1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
3 @c Free Software Foundation, Inc.
4 @c This is part of the GCC manual.
5 @c For copying conditions, see the file gcc.texi.
12 @c man begin COPYRIGHT
13 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
14 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
15 Free Software Foundation, Inc.
17 Permission is granted to copy, distribute and/or modify this document
18 under the terms of the GNU Free Documentation License, Version 1.2 or
19 any later version published by the Free Software Foundation; with the
20 Invariant Sections being ``GNU General Public License'' and ``Funding
21 Free Software'', the Front-Cover texts being (a) (see below), and with
22 the Back-Cover Texts being (b) (see below). A copy of the license is
23 included in the gfdl(7) man page.
25 (a) The FSF's Front-Cover Text is:
29 (b) The FSF's Back-Cover Text is:
31 You have freedom to copy and modify this GNU Manual, like GNU
32 software. Copies published by the Free Software Foundation raise
33 funds for GNU development.
35 @c Set file name and title for the man page.
37 @settitle GNU project C and C++ compiler
39 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
40 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
41 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
42 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
43 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
44 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
45 [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{}
47 Only the most useful options are listed here; see below for the
48 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
51 gpl(7), gfdl(7), fsf-funding(7),
52 cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
53 and the Info entries for @file{gcc}, @file{cpp}, @file{as},
54 @file{ld}, @file{binutils} and @file{gdb}.
57 For instructions on reporting bugs, see
61 See the Info entry for @command{gcc}, or
62 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
63 for contributors to GCC@.
68 @chapter GCC Command Options
69 @cindex GCC command options
70 @cindex command options
71 @cindex options, GCC command
73 @c man begin DESCRIPTION
74 When you invoke GCC, it normally does preprocessing, compilation,
75 assembly and linking. The ``overall options'' allow you to stop this
76 process at an intermediate stage. For example, the @option{-c} option
77 says not to run the linker. Then the output consists of object files
78 output by the assembler.
80 Other options are passed on to one stage of processing. Some options
81 control the preprocessor and others the compiler itself. Yet other
82 options control the assembler and linker; most of these are not
83 documented here, since you rarely need to use any of them.
85 @cindex C compilation options
86 Most of the command line options that you can use with GCC are useful
87 for C programs; when an option is only useful with another language
88 (usually C++), the explanation says so explicitly. If the description
89 for a particular option does not mention a source language, you can use
90 that option with all supported languages.
92 @cindex C++ compilation options
93 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
94 options for compiling C++ programs.
96 @cindex grouping options
97 @cindex options, grouping
98 The @command{gcc} program accepts options and file names as operands. Many
99 options have multi-letter names; therefore multiple single-letter options
100 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
103 @cindex order of options
104 @cindex options, order
105 You can mix options and other arguments. For the most part, the order
106 you use doesn't matter. Order does matter when you use several
107 options of the same kind; for example, if you specify @option{-L} more
108 than once, the directories are searched in the order specified. Also,
109 the placement of the @option{-l} option is significant.
111 Many options have long names starting with @samp{-f} or with
112 @samp{-W}---for example,
113 @option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of
114 these have both positive and negative forms; the negative form of
115 @option{-ffoo} would be @option{-fno-foo}. This manual documents
116 only one of these two forms, whichever one is not the default.
120 @xref{Option Index}, for an index to GCC's options.
123 * Option Summary:: Brief list of all options, without explanations.
124 * Overall Options:: Controlling the kind of output:
125 an executable, object files, assembler files,
126 or preprocessed source.
127 * Invoking G++:: Compiling C++ programs.
128 * C Dialect Options:: Controlling the variant of C language compiled.
129 * C++ Dialect Options:: Variations on C++.
130 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
132 * Language Independent Options:: Controlling how diagnostics should be
134 * Warning Options:: How picky should the compiler be?
135 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
136 * Optimize Options:: How much optimization?
137 * Preprocessor Options:: Controlling header files and macro definitions.
138 Also, getting dependency information for Make.
139 * Assembler Options:: Passing options to the assembler.
140 * Link Options:: Specifying libraries and so on.
141 * Directory Options:: Where to find header files and libraries.
142 Where to find the compiler executable files.
143 * Spec Files:: How to pass switches to sub-processes.
144 * Target Options:: Running a cross-compiler, or an old version of GCC.
145 * Submodel Options:: Specifying minor hardware or convention variations,
146 such as 68010 vs 68020.
147 * Code Gen Options:: Specifying conventions for function calls, data layout
149 * Environment Variables:: Env vars that affect GCC.
150 * Precompiled Headers:: Compiling a header once, and using it many times.
151 * Running Protoize:: Automatically adding or removing function prototypes.
157 @section Option Summary
159 Here is a summary of all the options, grouped by type. Explanations are
160 in the following sections.
163 @item Overall Options
164 @xref{Overall Options,,Options Controlling the Kind of Output}.
165 @gccoptlist{-c -S -E -o @var{file} -combine -pipe -pass-exit-codes @gol
166 -x @var{language} -v -### --help@r{[}=@var{class}@r{]} --target-help @gol
167 --version -wrapper@@@var{file}}
169 @item C Language Options
170 @xref{C Dialect Options,,Options Controlling C Dialect}.
171 @gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol
172 -aux-info @var{filename} @gol
173 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
174 -fhosted -ffreestanding -fopenmp -fms-extensions @gol
175 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
176 -fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol
177 -fsigned-bitfields -fsigned-char @gol
178 -funsigned-bitfields -funsigned-char}
180 @item C++ Language Options
181 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
182 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
183 -fconserve-space -ffriend-injection @gol
184 -fno-elide-constructors @gol
185 -fno-enforce-eh-specs @gol
186 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
187 -fno-implicit-templates @gol
188 -fno-implicit-inline-templates @gol
189 -fno-implement-inlines -fms-extensions @gol
190 -fno-nonansi-builtins -fno-operator-names @gol
191 -fno-optional-diags -fpermissive @gol
192 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
193 -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
194 -fno-default-inline -fvisibility-inlines-hidden @gol
195 -fvisibility-ms-compat @gol
196 -Wabi -Wctor-dtor-privacy @gol
197 -Wnon-virtual-dtor -Wreorder @gol
198 -Weffc++ -Wstrict-null-sentinel @gol
199 -Wno-non-template-friend -Wold-style-cast @gol
200 -Woverloaded-virtual -Wno-pmf-conversions @gol
203 @item Objective-C and Objective-C++ Language Options
204 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
205 Objective-C and Objective-C++ Dialects}.
206 @gccoptlist{-fconstant-string-class=@var{class-name} @gol
207 -fgnu-runtime -fnext-runtime @gol
208 -fno-nil-receivers @gol
209 -fobjc-call-cxx-cdtors @gol
210 -fobjc-direct-dispatch @gol
211 -fobjc-exceptions @gol
213 -freplace-objc-classes @gol
216 -Wassign-intercept @gol
217 -Wno-protocol -Wselector @gol
218 -Wstrict-selector-match @gol
219 -Wundeclared-selector}
221 @item Language Independent Options
222 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
223 @gccoptlist{-fmessage-length=@var{n} @gol
224 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol
225 -fdiagnostics-show-option}
227 @item Warning Options
228 @xref{Warning Options,,Options to Request or Suppress Warnings}.
229 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
230 -w -Wextra -Wall -Waddress -Waggregate-return -Warray-bounds @gol
231 -Wno-attributes -Wc++-compat -Wc++0x-compat -Wcast-align -Wcast-qual @gol
232 -Wchar-subscripts -Wclobbered -Wcomment @gol
233 -Wconversion -Wcoverage-mismatch -Wno-deprecated @gol
234 -Wno-deprecated-declarations -Wdisabled-optimization -Wno-div-by-zero @gol
235 -Wempty-body -Wenum-compare -Wno-endif-labels @gol
236 -Werror -Werror=* @gol
237 -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
238 -Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral @gol
239 -Wformat-security -Wformat-y2k @gol
240 -Wframe-larger-than=@var{len} -Wignored-qualifiers @gol
241 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
242 -Winit-self -Winline @gol
243 -Wno-int-to-pointer-cast -Wno-invalid-offsetof @gol
244 -Winvalid-pch -Wlarger-than=@var{len} -Wunsafe-loop-optimizations @gol
245 -Wlogical-op -Wlong-long @gol
246 -Wmain -Wmissing-braces -Wmissing-field-initializers @gol
247 -Wmissing-format-attribute -Wmissing-include-dirs @gol
248 -Wmissing-noreturn -Wno-mudflap @gol
249 -Wno-multichar -Wnonnull -Wno-overflow @gol
250 -Woverlength-strings -Wpacked -Wpadded @gol
251 -Wparentheses -Wpointer-arith -Wno-pointer-to-int-cast @gol
252 -Wredundant-decls @gol
253 -Wreturn-type -Wsequence-point -Wshadow @gol
254 -Wsign-compare -Wsign-conversion -Wstack-protector @gol
255 -Wstrict-aliasing -Wstrict-aliasing=n @gol
256 -Wstrict-overflow -Wstrict-overflow=@var{n} @gol
257 -Wswitch -Wswitch-default -Wswitch-enum @gol
258 -Wsystem-headers -Wtrigraphs -Wtype-limits -Wundef -Wuninitialized @gol
259 -Wunknown-pragmas -Wno-pragmas -Wunreachable-code @gol
260 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
261 -Wunused-value -Wunused-variable @gol
262 -Wvariadic-macros -Wvla @gol
263 -Wvolatile-register-var -Wwrite-strings}
265 @item C and Objective-C-only Warning Options
266 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
267 -Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol
268 -Wold-style-declaration -Wold-style-definition @gol
269 -Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol
270 -Wdeclaration-after-statement -Wpointer-sign}
272 @item Debugging Options
273 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
274 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
275 -fdbg-cnt-list -fdbg-cnt=@var{counter-value-list} @gol
276 -fdump-noaddr -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
277 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
278 -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol
279 -fdump-statistics @gol
281 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
282 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
283 -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol
285 -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
286 -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
287 -fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol
288 -fdump-tree-dom@r{[}-@var{n}@r{]} @gol
289 -fdump-tree-dse@r{[}-@var{n}@r{]} @gol
290 -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
291 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
292 -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
293 -fdump-tree-nrv -fdump-tree-vect @gol
294 -fdump-tree-sink @gol
295 -fdump-tree-sra@r{[}-@var{n}@r{]} @gol
296 -fdump-tree-fre@r{[}-@var{n}@r{]} @gol
297 -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
298 -ftree-vectorizer-verbose=@var{n} @gol
299 -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
300 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
301 -feliminate-unused-debug-symbols -femit-class-debug-always @gol
302 -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs @gol
303 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
304 -ftest-coverage -ftime-report -fvar-tracking @gol
305 -g -g@var{level} -gcoff -gdwarf-2 @gol
306 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
307 -fno-merge-debug-strings -fdebug-prefix-map=@var{old}=@var{new} @gol
308 -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
309 -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol
310 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
311 -print-multi-directory -print-multi-lib @gol
312 -print-prog-name=@var{program} -print-search-dirs -Q @gol
313 -print-sysroot -print-sysroot-headers-suffix @gol
316 @item Optimization Options
317 @xref{Optimize Options,,Options that Control Optimization}.
319 -falign-functions[=@var{n}] -falign-jumps[=@var{n}] @gol
320 -falign-labels[=@var{n}] -falign-loops[=@var{n}] -fassociative-math @gol
321 -fauto-inc-dec -fbranch-probabilities -fbranch-target-load-optimize @gol
322 -fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves @gol
323 -fcheck-data-deps -fcprop-registers -fcrossjumping -fcse-follow-jumps @gol
324 -fcse-skip-blocks -fcx-fortran-rules -fcx-limited-range @gol
325 -fdata-sections -fdce -fdce @gol
326 -fdelayed-branch -fdelete-null-pointer-checks -fdse -fdse @gol
327 -fearly-inlining -fexpensive-optimizations -ffast-math @gol
328 -ffinite-math-only -ffloat-store -fforward-propagate @gol
329 -ffunction-sections -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm @gol
330 -fgcse-sm -fif-conversion -fif-conversion2 -finline-functions @gol
331 -finline-functions-called-once -finline-limit=@var{n} @gol
332 -finline-small-functions -fipa-cp -fipa-marix-reorg -fipa-pta @gol
333 -fipa-pure-const -fipa-reference -fipa-struct-reorg @gol
334 -fipa-type-escape -fivopts -fkeep-inline-functions -fkeep-static-consts @gol
335 -fmerge-all-constants -fmerge-constants -fmodulo-sched @gol
336 -fmodulo-sched-allow-regmoves -fmove-loop-invariants -fmudflap @gol
337 -fmudflapir -fmudflapth -fno-branch-count-reg -fno-default-inline @gol
338 -fno-defer-pop -fno-function-cse -fno-guess-branch-probability @gol
339 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
340 -fno-sched-interblock -fno-sched-spec -fno-signed-zeros @gol
341 -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
342 -fomit-frame-pointer -foptimize-register-move -foptimize-sibling-calls @gol
343 -fpeel-loops -fpredictive-commoning -fprefetch-loop-arrays @gol
344 -fprofile-dir=@var{path} -fprofile-generate -fprofile-generate=@var{path} @gol
345 -fprofile-use -fprofile-use=@var{path} -fprofile-values @gol
346 -freciprocal-math -fregmove -frename-registers -freorder-blocks @gol
347 -freorder-blocks-and-partition -freorder-functions @gol
348 -frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol
349 -frounding-math -frtl-abstract-sequences -fsched2-use-superblocks @gol
350 -fsched2-use-traces -fsched-spec-load -fsched-spec-load-dangerous @gol
351 -fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol
352 -fschedule-insns -fschedule-insns2 -fsection-anchors -fsee @gol
353 -fsignaling-nans -fsingle-precision-constant -fsplit-ivs-in-unroller @gol
354 -fsplit-wide-types -fstack-protector -fstack-protector-all @gol
355 -fstrict-aliasing -fstrict-overflow -fthread-jumps -ftracer @gol
356 -ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-copy-prop @gol
357 -ftree-copyrename -ftree-dce @gol
358 -ftree-dominator-opts -ftree-dse -ftree-fre -ftree-loop-im @gol
359 -ftree-loop-distribution @gol
360 -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol
361 -ftree-parallelize-loops=@var{n} -ftree-pre -ftree-reassoc @gol
362 -ftree-sink -ftree-sra -ftree-store-ccp -ftree-switch-conversion @gol
363 -ftree-ter -ftree-vect-loop-version -ftree-vectorize -ftree-vrp @gol
364 -funit-at-a-time -funroll-all-loops -funroll-loops @gol
365 -funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops @gol
366 -fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb @gol
368 --param @var{name}=@var{value}
369 -O -O0 -O1 -O2 -O3 -Os}
371 @item Preprocessor Options
372 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
373 @gccoptlist{-A@var{question}=@var{answer} @gol
374 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
375 -C -dD -dI -dM -dN @gol
376 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
377 -idirafter @var{dir} @gol
378 -include @var{file} -imacros @var{file} @gol
379 -iprefix @var{file} -iwithprefix @var{dir} @gol
380 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
381 -imultilib @var{dir} -isysroot @var{dir} @gol
382 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
383 -P -fworking-directory -remap @gol
384 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
385 -Xpreprocessor @var{option}}
387 @item Assembler Option
388 @xref{Assembler Options,,Passing Options to the Assembler}.
389 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
392 @xref{Link Options,,Options for Linking}.
393 @gccoptlist{@var{object-file-name} -l@var{library} @gol
394 -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
395 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
396 -Wl,@var{option} -Xlinker @var{option} @gol
399 @item Directory Options
400 @xref{Directory Options,,Options for Directory Search}.
401 @gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} -L@var{dir}
402 -specs=@var{file} -I- --sysroot=@var{dir}}
405 @c I wrote this xref this way to avoid overfull hbox. -- rms
406 @xref{Target Options}.
407 @gccoptlist{-V @var{version} -b @var{machine}}
409 @item Machine Dependent Options
410 @xref{Submodel Options,,Hardware Models and Configurations}.
411 @c This list is ordered alphanumerically by subsection name.
412 @c Try and put the significant identifier (CPU or system) first,
413 @c so users have a clue at guessing where the ones they want will be.
416 @gccoptlist{-EB -EL @gol
417 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
418 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
421 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
422 -mabi=@var{name} @gol
423 -mapcs-stack-check -mno-apcs-stack-check @gol
424 -mapcs-float -mno-apcs-float @gol
425 -mapcs-reentrant -mno-apcs-reentrant @gol
426 -msched-prolog -mno-sched-prolog @gol
427 -mlittle-endian -mbig-endian -mwords-little-endian @gol
428 -mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
429 -mthumb-interwork -mno-thumb-interwork @gol
430 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
431 -mstructure-size-boundary=@var{n} @gol
432 -mabort-on-noreturn @gol
433 -mlong-calls -mno-long-calls @gol
434 -msingle-pic-base -mno-single-pic-base @gol
435 -mpic-register=@var{reg} @gol
436 -mnop-fun-dllimport @gol
437 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
438 -mpoke-function-name @gol
440 -mtpcs-frame -mtpcs-leaf-frame @gol
441 -mcaller-super-interworking -mcallee-super-interworking @gol
445 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
446 -mcall-prologues -mno-tablejump -mtiny-stack -mint8}
448 @emph{Blackfin Options}
449 @gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol
450 -msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
451 -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
452 -mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol
453 -mno-id-shared-library -mshared-library-id=@var{n} @gol
454 -mleaf-id-shared-library -mno-leaf-id-shared-library @gol
455 -msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol
456 -mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram}
459 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
460 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
461 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
462 -mstack-align -mdata-align -mconst-align @gol
463 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
464 -melf -maout -melinux -mlinux -sim -sim2 @gol
465 -mmul-bug-workaround -mno-mul-bug-workaround}
468 @gccoptlist{-mmac -mpush-args}
470 @emph{Darwin Options}
471 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
472 -arch_only -bind_at_load -bundle -bundle_loader @gol
473 -client_name -compatibility_version -current_version @gol
475 -dependency-file -dylib_file -dylinker_install_name @gol
476 -dynamic -dynamiclib -exported_symbols_list @gol
477 -filelist -flat_namespace -force_cpusubtype_ALL @gol
478 -force_flat_namespace -headerpad_max_install_names @gol
480 -image_base -init -install_name -keep_private_externs @gol
481 -multi_module -multiply_defined -multiply_defined_unused @gol
482 -noall_load -no_dead_strip_inits_and_terms @gol
483 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
484 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
485 -private_bundle -read_only_relocs -sectalign @gol
486 -sectobjectsymbols -whyload -seg1addr @gol
487 -sectcreate -sectobjectsymbols -sectorder @gol
488 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
489 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
490 -segprot -segs_read_only_addr -segs_read_write_addr @gol
491 -single_module -static -sub_library -sub_umbrella @gol
492 -twolevel_namespace -umbrella -undefined @gol
493 -unexported_symbols_list -weak_reference_mismatches @gol
494 -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
495 -mkernel -mone-byte-bool}
497 @emph{DEC Alpha Options}
498 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
499 -mieee -mieee-with-inexact -mieee-conformant @gol
500 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
501 -mtrap-precision=@var{mode} -mbuild-constants @gol
502 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
503 -mbwx -mmax -mfix -mcix @gol
504 -mfloat-vax -mfloat-ieee @gol
505 -mexplicit-relocs -msmall-data -mlarge-data @gol
506 -msmall-text -mlarge-text @gol
507 -mmemory-latency=@var{time}}
509 @emph{DEC Alpha/VMS Options}
510 @gccoptlist{-mvms-return-codes}
513 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
514 -mhard-float -msoft-float @gol
515 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
516 -mdouble -mno-double @gol
517 -mmedia -mno-media -mmuladd -mno-muladd @gol
518 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
519 -mlinked-fp -mlong-calls -malign-labels @gol
520 -mlibrary-pic -macc-4 -macc-8 @gol
521 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
522 -moptimize-membar -mno-optimize-membar @gol
523 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
524 -mvliw-branch -mno-vliw-branch @gol
525 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
526 -mno-nested-cond-exec -mtomcat-stats @gol
530 @emph{GNU/Linux Options}
531 @gccoptlist{-muclibc}
533 @emph{H8/300 Options}
534 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
537 @gccoptlist{-march=@var{architecture-type} @gol
538 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
539 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
540 -mfixed-range=@var{register-range} @gol
541 -mjump-in-delay -mlinker-opt -mlong-calls @gol
542 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
543 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
544 -mno-jump-in-delay -mno-long-load-store @gol
545 -mno-portable-runtime -mno-soft-float @gol
546 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
547 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
548 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
549 -munix=@var{unix-std} -nolibdld -static -threads}
551 @emph{i386 and x86-64 Options}
552 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
553 -mfpmath=@var{unit} @gol
554 -masm=@var{dialect} -mno-fancy-math-387 @gol
555 -mno-fp-ret-in-387 -msoft-float @gol
556 -mno-wide-multiply -mrtd -malign-double @gol
557 -mpreferred-stack-boundary=@var{num} -mcld -mcx16 -msahf -mrecip @gol
558 -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 @gol
560 -msse4a -m3dnow -mpopcnt -mabm -msse5 @gol
561 -mthreads -mno-align-stringops -minline-all-stringops @gol
562 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
563 -m96bit-long-double -mregparm=@var{num} -msseregparm @gol
564 -mveclibabi=@var{type} -mpc32 -mpc64 -mpc80 -mstackrealign @gol
565 -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
566 -mcmodel=@var{code-model} @gol
567 -m32 -m64 -mlarge-data-threshold=@var{num} @gol
568 -mfused-madd -mno-fused-madd}
571 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
572 -mvolatile-asm-stop -mregister-names -mno-sdata @gol
573 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
574 -minline-float-divide-max-throughput @gol
575 -minline-int-divide-min-latency @gol
576 -minline-int-divide-max-throughput @gol
577 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
578 -mno-dwarf2-asm -mearly-stop-bits @gol
579 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
580 -mtune=@var{cpu-type} -mt -pthread -milp32 -mlp64 @gol
581 -mno-sched-br-data-spec -msched-ar-data-spec -mno-sched-control-spec @gol
582 -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol
583 -msched-ldc -mno-sched-control-ldc -mno-sched-spec-verbose @gol
584 -mno-sched-prefer-non-data-spec-insns @gol
585 -mno-sched-prefer-non-control-spec-insns @gol
586 -mno-sched-count-spec-in-critical-path}
588 @emph{M32R/D Options}
589 @gccoptlist{-m32r2 -m32rx -m32r @gol
591 -malign-loops -mno-align-loops @gol
592 -missue-rate=@var{number} @gol
593 -mbranch-cost=@var{number} @gol
594 -mmodel=@var{code-size-model-type} @gol
595 -msdata=@var{sdata-type} @gol
596 -mno-flush-func -mflush-func=@var{name} @gol
597 -mno-flush-trap -mflush-trap=@var{number} @gol
601 @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
603 @emph{M680x0 Options}
604 @gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune}
605 -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
606 -m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol
607 -mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol
608 -mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol
609 -mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol
610 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
611 -mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol
614 @emph{M68hc1x Options}
615 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
616 -mauto-incdec -minmax -mlong-calls -mshort @gol
617 -msoft-reg-count=@var{count}}
620 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
621 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
622 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
623 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
624 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
627 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
628 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
629 -mips16 -mno-mips16 -mflip-mips16 @gol
630 -minterlink-mips16 -mno-interlink-mips16 @gol
631 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
632 -mshared -mno-shared -mxgot -mno-xgot -mgp32 -mgp64 @gol
633 -mfp32 -mfp64 -mhard-float -msoft-float @gol
634 -msingle-float -mdouble-float -mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol
635 -msmartmips -mno-smartmips @gol
636 -mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol
637 -mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol
638 -mlong64 -mlong32 -msym32 -mno-sym32 @gol
639 -G@var{num} -mlocal-sdata -mno-local-sdata @gol
640 -mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol
641 -membedded-data -mno-embedded-data @gol
642 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
643 -mcode-readable=@var{setting} @gol
644 -msplit-addresses -mno-split-addresses @gol
645 -mexplicit-relocs -mno-explicit-relocs @gol
646 -mcheck-zero-division -mno-check-zero-division @gol
647 -mdivide-traps -mdivide-breaks @gol
648 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
649 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
650 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
651 -mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130 -mno-fix-vr4130 @gol
652 -mfix-sb1 -mno-fix-sb1 @gol
653 -mflush-func=@var{func} -mno-flush-func @gol
654 -mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol
655 -mfp-exceptions -mno-fp-exceptions @gol
656 -mvr4130-align -mno-vr4130-align}
659 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
660 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
661 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
662 -mno-base-addresses -msingle-exit -mno-single-exit}
664 @emph{MN10300 Options}
665 @gccoptlist{-mmult-bug -mno-mult-bug @gol
666 -mam33 -mno-am33 @gol
667 -mam33-2 -mno-am33-2 @gol
668 -mreturn-pointer-on-d0 @gol
671 @emph{PDP-11 Options}
672 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
673 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
674 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
675 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
676 -mbranch-expensive -mbranch-cheap @gol
677 -msplit -mno-split -munix-asm -mdec-asm}
679 @emph{PowerPC Options}
680 See RS/6000 and PowerPC Options.
682 @emph{RS/6000 and PowerPC Options}
683 @gccoptlist{-mcpu=@var{cpu-type} @gol
684 -mtune=@var{cpu-type} @gol
685 -mpower -mno-power -mpower2 -mno-power2 @gol
686 -mpowerpc -mpowerpc64 -mno-powerpc @gol
687 -maltivec -mno-altivec @gol
688 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
689 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
690 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd @gol
691 -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp @gol
692 -mnew-mnemonics -mold-mnemonics @gol
693 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
694 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
695 -malign-power -malign-natural @gol
696 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
697 -mstring -mno-string -mupdate -mno-update @gol
698 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
699 -mstrict-align -mno-strict-align -mrelocatable @gol
700 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
701 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
702 -mdynamic-no-pic -maltivec -mswdiv @gol
703 -mprioritize-restricted-insns=@var{priority} @gol
704 -msched-costly-dep=@var{dependence_type} @gol
705 -minsert-sched-nops=@var{scheme} @gol
706 -mcall-sysv -mcall-netbsd @gol
707 -maix-struct-return -msvr4-struct-return @gol
708 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
709 -misel -mno-isel @gol
710 -misel=yes -misel=no @gol
712 -mspe=yes -mspe=no @gol
714 -mvrsave -mno-vrsave @gol
715 -mmulhw -mno-mulhw @gol
716 -mdlmzb -mno-dlmzb @gol
717 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
718 -mprototype -mno-prototype @gol
719 -msim -mmvme -mads -myellowknife -memb -msdata @gol
720 -msdata=@var{opt} -mvxworks -G @var{num} -pthread}
722 @emph{S/390 and zSeries Options}
723 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
724 -mhard-float -msoft-float -mlong-double-64 -mlong-double-128 @gol
725 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
726 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
727 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
728 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
729 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
732 @gccoptlist{-meb -mel @gol
736 -mscore5 -mscore5u -mscore7 -mscore7d}
739 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
740 -m4-nofpu -m4-single-only -m4-single -m4 @gol
741 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
742 -m5-64media -m5-64media-nofpu @gol
743 -m5-32media -m5-32media-nofpu @gol
744 -m5-compact -m5-compact-nofpu @gol
745 -mb -ml -mdalign -mrelax @gol
746 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
747 -mieee -mbitops -misize -minline-ic_invalidate -mpadstruct -mspace @gol
748 -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
749 -mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol
750 -madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
754 @gccoptlist{-mcpu=@var{cpu-type} @gol
755 -mtune=@var{cpu-type} @gol
756 -mcmodel=@var{code-model} @gol
757 -m32 -m64 -mapp-regs -mno-app-regs @gol
758 -mfaster-structs -mno-faster-structs @gol
759 -mfpu -mno-fpu -mhard-float -msoft-float @gol
760 -mhard-quad-float -msoft-quad-float @gol
761 -mimpure-text -mno-impure-text -mlittle-endian @gol
762 -mstack-bias -mno-stack-bias @gol
763 -munaligned-doubles -mno-unaligned-doubles @gol
764 -mv8plus -mno-v8plus -mvis -mno-vis
765 -threads -pthreads -pthread}
768 @gccoptlist{-mwarn-reloc -merror-reloc @gol
769 -msafe-dma -munsafe-dma @gol
771 -msmall-mem -mlarge-mem -mstdmain @gol
772 -mfixed-range=@var{register-range}}
774 @emph{System V Options}
775 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
778 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
779 -mprolog-function -mno-prolog-function -mspace @gol
780 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
781 -mapp-regs -mno-app-regs @gol
782 -mdisable-callt -mno-disable-callt @gol
788 @gccoptlist{-mg -mgnu -munix}
790 @emph{VxWorks Options}
791 @gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol
792 -Xbind-lazy -Xbind-now}
794 @emph{x86-64 Options}
795 See i386 and x86-64 Options.
797 @emph{Xstormy16 Options}
800 @emph{Xtensa Options}
801 @gccoptlist{-mconst16 -mno-const16 @gol
802 -mfused-madd -mno-fused-madd @gol
803 -mserialize-volatile -mno-serialize-volatile @gol
804 -mtext-section-literals -mno-text-section-literals @gol
805 -mtarget-align -mno-target-align @gol
806 -mlongcalls -mno-longcalls}
808 @emph{zSeries Options}
809 See S/390 and zSeries Options.
811 @item Code Generation Options
812 @xref{Code Gen Options,,Options for Code Generation Conventions}.
813 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
814 -ffixed-@var{reg} -fexceptions @gol
815 -fnon-call-exceptions -funwind-tables @gol
816 -fasynchronous-unwind-tables @gol
817 -finhibit-size-directive -finstrument-functions @gol
818 -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol
819 -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} @gol
820 -fno-common -fno-ident @gol
821 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
822 -fno-jump-tables @gol
823 -frecord-gcc-switches @gol
824 -freg-struct-return -fshort-enums @gol
825 -fshort-double -fshort-wchar @gol
826 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
827 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
828 -fno-stack-limit -fargument-alias -fargument-noalias @gol
829 -fargument-noalias-global -fargument-noalias-anything @gol
830 -fleading-underscore -ftls-model=@var{model} @gol
831 -ftrapv -fwrapv -fbounds-check @gol
836 * Overall Options:: Controlling the kind of output:
837 an executable, object files, assembler files,
838 or preprocessed source.
839 * C Dialect Options:: Controlling the variant of C language compiled.
840 * C++ Dialect Options:: Variations on C++.
841 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
843 * Language Independent Options:: Controlling how diagnostics should be
845 * Warning Options:: How picky should the compiler be?
846 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
847 * Optimize Options:: How much optimization?
848 * Preprocessor Options:: Controlling header files and macro definitions.
849 Also, getting dependency information for Make.
850 * Assembler Options:: Passing options to the assembler.
851 * Link Options:: Specifying libraries and so on.
852 * Directory Options:: Where to find header files and libraries.
853 Where to find the compiler executable files.
854 * Spec Files:: How to pass switches to sub-processes.
855 * Target Options:: Running a cross-compiler, or an old version of GCC.
858 @node Overall Options
859 @section Options Controlling the Kind of Output
861 Compilation can involve up to four stages: preprocessing, compilation
862 proper, assembly and linking, always in that order. GCC is capable of
863 preprocessing and compiling several files either into several
864 assembler input files, or into one assembler input file; then each
865 assembler input file produces an object file, and linking combines all
866 the object files (those newly compiled, and those specified as input)
867 into an executable file.
869 @cindex file name suffix
870 For any given input file, the file name suffix determines what kind of
875 C source code which must be preprocessed.
878 C source code which should not be preprocessed.
881 C++ source code which should not be preprocessed.
884 Objective-C source code. Note that you must link with the @file{libobjc}
885 library to make an Objective-C program work.
888 Objective-C source code which should not be preprocessed.
892 Objective-C++ source code. Note that you must link with the @file{libobjc}
893 library to make an Objective-C++ program work. Note that @samp{.M} refers
894 to a literal capital M@.
897 Objective-C++ source code which should not be preprocessed.
900 C, C++, Objective-C or Objective-C++ header file to be turned into a
905 @itemx @var{file}.cxx
906 @itemx @var{file}.cpp
907 @itemx @var{file}.CPP
908 @itemx @var{file}.c++
910 C++ source code which must be preprocessed. Note that in @samp{.cxx},
911 the last two letters must both be literally @samp{x}. Likewise,
912 @samp{.C} refers to a literal capital C@.
916 Objective-C++ source code which must be preprocessed.
919 Objective-C++ source code which should not be preprocessed.
924 @itemx @var{file}.hxx
925 @itemx @var{file}.hpp
926 @itemx @var{file}.HPP
927 @itemx @var{file}.h++
928 @itemx @var{file}.tcc
929 C++ header file to be turned into a precompiled header.
932 @itemx @var{file}.for
933 @itemx @var{file}.ftn
934 Fixed form Fortran source code which should not be preprocessed.
937 @itemx @var{file}.FOR
938 @itemx @var{file}.fpp
939 @itemx @var{file}.FPP
940 @itemx @var{file}.FTN
941 Fixed form Fortran source code which must be preprocessed (with the traditional
945 @itemx @var{file}.f95
946 @itemx @var{file}.f03
947 @itemx @var{file}.f08
948 Free form Fortran source code which should not be preprocessed.
951 @itemx @var{file}.F95
952 @itemx @var{file}.F03
953 @itemx @var{file}.F08
954 Free form Fortran source code which must be preprocessed (with the
955 traditional preprocessor).
957 @c FIXME: Descriptions of Java file types.
964 Ada source code file which contains a library unit declaration (a
965 declaration of a package, subprogram, or generic, or a generic
966 instantiation), or a library unit renaming declaration (a package,
967 generic, or subprogram renaming declaration). Such files are also
971 Ada source code file containing a library unit body (a subprogram or
972 package body). Such files are also called @dfn{bodies}.
974 @c GCC also knows about some suffixes for languages not yet included:
986 Assembler code which must be preprocessed.
989 An object file to be fed straight into linking.
990 Any file name with no recognized suffix is treated this way.
994 You can specify the input language explicitly with the @option{-x} option:
997 @item -x @var{language}
998 Specify explicitly the @var{language} for the following input files
999 (rather than letting the compiler choose a default based on the file
1000 name suffix). This option applies to all following input files until
1001 the next @option{-x} option. Possible values for @var{language} are:
1003 c c-header c-cpp-output
1004 c++ c++-header c++-cpp-output
1005 objective-c objective-c-header objective-c-cpp-output
1006 objective-c++ objective-c++-header objective-c++-cpp-output
1007 assembler assembler-with-cpp
1009 f77 f77-cpp-input f95 f95-cpp-input
1014 Turn off any specification of a language, so that subsequent files are
1015 handled according to their file name suffixes (as they are if @option{-x}
1016 has not been used at all).
1018 @item -pass-exit-codes
1019 @opindex pass-exit-codes
1020 Normally the @command{gcc} program will exit with the code of 1 if any
1021 phase of the compiler returns a non-success return code. If you specify
1022 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
1023 numerically highest error produced by any phase that returned an error
1024 indication. The C, C++, and Fortran frontends return 4, if an internal
1025 compiler error is encountered.
1028 If you only want some of the stages of compilation, you can use
1029 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
1030 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
1031 @command{gcc} is to stop. Note that some combinations (for example,
1032 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
1037 Compile or assemble the source files, but do not link. The linking
1038 stage simply is not done. The ultimate output is in the form of an
1039 object file for each source file.
1041 By default, the object file name for a source file is made by replacing
1042 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
1044 Unrecognized input files, not requiring compilation or assembly, are
1049 Stop after the stage of compilation proper; do not assemble. The output
1050 is in the form of an assembler code file for each non-assembler input
1053 By default, the assembler file name for a source file is made by
1054 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
1056 Input files that don't require compilation are ignored.
1060 Stop after the preprocessing stage; do not run the compiler proper. The
1061 output is in the form of preprocessed source code, which is sent to the
1064 Input files which don't require preprocessing are ignored.
1066 @cindex output file option
1069 Place output in file @var{file}. This applies regardless to whatever
1070 sort of output is being produced, whether it be an executable file,
1071 an object file, an assembler file or preprocessed C code.
1073 If @option{-o} is not specified, the default is to put an executable
1074 file in @file{a.out}, the object file for
1075 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
1076 assembler file in @file{@var{source}.s}, a precompiled header file in
1077 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
1082 Print (on standard error output) the commands executed to run the stages
1083 of compilation. Also print the version number of the compiler driver
1084 program and of the preprocessor and the compiler proper.
1088 Like @option{-v} except the commands are not executed and all command
1089 arguments are quoted. This is useful for shell scripts to capture the
1090 driver-generated command lines.
1094 Use pipes rather than temporary files for communication between the
1095 various stages of compilation. This fails to work on some systems where
1096 the assembler is unable to read from a pipe; but the GNU assembler has
1101 If you are compiling multiple source files, this option tells the driver
1102 to pass all the source files to the compiler at once (for those
1103 languages for which the compiler can handle this). This will allow
1104 intermodule analysis (IMA) to be performed by the compiler. Currently the only
1105 language for which this is supported is C@. If you pass source files for
1106 multiple languages to the driver, using this option, the driver will invoke
1107 the compiler(s) that support IMA once each, passing each compiler all the
1108 source files appropriate for it. For those languages that do not support
1109 IMA this option will be ignored, and the compiler will be invoked once for
1110 each source file in that language. If you use this option in conjunction
1111 with @option{-save-temps}, the compiler will generate multiple
1113 (one for each source file), but only one (combined) @file{.o} or
1118 Print (on the standard output) a description of the command line options
1119 understood by @command{gcc}. If the @option{-v} option is also specified
1120 then @option{--help} will also be passed on to the various processes
1121 invoked by @command{gcc}, so that they can display the command line options
1122 they accept. If the @option{-Wextra} option has also been specified
1123 (prior to the @option{--help} option), then command line options which
1124 have no documentation associated with them will also be displayed.
1127 @opindex target-help
1128 Print (on the standard output) a description of target-specific command
1129 line options for each tool. For some targets extra target-specific
1130 information may also be printed.
1132 @item --help=@var{class}@r{[},@var{qualifier}@r{]}
1133 Print (on the standard output) a description of the command line
1134 options understood by the compiler that fit into a specific class.
1135 The class can be one of @samp{optimizers}, @samp{warnings}, @samp{target},
1136 @samp{params}, or @var{language}:
1139 @item @samp{optimizers}
1140 This will display all of the optimization options supported by the
1143 @item @samp{warnings}
1144 This will display all of the options controlling warning messages
1145 produced by the compiler.
1148 This will display target-specific options. Unlike the
1149 @option{--target-help} option however, target-specific options of the
1150 linker and assembler will not be displayed. This is because those
1151 tools do not currently support the extended @option{--help=} syntax.
1154 This will display the values recognized by the @option{--param}
1157 @item @var{language}
1158 This will display the options supported for @var{language}, where
1159 @var{language} is the name of one of the languages supported in this
1163 This will display the options that are common to all languages.
1166 It is possible to further refine the output of the @option{--help=}
1167 option by adding a comma separated list of qualifiers after the
1168 class. These can be any from the following list:
1171 @item @samp{undocumented}
1172 Display only those options which are undocumented.
1175 Display options which take an argument that appears after an equal
1176 sign in the same continuous piece of text, such as:
1177 @samp{--help=target}.
1179 @item @samp{separate}
1180 Display options which take an argument that appears as a separate word
1181 following the original option, such as: @samp{-o output-file}.
1184 Thus for example to display all the undocumented target-specific
1185 switches supported by the compiler the following can be used:
1188 --help=target,undocumented
1191 The sense of a qualifier can be inverted by prefixing it with the
1192 @var{^} character, so for example to display all binary warning
1193 options (i.e., ones that are either on or off and that do not take an
1194 argument), which have a description the following can be used:
1197 --help=warnings,^joined,^undocumented
1200 A class can also be used as a qualifier, although this usually
1201 restricts the output by so much that there is nothing to display. One
1202 case where it does work however is when one of the classes is
1203 @var{target}. So for example to display all the target-specific
1204 optimization options the following can be used:
1207 --help=target,optimizers
1210 The @option{--help=} option can be repeated on the command line. Each
1211 successive use will display its requested class of options, skipping
1212 those that have already been displayed.
1214 If the @option{-Q} option appears on the command line before the
1215 @option{--help=} option, then the descriptive text displayed by
1216 @option{--help=} is changed. Instead of describing the displayed
1217 options, an indication is given as to whether the option is enabled,
1218 disabled or set to a specific value (assuming that the compiler
1219 knows this at the point where the @option{--help=} option is used).
1221 Here is a truncated example from the ARM port of @command{gcc}:
1224 % gcc -Q -mabi=2 --help=target -c
1225 The following options are target specific:
1227 -mabort-on-noreturn [disabled]
1231 The output is sensitive to the effects of previous command line
1232 options, so for example it is possible to find out which optimizations
1233 are enabled at @option{-O2} by using:
1236 -O2 --help=optimizers
1239 Alternatively you can discover which binary optimizations are enabled
1240 by @option{-O3} by using:
1243 gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
1244 gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
1245 diff /tmp/O2-opts /tmp/O3-opts | grep enabled
1250 Display the version number and copyrights of the invoked GCC@.
1254 Invoke all subcommands under a wrapper program. It takes a single
1255 comma separated list as an argument, which will be used to invoke
1259 gcc -c t.c -wrapper gdb,--args
1262 This will invoke all subprograms of gcc under "gdb --args",
1263 thus cc1 invocation will be "gdb --args cc1 ...".
1265 @include @value{srcdir}/../libiberty/at-file.texi
1269 @section Compiling C++ Programs
1271 @cindex suffixes for C++ source
1272 @cindex C++ source file suffixes
1273 C++ source files conventionally use one of the suffixes @samp{.C},
1274 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1275 @samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp},
1276 @samp{.H}, or (for shared template code) @samp{.tcc}; and
1277 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1278 files with these names and compiles them as C++ programs even if you
1279 call the compiler the same way as for compiling C programs (usually
1280 with the name @command{gcc}).
1284 However, the use of @command{gcc} does not add the C++ library.
1285 @command{g++} is a program that calls GCC and treats @samp{.c},
1286 @samp{.h} and @samp{.i} files as C++ source files instead of C source
1287 files unless @option{-x} is used, and automatically specifies linking
1288 against the C++ library. This program is also useful when
1289 precompiling a C header file with a @samp{.h} extension for use in C++
1290 compilations. On many systems, @command{g++} is also installed with
1291 the name @command{c++}.
1293 @cindex invoking @command{g++}
1294 When you compile C++ programs, you may specify many of the same
1295 command-line options that you use for compiling programs in any
1296 language; or command-line options meaningful for C and related
1297 languages; or options that are meaningful only for C++ programs.
1298 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1299 explanations of options for languages related to C@.
1300 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1301 explanations of options that are meaningful only for C++ programs.
1303 @node C Dialect Options
1304 @section Options Controlling C Dialect
1305 @cindex dialect options
1306 @cindex language dialect options
1307 @cindex options, dialect
1309 The following options control the dialect of C (or languages derived
1310 from C, such as C++, Objective-C and Objective-C++) that the compiler
1314 @cindex ANSI support
1318 In C mode, this is equivalent to @samp{-std=c89}. In C++ mode, it is
1319 equivalent to @samp{-std=c++98}.
1321 This turns off certain features of GCC that are incompatible with ISO
1322 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1323 such as the @code{asm} and @code{typeof} keywords, and
1324 predefined macros such as @code{unix} and @code{vax} that identify the
1325 type of system you are using. It also enables the undesirable and
1326 rarely used ISO trigraph feature. For the C compiler,
1327 it disables recognition of C++ style @samp{//} comments as well as
1328 the @code{inline} keyword.
1330 The alternate keywords @code{__asm__}, @code{__extension__},
1331 @code{__inline__} and @code{__typeof__} continue to work despite
1332 @option{-ansi}. You would not want to use them in an ISO C program, of
1333 course, but it is useful to put them in header files that might be included
1334 in compilations done with @option{-ansi}. Alternate predefined macros
1335 such as @code{__unix__} and @code{__vax__} are also available, with or
1336 without @option{-ansi}.
1338 The @option{-ansi} option does not cause non-ISO programs to be
1339 rejected gratuitously. For that, @option{-pedantic} is required in
1340 addition to @option{-ansi}. @xref{Warning Options}.
1342 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1343 option is used. Some header files may notice this macro and refrain
1344 from declaring certain functions or defining certain macros that the
1345 ISO standard doesn't call for; this is to avoid interfering with any
1346 programs that might use these names for other things.
1348 Functions that would normally be built in but do not have semantics
1349 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1350 functions when @option{-ansi} is used. @xref{Other Builtins,,Other
1351 built-in functions provided by GCC}, for details of the functions
1356 Determine the language standard. @xref{Standards,,Language Standards
1357 Supported by GCC}, for details of these standard versions. This option
1358 is currently only supported when compiling C or C++.
1360 The compiler can accept several base standards, such as @samp{c89} or
1361 @samp{c++98}, and GNU dialects of those standards, such as
1362 @samp{gnu89} or @samp{gnu++98}. By specifing a base standard, the
1363 compiler will accept all programs following that standard and those
1364 using GNU extensions that do not contradict it. For example,
1365 @samp{-std=c89} turns off certain features of GCC that are
1366 incompatible with ISO C90, such as the @code{asm} and @code{typeof}
1367 keywords, but not other GNU extensions that do not have a meaning in
1368 ISO C90, such as omitting the middle term of a @code{?:}
1369 expression. On the other hand, by specifing a GNU dialect of a
1370 standard, all features the compiler support are enabled, even when
1371 those features change the meaning of the base standard and some
1372 strict-conforming programs may be rejected. The particular standard
1373 is used by @option{-pedantic} to identify which features are GNU
1374 extensions given that version of the standard. For example
1375 @samp{-std=gnu89 -pedantic} would warn about C++ style @samp{//}
1376 comments, while @samp{-std=gnu99 -pedantic} would not.
1378 A value for this option must be provided; possible values are
1383 Support all ISO C90 programs (certain GNU extensions that conflict
1384 with ISO C90 are disabled). Same as @option{-ansi} for C code.
1386 @item iso9899:199409
1387 ISO C90 as modified in amendment 1.
1393 ISO C99. Note that this standard is not yet fully supported; see
1394 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1395 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1398 GNU dialect of ISO C90 (including some C99 features). This
1399 is the default for C code.
1403 GNU dialect of ISO C99. When ISO C99 is fully implemented in GCC,
1404 this will become the default. The name @samp{gnu9x} is deprecated.
1407 The 1998 ISO C++ standard plus amendments. Same as @option{-ansi} for
1411 GNU dialect of @option{-std=c++98}. This is the default for
1415 The working draft of the upcoming ISO C++0x standard. This option
1416 enables experimental features that are likely to be included in
1417 C++0x. The working draft is constantly changing, and any feature that is
1418 enabled by this flag may be removed from future versions of GCC if it is
1419 not part of the C++0x standard.
1422 GNU dialect of @option{-std=c++0x}. This option enables
1423 experimental features that may be removed in future versions of GCC.
1426 @item -fgnu89-inline
1427 @opindex fgnu89-inline
1428 The option @option{-fgnu89-inline} tells GCC to use the traditional
1429 GNU semantics for @code{inline} functions when in C99 mode.
1430 @xref{Inline,,An Inline Function is As Fast As a Macro}. This option
1431 is accepted and ignored by GCC versions 4.1.3 up to but not including
1432 4.3. In GCC versions 4.3 and later it changes the behavior of GCC in
1433 C99 mode. Using this option is roughly equivalent to adding the
1434 @code{gnu_inline} function attribute to all inline functions
1435 (@pxref{Function Attributes}).
1437 The option @option{-fno-gnu89-inline} explicitly tells GCC to use the
1438 C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it
1439 specifies the default behavior). This option was first supported in
1440 GCC 4.3. This option is not supported in C89 or gnu89 mode.
1442 The preprocessor macros @code{__GNUC_GNU_INLINE__} and
1443 @code{__GNUC_STDC_INLINE__} may be used to check which semantics are
1444 in effect for @code{inline} functions. @xref{Common Predefined
1445 Macros,,,cpp,The C Preprocessor}.
1447 @item -aux-info @var{filename}
1449 Output to the given filename prototyped declarations for all functions
1450 declared and/or defined in a translation unit, including those in header
1451 files. This option is silently ignored in any language other than C@.
1453 Besides declarations, the file indicates, in comments, the origin of
1454 each declaration (source file and line), whether the declaration was
1455 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1456 @samp{O} for old, respectively, in the first character after the line
1457 number and the colon), and whether it came from a declaration or a
1458 definition (@samp{C} or @samp{F}, respectively, in the following
1459 character). In the case of function definitions, a K&R-style list of
1460 arguments followed by their declarations is also provided, inside
1461 comments, after the declaration.
1465 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1466 keyword, so that code can use these words as identifiers. You can use
1467 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1468 instead. @option{-ansi} implies @option{-fno-asm}.
1470 In C++, this switch only affects the @code{typeof} keyword, since
1471 @code{asm} and @code{inline} are standard keywords. You may want to
1472 use the @option{-fno-gnu-keywords} flag instead, which has the same
1473 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1474 switch only affects the @code{asm} and @code{typeof} keywords, since
1475 @code{inline} is a standard keyword in ISO C99.
1478 @itemx -fno-builtin-@var{function}
1479 @opindex fno-builtin
1480 @cindex built-in functions
1481 Don't recognize built-in functions that do not begin with
1482 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1483 functions provided by GCC}, for details of the functions affected,
1484 including those which are not built-in functions when @option{-ansi} or
1485 @option{-std} options for strict ISO C conformance are used because they
1486 do not have an ISO standard meaning.
1488 GCC normally generates special code to handle certain built-in functions
1489 more efficiently; for instance, calls to @code{alloca} may become single
1490 instructions that adjust the stack directly, and calls to @code{memcpy}
1491 may become inline copy loops. The resulting code is often both smaller
1492 and faster, but since the function calls no longer appear as such, you
1493 cannot set a breakpoint on those calls, nor can you change the behavior
1494 of the functions by linking with a different library. In addition,
1495 when a function is recognized as a built-in function, GCC may use
1496 information about that function to warn about problems with calls to
1497 that function, or to generate more efficient code, even if the
1498 resulting code still contains calls to that function. For example,
1499 warnings are given with @option{-Wformat} for bad calls to
1500 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1501 known not to modify global memory.
1503 With the @option{-fno-builtin-@var{function}} option
1504 only the built-in function @var{function} is
1505 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1506 function is named this is not built-in in this version of GCC, this
1507 option is ignored. There is no corresponding
1508 @option{-fbuiltin-@var{function}} option; if you wish to enable
1509 built-in functions selectively when using @option{-fno-builtin} or
1510 @option{-ffreestanding}, you may define macros such as:
1513 #define abs(n) __builtin_abs ((n))
1514 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1519 @cindex hosted environment
1521 Assert that compilation takes place in a hosted environment. This implies
1522 @option{-fbuiltin}. A hosted environment is one in which the
1523 entire standard library is available, and in which @code{main} has a return
1524 type of @code{int}. Examples are nearly everything except a kernel.
1525 This is equivalent to @option{-fno-freestanding}.
1527 @item -ffreestanding
1528 @opindex ffreestanding
1529 @cindex hosted environment
1531 Assert that compilation takes place in a freestanding environment. This
1532 implies @option{-fno-builtin}. A freestanding environment
1533 is one in which the standard library may not exist, and program startup may
1534 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1535 This is equivalent to @option{-fno-hosted}.
1537 @xref{Standards,,Language Standards Supported by GCC}, for details of
1538 freestanding and hosted environments.
1542 @cindex openmp parallel
1543 Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
1544 @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
1545 compiler generates parallel code according to the OpenMP Application
1546 Program Interface v2.5 @w{@uref{http://www.openmp.org/}}. This option
1547 implies @option{-pthread}, and thus is only supported on targets that
1548 have support for @option{-pthread}.
1550 @item -fms-extensions
1551 @opindex fms-extensions
1552 Accept some non-standard constructs used in Microsoft header files.
1554 Some cases of unnamed fields in structures and unions are only
1555 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1556 fields within structs/unions}, for details.
1560 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1561 options for strict ISO C conformance) implies @option{-trigraphs}.
1563 @item -no-integrated-cpp
1564 @opindex no-integrated-cpp
1565 Performs a compilation in two passes: preprocessing and compiling. This
1566 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1567 @option{-B} option. The user supplied compilation step can then add in
1568 an additional preprocessing step after normal preprocessing but before
1569 compiling. The default is to use the integrated cpp (internal cpp)
1571 The semantics of this option will change if "cc1", "cc1plus", and
1572 "cc1obj" are merged.
1574 @cindex traditional C language
1575 @cindex C language, traditional
1577 @itemx -traditional-cpp
1578 @opindex traditional-cpp
1579 @opindex traditional
1580 Formerly, these options caused GCC to attempt to emulate a pre-standard
1581 C compiler. They are now only supported with the @option{-E} switch.
1582 The preprocessor continues to support a pre-standard mode. See the GNU
1583 CPP manual for details.
1585 @item -fcond-mismatch
1586 @opindex fcond-mismatch
1587 Allow conditional expressions with mismatched types in the second and
1588 third arguments. The value of such an expression is void. This option
1589 is not supported for C++.
1591 @item -flax-vector-conversions
1592 @opindex flax-vector-conversions
1593 Allow implicit conversions between vectors with differing numbers of
1594 elements and/or incompatible element types. This option should not be
1597 @item -funsigned-char
1598 @opindex funsigned-char
1599 Let the type @code{char} be unsigned, like @code{unsigned char}.
1601 Each kind of machine has a default for what @code{char} should
1602 be. It is either like @code{unsigned char} by default or like
1603 @code{signed char} by default.
1605 Ideally, a portable program should always use @code{signed char} or
1606 @code{unsigned char} when it depends on the signedness of an object.
1607 But many programs have been written to use plain @code{char} and
1608 expect it to be signed, or expect it to be unsigned, depending on the
1609 machines they were written for. This option, and its inverse, let you
1610 make such a program work with the opposite default.
1612 The type @code{char} is always a distinct type from each of
1613 @code{signed char} or @code{unsigned char}, even though its behavior
1614 is always just like one of those two.
1617 @opindex fsigned-char
1618 Let the type @code{char} be signed, like @code{signed char}.
1620 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1621 the negative form of @option{-funsigned-char}. Likewise, the option
1622 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1624 @item -fsigned-bitfields
1625 @itemx -funsigned-bitfields
1626 @itemx -fno-signed-bitfields
1627 @itemx -fno-unsigned-bitfields
1628 @opindex fsigned-bitfields
1629 @opindex funsigned-bitfields
1630 @opindex fno-signed-bitfields
1631 @opindex fno-unsigned-bitfields
1632 These options control whether a bit-field is signed or unsigned, when the
1633 declaration does not use either @code{signed} or @code{unsigned}. By
1634 default, such a bit-field is signed, because this is consistent: the
1635 basic integer types such as @code{int} are signed types.
1638 @node C++ Dialect Options
1639 @section Options Controlling C++ Dialect
1641 @cindex compiler options, C++
1642 @cindex C++ options, command line
1643 @cindex options, C++
1644 This section describes the command-line options that are only meaningful
1645 for C++ programs; but you can also use most of the GNU compiler options
1646 regardless of what language your program is in. For example, you
1647 might compile a file @code{firstClass.C} like this:
1650 g++ -g -frepo -O -c firstClass.C
1654 In this example, only @option{-frepo} is an option meant
1655 only for C++ programs; you can use the other options with any
1656 language supported by GCC@.
1658 Here is a list of options that are @emph{only} for compiling C++ programs:
1662 @item -fabi-version=@var{n}
1663 @opindex fabi-version
1664 Use version @var{n} of the C++ ABI@. Version 2 is the version of the
1665 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1666 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1667 the version that conforms most closely to the C++ ABI specification.
1668 Therefore, the ABI obtained using version 0 will change as ABI bugs
1671 The default is version 2.
1673 @item -fno-access-control
1674 @opindex fno-access-control
1675 Turn off all access checking. This switch is mainly useful for working
1676 around bugs in the access control code.
1680 Check that the pointer returned by @code{operator new} is non-null
1681 before attempting to modify the storage allocated. This check is
1682 normally unnecessary because the C++ standard specifies that
1683 @code{operator new} will only return @code{0} if it is declared
1684 @samp{throw()}, in which case the compiler will always check the
1685 return value even without this option. In all other cases, when
1686 @code{operator new} has a non-empty exception specification, memory
1687 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1688 @samp{new (nothrow)}.
1690 @item -fconserve-space
1691 @opindex fconserve-space
1692 Put uninitialized or runtime-initialized global variables into the
1693 common segment, as C does. This saves space in the executable at the
1694 cost of not diagnosing duplicate definitions. If you compile with this
1695 flag and your program mysteriously crashes after @code{main()} has
1696 completed, you may have an object that is being destroyed twice because
1697 two definitions were merged.
1699 This option is no longer useful on most targets, now that support has
1700 been added for putting variables into BSS without making them common.
1702 @item -ffriend-injection
1703 @opindex ffriend-injection
1704 Inject friend functions into the enclosing namespace, so that they are
1705 visible outside the scope of the class in which they are declared.
1706 Friend functions were documented to work this way in the old Annotated
1707 C++ Reference Manual, and versions of G++ before 4.1 always worked
1708 that way. However, in ISO C++ a friend function which is not declared
1709 in an enclosing scope can only be found using argument dependent
1710 lookup. This option causes friends to be injected as they were in
1713 This option is for compatibility, and may be removed in a future
1716 @item -fno-elide-constructors
1717 @opindex fno-elide-constructors
1718 The C++ standard allows an implementation to omit creating a temporary
1719 which is only used to initialize another object of the same type.
1720 Specifying this option disables that optimization, and forces G++ to
1721 call the copy constructor in all cases.
1723 @item -fno-enforce-eh-specs
1724 @opindex fno-enforce-eh-specs
1725 Don't generate code to check for violation of exception specifications
1726 at runtime. This option violates the C++ standard, but may be useful
1727 for reducing code size in production builds, much like defining
1728 @samp{NDEBUG}. This does not give user code permission to throw
1729 exceptions in violation of the exception specifications; the compiler
1730 will still optimize based on the specifications, so throwing an
1731 unexpected exception will result in undefined behavior.
