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{-fstrength-reduce}, @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 -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 -fno-const-strings @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}.
201 -fconstant-string-class=@var{class-name} @gol
202 -fgnu-runtime -fnext-runtime @gol
203 -fno-nil-receivers @gol
204 -fobjc-call-cxx-cdtors @gol
205 -fobjc-direct-dispatch @gol
206 -fobjc-exceptions @gol
208 -freplace-objc-classes @gol
211 -Wassign-intercept @gol
212 -Wno-protocol -Wselector @gol
213 -Wstrict-selector-match @gol
214 -Wundeclared-selector}
216 @item Language Independent Options
217 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
218 @gccoptlist{-fmessage-length=@var{n} @gol
219 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}} @gol
220 -fdiagnostics-show-options
222 @item Warning Options
223 @xref{Warning Options,,Options to Request or Suppress Warnings}.
224 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
225 -w -Wextra -Wall -Waggregate-return -Walways-true -Wno-attributes @gol
226 -Wc++-compat -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
227 -Wconversion -Wno-deprecated-declarations @gol
228 -Wdisabled-optimization -Wno-div-by-zero -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 -Woverlength-strings -Wpacked -Wpadded @gol
242 -Wparentheses -Wpointer-arith -Wno-pointer-to-int-cast @gol
243 -Wredundant-decls @gol
244 -Wreturn-type -Wsequence-point -Wshadow @gol
245 -Wsign-compare -Wstack-protector @gol
246 -Wstrict-aliasing -Wstrict-aliasing=2 @gol
247 -Wstring-literal-comparison @gol
248 -Wswitch -Wswitch-default -Wswitch-enum @gol
249 -Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized @gol
250 -Wunknown-pragmas -Wno-pragmas -Wunreachable-code @gol
251 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
252 -Wunused-value -Wunused-variable -Wvariadic-macros @gol
253 -Wvolatile-register-var -Wwrite-strings}
255 @item C-only Warning Options
256 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
257 -Wmissing-prototypes -Wnested-externs -Wold-style-definition @gol
258 -Wstrict-prototypes -Wtraditional @gol
259 -Wdeclaration-after-statement -Wpointer-sign}
261 @item Debugging Options
262 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
263 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
264 -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
265 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
266 -fdump-ipa-all -fdump-ipa-cgraph @gol
268 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
269 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
270 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
271 -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol
273 -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
274 -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
275 -fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol
276 -fdump-tree-dom@r{[}-@var{n}@r{]} @gol
277 -fdump-tree-dse@r{[}-@var{n}@r{]} @gol
278 -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
279 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
280 -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
281 -fdump-tree-nrv -fdump-tree-vect @gol
282 -fdump-tree-sink @gol
283 -fdump-tree-sra@r{[}-@var{n}@r{]} @gol
284 -fdump-tree-salias @gol
285 -fdump-tree-fre@r{[}-@var{n}@r{]} @gol
286 -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
287 -ftree-vectorizer-verbose=@var{n} @gol
288 -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
289 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
290 -feliminate-unused-debug-symbols -fmem-report -fprofile-arcs @gol
291 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
292 -ftest-coverage -ftime-report -fvar-tracking @gol
293 -g -g@var{level} -gcoff -gdwarf-2 @gol
294 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
295 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
296 -print-multi-directory -print-multi-lib @gol
297 -print-prog-name=@var{program} -print-search-dirs -Q @gol
300 @item Optimization Options
301 @xref{Optimize Options,,Options that Control Optimization}.
302 @gccoptlist{-falign-functions=@var{n} -falign-jumps=@var{n} @gol
303 -falign-labels=@var{n} -falign-loops=@var{n} @gol
304 -fbounds-check -fmudflap -fmudflapth -fmudflapir @gol
305 -fbranch-probabilities -fprofile-values -fvpt -fbranch-target-load-optimize @gol
306 -fbranch-target-load-optimize2 -fbtr-bb-exclusive @gol
307 -fcaller-saves -fcprop-registers -fcse-follow-jumps @gol
308 -fcse-skip-blocks -fcx-limited-range -fdata-sections @gol
309 -fdelayed-branch -fdelete-null-pointer-checks -fearly-inlining @gol
310 -fexpensive-optimizations -ffast-math -ffloat-store @gol
311 -fforce-addr -ffunction-sections @gol
312 -fgcse -fgcse-lm -fgcse-sm -fgcse-las -fgcse-after-reload @gol
313 -floop-optimize -fcrossjumping -fif-conversion -fif-conversion2 @gol
314 -finline-functions -finline-functions-called-once @gol
315 -finline-limit=@var{n} -fkeep-inline-functions @gol
316 -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
317 -fmodulo-sched -fno-branch-count-reg @gol
318 -fno-default-inline -fno-defer-pop -floop-optimize2 -fmove-loop-invariants @gol
319 -fno-function-cse -fno-guess-branch-probability @gol
320 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
321 -funsafe-math-optimizations -funsafe-loop-optimizations -ffinite-math-only @gol
322 -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
323 -fomit-frame-pointer -foptimize-register-move @gol
324 -foptimize-sibling-calls -fprefetch-loop-arrays @gol
325 -fprofile-generate -fprofile-use @gol
326 -fregmove -frename-registers @gol
327 -freorder-blocks -freorder-blocks-and-partition -freorder-functions @gol
328 -frerun-cse-after-loop -frerun-loop-opt @gol
329 -frounding-math -frtl-abstract-sequences @gol
330 -fschedule-insns -fschedule-insns2 @gol
331 -fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
332 -fsched-spec-load-dangerous @gol
333 -fsched-stalled-insns=@var{n} -fsched-stalled-insns-dep=@var{n} @gol
334 -fsched2-use-superblocks @gol
335 -fsched2-use-traces -freschedule-modulo-scheduled-loops @gol
336 -fsignaling-nans -fsingle-precision-constant @gol
337 -fstack-protector -fstack-protector-all @gol
338 -fstrength-reduce -fstrict-aliasing -ftracer -fthread-jumps @gol
339 -funroll-all-loops -funroll-loops -fpeel-loops @gol
340 -fsplit-ivs-in-unroller -funswitch-loops @gol
341 -fvariable-expansion-in-unroller @gol
342 -ftree-pre -ftree-ccp -ftree-dce -ftree-loop-optimize @gol
343 -ftree-loop-linear -ftree-loop-im -ftree-loop-ivcanon -fivopts @gol
344 -ftree-dominator-opts -ftree-dse -ftree-copyrename -ftree-sink @gol
345 -ftree-ch -ftree-sra -ftree-ter -ftree-lrs -ftree-fre -ftree-vectorize @gol
346 -ftree-vect-loop-version -ftree-salias -fweb @gol
347 -ftree-copy-prop -ftree-store-ccp -ftree-store-copy-prop -fwhole-program @gol
348 --param @var{name}=@var{value}
349 -O -O0 -O1 -O2 -O3 -Os}
351 @item Preprocessor Options
352 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
353 @gccoptlist{-A@var{question}=@var{answer} @gol
354 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
355 -C -dD -dI -dM -dN @gol
356 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
357 -idirafter @var{dir} @gol
358 -include @var{file} -imacros @var{file} @gol
359 -iprefix @var{file} -iwithprefix @var{dir} @gol
360 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
361 -imultilib @var{dir} -isysroot @var{dir} @gol
362 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
363 -P -fworking-directory -remap @gol
364 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
365 -Xpreprocessor @var{option}}
367 @item Assembler Option
368 @xref{Assembler Options,,Passing Options to the Assembler}.
369 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
372 @xref{Link Options,,Options for Linking}.
373 @gccoptlist{@var{object-file-name} -l@var{library} @gol
374 -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
375 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
376 -Wl,@var{option} -Xlinker @var{option} @gol
379 @item Directory Options
380 @xref{Directory Options,,Options for Directory Search}.
381 @gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} -L@var{dir}
382 -specs=@var{file} -I- --sysroot=@var{dir}}
385 @c I wrote this xref this way to avoid overfull hbox. -- rms
386 @xref{Target Options}.
387 @gccoptlist{-V @var{version} -b @var{machine}}
389 @item Machine Dependent Options
390 @xref{Submodel Options,,Hardware Models and Configurations}.
391 @c This list is ordered alphanumerically by subsection name.
392 @c Try and put the significant identifier (CPU or system) first,
393 @c so users have a clue at guessing where the ones they want will be.
396 @gccoptlist{-EB -EL @gol
397 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
398 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
401 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
402 -mabi=@var{name} @gol
403 -mapcs-stack-check -mno-apcs-stack-check @gol
404 -mapcs-float -mno-apcs-float @gol
405 -mapcs-reentrant -mno-apcs-reentrant @gol
406 -msched-prolog -mno-sched-prolog @gol
407 -mlittle-endian -mbig-endian -mwords-little-endian @gol
408 -mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
409 -mthumb-interwork -mno-thumb-interwork @gol
410 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
411 -mstructure-size-boundary=@var{n} @gol
412 -mabort-on-noreturn @gol
413 -mlong-calls -mno-long-calls @gol
414 -msingle-pic-base -mno-single-pic-base @gol
415 -mpic-register=@var{reg} @gol
416 -mnop-fun-dllimport @gol
417 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
418 -mpoke-function-name @gol
420 -mtpcs-frame -mtpcs-leaf-frame @gol
421 -mcaller-super-interworking -mcallee-super-interworking @gol
425 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
426 -mcall-prologues -mno-tablejump -mtiny-stack -mint8}
428 @emph{Blackfin Options}
429 @gccoptlist{-momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
430 -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
431 -mlow-64k -mno-low64k -mid-shared-library @gol
432 -mno-id-shared-library -mshared-library-id=@var{n} @gol
433 -mlong-calls -mno-long-calls}
436 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
437 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
438 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
439 -mstack-align -mdata-align -mconst-align @gol
440 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
441 -melf -maout -melinux -mlinux -sim -sim2 @gol
442 -mmul-bug-workaround -mno-mul-bug-workaround}
445 @gccoptlist{-mmac -mpush-args}
447 @emph{Darwin Options}
448 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
449 -arch_only -bind_at_load -bundle -bundle_loader @gol
450 -client_name -compatibility_version -current_version @gol
452 -dependency-file -dylib_file -dylinker_install_name @gol
453 -dynamic -dynamiclib -exported_symbols_list @gol
454 -filelist -flat_namespace -force_cpusubtype_ALL @gol
455 -force_flat_namespace -headerpad_max_install_names @gol
456 -image_base -init -install_name -keep_private_externs @gol
457 -multi_module -multiply_defined -multiply_defined_unused @gol
458 -noall_load -no_dead_strip_inits_and_terms @gol
459 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
460 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
461 -private_bundle -read_only_relocs -sectalign @gol
462 -sectobjectsymbols -whyload -seg1addr @gol
463 -sectcreate -sectobjectsymbols -sectorder @gol
464 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
465 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
466 -segprot -segs_read_only_addr -segs_read_write_addr @gol
467 -single_module -static -sub_library -sub_umbrella @gol
468 -twolevel_namespace -umbrella -undefined @gol
469 -unexported_symbols_list -weak_reference_mismatches @gol
470 -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
473 @emph{DEC Alpha Options}
474 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
475 -mieee -mieee-with-inexact -mieee-conformant @gol
476 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
477 -mtrap-precision=@var{mode} -mbuild-constants @gol
478 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
479 -mbwx -mmax -mfix -mcix @gol
480 -mfloat-vax -mfloat-ieee @gol
481 -mexplicit-relocs -msmall-data -mlarge-data @gol
482 -msmall-text -mlarge-text @gol
483 -mmemory-latency=@var{time}}
485 @emph{DEC Alpha/VMS Options}
486 @gccoptlist{-mvms-return-codes}
489 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
490 -mhard-float -msoft-float @gol
491 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
492 -mdouble -mno-double @gol
493 -mmedia -mno-media -mmuladd -mno-muladd @gol
494 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
495 -mlinked-fp -mlong-calls -malign-labels @gol
496 -mlibrary-pic -macc-4 -macc-8 @gol
497 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
498 -moptimize-membar -mno-optimize-membar @gol
499 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
500 -mvliw-branch -mno-vliw-branch @gol
501 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
502 -mno-nested-cond-exec -mtomcat-stats @gol
506 @emph{H8/300 Options}
507 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
510 @gccoptlist{-march=@var{architecture-type} @gol
511 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
512 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
513 -mfixed-range=@var{register-range} @gol
514 -mjump-in-delay -mlinker-opt -mlong-calls @gol
515 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
516 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
517 -mno-jump-in-delay -mno-long-load-store @gol
518 -mno-portable-runtime -mno-soft-float @gol
519 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
520 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
521 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
522 -munix=@var{unix-std} -nolibdld -static -threads}
524 @emph{i386 and x86-64 Options}
525 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
526 -mfpmath=@var{unit} @gol
527 -masm=@var{dialect} -mno-fancy-math-387 @gol
528 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
529 -mno-wide-multiply -mrtd -malign-double @gol
530 -mpreferred-stack-boundary=@var{num} @gol
531 -mmmx -msse -msse2 -msse3 -m3dnow -msselibm @gol
532 -mthreads -mno-align-stringops -minline-all-stringops @gol
533 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
534 -m96bit-long-double -mregparm=@var{num} -msseregparm @gol
535 -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
536 -mcmodel=@var{code-model} @gol
537 -m32 -m64 -mlarge-data-threshold=@var{num}}
540 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
541 -mvolatile-asm-stop -mregister-names -mno-sdata @gol
542 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
543 -minline-float-divide-max-throughput @gol
544 -minline-int-divide-min-latency @gol
545 -minline-int-divide-max-throughput @gol
546 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
547 -mno-dwarf2-asm -mearly-stop-bits @gol
548 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
549 -mtune=@var{cpu-type} -mt -pthread -milp32 -mlp64}
551 @emph{M32R/D Options}
552 @gccoptlist{-m32r2 -m32rx -m32r @gol
554 -malign-loops -mno-align-loops @gol
555 -missue-rate=@var{number} @gol
556 -mbranch-cost=@var{number} @gol
557 -mmodel=@var{code-size-model-type} @gol
558 -msdata=@var{sdata-type} @gol
559 -mno-flush-func -mflush-func=@var{name} @gol
560 -mno-flush-trap -mflush-trap=@var{number} @gol
564 @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
566 @emph{M680x0 Options}
567 @gccoptlist{-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
568 -m68060 -mcpu32 -m5200 -mcfv4e -m68881 -mbitfield @gol
569 -mc68000 -mc68020 @gol
570 -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
571 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
572 -mshared-library-id=n -mid-shared-library -mno-id-shared-library}
574 @emph{M68hc1x Options}
575 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
576 -mauto-incdec -minmax -mlong-calls -mshort @gol
577 -msoft-reg-count=@var{count}}
580 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
581 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
582 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
583 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
584 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
587 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
588 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
589 -mips16 -mno-mips16 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
590 -mxgot -mno-xgot -mgp32 -mgp64 -mfp32 -mfp64 @gol
591 -mhard-float -msoft-float -msingle-float -mdouble-float @gol
592 -mdsp -mpaired-single -mips3d @gol
593 -mlong64 -mlong32 -msym32 -mno-sym32 @gol
594 -G@var{num} -membedded-data -mno-embedded-data @gol
595 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
596 -msplit-addresses -mno-split-addresses @gol
597 -mexplicit-relocs -mno-explicit-relocs @gol
598 -mcheck-zero-division -mno-check-zero-division @gol
599 -mdivide-traps -mdivide-breaks @gol
600 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
601 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
602 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
603 -mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130 @gol
604 -mfix-sb1 -mno-fix-sb1 @gol
605 -mflush-func=@var{func} -mno-flush-func @gol
606 -mbranch-likely -mno-branch-likely @gol
607 -mfp-exceptions -mno-fp-exceptions @gol
608 -mvr4130-align -mno-vr4130-align}
611 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
612 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
613 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
614 -mno-base-addresses -msingle-exit -mno-single-exit}
616 @emph{MN10300 Options}
617 @gccoptlist{-mmult-bug -mno-mult-bug @gol
618 -mam33 -mno-am33 @gol
619 -mam33-2 -mno-am33-2 @gol
620 -mreturn-pointer-on-d0 @gol
624 @gccoptlist{-mno-crt0 -mbacc -msim @gol
625 -march=@var{cpu-type} }
627 @emph{PDP-11 Options}
628 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
629 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
630 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
631 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
632 -mbranch-expensive -mbranch-cheap @gol
633 -msplit -mno-split -munix-asm -mdec-asm}
635 @emph{PowerPC Options}
636 See RS/6000 and PowerPC Options.
638 @emph{RS/6000 and PowerPC Options}
639 @gccoptlist{-mcpu=@var{cpu-type} @gol
640 -mtune=@var{cpu-type} @gol
641 -mpower -mno-power -mpower2 -mno-power2 @gol
642 -mpowerpc -mpowerpc64 -mno-powerpc @gol
643 -maltivec -mno-altivec @gol
644 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
645 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
646 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd @gol
647 -mnew-mnemonics -mold-mnemonics @gol
648 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
649 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
650 -malign-power -malign-natural @gol
651 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
652 -mstring -mno-string -mupdate -mno-update @gol
653 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
654 -mstrict-align -mno-strict-align -mrelocatable @gol
655 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
656 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
657 -mdynamic-no-pic -maltivec -mswdiv @gol
658 -mprioritize-restricted-insns=@var{priority} @gol
659 -msched-costly-dep=@var{dependence_type} @gol
660 -minsert-sched-nops=@var{scheme} @gol
661 -mcall-sysv -mcall-netbsd @gol
662 -maix-struct-return -msvr4-struct-return @gol
663 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
664 -misel -mno-isel @gol
665 -misel=yes -misel=no @gol
667 -mspe=yes -mspe=no @gol
668 -mvrsave -mno-vrsave @gol
669 -mmulhw -mno-mulhw @gol
670 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
671 -mprototype -mno-prototype @gol
672 -msim -mmvme -mads -myellowknife -memb -msdata @gol
673 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
675 @emph{S/390 and zSeries Options}
676 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
677 -mhard-float -msoft-float -mlong-double-64 -mlong-double-128 @gol
678 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
679 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
680 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
681 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
682 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
685 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
686 -m4-nofpu -m4-single-only -m4-single -m4 @gol
687 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
688 -m5-64media -m5-64media-nofpu @gol
689 -m5-32media -m5-32media-nofpu @gol
690 -m5-compact -m5-compact-nofpu @gol
691 -mb -ml -mdalign -mrelax @gol
692 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
693 -mieee -misize -mpadstruct -mspace @gol
694 -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
695 -mdivsi3_libfunc=@var{name} @gol
696 -madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
700 @gccoptlist{-mcpu=@var{cpu-type} @gol
701 -mtune=@var{cpu-type} @gol
702 -mcmodel=@var{code-model} @gol
703 -m32 -m64 -mapp-regs -mno-app-regs @gol
704 -mfaster-structs -mno-faster-structs @gol
705 -mfpu -mno-fpu -mhard-float -msoft-float @gol
706 -mhard-quad-float -msoft-quad-float @gol
707 -mimpure-text -mno-impure-text -mlittle-endian @gol
708 -mstack-bias -mno-stack-bias @gol
709 -munaligned-doubles -mno-unaligned-doubles @gol
710 -mv8plus -mno-v8plus -mvis -mno-vis
713 @emph{System V Options}
714 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
716 @emph{TMS320C3x/C4x Options}
717 @gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
718 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
719 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
720 -mparallel-insns -mparallel-mpy -mpreserve-float}
723 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
724 -mprolog-function -mno-prolog-function -mspace @gol
725 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
726 -mapp-regs -mno-app-regs @gol
727 -mdisable-callt -mno-disable-callt @gol
733 @gccoptlist{-mg -mgnu -munix}
735 @emph{x86-64 Options}
736 See i386 and x86-64 Options.
738 @emph{Xstormy16 Options}
741 @emph{Xtensa Options}
742 @gccoptlist{-mconst16 -mno-const16 @gol
743 -mfused-madd -mno-fused-madd @gol
744 -mtext-section-literals -mno-text-section-literals @gol
745 -mtarget-align -mno-target-align @gol
746 -mlongcalls -mno-longcalls}
748 @emph{zSeries Options}
749 See S/390 and zSeries Options.
751 @item Code Generation Options
752 @xref{Code Gen Options,,Options for Code Generation Conventions}.
753 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
754 -ffixed-@var{reg} -fexceptions @gol
755 -fnon-call-exceptions -funwind-tables @gol
756 -fasynchronous-unwind-tables @gol
757 -finhibit-size-directive -finstrument-functions @gol
758 -fno-common -fno-ident @gol
759 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
760 -fno-jump-tables @gol
761 -freg-struct-return -fshared-data -fshort-enums @gol
762 -fshort-double -fshort-wchar @gol
763 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
764 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
765 -fargument-alias -fargument-noalias @gol
766 -fargument-noalias-global -fleading-underscore @gol
767 -ftls-model=@var{model} @gol
768 -ftrapv -fwrapv -fbounds-check @gol
769 -fvisibility -fopenmp}
773 * Overall Options:: Controlling the kind of output:
774 an executable, object files, assembler files,
775 or preprocessed source.
776 * C Dialect Options:: Controlling the variant of C language compiled.
777 * C++ Dialect Options:: Variations on C++.
778 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
780 * Language Independent Options:: Controlling how diagnostics should be
782 * Warning Options:: How picky should the compiler be?
783 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
784 * Optimize Options:: How much optimization?
785 * Preprocessor Options:: Controlling header files and macro definitions.
786 Also, getting dependency information for Make.
787 * Assembler Options:: Passing options to the assembler.
788 * Link Options:: Specifying libraries and so on.
789 * Directory Options:: Where to find header files and libraries.
790 Where to find the compiler executable files.
791 * Spec Files:: How to pass switches to sub-processes.
792 * Target Options:: Running a cross-compiler, or an old version of GCC.
795 @node Overall Options
796 @section Options Controlling the Kind of Output
798 Compilation can involve up to four stages: preprocessing, compilation
799 proper, assembly and linking, always in that order. GCC is capable of
800 preprocessing and compiling several files either into several
801 assembler input files, or into one assembler input file; then each
802 assembler input file produces an object file, and linking combines all
803 the object files (those newly compiled, and those specified as input)
804 into an executable file.
806 @cindex file name suffix
807 For any given input file, the file name suffix determines what kind of
812 C source code which must be preprocessed.
815 C source code which should not be preprocessed.
818 C++ source code which should not be preprocessed.
821 Objective-C source code. Note that you must link with the @file{libobjc}
822 library to make an Objective-C program work.
825 Objective-C source code which should not be preprocessed.
829 Objective-C++ source code. Note that you must link with the @file{libobjc}
830 library to make an Objective-C++ program work. Note that @samp{.M} refers
831 to a literal capital M@.
834 Objective-C++ source code which should not be preprocessed.
837 C, C++, Objective-C or Objective-C++ header file to be turned into a
842 @itemx @var{file}.cxx
843 @itemx @var{file}.cpp
844 @itemx @var{file}.CPP
845 @itemx @var{file}.c++
847 C++ source code which must be preprocessed. Note that in @samp{.cxx},
848 the last two letters must both be literally @samp{x}. Likewise,
849 @samp{.C} refers to a literal capital C@.
853 Objective-C++ source code which must be preprocessed.
856 Objective-C++ source code which should not be preprocessed.
860 C++ header file to be turned into a precompiled header.
863 @itemx @var{file}.for
864 @itemx @var{file}.FOR
865 Fixed form Fortran source code which should not be preprocessed.
868 @itemx @var{file}.fpp
869 @itemx @var{file}.FPP
870 Fixed form Fortran source code which must be preprocessed (with the traditional
874 @itemx @var{file}.f95
875 Free form Fortran source code which should not be preprocessed.
878 @itemx @var{file}.F95
879 Free form Fortran source code which must be preprocessed (with the
880 traditional preprocessor).
882 @c FIXME: Descriptions of Java file types.
889 Ada source code file which contains a library unit declaration (a
890 declaration of a package, subprogram, or generic, or a generic
891 instantiation), or a library unit renaming declaration (a package,
892 generic, or subprogram renaming declaration). Such files are also
895 @itemx @var{file}.adb
896 Ada source code file containing a library unit body (a subprogram or
897 package body). Such files are also called @dfn{bodies}.
899 @c GCC also knows about some suffixes for languages not yet included:
910 Assembler code which must be preprocessed.
913 An object file to be fed straight into linking.
914 Any file name with no recognized suffix is treated this way.
918 You can specify the input language explicitly with the @option{-x} option:
921 @item -x @var{language}
922 Specify explicitly the @var{language} for the following input files
923 (rather than letting the compiler choose a default based on the file
924 name suffix). This option applies to all following input files until
925 the next @option{-x} option. Possible values for @var{language} are:
927 c c-header c-cpp-output
928 c++ c++-header c++-cpp-output
929 objective-c objective-c-header objective-c-cpp-output
930 objective-c++ objective-c++-header objective-c++-cpp-output
931 assembler assembler-with-cpp
940 Turn off any specification of a language, so that subsequent files are
941 handled according to their file name suffixes (as they are if @option{-x}
942 has not been used at all).
944 @item -pass-exit-codes
945 @opindex pass-exit-codes
946 Normally the @command{gcc} program will exit with the code of 1 if any
947 phase of the compiler returns a non-success return code. If you specify
948 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
949 numerically highest error produced by any phase that returned an error
953 If you only want some of the stages of compilation, you can use
954 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
955 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
956 @command{gcc} is to stop. Note that some combinations (for example,
957 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
962 Compile or assemble the source files, but do not link. The linking
963 stage simply is not done. The ultimate output is in the form of an
964 object file for each source file.
966 By default, the object file name for a source file is made by replacing
967 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
969 Unrecognized input files, not requiring compilation or assembly, are
974 Stop after the stage of compilation proper; do not assemble. The output
975 is in the form of an assembler code file for each non-assembler input
978 By default, the assembler file name for a source file is made by
979 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
981 Input files that don't require compilation are ignored.
985 Stop after the preprocessing stage; do not run the compiler proper. The
986 output is in the form of preprocessed source code, which is sent to the
989 Input files which don't require preprocessing are ignored.
991 @cindex output file option
994 Place output in file @var{file}. This applies regardless to whatever
995 sort of output is being produced, whether it be an executable file,
996 an object file, an assembler file or preprocessed C code.
998 If @option{-o} is not specified, the default is to put an executable
999 file in @file{a.out}, the object file for
1000 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
1001 assembler file in @file{@var{source}.s}, a precompiled header file in
1002 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
1007 Print (on standard error output) the commands executed to run the stages
1008 of compilation. Also print the version number of the compiler driver
1009 program and of the preprocessor and the compiler proper.
1013 Like @option{-v} except the commands are not executed and all command
1014 arguments are quoted. This is useful for shell scripts to capture the
1015 driver-generated command lines.
1019 Use pipes rather than temporary files for communication between the
1020 various stages of compilation. This fails to work on some systems where
1021 the assembler is unable to read from a pipe; but the GNU assembler has
1026 If you are compiling multiple source files, this option tells the driver
1027 to pass all the source files to the compiler at once (for those
1028 languages for which the compiler can handle this). This will allow
1029 intermodule analysis (IMA) to be performed by the compiler. Currently the only
1030 language for which this is supported is C@. If you pass source files for
1031 multiple languages to the driver, using this option, the driver will invoke
1032 the compiler(s) that support IMA once each, passing each compiler all the
1033 source files appropriate for it. For those languages that do not support
1034 IMA this option will be ignored, and the compiler will be invoked once for
1035 each source file in that language. If you use this option in conjunction
1036 with @option{-save-temps}, the compiler will generate multiple
1038 (one for each source file), but only one (combined) @file{.o} or
1043 Print (on the standard output) a description of the command line options
1044 understood by @command{gcc}. If the @option{-v} option is also specified
1045 then @option{--help} will also be passed on to the various processes
1046 invoked by @command{gcc}, so that they can display the command line options
1047 they accept. If the @option{-Wextra} option is also specified then command
1048 line options which have no documentation associated with them will also
1052 @opindex target-help
1053 Print (on the standard output) a description of target specific command
1054 line options for each tool.
1058 Display the version number and copyrights of the invoked GCC@.
1060 @include @value{srcdir}/../libiberty/at-file.texi
1064 @section Compiling C++ Programs
1066 @cindex suffixes for C++ source
1067 @cindex C++ source file suffixes
1068 C++ source files conventionally use one of the suffixes @samp{.C},
1069 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1070 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
1071 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1072 files with these names and compiles them as C++ programs even if you
1073 call the compiler the same way as for compiling C programs (usually
1074 with the name @command{gcc}).
1078 However, C++ programs often require class libraries as well as a
1079 compiler that understands the C++ language---and under some
1080 circumstances, you might want to compile programs or header files from
1081 standard input, or otherwise without a suffix that flags them as C++
1082 programs. You might also like to precompile a C header file with a
1083 @samp{.h} extension to be used in C++ compilations. @command{g++} is a
1084 program that calls GCC with the default language set to C++, and
1085 automatically specifies linking against the C++ library. On many
1086 systems, @command{g++} is also installed with the name @command{c++}.
1088 @cindex invoking @command{g++}
1089 When you compile C++ programs, you may specify many of the same
1090 command-line options that you use for compiling programs in any
1091 language; or command-line options meaningful for C and related
1092 languages; or options that are meaningful only for C++ programs.
1093 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1094 explanations of options for languages related to C@.
1095 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1096 explanations of options that are meaningful only for C++ programs.
1098 @node C Dialect Options
1099 @section Options Controlling C Dialect
1100 @cindex dialect options
1101 @cindex language dialect options
1102 @cindex options, dialect
1104 The following options control the dialect of C (or languages derived
1105 from C, such as C++, Objective-C and Objective-C++) that the compiler
1109 @cindex ANSI support
1113 In C mode, support all ISO C90 programs. In C++ mode,
1114 remove GNU extensions that conflict with ISO C++.
1116 This turns off certain features of GCC that are incompatible with ISO
1117 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1118 such as the @code{asm} and @code{typeof} keywords, and
1119 predefined macros such as @code{unix} and @code{vax} that identify the
1120 type of system you are using. It also enables the undesirable and
1121 rarely used ISO trigraph feature. For the C compiler,
1122 it disables recognition of C++ style @samp{//} comments as well as
1123 the @code{inline} keyword.
1125 The alternate keywords @code{__asm__}, @code{__extension__},
1126 @code{__inline__} and @code{__typeof__} continue to work despite
1127 @option{-ansi}. You would not want to use them in an ISO C program, of
1128 course, but it is useful to put them in header files that might be included
1129 in compilations done with @option{-ansi}. Alternate predefined macros
1130 such as @code{__unix__} and @code{__vax__} are also available, with or
1131 without @option{-ansi}.
1133 The @option{-ansi} option does not cause non-ISO programs to be
1134 rejected gratuitously. For that, @option{-pedantic} is required in
1135 addition to @option{-ansi}. @xref{Warning Options}.
1137 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1138 option is used. Some header files may notice this macro and refrain
1139 from declaring certain functions or defining certain macros that the
1140 ISO standard doesn't call for; this is to avoid interfering with any
1141 programs that might use these names for other things.
1143 Functions which would normally be built in but do not have semantics
1144 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1145 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1146 built-in functions provided by GCC}, for details of the functions
1151 Determine the language standard. This option is currently only
1152 supported when compiling C or C++. A value for this option must be
1153 provided; possible values are
1158 ISO C90 (same as @option{-ansi}).
1160 @item iso9899:199409
1161 ISO C90 as modified in amendment 1.
1167 ISO C99. Note that this standard is not yet fully supported; see
1168 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1169 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1172 Default, ISO C90 plus GNU extensions (including some C99 features).
1176 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1177 this will become the default. The name @samp{gnu9x} is deprecated.
1180 The 1998 ISO C++ standard plus amendments.
1183 The same as @option{-std=c++98} plus GNU extensions. This is the
1184 default for C++ code.
1187 Even when this option is not specified, you can still use some of the
1188 features of newer standards in so far as they do not conflict with
1189 previous C standards. For example, you may use @code{__restrict__} even
1190 when @option{-std=c99} is not specified.
1192 The @option{-std} options specifying some version of ISO C have the same
1193 effects as @option{-ansi}, except that features that were not in ISO C90
1194 but are in the specified version (for example, @samp{//} comments and
1195 the @code{inline} keyword in ISO C99) are not disabled.
1197 @xref{Standards,,Language Standards Supported by GCC}, for details of
1198 these standard versions.
1200 @item -aux-info @var{filename}
1202 Output to the given filename prototyped declarations for all functions
1203 declared and/or defined in a translation unit, including those in header
1204 files. This option is silently ignored in any language other than C@.
1206 Besides declarations, the file indicates, in comments, the origin of
1207 each declaration (source file and line), whether the declaration was
1208 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1209 @samp{O} for old, respectively, in the first character after the line
1210 number and the colon), and whether it came from a declaration or a
1211 definition (@samp{C} or @samp{F}, respectively, in the following
1212 character). In the case of function definitions, a K&R-style list of
1213 arguments followed by their declarations is also provided, inside
1214 comments, after the declaration.
1218 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1219 keyword, so that code can use these words as identifiers. You can use
1220 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1221 instead. @option{-ansi} implies @option{-fno-asm}.
1223 In C++, this switch only affects the @code{typeof} keyword, since
1224 @code{asm} and @code{inline} are standard keywords. You may want to
1225 use the @option{-fno-gnu-keywords} flag instead, which has the same
1226 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1227 switch only affects the @code{asm} and @code{typeof} keywords, since
1228 @code{inline} is a standard keyword in ISO C99.
1231 @itemx -fno-builtin-@var{function}
1232 @opindex fno-builtin
1233 @cindex built-in functions
1234 Don't recognize built-in functions that do not begin with
1235 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1236 functions provided by GCC}, for details of the functions affected,
1237 including those which are not built-in functions when @option{-ansi} or
1238 @option{-std} options for strict ISO C conformance are used because they
1239 do not have an ISO standard meaning.
1241 GCC normally generates special code to handle certain built-in functions
1242 more efficiently; for instance, calls to @code{alloca} may become single
1243 instructions that adjust the stack directly, and calls to @code{memcpy}
1244 may become inline copy loops. The resulting code is often both smaller
1245 and faster, but since the function calls no longer appear as such, you
1246 cannot set a breakpoint on those calls, nor can you change the behavior
1247 of the functions by linking with a different library. In addition,
1248 when a function is recognized as a built-in function, GCC may use
1249 information about that function to warn about problems with calls to
1250 that function, or to generate more efficient code, even if the
1251 resulting code still contains calls to that function. For example,
1252 warnings are given with @option{-Wformat} for bad calls to
1253 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1254 known not to modify global memory.
1256 With the @option{-fno-builtin-@var{function}} option
1257 only the built-in function @var{function} is
1258 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1259 function is named this is not built-in in this version of GCC, this
1260 option is ignored. There is no corresponding
1261 @option{-fbuiltin-@var{function}} option; if you wish to enable
1262 built-in functions selectively when using @option{-fno-builtin} or
1263 @option{-ffreestanding}, you may define macros such as:
1266 #define abs(n) __builtin_abs ((n))
1267 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1272 @cindex hosted environment
1274 Assert that compilation takes place in a hosted environment. This implies
1275 @option{-fbuiltin}. A hosted environment is one in which the
1276 entire standard library is available, and in which @code{main} has a return
1277 type of @code{int}. Examples are nearly everything except a kernel.
1278 This is equivalent to @option{-fno-freestanding}.
1280 @item -ffreestanding
1281 @opindex ffreestanding
1282 @cindex hosted environment
1284 Assert that compilation takes place in a freestanding environment. This
1285 implies @option{-fno-builtin}. A freestanding environment
1286 is one in which the standard library may not exist, and program startup may
1287 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1288 This is equivalent to @option{-fno-hosted}.
1290 @xref{Standards,,Language Standards Supported by GCC}, for details of
1291 freestanding and hosted environments.
1293 @item -fms-extensions
1294 @opindex fms-extensions
1295 Accept some non-standard constructs used in Microsoft header files.
1297 Some cases of unnamed fields in structures and unions are only
1298 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1299 fields within structs/unions}, for details.
1303 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1304 options for strict ISO C conformance) implies @option{-trigraphs}.
1306 @item -no-integrated-cpp
1307 @opindex no-integrated-cpp
1308 Performs a compilation in two passes: preprocessing and compiling. This
1309 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1310 @option{-B} option. The user supplied compilation step can then add in
1311 an additional preprocessing step after normal preprocessing but before
1312 compiling. The default is to use the integrated cpp (internal cpp)
1314 The semantics of this option will change if "cc1", "cc1plus", and
1315 "cc1obj" are merged.
1317 @cindex traditional C language
1318 @cindex C language, traditional
1320 @itemx -traditional-cpp
1321 @opindex traditional-cpp
1322 @opindex traditional
1323 Formerly, these options caused GCC to attempt to emulate a pre-standard
1324 C compiler. They are now only supported with the @option{-E} switch.
1325 The preprocessor continues to support a pre-standard mode. See the GNU
1326 CPP manual for details.
1328 @item -fcond-mismatch
1329 @opindex fcond-mismatch
1330 Allow conditional expressions with mismatched types in the second and
1331 third arguments. The value of such an expression is void. This option
1332 is not supported for C++.
1334 @item -funsigned-char
1335 @opindex funsigned-char
1336 Let the type @code{char} be unsigned, like @code{unsigned char}.
1338 Each kind of machine has a default for what @code{char} should
1339 be. It is either like @code{unsigned char} by default or like
1340 @code{signed char} by default.
1342 Ideally, a portable program should always use @code{signed char} or
1343 @code{unsigned char} when it depends on the signedness of an object.
1344 But many programs have been written to use plain @code{char} and
1345 expect it to be signed, or expect it to be unsigned, depending on the
1346 machines they were written for. This option, and its inverse, let you
1347 make such a program work with the opposite default.
1349 The type @code{char} is always a distinct type from each of
1350 @code{signed char} or @code{unsigned char}, even though its behavior
1351 is always just like one of those two.
1354 @opindex fsigned-char
1355 Let the type @code{char} be signed, like @code{signed char}.
1357 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1358 the negative form of @option{-funsigned-char}. Likewise, the option
1359 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1361 @item -fsigned-bitfields
1362 @itemx -funsigned-bitfields
1363 @itemx -fno-signed-bitfields
1364 @itemx -fno-unsigned-bitfields
1365 @opindex fsigned-bitfields
1366 @opindex funsigned-bitfields
1367 @opindex fno-signed-bitfields
1368 @opindex fno-unsigned-bitfields
1369 These options control whether a bit-field is signed or unsigned, when the
1370 declaration does not use either @code{signed} or @code{unsigned}. By
1371 default, such a bit-field is signed, because this is consistent: the
1372 basic integer types such as @code{int} are signed types.
1375 @node C++ Dialect Options
1376 @section Options Controlling C++ Dialect
1378 @cindex compiler options, C++
1379 @cindex C++ options, command line
1380 @cindex options, C++
1381 This section describes the command-line options that are only meaningful
1382 for C++ programs; but you can also use most of the GNU compiler options
1383 regardless of what language your program is in. For example, you
1384 might compile a file @code{firstClass.C} like this:
1387 g++ -g -frepo -O -c firstClass.C
1391 In this example, only @option{-frepo} is an option meant
1392 only for C++ programs; you can use the other options with any
1393 language supported by GCC@.
1395 Here is a list of options that are @emph{only} for compiling C++ programs:
1399 @item -fabi-version=@var{n}
1400 @opindex fabi-version
1401 Use version @var{n} of the C++ ABI@. Version 2 is the version of the
1402 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1403 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1404 the version that conforms most closely to the C++ ABI specification.
1405 Therefore, the ABI obtained using version 0 will change as ABI bugs
1408 The default is version 2.
1410 @item -fno-access-control
1411 @opindex fno-access-control
1412 Turn off all access checking. This switch is mainly useful for working
1413 around bugs in the access control code.
1417 Check that the pointer returned by @code{operator new} is non-null
1418 before attempting to modify the storage allocated. This check is
1419 normally unnecessary because the C++ standard specifies that
1420 @code{operator new} will only return @code{0} if it is declared
1421 @samp{throw()}, in which case the compiler will always check the
1422 return value even without this option. In all other cases, when
1423 @code{operator new} has a non-empty exception specification, memory
1424 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1425 @samp{new (nothrow)}.
1427 @item -fconserve-space
1428 @opindex fconserve-space
1429 Put uninitialized or runtime-initialized global variables into the
1430 common segment, as C does. This saves space in the executable at the
1431 cost of not diagnosing duplicate definitions. If you compile with this
1432 flag and your program mysteriously crashes after @code{main()} has
1433 completed, you may have an object that is being destroyed twice because
1434 two definitions were merged.
1436 This option is no longer useful on most targets, now that support has
1437 been added for putting variables into BSS without making them common.
1439 @item -ffriend-injection
1440 @opindex ffriend-injection
1441 Inject friend functions into the enclosing namespace, so that they are
1442 visible outside the scope of the class in which they are declared.
1443 Friend functions were documented to work this way in the old Annotated
1444 C++ Reference Manual, and versions of G++ before 4.1 always worked
1445 that way. However, in ISO C++ a friend function which is not declared
1446 in an enclosing scope can only be found using argument dependent
1447 lookup. This option causes friends to be injected as they were in
1450 This option is for compatibility, and may be removed in a future
1453 @item -fno-const-strings
1454 @opindex fno-const-strings
1455 Give string constants type @code{char *} instead of type @code{const
1456 char *}. By default, G++ uses type @code{const char *} as required by
1457 the standard. Even if you use @option{-fno-const-strings}, you cannot
1458 actually modify the value of a string constant.
1460 This option might be removed in a future release of G++. For maximum
1461 portability, you should structure your code so that it works with
1462 string constants that have type @code{const char *}.
1464 @item -fno-elide-constructors
1465 @opindex fno-elide-constructors
1466 The C++ standard allows an implementation to omit creating a temporary
1467 which is only used to initialize another object of the same type.
1468 Specifying this option disables that optimization, and forces G++ to
1469 call the copy constructor in all cases.
1471 @item -fno-enforce-eh-specs
1472 @opindex fno-enforce-eh-specs
1473 Don't generate code to check for violation of exception specifications
1474 at runtime. This option violates the C++ standard, but may be useful
1475 for reducing code size in production builds, much like defining
1476 @samp{NDEBUG}. This does not give user code permission to throw
1477 exceptions in violation of the exception specifications; the compiler
1478 will still optimize based on the specifications, so throwing an
1479 unexpected exception will result in undefined behavior.
1482 @itemx -fno-for-scope
1484 @opindex fno-for-scope
1485 If @option{-ffor-scope} is specified, the scope of variables declared in
1486 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1487 as specified by the C++ standard.
1488 If @option{-fno-for-scope} is specified, the scope of variables declared in
1489 a @i{for-init-statement} extends to the end of the enclosing scope,
1490 as was the case in old versions of G++, and other (traditional)
1491 implementations of C++.
1493 The default if neither flag is given to follow the standard,
1494 but to allow and give a warning for old-style code that would
1495 otherwise be invalid, or have different behavior.
1497 @item -fno-gnu-keywords
1498 @opindex fno-gnu-keywords
1499 Do not recognize @code{typeof} as a keyword, so that code can use this
1500 word as an identifier. You can use the keyword @code{__typeof__} instead.
1501 @option{-ansi} implies @option{-fno-gnu-keywords}.
1503 @item -fno-implicit-templates
1504 @opindex fno-implicit-templates
1505 Never emit code for non-inline templates which are instantiated
1506 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1507 @xref{Template Instantiation}, for more information.
1509 @item -fno-implicit-inline-templates
1510 @opindex fno-implicit-inline-templates
1511 Don't emit code for implicit instantiations of inline templates, either.
1512 The default is to handle inlines differently so that compiles with and
1513 without optimization will need the same set of explicit instantiations.
1515 @item -fno-implement-inlines
1516 @opindex fno-implement-inlines
1517 To save space, do not emit out-of-line copies of inline functions
1518 controlled by @samp{#pragma implementation}. This will cause linker
1519 errors if these functions are not inlined everywhere they are called.
1521 @item -fms-extensions
1522 @opindex fms-extensions
1523 Disable pedantic warnings about constructs used in MFC, such as implicit
1524 int and getting a pointer to member function via non-standard syntax.
1526 @item -fno-nonansi-builtins
1527 @opindex fno-nonansi-builtins
1528 Disable built-in declarations of functions that are not mandated by
1529 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1530 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1532 @item -fno-operator-names
1533 @opindex fno-operator-names
1534 Do not treat the operator name keywords @code{and}, @code{bitand},
1535 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1536 synonyms as keywords.
1538 @item -fno-optional-diags
1539 @opindex fno-optional-diags
1540 Disable diagnostics that the standard says a compiler does not need to
1541 issue. Currently, the only such diagnostic issued by G++ is the one for
1542 a name having multiple meanings within a class.
1545 @opindex fpermissive
1546 Downgrade some diagnostics about nonconformant code from errors to
1547 warnings. Thus, using @option{-fpermissive} will allow some
1548 nonconforming code to compile.
1552 Enable automatic template instantiation at link time. This option also
1553 implies @option{-fno-implicit-templates}. @xref{Template
1554 Instantiation}, for more information.
1558 Disable generation of information about every class with virtual
1559 functions for use by the C++ runtime type identification features
1560 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1561 of the language, you can save some space by using this flag. Note that
1562 exception handling uses the same information, but it will generate it as
1567 Emit statistics about front-end processing at the end of the compilation.
1568 This information is generally only useful to the G++ development team.
1570 @item -ftemplate-depth-@var{n}
1571 @opindex ftemplate-depth
1572 Set the maximum instantiation depth for template classes to @var{n}.
1573 A limit on the template instantiation depth is needed to detect
1574 endless recursions during template class instantiation. ANSI/ISO C++
1575 conforming programs must not rely on a maximum depth greater than 17.
1577 @item -fno-threadsafe-statics
1578 @opindex fno-threadsafe-statics
1579 Do not emit the extra code to use the routines specified in the C++
1580 ABI for thread-safe initialization of local statics. You can use this
1581 option to reduce code size slightly in code that doesn't need to be
1584 @item -fuse-cxa-atexit
1585 @opindex fuse-cxa-atexit
1586 Register destructors for objects with static storage duration with the
1587 @code{__cxa_atexit} function rather than the @code{atexit} function.
1588 This option is required for fully standards-compliant handling of static
1589 destructors, but will only work if your C library supports
1590 @code{__cxa_atexit}.
1592 @item -fvisibility-inlines-hidden
1593 @opindex fvisibility-inlines-hidden
1594 Causes all inlined methods to be marked with
1595 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1596 appear in the export table of a DSO and do not require a PLT indirection
1597 when used within the DSO@. Enabling this option can have a dramatic effect
1598 on load and link times of a DSO as it massively reduces the size of the
1599 dynamic export table when the library makes heavy use of templates. While
1600 it can cause bloating through duplication of code within each DSO where
1601 it is used, often the wastage is less than the considerable space occupied
1602 by a long symbol name in the export table which is typical when using
1603 templates and namespaces. For even more savings, combine with the
1604 @option{-fvisibility=hidden} switch.
1608 Do not use weak symbol support, even if it is provided by the linker.
1609 By default, G++ will use weak symbols if they are available. This
1610 option exists only for testing, and should not be used by end-users;
1611 it will result in inferior code and has no benefits. This option may
1612 be removed in a future release of G++.
1616 Do not search for header files in the standard directories specific to
1617 C++, but do still search the other standard directories. (This option
1618 is used when building the C++ library.)
1621 In addition, these optimization, warning, and code generation options
1622 have meanings only for C++ programs:
1625 @item -fno-default-inline
1626 @opindex fno-default-inline
1627 Do not assume @samp{inline} for functions defined inside a class scope.
1628 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1629 functions will have linkage like inline functions; they just won't be
1632 @item -Wabi @r{(C++ only)}
1634 Warn when G++ generates code that is probably not compatible with the
1635 vendor-neutral C++ ABI@. Although an effort has been made to warn about
1636 all such cases, there are probably some cases that are not warned about,
1637 even though G++ is generating incompatible code. There may also be
1638 cases where warnings are emitted even though the code that is generated
1641 You should rewrite your code to avoid these warnings if you are
1642 concerned about the fact that code generated by G++ may not be binary
1643 compatible with code generated by other compilers.
1645 The known incompatibilities at this point include:
1650 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1651 pack data into the same byte as a base class. For example:
1654 struct A @{ virtual void f(); int f1 : 1; @};
1655 struct B : public A @{ int f2 : 1; @};
1659 In this case, G++ will place @code{B::f2} into the same byte
1660 as@code{A::f1}; other compilers will not. You can avoid this problem
1661 by explicitly padding @code{A} so that its size is a multiple of the
1662 byte size on your platform; that will cause G++ and other compilers to
1663 layout @code{B} identically.
1666 Incorrect handling of tail-padding for virtual bases. G++ does not use
1667 tail padding when laying out virtual bases. For example:
1670 struct A @{ virtual void f(); char c1; @};
1671 struct B @{ B(); char c2; @};
1672 struct C : public A, public virtual B @{@};
1676 In this case, G++ will not place @code{B} into the tail-padding for
1677 @code{A}; other compilers will. You can avoid this problem by
1678 explicitly padding @code{A} so that its size is a multiple of its
1679 alignment (ignoring virtual base classes); that will cause G++ and other
1680 compilers to layout @code{C} identically.
1683 Incorrect handling of bit-fields with declared widths greater than that
1684 of their underlying types, when the bit-fields appear in a union. For
1688 union U @{ int i : 4096; @};
1692 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1693 union too small by the number of bits in an @code{int}.
1696 Empty classes can be placed at incorrect offsets. For example:
1706 struct C : public B, public A @{@};
1710 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1711 it should be placed at offset zero. G++ mistakenly believes that the
1712 @code{A} data member of @code{B} is already at offset zero.
1715 Names of template functions whose types involve @code{typename} or
1716 template template parameters can be mangled incorrectly.
1719 template <typename Q>
1720 void f(typename Q::X) @{@}
1722 template <template <typename> class Q>
1723 void f(typename Q<int>::X) @{@}
1727 Instantiations of these templates may be mangled incorrectly.
1731 @item -Wctor-dtor-privacy @r{(C++ only)}
1732 @opindex Wctor-dtor-privacy
1733 Warn when a class seems unusable because all the constructors or
1734 destructors in that class are private, and it has neither friends nor
1735 public static member functions.
1737 @item -Wnon-virtual-dtor @r{(C++ only)}
1738 @opindex Wnon-virtual-dtor
1739 Warn when a class appears to be polymorphic, thereby requiring a virtual
1740 destructor, yet it declares a non-virtual one. This warning is also
1741 enabled if -Weffc++ is specified.
1743 @item -Wreorder @r{(C++ only)}
1745 @cindex reordering, warning
1746 @cindex warning for reordering of member initializers
1747 Warn when the order of member initializers given in the code does not
1748 match the order in which they must be executed. For instance:
1754 A(): j (0), i (1) @{ @}
1758 The compiler will rearrange the member initializers for @samp{i}
1759 and @samp{j} to match the declaration order of the members, emitting
1760 a warning to that effect. This warning is enabled by @option{-Wall}.
1763 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1766 @item -Weffc++ @r{(C++ only)}
1768 Warn about violations of the following style guidelines from Scott Meyers'
1769 @cite{Effective C++} book:
1773 Item 11: Define a copy constructor and an assignment operator for classes
1774 with dynamically allocated memory.
1777 Item 12: Prefer initialization to assignment in constructors.
1780 Item 14: Make destructors virtual in base classes.
1783 Item 15: Have @code{operator=} return a reference to @code{*this}.
1786 Item 23: Don't try to return a reference when you must return an object.
1790 Also warn about violations of the following style guidelines from
1791 Scott Meyers' @cite{More Effective C++} book:
1795 Item 6: Distinguish between prefix and postfix forms of increment and
1796 decrement operators.
1799 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1803 When selecting this option, be aware that the standard library
1804 headers do not obey all of these guidelines; use @samp{grep -v}
1805 to filter out those warnings.
1807 @item -Wno-deprecated @r{(C++ only)}
1808 @opindex Wno-deprecated
1809 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1811 @item -Wstrict-null-sentinel @r{(C++ only)}
1812 @opindex Wstrict-null-sentinel
1813 Warn also about the use of an uncasted @code{NULL} as sentinel. When
1814 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
1815 to @code{__null}. Although it is a null pointer constant not a null pointer,
1816 it is guaranteed to of the same size as a pointer. But this use is
1817 not portable across different compilers.
1819 @item -Wno-non-template-friend @r{(C++ only)}
1820 @opindex Wno-non-template-friend
1821 Disable warnings when non-templatized friend functions are declared
1822 within a template. Since the advent of explicit template specification
1823 support in G++, if the name of the friend is an unqualified-id (i.e.,
1824 @samp{friend foo(int)}), the C++ language specification demands that the
1825 friend declare or define an ordinary, nontemplate function. (Section
1826 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1827 could be interpreted as a particular specialization of a templatized
1828 function. Because this non-conforming behavior is no longer the default
1829 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1830 check existing code for potential trouble spots and is on by default.
1831 This new compiler behavior can be turned off with
1832 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1833 but disables the helpful warning.
1835 @item -Wold-style-cast @r{(C++ only)}
1836 @opindex Wold-style-cast
1837 Warn if an old-style (C-style) cast to a non-void type is used within
1838 a C++ program. The new-style casts (@samp{dynamic_cast},
1839 @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are
1840 less vulnerable to unintended effects and much easier to search for.
