1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
3 @c This is part of the GCC manual.
4 @c For copying conditions, see the file gcc.texi.
11 @c man begin COPYRIGHT
12 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
13 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
15 Permission is granted to copy, distribute and/or modify this document
16 under the terms of the GNU Free Documentation License, Version 1.2 or
17 any later version published by the Free Software Foundation; with the
18 Invariant Sections being ``GNU General Public License'' and ``Funding
19 Free Software'', the Front-Cover texts being (a) (see below), and with
20 the Back-Cover Texts being (b) (see below). A copy of the license is
21 included in the gfdl(7) man page.
23 (a) The FSF's Front-Cover Text is:
27 (b) The FSF's Back-Cover Text is:
29 You have freedom to copy and modify this GNU Manual, like GNU
30 software. Copies published by the Free Software Foundation raise
31 funds for GNU development.
33 @c Set file name and title for the man page.
35 @settitle GNU project C and C++ compiler
37 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
38 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
39 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
40 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
41 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
42 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
43 [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{}
45 Only the most useful options are listed here; see below for the
46 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
49 gpl(7), gfdl(7), fsf-funding(7),
50 cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
51 and the Info entries for @file{gcc}, @file{cpp}, @file{as},
52 @file{ld}, @file{binutils} and @file{gdb}.
55 For instructions on reporting bugs, see
56 @w{@uref{http://gcc.gnu.org/bugs.html}}.
59 See the Info entry for @command{gcc}, or
60 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
61 for contributors to GCC@.
66 @chapter GCC Command Options
67 @cindex GCC command options
68 @cindex command options
69 @cindex options, GCC command
71 @c man begin DESCRIPTION
72 When you invoke GCC, it normally does preprocessing, compilation,
73 assembly and linking. The ``overall options'' allow you to stop this
74 process at an intermediate stage. For example, the @option{-c} option
75 says not to run the linker. Then the output consists of object files
76 output by the assembler.
78 Other options are passed on to one stage of processing. Some options
79 control the preprocessor and others the compiler itself. Yet other
80 options control the assembler and linker; most of these are not
81 documented here, since you rarely need to use any of them.
83 @cindex C compilation options
84 Most of the command line options that you can use with GCC are useful
85 for C programs; when an option is only useful with another language
86 (usually C++), the explanation says so explicitly. If the description
87 for a particular option does not mention a source language, you can use
88 that option with all supported languages.
90 @cindex C++ compilation options
91 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
92 options for compiling C++ programs.
94 @cindex grouping options
95 @cindex options, grouping
96 The @command{gcc} program accepts options and file names as operands. Many
97 options have multi-letter names; therefore multiple single-letter options
98 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
101 @cindex order of options
102 @cindex options, order
103 You can mix options and other arguments. For the most part, the order
104 you use doesn't matter. Order does matter when you use several options
105 of the same kind; for example, if you specify @option{-L} more than once,
106 the directories are searched in the order specified.
108 Many options have long names starting with @samp{-f} or with
109 @samp{-W}---for example,
110 @option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of
111 these have both positive and negative forms; the negative form of
112 @option{-ffoo} would be @option{-fno-foo}. This manual documents
113 only one of these two forms, whichever one is not the default.
117 @xref{Option Index}, for an index to GCC's options.
120 * Option Summary:: Brief list of all options, without explanations.
121 * Overall Options:: Controlling the kind of output:
122 an executable, object files, assembler files,
123 or preprocessed source.
124 * Invoking G++:: Compiling C++ programs.
125 * C Dialect Options:: Controlling the variant of C language compiled.
126 * C++ Dialect Options:: Variations on C++.
127 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
129 * Language Independent Options:: Controlling how diagnostics should be
131 * Warning Options:: How picky should the compiler be?
132 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
133 * Optimize Options:: How much optimization?
134 * Preprocessor Options:: Controlling header files and macro definitions.
135 Also, getting dependency information for Make.
136 * Assembler Options:: Passing options to the assembler.
137 * Link Options:: Specifying libraries and so on.
138 * Directory Options:: Where to find header files and libraries.
139 Where to find the compiler executable files.
140 * Spec Files:: How to pass switches to sub-processes.
141 * Target Options:: Running a cross-compiler, or an old version of GCC.
142 * Submodel Options:: Specifying minor hardware or convention variations,
143 such as 68010 vs 68020.
144 * Code Gen Options:: Specifying conventions for function calls, data layout
146 * Environment Variables:: Env vars that affect GCC.
147 * Precompiled Headers:: Compiling a header once, and using it many times.
148 * Running Protoize:: Automatically adding or removing function prototypes.
154 @section Option Summary
156 Here is a summary of all the options, grouped by type. Explanations are
157 in the following sections.
160 @item Overall Options
161 @xref{Overall Options,,Options Controlling the Kind of Output}.
162 @gccoptlist{-c -S -E -o @var{file} -combine -pipe -pass-exit-codes @gol
163 -x @var{language} -v -### --help --target-help --version @@@var{file}}
165 @item C Language Options
166 @xref{C Dialect Options,,Options Controlling C Dialect}.
167 @gccoptlist{-ansi -std=@var{standard} -aux-info @var{filename} @gol
168 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
169 -fhosted -ffreestanding -fopenmp -fms-extensions @gol
170 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
171 -fallow-single-precision -fcond-mismatch @gol
172 -fsigned-bitfields -fsigned-char @gol
173 -funsigned-bitfields -funsigned-char}
175 @item C++ Language Options
176 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
177 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
178 -fconserve-space -ffriend-injection @gol
179 -fno-elide-constructors @gol
180 -fno-enforce-eh-specs @gol
181 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
182 -fno-implicit-templates @gol
183 -fno-implicit-inline-templates @gol
184 -fno-implement-inlines -fms-extensions @gol
185 -fno-nonansi-builtins -fno-operator-names @gol
186 -fno-optional-diags -fpermissive @gol
187 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
188 -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
189 -fno-default-inline -fvisibility-inlines-hidden @gol
190 -Wabi -Wctor-dtor-privacy @gol
191 -Wnon-virtual-dtor -Wreorder @gol
192 -Weffc++ -Wno-deprecated -Wstrict-null-sentinel @gol
193 -Wno-non-template-friend -Wold-style-cast @gol
194 -Woverloaded-virtual -Wno-pmf-conversions @gol
197 @item Objective-C and Objective-C++ Language Options
198 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
199 Objective-C and Objective-C++ Dialects}.
200 @gccoptlist{-fconstant-string-class=@var{class-name} @gol
201 -fgnu-runtime -fnext-runtime @gol
202 -fno-nil-receivers @gol
203 -fobjc-call-cxx-cdtors @gol
204 -fobjc-direct-dispatch @gol
205 -fobjc-exceptions @gol
207 -freplace-objc-classes @gol
210 -Wassign-intercept @gol
211 -Wno-protocol -Wselector @gol
212 -Wstrict-selector-match @gol
213 -Wundeclared-selector}
215 @item Language Independent Options
216 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
217 @gccoptlist{-fmessage-length=@var{n} @gol
218 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol
219 -fdiagnostics-show-option}
221 @item Warning Options
222 @xref{Warning Options,,Options to Request or Suppress Warnings}.
223 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
224 -w -Wextra -Wall -Waggregate-return -Walways-true -Wno-attributes @gol
225 -Wc++-compat -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
226 -Wconversion -Wno-deprecated-declarations @gol
227 -Wdisabled-optimization -Wno-div-by-zero @gol
228 -Wempty-body -Wno-endif-labels @gol
229 -Werror -Werror-* -Werror-implicit-function-declaration @gol
230 -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
231 -Wno-format-extra-args -Wformat-nonliteral @gol
232 -Wformat-security -Wformat-y2k @gol
233 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
234 -Wimport -Wno-import -Winit-self -Winline @gol
235 -Wno-int-to-pointer-cast @gol
236 -Wno-invalid-offsetof -Winvalid-pch @gol
237 -Wlarger-than-@var{len} -Wunsafe-loop-optimizations -Wlong-long @gol
238 -Wmain -Wmissing-braces -Wmissing-field-initializers @gol
239 -Wmissing-format-attribute -Wmissing-include-dirs @gol
240 -Wmissing-noreturn @gol
241 -Wno-multichar -Wnonnull -Wno-overflow @gol
242 -Woverlength-strings -Wpacked -Wpadded @gol
243 -Wparentheses -Wpointer-arith -Wno-pointer-to-int-cast @gol
244 -Wredundant-decls @gol
245 -Wreturn-type -Wsequence-point -Wshadow @gol
246 -Wsign-compare -Wstack-protector @gol
247 -Wstrict-aliasing -Wstrict-aliasing=2 @gol
248 -Wstring-literal-comparison @gol
249 -Wswitch -Wswitch-default -Wswitch-enum @gol
250 -Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized @gol
251 -Wunknown-pragmas -Wno-pragmas -Wunreachable-code @gol
252 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
253 -Wunused-value -Wunused-variable -Wvariadic-macros @gol
254 -Wvolatile-register-var -Wwrite-strings}
256 @item C-only Warning Options
257 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
258 -Wmissing-prototypes -Wnested-externs -Wold-style-definition @gol
259 -Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol
260 -Wdeclaration-after-statement -Wpointer-sign}
262 @item Debugging Options
263 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
264 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
265 -fdump-noaddr -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
266 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
267 -fdump-ipa-all -fdump-ipa-cgraph @gol
269 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
270 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
271 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
272 -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol
274 -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
275 -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
276 -fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol
277 -fdump-tree-dom@r{[}-@var{n}@r{]} @gol
278 -fdump-tree-dse@r{[}-@var{n}@r{]} @gol
279 -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
280 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
281 -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
282 -fdump-tree-nrv -fdump-tree-vect @gol
283 -fdump-tree-sink @gol
284 -fdump-tree-sra@r{[}-@var{n}@r{]} @gol
285 -fdump-tree-salias @gol
286 -fdump-tree-fre@r{[}-@var{n}@r{]} @gol
287 -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
288 -ftree-vectorizer-verbose=@var{n} @gol
289 -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
290 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
291 -feliminate-unused-debug-symbols -femit-class-debug-always @gol
292 -fmem-report -fprofile-arcs @gol
293 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
294 -ftest-coverage -ftime-report -fvar-tracking @gol
295 -g -g@var{level} -gcoff -gdwarf-2 @gol
296 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
297 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
298 -print-multi-directory -print-multi-lib @gol
299 -print-prog-name=@var{program} -print-search-dirs -Q @gol
302 @item Optimization Options
303 @xref{Optimize Options,,Options that Control Optimization}.
304 @gccoptlist{-falign-functions=@var{n} -falign-jumps=@var{n} @gol
305 -falign-labels=@var{n} -falign-loops=@var{n} @gol
306 -fbounds-check -fmudflap -fmudflapth -fmudflapir @gol
307 -fbranch-probabilities -fprofile-values -fvpt -fbranch-target-load-optimize @gol
308 -fbranch-target-load-optimize2 -fbtr-bb-exclusive @gol
309 -fcaller-saves -fcprop-registers -fcse-follow-jumps @gol
310 -fcse-skip-blocks -fcx-limited-range -fdata-sections @gol
311 -fdelayed-branch -fdelete-null-pointer-checks -fearly-inlining @gol
312 -fexpensive-optimizations -ffast-math -ffloat-store @gol
313 -fforce-addr -fforward-propagate -ffunction-sections @gol
314 -fgcse -fgcse-lm -fgcse-sm -fgcse-las -fgcse-after-reload @gol
315 -fcrossjumping -fif-conversion -fif-conversion2 @gol
316 -finline-functions -finline-functions-called-once @gol
317 -finline-limit=@var{n} -fkeep-inline-functions @gol
318 -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
319 -fmodulo-sched -fno-branch-count-reg @gol
320 -fno-default-inline -fno-defer-pop -fmove-loop-invariants @gol
321 -fno-function-cse -fno-guess-branch-probability @gol
322 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
323 -funsafe-math-optimizations -funsafe-loop-optimizations -ffinite-math-only @gol
324 -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
325 -fomit-frame-pointer -foptimize-register-move @gol
326 -foptimize-sibling-calls -fprefetch-loop-arrays @gol
327 -fprofile-generate -fprofile-use @gol
328 -fregmove -frename-registers @gol
329 -freorder-blocks -freorder-blocks-and-partition -freorder-functions @gol
330 -frerun-cse-after-loop @gol
331 -frounding-math -frtl-abstract-sequences @gol
332 -fschedule-insns -fschedule-insns2 @gol
333 -fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
334 -fsched-spec-load-dangerous @gol
335 -fsched-stalled-insns=@var{n} -fsched-stalled-insns-dep=@var{n} @gol
336 -fsched2-use-superblocks @gol
337 -fsched2-use-traces -fsee -freschedule-modulo-scheduled-loops @gol
338 -fsection-anchors -fsignaling-nans -fsingle-precision-constant @gol
339 -fstack-protector -fstack-protector-all @gol
340 -fstrict-aliasing -ftracer -fthread-jumps @gol
341 -funroll-all-loops -funroll-loops -fpeel-loops @gol
342 -fsplit-ivs-in-unroller -funswitch-loops @gol
343 -fvariable-expansion-in-unroller @gol
344 -ftree-pre -ftree-ccp -ftree-dce -ftree-loop-optimize @gol
345 -ftree-loop-linear -ftree-loop-im -ftree-loop-ivcanon -fivopts @gol
346 -ftree-dominator-opts -ftree-dse -ftree-copyrename -ftree-sink @gol
347 -ftree-ch -ftree-sra -ftree-ter -ftree-lrs -ftree-fre -ftree-vectorize @gol
348 -ftree-vect-loop-version -ftree-salias -fipa-pta -fweb @gol
349 -ftree-copy-prop -ftree-store-ccp -ftree-store-copy-prop -fwhole-program @gol
350 --param @var{name}=@var{value}
351 -O -O0 -O1 -O2 -O3 -Os}
353 @item Preprocessor Options
354 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
355 @gccoptlist{-A@var{question}=@var{answer} @gol
356 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
357 -C -dD -dI -dM -dN @gol
358 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
359 -idirafter @var{dir} @gol
360 -include @var{file} -imacros @var{file} @gol
361 -iprefix @var{file} -iwithprefix @var{dir} @gol
362 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
363 -imultilib @var{dir} -isysroot @var{dir} @gol
364 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
365 -P -fworking-directory -remap @gol
366 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
367 -Xpreprocessor @var{option}}
369 @item Assembler Option
370 @xref{Assembler Options,,Passing Options to the Assembler}.
371 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
374 @xref{Link Options,,Options for Linking}.
375 @gccoptlist{@var{object-file-name} -l@var{library} @gol
376 -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
377 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
378 -Wl,@var{option} -Xlinker @var{option} @gol
381 @item Directory Options
382 @xref{Directory Options,,Options for Directory Search}.
383 @gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} -L@var{dir}
384 -specs=@var{file} -I- --sysroot=@var{dir}}
387 @c I wrote this xref this way to avoid overfull hbox. -- rms
388 @xref{Target Options}.
389 @gccoptlist{-V @var{version} -b @var{machine}}
391 @item Machine Dependent Options
392 @xref{Submodel Options,,Hardware Models and Configurations}.
393 @c This list is ordered alphanumerically by subsection name.
394 @c Try and put the significant identifier (CPU or system) first,
395 @c so users have a clue at guessing where the ones they want will be.
398 @gccoptlist{-EB -EL @gol
399 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
400 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
403 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
404 -mabi=@var{name} @gol
405 -mapcs-stack-check -mno-apcs-stack-check @gol
406 -mapcs-float -mno-apcs-float @gol
407 -mapcs-reentrant -mno-apcs-reentrant @gol
408 -msched-prolog -mno-sched-prolog @gol
409 -mlittle-endian -mbig-endian -mwords-little-endian @gol
410 -mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
411 -mthumb-interwork -mno-thumb-interwork @gol
412 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
413 -mstructure-size-boundary=@var{n} @gol
414 -mabort-on-noreturn @gol
415 -mlong-calls -mno-long-calls @gol
416 -msingle-pic-base -mno-single-pic-base @gol
417 -mpic-register=@var{reg} @gol
418 -mnop-fun-dllimport @gol
419 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
420 -mpoke-function-name @gol
422 -mtpcs-frame -mtpcs-leaf-frame @gol
423 -mcaller-super-interworking -mcallee-super-interworking @gol
427 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
428 -mcall-prologues -mno-tablejump -mtiny-stack -mint8}
430 @emph{Blackfin Options}
431 @gccoptlist{-momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
432 -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
433 -mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol
434 -mno-id-shared-library -mshared-library-id=@var{n} @gol
435 -mleaf-id-shared-library -mno-leaf-id-shared-library @gol
436 -msep-data -mno-sep-data -mlong-calls -mno-long-calls}
439 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
440 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
441 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
442 -mstack-align -mdata-align -mconst-align @gol
443 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
444 -melf -maout -melinux -mlinux -sim -sim2 @gol
445 -mmul-bug-workaround -mno-mul-bug-workaround}
448 @gccoptlist{-mmac -mpush-args}
450 @emph{Darwin Options}
451 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
452 -arch_only -bind_at_load -bundle -bundle_loader @gol
453 -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 -no_dead_strip_inits_and_terms @gol
462 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
463 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
464 -private_bundle -read_only_relocs -sectalign @gol
465 -sectobjectsymbols -whyload -seg1addr @gol
466 -sectcreate -sectobjectsymbols -sectorder @gol
467 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
468 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
469 -segprot -segs_read_only_addr -segs_read_write_addr @gol
470 -single_module -static -sub_library -sub_umbrella @gol
471 -twolevel_namespace -umbrella -undefined @gol
472 -unexported_symbols_list -weak_reference_mismatches @gol
473 -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
474 -mkernel -mone-byte-bool}
476 @emph{DEC Alpha Options}
477 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
478 -mieee -mieee-with-inexact -mieee-conformant @gol
479 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
480 -mtrap-precision=@var{mode} -mbuild-constants @gol
481 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
482 -mbwx -mmax -mfix -mcix @gol
483 -mfloat-vax -mfloat-ieee @gol
484 -mexplicit-relocs -msmall-data -mlarge-data @gol
485 -msmall-text -mlarge-text @gol
486 -mmemory-latency=@var{time}}
488 @emph{DEC Alpha/VMS Options}
489 @gccoptlist{-mvms-return-codes}
492 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
493 -mhard-float -msoft-float @gol
494 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
495 -mdouble -mno-double @gol
496 -mmedia -mno-media -mmuladd -mno-muladd @gol
497 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
498 -mlinked-fp -mlong-calls -malign-labels @gol
499 -mlibrary-pic -macc-4 -macc-8 @gol
500 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
501 -moptimize-membar -mno-optimize-membar @gol
502 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
503 -mvliw-branch -mno-vliw-branch @gol
504 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
505 -mno-nested-cond-exec -mtomcat-stats @gol
509 @emph{GNU/Linux Options}
510 @gccoptlist{-muclibc}
512 @emph{H8/300 Options}
513 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
516 @gccoptlist{-march=@var{architecture-type} @gol
517 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
518 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
519 -mfixed-range=@var{register-range} @gol
520 -mjump-in-delay -mlinker-opt -mlong-calls @gol
521 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
522 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
523 -mno-jump-in-delay -mno-long-load-store @gol
524 -mno-portable-runtime -mno-soft-float @gol
525 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
526 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
527 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
528 -munix=@var{unix-std} -nolibdld -static -threads}
530 @emph{i386 and x86-64 Options}
531 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
532 -mfpmath=@var{unit} @gol
533 -masm=@var{dialect} -mno-fancy-math-387 @gol
534 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
535 -mno-wide-multiply -mrtd -malign-double @gol
536 -mpreferred-stack-boundary=@var{num} @gol
537 -mmmx -msse -msse2 -msse3 -mssse3 -m3dnow @gol
538 -mthreads -mno-align-stringops -minline-all-stringops @gol
539 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
540 -m96bit-long-double -mregparm=@var{num} -msseregparm @gol
542 -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
543 -mcmodel=@var{code-model} @gol
544 -m32 -m64 -mlarge-data-threshold=@var{num}}
547 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
548 -mvolatile-asm-stop -mregister-names -mno-sdata @gol
549 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
550 -minline-float-divide-max-throughput @gol
551 -minline-int-divide-min-latency @gol
552 -minline-int-divide-max-throughput @gol
553 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
554 -mno-dwarf2-asm -mearly-stop-bits @gol
555 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
556 -mtune=@var{cpu-type} -mt -pthread -milp32 -mlp64 @gol
557 -mno-sched-br-data-spec -msched-ar-data-spec -mno-sched-control-spec @gol
558 -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol
559 -msched-ldc -mno-sched-control-ldc -mno-sched-spec-verbose @gol
560 -mno-sched-prefer-non-data-spec-insns @gol
561 -mno-sched-prefer-non-control-spec-insns @gol
562 -mno-sched-count-spec-in-critical-path}
564 @emph{M32R/D Options}
565 @gccoptlist{-m32r2 -m32rx -m32r @gol
567 -malign-loops -mno-align-loops @gol
568 -missue-rate=@var{number} @gol
569 -mbranch-cost=@var{number} @gol
570 -mmodel=@var{code-size-model-type} @gol
571 -msdata=@var{sdata-type} @gol
572 -mno-flush-func -mflush-func=@var{name} @gol
573 -mno-flush-trap -mflush-trap=@var{number} @gol
577 @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
579 @emph{M680x0 Options}
580 @gccoptlist{-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
581 -m68060 -mcpu32 -m5200 -mcfv4e -m68881 -mbitfield @gol
582 -mc68000 -mc68020 @gol
583 -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
584 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
585 -mshared-library-id=n -mid-shared-library -mno-id-shared-library}
587 @emph{M68hc1x Options}
588 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
589 -mauto-incdec -minmax -mlong-calls -mshort @gol
590 -msoft-reg-count=@var{count}}
593 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
594 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
595 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
596 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
597 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
600 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
601 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
602 -mips16 -mno-mips16 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
603 -mshared -mno-shared -mxgot -mno-xgot -mgp32 -mgp64 @gol
604 -mfp32 -mfp64 -mhard-float -msoft-float @gol
605 -msingle-float -mdouble-float -mdsp -mpaired-single -mips3d @gol
606 -mlong64 -mlong32 -msym32 -mno-sym32 @gol
607 -G@var{num} -membedded-data -mno-embedded-data @gol
608 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
609 -msplit-addresses -mno-split-addresses @gol
610 -mexplicit-relocs -mno-explicit-relocs @gol
611 -mcheck-zero-division -mno-check-zero-division @gol
612 -mdivide-traps -mdivide-breaks @gol
613 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
614 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
615 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
616 -mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130 @gol
617 -mfix-sb1 -mno-fix-sb1 @gol
618 -mflush-func=@var{func} -mno-flush-func @gol
619 -mbranch-likely -mno-branch-likely @gol
620 -mfp-exceptions -mno-fp-exceptions @gol
621 -mvr4130-align -mno-vr4130-align}
624 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
625 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
626 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
627 -mno-base-addresses -msingle-exit -mno-single-exit}
629 @emph{MN10300 Options}
630 @gccoptlist{-mmult-bug -mno-mult-bug @gol
631 -mam33 -mno-am33 @gol
632 -mam33-2 -mno-am33-2 @gol
633 -mreturn-pointer-on-d0 @gol
637 @gccoptlist{-mno-crt0 -mbacc -msim @gol
638 -march=@var{cpu-type} }
640 @emph{PDP-11 Options}
641 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
642 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
643 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
644 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
645 -mbranch-expensive -mbranch-cheap @gol
646 -msplit -mno-split -munix-asm -mdec-asm}
648 @emph{PowerPC Options}
649 See RS/6000 and PowerPC Options.
651 @emph{RS/6000 and PowerPC Options}
652 @gccoptlist{-mcpu=@var{cpu-type} @gol
653 -mtune=@var{cpu-type} @gol
654 -mpower -mno-power -mpower2 -mno-power2 @gol
655 -mpowerpc -mpowerpc64 -mno-powerpc @gol
656 -maltivec -mno-altivec @gol
657 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
658 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
659 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd @gol
660 -mmfpgpr -mno-mfpgpr @gol
661 -mnew-mnemonics -mold-mnemonics @gol
662 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
663 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
664 -malign-power -malign-natural @gol
665 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
666 -mstring -mno-string -mupdate -mno-update @gol
667 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
668 -mstrict-align -mno-strict-align -mrelocatable @gol
669 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
670 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
671 -mdynamic-no-pic -maltivec -mswdiv @gol
672 -mprioritize-restricted-insns=@var{priority} @gol
673 -msched-costly-dep=@var{dependence_type} @gol
674 -minsert-sched-nops=@var{scheme} @gol
675 -mcall-sysv -mcall-netbsd @gol
676 -maix-struct-return -msvr4-struct-return @gol
677 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
678 -misel -mno-isel @gol
679 -misel=yes -misel=no @gol
681 -mspe=yes -mspe=no @gol
682 -mvrsave -mno-vrsave @gol
683 -mmulhw -mno-mulhw @gol
684 -mdlmzb -mno-dlmzb @gol
685 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
686 -mprototype -mno-prototype @gol
687 -msim -mmvme -mads -myellowknife -memb -msdata @gol
688 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
690 @emph{S/390 and zSeries Options}
691 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
692 -mhard-float -msoft-float -mlong-double-64 -mlong-double-128 @gol
693 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
694 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
695 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
696 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
697 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
700 @gccoptlist{-mel -mel @gol
705 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
706 -m4-nofpu -m4-single-only -m4-single -m4 @gol
707 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
708 -m5-64media -m5-64media-nofpu @gol
709 -m5-32media -m5-32media-nofpu @gol
710 -m5-compact -m5-compact-nofpu @gol
711 -mb -ml -mdalign -mrelax @gol
712 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
713 -mieee -misize -minline-ic_invalidate -mpadstruct -mspace @gol
714 -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
715 -mdivsi3_libfunc=@var{name} @gol
716 -madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
720 @gccoptlist{-mcpu=@var{cpu-type} @gol
721 -mtune=@var{cpu-type} @gol
722 -mcmodel=@var{code-model} @gol
723 -m32 -m64 -mapp-regs -mno-app-regs @gol
724 -mfaster-structs -mno-faster-structs @gol
725 -mfpu -mno-fpu -mhard-float -msoft-float @gol
726 -mhard-quad-float -msoft-quad-float @gol
727 -mimpure-text -mno-impure-text -mlittle-endian @gol
728 -mstack-bias -mno-stack-bias @gol
729 -munaligned-doubles -mno-unaligned-doubles @gol
730 -mv8plus -mno-v8plus -mvis -mno-vis
731 -threads -pthreads -pthread}
734 @gccoptlist{-mwarn-reloc -merror-reloc @gol
735 -msafe-dma -munsafe-dma @gol
737 -msmall-mem -mlarge-mem -mstdmain @gol
738 -mfixed-range=@var{register-range}}
740 @emph{System V Options}
741 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
743 @emph{TMS320C3x/C4x Options}
744 @gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
745 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
746 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
747 -mparallel-insns -mparallel-mpy -mpreserve-float}
750 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
751 -mprolog-function -mno-prolog-function -mspace @gol
752 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
753 -mapp-regs -mno-app-regs @gol
754 -mdisable-callt -mno-disable-callt @gol
760 @gccoptlist{-mg -mgnu -munix}
762 @emph{x86-64 Options}
763 See i386 and x86-64 Options.
765 @emph{Xstormy16 Options}
768 @emph{Xtensa Options}
769 @gccoptlist{-mconst16 -mno-const16 @gol
770 -mfused-madd -mno-fused-madd @gol
771 -mtext-section-literals -mno-text-section-literals @gol
772 -mtarget-align -mno-target-align @gol
773 -mlongcalls -mno-longcalls}
775 @emph{zSeries Options}
776 See S/390 and zSeries Options.
778 @item Code Generation Options
779 @xref{Code Gen Options,,Options for Code Generation Conventions}.
780 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
781 -ffixed-@var{reg} -fexceptions @gol
782 -fnon-call-exceptions -funwind-tables @gol
783 -fasynchronous-unwind-tables @gol
784 -finhibit-size-directive -finstrument-functions @gol
785 -fno-common -fno-ident @gol
786 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
787 -fno-jump-tables @gol
788 -frecord-gcc-switches @gol
789 -freg-struct-return -fshort-enums @gol
790 -fshort-double -fshort-wchar @gol
791 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
792 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
793 -fargument-alias -fargument-noalias @gol
794 -fargument-noalias-global -fargument-noalias-anything
795 -fleading-underscore -ftls-model=@var{model} @gol
796 -ftrapv -fwrapv -fbounds-check @gol
801 * Overall Options:: Controlling the kind of output:
802 an executable, object files, assembler files,
803 or preprocessed source.
804 * C Dialect Options:: Controlling the variant of C language compiled.
805 * C++ Dialect Options:: Variations on C++.
806 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
808 * Language Independent Options:: Controlling how diagnostics should be
810 * Warning Options:: How picky should the compiler be?
811 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
812 * Optimize Options:: How much optimization?
813 * Preprocessor Options:: Controlling header files and macro definitions.
814 Also, getting dependency information for Make.
815 * Assembler Options:: Passing options to the assembler.
816 * Link Options:: Specifying libraries and so on.
817 * Directory Options:: Where to find header files and libraries.
818 Where to find the compiler executable files.
819 * Spec Files:: How to pass switches to sub-processes.
820 * Target Options:: Running a cross-compiler, or an old version of GCC.
823 @node Overall Options
824 @section Options Controlling the Kind of Output
826 Compilation can involve up to four stages: preprocessing, compilation
827 proper, assembly and linking, always in that order. GCC is capable of
828 preprocessing and compiling several files either into several
829 assembler input files, or into one assembler input file; then each
830 assembler input file produces an object file, and linking combines all
831 the object files (those newly compiled, and those specified as input)
832 into an executable file.
834 @cindex file name suffix
835 For any given input file, the file name suffix determines what kind of
840 C source code which must be preprocessed.
843 C source code which should not be preprocessed.
846 C++ source code which should not be preprocessed.
849 Objective-C source code. Note that you must link with the @file{libobjc}
850 library to make an Objective-C program work.
853 Objective-C source code which should not be preprocessed.
857 Objective-C++ source code. Note that you must link with the @file{libobjc}
858 library to make an Objective-C++ program work. Note that @samp{.M} refers
859 to a literal capital M@.
862 Objective-C++ source code which should not be preprocessed.
865 C, C++, Objective-C or Objective-C++ header file to be turned into a
870 @itemx @var{file}.cxx
871 @itemx @var{file}.cpp
872 @itemx @var{file}.CPP
873 @itemx @var{file}.c++
875 C++ source code which must be preprocessed. Note that in @samp{.cxx},
876 the last two letters must both be literally @samp{x}. Likewise,
877 @samp{.C} refers to a literal capital C@.
881 Objective-C++ source code which must be preprocessed.
884 Objective-C++ source code which should not be preprocessed.
888 C++ header file to be turned into a precompiled header.
891 @itemx @var{file}.for
892 @itemx @var{file}.FOR
893 Fixed form Fortran source code which should not be preprocessed.
896 @itemx @var{file}.fpp
897 @itemx @var{file}.FPP
898 Fixed form Fortran source code which must be preprocessed (with the traditional
902 @itemx @var{file}.f95
903 Free form Fortran source code which should not be preprocessed.
906 @itemx @var{file}.F95
907 Free form Fortran source code which must be preprocessed (with the
908 traditional preprocessor).
910 @c FIXME: Descriptions of Java file types.
917 Ada source code file which contains a library unit declaration (a
918 declaration of a package, subprogram, or generic, or a generic
919 instantiation), or a library unit renaming declaration (a package,
920 generic, or subprogram renaming declaration). Such files are also
923 @itemx @var{file}.adb
924 Ada source code file containing a library unit body (a subprogram or
925 package body). Such files are also called @dfn{bodies}.
927 @c GCC also knows about some suffixes for languages not yet included:
938 Assembler code which must be preprocessed.
941 An object file to be fed straight into linking.
942 Any file name with no recognized suffix is treated this way.
946 You can specify the input language explicitly with the @option{-x} option:
949 @item -x @var{language}
950 Specify explicitly the @var{language} for the following input files
951 (rather than letting the compiler choose a default based on the file
952 name suffix). This option applies to all following input files until
953 the next @option{-x} option. Possible values for @var{language} are:
955 c c-header c-cpp-output
956 c++ c++-header c++-cpp-output
957 objective-c objective-c-header objective-c-cpp-output
958 objective-c++ objective-c++-header objective-c++-cpp-output
959 assembler assembler-with-cpp
967 Turn off any specification of a language, so that subsequent files are
968 handled according to their file name suffixes (as they are if @option{-x}
969 has not been used at all).
971 @item -pass-exit-codes
972 @opindex pass-exit-codes
973 Normally the @command{gcc} program will exit with the code of 1 if any
974 phase of the compiler returns a non-success return code. If you specify
975 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
976 numerically highest error produced by any phase that returned an error
977 indication. The C, C++, and Fortran frontends return 4, if an internal
978 compiler error is encountered.
981 If you only want some of the stages of compilation, you can use
982 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
983 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
984 @command{gcc} is to stop. Note that some combinations (for example,
985 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
990 Compile or assemble the source files, but do not link. The linking
991 stage simply is not done. The ultimate output is in the form of an
992 object file for each source file.
994 By default, the object file name for a source file is made by replacing
995 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
997 Unrecognized input files, not requiring compilation or assembly, are
1002 Stop after the stage of compilation proper; do not assemble. The output
1003 is in the form of an assembler code file for each non-assembler input
1006 By default, the assembler file name for a source file is made by
1007 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
1009 Input files that don't require compilation are ignored.
1013 Stop after the preprocessing stage; do not run the compiler proper. The
1014 output is in the form of preprocessed source code, which is sent to the
1017 Input files which don't require preprocessing are ignored.
1019 @cindex output file option
1022 Place output in file @var{file}. This applies regardless to whatever
1023 sort of output is being produced, whether it be an executable file,
1024 an object file, an assembler file or preprocessed C code.
1026 If @option{-o} is not specified, the default is to put an executable
1027 file in @file{a.out}, the object file for
1028 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
1029 assembler file in @file{@var{source}.s}, a precompiled header file in
1030 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
1035 Print (on standard error output) the commands executed to run the stages
1036 of compilation. Also print the version number of the compiler driver
1037 program and of the preprocessor and the compiler proper.
1041 Like @option{-v} except the commands are not executed and all command
1042 arguments are quoted. This is useful for shell scripts to capture the
1043 driver-generated command lines.
1047 Use pipes rather than temporary files for communication between the
1048 various stages of compilation. This fails to work on some systems where
1049 the assembler is unable to read from a pipe; but the GNU assembler has
1054 If you are compiling multiple source files, this option tells the driver
1055 to pass all the source files to the compiler at once (for those
1056 languages for which the compiler can handle this). This will allow
1057 intermodule analysis (IMA) to be performed by the compiler. Currently the only
1058 language for which this is supported is C@. If you pass source files for
1059 multiple languages to the driver, using this option, the driver will invoke
1060 the compiler(s) that support IMA once each, passing each compiler all the
1061 source files appropriate for it. For those languages that do not support
1062 IMA this option will be ignored, and the compiler will be invoked once for
1063 each source file in that language. If you use this option in conjunction
1064 with @option{-save-temps}, the compiler will generate multiple
1066 (one for each source file), but only one (combined) @file{.o} or
1071 Print (on the standard output) a description of the command line options
1072 understood by @command{gcc}. If the @option{-v} option is also specified
1073 then @option{--help} will also be passed on to the various processes
1074 invoked by @command{gcc}, so that they can display the command line options
1075 they accept. If the @option{-Wextra} option is also specified then command
1076 line options which have no documentation associated with them will also
1080 @opindex target-help
1081 Print (on the standard output) a description of target specific command
1082 line options for each tool.
1086 Display the version number and copyrights of the invoked GCC@.
1088 @include @value{srcdir}/../libiberty/at-file.texi
1092 @section Compiling C++ Programs
1094 @cindex suffixes for C++ source
1095 @cindex C++ source file suffixes
1096 C++ source files conventionally use one of the suffixes @samp{.C},
1097 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1098 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
1099 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1100 files with these names and compiles them as C++ programs even if you
1101 call the compiler the same way as for compiling C programs (usually
1102 with the name @command{gcc}).
1106 However, the use of @command{gcc} does not add the C++ library.
1107 @command{g++} is a program that calls GCC and treats @samp{.c},
1108 @samp{.h} and @samp{.i} files as C++ source files instead of C source
1109 files unless @option{-x} is used, and automatically specifies linking
1110 against the C++ library. This program is also useful when
1111 precompiling a C header file with a @samp{.h} extension for use in C++
1112 compilations. On many systems, @command{g++} is also installed with
1113 the name @command{c++}.
1115 @cindex invoking @command{g++}
1116 When you compile C++ programs, you may specify many of the same
1117 command-line options that you use for compiling programs in any
1118 language; or command-line options meaningful for C and related
1119 languages; or options that are meaningful only for C++ programs.
1120 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1121 explanations of options for languages related to C@.
1122 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1123 explanations of options that are meaningful only for C++ programs.
1125 @node C Dialect Options
1126 @section Options Controlling C Dialect
1127 @cindex dialect options
1128 @cindex language dialect options
1129 @cindex options, dialect
1131 The following options control the dialect of C (or languages derived
1132 from C, such as C++, Objective-C and Objective-C++) that the compiler
1136 @cindex ANSI support
1140 In C mode, support all ISO C90 programs. In C++ mode,
1141 remove GNU extensions that conflict with ISO C++.
1143 This turns off certain features of GCC that are incompatible with ISO
1144 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1145 such as the @code{asm} and @code{typeof} keywords, and
1146 predefined macros such as @code{unix} and @code{vax} that identify the
1147 type of system you are using. It also enables the undesirable and
1148 rarely used ISO trigraph feature. For the C compiler,
1149 it disables recognition of C++ style @samp{//} comments as well as
1150 the @code{inline} keyword.
1152 The alternate keywords @code{__asm__}, @code{__extension__},
1153 @code{__inline__} and @code{__typeof__} continue to work despite
1154 @option{-ansi}. You would not want to use them in an ISO C program, of
1155 course, but it is useful to put them in header files that might be included
1156 in compilations done with @option{-ansi}. Alternate predefined macros
1157 such as @code{__unix__} and @code{__vax__} are also available, with or
1158 without @option{-ansi}.
1160 The @option{-ansi} option does not cause non-ISO programs to be
1161 rejected gratuitously. For that, @option{-pedantic} is required in
1162 addition to @option{-ansi}. @xref{Warning Options}.
1164 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1165 option is used. Some header files may notice this macro and refrain
1166 from declaring certain functions or defining certain macros that the
1167 ISO standard doesn't call for; this is to avoid interfering with any
1168 programs that might use these names for other things.
1170 Functions which would normally be built in but do not have semantics
1171 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1172 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1173 built-in functions provided by GCC}, for details of the functions
1178 Determine the language standard. This option is currently only
1179 supported when compiling C or C++. A value for this option must be
1180 provided; possible values are
1185 ISO C90 (same as @option{-ansi}).
1187 @item iso9899:199409
1188 ISO C90 as modified in amendment 1.
1194 ISO C99. Note that this standard is not yet fully supported; see
1195 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1196 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1199 Default, ISO C90 plus GNU extensions (including some C99 features).
1203 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1204 this will become the default. The name @samp{gnu9x} is deprecated.
1207 The 1998 ISO C++ standard plus amendments.
1210 The same as @option{-std=c++98} plus GNU extensions. This is the
1211 default for C++ code.
1214 The working draft of the upcoming ISO C++0x standard. This option
1215 enables experimental features that are likely to be included in
1216 C++0x. The working draft is constantly changing, and any feature that is
1217 enabled by this flag may be removed from future versions of GCC if it is
1218 not part of the C++0x standard.
1221 The same as @option{-std=c++0x} plus GNU extensions. As with
1222 @option{-std=c++0x}, this option enables experimental features that may
1223 be removed in future versions of GCC.
1226 Even when this option is not specified, you can still use some of the
1227 features of newer standards in so far as they do not conflict with
1228 previous C standards. For example, you may use @code{__restrict__} even
1229 when @option{-std=c99} is not specified.
1231 The @option{-std} options specifying some version of ISO C have the same
1232 effects as @option{-ansi}, except that features that were not in ISO C90
1233 but are in the specified version (for example, @samp{//} comments and
1234 the @code{inline} keyword in ISO C99) are not disabled.
1236 @xref{Standards,,Language Standards Supported by GCC}, for details of
1237 these standard versions.
1239 @item -aux-info @var{filename}
1241 Output to the given filename prototyped declarations for all functions
1242 declared and/or defined in a translation unit, including those in header
1243 files. This option is silently ignored in any language other than C@.
1245 Besides declarations, the file indicates, in comments, the origin of
1246 each declaration (source file and line), whether the declaration was
1247 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1248 @samp{O} for old, respectively, in the first character after the line
1249 number and the colon), and whether it came from a declaration or a
1250 definition (@samp{C} or @samp{F}, respectively, in the following
1251 character). In the case of function definitions, a K&R-style list of
1252 arguments followed by their declarations is also provided, inside
1253 comments, after the declaration.
1257 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1258 keyword, so that code can use these words as identifiers. You can use
1259 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1260 instead. @option{-ansi} implies @option{-fno-asm}.
1262 In C++, this switch only affects the @code{typeof} keyword, since
1263 @code{asm} and @code{inline} are standard keywords. You may want to
1264 use the @option{-fno-gnu-keywords} flag instead, which has the same
1265 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1266 switch only affects the @code{asm} and @code{typeof} keywords, since
1267 @code{inline} is a standard keyword in ISO C99.
1270 @itemx -fno-builtin-@var{function}
1271 @opindex fno-builtin
1272 @cindex built-in functions
1273 Don't recognize built-in functions that do not begin with
1274 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1275 functions provided by GCC}, for details of the functions affected,
1276 including those which are not built-in functions when @option{-ansi} or
1277 @option{-std} options for strict ISO C conformance are used because they
1278 do not have an ISO standard meaning.
1280 GCC normally generates special code to handle certain built-in functions
1281 more efficiently; for instance, calls to @code{alloca} may become single
1282 instructions that adjust the stack directly, and calls to @code{memcpy}
1283 may become inline copy loops. The resulting code is often both smaller
1284 and faster, but since the function calls no longer appear as such, you
1285 cannot set a breakpoint on those calls, nor can you change the behavior
1286 of the functions by linking with a different library. In addition,
1287 when a function is recognized as a built-in function, GCC may use
1288 information about that function to warn about problems with calls to
1289 that function, or to generate more efficient code, even if the
1290 resulting code still contains calls to that function. For example,
1291 warnings are given with @option{-Wformat} for bad calls to
1292 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1293 known not to modify global memory.
1295 With the @option{-fno-builtin-@var{function}} option
1296 only the built-in function @var{function} is
1297 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1298 function is named this is not built-in in this version of GCC, this
1299 option is ignored. There is no corresponding
1300 @option{-fbuiltin-@var{function}} option; if you wish to enable
1301 built-in functions selectively when using @option{-fno-builtin} or
1302 @option{-ffreestanding}, you may define macros such as:
1305 #define abs(n) __builtin_abs ((n))
1306 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1311 @cindex hosted environment
1313 Assert that compilation takes place in a hosted environment. This implies
1314 @option{-fbuiltin}. A hosted environment is one in which the
1315 entire standard library is available, and in which @code{main} has a return
1316 type of @code{int}. Examples are nearly everything except a kernel.
1317 This is equivalent to @option{-fno-freestanding}.
1319 @item -ffreestanding
1320 @opindex ffreestanding
1321 @cindex hosted environment
1323 Assert that compilation takes place in a freestanding environment. This
1324 implies @option{-fno-builtin}. A freestanding environment
1325 is one in which the standard library may not exist, and program startup may
1326 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1327 This is equivalent to @option{-fno-hosted}.
1329 @xref{Standards,,Language Standards Supported by GCC}, for details of
1330 freestanding and hosted environments.
1334 @cindex openmp parallel
1335 Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
1336 @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
1337 compiler generates parallel code according to the OpenMP Application
1338 Program Interface v2.5 @w{@uref{http://www.openmp.org/}}.
1340 @item -fms-extensions
1341 @opindex fms-extensions
1342 Accept some non-standard constructs used in Microsoft header files.
1344 Some cases of unnamed fields in structures and unions are only
1345 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1346 fields within structs/unions}, for details.
1350 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1351 options for strict ISO C conformance) implies @option{-trigraphs}.
1353 @item -no-integrated-cpp
1354 @opindex no-integrated-cpp
1355 Performs a compilation in two passes: preprocessing and compiling. This
1356 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1357 @option{-B} option. The user supplied compilation step can then add in
1358 an additional preprocessing step after normal preprocessing but before
1359 compiling. The default is to use the integrated cpp (internal cpp)
1361 The semantics of this option will change if "cc1", "cc1plus", and
1362 "cc1obj" are merged.
1364 @cindex traditional C language
1365 @cindex C language, traditional
1367 @itemx -traditional-cpp
1368 @opindex traditional-cpp
1369 @opindex traditional
1370 Formerly, these options caused GCC to attempt to emulate a pre-standard
1371 C compiler. They are now only supported with the @option{-E} switch.
1372 The preprocessor continues to support a pre-standard mode. See the GNU
1373 CPP manual for details.
1375 @item -fcond-mismatch
1376 @opindex fcond-mismatch
1377 Allow conditional expressions with mismatched types in the second and
1378 third arguments. The value of such an expression is void. This option
1379 is not supported for C++.
1381 @item -funsigned-char
1382 @opindex funsigned-char
1383 Let the type @code{char} be unsigned, like @code{unsigned char}.
1385 Each kind of machine has a default for what @code{char} should
1386 be. It is either like @code{unsigned char} by default or like
1387 @code{signed char} by default.
1389 Ideally, a portable program should always use @code{signed char} or
1390 @code{unsigned char} when it depends on the signedness of an object.
1391 But many programs have been written to use plain @code{char} and
1392 expect it to be signed, or expect it to be unsigned, depending on the
1393 machines they were written for. This option, and its inverse, let you
1394 make such a program work with the opposite default.
1396 The type @code{char} is always a distinct type from each of
1397 @code{signed char} or @code{unsigned char}, even though its behavior
1398 is always just like one of those two.
1401 @opindex fsigned-char
1402 Let the type @code{char} be signed, like @code{signed char}.
1404 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1405 the negative form of @option{-funsigned-char}. Likewise, the option
1406 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1408 @item -fsigned-bitfields
1409 @itemx -funsigned-bitfields
1410 @itemx -fno-signed-bitfields
1411 @itemx -fno-unsigned-bitfields
1412 @opindex fsigned-bitfields
1413 @opindex funsigned-bitfields
1414 @opindex fno-signed-bitfields
1415 @opindex fno-unsigned-bitfields
1416 These options control whether a bit-field is signed or unsigned, when the
1417 declaration does not use either @code{signed} or @code{unsigned}. By
1418 default, such a bit-field is signed, because this is consistent: the
1419 basic integer types such as @code{int} are signed types.
1422 @node C++ Dialect Options
1423 @section Options Controlling C++ Dialect
1425 @cindex compiler options, C++
1426 @cindex C++ options, command line
1427 @cindex options, C++
1428 This section describes the command-line options that are only meaningful
1429 for C++ programs; but you can also use most of the GNU compiler options
1430 regardless of what language your program is in. For example, you
1431 might compile a file @code{firstClass.C} like this:
1434 g++ -g -frepo -O -c firstClass.C
1438 In this example, only @option{-frepo} is an option meant
1439 only for C++ programs; you can use the other options with any
1440 language supported by GCC@.
1442 Here is a list of options that are @emph{only} for compiling C++ programs:
1446 @item -fabi-version=@var{n}
1447 @opindex fabi-version
1448 Use version @var{n} of the C++ ABI@. Version 2 is the version of the
1449 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1450 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1451 the version that conforms most closely to the C++ ABI specification.
1452 Therefore, the ABI obtained using version 0 will change as ABI bugs
1455 The default is version 2.
1457 @item -fno-access-control
1458 @opindex fno-access-control
1459 Turn off all access checking. This switch is mainly useful for working
1460 around bugs in the access control code.
1464 Check that the pointer returned by @code{operator new} is non-null
1465 before attempting to modify the storage allocated. This check is
1466 normally unnecessary because the C++ standard specifies that
1467 @code{operator new} will only return @code{0} if it is declared
1468 @samp{throw()}, in which case the compiler will always check the
1469 return value even without this option. In all other cases, when
1470 @code{operator new} has a non-empty exception specification, memory
1471 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1472 @samp{new (nothrow)}.
1474 @item -fconserve-space
1475 @opindex fconserve-space
1476 Put uninitialized or runtime-initialized global variables into the
1477 common segment, as C does. This saves space in the executable at the
1478 cost of not diagnosing duplicate definitions. If you compile with this
1479 flag and your program mysteriously crashes after @code{main()} has
1480 completed, you may have an object that is being destroyed twice because
1481 two definitions were merged.
1483 This option is no longer useful on most targets, now that support has
1484 been added for putting variables into BSS without making them common.
1486 @item -ffriend-injection
1487 @opindex ffriend-injection
1488 Inject friend functions into the enclosing namespace, so that they are
1489 visible outside the scope of the class in which they are declared.
1490 Friend functions were documented to work this way in the old Annotated
1491 C++ Reference Manual, and versions of G++ before 4.1 always worked
1492 that way. However, in ISO C++ a friend function which is not declared
1493 in an enclosing scope can only be found using argument dependent
1494 lookup. This option causes friends to be injected as they were in
1497 This option is for compatibility, and may be removed in a future
1500 @item -fno-elide-constructors
1501 @opindex fno-elide-constructors
1502 The C++ standard allows an implementation to omit creating a temporary
1503 which is only used to initialize another object of the same type.
1504 Specifying this option disables that optimization, and forces G++ to
1505 call the copy constructor in all cases.
1507 @item -fno-enforce-eh-specs
1508 @opindex fno-enforce-eh-specs
1509 Don't generate code to check for violation of exception specifications
1510 at runtime. This option violates the C++ standard, but may be useful
1511 for reducing code size in production builds, much like defining
1512 @samp{NDEBUG}. This does not give user code permission to throw
1513 exceptions in violation of the exception specifications; the compiler
1514 will still optimize based on the specifications, so throwing an
1515 unexpected exception will result in undefined behavior.
1518 @itemx -fno-for-scope
1520 @opindex fno-for-scope
1521 If @option{-ffor-scope} is specified, the scope of variables declared in
1522 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1523 as specified by the C++ standard.
1524 If @option{-fno-for-scope} is specified, the scope of variables declared in
1525 a @i{for-init-statement} extends to the end of the enclosing scope,
1526 as was the case in old versions of G++, and other (traditional)
1527 implementations of C++.
1529 The default if neither flag is given to follow the standard,
1530 but to allow and give a warning for old-style code that would
1531 otherwise be invalid, or have different behavior.
1533 @item -fno-gnu-keywords
1534 @opindex fno-gnu-keywords
1535 Do not recognize @code{typeof} as a keyword, so that code can use this
1536 word as an identifier. You can use the keyword @code{__typeof__} instead.
1537 @option{-ansi} implies @option{-fno-gnu-keywords}.
1539 @item -fno-implicit-templates
1540 @opindex fno-implicit-templates
1541 Never emit code for non-inline templates which are instantiated
1542 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1543 @xref{Template Instantiation}, for more information.
1545 @item -fno-implicit-inline-templates
1546 @opindex fno-implicit-inline-templates
1547 Don't emit code for implicit instantiations of inline templates, either.
1548 The default is to handle inlines differently so that compiles with and
1549 without optimization will need the same set of explicit instantiations.
1551 @item -fno-implement-inlines
1552 @opindex fno-implement-inlines
1553 To save space, do not emit out-of-line copies of inline functions
1554 controlled by @samp{#pragma implementation}. This will cause linker
1555 errors if these functions are not inlined everywhere they are called.
1557 @item -fms-extensions
1558 @opindex fms-extensions
1559 Disable pedantic warnings about constructs used in MFC, such as implicit
1560 int and getting a pointer to member function via non-standard syntax.
1562 @item -fno-nonansi-builtins
1563 @opindex fno-nonansi-builtins
1564 Disable built-in declarations of functions that are not mandated by
1565 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1566 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1568 @item -fno-operator-names
1569 @opindex fno-operator-names
1570 Do not treat the operator name keywords @code{and}, @code{bitand},
1571 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1572 synonyms as keywords.
1574 @item -fno-optional-diags
1575 @opindex fno-optional-diags
1576 Disable diagnostics that the standard says a compiler does not need to
1577 issue. Currently, the only such diagnostic issued by G++ is the one for
1578 a name having multiple meanings within a class.
1581 @opindex fpermissive
1582 Downgrade some diagnostics about nonconformant code from errors to
1583 warnings. Thus, using @option{-fpermissive} will allow some
1584 nonconforming code to compile.
1588 Enable automatic template instantiation at link time. This option also
1589 implies @option{-fno-implicit-templates}. @xref{Template
1590 Instantiation}, for more information.
1594 Disable generation of information about every class with virtual
1595 functions for use by the C++ runtime type identification features
1596 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1597 of the language, you can save some space by using this flag. Note that
1598 exception handling uses the same information, but it will generate it as
1599 needed. The @samp{dynamic_cast} operator can still be used for casts that
1600 do not require runtime type information, i.e. casts to @code{void *} or to
1601 unambiguous base classes.
1605 Emit statistics about front-end processing at the end of the compilation.
1606 This information is generally only useful to the G++ development team.
1608 @item -ftemplate-depth-@var{n}
1609 @opindex ftemplate-depth
1610 Set the maximum instantiation depth for template classes to @var{n}.
1611 A limit on the template instantiation depth is needed to detect
1612 endless recursions during template class instantiation. ANSI/ISO C++
1613 conforming programs must not rely on a maximum depth greater than 17.
1615 @item -fno-threadsafe-statics
1616 @opindex fno-threadsafe-statics
1617 Do not emit the extra code to use the routines specified in the C++
1618 ABI for thread-safe initialization of local statics. You can use this
1619 option to reduce code size slightly in code that doesn't need to be
1622 @item -fuse-cxa-atexit
1623 @opindex fuse-cxa-atexit
1624 Register destructors for objects with static storage duration with the
1625 @code{__cxa_atexit} function rather than the @code{atexit} function.
1626 This option is required for fully standards-compliant handling of static
1627 destructors, but will only work if your C library supports
1628 @code{__cxa_atexit}.
1630 @item -fno-use-cxa-get-exception-ptr
1631 @opindex fno-use-cxa-get-exception-ptr
1632 Don't use the @code{__cxa_get_exception_ptr} runtime routine. This
1633 will cause @code{std::uncaught_exception} to be incorrect, but is necessary
1634 if the runtime routine is not available.
1636 @item -fvisibility-inlines-hidden
1637 @opindex fvisibility-inlines-hidden
1638 This switch declares that the user does not attempt to compare
1639 pointers to inline methods where the addresses of the two functions
1640 were taken in different shared objects.
1642 The effect of this is that GCC may, effectively, mark inline methods with
1643 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1644 appear in the export table of a DSO and do not require a PLT indirection
1645 when used within the DSO@. Enabling this option can have a dramatic effect
1646 on load and link times of a DSO as it massively reduces the size of the
1647 dynamic export table when the library makes heavy use of templates.
1649 The behaviour of this switch is not quite the same as marking the
1650 methods as hidden directly, because it does not affect static variables
1651 local to the function or cause the compiler to deduce that
1652 the function is defined in only one shared object.
1654 You may mark a method as having a visibility explicitly to negate the
1655 effect of the switch for that method. For example, if you do want to
1656 compare pointers to a particular inline method, you might mark it as
1657 having default visibility. Marking the enclosing class with explicit
1658 visibility will have no effect.
1660 Explicitly instantiated inline methods are unaffected by this option
1661 as their linkage might otherwise cross a shared library boundary.
1662 @xref{Template Instantiation}.
1666 Do not use weak symbol support, even if it is provided by the linker.
1667 By default, G++ will use weak symbols if they are available. This
1668 option exists only for testing, and should not be used by end-users;
1669 it will result in inferior code and has no benefits. This option may
1670 be removed in a future release of G++.
1674 Do not search for header files in the standard directories specific to
1675 C++, but do still search the other standard directories. (This option
1676 is used when building the C++ library.)
1679 In addition, these optimization, warning, and code generation options
1680 have meanings only for C++ programs:
1683 @item -fno-default-inline
1684 @opindex fno-default-inline
1685 Do not assume @samp{inline} for functions defined inside a class scope.
1686 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1687 functions will have linkage like inline functions; they just won't be
1690 @item -Wabi @r{(C++ only)}
1692 Warn when G++ generates code that is probably not compatible with the
1693 vendor-neutral C++ ABI@. Although an effort has been made to warn about
1694 all such cases, there are probably some cases that are not warned about,
1695 even though G++ is generating incompatible code. There may also be
1696 cases where warnings are emitted even though the code that is generated
1699 You should rewrite your code to avoid these warnings if you are
1700 concerned about the fact that code generated by G++ may not be binary
1701 compatible with code generated by other compilers.