1734 @itemx -fno-for-scope
1736 @opindex fno-for-scope
1737 If @option{-ffor-scope} is specified, the scope of variables declared in
1738 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1739 as specified by the C++ standard.
1740 If @option{-fno-for-scope} is specified, the scope of variables declared in
1741 a @i{for-init-statement} extends to the end of the enclosing scope,
1742 as was the case in old versions of G++, and other (traditional)
1743 implementations of C++.
1745 The default if neither flag is given to follow the standard,
1746 but to allow and give a warning for old-style code that would
1747 otherwise be invalid, or have different behavior.
1749 @item -fno-gnu-keywords
1750 @opindex fno-gnu-keywords
1751 Do not recognize @code{typeof} as a keyword, so that code can use this
1752 word as an identifier. You can use the keyword @code{__typeof__} instead.
1753 @option{-ansi} implies @option{-fno-gnu-keywords}.
1755 @item -fno-implicit-templates
1756 @opindex fno-implicit-templates
1757 Never emit code for non-inline templates which are instantiated
1758 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1759 @xref{Template Instantiation}, for more information.
1761 @item -fno-implicit-inline-templates
1762 @opindex fno-implicit-inline-templates
1763 Don't emit code for implicit instantiations of inline templates, either.
1764 The default is to handle inlines differently so that compiles with and
1765 without optimization will need the same set of explicit instantiations.
1767 @item -fno-implement-inlines
1768 @opindex fno-implement-inlines
1769 To save space, do not emit out-of-line copies of inline functions
1770 controlled by @samp{#pragma implementation}. This will cause linker
1771 errors if these functions are not inlined everywhere they are called.
1773 @item -fms-extensions
1774 @opindex fms-extensions
1775 Disable pedantic warnings about constructs used in MFC, such as implicit
1776 int and getting a pointer to member function via non-standard syntax.
1778 @item -fno-nonansi-builtins
1779 @opindex fno-nonansi-builtins
1780 Disable built-in declarations of functions that are not mandated by
1781 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1782 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1784 @item -fno-operator-names
1785 @opindex fno-operator-names
1786 Do not treat the operator name keywords @code{and}, @code{bitand},
1787 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1788 synonyms as keywords.
1790 @item -fno-optional-diags
1791 @opindex fno-optional-diags
1792 Disable diagnostics that the standard says a compiler does not need to
1793 issue. Currently, the only such diagnostic issued by G++ is the one for
1794 a name having multiple meanings within a class.
1797 @opindex fpermissive
1798 Downgrade some diagnostics about nonconformant code from errors to
1799 warnings. Thus, using @option{-fpermissive} will allow some
1800 nonconforming code to compile.
1804 Enable automatic template instantiation at link time. This option also
1805 implies @option{-fno-implicit-templates}. @xref{Template
1806 Instantiation}, for more information.
1810 Disable generation of information about every class with virtual
1811 functions for use by the C++ runtime type identification features
1812 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1813 of the language, you can save some space by using this flag. Note that
1814 exception handling uses the same information, but it will generate it as
1815 needed. The @samp{dynamic_cast} operator can still be used for casts that
1816 do not require runtime type information, i.e.@: casts to @code{void *} or to
1817 unambiguous base classes.
1821 Emit statistics about front-end processing at the end of the compilation.
1822 This information is generally only useful to the G++ development team.
1824 @item -ftemplate-depth-@var{n}
1825 @opindex ftemplate-depth
1826 Set the maximum instantiation depth for template classes to @var{n}.
1827 A limit on the template instantiation depth is needed to detect
1828 endless recursions during template class instantiation. ANSI/ISO C++
1829 conforming programs must not rely on a maximum depth greater than 17.
1831 @item -fno-threadsafe-statics
1832 @opindex fno-threadsafe-statics
1833 Do not emit the extra code to use the routines specified in the C++
1834 ABI for thread-safe initialization of local statics. You can use this
1835 option to reduce code size slightly in code that doesn't need to be
1838 @item -fuse-cxa-atexit
1839 @opindex fuse-cxa-atexit
1840 Register destructors for objects with static storage duration with the
1841 @code{__cxa_atexit} function rather than the @code{atexit} function.
1842 This option is required for fully standards-compliant handling of static
1843 destructors, but will only work if your C library supports
1844 @code{__cxa_atexit}.
1846 @item -fno-use-cxa-get-exception-ptr
1847 @opindex fno-use-cxa-get-exception-ptr
1848 Don't use the @code{__cxa_get_exception_ptr} runtime routine. This
1849 will cause @code{std::uncaught_exception} to be incorrect, but is necessary
1850 if the runtime routine is not available.
1852 @item -fvisibility-inlines-hidden
1853 @opindex fvisibility-inlines-hidden
1854 This switch declares that the user does not attempt to compare
1855 pointers to inline methods where the addresses of the two functions
1856 were taken in different shared objects.
1858 The effect of this is that GCC may, effectively, mark inline methods with
1859 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1860 appear in the export table of a DSO and do not require a PLT indirection
1861 when used within the DSO@. Enabling this option can have a dramatic effect
1862 on load and link times of a DSO as it massively reduces the size of the
1863 dynamic export table when the library makes heavy use of templates.
1865 The behavior of this switch is not quite the same as marking the
1866 methods as hidden directly, because it does not affect static variables
1867 local to the function or cause the compiler to deduce that
1868 the function is defined in only one shared object.
1870 You may mark a method as having a visibility explicitly to negate the
1871 effect of the switch for that method. For example, if you do want to
1872 compare pointers to a particular inline method, you might mark it as
1873 having default visibility. Marking the enclosing class with explicit
1874 visibility will have no effect.
1876 Explicitly instantiated inline methods are unaffected by this option
1877 as their linkage might otherwise cross a shared library boundary.
1878 @xref{Template Instantiation}.
1880 @item -fvisibility-ms-compat
1881 @opindex fvisibility-ms-compat
1882 This flag attempts to use visibility settings to make GCC's C++
1883 linkage model compatible with that of Microsoft Visual Studio.
1885 The flag makes these changes to GCC's linkage model:
1889 It sets the default visibility to @code{hidden}, like
1890 @option{-fvisibility=hidden}.
1893 Types, but not their members, are not hidden by default.
1896 The One Definition Rule is relaxed for types without explicit
1897 visibility specifications which are defined in more than one different
1898 shared object: those declarations are permitted if they would have
1899 been permitted when this option was not used.
1902 In new code it is better to use @option{-fvisibility=hidden} and
1903 export those classes which are intended to be externally visible.
1904 Unfortunately it is possible for code to rely, perhaps accidentally,
1905 on the Visual Studio behavior.
1907 Among the consequences of these changes are that static data members
1908 of the same type with the same name but defined in different shared
1909 objects will be different, so changing one will not change the other;
1910 and that pointers to function members defined in different shared
1911 objects may not compare equal. When this flag is given, it is a
1912 violation of the ODR to define types with the same name differently.
1916 Do not use weak symbol support, even if it is provided by the linker.
1917 By default, G++ will use weak symbols if they are available. This
1918 option exists only for testing, and should not be used by end-users;
1919 it will result in inferior code and has no benefits. This option may
1920 be removed in a future release of G++.
1924 Do not search for header files in the standard directories specific to
1925 C++, but do still search the other standard directories. (This option
1926 is used when building the C++ library.)
1929 In addition, these optimization, warning, and code generation options
1930 have meanings only for C++ programs:
1933 @item -fno-default-inline
1934 @opindex fno-default-inline
1935 Do not assume @samp{inline} for functions defined inside a class scope.
1936 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1937 functions will have linkage like inline functions; they just won't be
1940 @item -Wabi @r{(C++ and Objective-C++ only)}
1943 Warn when G++ generates code that is probably not compatible with the
1944 vendor-neutral C++ ABI@. Although an effort has been made to warn about
1945 all such cases, there are probably some cases that are not warned about,
1946 even though G++ is generating incompatible code. There may also be
1947 cases where warnings are emitted even though the code that is generated
1950 You should rewrite your code to avoid these warnings if you are
1951 concerned about the fact that code generated by G++ may not be binary
1952 compatible with code generated by other compilers.
1954 The known incompatibilities at this point include:
1959 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1960 pack data into the same byte as a base class. For example:
1963 struct A @{ virtual void f(); int f1 : 1; @};
1964 struct B : public A @{ int f2 : 1; @};
1968 In this case, G++ will place @code{B::f2} into the same byte
1969 as@code{A::f1}; other compilers will not. You can avoid this problem
1970 by explicitly padding @code{A} so that its size is a multiple of the
1971 byte size on your platform; that will cause G++ and other compilers to
1972 layout @code{B} identically.
1975 Incorrect handling of tail-padding for virtual bases. G++ does not use
1976 tail padding when laying out virtual bases. For example:
1979 struct A @{ virtual void f(); char c1; @};
1980 struct B @{ B(); char c2; @};
1981 struct C : public A, public virtual B @{@};
1985 In this case, G++ will not place @code{B} into the tail-padding for
1986 @code{A}; other compilers will. You can avoid this problem by
1987 explicitly padding @code{A} so that its size is a multiple of its
1988 alignment (ignoring virtual base classes); that will cause G++ and other
1989 compilers to layout @code{C} identically.
1992 Incorrect handling of bit-fields with declared widths greater than that
1993 of their underlying types, when the bit-fields appear in a union. For
1997 union U @{ int i : 4096; @};
2001 Assuming that an @code{int} does not have 4096 bits, G++ will make the
2002 union too small by the number of bits in an @code{int}.
2005 Empty classes can be placed at incorrect offsets. For example:
2015 struct C : public B, public A @{@};
2019 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
2020 it should be placed at offset zero. G++ mistakenly believes that the
2021 @code{A} data member of @code{B} is already at offset zero.
2024 Names of template functions whose types involve @code{typename} or
2025 template template parameters can be mangled incorrectly.
2028 template <typename Q>
2029 void f(typename Q::X) @{@}
2031 template <template <typename> class Q>
2032 void f(typename Q<int>::X) @{@}
2036 Instantiations of these templates may be mangled incorrectly.
2040 @item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)}
2041 @opindex Wctor-dtor-privacy
2042 @opindex Wno-ctor-dtor-privacy
2043 Warn when a class seems unusable because all the constructors or
2044 destructors in that class are private, and it has neither friends nor
2045 public static member functions.
2047 @item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)}
2048 @opindex Wnon-virtual-dtor
2049 @opindex Wno-non-virtual-dtor
2050 Warn when a class has virtual functions and accessible non-virtual
2051 destructor, in which case it would be possible but unsafe to delete
2052 an instance of a derived class through a pointer to the base class.
2053 This warning is also enabled if -Weffc++ is specified.
2055 @item -Wreorder @r{(C++ and Objective-C++ only)}
2057 @opindex Wno-reorder
2058 @cindex reordering, warning
2059 @cindex warning for reordering of member initializers
2060 Warn when the order of member initializers given in the code does not
2061 match the order in which they must be executed. For instance:
2067 A(): j (0), i (1) @{ @}
2071 The compiler will rearrange the member initializers for @samp{i}
2072 and @samp{j} to match the declaration order of the members, emitting
2073 a warning to that effect. This warning is enabled by @option{-Wall}.
2076 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
2079 @item -Weffc++ @r{(C++ and Objective-C++ only)}
2082 Warn about violations of the following style guidelines from Scott Meyers'
2083 @cite{Effective C++} book:
2087 Item 11: Define a copy constructor and an assignment operator for classes
2088 with dynamically allocated memory.
2091 Item 12: Prefer initialization to assignment in constructors.
2094 Item 14: Make destructors virtual in base classes.
2097 Item 15: Have @code{operator=} return a reference to @code{*this}.
2100 Item 23: Don't try to return a reference when you must return an object.
2104 Also warn about violations of the following style guidelines from
2105 Scott Meyers' @cite{More Effective C++} book:
2109 Item 6: Distinguish between prefix and postfix forms of increment and
2110 decrement operators.
2113 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
2117 When selecting this option, be aware that the standard library
2118 headers do not obey all of these guidelines; use @samp{grep -v}
2119 to filter out those warnings.
2121 @item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)}
2122 @opindex Wstrict-null-sentinel
2123 @opindex Wno-strict-null-sentinel
2124 Warn also about the use of an uncasted @code{NULL} as sentinel. When
2125 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
2126 to @code{__null}. Although it is a null pointer constant not a null pointer,
2127 it is guaranteed to of the same size as a pointer. But this use is
2128 not portable across different compilers.
2130 @item -Wno-non-template-friend @r{(C++ and Objective-C++ only)}
2131 @opindex Wno-non-template-friend
2132 @opindex Wnon-template-friend
2133 Disable warnings when non-templatized friend functions are declared
2134 within a template. Since the advent of explicit template specification
2135 support in G++, if the name of the friend is an unqualified-id (i.e.,
2136 @samp{friend foo(int)}), the C++ language specification demands that the
2137 friend declare or define an ordinary, nontemplate function. (Section
2138 14.5.3). Before G++ implemented explicit specification, unqualified-ids
2139 could be interpreted as a particular specialization of a templatized
2140 function. Because this non-conforming behavior is no longer the default
2141 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
2142 check existing code for potential trouble spots and is on by default.
2143 This new compiler behavior can be turned off with
2144 @option{-Wno-non-template-friend} which keeps the conformant compiler code
2145 but disables the helpful warning.
2147 @item -Wold-style-cast @r{(C++ and Objective-C++ only)}
2148 @opindex Wold-style-cast
2149 @opindex Wno-old-style-cast
2150 Warn if an old-style (C-style) cast to a non-void type is used within
2151 a C++ program. The new-style casts (@samp{dynamic_cast},
2152 @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are
2153 less vulnerable to unintended effects and much easier to search for.
2155 @item -Woverloaded-virtual @r{(C++ and Objective-C++ only)}
2156 @opindex Woverloaded-virtual
2157 @opindex Wno-overloaded-virtual
2158 @cindex overloaded virtual fn, warning
2159 @cindex warning for overloaded virtual fn
2160 Warn when a function declaration hides virtual functions from a
2161 base class. For example, in:
2168 struct B: public A @{
2173 the @code{A} class version of @code{f} is hidden in @code{B}, and code
2181 will fail to compile.
2183 @item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)}
2184 @opindex Wno-pmf-conversions
2185 @opindex Wpmf-conversions
2186 Disable the diagnostic for converting a bound pointer to member function
2189 @item -Wsign-promo @r{(C++ and Objective-C++ only)}
2190 @opindex Wsign-promo
2191 @opindex Wno-sign-promo
2192 Warn when overload resolution chooses a promotion from unsigned or
2193 enumerated type to a signed type, over a conversion to an unsigned type of
2194 the same size. Previous versions of G++ would try to preserve
2195 unsignedness, but the standard mandates the current behavior.
2200 A& operator = (int);
2210 In this example, G++ will synthesize a default @samp{A& operator =
2211 (const A&);}, while cfront will use the user-defined @samp{operator =}.
2214 @node Objective-C and Objective-C++ Dialect Options
2215 @section Options Controlling Objective-C and Objective-C++ Dialects
2217 @cindex compiler options, Objective-C and Objective-C++
2218 @cindex Objective-C and Objective-C++ options, command line
2219 @cindex options, Objective-C and Objective-C++
2220 (NOTE: This manual does not describe the Objective-C and Objective-C++
2221 languages themselves. See @xref{Standards,,Language Standards
2222 Supported by GCC}, for references.)
2224 This section describes the command-line options that are only meaningful
2225 for Objective-C and Objective-C++ programs, but you can also use most of
2226 the language-independent GNU compiler options.
2227 For example, you might compile a file @code{some_class.m} like this:
2230 gcc -g -fgnu-runtime -O -c some_class.m
2234 In this example, @option{-fgnu-runtime} is an option meant only for
2235 Objective-C and Objective-C++ programs; you can use the other options with
2236 any language supported by GCC@.
2238 Note that since Objective-C is an extension of the C language, Objective-C
2239 compilations may also use options specific to the C front-end (e.g.,
2240 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
2241 C++-specific options (e.g., @option{-Wabi}).
2243 Here is a list of options that are @emph{only} for compiling Objective-C
2244 and Objective-C++ programs:
2247 @item -fconstant-string-class=@var{class-name}
2248 @opindex fconstant-string-class
2249 Use @var{class-name} as the name of the class to instantiate for each
2250 literal string specified with the syntax @code{@@"@dots{}"}. The default
2251 class name is @code{NXConstantString} if the GNU runtime is being used, and
2252 @code{NSConstantString} if the NeXT runtime is being used (see below). The
2253 @option{-fconstant-cfstrings} option, if also present, will override the
2254 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
2255 to be laid out as constant CoreFoundation strings.
2258 @opindex fgnu-runtime
2259 Generate object code compatible with the standard GNU Objective-C
2260 runtime. This is the default for most types of systems.
2262 @item -fnext-runtime
2263 @opindex fnext-runtime
2264 Generate output compatible with the NeXT runtime. This is the default
2265 for NeXT-based systems, including Darwin and Mac OS X@. The macro
2266 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
2269 @item -fno-nil-receivers
2270 @opindex fno-nil-receivers
2271 Assume that all Objective-C message dispatches (e.g.,
2272 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
2273 is not @code{nil}. This allows for more efficient entry points in the runtime
2274 to be used. Currently, this option is only available in conjunction with
2275 the NeXT runtime on Mac OS X 10.3 and later.
2277 @item -fobjc-call-cxx-cdtors
2278 @opindex fobjc-call-cxx-cdtors
2279 For each Objective-C class, check if any of its instance variables is a
2280 C++ object with a non-trivial default constructor. If so, synthesize a
2281 special @code{- (id) .cxx_construct} instance method that will run
2282 non-trivial default constructors on any such instance variables, in order,
2283 and then return @code{self}. Similarly, check if any instance variable
2284 is a C++ object with a non-trivial destructor, and if so, synthesize a
2285 special @code{- (void) .cxx_destruct} method that will run
2286 all such default destructors, in reverse order.
2288 The @code{- (id) .cxx_construct} and/or @code{- (void) .cxx_destruct} methods
2289 thusly generated will only operate on instance variables declared in the
2290 current Objective-C class, and not those inherited from superclasses. It
2291 is the responsibility of the Objective-C runtime to invoke all such methods
2292 in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods
2293 will be invoked by the runtime immediately after a new object
2294 instance is allocated; the @code{- (void) .cxx_destruct} methods will
2295 be invoked immediately before the runtime deallocates an object instance.
2297 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
2298 support for invoking the @code{- (id) .cxx_construct} and
2299 @code{- (void) .cxx_destruct} methods.
2301 @item -fobjc-direct-dispatch
2302 @opindex fobjc-direct-dispatch
2303 Allow fast jumps to the message dispatcher. On Darwin this is
2304 accomplished via the comm page.
2306 @item -fobjc-exceptions
2307 @opindex fobjc-exceptions
2308 Enable syntactic support for structured exception handling in Objective-C,
2309 similar to what is offered by C++ and Java. This option is
2310 unavailable in conjunction with the NeXT runtime on Mac OS X 10.2 and
2319 @@catch (AnObjCClass *exc) @{
2326 @@catch (AnotherClass *exc) @{
2329 @@catch (id allOthers) @{
2339 The @code{@@throw} statement may appear anywhere in an Objective-C or
2340 Objective-C++ program; when used inside of a @code{@@catch} block, the
2341 @code{@@throw} may appear without an argument (as shown above), in which case
2342 the object caught by the @code{@@catch} will be rethrown.
2344 Note that only (pointers to) Objective-C objects may be thrown and
2345 caught using this scheme. When an object is thrown, it will be caught
2346 by the nearest @code{@@catch} clause capable of handling objects of that type,
2347 analogously to how @code{catch} blocks work in C++ and Java. A
2348 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
2349 any and all Objective-C exceptions not caught by previous @code{@@catch}
2352 The @code{@@finally} clause, if present, will be executed upon exit from the
2353 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
2354 regardless of whether any exceptions are thrown, caught or rethrown
2355 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
2356 of the @code{finally} clause in Java.
2358 There are several caveats to using the new exception mechanism:
2362 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
2363 idioms provided by the @code{NSException} class, the new
2364 exceptions can only be used on Mac OS X 10.3 (Panther) and later
2365 systems, due to additional functionality needed in the (NeXT) Objective-C
2369 As mentioned above, the new exceptions do not support handling
2370 types other than Objective-C objects. Furthermore, when used from
2371 Objective-C++, the Objective-C exception model does not interoperate with C++
2372 exceptions at this time. This means you cannot @code{@@throw} an exception
2373 from Objective-C and @code{catch} it in C++, or vice versa
2374 (i.e., @code{throw @dots{} @@catch}).
2377 The @option{-fobjc-exceptions} switch also enables the use of synchronization
2378 blocks for thread-safe execution:
2381 @@synchronized (ObjCClass *guard) @{
2386 Upon entering the @code{@@synchronized} block, a thread of execution shall
2387 first check whether a lock has been placed on the corresponding @code{guard}
2388 object by another thread. If it has, the current thread shall wait until
2389 the other thread relinquishes its lock. Once @code{guard} becomes available,
2390 the current thread will place its own lock on it, execute the code contained in
2391 the @code{@@synchronized} block, and finally relinquish the lock (thereby
2392 making @code{guard} available to other threads).
2394 Unlike Java, Objective-C does not allow for entire methods to be marked
2395 @code{@@synchronized}. Note that throwing exceptions out of
2396 @code{@@synchronized} blocks is allowed, and will cause the guarding object
2397 to be unlocked properly.
2401 Enable garbage collection (GC) in Objective-C and Objective-C++ programs.
2403 @item -freplace-objc-classes
2404 @opindex freplace-objc-classes
2405 Emit a special marker instructing @command{ld(1)} not to statically link in
2406 the resulting object file, and allow @command{dyld(1)} to load it in at
2407 run time instead. This is used in conjunction with the Fix-and-Continue
2408 debugging mode, where the object file in question may be recompiled and
2409 dynamically reloaded in the course of program execution, without the need
2410 to restart the program itself. Currently, Fix-and-Continue functionality
2411 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
2416 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
2417 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
2418 compile time) with static class references that get initialized at load time,
2419 which improves run-time performance. Specifying the @option{-fzero-link} flag
2420 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
2421 to be retained. This is useful in Zero-Link debugging mode, since it allows
2422 for individual class implementations to be modified during program execution.
2426 Dump interface declarations for all classes seen in the source file to a
2427 file named @file{@var{sourcename}.decl}.
2429 @item -Wassign-intercept @r{(Objective-C and Objective-C++ only)}
2430 @opindex Wassign-intercept
2431 @opindex Wno-assign-intercept
2432 Warn whenever an Objective-C assignment is being intercepted by the
2435 @item -Wno-protocol @r{(Objective-C and Objective-C++ only)}
2436 @opindex Wno-protocol
2438 If a class is declared to implement a protocol, a warning is issued for
2439 every method in the protocol that is not implemented by the class. The
2440 default behavior is to issue a warning for every method not explicitly
2441 implemented in the class, even if a method implementation is inherited
2442 from the superclass. If you use the @option{-Wno-protocol} option, then
2443 methods inherited from the superclass are considered to be implemented,
2444 and no warning is issued for them.
2446 @item -Wselector @r{(Objective-C and Objective-C++ only)}
2448 @opindex Wno-selector
2449 Warn if multiple methods of different types for the same selector are
2450 found during compilation. The check is performed on the list of methods
2451 in the final stage of compilation. Additionally, a check is performed
2452 for each selector appearing in a @code{@@selector(@dots{})}
2453 expression, and a corresponding method for that selector has been found
2454 during compilation. Because these checks scan the method table only at
2455 the end of compilation, these warnings are not produced if the final
2456 stage of compilation is not reached, for example because an error is
2457 found during compilation, or because the @option{-fsyntax-only} option is
2460 @item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)}
2461 @opindex Wstrict-selector-match
2462 @opindex Wno-strict-selector-match
2463 Warn if multiple methods with differing argument and/or return types are
2464 found for a given selector when attempting to send a message using this
2465 selector to a receiver of type @code{id} or @code{Class}. When this flag
2466 is off (which is the default behavior), the compiler will omit such warnings
2467 if any differences found are confined to types which share the same size
2470 @item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)}
2471 @opindex Wundeclared-selector
2472 @opindex Wno-undeclared-selector
2473 Warn if a @code{@@selector(@dots{})} expression referring to an
2474 undeclared selector is found. A selector is considered undeclared if no
2475 method with that name has been declared before the
2476 @code{@@selector(@dots{})} expression, either explicitly in an
2477 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2478 an @code{@@implementation} section. This option always performs its
2479 checks as soon as a @code{@@selector(@dots{})} expression is found,
2480 while @option{-Wselector} only performs its checks in the final stage of
2481 compilation. This also enforces the coding style convention
2482 that methods and selectors must be declared before being used.
2484 @item -print-objc-runtime-info
2485 @opindex print-objc-runtime-info
2486 Generate C header describing the largest structure that is passed by
2491 @node Language Independent Options
2492 @section Options to Control Diagnostic Messages Formatting
2493 @cindex options to control diagnostics formatting
2494 @cindex diagnostic messages
2495 @cindex message formatting
2497 Traditionally, diagnostic messages have been formatted irrespective of
2498 the output device's aspect (e.g.@: its width, @dots{}). The options described
2499 below can be used to control the diagnostic messages formatting
2500 algorithm, e.g.@: how many characters per line, how often source location
2501 information should be reported. Right now, only the C++ front end can
2502 honor these options. However it is expected, in the near future, that
2503 the remaining front ends would be able to digest them correctly.
2506 @item -fmessage-length=@var{n}
2507 @opindex fmessage-length
2508 Try to format error messages so that they fit on lines of about @var{n}
2509 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2510 the front ends supported by GCC@. If @var{n} is zero, then no
2511 line-wrapping will be done; each error message will appear on a single
2514 @opindex fdiagnostics-show-location
2515 @item -fdiagnostics-show-location=once
2516 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2517 reporter to emit @emph{once} source location information; that is, in
2518 case the message is too long to fit on a single physical line and has to
2519 be wrapped, the source location won't be emitted (as prefix) again,
2520 over and over, in subsequent continuation lines. This is the default
2523 @item -fdiagnostics-show-location=every-line
2524 Only meaningful in line-wrapping mode. Instructs the diagnostic
2525 messages reporter to emit the same source location information (as
2526 prefix) for physical lines that result from the process of breaking
2527 a message which is too long to fit on a single line.
2529 @item -fdiagnostics-show-option
2530 @opindex fdiagnostics-show-option
2531 This option instructs the diagnostic machinery to add text to each
2532 diagnostic emitted, which indicates which command line option directly
2533 controls that diagnostic, when such an option is known to the
2534 diagnostic machinery.
2536 @item -Wcoverage-mismatch
2537 @opindex Wcoverage-mismatch
2538 Warn if feedback profiles do not match when using the
2539 @option{-fprofile-use} option.
2540 If a source file was changed between @option{-fprofile-gen} and
2541 @option{-fprofile-use}, the files with the profile feedback can fail
2542 to match the source file and GCC can not use the profile feedback
2543 information. By default, GCC emits an error message in this case.
2544 The option @option{-Wcoverage-mismatch} emits a warning instead of an
2545 error. GCC does not use appropriate feedback profiles, so using this
2546 option can result in poorly optimized code. This option is useful
2547 only in the case of very minor changes such as bug fixes to an
2552 @node Warning Options
2553 @section Options to Request or Suppress Warnings
2554 @cindex options to control warnings
2555 @cindex warning messages
2556 @cindex messages, warning
2557 @cindex suppressing warnings
2559 Warnings are diagnostic messages that report constructions which
2560 are not inherently erroneous but which are risky or suggest there
2561 may have been an error.
2563 The following language-independent options do not enable specific
2564 warnings but control the kinds of diagnostics produced by GCC.
2567 @cindex syntax checking
2569 @opindex fsyntax-only
2570 Check the code for syntax errors, but don't do anything beyond that.
2574 Inhibit all warning messages.
2579 Make all warnings into errors.
2584 Make the specified warning into an error. The specifier for a warning
2585 is appended, for example @option{-Werror=switch} turns the warnings
2586 controlled by @option{-Wswitch} into errors. This switch takes a
2587 negative form, to be used to negate @option{-Werror} for specific
2588 warnings, for example @option{-Wno-error=switch} makes
2589 @option{-Wswitch} warnings not be errors, even when @option{-Werror}
2590 is in effect. You can use the @option{-fdiagnostics-show-option}
2591 option to have each controllable warning amended with the option which
2592 controls it, to determine what to use with this option.
2594 Note that specifying @option{-Werror=}@var{foo} automatically implies
2595 @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
2598 @item -Wfatal-errors
2599 @opindex Wfatal-errors
2600 @opindex Wno-fatal-errors
2601 This option causes the compiler to abort compilation on the first error
2602 occurred rather than trying to keep going and printing further error
2607 You can request many specific warnings with options beginning
2608 @samp{-W}, for example @option{-Wimplicit} to request warnings on
2609 implicit declarations. Each of these specific warning options also
2610 has a negative form beginning @samp{-Wno-} to turn off warnings; for
2611 example, @option{-Wno-implicit}. This manual lists only one of the
2612 two forms, whichever is not the default. For further,
2613 language-specific options also refer to @ref{C++ Dialect Options} and
2614 @ref{Objective-C and Objective-C++ Dialect Options}.
2619 Issue all the warnings demanded by strict ISO C and ISO C++;
2620 reject all programs that use forbidden extensions, and some other
2621 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2622 version of the ISO C standard specified by any @option{-std} option used.
2624 Valid ISO C and ISO C++ programs should compile properly with or without
2625 this option (though a rare few will require @option{-ansi} or a
2626 @option{-std} option specifying the required version of ISO C)@. However,
2627 without this option, certain GNU extensions and traditional C and C++
2628 features are supported as well. With this option, they are rejected.
2630 @option{-pedantic} does not cause warning messages for use of the
2631 alternate keywords whose names begin and end with @samp{__}. Pedantic
2632 warnings are also disabled in the expression that follows
2633 @code{__extension__}. However, only system header files should use
2634 these escape routes; application programs should avoid them.
2635 @xref{Alternate Keywords}.
2637 Some users try to use @option{-pedantic} to check programs for strict ISO
2638 C conformance. They soon find that it does not do quite what they want:
2639 it finds some non-ISO practices, but not all---only those for which
2640 ISO C @emph{requires} a diagnostic, and some others for which
2641 diagnostics have been added.
2643 A feature to report any failure to conform to ISO C might be useful in
2644 some instances, but would require considerable additional work and would
2645 be quite different from @option{-pedantic}. We don't have plans to
2646 support such a feature in the near future.
2648 Where the standard specified with @option{-std} represents a GNU
2649 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2650 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2651 extended dialect is based. Warnings from @option{-pedantic} are given
2652 where they are required by the base standard. (It would not make sense
2653 for such warnings to be given only for features not in the specified GNU
2654 C dialect, since by definition the GNU dialects of C include all
2655 features the compiler supports with the given option, and there would be
2656 nothing to warn about.)
2658 @item -pedantic-errors
2659 @opindex pedantic-errors
2660 Like @option{-pedantic}, except that errors are produced rather than
2666 This enables all the warnings about constructions that some users
2667 consider questionable, and that are easy to avoid (or modify to
2668 prevent the warning), even in conjunction with macros. This also
2669 enables some language-specific warnings described in @ref{C++ Dialect
2670 Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
2672 @option{-Wall} turns on the following warning flags:
2674 @gccoptlist{-Waddress @gol
2675 -Warray-bounds @r{(only with} @option{-O2}@r{)} @gol
2677 -Wchar-subscripts @gol
2679 -Wimplicit-function-declaration @gol
2682 -Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol
2683 -Wmissing-braces @gol
2689 -Wsequence-point @gol
2690 -Wsign-compare @r{(only in C++)} @gol
2691 -Wstrict-aliasing @gol
2692 -Wstrict-overflow=1 @gol
2695 -Wuninitialized @r{(only with} @option{-O1} @r{and above)} @gol
2696 -Wunknown-pragmas @gol
2697 -Wunused-function @gol
2700 -Wunused-variable @gol
2701 -Wvolatile-register-var @gol
2704 Note that some warning flags are not implied by @option{-Wall}. Some of
2705 them warn about constructions that users generally do not consider
2706 questionable, but which occasionally you might wish to check for;
2707 others warn about constructions that are necessary or hard to avoid in
2708 some cases, and there is no simple way to modify the code to suppress
2709 the warning. Some of them are enabled by @option{-Wextra} but many of
2710 them must be enabled individually.
2716 This enables some extra warning flags that are not enabled by
2717 @option{-Wall}. (This option used to be called @option{-W}. The older
2718 name is still supported, but the newer name is more descriptive.)
2720 @gccoptlist{-Wclobbered @gol
2722 -Wignored-qualifiers @gol
2723 -Wmissing-field-initializers @gol
2724 -Wmissing-parameter-type @r{(C only)} @gol
2725 -Wold-style-declaration @r{(C only)} @gol
2726 -Woverride-init @gol
2729 -Wuninitialized @r{(only with} @option{-O1} @r{and above)} @gol
2730 -Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
2733 The option @option{-Wextra} also prints warning messages for the
2739 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2740 @samp{>}, or @samp{>=}.
2743 (C++ only) An enumerator and a non-enumerator both appear in a
2744 conditional expression.
2747 (C++ only) A non-static reference or non-static @samp{const} member
2748 appears in a class without constructors.
2751 (C++ only) Ambiguous virtual bases.
2754 (C++ only) Subscripting an array which has been declared @samp{register}.
2757 (C++ only) Taking the address of a variable which has been declared
2761 (C++ only) A base class is not initialized in a derived class' copy
2766 @item -Wchar-subscripts
2767 @opindex Wchar-subscripts
2768 @opindex Wno-char-subscripts
2769 Warn if an array subscript has type @code{char}. This is a common cause
2770 of error, as programmers often forget that this type is signed on some
2772 This warning is enabled by @option{-Wall}.
2776 @opindex Wno-comment
2777 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2778 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2779 This warning is enabled by @option{-Wall}.
2784 @opindex ffreestanding
2785 @opindex fno-builtin
2786 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2787 the arguments supplied have types appropriate to the format string
2788 specified, and that the conversions specified in the format string make
2789 sense. This includes standard functions, and others specified by format
2790 attributes (@pxref{Function Attributes}), in the @code{printf},
2791 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2792 not in the C standard) families (or other target-specific families).
2793 Which functions are checked without format attributes having been
2794 specified depends on the standard version selected, and such checks of
2795 functions without the attribute specified are disabled by
2796 @option{-ffreestanding} or @option{-fno-builtin}.
2798 The formats are checked against the format features supported by GNU
2799 libc version 2.2. These include all ISO C90 and C99 features, as well
2800 as features from the Single Unix Specification and some BSD and GNU
2801 extensions. Other library implementations may not support all these
2802 features; GCC does not support warning about features that go beyond a
2803 particular library's limitations. However, if @option{-pedantic} is used
2804 with @option{-Wformat}, warnings will be given about format features not
2805 in the selected standard version (but not for @code{strfmon} formats,
2806 since those are not in any version of the C standard). @xref{C Dialect
2807 Options,,Options Controlling C Dialect}.
2809 Since @option{-Wformat} also checks for null format arguments for
2810 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2812 @option{-Wformat} is included in @option{-Wall}. For more control over some
2813 aspects of format checking, the options @option{-Wformat-y2k},
2814 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2815 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2816 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2819 @opindex Wformat-y2k
2820 @opindex Wno-format-y2k
2821 If @option{-Wformat} is specified, also warn about @code{strftime}
2822 formats which may yield only a two-digit year.
2824 @item -Wno-format-contains-nul
2825 @opindex Wno-format-contains-nul
2826 @opindex Wformat-contains-nul
2827 If @option{-Wformat} is specified, do not warn about format strings that
2830 @item -Wno-format-extra-args
2831 @opindex Wno-format-extra-args
2832 @opindex Wformat-extra-args
2833 If @option{-Wformat} is specified, do not warn about excess arguments to a
2834 @code{printf} or @code{scanf} format function. The C standard specifies
2835 that such arguments are ignored.
2837 Where the unused arguments lie between used arguments that are
2838 specified with @samp{$} operand number specifications, normally
2839 warnings are still given, since the implementation could not know what
2840 type to pass to @code{va_arg} to skip the unused arguments. However,
2841 in the case of @code{scanf} formats, this option will suppress the
2842 warning if the unused arguments are all pointers, since the Single
2843 Unix Specification says that such unused arguments are allowed.
2845 @item -Wno-format-zero-length @r{(C and Objective-C only)}
2846 @opindex Wno-format-zero-length
2847 @opindex Wformat-zero-length
2848 If @option{-Wformat} is specified, do not warn about zero-length formats.
2849 The C standard specifies that zero-length formats are allowed.
2851 @item -Wformat-nonliteral
2852 @opindex Wformat-nonliteral
2853 @opindex Wno-format-nonliteral
2854 If @option{-Wformat} is specified, also warn if the format string is not a
2855 string literal and so cannot be checked, unless the format function
2856 takes its format arguments as a @code{va_list}.
2858 @item -Wformat-security
2859 @opindex Wformat-security
2860 @opindex Wno-format-security
2861 If @option{-Wformat} is specified, also warn about uses of format
2862 functions that represent possible security problems. At present, this
2863 warns about calls to @code{printf} and @code{scanf} functions where the
2864 format string is not a string literal and there are no format arguments,
2865 as in @code{printf (foo);}. This may be a security hole if the format
2866 string came from untrusted input and contains @samp{%n}. (This is
2867 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2868 in future warnings may be added to @option{-Wformat-security} that are not
2869 included in @option{-Wformat-nonliteral}.)
2873 @opindex Wno-format=2
2874 Enable @option{-Wformat} plus format checks not included in
2875 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2876 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2878 @item -Wnonnull @r{(C and Objective-C only)}
2880 @opindex Wno-nonnull
2881 Warn about passing a null pointer for arguments marked as
2882 requiring a non-null value by the @code{nonnull} function attribute.
2884 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2885 can be disabled with the @option{-Wno-nonnull} option.
2887 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
2889 @opindex Wno-init-self
2890 Warn about uninitialized variables which are initialized with themselves.
2891 Note this option can only be used with the @option{-Wuninitialized} option,
2892 which in turn only works with @option{-O1} and above.
2894 For example, GCC will warn about @code{i} being uninitialized in the
2895 following snippet only when @option{-Winit-self} has been specified:
2906 @item -Wimplicit-int @r{(C and Objective-C only)}
2907 @opindex Wimplicit-int
2908 @opindex Wno-implicit-int
2909 Warn when a declaration does not specify a type.
2910 This warning is enabled by @option{-Wall}.
2912 @item -Wimplicit-function-declaration @r{(C and Objective-C only)}
2913 @opindex Wimplicit-function-declaration
2914 @opindex Wno-implicit-function-declaration
2915 Give a warning whenever a function is used before being declared. In
2916 C99 mode (@option{-std=c99} or @option{-std=gnu99}), this warning is
2917 enabled by default and it is made into an error by
2918 @option{-pedantic-errors}. This warning is also enabled by
2923 @opindex Wno-implicit
2924 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2925 This warning is enabled by @option{-Wall}.
2927 @item -Wignored-qualifiers @r{(C and C++ only)}
2928 @opindex Wignored-qualifiers
2929 @opindex Wno-ignored-qualifiers
2930 Warn if the return type of a function has a type qualifier
2931 such as @code{const}. For ISO C such a type qualifier has no effect,
2932 since the value returned by a function is not an lvalue.
2933 For C++, the warning is only emitted for scalar types or @code{void}.
2934 ISO C prohibits qualified @code{void} return types on function
2935 definitions, so such return types always receive a warning
2936 even without this option.
2938 This warning is also enabled by @option{-Wextra}.
2943 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2944 function with external linkage, returning int, taking either zero
2945 arguments, two, or three arguments of appropriate types.
2946 This warning is enabled by @option{-Wall}.
2948 @item -Wmissing-braces
2949 @opindex Wmissing-braces
2950 @opindex Wno-missing-braces
2951 Warn if an aggregate or union initializer is not fully bracketed. In
2952 the following example, the initializer for @samp{a} is not fully
2953 bracketed, but that for @samp{b} is fully bracketed.
2956 int a[2][2] = @{ 0, 1, 2, 3 @};
2957 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2960 This warning is enabled by @option{-Wall}.
2962 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
2963 @opindex Wmissing-include-dirs
2964 @opindex Wno-missing-include-dirs
2965 Warn if a user-supplied include directory does not exist.
2968 @opindex Wparentheses
2969 @opindex Wno-parentheses
2970 Warn if parentheses are omitted in certain contexts, such
2971 as when there is an assignment in a context where a truth value
2972 is expected, or when operators are nested whose precedence people
2973 often get confused about.
2975 Also warn if a comparison like @samp{x<=y<=z} appears; this is
2976 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
2977 interpretation from that of ordinary mathematical notation.
2979 Also warn about constructions where there may be confusion to which
2980 @code{if} statement an @code{else} branch belongs. Here is an example of
2995 In C/C++, every @code{else} branch belongs to the innermost possible
2996 @code{if} statement, which in this example is @code{if (b)}. This is
2997 often not what the programmer expected, as illustrated in the above
2998 example by indentation the programmer chose. When there is the
2999 potential for this confusion, GCC will issue a warning when this flag
3000 is specified. To eliminate the warning, add explicit braces around
3001 the innermost @code{if} statement so there is no way the @code{else}
3002 could belong to the enclosing @code{if}. The resulting code would
3019 This warning is enabled by @option{-Wall}.
3021 @item -Wsequence-point
3022 @opindex Wsequence-point
3023 @opindex Wno-sequence-point
3024 Warn about code that may have undefined semantics because of violations
3025 of sequence point rules in the C and C++ standards.
3027 The C and C++ standards defines the order in which expressions in a C/C++
3028 program are evaluated in terms of @dfn{sequence points}, which represent
3029 a partial ordering between the execution of parts of the program: those
3030 executed before the sequence point, and those executed after it. These
3031 occur after the evaluation of a full expression (one which is not part
3032 of a larger expression), after the evaluation of the first operand of a
3033 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
3034 function is called (but after the evaluation of its arguments and the
3035 expression denoting the called function), and in certain other places.
3036 Other than as expressed by the sequence point rules, the order of
3037 evaluation of subexpressions of an expression is not specified. All
3038 these rules describe only a partial order rather than a total order,
3039 since, for example, if two functions are called within one expression
3040 with no sequence point between them, the order in which the functions
3041 are called is not specified. However, the standards committee have
3042 ruled that function calls do not overlap.
3044 It is not specified when between sequence points modifications to the
3045 values of objects take effect. Programs whose behavior depends on this
3046 have undefined behavior; the C and C++ standards specify that ``Between
3047 the previous and next sequence point an object shall have its stored
3048 value modified at most once by the evaluation of an expression.
3049 Furthermore, the prior value shall be read only to determine the value
3050 to be stored.''. If a program breaks these rules, the results on any
3051 particular implementation are entirely unpredictable.
3053 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
3054 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
3055 diagnosed by this option, and it may give an occasional false positive
3056 result, but in general it has been found fairly effective at detecting
3057 this sort of problem in programs.
3059 The standard is worded confusingly, therefore there is some debate
3060 over the precise meaning of the sequence point rules in subtle cases.
3061 Links to discussions of the problem, including proposed formal
3062 definitions, may be found on the GCC readings page, at
3063 @w{@uref{http://gcc.gnu.org/readings.html}}.
3065 This warning is enabled by @option{-Wall} for C and C++.
3068 @opindex Wreturn-type
3069 @opindex Wno-return-type
3070 Warn whenever a function is defined with a return-type that defaults
3071 to @code{int}. Also warn about any @code{return} statement with no
3072 return-value in a function whose return-type is not @code{void}
3073 (falling off the end of the function body is considered returning
3074 without a value), and about a @code{return} statement with a
3075 expression in a function whose return-type is @code{void}.
3077 For C++, a function without return type always produces a diagnostic
3078 message, even when @option{-Wno-return-type} is specified. The only
3079 exceptions are @samp{main} and functions defined in system headers.
3081 This warning is enabled by @option{-Wall}.
3086 Warn whenever a @code{switch} statement has an index of enumerated type
3087 and lacks a @code{case} for one or more of the named codes of that
3088 enumeration. (The presence of a @code{default} label prevents this
3089 warning.) @code{case} labels outside the enumeration range also
3090 provoke warnings when this option is used.
3091 This warning is enabled by @option{-Wall}.
3093 @item -Wswitch-default
3094 @opindex Wswitch-default
3095 @opindex Wno-switch-default
3096 Warn whenever a @code{switch} statement does not have a @code{default}
3100 @opindex Wswitch-enum
3101 @opindex Wno-switch-enum
3102 Warn whenever a @code{switch} statement has an index of enumerated type
3103 and lacks a @code{case} for one or more of the named codes of that
3104 enumeration. @code{case} labels outside the enumeration range also
3105 provoke warnings when this option is used.
3109 @opindex Wno-trigraphs
3110 Warn if any trigraphs are encountered that might change the meaning of
3111 the program (trigraphs within comments are not warned about).
3112 This warning is enabled by @option{-Wall}.
3114 @item -Wunused-function
3115 @opindex Wunused-function
3116 @opindex Wno-unused-function
3117 Warn whenever a static function is declared but not defined or a
3118 non-inline static function is unused.
3119 This warning is enabled by @option{-Wall}.
3121 @item -Wunused-label
3122 @opindex Wunused-label
3123 @opindex Wno-unused-label
3124 Warn whenever a label is declared but not used.
3125 This warning is enabled by @option{-Wall}.
3127 To suppress this warning use the @samp{unused} attribute
3128 (@pxref{Variable Attributes}).
3130 @item -Wunused-parameter
3131 @opindex Wunused-parameter
3132 @opindex Wno-unused-parameter
3133 Warn whenever a function parameter is unused aside from its declaration.
3135 To suppress this warning use the @samp{unused} attribute
3136 (@pxref{Variable Attributes}).
3138 @item -Wunused-variable
3139 @opindex Wunused-variable
3140 @opindex Wno-unused-variable
3141 Warn whenever a local variable or non-constant static variable is unused
3142 aside from its declaration.
3143 This warning is enabled by @option{-Wall}.
3145 To suppress this warning use the @samp{unused} attribute
3146 (@pxref{Variable Attributes}).
3148 @item -Wunused-value
3149 @opindex Wunused-value
3150 @opindex Wno-unused-value
3151 Warn whenever a statement computes a result that is explicitly not
3152 used. To suppress this warning cast the unused expression to
3153 @samp{void}. This includes an expression-statement or the left-hand
3154 side of a comma expression that contains no side effects. For example,
3155 an expression such as @samp{x[i,j]} will cause a warning, while
3156 @samp{x[(void)i,j]} will not.
3158 This warning is enabled by @option{-Wall}.
3163 All the above @option{-Wunused} options combined.
3165 In order to get a warning about an unused function parameter, you must
3166 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
3167 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
3169 @item -Wuninitialized
3170 @opindex Wuninitialized
3171 @opindex Wno-uninitialized
3172 Warn if an automatic variable is used without first being initialized or
3173 if a variable may be clobbered by a @code{setjmp} call.
3175 These warnings are possible only in optimizing compilation,
3176 because they require data flow information that is computed only
3177 when optimizing. If you do not specify @option{-O}, you will not get
3178 these warnings. Instead, GCC will issue a warning about @option{-Wuninitialized}
3179 requiring @option{-O}.
3181 If you want to warn about code which uses the uninitialized value of the
3182 variable in its own initializer, use the @option{-Winit-self} option.
3184 These warnings occur for individual uninitialized or clobbered
3185 elements of structure, union or array variables as well as for
3186 variables which are uninitialized or clobbered as a whole. They do
3187 not occur for variables or elements declared @code{volatile}. Because
3188 these warnings depend on optimization, the exact variables or elements
3189 for which there are warnings will depend on the precise optimization
3190 options and version of GCC used.
3192 Note that there may be no warning about a variable that is used only
3193 to compute a value that itself is never used, because such
3194 computations may be deleted by data flow analysis before the warnings
3197 These warnings are made optional because GCC is not smart
3198 enough to see all the reasons why the code might be correct
3199 despite appearing to have an error. Here is one example of how
3220 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
3221 always initialized, but GCC doesn't know this. Here is
3222 another common case:
3227 if (change_y) save_y = y, y = new_y;
3229 if (change_y) y = save_y;
3234 This has no bug because @code{save_y} is used only if it is set.
3236 @cindex @code{longjmp} warnings
3237 This option also warns when a non-volatile automatic variable might be
3238 changed by a call to @code{longjmp}. These warnings as well are possible
3239 only in optimizing compilation.
3241 The compiler sees only the calls to @code{setjmp}. It cannot know
3242 where @code{longjmp} will be called; in fact, a signal handler could
3243 call it at any point in the code. As a result, you may get a warning
3244 even when there is in fact no problem because @code{longjmp} cannot
3245 in fact be called at the place which would cause a problem.
3247 Some spurious warnings can be avoided if you declare all the functions
3248 you use that never return as @code{noreturn}. @xref{Function
3251 This warning is enabled by @option{-Wall} or @option{-Wextra} in
3252 optimizing compilations (@option{-O1} and above).
3254 @item -Wunknown-pragmas
3255 @opindex Wunknown-pragmas
3256 @opindex Wno-unknown-pragmas
3257 @cindex warning for unknown pragmas
3258 @cindex unknown pragmas, warning
3259 @cindex pragmas, warning of unknown
3260 Warn when a #pragma directive is encountered which is not understood by
3261 GCC@. If this command line option is used, warnings will even be issued
3262 for unknown pragmas in system header files. This is not the case if
3263 the warnings were only enabled by the @option{-Wall} command line option.
3266 @opindex Wno-pragmas
3268 Do not warn about misuses of pragmas, such as incorrect parameters,
3269 invalid syntax, or conflicts between pragmas. See also
3270 @samp{-Wunknown-pragmas}.
3272 @item -Wstrict-aliasing
3273 @opindex Wstrict-aliasing
3274 @opindex Wno-strict-aliasing
3275 This option is only active when @option{-fstrict-aliasing} is active.
3276 It warns about code which might break the strict aliasing rules that the
3277 compiler is using for optimization. The warning does not catch all
3278 cases, but does attempt to catch the more common pitfalls. It is
3279 included in @option{-Wall}.
3280 It is equivalent to @option{-Wstrict-aliasing=3}
3282 @item -Wstrict-aliasing=n
3283 @opindex Wstrict-aliasing=n
3284 @opindex Wno-strict-aliasing=n
3285 This option is only active when @option{-fstrict-aliasing} is active.
3286 It warns about code which might break the strict aliasing rules that the
3287 compiler is using for optimization.
3288 Higher levels correspond to higher accuracy (fewer false positives).
3289 Higher levels also correspond to more effort, similar to the way -O works.
3290 @option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=n},
3293 Level 1: Most aggressive, quick, least accurate.
3294 Possibly useful when higher levels
3295 do not warn but -fstrict-aliasing still breaks the code, as it has very few
3296 false negatives. However, it has many false positives.
3297 Warns for all pointer conversions between possibly incompatible types,
3298 even if never dereferenced. Runs in the frontend only.
3300 Level 2: Aggressive, quick, not too precise.
3301 May still have many false positives (not as many as level 1 though),
3302 and few false negatives (but possibly more than level 1).
3303 Unlike level 1, it only warns when an address is taken. Warns about
3304 incomplete types. Runs in the frontend only.
3306 Level 3 (default for @option{-Wstrict-aliasing}):
3307 Should have very few false positives and few false
3308 negatives. Slightly slower than levels 1 or 2 when optimization is enabled.
3309 Takes care of the common punn+dereference pattern in the frontend:
3310 @code{*(int*)&some_float}.
3311 If optimization is enabled, it also runs in the backend, where it deals
3312 with multiple statement cases using flow-sensitive points-to information.
3313 Only warns when the converted pointer is dereferenced.
3314 Does not warn about incomplete types.
3316 @item -Wstrict-overflow
3317 @itemx -Wstrict-overflow=@var{n}
3318 @opindex Wstrict-overflow
3319 @opindex Wno-strict-overflow
3320 This option is only active when @option{-fstrict-overflow} is active.
3321 It warns about cases where the compiler optimizes based on the
3322 assumption that signed overflow does not occur. Note that it does not
3323 warn about all cases where the code might overflow: it only warns
3324 about cases where the compiler implements some optimization. Thus
3325 this warning depends on the optimization level.
3327 An optimization which assumes that signed overflow does not occur is
3328 perfectly safe if the values of the variables involved are such that
3329 overflow never does, in fact, occur. Therefore this warning can
3330 easily give a false positive: a warning about code which is not
3331 actually a problem. To help focus on important issues, several
3332 warning levels are defined. No warnings are issued for the use of
3333 undefined signed overflow when estimating how many iterations a loop
3334 will require, in particular when determining whether a loop will be
3338 @item -Wstrict-overflow=1
3339 Warn about cases which are both questionable and easy to avoid. For
3340 example: @code{x + 1 > x}; with @option{-fstrict-overflow}, the
3341 compiler will simplify this to @code{1}. This level of
3342 @option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels
3343 are not, and must be explicitly requested.
3345 @item -Wstrict-overflow=2
3346 Also warn about other cases where a comparison is simplified to a
3347 constant. For example: @code{abs (x) >= 0}. This can only be
3348 simplified when @option{-fstrict-overflow} is in effect, because
3349 @code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than
3350 zero. @option{-Wstrict-overflow} (with no level) is the same as
3351 @option{-Wstrict-overflow=2}.
3353 @item -Wstrict-overflow=3
3354 Also warn about other cases where a comparison is simplified. For
3355 example: @code{x + 1 > 1} will be simplified to @code{x > 0}.
3357 @item -Wstrict-overflow=4
3358 Also warn about other simplifications not covered by the above cases.
3359 For example: @code{(x * 10) / 5} will be simplified to @code{x * 2}.
3361 @item -Wstrict-overflow=5
3362 Also warn about cases where the compiler reduces the magnitude of a
3363 constant involved in a comparison. For example: @code{x + 2 > y} will
3364 be simplified to @code{x + 1 >= y}. This is reported only at the
3365 highest warning level because this simplification applies to many
3366 comparisons, so this warning level will give a very large number of
3370 @item -Warray-bounds
3371 @opindex Wno-array-bounds
3372 @opindex Warray-bounds
3373 This option is only active when @option{-ftree-vrp} is active
3374 (default for -O2 and above). It warns about subscripts to arrays
3375 that are always out of bounds. This warning is enabled by @option{-Wall}.
3377 @item -Wno-div-by-zero
3378 @opindex Wno-div-by-zero
3379 @opindex Wdiv-by-zero
3380 Do not warn about compile-time integer division by zero. Floating point
3381 division by zero is not warned about, as it can be a legitimate way of
3382 obtaining infinities and NaNs.
3384 @item -Wsystem-headers
3385 @opindex Wsystem-headers
3386 @opindex Wno-system-headers
3387 @cindex warnings from system headers
3388 @cindex system headers, warnings from
3389 Print warning messages for constructs found in system header files.
3390 Warnings from system headers are normally suppressed, on the assumption
3391 that they usually do not indicate real problems and would only make the
3392 compiler output harder to read. Using this command line option tells
3393 GCC to emit warnings from system headers as if they occurred in user
3394 code. However, note that using @option{-Wall} in conjunction with this
3395 option will @emph{not} warn about unknown pragmas in system
3396 headers---for that, @option{-Wunknown-pragmas} must also be used.
3399 @opindex Wfloat-equal
3400 @opindex Wno-float-equal
3401 Warn if floating point values are used in equality comparisons.
3403 The idea behind this is that sometimes it is convenient (for the
3404 programmer) to consider floating-point values as approximations to
3405 infinitely precise real numbers. If you are doing this, then you need
3406 to compute (by analyzing the code, or in some other way) the maximum or
3407 likely maximum error that the computation introduces, and allow for it
3408 when performing comparisons (and when producing output, but that's a
3409 different problem). In particular, instead of testing for equality, you
3410 would check to see whether the two values have ranges that overlap; and
3411 this is done with the relational operators, so equality comparisons are
3414 @item -Wtraditional @r{(C and Objective-C only)}
3415 @opindex Wtraditional
3416 @opindex Wno-traditional
3417 Warn about certain constructs that behave differently in traditional and
3418 ISO C@. Also warn about ISO C constructs that have no traditional C
3419 equivalent, and/or problematic constructs which should be avoided.
3423 Macro parameters that appear within string literals in the macro body.
3424 In traditional C macro replacement takes place within string literals,
3425 but does not in ISO C@.
3428 In traditional C, some preprocessor directives did not exist.
3429 Traditional preprocessors would only consider a line to be a directive
3430 if the @samp{#} appeared in column 1 on the line. Therefore
3431 @option{-Wtraditional} warns about directives that traditional C
3432 understands but would ignore because the @samp{#} does not appear as the
3433 first character on the line. It also suggests you hide directives like
3434 @samp{#pragma} not understood by traditional C by indenting them. Some
3435 traditional implementations would not recognize @samp{#elif}, so it
3436 suggests avoiding it altogether.
3439 A function-like macro that appears without arguments.
3442 The unary plus operator.
3445 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
3446 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
3447 constants.) Note, these suffixes appear in macros defined in the system
3448 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
3449 Use of these macros in user code might normally lead to spurious
3450 warnings, however GCC's integrated preprocessor has enough context to
3451 avoid warning in these cases.
3454 A function declared external in one block and then used after the end of
3458 A @code{switch} statement has an operand of type @code{long}.
3461 A non-@code{static} function declaration follows a @code{static} one.
3462 This construct is not accepted by some traditional C compilers.
3465 The ISO type of an integer constant has a different width or
3466 signedness from its traditional type. This warning is only issued if
3467 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
3468 typically represent bit patterns, are not warned about.
3471 Usage of ISO string concatenation is detected.
3474 Initialization of automatic aggregates.
3477 Identifier conflicts with labels. Traditional C lacks a separate
3478 namespace for labels.
3481 Initialization of unions. If the initializer is zero, the warning is
3482 omitted. This is done under the assumption that the zero initializer in
3483 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
3484 initializer warnings and relies on default initialization to zero in the
3488 Conversions by prototypes between fixed/floating point values and vice
3489 versa. The absence of these prototypes when compiling with traditional
3490 C would cause serious problems. This is a subset of the possible
3491 conversion warnings, for the full set use @option{-Wtraditional-conversion}.
