @samp{EV}
9387 style name or the corresponding chip number. GCC supports scheduling
9388 parameters for the EV4, EV5 and EV6 family of processors and will
9389 choose the default values for the instruction set from the processor
9390 you specify. If you do not specify a processor type, GCC will default
9391 to the processor on which the compiler was built.
9393 Supported values for @var{cpu_type} are
9399 Schedules as an EV4 and has no instruction set extensions.
9403 Schedules as an EV5 and has no instruction set extensions.
9407 Schedules as an EV5 and supports the BWX extension.
9412 Schedules as an EV5 and supports the BWX and MAX extensions.
9416 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
9420 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
9423 @item -mtune=@var{cpu_type}
9425 Set only the instruction scheduling parameters for machine type
9426 @var{cpu_type}. The instruction set is not changed.
9428 @item -mmemory-latency=@var{time}
9429 @opindex mmemory-latency
9430 Sets the latency the scheduler should assume for typical memory
9431 references as seen by the application. This number is highly
9432 dependent on the memory access patterns used by the application
9433 and the size of the external cache on the machine.
9435 Valid options for @var{time} are
9439 A decimal number representing clock cycles.
9445 The compiler contains estimates of the number of clock cycles for
9446 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
9447 (also called Dcache, Scache, and Bcache), as well as to main memory.
9448 Note that L3 is only valid for EV5.
9453 @node DEC Alpha/VMS Options
9454 @subsection DEC Alpha/VMS Options
9456 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
9459 @item -mvms-return-codes
9460 @opindex mvms-return-codes
9461 Return VMS condition codes from main. The default is to return POSIX
9462 style condition (e.g.@ error) codes.
9465 @node H8/300 Options
9466 @subsection H8/300 Options
9468 These @samp{-m} options are defined for the H8/300 implementations:
9473 Shorten some address references at link time, when possible; uses the
9474 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
9475 ld, Using ld}, for a fuller description.
9479 Generate code for the H8/300H@.
9483 Generate code for the H8S@.
9487 Generate code for the H8S and H8/300H in the normal mode. This switch
9488 must be used either with -mh or -ms.
9492 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
9496 Make @code{int} data 32 bits by default.
9500 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
9501 The default for the H8/300H and H8S is to align longs and floats on 4
9503 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
9504 This option has no effect on the H8/300.
9508 @subsection SH Options
9510 These @samp{-m} options are defined for the SH implementations:
9515 Generate code for the SH1.
9519 Generate code for the SH2.
9522 Generate code for the SH2e.
9526 Generate code for the SH3.
9530 Generate code for the SH3e.
9534 Generate code for the SH4 without a floating-point unit.
9536 @item -m4-single-only
9537 @opindex m4-single-only
9538 Generate code for the SH4 with a floating-point unit that only
9539 supports single-precision arithmetic.
9543 Generate code for the SH4 assuming the floating-point unit is in
9544 single-precision mode by default.
9548 Generate code for the SH4.
9552 Compile code for the processor in big endian mode.
9556 Compile code for the processor in little endian mode.
9560 Align doubles at 64-bit boundaries. Note that this changes the calling
9561 conventions, and thus some functions from the standard C library will
9562 not work unless you recompile it first with @option{-mdalign}.
9566 Shorten some address references at link time, when possible; uses the
9567 linker option @option{-relax}.
9571 Use 32-bit offsets in @code{switch} tables. The default is to use
9576 Enable the use of the instruction @code{fmovd}.
9580 Comply with the calling conventions defined by Renesas.
9584 Mark the @code{MAC} register as call-clobbered, even if
9585 @option{-mhitachi} is given.
9589 Increase IEEE-compliance of floating-point code.
9593 Dump instruction size and location in the assembly code.
9597 This option is deprecated. It pads structures to multiple of 4 bytes,
9598 which is incompatible with the SH ABI@.
9602 Optimize for space instead of speed. Implied by @option{-Os}.
9606 When generating position-independent code, emit function calls using
9607 the Global Offset Table instead of the Procedure Linkage Table.
9611 Generate a library function call to invalidate instruction cache
9612 entries, after fixing up a trampoline. This library function call
9613 doesn't assume it can write to the whole memory address space. This
9614 is the default when the target is @code{sh-*-linux*}.
9617 @node System V Options
9618 @subsection Options for System V
9620 These additional options are available on System V Release 4 for
9621 compatibility with other compilers on those systems:
9626 Create a shared object.
9627 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
9631 Identify the versions of each tool used by the compiler, in a
9632 @code{.ident} assembler directive in the output.
9636 Refrain from adding @code{.ident} directives to the output file (this is
9639 @item -YP,@var{dirs}
9641 Search the directories @var{dirs}, and no others, for libraries
9642 specified with @option{-l}.
9646 Look in the directory @var{dir} to find the M4 preprocessor.
9647 The assembler uses this option.
9648 @c This is supposed to go with a -Yd for predefined M4 macro files, but
9649 @c the generic assembler that comes with Solaris takes just -Ym.
9652 @node TMS320C3x/C4x Options
9653 @subsection TMS320C3x/C4x Options
9654 @cindex TMS320C3x/C4x Options
9656 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
9660 @item -mcpu=@var{cpu_type}
9662 Set the instruction set, register set, and instruction scheduling
9663 parameters for machine type @var{cpu_type}. Supported values for
9664 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
9665 @samp{c44}. The default is @samp{c40} to generate code for the
9670 @itemx -msmall-memory
9672 @opindex mbig-memory
9674 @opindex msmall-memory
9676 Generates code for the big or small memory model. The small memory
9677 model assumed that all data fits into one 64K word page. At run-time
9678 the data page (DP) register must be set to point to the 64K page
9679 containing the .bss and .data program sections. The big memory model is
9680 the default and requires reloading of the DP register for every direct
9687 Allow (disallow) allocation of general integer operands into the block
9694 Enable (disable) generation of code using decrement and branch,
9695 DBcond(D), instructions. This is enabled by default for the C4x. To be
9696 on the safe side, this is disabled for the C3x, since the maximum
9697 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
9698 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
9699 that it can utilize the decrement and branch instruction, but will give
9700 up if there is more than one memory reference in the loop. Thus a loop
9701 where the loop counter is decremented can generate slightly more
9702 efficient code, in cases where the RPTB instruction cannot be utilized.
9704 @item -mdp-isr-reload
9706 @opindex mdp-isr-reload
9708 Force the DP register to be saved on entry to an interrupt service
9709 routine (ISR), reloaded to point to the data section, and restored on
9710 exit from the ISR@. This should not be required unless someone has
9711 violated the small memory model by modifying the DP register, say within
9718 For the C3x use the 24-bit MPYI instruction for integer multiplies
9719 instead of a library call to guarantee 32-bit results. Note that if one
9720 of the operands is a constant, then the multiplication will be performed
9721 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
9722 then squaring operations are performed inline instead of a library call.
9725 @itemx -mno-fast-fix
9727 @opindex mno-fast-fix
9728 The C3x/C4x FIX instruction to convert a floating point value to an
9729 integer value chooses the nearest integer less than or equal to the
9730 floating point value rather than to the nearest integer. Thus if the
9731 floating point number is negative, the result will be incorrectly
9732 truncated an additional code is necessary to detect and correct this
9733 case. This option can be used to disable generation of the additional
9734 code required to correct the result.
9740 Enable (disable) generation of repeat block sequences using the RPTB
9741 instruction for zero overhead looping. The RPTB construct is only used
9742 for innermost loops that do not call functions or jump across the loop
9743 boundaries. There is no advantage having nested RPTB loops due to the
9744 overhead required to save and restore the RC, RS, and RE registers.
9745 This is enabled by default with @option{-O2}.
9747 @item -mrpts=@var{count}
9751 Enable (disable) the use of the single instruction repeat instruction
9752 RPTS@. If a repeat block contains a single instruction, and the loop
9753 count can be guaranteed to be less than the value @var{count}, GCC will
9754 emit a RPTS instruction instead of a RPTB@. If no value is specified,
9755 then a RPTS will be emitted even if the loop count cannot be determined
9756 at compile time. Note that the repeated instruction following RPTS does
9757 not have to be reloaded from memory each iteration, thus freeing up the
9758 CPU buses for operands. However, since interrupts are blocked by this
9759 instruction, it is disabled by default.
9761 @item -mloop-unsigned
9762 @itemx -mno-loop-unsigned
9763 @opindex mloop-unsigned
9764 @opindex mno-loop-unsigned
9765 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
9766 is @math{2^{31} + 1} since these instructions test if the iteration count is
9767 negative to terminate the loop. If the iteration count is unsigned
9768 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
9769 exceeded. This switch allows an unsigned iteration count.
9773 Try to emit an assembler syntax that the TI assembler (asm30) is happy
9774 with. This also enforces compatibility with the API employed by the TI
9775 C3x C compiler. For example, long doubles are passed as structures
9776 rather than in floating point registers.
9782 Generate code that uses registers (stack) for passing arguments to functions.
9783 By default, arguments are passed in registers where possible rather
9784 than by pushing arguments on to the stack.