1703 The known incompatibilities at this point include:
1708 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1709 pack data into the same byte as a base class. For example:
1712 struct A @{ virtual void f(); int f1 : 1; @};
1713 struct B : public A @{ int f2 : 1; @};
1717 In this case, G++ will place @code{B::f2} into the same byte
1718 as@code{A::f1}; other compilers will not. You can avoid this problem
1719 by explicitly padding @code{A} so that its size is a multiple of the
1720 byte size on your platform; that will cause G++ and other compilers to
1721 layout @code{B} identically.
1724 Incorrect handling of tail-padding for virtual bases. G++ does not use
1725 tail padding when laying out virtual bases. For example:
1728 struct A @{ virtual void f(); char c1; @};
1729 struct B @{ B(); char c2; @};
1730 struct C : public A, public virtual B @{@};
1734 In this case, G++ will not place @code{B} into the tail-padding for
1735 @code{A}; other compilers will. You can avoid this problem by
1736 explicitly padding @code{A} so that its size is a multiple of its
1737 alignment (ignoring virtual base classes); that will cause G++ and other
1738 compilers to layout @code{C} identically.
1741 Incorrect handling of bit-fields with declared widths greater than that
1742 of their underlying types, when the bit-fields appear in a union. For
1746 union U @{ int i : 4096; @};
1750 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1751 union too small by the number of bits in an @code{int}.
1754 Empty classes can be placed at incorrect offsets. For example:
1764 struct C : public B, public A @{@};
1768 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1769 it should be placed at offset zero. G++ mistakenly believes that the
1770 @code{A} data member of @code{B} is already at offset zero.
1773 Names of template functions whose types involve @code{typename} or
1774 template template parameters can be mangled incorrectly.
1777 template <typename Q>
1778 void f(typename Q::X) @{@}
1780 template <template <typename> class Q>
1781 void f(typename Q<int>::X) @{@}
1785 Instantiations of these templates may be mangled incorrectly.
1789 @item -Wctor-dtor-privacy @r{(C++ only)}
1790 @opindex Wctor-dtor-privacy
1791 Warn when a class seems unusable because all the constructors or
1792 destructors in that class are private, and it has neither friends nor
1793 public static member functions.
1795 @item -Wnon-virtual-dtor @r{(C++ only)}
1796 @opindex Wnon-virtual-dtor
1797 Warn when a class appears to be polymorphic, thereby requiring a virtual
1798 destructor, yet it declares a non-virtual one. This warning is also
1799 enabled if -Weffc++ is specified.
1801 @item -Wreorder @r{(C++ only)}
1803 @cindex reordering, warning
1804 @cindex warning for reordering of member initializers
1805 Warn when the order of member initializers given in the code does not
1806 match the order in which they must be executed. For instance:
1812 A(): j (0), i (1) @{ @}
1816 The compiler will rearrange the member initializers for @samp{i}
1817 and @samp{j} to match the declaration order of the members, emitting
1818 a warning to that effect. This warning is enabled by @option{-Wall}.
1821 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1824 @item -Weffc++ @r{(C++ only)}
1826 Warn about violations of the following style guidelines from Scott Meyers'
1827 @cite{Effective C++} book:
1831 Item 11: Define a copy constructor and an assignment operator for classes
1832 with dynamically allocated memory.
1835 Item 12: Prefer initialization to assignment in constructors.
1838 Item 14: Make destructors virtual in base classes.
1841 Item 15: Have @code{operator=} return a reference to @code{*this}.
1844 Item 23: Don't try to return a reference when you must return an object.
1848 Also warn about violations of the following style guidelines from
1849 Scott Meyers' @cite{More Effective C++} book:
1853 Item 6: Distinguish between prefix and postfix forms of increment and
1854 decrement operators.
1857 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1861 When selecting this option, be aware that the standard library
1862 headers do not obey all of these guidelines; use @samp{grep -v}
1863 to filter out those warnings.
1865 @item -Wno-deprecated @r{(C++ only)}
1866 @opindex Wno-deprecated
1867 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1869 @item -Wstrict-null-sentinel @r{(C++ only)}
1870 @opindex Wstrict-null-sentinel
1871 Warn also about the use of an uncasted @code{NULL} as sentinel. When
1872 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
1873 to @code{__null}. Although it is a null pointer constant not a null pointer,
1874 it is guaranteed to of the same size as a pointer. But this use is
1875 not portable across different compilers.
1877 @item -Wno-non-template-friend @r{(C++ only)}
1878 @opindex Wno-non-template-friend
1879 Disable warnings when non-templatized friend functions are declared
1880 within a template. Since the advent of explicit template specification
1881 support in G++, if the name of the friend is an unqualified-id (i.e.,
1882 @samp{friend foo(int)}), the C++ language specification demands that the
1883 friend declare or define an ordinary, nontemplate function. (Section
1884 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1885 could be interpreted as a particular specialization of a templatized
1886 function. Because this non-conforming behavior is no longer the default
1887 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1888 check existing code for potential trouble spots and is on by default.
1889 This new compiler behavior can be turned off with
1890 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1891 but disables the helpful warning.
1893 @item -Wold-style-cast @r{(C++ only)}
1894 @opindex Wold-style-cast
1895 Warn if an old-style (C-style) cast to a non-void type is used within
1896 a C++ program. The new-style casts (@samp{dynamic_cast},
1897 @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are
1898 less vulnerable to unintended effects and much easier to search for.
1900 @item -Woverloaded-virtual @r{(C++ only)}
1901 @opindex Woverloaded-virtual
1902 @cindex overloaded virtual fn, warning
1903 @cindex warning for overloaded virtual fn
1904 Warn when a function declaration hides virtual functions from a
1905 base class. For example, in:
1912 struct B: public A @{
1917 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1925 will fail to compile.
1927 @item -Wno-pmf-conversions @r{(C++ only)}
1928 @opindex Wno-pmf-conversions
1929 Disable the diagnostic for converting a bound pointer to member function
1932 @item -Wsign-promo @r{(C++ only)}
1933 @opindex Wsign-promo
1934 Warn when overload resolution chooses a promotion from unsigned or
1935 enumerated type to a signed type, over a conversion to an unsigned type of
1936 the same size. Previous versions of G++ would try to preserve
1937 unsignedness, but the standard mandates the current behavior.
1942 A& operator = (int);
1952 In this example, G++ will synthesize a default @samp{A& operator =
1953 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1956 @node Objective-C and Objective-C++ Dialect Options
1957 @section Options Controlling Objective-C and Objective-C++ Dialects
1959 @cindex compiler options, Objective-C and Objective-C++
1960 @cindex Objective-C and Objective-C++ options, command line
1961 @cindex options, Objective-C and Objective-C++
1962 (NOTE: This manual does not describe the Objective-C and Objective-C++
1963 languages themselves. See @xref{Standards,,Language Standards
1964 Supported by GCC}, for references.)
1966 This section describes the command-line options that are only meaningful
1967 for Objective-C and Objective-C++ programs, but you can also use most of
1968 the language-independent GNU compiler options.
1969 For example, you might compile a file @code{some_class.m} like this:
1972 gcc -g -fgnu-runtime -O -c some_class.m
1976 In this example, @option{-fgnu-runtime} is an option meant only for
1977 Objective-C and Objective-C++ programs; you can use the other options with
1978 any language supported by GCC@.
1980 Note that since Objective-C is an extension of the C language, Objective-C
1981 compilations may also use options specific to the C front-end (e.g.,
1982 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
1983 C++-specific options (e.g., @option{-Wabi}).
1985 Here is a list of options that are @emph{only} for compiling Objective-C
1986 and Objective-C++ programs:
1989 @item -fconstant-string-class=@var{class-name}
1990 @opindex fconstant-string-class
1991 Use @var{class-name} as the name of the class to instantiate for each
1992 literal string specified with the syntax @code{@@"@dots{}"}. The default
1993 class name is @code{NXConstantString} if the GNU runtime is being used, and
1994 @code{NSConstantString} if the NeXT runtime is being used (see below). The
1995 @option{-fconstant-cfstrings} option, if also present, will override the
1996 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
1997 to be laid out as constant CoreFoundation strings.
2000 @opindex fgnu-runtime
2001 Generate object code compatible with the standard GNU Objective-C
2002 runtime. This is the default for most types of systems.
2004 @item -fnext-runtime
2005 @opindex fnext-runtime
2006 Generate output compatible with the NeXT runtime. This is the default
2007 for NeXT-based systems, including Darwin and Mac OS X@. The macro
2008 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
2011 @item -fno-nil-receivers
2012 @opindex fno-nil-receivers
2013 Assume that all Objective-C message dispatches (e.g.,
2014 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
2015 is not @code{nil}. This allows for more efficient entry points in the runtime
2016 to be used. Currently, this option is only available in conjunction with
2017 the NeXT runtime on Mac OS X 10.3 and later.
2019 @item -fobjc-call-cxx-cdtors
2020 @opindex fobjc-call-cxx-cdtors
2021 For each Objective-C class, check if any of its instance variables is a
2022 C++ object with a non-trivial default constructor. If so, synthesize a
2023 special @code{- (id) .cxx_construct} instance method that will run
2024 non-trivial default constructors on any such instance variables, in order,
2025 and then return @code{self}. Similarly, check if any instance variable
2026 is a C++ object with a non-trivial destructor, and if so, synthesize a
2027 special @code{- (void) .cxx_destruct} method that will run
2028 all such default destructors, in reverse order.
2030 The @code{- (id) .cxx_construct} and/or @code{- (void) .cxx_destruct} methods
2031 thusly generated will only operate on instance variables declared in the
2032 current Objective-C class, and not those inherited from superclasses. It
2033 is the responsibility of the Objective-C runtime to invoke all such methods
2034 in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods
2035 will be invoked by the runtime immediately after a new object
2036 instance is allocated; the @code{- (void) .cxx_destruct} methods will
2037 be invoked immediately before the runtime deallocates an object instance.
2039 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
2040 support for invoking the @code{- (id) .cxx_construct} and
2041 @code{- (void) .cxx_destruct} methods.
2043 @item -fobjc-direct-dispatch
2044 @opindex fobjc-direct-dispatch
2045 Allow fast jumps to the message dispatcher. On Darwin this is
2046 accomplished via the comm page.
2048 @item -fobjc-exceptions
2049 @opindex fobjc-exceptions
2050 Enable syntactic support for structured exception handling in Objective-C,
2051 similar to what is offered by C++ and Java. This option is
2052 unavailable in conjunction with the NeXT runtime on Mac OS X 10.2 and
2061 @@catch (AnObjCClass *exc) @{
2068 @@catch (AnotherClass *exc) @{
2071 @@catch (id allOthers) @{
2081 The @code{@@throw} statement may appear anywhere in an Objective-C or
2082 Objective-C++ program; when used inside of a @code{@@catch} block, the
2083 @code{@@throw} may appear without an argument (as shown above), in which case
2084 the object caught by the @code{@@catch} will be rethrown.
2086 Note that only (pointers to) Objective-C objects may be thrown and
2087 caught using this scheme. When an object is thrown, it will be caught
2088 by the nearest @code{@@catch} clause capable of handling objects of that type,
2089 analogously to how @code{catch} blocks work in C++ and Java. A
2090 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
2091 any and all Objective-C exceptions not caught by previous @code{@@catch}
2094 The @code{@@finally} clause, if present, will be executed upon exit from the
2095 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
2096 regardless of whether any exceptions are thrown, caught or rethrown
2097 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
2098 of the @code{finally} clause in Java.
2100 There are several caveats to using the new exception mechanism:
2104 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
2105 idioms provided by the @code{NSException} class, the new
2106 exceptions can only be used on Mac OS X 10.3 (Panther) and later
2107 systems, due to additional functionality needed in the (NeXT) Objective-C
2111 As mentioned above, the new exceptions do not support handling
2112 types other than Objective-C objects. Furthermore, when used from
2113 Objective-C++, the Objective-C exception model does not interoperate with C++
2114 exceptions at this time. This means you cannot @code{@@throw} an exception
2115 from Objective-C and @code{catch} it in C++, or vice versa
2116 (i.e., @code{throw @dots{} @@catch}).
2119 The @option{-fobjc-exceptions} switch also enables the use of synchronization
2120 blocks for thread-safe execution:
2123 @@synchronized (ObjCClass *guard) @{
2128 Upon entering the @code{@@synchronized} block, a thread of execution shall
2129 first check whether a lock has been placed on the corresponding @code{guard}
2130 object by another thread. If it has, the current thread shall wait until
2131 the other thread relinquishes its lock. Once @code{guard} becomes available,
2132 the current thread will place its own lock on it, execute the code contained in
2133 the @code{@@synchronized} block, and finally relinquish the lock (thereby
2134 making @code{guard} available to other threads).
2136 Unlike Java, Objective-C does not allow for entire methods to be marked
2137 @code{@@synchronized}. Note that throwing exceptions out of
2138 @code{@@synchronized} blocks is allowed, and will cause the guarding object
2139 to be unlocked properly.
2143 Enable garbage collection (GC) in Objective-C and Objective-C++ programs.
2145 @item -freplace-objc-classes
2146 @opindex freplace-objc-classes
2147 Emit a special marker instructing @command{ld(1)} not to statically link in
2148 the resulting object file, and allow @command{dyld(1)} to load it in at
2149 run time instead. This is used in conjunction with the Fix-and-Continue
2150 debugging mode, where the object file in question may be recompiled and
2151 dynamically reloaded in the course of program execution, without the need
2152 to restart the program itself. Currently, Fix-and-Continue functionality
2153 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
2158 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
2159 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
2160 compile time) with static class references that get initialized at load time,
2161 which improves run-time performance. Specifying the @option{-fzero-link} flag
2162 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
2163 to be retained. This is useful in Zero-Link debugging mode, since it allows
2164 for individual class implementations to be modified during program execution.
2168 Dump interface declarations for all classes seen in the source file to a
2169 file named @file{@var{sourcename}.decl}.
2171 @item -Wassign-intercept
2172 @opindex Wassign-intercept
2173 Warn whenever an Objective-C assignment is being intercepted by the
2177 @opindex Wno-protocol
2178 If a class is declared to implement a protocol, a warning is issued for
2179 every method in the protocol that is not implemented by the class. The
2180 default behavior is to issue a warning for every method not explicitly
2181 implemented in the class, even if a method implementation is inherited
2182 from the superclass. If you use the @option{-Wno-protocol} option, then
2183 methods inherited from the superclass are considered to be implemented,
2184 and no warning is issued for them.
2188 Warn if multiple methods of different types for the same selector are
2189 found during compilation. The check is performed on the list of methods
2190 in the final stage of compilation. Additionally, a check is performed
2191 for each selector appearing in a @code{@@selector(@dots{})}
2192 expression, and a corresponding method for that selector has been found
2193 during compilation. Because these checks scan the method table only at
2194 the end of compilation, these warnings are not produced if the final
2195 stage of compilation is not reached, for example because an error is
2196 found during compilation, or because the @option{-fsyntax-only} option is
2199 @item -Wstrict-selector-match
2200 @opindex Wstrict-selector-match
2201 Warn if multiple methods with differing argument and/or return types are
2202 found for a given selector when attempting to send a message using this
2203 selector to a receiver of type @code{id} or @code{Class}. When this flag
2204 is off (which is the default behavior), the compiler will omit such warnings
2205 if any differences found are confined to types which share the same size
2208 @item -Wundeclared-selector
2209 @opindex Wundeclared-selector
2210 Warn if a @code{@@selector(@dots{})} expression referring to an
2211 undeclared selector is found. A selector is considered undeclared if no
2212 method with that name has been declared before the
2213 @code{@@selector(@dots{})} expression, either explicitly in an
2214 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2215 an @code{@@implementation} section. This option always performs its
2216 checks as soon as a @code{@@selector(@dots{})} expression is found,
2217 while @option{-Wselector} only performs its checks in the final stage of
2218 compilation. This also enforces the coding style convention
2219 that methods and selectors must be declared before being used.
2221 @item -print-objc-runtime-info
2222 @opindex print-objc-runtime-info
2223 Generate C header describing the largest structure that is passed by
2228 @node Language Independent Options
2229 @section Options to Control Diagnostic Messages Formatting
2230 @cindex options to control diagnostics formatting
2231 @cindex diagnostic messages
2232 @cindex message formatting
2234 Traditionally, diagnostic messages have been formatted irrespective of
2235 the output device's aspect (e.g.@: its width, @dots{}). The options described
2236 below can be used to control the diagnostic messages formatting
2237 algorithm, e.g.@: how many characters per line, how often source location
2238 information should be reported. Right now, only the C++ front end can
2239 honor these options. However it is expected, in the near future, that
2240 the remaining front ends would be able to digest them correctly.
2243 @item -fmessage-length=@var{n}
2244 @opindex fmessage-length
2245 Try to format error messages so that they fit on lines of about @var{n}
2246 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2247 the front ends supported by GCC@. If @var{n} is zero, then no
2248 line-wrapping will be done; each error message will appear on a single
2251 @opindex fdiagnostics-show-location
2252 @item -fdiagnostics-show-location=once
2253 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2254 reporter to emit @emph{once} source location information; that is, in
2255 case the message is too long to fit on a single physical line and has to
2256 be wrapped, the source location won't be emitted (as prefix) again,
2257 over and over, in subsequent continuation lines. This is the default
2260 @item -fdiagnostics-show-location=every-line
2261 Only meaningful in line-wrapping mode. Instructs the diagnostic
2262 messages reporter to emit the same source location information (as
2263 prefix) for physical lines that result from the process of breaking
2264 a message which is too long to fit on a single line.
2266 @item -fdiagnostics-show-option
2267 @opindex fdiagnostics-show-option
2268 This option instructs the diagnostic machinery to add text to each
2269 diagnostic emitted, which indicates which command line option directly
2270 controls that diagnostic, when such an option is known to the
2271 diagnostic machinery.
2275 @node Warning Options
2276 @section Options to Request or Suppress Warnings
2277 @cindex options to control warnings
2278 @cindex warning messages
2279 @cindex messages, warning
2280 @cindex suppressing warnings
2282 Warnings are diagnostic messages that report constructions which
2283 are not inherently erroneous but which are risky or suggest there
2284 may have been an error.
2286 You can request many specific warnings with options beginning @samp{-W},
2287 for example @option{-Wimplicit} to request warnings on implicit
2288 declarations. Each of these specific warning options also has a
2289 negative form beginning @samp{-Wno-} to turn off warnings;
2290 for example, @option{-Wno-implicit}. This manual lists only one of the
2291 two forms, whichever is not the default.
2293 The following options control the amount and kinds of warnings produced
2294 by GCC; for further, language-specific options also refer to
2295 @ref{C++ Dialect Options} and @ref{Objective-C and Objective-C++ Dialect
2299 @cindex syntax checking
2301 @opindex fsyntax-only
2302 Check the code for syntax errors, but don't do anything beyond that.
2306 Issue all the warnings demanded by strict ISO C and ISO C++;
2307 reject all programs that use forbidden extensions, and some other
2308 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2309 version of the ISO C standard specified by any @option{-std} option used.
2311 Valid ISO C and ISO C++ programs should compile properly with or without
2312 this option (though a rare few will require @option{-ansi} or a
2313 @option{-std} option specifying the required version of ISO C)@. However,
2314 without this option, certain GNU extensions and traditional C and C++
2315 features are supported as well. With this option, they are rejected.
2317 @option{-pedantic} does not cause warning messages for use of the
2318 alternate keywords whose names begin and end with @samp{__}. Pedantic
2319 warnings are also disabled in the expression that follows
2320 @code{__extension__}. However, only system header files should use
2321 these escape routes; application programs should avoid them.
2322 @xref{Alternate Keywords}.
2324 Some users try to use @option{-pedantic} to check programs for strict ISO
2325 C conformance. They soon find that it does not do quite what they want:
2326 it finds some non-ISO practices, but not all---only those for which
2327 ISO C @emph{requires} a diagnostic, and some others for which
2328 diagnostics have been added.
2330 A feature to report any failure to conform to ISO C might be useful in
2331 some instances, but would require considerable additional work and would
2332 be quite different from @option{-pedantic}. We don't have plans to
2333 support such a feature in the near future.
2335 Where the standard specified with @option{-std} represents a GNU
2336 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2337 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2338 extended dialect is based. Warnings from @option{-pedantic} are given
2339 where they are required by the base standard. (It would not make sense
2340 for such warnings to be given only for features not in the specified GNU
2341 C dialect, since by definition the GNU dialects of C include all
2342 features the compiler supports with the given option, and there would be
2343 nothing to warn about.)
2345 @item -pedantic-errors
2346 @opindex pedantic-errors
2347 Like @option{-pedantic}, except that errors are produced rather than
2352 Inhibit all warning messages.
2356 Inhibit warning messages about the use of @samp{#import}.
2358 @item -Wchar-subscripts
2359 @opindex Wchar-subscripts
2360 Warn if an array subscript has type @code{char}. This is a common cause
2361 of error, as programmers often forget that this type is signed on some
2363 This warning is enabled by @option{-Wall}.
2367 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2368 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2369 This warning is enabled by @option{-Wall}.
2371 @item -Wfatal-errors
2372 @opindex Wfatal-errors
2373 This option causes the compiler to abort compilation on the first error
2374 occurred rather than trying to keep going and printing further error
2379 @opindex ffreestanding
2380 @opindex fno-builtin
2381 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2382 the arguments supplied have types appropriate to the format string
2383 specified, and that the conversions specified in the format string make
2384 sense. This includes standard functions, and others specified by format
2385 attributes (@pxref{Function Attributes}), in the @code{printf},
2386 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2387 not in the C standard) families (or other target-specific families).
2388 Which functions are checked without format attributes having been
2389 specified depends on the standard version selected, and such checks of
2390 functions without the attribute specified are disabled by
2391 @option{-ffreestanding} or @option{-fno-builtin}.
2393 The formats are checked against the format features supported by GNU
2394 libc version 2.2. These include all ISO C90 and C99 features, as well
2395 as features from the Single Unix Specification and some BSD and GNU
2396 extensions. Other library implementations may not support all these
2397 features; GCC does not support warning about features that go beyond a
2398 particular library's limitations. However, if @option{-pedantic} is used
2399 with @option{-Wformat}, warnings will be given about format features not
2400 in the selected standard version (but not for @code{strfmon} formats,
2401 since those are not in any version of the C standard). @xref{C Dialect
2402 Options,,Options Controlling C Dialect}.
2404 Since @option{-Wformat} also checks for null format arguments for
2405 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2407 @option{-Wformat} is included in @option{-Wall}. For more control over some
2408 aspects of format checking, the options @option{-Wformat-y2k},
2409 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2410 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2411 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2414 @opindex Wformat-y2k
2415 If @option{-Wformat} is specified, also warn about @code{strftime}
2416 formats which may yield only a two-digit year.
2418 @item -Wno-format-extra-args
2419 @opindex Wno-format-extra-args
2420 If @option{-Wformat} is specified, do not warn about excess arguments to a
2421 @code{printf} or @code{scanf} format function. The C standard specifies
2422 that such arguments are ignored.
2424 Where the unused arguments lie between used arguments that are
2425 specified with @samp{$} operand number specifications, normally
2426 warnings are still given, since the implementation could not know what
2427 type to pass to @code{va_arg} to skip the unused arguments. However,
2428 in the case of @code{scanf} formats, this option will suppress the
2429 warning if the unused arguments are all pointers, since the Single
2430 Unix Specification says that such unused arguments are allowed.
2432 @item -Wno-format-zero-length
2433 @opindex Wno-format-zero-length
2434 If @option{-Wformat} is specified, do not warn about zero-length formats.
2435 The C standard specifies that zero-length formats are allowed.
2437 @item -Wformat-nonliteral
2438 @opindex Wformat-nonliteral
2439 If @option{-Wformat} is specified, also warn if the format string is not a
2440 string literal and so cannot be checked, unless the format function
2441 takes its format arguments as a @code{va_list}.
2443 @item -Wformat-security
2444 @opindex Wformat-security
2445 If @option{-Wformat} is specified, also warn about uses of format
2446 functions that represent possible security problems. At present, this
2447 warns about calls to @code{printf} and @code{scanf} functions where the
2448 format string is not a string literal and there are no format arguments,
2449 as in @code{printf (foo);}. This may be a security hole if the format
2450 string came from untrusted input and contains @samp{%n}. (This is
2451 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2452 in future warnings may be added to @option{-Wformat-security} that are not
2453 included in @option{-Wformat-nonliteral}.)
2457 Enable @option{-Wformat} plus format checks not included in
2458 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2459 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2463 Warn about passing a null pointer for arguments marked as
2464 requiring a non-null value by the @code{nonnull} function attribute.
2466 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2467 can be disabled with the @option{-Wno-nonnull} option.
2469 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
2471 Warn about uninitialized variables which are initialized with themselves.
2472 Note this option can only be used with the @option{-Wuninitialized} option,
2473 which in turn only works with @option{-O1} and above.
2475 For example, GCC will warn about @code{i} being uninitialized in the
2476 following snippet only when @option{-Winit-self} has been specified:
2487 @item -Wimplicit-int
2488 @opindex Wimplicit-int
2489 Warn when a declaration does not specify a type.
2490 This warning is enabled by @option{-Wall}.
2492 @item -Wimplicit-function-declaration
2493 @itemx -Werror-implicit-function-declaration
2494 @opindex Wimplicit-function-declaration
2495 @opindex Werror-implicit-function-declaration
2496 Give a warning (or error) whenever a function is used before being
2497 declared. The form @option{-Wno-error-implicit-function-declaration}
2499 This warning is enabled by @option{-Wall} (as a warning, not an error).
2503 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2504 This warning is enabled by @option{-Wall}.
2508 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2509 function with external linkage, returning int, taking either zero
2510 arguments, two, or three arguments of appropriate types.
2511 This warning is enabled by @option{-Wall}.
2513 @item -Wmissing-braces
2514 @opindex Wmissing-braces
2515 Warn if an aggregate or union initializer is not fully bracketed. In
2516 the following example, the initializer for @samp{a} is not fully
2517 bracketed, but that for @samp{b} is fully bracketed.
2520 int a[2][2] = @{ 0, 1, 2, 3 @};
2521 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2524 This warning is enabled by @option{-Wall}.
2526 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
2527 @opindex Wmissing-include-dirs
2528 Warn if a user-supplied include directory does not exist.
2531 @opindex Wparentheses
2532 Warn if parentheses are omitted in certain contexts, such
2533 as when there is an assignment in a context where a truth value
2534 is expected, or when operators are nested whose precedence people
2535 often get confused about.
2537 Also warn if a comparison like @samp{x<=y<=z} appears; this is
2538 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
2539 interpretation from that of ordinary mathematical notation.
2541 Also warn about constructions where there may be confusion to which
2542 @code{if} statement an @code{else} branch belongs. Here is an example of
2557 In C/C++, every @code{else} branch belongs to the innermost possible
2558 @code{if} statement, which in this example is @code{if (b)}. This is
2559 often not what the programmer expected, as illustrated in the above
2560 example by indentation the programmer chose. When there is the
2561 potential for this confusion, GCC will issue a warning when this flag
2562 is specified. To eliminate the warning, add explicit braces around
2563 the innermost @code{if} statement so there is no way the @code{else}
2564 could belong to the enclosing @code{if}. The resulting code would
2581 This warning is enabled by @option{-Wall}.
2583 @item -Wsequence-point
2584 @opindex Wsequence-point
2585 Warn about code that may have undefined semantics because of violations
2586 of sequence point rules in the C and C++ standards.
2588 The C and C++ standards defines the order in which expressions in a C/C++
2589 program are evaluated in terms of @dfn{sequence points}, which represent
2590 a partial ordering between the execution of parts of the program: those
2591 executed before the sequence point, and those executed after it. These
2592 occur after the evaluation of a full expression (one which is not part
2593 of a larger expression), after the evaluation of the first operand of a
2594 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2595 function is called (but after the evaluation of its arguments and the
2596 expression denoting the called function), and in certain other places.
2597 Other than as expressed by the sequence point rules, the order of
2598 evaluation of subexpressions of an expression is not specified. All
2599 these rules describe only a partial order rather than a total order,
2600 since, for example, if two functions are called within one expression
2601 with no sequence point between them, the order in which the functions
2602 are called is not specified. However, the standards committee have
2603 ruled that function calls do not overlap.
2605 It is not specified when between sequence points modifications to the
2606 values of objects take effect. Programs whose behavior depends on this
2607 have undefined behavior; the C and C++ standards specify that ``Between
2608 the previous and next sequence point an object shall have its stored
2609 value modified at most once by the evaluation of an expression.
2610 Furthermore, the prior value shall be read only to determine the value
2611 to be stored.''. If a program breaks these rules, the results on any
2612 particular implementation are entirely unpredictable.
2614 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2615 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2616 diagnosed by this option, and it may give an occasional false positive
2617 result, but in general it has been found fairly effective at detecting
2618 this sort of problem in programs.
2620 The standard is worded confusingly, therefore there is some debate
2621 over the precise meaning of the sequence point rules in subtle cases.
2622 Links to discussions of the problem, including proposed formal
2623 definitions, may be found on the GCC readings page, at
2624 @w{@uref{http://gcc.gnu.org/readings.html}}.
2626 This warning is enabled by @option{-Wall} for C and C++.
2629 @opindex Wreturn-type
2630 Warn whenever a function is defined with a return-type that defaults to
2631 @code{int}. Also warn about any @code{return} statement with no
2632 return-value in a function whose return-type is not @code{void}.
2634 For C, also warn if the return type of a function has a type qualifier
2635 such as @code{const}. Such a type qualifier has no effect, since the
2636 value returned by a function is not an lvalue. ISO C prohibits
2637 qualified @code{void} return types on function definitions, so such
2638 return types always receive a warning even without this option.
2640 For C++, a function without return type always produces a diagnostic
2641 message, even when @option{-Wno-return-type} is specified. The only
2642 exceptions are @samp{main} and functions defined in system headers.
2644 This warning is enabled by @option{-Wall}.
2648 Warn whenever a @code{switch} statement has an index of enumerated type
2649 and lacks a @code{case} for one or more of the named codes of that
2650 enumeration. (The presence of a @code{default} label prevents this
2651 warning.) @code{case} labels outside the enumeration range also
2652 provoke warnings when this option is used.
2653 This warning is enabled by @option{-Wall}.
2655 @item -Wswitch-default
2656 @opindex Wswitch-switch
2657 Warn whenever a @code{switch} statement does not have a @code{default}
2661 @opindex Wswitch-enum
2662 Warn whenever a @code{switch} statement has an index of enumerated type
2663 and lacks a @code{case} for one or more of the named codes of that
2664 enumeration. @code{case} labels outside the enumeration range also
2665 provoke warnings when this option is used.
2669 Warn if any trigraphs are encountered that might change the meaning of
2670 the program (trigraphs within comments are not warned about).
2671 This warning is enabled by @option{-Wall}.
2673 @item -Wunused-function
2674 @opindex Wunused-function
2675 Warn whenever a static function is declared but not defined or a
2676 non-inline static function is unused.
2677 This warning is enabled by @option{-Wall}.
2679 @item -Wunused-label
2680 @opindex Wunused-label
2681 Warn whenever a label is declared but not used.
2682 This warning is enabled by @option{-Wall}.
2684 To suppress this warning use the @samp{unused} attribute
2685 (@pxref{Variable Attributes}).
2687 @item -Wunused-parameter
2688 @opindex Wunused-parameter
2689 Warn whenever a function parameter is unused aside from its declaration.
2691 To suppress this warning use the @samp{unused} attribute
2692 (@pxref{Variable Attributes}).
2694 @item -Wunused-variable
2695 @opindex Wunused-variable
2696 Warn whenever a local variable or non-constant static variable is unused
2697 aside from its declaration.
2698 This warning is enabled by @option{-Wall}.
2700 To suppress this warning use the @samp{unused} attribute
2701 (@pxref{Variable Attributes}).
2703 @item -Wunused-value
2704 @opindex Wunused-value
2705 Warn whenever a statement computes a result that is explicitly not used.
2706 This warning is enabled by @option{-Wall}.
2708 To suppress this warning cast the expression to @samp{void}.
2712 All the above @option{-Wunused} options combined.
2714 In order to get a warning about an unused function parameter, you must
2715 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2716 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2718 @item -Wuninitialized
2719 @opindex Wuninitialized
2720 Warn if an automatic variable is used without first being initialized or
2721 if a variable may be clobbered by a @code{setjmp} call.
2723 These warnings are possible only in optimizing compilation,
2724 because they require data flow information that is computed only
2725 when optimizing. If you do not specify @option{-O}, you will not get
2726 these warnings. Instead, GCC will issue a warning about @option{-Wuninitialized}
2727 requiring @option{-O}.
2729 If you want to warn about code which uses the uninitialized value of the
2730 variable in its own initializer, use the @option{-Winit-self} option.
2732 These warnings occur for individual uninitialized or clobbered
2733 elements of structure, union or array variables as well as for
2734 variables which are uninitialized or clobbered as a whole. They do
2735 not occur for variables or elements declared @code{volatile}. Because
2736 these warnings depend on optimization, the exact variables or elements
2737 for which there are warnings will depend on the precise optimization
2738 options and version of GCC used.
2740 Note that there may be no warning about a variable that is used only
2741 to compute a value that itself is never used, because such
2742 computations may be deleted by data flow analysis before the warnings
2745 These warnings are made optional because GCC is not smart
2746 enough to see all the reasons why the code might be correct
2747 despite appearing to have an error. Here is one example of how
2768 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2769 always initialized, but GCC doesn't know this. Here is
2770 another common case:
2775 if (change_y) save_y = y, y = new_y;
2777 if (change_y) y = save_y;
2782 This has no bug because @code{save_y} is used only if it is set.
2784 @cindex @code{longjmp} warnings
2785 This option also warns when a non-volatile automatic variable might be
2786 changed by a call to @code{longjmp}. These warnings as well are possible
2787 only in optimizing compilation.
2789 The compiler sees only the calls to @code{setjmp}. It cannot know
2790 where @code{longjmp} will be called; in fact, a signal handler could
2791 call it at any point in the code. As a result, you may get a warning
2792 even when there is in fact no problem because @code{longjmp} cannot
2793 in fact be called at the place which would cause a problem.
2795 Some spurious warnings can be avoided if you declare all the functions
2796 you use that never return as @code{noreturn}. @xref{Function
2799 This warning is enabled by @option{-Wall}.
2801 @item -Wunknown-pragmas
2802 @opindex Wunknown-pragmas
2803 @cindex warning for unknown pragmas
2804 @cindex unknown pragmas, warning
2805 @cindex pragmas, warning of unknown
2806 Warn when a #pragma directive is encountered which is not understood by
2807 GCC@. If this command line option is used, warnings will even be issued
2808 for unknown pragmas in system header files. This is not the case if
2809 the warnings were only enabled by the @option{-Wall} command line option.
2812 @opindex Wno-pragmas
2814 Do not warn about misuses of pragmas, such as incorrect parameters,
2815 invalid syntax, or conflicts between pragmas. See also
2816 @samp{-Wunknown-pragmas}.
2818 @item -Wstrict-aliasing
2819 @opindex Wstrict-aliasing
2820 This option is only active when @option{-fstrict-aliasing} is active.
2821 It warns about code which might break the strict aliasing rules that the
2822 compiler is using for optimization. The warning does not catch all
2823 cases, but does attempt to catch the more common pitfalls. It is
2824 included in @option{-Wall}.
2826 @item -Wstrict-aliasing=2
2827 @opindex Wstrict-aliasing=2
2828 This option is only active when @option{-fstrict-aliasing} is active.
2829 It warns about code which might break the strict aliasing rules that the
2830 compiler is using for optimization. This warning catches more cases than
2831 @option{-Wstrict-aliasing}, but it will also give a warning for some ambiguous
2832 cases that are safe.
2836 All of the above @samp{-W} options combined. This enables all the
2837 warnings about constructions that some users consider questionable, and
2838 that are easy to avoid (or modify to prevent the warning), even in
2839 conjunction with macros. This also enables some language-specific
2840 warnings described in @ref{C++ Dialect Options} and
2841 @ref{Objective-C and Objective-C++ Dialect Options}.
2844 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2845 Some of them warn about constructions that users generally do not
2846 consider questionable, but which occasionally you might wish to check
2847 for; others warn about constructions that are necessary or hard to avoid
2848 in some cases, and there is no simple way to modify the code to suppress
2855 (This option used to be called @option{-W}. The older name is still
2856 supported, but the newer name is more descriptive.) Print extra warning
2857 messages for these events:
2861 A function can return either with or without a value. (Falling
2862 off the end of the function body is considered returning without
2863 a value.) For example, this function would evoke such a
2877 An expression-statement or the left-hand side of a comma expression
2878 contains no side effects.
2879 To suppress the warning, cast the unused expression to void.
2880 For example, an expression such as @samp{x[i,j]} will cause a warning,
2881 but @samp{x[(void)i,j]} will not.
2884 An unsigned value is compared against zero with @samp{<} or @samp{>=}.
2887 Storage-class specifiers like @code{static} are not the first things in
2888 a declaration. According to the C Standard, this usage is obsolescent.
2891 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2895 A comparison between signed and unsigned values could produce an
2896 incorrect result when the signed value is converted to unsigned.
2897 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2900 An aggregate has an initializer which does not initialize all members.
2901 This warning can be independently controlled by
2902 @option{-Wmissing-field-initializers}.
2905 An initialized field without side effects is overridden when using
2906 designated initializers (@pxref{Designated Inits, , Designated
2907 Initializers}). This warning can be independently controlled by
2908 @option{-Woverride-init}.
2911 A function parameter is declared without a type specifier in K&R-style
2919 An empty body occurs in an @samp{if} or @samp{else} statement. This
2920 warning can be independently controlled by @option{-Wempty-body}.
2923 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2924 @samp{>}, or @samp{>=}.
2927 A variable might be changed by @samp{longjmp} or @samp{vfork}.
2930 Any of several floating-point events that often indicate errors, such as
2931 overflow, underflow, loss of precision, etc.
2933 @item @r{(C++ only)}
2934 An enumerator and a non-enumerator both appear in a conditional expression.
2936 @item @r{(C++ only)}
2937 A non-static reference or non-static @samp{const} member appears in a
2938 class without constructors.
2940 @item @r{(C++ only)}
2941 Ambiguous virtual bases.
2943 @item @r{(C++ only)}
2944 Subscripting an array which has been declared @samp{register}.
2946 @item @r{(C++ only)}
2947 Taking the address of a variable which has been declared @samp{register}.
2949 @item @r{(C++ only)}
2950 A base class is not initialized in a derived class' copy constructor.
2953 @item -Wno-div-by-zero
2954 @opindex Wno-div-by-zero
2955 @opindex Wdiv-by-zero
2956 Do not warn about compile-time integer division by zero. Floating point
2957 division by zero is not warned about, as it can be a legitimate way of
2958 obtaining infinities and NaNs.
2960 @item -Wsystem-headers
2961 @opindex Wsystem-headers
2962 @cindex warnings from system headers
2963 @cindex system headers, warnings from
2964 Print warning messages for constructs found in system header files.
2965 Warnings from system headers are normally suppressed, on the assumption
2966 that they usually do not indicate real problems and would only make the
2967 compiler output harder to read. Using this command line option tells
2968 GCC to emit warnings from system headers as if they occurred in user
2969 code. However, note that using @option{-Wall} in conjunction with this
2970 option will @emph{not} warn about unknown pragmas in system
2971 headers---for that, @option{-Wunknown-pragmas} must also be used.
2974 @opindex Wfloat-equal
2975 Warn if floating point values are used in equality comparisons.
2977 The idea behind this is that sometimes it is convenient (for the
2978 programmer) to consider floating-point values as approximations to
2979 infinitely precise real numbers. If you are doing this, then you need
2980 to compute (by analyzing the code, or in some other way) the maximum or
2981 likely maximum error that the computation introduces, and allow for it
2982 when performing comparisons (and when producing output, but that's a
2983 different problem). In particular, instead of testing for equality, you
2984 would check to see whether the two values have ranges that overlap; and
2985 this is done with the relational operators, so equality comparisons are
2988 @item -Wtraditional @r{(C only)}
2989 @opindex Wtraditional
2990 Warn about certain constructs that behave differently in traditional and
2991 ISO C@. Also warn about ISO C constructs that have no traditional C
2992 equivalent, and/or problematic constructs which should be avoided.
2996 Macro parameters that appear within string literals in the macro body.
2997 In traditional C macro replacement takes place within string literals,
2998 but does not in ISO C@.
3001 In traditional C, some preprocessor directives did not exist.
3002 Traditional preprocessors would only consider a line to be a directive
3003 if the @samp{#} appeared in column 1 on the line. Therefore
3004 @option{-Wtraditional} warns about directives that traditional C
3005 understands but would ignore because the @samp{#} does not appear as the
3006 first character on the line. It also suggests you hide directives like
3007 @samp{#pragma} not understood by traditional C by indenting them. Some
3008 traditional implementations would not recognize @samp{#elif}, so it
3009 suggests avoiding it altogether.
3012 A function-like macro that appears without arguments.
3015 The unary plus operator.
3018 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
3019 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
3020 constants.) Note, these suffixes appear in macros defined in the system
3021 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
3022 Use of these macros in user code might normally lead to spurious
3023 warnings, however GCC's integrated preprocessor has enough context to
3024 avoid warning in these cases.
3027 A function declared external in one block and then used after the end of
3031 A @code{switch} statement has an operand of type @code{long}.
3034 A non-@code{static} function declaration follows a @code{static} one.
3035 This construct is not accepted by some traditional C compilers.
3038 The ISO type of an integer constant has a different width or
3039 signedness from its traditional type. This warning is only issued if
3040 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
3041 typically represent bit patterns, are not warned about.
3044 Usage of ISO string concatenation is detected.
3047 Initialization of automatic aggregates.
3050 Identifier conflicts with labels. Traditional C lacks a separate
3051 namespace for labels.
3054 Initialization of unions. If the initializer is zero, the warning is
3055 omitted. This is done under the assumption that the zero initializer in
3056 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
3057 initializer warnings and relies on default initialization to zero in the
3061 Conversions by prototypes between fixed/floating point values and vice
3062 versa. The absence of these prototypes when compiling with traditional
3063 C would cause serious problems. This is a subset of the possible
3064 conversion warnings, for the full set use @option{-Wtraditional-conversion}.
3067 Use of ISO C style function definitions. This warning intentionally is
3068 @emph{not} issued for prototype declarations or variadic functions
3069 because these ISO C features will appear in your code when using
3070 libiberty's traditional C compatibility macros, @code{PARAMS} and
3071 @code{VPARAMS}. This warning is also bypassed for nested functions
3072 because that feature is already a GCC extension and thus not relevant to
3073 traditional C compatibility.
3076 @item -Wtraditional-conversion @r{(C only)}
3077 @opindex Wtraditional-conversion
3078 Warn if a prototype causes a type conversion that is different from what
3079 would happen to the same argument in the absence of a prototype. This
3080 includes conversions of fixed point to floating and vice versa, and
3081 conversions changing the width or signedness of a fixed point argument
3082 except when the same as the default promotion.
3084 @item -Wdeclaration-after-statement @r{(C only)}
3085 @opindex Wdeclaration-after-statement
3086 Warn when a declaration is found after a statement in a block. This
3087 construct, known from C++, was introduced with ISO C99 and is by default
3088 allowed in GCC@. It is not supported by ISO C90 and was not supported by
3089 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
3093 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
3095 @item -Wno-endif-labels
3096 @opindex Wno-endif-labels
3097 @opindex Wendif-labels
3098 Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
3102 Warn whenever a local variable shadows another local variable, parameter or
3103 global variable or whenever a built-in function is shadowed.
3105 @item -Wlarger-than-@var{len}
3106 @opindex Wlarger-than
3107 Warn whenever an object of larger than @var{len} bytes is defined.
3109 @item -Wunsafe-loop-optimizations
3110 @opindex Wunsafe-loop-optimizations
3111 Warn if the loop cannot be optimized because the compiler could not
3112 assume anything on the bounds of the loop indices. With
3113 @option{-funsafe-loop-optimizations} warn if the compiler made
3116 @item -Wpointer-arith
3117 @opindex Wpointer-arith
3118 Warn about anything that depends on the ``size of'' a function type or
3119 of @code{void}. GNU C assigns these types a size of 1, for
3120 convenience in calculations with @code{void *} pointers and pointers
3123 @item -Wbad-function-cast @r{(C only)}
3124 @opindex Wbad-function-cast
3125 Warn whenever a function call is cast to a non-matching type.
3126 For example, warn if @code{int malloc()} is cast to @code{anything *}.
3129 Warn about ISO C constructs that are outside of the common subset of
3130 ISO C and ISO C++, e.g.@: request for implicit conversion from
3131 @code{void *} to a pointer to non-@code{void} type.
3135 Warn whenever a pointer is cast so as to remove a type qualifier from
3136 the target type. For example, warn if a @code{const char *} is cast
3137 to an ordinary @code{char *}.
3140 @opindex Wcast-align
3141 Warn whenever a pointer is cast such that the required alignment of the
3142 target is increased. For example, warn if a @code{char *} is cast to
3143 an @code{int *} on machines where integers can only be accessed at
3144 two- or four-byte boundaries.
3146 @item -Wwrite-strings
3147 @opindex Wwrite-strings
3148 When compiling C, give string constants the type @code{const
3149 char[@var{length}]} so that
3150 copying the address of one into a non-@code{const} @code{char *}
3151 pointer will get a warning; when compiling C++, warn about the
3152 deprecated conversion from string literals to @code{char *}. This
3153 warning, by default, is enabled for C++ programs.
3154 These warnings will help you find at
3155 compile time code that can try to write into a string constant, but
3156 only if you have been very careful about using @code{const} in
3157 declarations and prototypes. Otherwise, it will just be a nuisance;
3158 this is why we did not make @option{-Wall} request these warnings.
3161 @opindex Wconversion
3162 Warn for implicit conversions that may alter a value. This includes
3163 conversions between real and integer, like @code{abs (x)} when
3164 @code{x} is @code{double}; conversions between signed and unsigned,
3165 like @code{unsigned ui = -1}; and conversions to smaller types, like
3166 @code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs
3167 ((int) x)} and @code{ui = (unsigned) -1}, or if the value is not
3168 changed by the conversion like in @code{abs (2.0)}.
3171 @opindex Wempty-body
3172 An empty body occurs in an @samp{if} or @samp{else} statement.
3173 This warning is also enabled by @option{-Wextra}.
3175 @item -Wsign-compare
3176 @opindex Wsign-compare
3177 @cindex warning for comparison of signed and unsigned values
3178 @cindex comparison of signed and unsigned values, warning
3179 @cindex signed and unsigned values, comparison warning
3180 Warn when a comparison between signed and unsigned values could produce
3181 an incorrect result when the signed value is converted to unsigned.
3182 This warning is also enabled by @option{-Wextra}; to get the other warnings
3183 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
3185 @item -Waggregate-return
3186 @opindex Waggregate-return
3187 Warn if any functions that return structures or unions are defined or
3188 called. (In languages where you can return an array, this also elicits
3192 @opindex Walways-true
3193 Warn about comparisons which are always true such as testing if
3194 unsigned values are greater than or equal to zero. This warning is
3195 enabled by @option{-Wall}.
3197 @item -Wno-attributes
3198 @opindex Wno-attributes
3199 @opindex Wattributes
3200 Do not warn if an unexpected @code{__attribute__} is used, such as
3201 unrecognized attributes, function attributes applied to variables,
3202 etc. This will not stop errors for incorrect use of supported
3205 @item -Wstrict-prototypes @r{(C only)}
3206 @opindex Wstrict-prototypes
3207 Warn if a function is declared or defined without specifying the
3208 argument types. (An old-style function definition is permitted without
3209 a warning if preceded by a declaration which specifies the argument
3212 @item -Wold-style-definition @r{(C only)}
3213 @opindex Wold-style-definition
3214 Warn if an old-style function definition is used. A warning is given
3215 even if there is a previous prototype.
3217 @item -Wmissing-prototypes @r{(C only)}
3218 @opindex Wmissing-prototypes
3219 Warn if a global function is defined without a previous prototype
3220 declaration. This warning is issued even if the definition itself
3221 provides a prototype. The aim is to detect global functions that fail
3222 to be declared in header files.
3224 @item -Wmissing-declarations @r{(C and C++ only)}
3225 @opindex Wmissing-declarations
3226 Warn if a global function is defined without a previous declaration.
3227 Do so even if the definition itself provides a prototype.
3228 Use this option to detect global functions that are not declared in
3229 header files. In C++, no warnings are issued for function templates,
3230 or for inline functions, or for functions in anonymous namespaces.
3232 @item -Wmissing-field-initializers
3233 @opindex Wmissing-field-initializers
3236 Warn if a structure's initializer has some fields missing. For
3237 example, the following code would cause such a warning, because
3238 @code{x.h} is implicitly zero:
3241 struct s @{ int f, g, h; @};
3242 struct s x = @{ 3, 4 @};
3245 This option does not warn about designated initializers, so the following
3246 modification would not trigger a warning:
3249 struct s @{ int f, g, h; @};
3250 struct s x = @{ .f = 3, .g = 4 @};
3253 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
3254 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
3256 @item -Wmissing-noreturn
3257 @opindex Wmissing-noreturn
3258 Warn about functions which might be candidates for attribute @code{noreturn}.
3259 Note these are only possible candidates, not absolute ones. Care should
3260 be taken to manually verify functions actually do not ever return before
3261 adding the @code{noreturn} attribute, otherwise subtle code generation
3262 bugs could be introduced. You will not get a warning for @code{main} in
3263 hosted C environments.
3265 @item -Wmissing-format-attribute
3266 @opindex Wmissing-format-attribute
3268 Warn about function pointers which might be candidates for @code{format}
3269 attributes. Note these are only possible candidates, not absolute ones.
3270 GCC will guess that function pointers with @code{format} attributes that
3271 are used in assignment, initialization, parameter passing or return
3272 statements should have a corresponding @code{format} attribute in the
3273 resulting type. I.e.@: the left-hand side of the assignment or
3274 initialization, the type of the parameter variable, or the return type
3275 of the containing function respectively should also have a @code{format}
3276 attribute to avoid the warning.
3278 GCC will also warn about function definitions which might be
3279 candidates for @code{format} attributes. Again, these are only
3280 possible candidates. GCC will guess that @code{format} attributes
3281 might be appropriate for any function that calls a function like
3282 @code{vprintf} or @code{vscanf}, but this might not always be the
3283 case, and some functions for which @code{format} attributes are
3284 appropriate may not be detected.
3286 @item -Wno-multichar
3287 @opindex Wno-multichar
3289 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
3290 Usually they indicate a typo in the user's code, as they have
3291 implementation-defined values, and should not be used in portable code.
3293 @item -Wnormalized=<none|id|nfc|nfkc>
3294 @opindex Wnormalized
3297 @cindex character set, input normalization
3298 In ISO C and ISO C++, two identifiers are different if they are
3299 different sequences of characters. However, sometimes when characters
3300 outside the basic ASCII character set are used, you can have two
3301 different character sequences that look the same. To avoid confusion,
3302 the ISO 10646 standard sets out some @dfn{normalization rules} which
3303 when applied ensure that two sequences that look the same are turned into
3304 the same sequence. GCC can warn you if you are using identifiers which
3305 have not been normalized; this option controls that warning.
3307 There are four levels of warning that GCC supports. The default is
3308 @option{-Wnormalized=nfc}, which warns about any identifier which is
3309 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
3310 recommended form for most uses.
3312 Unfortunately, there are some characters which ISO C and ISO C++ allow
3313 in identifiers that when turned into NFC aren't allowable as
3314 identifiers. That is, there's no way to use these symbols in portable
3315 ISO C or C++ and have all your identifiers in NFC.
3316 @option{-Wnormalized=id} suppresses the warning for these characters.
3317 It is hoped that future versions of the standards involved will correct
3318 this, which is why this option is not the default.
3320 You can switch the warning off for all characters by writing
3321 @option{-Wnormalized=none}. You would only want to do this if you
3322 were using some other normalization scheme (like ``D''), because
3323 otherwise you can easily create bugs that are literally impossible to see.
3325 Some characters in ISO 10646 have distinct meanings but look identical
3326 in some fonts or display methodologies, especially once formatting has
3327 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
3328 LETTER N'', will display just like a regular @code{n} which has been
3329 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
3330 normalization scheme to convert all these into a standard form as
3331 well, and GCC will warn if your code is not in NFKC if you use
3332 @option{-Wnormalized=nfkc}. This warning is comparable to warning
3333 about every identifier that contains the letter O because it might be
3334 confused with the digit 0, and so is not the default, but may be
3335 useful as a local coding convention if the programming environment is
3336 unable to be fixed to display these characters distinctly.
3338 @item -Wno-deprecated-declarations
3339 @opindex Wno-deprecated-declarations
3340 Do not warn about uses of functions (@pxref{Function Attributes}),
3341 variables (@pxref{Variable Attributes}), and types (@pxref{Type
3342 Attributes}) marked as deprecated by using the @code{deprecated}
3346 @opindex Wno-overflow
3347 Do not warn about compile-time overflow in constant expressions.
3349 @item -Woverride-init
3350 @opindex Woverride-init
3353 Warn if an initialized field without side effects is overridden when
3354 using designated initializers (@pxref{Designated Inits, , Designated
3357 This warning is included in @option{-Wextra}. To get other
3358 @option{-Wextra} warnings without this one, use @samp{-Wextra
3359 -Wno-override-init}.
3363 Warn if a structure is given the packed attribute, but the packed
3364 attribute has no effect on the layout or size of the structure.
3365 Such structures may be mis-aligned for little benefit. For
3366 instance, in this code, the variable @code{f.x} in @code{struct bar}
3367 will be misaligned even though @code{struct bar} does not itself
3368 have the packed attribute:
3375 @} __attribute__((packed));
3385 Warn if padding is included in a structure, either to align an element
3386 of the structure or to align the whole structure. Sometimes when this
3387 happens it is possible to rearrange the fields of the structure to
3388 reduce the padding and so make the structure smaller.
3390 @item -Wredundant-decls
3391 @opindex Wredundant-decls
3392 Warn if anything is declared more than once in the same scope, even in
3393 cases where multiple declaration is valid and changes nothing.
3395 @item -Wnested-externs @r{(C only)}
3396 @opindex Wnested-externs
3397 Warn if an @code{extern} declaration is encountered within a function.
3399 @item -Wunreachable-code
3400 @opindex Wunreachable-code
3401 Warn if the compiler detects that code will never be executed.
3403 This option is intended to warn when the compiler detects that at
3404 least a whole line of source code will never be executed, because
3405 some condition is never satisfied or because it is after a
3406 procedure that never returns.
3408 It is possible for this option to produce a warning even though there
3409 are circumstances under which part of the affected line can be executed,
3410 so care should be taken when removing apparently-unreachable code.
3412 For instance, when a function is inlined, a warning may mean that the
3413 line is unreachable in only one inlined copy of the function.
3415 This option is not made part of @option{-Wall} because in a debugging
3416 version of a program there is often substantial code which checks
3417 correct functioning of the program and is, hopefully, unreachable
3418 because the program does work. Another common use of unreachable
3419 code is to provide behavior which is selectable at compile-time.
3423 Warn if a function can not be inlined and it was declared as inline.
3424 Even with this option, the compiler will not warn about failures to
3425 inline functions declared in system headers.
3427 The compiler uses a variety of heuristics to determine whether or not
3428 to inline a function. For example, the compiler takes into account
3429 the size of the function being inlined and the amount of inlining
3430 that has already been done in the current function. Therefore,
3431 seemingly insignificant changes in the source program can cause the
3432 warnings produced by @option{-Winline} to appear or disappear.
3434 @item -Wno-invalid-offsetof @r{(C++ only)}
3435 @opindex Wno-invalid-offsetof
3436 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
3437 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
3438 to a non-POD type is undefined. In existing C++ implementations,
3439 however, @samp{offsetof} typically gives meaningful results even when
3440 applied to certain kinds of non-POD types. (Such as a simple
3441 @samp{struct} that fails to be a POD type only by virtue of having a
3442 constructor.) This flag is for users who are aware that they are
3443 writing nonportable code and who have deliberately chosen to ignore the
3446 The restrictions on @samp{offsetof} may be relaxed in a future version
3447 of the C++ standard.
3449 @item -Wno-int-to-pointer-cast @r{(C only)}
3450 @opindex Wno-int-to-pointer-cast
3451 Suppress warnings from casts to pointer type of an integer of a
3454 @item -Wno-pointer-to-int-cast @r{(C only)}
3455 @opindex Wno-pointer-to-int-cast
3456 Suppress warnings from casts from a pointer to an integer type of a
3460 @opindex Winvalid-pch
3461 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
3462 the search path but can't be used.
3466 @opindex Wno-long-long
3467 Warn if @samp{long long} type is used. This is default. To inhibit
3468 the warning messages, use @option{-Wno-long-long}. Flags
3469 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
3470 only when @option{-pedantic} flag is used.
3472 @item -Wvariadic-macros
3473 @opindex Wvariadic-macros
3474 @opindex Wno-variadic-macros
3475 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
3476 alternate syntax when in pedantic ISO C99 mode. This is default.