1842 @item -Woverloaded-virtual @r{(C++ only)}
1843 @opindex Woverloaded-virtual
1844 @cindex overloaded virtual fn, warning
1845 @cindex warning for overloaded virtual fn
1846 Warn when a function declaration hides virtual functions from a
1847 base class. For example, in:
1854 struct B: public A @{
1859 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1867 will fail to compile.
1869 @item -Wno-pmf-conversions @r{(C++ only)}
1870 @opindex Wno-pmf-conversions
1871 Disable the diagnostic for converting a bound pointer to member function
1874 @item -Wsign-promo @r{(C++ only)}
1875 @opindex Wsign-promo
1876 Warn when overload resolution chooses a promotion from unsigned or
1877 enumerated type to a signed type, over a conversion to an unsigned type of
1878 the same size. Previous versions of G++ would try to preserve
1879 unsignedness, but the standard mandates the current behavior.
1884 A& operator = (int);
1894 In this example, G++ will synthesize a default @samp{A& operator =
1895 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1898 @node Objective-C and Objective-C++ Dialect Options
1899 @section Options Controlling Objective-C and Objective-C++ Dialects
1901 @cindex compiler options, Objective-C and Objective-C++
1902 @cindex Objective-C and Objective-C++ options, command line
1903 @cindex options, Objective-C and Objective-C++
1904 (NOTE: This manual does not describe the Objective-C and Objective-C++
1905 languages themselves. See @xref{Standards,,Language Standards
1906 Supported by GCC}, for references.)
1908 This section describes the command-line options that are only meaningful
1909 for Objective-C and Objective-C++ programs, but you can also use most of
1910 the language-independent GNU compiler options.
1911 For example, you might compile a file @code{some_class.m} like this:
1914 gcc -g -fgnu-runtime -O -c some_class.m
1918 In this example, @option{-fgnu-runtime} is an option meant only for
1919 Objective-C and Objective-C++ programs; you can use the other options with
1920 any language supported by GCC@.
1922 Note that since Objective-C is an extension of the C language, Objective-C
1923 compilations may also use options specific to the C front-end (e.g.,
1924 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
1925 C++-specific options (e.g., @option{-Wabi}).
1927 Here is a list of options that are @emph{only} for compiling Objective-C
1928 and Objective-C++ programs:
1931 @item -fconstant-string-class=@var{class-name}
1932 @opindex fconstant-string-class
1933 Use @var{class-name} as the name of the class to instantiate for each
1934 literal string specified with the syntax @code{@@"@dots{}"}. The default
1935 class name is @code{NXConstantString} if the GNU runtime is being used, and
1936 @code{NSConstantString} if the NeXT runtime is being used (see below). The
1937 @option{-fconstant-cfstrings} option, if also present, will override the
1938 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
1939 to be laid out as constant CoreFoundation strings.
1942 @opindex fgnu-runtime
1943 Generate object code compatible with the standard GNU Objective-C
1944 runtime. This is the default for most types of systems.
1946 @item -fnext-runtime
1947 @opindex fnext-runtime
1948 Generate output compatible with the NeXT runtime. This is the default
1949 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1950 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1953 @item -fno-nil-receivers
1954 @opindex fno-nil-receivers
1955 Assume that all Objective-C message dispatches (e.g.,
1956 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
1957 is not @code{nil}. This allows for more efficient entry points in the runtime
1958 to be used. Currently, this option is only available in conjunction with
1959 the NeXT runtime on Mac OS X 10.3 and later.
1961 @item -fobjc-call-cxx-cdtors
1962 @opindex fobjc-call-cxx-cdtors
1963 For each Objective-C class, check if any of its instance variables is a
1964 C++ object with a non-trivial default constructor. If so, synthesize a
1965 special @code{- (id) .cxx_construct} instance method that will run
1966 non-trivial default constructors on any such instance variables, in order,
1967 and then return @code{self}. Similarly, check if any instance variable
1968 is a C++ object with a non-trivial destructor, and if so, synthesize a
1969 special @code{- (void) .cxx_destruct} method that will run
1970 all such default destructors, in reverse order.
1972 The @code{- (id) .cxx_construct} and/or @code{- (void) .cxx_destruct} methods
1973 thusly generated will only operate on instance variables declared in the
1974 current Objective-C class, and not those inherited from superclasses. It
1975 is the responsibility of the Objective-C runtime to invoke all such methods
1976 in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods
1977 will be invoked by the runtime immediately after a new object
1978 instance is allocated; the @code{- (void) .cxx_destruct} methods will
1979 be invoked immediately before the runtime deallocates an object instance.
1981 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
1982 support for invoking the @code{- (id) .cxx_construct} and
1983 @code{- (void) .cxx_destruct} methods.
1985 @item -fobjc-direct-dispatch
1986 @opindex fobjc-direct-dispatch
1987 Allow fast jumps to the message dispatcher. On Darwin this is
1988 accomplished via the comm page.
1990 @item -fobjc-exceptions
1991 @opindex fobjc-exceptions
1992 Enable syntactic support for structured exception handling in Objective-C,
1993 similar to what is offered by C++ and Java. This option is
1994 unavailable in conjunction with the NeXT runtime on Mac OS X 10.2 and
2003 @@catch (AnObjCClass *exc) @{
2010 @@catch (AnotherClass *exc) @{
2013 @@catch (id allOthers) @{
2023 The @code{@@throw} statement may appear anywhere in an Objective-C or
2024 Objective-C++ program; when used inside of a @code{@@catch} block, the
2025 @code{@@throw} may appear without an argument (as shown above), in which case
2026 the object caught by the @code{@@catch} will be rethrown.
2028 Note that only (pointers to) Objective-C objects may be thrown and
2029 caught using this scheme. When an object is thrown, it will be caught
2030 by the nearest @code{@@catch} clause capable of handling objects of that type,
2031 analogously to how @code{catch} blocks work in C++ and Java. A
2032 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
2033 any and all Objective-C exceptions not caught by previous @code{@@catch}
2036 The @code{@@finally} clause, if present, will be executed upon exit from the
2037 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
2038 regardless of whether any exceptions are thrown, caught or rethrown
2039 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
2040 of the @code{finally} clause in Java.
2042 There are several caveats to using the new exception mechanism:
2046 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
2047 idioms provided by the @code{NSException} class, the new
2048 exceptions can only be used on Mac OS X 10.3 (Panther) and later
2049 systems, due to additional functionality needed in the (NeXT) Objective-C
2053 As mentioned above, the new exceptions do not support handling
2054 types other than Objective-C objects. Furthermore, when used from
2055 Objective-C++, the Objective-C exception model does not interoperate with C++
2056 exceptions at this time. This means you cannot @code{@@throw} an exception
2057 from Objective-C and @code{catch} it in C++, or vice versa
2058 (i.e., @code{throw @dots{} @@catch}).
2061 The @option{-fobjc-exceptions} switch also enables the use of synchronization
2062 blocks for thread-safe execution:
2065 @@synchronized (ObjCClass *guard) @{
2070 Upon entering the @code{@@synchronized} block, a thread of execution shall
2071 first check whether a lock has been placed on the corresponding @code{guard}
2072 object by another thread. If it has, the current thread shall wait until
2073 the other thread relinquishes its lock. Once @code{guard} becomes available,
2074 the current thread will place its own lock on it, execute the code contained in
2075 the @code{@@synchronized} block, and finally relinquish the lock (thereby
2076 making @code{guard} available to other threads).
2078 Unlike Java, Objective-C does not allow for entire methods to be marked
2079 @code{@@synchronized}. Note that throwing exceptions out of
2080 @code{@@synchronized} blocks is allowed, and will cause the guarding object
2081 to be unlocked properly.
2085 Enable garbage collection (GC) in Objective-C and Objective-C++ programs.
2087 @item -freplace-objc-classes
2088 @opindex freplace-objc-classes
2089 Emit a special marker instructing @command{ld(1)} not to statically link in
2090 the resulting object file, and allow @command{dyld(1)} to load it in at
2091 run time instead. This is used in conjunction with the Fix-and-Continue
2092 debugging mode, where the object file in question may be recompiled and
2093 dynamically reloaded in the course of program execution, without the need
2094 to restart the program itself. Currently, Fix-and-Continue functionality
2095 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
2100 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
2101 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
2102 compile time) with static class references that get initialized at load time,
2103 which improves run-time performance. Specifying the @option{-fzero-link} flag
2104 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
2105 to be retained. This is useful in Zero-Link debugging mode, since it allows
2106 for individual class implementations to be modified during program execution.
2110 Dump interface declarations for all classes seen in the source file to a
2111 file named @file{@var{sourcename}.decl}.
2113 @item -Wassign-intercept
2114 @opindex Wassign-intercept
2115 Warn whenever an Objective-C assignment is being intercepted by the
2119 @opindex Wno-protocol
2120 If a class is declared to implement a protocol, a warning is issued for
2121 every method in the protocol that is not implemented by the class. The
2122 default behavior is to issue a warning for every method not explicitly
2123 implemented in the class, even if a method implementation is inherited
2124 from the superclass. If you use the @option{-Wno-protocol} option, then
2125 methods inherited from the superclass are considered to be implemented,
2126 and no warning is issued for them.
2130 Warn if multiple methods of different types for the same selector are
2131 found during compilation. The check is performed on the list of methods
2132 in the final stage of compilation. Additionally, a check is performed
2133 for each selector appearing in a @code{@@selector(@dots{})}
2134 expression, and a corresponding method for that selector has been found
2135 during compilation. Because these checks scan the method table only at
2136 the end of compilation, these warnings are not produced if the final
2137 stage of compilation is not reached, for example because an error is
2138 found during compilation, or because the @option{-fsyntax-only} option is
2141 @item -Wstrict-selector-match
2142 @opindex Wstrict-selector-match
2143 Warn if multiple methods with differing argument and/or return types are
2144 found for a given selector when attempting to send a message using this
2145 selector to a receiver of type @code{id} or @code{Class}. When this flag
2146 is off (which is the default behavior), the compiler will omit such warnings
2147 if any differences found are confined to types which share the same size
2150 @item -Wundeclared-selector
2151 @opindex Wundeclared-selector
2152 Warn if a @code{@@selector(@dots{})} expression referring to an
2153 undeclared selector is found. A selector is considered undeclared if no
2154 method with that name has been declared before the
2155 @code{@@selector(@dots{})} expression, either explicitly in an
2156 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2157 an @code{@@implementation} section. This option always performs its
2158 checks as soon as a @code{@@selector(@dots{})} expression is found,
2159 while @option{-Wselector} only performs its checks in the final stage of
2160 compilation. This also enforces the coding style convention
2161 that methods and selectors must be declared before being used.
2163 @item -print-objc-runtime-info
2164 @opindex print-objc-runtime-info
2165 Generate C header describing the largest structure that is passed by
2170 @node Language Independent Options
2171 @section Options to Control Diagnostic Messages Formatting
2172 @cindex options to control diagnostics formatting
2173 @cindex diagnostic messages
2174 @cindex message formatting
2176 Traditionally, diagnostic messages have been formatted irrespective of
2177 the output device's aspect (e.g.@: its width, @dots{}). The options described
2178 below can be used to control the diagnostic messages formatting
2179 algorithm, e.g.@: how many characters per line, how often source location
2180 information should be reported. Right now, only the C++ front end can
2181 honor these options. However it is expected, in the near future, that
2182 the remaining front ends would be able to digest them correctly.
2185 @item -fmessage-length=@var{n}
2186 @opindex fmessage-length
2187 Try to format error messages so that they fit on lines of about @var{n}
2188 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2189 the front ends supported by GCC@. If @var{n} is zero, then no
2190 line-wrapping will be done; each error message will appear on a single
2193 @opindex fdiagnostics-show-location
2194 @item -fdiagnostics-show-location=once
2195 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2196 reporter to emit @emph{once} source location information; that is, in
2197 case the message is too long to fit on a single physical line and has to
2198 be wrapped, the source location won't be emitted (as prefix) again,
2199 over and over, in subsequent continuation lines. This is the default
2202 @item -fdiagnostics-show-location=every-line
2203 Only meaningful in line-wrapping mode. Instructs the diagnostic
2204 messages reporter to emit the same source location information (as
2205 prefix) for physical lines that result from the process of breaking
2206 a message which is too long to fit on a single line.
2208 @item -fdiagnostics-show-options
2209 @opindex fdiagnostics-show-options
2210 This option instructs the diagnostic machinery to add text to each
2211 diagnostic emitted, which indicates which command line option directly
2212 controls that diagnostic, when such an option is known to the
2213 diagnostic machinery.
2217 @node Warning Options
2218 @section Options to Request or Suppress Warnings
2219 @cindex options to control warnings
2220 @cindex warning messages
2221 @cindex messages, warning
2222 @cindex suppressing warnings
2224 Warnings are diagnostic messages that report constructions which
2225 are not inherently erroneous but which are risky or suggest there
2226 may have been an error.
2228 You can request many specific warnings with options beginning @samp{-W},
2229 for example @option{-Wimplicit} to request warnings on implicit
2230 declarations. Each of these specific warning options also has a
2231 negative form beginning @samp{-Wno-} to turn off warnings;
2232 for example, @option{-Wno-implicit}. This manual lists only one of the
2233 two forms, whichever is not the default.
2235 The following options control the amount and kinds of warnings produced
2236 by GCC; for further, language-specific options also refer to
2237 @ref{C++ Dialect Options} and @ref{Objective-C and Objective-C++ Dialect
2241 @cindex syntax checking
2243 @opindex fsyntax-only
2244 Check the code for syntax errors, but don't do anything beyond that.
2248 Issue all the warnings demanded by strict ISO C and ISO C++;
2249 reject all programs that use forbidden extensions, and some other
2250 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2251 version of the ISO C standard specified by any @option{-std} option used.
2253 Valid ISO C and ISO C++ programs should compile properly with or without
2254 this option (though a rare few will require @option{-ansi} or a
2255 @option{-std} option specifying the required version of ISO C)@. However,
2256 without this option, certain GNU extensions and traditional C and C++
2257 features are supported as well. With this option, they are rejected.
2259 @option{-pedantic} does not cause warning messages for use of the
2260 alternate keywords whose names begin and end with @samp{__}. Pedantic
2261 warnings are also disabled in the expression that follows
2262 @code{__extension__}. However, only system header files should use
2263 these escape routes; application programs should avoid them.
2264 @xref{Alternate Keywords}.
2266 Some users try to use @option{-pedantic} to check programs for strict ISO
2267 C conformance. They soon find that it does not do quite what they want:
2268 it finds some non-ISO practices, but not all---only those for which
2269 ISO C @emph{requires} a diagnostic, and some others for which
2270 diagnostics have been added.
2272 A feature to report any failure to conform to ISO C might be useful in
2273 some instances, but would require considerable additional work and would
2274 be quite different from @option{-pedantic}. We don't have plans to
2275 support such a feature in the near future.
2277 Where the standard specified with @option{-std} represents a GNU
2278 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2279 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2280 extended dialect is based. Warnings from @option{-pedantic} are given
2281 where they are required by the base standard. (It would not make sense
2282 for such warnings to be given only for features not in the specified GNU
2283 C dialect, since by definition the GNU dialects of C include all
2284 features the compiler supports with the given option, and there would be
2285 nothing to warn about.)
2287 @item -pedantic-errors
2288 @opindex pedantic-errors
2289 Like @option{-pedantic}, except that errors are produced rather than
2294 Inhibit all warning messages.
2298 Inhibit warning messages about the use of @samp{#import}.
2300 @item -Wchar-subscripts
2301 @opindex Wchar-subscripts
2302 Warn if an array subscript has type @code{char}. This is a common cause
2303 of error, as programmers often forget that this type is signed on some
2305 This warning is enabled by @option{-Wall}.
2309 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2310 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2311 This warning is enabled by @option{-Wall}.
2313 @item -Wfatal-errors
2314 @opindex Wfatal-errors
2315 This option causes the compiler to abort compilation on the first error
2316 occurred rather than trying to keep going and printing further error
2321 @opindex ffreestanding
2322 @opindex fno-builtin
2323 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2324 the arguments supplied have types appropriate to the format string
2325 specified, and that the conversions specified in the format string make
2326 sense. This includes standard functions, and others specified by format
2327 attributes (@pxref{Function Attributes}), in the @code{printf},
2328 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2329 not in the C standard) families (or other target-specific families).
2330 Which functions are checked without format attributes having been
2331 specified depends on the standard version selected, and such checks of
2332 functions without the attribute specified are disabled by
2333 @option{-ffreestanding} or @option{-fno-builtin}.
2335 The formats are checked against the format features supported by GNU
2336 libc version 2.2. These include all ISO C90 and C99 features, as well
2337 as features from the Single Unix Specification and some BSD and GNU
2338 extensions. Other library implementations may not support all these
2339 features; GCC does not support warning about features that go beyond a
2340 particular library's limitations. However, if @option{-pedantic} is used
2341 with @option{-Wformat}, warnings will be given about format features not
2342 in the selected standard version (but not for @code{strfmon} formats,
2343 since those are not in any version of the C standard). @xref{C Dialect
2344 Options,,Options Controlling C Dialect}.
2346 Since @option{-Wformat} also checks for null format arguments for
2347 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2349 @option{-Wformat} is included in @option{-Wall}. For more control over some
2350 aspects of format checking, the options @option{-Wformat-y2k},
2351 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2352 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2353 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2356 @opindex Wformat-y2k
2357 If @option{-Wformat} is specified, also warn about @code{strftime}
2358 formats which may yield only a two-digit year.
2360 @item -Wno-format-extra-args
2361 @opindex Wno-format-extra-args
2362 If @option{-Wformat} is specified, do not warn about excess arguments to a
2363 @code{printf} or @code{scanf} format function. The C standard specifies
2364 that such arguments are ignored.
2366 Where the unused arguments lie between used arguments that are
2367 specified with @samp{$} operand number specifications, normally
2368 warnings are still given, since the implementation could not know what
2369 type to pass to @code{va_arg} to skip the unused arguments. However,
2370 in the case of @code{scanf} formats, this option will suppress the
2371 warning if the unused arguments are all pointers, since the Single
2372 Unix Specification says that such unused arguments are allowed.
2374 @item -Wno-format-zero-length
2375 @opindex Wno-format-zero-length
2376 If @option{-Wformat} is specified, do not warn about zero-length formats.
2377 The C standard specifies that zero-length formats are allowed.
2379 @item -Wformat-nonliteral
2380 @opindex Wformat-nonliteral
2381 If @option{-Wformat} is specified, also warn if the format string is not a
2382 string literal and so cannot be checked, unless the format function
2383 takes its format arguments as a @code{va_list}.
2385 @item -Wformat-security
2386 @opindex Wformat-security
2387 If @option{-Wformat} is specified, also warn about uses of format
2388 functions that represent possible security problems. At present, this
2389 warns about calls to @code{printf} and @code{scanf} functions where the
2390 format string is not a string literal and there are no format arguments,
2391 as in @code{printf (foo);}. This may be a security hole if the format
2392 string came from untrusted input and contains @samp{%n}. (This is
2393 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2394 in future warnings may be added to @option{-Wformat-security} that are not
2395 included in @option{-Wformat-nonliteral}.)
2399 Enable @option{-Wformat} plus format checks not included in
2400 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2401 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2405 Warn about passing a null pointer for arguments marked as
2406 requiring a non-null value by the @code{nonnull} function attribute.
2408 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2409 can be disabled with the @option{-Wno-nonnull} option.
2411 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
2413 Warn about uninitialized variables which are initialized with themselves.
2414 Note this option can only be used with the @option{-Wuninitialized} option,
2415 which in turn only works with @option{-O1} and above.
2417 For example, GCC will warn about @code{i} being uninitialized in the
2418 following snippet only when @option{-Winit-self} has been specified:
2429 @item -Wimplicit-int
2430 @opindex Wimplicit-int
2431 Warn when a declaration does not specify a type.
2432 This warning is enabled by @option{-Wall}.
2434 @item -Wimplicit-function-declaration
2435 @itemx -Werror-implicit-function-declaration
2436 @opindex Wimplicit-function-declaration
2437 @opindex Werror-implicit-function-declaration
2438 Give a warning (or error) whenever a function is used before being
2439 declared. The form @option{-Wno-error-implicit-function-declaration}
2441 This warning is enabled by @option{-Wall} (as a warning, not an error).
2445 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2446 This warning is enabled by @option{-Wall}.
2450 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2451 function with external linkage, returning int, taking either zero
2452 arguments, two, or three arguments of appropriate types.
2453 This warning is enabled by @option{-Wall}.
2455 @item -Wmissing-braces
2456 @opindex Wmissing-braces
2457 Warn if an aggregate or union initializer is not fully bracketed. In
2458 the following example, the initializer for @samp{a} is not fully
2459 bracketed, but that for @samp{b} is fully bracketed.
2462 int a[2][2] = @{ 0, 1, 2, 3 @};
2463 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2466 This warning is enabled by @option{-Wall}.
2468 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
2469 @opindex Wmissing-include-dirs
2470 Warn if a user-supplied include directory does not exist.
2473 @opindex Wparentheses
2474 Warn if parentheses are omitted in certain contexts, such
2475 as when there is an assignment in a context where a truth value
2476 is expected, or when operators are nested whose precedence people
2477 often get confused about. Only the warning for an assignment used as
2478 a truth value is supported when compiling C++; the other warnings are
2479 only supported when compiling C@.
2481 Also warn if a comparison like @samp{x<=y<=z} appears; this is
2482 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
2483 interpretation from that of ordinary mathematical notation.
2485 Also warn about constructions where there may be confusion to which
2486 @code{if} statement an @code{else} branch belongs. Here is an example of
2501 In C, every @code{else} branch belongs to the innermost possible @code{if}
2502 statement, which in this example is @code{if (b)}. This is often not
2503 what the programmer expected, as illustrated in the above example by
2504 indentation the programmer chose. When there is the potential for this
2505 confusion, GCC will issue a warning when this flag is specified.
2506 To eliminate the warning, add explicit braces around the innermost
2507 @code{if} statement so there is no way the @code{else} could belong to
2508 the enclosing @code{if}. The resulting code would look like this:
2524 This warning is enabled by @option{-Wall}.
2526 @item -Wsequence-point
2527 @opindex Wsequence-point
2528 Warn about code that may have undefined semantics because of violations
2529 of sequence point rules in the C standard.
2531 The C standard defines the order in which expressions in a C program are
2532 evaluated in terms of @dfn{sequence points}, which represent a partial
2533 ordering between the execution of parts of the program: those executed
2534 before the sequence point, and those executed after it. These occur
2535 after the evaluation of a full expression (one which is not part of a
2536 larger expression), after the evaluation of the first operand of a
2537 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2538 function is called (but after the evaluation of its arguments and the
2539 expression denoting the called function), and in certain other places.
2540 Other than as expressed by the sequence point rules, the order of
2541 evaluation of subexpressions of an expression is not specified. All
2542 these rules describe only a partial order rather than a total order,
2543 since, for example, if two functions are called within one expression
2544 with no sequence point between them, the order in which the functions
2545 are called is not specified. However, the standards committee have
2546 ruled that function calls do not overlap.
2548 It is not specified when between sequence points modifications to the
2549 values of objects take effect. Programs whose behavior depends on this
2550 have undefined behavior; the C standard specifies that ``Between the
2551 previous and next sequence point an object shall have its stored value
2552 modified at most once by the evaluation of an expression. Furthermore,
2553 the prior value shall be read only to determine the value to be
2554 stored.''. If a program breaks these rules, the results on any
2555 particular implementation are entirely unpredictable.
2557 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2558 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2559 diagnosed by this option, and it may give an occasional false positive
2560 result, but in general it has been found fairly effective at detecting
2561 this sort of problem in programs.
2563 The present implementation of this option only works for C programs. A
2564 future implementation may also work for C++ programs.
2566 The C standard is worded confusingly, therefore there is some debate
2567 over the precise meaning of the sequence point rules in subtle cases.
2568 Links to discussions of the problem, including proposed formal
2569 definitions, may be found on the GCC readings page, at
2570 @w{@uref{http://gcc.gnu.org/readings.html}}.
2572 This warning is enabled by @option{-Wall}.
2575 @opindex Wreturn-type
2576 Warn whenever a function is defined with a return-type that defaults to
2577 @code{int}. Also warn about any @code{return} statement with no
2578 return-value in a function whose return-type is not @code{void}.
2580 For C, also warn if the return type of a function has a type qualifier
2581 such as @code{const}. Such a type qualifier has no effect, since the
2582 value returned by a function is not an lvalue. ISO C prohibits
2583 qualified @code{void} return types on function definitions, so such
2584 return types always receive a warning even without this option.
2586 For C++, a function without return type always produces a diagnostic
2587 message, even when @option{-Wno-return-type} is specified. The only
2588 exceptions are @samp{main} and functions defined in system headers.
2590 This warning is enabled by @option{-Wall}.
2594 Warn whenever a @code{switch} statement has an index of enumerated type
2595 and lacks a @code{case} for one or more of the named codes of that
2596 enumeration. (The presence of a @code{default} label prevents this
2597 warning.) @code{case} labels outside the enumeration range also
2598 provoke warnings when this option is used.
2599 This warning is enabled by @option{-Wall}.
2601 @item -Wswitch-default
2602 @opindex Wswitch-switch
2603 Warn whenever a @code{switch} statement does not have a @code{default}
2607 @opindex Wswitch-enum
2608 Warn whenever a @code{switch} statement has an index of enumerated type
2609 and lacks a @code{case} for one or more of the named codes of that
2610 enumeration. @code{case} labels outside the enumeration range also
2611 provoke warnings when this option is used.
2615 Warn if any trigraphs are encountered that might change the meaning of
2616 the program (trigraphs within comments are not warned about).
2617 This warning is enabled by @option{-Wall}.
2619 @item -Wunused-function
2620 @opindex Wunused-function
2621 Warn whenever a static function is declared but not defined or a
2622 non-inline static function is unused.
2623 This warning is enabled by @option{-Wall}.
2625 @item -Wunused-label
2626 @opindex Wunused-label
2627 Warn whenever a label is declared but not used.
2628 This warning is enabled by @option{-Wall}.
2630 To suppress this warning use the @samp{unused} attribute
2631 (@pxref{Variable Attributes}).
2633 @item -Wunused-parameter
2634 @opindex Wunused-parameter
2635 Warn whenever a function parameter is unused aside from its declaration.
2637 To suppress this warning use the @samp{unused} attribute
2638 (@pxref{Variable Attributes}).
2640 @item -Wunused-variable
2641 @opindex Wunused-variable
2642 Warn whenever a local variable or non-constant static variable is unused
2643 aside from its declaration
2644 This warning is enabled by @option{-Wall}.
2646 To suppress this warning use the @samp{unused} attribute
2647 (@pxref{Variable Attributes}).
2649 @item -Wunused-value
2650 @opindex Wunused-value
2651 Warn whenever a statement computes a result that is explicitly not used.
2652 This warning is enabled by @option{-Wall}.
2654 To suppress this warning cast the expression to @samp{void}.
2658 All the above @option{-Wunused} options combined.
2660 In order to get a warning about an unused function parameter, you must
2661 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2662 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2664 @item -Wuninitialized
2665 @opindex Wuninitialized
2666 Warn if an automatic variable is used without first being initialized or
2667 if a variable may be clobbered by a @code{setjmp} call.
2669 These warnings are possible only in optimizing compilation,
2670 because they require data flow information that is computed only
2671 when optimizing. If you don't specify @option{-O}, you simply won't
2674 If you want to warn about code which uses the uninitialized value of the
2675 variable in its own initializer, use the @option{-Winit-self} option.
2677 These warnings occur for individual uninitialized or clobbered
2678 elements of structure, union or array variables as well as for
2679 variables which are uninitialized or clobbered as a whole. They do
2680 not occur for variables or elements declared @code{volatile}. Because
2681 these warnings depend on optimization, the exact variables or elements
2682 for which there are warnings will depend on the precise optimization
2683 options and version of GCC used.
2685 Note that there may be no warning about a variable that is used only
2686 to compute a value that itself is never used, because such
2687 computations may be deleted by data flow analysis before the warnings
2690 These warnings are made optional because GCC is not smart
2691 enough to see all the reasons why the code might be correct
2692 despite appearing to have an error. Here is one example of how
2713 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2714 always initialized, but GCC doesn't know this. Here is
2715 another common case:
2720 if (change_y) save_y = y, y = new_y;
2722 if (change_y) y = save_y;
2727 This has no bug because @code{save_y} is used only if it is set.
2729 @cindex @code{longjmp} warnings
2730 This option also warns when a non-volatile automatic variable might be
2731 changed by a call to @code{longjmp}. These warnings as well are possible
2732 only in optimizing compilation.
2734 The compiler sees only the calls to @code{setjmp}. It cannot know
2735 where @code{longjmp} will be called; in fact, a signal handler could
2736 call it at any point in the code. As a result, you may get a warning
2737 even when there is in fact no problem because @code{longjmp} cannot
2738 in fact be called at the place which would cause a problem.
2740 Some spurious warnings can be avoided if you declare all the functions
2741 you use that never return as @code{noreturn}. @xref{Function
2744 This warning is enabled by @option{-Wall}.
2746 @item -Wunknown-pragmas
2747 @opindex Wunknown-pragmas
2748 @cindex warning for unknown pragmas
2749 @cindex unknown pragmas, warning
2750 @cindex pragmas, warning of unknown
2751 Warn when a #pragma directive is encountered which is not understood by
2752 GCC@. If this command line option is used, warnings will even be issued
2753 for unknown pragmas in system header files. This is not the case if
2754 the warnings were only enabled by the @option{-Wall} command line option.
2757 @opindex Wno-pragmas
2759 Do not warn about misuses of pragmas, such as incorrect parameters,
2760 invalid syntax, or conflicts between pragmas. See also
2761 @samp{-Wunknown-pragmas}.
2763 @item -Wstrict-aliasing
2764 @opindex Wstrict-aliasing
2765 This option is only active when @option{-fstrict-aliasing} is active.
2766 It warns about code which might break the strict aliasing rules that the
2767 compiler is using for optimization. The warning does not catch all
2768 cases, but does attempt to catch the more common pitfalls. It is
2769 included in @option{-Wall}.
2771 @item -Wstrict-aliasing=2
2772 @opindex Wstrict-aliasing=2
2773 This option is only active when @option{-fstrict-aliasing} is active.
2774 It warns about code which might break the strict aliasing rules that the
2775 compiler is using for optimization. This warning catches more cases than
2776 @option{-Wstrict-aliasing}, but it will also give a warning for some ambiguous
2777 cases that are safe.
2781 All of the above @samp{-W} options combined. This enables all the
2782 warnings about constructions that some users consider questionable, and
2783 that are easy to avoid (or modify to prevent the warning), even in
2784 conjunction with macros. This also enables some language-specific
2785 warnings described in @ref{C++ Dialect Options} and
2786 @ref{Objective-C and Objective-C++ Dialect Options}.
2789 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2790 Some of them warn about constructions that users generally do not
2791 consider questionable, but which occasionally you might wish to check
2792 for; others warn about constructions that are necessary or hard to avoid
2793 in some cases, and there is no simple way to modify the code to suppress
2800 (This option used to be called @option{-W}. The older name is still
2801 supported, but the newer name is more descriptive.) Print extra warning
2802 messages for these events:
2806 A function can return either with or without a value. (Falling
2807 off the end of the function body is considered returning without
2808 a value.) For example, this function would evoke such a
2822 An expression-statement or the left-hand side of a comma expression
2823 contains no side effects.
2824 To suppress the warning, cast the unused expression to void.
2825 For example, an expression such as @samp{x[i,j]} will cause a warning,
2826 but @samp{x[(void)i,j]} will not.
2829 An unsigned value is compared against zero with @samp{<} or @samp{>=}.
2832 Storage-class specifiers like @code{static} are not the first things in
2833 a declaration. According to the C Standard, this usage is obsolescent.
2836 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2840 A comparison between signed and unsigned values could produce an
2841 incorrect result when the signed value is converted to unsigned.
2842 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2845 An aggregate has an initializer which does not initialize all members.
2846 This warning can be independently controlled by
2847 @option{-Wmissing-field-initializers}.
2850 A function parameter is declared without a type specifier in K&R-style
2858 An empty body occurs in an @samp{if} or @samp{else} statement.
2861 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2862 @samp{>}, or @samp{>=}.
2865 A variable might be changed by @samp{longjmp} or @samp{vfork}.
2868 Any of several floating-point events that often indicate errors, such as
2869 overflow, underflow, loss of precision, etc.
2871 @item @r{(C++ only)}
2872 An enumerator and a non-enumerator both appear in a conditional expression.
2874 @item @r{(C++ only)}
2875 A non-static reference or non-static @samp{const} member appears in a
2876 class without constructors.
2878 @item @r{(C++ only)}
2879 Ambiguous virtual bases.
2881 @item @r{(C++ only)}
2882 Subscripting an array which has been declared @samp{register}.
2884 @item @r{(C++ only)}
2885 Taking the address of a variable which has been declared @samp{register}.
2887 @item @r{(C++ only)}
2888 A base class is not initialized in a derived class' copy constructor.
2891 @item -Wno-div-by-zero
2892 @opindex Wno-div-by-zero
2893 @opindex Wdiv-by-zero
2894 Do not warn about compile-time integer division by zero. Floating point
2895 division by zero is not warned about, as it can be a legitimate way of
2896 obtaining infinities and NaNs.
2898 @item -Wsystem-headers
2899 @opindex Wsystem-headers
2900 @cindex warnings from system headers
2901 @cindex system headers, warnings from
2902 Print warning messages for constructs found in system header files.
2903 Warnings from system headers are normally suppressed, on the assumption
2904 that they usually do not indicate real problems and would only make the
2905 compiler output harder to read. Using this command line option tells
2906 GCC to emit warnings from system headers as if they occurred in user
2907 code. However, note that using @option{-Wall} in conjunction with this
2908 option will @emph{not} warn about unknown pragmas in system
2909 headers---for that, @option{-Wunknown-pragmas} must also be used.
2912 @opindex Wfloat-equal
2913 Warn if floating point values are used in equality comparisons.
2915 The idea behind this is that sometimes it is convenient (for the
2916 programmer) to consider floating-point values as approximations to
2917 infinitely precise real numbers. If you are doing this, then you need
2918 to compute (by analyzing the code, or in some other way) the maximum or
2919 likely maximum error that the computation introduces, and allow for it
2920 when performing comparisons (and when producing output, but that's a
2921 different problem). In particular, instead of testing for equality, you
2922 would check to see whether the two values have ranges that overlap; and
2923 this is done with the relational operators, so equality comparisons are
2926 @item -Wtraditional @r{(C only)}
2927 @opindex Wtraditional
2928 Warn about certain constructs that behave differently in traditional and
2929 ISO C@. Also warn about ISO C constructs that have no traditional C
2930 equivalent, and/or problematic constructs which should be avoided.
2934 Macro parameters that appear within string literals in the macro body.
2935 In traditional C macro replacement takes place within string literals,
2936 but does not in ISO C@.
2939 In traditional C, some preprocessor directives did not exist.
2940 Traditional preprocessors would only consider a line to be a directive
2941 if the @samp{#} appeared in column 1 on the line. Therefore
2942 @option{-Wtraditional} warns about directives that traditional C
2943 understands but would ignore because the @samp{#} does not appear as the
2944 first character on the line. It also suggests you hide directives like
2945 @samp{#pragma} not understood by traditional C by indenting them. Some
2946 traditional implementations would not recognize @samp{#elif}, so it
2947 suggests avoiding it altogether.
2950 A function-like macro that appears without arguments.
2953 The unary plus operator.
2956 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2957 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2958 constants.) Note, these suffixes appear in macros defined in the system
2959 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2960 Use of these macros in user code might normally lead to spurious
2961 warnings, however GCC's integrated preprocessor has enough context to
2962 avoid warning in these cases.
2965 A function declared external in one block and then used after the end of
2969 A @code{switch} statement has an operand of type @code{long}.
2972 A non-@code{static} function declaration follows a @code{static} one.
2973 This construct is not accepted by some traditional C compilers.
2976 The ISO type of an integer constant has a different width or
2977 signedness from its traditional type. This warning is only issued if
2978 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2979 typically represent bit patterns, are not warned about.
2982 Usage of ISO string concatenation is detected.
2985 Initialization of automatic aggregates.
2988 Identifier conflicts with labels. Traditional C lacks a separate
2989 namespace for labels.
2992 Initialization of unions. If the initializer is zero, the warning is
2993 omitted. This is done under the assumption that the zero initializer in
2994 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2995 initializer warnings and relies on default initialization to zero in the
2999 Conversions by prototypes between fixed/floating point values and vice
3000 versa. The absence of these prototypes when compiling with traditional
3001 C would cause serious problems. This is a subset of the possible
3002 conversion warnings, for the full set use @option{-Wconversion}.
3005 Use of ISO C style function definitions. This warning intentionally is
3006 @emph{not} issued for prototype declarations or variadic functions
3007 because these ISO C features will appear in your code when using
3008 libiberty's traditional C compatibility macros, @code{PARAMS} and
3009 @code{VPARAMS}. This warning is also bypassed for nested functions
3010 because that feature is already a GCC extension and thus not relevant to
3011 traditional C compatibility.
3014 @item -Wdeclaration-after-statement @r{(C only)}
3015 @opindex Wdeclaration-after-statement
3016 Warn when a declaration is found after a statement in a block. This
3017 construct, known from C++, was introduced with ISO C99 and is by default
3018 allowed in GCC@. It is not supported by ISO C90 and was not supported by
3019 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
3023 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
3025 @item -Wno-endif-labels
3026 @opindex Wno-endif-labels
3027 @opindex Wendif-labels
3028 Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
3032 Warn whenever a local variable shadows another local variable, parameter or
3033 global variable or whenever a built-in function is shadowed.
3035 @item -Wlarger-than-@var{len}
3036 @opindex Wlarger-than
3037 Warn whenever an object of larger than @var{len} bytes is defined.
3039 @item -Wunsafe-loop-optimizations
3040 @opindex Wunsafe-loop-optimizations
3041 Warn if the loop cannot be optimized because the compiler could not
3042 assume anything on the bounds of the loop indices. With
3043 @option{-funsafe-loop-optimizations} warn if the compiler made
3046 @item -Wpointer-arith
3047 @opindex Wpointer-arith
3048 Warn about anything that depends on the ``size of'' a function type or
3049 of @code{void}. GNU C assigns these types a size of 1, for
3050 convenience in calculations with @code{void *} pointers and pointers
3053 @item -Wbad-function-cast @r{(C only)}
3054 @opindex Wbad-function-cast
3055 Warn whenever a function call is cast to a non-matching type.
3056 For example, warn if @code{int malloc()} is cast to @code{anything *}.
3059 Warn about ISO C constructs that are outside of the common subset of
3060 ISO C and ISO C++, e.g.@: request for implicit conversion from
3061 @code{void *} to a pointer to non-@code{void} type.
3065 Warn whenever a pointer is cast so as to remove a type qualifier from
3066 the target type. For example, warn if a @code{const char *} is cast
3067 to an ordinary @code{char *}.
3070 @opindex Wcast-align
3071 Warn whenever a pointer is cast such that the required alignment of the
3072 target is increased. For example, warn if a @code{char *} is cast to
3073 an @code{int *} on machines where integers can only be accessed at
3074 two- or four-byte boundaries.
3076 @item -Wwrite-strings
3077 @opindex Wwrite-strings
3078 When compiling C, give string constants the type @code{const
3079 char[@var{length}]} so that
3080 copying the address of one into a non-@code{const} @code{char *}
3081 pointer will get a warning; when compiling C++, warn about the
3082 deprecated conversion from string constants to @code{char *}.
3083 These warnings will help you find at
3084 compile time code that can try to write into a string constant, but
3085 only if you have been very careful about using @code{const} in
3086 declarations and prototypes. Otherwise, it will just be a nuisance;
3087 this is why we did not make @option{-Wall} request these warnings.
3090 @opindex Wconversion
3091 Warn if a prototype causes a type conversion that is different from what
3092 would happen to the same argument in the absence of a prototype. This
3093 includes conversions of fixed point to floating and vice versa, and
3094 conversions changing the width or signedness of a fixed point argument
3095 except when the same as the default promotion.
3097 Also, warn if a negative integer constant expression is implicitly
3098 converted to an unsigned type. For example, warn about the assignment
3099 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
3100 casts like @code{(unsigned) -1}.
3102 @item -Wsign-compare
3103 @opindex Wsign-compare
3104 @cindex warning for comparison of signed and unsigned values
3105 @cindex comparison of signed and unsigned values, warning
3106 @cindex signed and unsigned values, comparison warning
3107 Warn when a comparison between signed and unsigned values could produce
3108 an incorrect result when the signed value is converted to unsigned.
3109 This warning is also enabled by @option{-Wextra}; to get the other warnings
3110 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
3112 @item -Waggregate-return
3113 @opindex Waggregate-return
3114 Warn if any functions that return structures or unions are defined or
3115 called. (In languages where you can return an array, this also elicits
3119 @opindex Walways-true
3120 Warn about comparisons which are always true such as testing if
3121 unsigned values are greater than or equal to zero. This warning is
3122 enabled by @option{-Wall}.
3124 @item -Wno-attributes
3125 @opindex Wno-attributes
3126 @opindex Wattributes
3127 Do not warn if an unexpected @code{__attribute__} is used, such as
3128 unrecognized attributes, function attributes applied to variables,
3129 etc. This will not stop errors for incorrect use of supported
3132 @item -Wstrict-prototypes @r{(C only)}
3133 @opindex Wstrict-prototypes
3134 Warn if a function is declared or defined without specifying the
3135 argument types. (An old-style function definition is permitted without
3136 a warning if preceded by a declaration which specifies the argument
3139 @item -Wold-style-definition @r{(C only)}
3140 @opindex Wold-style-definition
3141 Warn if an old-style function definition is used. A warning is given
3142 even if there is a previous prototype.
3144 @item -Wmissing-prototypes @r{(C only)}
3145 @opindex Wmissing-prototypes
3146 Warn if a global function is defined without a previous prototype
3147 declaration. This warning is issued even if the definition itself
3148 provides a prototype. The aim is to detect global functions that fail
3149 to be declared in header files.
3151 @item -Wmissing-declarations @r{(C only)}
3152 @opindex Wmissing-declarations
3153 Warn if a global function is defined without a previous declaration.
3154 Do so even if the definition itself provides a prototype.
3155 Use this option to detect global functions that are not declared in
3158 @item -Wmissing-field-initializers
3159 @opindex Wmissing-field-initializers
3162 Warn if a structure's initializer has some fields missing. For
3163 example, the following code would cause such a warning, because
3164 @code{x.h} is implicitly zero:
3167 struct s @{ int f, g, h; @};
3168 struct s x = @{ 3, 4 @};
3171 This option does not warn about designated initializers, so the following
3172 modification would not trigger a warning:
3175 struct s @{ int f, g, h; @};
3176 struct s x = @{ .f = 3, .g = 4 @};
3179 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
3180 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
3182 @item -Wmissing-noreturn
3183 @opindex Wmissing-noreturn
3184 Warn about functions which might be candidates for attribute @code{noreturn}.
3185 Note these are only possible candidates, not absolute ones. Care should
3186 be taken to manually verify functions actually do not ever return before
3187 adding the @code{noreturn} attribute, otherwise subtle code generation
3188 bugs could be introduced. You will not get a warning for @code{main} in
3189 hosted C environments.
3191 @item -Wmissing-format-attribute
3192 @opindex Wmissing-format-attribute
3194 Warn about function pointers which might be candidates for @code{format}
3195 attributes. Note these are only possible candidates, not absolute ones.
3196 GCC will guess that function pointers with @code{format} attributes that
3197 are used in assignment, initialization, parameter passing or return
3198 statements should have a corresponding @code{format} attribute in the
3199 resulting type. I.e.@: the left-hand side of the assignment or
3200 initialization, the type of the parameter variable, or the return type
3201 of the containing function respectively should also have a @code{format}
3202 attribute to avoid the warning.
3204 GCC will also warn about function definitions which might be
3205 candidates for @code{format} attributes. Again, these are only
3206 possible candidates. GCC will guess that @code{format} attributes
3207 might be appropriate for any function that calls a function like
3208 @code{vprintf} or @code{vscanf}, but this might not always be the
3209 case, and some functions for which @code{format} attributes are
3210 appropriate may not be detected.
3212 @item -Wno-multichar
3213 @opindex Wno-multichar
3215 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
3216 Usually they indicate a typo in the user's code, as they have
3217 implementation-defined values, and should not be used in portable code.
3219 @item -Wnormalized=<none|id|nfc|nfkc>
3220 @opindex Wnormalized
3223 @cindex character set, input normalization
3224 In ISO C and ISO C++, two identifiers are different if they are
3225 different sequences of characters. However, sometimes when characters
3226 outside the basic ASCII character set are used, you can have two
3227 different character sequences that look the same. To avoid confusion,
3228 the ISO 10646 standard sets out some @dfn{normalization rules} which
3229 when applied ensure that two sequences that look the same are turned into
3230 the same sequence. GCC can warn you if you are using identifiers which
3231 have not been normalized; this option controls that warning.
3233 There are four levels of warning that GCC supports. The default is
3234 @option{-Wnormalized=nfc}, which warns about any identifier which is
3235 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
3236 recommended form for most uses.
3238 Unfortunately, there are some characters which ISO C and ISO C++ allow
3239 in identifiers that when turned into NFC aren't allowable as
3240 identifiers. That is, there's no way to use these symbols in portable
3241 ISO C or C++ and have all your identifiers in NFC.
3242 @option{-Wnormalized=id} suppresses the warning for these characters.
3243 It is hoped that future versions of the standards involved will correct
3244 this, which is why this option is not the default.
3246 You can switch the warning off for all characters by writing
3247 @option{-Wnormalized=none}. You would only want to do this if you
3248 were using some other normalization scheme (like ``D''), because
3249 otherwise you can easily create bugs that are literally impossible to see.
3251 Some characters in ISO 10646 have distinct meanings but look identical
3252 in some fonts or display methodologies, especially once formatting has
3253 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
3254 LETTER N'', will display just like a regular @code{n} which has been
3255 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
3256 normalisation scheme to convert all these into a standard form as
3257 well, and GCC will warn if your code is not in NFKC if you use
3258 @option{-Wnormalized=nfkc}. This warning is comparable to warning
3259 about every identifier that contains the letter O because it might be
3260 confused with the digit 0, and so is not the default, but may be
3261 useful as a local coding convention if the programming environment is
3262 unable to be fixed to display these characters distinctly.
3264 @item -Wno-deprecated-declarations
3265 @opindex Wno-deprecated-declarations
3266 Do not warn about uses of functions, variables, and types marked as
3267 deprecated by using the @code{deprecated} attribute.
3268 (@pxref{Function Attributes}, @pxref{Variable Attributes},
3269 @pxref{Type Attributes}.)
3273 Warn if a structure is given the packed attribute, but the packed
3274 attribute has no effect on the layout or size of the structure.
3275 Such structures may be mis-aligned for little benefit. For
3276 instance, in this code, the variable @code{f.x} in @code{struct bar}
3277 will be misaligned even though @code{struct bar} does not itself
3278 have the packed attribute:
3285 @} __attribute__((packed));
3295 Warn if padding is included in a structure, either to align an element
3296 of the structure or to align the whole structure. Sometimes when this
3297 happens it is possible to rearrange the fields of the structure to
3298 reduce the padding and so make the structure smaller.
3300 @item -Wredundant-decls
3301 @opindex Wredundant-decls
3302 Warn if anything is declared more than once in the same scope, even in
3303 cases where multiple declaration is valid and changes nothing.
3305 @item -Wnested-externs @r{(C only)}
3306 @opindex Wnested-externs
3307 Warn if an @code{extern} declaration is encountered within a function.
3309 @item -Wunreachable-code
3310 @opindex Wunreachable-code
3311 Warn if the compiler detects that code will never be executed.
3313 This option is intended to warn when the compiler detects that at
3314 least a whole line of source code will never be executed, because
3315 some condition is never satisfied or because it is after a
3316 procedure that never returns.
3318 It is possible for this option to produce a warning even though there
3319 are circumstances under which part of the affected line can be executed,
3320 so care should be taken when removing apparently-unreachable code.
3322 For instance, when a function is inlined, a warning may mean that the
3323 line is unreachable in only one inlined copy of the function.
3325 This option is not made part of @option{-Wall} because in a debugging
3326 version of a program there is often substantial code which checks
3327 correct functioning of the program and is, hopefully, unreachable
3328 because the program does work. Another common use of unreachable
3329 code is to provide behavior which is selectable at compile-time.
3333 Warn if a function can not be inlined and it was declared as inline.
3334 Even with this option, the compiler will not warn about failures to
3335 inline functions declared in system headers.
3337 The compiler uses a variety of heuristics to determine whether or not
3338 to inline a function. For example, the compiler takes into account
3339 the size of the function being inlined and the amount of inlining
3340 that has already been done in the current function. Therefore,
3341 seemingly insignificant changes in the source program can cause the
3342 warnings produced by @option{-Winline} to appear or disappear.
3344 @item -Wno-invalid-offsetof @r{(C++ only)}
3345 @opindex Wno-invalid-offsetof
3346 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
3347 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
3348 to a non-POD type is undefined. In existing C++ implementations,
3349 however, @samp{offsetof} typically gives meaningful results even when
3350 applied to certain kinds of non-POD types. (Such as a simple
3351 @samp{struct} that fails to be a POD type only by virtue of having a
3352 constructor.) This flag is for users who are aware that they are
3353 writing nonportable code and who have deliberately chosen to ignore the
3356 The restrictions on @samp{offsetof} may be relaxed in a future version
3357 of the C++ standard.
3359 @item -Wno-int-to-pointer-cast @r{(C only)}
3360 @opindex Wno-int-to-pointer-cast
3361 Suppress warnings from casts to pointer type of an integer of a
3364 @item -Wno-pointer-to-int-cast @r{(C only)}
3365 @opindex Wno-pointer-to-int-cast
3366 Suppress warnings from casts from a pointer to an integer type of a
3370 @opindex Winvalid-pch
3371 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
3372 the search path but can't be used.
3376 @opindex Wno-long-long
3377 Warn if @samp{long long} type is used. This is default. To inhibit
3378 the warning messages, use @option{-Wno-long-long}. Flags
3379 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
3380 only when @option{-pedantic} flag is used.
3382 @item -Wvariadic-macros
3383 @opindex Wvariadic-macros
3384 @opindex Wno-variadic-macros
3385 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
3386 alternate syntax when in pedantic ISO C99 mode. This is default.
3387 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
3389 @item -Wvolatile-register-var
3390 @opindex Wvolatile-register-var
3391 @opindex Wno-volatile-register-var
3392 Warn if a register variable is declared volatile. The volatile
3393 modifier does not inhibit all optimizations that may eliminate reads
3394 and/or writes to register variables.
3396 @item -Wdisabled-optimization
3397 @opindex Wdisabled-optimization
3398 Warn if a requested optimization pass is disabled. This warning does
3399 not generally indicate that there is anything wrong with your code; it
3400 merely indicates that GCC's optimizers were unable to handle the code
3401 effectively. Often, the problem is that your code is too big or too
3402 complex; GCC will refuse to optimize programs when the optimization
3403 itself is likely to take inordinate amounts of time.
3405 @item -Wpointer-sign
3406 @opindex Wpointer-sign
3407 @opindex Wno-pointer-sign
3408 Warn for pointer argument passing or assignment with different signedness.
3409 This option is only supported for C and Objective-C@. It is implied by
3410 @option{-Wall} and by @option{-pedantic}, which can be disabled with
3411 @option{-Wno-pointer-sign}.
3415 Make all warnings into errors.
3419 Make the specified warning into an errors. The specifier for a
3420 warning is appended, for example @option{-Werror=switch} turns the
3421 warnings controlled by @option{-Wswitch} into errors. This switch
3422 takes a negative form, to be used to negate @option{-Werror} for
3423 specific warnings, for example @option{-Wno-error=switch} makes
3424 @option{-Wswitch} warnings not be errors, even when @option{-Werror}
3425 is in effect. You can use the @option{-fdiagnostics-show-option}
3426 option to have each controllable warning amended with the option which
3427 controls it, to determine what to use with this option.
3429 Note that specifying @option{-Werror=}@var{foo} automatically implies
3430 @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
3433 @item -Wstack-protector
3434 @opindex Wstack-protector
3435 This option is only active when @option{-fstack-protector} is active. It
3436 warns about functions that will not be protected against stack smashing.
3438 @item -Wstring-literal-comparison
3439 @opindex Wstring-literal-comparison
3440 Warn about suspicious comparisons to string literal constants. In C,
3441 direct comparisons against the memory address of a string literal, such
3442 as @code{if (x == "abc")}, typically indicate a programmer error, and
3443 even when intentional, result in unspecified behavior and are not portable.
3444 Usually these warnings alert that the programmer intended to use
3445 @code{strcmp}. This warning is enabled by @option{-Wall}.
3447 @item -Woverlength-strings
3448 @opindex Woverlength-strings
3449 Warn about string constants which are longer than the ``minimum
3450 maximum'' length specified in the C standard. Modern compilers
3451 generally allow string constants which are much longer than the
3452 standard's minimum limit, but very portable programs should avoid
3453 using longer strings.
3455 The limit applies @emph{after} string constant concatenation, and does
3456 not count the trailing NUL@. In C89, the limit was 509 characters; in
3457 C99, it was raised to 4095. C++98 does not specify a normative
3458 minimum maximum, so we do not diagnose overlength strings in C++@.
3460 This option is implied by @option{-pedantic}, and can be disabled with
3461 @option{-Wno-overlength-strings}.