9786 @item -mparallel-insns
9787 @itemx -mno-parallel-insns
9788 @opindex mparallel-insns
9789 @opindex mno-parallel-insns
9790 Allow the generation of parallel instructions. This is enabled by
9791 default with @option{-O2}.
9793 @item -mparallel-mpy
9794 @itemx -mno-parallel-mpy
9795 @opindex mparallel-mpy
9796 @opindex mno-parallel-mpy
9797 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
9798 provided @option{-mparallel-insns} is also specified. These instructions have
9799 tight register constraints which can pessimize the code generation
9805 @subsection V850 Options
9806 @cindex V850 Options
9808 These @samp{-m} options are defined for V850 implementations:
9812 @itemx -mno-long-calls
9813 @opindex mlong-calls
9814 @opindex mno-long-calls
9815 Treat all calls as being far away (near). If calls are assumed to be
9816 far away, the compiler will always load the functions address up into a
9817 register, and call indirect through the pointer.
9823 Do not optimize (do optimize) basic blocks that use the same index
9824 pointer 4 or more times to copy pointer into the @code{ep} register, and
9825 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
9826 option is on by default if you optimize.
9828 @item -mno-prolog-function
9829 @itemx -mprolog-function
9830 @opindex mno-prolog-function
9831 @opindex mprolog-function
9832 Do not use (do use) external functions to save and restore registers
9833 at the prologue and epilogue of a function. The external functions
9834 are slower, but use less code space if more than one function saves
9835 the same number of registers. The @option{-mprolog-function} option
9836 is on by default if you optimize.
9840 Try to make the code as small as possible. At present, this just turns
9841 on the @option{-mep} and @option{-mprolog-function} options.
9845 Put static or global variables whose size is @var{n} bytes or less into
9846 the tiny data area that register @code{ep} points to. The tiny data
9847 area can hold up to 256 bytes in total (128 bytes for byte references).
9851 Put static or global variables whose size is @var{n} bytes or less into
9852 the small data area that register @code{gp} points to. The small data
9853 area can hold up to 64 kilobytes.
9857 Put static or global variables whose size is @var{n} bytes or less into
9858 the first 32 kilobytes of memory.
9862 Specify that the target processor is the V850.
9865 @opindex mbig-switch
9866 Generate code suitable for big switch tables. Use this option only if
9867 the assembler/linker complain about out of range branches within a switch
9872 This option will cause r2 and r5 to be used in the code generated by
9873 the compiler. This setting is the default.
9876 @opindex mno-app-regs
9877 This option will cause r2 and r5 to be treated as fixed registers.
9881 Specify that the target processor is the V850E1. The preprocessor
9882 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
9883 this option is used.
9887 Specify that the target processor is the V850E. The preprocessor
9888 constant @samp{__v850e__} will be defined if this option is used.
9890 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
9891 are defined then a default target processor will be chosen and the
9892 relevant @samp{__v850*__} preprocessor constant will be defined.
9894 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
9895 defined, regardless of which processor variant is the target.
9897 @item -mdisable-callt
9898 @opindex mdisable-callt
9899 This option will suppress generation of the CALLT instruction for the
9900 v850e and v850e1 flavors of the v850 architecture. The default is
9901 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
9906 @subsection ARC Options
9909 These options are defined for ARC implementations:
9914 Compile code for little endian mode. This is the default.
9918 Compile code for big endian mode.
9921 @opindex mmangle-cpu
9922 Prepend the name of the cpu to all public symbol names.
9923 In multiple-processor systems, there are many ARC variants with different
9924 instruction and register set characteristics. This flag prevents code
9925 compiled for one cpu to be linked with code compiled for another.
9926 No facility exists for handling variants that are ``almost identical''.
9927 This is an all or nothing option.
9929 @item -mcpu=@var{cpu}
9931 Compile code for ARC variant @var{cpu}.
9932 Which variants are supported depend on the configuration.
9933 All variants support @option{-mcpu=base}, this is the default.
9935 @item -mtext=@var{text-section}
9936 @itemx -mdata=@var{data-section}
9937 @itemx -mrodata=@var{readonly-data-section}
9941 Put functions, data, and readonly data in @var{text-section},
9942 @var{data-section}, and @var{readonly-data-section} respectively
9943 by default. This can be overridden with the @code{section} attribute.
9944 @xref{Variable Attributes}.
9949 @subsection NS32K Options
9950 @cindex NS32K options
9952 These are the @samp{-m} options defined for the 32000 series. The default
9953 values for these options depends on which style of 32000 was selected when
9954 the compiler was configured; the defaults for the most common choices are
9962 Generate output for a 32032. This is the default
9963 when the compiler is configured for 32032 and 32016 based systems.
9969 Generate output for a 32332. This is the default
9970 when the compiler is configured for 32332-based systems.
9976 Generate output for a 32532. This is the default
9977 when the compiler is configured for 32532-based systems.
9981 Generate output containing 32081 instructions for floating point.
9982 This is the default for all systems.
9986 Generate output containing 32381 instructions for floating point. This
9987 also implies @option{-m32081}. The 32381 is only compatible with the 32332
9988 and 32532 cpus. This is the default for the pc532-netbsd configuration.
9992 Try and generate multiply-add floating point instructions @code{polyF}
9993 and @code{dotF}. This option is only available if the @option{-m32381}
9994 option is in effect. Using these instructions requires changes to
9995 register allocation which generally has a negative impact on
9996 performance. This option should only be enabled when compiling code
9997 particularly likely to make heavy use of multiply-add instructions.
10000 @opindex mnomulti-add
10001 Do not try and generate multiply-add floating point instructions
10002 @code{polyF} and @code{dotF}. This is the default on all platforms.
10005 @opindex msoft-float
10006 Generate output containing library calls for floating point.
10007 @strong{Warning:} the requisite libraries may not be available.
10009 @item -mieee-compare
10010 @itemx -mno-ieee-compare
10011 @opindex mieee-compare
10012 @opindex mno-ieee-compare
10013 Control whether or not the compiler uses IEEE floating point
10014 comparisons. These handle correctly the case where the result of a
10015 comparison is unordered.
10016 @strong{Warning:} the requisite kernel support may not be available.
10019 @opindex mnobitfield
10020 Do not use the bit-field instructions. On some machines it is faster to
10021 use shifting and masking operations. This is the default for the pc532.
10025 Do use the bit-field instructions. This is the default for all platforms
10030 Use a different function-calling convention, in which functions
10031 that take a fixed number of arguments return pop their
10032 arguments on return with the @code{ret} instruction.
10034 This calling convention is incompatible with the one normally
10035 used on Unix, so you cannot use it if you need to call libraries
10036 compiled with the Unix compiler.
10038 Also, you must provide function prototypes for all functions that
10039 take variable numbers of arguments (including @code{printf});
10040 otherwise incorrect code will be generated for calls to those
10043 In addition, seriously incorrect code will result if you call a
10044 function with too many arguments. (Normally, extra arguments are
10045 harmlessly ignored.)
10047 This option takes its name from the 680x0 @code{rtd} instruction.
10052 Use a different function-calling convention where the first two arguments
10053 are passed in registers.
10055 This calling convention is incompatible with the one normally
10056 used on Unix, so you cannot use it if you need to call libraries
10057 compiled with the Unix compiler.
10060 @opindex mnoregparam
10061 Do not pass any arguments in registers. This is the default for all
10066 It is OK to use the sb as an index register which is always loaded with
10067 zero. This is the default for the pc532-netbsd target.
10071 The sb register is not available for use or has not been initialized to
10072 zero by the run time system. This is the default for all targets except
10073 the pc532-netbsd. It is also implied whenever @option{-mhimem} or
10074 @option{-fpic} is set.
10078 Many ns32000 series addressing modes use displacements of up to 512MB@.
10079 If an address is above 512MB then displacements from zero can not be used.
10080 This option causes code to be generated which can be loaded above 512MB@.
10081 This may be useful for operating systems or ROM code.
10085 Assume code will be loaded in the first 512MB of virtual address space.
10086 This is the default for all platforms.
10092 @subsection AVR Options
10093 @cindex AVR Options
10095 These options are defined for AVR implementations:
10098 @item -mmcu=@var{mcu}
10100 Specify ATMEL AVR instruction set or MCU type.
10102 Instruction set avr1 is for the minimal AVR core, not supported by the C
10103 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
10104 attiny11, attiny12, attiny15, attiny28).
10106 Instruction set avr2 (default) is for the classic AVR core with up to
10107 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
10108 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
10109 at90c8534, at90s8535).
10111 Instruction set avr3 is for the classic AVR core with up to 128K program
10112 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
10114 Instruction set avr4 is for the enhanced AVR core with up to 8K program
10115 memory space (MCU types: atmega8, atmega83, atmega85).
10117 Instruction set avr5 is for the enhanced AVR core with up to 128K program
10118 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
10119 atmega64, atmega128, at43usb355, at94k).
10123 Output instruction sizes to the asm file.
10125 @item -minit-stack=@var{N}
10126 @opindex minit-stack
10127 Specify the initial stack address, which may be a symbol or numeric value,
10128 @samp{__stack} is the default.