3494 Use of ISO C style function definitions. This warning intentionally is
3495 @emph{not} issued for prototype declarations or variadic functions
3496 because these ISO C features will appear in your code when using
3497 libiberty's traditional C compatibility macros, @code{PARAMS} and
3498 @code{VPARAMS}. This warning is also bypassed for nested functions
3499 because that feature is already a GCC extension and thus not relevant to
3500 traditional C compatibility.
3503 @item -Wtraditional-conversion @r{(C and Objective-C only)}
3504 @opindex Wtraditional-conversion
3505 @opindex Wno-traditional-conversion
3506 Warn if a prototype causes a type conversion that is different from what
3507 would happen to the same argument in the absence of a prototype. This
3508 includes conversions of fixed point to floating and vice versa, and
3509 conversions changing the width or signedness of a fixed point argument
3510 except when the same as the default promotion.
3512 @item -Wdeclaration-after-statement @r{(C and Objective-C only)}
3513 @opindex Wdeclaration-after-statement
3514 @opindex Wno-declaration-after-statement
3515 Warn when a declaration is found after a statement in a block. This
3516 construct, known from C++, was introduced with ISO C99 and is by default
3517 allowed in GCC@. It is not supported by ISO C90 and was not supported by
3518 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
3523 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
3525 @item -Wno-endif-labels
3526 @opindex Wno-endif-labels
3527 @opindex Wendif-labels
3528 Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
3533 Warn whenever a local variable shadows another local variable, parameter or
3534 global variable or whenever a built-in function is shadowed.
3536 @item -Wlarger-than=@var{len}
3537 @opindex Wlarger-than=@var{len}
3538 @opindex Wlarger-than-@var{len}
3539 Warn whenever an object of larger than @var{len} bytes is defined.
3541 @item -Wframe-larger-than=@var{len}
3542 @opindex Wframe-larger-than
3543 Warn if the size of a function frame is larger than @var{len} bytes.
3544 The computation done to determine the stack frame size is approximate
3545 and not conservative.
3546 The actual requirements may be somewhat greater than @var{len}
3547 even if you do not get a warning. In addition, any space allocated
3548 via @code{alloca}, variable-length arrays, or related constructs
3549 is not included by the compiler when determining
3550 whether or not to issue a warning.
3552 @item -Wunsafe-loop-optimizations
3553 @opindex Wunsafe-loop-optimizations
3554 @opindex Wno-unsafe-loop-optimizations
3555 Warn if the loop cannot be optimized because the compiler could not
3556 assume anything on the bounds of the loop indices. With
3557 @option{-funsafe-loop-optimizations} warn if the compiler made
3560 @item -Wpointer-arith
3561 @opindex Wpointer-arith
3562 @opindex Wno-pointer-arith
3563 Warn about anything that depends on the ``size of'' a function type or
3564 of @code{void}. GNU C assigns these types a size of 1, for
3565 convenience in calculations with @code{void *} pointers and pointers
3566 to functions. In C++, warn also when an arithmetic operation involves
3567 @code{NULL}. This warning is also enabled by @option{-pedantic}.
3570 @opindex Wtype-limits
3571 @opindex Wno-type-limits
3572 Warn if a comparison is always true or always false due to the limited
3573 range of the data type, but do not warn for constant expressions. For
3574 example, warn if an unsigned variable is compared against zero with
3575 @samp{<} or @samp{>=}. This warning is also enabled by
3578 @item -Wbad-function-cast @r{(C and Objective-C only)}
3579 @opindex Wbad-function-cast
3580 @opindex Wno-bad-function-cast
3581 Warn whenever a function call is cast to a non-matching type.
3582 For example, warn if @code{int malloc()} is cast to @code{anything *}.
3584 @item -Wc++-compat @r{(C and Objective-C only)}
3585 Warn about ISO C constructs that are outside of the common subset of
3586 ISO C and ISO C++, e.g.@: request for implicit conversion from
3587 @code{void *} to a pointer to non-@code{void} type.
3589 @item -Wc++0x-compat @r{(C++ and Objective-C++ only)}
3590 Warn about C++ constructs whose meaning differs between ISO C++ 1998 and
3591 ISO C++ 200x, e.g., identifiers in ISO C++ 1998 that will become keywords
3592 in ISO C++ 200x. This warning is enabled by @option{-Wall}.
3596 @opindex Wno-cast-qual
3597 Warn whenever a pointer is cast so as to remove a type qualifier from
3598 the target type. For example, warn if a @code{const char *} is cast
3599 to an ordinary @code{char *}.
3602 @opindex Wcast-align
3603 @opindex Wno-cast-align
3604 Warn whenever a pointer is cast such that the required alignment of the
3605 target is increased. For example, warn if a @code{char *} is cast to
3606 an @code{int *} on machines where integers can only be accessed at
3607 two- or four-byte boundaries.
3609 @item -Wwrite-strings
3610 @opindex Wwrite-strings
3611 @opindex Wno-write-strings
3612 When compiling C, give string constants the type @code{const
3613 char[@var{length}]} so that
3614 copying the address of one into a non-@code{const} @code{char *}
3615 pointer will get a warning; when compiling C++, warn about the
3616 deprecated conversion from string literals to @code{char *}. This
3617 warning, by default, is enabled for C++ programs.
3618 These warnings will help you find at
3619 compile time code that can try to write into a string constant, but
3620 only if you have been very careful about using @code{const} in
3621 declarations and prototypes. Otherwise, it will just be a nuisance;
3622 this is why we did not make @option{-Wall} request these warnings.
3626 @opindex Wno-clobbered
3627 Warn for variables that might be changed by @samp{longjmp} or
3628 @samp{vfork}. This warning is also enabled by @option{-Wextra}.
3631 @opindex Wconversion
3632 @opindex Wno-conversion
3633 Warn for implicit conversions that may alter a value. This includes
3634 conversions between real and integer, like @code{abs (x)} when
3635 @code{x} is @code{double}; conversions between signed and unsigned,
3636 like @code{unsigned ui = -1}; and conversions to smaller types, like
3637 @code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs
3638 ((int) x)} and @code{ui = (unsigned) -1}, or if the value is not
3639 changed by the conversion like in @code{abs (2.0)}. Warnings about
3640 conversions between signed and unsigned integers can be disabled by
3641 using @option{-Wno-sign-conversion}.
3643 For C++, also warn for conversions between @code{NULL} and non-pointer
3644 types; confusing overload resolution for user-defined conversions; and
3645 conversions that will never use a type conversion operator:
3646 conversions to @code{void}, the same type, a base class or a reference
3647 to them. Warnings about conversions between signed and unsigned
3648 integers are disabled by default in C++ unless
3649 @option{-Wsign-conversion} is explicitly enabled.
3652 @opindex Wempty-body
3653 @opindex Wno-empty-body
3654 Warn if an empty body occurs in an @samp{if}, @samp{else} or @samp{do
3655 while} statement. Additionally, in C++, warn when an empty body occurs
3656 in a @samp{while} or @samp{for} statement with no whitespacing before
3657 the semicolon. This warning is also enabled by @option{-Wextra}.
3659 @item -Wenum-compare @r{(C++ and Objective-C++ only)}
3660 @opindex Wenum-compare
3661 @opindex Wno-enum-compare
3662 Warn about a comparison between values of different enum types. This
3663 warning is enabled by default.
3665 @item -Wsign-compare
3666 @opindex Wsign-compare
3667 @opindex Wno-sign-compare
3668 @cindex warning for comparison of signed and unsigned values
3669 @cindex comparison of signed and unsigned values, warning
3670 @cindex signed and unsigned values, comparison warning
3671 Warn when a comparison between signed and unsigned values could produce
3672 an incorrect result when the signed value is converted to unsigned.
3673 This warning is also enabled by @option{-Wextra}; to get the other warnings
3674 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
3676 @item -Wsign-conversion
3677 @opindex Wsign-conversion
3678 @opindex Wno-sign-conversion
3679 Warn for implicit conversions that may change the sign of an integer
3680 value, like assigning a signed integer expression to an unsigned
3681 integer variable. An explicit cast silences the warning. In C, this
3682 option is enabled also by @option{-Wconversion}.
3686 @opindex Wno-address
3687 Warn about suspicious uses of memory addresses. These include using
3688 the address of a function in a conditional expression, such as
3689 @code{void func(void); if (func)}, and comparisons against the memory
3690 address of a string literal, such as @code{if (x == "abc")}. Such
3691 uses typically indicate a programmer error: the address of a function
3692 always evaluates to true, so their use in a conditional usually
3693 indicate that the programmer forgot the parentheses in a function
3694 call; and comparisons against string literals result in unspecified
3695 behavior and are not portable in C, so they usually indicate that the
3696 programmer intended to use @code{strcmp}. This warning is enabled by
3700 @opindex Wlogical-op
3701 @opindex Wno-logical-op
3702 Warn about suspicious uses of logical operators in expressions.
3703 This includes using logical operators in contexts where a
3704 bit-wise operator is likely to be expected.
3706 @item -Waggregate-return
3707 @opindex Waggregate-return
3708 @opindex Wno-aggregate-return
3709 Warn if any functions that return structures or unions are defined or
3710 called. (In languages where you can return an array, this also elicits
3713 @item -Wno-attributes
3714 @opindex Wno-attributes
3715 @opindex Wattributes
3716 Do not warn if an unexpected @code{__attribute__} is used, such as
3717 unrecognized attributes, function attributes applied to variables,
3718 etc. This will not stop errors for incorrect use of supported
3721 @item -Wstrict-prototypes @r{(C and Objective-C only)}
3722 @opindex Wstrict-prototypes
3723 @opindex Wno-strict-prototypes
3724 Warn if a function is declared or defined without specifying the
3725 argument types. (An old-style function definition is permitted without
3726 a warning if preceded by a declaration which specifies the argument
3729 @item -Wold-style-declaration @r{(C and Objective-C only)}
3730 @opindex Wold-style-declaration
3731 @opindex Wno-old-style-declaration
3732 Warn for obsolescent usages, according to the C Standard, in a
3733 declaration. For example, warn if storage-class specifiers like
3734 @code{static} are not the first things in a declaration. This warning
3735 is also enabled by @option{-Wextra}.
3737 @item -Wold-style-definition @r{(C and Objective-C only)}
3738 @opindex Wold-style-definition
3739 @opindex Wno-old-style-definition
3740 Warn if an old-style function definition is used. A warning is given
3741 even if there is a previous prototype.
3743 @item -Wmissing-parameter-type @r{(C and Objective-C only)}
3744 @opindex Wmissing-parameter-type
3745 @opindex Wno-missing-parameter-type
3746 A function parameter is declared without a type specifier in K&R-style
3753 This warning is also enabled by @option{-Wextra}.
3755 @item -Wmissing-prototypes @r{(C and Objective-C only)}
3756 @opindex Wmissing-prototypes
3757 @opindex Wno-missing-prototypes
3758 Warn if a global function is defined without a previous prototype
3759 declaration. This warning is issued even if the definition itself
3760 provides a prototype. The aim is to detect global functions that fail
3761 to be declared in header files.
3763 @item -Wmissing-declarations
3764 @opindex Wmissing-declarations
3765 @opindex Wno-missing-declarations
3766 Warn if a global function is defined without a previous declaration.
3767 Do so even if the definition itself provides a prototype.
3768 Use this option to detect global functions that are not declared in
3769 header files. In C++, no warnings are issued for function templates,
3770 or for inline functions, or for functions in anonymous namespaces.
3772 @item -Wmissing-field-initializers
3773 @opindex Wmissing-field-initializers
3774 @opindex Wno-missing-field-initializers
3778 Warn if a structure's initializer has some fields missing. For
3779 example, the following code would cause such a warning, because
3780 @code{x.h} is implicitly zero:
3783 struct s @{ int f, g, h; @};
3784 struct s x = @{ 3, 4 @};
3787 This option does not warn about designated initializers, so the following
3788 modification would not trigger a warning:
3791 struct s @{ int f, g, h; @};
3792 struct s x = @{ .f = 3, .g = 4 @};
3795 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
3796 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
3798 @item -Wmissing-noreturn
3799 @opindex Wmissing-noreturn
3800 @opindex Wno-missing-noreturn
3801 Warn about functions which might be candidates for attribute @code{noreturn}.
3802 Note these are only possible candidates, not absolute ones. Care should
3803 be taken to manually verify functions actually do not ever return before
3804 adding the @code{noreturn} attribute, otherwise subtle code generation
3805 bugs could be introduced. You will not get a warning for @code{main} in
3806 hosted C environments.
3808 @item -Wmissing-format-attribute
3809 @opindex Wmissing-format-attribute
3810 @opindex Wno-missing-format-attribute
3813 Warn about function pointers which might be candidates for @code{format}
3814 attributes. Note these are only possible candidates, not absolute ones.
3815 GCC will guess that function pointers with @code{format} attributes that
3816 are used in assignment, initialization, parameter passing or return
3817 statements should have a corresponding @code{format} attribute in the
3818 resulting type. I.e.@: the left-hand side of the assignment or
3819 initialization, the type of the parameter variable, or the return type
3820 of the containing function respectively should also have a @code{format}
3821 attribute to avoid the warning.
3823 GCC will also warn about function definitions which might be
3824 candidates for @code{format} attributes. Again, these are only
3825 possible candidates. GCC will guess that @code{format} attributes
3826 might be appropriate for any function that calls a function like
3827 @code{vprintf} or @code{vscanf}, but this might not always be the
3828 case, and some functions for which @code{format} attributes are
3829 appropriate may not be detected.
3831 @item -Wno-multichar
3832 @opindex Wno-multichar
3834 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
3835 Usually they indicate a typo in the user's code, as they have
3836 implementation-defined values, and should not be used in portable code.
3838 @item -Wnormalized=<none|id|nfc|nfkc>
3839 @opindex Wnormalized=
3842 @cindex character set, input normalization
3843 In ISO C and ISO C++, two identifiers are different if they are
3844 different sequences of characters. However, sometimes when characters
3845 outside the basic ASCII character set are used, you can have two
3846 different character sequences that look the same. To avoid confusion,
3847 the ISO 10646 standard sets out some @dfn{normalization rules} which
3848 when applied ensure that two sequences that look the same are turned into
3849 the same sequence. GCC can warn you if you are using identifiers which
3850 have not been normalized; this option controls that warning.
3852 There are four levels of warning that GCC supports. The default is
3853 @option{-Wnormalized=nfc}, which warns about any identifier which is
3854 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
3855 recommended form for most uses.
3857 Unfortunately, there are some characters which ISO C and ISO C++ allow
3858 in identifiers that when turned into NFC aren't allowable as
3859 identifiers. That is, there's no way to use these symbols in portable
3860 ISO C or C++ and have all your identifiers in NFC@.
3861 @option{-Wnormalized=id} suppresses the warning for these characters.
3862 It is hoped that future versions of the standards involved will correct
3863 this, which is why this option is not the default.
3865 You can switch the warning off for all characters by writing
3866 @option{-Wnormalized=none}. You would only want to do this if you
3867 were using some other normalization scheme (like ``D''), because
3868 otherwise you can easily create bugs that are literally impossible to see.
3870 Some characters in ISO 10646 have distinct meanings but look identical
3871 in some fonts or display methodologies, especially once formatting has
3872 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
3873 LETTER N'', will display just like a regular @code{n} which has been
3874 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
3875 normalization scheme to convert all these into a standard form as
3876 well, and GCC will warn if your code is not in NFKC if you use
3877 @option{-Wnormalized=nfkc}. This warning is comparable to warning
3878 about every identifier that contains the letter O because it might be
3879 confused with the digit 0, and so is not the default, but may be
3880 useful as a local coding convention if the programming environment is
3881 unable to be fixed to display these characters distinctly.
3883 @item -Wno-deprecated
3884 @opindex Wno-deprecated
3885 @opindex Wdeprecated
3886 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
3888 @item -Wno-deprecated-declarations
3889 @opindex Wno-deprecated-declarations
3890 @opindex Wdeprecated-declarations
3891 Do not warn about uses of functions (@pxref{Function Attributes}),
3892 variables (@pxref{Variable Attributes}), and types (@pxref{Type
3893 Attributes}) marked as deprecated by using the @code{deprecated}
3897 @opindex Wno-overflow
3899 Do not warn about compile-time overflow in constant expressions.
3901 @item -Woverride-init @r{(C and Objective-C only)}
3902 @opindex Woverride-init
3903 @opindex Wno-override-init
3907 Warn if an initialized field without side effects is overridden when
3908 using designated initializers (@pxref{Designated Inits, , Designated
3911 This warning is included in @option{-Wextra}. To get other
3912 @option{-Wextra} warnings without this one, use @samp{-Wextra
3913 -Wno-override-init}.
3918 Warn if a structure is given the packed attribute, but the packed
3919 attribute has no effect on the layout or size of the structure.
3920 Such structures may be mis-aligned for little benefit. For
3921 instance, in this code, the variable @code{f.x} in @code{struct bar}
3922 will be misaligned even though @code{struct bar} does not itself
3923 have the packed attribute:
3930 @} __attribute__((packed));
3941 Warn if padding is included in a structure, either to align an element
3942 of the structure or to align the whole structure. Sometimes when this
3943 happens it is possible to rearrange the fields of the structure to
3944 reduce the padding and so make the structure smaller.
3946 @item -Wredundant-decls
3947 @opindex Wredundant-decls
3948 @opindex Wno-redundant-decls
3949 Warn if anything is declared more than once in the same scope, even in
3950 cases where multiple declaration is valid and changes nothing.
3952 @item -Wnested-externs @r{(C and Objective-C only)}
3953 @opindex Wnested-externs
3954 @opindex Wno-nested-externs
3955 Warn if an @code{extern} declaration is encountered within a function.
3957 @item -Wunreachable-code
3958 @opindex Wunreachable-code
3959 @opindex Wno-unreachable-code
3960 Warn if the compiler detects that code will never be executed.
3962 This option is intended to warn when the compiler detects that at
3963 least a whole line of source code will never be executed, because
3964 some condition is never satisfied or because it is after a
3965 procedure that never returns.
3967 It is possible for this option to produce a warning even though there
3968 are circumstances under which part of the affected line can be executed,
3969 so care should be taken when removing apparently-unreachable code.
3971 For instance, when a function is inlined, a warning may mean that the
3972 line is unreachable in only one inlined copy of the function.
3974 This option is not made part of @option{-Wall} because in a debugging
3975 version of a program there is often substantial code which checks
3976 correct functioning of the program and is, hopefully, unreachable
3977 because the program does work. Another common use of unreachable
3978 code is to provide behavior which is selectable at compile-time.
3983 Warn if a function can not be inlined and it was declared as inline.
3984 Even with this option, the compiler will not warn about failures to
3985 inline functions declared in system headers.
3987 The compiler uses a variety of heuristics to determine whether or not
3988 to inline a function. For example, the compiler takes into account
3989 the size of the function being inlined and the amount of inlining
3990 that has already been done in the current function. Therefore,
3991 seemingly insignificant changes in the source program can cause the
3992 warnings produced by @option{-Winline} to appear or disappear.
3994 @item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)}
3995 @opindex Wno-invalid-offsetof
3996 @opindex Winvalid-offsetof
3997 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
3998 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
3999 to a non-POD type is undefined. In existing C++ implementations,
4000 however, @samp{offsetof} typically gives meaningful results even when
4001 applied to certain kinds of non-POD types. (Such as a simple
4002 @samp{struct} that fails to be a POD type only by virtue of having a
4003 constructor.) This flag is for users who are aware that they are
4004 writing nonportable code and who have deliberately chosen to ignore the
4007 The restrictions on @samp{offsetof} may be relaxed in a future version
4008 of the C++ standard.
4010 @item -Wno-int-to-pointer-cast @r{(C and Objective-C only)}
4011 @opindex Wno-int-to-pointer-cast
4012 @opindex Wint-to-pointer-cast
4013 Suppress warnings from casts to pointer type of an integer of a
4016 @item -Wno-pointer-to-int-cast @r{(C and Objective-C only)}
4017 @opindex Wno-pointer-to-int-cast
4018 @opindex Wpointer-to-int-cast
4019 Suppress warnings from casts from a pointer to an integer type of a
4023 @opindex Winvalid-pch
4024 @opindex Wno-invalid-pch
4025 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
4026 the search path but can't be used.
4030 @opindex Wno-long-long
4031 Warn if @samp{long long} type is used. This is default. To inhibit
4032 the warning messages, use @option{-Wno-long-long}. Flags
4033 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
4034 only when @option{-pedantic} flag is used.
4036 @item -Wvariadic-macros
4037 @opindex Wvariadic-macros
4038 @opindex Wno-variadic-macros
4039 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
4040 alternate syntax when in pedantic ISO C99 mode. This is default.
4041 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
4046 Warn if variable length array is used in the code.
4047 @option{-Wno-vla} will prevent the @option{-pedantic} warning of
4048 the variable length array.
4050 @item -Wvolatile-register-var
4051 @opindex Wvolatile-register-var
4052 @opindex Wno-volatile-register-var
4053 Warn if a register variable is declared volatile. The volatile
4054 modifier does not inhibit all optimizations that may eliminate reads
4055 and/or writes to register variables. This warning is enabled by
4058 @item -Wdisabled-optimization
4059 @opindex Wdisabled-optimization
4060 @opindex Wno-disabled-optimization
4061 Warn if a requested optimization pass is disabled. This warning does
4062 not generally indicate that there is anything wrong with your code; it
4063 merely indicates that GCC's optimizers were unable to handle the code
4064 effectively. Often, the problem is that your code is too big or too
4065 complex; GCC will refuse to optimize programs when the optimization
4066 itself is likely to take inordinate amounts of time.
4068 @item -Wpointer-sign @r{(C and Objective-C only)}
4069 @opindex Wpointer-sign
4070 @opindex Wno-pointer-sign
4071 Warn for pointer argument passing or assignment with different signedness.
4072 This option is only supported for C and Objective-C@. It is implied by
4073 @option{-Wall} and by @option{-pedantic}, which can be disabled with
4074 @option{-Wno-pointer-sign}.
4076 @item -Wstack-protector
4077 @opindex Wstack-protector
4078 @opindex Wno-stack-protector
4079 This option is only active when @option{-fstack-protector} is active. It
4080 warns about functions that will not be protected against stack smashing.
4083 @opindex Wno-mudflap
4084 Suppress warnings about constructs that cannot be instrumented by
4087 @item -Woverlength-strings
4088 @opindex Woverlength-strings
4089 @opindex Wno-overlength-strings
4090 Warn about string constants which are longer than the ``minimum
4091 maximum'' length specified in the C standard. Modern compilers
4092 generally allow string constants which are much longer than the
4093 standard's minimum limit, but very portable programs should avoid
4094 using longer strings.
4096 The limit applies @emph{after} string constant concatenation, and does
4097 not count the trailing NUL@. In C89, the limit was 509 characters; in
4098 C99, it was raised to 4095. C++98 does not specify a normative
4099 minimum maximum, so we do not diagnose overlength strings in C++@.
4101 This option is implied by @option{-pedantic}, and can be disabled with
4102 @option{-Wno-overlength-strings}.
4105 @node Debugging Options
4106 @section Options for Debugging Your Program or GCC
4107 @cindex options, debugging
4108 @cindex debugging information options
4110 GCC has various special options that are used for debugging
4111 either your program or GCC:
4116 Produce debugging information in the operating system's native format
4117 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
4120 On most systems that use stabs format, @option{-g} enables use of extra
4121 debugging information that only GDB can use; this extra information
4122 makes debugging work better in GDB but will probably make other debuggers
4124 refuse to read the program. If you want to control for certain whether
4125 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
4126 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
4128 GCC allows you to use @option{-g} with
4129 @option{-O}. The shortcuts taken by optimized code may occasionally
4130 produce surprising results: some variables you declared may not exist
4131 at all; flow of control may briefly move where you did not expect it;
4132 some statements may not be executed because they compute constant
4133 results or their values were already at hand; some statements may
4134 execute in different places because they were moved out of loops.
4136 Nevertheless it proves possible to debug optimized output. This makes
4137 it reasonable to use the optimizer for programs that might have bugs.
4139 The following options are useful when GCC is generated with the
4140 capability for more than one debugging format.
4144 Produce debugging information for use by GDB@. This means to use the
4145 most expressive format available (DWARF 2, stabs, or the native format
4146 if neither of those are supported), including GDB extensions if at all
4151 Produce debugging information in stabs format (if that is supported),
4152 without GDB extensions. This is the format used by DBX on most BSD
4153 systems. On MIPS, Alpha and System V Release 4 systems this option
4154 produces stabs debugging output which is not understood by DBX or SDB@.
4155 On System V Release 4 systems this option requires the GNU assembler.
4157 @item -feliminate-unused-debug-symbols
4158 @opindex feliminate-unused-debug-symbols
4159 Produce debugging information in stabs format (if that is supported),
4160 for only symbols that are actually used.
4162 @item -femit-class-debug-always
4163 Instead of emitting debugging information for a C++ class in only one
4164 object file, emit it in all object files using the class. This option
4165 should be used only with debuggers that are unable to handle the way GCC
4166 normally emits debugging information for classes because using this
4167 option will increase the size of debugging information by as much as a
4172 Produce debugging information in stabs format (if that is supported),
4173 using GNU extensions understood only by the GNU debugger (GDB)@. The
4174 use of these extensions is likely to make other debuggers crash or
4175 refuse to read the program.
4179 Produce debugging information in COFF format (if that is supported).
4180 This is the format used by SDB on most System V systems prior to
4185 Produce debugging information in XCOFF format (if that is supported).
4186 This is the format used by the DBX debugger on IBM RS/6000 systems.
4190 Produce debugging information in XCOFF format (if that is supported),
4191 using GNU extensions understood only by the GNU debugger (GDB)@. The
4192 use of these extensions is likely to make other debuggers crash or
4193 refuse to read the program, and may cause assemblers other than the GNU
4194 assembler (GAS) to fail with an error.
4198 Produce debugging information in DWARF version 2 format (if that is
4199 supported). This is the format used by DBX on IRIX 6. With this
4200 option, GCC uses features of DWARF version 3 when they are useful;
4201 version 3 is upward compatible with version 2, but may still cause
4202 problems for older debuggers.
4206 Produce debugging information in VMS debug format (if that is
4207 supported). This is the format used by DEBUG on VMS systems.
4210 @itemx -ggdb@var{level}
4211 @itemx -gstabs@var{level}
4212 @itemx -gcoff@var{level}
4213 @itemx -gxcoff@var{level}
4214 @itemx -gvms@var{level}
4215 Request debugging information and also use @var{level} to specify how
4216 much information. The default level is 2.
4218 Level 0 produces no debug information at all. Thus, @option{-g0} negates
4221 Level 1 produces minimal information, enough for making backtraces in
4222 parts of the program that you don't plan to debug. This includes
4223 descriptions of functions and external variables, but no information
4224 about local variables and no line numbers.
4226 Level 3 includes extra information, such as all the macro definitions
4227 present in the program. Some debuggers support macro expansion when
4228 you use @option{-g3}.
4230 @option{-gdwarf-2} does not accept a concatenated debug level, because
4231 GCC used to support an option @option{-gdwarf} that meant to generate
4232 debug information in version 1 of the DWARF format (which is very
4233 different from version 2), and it would have been too confusing. That
4234 debug format is long obsolete, but the option cannot be changed now.
4235 Instead use an additional @option{-g@var{level}} option to change the
4236 debug level for DWARF2.
4238 @item -feliminate-dwarf2-dups
4239 @opindex feliminate-dwarf2-dups
4240 Compress DWARF2 debugging information by eliminating duplicated
4241 information about each symbol. This option only makes sense when
4242 generating DWARF2 debugging information with @option{-gdwarf-2}.
4244 @item -femit-struct-debug-baseonly
4245 Emit debug information for struct-like types
4246 only when the base name of the compilation source file
4247 matches the base name of file in which the struct was defined.
4249 This option substantially reduces the size of debugging information,
4250 but at significant potential loss in type information to the debugger.
4251 See @option{-femit-struct-debug-reduced} for a less aggressive option.
4252 See @option{-femit-struct-debug-detailed} for more detailed control.
4254 This option works only with DWARF 2.
4256 @item -femit-struct-debug-reduced
4257 Emit debug information for struct-like types
4258 only when the base name of the compilation source file
4259 matches the base name of file in which the type was defined,
4260 unless the struct is a template or defined in a system header.
4262 This option significantly reduces the size of debugging information,
4263 with some potential loss in type information to the debugger.
4264 See @option{-femit-struct-debug-baseonly} for a more aggressive option.
4265 See @option{-femit-struct-debug-detailed} for more detailed control.
4267 This option works only with DWARF 2.
4269 @item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]}
4270 Specify the struct-like types
4271 for which the compiler will generate debug information.
4272 The intent is to reduce duplicate struct debug information
4273 between different object files within the same program.
4275 This option is a detailed version of
4276 @option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly},
4277 which will serve for most needs.
4279 A specification has the syntax
4280 [@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none})
4282 The optional first word limits the specification to
4283 structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}).
4284 A struct type is used directly when it is the type of a variable, member.
4285 Indirect uses arise through pointers to structs.
4286 That is, when use of an incomplete struct would be legal, the use is indirect.
4288 @samp{struct one direct; struct two * indirect;}.
4290 The optional second word limits the specification to
4291 ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}).
4292 Generic structs are a bit complicated to explain.
4293 For C++, these are non-explicit specializations of template classes,
4294 or non-template classes within the above.
4295 Other programming languages have generics,
4296 but @samp{-femit-struct-debug-detailed} does not yet implement them.
4298 The third word specifies the source files for those
4299 structs for which the compiler will emit debug information.
4300 The values @samp{none} and @samp{any} have the normal meaning.
4301 The value @samp{base} means that
4302 the base of name of the file in which the type declaration appears
4303 must match the base of the name of the main compilation file.
4304 In practice, this means that
4305 types declared in @file{foo.c} and @file{foo.h} will have debug information,
4306 but types declared in other header will not.
4307 The value @samp{sys} means those types satisfying @samp{base}
4308 or declared in system or compiler headers.
4310 You may need to experiment to determine the best settings for your application.
4312 The default is @samp{-femit-struct-debug-detailed=all}.
4314 This option works only with DWARF 2.
4316 @item -fno-merge-debug-strings
4317 @opindex fmerge-debug-strings
4318 @opindex fno-merge-debug-strings
4319 Direct the linker to merge together strings which are identical in
4320 different object files. This is not supported by all assemblers or
4321 linker. This decreases the size of the debug information in the
4322 output file at the cost of increasing link processing time. This is
4325 @item -fdebug-prefix-map=@var{old}=@var{new}
4326 @opindex fdebug-prefix-map
4327 When compiling files in directory @file{@var{old}}, record debugging
4328 information describing them as in @file{@var{new}} instead.
4330 @cindex @command{prof}
4333 Generate extra code to write profile information suitable for the
4334 analysis program @command{prof}. You must use this option when compiling
4335 the source files you want data about, and you must also use it when
4338 @cindex @command{gprof}
4341 Generate extra code to write profile information suitable for the
4342 analysis program @command{gprof}. You must use this option when compiling
4343 the source files you want data about, and you must also use it when
4348 Makes the compiler print out each function name as it is compiled, and
4349 print some statistics about each pass when it finishes.
4352 @opindex ftime-report
4353 Makes the compiler print some statistics about the time consumed by each
4354 pass when it finishes.
4357 @opindex fmem-report
4358 Makes the compiler print some statistics about permanent memory
4359 allocation when it finishes.
4361 @item -fpre-ipa-mem-report
4362 @opindex fpre-ipa-mem-report
4363 @item -fpost-ipa-mem-report
4364 @opindex fpost-ipa-mem-report
4365 Makes the compiler print some statistics about permanent memory
4366 allocation before or after interprocedural optimization.
4368 @item -fprofile-arcs
4369 @opindex fprofile-arcs
4370 Add code so that program flow @dfn{arcs} are instrumented. During
4371 execution the program records how many times each branch and call is
4372 executed and how many times it is taken or returns. When the compiled
4373 program exits it saves this data to a file called
4374 @file{@var{auxname}.gcda} for each source file. The data may be used for
4375 profile-directed optimizations (@option{-fbranch-probabilities}), or for
4376 test coverage analysis (@option{-ftest-coverage}). Each object file's
4377 @var{auxname} is generated from the name of the output file, if
4378 explicitly specified and it is not the final executable, otherwise it is
4379 the basename of the source file. In both cases any suffix is removed
4380 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
4381 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
4382 @xref{Cross-profiling}.
4384 @cindex @command{gcov}
4388 This option is used to compile and link code instrumented for coverage
4389 analysis. The option is a synonym for @option{-fprofile-arcs}
4390 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
4391 linking). See the documentation for those options for more details.
4396 Compile the source files with @option{-fprofile-arcs} plus optimization
4397 and code generation options. For test coverage analysis, use the
4398 additional @option{-ftest-coverage} option. You do not need to profile
4399 every source file in a program.
4402 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
4403 (the latter implies the former).
4406 Run the program on a representative workload to generate the arc profile
4407 information. This may be repeated any number of times. You can run
4408 concurrent instances of your program, and provided that the file system
4409 supports locking, the data files will be correctly updated. Also
4410 @code{fork} calls are detected and correctly handled (double counting
4414 For profile-directed optimizations, compile the source files again with
4415 the same optimization and code generation options plus
4416 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
4417 Control Optimization}).
4420 For test coverage analysis, use @command{gcov} to produce human readable
4421 information from the @file{.gcno} and @file{.gcda} files. Refer to the
4422 @command{gcov} documentation for further information.
4426 With @option{-fprofile-arcs}, for each function of your program GCC
4427 creates a program flow graph, then finds a spanning tree for the graph.
4428 Only arcs that are not on the spanning tree have to be instrumented: the
4429 compiler adds code to count the number of times that these arcs are
4430 executed. When an arc is the only exit or only entrance to a block, the
4431 instrumentation code can be added to the block; otherwise, a new basic
4432 block must be created to hold the instrumentation code.
4435 @item -ftest-coverage
4436 @opindex ftest-coverage
4437 Produce a notes file that the @command{gcov} code-coverage utility
4438 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
4439 show program coverage. Each source file's note file is called
4440 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
4441 above for a description of @var{auxname} and instructions on how to
4442 generate test coverage data. Coverage data will match the source files
4443 more closely, if you do not optimize.
4445 @item -fdbg-cnt-list
4446 @opindex fdbg-cnt-list
4447 Print the name and the counter upperbound for all debug counters.
4449 @item -fdbg-cnt=@var{counter-value-list}
4451 Set the internal debug counter upperbound. @var{counter-value-list}
4452 is a comma-separated list of @var{name}:@var{value} pairs
4453 which sets the upperbound of each debug counter @var{name} to @var{value}.
4454 All debug counters have the initial upperbound of @var{UINT_MAX},
4455 thus dbg_cnt() returns true always unless the upperbound is set by this option.
4456 e.g. With -fdbg-cnt=dce:10,tail_call:0
4457 dbg_cnt(dce) will return true only for first 10 invocations
4458 and dbg_cnt(tail_call) will return false always.
4460 @item -d@var{letters}
4461 @itemx -fdump-rtl-@var{pass}
4463 Says to make debugging dumps during compilation at times specified by
4464 @var{letters}. This is used for debugging the RTL-based passes of the
4465 compiler. The file names for most of the dumps are made by appending a
4466 pass number and a word to the @var{dumpname}. @var{dumpname} is generated
4467 from the name of the output file, if explicitly specified and it is not
4468 an executable, otherwise it is the basename of the source file. These
4469 switches may have different effects when @option{-E} is used for
4472 Most debug dumps can be enabled either passing a letter to the @option{-d}
4473 option, or with a long @option{-fdump-rtl} switch; here are the possible
4474 letters for use in @var{letters} and @var{pass}, and their meanings:
4479 Annotate the assembler output with miscellaneous debugging information.
4481 @item -fdump-rtl-bbro
4482 @opindex fdump-rtl-bbro
4483 Dump after block reordering, to @file{@var{file}.148r.bbro}.
4485 @item -fdump-rtl-combine
4486 @opindex fdump-rtl-combine
4487 Dump after the RTL instruction combination pass, to the file
4488 @file{@var{file}.129r.combine}.
4490 @item -fdump-rtl-ce1
4491 @itemx -fdump-rtl-ce2
4492 @opindex fdump-rtl-ce1
4493 @opindex fdump-rtl-ce2
4494 @option{-fdump-rtl-ce1} enable dumping after the
4495 first if conversion, to the file @file{@var{file}.117r.ce1}.
4496 @option{-fdump-rtl-ce2} enable dumping after the second if
4497 conversion, to the file @file{@var{file}.130r.ce2}.
4499 @item -fdump-rtl-btl
4500 @itemx -fdump-rtl-dbr
4501 @opindex fdump-rtl-btl
4502 @opindex fdump-rtl-dbr
4503 @option{-fdump-rtl-btl} enable dumping after branch
4504 target load optimization, to @file{@var{file}.31.btl}.
4505 @option{-fdump-rtl-dbr} enable dumping after delayed branch
4506 scheduling, to @file{@var{file}.36.dbr}.
4510 Dump all macro definitions, at the end of preprocessing, in addition to
4513 @item -fdump-rtl-ce3
4514 @opindex fdump-rtl-ce3
4515 Dump after the third if conversion, to @file{@var{file}.146r.ce3}.
4517 @item -fdump-rtl-cfg
4518 @itemx -fdump-rtl-life
4519 @opindex fdump-rtl-cfg
4520 @opindex fdump-rtl-life
4521 @option{-fdump-rtl-cfg} enable dumping after control
4522 and data flow analysis, to @file{@var{file}.116r.cfg}.
4523 @option{-fdump-rtl-cfg} enable dumping dump after life analysis,
4524 to @file{@var{file}.128r.life1} and @file{@var{file}.135r.life2}.
4526 @item -fdump-rtl-greg
4527 @opindex fdump-rtl-greg
4528 Dump after global register allocation, to @file{@var{file}.139r.greg}.
4530 @item -fdump-rtl-gcse
4531 @itemx -fdump-rtl-bypass
4532 @opindex fdump-rtl-gcse
4533 @opindex fdump-rtl-bypass
4534 @option{-fdump-rtl-gcse} enable dumping after GCSE, to
4535 @file{@var{file}.114r.gcse}. @option{-fdump-rtl-bypass}
4536 enable dumping after jump bypassing and control flow optimizations, to
4537 @file{@var{file}.115r.bypass}.
4540 @opindex fdump-rtl-eh
4541 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
4543 @item -fdump-rtl-sibling
4544 @opindex fdump-rtl-sibling
4545 Dump after sibling call optimizations, to @file{@var{file}.106r.sibling}.
4547 @item -fdump-rtl-jump
4548 @opindex fdump-rtl-jump
4549 Dump after the first jump optimization, to @file{@var{file}.112r.jump}.
4551 @item -fdump-rtl-stack
4552 @opindex fdump-rtl-stack
4553 Dump after conversion from GCC's "flat register file" registers to the
4554 x87's stack-like registers, to @file{@var{file}.152r.stack}.
4556 @item -fdump-rtl-lreg
4557 @opindex fdump-rtl-lreg
4558 Dump after local register allocation, to @file{@var{file}.138r.lreg}.
4560 @item -fdump-rtl-loop2
4561 @opindex fdump-rtl-loop2
4562 @option{-dL} and @option{-fdump-rtl-loop2} enable dumping after the
4563 loop optimization pass, to @file{@var{file}.119r.loop2},
4564 @file{@var{file}.120r.loop2_init},
4565 @file{@var{file}.121r.loop2_invariant}, and
4566 @file{@var{file}.125r.loop2_done}.
4568 @item -fdump-rtl-sms
4569 @opindex fdump-rtl-sms
4570 Dump after modulo scheduling, to @file{@var{file}.136r.sms}.
4572 @item -fdump-rtl-mach
4573 @opindex fdump-rtl-mach
4574 Dump after performing the machine dependent reorganization pass, to
4575 @file{@var{file}.155r.mach} if that pass exists.
4577 @item -fdump-rtl-rnreg
4578 @opindex fdump-rtl-rnreg
4579 Dump after register renumbering, to @file{@var{file}.147r.rnreg}.
4581 @item -fdump-rtl-regmove
4582 @opindex fdump-rtl-regmove
4583 Dump after the register move pass, to @file{@var{file}.132r.regmove}.
4585 @item -fdump-rtl-postreload
4586 @opindex fdump-rtl-postreload
4587 Dump after post-reload optimizations, to @file{@var{file}.24.postreload}.
4589 @item -fdump-rtl-expand
4590 @opindex fdump-rtl-expand
4591 Dump after RTL generation, to @file{@var{file}.104r.expand}.
4593 @item -fdump-rtl-sched2
4594 @opindex fdump-rtl-sched2
4595 Dump after the second scheduling pass, to @file{@var{file}.149r.sched2}.
4597 @item -fdump-rtl-cse
4598 @opindex fdump-rtl-cse
4599 Dump after CSE (including the jump optimization that sometimes follows
4600 CSE), to @file{@var{file}.113r.cse}.
4602 @item -fdump-rtl-sched1
4603 @opindex fdump-rtl-sched1
4604 Dump after the first scheduling pass, to @file{@var{file}.136r.sched1}.
4606 @item -fdump-rtl-cse2
4607 @opindex fdump-rtl-cse2
4608 Dump after the second CSE pass (including the jump optimization that
4609 sometimes follows CSE), to @file{@var{file}.127r.cse2}.
4611 @item -fdump-rtl-tracer
4612 @opindex fdump-rtl-tracer
4613 Dump after running tracer, to @file{@var{file}.118r.tracer}.
4615 @item -fdump-rtl-vpt
4616 @itemx -fdump-rtl-vartrack
4617 @opindex fdump-rtl-vpt
4618 @opindex fdump-rtl-vartrack
4619 @option{-fdump-rtl-vpt} enable dumping after the value
4620 profile transformations, to @file{@var{file}.10.vpt}.
4621 @option{-fdump-rtl-vartrack} enable dumping after variable tracking,
4622 to @file{@var{file}.154r.vartrack}.
4624 @item -fdump-rtl-flow2
4625 @opindex fdump-rtl-flow2
4626 Dump after the second flow pass, to @file{@var{file}.142r.flow2}.
4628 @item -fdump-rtl-peephole2
4629 @opindex fdump-rtl-peephole2
4630 Dump after the peephole pass, to @file{@var{file}.145r.peephole2}.
4632 @item -fdump-rtl-web
4633 @opindex fdump-rtl-web
4634 Dump after live range splitting, to @file{@var{file}.126r.web}.
4636 @item -fdump-rtl-all
4637 @opindex fdump-rtl-all
4638 Produce all the dumps listed above.
4642 Produce a core dump whenever an error occurs.
4646 Print statistics on memory usage, at the end of the run, to
4651 Annotate the assembler output with a comment indicating which
4652 pattern and alternative was used. The length of each instruction is
4657 Dump the RTL in the assembler output as a comment before each instruction.
4658 Also turns on @option{-dp} annotation.
4662 For each of the other indicated dump files (either with @option{-d} or
4663 @option{-fdump-rtl-@var{pass}}), dump a representation of the control flow
4664 graph suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
4668 Just generate RTL for a function instead of compiling it. Usually used
4669 with @samp{r} (@option{-fdump-rtl-expand}).
4673 Dump debugging information during parsing, to standard error.
4677 @opindex fdump-noaddr
4678 When doing debugging dumps (see @option{-d} option above), suppress
4679 address output. This makes it more feasible to use diff on debugging
4680 dumps for compiler invocations with different compiler binaries and/or
4681 different text / bss / data / heap / stack / dso start locations.
4683 @item -fdump-unnumbered
4684 @opindex fdump-unnumbered
4685 When doing debugging dumps (see @option{-d} option above), suppress instruction
4686 numbers and address output. This makes it more feasible to
4687 use diff on debugging dumps for compiler invocations with different
4688 options, in particular with and without @option{-g}.
4690 @item -fdump-translation-unit @r{(C++ only)}
4691 @itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
4692 @opindex fdump-translation-unit
4693 Dump a representation of the tree structure for the entire translation
4694 unit to a file. The file name is made by appending @file{.tu} to the
4695 source file name. If the @samp{-@var{options}} form is used, @var{options}
4696 controls the details of the dump as described for the
4697 @option{-fdump-tree} options.
4699 @item -fdump-class-hierarchy @r{(C++ only)}
4700 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
4701 @opindex fdump-class-hierarchy
4702 Dump a representation of each class's hierarchy and virtual function
4703 table layout to a file. The file name is made by appending @file{.class}
4704 to the source file name. If the @samp{-@var{options}} form is used,
4705 @var{options} controls the details of the dump as described for the
4706 @option{-fdump-tree} options.
4708 @item -fdump-ipa-@var{switch}
4710 Control the dumping at various stages of inter-procedural analysis
4711 language tree to a file. The file name is generated by appending a switch
4712 specific suffix to the source file name. The following dumps are possible:
4716 Enables all inter-procedural analysis dumps.
4719 Dumps information about call-graph optimization, unused function removal,
4720 and inlining decisions.
4723 Dump after function inlining.
4727 @item -fdump-statistics-@var{option}
4728 @opindex -fdump-statistics
4729 Enable and control dumping of pass statistics in a separate file. The
4730 file name is generated by appending a suffix ending in @samp{.statistics}
4731 to the source file name. If the @samp{-@var{option}} form is used,
4732 @samp{-stats} will cause counters to be summed over the whole compilation unit
4733 while @samp{-details} will dump every event as the passes generate them.
4734 The default with no option is to sum counters for each function compiled.
4736 @item -fdump-tree-@var{switch}
4737 @itemx -fdump-tree-@var{switch}-@var{options}
4739 Control the dumping at various stages of processing the intermediate
4740 language tree to a file. The file name is generated by appending a switch
4741 specific suffix to the source file name. If the @samp{-@var{options}}
4742 form is used, @var{options} is a list of @samp{-} separated options that
4743 control the details of the dump. Not all options are applicable to all
4744 dumps, those which are not meaningful will be ignored. The following
4745 options are available
4749 Print the address of each node. Usually this is not meaningful as it
4750 changes according to the environment and source file. Its primary use
4751 is for tying up a dump file with a debug environment.
4753 Inhibit dumping of members of a scope or body of a function merely
4754 because that scope has been reached. Only dump such items when they
4755 are directly reachable by some other path. When dumping pretty-printed
4756 trees, this option inhibits dumping the bodies of control structures.
4758 Print a raw representation of the tree. By default, trees are
4759 pretty-printed into a C-like representation.
4761 Enable more detailed dumps (not honored by every dump option).
4763 Enable dumping various statistics about the pass (not honored by every dump
4766 Enable showing basic block boundaries (disabled in raw dumps).
4768 Enable showing virtual operands for every statement.
4770 Enable showing line numbers for statements.
4772 Enable showing the unique ID (@code{DECL_UID}) for each variable.
4774 Enable showing the tree dump for each statement.
4776 Turn on all options, except @option{raw}, @option{slim}, @option{verbose}
4777 and @option{lineno}.
4780 The following tree dumps are possible:
4784 Dump before any tree based optimization, to @file{@var{file}.original}.
4787 Dump after all tree based optimization, to @file{@var{file}.optimized}.
4790 @opindex fdump-tree-gimple
4791 Dump each function before and after the gimplification pass to a file. The
4792 file name is made by appending @file{.gimple} to the source file name.
4795 @opindex fdump-tree-cfg
4796 Dump the control flow graph of each function to a file. The file name is
4797 made by appending @file{.cfg} to the source file name.
4800 @opindex fdump-tree-vcg
4801 Dump the control flow graph of each function to a file in VCG format. The
4802 file name is made by appending @file{.vcg} to the source file name. Note
4803 that if the file contains more than one function, the generated file cannot
4804 be used directly by VCG@. You will need to cut and paste each function's
4805 graph into its own separate file first.
4808 @opindex fdump-tree-ch
4809 Dump each function after copying loop headers. The file name is made by
4810 appending @file{.ch} to the source file name.
4813 @opindex fdump-tree-ssa
4814 Dump SSA related information to a file. The file name is made by appending
4815 @file{.ssa} to the source file name.
4818 @opindex fdump-tree-alias
4819 Dump aliasing information for each function. The file name is made by
4820 appending @file{.alias} to the source file name.
4823 @opindex fdump-tree-ccp
4824 Dump each function after CCP@. The file name is made by appending
4825 @file{.ccp} to the source file name.
4828 @opindex fdump-tree-storeccp
4829 Dump each function after STORE-CCP@. The file name is made by appending
4830 @file{.storeccp} to the source file name.
4833 @opindex fdump-tree-pre
4834 Dump trees after partial redundancy elimination. The file name is made
4835 by appending @file{.pre} to the source file name.
4838 @opindex fdump-tree-fre
4839 Dump trees after full redundancy elimination. The file name is made
4840 by appending @file{.fre} to the source file name.
4843 @opindex fdump-tree-copyprop
4844 Dump trees after copy propagation. The file name is made
4845 by appending @file{.copyprop} to the source file name.
4847 @item store_copyprop
4848 @opindex fdump-tree-store_copyprop
4849 Dump trees after store copy-propagation. The file name is made
4850 by appending @file{.store_copyprop} to the source file name.
4853 @opindex fdump-tree-dce
4854 Dump each function after dead code elimination. The file name is made by
4855 appending @file{.dce} to the source file name.
4858 @opindex fdump-tree-mudflap
4859 Dump each function after adding mudflap instrumentation. The file name is
4860 made by appending @file{.mudflap} to the source file name.
4863 @opindex fdump-tree-sra
4864 Dump each function after performing scalar replacement of aggregates. The
4865 file name is made by appending @file{.sra} to the source file name.
4868 @opindex fdump-tree-sink
4869 Dump each function after performing code sinking. The file name is made
4870 by appending @file{.sink} to the source file name.
4873 @opindex fdump-tree-dom
4874 Dump each function after applying dominator tree optimizations. The file
4875 name is made by appending @file{.dom} to the source file name.
4878 @opindex fdump-tree-dse
4879 Dump each function after applying dead store elimination. The file
4880 name is made by appending @file{.dse} to the source file name.
4883 @opindex fdump-tree-phiopt
4884 Dump each function after optimizing PHI nodes into straightline code. The file
4885 name is made by appending @file{.phiopt} to the source file name.
4888 @opindex fdump-tree-forwprop
4889 Dump each function after forward propagating single use variables. The file
4890 name is made by appending @file{.forwprop} to the source file name.
4893 @opindex fdump-tree-copyrename
4894 Dump each function after applying the copy rename optimization. The file
4895 name is made by appending @file{.copyrename} to the source file name.
4898 @opindex fdump-tree-nrv
4899 Dump each function after applying the named return value optimization on
4900 generic trees. The file name is made by appending @file{.nrv} to the source
4904 @opindex fdump-tree-vect
4905 Dump each function after applying vectorization of loops. The file name is
4906 made by appending @file{.vect} to the source file name.
4909 @opindex fdump-tree-vrp
4910 Dump each function after Value Range Propagation (VRP). The file name
4911 is made by appending @file{.vrp} to the source file name.
4914 @opindex fdump-tree-all
4915 Enable all the available tree dumps with the flags provided in this option.
4918 @item -ftree-vectorizer-verbose=@var{n}
4919 @opindex ftree-vectorizer-verbose
4920 This option controls the amount of debugging output the vectorizer prints.
4921 This information is written to standard error, unless
4922 @option{-fdump-tree-all} or @option{-fdump-tree-vect} is specified,
4923 in which case it is output to the usual dump listing file, @file{.vect}.
4924 For @var{n}=0 no diagnostic information is reported.
4925 If @var{n}=1 the vectorizer reports each loop that got vectorized,
4926 and the total number of loops that got vectorized.
4927 If @var{n}=2 the vectorizer also reports non-vectorized loops that passed
4928 the first analysis phase (vect_analyze_loop_form) - i.e.@: countable,
4929 inner-most, single-bb, single-entry/exit loops. This is the same verbosity
4930 level that @option{-fdump-tree-vect-stats} uses.
4931 Higher verbosity levels mean either more information dumped for each
4932 reported loop, or same amount of information reported for more loops:
4933 If @var{n}=3, alignment related information is added to the reports.
4934 If @var{n}=4, data-references related information (e.g.@: memory dependences,
4935 memory access-patterns) is added to the reports.
4936 If @var{n}=5, the vectorizer reports also non-vectorized inner-most loops
4937 that did not pass the first analysis phase (i.e., may not be countable, or
4938 may have complicated control-flow).
4939 If @var{n}=6, the vectorizer reports also non-vectorized nested loops.
4940 For @var{n}=7, all the information the vectorizer generates during its
4941 analysis and transformation is reported. This is the same verbosity level
4942 that @option{-fdump-tree-vect-details} uses.
4944 @item -frandom-seed=@var{string}
4945 @opindex frandom-string
4946 This option provides a seed that GCC uses when it would otherwise use
4947 random numbers. It is used to generate certain symbol names
4948 that have to be different in every compiled file. It is also used to
4949 place unique stamps in coverage data files and the object files that
4950 produce them. You can use the @option{-frandom-seed} option to produce
4951 reproducibly identical object files.
4953 The @var{string} should be different for every file you compile.
4955 @item -fsched-verbose=@var{n}
4956 @opindex fsched-verbose
4957 On targets that use instruction scheduling, this option controls the
4958 amount of debugging output the scheduler prints. This information is
4959 written to standard error, unless @option{-dS} or @option{-dR} is
4960 specified, in which case it is output to the usual dump
4961 listing file, @file{.sched} or @file{.sched2} respectively. However
4962 for @var{n} greater than nine, the output is always printed to standard
4965 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
4966 same information as @option{-dRS}. For @var{n} greater than one, it
4967 also output basic block probabilities, detailed ready list information
4968 and unit/insn info. For @var{n} greater than two, it includes RTL
4969 at abort point, control-flow and regions info. And for @var{n} over
4970 four, @option{-fsched-verbose} also includes dependence info.
4974 Store the usual ``temporary'' intermediate files permanently; place them
4975 in the current directory and name them based on the source file. Thus,
4976 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
4977 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
4978 preprocessed @file{foo.i} output file even though the compiler now
4979 normally uses an integrated preprocessor.
4981 When used in combination with the @option{-x} command line option,
4982 @option{-save-temps} is sensible enough to avoid over writing an
4983 input source file with the same extension as an intermediate file.
4984 The corresponding intermediate file may be obtained by renaming the
4985 source file before using @option{-save-temps}.
4989 Report the CPU time taken by each subprocess in the compilation
4990 sequence. For C source files, this is the compiler proper and assembler
4991 (plus the linker if linking is done). The output looks like this:
4998 The first number on each line is the ``user time'', that is time spent
4999 executing the program itself. The second number is ``system time'',
5000 time spent executing operating system routines on behalf of the program.
5001 Both numbers are in seconds.
5003 @item -fvar-tracking
5004 @opindex fvar-tracking
5005 Run variable tracking pass. It computes where variables are stored at each
5006 position in code. Better debugging information is then generated
5007 (if the debugging information format supports this information).
5009 It is enabled by default when compiling with optimization (@option{-Os},
5010 @option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and
5011 the debug info format supports it.
5013 @item -print-file-name=@var{library}
5014 @opindex print-file-name
5015 Print the full absolute name of the library file @var{library} that
5016 would be used when linking---and don't do anything else. With this
5017 option, GCC does not compile or link anything; it just prints the
5020 @item -print-multi-directory
5021 @opindex print-multi-directory
5022 Print the directory name corresponding to the multilib selected by any
5023 other switches present in the command line. This directory is supposed
5024 to exist in @env{GCC_EXEC_PREFIX}.
5026 @item -print-multi-lib
5027 @opindex print-multi-lib
5028 Print the mapping from multilib directory names to compiler switches
5029 that enable them. The directory name is separated from the switches by
5030 @samp{;}, and each switch starts with an @samp{@@} instead of the
5031 @samp{-}, without spaces between multiple switches. This is supposed to
5032 ease shell-processing.
5034 @item -print-prog-name=@var{program}
5035 @opindex print-prog-name
5036 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
5038 @item -print-libgcc-file-name
5039 @opindex print-libgcc-file-name
5040 Same as @option{-print-file-name=libgcc.a}.
5042 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
5043 but you do want to link with @file{libgcc.a}. You can do
5046 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
5049 @item -print-search-dirs
5050 @opindex print-search-dirs
5051 Print the name of the configured installation directory and a list of
5052 program and library directories @command{gcc} will search---and don't do anything else.
5054 This is useful when @command{gcc} prints the error message
5055 @samp{installation problem, cannot exec cpp0: No such file or directory}.
5056 To resolve this you either need to put @file{cpp0} and the other compiler
5057 components where @command{gcc} expects to find them, or you can set the environment
5058 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
5059 Don't forget the trailing @samp{/}.
5060 @xref{Environment Variables}.
5062 @item -print-sysroot
5063 @opindex print-sysroot
5064 Print the target sysroot directory that will be used during
5065 compilation. This is the target sysroot specified either at configure
5066 time or or using the @option{--sysroot} option, possibly with an extra
5067 suffix that depends on compilation options. If no target sysroot is
5068 specified, the option prints nothing.
5070 @item -print-sysroot-headers-suffix
5071 @opindex print-sysroot-headers-suffix
5072 Print the suffix added to the target sysroot when searching for
5073 headers, or give an error if the compiler is not configured with such
5074 a suffix---and don't do anything else.
5077 @opindex dumpmachine
5078 Print the compiler's target machine (for example,
5079 @samp{i686-pc-linux-gnu})---and don't do anything else.
5082 @opindex dumpversion
5083 Print the compiler version (for example, @samp{3.0})---and don't do
5088 Print the compiler's built-in specs---and don't do anything else. (This
5089 is used when GCC itself is being built.) @xref{Spec Files}.
5091 @item -feliminate-unused-debug-types
5092 @opindex feliminate-unused-debug-types
5093 Normally, when producing DWARF2 output, GCC will emit debugging
5094 information for all types declared in a compilation
5095 unit, regardless of whether or not they are actually used
5096 in that compilation unit. Sometimes this is useful, such as
5097 if, in the debugger, you want to cast a value to a type that is
5098 not actually used in your program (but is declared). More often,
5099 however, this results in a significant amount of wasted space.
5100 With this option, GCC will avoid producing debug symbol output
5101 for types that are nowhere used in the source file being compiled.
5104 @node Optimize Options
5105 @section Options That Control Optimization
5106 @cindex optimize options
5107 @cindex options, optimization
5109 These options control various sorts of optimizations.
5111 Without any optimization option, the compiler's goal is to reduce the
5112 cost of compilation and to make debugging produce the expected
5113 results. Statements are independent: if you stop the program with a
5114 breakpoint between statements, you can then assign a new value to any
5115 variable or change the program counter to any other statement in the
5116 function and get exactly the results you would expect from the source
5119 Turning on optimization flags makes the compiler attempt to improve
5120 the performance and/or code size at the expense of compilation time
5121 and possibly the ability to debug the program.