3464 @node Debugging Options
3465 @section Options for Debugging Your Program or GCC
3466 @cindex options, debugging
3467 @cindex debugging information options
3469 GCC has various special options that are used for debugging
3470 either your program or GCC:
3475 Produce debugging information in the operating system's native format
3476 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
3479 On most systems that use stabs format, @option{-g} enables use of extra
3480 debugging information that only GDB can use; this extra information
3481 makes debugging work better in GDB but will probably make other debuggers
3483 refuse to read the program. If you want to control for certain whether
3484 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
3485 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
3487 GCC allows you to use @option{-g} with
3488 @option{-O}. The shortcuts taken by optimized code may occasionally
3489 produce surprising results: some variables you declared may not exist
3490 at all; flow of control may briefly move where you did not expect it;
3491 some statements may not be executed because they compute constant
3492 results or their values were already at hand; some statements may
3493 execute in different places because they were moved out of loops.
3495 Nevertheless it proves possible to debug optimized output. This makes
3496 it reasonable to use the optimizer for programs that might have bugs.
3498 The following options are useful when GCC is generated with the
3499 capability for more than one debugging format.
3503 Produce debugging information for use by GDB@. This means to use the
3504 most expressive format available (DWARF 2, stabs, or the native format
3505 if neither of those are supported), including GDB extensions if at all
3510 Produce debugging information in stabs format (if that is supported),
3511 without GDB extensions. This is the format used by DBX on most BSD
3512 systems. On MIPS, Alpha and System V Release 4 systems this option
3513 produces stabs debugging output which is not understood by DBX or SDB@.
3514 On System V Release 4 systems this option requires the GNU assembler.
3516 @item -feliminate-unused-debug-symbols
3517 @opindex feliminate-unused-debug-symbols
3518 Produce debugging information in stabs format (if that is supported),
3519 for only symbols that are actually used.
3523 Produce debugging information in stabs format (if that is supported),
3524 using GNU extensions understood only by the GNU debugger (GDB)@. The
3525 use of these extensions is likely to make other debuggers crash or
3526 refuse to read the program.
3530 Produce debugging information in COFF format (if that is supported).
3531 This is the format used by SDB on most System V systems prior to
3536 Produce debugging information in XCOFF format (if that is supported).
3537 This is the format used by the DBX debugger on IBM RS/6000 systems.
3541 Produce debugging information in XCOFF format (if that is supported),
3542 using GNU extensions understood only by the GNU debugger (GDB)@. The
3543 use of these extensions is likely to make other debuggers crash or
3544 refuse to read the program, and may cause assemblers other than the GNU
3545 assembler (GAS) to fail with an error.
3549 Produce debugging information in DWARF version 2 format (if that is
3550 supported). This is the format used by DBX on IRIX 6. With this
3551 option, GCC uses features of DWARF version 3 when they are useful;
3552 version 3 is upward compatible with version 2, but may still cause
3553 problems for older debuggers.
3557 Produce debugging information in VMS debug format (if that is
3558 supported). This is the format used by DEBUG on VMS systems.
3561 @itemx -ggdb@var{level}
3562 @itemx -gstabs@var{level}
3563 @itemx -gcoff@var{level}
3564 @itemx -gxcoff@var{level}
3565 @itemx -gvms@var{level}
3566 Request debugging information and also use @var{level} to specify how
3567 much information. The default level is 2.
3569 Level 1 produces minimal information, enough for making backtraces in
3570 parts of the program that you don't plan to debug. This includes
3571 descriptions of functions and external variables, but no information
3572 about local variables and no line numbers.
3574 Level 3 includes extra information, such as all the macro definitions
3575 present in the program. Some debuggers support macro expansion when
3576 you use @option{-g3}.
3578 @option{-gdwarf-2} does not accept a concatenated debug level, because
3579 GCC used to support an option @option{-gdwarf} that meant to generate
3580 debug information in version 1 of the DWARF format (which is very
3581 different from version 2), and it would have been too confusing. That
3582 debug format is long obsolete, but the option cannot be changed now.
3583 Instead use an additional @option{-g@var{level}} option to change the
3584 debug level for DWARF2.
3586 @item -feliminate-dwarf2-dups
3587 @opindex feliminate-dwarf2-dups
3588 Compress DWARF2 debugging information by eliminating duplicated
3589 information about each symbol. This option only makes sense when
3590 generating DWARF2 debugging information with @option{-gdwarf-2}.
3592 @cindex @command{prof}
3595 Generate extra code to write profile information suitable for the
3596 analysis program @command{prof}. You must use this option when compiling
3597 the source files you want data about, and you must also use it when
3600 @cindex @command{gprof}
3603 Generate extra code to write profile information suitable for the
3604 analysis program @command{gprof}. You must use this option when compiling
3605 the source files you want data about, and you must also use it when
3610 Makes the compiler print out each function name as it is compiled, and
3611 print some statistics about each pass when it finishes.
3614 @opindex ftime-report
3615 Makes the compiler print some statistics about the time consumed by each
3616 pass when it finishes.
3619 @opindex fmem-report
3620 Makes the compiler print some statistics about permanent memory
3621 allocation when it finishes.
3623 @item -fprofile-arcs
3624 @opindex fprofile-arcs
3625 Add code so that program flow @dfn{arcs} are instrumented. During
3626 execution the program records how many times each branch and call is
3627 executed and how many times it is taken or returns. When the compiled
3628 program exits it saves this data to a file called
3629 @file{@var{auxname}.gcda} for each source file. The data may be used for
3630 profile-directed optimizations (@option{-fbranch-probabilities}), or for
3631 test coverage analysis (@option{-ftest-coverage}). Each object file's
3632 @var{auxname} is generated from the name of the output file, if
3633 explicitly specified and it is not the final executable, otherwise it is
3634 the basename of the source file. In both cases any suffix is removed
3635 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
3636 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
3637 @xref{Cross-profiling}.
3639 @cindex @command{gcov}
3643 This option is used to compile and link code instrumented for coverage
3644 analysis. The option is a synonym for @option{-fprofile-arcs}
3645 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
3646 linking). See the documentation for those options for more details.
3651 Compile the source files with @option{-fprofile-arcs} plus optimization
3652 and code generation options. For test coverage analysis, use the
3653 additional @option{-ftest-coverage} option. You do not need to profile
3654 every source file in a program.
3657 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
3658 (the latter implies the former).
3661 Run the program on a representative workload to generate the arc profile
3662 information. This may be repeated any number of times. You can run
3663 concurrent instances of your program, and provided that the file system
3664 supports locking, the data files will be correctly updated. Also
3665 @code{fork} calls are detected and correctly handled (double counting
3669 For profile-directed optimizations, compile the source files again with
3670 the same optimization and code generation options plus
3671 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
3672 Control Optimization}).
3675 For test coverage analysis, use @command{gcov} to produce human readable
3676 information from the @file{.gcno} and @file{.gcda} files. Refer to the
3677 @command{gcov} documentation for further information.
3681 With @option{-fprofile-arcs}, for each function of your program GCC
3682 creates a program flow graph, then finds a spanning tree for the graph.
3683 Only arcs that are not on the spanning tree have to be instrumented: the
3684 compiler adds code to count the number of times that these arcs are
3685 executed. When an arc is the only exit or only entrance to a block, the
3686 instrumentation code can be added to the block; otherwise, a new basic
3687 block must be created to hold the instrumentation code.
3690 @item -ftest-coverage
3691 @opindex ftest-coverage
3692 Produce a notes file that the @command{gcov} code-coverage utility
3693 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
3694 show program coverage. Each source file's note file is called
3695 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
3696 above for a description of @var{auxname} and instructions on how to
3697 generate test coverage data. Coverage data will match the source files
3698 more closely, if you do not optimize.
3700 @item -d@var{letters}
3701 @item -fdump-rtl-@var{pass}
3703 Says to make debugging dumps during compilation at times specified by
3704 @var{letters}. This is used for debugging the RTL-based passes of the
3705 compiler. The file names for most of the dumps are made by appending a
3706 pass number and a word to the @var{dumpname}. @var{dumpname} is generated
3707 from the name of the output file, if explicitly specified and it is not
3708 an executable, otherwise it is the basename of the source file.
3710 Most debug dumps can be enabled either passing a letter to the @option{-d}
3711 option, or with a long @option{-fdump-rtl} switch; here are the possible
3712 letters for use in @var{letters} and @var{pass}, and their meanings:
3717 Annotate the assembler output with miscellaneous debugging information.
3720 @itemx -fdump-rtl-bp
3722 @opindex fdump-rtl-bp
3723 Dump after computing branch probabilities, to @file{@var{file}.09.bp}.
3726 @itemx -fdump-rtl-bbro
3728 @opindex fdump-rtl-bbro
3729 Dump after block reordering, to @file{@var{file}.30.bbro}.
3732 @itemx -fdump-rtl-combine
3734 @opindex fdump-rtl-combine
3735 Dump after instruction combination, to the file @file{@var{file}.17.combine}.
3738 @itemx -fdump-rtl-ce1
3739 @itemx -fdump-rtl-ce2
3741 @opindex fdump-rtl-ce1
3742 @opindex fdump-rtl-ce2
3743 @option{-dC} and @option{-fdump-rtl-ce1} enable dumping after the
3744 first if conversion, to the file @file{@var{file}.11.ce1}. @option{-dC}
3745 and @option{-fdump-rtl-ce2} enable dumping after the second if
3746 conversion, to the file @file{@var{file}.18.ce2}.
3749 @itemx -fdump-rtl-btl
3750 @itemx -fdump-rtl-dbr
3752 @opindex fdump-rtl-btl
3753 @opindex fdump-rtl-dbr
3754 @option{-dd} and @option{-fdump-rtl-btl} enable dumping after branch
3755 target load optimization, to @file{@var{file}.31.btl}. @option{-dd}
3756 and @option{-fdump-rtl-dbr} enable dumping after delayed branch
3757 scheduling, to @file{@var{file}.36.dbr}.
3761 Dump all macro definitions, at the end of preprocessing, in addition to
3765 @itemx -fdump-rtl-ce3
3767 @opindex fdump-rtl-ce3
3768 Dump after the third if conversion, to @file{@var{file}.28.ce3}.
3771 @itemx -fdump-rtl-cfg
3772 @itemx -fdump-rtl-life
3774 @opindex fdump-rtl-cfg
3775 @opindex fdump-rtl-life
3776 @option{-df} and @option{-fdump-rtl-cfg} enable dumping after control
3777 and data flow analysis, to @file{@var{file}.08.cfg}. @option{-df}
3778 and @option{-fdump-rtl-cfg} enable dumping dump after life analysis,
3779 to @file{@var{file}.16.life}.
3782 @itemx -fdump-rtl-greg
3784 @opindex fdump-rtl-greg
3785 Dump after global register allocation, to @file{@var{file}.23.greg}.
3788 @itemx -fdump-rtl-gcse
3789 @itemx -fdump-rtl-bypass
3791 @opindex fdump-rtl-gcse
3792 @opindex fdump-rtl-bypass
3793 @option{-dG} and @option{-fdump-rtl-gcse} enable dumping after GCSE, to
3794 @file{@var{file}.05.gcse}. @option{-dG} and @option{-fdump-rtl-bypass}
3795 enable dumping after jump bypassing and control flow optimizations, to
3796 @file{@var{file}.07.bypass}.
3799 @itemx -fdump-rtl-eh
3801 @opindex fdump-rtl-eh
3802 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
3805 @itemx -fdump-rtl-sibling
3807 @opindex fdump-rtl-sibling
3808 Dump after sibling call optimizations, to @file{@var{file}.01.sibling}.
3811 @itemx -fdump-rtl-jump
3813 @opindex fdump-rtl-jump
3814 Dump after the first jump optimization, to @file{@var{file}.03.jump}.
3817 @itemx -fdump-rtl-stack
3819 @opindex fdump-rtl-stack
3820 Dump after conversion from registers to stack, to @file{@var{file}.33.stack}.
3823 @itemx -fdump-rtl-lreg
3825 @opindex fdump-rtl-lreg
3826 Dump after local register allocation, to @file{@var{file}.22.lreg}.
3829 @itemx -fdump-rtl-loop
3830 @itemx -fdump-rtl-loop2
3832 @opindex fdump-rtl-loop
3833 @opindex fdump-rtl-loop2
3834 @option{-dL} and @option{-fdump-rtl-loop} enable dumping after the first
3835 loop optimization pass, to @file{@var{file}.06.loop}. @option{-dL} and
3836 @option{-fdump-rtl-loop2} enable dumping after the second pass, to
3837 @file{@var{file}.13.loop2}.
3840 @itemx -fdump-rtl-sms
3842 @opindex fdump-rtl-sms
3843 Dump after modulo scheduling, to @file{@var{file}.20.sms}.
3846 @itemx -fdump-rtl-mach
3848 @opindex fdump-rtl-mach
3849 Dump after performing the machine dependent reorganization pass, to
3850 @file{@var{file}.35.mach}.
3853 @itemx -fdump-rtl-rnreg
3855 @opindex fdump-rtl-rnreg
3856 Dump after register renumbering, to @file{@var{file}.29.rnreg}.
3859 @itemx -fdump-rtl-regmove
3861 @opindex fdump-rtl-regmove
3862 Dump after the register move pass, to @file{@var{file}.19.regmove}.
3865 @itemx -fdump-rtl-postreload
3867 @opindex fdump-rtl-postreload
3868 Dump after post-reload optimizations, to @file{@var{file}.24.postreload}.
3871 @itemx -fdump-rtl-expand
3873 @opindex fdump-rtl-expand
3874 Dump after RTL generation, to @file{@var{file}.00.expand}.
3877 @itemx -fdump-rtl-sched2
3879 @opindex fdump-rtl-sched2
3880 Dump after the second scheduling pass, to @file{@var{file}.32.sched2}.
3883 @itemx -fdump-rtl-cse
3885 @opindex fdump-rtl-cse
3886 Dump after CSE (including the jump optimization that sometimes follows
3887 CSE), to @file{@var{file}.04.cse}.
3890 @itemx -fdump-rtl-sched
3892 @opindex fdump-rtl-sched
3893 Dump after the first scheduling pass, to @file{@var{file}.21.sched}.
3896 @itemx -fdump-rtl-cse2
3898 @opindex fdump-rtl-cse2
3899 Dump after the second CSE pass (including the jump optimization that
3900 sometimes follows CSE), to @file{@var{file}.15.cse2}.
3903 @itemx -fdump-rtl-tracer
3905 @opindex fdump-rtl-tracer
3906 Dump after running tracer, to @file{@var{file}.12.tracer}.
3909 @itemx -fdump-rtl-vpt
3910 @itemx -fdump-rtl-vartrack
3912 @opindex fdump-rtl-vpt
3913 @opindex fdump-rtl-vartrack
3914 @option{-dV} and @option{-fdump-rtl-vpt} enable dumping after the value
3915 profile transformations, to @file{@var{file}.10.vpt}. @option{-dV}
3916 and @option{-fdump-rtl-vartrack} enable dumping after variable tracking,
3917 to @file{@var{file}.34.vartrack}.
3920 @itemx -fdump-rtl-flow2
3922 @opindex fdump-rtl-flow2
3923 Dump after the second flow pass, to @file{@var{file}.26.flow2}.
3926 @itemx -fdump-rtl-peephole2
3928 @opindex fdump-rtl-peephole2
3929 Dump after the peephole pass, to @file{@var{file}.27.peephole2}.
3932 @itemx -fdump-rtl-web
3934 @opindex fdump-rtl-web
3935 Dump after live range splitting, to @file{@var{file}.14.web}.
3938 @itemx -fdump-rtl-all
3940 @opindex fdump-rtl-all
3941 Produce all the dumps listed above.
3945 Produce a core dump whenever an error occurs.
3949 Print statistics on memory usage, at the end of the run, to
3954 Annotate the assembler output with a comment indicating which
3955 pattern and alternative was used. The length of each instruction is
3960 Dump the RTL in the assembler output as a comment before each instruction.
3961 Also turns on @option{-dp} annotation.
3965 For each of the other indicated dump files (either with @option{-d} or
3966 @option{-fdump-rtl-@var{pass}}), dump a representation of the control flow
3967 graph suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3971 Just generate RTL for a function instead of compiling it. Usually used
3972 with @samp{r} (@option{-fdump-rtl-expand}).
3976 Dump debugging information during parsing, to standard error.
3979 @item -fdump-unnumbered
3980 @opindex fdump-unnumbered
3981 When doing debugging dumps (see @option{-d} option above), suppress instruction
3982 numbers and line number note output. This makes it more feasible to
3983 use diff on debugging dumps for compiler invocations with different
3984 options, in particular with and without @option{-g}.
3986 @item -fdump-translation-unit @r{(C++ only)}
3987 @itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
3988 @opindex fdump-translation-unit
3989 Dump a representation of the tree structure for the entire translation
3990 unit to a file. The file name is made by appending @file{.tu} to the
3991 source file name. If the @samp{-@var{options}} form is used, @var{options}
3992 controls the details of the dump as described for the
3993 @option{-fdump-tree} options.
3995 @item -fdump-class-hierarchy @r{(C++ only)}
3996 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3997 @opindex fdump-class-hierarchy
3998 Dump a representation of each class's hierarchy and virtual function
3999 table layout to a file. The file name is made by appending @file{.class}
4000 to the source file name. If the @samp{-@var{options}} form is used,
4001 @var{options} controls the details of the dump as described for the
4002 @option{-fdump-tree} options.
4004 @item -fdump-ipa-@var{switch}
4006 Control the dumping at various stages of inter-procedural analysis
4007 language tree to a file. The file name is generated by appending a switch
4008 specific suffix to the source file name. The following dumps are possible:
4012 Enables all inter-procedural analysis dumps; currently the only produced
4013 dump is the @samp{cgraph} dump.
4016 Dumps information about call-graph optimization, unused function removal,
4017 and inlining decisions.
4020 @item -fdump-tree-@var{switch}
4021 @itemx -fdump-tree-@var{switch}-@var{options}
4023 Control the dumping at various stages of processing the intermediate
4024 language tree to a file. The file name is generated by appending a switch
4025 specific suffix to the source file name. If the @samp{-@var{options}}
4026 form is used, @var{options} is a list of @samp{-} separated options that
4027 control the details of the dump. Not all options are applicable to all
4028 dumps, those which are not meaningful will be ignored. The following
4029 options are available
4033 Print the address of each node. Usually this is not meaningful as it
4034 changes according to the environment and source file. Its primary use
4035 is for tying up a dump file with a debug environment.
4037 Inhibit dumping of members of a scope or body of a function merely
4038 because that scope has been reached. Only dump such items when they
4039 are directly reachable by some other path. When dumping pretty-printed
4040 trees, this option inhibits dumping the bodies of control structures.
4042 Print a raw representation of the tree. By default, trees are
4043 pretty-printed into a C-like representation.
4045 Enable more detailed dumps (not honored by every dump option).
4047 Enable dumping various statistics about the pass (not honored by every dump
4050 Enable showing basic block boundaries (disabled in raw dumps).
4052 Enable showing virtual operands for every statement.
4054 Enable showing line numbers for statements.
4056 Enable showing the unique ID (@code{DECL_UID}) for each variable.
4058 Turn on all options, except @option{raw}, @option{slim} and @option{lineno}.
4061 The following tree dumps are possible:
4065 Dump before any tree based optimization, to @file{@var{file}.original}.
4068 Dump after all tree based optimization, to @file{@var{file}.optimized}.
4071 Dump after function inlining, to @file{@var{file}.inlined}.
4074 @opindex fdump-tree-gimple
4075 Dump each function before and after the gimplification pass to a file. The
4076 file name is made by appending @file{.gimple} to the source file name.
4079 @opindex fdump-tree-cfg
4080 Dump the control flow graph of each function to a file. The file name is
4081 made by appending @file{.cfg} to the source file name.
4084 @opindex fdump-tree-vcg
4085 Dump the control flow graph of each function to a file in VCG format. The
4086 file name is made by appending @file{.vcg} to the source file name. Note
4087 that if the file contains more than one function, the generated file cannot
4088 be used directly by VCG@. You will need to cut and paste each function's
4089 graph into its own separate file first.
4092 @opindex fdump-tree-ch
4093 Dump each function after copying loop headers. The file name is made by
4094 appending @file{.ch} to the source file name.
4097 @opindex fdump-tree-ssa
4098 Dump SSA related information to a file. The file name is made by appending
4099 @file{.ssa} to the source file name.
4102 @opindex fdump-tree-salias
4103 Dump structure aliasing variable information to a file. This file name
4104 is made by appending @file{.salias} to the source file name.
4107 @opindex fdump-tree-alias
4108 Dump aliasing information for each function. The file name is made by
4109 appending @file{.alias} to the source file name.
4112 @opindex fdump-tree-ccp
4113 Dump each function after CCP@. The file name is made by appending
4114 @file{.ccp} to the source file name.
4117 @opindex fdump-tree-storeccp
4118 Dump each function after STORE-CCP. The file name is made by appending
4119 @file{.storeccp} to the source file name.
4122 @opindex fdump-tree-pre
4123 Dump trees after partial redundancy elimination. The file name is made
4124 by appending @file{.pre} to the source file name.
4127 @opindex fdump-tree-fre
4128 Dump trees after full redundancy elimination. The file name is made
4129 by appending @file{.fre} to the source file name.
4132 @opindex fdump-tree-copyprop
4133 Dump trees after copy propagation. The file name is made
4134 by appending @file{.copyprop} to the source file name.
4136 @item store_copyprop
4137 @opindex fdump-tree-store_copyprop
4138 Dump trees after store copy-propagation. The file name is made
4139 by appending @file{.store_copyprop} to the source file name.
4142 @opindex fdump-tree-dce
4143 Dump each function after dead code elimination. The file name is made by
4144 appending @file{.dce} to the source file name.
4147 @opindex fdump-tree-mudflap
4148 Dump each function after adding mudflap instrumentation. The file name is
4149 made by appending @file{.mudflap} to the source file name.
4152 @opindex fdump-tree-sra
4153 Dump each function after performing scalar replacement of aggregates. The
4154 file name is made by appending @file{.sra} to the source file name.
4157 @opindex fdump-tree-sink
4158 Dump each function after performing code sinking. The file name is made
4159 by appending @file{.sink} to the source file name.
4162 @opindex fdump-tree-dom
4163 Dump each function after applying dominator tree optimizations. The file
4164 name is made by appending @file{.dom} to the source file name.
4167 @opindex fdump-tree-dse
4168 Dump each function after applying dead store elimination. The file
4169 name is made by appending @file{.dse} to the source file name.
4172 @opindex fdump-tree-phiopt
4173 Dump each function after optimizing PHI nodes into straightline code. The file
4174 name is made by appending @file{.phiopt} to the source file name.
4177 @opindex fdump-tree-forwprop
4178 Dump each function after forward propagating single use variables. The file
4179 name is made by appending @file{.forwprop} to the source file name.
4182 @opindex fdump-tree-copyrename
4183 Dump each function after applying the copy rename optimization. The file
4184 name is made by appending @file{.copyrename} to the source file name.
4187 @opindex fdump-tree-nrv
4188 Dump each function after applying the named return value optimization on
4189 generic trees. The file name is made by appending @file{.nrv} to the source
4193 @opindex fdump-tree-vect
4194 Dump each function after applying vectorization of loops. The file name is
4195 made by appending @file{.vect} to the source file name.
4198 @opindex fdump-tree-vrp
4199 Dump each function after Value Range Propagation (VRP). The file name
4200 is made by appending @file{.vrp} to the source file name.
4203 @opindex fdump-tree-all
4204 Enable all the available tree dumps with the flags provided in this option.
4207 @item -ftree-vectorizer-verbose=@var{n}
4208 @opindex ftree-vectorizer-verbose
4209 This option controls the amount of debugging output the vectorizer prints.
4210 This information is written to standard error, unless @option{-fdump-tree-all}
4211 or @option{-fdump-tree-vect} is specified, in which case it is output to the
4212 usual dump listing file, @file{.vect}.
4214 @item -frandom-seed=@var{string}
4215 @opindex frandom-string
4216 This option provides a seed that GCC uses when it would otherwise use
4217 random numbers. It is used to generate certain symbol names
4218 that have to be different in every compiled file. It is also used to
4219 place unique stamps in coverage data files and the object files that
4220 produce them. You can use the @option{-frandom-seed} option to produce
4221 reproducibly identical object files.
4223 The @var{string} should be different for every file you compile.
4225 @item -fsched-verbose=@var{n}
4226 @opindex fsched-verbose
4227 On targets that use instruction scheduling, this option controls the
4228 amount of debugging output the scheduler prints. This information is
4229 written to standard error, unless @option{-dS} or @option{-dR} is
4230 specified, in which case it is output to the usual dump
4231 listing file, @file{.sched} or @file{.sched2} respectively. However
4232 for @var{n} greater than nine, the output is always printed to standard
4235 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
4236 same information as @option{-dRS}. For @var{n} greater than one, it
4237 also output basic block probabilities, detailed ready list information
4238 and unit/insn info. For @var{n} greater than two, it includes RTL
4239 at abort point, control-flow and regions info. And for @var{n} over
4240 four, @option{-fsched-verbose} also includes dependence info.
4244 Store the usual ``temporary'' intermediate files permanently; place them
4245 in the current directory and name them based on the source file. Thus,
4246 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
4247 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
4248 preprocessed @file{foo.i} output file even though the compiler now
4249 normally uses an integrated preprocessor.
4251 When used in combination with the @option{-x} command line option,
4252 @option{-save-temps} is sensible enough to avoid over writing an
4253 input source file with the same extension as an intermediate file.
4254 The corresponding intermediate file may be obtained by renaming the
4255 source file before using @option{-save-temps}.
4259 Report the CPU time taken by each subprocess in the compilation
4260 sequence. For C source files, this is the compiler proper and assembler
4261 (plus the linker if linking is done). The output looks like this:
4268 The first number on each line is the ``user time'', that is time spent
4269 executing the program itself. The second number is ``system time'',
4270 time spent executing operating system routines on behalf of the program.
4271 Both numbers are in seconds.
4273 @item -fvar-tracking
4274 @opindex fvar-tracking
4275 Run variable tracking pass. It computes where variables are stored at each
4276 position in code. Better debugging information is then generated
4277 (if the debugging information format supports this information).
4279 It is enabled by default when compiling with optimization (@option{-Os},
4280 @option{-O}, @option{-O2}, ...), debugging information (@option{-g}) and
4281 the debug info format supports it.
4283 @item -print-file-name=@var{library}
4284 @opindex print-file-name
4285 Print the full absolute name of the library file @var{library} that
4286 would be used when linking---and don't do anything else. With this
4287 option, GCC does not compile or link anything; it just prints the
4290 @item -print-multi-directory
4291 @opindex print-multi-directory
4292 Print the directory name corresponding to the multilib selected by any
4293 other switches present in the command line. This directory is supposed
4294 to exist in @env{GCC_EXEC_PREFIX}.
4296 @item -print-multi-lib
4297 @opindex print-multi-lib
4298 Print the mapping from multilib directory names to compiler switches
4299 that enable them. The directory name is separated from the switches by
4300 @samp{;}, and each switch starts with an @samp{@@} instead of the
4301 @samp{-}, without spaces between multiple switches. This is supposed to
4302 ease shell-processing.
4304 @item -print-prog-name=@var{program}
4305 @opindex print-prog-name
4306 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
4308 @item -print-libgcc-file-name
4309 @opindex print-libgcc-file-name
4310 Same as @option{-print-file-name=libgcc.a}.
4312 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
4313 but you do want to link with @file{libgcc.a}. You can do
4316 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
4319 @item -print-search-dirs
4320 @opindex print-search-dirs
4321 Print the name of the configured installation directory and a list of
4322 program and library directories @command{gcc} will search---and don't do anything else.
4324 This is useful when @command{gcc} prints the error message
4325 @samp{installation problem, cannot exec cpp0: No such file or directory}.
4326 To resolve this you either need to put @file{cpp0} and the other compiler
4327 components where @command{gcc} expects to find them, or you can set the environment
4328 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
4329 Don't forget the trailing @samp{/}.
4330 @xref{Environment Variables}.
4333 @opindex dumpmachine
4334 Print the compiler's target machine (for example,
4335 @samp{i686-pc-linux-gnu})---and don't do anything else.
4338 @opindex dumpversion
4339 Print the compiler version (for example, @samp{3.0})---and don't do
4344 Print the compiler's built-in specs---and don't do anything else. (This
4345 is used when GCC itself is being built.) @xref{Spec Files}.
4347 @item -feliminate-unused-debug-types
4348 @opindex feliminate-unused-debug-types
4349 Normally, when producing DWARF2 output, GCC will emit debugging
4350 information for all types declared in a compilation
4351 unit, regardless of whether or not they are actually used
4352 in that compilation unit. Sometimes this is useful, such as
4353 if, in the debugger, you want to cast a value to a type that is
4354 not actually used in your program (but is declared). More often,
4355 however, this results in a significant amount of wasted space.
4356 With this option, GCC will avoid producing debug symbol output
4357 for types that are nowhere used in the source file being compiled.
4360 @node Optimize Options
4361 @section Options That Control Optimization
4362 @cindex optimize options
4363 @cindex options, optimization
4365 These options control various sorts of optimizations.
4367 Without any optimization option, the compiler's goal is to reduce the
4368 cost of compilation and to make debugging produce the expected
4369 results. Statements are independent: if you stop the program with a
4370 breakpoint between statements, you can then assign a new value to any
4371 variable or change the program counter to any other statement in the
4372 function and get exactly the results you would expect from the source
4375 Turning on optimization flags makes the compiler attempt to improve
4376 the performance and/or code size at the expense of compilation time
4377 and possibly the ability to debug the program.
4379 The compiler performs optimization based on the knowledge it has of
4380 the program. Optimization levels @option{-O2} and above, in
4381 particular, enable @emph{unit-at-a-time} mode, which allows the
4382 compiler to consider information gained from later functions in
4383 the file when compiling a function. Compiling multiple files at
4384 once to a single output file in @emph{unit-at-a-time} mode allows
4385 the compiler to use information gained from all of the files when
4386 compiling each of them.
4388 Not all optimizations are controlled directly by a flag. Only
4389 optimizations that have a flag are listed.
4396 Optimize. Optimizing compilation takes somewhat more time, and a lot
4397 more memory for a large function.
4399 With @option{-O}, the compiler tries to reduce code size and execution
4400 time, without performing any optimizations that take a great deal of
4403 @option{-O} turns on the following optimization flags:
4404 @gccoptlist{-fdefer-pop @gol
4405 -fdelayed-branch @gol
4406 -fguess-branch-probability @gol
4407 -fcprop-registers @gol
4408 -floop-optimize @gol
4409 -fif-conversion @gol
4410 -fif-conversion2 @gol
4413 -ftree-dominator-opts @gol
4418 -ftree-copyrename @gol
4423 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
4424 where doing so does not interfere with debugging.
4428 Optimize even more. GCC performs nearly all supported optimizations
4429 that do not involve a space-speed tradeoff. The compiler does not
4430 perform loop unrolling or function inlining when you specify @option{-O2}.
4431 As compared to @option{-O}, this option increases both compilation time
4432 and the performance of the generated code.
4434 @option{-O2} turns on all optimization flags specified by @option{-O}. It
4435 also turns on the following optimization flags:
4436 @gccoptlist{-fthread-jumps @gol
4438 -foptimize-sibling-calls @gol
4439 -fcse-follow-jumps -fcse-skip-blocks @gol
4440 -fgcse -fgcse-lm @gol
4441 -fexpensive-optimizations @gol
4442 -fstrength-reduce @gol
4443 -frerun-cse-after-loop -frerun-loop-opt @gol
4446 -fschedule-insns -fschedule-insns2 @gol
4447 -fsched-interblock -fsched-spec @gol
4449 -fstrict-aliasing @gol
4450 -fdelete-null-pointer-checks @gol
4451 -freorder-blocks -freorder-functions @gol
4452 -funit-at-a-time @gol
4453 -falign-functions -falign-jumps @gol
4454 -falign-loops -falign-labels @gol
4458 Please note the warning under @option{-fgcse} about
4459 invoking @option{-O2} on programs that use computed gotos.
4463 Optimize yet more. @option{-O3} turns on all optimizations specified by
4464 @option{-O2} and also turns on the @option{-finline-functions},
4465 @option{-funswitch-loops} and @option{-fgcse-after-reload} options.
4469 Do not optimize. This is the default.
4473 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
4474 do not typically increase code size. It also performs further
4475 optimizations designed to reduce code size.
4477 @option{-Os} disables the following optimization flags:
4478 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
4479 -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
4480 -fprefetch-loop-arrays -ftree-vect-loop-version}
4482 If you use multiple @option{-O} options, with or without level numbers,
4483 the last such option is the one that is effective.
4486 Options of the form @option{-f@var{flag}} specify machine-independent
4487 flags. Most flags have both positive and negative forms; the negative
4488 form of @option{-ffoo} would be @option{-fno-foo}. In the table
4489 below, only one of the forms is listed---the one you typically will
4490 use. You can figure out the other form by either removing @samp{no-}
4493 The following options control specific optimizations. They are either
4494 activated by @option{-O} options or are related to ones that are. You
4495 can use the following flags in the rare cases when ``fine-tuning'' of
4496 optimizations to be performed is desired.
4499 @item -fno-default-inline
4500 @opindex fno-default-inline
4501 Do not make member functions inline by default merely because they are
4502 defined inside the class scope (C++ only). Otherwise, when you specify
4503 @w{@option{-O}}, member functions defined inside class scope are compiled
4504 inline by default; i.e., you don't need to add @samp{inline} in front of
4505 the member function name.
4507 @item -fno-defer-pop
4508 @opindex fno-defer-pop
4509 Always pop the arguments to each function call as soon as that function
4510 returns. For machines which must pop arguments after a function call,
4511 the compiler normally lets arguments accumulate on the stack for several
4512 function calls and pops them all at once.
4514 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4518 Force memory operands to be copied into registers before doing
4519 arithmetic on them. This produces better code by making all memory
4520 references potential common subexpressions. When they are not common
4521 subexpressions, instruction combination should eliminate the separate
4522 register-load. This option is now a nop and will be removed in 4.2.
4525 @opindex fforce-addr
4526 Force memory address constants to be copied into registers before
4527 doing arithmetic on them.
4529 @item -fomit-frame-pointer
4530 @opindex fomit-frame-pointer
4531 Don't keep the frame pointer in a register for functions that
4532 don't need one. This avoids the instructions to save, set up and
4533 restore frame pointers; it also makes an extra register available
4534 in many functions. @strong{It also makes debugging impossible on
4537 On some machines, such as the VAX, this flag has no effect, because
4538 the standard calling sequence automatically handles the frame pointer
4539 and nothing is saved by pretending it doesn't exist. The
4540 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
4541 whether a target machine supports this flag. @xref{Registers,,Register
4542 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
4544 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4546 @item -foptimize-sibling-calls
4547 @opindex foptimize-sibling-calls
4548 Optimize sibling and tail recursive calls.
4550 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4554 Don't pay attention to the @code{inline} keyword. Normally this option
4555 is used to keep the compiler from expanding any functions inline.
4556 Note that if you are not optimizing, no functions can be expanded inline.
4558 @item -finline-functions
4559 @opindex finline-functions
4560 Integrate all simple functions into their callers. The compiler
4561 heuristically decides which functions are simple enough to be worth
4562 integrating in this way.
4564 If all calls to a given function are integrated, and the function is
4565 declared @code{static}, then the function is normally not output as
4566 assembler code in its own right.
4568 Enabled at level @option{-O3}.
4570 @item -finline-functions-called-once
4571 @opindex finline-functions-called-once
4572 Consider all @code{static} functions called once for inlining into their
4573 caller even if they are not marked @code{inline}. If a call to a given
4574 function is integrated, then the function is not output as assembler code
4577 Enabled if @option{-funit-at-a-time} is enabled.
4579 @item -fearly-inlining
4580 @opindex fearly-inlining
4581 Inline functions marked by @code{always_inline} and functions whose body seems
4582 smaller than the function call overhead early before doing
4583 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
4584 makes profiling significantly cheaper and usually inlining faster on programs
4585 having large chains of nested wrapper functions.
4589 @item -finline-limit=@var{n}
4590 @opindex finline-limit
4591 By default, GCC limits the size of functions that can be inlined. This flag
4592 allows the control of this limit for functions that are explicitly marked as
4593 inline (i.e., marked with the inline keyword or defined within the class
4594 definition in c++). @var{n} is the size of functions that can be inlined in
4595 number of pseudo instructions (not counting parameter handling). The default
4596 value of @var{n} is 600.
4597 Increasing this value can result in more inlined code at
4598 the cost of compilation time and memory consumption. Decreasing usually makes
4599 the compilation faster and less code will be inlined (which presumably
4600 means slower programs). This option is particularly useful for programs that
4601 use inlining heavily such as those based on recursive templates with C++.
4603 Inlining is actually controlled by a number of parameters, which may be
4604 specified individually by using @option{--param @var{name}=@var{value}}.
4605 The @option{-finline-limit=@var{n}} option sets some of these parameters
4609 @item max-inline-insns-single
4610 is set to @var{n}/2.
4611 @item max-inline-insns-auto
4612 is set to @var{n}/2.
4613 @item min-inline-insns
4614 is set to 130 or @var{n}/4, whichever is smaller.
4615 @item max-inline-insns-rtl
4619 See below for a documentation of the individual
4620 parameters controlling inlining.
4622 @emph{Note:} pseudo instruction represents, in this particular context, an
4623 abstract measurement of function's size. In no way does it represent a count
4624 of assembly instructions and as such its exact meaning might change from one
4625 release to an another.
4627 @item -fkeep-inline-functions
4628 @opindex fkeep-inline-functions
4629 In C, emit @code{static} functions that are declared @code{inline}
4630 into the object file, even if the function has been inlined into all
4631 of its callers. This switch does not affect functions using the
4632 @code{extern inline} extension in GNU C@. In C++, emit any and all
4633 inline functions into the object file.
4635 @item -fkeep-static-consts
4636 @opindex fkeep-static-consts
4637 Emit variables declared @code{static const} when optimization isn't turned
4638 on, even if the variables aren't referenced.
4640 GCC enables this option by default. If you want to force the compiler to
4641 check if the variable was referenced, regardless of whether or not
4642 optimization is turned on, use the @option{-fno-keep-static-consts} option.
4644 @item -fmerge-constants
4645 Attempt to merge identical constants (string constants and floating point
4646 constants) across compilation units.
4648 This option is the default for optimized compilation if the assembler and
4649 linker support it. Use @option{-fno-merge-constants} to inhibit this
4652 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4654 @item -fmerge-all-constants
4655 Attempt to merge identical constants and identical variables.
4657 This option implies @option{-fmerge-constants}. In addition to
4658 @option{-fmerge-constants} this considers e.g.@: even constant initialized
4659 arrays or initialized constant variables with integral or floating point
4660 types. Languages like C or C++ require each non-automatic variable to
4661 have distinct location, so using this option will result in non-conforming
4664 @item -fmodulo-sched
4665 @opindex fmodulo-sched
4666 Perform swing modulo scheduling immediately before the first scheduling
4667 pass. This pass looks at innermost loops and reorders their
4668 instructions by overlapping different iterations.
4670 @item -fno-branch-count-reg
4671 @opindex fno-branch-count-reg
4672 Do not use ``decrement and branch'' instructions on a count register,
4673 but instead generate a sequence of instructions that decrement a
4674 register, compare it against zero, then branch based upon the result.
4675 This option is only meaningful on architectures that support such
4676 instructions, which include x86, PowerPC, IA-64 and S/390.
4678 The default is @option{-fbranch-count-reg}, enabled when
4679 @option{-fstrength-reduce} is enabled.
4681 @item -fno-function-cse
4682 @opindex fno-function-cse
4683 Do not put function addresses in registers; make each instruction that
4684 calls a constant function contain the function's address explicitly.
4686 This option results in less efficient code, but some strange hacks
4687 that alter the assembler output may be confused by the optimizations
4688 performed when this option is not used.
4690 The default is @option{-ffunction-cse}
4692 @item -fno-zero-initialized-in-bss
4693 @opindex fno-zero-initialized-in-bss
4694 If the target supports a BSS section, GCC by default puts variables that
4695 are initialized to zero into BSS@. This can save space in the resulting
4698 This option turns off this behavior because some programs explicitly
4699 rely on variables going to the data section. E.g., so that the
4700 resulting executable can find the beginning of that section and/or make
4701 assumptions based on that.
4703 The default is @option{-fzero-initialized-in-bss}.
4705 @item -fbounds-check
4706 @opindex fbounds-check
4707 For front-ends that support it, generate additional code to check that
4708 indices used to access arrays are within the declared range. This is
4709 currently only supported by the Java and Fortran front-ends, where
4710 this option defaults to true and false respectively.
4712 @item -fmudflap -fmudflapth -fmudflapir
4716 @cindex bounds checking
4718 For front-ends that support it (C and C++), instrument all risky
4719 pointer/array dereferencing operations, some standard library
4720 string/heap functions, and some other associated constructs with
4721 range/validity tests. Modules so instrumented should be immune to
4722 buffer overflows, invalid heap use, and some other classes of C/C++
4723 programming errors. The instrumentation relies on a separate runtime
4724 library (@file{libmudflap}), which will be linked into a program if
4725 @option{-fmudflap} is given at link time. Run-time behavior of the
4726 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
4727 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
4730 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
4731 link if your program is multi-threaded. Use @option{-fmudflapir}, in
4732 addition to @option{-fmudflap} or @option{-fmudflapth}, if
4733 instrumentation should ignore pointer reads. This produces less
4734 instrumentation (and therefore faster execution) and still provides
4735 some protection against outright memory corrupting writes, but allows
4736 erroneously read data to propagate within a program.
4740 @cindex openmp parallel
4741 Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
4742 @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
4743 compiler generates parallel code according to the OpenMP Application
4744 Program Interface v2.5. To generate the final exectuable, the runtime
4745 library @code{libgomp} must be linked in using @option{-lgomp}.
4747 @item -fstrength-reduce
4748 @opindex fstrength-reduce
4749 Perform the optimizations of loop strength reduction and
4750 elimination of iteration variables.
4752 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4754 @item -fthread-jumps
4755 @opindex fthread-jumps
4756 Perform optimizations where we check to see if a jump branches to a
4757 location where another comparison subsumed by the first is found. If
4758 so, the first branch is redirected to either the destination of the
4759 second branch or a point immediately following it, depending on whether
4760 the condition is known to be true or false.
4762 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4764 @item -fcse-follow-jumps
4765 @opindex fcse-follow-jumps
4766 In common subexpression elimination, scan through jump instructions
4767 when the target of the jump is not reached by any other path. For
4768 example, when CSE encounters an @code{if} statement with an
4769 @code{else} clause, CSE will follow the jump when the condition
4772 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4774 @item -fcse-skip-blocks
4775 @opindex fcse-skip-blocks
4776 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
4777 follow jumps which conditionally skip over blocks. When CSE
4778 encounters a simple @code{if} statement with no else clause,
4779 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
4780 body of the @code{if}.
4782 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4784 @item -frerun-cse-after-loop
4785 @opindex frerun-cse-after-loop
4786 Re-run common subexpression elimination after loop optimizations has been
4789 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4791 @item -frerun-loop-opt
4792 @opindex frerun-loop-opt
4793 Run the loop optimizer twice.
4795 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4799 Perform a global common subexpression elimination pass.
4800 This pass also performs global constant and copy propagation.
4802 @emph{Note:} When compiling a program using computed gotos, a GCC
4803 extension, you may get better runtime performance if you disable
4804 the global common subexpression elimination pass by adding
4805 @option{-fno-gcse} to the command line.
4807 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4811 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
4812 attempt to move loads which are only killed by stores into themselves. This
4813 allows a loop containing a load/store sequence to be changed to a load outside
4814 the loop, and a copy/store within the loop.
4816 Enabled by default when gcse is enabled.
4820 When @option{-fgcse-sm} is enabled, a store motion pass is run after
4821 global common subexpression elimination. This pass will attempt to move
4822 stores out of loops. When used in conjunction with @option{-fgcse-lm},
4823 loops containing a load/store sequence can be changed to a load before
4824 the loop and a store after the loop.
4826 Not enabled at any optimization level.
4830 When @option{-fgcse-las} is enabled, the global common subexpression
4831 elimination pass eliminates redundant loads that come after stores to the
4832 same memory location (both partial and full redundancies).
4834 Not enabled at any optimization level.
4836 @item -fgcse-after-reload
4837 @opindex fgcse-after-reload
4838 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
4839 pass is performed after reload. The purpose of this pass is to cleanup
4842 @item -floop-optimize
4843 @opindex floop-optimize
4844 Perform loop optimizations: move constant expressions out of loops, simplify
4845 exit test conditions and optionally do strength-reduction as well.
4847 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4849 @item -floop-optimize2
4850 @opindex floop-optimize2
4851 Perform loop optimizations using the new loop optimizer. The optimizations
4852 (loop unrolling, peeling and unswitching, loop invariant motion) are enabled
4855 @item -funsafe-loop-optimizations
4856 @opindex funsafe-loop-optimizations
4857 If given, the loop optimizer will assume that loop indices do not
4858 overflow, and that the loops with nontrivial exit condition are not
4859 infinite. This enables a wider range of loop optimizations even if
4860 the loop optimizer itself cannot prove that these assumptions are valid.
4861 Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you
4862 if it finds this kind of loop.
4864 @item -fcrossjumping
4865 @opindex crossjumping
4866 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
4867 resulting code may or may not perform better than without cross-jumping.
4869 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4871 @item -fif-conversion
4872 @opindex if-conversion
4873 Attempt to transform conditional jumps into branch-less equivalents. This
4874 include use of conditional moves, min, max, set flags and abs instructions, and
4875 some tricks doable by standard arithmetics. The use of conditional execution
4876 on chips where it is available is controlled by @code{if-conversion2}.
4878 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4880 @item -fif-conversion2
4881 @opindex if-conversion2
4882 Use conditional execution (where available) to transform conditional jumps into
4883 branch-less equivalents.
4885 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4887 @item -fdelete-null-pointer-checks
4888 @opindex fdelete-null-pointer-checks
4889 Use global dataflow analysis to identify and eliminate useless checks
4890 for null pointers. The compiler assumes that dereferencing a null
4891 pointer would have halted the program. If a pointer is checked after
4892 it has already been dereferenced, it cannot be null.
4894 In some environments, this assumption is not true, and programs can
4895 safely dereference null pointers. Use
4896 @option{-fno-delete-null-pointer-checks} to disable this optimization
4897 for programs which depend on that behavior.
4899 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4901 @item -fexpensive-optimizations
4902 @opindex fexpensive-optimizations
4903 Perform a number of minor optimizations that are relatively expensive.
4905 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4907 @item -foptimize-register-move
4909 @opindex foptimize-register-move
4911 Attempt to reassign register numbers in move instructions and as
4912 operands of other simple instructions in order to maximize the amount of
4913 register tying. This is especially helpful on machines with two-operand
4916 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
4919 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4921 @item -fdelayed-branch
4922 @opindex fdelayed-branch
4923 If supported for the target machine, attempt to reorder instructions
4924 to exploit instruction slots available after delayed branch
4927 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4929 @item -fschedule-insns
4930 @opindex fschedule-insns
4931 If supported for the target machine, attempt to reorder instructions to
4932 eliminate execution stalls due to required data being unavailable. This
4933 helps machines that have slow floating point or memory load instructions
4934 by allowing other instructions to be issued until the result of the load
4935 or floating point instruction is required.
4937 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4939 @item -fschedule-insns2
4940 @opindex fschedule-insns2
4941 Similar to @option{-fschedule-insns}, but requests an additional pass of
4942 instruction scheduling after register allocation has been done. This is
4943 especially useful on machines with a relatively small number of
4944 registers and where memory load instructions take more than one cycle.
4946 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4948 @item -fno-sched-interblock
4949 @opindex fno-sched-interblock
4950 Don't schedule instructions across basic blocks. This is normally
4951 enabled by default when scheduling before register allocation, i.e.@:
4952 with @option{-fschedule-insns} or at @option{-O2} or higher.
4954 @item -fno-sched-spec
4955 @opindex fno-sched-spec
4956 Don't allow speculative motion of non-load instructions. This is normally
4957 enabled by default when scheduling before register allocation, i.e.@:
4958 with @option{-fschedule-insns} or at @option{-O2} or higher.
4960 @item -fsched-spec-load
4961 @opindex fsched-spec-load
4962 Allow speculative motion of some load instructions. This only makes
4963 sense when scheduling before register allocation, i.e.@: with
4964 @option{-fschedule-insns} or at @option{-O2} or higher.
4966 @item -fsched-spec-load-dangerous
4967 @opindex fsched-spec-load-dangerous
4968 Allow speculative motion of more load instructions. This only makes
4969 sense when scheduling before register allocation, i.e.@: with
4970 @option{-fschedule-insns} or at @option{-O2} or higher.
4972 @item -fsched-stalled-insns=@var{n}
4973 @opindex fsched-stalled-insns
4974 Define how many insns (if any) can be moved prematurely from the queue
4975 of stalled insns into the ready list, during the second scheduling pass.
4977 @item -fsched-stalled-insns-dep=@var{n}
4978 @opindex fsched-stalled-insns-dep
4979 Define how many insn groups (cycles) will be examined for a dependency
4980 on a stalled insn that is candidate for premature removal from the queue
4981 of stalled insns. Has an effect only during the second scheduling pass,
4982 and only if @option{-fsched-stalled-insns} is used and its value is not zero.
4984 @item -fsched2-use-superblocks
4985 @opindex fsched2-use-superblocks
4986 When scheduling after register allocation, do use superblock scheduling
4987 algorithm. Superblock scheduling allows motion across basic block boundaries
4988 resulting on faster schedules. This option is experimental, as not all machine
4989 descriptions used by GCC model the CPU closely enough to avoid unreliable
4990 results from the algorithm.
4992 This only makes sense when scheduling after register allocation, i.e.@: with
4993 @option{-fschedule-insns2} or at @option{-O2} or higher.
4995 @item -fsched2-use-traces
4996 @opindex fsched2-use-traces
4997 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
4998 allocation and additionally perform code duplication in order to increase the
4999 size of superblocks using tracer pass. See @option{-ftracer} for details on
5002 This mode should produce faster but significantly longer programs. Also
5003 without @option{-fbranch-probabilities} the traces constructed may not
5004 match the reality and hurt the performance. This only makes
5005 sense when scheduling after register allocation, i.e.@: with
5006 @option{-fschedule-insns2} or at @option{-O2} or higher.
5008 @item -freschedule-modulo-scheduled-loops
5009 @opindex fscheduling-in-modulo-scheduled-loops
5010 The modulo scheduling comes before the traditional scheduling, if a loop was modulo scheduled
5011 we may want to prevent the later scheduling passes from changing its schedule, we use this
5012 option to control that.
5014 @item -fcaller-saves
5015 @opindex fcaller-saves
5016 Enable values to be allocated in registers that will be clobbered by
5017 function calls, by emitting extra instructions to save and restore the
5018 registers around such calls. Such allocation is done only when it
5019 seems to result in better code than would otherwise be produced.
5021 This option is always enabled by default on certain machines, usually
5022 those which have no call-preserved registers to use instead.
5024 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5027 Perform Partial Redundancy Elimination (PRE) on trees. This flag is
5028 enabled by default at @option{-O2} and @option{-O3}.
5031 Perform Full Redundancy Elimination (FRE) on trees. The difference
5032 between FRE and PRE is that FRE only considers expressions
5033 that are computed on all paths leading to the redundant computation.
5034 This analysis faster than PRE, though it exposes fewer redundancies.
5035 This flag is enabled by default at @option{-O} and higher.
5037 @item -ftree-copy-prop
5038 Perform copy propagation on trees. This pass eliminates unnecessary
5039 copy operations. This flag is enabled by default at @option{-O} and
5042 @item -ftree-store-copy-prop
5043 Perform copy propagation of memory loads and stores. This pass
5044 eliminates unnecessary copy operations in memory references
5045 (structures, global variables, arrays, etc). This flag is enabled by
5046 default at @option{-O2} and higher.
5049 Perform structural alias analysis on trees. This flag
5050 is enabled by default at @option{-O} and higher.
5053 Perform forward store motion on trees. This flag is
5054 enabled by default at @option{-O} and higher.
5057 Perform sparse conditional constant propagation (CCP) on trees. This
5058 pass only operates on local scalar variables and is enabled by default
5059 at @option{-O} and higher.
5061 @item -ftree-store-ccp
5062 Perform sparse conditional constant propagation (CCP) on trees. This
5063 pass operates on both local scalar variables and memory stores and
5064 loads (global variables, structures, arrays, etc). This flag is
5065 enabled by default at @option{-O2} and higher.
5068 Perform dead code elimination (DCE) on trees. This flag is enabled by
5069 default at @option{-O} and higher.
5071 @item -ftree-dominator-opts
5072 Perform a variety of simple scalar cleanups (constant/copy
5073 propagation, redundancy elimination, range propagation and expression
5074 simplification) based on a dominator tree traversal. This also
5075 performs jump threading (to reduce jumps to jumps). This flag is
5076 enabled by default at @option{-O} and higher.
5079 Perform loop header copying on trees. This is beneficial since it increases
5080 effectiveness of code motion optimizations. It also saves one jump. This flag
5081 is enabled by default at @option{-O} and higher. It is not enabled
5082 for @option{-Os}, since it usually increases code size.
5084 @item -ftree-loop-optimize
5085 Perform loop optimizations on trees. This flag is enabled by default
5086 at @option{-O} and higher.
5088 @item -ftree-loop-linear
5089 Perform linear loop transformations on tree. This flag can improve cache
5090 performance and allow further loop optimizations to take place.