10130 @item -mno-interrupts
10131 @opindex mno-interrupts
10132 Generated code is not compatible with hardware interrupts.
10133 Code size will be smaller.
10135 @item -mcall-prologues
10136 @opindex mcall-prologues
10137 Functions prologues/epilogues expanded as call to appropriate
10138 subroutines. Code size will be smaller.
10140 @item -mno-tablejump
10141 @opindex mno-tablejump
10142 Do not generate tablejump insns which sometimes increase code size.
10145 @opindex mtiny-stack
10146 Change only the low 8 bits of the stack pointer.
10149 @node MCore Options
10150 @subsection MCore Options
10151 @cindex MCore options
10153 These are the @samp{-m} options defined for the Motorola M*Core
10159 @itemx -mno-hardlit
10161 @opindex mno-hardlit
10162 Inline constants into the code stream if it can be done in two
10163 instructions or less.
10169 Use the divide instruction. (Enabled by default).
10171 @item -mrelax-immediate
10172 @itemx -mno-relax-immediate
10173 @opindex mrelax-immediate
10174 @opindex mno-relax-immediate
10175 Allow arbitrary sized immediates in bit operations.
10177 @item -mwide-bitfields
10178 @itemx -mno-wide-bitfields
10179 @opindex mwide-bitfields
10180 @opindex mno-wide-bitfields
10181 Always treat bit-fields as int-sized.
10183 @item -m4byte-functions
10184 @itemx -mno-4byte-functions
10185 @opindex m4byte-functions
10186 @opindex mno-4byte-functions
10187 Force all functions to be aligned to a four byte boundary.
10189 @item -mcallgraph-data
10190 @itemx -mno-callgraph-data
10191 @opindex mcallgraph-data
10192 @opindex mno-callgraph-data
10193 Emit callgraph information.
10196 @itemx -mno-slow-bytes
10197 @opindex mslow-bytes
10198 @opindex mno-slow-bytes
10199 Prefer word access when reading byte quantities.
10201 @item -mlittle-endian
10202 @itemx -mbig-endian
10203 @opindex mlittle-endian
10204 @opindex mbig-endian
10205 Generate code for a little endian target.
10211 Generate code for the 210 processor.
10214 @node IA-64 Options
10215 @subsection IA-64 Options
10216 @cindex IA-64 Options
10218 These are the @samp{-m} options defined for the Intel IA-64 architecture.
10222 @opindex mbig-endian
10223 Generate code for a big endian target. This is the default for HP-UX@.
10225 @item -mlittle-endian
10226 @opindex mlittle-endian
10227 Generate code for a little endian target. This is the default for AIX5
10233 @opindex mno-gnu-as
10234 Generate (or don't) code for the GNU assembler. This is the default.
10235 @c Also, this is the default if the configure option @option{--with-gnu-as}
10241 @opindex mno-gnu-ld
10242 Generate (or don't) code for the GNU linker. This is the default.
10243 @c Also, this is the default if the configure option @option{--with-gnu-ld}
10248 Generate code that does not use a global pointer register. The result
10249 is not position independent code, and violates the IA-64 ABI@.
10251 @item -mvolatile-asm-stop
10252 @itemx -mno-volatile-asm-stop
10253 @opindex mvolatile-asm-stop
10254 @opindex mno-volatile-asm-stop
10255 Generate (or don't) a stop bit immediately before and after volatile asm
10260 Generate code that works around Itanium B step errata.
10262 @item -mregister-names
10263 @itemx -mno-register-names
10264 @opindex mregister-names
10265 @opindex mno-register-names
10266 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
10267 the stacked registers. This may make assembler output more readable.
10273 Disable (or enable) optimizations that use the small data section. This may
10274 be useful for working around optimizer bugs.
10276 @item -mconstant-gp
10277 @opindex mconstant-gp
10278 Generate code that uses a single constant global pointer value. This is
10279 useful when compiling kernel code.
10283 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
10284 This is useful when compiling firmware code.
10286 @item -minline-float-divide-min-latency
10287 @opindex minline-float-divide-min-latency
10288 Generate code for inline divides of floating point values
10289 using the minimum latency algorithm.
10291 @item -minline-float-divide-max-throughput
10292 @opindex minline-float-divide-max-throughput
10293 Generate code for inline divides of floating point values
10294 using the maximum throughput algorithm.
10296 @item -minline-int-divide-min-latency
10297 @opindex minline-int-divide-min-latency
10298 Generate code for inline divides of integer values
10299 using the minimum latency algorithm.
10301 @item -minline-int-divide-max-throughput
10302 @opindex minline-int-divide-max-throughput
10303 Generate code for inline divides of integer values
10304 using the maximum throughput algorithm.
10306 @item -mno-dwarf2-asm
10307 @itemx -mdwarf2-asm
10308 @opindex mno-dwarf2-asm
10309 @opindex mdwarf2-asm
10310 Don't (or do) generate assembler code for the DWARF2 line number debugging
10311 info. This may be useful when not using the GNU assembler.
10313 @item -mfixed-range=@var{register-range}
10314 @opindex mfixed-range
10315 Generate code treating the given register range as fixed registers.
10316 A fixed register is one that the register allocator can not use. This is
10317 useful when compiling kernel code. A register range is specified as
10318 two registers separated by a dash. Multiple register ranges can be
10319 specified separated by a comma.
10321 @item -mearly-stop-bits
10322 @itemx -mno-early-stop-bits
10323 @opindex mearly-stop-bits
10324 @opindex mno-early-stop-bits
10325 Allow stop bits to be placed earlier than immediately preceding the
10326 instruction that triggered the stop bit. This can improve instruction
10327 scheduling, but does not always do so.
10331 @subsection D30V Options
10332 @cindex D30V Options
10334 These @samp{-m} options are defined for D30V implementations:
10339 Link the @samp{.text}, @samp{.data}, @samp{.bss}, @samp{.strings},
10340 @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into external
10341 memory, which starts at location @code{0x80000000}.
10344 @opindex mextmemory
10345 Same as the @option{-mextmem} switch.
10349 Link the @samp{.text} section into onchip text memory, which starts at
10350 location @code{0x0}. Also link @samp{.data}, @samp{.bss},
10351 @samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections
10352 into onchip data memory, which starts at location @code{0x20000000}.
10354 @item -mno-asm-optimize
10355 @itemx -masm-optimize
10356 @opindex mno-asm-optimize
10357 @opindex masm-optimize
10358 Disable (enable) passing @option{-O} to the assembler when optimizing.
10359 The assembler uses the @option{-O} option to automatically parallelize
10360 adjacent short instructions where possible.
10362 @item -mbranch-cost=@var{n}
10363 @opindex mbranch-cost
10364 Increase the internal costs of branches to @var{n}. Higher costs means
10365 that the compiler will issue more instructions to avoid doing a branch.
10368 @item -mcond-exec=@var{n}
10369 @opindex mcond-exec
10370 Specify the maximum number of conditionally executed instructions that
10371 replace a branch. The default is 4.
10374 @node S/390 and zSeries Options
10375 @subsection S/390 and zSeries Options
10376 @cindex S/390 and zSeries Options
10378 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
10382 @itemx -msoft-float
10383 @opindex mhard-float
10384 @opindex msoft-float
10385 Use (do not use) the hardware floating-point instructions and registers
10386 for floating-point operations. When @option{-msoft-float} is specified,
10387 functions in @file{libgcc.a} will be used to perform floating-point
10388 operations. When @option{-mhard-float} is specified, the compiler
10389 generates IEEE floating-point instructions. This is the default.
10392 @itemx -mno-backchain
10393 @opindex mbackchain
10394 @opindex mno-backchain
10395 Generate (or do not generate) code which maintains an explicit
10396 backchain within the stack frame that points to the caller's frame.
10397 This is currently needed to allow debugging. The default is to
10398 generate the backchain.
10401 @itemx -mno-small-exec
10402 @opindex msmall-exec
10403 @opindex mno-small-exec
10404 Generate (or do not generate) code using the @code{bras} instruction
10405 to do subroutine calls.
10406 This only works reliably if the total executable size does not
10407 exceed 64k. The default is to use the @code{basr} instruction instead,
10408 which does not have this limitation.
10414 When @option{-m31} is specified, generate code compliant to the
10415 Linux for S/390 ABI@. When @option{-m64} is specified, generate
10416 code compliant to the Linux for zSeries ABI@. This allows GCC in
10417 particular to generate 64-bit instructions. For the @samp{s390}
10418 targets, the default is @option{-m31}, while the @samp{s390x}
10419 targets default to @option{-m64}.
10425 When @option{-mzarch} is specified, generate code using the
10426 instructions available on z/Architecture.
10427 When @option{-mesa} is specified, generate code using the
10428 instructions available on ESA/390. Note that @option{-mesa} is
10429 not possible with @option{-m64}.
10430 When generating code compliant to the Linux for S/390 ABI,
10431 the default is @option{-mesa}. When generating code compliant
10432 to the Linux for zSeries ABI, the default is @option{-mzarch}.