5123 The compiler performs optimization based on the knowledge it has of
5124 the program. Optimization levels @option{-O} and above, in
5125 particular, enable @emph{unit-at-a-time} mode, which allows the
5126 compiler to consider information gained from later functions in
5127 the file when compiling a function. Compiling multiple files at
5128 once to a single output file in @emph{unit-at-a-time} mode allows
5129 the compiler to use information gained from all of the files when
5130 compiling each of them.
5132 Not all optimizations are controlled directly by a flag. Only
5133 optimizations that have a flag are listed.
5140 Optimize. Optimizing compilation takes somewhat more time, and a lot
5141 more memory for a large function.
5143 With @option{-O}, the compiler tries to reduce code size and execution
5144 time, without performing any optimizations that take a great deal of
5147 @option{-O} turns on the following optimization flags:
5150 -fcprop-registers @gol
5153 -fdelayed-branch @gol
5155 -fguess-branch-probability @gol
5156 -fif-conversion2 @gol
5157 -fif-conversion @gol
5158 -finline-small-functions @gol
5159 -fipa-pure-const @gol
5160 -fipa-reference @gol
5162 -fsplit-wide-types @gol
5163 -ftree-builtin-call-dce @gol
5166 -ftree-copyrename @gol
5168 -ftree-dominator-opts @gol
5175 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
5176 where doing so does not interfere with debugging.
5180 Optimize even more. GCC performs nearly all supported optimizations
5181 that do not involve a space-speed tradeoff. The compiler does not
5182 perform loop unrolling or function inlining when you specify @option{-O2}.
5183 As compared to @option{-O}, this option increases both compilation time
5184 and the performance of the generated code.
5186 @option{-O2} turns on all optimization flags specified by @option{-O}. It
5187 also turns on the following optimization flags:
5188 @gccoptlist{-fthread-jumps @gol
5189 -falign-functions -falign-jumps @gol
5190 -falign-loops -falign-labels @gol
5193 -fcse-follow-jumps -fcse-skip-blocks @gol
5194 -fdelete-null-pointer-checks @gol
5195 -fexpensive-optimizations @gol
5196 -fgcse -fgcse-lm @gol
5197 -foptimize-sibling-calls @gol
5200 -freorder-blocks -freorder-functions @gol
5201 -frerun-cse-after-loop @gol
5202 -fsched-interblock -fsched-spec @gol
5203 -fschedule-insns -fschedule-insns2 @gol
5204 -fstrict-aliasing -fstrict-overflow @gol
5205 -ftree-switch-conversion @gol
5209 Please note the warning under @option{-fgcse} about
5210 invoking @option{-O2} on programs that use computed gotos.
5214 Optimize yet more. @option{-O3} turns on all optimizations specified by
5215 @option{-O2} and also turns on the @option{-finline-functions},
5216 @option{-funswitch-loops}, @option{-fpredictive-commoning},
5217 @option{-fgcse-after-reload} and @option{-ftree-vectorize} options.
5221 Reduce compilation time and make debugging produce the expected
5222 results. This is the default.
5226 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
5227 do not typically increase code size. It also performs further
5228 optimizations designed to reduce code size.
5230 @option{-Os} disables the following optimization flags:
5231 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
5232 -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
5233 -fprefetch-loop-arrays -ftree-vect-loop-version}
5235 If you use multiple @option{-O} options, with or without level numbers,
5236 the last such option is the one that is effective.
5239 Options of the form @option{-f@var{flag}} specify machine-independent
5240 flags. Most flags have both positive and negative forms; the negative
5241 form of @option{-ffoo} would be @option{-fno-foo}. In the table
5242 below, only one of the forms is listed---the one you typically will
5243 use. You can figure out the other form by either removing @samp{no-}
5246 The following options control specific optimizations. They are either
5247 activated by @option{-O} options or are related to ones that are. You
5248 can use the following flags in the rare cases when ``fine-tuning'' of
5249 optimizations to be performed is desired.
5252 @item -fno-default-inline
5253 @opindex fno-default-inline
5254 Do not make member functions inline by default merely because they are
5255 defined inside the class scope (C++ only). Otherwise, when you specify
5256 @w{@option{-O}}, member functions defined inside class scope are compiled
5257 inline by default; i.e., you don't need to add @samp{inline} in front of
5258 the member function name.
5260 @item -fno-defer-pop
5261 @opindex fno-defer-pop
5262 Always pop the arguments to each function call as soon as that function
5263 returns. For machines which must pop arguments after a function call,
5264 the compiler normally lets arguments accumulate on the stack for several
5265 function calls and pops them all at once.
5267 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5269 @item -fforward-propagate
5270 @opindex fforward-propagate
5271 Perform a forward propagation pass on RTL@. The pass tries to combine two
5272 instructions and checks if the result can be simplified. If loop unrolling
5273 is active, two passes are performed and the second is scheduled after
5276 This option is enabled by default at optimization levels @option{-O2},
5277 @option{-O3}, @option{-Os}.
5279 @item -fomit-frame-pointer
5280 @opindex fomit-frame-pointer
5281 Don't keep the frame pointer in a register for functions that
5282 don't need one. This avoids the instructions to save, set up and
5283 restore frame pointers; it also makes an extra register available
5284 in many functions. @strong{It also makes debugging impossible on
5287 On some machines, such as the VAX, this flag has no effect, because
5288 the standard calling sequence automatically handles the frame pointer
5289 and nothing is saved by pretending it doesn't exist. The
5290 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
5291 whether a target machine supports this flag. @xref{Registers,,Register
5292 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
5294 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5296 @item -foptimize-sibling-calls
5297 @opindex foptimize-sibling-calls
5298 Optimize sibling and tail recursive calls.
5300 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5304 Don't pay attention to the @code{inline} keyword. Normally this option
5305 is used to keep the compiler from expanding any functions inline.
5306 Note that if you are not optimizing, no functions can be expanded inline.
5308 @item -finline-small-functions
5309 @opindex finline-small-functions
5310 Integrate functions into their callers when their body is smaller than expected
5311 function call code (so overall size of program gets smaller). The compiler
5312 heuristically decides which functions are simple enough to be worth integrating
5315 Enabled at level @option{-O2}.
5317 @item -finline-functions
5318 @opindex finline-functions
5319 Integrate all simple functions into their callers. The compiler
5320 heuristically decides which functions are simple enough to be worth
5321 integrating in this way.
5323 If all calls to a given function are integrated, and the function is
5324 declared @code{static}, then the function is normally not output as
5325 assembler code in its own right.
5327 Enabled at level @option{-O3}.
5329 @item -finline-functions-called-once
5330 @opindex finline-functions-called-once
5331 Consider all @code{static} functions called once for inlining into their
5332 caller even if they are not marked @code{inline}. If a call to a given
5333 function is integrated, then the function is not output as assembler code
5336 Enabled if @option{-funit-at-a-time} is enabled.
5338 @item -fearly-inlining
5339 @opindex fearly-inlining
5340 Inline functions marked by @code{always_inline} and functions whose body seems
5341 smaller than the function call overhead early before doing
5342 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
5343 makes profiling significantly cheaper and usually inlining faster on programs
5344 having large chains of nested wrapper functions.
5348 @item -finline-limit=@var{n}
5349 @opindex finline-limit
5350 By default, GCC limits the size of functions that can be inlined. This flag
5351 allows coarse control of this limit. @var{n} is the size of functions that
5352 can be inlined in number of pseudo instructions.
5354 Inlining is actually controlled by a number of parameters, which may be
5355 specified individually by using @option{--param @var{name}=@var{value}}.
5356 The @option{-finline-limit=@var{n}} option sets some of these parameters
5360 @item max-inline-insns-single
5361 is set to @var{n}/2.
5362 @item max-inline-insns-auto
5363 is set to @var{n}/2.
5366 See below for a documentation of the individual
5367 parameters controlling inlining and for the defaults of these parameters.
5369 @emph{Note:} there may be no value to @option{-finline-limit} that results
5370 in default behavior.
5372 @emph{Note:} pseudo instruction represents, in this particular context, an
5373 abstract measurement of function's size. In no way does it represent a count
5374 of assembly instructions and as such its exact meaning might change from one
5375 release to an another.
5377 @item -fkeep-inline-functions
5378 @opindex fkeep-inline-functions
5379 In C, emit @code{static} functions that are declared @code{inline}
5380 into the object file, even if the function has been inlined into all
5381 of its callers. This switch does not affect functions using the
5382 @code{extern inline} extension in GNU C89@. In C++, emit any and all
5383 inline functions into the object file.
5385 @item -fkeep-static-consts
5386 @opindex fkeep-static-consts
5387 Emit variables declared @code{static const} when optimization isn't turned
5388 on, even if the variables aren't referenced.
5390 GCC enables this option by default. If you want to force the compiler to
5391 check if the variable was referenced, regardless of whether or not
5392 optimization is turned on, use the @option{-fno-keep-static-consts} option.
5394 @item -fmerge-constants
5395 @opindex fmerge-constants
5396 Attempt to merge identical constants (string constants and floating point
5397 constants) across compilation units.
5399 This option is the default for optimized compilation if the assembler and
5400 linker support it. Use @option{-fno-merge-constants} to inhibit this
5403 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5405 @item -fmerge-all-constants
5406 @opindex fmerge-all-constants
5407 Attempt to merge identical constants and identical variables.
5409 This option implies @option{-fmerge-constants}. In addition to
5410 @option{-fmerge-constants} this considers e.g.@: even constant initialized
5411 arrays or initialized constant variables with integral or floating point
5412 types. Languages like C or C++ require each non-automatic variable to
5413 have distinct location, so using this option will result in non-conforming
5416 @item -fmodulo-sched
5417 @opindex fmodulo-sched
5418 Perform swing modulo scheduling immediately before the first scheduling
5419 pass. This pass looks at innermost loops and reorders their
5420 instructions by overlapping different iterations.
5422 @item -fmodulo-sched-allow-regmoves
5423 @opindex fmodulo-sched-allow-regmoves
5424 Perform more aggressive SMS based modulo scheduling with register moves
5425 allowed. By setting this flag certain anti-dependences edges will be
5426 deleted which will trigger the generation of reg-moves based on the
5427 life-range analysis. This option is effective only with
5428 @option{-fmodulo-sched} enabled.
5430 @item -fno-branch-count-reg
5431 @opindex fno-branch-count-reg
5432 Do not use ``decrement and branch'' instructions on a count register,
5433 but instead generate a sequence of instructions that decrement a
5434 register, compare it against zero, then branch based upon the result.
5435 This option is only meaningful on architectures that support such
5436 instructions, which include x86, PowerPC, IA-64 and S/390.
5438 The default is @option{-fbranch-count-reg}.
5440 @item -fno-function-cse
5441 @opindex fno-function-cse
5442 Do not put function addresses in registers; make each instruction that
5443 calls a constant function contain the function's address explicitly.
5445 This option results in less efficient code, but some strange hacks
5446 that alter the assembler output may be confused by the optimizations
5447 performed when this option is not used.
5449 The default is @option{-ffunction-cse}
5451 @item -fno-zero-initialized-in-bss
5452 @opindex fno-zero-initialized-in-bss
5453 If the target supports a BSS section, GCC by default puts variables that
5454 are initialized to zero into BSS@. This can save space in the resulting
5457 This option turns off this behavior because some programs explicitly
5458 rely on variables going to the data section. E.g., so that the
5459 resulting executable can find the beginning of that section and/or make
5460 assumptions based on that.
5462 The default is @option{-fzero-initialized-in-bss}.
5464 @item -fmudflap -fmudflapth -fmudflapir
5468 @cindex bounds checking
5470 For front-ends that support it (C and C++), instrument all risky
5471 pointer/array dereferencing operations, some standard library
5472 string/heap functions, and some other associated constructs with
5473 range/validity tests. Modules so instrumented should be immune to
5474 buffer overflows, invalid heap use, and some other classes of C/C++
5475 programming errors. The instrumentation relies on a separate runtime
5476 library (@file{libmudflap}), which will be linked into a program if
5477 @option{-fmudflap} is given at link time. Run-time behavior of the
5478 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
5479 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
5482 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
5483 link if your program is multi-threaded. Use @option{-fmudflapir}, in
5484 addition to @option{-fmudflap} or @option{-fmudflapth}, if
5485 instrumentation should ignore pointer reads. This produces less
5486 instrumentation (and therefore faster execution) and still provides
5487 some protection against outright memory corrupting writes, but allows
5488 erroneously read data to propagate within a program.
5490 @item -fthread-jumps
5491 @opindex fthread-jumps
5492 Perform optimizations where we check to see if a jump branches to a
5493 location where another comparison subsumed by the first is found. If
5494 so, the first branch is redirected to either the destination of the
5495 second branch or a point immediately following it, depending on whether
5496 the condition is known to be true or false.
5498 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5500 @item -fsplit-wide-types
5501 @opindex fsplit-wide-types
5502 When using a type that occupies multiple registers, such as @code{long
5503 long} on a 32-bit system, split the registers apart and allocate them
5504 independently. This normally generates better code for those types,
5505 but may make debugging more difficult.
5507 Enabled at levels @option{-O}, @option{-O2}, @option{-O3},
5510 @item -fcse-follow-jumps
5511 @opindex fcse-follow-jumps
5512 In common subexpression elimination (CSE), scan through jump instructions
5513 when the target of the jump is not reached by any other path. For
5514 example, when CSE encounters an @code{if} statement with an
5515 @code{else} clause, CSE will follow the jump when the condition
5518 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5520 @item -fcse-skip-blocks
5521 @opindex fcse-skip-blocks
5522 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
5523 follow jumps which conditionally skip over blocks. When CSE
5524 encounters a simple @code{if} statement with no else clause,
5525 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
5526 body of the @code{if}.
5528 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5530 @item -frerun-cse-after-loop
5531 @opindex frerun-cse-after-loop
5532 Re-run common subexpression elimination after loop optimizations has been
5535 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5539 Perform a global common subexpression elimination pass.
5540 This pass also performs global constant and copy propagation.
5542 @emph{Note:} When compiling a program using computed gotos, a GCC
5543 extension, you may get better runtime performance if you disable
5544 the global common subexpression elimination pass by adding
5545 @option{-fno-gcse} to the command line.
5547 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5551 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
5552 attempt to move loads which are only killed by stores into themselves. This
5553 allows a loop containing a load/store sequence to be changed to a load outside
5554 the loop, and a copy/store within the loop.
5556 Enabled by default when gcse is enabled.
5560 When @option{-fgcse-sm} is enabled, a store motion pass is run after
5561 global common subexpression elimination. This pass will attempt to move
5562 stores out of loops. When used in conjunction with @option{-fgcse-lm},
5563 loops containing a load/store sequence can be changed to a load before
5564 the loop and a store after the loop.
5566 Not enabled at any optimization level.
5570 When @option{-fgcse-las} is enabled, the global common subexpression
5571 elimination pass eliminates redundant loads that come after stores to the
5572 same memory location (both partial and full redundancies).
5574 Not enabled at any optimization level.
5576 @item -fgcse-after-reload
5577 @opindex fgcse-after-reload
5578 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
5579 pass is performed after reload. The purpose of this pass is to cleanup
5582 @item -funsafe-loop-optimizations
5583 @opindex funsafe-loop-optimizations
5584 If given, the loop optimizer will assume that loop indices do not
5585 overflow, and that the loops with nontrivial exit condition are not
5586 infinite. This enables a wider range of loop optimizations even if
5587 the loop optimizer itself cannot prove that these assumptions are valid.
5588 Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you
5589 if it finds this kind of loop.
5591 @item -fcrossjumping
5592 @opindex fcrossjumping
5593 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
5594 resulting code may or may not perform better than without cross-jumping.
5596 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5598 @item -fauto-inc-dec
5599 @opindex fauto-inc-dec
5600 Combine increments or decrements of addresses with memory accesses.
5601 This pass is always skipped on architectures that do not have
5602 instructions to support this. Enabled by default at @option{-O} and
5603 higher on architectures that support this.
5607 Perform dead code elimination (DCE) on RTL@.
5608 Enabled by default at @option{-O} and higher.
5612 Perform dead store elimination (DSE) on RTL@.
5613 Enabled by default at @option{-O} and higher.
5615 @item -fif-conversion
5616 @opindex fif-conversion
5617 Attempt to transform conditional jumps into branch-less equivalents. This
5618 include use of conditional moves, min, max, set flags and abs instructions, and
5619 some tricks doable by standard arithmetics. The use of conditional execution
5620 on chips where it is available is controlled by @code{if-conversion2}.
5622 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5624 @item -fif-conversion2
5625 @opindex fif-conversion2
5626 Use conditional execution (where available) to transform conditional jumps into
5627 branch-less equivalents.
5629 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5631 @item -fdelete-null-pointer-checks
5632 @opindex fdelete-null-pointer-checks
5633 Use global dataflow analysis to identify and eliminate useless checks
5634 for null pointers. The compiler assumes that dereferencing a null
5635 pointer would have halted the program. If a pointer is checked after
5636 it has already been dereferenced, it cannot be null.
5638 In some environments, this assumption is not true, and programs can
5639 safely dereference null pointers. Use
5640 @option{-fno-delete-null-pointer-checks} to disable this optimization
5641 for programs which depend on that behavior.
5643 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5645 @item -fexpensive-optimizations
5646 @opindex fexpensive-optimizations
5647 Perform a number of minor optimizations that are relatively expensive.
5649 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5651 @item -foptimize-register-move
5653 @opindex foptimize-register-move
5655 Attempt to reassign register numbers in move instructions and as
5656 operands of other simple instructions in order to maximize the amount of
5657 register tying. This is especially helpful on machines with two-operand
5660 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
5663 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5665 @item -fdelayed-branch
5666 @opindex fdelayed-branch
5667 If supported for the target machine, attempt to reorder instructions
5668 to exploit instruction slots available after delayed branch
5671 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5673 @item -fschedule-insns
5674 @opindex fschedule-insns
5675 If supported for the target machine, attempt to reorder instructions to
5676 eliminate execution stalls due to required data being unavailable. This
5677 helps machines that have slow floating point or memory load instructions
5678 by allowing other instructions to be issued until the result of the load
5679 or floating point instruction is required.
5681 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5683 @item -fschedule-insns2
5684 @opindex fschedule-insns2
5685 Similar to @option{-fschedule-insns}, but requests an additional pass of
5686 instruction scheduling after register allocation has been done. This is
5687 especially useful on machines with a relatively small number of
5688 registers and where memory load instructions take more than one cycle.
5690 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5692 @item -fno-sched-interblock
5693 @opindex fno-sched-interblock
5694 Don't schedule instructions across basic blocks. This is normally
5695 enabled by default when scheduling before register allocation, i.e.@:
5696 with @option{-fschedule-insns} or at @option{-O2} or higher.
5698 @item -fno-sched-spec
5699 @opindex fno-sched-spec
5700 Don't allow speculative motion of non-load instructions. This is normally
5701 enabled by default when scheduling before register allocation, i.e.@:
5702 with @option{-fschedule-insns} or at @option{-O2} or higher.
5704 @item -fsched-spec-load
5705 @opindex fsched-spec-load
5706 Allow speculative motion of some load instructions. This only makes
5707 sense when scheduling before register allocation, i.e.@: with
5708 @option{-fschedule-insns} or at @option{-O2} or higher.
5710 @item -fsched-spec-load-dangerous
5711 @opindex fsched-spec-load-dangerous
5712 Allow speculative motion of more load instructions. This only makes
5713 sense when scheduling before register allocation, i.e.@: with
5714 @option{-fschedule-insns} or at @option{-O2} or higher.
5716 @item -fsched-stalled-insns
5717 @itemx -fsched-stalled-insns=@var{n}
5718 @opindex fsched-stalled-insns
5719 Define how many insns (if any) can be moved prematurely from the queue
5720 of stalled insns into the ready list, during the second scheduling pass.
5721 @option{-fno-sched-stalled-insns} means that no insns will be moved
5722 prematurely, @option{-fsched-stalled-insns=0} means there is no limit
5723 on how many queued insns can be moved prematurely.
5724 @option{-fsched-stalled-insns} without a value is equivalent to
5725 @option{-fsched-stalled-insns=1}.
5727 @item -fsched-stalled-insns-dep
5728 @itemx -fsched-stalled-insns-dep=@var{n}
5729 @opindex fsched-stalled-insns-dep
5730 Define how many insn groups (cycles) will be examined for a dependency
5731 on a stalled insn that is candidate for premature removal from the queue
5732 of stalled insns. This has an effect only during the second scheduling pass,
5733 and only if @option{-fsched-stalled-insns} is used.
5734 @option{-fno-sched-stalled-insns-dep} is equivalent to
5735 @option{-fsched-stalled-insns-dep=0}.
5736 @option{-fsched-stalled-insns-dep} without a value is equivalent to
5737 @option{-fsched-stalled-insns-dep=1}.
5739 @item -fsched2-use-superblocks
5740 @opindex fsched2-use-superblocks
5741 When scheduling after register allocation, do use superblock scheduling
5742 algorithm. Superblock scheduling allows motion across basic block boundaries
5743 resulting on faster schedules. This option is experimental, as not all machine
5744 descriptions used by GCC model the CPU closely enough to avoid unreliable
5745 results from the algorithm.
5747 This only makes sense when scheduling after register allocation, i.e.@: with
5748 @option{-fschedule-insns2} or at @option{-O2} or higher.
5750 @item -fsched2-use-traces
5751 @opindex fsched2-use-traces
5752 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
5753 allocation and additionally perform code duplication in order to increase the
5754 size of superblocks using tracer pass. See @option{-ftracer} for details on
5757 This mode should produce faster but significantly longer programs. Also
5758 without @option{-fbranch-probabilities} the traces constructed may not
5759 match the reality and hurt the performance. This only makes
5760 sense when scheduling after register allocation, i.e.@: with
5761 @option{-fschedule-insns2} or at @option{-O2} or higher.
5765 Eliminate redundant sign extension instructions and move the non-redundant
5766 ones to optimal placement using lazy code motion (LCM).
5768 @item -freschedule-modulo-scheduled-loops
5769 @opindex freschedule-modulo-scheduled-loops
5770 The modulo scheduling comes before the traditional scheduling, if a loop
5771 was modulo scheduled we may want to prevent the later scheduling passes
5772 from changing its schedule, we use this option to control that.
5774 @item -fcaller-saves
5775 @opindex fcaller-saves
5776 Enable values to be allocated in registers that will be clobbered by
5777 function calls, by emitting extra instructions to save and restore the
5778 registers around such calls. Such allocation is done only when it
5779 seems to result in better code than would otherwise be produced.
5781 This option is always enabled by default on certain machines, usually
5782 those which have no call-preserved registers to use instead.
5784 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5786 @item -ftree-reassoc
5787 @opindex ftree-reassoc
5788 Perform reassociation on trees. This flag is enabled by default
5789 at @option{-O} and higher.
5793 Perform partial redundancy elimination (PRE) on trees. This flag is
5794 enabled by default at @option{-O2} and @option{-O3}.
5798 Perform full redundancy elimination (FRE) on trees. The difference
5799 between FRE and PRE is that FRE only considers expressions
5800 that are computed on all paths leading to the redundant computation.
5801 This analysis is faster than PRE, though it exposes fewer redundancies.
5802 This flag is enabled by default at @option{-O} and higher.
5804 @item -ftree-copy-prop
5805 @opindex ftree-copy-prop
5806 Perform copy propagation on trees. This pass eliminates unnecessary
5807 copy operations. This flag is enabled by default at @option{-O} and
5810 @item -fipa-pure-const
5811 @opindex fipa-pure-const
5812 Discover which functions are pure or constant.
5813 Enabled by default at @option{-O} and higher.
5815 @item -fipa-reference
5816 @opindex fipa-reference
5817 Discover which static variables do not escape cannot escape the
5819 Enabled by default at @option{-O} and higher.
5821 @item -fipa-struct-reorg
5822 @opindex fipa-struct-reorg
5823 Perform structure reorganization optimization, that change C-like structures
5824 layout in order to better utilize spatial locality. This transformation is
5825 affective for programs containing arrays of structures. Available in two
5826 compilation modes: profile-based (enabled with @option{-fprofile-generate})
5827 or static (which uses built-in heuristics). Require @option{-fipa-type-escape}
5828 to provide the safety of this transformation. It works only in whole program
5829 mode, so it requires @option{-fwhole-program} and @option{-combine} to be
5830 enabled. Structures considered @samp{cold} by this transformation are not
5831 affected (see @option{--param struct-reorg-cold-struct-ratio=@var{value}}).
5833 With this flag, the program debug info reflects a new structure layout.
5837 Perform interprocedural pointer analysis.
5841 Perform interprocedural constant propagation.
5842 This optimization analyzes the program to determine when values passed
5843 to functions are constants and then optimizes accordingly.
5844 This optimization can substantially increase performance
5845 if the application has constants passed to functions, but
5846 because this optimization can create multiple copies of functions,
5847 it may significantly increase code size.
5849 @item -fipa-matrix-reorg
5850 @opindex fipa-matrix-reorg
5851 Perform matrix flattening and transposing.
5852 Matrix flattening tries to replace a m-dimensional matrix
5853 with its equivalent n-dimensional matrix, where n < m.
5854 This reduces the level of indirection needed for accessing the elements
5855 of the matrix. The second optimization is matrix transposing that
5856 attemps to change the order of the matrix's dimensions in order to
5857 improve cache locality.
5858 Both optimizations need fwhole-program flag.
5859 Transposing is enabled only if profiling information is avaliable.
5864 Perform forward store motion on trees. This flag is
5865 enabled by default at @option{-O} and higher.
5869 Perform sparse conditional constant propagation (CCP) on trees. This
5870 pass only operates on local scalar variables and is enabled by default
5871 at @option{-O} and higher.
5873 @item -ftree-store-ccp
5874 @opindex ftree-store-ccp
5875 Perform sparse conditional constant propagation (CCP) on trees. This
5876 pass operates on both local scalar variables and memory stores and
5877 loads (global variables, structures, arrays, etc). This flag is
5878 enabled by default at @option{-O2} and higher.
5880 @item -ftree-switch-conversion
5881 Perform conversion of simple initializations in a switch to
5882 initializations from a scalar array. This flag is enabled by default
5883 at @option{-O2} and higher.
5887 Perform dead code elimination (DCE) on trees. This flag is enabled by
5888 default at @option{-O} and higher.
5890 @item -ftree-builtin-call-dce
5891 @opindex ftree-builtin-call-dce
5892 Perform conditional dead code elimination (DCE) for calls to builtin functions
5893 that may set @code{errno} but are otherwise side-effect free. This flag is
5894 enabled by default at @option{-O2} and higher if @option{-Os} is not also
5897 @item -ftree-dominator-opts
5898 @opindex ftree-dominator-opts
5899 Perform a variety of simple scalar cleanups (constant/copy
5900 propagation, redundancy elimination, range propagation and expression
5901 simplification) based on a dominator tree traversal. This also
5902 performs jump threading (to reduce jumps to jumps). This flag is
5903 enabled by default at @option{-O} and higher.
5907 Perform dead store elimination (DSE) on trees. A dead store is a store into
5908 a memory location which will later be overwritten by another store without
5909 any intervening loads. In this case the earlier store can be deleted. This
5910 flag is enabled by default at @option{-O} and higher.
5914 Perform loop header copying on trees. This is beneficial since it increases
5915 effectiveness of code motion optimizations. It also saves one jump. This flag
5916 is enabled by default at @option{-O} and higher. It is not enabled
5917 for @option{-Os}, since it usually increases code size.
5919 @item -ftree-loop-optimize
5920 @opindex ftree-loop-optimize
5921 Perform loop optimizations on trees. This flag is enabled by default
5922 at @option{-O} and higher.
5924 @item -ftree-loop-linear
5925 @opindex ftree-loop-linear
5926 Perform linear loop transformations on tree. This flag can improve cache
5927 performance and allow further loop optimizations to take place.
5929 @item -fcheck-data-deps
5930 @opindex fcheck-data-deps
5931 Compare the results of several data dependence analyzers. This option
5932 is used for debugging the data dependence analyzers.
5934 @item -ftree-loop-distribution
5935 Perform loop distribution. This flag can improve cache performance on
5936 big loop bodies and allow further loop optimizations, like
5937 parallelization or vectorization, to take place. For example, the loop
5954 @item -ftree-loop-im
5955 @opindex ftree-loop-im
5956 Perform loop invariant motion on trees. This pass moves only invariants that
5957 would be hard to handle at RTL level (function calls, operations that expand to
5958 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
5959 operands of conditions that are invariant out of the loop, so that we can use
5960 just trivial invariantness analysis in loop unswitching. The pass also includes
5963 @item -ftree-loop-ivcanon
5964 @opindex ftree-loop-ivcanon
5965 Create a canonical counter for number of iterations in the loop for that
5966 determining number of iterations requires complicated analysis. Later
5967 optimizations then may determine the number easily. Useful especially
5968 in connection with unrolling.
5972 Perform induction variable optimizations (strength reduction, induction
5973 variable merging and induction variable elimination) on trees.
5975 @item -ftree-parallelize-loops=n
5976 @opindex ftree-parallelize-loops
5977 Parallelize loops, i.e., split their iteration space to run in n threads.
5978 This is only possible for loops whose iterations are independent
5979 and can be arbitrarily reordered. The optimization is only
5980 profitable on multiprocessor machines, for loops that are CPU-intensive,
5981 rather than constrained e.g.@: by memory bandwidth. This option
5982 implies @option{-pthread}, and thus is only supported on targets
5983 that have support for @option{-pthread}.
5987 Perform scalar replacement of aggregates. This pass replaces structure
5988 references with scalars to prevent committing structures to memory too
5989 early. This flag is enabled by default at @option{-O} and higher.
5991 @item -ftree-copyrename
5992 @opindex ftree-copyrename
5993 Perform copy renaming on trees. This pass attempts to rename compiler
5994 temporaries to other variables at copy locations, usually resulting in
5995 variable names which more closely resemble the original variables. This flag
5996 is enabled by default at @option{-O} and higher.
6000 Perform temporary expression replacement during the SSA->normal phase. Single
6001 use/single def temporaries are replaced at their use location with their
6002 defining expression. This results in non-GIMPLE code, but gives the expanders
6003 much more complex trees to work on resulting in better RTL generation. This is
6004 enabled by default at @option{-O} and higher.
6006 @item -ftree-vectorize
6007 @opindex ftree-vectorize
6008 Perform loop vectorization on trees. This flag is enabled by default at
6011 @item -ftree-vect-loop-version
6012 @opindex ftree-vect-loop-version
6013 Perform loop versioning when doing loop vectorization on trees. When a loop
6014 appears to be vectorizable except that data alignment or data dependence cannot
6015 be determined at compile time then vectorized and non-vectorized versions of
6016 the loop are generated along with runtime checks for alignment or dependence
6017 to control which version is executed. This option is enabled by default
6018 except at level @option{-Os} where it is disabled.
6020 @item -fvect-cost-model
6021 @opindex fvect-cost-model
6022 Enable cost model for vectorization.
6026 Perform Value Range Propagation on trees. This is similar to the
6027 constant propagation pass, but instead of values, ranges of values are
6028 propagated. This allows the optimizers to remove unnecessary range
6029 checks like array bound checks and null pointer checks. This is
6030 enabled by default at @option{-O2} and higher. Null pointer check
6031 elimination is only done if @option{-fdelete-null-pointer-checks} is
6036 Perform tail duplication to enlarge superblock size. This transformation
6037 simplifies the control flow of the function allowing other optimizations to do
6040 @item -funroll-loops
6041 @opindex funroll-loops
6042 Unroll loops whose number of iterations can be determined at compile
6043 time or upon entry to the loop. @option{-funroll-loops} implies
6044 @option{-frerun-cse-after-loop}. This option makes code larger,
6045 and may or may not make it run faster.
6047 @item -funroll-all-loops
6048 @opindex funroll-all-loops
6049 Unroll all loops, even if their number of iterations is uncertain when
6050 the loop is entered. This usually makes programs run more slowly.
6051 @option{-funroll-all-loops} implies the same options as
6052 @option{-funroll-loops},
6054 @item -fsplit-ivs-in-unroller
6055 @opindex fsplit-ivs-in-unroller
6056 Enables expressing of values of induction variables in later iterations
6057 of the unrolled loop using the value in the first iteration. This breaks
6058 long dependency chains, thus improving efficiency of the scheduling passes.
6060 Combination of @option{-fweb} and CSE is often sufficient to obtain the
6061 same effect. However in cases the loop body is more complicated than
6062 a single basic block, this is not reliable. It also does not work at all
6063 on some of the architectures due to restrictions in the CSE pass.
6065 This optimization is enabled by default.
6067 @item -fvariable-expansion-in-unroller
6068 @opindex fvariable-expansion-in-unroller
6069 With this option, the compiler will create multiple copies of some
6070 local variables when unrolling a loop which can result in superior code.
6072 @item -fpredictive-commoning
6073 @opindex fpredictive-commoning
6074 Perform predictive commoning optimization, i.e., reusing computations
6075 (especially memory loads and stores) performed in previous
6076 iterations of loops.
6078 This option is enabled at level @option{-O3}.
6080 @item -fprefetch-loop-arrays
6081 @opindex fprefetch-loop-arrays
6082 If supported by the target machine, generate instructions to prefetch
6083 memory to improve the performance of loops that access large arrays.
6085 This option may generate better or worse code; results are highly
6086 dependent on the structure of loops within the source code.
6088 Disabled at level @option{-Os}.
6091 @itemx -fno-peephole2
6092 @opindex fno-peephole
6093 @opindex fno-peephole2
6094 Disable any machine-specific peephole optimizations. The difference
6095 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
6096 are implemented in the compiler; some targets use one, some use the
6097 other, a few use both.
6099 @option{-fpeephole} is enabled by default.
6100 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6102 @item -fno-guess-branch-probability
6103 @opindex fno-guess-branch-probability
6104 Do not guess branch probabilities using heuristics.
6106 GCC will use heuristics to guess branch probabilities if they are
6107 not provided by profiling feedback (@option{-fprofile-arcs}). These
6108 heuristics are based on the control flow graph. If some branch probabilities
6109 are specified by @samp{__builtin_expect}, then the heuristics will be
6110 used to guess branch probabilities for the rest of the control flow graph,
6111 taking the @samp{__builtin_expect} info into account. The interactions
6112 between the heuristics and @samp{__builtin_expect} can be complex, and in
6113 some cases, it may be useful to disable the heuristics so that the effects
6114 of @samp{__builtin_expect} are easier to understand.
6116 The default is @option{-fguess-branch-probability} at levels
6117 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6119 @item -freorder-blocks
6120 @opindex freorder-blocks
6121 Reorder basic blocks in the compiled function in order to reduce number of
6122 taken branches and improve code locality.
6124 Enabled at levels @option{-O2}, @option{-O3}.
6126 @item -freorder-blocks-and-partition
6127 @opindex freorder-blocks-and-partition
6128 In addition to reordering basic blocks in the compiled function, in order
6129 to reduce number of taken branches, partitions hot and cold basic blocks
6130 into separate sections of the assembly and .o files, to improve
6131 paging and cache locality performance.
6133 This optimization is automatically turned off in the presence of
6134 exception handling, for linkonce sections, for functions with a user-defined
6135 section attribute and on any architecture that does not support named
6138 @item -freorder-functions
6139 @opindex freorder-functions
6140 Reorder functions in the object file in order to
6141 improve code locality. This is implemented by using special
6142 subsections @code{.text.hot} for most frequently executed functions and
6143 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
6144 the linker so object file format must support named sections and linker must
6145 place them in a reasonable way.
6147 Also profile feedback must be available in to make this option effective. See
6148 @option{-fprofile-arcs} for details.
6150 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6152 @item -fstrict-aliasing
6153 @opindex fstrict-aliasing
6154 Allows the compiler to assume the strictest aliasing rules applicable to
6155 the language being compiled. For C (and C++), this activates
6156 optimizations based on the type of expressions. In particular, an
6157 object of one type is assumed never to reside at the same address as an
6158 object of a different type, unless the types are almost the same. For
6159 example, an @code{unsigned int} can alias an @code{int}, but not a
6160 @code{void*} or a @code{double}. A character type may alias any other
6163 @anchor{Type-punning}Pay special attention to code like this:
6176 The practice of reading from a different union member than the one most
6177 recently written to (called ``type-punning'') is common. Even with
6178 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
6179 is accessed through the union type. So, the code above will work as
6180 expected. @xref{Structures unions enumerations and bit-fields
6181 implementation}. However, this code might not:
6192 Similarly, access by taking the address, casting the resulting pointer
6193 and dereferencing the result has undefined behavior, even if the cast
6194 uses a union type, e.g.:
6198 return ((union a_union *) &d)->i;
6202 The @option{-fstrict-aliasing} option is enabled at levels
6203 @option{-O2}, @option{-O3}, @option{-Os}.
6205 @item -fstrict-overflow
6206 @opindex fstrict-overflow
6207 Allow the compiler to assume strict signed overflow rules, depending
6208 on the language being compiled. For C (and C++) this means that
6209 overflow when doing arithmetic with signed numbers is undefined, which
6210 means that the compiler may assume that it will not happen. This
6211 permits various optimizations. For example, the compiler will assume
6212 that an expression like @code{i + 10 > i} will always be true for
6213 signed @code{i}. This assumption is only valid if signed overflow is
6214 undefined, as the expression is false if @code{i + 10} overflows when
6215 using twos complement arithmetic. When this option is in effect any
6216 attempt to determine whether an operation on signed numbers will
6217 overflow must be written carefully to not actually involve overflow.
6219 This option also allows the compiler to assume strict pointer
6220 semantics: given a pointer to an object, if adding an offset to that
6221 pointer does not produce a pointer to the same object, the addition is
6222 undefined. This permits the compiler to conclude that @code{p + u >
6223 p} is always true for a pointer @code{p} and unsigned integer
6224 @code{u}. This assumption is only valid because pointer wraparound is
6225 undefined, as the expression is false if @code{p + u} overflows using
6226 twos complement arithmetic.
6228 See also the @option{-fwrapv} option. Using @option{-fwrapv} means
6229 that integer signed overflow is fully defined: it wraps. When
6230 @option{-fwrapv} is used, there is no difference between
6231 @option{-fstrict-overflow} and @option{-fno-strict-overflow} for
6232 integers. With @option{-fwrapv} certain types of overflow are
6233 permitted. For example, if the compiler gets an overflow when doing
6234 arithmetic on constants, the overflowed value can still be used with
6235 @option{-fwrapv}, but not otherwise.
6237 The @option{-fstrict-overflow} option is enabled at levels
6238 @option{-O2}, @option{-O3}, @option{-Os}.
6240 @item -falign-functions
6241 @itemx -falign-functions=@var{n}
6242 @opindex falign-functions
6243 Align the start of functions to the next power-of-two greater than
6244 @var{n}, skipping up to @var{n} bytes. For instance,
6245 @option{-falign-functions=32} aligns functions to the next 32-byte
6246 boundary, but @option{-falign-functions=24} would align to the next
6247 32-byte boundary only if this can be done by skipping 23 bytes or less.
6249 @option{-fno-align-functions} and @option{-falign-functions=1} are
6250 equivalent and mean that functions will not be aligned.
6252 Some assemblers only support this flag when @var{n} is a power of two;
6253 in that case, it is rounded up.
6255 If @var{n} is not specified or is zero, use a machine-dependent default.
6257 Enabled at levels @option{-O2}, @option{-O3}.
6259 @item -falign-labels
6260 @itemx -falign-labels=@var{n}
6261 @opindex falign-labels
6262 Align all branch targets to a power-of-two boundary, skipping up to
6263 @var{n} bytes like @option{-falign-functions}. This option can easily
6264 make code slower, because it must insert dummy operations for when the
6265 branch target is reached in the usual flow of the code.
6267 @option{-fno-align-labels} and @option{-falign-labels=1} are
6268 equivalent and mean that labels will not be aligned.
6270 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
6271 are greater than this value, then their values are used instead.
6273 If @var{n} is not specified or is zero, use a machine-dependent default
6274 which is very likely to be @samp{1}, meaning no alignment.
6276 Enabled at levels @option{-O2}, @option{-O3}.
6279 @itemx -falign-loops=@var{n}
6280 @opindex falign-loops
6281 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
6282 like @option{-falign-functions}. The hope is that the loop will be
6283 executed many times, which will make up for any execution of the dummy
6286 @option{-fno-align-loops} and @option{-falign-loops=1} are
6287 equivalent and mean that loops will not be aligned.
6289 If @var{n} is not specified or is zero, use a machine-dependent default.
6291 Enabled at levels @option{-O2}, @option{-O3}.
6294 @itemx -falign-jumps=@var{n}
6295 @opindex falign-jumps
6296 Align branch targets to a power-of-two boundary, for branch targets
6297 where the targets can only be reached by jumping, skipping up to @var{n}
6298 bytes like @option{-falign-functions}. In this case, no dummy operations
6301 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
6302 equivalent and mean that loops will not be aligned.
6304 If @var{n} is not specified or is zero, use a machine-dependent default.
6306 Enabled at levels @option{-O2}, @option{-O3}.
6308 @item -funit-at-a-time
6309 @opindex funit-at-a-time
6310 Parse the whole compilation unit before starting to produce code.
6311 This allows some extra optimizations to take place but consumes
6312 more memory (in general). There are some compatibility issues
6313 with @emph{unit-at-a-time} mode:
6316 enabling @emph{unit-at-a-time} mode may change the order
6317 in which functions, variables, and top-level @code{asm} statements
6318 are emitted, and will likely break code relying on some particular
6319 ordering. The majority of such top-level @code{asm} statements,
6320 though, can be replaced by @code{section} attributes. The
6321 @option{fno-toplevel-reorder} option may be used to keep the ordering
6322 used in the input file, at the cost of some optimizations.
6325 @emph{unit-at-a-time} mode removes unreferenced static variables
6326 and functions. This may result in undefined references
6327 when an @code{asm} statement refers directly to variables or functions
6328 that are otherwise unused. In that case either the variable/function
6329 shall be listed as an operand of the @code{asm} statement operand or,
6330 in the case of top-level @code{asm} statements the attribute @code{used}
6331 shall be used on the declaration.
6334 Static functions now can use non-standard passing conventions that
6335 may break @code{asm} statements calling functions directly. Again,
6336 attribute @code{used} will prevent this behavior.
6339 As a temporary workaround, @option{-fno-unit-at-a-time} can be used,
6340 but this scheme may not be supported by future releases of GCC@.
6342 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6344 @item -fno-toplevel-reorder
6345 @opindex fno-toplevel-reorder
6346 Do not reorder top-level functions, variables, and @code{asm}
6347 statements. Output them in the same order that they appear in the
6348 input file. When this option is used, unreferenced static variables
6349 will not be removed. This option is intended to support existing code
6350 which relies on a particular ordering. For new code, it is better to
6355 Constructs webs as commonly used for register allocation purposes and assign
6356 each web individual pseudo register. This allows the register allocation pass
6357 to operate on pseudos directly, but also strengthens several other optimization
6358 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
6359 however, make debugging impossible, since variables will no longer stay in a
6362 Enabled by default with @option{-funroll-loops}.
6364 @item -fwhole-program
6365 @opindex fwhole-program
6366 Assume that the current compilation unit represents whole program being
6367 compiled. All public functions and variables with the exception of @code{main}
6368 and those merged by attribute @code{externally_visible} become static functions
6369 and in a affect gets more aggressively optimized by interprocedural optimizers.
6370 While this option is equivalent to proper use of @code{static} keyword for
6371 programs consisting of single file, in combination with option
6372 @option{--combine} this flag can be used to compile most of smaller scale C
6373 programs since the functions and variables become local for the whole combined
6374 compilation unit, not for the single source file itself.
6376 This option is not supported for Fortran programs.
6378 @item -fcprop-registers
6379 @opindex fcprop-registers
6380 After register allocation and post-register allocation instruction splitting,
6381 we perform a copy-propagation pass to try to reduce scheduling dependencies
6382 and occasionally eliminate the copy.
6384 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6386 @item -fprofile-dir=@var{path}
6387 @opindex fprofile-dir
6389 Set the directory to search the profile data files in to @var{path}.
6390 This option affects only the profile data generated by
6391 @option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs}
6392 and used by @option{-fprofile-use} and @option{-fbranch-probabilities}
6393 and its related options.
6394 By default, GCC will use the current directory as @var{path}
6395 thus the profile data file will appear in the same directory as the object file.
6397 @item -fprofile-generate
6398 @itemx -fprofile-generate=@var{path}
6399 @opindex fprofile-generate
6401 Enable options usually used for instrumenting application to produce
6402 profile useful for later recompilation with profile feedback based
6403 optimization. You must use @option{-fprofile-generate} both when
6404 compiling and when linking your program.
6406 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
6408 If @var{path} is specified, GCC will look at the @var{path} to find
6409 the profile feeedback data files. See @option{-fprofile-dir}.
6412 @itemx -fprofile-use=@var{path}
6413 @opindex fprofile-use
6414 Enable profile feedback directed optimizations, and optimizations
6415 generally profitable only with profile feedback available.
6417 The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt},
6418 @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}
6420 By default, GCC emits an error message if the feedback profiles do not
6421 match the source code. This error can be turned into a warning by using
6422 @option{-Wcoverage-mismatch}. Note this may result in poorly optimized
6425 If @var{path} is specified, GCC will look at the @var{path} to find
6426 the profile feedback data files. See @option{-fprofile-dir}.
6429 The following options control compiler behavior regarding floating
6430 point arithmetic. These options trade off between speed and
6431 correctness. All must be specifically enabled.
6435 @opindex ffloat-store
6436 Do not store floating point variables in registers, and inhibit other
6437 options that might change whether a floating point value is taken from a
6440 @cindex floating point precision
6441 This option prevents undesirable excess precision on machines such as
6442 the 68000 where the floating registers (of the 68881) keep more
6443 precision than a @code{double} is supposed to have. Similarly for the
6444 x86 architecture. For most programs, the excess precision does only
6445 good, but a few programs rely on the precise definition of IEEE floating
6446 point. Use @option{-ffloat-store} for such programs, after modifying
6447 them to store all pertinent intermediate computations into variables.
6451 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations},
6452 @option{-ffinite-math-only}, @option{-fno-rounding-math},
6453 @option{-fno-signaling-nans} and @option{-fcx-limited-range}.
6455 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
6457 This option is not turned on by any @option{-O} option since
6458 it can result in incorrect output for programs which depend on
6459 an exact implementation of IEEE or ISO rules/specifications for
6460 math functions. It may, however, yield faster code for programs
6461 that do not require the guarantees of these specifications.
6463 @item -fno-math-errno
6464 @opindex fno-math-errno
6465 Do not set ERRNO after calling math functions that are executed
6466 with a single instruction, e.g., sqrt. A program that relies on
6467 IEEE exceptions for math error handling may want to use this flag
6468 for speed while maintaining IEEE arithmetic compatibility.
6470 This option is not turned on by any @option{-O} option since
6471 it can result in incorrect output for programs which depend on
6472 an exact implementation of IEEE or ISO rules/specifications for
6473 math functions. It may, however, yield faster code for programs
6474 that do not require the guarantees of these specifications.
6476 The default is @option{-fmath-errno}.
6478 On Darwin systems, the math library never sets @code{errno}. There is
6479 therefore no reason for the compiler to consider the possibility that
6480 it might, and @option{-fno-math-errno} is the default.
6482 @item -funsafe-math-optimizations
6483 @opindex funsafe-math-optimizations
6485 Allow optimizations for floating-point arithmetic that (a) assume
6486 that arguments and results are valid and (b) may violate IEEE or
6487 ANSI standards. When used at link-time, it may include libraries
6488 or startup files that change the default FPU control word or other
6489 similar optimizations.
6491 This option is not turned on by any @option{-O} option since
6492 it can result in incorrect output for programs which depend on
6493 an exact implementation of IEEE or ISO rules/specifications for
6494 math functions. It may, however, yield faster code for programs
6495 that do not require the guarantees of these specifications.
6496 Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math},
6497 @option{-fassociative-math} and @option{-freciprocal-math}.
6499 The default is @option{-fno-unsafe-math-optimizations}.
6501 @item -fassociative-math
6502 @opindex fassociative-math
6504 Allow re-association of operands in series of floating-point operations.
6505 This violates the ISO C and C++ language standard by possibly changing
6506 computation result. NOTE: re-ordering may change the sign of zero as
6507 well as ignore NaNs and inhibit or create underflow or overflow (and
6508 thus cannot be used on a code which relies on rounding behavior like
6509 @code{(x + 2**52) - 2**52)}. May also reorder floating-point comparisons
6510 and thus may not be used when ordered comparisons are required.
6511 This option requires that both @option{-fno-signed-zeros} and
6512 @option{-fno-trapping-math} be in effect. Moreover, it doesn't make
6513 much sense with @option{-frounding-math}.
6515 The default is @option{-fno-associative-math}.
6517 @item -freciprocal-math
6518 @opindex freciprocal-math
6520 Allow the reciprocal of a value to be used instead of dividing by
6521 the value if this enables optimizations. For example @code{x / y}
6522 can be replaced with @code{x * (1/y)} which is useful if @code{(1/y)}
6523 is subject to common subexpression elimination. Note that this loses
6524 precision and increases the number of flops operating on the value.
6526 The default is @option{-fno-reciprocal-math}.
6528 @item -ffinite-math-only
6529 @opindex ffinite-math-only
6530 Allow optimizations for floating-point arithmetic that assume
6531 that arguments and results are not NaNs or +-Infs.
6533 This option is not turned on by any @option{-O} option since
6534 it can result in incorrect output for programs which depend on
6535 an exact implementation of IEEE or ISO rules/specifications for
6536 math functions. It may, however, yield faster code for programs
6537 that do not require the guarantees of these specifications.
6539 The default is @option{-fno-finite-math-only}.
6541 @item -fno-signed-zeros
6542 @opindex fno-signed-zeros
6543 Allow optimizations for floating point arithmetic that ignore the
6544 signedness of zero. IEEE arithmetic specifies the behavior of
6545 distinct +0.0 and @minus{}0.0 values, which then prohibits simplification
6546 of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}).
6547 This option implies that the sign of a zero result isn't significant.
6549 The default is @option{-fsigned-zeros}.
6551 @item -fno-trapping-math
6552 @opindex fno-trapping-math
6553 Compile code assuming that floating-point operations cannot generate
6554 user-visible traps. These traps include division by zero, overflow,
6555 underflow, inexact result and invalid operation. This option requires
6556 that @option{-fno-signaling-nans} be in effect. Setting this option may
6557 allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example.
6559 This option should never be turned on by any @option{-O} option since
6560 it can result in incorrect output for programs which depend on
6561 an exact implementation of IEEE or ISO rules/specifications for
6564 The default is @option{-ftrapping-math}.
6566 @item -frounding-math
6567 @opindex frounding-math
6568 Disable transformations and optimizations that assume default floating
6569 point rounding behavior. This is round-to-zero for all floating point
6570 to integer conversions, and round-to-nearest for all other arithmetic
6571 truncations. This option should be specified for programs that change
6572 the FP rounding mode dynamically, or that may be executed with a
6573 non-default rounding mode. This option disables constant folding of
6574 floating point expressions at compile-time (which may be affected by
6575 rounding mode) and arithmetic transformations that are unsafe in the
6576 presence of sign-dependent rounding modes.
6578 The default is @option{-fno-rounding-math}.
6580 This option is experimental and does not currently guarantee to
6581 disable all GCC optimizations that are affected by rounding mode.
6582 Future versions of GCC may provide finer control of this setting
6583 using C99's @code{FENV_ACCESS} pragma. This command line option
6584 will be used to specify the default state for @code{FENV_ACCESS}.
6586 @item -frtl-abstract-sequences
6587 @opindex frtl-abstract-sequences
6588 It is a size optimization method. This option is to find identical
6589 sequences of code, which can be turned into pseudo-procedures and
6590 then replace all occurrences with calls to the newly created
6591 subroutine. It is kind of an opposite of @option{-finline-functions}.
6592 This optimization runs at RTL level.
6594 @item -fsignaling-nans
6595 @opindex fsignaling-nans
6596 Compile code assuming that IEEE signaling NaNs may generate user-visible
6597 traps during floating-point operations. Setting this option disables
6598 optimizations that may change the number of exceptions visible with
6599 signaling NaNs. This option implies @option{-ftrapping-math}.
6601 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
6604 The default is @option{-fno-signaling-nans}.
6606 This option is experimental and does not currently guarantee to
6607 disable all GCC optimizations that affect signaling NaN behavior.
6609 @item -fsingle-precision-constant
6610 @opindex fsingle-precision-constant
6611 Treat floating point constant as single precision constant instead of
6612 implicitly converting it to double precision constant.
6614 @item -fcx-limited-range
6615 @opindex fcx-limited-range
6616 When enabled, this option states that a range reduction step is not
6617 needed when performing complex division. Also, there is no checking
6618 whether the result of a complex multiplication or division is @code{NaN
6619 + I*NaN}, with an attempt to rescue the situation in that case. The
6620 default is @option{-fno-cx-limited-range}, but is enabled by
6621 @option{-ffast-math}.
6623 This option controls the default setting of the ISO C99
6624 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
6627 @item -fcx-fortran-rules
6628 @opindex fcx-fortran-rules
6629 Complex multiplication and division follow Fortran rules. Range
6630 reduction is done as part of complex division, but there is no checking
6631 whether the result of a complex multiplication or division is @code{NaN
6632 + I*NaN}, with an attempt to rescue the situation in that case.
6634 The default is @option{-fno-cx-fortran-rules}.
6638 The following options control optimizations that may improve
6639 performance, but are not enabled by any @option{-O} options. This
6640 section includes experimental options that may produce broken code.
6643 @item -fbranch-probabilities
6644 @opindex fbranch-probabilities
6645 After running a program compiled with @option{-fprofile-arcs}
6646 (@pxref{Debugging Options,, Options for Debugging Your Program or
6647 @command{gcc}}), you can compile it a second time using
6648 @option{-fbranch-probabilities}, to improve optimizations based on
6649 the number of times each branch was taken. When the program
6650 compiled with @option{-fprofile-arcs} exits it saves arc execution
6651 counts to a file called @file{@var{sourcename}.gcda} for each source
6652 file. The information in this data file is very dependent on the
6653 structure of the generated code, so you must use the same source code
6654 and the same optimization options for both compilations.
6656 With @option{-fbranch-probabilities}, GCC puts a
6657 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
6658 These can be used to improve optimization. Currently, they are only
6659 used in one place: in @file{reorg.c}, instead of guessing which path a
6660 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
6661 exactly determine which path is taken more often.
6663 @item -fprofile-values
6664 @opindex fprofile-values
6665 If combined with @option{-fprofile-arcs}, it adds code so that some
6666 data about values of expressions in the program is gathered.
6668 With @option{-fbranch-probabilities}, it reads back the data gathered
6669 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
6670 notes to instructions for their later usage in optimizations.
6672 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
6676 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
6677 a code to gather information about values of expressions.
6679 With @option{-fbranch-probabilities}, it reads back the data gathered
6680 and actually performs the optimizations based on them.
6681 Currently the optimizations include specialization of division operation
6682 using the knowledge about the value of the denominator.
6684 @item -frename-registers
6685 @opindex frename-registers
6686 Attempt to avoid false dependencies in scheduled code by making use
6687 of registers left over after register allocation. This optimization
6688 will most benefit processors with lots of registers. Depending on the
6689 debug information format adopted by the target, however, it can
6690 make debugging impossible, since variables will no longer stay in
6691 a ``home register''.
6693 Enabled by default with @option{-funroll-loops}.
6697 Perform tail duplication to enlarge superblock size. This transformation
6698 simplifies the control flow of the function allowing other optimizations to do
6701 Enabled with @option{-fprofile-use}.
6703 @item -funroll-loops
6704 @opindex funroll-loops
6705 Unroll loops whose number of iterations can be determined at compile time or
6706 upon entry to the loop. @option{-funroll-loops} implies
6707 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
6708 It also turns on complete loop peeling (i.e.@: complete removal of loops with
6709 small constant number of iterations). This option makes code larger, and may
6710 or may not make it run faster.
6712 Enabled with @option{-fprofile-use}.
6714 @item -funroll-all-loops
6715 @opindex funroll-all-loops
6716 Unroll all loops, even if their number of iterations is uncertain when
6717 the loop is entered. This usually makes programs run more slowly.
6718 @option{-funroll-all-loops} implies the same options as
6719 @option{-funroll-loops}.
6722 @opindex fpeel-loops
6723 Peels the loops for that there is enough information that they do not
6724 roll much (from profile feedback). It also turns on complete loop peeling
6725 (i.e.@: complete removal of loops with small constant number of iterations).
6727 Enabled with @option{-fprofile-use}.
6729 @item -fmove-loop-invariants
6730 @opindex fmove-loop-invariants
6731 Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
6732 at level @option{-O1}
6734 @item -funswitch-loops
6735 @opindex funswitch-loops
6736 Move branches with loop invariant conditions out of the loop, with duplicates
6737 of the loop on both branches (modified according to result of the condition).
6739 @item -ffunction-sections
6740 @itemx -fdata-sections
6741 @opindex ffunction-sections
6742 @opindex fdata-sections
6743 Place each function or data item into its own section in the output
6744 file if the target supports arbitrary sections. The name of the
6745 function or the name of the data item determines the section's name
6748 Use these options on systems where the linker can perform optimizations
6749 to improve locality of reference in the instruction space. Most systems
6750 using the ELF object format and SPARC processors running Solaris 2 have
6751 linkers with such optimizations. AIX may have these optimizations in
6754 Only use these options when there are significant benefits from doing
6755 so. When you specify these options, the assembler and linker will
6756 create larger object and executable files and will also be slower.
6757 You will not be able to use @code{gprof} on all systems if you
6758 specify this option and you may have problems with debugging if
6759 you specify both this option and @option{-g}.
6761 @item -fbranch-target-load-optimize
6762 @opindex fbranch-target-load-optimize
6763 Perform branch target register load optimization before prologue / epilogue
6765 The use of target registers can typically be exposed only during reload,
6766 thus hoisting loads out of loops and doing inter-block scheduling needs
6767 a separate optimization pass.