3477 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
3479 @item -Wvolatile-register-var
3480 @opindex Wvolatile-register-var
3481 @opindex Wno-volatile-register-var
3482 Warn if a register variable is declared volatile. The volatile
3483 modifier does not inhibit all optimizations that may eliminate reads
3484 and/or writes to register variables.
3486 @item -Wdisabled-optimization
3487 @opindex Wdisabled-optimization
3488 Warn if a requested optimization pass is disabled. This warning does
3489 not generally indicate that there is anything wrong with your code; it
3490 merely indicates that GCC's optimizers were unable to handle the code
3491 effectively. Often, the problem is that your code is too big or too
3492 complex; GCC will refuse to optimize programs when the optimization
3493 itself is likely to take inordinate amounts of time.
3495 @item -Wpointer-sign
3496 @opindex Wpointer-sign
3497 @opindex Wno-pointer-sign
3498 Warn for pointer argument passing or assignment with different signedness.
3499 This option is only supported for C and Objective-C@. It is implied by
3500 @option{-Wall} and by @option{-pedantic}, which can be disabled with
3501 @option{-Wno-pointer-sign}.
3505 Make all warnings into errors.
3509 Make the specified warning into an errors. The specifier for a
3510 warning is appended, for example @option{-Werror=switch} turns the
3511 warnings controlled by @option{-Wswitch} into errors. This switch
3512 takes a negative form, to be used to negate @option{-Werror} for
3513 specific warnings, for example @option{-Wno-error=switch} makes
3514 @option{-Wswitch} warnings not be errors, even when @option{-Werror}
3515 is in effect. You can use the @option{-fdiagnostics-show-option}
3516 option to have each controllable warning amended with the option which
3517 controls it, to determine what to use with this option.
3519 Note that specifying @option{-Werror=}@var{foo} automatically implies
3520 @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
3523 @item -Wstack-protector
3524 @opindex Wstack-protector
3525 This option is only active when @option{-fstack-protector} is active. It
3526 warns about functions that will not be protected against stack smashing.
3528 @item -Wstring-literal-comparison
3529 @opindex Wstring-literal-comparison
3530 Warn about suspicious comparisons to string literal constants. In C,
3531 direct comparisons against the memory address of a string literal, such
3532 as @code{if (x == "abc")}, typically indicate a programmer error, and
3533 even when intentional, result in unspecified behavior and are not portable.
3534 Usually these warnings alert that the programmer intended to use
3535 @code{strcmp}. This warning is enabled by @option{-Wall}.
3537 @item -Woverlength-strings
3538 @opindex Woverlength-strings
3539 Warn about string constants which are longer than the ``minimum
3540 maximum'' length specified in the C standard. Modern compilers
3541 generally allow string constants which are much longer than the
3542 standard's minimum limit, but very portable programs should avoid
3543 using longer strings.
3545 The limit applies @emph{after} string constant concatenation, and does
3546 not count the trailing NUL@. In C89, the limit was 509 characters; in
3547 C99, it was raised to 4095. C++98 does not specify a normative
3548 minimum maximum, so we do not diagnose overlength strings in C++@.
3550 This option is implied by @option{-pedantic}, and can be disabled with
3551 @option{-Wno-overlength-strings}.
3554 @node Debugging Options
3555 @section Options for Debugging Your Program or GCC
3556 @cindex options, debugging
3557 @cindex debugging information options
3559 GCC has various special options that are used for debugging
3560 either your program or GCC:
3565 Produce debugging information in the operating system's native format
3566 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
3569 On most systems that use stabs format, @option{-g} enables use of extra
3570 debugging information that only GDB can use; this extra information
3571 makes debugging work better in GDB but will probably make other debuggers
3573 refuse to read the program. If you want to control for certain whether
3574 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
3575 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
3577 GCC allows you to use @option{-g} with
3578 @option{-O}. The shortcuts taken by optimized code may occasionally
3579 produce surprising results: some variables you declared may not exist
3580 at all; flow of control may briefly move where you did not expect it;
3581 some statements may not be executed because they compute constant
3582 results or their values were already at hand; some statements may
3583 execute in different places because they were moved out of loops.
3585 Nevertheless it proves possible to debug optimized output. This makes
3586 it reasonable to use the optimizer for programs that might have bugs.
3588 The following options are useful when GCC is generated with the
3589 capability for more than one debugging format.
3593 Produce debugging information for use by GDB@. This means to use the
3594 most expressive format available (DWARF 2, stabs, or the native format
3595 if neither of those are supported), including GDB extensions if at all
3600 Produce debugging information in stabs format (if that is supported),
3601 without GDB extensions. This is the format used by DBX on most BSD
3602 systems. On MIPS, Alpha and System V Release 4 systems this option
3603 produces stabs debugging output which is not understood by DBX or SDB@.
3604 On System V Release 4 systems this option requires the GNU assembler.
3606 @item -feliminate-unused-debug-symbols
3607 @opindex feliminate-unused-debug-symbols
3608 Produce debugging information in stabs format (if that is supported),
3609 for only symbols that are actually used.
3611 @item -femit-class-debug-always
3612 Instead of emitting debugging information for a C++ class in only one
3613 object file, emit it in all object files using the class. This option
3614 should be used only with debuggers that are unable to handle the way GCC
3615 normally emits debugging information for classes because using this
3616 option will increase the size of debugging information by as much as a
3621 Produce debugging information in stabs format (if that is supported),
3622 using GNU extensions understood only by the GNU debugger (GDB)@. The
3623 use of these extensions is likely to make other debuggers crash or
3624 refuse to read the program.
3628 Produce debugging information in COFF format (if that is supported).
3629 This is the format used by SDB on most System V systems prior to
3634 Produce debugging information in XCOFF format (if that is supported).
3635 This is the format used by the DBX debugger on IBM RS/6000 systems.
3639 Produce debugging information in XCOFF format (if that is supported),
3640 using GNU extensions understood only by the GNU debugger (GDB)@. The
3641 use of these extensions is likely to make other debuggers crash or
3642 refuse to read the program, and may cause assemblers other than the GNU
3643 assembler (GAS) to fail with an error.
3647 Produce debugging information in DWARF version 2 format (if that is
3648 supported). This is the format used by DBX on IRIX 6. With this
3649 option, GCC uses features of DWARF version 3 when they are useful;
3650 version 3 is upward compatible with version 2, but may still cause
3651 problems for older debuggers.
3655 Produce debugging information in VMS debug format (if that is
3656 supported). This is the format used by DEBUG on VMS systems.
3659 @itemx -ggdb@var{level}
3660 @itemx -gstabs@var{level}
3661 @itemx -gcoff@var{level}
3662 @itemx -gxcoff@var{level}
3663 @itemx -gvms@var{level}
3664 Request debugging information and also use @var{level} to specify how
3665 much information. The default level is 2.
3667 Level 1 produces minimal information, enough for making backtraces in
3668 parts of the program that you don't plan to debug. This includes
3669 descriptions of functions and external variables, but no information
3670 about local variables and no line numbers.
3672 Level 3 includes extra information, such as all the macro definitions
3673 present in the program. Some debuggers support macro expansion when
3674 you use @option{-g3}.
3676 @option{-gdwarf-2} does not accept a concatenated debug level, because
3677 GCC used to support an option @option{-gdwarf} that meant to generate
3678 debug information in version 1 of the DWARF format (which is very
3679 different from version 2), and it would have been too confusing. That
3680 debug format is long obsolete, but the option cannot be changed now.
3681 Instead use an additional @option{-g@var{level}} option to change the
3682 debug level for DWARF2.
3684 @item -feliminate-dwarf2-dups
3685 @opindex feliminate-dwarf2-dups
3686 Compress DWARF2 debugging information by eliminating duplicated
3687 information about each symbol. This option only makes sense when
3688 generating DWARF2 debugging information with @option{-gdwarf-2}.
3690 @cindex @command{prof}
3693 Generate extra code to write profile information suitable for the
3694 analysis program @command{prof}. You must use this option when compiling
3695 the source files you want data about, and you must also use it when
3698 @cindex @command{gprof}
3701 Generate extra code to write profile information suitable for the
3702 analysis program @command{gprof}. You must use this option when compiling
3703 the source files you want data about, and you must also use it when
3708 Makes the compiler print out each function name as it is compiled, and
3709 print some statistics about each pass when it finishes.
3712 @opindex ftime-report
3713 Makes the compiler print some statistics about the time consumed by each
3714 pass when it finishes.
3717 @opindex fmem-report
3718 Makes the compiler print some statistics about permanent memory
3719 allocation when it finishes.
3721 @item -fprofile-arcs
3722 @opindex fprofile-arcs
3723 Add code so that program flow @dfn{arcs} are instrumented. During
3724 execution the program records how many times each branch and call is
3725 executed and how many times it is taken or returns. When the compiled
3726 program exits it saves this data to a file called
3727 @file{@var{auxname}.gcda} for each source file. The data may be used for
3728 profile-directed optimizations (@option{-fbranch-probabilities}), or for
3729 test coverage analysis (@option{-ftest-coverage}). Each object file's
3730 @var{auxname} is generated from the name of the output file, if
3731 explicitly specified and it is not the final executable, otherwise it is
3732 the basename of the source file. In both cases any suffix is removed
3733 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
3734 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
3735 @xref{Cross-profiling}.
3737 @cindex @command{gcov}
3741 This option is used to compile and link code instrumented for coverage
3742 analysis. The option is a synonym for @option{-fprofile-arcs}
3743 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
3744 linking). See the documentation for those options for more details.
3749 Compile the source files with @option{-fprofile-arcs} plus optimization
3750 and code generation options. For test coverage analysis, use the
3751 additional @option{-ftest-coverage} option. You do not need to profile
3752 every source file in a program.
3755 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
3756 (the latter implies the former).
3759 Run the program on a representative workload to generate the arc profile
3760 information. This may be repeated any number of times. You can run
3761 concurrent instances of your program, and provided that the file system
3762 supports locking, the data files will be correctly updated. Also
3763 @code{fork} calls are detected and correctly handled (double counting
3767 For profile-directed optimizations, compile the source files again with
3768 the same optimization and code generation options plus
3769 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
3770 Control Optimization}).
3773 For test coverage analysis, use @command{gcov} to produce human readable
3774 information from the @file{.gcno} and @file{.gcda} files. Refer to the
3775 @command{gcov} documentation for further information.
3779 With @option{-fprofile-arcs}, for each function of your program GCC
3780 creates a program flow graph, then finds a spanning tree for the graph.
3781 Only arcs that are not on the spanning tree have to be instrumented: the
3782 compiler adds code to count the number of times that these arcs are
3783 executed. When an arc is the only exit or only entrance to a block, the
3784 instrumentation code can be added to the block; otherwise, a new basic
3785 block must be created to hold the instrumentation code.
3788 @item -ftest-coverage
3789 @opindex ftest-coverage
3790 Produce a notes file that the @command{gcov} code-coverage utility
3791 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
3792 show program coverage. Each source file's note file is called
3793 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
3794 above for a description of @var{auxname} and instructions on how to
3795 generate test coverage data. Coverage data will match the source files
3796 more closely, if you do not optimize.
3798 @item -d@var{letters}
3799 @item -fdump-rtl-@var{pass}
3801 Says to make debugging dumps during compilation at times specified by
3802 @var{letters}. This is used for debugging the RTL-based passes of the
3803 compiler. The file names for most of the dumps are made by appending a
3804 pass number and a word to the @var{dumpname}. @var{dumpname} is generated
3805 from the name of the output file, if explicitly specified and it is not
3806 an executable, otherwise it is the basename of the source file.
3808 Most debug dumps can be enabled either passing a letter to the @option{-d}
3809 option, or with a long @option{-fdump-rtl} switch; here are the possible
3810 letters for use in @var{letters} and @var{pass}, and their meanings:
3815 Annotate the assembler output with miscellaneous debugging information.
3818 @itemx -fdump-rtl-bbro
3820 @opindex fdump-rtl-bbro
3821 Dump after block reordering, to @file{@var{file}.148r.bbro}.
3824 @itemx -fdump-rtl-combine
3826 @opindex fdump-rtl-combine
3827 Dump after instruction combination, to the file @file{@var{file}.129r.combine}.
3830 @itemx -fdump-rtl-ce1
3831 @itemx -fdump-rtl-ce2
3833 @opindex fdump-rtl-ce1
3834 @opindex fdump-rtl-ce2
3835 @option{-dC} and @option{-fdump-rtl-ce1} enable dumping after the
3836 first if conversion, to the file @file{@var{file}.117r.ce1}. @option{-dC}
3837 and @option{-fdump-rtl-ce2} enable dumping after the second if
3838 conversion, to the file @file{@var{file}.130r.ce2}.
3841 @itemx -fdump-rtl-btl
3842 @itemx -fdump-rtl-dbr
3844 @opindex fdump-rtl-btl
3845 @opindex fdump-rtl-dbr
3846 @option{-dd} and @option{-fdump-rtl-btl} enable dumping after branch
3847 target load optimization, to @file{@var{file}.31.btl}. @option{-dd}
3848 and @option{-fdump-rtl-dbr} enable dumping after delayed branch
3849 scheduling, to @file{@var{file}.36.dbr}.
3853 Dump all macro definitions, at the end of preprocessing, in addition to
3857 @itemx -fdump-rtl-ce3
3859 @opindex fdump-rtl-ce3
3860 Dump after the third if conversion, to @file{@var{file}.146r.ce3}.
3863 @itemx -fdump-rtl-cfg
3864 @itemx -fdump-rtl-life
3866 @opindex fdump-rtl-cfg
3867 @opindex fdump-rtl-life
3868 @option{-df} and @option{-fdump-rtl-cfg} enable dumping after control
3869 and data flow analysis, to @file{@var{file}.116r.cfg}. @option{-df}
3870 and @option{-fdump-rtl-cfg} enable dumping dump after life analysis,
3871 to @file{@var{file}.128r.life1} and @file{@var{file}.135r.life2}.
3874 @itemx -fdump-rtl-greg
3876 @opindex fdump-rtl-greg
3877 Dump after global register allocation, to @file{@var{file}.139r.greg}.
3880 @itemx -fdump-rtl-gcse
3881 @itemx -fdump-rtl-bypass
3883 @opindex fdump-rtl-gcse
3884 @opindex fdump-rtl-bypass
3885 @option{-dG} and @option{-fdump-rtl-gcse} enable dumping after GCSE, to
3886 @file{@var{file}.114r.gcse}. @option{-dG} and @option{-fdump-rtl-bypass}
3887 enable dumping after jump bypassing and control flow optimizations, to
3888 @file{@var{file}.115r.bypass}.
3891 @itemx -fdump-rtl-eh
3893 @opindex fdump-rtl-eh
3894 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
3897 @itemx -fdump-rtl-sibling
3899 @opindex fdump-rtl-sibling
3900 Dump after sibling call optimizations, to @file{@var{file}.106r.sibling}.
3903 @itemx -fdump-rtl-jump
3905 @opindex fdump-rtl-jump
3906 Dump after the first jump optimization, to @file{@var{file}.112r.jump}.
3909 @itemx -fdump-rtl-stack
3911 @opindex fdump-rtl-stack
3912 Dump after conversion from registers to stack, to @file{@var{file}.152r.stack}.
3915 @itemx -fdump-rtl-lreg
3917 @opindex fdump-rtl-lreg
3918 Dump after local register allocation, to @file{@var{file}.138r.lreg}.
3921 @itemx -fdump-rtl-loop2
3923 @opindex fdump-rtl-loop2
3924 @option{-dL} and @option{-fdump-rtl-loop2} enable dumping after the
3925 loop optimization pass, to @file{@var{file}.119r.loop2},
3926 @file{@var{file}.120r.loop2_init},
3927 @file{@var{file}.121r.loop2_invariant}, and
3928 @file{@var{file}.125r.loop2_done}.
3931 @itemx -fdump-rtl-sms
3933 @opindex fdump-rtl-sms
3934 Dump after modulo scheduling, to @file{@var{file}.136r.sms}.
3937 @itemx -fdump-rtl-mach
3939 @opindex fdump-rtl-mach
3940 Dump after performing the machine dependent reorganization pass, to
3941 @file{@var{file}.155r.mach}.
3944 @itemx -fdump-rtl-rnreg
3946 @opindex fdump-rtl-rnreg
3947 Dump after register renumbering, to @file{@var{file}.147r.rnreg}.
3950 @itemx -fdump-rtl-regmove
3952 @opindex fdump-rtl-regmove
3953 Dump after the register move pass, to @file{@var{file}.132r.regmove}.
3956 @itemx -fdump-rtl-postreload
3958 @opindex fdump-rtl-postreload
3959 Dump after post-reload optimizations, to @file{@var{file}.24.postreload}.
3962 @itemx -fdump-rtl-expand
3964 @opindex fdump-rtl-expand
3965 Dump after RTL generation, to @file{@var{file}.104r.expand}.
3968 @itemx -fdump-rtl-sched2
3970 @opindex fdump-rtl-sched2
3971 Dump after the second scheduling pass, to @file{@var{file}.149r.sched2}.
3974 @itemx -fdump-rtl-cse
3976 @opindex fdump-rtl-cse
3977 Dump after CSE (including the jump optimization that sometimes follows
3978 CSE), to @file{@var{file}.113r.cse}.
3981 @itemx -fdump-rtl-sched1
3983 @opindex fdump-rtl-sched1
3984 Dump after the first scheduling pass, to @file{@var{file}.136r.sched1}.
3987 @itemx -fdump-rtl-cse2
3989 @opindex fdump-rtl-cse2
3990 Dump after the second CSE pass (including the jump optimization that
3991 sometimes follows CSE), to @file{@var{file}.127r.cse2}.
3994 @itemx -fdump-rtl-tracer
3996 @opindex fdump-rtl-tracer
3997 Dump after running tracer, to @file{@var{file}.118r.tracer}.
4000 @itemx -fdump-rtl-vpt
4001 @itemx -fdump-rtl-vartrack
4003 @opindex fdump-rtl-vpt
4004 @opindex fdump-rtl-vartrack
4005 @option{-dV} and @option{-fdump-rtl-vpt} enable dumping after the value
4006 profile transformations, to @file{@var{file}.10.vpt}. @option{-dV}
4007 and @option{-fdump-rtl-vartrack} enable dumping after variable tracking,
4008 to @file{@var{file}.154r.vartrack}.
4011 @itemx -fdump-rtl-flow2
4013 @opindex fdump-rtl-flow2
4014 Dump after the second flow pass, to @file{@var{file}.142r.flow2}.
4017 @itemx -fdump-rtl-peephole2
4019 @opindex fdump-rtl-peephole2
4020 Dump after the peephole pass, to @file{@var{file}.145r.peephole2}.
4023 @itemx -fdump-rtl-web
4025 @opindex fdump-rtl-web
4026 Dump after live range splitting, to @file{@var{file}.126r.web}.
4029 @itemx -fdump-rtl-all
4031 @opindex fdump-rtl-all
4032 Produce all the dumps listed above.
4036 Produce a core dump whenever an error occurs.
4040 Print statistics on memory usage, at the end of the run, to
4045 Annotate the assembler output with a comment indicating which
4046 pattern and alternative was used. The length of each instruction is
4051 Dump the RTL in the assembler output as a comment before each instruction.
4052 Also turns on @option{-dp} annotation.
4056 For each of the other indicated dump files (either with @option{-d} or
4057 @option{-fdump-rtl-@var{pass}}), dump a representation of the control flow
4058 graph suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
4062 Just generate RTL for a function instead of compiling it. Usually used
4063 with @samp{r} (@option{-fdump-rtl-expand}).
4067 Dump debugging information during parsing, to standard error.
4071 @opindex fdump-noaddr
4072 When doing debugging dumps (see @option{-d} option above), suppress
4073 address output. This makes it more feasible to use diff on debugging
4074 dumps for compiler invocations with different compiler binaries and/or
4075 different text / bss / data / heap / stack / dso start locations.
4077 @item -fdump-unnumbered
4078 @opindex fdump-unnumbered
4079 When doing debugging dumps (see @option{-d} option above), suppress instruction
4080 numbers, line number note and address output. This makes it more feasible to
4081 use diff on debugging dumps for compiler invocations with different
4082 options, in particular with and without @option{-g}.
4084 @item -fdump-translation-unit @r{(C++ only)}
4085 @itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
4086 @opindex fdump-translation-unit
4087 Dump a representation of the tree structure for the entire translation
4088 unit to a file. The file name is made by appending @file{.tu} to the
4089 source file name. If the @samp{-@var{options}} form is used, @var{options}
4090 controls the details of the dump as described for the
4091 @option{-fdump-tree} options.
4093 @item -fdump-class-hierarchy @r{(C++ only)}
4094 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
4095 @opindex fdump-class-hierarchy
4096 Dump a representation of each class's hierarchy and virtual function
4097 table layout to a file. The file name is made by appending @file{.class}
4098 to the source file name. If the @samp{-@var{options}} form is used,
4099 @var{options} controls the details of the dump as described for the
4100 @option{-fdump-tree} options.
4102 @item -fdump-ipa-@var{switch}
4104 Control the dumping at various stages of inter-procedural analysis
4105 language tree to a file. The file name is generated by appending a switch
4106 specific suffix to the source file name. The following dumps are possible:
4110 Enables all inter-procedural analysis dumps; currently the only produced
4111 dump is the @samp{cgraph} dump.
4114 Dumps information about call-graph optimization, unused function removal,
4115 and inlining decisions.
4118 @item -fdump-tree-@var{switch}
4119 @itemx -fdump-tree-@var{switch}-@var{options}
4121 Control the dumping at various stages of processing the intermediate
4122 language tree to a file. The file name is generated by appending a switch
4123 specific suffix to the source file name. If the @samp{-@var{options}}
4124 form is used, @var{options} is a list of @samp{-} separated options that
4125 control the details of the dump. Not all options are applicable to all
4126 dumps, those which are not meaningful will be ignored. The following
4127 options are available
4131 Print the address of each node. Usually this is not meaningful as it
4132 changes according to the environment and source file. Its primary use
4133 is for tying up a dump file with a debug environment.
4135 Inhibit dumping of members of a scope or body of a function merely
4136 because that scope has been reached. Only dump such items when they
4137 are directly reachable by some other path. When dumping pretty-printed
4138 trees, this option inhibits dumping the bodies of control structures.
4140 Print a raw representation of the tree. By default, trees are
4141 pretty-printed into a C-like representation.
4143 Enable more detailed dumps (not honored by every dump option).
4145 Enable dumping various statistics about the pass (not honored by every dump
4148 Enable showing basic block boundaries (disabled in raw dumps).
4150 Enable showing virtual operands for every statement.
4152 Enable showing line numbers for statements.
4154 Enable showing the unique ID (@code{DECL_UID}) for each variable.
4156 Turn on all options, except @option{raw}, @option{slim} and @option{lineno}.
4159 The following tree dumps are possible:
4163 Dump before any tree based optimization, to @file{@var{file}.original}.
4166 Dump after all tree based optimization, to @file{@var{file}.optimized}.
4169 Dump after function inlining, to @file{@var{file}.inlined}.
4172 @opindex fdump-tree-gimple
4173 Dump each function before and after the gimplification pass to a file. The
4174 file name is made by appending @file{.gimple} to the source file name.
4177 @opindex fdump-tree-cfg
4178 Dump the control flow graph of each function to a file. The file name is
4179 made by appending @file{.cfg} to the source file name.
4182 @opindex fdump-tree-vcg
4183 Dump the control flow graph of each function to a file in VCG format. The
4184 file name is made by appending @file{.vcg} to the source file name. Note
4185 that if the file contains more than one function, the generated file cannot
4186 be used directly by VCG@. You will need to cut and paste each function's
4187 graph into its own separate file first.
4190 @opindex fdump-tree-ch
4191 Dump each function after copying loop headers. The file name is made by
4192 appending @file{.ch} to the source file name.
4195 @opindex fdump-tree-ssa
4196 Dump SSA related information to a file. The file name is made by appending
4197 @file{.ssa} to the source file name.
4200 @opindex fdump-tree-salias
4201 Dump structure aliasing variable information to a file. This file name
4202 is made by appending @file{.salias} to the source file name.
4205 @opindex fdump-tree-alias
4206 Dump aliasing information for each function. The file name is made by
4207 appending @file{.alias} to the source file name.
4210 @opindex fdump-tree-ccp
4211 Dump each function after CCP@. The file name is made by appending
4212 @file{.ccp} to the source file name.
4215 @opindex fdump-tree-storeccp
4216 Dump each function after STORE-CCP. The file name is made by appending
4217 @file{.storeccp} to the source file name.
4220 @opindex fdump-tree-pre
4221 Dump trees after partial redundancy elimination. The file name is made
4222 by appending @file{.pre} to the source file name.
4225 @opindex fdump-tree-fre
4226 Dump trees after full redundancy elimination. The file name is made
4227 by appending @file{.fre} to the source file name.
4230 @opindex fdump-tree-copyprop
4231 Dump trees after copy propagation. The file name is made
4232 by appending @file{.copyprop} to the source file name.
4234 @item store_copyprop
4235 @opindex fdump-tree-store_copyprop
4236 Dump trees after store copy-propagation. The file name is made
4237 by appending @file{.store_copyprop} to the source file name.
4240 @opindex fdump-tree-dce
4241 Dump each function after dead code elimination. The file name is made by
4242 appending @file{.dce} to the source file name.
4245 @opindex fdump-tree-mudflap
4246 Dump each function after adding mudflap instrumentation. The file name is
4247 made by appending @file{.mudflap} to the source file name.
4250 @opindex fdump-tree-sra
4251 Dump each function after performing scalar replacement of aggregates. The
4252 file name is made by appending @file{.sra} to the source file name.
4255 @opindex fdump-tree-sink
4256 Dump each function after performing code sinking. The file name is made
4257 by appending @file{.sink} to the source file name.
4260 @opindex fdump-tree-dom
4261 Dump each function after applying dominator tree optimizations. The file
4262 name is made by appending @file{.dom} to the source file name.
4265 @opindex fdump-tree-dse
4266 Dump each function after applying dead store elimination. The file
4267 name is made by appending @file{.dse} to the source file name.
4270 @opindex fdump-tree-phiopt
4271 Dump each function after optimizing PHI nodes into straightline code. The file
4272 name is made by appending @file{.phiopt} to the source file name.
4275 @opindex fdump-tree-forwprop
4276 Dump each function after forward propagating single use variables. The file
4277 name is made by appending @file{.forwprop} to the source file name.
4280 @opindex fdump-tree-copyrename
4281 Dump each function after applying the copy rename optimization. The file
4282 name is made by appending @file{.copyrename} to the source file name.
4285 @opindex fdump-tree-nrv
4286 Dump each function after applying the named return value optimization on
4287 generic trees. The file name is made by appending @file{.nrv} to the source
4291 @opindex fdump-tree-vect
4292 Dump each function after applying vectorization of loops. The file name is
4293 made by appending @file{.vect} to the source file name.
4296 @opindex fdump-tree-vrp
4297 Dump each function after Value Range Propagation (VRP). The file name
4298 is made by appending @file{.vrp} to the source file name.
4301 @opindex fdump-tree-all
4302 Enable all the available tree dumps with the flags provided in this option.
4305 @item -ftree-vectorizer-verbose=@var{n}
4306 @opindex ftree-vectorizer-verbose
4307 This option controls the amount of debugging output the vectorizer prints.
4308 This information is written to standard error, unless
4309 @option{-fdump-tree-all} or @option{-fdump-tree-vect} is specified,
4310 in which case it is output to the usual dump listing file, @file{.vect}.
4311 For @var{n}=0 no diagnostic information is reported.
4312 If @var{n}=1 the vectorizer reports each loop that got vectorized,
4313 and the total number of loops that got vectorized.
4314 If @var{n}=2 the vectorizer also reports non-vectorized loops that passed
4315 the first analysis phase (vect_analyze_loop_form) - i.e. countable,
4316 inner-most, single-bb, single-entry/exit loops. This is the same verbosity
4317 level that @option{-fdump-tree-vect-stats} uses.
4318 Higher verbosity levels mean either more information dumped for each
4319 reported loop, or same amount of information reported for more loops:
4320 If @var{n}=3, alignment related information is added to the reports.
4321 If @var{n}=4, data-references related information (e.g. memory dependences,
4322 memory access-patterns) is added to the reports.
4323 If @var{n}=5, the vectorizer reports also non-vectorized inner-most loops
4324 that did not pass the first analysis phase (i.e. may not be countable, or
4325 may have complicated control-flow).
4326 If @var{n}=6, the vectorizer reports also non-vectorized nested loops.
4327 For @var{n}=7, all the information the vectorizer generates during its
4328 analysis and transformation is reported. This is the same verbosity level
4329 that @option{-fdump-tree-vect-details} uses.
4331 @item -frandom-seed=@var{string}
4332 @opindex frandom-string
4333 This option provides a seed that GCC uses when it would otherwise use
4334 random numbers. It is used to generate certain symbol names
4335 that have to be different in every compiled file. It is also used to
4336 place unique stamps in coverage data files and the object files that
4337 produce them. You can use the @option{-frandom-seed} option to produce
4338 reproducibly identical object files.
4340 The @var{string} should be different for every file you compile.
4342 @item -fsched-verbose=@var{n}
4343 @opindex fsched-verbose
4344 On targets that use instruction scheduling, this option controls the
4345 amount of debugging output the scheduler prints. This information is
4346 written to standard error, unless @option{-dS} or @option{-dR} is
4347 specified, in which case it is output to the usual dump
4348 listing file, @file{.sched} or @file{.sched2} respectively. However
4349 for @var{n} greater than nine, the output is always printed to standard
4352 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
4353 same information as @option{-dRS}. For @var{n} greater than one, it
4354 also output basic block probabilities, detailed ready list information
4355 and unit/insn info. For @var{n} greater than two, it includes RTL
4356 at abort point, control-flow and regions info. And for @var{n} over
4357 four, @option{-fsched-verbose} also includes dependence info.
4361 Store the usual ``temporary'' intermediate files permanently; place them
4362 in the current directory and name them based on the source file. Thus,
4363 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
4364 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
4365 preprocessed @file{foo.i} output file even though the compiler now
4366 normally uses an integrated preprocessor.
4368 When used in combination with the @option{-x} command line option,
4369 @option{-save-temps} is sensible enough to avoid over writing an
4370 input source file with the same extension as an intermediate file.
4371 The corresponding intermediate file may be obtained by renaming the
4372 source file before using @option{-save-temps}.
4376 Report the CPU time taken by each subprocess in the compilation
4377 sequence. For C source files, this is the compiler proper and assembler
4378 (plus the linker if linking is done). The output looks like this:
4385 The first number on each line is the ``user time'', that is time spent
4386 executing the program itself. The second number is ``system time'',
4387 time spent executing operating system routines on behalf of the program.
4388 Both numbers are in seconds.
4390 @item -fvar-tracking
4391 @opindex fvar-tracking
4392 Run variable tracking pass. It computes where variables are stored at each
4393 position in code. Better debugging information is then generated
4394 (if the debugging information format supports this information).
4396 It is enabled by default when compiling with optimization (@option{-Os},
4397 @option{-O}, @option{-O2}, ...), debugging information (@option{-g}) and
4398 the debug info format supports it.
4400 @item -print-file-name=@var{library}
4401 @opindex print-file-name
4402 Print the full absolute name of the library file @var{library} that
4403 would be used when linking---and don't do anything else. With this
4404 option, GCC does not compile or link anything; it just prints the
4407 @item -print-multi-directory
4408 @opindex print-multi-directory
4409 Print the directory name corresponding to the multilib selected by any
4410 other switches present in the command line. This directory is supposed
4411 to exist in @env{GCC_EXEC_PREFIX}.
4413 @item -print-multi-lib
4414 @opindex print-multi-lib
4415 Print the mapping from multilib directory names to compiler switches
4416 that enable them. The directory name is separated from the switches by
4417 @samp{;}, and each switch starts with an @samp{@@} instead of the
4418 @samp{-}, without spaces between multiple switches. This is supposed to
4419 ease shell-processing.
4421 @item -print-prog-name=@var{program}
4422 @opindex print-prog-name
4423 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
4425 @item -print-libgcc-file-name
4426 @opindex print-libgcc-file-name
4427 Same as @option{-print-file-name=libgcc.a}.
4429 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
4430 but you do want to link with @file{libgcc.a}. You can do
4433 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
4436 @item -print-search-dirs
4437 @opindex print-search-dirs
4438 Print the name of the configured installation directory and a list of
4439 program and library directories @command{gcc} will search---and don't do anything else.
4441 This is useful when @command{gcc} prints the error message
4442 @samp{installation problem, cannot exec cpp0: No such file or directory}.
4443 To resolve this you either need to put @file{cpp0} and the other compiler
4444 components where @command{gcc} expects to find them, or you can set the environment
4445 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
4446 Don't forget the trailing @samp{/}.
4447 @xref{Environment Variables}.
4450 @opindex dumpmachine
4451 Print the compiler's target machine (for example,
4452 @samp{i686-pc-linux-gnu})---and don't do anything else.
4455 @opindex dumpversion
4456 Print the compiler version (for example, @samp{3.0})---and don't do
4461 Print the compiler's built-in specs---and don't do anything else. (This
4462 is used when GCC itself is being built.) @xref{Spec Files}.
4464 @item -feliminate-unused-debug-types
4465 @opindex feliminate-unused-debug-types
4466 Normally, when producing DWARF2 output, GCC will emit debugging
4467 information for all types declared in a compilation
4468 unit, regardless of whether or not they are actually used
4469 in that compilation unit. Sometimes this is useful, such as
4470 if, in the debugger, you want to cast a value to a type that is
4471 not actually used in your program (but is declared). More often,
4472 however, this results in a significant amount of wasted space.
4473 With this option, GCC will avoid producing debug symbol output
4474 for types that are nowhere used in the source file being compiled.
4477 @node Optimize Options
4478 @section Options That Control Optimization
4479 @cindex optimize options
4480 @cindex options, optimization
4482 These options control various sorts of optimizations.
4484 Without any optimization option, the compiler's goal is to reduce the
4485 cost of compilation and to make debugging produce the expected
4486 results. Statements are independent: if you stop the program with a
4487 breakpoint between statements, you can then assign a new value to any
4488 variable or change the program counter to any other statement in the
4489 function and get exactly the results you would expect from the source
4492 Turning on optimization flags makes the compiler attempt to improve
4493 the performance and/or code size at the expense of compilation time
4494 and possibly the ability to debug the program.
4496 The compiler performs optimization based on the knowledge it has of
4497 the program. Optimization levels @option{-O} and above, in
4498 particular, enable @emph{unit-at-a-time} mode, which allows the
4499 compiler to consider information gained from later functions in
4500 the file when compiling a function. Compiling multiple files at
4501 once to a single output file in @emph{unit-at-a-time} mode allows
4502 the compiler to use information gained from all of the files when
4503 compiling each of them.
4505 Not all optimizations are controlled directly by a flag. Only
4506 optimizations that have a flag are listed.
4513 Optimize. Optimizing compilation takes somewhat more time, and a lot
4514 more memory for a large function.
4516 With @option{-O}, the compiler tries to reduce code size and execution
4517 time, without performing any optimizations that take a great deal of
4520 @option{-O} turns on the following optimization flags:
4521 @gccoptlist{-fdefer-pop @gol
4522 -fdelayed-branch @gol
4523 -fguess-branch-probability @gol
4524 -fcprop-registers @gol
4525 -fif-conversion @gol
4526 -fif-conversion2 @gol
4529 -ftree-dominator-opts @gol
4534 -ftree-copyrename @gol
4537 -funit-at-a-time @gol
4540 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
4541 where doing so does not interfere with debugging.
4545 Optimize even more. GCC performs nearly all supported optimizations
4546 that do not involve a space-speed tradeoff. The compiler does not
4547 perform loop unrolling or function inlining when you specify @option{-O2}.
4548 As compared to @option{-O}, this option increases both compilation time
4549 and the performance of the generated code.
4551 @option{-O2} turns on all optimization flags specified by @option{-O}. It
4552 also turns on the following optimization flags:
4553 @gccoptlist{-fthread-jumps @gol
4555 -foptimize-sibling-calls @gol
4556 -fcse-follow-jumps -fcse-skip-blocks @gol
4557 -fgcse -fgcse-lm @gol
4558 -fexpensive-optimizations @gol
4559 -frerun-cse-after-loop @gol
4562 -fschedule-insns -fschedule-insns2 @gol
4563 -fsched-interblock -fsched-spec @gol
4565 -fstrict-aliasing @gol
4566 -fdelete-null-pointer-checks @gol
4567 -freorder-blocks -freorder-functions @gol
4568 -falign-functions -falign-jumps @gol
4569 -falign-loops -falign-labels @gol
4573 Please note the warning under @option{-fgcse} about
4574 invoking @option{-O2} on programs that use computed gotos.
4578 Optimize yet more. @option{-O3} turns on all optimizations specified by
4579 @option{-O2} and also turns on the @option{-finline-functions},
4580 @option{-funswitch-loops} and @option{-fgcse-after-reload} options.
4584 Do not optimize. This is the default.
4588 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
4589 do not typically increase code size. It also performs further
4590 optimizations designed to reduce code size.
4592 @option{-Os} disables the following optimization flags:
4593 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
4594 -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
4595 -fprefetch-loop-arrays -ftree-vect-loop-version}
4597 If you use multiple @option{-O} options, with or without level numbers,
4598 the last such option is the one that is effective.
4601 Options of the form @option{-f@var{flag}} specify machine-independent
4602 flags. Most flags have both positive and negative forms; the negative
4603 form of @option{-ffoo} would be @option{-fno-foo}. In the table
4604 below, only one of the forms is listed---the one you typically will
4605 use. You can figure out the other form by either removing @samp{no-}
4608 The following options control specific optimizations. They are either
4609 activated by @option{-O} options or are related to ones that are. You
4610 can use the following flags in the rare cases when ``fine-tuning'' of
4611 optimizations to be performed is desired.
4614 @item -fno-default-inline
4615 @opindex fno-default-inline
4616 Do not make member functions inline by default merely because they are
4617 defined inside the class scope (C++ only). Otherwise, when you specify
4618 @w{@option{-O}}, member functions defined inside class scope are compiled
4619 inline by default; i.e., you don't need to add @samp{inline} in front of
4620 the member function name.
4622 @item -fno-defer-pop
4623 @opindex fno-defer-pop
4624 Always pop the arguments to each function call as soon as that function
4625 returns. For machines which must pop arguments after a function call,
4626 the compiler normally lets arguments accumulate on the stack for several
4627 function calls and pops them all at once.
4629 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4633 Force memory operands to be copied into registers before doing
4634 arithmetic on them. This produces better code by making all memory
4635 references potential common subexpressions. When they are not common
4636 subexpressions, instruction combination should eliminate the separate
4637 register-load. This option is now a nop and will be removed in 4.2.
4640 @opindex fforce-addr
4641 Force memory address constants to be copied into registers before
4642 doing arithmetic on them.
4644 @item -fforward-propagate
4645 @opindex fforward-propagate
4646 Perform a forward propagation pass on RTL. The pass tries to combine two
4647 instructions and checks if the result can be simplified. If loop unrolling
4648 is active, two passes are performed and the second is scheduled after
4651 This option is enabled by default at optimization levels @option{-O2},
4652 @option{-O3}, @option{-Os}.
4654 @item -fomit-frame-pointer
4655 @opindex fomit-frame-pointer
4656 Don't keep the frame pointer in a register for functions that
4657 don't need one. This avoids the instructions to save, set up and
4658 restore frame pointers; it also makes an extra register available
4659 in many functions. @strong{It also makes debugging impossible on
4662 On some machines, such as the VAX, this flag has no effect, because
4663 the standard calling sequence automatically handles the frame pointer
4664 and nothing is saved by pretending it doesn't exist. The
4665 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
4666 whether a target machine supports this flag. @xref{Registers,,Register
4667 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
4669 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4671 @item -foptimize-sibling-calls
4672 @opindex foptimize-sibling-calls
4673 Optimize sibling and tail recursive calls.
4675 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4679 Don't pay attention to the @code{inline} keyword. Normally this option
4680 is used to keep the compiler from expanding any functions inline.
4681 Note that if you are not optimizing, no functions can be expanded inline.
4683 @item -finline-functions
4684 @opindex finline-functions
4685 Integrate all simple functions into their callers. The compiler
4686 heuristically decides which functions are simple enough to be worth
4687 integrating in this way.
4689 If all calls to a given function are integrated, and the function is
4690 declared @code{static}, then the function is normally not output as
4691 assembler code in its own right.
4693 Enabled at level @option{-O3}.
4695 @item -finline-functions-called-once
4696 @opindex finline-functions-called-once
4697 Consider all @code{static} functions called once for inlining into their
4698 caller even if they are not marked @code{inline}. If a call to a given
4699 function is integrated, then the function is not output as assembler code
4702 Enabled if @option{-funit-at-a-time} is enabled.
4704 @item -fearly-inlining
4705 @opindex fearly-inlining
4706 Inline functions marked by @code{always_inline} and functions whose body seems
4707 smaller than the function call overhead early before doing
4708 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
4709 makes profiling significantly cheaper and usually inlining faster on programs
4710 having large chains of nested wrapper functions.
4714 @item -finline-limit=@var{n}
4715 @opindex finline-limit
4716 By default, GCC limits the size of functions that can be inlined. This flag
4717 allows the control of this limit for functions that are explicitly marked as
4718 inline (i.e., marked with the inline keyword or defined within the class
4719 definition in c++). @var{n} is the size of functions that can be inlined in
4720 number of pseudo instructions (not counting parameter handling). The default
4721 value of @var{n} is 600.
4722 Increasing this value can result in more inlined code at
4723 the cost of compilation time and memory consumption. Decreasing usually makes
4724 the compilation faster and less code will be inlined (which presumably
4725 means slower programs). This option is particularly useful for programs that
4726 use inlining heavily such as those based on recursive templates with C++.
4728 Inlining is actually controlled by a number of parameters, which may be
4729 specified individually by using @option{--param @var{name}=@var{value}}.
4730 The @option{-finline-limit=@var{n}} option sets some of these parameters
4734 @item max-inline-insns-single
4735 is set to @var{n}/2.
4736 @item max-inline-insns-auto
4737 is set to @var{n}/2.
4738 @item min-inline-insns
4739 is set to 130 or @var{n}/4, whichever is smaller.
4740 @item max-inline-insns-rtl
4744 See below for a documentation of the individual
4745 parameters controlling inlining.
4747 @emph{Note:} pseudo instruction represents, in this particular context, an
4748 abstract measurement of function's size. In no way does it represent a count
4749 of assembly instructions and as such its exact meaning might change from one
4750 release to an another.
4752 @item -fkeep-inline-functions
4753 @opindex fkeep-inline-functions
4754 In C, emit @code{static} functions that are declared @code{inline}
4755 into the object file, even if the function has been inlined into all
4756 of its callers. This switch does not affect functions using the
4757 @code{extern inline} extension in GNU C89@. In C++, emit any and all
4758 inline functions into the object file.
4760 @item -fkeep-static-consts
4761 @opindex fkeep-static-consts
4762 Emit variables declared @code{static const} when optimization isn't turned
4763 on, even if the variables aren't referenced.
4765 GCC enables this option by default. If you want to force the compiler to
4766 check if the variable was referenced, regardless of whether or not
4767 optimization is turned on, use the @option{-fno-keep-static-consts} option.
4769 @item -fmerge-constants
4770 Attempt to merge identical constants (string constants and floating point
4771 constants) across compilation units.
4773 This option is the default for optimized compilation if the assembler and
4774 linker support it. Use @option{-fno-merge-constants} to inhibit this
4777 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4779 @item -fmerge-all-constants
4780 Attempt to merge identical constants and identical variables.
4782 This option implies @option{-fmerge-constants}. In addition to
4783 @option{-fmerge-constants} this considers e.g.@: even constant initialized
4784 arrays or initialized constant variables with integral or floating point
4785 types. Languages like C or C++ require each non-automatic variable to
4786 have distinct location, so using this option will result in non-conforming
4789 @item -fmodulo-sched
4790 @opindex fmodulo-sched
4791 Perform swing modulo scheduling immediately before the first scheduling
4792 pass. This pass looks at innermost loops and reorders their
4793 instructions by overlapping different iterations.
4795 @item -fno-branch-count-reg
4796 @opindex fno-branch-count-reg
4797 Do not use ``decrement and branch'' instructions on a count register,
4798 but instead generate a sequence of instructions that decrement a
4799 register, compare it against zero, then branch based upon the result.
4800 This option is only meaningful on architectures that support such
4801 instructions, which include x86, PowerPC, IA-64 and S/390.
4803 The default is @option{-fbranch-count-reg}.
4805 @item -fno-function-cse
4806 @opindex fno-function-cse
4807 Do not put function addresses in registers; make each instruction that
4808 calls a constant function contain the function's address explicitly.
4810 This option results in less efficient code, but some strange hacks
4811 that alter the assembler output may be confused by the optimizations
4812 performed when this option is not used.
4814 The default is @option{-ffunction-cse}
4816 @item -fno-zero-initialized-in-bss
4817 @opindex fno-zero-initialized-in-bss
4818 If the target supports a BSS section, GCC by default puts variables that
4819 are initialized to zero into BSS@. This can save space in the resulting
4822 This option turns off this behavior because some programs explicitly
4823 rely on variables going to the data section. E.g., so that the
4824 resulting executable can find the beginning of that section and/or make
4825 assumptions based on that.
4827 The default is @option{-fzero-initialized-in-bss}.
4829 @item -fbounds-check
4830 @opindex fbounds-check
4831 For front-ends that support it, generate additional code to check that
4832 indices used to access arrays are within the declared range. This is
4833 currently only supported by the Java and Fortran front-ends, where
4834 this option defaults to true and false respectively.
4836 @item -fmudflap -fmudflapth -fmudflapir
4840 @cindex bounds checking
4842 For front-ends that support it (C and C++), instrument all risky
4843 pointer/array dereferencing operations, some standard library
4844 string/heap functions, and some other associated constructs with
4845 range/validity tests. Modules so instrumented should be immune to
4846 buffer overflows, invalid heap use, and some other classes of C/C++
4847 programming errors. The instrumentation relies on a separate runtime
4848 library (@file{libmudflap}), which will be linked into a program if
4849 @option{-fmudflap} is given at link time. Run-time behavior of the
4850 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
4851 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
4854 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
4855 link if your program is multi-threaded. Use @option{-fmudflapir}, in
4856 addition to @option{-fmudflap} or @option{-fmudflapth}, if
4857 instrumentation should ignore pointer reads. This produces less
4858 instrumentation (and therefore faster execution) and still provides
4859 some protection against outright memory corrupting writes, but allows
4860 erroneously read data to propagate within a program.
4862 @item -fthread-jumps
4863 @opindex fthread-jumps
4864 Perform optimizations where we check to see if a jump branches to a
4865 location where another comparison subsumed by the first is found. If
4866 so, the first branch is redirected to either the destination of the
4867 second branch or a point immediately following it, depending on whether
4868 the condition is known to be true or false.
4870 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4872 @item -fcse-follow-jumps
4873 @opindex fcse-follow-jumps
4874 In common subexpression elimination, scan through jump instructions
4875 when the target of the jump is not reached by any other path. For
4876 example, when CSE encounters an @code{if} statement with an
4877 @code{else} clause, CSE will follow the jump when the condition
4880 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4882 @item -fcse-skip-blocks
4883 @opindex fcse-skip-blocks
4884 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
4885 follow jumps which conditionally skip over blocks. When CSE
4886 encounters a simple @code{if} statement with no else clause,
4887 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
4888 body of the @code{if}.
4890 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4892 @item -frerun-cse-after-loop
4893 @opindex frerun-cse-after-loop
4894 Re-run common subexpression elimination after loop optimizations has been
4897 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4901 Perform a global common subexpression elimination pass.
4902 This pass also performs global constant and copy propagation.
4904 @emph{Note:} When compiling a program using computed gotos, a GCC
4905 extension, you may get better runtime performance if you disable
4906 the global common subexpression elimination pass by adding
4907 @option{-fno-gcse} to the command line.
4909 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4913 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
4914 attempt to move loads which are only killed by stores into themselves. This
4915 allows a loop containing a load/store sequence to be changed to a load outside
4916 the loop, and a copy/store within the loop.
4918 Enabled by default when gcse is enabled.
4922 When @option{-fgcse-sm} is enabled, a store motion pass is run after
4923 global common subexpression elimination. This pass will attempt to move
4924 stores out of loops. When used in conjunction with @option{-fgcse-lm},
4925 loops containing a load/store sequence can be changed to a load before
4926 the loop and a store after the loop.
4928 Not enabled at any optimization level.
4932 When @option{-fgcse-las} is enabled, the global common subexpression
4933 elimination pass eliminates redundant loads that come after stores to the
4934 same memory location (both partial and full redundancies).
4936 Not enabled at any optimization level.
4938 @item -fgcse-after-reload
4939 @opindex fgcse-after-reload
4940 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
4941 pass is performed after reload. The purpose of this pass is to cleanup
4944 @item -funsafe-loop-optimizations
4945 @opindex funsafe-loop-optimizations
4946 If given, the loop optimizer will assume that loop indices do not
4947 overflow, and that the loops with nontrivial exit condition are not
4948 infinite. This enables a wider range of loop optimizations even if
4949 the loop optimizer itself cannot prove that these assumptions are valid.
4950 Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you
4951 if it finds this kind of loop.
4953 @item -fcrossjumping
4954 @opindex crossjumping
4955 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
4956 resulting code may or may not perform better than without cross-jumping.
4958 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4960 @item -fif-conversion
4961 @opindex if-conversion
4962 Attempt to transform conditional jumps into branch-less equivalents. This
4963 include use of conditional moves, min, max, set flags and abs instructions, and
4964 some tricks doable by standard arithmetics. The use of conditional execution
4965 on chips where it is available is controlled by @code{if-conversion2}.
4967 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4969 @item -fif-conversion2
4970 @opindex if-conversion2
4971 Use conditional execution (where available) to transform conditional jumps into
4972 branch-less equivalents.
4974 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4976 @item -fdelete-null-pointer-checks
4977 @opindex fdelete-null-pointer-checks
4978 Use global dataflow analysis to identify and eliminate useless checks
4979 for null pointers. The compiler assumes that dereferencing a null
4980 pointer would have halted the program. If a pointer is checked after
4981 it has already been dereferenced, it cannot be null.
4983 In some environments, this assumption is not true, and programs can
4984 safely dereference null pointers. Use
4985 @option{-fno-delete-null-pointer-checks} to disable this optimization
4986 for programs which depend on that behavior.
4988 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4990 @item -fexpensive-optimizations
4991 @opindex fexpensive-optimizations
4992 Perform a number of minor optimizations that are relatively expensive.
4994 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4996 @item -foptimize-register-move
4998 @opindex foptimize-register-move
5000 Attempt to reassign register numbers in move instructions and as
5001 operands of other simple instructions in order to maximize the amount of
5002 register tying. This is especially helpful on machines with two-operand
5005 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
5008 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5010 @item -fdelayed-branch
5011 @opindex fdelayed-branch
5012 If supported for the target machine, attempt to reorder instructions
5013 to exploit instruction slots available after delayed branch
5016 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5018 @item -fschedule-insns
5019 @opindex fschedule-insns
5020 If supported for the target machine, attempt to reorder instructions to
5021 eliminate execution stalls due to required data being unavailable. This
5022 helps machines that have slow floating point or memory load instructions
5023 by allowing other instructions to be issued until the result of the load
5024 or floating point instruction is required.
5026 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5028 @item -fschedule-insns2
5029 @opindex fschedule-insns2
5030 Similar to @option{-fschedule-insns}, but requests an additional pass of
5031 instruction scheduling after register allocation has been done. This is
5032 especially useful on machines with a relatively small number of
5033 registers and where memory load instructions take more than one cycle.
5035 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5037 @item -fno-sched-interblock
5038 @opindex fno-sched-interblock
5039 Don't schedule instructions across basic blocks. This is normally
5040 enabled by default when scheduling before register allocation, i.e.@:
5041 with @option{-fschedule-insns} or at @option{-O2} or higher.
5043 @item -fno-sched-spec
5044 @opindex fno-sched-spec
5045 Don't allow speculative motion of non-load instructions. This is normally
5046 enabled by default when scheduling before register allocation, i.e.@:
5047 with @option{-fschedule-insns} or at @option{-O2} or higher.
5049 @item -fsched-spec-load
5050 @opindex fsched-spec-load
5051 Allow speculative motion of some load instructions. This only makes
5052 sense when scheduling before register allocation, i.e.@: with
5053 @option{-fschedule-insns} or at @option{-O2} or higher.
5055 @item -fsched-spec-load-dangerous
5056 @opindex fsched-spec-load-dangerous
5057 Allow speculative motion of more load instructions. This only makes
5058 sense when scheduling before register allocation, i.e.@: with
5059 @option{-fschedule-insns} or at @option{-O2} or higher.
5061 @item -fsched-stalled-insns=@var{n}
5062 @opindex fsched-stalled-insns
5063 Define how many insns (if any) can be moved prematurely from the queue
5064 of stalled insns into the ready list, during the second scheduling pass.
5066 @item -fsched-stalled-insns-dep=@var{n}
5067 @opindex fsched-stalled-insns-dep
5068 Define how many insn groups (cycles) will be examined for a dependency
5069 on a stalled insn that is candidate for premature removal from the queue
5070 of stalled insns. Has an effect only during the second scheduling pass,
5071 and only if @option{-fsched-stalled-insns} is used and its value is not zero.
5073 @item -fsched2-use-superblocks
5074 @opindex fsched2-use-superblocks
5075 When scheduling after register allocation, do use superblock scheduling
5076 algorithm. Superblock scheduling allows motion across basic block boundaries
5077 resulting on faster schedules. This option is experimental, as not all machine
5078 descriptions used by GCC model the CPU closely enough to avoid unreliable
5079 results from the algorithm.
5081 This only makes sense when scheduling after register allocation, i.e.@: with
5082 @option{-fschedule-insns2} or at @option{-O2} or higher.
5084 @item -fsched2-use-traces
5085 @opindex fsched2-use-traces
5086 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
5087 allocation and additionally perform code duplication in order to increase the
5088 size of superblocks using tracer pass. See @option{-ftracer} for details on
5091 This mode should produce faster but significantly longer programs. Also
5092 without @option{-fbranch-probabilities} the traces constructed may not
5093 match the reality and hurt the performance. This only makes
5094 sense when scheduling after register allocation, i.e.@: with
5095 @option{-fschedule-insns2} or at @option{-O2} or higher.
5099 Eliminates redundant extension instructions and move the non redundant
5100 ones to optimal placement using LCM.
5102 @item -freschedule-modulo-scheduled-loops
5103 @opindex fscheduling-in-modulo-scheduled-loops
5104 The modulo scheduling comes before the traditional scheduling, if a loop was modulo scheduled
5105 we may want to prevent the later scheduling passes from changing its schedule, we use this
5106 option to control that.
5108 @item -fcaller-saves
5109 @opindex fcaller-saves
5110 Enable values to be allocated in registers that will be clobbered by
5111 function calls, by emitting extra instructions to save and restore the
5112 registers around such calls. Such allocation is done only when it
5113 seems to result in better code than would otherwise be produced.
5115 This option is always enabled by default on certain machines, usually
5116 those which have no call-preserved registers to use instead.
5118 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5121 Perform Partial Redundancy Elimination (PRE) on trees. This flag is
5122 enabled by default at @option{-O2} and @option{-O3}.
5125 Perform Full Redundancy Elimination (FRE) on trees. The difference
5126 between FRE and PRE is that FRE only considers expressions
5127 that are computed on all paths leading to the redundant computation.
5128 This analysis faster than PRE, though it exposes fewer redundancies.
5129 This flag is enabled by default at @option{-O} and higher.
5131 @item -ftree-copy-prop
5132 Perform copy propagation on trees. This pass eliminates unnecessary
5133 copy operations. This flag is enabled by default at @option{-O} and
5136 @item -ftree-store-copy-prop
5137 Perform copy propagation of memory loads and stores. This pass
5138 eliminates unnecessary copy operations in memory references
5139 (structures, global variables, arrays, etc). This flag is enabled by
5140 default at @option{-O2} and higher.
5143 Perform structural alias analysis on trees. This flag
5144 is enabled by default at @option{-O} and higher.
5147 Perform interprocedural pointer analysis.
5150 Perform forward store motion on trees. This flag is
5151 enabled by default at @option{-O} and higher.
5154 Perform sparse conditional constant propagation (CCP) on trees. This
5155 pass only operates on local scalar variables and is enabled by default
5156 at @option{-O} and higher.
5158 @item -ftree-store-ccp
5159 Perform sparse conditional constant propagation (CCP) on trees. This
5160 pass operates on both local scalar variables and memory stores and
5161 loads (global variables, structures, arrays, etc). This flag is
5162 enabled by default at @option{-O2} and higher.
5165 Perform dead code elimination (DCE) on trees. This flag is enabled by
5166 default at @option{-O} and higher.
5168 @item -ftree-dominator-opts
5169 Perform a variety of simple scalar cleanups (constant/copy
5170 propagation, redundancy elimination, range propagation and expression
5171 simplification) based on a dominator tree traversal. This also
5172 performs jump threading (to reduce jumps to jumps). This flag is
5173 enabled by default at @option{-O} and higher.