10438 Generate (or do not generate) code using the @code{mvcle} instruction
10439 to perform block moves. When @option{-mno-mvcle} is specified,
10440 use a @code{mvc} loop instead. This is the default.
10446 Print (or do not print) additional debug information when compiling.
10447 The default is to not print debug information.
10449 @item -march=@var{cpu-type}
10451 Generate code that will run on @var{cpu-type}, which is the name of a system
10452 representing a certain processor type. Possible values for
10453 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
10454 When generating code using the instructions available on z/Architecture,
10455 the default is @option{-march=z900}. Otherwise, the default is
10456 @option{-march=g5}.
10458 @item -mtune=@var{cpu-type}
10460 Tune to @var{cpu-type} everything applicable about the generated code,
10461 except for the ABI and the set of available instructions.
10462 The list of @var{cpu-type} values is the same as for @option{-march}.
10463 The default is the value used for @option{-march}.
10466 @itemx -mno-fused-madd
10467 @opindex mfused-madd
10468 @opindex mno-fused-madd
10469 Generate code that uses (does not use) the floating point multiply and
10470 accumulate instructions. These instructions are generated by default if
10471 hardware floating point is used.
10475 @subsection CRIS Options
10476 @cindex CRIS Options
10478 These options are defined specifically for the CRIS ports.
10481 @item -march=@var{architecture-type}
10482 @itemx -mcpu=@var{architecture-type}
10485 Generate code for the specified architecture. The choices for
10486 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
10487 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX.
10488 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
10491 @item -mtune=@var{architecture-type}
10493 Tune to @var{architecture-type} everything applicable about the generated
10494 code, except for the ABI and the set of available instructions. The
10495 choices for @var{architecture-type} are the same as for
10496 @option{-march=@var{architecture-type}}.
10498 @item -mmax-stack-frame=@var{n}
10499 @opindex mmax-stack-frame
10500 Warn when the stack frame of a function exceeds @var{n} bytes.
10502 @item -melinux-stacksize=@var{n}
10503 @opindex melinux-stacksize
10504 Only available with the @samp{cris-axis-aout} target. Arranges for
10505 indications in the program to the kernel loader that the stack of the
10506 program should be set to @var{n} bytes.
10512 The options @option{-metrax4} and @option{-metrax100} are synonyms for
10513 @option{-march=v3} and @option{-march=v8} respectively.
10517 Enable CRIS-specific verbose debug-related information in the assembly
10518 code. This option also has the effect to turn off the @samp{#NO_APP}
10519 formatted-code indicator to the assembler at the beginning of the
10524 Do not use condition-code results from previous instruction; always emit
10525 compare and test instructions before use of condition codes.
10527 @item -mno-side-effects
10528 @opindex mno-side-effects
10529 Do not emit instructions with side-effects in addressing modes other than
10532 @item -mstack-align
10533 @itemx -mno-stack-align
10534 @itemx -mdata-align
10535 @itemx -mno-data-align
10536 @itemx -mconst-align
10537 @itemx -mno-const-align
10538 @opindex mstack-align
10539 @opindex mno-stack-align
10540 @opindex mdata-align
10541 @opindex mno-data-align
10542 @opindex mconst-align
10543 @opindex mno-const-align
10544 These options (no-options) arranges (eliminate arrangements) for the
10545 stack-frame, individual data and constants to be aligned for the maximum
10546 single data access size for the chosen CPU model. The default is to
10547 arrange for 32-bit alignment. ABI details such as structure layout are
10548 not affected by these options.
10556 Similar to the stack- data- and const-align options above, these options
10557 arrange for stack-frame, writable data and constants to all be 32-bit,
10558 16-bit or 8-bit aligned. The default is 32-bit alignment.
10560 @item -mno-prologue-epilogue
10561 @itemx -mprologue-epilogue
10562 @opindex mno-prologue-epilogue
10563 @opindex mprologue-epilogue
10564 With @option{-mno-prologue-epilogue}, the normal function prologue and
10565 epilogue that sets up the stack-frame are omitted and no return
10566 instructions or return sequences are generated in the code. Use this
10567 option only together with visual inspection of the compiled code: no
10568 warnings or errors are generated when call-saved registers must be saved,
10569 or storage for local variable needs to be allocated.
10573 @opindex mno-gotplt
10575 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
10576 instruction sequences that load addresses for functions from the PLT part
10577 of the GOT rather than (traditional on other architectures) calls to the
10578 PLT. The default is @option{-mgotplt}.
10582 Legacy no-op option only recognized with the cris-axis-aout target.
10586 Legacy no-op option only recognized with the cris-axis-elf and
10587 cris-axis-linux-gnu targets.
10591 Only recognized with the cris-axis-aout target, where it selects a
10592 GNU/linux-like multilib, include files and instruction set for
10593 @option{-march=v8}.
10597 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
10601 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
10602 to link with input-output functions from a simulator library. Code,
10603 initialized data and zero-initialized data are allocated consecutively.
10607 Like @option{-sim}, but pass linker options to locate initialized data at
10608 0x40000000 and zero-initialized data at 0x80000000.
10612 @subsection MMIX Options
10613 @cindex MMIX Options
10615 These options are defined for the MMIX:
10619 @itemx -mno-libfuncs
10621 @opindex mno-libfuncs
10622 Specify that intrinsic library functions are being compiled, passing all
10623 values in registers, no matter the size.
10626 @itemx -mno-epsilon
10628 @opindex mno-epsilon
10629 Generate floating-point comparison instructions that compare with respect
10630 to the @code{rE} epsilon register.
10632 @item -mabi=mmixware
10634 @opindex mabi-mmixware
10636 Generate code that passes function parameters and return values that (in
10637 the called function) are seen as registers @code{$0} and up, as opposed to
10638 the GNU ABI which uses global registers @code{$231} and up.
10640 @item -mzero-extend
10641 @itemx -mno-zero-extend
10642 @opindex mzero-extend
10643 @opindex mno-zero-extend
10644 When reading data from memory in sizes shorter than 64 bits, use (do not
10645 use) zero-extending load instructions by default, rather than
10646 sign-extending ones.
10649 @itemx -mno-knuthdiv
10651 @opindex mno-knuthdiv
10652 Make the result of a division yielding a remainder have the same sign as
10653 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
10654 remainder follows the sign of the dividend. Both methods are
10655 arithmetically valid, the latter being almost exclusively used.
10657 @item -mtoplevel-symbols
10658 @itemx -mno-toplevel-symbols
10659 @opindex mtoplevel-symbols
10660 @opindex mno-toplevel-symbols
10661 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
10662 code can be used with the @code{PREFIX} assembly directive.
10666 Generate an executable in the ELF format, rather than the default
10667 @samp{mmo} format used by the @command{mmix} simulator.
10669 @item -mbranch-predict
10670 @itemx -mno-branch-predict
10671 @opindex mbranch-predict
10672 @opindex mno-branch-predict
10673 Use (do not use) the probable-branch instructions, when static branch
10674 prediction indicates a probable branch.
10676 @item -mbase-addresses
10677 @itemx -mno-base-addresses
10678 @opindex mbase-addresses
10679 @opindex mno-base-addresses
10680 Generate (do not generate) code that uses @emph{base addresses}. Using a
10681 base address automatically generates a request (handled by the assembler
10682 and the linker) for a constant to be set up in a global register. The
10683 register is used for one or more base address requests within the range 0
10684 to 255 from the value held in the register. The generally leads to short
10685 and fast code, but the number of different data items that can be
10686 addressed is limited. This means that a program that uses lots of static
10687 data may require @option{-mno-base-addresses}.
10689 @item -msingle-exit
10690 @itemx -mno-single-exit
10691 @opindex msingle-exit
10692 @opindex mno-single-exit
10693 Force (do not force) generated code to have a single exit point in each
10697 @node PDP-11 Options
10698 @subsection PDP-11 Options
10699 @cindex PDP-11 Options
10701 These options are defined for the PDP-11:
10706 Use hardware FPP floating point. This is the default. (FIS floating
10707 point on the PDP-11/40 is not supported.)
10710 @opindex msoft-float
10711 Do not use hardware floating point.
10715 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
10719 Return floating-point results in memory. This is the default.
10723 Generate code for a PDP-11/40.
10727 Generate code for a PDP-11/45. This is the default.
10731 Generate code for a PDP-11/10.
10733 @item -mbcopy-builtin
10734 @opindex bcopy-builtin
10735 Use inline @code{movstrhi} patterns for copying memory. This is the
10740 Do not use inline @code{movstrhi} patterns for copying memory.
10746 Use 16-bit @code{int}. This is the default.
10752 Use 32-bit @code{int}.
10755 @itemx -mno-float32
10757 @opindex mno-float32
10758 Use 64-bit @code{float}. This is the default.
10763 @opindex mno-float64
10764 Use 32-bit @code{float}.
10768 Use @code{abshi2} pattern. This is the default.
10772 Do not use @code{abshi2} pattern.
10774 @item -mbranch-expensive
10775 @opindex mbranch-expensive
10776 Pretend that branches are expensive. This is for experimenting with
10777 code generation only.