6769 @item -fbranch-target-load-optimize2
6770 @opindex fbranch-target-load-optimize2
6771 Perform branch target register load optimization after prologue / epilogue
6774 @item -fbtr-bb-exclusive
6775 @opindex fbtr-bb-exclusive
6776 When performing branch target register load optimization, don't reuse
6777 branch target registers in within any basic block.
6779 @item -fstack-protector
6780 @opindex fstack-protector
6781 Emit extra code to check for buffer overflows, such as stack smashing
6782 attacks. This is done by adding a guard variable to functions with
6783 vulnerable objects. This includes functions that call alloca, and
6784 functions with buffers larger than 8 bytes. The guards are initialized
6785 when a function is entered and then checked when the function exits.
6786 If a guard check fails, an error message is printed and the program exits.
6788 @item -fstack-protector-all
6789 @opindex fstack-protector-all
6790 Like @option{-fstack-protector} except that all functions are protected.
6792 @item -fsection-anchors
6793 @opindex fsection-anchors
6794 Try to reduce the number of symbolic address calculations by using
6795 shared ``anchor'' symbols to address nearby objects. This transformation
6796 can help to reduce the number of GOT entries and GOT accesses on some
6799 For example, the implementation of the following function @code{foo}:
6803 int foo (void) @{ return a + b + c; @}
6806 would usually calculate the addresses of all three variables, but if you
6807 compile it with @option{-fsection-anchors}, it will access the variables
6808 from a common anchor point instead. The effect is similar to the
6809 following pseudocode (which isn't valid C):
6814 register int *xr = &x;
6815 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
6819 Not all targets support this option.
6821 @item --param @var{name}=@var{value}
6823 In some places, GCC uses various constants to control the amount of
6824 optimization that is done. For example, GCC will not inline functions
6825 that contain more that a certain number of instructions. You can
6826 control some of these constants on the command-line using the
6827 @option{--param} option.
6829 The names of specific parameters, and the meaning of the values, are
6830 tied to the internals of the compiler, and are subject to change
6831 without notice in future releases.
6833 In each case, the @var{value} is an integer. The allowable choices for
6834 @var{name} are given in the following table:
6837 @item sra-max-structure-size
6838 The maximum structure size, in bytes, at which the scalar replacement
6839 of aggregates (SRA) optimization will perform block copies. The
6840 default value, 0, implies that GCC will select the most appropriate
6843 @item sra-field-structure-ratio
6844 The threshold ratio (as a percentage) between instantiated fields and
6845 the complete structure size. We say that if the ratio of the number
6846 of bytes in instantiated fields to the number of bytes in the complete
6847 structure exceeds this parameter, then block copies are not used. The
6850 @item struct-reorg-cold-struct-ratio
6851 The threshold ratio (as a percentage) between a structure frequency
6852 and the frequency of the hottest structure in the program. This parameter
6853 is used by struct-reorg optimization enabled by @option{-fipa-struct-reorg}.
6854 We say that if the ratio of a structure frequency, calculated by profiling,
6855 to the hottest structure frequency in the program is less than this
6856 parameter, then structure reorganization is not applied to this structure.
6859 @item max-crossjump-edges
6860 The maximum number of incoming edges to consider for crossjumping.
6861 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
6862 the number of edges incoming to each block. Increasing values mean
6863 more aggressive optimization, making the compile time increase with
6864 probably small improvement in executable size.
6866 @item min-crossjump-insns
6867 The minimum number of instructions which must be matched at the end
6868 of two blocks before crossjumping will be performed on them. This
6869 value is ignored in the case where all instructions in the block being
6870 crossjumped from are matched. The default value is 5.
6872 @item max-grow-copy-bb-insns
6873 The maximum code size expansion factor when copying basic blocks
6874 instead of jumping. The expansion is relative to a jump instruction.
6875 The default value is 8.
6877 @item max-goto-duplication-insns
6878 The maximum number of instructions to duplicate to a block that jumps
6879 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
6880 passes, GCC factors computed gotos early in the compilation process,
6881 and unfactors them as late as possible. Only computed jumps at the
6882 end of a basic blocks with no more than max-goto-duplication-insns are
6883 unfactored. The default value is 8.
6885 @item max-delay-slot-insn-search
6886 The maximum number of instructions to consider when looking for an
6887 instruction to fill a delay slot. If more than this arbitrary number of
6888 instructions is searched, the time savings from filling the delay slot
6889 will be minimal so stop searching. Increasing values mean more
6890 aggressive optimization, making the compile time increase with probably
6891 small improvement in executable run time.
6893 @item max-delay-slot-live-search
6894 When trying to fill delay slots, the maximum number of instructions to
6895 consider when searching for a block with valid live register
6896 information. Increasing this arbitrarily chosen value means more
6897 aggressive optimization, increasing the compile time. This parameter
6898 should be removed when the delay slot code is rewritten to maintain the
6901 @item max-gcse-memory
6902 The approximate maximum amount of memory that will be allocated in
6903 order to perform the global common subexpression elimination
6904 optimization. If more memory than specified is required, the
6905 optimization will not be done.
6907 @item max-gcse-passes
6908 The maximum number of passes of GCSE to run. The default is 1.
6910 @item max-pending-list-length
6911 The maximum number of pending dependencies scheduling will allow
6912 before flushing the current state and starting over. Large functions
6913 with few branches or calls can create excessively large lists which
6914 needlessly consume memory and resources.
6916 @item max-inline-insns-single
6917 Several parameters control the tree inliner used in gcc.
6918 This number sets the maximum number of instructions (counted in GCC's
6919 internal representation) in a single function that the tree inliner
6920 will consider for inlining. This only affects functions declared
6921 inline and methods implemented in a class declaration (C++).
6922 The default value is 450.
6924 @item max-inline-insns-auto
6925 When you use @option{-finline-functions} (included in @option{-O3}),
6926 a lot of functions that would otherwise not be considered for inlining
6927 by the compiler will be investigated. To those functions, a different
6928 (more restrictive) limit compared to functions declared inline can
6930 The default value is 90.
6932 @item large-function-insns
6933 The limit specifying really large functions. For functions larger than this
6934 limit after inlining inlining is constrained by
6935 @option{--param large-function-growth}. This parameter is useful primarily
6936 to avoid extreme compilation time caused by non-linear algorithms used by the
6938 This parameter is ignored when @option{-funit-at-a-time} is not used.
6939 The default value is 2700.
6941 @item large-function-growth
6942 Specifies maximal growth of large function caused by inlining in percents.
6943 This parameter is ignored when @option{-funit-at-a-time} is not used.
6944 The default value is 100 which limits large function growth to 2.0 times
6947 @item large-unit-insns
6948 The limit specifying large translation unit. Growth caused by inlining of
6949 units larger than this limit is limited by @option{--param inline-unit-growth}.
6950 For small units this might be too tight (consider unit consisting of function A
6951 that is inline and B that just calls A three time. If B is small relative to
6952 A, the growth of unit is 300\% and yet such inlining is very sane. For very
6953 large units consisting of small inlineable functions however the overall unit
6954 growth limit is needed to avoid exponential explosion of code size. Thus for
6955 smaller units, the size is increased to @option{--param large-unit-insns}
6956 before applying @option{--param inline-unit-growth}. The default is 10000
6958 @item inline-unit-growth
6959 Specifies maximal overall growth of the compilation unit caused by inlining.
6960 This parameter is ignored when @option{-funit-at-a-time} is not used.
6961 The default value is 30 which limits unit growth to 1.3 times the original
6964 @item large-stack-frame
6965 The limit specifying large stack frames. While inlining the algorithm is trying
6966 to not grow past this limit too much. Default value is 256 bytes.
6968 @item large-stack-frame-growth
6969 Specifies maximal growth of large stack frames caused by inlining in percents.
6970 The default value is 1000 which limits large stack frame growth to 11 times
6973 @item max-inline-insns-recursive
6974 @itemx max-inline-insns-recursive-auto
6975 Specifies maximum number of instructions out-of-line copy of self recursive inline
6976 function can grow into by performing recursive inlining.
6978 For functions declared inline @option{--param max-inline-insns-recursive} is
6979 taken into account. For function not declared inline, recursive inlining
6980 happens only when @option{-finline-functions} (included in @option{-O3}) is
6981 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
6982 default value is 450.
6984 @item max-inline-recursive-depth
6985 @itemx max-inline-recursive-depth-auto
6986 Specifies maximum recursion depth used by the recursive inlining.
6988 For functions declared inline @option{--param max-inline-recursive-depth} is
6989 taken into account. For function not declared inline, recursive inlining
6990 happens only when @option{-finline-functions} (included in @option{-O3}) is
6991 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
6994 @item min-inline-recursive-probability
6995 Recursive inlining is profitable only for function having deep recursion
6996 in average and can hurt for function having little recursion depth by
6997 increasing the prologue size or complexity of function body to other
7000 When profile feedback is available (see @option{-fprofile-generate}) the actual
7001 recursion depth can be guessed from probability that function will recurse via
7002 given call expression. This parameter limits inlining only to call expression
7003 whose probability exceeds given threshold (in percents). The default value is
7006 @item inline-call-cost
7007 Specify cost of call instruction relative to simple arithmetics operations
7008 (having cost of 1). Increasing this cost disqualifies inlining of non-leaf
7009 functions and at the same time increases size of leaf function that is believed to
7010 reduce function size by being inlined. In effect it increases amount of
7011 inlining for code having large abstraction penalty (many functions that just
7012 pass the arguments to other functions) and decrease inlining for code with low
7013 abstraction penalty. The default value is 12.
7015 @item min-vect-loop-bound
7016 The minimum number of iterations under which a loop will not get vectorized
7017 when @option{-ftree-vectorize} is used. The number of iterations after
7018 vectorization needs to be greater than the value specified by this option
7019 to allow vectorization. The default value is 0.
7021 @item max-unrolled-insns
7022 The maximum number of instructions that a loop should have if that loop
7023 is unrolled, and if the loop is unrolled, it determines how many times
7024 the loop code is unrolled.
7026 @item max-average-unrolled-insns
7027 The maximum number of instructions biased by probabilities of their execution
7028 that a loop should have if that loop is unrolled, and if the loop is unrolled,
7029 it determines how many times the loop code is unrolled.
7031 @item max-unroll-times
7032 The maximum number of unrollings of a single loop.
7034 @item max-peeled-insns
7035 The maximum number of instructions that a loop should have if that loop
7036 is peeled, and if the loop is peeled, it determines how many times
7037 the loop code is peeled.
7039 @item max-peel-times
7040 The maximum number of peelings of a single loop.
7042 @item max-completely-peeled-insns
7043 The maximum number of insns of a completely peeled loop.
7045 @item max-completely-peel-times
7046 The maximum number of iterations of a loop to be suitable for complete peeling.
7048 @item max-unswitch-insns
7049 The maximum number of insns of an unswitched loop.
7051 @item max-unswitch-level
7052 The maximum number of branches unswitched in a single loop.
7055 The minimum cost of an expensive expression in the loop invariant motion.
7057 @item iv-consider-all-candidates-bound
7058 Bound on number of candidates for induction variables below that
7059 all candidates are considered for each use in induction variable
7060 optimizations. Only the most relevant candidates are considered
7061 if there are more candidates, to avoid quadratic time complexity.
7063 @item iv-max-considered-uses
7064 The induction variable optimizations give up on loops that contain more
7065 induction variable uses.
7067 @item iv-always-prune-cand-set-bound
7068 If number of candidates in the set is smaller than this value,
7069 we always try to remove unnecessary ivs from the set during its
7070 optimization when a new iv is added to the set.
7072 @item scev-max-expr-size
7073 Bound on size of expressions used in the scalar evolutions analyzer.
7074 Large expressions slow the analyzer.
7076 @item omega-max-vars
7077 The maximum number of variables in an Omega constraint system.
7078 The default value is 128.
7080 @item omega-max-geqs
7081 The maximum number of inequalities in an Omega constraint system.
7082 The default value is 256.
7085 The maximum number of equalities in an Omega constraint system.
7086 The default value is 128.
7088 @item omega-max-wild-cards
7089 The maximum number of wildcard variables that the Omega solver will
7090 be able to insert. The default value is 18.
7092 @item omega-hash-table-size
7093 The size of the hash table in the Omega solver. The default value is
7096 @item omega-max-keys
7097 The maximal number of keys used by the Omega solver. The default
7100 @item omega-eliminate-redundant-constraints
7101 When set to 1, use expensive methods to eliminate all redundant
7102 constraints. The default value is 0.
7104 @item vect-max-version-for-alignment-checks
7105 The maximum number of runtime checks that can be performed when
7106 doing loop versioning for alignment in the vectorizer. See option
7107 ftree-vect-loop-version for more information.
7109 @item vect-max-version-for-alias-checks
7110 The maximum number of runtime checks that can be performed when
7111 doing loop versioning for alias in the vectorizer. See option
7112 ftree-vect-loop-version for more information.
7114 @item max-iterations-to-track
7116 The maximum number of iterations of a loop the brute force algorithm
7117 for analysis of # of iterations of the loop tries to evaluate.
7119 @item hot-bb-count-fraction
7120 Select fraction of the maximal count of repetitions of basic block in program
7121 given basic block needs to have to be considered hot.
7123 @item hot-bb-frequency-fraction
7124 Select fraction of the maximal frequency of executions of basic block in
7125 function given basic block needs to have to be considered hot
7127 @item max-predicted-iterations
7128 The maximum number of loop iterations we predict statically. This is useful
7129 in cases where function contain single loop with known bound and other loop
7130 with unknown. We predict the known number of iterations correctly, while
7131 the unknown number of iterations average to roughly 10. This means that the
7132 loop without bounds would appear artificially cold relative to the other one.
7134 @item align-threshold
7136 Select fraction of the maximal frequency of executions of basic block in
7137 function given basic block will get aligned.
7139 @item align-loop-iterations
7141 A loop expected to iterate at lest the selected number of iterations will get
7144 @item tracer-dynamic-coverage
7145 @itemx tracer-dynamic-coverage-feedback
7147 This value is used to limit superblock formation once the given percentage of
7148 executed instructions is covered. This limits unnecessary code size
7151 The @option{tracer-dynamic-coverage-feedback} is used only when profile
7152 feedback is available. The real profiles (as opposed to statically estimated
7153 ones) are much less balanced allowing the threshold to be larger value.
7155 @item tracer-max-code-growth
7156 Stop tail duplication once code growth has reached given percentage. This is
7157 rather hokey argument, as most of the duplicates will be eliminated later in
7158 cross jumping, so it may be set to much higher values than is the desired code
7161 @item tracer-min-branch-ratio
7163 Stop reverse growth when the reverse probability of best edge is less than this
7164 threshold (in percent).
7166 @item tracer-min-branch-ratio
7167 @itemx tracer-min-branch-ratio-feedback
7169 Stop forward growth if the best edge do have probability lower than this
7172 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
7173 compilation for profile feedback and one for compilation without. The value
7174 for compilation with profile feedback needs to be more conservative (higher) in
7175 order to make tracer effective.
7177 @item max-cse-path-length
7179 Maximum number of basic blocks on path that cse considers. The default is 10.
7182 The maximum instructions CSE process before flushing. The default is 1000.
7184 @item max-aliased-vops
7186 Maximum number of virtual operands per function allowed to represent
7187 aliases before triggering the alias partitioning heuristic. Alias
7188 partitioning reduces compile times and memory consumption needed for
7189 aliasing at the expense of precision loss in alias information. The
7190 default value for this parameter is 100 for -O1, 500 for -O2 and 1000
7193 Notice that if a function contains more memory statements than the
7194 value of this parameter, it is not really possible to achieve this
7195 reduction. In this case, the compiler will use the number of memory
7196 statements as the value for @option{max-aliased-vops}.
7198 @item avg-aliased-vops
7200 Average number of virtual operands per statement allowed to represent
7201 aliases before triggering the alias partitioning heuristic. This
7202 works in conjunction with @option{max-aliased-vops}. If a function
7203 contains more than @option{max-aliased-vops} virtual operators, then
7204 memory symbols will be grouped into memory partitions until either the
7205 total number of virtual operators is below @option{max-aliased-vops}
7206 or the average number of virtual operators per memory statement is
7207 below @option{avg-aliased-vops}. The default value for this parameter
7208 is 1 for -O1 and -O2, and 3 for -O3.
7210 @item ggc-min-expand
7212 GCC uses a garbage collector to manage its own memory allocation. This
7213 parameter specifies the minimum percentage by which the garbage
7214 collector's heap should be allowed to expand between collections.
7215 Tuning this may improve compilation speed; it has no effect on code
7218 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
7219 RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
7220 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
7221 GCC is not able to calculate RAM on a particular platform, the lower
7222 bound of 30% is used. Setting this parameter and
7223 @option{ggc-min-heapsize} to zero causes a full collection to occur at
7224 every opportunity. This is extremely slow, but can be useful for
7227 @item ggc-min-heapsize
7229 Minimum size of the garbage collector's heap before it begins bothering
7230 to collect garbage. The first collection occurs after the heap expands
7231 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
7232 tuning this may improve compilation speed, and has no effect on code
7235 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
7236 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
7237 with a lower bound of 4096 (four megabytes) and an upper bound of
7238 131072 (128 megabytes). If GCC is not able to calculate RAM on a
7239 particular platform, the lower bound is used. Setting this parameter
7240 very large effectively disables garbage collection. Setting this
7241 parameter and @option{ggc-min-expand} to zero causes a full collection
7242 to occur at every opportunity.
7244 @item max-reload-search-insns
7245 The maximum number of instruction reload should look backward for equivalent
7246 register. Increasing values mean more aggressive optimization, making the
7247 compile time increase with probably slightly better performance. The default
7250 @item max-cselib-memory-locations
7251 The maximum number of memory locations cselib should take into account.
7252 Increasing values mean more aggressive optimization, making the compile time
7253 increase with probably slightly better performance. The default value is 500.
7255 @item reorder-blocks-duplicate
7256 @itemx reorder-blocks-duplicate-feedback
7258 Used by basic block reordering pass to decide whether to use unconditional
7259 branch or duplicate the code on its destination. Code is duplicated when its
7260 estimated size is smaller than this value multiplied by the estimated size of
7261 unconditional jump in the hot spots of the program.
7263 The @option{reorder-block-duplicate-feedback} is used only when profile
7264 feedback is available and may be set to higher values than
7265 @option{reorder-block-duplicate} since information about the hot spots is more
7268 @item max-sched-ready-insns
7269 The maximum number of instructions ready to be issued the scheduler should
7270 consider at any given time during the first scheduling pass. Increasing
7271 values mean more thorough searches, making the compilation time increase
7272 with probably little benefit. The default value is 100.
7274 @item max-sched-region-blocks
7275 The maximum number of blocks in a region to be considered for
7276 interblock scheduling. The default value is 10.
7278 @item max-sched-region-insns
7279 The maximum number of insns in a region to be considered for
7280 interblock scheduling. The default value is 100.
7283 The minimum probability (in percents) of reaching a source block
7284 for interblock speculative scheduling. The default value is 40.
7286 @item max-sched-extend-regions-iters
7287 The maximum number of iterations through CFG to extend regions.
7288 0 - disable region extension,
7289 N - do at most N iterations.
7290 The default value is 0.
7292 @item max-sched-insn-conflict-delay
7293 The maximum conflict delay for an insn to be considered for speculative motion.
7294 The default value is 3.
7296 @item sched-spec-prob-cutoff
7297 The minimal probability of speculation success (in percents), so that
7298 speculative insn will be scheduled.
7299 The default value is 40.
7301 @item max-last-value-rtl
7303 The maximum size measured as number of RTLs that can be recorded in an expression
7304 in combiner for a pseudo register as last known value of that register. The default
7307 @item integer-share-limit
7308 Small integer constants can use a shared data structure, reducing the
7309 compiler's memory usage and increasing its speed. This sets the maximum
7310 value of a shared integer constant. The default value is 256.
7312 @item min-virtual-mappings
7313 Specifies the minimum number of virtual mappings in the incremental
7314 SSA updater that should be registered to trigger the virtual mappings
7315 heuristic defined by virtual-mappings-ratio. The default value is
7318 @item virtual-mappings-ratio
7319 If the number of virtual mappings is virtual-mappings-ratio bigger
7320 than the number of virtual symbols to be updated, then the incremental
7321 SSA updater switches to a full update for those symbols. The default
7324 @item ssp-buffer-size
7325 The minimum size of buffers (i.e.@: arrays) that will receive stack smashing
7326 protection when @option{-fstack-protection} is used.
7328 @item max-jump-thread-duplication-stmts
7329 Maximum number of statements allowed in a block that needs to be
7330 duplicated when threading jumps.
7332 @item max-fields-for-field-sensitive
7333 Maximum number of fields in a structure we will treat in
7334 a field sensitive manner during pointer analysis. The default is zero
7335 for -O0, and -O1 and 100 for -Os, -O2, and -O3.
7337 @item prefetch-latency
7338 Estimate on average number of instructions that are executed before
7339 prefetch finishes. The distance we prefetch ahead is proportional
7340 to this constant. Increasing this number may also lead to less
7341 streams being prefetched (see @option{simultaneous-prefetches}).
7343 @item simultaneous-prefetches
7344 Maximum number of prefetches that can run at the same time.
7346 @item l1-cache-line-size
7347 The size of cache line in L1 cache, in bytes.
7350 The size of L1 cache, in kilobytes.
7353 The size of L2 cache, in kilobytes.
7355 @item use-canonical-types
7356 Whether the compiler should use the ``canonical'' type system. By
7357 default, this should always be 1, which uses a more efficient internal
7358 mechanism for comparing types in C++ and Objective-C++. However, if
7359 bugs in the canonical type system are causing compilation failures,
7360 set this value to 0 to disable canonical types.
7362 @item switch-conversion-max-branch-ratio
7363 Switch initialization conversion will refuse to create arrays that are
7364 bigger than @option{switch-conversion-max-branch-ratio} times the number of
7365 branches in the switch.
7367 @item max-partial-antic-length
7368 Maximum length of the partial antic set computed during the tree
7369 partial redundancy elimination optimization (@option{-ftree-pre}) when
7370 optimizing at @option{-O3} and above. For some sorts of source code
7371 the enhanced partial redundancy elimination optimization can run away,
7372 consuming all of the memory available on the host machine. This
7373 parameter sets a limit on the length of the sets that are computed,
7374 which prevents the runaway behaviour. Setting a value of 0 for
7375 this paramter will allow an unlimited set length.
7377 @item sccvn-max-scc-size
7378 Maximum size of a strongly connected component (SCC) during SCCVN
7379 processing. If this limit is hit, SCCVN processing for the whole
7380 function will not be done and optimizations depending on it will
7381 be disabled. The default maximum SCC size is 10000.
7386 @node Preprocessor Options
7387 @section Options Controlling the Preprocessor
7388 @cindex preprocessor options
7389 @cindex options, preprocessor
7391 These options control the C preprocessor, which is run on each C source
7392 file before actual compilation.
7394 If you use the @option{-E} option, nothing is done except preprocessing.
7395 Some of these options make sense only together with @option{-E} because
7396 they cause the preprocessor output to be unsuitable for actual
7401 You can use @option{-Wp,@var{option}} to bypass the compiler driver
7402 and pass @var{option} directly through to the preprocessor. If
7403 @var{option} contains commas, it is split into multiple options at the
7404 commas. However, many options are modified, translated or interpreted
7405 by the compiler driver before being passed to the preprocessor, and
7406 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
7407 interface is undocumented and subject to change, so whenever possible
7408 you should avoid using @option{-Wp} and let the driver handle the
7411 @item -Xpreprocessor @var{option}
7412 @opindex preprocessor
7413 Pass @var{option} as an option to the preprocessor. You can use this to
7414 supply system-specific preprocessor options which GCC does not know how to
7417 If you want to pass an option that takes an argument, you must use
7418 @option{-Xpreprocessor} twice, once for the option and once for the argument.
7421 @include cppopts.texi
7423 @node Assembler Options
7424 @section Passing Options to the Assembler
7426 @c prevent bad page break with this line
7427 You can pass options to the assembler.
7430 @item -Wa,@var{option}
7432 Pass @var{option} as an option to the assembler. If @var{option}
7433 contains commas, it is split into multiple options at the commas.
7435 @item -Xassembler @var{option}
7437 Pass @var{option} as an option to the assembler. You can use this to
7438 supply system-specific assembler options which GCC does not know how to
7441 If you want to pass an option that takes an argument, you must use
7442 @option{-Xassembler} twice, once for the option and once for the argument.
7447 @section Options for Linking
7448 @cindex link options
7449 @cindex options, linking
7451 These options come into play when the compiler links object files into
7452 an executable output file. They are meaningless if the compiler is
7453 not doing a link step.
7457 @item @var{object-file-name}
7458 A file name that does not end in a special recognized suffix is
7459 considered to name an object file or library. (Object files are
7460 distinguished from libraries by the linker according to the file
7461 contents.) If linking is done, these object files are used as input
7470 If any of these options is used, then the linker is not run, and
7471 object file names should not be used as arguments. @xref{Overall
7475 @item -l@var{library}
7476 @itemx -l @var{library}
7478 Search the library named @var{library} when linking. (The second
7479 alternative with the library as a separate argument is only for
7480 POSIX compliance and is not recommended.)
7482 It makes a difference where in the command you write this option; the
7483 linker searches and processes libraries and object files in the order they
7484 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
7485 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
7486 to functions in @samp{z}, those functions may not be loaded.
7488 The linker searches a standard list of directories for the library,
7489 which is actually a file named @file{lib@var{library}.a}. The linker
7490 then uses this file as if it had been specified precisely by name.
7492 The directories searched include several standard system directories
7493 plus any that you specify with @option{-L}.
7495 Normally the files found this way are library files---archive files
7496 whose members are object files. The linker handles an archive file by
7497 scanning through it for members which define symbols that have so far
7498 been referenced but not defined. But if the file that is found is an
7499 ordinary object file, it is linked in the usual fashion. The only
7500 difference between using an @option{-l} option and specifying a file name
7501 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
7502 and searches several directories.
7506 You need this special case of the @option{-l} option in order to
7507 link an Objective-C or Objective-C++ program.
7510 @opindex nostartfiles
7511 Do not use the standard system startup files when linking.
7512 The standard system libraries are used normally, unless @option{-nostdlib}
7513 or @option{-nodefaultlibs} is used.
7515 @item -nodefaultlibs
7516 @opindex nodefaultlibs
7517 Do not use the standard system libraries when linking.
7518 Only the libraries you specify will be passed to the linker.
7519 The standard startup files are used normally, unless @option{-nostartfiles}
7520 is used. The compiler may generate calls to @code{memcmp},
7521 @code{memset}, @code{memcpy} and @code{memmove}.
7522 These entries are usually resolved by entries in
7523 libc. These entry points should be supplied through some other
7524 mechanism when this option is specified.
7528 Do not use the standard system startup files or libraries when linking.
7529 No startup files and only the libraries you specify will be passed to
7530 the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
7531 @code{memcpy} and @code{memmove}.
7532 These entries are usually resolved by entries in
7533 libc. These entry points should be supplied through some other
7534 mechanism when this option is specified.
7536 @cindex @option{-lgcc}, use with @option{-nostdlib}
7537 @cindex @option{-nostdlib} and unresolved references
7538 @cindex unresolved references and @option{-nostdlib}
7539 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
7540 @cindex @option{-nodefaultlibs} and unresolved references
7541 @cindex unresolved references and @option{-nodefaultlibs}
7542 One of the standard libraries bypassed by @option{-nostdlib} and
7543 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
7544 that GCC uses to overcome shortcomings of particular machines, or special
7545 needs for some languages.
7546 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
7547 Collection (GCC) Internals},
7548 for more discussion of @file{libgcc.a}.)
7549 In most cases, you need @file{libgcc.a} even when you want to avoid
7550 other standard libraries. In other words, when you specify @option{-nostdlib}
7551 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
7552 This ensures that you have no unresolved references to internal GCC
7553 library subroutines. (For example, @samp{__main}, used to ensure C++
7554 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
7555 GNU Compiler Collection (GCC) Internals}.)
7559 Produce a position independent executable on targets which support it.
7560 For predictable results, you must also specify the same set of options
7561 that were used to generate code (@option{-fpie}, @option{-fPIE},
7562 or model suboptions) when you specify this option.
7566 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
7567 that support it. This instructs the linker to add all symbols, not
7568 only used ones, to the dynamic symbol table. This option is needed
7569 for some uses of @code{dlopen} or to allow obtaining backtraces
7570 from within a program.
7574 Remove all symbol table and relocation information from the executable.
7578 On systems that support dynamic linking, this prevents linking with the shared
7579 libraries. On other systems, this option has no effect.
7583 Produce a shared object which can then be linked with other objects to
7584 form an executable. Not all systems support this option. For predictable
7585 results, you must also specify the same set of options that were used to
7586 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
7587 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
7588 needs to build supplementary stub code for constructors to work. On
7589 multi-libbed systems, @samp{gcc -shared} must select the correct support
7590 libraries to link against. Failing to supply the correct flags may lead
7591 to subtle defects. Supplying them in cases where they are not necessary
7594 @item -shared-libgcc
7595 @itemx -static-libgcc
7596 @opindex shared-libgcc
7597 @opindex static-libgcc
7598 On systems that provide @file{libgcc} as a shared library, these options
7599 force the use of either the shared or static version respectively.
7600 If no shared version of @file{libgcc} was built when the compiler was
7601 configured, these options have no effect.
7603 There are several situations in which an application should use the
7604 shared @file{libgcc} instead of the static version. The most common
7605 of these is when the application wishes to throw and catch exceptions
7606 across different shared libraries. In that case, each of the libraries
7607 as well as the application itself should use the shared @file{libgcc}.
7609 Therefore, the G++ and GCJ drivers automatically add
7610 @option{-shared-libgcc} whenever you build a shared library or a main
7611 executable, because C++ and Java programs typically use exceptions, so
7612 this is the right thing to do.
7614 If, instead, you use the GCC driver to create shared libraries, you may
7615 find that they will not always be linked with the shared @file{libgcc}.
7616 If GCC finds, at its configuration time, that you have a non-GNU linker
7617 or a GNU linker that does not support option @option{--eh-frame-hdr},
7618 it will link the shared version of @file{libgcc} into shared libraries
7619 by default. Otherwise, it will take advantage of the linker and optimize
7620 away the linking with the shared version of @file{libgcc}, linking with
7621 the static version of libgcc by default. This allows exceptions to
7622 propagate through such shared libraries, without incurring relocation
7623 costs at library load time.
7625 However, if a library or main executable is supposed to throw or catch
7626 exceptions, you must link it using the G++ or GCJ driver, as appropriate
7627 for the languages used in the program, or using the option
7628 @option{-shared-libgcc}, such that it is linked with the shared
7633 Bind references to global symbols when building a shared object. Warn
7634 about any unresolved references (unless overridden by the link editor
7635 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
7638 @item -Xlinker @var{option}
7640 Pass @var{option} as an option to the linker. You can use this to
7641 supply system-specific linker options which GCC does not know how to
7644 If you want to pass an option that takes an argument, you must use
7645 @option{-Xlinker} twice, once for the option and once for the argument.
7646 For example, to pass @option{-assert definitions}, you must write
7647 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
7648 @option{-Xlinker "-assert definitions"}, because this passes the entire
7649 string as a single argument, which is not what the linker expects.
7651 @item -Wl,@var{option}
7653 Pass @var{option} as an option to the linker. If @var{option} contains
7654 commas, it is split into multiple options at the commas.
7656 @item -u @var{symbol}
7658 Pretend the symbol @var{symbol} is undefined, to force linking of
7659 library modules to define it. You can use @option{-u} multiple times with
7660 different symbols to force loading of additional library modules.
7663 @node Directory Options
7664 @section Options for Directory Search
7665 @cindex directory options
7666 @cindex options, directory search
7669 These options specify directories to search for header files, for
7670 libraries and for parts of the compiler:
7675 Add the directory @var{dir} to the head of the list of directories to be
7676 searched for header files. This can be used to override a system header
7677 file, substituting your own version, since these directories are
7678 searched before the system header file directories. However, you should
7679 not use this option to add directories that contain vendor-supplied
7680 system header files (use @option{-isystem} for that). If you use more than
7681 one @option{-I} option, the directories are scanned in left-to-right
7682 order; the standard system directories come after.
7684 If a standard system include directory, or a directory specified with
7685 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
7686 option will be ignored. The directory will still be searched but as a
7687 system directory at its normal position in the system include chain.
7688 This is to ensure that GCC's procedure to fix buggy system headers and
7689 the ordering for the include_next directive are not inadvertently changed.
7690 If you really need to change the search order for system directories,
7691 use the @option{-nostdinc} and/or @option{-isystem} options.
7693 @item -iquote@var{dir}
7695 Add the directory @var{dir} to the head of the list of directories to
7696 be searched for header files only for the case of @samp{#include
7697 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
7698 otherwise just like @option{-I}.
7702 Add directory @var{dir} to the list of directories to be searched
7705 @item -B@var{prefix}
7707 This option specifies where to find the executables, libraries,
7708 include files, and data files of the compiler itself.
7710 The compiler driver program runs one or more of the subprograms
7711 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
7712 @var{prefix} as a prefix for each program it tries to run, both with and
7713 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
7715 For each subprogram to be run, the compiler driver first tries the
7716 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
7717 was not specified, the driver tries two standard prefixes, which are
7718 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
7719 those results in a file name that is found, the unmodified program
7720 name is searched for using the directories specified in your
7721 @env{PATH} environment variable.
7723 The compiler will check to see if the path provided by the @option{-B}
7724 refers to a directory, and if necessary it will add a directory
7725 separator character at the end of the path.
7727 @option{-B} prefixes that effectively specify directory names also apply
7728 to libraries in the linker, because the compiler translates these
7729 options into @option{-L} options for the linker. They also apply to
7730 includes files in the preprocessor, because the compiler translates these
7731 options into @option{-isystem} options for the preprocessor. In this case,
7732 the compiler appends @samp{include} to the prefix.
7734 The run-time support file @file{libgcc.a} can also be searched for using
7735 the @option{-B} prefix, if needed. If it is not found there, the two
7736 standard prefixes above are tried, and that is all. The file is left
7737 out of the link if it is not found by those means.
7739 Another way to specify a prefix much like the @option{-B} prefix is to use
7740 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
7743 As a special kludge, if the path provided by @option{-B} is
7744 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
7745 9, then it will be replaced by @file{[dir/]include}. This is to help
7746 with boot-strapping the compiler.
7748 @item -specs=@var{file}
7750 Process @var{file} after the compiler reads in the standard @file{specs}
7751 file, in order to override the defaults that the @file{gcc} driver
7752 program uses when determining what switches to pass to @file{cc1},
7753 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
7754 @option{-specs=@var{file}} can be specified on the command line, and they
7755 are processed in order, from left to right.
7757 @item --sysroot=@var{dir}
7759 Use @var{dir} as the logical root directory for headers and libraries.
7760 For example, if the compiler would normally search for headers in
7761 @file{/usr/include} and libraries in @file{/usr/lib}, it will instead
7762 search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
7764 If you use both this option and the @option{-isysroot} option, then
7765 the @option{--sysroot} option will apply to libraries, but the
7766 @option{-isysroot} option will apply to header files.
7768 The GNU linker (beginning with version 2.16) has the necessary support
7769 for this option. If your linker does not support this option, the
7770 header file aspect of @option{--sysroot} will still work, but the
7771 library aspect will not.
7775 This option has been deprecated. Please use @option{-iquote} instead for
7776 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
7777 Any directories you specify with @option{-I} options before the @option{-I-}
7778 option are searched only for the case of @samp{#include "@var{file}"};
7779 they are not searched for @samp{#include <@var{file}>}.
7781 If additional directories are specified with @option{-I} options after
7782 the @option{-I-}, these directories are searched for all @samp{#include}
7783 directives. (Ordinarily @emph{all} @option{-I} directories are used
7786 In addition, the @option{-I-} option inhibits the use of the current
7787 directory (where the current input file came from) as the first search
7788 directory for @samp{#include "@var{file}"}. There is no way to
7789 override this effect of @option{-I-}. With @option{-I.} you can specify
7790 searching the directory which was current when the compiler was
7791 invoked. That is not exactly the same as what the preprocessor does
7792 by default, but it is often satisfactory.
7794 @option{-I-} does not inhibit the use of the standard system directories
7795 for header files. Thus, @option{-I-} and @option{-nostdinc} are
7802 @section Specifying subprocesses and the switches to pass to them
7805 @command{gcc} is a driver program. It performs its job by invoking a
7806 sequence of other programs to do the work of compiling, assembling and
7807 linking. GCC interprets its command-line parameters and uses these to
7808 deduce which programs it should invoke, and which command-line options
7809 it ought to place on their command lines. This behavior is controlled
7810 by @dfn{spec strings}. In most cases there is one spec string for each
7811 program that GCC can invoke, but a few programs have multiple spec
7812 strings to control their behavior. The spec strings built into GCC can
7813 be overridden by using the @option{-specs=} command-line switch to specify
7816 @dfn{Spec files} are plaintext files that are used to construct spec
7817 strings. They consist of a sequence of directives separated by blank
7818 lines. The type of directive is determined by the first non-whitespace
7819 character on the line and it can be one of the following:
7822 @item %@var{command}
7823 Issues a @var{command} to the spec file processor. The commands that can
7827 @item %include <@var{file}>
7829 Search for @var{file} and insert its text at the current point in the
7832 @item %include_noerr <@var{file}>
7833 @cindex %include_noerr
7834 Just like @samp{%include}, but do not generate an error message if the include
7835 file cannot be found.
7837 @item %rename @var{old_name} @var{new_name}
7839 Rename the spec string @var{old_name} to @var{new_name}.
7843 @item *[@var{spec_name}]:
7844 This tells the compiler to create, override or delete the named spec
7845 string. All lines after this directive up to the next directive or
7846 blank line are considered to be the text for the spec string. If this
7847 results in an empty string then the spec will be deleted. (Or, if the
7848 spec did not exist, then nothing will happened.) Otherwise, if the spec
7849 does not currently exist a new spec will be created. If the spec does
7850 exist then its contents will be overridden by the text of this
7851 directive, unless the first character of that text is the @samp{+}
7852 character, in which case the text will be appended to the spec.
7854 @item [@var{suffix}]:
7855 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
7856 and up to the next directive or blank line are considered to make up the
7857 spec string for the indicated suffix. When the compiler encounters an
7858 input file with the named suffix, it will processes the spec string in
7859 order to work out how to compile that file. For example:
7866 This says that any input file whose name ends in @samp{.ZZ} should be
7867 passed to the program @samp{z-compile}, which should be invoked with the
7868 command-line switch @option{-input} and with the result of performing the
7869 @samp{%i} substitution. (See below.)
7871 As an alternative to providing a spec string, the text that follows a
7872 suffix directive can be one of the following:
7875 @item @@@var{language}
7876 This says that the suffix is an alias for a known @var{language}. This is
7877 similar to using the @option{-x} command-line switch to GCC to specify a
7878 language explicitly. For example:
7885 Says that .ZZ files are, in fact, C++ source files.
7888 This causes an error messages saying:
7891 @var{name} compiler not installed on this system.
7895 GCC already has an extensive list of suffixes built into it.
7896 This directive will add an entry to the end of the list of suffixes, but
7897 since the list is searched from the end backwards, it is effectively
7898 possible to override earlier entries using this technique.
7902 GCC has the following spec strings built into it. Spec files can
7903 override these strings or create their own. Note that individual
7904 targets can also add their own spec strings to this list.
7907 asm Options to pass to the assembler
7908 asm_final Options to pass to the assembler post-processor
7909 cpp Options to pass to the C preprocessor
7910 cc1 Options to pass to the C compiler
7911 cc1plus Options to pass to the C++ compiler
7912 endfile Object files to include at the end of the link
7913 link Options to pass to the linker
7914 lib Libraries to include on the command line to the linker
7915 libgcc Decides which GCC support library to pass to the linker
7916 linker Sets the name of the linker
7917 predefines Defines to be passed to the C preprocessor
7918 signed_char Defines to pass to CPP to say whether @code{char} is signed
7920 startfile Object files to include at the start of the link
7923 Here is a small example of a spec file:
7929 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
7932 This example renames the spec called @samp{lib} to @samp{old_lib} and
7933 then overrides the previous definition of @samp{lib} with a new one.
7934 The new definition adds in some extra command-line options before
7935 including the text of the old definition.
7937 @dfn{Spec strings} are a list of command-line options to be passed to their
7938 corresponding program. In addition, the spec strings can contain
7939 @samp{%}-prefixed sequences to substitute variable text or to
7940 conditionally insert text into the command line. Using these constructs
7941 it is possible to generate quite complex command lines.
7943 Here is a table of all defined @samp{%}-sequences for spec
7944 strings. Note that spaces are not generated automatically around the
7945 results of expanding these sequences. Therefore you can concatenate them
7946 together or combine them with constant text in a single argument.
7950 Substitute one @samp{%} into the program name or argument.
7953 Substitute the name of the input file being processed.
7956 Substitute the basename of the input file being processed.
7957 This is the substring up to (and not including) the last period
7958 and not including the directory.
7961 This is the same as @samp{%b}, but include the file suffix (text after
7965 Marks the argument containing or following the @samp{%d} as a
7966 temporary file name, so that that file will be deleted if GCC exits
7967 successfully. Unlike @samp{%g}, this contributes no text to the
7970 @item %g@var{suffix}
7971 Substitute a file name that has suffix @var{suffix} and is chosen
7972 once per compilation, and mark the argument in the same way as
7973 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
7974 name is now chosen in a way that is hard to predict even when previously
7975 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
7976 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
7977 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
7978 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
7979 was simply substituted with a file name chosen once per compilation,
7980 without regard to any appended suffix (which was therefore treated
7981 just like ordinary text), making such attacks more likely to succeed.
7983 @item %u@var{suffix}
7984 Like @samp{%g}, but generates a new temporary file name even if
7985 @samp{%u@var{suffix}} was already seen.
7987 @item %U@var{suffix}
7988 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
7989 new one if there is no such last file name. In the absence of any
7990 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
7991 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
7992 would involve the generation of two distinct file names, one
7993 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
7994 simply substituted with a file name chosen for the previous @samp{%u},
7995 without regard to any appended suffix.
7997 @item %j@var{suffix}
7998 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
7999 writable, and if save-temps is off; otherwise, substitute the name
8000 of a temporary file, just like @samp{%u}. This temporary file is not
8001 meant for communication between processes, but rather as a junk
8004 @item %|@var{suffix}
8005 @itemx %m@var{suffix}
8006 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
8007 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
8008 all. These are the two most common ways to instruct a program that it
8009 should read from standard input or write to standard output. If you
8010 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
8011 construct: see for example @file{f/lang-specs.h}.
8013 @item %.@var{SUFFIX}
8014 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
8015 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
8016 terminated by the next space or %.
8019 Marks the argument containing or following the @samp{%w} as the
8020 designated output file of this compilation. This puts the argument
8021 into the sequence of arguments that @samp{%o} will substitute later.
8024 Substitutes the names of all the output files, with spaces
8025 automatically placed around them. You should write spaces
8026 around the @samp{%o} as well or the results are undefined.
8027 @samp{%o} is for use in the specs for running the linker.
8028 Input files whose names have no recognized suffix are not compiled
8029 at all, but they are included among the output files, so they will
8033 Substitutes the suffix for object files. Note that this is
8034 handled specially when it immediately follows @samp{%g, %u, or %U},
8035 because of the need for those to form complete file names. The
8036 handling is such that @samp{%O} is treated exactly as if it had already
8037 been substituted, except that @samp{%g, %u, and %U} do not currently
8038 support additional @var{suffix} characters following @samp{%O} as they would
8039 following, for example, @samp{.o}.
8042 Substitutes the standard macro predefinitions for the
8043 current target machine. Use this when running @code{cpp}.
8046 Like @samp{%p}, but puts @samp{__} before and after the name of each
8047 predefined macro, except for macros that start with @samp{__} or with
8048 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
8052 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
8053 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
8054 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
8055 and @option{-imultilib} as necessary.
8058 Current argument is the name of a library or startup file of some sort.
8059 Search for that file in a standard list of directories and substitute
8060 the full name found.
8063 Print @var{str} as an error message. @var{str} is terminated by a newline.
8064 Use this when inconsistent options are detected.
8067 Substitute the contents of spec string @var{name} at this point.
8070 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
8072 @item %x@{@var{option}@}
8073 Accumulate an option for @samp{%X}.
8076 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
8080 Output the accumulated assembler options specified by @option{-Wa}.
8083 Output the accumulated preprocessor options specified by @option{-Wp}.
8086 Process the @code{asm} spec. This is used to compute the
8087 switches to be passed to the assembler.
8090 Process the @code{asm_final} spec. This is a spec string for
8091 passing switches to an assembler post-processor, if such a program is
8095 Process the @code{link} spec. This is the spec for computing the
8096 command line passed to the linker. Typically it will make use of the
8097 @samp{%L %G %S %D and %E} sequences.
8100 Dump out a @option{-L} option for each directory that GCC believes might
8101 contain startup files. If the target supports multilibs then the
8102 current multilib directory will be prepended to each of these paths.
8105 Process the @code{lib} spec. This is a spec string for deciding which
8106 libraries should be included on the command line to the linker.
8109 Process the @code{libgcc} spec. This is a spec string for deciding
8110 which GCC support library should be included on the command line to the linker.
8113 Process the @code{startfile} spec. This is a spec for deciding which
8114 object files should be the first ones passed to the linker. Typically
8115 this might be a file named @file{crt0.o}.
8118 Process the @code{endfile} spec. This is a spec string that specifies
8119 the last object files that will be passed to the linker.
8122 Process the @code{cpp} spec. This is used to construct the arguments
8123 to be passed to the C preprocessor.
8126 Process the @code{cc1} spec. This is used to construct the options to be
8127 passed to the actual C compiler (@samp{cc1}).
8130 Process the @code{cc1plus} spec. This is used to construct the options to be
8131 passed to the actual C++ compiler (@samp{cc1plus}).
8134 Substitute the variable part of a matched option. See below.
8135 Note that each comma in the substituted string is replaced by
8139 Remove all occurrences of @code{-S} from the command line. Note---this
8140 command is position dependent. @samp{%} commands in the spec string
8141 before this one will see @code{-S}, @samp{%} commands in the spec string
8142 after this one will not.
8144 @item %:@var{function}(@var{args})
8145 Call the named function @var{function}, passing it @var{args}.
8146 @var{args} is first processed as a nested spec string, then split
8147 into an argument vector in the usual fashion. The function returns
8148 a string which is processed as if it had appeared literally as part
8149 of the current spec.
8151 The following built-in spec functions are provided:
8155 The @code{getenv} spec function takes two arguments: an environment
8156 variable name and a string. If the environment variable is not
8157 defined, a fatal error is issued. Otherwise, the return value is the
8158 value of the environment variable concatenated with the string. For
8159 example, if @env{TOPDIR} is defined as @file{/path/to/top}, then:
8162 %:getenv(TOPDIR /include)
8165 expands to @file{/path/to/top/include}.
8167 @item @code{if-exists}
8168 The @code{if-exists} spec function takes one argument, an absolute
8169 pathname to a file. If the file exists, @code{if-exists} returns the
8170 pathname. Here is a small example of its usage:
8174 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
8177 @item @code{if-exists-else}
8178 The @code{if-exists-else} spec function is similar to the @code{if-exists}
8179 spec function, except that it takes two arguments. The first argument is
8180 an absolute pathname to a file. If the file exists, @code{if-exists-else}
8181 returns the pathname. If it does not exist, it returns the second argument.
8182 This way, @code{if-exists-else} can be used to select one file or another,
8183 based on the existence of the first. Here is a small example of its usage:
8187 crt0%O%s %:if-exists(crti%O%s) \
8188 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
8191 @item @code{replace-outfile}
8192 The @code{replace-outfile} spec function takes two arguments. It looks for the
8193 first argument in the outfiles array and replaces it with the second argument. Here
8194 is a small example of its usage:
8197 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
8200 @item @code{print-asm-header}
8201 The @code{print-asm-header} function takes no arguments and simply
8202 prints a banner like:
8208 Use "-Wa,OPTION" to pass "OPTION" to the assembler.
8211 It is used to separate compiler options from assembler options
8212 in the @option{--target-help} output.
8216 Substitutes the @code{-S} switch, if that switch was given to GCC@.
8217 If that switch was not specified, this substitutes nothing. Note that
8218 the leading dash is omitted when specifying this option, and it is
8219 automatically inserted if the substitution is performed. Thus the spec
8220 string @samp{%@{foo@}} would match the command-line option @option{-foo}
8221 and would output the command line option @option{-foo}.
8223 @item %W@{@code{S}@}
8224 Like %@{@code{S}@} but mark last argument supplied within as a file to be
8227 @item %@{@code{S}*@}
8228 Substitutes all the switches specified to GCC whose names start
8229 with @code{-S}, but which also take an argument. This is used for
8230 switches like @option{-o}, @option{-D}, @option{-I}, etc.
8231 GCC considers @option{-o foo} as being
8232 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
8233 text, including the space. Thus two arguments would be generated.
8235 @item %@{@code{S}*&@code{T}*@}
8236 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
8237 (the order of @code{S} and @code{T} in the spec is not significant).
8238 There can be any number of ampersand-separated variables; for each the
8239 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
8241 @item %@{@code{S}:@code{X}@}
8242 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
8244 @item %@{!@code{S}:@code{X}@}
8245 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
8247 @item %@{@code{S}*:@code{X}@}
8248 Substitutes @code{X} if one or more switches whose names start with
8249 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
8250 once, no matter how many such switches appeared. However, if @code{%*}
8251 appears somewhere in @code{X}, then @code{X} will be substituted once
8252 for each matching switch, with the @code{%*} replaced by the part of
8253 that switch that matched the @code{*}.
8255 @item %@{.@code{S}:@code{X}@}
8256 Substitutes @code{X}, if processing a file with suffix @code{S}.
8258 @item %@{!.@code{S}:@code{X}@}
8259 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
8261 @item %@{,@code{S}:@code{X}@}
8262 Substitutes @code{X}, if processing a file for language @code{S}.
8264 @item %@{!,@code{S}:@code{X}@}
8265 Substitutes @code{X}, if not processing a file for language @code{S}.
8267 @item %@{@code{S}|@code{P}:@code{X}@}
8268 Substitutes @code{X} if either @code{-S} or @code{-P} was given to
8269 GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and
8270 @code{*} sequences as well, although they have a stronger binding than
8271 the @samp{|}. If @code{%*} appears in @code{X}, all of the
8272 alternatives must be starred, and only the first matching alternative
8275 For example, a spec string like this:
8278 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
8281 will output the following command-line options from the following input
8282 command-line options:
8287 -d fred.c -foo -baz -boggle
8288 -d jim.d -bar -baz -boggle
8291 @item %@{S:X; T:Y; :D@}
8293 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
8294 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
8295 be as many clauses as you need. This may be combined with @code{.},
8296 @code{,}, @code{!}, @code{|}, and @code{*} as needed.
8301 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
8302 construct may contain other nested @samp{%} constructs or spaces, or
8303 even newlines. They are processed as usual, as described above.
8304 Trailing white space in @code{X} is ignored. White space may also
8305 appear anywhere on the left side of the colon in these constructs,
8306 except between @code{.} or @code{*} and the corresponding word.
8308 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
8309 handled specifically in these constructs. If another value of
8310 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
8311 @option{-W} switch is found later in the command line, the earlier
8312 switch value is ignored, except with @{@code{S}*@} where @code{S} is
8313 just one letter, which passes all matching options.
8315 The character @samp{|} at the beginning of the predicate text is used to
8316 indicate that a command should be piped to the following command, but
8317 only if @option{-pipe} is specified.
8319 It is built into GCC which switches take arguments and which do not.
8320 (You might think it would be useful to generalize this to allow each
8321 compiler's spec to say which switches take arguments. But this cannot
8322 be done in a consistent fashion. GCC cannot even decide which input
8323 files have been specified without knowing which switches take arguments,
8324 and it must know which input files to compile in order to tell which
8327 GCC also knows implicitly that arguments starting in @option{-l} are to be
8328 treated as compiler output files, and passed to the linker in their
8329 proper position among the other output files.
8331 @c man begin OPTIONS
8333 @node Target Options
8334 @section Specifying Target Machine and Compiler Version
8335 @cindex target options
8336 @cindex cross compiling
8337 @cindex specifying machine version
8338 @cindex specifying compiler version and target machine
8339 @cindex compiler version, specifying
8340 @cindex target machine, specifying
8342 The usual way to run GCC is to run the executable called @file{gcc}, or
8343 @file{<machine>-gcc} when cross-compiling, or
8344 @file{<machine>-gcc-<version>} to run a version other than the one that
8345 was installed last. Sometimes this is inconvenient, so GCC provides
8346 options that will switch to another cross-compiler or version.
8349 @item -b @var{machine}
8351 The argument @var{machine} specifies the target machine for compilation.
8353 The value to use for @var{machine} is the same as was specified as the
8354 machine type when configuring GCC as a cross-compiler. For
8355 example, if a cross-compiler was configured with @samp{configure
8356 arm-elf}, meaning to compile for an arm processor with elf binaries,
8357 then you would specify @option{-b arm-elf} to run that cross compiler.
8358 Because there are other options beginning with @option{-b}, the
8359 configuration must contain a hyphen.
8361 @item -V @var{version}
8363 The argument @var{version} specifies which version of GCC to run.
8364 This is useful when multiple versions are installed. For example,
8365 @var{version} might be @samp{4.0}, meaning to run GCC version 4.0.
8368 The @option{-V} and @option{-b} options work by running the
8369 @file{<machine>-gcc-<version>} executable, so there's no real reason to
8370 use them if you can just run that directly.
8372 @node Submodel Options
8373 @section Hardware Models and Configurations
8374 @cindex submodel options
8375 @cindex specifying hardware config
8376 @cindex hardware models and configurations, specifying
8377 @cindex machine dependent options
8379 Earlier we discussed the standard option @option{-b} which chooses among
8380 different installed compilers for completely different target
8381 machines, such as VAX vs.@: 68000 vs.@: 80386.
8383 In addition, each of these target machine types can have its own
8384 special options, starting with @samp{-m}, to choose among various
8385 hardware models or configurations---for example, 68010 vs 68020,
8386 floating coprocessor or none. A single installed version of the
8387 compiler can compile for any model or configuration, according to the
8390 Some configurations of the compiler also support additional special
8391 options, usually for compatibility with other compilers on the same
8394 @c This list is ordered alphanumerically by subsection name.
8395 @c It should be the same order and spelling as these options are listed
8396 @c in Machine Dependent Options
8402 * Blackfin Options::
8406 * DEC Alpha Options::
8407 * DEC Alpha/VMS Options::
8409 * GNU/Linux Options::
8412 * i386 and x86-64 Options::
8424 * RS/6000 and PowerPC Options::
8425 * S/390 and zSeries Options::
8430 * System V Options::
8435 * Xstormy16 Options::
8441 @subsection ARC Options
8444 These options are defined for ARC implementations:
8449 Compile code for little endian mode. This is the default.
8453 Compile code for big endian mode.
8456 @opindex mmangle-cpu
8457 Prepend the name of the cpu to all public symbol names.
8458 In multiple-processor systems, there are many ARC variants with different
8459 instruction and register set characteristics. This flag prevents code
8460 compiled for one cpu to be linked with code compiled for another.
8461 No facility exists for handling variants that are ``almost identical''.
8462 This is an all or nothing option.
8464 @item -mcpu=@var{cpu}
8466 Compile code for ARC variant @var{cpu}.
8467 Which variants are supported depend on the configuration.
8468 All variants support @option{-mcpu=base}, this is the default.
8470 @item -mtext=@var{text-section}
8471 @itemx -mdata=@var{data-section}
8472 @itemx -mrodata=@var{readonly-data-section}
8476 Put functions, data, and readonly data in @var{text-section},
8477 @var{data-section}, and @var{readonly-data-section} respectively
8478 by default. This can be overridden with the @code{section} attribute.
8479 @xref{Variable Attributes}.
8484 @subsection ARM Options
8487 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
8491 @item -mabi=@var{name}
8493 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
8494 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
8497 @opindex mapcs-frame
8498 Generate a stack frame that is compliant with the ARM Procedure Call
8499 Standard for all functions, even if this is not strictly necessary for
8500 correct execution of the code. Specifying @option{-fomit-frame-pointer}
8501 with this option will cause the stack frames not to be generated for
8502 leaf functions. The default is @option{-mno-apcs-frame}.
8506 This is a synonym for @option{-mapcs-frame}.
8509 @c not currently implemented
8510 @item -mapcs-stack-check
8511 @opindex mapcs-stack-check
8512 Generate code to check the amount of stack space available upon entry to
8513 every function (that actually uses some stack space). If there is
8514 insufficient space available then either the function
8515 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
8516 called, depending upon the amount of stack space required. The run time
8517 system is required to provide these functions. The default is
8518 @option{-mno-apcs-stack-check}, since this produces smaller code.
8520 @c not currently implemented
8522 @opindex mapcs-float
8523 Pass floating point arguments using the float point registers. This is
8524 one of the variants of the APCS@. This option is recommended if the
8525 target hardware has a floating point unit or if a lot of floating point
8526 arithmetic is going to be performed by the code. The default is
8527 @option{-mno-apcs-float}, since integer only code is slightly increased in
8528 size if @option{-mapcs-float} is used.
8530 @c not currently implemented
8531 @item -mapcs-reentrant
8532 @opindex mapcs-reentrant
8533 Generate reentrant, position independent code. The default is
8534 @option{-mno-apcs-reentrant}.
8537 @item -mthumb-interwork
8538 @opindex mthumb-interwork
8539 Generate code which supports calling between the ARM and Thumb
8540 instruction sets. Without this option the two instruction sets cannot
8541 be reliably used inside one program. The default is
8542 @option{-mno-thumb-interwork}, since slightly larger code is generated
8543 when @option{-mthumb-interwork} is specified.
8545 @item -mno-sched-prolog
8546 @opindex mno-sched-prolog
8547 Prevent the reordering of instructions in the function prolog, or the
8548 merging of those instruction with the instructions in the function's
8549 body. This means that all functions will start with a recognizable set
8550 of instructions (or in fact one of a choice from a small set of
8551 different function prologues), and this information can be used to
8552 locate the start if functions inside an executable piece of code. The
8553 default is @option{-msched-prolog}.