5176 Perform loop header copying on trees. This is beneficial since it increases
5177 effectiveness of code motion optimizations. It also saves one jump. This flag
5178 is enabled by default at @option{-O} and higher. It is not enabled
5179 for @option{-Os}, since it usually increases code size.
5181 @item -ftree-loop-optimize
5182 Perform loop optimizations on trees. This flag is enabled by default
5183 at @option{-O} and higher.
5185 @item -ftree-loop-linear
5186 Perform linear loop transformations on tree. This flag can improve cache
5187 performance and allow further loop optimizations to take place.
5189 @item -ftree-loop-im
5190 Perform loop invariant motion on trees. This pass moves only invariants that
5191 would be hard to handle at RTL level (function calls, operations that expand to
5192 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
5193 operands of conditions that are invariant out of the loop, so that we can use
5194 just trivial invariantness analysis in loop unswitching. The pass also includes
5197 @item -ftree-loop-ivcanon
5198 Create a canonical counter for number of iterations in the loop for that
5199 determining number of iterations requires complicated analysis. Later
5200 optimizations then may determine the number easily. Useful especially
5201 in connection with unrolling.
5204 Perform induction variable optimizations (strength reduction, induction
5205 variable merging and induction variable elimination) on trees.
5208 Perform scalar replacement of aggregates. This pass replaces structure
5209 references with scalars to prevent committing structures to memory too
5210 early. This flag is enabled by default at @option{-O} and higher.
5212 @item -ftree-copyrename
5213 Perform copy renaming on trees. This pass attempts to rename compiler
5214 temporaries to other variables at copy locations, usually resulting in
5215 variable names which more closely resemble the original variables. This flag
5216 is enabled by default at @option{-O} and higher.
5219 Perform temporary expression replacement during the SSA->normal phase. Single
5220 use/single def temporaries are replaced at their use location with their
5221 defining expression. This results in non-GIMPLE code, but gives the expanders
5222 much more complex trees to work on resulting in better RTL generation. This is
5223 enabled by default at @option{-O} and higher.
5226 Perform live range splitting during the SSA->normal phase. Distinct live
5227 ranges of a variable are split into unique variables, allowing for better
5228 optimization later. This is enabled by default at @option{-O} and higher.
5230 @item -ftree-vectorize
5231 Perform loop vectorization on trees.
5233 @item -ftree-vect-loop-version
5234 @opindex ftree-vect-loop-version
5235 Perform loop versioning when doing loop vectorization on trees. When a loop
5236 appears to be vectorizable except that data alignment or data dependence cannot
5237 be determined at compile time then vectorized and non-vectorized versions of
5238 the loop are generated along with runtime checks for alignment or dependence
5239 to control which version is executed. This option is enabled by default
5240 except at level @option{-Os} where it is disabled.
5243 Perform Value Range Propagation on trees. This is similar to the
5244 constant propagation pass, but instead of values, ranges of values are
5245 propagated. This allows the optimizers to remove unnecessary range
5246 checks like array bound checks and null pointer checks. This is
5247 enabled by default at @option{-O2} and higher. Null pointer check
5248 elimination is only done if @option{-fdelete-null-pointer-checks} is
5253 Perform tail duplication to enlarge superblock size. This transformation
5254 simplifies the control flow of the function allowing other optimizations to do
5257 @item -funroll-loops
5258 @opindex funroll-loops
5259 Unroll loops whose number of iterations can be determined at compile
5260 time or upon entry to the loop. @option{-funroll-loops} implies
5261 @option{-frerun-cse-after-loop}. This option makes code larger,
5262 and may or may not make it run faster.
5264 @item -funroll-all-loops
5265 @opindex funroll-all-loops
5266 Unroll all loops, even if their number of iterations is uncertain when
5267 the loop is entered. This usually makes programs run more slowly.
5268 @option{-funroll-all-loops} implies the same options as
5269 @option{-funroll-loops},
5271 @item -fsplit-ivs-in-unroller
5272 @opindex -fsplit-ivs-in-unroller
5273 Enables expressing of values of induction variables in later iterations
5274 of the unrolled loop using the value in the first iteration. This breaks
5275 long dependency chains, thus improving efficiency of the scheduling passes.
5277 Combination of @option{-fweb} and CSE is often sufficient to obtain the
5278 same effect. However in cases the loop body is more complicated than
5279 a single basic block, this is not reliable. It also does not work at all
5280 on some of the architectures due to restrictions in the CSE pass.
5282 This optimization is enabled by default.
5284 @item -fvariable-expansion-in-unroller
5285 @opindex -fvariable-expansion-in-unroller
5286 With this option, the compiler will create multiple copies of some
5287 local variables when unrolling a loop which can result in superior code.
5289 @item -fprefetch-loop-arrays
5290 @opindex fprefetch-loop-arrays
5291 If supported by the target machine, generate instructions to prefetch
5292 memory to improve the performance of loops that access large arrays.
5294 This option may generate better or worse code; results are highly
5295 dependent on the structure of loops within the source code.
5297 Disabled at level @option{-Os}.
5300 @itemx -fno-peephole2
5301 @opindex fno-peephole
5302 @opindex fno-peephole2
5303 Disable any machine-specific peephole optimizations. The difference
5304 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
5305 are implemented in the compiler; some targets use one, some use the
5306 other, a few use both.
5308 @option{-fpeephole} is enabled by default.
5309 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5311 @item -fno-guess-branch-probability
5312 @opindex fno-guess-branch-probability
5313 Do not guess branch probabilities using heuristics.
5315 GCC will use heuristics to guess branch probabilities if they are
5316 not provided by profiling feedback (@option{-fprofile-arcs}). These
5317 heuristics are based on the control flow graph. If some branch probabilities
5318 are specified by @samp{__builtin_expect}, then the heuristics will be
5319 used to guess branch probabilities for the rest of the control flow graph,
5320 taking the @samp{__builtin_expect} info into account. The interactions
5321 between the heuristics and @samp{__builtin_expect} can be complex, and in
5322 some cases, it may be useful to disable the heuristics so that the effects
5323 of @samp{__builtin_expect} are easier to understand.
5325 The default is @option{-fguess-branch-probability} at levels
5326 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5328 @item -freorder-blocks
5329 @opindex freorder-blocks
5330 Reorder basic blocks in the compiled function in order to reduce number of
5331 taken branches and improve code locality.
5333 Enabled at levels @option{-O2}, @option{-O3}.
5335 @item -freorder-blocks-and-partition
5336 @opindex freorder-blocks-and-partition
5337 In addition to reordering basic blocks in the compiled function, in order
5338 to reduce number of taken branches, partitions hot and cold basic blocks
5339 into separate sections of the assembly and .o files, to improve
5340 paging and cache locality performance.
5342 This optimization is automatically turned off in the presence of
5343 exception handling, for linkonce sections, for functions with a user-defined
5344 section attribute and on any architecture that does not support named
5347 @item -freorder-functions
5348 @opindex freorder-functions
5349 Reorder functions in the object file in order to
5350 improve code locality. This is implemented by using special
5351 subsections @code{.text.hot} for most frequently executed functions and
5352 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
5353 the linker so object file format must support named sections and linker must
5354 place them in a reasonable way.
5356 Also profile feedback must be available in to make this option effective. See
5357 @option{-fprofile-arcs} for details.
5359 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5361 @item -fstrict-aliasing
5362 @opindex fstrict-aliasing
5363 Allows the compiler to assume the strictest aliasing rules applicable to
5364 the language being compiled. For C (and C++), this activates
5365 optimizations based on the type of expressions. In particular, an
5366 object of one type is assumed never to reside at the same address as an
5367 object of a different type, unless the types are almost the same. For
5368 example, an @code{unsigned int} can alias an @code{int}, but not a
5369 @code{void*} or a @code{double}. A character type may alias any other
5372 Pay special attention to code like this:
5385 The practice of reading from a different union member than the one most
5386 recently written to (called ``type-punning'') is common. Even with
5387 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
5388 is accessed through the union type. So, the code above will work as
5389 expected. However, this code might not:
5400 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5402 @item -falign-functions
5403 @itemx -falign-functions=@var{n}
5404 @opindex falign-functions
5405 Align the start of functions to the next power-of-two greater than
5406 @var{n}, skipping up to @var{n} bytes. For instance,
5407 @option{-falign-functions=32} aligns functions to the next 32-byte
5408 boundary, but @option{-falign-functions=24} would align to the next
5409 32-byte boundary only if this can be done by skipping 23 bytes or less.
5411 @option{-fno-align-functions} and @option{-falign-functions=1} are
5412 equivalent and mean that functions will not be aligned.
5414 Some assemblers only support this flag when @var{n} is a power of two;
5415 in that case, it is rounded up.
5417 If @var{n} is not specified or is zero, use a machine-dependent default.
5419 Enabled at levels @option{-O2}, @option{-O3}.
5421 @item -falign-labels
5422 @itemx -falign-labels=@var{n}
5423 @opindex falign-labels
5424 Align all branch targets to a power-of-two boundary, skipping up to
5425 @var{n} bytes like @option{-falign-functions}. This option can easily
5426 make code slower, because it must insert dummy operations for when the
5427 branch target is reached in the usual flow of the code.
5429 @option{-fno-align-labels} and @option{-falign-labels=1} are
5430 equivalent and mean that labels will not be aligned.
5432 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
5433 are greater than this value, then their values are used instead.
5435 If @var{n} is not specified or is zero, use a machine-dependent default
5436 which is very likely to be @samp{1}, meaning no alignment.
5438 Enabled at levels @option{-O2}, @option{-O3}.
5441 @itemx -falign-loops=@var{n}
5442 @opindex falign-loops
5443 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
5444 like @option{-falign-functions}. The hope is that the loop will be
5445 executed many times, which will make up for any execution of the dummy
5448 @option{-fno-align-loops} and @option{-falign-loops=1} are
5449 equivalent and mean that loops will not be aligned.
5451 If @var{n} is not specified or is zero, use a machine-dependent default.
5453 Enabled at levels @option{-O2}, @option{-O3}.
5456 @itemx -falign-jumps=@var{n}
5457 @opindex falign-jumps
5458 Align branch targets to a power-of-two boundary, for branch targets
5459 where the targets can only be reached by jumping, skipping up to @var{n}
5460 bytes like @option{-falign-functions}. In this case, no dummy operations
5463 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
5464 equivalent and mean that loops will not be aligned.
5466 If @var{n} is not specified or is zero, use a machine-dependent default.
5468 Enabled at levels @option{-O2}, @option{-O3}.
5470 @item -funit-at-a-time
5471 @opindex funit-at-a-time
5472 Parse the whole compilation unit before starting to produce code.
5473 This allows some extra optimizations to take place but consumes
5474 more memory (in general). There are some compatibility issues
5475 with @emph{unit-at-a-time} mode:
5478 enabling @emph{unit-at-a-time} mode may change the order
5479 in which functions, variables, and top-level @code{asm} statements
5480 are emitted, and will likely break code relying on some particular
5481 ordering. The majority of such top-level @code{asm} statements,
5482 though, can be replaced by @code{section} attributes. The
5483 @option{fno-toplevel-reorder} option may be used to keep the ordering
5484 used in the input file, at the cost of some optimizations.
5487 @emph{unit-at-a-time} mode removes unreferenced static variables
5488 and functions. This may result in undefined references
5489 when an @code{asm} statement refers directly to variables or functions
5490 that are otherwise unused. In that case either the variable/function
5491 shall be listed as an operand of the @code{asm} statement operand or,
5492 in the case of top-level @code{asm} statements the attribute @code{used}
5493 shall be used on the declaration.
5496 Static functions now can use non-standard passing conventions that
5497 may break @code{asm} statements calling functions directly. Again,
5498 attribute @code{used} will prevent this behavior.
5501 As a temporary workaround, @option{-fno-unit-at-a-time} can be used,
5502 but this scheme may not be supported by future releases of GCC@.
5504 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5506 @item -fno-toplevel-reorder
5507 Do not reorder top-level functions, variables, and @code{asm}
5508 statements. Output them in the same order that they appear in the
5509 input file. When this option is used, unreferenced static variables
5510 will not be removed. This option is intended to support existing code
5511 which relies on a particular ordering. For new code, it is better to
5516 Constructs webs as commonly used for register allocation purposes and assign
5517 each web individual pseudo register. This allows the register allocation pass
5518 to operate on pseudos directly, but also strengthens several other optimization
5519 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
5520 however, make debugging impossible, since variables will no longer stay in a
5523 Enabled by default with @option{-funroll-loops}.
5525 @item -fwhole-program
5526 @opindex fwhole-program
5527 Assume that the current compilation unit represents whole program being
5528 compiled. All public functions and variables with the exception of @code{main}
5529 and those merged by attribute @code{externally_visible} become static functions
5530 and in a affect gets more aggressively optimized by interprocedural optimizers.
5531 While this option is equivalent to proper use of @code{static} keyword for
5532 programs consisting of single file, in combination with option
5533 @option{--combine} this flag can be used to compile most of smaller scale C
5534 programs since the functions and variables become local for the whole combined
5535 compilation unit, not for the single source file itself.
5538 @item -fno-cprop-registers
5539 @opindex fno-cprop-registers
5540 After register allocation and post-register allocation instruction splitting,
5541 we perform a copy-propagation pass to try to reduce scheduling dependencies
5542 and occasionally eliminate the copy.
5544 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5546 @item -fprofile-generate
5547 @opindex fprofile-generate
5549 Enable options usually used for instrumenting application to produce
5550 profile useful for later recompilation with profile feedback based
5551 optimization. You must use @option{-fprofile-generate} both when
5552 compiling and when linking your program.
5554 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
5557 @opindex fprofile-use
5558 Enable profile feedback directed optimizations, and optimizations
5559 generally profitable only with profile feedback available.
5561 The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt},
5562 @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}
5566 The following options control compiler behavior regarding floating
5567 point arithmetic. These options trade off between speed and
5568 correctness. All must be specifically enabled.
5572 @opindex ffloat-store
5573 Do not store floating point variables in registers, and inhibit other
5574 options that might change whether a floating point value is taken from a
5577 @cindex floating point precision
5578 This option prevents undesirable excess precision on machines such as
5579 the 68000 where the floating registers (of the 68881) keep more
5580 precision than a @code{double} is supposed to have. Similarly for the
5581 x86 architecture. For most programs, the excess precision does only
5582 good, but a few programs rely on the precise definition of IEEE floating
5583 point. Use @option{-ffloat-store} for such programs, after modifying
5584 them to store all pertinent intermediate computations into variables.
5588 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
5589 @option{-fno-trapping-math}, @option{-ffinite-math-only},
5590 @option{-fno-rounding-math}, @option{-fno-signaling-nans}
5591 and @option{fcx-limited-range}.
5593 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
5595 This option should never be turned on by any @option{-O} option since
5596 it can result in incorrect output for programs which depend on
5597 an exact implementation of IEEE or ISO rules/specifications for
5600 @item -fno-math-errno
5601 @opindex fno-math-errno
5602 Do not set ERRNO after calling math functions that are executed
5603 with a single instruction, e.g., sqrt. A program that relies on
5604 IEEE exceptions for math error handling may want to use this flag
5605 for speed while maintaining IEEE arithmetic compatibility.
5607 This option should never be turned on by any @option{-O} option since
5608 it can result in incorrect output for programs which depend on
5609 an exact implementation of IEEE or ISO rules/specifications for
5612 The default is @option{-fmath-errno}.
5614 On Darwin systems, the math library never sets @code{errno}. There is therefore
5615 no reason for the compiler to consider the possibility that it might,
5616 and @option{-fno-math-errno} is the default.
5618 @item -funsafe-math-optimizations
5619 @opindex funsafe-math-optimizations
5620 Allow optimizations for floating-point arithmetic that (a) assume
5621 that arguments and results are valid and (b) may violate IEEE or
5622 ANSI standards. When used at link-time, it may include libraries
5623 or startup files that change the default FPU control word or other
5624 similar optimizations.
5626 This option should never be turned on by any @option{-O} option since
5627 it can result in incorrect output for programs which depend on
5628 an exact implementation of IEEE or ISO rules/specifications for
5631 The default is @option{-fno-unsafe-math-optimizations}.
5633 @item -ffinite-math-only
5634 @opindex ffinite-math-only
5635 Allow optimizations for floating-point arithmetic that assume
5636 that arguments and results are not NaNs or +-Infs.
5638 This option should never be turned on by any @option{-O} option since
5639 it can result in incorrect output for programs which depend on
5640 an exact implementation of IEEE or ISO rules/specifications.
5642 The default is @option{-fno-finite-math-only}.
5644 @item -fno-trapping-math
5645 @opindex fno-trapping-math
5646 Compile code assuming that floating-point operations cannot generate
5647 user-visible traps. These traps include division by zero, overflow,
5648 underflow, inexact result and invalid operation. This option implies
5649 @option{-fno-signaling-nans}. Setting this option may allow faster
5650 code if one relies on ``non-stop'' IEEE arithmetic, for example.
5652 This option should never be turned on by any @option{-O} option since
5653 it can result in incorrect output for programs which depend on
5654 an exact implementation of IEEE or ISO rules/specifications for
5657 The default is @option{-ftrapping-math}.
5659 @item -frounding-math
5660 @opindex frounding-math
5661 Disable transformations and optimizations that assume default floating
5662 point rounding behavior. This is round-to-zero for all floating point
5663 to integer conversions, and round-to-nearest for all other arithmetic
5664 truncations. This option should be specified for programs that change
5665 the FP rounding mode dynamically, or that may be executed with a
5666 non-default rounding mode. This option disables constant folding of
5667 floating point expressions at compile-time (which may be affected by
5668 rounding mode) and arithmetic transformations that are unsafe in the
5669 presence of sign-dependent rounding modes.
5671 The default is @option{-fno-rounding-math}.
5673 This option is experimental and does not currently guarantee to
5674 disable all GCC optimizations that are affected by rounding mode.
5675 Future versions of GCC may provide finer control of this setting
5676 using C99's @code{FENV_ACCESS} pragma. This command line option
5677 will be used to specify the default state for @code{FENV_ACCESS}.
5679 @item -frtl-abstract-sequences
5680 @opindex frtl-abstract-sequences
5681 It is a size optimization method. This option is to find identical
5682 sequences of code, which can be turned into pseudo-procedures and
5683 then replace all occurrences with calls to the newly created
5684 subroutine. It is kind of an opposite of @option{-finline-functions}.
5685 This optimization runs at RTL level.
5687 @item -fsignaling-nans
5688 @opindex fsignaling-nans
5689 Compile code assuming that IEEE signaling NaNs may generate user-visible
5690 traps during floating-point operations. Setting this option disables
5691 optimizations that may change the number of exceptions visible with
5692 signaling NaNs. This option implies @option{-ftrapping-math}.
5694 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
5697 The default is @option{-fno-signaling-nans}.
5699 This option is experimental and does not currently guarantee to
5700 disable all GCC optimizations that affect signaling NaN behavior.
5702 @item -fsingle-precision-constant
5703 @opindex fsingle-precision-constant
5704 Treat floating point constant as single precision constant instead of
5705 implicitly converting it to double precision constant.
5707 @item -fcx-limited-range
5708 @itemx -fno-cx-limited-range
5709 @opindex fcx-limited-range
5710 @opindex fno-cx-limited-range
5711 When enabled, this option states that a range reduction step is not
5712 needed when performing complex division. The default is
5713 @option{-fno-cx-limited-range}, but is enabled by @option{-ffast-math}.
5715 This option controls the default setting of the ISO C99
5716 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
5721 The following options control optimizations that may improve
5722 performance, but are not enabled by any @option{-O} options. This
5723 section includes experimental options that may produce broken code.
5726 @item -fbranch-probabilities
5727 @opindex fbranch-probabilities
5728 After running a program compiled with @option{-fprofile-arcs}
5729 (@pxref{Debugging Options,, Options for Debugging Your Program or
5730 @command{gcc}}), you can compile it a second time using
5731 @option{-fbranch-probabilities}, to improve optimizations based on
5732 the number of times each branch was taken. When the program
5733 compiled with @option{-fprofile-arcs} exits it saves arc execution
5734 counts to a file called @file{@var{sourcename}.gcda} for each source
5735 file The information in this data file is very dependent on the
5736 structure of the generated code, so you must use the same source code
5737 and the same optimization options for both compilations.
5739 With @option{-fbranch-probabilities}, GCC puts a
5740 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
5741 These can be used to improve optimization. Currently, they are only
5742 used in one place: in @file{reorg.c}, instead of guessing which path a
5743 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
5744 exactly determine which path is taken more often.
5746 @item -fprofile-values
5747 @opindex fprofile-values
5748 If combined with @option{-fprofile-arcs}, it adds code so that some
5749 data about values of expressions in the program is gathered.
5751 With @option{-fbranch-probabilities}, it reads back the data gathered
5752 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
5753 notes to instructions for their later usage in optimizations.
5755 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
5759 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
5760 a code to gather information about values of expressions.
5762 With @option{-fbranch-probabilities}, it reads back the data gathered
5763 and actually performs the optimizations based on them.
5764 Currently the optimizations include specialization of division operation
5765 using the knowledge about the value of the denominator.
5767 @item -frename-registers
5768 @opindex frename-registers
5769 Attempt to avoid false dependencies in scheduled code by making use
5770 of registers left over after register allocation. This optimization
5771 will most benefit processors with lots of registers. Depending on the
5772 debug information format adopted by the target, however, it can
5773 make debugging impossible, since variables will no longer stay in
5774 a ``home register''.
5776 Enabled by default with @option{-funroll-loops}.
5780 Perform tail duplication to enlarge superblock size. This transformation
5781 simplifies the control flow of the function allowing other optimizations to do
5784 Enabled with @option{-fprofile-use}.
5786 @item -funroll-loops
5787 @opindex funroll-loops
5788 Unroll loops whose number of iterations can be determined at compile time or
5789 upon entry to the loop. @option{-funroll-loops} implies
5790 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
5791 It also turns on complete loop peeling (i.e.@: complete removal of loops with
5792 small constant number of iterations). This option makes code larger, and may
5793 or may not make it run faster.
5795 Enabled with @option{-fprofile-use}.
5797 @item -funroll-all-loops
5798 @opindex funroll-all-loops
5799 Unroll all loops, even if their number of iterations is uncertain when
5800 the loop is entered. This usually makes programs run more slowly.
5801 @option{-funroll-all-loops} implies the same options as
5802 @option{-funroll-loops}.
5805 @opindex fpeel-loops
5806 Peels the loops for that there is enough information that they do not
5807 roll much (from profile feedback). It also turns on complete loop peeling
5808 (i.e.@: complete removal of loops with small constant number of iterations).
5810 Enabled with @option{-fprofile-use}.
5812 @item -fmove-loop-invariants
5813 @opindex fmove-loop-invariants
5814 Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
5815 at level @option{-O1}
5817 @item -funswitch-loops
5818 @opindex funswitch-loops
5819 Move branches with loop invariant conditions out of the loop, with duplicates
5820 of the loop on both branches (modified according to result of the condition).
5822 @item -ffunction-sections
5823 @itemx -fdata-sections
5824 @opindex ffunction-sections
5825 @opindex fdata-sections
5826 Place each function or data item into its own section in the output
5827 file if the target supports arbitrary sections. The name of the
5828 function or the name of the data item determines the section's name
5831 Use these options on systems where the linker can perform optimizations
5832 to improve locality of reference in the instruction space. Most systems
5833 using the ELF object format and SPARC processors running Solaris 2 have
5834 linkers with such optimizations. AIX may have these optimizations in
5837 Only use these options when there are significant benefits from doing
5838 so. When you specify these options, the assembler and linker will
5839 create larger object and executable files and will also be slower.
5840 You will not be able to use @code{gprof} on all systems if you
5841 specify this option and you may have problems with debugging if
5842 you specify both this option and @option{-g}.
5844 @item -fbranch-target-load-optimize
5845 @opindex fbranch-target-load-optimize
5846 Perform branch target register load optimization before prologue / epilogue
5848 The use of target registers can typically be exposed only during reload,
5849 thus hoisting loads out of loops and doing inter-block scheduling needs
5850 a separate optimization pass.
5852 @item -fbranch-target-load-optimize2
5853 @opindex fbranch-target-load-optimize2
5854 Perform branch target register load optimization after prologue / epilogue
5857 @item -fbtr-bb-exclusive
5858 @opindex fbtr-bb-exclusive
5859 When performing branch target register load optimization, don't reuse
5860 branch target registers in within any basic block.
5862 @item -fstack-protector
5863 Emit extra code to check for buffer overflows, such as stack smashing
5864 attacks. This is done by adding a guard variable to functions with
5865 vulnerable objects. This includes functions that call alloca, and
5866 functions with buffers larger than 8 bytes. The guards are initialized
5867 when a function is entered and then checked when the function exits.
5868 If a guard check fails, an error message is printed and the program exits.
5870 @item -fstack-protector-all
5871 Like @option{-fstack-protector} except that all functions are protected.
5873 @item -fsection-anchors
5874 @opindex fsection-anchors
5875 Try to reduce the number of symbolic address calculations by using
5876 shared ``anchor'' symbols to address nearby objects. This transformation
5877 can help to reduce the number of GOT entries and GOT accesses on some
5880 For example, the implementation of the following function @code{foo}:
5884 int foo (void) @{ return a + b + c; @}
5887 would usually calculate the addresses of all three variables, but if you
5888 compile it with @option{-fsection-anchors}, it will access the variables
5889 from a common anchor point instead. The effect is similar to the
5890 following pseudocode (which isn't valid C):
5895 register int *xr = &x;
5896 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
5900 Not all targets support this option.
5902 @item --param @var{name}=@var{value}
5904 In some places, GCC uses various constants to control the amount of
5905 optimization that is done. For example, GCC will not inline functions
5906 that contain more that a certain number of instructions. You can
5907 control some of these constants on the command-line using the
5908 @option{--param} option.
5910 The names of specific parameters, and the meaning of the values, are
5911 tied to the internals of the compiler, and are subject to change
5912 without notice in future releases.
5914 In each case, the @var{value} is an integer. The allowable choices for
5915 @var{name} are given in the following table:
5918 @item salias-max-implicit-fields
5919 The maximum number of fields in a variable without direct
5920 structure accesses for which structure aliasing will consider trying
5921 to track each field. The default is 5
5923 @item salias-max-array-elements
5924 The maximum number of elements an array can have and its elements
5925 still be tracked individually by structure aliasing. The default is 4
5927 @item sra-max-structure-size
5928 The maximum structure size, in bytes, at which the scalar replacement
5929 of aggregates (SRA) optimization will perform block copies. The
5930 default value, 0, implies that GCC will select the most appropriate
5933 @item sra-field-structure-ratio
5934 The threshold ratio (as a percentage) between instantiated fields and
5935 the complete structure size. We say that if the ratio of the number
5936 of bytes in instantiated fields to the number of bytes in the complete
5937 structure exceeds this parameter, then block copies are not used. The
5940 @item max-crossjump-edges
5941 The maximum number of incoming edges to consider for crossjumping.
5942 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
5943 the number of edges incoming to each block. Increasing values mean
5944 more aggressive optimization, making the compile time increase with
5945 probably small improvement in executable size.
5947 @item min-crossjump-insns
5948 The minimum number of instructions which must be matched at the end
5949 of two blocks before crossjumping will be performed on them. This
5950 value is ignored in the case where all instructions in the block being
5951 crossjumped from are matched. The default value is 5.
5953 @item max-grow-copy-bb-insns
5954 The maximum code size expansion factor when copying basic blocks
5955 instead of jumping. The expansion is relative to a jump instruction.
5956 The default value is 8.
5958 @item max-goto-duplication-insns
5959 The maximum number of instructions to duplicate to a block that jumps
5960 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
5961 passes, GCC factors computed gotos early in the compilation process,
5962 and unfactors them as late as possible. Only computed jumps at the
5963 end of a basic blocks with no more than max-goto-duplication-insns are
5964 unfactored. The default value is 8.
5966 @item max-delay-slot-insn-search
5967 The maximum number of instructions to consider when looking for an
5968 instruction to fill a delay slot. If more than this arbitrary number of
5969 instructions is searched, the time savings from filling the delay slot
5970 will be minimal so stop searching. Increasing values mean more
5971 aggressive optimization, making the compile time increase with probably
5972 small improvement in executable run time.
5974 @item max-delay-slot-live-search
5975 When trying to fill delay slots, the maximum number of instructions to
5976 consider when searching for a block with valid live register
5977 information. Increasing this arbitrarily chosen value means more
5978 aggressive optimization, increasing the compile time. This parameter
5979 should be removed when the delay slot code is rewritten to maintain the
5982 @item max-gcse-memory
5983 The approximate maximum amount of memory that will be allocated in
5984 order to perform the global common subexpression elimination
5985 optimization. If more memory than specified is required, the
5986 optimization will not be done.
5988 @item max-gcse-passes
5989 The maximum number of passes of GCSE to run. The default is 1.
5991 @item max-pending-list-length
5992 The maximum number of pending dependencies scheduling will allow
5993 before flushing the current state and starting over. Large functions
5994 with few branches or calls can create excessively large lists which
5995 needlessly consume memory and resources.
5997 @item max-inline-insns-single
5998 Several parameters control the tree inliner used in gcc.
5999 This number sets the maximum number of instructions (counted in GCC's
6000 internal representation) in a single function that the tree inliner
6001 will consider for inlining. This only affects functions declared
6002 inline and methods implemented in a class declaration (C++).
6003 The default value is 450.
6005 @item max-inline-insns-auto
6006 When you use @option{-finline-functions} (included in @option{-O3}),
6007 a lot of functions that would otherwise not be considered for inlining
6008 by the compiler will be investigated. To those functions, a different
6009 (more restrictive) limit compared to functions declared inline can
6011 The default value is 90.
6013 @item large-function-insns
6014 The limit specifying really large functions. For functions larger than this
6015 limit after inlining inlining is constrained by
6016 @option{--param large-function-growth}. This parameter is useful primarily
6017 to avoid extreme compilation time caused by non-linear algorithms used by the
6019 This parameter is ignored when @option{-funit-at-a-time} is not used.
6020 The default value is 2700.
6022 @item large-function-growth
6023 Specifies maximal growth of large function caused by inlining in percents.
6024 This parameter is ignored when @option{-funit-at-a-time} is not used.
6025 The default value is 100 which limits large function growth to 2.0 times
6028 @item large-unit-insns
6029 The limit specifying large translation unit. Growth caused by inlining of
6030 units larger than this limit is limited by @option{--param inline-unit-growth}.
6031 For small units this might be too tight (consider unit consisting of function A
6032 that is inline and B that just calls A three time. If B is small relative to
6033 A, the growth of unit is 300\% and yet such inlining is very sane. For very
6034 large units consisting of small inlininable functions however the overall unit
6035 growth limit is needed to avoid exponential explosion of code size. Thus for
6036 smaller units, the size is increased to @option{--param large-unit-insns}
6037 before applying @option{--param inline-unit-growth}. The default is 10000
6039 @item inline-unit-growth
6040 Specifies maximal overall growth of the compilation unit caused by inlining.
6041 This parameter is ignored when @option{-funit-at-a-time} is not used.
6042 The default value is 50 which limits unit growth to 1.5 times the original
6045 @item large-stack-frame
6046 The limit specifying large stack frames. While inlining the algorithm is trying
6047 to not grow past this limit too much. Default value is 256 bytes.
6049 @item large-stack-frame-growth
6050 Specifies maximal growth of large stack frames caused by inlining in percents.
6051 The default value is 1000 which limits large stack frame growth to 11 times
6054 @item max-inline-insns-recursive
6055 @itemx max-inline-insns-recursive-auto
6056 Specifies maximum number of instructions out-of-line copy of self recursive inline
6057 function can grow into by performing recursive inlining.
6059 For functions declared inline @option{--param max-inline-insns-recursive} is
6060 taken into account. For function not declared inline, recursive inlining
6061 happens only when @option{-finline-functions} (included in @option{-O3}) is
6062 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
6063 default value is 450.
6065 @item max-inline-recursive-depth
6066 @itemx max-inline-recursive-depth-auto
6067 Specifies maximum recursion depth used by the recursive inlining.
6069 For functions declared inline @option{--param max-inline-recursive-depth} is
6070 taken into account. For function not declared inline, recursive inlining
6071 happens only when @option{-finline-functions} (included in @option{-O3}) is
6072 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
6073 default value is 450.
6075 @item min-inline-recursive-probability
6076 Recursive inlining is profitable only for function having deep recursion
6077 in average and can hurt for function having little recursion depth by
6078 increasing the prologue size or complexity of function body to other
6081 When profile feedback is available (see @option{-fprofile-generate}) the actual
6082 recursion depth can be guessed from probability that function will recurse via
6083 given call expression. This parameter limits inlining only to call expression
6084 whose probability exceeds given threshold (in percents). The default value is
6087 @item inline-call-cost
6088 Specify cost of call instruction relative to simple arithmetics operations
6089 (having cost of 1). Increasing this cost disqualifies inlining of non-leaf
6090 functions and at the same time increases size of leaf function that is believed to
6091 reduce function size by being inlined. In effect it increases amount of
6092 inlining for code having large abstraction penalty (many functions that just
6093 pass the arguments to other functions) and decrease inlining for code with low
6094 abstraction penalty. The default value is 16.
6096 @item max-unrolled-insns
6097 The maximum number of instructions that a loop should have if that loop
6098 is unrolled, and if the loop is unrolled, it determines how many times
6099 the loop code is unrolled.
6101 @item max-average-unrolled-insns
6102 The maximum number of instructions biased by probabilities of their execution
6103 that a loop should have if that loop is unrolled, and if the loop is unrolled,
6104 it determines how many times the loop code is unrolled.
6106 @item max-unroll-times
6107 The maximum number of unrollings of a single loop.
6109 @item max-peeled-insns
6110 The maximum number of instructions that a loop should have if that loop
6111 is peeled, and if the loop is peeled, it determines how many times
6112 the loop code is peeled.
6114 @item max-peel-times
6115 The maximum number of peelings of a single loop.
6117 @item max-completely-peeled-insns
6118 The maximum number of insns of a completely peeled loop.
6120 @item max-completely-peel-times
6121 The maximum number of iterations of a loop to be suitable for complete peeling.
6123 @item max-unswitch-insns
6124 The maximum number of insns of an unswitched loop.
6126 @item max-unswitch-level
6127 The maximum number of branches unswitched in a single loop.
6130 The minimum cost of an expensive expression in the loop invariant motion.
6132 @item iv-consider-all-candidates-bound
6133 Bound on number of candidates for induction variables below that
6134 all candidates are considered for each use in induction variable
6135 optimizations. Only the most relevant candidates are considered
6136 if there are more candidates, to avoid quadratic time complexity.
6138 @item iv-max-considered-uses
6139 The induction variable optimizations give up on loops that contain more
6140 induction variable uses.
6142 @item iv-always-prune-cand-set-bound
6143 If number of candidates in the set is smaller than this value,
6144 we always try to remove unnecessary ivs from the set during its
6145 optimization when a new iv is added to the set.
6147 @item scev-max-expr-size
6148 Bound on size of expressions used in the scalar evolutions analyzer.
6149 Large expressions slow the analyzer.
6151 @item vect-max-version-checks
6152 The maximum number of runtime checks that can be performed when doing
6153 loop versioning in the vectorizer. See option ftree-vect-loop-version
6154 for more information.
6156 @item max-iterations-to-track
6158 The maximum number of iterations of a loop the brute force algorithm
6159 for analysis of # of iterations of the loop tries to evaluate.
6161 @item hot-bb-count-fraction
6162 Select fraction of the maximal count of repetitions of basic block in program
6163 given basic block needs to have to be considered hot.
6165 @item hot-bb-frequency-fraction
6166 Select fraction of the maximal frequency of executions of basic block in
6167 function given basic block needs to have to be considered hot
6169 @item max-predicted-iterations
6170 The maximum number of loop iterations we predict statically. This is useful
6171 in cases where function contain single loop with known bound and other loop
6172 with unknown. We predict the known number of iterations correctly, while
6173 the unknown number of iterations average to roughly 10. This means that the
6174 loop without bounds would appear artificially cold relative to the other one.
6176 @item tracer-dynamic-coverage
6177 @itemx tracer-dynamic-coverage-feedback
6179 This value is used to limit superblock formation once the given percentage of
6180 executed instructions is covered. This limits unnecessary code size
6183 The @option{tracer-dynamic-coverage-feedback} is used only when profile
6184 feedback is available. The real profiles (as opposed to statically estimated
6185 ones) are much less balanced allowing the threshold to be larger value.
6187 @item tracer-max-code-growth
6188 Stop tail duplication once code growth has reached given percentage. This is
6189 rather hokey argument, as most of the duplicates will be eliminated later in
6190 cross jumping, so it may be set to much higher values than is the desired code
6193 @item tracer-min-branch-ratio
6195 Stop reverse growth when the reverse probability of best edge is less than this
6196 threshold (in percent).
6198 @item tracer-min-branch-ratio
6199 @itemx tracer-min-branch-ratio-feedback
6201 Stop forward growth if the best edge do have probability lower than this
6204 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
6205 compilation for profile feedback and one for compilation without. The value
6206 for compilation with profile feedback needs to be more conservative (higher) in
6207 order to make tracer effective.
6209 @item max-cse-path-length
6211 Maximum number of basic blocks on path that cse considers. The default is 10.
6214 The maximum instructions CSE process before flushing. The default is 1000.
6216 @item max-aliased-vops
6218 Maximum number of virtual operands per statement allowed to represent
6219 aliases before triggering the alias grouping heuristic. Alias
6220 grouping reduces compile times and memory consumption needed for
6221 aliasing at the expense of precision loss in alias information.
6223 @item ggc-min-expand
6225 GCC uses a garbage collector to manage its own memory allocation. This
6226 parameter specifies the minimum percentage by which the garbage
6227 collector's heap should be allowed to expand between collections.
6228 Tuning this may improve compilation speed; it has no effect on code
6231 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
6232 RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
6233 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
6234 GCC is not able to calculate RAM on a particular platform, the lower
6235 bound of 30% is used. Setting this parameter and
6236 @option{ggc-min-heapsize} to zero causes a full collection to occur at
6237 every opportunity. This is extremely slow, but can be useful for
6240 @item ggc-min-heapsize
6242 Minimum size of the garbage collector's heap before it begins bothering
6243 to collect garbage. The first collection occurs after the heap expands
6244 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
6245 tuning this may improve compilation speed, and has no effect on code
6248 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
6249 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
6250 with a lower bound of 4096 (four megabytes) and an upper bound of
6251 131072 (128 megabytes). If GCC is not able to calculate RAM on a
6252 particular platform, the lower bound is used. Setting this parameter
6253 very large effectively disables garbage collection. Setting this
6254 parameter and @option{ggc-min-expand} to zero causes a full collection
6255 to occur at every opportunity.
6257 @item max-reload-search-insns
6258 The maximum number of instruction reload should look backward for equivalent
6259 register. Increasing values mean more aggressive optimization, making the
6260 compile time increase with probably slightly better performance. The default
6263 @item max-cselib-memory-locations
6264 The maximum number of memory locations cselib should take into account.
6265 Increasing values mean more aggressive optimization, making the compile time
6266 increase with probably slightly better performance. The default value is 500.
6268 @item max-flow-memory-locations
6269 Similar as @option{max-cselib-memory-locations} but for dataflow liveness.
6270 The default value is 100.
6272 @item reorder-blocks-duplicate
6273 @itemx reorder-blocks-duplicate-feedback
6275 Used by basic block reordering pass to decide whether to use unconditional
6276 branch or duplicate the code on its destination. Code is duplicated when its
6277 estimated size is smaller than this value multiplied by the estimated size of
6278 unconditional jump in the hot spots of the program.
6280 The @option{reorder-block-duplicate-feedback} is used only when profile
6281 feedback is available and may be set to higher values than
6282 @option{reorder-block-duplicate} since information about the hot spots is more
6285 @item max-sched-ready-insns
6286 The maximum number of instructions ready to be issued the scheduler should
6287 consider at any given time during the first scheduling pass. Increasing
6288 values mean more thorough searches, making the compilation time increase
6289 with probably little benefit. The default value is 100.
6291 @item max-sched-region-blocks
6292 The maximum number of blocks in a region to be considered for
6293 interblock scheduling. The default value is 10.
6295 @item max-sched-region-insns
6296 The maximum number of insns in a region to be considered for
6297 interblock scheduling. The default value is 100.
6300 The minimum probability (in percents) of reaching a source block
6301 for interblock speculative scheduling. The default value is 40.
6303 @item max-sched-extend-regions-iters
6304 The maximum number of iterations through CFG to extend regions.
6305 0 - disable region extension,
6306 N - do at most N iterations.
6307 The default value is 0.
6309 @item max-sched-insn-conflict-delay
6310 The maximum conflict delay for an insn to be considered for speculative motion.
6311 The default value is 3.
6313 @item sched-spec-prob-cutoff
6314 The minimal probability of speculation success (in percents), so that
6315 speculative insn will be scheduled.
6316 The default value is 40.
6318 @item max-last-value-rtl
6320 The maximum size measured as number of RTLs that can be recorded in an expression
6321 in combiner for a pseudo register as last known value of that register. The default
6324 @item integer-share-limit
6325 Small integer constants can use a shared data structure, reducing the
6326 compiler's memory usage and increasing its speed. This sets the maximum
6327 value of a shared integer constant's. The default value is 256.
6329 @item min-virtual-mappings
6330 Specifies the minimum number of virtual mappings in the incremental
6331 SSA updater that should be registered to trigger the virtual mappings
6332 heuristic defined by virtual-mappings-ratio. The default value is
6335 @item virtual-mappings-ratio
6336 If the number of virtual mappings is virtual-mappings-ratio bigger
6337 than the number of virtual symbols to be updated, then the incremental
6338 SSA updater switches to a full update for those symbols. The default
6341 @item ssp-buffer-size
6342 The minimum size of buffers (i.e. arrays) that will receive stack smashing
6343 protection when @option{-fstack-protection} is used.
6345 @item max-jump-thread-duplication-stmts
6346 Maximum number of statements allowed in a block that needs to be
6347 duplicated when threading jumps.
6349 @item max-fields-for-field-sensitive
6350 Maximum number of fields in a structure we will treat in
6351 a field sensitive manner during pointer analysis.
6353 @item prefetch-latency
6354 Estimate on average number of instructions that are executed before
6355 prefetch finishes. The distance we prefetch ahead is proportional
6356 to this constant. Increasing this number may also lead to less
6357 streams being prefetched (see @option{simultaneous-prefetches}).
6359 @item simultaneous-prefetches
6360 Maximum number of prefetches that can run at the same time.
6362 @item l1-cache-line-size
6363 The size of cache line in L1 cache, in bytes.
6366 The number of cache lines in L1 cache.
6371 @node Preprocessor Options
6372 @section Options Controlling the Preprocessor
6373 @cindex preprocessor options
6374 @cindex options, preprocessor
6376 These options control the C preprocessor, which is run on each C source
6377 file before actual compilation.
6379 If you use the @option{-E} option, nothing is done except preprocessing.
6380 Some of these options make sense only together with @option{-E} because
6381 they cause the preprocessor output to be unsuitable for actual
6386 You can use @option{-Wp,@var{option}} to bypass the compiler driver
6387 and pass @var{option} directly through to the preprocessor. If
6388 @var{option} contains commas, it is split into multiple options at the
6389 commas. However, many options are modified, translated or interpreted
6390 by the compiler driver before being passed to the preprocessor, and
6391 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
6392 interface is undocumented and subject to change, so whenever possible
6393 you should avoid using @option{-Wp} and let the driver handle the
6396 @item -Xpreprocessor @var{option}
6397 @opindex preprocessor
6398 Pass @var{option} as an option to the preprocessor. You can use this to
6399 supply system-specific preprocessor options which GCC does not know how to
6402 If you want to pass an option that takes an argument, you must use
6403 @option{-Xpreprocessor} twice, once for the option and once for the argument.
6406 @include cppopts.texi
6408 @node Assembler Options
6409 @section Passing Options to the Assembler
6411 @c prevent bad page break with this line
6412 You can pass options to the assembler.
6415 @item -Wa,@var{option}
6417 Pass @var{option} as an option to the assembler. If @var{option}
6418 contains commas, it is split into multiple options at the commas.
6420 @item -Xassembler @var{option}
6422 Pass @var{option} as an option to the assembler. You can use this to
6423 supply system-specific assembler options which GCC does not know how to
6426 If you want to pass an option that takes an argument, you must use
6427 @option{-Xassembler} twice, once for the option and once for the argument.
6432 @section Options for Linking
6433 @cindex link options
6434 @cindex options, linking
6436 These options come into play when the compiler links object files into
6437 an executable output file. They are meaningless if the compiler is
6438 not doing a link step.
6442 @item @var{object-file-name}
6443 A file name that does not end in a special recognized suffix is
6444 considered to name an object file or library. (Object files are
6445 distinguished from libraries by the linker according to the file
6446 contents.) If linking is done, these object files are used as input
6455 If any of these options is used, then the linker is not run, and
6456 object file names should not be used as arguments. @xref{Overall
6460 @item -l@var{library}
6461 @itemx -l @var{library}
6463 Search the library named @var{library} when linking. (The second
6464 alternative with the library as a separate argument is only for
6465 POSIX compliance and is not recommended.)
6467 It makes a difference where in the command you write this option; the
6468 linker searches and processes libraries and object files in the order they
6469 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
6470 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
6471 to functions in @samp{z}, those functions may not be loaded.
6473 The linker searches a standard list of directories for the library,
6474 which is actually a file named @file{lib@var{library}.a}. The linker
6475 then uses this file as if it had been specified precisely by name.
6477 The directories searched include several standard system directories
6478 plus any that you specify with @option{-L}.
6480 Normally the files found this way are library files---archive files
6481 whose members are object files. The linker handles an archive file by
6482 scanning through it for members which define symbols that have so far
6483 been referenced but not defined. But if the file that is found is an
6484 ordinary object file, it is linked in the usual fashion. The only
6485 difference between using an @option{-l} option and specifying a file name
6486 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
6487 and searches several directories.
6491 You need this special case of the @option{-l} option in order to
6492 link an Objective-C or Objective-C++ program.
6495 @opindex nostartfiles
6496 Do not use the standard system startup files when linking.
6497 The standard system libraries are used normally, unless @option{-nostdlib}
6498 or @option{-nodefaultlibs} is used.
6500 @item -nodefaultlibs
6501 @opindex nodefaultlibs
6502 Do not use the standard system libraries when linking.
6503 Only the libraries you specify will be passed to the linker.
6504 The standard startup files are used normally, unless @option{-nostartfiles}
6505 is used. The compiler may generate calls to @code{memcmp},
6506 @code{memset}, @code{memcpy} and @code{memmove}.
6507 These entries are usually resolved by entries in
6508 libc. These entry points should be supplied through some other
6509 mechanism when this option is specified.
6513 Do not use the standard system startup files or libraries when linking.
6514 No startup files and only the libraries you specify will be passed to
6515 the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
6516 @code{memcpy} and @code{memmove}.
6517 These entries are usually resolved by entries in
6518 libc. These entry points should be supplied through some other
6519 mechanism when this option is specified.
6521 @cindex @option{-lgcc}, use with @option{-nostdlib}
6522 @cindex @option{-nostdlib} and unresolved references
6523 @cindex unresolved references and @option{-nostdlib}
6524 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
6525 @cindex @option{-nodefaultlibs} and unresolved references
6526 @cindex unresolved references and @option{-nodefaultlibs}
6527 One of the standard libraries bypassed by @option{-nostdlib} and
6528 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
6529 that GCC uses to overcome shortcomings of particular machines, or special
6530 needs for some languages.
6531 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
6532 Collection (GCC) Internals},
6533 for more discussion of @file{libgcc.a}.)
6534 In most cases, you need @file{libgcc.a} even when you want to avoid
6535 other standard libraries. In other words, when you specify @option{-nostdlib}
6536 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
6537 This ensures that you have no unresolved references to internal GCC
6538 library subroutines. (For example, @samp{__main}, used to ensure C++
6539 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
6540 GNU Compiler Collection (GCC) Internals}.)
6544 Produce a position independent executable on targets which support it.
6545 For predictable results, you must also specify the same set of options
6546 that were used to generate code (@option{-fpie}, @option{-fPIE},
6547 or model suboptions) when you specify this option.
6551 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
6552 that support it. This instructs the linker to add all symbols, not
6553 only used ones, to the dynamic symbol table. This option is needed
6554 for some uses of @code{dlopen} or to allow obtaining backtraces
6555 from within a program.
6559 Remove all symbol table and relocation information from the executable.
6563 On systems that support dynamic linking, this prevents linking with the shared
6564 libraries. On other systems, this option has no effect.
6568 Produce a shared object which can then be linked with other objects to
6569 form an executable. Not all systems support this option. For predictable
6570 results, you must also specify the same set of options that were used to
6571 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
6572 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
6573 needs to build supplementary stub code for constructors to work. On
6574 multi-libbed systems, @samp{gcc -shared} must select the correct support
6575 libraries to link against. Failing to supply the correct flags may lead
6576 to subtle defects. Supplying them in cases where they are not necessary
6579 @item -shared-libgcc
6580 @itemx -static-libgcc
6581 @opindex shared-libgcc
6582 @opindex static-libgcc
6583 On systems that provide @file{libgcc} as a shared library, these options
6584 force the use of either the shared or static version respectively.
6585 If no shared version of @file{libgcc} was built when the compiler was
6586 configured, these options have no effect.
6588 There are several situations in which an application should use the
6589 shared @file{libgcc} instead of the static version. The most common
6590 of these is when the application wishes to throw and catch exceptions
6591 across different shared libraries. In that case, each of the libraries
6592 as well as the application itself should use the shared @file{libgcc}.
6594 Therefore, the G++ and GCJ drivers automatically add
6595 @option{-shared-libgcc} whenever you build a shared library or a main
6596 executable, because C++ and Java programs typically use exceptions, so
6597 this is the right thing to do.
6599 If, instead, you use the GCC driver to create shared libraries, you may
6600 find that they will not always be linked with the shared @file{libgcc}.
6601 If GCC finds, at its configuration time, that you have a non-GNU linker
6602 or a GNU linker that does not support option @option{--eh-frame-hdr},
6603 it will link the shared version of @file{libgcc} into shared libraries
6604 by default. Otherwise, it will take advantage of the linker and optimize
6605 away the linking with the shared version of @file{libgcc}, linking with
6606 the static version of libgcc by default. This allows exceptions to
6607 propagate through such shared libraries, without incurring relocation
6608 costs at library load time.
6610 However, if a library or main executable is supposed to throw or catch
6611 exceptions, you must link it using the G++ or GCJ driver, as appropriate
6612 for the languages used in the program, or using the option
6613 @option{-shared-libgcc}, such that it is linked with the shared
6618 Bind references to global symbols when building a shared object. Warn
6619 about any unresolved references (unless overridden by the link editor
6620 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
6623 @item -Xlinker @var{option}
6625 Pass @var{option} as an option to the linker. You can use this to
6626 supply system-specific linker options which GCC does not know how to
6629 If you want to pass an option that takes an argument, you must use
6630 @option{-Xlinker} twice, once for the option and once for the argument.
6631 For example, to pass @option{-assert definitions}, you must write
6632 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
6633 @option{-Xlinker "-assert definitions"}, because this passes the entire
6634 string as a single argument, which is not what the linker expects.
6636 @item -Wl,@var{option}
6638 Pass @var{option} as an option to the linker. If @var{option} contains
6639 commas, it is split into multiple options at the commas.
6641 @item -u @var{symbol}
6643 Pretend the symbol @var{symbol} is undefined, to force linking of
6644 library modules to define it. You can use @option{-u} multiple times with
6645 different symbols to force loading of additional library modules.
6648 @node Directory Options
6649 @section Options for Directory Search
6650 @cindex directory options
6651 @cindex options, directory search
6654 These options specify directories to search for header files, for
6655 libraries and for parts of the compiler:
6660 Add the directory @var{dir} to the head of the list of directories to be
6661 searched for header files. This can be used to override a system header
6662 file, substituting your own version, since these directories are
6663 searched before the system header file directories. However, you should
6664 not use this option to add directories that contain vendor-supplied
6665 system header files (use @option{-isystem} for that). If you use more than
6666 one @option{-I} option, the directories are scanned in left-to-right
6667 order; the standard system directories come after.
6669 If a standard system include directory, or a directory specified with
6670 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
6671 option will be ignored. The directory will still be searched but as a
6672 system directory at its normal position in the system include chain.
6673 This is to ensure that GCC's procedure to fix buggy system headers and
6674 the ordering for the include_next directive are not inadvertently changed.
6675 If you really need to change the search order for system directories,
6676 use the @option{-nostdinc} and/or @option{-isystem} options.
6678 @item -iquote@var{dir}
6680 Add the directory @var{dir} to the head of the list of directories to
6681 be searched for header files only for the case of @samp{#include
6682 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
6683 otherwise just like @option{-I}.
6687 Add directory @var{dir} to the list of directories to be searched
6690 @item -B@var{prefix}
6692 This option specifies where to find the executables, libraries,
6693 include files, and data files of the compiler itself.
6695 The compiler driver program runs one or more of the subprograms
6696 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
6697 @var{prefix} as a prefix for each program it tries to run, both with and
6698 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
6700 For each subprogram to be run, the compiler driver first tries the
6701 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
6702 was not specified, the driver tries two standard prefixes, which are
6703 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
6704 those results in a file name that is found, the unmodified program
6705 name is searched for using the directories specified in your
6706 @env{PATH} environment variable.
6708 The compiler will check to see if the path provided by the @option{-B}
6709 refers to a directory, and if necessary it will add a directory
6710 separator character at the end of the path.
6712 @option{-B} prefixes that effectively specify directory names also apply
6713 to libraries in the linker, because the compiler translates these
6714 options into @option{-L} options for the linker. They also apply to
6715 includes files in the preprocessor, because the compiler translates these
6716 options into @option{-isystem} options for the preprocessor. In this case,
6717 the compiler appends @samp{include} to the prefix.
6719 The run-time support file @file{libgcc.a} can also be searched for using
6720 the @option{-B} prefix, if needed. If it is not found there, the two
6721 standard prefixes above are tried, and that is all. The file is left
6722 out of the link if it is not found by those means.
6724 Another way to specify a prefix much like the @option{-B} prefix is to use
6725 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
6728 As a special kludge, if the path provided by @option{-B} is
6729 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
6730 9, then it will be replaced by @file{[dir/]include}. This is to help
6731 with boot-strapping the compiler.
6733 @item -specs=@var{file}
6735 Process @var{file} after the compiler reads in the standard @file{specs}
6736 file, in order to override the defaults that the @file{gcc} driver
6737 program uses when determining what switches to pass to @file{cc1},
6738 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
6739 @option{-specs=@var{file}} can be specified on the command line, and they
6740 are processed in order, from left to right.
6742 @item --sysroot=@var{dir}
6744 Use @var{dir} as the logical root directory for headers and libraries.
6745 For example, if the compiler would normally search for headers in
6746 @file{/usr/include} and libraries in @file{/usr/lib}, it will instead
6747 search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
6749 If you use both this option and the @option{-isysroot} option, then
6750 the @option{--sysroot} option will apply to libraries, but the
6751 @option{-isysroot} option will apply to header files.
6753 The GNU linker (beginning with version 2.16) has the necessary support
6754 for this option. If your linker does not support this option, the
6755 header file aspect of @option{--sysroot} will still work, but the
6756 library aspect will not.
6760 This option has been deprecated. Please use @option{-iquote} instead for
6761 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
6762 Any directories you specify with @option{-I} options before the @option{-I-}
6763 option are searched only for the case of @samp{#include "@var{file}"};
6764 they are not searched for @samp{#include <@var{file}>}.
6766 If additional directories are specified with @option{-I} options after
6767 the @option{-I-}, these directories are searched for all @samp{#include}
6768 directives. (Ordinarily @emph{all} @option{-I} directories are used
6771 In addition, the @option{-I-} option inhibits the use of the current
6772 directory (where the current input file came from) as the first search
6773 directory for @samp{#include "@var{file}"}. There is no way to
6774 override this effect of @option{-I-}. With @option{-I.} you can specify
6775 searching the directory which was current when the compiler was
6776 invoked. That is not exactly the same as what the preprocessor does
6777 by default, but it is often satisfactory.
6779 @option{-I-} does not inhibit the use of the standard system directories
6780 for header files. Thus, @option{-I-} and @option{-nostdinc} are
6787 @section Specifying subprocesses and the switches to pass to them
6790 @command{gcc} is a driver program. It performs its job by invoking a
6791 sequence of other programs to do the work of compiling, assembling and
6792 linking. GCC interprets its command-line parameters and uses these to
6793 deduce which programs it should invoke, and which command-line options
6794 it ought to place on their command lines. This behavior is controlled
6795 by @dfn{spec strings}. In most cases there is one spec string for each
6796 program that GCC can invoke, but a few programs have multiple spec
6797 strings to control their behavior. The spec strings built into GCC can
6798 be overridden by using the @option{-specs=} command-line switch to specify
6801 @dfn{Spec files} are plaintext files that are used to construct spec
6802 strings. They consist of a sequence of directives separated by blank
6803 lines. The type of directive is determined by the first non-whitespace
6804 character on the line and it can be one of the following:
6807 @item %@var{command}
6808 Issues a @var{command} to the spec file processor. The commands that can
6812 @item %include <@var{file}>
6814 Search for @var{file} and insert its text at the current point in the
6817 @item %include_noerr <@var{file}>
6818 @cindex %include_noerr
6819 Just like @samp{%include}, but do not generate an error message if the include
6820 file cannot be found.