10779 @item -mbranch-cheap
10780 @opindex mbranch-cheap
10781 Do not pretend that branches are expensive. This is the default.
10785 Generate code for a system with split I&D.
10789 Generate code for a system without split I&D. This is the default.
10793 Use Unix assembler syntax. This is the default when configured for
10794 @samp{pdp11-*-bsd}.
10798 Use DEC assembler syntax. This is the default when configured for any
10799 PDP-11 target other than @samp{pdp11-*-bsd}.
10802 @node Xstormy16 Options
10803 @subsection Xstormy16 Options
10804 @cindex Xstormy16 Options
10806 These options are defined for Xstormy16:
10811 Choose startup files and linker script suitable for the simulator.
10815 @subsection FRV Options
10816 @cindex FRV Options
10822 Only use the first 32 general purpose registers.
10827 Use all 64 general purpose registers.
10832 Use only the first 32 floating point registers.
10837 Use all 64 floating point registers
10840 @opindex mhard-float
10842 Use hardware instructions for floating point operations.
10845 @opindex msoft-float
10847 Use library routines for floating point operations.
10852 Dynamically allocate condition code registers.
10857 Do not try to dynamically allocate condition code registers, only
10858 use @code{icc0} and @code{fcc0}.
10863 Change ABI to use double word insns.
10868 Do not use double word instructions.
10873 Use floating point double instructions.
10876 @opindex mno-double
10878 Do not use floating point double instructions.
10883 Use media instructions.
10888 Do not use media instructions.
10893 Use multiply and add/subtract instructions.
10896 @opindex mno-muladd
10898 Do not use multiply and add/subtract instructions.
10900 @item -mlibrary-pic
10901 @opindex mlibrary-pic
10903 Enable PIC support for building libraries
10908 Use only the first four media accumulator registers.
10913 Use all eight media accumulator registers.
10918 Pack VLIW instructions.
10923 Do not pack VLIW instructions.
10926 @opindex mno-eflags
10928 Do not mark ABI switches in e_flags.
10931 @opindex mcond-move
10933 Enable the use of conditional-move instructions (default).
10935 This switch is mainly for debugging the compiler and will likely be removed
10936 in a future version.
10938 @item -mno-cond-move
10939 @opindex mno-cond-move
10941 Disable the use of conditional-move instructions.
10943 This switch is mainly for debugging the compiler and will likely be removed
10944 in a future version.
10949 Enable the use of conditional set instructions (default).
10951 This switch is mainly for debugging the compiler and will likely be removed
10952 in a future version.
10957 Disable the use of conditional set instructions.
10959 This switch is mainly for debugging the compiler and will likely be removed
10960 in a future version.
10963 @opindex mcond-exec
10965 Enable the use of conditional execution (default).
10967 This switch is mainly for debugging the compiler and will likely be removed
10968 in a future version.
10970 @item -mno-cond-exec
10971 @opindex mno-cond-exec
10973 Disable the use of conditional execution.
10975 This switch is mainly for debugging the compiler and will likely be removed
10976 in a future version.
10978 @item -mvliw-branch
10979 @opindex mvliw-branch
10981 Run a pass to pack branches into VLIW instructions (default).
10983 This switch is mainly for debugging the compiler and will likely be removed
10984 in a future version.
10986 @item -mno-vliw-branch
10987 @opindex mno-vliw-branch
10989 Do not run a pass to pack branches into VLIW instructions.
10991 This switch is mainly for debugging the compiler and will likely be removed
10992 in a future version.
10994 @item -mmulti-cond-exec
10995 @opindex mmulti-cond-exec
10997 Enable optimization of @code{&&} and @code{||} in conditional execution
11000 This switch is mainly for debugging the compiler and will likely be removed
11001 in a future version.
11003 @item -mno-multi-cond-exec
11004 @opindex mno-multi-cond-exec
11006 Disable optimization of @code{&&} and @code{||} in conditional execution.
11008 This switch is mainly for debugging the compiler and will likely be removed
11009 in a future version.
11011 @item -mnested-cond-exec
11012 @opindex mnested-cond-exec
11014 Enable nested conditional execution optimizations (default).
11016 This switch is mainly for debugging the compiler and will likely be removed
11017 in a future version.
11019 @item -mno-nested-cond-exec
11020 @opindex mno-nested-cond-exec
11022 Disable nested conditional execution optimizations.
11024 This switch is mainly for debugging the compiler and will likely be removed
11025 in a future version.
11027 @item -mtomcat-stats
11028 @opindex mtomcat-stats
11030 Cause gas to print out tomcat statistics.
11032 @item -mcpu=@var{cpu}
11035 Select the processor type for which to generate code. Possible values are
11036 @samp{simple}, @samp{tomcat}, @samp{fr500}, @samp{fr400}, @samp{fr300},
11041 @node Xtensa Options
11042 @subsection Xtensa Options
11043 @cindex Xtensa Options
11045 These options are supported for Xtensa targets:
11049 @itemx -mno-const16
11051 @opindex mno-const16
11052 Enable or disable use of @code{CONST16} instructions for loading
11053 constant values. The @code{CONST16} instruction is currently not a
11054 standard option from Tensilica. When enabled, @code{CONST16}
11055 instructions are always used in place of the standard @code{L32R}
11056 instructions. The use of @code{CONST16} is enabled by default only if
11057 the @code{L32R} instruction is not available.
11060 @itemx -mno-fused-madd
11061 @opindex mfused-madd
11062 @opindex mno-fused-madd
11063 Enable or disable use of fused multiply/add and multiply/subtract
11064 instructions in the floating-point option. This has no effect if the
11065 floating-point option is not also enabled. Disabling fused multiply/add
11066 and multiply/subtract instructions forces the compiler to use separate
11067 instructions for the multiply and add/subtract operations. This may be
11068 desirable in some cases where strict IEEE 754-compliant results are
11069 required: the fused multiply add/subtract instructions do not round the
11070 intermediate result, thereby producing results with @emph{more} bits of
11071 precision than specified by the IEEE standard. Disabling fused multiply
11072 add/subtract instructions also ensures that the program output is not
11073 sensitive to the compiler's ability to combine multiply and add/subtract
11076 @item -mtext-section-literals
11077 @itemx -mno-text-section-literals
11078 @opindex mtext-section-literals
11079 @opindex mno-text-section-literals
11080 Control the treatment of literal pools. The default is
11081 @option{-mno-text-section-literals}, which places literals in a separate
11082 section in the output file. This allows the literal pool to be placed
11083 in a data RAM/ROM, and it also allows the linker to combine literal
11084 pools from separate object files to remove redundant literals and
11085 improve code size. With @option{-mtext-section-literals}, the literals
11086 are interspersed in the text section in order to keep them as close as
11087 possible to their references. This may be necessary for large assembly
11090 @item -mtarget-align
11091 @itemx -mno-target-align
11092 @opindex mtarget-align
11093 @opindex mno-target-align
11094 When this option is enabled, GCC instructs the assembler to
11095 automatically align instructions to reduce branch penalties at the
11096 expense of some code density. The assembler attempts to widen density
11097 instructions to align branch targets and the instructions following call
11098 instructions. If there are not enough preceding safe density
11099 instructions to align a target, no widening will be performed. The
11100 default is @option{-mtarget-align}. These options do not affect the
11101 treatment of auto-aligned instructions like @code{LOOP}, which the
11102 assembler will always align, either by widening density instructions or
11103 by inserting no-op instructions.
11106 @itemx -mno-longcalls
11107 @opindex mlongcalls
11108 @opindex mno-longcalls
11109 When this option is enabled, GCC instructs the assembler to translate
11110 direct calls to indirect calls unless it can determine that the target
11111 of a direct call is in the range allowed by the call instruction. This
11112 translation typically occurs for calls to functions in other source
11113 files. Specifically, the assembler translates a direct @code{CALL}
11114 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
11115 The default is @option{-mno-longcalls}. This option should be used in
11116 programs where the call target can potentially be out of range. This
11117 option is implemented in the assembler, not the compiler, so the
11118 assembly code generated by GCC will still show direct call
11119 instructions---look at the disassembled object code to see the actual
11120 instructions. Note that the assembler will use an indirect call for
11121 every cross-file call, not just those that really will be out of range.
11124 @node Code Gen Options
11125 @section Options for Code Generation Conventions
11126 @cindex code generation conventions
11127 @cindex options, code generation
11128 @cindex run-time options
11130 These machine-independent options control the interface conventions
11131 used in code generation.
11133 Most of them have both positive and negative forms; the negative form
11134 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
11135 one of the forms is listed---the one which is not the default. You
11136 can figure out the other form by either removing @samp{no-} or adding
11140 @item -fbounds-check
11141 @opindex fbounds-check
11142 For front-ends that support it, generate additional code to check that
11143 indices used to access arrays are within the declared range. This is
11144 currently only supported by the Java and Fortran 77 front-ends, where
11145 this option defaults to true and false respectively.
11149 This option generates traps for signed overflow on addition, subtraction,
11150 multiplication operations.