5092 @item -ftree-loop-im
5093 Perform loop invariant motion on trees. This pass moves only invariants that
5094 would be hard to handle at RTL level (function calls, operations that expand to
5095 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
5096 operands of conditions that are invariant out of the loop, so that we can use
5097 just trivial invariantness analysis in loop unswitching. The pass also includes
5100 @item -ftree-loop-ivcanon
5101 Create a canonical counter for number of iterations in the loop for that
5102 determining number of iterations requires complicated analysis. Later
5103 optimizations then may determine the number easily. Useful especially
5104 in connection with unrolling.
5107 Perform induction variable optimizations (strength reduction, induction
5108 variable merging and induction variable elimination) on trees.
5111 Perform scalar replacement of aggregates. This pass replaces structure
5112 references with scalars to prevent committing structures to memory too
5113 early. This flag is enabled by default at @option{-O} and higher.
5115 @item -ftree-copyrename
5116 Perform copy renaming on trees. This pass attempts to rename compiler
5117 temporaries to other variables at copy locations, usually resulting in
5118 variable names which more closely resemble the original variables. This flag
5119 is enabled by default at @option{-O} and higher.
5122 Perform temporary expression replacement during the SSA->normal phase. Single
5123 use/single def temporaries are replaced at their use location with their
5124 defining expression. This results in non-GIMPLE code, but gives the expanders
5125 much more complex trees to work on resulting in better RTL generation. This is
5126 enabled by default at @option{-O} and higher.
5129 Perform live range splitting during the SSA->normal phase. Distinct live
5130 ranges of a variable are split into unique variables, allowing for better
5131 optimization later. This is enabled by default at @option{-O} and higher.
5133 @item -ftree-vectorize
5134 Perform loop vectorization on trees.
5136 @item -ftree-vect-loop-version
5137 @opindex ftree-vect-loop-version
5138 Perform loop versioning when doing loop vectorization on trees. When a loop
5139 appears to be vectorizable except that data alignment or data dependence cannot
5140 be determined at compile time then vectorized and non-vectorized versions of
5141 the loop are generated along with runtime checks for alignment or dependence
5142 to control which version is executed. This option is enabled by default
5143 except at level @option{-Os} where it is disabled.
5146 Perform Value Range Propagation on trees. This is similar to the
5147 constant propagation pass, but instead of values, ranges of values are
5148 propagated. This allows the optimizers to remove unnecessary range
5149 checks like array bound checks and null pointer checks. This is
5150 enabled by default at @option{-O2} and higher. Null pointer check
5151 elimination is only done if @option{-fdelete-null-pointer-checks} is
5156 Perform tail duplication to enlarge superblock size. This transformation
5157 simplifies the control flow of the function allowing other optimizations to do
5160 @item -funroll-loops
5161 @opindex funroll-loops
5162 Unroll loops whose number of iterations can be determined at compile
5163 time or upon entry to the loop. @option{-funroll-loops} implies both
5164 @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
5165 option makes code larger, and may or may not make it run faster.
5167 @item -funroll-all-loops
5168 @opindex funroll-all-loops
5169 Unroll all loops, even if their number of iterations is uncertain when
5170 the loop is entered. This usually makes programs run more slowly.
5171 @option{-funroll-all-loops} implies the same options as
5172 @option{-funroll-loops},
5174 @item -fsplit-ivs-in-unroller
5175 @opindex -fsplit-ivs-in-unroller
5176 Enables expressing of values of induction variables in later iterations
5177 of the unrolled loop using the value in the first iteration. This breaks
5178 long dependency chains, thus improving efficiency of the scheduling passes.
5180 Combination of @option{-fweb} and CSE is often sufficient to obtain the
5181 same effect. However in cases the loop body is more complicated than
5182 a single basic block, this is not reliable. It also does not work at all
5183 on some of the architectures due to restrictions in the CSE pass.
5185 This optimization is enabled by default.
5187 @item -fvariable-expansion-in-unroller
5188 @opindex -fvariable-expansion-in-unroller
5189 With this option, the compiler will create multiple copies of some
5190 local variables when unrolling a loop which can result in superior code.
5192 @item -fprefetch-loop-arrays
5193 @opindex fprefetch-loop-arrays
5194 If supported by the target machine, generate instructions to prefetch
5195 memory to improve the performance of loops that access large arrays.
5197 These options may generate better or worse code; results are highly
5198 dependent on the structure of loops within the source code.
5201 @itemx -fno-peephole2
5202 @opindex fno-peephole
5203 @opindex fno-peephole2
5204 Disable any machine-specific peephole optimizations. The difference
5205 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
5206 are implemented in the compiler; some targets use one, some use the
5207 other, a few use both.
5209 @option{-fpeephole} is enabled by default.
5210 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5212 @item -fno-guess-branch-probability
5213 @opindex fno-guess-branch-probability
5214 Do not guess branch probabilities using heuristics.
5216 GCC will use heuristics to guess branch probabilities if they are
5217 not provided by profiling feedback (@option{-fprofile-arcs}). These
5218 heuristics are based on the control flow graph. If some branch probabilities
5219 are specified by @samp{__builtin_expect}, then the heuristics will be
5220 used to guess branch probabilities for the rest of the control flow graph,
5221 taking the @samp{__builtin_expect} info into account. The interactions
5222 between the heuristics and @samp{__builtin_expect} can be complex, and in
5223 some cases, it may be useful to disable the heuristics so that the effects
5224 of @samp{__builtin_expect} are easier to understand.
5226 The default is @option{-fguess-branch-probability} at levels
5227 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5229 @item -freorder-blocks
5230 @opindex freorder-blocks
5231 Reorder basic blocks in the compiled function in order to reduce number of
5232 taken branches and improve code locality.
5234 Enabled at levels @option{-O2}, @option{-O3}.
5236 @item -freorder-blocks-and-partition
5237 @opindex freorder-blocks-and-partition
5238 In addition to reordering basic blocks in the compiled function, in order
5239 to reduce number of taken branches, partitions hot and cold basic blocks
5240 into separate sections of the assembly and .o files, to improve
5241 paging and cache locality performance.
5243 This optimization is automatically turned off in the presence of
5244 exception handling, for linkonce sections, for functions with a user-defined
5245 section attribute and on any architecture that does not support named
5248 @item -freorder-functions
5249 @opindex freorder-functions
5250 Reorder functions in the object file in order to
5251 improve code locality. This is implemented by using special
5252 subsections @code{.text.hot} for most frequently executed functions and
5253 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
5254 the linker so object file format must support named sections and linker must
5255 place them in a reasonable way.
5257 Also profile feedback must be available in to make this option effective. See
5258 @option{-fprofile-arcs} for details.
5260 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5262 @item -fstrict-aliasing
5263 @opindex fstrict-aliasing
5264 Allows the compiler to assume the strictest aliasing rules applicable to
5265 the language being compiled. For C (and C++), this activates
5266 optimizations based on the type of expressions. In particular, an
5267 object of one type is assumed never to reside at the same address as an
5268 object of a different type, unless the types are almost the same. For
5269 example, an @code{unsigned int} can alias an @code{int}, but not a
5270 @code{void*} or a @code{double}. A character type may alias any other
5273 Pay special attention to code like this:
5286 The practice of reading from a different union member than the one most
5287 recently written to (called ``type-punning'') is common. Even with
5288 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
5289 is accessed through the union type. So, the code above will work as
5290 expected. However, this code might not:
5301 Every language that wishes to perform language-specific alias analysis
5302 should define a function that computes, given an @code{tree}
5303 node, an alias set for the node. Nodes in different alias sets are not
5304 allowed to alias. For an example, see the C front-end function
5305 @code{c_get_alias_set}.
5307 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5309 @item -falign-functions
5310 @itemx -falign-functions=@var{n}
5311 @opindex falign-functions
5312 Align the start of functions to the next power-of-two greater than
5313 @var{n}, skipping up to @var{n} bytes. For instance,
5314 @option{-falign-functions=32} aligns functions to the next 32-byte
5315 boundary, but @option{-falign-functions=24} would align to the next
5316 32-byte boundary only if this can be done by skipping 23 bytes or less.
5318 @option{-fno-align-functions} and @option{-falign-functions=1} are
5319 equivalent and mean that functions will not be aligned.
5321 Some assemblers only support this flag when @var{n} is a power of two;
5322 in that case, it is rounded up.
5324 If @var{n} is not specified or is zero, use a machine-dependent default.
5326 Enabled at levels @option{-O2}, @option{-O3}.
5328 @item -falign-labels
5329 @itemx -falign-labels=@var{n}
5330 @opindex falign-labels
5331 Align all branch targets to a power-of-two boundary, skipping up to
5332 @var{n} bytes like @option{-falign-functions}. This option can easily
5333 make code slower, because it must insert dummy operations for when the
5334 branch target is reached in the usual flow of the code.
5336 @option{-fno-align-labels} and @option{-falign-labels=1} are
5337 equivalent and mean that labels will not be aligned.
5339 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
5340 are greater than this value, then their values are used instead.
5342 If @var{n} is not specified or is zero, use a machine-dependent default
5343 which is very likely to be @samp{1}, meaning no alignment.
5345 Enabled at levels @option{-O2}, @option{-O3}.
5348 @itemx -falign-loops=@var{n}
5349 @opindex falign-loops
5350 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
5351 like @option{-falign-functions}. The hope is that the loop will be
5352 executed many times, which will make up for any execution of the dummy
5355 @option{-fno-align-loops} and @option{-falign-loops=1} are
5356 equivalent and mean that loops will not be aligned.
5358 If @var{n} is not specified or is zero, use a machine-dependent default.
5360 Enabled at levels @option{-O2}, @option{-O3}.
5363 @itemx -falign-jumps=@var{n}
5364 @opindex falign-jumps
5365 Align branch targets to a power-of-two boundary, for branch targets
5366 where the targets can only be reached by jumping, skipping up to @var{n}
5367 bytes like @option{-falign-functions}. In this case, no dummy operations
5370 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
5371 equivalent and mean that loops will not be aligned.
5373 If @var{n} is not specified or is zero, use a machine-dependent default.
5375 Enabled at levels @option{-O2}, @option{-O3}.
5377 @item -funit-at-a-time
5378 @opindex funit-at-a-time
5379 Parse the whole compilation unit before starting to produce code.
5380 This allows some extra optimizations to take place but consumes
5381 more memory (in general). There are some compatibility issues
5382 with @emph{unit-at-a-time} mode:
5385 enabling @emph{unit-at-a-time} mode may change the order
5386 in which functions, variables, and top-level @code{asm} statements
5387 are emitted, and will likely break code relying on some particular
5388 ordering. The majority of such top-level @code{asm} statements,
5389 though, can be replaced by @code{section} attributes. The
5390 @option{fno-toplevel-reorder} option may be used to keep the ordering
5391 used in the input file, at the cost of some optimizations.
5394 @emph{unit-at-a-time} mode removes unreferenced static variables
5395 and functions. This may result in undefined references
5396 when an @code{asm} statement refers directly to variables or functions
5397 that are otherwise unused. In that case either the variable/function
5398 shall be listed as an operand of the @code{asm} statement operand or,
5399 in the case of top-level @code{asm} statements the attribute @code{used}
5400 shall be used on the declaration.
5403 Static functions now can use non-standard passing conventions that
5404 may break @code{asm} statements calling functions directly. Again,
5405 attribute @code{used} will prevent this behavior.
5408 As a temporary workaround, @option{-fno-unit-at-a-time} can be used,
5409 but this scheme may not be supported by future releases of GCC@.
5411 Enabled at levels @option{-O2}, @option{-O3}.
5413 @item -fno-toplevel-reorder
5414 Do not reorder top-level functions, variables, and @code{asm}
5415 statements. Output them in the same order that they appear in the
5416 input file. When this option is used, unreferenced static variables
5417 will not be removed. This option is intended to support existing code
5418 which relies on a particular ordering. For new code, it is better to
5423 Constructs webs as commonly used for register allocation purposes and assign
5424 each web individual pseudo register. This allows the register allocation pass
5425 to operate on pseudos directly, but also strengthens several other optimization
5426 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
5427 however, make debugging impossible, since variables will no longer stay in a
5430 Enabled by default with @option{-funroll-loops}.
5432 @item -fwhole-program
5433 @opindex fwhole-program
5434 Assume that the current compilation unit represents whole program being
5435 compiled. All public functions and variables with the exception of @code{main}
5436 and those merged by attribute @code{externally_visible} become static functions
5437 and in a affect gets more aggressively optimized by interprocedural optimizers.
5438 While this option is equivalent to proper use of @code{static} keyword for
5439 programs consisting of single file, in combination with option
5440 @option{--combine} this flag can be used to compile most of smaller scale C
5441 programs since the functions and variables become local for the whole combined
5442 compilation unit, not for the single source file itself.
5445 @item -fno-cprop-registers
5446 @opindex fno-cprop-registers
5447 After register allocation and post-register allocation instruction splitting,
5448 we perform a copy-propagation pass to try to reduce scheduling dependencies
5449 and occasionally eliminate the copy.
5451 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5453 @item -fprofile-generate
5454 @opindex fprofile-generate
5456 Enable options usually used for instrumenting application to produce
5457 profile useful for later recompilation with profile feedback based
5458 optimization. You must use @option{-fprofile-generate} both when
5459 compiling and when linking your program.
5461 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
5464 @opindex fprofile-use
5465 Enable profile feedback directed optimizations, and optimizations
5466 generally profitable only with profile feedback available.
5468 The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt},
5469 @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer},
5470 @code{-fno-loop-optimize}.
5474 The following options control compiler behavior regarding floating
5475 point arithmetic. These options trade off between speed and
5476 correctness. All must be specifically enabled.
5480 @opindex ffloat-store
5481 Do not store floating point variables in registers, and inhibit other
5482 options that might change whether a floating point value is taken from a
5485 @cindex floating point precision
5486 This option prevents undesirable excess precision on machines such as
5487 the 68000 where the floating registers (of the 68881) keep more
5488 precision than a @code{double} is supposed to have. Similarly for the
5489 x86 architecture. For most programs, the excess precision does only
5490 good, but a few programs rely on the precise definition of IEEE floating
5491 point. Use @option{-ffloat-store} for such programs, after modifying
5492 them to store all pertinent intermediate computations into variables.
5496 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
5497 @option{-fno-trapping-math}, @option{-ffinite-math-only},
5498 @option{-fno-rounding-math}, @option{-fno-signaling-nans}
5499 and @option{fcx-limited-range}.
5501 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
5503 This option should never be turned on by any @option{-O} option since
5504 it can result in incorrect output for programs which depend on
5505 an exact implementation of IEEE or ISO rules/specifications for
5508 @item -fno-math-errno
5509 @opindex fno-math-errno
5510 Do not set ERRNO after calling math functions that are executed
5511 with a single instruction, e.g., sqrt. A program that relies on
5512 IEEE exceptions for math error handling may want to use this flag
5513 for speed while maintaining IEEE arithmetic compatibility.
5515 This option should never be turned on by any @option{-O} option since
5516 it can result in incorrect output for programs which depend on
5517 an exact implementation of IEEE or ISO rules/specifications for
5520 The default is @option{-fmath-errno}.
5522 On Darwin systems, the math library never sets @code{errno}. There is therefore
5523 no reason for the compiler to consider the possibility that it might,
5524 and @option{-fno-math-errno} is the default.
5526 @item -funsafe-math-optimizations
5527 @opindex funsafe-math-optimizations
5528 Allow optimizations for floating-point arithmetic that (a) assume
5529 that arguments and results are valid and (b) may violate IEEE or
5530 ANSI standards. When used at link-time, it may include libraries
5531 or startup files that change the default FPU control word or other
5532 similar optimizations.
5534 This option should never be turned on by any @option{-O} option since
5535 it can result in incorrect output for programs which depend on
5536 an exact implementation of IEEE or ISO rules/specifications for
5539 The default is @option{-fno-unsafe-math-optimizations}.
5541 @item -ffinite-math-only
5542 @opindex ffinite-math-only
5543 Allow optimizations for floating-point arithmetic that assume
5544 that arguments and results are not NaNs or +-Infs.
5546 This option should never be turned on by any @option{-O} option since
5547 it can result in incorrect output for programs which depend on
5548 an exact implementation of IEEE or ISO rules/specifications.
5550 The default is @option{-fno-finite-math-only}.
5552 @item -fno-trapping-math
5553 @opindex fno-trapping-math
5554 Compile code assuming that floating-point operations cannot generate
5555 user-visible traps. These traps include division by zero, overflow,
5556 underflow, inexact result and invalid operation. This option implies
5557 @option{-fno-signaling-nans}. Setting this option may allow faster
5558 code if one relies on ``non-stop'' IEEE arithmetic, for example.
5560 This option should never be turned on by any @option{-O} option since
5561 it can result in incorrect output for programs which depend on
5562 an exact implementation of IEEE or ISO rules/specifications for
5565 The default is @option{-ftrapping-math}.
5567 @item -frounding-math
5568 @opindex frounding-math
5569 Disable transformations and optimizations that assume default floating
5570 point rounding behavior. This is round-to-zero for all floating point
5571 to integer conversions, and round-to-nearest for all other arithmetic
5572 truncations. This option should be specified for programs that change
5573 the FP rounding mode dynamically, or that may be executed with a
5574 non-default rounding mode. This option disables constant folding of
5575 floating point expressions at compile-time (which may be affected by
5576 rounding mode) and arithmetic transformations that are unsafe in the
5577 presence of sign-dependent rounding modes.
5579 The default is @option{-fno-rounding-math}.
5581 This option is experimental and does not currently guarantee to
5582 disable all GCC optimizations that are affected by rounding mode.
5583 Future versions of GCC may provide finer control of this setting
5584 using C99's @code{FENV_ACCESS} pragma. This command line option
5585 will be used to specify the default state for @code{FENV_ACCESS}.
5587 @item -frtl-abstract-sequences
5588 @opindex frtl-abstract-sequences
5589 It is a size optimization method. This option is to find identical
5590 sequences of code, which can be turned into pseudo-procedures and
5591 then replace all occurrences with calls to the newly created
5592 subroutine. It is kind of an opposite of @option{-finline-functions}.
5593 This optimization runs at RTL level.
5595 @item -fsignaling-nans
5596 @opindex fsignaling-nans
5597 Compile code assuming that IEEE signaling NaNs may generate user-visible
5598 traps during floating-point operations. Setting this option disables
5599 optimizations that may change the number of exceptions visible with
5600 signaling NaNs. This option implies @option{-ftrapping-math}.
5602 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
5605 The default is @option{-fno-signaling-nans}.
5607 This option is experimental and does not currently guarantee to
5608 disable all GCC optimizations that affect signaling NaN behavior.
5610 @item -fsingle-precision-constant
5611 @opindex fsingle-precision-constant
5612 Treat floating point constant as single precision constant instead of
5613 implicitly converting it to double precision constant.
5615 @item -fcx-limited-range
5616 @itemx -fno-cx-limited-range
5617 @opindex fcx-limited-range
5618 @opindex fno-cx-limited-range
5619 When enabled, this option states that a range reduction step is not
5620 needed when performing complex division. The default is
5621 @option{-fno-cx-limited-range}, but is enabled by @option{-ffast-math}.
5623 This option controls the default setting of the ISO C99
5624 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
5629 The following options control optimizations that may improve
5630 performance, but are not enabled by any @option{-O} options. This
5631 section includes experimental options that may produce broken code.
5634 @item -fbranch-probabilities
5635 @opindex fbranch-probabilities
5636 After running a program compiled with @option{-fprofile-arcs}
5637 (@pxref{Debugging Options,, Options for Debugging Your Program or
5638 @command{gcc}}), you can compile it a second time using
5639 @option{-fbranch-probabilities}, to improve optimizations based on
5640 the number of times each branch was taken. When the program
5641 compiled with @option{-fprofile-arcs} exits it saves arc execution
5642 counts to a file called @file{@var{sourcename}.gcda} for each source
5643 file The information in this data file is very dependent on the
5644 structure of the generated code, so you must use the same source code
5645 and the same optimization options for both compilations.
5647 With @option{-fbranch-probabilities}, GCC puts a
5648 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
5649 These can be used to improve optimization. Currently, they are only
5650 used in one place: in @file{reorg.c}, instead of guessing which path a
5651 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
5652 exactly determine which path is taken more often.
5654 @item -fprofile-values
5655 @opindex fprofile-values
5656 If combined with @option{-fprofile-arcs}, it adds code so that some
5657 data about values of expressions in the program is gathered.
5659 With @option{-fbranch-probabilities}, it reads back the data gathered
5660 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
5661 notes to instructions for their later usage in optimizations.
5663 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
5667 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
5668 a code to gather information about values of expressions.
5670 With @option{-fbranch-probabilities}, it reads back the data gathered
5671 and actually performs the optimizations based on them.
5672 Currently the optimizations include specialization of division operation
5673 using the knowledge about the value of the denominator.
5675 @item -frename-registers
5676 @opindex frename-registers
5677 Attempt to avoid false dependencies in scheduled code by making use
5678 of registers left over after register allocation. This optimization
5679 will most benefit processors with lots of registers. Depending on the
5680 debug information format adopted by the target, however, it can
5681 make debugging impossible, since variables will no longer stay in
5682 a ``home register''.
5684 Enabled by default with @option{-funroll-loops}.
5688 Perform tail duplication to enlarge superblock size. This transformation
5689 simplifies the control flow of the function allowing other optimizations to do
5692 Enabled with @option{-fprofile-use}.
5694 @item -funroll-loops
5695 @opindex funroll-loops
5696 Unroll loops whose number of iterations can be determined at compile time or
5697 upon entry to the loop. @option{-funroll-loops} implies
5698 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
5699 It also turns on complete loop peeling (i.e.@: complete removal of loops with
5700 small constant number of iterations). This option makes code larger, and may
5701 or may not make it run faster.
5703 Enabled with @option{-fprofile-use}.
5705 @item -funroll-all-loops
5706 @opindex funroll-all-loops
5707 Unroll all loops, even if their number of iterations is uncertain when
5708 the loop is entered. This usually makes programs run more slowly.
5709 @option{-funroll-all-loops} implies the same options as
5710 @option{-funroll-loops}.
5713 @opindex fpeel-loops
5714 Peels the loops for that there is enough information that they do not
5715 roll much (from profile feedback). It also turns on complete loop peeling
5716 (i.e.@: complete removal of loops with small constant number of iterations).
5718 Enabled with @option{-fprofile-use}.
5720 @item -fmove-loop-invariants
5721 @opindex fmove-loop-invariants
5722 Enables the loop invariant motion pass in the new loop optimizer. Enabled
5723 at level @option{-O1}
5725 @item -funswitch-loops
5726 @opindex funswitch-loops
5727 Move branches with loop invariant conditions out of the loop, with duplicates
5728 of the loop on both branches (modified according to result of the condition).
5730 @item -fprefetch-loop-arrays
5731 @opindex fprefetch-loop-arrays
5732 If supported by the target machine, generate instructions to prefetch
5733 memory to improve the performance of loops that access large arrays.
5735 Disabled at level @option{-Os}.
5737 @item -ffunction-sections
5738 @itemx -fdata-sections
5739 @opindex ffunction-sections
5740 @opindex fdata-sections
5741 Place each function or data item into its own section in the output
5742 file if the target supports arbitrary sections. The name of the
5743 function or the name of the data item determines the section's name
5746 Use these options on systems where the linker can perform optimizations
5747 to improve locality of reference in the instruction space. Most systems
5748 using the ELF object format and SPARC processors running Solaris 2 have
5749 linkers with such optimizations. AIX may have these optimizations in
5752 Only use these options when there are significant benefits from doing
5753 so. When you specify these options, the assembler and linker will
5754 create larger object and executable files and will also be slower.
5755 You will not be able to use @code{gprof} on all systems if you
5756 specify this option and you may have problems with debugging if
5757 you specify both this option and @option{-g}.
5759 @item -fbranch-target-load-optimize
5760 @opindex fbranch-target-load-optimize
5761 Perform branch target register load optimization before prologue / epilogue
5763 The use of target registers can typically be exposed only during reload,
5764 thus hoisting loads out of loops and doing inter-block scheduling needs
5765 a separate optimization pass.
5767 @item -fbranch-target-load-optimize2
5768 @opindex fbranch-target-load-optimize2
5769 Perform branch target register load optimization after prologue / epilogue
5772 @item -fbtr-bb-exclusive
5773 @opindex fbtr-bb-exclusive
5774 When performing branch target register load optimization, don't reuse
5775 branch target registers in within any basic block.
5777 @item -fstack-protector
5778 Emit extra code to check for buffer overflows, such as stack smashing
5779 attacks. This is done by adding a guard variable to functions with
5780 vulnerable objects. This includes functions that call alloca, and
5781 functions with buffers larger than 8 bytes. The guards are initialized
5782 when a function is entered and then checked when the function exits.
5783 If a guard check fails, an error message is printed and the program exits.
5785 @item -fstack-protector-all
5786 Like @option{-fstack-protector} except that all functions are protected.
5788 @item --param @var{name}=@var{value}
5790 In some places, GCC uses various constants to control the amount of
5791 optimization that is done. For example, GCC will not inline functions
5792 that contain more that a certain number of instructions. You can
5793 control some of these constants on the command-line using the
5794 @option{--param} option.
5796 The names of specific parameters, and the meaning of the values, are
5797 tied to the internals of the compiler, and are subject to change
5798 without notice in future releases.
5800 In each case, the @var{value} is an integer. The allowable choices for
5801 @var{name} are given in the following table:
5804 @item salias-max-implicit-fields
5805 The maximum number of fields in a variable without direct
5806 structure accesses for which structure aliasing will consider trying
5807 to track each field. The default is 5
5809 @item salias-max-array-elements
5810 The maximum number of elements an array can have and its elements
5811 still be tracked individually by structure aliasing. The default is 4
5813 @item sra-max-structure-size
5814 The maximum structure size, in bytes, at which the scalar replacement
5815 of aggregates (SRA) optimization will perform block copies. The
5816 default value, 0, implies that GCC will select the most appropriate
5819 @item sra-field-structure-ratio
5820 The threshold ratio (as a percentage) between instantiated fields and
5821 the complete structure size. We say that if the ratio of the number
5822 of bytes in instantiated fields to the number of bytes in the complete
5823 structure exceeds this parameter, then block copies are not used. The
5826 @item max-crossjump-edges
5827 The maximum number of incoming edges to consider for crossjumping.
5828 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
5829 the number of edges incoming to each block. Increasing values mean
5830 more aggressive optimization, making the compile time increase with
5831 probably small improvement in executable size.
5833 @item min-crossjump-insns
5834 The minimum number of instructions which must be matched at the end
5835 of two blocks before crossjumping will be performed on them. This
5836 value is ignored in the case where all instructions in the block being
5837 crossjumped from are matched. The default value is 5.
5839 @item max-grow-copy-bb-insns
5840 The maximum code size expansion factor when copying basic blocks
5841 instead of jumping. The expansion is relative to a jump instruction.
5842 The default value is 8.
5844 @item max-goto-duplication-insns
5845 The maximum number of instructions to duplicate to a block that jumps
5846 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
5847 passes, GCC factors computed gotos early in the compilation process,
5848 and unfactors them as late as possible. Only computed jumps at the
5849 end of a basic blocks with no more than max-goto-duplication-insns are
5850 unfactored. The default value is 8.
5852 @item max-delay-slot-insn-search
5853 The maximum number of instructions to consider when looking for an
5854 instruction to fill a delay slot. If more than this arbitrary number of
5855 instructions is searched, the time savings from filling the delay slot
5856 will be minimal so stop searching. Increasing values mean more
5857 aggressive optimization, making the compile time increase with probably
5858 small improvement in executable run time.
5860 @item max-delay-slot-live-search
5861 When trying to fill delay slots, the maximum number of instructions to
5862 consider when searching for a block with valid live register
5863 information. Increasing this arbitrarily chosen value means more
5864 aggressive optimization, increasing the compile time. This parameter
5865 should be removed when the delay slot code is rewritten to maintain the
5868 @item max-gcse-memory
5869 The approximate maximum amount of memory that will be allocated in
5870 order to perform the global common subexpression elimination
5871 optimization. If more memory than specified is required, the
5872 optimization will not be done.
5874 @item max-gcse-passes
5875 The maximum number of passes of GCSE to run. The default is 1.
5877 @item max-pending-list-length
5878 The maximum number of pending dependencies scheduling will allow
5879 before flushing the current state and starting over. Large functions
5880 with few branches or calls can create excessively large lists which
5881 needlessly consume memory and resources.
5883 @item max-inline-insns-single
5884 Several parameters control the tree inliner used in gcc.
5885 This number sets the maximum number of instructions (counted in GCC's
5886 internal representation) in a single function that the tree inliner
5887 will consider for inlining. This only affects functions declared
5888 inline and methods implemented in a class declaration (C++).
5889 The default value is 450.
5891 @item max-inline-insns-auto
5892 When you use @option{-finline-functions} (included in @option{-O3}),
5893 a lot of functions that would otherwise not be considered for inlining
5894 by the compiler will be investigated. To those functions, a different
5895 (more restrictive) limit compared to functions declared inline can
5897 The default value is 90.
5899 @item large-function-insns
5900 The limit specifying really large functions. For functions larger than this
5901 limit after inlining inlining is constrained by
5902 @option{--param large-function-growth}. This parameter is useful primarily
5903 to avoid extreme compilation time caused by non-linear algorithms used by the
5905 This parameter is ignored when @option{-funit-at-a-time} is not used.
5906 The default value is 2700.
5908 @item large-function-growth
5909 Specifies maximal growth of large function caused by inlining in percents.
5910 This parameter is ignored when @option{-funit-at-a-time} is not used.
5911 The default value is 100 which limits large function growth to 2.0 times
5914 @item large-unit-insns
5915 The limit specifying large translation unit. Growth caused by inlining of
5916 units larger than this limit is limited by @option{--param inline-unit-growth}.
5917 For small units this might be too tight (consider unit consisting of function A
5918 that is inline and B that just calls A three time. If B is small relative to
5919 A, the growth of unit is 300\% and yet such inlining is very sane. For very
5920 large units consisting of small inlininable functions however the overall unit
5921 growth limit is needed to avoid exponential explosion of code size. Thus for
5922 smaller units, the size is increased to @option{--param large-unit-insns}
5923 before applying @option{--param inline-unit-growth}. The default is 10000
5925 @item inline-unit-growth
5926 Specifies maximal overall growth of the compilation unit caused by inlining.
5927 This parameter is ignored when @option{-funit-at-a-time} is not used.
5928 The default value is 50 which limits unit growth to 1.5 times the original
5931 @item max-inline-insns-recursive
5932 @itemx max-inline-insns-recursive-auto
5933 Specifies maximum number of instructions out-of-line copy of self recursive inline
5934 function can grow into by performing recursive inlining.
5936 For functions declared inline @option{--param max-inline-insns-recursive} is
5937 taken into acount. For function not declared inline, recursive inlining
5938 happens only when @option{-finline-functions} (included in @option{-O3}) is
5939 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
5940 default value is 450.
5942 @item max-inline-recursive-depth
5943 @itemx max-inline-recursive-depth-auto
5944 Specifies maximum recursion depth used by the recursive inlining.
5946 For functions declared inline @option{--param max-inline-recursive-depth} is
5947 taken into acount. For function not declared inline, recursive inlining
5948 happens only when @option{-finline-functions} (included in @option{-O3}) is
5949 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
5950 default value is 450.
5952 @item min-inline-recursive-probability
5953 Recursive inlining is profitable only for function having deep recursion
5954 in average and can hurt for function having little recursion depth by
5955 increasing the prologue size or complexity of function body to other
5958 When profile feedback is available (see @option{-fprofile-generate}) the actual
5959 recursion depth can be guessed from probability that function will recurse via
5960 given call expression. This parameter limits inlining only to call expression
5961 whose probability exceeds given threshold (in percents). The default value is
5964 @item inline-call-cost
5965 Specify cost of call instruction relative to simple arithmetics operations
5966 (having cost of 1). Increasing this cost disqualifies inlining of non-leaf
5967 functions and at the same time increases size of leaf function that is believed to
5968 reduce function size by being inlined. In effect it increases amount of
5969 inlining for code having large abstraction penalty (many functions that just
5970 pass the arguments to other functions) and decrease inlining for code with low
5971 abstraction penalty. The default value is 16.
5973 @item max-unrolled-insns
5974 The maximum number of instructions that a loop should have if that loop
5975 is unrolled, and if the loop is unrolled, it determines how many times
5976 the loop code is unrolled.
5978 @item max-average-unrolled-insns
5979 The maximum number of instructions biased by probabilities of their execution
5980 that a loop should have if that loop is unrolled, and if the loop is unrolled,
5981 it determines how many times the loop code is unrolled.
5983 @item max-unroll-times
5984 The maximum number of unrollings of a single loop.
5986 @item max-peeled-insns
5987 The maximum number of instructions that a loop should have if that loop
5988 is peeled, and if the loop is peeled, it determines how many times
5989 the loop code is peeled.
5991 @item max-peel-times
5992 The maximum number of peelings of a single loop.
5994 @item max-completely-peeled-insns
5995 The maximum number of insns of a completely peeled loop.
5997 @item max-completely-peel-times
5998 The maximum number of iterations of a loop to be suitable for complete peeling.
6000 @item max-unswitch-insns
6001 The maximum number of insns of an unswitched loop.
6003 @item max-unswitch-level
6004 The maximum number of branches unswitched in a single loop.
6007 The minimum cost of an expensive expression in the loop invariant motion.
6009 @item iv-consider-all-candidates-bound
6010 Bound on number of candidates for induction variables below that
6011 all candidates are considered for each use in induction variable
6012 optimizations. Only the most relevant candidates are considered
6013 if there are more candidates, to avoid quadratic time complexity.
6015 @item iv-max-considered-uses
6016 The induction variable optimizations give up on loops that contain more
6017 induction variable uses.
6019 @item iv-always-prune-cand-set-bound
6020 If number of candidates in the set is smaller than this value,
6021 we always try to remove unnecessary ivs from the set during its
6022 optimization when a new iv is added to the set.
6024 @item scev-max-expr-size
6025 Bound on size of expressions used in the scalar evolutions analyzer.
6026 Large expressions slow the analyzer.
6028 @item vect-max-version-checks
6029 The maximum number of runtime checks that can be performed when doing
6030 loop versioning in the vectorizer. See option ftree-vect-loop-version
6031 for more information.
6033 @item max-iterations-to-track
6035 The maximum number of iterations of a loop the brute force algorithm
6036 for analysis of # of iterations of the loop tries to evaluate.
6038 @item hot-bb-count-fraction
6039 Select fraction of the maximal count of repetitions of basic block in program
6040 given basic block needs to have to be considered hot.
6042 @item hot-bb-frequency-fraction
6043 Select fraction of the maximal frequency of executions of basic block in
6044 function given basic block needs to have to be considered hot
6046 @item max-predicted-iterations
6047 The maximum number of loop iterations we predict statically. This is useful
6048 in cases where function contain single loop with known bound and other loop
6049 with unknown. We predict the known number of iterations correctly, while
6050 the unknown number of iterations average to roughly 10. This means that the
6051 loop without bounds would appear artificially cold relative to the other one.
6053 @item tracer-dynamic-coverage
6054 @itemx tracer-dynamic-coverage-feedback
6056 This value is used to limit superblock formation once the given percentage of
6057 executed instructions is covered. This limits unnecessary code size
6060 The @option{tracer-dynamic-coverage-feedback} is used only when profile
6061 feedback is available. The real profiles (as opposed to statically estimated
6062 ones) are much less balanced allowing the threshold to be larger value.
6064 @item tracer-max-code-growth
6065 Stop tail duplication once code growth has reached given percentage. This is
6066 rather hokey argument, as most of the duplicates will be eliminated later in
6067 cross jumping, so it may be set to much higher values than is the desired code
6070 @item tracer-min-branch-ratio
6072 Stop reverse growth when the reverse probability of best edge is less than this
6073 threshold (in percent).
6075 @item tracer-min-branch-ratio
6076 @itemx tracer-min-branch-ratio-feedback
6078 Stop forward growth if the best edge do have probability lower than this
6081 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
6082 compilation for profile feedback and one for compilation without. The value
6083 for compilation with profile feedback needs to be more conservative (higher) in
6084 order to make tracer effective.
6086 @item max-cse-path-length
6088 Maximum number of basic blocks on path that cse considers. The default is 10.
6091 The maximum instructions CSE process before flushing. The default is 1000.
6093 @item global-var-threshold
6095 Counts the number of function calls (@var{n}) and the number of
6096 call-clobbered variables (@var{v}). If @var{n}x@var{v} is larger than this limit, a
6097 single artificial variable will be created to represent all the
6098 call-clobbered variables at function call sites. This artificial
6099 variable will then be made to alias every call-clobbered variable.
6100 (done as @code{int * size_t} on the host machine; beware overflow).
6102 @item max-aliased-vops
6104 Maximum number of virtual operands allowed to represent aliases
6105 before triggering the alias grouping heuristic. Alias grouping
6106 reduces compile times and memory consumption needed for aliasing at
6107 the expense of precision loss in alias information.
6109 @item ggc-min-expand
6111 GCC uses a garbage collector to manage its own memory allocation. This
6112 parameter specifies the minimum percentage by which the garbage
6113 collector's heap should be allowed to expand between collections.
6114 Tuning this may improve compilation speed; it has no effect on code
6117 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
6118 RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
6119 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
6120 GCC is not able to calculate RAM on a particular platform, the lower
6121 bound of 30% is used. Setting this parameter and
6122 @option{ggc-min-heapsize} to zero causes a full collection to occur at
6123 every opportunity. This is extremely slow, but can be useful for
6126 @item ggc-min-heapsize
6128 Minimum size of the garbage collector's heap before it begins bothering
6129 to collect garbage. The first collection occurs after the heap expands
6130 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
6131 tuning this may improve compilation speed, and has no effect on code
6134 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
6135 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
6136 with a lower bound of 4096 (four megabytes) and an upper bound of
6137 131072 (128 megabytes). If GCC is not able to calculate RAM on a
6138 particular platform, the lower bound is used. Setting this parameter
6139 very large effectively disables garbage collection. Setting this
6140 parameter and @option{ggc-min-expand} to zero causes a full collection
6141 to occur at every opportunity.
6143 @item max-reload-search-insns
6144 The maximum number of instruction reload should look backward for equivalent
6145 register. Increasing values mean more aggressive optimization, making the
6146 compile time increase with probably slightly better performance. The default
6149 @item max-cselib-memory-location
6150 The maximum number of memory locations cselib should take into acount.
6151 Increasing values mean more aggressive optimization, making the compile time
6152 increase with probably slightly better performance. The default value is 500.
6154 @item max-flow-memory-location
6155 Similar as @option{max-cselib-memory-location} but for dataflow liveness.
6156 The default value is 100.
6158 @item reorder-blocks-duplicate
6159 @itemx reorder-blocks-duplicate-feedback
6161 Used by basic block reordering pass to decide whether to use unconditional
6162 branch or duplicate the code on its destination. Code is duplicated when its
6163 estimated size is smaller than this value multiplied by the estimated size of
6164 unconditional jump in the hot spots of the program.
6166 The @option{reorder-block-duplicate-feedback} is used only when profile
6167 feedback is available and may be set to higher values than
6168 @option{reorder-block-duplicate} since information about the hot spots is more
6171 @item max-sched-region-blocks
6172 The maximum number of blocks in a region to be considered for
6173 interblock scheduling. The default value is 10.
6175 @item max-sched-region-insns
6176 The maximum number of insns in a region to be considered for
6177 interblock scheduling. The default value is 100.
6180 The minimum probability (in percents) of reaching a source block
6181 for interblock speculative scheduling. The default value is 40.
6183 @item max-last-value-rtl
6185 The maximum size measured as number of RTLs that can be recorded in an expression
6186 in combiner for a pseudo register as last known value of that register. The default
6189 @item integer-share-limit
6190 Small integer constants can use a shared data structure, reducing the
6191 compiler's memory usage and increasing its speed. This sets the maximum
6192 value of a shared integer constant's. The default value is 256.
6194 @item min-virtual-mappings
6195 Specifies the minimum number of virtual mappings in the incremental
6196 SSA updater that should be registered to trigger the virtual mappings
6197 heuristic defined by virtual-mappings-ratio. The default value is
6200 @item virtual-mappings-ratio
6201 If the number of virtual mappings is virtual-mappings-ratio bigger
6202 than the number of virtual symbols to be updated, then the incremental
6203 SSA updater switches to a full update for those symbols. The default
6206 @item ssp-buffer-size
6207 The minimum size of buffers (i.e. arrays) that will receive stack smashing
6208 protection when @option{-fstack-protection} is used.
6210 @item max-jump-thread-duplication-stmts
6211 Maximum number of statements allowed in a block that needs to be
6212 duplicated when threading jumps.
6216 @node Preprocessor Options
6217 @section Options Controlling the Preprocessor
6218 @cindex preprocessor options
6219 @cindex options, preprocessor
6221 These options control the C preprocessor, which is run on each C source
6222 file before actual compilation.
6224 If you use the @option{-E} option, nothing is done except preprocessing.
6225 Some of these options make sense only together with @option{-E} because
6226 they cause the preprocessor output to be unsuitable for actual
6231 You can use @option{-Wp,@var{option}} to bypass the compiler driver
6232 and pass @var{option} directly through to the preprocessor. If
6233 @var{option} contains commas, it is split into multiple options at the
6234 commas. However, many options are modified, translated or interpreted
6235 by the compiler driver before being passed to the preprocessor, and
6236 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
6237 interface is undocumented and subject to change, so whenever possible
6238 you should avoid using @option{-Wp} and let the driver handle the
6241 @item -Xpreprocessor @var{option}
6242 @opindex preprocessor
6243 Pass @var{option} as an option to the preprocessor. You can use this to
6244 supply system-specific preprocessor options which GCC does not know how to
6247 If you want to pass an option that takes an argument, you must use
6248 @option{-Xpreprocessor} twice, once for the option and once for the argument.
6251 @include cppopts.texi
6253 @node Assembler Options
6254 @section Passing Options to the Assembler
6256 @c prevent bad page break with this line
6257 You can pass options to the assembler.
6260 @item -Wa,@var{option}
6262 Pass @var{option} as an option to the assembler. If @var{option}
6263 contains commas, it is split into multiple options at the commas.
6265 @item -Xassembler @var{option}
6267 Pass @var{option} as an option to the assembler. You can use this to
6268 supply system-specific assembler options which GCC does not know how to
6271 If you want to pass an option that takes an argument, you must use
6272 @option{-Xassembler} twice, once for the option and once for the argument.
6277 @section Options for Linking
6278 @cindex link options
6279 @cindex options, linking
6281 These options come into play when the compiler links object files into
6282 an executable output file. They are meaningless if the compiler is
6283 not doing a link step.
6287 @item @var{object-file-name}
6288 A file name that does not end in a special recognized suffix is
6289 considered to name an object file or library. (Object files are
6290 distinguished from libraries by the linker according to the file
6291 contents.) If linking is done, these object files are used as input
6300 If any of these options is used, then the linker is not run, and
6301 object file names should not be used as arguments. @xref{Overall
6305 @item -l@var{library}
6306 @itemx -l @var{library}
6308 Search the library named @var{library} when linking. (The second
6309 alternative with the library as a separate argument is only for
6310 POSIX compliance and is not recommended.)
6312 It makes a difference where in the command you write this option; the
6313 linker searches and processes libraries and object files in the order they
6314 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
6315 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
6316 to functions in @samp{z}, those functions may not be loaded.
6318 The linker searches a standard list of directories for the library,
6319 which is actually a file named @file{lib@var{library}.a}. The linker
6320 then uses this file as if it had been specified precisely by name.
6322 The directories searched include several standard system directories
6323 plus any that you specify with @option{-L}.
6325 Normally the files found this way are library files---archive files
6326 whose members are object files. The linker handles an archive file by
6327 scanning through it for members which define symbols that have so far
6328 been referenced but not defined. But if the file that is found is an
6329 ordinary object file, it is linked in the usual fashion. The only
6330 difference between using an @option{-l} option and specifying a file name
6331 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
6332 and searches several directories.
6336 You need this special case of the @option{-l} option in order to
6337 link an Objective-C or Objective-C++ program.
6340 @opindex nostartfiles
6341 Do not use the standard system startup files when linking.
6342 The standard system libraries are used normally, unless @option{-nostdlib}
6343 or @option{-nodefaultlibs} is used.
6345 @item -nodefaultlibs
6346 @opindex nodefaultlibs
6347 Do not use the standard system libraries when linking.
6348 Only the libraries you specify will be passed to the linker.
6349 The standard startup files are used normally, unless @option{-nostartfiles}
6350 is used. The compiler may generate calls to @code{memcmp},
6351 @code{memset}, @code{memcpy} and @code{memmove}.
6352 These entries are usually resolved by entries in
6353 libc. These entry points should be supplied through some other
6354 mechanism when this option is specified.
6358 Do not use the standard system startup files or libraries when linking.
6359 No startup files and only the libraries you specify will be passed to
6360 the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
6361 @code{memcpy} and @code{memmove}.
6362 These entries are usually resolved by entries in
6363 libc. These entry points should be supplied through some other
6364 mechanism when this option is specified.
6366 @cindex @option{-lgcc}, use with @option{-nostdlib}
6367 @cindex @option{-nostdlib} and unresolved references
6368 @cindex unresolved references and @option{-nostdlib}
6369 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
6370 @cindex @option{-nodefaultlibs} and unresolved references
6371 @cindex unresolved references and @option{-nodefaultlibs}
6372 One of the standard libraries bypassed by @option{-nostdlib} and
6373 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
6374 that GCC uses to overcome shortcomings of particular machines, or special
6375 needs for some languages.
6376 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
6377 Collection (GCC) Internals},
6378 for more discussion of @file{libgcc.a}.)
6379 In most cases, you need @file{libgcc.a} even when you want to avoid
6380 other standard libraries. In other words, when you specify @option{-nostdlib}
6381 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
6382 This ensures that you have no unresolved references to internal GCC
6383 library subroutines. (For example, @samp{__main}, used to ensure C++
6384 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
6385 GNU Compiler Collection (GCC) Internals}.)
6389 Produce a position independent executable on targets which support it.
6390 For predictable results, you must also specify the same set of options
6391 that were used to generate code (@option{-fpie}, @option{-fPIE},
6392 or model suboptions) when you specify this option.
6396 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
6397 that support it. This instructs the linker to add all symbols, not
6398 only used ones, to the dynamic symbol table. This option is needed
6399 for some uses of @code{dlopen} or to allow obtaining backtraces
6400 from within a program.
6404 Remove all symbol table and relocation information from the executable.
6408 On systems that support dynamic linking, this prevents linking with the shared
6409 libraries. On other systems, this option has no effect.
6413 Produce a shared object which can then be linked with other objects to
6414 form an executable. Not all systems support this option. For predictable
6415 results, you must also specify the same set of options that were used to
6416 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
6417 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
6418 needs to build supplementary stub code for constructors to work. On
6419 multi-libbed systems, @samp{gcc -shared} must select the correct support
6420 libraries to link against. Failing to supply the correct flags may lead
6421 to subtle defects. Supplying them in cases where they are not necessary
6424 @item -shared-libgcc
6425 @itemx -static-libgcc
6426 @opindex shared-libgcc
6427 @opindex static-libgcc
6428 On systems that provide @file{libgcc} as a shared library, these options
6429 force the use of either the shared or static version respectively.
6430 If no shared version of @file{libgcc} was built when the compiler was
6431 configured, these options have no effect.
6433 There are several situations in which an application should use the
6434 shared @file{libgcc} instead of the static version. The most common
6435 of these is when the application wishes to throw and catch exceptions
6436 across different shared libraries. In that case, each of the libraries
6437 as well as the application itself should use the shared @file{libgcc}.
6439 Therefore, the G++ and GCJ drivers automatically add
6440 @option{-shared-libgcc} whenever you build a shared library or a main
6441 executable, because C++ and Java programs typically use exceptions, so
6442 this is the right thing to do.
6444 If, instead, you use the GCC driver to create shared libraries, you may
6445 find that they will not always be linked with the shared @file{libgcc}.
6446 If GCC finds, at its configuration time, that you have a non-GNU linker
6447 or a GNU linker that does not support option @option{--eh-frame-hdr},
6448 it will link the shared version of @file{libgcc} into shared libraries
6449 by default. Otherwise, it will take advantage of the linker and optimize
6450 away the linking with the shared version of @file{libgcc}, linking with
6451 the static version of libgcc by default. This allows exceptions to
6452 propagate through such shared libraries, without incurring relocation
6453 costs at library load time.
6455 However, if a library or main executable is supposed to throw or catch
6456 exceptions, you must link it using the G++ or GCJ driver, as appropriate
6457 for the languages used in the program, or using the option
6458 @option{-shared-libgcc}, such that it is linked with the shared
6463 Bind references to global symbols when building a shared object. Warn
6464 about any unresolved references (unless overridden by the link editor
6465 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
6468 @item -Xlinker @var{option}
6470 Pass @var{option} as an option to the linker. You can use this to
6471 supply system-specific linker options which GCC does not know how to
6474 If you want to pass an option that takes an argument, you must use
6475 @option{-Xlinker} twice, once for the option and once for the argument.
6476 For example, to pass @option{-assert definitions}, you must write
6477 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
6478 @option{-Xlinker "-assert definitions"}, because this passes the entire
6479 string as a single argument, which is not what the linker expects.
6481 @item -Wl,@var{option}
6483 Pass @var{option} as an option to the linker. If @var{option} contains
6484 commas, it is split into multiple options at the commas.
6486 @item -u @var{symbol}
6488 Pretend the symbol @var{symbol} is undefined, to force linking of
6489 library modules to define it. You can use @option{-u} multiple times with
6490 different symbols to force loading of additional library modules.
6493 @node Directory Options
6494 @section Options for Directory Search
6495 @cindex directory options
6496 @cindex options, directory search
6499 These options specify directories to search for header files, for
6500 libraries and for parts of the compiler:
6505 Add the directory @var{dir} to the head of the list of directories to be
6506 searched for header files. This can be used to override a system header
6507 file, substituting your own version, since these directories are
6508 searched before the system header file directories. However, you should
6509 not use this option to add directories that contain vendor-supplied
6510 system header files (use @option{-isystem} for that). If you use more than
6511 one @option{-I} option, the directories are scanned in left-to-right
6512 order; the standard system directories come after.
6514 If a standard system include directory, or a directory specified with
6515 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
6516 option will be ignored. The directory will still be searched but as a
6517 system directory at its normal position in the system include chain.
6518 This is to ensure that GCC's procedure to fix buggy system headers and
6519 the ordering for the include_next directive are not inadvertently changed.
6520 If you really need to change the search order for system directories,
6521 use the @option{-nostdinc} and/or @option{-isystem} options.
6523 @item -iquote@var{dir}
6525 Add the directory @var{dir} to the head of the list of directories to
6526 be searched for header files only for the case of @samp{#include
6527 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
6528 otherwise just like @option{-I}.
6532 Add directory @var{dir} to the list of directories to be searched
6535 @item -B@var{prefix}
6537 This option specifies where to find the executables, libraries,
6538 include files, and data files of the compiler itself.
6540 The compiler driver program runs one or more of the subprograms
6541 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
6542 @var{prefix} as a prefix for each program it tries to run, both with and
6543 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
6545 For each subprogram to be run, the compiler driver first tries the
6546 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
6547 was not specified, the driver tries two standard prefixes, which are
6548 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
6549 those results in a file name that is found, the unmodified program
6550 name is searched for using the directories specified in your
6551 @env{PATH} environment variable.
6553 The compiler will check to see if the path provided by the @option{-B}
6554 refers to a directory, and if necessary it will add a directory
6555 separator character at the end of the path.
6557 @option{-B} prefixes that effectively specify directory names also apply
6558 to libraries in the linker, because the compiler translates these
6559 options into @option{-L} options for the linker. They also apply to
6560 includes files in the preprocessor, because the compiler translates these
6561 options into @option{-isystem} options for the preprocessor. In this case,
6562 the compiler appends @samp{include} to the prefix.
6564 The run-time support file @file{libgcc.a} can also be searched for using
6565 the @option{-B} prefix, if needed. If it is not found there, the two
6566 standard prefixes above are tried, and that is all. The file is left
6567 out of the link if it is not found by those means.
6569 Another way to specify a prefix much like the @option{-B} prefix is to use
6570 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
6573 As a special kludge, if the path provided by @option{-B} is
6574 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
6575 9, then it will be replaced by @file{[dir/]include}. This is to help
6576 with boot-strapping the compiler.
6578 @item -specs=@var{file}
6580 Process @var{file} after the compiler reads in the standard @file{specs}
6581 file, in order to override the defaults that the @file{gcc} driver
6582 program uses when determining what switches to pass to @file{cc1},
6583 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
6584 @option{-specs=@var{file}} can be specified on the command line, and they
6585 are processed in order, from left to right.
6587 @item --sysroot=@var{dir}
6589 Use @var{dir} as the logical root directory for headers and libraries.
6590 For example, if the compiler would normally search for headers in
6591 @file{/usr/include} and libraries in @file{/usr/lib}, it will instead
6592 search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
6594 If you use both this option and the @option{-isysroot} option, then
6595 the @option{--sysroot} option will apply to libraries, but the
6596 @option{-isysroot} option will apply to header files.
6598 The GNU linker (beginning with version 2.16) has the necessary support
6599 for this option. If your linker does not support this option, the
6600 header file aspect of @option{--sysroot} will still work, but the
6601 library aspect will not.
6605 This option has been deprecated. Please use @option{-iquote} instead for
6606 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
6607 Any directories you specify with @option{-I} options before the @option{-I-}
6608 option are searched only for the case of @samp{#include "@var{file}"};
6609 they are not searched for @samp{#include <@var{file}>}.