8556 @opindex mhard-float
8557 Generate output containing floating point instructions. This is the
8561 @opindex msoft-float
8562 Generate output containing library calls for floating point.
8563 @strong{Warning:} the requisite libraries are not available for all ARM
8564 targets. Normally the facilities of the machine's usual C compiler are
8565 used, but this cannot be done directly in cross-compilation. You must make
8566 your own arrangements to provide suitable library functions for
8569 @option{-msoft-float} changes the calling convention in the output file;
8570 therefore, it is only useful if you compile @emph{all} of a program with
8571 this option. In particular, you need to compile @file{libgcc.a}, the
8572 library that comes with GCC, with @option{-msoft-float} in order for
8575 @item -mfloat-abi=@var{name}
8577 Specifies which ABI to use for floating point values. Permissible values
8578 are: @samp{soft}, @samp{softfp} and @samp{hard}.
8580 @samp{soft} and @samp{hard} are equivalent to @option{-msoft-float}
8581 and @option{-mhard-float} respectively. @samp{softfp} allows the generation
8582 of floating point instructions, but still uses the soft-float calling
8585 @item -mlittle-endian
8586 @opindex mlittle-endian
8587 Generate code for a processor running in little-endian mode. This is
8588 the default for all standard configurations.
8591 @opindex mbig-endian
8592 Generate code for a processor running in big-endian mode; the default is
8593 to compile code for a little-endian processor.
8595 @item -mwords-little-endian
8596 @opindex mwords-little-endian
8597 This option only applies when generating code for big-endian processors.
8598 Generate code for a little-endian word order but a big-endian byte
8599 order. That is, a byte order of the form @samp{32107654}. Note: this
8600 option should only be used if you require compatibility with code for
8601 big-endian ARM processors generated by versions of the compiler prior to
8604 @item -mcpu=@var{name}
8606 This specifies the name of the target ARM processor. GCC uses this name
8607 to determine what kind of instructions it can emit when generating
8608 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
8609 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
8610 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
8611 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
8612 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
8613 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
8614 @samp{arm8}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
8615 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
8616 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
8617 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
8618 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
8619 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
8620 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
8621 @samp{arm1156t2-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s},
8622 @samp{cortex-a8}, @samp{cortex-r4}, @samp{cortex-m3}, @samp{cortex-m1},
8623 @samp{xscale}, @samp{iwmmxt}, @samp{ep9312}.
8625 @item -mtune=@var{name}
8627 This option is very similar to the @option{-mcpu=} option, except that
8628 instead of specifying the actual target processor type, and hence
8629 restricting which instructions can be used, it specifies that GCC should
8630 tune the performance of the code as if the target were of the type
8631 specified in this option, but still choosing the instructions that it
8632 will generate based on the cpu specified by a @option{-mcpu=} option.
8633 For some ARM implementations better performance can be obtained by using
8636 @item -march=@var{name}
8638 This specifies the name of the target ARM architecture. GCC uses this
8639 name to determine what kind of instructions it can emit when generating
8640 assembly code. This option can be used in conjunction with or instead
8641 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
8642 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
8643 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6}, @samp{armv6j},
8644 @samp{armv6t2}, @samp{armv6z}, @samp{armv6zk}, @samp{armv6-m},
8645 @samp{armv7}, @samp{armv7-a}, @samp{armv7-r}, @samp{armv7-m},
8646 @samp{iwmmxt}, @samp{ep9312}.
8648 @item -mfpu=@var{name}
8649 @itemx -mfpe=@var{number}
8650 @itemx -mfp=@var{number}
8654 This specifies what floating point hardware (or hardware emulation) is
8655 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
8656 @samp{fpe3}, @samp{maverick}, @samp{vfp}. @option{-mfp} and @option{-mfpe}
8657 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
8658 with older versions of GCC@.
8660 If @option{-msoft-float} is specified this specifies the format of
8661 floating point values.
8663 @item -mstructure-size-boundary=@var{n}
8664 @opindex mstructure-size-boundary
8665 The size of all structures and unions will be rounded up to a multiple
8666 of the number of bits set by this option. Permissible values are 8, 32
8667 and 64. The default value varies for different toolchains. For the COFF
8668 targeted toolchain the default value is 8. A value of 64 is only allowed
8669 if the underlying ABI supports it.
8671 Specifying the larger number can produce faster, more efficient code, but
8672 can also increase the size of the program. Different values are potentially
8673 incompatible. Code compiled with one value cannot necessarily expect to
8674 work with code or libraries compiled with another value, if they exchange
8675 information using structures or unions.
8677 @item -mabort-on-noreturn
8678 @opindex mabort-on-noreturn
8679 Generate a call to the function @code{abort} at the end of a
8680 @code{noreturn} function. It will be executed if the function tries to
8684 @itemx -mno-long-calls
8685 @opindex mlong-calls
8686 @opindex mno-long-calls
8687 Tells the compiler to perform function calls by first loading the
8688 address of the function into a register and then performing a subroutine
8689 call on this register. This switch is needed if the target function
8690 will lie outside of the 64 megabyte addressing range of the offset based
8691 version of subroutine call instruction.
8693 Even if this switch is enabled, not all function calls will be turned
8694 into long calls. The heuristic is that static functions, functions
8695 which have the @samp{short-call} attribute, functions that are inside
8696 the scope of a @samp{#pragma no_long_calls} directive and functions whose
8697 definitions have already been compiled within the current compilation
8698 unit, will not be turned into long calls. The exception to this rule is
8699 that weak function definitions, functions with the @samp{long-call}
8700 attribute or the @samp{section} attribute, and functions that are within
8701 the scope of a @samp{#pragma long_calls} directive, will always be
8702 turned into long calls.
8704 This feature is not enabled by default. Specifying
8705 @option{-mno-long-calls} will restore the default behavior, as will
8706 placing the function calls within the scope of a @samp{#pragma
8707 long_calls_off} directive. Note these switches have no effect on how
8708 the compiler generates code to handle function calls via function
8711 @item -mnop-fun-dllimport
8712 @opindex mnop-fun-dllimport
8713 Disable support for the @code{dllimport} attribute.
8715 @item -msingle-pic-base
8716 @opindex msingle-pic-base
8717 Treat the register used for PIC addressing as read-only, rather than
8718 loading it in the prologue for each function. The run-time system is
8719 responsible for initializing this register with an appropriate value
8720 before execution begins.
8722 @item -mpic-register=@var{reg}
8723 @opindex mpic-register
8724 Specify the register to be used for PIC addressing. The default is R10
8725 unless stack-checking is enabled, when R9 is used.
8727 @item -mcirrus-fix-invalid-insns
8728 @opindex mcirrus-fix-invalid-insns
8729 @opindex mno-cirrus-fix-invalid-insns
8730 Insert NOPs into the instruction stream to in order to work around
8731 problems with invalid Maverick instruction combinations. This option
8732 is only valid if the @option{-mcpu=ep9312} option has been used to
8733 enable generation of instructions for the Cirrus Maverick floating
8734 point co-processor. This option is not enabled by default, since the
8735 problem is only present in older Maverick implementations. The default
8736 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
8739 @item -mpoke-function-name
8740 @opindex mpoke-function-name
8741 Write the name of each function into the text section, directly
8742 preceding the function prologue. The generated code is similar to this:
8746 .ascii "arm_poke_function_name", 0
8749 .word 0xff000000 + (t1 - t0)
8750 arm_poke_function_name
8752 stmfd sp!, @{fp, ip, lr, pc@}
8756 When performing a stack backtrace, code can inspect the value of
8757 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
8758 location @code{pc - 12} and the top 8 bits are set, then we know that
8759 there is a function name embedded immediately preceding this location
8760 and has length @code{((pc[-3]) & 0xff000000)}.
8764 Generate code for the Thumb instruction set. The default is to
8765 use the 32-bit ARM instruction set.
8766 This option automatically enables either 16-bit Thumb-1 or
8767 mixed 16/32-bit Thumb-2 instructions based on the @option{-mcpu=@var{name}}
8768 and @option{-march=@var{name}} options.
8771 @opindex mtpcs-frame
8772 Generate a stack frame that is compliant with the Thumb Procedure Call
8773 Standard for all non-leaf functions. (A leaf function is one that does
8774 not call any other functions.) The default is @option{-mno-tpcs-frame}.
8776 @item -mtpcs-leaf-frame
8777 @opindex mtpcs-leaf-frame
8778 Generate a stack frame that is compliant with the Thumb Procedure Call
8779 Standard for all leaf functions. (A leaf function is one that does
8780 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
8782 @item -mcallee-super-interworking
8783 @opindex mcallee-super-interworking
8784 Gives all externally visible functions in the file being compiled an ARM
8785 instruction set header which switches to Thumb mode before executing the
8786 rest of the function. This allows these functions to be called from
8787 non-interworking code.
8789 @item -mcaller-super-interworking
8790 @opindex mcaller-super-interworking
8791 Allows calls via function pointers (including virtual functions) to
8792 execute correctly regardless of whether the target code has been
8793 compiled for interworking or not. There is a small overhead in the cost
8794 of executing a function pointer if this option is enabled.
8796 @item -mtp=@var{name}
8798 Specify the access model for the thread local storage pointer. The valid
8799 models are @option{soft}, which generates calls to @code{__aeabi_read_tp},
8800 @option{cp15}, which fetches the thread pointer from @code{cp15} directly
8801 (supported in the arm6k architecture), and @option{auto}, which uses the
8802 best available method for the selected processor. The default setting is
8808 @subsection AVR Options
8811 These options are defined for AVR implementations:
8814 @item -mmcu=@var{mcu}
8816 Specify ATMEL AVR instruction set or MCU type.
8818 Instruction set avr1 is for the minimal AVR core, not supported by the C
8819 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
8820 attiny11, attiny12, attiny15, attiny28).
8822 Instruction set avr2 (default) is for the classic AVR core with up to
8823 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
8824 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
8825 at90c8534, at90s8535).
8827 Instruction set avr3 is for the classic AVR core with up to 128K program
8828 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
8830 Instruction set avr4 is for the enhanced AVR core with up to 8K program
8831 memory space (MCU types: atmega8, atmega83, atmega85).
8833 Instruction set avr5 is for the enhanced AVR core with up to 128K program
8834 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
8835 atmega64, atmega128, at43usb355, at94k).
8839 Output instruction sizes to the asm file.
8841 @item -minit-stack=@var{N}
8842 @opindex minit-stack
8843 Specify the initial stack address, which may be a symbol or numeric value,
8844 @samp{__stack} is the default.
8846 @item -mno-interrupts
8847 @opindex mno-interrupts
8848 Generated code is not compatible with hardware interrupts.
8849 Code size will be smaller.
8851 @item -mcall-prologues
8852 @opindex mcall-prologues
8853 Functions prologues/epilogues expanded as call to appropriate
8854 subroutines. Code size will be smaller.
8856 @item -mno-tablejump
8857 @opindex mno-tablejump
8858 Do not generate tablejump insns which sometimes increase code size.
8861 @opindex mtiny-stack
8862 Change only the low 8 bits of the stack pointer.
8866 Assume int to be 8 bit integer. This affects the sizes of all types: A
8867 char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
8868 and long long will be 4 bytes. Please note that this option does not
8869 comply to the C standards, but it will provide you with smaller code
8873 @node Blackfin Options
8874 @subsection Blackfin Options
8875 @cindex Blackfin Options
8878 @item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]}
8880 Specifies the name of the target Blackfin processor. Currently, @var{cpu}
8881 can be one of @samp{bf522}, @samp{bf523}, @samp{bf524},
8882 @samp{bf525}, @samp{bf526}, @samp{bf527},
8883 @samp{bf531}, @samp{bf532}, @samp{bf533}, @samp{bf534},
8884 @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539},
8885 @samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549},
8887 The optional @var{sirevision} specifies the silicon revision of the target
8888 Blackfin processor. Any workarounds available for the targeted silicon revision
8889 will be enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled.
8890 If @var{sirevision} is @samp{any}, all workarounds for the targeted processor
8891 will be enabled. The @code{__SILICON_REVISION__} macro is defined to two
8892 hexadecimal digits representing the major and minor numbers in the silicon
8893 revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__}
8894 is not defined. If @var{sirevision} is @samp{any}, the
8895 @code{__SILICON_REVISION__} is defined to be @code{0xffff}.
8896 If this optional @var{sirevision} is not used, GCC assumes the latest known
8897 silicon revision of the targeted Blackfin processor.
8899 Support for @samp{bf561} is incomplete. For @samp{bf561},
8900 Only the processor macro is defined.
8901 Without this option, @samp{bf532} is used as the processor by default.
8902 The corresponding predefined processor macros for @var{cpu} is to
8903 be defined. And for @samp{bfin-elf} toolchain, this causes the hardware BSP
8904 provided by libgloss to be linked in if @option{-msim} is not given.
8908 Specifies that the program will be run on the simulator. This causes
8909 the simulator BSP provided by libgloss to be linked in. This option
8910 has effect only for @samp{bfin-elf} toolchain.
8911 Certain other options, such as @option{-mid-shared-library} and
8912 @option{-mfdpic}, imply @option{-msim}.
8914 @item -momit-leaf-frame-pointer
8915 @opindex momit-leaf-frame-pointer
8916 Don't keep the frame pointer in a register for leaf functions. This
8917 avoids the instructions to save, set up and restore frame pointers and
8918 makes an extra register available in leaf functions. The option
8919 @option{-fomit-frame-pointer} removes the frame pointer for all functions
8920 which might make debugging harder.
8922 @item -mspecld-anomaly
8923 @opindex mspecld-anomaly
8924 When enabled, the compiler will ensure that the generated code does not
8925 contain speculative loads after jump instructions. If this option is used,
8926 @code{__WORKAROUND_SPECULATIVE_LOADS} is defined.
8928 @item -mno-specld-anomaly
8929 @opindex mno-specld-anomaly
8930 Don't generate extra code to prevent speculative loads from occurring.
8932 @item -mcsync-anomaly
8933 @opindex mcsync-anomaly
8934 When enabled, the compiler will ensure that the generated code does not
8935 contain CSYNC or SSYNC instructions too soon after conditional branches.
8936 If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined.
8938 @item -mno-csync-anomaly
8939 @opindex mno-csync-anomaly
8940 Don't generate extra code to prevent CSYNC or SSYNC instructions from
8941 occurring too soon after a conditional branch.
8945 When enabled, the compiler is free to take advantage of the knowledge that
8946 the entire program fits into the low 64k of memory.
8949 @opindex mno-low-64k
8950 Assume that the program is arbitrarily large. This is the default.
8952 @item -mstack-check-l1
8953 @opindex mstack-check-l1
8954 Do stack checking using information placed into L1 scratchpad memory by the
8957 @item -mid-shared-library
8958 @opindex mid-shared-library
8959 Generate code that supports shared libraries via the library ID method.
8960 This allows for execute in place and shared libraries in an environment
8961 without virtual memory management. This option implies @option{-fPIC}.
8962 With a @samp{bfin-elf} target, this option implies @option{-msim}.
8964 @item -mno-id-shared-library
8965 @opindex mno-id-shared-library
8966 Generate code that doesn't assume ID based shared libraries are being used.
8967 This is the default.
8969 @item -mleaf-id-shared-library
8970 @opindex mleaf-id-shared-library
8971 Generate code that supports shared libraries via the library ID method,
8972 but assumes that this library or executable won't link against any other
8973 ID shared libraries. That allows the compiler to use faster code for jumps
8976 @item -mno-leaf-id-shared-library
8977 @opindex mno-leaf-id-shared-library
8978 Do not assume that the code being compiled won't link against any ID shared
8979 libraries. Slower code will be generated for jump and call insns.
8981 @item -mshared-library-id=n
8982 @opindex mshared-library-id
8983 Specified the identification number of the ID based shared library being
8984 compiled. Specifying a value of 0 will generate more compact code, specifying
8985 other values will force the allocation of that number to the current
8986 library but is no more space or time efficient than omitting this option.
8990 Generate code that allows the data segment to be located in a different
8991 area of memory from the text segment. This allows for execute in place in
8992 an environment without virtual memory management by eliminating relocations
8993 against the text section.
8996 @opindex mno-sep-data
8997 Generate code that assumes that the data segment follows the text segment.
8998 This is the default.
9001 @itemx -mno-long-calls
9002 @opindex mlong-calls
9003 @opindex mno-long-calls
9004 Tells the compiler to perform function calls by first loading the
9005 address of the function into a register and then performing a subroutine
9006 call on this register. This switch is needed if the target function
9007 will lie outside of the 24 bit addressing range of the offset based
9008 version of subroutine call instruction.
9010 This feature is not enabled by default. Specifying
9011 @option{-mno-long-calls} will restore the default behavior. Note these
9012 switches have no effect on how the compiler generates code to handle
9013 function calls via function pointers.
9017 Link with the fast floating-point library. This library relaxes some of
9018 the IEEE floating-point standard's rules for checking inputs against
9019 Not-a-Number (NAN), in the interest of performance.
9022 @opindex minline-plt
9023 Enable inlining of PLT entries in function calls to functions that are
9024 not known to bind locally. It has no effect without @option{-mfdpic}.
9028 Build standalone application for multicore Blackfin processor. Proper
9029 start files and link scripts will be used to support multicore.
9030 This option defines @code{__BFIN_MULTICORE}. It can only be used with
9031 @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}. It can be used with
9032 @option{-mcorea} or @option{-mcoreb}. If it's used without
9033 @option{-mcorea} or @option{-mcoreb}, single application/dual core
9034 programming model is used. In this model, the main function of Core B
9035 should be named as coreb_main. If it's used with @option{-mcorea} or
9036 @option{-mcoreb}, one application per core programming model is used.
9037 If this option is not used, single core application programming
9042 Build standalone application for Core A of BF561 when using
9043 one application per core programming model. Proper start files
9044 and link scripts will be used to support Core A. This option
9045 defines @code{__BFIN_COREA}. It must be used with @option{-mmulticore}.
9049 Build standalone application for Core B of BF561 when using
9050 one application per core programming model. Proper start files
9051 and link scripts will be used to support Core B. This option
9052 defines @code{__BFIN_COREB}. When this option is used, coreb_main
9053 should be used instead of main. It must be used with
9054 @option{-mmulticore}.
9058 Build standalone application for SDRAM. Proper start files and
9059 link scripts will be used to put the application into SDRAM.
9060 Loader should initialize SDRAM before loading the application
9061 into SDRAM. This option defines @code{__BFIN_SDRAM}.
9065 @subsection CRIS Options
9066 @cindex CRIS Options
9068 These options are defined specifically for the CRIS ports.
9071 @item -march=@var{architecture-type}
9072 @itemx -mcpu=@var{architecture-type}
9075 Generate code for the specified architecture. The choices for
9076 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
9077 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
9078 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
9081 @item -mtune=@var{architecture-type}
9083 Tune to @var{architecture-type} everything applicable about the generated
9084 code, except for the ABI and the set of available instructions. The
9085 choices for @var{architecture-type} are the same as for
9086 @option{-march=@var{architecture-type}}.
9088 @item -mmax-stack-frame=@var{n}
9089 @opindex mmax-stack-frame
9090 Warn when the stack frame of a function exceeds @var{n} bytes.
9096 The options @option{-metrax4} and @option{-metrax100} are synonyms for
9097 @option{-march=v3} and @option{-march=v8} respectively.
9099 @item -mmul-bug-workaround
9100 @itemx -mno-mul-bug-workaround
9101 @opindex mmul-bug-workaround
9102 @opindex mno-mul-bug-workaround
9103 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
9104 models where it applies. This option is active by default.
9108 Enable CRIS-specific verbose debug-related information in the assembly
9109 code. This option also has the effect to turn off the @samp{#NO_APP}
9110 formatted-code indicator to the assembler at the beginning of the
9115 Do not use condition-code results from previous instruction; always emit
9116 compare and test instructions before use of condition codes.
9118 @item -mno-side-effects
9119 @opindex mno-side-effects
9120 Do not emit instructions with side-effects in addressing modes other than
9124 @itemx -mno-stack-align
9126 @itemx -mno-data-align
9127 @itemx -mconst-align
9128 @itemx -mno-const-align
9129 @opindex mstack-align
9130 @opindex mno-stack-align
9131 @opindex mdata-align
9132 @opindex mno-data-align
9133 @opindex mconst-align
9134 @opindex mno-const-align
9135 These options (no-options) arranges (eliminate arrangements) for the
9136 stack-frame, individual data and constants to be aligned for the maximum
9137 single data access size for the chosen CPU model. The default is to
9138 arrange for 32-bit alignment. ABI details such as structure layout are
9139 not affected by these options.
9147 Similar to the stack- data- and const-align options above, these options
9148 arrange for stack-frame, writable data and constants to all be 32-bit,
9149 16-bit or 8-bit aligned. The default is 32-bit alignment.
9151 @item -mno-prologue-epilogue
9152 @itemx -mprologue-epilogue
9153 @opindex mno-prologue-epilogue
9154 @opindex mprologue-epilogue
9155 With @option{-mno-prologue-epilogue}, the normal function prologue and
9156 epilogue that sets up the stack-frame are omitted and no return
9157 instructions or return sequences are generated in the code. Use this
9158 option only together with visual inspection of the compiled code: no
9159 warnings or errors are generated when call-saved registers must be saved,
9160 or storage for local variable needs to be allocated.
9166 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
9167 instruction sequences that load addresses for functions from the PLT part
9168 of the GOT rather than (traditional on other architectures) calls to the
9169 PLT@. The default is @option{-mgotplt}.
9173 Legacy no-op option only recognized with the cris-axis-elf and
9174 cris-axis-linux-gnu targets.
9178 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
9182 This option, recognized for the cris-axis-elf arranges
9183 to link with input-output functions from a simulator library. Code,
9184 initialized data and zero-initialized data are allocated consecutively.
9188 Like @option{-sim}, but pass linker options to locate initialized data at
9189 0x40000000 and zero-initialized data at 0x80000000.
9193 @subsection CRX Options
9196 These options are defined specifically for the CRX ports.
9202 Enable the use of multiply-accumulate instructions. Disabled by default.
9206 Push instructions will be used to pass outgoing arguments when functions
9207 are called. Enabled by default.
9210 @node Darwin Options
9211 @subsection Darwin Options
9212 @cindex Darwin options
9214 These options are defined for all architectures running the Darwin operating
9217 FSF GCC on Darwin does not create ``fat'' object files; it will create
9218 an object file for the single architecture that it was built to
9219 target. Apple's GCC on Darwin does create ``fat'' files if multiple
9220 @option{-arch} options are used; it does so by running the compiler or
9221 linker multiple times and joining the results together with
9224 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
9225 @samp{i686}) is determined by the flags that specify the ISA
9226 that GCC is targetting, like @option{-mcpu} or @option{-march}. The
9227 @option{-force_cpusubtype_ALL} option can be used to override this.
9229 The Darwin tools vary in their behavior when presented with an ISA
9230 mismatch. The assembler, @file{as}, will only permit instructions to
9231 be used that are valid for the subtype of the file it is generating,
9232 so you cannot put 64-bit instructions in an @samp{ppc750} object file.
9233 The linker for shared libraries, @file{/usr/bin/libtool}, will fail
9234 and print an error if asked to create a shared library with a less
9235 restrictive subtype than its input files (for instance, trying to put
9236 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
9237 for executables, @file{ld}, will quietly give the executable the most
9238 restrictive subtype of any of its input files.
9243 Add the framework directory @var{dir} to the head of the list of
9244 directories to be searched for header files. These directories are
9245 interleaved with those specified by @option{-I} options and are
9246 scanned in a left-to-right order.
9248 A framework directory is a directory with frameworks in it. A
9249 framework is a directory with a @samp{"Headers"} and/or
9250 @samp{"PrivateHeaders"} directory contained directly in it that ends
9251 in @samp{".framework"}. The name of a framework is the name of this
9252 directory excluding the @samp{".framework"}. Headers associated with
9253 the framework are found in one of those two directories, with
9254 @samp{"Headers"} being searched first. A subframework is a framework
9255 directory that is in a framework's @samp{"Frameworks"} directory.
9256 Includes of subframework headers can only appear in a header of a
9257 framework that contains the subframework, or in a sibling subframework
9258 header. Two subframeworks are siblings if they occur in the same
9259 framework. A subframework should not have the same name as a
9260 framework, a warning will be issued if this is violated. Currently a
9261 subframework cannot have subframeworks, in the future, the mechanism
9262 may be extended to support this. The standard frameworks can be found
9263 in @samp{"/System/Library/Frameworks"} and
9264 @samp{"/Library/Frameworks"}. An example include looks like
9265 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
9266 the name of the framework and header.h is found in the
9267 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
9269 @item -iframework@var{dir}
9271 Like @option{-F} except the directory is a treated as a system
9272 directory. The main difference between this @option{-iframework} and
9273 @option{-F} is that with @option{-iframework} the compiler does not
9274 warn about constructs contained within header files found via
9275 @var{dir}. This option is valid only for the C family of languages.
9279 Emit debugging information for symbols that are used. For STABS
9280 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
9281 This is by default ON@.
9285 Emit debugging information for all symbols and types.
9287 @item -mmacosx-version-min=@var{version}
9288 The earliest version of MacOS X that this executable will run on
9289 is @var{version}. Typical values of @var{version} include @code{10.1},
9290 @code{10.2}, and @code{10.3.9}.
9292 If the compiler was built to use the system's headers by default,
9293 then the default for this option is the system version on which the
9294 compiler is running, otherwise the default is to make choices which
9295 are compatible with as many systems and code bases as possible.
9299 Enable kernel development mode. The @option{-mkernel} option sets
9300 @option{-static}, @option{-fno-common}, @option{-fno-cxa-atexit},
9301 @option{-fno-exceptions}, @option{-fno-non-call-exceptions},
9302 @option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where
9303 applicable. This mode also sets @option{-mno-altivec},
9304 @option{-msoft-float}, @option{-fno-builtin} and
9305 @option{-mlong-branch} for PowerPC targets.
9307 @item -mone-byte-bool
9308 @opindex mone-byte-bool
9309 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
9310 By default @samp{sizeof(bool)} is @samp{4} when compiling for
9311 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
9312 option has no effect on x86.
9314 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
9315 to generate code that is not binary compatible with code generated
9316 without that switch. Using this switch may require recompiling all
9317 other modules in a program, including system libraries. Use this
9318 switch to conform to a non-default data model.
9320 @item -mfix-and-continue
9321 @itemx -ffix-and-continue
9322 @itemx -findirect-data
9323 @opindex mfix-and-continue
9324 @opindex ffix-and-continue
9325 @opindex findirect-data
9326 Generate code suitable for fast turn around development. Needed to
9327 enable gdb to dynamically load @code{.o} files into already running
9328 programs. @option{-findirect-data} and @option{-ffix-and-continue}
9329 are provided for backwards compatibility.
9333 Loads all members of static archive libraries.
9334 See man ld(1) for more information.
9336 @item -arch_errors_fatal
9337 @opindex arch_errors_fatal
9338 Cause the errors having to do with files that have the wrong architecture
9342 @opindex bind_at_load
9343 Causes the output file to be marked such that the dynamic linker will
9344 bind all undefined references when the file is loaded or launched.
9348 Produce a Mach-o bundle format file.
9349 See man ld(1) for more information.
9351 @item -bundle_loader @var{executable}
9352 @opindex bundle_loader
9353 This option specifies the @var{executable} that will be loading the build
9354 output file being linked. See man ld(1) for more information.
9358 When passed this option, GCC will produce a dynamic library instead of
9359 an executable when linking, using the Darwin @file{libtool} command.
9361 @item -force_cpusubtype_ALL
9362 @opindex force_cpusubtype_ALL
9363 This causes GCC's output file to have the @var{ALL} subtype, instead of
9364 one controlled by the @option{-mcpu} or @option{-march} option.
9366 @item -allowable_client @var{client_name}
9368 @itemx -compatibility_version
9369 @itemx -current_version
9371 @itemx -dependency-file
9373 @itemx -dylinker_install_name
9375 @itemx -exported_symbols_list
9377 @itemx -flat_namespace
9378 @itemx -force_flat_namespace
9379 @itemx -headerpad_max_install_names
9382 @itemx -install_name
9383 @itemx -keep_private_externs
9384 @itemx -multi_module
9385 @itemx -multiply_defined
9386 @itemx -multiply_defined_unused
9388 @itemx -no_dead_strip_inits_and_terms
9389 @itemx -nofixprebinding
9392 @itemx -noseglinkedit
9393 @itemx -pagezero_size
9395 @itemx -prebind_all_twolevel_modules
9396 @itemx -private_bundle
9397 @itemx -read_only_relocs
9399 @itemx -sectobjectsymbols
9403 @itemx -sectobjectsymbols
9406 @itemx -segs_read_only_addr
9407 @itemx -segs_read_write_addr
9408 @itemx -seg_addr_table
9409 @itemx -seg_addr_table_filename
9412 @itemx -segs_read_only_addr
9413 @itemx -segs_read_write_addr
9414 @itemx -single_module
9417 @itemx -sub_umbrella
9418 @itemx -twolevel_namespace
9421 @itemx -unexported_symbols_list
9422 @itemx -weak_reference_mismatches
9424 @opindex allowable_client
9425 @opindex client_name
9426 @opindex compatibility_version
9427 @opindex current_version
9429 @opindex dependency-file
9431 @opindex dylinker_install_name
9433 @opindex exported_symbols_list
9435 @opindex flat_namespace
9436 @opindex force_flat_namespace
9437 @opindex headerpad_max_install_names
9440 @opindex install_name
9441 @opindex keep_private_externs
9442 @opindex multi_module
9443 @opindex multiply_defined
9444 @opindex multiply_defined_unused
9446 @opindex no_dead_strip_inits_and_terms
9447 @opindex nofixprebinding
9448 @opindex nomultidefs
9450 @opindex noseglinkedit
9451 @opindex pagezero_size
9453 @opindex prebind_all_twolevel_modules
9454 @opindex private_bundle
9455 @opindex read_only_relocs
9457 @opindex sectobjectsymbols
9461 @opindex sectobjectsymbols
9464 @opindex segs_read_only_addr
9465 @opindex segs_read_write_addr
9466 @opindex seg_addr_table
9467 @opindex seg_addr_table_filename
9468 @opindex seglinkedit
9470 @opindex segs_read_only_addr
9471 @opindex segs_read_write_addr
9472 @opindex single_module
9474 @opindex sub_library
9475 @opindex sub_umbrella
9476 @opindex twolevel_namespace
9479 @opindex unexported_symbols_list
9480 @opindex weak_reference_mismatches
9481 @opindex whatsloaded
9482 These options are passed to the Darwin linker. The Darwin linker man page
9483 describes them in detail.
9486 @node DEC Alpha Options
9487 @subsection DEC Alpha Options
9489 These @samp{-m} options are defined for the DEC Alpha implementations:
9492 @item -mno-soft-float
9494 @opindex mno-soft-float
9495 @opindex msoft-float
9496 Use (do not use) the hardware floating-point instructions for
9497 floating-point operations. When @option{-msoft-float} is specified,
9498 functions in @file{libgcc.a} will be used to perform floating-point
9499 operations. Unless they are replaced by routines that emulate the
9500 floating-point operations, or compiled in such a way as to call such
9501 emulations routines, these routines will issue floating-point
9502 operations. If you are compiling for an Alpha without floating-point
9503 operations, you must ensure that the library is built so as not to call
9506 Note that Alpha implementations without floating-point operations are
9507 required to have floating-point registers.
9512 @opindex mno-fp-regs
9513 Generate code that uses (does not use) the floating-point register set.
9514 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
9515 register set is not used, floating point operands are passed in integer
9516 registers as if they were integers and floating-point results are passed
9517 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
9518 so any function with a floating-point argument or return value called by code
9519 compiled with @option{-mno-fp-regs} must also be compiled with that
9522 A typical use of this option is building a kernel that does not use,
9523 and hence need not save and restore, any floating-point registers.
9527 The Alpha architecture implements floating-point hardware optimized for
9528 maximum performance. It is mostly compliant with the IEEE floating
9529 point standard. However, for full compliance, software assistance is
9530 required. This option generates code fully IEEE compliant code
9531 @emph{except} that the @var{inexact-flag} is not maintained (see below).
9532 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
9533 defined during compilation. The resulting code is less efficient but is
9534 able to correctly support denormalized numbers and exceptional IEEE
9535 values such as not-a-number and plus/minus infinity. Other Alpha
9536 compilers call this option @option{-ieee_with_no_inexact}.
9538 @item -mieee-with-inexact
9539 @opindex mieee-with-inexact
9540 This is like @option{-mieee} except the generated code also maintains
9541 the IEEE @var{inexact-flag}. Turning on this option causes the
9542 generated code to implement fully-compliant IEEE math. In addition to
9543 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
9544 macro. On some Alpha implementations the resulting code may execute
9545 significantly slower than the code generated by default. Since there is
9546 very little code that depends on the @var{inexact-flag}, you should
9547 normally not specify this option. Other Alpha compilers call this
9548 option @option{-ieee_with_inexact}.
9550 @item -mfp-trap-mode=@var{trap-mode}
9551 @opindex mfp-trap-mode
9552 This option controls what floating-point related traps are enabled.
9553 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
9554 The trap mode can be set to one of four values:
9558 This is the default (normal) setting. The only traps that are enabled
9559 are the ones that cannot be disabled in software (e.g., division by zero
9563 In addition to the traps enabled by @samp{n}, underflow traps are enabled
9567 Like @samp{u}, but the instructions are marked to be safe for software
9568 completion (see Alpha architecture manual for details).
9571 Like @samp{su}, but inexact traps are enabled as well.
9574 @item -mfp-rounding-mode=@var{rounding-mode}
9575 @opindex mfp-rounding-mode
9576 Selects the IEEE rounding mode. Other Alpha compilers call this option
9577 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
9582 Normal IEEE rounding mode. Floating point numbers are rounded towards
9583 the nearest machine number or towards the even machine number in case
9587 Round towards minus infinity.
9590 Chopped rounding mode. Floating point numbers are rounded towards zero.
9593 Dynamic rounding mode. A field in the floating point control register
9594 (@var{fpcr}, see Alpha architecture reference manual) controls the
9595 rounding mode in effect. The C library initializes this register for
9596 rounding towards plus infinity. Thus, unless your program modifies the
9597 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
9600 @item -mtrap-precision=@var{trap-precision}
9601 @opindex mtrap-precision
9602 In the Alpha architecture, floating point traps are imprecise. This
9603 means without software assistance it is impossible to recover from a
9604 floating trap and program execution normally needs to be terminated.
9605 GCC can generate code that can assist operating system trap handlers
9606 in determining the exact location that caused a floating point trap.
9607 Depending on the requirements of an application, different levels of
9608 precisions can be selected:
9612 Program precision. This option is the default and means a trap handler
9613 can only identify which program caused a floating point exception.
9616 Function precision. The trap handler can determine the function that
9617 caused a floating point exception.
9620 Instruction precision. The trap handler can determine the exact
9621 instruction that caused a floating point exception.
9624 Other Alpha compilers provide the equivalent options called
9625 @option{-scope_safe} and @option{-resumption_safe}.
9627 @item -mieee-conformant
9628 @opindex mieee-conformant
9629 This option marks the generated code as IEEE conformant. You must not
9630 use this option unless you also specify @option{-mtrap-precision=i} and either
9631 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
9632 is to emit the line @samp{.eflag 48} in the function prologue of the
9633 generated assembly file. Under DEC Unix, this has the effect that
9634 IEEE-conformant math library routines will be linked in.
9636 @item -mbuild-constants
9637 @opindex mbuild-constants
9638 Normally GCC examines a 32- or 64-bit integer constant to
9639 see if it can construct it from smaller constants in two or three
9640 instructions. If it cannot, it will output the constant as a literal and
9641 generate code to load it from the data segment at runtime.
9643 Use this option to require GCC to construct @emph{all} integer constants
9644 using code, even if it takes more instructions (the maximum is six).
9646 You would typically use this option to build a shared library dynamic
9647 loader. Itself a shared library, it must relocate itself in memory
9648 before it can find the variables and constants in its own data segment.
9654 Select whether to generate code to be assembled by the vendor-supplied
9655 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
9673 Indicate whether GCC should generate code to use the optional BWX,
9674 CIX, FIX and MAX instruction sets. The default is to use the instruction
9675 sets supported by the CPU type specified via @option{-mcpu=} option or that
9676 of the CPU on which GCC was built if none was specified.
9681 @opindex mfloat-ieee
9682 Generate code that uses (does not use) VAX F and G floating point
9683 arithmetic instead of IEEE single and double precision.
9685 @item -mexplicit-relocs
9686 @itemx -mno-explicit-relocs
9687 @opindex mexplicit-relocs
9688 @opindex mno-explicit-relocs
9689 Older Alpha assemblers provided no way to generate symbol relocations
9690 except via assembler macros. Use of these macros does not allow
9691 optimal instruction scheduling. GNU binutils as of version 2.12
9692 supports a new syntax that allows the compiler to explicitly mark
9693 which relocations should apply to which instructions. This option
9694 is mostly useful for debugging, as GCC detects the capabilities of
9695 the assembler when it is built and sets the default accordingly.
9699 @opindex msmall-data
9700 @opindex mlarge-data
9701 When @option{-mexplicit-relocs} is in effect, static data is
9702 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
9703 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
9704 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
9705 16-bit relocations off of the @code{$gp} register. This limits the
9706 size of the small data area to 64KB, but allows the variables to be
9707 directly accessed via a single instruction.
9709 The default is @option{-mlarge-data}. With this option the data area
9710 is limited to just below 2GB@. Programs that require more than 2GB of
9711 data must use @code{malloc} or @code{mmap} to allocate the data in the
9712 heap instead of in the program's data segment.
9714 When generating code for shared libraries, @option{-fpic} implies
9715 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
9719 @opindex msmall-text
9720 @opindex mlarge-text
9721 When @option{-msmall-text} is used, the compiler assumes that the
9722 code of the entire program (or shared library) fits in 4MB, and is
9723 thus reachable with a branch instruction. When @option{-msmall-data}
9724 is used, the compiler can assume that all local symbols share the
9725 same @code{$gp} value, and thus reduce the number of instructions
9726 required for a function call from 4 to 1.
9728 The default is @option{-mlarge-text}.
9730 @item -mcpu=@var{cpu_type}
9732 Set the instruction set and instruction scheduling parameters for
9733 machine type @var{cpu_type}. You can specify either the @samp{EV}
9734 style name or the corresponding chip number. GCC supports scheduling
9735 parameters for the EV4, EV5 and EV6 family of processors and will
9736 choose the default values for the instruction set from the processor
9737 you specify. If you do not specify a processor type, GCC will default
9738 to the processor on which the compiler was built.
9740 Supported values for @var{cpu_type} are
9746 Schedules as an EV4 and has no instruction set extensions.
9750 Schedules as an EV5 and has no instruction set extensions.
9754 Schedules as an EV5 and supports the BWX extension.
9759 Schedules as an EV5 and supports the BWX and MAX extensions.
9763 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
9767 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
9770 @item -mtune=@var{cpu_type}
9772 Set only the instruction scheduling parameters for machine type
9773 @var{cpu_type}. The instruction set is not changed.
9775 @item -mmemory-latency=@var{time}
9776 @opindex mmemory-latency
9777 Sets the latency the scheduler should assume for typical memory
9778 references as seen by the application. This number is highly
9779 dependent on the memory access patterns used by the application
9780 and the size of the external cache on the machine.
9782 Valid options for @var{time} are
9786 A decimal number representing clock cycles.
9792 The compiler contains estimates of the number of clock cycles for
9793 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
9794 (also called Dcache, Scache, and Bcache), as well as to main memory.
9795 Note that L3 is only valid for EV5.
9800 @node DEC Alpha/VMS Options
9801 @subsection DEC Alpha/VMS Options
9803 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
9806 @item -mvms-return-codes
9807 @opindex mvms-return-codes
9808 Return VMS condition codes from main. The default is to return POSIX
9809 style condition (e.g.@: error) codes.
9813 @subsection FRV Options
9820 Only use the first 32 general purpose registers.
9825 Use all 64 general purpose registers.
9830 Use only the first 32 floating point registers.
9835 Use all 64 floating point registers
9838 @opindex mhard-float
9840 Use hardware instructions for floating point operations.
9843 @opindex msoft-float
9845 Use library routines for floating point operations.
9850 Dynamically allocate condition code registers.
9855 Do not try to dynamically allocate condition code registers, only
9856 use @code{icc0} and @code{fcc0}.
9861 Change ABI to use double word insns.
9866 Do not use double word instructions.
9871 Use floating point double instructions.
9876 Do not use floating point double instructions.
9881 Use media instructions.
9886 Do not use media instructions.
9891 Use multiply and add/subtract instructions.
9896 Do not use multiply and add/subtract instructions.
9901 Select the FDPIC ABI, that uses function descriptors to represent
9902 pointers to functions. Without any PIC/PIE-related options, it
9903 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
9904 assumes GOT entries and small data are within a 12-bit range from the
9905 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
9906 are computed with 32 bits.
9907 With a @samp{bfin-elf} target, this option implies @option{-msim}.
9910 @opindex minline-plt
9912 Enable inlining of PLT entries in function calls to functions that are
9913 not known to bind locally. It has no effect without @option{-mfdpic}.
9914 It's enabled by default if optimizing for speed and compiling for
9915 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
9916 optimization option such as @option{-O3} or above is present in the
9922 Assume a large TLS segment when generating thread-local code.
9927 Do not assume a large TLS segment when generating thread-local code.
9932 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
9933 that is known to be in read-only sections. It's enabled by default,
9934 except for @option{-fpic} or @option{-fpie}: even though it may help
9935 make the global offset table smaller, it trades 1 instruction for 4.
9936 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
9937 one of which may be shared by multiple symbols, and it avoids the need
9938 for a GOT entry for the referenced symbol, so it's more likely to be a
9939 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
9941 @item -multilib-library-pic
9942 @opindex multilib-library-pic
9944 Link with the (library, not FD) pic libraries. It's implied by
9945 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
9946 @option{-fpic} without @option{-mfdpic}. You should never have to use
9952 Follow the EABI requirement of always creating a frame pointer whenever
9953 a stack frame is allocated. This option is enabled by default and can
9954 be disabled with @option{-mno-linked-fp}.
9957 @opindex mlong-calls
9959 Use indirect addressing to call functions outside the current
9960 compilation unit. This allows the functions to be placed anywhere
9961 within the 32-bit address space.
9963 @item -malign-labels
9964 @opindex malign-labels
9966 Try to align labels to an 8-byte boundary by inserting nops into the
9967 previous packet. This option only has an effect when VLIW packing
9968 is enabled. It doesn't create new packets; it merely adds nops to
9972 @opindex mlibrary-pic
9974 Generate position-independent EABI code.
9979 Use only the first four media accumulator registers.
9984 Use all eight media accumulator registers.
9989 Pack VLIW instructions.
9994 Do not pack VLIW instructions.
9999 Do not mark ABI switches in e_flags.
10002 @opindex mcond-move
10004 Enable the use of conditional-move instructions (default).
10006 This switch is mainly for debugging the compiler and will likely be removed
10007 in a future version.
10009 @item -mno-cond-move
10010 @opindex mno-cond-move
10012 Disable the use of conditional-move instructions.
10014 This switch is mainly for debugging the compiler and will likely be removed
10015 in a future version.
10020 Enable the use of conditional set instructions (default).
10022 This switch is mainly for debugging the compiler and will likely be removed
10023 in a future version.
10028 Disable the use of conditional set instructions.
10030 This switch is mainly for debugging the compiler and will likely be removed
10031 in a future version.
10034 @opindex mcond-exec
10036 Enable the use of conditional execution (default).
10038 This switch is mainly for debugging the compiler and will likely be removed
10039 in a future version.
10041 @item -mno-cond-exec
10042 @opindex mno-cond-exec
10044 Disable the use of conditional execution.
10046 This switch is mainly for debugging the compiler and will likely be removed
10047 in a future version.
10049 @item -mvliw-branch
10050 @opindex mvliw-branch
10052 Run a pass to pack branches into VLIW instructions (default).
10054 This switch is mainly for debugging the compiler and will likely be removed
10055 in a future version.
10057 @item -mno-vliw-branch
10058 @opindex mno-vliw-branch
10060 Do not run a pass to pack branches into VLIW instructions.
10062 This switch is mainly for debugging the compiler and will likely be removed
10063 in a future version.
10065 @item -mmulti-cond-exec
10066 @opindex mmulti-cond-exec
10068 Enable optimization of @code{&&} and @code{||} in conditional execution
10071 This switch is mainly for debugging the compiler and will likely be removed
10072 in a future version.
10074 @item -mno-multi-cond-exec
10075 @opindex mno-multi-cond-exec
10077 Disable optimization of @code{&&} and @code{||} in conditional execution.
10079 This switch is mainly for debugging the compiler and will likely be removed
10080 in a future version.
10082 @item -mnested-cond-exec
10083 @opindex mnested-cond-exec
10085 Enable nested conditional execution optimizations (default).
10087 This switch is mainly for debugging the compiler and will likely be removed
10088 in a future version.
10090 @item -mno-nested-cond-exec
10091 @opindex mno-nested-cond-exec
10093 Disable nested conditional execution optimizations.
10095 This switch is mainly for debugging the compiler and will likely be removed
10096 in a future version.
10098 @item -moptimize-membar
10099 @opindex moptimize-membar
10101 This switch removes redundant @code{membar} instructions from the
10102 compiler generated code. It is enabled by default.
10104 @item -mno-optimize-membar
10105 @opindex mno-optimize-membar
10107 This switch disables the automatic removal of redundant @code{membar}
10108 instructions from the generated code.
10110 @item -mtomcat-stats
10111 @opindex mtomcat-stats
10113 Cause gas to print out tomcat statistics.
10115 @item -mcpu=@var{cpu}
10118 Select the processor type for which to generate code. Possible values are
10119 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
10120 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
10124 @node GNU/Linux Options
10125 @subsection GNU/Linux Options
10127 These @samp{-m} options are defined for GNU/Linux targets:
10132 Use the GNU C library instead of uClibc. This is the default except
10133 on @samp{*-*-linux-*uclibc*} targets.
10137 Use uClibc instead of the GNU C library. This is the default on
10138 @samp{*-*-linux-*uclibc*} targets.
10141 @node H8/300 Options
10142 @subsection H8/300 Options
10144 These @samp{-m} options are defined for the H8/300 implementations:
10149 Shorten some address references at link time, when possible; uses the
10150 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
10151 ld, Using ld}, for a fuller description.
10155 Generate code for the H8/300H@.
10159 Generate code for the H8S@.
10163 Generate code for the H8S and H8/300H in the normal mode. This switch
10164 must be used either with @option{-mh} or @option{-ms}.
10168 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
10172 Make @code{int} data 32 bits by default.
10175 @opindex malign-300
10176 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
10177 The default for the H8/300H and H8S is to align longs and floats on 4
10179 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
10180 This option has no effect on the H8/300.
10184 @subsection HPPA Options
10185 @cindex HPPA Options
10187 These @samp{-m} options are defined for the HPPA family of computers:
10190 @item -march=@var{architecture-type}
10192 Generate code for the specified architecture. The choices for
10193 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
10194 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
10195 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
10196 architecture option for your machine. Code compiled for lower numbered
10197 architectures will run on higher numbered architectures, but not the
10200 @item -mpa-risc-1-0
10201 @itemx -mpa-risc-1-1
10202 @itemx -mpa-risc-2-0
10203 @opindex mpa-risc-1-0
10204 @opindex mpa-risc-1-1
10205 @opindex mpa-risc-2-0
10206 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
10209 @opindex mbig-switch
10210 Generate code suitable for big switch tables. Use this option only if
10211 the assembler/linker complain about out of range branches within a switch
10214 @item -mjump-in-delay
10215 @opindex mjump-in-delay
10216 Fill delay slots of function calls with unconditional jump instructions
10217 by modifying the return pointer for the function call to be the target
10218 of the conditional jump.
10220 @item -mdisable-fpregs
10221 @opindex mdisable-fpregs
10222 Prevent floating point registers from being used in any manner. This is
10223 necessary for compiling kernels which perform lazy context switching of
10224 floating point registers. If you use this option and attempt to perform
10225 floating point operations, the compiler will abort.
10227 @item -mdisable-indexing
10228 @opindex mdisable-indexing
10229 Prevent the compiler from using indexing address modes. This avoids some
10230 rather obscure problems when compiling MIG generated code under MACH@.
10232 @item -mno-space-regs
10233 @opindex mno-space-regs
10234 Generate code that assumes the target has no space registers. This allows
10235 GCC to generate faster indirect calls and use unscaled index address modes.
10237 Such code is suitable for level 0 PA systems and kernels.
10239 @item -mfast-indirect-calls
10240 @opindex mfast-indirect-calls
10241 Generate code that assumes calls never cross space boundaries. This
10242 allows GCC to emit code which performs faster indirect calls.
10244 This option will not work in the presence of shared libraries or nested
10247 @item -mfixed-range=@var{register-range}
10248 @opindex mfixed-range
10249 Generate code treating the given register range as fixed registers.
10250 A fixed register is one that the register allocator can not use. This is
10251 useful when compiling kernel code. A register range is specified as
10252 two registers separated by a dash. Multiple register ranges can be
10253 specified separated by a comma.
10255 @item -mlong-load-store
10256 @opindex mlong-load-store
10257 Generate 3-instruction load and store sequences as sometimes required by
10258 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
10261 @item -mportable-runtime
10262 @opindex mportable-runtime
10263 Use the portable calling conventions proposed by HP for ELF systems.
10267 Enable the use of assembler directives only GAS understands.
10269 @item -mschedule=@var{cpu-type}
10271 Schedule code according to the constraints for the machine type
10272 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
10273 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
10274 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
10275 proper scheduling option for your machine. The default scheduling is
10279 @opindex mlinker-opt
10280 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
10281 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
10282 linkers in which they give bogus error messages when linking some programs.
10285 @opindex msoft-float
10286 Generate output containing library calls for floating point.
10287 @strong{Warning:} the requisite libraries are not available for all HPPA
10288 targets. Normally the facilities of the machine's usual C compiler are
10289 used, but this cannot be done directly in cross-compilation. You must make
10290 your own arrangements to provide suitable library functions for
10293 @option{-msoft-float} changes the calling convention in the output file;
10294 therefore, it is only useful if you compile @emph{all} of a program with
10295 this option. In particular, you need to compile @file{libgcc.a}, the
10296 library that comes with GCC, with @option{-msoft-float} in order for
10301 Generate the predefine, @code{_SIO}, for server IO@. The default is
10302 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
10303 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
10304 options are available under HP-UX and HI-UX@.
10308 Use GNU ld specific options. This passes @option{-shared} to ld when
10309 building a shared library. It is the default when GCC is configured,
10310 explicitly or implicitly, with the GNU linker. This option does not
10311 have any affect on which ld is called, it only changes what parameters
10312 are passed to that ld. The ld that is called is determined by the
10313 @option{--with-ld} configure option, GCC's program search path, and
10314 finally by the user's @env{PATH}. The linker used by GCC can be printed
10315 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
10316 on the 64 bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
10320 Use HP ld specific options. This passes @option{-b} to ld when building
10321 a shared library and passes @option{+Accept TypeMismatch} to ld on all
10322 links. It is the default when GCC is configured, explicitly or
10323 implicitly, with the HP linker. This option does not have any affect on
10324 which ld is called, it only changes what parameters are passed to that
10325 ld. The ld that is called is determined by the @option{--with-ld}
10326 configure option, GCC's program search path, and finally by the user's
10327 @env{PATH}. The linker used by GCC can be printed using @samp{which
10328 `gcc -print-prog-name=ld`}. This option is only available on the 64 bit
10329 HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
10332 @opindex mno-long-calls
10333 Generate code that uses long call sequences. This ensures that a call
10334 is always able to reach linker generated stubs. The default is to generate
10335 long calls only when the distance from the call site to the beginning
10336 of the function or translation unit, as the case may be, exceeds a
10337 predefined limit set by the branch type being used. The limits for
10338 normal calls are 7,600,000 and 240,000 bytes, respectively for the
10339 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
10342 Distances are measured from the beginning of functions when using the
10343 @option{-ffunction-sections} option, or when using the @option{-mgas}
10344 and @option{-mno-portable-runtime} options together under HP-UX with
10347 It is normally not desirable to use this option as it will degrade
10348 performance. However, it may be useful in large applications,
10349 particularly when partial linking is used to build the application.
10351 The types of long calls used depends on the capabilities of the
10352 assembler and linker, and the type of code being generated. The
10353 impact on systems that support long absolute calls, and long pic
10354 symbol-difference or pc-relative calls should be relatively small.
10355 However, an indirect call is used on 32-bit ELF systems in pic code
10356 and it is quite long.
10358 @item -munix=@var{unix-std}
10360 Generate compiler predefines and select a startfile for the specified
10361 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
10362 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
10363 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
10364 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
10365 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
10368 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
10369 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
10370 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
10371 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
10372 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
10373 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
10375 It is @emph{important} to note that this option changes the interfaces
10376 for various library routines. It also affects the operational behavior
10377 of the C library. Thus, @emph{extreme} care is needed in using this
10380 Library code that is intended to operate with more than one UNIX
10381 standard must test, set and restore the variable @var{__xpg4_extended_mask}
10382 as appropriate. Most GNU software doesn't provide this capability.
10386 Suppress the generation of link options to search libdld.sl when the
10387 @option{-static} option is specified on HP-UX 10 and later.
10391 The HP-UX implementation of setlocale in libc has a dependency on
10392 libdld.sl. There isn't an archive version of libdld.sl. Thus,
10393 when the @option{-static} option is specified, special link options
10394 are needed to resolve this dependency.
10396 On HP-UX 10 and later, the GCC driver adds the necessary options to
10397 link with libdld.sl when the @option{-static} option is specified.
10398 This causes the resulting binary to be dynamic. On the 64-bit port,
10399 the linkers generate dynamic binaries by default in any case. The
10400 @option{-nolibdld} option can be used to prevent the GCC driver from
10401 adding these link options.
10405 Add support for multithreading with the @dfn{dce thread} library
10406 under HP-UX@. This option sets flags for both the preprocessor and
10410 @node i386 and x86-64 Options
10411 @subsection Intel 386 and AMD x86-64 Options
10412 @cindex i386 Options
10413 @cindex x86-64 Options
10414 @cindex Intel 386 Options
10415 @cindex AMD x86-64 Options
10417 These @samp{-m} options are defined for the i386 and x86-64 family of
10421 @item -mtune=@var{cpu-type}
10423 Tune to @var{cpu-type} everything applicable about the generated code, except
10424 for the ABI and the set of available instructions. The choices for
10425 @var{cpu-type} are:
10428 Produce code optimized for the most common IA32/AMD64/EM64T processors.
10429 If you know the CPU on which your code will run, then you should use
10430 the corresponding @option{-mtune} option instead of
10431 @option{-mtune=generic}. But, if you do not know exactly what CPU users
10432 of your application will have, then you should use this option.
10434 As new processors are deployed in the marketplace, the behavior of this
10435 option will change. Therefore, if you upgrade to a newer version of
10436 GCC, the code generated option will change to reflect the processors
10437 that were most common when that version of GCC was released.
10439 There is no @option{-march=generic} option because @option{-march}
10440 indicates the instruction set the compiler can use, and there is no
10441 generic instruction set applicable to all processors. In contrast,
10442 @option{-mtune} indicates the processor (or, in this case, collection of
10443 processors) for which the code is optimized.
10445 This selects the CPU to tune for at compilation time by determining
10446 the processor type of the compiling machine. Using @option{-mtune=native}
10447 will produce code optimized for the local machine under the constraints
10448 of the selected instruction set. Using @option{-march=native} will
10449 enable all instruction subsets supported by the local machine (hence
10450 the result might not run on different machines).
10452 Original Intel's i386 CPU@.
10454 Intel's i486 CPU@. (No scheduling is implemented for this chip.)
10455 @item i586, pentium
10456 Intel Pentium CPU with no MMX support.
10458 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
10460 Intel PentiumPro CPU@.
10462 Same as @code{generic}, but when used as @code{march} option, PentiumPro
10463 instruction set will be used, so the code will run on all i686 family chips.
10465 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
10466 @item pentium3, pentium3m
10467 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
10470 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
10471 support. Used by Centrino notebooks.
10472 @item pentium4, pentium4m
10473 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
10475 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
10478 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
10479 SSE2 and SSE3 instruction set support.
10481 Intel Core2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
10482 instruction set support.
10484 AMD K6 CPU with MMX instruction set support.
10486 Improved versions of AMD K6 CPU with MMX and 3dNOW!@: instruction set support.
10487 @item athlon, athlon-tbird
10488 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW!@: and SSE prefetch instructions
10490 @item athlon-4, athlon-xp, athlon-mp
10491 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW!@: and full SSE
10492 instruction set support.
10493 @item k8, opteron, athlon64, athlon-fx
10494 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
10495 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW!@: and 64-bit instruction set extensions.)
10496 @item k8-sse3, opteron-sse3, athlon64-sse3
10497 Improved versions of k8, opteron and athlon64 with SSE3 instruction set support.
10498 @item amdfam10, barcelona
10499 AMD Family 10h core based CPUs with x86-64 instruction set support. (This
10500 supersets MMX, SSE, SSE2, SSE3, SSE4A, 3dNOW!, enhanced 3dNOW!, ABM and 64-bit
10501 instruction set extensions.)
10503 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
10506 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!@:
10507 instruction set support.
10509 Via C3 CPU with MMX and 3dNOW!@: instruction set support. (No scheduling is
10510 implemented for this chip.)
10512 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
10513 implemented for this chip.)
10515 Embedded AMD CPU with MMX and 3dNOW! instruction set support.
10518 While picking a specific @var{cpu-type} will schedule things appropriately
10519 for that particular chip, the compiler will not generate any code that
10520 does not run on the i386 without the @option{-march=@var{cpu-type}} option
10523 @item -march=@var{cpu-type}
10525 Generate instructions for the machine type @var{cpu-type}. The choices
10526 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
10527 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
10529 @item -mcpu=@var{cpu-type}
10531 A deprecated synonym for @option{-mtune}.
10533 @item -mfpmath=@var{unit}
10535 Generate floating point arithmetics for selected unit @var{unit}. The choices
10536 for @var{unit} are:
10540 Use the standard 387 floating point coprocessor present majority of chips and
10541 emulated otherwise. Code compiled with this option will run almost everywhere.
10542 The temporary results are computed in 80bit precision instead of precision
10543 specified by the type resulting in slightly different results compared to most
10544 of other chips. See @option{-ffloat-store} for more detailed description.