11154 This option instructs the compiler to assume that signed arithmetic
11155 overflow of addition, subtraction and multiplication wraps around
11156 using twos-complement representation. This flag enables some optimizations
11157 and disables other. This option is enabled by default for the Java
11158 front-end, as required by the Java language specification.
11161 @opindex fexceptions
11162 Enable exception handling. Generates extra code needed to propagate
11163 exceptions. For some targets, this implies GCC will generate frame
11164 unwind information for all functions, which can produce significant data
11165 size overhead, although it does not affect execution. If you do not
11166 specify this option, GCC will enable it by default for languages like
11167 C++ which normally require exception handling, and disable it for
11168 languages like C that do not normally require it. However, you may need
11169 to enable this option when compiling C code that needs to interoperate
11170 properly with exception handlers written in C++. You may also wish to
11171 disable this option if you are compiling older C++ programs that don't
11172 use exception handling.
11174 @item -fnon-call-exceptions
11175 @opindex fnon-call-exceptions
11176 Generate code that allows trapping instructions to throw exceptions.
11177 Note that this requires platform-specific runtime support that does
11178 not exist everywhere. Moreover, it only allows @emph{trapping}
11179 instructions to throw exceptions, i.e.@: memory references or floating
11180 point instructions. It does not allow exceptions to be thrown from
11181 arbitrary signal handlers such as @code{SIGALRM}.
11183 @item -funwind-tables
11184 @opindex funwind-tables
11185 Similar to @option{-fexceptions}, except that it will just generate any needed
11186 static data, but will not affect the generated code in any other way.
11187 You will normally not enable this option; instead, a language processor
11188 that needs this handling would enable it on your behalf.
11190 @item -fasynchronous-unwind-tables
11191 @opindex funwind-tables
11192 Generate unwind table in dwarf2 format, if supported by target machine. The
11193 table is exact at each instruction boundary, so it can be used for stack
11194 unwinding from asynchronous events (such as debugger or garbage collector).
11196 @item -fpcc-struct-return
11197 @opindex fpcc-struct-return
11198 Return ``short'' @code{struct} and @code{union} values in memory like
11199 longer ones, rather than in registers. This convention is less
11200 efficient, but it has the advantage of allowing intercallability between
11201 GCC-compiled files and files compiled with other compilers, particularly
11202 the Portable C Compiler (pcc).
11204 The precise convention for returning structures in memory depends
11205 on the target configuration macros.
11207 Short structures and unions are those whose size and alignment match
11208 that of some integer type.
11210 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
11211 switch is not binary compatible with code compiled with the
11212 @option{-freg-struct-return} switch.
11213 Use it to conform to a non-default application binary interface.
11215 @item -freg-struct-return
11216 @opindex freg-struct-return
11217 Return @code{struct} and @code{union} values in registers when possible.
11218 This is more efficient for small structures than
11219 @option{-fpcc-struct-return}.
11221 If you specify neither @option{-fpcc-struct-return} nor
11222 @option{-freg-struct-return}, GCC defaults to whichever convention is
11223 standard for the target. If there is no standard convention, GCC
11224 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
11225 the principal compiler. In those cases, we can choose the standard, and
11226 we chose the more efficient register return alternative.
11228 @strong{Warning:} code compiled with the @option{-freg-struct-return}
11229 switch is not binary compatible with code compiled with the
11230 @option{-fpcc-struct-return} switch.
11231 Use it to conform to a non-default application binary interface.
11233 @item -fshort-enums
11234 @opindex fshort-enums
11235 Allocate to an @code{enum} type only as many bytes as it needs for the
11236 declared range of possible values. Specifically, the @code{enum} type
11237 will be equivalent to the smallest integer type which has enough room.
11239 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
11240 code that is not binary compatible with code generated without that switch.
11241 Use it to conform to a non-default application binary interface.
11243 @item -fshort-double
11244 @opindex fshort-double
11245 Use the same size for @code{double} as for @code{float}.
11247 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
11248 code that is not binary compatible with code generated without that switch.
11249 Use it to conform to a non-default application binary interface.
11251 @item -fshort-wchar
11252 @opindex fshort-wchar
11253 Override the underlying type for @samp{wchar_t} to be @samp{short
11254 unsigned int} instead of the default for the target. This option is
11255 useful for building programs to run under WINE@.
11257 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
11258 code that is not binary compatible with code generated without that switch.
11259 Use it to conform to a non-default application binary interface.
11261 @item -fshared-data
11262 @opindex fshared-data
11263 Requests that the data and non-@code{const} variables of this
11264 compilation be shared data rather than private data. The distinction
11265 makes sense only on certain operating systems, where shared data is
11266 shared between processes running the same program, while private data
11267 exists in one copy per process.
11270 @opindex fno-common
11271 In C, allocate even uninitialized global variables in the data section of the
11272 object file, rather than generating them as common blocks. This has the
11273 effect that if the same variable is declared (without @code{extern}) in
11274 two different compilations, you will get an error when you link them.
11275 The only reason this might be useful is if you wish to verify that the
11276 program will work on other systems which always work this way.
11280 Ignore the @samp{#ident} directive.
11282 @item -fno-gnu-linker
11283 @opindex fno-gnu-linker
11284 Do not output global initializations (such as C++ constructors and
11285 destructors) in the form used by the GNU linker (on systems where the GNU
11286 linker is the standard method of handling them). Use this option when
11287 you want to use a non-GNU linker, which also requires using the
11288 @command{collect2} program to make sure the system linker includes
11289 constructors and destructors. (@command{collect2} is included in the GCC
11290 distribution.) For systems which @emph{must} use @command{collect2}, the
11291 compiler driver @command{gcc} is configured to do this automatically.
11293 @item -finhibit-size-directive
11294 @opindex finhibit-size-directive
11295 Don't output a @code{.size} assembler directive, or anything else that
11296 would cause trouble if the function is split in the middle, and the
11297 two halves are placed at locations far apart in memory. This option is
11298 used when compiling @file{crtstuff.c}; you should not need to use it
11301 @item -fverbose-asm
11302 @opindex fverbose-asm
11303 Put extra commentary information in the generated assembly code to
11304 make it more readable. This option is generally only of use to those
11305 who actually need to read the generated assembly code (perhaps while
11306 debugging the compiler itself).
11308 @option{-fno-verbose-asm}, the default, causes the
11309 extra information to be omitted and is useful when comparing two assembler
11314 @cindex global offset table
11316 Generate position-independent code (PIC) suitable for use in a shared
11317 library, if supported for the target machine. Such code accesses all
11318 constant addresses through a global offset table (GOT)@. The dynamic
11319 loader resolves the GOT entries when the program starts (the dynamic
11320 loader is not part of GCC; it is part of the operating system). If
11321 the GOT size for the linked executable exceeds a machine-specific
11322 maximum size, you get an error message from the linker indicating that
11323 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
11324 instead. (These maximums are 16k on the m88k, 8k on the SPARC, and 32k
11325 on the m68k and RS/6000. The 386 has no such limit.)
11327 Position-independent code requires special support, and therefore works
11328 only on certain machines. For the 386, GCC supports PIC for System V
11329 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
11330 position-independent.
11334 If supported for the target machine, emit position-independent code,
11335 suitable for dynamic linking and avoiding any limit on the size of the
11336 global offset table. This option makes a difference on the m68k, m88k,
11339 Position-independent code requires special support, and therefore works
11340 only on certain machines.
11346 These options are similar to @option{-fpic} and @option{-fPIC}, but
11347 generated position independent code can be only linked into executables.
11348 Usually these options are used when @option{-pie} GCC option will be
11349 used during linking.
11351 @item -ffixed-@var{reg}
11353 Treat the register named @var{reg} as a fixed register; generated code
11354 should never refer to it (except perhaps as a stack pointer, frame
11355 pointer or in some other fixed role).
11357 @var{reg} must be the name of a register. The register names accepted
11358 are machine-specific and are defined in the @code{REGISTER_NAMES}
11359 macro in the machine description macro file.
11361 This flag does not have a negative form, because it specifies a
11364 @item -fcall-used-@var{reg}
11365 @opindex fcall-used
11366 Treat the register named @var{reg} as an allocable register that is
11367 clobbered by function calls. It may be allocated for temporaries or
11368 variables that do not live across a call. Functions compiled this way
11369 will not save and restore the register @var{reg}.
11371 It is an error to used this flag with the frame pointer or stack pointer.
11372 Use of this flag for other registers that have fixed pervasive roles in
11373 the machine's execution model will produce disastrous results.
11375 This flag does not have a negative form, because it specifies a
11378 @item -fcall-saved-@var{reg}
11379 @opindex fcall-saved
11380 Treat the register named @var{reg} as an allocable register saved by
11381 functions. It may be allocated even for temporaries or variables that
11382 live across a call. Functions compiled this way will save and restore
11383 the register @var{reg} if they use it.
11385 It is an error to used this flag with the frame pointer or stack pointer.
11386 Use of this flag for other registers that have fixed pervasive roles in
11387 the machine's execution model will produce disastrous results.
11389 A different sort of disaster will result from the use of this flag for
11390 a register in which function values may be returned.