6822 @item %rename @var{old_name} @var{new_name}
6824 Rename the spec string @var{old_name} to @var{new_name}.
6828 @item *[@var{spec_name}]:
6829 This tells the compiler to create, override or delete the named spec
6830 string. All lines after this directive up to the next directive or
6831 blank line are considered to be the text for the spec string. If this
6832 results in an empty string then the spec will be deleted. (Or, if the
6833 spec did not exist, then nothing will happened.) Otherwise, if the spec
6834 does not currently exist a new spec will be created. If the spec does
6835 exist then its contents will be overridden by the text of this
6836 directive, unless the first character of that text is the @samp{+}
6837 character, in which case the text will be appended to the spec.
6839 @item [@var{suffix}]:
6840 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
6841 and up to the next directive or blank line are considered to make up the
6842 spec string for the indicated suffix. When the compiler encounters an
6843 input file with the named suffix, it will processes the spec string in
6844 order to work out how to compile that file. For example:
6851 This says that any input file whose name ends in @samp{.ZZ} should be
6852 passed to the program @samp{z-compile}, which should be invoked with the
6853 command-line switch @option{-input} and with the result of performing the
6854 @samp{%i} substitution. (See below.)
6856 As an alternative to providing a spec string, the text that follows a
6857 suffix directive can be one of the following:
6860 @item @@@var{language}
6861 This says that the suffix is an alias for a known @var{language}. This is
6862 similar to using the @option{-x} command-line switch to GCC to specify a
6863 language explicitly. For example:
6870 Says that .ZZ files are, in fact, C++ source files.
6873 This causes an error messages saying:
6876 @var{name} compiler not installed on this system.
6880 GCC already has an extensive list of suffixes built into it.
6881 This directive will add an entry to the end of the list of suffixes, but
6882 since the list is searched from the end backwards, it is effectively
6883 possible to override earlier entries using this technique.
6887 GCC has the following spec strings built into it. Spec files can
6888 override these strings or create their own. Note that individual
6889 targets can also add their own spec strings to this list.
6892 asm Options to pass to the assembler
6893 asm_final Options to pass to the assembler post-processor
6894 cpp Options to pass to the C preprocessor
6895 cc1 Options to pass to the C compiler
6896 cc1plus Options to pass to the C++ compiler
6897 endfile Object files to include at the end of the link
6898 link Options to pass to the linker
6899 lib Libraries to include on the command line to the linker
6900 libgcc Decides which GCC support library to pass to the linker
6901 linker Sets the name of the linker
6902 predefines Defines to be passed to the C preprocessor
6903 signed_char Defines to pass to CPP to say whether @code{char} is signed
6905 startfile Object files to include at the start of the link
6908 Here is a small example of a spec file:
6914 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
6917 This example renames the spec called @samp{lib} to @samp{old_lib} and
6918 then overrides the previous definition of @samp{lib} with a new one.
6919 The new definition adds in some extra command-line options before
6920 including the text of the old definition.
6922 @dfn{Spec strings} are a list of command-line options to be passed to their
6923 corresponding program. In addition, the spec strings can contain
6924 @samp{%}-prefixed sequences to substitute variable text or to
6925 conditionally insert text into the command line. Using these constructs
6926 it is possible to generate quite complex command lines.
6928 Here is a table of all defined @samp{%}-sequences for spec
6929 strings. Note that spaces are not generated automatically around the
6930 results of expanding these sequences. Therefore you can concatenate them
6931 together or combine them with constant text in a single argument.
6935 Substitute one @samp{%} into the program name or argument.
6938 Substitute the name of the input file being processed.
6941 Substitute the basename of the input file being processed.
6942 This is the substring up to (and not including) the last period
6943 and not including the directory.
6946 This is the same as @samp{%b}, but include the file suffix (text after
6950 Marks the argument containing or following the @samp{%d} as a
6951 temporary file name, so that that file will be deleted if GCC exits
6952 successfully. Unlike @samp{%g}, this contributes no text to the
6955 @item %g@var{suffix}
6956 Substitute a file name that has suffix @var{suffix} and is chosen
6957 once per compilation, and mark the argument in the same way as
6958 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
6959 name is now chosen in a way that is hard to predict even when previously
6960 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
6961 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
6962 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
6963 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
6964 was simply substituted with a file name chosen once per compilation,
6965 without regard to any appended suffix (which was therefore treated
6966 just like ordinary text), making such attacks more likely to succeed.
6968 @item %u@var{suffix}
6969 Like @samp{%g}, but generates a new temporary file name even if
6970 @samp{%u@var{suffix}} was already seen.
6972 @item %U@var{suffix}
6973 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
6974 new one if there is no such last file name. In the absence of any
6975 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
6976 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
6977 would involve the generation of two distinct file names, one
6978 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
6979 simply substituted with a file name chosen for the previous @samp{%u},
6980 without regard to any appended suffix.
6982 @item %j@var{suffix}
6983 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
6984 writable, and if save-temps is off; otherwise, substitute the name
6985 of a temporary file, just like @samp{%u}. This temporary file is not
6986 meant for communication between processes, but rather as a junk
6989 @item %|@var{suffix}
6990 @itemx %m@var{suffix}
6991 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
6992 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
6993 all. These are the two most common ways to instruct a program that it
6994 should read from standard input or write to standard output. If you
6995 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
6996 construct: see for example @file{f/lang-specs.h}.
6998 @item %.@var{SUFFIX}
6999 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
7000 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
7001 terminated by the next space or %.
7004 Marks the argument containing or following the @samp{%w} as the
7005 designated output file of this compilation. This puts the argument
7006 into the sequence of arguments that @samp{%o} will substitute later.
7009 Substitutes the names of all the output files, with spaces
7010 automatically placed around them. You should write spaces
7011 around the @samp{%o} as well or the results are undefined.
7012 @samp{%o} is for use in the specs for running the linker.
7013 Input files whose names have no recognized suffix are not compiled
7014 at all, but they are included among the output files, so they will
7018 Substitutes the suffix for object files. Note that this is
7019 handled specially when it immediately follows @samp{%g, %u, or %U},
7020 because of the need for those to form complete file names. The
7021 handling is such that @samp{%O} is treated exactly as if it had already
7022 been substituted, except that @samp{%g, %u, and %U} do not currently
7023 support additional @var{suffix} characters following @samp{%O} as they would
7024 following, for example, @samp{.o}.
7027 Substitutes the standard macro predefinitions for the
7028 current target machine. Use this when running @code{cpp}.
7031 Like @samp{%p}, but puts @samp{__} before and after the name of each
7032 predefined macro, except for macros that start with @samp{__} or with
7033 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
7037 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
7038 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
7039 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
7040 and @option{-imultilib} as necessary.
7043 Current argument is the name of a library or startup file of some sort.
7044 Search for that file in a standard list of directories and substitute
7045 the full name found.
7048 Print @var{str} as an error message. @var{str} is terminated by a newline.
7049 Use this when inconsistent options are detected.
7052 Substitute the contents of spec string @var{name} at this point.
7055 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
7057 @item %x@{@var{option}@}
7058 Accumulate an option for @samp{%X}.
7061 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
7065 Output the accumulated assembler options specified by @option{-Wa}.
7068 Output the accumulated preprocessor options specified by @option{-Wp}.
7071 Process the @code{asm} spec. This is used to compute the
7072 switches to be passed to the assembler.
7075 Process the @code{asm_final} spec. This is a spec string for
7076 passing switches to an assembler post-processor, if such a program is
7080 Process the @code{link} spec. This is the spec for computing the
7081 command line passed to the linker. Typically it will make use of the
7082 @samp{%L %G %S %D and %E} sequences.
7085 Dump out a @option{-L} option for each directory that GCC believes might
7086 contain startup files. If the target supports multilibs then the
7087 current multilib directory will be prepended to each of these paths.
7090 Process the @code{lib} spec. This is a spec string for deciding which
7091 libraries should be included on the command line to the linker.
7094 Process the @code{libgcc} spec. This is a spec string for deciding
7095 which GCC support library should be included on the command line to the linker.
7098 Process the @code{startfile} spec. This is a spec for deciding which
7099 object files should be the first ones passed to the linker. Typically
7100 this might be a file named @file{crt0.o}.
7103 Process the @code{endfile} spec. This is a spec string that specifies
7104 the last object files that will be passed to the linker.
7107 Process the @code{cpp} spec. This is used to construct the arguments
7108 to be passed to the C preprocessor.
7111 Process the @code{cc1} spec. This is used to construct the options to be
7112 passed to the actual C compiler (@samp{cc1}).
7115 Process the @code{cc1plus} spec. This is used to construct the options to be
7116 passed to the actual C++ compiler (@samp{cc1plus}).
7119 Substitute the variable part of a matched option. See below.
7120 Note that each comma in the substituted string is replaced by
7124 Remove all occurrences of @code{-S} from the command line. Note---this
7125 command is position dependent. @samp{%} commands in the spec string
7126 before this one will see @code{-S}, @samp{%} commands in the spec string
7127 after this one will not.
7129 @item %:@var{function}(@var{args})
7130 Call the named function @var{function}, passing it @var{args}.
7131 @var{args} is first processed as a nested spec string, then split
7132 into an argument vector in the usual fashion. The function returns
7133 a string which is processed as if it had appeared literally as part
7134 of the current spec.
7136 The following built-in spec functions are provided:
7139 @item @code{if-exists}
7140 The @code{if-exists} spec function takes one argument, an absolute
7141 pathname to a file. If the file exists, @code{if-exists} returns the
7142 pathname. Here is a small example of its usage:
7146 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
7149 @item @code{if-exists-else}
7150 The @code{if-exists-else} spec function is similar to the @code{if-exists}
7151 spec function, except that it takes two arguments. The first argument is
7152 an absolute pathname to a file. If the file exists, @code{if-exists-else}
7153 returns the pathname. If it does not exist, it returns the second argument.
7154 This way, @code{if-exists-else} can be used to select one file or another,
7155 based on the existence of the first. Here is a small example of its usage:
7159 crt0%O%s %:if-exists(crti%O%s) \
7160 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
7163 @item @code{replace-outfile}
7164 The @code{replace-outfile} spec function takes two arguments. It looks for the
7165 first argument in the outfiles array and replaces it with the second argument. Here
7166 is a small example of its usage:
7169 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
7175 Substitutes the @code{-S} switch, if that switch was given to GCC@.
7176 If that switch was not specified, this substitutes nothing. Note that
7177 the leading dash is omitted when specifying this option, and it is
7178 automatically inserted if the substitution is performed. Thus the spec
7179 string @samp{%@{foo@}} would match the command-line option @option{-foo}
7180 and would output the command line option @option{-foo}.
7182 @item %W@{@code{S}@}
7183 Like %@{@code{S}@} but mark last argument supplied within as a file to be
7186 @item %@{@code{S}*@}
7187 Substitutes all the switches specified to GCC whose names start
7188 with @code{-S}, but which also take an argument. This is used for
7189 switches like @option{-o}, @option{-D}, @option{-I}, etc.
7190 GCC considers @option{-o foo} as being
7191 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
7192 text, including the space. Thus two arguments would be generated.
7194 @item %@{@code{S}*&@code{T}*@}
7195 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
7196 (the order of @code{S} and @code{T} in the spec is not significant).
7197 There can be any number of ampersand-separated variables; for each the
7198 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
7200 @item %@{@code{S}:@code{X}@}
7201 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
7203 @item %@{!@code{S}:@code{X}@}
7204 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
7206 @item %@{@code{S}*:@code{X}@}
7207 Substitutes @code{X} if one or more switches whose names start with
7208 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
7209 once, no matter how many such switches appeared. However, if @code{%*}
7210 appears somewhere in @code{X}, then @code{X} will be substituted once
7211 for each matching switch, with the @code{%*} replaced by the part of
7212 that switch that matched the @code{*}.
7214 @item %@{.@code{S}:@code{X}@}
7215 Substitutes @code{X}, if processing a file with suffix @code{S}.
7217 @item %@{!.@code{S}:@code{X}@}
7218 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
7220 @item %@{@code{S}|@code{P}:@code{X}@}
7221 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
7222 This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
7223 although they have a stronger binding than the @samp{|}. If @code{%*}
7224 appears in @code{X}, all of the alternatives must be starred, and only
7225 the first matching alternative is substituted.
7227 For example, a spec string like this:
7230 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
7233 will output the following command-line options from the following input
7234 command-line options:
7239 -d fred.c -foo -baz -boggle
7240 -d jim.d -bar -baz -boggle
7243 @item %@{S:X; T:Y; :D@}
7245 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
7246 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
7247 be as many clauses as you need. This may be combined with @code{.},
7248 @code{!}, @code{|}, and @code{*} as needed.
7253 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
7254 construct may contain other nested @samp{%} constructs or spaces, or
7255 even newlines. They are processed as usual, as described above.
7256 Trailing white space in @code{X} is ignored. White space may also
7257 appear anywhere on the left side of the colon in these constructs,
7258 except between @code{.} or @code{*} and the corresponding word.
7260 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
7261 handled specifically in these constructs. If another value of
7262 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
7263 @option{-W} switch is found later in the command line, the earlier
7264 switch value is ignored, except with @{@code{S}*@} where @code{S} is
7265 just one letter, which passes all matching options.
7267 The character @samp{|} at the beginning of the predicate text is used to
7268 indicate that a command should be piped to the following command, but
7269 only if @option{-pipe} is specified.
7271 It is built into GCC which switches take arguments and which do not.
7272 (You might think it would be useful to generalize this to allow each
7273 compiler's spec to say which switches take arguments. But this cannot
7274 be done in a consistent fashion. GCC cannot even decide which input
7275 files have been specified without knowing which switches take arguments,
7276 and it must know which input files to compile in order to tell which
7279 GCC also knows implicitly that arguments starting in @option{-l} are to be
7280 treated as compiler output files, and passed to the linker in their
7281 proper position among the other output files.
7283 @c man begin OPTIONS
7285 @node Target Options
7286 @section Specifying Target Machine and Compiler Version
7287 @cindex target options
7288 @cindex cross compiling
7289 @cindex specifying machine version
7290 @cindex specifying compiler version and target machine
7291 @cindex compiler version, specifying
7292 @cindex target machine, specifying
7294 The usual way to run GCC is to run the executable called @file{gcc}, or
7295 @file{<machine>-gcc} when cross-compiling, or
7296 @file{<machine>-gcc-<version>} to run a version other than the one that
7297 was installed last. Sometimes this is inconvenient, so GCC provides
7298 options that will switch to another cross-compiler or version.
7301 @item -b @var{machine}
7303 The argument @var{machine} specifies the target machine for compilation.
7305 The value to use for @var{machine} is the same as was specified as the
7306 machine type when configuring GCC as a cross-compiler. For
7307 example, if a cross-compiler was configured with @samp{configure
7308 arm-elf}, meaning to compile for an arm processor with elf binaries,
7309 then you would specify @option{-b arm-elf} to run that cross compiler.
7310 Because there are other options beginning with @option{-b}, the
7311 configuration must contain a hyphen.
7313 @item -V @var{version}
7315 The argument @var{version} specifies which version of GCC to run.
7316 This is useful when multiple versions are installed. For example,
7317 @var{version} might be @samp{4.0}, meaning to run GCC version 4.0.
7320 The @option{-V} and @option{-b} options work by running the
7321 @file{<machine>-gcc-<version>} executable, so there's no real reason to
7322 use them if you can just run that directly.
7324 @node Submodel Options
7325 @section Hardware Models and Configurations
7326 @cindex submodel options
7327 @cindex specifying hardware config
7328 @cindex hardware models and configurations, specifying
7329 @cindex machine dependent options
7331 Earlier we discussed the standard option @option{-b} which chooses among
7332 different installed compilers for completely different target
7333 machines, such as VAX vs.@: 68000 vs.@: 80386.
7335 In addition, each of these target machine types can have its own
7336 special options, starting with @samp{-m}, to choose among various
7337 hardware models or configurations---for example, 68010 vs 68020,
7338 floating coprocessor or none. A single installed version of the
7339 compiler can compile for any model or configuration, according to the
7342 Some configurations of the compiler also support additional special
7343 options, usually for compatibility with other compilers on the same
7346 @c This list is ordered alphanumerically by subsection name.
7347 @c It should be the same order and spelling as these options are listed
7348 @c in Machine Dependent Options
7354 * Blackfin Options::
7358 * DEC Alpha Options::
7359 * DEC Alpha/VMS Options::
7361 * GNU/Linux Options::
7364 * i386 and x86-64 Options::
7377 * RS/6000 and PowerPC Options::
7378 * S/390 and zSeries Options::
7383 * System V Options::
7384 * TMS320C3x/C4x Options::
7388 * Xstormy16 Options::
7394 @subsection ARC Options
7397 These options are defined for ARC implementations:
7402 Compile code for little endian mode. This is the default.
7406 Compile code for big endian mode.
7409 @opindex mmangle-cpu
7410 Prepend the name of the cpu to all public symbol names.
7411 In multiple-processor systems, there are many ARC variants with different
7412 instruction and register set characteristics. This flag prevents code
7413 compiled for one cpu to be linked with code compiled for another.
7414 No facility exists for handling variants that are ``almost identical''.
7415 This is an all or nothing option.
7417 @item -mcpu=@var{cpu}
7419 Compile code for ARC variant @var{cpu}.
7420 Which variants are supported depend on the configuration.
7421 All variants support @option{-mcpu=base}, this is the default.
7423 @item -mtext=@var{text-section}
7424 @itemx -mdata=@var{data-section}
7425 @itemx -mrodata=@var{readonly-data-section}
7429 Put functions, data, and readonly data in @var{text-section},
7430 @var{data-section}, and @var{readonly-data-section} respectively
7431 by default. This can be overridden with the @code{section} attribute.
7432 @xref{Variable Attributes}.
7437 @subsection ARM Options
7440 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
7444 @item -mabi=@var{name}
7446 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
7447 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
7450 @opindex mapcs-frame
7451 Generate a stack frame that is compliant with the ARM Procedure Call
7452 Standard for all functions, even if this is not strictly necessary for
7453 correct execution of the code. Specifying @option{-fomit-frame-pointer}
7454 with this option will cause the stack frames not to be generated for
7455 leaf functions. The default is @option{-mno-apcs-frame}.
7459 This is a synonym for @option{-mapcs-frame}.
7462 @c not currently implemented
7463 @item -mapcs-stack-check
7464 @opindex mapcs-stack-check
7465 Generate code to check the amount of stack space available upon entry to
7466 every function (that actually uses some stack space). If there is
7467 insufficient space available then either the function
7468 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
7469 called, depending upon the amount of stack space required. The run time
7470 system is required to provide these functions. The default is
7471 @option{-mno-apcs-stack-check}, since this produces smaller code.
7473 @c not currently implemented
7475 @opindex mapcs-float
7476 Pass floating point arguments using the float point registers. This is
7477 one of the variants of the APCS@. This option is recommended if the
7478 target hardware has a floating point unit or if a lot of floating point
7479 arithmetic is going to be performed by the code. The default is
7480 @option{-mno-apcs-float}, since integer only code is slightly increased in
7481 size if @option{-mapcs-float} is used.
7483 @c not currently implemented
7484 @item -mapcs-reentrant
7485 @opindex mapcs-reentrant
7486 Generate reentrant, position independent code. The default is
7487 @option{-mno-apcs-reentrant}.
7490 @item -mthumb-interwork
7491 @opindex mthumb-interwork
7492 Generate code which supports calling between the ARM and Thumb
7493 instruction sets. Without this option the two instruction sets cannot
7494 be reliably used inside one program. The default is
7495 @option{-mno-thumb-interwork}, since slightly larger code is generated
7496 when @option{-mthumb-interwork} is specified.
7498 @item -mno-sched-prolog
7499 @opindex mno-sched-prolog
7500 Prevent the reordering of instructions in the function prolog, or the
7501 merging of those instruction with the instructions in the function's
7502 body. This means that all functions will start with a recognizable set
7503 of instructions (or in fact one of a choice from a small set of
7504 different function prologues), and this information can be used to
7505 locate the start if functions inside an executable piece of code. The
7506 default is @option{-msched-prolog}.
7509 @opindex mhard-float
7510 Generate output containing floating point instructions. This is the
7514 @opindex msoft-float
7515 Generate output containing library calls for floating point.
7516 @strong{Warning:} the requisite libraries are not available for all ARM
7517 targets. Normally the facilities of the machine's usual C compiler are
7518 used, but this cannot be done directly in cross-compilation. You must make
7519 your own arrangements to provide suitable library functions for
7522 @option{-msoft-float} changes the calling convention in the output file;
7523 therefore, it is only useful if you compile @emph{all} of a program with
7524 this option. In particular, you need to compile @file{libgcc.a}, the
7525 library that comes with GCC, with @option{-msoft-float} in order for
7528 @item -mfloat-abi=@var{name}
7530 Specifies which ABI to use for floating point values. Permissible values
7531 are: @samp{soft}, @samp{softfp} and @samp{hard}.
7533 @samp{soft} and @samp{hard} are equivalent to @option{-msoft-float}
7534 and @option{-mhard-float} respectively. @samp{softfp} allows the generation
7535 of floating point instructions, but still uses the soft-float calling
7538 @item -mlittle-endian
7539 @opindex mlittle-endian
7540 Generate code for a processor running in little-endian mode. This is
7541 the default for all standard configurations.
7544 @opindex mbig-endian
7545 Generate code for a processor running in big-endian mode; the default is
7546 to compile code for a little-endian processor.
7548 @item -mwords-little-endian
7549 @opindex mwords-little-endian
7550 This option only applies when generating code for big-endian processors.
7551 Generate code for a little-endian word order but a big-endian byte
7552 order. That is, a byte order of the form @samp{32107654}. Note: this
7553 option should only be used if you require compatibility with code for
7554 big-endian ARM processors generated by versions of the compiler prior to
7557 @item -mcpu=@var{name}
7559 This specifies the name of the target ARM processor. GCC uses this name
7560 to determine what kind of instructions it can emit when generating
7561 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
7562 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
7563 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
7564 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
7565 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
7566 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
7567 @samp{arm8}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
7568 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
7569 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
7570 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
7571 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
7572 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
7573 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
7574 @samp{arm1176jz-s}, @samp{arm1176jzf-s}, @samp{xscale}, @samp{iwmmxt},
7577 @itemx -mtune=@var{name}
7579 This option is very similar to the @option{-mcpu=} option, except that
7580 instead of specifying the actual target processor type, and hence
7581 restricting which instructions can be used, it specifies that GCC should
7582 tune the performance of the code as if the target were of the type
7583 specified in this option, but still choosing the instructions that it
7584 will generate based on the cpu specified by a @option{-mcpu=} option.
7585 For some ARM implementations better performance can be obtained by using
7588 @item -march=@var{name}
7590 This specifies the name of the target ARM architecture. GCC uses this
7591 name to determine what kind of instructions it can emit when generating
7592 assembly code. This option can be used in conjunction with or instead
7593 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
7594 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
7595 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6}, @samp{armv6j},
7596 @samp{iwmmxt}, @samp{ep9312}.
7598 @item -mfpu=@var{name}
7599 @itemx -mfpe=@var{number}
7600 @itemx -mfp=@var{number}
7604 This specifies what floating point hardware (or hardware emulation) is
7605 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
7606 @samp{fpe3}, @samp{maverick}, @samp{vfp}. @option{-mfp} and @option{-mfpe}
7607 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
7608 with older versions of GCC@.
7610 If @option{-msoft-float} is specified this specifies the format of
7611 floating point values.
7613 @item -mstructure-size-boundary=@var{n}
7614 @opindex mstructure-size-boundary
7615 The size of all structures and unions will be rounded up to a multiple
7616 of the number of bits set by this option. Permissible values are 8, 32
7617 and 64. The default value varies for different toolchains. For the COFF
7618 targeted toolchain the default value is 8. A value of 64 is only allowed
7619 if the underlying ABI supports it.
7621 Specifying the larger number can produce faster, more efficient code, but
7622 can also increase the size of the program. Different values are potentially
7623 incompatible. Code compiled with one value cannot necessarily expect to
7624 work with code or libraries compiled with another value, if they exchange
7625 information using structures or unions.
7627 @item -mabort-on-noreturn
7628 @opindex mabort-on-noreturn
7629 Generate a call to the function @code{abort} at the end of a
7630 @code{noreturn} function. It will be executed if the function tries to
7634 @itemx -mno-long-calls
7635 @opindex mlong-calls
7636 @opindex mno-long-calls
7637 Tells the compiler to perform function calls by first loading the
7638 address of the function into a register and then performing a subroutine
7639 call on this register. This switch is needed if the target function
7640 will lie outside of the 64 megabyte addressing range of the offset based
7641 version of subroutine call instruction.
7643 Even if this switch is enabled, not all function calls will be turned
7644 into long calls. The heuristic is that static functions, functions
7645 which have the @samp{short-call} attribute, functions that are inside
7646 the scope of a @samp{#pragma no_long_calls} directive and functions whose
7647 definitions have already been compiled within the current compilation
7648 unit, will not be turned into long calls. The exception to this rule is
7649 that weak function definitions, functions with the @samp{long-call}
7650 attribute or the @samp{section} attribute, and functions that are within
7651 the scope of a @samp{#pragma long_calls} directive, will always be
7652 turned into long calls.
7654 This feature is not enabled by default. Specifying
7655 @option{-mno-long-calls} will restore the default behavior, as will
7656 placing the function calls within the scope of a @samp{#pragma
7657 long_calls_off} directive. Note these switches have no effect on how
7658 the compiler generates code to handle function calls via function
7661 @item -mnop-fun-dllimport
7662 @opindex mnop-fun-dllimport
7663 Disable support for the @code{dllimport} attribute.
7665 @item -msingle-pic-base
7666 @opindex msingle-pic-base
7667 Treat the register used for PIC addressing as read-only, rather than
7668 loading it in the prologue for each function. The run-time system is
7669 responsible for initializing this register with an appropriate value
7670 before execution begins.
7672 @item -mpic-register=@var{reg}
7673 @opindex mpic-register
7674 Specify the register to be used for PIC addressing. The default is R10
7675 unless stack-checking is enabled, when R9 is used.
7677 @item -mcirrus-fix-invalid-insns
7678 @opindex mcirrus-fix-invalid-insns
7679 @opindex mno-cirrus-fix-invalid-insns
7680 Insert NOPs into the instruction stream to in order to work around
7681 problems with invalid Maverick instruction combinations. This option
7682 is only valid if the @option{-mcpu=ep9312} option has been used to
7683 enable generation of instructions for the Cirrus Maverick floating
7684 point co-processor. This option is not enabled by default, since the
7685 problem is only present in older Maverick implementations. The default
7686 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
7689 @item -mpoke-function-name
7690 @opindex mpoke-function-name
7691 Write the name of each function into the text section, directly
7692 preceding the function prologue. The generated code is similar to this:
7696 .ascii "arm_poke_function_name", 0
7699 .word 0xff000000 + (t1 - t0)
7700 arm_poke_function_name
7702 stmfd sp!, @{fp, ip, lr, pc@}
7706 When performing a stack backtrace, code can inspect the value of
7707 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
7708 location @code{pc - 12} and the top 8 bits are set, then we know that
7709 there is a function name embedded immediately preceding this location
7710 and has length @code{((pc[-3]) & 0xff000000)}.
7714 Generate code for the 16-bit Thumb instruction set. The default is to
7715 use the 32-bit ARM instruction set.
7718 @opindex mtpcs-frame
7719 Generate a stack frame that is compliant with the Thumb Procedure Call
7720 Standard for all non-leaf functions. (A leaf function is one that does
7721 not call any other functions.) The default is @option{-mno-tpcs-frame}.
7723 @item -mtpcs-leaf-frame
7724 @opindex mtpcs-leaf-frame
7725 Generate a stack frame that is compliant with the Thumb Procedure Call
7726 Standard for all leaf functions. (A leaf function is one that does
7727 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
7729 @item -mcallee-super-interworking
7730 @opindex mcallee-super-interworking
7731 Gives all externally visible functions in the file being compiled an ARM
7732 instruction set header which switches to Thumb mode before executing the
7733 rest of the function. This allows these functions to be called from
7734 non-interworking code.
7736 @item -mcaller-super-interworking
7737 @opindex mcaller-super-interworking
7738 Allows calls via function pointers (including virtual functions) to
7739 execute correctly regardless of whether the target code has been
7740 compiled for interworking or not. There is a small overhead in the cost
7741 of executing a function pointer if this option is enabled.
7743 @item -mtp=@var{name}
7745 Specify the access model for the thread local storage pointer. The valid
7746 models are @option{soft}, which generates calls to @code{__aeabi_read_tp},
7747 @option{cp15}, which fetches the thread pointer from @code{cp15} directly
7748 (supported in the arm6k architecture), and @option{auto}, which uses the
7749 best available method for the selected processor. The default setting is
7755 @subsection AVR Options
7758 These options are defined for AVR implementations:
7761 @item -mmcu=@var{mcu}
7763 Specify ATMEL AVR instruction set or MCU type.
7765 Instruction set avr1 is for the minimal AVR core, not supported by the C
7766 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
7767 attiny11, attiny12, attiny15, attiny28).
7769 Instruction set avr2 (default) is for the classic AVR core with up to
7770 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
7771 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
7772 at90c8534, at90s8535).
7774 Instruction set avr3 is for the classic AVR core with up to 128K program
7775 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
7777 Instruction set avr4 is for the enhanced AVR core with up to 8K program
7778 memory space (MCU types: atmega8, atmega83, atmega85).
7780 Instruction set avr5 is for the enhanced AVR core with up to 128K program
7781 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
7782 atmega64, atmega128, at43usb355, at94k).
7786 Output instruction sizes to the asm file.
7788 @item -minit-stack=@var{N}
7789 @opindex minit-stack
7790 Specify the initial stack address, which may be a symbol or numeric value,
7791 @samp{__stack} is the default.
7793 @item -mno-interrupts
7794 @opindex mno-interrupts
7795 Generated code is not compatible with hardware interrupts.
7796 Code size will be smaller.
7798 @item -mcall-prologues
7799 @opindex mcall-prologues
7800 Functions prologues/epilogues expanded as call to appropriate
7801 subroutines. Code size will be smaller.
7803 @item -mno-tablejump
7804 @opindex mno-tablejump
7805 Do not generate tablejump insns which sometimes increase code size.
7808 @opindex mtiny-stack
7809 Change only the low 8 bits of the stack pointer.
7813 Assume int to be 8 bit integer. This affects the sizes of all types: A
7814 char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
7815 and long long will be 4 bytes. Please note that this option does not
7816 comply to the C standards, but it will provide you with smaller code
7820 @node Blackfin Options
7821 @subsection Blackfin Options
7822 @cindex Blackfin Options
7825 @item -momit-leaf-frame-pointer
7826 @opindex momit-leaf-frame-pointer
7827 Don't keep the frame pointer in a register for leaf functions. This
7828 avoids the instructions to save, set up and restore frame pointers and
7829 makes an extra register available in leaf functions. The option
7830 @option{-fomit-frame-pointer} removes the frame pointer for all functions
7831 which might make debugging harder.
7833 @item -mspecld-anomaly
7834 @opindex mspecld-anomaly
7835 When enabled, the compiler will ensure that the generated code does not
7836 contain speculative loads after jump instructions. This option is enabled
7839 @item -mno-specld-anomaly
7840 @opindex mno-specld-anomaly
7841 Don't generate extra code to prevent speculative loads from occurring.
7843 @item -mcsync-anomaly
7844 @opindex mcsync-anomaly
7845 When enabled, the compiler will ensure that the generated code does not
7846 contain CSYNC or SSYNC instructions too soon after conditional branches.
7847 This option is enabled by default.
7849 @item -mno-csync-anomaly
7850 @opindex mno-csync-anomaly
7851 Don't generate extra code to prevent CSYNC or SSYNC instructions from
7852 occurring too soon after a conditional branch.
7856 When enabled, the compiler is free to take advantage of the knowledge that
7857 the entire program fits into the low 64k of memory.
7860 @opindex mno-low-64k
7861 Assume that the program is arbitrarily large. This is the default.
7863 @item -mstack-check-l1
7864 @opindex mstack-check-l1
7865 Do stack checking using information placed into L1 scratchpad memory by the
7868 @item -mid-shared-library
7869 @opindex mid-shared-library
7870 Generate code that supports shared libraries via the library ID method.
7871 This allows for execute in place and shared libraries in an environment
7872 without virtual memory management. This option implies @option{-fPIC}.
7874 @item -mno-id-shared-library
7875 @opindex mno-id-shared-library
7876 Generate code that doesn't assume ID based shared libraries are being used.
7877 This is the default.
7879 @item -mleaf-id-shared-library
7880 @opindex mleaf-id-shared-library
7881 Generate code that supports shared libraries via the library ID method,
7882 but assumes that this library or executable won't link against any other
7883 ID shared libraries. That allows the compiler to use faster code for jumps
7886 @item -mno-leaf-id-shared-library
7887 @opindex mno-leaf-id-shared-library
7888 Do not assume that the code being compiled won't link against any ID shared
7889 libraries. Slower code will be generated for jump and call insns.
7891 @item -mshared-library-id=n
7892 @opindex mshared-library-id
7893 Specified the identification number of the ID based shared library being
7894 compiled. Specifying a value of 0 will generate more compact code, specifying
7895 other values will force the allocation of that number to the current
7896 library but is no more space or time efficient than omitting this option.
7900 Generate code that allows the data segment to be located in a different
7901 area of memory from the text segment. This allows for execute in place in
7902 an environment without virtual memory management by eliminating relocations
7903 against the text section.
7906 @opindex mno-sep-data
7907 Generate code that assumes that the data segment follows the text segment.
7908 This is the default.
7911 @itemx -mno-long-calls
7912 @opindex mlong-calls
7913 @opindex mno-long-calls
7914 Tells the compiler to perform function calls by first loading the
7915 address of the function into a register and then performing a subroutine
7916 call on this register. This switch is needed if the target function
7917 will lie outside of the 24 bit addressing range of the offset based
7918 version of subroutine call instruction.
7920 This feature is not enabled by default. Specifying
7921 @option{-mno-long-calls} will restore the default behavior. Note these
7922 switches have no effect on how the compiler generates code to handle
7923 function calls via function pointers.
7927 @subsection CRIS Options
7928 @cindex CRIS Options
7930 These options are defined specifically for the CRIS ports.
7933 @item -march=@var{architecture-type}
7934 @itemx -mcpu=@var{architecture-type}
7937 Generate code for the specified architecture. The choices for
7938 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
7939 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
7940 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
7943 @item -mtune=@var{architecture-type}
7945 Tune to @var{architecture-type} everything applicable about the generated
7946 code, except for the ABI and the set of available instructions. The
7947 choices for @var{architecture-type} are the same as for
7948 @option{-march=@var{architecture-type}}.
7950 @item -mmax-stack-frame=@var{n}
7951 @opindex mmax-stack-frame
7952 Warn when the stack frame of a function exceeds @var{n} bytes.
7954 @item -melinux-stacksize=@var{n}
7955 @opindex melinux-stacksize
7956 Only available with the @samp{cris-axis-aout} target. Arranges for
7957 indications in the program to the kernel loader that the stack of the
7958 program should be set to @var{n} bytes.
7964 The options @option{-metrax4} and @option{-metrax100} are synonyms for
7965 @option{-march=v3} and @option{-march=v8} respectively.
7967 @item -mmul-bug-workaround
7968 @itemx -mno-mul-bug-workaround
7969 @opindex mmul-bug-workaround
7970 @opindex mno-mul-bug-workaround
7971 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
7972 models where it applies. This option is active by default.
7976 Enable CRIS-specific verbose debug-related information in the assembly
7977 code. This option also has the effect to turn off the @samp{#NO_APP}
7978 formatted-code indicator to the assembler at the beginning of the
7983 Do not use condition-code results from previous instruction; always emit
7984 compare and test instructions before use of condition codes.
7986 @item -mno-side-effects
7987 @opindex mno-side-effects
7988 Do not emit instructions with side-effects in addressing modes other than
7992 @itemx -mno-stack-align
7994 @itemx -mno-data-align
7995 @itemx -mconst-align
7996 @itemx -mno-const-align
7997 @opindex mstack-align
7998 @opindex mno-stack-align
7999 @opindex mdata-align
8000 @opindex mno-data-align
8001 @opindex mconst-align
8002 @opindex mno-const-align
8003 These options (no-options) arranges (eliminate arrangements) for the
8004 stack-frame, individual data and constants to be aligned for the maximum
8005 single data access size for the chosen CPU model. The default is to
8006 arrange for 32-bit alignment. ABI details such as structure layout are
8007 not affected by these options.
8015 Similar to the stack- data- and const-align options above, these options
8016 arrange for stack-frame, writable data and constants to all be 32-bit,
8017 16-bit or 8-bit aligned. The default is 32-bit alignment.
8019 @item -mno-prologue-epilogue
8020 @itemx -mprologue-epilogue
8021 @opindex mno-prologue-epilogue
8022 @opindex mprologue-epilogue
8023 With @option{-mno-prologue-epilogue}, the normal function prologue and
8024 epilogue that sets up the stack-frame are omitted and no return
8025 instructions or return sequences are generated in the code. Use this
8026 option only together with visual inspection of the compiled code: no
8027 warnings or errors are generated when call-saved registers must be saved,
8028 or storage for local variable needs to be allocated.
8034 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
8035 instruction sequences that load addresses for functions from the PLT part
8036 of the GOT rather than (traditional on other architectures) calls to the
8037 PLT@. The default is @option{-mgotplt}.
8041 Legacy no-op option only recognized with the cris-axis-aout target.
8045 Legacy no-op option only recognized with the cris-axis-elf and
8046 cris-axis-linux-gnu targets.
8050 Only recognized with the cris-axis-aout target, where it selects a
8051 GNU/linux-like multilib, include files and instruction set for
8056 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
8060 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
8061 to link with input-output functions from a simulator library. Code,
8062 initialized data and zero-initialized data are allocated consecutively.
8066 Like @option{-sim}, but pass linker options to locate initialized data at
8067 0x40000000 and zero-initialized data at 0x80000000.
8071 @subsection CRX Options
8074 These options are defined specifically for the CRX ports.
8080 Enable the use of multiply-accumulate instructions. Disabled by default.
8084 Push instructions will be used to pass outgoing arguments when functions
8085 are called. Enabled by default.
8088 @node Darwin Options
8089 @subsection Darwin Options
8090 @cindex Darwin options
8092 These options are defined for all architectures running the Darwin operating
8095 FSF GCC on Darwin does not create ``fat'' object files; it will create
8096 an object file for the single architecture that it was built to
8097 target. Apple's GCC on Darwin does create ``fat'' files if multiple
8098 @option{-arch} options are used; it does so by running the compiler or
8099 linker multiple times and joining the results together with
8102 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
8103 @samp{i686}) is determined by the flags that specify the ISA
8104 that GCC is targetting, like @option{-mcpu} or @option{-march}. The
8105 @option{-force_cpusubtype_ALL} option can be used to override this.
8107 The Darwin tools vary in their behavior when presented with an ISA
8108 mismatch. The assembler, @file{as}, will only permit instructions to
8109 be used that are valid for the subtype of the file it is generating,
8110 so you cannot put 64-bit instructions in an @samp{ppc750} object file.
8111 The linker for shared libraries, @file{/usr/bin/libtool}, will fail
8112 and print an error if asked to create a shared library with a less
8113 restrictive subtype than its input files (for instance, trying to put
8114 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
8115 for executables, @file{ld}, will quietly give the executable the most
8116 restrictive subtype of any of its input files.
8121 Add the framework directory @var{dir} to the head of the list of
8122 directories to be searched for header files. These directories are
8123 interleaved with those specified by @option{-I} options and are
8124 scanned in a left-to-right order.
8126 A framework directory is a directory with frameworks in it. A
8127 framework is a directory with a @samp{"Headers"} and/or
8128 @samp{"PrivateHeaders"} directory contained directly in it that ends
8129 in @samp{".framework"}. The name of a framework is the name of this
8130 directory excluding the @samp{".framework"}. Headers associated with
8131 the framework are found in one of those two directories, with
8132 @samp{"Headers"} being searched first. A subframework is a framework
8133 directory that is in a framework's @samp{"Frameworks"} directory.
8134 Includes of subframework headers can only appear in a header of a
8135 framework that contains the subframework, or in a sibling subframework
8136 header. Two subframeworks are siblings if they occur in the same
8137 framework. A subframework should not have the same name as a
8138 framework, a warning will be issued if this is violated. Currently a
8139 subframework cannot have subframeworks, in the future, the mechanism
8140 may be extended to support this. The standard frameworks can be found
8141 in @samp{"/System/Library/Frameworks"} and
8142 @samp{"/Library/Frameworks"}. An example include looks like
8143 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
8144 the name of the framework and header.h is found in the
8145 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
8149 Emit debugging information for symbols that are used. For STABS
8150 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
8151 This is by default ON@.
8155 Emit debugging information for all symbols and types.
8157 @item -mmacosx-version-min=@var{version}
8158 The earliest version of MacOS X that this executable will run on
8159 is @var{version}. Typical values of @var{version} include @code{10.1},
8160 @code{10.2}, and @code{10.3.9}.
8162 The default for this option is to make choices that seem to be most
8167 Enable kernel development mode. The @option{-mkernel} option sets
8168 @option{-static}, @option{-fno-common}, @option{-fno-cxa-atexit},
8169 @option{-fno-exceptions}, @option{-fno-non-call-exceptions},
8170 @option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where
8171 applicable. This mode also sets @option{-mno-altivec},
8172 @option{-msoft-float}, @option{-fno-builtin} and
8173 @option{-mlong-branch} for PowerPC targets.
8175 @item -mone-byte-bool
8176 @opindex -mone-byte-bool
8177 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
8178 By default @samp{sizeof(bool)} is @samp{4} when compiling for
8179 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
8180 option has no effect on x86.
8182 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
8183 to generate code that is not binary compatible with code generated
8184 without that switch. Using this switch may require recompiling all
8185 other modules in a program, including system libraries. Use this
8186 switch to conform to a non-default data model.
8188 @item -mfix-and-continue
8189 @itemx -ffix-and-continue
8190 @itemx -findirect-data
8191 @opindex mfix-and-continue
8192 @opindex ffix-and-continue
8193 @opindex findirect-data
8194 Generate code suitable for fast turn around development. Needed to
8195 enable gdb to dynamically load @code{.o} files into already running
8196 programs. @option{-findirect-data} and @option{-ffix-and-continue}
8197 are provided for backwards compatibility.
8201 Loads all members of static archive libraries.
8202 See man ld(1) for more information.
8204 @item -arch_errors_fatal
8205 @opindex arch_errors_fatal
8206 Cause the errors having to do with files that have the wrong architecture
8210 @opindex bind_at_load
8211 Causes the output file to be marked such that the dynamic linker will
8212 bind all undefined references when the file is loaded or launched.
8216 Produce a Mach-o bundle format file.
8217 See man ld(1) for more information.
8219 @item -bundle_loader @var{executable}
8220 @opindex bundle_loader
8221 This option specifies the @var{executable} that will be loading the build
8222 output file being linked. See man ld(1) for more information.
8225 @opindex -dynamiclib
8226 When passed this option, GCC will produce a dynamic library instead of
8227 an executable when linking, using the Darwin @file{libtool} command.
8229 @item -force_cpusubtype_ALL
8230 @opindex -force_cpusubtype_ALL
8231 This causes GCC's output file to have the @var{ALL} subtype, instead of
8232 one controlled by the @option{-mcpu} or @option{-march} option.
8234 @item -allowable_client @var{client_name}
8236 @itemx -compatibility_version
8237 @itemx -current_version
8239 @itemx -dependency-file
8241 @itemx -dylinker_install_name
8243 @itemx -exported_symbols_list
8245 @itemx -flat_namespace
8246 @itemx -force_flat_namespace
8247 @itemx -headerpad_max_install_names
8250 @itemx -install_name
8251 @itemx -keep_private_externs
8252 @itemx -multi_module
8253 @itemx -multiply_defined
8254 @itemx -multiply_defined_unused
8256 @itemx -no_dead_strip_inits_and_terms
8257 @itemx -nofixprebinding
8260 @itemx -noseglinkedit
8261 @itemx -pagezero_size
8263 @itemx -prebind_all_twolevel_modules
8264 @itemx -private_bundle
8265 @itemx -read_only_relocs
8267 @itemx -sectobjectsymbols
8271 @itemx -sectobjectsymbols
8274 @itemx -segs_read_only_addr
8275 @itemx -segs_read_write_addr
8276 @itemx -seg_addr_table
8277 @itemx -seg_addr_table_filename
8280 @itemx -segs_read_only_addr
8281 @itemx -segs_read_write_addr
8282 @itemx -single_module
8285 @itemx -sub_umbrella
8286 @itemx -twolevel_namespace
8289 @itemx -unexported_symbols_list
8290 @itemx -weak_reference_mismatches
8293 @opindex allowable_client
8294 @opindex client_name
8295 @opindex compatibility_version
8296 @opindex current_version
8298 @opindex dependency-file
8300 @opindex dylinker_install_name
8302 @opindex exported_symbols_list
8304 @opindex flat_namespace
8305 @opindex force_flat_namespace
8306 @opindex headerpad_max_install_names
8309 @opindex install_name
8310 @opindex keep_private_externs
8311 @opindex multi_module
8312 @opindex multiply_defined
8313 @opindex multiply_defined_unused
8315 @opindex no_dead_strip_inits_and_terms
8316 @opindex nofixprebinding
8317 @opindex nomultidefs
8319 @opindex noseglinkedit
8320 @opindex pagezero_size
8322 @opindex prebind_all_twolevel_modules
8323 @opindex private_bundle
8324 @opindex read_only_relocs
8326 @opindex sectobjectsymbols
8330 @opindex sectobjectsymbols
8333 @opindex segs_read_only_addr
8334 @opindex segs_read_write_addr
8335 @opindex seg_addr_table
8336 @opindex seg_addr_table_filename
8337 @opindex seglinkedit
8339 @opindex segs_read_only_addr
8340 @opindex segs_read_write_addr
8341 @opindex single_module
8343 @opindex sub_library
8344 @opindex sub_umbrella
8345 @opindex twolevel_namespace
8348 @opindex unexported_symbols_list
8349 @opindex weak_reference_mismatches
8350 @opindex whatsloaded
8352 These options are passed to the Darwin linker. The Darwin linker man page
8353 describes them in detail.
8356 @node DEC Alpha Options
8357 @subsection DEC Alpha Options
8359 These @samp{-m} options are defined for the DEC Alpha implementations:
8362 @item -mno-soft-float
8364 @opindex mno-soft-float
8365 @opindex msoft-float
8366 Use (do not use) the hardware floating-point instructions for
8367 floating-point operations. When @option{-msoft-float} is specified,
8368 functions in @file{libgcc.a} will be used to perform floating-point
8369 operations. Unless they are replaced by routines that emulate the
8370 floating-point operations, or compiled in such a way as to call such
8371 emulations routines, these routines will issue floating-point
8372 operations. If you are compiling for an Alpha without floating-point
8373 operations, you must ensure that the library is built so as not to call
8376 Note that Alpha implementations without floating-point operations are
8377 required to have floating-point registers.
8382 @opindex mno-fp-regs
8383 Generate code that uses (does not use) the floating-point register set.
8384 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
8385 register set is not used, floating point operands are passed in integer
8386 registers as if they were integers and floating-point results are passed
8387 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
8388 so any function with a floating-point argument or return value called by code
8389 compiled with @option{-mno-fp-regs} must also be compiled with that
8392 A typical use of this option is building a kernel that does not use,
8393 and hence need not save and restore, any floating-point registers.
8397 The Alpha architecture implements floating-point hardware optimized for
8398 maximum performance. It is mostly compliant with the IEEE floating
8399 point standard. However, for full compliance, software assistance is
8400 required. This option generates code fully IEEE compliant code
8401 @emph{except} that the @var{inexact-flag} is not maintained (see below).
8402 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
8403 defined during compilation. The resulting code is less efficient but is
8404 able to correctly support denormalized numbers and exceptional IEEE
8405 values such as not-a-number and plus/minus infinity. Other Alpha
8406 compilers call this option @option{-ieee_with_no_inexact}.
8408 @item -mieee-with-inexact
8409 @opindex mieee-with-inexact
8410 This is like @option{-mieee} except the generated code also maintains
8411 the IEEE @var{inexact-flag}. Turning on this option causes the
8412 generated code to implement fully-compliant IEEE math. In addition to
8413 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
8414 macro. On some Alpha implementations the resulting code may execute
8415 significantly slower than the code generated by default. Since there is
8416 very little code that depends on the @var{inexact-flag}, you should
8417 normally not specify this option. Other Alpha compilers call this
8418 option @option{-ieee_with_inexact}.
8420 @item -mfp-trap-mode=@var{trap-mode}
8421 @opindex mfp-trap-mode
8422 This option controls what floating-point related traps are enabled.
8423 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
8424 The trap mode can be set to one of four values:
8428 This is the default (normal) setting. The only traps that are enabled
8429 are the ones that cannot be disabled in software (e.g., division by zero
8433 In addition to the traps enabled by @samp{n}, underflow traps are enabled
8437 Like @samp{u}, but the instructions are marked to be safe for software
8438 completion (see Alpha architecture manual for details).
8441 Like @samp{su}, but inexact traps are enabled as well.
8444 @item -mfp-rounding-mode=@var{rounding-mode}
8445 @opindex mfp-rounding-mode
8446 Selects the IEEE rounding mode. Other Alpha compilers call this option
8447 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
8452 Normal IEEE rounding mode. Floating point numbers are rounded towards
8453 the nearest machine number or towards the even machine number in case
8457 Round towards minus infinity.
8460 Chopped rounding mode. Floating point numbers are rounded towards zero.
8463 Dynamic rounding mode. A field in the floating point control register
8464 (@var{fpcr}, see Alpha architecture reference manual) controls the
8465 rounding mode in effect. The C library initializes this register for
8466 rounding towards plus infinity. Thus, unless your program modifies the
8467 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
8470 @item -mtrap-precision=@var{trap-precision}
8471 @opindex mtrap-precision
8472 In the Alpha architecture, floating point traps are imprecise. This
8473 means without software assistance it is impossible to recover from a
8474 floating trap and program execution normally needs to be terminated.
8475 GCC can generate code that can assist operating system trap handlers
8476 in determining the exact location that caused a floating point trap.
8477 Depending on the requirements of an application, different levels of
8478 precisions can be selected:
8482 Program precision. This option is the default and means a trap handler
8483 can only identify which program caused a floating point exception.
8486 Function precision. The trap handler can determine the function that
8487 caused a floating point exception.
8490 Instruction precision. The trap handler can determine the exact
8491 instruction that caused a floating point exception.
8494 Other Alpha compilers provide the equivalent options called
8495 @option{-scope_safe} and @option{-resumption_safe}.
8497 @item -mieee-conformant
8498 @opindex mieee-conformant
8499 This option marks the generated code as IEEE conformant. You must not
8500 use this option unless you also specify @option{-mtrap-precision=i} and either
8501 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
8502 is to emit the line @samp{.eflag 48} in the function prologue of the
8503 generated assembly file. Under DEC Unix, this has the effect that
8504 IEEE-conformant math library routines will be linked in.
8506 @item -mbuild-constants
8507 @opindex mbuild-constants
8508 Normally GCC examines a 32- or 64-bit integer constant to
8509 see if it can construct it from smaller constants in two or three
8510 instructions. If it cannot, it will output the constant as a literal and
8511 generate code to load it from the data segment at runtime.
8513 Use this option to require GCC to construct @emph{all} integer constants
8514 using code, even if it takes more instructions (the maximum is six).
8516 You would typically use this option to build a shared library dynamic
8517 loader. Itself a shared library, it must relocate itself in memory
8518 before it can find the variables and constants in its own data segment.
8524 Select whether to generate code to be assembled by the vendor-supplied
8525 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
8543 Indicate whether GCC should generate code to use the optional BWX,
8544 CIX, FIX and MAX instruction sets. The default is to use the instruction
8545 sets supported by the CPU type specified via @option{-mcpu=} option or that
8546 of the CPU on which GCC was built if none was specified.
8551 @opindex mfloat-ieee
8552 Generate code that uses (does not use) VAX F and G floating point
8553 arithmetic instead of IEEE single and double precision.
8555 @item -mexplicit-relocs
8556 @itemx -mno-explicit-relocs
8557 @opindex mexplicit-relocs
8558 @opindex mno-explicit-relocs
8559 Older Alpha assemblers provided no way to generate symbol relocations
8560 except via assembler macros. Use of these macros does not allow
8561 optimal instruction scheduling. GNU binutils as of version 2.12
8562 supports a new syntax that allows the compiler to explicitly mark
8563 which relocations should apply to which instructions. This option
8564 is mostly useful for debugging, as GCC detects the capabilities of
8565 the assembler when it is built and sets the default accordingly.
8569 @opindex msmall-data
8570 @opindex mlarge-data
8571 When @option{-mexplicit-relocs} is in effect, static data is
8572 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
8573 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
8574 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
8575 16-bit relocations off of the @code{$gp} register. This limits the
8576 size of the small data area to 64KB, but allows the variables to be
8577 directly accessed via a single instruction.
8579 The default is @option{-mlarge-data}. With this option the data area
8580 is limited to just below 2GB@. Programs that require more than 2GB of
8581 data must use @code{malloc} or @code{mmap} to allocate the data in the
8582 heap instead of in the program's data segment.
8584 When generating code for shared libraries, @option{-fpic} implies
8585 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
8589 @opindex msmall-text
8590 @opindex mlarge-text
8591 When @option{-msmall-text} is used, the compiler assumes that the
8592 code of the entire program (or shared library) fits in 4MB, and is
8593 thus reachable with a branch instruction. When @option{-msmall-data}
8594 is used, the compiler can assume that all local symbols share the
8595 same @code{$gp} value, and thus reduce the number of instructions
8596 required for a function call from 4 to 1.
8598 The default is @option{-mlarge-text}.
8600 @item -mcpu=@var{cpu_type}
8602 Set the instruction set and instruction scheduling parameters for
8603 machine type @var{cpu_type}. You can specify either the @samp{EV}
8604 style name or the corresponding chip number. GCC supports scheduling
8605 parameters for the EV4, EV5 and EV6 family of processors and will
8606 choose the default values for the instruction set from the processor
8607 you specify. If you do not specify a processor type, GCC will default
8608 to the processor on which the compiler was built.
8610 Supported values for @var{cpu_type} are
8616 Schedules as an EV4 and has no instruction set extensions.
8620 Schedules as an EV5 and has no instruction set extensions.
8624 Schedules as an EV5 and supports the BWX extension.
8629 Schedules as an EV5 and supports the BWX and MAX extensions.
8633 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
8637 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
8640 @item -mtune=@var{cpu_type}
8642 Set only the instruction scheduling parameters for machine type
8643 @var{cpu_type}. The instruction set is not changed.
8645 @item -mmemory-latency=@var{time}
8646 @opindex mmemory-latency
8647 Sets the latency the scheduler should assume for typical memory
8648 references as seen by the application. This number is highly
8649 dependent on the memory access patterns used by the application
8650 and the size of the external cache on the machine.
8652 Valid options for @var{time} are
8656 A decimal number representing clock cycles.
8662 The compiler contains estimates of the number of clock cycles for
8663 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
8664 (also called Dcache, Scache, and Bcache), as well as to main memory.
8665 Note that L3 is only valid for EV5.
8670 @node DEC Alpha/VMS Options
8671 @subsection DEC Alpha/VMS Options
8673 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
8676 @item -mvms-return-codes
8677 @opindex mvms-return-codes
8678 Return VMS condition codes from main. The default is to return POSIX
8679 style condition (e.g.@ error) codes.
8683 @subsection FRV Options
8690 Only use the first 32 general purpose registers.
8695 Use all 64 general purpose registers.
8700 Use only the first 32 floating point registers.
8705 Use all 64 floating point registers
8708 @opindex mhard-float
8710 Use hardware instructions for floating point operations.
8713 @opindex msoft-float
8715 Use library routines for floating point operations.
8720 Dynamically allocate condition code registers.
8725 Do not try to dynamically allocate condition code registers, only
8726 use @code{icc0} and @code{fcc0}.
8731 Change ABI to use double word insns.
8736 Do not use double word instructions.
8741 Use floating point double instructions.
8746 Do not use floating point double instructions.
8751 Use media instructions.
8756 Do not use media instructions.
8761 Use multiply and add/subtract instructions.
8766 Do not use multiply and add/subtract instructions.
8771 Select the FDPIC ABI, that uses function descriptors to represent
8772 pointers to functions. Without any PIC/PIE-related options, it
8773 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
8774 assumes GOT entries and small data are within a 12-bit range from the
8775 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
8776 are computed with 32 bits.