6611 If additional directories are specified with @option{-I} options after
6612 the @option{-I-}, these directories are searched for all @samp{#include}
6613 directives. (Ordinarily @emph{all} @option{-I} directories are used
6616 In addition, the @option{-I-} option inhibits the use of the current
6617 directory (where the current input file came from) as the first search
6618 directory for @samp{#include "@var{file}"}. There is no way to
6619 override this effect of @option{-I-}. With @option{-I.} you can specify
6620 searching the directory which was current when the compiler was
6621 invoked. That is not exactly the same as what the preprocessor does
6622 by default, but it is often satisfactory.
6624 @option{-I-} does not inhibit the use of the standard system directories
6625 for header files. Thus, @option{-I-} and @option{-nostdinc} are
6632 @section Specifying subprocesses and the switches to pass to them
6635 @command{gcc} is a driver program. It performs its job by invoking a
6636 sequence of other programs to do the work of compiling, assembling and
6637 linking. GCC interprets its command-line parameters and uses these to
6638 deduce which programs it should invoke, and which command-line options
6639 it ought to place on their command lines. This behavior is controlled
6640 by @dfn{spec strings}. In most cases there is one spec string for each
6641 program that GCC can invoke, but a few programs have multiple spec
6642 strings to control their behavior. The spec strings built into GCC can
6643 be overridden by using the @option{-specs=} command-line switch to specify
6646 @dfn{Spec files} are plaintext files that are used to construct spec
6647 strings. They consist of a sequence of directives separated by blank
6648 lines. The type of directive is determined by the first non-whitespace
6649 character on the line and it can be one of the following:
6652 @item %@var{command}
6653 Issues a @var{command} to the spec file processor. The commands that can
6657 @item %include <@var{file}>
6659 Search for @var{file} and insert its text at the current point in the
6662 @item %include_noerr <@var{file}>
6663 @cindex %include_noerr
6664 Just like @samp{%include}, but do not generate an error message if the include
6665 file cannot be found.
6667 @item %rename @var{old_name} @var{new_name}
6669 Rename the spec string @var{old_name} to @var{new_name}.
6673 @item *[@var{spec_name}]:
6674 This tells the compiler to create, override or delete the named spec
6675 string. All lines after this directive up to the next directive or
6676 blank line are considered to be the text for the spec string. If this
6677 results in an empty string then the spec will be deleted. (Or, if the
6678 spec did not exist, then nothing will happened.) Otherwise, if the spec
6679 does not currently exist a new spec will be created. If the spec does
6680 exist then its contents will be overridden by the text of this
6681 directive, unless the first character of that text is the @samp{+}
6682 character, in which case the text will be appended to the spec.
6684 @item [@var{suffix}]:
6685 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
6686 and up to the next directive or blank line are considered to make up the
6687 spec string for the indicated suffix. When the compiler encounters an
6688 input file with the named suffix, it will processes the spec string in
6689 order to work out how to compile that file. For example:
6696 This says that any input file whose name ends in @samp{.ZZ} should be
6697 passed to the program @samp{z-compile}, which should be invoked with the
6698 command-line switch @option{-input} and with the result of performing the
6699 @samp{%i} substitution. (See below.)
6701 As an alternative to providing a spec string, the text that follows a
6702 suffix directive can be one of the following:
6705 @item @@@var{language}
6706 This says that the suffix is an alias for a known @var{language}. This is
6707 similar to using the @option{-x} command-line switch to GCC to specify a
6708 language explicitly. For example:
6715 Says that .ZZ files are, in fact, C++ source files.
6718 This causes an error messages saying:
6721 @var{name} compiler not installed on this system.
6725 GCC already has an extensive list of suffixes built into it.
6726 This directive will add an entry to the end of the list of suffixes, but
6727 since the list is searched from the end backwards, it is effectively
6728 possible to override earlier entries using this technique.
6732 GCC has the following spec strings built into it. Spec files can
6733 override these strings or create their own. Note that individual
6734 targets can also add their own spec strings to this list.
6737 asm Options to pass to the assembler
6738 asm_final Options to pass to the assembler post-processor
6739 cpp Options to pass to the C preprocessor
6740 cc1 Options to pass to the C compiler
6741 cc1plus Options to pass to the C++ compiler
6742 endfile Object files to include at the end of the link
6743 link Options to pass to the linker
6744 lib Libraries to include on the command line to the linker
6745 libgcc Decides which GCC support library to pass to the linker
6746 linker Sets the name of the linker
6747 predefines Defines to be passed to the C preprocessor
6748 signed_char Defines to pass to CPP to say whether @code{char} is signed
6750 startfile Object files to include at the start of the link
6753 Here is a small example of a spec file:
6759 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
6762 This example renames the spec called @samp{lib} to @samp{old_lib} and
6763 then overrides the previous definition of @samp{lib} with a new one.
6764 The new definition adds in some extra command-line options before
6765 including the text of the old definition.
6767 @dfn{Spec strings} are a list of command-line options to be passed to their
6768 corresponding program. In addition, the spec strings can contain
6769 @samp{%}-prefixed sequences to substitute variable text or to
6770 conditionally insert text into the command line. Using these constructs
6771 it is possible to generate quite complex command lines.
6773 Here is a table of all defined @samp{%}-sequences for spec
6774 strings. Note that spaces are not generated automatically around the
6775 results of expanding these sequences. Therefore you can concatenate them
6776 together or combine them with constant text in a single argument.
6780 Substitute one @samp{%} into the program name or argument.
6783 Substitute the name of the input file being processed.
6786 Substitute the basename of the input file being processed.
6787 This is the substring up to (and not including) the last period
6788 and not including the directory.
6791 This is the same as @samp{%b}, but include the file suffix (text after
6795 Marks the argument containing or following the @samp{%d} as a
6796 temporary file name, so that that file will be deleted if GCC exits
6797 successfully. Unlike @samp{%g}, this contributes no text to the
6800 @item %g@var{suffix}
6801 Substitute a file name that has suffix @var{suffix} and is chosen
6802 once per compilation, and mark the argument in the same way as
6803 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
6804 name is now chosen in a way that is hard to predict even when previously
6805 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
6806 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
6807 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
6808 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
6809 was simply substituted with a file name chosen once per compilation,
6810 without regard to any appended suffix (which was therefore treated
6811 just like ordinary text), making such attacks more likely to succeed.
6813 @item %u@var{suffix}
6814 Like @samp{%g}, but generates a new temporary file name even if
6815 @samp{%u@var{suffix}} was already seen.
6817 @item %U@var{suffix}
6818 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
6819 new one if there is no such last file name. In the absence of any
6820 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
6821 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
6822 would involve the generation of two distinct file names, one
6823 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
6824 simply substituted with a file name chosen for the previous @samp{%u},
6825 without regard to any appended suffix.
6827 @item %j@var{suffix}
6828 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
6829 writable, and if save-temps is off; otherwise, substitute the name
6830 of a temporary file, just like @samp{%u}. This temporary file is not
6831 meant for communication between processes, but rather as a junk
6834 @item %|@var{suffix}
6835 @itemx %m@var{suffix}
6836 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
6837 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
6838 all. These are the two most common ways to instruct a program that it
6839 should read from standard input or write to standard output. If you
6840 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
6841 construct: see for example @file{f/lang-specs.h}.
6843 @item %.@var{SUFFIX}
6844 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
6845 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
6846 terminated by the next space or %.
6849 Marks the argument containing or following the @samp{%w} as the
6850 designated output file of this compilation. This puts the argument
6851 into the sequence of arguments that @samp{%o} will substitute later.
6854 Substitutes the names of all the output files, with spaces
6855 automatically placed around them. You should write spaces
6856 around the @samp{%o} as well or the results are undefined.
6857 @samp{%o} is for use in the specs for running the linker.
6858 Input files whose names have no recognized suffix are not compiled
6859 at all, but they are included among the output files, so they will
6863 Substitutes the suffix for object files. Note that this is
6864 handled specially when it immediately follows @samp{%g, %u, or %U},
6865 because of the need for those to form complete file names. The
6866 handling is such that @samp{%O} is treated exactly as if it had already
6867 been substituted, except that @samp{%g, %u, and %U} do not currently
6868 support additional @var{suffix} characters following @samp{%O} as they would
6869 following, for example, @samp{.o}.
6872 Substitutes the standard macro predefinitions for the
6873 current target machine. Use this when running @code{cpp}.
6876 Like @samp{%p}, but puts @samp{__} before and after the name of each
6877 predefined macro, except for macros that start with @samp{__} or with
6878 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
6882 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
6883 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
6884 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
6885 and @option{-imultilib} as necessary.
6888 Current argument is the name of a library or startup file of some sort.
6889 Search for that file in a standard list of directories and substitute
6890 the full name found.
6893 Print @var{str} as an error message. @var{str} is terminated by a newline.
6894 Use this when inconsistent options are detected.
6897 Substitute the contents of spec string @var{name} at this point.
6900 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
6902 @item %x@{@var{option}@}
6903 Accumulate an option for @samp{%X}.
6906 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
6910 Output the accumulated assembler options specified by @option{-Wa}.
6913 Output the accumulated preprocessor options specified by @option{-Wp}.
6916 Process the @code{asm} spec. This is used to compute the
6917 switches to be passed to the assembler.
6920 Process the @code{asm_final} spec. This is a spec string for
6921 passing switches to an assembler post-processor, if such a program is
6925 Process the @code{link} spec. This is the spec for computing the
6926 command line passed to the linker. Typically it will make use of the
6927 @samp{%L %G %S %D and %E} sequences.
6930 Dump out a @option{-L} option for each directory that GCC believes might
6931 contain startup files. If the target supports multilibs then the
6932 current multilib directory will be prepended to each of these paths.
6935 Process the @code{lib} spec. This is a spec string for deciding which
6936 libraries should be included on the command line to the linker.
6939 Process the @code{libgcc} spec. This is a spec string for deciding
6940 which GCC support library should be included on the command line to the linker.
6943 Process the @code{startfile} spec. This is a spec for deciding which
6944 object files should be the first ones passed to the linker. Typically
6945 this might be a file named @file{crt0.o}.
6948 Process the @code{endfile} spec. This is a spec string that specifies
6949 the last object files that will be passed to the linker.
6952 Process the @code{cpp} spec. This is used to construct the arguments
6953 to be passed to the C preprocessor.
6956 Process the @code{cc1} spec. This is used to construct the options to be
6957 passed to the actual C compiler (@samp{cc1}).
6960 Process the @code{cc1plus} spec. This is used to construct the options to be
6961 passed to the actual C++ compiler (@samp{cc1plus}).
6964 Substitute the variable part of a matched option. See below.
6965 Note that each comma in the substituted string is replaced by
6969 Remove all occurrences of @code{-S} from the command line. Note---this
6970 command is position dependent. @samp{%} commands in the spec string
6971 before this one will see @code{-S}, @samp{%} commands in the spec string
6972 after this one will not.
6974 @item %:@var{function}(@var{args})
6975 Call the named function @var{function}, passing it @var{args}.
6976 @var{args} is first processed as a nested spec string, then split
6977 into an argument vector in the usual fashion. The function returns
6978 a string which is processed as if it had appeared literally as part
6979 of the current spec.
6981 The following built-in spec functions are provided:
6984 @item @code{if-exists}
6985 The @code{if-exists} spec function takes one argument, an absolute
6986 pathname to a file. If the file exists, @code{if-exists} returns the
6987 pathname. Here is a small example of its usage:
6991 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
6994 @item @code{if-exists-else}
6995 The @code{if-exists-else} spec function is similar to the @code{if-exists}
6996 spec function, except that it takes two arguments. The first argument is
6997 an absolute pathname to a file. If the file exists, @code{if-exists-else}
6998 returns the pathname. If it does not exist, it returns the second argument.
6999 This way, @code{if-exists-else} can be used to select one file or another,
7000 based on the existence of the first. Here is a small example of its usage:
7004 crt0%O%s %:if-exists(crti%O%s) \
7005 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
7008 @item @code{replace-outfile}
7009 The @code{replace-outfile} spec function takes two arguments. It looks for the
7010 first argument in the outfiles array and replaces it with the second argument. Here
7011 is a small example of its usage:
7014 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
7020 Substitutes the @code{-S} switch, if that switch was given to GCC@.
7021 If that switch was not specified, this substitutes nothing. Note that
7022 the leading dash is omitted when specifying this option, and it is
7023 automatically inserted if the substitution is performed. Thus the spec
7024 string @samp{%@{foo@}} would match the command-line option @option{-foo}
7025 and would output the command line option @option{-foo}.
7027 @item %W@{@code{S}@}
7028 Like %@{@code{S}@} but mark last argument supplied within as a file to be
7031 @item %@{@code{S}*@}
7032 Substitutes all the switches specified to GCC whose names start
7033 with @code{-S}, but which also take an argument. This is used for
7034 switches like @option{-o}, @option{-D}, @option{-I}, etc.
7035 GCC considers @option{-o foo} as being
7036 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
7037 text, including the space. Thus two arguments would be generated.
7039 @item %@{@code{S}*&@code{T}*@}
7040 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
7041 (the order of @code{S} and @code{T} in the spec is not significant).
7042 There can be any number of ampersand-separated variables; for each the
7043 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
7045 @item %@{@code{S}:@code{X}@}
7046 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
7048 @item %@{!@code{S}:@code{X}@}
7049 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
7051 @item %@{@code{S}*:@code{X}@}
7052 Substitutes @code{X} if one or more switches whose names start with
7053 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
7054 once, no matter how many such switches appeared. However, if @code{%*}
7055 appears somewhere in @code{X}, then @code{X} will be substituted once
7056 for each matching switch, with the @code{%*} replaced by the part of
7057 that switch that matched the @code{*}.
7059 @item %@{.@code{S}:@code{X}@}
7060 Substitutes @code{X}, if processing a file with suffix @code{S}.
7062 @item %@{!.@code{S}:@code{X}@}
7063 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
7065 @item %@{@code{S}|@code{P}:@code{X}@}
7066 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
7067 This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
7068 although they have a stronger binding than the @samp{|}. If @code{%*}
7069 appears in @code{X}, all of the alternatives must be starred, and only
7070 the first matching alternative is substituted.
7072 For example, a spec string like this:
7075 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
7078 will output the following command-line options from the following input
7079 command-line options:
7084 -d fred.c -foo -baz -boggle
7085 -d jim.d -bar -baz -boggle
7088 @item %@{S:X; T:Y; :D@}
7090 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
7091 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
7092 be as many clauses as you need. This may be combined with @code{.},
7093 @code{!}, @code{|}, and @code{*} as needed.
7098 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
7099 construct may contain other nested @samp{%} constructs or spaces, or
7100 even newlines. They are processed as usual, as described above.
7101 Trailing white space in @code{X} is ignored. White space may also
7102 appear anywhere on the left side of the colon in these constructs,
7103 except between @code{.} or @code{*} and the corresponding word.
7105 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
7106 handled specifically in these constructs. If another value of
7107 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
7108 @option{-W} switch is found later in the command line, the earlier
7109 switch value is ignored, except with @{@code{S}*@} where @code{S} is
7110 just one letter, which passes all matching options.
7112 The character @samp{|} at the beginning of the predicate text is used to
7113 indicate that a command should be piped to the following command, but
7114 only if @option{-pipe} is specified.
7116 It is built into GCC which switches take arguments and which do not.
7117 (You might think it would be useful to generalize this to allow each
7118 compiler's spec to say which switches take arguments. But this cannot
7119 be done in a consistent fashion. GCC cannot even decide which input
7120 files have been specified without knowing which switches take arguments,
7121 and it must know which input files to compile in order to tell which
7124 GCC also knows implicitly that arguments starting in @option{-l} are to be
7125 treated as compiler output files, and passed to the linker in their
7126 proper position among the other output files.
7128 @c man begin OPTIONS
7130 @node Target Options
7131 @section Specifying Target Machine and Compiler Version
7132 @cindex target options
7133 @cindex cross compiling
7134 @cindex specifying machine version
7135 @cindex specifying compiler version and target machine
7136 @cindex compiler version, specifying
7137 @cindex target machine, specifying
7139 The usual way to run GCC is to run the executable called @file{gcc}, or
7140 @file{<machine>-gcc} when cross-compiling, or
7141 @file{<machine>-gcc-<version>} to run a version other than the one that
7142 was installed last. Sometimes this is inconvenient, so GCC provides
7143 options that will switch to another cross-compiler or version.
7146 @item -b @var{machine}
7148 The argument @var{machine} specifies the target machine for compilation.
7150 The value to use for @var{machine} is the same as was specified as the
7151 machine type when configuring GCC as a cross-compiler. For
7152 example, if a cross-compiler was configured with @samp{configure
7153 arm-elf}, meaning to compile for an arm processor with elf binaries,
7154 then you would specify @option{-b arm-elf} to run that cross compiler.
7155 Because there are other options beginning with @option{-b}, the
7156 configuration must contain a hyphen.
7158 @item -V @var{version}
7160 The argument @var{version} specifies which version of GCC to run.
7161 This is useful when multiple versions are installed. For example,
7162 @var{version} might be @samp{4.0}, meaning to run GCC version 4.0.
7165 The @option{-V} and @option{-b} options work by running the
7166 @file{<machine>-gcc-<version>} executable, so there's no real reason to
7167 use them if you can just run that directly.
7169 @node Submodel Options
7170 @section Hardware Models and Configurations
7171 @cindex submodel options
7172 @cindex specifying hardware config
7173 @cindex hardware models and configurations, specifying
7174 @cindex machine dependent options
7176 Earlier we discussed the standard option @option{-b} which chooses among
7177 different installed compilers for completely different target
7178 machines, such as VAX vs.@: 68000 vs.@: 80386.
7180 In addition, each of these target machine types can have its own
7181 special options, starting with @samp{-m}, to choose among various
7182 hardware models or configurations---for example, 68010 vs 68020,
7183 floating coprocessor or none. A single installed version of the
7184 compiler can compile for any model or configuration, according to the
7187 Some configurations of the compiler also support additional special
7188 options, usually for compatibility with other compilers on the same
7191 @c This list is ordered alphanumerically by subsection name.
7192 @c It should be the same order and spelling as these options are listed
7193 @c in Machine Dependent Options
7199 * Blackfin Options::
7203 * DEC Alpha Options::
7204 * DEC Alpha/VMS Options::
7208 * i386 and x86-64 Options::
7221 * RS/6000 and PowerPC Options::
7222 * S/390 and zSeries Options::
7225 * System V Options::
7226 * TMS320C3x/C4x Options::
7230 * Xstormy16 Options::
7236 @subsection ARC Options
7239 These options are defined for ARC implementations:
7244 Compile code for little endian mode. This is the default.
7248 Compile code for big endian mode.
7251 @opindex mmangle-cpu
7252 Prepend the name of the cpu to all public symbol names.
7253 In multiple-processor systems, there are many ARC variants with different
7254 instruction and register set characteristics. This flag prevents code
7255 compiled for one cpu to be linked with code compiled for another.
7256 No facility exists for handling variants that are ``almost identical''.
7257 This is an all or nothing option.
7259 @item -mcpu=@var{cpu}
7261 Compile code for ARC variant @var{cpu}.
7262 Which variants are supported depend on the configuration.
7263 All variants support @option{-mcpu=base}, this is the default.
7265 @item -mtext=@var{text-section}
7266 @itemx -mdata=@var{data-section}
7267 @itemx -mrodata=@var{readonly-data-section}
7271 Put functions, data, and readonly data in @var{text-section},
7272 @var{data-section}, and @var{readonly-data-section} respectively
7273 by default. This can be overridden with the @code{section} attribute.
7274 @xref{Variable Attributes}.
7279 @subsection ARM Options
7282 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
7286 @item -mabi=@var{name}
7288 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
7289 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
7292 @opindex mapcs-frame
7293 Generate a stack frame that is compliant with the ARM Procedure Call
7294 Standard for all functions, even if this is not strictly necessary for
7295 correct execution of the code. Specifying @option{-fomit-frame-pointer}
7296 with this option will cause the stack frames not to be generated for
7297 leaf functions. The default is @option{-mno-apcs-frame}.
7301 This is a synonym for @option{-mapcs-frame}.
7304 @c not currently implemented
7305 @item -mapcs-stack-check
7306 @opindex mapcs-stack-check
7307 Generate code to check the amount of stack space available upon entry to
7308 every function (that actually uses some stack space). If there is
7309 insufficient space available then either the function
7310 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
7311 called, depending upon the amount of stack space required. The run time
7312 system is required to provide these functions. The default is
7313 @option{-mno-apcs-stack-check}, since this produces smaller code.
7315 @c not currently implemented
7317 @opindex mapcs-float
7318 Pass floating point arguments using the float point registers. This is
7319 one of the variants of the APCS@. This option is recommended if the
7320 target hardware has a floating point unit or if a lot of floating point
7321 arithmetic is going to be performed by the code. The default is
7322 @option{-mno-apcs-float}, since integer only code is slightly increased in
7323 size if @option{-mapcs-float} is used.
7325 @c not currently implemented
7326 @item -mapcs-reentrant
7327 @opindex mapcs-reentrant
7328 Generate reentrant, position independent code. The default is
7329 @option{-mno-apcs-reentrant}.
7332 @item -mthumb-interwork
7333 @opindex mthumb-interwork
7334 Generate code which supports calling between the ARM and Thumb
7335 instruction sets. Without this option the two instruction sets cannot
7336 be reliably used inside one program. The default is
7337 @option{-mno-thumb-interwork}, since slightly larger code is generated
7338 when @option{-mthumb-interwork} is specified.
7340 @item -mno-sched-prolog
7341 @opindex mno-sched-prolog
7342 Prevent the reordering of instructions in the function prolog, or the
7343 merging of those instruction with the instructions in the function's
7344 body. This means that all functions will start with a recognizable set
7345 of instructions (or in fact one of a choice from a small set of
7346 different function prologues), and this information can be used to
7347 locate the start if functions inside an executable piece of code. The
7348 default is @option{-msched-prolog}.
7351 @opindex mhard-float
7352 Generate output containing floating point instructions. This is the
7356 @opindex msoft-float
7357 Generate output containing library calls for floating point.
7358 @strong{Warning:} the requisite libraries are not available for all ARM
7359 targets. Normally the facilities of the machine's usual C compiler are
7360 used, but this cannot be done directly in cross-compilation. You must make
7361 your own arrangements to provide suitable library functions for
7364 @option{-msoft-float} changes the calling convention in the output file;
7365 therefore, it is only useful if you compile @emph{all} of a program with
7366 this option. In particular, you need to compile @file{libgcc.a}, the
7367 library that comes with GCC, with @option{-msoft-float} in order for
7370 @item -mfloat-abi=@var{name}
7372 Specifies which ABI to use for floating point values. Permissible values
7373 are: @samp{soft}, @samp{softfp} and @samp{hard}.
7375 @samp{soft} and @samp{hard} are equivalent to @option{-msoft-float}
7376 and @option{-mhard-float} respectively. @samp{softfp} allows the generation
7377 of floating point instructions, but still uses the soft-float calling
7380 @item -mlittle-endian
7381 @opindex mlittle-endian
7382 Generate code for a processor running in little-endian mode. This is
7383 the default for all standard configurations.
7386 @opindex mbig-endian
7387 Generate code for a processor running in big-endian mode; the default is
7388 to compile code for a little-endian processor.
7390 @item -mwords-little-endian
7391 @opindex mwords-little-endian
7392 This option only applies when generating code for big-endian processors.
7393 Generate code for a little-endian word order but a big-endian byte
7394 order. That is, a byte order of the form @samp{32107654}. Note: this
7395 option should only be used if you require compatibility with code for
7396 big-endian ARM processors generated by versions of the compiler prior to
7399 @item -mcpu=@var{name}
7401 This specifies the name of the target ARM processor. GCC uses this name
7402 to determine what kind of instructions it can emit when generating
7403 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
7404 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
7405 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
7406 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
7407 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
7408 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
7409 @samp{arm8}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
7410 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
7411 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
7412 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
7413 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
7414 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
7415 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
7416 @samp{arm1176jz-s}, @samp{arm1176jzf-s}, @samp{xscale}, @samp{iwmmxt},
7419 @itemx -mtune=@var{name}
7421 This option is very similar to the @option{-mcpu=} option, except that
7422 instead of specifying the actual target processor type, and hence
7423 restricting which instructions can be used, it specifies that GCC should
7424 tune the performance of the code as if the target were of the type
7425 specified in this option, but still choosing the instructions that it
7426 will generate based on the cpu specified by a @option{-mcpu=} option.
7427 For some ARM implementations better performance can be obtained by using
7430 @item -march=@var{name}
7432 This specifies the name of the target ARM architecture. GCC uses this
7433 name to determine what kind of instructions it can emit when generating
7434 assembly code. This option can be used in conjunction with or instead
7435 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
7436 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
7437 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6}, @samp{armv6j},
7438 @samp{iwmmxt}, @samp{ep9312}.
7440 @item -mfpu=@var{name}
7441 @itemx -mfpe=@var{number}
7442 @itemx -mfp=@var{number}
7446 This specifies what floating point hardware (or hardware emulation) is
7447 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
7448 @samp{fpe3}, @samp{maverick}, @samp{vfp}. @option{-mfp} and @option{-mfpe}
7449 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
7450 with older versions of GCC@.
7452 If @option{-msoft-float} is specified this specifies the format of
7453 floating point values.
7455 @item -mstructure-size-boundary=@var{n}
7456 @opindex mstructure-size-boundary
7457 The size of all structures and unions will be rounded up to a multiple
7458 of the number of bits set by this option. Permissible values are 8, 32
7459 and 64. The default value varies for different toolchains. For the COFF
7460 targeted toolchain the default value is 8. A value of 64 is only allowed
7461 if the underlying ABI supports it.
7463 Specifying the larger number can produce faster, more efficient code, but
7464 can also increase the size of the program. Different values are potentially
7465 incompatible. Code compiled with one value cannot necessarily expect to
7466 work with code or libraries compiled with another value, if they exchange
7467 information using structures or unions.
7469 @item -mabort-on-noreturn
7470 @opindex mabort-on-noreturn
7471 Generate a call to the function @code{abort} at the end of a
7472 @code{noreturn} function. It will be executed if the function tries to
7476 @itemx -mno-long-calls
7477 @opindex mlong-calls
7478 @opindex mno-long-calls
7479 Tells the compiler to perform function calls by first loading the
7480 address of the function into a register and then performing a subroutine
7481 call on this register. This switch is needed if the target function
7482 will lie outside of the 64 megabyte addressing range of the offset based
7483 version of subroutine call instruction.
7485 Even if this switch is enabled, not all function calls will be turned
7486 into long calls. The heuristic is that static functions, functions
7487 which have the @samp{short-call} attribute, functions that are inside
7488 the scope of a @samp{#pragma no_long_calls} directive and functions whose
7489 definitions have already been compiled within the current compilation
7490 unit, will not be turned into long calls. The exception to this rule is
7491 that weak function definitions, functions with the @samp{long-call}
7492 attribute or the @samp{section} attribute, and functions that are within
7493 the scope of a @samp{#pragma long_calls} directive, will always be
7494 turned into long calls.
7496 This feature is not enabled by default. Specifying
7497 @option{-mno-long-calls} will restore the default behavior, as will
7498 placing the function calls within the scope of a @samp{#pragma
7499 long_calls_off} directive. Note these switches have no effect on how
7500 the compiler generates code to handle function calls via function
7503 @item -mnop-fun-dllimport
7504 @opindex mnop-fun-dllimport
7505 Disable support for the @code{dllimport} attribute.
7507 @item -msingle-pic-base
7508 @opindex msingle-pic-base
7509 Treat the register used for PIC addressing as read-only, rather than
7510 loading it in the prologue for each function. The run-time system is
7511 responsible for initializing this register with an appropriate value
7512 before execution begins.
7514 @item -mpic-register=@var{reg}
7515 @opindex mpic-register
7516 Specify the register to be used for PIC addressing. The default is R10
7517 unless stack-checking is enabled, when R9 is used.
7519 @item -mcirrus-fix-invalid-insns
7520 @opindex mcirrus-fix-invalid-insns
7521 @opindex mno-cirrus-fix-invalid-insns
7522 Insert NOPs into the instruction stream to in order to work around
7523 problems with invalid Maverick instruction combinations. This option
7524 is only valid if the @option{-mcpu=ep9312} option has been used to
7525 enable generation of instructions for the Cirrus Maverick floating
7526 point co-processor. This option is not enabled by default, since the
7527 problem is only present in older Maverick implementations. The default
7528 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
7531 @item -mpoke-function-name
7532 @opindex mpoke-function-name
7533 Write the name of each function into the text section, directly
7534 preceding the function prologue. The generated code is similar to this:
7538 .ascii "arm_poke_function_name", 0
7541 .word 0xff000000 + (t1 - t0)
7542 arm_poke_function_name
7544 stmfd sp!, @{fp, ip, lr, pc@}
7548 When performing a stack backtrace, code can inspect the value of
7549 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
7550 location @code{pc - 12} and the top 8 bits are set, then we know that
7551 there is a function name embedded immediately preceding this location
7552 and has length @code{((pc[-3]) & 0xff000000)}.
7556 Generate code for the 16-bit Thumb instruction set. The default is to
7557 use the 32-bit ARM instruction set.
7560 @opindex mtpcs-frame
7561 Generate a stack frame that is compliant with the Thumb Procedure Call
7562 Standard for all non-leaf functions. (A leaf function is one that does
7563 not call any other functions.) The default is @option{-mno-tpcs-frame}.
7565 @item -mtpcs-leaf-frame
7566 @opindex mtpcs-leaf-frame
7567 Generate a stack frame that is compliant with the Thumb Procedure Call
7568 Standard for all leaf functions. (A leaf function is one that does
7569 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
7571 @item -mcallee-super-interworking
7572 @opindex mcallee-super-interworking
7573 Gives all externally visible functions in the file being compiled an ARM
7574 instruction set header which switches to Thumb mode before executing the
7575 rest of the function. This allows these functions to be called from
7576 non-interworking code.
7578 @item -mcaller-super-interworking
7579 @opindex mcaller-super-interworking
7580 Allows calls via function pointers (including virtual functions) to
7581 execute correctly regardless of whether the target code has been
7582 compiled for interworking or not. There is a small overhead in the cost
7583 of executing a function pointer if this option is enabled.
7585 @item -mtp=@var{name}
7587 Specify the access model for the thread local storage pointer. The valid
7588 models are @option{soft}, which generates calls to @code{__aeabi_read_tp},
7589 @option{cp15}, which fetches the thread pointer from @code{cp15} directly
7590 (supported in the arm6k architecture), and @option{auto}, which uses the
7591 best available method for the selected processor. The default setting is
7597 @subsection AVR Options
7600 These options are defined for AVR implementations:
7603 @item -mmcu=@var{mcu}
7605 Specify ATMEL AVR instruction set or MCU type.
7607 Instruction set avr1 is for the minimal AVR core, not supported by the C
7608 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
7609 attiny11, attiny12, attiny15, attiny28).
7611 Instruction set avr2 (default) is for the classic AVR core with up to
7612 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
7613 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
7614 at90c8534, at90s8535).
7616 Instruction set avr3 is for the classic AVR core with up to 128K program
7617 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
7619 Instruction set avr4 is for the enhanced AVR core with up to 8K program
7620 memory space (MCU types: atmega8, atmega83, atmega85).
7622 Instruction set avr5 is for the enhanced AVR core with up to 128K program
7623 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
7624 atmega64, atmega128, at43usb355, at94k).
7628 Output instruction sizes to the asm file.
7630 @item -minit-stack=@var{N}
7631 @opindex minit-stack
7632 Specify the initial stack address, which may be a symbol or numeric value,
7633 @samp{__stack} is the default.
7635 @item -mno-interrupts
7636 @opindex mno-interrupts
7637 Generated code is not compatible with hardware interrupts.
7638 Code size will be smaller.
7640 @item -mcall-prologues
7641 @opindex mcall-prologues
7642 Functions prologues/epilogues expanded as call to appropriate
7643 subroutines. Code size will be smaller.
7645 @item -mno-tablejump
7646 @opindex mno-tablejump
7647 Do not generate tablejump insns which sometimes increase code size.
7650 @opindex mtiny-stack
7651 Change only the low 8 bits of the stack pointer.
7655 Assume int to be 8 bit integer. This affects the sizes of all types: A
7656 char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
7657 and long long will be 4 bytes. Please note that this option does not
7658 comply to the C standards, but it will provide you with smaller code
7662 @node Blackfin Options
7663 @subsection Blackfin Options
7664 @cindex Blackfin Options
7667 @item -momit-leaf-frame-pointer
7668 @opindex momit-leaf-frame-pointer
7669 Don't keep the frame pointer in a register for leaf functions. This
7670 avoids the instructions to save, set up and restore frame pointers and
7671 makes an extra register available in leaf functions. The option
7672 @option{-fomit-frame-pointer} removes the frame pointer for all functions
7673 which might make debugging harder.
7675 @item -mspecld-anomaly
7676 @opindex mspecld-anomaly
7677 When enabled, the compiler will ensure that the generated code does not
7678 contain speculative loads after jump instructions. This option is enabled
7681 @item -mno-specld-anomaly
7682 @opindex mno-specld-anomaly
7683 Don't generate extra code to prevent speculative loads from occurring.
7685 @item -mcsync-anomaly
7686 @opindex mcsync-anomaly
7687 When enabled, the compiler will ensure that the generated code does not
7688 contain CSYNC or SSYNC instructions too soon after conditional branches.
7689 This option is enabled by default.
7691 @item -mno-csync-anomaly
7692 @opindex mno-csync-anomaly
7693 Don't generate extra code to prevent CSYNC or SSYNC instructions from
7694 occurring too soon after a conditional branch.
7698 When enabled, the compiler is free to take advantage of the knowledge that
7699 the entire program fits into the low 64k of memory.
7702 @opindex mno-low-64k
7703 Assume that the program is arbitrarily large. This is the default.
7705 @item -mid-shared-library
7706 @opindex mid-shared-library
7707 Generate code that supports shared libraries via the library ID method.
7708 This allows for execute in place and shared libraries in an environment
7709 without virtual memory management. This option implies @option{-fPIC}.
7711 @item -mno-id-shared-library
7712 @opindex mno-id-shared-library
7713 Generate code that doesn't assume ID based shared libraries are being used.
7714 This is the default.
7716 @item -mshared-library-id=n
7717 @opindex mshared-library-id
7718 Specified the identification number of the ID based shared library being
7719 compiled. Specifying a value of 0 will generate more compact code, specifying
7720 other values will force the allocation of that number to the current
7721 library but is no more space or time efficient than omitting this option.
7724 @itemx -mno-long-calls
7725 @opindex mlong-calls
7726 @opindex mno-long-calls
7727 Tells the compiler to perform function calls by first loading the
7728 address of the function into a register and then performing a subroutine
7729 call on this register. This switch is needed if the target function
7730 will lie outside of the 24 bit addressing range of the offset based
7731 version of subroutine call instruction.
7733 This feature is not enabled by default. Specifying
7734 @option{-mno-long-calls} will restore the default behavior. Note these
7735 switches have no effect on how the compiler generates code to handle
7736 function calls via function pointers.
7740 @subsection CRIS Options
7741 @cindex CRIS Options
7743 These options are defined specifically for the CRIS ports.
7746 @item -march=@var{architecture-type}
7747 @itemx -mcpu=@var{architecture-type}
7750 Generate code for the specified architecture. The choices for
7751 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
7752 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
7753 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
7756 @item -mtune=@var{architecture-type}
7758 Tune to @var{architecture-type} everything applicable about the generated
7759 code, except for the ABI and the set of available instructions. The
7760 choices for @var{architecture-type} are the same as for
7761 @option{-march=@var{architecture-type}}.
7763 @item -mmax-stack-frame=@var{n}
7764 @opindex mmax-stack-frame
7765 Warn when the stack frame of a function exceeds @var{n} bytes.
7767 @item -melinux-stacksize=@var{n}
7768 @opindex melinux-stacksize
7769 Only available with the @samp{cris-axis-aout} target. Arranges for
7770 indications in the program to the kernel loader that the stack of the
7771 program should be set to @var{n} bytes.
7777 The options @option{-metrax4} and @option{-metrax100} are synonyms for
7778 @option{-march=v3} and @option{-march=v8} respectively.
7780 @item -mmul-bug-workaround
7781 @itemx -mno-mul-bug-workaround
7782 @opindex mmul-bug-workaround
7783 @opindex mno-mul-bug-workaround
7784 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
7785 models where it applies. This option is active by default.
7789 Enable CRIS-specific verbose debug-related information in the assembly
7790 code. This option also has the effect to turn off the @samp{#NO_APP}
7791 formatted-code indicator to the assembler at the beginning of the
7796 Do not use condition-code results from previous instruction; always emit
7797 compare and test instructions before use of condition codes.
7799 @item -mno-side-effects
7800 @opindex mno-side-effects
7801 Do not emit instructions with side-effects in addressing modes other than
7805 @itemx -mno-stack-align
7807 @itemx -mno-data-align
7808 @itemx -mconst-align
7809 @itemx -mno-const-align
7810 @opindex mstack-align
7811 @opindex mno-stack-align
7812 @opindex mdata-align
7813 @opindex mno-data-align
7814 @opindex mconst-align
7815 @opindex mno-const-align
7816 These options (no-options) arranges (eliminate arrangements) for the
7817 stack-frame, individual data and constants to be aligned for the maximum
7818 single data access size for the chosen CPU model. The default is to
7819 arrange for 32-bit alignment. ABI details such as structure layout are
7820 not affected by these options.
7828 Similar to the stack- data- and const-align options above, these options
7829 arrange for stack-frame, writable data and constants to all be 32-bit,
7830 16-bit or 8-bit aligned. The default is 32-bit alignment.
7832 @item -mno-prologue-epilogue
7833 @itemx -mprologue-epilogue
7834 @opindex mno-prologue-epilogue
7835 @opindex mprologue-epilogue
7836 With @option{-mno-prologue-epilogue}, the normal function prologue and
7837 epilogue that sets up the stack-frame are omitted and no return
7838 instructions or return sequences are generated in the code. Use this
7839 option only together with visual inspection of the compiled code: no
7840 warnings or errors are generated when call-saved registers must be saved,
7841 or storage for local variable needs to be allocated.
7847 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
7848 instruction sequences that load addresses for functions from the PLT part
7849 of the GOT rather than (traditional on other architectures) calls to the
7850 PLT@. The default is @option{-mgotplt}.
7854 Legacy no-op option only recognized with the cris-axis-aout target.
7858 Legacy no-op option only recognized with the cris-axis-elf and
7859 cris-axis-linux-gnu targets.
7863 Only recognized with the cris-axis-aout target, where it selects a
7864 GNU/linux-like multilib, include files and instruction set for
7869 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
7873 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
7874 to link with input-output functions from a simulator library. Code,
7875 initialized data and zero-initialized data are allocated consecutively.
7879 Like @option{-sim}, but pass linker options to locate initialized data at
7880 0x40000000 and zero-initialized data at 0x80000000.
7884 @subsection CRX Options
7887 These options are defined specifically for the CRX ports.
7893 Enable the use of multiply-accumulate instructions. Disabled by default.
7897 Push instructions will be used to pass outgoing arguments when functions
7898 are called. Enabled by default.
7901 @node Darwin Options
7902 @subsection Darwin Options
7903 @cindex Darwin options
7905 These options are defined for all architectures running the Darwin operating
7908 FSF GCC on Darwin does not create ``fat'' object files; it will create
7909 an object file for the single architecture that it was built to
7910 target. Apple's GCC on Darwin does create ``fat'' files if multiple
7911 @option{-arch} options are used; it does so by running the compiler or
7912 linker multiple times and joining the results together with
7915 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
7916 @samp{i686}) is determined by the flags that specify the ISA
7917 that GCC is targetting, like @option{-mcpu} or @option{-march}. The
7918 @option{-force_cpusubtype_ALL} option can be used to override this.
7920 The Darwin tools vary in their behavior when presented with an ISA
7921 mismatch. The assembler, @file{as}, will only permit instructions to
7922 be used that are valid for the subtype of the file it is generating,
7923 so you cannot put 64-bit instructions in an @samp{ppc750} object file.
7924 The linker for shared libraries, @file{/usr/bin/libtool}, will fail
7925 and print an error if asked to create a shared library with a less
7926 restrictive subtype than its input files (for instance, trying to put
7927 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
7928 for executables, @file{ld}, will quietly give the executable the most
7929 restrictive subtype of any of its input files.
7934 Add the framework directory @var{dir} to the head of the list of
7935 directories to be searched for header files. These directories are
7936 interleaved with those specified by @option{-I} options and are
7937 scanned in a left-to-right order.
7939 A framework directory is a directory with frameworks in it. A
7940 framework is a directory with a @samp{"Headers"} and/or
7941 @samp{"PrivateHeaders"} directory contained directly in it that ends
7942 in @samp{".framework"}. The name of a framework is the name of this
7943 directory excluding the @samp{".framework"}. Headers associated with
7944 the framework are found in one of those two directories, with
7945 @samp{"Headers"} being searched first. A subframework is a framework
7946 directory that is in a framework's @samp{"Frameworks"} directory.
7947 Includes of subframework headers can only appear in a header of a
7948 framework that contains the subframework, or in a sibling subframework
7949 header. Two subframeworks are siblings if they occur in the same
7950 framework. A subframework should not have the same name as a
7951 framework, a warning will be issued if this is violated. Currently a
7952 subframework cannot have subframeworks, in the future, the mechanism
7953 may be extended to support this. The standard frameworks can be found
7954 in @samp{"/System/Library/Frameworks"} and
7955 @samp{"/Library/Frameworks"}. An example include looks like
7956 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
7957 the name of the framework and header.h is found in the
7958 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
7962 Emit debugging information for symbols that are used. For STABS
7963 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
7964 This is by default ON@.
7968 Emit debugging information for all symbols and types.
7970 @item -mmacosx-version-min=@var{version}
7971 The earliest version of MacOS X that this executable will run on
7972 is @var{version}. Typical values of @var{version} include @code{10.1},
7973 @code{10.2}, and @code{10.3.9}.
7975 The default for this option is to make choices that seem to be most
7978 @item -mone-byte-bool
7979 @opindex -mone-byte-bool
7980 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
7981 By default @samp{sizeof(bool)} is @samp{4} when compiling for
7982 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
7983 option has no effect on x86.
7985 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
7986 to generate code that is not binary compatible with code generated
7987 without that switch. Using this switch may require recompiling all
7988 other modules in a program, including system libraries. Use this
7989 switch to conform to a non-default data model.
7991 @item -mfix-and-continue
7992 @itemx -ffix-and-continue
7993 @itemx -findirect-data
7994 @opindex mfix-and-continue
7995 @opindex ffix-and-continue
7996 @opindex findirect-data
7997 Generate code suitable for fast turn around development. Needed to
7998 enable gdb to dynamically load @code{.o} files into already running
7999 programs. @option{-findirect-data} and @option{-ffix-and-continue}
8000 are provided for backwards compatibility.
8004 Loads all members of static archive libraries.
8005 See man ld(1) for more information.
8007 @item -arch_errors_fatal
8008 @opindex arch_errors_fatal
8009 Cause the errors having to do with files that have the wrong architecture
8013 @opindex bind_at_load
8014 Causes the output file to be marked such that the dynamic linker will
8015 bind all undefined references when the file is loaded or launched.
8019 Produce a Mach-o bundle format file.
8020 See man ld(1) for more information.
8022 @item -bundle_loader @var{executable}
8023 @opindex bundle_loader
8024 This option specifies the @var{executable} that will be loading the build
8025 output file being linked. See man ld(1) for more information.
8028 @opindex -dynamiclib
8029 When passed this option, GCC will produce a dynamic library instead of
8030 an executable when linking, using the Darwin @file{libtool} command.
8032 @item -force_cpusubtype_ALL
8033 @opindex -force_cpusubtype_ALL
8034 This causes GCC's output file to have the @var{ALL} subtype, instead of
8035 one controlled by the @option{-mcpu} or @option{-march} option.
8037 @item -allowable_client @var{client_name}
8039 @itemx -compatibility_version
8040 @itemx -current_version
8042 @itemx -dependency-file
8044 @itemx -dylinker_install_name
8046 @itemx -exported_symbols_list
8048 @itemx -flat_namespace
8049 @itemx -force_flat_namespace
8050 @itemx -headerpad_max_install_names
8053 @itemx -install_name
8054 @itemx -keep_private_externs
8055 @itemx -multi_module
8056 @itemx -multiply_defined
8057 @itemx -multiply_defined_unused
8059 @itemx -no_dead_strip_inits_and_terms
8060 @itemx -nofixprebinding
8063 @itemx -noseglinkedit
8064 @itemx -pagezero_size
8066 @itemx -prebind_all_twolevel_modules
8067 @itemx -private_bundle
8068 @itemx -read_only_relocs
8070 @itemx -sectobjectsymbols
8074 @itemx -sectobjectsymbols
8077 @itemx -segs_read_only_addr
8078 @itemx -segs_read_write_addr
8079 @itemx -seg_addr_table
8080 @itemx -seg_addr_table_filename
8083 @itemx -segs_read_only_addr
8084 @itemx -segs_read_write_addr
8085 @itemx -single_module
8088 @itemx -sub_umbrella
8089 @itemx -twolevel_namespace
8092 @itemx -unexported_symbols_list
8093 @itemx -weak_reference_mismatches
8096 @opindex allowable_client
8097 @opindex client_name
8098 @opindex compatibility_version
8099 @opindex current_version
8101 @opindex dependency-file
8103 @opindex dylinker_install_name
8105 @opindex exported_symbols_list
8107 @opindex flat_namespace
8108 @opindex force_flat_namespace
8109 @opindex headerpad_max_install_names
8112 @opindex install_name
8113 @opindex keep_private_externs
8114 @opindex multi_module
8115 @opindex multiply_defined
8116 @opindex multiply_defined_unused
8118 @opindex no_dead_strip_inits_and_terms
8119 @opindex nofixprebinding
8120 @opindex nomultidefs
8122 @opindex noseglinkedit
8123 @opindex pagezero_size
8125 @opindex prebind_all_twolevel_modules
8126 @opindex private_bundle
8127 @opindex read_only_relocs
8129 @opindex sectobjectsymbols
8133 @opindex sectobjectsymbols
8136 @opindex segs_read_only_addr
8137 @opindex segs_read_write_addr
8138 @opindex seg_addr_table
8139 @opindex seg_addr_table_filename
8140 @opindex seglinkedit
8142 @opindex segs_read_only_addr
8143 @opindex segs_read_write_addr
8144 @opindex single_module
8146 @opindex sub_library
8147 @opindex sub_umbrella
8148 @opindex twolevel_namespace
8151 @opindex unexported_symbols_list
8152 @opindex weak_reference_mismatches
8153 @opindex whatsloaded
8155 These options are passed to the Darwin linker. The Darwin linker man page
8156 describes them in detail.
8159 @node DEC Alpha Options
8160 @subsection DEC Alpha Options
8162 These @samp{-m} options are defined for the DEC Alpha implementations:
8165 @item -mno-soft-float
8167 @opindex mno-soft-float
8168 @opindex msoft-float
8169 Use (do not use) the hardware floating-point instructions for
8170 floating-point operations. When @option{-msoft-float} is specified,
8171 functions in @file{libgcc.a} will be used to perform floating-point
8172 operations. Unless they are replaced by routines that emulate the
8173 floating-point operations, or compiled in such a way as to call such
8174 emulations routines, these routines will issue floating-point
8175 operations. If you are compiling for an Alpha without floating-point
8176 operations, you must ensure that the library is built so as not to call
8179 Note that Alpha implementations without floating-point operations are
8180 required to have floating-point registers.
8185 @opindex mno-fp-regs
8186 Generate code that uses (does not use) the floating-point register set.
8187 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
8188 register set is not used, floating point operands are passed in integer
8189 registers as if they were integers and floating-point results are passed
8190 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
8191 so any function with a floating-point argument or return value called by code
8192 compiled with @option{-mno-fp-regs} must also be compiled with that
8195 A typical use of this option is building a kernel that does not use,
8196 and hence need not save and restore, any floating-point registers.
8200 The Alpha architecture implements floating-point hardware optimized for
8201 maximum performance. It is mostly compliant with the IEEE floating
8202 point standard. However, for full compliance, software assistance is
8203 required. This option generates code fully IEEE compliant code
8204 @emph{except} that the @var{inexact-flag} is not maintained (see below).
8205 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
8206 defined during compilation. The resulting code is less efficient but is
8207 able to correctly support denormalized numbers and exceptional IEEE
8208 values such as not-a-number and plus/minus infinity. Other Alpha
8209 compilers call this option @option{-ieee_with_no_inexact}.
8211 @item -mieee-with-inexact
8212 @opindex mieee-with-inexact
8213 This is like @option{-mieee} except the generated code also maintains
8214 the IEEE @var{inexact-flag}. Turning on this option causes the
8215 generated code to implement fully-compliant IEEE math. In addition to
8216 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
8217 macro. On some Alpha implementations the resulting code may execute
8218 significantly slower than the code generated by default. Since there is
8219 very little code that depends on the @var{inexact-flag}, you should
8220 normally not specify this option. Other Alpha compilers call this
8221 option @option{-ieee_with_inexact}.
8223 @item -mfp-trap-mode=@var{trap-mode}
8224 @opindex mfp-trap-mode
8225 This option controls what floating-point related traps are enabled.
8226 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
8227 The trap mode can be set to one of four values:
8231 This is the default (normal) setting. The only traps that are enabled
8232 are the ones that cannot be disabled in software (e.g., division by zero
8236 In addition to the traps enabled by @samp{n}, underflow traps are enabled
8240 Like @samp{su}, but the instructions are marked to be safe for software
8241 completion (see Alpha architecture manual for details).
8244 Like @samp{su}, but inexact traps are enabled as well.
8247 @item -mfp-rounding-mode=@var{rounding-mode}
8248 @opindex mfp-rounding-mode
8249 Selects the IEEE rounding mode. Other Alpha compilers call this option
8250 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
8255 Normal IEEE rounding mode. Floating point numbers are rounded towards
8256 the nearest machine number or towards the even machine number in case
8260 Round towards minus infinity.
8263 Chopped rounding mode. Floating point numbers are rounded towards zero.
8266 Dynamic rounding mode. A field in the floating point control register
8267 (@var{fpcr}, see Alpha architecture reference manual) controls the
8268 rounding mode in effect. The C library initializes this register for
8269 rounding towards plus infinity. Thus, unless your program modifies the
8270 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
8273 @item -mtrap-precision=@var{trap-precision}
8274 @opindex mtrap-precision
8275 In the Alpha architecture, floating point traps are imprecise. This
8276 means without software assistance it is impossible to recover from a
8277 floating trap and program execution normally needs to be terminated.
8278 GCC can generate code that can assist operating system trap handlers
8279 in determining the exact location that caused a floating point trap.
8280 Depending on the requirements of an application, different levels of
8281 precisions can be selected:
8285 Program precision. This option is the default and means a trap handler
8286 can only identify which program caused a floating point exception.
8289 Function precision. The trap handler can determine the function that
8290 caused a floating point exception.
8293 Instruction precision. The trap handler can determine the exact
8294 instruction that caused a floating point exception.
8297 Other Alpha compilers provide the equivalent options called
8298 @option{-scope_safe} and @option{-resumption_safe}.
8300 @item -mieee-conformant
8301 @opindex mieee-conformant
8302 This option marks the generated code as IEEE conformant. You must not
8303 use this option unless you also specify @option{-mtrap-precision=i} and either
8304 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
8305 is to emit the line @samp{.eflag 48} in the function prologue of the
8306 generated assembly file. Under DEC Unix, this has the effect that
8307 IEEE-conformant math library routines will be linked in.
8309 @item -mbuild-constants
8310 @opindex mbuild-constants
8311 Normally GCC examines a 32- or 64-bit integer constant to
8312 see if it can construct it from smaller constants in two or three
8313 instructions. If it cannot, it will output the constant as a literal and
8314 generate code to load it from the data segment at runtime.
8316 Use this option to require GCC to construct @emph{all} integer constants
8317 using code, even if it takes more instructions (the maximum is six).
8319 You would typically use this option to build a shared library dynamic
8320 loader. Itself a shared library, it must relocate itself in memory
8321 before it can find the variables and constants in its own data segment.
8327 Select whether to generate code to be assembled by the vendor-supplied
8328 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
8346 Indicate whether GCC should generate code to use the optional BWX,
8347 CIX, FIX and MAX instruction sets. The default is to use the instruction
8348 sets supported by the CPU type specified via @option{-mcpu=} option or that
8349 of the CPU on which GCC was built if none was specified.
8354 @opindex mfloat-ieee
8355 Generate code that uses (does not use) VAX F and G floating point
8356 arithmetic instead of IEEE single and double precision.
8358 @item -mexplicit-relocs
8359 @itemx -mno-explicit-relocs
8360 @opindex mexplicit-relocs
8361 @opindex mno-explicit-relocs
8362 Older Alpha assemblers provided no way to generate symbol relocations
8363 except via assembler macros. Use of these macros does not allow
8364 optimal instruction scheduling. GNU binutils as of version 2.12
8365 supports a new syntax that allows the compiler to explicitly mark
8366 which relocations should apply to which instructions. This option
8367 is mostly useful for debugging, as GCC detects the capabilities of
8368 the assembler when it is built and sets the default accordingly.
8372 @opindex msmall-data
8373 @opindex mlarge-data
8374 When @option{-mexplicit-relocs} is in effect, static data is
8375 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
8376 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
8377 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
8378 16-bit relocations off of the @code{$gp} register. This limits the
8379 size of the small data area to 64KB, but allows the variables to be
8380 directly accessed via a single instruction.
8382 The default is @option{-mlarge-data}. With this option the data area
8383 is limited to just below 2GB@. Programs that require more than 2GB of
8384 data must use @code{malloc} or @code{mmap} to allocate the data in the
8385 heap instead of in the program's data segment.