11392 This flag does not have a negative form, because it specifies a
11395 @item -fpack-struct
11396 @opindex fpack-struct
11397 Pack all structure members together without holes.
11399 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
11400 code that is not binary compatible with code generated without that switch.
11401 Additionally, it makes the code suboptimal.
11402 Use it to conform to a non-default application binary interface.
11404 @item -finstrument-functions
11405 @opindex finstrument-functions
11406 Generate instrumentation calls for entry and exit to functions. Just
11407 after function entry and just before function exit, the following
11408 profiling functions will be called with the address of the current
11409 function and its call site. (On some platforms,
11410 @code{__builtin_return_address} does not work beyond the current
11411 function, so the call site information may not be available to the
11412 profiling functions otherwise.)
11415 void __cyg_profile_func_enter (void *this_fn,
11417 void __cyg_profile_func_exit (void *this_fn,
11421 The first argument is the address of the start of the current function,
11422 which may be looked up exactly in the symbol table.
11424 This instrumentation is also done for functions expanded inline in other
11425 functions. The profiling calls will indicate where, conceptually, the
11426 inline function is entered and exited. This means that addressable
11427 versions of such functions must be available. If all your uses of a
11428 function are expanded inline, this may mean an additional expansion of
11429 code size. If you use @samp{extern inline} in your C code, an
11430 addressable version of such functions must be provided. (This is
11431 normally the case anyways, but if you get lucky and the optimizer always
11432 expands the functions inline, you might have gotten away without
11433 providing static copies.)
11435 A function may be given the attribute @code{no_instrument_function}, in
11436 which case this instrumentation will not be done. This can be used, for
11437 example, for the profiling functions listed above, high-priority
11438 interrupt routines, and any functions from which the profiling functions
11439 cannot safely be called (perhaps signal handlers, if the profiling
11440 routines generate output or allocate memory).
11442 @item -fstack-check
11443 @opindex fstack-check
11444 Generate code to verify that you do not go beyond the boundary of the
11445 stack. You should specify this flag if you are running in an
11446 environment with multiple threads, but only rarely need to specify it in
11447 a single-threaded environment since stack overflow is automatically
11448 detected on nearly all systems if there is only one stack.
11450 Note that this switch does not actually cause checking to be done; the
11451 operating system must do that. The switch causes generation of code
11452 to ensure that the operating system sees the stack being extended.
11454 @item -fstack-limit-register=@var{reg}
11455 @itemx -fstack-limit-symbol=@var{sym}
11456 @itemx -fno-stack-limit
11457 @opindex fstack-limit-register
11458 @opindex fstack-limit-symbol
11459 @opindex fno-stack-limit
11460 Generate code to ensure that the stack does not grow beyond a certain value,
11461 either the value of a register or the address of a symbol. If the stack
11462 would grow beyond the value, a signal is raised. For most targets,
11463 the signal is raised before the stack overruns the boundary, so
11464 it is possible to catch the signal without taking special precautions.
11466 For instance, if the stack starts at absolute address @samp{0x80000000}
11467 and grows downwards, you can use the flags
11468 @option{-fstack-limit-symbol=__stack_limit} and
11469 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
11470 of 128KB@. Note that this may only work with the GNU linker.
11472 @cindex aliasing of parameters
11473 @cindex parameters, aliased
11474 @item -fargument-alias
11475 @itemx -fargument-noalias
11476 @itemx -fargument-noalias-global
11477 @opindex fargument-alias
11478 @opindex fargument-noalias
11479 @opindex fargument-noalias-global
11480 Specify the possible relationships among parameters and between
11481 parameters and global data.
11483 @option{-fargument-alias} specifies that arguments (parameters) may
11484 alias each other and may alias global storage.@*
11485 @option{-fargument-noalias} specifies that arguments do not alias
11486 each other, but may alias global storage.@*
11487 @option{-fargument-noalias-global} specifies that arguments do not
11488 alias each other and do not alias global storage.
11490 Each language will automatically use whatever option is required by
11491 the language standard. You should not need to use these options yourself.
11493 @item -fleading-underscore
11494 @opindex fleading-underscore
11495 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
11496 change the way C symbols are represented in the object file. One use
11497 is to help link with legacy assembly code.
11499 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
11500 generate code that is not binary compatible with code generated without that
11501 switch. Use it to conform to a non-default application binary interface.
11502 Not all targets provide complete support for this switch.
11504 @item -ftls-model=@var{model}
11505 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
11506 The @var{model} argument should be one of @code{global-dynamic},
11507 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
11509 The default without @option{-fpic} is @code{initial-exec}; with
11510 @option{-fpic} the default is @code{global-dynamic}.
11515 @node Environment Variables
11516 @section Environment Variables Affecting GCC
11517 @cindex environment variables
11519 @c man begin ENVIRONMENT
11520 This section describes several environment variables that affect how GCC
11521 operates. Some of them work by specifying directories or prefixes to use
11522 when searching for various kinds of files. Some are used to specify other
11523 aspects of the compilation environment.
11525 Note that you can also specify places to search using options such as
11526 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
11527 take precedence over places specified using environment variables, which
11528 in turn take precedence over those specified by the configuration of GCC@.
11529 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
11530 GNU Compiler Collection (GCC) Internals}.
11535 @c @itemx LC_COLLATE
11537 @c @itemx LC_MONETARY
11538 @c @itemx LC_NUMERIC
11543 @c @findex LC_COLLATE
11544 @findex LC_MESSAGES
11545 @c @findex LC_MONETARY
11546 @c @findex LC_NUMERIC
11550 These environment variables control the way that GCC uses
11551 localization information that allow GCC to work with different
11552 national conventions. GCC inspects the locale categories
11553 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
11554 so. These locale categories can be set to any value supported by your
11555 installation. A typical value is @samp{en_UK} for English in the United
11558 The @env{LC_CTYPE} environment variable specifies character
11559 classification. GCC uses it to determine the character boundaries in
11560 a string; this is needed for some multibyte encodings that contain quote
11561 and escape characters that would otherwise be interpreted as a string
11564 The @env{LC_MESSAGES} environment variable specifies the language to
11565 use in diagnostic messages.
11567 If the @env{LC_ALL} environment variable is set, it overrides the value
11568 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
11569 and @env{LC_MESSAGES} default to the value of the @env{LANG}
11570 environment variable. If none of these variables are set, GCC
11571 defaults to traditional C English behavior.
11575 If @env{TMPDIR} is set, it specifies the directory to use for temporary
11576 files. GCC uses temporary files to hold the output of one stage of
11577 compilation which is to be used as input to the next stage: for example,
11578 the output of the preprocessor, which is the input to the compiler
11581 @item GCC_EXEC_PREFIX
11582 @findex GCC_EXEC_PREFIX
11583 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
11584 names of the subprograms executed by the compiler. No slash is added
11585 when this prefix is combined with the name of a subprogram, but you can
11586 specify a prefix that ends with a slash if you wish.
11588 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
11589 an appropriate prefix to use based on the pathname it was invoked with.
11591 If GCC cannot find the subprogram using the specified prefix, it
11592 tries looking in the usual places for the subprogram.
11594 The default value of @env{GCC_EXEC_PREFIX} is
11595 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the value
11596 of @code{prefix} when you ran the @file{configure} script.
11598 Other prefixes specified with @option{-B} take precedence over this prefix.
11600 This prefix is also used for finding files such as @file{crt0.o} that are
11603 In addition, the prefix is used in an unusual way in finding the
11604 directories to search for header files. For each of the standard
11605 directories whose name normally begins with @samp{/usr/local/lib/gcc}
11606 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
11607 replacing that beginning with the specified prefix to produce an
11608 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
11609 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
11610 These alternate directories are searched first; the standard directories
11613 @item COMPILER_PATH
11614 @findex COMPILER_PATH
11615 The value of @env{COMPILER_PATH} is a colon-separated list of
11616 directories, much like @env{PATH}. GCC tries the directories thus
11617 specified when searching for subprograms, if it can't find the
11618 subprograms using @env{GCC_EXEC_PREFIX}.
11621 @findex LIBRARY_PATH
11622 The value of @env{LIBRARY_PATH} is a colon-separated list of
11623 directories, much like @env{PATH}. When configured as a native compiler,
11624 GCC tries the directories thus specified when searching for special
11625 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
11626 using GCC also uses these directories when searching for ordinary
11627 libraries for the @option{-l} option (but directories specified with
11628 @option{-L} come first).
11632 @cindex locale definition
11633 This variable is used to pass locale information to the compiler. One way in
11634 which this information is used is to determine the character set to be used
11635 when character literals, string literals and comments are parsed in C and C++.
11636 When the compiler is configured to allow multibyte characters,
11637 the following values for @env{LANG} are recognized:
11641 Recognize JIS characters.
11643 Recognize SJIS characters.
11645 Recognize EUCJP characters.
11648 If @env{LANG} is not defined, or if it has some other value, then the
11649 compiler will use mblen and mbtowc as defined by the default locale to
11650 recognize and translate multibyte characters.