10546 This is the default choice for i386 compiler.
10549 Use scalar floating point instructions present in the SSE instruction set.
10550 This instruction set is supported by Pentium3 and newer chips, in the AMD line
10551 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
10552 instruction set supports only single precision arithmetics, thus the double and
10553 extended precision arithmetics is still done using 387. Later version, present
10554 only in Pentium4 and the future AMD x86-64 chips supports double precision
10557 For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse}
10558 or @option{-msse2} switches to enable SSE extensions and make this option
10559 effective. For the x86-64 compiler, these extensions are enabled by default.
10561 The resulting code should be considerably faster in the majority of cases and avoid
10562 the numerical instability problems of 387 code, but may break some existing
10563 code that expects temporaries to be 80bit.
10565 This is the default choice for the x86-64 compiler.
10568 Attempt to utilize both instruction sets at once. This effectively double the
10569 amount of available registers and on chips with separate execution units for
10570 387 and SSE the execution resources too. Use this option with care, as it is
10571 still experimental, because the GCC register allocator does not model separate
10572 functional units well resulting in instable performance.
10575 @item -masm=@var{dialect}
10576 @opindex masm=@var{dialect}
10577 Output asm instructions using selected @var{dialect}. Supported
10578 choices are @samp{intel} or @samp{att} (the default one). Darwin does
10579 not support @samp{intel}.
10582 @itemx -mno-ieee-fp
10584 @opindex mno-ieee-fp
10585 Control whether or not the compiler uses IEEE floating point
10586 comparisons. These handle correctly the case where the result of a
10587 comparison is unordered.
10590 @opindex msoft-float
10591 Generate output containing library calls for floating point.
10592 @strong{Warning:} the requisite libraries are not part of GCC@.
10593 Normally the facilities of the machine's usual C compiler are used, but
10594 this can't be done directly in cross-compilation. You must make your
10595 own arrangements to provide suitable library functions for
10598 On machines where a function returns floating point results in the 80387
10599 register stack, some floating point opcodes may be emitted even if
10600 @option{-msoft-float} is used.
10602 @item -mno-fp-ret-in-387
10603 @opindex mno-fp-ret-in-387
10604 Do not use the FPU registers for return values of functions.
10606 The usual calling convention has functions return values of types
10607 @code{float} and @code{double} in an FPU register, even if there
10608 is no FPU@. The idea is that the operating system should emulate
10611 The option @option{-mno-fp-ret-in-387} causes such values to be returned
10612 in ordinary CPU registers instead.
10614 @item -mno-fancy-math-387
10615 @opindex mno-fancy-math-387
10616 Some 387 emulators do not support the @code{sin}, @code{cos} and
10617 @code{sqrt} instructions for the 387. Specify this option to avoid
10618 generating those instructions. This option is the default on FreeBSD,
10619 OpenBSD and NetBSD@. This option is overridden when @option{-march}
10620 indicates that the target cpu will always have an FPU and so the
10621 instruction will not need emulation. As of revision 2.6.1, these
10622 instructions are not generated unless you also use the
10623 @option{-funsafe-math-optimizations} switch.
10625 @item -malign-double
10626 @itemx -mno-align-double
10627 @opindex malign-double
10628 @opindex mno-align-double
10629 Control whether GCC aligns @code{double}, @code{long double}, and
10630 @code{long long} variables on a two word boundary or a one word
10631 boundary. Aligning @code{double} variables on a two word boundary will
10632 produce code that runs somewhat faster on a @samp{Pentium} at the
10633 expense of more memory.
10635 On x86-64, @option{-malign-double} is enabled by default.
10637 @strong{Warning:} if you use the @option{-malign-double} switch,
10638 structures containing the above types will be aligned differently than
10639 the published application binary interface specifications for the 386
10640 and will not be binary compatible with structures in code compiled
10641 without that switch.
10643 @item -m96bit-long-double
10644 @itemx -m128bit-long-double
10645 @opindex m96bit-long-double
10646 @opindex m128bit-long-double
10647 These switches control the size of @code{long double} type. The i386
10648 application binary interface specifies the size to be 96 bits,
10649 so @option{-m96bit-long-double} is the default in 32 bit mode.
10651 Modern architectures (Pentium and newer) would prefer @code{long double}
10652 to be aligned to an 8 or 16 byte boundary. In arrays or structures
10653 conforming to the ABI, this would not be possible. So specifying a
10654 @option{-m128bit-long-double} will align @code{long double}
10655 to a 16 byte boundary by padding the @code{long double} with an additional
10658 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
10659 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
10661 Notice that neither of these options enable any extra precision over the x87
10662 standard of 80 bits for a @code{long double}.
10664 @strong{Warning:} if you override the default value for your target ABI, the
10665 structures and arrays containing @code{long double} variables will change
10666 their size as well as function calling convention for function taking
10667 @code{long double} will be modified. Hence they will not be binary
10668 compatible with arrays or structures in code compiled without that switch.
10670 @item -mmlarge-data-threshold=@var{number}
10671 @opindex mlarge-data-threshold=@var{number}
10672 When @option{-mcmodel=medium} is specified, the data greater than
10673 @var{threshold} are placed in large data section. This value must be the
10674 same across all object linked into the binary and defaults to 65535.
10678 Use a different function-calling convention, in which functions that
10679 take a fixed number of arguments return with the @code{ret} @var{num}
10680 instruction, which pops their arguments while returning. This saves one
10681 instruction in the caller since there is no need to pop the arguments
10684 You can specify that an individual function is called with this calling
10685 sequence with the function attribute @samp{stdcall}. You can also
10686 override the @option{-mrtd} option by using the function attribute
10687 @samp{cdecl}. @xref{Function Attributes}.
10689 @strong{Warning:} this calling convention is incompatible with the one
10690 normally used on Unix, so you cannot use it if you need to call
10691 libraries compiled with the Unix compiler.
10693 Also, you must provide function prototypes for all functions that
10694 take variable numbers of arguments (including @code{printf});
10695 otherwise incorrect code will be generated for calls to those
10698 In addition, seriously incorrect code will result if you call a
10699 function with too many arguments. (Normally, extra arguments are
10700 harmlessly ignored.)
10702 @item -mregparm=@var{num}
10704 Control how many registers are used to pass integer arguments. By
10705 default, no registers are used to pass arguments, and at most 3
10706 registers can be used. You can control this behavior for a specific
10707 function by using the function attribute @samp{regparm}.
10708 @xref{Function Attributes}.
10710 @strong{Warning:} if you use this switch, and
10711 @var{num} is nonzero, then you must build all modules with the same
10712 value, including any libraries. This includes the system libraries and
10716 @opindex msseregparm
10717 Use SSE register passing conventions for float and double arguments
10718 and return values. You can control this behavior for a specific
10719 function by using the function attribute @samp{sseregparm}.
10720 @xref{Function Attributes}.
10722 @strong{Warning:} if you use this switch then you must build all
10723 modules with the same value, including any libraries. This includes
10724 the system libraries and startup modules.
10733 Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32}
10734 is specified, the significands of results of floating-point operations are
10735 rounded to 24 bits (single precision); @option{-mpc64} rounds the the
10736 significands of results of floating-point operations to 53 bits (double
10737 precision) and @option{-mpc80} rounds the significands of results of
10738 floating-point operations to 64 bits (extended double precision), which is
10739 the default. When this option is used, floating-point operations in higher
10740 precisions are not available to the programmer without setting the FPU
10741 control word explicitly.
10743 Setting the rounding of floating-point operations to less than the default
10744 80 bits can speed some programs by 2% or more. Note that some mathematical
10745 libraries assume that extended precision (80 bit) floating-point operations
10746 are enabled by default; routines in such libraries could suffer significant
10747 loss of accuracy, typically through so-called "catastrophic cancellation",
10748 when this option is used to set the precision to less than extended precision.
10750 @item -mstackrealign
10751 @opindex mstackrealign
10752 Realign the stack at entry. On the Intel x86, the
10753 @option{-mstackrealign} option will generate an alternate prologue and
10754 epilogue that realigns the runtime stack. This supports mixing legacy
10755 codes that keep a 4-byte aligned stack with modern codes that keep a
10756 16-byte stack for SSE compatibility. The alternate prologue and
10757 epilogue are slower and bigger than the regular ones, and the
10758 alternate prologue requires an extra scratch register; this lowers the
10759 number of registers available if used in conjunction with the
10760 @code{regparm} attribute. The @option{-mstackrealign} option is
10761 incompatible with the nested function prologue; this is considered a
10762 hard error. See also the attribute @code{force_align_arg_pointer},
10763 applicable to individual functions.
10765 @item -mpreferred-stack-boundary=@var{num}
10766 @opindex mpreferred-stack-boundary
10767 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
10768 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
10769 the default is 4 (16 bytes or 128 bits).
10771 On Pentium and PentiumPro, @code{double} and @code{long double} values
10772 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
10773 suffer significant run time performance penalties. On Pentium III, the
10774 Streaming SIMD Extension (SSE) data type @code{__m128} may not work
10775 properly if it is not 16 byte aligned.
10777 To ensure proper alignment of this values on the stack, the stack boundary
10778 must be as aligned as that required by any value stored on the stack.
10779 Further, every function must be generated such that it keeps the stack
10780 aligned. Thus calling a function compiled with a higher preferred
10781 stack boundary from a function compiled with a lower preferred stack
10782 boundary will most likely misalign the stack. It is recommended that
10783 libraries that use callbacks always use the default setting.
10785 This extra alignment does consume extra stack space, and generally
10786 increases code size. Code that is sensitive to stack space usage, such
10787 as embedded systems and operating system kernels, may want to reduce the
10788 preferred alignment to @option{-mpreferred-stack-boundary=2}.
10826 These switches enable or disable the use of instructions in the MMX,
10827 SSE, SSE2, SSE3, SSSE3, SSE4.1, AES, PCLMUL, SSE4A, SSE5, ABM or
10828 3DNow!@: extended instruction sets.
10829 These extensions are also available as built-in functions: see
10830 @ref{X86 Built-in Functions}, for details of the functions enabled and
10831 disabled by these switches.
10833 To have SSE/SSE2 instructions generated automatically from floating-point
10834 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
10836 These options will enable GCC to use these extended instructions in
10837 generated code, even without @option{-mfpmath=sse}. Applications which
10838 perform runtime CPU detection must compile separate files for each
10839 supported architecture, using the appropriate flags. In particular,
10840 the file containing the CPU detection code should be compiled without
10845 This option instructs GCC to emit a @code{cld} instruction in the prologue
10846 of functions that use string instructions. String instructions depend on
10847 the DF flag to select between autoincrement or autodecrement mode. While the
10848 ABI specifies the DF flag to be cleared on function entry, some operating
10849 systems violate this specification by not clearing the DF flag in their
10850 exception dispatchers. The exception handler can be invoked with the DF flag
10851 set which leads to wrong direction mode, when string instructions are used.
10852 This option can be enabled by default on 32-bit x86 targets by configuring
10853 GCC with the @option{--enable-cld} configure option. Generation of @code{cld}
10854 instructions can be suppressed with the @option{-mno-cld} compiler option
10859 This option will enable GCC to use CMPXCHG16B instruction in generated code.
10860 CMPXCHG16B allows for atomic operations on 128-bit double quadword (or oword)
10861 data types. This is useful for high resolution counters that could be updated
10862 by multiple processors (or cores). This instruction is generated as part of
10863 atomic built-in functions: see @ref{Atomic Builtins} for details.
10867 This option will enable GCC to use SAHF instruction in generated 64-bit code.
10868 Early Intel CPUs with Intel 64 lacked LAHF and SAHF instructions supported
10869 by AMD64 until introduction of Pentium 4 G1 step in December 2005. LAHF and
10870 SAHF are load and store instructions, respectively, for certain status flags.
10871 In 64-bit mode, SAHF instruction is used to optimize @code{fmod}, @code{drem}
10872 or @code{remainder} built-in functions: see @ref{Other Builtins} for details.
10876 This option will enable GCC to use RCPSS and RSQRTSS instructions (and their
10877 vectorized variants RCPPS and RSQRTPS) with an additional Newton-Rhapson step
10878 to increase precision instead of DIVSS and SQRTSS (and their vectorized
10879 variants) for single precision floating point arguments. These instructions
10880 are generated only when @option{-funsafe-math-optimizations} is enabled
10881 together with @option{-finite-math-only} and @option{-fno-trapping-math}.
10882 Note that while the throughput of the sequence is higher than the throughput
10883 of the non-reciprocal instruction, the precision of the sequence can be
10884 decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).
10886 @item -mveclibabi=@var{type}
10887 @opindex mveclibabi
10888 Specifies the ABI type to use for vectorizing intrinsics using an
10889 external library. Supported types are @code{svml} for the Intel short
10890 vector math library and @code{acml} for the AMD math core library style
10891 of interfacing. GCC will currently emit calls to @code{vmldExp2},
10892 @code{vmldLn2}, @code{vmldLog102}, @code{vmldLog102}, @code{vmldPow2},
10893 @code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2},
10894 @code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2},
10895 @code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2},
10896 @code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, @code{vmlsLog104},
10897 @code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4},
10898 @code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4},
10899 @code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4},
10900 @code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding
10901 function type when @option{-mveclibabi=svml} is used and @code{__vrd2_sin},
10902 @code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2},
10903 @code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf},
10904 @code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f},
10905 @code{__vrs4_log10f} and @code{__vrs4_powf} for corresponding function type
10906 when @option{-mveclibabi=acml} is used. Both @option{-ftree-vectorize} and
10907 @option{-funsafe-math-optimizations} have to be enabled. A SVML or ACML ABI
10908 compatible library will have to be specified at link time.
10911 @itemx -mno-push-args
10912 @opindex mpush-args
10913 @opindex mno-push-args
10914 Use PUSH operations to store outgoing parameters. This method is shorter
10915 and usually equally fast as method using SUB/MOV operations and is enabled
10916 by default. In some cases disabling it may improve performance because of
10917 improved scheduling and reduced dependencies.
10919 @item -maccumulate-outgoing-args
10920 @opindex maccumulate-outgoing-args
10921 If enabled, the maximum amount of space required for outgoing arguments will be
10922 computed in the function prologue. This is faster on most modern CPUs
10923 because of reduced dependencies, improved scheduling and reduced stack usage
10924 when preferred stack boundary is not equal to 2. The drawback is a notable
10925 increase in code size. This switch implies @option{-mno-push-args}.
10929 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
10930 on thread-safe exception handling must compile and link all code with the
10931 @option{-mthreads} option. When compiling, @option{-mthreads} defines
10932 @option{-D_MT}; when linking, it links in a special thread helper library
10933 @option{-lmingwthrd} which cleans up per thread exception handling data.
10935 @item -mno-align-stringops
10936 @opindex mno-align-stringops
10937 Do not align destination of inlined string operations. This switch reduces
10938 code size and improves performance in case the destination is already aligned,
10939 but GCC doesn't know about it.
10941 @item -minline-all-stringops
10942 @opindex minline-all-stringops
10943 By default GCC inlines string operations only when destination is known to be
10944 aligned at least to 4 byte boundary. This enables more inlining, increase code
10945 size, but may improve performance of code that depends on fast memcpy, strlen
10946 and memset for short lengths.
10948 @item -minline-stringops-dynamically
10949 @opindex minline-stringops-dynamically
10950 For string operation of unknown size, inline runtime checks so for small
10951 blocks inline code is used, while for large blocks library call is used.
10953 @item -mstringop-strategy=@var{alg}
10954 @opindex mstringop-strategy=@var{alg}
10955 Overwrite internal decision heuristic about particular algorithm to inline
10956 string operation with. The allowed values are @code{rep_byte},
10957 @code{rep_4byte}, @code{rep_8byte} for expanding using i386 @code{rep} prefix
10958 of specified size, @code{byte_loop}, @code{loop}, @code{unrolled_loop} for
10959 expanding inline loop, @code{libcall} for always expanding library call.
10961 @item -momit-leaf-frame-pointer
10962 @opindex momit-leaf-frame-pointer
10963 Don't keep the frame pointer in a register for leaf functions. This
10964 avoids the instructions to save, set up and restore frame pointers and
10965 makes an extra register available in leaf functions. The option
10966 @option{-fomit-frame-pointer} removes the frame pointer for all functions
10967 which might make debugging harder.
10969 @item -mtls-direct-seg-refs
10970 @itemx -mno-tls-direct-seg-refs
10971 @opindex mtls-direct-seg-refs
10972 Controls whether TLS variables may be accessed with offsets from the
10973 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
10974 or whether the thread base pointer must be added. Whether or not this
10975 is legal depends on the operating system, and whether it maps the
10976 segment to cover the entire TLS area.
10978 For systems that use GNU libc, the default is on.
10981 @itemx -mno-fused-madd
10982 @opindex mfused-madd
10983 Enable automatic generation of fused floating point multiply-add instructions
10984 if the ISA supports such instructions. The -mfused-madd option is on by
10985 default. The fused multiply-add instructions have a different
10986 rounding behavior compared to executing a multiply followed by an add.
10989 These @samp{-m} switches are supported in addition to the above
10990 on AMD x86-64 processors in 64-bit environments.
10997 Generate code for a 32-bit or 64-bit environment.
10998 The 32-bit environment sets int, long and pointer to 32 bits and
10999 generates code that runs on any i386 system.
11000 The 64-bit environment sets int to 32 bits and long and pointer
11001 to 64 bits and generates code for AMD's x86-64 architecture. For
11002 darwin only the -m64 option turns off the @option{-fno-pic} and
11003 @option{-mdynamic-no-pic} options.
11005 @item -mno-red-zone
11006 @opindex no-red-zone
11007 Do not use a so called red zone for x86-64 code. The red zone is mandated
11008 by the x86-64 ABI, it is a 128-byte area beyond the location of the
11009 stack pointer that will not be modified by signal or interrupt handlers
11010 and therefore can be used for temporary data without adjusting the stack
11011 pointer. The flag @option{-mno-red-zone} disables this red zone.
11013 @item -mcmodel=small
11014 @opindex mcmodel=small
11015 Generate code for the small code model: the program and its symbols must
11016 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
11017 Programs can be statically or dynamically linked. This is the default
11020 @item -mcmodel=kernel
11021 @opindex mcmodel=kernel
11022 Generate code for the kernel code model. The kernel runs in the
11023 negative 2 GB of the address space.
11024 This model has to be used for Linux kernel code.
11026 @item -mcmodel=medium
11027 @opindex mcmodel=medium
11028 Generate code for the medium model: The program is linked in the lower 2
11029 GB of the address space but symbols can be located anywhere in the
11030 address space. Programs can be statically or dynamically linked, but
11031 building of shared libraries are not supported with the medium model.
11033 @item -mcmodel=large
11034 @opindex mcmodel=large
11035 Generate code for the large model: This model makes no assumptions
11036 about addresses and sizes of sections.
11039 @node IA-64 Options
11040 @subsection IA-64 Options
11041 @cindex IA-64 Options
11043 These are the @samp{-m} options defined for the Intel IA-64 architecture.
11047 @opindex mbig-endian
11048 Generate code for a big endian target. This is the default for HP-UX@.
11050 @item -mlittle-endian
11051 @opindex mlittle-endian
11052 Generate code for a little endian target. This is the default for AIX5
11058 @opindex mno-gnu-as
11059 Generate (or don't) code for the GNU assembler. This is the default.
11060 @c Also, this is the default if the configure option @option{--with-gnu-as}
11066 @opindex mno-gnu-ld
11067 Generate (or don't) code for the GNU linker. This is the default.
11068 @c Also, this is the default if the configure option @option{--with-gnu-ld}
11073 Generate code that does not use a global pointer register. The result
11074 is not position independent code, and violates the IA-64 ABI@.
11076 @item -mvolatile-asm-stop
11077 @itemx -mno-volatile-asm-stop
11078 @opindex mvolatile-asm-stop
11079 @opindex mno-volatile-asm-stop
11080 Generate (or don't) a stop bit immediately before and after volatile asm
11083 @item -mregister-names
11084 @itemx -mno-register-names
11085 @opindex mregister-names
11086 @opindex mno-register-names
11087 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
11088 the stacked registers. This may make assembler output more readable.
11094 Disable (or enable) optimizations that use the small data section. This may
11095 be useful for working around optimizer bugs.
11097 @item -mconstant-gp
11098 @opindex mconstant-gp
11099 Generate code that uses a single constant global pointer value. This is
11100 useful when compiling kernel code.
11104 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
11105 This is useful when compiling firmware code.
11107 @item -minline-float-divide-min-latency
11108 @opindex minline-float-divide-min-latency
11109 Generate code for inline divides of floating point values
11110 using the minimum latency algorithm.
11112 @item -minline-float-divide-max-throughput
11113 @opindex minline-float-divide-max-throughput
11114 Generate code for inline divides of floating point values
11115 using the maximum throughput algorithm.
11117 @item -minline-int-divide-min-latency
11118 @opindex minline-int-divide-min-latency
11119 Generate code for inline divides of integer values
11120 using the minimum latency algorithm.
11122 @item -minline-int-divide-max-throughput
11123 @opindex minline-int-divide-max-throughput
11124 Generate code for inline divides of integer values
11125 using the maximum throughput algorithm.
11127 @item -minline-sqrt-min-latency
11128 @opindex minline-sqrt-min-latency
11129 Generate code for inline square roots
11130 using the minimum latency algorithm.
11132 @item -minline-sqrt-max-throughput
11133 @opindex minline-sqrt-max-throughput
11134 Generate code for inline square roots
11135 using the maximum throughput algorithm.
11137 @item -mno-dwarf2-asm
11138 @itemx -mdwarf2-asm
11139 @opindex mno-dwarf2-asm
11140 @opindex mdwarf2-asm
11141 Don't (or do) generate assembler code for the DWARF2 line number debugging
11142 info. This may be useful when not using the GNU assembler.
11144 @item -mearly-stop-bits
11145 @itemx -mno-early-stop-bits
11146 @opindex mearly-stop-bits
11147 @opindex mno-early-stop-bits
11148 Allow stop bits to be placed earlier than immediately preceding the
11149 instruction that triggered the stop bit. This can improve instruction
11150 scheduling, but does not always do so.
11152 @item -mfixed-range=@var{register-range}
11153 @opindex mfixed-range
11154 Generate code treating the given register range as fixed registers.
11155 A fixed register is one that the register allocator can not use. This is
11156 useful when compiling kernel code. A register range is specified as
11157 two registers separated by a dash. Multiple register ranges can be
11158 specified separated by a comma.
11160 @item -mtls-size=@var{tls-size}
11162 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
11165 @item -mtune=@var{cpu-type}
11167 Tune the instruction scheduling for a particular CPU, Valid values are
11168 itanium, itanium1, merced, itanium2, and mckinley.
11174 Add support for multithreading using the POSIX threads library. This
11175 option sets flags for both the preprocessor and linker. It does
11176 not affect the thread safety of object code produced by the compiler or
11177 that of libraries supplied with it. These are HP-UX specific flags.
11183 Generate code for a 32-bit or 64-bit environment.
11184 The 32-bit environment sets int, long and pointer to 32 bits.
11185 The 64-bit environment sets int to 32 bits and long and pointer
11186 to 64 bits. These are HP-UX specific flags.
11188 @item -mno-sched-br-data-spec
11189 @itemx -msched-br-data-spec
11190 @opindex mno-sched-br-data-spec
11191 @opindex msched-br-data-spec
11192 (Dis/En)able data speculative scheduling before reload.
11193 This will result in generation of the ld.a instructions and
11194 the corresponding check instructions (ld.c / chk.a).
11195 The default is 'disable'.
11197 @item -msched-ar-data-spec
11198 @itemx -mno-sched-ar-data-spec
11199 @opindex msched-ar-data-spec
11200 @opindex mno-sched-ar-data-spec
11201 (En/Dis)able data speculative scheduling after reload.
11202 This will result in generation of the ld.a instructions and
11203 the corresponding check instructions (ld.c / chk.a).
11204 The default is 'enable'.
11206 @item -mno-sched-control-spec
11207 @itemx -msched-control-spec
11208 @opindex mno-sched-control-spec
11209 @opindex msched-control-spec
11210 (Dis/En)able control speculative scheduling. This feature is
11211 available only during region scheduling (i.e.@: before reload).
11212 This will result in generation of the ld.s instructions and
11213 the corresponding check instructions chk.s .
11214 The default is 'disable'.
11216 @item -msched-br-in-data-spec
11217 @itemx -mno-sched-br-in-data-spec
11218 @opindex msched-br-in-data-spec
11219 @opindex mno-sched-br-in-data-spec
11220 (En/Dis)able speculative scheduling of the instructions that
11221 are dependent on the data speculative loads before reload.
11222 This is effective only with @option{-msched-br-data-spec} enabled.
11223 The default is 'enable'.
11225 @item -msched-ar-in-data-spec
11226 @itemx -mno-sched-ar-in-data-spec
11227 @opindex msched-ar-in-data-spec
11228 @opindex mno-sched-ar-in-data-spec
11229 (En/Dis)able speculative scheduling of the instructions that
11230 are dependent on the data speculative loads after reload.
11231 This is effective only with @option{-msched-ar-data-spec} enabled.
11232 The default is 'enable'.
11234 @item -msched-in-control-spec
11235 @itemx -mno-sched-in-control-spec
11236 @opindex msched-in-control-spec
11237 @opindex mno-sched-in-control-spec
11238 (En/Dis)able speculative scheduling of the instructions that
11239 are dependent on the control speculative loads.
11240 This is effective only with @option{-msched-control-spec} enabled.
11241 The default is 'enable'.
11244 @itemx -mno-sched-ldc
11245 @opindex msched-ldc
11246 @opindex mno-sched-ldc
11247 (En/Dis)able use of simple data speculation checks ld.c .
11248 If disabled, only chk.a instructions will be emitted to check
11249 data speculative loads.
11250 The default is 'enable'.
11252 @item -mno-sched-control-ldc
11253 @itemx -msched-control-ldc
11254 @opindex mno-sched-control-ldc
11255 @opindex msched-control-ldc
11256 (Dis/En)able use of ld.c instructions to check control speculative loads.
11257 If enabled, in case of control speculative load with no speculatively
11258 scheduled dependent instructions this load will be emitted as ld.sa and
11259 ld.c will be used to check it.
11260 The default is 'disable'.
11262 @item -mno-sched-spec-verbose
11263 @itemx -msched-spec-verbose
11264 @opindex mno-sched-spec-verbose
11265 @opindex msched-spec-verbose
11266 (Dis/En)able printing of the information about speculative motions.
11268 @item -mno-sched-prefer-non-data-spec-insns
11269 @itemx -msched-prefer-non-data-spec-insns
11270 @opindex mno-sched-prefer-non-data-spec-insns
11271 @opindex msched-prefer-non-data-spec-insns
11272 If enabled, data speculative instructions will be chosen for schedule
11273 only if there are no other choices at the moment. This will make
11274 the use of the data speculation much more conservative.
11275 The default is 'disable'.
11277 @item -mno-sched-prefer-non-control-spec-insns
11278 @itemx -msched-prefer-non-control-spec-insns
11279 @opindex mno-sched-prefer-non-control-spec-insns
11280 @opindex msched-prefer-non-control-spec-insns
11281 If enabled, control speculative instructions will be chosen for schedule
11282 only if there are no other choices at the moment. This will make
11283 the use of the control speculation much more conservative.
11284 The default is 'disable'.
11286 @item -mno-sched-count-spec-in-critical-path
11287 @itemx -msched-count-spec-in-critical-path
11288 @opindex mno-sched-count-spec-in-critical-path
11289 @opindex msched-count-spec-in-critical-path
11290 If enabled, speculative dependencies will be considered during
11291 computation of the instructions priorities. This will make the use of the
11292 speculation a bit more conservative.
11293 The default is 'disable'.
11298 @subsection M32C Options
11299 @cindex M32C options
11302 @item -mcpu=@var{name}
11304 Select the CPU for which code is generated. @var{name} may be one of
11305 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
11306 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
11307 the M32C/80 series.
11311 Specifies that the program will be run on the simulator. This causes
11312 an alternate runtime library to be linked in which supports, for
11313 example, file I/O@. You must not use this option when generating
11314 programs that will run on real hardware; you must provide your own
11315 runtime library for whatever I/O functions are needed.
11317 @item -memregs=@var{number}
11319 Specifies the number of memory-based pseudo-registers GCC will use
11320 during code generation. These pseudo-registers will be used like real
11321 registers, so there is a tradeoff between GCC's ability to fit the
11322 code into available registers, and the performance penalty of using
11323 memory instead of registers. Note that all modules in a program must
11324 be compiled with the same value for this option. Because of that, you
11325 must not use this option with the default runtime libraries gcc
11330 @node M32R/D Options
11331 @subsection M32R/D Options
11332 @cindex M32R/D options
11334 These @option{-m} options are defined for Renesas M32R/D architectures:
11339 Generate code for the M32R/2@.
11343 Generate code for the M32R/X@.
11347 Generate code for the M32R@. This is the default.
11349 @item -mmodel=small
11350 @opindex mmodel=small
11351 Assume all objects live in the lower 16MB of memory (so that their addresses
11352 can be loaded with the @code{ld24} instruction), and assume all subroutines
11353 are reachable with the @code{bl} instruction.
11354 This is the default.
11356 The addressability of a particular object can be set with the
11357 @code{model} attribute.
11359 @item -mmodel=medium
11360 @opindex mmodel=medium
11361 Assume objects may be anywhere in the 32-bit address space (the compiler
11362 will generate @code{seth/add3} instructions to load their addresses), and
11363 assume all subroutines are reachable with the @code{bl} instruction.
11365 @item -mmodel=large
11366 @opindex mmodel=large
11367 Assume objects may be anywhere in the 32-bit address space (the compiler
11368 will generate @code{seth/add3} instructions to load their addresses), and
11369 assume subroutines may not be reachable with the @code{bl} instruction
11370 (the compiler will generate the much slower @code{seth/add3/jl}
11371 instruction sequence).
11374 @opindex msdata=none
11375 Disable use of the small data area. Variables will be put into
11376 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
11377 @code{section} attribute has been specified).
11378 This is the default.
11380 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
11381 Objects may be explicitly put in the small data area with the
11382 @code{section} attribute using one of these sections.
11384 @item -msdata=sdata
11385 @opindex msdata=sdata
11386 Put small global and static data in the small data area, but do not
11387 generate special code to reference them.
11390 @opindex msdata=use
11391 Put small global and static data in the small data area, and generate
11392 special instructions to reference them.
11396 @cindex smaller data references
11397 Put global and static objects less than or equal to @var{num} bytes
11398 into the small data or bss sections instead of the normal data or bss
11399 sections. The default value of @var{num} is 8.
11400 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
11401 for this option to have any effect.
11403 All modules should be compiled with the same @option{-G @var{num}} value.
11404 Compiling with different values of @var{num} may or may not work; if it
11405 doesn't the linker will give an error message---incorrect code will not be
11410 Makes the M32R specific code in the compiler display some statistics
11411 that might help in debugging programs.
11413 @item -malign-loops
11414 @opindex malign-loops
11415 Align all loops to a 32-byte boundary.
11417 @item -mno-align-loops
11418 @opindex mno-align-loops
11419 Do not enforce a 32-byte alignment for loops. This is the default.
11421 @item -missue-rate=@var{number}
11422 @opindex missue-rate=@var{number}
11423 Issue @var{number} instructions per cycle. @var{number} can only be 1
11426 @item -mbranch-cost=@var{number}
11427 @opindex mbranch-cost=@var{number}
11428 @var{number} can only be 1 or 2. If it is 1 then branches will be
11429 preferred over conditional code, if it is 2, then the opposite will
11432 @item -mflush-trap=@var{number}
11433 @opindex mflush-trap=@var{number}
11434 Specifies the trap number to use to flush the cache. The default is
11435 12. Valid numbers are between 0 and 15 inclusive.
11437 @item -mno-flush-trap
11438 @opindex mno-flush-trap
11439 Specifies that the cache cannot be flushed by using a trap.
11441 @item -mflush-func=@var{name}
11442 @opindex mflush-func=@var{name}
11443 Specifies the name of the operating system function to call to flush
11444 the cache. The default is @emph{_flush_cache}, but a function call
11445 will only be used if a trap is not available.
11447 @item -mno-flush-func
11448 @opindex mno-flush-func
11449 Indicates that there is no OS function for flushing the cache.
11453 @node M680x0 Options
11454 @subsection M680x0 Options
11455 @cindex M680x0 options
11457 These are the @samp{-m} options defined for M680x0 and ColdFire processors.
11458 The default settings depend on which architecture was selected when
11459 the compiler was configured; the defaults for the most common choices
11463 @item -march=@var{arch}
11465 Generate code for a specific M680x0 or ColdFire instruction set
11466 architecture. Permissible values of @var{arch} for M680x0
11467 architectures are: @samp{68000}, @samp{68010}, @samp{68020},
11468 @samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire
11469 architectures are selected according to Freescale's ISA classification
11470 and the permissible values are: @samp{isaa}, @samp{isaaplus},
11471 @samp{isab} and @samp{isac}.
11473 gcc defines a macro @samp{__mcf@var{arch}__} whenever it is generating
11474 code for a ColdFire target. The @var{arch} in this macro is one of the
11475 @option{-march} arguments given above.
11477 When used together, @option{-march} and @option{-mtune} select code
11478 that runs on a family of similar processors but that is optimized
11479 for a particular microarchitecture.
11481 @item -mcpu=@var{cpu}
11483 Generate code for a specific M680x0 or ColdFire processor.
11484 The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020},
11485 @samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332}
11486 and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table
11487 below, which also classifies the CPUs into families:
11489 @multitable @columnfractions 0.20 0.80
11490 @item @strong{Family} @tab @strong{@samp{-mcpu} arguments}
11491 @item @samp{51qe} @tab @samp{51qe}
11492 @item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206}
11493 @item @samp{5206e} @tab @samp{5206e}
11494 @item @samp{5208} @tab @samp{5207} @samp{5208}
11495 @item @samp{5211a} @tab @samp{5210a} @samp{5211a}
11496 @item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213}
11497 @item @samp{5216} @tab @samp{5214} @samp{5216}
11498 @item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235}
11499 @item @samp{5225} @tab @samp{5224} @samp{5225}
11500 @item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x}
11501 @item @samp{5249} @tab @samp{5249}
11502 @item @samp{5250} @tab @samp{5250}
11503 @item @samp{5271} @tab @samp{5270} @samp{5271}
11504 @item @samp{5272} @tab @samp{5272}
11505 @item @samp{5275} @tab @samp{5274} @samp{5275}
11506 @item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x}
11507 @item @samp{5307} @tab @samp{5307}
11508 @item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x}
11509 @item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x}
11510 @item @samp{5407} @tab @samp{5407}
11511 @item @samp{5475} @tab @samp{5470} @samp{5471} @samp{5472} @samp{5473} @samp{5474} @samp{5475} @samp{547x} @samp{5480} @samp{5481} @samp{5482} @samp{5483} @samp{5484} @samp{5485}
11514 @option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if
11515 @var{arch} is compatible with @var{cpu}. Other combinations of
11516 @option{-mcpu} and @option{-march} are rejected.
11518 gcc defines the macro @samp{__mcf_cpu_@var{cpu}} when ColdFire target
11519 @var{cpu} is selected. It also defines @samp{__mcf_family_@var{family}},
11520 where the value of @var{family} is given by the table above.
11522 @item -mtune=@var{tune}
11524 Tune the code for a particular microarchitecture, within the
11525 constraints set by @option{-march} and @option{-mcpu}.
11526 The M680x0 microarchitectures are: @samp{68000}, @samp{68010},
11527 @samp{68020}, @samp{68030}, @samp{68040}, @samp{68060}
11528 and @samp{cpu32}. The ColdFire microarchitectures
11529 are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}.
11531 You can also use @option{-mtune=68020-40} for code that needs
11532 to run relatively well on 68020, 68030 and 68040 targets.
11533 @option{-mtune=68020-60} is similar but includes 68060 targets
11534 as well. These two options select the same tuning decisions as
11535 @option{-m68020-40} and @option{-m68020-60} respectively.
11537 gcc defines the macros @samp{__mc@var{arch}} and @samp{__mc@var{arch}__}
11538 when tuning for 680x0 architecture @var{arch}. It also defines
11539 @samp{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std}
11540 option is used. If gcc is tuning for a range of architectures,
11541 as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60},
11542 it defines the macros for every architecture in the range.
11544 gcc also defines the macro @samp{__m@var{uarch}__} when tuning for
11545 ColdFire microarchitecture @var{uarch}, where @var{uarch} is one
11546 of the arguments given above.
11552 Generate output for a 68000. This is the default
11553 when the compiler is configured for 68000-based systems.
11554 It is equivalent to @option{-march=68000}.
11556 Use this option for microcontrollers with a 68000 or EC000 core,
11557 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
11561 Generate output for a 68010. This is the default
11562 when the compiler is configured for 68010-based systems.
11563 It is equivalent to @option{-march=68010}.
11569 Generate output for a 68020. This is the default
11570 when the compiler is configured for 68020-based systems.
11571 It is equivalent to @option{-march=68020}.
11575 Generate output for a 68030. This is the default when the compiler is
11576 configured for 68030-based systems. It is equivalent to
11577 @option{-march=68030}.
11581 Generate output for a 68040. This is the default when the compiler is
11582 configured for 68040-based systems. It is equivalent to
11583 @option{-march=68040}.
11585 This option inhibits the use of 68881/68882 instructions that have to be
11586 emulated by software on the 68040. Use this option if your 68040 does not
11587 have code to emulate those instructions.
11591 Generate output for a 68060. This is the default when the compiler is
11592 configured for 68060-based systems. It is equivalent to
11593 @option{-march=68060}.
11595 This option inhibits the use of 68020 and 68881/68882 instructions that
11596 have to be emulated by software on the 68060. Use this option if your 68060
11597 does not have code to emulate those instructions.
11601 Generate output for a CPU32. This is the default
11602 when the compiler is configured for CPU32-based systems.
11603 It is equivalent to @option{-march=cpu32}.
11605 Use this option for microcontrollers with a
11606 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
11607 68336, 68340, 68341, 68349 and 68360.
11611 Generate output for a 520X ColdFire CPU@. This is the default
11612 when the compiler is configured for 520X-based systems.
11613 It is equivalent to @option{-mcpu=5206}, and is now deprecated
11614 in favor of that option.
11616 Use this option for microcontroller with a 5200 core, including
11617 the MCF5202, MCF5203, MCF5204 and MCF5206.
11621 Generate output for a 5206e ColdFire CPU@. The option is now
11622 deprecated in favor of the equivalent @option{-mcpu=5206e}.
11626 Generate output for a member of the ColdFire 528X family.
11627 The option is now deprecated in favor of the equivalent
11628 @option{-mcpu=528x}.
11632 Generate output for a ColdFire 5307 CPU@. The option is now deprecated
11633 in favor of the equivalent @option{-mcpu=5307}.
11637 Generate output for a ColdFire 5407 CPU@. The option is now deprecated
11638 in favor of the equivalent @option{-mcpu=5407}.
11642 Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x).
11643 This includes use of hardware floating point instructions.
11644 The option is equivalent to @option{-mcpu=547x}, and is now
11645 deprecated in favor of that option.
11649 Generate output for a 68040, without using any of the new instructions.
11650 This results in code which can run relatively efficiently on either a
11651 68020/68881 or a 68030 or a 68040. The generated code does use the
11652 68881 instructions that are emulated on the 68040.
11654 The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}.
11658 Generate output for a 68060, without using any of the new instructions.
11659 This results in code which can run relatively efficiently on either a
11660 68020/68881 or a 68030 or a 68040. The generated code does use the
11661 68881 instructions that are emulated on the 68060.
11663 The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}.
11667 @opindex mhard-float
11669 Generate floating-point instructions. This is the default for 68020
11670 and above, and for ColdFire devices that have an FPU@. It defines the
11671 macro @samp{__HAVE_68881__} on M680x0 targets and @samp{__mcffpu__}
11672 on ColdFire targets.
11675 @opindex msoft-float
11676 Do not generate floating-point instructions; use library calls instead.
11677 This is the default for 68000, 68010, and 68832 targets. It is also
11678 the default for ColdFire devices that have no FPU.
11684 Generate (do not generate) ColdFire hardware divide and remainder
11685 instructions. If @option{-march} is used without @option{-mcpu},
11686 the default is ``on'' for ColdFire architectures and ``off'' for M680x0
11687 architectures. Otherwise, the default is taken from the target CPU
11688 (either the default CPU, or the one specified by @option{-mcpu}). For
11689 example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for
11690 @option{-mcpu=5206e}.
11692 gcc defines the macro @samp{__mcfhwdiv__} when this option is enabled.
11696 Consider type @code{int} to be 16 bits wide, like @code{short int}.
11697 Additionally, parameters passed on the stack are also aligned to a
11698 16-bit boundary even on targets whose API mandates promotion to 32-bit.
11702 Do not consider type @code{int} to be 16 bits wide. This is the default.
11705 @itemx -mno-bitfield
11706 @opindex mnobitfield
11707 @opindex mno-bitfield
11708 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
11709 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
11713 Do use the bit-field instructions. The @option{-m68020} option implies
11714 @option{-mbitfield}. This is the default if you use a configuration
11715 designed for a 68020.
11719 Use a different function-calling convention, in which functions
11720 that take a fixed number of arguments return with the @code{rtd}
11721 instruction, which pops their arguments while returning. This
11722 saves one instruction in the caller since there is no need to pop
11723 the arguments there.
11725 This calling convention is incompatible with the one normally
11726 used on Unix, so you cannot use it if you need to call libraries
11727 compiled with the Unix compiler.
11729 Also, you must provide function prototypes for all functions that
11730 take variable numbers of arguments (including @code{printf});
11731 otherwise incorrect code will be generated for calls to those
11734 In addition, seriously incorrect code will result if you call a
11735 function with too many arguments. (Normally, extra arguments are
11736 harmlessly ignored.)
11738 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
11739 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
11743 Do not use the calling conventions selected by @option{-mrtd}.
11744 This is the default.
11747 @itemx -mno-align-int
11748 @opindex malign-int
11749 @opindex mno-align-int
11750 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
11751 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
11752 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
11753 Aligning variables on 32-bit boundaries produces code that runs somewhat
11754 faster on processors with 32-bit busses at the expense of more memory.
11756 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
11757 align structures containing the above types differently than
11758 most published application binary interface specifications for the m68k.
11762 Use the pc-relative addressing mode of the 68000 directly, instead of
11763 using a global offset table. At present, this option implies @option{-fpic},
11764 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
11765 not presently supported with @option{-mpcrel}, though this could be supported for
11766 68020 and higher processors.
11768 @item -mno-strict-align
11769 @itemx -mstrict-align
11770 @opindex mno-strict-align
11771 @opindex mstrict-align
11772 Do not (do) assume that unaligned memory references will be handled by
11776 Generate code that allows the data segment to be located in a different
11777 area of memory from the text segment. This allows for execute in place in
11778 an environment without virtual memory management. This option implies
11781 @item -mno-sep-data
11782 Generate code that assumes that the data segment follows the text segment.
11783 This is the default.
11785 @item -mid-shared-library
11786 Generate code that supports shared libraries via the library ID method.
11787 This allows for execute in place and shared libraries in an environment
11788 without virtual memory management. This option implies @option{-fPIC}.
11790 @item -mno-id-shared-library
11791 Generate code that doesn't assume ID based shared libraries are being used.
11792 This is the default.
11794 @item -mshared-library-id=n
11795 Specified the identification number of the ID based shared library being
11796 compiled. Specifying a value of 0 will generate more compact code, specifying
11797 other values will force the allocation of that number to the current
11798 library but is no more space or time efficient than omitting this option.
11804 When generating position-independent code for ColdFire, generate code
11805 that works if the GOT has more than 8192 entries. This code is
11806 larger and slower than code generated without this option. On M680x0
11807 processors, this option is not needed; @option{-fPIC} suffices.
11809 GCC normally uses a single instruction to load values from the GOT@.
11810 While this is relatively efficient, it only works if the GOT
11811 is smaller than about 64k. Anything larger causes the linker
11812 to report an error such as:
11814 @cindex relocation truncated to fit (ColdFire)
11816 relocation truncated to fit: R_68K_GOT16O foobar
11819 If this happens, you should recompile your code with @option{-mxgot}.
11820 It should then work with very large GOTs. However, code generated with
11821 @option{-mxgot} is less efficient, since it takes 4 instructions to fetch
11822 the value of a global symbol.
11824 Note that some linkers, including newer versions of the GNU linker,
11825 can create multiple GOTs and sort GOT entries. If you have such a linker,
11826 you should only need to use @option{-mxgot} when compiling a single
11827 object file that accesses more than 8192 GOT entries. Very few do.
11829 These options have no effect unless GCC is generating
11830 position-independent code.
11834 @node M68hc1x Options
11835 @subsection M68hc1x Options
11836 @cindex M68hc1x options
11838 These are the @samp{-m} options defined for the 68hc11 and 68hc12
11839 microcontrollers. The default values for these options depends on
11840 which style of microcontroller was selected when the compiler was configured;
11841 the defaults for the most common choices are given below.
11848 Generate output for a 68HC11. This is the default
11849 when the compiler is configured for 68HC11-based systems.
11855 Generate output for a 68HC12. This is the default
11856 when the compiler is configured for 68HC12-based systems.
11862 Generate output for a 68HCS12.
11864 @item -mauto-incdec
11865 @opindex mauto-incdec
11866 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
11873 Enable the use of 68HC12 min and max instructions.
11876 @itemx -mno-long-calls
11877 @opindex mlong-calls
11878 @opindex mno-long-calls
11879 Treat all calls as being far away (near). If calls are assumed to be
11880 far away, the compiler will use the @code{call} instruction to
11881 call a function and the @code{rtc} instruction for returning.
11885 Consider type @code{int} to be 16 bits wide, like @code{short int}.
11887 @item -msoft-reg-count=@var{count}
11888 @opindex msoft-reg-count
11889 Specify the number of pseudo-soft registers which are used for the
11890 code generation. The maximum number is 32. Using more pseudo-soft
11891 register may or may not result in better code depending on the program.
11892 The default is 4 for 68HC11 and 2 for 68HC12.
11896 @node MCore Options
11897 @subsection MCore Options
11898 @cindex MCore options
11900 These are the @samp{-m} options defined for the Motorola M*Core
11906 @itemx -mno-hardlit
11908 @opindex mno-hardlit
11909 Inline constants into the code stream if it can be done in two
11910 instructions or less.
11916 Use the divide instruction. (Enabled by default).
11918 @item -mrelax-immediate
11919 @itemx -mno-relax-immediate
11920 @opindex mrelax-immediate
11921 @opindex mno-relax-immediate
11922 Allow arbitrary sized immediates in bit operations.
11924 @item -mwide-bitfields
11925 @itemx -mno-wide-bitfields
11926 @opindex mwide-bitfields
11927 @opindex mno-wide-bitfields
11928 Always treat bit-fields as int-sized.
11930 @item -m4byte-functions
11931 @itemx -mno-4byte-functions
11932 @opindex m4byte-functions
11933 @opindex mno-4byte-functions
11934 Force all functions to be aligned to a four byte boundary.
11936 @item -mcallgraph-data
11937 @itemx -mno-callgraph-data
11938 @opindex mcallgraph-data
11939 @opindex mno-callgraph-data
11940 Emit callgraph information.
11943 @itemx -mno-slow-bytes
11944 @opindex mslow-bytes
11945 @opindex mno-slow-bytes
11946 Prefer word access when reading byte quantities.
11948 @item -mlittle-endian
11949 @itemx -mbig-endian
11950 @opindex mlittle-endian
11951 @opindex mbig-endian
11952 Generate code for a little endian target.
11958 Generate code for the 210 processor.
11962 @subsection MIPS Options
11963 @cindex MIPS options
11969 Generate big-endian code.
11973 Generate little-endian code. This is the default for @samp{mips*el-*-*}
11976 @item -march=@var{arch}
11978 Generate code that will run on @var{arch}, which can be the name of a
11979 generic MIPS ISA, or the name of a particular processor.
11981 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
11982 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
11983 The processor names are:
11984 @samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc},
11985 @samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd},
11986 @samp{5kc}, @samp{5kf},
11988 @samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1},
11989 @samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1},
11990 @samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1},
11991 @samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2},
11992 @samp{loongson2e}, @samp{loongson2f},
11995 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
11996 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
11997 @samp{rm7000}, @samp{rm9000},
12000 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
12001 @samp{vr5000}, @samp{vr5400}, @samp{vr5500}
12003 The special value @samp{from-abi} selects the
12004 most compatible architecture for the selected ABI (that is,
12005 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
12007 Native Linux/GNU toolchains also support the value @samp{native},
12008 which selects the best architecture option for the host processor.
12009 @option{-march=native} has no effect if GCC does not recognize
12012 In processor names, a final @samp{000} can be abbreviated as @samp{k}
12013 (for example, @samp{-march=r2k}). Prefixes are optional, and
12014 @samp{vr} may be written @samp{r}.
12016 Names of the form @samp{@var{n}f2_1} refer to processors with
12017 FPUs clocked at half the rate of the core, names of the form
12018 @samp{@var{n}f1_1} refer to processors with FPUs clocked at the same
12019 rate as the core, and names of the form @samp{@var{n}f3_2} refer to
12020 processors with FPUs clocked a ratio of 3:2 with respect to the core.
12021 For compatibility reasons, @samp{@var{n}f} is accepted as a synonym
12022 for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are
12023 accepted as synonyms for @samp{@var{n}f1_1}.
12025 GCC defines two macros based on the value of this option. The first
12026 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
12027 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
12028 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
12029 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
12030 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
12032 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
12033 above. In other words, it will have the full prefix and will not
12034 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
12035 the macro names the resolved architecture (either @samp{"mips1"} or
12036 @samp{"mips3"}). It names the default architecture when no
12037 @option{-march} option is given.
12039 @item -mtune=@var{arch}
12041 Optimize for @var{arch}. Among other things, this option controls
12042 the way instructions are scheduled, and the perceived cost of arithmetic
12043 operations. The list of @var{arch} values is the same as for
12046 When this option is not used, GCC will optimize for the processor
12047 specified by @option{-march}. By using @option{-march} and
12048 @option{-mtune} together, it is possible to generate code that will
12049 run on a family of processors, but optimize the code for one
12050 particular member of that family.
12052 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
12053 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
12054 @samp{-march} ones described above.
12058 Equivalent to @samp{-march=mips1}.
12062 Equivalent to @samp{-march=mips2}.
12066 Equivalent to @samp{-march=mips3}.
12070 Equivalent to @samp{-march=mips4}.
12074 Equivalent to @samp{-march=mips32}.
12078 Equivalent to @samp{-march=mips32r2}.
12082 Equivalent to @samp{-march=mips64}.
12087 @opindex mno-mips16
12088 Generate (do not generate) MIPS16 code. If GCC is targetting a
12089 MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
12091 MIPS16 code generation can also be controlled on a per-function basis
12092 by means of @code{mips16} and @code{nomips16} attributes.
12093 @xref{Function Attributes}, for more information.
12095 @item -mflip-mips16
12096 @opindex mflip-mips16
12097 Generate MIPS16 code on alternating functions. This option is provided
12098 for regression testing of mixed MIPS16/non-MIPS16 code generation, and is
12099 not intended for ordinary use in compiling user code.
12101 @item -minterlink-mips16
12102 @itemx -mno-interlink-mips16
12103 @opindex minterlink-mips16
12104 @opindex mno-interlink-mips16
12105 Require (do not require) that non-MIPS16 code be link-compatible with
12108 For example, non-MIPS16 code cannot jump directly to MIPS16 code;
12109 it must either use a call or an indirect jump. @option{-minterlink-mips16}
12110 therefore disables direct jumps unless GCC knows that the target of the
12111 jump is not MIPS16.
12123 Generate code for the given ABI@.
12125 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
12126 generates 64-bit code when you select a 64-bit architecture, but you
12127 can use @option{-mgp32} to get 32-bit code instead.
12129 For information about the O64 ABI, see
12130 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
12132 GCC supports a variant of the o32 ABI in which floating-point registers
12133 are 64 rather than 32 bits wide. You can select this combination with
12134 @option{-mabi=32} @option{-mfp64}. This ABI relies on the @samp{mthc1}
12135 and @samp{mfhc1} instructions and is therefore only supported for
12136 MIPS32R2 processors.
12138 The register assignments for arguments and return values remain the
12139 same, but each scalar value is passed in a single 64-bit register
12140 rather than a pair of 32-bit registers. For example, scalar
12141 floating-point values are returned in @samp{$f0} only, not a
12142 @samp{$f0}/@samp{$f1} pair. The set of call-saved registers also
12143 remains the same, but all 64 bits are saved.
12146 @itemx -mno-abicalls
12148 @opindex mno-abicalls
12149 Generate (do not generate) code that is suitable for SVR4-style
12150 dynamic objects. @option{-mabicalls} is the default for SVR4-based
12155 Generate (do not generate) code that is fully position-independent,
12156 and that can therefore be linked into shared libraries. This option
12157 only affects @option{-mabicalls}.
12159 All @option{-mabicalls} code has traditionally been position-independent,
12160 regardless of options like @option{-fPIC} and @option{-fpic}. However,
12161 as an extension, the GNU toolchain allows executables to use absolute
12162 accesses for locally-binding symbols. It can also use shorter GP
12163 initialization sequences and generate direct calls to locally-defined
12164 functions. This mode is selected by @option{-mno-shared}.
12166 @option{-mno-shared} depends on binutils 2.16 or higher and generates
12167 objects that can only be linked by the GNU linker. However, the option
12168 does not affect the ABI of the final executable; it only affects the ABI
12169 of relocatable objects. Using @option{-mno-shared} will generally make
12170 executables both smaller and quicker.
12172 @option{-mshared} is the default.
12178 Lift (do not lift) the usual restrictions on the size of the global
12181 GCC normally uses a single instruction to load values from the GOT@.
12182 While this is relatively efficient, it will only work if the GOT
12183 is smaller than about 64k. Anything larger will cause the linker
12184 to report an error such as:
12186 @cindex relocation truncated to fit (MIPS)
12188 relocation truncated to fit: R_MIPS_GOT16 foobar
12191 If this happens, you should recompile your code with @option{-mxgot}.
12192 It should then work with very large GOTs, although it will also be
12193 less efficient, since it will take three instructions to fetch the
12194 value of a global symbol.
12196 Note that some linkers can create multiple GOTs. If you have such a
12197 linker, you should only need to use @option{-mxgot} when a single object
12198 file accesses more than 64k's worth of GOT entries. Very few do.
12200 These options have no effect unless GCC is generating position
12205 Assume that general-purpose registers are 32 bits wide.
12209 Assume that general-purpose registers are 64 bits wide.
12213 Assume that floating-point registers are 32 bits wide.
12217 Assume that floating-point registers are 64 bits wide.
12220 @opindex mhard-float
12221 Use floating-point coprocessor instructions.
12224 @opindex msoft-float
12225 Do not use floating-point coprocessor instructions. Implement
12226 floating-point calculations using library calls instead.
12228 @item -msingle-float
12229 @opindex msingle-float
12230 Assume that the floating-point coprocessor only supports single-precision
12233 @item -mdouble-float
12234 @opindex mdouble-float
12235 Assume that the floating-point coprocessor supports double-precision
12236 operations. This is the default.
12242 Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to
12243 implement atomic memory built-in functions. When neither option is
12244 specified, GCC will use the instructions if the target architecture
12247 @option{-mllsc} is useful if the runtime environment can emulate the
12248 instructions and @option{-mno-llsc} can be useful when compiling for
12249 nonstandard ISAs. You can make either option the default by
12250 configuring GCC with @option{--with-llsc} and @option{--without-llsc}
12251 respectively. @option{--with-llsc} is the default for some
12252 configurations; see the installation documentation for details.
12258 Use (do not use) revision 1 of the MIPS DSP ASE@.
12259 @xref{MIPS DSP Built-in Functions}. This option defines the
12260 preprocessor macro @samp{__mips_dsp}. It also defines
12261 @samp{__mips_dsp_rev} to 1.
12267 Use (do not use) revision 2 of the MIPS DSP ASE@.
12268 @xref{MIPS DSP Built-in Functions}. This option defines the
12269 preprocessor macros @samp{__mips_dsp} and @samp{__mips_dspr2}.
12270 It also defines @samp{__mips_dsp_rev} to 2.
12273 @itemx -mno-smartmips
12274 @opindex msmartmips
12275 @opindex mno-smartmips
12276 Use (do not use) the MIPS SmartMIPS ASE.
12278 @item -mpaired-single
12279 @itemx -mno-paired-single
12280 @opindex mpaired-single
12281 @opindex mno-paired-single
12282 Use (do not use) paired-single floating-point instructions.
12283 @xref{MIPS Paired-Single Support}. This option requires
12284 hardware floating-point support to be enabled.
12290 Use (do not use) MIPS Digital Media Extension instructions.
12291 This option can only be used when generating 64-bit code and requires
12292 hardware floating-point support to be enabled.
12297 @opindex mno-mips3d
12298 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
12299 The option @option{-mips3d} implies @option{-mpaired-single}.
12305 Use (do not use) MT Multithreading instructions.
12309 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
12310 an explanation of the default and the way that the pointer size is
12315 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
12317 The default size of @code{int}s, @code{long}s and pointers depends on
12318 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
12319 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
12320 32-bit @code{long}s. Pointers are the same size as @code{long}s,
12321 or the same size as integer registers, whichever is smaller.
12327 Assume (do not assume) that all symbols have 32-bit values, regardless
12328 of the selected ABI@. This option is useful in combination with
12329 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
12330 to generate shorter and faster references to symbolic addresses.
12334 Put definitions of externally-visible data in a small data section
12335 if that data is no bigger than @var{num} bytes. GCC can then access
12336 the data more efficiently; see @option{-mgpopt} for details.
12338 The default @option{-G} option depends on the configuration.
12340 @item -mlocal-sdata
12341 @itemx -mno-local-sdata
12342 @opindex mlocal-sdata
12343 @opindex mno-local-sdata
12344 Extend (do not extend) the @option{-G} behavior to local data too,
12345 such as to static variables in C@. @option{-mlocal-sdata} is the
12346 default for all configurations.
12348 If the linker complains that an application is using too much small data,
12349 you might want to try rebuilding the less performance-critical parts with
12350 @option{-mno-local-sdata}. You might also want to build large
12351 libraries with @option{-mno-local-sdata}, so that the libraries leave
12352 more room for the main program.