8387 When generating code for shared libraries, @option{-fpic} implies
8388 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
8392 @opindex msmall-text
8393 @opindex mlarge-text
8394 When @option{-msmall-text} is used, the compiler assumes that the
8395 code of the entire program (or shared library) fits in 4MB, and is
8396 thus reachable with a branch instruction. When @option{-msmall-data}
8397 is used, the compiler can assume that all local symbols share the
8398 same @code{$gp} value, and thus reduce the number of instructions
8399 required for a function call from 4 to 1.
8401 The default is @option{-mlarge-text}.
8403 @item -mcpu=@var{cpu_type}
8405 Set the instruction set and instruction scheduling parameters for
8406 machine type @var{cpu_type}. You can specify either the @samp{EV}
8407 style name or the corresponding chip number. GCC supports scheduling
8408 parameters for the EV4, EV5 and EV6 family of processors and will
8409 choose the default values for the instruction set from the processor
8410 you specify. If you do not specify a processor type, GCC will default
8411 to the processor on which the compiler was built.
8413 Supported values for @var{cpu_type} are
8419 Schedules as an EV4 and has no instruction set extensions.
8423 Schedules as an EV5 and has no instruction set extensions.
8427 Schedules as an EV5 and supports the BWX extension.
8432 Schedules as an EV5 and supports the BWX and MAX extensions.
8436 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
8440 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
8443 @item -mtune=@var{cpu_type}
8445 Set only the instruction scheduling parameters for machine type
8446 @var{cpu_type}. The instruction set is not changed.
8448 @item -mmemory-latency=@var{time}
8449 @opindex mmemory-latency
8450 Sets the latency the scheduler should assume for typical memory
8451 references as seen by the application. This number is highly
8452 dependent on the memory access patterns used by the application
8453 and the size of the external cache on the machine.
8455 Valid options for @var{time} are
8459 A decimal number representing clock cycles.
8465 The compiler contains estimates of the number of clock cycles for
8466 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
8467 (also called Dcache, Scache, and Bcache), as well as to main memory.
8468 Note that L3 is only valid for EV5.
8473 @node DEC Alpha/VMS Options
8474 @subsection DEC Alpha/VMS Options
8476 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
8479 @item -mvms-return-codes
8480 @opindex mvms-return-codes
8481 Return VMS condition codes from main. The default is to return POSIX
8482 style condition (e.g.@ error) codes.
8486 @subsection FRV Options
8493 Only use the first 32 general purpose registers.
8498 Use all 64 general purpose registers.
8503 Use only the first 32 floating point registers.
8508 Use all 64 floating point registers
8511 @opindex mhard-float
8513 Use hardware instructions for floating point operations.
8516 @opindex msoft-float
8518 Use library routines for floating point operations.
8523 Dynamically allocate condition code registers.
8528 Do not try to dynamically allocate condition code registers, only
8529 use @code{icc0} and @code{fcc0}.
8534 Change ABI to use double word insns.
8539 Do not use double word instructions.
8544 Use floating point double instructions.
8549 Do not use floating point double instructions.
8554 Use media instructions.
8559 Do not use media instructions.
8564 Use multiply and add/subtract instructions.
8569 Do not use multiply and add/subtract instructions.
8574 Select the FDPIC ABI, that uses function descriptors to represent
8575 pointers to functions. Without any PIC/PIE-related options, it
8576 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
8577 assumes GOT entries and small data are within a 12-bit range from the
8578 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
8579 are computed with 32 bits.
8582 @opindex minline-plt
8584 Enable inlining of PLT entries in function calls to functions that are
8585 not known to bind locally. It has no effect without @option{-mfdpic}.
8586 It's enabled by default if optimizing for speed and compiling for
8587 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
8588 optimization option such as @option{-O3} or above is present in the
8594 Assume a large TLS segment when generating thread-local code.
8599 Do not assume a large TLS segment when generating thread-local code.
8604 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
8605 that is known to be in read-only sections. It's enabled by default,
8606 except for @option{-fpic} or @option{-fpie}: even though it may help
8607 make the global offset table smaller, it trades 1 instruction for 4.
8608 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
8609 one of which may be shared by multiple symbols, and it avoids the need
8610 for a GOT entry for the referenced symbol, so it's more likely to be a
8611 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
8613 @item -multilib-library-pic
8614 @opindex multilib-library-pic
8616 Link with the (library, not FD) pic libraries. It's implied by
8617 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
8618 @option{-fpic} without @option{-mfdpic}. You should never have to use
8624 Follow the EABI requirement of always creating a frame pointer whenever
8625 a stack frame is allocated. This option is enabled by default and can
8626 be disabled with @option{-mno-linked-fp}.
8629 @opindex mlong-calls
8631 Use indirect addressing to call functions outside the current
8632 compilation unit. This allows the functions to be placed anywhere
8633 within the 32-bit address space.
8635 @item -malign-labels
8636 @opindex malign-labels
8638 Try to align labels to an 8-byte boundary by inserting nops into the
8639 previous packet. This option only has an effect when VLIW packing
8640 is enabled. It doesn't create new packets; it merely adds nops to
8644 @opindex mlibrary-pic
8646 Generate position-independent EABI code.
8651 Use only the first four media accumulator registers.
8656 Use all eight media accumulator registers.
8661 Pack VLIW instructions.
8666 Do not pack VLIW instructions.
8671 Do not mark ABI switches in e_flags.
8676 Enable the use of conditional-move instructions (default).
8678 This switch is mainly for debugging the compiler and will likely be removed
8679 in a future version.
8681 @item -mno-cond-move
8682 @opindex mno-cond-move
8684 Disable the use of conditional-move instructions.
8686 This switch is mainly for debugging the compiler and will likely be removed
8687 in a future version.
8692 Enable the use of conditional set instructions (default).
8694 This switch is mainly for debugging the compiler and will likely be removed
8695 in a future version.
8700 Disable the use of conditional set instructions.
8702 This switch is mainly for debugging the compiler and will likely be removed
8703 in a future version.
8708 Enable the use of conditional execution (default).
8710 This switch is mainly for debugging the compiler and will likely be removed
8711 in a future version.
8713 @item -mno-cond-exec
8714 @opindex mno-cond-exec
8716 Disable the use of conditional execution.
8718 This switch is mainly for debugging the compiler and will likely be removed
8719 in a future version.
8722 @opindex mvliw-branch
8724 Run a pass to pack branches into VLIW instructions (default).
8726 This switch is mainly for debugging the compiler and will likely be removed
8727 in a future version.
8729 @item -mno-vliw-branch
8730 @opindex mno-vliw-branch
8732 Do not run a pass to pack branches into VLIW instructions.
8734 This switch is mainly for debugging the compiler and will likely be removed
8735 in a future version.
8737 @item -mmulti-cond-exec
8738 @opindex mmulti-cond-exec
8740 Enable optimization of @code{&&} and @code{||} in conditional execution
8743 This switch is mainly for debugging the compiler and will likely be removed
8744 in a future version.
8746 @item -mno-multi-cond-exec
8747 @opindex mno-multi-cond-exec
8749 Disable optimization of @code{&&} and @code{||} in conditional execution.
8751 This switch is mainly for debugging the compiler and will likely be removed
8752 in a future version.
8754 @item -mnested-cond-exec
8755 @opindex mnested-cond-exec
8757 Enable nested conditional execution optimizations (default).
8759 This switch is mainly for debugging the compiler and will likely be removed
8760 in a future version.
8762 @item -mno-nested-cond-exec
8763 @opindex mno-nested-cond-exec
8765 Disable nested conditional execution optimizations.
8767 This switch is mainly for debugging the compiler and will likely be removed
8768 in a future version.
8770 @item -moptimize-membar
8771 @opindex moptimize-membar
8773 This switch removes redundant @code{membar} instructions from the
8774 compiler generated code. It is enabled by default.
8776 @item -mno-optimize-membar
8777 @opindex mno-optimize-membar
8779 This switch disables the automatic removal of redundant @code{membar}
8780 instructions from the generated code.
8782 @item -mtomcat-stats
8783 @opindex mtomcat-stats
8785 Cause gas to print out tomcat statistics.
8787 @item -mcpu=@var{cpu}
8790 Select the processor type for which to generate code. Possible values are
8791 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
8792 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
8796 @node H8/300 Options
8797 @subsection H8/300 Options
8799 These @samp{-m} options are defined for the H8/300 implementations:
8804 Shorten some address references at link time, when possible; uses the
8805 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
8806 ld, Using ld}, for a fuller description.
8810 Generate code for the H8/300H@.
8814 Generate code for the H8S@.
8818 Generate code for the H8S and H8/300H in the normal mode. This switch
8819 must be used either with @option{-mh} or @option{-ms}.
8823 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
8827 Make @code{int} data 32 bits by default.
8831 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
8832 The default for the H8/300H and H8S is to align longs and floats on 4
8834 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
8835 This option has no effect on the H8/300.
8839 @subsection HPPA Options
8840 @cindex HPPA Options
8842 These @samp{-m} options are defined for the HPPA family of computers:
8845 @item -march=@var{architecture-type}
8847 Generate code for the specified architecture. The choices for
8848 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8849 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8850 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8851 architecture option for your machine. Code compiled for lower numbered
8852 architectures will run on higher numbered architectures, but not the
8856 @itemx -mpa-risc-1-1
8857 @itemx -mpa-risc-2-0
8858 @opindex mpa-risc-1-0
8859 @opindex mpa-risc-1-1
8860 @opindex mpa-risc-2-0
8861 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8864 @opindex mbig-switch
8865 Generate code suitable for big switch tables. Use this option only if
8866 the assembler/linker complain about out of range branches within a switch
8869 @item -mjump-in-delay
8870 @opindex mjump-in-delay
8871 Fill delay slots of function calls with unconditional jump instructions
8872 by modifying the return pointer for the function call to be the target
8873 of the conditional jump.
8875 @item -mdisable-fpregs
8876 @opindex mdisable-fpregs
8877 Prevent floating point registers from being used in any manner. This is
8878 necessary for compiling kernels which perform lazy context switching of
8879 floating point registers. If you use this option and attempt to perform
8880 floating point operations, the compiler will abort.
8882 @item -mdisable-indexing
8883 @opindex mdisable-indexing
8884 Prevent the compiler from using indexing address modes. This avoids some
8885 rather obscure problems when compiling MIG generated code under MACH@.
8887 @item -mno-space-regs
8888 @opindex mno-space-regs
8889 Generate code that assumes the target has no space registers. This allows
8890 GCC to generate faster indirect calls and use unscaled index address modes.
8892 Such code is suitable for level 0 PA systems and kernels.
8894 @item -mfast-indirect-calls
8895 @opindex mfast-indirect-calls
8896 Generate code that assumes calls never cross space boundaries. This
8897 allows GCC to emit code which performs faster indirect calls.
8899 This option will not work in the presence of shared libraries or nested
8902 @item -mfixed-range=@var{register-range}
8903 @opindex mfixed-range
8904 Generate code treating the given register range as fixed registers.
8905 A fixed register is one that the register allocator can not use. This is
8906 useful when compiling kernel code. A register range is specified as
8907 two registers separated by a dash. Multiple register ranges can be
8908 specified separated by a comma.
8910 @item -mlong-load-store
8911 @opindex mlong-load-store
8912 Generate 3-instruction load and store sequences as sometimes required by
8913 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8916 @item -mportable-runtime
8917 @opindex mportable-runtime
8918 Use the portable calling conventions proposed by HP for ELF systems.
8922 Enable the use of assembler directives only GAS understands.
8924 @item -mschedule=@var{cpu-type}
8926 Schedule code according to the constraints for the machine type
8927 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8928 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
8929 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
8930 proper scheduling option for your machine. The default scheduling is
8934 @opindex mlinker-opt
8935 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
8936 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
8937 linkers in which they give bogus error messages when linking some programs.
8940 @opindex msoft-float
8941 Generate output containing library calls for floating point.
8942 @strong{Warning:} the requisite libraries are not available for all HPPA
8943 targets. Normally the facilities of the machine's usual C compiler are
8944 used, but this cannot be done directly in cross-compilation. You must make
8945 your own arrangements to provide suitable library functions for
8946 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8947 does provide software floating point support.
8949 @option{-msoft-float} changes the calling convention in the output file;
8950 therefore, it is only useful if you compile @emph{all} of a program with
8951 this option. In particular, you need to compile @file{libgcc.a}, the
8952 library that comes with GCC, with @option{-msoft-float} in order for
8957 Generate the predefine, @code{_SIO}, for server IO@. The default is
8958 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
8959 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
8960 options are available under HP-UX and HI-UX@.
8964 Use GNU ld specific options. This passes @option{-shared} to ld when
8965 building a shared library. It is the default when GCC is configured,
8966 explicitly or implicitly, with the GNU linker. This option does not
8967 have any affect on which ld is called, it only changes what parameters
8968 are passed to that ld. The ld that is called is determined by the
8969 @option{--with-ld} configure option, GCC's program search path, and
8970 finally by the user's @env{PATH}. The linker used by GCC can be printed
8971 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
8972 on the 64 bit HP-UX GCC, i.e. configured with @samp{hppa*64*-*-hpux*}.
8976 Use HP ld specific options. This passes @option{-b} to ld when building
8977 a shared library and passes @option{+Accept TypeMismatch} to ld on all
8978 links. It is the default when GCC is configured, explicitly or
8979 implicitly, with the HP linker. This option does not have any affect on
8980 which ld is called, it only changes what parameters are passed to that
8981 ld. The ld that is called is determined by the @option{--with-ld}
8982 configure option, GCC's program search path, and finally by the user's
8983 @env{PATH}. The linker used by GCC can be printed using @samp{which
8984 `gcc -print-prog-name=ld`}. This option is only available on the 64 bit
8985 HP-UX GCC, i.e. configured with @samp{hppa*64*-*-hpux*}.
8988 @opindex mno-long-calls
8989 Generate code that uses long call sequences. This ensures that a call
8990 is always able to reach linker generated stubs. The default is to generate
8991 long calls only when the distance from the call site to the beginning
8992 of the function or translation unit, as the case may be, exceeds a
8993 predefined limit set by the branch type being used. The limits for
8994 normal calls are 7,600,000 and 240,000 bytes, respectively for the
8995 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
8998 Distances are measured from the beginning of functions when using the
8999 @option{-ffunction-sections} option, or when using the @option{-mgas}
9000 and @option{-mno-portable-runtime} options together under HP-UX with
9003 It is normally not desirable to use this option as it will degrade
9004 performance. However, it may be useful in large applications,
9005 particularly when partial linking is used to build the application.
9007 The types of long calls used depends on the capabilities of the
9008 assembler and linker, and the type of code being generated. The
9009 impact on systems that support long absolute calls, and long pic
9010 symbol-difference or pc-relative calls should be relatively small.
9011 However, an indirect call is used on 32-bit ELF systems in pic code
9012 and it is quite long.
9014 @item -munix=@var{unix-std}
9016 Generate compiler predefines and select a startfile for the specified
9017 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
9018 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
9019 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
9020 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
9021 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
9024 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
9025 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
9026 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
9027 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
9028 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
9029 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
9031 It is @emph{important} to note that this option changes the interfaces
9032 for various library routines. It also affects the operational behavior
9033 of the C library. Thus, @emph{extreme} care is needed in using this
9036 Library code that is intended to operate with more than one UNIX
9037 standard must test, set and restore the variable @var{__xpg4_extended_mask}
9038 as appropriate. Most GNU software doesn't provide this capability.
9042 Suppress the generation of link options to search libdld.sl when the
9043 @option{-static} option is specified on HP-UX 10 and later.
9047 The HP-UX implementation of setlocale in libc has a dependency on
9048 libdld.sl. There isn't an archive version of libdld.sl. Thus,
9049 when the @option{-static} option is specified, special link options
9050 are needed to resolve this dependency.
9052 On HP-UX 10 and later, the GCC driver adds the necessary options to
9053 link with libdld.sl when the @option{-static} option is specified.
9054 This causes the resulting binary to be dynamic. On the 64-bit port,
9055 the linkers generate dynamic binaries by default in any case. The
9056 @option{-nolibdld} option can be used to prevent the GCC driver from
9057 adding these link options.
9061 Add support for multithreading with the @dfn{dce thread} library
9062 under HP-UX@. This option sets flags for both the preprocessor and
9066 @node i386 and x86-64 Options
9067 @subsection Intel 386 and AMD x86-64 Options
9068 @cindex i386 Options
9069 @cindex x86-64 Options
9070 @cindex Intel 386 Options
9071 @cindex AMD x86-64 Options
9073 These @samp{-m} options are defined for the i386 and x86-64 family of
9077 @item -mtune=@var{cpu-type}
9079 Tune to @var{cpu-type} everything applicable about the generated code, except
9080 for the ABI and the set of available instructions. The choices for
9084 Produce code optimized for the most common IA32/AMD64/EM64T processors.
9085 If you know the CPU on which your code will run, then you should use
9086 the corresponding @option{-mtune} option instead of
9087 @option{-mtune=generic}. But, if you do not know exactly what CPU users
9088 of your application will have, then you should use this option.
9090 As new processors are deployed in the marketplace, the behavior of this
9091 option will change. Therefore, if you upgrade to a newer version of
9092 GCC, the code generated option will change to reflect the processors
9093 that were most common when that version of GCC was released.
9095 There is no @option{-march=generic} option because @option{-march}
9096 indicates the instruction set the compiler can use, and there is no
9097 generic instruction set applicable to all processors. In contrast,
9098 @option{-mtune} indicates the processor (or, in this case, collection of
9099 processors) for which the code is optimized.
9101 Original Intel's i386 CPU@.
9103 Intel's i486 CPU@. (No scheduling is implemented for this chip.)
9105 Intel Pentium CPU with no MMX support.
9107 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
9109 Intel PentiumPro CPU@.
9111 Same as @code{generic}, but when used as @code{march} option, PentiumPro
9112 instruction set will be used, so the code will run on all i686 familly chips.
9114 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
9115 @item pentium3, pentium3m
9116 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
9119 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
9120 support. Used by Centrino notebooks.
9121 @item pentium4, pentium4m
9122 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
9124 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
9127 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
9128 SSE2 and SSE3 instruction set support.
9130 AMD K6 CPU with MMX instruction set support.
9132 Improved versions of AMD K6 CPU with MMX and 3dNOW! instruction set support.
9133 @item athlon, athlon-tbird
9134 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and SSE prefetch instructions
9136 @item athlon-4, athlon-xp, athlon-mp
9137 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and full SSE
9138 instruction set support.
9139 @item k8, opteron, athlon64, athlon-fx
9140 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
9141 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW! and 64-bit instruction set extensions.)
9143 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
9146 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!
9147 instruction set support.
9149 Via C3 CPU with MMX and 3dNOW! instruction set support. (No scheduling is
9150 implemented for this chip.)
9152 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
9153 implemented for this chip.)
9156 While picking a specific @var{cpu-type} will schedule things appropriately
9157 for that particular chip, the compiler will not generate any code that
9158 does not run on the i386 without the @option{-march=@var{cpu-type}} option
9161 @item -march=@var{cpu-type}
9163 Generate instructions for the machine type @var{cpu-type}. The choices
9164 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
9165 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
9167 @item -mcpu=@var{cpu-type}
9169 A deprecated synonym for @option{-mtune}.
9178 @opindex mpentiumpro
9179 These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
9180 @option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
9181 These synonyms are deprecated.
9183 @item -mfpmath=@var{unit}
9185 Generate floating point arithmetics for selected unit @var{unit}. The choices
9190 Use the standard 387 floating point coprocessor present majority of chips and
9191 emulated otherwise. Code compiled with this option will run almost everywhere.
9192 The temporary results are computed in 80bit precision instead of precision
9193 specified by the type resulting in slightly different results compared to most
9194 of other chips. See @option{-ffloat-store} for more detailed description.
9196 This is the default choice for i386 compiler.
9199 Use scalar floating point instructions present in the SSE instruction set.
9200 This instruction set is supported by Pentium3 and newer chips, in the AMD line
9201 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
9202 instruction set supports only single precision arithmetics, thus the double and
9203 extended precision arithmetics is still done using 387. Later version, present
9204 only in Pentium4 and the future AMD x86-64 chips supports double precision
9207 For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse}
9208 or @option{-msse2} switches to enable SSE extensions and make this option
9209 effective. For the x86-64 compiler, these extensions are enabled by default.
9211 The resulting code should be considerably faster in the majority of cases and avoid
9212 the numerical instability problems of 387 code, but may break some existing
9213 code that expects temporaries to be 80bit.
9215 This is the default choice for the x86-64 compiler.
9218 Attempt to utilize both instruction sets at once. This effectively double the
9219 amount of available registers and on chips with separate execution units for
9220 387 and SSE the execution resources too. Use this option with care, as it is
9221 still experimental, because the GCC register allocator does not model separate
9222 functional units well resulting in instable performance.
9225 @item -masm=@var{dialect}
9226 @opindex masm=@var{dialect}
9227 Output asm instructions using selected @var{dialect}. Supported
9228 choices are @samp{intel} or @samp{att} (the default one). Darwin does
9229 not support @samp{intel}.
9234 @opindex mno-ieee-fp
9235 Control whether or not the compiler uses IEEE floating point
9236 comparisons. These handle correctly the case where the result of a
9237 comparison is unordered.
9240 @opindex msoft-float
9241 Generate output containing library calls for floating point.
9242 @strong{Warning:} the requisite libraries are not part of GCC@.
9243 Normally the facilities of the machine's usual C compiler are used, but
9244 this can't be done directly in cross-compilation. You must make your
9245 own arrangements to provide suitable library functions for
9248 On machines where a function returns floating point results in the 80387
9249 register stack, some floating point opcodes may be emitted even if
9250 @option{-msoft-float} is used.
9252 @item -mno-fp-ret-in-387
9253 @opindex mno-fp-ret-in-387
9254 Do not use the FPU registers for return values of functions.
9256 The usual calling convention has functions return values of types
9257 @code{float} and @code{double} in an FPU register, even if there
9258 is no FPU@. The idea is that the operating system should emulate
9261 The option @option{-mno-fp-ret-in-387} causes such values to be returned
9262 in ordinary CPU registers instead.
9264 @item -mno-fancy-math-387
9265 @opindex mno-fancy-math-387
9266 Some 387 emulators do not support the @code{sin}, @code{cos} and
9267 @code{sqrt} instructions for the 387. Specify this option to avoid
9268 generating those instructions. This option is the default on FreeBSD,
9269 OpenBSD and NetBSD@. This option is overridden when @option{-march}
9270 indicates that the target cpu will always have an FPU and so the
9271 instruction will not need emulation. As of revision 2.6.1, these
9272 instructions are not generated unless you also use the
9273 @option{-funsafe-math-optimizations} switch.
9275 @item -malign-double
9276 @itemx -mno-align-double
9277 @opindex malign-double
9278 @opindex mno-align-double
9279 Control whether GCC aligns @code{double}, @code{long double}, and
9280 @code{long long} variables on a two word boundary or a one word
9281 boundary. Aligning @code{double} variables on a two word boundary will
9282 produce code that runs somewhat faster on a @samp{Pentium} at the
9283 expense of more memory.
9285 @strong{Warning:} if you use the @option{-malign-double} switch,
9286 structures containing the above types will be aligned differently than
9287 the published application binary interface specifications for the 386
9288 and will not be binary compatible with structures in code compiled
9289 without that switch.
9291 @item -m96bit-long-double
9292 @itemx -m128bit-long-double
9293 @opindex m96bit-long-double
9294 @opindex m128bit-long-double
9295 These switches control the size of @code{long double} type. The i386
9296 application binary interface specifies the size to be 96 bits,
9297 so @option{-m96bit-long-double} is the default in 32 bit mode.
9299 Modern architectures (Pentium and newer) would prefer @code{long double}
9300 to be aligned to an 8 or 16 byte boundary. In arrays or structures
9301 conforming to the ABI, this would not be possible. So specifying a
9302 @option{-m128bit-long-double} will align @code{long double}
9303 to a 16 byte boundary by padding the @code{long double} with an additional
9306 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
9307 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
9309 Notice that neither of these options enable any extra precision over the x87
9310 standard of 80 bits for a @code{long double}.
9312 @strong{Warning:} if you override the default value for your target ABI, the
9313 structures and arrays containing @code{long double} variables will change
9314 their size as well as function calling convention for function taking
9315 @code{long double} will be modified. Hence they will not be binary
9316 compatible with arrays or structures in code compiled without that switch.
9318 @item -mmlarge-data-threshold=@var{number}
9319 @opindex mlarge-data-threshold=@var{number}
9320 When @option{-mcmodel=medium} is specified, the data greater than
9321 @var{threshold} are placed in large data section. This value must be the
9322 same across all object linked into the binary and defaults to 65535.
9325 @itemx -mno-svr3-shlib
9326 @opindex msvr3-shlib
9327 @opindex mno-svr3-shlib
9328 Control whether GCC places uninitialized local variables into the
9329 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
9330 into @code{bss}. These options are meaningful only on System V Release 3.
9334 Use a different function-calling convention, in which functions that
9335 take a fixed number of arguments return with the @code{ret} @var{num}
9336 instruction, which pops their arguments while returning. This saves one
9337 instruction in the caller since there is no need to pop the arguments
9340 You can specify that an individual function is called with this calling
9341 sequence with the function attribute @samp{stdcall}. You can also
9342 override the @option{-mrtd} option by using the function attribute
9343 @samp{cdecl}. @xref{Function Attributes}.
9345 @strong{Warning:} this calling convention is incompatible with the one
9346 normally used on Unix, so you cannot use it if you need to call
9347 libraries compiled with the Unix compiler.
9349 Also, you must provide function prototypes for all functions that
9350 take variable numbers of arguments (including @code{printf});
9351 otherwise incorrect code will be generated for calls to those
9354 In addition, seriously incorrect code will result if you call a
9355 function with too many arguments. (Normally, extra arguments are
9356 harmlessly ignored.)
9358 @item -mregparm=@var{num}
9360 Control how many registers are used to pass integer arguments. By
9361 default, no registers are used to pass arguments, and at most 3
9362 registers can be used. You can control this behavior for a specific
9363 function by using the function attribute @samp{regparm}.
9364 @xref{Function Attributes}.
9366 @strong{Warning:} if you use this switch, and
9367 @var{num} is nonzero, then you must build all modules with the same
9368 value, including any libraries. This includes the system libraries and
9372 @opindex msseregparm
9373 Use SSE register passing conventions for float and double arguments
9374 and return values. You can control this behavior for a specific
9375 function by using the function attribute @samp{sseregparm}.
9376 @xref{Function Attributes}.
9378 @strong{Warning:} if you use this switch then you must build all
9379 modules with the same value, including any libraries. This includes
9380 the system libraries and startup modules.
9382 @item -mpreferred-stack-boundary=@var{num}
9383 @opindex mpreferred-stack-boundary
9384 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
9385 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
9386 the default is 4 (16 bytes or 128 bits), except when optimizing for code
9387 size (@option{-Os}), in which case the default is the minimum correct
9388 alignment (4 bytes for x86, and 8 bytes for x86-64).
9390 On Pentium and PentiumPro, @code{double} and @code{long double} values
9391 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
9392 suffer significant run time performance penalties. On Pentium III, the
9393 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
9394 penalties if it is not 16 byte aligned.
9396 To ensure proper alignment of this values on the stack, the stack boundary
9397 must be as aligned as that required by any value stored on the stack.
9398 Further, every function must be generated such that it keeps the stack
9399 aligned. Thus calling a function compiled with a higher preferred
9400 stack boundary from a function compiled with a lower preferred stack
9401 boundary will most likely misalign the stack. It is recommended that
9402 libraries that use callbacks always use the default setting.
9404 This extra alignment does consume extra stack space, and generally
9405 increases code size. Code that is sensitive to stack space usage, such
9406 as embedded systems and operating system kernels, may want to reduce the
9407 preferred alignment to @option{-mpreferred-stack-boundary=2}.
9425 These switches enable or disable the use of instructions in the MMX,
9426 SSE, SSE2 or 3DNow! extended instruction sets. These extensions are
9427 also available as built-in functions: see @ref{X86 Built-in Functions},
9428 for details of the functions enabled and disabled by these switches.
9430 To have SSE/SSE2 instructions generated automatically from floating-point
9431 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
9433 These options will enable GCC to use these extended instructions in
9434 generated code, even without @option{-mfpmath=sse}. Applications which
9435 perform runtime CPU detection must compile separate files for each
9436 supported architecture, using the appropriate flags. In particular,
9437 the file containing the CPU detection code should be compiled without
9442 Use special versions of certain libm routines that come with an SSE
9443 ABI and an SSE implementation. Useful together with @option{-mfpmath=sse}
9444 to avoid moving values between SSE registers and the x87 FP stack.
9447 @itemx -mno-push-args
9449 @opindex mno-push-args
9450 Use PUSH operations to store outgoing parameters. This method is shorter
9451 and usually equally fast as method using SUB/MOV operations and is enabled
9452 by default. In some cases disabling it may improve performance because of
9453 improved scheduling and reduced dependencies.
9455 @item -maccumulate-outgoing-args
9456 @opindex maccumulate-outgoing-args
9457 If enabled, the maximum amount of space required for outgoing arguments will be
9458 computed in the function prologue. This is faster on most modern CPUs
9459 because of reduced dependencies, improved scheduling and reduced stack usage
9460 when preferred stack boundary is not equal to 2. The drawback is a notable
9461 increase in code size. This switch implies @option{-mno-push-args}.
9465 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
9466 on thread-safe exception handling must compile and link all code with the
9467 @option{-mthreads} option. When compiling, @option{-mthreads} defines
9468 @option{-D_MT}; when linking, it links in a special thread helper library
9469 @option{-lmingwthrd} which cleans up per thread exception handling data.
9471 @item -mno-align-stringops
9472 @opindex mno-align-stringops
9473 Do not align destination of inlined string operations. This switch reduces
9474 code size and improves performance in case the destination is already aligned,
9475 but GCC doesn't know about it.
9477 @item -minline-all-stringops
9478 @opindex minline-all-stringops
9479 By default GCC inlines string operations only when destination is known to be
9480 aligned at least to 4 byte boundary. This enables more inlining, increase code
9481 size, but may improve performance of code that depends on fast memcpy, strlen
9482 and memset for short lengths.
9484 @item -momit-leaf-frame-pointer
9485 @opindex momit-leaf-frame-pointer
9486 Don't keep the frame pointer in a register for leaf functions. This
9487 avoids the instructions to save, set up and restore frame pointers and
9488 makes an extra register available in leaf functions. The option
9489 @option{-fomit-frame-pointer} removes the frame pointer for all functions
9490 which might make debugging harder.
9492 @item -mtls-direct-seg-refs
9493 @itemx -mno-tls-direct-seg-refs
9494 @opindex mtls-direct-seg-refs
9495 Controls whether TLS variables may be accessed with offsets from the
9496 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
9497 or whether the thread base pointer must be added. Whether or not this
9498 is legal depends on the operating system, and whether it maps the
9499 segment to cover the entire TLS area.
9501 For systems that use GNU libc, the default is on.
9504 These @samp{-m} switches are supported in addition to the above
9505 on AMD x86-64 processors in 64-bit environments.
9512 Generate code for a 32-bit or 64-bit environment.
9513 The 32-bit environment sets int, long and pointer to 32 bits and
9514 generates code that runs on any i386 system.
9515 The 64-bit environment sets int to 32 bits and long and pointer
9516 to 64 bits and generates code for AMD's x86-64 architecture.
9519 @opindex no-red-zone
9520 Do not use a so called red zone for x86-64 code. The red zone is mandated
9521 by the x86-64 ABI, it is a 128-byte area beyond the location of the
9522 stack pointer that will not be modified by signal or interrupt handlers
9523 and therefore can be used for temporary data without adjusting the stack
9524 pointer. The flag @option{-mno-red-zone} disables this red zone.
9526 @item -mcmodel=small
9527 @opindex mcmodel=small
9528 Generate code for the small code model: the program and its symbols must
9529 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
9530 Programs can be statically or dynamically linked. This is the default
9533 @item -mcmodel=kernel
9534 @opindex mcmodel=kernel
9535 Generate code for the kernel code model. The kernel runs in the
9536 negative 2 GB of the address space.
9537 This model has to be used for Linux kernel code.
9539 @item -mcmodel=medium
9540 @opindex mcmodel=medium
9541 Generate code for the medium model: The program is linked in the lower 2
9542 GB of the address space but symbols can be located anywhere in the
9543 address space. Programs can be statically or dynamically linked, but
9544 building of shared libraries are not supported with the medium model.
9546 @item -mcmodel=large
9547 @opindex mcmodel=large
9548 Generate code for the large model: This model makes no assumptions
9549 about addresses and sizes of sections. Currently GCC does not implement
9554 @subsection IA-64 Options
9555 @cindex IA-64 Options
9557 These are the @samp{-m} options defined for the Intel IA-64 architecture.
9561 @opindex mbig-endian
9562 Generate code for a big endian target. This is the default for HP-UX@.
9564 @item -mlittle-endian
9565 @opindex mlittle-endian
9566 Generate code for a little endian target. This is the default for AIX5
9573 Generate (or don't) code for the GNU assembler. This is the default.
9574 @c Also, this is the default if the configure option @option{--with-gnu-as}
9581 Generate (or don't) code for the GNU linker. This is the default.
9582 @c Also, this is the default if the configure option @option{--with-gnu-ld}
9587 Generate code that does not use a global pointer register. The result
9588 is not position independent code, and violates the IA-64 ABI@.
9590 @item -mvolatile-asm-stop
9591 @itemx -mno-volatile-asm-stop
9592 @opindex mvolatile-asm-stop
9593 @opindex mno-volatile-asm-stop
9594 Generate (or don't) a stop bit immediately before and after volatile asm
9597 @item -mregister-names
9598 @itemx -mno-register-names
9599 @opindex mregister-names
9600 @opindex mno-register-names
9601 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
9602 the stacked registers. This may make assembler output more readable.
9608 Disable (or enable) optimizations that use the small data section. This may
9609 be useful for working around optimizer bugs.
9612 @opindex mconstant-gp
9613 Generate code that uses a single constant global pointer value. This is
9614 useful when compiling kernel code.
9618 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
9619 This is useful when compiling firmware code.
9621 @item -minline-float-divide-min-latency
9622 @opindex minline-float-divide-min-latency
9623 Generate code for inline divides of floating point values
9624 using the minimum latency algorithm.
9626 @item -minline-float-divide-max-throughput
9627 @opindex minline-float-divide-max-throughput
9628 Generate code for inline divides of floating point values
9629 using the maximum throughput algorithm.
9631 @item -minline-int-divide-min-latency
9632 @opindex minline-int-divide-min-latency
9633 Generate code for inline divides of integer values
9634 using the minimum latency algorithm.
9636 @item -minline-int-divide-max-throughput
9637 @opindex minline-int-divide-max-throughput
9638 Generate code for inline divides of integer values
9639 using the maximum throughput algorithm.
9641 @item -minline-sqrt-min-latency
9642 @opindex minline-sqrt-min-latency
9643 Generate code for inline square roots
9644 using the minimum latency algorithm.
9646 @item -minline-sqrt-max-throughput
9647 @opindex minline-sqrt-max-throughput
9648 Generate code for inline square roots
9649 using the maximum throughput algorithm.
9651 @item -mno-dwarf2-asm
9653 @opindex mno-dwarf2-asm
9654 @opindex mdwarf2-asm
9655 Don't (or do) generate assembler code for the DWARF2 line number debugging
9656 info. This may be useful when not using the GNU assembler.
9658 @item -mearly-stop-bits
9659 @itemx -mno-early-stop-bits
9660 @opindex mearly-stop-bits
9661 @opindex mno-early-stop-bits
9662 Allow stop bits to be placed earlier than immediately preceding the
9663 instruction that triggered the stop bit. This can improve instruction
9664 scheduling, but does not always do so.
9666 @item -mfixed-range=@var{register-range}
9667 @opindex mfixed-range
9668 Generate code treating the given register range as fixed registers.
9669 A fixed register is one that the register allocator can not use. This is
9670 useful when compiling kernel code. A register range is specified as
9671 two registers separated by a dash. Multiple register ranges can be
9672 specified separated by a comma.
9674 @item -mtls-size=@var{tls-size}
9676 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
9679 @item -mtune=@var{cpu-type}
9681 Tune the instruction scheduling for a particular CPU, Valid values are
9682 itanium, itanium1, merced, itanium2, and mckinley.
9688 Add support for multithreading using the POSIX threads library. This
9689 option sets flags for both the preprocessor and linker. It does
9690 not affect the thread safety of object code produced by the compiler or
9691 that of libraries supplied with it. These are HP-UX specific flags.
9697 Generate code for a 32-bit or 64-bit environment.
9698 The 32-bit environment sets int, long and pointer to 32 bits.
9699 The 64-bit environment sets int to 32 bits and long and pointer
9700 to 64 bits. These are HP-UX specific flags.
9705 @subsection M32C Options
9706 @cindex M32C options
9709 @item -mcpu=@var{name}
9711 Select the CPU for which code is generated. @var{name} may be one of
9712 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
9713 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
9718 Specifies that the program will be run on the simulator. This causes
9719 an alternate runtime library to be linked in which supports, for
9720 example, file I/O. You must not use this option when generating
9721 programs that will run on real hardware; you must provide your own
9722 runtime library for whatever I/O functions are needed.
9724 @item -memregs=@var{number}
9726 Specifies the number of memory-based pseudo-registers GCC will use
9727 during code generation. These pseudo-registers will be used like real
9728 registers, so there is a tradeoff between GCC's ability to fit the
9729 code into available registers, and the performance penalty of using
9730 memory instead of registers. Note that all modules in a program must
9731 be compiled with the same value for this option. Because of that, you
9732 must not use this option with the default runtime libraries gcc
9737 @node M32R/D Options
9738 @subsection M32R/D Options
9739 @cindex M32R/D options
9741 These @option{-m} options are defined for Renesas M32R/D architectures:
9746 Generate code for the M32R/2@.
9750 Generate code for the M32R/X@.
9754 Generate code for the M32R@. This is the default.
9757 @opindex mmodel=small
9758 Assume all objects live in the lower 16MB of memory (so that their addresses
9759 can be loaded with the @code{ld24} instruction), and assume all subroutines
9760 are reachable with the @code{bl} instruction.
9761 This is the default.
9763 The addressability of a particular object can be set with the
9764 @code{model} attribute.
9766 @item -mmodel=medium
9767 @opindex mmodel=medium
9768 Assume objects may be anywhere in the 32-bit address space (the compiler
9769 will generate @code{seth/add3} instructions to load their addresses), and
9770 assume all subroutines are reachable with the @code{bl} instruction.
9773 @opindex mmodel=large
9774 Assume objects may be anywhere in the 32-bit address space (the compiler
9775 will generate @code{seth/add3} instructions to load their addresses), and
9776 assume subroutines may not be reachable with the @code{bl} instruction
9777 (the compiler will generate the much slower @code{seth/add3/jl}
9778 instruction sequence).
9781 @opindex msdata=none
9782 Disable use of the small data area. Variables will be put into
9783 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
9784 @code{section} attribute has been specified).
9785 This is the default.
9787 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
9788 Objects may be explicitly put in the small data area with the
9789 @code{section} attribute using one of these sections.
9792 @opindex msdata=sdata
9793 Put small global and static data in the small data area, but do not
9794 generate special code to reference them.
9798 Put small global and static data in the small data area, and generate
9799 special instructions to reference them.
9803 @cindex smaller data references
9804 Put global and static objects less than or equal to @var{num} bytes
9805 into the small data or bss sections instead of the normal data or bss
9806 sections. The default value of @var{num} is 8.
9807 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
9808 for this option to have any effect.
9810 All modules should be compiled with the same @option{-G @var{num}} value.
9811 Compiling with different values of @var{num} may or may not work; if it
9812 doesn't the linker will give an error message---incorrect code will not be
9817 Makes the M32R specific code in the compiler display some statistics
9818 that might help in debugging programs.
9821 @opindex malign-loops
9822 Align all loops to a 32-byte boundary.
9824 @item -mno-align-loops
9825 @opindex mno-align-loops
9826 Do not enforce a 32-byte alignment for loops. This is the default.
9828 @item -missue-rate=@var{number}
9829 @opindex missue-rate=@var{number}
9830 Issue @var{number} instructions per cycle. @var{number} can only be 1
9833 @item -mbranch-cost=@var{number}
9834 @opindex mbranch-cost=@var{number}
9835 @var{number} can only be 1 or 2. If it is 1 then branches will be
9836 preferred over conditional code, if it is 2, then the opposite will
9839 @item -mflush-trap=@var{number}
9840 @opindex mflush-trap=@var{number}
9841 Specifies the trap number to use to flush the cache. The default is
9842 12. Valid numbers are between 0 and 15 inclusive.
9844 @item -mno-flush-trap
9845 @opindex mno-flush-trap
9846 Specifies that the cache cannot be flushed by using a trap.
9848 @item -mflush-func=@var{name}
9849 @opindex mflush-func=@var{name}
9850 Specifies the name of the operating system function to call to flush
9851 the cache. The default is @emph{_flush_cache}, but a function call
9852 will only be used if a trap is not available.
9854 @item -mno-flush-func
9855 @opindex mno-flush-func
9856 Indicates that there is no OS function for flushing the cache.
9860 @node M680x0 Options
9861 @subsection M680x0 Options
9862 @cindex M680x0 options
9864 These are the @samp{-m} options defined for the 68000 series. The default
9865 values for these options depends on which style of 68000 was selected when
9866 the compiler was configured; the defaults for the most common choices are
9874 Generate output for a 68000. This is the default
9875 when the compiler is configured for 68000-based systems.
9877 Use this option for microcontrollers with a 68000 or EC000 core,
9878 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
9884 Generate output for a 68020. This is the default
9885 when the compiler is configured for 68020-based systems.
9889 Generate output containing 68881 instructions for floating point.
9890 This is the default for most 68020 systems unless @option{--nfp} was
9891 specified when the compiler was configured.
9895 Generate output for a 68030. This is the default when the compiler is
9896 configured for 68030-based systems.
9900 Generate output for a 68040. This is the default when the compiler is
9901 configured for 68040-based systems.
9903 This option inhibits the use of 68881/68882 instructions that have to be
9904 emulated by software on the 68040. Use this option if your 68040 does not
9905 have code to emulate those instructions.
9909 Generate output for a 68060. This is the default when the compiler is
9910 configured for 68060-based systems.
9912 This option inhibits the use of 68020 and 68881/68882 instructions that
9913 have to be emulated by software on the 68060. Use this option if your 68060
9914 does not have code to emulate those instructions.
9918 Generate output for a CPU32. This is the default
9919 when the compiler is configured for CPU32-based systems.
9921 Use this option for microcontrollers with a
9922 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
9923 68336, 68340, 68341, 68349 and 68360.
9927 Generate output for a 520X ``coldfire'' family cpu. This is the default
9928 when the compiler is configured for 520X-based systems.
9930 Use this option for microcontroller with a 5200 core, including
9931 the MCF5202, MCF5203, MCF5204 and MCF5202.
9935 Generate output for a ColdFire V4e family cpu (e.g.@: 547x/548x).
9936 This includes use of hardware floating point instructions.
9940 Generate output for a 68040, without using any of the new instructions.
9941 This results in code which can run relatively efficiently on either a
9942 68020/68881 or a 68030 or a 68040. The generated code does use the
9943 68881 instructions that are emulated on the 68040.
9947 Generate output for a 68060, without using any of the new instructions.
9948 This results in code which can run relatively efficiently on either a
9949 68020/68881 or a 68030 or a 68040. The generated code does use the
9950 68881 instructions that are emulated on the 68060.
9953 @opindex msoft-float
9954 Generate output containing library calls for floating point.
9955 @strong{Warning:} the requisite libraries are not available for all m68k
9956 targets. Normally the facilities of the machine's usual C compiler are
9957 used, but this can't be done directly in cross-compilation. You must
9958 make your own arrangements to provide suitable library functions for
9959 cross-compilation. The embedded targets @samp{m68k-*-aout} and
9960 @samp{m68k-*-coff} do provide software floating point support.
9964 Consider type @code{int} to be 16 bits wide, like @code{short int}.
9965 Additionally, parameters passed on the stack are also aligned to a
9966 16-bit boundary even on targets whose API mandates promotion to 32-bit.
9969 @opindex mnobitfield
9970 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
9971 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
9975 Do use the bit-field instructions. The @option{-m68020} option implies
9976 @option{-mbitfield}. This is the default if you use a configuration
9977 designed for a 68020.
9981 Use a different function-calling convention, in which functions
9982 that take a fixed number of arguments return with the @code{rtd}
9983 instruction, which pops their arguments while returning. This
9984 saves one instruction in the caller since there is no need to pop
9985 the arguments there.
9987 This calling convention is incompatible with the one normally
9988 used on Unix, so you cannot use it if you need to call libraries
9989 compiled with the Unix compiler.
9991 Also, you must provide function prototypes for all functions that
9992 take variable numbers of arguments (including @code{printf});
9993 otherwise incorrect code will be generated for calls to those
9996 In addition, seriously incorrect code will result if you call a
9997 function with too many arguments. (Normally, extra arguments are
9998 harmlessly ignored.)
10000 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
10001 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
10004 @itemx -mno-align-int
10005 @opindex malign-int
10006 @opindex mno-align-int
10007 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
10008 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
10009 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
10010 Aligning variables on 32-bit boundaries produces code that runs somewhat
10011 faster on processors with 32-bit busses at the expense of more memory.
10013 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
10014 align structures containing the above types differently than
10015 most published application binary interface specifications for the m68k.
10019 Use the pc-relative addressing mode of the 68000 directly, instead of
10020 using a global offset table. At present, this option implies @option{-fpic},
10021 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
10022 not presently supported with @option{-mpcrel}, though this could be supported for
10023 68020 and higher processors.
10025 @item -mno-strict-align
10026 @itemx -mstrict-align
10027 @opindex mno-strict-align
10028 @opindex mstrict-align
10029 Do not (do) assume that unaligned memory references will be handled by
10033 Generate code that allows the data segment to be located in a different
10034 area of memory from the text segment. This allows for execute in place in
10035 an environment without virtual memory management. This option implies
10038 @item -mno-sep-data
10039 Generate code that assumes that the data segment follows the text segment.
10040 This is the default.
10042 @item -mid-shared-library
10043 Generate code that supports shared libraries via the library ID method.
10044 This allows for execute in place and shared libraries in an environment
10045 without virtual memory management. This option implies @option{-fPIC}.
10047 @item -mno-id-shared-library
10048 Generate code that doesn't assume ID based shared libraries are being used.
10049 This is the default.
10051 @item -mshared-library-id=n
10052 Specified the identification number of the ID based shared library being
10053 compiled. Specifying a value of 0 will generate more compact code, specifying
10054 other values will force the allocation of that number to the current
10055 library but is no more space or time efficient than omitting this option.
10059 @node M68hc1x Options
10060 @subsection M68hc1x Options
10061 @cindex M68hc1x options
10063 These are the @samp{-m} options defined for the 68hc11 and 68hc12
10064 microcontrollers. The default values for these options depends on
10065 which style of microcontroller was selected when the compiler was configured;
10066 the defaults for the most common choices are given below.
10073 Generate output for a 68HC11. This is the default
10074 when the compiler is configured for 68HC11-based systems.
10080 Generate output for a 68HC12. This is the default
10081 when the compiler is configured for 68HC12-based systems.
10087 Generate output for a 68HCS12.
10089 @item -mauto-incdec
10090 @opindex mauto-incdec
10091 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
10098 Enable the use of 68HC12 min and max instructions.
10101 @itemx -mno-long-calls
10102 @opindex mlong-calls
10103 @opindex mno-long-calls
10104 Treat all calls as being far away (near). If calls are assumed to be
10105 far away, the compiler will use the @code{call} instruction to
10106 call a function and the @code{rtc} instruction for returning.
10110 Consider type @code{int} to be 16 bits wide, like @code{short int}.
10112 @item -msoft-reg-count=@var{count}
10113 @opindex msoft-reg-count
10114 Specify the number of pseudo-soft registers which are used for the
10115 code generation. The maximum number is 32. Using more pseudo-soft
10116 register may or may not result in better code depending on the program.
10117 The default is 4 for 68HC11 and 2 for 68HC12.
10121 @node MCore Options
10122 @subsection MCore Options
10123 @cindex MCore options
10125 These are the @samp{-m} options defined for the Motorola M*Core
10131 @itemx -mno-hardlit
10133 @opindex mno-hardlit
10134 Inline constants into the code stream if it can be done in two
10135 instructions or less.
10141 Use the divide instruction. (Enabled by default).
10143 @item -mrelax-immediate
10144 @itemx -mno-relax-immediate
10145 @opindex mrelax-immediate
10146 @opindex mno-relax-immediate
10147 Allow arbitrary sized immediates in bit operations.
10149 @item -mwide-bitfields
10150 @itemx -mno-wide-bitfields
10151 @opindex mwide-bitfields
10152 @opindex mno-wide-bitfields
10153 Always treat bit-fields as int-sized.
10155 @item -m4byte-functions
10156 @itemx -mno-4byte-functions
10157 @opindex m4byte-functions
10158 @opindex mno-4byte-functions
10159 Force all functions to be aligned to a four byte boundary.
10161 @item -mcallgraph-data
10162 @itemx -mno-callgraph-data
10163 @opindex mcallgraph-data
10164 @opindex mno-callgraph-data
10165 Emit callgraph information.
10168 @itemx -mno-slow-bytes
10169 @opindex mslow-bytes
10170 @opindex mno-slow-bytes
10171 Prefer word access when reading byte quantities.
10173 @item -mlittle-endian
10174 @itemx -mbig-endian
10175 @opindex mlittle-endian
10176 @opindex mbig-endian
10177 Generate code for a little endian target.
10183 Generate code for the 210 processor.
10187 @subsection MIPS Options
10188 @cindex MIPS options
10194 Generate big-endian code.
10198 Generate little-endian code. This is the default for @samp{mips*el-*-*}
10201 @item -march=@var{arch}
10203 Generate code that will run on @var{arch}, which can be the name of a
10204 generic MIPS ISA, or the name of a particular processor.
10206 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
10207 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
10208 The processor names are:
10209 @samp{4kc}, @samp{4km}, @samp{4kp},
10210 @samp{5kc}, @samp{5kf},
10212 @samp{24k}, @samp{24kc}, @samp{24kf}, @samp{24kx},
10215 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
10216 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
10217 @samp{rm7000}, @samp{rm9000},
10220 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
10221 @samp{vr5000}, @samp{vr5400} and @samp{vr5500}.
10222 The special value @samp{from-abi} selects the
10223 most compatible architecture for the selected ABI (that is,
10224 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
10226 In processor names, a final @samp{000} can be abbreviated as @samp{k}
10227 (for example, @samp{-march=r2k}). Prefixes are optional, and
10228 @samp{vr} may be written @samp{r}.
10230 GCC defines two macros based on the value of this option. The first
10231 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
10232 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
10233 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
10234 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
10235 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
10237 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
10238 above. In other words, it will have the full prefix and will not
10239 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
10240 the macro names the resolved architecture (either @samp{"mips1"} or
10241 @samp{"mips3"}). It names the default architecture when no
10242 @option{-march} option is given.
10244 @item -mtune=@var{arch}
10246 Optimize for @var{arch}. Among other things, this option controls
10247 the way instructions are scheduled, and the perceived cost of arithmetic
10248 operations. The list of @var{arch} values is the same as for
10251 When this option is not used, GCC will optimize for the processor
10252 specified by @option{-march}. By using @option{-march} and
10253 @option{-mtune} together, it is possible to generate code that will
10254 run on a family of processors, but optimize the code for one
10255 particular member of that family.
10257 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
10258 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
10259 @samp{-march} ones described above.
10263 Equivalent to @samp{-march=mips1}.
10267 Equivalent to @samp{-march=mips2}.
10271 Equivalent to @samp{-march=mips3}.
10275 Equivalent to @samp{-march=mips4}.
10279 Equivalent to @samp{-march=mips32}.
10283 Equivalent to @samp{-march=mips32r2}.
10287 Equivalent to @samp{-march=mips64}.
10292 @opindex mno-mips16
10293 Generate (do not generate) MIPS16 code. If GCC is targetting a
10294 MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
10306 Generate code for the given ABI@.
10308 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
10309 generates 64-bit code when you select a 64-bit architecture, but you
10310 can use @option{-mgp32} to get 32-bit code instead.
10312 For information about the O64 ABI, see
10313 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
10316 @itemx -mno-abicalls
10318 @opindex mno-abicalls
10319 Generate (do not generate) SVR4-style position-independent code.
10320 @option{-mabicalls} is the default for SVR4-based systems.
10326 Lift (do not lift) the usual restrictions on the size of the global
10329 GCC normally uses a single instruction to load values from the GOT@.
10330 While this is relatively efficient, it will only work if the GOT
10331 is smaller than about 64k. Anything larger will cause the linker
10332 to report an error such as:
10334 @cindex relocation truncated to fit (MIPS)
10336 relocation truncated to fit: R_MIPS_GOT16 foobar
10339 If this happens, you should recompile your code with @option{-mxgot}.
10340 It should then work with very large GOTs, although it will also be
10341 less efficient, since it will take three instructions to fetch the
10342 value of a global symbol.
10344 Note that some linkers can create multiple GOTs. If you have such a
10345 linker, you should only need to use @option{-mxgot} when a single object
10346 file accesses more than 64k's worth of GOT entries. Very few do.