11654 Some additional environments variables affect the behavior of the
11657 @include cppenv.texi
11661 @node Precompiled Headers
11662 @section Using Precompiled Headers
11663 @cindex precompiled headers
11664 @cindex speed of compilation
11666 Often large projects have many header files that are included in every
11667 source file. The time the compiler takes to process these header files
11668 over and over again can account for nearly all of the time required to
11669 build the project. To make builds faster, GCC allows users to
11670 `precompile' a header file; then, if builds can use the precompiled
11671 header file they will be much faster.
11673 To create a precompiled header file, simply compile it as you would any
11674 other file, if necessary using the @option{-x} option to make the driver
11675 treat it as a C or C++ header file. You will probably want to use a
11676 tool like @command{make} to keep the precompiled header up-to-date when
11677 the headers it contains change.
11679 A precompiled header file will be searched for when @code{#include} is
11680 seen in the compilation. As it searches for the included file
11681 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
11682 compiler looks for a precompiled header in each directory just before it
11683 looks for the include file in that directory. The name searched for is
11684 the name specified in the @code{#include} with @samp{.gch} appended. If
11685 the precompiled header file can't be used, it is ignored.
11687 For instance, if you have @code{#include "all.h"}, and you have
11688 @file{all.h.gch} in the same directory as @file{all.h}, then the
11689 precompiled header file will be used if possible, and the original
11690 header will be used otherwise.
11692 Alternatively, you might decide to put the precompiled header file in a
11693 directory and use @option{-I} to ensure that directory is searched
11694 before (or instead of) the directory containing the original header.
11695 Then, if you want to check that the precompiled header file is always
11696 used, you can put a file of the same name as the original header in this
11697 directory containing an @code{#error} command.
11699 This also works with @option{-include}. So yet another way to use
11700 precompiled headers, good for projects not designed with precompiled
11701 header files in mind, is to simply take most of the header files used by
11702 a project, include them from another header file, precompile that header
11703 file, and @option{-include} the precompiled header. If the header files
11704 have guards against multiple inclusion, they will be skipped because
11705 they've already been included (in the precompiled header).
11707 If you need to precompile the same header file for different
11708 languages, targets, or compiler options, you can instead make a
11709 @emph{directory} named like @file{all.h.gch}, and put each precompiled
11710 header in the directory. (It doesn't matter what you call the files
11711 in the directory, every precompiled header in the directory will be
11712 considered.) The first precompiled header encountered in the
11713 directory that is valid for this compilation will be used; they're
11714 searched in no particular order.
11716 There are many other possibilities, limited only by your imagination,
11717 good sense, and the constraints of your build system.
11719 A precompiled header file can be used only when these conditions apply:
11723 Only one precompiled header can be used in a particular compilation.
11725 A precompiled header can't be used once the first C token is seen. You
11726 can have preprocessor directives before a precompiled header; you can
11727 even include a precompiled header from inside another header, so long as
11728 there are no C tokens before the @code{#include}.
11730 The precompiled header file must be produced for the same language as
11731 the current compilation. You can't use a C precompiled header for a C++
11734 The precompiled header file must be produced by the same compiler
11735 version and configuration as the current compilation is using.
11736 The easiest way to guarantee this is to use the same compiler binary
11737 for creating and using precompiled headers.
11739 Any macros defined before the precompiled header (including with
11740 @option{-D}) must either be defined in the same way as when the
11741 precompiled header was generated, or must not affect the precompiled
11742 header, which usually means that the they don't appear in the
11743 precompiled header at all.
11745 Certain command-line options must be defined in the same way as when the
11746 precompiled header was generated. At present, it's not clear which
11747 options are safe to change and which are not; the safest choice is to
11748 use exactly the same options when generating and using the precompiled
11752 For all of these but the last, the compiler will automatically ignore
11753 the precompiled header if the conditions aren't met. For the last item,
11754 some option changes will cause the precompiled header to be rejected,
11755 but not all incompatible option combinations have yet been found. If
11756 you find a new incompatible combination, please consider filing a bug
11757 report, see @ref{Bugs}.
11759 @node Running Protoize
11760 @section Running Protoize
11762 The program @code{protoize} is an optional part of GCC@. You can use
11763 it to add prototypes to a program, thus converting the program to ISO
11764 C in one respect. The companion program @code{unprotoize} does the
11765 reverse: it removes argument types from any prototypes that are found.
11767 When you run these programs, you must specify a set of source files as
11768 command line arguments. The conversion programs start out by compiling
11769 these files to see what functions they define. The information gathered
11770 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
11772 After scanning comes actual conversion. The specified files are all
11773 eligible to be converted; any files they include (whether sources or
11774 just headers) are eligible as well.
11776 But not all the eligible files are converted. By default,
11777 @code{protoize} and @code{unprotoize} convert only source and header
11778 files in the current directory. You can specify additional directories
11779 whose files should be converted with the @option{-d @var{directory}}
11780 option. You can also specify particular files to exclude with the
11781 @option{-x @var{file}} option. A file is converted if it is eligible, its
11782 directory name matches one of the specified directory names, and its
11783 name within the directory has not been excluded.
11785 Basic conversion with @code{protoize} consists of rewriting most
11786 function definitions and function declarations to specify the types of
11787 the arguments. The only ones not rewritten are those for varargs
11790 @code{protoize} optionally inserts prototype declarations at the
11791 beginning of the source file, to make them available for any calls that
11792 precede the function's definition. Or it can insert prototype
11793 declarations with block scope in the blocks where undeclared functions
11796 Basic conversion with @code{unprotoize} consists of rewriting most
11797 function declarations to remove any argument types, and rewriting
11798 function definitions to the old-style pre-ISO form.
11800 Both conversion programs print a warning for any function declaration or
11801 definition that they can't convert. You can suppress these warnings
11804 The output from @code{protoize} or @code{unprotoize} replaces the
11805 original source file. The original file is renamed to a name ending
11806 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
11807 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
11808 for DOS) file already exists, then the source file is simply discarded.
11810 @code{protoize} and @code{unprotoize} both depend on GCC itself to
11811 scan the program and collect information about the functions it uses.
11812 So neither of these programs will work until GCC is installed.
11814 Here is a table of the options you can use with @code{protoize} and
11815 @code{unprotoize}. Each option works with both programs unless
11819 @item -B @var{directory}
11820 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
11821 usual directory (normally @file{/usr/local/lib}). This file contains
11822 prototype information about standard system functions. This option
11823 applies only to @code{protoize}.
11825 @item -c @var{compilation-options}
11826 Use @var{compilation-options} as the options when running @command{gcc} to
11827 produce the @samp{.X} files. The special option @option{-aux-info} is
11828 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
11830 Note that the compilation options must be given as a single argument to
11831 @code{protoize} or @code{unprotoize}. If you want to specify several
11832 @command{gcc} options, you must quote the entire set of compilation options
11833 to make them a single word in the shell.
11835 There are certain @command{gcc} arguments that you cannot use, because they
11836 would produce the wrong kind of output. These include @option{-g},
11837 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
11838 the @var{compilation-options}, they are ignored.
11841 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
11842 systems) instead of @samp{.c}. This is convenient if you are converting
11843 a C program to C++. This option applies only to @code{protoize}.
11846 Add explicit global declarations. This means inserting explicit
11847 declarations at the beginning of each source file for each function
11848 that is called in the file and was not declared. These declarations
11849 precede the first function definition that contains a call to an
11850 undeclared function. This option applies only to @code{protoize}.
11852 @item -i @var{string}
11853 Indent old-style parameter declarations with the string @var{string}.
11854 This option applies only to @code{protoize}.
11856 @code{unprotoize} converts prototyped function definitions to old-style
11857 function definitions, where the arguments are declared between the
11858 argument list and the initial @samp{@{}. By default, @code{unprotoize}
11859 uses five spaces as the indentation. If you want to indent with just
11860 one space instead, use @option{-i " "}.
11863 Keep the @samp{.X} files. Normally, they are deleted after conversion
11867 Add explicit local declarations. @code{protoize} with @option{-l} inserts
11868 a prototype declaration for each function in each block which calls the
11869 function without any declaration. This option applies only to
11873 Make no real changes. This mode just prints information about the conversions
11874 that would have been done without @option{-n}.
11877 Make no @samp{.save} files. The original files are simply deleted.
11878 Use this option with caution.
11880 @item -p @var{program}
11881 Use the program @var{program} as the compiler. Normally, the name
11882 @file{gcc} is used.
11885 Work quietly. Most warnings are suppressed.
11888 Print the version number, just like @option{-v} for @command{gcc}.
11891 If you need special compiler options to compile one of your program's
11892 source files, then you should generate that file's @samp{.X} file
11893 specially, by running @command{gcc} on that source file with the
11894 appropriate options and the option @option{-aux-info}. Then run
11895 @code{protoize} on the entire set of files. @code{protoize} will use
11896 the existing @samp{.X} file because it is newer than the source file.
11900 gcc -Dfoo=bar file1.c -aux-info file1.X
11905 You need to include the special files along with the rest in the
11906 @code{protoize} command, even though their @samp{.X} files already
11907 exist, because otherwise they won't get converted.
11909 @xref{Protoize Caveats}, for more information on how to use
11910 @code{protoize} successfully.