8779 @opindex minline-plt
8781 Enable inlining of PLT entries in function calls to functions that are
8782 not known to bind locally. It has no effect without @option{-mfdpic}.
8783 It's enabled by default if optimizing for speed and compiling for
8784 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
8785 optimization option such as @option{-O3} or above is present in the
8791 Assume a large TLS segment when generating thread-local code.
8796 Do not assume a large TLS segment when generating thread-local code.
8801 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
8802 that is known to be in read-only sections. It's enabled by default,
8803 except for @option{-fpic} or @option{-fpie}: even though it may help
8804 make the global offset table smaller, it trades 1 instruction for 4.
8805 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
8806 one of which may be shared by multiple symbols, and it avoids the need
8807 for a GOT entry for the referenced symbol, so it's more likely to be a
8808 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
8810 @item -multilib-library-pic
8811 @opindex multilib-library-pic
8813 Link with the (library, not FD) pic libraries. It's implied by
8814 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
8815 @option{-fpic} without @option{-mfdpic}. You should never have to use
8821 Follow the EABI requirement of always creating a frame pointer whenever
8822 a stack frame is allocated. This option is enabled by default and can
8823 be disabled with @option{-mno-linked-fp}.
8826 @opindex mlong-calls
8828 Use indirect addressing to call functions outside the current
8829 compilation unit. This allows the functions to be placed anywhere
8830 within the 32-bit address space.
8832 @item -malign-labels
8833 @opindex malign-labels
8835 Try to align labels to an 8-byte boundary by inserting nops into the
8836 previous packet. This option only has an effect when VLIW packing
8837 is enabled. It doesn't create new packets; it merely adds nops to
8841 @opindex mlibrary-pic
8843 Generate position-independent EABI code.
8848 Use only the first four media accumulator registers.
8853 Use all eight media accumulator registers.
8858 Pack VLIW instructions.
8863 Do not pack VLIW instructions.
8868 Do not mark ABI switches in e_flags.
8873 Enable the use of conditional-move instructions (default).
8875 This switch is mainly for debugging the compiler and will likely be removed
8876 in a future version.
8878 @item -mno-cond-move
8879 @opindex mno-cond-move
8881 Disable the use of conditional-move instructions.
8883 This switch is mainly for debugging the compiler and will likely be removed
8884 in a future version.
8889 Enable the use of conditional set instructions (default).
8891 This switch is mainly for debugging the compiler and will likely be removed
8892 in a future version.
8897 Disable the use of conditional set instructions.
8899 This switch is mainly for debugging the compiler and will likely be removed
8900 in a future version.
8905 Enable the use of conditional execution (default).
8907 This switch is mainly for debugging the compiler and will likely be removed
8908 in a future version.
8910 @item -mno-cond-exec
8911 @opindex mno-cond-exec
8913 Disable the use of conditional execution.
8915 This switch is mainly for debugging the compiler and will likely be removed
8916 in a future version.
8919 @opindex mvliw-branch
8921 Run a pass to pack branches into VLIW instructions (default).
8923 This switch is mainly for debugging the compiler and will likely be removed
8924 in a future version.
8926 @item -mno-vliw-branch
8927 @opindex mno-vliw-branch
8929 Do not run a pass to pack branches into VLIW instructions.
8931 This switch is mainly for debugging the compiler and will likely be removed
8932 in a future version.
8934 @item -mmulti-cond-exec
8935 @opindex mmulti-cond-exec
8937 Enable optimization of @code{&&} and @code{||} in conditional execution
8940 This switch is mainly for debugging the compiler and will likely be removed
8941 in a future version.
8943 @item -mno-multi-cond-exec
8944 @opindex mno-multi-cond-exec
8946 Disable optimization of @code{&&} and @code{||} in conditional execution.
8948 This switch is mainly for debugging the compiler and will likely be removed
8949 in a future version.
8951 @item -mnested-cond-exec
8952 @opindex mnested-cond-exec
8954 Enable nested conditional execution optimizations (default).
8956 This switch is mainly for debugging the compiler and will likely be removed
8957 in a future version.
8959 @item -mno-nested-cond-exec
8960 @opindex mno-nested-cond-exec
8962 Disable nested conditional execution optimizations.
8964 This switch is mainly for debugging the compiler and will likely be removed
8965 in a future version.
8967 @item -moptimize-membar
8968 @opindex moptimize-membar
8970 This switch removes redundant @code{membar} instructions from the
8971 compiler generated code. It is enabled by default.
8973 @item -mno-optimize-membar
8974 @opindex mno-optimize-membar
8976 This switch disables the automatic removal of redundant @code{membar}
8977 instructions from the generated code.
8979 @item -mtomcat-stats
8980 @opindex mtomcat-stats
8982 Cause gas to print out tomcat statistics.
8984 @item -mcpu=@var{cpu}
8987 Select the processor type for which to generate code. Possible values are
8988 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
8989 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
8993 @node GNU/Linux Options
8994 @subsection GNU/Linux Options
8996 These @samp{-m} options are defined for GNU/Linux targets:
9001 Use the GNU C library instead of uClibc. This is the default except
9002 on @samp{*-*-linux-*uclibc*} targets.
9006 Use uClibc instead of the GNU C library. This is the default on
9007 @samp{*-*-linux-*uclibc*} targets.
9010 @node H8/300 Options
9011 @subsection H8/300 Options
9013 These @samp{-m} options are defined for the H8/300 implementations:
9018 Shorten some address references at link time, when possible; uses the
9019 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
9020 ld, Using ld}, for a fuller description.
9024 Generate code for the H8/300H@.
9028 Generate code for the H8S@.
9032 Generate code for the H8S and H8/300H in the normal mode. This switch
9033 must be used either with @option{-mh} or @option{-ms}.
9037 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
9041 Make @code{int} data 32 bits by default.
9045 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
9046 The default for the H8/300H and H8S is to align longs and floats on 4
9048 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
9049 This option has no effect on the H8/300.
9053 @subsection HPPA Options
9054 @cindex HPPA Options
9056 These @samp{-m} options are defined for the HPPA family of computers:
9059 @item -march=@var{architecture-type}
9061 Generate code for the specified architecture. The choices for
9062 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
9063 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
9064 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
9065 architecture option for your machine. Code compiled for lower numbered
9066 architectures will run on higher numbered architectures, but not the
9070 @itemx -mpa-risc-1-1
9071 @itemx -mpa-risc-2-0
9072 @opindex mpa-risc-1-0
9073 @opindex mpa-risc-1-1
9074 @opindex mpa-risc-2-0
9075 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
9078 @opindex mbig-switch
9079 Generate code suitable for big switch tables. Use this option only if
9080 the assembler/linker complain about out of range branches within a switch
9083 @item -mjump-in-delay
9084 @opindex mjump-in-delay
9085 Fill delay slots of function calls with unconditional jump instructions
9086 by modifying the return pointer for the function call to be the target
9087 of the conditional jump.
9089 @item -mdisable-fpregs
9090 @opindex mdisable-fpregs
9091 Prevent floating point registers from being used in any manner. This is
9092 necessary for compiling kernels which perform lazy context switching of
9093 floating point registers. If you use this option and attempt to perform
9094 floating point operations, the compiler will abort.
9096 @item -mdisable-indexing
9097 @opindex mdisable-indexing
9098 Prevent the compiler from using indexing address modes. This avoids some
9099 rather obscure problems when compiling MIG generated code under MACH@.
9101 @item -mno-space-regs
9102 @opindex mno-space-regs
9103 Generate code that assumes the target has no space registers. This allows
9104 GCC to generate faster indirect calls and use unscaled index address modes.
9106 Such code is suitable for level 0 PA systems and kernels.
9108 @item -mfast-indirect-calls
9109 @opindex mfast-indirect-calls
9110 Generate code that assumes calls never cross space boundaries. This
9111 allows GCC to emit code which performs faster indirect calls.
9113 This option will not work in the presence of shared libraries or nested
9116 @item -mfixed-range=@var{register-range}
9117 @opindex mfixed-range
9118 Generate code treating the given register range as fixed registers.
9119 A fixed register is one that the register allocator can not use. This is
9120 useful when compiling kernel code. A register range is specified as
9121 two registers separated by a dash. Multiple register ranges can be
9122 specified separated by a comma.
9124 @item -mlong-load-store
9125 @opindex mlong-load-store
9126 Generate 3-instruction load and store sequences as sometimes required by
9127 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
9130 @item -mportable-runtime
9131 @opindex mportable-runtime
9132 Use the portable calling conventions proposed by HP for ELF systems.
9136 Enable the use of assembler directives only GAS understands.
9138 @item -mschedule=@var{cpu-type}
9140 Schedule code according to the constraints for the machine type
9141 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
9142 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
9143 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
9144 proper scheduling option for your machine. The default scheduling is
9148 @opindex mlinker-opt
9149 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
9150 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
9151 linkers in which they give bogus error messages when linking some programs.
9154 @opindex msoft-float
9155 Generate output containing library calls for floating point.
9156 @strong{Warning:} the requisite libraries are not available for all HPPA
9157 targets. Normally the facilities of the machine's usual C compiler are
9158 used, but this cannot be done directly in cross-compilation. You must make
9159 your own arrangements to provide suitable library functions for
9160 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
9161 does provide software floating point support.
9163 @option{-msoft-float} changes the calling convention in the output file;
9164 therefore, it is only useful if you compile @emph{all} of a program with
9165 this option. In particular, you need to compile @file{libgcc.a}, the
9166 library that comes with GCC, with @option{-msoft-float} in order for
9171 Generate the predefine, @code{_SIO}, for server IO@. The default is
9172 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
9173 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
9174 options are available under HP-UX and HI-UX@.
9178 Use GNU ld specific options. This passes @option{-shared} to ld when
9179 building a shared library. It is the default when GCC is configured,
9180 explicitly or implicitly, with the GNU linker. This option does not
9181 have any affect on which ld is called, it only changes what parameters
9182 are passed to that ld. The ld that is called is determined by the
9183 @option{--with-ld} configure option, GCC's program search path, and
9184 finally by the user's @env{PATH}. The linker used by GCC can be printed
9185 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
9186 on the 64 bit HP-UX GCC, i.e. configured with @samp{hppa*64*-*-hpux*}.
9190 Use HP ld specific options. This passes @option{-b} to ld when building
9191 a shared library and passes @option{+Accept TypeMismatch} to ld on all
9192 links. It is the default when GCC is configured, explicitly or
9193 implicitly, with the HP linker. This option does not have any affect on
9194 which ld is called, it only changes what parameters are passed to that
9195 ld. The ld that is called is determined by the @option{--with-ld}
9196 configure option, GCC's program search path, and finally by the user's
9197 @env{PATH}. The linker used by GCC can be printed using @samp{which
9198 `gcc -print-prog-name=ld`}. This option is only available on the 64 bit
9199 HP-UX GCC, i.e. configured with @samp{hppa*64*-*-hpux*}.
9202 @opindex mno-long-calls
9203 Generate code that uses long call sequences. This ensures that a call
9204 is always able to reach linker generated stubs. The default is to generate
9205 long calls only when the distance from the call site to the beginning
9206 of the function or translation unit, as the case may be, exceeds a
9207 predefined limit set by the branch type being used. The limits for
9208 normal calls are 7,600,000 and 240,000 bytes, respectively for the
9209 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
9212 Distances are measured from the beginning of functions when using the
9213 @option{-ffunction-sections} option, or when using the @option{-mgas}
9214 and @option{-mno-portable-runtime} options together under HP-UX with
9217 It is normally not desirable to use this option as it will degrade
9218 performance. However, it may be useful in large applications,
9219 particularly when partial linking is used to build the application.
9221 The types of long calls used depends on the capabilities of the
9222 assembler and linker, and the type of code being generated. The
9223 impact on systems that support long absolute calls, and long pic
9224 symbol-difference or pc-relative calls should be relatively small.
9225 However, an indirect call is used on 32-bit ELF systems in pic code
9226 and it is quite long.
9228 @item -munix=@var{unix-std}
9230 Generate compiler predefines and select a startfile for the specified
9231 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
9232 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
9233 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
9234 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
9235 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
9238 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
9239 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
9240 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
9241 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
9242 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
9243 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
9245 It is @emph{important} to note that this option changes the interfaces
9246 for various library routines. It also affects the operational behavior
9247 of the C library. Thus, @emph{extreme} care is needed in using this
9250 Library code that is intended to operate with more than one UNIX
9251 standard must test, set and restore the variable @var{__xpg4_extended_mask}
9252 as appropriate. Most GNU software doesn't provide this capability.
9256 Suppress the generation of link options to search libdld.sl when the
9257 @option{-static} option is specified on HP-UX 10 and later.
9261 The HP-UX implementation of setlocale in libc has a dependency on
9262 libdld.sl. There isn't an archive version of libdld.sl. Thus,
9263 when the @option{-static} option is specified, special link options
9264 are needed to resolve this dependency.
9266 On HP-UX 10 and later, the GCC driver adds the necessary options to
9267 link with libdld.sl when the @option{-static} option is specified.
9268 This causes the resulting binary to be dynamic. On the 64-bit port,
9269 the linkers generate dynamic binaries by default in any case. The
9270 @option{-nolibdld} option can be used to prevent the GCC driver from
9271 adding these link options.
9275 Add support for multithreading with the @dfn{dce thread} library
9276 under HP-UX@. This option sets flags for both the preprocessor and
9280 @node i386 and x86-64 Options
9281 @subsection Intel 386 and AMD x86-64 Options
9282 @cindex i386 Options
9283 @cindex x86-64 Options
9284 @cindex Intel 386 Options
9285 @cindex AMD x86-64 Options
9287 These @samp{-m} options are defined for the i386 and x86-64 family of
9291 @item -mtune=@var{cpu-type}
9293 Tune to @var{cpu-type} everything applicable about the generated code, except
9294 for the ABI and the set of available instructions. The choices for
9298 Produce code optimized for the most common IA32/AMD64/EM64T processors.
9299 If you know the CPU on which your code will run, then you should use
9300 the corresponding @option{-mtune} option instead of
9301 @option{-mtune=generic}. But, if you do not know exactly what CPU users
9302 of your application will have, then you should use this option.
9304 As new processors are deployed in the marketplace, the behavior of this
9305 option will change. Therefore, if you upgrade to a newer version of
9306 GCC, the code generated option will change to reflect the processors
9307 that were most common when that version of GCC was released.
9309 There is no @option{-march=generic} option because @option{-march}
9310 indicates the instruction set the compiler can use, and there is no
9311 generic instruction set applicable to all processors. In contrast,
9312 @option{-mtune} indicates the processor (or, in this case, collection of
9313 processors) for which the code is optimized.
9315 This selects the CPU to tune for at compilation time by determining
9316 the processor type of the compiling machine. Using @option{-mtune=native}
9317 will produce code optimized for the local machine under the constraints
9318 of the selected instruction set. Using @option{-march=native} will
9319 enable all instruction subsets supported by the local machine (hence
9320 the result might not run on different machines).
9322 Original Intel's i386 CPU@.
9324 Intel's i486 CPU@. (No scheduling is implemented for this chip.)
9326 Intel Pentium CPU with no MMX support.
9328 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
9330 Intel PentiumPro CPU@.
9332 Same as @code{generic}, but when used as @code{march} option, PentiumPro
9333 instruction set will be used, so the code will run on all i686 family chips.
9335 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
9336 @item pentium3, pentium3m
9337 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
9340 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
9341 support. Used by Centrino notebooks.
9342 @item pentium4, pentium4m
9343 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
9345 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
9348 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
9349 SSE2 and SSE3 instruction set support.
9351 Intel Core2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
9352 instruction set support.
9354 AMD K6 CPU with MMX instruction set support.
9356 Improved versions of AMD K6 CPU with MMX and 3dNOW! instruction set support.
9357 @item athlon, athlon-tbird
9358 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and SSE prefetch instructions
9360 @item athlon-4, athlon-xp, athlon-mp
9361 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and full SSE
9362 instruction set support.
9363 @item k8, opteron, athlon64, athlon-fx
9364 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
9365 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW! and 64-bit instruction set extensions.)
9367 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
9370 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!
9371 instruction set support.
9373 Via C3 CPU with MMX and 3dNOW! instruction set support. (No scheduling is
9374 implemented for this chip.)
9376 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
9377 implemented for this chip.)
9379 Embedded AMD CPU with MMX and 3dNOW! instruction set support.
9382 While picking a specific @var{cpu-type} will schedule things appropriately
9383 for that particular chip, the compiler will not generate any code that
9384 does not run on the i386 without the @option{-march=@var{cpu-type}} option
9387 @item -march=@var{cpu-type}
9389 Generate instructions for the machine type @var{cpu-type}. The choices
9390 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
9391 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
9393 @item -mcpu=@var{cpu-type}
9395 A deprecated synonym for @option{-mtune}.
9404 @opindex mpentiumpro
9405 These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
9406 @option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
9407 These synonyms are deprecated.
9409 @item -mfpmath=@var{unit}
9411 Generate floating point arithmetics for selected unit @var{unit}. The choices
9416 Use the standard 387 floating point coprocessor present majority of chips and
9417 emulated otherwise. Code compiled with this option will run almost everywhere.
9418 The temporary results are computed in 80bit precision instead of precision
9419 specified by the type resulting in slightly different results compared to most
9420 of other chips. See @option{-ffloat-store} for more detailed description.
9422 This is the default choice for i386 compiler.
9425 Use scalar floating point instructions present in the SSE instruction set.
9426 This instruction set is supported by Pentium3 and newer chips, in the AMD line
9427 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
9428 instruction set supports only single precision arithmetics, thus the double and
9429 extended precision arithmetics is still done using 387. Later version, present
9430 only in Pentium4 and the future AMD x86-64 chips supports double precision
9433 For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse}
9434 or @option{-msse2} switches to enable SSE extensions and make this option
9435 effective. For the x86-64 compiler, these extensions are enabled by default.
9437 The resulting code should be considerably faster in the majority of cases and avoid
9438 the numerical instability problems of 387 code, but may break some existing
9439 code that expects temporaries to be 80bit.
9441 This is the default choice for the x86-64 compiler.
9444 Attempt to utilize both instruction sets at once. This effectively double the
9445 amount of available registers and on chips with separate execution units for
9446 387 and SSE the execution resources too. Use this option with care, as it is
9447 still experimental, because the GCC register allocator does not model separate
9448 functional units well resulting in instable performance.
9451 @item -masm=@var{dialect}
9452 @opindex masm=@var{dialect}
9453 Output asm instructions using selected @var{dialect}. Supported
9454 choices are @samp{intel} or @samp{att} (the default one). Darwin does
9455 not support @samp{intel}.
9460 @opindex mno-ieee-fp
9461 Control whether or not the compiler uses IEEE floating point
9462 comparisons. These handle correctly the case where the result of a
9463 comparison is unordered.
9466 @opindex msoft-float
9467 Generate output containing library calls for floating point.
9468 @strong{Warning:} the requisite libraries are not part of GCC@.
9469 Normally the facilities of the machine's usual C compiler are used, but
9470 this can't be done directly in cross-compilation. You must make your
9471 own arrangements to provide suitable library functions for
9474 On machines where a function returns floating point results in the 80387
9475 register stack, some floating point opcodes may be emitted even if
9476 @option{-msoft-float} is used.
9478 @item -mno-fp-ret-in-387
9479 @opindex mno-fp-ret-in-387
9480 Do not use the FPU registers for return values of functions.
9482 The usual calling convention has functions return values of types
9483 @code{float} and @code{double} in an FPU register, even if there
9484 is no FPU@. The idea is that the operating system should emulate
9487 The option @option{-mno-fp-ret-in-387} causes such values to be returned
9488 in ordinary CPU registers instead.
9490 @item -mno-fancy-math-387
9491 @opindex mno-fancy-math-387
9492 Some 387 emulators do not support the @code{sin}, @code{cos} and
9493 @code{sqrt} instructions for the 387. Specify this option to avoid
9494 generating those instructions. This option is the default on FreeBSD,
9495 OpenBSD and NetBSD@. This option is overridden when @option{-march}
9496 indicates that the target cpu will always have an FPU and so the
9497 instruction will not need emulation. As of revision 2.6.1, these
9498 instructions are not generated unless you also use the
9499 @option{-funsafe-math-optimizations} switch.
9501 @item -malign-double
9502 @itemx -mno-align-double
9503 @opindex malign-double
9504 @opindex mno-align-double
9505 Control whether GCC aligns @code{double}, @code{long double}, and
9506 @code{long long} variables on a two word boundary or a one word
9507 boundary. Aligning @code{double} variables on a two word boundary will
9508 produce code that runs somewhat faster on a @samp{Pentium} at the
9509 expense of more memory.
9511 On x86-64, @option{-malign-double} is enabled by default.
9513 @strong{Warning:} if you use the @option{-malign-double} switch,
9514 structures containing the above types will be aligned differently than
9515 the published application binary interface specifications for the 386
9516 and will not be binary compatible with structures in code compiled
9517 without that switch.
9519 @item -m96bit-long-double
9520 @itemx -m128bit-long-double
9521 @opindex m96bit-long-double
9522 @opindex m128bit-long-double
9523 These switches control the size of @code{long double} type. The i386
9524 application binary interface specifies the size to be 96 bits,
9525 so @option{-m96bit-long-double} is the default in 32 bit mode.
9527 Modern architectures (Pentium and newer) would prefer @code{long double}
9528 to be aligned to an 8 or 16 byte boundary. In arrays or structures
9529 conforming to the ABI, this would not be possible. So specifying a
9530 @option{-m128bit-long-double} will align @code{long double}
9531 to a 16 byte boundary by padding the @code{long double} with an additional
9534 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
9535 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
9537 Notice that neither of these options enable any extra precision over the x87
9538 standard of 80 bits for a @code{long double}.
9540 @strong{Warning:} if you override the default value for your target ABI, the
9541 structures and arrays containing @code{long double} variables will change
9542 their size as well as function calling convention for function taking
9543 @code{long double} will be modified. Hence they will not be binary
9544 compatible with arrays or structures in code compiled without that switch.
9546 @item -mmlarge-data-threshold=@var{number}
9547 @opindex mlarge-data-threshold=@var{number}
9548 When @option{-mcmodel=medium} is specified, the data greater than
9549 @var{threshold} are placed in large data section. This value must be the
9550 same across all object linked into the binary and defaults to 65535.
9553 @itemx -mno-svr3-shlib
9554 @opindex msvr3-shlib
9555 @opindex mno-svr3-shlib
9556 Control whether GCC places uninitialized local variables into the
9557 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
9558 into @code{bss}. These options are meaningful only on System V Release 3.
9562 Use a different function-calling convention, in which functions that
9563 take a fixed number of arguments return with the @code{ret} @var{num}
9564 instruction, which pops their arguments while returning. This saves one
9565 instruction in the caller since there is no need to pop the arguments
9568 You can specify that an individual function is called with this calling
9569 sequence with the function attribute @samp{stdcall}. You can also
9570 override the @option{-mrtd} option by using the function attribute
9571 @samp{cdecl}. @xref{Function Attributes}.
9573 @strong{Warning:} this calling convention is incompatible with the one
9574 normally used on Unix, so you cannot use it if you need to call
9575 libraries compiled with the Unix compiler.
9577 Also, you must provide function prototypes for all functions that
9578 take variable numbers of arguments (including @code{printf});
9579 otherwise incorrect code will be generated for calls to those
9582 In addition, seriously incorrect code will result if you call a
9583 function with too many arguments. (Normally, extra arguments are
9584 harmlessly ignored.)
9586 @item -mregparm=@var{num}
9588 Control how many registers are used to pass integer arguments. By
9589 default, no registers are used to pass arguments, and at most 3
9590 registers can be used. You can control this behavior for a specific
9591 function by using the function attribute @samp{regparm}.
9592 @xref{Function Attributes}.
9594 @strong{Warning:} if you use this switch, and
9595 @var{num} is nonzero, then you must build all modules with the same
9596 value, including any libraries. This includes the system libraries and
9600 @opindex msseregparm
9601 Use SSE register passing conventions for float and double arguments
9602 and return values. You can control this behavior for a specific
9603 function by using the function attribute @samp{sseregparm}.
9604 @xref{Function Attributes}.
9606 @strong{Warning:} if you use this switch then you must build all
9607 modules with the same value, including any libraries. This includes
9608 the system libraries and startup modules.
9610 @item -mstackrealign
9611 @opindex mstackrealign
9612 Realign the stack at entry. On the Intel x86, the
9613 @option{-mstackrealign} option will generate an alternate prologue and
9614 epilogue that realigns the runtime stack. This supports mixing legacy
9615 codes that keep a 4-byte aligned stack with modern codes that keep a
9616 16-byte stack for SSE compatibility. The alternate prologue and
9617 epilogue are slower and bigger than the regular ones, and the
9618 alternate prologue requires an extra scratch register; this lowers the
9619 number of registers available if used in conjunction with the
9620 @code{regparm} attribute. The @option{-mstackrealign} option is
9621 incompatible with the nested function prologue; this is considered a
9622 hard error. See also the attribute @code{force_align_arg_pointer},
9623 applicable to individual functions.
9625 @item -mpreferred-stack-boundary=@var{num}
9626 @opindex mpreferred-stack-boundary
9627 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
9628 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
9629 the default is 4 (16 bytes or 128 bits).
9631 On Pentium and PentiumPro, @code{double} and @code{long double} values
9632 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
9633 suffer significant run time performance penalties. On Pentium III, the
9634 Streaming SIMD Extension (SSE) data type @code{__m128} may not work
9635 properly if it is not 16 byte aligned.
9637 To ensure proper alignment of this values on the stack, the stack boundary
9638 must be as aligned as that required by any value stored on the stack.
9639 Further, every function must be generated such that it keeps the stack
9640 aligned. Thus calling a function compiled with a higher preferred
9641 stack boundary from a function compiled with a lower preferred stack
9642 boundary will most likely misalign the stack. It is recommended that
9643 libraries that use callbacks always use the default setting.
9645 This extra alignment does consume extra stack space, and generally
9646 increases code size. Code that is sensitive to stack space usage, such
9647 as embedded systems and operating system kernels, may want to reduce the
9648 preferred alignment to @option{-mpreferred-stack-boundary=2}.
9668 These switches enable or disable the use of instructions in the MMX,
9669 SSE, SSE2, SSE3, SSSE3 or 3DNow! extended instruction sets.
9670 These extensions are also available as built-in functions: see
9671 @ref{X86 Built-in Functions}, for details of the functions enabled and
9672 disabled by these switches.
9674 To have SSE/SSE2 instructions generated automatically from floating-point
9675 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
9677 These options will enable GCC to use these extended instructions in
9678 generated code, even without @option{-mfpmath=sse}. Applications which
9679 perform runtime CPU detection must compile separate files for each
9680 supported architecture, using the appropriate flags. In particular,
9681 the file containing the CPU detection code should be compiled without
9685 @itemx -mno-push-args
9687 @opindex mno-push-args
9688 Use PUSH operations to store outgoing parameters. This method is shorter
9689 and usually equally fast as method using SUB/MOV operations and is enabled
9690 by default. In some cases disabling it may improve performance because of
9691 improved scheduling and reduced dependencies.
9693 @item -maccumulate-outgoing-args
9694 @opindex maccumulate-outgoing-args
9695 If enabled, the maximum amount of space required for outgoing arguments will be
9696 computed in the function prologue. This is faster on most modern CPUs
9697 because of reduced dependencies, improved scheduling and reduced stack usage
9698 when preferred stack boundary is not equal to 2. The drawback is a notable
9699 increase in code size. This switch implies @option{-mno-push-args}.
9703 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
9704 on thread-safe exception handling must compile and link all code with the
9705 @option{-mthreads} option. When compiling, @option{-mthreads} defines
9706 @option{-D_MT}; when linking, it links in a special thread helper library
9707 @option{-lmingwthrd} which cleans up per thread exception handling data.
9709 @item -mno-align-stringops
9710 @opindex mno-align-stringops
9711 Do not align destination of inlined string operations. This switch reduces
9712 code size and improves performance in case the destination is already aligned,
9713 but GCC doesn't know about it.
9715 @item -minline-all-stringops
9716 @opindex minline-all-stringops
9717 By default GCC inlines string operations only when destination is known to be
9718 aligned at least to 4 byte boundary. This enables more inlining, increase code
9719 size, but may improve performance of code that depends on fast memcpy, strlen
9720 and memset for short lengths.
9722 @item -minline-stringops-dynamically
9723 @opindex minline-stringops-dynamically
9724 For string operation of unknown size, inline runtime checks so for small
9725 blocks inline code is used, while for large blocks library call is used.
9727 @item -mstringop-strategy=@var{alg}
9728 @opindex mstringop-strategy=@var{alg}
9729 Overwrite internal decision heuristic about particular algorithm to inline
9730 string operation with. The allowed values are @code{rep_byte},
9731 @code{rep_4byte}, @code{rep_8byte} for expanding using i386 @code{rep} prefix
9732 of specified size, @code{byte_loop}, @code{loop}, @code{unrolled_loop} for
9733 expanding inline loop, @code{libcall} for always expanding library call.
9735 @item -momit-leaf-frame-pointer
9736 @opindex momit-leaf-frame-pointer
9737 Don't keep the frame pointer in a register for leaf functions. This
9738 avoids the instructions to save, set up and restore frame pointers and
9739 makes an extra register available in leaf functions. The option
9740 @option{-fomit-frame-pointer} removes the frame pointer for all functions
9741 which might make debugging harder.
9743 @item -mtls-direct-seg-refs
9744 @itemx -mno-tls-direct-seg-refs
9745 @opindex mtls-direct-seg-refs
9746 Controls whether TLS variables may be accessed with offsets from the
9747 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
9748 or whether the thread base pointer must be added. Whether or not this
9749 is legal depends on the operating system, and whether it maps the
9750 segment to cover the entire TLS area.
9752 For systems that use GNU libc, the default is on.
9755 These @samp{-m} switches are supported in addition to the above
9756 on AMD x86-64 processors in 64-bit environments.
9763 Generate code for a 32-bit or 64-bit environment.
9764 The 32-bit environment sets int, long and pointer to 32 bits and
9765 generates code that runs on any i386 system.
9766 The 64-bit environment sets int to 32 bits and long and pointer
9767 to 64 bits and generates code for AMD's x86-64 architecture.
9770 @opindex no-red-zone
9771 Do not use a so called red zone for x86-64 code. The red zone is mandated
9772 by the x86-64 ABI, it is a 128-byte area beyond the location of the
9773 stack pointer that will not be modified by signal or interrupt handlers
9774 and therefore can be used for temporary data without adjusting the stack
9775 pointer. The flag @option{-mno-red-zone} disables this red zone.
9777 @item -mcmodel=small
9778 @opindex mcmodel=small
9779 Generate code for the small code model: the program and its symbols must
9780 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
9781 Programs can be statically or dynamically linked. This is the default
9784 @item -mcmodel=kernel
9785 @opindex mcmodel=kernel
9786 Generate code for the kernel code model. The kernel runs in the
9787 negative 2 GB of the address space.
9788 This model has to be used for Linux kernel code.
9790 @item -mcmodel=medium
9791 @opindex mcmodel=medium
9792 Generate code for the medium model: The program is linked in the lower 2
9793 GB of the address space but symbols can be located anywhere in the
9794 address space. Programs can be statically or dynamically linked, but
9795 building of shared libraries are not supported with the medium model.
9797 @item -mcmodel=large
9798 @opindex mcmodel=large
9799 Generate code for the large model: This model makes no assumptions
9800 about addresses and sizes of sections. Currently GCC does not implement
9805 @subsection IA-64 Options
9806 @cindex IA-64 Options
9808 These are the @samp{-m} options defined for the Intel IA-64 architecture.
9812 @opindex mbig-endian
9813 Generate code for a big endian target. This is the default for HP-UX@.
9815 @item -mlittle-endian
9816 @opindex mlittle-endian
9817 Generate code for a little endian target. This is the default for AIX5
9824 Generate (or don't) code for the GNU assembler. This is the default.
9825 @c Also, this is the default if the configure option @option{--with-gnu-as}
9832 Generate (or don't) code for the GNU linker. This is the default.
9833 @c Also, this is the default if the configure option @option{--with-gnu-ld}
9838 Generate code that does not use a global pointer register. The result
9839 is not position independent code, and violates the IA-64 ABI@.
9841 @item -mvolatile-asm-stop
9842 @itemx -mno-volatile-asm-stop
9843 @opindex mvolatile-asm-stop
9844 @opindex mno-volatile-asm-stop
9845 Generate (or don't) a stop bit immediately before and after volatile asm
9848 @item -mregister-names
9849 @itemx -mno-register-names
9850 @opindex mregister-names
9851 @opindex mno-register-names
9852 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
9853 the stacked registers. This may make assembler output more readable.
9859 Disable (or enable) optimizations that use the small data section. This may
9860 be useful for working around optimizer bugs.
9863 @opindex mconstant-gp
9864 Generate code that uses a single constant global pointer value. This is
9865 useful when compiling kernel code.
9869 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
9870 This is useful when compiling firmware code.
9872 @item -minline-float-divide-min-latency
9873 @opindex minline-float-divide-min-latency
9874 Generate code for inline divides of floating point values
9875 using the minimum latency algorithm.
9877 @item -minline-float-divide-max-throughput
9878 @opindex minline-float-divide-max-throughput
9879 Generate code for inline divides of floating point values
9880 using the maximum throughput algorithm.
9882 @item -minline-int-divide-min-latency
9883 @opindex minline-int-divide-min-latency
9884 Generate code for inline divides of integer values
9885 using the minimum latency algorithm.
9887 @item -minline-int-divide-max-throughput
9888 @opindex minline-int-divide-max-throughput
9889 Generate code for inline divides of integer values
9890 using the maximum throughput algorithm.
9892 @item -minline-sqrt-min-latency
9893 @opindex minline-sqrt-min-latency
9894 Generate code for inline square roots
9895 using the minimum latency algorithm.
9897 @item -minline-sqrt-max-throughput
9898 @opindex minline-sqrt-max-throughput
9899 Generate code for inline square roots
9900 using the maximum throughput algorithm.
9902 @item -mno-dwarf2-asm
9904 @opindex mno-dwarf2-asm
9905 @opindex mdwarf2-asm
9906 Don't (or do) generate assembler code for the DWARF2 line number debugging
9907 info. This may be useful when not using the GNU assembler.
9909 @item -mearly-stop-bits
9910 @itemx -mno-early-stop-bits
9911 @opindex mearly-stop-bits
9912 @opindex mno-early-stop-bits
9913 Allow stop bits to be placed earlier than immediately preceding the
9914 instruction that triggered the stop bit. This can improve instruction
9915 scheduling, but does not always do so.
9917 @item -mfixed-range=@var{register-range}
9918 @opindex mfixed-range
9919 Generate code treating the given register range as fixed registers.
9920 A fixed register is one that the register allocator can not use. This is
9921 useful when compiling kernel code. A register range is specified as
9922 two registers separated by a dash. Multiple register ranges can be
9923 specified separated by a comma.
9925 @item -mtls-size=@var{tls-size}
9927 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
9930 @item -mtune=@var{cpu-type}
9932 Tune the instruction scheduling for a particular CPU, Valid values are
9933 itanium, itanium1, merced, itanium2, and mckinley.
9939 Add support for multithreading using the POSIX threads library. This
9940 option sets flags for both the preprocessor and linker. It does
9941 not affect the thread safety of object code produced by the compiler or
9942 that of libraries supplied with it. These are HP-UX specific flags.
9948 Generate code for a 32-bit or 64-bit environment.
9949 The 32-bit environment sets int, long and pointer to 32 bits.
9950 The 64-bit environment sets int to 32 bits and long and pointer
9951 to 64 bits. These are HP-UX specific flags.
9953 @item -mno-sched-br-data-spec
9954 @itemx -msched-br-data-spec
9955 @opindex -mno-sched-br-data-spec
9956 @opindex -msched-br-data-spec
9957 (Dis/En)able data speculative scheduling before reload.
9958 This will result in generation of the ld.a instructions and
9959 the corresponding check instructions (ld.c / chk.a).
9960 The default is 'disable'.
9962 @item -msched-ar-data-spec
9963 @itemx -mno-sched-ar-data-spec
9964 @opindex -msched-ar-data-spec
9965 @opindex -mno-sched-ar-data-spec
9966 (En/Dis)able data speculative scheduling after reload.
9967 This will result in generation of the ld.a instructions and
9968 the corresponding check instructions (ld.c / chk.a).
9969 The default is 'enable'.
9971 @item -mno-sched-control-spec
9972 @itemx -msched-control-spec
9973 @opindex -mno-sched-control-spec
9974 @opindex -msched-control-spec
9975 (Dis/En)able control speculative scheduling. This feature is
9976 available only during region scheduling (i.e. before reload).
9977 This will result in generation of the ld.s instructions and
9978 the corresponding check instructions chk.s .
9979 The default is 'disable'.
9981 @item -msched-br-in-data-spec
9982 @itemx -mno-sched-br-in-data-spec
9983 @opindex -msched-br-in-data-spec
9984 @opindex -mno-sched-br-in-data-spec
9985 (En/Dis)able speculative scheduling of the instructions that
9986 are dependent on the data speculative loads before reload.
9987 This is effective only with @option{-msched-br-data-spec} enabled.
9988 The default is 'enable'.
9990 @item -msched-ar-in-data-spec
9991 @itemx -mno-sched-ar-in-data-spec
9992 @opindex -msched-ar-in-data-spec
9993 @opindex -mno-sched-ar-in-data-spec
9994 (En/Dis)able speculative scheduling of the instructions that
9995 are dependent on the data speculative loads after reload.
9996 This is effective only with @option{-msched-ar-data-spec} enabled.
9997 The default is 'enable'.
9999 @item -msched-in-control-spec
10000 @itemx -mno-sched-in-control-spec
10001 @opindex -msched-in-control-spec
10002 @opindex -mno-sched-in-control-spec
10003 (En/Dis)able speculative scheduling of the instructions that
10004 are dependent on the control speculative loads.
10005 This is effective only with @option{-msched-control-spec} enabled.
10006 The default is 'enable'.
10009 @itemx -mno-sched-ldc
10010 @opindex -msched-ldc
10011 @opindex -mno-sched-ldc
10012 (En/Dis)able use of simple data speculation checks ld.c .
10013 If disabled, only chk.a instructions will be emitted to check
10014 data speculative loads.
10015 The default is 'enable'.
10017 @item -mno-sched-control-ldc
10018 @itemx -msched-control-ldc
10019 @opindex -mno-sched-control-ldc
10020 @opindex -msched-control-ldc
10021 (Dis/En)able use of ld.c instructions to check control speculative loads.
10022 If enabled, in case of control speculative load with no speculatively
10023 scheduled dependent instructions this load will be emitted as ld.sa and
10024 ld.c will be used to check it.
10025 The default is 'disable'.
10027 @item -mno-sched-spec-verbose
10028 @itemx -msched-spec-verbose
10029 @opindex -mno-sched-spec-verbose
10030 @opindex -msched-spec-verbose
10031 (Dis/En)able printing of the information about speculative motions.
10033 @item -mno-sched-prefer-non-data-spec-insns
10034 @itemx -msched-prefer-non-data-spec-insns
10035 @opindex -mno-sched-prefer-non-data-spec-insns
10036 @opindex -msched-prefer-non-data-spec-insns
10037 If enabled, data speculative instructions will be chosen for schedule
10038 only if there are no other choices at the moment. This will make
10039 the use of the data speculation much more conservative.
10040 The default is 'disable'.
10042 @item -mno-sched-prefer-non-control-spec-insns
10043 @itemx -msched-prefer-non-control-spec-insns
10044 @opindex -mno-sched-prefer-non-control-spec-insns
10045 @opindex -msched-prefer-non-control-spec-insns
10046 If enabled, control speculative instructions will be chosen for schedule
10047 only if there are no other choices at the moment. This will make
10048 the use of the control speculation much more conservative.
10049 The default is 'disable'.
10051 @item -mno-sched-count-spec-in-critical-path
10052 @itemx -msched-count-spec-in-critical-path
10053 @opindex -mno-sched-count-spec-in-critical-path
10054 @opindex -msched-count-spec-in-critical-path
10055 If enabled, speculative dependencies will be considered during
10056 computation of the instructions priorities. This will make the use of the
10057 speculation a bit more conservative.
10058 The default is 'disable'.
10063 @subsection M32C Options
10064 @cindex M32C options
10067 @item -mcpu=@var{name}
10069 Select the CPU for which code is generated. @var{name} may be one of
10070 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
10071 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
10072 the M32C/80 series.
10076 Specifies that the program will be run on the simulator. This causes
10077 an alternate runtime library to be linked in which supports, for
10078 example, file I/O. You must not use this option when generating
10079 programs that will run on real hardware; you must provide your own
10080 runtime library for whatever I/O functions are needed.
10082 @item -memregs=@var{number}
10084 Specifies the number of memory-based pseudo-registers GCC will use
10085 during code generation. These pseudo-registers will be used like real
10086 registers, so there is a tradeoff between GCC's ability to fit the
10087 code into available registers, and the performance penalty of using
10088 memory instead of registers. Note that all modules in a program must
10089 be compiled with the same value for this option. Because of that, you
10090 must not use this option with the default runtime libraries gcc
10095 @node M32R/D Options
10096 @subsection M32R/D Options
10097 @cindex M32R/D options
10099 These @option{-m} options are defined for Renesas M32R/D architectures:
10104 Generate code for the M32R/2@.
10108 Generate code for the M32R/X@.
10112 Generate code for the M32R@. This is the default.
10114 @item -mmodel=small
10115 @opindex mmodel=small
10116 Assume all objects live in the lower 16MB of memory (so that their addresses
10117 can be loaded with the @code{ld24} instruction), and assume all subroutines
10118 are reachable with the @code{bl} instruction.
10119 This is the default.
10121 The addressability of a particular object can be set with the
10122 @code{model} attribute.
10124 @item -mmodel=medium
10125 @opindex mmodel=medium
10126 Assume objects may be anywhere in the 32-bit address space (the compiler
10127 will generate @code{seth/add3} instructions to load their addresses), and
10128 assume all subroutines are reachable with the @code{bl} instruction.
10130 @item -mmodel=large
10131 @opindex mmodel=large
10132 Assume objects may be anywhere in the 32-bit address space (the compiler
10133 will generate @code{seth/add3} instructions to load their addresses), and
10134 assume subroutines may not be reachable with the @code{bl} instruction
10135 (the compiler will generate the much slower @code{seth/add3/jl}
10136 instruction sequence).
10139 @opindex msdata=none
10140 Disable use of the small data area. Variables will be put into
10141 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
10142 @code{section} attribute has been specified).
10143 This is the default.
10145 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
10146 Objects may be explicitly put in the small data area with the
10147 @code{section} attribute using one of these sections.
10149 @item -msdata=sdata
10150 @opindex msdata=sdata
10151 Put small global and static data in the small data area, but do not
10152 generate special code to reference them.
10155 @opindex msdata=use
10156 Put small global and static data in the small data area, and generate
10157 special instructions to reference them.
10161 @cindex smaller data references
10162 Put global and static objects less than or equal to @var{num} bytes
10163 into the small data or bss sections instead of the normal data or bss
10164 sections. The default value of @var{num} is 8.
10165 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
10166 for this option to have any effect.
10168 All modules should be compiled with the same @option{-G @var{num}} value.
10169 Compiling with different values of @var{num} may or may not work; if it
10170 doesn't the linker will give an error message---incorrect code will not be
10175 Makes the M32R specific code in the compiler display some statistics
10176 that might help in debugging programs.
10178 @item -malign-loops
10179 @opindex malign-loops
10180 Align all loops to a 32-byte boundary.
10182 @item -mno-align-loops
10183 @opindex mno-align-loops
10184 Do not enforce a 32-byte alignment for loops. This is the default.
10186 @item -missue-rate=@var{number}
10187 @opindex missue-rate=@var{number}
10188 Issue @var{number} instructions per cycle. @var{number} can only be 1
10191 @item -mbranch-cost=@var{number}
10192 @opindex mbranch-cost=@var{number}
10193 @var{number} can only be 1 or 2. If it is 1 then branches will be
10194 preferred over conditional code, if it is 2, then the opposite will
10197 @item -mflush-trap=@var{number}
10198 @opindex mflush-trap=@var{number}
10199 Specifies the trap number to use to flush the cache. The default is
10200 12. Valid numbers are between 0 and 15 inclusive.
10202 @item -mno-flush-trap
10203 @opindex mno-flush-trap
10204 Specifies that the cache cannot be flushed by using a trap.
10206 @item -mflush-func=@var{name}
10207 @opindex mflush-func=@var{name}
10208 Specifies the name of the operating system function to call to flush
10209 the cache. The default is @emph{_flush_cache}, but a function call
10210 will only be used if a trap is not available.
10212 @item -mno-flush-func
10213 @opindex mno-flush-func
10214 Indicates that there is no OS function for flushing the cache.
10218 @node M680x0 Options
10219 @subsection M680x0 Options
10220 @cindex M680x0 options
10222 These are the @samp{-m} options defined for the 68000 series. The default
10223 values for these options depends on which style of 68000 was selected when
10224 the compiler was configured; the defaults for the most common choices are
10232 Generate output for a 68000. This is the default
10233 when the compiler is configured for 68000-based systems.
10235 Use this option for microcontrollers with a 68000 or EC000 core,
10236 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
10242 Generate output for a 68020. This is the default
10243 when the compiler is configured for 68020-based systems.
10247 Generate output containing 68881 instructions for floating point.
10248 This is the default for most 68020 systems unless @option{--nfp} was
10249 specified when the compiler was configured.
10253 Generate output for a 68030. This is the default when the compiler is
10254 configured for 68030-based systems.
10258 Generate output for a 68040. This is the default when the compiler is
10259 configured for 68040-based systems.
10261 This option inhibits the use of 68881/68882 instructions that have to be
10262 emulated by software on the 68040. Use this option if your 68040 does not
10263 have code to emulate those instructions.
10267 Generate output for a 68060. This is the default when the compiler is
10268 configured for 68060-based systems.
10270 This option inhibits the use of 68020 and 68881/68882 instructions that
10271 have to be emulated by software on the 68060. Use this option if your 68060
10272 does not have code to emulate those instructions.
10276 Generate output for a CPU32. This is the default
10277 when the compiler is configured for CPU32-based systems.
10279 Use this option for microcontrollers with a
10280 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
10281 68336, 68340, 68341, 68349 and 68360.
10285 Generate output for a 520X ``coldfire'' family cpu. This is the default
10286 when the compiler is configured for 520X-based systems.
10288 Use this option for microcontroller with a 5200 core, including
10289 the MCF5202, MCF5203, MCF5204 and MCF5202.
10293 Generate output for a ColdFire V4e family cpu (e.g.@: 547x/548x).
10294 This includes use of hardware floating point instructions.
10298 Generate output for a 68040, without using any of the new instructions.
10299 This results in code which can run relatively efficiently on either a
10300 68020/68881 or a 68030 or a 68040. The generated code does use the
10301 68881 instructions that are emulated on the 68040.
10305 Generate output for a 68060, without using any of the new instructions.
10306 This results in code which can run relatively efficiently on either a
10307 68020/68881 or a 68030 or a 68040. The generated code does use the
10308 68881 instructions that are emulated on the 68060.
10311 @opindex msoft-float
10312 Generate output containing library calls for floating point.
10313 @strong{Warning:} the requisite libraries are not available for all m68k
10314 targets. Normally the facilities of the machine's usual C compiler are
10315 used, but this can't be done directly in cross-compilation. You must
10316 make your own arrangements to provide suitable library functions for
10317 cross-compilation. The embedded targets @samp{m68k-*-aout} and
10318 @samp{m68k-*-coff} do provide software floating point support.
10322 Consider type @code{int} to be 16 bits wide, like @code{short int}.
10323 Additionally, parameters passed on the stack are also aligned to a
10324 16-bit boundary even on targets whose API mandates promotion to 32-bit.
10327 @opindex mnobitfield
10328 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
10329 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
10333 Do use the bit-field instructions. The @option{-m68020} option implies
10334 @option{-mbitfield}. This is the default if you use a configuration
10335 designed for a 68020.
10339 Use a different function-calling convention, in which functions
10340 that take a fixed number of arguments return with the @code{rtd}
10341 instruction, which pops their arguments while returning. This
10342 saves one instruction in the caller since there is no need to pop
10343 the arguments there.
10345 This calling convention is incompatible with the one normally
10346 used on Unix, so you cannot use it if you need to call libraries
10347 compiled with the Unix compiler.
10349 Also, you must provide function prototypes for all functions that
10350 take variable numbers of arguments (including @code{printf});
10351 otherwise incorrect code will be generated for calls to those
10354 In addition, seriously incorrect code will result if you call a
10355 function with too many arguments. (Normally, extra arguments are
10356 harmlessly ignored.)
10358 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
10359 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
10362 @itemx -mno-align-int
10363 @opindex malign-int
10364 @opindex mno-align-int
10365 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
10366 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
10367 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
10368 Aligning variables on 32-bit boundaries produces code that runs somewhat
10369 faster on processors with 32-bit busses at the expense of more memory.
10371 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
10372 align structures containing the above types differently than
10373 most published application binary interface specifications for the m68k.
10377 Use the pc-relative addressing mode of the 68000 directly, instead of
10378 using a global offset table. At present, this option implies @option{-fpic},
10379 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
10380 not presently supported with @option{-mpcrel}, though this could be supported for
10381 68020 and higher processors.
10383 @item -mno-strict-align
10384 @itemx -mstrict-align
10385 @opindex mno-strict-align
10386 @opindex mstrict-align
10387 Do not (do) assume that unaligned memory references will be handled by
10391 Generate code that allows the data segment to be located in a different
10392 area of memory from the text segment. This allows for execute in place in
10393 an environment without virtual memory management. This option implies
10396 @item -mno-sep-data
10397 Generate code that assumes that the data segment follows the text segment.
10398 This is the default.
10400 @item -mid-shared-library
10401 Generate code that supports shared libraries via the library ID method.
10402 This allows for execute in place and shared libraries in an environment
10403 without virtual memory management. This option implies @option{-fPIC}.
10405 @item -mno-id-shared-library
10406 Generate code that doesn't assume ID based shared libraries are being used.
10407 This is the default.
10409 @item -mshared-library-id=n
10410 Specified the identification number of the ID based shared library being
10411 compiled. Specifying a value of 0 will generate more compact code, specifying
10412 other values will force the allocation of that number to the current
10413 library but is no more space or time efficient than omitting this option.
10417 @node M68hc1x Options
10418 @subsection M68hc1x Options
10419 @cindex M68hc1x options
10421 These are the @samp{-m} options defined for the 68hc11 and 68hc12
10422 microcontrollers. The default values for these options depends on
10423 which style of microcontroller was selected when the compiler was configured;
10424 the defaults for the most common choices are given below.
10431 Generate output for a 68HC11. This is the default
10432 when the compiler is configured for 68HC11-based systems.
10438 Generate output for a 68HC12. This is the default
10439 when the compiler is configured for 68HC12-based systems.
10445 Generate output for a 68HCS12.
10447 @item -mauto-incdec
10448 @opindex mauto-incdec
10449 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
10456 Enable the use of 68HC12 min and max instructions.
10459 @itemx -mno-long-calls
10460 @opindex mlong-calls
10461 @opindex mno-long-calls
10462 Treat all calls as being far away (near). If calls are assumed to be
10463 far away, the compiler will use the @code{call} instruction to
10464 call a function and the @code{rtc} instruction for returning.
10468 Consider type @code{int} to be 16 bits wide, like @code{short int}.
10470 @item -msoft-reg-count=@var{count}
10471 @opindex msoft-reg-count
10472 Specify the number of pseudo-soft registers which are used for the
10473 code generation. The maximum number is 32. Using more pseudo-soft
10474 register may or may not result in better code depending on the program.
10475 The default is 4 for 68HC11 and 2 for 68HC12.
10479 @node MCore Options
10480 @subsection MCore Options
10481 @cindex MCore options
10483 These are the @samp{-m} options defined for the Motorola M*Core
10489 @itemx -mno-hardlit
10491 @opindex mno-hardlit
10492 Inline constants into the code stream if it can be done in two
10493 instructions or less.
10499 Use the divide instruction. (Enabled by default).
10501 @item -mrelax-immediate
10502 @itemx -mno-relax-immediate
10503 @opindex mrelax-immediate
10504 @opindex mno-relax-immediate
10505 Allow arbitrary sized immediates in bit operations.
10507 @item -mwide-bitfields
10508 @itemx -mno-wide-bitfields
10509 @opindex mwide-bitfields
10510 @opindex mno-wide-bitfields
10511 Always treat bit-fields as int-sized.
10513 @item -m4byte-functions
10514 @itemx -mno-4byte-functions
10515 @opindex m4byte-functions
10516 @opindex mno-4byte-functions
10517 Force all functions to be aligned to a four byte boundary.
10519 @item -mcallgraph-data
10520 @itemx -mno-callgraph-data
10521 @opindex mcallgraph-data
10522 @opindex mno-callgraph-data
10523 Emit callgraph information.
10526 @itemx -mno-slow-bytes
10527 @opindex mslow-bytes
10528 @opindex mno-slow-bytes
10529 Prefer word access when reading byte quantities.
10531 @item -mlittle-endian
10532 @itemx -mbig-endian
10533 @opindex mlittle-endian
10534 @opindex mbig-endian
10535 Generate code for a little endian target.
10541 Generate code for the 210 processor.
10545 @subsection MIPS Options
10546 @cindex MIPS options
10552 Generate big-endian code.
10556 Generate little-endian code. This is the default for @samp{mips*el-*-*}
10559 @item -march=@var{arch}
10561 Generate code that will run on @var{arch}, which can be the name of a
10562 generic MIPS ISA, or the name of a particular processor.
10564 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
10565 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
10566 The processor names are:
10567 @samp{4kc}, @samp{4km}, @samp{4kp},
10568 @samp{4kec}, @samp{4kem}, @samp{4kep},
10569 @samp{5kc}, @samp{5kf},
10571 @samp{24kc}, @samp{24kf}, @samp{24kx},
10572 @samp{24kec}, @samp{24kef}, @samp{24kex},
10573 @samp{34kc}, @samp{34kf}, @samp{34kx},
10576 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
10577 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
10578 @samp{rm7000}, @samp{rm9000},
10581 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
10582 @samp{vr5000}, @samp{vr5400} and @samp{vr5500}.
10583 The special value @samp{from-abi} selects the
10584 most compatible architecture for the selected ABI (that is,
10585 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
10587 In processor names, a final @samp{000} can be abbreviated as @samp{k}
10588 (for example, @samp{-march=r2k}). Prefixes are optional, and
10589 @samp{vr} may be written @samp{r}.
10591 GCC defines two macros based on the value of this option. The first
10592 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
10593 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
10594 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
10595 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
10596 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
10598 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
10599 above. In other words, it will have the full prefix and will not
10600 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
10601 the macro names the resolved architecture (either @samp{"mips1"} or
10602 @samp{"mips3"}). It names the default architecture when no
10603 @option{-march} option is given.
10605 @item -mtune=@var{arch}
10607 Optimize for @var{arch}. Among other things, this option controls
10608 the way instructions are scheduled, and the perceived cost of arithmetic
10609 operations. The list of @var{arch} values is the same as for
10612 When this option is not used, GCC will optimize for the processor
10613 specified by @option{-march}. By using @option{-march} and
10614 @option{-mtune} together, it is possible to generate code that will
10615 run on a family of processors, but optimize the code for one
10616 particular member of that family.
10618 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
10619 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
10620 @samp{-march} ones described above.
10624 Equivalent to @samp{-march=mips1}.
10628 Equivalent to @samp{-march=mips2}.
10632 Equivalent to @samp{-march=mips3}.
10636 Equivalent to @samp{-march=mips4}.
10640 Equivalent to @samp{-march=mips32}.
10644 Equivalent to @samp{-march=mips32r2}.
10648 Equivalent to @samp{-march=mips64}.
10653 @opindex mno-mips16
10654 Generate (do not generate) MIPS16 code. If GCC is targetting a
10655 MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
10667 Generate code for the given ABI@.
10669 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
10670 generates 64-bit code when you select a 64-bit architecture, but you
10671 can use @option{-mgp32} to get 32-bit code instead.
10673 For information about the O64 ABI, see
10674 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
10676 GCC supports a variant of the o32 ABI in which floating-point registers
10677 are 64 rather than 32 bits wide. You can select this combination with
10678 @option{-mabi=32} @option{-mfp64}. This ABI relies on the @samp{mthc1}
10679 and @samp{mfhc1} instructions and is therefore only supported for
10680 MIPS32R2 processors.
10682 The register assignments for arguments and return values remain the
10683 same, but each scalar value is passed in a single 64-bit register
10684 rather than a pair of 32-bit registers. For example, scalar
10685 floating-point values are returned in @samp{$f0} only, not a
10686 @samp{$f0}/@samp{$f1} pair. The set of call-saved registers also
10687 remains the same, but all 64 bits are saved.
10690 @itemx -mno-abicalls
10692 @opindex mno-abicalls
10693 Generate (do not generate) code that is suitable for SVR4-style
10694 dynamic objects. @option{-mabicalls} is the default for SVR4-based
10699 Generate (do not generate) code that is fully position-independent,
10700 and that can therefore be linked into shared libraries. This option
10701 only affects @option{-mabicalls}.