10348 These options have no effect unless GCC is generating position
10353 Assume that general-purpose registers are 32 bits wide.
10357 Assume that general-purpose registers are 64 bits wide.
10361 Assume that floating-point registers are 32 bits wide.
10365 Assume that floating-point registers are 64 bits wide.
10368 @opindex mhard-float
10369 Use floating-point coprocessor instructions.
10372 @opindex msoft-float
10373 Do not use floating-point coprocessor instructions. Implement
10374 floating-point calculations using library calls instead.
10376 @item -msingle-float
10377 @opindex msingle-float
10378 Assume that the floating-point coprocessor only supports single-precision
10381 @itemx -mdouble-float
10382 @opindex mdouble-float
10383 Assume that the floating-point coprocessor supports double-precision
10384 operations. This is the default.
10390 Use (do not use) the MIPS DSP ASE. @xref{MIPS DSP Built-in Functions}.
10392 @itemx -mpaired-single
10393 @itemx -mno-paired-single
10394 @opindex mpaired-single
10395 @opindex mno-paired-single
10396 Use (do not use) paired-single floating-point instructions.
10397 @xref{MIPS Paired-Single Support}. This option can only be used
10398 when generating 64-bit code and requires hardware floating-point
10399 support to be enabled.
10404 @opindex mno-mips3d
10405 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
10406 The option @option{-mips3d} implies @option{-mpaired-single}.
10410 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
10411 an explanation of the default and the way that the pointer size is
10416 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
10418 The default size of @code{int}s, @code{long}s and pointers depends on
10419 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
10420 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
10421 32-bit @code{long}s. Pointers are the same size as @code{long}s,
10422 or the same size as integer registers, whichever is smaller.
10428 Assume (do not assume) that all symbols have 32-bit values, regardless
10429 of the selected ABI@. This option is useful in combination with
10430 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
10431 to generate shorter and faster references to symbolic addresses.
10435 @cindex smaller data references (MIPS)
10436 @cindex gp-relative references (MIPS)
10437 Put global and static items less than or equal to @var{num} bytes into
10438 the small data or bss section instead of the normal data or bss section.
10439 This allows the data to be accessed using a single instruction.
10441 All modules should be compiled with the same @option{-G @var{num}}
10444 @item -membedded-data
10445 @itemx -mno-embedded-data
10446 @opindex membedded-data
10447 @opindex mno-embedded-data
10448 Allocate variables to the read-only data section first if possible, then
10449 next in the small data section if possible, otherwise in data. This gives
10450 slightly slower code than the default, but reduces the amount of RAM required
10451 when executing, and thus may be preferred for some embedded systems.
10453 @item -muninit-const-in-rodata
10454 @itemx -mno-uninit-const-in-rodata
10455 @opindex muninit-const-in-rodata
10456 @opindex mno-uninit-const-in-rodata
10457 Put uninitialized @code{const} variables in the read-only data section.
10458 This option is only meaningful in conjunction with @option{-membedded-data}.
10460 @item -msplit-addresses
10461 @itemx -mno-split-addresses
10462 @opindex msplit-addresses
10463 @opindex mno-split-addresses
10464 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
10465 relocation operators. This option has been superseded by
10466 @option{-mexplicit-relocs} but is retained for backwards compatibility.
10468 @item -mexplicit-relocs
10469 @itemx -mno-explicit-relocs
10470 @opindex mexplicit-relocs
10471 @opindex mno-explicit-relocs
10472 Use (do not use) assembler relocation operators when dealing with symbolic
10473 addresses. The alternative, selected by @option{-mno-explicit-relocs},
10474 is to use assembler macros instead.
10476 @option{-mexplicit-relocs} is the default if GCC was configured
10477 to use an assembler that supports relocation operators.
10479 @item -mcheck-zero-division
10480 @itemx -mno-check-zero-division
10481 @opindex mcheck-zero-division
10482 @opindex mno-check-zero-division
10483 Trap (do not trap) on integer division by zero. The default is
10484 @option{-mcheck-zero-division}.
10486 @item -mdivide-traps
10487 @itemx -mdivide-breaks
10488 @opindex mdivide-traps
10489 @opindex mdivide-breaks
10490 MIPS systems check for division by zero by generating either a
10491 conditional trap or a break instruction. Using traps results in
10492 smaller code, but is only supported on MIPS II and later. Also, some
10493 versions of the Linux kernel have a bug that prevents trap from
10494 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
10495 allow conditional traps on architectures that support them and
10496 @option{-mdivide-breaks} to force the use of breaks.
10498 The default is usually @option{-mdivide-traps}, but this can be
10499 overridden at configure time using @option{--with-divide=breaks}.
10500 Divide-by-zero checks can be completely disabled using
10501 @option{-mno-check-zero-division}.
10506 @opindex mno-memcpy
10507 Force (do not force) the use of @code{memcpy()} for non-trivial block
10508 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
10509 most constant-sized copies.
10512 @itemx -mno-long-calls
10513 @opindex mlong-calls
10514 @opindex mno-long-calls
10515 Disable (do not disable) use of the @code{jal} instruction. Calling
10516 functions using @code{jal} is more efficient but requires the caller
10517 and callee to be in the same 256 megabyte segment.
10519 This option has no effect on abicalls code. The default is
10520 @option{-mno-long-calls}.
10526 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
10527 instructions, as provided by the R4650 ISA@.
10530 @itemx -mno-fused-madd
10531 @opindex mfused-madd
10532 @opindex mno-fused-madd
10533 Enable (disable) use of the floating point multiply-accumulate
10534 instructions, when they are available. The default is
10535 @option{-mfused-madd}.
10537 When multiply-accumulate instructions are used, the intermediate
10538 product is calculated to infinite precision and is not subject to
10539 the FCSR Flush to Zero bit. This may be undesirable in some
10544 Tell the MIPS assembler to not run its preprocessor over user
10545 assembler files (with a @samp{.s} suffix) when assembling them.
10548 @itemx -mno-fix-r4000
10549 @opindex mfix-r4000
10550 @opindex mno-fix-r4000
10551 Work around certain R4000 CPU errata:
10554 A double-word or a variable shift may give an incorrect result if executed
10555 immediately after starting an integer division.
10557 A double-word or a variable shift may give an incorrect result if executed
10558 while an integer multiplication is in progress.
10560 An integer division may give an incorrect result if started in a delay slot
10561 of a taken branch or a jump.
10565 @itemx -mno-fix-r4400
10566 @opindex mfix-r4400
10567 @opindex mno-fix-r4400
10568 Work around certain R4400 CPU errata:
10571 A double-word or a variable shift may give an incorrect result if executed
10572 immediately after starting an integer division.
10576 @itemx -mno-fix-vr4120
10577 @opindex mfix-vr4120
10578 Work around certain VR4120 errata:
10581 @code{dmultu} does not always produce the correct result.
10583 @code{div} and @code{ddiv} do not always produce the correct result if one
10584 of the operands is negative.
10586 The workarounds for the division errata rely on special functions in
10587 @file{libgcc.a}. At present, these functions are only provided by
10588 the @code{mips64vr*-elf} configurations.
10590 Other VR4120 errata require a nop to be inserted between certain pairs of
10591 instructions. These errata are handled by the assembler, not by GCC itself.
10594 @opindex mfix-vr4130
10595 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
10596 workarounds are implemented by the assembler rather than by GCC,
10597 although GCC will avoid using @code{mflo} and @code{mfhi} if the
10598 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
10599 instructions are available instead.
10602 @itemx -mno-fix-sb1
10604 Work around certain SB-1 CPU core errata.
10605 (This flag currently works around the SB-1 revision 2
10606 ``F1'' and ``F2'' floating point errata.)
10608 @item -mflush-func=@var{func}
10609 @itemx -mno-flush-func
10610 @opindex mflush-func
10611 Specifies the function to call to flush the I and D caches, or to not
10612 call any such function. If called, the function must take the same
10613 arguments as the common @code{_flush_func()}, that is, the address of the
10614 memory range for which the cache is being flushed, the size of the
10615 memory range, and the number 3 (to flush both caches). The default
10616 depends on the target GCC was configured for, but commonly is either
10617 @samp{_flush_func} or @samp{__cpu_flush}.
10619 @item -mbranch-likely
10620 @itemx -mno-branch-likely
10621 @opindex mbranch-likely
10622 @opindex mno-branch-likely
10623 Enable or disable use of Branch Likely instructions, regardless of the
10624 default for the selected architecture. By default, Branch Likely
10625 instructions may be generated if they are supported by the selected
10626 architecture. An exception is for the MIPS32 and MIPS64 architectures
10627 and processors which implement those architectures; for those, Branch
10628 Likely instructions will not be generated by default because the MIPS32
10629 and MIPS64 architectures specifically deprecate their use.
10631 @item -mfp-exceptions
10632 @itemx -mno-fp-exceptions
10633 @opindex mfp-exceptions
10634 Specifies whether FP exceptions are enabled. This affects how we schedule
10635 FP instructions for some processors. The default is that FP exceptions are
10638 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
10639 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
10642 @item -mvr4130-align
10643 @itemx -mno-vr4130-align
10644 @opindex mvr4130-align
10645 The VR4130 pipeline is two-way superscalar, but can only issue two
10646 instructions together if the first one is 8-byte aligned. When this
10647 option is enabled, GCC will align pairs of instructions that it
10648 thinks should execute in parallel.
10650 This option only has an effect when optimizing for the VR4130.
10651 It normally makes code faster, but at the expense of making it bigger.
10652 It is enabled by default at optimization level @option{-O3}.
10656 @subsection MMIX Options
10657 @cindex MMIX Options
10659 These options are defined for the MMIX:
10663 @itemx -mno-libfuncs
10665 @opindex mno-libfuncs
10666 Specify that intrinsic library functions are being compiled, passing all
10667 values in registers, no matter the size.
10670 @itemx -mno-epsilon
10672 @opindex mno-epsilon
10673 Generate floating-point comparison instructions that compare with respect
10674 to the @code{rE} epsilon register.
10676 @item -mabi=mmixware
10678 @opindex mabi-mmixware
10680 Generate code that passes function parameters and return values that (in
10681 the called function) are seen as registers @code{$0} and up, as opposed to
10682 the GNU ABI which uses global registers @code{$231} and up.
10684 @item -mzero-extend
10685 @itemx -mno-zero-extend
10686 @opindex mzero-extend
10687 @opindex mno-zero-extend
10688 When reading data from memory in sizes shorter than 64 bits, use (do not
10689 use) zero-extending load instructions by default, rather than
10690 sign-extending ones.
10693 @itemx -mno-knuthdiv
10695 @opindex mno-knuthdiv
10696 Make the result of a division yielding a remainder have the same sign as
10697 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
10698 remainder follows the sign of the dividend. Both methods are
10699 arithmetically valid, the latter being almost exclusively used.
10701 @item -mtoplevel-symbols
10702 @itemx -mno-toplevel-symbols
10703 @opindex mtoplevel-symbols
10704 @opindex mno-toplevel-symbols
10705 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
10706 code can be used with the @code{PREFIX} assembly directive.
10710 Generate an executable in the ELF format, rather than the default
10711 @samp{mmo} format used by the @command{mmix} simulator.
10713 @item -mbranch-predict
10714 @itemx -mno-branch-predict
10715 @opindex mbranch-predict
10716 @opindex mno-branch-predict
10717 Use (do not use) the probable-branch instructions, when static branch
10718 prediction indicates a probable branch.
10720 @item -mbase-addresses
10721 @itemx -mno-base-addresses
10722 @opindex mbase-addresses
10723 @opindex mno-base-addresses
10724 Generate (do not generate) code that uses @emph{base addresses}. Using a
10725 base address automatically generates a request (handled by the assembler
10726 and the linker) for a constant to be set up in a global register. The
10727 register is used for one or more base address requests within the range 0
10728 to 255 from the value held in the register. The generally leads to short
10729 and fast code, but the number of different data items that can be
10730 addressed is limited. This means that a program that uses lots of static
10731 data may require @option{-mno-base-addresses}.
10733 @item -msingle-exit
10734 @itemx -mno-single-exit
10735 @opindex msingle-exit
10736 @opindex mno-single-exit
10737 Force (do not force) generated code to have a single exit point in each
10741 @node MN10300 Options
10742 @subsection MN10300 Options
10743 @cindex MN10300 options
10745 These @option{-m} options are defined for Matsushita MN10300 architectures:
10750 Generate code to avoid bugs in the multiply instructions for the MN10300
10751 processors. This is the default.
10753 @item -mno-mult-bug
10754 @opindex mno-mult-bug
10755 Do not generate code to avoid bugs in the multiply instructions for the
10756 MN10300 processors.
10760 Generate code which uses features specific to the AM33 processor.
10764 Do not generate code which uses features specific to the AM33 processor. This
10767 @item -mreturn-pointer-on-d0
10768 @opindex mreturn-pointer-on-d0
10769 When generating a function which returns a pointer, return the pointer
10770 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
10771 only in a0, and attempts to call such functions without a prototype
10772 would result in errors. Note that this option is on by default; use
10773 @option{-mno-return-pointer-on-d0} to disable it.
10777 Do not link in the C run-time initialization object file.
10781 Indicate to the linker that it should perform a relaxation optimization pass
10782 to shorten branches, calls and absolute memory addresses. This option only
10783 has an effect when used on the command line for the final link step.
10785 This option makes symbolic debugging impossible.
10789 @subsection MT Options
10792 These @option{-m} options are defined for Morpho MT architectures:
10796 @item -march=@var{cpu-type}
10798 Generate code that will run on @var{cpu-type}, which is the name of a system
10799 representing a certain processor type. Possible values for
10800 @var{cpu-type} are @samp{ms1-64-001}, @samp{ms1-16-002},
10801 @samp{ms1-16-003} and @samp{ms2}.
10803 When this option is not used, the default is @option{-march=ms1-16-002}.
10807 Use byte loads and stores when generating code.
10811 Do not use byte loads and stores when generating code.
10815 Use simulator runtime
10819 Do not link in the C run-time initialization object file
10820 @file{crti.o}. Other run-time initialization and termination files
10821 such as @file{startup.o} and @file{exit.o} are still included on the
10822 linker command line.
10826 @node PDP-11 Options
10827 @subsection PDP-11 Options
10828 @cindex PDP-11 Options
10830 These options are defined for the PDP-11:
10835 Use hardware FPP floating point. This is the default. (FIS floating
10836 point on the PDP-11/40 is not supported.)
10839 @opindex msoft-float
10840 Do not use hardware floating point.
10844 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
10848 Return floating-point results in memory. This is the default.
10852 Generate code for a PDP-11/40.
10856 Generate code for a PDP-11/45. This is the default.
10860 Generate code for a PDP-11/10.
10862 @item -mbcopy-builtin
10863 @opindex bcopy-builtin
10864 Use inline @code{movmemhi} patterns for copying memory. This is the
10869 Do not use inline @code{movmemhi} patterns for copying memory.
10875 Use 16-bit @code{int}. This is the default.
10881 Use 32-bit @code{int}.
10884 @itemx -mno-float32
10886 @opindex mno-float32
10887 Use 64-bit @code{float}. This is the default.
10890 @itemx -mno-float64
10892 @opindex mno-float64
10893 Use 32-bit @code{float}.
10897 Use @code{abshi2} pattern. This is the default.
10901 Do not use @code{abshi2} pattern.
10903 @item -mbranch-expensive
10904 @opindex mbranch-expensive
10905 Pretend that branches are expensive. This is for experimenting with
10906 code generation only.
10908 @item -mbranch-cheap
10909 @opindex mbranch-cheap
10910 Do not pretend that branches are expensive. This is the default.
10914 Generate code for a system with split I&D@.
10918 Generate code for a system without split I&D@. This is the default.
10922 Use Unix assembler syntax. This is the default when configured for
10923 @samp{pdp11-*-bsd}.
10927 Use DEC assembler syntax. This is the default when configured for any
10928 PDP-11 target other than @samp{pdp11-*-bsd}.
10931 @node PowerPC Options
10932 @subsection PowerPC Options
10933 @cindex PowerPC options
10935 These are listed under @xref{RS/6000 and PowerPC Options}.
10937 @node RS/6000 and PowerPC Options
10938 @subsection IBM RS/6000 and PowerPC Options
10939 @cindex RS/6000 and PowerPC Options
10940 @cindex IBM RS/6000 and PowerPC Options
10942 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
10949 @itemx -mno-powerpc
10950 @itemx -mpowerpc-gpopt
10951 @itemx -mno-powerpc-gpopt
10952 @itemx -mpowerpc-gfxopt
10953 @itemx -mno-powerpc-gfxopt
10955 @itemx -mno-powerpc64
10959 @itemx -mno-popcntb
10965 @opindex mno-power2
10967 @opindex mno-powerpc
10968 @opindex mpowerpc-gpopt
10969 @opindex mno-powerpc-gpopt
10970 @opindex mpowerpc-gfxopt
10971 @opindex mno-powerpc-gfxopt
10972 @opindex mpowerpc64
10973 @opindex mno-powerpc64
10977 @opindex mno-popcntb
10980 GCC supports two related instruction set architectures for the
10981 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
10982 instructions supported by the @samp{rios} chip set used in the original
10983 RS/6000 systems and the @dfn{PowerPC} instruction set is the
10984 architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and
10985 the IBM 4xx, 6xx, and follow-on microprocessors.
10987 Neither architecture is a subset of the other. However there is a
10988 large common subset of instructions supported by both. An MQ
10989 register is included in processors supporting the POWER architecture.
10991 You use these options to specify which instructions are available on the
10992 processor you are using. The default value of these options is
10993 determined when configuring GCC@. Specifying the
10994 @option{-mcpu=@var{cpu_type}} overrides the specification of these
10995 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
10996 rather than the options listed above.
10998 The @option{-mpower} option allows GCC to generate instructions that
10999 are found only in the POWER architecture and to use the MQ register.
11000 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
11001 to generate instructions that are present in the POWER2 architecture but
11002 not the original POWER architecture.
11004 The @option{-mpowerpc} option allows GCC to generate instructions that
11005 are found only in the 32-bit subset of the PowerPC architecture.
11006 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
11007 GCC to use the optional PowerPC architecture instructions in the
11008 General Purpose group, including floating-point square root. Specifying
11009 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
11010 use the optional PowerPC architecture instructions in the Graphics
11011 group, including floating-point select.
11013 The @option{-mmfcrf} option allows GCC to generate the move from
11014 condition register field instruction implemented on the POWER4
11015 processor and other processors that support the PowerPC V2.01
11017 The @option{-mpopcntb} option allows GCC to generate the popcount and
11018 double precision FP reciprocal estimate instruction implemented on the
11019 POWER5 processor and other processors that support the PowerPC V2.02
11021 The @option{-mfprnd} option allows GCC to generate the FP round to
11022 integer instructions implemented on the POWER5+ processor and other
11023 processors that support the PowerPC V2.03 architecture.
11025 The @option{-mpowerpc64} option allows GCC to generate the additional
11026 64-bit instructions that are found in the full PowerPC64 architecture
11027 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
11028 @option{-mno-powerpc64}.
11030 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
11031 will use only the instructions in the common subset of both
11032 architectures plus some special AIX common-mode calls, and will not use
11033 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
11034 permits GCC to use any instruction from either architecture and to
11035 allow use of the MQ register; specify this for the Motorola MPC601.
11037 @item -mnew-mnemonics
11038 @itemx -mold-mnemonics
11039 @opindex mnew-mnemonics
11040 @opindex mold-mnemonics
11041 Select which mnemonics to use in the generated assembler code. With
11042 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
11043 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
11044 assembler mnemonics defined for the POWER architecture. Instructions
11045 defined in only one architecture have only one mnemonic; GCC uses that
11046 mnemonic irrespective of which of these options is specified.
11048 GCC defaults to the mnemonics appropriate for the architecture in
11049 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
11050 value of these option. Unless you are building a cross-compiler, you
11051 should normally not specify either @option{-mnew-mnemonics} or
11052 @option{-mold-mnemonics}, but should instead accept the default.
11054 @item -mcpu=@var{cpu_type}
11056 Set architecture type, register usage, choice of mnemonics, and
11057 instruction scheduling parameters for machine type @var{cpu_type}.
11058 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
11059 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{505},
11060 @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
11061 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
11062 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
11063 @samp{860}, @samp{970}, @samp{8540}, @samp{ec603e}, @samp{G3},
11064 @samp{G4}, @samp{G5}, @samp{power}, @samp{power2}, @samp{power3},
11065 @samp{power4}, @samp{power5}, @samp{power5+},
11066 @samp{common}, @samp{powerpc}, @samp{powerpc64},
11067 @samp{rios}, @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
11069 @option{-mcpu=common} selects a completely generic processor. Code
11070 generated under this option will run on any POWER or PowerPC processor.
11071 GCC will use only the instructions in the common subset of both
11072 architectures, and will not use the MQ register. GCC assumes a generic
11073 processor model for scheduling purposes.
11075 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
11076 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
11077 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
11078 types, with an appropriate, generic processor model assumed for
11079 scheduling purposes.
11081 The other options specify a specific processor. Code generated under
11082 those options will run best on that processor, and may not run at all on
11085 The @option{-mcpu} options automatically enable or disable the
11086 following options: @option{-maltivec}, @option{-mfprnd},
11087 @option{-mhard-float}, @option{-mmfcrf}, @option{-mmultiple},
11088 @option{-mnew-mnemonics}, @option{-mpopcntb}, @option{-mpower},
11089 @option{-mpower2}, @option{-mpowerpc64}, @option{-mpowerpc-gpopt},
11090 @option{-mpowerpc-gfxopt}, @option{-mstring}, @option{-mmulhw}.
11091 The particular options
11092 set for any particular CPU will vary between compiler versions,
11093 depending on what setting seems to produce optimal code for that CPU;
11094 it doesn't necessarily reflect the actual hardware's capabilities. If
11095 you wish to set an individual option to a particular value, you may
11096 specify it after the @option{-mcpu} option, like @samp{-mcpu=970
11099 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
11100 not enabled or disabled by the @option{-mcpu} option at present because
11101 AIX does not have full support for these options. You may still
11102 enable or disable them individually if you're sure it'll work in your
11105 @item -mtune=@var{cpu_type}
11107 Set the instruction scheduling parameters for machine type
11108 @var{cpu_type}, but do not set the architecture type, register usage, or
11109 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
11110 values for @var{cpu_type} are used for @option{-mtune} as for
11111 @option{-mcpu}. If both are specified, the code generated will use the
11112 architecture, registers, and mnemonics set by @option{-mcpu}, but the
11113 scheduling parameters set by @option{-mtune}.
11119 Generate code to compute division as reciprocal estimate and iterative
11120 refinement, creating opportunities for increased throughput. This
11121 feature requires: optional PowerPC Graphics instruction set for single
11122 precision and FRE instruction for double precision, assuming divides
11123 cannot generate user-visible traps, and the domain values not include
11124 Infinities, denormals or zero denominator.
11127 @itemx -mno-altivec
11129 @opindex mno-altivec
11130 Generate code that uses (does not use) AltiVec instructions, and also
11131 enable the use of built-in functions that allow more direct access to
11132 the AltiVec instruction set. You may also need to set
11133 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
11139 @opindex mno-vrsave
11140 Generate VRSAVE instructions when generating AltiVec code.
11143 @opindex msecure-plt
11144 Generate code that allows ld and ld.so to build executables and shared
11145 libraries with non-exec .plt and .got sections. This is a PowerPC
11146 32-bit SYSV ABI option.
11150 Generate code that uses a BSS .plt section that ld.so fills in, and
11151 requires .plt and .got sections that are both writable and executable.
11152 This is a PowerPC 32-bit SYSV ABI option.
11158 This switch enables or disables the generation of ISEL instructions.
11160 @item -misel=@var{yes/no}
11161 This switch has been deprecated. Use @option{-misel} and
11162 @option{-mno-isel} instead.
11168 This switch enables or disables the generation of SPE simd
11171 @item -mspe=@var{yes/no}
11172 This option has been deprecated. Use @option{-mspe} and
11173 @option{-mno-spe} instead.
11175 @item -mfloat-gprs=@var{yes/single/double/no}
11176 @itemx -mfloat-gprs
11177 @opindex mfloat-gprs
11178 This switch enables or disables the generation of floating point
11179 operations on the general purpose registers for architectures that
11182 The argument @var{yes} or @var{single} enables the use of
11183 single-precision floating point operations.
11185 The argument @var{double} enables the use of single and
11186 double-precision floating point operations.
11188 The argument @var{no} disables floating point operations on the
11189 general purpose registers.
11191 This option is currently only available on the MPC854x.
11197 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
11198 targets (including GNU/Linux). The 32-bit environment sets int, long
11199 and pointer to 32 bits and generates code that runs on any PowerPC
11200 variant. The 64-bit environment sets int to 32 bits and long and
11201 pointer to 64 bits, and generates code for PowerPC64, as for
11202 @option{-mpowerpc64}.
11205 @itemx -mno-fp-in-toc
11206 @itemx -mno-sum-in-toc
11207 @itemx -mminimal-toc
11209 @opindex mno-fp-in-toc
11210 @opindex mno-sum-in-toc
11211 @opindex mminimal-toc
11212 Modify generation of the TOC (Table Of Contents), which is created for
11213 every executable file. The @option{-mfull-toc} option is selected by
11214 default. In that case, GCC will allocate at least one TOC entry for
11215 each unique non-automatic variable reference in your program. GCC
11216 will also place floating-point constants in the TOC@. However, only
11217 16,384 entries are available in the TOC@.
11219 If you receive a linker error message that saying you have overflowed
11220 the available TOC space, you can reduce the amount of TOC space used
11221 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
11222 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
11223 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
11224 generate code to calculate the sum of an address and a constant at
11225 run-time instead of putting that sum into the TOC@. You may specify one
11226 or both of these options. Each causes GCC to produce very slightly
11227 slower and larger code at the expense of conserving TOC space.
11229 If you still run out of space in the TOC even when you specify both of
11230 these options, specify @option{-mminimal-toc} instead. This option causes
11231 GCC to make only one TOC entry for every file. When you specify this
11232 option, GCC will produce code that is slower and larger but which
11233 uses extremely little TOC space. You may wish to use this option
11234 only on files that contain less frequently executed code.
11240 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
11241 @code{long} type, and the infrastructure needed to support them.
11242 Specifying @option{-maix64} implies @option{-mpowerpc64} and
11243 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
11244 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
11247 @itemx -mno-xl-compat
11248 @opindex mxl-compat
11249 @opindex mno-xl-compat
11250 Produce code that conforms more closely to IBM XL compiler semantics
11251 when using AIX-compatible ABI. Pass floating-point arguments to
11252 prototyped functions beyond the register save area (RSA) on the stack
11253 in addition to argument FPRs. Do not assume that most significant
11254 double in 128-bit long double value is properly rounded when comparing
11255 values and converting to double. Use XL symbol names for long double
11258 The AIX calling convention was extended but not initially documented to
11259 handle an obscure K&R C case of calling a function that takes the
11260 address of its arguments with fewer arguments than declared. IBM XL
11261 compilers access floating point arguments which do not fit in the
11262 RSA from the stack when a subroutine is compiled without
11263 optimization. Because always storing floating-point arguments on the
11264 stack is inefficient and rarely needed, this option is not enabled by
11265 default and only is necessary when calling subroutines compiled by IBM
11266 XL compilers without optimization.
11270 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
11271 application written to use message passing with special startup code to
11272 enable the application to run. The system must have PE installed in the
11273 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
11274 must be overridden with the @option{-specs=} option to specify the
11275 appropriate directory location. The Parallel Environment does not
11276 support threads, so the @option{-mpe} option and the @option{-pthread}
11277 option are incompatible.
11279 @item -malign-natural
11280 @itemx -malign-power
11281 @opindex malign-natural
11282 @opindex malign-power
11283 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
11284 @option{-malign-natural} overrides the ABI-defined alignment of larger
11285 types, such as floating-point doubles, on their natural size-based boundary.
11286 The option @option{-malign-power} instructs GCC to follow the ABI-specified
11287 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
11289 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
11293 @itemx -mhard-float
11294 @opindex msoft-float
11295 @opindex mhard-float
11296 Generate code that does not use (uses) the floating-point register set.
11297 Software floating point emulation is provided if you use the
11298 @option{-msoft-float} option, and pass the option to GCC when linking.
11301 @itemx -mno-multiple
11303 @opindex mno-multiple
11304 Generate code that uses (does not use) the load multiple word
11305 instructions and the store multiple word instructions. These
11306 instructions are generated by default on POWER systems, and not
11307 generated on PowerPC systems. Do not use @option{-mmultiple} on little
11308 endian PowerPC systems, since those instructions do not work when the
11309 processor is in little endian mode. The exceptions are PPC740 and
11310 PPC750 which permit the instructions usage in little endian mode.
11315 @opindex mno-string
11316 Generate code that uses (does not use) the load string instructions
11317 and the store string word instructions to save multiple registers and
11318 do small block moves. These instructions are generated by default on
11319 POWER systems, and not generated on PowerPC systems. Do not use
11320 @option{-mstring} on little endian PowerPC systems, since those
11321 instructions do not work when the processor is in little endian mode.
11322 The exceptions are PPC740 and PPC750 which permit the instructions
11323 usage in little endian mode.
11328 @opindex mno-update
11329 Generate code that uses (does not use) the load or store instructions
11330 that update the base register to the address of the calculated memory
11331 location. These instructions are generated by default. If you use
11332 @option{-mno-update}, there is a small window between the time that the
11333 stack pointer is updated and the address of the previous frame is
11334 stored, which means code that walks the stack frame across interrupts or
11335 signals may get corrupted data.
11338 @itemx -mno-fused-madd
11339 @opindex mfused-madd
11340 @opindex mno-fused-madd
11341 Generate code that uses (does not use) the floating point multiply and
11342 accumulate instructions. These instructions are generated by default if
11343 hardware floating is used.
11349 Generate code that uses (does not use) the half-word multiply and
11350 multiply-accumulate instructions on the IBM 405 and 440 processors.
11351 These instructions are generated by default when targetting those
11354 @item -mno-bit-align
11356 @opindex mno-bit-align
11357 @opindex mbit-align
11358 On System V.4 and embedded PowerPC systems do not (do) force structures
11359 and unions that contain bit-fields to be aligned to the base type of the
11362 For example, by default a structure containing nothing but 8
11363 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
11364 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
11365 the structure would be aligned to a 1 byte boundary and be one byte in
11368 @item -mno-strict-align
11369 @itemx -mstrict-align
11370 @opindex mno-strict-align
11371 @opindex mstrict-align
11372 On System V.4 and embedded PowerPC systems do not (do) assume that
11373 unaligned memory references will be handled by the system.
11375 @item -mrelocatable
11376 @itemx -mno-relocatable
11377 @opindex mrelocatable
11378 @opindex mno-relocatable
11379 On embedded PowerPC systems generate code that allows (does not allow)
11380 the program to be relocated to a different address at runtime. If you
11381 use @option{-mrelocatable} on any module, all objects linked together must
11382 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
11384 @item -mrelocatable-lib
11385 @itemx -mno-relocatable-lib
11386 @opindex mrelocatable-lib
11387 @opindex mno-relocatable-lib
11388 On embedded PowerPC systems generate code that allows (does not allow)
11389 the program to be relocated to a different address at runtime. Modules
11390 compiled with @option{-mrelocatable-lib} can be linked with either modules
11391 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
11392 with modules compiled with the @option{-mrelocatable} options.
11398 On System V.4 and embedded PowerPC systems do not (do) assume that
11399 register 2 contains a pointer to a global area pointing to the addresses
11400 used in the program.
11403 @itemx -mlittle-endian
11405 @opindex mlittle-endian
11406 On System V.4 and embedded PowerPC systems compile code for the
11407 processor in little endian mode. The @option{-mlittle-endian} option is
11408 the same as @option{-mlittle}.
11411 @itemx -mbig-endian
11413 @opindex mbig-endian
11414 On System V.4 and embedded PowerPC systems compile code for the
11415 processor in big endian mode. The @option{-mbig-endian} option is
11416 the same as @option{-mbig}.
11418 @item -mdynamic-no-pic
11419 @opindex mdynamic-no-pic
11420 On Darwin and Mac OS X systems, compile code so that it is not
11421 relocatable, but that its external references are relocatable. The
11422 resulting code is suitable for applications, but not shared
11425 @item -mprioritize-restricted-insns=@var{priority}
11426 @opindex mprioritize-restricted-insns
11427 This option controls the priority that is assigned to
11428 dispatch-slot restricted instructions during the second scheduling
11429 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
11430 @var{no/highest/second-highest} priority to dispatch slot restricted
11433 @item -msched-costly-dep=@var{dependence_type}
11434 @opindex msched-costly-dep
11435 This option controls which dependences are considered costly
11436 by the target during instruction scheduling. The argument
11437 @var{dependence_type} takes one of the following values:
11438 @var{no}: no dependence is costly,
11439 @var{all}: all dependences are costly,
11440 @var{true_store_to_load}: a true dependence from store to load is costly,
11441 @var{store_to_load}: any dependence from store to load is costly,
11442 @var{number}: any dependence which latency >= @var{number} is costly.
11444 @item -minsert-sched-nops=@var{scheme}
11445 @opindex minsert-sched-nops
11446 This option controls which nop insertion scheme will be used during
11447 the second scheduling pass. The argument @var{scheme} takes one of the
11449 @var{no}: Don't insert nops.
11450 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
11451 according to the scheduler's grouping.
11452 @var{regroup_exact}: Insert nops to force costly dependent insns into
11453 separate groups. Insert exactly as many nops as needed to force an insn
11454 to a new group, according to the estimated processor grouping.
11455 @var{number}: Insert nops to force costly dependent insns into
11456 separate groups. Insert @var{number} nops to force an insn to a new group.
11459 @opindex mcall-sysv
11460 On System V.4 and embedded PowerPC systems compile code using calling
11461 conventions that adheres to the March 1995 draft of the System V
11462 Application Binary Interface, PowerPC processor supplement. This is the
11463 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
11465 @item -mcall-sysv-eabi
11466 @opindex mcall-sysv-eabi
11467 Specify both @option{-mcall-sysv} and @option{-meabi} options.
11469 @item -mcall-sysv-noeabi
11470 @opindex mcall-sysv-noeabi
11471 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
11473 @item -mcall-solaris
11474 @opindex mcall-solaris
11475 On System V.4 and embedded PowerPC systems compile code for the Solaris
11479 @opindex mcall-linux
11480 On System V.4 and embedded PowerPC systems compile code for the
11481 Linux-based GNU system.
11485 On System V.4 and embedded PowerPC systems compile code for the
11486 Hurd-based GNU system.
11488 @item -mcall-netbsd
11489 @opindex mcall-netbsd
11490 On System V.4 and embedded PowerPC systems compile code for the
11491 NetBSD operating system.
11493 @item -maix-struct-return
11494 @opindex maix-struct-return
11495 Return all structures in memory (as specified by the AIX ABI)@.
11497 @item -msvr4-struct-return
11498 @opindex msvr4-struct-return
11499 Return structures smaller than 8 bytes in registers (as specified by the
11502 @item -mabi=@var{abi-type}
11504 Extend the current ABI with a particular extension, or remove such extension.
11505 Valid values are @var{altivec}, @var{no-altivec}, @var{spe},
11506 @var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}@.
11510 Extend the current ABI with SPE ABI extensions. This does not change
11511 the default ABI, instead it adds the SPE ABI extensions to the current
11515 @opindex mabi=no-spe
11516 Disable Booke SPE ABI extensions for the current ABI@.
11518 @item -mabi=ibmlongdouble
11519 @opindex mabi=ibmlongdouble
11520 Change the current ABI to use IBM extended precision long double.
11521 This is a PowerPC 32-bit SYSV ABI option.
11523 @item -mabi=ieeelongdouble
11524 @opindex mabi=ieeelongdouble
11525 Change the current ABI to use IEEE extended precision long double.
11526 This is a PowerPC 32-bit Linux ABI option.
11529 @itemx -mno-prototype
11530 @opindex mprototype
11531 @opindex mno-prototype
11532 On System V.4 and embedded PowerPC systems assume that all calls to
11533 variable argument functions are properly prototyped. Otherwise, the
11534 compiler must insert an instruction before every non prototyped call to
11535 set or clear bit 6 of the condition code register (@var{CR}) to
11536 indicate whether floating point values were passed in the floating point
11537 registers in case the function takes a variable arguments. With
11538 @option{-mprototype}, only calls to prototyped variable argument functions
11539 will set or clear the bit.
11543 On embedded PowerPC systems, assume that the startup module is called
11544 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
11545 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
11550 On embedded PowerPC systems, assume that the startup module is called
11551 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
11556 On embedded PowerPC systems, assume that the startup module is called
11557 @file{crt0.o} and the standard C libraries are @file{libads.a} and
11560 @item -myellowknife
11561 @opindex myellowknife
11562 On embedded PowerPC systems, assume that the startup module is called
11563 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
11568 On System V.4 and embedded PowerPC systems, specify that you are
11569 compiling for a VxWorks system.
11573 Specify that you are compiling for the WindISS simulation environment.
11577 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
11578 header to indicate that @samp{eabi} extended relocations are used.
11584 On System V.4 and embedded PowerPC systems do (do not) adhere to the
11585 Embedded Applications Binary Interface (eabi) which is a set of
11586 modifications to the System V.4 specifications. Selecting @option{-meabi}
11587 means that the stack is aligned to an 8 byte boundary, a function
11588 @code{__eabi} is called to from @code{main} to set up the eabi
11589 environment, and the @option{-msdata} option can use both @code{r2} and
11590 @code{r13} to point to two separate small data areas. Selecting
11591 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
11592 do not call an initialization function from @code{main}, and the
11593 @option{-msdata} option will only use @code{r13} to point to a single
11594 small data area. The @option{-meabi} option is on by default if you
11595 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
11598 @opindex msdata=eabi
11599 On System V.4 and embedded PowerPC systems, put small initialized
11600 @code{const} global and static data in the @samp{.sdata2} section, which
11601 is pointed to by register @code{r2}. Put small initialized
11602 non-@code{const} global and static data in the @samp{.sdata} section,
11603 which is pointed to by register @code{r13}. Put small uninitialized
11604 global and static data in the @samp{.sbss} section, which is adjacent to
11605 the @samp{.sdata} section. The @option{-msdata=eabi} option is
11606 incompatible with the @option{-mrelocatable} option. The
11607 @option{-msdata=eabi} option also sets the @option{-memb} option.
11610 @opindex msdata=sysv
11611 On System V.4 and embedded PowerPC systems, put small global and static
11612 data in the @samp{.sdata} section, which is pointed to by register
11613 @code{r13}. Put small uninitialized global and static data in the
11614 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
11615 The @option{-msdata=sysv} option is incompatible with the
11616 @option{-mrelocatable} option.
11618 @item -msdata=default
11620 @opindex msdata=default
11622 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
11623 compile code the same as @option{-msdata=eabi}, otherwise compile code the
11624 same as @option{-msdata=sysv}.
11627 @opindex msdata-data
11628 On System V.4 and embedded PowerPC systems, put small global
11629 data in the @samp{.sdata} section. Put small uninitialized global
11630 data in the @samp{.sbss} section. Do not use register @code{r13}
11631 to address small data however. This is the default behavior unless
11632 other @option{-msdata} options are used.
11636 @opindex msdata=none
11638 On embedded PowerPC systems, put all initialized global and static data
11639 in the @samp{.data} section, and all uninitialized data in the
11640 @samp{.bss} section.
11644 @cindex smaller data references (PowerPC)
11645 @cindex .sdata/.sdata2 references (PowerPC)
11646 On embedded PowerPC systems, put global and static items less than or
11647 equal to @var{num} bytes into the small data or bss sections instead of
11648 the normal data or bss section. By default, @var{num} is 8. The
11649 @option{-G @var{num}} switch is also passed to the linker.
11650 All modules should be compiled with the same @option{-G @var{num}} value.
11653 @itemx -mno-regnames
11655 @opindex mno-regnames
11656 On System V.4 and embedded PowerPC systems do (do not) emit register
11657 names in the assembly language output using symbolic forms.
11660 @itemx -mno-longcall
11662 @opindex mno-longcall
11663 Default to making all function calls indirectly, using a register, so
11664 that functions which reside further than 32 megabytes (33,554,432
11665 bytes) from the current location can be called. This setting can be
11666 overridden by the @code{shortcall} function attribute, or by
11667 @code{#pragma longcall(0)}.
11669 Some linkers are capable of detecting out-of-range calls and generating
11670 glue code on the fly. On these systems, long calls are unnecessary and
11671 generate slower code. As of this writing, the AIX linker can do this,
11672 as can the GNU linker for PowerPC/64. It is planned to add this feature
11673 to the GNU linker for 32-bit PowerPC systems as well.
11675 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
11676 callee, L42'', plus a ``branch island'' (glue code). The two target
11677 addresses represent the callee and the ``branch island''. The
11678 Darwin/PPC linker will prefer the first address and generate a ``bl
11679 callee'' if the PPC ``bl'' instruction will reach the callee directly;
11680 otherwise, the linker will generate ``bl L42'' to call the ``branch
11681 island''. The ``branch island'' is appended to the body of the
11682 calling function; it computes the full 32-bit address of the callee
11685 On Mach-O (Darwin) systems, this option directs the compiler emit to
11686 the glue for every direct call, and the Darwin linker decides whether
11687 to use or discard it.
11689 In the future, we may cause GCC to ignore all longcall specifications
11690 when the linker is known to generate glue.
11694 Adds support for multithreading with the @dfn{pthreads} library.
11695 This option sets flags for both the preprocessor and linker.
11699 @node S/390 and zSeries Options
11700 @subsection S/390 and zSeries Options
11701 @cindex S/390 and zSeries Options
11703 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
11707 @itemx -msoft-float
11708 @opindex mhard-float
11709 @opindex msoft-float
11710 Use (do not use) the hardware floating-point instructions and registers
11711 for floating-point operations. When @option{-msoft-float} is specified,
11712 functions in @file{libgcc.a} will be used to perform floating-point
11713 operations. When @option{-mhard-float} is specified, the compiler
11714 generates IEEE floating-point instructions. This is the default.
11716 @item -mlong-double-64
11717 @itemx -mlong-double-128
11718 @opindex mlong-double-64
11719 @opindex mlong-double-128
11720 These switches control the size of @code{long double} type. A size
11721 of 64bit makes the @code{long double} type equivalent to the @code{double}
11722 type. This is the default.
11725 @itemx -mno-backchain
11726 @opindex mbackchain
11727 @opindex mno-backchain
11728 Store (do not store) the address of the caller's frame as backchain pointer
11729 into the callee's stack frame.
11730 A backchain may be needed to allow debugging using tools that do not understand
11731 DWARF-2 call frame information.
11732 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
11733 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
11734 the backchain is placed into the topmost word of the 96/160 byte register
11737 In general, code compiled with @option{-mbackchain} is call-compatible with
11738 code compiled with @option{-mmo-backchain}; however, use of the backchain
11739 for debugging purposes usually requires that the whole binary is built with
11740 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
11741 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
11742 to build a linux kernel use @option{-msoft-float}.
11744 The default is to not maintain the backchain.
11746 @item -mpacked-stack
11747 @item -mno-packed-stack
11748 @opindex mpacked-stack
11749 @opindex mno-packed-stack
11750 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
11751 specified, the compiler uses the all fields of the 96/160 byte register save
11752 area only for their default purpose; unused fields still take up stack space.
11753 When @option{-mpacked-stack} is specified, register save slots are densely
11754 packed at the top of the register save area; unused space is reused for other
11755 purposes, allowing for more efficient use of the available stack space.
11756 However, when @option{-mbackchain} is also in effect, the topmost word of
11757 the save area is always used to store the backchain, and the return address
11758 register is always saved two words below the backchain.
11760 As long as the stack frame backchain is not used, code generated with
11761 @option{-mpacked-stack} is call-compatible with code generated with
11762 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
11763 S/390 or zSeries generated code that uses the stack frame backchain at run
11764 time, not just for debugging purposes. Such code is not call-compatible
11765 with code compiled with @option{-mpacked-stack}. Also, note that the
11766 combination of @option{-mbackchain},
11767 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
11768 to build a linux kernel use @option{-msoft-float}.
11770 The default is to not use the packed stack layout.
11773 @itemx -mno-small-exec
11774 @opindex msmall-exec
11775 @opindex mno-small-exec
11776 Generate (or do not generate) code using the @code{bras} instruction
11777 to do subroutine calls.
11778 This only works reliably if the total executable size does not
11779 exceed 64k. The default is to use the @code{basr} instruction instead,
11780 which does not have this limitation.
11786 When @option{-m31} is specified, generate code compliant to the
11787 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
11788 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
11789 particular to generate 64-bit instructions. For the @samp{s390}
11790 targets, the default is @option{-m31}, while the @samp{s390x}
11791 targets default to @option{-m64}.
11797 When @option{-mzarch} is specified, generate code using the
11798 instructions available on z/Architecture.
11799 When @option{-mesa} is specified, generate code using the
11800 instructions available on ESA/390. Note that @option{-mesa} is
11801 not possible with @option{-m64}.
11802 When generating code compliant to the GNU/Linux for S/390 ABI,
11803 the default is @option{-mesa}. When generating code compliant
11804 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
11810 Generate (or do not generate) code using the @code{mvcle} instruction
11811 to perform block moves. When @option{-mno-mvcle} is specified,
11812 use a @code{mvc} loop instead. This is the default unless optimizing for
11819 Print (or do not print) additional debug information when compiling.
11820 The default is to not print debug information.
11822 @item -march=@var{cpu-type}
11824 Generate code that will run on @var{cpu-type}, which is the name of a system
11825 representing a certain processor type. Possible values for
11826 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
11827 When generating code using the instructions available on z/Architecture,
11828 the default is @option{-march=z900}. Otherwise, the default is
11829 @option{-march=g5}.
11831 @item -mtune=@var{cpu-type}
11833 Tune to @var{cpu-type} everything applicable about the generated code,
11834 except for the ABI and the set of available instructions.
11835 The list of @var{cpu-type} values is the same as for @option{-march}.
11836 The default is the value used for @option{-march}.
11839 @itemx -mno-tpf-trace
11840 @opindex mtpf-trace
11841 @opindex mno-tpf-trace
11842 Generate code that adds (does not add) in TPF OS specific branches to trace
11843 routines in the operating system. This option is off by default, even
11844 when compiling for the TPF OS@.
11847 @itemx -mno-fused-madd
11848 @opindex mfused-madd
11849 @opindex mno-fused-madd
11850 Generate code that uses (does not use) the floating point multiply and
11851 accumulate instructions. These instructions are generated by default if
11852 hardware floating point is used.
11854 @item -mwarn-framesize=@var{framesize}
11855 @opindex mwarn-framesize
11856 Emit a warning if the current function exceeds the given frame size. Because
11857 this is a compile time check it doesn't need to be a real problem when the program
11858 runs. It is intended to identify functions which most probably cause
11859 a stack overflow. It is useful to be used in an environment with limited stack
11860 size e.g.@: the linux kernel.
11862 @item -mwarn-dynamicstack
11863 @opindex mwarn-dynamicstack
11864 Emit a warning if the function calls alloca or uses dynamically
11865 sized arrays. This is generally a bad idea with a limited stack size.
11867 @item -mstack-guard=@var{stack-guard}
11868 @item -mstack-size=@var{stack-size}
11869 @opindex mstack-guard
11870 @opindex mstack-size
11871 These arguments always have to be used in conjunction. If they are present the s390
11872 back end emits additional instructions in the function prologue which trigger a trap
11873 if the stack size is @var{stack-guard} bytes above the @var{stack-size}
11874 (remember that the stack on s390 grows downward). These options are intended to
11875 be used to help debugging stack overflow problems. The additionally emitted code
11876 causes only little overhead and hence can also be used in production like systems
11877 without greater performance degradation. The given values have to be exact
11878 powers of 2 and @var{stack-size} has to be greater than @var{stack-guard} without
11880 In order to be efficient the extra code makes the assumption that the stack starts
11881 at an address aligned to the value given by @var{stack-size}.
11885 @subsection SH Options
11887 These @samp{-m} options are defined for the SH implementations:
11892 Generate code for the SH1.
11896 Generate code for the SH2.
11899 Generate code for the SH2e.
11903 Generate code for the SH3.
11907 Generate code for the SH3e.
11911 Generate code for the SH4 without a floating-point unit.
11913 @item -m4-single-only
11914 @opindex m4-single-only
11915 Generate code for the SH4 with a floating-point unit that only
11916 supports single-precision arithmetic.
11920 Generate code for the SH4 assuming the floating-point unit is in
11921 single-precision mode by default.
11925 Generate code for the SH4.
11929 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
11930 floating-point unit is not used.
11932 @item -m4a-single-only
11933 @opindex m4a-single-only
11934 Generate code for the SH4a, in such a way that no double-precision
11935 floating point operations are used.
11938 @opindex m4a-single
11939 Generate code for the SH4a assuming the floating-point unit is in
11940 single-precision mode by default.
11944 Generate code for the SH4a.
11948 Same as @option{-m4a-nofpu}, except that it implicitly passes
11949 @option{-dsp} to the assembler. GCC doesn't generate any DSP
11950 instructions at the moment.
11954 Compile code for the processor in big endian mode.
11958 Compile code for the processor in little endian mode.
11962 Align doubles at 64-bit boundaries. Note that this changes the calling
11963 conventions, and thus some functions from the standard C library will
11964 not work unless you recompile it first with @option{-mdalign}.
11968 Shorten some address references at link time, when possible; uses the
11969 linker option @option{-relax}.
11973 Use 32-bit offsets in @code{switch} tables. The default is to use
11978 Enable the use of the instruction @code{fmovd}.
11982 Comply with the calling conventions defined by Renesas.
11986 Comply with the calling conventions defined by Renesas.
11990 Comply with the calling conventions defined for GCC before the Renesas
11991 conventions were available. This option is the default for all
11992 targets of the SH toolchain except for @samp{sh-symbianelf}.
11995 @opindex mnomacsave
11996 Mark the @code{MAC} register as call-clobbered, even if
11997 @option{-mhitachi} is given.
12001 Increase IEEE-compliance of floating-point code.
12002 At the moment, this is equivalent to @option{-fno-finite-math-only}.
12003 When generating 16 bit SH opcodes, getting IEEE-conforming results for
12004 comparisons of NANs / infinities incurs extra overhead in every
12005 floating point comparison, therefore the default is set to
12006 @option{-ffinite-math-only}.
12010 Dump instruction size and location in the assembly code.
12013 @opindex mpadstruct
12014 This option is deprecated. It pads structures to multiple of 4 bytes,
12015 which is incompatible with the SH ABI@.
12019 Optimize for space instead of speed. Implied by @option{-Os}.
12022 @opindex mprefergot
12023 When generating position-independent code, emit function calls using
12024 the Global Offset Table instead of the Procedure Linkage Table.
12028 Generate a library function call to invalidate instruction cache
12029 entries, after fixing up a trampoline. This library function call
12030 doesn't assume it can write to the whole memory address space. This
12031 is the default when the target is @code{sh-*-linux*}.
12033 @item -multcost=@var{number}
12034 @opindex multcost=@var{number}
12035 Set the cost to assume for a multiply insn.
12037 @item -mdiv=@var{strategy}
12038 @opindex mdiv=@var{strategy}
12039 Set the division strategy to use for SHmedia code. @var{strategy} must be
12040 one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
12041 inv:call2, inv:fp .
12042 "fp" performs the operation in floating point. This has a very high latency,
12043 but needs only a few instructions, so it might be a good choice if
12044 your code has enough easily exploitable ILP to allow the compiler to
12045 schedule the floating point instructions together with other instructions.
12046 Division by zero causes a floating point exception.
12047 "inv" uses integer operations to calculate the inverse of the divisor,
12048 and then multiplies the dividend with the inverse. This strategy allows
12049 cse and hoisting of the inverse calculation. Division by zero calculates
12050 an unspecified result, but does not trap.
12051 "inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
12052 have been found, or if the entire operation has been hoisted to the same
12053 place, the last stages of the inverse calculation are intertwined with the
12054 final multiply to reduce the overall latency, at the expense of using a few
12055 more instructions, and thus offering fewer scheduling opportunities with
12057 "call" calls a library function that usually implements the inv:minlat
12059 This gives high code density for m5-*media-nofpu compilations.
12060 "call2" uses a different entry point of the same library function, where it
12061 assumes that a pointer to a lookup table has already been set up, which
12062 exposes the pointer load to cse / code hoisting optimizations.
12063 "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
12064 code generation, but if the code stays unoptimized, revert to the "call",
12065 "call2", or "fp" strategies, respectively. Note that the
12066 potentially-trapping side effect of division by zero is carried by a
12067 separate instruction, so it is possible that all the integer instructions
12068 are hoisted out, but the marker for the side effect stays where it is.
12069 A recombination to fp operations or a call is not possible in that case.
12070 "inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
12071 that the inverse calculation was nor separated from the multiply, they speed
12072 up division where the dividend fits into 20 bits (plus sign where applicable),
12073 by inserting a test to skip a number of operations in this case; this test
12074 slows down the case of larger dividends. inv20u assumes the case of a such
12075 a small dividend to be unlikely, and inv20l assumes it to be likely.
12077 @item -mdivsi3_libfunc=@var{name}
12078 @opindex mdivsi3_libfunc=@var{name}
12079 Set the name of the library function used for 32 bit signed division to
12080 @var{name}. This only affect the name used in the call and inv:call
12081 division strategies, and the compiler will still expect the same
12082 sets of input/output/clobbered registers as if this option was not present.