10703 All @option{-mabicalls} code has traditionally been position-independent,
10704 regardless of options like @option{-fPIC} and @option{-fpic}. However,
10705 as an extension, the GNU toolchain allows executables to use absolute
10706 accesses for locally-binding symbols. It can also use shorter GP
10707 initialization sequences and generate direct calls to locally-defined
10708 functions. This mode is selected by @option{-mno-shared}.
10710 @option{-mno-shared} depends on binutils 2.16 or higher and generates
10711 objects that can only be linked by the GNU linker. However, the option
10712 does not affect the ABI of the final executable; it only affects the ABI
10713 of relocatable objects. Using @option{-mno-shared} will generally make
10714 executables both smaller and quicker.
10716 @option{-mshared} is the default.
10722 Lift (do not lift) the usual restrictions on the size of the global
10725 GCC normally uses a single instruction to load values from the GOT@.
10726 While this is relatively efficient, it will only work if the GOT
10727 is smaller than about 64k. Anything larger will cause the linker
10728 to report an error such as:
10730 @cindex relocation truncated to fit (MIPS)
10732 relocation truncated to fit: R_MIPS_GOT16 foobar
10735 If this happens, you should recompile your code with @option{-mxgot}.
10736 It should then work with very large GOTs, although it will also be
10737 less efficient, since it will take three instructions to fetch the
10738 value of a global symbol.
10740 Note that some linkers can create multiple GOTs. If you have such a
10741 linker, you should only need to use @option{-mxgot} when a single object
10742 file accesses more than 64k's worth of GOT entries. Very few do.
10744 These options have no effect unless GCC is generating position
10749 Assume that general-purpose registers are 32 bits wide.
10753 Assume that general-purpose registers are 64 bits wide.
10757 Assume that floating-point registers are 32 bits wide.
10761 Assume that floating-point registers are 64 bits wide.
10764 @opindex mhard-float
10765 Use floating-point coprocessor instructions.
10768 @opindex msoft-float
10769 Do not use floating-point coprocessor instructions. Implement
10770 floating-point calculations using library calls instead.
10772 @item -msingle-float
10773 @opindex msingle-float
10774 Assume that the floating-point coprocessor only supports single-precision
10777 @itemx -mdouble-float
10778 @opindex mdouble-float
10779 Assume that the floating-point coprocessor supports double-precision
10780 operations. This is the default.
10786 Use (do not use) the MIPS DSP ASE. @xref{MIPS DSP Built-in Functions}.
10788 @itemx -mpaired-single
10789 @itemx -mno-paired-single
10790 @opindex mpaired-single
10791 @opindex mno-paired-single
10792 Use (do not use) paired-single floating-point instructions.
10793 @xref{MIPS Paired-Single Support}. This option can only be used
10794 when generating 64-bit code and requires hardware floating-point
10795 support to be enabled.
10800 @opindex mno-mips3d
10801 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
10802 The option @option{-mips3d} implies @option{-mpaired-single}.
10806 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
10807 an explanation of the default and the way that the pointer size is
10812 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
10814 The default size of @code{int}s, @code{long}s and pointers depends on
10815 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
10816 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
10817 32-bit @code{long}s. Pointers are the same size as @code{long}s,
10818 or the same size as integer registers, whichever is smaller.
10824 Assume (do not assume) that all symbols have 32-bit values, regardless
10825 of the selected ABI@. This option is useful in combination with
10826 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
10827 to generate shorter and faster references to symbolic addresses.
10831 @cindex smaller data references (MIPS)
10832 @cindex gp-relative references (MIPS)
10833 Put global and static items less than or equal to @var{num} bytes into
10834 the small data or bss section instead of the normal data or bss section.
10835 This allows the data to be accessed using a single instruction.
10837 All modules should be compiled with the same @option{-G @var{num}}
10840 @item -membedded-data
10841 @itemx -mno-embedded-data
10842 @opindex membedded-data
10843 @opindex mno-embedded-data
10844 Allocate variables to the read-only data section first if possible, then
10845 next in the small data section if possible, otherwise in data. This gives
10846 slightly slower code than the default, but reduces the amount of RAM required
10847 when executing, and thus may be preferred for some embedded systems.
10849 @item -muninit-const-in-rodata
10850 @itemx -mno-uninit-const-in-rodata
10851 @opindex muninit-const-in-rodata
10852 @opindex mno-uninit-const-in-rodata
10853 Put uninitialized @code{const} variables in the read-only data section.
10854 This option is only meaningful in conjunction with @option{-membedded-data}.
10856 @item -msplit-addresses
10857 @itemx -mno-split-addresses
10858 @opindex msplit-addresses
10859 @opindex mno-split-addresses
10860 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
10861 relocation operators. This option has been superseded by
10862 @option{-mexplicit-relocs} but is retained for backwards compatibility.
10864 @item -mexplicit-relocs
10865 @itemx -mno-explicit-relocs
10866 @opindex mexplicit-relocs
10867 @opindex mno-explicit-relocs
10868 Use (do not use) assembler relocation operators when dealing with symbolic
10869 addresses. The alternative, selected by @option{-mno-explicit-relocs},
10870 is to use assembler macros instead.
10872 @option{-mexplicit-relocs} is the default if GCC was configured
10873 to use an assembler that supports relocation operators.
10875 @item -mcheck-zero-division
10876 @itemx -mno-check-zero-division
10877 @opindex mcheck-zero-division
10878 @opindex mno-check-zero-division
10879 Trap (do not trap) on integer division by zero. The default is
10880 @option{-mcheck-zero-division}.
10882 @item -mdivide-traps
10883 @itemx -mdivide-breaks
10884 @opindex mdivide-traps
10885 @opindex mdivide-breaks
10886 MIPS systems check for division by zero by generating either a
10887 conditional trap or a break instruction. Using traps results in
10888 smaller code, but is only supported on MIPS II and later. Also, some
10889 versions of the Linux kernel have a bug that prevents trap from
10890 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
10891 allow conditional traps on architectures that support them and
10892 @option{-mdivide-breaks} to force the use of breaks.
10894 The default is usually @option{-mdivide-traps}, but this can be
10895 overridden at configure time using @option{--with-divide=breaks}.
10896 Divide-by-zero checks can be completely disabled using
10897 @option{-mno-check-zero-division}.
10902 @opindex mno-memcpy
10903 Force (do not force) the use of @code{memcpy()} for non-trivial block
10904 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
10905 most constant-sized copies.
10908 @itemx -mno-long-calls
10909 @opindex mlong-calls
10910 @opindex mno-long-calls
10911 Disable (do not disable) use of the @code{jal} instruction. Calling
10912 functions using @code{jal} is more efficient but requires the caller
10913 and callee to be in the same 256 megabyte segment.
10915 This option has no effect on abicalls code. The default is
10916 @option{-mno-long-calls}.
10922 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
10923 instructions, as provided by the R4650 ISA@.
10926 @itemx -mno-fused-madd
10927 @opindex mfused-madd
10928 @opindex mno-fused-madd
10929 Enable (disable) use of the floating point multiply-accumulate
10930 instructions, when they are available. The default is
10931 @option{-mfused-madd}.
10933 When multiply-accumulate instructions are used, the intermediate
10934 product is calculated to infinite precision and is not subject to
10935 the FCSR Flush to Zero bit. This may be undesirable in some
10940 Tell the MIPS assembler to not run its preprocessor over user
10941 assembler files (with a @samp{.s} suffix) when assembling them.
10944 @itemx -mno-fix-r4000
10945 @opindex mfix-r4000
10946 @opindex mno-fix-r4000
10947 Work around certain R4000 CPU errata:
10950 A double-word or a variable shift may give an incorrect result if executed
10951 immediately after starting an integer division.
10953 A double-word or a variable shift may give an incorrect result if executed
10954 while an integer multiplication is in progress.
10956 An integer division may give an incorrect result if started in a delay slot
10957 of a taken branch or a jump.
10961 @itemx -mno-fix-r4400
10962 @opindex mfix-r4400
10963 @opindex mno-fix-r4400
10964 Work around certain R4400 CPU errata:
10967 A double-word or a variable shift may give an incorrect result if executed
10968 immediately after starting an integer division.
10972 @itemx -mno-fix-vr4120
10973 @opindex mfix-vr4120
10974 Work around certain VR4120 errata:
10977 @code{dmultu} does not always produce the correct result.
10979 @code{div} and @code{ddiv} do not always produce the correct result if one
10980 of the operands is negative.
10982 The workarounds for the division errata rely on special functions in
10983 @file{libgcc.a}. At present, these functions are only provided by
10984 the @code{mips64vr*-elf} configurations.
10986 Other VR4120 errata require a nop to be inserted between certain pairs of
10987 instructions. These errata are handled by the assembler, not by GCC itself.
10990 @opindex mfix-vr4130
10991 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
10992 workarounds are implemented by the assembler rather than by GCC,
10993 although GCC will avoid using @code{mflo} and @code{mfhi} if the
10994 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
10995 instructions are available instead.
10998 @itemx -mno-fix-sb1
11000 Work around certain SB-1 CPU core errata.
11001 (This flag currently works around the SB-1 revision 2
11002 ``F1'' and ``F2'' floating point errata.)
11004 @item -mflush-func=@var{func}
11005 @itemx -mno-flush-func
11006 @opindex mflush-func
11007 Specifies the function to call to flush the I and D caches, or to not
11008 call any such function. If called, the function must take the same
11009 arguments as the common @code{_flush_func()}, that is, the address of the
11010 memory range for which the cache is being flushed, the size of the
11011 memory range, and the number 3 (to flush both caches). The default
11012 depends on the target GCC was configured for, but commonly is either
11013 @samp{_flush_func} or @samp{__cpu_flush}.
11015 @item -mbranch-likely
11016 @itemx -mno-branch-likely
11017 @opindex mbranch-likely
11018 @opindex mno-branch-likely
11019 Enable or disable use of Branch Likely instructions, regardless of the
11020 default for the selected architecture. By default, Branch Likely
11021 instructions may be generated if they are supported by the selected
11022 architecture. An exception is for the MIPS32 and MIPS64 architectures
11023 and processors which implement those architectures; for those, Branch
11024 Likely instructions will not be generated by default because the MIPS32
11025 and MIPS64 architectures specifically deprecate their use.
11027 @item -mfp-exceptions
11028 @itemx -mno-fp-exceptions
11029 @opindex mfp-exceptions
11030 Specifies whether FP exceptions are enabled. This affects how we schedule
11031 FP instructions for some processors. The default is that FP exceptions are
11034 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
11035 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
11038 @item -mvr4130-align
11039 @itemx -mno-vr4130-align
11040 @opindex mvr4130-align
11041 The VR4130 pipeline is two-way superscalar, but can only issue two
11042 instructions together if the first one is 8-byte aligned. When this
11043 option is enabled, GCC will align pairs of instructions that it
11044 thinks should execute in parallel.
11046 This option only has an effect when optimizing for the VR4130.
11047 It normally makes code faster, but at the expense of making it bigger.
11048 It is enabled by default at optimization level @option{-O3}.
11052 @subsection MMIX Options
11053 @cindex MMIX Options
11055 These options are defined for the MMIX:
11059 @itemx -mno-libfuncs
11061 @opindex mno-libfuncs
11062 Specify that intrinsic library functions are being compiled, passing all
11063 values in registers, no matter the size.
11066 @itemx -mno-epsilon
11068 @opindex mno-epsilon
11069 Generate floating-point comparison instructions that compare with respect
11070 to the @code{rE} epsilon register.
11072 @item -mabi=mmixware
11074 @opindex mabi-mmixware
11076 Generate code that passes function parameters and return values that (in
11077 the called function) are seen as registers @code{$0} and up, as opposed to
11078 the GNU ABI which uses global registers @code{$231} and up.
11080 @item -mzero-extend
11081 @itemx -mno-zero-extend
11082 @opindex mzero-extend
11083 @opindex mno-zero-extend
11084 When reading data from memory in sizes shorter than 64 bits, use (do not
11085 use) zero-extending load instructions by default, rather than
11086 sign-extending ones.
11089 @itemx -mno-knuthdiv
11091 @opindex mno-knuthdiv
11092 Make the result of a division yielding a remainder have the same sign as
11093 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
11094 remainder follows the sign of the dividend. Both methods are
11095 arithmetically valid, the latter being almost exclusively used.
11097 @item -mtoplevel-symbols
11098 @itemx -mno-toplevel-symbols
11099 @opindex mtoplevel-symbols
11100 @opindex mno-toplevel-symbols
11101 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
11102 code can be used with the @code{PREFIX} assembly directive.
11106 Generate an executable in the ELF format, rather than the default
11107 @samp{mmo} format used by the @command{mmix} simulator.
11109 @item -mbranch-predict
11110 @itemx -mno-branch-predict
11111 @opindex mbranch-predict
11112 @opindex mno-branch-predict
11113 Use (do not use) the probable-branch instructions, when static branch
11114 prediction indicates a probable branch.
11116 @item -mbase-addresses
11117 @itemx -mno-base-addresses
11118 @opindex mbase-addresses
11119 @opindex mno-base-addresses
11120 Generate (do not generate) code that uses @emph{base addresses}. Using a
11121 base address automatically generates a request (handled by the assembler
11122 and the linker) for a constant to be set up in a global register. The
11123 register is used for one or more base address requests within the range 0
11124 to 255 from the value held in the register. The generally leads to short
11125 and fast code, but the number of different data items that can be
11126 addressed is limited. This means that a program that uses lots of static
11127 data may require @option{-mno-base-addresses}.
11129 @item -msingle-exit
11130 @itemx -mno-single-exit
11131 @opindex msingle-exit
11132 @opindex mno-single-exit
11133 Force (do not force) generated code to have a single exit point in each
11137 @node MN10300 Options
11138 @subsection MN10300 Options
11139 @cindex MN10300 options
11141 These @option{-m} options are defined for Matsushita MN10300 architectures:
11146 Generate code to avoid bugs in the multiply instructions for the MN10300
11147 processors. This is the default.
11149 @item -mno-mult-bug
11150 @opindex mno-mult-bug
11151 Do not generate code to avoid bugs in the multiply instructions for the
11152 MN10300 processors.
11156 Generate code which uses features specific to the AM33 processor.
11160 Do not generate code which uses features specific to the AM33 processor. This
11163 @item -mreturn-pointer-on-d0
11164 @opindex mreturn-pointer-on-d0
11165 When generating a function which returns a pointer, return the pointer
11166 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
11167 only in a0, and attempts to call such functions without a prototype
11168 would result in errors. Note that this option is on by default; use
11169 @option{-mno-return-pointer-on-d0} to disable it.
11173 Do not link in the C run-time initialization object file.
11177 Indicate to the linker that it should perform a relaxation optimization pass
11178 to shorten branches, calls and absolute memory addresses. This option only
11179 has an effect when used on the command line for the final link step.
11181 This option makes symbolic debugging impossible.
11185 @subsection MT Options
11188 These @option{-m} options are defined for Morpho MT architectures:
11192 @item -march=@var{cpu-type}
11194 Generate code that will run on @var{cpu-type}, which is the name of a system
11195 representing a certain processor type. Possible values for
11196 @var{cpu-type} are @samp{ms1-64-001}, @samp{ms1-16-002},
11197 @samp{ms1-16-003} and @samp{ms2}.
11199 When this option is not used, the default is @option{-march=ms1-16-002}.
11203 Use byte loads and stores when generating code.
11207 Do not use byte loads and stores when generating code.
11211 Use simulator runtime
11215 Do not link in the C run-time initialization object file
11216 @file{crti.o}. Other run-time initialization and termination files
11217 such as @file{startup.o} and @file{exit.o} are still included on the
11218 linker command line.
11222 @node PDP-11 Options
11223 @subsection PDP-11 Options
11224 @cindex PDP-11 Options
11226 These options are defined for the PDP-11:
11231 Use hardware FPP floating point. This is the default. (FIS floating
11232 point on the PDP-11/40 is not supported.)
11235 @opindex msoft-float
11236 Do not use hardware floating point.
11240 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
11244 Return floating-point results in memory. This is the default.
11248 Generate code for a PDP-11/40.
11252 Generate code for a PDP-11/45. This is the default.
11256 Generate code for a PDP-11/10.
11258 @item -mbcopy-builtin
11259 @opindex bcopy-builtin
11260 Use inline @code{movmemhi} patterns for copying memory. This is the
11265 Do not use inline @code{movmemhi} patterns for copying memory.
11271 Use 16-bit @code{int}. This is the default.
11277 Use 32-bit @code{int}.
11280 @itemx -mno-float32
11282 @opindex mno-float32
11283 Use 64-bit @code{float}. This is the default.
11286 @itemx -mno-float64
11288 @opindex mno-float64
11289 Use 32-bit @code{float}.
11293 Use @code{abshi2} pattern. This is the default.
11297 Do not use @code{abshi2} pattern.
11299 @item -mbranch-expensive
11300 @opindex mbranch-expensive
11301 Pretend that branches are expensive. This is for experimenting with
11302 code generation only.
11304 @item -mbranch-cheap
11305 @opindex mbranch-cheap
11306 Do not pretend that branches are expensive. This is the default.
11310 Generate code for a system with split I&D@.
11314 Generate code for a system without split I&D@. This is the default.
11318 Use Unix assembler syntax. This is the default when configured for
11319 @samp{pdp11-*-bsd}.
11323 Use DEC assembler syntax. This is the default when configured for any
11324 PDP-11 target other than @samp{pdp11-*-bsd}.
11327 @node PowerPC Options
11328 @subsection PowerPC Options
11329 @cindex PowerPC options
11331 These are listed under @xref{RS/6000 and PowerPC Options}.
11333 @node RS/6000 and PowerPC Options
11334 @subsection IBM RS/6000 and PowerPC Options
11335 @cindex RS/6000 and PowerPC Options
11336 @cindex IBM RS/6000 and PowerPC Options
11338 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
11345 @itemx -mno-powerpc
11346 @itemx -mpowerpc-gpopt
11347 @itemx -mno-powerpc-gpopt
11348 @itemx -mpowerpc-gfxopt
11349 @itemx -mno-powerpc-gfxopt
11351 @itemx -mno-powerpc64
11355 @itemx -mno-popcntb
11363 @opindex mno-power2
11365 @opindex mno-powerpc
11366 @opindex mpowerpc-gpopt
11367 @opindex mno-powerpc-gpopt
11368 @opindex mpowerpc-gfxopt
11369 @opindex mno-powerpc-gfxopt
11370 @opindex mpowerpc64
11371 @opindex mno-powerpc64
11375 @opindex mno-popcntb
11379 @opindex mno-mfpgpr
11380 GCC supports two related instruction set architectures for the
11381 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
11382 instructions supported by the @samp{rios} chip set used in the original
11383 RS/6000 systems and the @dfn{PowerPC} instruction set is the
11384 architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and
11385 the IBM 4xx, 6xx, and follow-on microprocessors.
11387 Neither architecture is a subset of the other. However there is a
11388 large common subset of instructions supported by both. An MQ
11389 register is included in processors supporting the POWER architecture.
11391 You use these options to specify which instructions are available on the
11392 processor you are using. The default value of these options is
11393 determined when configuring GCC@. Specifying the
11394 @option{-mcpu=@var{cpu_type}} overrides the specification of these
11395 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
11396 rather than the options listed above.
11398 The @option{-mpower} option allows GCC to generate instructions that
11399 are found only in the POWER architecture and to use the MQ register.
11400 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
11401 to generate instructions that are present in the POWER2 architecture but
11402 not the original POWER architecture.
11404 The @option{-mpowerpc} option allows GCC to generate instructions that
11405 are found only in the 32-bit subset of the PowerPC architecture.
11406 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
11407 GCC to use the optional PowerPC architecture instructions in the
11408 General Purpose group, including floating-point square root. Specifying
11409 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
11410 use the optional PowerPC architecture instructions in the Graphics
11411 group, including floating-point select.
11413 The @option{-mmfcrf} option allows GCC to generate the move from
11414 condition register field instruction implemented on the POWER4
11415 processor and other processors that support the PowerPC V2.01
11417 The @option{-mpopcntb} option allows GCC to generate the popcount and
11418 double precision FP reciprocal estimate instruction implemented on the
11419 POWER5 processor and other processors that support the PowerPC V2.02
11421 The @option{-mfprnd} option allows GCC to generate the FP round to
11422 integer instructions implemented on the POWER5+ processor and other
11423 processors that support the PowerPC V2.03 architecture.
11424 The @option{-mmfpgpr} option allows GCC to generate the FP move to/from
11425 general purpose register instructions implemented on the POWER6X
11426 processor and other processors that support the extended PowerPC V2.05
11429 The @option{-mpowerpc64} option allows GCC to generate the additional
11430 64-bit instructions that are found in the full PowerPC64 architecture
11431 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
11432 @option{-mno-powerpc64}.
11434 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
11435 will use only the instructions in the common subset of both
11436 architectures plus some special AIX common-mode calls, and will not use
11437 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
11438 permits GCC to use any instruction from either architecture and to
11439 allow use of the MQ register; specify this for the Motorola MPC601.
11441 @item -mnew-mnemonics
11442 @itemx -mold-mnemonics
11443 @opindex mnew-mnemonics
11444 @opindex mold-mnemonics
11445 Select which mnemonics to use in the generated assembler code. With
11446 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
11447 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
11448 assembler mnemonics defined for the POWER architecture. Instructions
11449 defined in only one architecture have only one mnemonic; GCC uses that
11450 mnemonic irrespective of which of these options is specified.
11452 GCC defaults to the mnemonics appropriate for the architecture in
11453 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
11454 value of these option. Unless you are building a cross-compiler, you
11455 should normally not specify either @option{-mnew-mnemonics} or
11456 @option{-mold-mnemonics}, but should instead accept the default.
11458 @item -mcpu=@var{cpu_type}
11460 Set architecture type, register usage, choice of mnemonics, and
11461 instruction scheduling parameters for machine type @var{cpu_type}.
11462 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
11463 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{505},
11464 @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
11465 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
11466 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
11467 @samp{860}, @samp{970}, @samp{8540}, @samp{ec603e}, @samp{G3},
11468 @samp{G4}, @samp{G5}, @samp{power}, @samp{power2}, @samp{power3},
11469 @samp{power4}, @samp{power5}, @samp{power5+}, @samp{power6},
11470 @samp{power6x}, @samp{common}, @samp{powerpc}, @samp{powerpc64},
11471 @samp{rios}, @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
11473 @option{-mcpu=common} selects a completely generic processor. Code
11474 generated under this option will run on any POWER or PowerPC processor.
11475 GCC will use only the instructions in the common subset of both
11476 architectures, and will not use the MQ register. GCC assumes a generic
11477 processor model for scheduling purposes.
11479 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
11480 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
11481 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
11482 types, with an appropriate, generic processor model assumed for
11483 scheduling purposes.
11485 The other options specify a specific processor. Code generated under
11486 those options will run best on that processor, and may not run at all on
11489 The @option{-mcpu} options automatically enable or disable the
11490 following options: @option{-maltivec}, @option{-mfprnd},
11491 @option{-mhard-float}, @option{-mmfcrf}, @option{-mmultiple},
11492 @option{-mnew-mnemonics}, @option{-mpopcntb}, @option{-mpower},
11493 @option{-mpower2}, @option{-mpowerpc64}, @option{-mpowerpc-gpopt},
11494 @option{-mpowerpc-gfxopt}, @option{-mstring}, @option{-mmulhw},
11495 @option{-mdlmzb}, @option{-mmfpgpr}.
11496 The particular options set for any particular CPU will vary between
11497 compiler versions, depending on what setting seems to produce optimal
11498 code for that CPU; it doesn't necessarily reflect the actual hardware's
11499 capabilities. If you wish to set an individual option to a particular
11500 value, you may specify it after the @option{-mcpu} option, like
11501 @samp{-mcpu=970 -mno-altivec}.
11503 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
11504 not enabled or disabled by the @option{-mcpu} option at present because
11505 AIX does not have full support for these options. You may still
11506 enable or disable them individually if you're sure it'll work in your
11509 @item -mtune=@var{cpu_type}
11511 Set the instruction scheduling parameters for machine type
11512 @var{cpu_type}, but do not set the architecture type, register usage, or
11513 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
11514 values for @var{cpu_type} are used for @option{-mtune} as for
11515 @option{-mcpu}. If both are specified, the code generated will use the
11516 architecture, registers, and mnemonics set by @option{-mcpu}, but the
11517 scheduling parameters set by @option{-mtune}.
11523 Generate code to compute division as reciprocal estimate and iterative
11524 refinement, creating opportunities for increased throughput. This
11525 feature requires: optional PowerPC Graphics instruction set for single
11526 precision and FRE instruction for double precision, assuming divides
11527 cannot generate user-visible traps, and the domain values not include
11528 Infinities, denormals or zero denominator.
11531 @itemx -mno-altivec
11533 @opindex mno-altivec
11534 Generate code that uses (does not use) AltiVec instructions, and also
11535 enable the use of built-in functions that allow more direct access to
11536 the AltiVec instruction set. You may also need to set
11537 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
11543 @opindex mno-vrsave
11544 Generate VRSAVE instructions when generating AltiVec code.
11547 @opindex msecure-plt
11548 Generate code that allows ld and ld.so to build executables and shared
11549 libraries with non-exec .plt and .got sections. This is a PowerPC
11550 32-bit SYSV ABI option.
11554 Generate code that uses a BSS .plt section that ld.so fills in, and
11555 requires .plt and .got sections that are both writable and executable.
11556 This is a PowerPC 32-bit SYSV ABI option.
11562 This switch enables or disables the generation of ISEL instructions.
11564 @item -misel=@var{yes/no}
11565 This switch has been deprecated. Use @option{-misel} and
11566 @option{-mno-isel} instead.
11572 This switch enables or disables the generation of SPE simd
11575 @item -mspe=@var{yes/no}
11576 This option has been deprecated. Use @option{-mspe} and
11577 @option{-mno-spe} instead.
11579 @item -mfloat-gprs=@var{yes/single/double/no}
11580 @itemx -mfloat-gprs
11581 @opindex mfloat-gprs
11582 This switch enables or disables the generation of floating point
11583 operations on the general purpose registers for architectures that
11586 The argument @var{yes} or @var{single} enables the use of
11587 single-precision floating point operations.
11589 The argument @var{double} enables the use of single and
11590 double-precision floating point operations.
11592 The argument @var{no} disables floating point operations on the
11593 general purpose registers.
11595 This option is currently only available on the MPC854x.
11601 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
11602 targets (including GNU/Linux). The 32-bit environment sets int, long
11603 and pointer to 32 bits and generates code that runs on any PowerPC
11604 variant. The 64-bit environment sets int to 32 bits and long and
11605 pointer to 64 bits, and generates code for PowerPC64, as for
11606 @option{-mpowerpc64}.
11609 @itemx -mno-fp-in-toc
11610 @itemx -mno-sum-in-toc
11611 @itemx -mminimal-toc
11613 @opindex mno-fp-in-toc
11614 @opindex mno-sum-in-toc
11615 @opindex mminimal-toc
11616 Modify generation of the TOC (Table Of Contents), which is created for
11617 every executable file. The @option{-mfull-toc} option is selected by
11618 default. In that case, GCC will allocate at least one TOC entry for
11619 each unique non-automatic variable reference in your program. GCC
11620 will also place floating-point constants in the TOC@. However, only
11621 16,384 entries are available in the TOC@.
11623 If you receive a linker error message that saying you have overflowed
11624 the available TOC space, you can reduce the amount of TOC space used
11625 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
11626 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
11627 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
11628 generate code to calculate the sum of an address and a constant at
11629 run-time instead of putting that sum into the TOC@. You may specify one
11630 or both of these options. Each causes GCC to produce very slightly
11631 slower and larger code at the expense of conserving TOC space.
11633 If you still run out of space in the TOC even when you specify both of
11634 these options, specify @option{-mminimal-toc} instead. This option causes
11635 GCC to make only one TOC entry for every file. When you specify this
11636 option, GCC will produce code that is slower and larger but which
11637 uses extremely little TOC space. You may wish to use this option
11638 only on files that contain less frequently executed code.
11644 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
11645 @code{long} type, and the infrastructure needed to support them.
11646 Specifying @option{-maix64} implies @option{-mpowerpc64} and
11647 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
11648 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
11651 @itemx -mno-xl-compat
11652 @opindex mxl-compat
11653 @opindex mno-xl-compat
11654 Produce code that conforms more closely to IBM XL compiler semantics
11655 when using AIX-compatible ABI. Pass floating-point arguments to
11656 prototyped functions beyond the register save area (RSA) on the stack
11657 in addition to argument FPRs. Do not assume that most significant
11658 double in 128-bit long double value is properly rounded when comparing
11659 values and converting to double. Use XL symbol names for long double
11662 The AIX calling convention was extended but not initially documented to
11663 handle an obscure K&R C case of calling a function that takes the
11664 address of its arguments with fewer arguments than declared. IBM XL
11665 compilers access floating point arguments which do not fit in the
11666 RSA from the stack when a subroutine is compiled without
11667 optimization. Because always storing floating-point arguments on the
11668 stack is inefficient and rarely needed, this option is not enabled by
11669 default and only is necessary when calling subroutines compiled by IBM
11670 XL compilers without optimization.
11674 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
11675 application written to use message passing with special startup code to
11676 enable the application to run. The system must have PE installed in the
11677 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
11678 must be overridden with the @option{-specs=} option to specify the
11679 appropriate directory location. The Parallel Environment does not
11680 support threads, so the @option{-mpe} option and the @option{-pthread}
11681 option are incompatible.
11683 @item -malign-natural
11684 @itemx -malign-power
11685 @opindex malign-natural
11686 @opindex malign-power
11687 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
11688 @option{-malign-natural} overrides the ABI-defined alignment of larger
11689 types, such as floating-point doubles, on their natural size-based boundary.
11690 The option @option{-malign-power} instructs GCC to follow the ABI-specified
11691 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
11693 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
11697 @itemx -mhard-float
11698 @opindex msoft-float
11699 @opindex mhard-float
11700 Generate code that does not use (uses) the floating-point register set.
11701 Software floating point emulation is provided if you use the
11702 @option{-msoft-float} option, and pass the option to GCC when linking.
11705 @itemx -mno-multiple
11707 @opindex mno-multiple
11708 Generate code that uses (does not use) the load multiple word
11709 instructions and the store multiple word instructions. These
11710 instructions are generated by default on POWER systems, and not
11711 generated on PowerPC systems. Do not use @option{-mmultiple} on little
11712 endian PowerPC systems, since those instructions do not work when the
11713 processor is in little endian mode. The exceptions are PPC740 and
11714 PPC750 which permit the instructions usage in little endian mode.
11719 @opindex mno-string
11720 Generate code that uses (does not use) the load string instructions
11721 and the store string word instructions to save multiple registers and
11722 do small block moves. These instructions are generated by default on
11723 POWER systems, and not generated on PowerPC systems. Do not use
11724 @option{-mstring} on little endian PowerPC systems, since those
11725 instructions do not work when the processor is in little endian mode.
11726 The exceptions are PPC740 and PPC750 which permit the instructions
11727 usage in little endian mode.
11732 @opindex mno-update
11733 Generate code that uses (does not use) the load or store instructions
11734 that update the base register to the address of the calculated memory
11735 location. These instructions are generated by default. If you use
11736 @option{-mno-update}, there is a small window between the time that the
11737 stack pointer is updated and the address of the previous frame is
11738 stored, which means code that walks the stack frame across interrupts or
11739 signals may get corrupted data.
11742 @itemx -mno-fused-madd
11743 @opindex mfused-madd
11744 @opindex mno-fused-madd
11745 Generate code that uses (does not use) the floating point multiply and
11746 accumulate instructions. These instructions are generated by default if
11747 hardware floating is used.
11753 Generate code that uses (does not use) the half-word multiply and
11754 multiply-accumulate instructions on the IBM 405 and 440 processors.
11755 These instructions are generated by default when targetting those
11762 Generate code that uses (does not use) the string-search @samp{dlmzb}
11763 instruction on the IBM 405 and 440 processors. This instruction is
11764 generated by default when targetting those processors.
11766 @item -mno-bit-align
11768 @opindex mno-bit-align
11769 @opindex mbit-align
11770 On System V.4 and embedded PowerPC systems do not (do) force structures
11771 and unions that contain bit-fields to be aligned to the base type of the
11774 For example, by default a structure containing nothing but 8
11775 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
11776 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
11777 the structure would be aligned to a 1 byte boundary and be one byte in
11780 @item -mno-strict-align
11781 @itemx -mstrict-align
11782 @opindex mno-strict-align
11783 @opindex mstrict-align
11784 On System V.4 and embedded PowerPC systems do not (do) assume that
11785 unaligned memory references will be handled by the system.
11787 @item -mrelocatable
11788 @itemx -mno-relocatable
11789 @opindex mrelocatable
11790 @opindex mno-relocatable
11791 On embedded PowerPC systems generate code that allows (does not allow)
11792 the program to be relocated to a different address at runtime. If you
11793 use @option{-mrelocatable} on any module, all objects linked together must
11794 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
11796 @item -mrelocatable-lib
11797 @itemx -mno-relocatable-lib
11798 @opindex mrelocatable-lib
11799 @opindex mno-relocatable-lib
11800 On embedded PowerPC systems generate code that allows (does not allow)
11801 the program to be relocated to a different address at runtime. Modules
11802 compiled with @option{-mrelocatable-lib} can be linked with either modules
11803 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
11804 with modules compiled with the @option{-mrelocatable} options.
11810 On System V.4 and embedded PowerPC systems do not (do) assume that
11811 register 2 contains a pointer to a global area pointing to the addresses
11812 used in the program.
11815 @itemx -mlittle-endian
11817 @opindex mlittle-endian
11818 On System V.4 and embedded PowerPC systems compile code for the
11819 processor in little endian mode. The @option{-mlittle-endian} option is
11820 the same as @option{-mlittle}.
11823 @itemx -mbig-endian
11825 @opindex mbig-endian
11826 On System V.4 and embedded PowerPC systems compile code for the
11827 processor in big endian mode. The @option{-mbig-endian} option is
11828 the same as @option{-mbig}.
11830 @item -mdynamic-no-pic
11831 @opindex mdynamic-no-pic
11832 On Darwin and Mac OS X systems, compile code so that it is not
11833 relocatable, but that its external references are relocatable. The
11834 resulting code is suitable for applications, but not shared
11837 @item -mprioritize-restricted-insns=@var{priority}
11838 @opindex mprioritize-restricted-insns
11839 This option controls the priority that is assigned to
11840 dispatch-slot restricted instructions during the second scheduling
11841 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
11842 @var{no/highest/second-highest} priority to dispatch slot restricted
11845 @item -msched-costly-dep=@var{dependence_type}
11846 @opindex msched-costly-dep
11847 This option controls which dependences are considered costly
11848 by the target during instruction scheduling. The argument
11849 @var{dependence_type} takes one of the following values:
11850 @var{no}: no dependence is costly,
11851 @var{all}: all dependences are costly,
11852 @var{true_store_to_load}: a true dependence from store to load is costly,
11853 @var{store_to_load}: any dependence from store to load is costly,
11854 @var{number}: any dependence which latency >= @var{number} is costly.
11856 @item -minsert-sched-nops=@var{scheme}
11857 @opindex minsert-sched-nops
11858 This option controls which nop insertion scheme will be used during
11859 the second scheduling pass. The argument @var{scheme} takes one of the
11861 @var{no}: Don't insert nops.
11862 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
11863 according to the scheduler's grouping.
11864 @var{regroup_exact}: Insert nops to force costly dependent insns into
11865 separate groups. Insert exactly as many nops as needed to force an insn
11866 to a new group, according to the estimated processor grouping.
11867 @var{number}: Insert nops to force costly dependent insns into
11868 separate groups. Insert @var{number} nops to force an insn to a new group.
11871 @opindex mcall-sysv
11872 On System V.4 and embedded PowerPC systems compile code using calling
11873 conventions that adheres to the March 1995 draft of the System V
11874 Application Binary Interface, PowerPC processor supplement. This is the
11875 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
11877 @item -mcall-sysv-eabi
11878 @opindex mcall-sysv-eabi
11879 Specify both @option{-mcall-sysv} and @option{-meabi} options.
11881 @item -mcall-sysv-noeabi
11882 @opindex mcall-sysv-noeabi
11883 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
11885 @item -mcall-solaris
11886 @opindex mcall-solaris
11887 On System V.4 and embedded PowerPC systems compile code for the Solaris
11891 @opindex mcall-linux
11892 On System V.4 and embedded PowerPC systems compile code for the
11893 Linux-based GNU system.
11897 On System V.4 and embedded PowerPC systems compile code for the
11898 Hurd-based GNU system.
11900 @item -mcall-netbsd
11901 @opindex mcall-netbsd
11902 On System V.4 and embedded PowerPC systems compile code for the
11903 NetBSD operating system.
11905 @item -maix-struct-return
11906 @opindex maix-struct-return
11907 Return all structures in memory (as specified by the AIX ABI)@.
11909 @item -msvr4-struct-return
11910 @opindex msvr4-struct-return
11911 Return structures smaller than 8 bytes in registers (as specified by the
11914 @item -mabi=@var{abi-type}
11916 Extend the current ABI with a particular extension, or remove such extension.
11917 Valid values are @var{altivec}, @var{no-altivec}, @var{spe},
11918 @var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}@.
11922 Extend the current ABI with SPE ABI extensions. This does not change
11923 the default ABI, instead it adds the SPE ABI extensions to the current
11927 @opindex mabi=no-spe
11928 Disable Booke SPE ABI extensions for the current ABI@.
11930 @item -mabi=ibmlongdouble
11931 @opindex mabi=ibmlongdouble
11932 Change the current ABI to use IBM extended precision long double.
11933 This is a PowerPC 32-bit SYSV ABI option.
11935 @item -mabi=ieeelongdouble
11936 @opindex mabi=ieeelongdouble
11937 Change the current ABI to use IEEE extended precision long double.
11938 This is a PowerPC 32-bit Linux ABI option.
11941 @itemx -mno-prototype
11942 @opindex mprototype
11943 @opindex mno-prototype
11944 On System V.4 and embedded PowerPC systems assume that all calls to
11945 variable argument functions are properly prototyped. Otherwise, the
11946 compiler must insert an instruction before every non prototyped call to
11947 set or clear bit 6 of the condition code register (@var{CR}) to
11948 indicate whether floating point values were passed in the floating point
11949 registers in case the function takes a variable arguments. With
11950 @option{-mprototype}, only calls to prototyped variable argument functions
11951 will set or clear the bit.
11955 On embedded PowerPC systems, assume that the startup module is called
11956 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
11957 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
11962 On embedded PowerPC systems, assume that the startup module is called
11963 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
11968 On embedded PowerPC systems, assume that the startup module is called
11969 @file{crt0.o} and the standard C libraries are @file{libads.a} and
11972 @item -myellowknife
11973 @opindex myellowknife
11974 On embedded PowerPC systems, assume that the startup module is called
11975 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
11980 On System V.4 and embedded PowerPC systems, specify that you are
11981 compiling for a VxWorks system.
11985 Specify that you are compiling for the WindISS simulation environment.
11989 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
11990 header to indicate that @samp{eabi} extended relocations are used.
11996 On System V.4 and embedded PowerPC systems do (do not) adhere to the
11997 Embedded Applications Binary Interface (eabi) which is a set of
11998 modifications to the System V.4 specifications. Selecting @option{-meabi}
11999 means that the stack is aligned to an 8 byte boundary, a function
12000 @code{__eabi} is called to from @code{main} to set up the eabi
12001 environment, and the @option{-msdata} option can use both @code{r2} and
12002 @code{r13} to point to two separate small data areas. Selecting
12003 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
12004 do not call an initialization function from @code{main}, and the
12005 @option{-msdata} option will only use @code{r13} to point to a single
12006 small data area. The @option{-meabi} option is on by default if you
12007 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
12010 @opindex msdata=eabi
12011 On System V.4 and embedded PowerPC systems, put small initialized
12012 @code{const} global and static data in the @samp{.sdata2} section, which
12013 is pointed to by register @code{r2}. Put small initialized
12014 non-@code{const} global and static data in the @samp{.sdata} section,
12015 which is pointed to by register @code{r13}. Put small uninitialized
12016 global and static data in the @samp{.sbss} section, which is adjacent to
12017 the @samp{.sdata} section. The @option{-msdata=eabi} option is
12018 incompatible with the @option{-mrelocatable} option. The
12019 @option{-msdata=eabi} option also sets the @option{-memb} option.
12022 @opindex msdata=sysv
12023 On System V.4 and embedded PowerPC systems, put small global and static
12024 data in the @samp{.sdata} section, which is pointed to by register
12025 @code{r13}. Put small uninitialized global and static data in the
12026 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
12027 The @option{-msdata=sysv} option is incompatible with the
12028 @option{-mrelocatable} option.
12030 @item -msdata=default
12032 @opindex msdata=default
12034 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
12035 compile code the same as @option{-msdata=eabi}, otherwise compile code the
12036 same as @option{-msdata=sysv}.
12039 @opindex msdata-data
12040 On System V.4 and embedded PowerPC systems, put small global
12041 data in the @samp{.sdata} section. Put small uninitialized global
12042 data in the @samp{.sbss} section. Do not use register @code{r13}
12043 to address small data however. This is the default behavior unless
12044 other @option{-msdata} options are used.
12048 @opindex msdata=none
12050 On embedded PowerPC systems, put all initialized global and static data
12051 in the @samp{.data} section, and all uninitialized data in the
12052 @samp{.bss} section.
12056 @cindex smaller data references (PowerPC)
12057 @cindex .sdata/.sdata2 references (PowerPC)
12058 On embedded PowerPC systems, put global and static items less than or
12059 equal to @var{num} bytes into the small data or bss sections instead of
12060 the normal data or bss section. By default, @var{num} is 8. The
12061 @option{-G @var{num}} switch is also passed to the linker.
12062 All modules should be compiled with the same @option{-G @var{num}} value.
12065 @itemx -mno-regnames
12067 @opindex mno-regnames
12068 On System V.4 and embedded PowerPC systems do (do not) emit register
12069 names in the assembly language output using symbolic forms.
12072 @itemx -mno-longcall
12074 @opindex mno-longcall
12075 By default assume that all calls are far away so that a longer more
12076 expensive calling sequence is required. This is required for calls
12077 further than 32 megabytes (33,554,432 bytes) from the current location.
12078 A short call will be generated if the compiler knows
12079 the call cannot be that far away. This setting can be overridden by
12080 the @code{shortcall} function attribute, or by @code{#pragma
12083 Some linkers are capable of detecting out-of-range calls and generating
12084 glue code on the fly. On these systems, long calls are unnecessary and
12085 generate slower code. As of this writing, the AIX linker can do this,
12086 as can the GNU linker for PowerPC/64. It is planned to add this feature
12087 to the GNU linker for 32-bit PowerPC systems as well.
12089 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
12090 callee, L42'', plus a ``branch island'' (glue code). The two target
12091 addresses represent the callee and the ``branch island''. The
12092 Darwin/PPC linker will prefer the first address and generate a ``bl
12093 callee'' if the PPC ``bl'' instruction will reach the callee directly;
12094 otherwise, the linker will generate ``bl L42'' to call the ``branch
12095 island''. The ``branch island'' is appended to the body of the
12096 calling function; it computes the full 32-bit address of the callee
12099 On Mach-O (Darwin) systems, this option directs the compiler emit to
12100 the glue for every direct call, and the Darwin linker decides whether
12101 to use or discard it.
12103 In the future, we may cause GCC to ignore all longcall specifications
12104 when the linker is known to generate glue.
12108 Adds support for multithreading with the @dfn{pthreads} library.
12109 This option sets flags for both the preprocessor and linker.
12113 @node S/390 and zSeries Options
12114 @subsection S/390 and zSeries Options
12115 @cindex S/390 and zSeries Options
12117 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
12121 @itemx -msoft-float
12122 @opindex mhard-float
12123 @opindex msoft-float
12124 Use (do not use) the hardware floating-point instructions and registers
12125 for floating-point operations. When @option{-msoft-float} is specified,
12126 functions in @file{libgcc.a} will be used to perform floating-point
12127 operations. When @option{-mhard-float} is specified, the compiler
12128 generates IEEE floating-point instructions. This is the default.
12130 @item -mlong-double-64
12131 @itemx -mlong-double-128
12132 @opindex mlong-double-64
12133 @opindex mlong-double-128
12134 These switches control the size of @code{long double} type. A size
12135 of 64bit makes the @code{long double} type equivalent to the @code{double}
12136 type. This is the default.
12139 @itemx -mno-backchain
12140 @opindex mbackchain
12141 @opindex mno-backchain
12142 Store (do not store) the address of the caller's frame as backchain pointer
12143 into the callee's stack frame.
12144 A backchain may be needed to allow debugging using tools that do not understand
12145 DWARF-2 call frame information.
12146 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
12147 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
12148 the backchain is placed into the topmost word of the 96/160 byte register
12151 In general, code compiled with @option{-mbackchain} is call-compatible with
12152 code compiled with @option{-mmo-backchain}; however, use of the backchain
12153 for debugging purposes usually requires that the whole binary is built with
12154 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
12155 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
12156 to build a linux kernel use @option{-msoft-float}.
12158 The default is to not maintain the backchain.
12160 @item -mpacked-stack
12161 @item -mno-packed-stack
12162 @opindex mpacked-stack
12163 @opindex mno-packed-stack
12164 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
12165 specified, the compiler uses the all fields of the 96/160 byte register save
12166 area only for their default purpose; unused fields still take up stack space.
12167 When @option{-mpacked-stack} is specified, register save slots are densely
12168 packed at the top of the register save area; unused space is reused for other
12169 purposes, allowing for more efficient use of the available stack space.
12170 However, when @option{-mbackchain} is also in effect, the topmost word of
12171 the save area is always used to store the backchain, and the return address
12172 register is always saved two words below the backchain.
12174 As long as the stack frame backchain is not used, code generated with
12175 @option{-mpacked-stack} is call-compatible with code generated with
12176 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
12177 S/390 or zSeries generated code that uses the stack frame backchain at run
12178 time, not just for debugging purposes. Such code is not call-compatible
12179 with code compiled with @option{-mpacked-stack}. Also, note that the
12180 combination of @option{-mbackchain},
12181 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
12182 to build a linux kernel use @option{-msoft-float}.
12184 The default is to not use the packed stack layout.
12187 @itemx -mno-small-exec
12188 @opindex msmall-exec
12189 @opindex mno-small-exec
12190 Generate (or do not generate) code using the @code{bras} instruction
12191 to do subroutine calls.
12192 This only works reliably if the total executable size does not
12193 exceed 64k. The default is to use the @code{basr} instruction instead,
12194 which does not have this limitation.
12200 When @option{-m31} is specified, generate code compliant to the
12201 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
12202 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
12203 particular to generate 64-bit instructions. For the @samp{s390}
12204 targets, the default is @option{-m31}, while the @samp{s390x}
12205 targets default to @option{-m64}.
12211 When @option{-mzarch} is specified, generate code using the
12212 instructions available on z/Architecture.
12213 When @option{-mesa} is specified, generate code using the
12214 instructions available on ESA/390. Note that @option{-mesa} is
12215 not possible with @option{-m64}.
12216 When generating code compliant to the GNU/Linux for S/390 ABI,
12217 the default is @option{-mesa}. When generating code compliant
12218 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
12224 Generate (or do not generate) code using the @code{mvcle} instruction
12225 to perform block moves. When @option{-mno-mvcle} is specified,
12226 use a @code{mvc} loop instead. This is the default unless optimizing for
12233 Print (or do not print) additional debug information when compiling.
12234 The default is to not print debug information.
12236 @item -march=@var{cpu-type}
12238 Generate code that will run on @var{cpu-type}, which is the name of a system
12239 representing a certain processor type. Possible values for
12240 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
12241 When generating code using the instructions available on z/Architecture,
12242 the default is @option{-march=z900}. Otherwise, the default is
12243 @option{-march=g5}.
12245 @item -mtune=@var{cpu-type}
12247 Tune to @var{cpu-type} everything applicable about the generated code,
12248 except for the ABI and the set of available instructions.
12249 The list of @var{cpu-type} values is the same as for @option{-march}.
12250 The default is the value used for @option{-march}.
12253 @itemx -mno-tpf-trace
12254 @opindex mtpf-trace
12255 @opindex mno-tpf-trace
12256 Generate code that adds (does not add) in TPF OS specific branches to trace
12257 routines in the operating system. This option is off by default, even
12258 when compiling for the TPF OS@.
12261 @itemx -mno-fused-madd
12262 @opindex mfused-madd
12263 @opindex mno-fused-madd
12264 Generate code that uses (does not use) the floating point multiply and
12265 accumulate instructions. These instructions are generated by default if
12266 hardware floating point is used.
12268 @item -mwarn-framesize=@var{framesize}
12269 @opindex mwarn-framesize
12270 Emit a warning if the current function exceeds the given frame size. Because
12271 this is a compile time check it doesn't need to be a real problem when the program
12272 runs. It is intended to identify functions which most probably cause
12273 a stack overflow. It is useful to be used in an environment with limited stack
12274 size e.g.@: the linux kernel.
12276 @item -mwarn-dynamicstack
12277 @opindex mwarn-dynamicstack
12278 Emit a warning if the function calls alloca or uses dynamically
12279 sized arrays. This is generally a bad idea with a limited stack size.
12281 @item -mstack-guard=@var{stack-guard}
12282 @item -mstack-size=@var{stack-size}
12283 @opindex mstack-guard
12284 @opindex mstack-size
12285 These arguments always have to be used in conjunction. If they are present the s390
12286 back end emits additional instructions in the function prologue which trigger a trap
12287 if the stack size is @var{stack-guard} bytes above the @var{stack-size}
12288 (remember that the stack on s390 grows downward). These options are intended to
12289 be used to help debugging stack overflow problems. The additionally emitted code
12290 causes only little overhead and hence can also be used in production like systems
12291 without greater performance degradation. The given values have to be exact
12292 powers of 2 and @var{stack-size} has to be greater than @var{stack-guard} without
12294 In order to be efficient the extra code makes the assumption that the stack starts
12295 at an address aligned to the value given by @var{stack-size}.
12298 @node Score Options
12299 @subsection Score Options
12300 @cindex Score Options
12302 These options are defined for Score implementations:
12307 Compile code for little endian mode.
12311 Compile code for big endian mode. This is the default.
12315 Enable the use of multiply-accumulate instructions. Disabled by default.
12319 Specify the SCORE5U of the target architecture.
12323 Specify the SCORE7 of the target architecture. This is the default.
12327 @subsection SH Options
12329 These @samp{-m} options are defined for the SH implementations:
12334 Generate code for the SH1.
12338 Generate code for the SH2.
12341 Generate code for the SH2e.
12345 Generate code for the SH3.
12349 Generate code for the SH3e.
12353 Generate code for the SH4 without a floating-point unit.
12355 @item -m4-single-only
12356 @opindex m4-single-only
12357 Generate code for the SH4 with a floating-point unit that only
12358 supports single-precision arithmetic.
12362 Generate code for the SH4 assuming the floating-point unit is in
12363 single-precision mode by default.
12367 Generate code for the SH4.
12371 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
12372 floating-point unit is not used.
12374 @item -m4a-single-only
12375 @opindex m4a-single-only
12376 Generate code for the SH4a, in such a way that no double-precision
12377 floating point operations are used.
12380 @opindex m4a-single
12381 Generate code for the SH4a assuming the floating-point unit is in
12382 single-precision mode by default.
12386 Generate code for the SH4a.
12390 Same as @option{-m4a-nofpu}, except that it implicitly passes
12391 @option{-dsp} to the assembler. GCC doesn't generate any DSP
12392 instructions at the moment.
12396 Compile code for the processor in big endian mode.
12400 Compile code for the processor in little endian mode.
12404 Align doubles at 64-bit boundaries. Note that this changes the calling
12405 conventions, and thus some functions from the standard C library will
12406 not work unless you recompile it first with @option{-mdalign}.
12410 Shorten some address references at link time, when possible; uses the
12411 linker option @option{-relax}.
12415 Use 32-bit offsets in @code{switch} tables. The default is to use
12420 Enable the use of the instruction @code{fmovd}.
12424 Comply with the calling conventions defined by Renesas.
12428 Comply with the calling conventions defined by Renesas.
12432 Comply with the calling conventions defined for GCC before the Renesas
12433 conventions were available. This option is the default for all
12434 targets of the SH toolchain except for @samp{sh-symbianelf}.
12437 @opindex mnomacsave
12438 Mark the @code{MAC} register as call-clobbered, even if
12439 @option{-mhitachi} is given.
12443 Increase IEEE-compliance of floating-point code.
12444 At the moment, this is equivalent to @option{-fno-finite-math-only}.
12445 When generating 16 bit SH opcodes, getting IEEE-conforming results for
12446 comparisons of NANs / infinities incurs extra overhead in every
12447 floating point comparison, therefore the default is set to
12448 @option{-ffinite-math-only}.
12450 @item -minline-ic_invalidate
12451 @opindex minline-ic_invalidate
12452 Inline code to invalidate instruction cache entries after setting up
12453 nested function trampolines.
12454 This option has no effect if -musermode is in effect and the selected
12455 code generation option (e.g. -m4) does not allow the use of the icbi
12457 If the selected code generation option does not allow the use of the icbi
12458 instruction, and -musermode is not in effect, the inlined code will
12459 manipulate the instruction cache address array directly with an associative
12460 write. This not only requires privileged mode, but it will also
12461 fail if the cache line had been mapped via the TLB and has become unmapped.
12465 Dump instruction size and location in the assembly code.
12468 @opindex mpadstruct
12469 This option is deprecated. It pads structures to multiple of 4 bytes,
12470 which is incompatible with the SH ABI@.
12474 Optimize for space instead of speed. Implied by @option{-Os}.
12477 @opindex mprefergot
12478 When generating position-independent code, emit function calls using
12479 the Global Offset Table instead of the Procedure Linkage Table.
12483 Don't generate privileged mode only code; implies -mno-inline-ic_invalidate
12484 if the inlined code would not work in user mode.
12485 This is the default when the target is @code{sh-*-linux*}.
12487 @item -multcost=@var{number}
12488 @opindex multcost=@var{number}
12489 Set the cost to assume for a multiply insn.
12491 @item -mdiv=@var{strategy}
12492 @opindex mdiv=@var{strategy}
12493 Set the division strategy to use for SHmedia code. @var{strategy} must be
12494 one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
12495 inv:call2, inv:fp .
12496 "fp" performs the operation in floating point. This has a very high latency,
12497 but needs only a few instructions, so it might be a good choice if
12498 your code has enough easily exploitable ILP to allow the compiler to
12499 schedule the floating point instructions together with other instructions.
12500 Division by zero causes a floating point exception.
12501 "inv" uses integer operations to calculate the inverse of the divisor,
12502 and then multiplies the dividend with the inverse. This strategy allows
12503 cse and hoisting of the inverse calculation. Division by zero calculates
12504 an unspecified result, but does not trap.
12505 "inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
12506 have been found, or if the entire operation has been hoisted to the same
12507 place, the last stages of the inverse calculation are intertwined with the
12508 final multiply to reduce the overall latency, at the expense of using a few
12509 more instructions, and thus offering fewer scheduling opportunities with
12511 "call" calls a library function that usually implements the inv:minlat
12513 This gives high code density for m5-*media-nofpu compilations.
12514 "call2" uses a different entry point of the same library function, where it
12515 assumes that a pointer to a lookup table has already been set up, which
12516 exposes the pointer load to cse / code hoisting optimizations.
12517 "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
12518 code generation, but if the code stays unoptimized, revert to the "call",
12519 "call2", or "fp" strategies, respectively. Note that the
12520 potentially-trapping side effect of division by zero is carried by a
12521 separate instruction, so it is possible that all the integer instructions
12522 are hoisted out, but the marker for the side effect stays where it is.
12523 A recombination to fp operations or a call is not possible in that case.
12524 "inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
12525 that the inverse calculation was nor separated from the multiply, they speed
12526 up division where the dividend fits into 20 bits (plus sign where applicable),
12527 by inserting a test to skip a number of operations in this case; this test
12528 slows down the case of larger dividends. inv20u assumes the case of a such
12529 a small dividend to be unlikely, and inv20l assumes it to be likely.
12531 @item -mdivsi3_libfunc=@var{name}
12532 @opindex mdivsi3_libfunc=@var{name}
12533 Set the name of the library function used for 32 bit signed division to
12534 @var{name}. This only affect the name used in the call and inv:call
12535 division strategies, and the compiler will still expect the same
12536 sets of input/output/clobbered registers as if this option was not present.
12538 @item -madjust-unroll
12539 @opindex madjust-unroll
12540 Throttle unrolling to avoid thrashing target registers.
12541 This option only has an effect if the gcc code base supports the
12542 TARGET_ADJUST_UNROLL_MAX target hook.
12544 @item -mindexed-addressing
12545 @opindex mindexed-addressing
12546 Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
12547 This is only safe if the hardware and/or OS implement 32 bit wrap-around
12548 semantics for the indexed addressing mode. The architecture allows the
12549 implementation of processors with 64 bit MMU, which the OS could use to
12550 get 32 bit addressing, but since no current hardware implementation supports
12551 this or any other way to make the indexed addressing mode safe to use in
12552 the 32 bit ABI, the default is -mno-indexed-addressing.