12084 @item -madjust-unroll
12085 @opindex madjust-unroll
12086 Throttle unrolling to avoid thrashing target registers.
12087 This option only has an effect if the gcc code base supports the
12088 TARGET_ADJUST_UNROLL_MAX target hook.
12090 @item -mindexed-addressing
12091 @opindex mindexed-addressing
12092 Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
12093 This is only safe if the hardware and/or OS implement 32 bit wrap-around
12094 semantics for the indexed addressing mode. The architecture allows the
12095 implementation of processors with 64 bit MMU, which the OS could use to
12096 get 32 bit addressing, but since no current hardware implementation supports
12097 this or any other way to make the indexed addressing mode safe to use in
12098 the 32 bit ABI, the default is -mno-indexed-addressing.
12100 @item -mgettrcost=@var{number}
12101 @opindex mgettrcost=@var{number}
12102 Set the cost assumed for the gettr instruction to @var{number}.
12103 The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
12107 Assume pt* instructions won't trap. This will generally generate better
12108 scheduled code, but is unsafe on current hardware. The current architecture
12109 definition says that ptabs and ptrel trap when the target anded with 3 is 3.
12110 This has the unintentional effect of making it unsafe to schedule ptabs /
12111 ptrel before a branch, or hoist it out of a loop. For example,
12112 __do_global_ctors, a part of libgcc that runs constructors at program
12113 startup, calls functions in a list which is delimited by -1. With the
12114 -mpt-fixed option, the ptabs will be done before testing against -1.
12115 That means that all the constructors will be run a bit quicker, but when
12116 the loop comes to the end of the list, the program crashes because ptabs
12117 loads -1 into a target register. Since this option is unsafe for any
12118 hardware implementing the current architecture specification, the default
12119 is -mno-pt-fixed. Unless the user specifies a specific cost with
12120 @option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100};
12121 this deters register allocation using target registers for storing
12124 @item -minvalid-symbols
12125 @opindex minvalid-symbols
12126 Assume symbols might be invalid. Ordinary function symbols generated by
12127 the compiler will always be valid to load with movi/shori/ptabs or
12128 movi/shori/ptrel, but with assembler and/or linker tricks it is possible
12129 to generate symbols that will cause ptabs / ptrel to trap.
12130 This option is only meaningful when @option{-mno-pt-fixed} is in effect.
12131 It will then prevent cross-basic-block cse, hoisting and most scheduling
12132 of symbol loads. The default is @option{-mno-invalid-symbols}.
12135 @node SPARC Options
12136 @subsection SPARC Options
12137 @cindex SPARC options
12139 These @samp{-m} options are supported on the SPARC:
12142 @item -mno-app-regs
12144 @opindex mno-app-regs
12146 Specify @option{-mapp-regs} to generate output using the global registers
12147 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
12150 To be fully SVR4 ABI compliant at the cost of some performance loss,
12151 specify @option{-mno-app-regs}. You should compile libraries and system
12152 software with this option.
12155 @itemx -mhard-float
12157 @opindex mhard-float
12158 Generate output containing floating point instructions. This is the
12162 @itemx -msoft-float
12164 @opindex msoft-float
12165 Generate output containing library calls for floating point.
12166 @strong{Warning:} the requisite libraries are not available for all SPARC
12167 targets. Normally the facilities of the machine's usual C compiler are
12168 used, but this cannot be done directly in cross-compilation. You must make
12169 your own arrangements to provide suitable library functions for
12170 cross-compilation. The embedded targets @samp{sparc-*-aout} and
12171 @samp{sparclite-*-*} do provide software floating point support.
12173 @option{-msoft-float} changes the calling convention in the output file;
12174 therefore, it is only useful if you compile @emph{all} of a program with
12175 this option. In particular, you need to compile @file{libgcc.a}, the
12176 library that comes with GCC, with @option{-msoft-float} in order for
12179 @item -mhard-quad-float
12180 @opindex mhard-quad-float
12181 Generate output containing quad-word (long double) floating point
12184 @item -msoft-quad-float
12185 @opindex msoft-quad-float
12186 Generate output containing library calls for quad-word (long double)
12187 floating point instructions. The functions called are those specified
12188 in the SPARC ABI@. This is the default.
12190 As of this writing, there are no SPARC implementations that have hardware
12191 support for the quad-word floating point instructions. They all invoke
12192 a trap handler for one of these instructions, and then the trap handler
12193 emulates the effect of the instruction. Because of the trap handler overhead,
12194 this is much slower than calling the ABI library routines. Thus the
12195 @option{-msoft-quad-float} option is the default.
12197 @item -mno-unaligned-doubles
12198 @itemx -munaligned-doubles
12199 @opindex mno-unaligned-doubles
12200 @opindex munaligned-doubles
12201 Assume that doubles have 8 byte alignment. This is the default.
12203 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
12204 alignment only if they are contained in another type, or if they have an
12205 absolute address. Otherwise, it assumes they have 4 byte alignment.
12206 Specifying this option avoids some rare compatibility problems with code
12207 generated by other compilers. It is not the default because it results
12208 in a performance loss, especially for floating point code.
12210 @item -mno-faster-structs
12211 @itemx -mfaster-structs
12212 @opindex mno-faster-structs
12213 @opindex mfaster-structs
12214 With @option{-mfaster-structs}, the compiler assumes that structures
12215 should have 8 byte alignment. This enables the use of pairs of
12216 @code{ldd} and @code{std} instructions for copies in structure
12217 assignment, in place of twice as many @code{ld} and @code{st} pairs.
12218 However, the use of this changed alignment directly violates the SPARC
12219 ABI@. Thus, it's intended only for use on targets where the developer
12220 acknowledges that their resulting code will not be directly in line with
12221 the rules of the ABI@.
12223 @item -mimpure-text
12224 @opindex mimpure-text
12225 @option{-mimpure-text}, used in addition to @option{-shared}, tells
12226 the compiler to not pass @option{-z text} to the linker when linking a
12227 shared object. Using this option, you can link position-dependent
12228 code into a shared object.
12230 @option{-mimpure-text} suppresses the ``relocations remain against
12231 allocatable but non-writable sections'' linker error message.
12232 However, the necessary relocations will trigger copy-on-write, and the
12233 shared object is not actually shared across processes. Instead of
12234 using @option{-mimpure-text}, you should compile all source code with
12235 @option{-fpic} or @option{-fPIC}.
12237 This option is only available on SunOS and Solaris.
12239 @item -mcpu=@var{cpu_type}
12241 Set the instruction set, register set, and instruction scheduling parameters
12242 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
12243 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
12244 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
12245 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, and
12246 @samp{ultrasparc3}.
12248 Default instruction scheduling parameters are used for values that select
12249 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
12250 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
12252 Here is a list of each supported architecture and their supported
12257 v8: supersparc, hypersparc
12258 sparclite: f930, f934, sparclite86x
12260 v9: ultrasparc, ultrasparc3
12263 By default (unless configured otherwise), GCC generates code for the V7
12264 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
12265 additionally optimizes it for the Cypress CY7C602 chip, as used in the
12266 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
12267 SPARCStation 1, 2, IPX etc.
12269 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
12270 architecture. The only difference from V7 code is that the compiler emits
12271 the integer multiply and integer divide instructions which exist in SPARC-V8
12272 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
12273 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
12276 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
12277 the SPARC architecture. This adds the integer multiply, integer divide step
12278 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
12279 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
12280 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
12281 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
12282 MB86934 chip, which is the more recent SPARClite with FPU@.
12284 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
12285 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
12286 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
12287 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
12288 optimizes it for the TEMIC SPARClet chip.
12290 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
12291 architecture. This adds 64-bit integer and floating-point move instructions,
12292 3 additional floating-point condition code registers and conditional move
12293 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
12294 optimizes it for the Sun UltraSPARC I/II chips. With
12295 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
12296 Sun UltraSPARC III chip.
12298 @item -mtune=@var{cpu_type}
12300 Set the instruction scheduling parameters for machine type
12301 @var{cpu_type}, but do not set the instruction set or register set that the
12302 option @option{-mcpu=@var{cpu_type}} would.
12304 The same values for @option{-mcpu=@var{cpu_type}} can be used for
12305 @option{-mtune=@var{cpu_type}}, but the only useful values are those
12306 that select a particular cpu implementation. Those are @samp{cypress},
12307 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
12308 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, and
12309 @samp{ultrasparc3}.
12314 @opindex mno-v8plus
12315 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
12316 difference from the V8 ABI is that the global and out registers are
12317 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
12318 mode for all SPARC-V9 processors.
12324 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
12325 Visual Instruction Set extensions. The default is @option{-mno-vis}.
12328 These @samp{-m} options are supported in addition to the above
12329 on SPARC-V9 processors in 64-bit environments:
12332 @item -mlittle-endian
12333 @opindex mlittle-endian
12334 Generate code for a processor running in little-endian mode. It is only
12335 available for a few configurations and most notably not on Solaris and Linux.
12341 Generate code for a 32-bit or 64-bit environment.
12342 The 32-bit environment sets int, long and pointer to 32 bits.
12343 The 64-bit environment sets int to 32 bits and long and pointer
12346 @item -mcmodel=medlow
12347 @opindex mcmodel=medlow
12348 Generate code for the Medium/Low code model: 64-bit addresses, programs
12349 must be linked in the low 32 bits of memory. Programs can be statically
12350 or dynamically linked.
12352 @item -mcmodel=medmid
12353 @opindex mcmodel=medmid
12354 Generate code for the Medium/Middle code model: 64-bit addresses, programs
12355 must be linked in the low 44 bits of memory, the text and data segments must
12356 be less than 2GB in size and the data segment must be located within 2GB of
12359 @item -mcmodel=medany
12360 @opindex mcmodel=medany
12361 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
12362 may be linked anywhere in memory, the text and data segments must be less
12363 than 2GB in size and the data segment must be located within 2GB of the
12366 @item -mcmodel=embmedany
12367 @opindex mcmodel=embmedany
12368 Generate code for the Medium/Anywhere code model for embedded systems:
12369 64-bit addresses, the text and data segments must be less than 2GB in
12370 size, both starting anywhere in memory (determined at link time). The
12371 global register %g4 points to the base of the data segment. Programs
12372 are statically linked and PIC is not supported.
12375 @itemx -mno-stack-bias
12376 @opindex mstack-bias
12377 @opindex mno-stack-bias
12378 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
12379 frame pointer if present, are offset by @minus{}2047 which must be added back
12380 when making stack frame references. This is the default in 64-bit mode.
12381 Otherwise, assume no such offset is present.
12384 These switches are supported in addition to the above on Solaris:
12389 Add support for multithreading using the Solaris threads library. This
12390 option sets flags for both the preprocessor and linker. This option does
12391 not affect the thread safety of object code produced by the compiler or
12392 that of libraries supplied with it.
12396 Add support for multithreading using the POSIX threads library. This
12397 option sets flags for both the preprocessor and linker. This option does
12398 not affect the thread safety of object code produced by the compiler or
12399 that of libraries supplied with it.
12402 @node System V Options
12403 @subsection Options for System V
12405 These additional options are available on System V Release 4 for
12406 compatibility with other compilers on those systems:
12411 Create a shared object.
12412 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
12416 Identify the versions of each tool used by the compiler, in a
12417 @code{.ident} assembler directive in the output.
12421 Refrain from adding @code{.ident} directives to the output file (this is
12424 @item -YP,@var{dirs}
12426 Search the directories @var{dirs}, and no others, for libraries
12427 specified with @option{-l}.
12429 @item -Ym,@var{dir}
12431 Look in the directory @var{dir} to find the M4 preprocessor.
12432 The assembler uses this option.
12433 @c This is supposed to go with a -Yd for predefined M4 macro files, but
12434 @c the generic assembler that comes with Solaris takes just -Ym.
12437 @node TMS320C3x/C4x Options
12438 @subsection TMS320C3x/C4x Options
12439 @cindex TMS320C3x/C4x Options
12441 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
12445 @item -mcpu=@var{cpu_type}
12447 Set the instruction set, register set, and instruction scheduling
12448 parameters for machine type @var{cpu_type}. Supported values for
12449 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
12450 @samp{c44}. The default is @samp{c40} to generate code for the
12455 @itemx -msmall-memory
12457 @opindex mbig-memory
12459 @opindex msmall-memory
12461 Generates code for the big or small memory model. The small memory
12462 model assumed that all data fits into one 64K word page. At run-time
12463 the data page (DP) register must be set to point to the 64K page
12464 containing the .bss and .data program sections. The big memory model is
12465 the default and requires reloading of the DP register for every direct
12472 Allow (disallow) allocation of general integer operands into the block
12473 count register BK@.
12479 Enable (disable) generation of code using decrement and branch,
12480 DBcond(D), instructions. This is enabled by default for the C4x. To be
12481 on the safe side, this is disabled for the C3x, since the maximum
12482 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
12483 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
12484 that it can utilize the decrement and branch instruction, but will give
12485 up if there is more than one memory reference in the loop. Thus a loop
12486 where the loop counter is decremented can generate slightly more
12487 efficient code, in cases where the RPTB instruction cannot be utilized.
12489 @item -mdp-isr-reload
12491 @opindex mdp-isr-reload
12493 Force the DP register to be saved on entry to an interrupt service
12494 routine (ISR), reloaded to point to the data section, and restored on
12495 exit from the ISR@. This should not be required unless someone has
12496 violated the small memory model by modifying the DP register, say within
12503 For the C3x use the 24-bit MPYI instruction for integer multiplies
12504 instead of a library call to guarantee 32-bit results. Note that if one
12505 of the operands is a constant, then the multiplication will be performed
12506 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
12507 then squaring operations are performed inline instead of a library call.
12510 @itemx -mno-fast-fix
12512 @opindex mno-fast-fix
12513 The C3x/C4x FIX instruction to convert a floating point value to an
12514 integer value chooses the nearest integer less than or equal to the
12515 floating point value rather than to the nearest integer. Thus if the
12516 floating point number is negative, the result will be incorrectly
12517 truncated an additional code is necessary to detect and correct this
12518 case. This option can be used to disable generation of the additional
12519 code required to correct the result.
12525 Enable (disable) generation of repeat block sequences using the RPTB
12526 instruction for zero overhead looping. The RPTB construct is only used
12527 for innermost loops that do not call functions or jump across the loop
12528 boundaries. There is no advantage having nested RPTB loops due to the
12529 overhead required to save and restore the RC, RS, and RE registers.
12530 This is enabled by default with @option{-O2}.
12532 @item -mrpts=@var{count}
12536 Enable (disable) the use of the single instruction repeat instruction
12537 RPTS@. If a repeat block contains a single instruction, and the loop
12538 count can be guaranteed to be less than the value @var{count}, GCC will
12539 emit a RPTS instruction instead of a RPTB@. If no value is specified,
12540 then a RPTS will be emitted even if the loop count cannot be determined
12541 at compile time. Note that the repeated instruction following RPTS does
12542 not have to be reloaded from memory each iteration, thus freeing up the
12543 CPU buses for operands. However, since interrupts are blocked by this
12544 instruction, it is disabled by default.
12546 @item -mloop-unsigned
12547 @itemx -mno-loop-unsigned
12548 @opindex mloop-unsigned
12549 @opindex mno-loop-unsigned
12550 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
12551 is @math{2^{31} + 1} since these instructions test if the iteration count is
12552 negative to terminate the loop. If the iteration count is unsigned
12553 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
12554 exceeded. This switch allows an unsigned iteration count.
12558 Try to emit an assembler syntax that the TI assembler (asm30) is happy
12559 with. This also enforces compatibility with the API employed by the TI
12560 C3x C compiler. For example, long doubles are passed as structures
12561 rather than in floating point registers.
12567 Generate code that uses registers (stack) for passing arguments to functions.
12568 By default, arguments are passed in registers where possible rather
12569 than by pushing arguments on to the stack.
12571 @item -mparallel-insns
12572 @itemx -mno-parallel-insns
12573 @opindex mparallel-insns
12574 @opindex mno-parallel-insns
12575 Allow the generation of parallel instructions. This is enabled by
12576 default with @option{-O2}.
12578 @item -mparallel-mpy
12579 @itemx -mno-parallel-mpy
12580 @opindex mparallel-mpy
12581 @opindex mno-parallel-mpy
12582 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
12583 provided @option{-mparallel-insns} is also specified. These instructions have
12584 tight register constraints which can pessimize the code generation
12585 of large functions.
12590 @subsection V850 Options
12591 @cindex V850 Options
12593 These @samp{-m} options are defined for V850 implementations:
12597 @itemx -mno-long-calls
12598 @opindex mlong-calls
12599 @opindex mno-long-calls
12600 Treat all calls as being far away (near). If calls are assumed to be
12601 far away, the compiler will always load the functions address up into a
12602 register, and call indirect through the pointer.
12608 Do not optimize (do optimize) basic blocks that use the same index
12609 pointer 4 or more times to copy pointer into the @code{ep} register, and
12610 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
12611 option is on by default if you optimize.
12613 @item -mno-prolog-function
12614 @itemx -mprolog-function
12615 @opindex mno-prolog-function
12616 @opindex mprolog-function
12617 Do not use (do use) external functions to save and restore registers
12618 at the prologue and epilogue of a function. The external functions
12619 are slower, but use less code space if more than one function saves
12620 the same number of registers. The @option{-mprolog-function} option
12621 is on by default if you optimize.
12625 Try to make the code as small as possible. At present, this just turns
12626 on the @option{-mep} and @option{-mprolog-function} options.
12628 @item -mtda=@var{n}
12630 Put static or global variables whose size is @var{n} bytes or less into
12631 the tiny data area that register @code{ep} points to. The tiny data
12632 area can hold up to 256 bytes in total (128 bytes for byte references).
12634 @item -msda=@var{n}
12636 Put static or global variables whose size is @var{n} bytes or less into
12637 the small data area that register @code{gp} points to. The small data
12638 area can hold up to 64 kilobytes.
12640 @item -mzda=@var{n}
12642 Put static or global variables whose size is @var{n} bytes or less into
12643 the first 32 kilobytes of memory.
12647 Specify that the target processor is the V850.
12650 @opindex mbig-switch
12651 Generate code suitable for big switch tables. Use this option only if
12652 the assembler/linker complain about out of range branches within a switch
12657 This option will cause r2 and r5 to be used in the code generated by
12658 the compiler. This setting is the default.
12660 @item -mno-app-regs
12661 @opindex mno-app-regs
12662 This option will cause r2 and r5 to be treated as fixed registers.
12666 Specify that the target processor is the V850E1. The preprocessor
12667 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
12668 this option is used.
12672 Specify that the target processor is the V850E@. The preprocessor
12673 constant @samp{__v850e__} will be defined if this option is used.
12675 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
12676 are defined then a default target processor will be chosen and the
12677 relevant @samp{__v850*__} preprocessor constant will be defined.
12679 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
12680 defined, regardless of which processor variant is the target.
12682 @item -mdisable-callt
12683 @opindex mdisable-callt
12684 This option will suppress generation of the CALLT instruction for the
12685 v850e and v850e1 flavors of the v850 architecture. The default is
12686 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
12691 @subsection VAX Options
12692 @cindex VAX options
12694 These @samp{-m} options are defined for the VAX:
12699 Do not output certain jump instructions (@code{aobleq} and so on)
12700 that the Unix assembler for the VAX cannot handle across long
12705 Do output those jump instructions, on the assumption that you
12706 will assemble with the GNU assembler.
12710 Output code for g-format floating point numbers instead of d-format.
12713 @node x86-64 Options
12714 @subsection x86-64 Options
12715 @cindex x86-64 options
12717 These are listed under @xref{i386 and x86-64 Options}.
12719 @node Xstormy16 Options
12720 @subsection Xstormy16 Options
12721 @cindex Xstormy16 Options
12723 These options are defined for Xstormy16:
12728 Choose startup files and linker script suitable for the simulator.
12731 @node Xtensa Options
12732 @subsection Xtensa Options
12733 @cindex Xtensa Options
12735 These options are supported for Xtensa targets:
12739 @itemx -mno-const16
12741 @opindex mno-const16
12742 Enable or disable use of @code{CONST16} instructions for loading
12743 constant values. The @code{CONST16} instruction is currently not a
12744 standard option from Tensilica. When enabled, @code{CONST16}
12745 instructions are always used in place of the standard @code{L32R}
12746 instructions. The use of @code{CONST16} is enabled by default only if
12747 the @code{L32R} instruction is not available.
12750 @itemx -mno-fused-madd
12751 @opindex mfused-madd
12752 @opindex mno-fused-madd
12753 Enable or disable use of fused multiply/add and multiply/subtract
12754 instructions in the floating-point option. This has no effect if the
12755 floating-point option is not also enabled. Disabling fused multiply/add
12756 and multiply/subtract instructions forces the compiler to use separate
12757 instructions for the multiply and add/subtract operations. This may be
12758 desirable in some cases where strict IEEE 754-compliant results are
12759 required: the fused multiply add/subtract instructions do not round the
12760 intermediate result, thereby producing results with @emph{more} bits of
12761 precision than specified by the IEEE standard. Disabling fused multiply
12762 add/subtract instructions also ensures that the program output is not
12763 sensitive to the compiler's ability to combine multiply and add/subtract
12766 @item -mtext-section-literals
12767 @itemx -mno-text-section-literals
12768 @opindex mtext-section-literals
12769 @opindex mno-text-section-literals
12770 Control the treatment of literal pools. The default is
12771 @option{-mno-text-section-literals}, which places literals in a separate
12772 section in the output file. This allows the literal pool to be placed
12773 in a data RAM/ROM, and it also allows the linker to combine literal
12774 pools from separate object files to remove redundant literals and
12775 improve code size. With @option{-mtext-section-literals}, the literals
12776 are interspersed in the text section in order to keep them as close as
12777 possible to their references. This may be necessary for large assembly
12780 @item -mtarget-align
12781 @itemx -mno-target-align
12782 @opindex mtarget-align
12783 @opindex mno-target-align
12784 When this option is enabled, GCC instructs the assembler to
12785 automatically align instructions to reduce branch penalties at the
12786 expense of some code density. The assembler attempts to widen density
12787 instructions to align branch targets and the instructions following call
12788 instructions. If there are not enough preceding safe density
12789 instructions to align a target, no widening will be performed. The
12790 default is @option{-mtarget-align}. These options do not affect the
12791 treatment of auto-aligned instructions like @code{LOOP}, which the
12792 assembler will always align, either by widening density instructions or
12793 by inserting no-op instructions.
12796 @itemx -mno-longcalls
12797 @opindex mlongcalls
12798 @opindex mno-longcalls
12799 When this option is enabled, GCC instructs the assembler to translate
12800 direct calls to indirect calls unless it can determine that the target
12801 of a direct call is in the range allowed by the call instruction. This
12802 translation typically occurs for calls to functions in other source
12803 files. Specifically, the assembler translates a direct @code{CALL}
12804 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
12805 The default is @option{-mno-longcalls}. This option should be used in
12806 programs where the call target can potentially be out of range. This
12807 option is implemented in the assembler, not the compiler, so the
12808 assembly code generated by GCC will still show direct call
12809 instructions---look at the disassembled object code to see the actual
12810 instructions. Note that the assembler will use an indirect call for
12811 every cross-file call, not just those that really will be out of range.
12814 @node zSeries Options
12815 @subsection zSeries Options
12816 @cindex zSeries options
12818 These are listed under @xref{S/390 and zSeries Options}.
12820 @node Code Gen Options
12821 @section Options for Code Generation Conventions
12822 @cindex code generation conventions
12823 @cindex options, code generation
12824 @cindex run-time options
12826 These machine-independent options control the interface conventions
12827 used in code generation.
12829 Most of them have both positive and negative forms; the negative form
12830 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
12831 one of the forms is listed---the one which is not the default. You
12832 can figure out the other form by either removing @samp{no-} or adding
12836 @item -fbounds-check
12837 @opindex fbounds-check
12838 For front-ends that support it, generate additional code to check that
12839 indices used to access arrays are within the declared range. This is
12840 currently only supported by the Java and Fortran 77 front-ends, where
12841 this option defaults to true and false respectively.
12845 This option generates traps for signed overflow on addition, subtraction,
12846 multiplication operations.
12850 This option instructs the compiler to assume that signed arithmetic
12851 overflow of addition, subtraction and multiplication wraps around
12852 using twos-complement representation. This flag enables some optimizations
12853 and disables others. This option is enabled by default for the Java
12854 front-end, as required by the Java language specification.
12857 @opindex fexceptions
12858 Enable exception handling. Generates extra code needed to propagate
12859 exceptions. For some targets, this implies GCC will generate frame
12860 unwind information for all functions, which can produce significant data
12861 size overhead, although it does not affect execution. If you do not
12862 specify this option, GCC will enable it by default for languages like
12863 C++ which normally require exception handling, and disable it for
12864 languages like C that do not normally require it. However, you may need
12865 to enable this option when compiling C code that needs to interoperate
12866 properly with exception handlers written in C++. You may also wish to
12867 disable this option if you are compiling older C++ programs that don't
12868 use exception handling.
12870 @item -fnon-call-exceptions
12871 @opindex fnon-call-exceptions
12872 Generate code that allows trapping instructions to throw exceptions.
12873 Note that this requires platform-specific runtime support that does
12874 not exist everywhere. Moreover, it only allows @emph{trapping}
12875 instructions to throw exceptions, i.e.@: memory references or floating
12876 point instructions. It does not allow exceptions to be thrown from
12877 arbitrary signal handlers such as @code{SIGALRM}.
12879 @item -funwind-tables
12880 @opindex funwind-tables
12881 Similar to @option{-fexceptions}, except that it will just generate any needed
12882 static data, but will not affect the generated code in any other way.
12883 You will normally not enable this option; instead, a language processor
12884 that needs this handling would enable it on your behalf.
12886 @item -fasynchronous-unwind-tables
12887 @opindex fasynchronous-unwind-tables
12888 Generate unwind table in dwarf2 format, if supported by target machine. The
12889 table is exact at each instruction boundary, so it can be used for stack
12890 unwinding from asynchronous events (such as debugger or garbage collector).
12892 @item -fpcc-struct-return
12893 @opindex fpcc-struct-return
12894 Return ``short'' @code{struct} and @code{union} values in memory like
12895 longer ones, rather than in registers. This convention is less
12896 efficient, but it has the advantage of allowing intercallability between
12897 GCC-compiled files and files compiled with other compilers, particularly
12898 the Portable C Compiler (pcc).
12900 The precise convention for returning structures in memory depends
12901 on the target configuration macros.
12903 Short structures and unions are those whose size and alignment match
12904 that of some integer type.
12906 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
12907 switch is not binary compatible with code compiled with the
12908 @option{-freg-struct-return} switch.
12909 Use it to conform to a non-default application binary interface.
12911 @item -freg-struct-return
12912 @opindex freg-struct-return
12913 Return @code{struct} and @code{union} values in registers when possible.
12914 This is more efficient for small structures than
12915 @option{-fpcc-struct-return}.
12917 If you specify neither @option{-fpcc-struct-return} nor
12918 @option{-freg-struct-return}, GCC defaults to whichever convention is
12919 standard for the target. If there is no standard convention, GCC
12920 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
12921 the principal compiler. In those cases, we can choose the standard, and
12922 we chose the more efficient register return alternative.
12924 @strong{Warning:} code compiled with the @option{-freg-struct-return}
12925 switch is not binary compatible with code compiled with the
12926 @option{-fpcc-struct-return} switch.
12927 Use it to conform to a non-default application binary interface.
12929 @item -fshort-enums
12930 @opindex fshort-enums
12931 Allocate to an @code{enum} type only as many bytes as it needs for the
12932 declared range of possible values. Specifically, the @code{enum} type
12933 will be equivalent to the smallest integer type which has enough room.
12935 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
12936 code that is not binary compatible with code generated without that switch.
12937 Use it to conform to a non-default application binary interface.
12939 @item -fshort-double
12940 @opindex fshort-double
12941 Use the same size for @code{double} as for @code{float}.
12943 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
12944 code that is not binary compatible with code generated without that switch.
12945 Use it to conform to a non-default application binary interface.
12947 @item -fshort-wchar
12948 @opindex fshort-wchar
12949 Override the underlying type for @samp{wchar_t} to be @samp{short
12950 unsigned int} instead of the default for the target. This option is
12951 useful for building programs to run under WINE@.
12953 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
12954 code that is not binary compatible with code generated without that switch.
12955 Use it to conform to a non-default application binary interface.
12957 @item -fshared-data
12958 @opindex fshared-data
12959 Requests that the data and non-@code{const} variables of this
12960 compilation be shared data rather than private data. The distinction
12961 makes sense only on certain operating systems, where shared data is
12962 shared between processes running the same program, while private data
12963 exists in one copy per process.
12966 @opindex fno-common
12967 In C, allocate even uninitialized global variables in the data section of the
12968 object file, rather than generating them as common blocks. This has the
12969 effect that if the same variable is declared (without @code{extern}) in
12970 two different compilations, you will get an error when you link them.
12971 The only reason this might be useful is if you wish to verify that the
12972 program will work on other systems which always work this way.
12976 Ignore the @samp{#ident} directive.
12978 @item -finhibit-size-directive
12979 @opindex finhibit-size-directive
12980 Don't output a @code{.size} assembler directive, or anything else that
12981 would cause trouble if the function is split in the middle, and the
12982 two halves are placed at locations far apart in memory. This option is
12983 used when compiling @file{crtstuff.c}; you should not need to use it
12986 @item -fverbose-asm
12987 @opindex fverbose-asm
12988 Put extra commentary information in the generated assembly code to
12989 make it more readable. This option is generally only of use to those
12990 who actually need to read the generated assembly code (perhaps while
12991 debugging the compiler itself).
12993 @option{-fno-verbose-asm}, the default, causes the
12994 extra information to be omitted and is useful when comparing two assembler
12999 @cindex global offset table
13001 Generate position-independent code (PIC) suitable for use in a shared
13002 library, if supported for the target machine. Such code accesses all
13003 constant addresses through a global offset table (GOT)@. The dynamic
13004 loader resolves the GOT entries when the program starts (the dynamic
13005 loader is not part of GCC; it is part of the operating system). If
13006 the GOT size for the linked executable exceeds a machine-specific
13007 maximum size, you get an error message from the linker indicating that
13008 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
13009 instead. (These maximums are 8k on the SPARC and 32k
13010 on the m68k and RS/6000. The 386 has no such limit.)
13012 Position-independent code requires special support, and therefore works
13013 only on certain machines. For the 386, GCC supports PIC for System V
13014 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
13015 position-independent.
13017 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
13022 If supported for the target machine, emit position-independent code,
13023 suitable for dynamic linking and avoiding any limit on the size of the
13024 global offset table. This option makes a difference on the m68k,
13025 PowerPC and SPARC@.
13027 Position-independent code requires special support, and therefore works
13028 only on certain machines.
13030 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
13037 These options are similar to @option{-fpic} and @option{-fPIC}, but
13038 generated position independent code can be only linked into executables.
13039 Usually these options are used when @option{-pie} GCC option will be
13040 used during linking.
13042 @item -fno-jump-tables
13043 @opindex fno-jump-tables
13044 Do not use jump tables for switch statements even where it would be
13045 more efficient than other code generation strategies. This option is
13046 of use in conjunction with @option{-fpic} or @option{-fPIC} for
13047 building code which forms part of a dynamic linker and cannot
13048 reference the address of a jump table. On some targets, jump tables
13049 do not require a GOT and this option is not needed.
13051 @item -ffixed-@var{reg}
13053 Treat the register named @var{reg} as a fixed register; generated code
13054 should never refer to it (except perhaps as a stack pointer, frame
13055 pointer or in some other fixed role).
13057 @var{reg} must be the name of a register. The register names accepted
13058 are machine-specific and are defined in the @code{REGISTER_NAMES}
13059 macro in the machine description macro file.
13061 This flag does not have a negative form, because it specifies a
13064 @item -fcall-used-@var{reg}
13065 @opindex fcall-used
13066 Treat the register named @var{reg} as an allocable register that is
13067 clobbered by function calls. It may be allocated for temporaries or
13068 variables that do not live across a call. Functions compiled this way
13069 will not save and restore the register @var{reg}.
13071 It is an error to used this flag with the frame pointer or stack pointer.
13072 Use of this flag for other registers that have fixed pervasive roles in
13073 the machine's execution model will produce disastrous results.
13075 This flag does not have a negative form, because it specifies a
13078 @item -fcall-saved-@var{reg}
13079 @opindex fcall-saved
13080 Treat the register named @var{reg} as an allocable register saved by
13081 functions. It may be allocated even for temporaries or variables that
13082 live across a call. Functions compiled this way will save and restore
13083 the register @var{reg} if they use it.
13085 It is an error to used this flag with the frame pointer or stack pointer.
13086 Use of this flag for other registers that have fixed pervasive roles in
13087 the machine's execution model will produce disastrous results.
13089 A different sort of disaster will result from the use of this flag for
13090 a register in which function values may be returned.
13092 This flag does not have a negative form, because it specifies a
13095 @item -fpack-struct[=@var{n}]
13096 @opindex fpack-struct
13097 Without a value specified, pack all structure members together without
13098 holes. When a value is specified (which must be a small power of two), pack
13099 structure members according to this value, representing the maximum
13100 alignment (that is, objects with default alignment requirements larger than
13101 this will be output potentially unaligned at the next fitting location.
13103 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
13104 code that is not binary compatible with code generated without that switch.
13105 Additionally, it makes the code suboptimal.
13106 Use it to conform to a non-default application binary interface.
13108 @item -finstrument-functions
13109 @opindex finstrument-functions
13110 Generate instrumentation calls for entry and exit to functions. Just
13111 after function entry and just before function exit, the following
13112 profiling functions will be called with the address of the current
13113 function and its call site. (On some platforms,
13114 @code{__builtin_return_address} does not work beyond the current
13115 function, so the call site information may not be available to the
13116 profiling functions otherwise.)
13119 void __cyg_profile_func_enter (void *this_fn,
13121 void __cyg_profile_func_exit (void *this_fn,
13125 The first argument is the address of the start of the current function,
13126 which may be looked up exactly in the symbol table.
13128 This instrumentation is also done for functions expanded inline in other
13129 functions. The profiling calls will indicate where, conceptually, the
13130 inline function is entered and exited. This means that addressable
13131 versions of such functions must be available. If all your uses of a
13132 function are expanded inline, this may mean an additional expansion of
13133 code size. If you use @samp{extern inline} in your C code, an
13134 addressable version of such functions must be provided. (This is
13135 normally the case anyways, but if you get lucky and the optimizer always
13136 expands the functions inline, you might have gotten away without
13137 providing static copies.)
13139 A function may be given the attribute @code{no_instrument_function}, in
13140 which case this instrumentation will not be done. This can be used, for
13141 example, for the profiling functions listed above, high-priority
13142 interrupt routines, and any functions from which the profiling functions
13143 cannot safely be called (perhaps signal handlers, if the profiling
13144 routines generate output or allocate memory).
13146 @item -fstack-check
13147 @opindex fstack-check
13148 Generate code to verify that you do not go beyond the boundary of the
13149 stack. You should specify this flag if you are running in an
13150 environment with multiple threads, but only rarely need to specify it in
13151 a single-threaded environment since stack overflow is automatically
13152 detected on nearly all systems if there is only one stack.
13154 Note that this switch does not actually cause checking to be done; the
13155 operating system must do that. The switch causes generation of code
13156 to ensure that the operating system sees the stack being extended.
13158 @item -fstack-limit-register=@var{reg}
13159 @itemx -fstack-limit-symbol=@var{sym}
13160 @itemx -fno-stack-limit
13161 @opindex fstack-limit-register
13162 @opindex fstack-limit-symbol
13163 @opindex fno-stack-limit
13164 Generate code to ensure that the stack does not grow beyond a certain value,
13165 either the value of a register or the address of a symbol. If the stack
13166 would grow beyond the value, a signal is raised. For most targets,
13167 the signal is raised before the stack overruns the boundary, so
13168 it is possible to catch the signal without taking special precautions.
13170 For instance, if the stack starts at absolute address @samp{0x80000000}
13171 and grows downwards, you can use the flags
13172 @option{-fstack-limit-symbol=__stack_limit} and
13173 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
13174 of 128KB@. Note that this may only work with the GNU linker.
13176 @cindex aliasing of parameters
13177 @cindex parameters, aliased
13178 @item -fargument-alias
13179 @itemx -fargument-noalias
13180 @itemx -fargument-noalias-global
13181 @opindex fargument-alias
13182 @opindex fargument-noalias
13183 @opindex fargument-noalias-global
13184 Specify the possible relationships among parameters and between
13185 parameters and global data.
13187 @option{-fargument-alias} specifies that arguments (parameters) may
13188 alias each other and may alias global storage.@*
13189 @option{-fargument-noalias} specifies that arguments do not alias
13190 each other, but may alias global storage.@*
13191 @option{-fargument-noalias-global} specifies that arguments do not
13192 alias each other and do not alias global storage.
13194 Each language will automatically use whatever option is required by
13195 the language standard. You should not need to use these options yourself.
13197 @item -fleading-underscore
13198 @opindex fleading-underscore
13199 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
13200 change the way C symbols are represented in the object file. One use
13201 is to help link with legacy assembly code.
13203 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
13204 generate code that is not binary compatible with code generated without that
13205 switch. Use it to conform to a non-default application binary interface.
13206 Not all targets provide complete support for this switch.
13208 @item -ftls-model=@var{model}
13209 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
13210 The @var{model} argument should be one of @code{global-dynamic},
13211 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
13213 The default without @option{-fpic} is @code{initial-exec}; with
13214 @option{-fpic} the default is @code{global-dynamic}.
13216 @item -fvisibility=@var{default|internal|hidden|protected}
13217 @opindex fvisibility
13218 Set the default ELF image symbol visibility to the specified option---all
13219 symbols will be marked with this unless overridden within the code.
13220 Using this feature can very substantially improve linking and
13221 load times of shared object libraries, produce more optimized
13222 code, provide near-perfect API export and prevent symbol clashes.
13223 It is @strong{strongly} recommended that you use this in any shared objects
13226 Despite the nomenclature, @code{default} always means public ie;
13227 available to be linked against from outside the shared object.
13228 @code{protected} and @code{internal} are pretty useless in real-world
13229 usage so the only other commonly used option will be @code{hidden}.
13230 The default if @option{-fvisibility} isn't specified is
13231 @code{default}, i.e., make every
13232 symbol public---this causes the same behavior as previous versions of
13235 A good explanation of the benefits offered by ensuring ELF
13236 symbols have the correct visibility is given by ``How To Write
13237 Shared Libraries'' by Ulrich Drepper (which can be found at
13238 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
13239 solution made possible by this option to marking things hidden when
13240 the default is public is to make the default hidden and mark things
13241 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
13242 and @code{__attribute__ ((visibility("default")))} instead of
13243 @code{__declspec(dllexport)} you get almost identical semantics with
13244 identical syntax. This is a great boon to those working with
13245 cross-platform projects.
13247 For those adding visibility support to existing code, you may find
13248 @samp{#pragma GCC visibility} of use. This works by you enclosing
13249 the declarations you wish to set visibility for with (for example)
13250 @samp{#pragma GCC visibility push(hidden)} and
13251 @samp{#pragma GCC visibility pop}.
13252 Bear in mind that symbol visibility should be viewed @strong{as
13253 part of the API interface contract} and thus all new code should
13254 always specify visibility when it is not the default ie; declarations
13255 only for use within the local DSO should @strong{always} be marked explicitly
13256 as hidden as so to avoid PLT indirection overheads---making this
13257 abundantly clear also aids readability and self-documentation of the code.
13258 Note that due to ISO C++ specification requirements, operator new and
13259 operator delete must always be of default visibility.
13261 An overview of these techniques, their benefits and how to use them
13262 is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}.
13268 @node Environment Variables
13269 @section Environment Variables Affecting GCC
13270 @cindex environment variables
13272 @c man begin ENVIRONMENT
13273 This section describes several environment variables that affect how GCC
13274 operates. Some of them work by specifying directories or prefixes to use
13275 when searching for various kinds of files. Some are used to specify other
13276 aspects of the compilation environment.
13278 Note that you can also specify places to search using options such as
13279 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
13280 take precedence over places specified using environment variables, which
13281 in turn take precedence over those specified by the configuration of GCC@.
13282 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
13283 GNU Compiler Collection (GCC) Internals}.
13288 @c @itemx LC_COLLATE
13290 @c @itemx LC_MONETARY
13291 @c @itemx LC_NUMERIC
13296 @c @findex LC_COLLATE
13297 @findex LC_MESSAGES
13298 @c @findex LC_MONETARY
13299 @c @findex LC_NUMERIC
13303 These environment variables control the way that GCC uses
13304 localization information that allow GCC to work with different
13305 national conventions. GCC inspects the locale categories
13306 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
13307 so. These locale categories can be set to any value supported by your
13308 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
13309 Kingdom encoded in UTF-8.
13311 The @env{LC_CTYPE} environment variable specifies character
13312 classification. GCC uses it to determine the character boundaries in
13313 a string; this is needed for some multibyte encodings that contain quote
13314 and escape characters that would otherwise be interpreted as a string
13317 The @env{LC_MESSAGES} environment variable specifies the language to
13318 use in diagnostic messages.
13320 If the @env{LC_ALL} environment variable is set, it overrides the value
13321 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
13322 and @env{LC_MESSAGES} default to the value of the @env{LANG}
13323 environment variable. If none of these variables are set, GCC
13324 defaults to traditional C English behavior.
13328 If @env{TMPDIR} is set, it specifies the directory to use for temporary
13329 files. GCC uses temporary files to hold the output of one stage of
13330 compilation which is to be used as input to the next stage: for example,
13331 the output of the preprocessor, which is the input to the compiler
13334 @item GCC_EXEC_PREFIX
13335 @findex GCC_EXEC_PREFIX
13336 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
13337 names of the subprograms executed by the compiler. No slash is added
13338 when this prefix is combined with the name of a subprogram, but you can
13339 specify a prefix that ends with a slash if you wish.
13341 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
13342 an appropriate prefix to use based on the pathname it was invoked with.
13344 If GCC cannot find the subprogram using the specified prefix, it
13345 tries looking in the usual places for the subprogram.
13347 The default value of @env{GCC_EXEC_PREFIX} is
13348 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the value
13349 of @code{prefix} when you ran the @file{configure} script.
13351 Other prefixes specified with @option{-B} take precedence over this prefix.
13353 This prefix is also used for finding files such as @file{crt0.o} that are
13356 In addition, the prefix is used in an unusual way in finding the
13357 directories to search for header files. For each of the standard
13358 directories whose name normally begins with @samp{/usr/local/lib/gcc}
13359 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
13360 replacing that beginning with the specified prefix to produce an
13361 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
13362 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
13363 These alternate directories are searched first; the standard directories
13366 @item COMPILER_PATH
13367 @findex COMPILER_PATH
13368 The value of @env{COMPILER_PATH} is a colon-separated list of
13369 directories, much like @env{PATH}. GCC tries the directories thus
13370 specified when searching for subprograms, if it can't find the
13371 subprograms using @env{GCC_EXEC_PREFIX}.
13374 @findex LIBRARY_PATH
13375 The value of @env{LIBRARY_PATH} is a colon-separated list of
13376 directories, much like @env{PATH}. When configured as a native compiler,
13377 GCC tries the directories thus specified when searching for special
13378 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
13379 using GCC also uses these directories when searching for ordinary
13380 libraries for the @option{-l} option (but directories specified with
13381 @option{-L} come first).
13385 @cindex locale definition
13386 This variable is used to pass locale information to the compiler. One way in
13387 which this information is used is to determine the character set to be used
13388 when character literals, string literals and comments are parsed in C and C++.
13389 When the compiler is configured to allow multibyte characters,
13390 the following values for @env{LANG} are recognized:
13394 Recognize JIS characters.
13396 Recognize SJIS characters.
13398 Recognize EUCJP characters.
13401 If @env{LANG} is not defined, or if it has some other value, then the
13402 compiler will use mblen and mbtowc as defined by the default locale to
13403 recognize and translate multibyte characters.
13407 Some additional environments variables affect the behavior of the
13410 @include cppenv.texi
13414 @node Precompiled Headers
13415 @section Using Precompiled Headers
13416 @cindex precompiled headers
13417 @cindex speed of compilation
13419 Often large projects have many header files that are included in every
13420 source file. The time the compiler takes to process these header files
13421 over and over again can account for nearly all of the time required to
13422 build the project. To make builds faster, GCC allows users to
13423 `precompile' a header file; then, if builds can use the precompiled
13424 header file they will be much faster.
13426 To create a precompiled header file, simply compile it as you would any
13427 other file, if necessary using the @option{-x} option to make the driver
13428 treat it as a C or C++ header file. You will probably want to use a
13429 tool like @command{make} to keep the precompiled header up-to-date when
13430 the headers it contains change.
13432 A precompiled header file will be searched for when @code{#include} is
13433 seen in the compilation. As it searches for the included file
13434 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
13435 compiler looks for a precompiled header in each directory just before it
13436 looks for the include file in that directory. The name searched for is
13437 the name specified in the @code{#include} with @samp{.gch} appended. If
13438 the precompiled header file can't be used, it is ignored.
13440 For instance, if you have @code{#include "all.h"}, and you have
13441 @file{all.h.gch} in the same directory as @file{all.h}, then the
13442 precompiled header file will be used if possible, and the original
13443 header will be used otherwise.
13445 Alternatively, you might decide to put the precompiled header file in a
13446 directory and use @option{-I} to ensure that directory is searched
13447 before (or instead of) the directory containing the original header.
13448 Then, if you want to check that the precompiled header file is always
13449 used, you can put a file of the same name as the original header in this
13450 directory containing an @code{#error} command.
13452 This also works with @option{-include}. So yet another way to use
13453 precompiled headers, good for projects not designed with precompiled
13454 header files in mind, is to simply take most of the header files used by
13455 a project, include them from another header file, precompile that header
13456 file, and @option{-include} the precompiled header. If the header files
13457 have guards against multiple inclusion, they will be skipped because
13458 they've already been included (in the precompiled header).
13460 If you need to precompile the same header file for different
13461 languages, targets, or compiler options, you can instead make a
13462 @emph{directory} named like @file{all.h.gch}, and put each precompiled
13463 header in the directory, perhaps using @option{-o}. It doesn't matter
13464 what you call the files in the directory, every precompiled header in
13465 the directory will be considered. The first precompiled header
13466 encountered in the directory that is valid for this compilation will
13467 be used; they're searched in no particular order.
13469 There are many other possibilities, limited only by your imagination,
13470 good sense, and the constraints of your build system.
13472 A precompiled header file can be used only when these conditions apply:
13476 Only one precompiled header can be used in a particular compilation.
13479 A precompiled header can't be used once the first C token is seen. You
13480 can have preprocessor directives before a precompiled header; you can
13481 even include a precompiled header from inside another header, so long as
13482 there are no C tokens before the @code{#include}.
13485 The precompiled header file must be produced for the same language as
13486 the current compilation. You can't use a C precompiled header for a C++
13490 The precompiled header file must have been produced by the same compiler
13491 binary as the current compilation is using.
13494 Any macros defined before the precompiled header is included must
13495 either be defined in the same way as when the precompiled header was
13496 generated, or must not affect the precompiled header, which usually
13497 means that they don't appear in the precompiled header at all.
13499 The @option{-D} option is one way to define a macro before a
13500 precompiled header is included; using a @code{#define} can also do it.
13501 There are also some options that define macros implicitly, like
13502 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
13505 @item If debugging information is output when using the precompiled
13506 header, using @option{-g} or similar, the same kind of debugging information
13507 must have been output when building the precompiled header. However,
13508 a precompiled header built using @option{-g} can be used in a compilation
13509 when no debugging information is being output.
13511 @item The same @option{-m} options must generally be used when building
13512 and using the precompiled header. @xref{Submodel Options},
13513 for any cases where this rule is relaxed.
13515 @item Each of the following options must be the same when building and using
13516 the precompiled header:
13518 @gccoptlist{-fexceptions -funit-at-a-time}
13521 Some other command-line options starting with @option{-f},
13522 @option{-p}, or @option{-O} must be defined in the same way as when
13523 the precompiled header was generated. At present, it's not clear
13524 which options are safe to change and which are not; the safest choice
13525 is to use exactly the same options when generating and using the
13526 precompiled header. The following are known to be safe:
13528 @gccoptlist{-fmessage-length= -fpreprocessed
13529 -fsched-interblock -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous
13530 -fsched-verbose=<number> -fschedule-insns -fvisibility=
13535 For all of these except the last, the compiler will automatically
13536 ignore the precompiled header if the conditions aren't met. If you
13537 find an option combination that doesn't work and doesn't cause the
13538 precompiled header to be ignored, please consider filing a bug report,
13541 If you do use differing options when generating and using the
13542 precompiled header, the actual behavior will be a mixture of the
13543 behavior for the options. For instance, if you use @option{-g} to
13544 generate the precompiled header but not when using it, you may or may
13545 not get debugging information for routines in the precompiled header.
13547 @node Running Protoize
13548 @section Running Protoize
13550 The program @code{protoize} is an optional part of GCC@. You can use
13551 it to add prototypes to a program, thus converting the program to ISO
13552 C in one respect. The companion program @code{unprotoize} does the
13553 reverse: it removes argument types from any prototypes that are found.
13555 When you run these programs, you must specify a set of source files as
13556 command line arguments. The conversion programs start out by compiling
13557 these files to see what functions they define. The information gathered
13558 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
13560 After scanning comes actual conversion. The specified files are all
13561 eligible to be converted; any files they include (whether sources or
13562 just headers) are eligible as well.
13564 But not all the eligible files are converted. By default,
13565 @code{protoize} and @code{unprotoize} convert only source and header
13566 files in the current directory. You can specify additional directories
13567 whose files should be converted with the @option{-d @var{directory}}
13568 option. You can also specify particular files to exclude with the
13569 @option{-x @var{file}} option. A file is converted if it is eligible, its
13570 directory name matches one of the specified directory names, and its
13571 name within the directory has not been excluded.
13573 Basic conversion with @code{protoize} consists of rewriting most
13574 function definitions and function declarations to specify the types of
13575 the arguments. The only ones not rewritten are those for varargs
13578 @code{protoize} optionally inserts prototype declarations at the
13579 beginning of the source file, to make them available for any calls that
13580 precede the function's definition. Or it can insert prototype
13581 declarations with block scope in the blocks where undeclared functions
13584 Basic conversion with @code{unprotoize} consists of rewriting most
13585 function declarations to remove any argument types, and rewriting
13586 function definitions to the old-style pre-ISO form.
13588 Both conversion programs print a warning for any function declaration or
13589 definition that they can't convert. You can suppress these warnings
13592 The output from @code{protoize} or @code{unprotoize} replaces the
13593 original source file. The original file is renamed to a name ending
13594 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
13595 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
13596 for DOS) file already exists, then the source file is simply discarded.
13598 @code{protoize} and @code{unprotoize} both depend on GCC itself to
13599 scan the program and collect information about the functions it uses.
13600 So neither of these programs will work until GCC is installed.
13602 Here is a table of the options you can use with @code{protoize} and
13603 @code{unprotoize}. Each option works with both programs unless
13607 @item -B @var{directory}
13608 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
13609 usual directory (normally @file{/usr/local/lib}). This file contains
13610 prototype information about standard system functions. This option
13611 applies only to @code{protoize}.
13613 @item -c @var{compilation-options}
13614 Use @var{compilation-options} as the options when running @command{gcc} to
13615 produce the @samp{.X} files. The special option @option{-aux-info} is
13616 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
13618 Note that the compilation options must be given as a single argument to
13619 @code{protoize} or @code{unprotoize}. If you want to specify several
13620 @command{gcc} options, you must quote the entire set of compilation options
13621 to make them a single word in the shell.
13623 There are certain @command{gcc} arguments that you cannot use, because they
13624 would produce the wrong kind of output. These include @option{-g},
13625 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
13626 the @var{compilation-options}, they are ignored.
13629 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
13630 systems) instead of @samp{.c}. This is convenient if you are converting
13631 a C program to C++. This option applies only to @code{protoize}.
13634 Add explicit global declarations. This means inserting explicit
13635 declarations at the beginning of each source file for each function
13636 that is called in the file and was not declared. These declarations
13637 precede the first function definition that contains a call to an
13638 undeclared function. This option applies only to @code{protoize}.
13640 @item -i @var{string}
13641 Indent old-style parameter declarations with the string @var{string}.
13642 This option applies only to @code{protoize}.
13644 @code{unprotoize} converts prototyped function definitions to old-style
13645 function definitions, where the arguments are declared between the
13646 argument list and the initial @samp{@{}. By default, @code{unprotoize}
13647 uses five spaces as the indentation. If you want to indent with just
13648 one space instead, use @option{-i " "}.
13651 Keep the @samp{.X} files. Normally, they are deleted after conversion
13655 Add explicit local declarations. @code{protoize} with @option{-l} inserts
13656 a prototype declaration for each function in each block which calls the
13657 function without any declaration. This option applies only to
13661 Make no real changes. This mode just prints information about the conversions
13662 that would have been done without @option{-n}.
13665 Make no @samp{.save} files. The original files are simply deleted.
13666 Use this option with caution.
13668 @item -p @var{program}
13669 Use the program @var{program} as the compiler. Normally, the name
13670 @file{gcc} is used.
13673 Work quietly. Most warnings are suppressed.
13676 Print the version number, just like @option{-v} for @command{gcc}.
13679 If you need special compiler options to compile one of your program's
13680 source files, then you should generate that file's @samp{.X} file
13681 specially, by running @command{gcc} on that source file with the
13682 appropriate options and the option @option{-aux-info}. Then run
13683 @code{protoize} on the entire set of files. @code{protoize} will use
13684 the existing @samp{.X} file because it is newer than the source file.
13688 gcc -Dfoo=bar file1.c -aux-info file1.X
13693 You need to include the special files along with the rest in the
13694 @code{protoize} command, even though their @samp{.X} files already
13695 exist, because otherwise they won't get converted.
13697 @xref{Protoize Caveats}, for more information on how to use
13698 @code{protoize} successfully.