12554 @item -mgettrcost=@var{number}
12555 @opindex mgettrcost=@var{number}
12556 Set the cost assumed for the gettr instruction to @var{number}.
12557 The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
12561 Assume pt* instructions won't trap. This will generally generate better
12562 scheduled code, but is unsafe on current hardware. The current architecture
12563 definition says that ptabs and ptrel trap when the target anded with 3 is 3.
12564 This has the unintentional effect of making it unsafe to schedule ptabs /
12565 ptrel before a branch, or hoist it out of a loop. For example,
12566 __do_global_ctors, a part of libgcc that runs constructors at program
12567 startup, calls functions in a list which is delimited by -1. With the
12568 -mpt-fixed option, the ptabs will be done before testing against -1.
12569 That means that all the constructors will be run a bit quicker, but when
12570 the loop comes to the end of the list, the program crashes because ptabs
12571 loads -1 into a target register. Since this option is unsafe for any
12572 hardware implementing the current architecture specification, the default
12573 is -mno-pt-fixed. Unless the user specifies a specific cost with
12574 @option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100};
12575 this deters register allocation using target registers for storing
12578 @item -minvalid-symbols
12579 @opindex minvalid-symbols
12580 Assume symbols might be invalid. Ordinary function symbols generated by
12581 the compiler will always be valid to load with movi/shori/ptabs or
12582 movi/shori/ptrel, but with assembler and/or linker tricks it is possible
12583 to generate symbols that will cause ptabs / ptrel to trap.
12584 This option is only meaningful when @option{-mno-pt-fixed} is in effect.
12585 It will then prevent cross-basic-block cse, hoisting and most scheduling
12586 of symbol loads. The default is @option{-mno-invalid-symbols}.
12589 @node SPARC Options
12590 @subsection SPARC Options
12591 @cindex SPARC options
12593 These @samp{-m} options are supported on the SPARC:
12596 @item -mno-app-regs
12598 @opindex mno-app-regs
12600 Specify @option{-mapp-regs} to generate output using the global registers
12601 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
12604 To be fully SVR4 ABI compliant at the cost of some performance loss,
12605 specify @option{-mno-app-regs}. You should compile libraries and system
12606 software with this option.
12609 @itemx -mhard-float
12611 @opindex mhard-float
12612 Generate output containing floating point instructions. This is the
12616 @itemx -msoft-float
12618 @opindex msoft-float
12619 Generate output containing library calls for floating point.
12620 @strong{Warning:} the requisite libraries are not available for all SPARC
12621 targets. Normally the facilities of the machine's usual C compiler are
12622 used, but this cannot be done directly in cross-compilation. You must make
12623 your own arrangements to provide suitable library functions for
12624 cross-compilation. The embedded targets @samp{sparc-*-aout} and
12625 @samp{sparclite-*-*} do provide software floating point support.
12627 @option{-msoft-float} changes the calling convention in the output file;
12628 therefore, it is only useful if you compile @emph{all} of a program with
12629 this option. In particular, you need to compile @file{libgcc.a}, the
12630 library that comes with GCC, with @option{-msoft-float} in order for
12633 @item -mhard-quad-float
12634 @opindex mhard-quad-float
12635 Generate output containing quad-word (long double) floating point
12638 @item -msoft-quad-float
12639 @opindex msoft-quad-float
12640 Generate output containing library calls for quad-word (long double)
12641 floating point instructions. The functions called are those specified
12642 in the SPARC ABI@. This is the default.
12644 As of this writing, there are no SPARC implementations that have hardware
12645 support for the quad-word floating point instructions. They all invoke
12646 a trap handler for one of these instructions, and then the trap handler
12647 emulates the effect of the instruction. Because of the trap handler overhead,
12648 this is much slower than calling the ABI library routines. Thus the
12649 @option{-msoft-quad-float} option is the default.
12651 @item -mno-unaligned-doubles
12652 @itemx -munaligned-doubles
12653 @opindex mno-unaligned-doubles
12654 @opindex munaligned-doubles
12655 Assume that doubles have 8 byte alignment. This is the default.
12657 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
12658 alignment only if they are contained in another type, or if they have an
12659 absolute address. Otherwise, it assumes they have 4 byte alignment.
12660 Specifying this option avoids some rare compatibility problems with code
12661 generated by other compilers. It is not the default because it results
12662 in a performance loss, especially for floating point code.
12664 @item -mno-faster-structs
12665 @itemx -mfaster-structs
12666 @opindex mno-faster-structs
12667 @opindex mfaster-structs
12668 With @option{-mfaster-structs}, the compiler assumes that structures
12669 should have 8 byte alignment. This enables the use of pairs of
12670 @code{ldd} and @code{std} instructions for copies in structure
12671 assignment, in place of twice as many @code{ld} and @code{st} pairs.
12672 However, the use of this changed alignment directly violates the SPARC
12673 ABI@. Thus, it's intended only for use on targets where the developer
12674 acknowledges that their resulting code will not be directly in line with
12675 the rules of the ABI@.
12677 @item -mimpure-text
12678 @opindex mimpure-text
12679 @option{-mimpure-text}, used in addition to @option{-shared}, tells
12680 the compiler to not pass @option{-z text} to the linker when linking a
12681 shared object. Using this option, you can link position-dependent
12682 code into a shared object.
12684 @option{-mimpure-text} suppresses the ``relocations remain against
12685 allocatable but non-writable sections'' linker error message.
12686 However, the necessary relocations will trigger copy-on-write, and the
12687 shared object is not actually shared across processes. Instead of
12688 using @option{-mimpure-text}, you should compile all source code with
12689 @option{-fpic} or @option{-fPIC}.
12691 This option is only available on SunOS and Solaris.
12693 @item -mcpu=@var{cpu_type}
12695 Set the instruction set, register set, and instruction scheduling parameters
12696 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
12697 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
12698 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
12699 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc},
12700 @samp{ultrasparc3}, and @samp{niagara}.
12702 Default instruction scheduling parameters are used for values that select
12703 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
12704 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
12706 Here is a list of each supported architecture and their supported
12711 v8: supersparc, hypersparc
12712 sparclite: f930, f934, sparclite86x
12714 v9: ultrasparc, ultrasparc3, niagara
12717 By default (unless configured otherwise), GCC generates code for the V7
12718 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
12719 additionally optimizes it for the Cypress CY7C602 chip, as used in the
12720 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
12721 SPARCStation 1, 2, IPX etc.
12723 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
12724 architecture. The only difference from V7 code is that the compiler emits
12725 the integer multiply and integer divide instructions which exist in SPARC-V8
12726 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
12727 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
12730 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
12731 the SPARC architecture. This adds the integer multiply, integer divide step
12732 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
12733 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
12734 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
12735 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
12736 MB86934 chip, which is the more recent SPARClite with FPU@.
12738 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
12739 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
12740 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
12741 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
12742 optimizes it for the TEMIC SPARClet chip.
12744 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
12745 architecture. This adds 64-bit integer and floating-point move instructions,
12746 3 additional floating-point condition code registers and conditional move
12747 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
12748 optimizes it for the Sun UltraSPARC I/II/IIi chips. With
12749 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
12750 Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With
12751 @option{-mcpu=niagara}, the compiler additionally optimizes it for
12752 Sun UltraSPARC T1 chips.
12754 @item -mtune=@var{cpu_type}
12756 Set the instruction scheduling parameters for machine type
12757 @var{cpu_type}, but do not set the instruction set or register set that the
12758 option @option{-mcpu=@var{cpu_type}} would.
12760 The same values for @option{-mcpu=@var{cpu_type}} can be used for
12761 @option{-mtune=@var{cpu_type}}, but the only useful values are those
12762 that select a particular cpu implementation. Those are @samp{cypress},
12763 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
12764 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc},
12765 @samp{ultrasparc3}, and @samp{niagara}.
12770 @opindex mno-v8plus
12771 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
12772 difference from the V8 ABI is that the global and out registers are
12773 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
12774 mode for all SPARC-V9 processors.
12780 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
12781 Visual Instruction Set extensions. The default is @option{-mno-vis}.
12784 These @samp{-m} options are supported in addition to the above
12785 on SPARC-V9 processors in 64-bit environments:
12788 @item -mlittle-endian
12789 @opindex mlittle-endian
12790 Generate code for a processor running in little-endian mode. It is only
12791 available for a few configurations and most notably not on Solaris and Linux.
12797 Generate code for a 32-bit or 64-bit environment.
12798 The 32-bit environment sets int, long and pointer to 32 bits.
12799 The 64-bit environment sets int to 32 bits and long and pointer
12802 @item -mcmodel=medlow
12803 @opindex mcmodel=medlow
12804 Generate code for the Medium/Low code model: 64-bit addresses, programs
12805 must be linked in the low 32 bits of memory. Programs can be statically
12806 or dynamically linked.
12808 @item -mcmodel=medmid
12809 @opindex mcmodel=medmid
12810 Generate code for the Medium/Middle code model: 64-bit addresses, programs
12811 must be linked in the low 44 bits of memory, the text and data segments must
12812 be less than 2GB in size and the data segment must be located within 2GB of
12815 @item -mcmodel=medany
12816 @opindex mcmodel=medany
12817 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
12818 may be linked anywhere in memory, the text and data segments must be less
12819 than 2GB in size and the data segment must be located within 2GB of the
12822 @item -mcmodel=embmedany
12823 @opindex mcmodel=embmedany
12824 Generate code for the Medium/Anywhere code model for embedded systems:
12825 64-bit addresses, the text and data segments must be less than 2GB in
12826 size, both starting anywhere in memory (determined at link time). The
12827 global register %g4 points to the base of the data segment. Programs
12828 are statically linked and PIC is not supported.
12831 @itemx -mno-stack-bias
12832 @opindex mstack-bias
12833 @opindex mno-stack-bias
12834 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
12835 frame pointer if present, are offset by @minus{}2047 which must be added back
12836 when making stack frame references. This is the default in 64-bit mode.
12837 Otherwise, assume no such offset is present.
12840 These switches are supported in addition to the above on Solaris:
12845 Add support for multithreading using the Solaris threads library. This
12846 option sets flags for both the preprocessor and linker. This option does
12847 not affect the thread safety of object code produced by the compiler or
12848 that of libraries supplied with it.
12852 Add support for multithreading using the POSIX threads library. This
12853 option sets flags for both the preprocessor and linker. This option does
12854 not affect the thread safety of object code produced by the compiler or
12855 that of libraries supplied with it.
12859 This is a synonym for @option{-pthreads}.
12863 @subsection SPU Options
12864 @cindex SPU options
12866 These @samp{-m} options are supported on the SPU:
12870 @itemx -merror-reloc
12871 @opindex mwarn-reloc
12872 @opindex merror-reloc
12874 The loader for SPU does not handle dynamic relocations. By default, GCC
12875 will give an error when it generates code that requires a dynamic
12876 relocation. @option{-mno-error-reloc} disables the error,
12877 @option{-mwarn-reloc} will generate a warning instead.
12880 @itemx -munsafe-dma
12882 @opindex munsafe-dma
12884 Instructions which initiate or test completion of DMA must not be
12885 reordered with respect to loads and stores of the memory which is being
12886 accessed. Users typically address this problem using the volatile
12887 keyword, but that can lead to inefficient code in places where the
12888 memory is known to not change. Rather than mark the memory as volatile
12889 we treat the DMA instructions as potentially effecting all memory. With
12890 @option{-munsafe-dma} users must use the volatile keyword to protect
12893 @item -mbranch-hints
12894 @opindex mbranch-hints
12896 By default, GCC will generate a branch hint instruction to avoid
12897 pipeline stalls for always taken or probably taken branches. A hint
12898 will not be generated closer than 8 instructions away from its branch.
12899 There is little reason to disable them, except for debugging purposes,
12900 or to make an object a little bit smaller.
12904 @opindex msmall-mem
12905 @opindex mlarge-mem
12907 By default, GCC generates code assuming that addresses are never larger
12908 than 18 bits. With @option{-mlarge-mem} code is generated that assumes
12909 a full 32 bit address.
12914 By default, GCC links against startup code that assumes the SPU-style
12915 main function interface (which has an unconventional parameter list).
12916 With @option{-mstdmain}, GCC will link your program against startup
12917 code that assumes a C99-style interface to @code{main}, including a
12918 local copy of @code{argv} strings.
12920 @item -mfixed-range=@var{register-range}
12921 @opindex mfixed-range
12922 Generate code treating the given register range as fixed registers.
12923 A fixed register is one that the register allocator can not use. This is
12924 useful when compiling kernel code. A register range is specified as
12925 two registers separated by a dash. Multiple register ranges can be
12926 specified separated by a comma.
12930 @node System V Options
12931 @subsection Options for System V
12933 These additional options are available on System V Release 4 for
12934 compatibility with other compilers on those systems:
12939 Create a shared object.
12940 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
12944 Identify the versions of each tool used by the compiler, in a
12945 @code{.ident} assembler directive in the output.
12949 Refrain from adding @code{.ident} directives to the output file (this is
12952 @item -YP,@var{dirs}
12954 Search the directories @var{dirs}, and no others, for libraries
12955 specified with @option{-l}.
12957 @item -Ym,@var{dir}
12959 Look in the directory @var{dir} to find the M4 preprocessor.
12960 The assembler uses this option.
12961 @c This is supposed to go with a -Yd for predefined M4 macro files, but
12962 @c the generic assembler that comes with Solaris takes just -Ym.
12965 @node TMS320C3x/C4x Options
12966 @subsection TMS320C3x/C4x Options
12967 @cindex TMS320C3x/C4x Options
12969 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
12973 @item -mcpu=@var{cpu_type}
12975 Set the instruction set, register set, and instruction scheduling
12976 parameters for machine type @var{cpu_type}. Supported values for
12977 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
12978 @samp{c44}. The default is @samp{c40} to generate code for the
12983 @itemx -msmall-memory
12985 @opindex mbig-memory
12987 @opindex msmall-memory
12989 Generates code for the big or small memory model. The small memory
12990 model assumed that all data fits into one 64K word page. At run-time
12991 the data page (DP) register must be set to point to the 64K page
12992 containing the .bss and .data program sections. The big memory model is
12993 the default and requires reloading of the DP register for every direct
13000 Allow (disallow) allocation of general integer operands into the block
13001 count register BK@.
13007 Enable (disable) generation of code using decrement and branch,
13008 DBcond(D), instructions. This is enabled by default for the C4x. To be
13009 on the safe side, this is disabled for the C3x, since the maximum
13010 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
13011 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
13012 that it can utilize the decrement and branch instruction, but will give
13013 up if there is more than one memory reference in the loop. Thus a loop
13014 where the loop counter is decremented can generate slightly more
13015 efficient code, in cases where the RPTB instruction cannot be utilized.
13017 @item -mdp-isr-reload
13019 @opindex mdp-isr-reload
13021 Force the DP register to be saved on entry to an interrupt service
13022 routine (ISR), reloaded to point to the data section, and restored on
13023 exit from the ISR@. This should not be required unless someone has
13024 violated the small memory model by modifying the DP register, say within
13031 For the C3x use the 24-bit MPYI instruction for integer multiplies
13032 instead of a library call to guarantee 32-bit results. Note that if one
13033 of the operands is a constant, then the multiplication will be performed
13034 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
13035 then squaring operations are performed inline instead of a library call.
13038 @itemx -mno-fast-fix
13040 @opindex mno-fast-fix
13041 The C3x/C4x FIX instruction to convert a floating point value to an
13042 integer value chooses the nearest integer less than or equal to the
13043 floating point value rather than to the nearest integer. Thus if the
13044 floating point number is negative, the result will be incorrectly
13045 truncated an additional code is necessary to detect and correct this
13046 case. This option can be used to disable generation of the additional
13047 code required to correct the result.
13053 Enable (disable) generation of repeat block sequences using the RPTB
13054 instruction for zero overhead looping. The RPTB construct is only used
13055 for innermost loops that do not call functions or jump across the loop
13056 boundaries. There is no advantage having nested RPTB loops due to the
13057 overhead required to save and restore the RC, RS, and RE registers.
13058 This is enabled by default with @option{-O2}.
13060 @item -mrpts=@var{count}
13064 Enable (disable) the use of the single instruction repeat instruction
13065 RPTS@. If a repeat block contains a single instruction, and the loop
13066 count can be guaranteed to be less than the value @var{count}, GCC will
13067 emit a RPTS instruction instead of a RPTB@. If no value is specified,
13068 then a RPTS will be emitted even if the loop count cannot be determined
13069 at compile time. Note that the repeated instruction following RPTS does
13070 not have to be reloaded from memory each iteration, thus freeing up the
13071 CPU buses for operands. However, since interrupts are blocked by this
13072 instruction, it is disabled by default.
13074 @item -mloop-unsigned
13075 @itemx -mno-loop-unsigned
13076 @opindex mloop-unsigned
13077 @opindex mno-loop-unsigned
13078 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
13079 is @math{2^{31} + 1} since these instructions test if the iteration count is
13080 negative to terminate the loop. If the iteration count is unsigned
13081 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
13082 exceeded. This switch allows an unsigned iteration count.
13086 Try to emit an assembler syntax that the TI assembler (asm30) is happy
13087 with. This also enforces compatibility with the API employed by the TI
13088 C3x C compiler. For example, long doubles are passed as structures
13089 rather than in floating point registers.
13095 Generate code that uses registers (stack) for passing arguments to functions.
13096 By default, arguments are passed in registers where possible rather
13097 than by pushing arguments on to the stack.
13099 @item -mparallel-insns
13100 @itemx -mno-parallel-insns
13101 @opindex mparallel-insns
13102 @opindex mno-parallel-insns
13103 Allow the generation of parallel instructions. This is enabled by
13104 default with @option{-O2}.
13106 @item -mparallel-mpy
13107 @itemx -mno-parallel-mpy
13108 @opindex mparallel-mpy
13109 @opindex mno-parallel-mpy
13110 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
13111 provided @option{-mparallel-insns} is also specified. These instructions have
13112 tight register constraints which can pessimize the code generation
13113 of large functions.
13118 @subsection V850 Options
13119 @cindex V850 Options
13121 These @samp{-m} options are defined for V850 implementations:
13125 @itemx -mno-long-calls
13126 @opindex mlong-calls
13127 @opindex mno-long-calls
13128 Treat all calls as being far away (near). If calls are assumed to be
13129 far away, the compiler will always load the functions address up into a
13130 register, and call indirect through the pointer.
13136 Do not optimize (do optimize) basic blocks that use the same index
13137 pointer 4 or more times to copy pointer into the @code{ep} register, and
13138 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
13139 option is on by default if you optimize.
13141 @item -mno-prolog-function
13142 @itemx -mprolog-function
13143 @opindex mno-prolog-function
13144 @opindex mprolog-function
13145 Do not use (do use) external functions to save and restore registers
13146 at the prologue and epilogue of a function. The external functions
13147 are slower, but use less code space if more than one function saves
13148 the same number of registers. The @option{-mprolog-function} option
13149 is on by default if you optimize.
13153 Try to make the code as small as possible. At present, this just turns
13154 on the @option{-mep} and @option{-mprolog-function} options.
13156 @item -mtda=@var{n}
13158 Put static or global variables whose size is @var{n} bytes or less into
13159 the tiny data area that register @code{ep} points to. The tiny data
13160 area can hold up to 256 bytes in total (128 bytes for byte references).
13162 @item -msda=@var{n}
13164 Put static or global variables whose size is @var{n} bytes or less into
13165 the small data area that register @code{gp} points to. The small data
13166 area can hold up to 64 kilobytes.
13168 @item -mzda=@var{n}
13170 Put static or global variables whose size is @var{n} bytes or less into
13171 the first 32 kilobytes of memory.
13175 Specify that the target processor is the V850.
13178 @opindex mbig-switch
13179 Generate code suitable for big switch tables. Use this option only if
13180 the assembler/linker complain about out of range branches within a switch
13185 This option will cause r2 and r5 to be used in the code generated by
13186 the compiler. This setting is the default.
13188 @item -mno-app-regs
13189 @opindex mno-app-regs
13190 This option will cause r2 and r5 to be treated as fixed registers.
13194 Specify that the target processor is the V850E1. The preprocessor
13195 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
13196 this option is used.
13200 Specify that the target processor is the V850E@. The preprocessor
13201 constant @samp{__v850e__} will be defined if this option is used.
13203 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
13204 are defined then a default target processor will be chosen and the
13205 relevant @samp{__v850*__} preprocessor constant will be defined.
13207 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
13208 defined, regardless of which processor variant is the target.
13210 @item -mdisable-callt
13211 @opindex mdisable-callt
13212 This option will suppress generation of the CALLT instruction for the
13213 v850e and v850e1 flavors of the v850 architecture. The default is
13214 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
13219 @subsection VAX Options
13220 @cindex VAX options
13222 These @samp{-m} options are defined for the VAX:
13227 Do not output certain jump instructions (@code{aobleq} and so on)
13228 that the Unix assembler for the VAX cannot handle across long
13233 Do output those jump instructions, on the assumption that you
13234 will assemble with the GNU assembler.
13238 Output code for g-format floating point numbers instead of d-format.
13241 @node x86-64 Options
13242 @subsection x86-64 Options
13243 @cindex x86-64 options
13245 These are listed under @xref{i386 and x86-64 Options}.
13247 @node Xstormy16 Options
13248 @subsection Xstormy16 Options
13249 @cindex Xstormy16 Options
13251 These options are defined for Xstormy16:
13256 Choose startup files and linker script suitable for the simulator.
13259 @node Xtensa Options
13260 @subsection Xtensa Options
13261 @cindex Xtensa Options
13263 These options are supported for Xtensa targets:
13267 @itemx -mno-const16
13269 @opindex mno-const16
13270 Enable or disable use of @code{CONST16} instructions for loading
13271 constant values. The @code{CONST16} instruction is currently not a
13272 standard option from Tensilica. When enabled, @code{CONST16}
13273 instructions are always used in place of the standard @code{L32R}
13274 instructions. The use of @code{CONST16} is enabled by default only if
13275 the @code{L32R} instruction is not available.
13278 @itemx -mno-fused-madd
13279 @opindex mfused-madd
13280 @opindex mno-fused-madd
13281 Enable or disable use of fused multiply/add and multiply/subtract
13282 instructions in the floating-point option. This has no effect if the
13283 floating-point option is not also enabled. Disabling fused multiply/add
13284 and multiply/subtract instructions forces the compiler to use separate
13285 instructions for the multiply and add/subtract operations. This may be
13286 desirable in some cases where strict IEEE 754-compliant results are
13287 required: the fused multiply add/subtract instructions do not round the
13288 intermediate result, thereby producing results with @emph{more} bits of
13289 precision than specified by the IEEE standard. Disabling fused multiply
13290 add/subtract instructions also ensures that the program output is not
13291 sensitive to the compiler's ability to combine multiply and add/subtract
13294 @item -mtext-section-literals
13295 @itemx -mno-text-section-literals
13296 @opindex mtext-section-literals
13297 @opindex mno-text-section-literals
13298 Control the treatment of literal pools. The default is
13299 @option{-mno-text-section-literals}, which places literals in a separate
13300 section in the output file. This allows the literal pool to be placed
13301 in a data RAM/ROM, and it also allows the linker to combine literal
13302 pools from separate object files to remove redundant literals and
13303 improve code size. With @option{-mtext-section-literals}, the literals
13304 are interspersed in the text section in order to keep them as close as
13305 possible to their references. This may be necessary for large assembly
13308 @item -mtarget-align
13309 @itemx -mno-target-align
13310 @opindex mtarget-align
13311 @opindex mno-target-align
13312 When this option is enabled, GCC instructs the assembler to
13313 automatically align instructions to reduce branch penalties at the
13314 expense of some code density. The assembler attempts to widen density
13315 instructions to align branch targets and the instructions following call
13316 instructions. If there are not enough preceding safe density
13317 instructions to align a target, no widening will be performed. The
13318 default is @option{-mtarget-align}. These options do not affect the
13319 treatment of auto-aligned instructions like @code{LOOP}, which the
13320 assembler will always align, either by widening density instructions or
13321 by inserting no-op instructions.
13324 @itemx -mno-longcalls
13325 @opindex mlongcalls
13326 @opindex mno-longcalls
13327 When this option is enabled, GCC instructs the assembler to translate
13328 direct calls to indirect calls unless it can determine that the target
13329 of a direct call is in the range allowed by the call instruction. This
13330 translation typically occurs for calls to functions in other source
13331 files. Specifically, the assembler translates a direct @code{CALL}
13332 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
13333 The default is @option{-mno-longcalls}. This option should be used in
13334 programs where the call target can potentially be out of range. This
13335 option is implemented in the assembler, not the compiler, so the
13336 assembly code generated by GCC will still show direct call
13337 instructions---look at the disassembled object code to see the actual
13338 instructions. Note that the assembler will use an indirect call for
13339 every cross-file call, not just those that really will be out of range.
13342 @node zSeries Options
13343 @subsection zSeries Options
13344 @cindex zSeries options
13346 These are listed under @xref{S/390 and zSeries Options}.
13348 @node Code Gen Options
13349 @section Options for Code Generation Conventions
13350 @cindex code generation conventions
13351 @cindex options, code generation
13352 @cindex run-time options
13354 These machine-independent options control the interface conventions
13355 used in code generation.
13357 Most of them have both positive and negative forms; the negative form
13358 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
13359 one of the forms is listed---the one which is not the default. You
13360 can figure out the other form by either removing @samp{no-} or adding
13364 @item -fbounds-check
13365 @opindex fbounds-check
13366 For front-ends that support it, generate additional code to check that
13367 indices used to access arrays are within the declared range. This is
13368 currently only supported by the Java and Fortran front-ends, where
13369 this option defaults to true and false respectively.
13373 This option generates traps for signed overflow on addition, subtraction,
13374 multiplication operations.
13378 This option instructs the compiler to assume that signed arithmetic
13379 overflow of addition, subtraction and multiplication wraps around
13380 using twos-complement representation. This flag enables some optimizations
13381 and disables others. This option is enabled by default for the Java
13382 front-end, as required by the Java language specification.
13385 @opindex fexceptions
13386 Enable exception handling. Generates extra code needed to propagate
13387 exceptions. For some targets, this implies GCC will generate frame
13388 unwind information for all functions, which can produce significant data
13389 size overhead, although it does not affect execution. If you do not
13390 specify this option, GCC will enable it by default for languages like
13391 C++ which normally require exception handling, and disable it for
13392 languages like C that do not normally require it. However, you may need
13393 to enable this option when compiling C code that needs to interoperate
13394 properly with exception handlers written in C++. You may also wish to
13395 disable this option if you are compiling older C++ programs that don't
13396 use exception handling.
13398 @item -fnon-call-exceptions
13399 @opindex fnon-call-exceptions
13400 Generate code that allows trapping instructions to throw exceptions.
13401 Note that this requires platform-specific runtime support that does
13402 not exist everywhere. Moreover, it only allows @emph{trapping}
13403 instructions to throw exceptions, i.e.@: memory references or floating
13404 point instructions. It does not allow exceptions to be thrown from
13405 arbitrary signal handlers such as @code{SIGALRM}.
13407 @item -funwind-tables
13408 @opindex funwind-tables
13409 Similar to @option{-fexceptions}, except that it will just generate any needed
13410 static data, but will not affect the generated code in any other way.
13411 You will normally not enable this option; instead, a language processor
13412 that needs this handling would enable it on your behalf.
13414 @item -fasynchronous-unwind-tables
13415 @opindex fasynchronous-unwind-tables
13416 Generate unwind table in dwarf2 format, if supported by target machine. The
13417 table is exact at each instruction boundary, so it can be used for stack
13418 unwinding from asynchronous events (such as debugger or garbage collector).
13420 @item -fpcc-struct-return
13421 @opindex fpcc-struct-return
13422 Return ``short'' @code{struct} and @code{union} values in memory like
13423 longer ones, rather than in registers. This convention is less
13424 efficient, but it has the advantage of allowing intercallability between
13425 GCC-compiled files and files compiled with other compilers, particularly
13426 the Portable C Compiler (pcc).
13428 The precise convention for returning structures in memory depends
13429 on the target configuration macros.
13431 Short structures and unions are those whose size and alignment match
13432 that of some integer type.
13434 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
13435 switch is not binary compatible with code compiled with the
13436 @option{-freg-struct-return} switch.
13437 Use it to conform to a non-default application binary interface.
13439 @item -freg-struct-return
13440 @opindex freg-struct-return
13441 Return @code{struct} and @code{union} values in registers when possible.
13442 This is more efficient for small structures than
13443 @option{-fpcc-struct-return}.
13445 If you specify neither @option{-fpcc-struct-return} nor
13446 @option{-freg-struct-return}, GCC defaults to whichever convention is
13447 standard for the target. If there is no standard convention, GCC
13448 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
13449 the principal compiler. In those cases, we can choose the standard, and
13450 we chose the more efficient register return alternative.
13452 @strong{Warning:} code compiled with the @option{-freg-struct-return}
13453 switch is not binary compatible with code compiled with the
13454 @option{-fpcc-struct-return} switch.
13455 Use it to conform to a non-default application binary interface.
13457 @item -fshort-enums
13458 @opindex fshort-enums
13459 Allocate to an @code{enum} type only as many bytes as it needs for the
13460 declared range of possible values. Specifically, the @code{enum} type
13461 will be equivalent to the smallest integer type which has enough room.
13463 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
13464 code that is not binary compatible with code generated without that switch.
13465 Use it to conform to a non-default application binary interface.
13467 @item -fshort-double
13468 @opindex fshort-double
13469 Use the same size for @code{double} as for @code{float}.
13471 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
13472 code that is not binary compatible with code generated without that switch.
13473 Use it to conform to a non-default application binary interface.
13475 @item -fshort-wchar
13476 @opindex fshort-wchar
13477 Override the underlying type for @samp{wchar_t} to be @samp{short
13478 unsigned int} instead of the default for the target. This option is
13479 useful for building programs to run under WINE@.
13481 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
13482 code that is not binary compatible with code generated without that switch.
13483 Use it to conform to a non-default application binary interface.
13486 @opindex fno-common
13487 In C, allocate even uninitialized global variables in the data section of the
13488 object file, rather than generating them as common blocks. This has the
13489 effect that if the same variable is declared (without @code{extern}) in
13490 two different compilations, you will get an error when you link them.
13491 The only reason this might be useful is if you wish to verify that the
13492 program will work on other systems which always work this way.
13496 Ignore the @samp{#ident} directive.
13498 @item -finhibit-size-directive
13499 @opindex finhibit-size-directive
13500 Don't output a @code{.size} assembler directive, or anything else that
13501 would cause trouble if the function is split in the middle, and the
13502 two halves are placed at locations far apart in memory. This option is
13503 used when compiling @file{crtstuff.c}; you should not need to use it
13506 @item -fverbose-asm
13507 @opindex fverbose-asm
13508 Put extra commentary information in the generated assembly code to
13509 make it more readable. This option is generally only of use to those
13510 who actually need to read the generated assembly code (perhaps while
13511 debugging the compiler itself).
13513 @option{-fno-verbose-asm}, the default, causes the
13514 extra information to be omitted and is useful when comparing two assembler
13517 @item -frecord-gcc-switches
13518 @opindex frecord-gcc-switches
13519 This switch causes the command line that was used to invoke the
13520 compiler to be recorded into the object file that is being created.
13521 This switch is only implemented on some targets and the exact format
13522 of the recording is target and binary file format dependent, but it
13523 usually takes the form of a section containing ASCII text. This
13524 switch is related to the @option{-fverbose-asm} switch, but that
13525 switch only records information in the assembler output file as
13526 comments, so it never reaches the object file.
13530 @cindex global offset table
13532 Generate position-independent code (PIC) suitable for use in a shared
13533 library, if supported for the target machine. Such code accesses all
13534 constant addresses through a global offset table (GOT)@. The dynamic
13535 loader resolves the GOT entries when the program starts (the dynamic
13536 loader is not part of GCC; it is part of the operating system). If
13537 the GOT size for the linked executable exceeds a machine-specific
13538 maximum size, you get an error message from the linker indicating that
13539 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
13540 instead. (These maximums are 8k on the SPARC and 32k
13541 on the m68k and RS/6000. The 386 has no such limit.)
13543 Position-independent code requires special support, and therefore works
13544 only on certain machines. For the 386, GCC supports PIC for System V
13545 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
13546 position-independent.
13548 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
13553 If supported for the target machine, emit position-independent code,
13554 suitable for dynamic linking and avoiding any limit on the size of the
13555 global offset table. This option makes a difference on the m68k,
13556 PowerPC and SPARC@.
13558 Position-independent code requires special support, and therefore works
13559 only on certain machines.
13561 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
13568 These options are similar to @option{-fpic} and @option{-fPIC}, but
13569 generated position independent code can be only linked into executables.
13570 Usually these options are used when @option{-pie} GCC option will be
13571 used during linking.
13573 @item -fno-jump-tables
13574 @opindex fno-jump-tables
13575 Do not use jump tables for switch statements even where it would be
13576 more efficient than other code generation strategies. This option is
13577 of use in conjunction with @option{-fpic} or @option{-fPIC} for
13578 building code which forms part of a dynamic linker and cannot
13579 reference the address of a jump table. On some targets, jump tables
13580 do not require a GOT and this option is not needed.
13582 @item -ffixed-@var{reg}
13584 Treat the register named @var{reg} as a fixed register; generated code
13585 should never refer to it (except perhaps as a stack pointer, frame
13586 pointer or in some other fixed role).
13588 @var{reg} must be the name of a register. The register names accepted
13589 are machine-specific and are defined in the @code{REGISTER_NAMES}
13590 macro in the machine description macro file.
13592 This flag does not have a negative form, because it specifies a
13595 @item -fcall-used-@var{reg}
13596 @opindex fcall-used
13597 Treat the register named @var{reg} as an allocable register that is
13598 clobbered by function calls. It may be allocated for temporaries or
13599 variables that do not live across a call. Functions compiled this way
13600 will not save and restore the register @var{reg}.
13602 It is an error to used this flag with the frame pointer or stack pointer.
13603 Use of this flag for other registers that have fixed pervasive roles in
13604 the machine's execution model will produce disastrous results.
13606 This flag does not have a negative form, because it specifies a
13609 @item -fcall-saved-@var{reg}
13610 @opindex fcall-saved
13611 Treat the register named @var{reg} as an allocable register saved by
13612 functions. It may be allocated even for temporaries or variables that
13613 live across a call. Functions compiled this way will save and restore
13614 the register @var{reg} if they use it.
13616 It is an error to used this flag with the frame pointer or stack pointer.
13617 Use of this flag for other registers that have fixed pervasive roles in
13618 the machine's execution model will produce disastrous results.
13620 A different sort of disaster will result from the use of this flag for
13621 a register in which function values may be returned.
13623 This flag does not have a negative form, because it specifies a
13626 @item -fpack-struct[=@var{n}]
13627 @opindex fpack-struct
13628 Without a value specified, pack all structure members together without
13629 holes. When a value is specified (which must be a small power of two), pack
13630 structure members according to this value, representing the maximum
13631 alignment (that is, objects with default alignment requirements larger than
13632 this will be output potentially unaligned at the next fitting location.
13634 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
13635 code that is not binary compatible with code generated without that switch.
13636 Additionally, it makes the code suboptimal.
13637 Use it to conform to a non-default application binary interface.
13639 @item -finstrument-functions
13640 @opindex finstrument-functions
13641 Generate instrumentation calls for entry and exit to functions. Just
13642 after function entry and just before function exit, the following
13643 profiling functions will be called with the address of the current
13644 function and its call site. (On some platforms,
13645 @code{__builtin_return_address} does not work beyond the current
13646 function, so the call site information may not be available to the
13647 profiling functions otherwise.)
13650 void __cyg_profile_func_enter (void *this_fn,
13652 void __cyg_profile_func_exit (void *this_fn,
13656 The first argument is the address of the start of the current function,
13657 which may be looked up exactly in the symbol table.
13659 This instrumentation is also done for functions expanded inline in other
13660 functions. The profiling calls will indicate where, conceptually, the
13661 inline function is entered and exited. This means that addressable
13662 versions of such functions must be available. If all your uses of a
13663 function are expanded inline, this may mean an additional expansion of
13664 code size. If you use @samp{extern inline} in your C code, an
13665 addressable version of such functions must be provided. (This is
13666 normally the case anyways, but if you get lucky and the optimizer always
13667 expands the functions inline, you might have gotten away without
13668 providing static copies.)
13670 A function may be given the attribute @code{no_instrument_function}, in
13671 which case this instrumentation will not be done. This can be used, for
13672 example, for the profiling functions listed above, high-priority
13673 interrupt routines, and any functions from which the profiling functions
13674 cannot safely be called (perhaps signal handlers, if the profiling
13675 routines generate output or allocate memory).
13677 @item -fstack-check
13678 @opindex fstack-check
13679 Generate code to verify that you do not go beyond the boundary of the
13680 stack. You should specify this flag if you are running in an
13681 environment with multiple threads, but only rarely need to specify it in
13682 a single-threaded environment since stack overflow is automatically
13683 detected on nearly all systems if there is only one stack.
13685 Note that this switch does not actually cause checking to be done; the
13686 operating system must do that. The switch causes generation of code
13687 to ensure that the operating system sees the stack being extended.
13689 @item -fstack-limit-register=@var{reg}
13690 @itemx -fstack-limit-symbol=@var{sym}
13691 @itemx -fno-stack-limit
13692 @opindex fstack-limit-register
13693 @opindex fstack-limit-symbol
13694 @opindex fno-stack-limit
13695 Generate code to ensure that the stack does not grow beyond a certain value,
13696 either the value of a register or the address of a symbol. If the stack
13697 would grow beyond the value, a signal is raised. For most targets,
13698 the signal is raised before the stack overruns the boundary, so
13699 it is possible to catch the signal without taking special precautions.
13701 For instance, if the stack starts at absolute address @samp{0x80000000}
13702 and grows downwards, you can use the flags
13703 @option{-fstack-limit-symbol=__stack_limit} and
13704 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
13705 of 128KB@. Note that this may only work with the GNU linker.
13707 @cindex aliasing of parameters
13708 @cindex parameters, aliased
13709 @item -fargument-alias
13710 @itemx -fargument-noalias
13711 @itemx -fargument-noalias-global
13712 @itemx -fargument-noalias-anything
13713 @opindex fargument-alias
13714 @opindex fargument-noalias
13715 @opindex fargument-noalias-global
13716 @opindex fargument-noalias-anything
13717 Specify the possible relationships among parameters and between
13718 parameters and global data.
13720 @option{-fargument-alias} specifies that arguments (parameters) may
13721 alias each other and may alias global storage.@*
13722 @option{-fargument-noalias} specifies that arguments do not alias
13723 each other, but may alias global storage.@*
13724 @option{-fargument-noalias-global} specifies that arguments do not
13725 alias each other and do not alias global storage.
13726 @option{-fargument-noalias-anything} specifies that arguments do not
13727 alias any other storage.
13729 Each language will automatically use whatever option is required by
13730 the language standard. You should not need to use these options yourself.
13732 @item -fleading-underscore
13733 @opindex fleading-underscore
13734 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
13735 change the way C symbols are represented in the object file. One use
13736 is to help link with legacy assembly code.
13738 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
13739 generate code that is not binary compatible with code generated without that
13740 switch. Use it to conform to a non-default application binary interface.
13741 Not all targets provide complete support for this switch.
13743 @item -ftls-model=@var{model}
13744 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
13745 The @var{model} argument should be one of @code{global-dynamic},
13746 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
13748 The default without @option{-fpic} is @code{initial-exec}; with
13749 @option{-fpic} the default is @code{global-dynamic}.
13751 @item -fvisibility=@var{default|internal|hidden|protected}
13752 @opindex fvisibility
13753 Set the default ELF image symbol visibility to the specified option---all
13754 symbols will be marked with this unless overridden within the code.
13755 Using this feature can very substantially improve linking and
13756 load times of shared object libraries, produce more optimized
13757 code, provide near-perfect API export and prevent symbol clashes.
13758 It is @strong{strongly} recommended that you use this in any shared objects
13761 Despite the nomenclature, @code{default} always means public ie;
13762 available to be linked against from outside the shared object.
13763 @code{protected} and @code{internal} are pretty useless in real-world
13764 usage so the only other commonly used option will be @code{hidden}.
13765 The default if @option{-fvisibility} isn't specified is
13766 @code{default}, i.e., make every
13767 symbol public---this causes the same behavior as previous versions of
13770 A good explanation of the benefits offered by ensuring ELF
13771 symbols have the correct visibility is given by ``How To Write
13772 Shared Libraries'' by Ulrich Drepper (which can be found at
13773 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
13774 solution made possible by this option to marking things hidden when
13775 the default is public is to make the default hidden and mark things
13776 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
13777 and @code{__attribute__ ((visibility("default")))} instead of
13778 @code{__declspec(dllexport)} you get almost identical semantics with
13779 identical syntax. This is a great boon to those working with
13780 cross-platform projects.
13782 For those adding visibility support to existing code, you may find
13783 @samp{#pragma GCC visibility} of use. This works by you enclosing
13784 the declarations you wish to set visibility for with (for example)
13785 @samp{#pragma GCC visibility push(hidden)} and
13786 @samp{#pragma GCC visibility pop}.
13787 Bear in mind that symbol visibility should be viewed @strong{as
13788 part of the API interface contract} and thus all new code should
13789 always specify visibility when it is not the default ie; declarations
13790 only for use within the local DSO should @strong{always} be marked explicitly
13791 as hidden as so to avoid PLT indirection overheads---making this
13792 abundantly clear also aids readability and self-documentation of the code.
13793 Note that due to ISO C++ specification requirements, operator new and
13794 operator delete must always be of default visibility.
13796 Be aware that headers from outside your project, in particular system
13797 headers and headers from any other library you use, may not be
13798 expecting to be compiled with visibility other than the default. You
13799 may need to explicitly say @samp{#pragma GCC visibility push(default)}
13800 before including any such headers.
13802 @samp{extern} declarations are not affected by @samp{-fvisibility}, so
13803 a lot of code can be recompiled with @samp{-fvisibility=hidden} with
13804 no modifications. However, this means that calls to @samp{extern}
13805 functions with no explicit visibility will use the PLT, so it is more
13806 effective to use @samp{__attribute ((visibility))} and/or
13807 @samp{#pragma GCC visibility} to tell the compiler which @samp{extern}
13808 declarations should be treated as hidden.
13810 Note that @samp{-fvisibility} does affect C++ vague linkage
13811 entities. This means that, for instance, an exception class that will
13812 be thrown between DSOs must be explicitly marked with default
13813 visibility so that the @samp{type_info} nodes will be unified between
13816 An overview of these techniques, their benefits and how to use them
13817 is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}.
13823 @node Environment Variables
13824 @section Environment Variables Affecting GCC
13825 @cindex environment variables
13827 @c man begin ENVIRONMENT
13828 This section describes several environment variables that affect how GCC
13829 operates. Some of them work by specifying directories or prefixes to use
13830 when searching for various kinds of files. Some are used to specify other
13831 aspects of the compilation environment.
13833 Note that you can also specify places to search using options such as
13834 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
13835 take precedence over places specified using environment variables, which
13836 in turn take precedence over those specified by the configuration of GCC@.
13837 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
13838 GNU Compiler Collection (GCC) Internals}.
13843 @c @itemx LC_COLLATE
13845 @c @itemx LC_MONETARY
13846 @c @itemx LC_NUMERIC
13851 @c @findex LC_COLLATE
13852 @findex LC_MESSAGES
13853 @c @findex LC_MONETARY
13854 @c @findex LC_NUMERIC
13858 These environment variables control the way that GCC uses
13859 localization information that allow GCC to work with different
13860 national conventions. GCC inspects the locale categories
13861 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
13862 so. These locale categories can be set to any value supported by your
13863 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
13864 Kingdom encoded in UTF-8.
13866 The @env{LC_CTYPE} environment variable specifies character
13867 classification. GCC uses it to determine the character boundaries in
13868 a string; this is needed for some multibyte encodings that contain quote
13869 and escape characters that would otherwise be interpreted as a string
13872 The @env{LC_MESSAGES} environment variable specifies the language to
13873 use in diagnostic messages.
13875 If the @env{LC_ALL} environment variable is set, it overrides the value
13876 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
13877 and @env{LC_MESSAGES} default to the value of the @env{LANG}
13878 environment variable. If none of these variables are set, GCC
13879 defaults to traditional C English behavior.
13883 If @env{TMPDIR} is set, it specifies the directory to use for temporary
13884 files. GCC uses temporary files to hold the output of one stage of
13885 compilation which is to be used as input to the next stage: for example,
13886 the output of the preprocessor, which is the input to the compiler
13889 @item GCC_EXEC_PREFIX
13890 @findex GCC_EXEC_PREFIX
13891 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
13892 names of the subprograms executed by the compiler. No slash is added
13893 when this prefix is combined with the name of a subprogram, but you can
13894 specify a prefix that ends with a slash if you wish.
13896 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
13897 an appropriate prefix to use based on the pathname it was invoked with.
13899 If GCC cannot find the subprogram using the specified prefix, it
13900 tries looking in the usual places for the subprogram.
13902 The default value of @env{GCC_EXEC_PREFIX} is
13903 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the value
13904 of @code{prefix} when you ran the @file{configure} script.
13906 Other prefixes specified with @option{-B} take precedence over this prefix.
13908 This prefix is also used for finding files such as @file{crt0.o} that are
13911 In addition, the prefix is used in an unusual way in finding the
13912 directories to search for header files. For each of the standard
13913 directories whose name normally begins with @samp{/usr/local/lib/gcc}
13914 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
13915 replacing that beginning with the specified prefix to produce an
13916 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
13917 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
13918 These alternate directories are searched first; the standard directories
13921 @item COMPILER_PATH
13922 @findex COMPILER_PATH
13923 The value of @env{COMPILER_PATH} is a colon-separated list of
13924 directories, much like @env{PATH}. GCC tries the directories thus
13925 specified when searching for subprograms, if it can't find the
13926 subprograms using @env{GCC_EXEC_PREFIX}.
13929 @findex LIBRARY_PATH
13930 The value of @env{LIBRARY_PATH} is a colon-separated list of
13931 directories, much like @env{PATH}. When configured as a native compiler,
13932 GCC tries the directories thus specified when searching for special
13933 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
13934 using GCC also uses these directories when searching for ordinary
13935 libraries for the @option{-l} option (but directories specified with
13936 @option{-L} come first).
13940 @cindex locale definition
13941 This variable is used to pass locale information to the compiler. One way in
13942 which this information is used is to determine the character set to be used
13943 when character literals, string literals and comments are parsed in C and C++.
13944 When the compiler is configured to allow multibyte characters,
13945 the following values for @env{LANG} are recognized:
13949 Recognize JIS characters.
13951 Recognize SJIS characters.
13953 Recognize EUCJP characters.
13956 If @env{LANG} is not defined, or if it has some other value, then the
13957 compiler will use mblen and mbtowc as defined by the default locale to
13958 recognize and translate multibyte characters.
13962 Some additional environments variables affect the behavior of the
13965 @include cppenv.texi
13969 @node Precompiled Headers
13970 @section Using Precompiled Headers
13971 @cindex precompiled headers
13972 @cindex speed of compilation
13974 Often large projects have many header files that are included in every
13975 source file. The time the compiler takes to process these header files
13976 over and over again can account for nearly all of the time required to
13977 build the project. To make builds faster, GCC allows users to
13978 `precompile' a header file; then, if builds can use the precompiled
13979 header file they will be much faster.
13981 To create a precompiled header file, simply compile it as you would any
13982 other file, if necessary using the @option{-x} option to make the driver
13983 treat it as a C or C++ header file. You will probably want to use a
13984 tool like @command{make} to keep the precompiled header up-to-date when
13985 the headers it contains change.
13987 A precompiled header file will be searched for when @code{#include} is
13988 seen in the compilation. As it searches for the included file
13989 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
13990 compiler looks for a precompiled header in each directory just before it
13991 looks for the include file in that directory. The name searched for is
13992 the name specified in the @code{#include} with @samp{.gch} appended. If
13993 the precompiled header file can't be used, it is ignored.
13995 For instance, if you have @code{#include "all.h"}, and you have
13996 @file{all.h.gch} in the same directory as @file{all.h}, then the
13997 precompiled header file will be used if possible, and the original
13998 header will be used otherwise.
14000 Alternatively, you might decide to put the precompiled header file in a
14001 directory and use @option{-I} to ensure that directory is searched
14002 before (or instead of) the directory containing the original header.
14003 Then, if you want to check that the precompiled header file is always
14004 used, you can put a file of the same name as the original header in this
14005 directory containing an @code{#error} command.
14007 This also works with @option{-include}. So yet another way to use
14008 precompiled headers, good for projects not designed with precompiled
14009 header files in mind, is to simply take most of the header files used by
14010 a project, include them from another header file, precompile that header
14011 file, and @option{-include} the precompiled header. If the header files
14012 have guards against multiple inclusion, they will be skipped because
14013 they've already been included (in the precompiled header).
14015 If you need to precompile the same header file for different
14016 languages, targets, or compiler options, you can instead make a
14017 @emph{directory} named like @file{all.h.gch}, and put each precompiled
14018 header in the directory, perhaps using @option{-o}. It doesn't matter
14019 what you call the files in the directory, every precompiled header in
14020 the directory will be considered. The first precompiled header
14021 encountered in the directory that is valid for this compilation will
14022 be used; they're searched in no particular order.
14024 There are many other possibilities, limited only by your imagination,
14025 good sense, and the constraints of your build system.
14027 A precompiled header file can be used only when these conditions apply:
14031 Only one precompiled header can be used in a particular compilation.
14034 A precompiled header can't be used once the first C token is seen. You
14035 can have preprocessor directives before a precompiled header; you can
14036 even include a precompiled header from inside another header, so long as
14037 there are no C tokens before the @code{#include}.
14040 The precompiled header file must be produced for the same language as
14041 the current compilation. You can't use a C precompiled header for a C++
14045 The precompiled header file must have been produced by the same compiler
14046 binary as the current compilation is using.
14049 Any macros defined before the precompiled header is included must
14050 either be defined in the same way as when the precompiled header was
14051 generated, or must not affect the precompiled header, which usually
14052 means that they don't appear in the precompiled header at all.
14054 The @option{-D} option is one way to define a macro before a
14055 precompiled header is included; using a @code{#define} can also do it.
14056 There are also some options that define macros implicitly, like
14057 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
14060 @item If debugging information is output when using the precompiled
14061 header, using @option{-g} or similar, the same kind of debugging information
14062 must have been output when building the precompiled header. However,
14063 a precompiled header built using @option{-g} can be used in a compilation
14064 when no debugging information is being output.
14066 @item The same @option{-m} options must generally be used when building
14067 and using the precompiled header. @xref{Submodel Options},
14068 for any cases where this rule is relaxed.
14070 @item Each of the following options must be the same when building and using
14071 the precompiled header:
14073 @gccoptlist{-fexceptions -funit-at-a-time}
14076 Some other command-line options starting with @option{-f},
14077 @option{-p}, or @option{-O} must be defined in the same way as when
14078 the precompiled header was generated. At present, it's not clear
14079 which options are safe to change and which are not; the safest choice
14080 is to use exactly the same options when generating and using the
14081 precompiled header. The following are known to be safe:
14083 @gccoptlist{-fmessage-length= -fpreprocessed
14084 -fsched-interblock -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous
14085 -fsched-verbose=<number> -fschedule-insns -fvisibility=
14090 For all of these except the last, the compiler will automatically
14091 ignore the precompiled header if the conditions aren't met. If you
14092 find an option combination that doesn't work and doesn't cause the
14093 precompiled header to be ignored, please consider filing a bug report,
14096 If you do use differing options when generating and using the
14097 precompiled header, the actual behavior will be a mixture of the
14098 behavior for the options. For instance, if you use @option{-g} to
14099 generate the precompiled header but not when using it, you may or may
14100 not get debugging information for routines in the precompiled header.
14102 @node Running Protoize
14103 @section Running Protoize
14105 The program @code{protoize} is an optional part of GCC@. You can use
14106 it to add prototypes to a program, thus converting the program to ISO
14107 C in one respect. The companion program @code{unprotoize} does the
14108 reverse: it removes argument types from any prototypes that are found.
14110 When you run these programs, you must specify a set of source files as
14111 command line arguments. The conversion programs start out by compiling
14112 these files to see what functions they define. The information gathered
14113 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
14115 After scanning comes actual conversion. The specified files are all
14116 eligible to be converted; any files they include (whether sources or
14117 just headers) are eligible as well.
14119 But not all the eligible files are converted. By default,
14120 @code{protoize} and @code{unprotoize} convert only source and header
14121 files in the current directory. You can specify additional directories
14122 whose files should be converted with the @option{-d @var{directory}}
14123 option. You can also specify particular files to exclude with the
14124 @option{-x @var{file}} option. A file is converted if it is eligible, its
14125 directory name matches one of the specified directory names, and its
14126 name within the directory has not been excluded.
14128 Basic conversion with @code{protoize} consists of rewriting most
14129 function definitions and function declarations to specify the types of
14130 the arguments. The only ones not rewritten are those for varargs
14133 @code{protoize} optionally inserts prototype declarations at the
14134 beginning of the source file, to make them available for any calls that
14135 precede the function's definition. Or it can insert prototype
14136 declarations with block scope in the blocks where undeclared functions
14139 Basic conversion with @code{unprotoize} consists of rewriting most
14140 function declarations to remove any argument types, and rewriting
14141 function definitions to the old-style pre-ISO form.
14143 Both conversion programs print a warning for any function declaration or
14144 definition that they can't convert. You can suppress these warnings
14147 The output from @code{protoize} or @code{unprotoize} replaces the
14148 original source file. The original file is renamed to a name ending
14149 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
14150 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
14151 for DOS) file already exists, then the source file is simply discarded.
14153 @code{protoize} and @code{unprotoize} both depend on GCC itself to
14154 scan the program and collect information about the functions it uses.
14155 So neither of these programs will work until GCC is installed.
14157 Here is a table of the options you can use with @code{protoize} and
14158 @code{unprotoize}. Each option works with both programs unless
14162 @item -B @var{directory}
14163 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
14164 usual directory (normally @file{/usr/local/lib}). This file contains
14165 prototype information about standard system functions. This option
14166 applies only to @code{protoize}.
14168 @item -c @var{compilation-options}
14169 Use @var{compilation-options} as the options when running @command{gcc} to
14170 produce the @samp{.X} files. The special option @option{-aux-info} is
14171 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
14173 Note that the compilation options must be given as a single argument to
14174 @code{protoize} or @code{unprotoize}. If you want to specify several
14175 @command{gcc} options, you must quote the entire set of compilation options
14176 to make them a single word in the shell.
14178 There are certain @command{gcc} arguments that you cannot use, because they
14179 would produce the wrong kind of output. These include @option{-g},
14180 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
14181 the @var{compilation-options}, they are ignored.
14184 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
14185 systems) instead of @samp{.c}. This is convenient if you are converting
14186 a C program to C++. This option applies only to @code{protoize}.
14189 Add explicit global declarations. This means inserting explicit
14190 declarations at the beginning of each source file for each function
14191 that is called in the file and was not declared. These declarations
14192 precede the first function definition that contains a call to an
14193 undeclared function. This option applies only to @code{protoize}.
14195 @item -i @var{string}
14196 Indent old-style parameter declarations with the string @var{string}.
14197 This option applies only to @code{protoize}.
14199 @code{unprotoize} converts prototyped function definitions to old-style
14200 function definitions, where the arguments are declared between the
14201 argument list and the initial @samp{@{}. By default, @code{unprotoize}
14202 uses five spaces as the indentation. If you want to indent with just
14203 one space instead, use @option{-i " "}.
14206 Keep the @samp{.X} files. Normally, they are deleted after conversion
14210 Add explicit local declarations. @code{protoize} with @option{-l} inserts
14211 a prototype declaration for each function in each block which calls the
14212 function without any declaration. This option applies only to
14216 Make no real changes. This mode just prints information about the conversions
14217 that would have been done without @option{-n}.
14220 Make no @samp{.save} files. The original files are simply deleted.
14221 Use this option with caution.
14223 @item -p @var{program}
14224 Use the program @var{program} as the compiler. Normally, the name
14225 @file{gcc} is used.
14228 Work quietly. Most warnings are suppressed.
14231 Print the version number, just like @option{-v} for @command{gcc}.
14234 If you need special compiler options to compile one of your program's
14235 source files, then you should generate that file's @samp{.X} file
14236 specially, by running @command{gcc} on that source file with the
14237 appropriate options and the option @option{-aux-info}. Then run
14238 @code{protoize} on the entire set of files. @code{protoize} will use
14239 the existing @samp{.X} file because it is newer than the source file.
14243 gcc -Dfoo=bar file1.c -aux-info file1.X
14248 You need to include the special files along with the rest in the
14249 @code{protoize} command, even though their @samp{.X} files already
14250 exist, because otherwise they won't get converted.
14252 @xref{Protoize Caveats}, for more information on how to use
14253 @code{protoize} successfully.