12354 @item -mextern-sdata
12355 @itemx -mno-extern-sdata
12356 @opindex mextern-sdata
12357 @opindex mno-extern-sdata
12358 Assume (do not assume) that externally-defined data will be in
12359 a small data section if that data is within the @option{-G} limit.
12360 @option{-mextern-sdata} is the default for all configurations.
12362 If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G
12363 @var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var}
12364 that is no bigger than @var{num} bytes, you must make sure that @var{Var}
12365 is placed in a small data section. If @var{Var} is defined by another
12366 module, you must either compile that module with a high-enough
12367 @option{-G} setting or attach a @code{section} attribute to @var{Var}'s
12368 definition. If @var{Var} is common, you must link the application
12369 with a high-enough @option{-G} setting.
12371 The easiest way of satisfying these restrictions is to compile
12372 and link every module with the same @option{-G} option. However,
12373 you may wish to build a library that supports several different
12374 small data limits. You can do this by compiling the library with
12375 the highest supported @option{-G} setting and additionally using
12376 @option{-mno-extern-sdata} to stop the library from making assumptions
12377 about externally-defined data.
12383 Use (do not use) GP-relative accesses for symbols that are known to be
12384 in a small data section; see @option{-G}, @option{-mlocal-sdata} and
12385 @option{-mextern-sdata}. @option{-mgpopt} is the default for all
12388 @option{-mno-gpopt} is useful for cases where the @code{$gp} register
12389 might not hold the value of @code{_gp}. For example, if the code is
12390 part of a library that might be used in a boot monitor, programs that
12391 call boot monitor routines will pass an unknown value in @code{$gp}.
12392 (In such situations, the boot monitor itself would usually be compiled
12393 with @option{-G0}.)
12395 @option{-mno-gpopt} implies @option{-mno-local-sdata} and
12396 @option{-mno-extern-sdata}.
12398 @item -membedded-data
12399 @itemx -mno-embedded-data
12400 @opindex membedded-data
12401 @opindex mno-embedded-data
12402 Allocate variables to the read-only data section first if possible, then
12403 next in the small data section if possible, otherwise in data. This gives
12404 slightly slower code than the default, but reduces the amount of RAM required
12405 when executing, and thus may be preferred for some embedded systems.
12407 @item -muninit-const-in-rodata
12408 @itemx -mno-uninit-const-in-rodata
12409 @opindex muninit-const-in-rodata
12410 @opindex mno-uninit-const-in-rodata
12411 Put uninitialized @code{const} variables in the read-only data section.
12412 This option is only meaningful in conjunction with @option{-membedded-data}.
12414 @item -mcode-readable=@var{setting}
12415 @opindex mcode-readable
12416 Specify whether GCC may generate code that reads from executable sections.
12417 There are three possible settings:
12420 @item -mcode-readable=yes
12421 Instructions may freely access executable sections. This is the
12424 @item -mcode-readable=pcrel
12425 MIPS16 PC-relative load instructions can access executable sections,
12426 but other instructions must not do so. This option is useful on 4KSc
12427 and 4KSd processors when the code TLBs have the Read Inhibit bit set.
12428 It is also useful on processors that can be configured to have a dual
12429 instruction/data SRAM interface and that, like the M4K, automatically
12430 redirect PC-relative loads to the instruction RAM.
12432 @item -mcode-readable=no
12433 Instructions must not access executable sections. This option can be
12434 useful on targets that are configured to have a dual instruction/data
12435 SRAM interface but that (unlike the M4K) do not automatically redirect
12436 PC-relative loads to the instruction RAM.
12439 @item -msplit-addresses
12440 @itemx -mno-split-addresses
12441 @opindex msplit-addresses
12442 @opindex mno-split-addresses
12443 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
12444 relocation operators. This option has been superseded by
12445 @option{-mexplicit-relocs} but is retained for backwards compatibility.
12447 @item -mexplicit-relocs
12448 @itemx -mno-explicit-relocs
12449 @opindex mexplicit-relocs
12450 @opindex mno-explicit-relocs
12451 Use (do not use) assembler relocation operators when dealing with symbolic
12452 addresses. The alternative, selected by @option{-mno-explicit-relocs},
12453 is to use assembler macros instead.
12455 @option{-mexplicit-relocs} is the default if GCC was configured
12456 to use an assembler that supports relocation operators.
12458 @item -mcheck-zero-division
12459 @itemx -mno-check-zero-division
12460 @opindex mcheck-zero-division
12461 @opindex mno-check-zero-division
12462 Trap (do not trap) on integer division by zero.
12464 The default is @option{-mcheck-zero-division}.
12466 @item -mdivide-traps
12467 @itemx -mdivide-breaks
12468 @opindex mdivide-traps
12469 @opindex mdivide-breaks
12470 MIPS systems check for division by zero by generating either a
12471 conditional trap or a break instruction. Using traps results in
12472 smaller code, but is only supported on MIPS II and later. Also, some
12473 versions of the Linux kernel have a bug that prevents trap from
12474 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
12475 allow conditional traps on architectures that support them and
12476 @option{-mdivide-breaks} to force the use of breaks.
12478 The default is usually @option{-mdivide-traps}, but this can be
12479 overridden at configure time using @option{--with-divide=breaks}.
12480 Divide-by-zero checks can be completely disabled using
12481 @option{-mno-check-zero-division}.
12486 @opindex mno-memcpy
12487 Force (do not force) the use of @code{memcpy()} for non-trivial block
12488 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
12489 most constant-sized copies.
12492 @itemx -mno-long-calls
12493 @opindex mlong-calls
12494 @opindex mno-long-calls
12495 Disable (do not disable) use of the @code{jal} instruction. Calling
12496 functions using @code{jal} is more efficient but requires the caller
12497 and callee to be in the same 256 megabyte segment.
12499 This option has no effect on abicalls code. The default is
12500 @option{-mno-long-calls}.
12506 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
12507 instructions, as provided by the R4650 ISA@.
12510 @itemx -mno-fused-madd
12511 @opindex mfused-madd
12512 @opindex mno-fused-madd
12513 Enable (disable) use of the floating point multiply-accumulate
12514 instructions, when they are available. The default is
12515 @option{-mfused-madd}.
12517 When multiply-accumulate instructions are used, the intermediate
12518 product is calculated to infinite precision and is not subject to
12519 the FCSR Flush to Zero bit. This may be undesirable in some
12524 Tell the MIPS assembler to not run its preprocessor over user
12525 assembler files (with a @samp{.s} suffix) when assembling them.
12528 @itemx -mno-fix-r4000
12529 @opindex mfix-r4000
12530 @opindex mno-fix-r4000
12531 Work around certain R4000 CPU errata:
12534 A double-word or a variable shift may give an incorrect result if executed
12535 immediately after starting an integer division.
12537 A double-word or a variable shift may give an incorrect result if executed
12538 while an integer multiplication is in progress.
12540 An integer division may give an incorrect result if started in a delay slot
12541 of a taken branch or a jump.
12545 @itemx -mno-fix-r4400
12546 @opindex mfix-r4400
12547 @opindex mno-fix-r4400
12548 Work around certain R4400 CPU errata:
12551 A double-word or a variable shift may give an incorrect result if executed
12552 immediately after starting an integer division.
12556 @itemx -mno-fix-vr4120
12557 @opindex mfix-vr4120
12558 Work around certain VR4120 errata:
12561 @code{dmultu} does not always produce the correct result.
12563 @code{div} and @code{ddiv} do not always produce the correct result if one
12564 of the operands is negative.
12566 The workarounds for the division errata rely on special functions in
12567 @file{libgcc.a}. At present, these functions are only provided by
12568 the @code{mips64vr*-elf} configurations.
12570 Other VR4120 errata require a nop to be inserted between certain pairs of
12571 instructions. These errata are handled by the assembler, not by GCC itself.
12574 @opindex mfix-vr4130
12575 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
12576 workarounds are implemented by the assembler rather than by GCC,
12577 although GCC will avoid using @code{mflo} and @code{mfhi} if the
12578 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
12579 instructions are available instead.
12582 @itemx -mno-fix-sb1
12584 Work around certain SB-1 CPU core errata.
12585 (This flag currently works around the SB-1 revision 2
12586 ``F1'' and ``F2'' floating point errata.)
12588 @item -mflush-func=@var{func}
12589 @itemx -mno-flush-func
12590 @opindex mflush-func
12591 Specifies the function to call to flush the I and D caches, or to not
12592 call any such function. If called, the function must take the same
12593 arguments as the common @code{_flush_func()}, that is, the address of the
12594 memory range for which the cache is being flushed, the size of the
12595 memory range, and the number 3 (to flush both caches). The default
12596 depends on the target GCC was configured for, but commonly is either
12597 @samp{_flush_func} or @samp{__cpu_flush}.
12599 @item mbranch-cost=@var{num}
12600 @opindex mbranch-cost
12601 Set the cost of branches to roughly @var{num} ``simple'' instructions.
12602 This cost is only a heuristic and is not guaranteed to produce
12603 consistent results across releases. A zero cost redundantly selects
12604 the default, which is based on the @option{-mtune} setting.
12606 @item -mbranch-likely
12607 @itemx -mno-branch-likely
12608 @opindex mbranch-likely
12609 @opindex mno-branch-likely
12610 Enable or disable use of Branch Likely instructions, regardless of the
12611 default for the selected architecture. By default, Branch Likely
12612 instructions may be generated if they are supported by the selected
12613 architecture. An exception is for the MIPS32 and MIPS64 architectures
12614 and processors which implement those architectures; for those, Branch
12615 Likely instructions will not be generated by default because the MIPS32
12616 and MIPS64 architectures specifically deprecate their use.
12618 @item -mfp-exceptions
12619 @itemx -mno-fp-exceptions
12620 @opindex mfp-exceptions
12621 Specifies whether FP exceptions are enabled. This affects how we schedule
12622 FP instructions for some processors. The default is that FP exceptions are
12625 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
12626 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
12629 @item -mvr4130-align
12630 @itemx -mno-vr4130-align
12631 @opindex mvr4130-align
12632 The VR4130 pipeline is two-way superscalar, but can only issue two
12633 instructions together if the first one is 8-byte aligned. When this
12634 option is enabled, GCC will align pairs of instructions that it
12635 thinks should execute in parallel.
12637 This option only has an effect when optimizing for the VR4130.
12638 It normally makes code faster, but at the expense of making it bigger.
12639 It is enabled by default at optimization level @option{-O3}.
12643 @subsection MMIX Options
12644 @cindex MMIX Options
12646 These options are defined for the MMIX:
12650 @itemx -mno-libfuncs
12652 @opindex mno-libfuncs
12653 Specify that intrinsic library functions are being compiled, passing all
12654 values in registers, no matter the size.
12657 @itemx -mno-epsilon
12659 @opindex mno-epsilon
12660 Generate floating-point comparison instructions that compare with respect
12661 to the @code{rE} epsilon register.
12663 @item -mabi=mmixware
12665 @opindex mabi-mmixware
12667 Generate code that passes function parameters and return values that (in
12668 the called function) are seen as registers @code{$0} and up, as opposed to
12669 the GNU ABI which uses global registers @code{$231} and up.
12671 @item -mzero-extend
12672 @itemx -mno-zero-extend
12673 @opindex mzero-extend
12674 @opindex mno-zero-extend
12675 When reading data from memory in sizes shorter than 64 bits, use (do not
12676 use) zero-extending load instructions by default, rather than
12677 sign-extending ones.
12680 @itemx -mno-knuthdiv
12682 @opindex mno-knuthdiv
12683 Make the result of a division yielding a remainder have the same sign as
12684 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
12685 remainder follows the sign of the dividend. Both methods are
12686 arithmetically valid, the latter being almost exclusively used.
12688 @item -mtoplevel-symbols
12689 @itemx -mno-toplevel-symbols
12690 @opindex mtoplevel-symbols
12691 @opindex mno-toplevel-symbols
12692 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
12693 code can be used with the @code{PREFIX} assembly directive.
12697 Generate an executable in the ELF format, rather than the default
12698 @samp{mmo} format used by the @command{mmix} simulator.
12700 @item -mbranch-predict
12701 @itemx -mno-branch-predict
12702 @opindex mbranch-predict
12703 @opindex mno-branch-predict
12704 Use (do not use) the probable-branch instructions, when static branch
12705 prediction indicates a probable branch.
12707 @item -mbase-addresses
12708 @itemx -mno-base-addresses
12709 @opindex mbase-addresses
12710 @opindex mno-base-addresses
12711 Generate (do not generate) code that uses @emph{base addresses}. Using a
12712 base address automatically generates a request (handled by the assembler
12713 and the linker) for a constant to be set up in a global register. The
12714 register is used for one or more base address requests within the range 0
12715 to 255 from the value held in the register. The generally leads to short
12716 and fast code, but the number of different data items that can be
12717 addressed is limited. This means that a program that uses lots of static
12718 data may require @option{-mno-base-addresses}.
12720 @item -msingle-exit
12721 @itemx -mno-single-exit
12722 @opindex msingle-exit
12723 @opindex mno-single-exit
12724 Force (do not force) generated code to have a single exit point in each
12728 @node MN10300 Options
12729 @subsection MN10300 Options
12730 @cindex MN10300 options
12732 These @option{-m} options are defined for Matsushita MN10300 architectures:
12737 Generate code to avoid bugs in the multiply instructions for the MN10300
12738 processors. This is the default.
12740 @item -mno-mult-bug
12741 @opindex mno-mult-bug
12742 Do not generate code to avoid bugs in the multiply instructions for the
12743 MN10300 processors.
12747 Generate code which uses features specific to the AM33 processor.
12751 Do not generate code which uses features specific to the AM33 processor. This
12754 @item -mreturn-pointer-on-d0
12755 @opindex mreturn-pointer-on-d0
12756 When generating a function which returns a pointer, return the pointer
12757 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
12758 only in a0, and attempts to call such functions without a prototype
12759 would result in errors. Note that this option is on by default; use
12760 @option{-mno-return-pointer-on-d0} to disable it.
12764 Do not link in the C run-time initialization object file.
12768 Indicate to the linker that it should perform a relaxation optimization pass
12769 to shorten branches, calls and absolute memory addresses. This option only
12770 has an effect when used on the command line for the final link step.
12772 This option makes symbolic debugging impossible.
12775 @node PDP-11 Options
12776 @subsection PDP-11 Options
12777 @cindex PDP-11 Options
12779 These options are defined for the PDP-11:
12784 Use hardware FPP floating point. This is the default. (FIS floating
12785 point on the PDP-11/40 is not supported.)
12788 @opindex msoft-float
12789 Do not use hardware floating point.
12793 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
12797 Return floating-point results in memory. This is the default.
12801 Generate code for a PDP-11/40.
12805 Generate code for a PDP-11/45. This is the default.
12809 Generate code for a PDP-11/10.
12811 @item -mbcopy-builtin
12812 @opindex bcopy-builtin
12813 Use inline @code{movmemhi} patterns for copying memory. This is the
12818 Do not use inline @code{movmemhi} patterns for copying memory.
12824 Use 16-bit @code{int}. This is the default.
12830 Use 32-bit @code{int}.
12833 @itemx -mno-float32
12835 @opindex mno-float32
12836 Use 64-bit @code{float}. This is the default.
12839 @itemx -mno-float64
12841 @opindex mno-float64
12842 Use 32-bit @code{float}.
12846 Use @code{abshi2} pattern. This is the default.
12850 Do not use @code{abshi2} pattern.
12852 @item -mbranch-expensive
12853 @opindex mbranch-expensive
12854 Pretend that branches are expensive. This is for experimenting with
12855 code generation only.
12857 @item -mbranch-cheap
12858 @opindex mbranch-cheap
12859 Do not pretend that branches are expensive. This is the default.
12863 Generate code for a system with split I&D@.
12867 Generate code for a system without split I&D@. This is the default.
12871 Use Unix assembler syntax. This is the default when configured for
12872 @samp{pdp11-*-bsd}.
12876 Use DEC assembler syntax. This is the default when configured for any
12877 PDP-11 target other than @samp{pdp11-*-bsd}.
12880 @node PowerPC Options
12881 @subsection PowerPC Options
12882 @cindex PowerPC options
12884 These are listed under @xref{RS/6000 and PowerPC Options}.
12886 @node RS/6000 and PowerPC Options
12887 @subsection IBM RS/6000 and PowerPC Options
12888 @cindex RS/6000 and PowerPC Options
12889 @cindex IBM RS/6000 and PowerPC Options
12891 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
12898 @itemx -mno-powerpc
12899 @itemx -mpowerpc-gpopt
12900 @itemx -mno-powerpc-gpopt
12901 @itemx -mpowerpc-gfxopt
12902 @itemx -mno-powerpc-gfxopt
12904 @itemx -mno-powerpc64
12908 @itemx -mno-popcntb
12916 @itemx -mno-hard-dfp
12920 @opindex mno-power2
12922 @opindex mno-powerpc
12923 @opindex mpowerpc-gpopt
12924 @opindex mno-powerpc-gpopt
12925 @opindex mpowerpc-gfxopt
12926 @opindex mno-powerpc-gfxopt
12927 @opindex mpowerpc64
12928 @opindex mno-powerpc64
12932 @opindex mno-popcntb
12938 @opindex mno-mfpgpr
12940 @opindex mno-hard-dfp
12941 GCC supports two related instruction set architectures for the
12942 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
12943 instructions supported by the @samp{rios} chip set used in the original
12944 RS/6000 systems and the @dfn{PowerPC} instruction set is the
12945 architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and
12946 the IBM 4xx, 6xx, and follow-on microprocessors.
12948 Neither architecture is a subset of the other. However there is a
12949 large common subset of instructions supported by both. An MQ
12950 register is included in processors supporting the POWER architecture.
12952 You use these options to specify which instructions are available on the
12953 processor you are using. The default value of these options is
12954 determined when configuring GCC@. Specifying the
12955 @option{-mcpu=@var{cpu_type}} overrides the specification of these
12956 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
12957 rather than the options listed above.
12959 The @option{-mpower} option allows GCC to generate instructions that
12960 are found only in the POWER architecture and to use the MQ register.
12961 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
12962 to generate instructions that are present in the POWER2 architecture but
12963 not the original POWER architecture.
12965 The @option{-mpowerpc} option allows GCC to generate instructions that
12966 are found only in the 32-bit subset of the PowerPC architecture.
12967 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
12968 GCC to use the optional PowerPC architecture instructions in the
12969 General Purpose group, including floating-point square root. Specifying
12970 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
12971 use the optional PowerPC architecture instructions in the Graphics
12972 group, including floating-point select.
12974 The @option{-mmfcrf} option allows GCC to generate the move from
12975 condition register field instruction implemented on the POWER4
12976 processor and other processors that support the PowerPC V2.01
12978 The @option{-mpopcntb} option allows GCC to generate the popcount and
12979 double precision FP reciprocal estimate instruction implemented on the
12980 POWER5 processor and other processors that support the PowerPC V2.02
12982 The @option{-mfprnd} option allows GCC to generate the FP round to
12983 integer instructions implemented on the POWER5+ processor and other
12984 processors that support the PowerPC V2.03 architecture.
12985 The @option{-mcmpb} option allows GCC to generate the compare bytes
12986 instruction implemented on the POWER6 processor and other processors
12987 that support the PowerPC V2.05 architecture.
12988 The @option{-mmfpgpr} option allows GCC to generate the FP move to/from
12989 general purpose register instructions implemented on the POWER6X
12990 processor and other processors that support the extended PowerPC V2.05
12992 The @option{-mhard-dfp} option allows GCC to generate the decimal floating
12993 point instructions implemented on some POWER processors.
12995 The @option{-mpowerpc64} option allows GCC to generate the additional
12996 64-bit instructions that are found in the full PowerPC64 architecture
12997 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
12998 @option{-mno-powerpc64}.
13000 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
13001 will use only the instructions in the common subset of both
13002 architectures plus some special AIX common-mode calls, and will not use
13003 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
13004 permits GCC to use any instruction from either architecture and to
13005 allow use of the MQ register; specify this for the Motorola MPC601.
13007 @item -mnew-mnemonics
13008 @itemx -mold-mnemonics
13009 @opindex mnew-mnemonics
13010 @opindex mold-mnemonics
13011 Select which mnemonics to use in the generated assembler code. With
13012 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
13013 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
13014 assembler mnemonics defined for the POWER architecture. Instructions
13015 defined in only one architecture have only one mnemonic; GCC uses that
13016 mnemonic irrespective of which of these options is specified.
13018 GCC defaults to the mnemonics appropriate for the architecture in
13019 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
13020 value of these option. Unless you are building a cross-compiler, you
13021 should normally not specify either @option{-mnew-mnemonics} or
13022 @option{-mold-mnemonics}, but should instead accept the default.
13024 @item -mcpu=@var{cpu_type}
13026 Set architecture type, register usage, choice of mnemonics, and
13027 instruction scheduling parameters for machine type @var{cpu_type}.
13028 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
13029 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp},
13030 @samp{505}, @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
13031 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
13032 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
13033 @samp{860}, @samp{970}, @samp{8540}, @samp{e300c2}, @samp{e300c3},
13034 @samp{e500mc}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5},
13035 @samp{power}, @samp{power2}, @samp{power3}, @samp{power4},
13036 @samp{power5}, @samp{power5+}, @samp{power6}, @samp{power6x},
13037 @samp{common}, @samp{powerpc}, @samp{powerpc64}, @samp{rios},
13038 @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
13040 @option{-mcpu=common} selects a completely generic processor. Code
13041 generated under this option will run on any POWER or PowerPC processor.
13042 GCC will use only the instructions in the common subset of both
13043 architectures, and will not use the MQ register. GCC assumes a generic
13044 processor model for scheduling purposes.
13046 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
13047 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
13048 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
13049 types, with an appropriate, generic processor model assumed for
13050 scheduling purposes.
13052 The other options specify a specific processor. Code generated under
13053 those options will run best on that processor, and may not run at all on
13056 The @option{-mcpu} options automatically enable or disable the
13059 @gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol
13060 -mnew-mnemonics -mpopcntb -mpower -mpower2 -mpowerpc64 @gol
13061 -mpowerpc-gpopt -mpowerpc-gfxopt -mstring -mmulhw -mdlmzb -mmfpgpr}
13063 The particular options set for any particular CPU will vary between
13064 compiler versions, depending on what setting seems to produce optimal
13065 code for that CPU; it doesn't necessarily reflect the actual hardware's
13066 capabilities. If you wish to set an individual option to a particular
13067 value, you may specify it after the @option{-mcpu} option, like
13068 @samp{-mcpu=970 -mno-altivec}.
13070 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
13071 not enabled or disabled by the @option{-mcpu} option at present because
13072 AIX does not have full support for these options. You may still
13073 enable or disable them individually if you're sure it'll work in your
13076 @item -mtune=@var{cpu_type}
13078 Set the instruction scheduling parameters for machine type
13079 @var{cpu_type}, but do not set the architecture type, register usage, or
13080 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
13081 values for @var{cpu_type} are used for @option{-mtune} as for
13082 @option{-mcpu}. If both are specified, the code generated will use the
13083 architecture, registers, and mnemonics set by @option{-mcpu}, but the
13084 scheduling parameters set by @option{-mtune}.
13090 Generate code to compute division as reciprocal estimate and iterative
13091 refinement, creating opportunities for increased throughput. This
13092 feature requires: optional PowerPC Graphics instruction set for single
13093 precision and FRE instruction for double precision, assuming divides
13094 cannot generate user-visible traps, and the domain values not include
13095 Infinities, denormals or zero denominator.
13098 @itemx -mno-altivec
13100 @opindex mno-altivec
13101 Generate code that uses (does not use) AltiVec instructions, and also
13102 enable the use of built-in functions that allow more direct access to
13103 the AltiVec instruction set. You may also need to set
13104 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
13110 @opindex mno-vrsave
13111 Generate VRSAVE instructions when generating AltiVec code.
13114 @opindex msecure-plt
13115 Generate code that allows ld and ld.so to build executables and shared
13116 libraries with non-exec .plt and .got sections. This is a PowerPC
13117 32-bit SYSV ABI option.
13121 Generate code that uses a BSS .plt section that ld.so fills in, and
13122 requires .plt and .got sections that are both writable and executable.
13123 This is a PowerPC 32-bit SYSV ABI option.
13129 This switch enables or disables the generation of ISEL instructions.
13131 @item -misel=@var{yes/no}
13132 This switch has been deprecated. Use @option{-misel} and
13133 @option{-mno-isel} instead.
13139 This switch enables or disables the generation of SPE simd
13145 @opindex mno-paired
13146 This switch enables or disables the generation of PAIRED simd
13149 @item -mspe=@var{yes/no}
13150 This option has been deprecated. Use @option{-mspe} and
13151 @option{-mno-spe} instead.
13153 @item -mfloat-gprs=@var{yes/single/double/no}
13154 @itemx -mfloat-gprs
13155 @opindex mfloat-gprs
13156 This switch enables or disables the generation of floating point
13157 operations on the general purpose registers for architectures that
13160 The argument @var{yes} or @var{single} enables the use of
13161 single-precision floating point operations.
13163 The argument @var{double} enables the use of single and
13164 double-precision floating point operations.
13166 The argument @var{no} disables floating point operations on the
13167 general purpose registers.
13169 This option is currently only available on the MPC854x.
13175 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
13176 targets (including GNU/Linux). The 32-bit environment sets int, long
13177 and pointer to 32 bits and generates code that runs on any PowerPC
13178 variant. The 64-bit environment sets int to 32 bits and long and
13179 pointer to 64 bits, and generates code for PowerPC64, as for
13180 @option{-mpowerpc64}.
13183 @itemx -mno-fp-in-toc
13184 @itemx -mno-sum-in-toc
13185 @itemx -mminimal-toc
13187 @opindex mno-fp-in-toc
13188 @opindex mno-sum-in-toc
13189 @opindex mminimal-toc
13190 Modify generation of the TOC (Table Of Contents), which is created for
13191 every executable file. The @option{-mfull-toc} option is selected by
13192 default. In that case, GCC will allocate at least one TOC entry for
13193 each unique non-automatic variable reference in your program. GCC
13194 will also place floating-point constants in the TOC@. However, only
13195 16,384 entries are available in the TOC@.
13197 If you receive a linker error message that saying you have overflowed
13198 the available TOC space, you can reduce the amount of TOC space used
13199 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
13200 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
13201 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
13202 generate code to calculate the sum of an address and a constant at
13203 run-time instead of putting that sum into the TOC@. You may specify one
13204 or both of these options. Each causes GCC to produce very slightly
13205 slower and larger code at the expense of conserving TOC space.
13207 If you still run out of space in the TOC even when you specify both of
13208 these options, specify @option{-mminimal-toc} instead. This option causes
13209 GCC to make only one TOC entry for every file. When you specify this
13210 option, GCC will produce code that is slower and larger but which
13211 uses extremely little TOC space. You may wish to use this option
13212 only on files that contain less frequently executed code.
13218 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
13219 @code{long} type, and the infrastructure needed to support them.
13220 Specifying @option{-maix64} implies @option{-mpowerpc64} and
13221 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
13222 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
13225 @itemx -mno-xl-compat
13226 @opindex mxl-compat
13227 @opindex mno-xl-compat
13228 Produce code that conforms more closely to IBM XL compiler semantics
13229 when using AIX-compatible ABI@. Pass floating-point arguments to
13230 prototyped functions beyond the register save area (RSA) on the stack
13231 in addition to argument FPRs. Do not assume that most significant
13232 double in 128-bit long double value is properly rounded when comparing
13233 values and converting to double. Use XL symbol names for long double
13236 The AIX calling convention was extended but not initially documented to
13237 handle an obscure K&R C case of calling a function that takes the
13238 address of its arguments with fewer arguments than declared. IBM XL
13239 compilers access floating point arguments which do not fit in the
13240 RSA from the stack when a subroutine is compiled without
13241 optimization. Because always storing floating-point arguments on the
13242 stack is inefficient and rarely needed, this option is not enabled by
13243 default and only is necessary when calling subroutines compiled by IBM
13244 XL compilers without optimization.
13248 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
13249 application written to use message passing with special startup code to
13250 enable the application to run. The system must have PE installed in the
13251 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
13252 must be overridden with the @option{-specs=} option to specify the
13253 appropriate directory location. The Parallel Environment does not
13254 support threads, so the @option{-mpe} option and the @option{-pthread}
13255 option are incompatible.
13257 @item -malign-natural
13258 @itemx -malign-power
13259 @opindex malign-natural
13260 @opindex malign-power
13261 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
13262 @option{-malign-natural} overrides the ABI-defined alignment of larger
13263 types, such as floating-point doubles, on their natural size-based boundary.
13264 The option @option{-malign-power} instructs GCC to follow the ABI-specified
13265 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
13267 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
13271 @itemx -mhard-float
13272 @opindex msoft-float
13273 @opindex mhard-float
13274 Generate code that does not use (uses) the floating-point register set.
13275 Software floating point emulation is provided if you use the
13276 @option{-msoft-float} option, and pass the option to GCC when linking.
13279 @itemx -mno-multiple
13281 @opindex mno-multiple
13282 Generate code that uses (does not use) the load multiple word
13283 instructions and the store multiple word instructions. These
13284 instructions are generated by default on POWER systems, and not
13285 generated on PowerPC systems. Do not use @option{-mmultiple} on little
13286 endian PowerPC systems, since those instructions do not work when the
13287 processor is in little endian mode. The exceptions are PPC740 and
13288 PPC750 which permit the instructions usage in little endian mode.
13293 @opindex mno-string
13294 Generate code that uses (does not use) the load string instructions
13295 and the store string word instructions to save multiple registers and
13296 do small block moves. These instructions are generated by default on
13297 POWER systems, and not generated on PowerPC systems. Do not use
13298 @option{-mstring} on little endian PowerPC systems, since those
13299 instructions do not work when the processor is in little endian mode.
13300 The exceptions are PPC740 and PPC750 which permit the instructions
13301 usage in little endian mode.
13306 @opindex mno-update
13307 Generate code that uses (does not use) the load or store instructions
13308 that update the base register to the address of the calculated memory
13309 location. These instructions are generated by default. If you use
13310 @option{-mno-update}, there is a small window between the time that the
13311 stack pointer is updated and the address of the previous frame is
13312 stored, which means code that walks the stack frame across interrupts or
13313 signals may get corrupted data.
13316 @itemx -mno-fused-madd
13317 @opindex mfused-madd
13318 @opindex mno-fused-madd
13319 Generate code that uses (does not use) the floating point multiply and
13320 accumulate instructions. These instructions are generated by default if
13321 hardware floating is used.
13327 Generate code that uses (does not use) the half-word multiply and
13328 multiply-accumulate instructions on the IBM 405, 440 and 464 processors.
13329 These instructions are generated by default when targetting those
13336 Generate code that uses (does not use) the string-search @samp{dlmzb}
13337 instruction on the IBM 405, 440 and 464 processors. This instruction is
13338 generated by default when targetting those processors.
13340 @item -mno-bit-align
13342 @opindex mno-bit-align
13343 @opindex mbit-align
13344 On System V.4 and embedded PowerPC systems do not (do) force structures
13345 and unions that contain bit-fields to be aligned to the base type of the
13348 For example, by default a structure containing nothing but 8
13349 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
13350 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
13351 the structure would be aligned to a 1 byte boundary and be one byte in
13354 @item -mno-strict-align
13355 @itemx -mstrict-align
13356 @opindex mno-strict-align
13357 @opindex mstrict-align
13358 On System V.4 and embedded PowerPC systems do not (do) assume that
13359 unaligned memory references will be handled by the system.
13361 @item -mrelocatable
13362 @itemx -mno-relocatable
13363 @opindex mrelocatable
13364 @opindex mno-relocatable
13365 On embedded PowerPC systems generate code that allows (does not allow)
13366 the program to be relocated to a different address at runtime. If you
13367 use @option{-mrelocatable} on any module, all objects linked together must
13368 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
13370 @item -mrelocatable-lib
13371 @itemx -mno-relocatable-lib
13372 @opindex mrelocatable-lib
13373 @opindex mno-relocatable-lib
13374 On embedded PowerPC systems generate code that allows (does not allow)
13375 the program to be relocated to a different address at runtime. Modules
13376 compiled with @option{-mrelocatable-lib} can be linked with either modules
13377 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
13378 with modules compiled with the @option{-mrelocatable} options.
13384 On System V.4 and embedded PowerPC systems do not (do) assume that
13385 register 2 contains a pointer to a global area pointing to the addresses
13386 used in the program.
13389 @itemx -mlittle-endian
13391 @opindex mlittle-endian
13392 On System V.4 and embedded PowerPC systems compile code for the
13393 processor in little endian mode. The @option{-mlittle-endian} option is
13394 the same as @option{-mlittle}.
13397 @itemx -mbig-endian
13399 @opindex mbig-endian
13400 On System V.4 and embedded PowerPC systems compile code for the
13401 processor in big endian mode. The @option{-mbig-endian} option is
13402 the same as @option{-mbig}.
13404 @item -mdynamic-no-pic
13405 @opindex mdynamic-no-pic
13406 On Darwin and Mac OS X systems, compile code so that it is not
13407 relocatable, but that its external references are relocatable. The
13408 resulting code is suitable for applications, but not shared
13411 @item -mprioritize-restricted-insns=@var{priority}
13412 @opindex mprioritize-restricted-insns
13413 This option controls the priority that is assigned to
13414 dispatch-slot restricted instructions during the second scheduling
13415 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
13416 @var{no/highest/second-highest} priority to dispatch slot restricted
13419 @item -msched-costly-dep=@var{dependence_type}
13420 @opindex msched-costly-dep
13421 This option controls which dependences are considered costly
13422 by the target during instruction scheduling. The argument
13423 @var{dependence_type} takes one of the following values:
13424 @var{no}: no dependence is costly,
13425 @var{all}: all dependences are costly,
13426 @var{true_store_to_load}: a true dependence from store to load is costly,
13427 @var{store_to_load}: any dependence from store to load is costly,
13428 @var{number}: any dependence which latency >= @var{number} is costly.
13430 @item -minsert-sched-nops=@var{scheme}
13431 @opindex minsert-sched-nops
13432 This option controls which nop insertion scheme will be used during
13433 the second scheduling pass. The argument @var{scheme} takes one of the
13435 @var{no}: Don't insert nops.
13436 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
13437 according to the scheduler's grouping.
13438 @var{regroup_exact}: Insert nops to force costly dependent insns into
13439 separate groups. Insert exactly as many nops as needed to force an insn
13440 to a new group, according to the estimated processor grouping.
13441 @var{number}: Insert nops to force costly dependent insns into
13442 separate groups. Insert @var{number} nops to force an insn to a new group.
13445 @opindex mcall-sysv
13446 On System V.4 and embedded PowerPC systems compile code using calling
13447 conventions that adheres to the March 1995 draft of the System V
13448 Application Binary Interface, PowerPC processor supplement. This is the
13449 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
13451 @item -mcall-sysv-eabi
13452 @opindex mcall-sysv-eabi
13453 Specify both @option{-mcall-sysv} and @option{-meabi} options.
13455 @item -mcall-sysv-noeabi
13456 @opindex mcall-sysv-noeabi
13457 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
13459 @item -mcall-solaris
13460 @opindex mcall-solaris
13461 On System V.4 and embedded PowerPC systems compile code for the Solaris
13465 @opindex mcall-linux
13466 On System V.4 and embedded PowerPC systems compile code for the
13467 Linux-based GNU system.
13471 On System V.4 and embedded PowerPC systems compile code for the
13472 Hurd-based GNU system.
13474 @item -mcall-netbsd
13475 @opindex mcall-netbsd
13476 On System V.4 and embedded PowerPC systems compile code for the
13477 NetBSD operating system.
13479 @item -maix-struct-return
13480 @opindex maix-struct-return
13481 Return all structures in memory (as specified by the AIX ABI)@.
13483 @item -msvr4-struct-return
13484 @opindex msvr4-struct-return
13485 Return structures smaller than 8 bytes in registers (as specified by the
13488 @item -mabi=@var{abi-type}
13490 Extend the current ABI with a particular extension, or remove such extension.
13491 Valid values are @var{altivec}, @var{no-altivec}, @var{spe},
13492 @var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}@.
13496 Extend the current ABI with SPE ABI extensions. This does not change
13497 the default ABI, instead it adds the SPE ABI extensions to the current
13501 @opindex mabi=no-spe
13502 Disable Booke SPE ABI extensions for the current ABI@.
13504 @item -mabi=ibmlongdouble
13505 @opindex mabi=ibmlongdouble
13506 Change the current ABI to use IBM extended precision long double.
13507 This is a PowerPC 32-bit SYSV ABI option.
13509 @item -mabi=ieeelongdouble
13510 @opindex mabi=ieeelongdouble
13511 Change the current ABI to use IEEE extended precision long double.
13512 This is a PowerPC 32-bit Linux ABI option.
13515 @itemx -mno-prototype
13516 @opindex mprototype
13517 @opindex mno-prototype
13518 On System V.4 and embedded PowerPC systems assume that all calls to
13519 variable argument functions are properly prototyped. Otherwise, the
13520 compiler must insert an instruction before every non prototyped call to
13521 set or clear bit 6 of the condition code register (@var{CR}) to
13522 indicate whether floating point values were passed in the floating point
13523 registers in case the function takes a variable arguments. With
13524 @option{-mprototype}, only calls to prototyped variable argument functions
13525 will set or clear the bit.
13529 On embedded PowerPC systems, assume that the startup module is called
13530 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
13531 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}
13536 On embedded PowerPC systems, assume that the startup module is called
13537 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
13542 On embedded PowerPC systems, assume that the startup module is called
13543 @file{crt0.o} and the standard C libraries are @file{libads.a} and
13546 @item -myellowknife
13547 @opindex myellowknife
13548 On embedded PowerPC systems, assume that the startup module is called
13549 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
13554 On System V.4 and embedded PowerPC systems, specify that you are
13555 compiling for a VxWorks system.
13559 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
13560 header to indicate that @samp{eabi} extended relocations are used.
13566 On System V.4 and embedded PowerPC systems do (do not) adhere to the
13567 Embedded Applications Binary Interface (eabi) which is a set of
13568 modifications to the System V.4 specifications. Selecting @option{-meabi}
13569 means that the stack is aligned to an 8 byte boundary, a function
13570 @code{__eabi} is called to from @code{main} to set up the eabi
13571 environment, and the @option{-msdata} option can use both @code{r2} and
13572 @code{r13} to point to two separate small data areas. Selecting
13573 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
13574 do not call an initialization function from @code{main}, and the
13575 @option{-msdata} option will only use @code{r13} to point to a single
13576 small data area. The @option{-meabi} option is on by default if you
13577 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
13580 @opindex msdata=eabi
13581 On System V.4 and embedded PowerPC systems, put small initialized
13582 @code{const} global and static data in the @samp{.sdata2} section, which
13583 is pointed to by register @code{r2}. Put small initialized
13584 non-@code{const} global and static data in the @samp{.sdata} section,
13585 which is pointed to by register @code{r13}. Put small uninitialized
13586 global and static data in the @samp{.sbss} section, which is adjacent to
13587 the @samp{.sdata} section. The @option{-msdata=eabi} option is
13588 incompatible with the @option{-mrelocatable} option. The
13589 @option{-msdata=eabi} option also sets the @option{-memb} option.
13592 @opindex msdata=sysv
13593 On System V.4 and embedded PowerPC systems, put small global and static
13594 data in the @samp{.sdata} section, which is pointed to by register
13595 @code{r13}. Put small uninitialized global and static data in the
13596 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
13597 The @option{-msdata=sysv} option is incompatible with the
13598 @option{-mrelocatable} option.
13600 @item -msdata=default
13602 @opindex msdata=default
13604 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
13605 compile code the same as @option{-msdata=eabi}, otherwise compile code the
13606 same as @option{-msdata=sysv}.
13609 @opindex msdata-data
13610 On System V.4 and embedded PowerPC systems, put small global
13611 data in the @samp{.sdata} section. Put small uninitialized global
13612 data in the @samp{.sbss} section. Do not use register @code{r13}
13613 to address small data however. This is the default behavior unless
13614 other @option{-msdata} options are used.
13618 @opindex msdata=none
13620 On embedded PowerPC systems, put all initialized global and static data
13621 in the @samp{.data} section, and all uninitialized data in the
13622 @samp{.bss} section.
13626 @cindex smaller data references (PowerPC)
13627 @cindex .sdata/.sdata2 references (PowerPC)
13628 On embedded PowerPC systems, put global and static items less than or
13629 equal to @var{num} bytes into the small data or bss sections instead of
13630 the normal data or bss section. By default, @var{num} is 8. The
13631 @option{-G @var{num}} switch is also passed to the linker.
13632 All modules should be compiled with the same @option{-G @var{num}} value.
13635 @itemx -mno-regnames
13637 @opindex mno-regnames
13638 On System V.4 and embedded PowerPC systems do (do not) emit register
13639 names in the assembly language output using symbolic forms.
13642 @itemx -mno-longcall
13644 @opindex mno-longcall
13645 By default assume that all calls are far away so that a longer more
13646 expensive calling sequence is required. This is required for calls
13647 further than 32 megabytes (33,554,432 bytes) from the current location.
13648 A short call will be generated if the compiler knows
13649 the call cannot be that far away. This setting can be overridden by
13650 the @code{shortcall} function attribute, or by @code{#pragma
13653 Some linkers are capable of detecting out-of-range calls and generating
13654 glue code on the fly. On these systems, long calls are unnecessary and
13655 generate slower code. As of this writing, the AIX linker can do this,
13656 as can the GNU linker for PowerPC/64. It is planned to add this feature
13657 to the GNU linker for 32-bit PowerPC systems as well.
13659 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
13660 callee, L42'', plus a ``branch island'' (glue code). The two target
13661 addresses represent the callee and the ``branch island''. The
13662 Darwin/PPC linker will prefer the first address and generate a ``bl
13663 callee'' if the PPC ``bl'' instruction will reach the callee directly;
13664 otherwise, the linker will generate ``bl L42'' to call the ``branch
13665 island''. The ``branch island'' is appended to the body of the
13666 calling function; it computes the full 32-bit address of the callee
13669 On Mach-O (Darwin) systems, this option directs the compiler emit to
13670 the glue for every direct call, and the Darwin linker decides whether
13671 to use or discard it.
13673 In the future, we may cause GCC to ignore all longcall specifications
13674 when the linker is known to generate glue.
13678 Adds support for multithreading with the @dfn{pthreads} library.
13679 This option sets flags for both the preprocessor and linker.
13683 @node S/390 and zSeries Options
13684 @subsection S/390 and zSeries Options
13685 @cindex S/390 and zSeries Options
13687 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
13691 @itemx -msoft-float
13692 @opindex mhard-float
13693 @opindex msoft-float
13694 Use (do not use) the hardware floating-point instructions and registers
13695 for floating-point operations. When @option{-msoft-float} is specified,
13696 functions in @file{libgcc.a} will be used to perform floating-point
13697 operations. When @option{-mhard-float} is specified, the compiler
13698 generates IEEE floating-point instructions. This is the default.
13700 @item -mlong-double-64
13701 @itemx -mlong-double-128
13702 @opindex mlong-double-64
13703 @opindex mlong-double-128
13704 These switches control the size of @code{long double} type. A size
13705 of 64bit makes the @code{long double} type equivalent to the @code{double}
13706 type. This is the default.
13709 @itemx -mno-backchain
13710 @opindex mbackchain
13711 @opindex mno-backchain
13712 Store (do not store) the address of the caller's frame as backchain pointer
13713 into the callee's stack frame.
13714 A backchain may be needed to allow debugging using tools that do not understand
13715 DWARF-2 call frame information.
13716 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
13717 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
13718 the backchain is placed into the topmost word of the 96/160 byte register
13721 In general, code compiled with @option{-mbackchain} is call-compatible with
13722 code compiled with @option{-mmo-backchain}; however, use of the backchain
13723 for debugging purposes usually requires that the whole binary is built with
13724 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
13725 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
13726 to build a linux kernel use @option{-msoft-float}.
13728 The default is to not maintain the backchain.
13730 @item -mpacked-stack
13731 @itemx -mno-packed-stack
13732 @opindex mpacked-stack
13733 @opindex mno-packed-stack
13734 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
13735 specified, the compiler uses the all fields of the 96/160 byte register save
13736 area only for their default purpose; unused fields still take up stack space.
13737 When @option{-mpacked-stack} is specified, register save slots are densely
13738 packed at the top of the register save area; unused space is reused for other
13739 purposes, allowing for more efficient use of the available stack space.
13740 However, when @option{-mbackchain} is also in effect, the topmost word of
13741 the save area is always used to store the backchain, and the return address
13742 register is always saved two words below the backchain.
13744 As long as the stack frame backchain is not used, code generated with
13745 @option{-mpacked-stack} is call-compatible with code generated with
13746 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
13747 S/390 or zSeries generated code that uses the stack frame backchain at run
13748 time, not just for debugging purposes. Such code is not call-compatible
13749 with code compiled with @option{-mpacked-stack}. Also, note that the
13750 combination of @option{-mbackchain},
13751 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
13752 to build a linux kernel use @option{-msoft-float}.
13754 The default is to not use the packed stack layout.
13757 @itemx -mno-small-exec
13758 @opindex msmall-exec
13759 @opindex mno-small-exec
13760 Generate (or do not generate) code using the @code{bras} instruction
13761 to do subroutine calls.
13762 This only works reliably if the total executable size does not
13763 exceed 64k. The default is to use the @code{basr} instruction instead,
13764 which does not have this limitation.
13770 When @option{-m31} is specified, generate code compliant to the
13771 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
13772 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
13773 particular to generate 64-bit instructions. For the @samp{s390}
13774 targets, the default is @option{-m31}, while the @samp{s390x}
13775 targets default to @option{-m64}.
13781 When @option{-mzarch} is specified, generate code using the
13782 instructions available on z/Architecture.
13783 When @option{-mesa} is specified, generate code using the
13784 instructions available on ESA/390. Note that @option{-mesa} is
13785 not possible with @option{-m64}.
13786 When generating code compliant to the GNU/Linux for S/390 ABI,
13787 the default is @option{-mesa}. When generating code compliant
13788 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
13794 Generate (or do not generate) code using the @code{mvcle} instruction
13795 to perform block moves. When @option{-mno-mvcle} is specified,
13796 use a @code{mvc} loop instead. This is the default unless optimizing for
13803 Print (or do not print) additional debug information when compiling.
13804 The default is to not print debug information.
13806 @item -march=@var{cpu-type}
13808 Generate code that will run on @var{cpu-type}, which is the name of a system
13809 representing a certain processor type. Possible values for
13810 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
13811 When generating code using the instructions available on z/Architecture,
13812 the default is @option{-march=z900}. Otherwise, the default is
13813 @option{-march=g5}.
13815 @item -mtune=@var{cpu-type}
13817 Tune to @var{cpu-type} everything applicable about the generated code,
13818 except for the ABI and the set of available instructions.
13819 The list of @var{cpu-type} values is the same as for @option{-march}.
13820 The default is the value used for @option{-march}.
13823 @itemx -mno-tpf-trace
13824 @opindex mtpf-trace
13825 @opindex mno-tpf-trace
13826 Generate code that adds (does not add) in TPF OS specific branches to trace
13827 routines in the operating system. This option is off by default, even
13828 when compiling for the TPF OS@.
13831 @itemx -mno-fused-madd
13832 @opindex mfused-madd
13833 @opindex mno-fused-madd
13834 Generate code that uses (does not use) the floating point multiply and
13835 accumulate instructions. These instructions are generated by default if
13836 hardware floating point is used.
13838 @item -mwarn-framesize=@var{framesize}
13839 @opindex mwarn-framesize
13840 Emit a warning if the current function exceeds the given frame size. Because
13841 this is a compile time check it doesn't need to be a real problem when the program
13842 runs. It is intended to identify functions which most probably cause
13843 a stack overflow. It is useful to be used in an environment with limited stack
13844 size e.g.@: the linux kernel.
13846 @item -mwarn-dynamicstack
13847 @opindex mwarn-dynamicstack
13848 Emit a warning if the function calls alloca or uses dynamically
13849 sized arrays. This is generally a bad idea with a limited stack size.
13851 @item -mstack-guard=@var{stack-guard}
13852 @itemx -mstack-size=@var{stack-size}
13853 @opindex mstack-guard
13854 @opindex mstack-size
13855 If these options are provided the s390 back end emits additional instructions in
13856 the function prologue which trigger a trap if the stack size is @var{stack-guard}
13857 bytes above the @var{stack-size} (remember that the stack on s390 grows downward).
13858 If the @var{stack-guard} option is omitted the smallest power of 2 larger than
13859 the frame size of the compiled function is chosen.
13860 These options are intended to be used to help debugging stack overflow problems.
13861 The additionally emitted code causes only little overhead and hence can also be
13862 used in production like systems without greater performance degradation. The given
13863 values have to be exact powers of 2 and @var{stack-size} has to be greater than
13864 @var{stack-guard} without exceeding 64k.
13865 In order to be efficient the extra code makes the assumption that the stack starts
13866 at an address aligned to the value given by @var{stack-size}.
13867 The @var{stack-guard} option can only be used in conjunction with @var{stack-size}.
13870 @node Score Options
13871 @subsection Score Options
13872 @cindex Score Options
13874 These options are defined for Score implementations:
13879 Compile code for big endian mode. This is the default.
13883 Compile code for little endian mode.
13887 Disable generate bcnz instruction.
13891 Enable generate unaligned load and store instruction.
13895 Enable the use of multiply-accumulate instructions. Disabled by default.
13899 Specify the SCORE5 as the target architecture.
13903 Specify the SCORE5U of the target architecture.
13907 Specify the SCORE7 as the target architecture. This is the default.
13911 Specify the SCORE7D as the target architecture.
13915 @subsection SH Options
13917 These @samp{-m} options are defined for the SH implementations:
13922 Generate code for the SH1.
13926 Generate code for the SH2.
13929 Generate code for the SH2e.
13933 Generate code for the SH3.
13937 Generate code for the SH3e.
13941 Generate code for the SH4 without a floating-point unit.
13943 @item -m4-single-only
13944 @opindex m4-single-only
13945 Generate code for the SH4 with a floating-point unit that only
13946 supports single-precision arithmetic.
13950 Generate code for the SH4 assuming the floating-point unit is in
13951 single-precision mode by default.
13955 Generate code for the SH4.
13959 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
13960 floating-point unit is not used.
13962 @item -m4a-single-only
13963 @opindex m4a-single-only
13964 Generate code for the SH4a, in such a way that no double-precision
13965 floating point operations are used.
13968 @opindex m4a-single
13969 Generate code for the SH4a assuming the floating-point unit is in
13970 single-precision mode by default.
13974 Generate code for the SH4a.
13978 Same as @option{-m4a-nofpu}, except that it implicitly passes
13979 @option{-dsp} to the assembler. GCC doesn't generate any DSP
13980 instructions at the moment.
13984 Compile code for the processor in big endian mode.
13988 Compile code for the processor in little endian mode.
13992 Align doubles at 64-bit boundaries. Note that this changes the calling
13993 conventions, and thus some functions from the standard C library will
13994 not work unless you recompile it first with @option{-mdalign}.
13998 Shorten some address references at link time, when possible; uses the
13999 linker option @option{-relax}.
14003 Use 32-bit offsets in @code{switch} tables. The default is to use
14008 Enable the use of bit manipulation instructions on SH2A.
14012 Enable the use of the instruction @code{fmovd}.
14016 Comply with the calling conventions defined by Renesas.
14020 Comply with the calling conventions defined by Renesas.
14024 Comply with the calling conventions defined for GCC before the Renesas
14025 conventions were available. This option is the default for all
14026 targets of the SH toolchain except for @samp{sh-symbianelf}.
14029 @opindex mnomacsave
14030 Mark the @code{MAC} register as call-clobbered, even if
14031 @option{-mhitachi} is given.
14035 Increase IEEE-compliance of floating-point code.
14036 At the moment, this is equivalent to @option{-fno-finite-math-only}.
14037 When generating 16 bit SH opcodes, getting IEEE-conforming results for
14038 comparisons of NANs / infinities incurs extra overhead in every
14039 floating point comparison, therefore the default is set to
14040 @option{-ffinite-math-only}.
14042 @item -minline-ic_invalidate
14043 @opindex minline-ic_invalidate
14044 Inline code to invalidate instruction cache entries after setting up
14045 nested function trampolines.
14046 This option has no effect if -musermode is in effect and the selected
14047 code generation option (e.g. -m4) does not allow the use of the icbi
14049 If the selected code generation option does not allow the use of the icbi
14050 instruction, and -musermode is not in effect, the inlined code will
14051 manipulate the instruction cache address array directly with an associative
14052 write. This not only requires privileged mode, but it will also
14053 fail if the cache line had been mapped via the TLB and has become unmapped.
14057 Dump instruction size and location in the assembly code.
14060 @opindex mpadstruct
14061 This option is deprecated. It pads structures to multiple of 4 bytes,
14062 which is incompatible with the SH ABI@.
14066 Optimize for space instead of speed. Implied by @option{-Os}.
14069 @opindex mprefergot
14070 When generating position-independent code, emit function calls using
14071 the Global Offset Table instead of the Procedure Linkage Table.
14075 Don't generate privileged mode only code; implies -mno-inline-ic_invalidate
14076 if the inlined code would not work in user mode.
14077 This is the default when the target is @code{sh-*-linux*}.
14079 @item -multcost=@var{number}
14080 @opindex multcost=@var{number}
14081 Set the cost to assume for a multiply insn.
14083 @item -mdiv=@var{strategy}
14084 @opindex mdiv=@var{strategy}
14085 Set the division strategy to use for SHmedia code. @var{strategy} must be
14086 one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
14087 inv:call2, inv:fp .
14088 "fp" performs the operation in floating point. This has a very high latency,
14089 but needs only a few instructions, so it might be a good choice if
14090 your code has enough easily exploitable ILP to allow the compiler to
14091 schedule the floating point instructions together with other instructions.
14092 Division by zero causes a floating point exception.
14093 "inv" uses integer operations to calculate the inverse of the divisor,
14094 and then multiplies the dividend with the inverse. This strategy allows
14095 cse and hoisting of the inverse calculation. Division by zero calculates
14096 an unspecified result, but does not trap.
14097 "inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
14098 have been found, or if the entire operation has been hoisted to the same
14099 place, the last stages of the inverse calculation are intertwined with the
14100 final multiply to reduce the overall latency, at the expense of using a few
14101 more instructions, and thus offering fewer scheduling opportunities with
14103 "call" calls a library function that usually implements the inv:minlat
14105 This gives high code density for m5-*media-nofpu compilations.
14106 "call2" uses a different entry point of the same library function, where it
14107 assumes that a pointer to a lookup table has already been set up, which
14108 exposes the pointer load to cse / code hoisting optimizations.
14109 "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
14110 code generation, but if the code stays unoptimized, revert to the "call",
14111 "call2", or "fp" strategies, respectively. Note that the
14112 potentially-trapping side effect of division by zero is carried by a
14113 separate instruction, so it is possible that all the integer instructions
14114 are hoisted out, but the marker for the side effect stays where it is.
14115 A recombination to fp operations or a call is not possible in that case.
14116 "inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
14117 that the inverse calculation was nor separated from the multiply, they speed
14118 up division where the dividend fits into 20 bits (plus sign where applicable),
14119 by inserting a test to skip a number of operations in this case; this test
14120 slows down the case of larger dividends. inv20u assumes the case of a such
14121 a small dividend to be unlikely, and inv20l assumes it to be likely.
14123 @item -mdivsi3_libfunc=@var{name}
14124 @opindex mdivsi3_libfunc=@var{name}
14125 Set the name of the library function used for 32 bit signed division to
14126 @var{name}. This only affect the name used in the call and inv:call
14127 division strategies, and the compiler will still expect the same
14128 sets of input/output/clobbered registers as if this option was not present.
14130 @item -mfixed-range=@var{register-range}
14131 @opindex mfixed-range
14132 Generate code treating the given register range as fixed registers.
14133 A fixed register is one that the register allocator can not use. This is
14134 useful when compiling kernel code. A register range is specified as
14135 two registers separated by a dash. Multiple register ranges can be
14136 specified separated by a comma.
14138 @item -madjust-unroll
14139 @opindex madjust-unroll
14140 Throttle unrolling to avoid thrashing target registers.
14141 This option only has an effect if the gcc code base supports the
14142 TARGET_ADJUST_UNROLL_MAX target hook.
14144 @item -mindexed-addressing
14145 @opindex mindexed-addressing
14146 Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
14147 This is only safe if the hardware and/or OS implement 32 bit wrap-around
14148 semantics for the indexed addressing mode. The architecture allows the
14149 implementation of processors with 64 bit MMU, which the OS could use to
14150 get 32 bit addressing, but since no current hardware implementation supports
14151 this or any other way to make the indexed addressing mode safe to use in
14152 the 32 bit ABI, the default is -mno-indexed-addressing.
14154 @item -mgettrcost=@var{number}
14155 @opindex mgettrcost=@var{number}
14156 Set the cost assumed for the gettr instruction to @var{number}.
14157 The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
14161 Assume pt* instructions won't trap. This will generally generate better
14162 scheduled code, but is unsafe on current hardware. The current architecture
14163 definition says that ptabs and ptrel trap when the target anded with 3 is 3.
14164 This has the unintentional effect of making it unsafe to schedule ptabs /
14165 ptrel before a branch, or hoist it out of a loop. For example,
14166 __do_global_ctors, a part of libgcc that runs constructors at program
14167 startup, calls functions in a list which is delimited by @minus{}1. With the
14168 -mpt-fixed option, the ptabs will be done before testing against @minus{}1.
14169 That means that all the constructors will be run a bit quicker, but when
14170 the loop comes to the end of the list, the program crashes because ptabs
14171 loads @minus{}1 into a target register. Since this option is unsafe for any
14172 hardware implementing the current architecture specification, the default
14173 is -mno-pt-fixed. Unless the user specifies a specific cost with
14174 @option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100};
14175 this deters register allocation using target registers for storing
14178 @item -minvalid-symbols
14179 @opindex minvalid-symbols
14180 Assume symbols might be invalid. Ordinary function symbols generated by
14181 the compiler will always be valid to load with movi/shori/ptabs or
14182 movi/shori/ptrel, but with assembler and/or linker tricks it is possible
14183 to generate symbols that will cause ptabs / ptrel to trap.
14184 This option is only meaningful when @option{-mno-pt-fixed} is in effect.
14185 It will then prevent cross-basic-block cse, hoisting and most scheduling
14186 of symbol loads. The default is @option{-mno-invalid-symbols}.
14189 @node SPARC Options
14190 @subsection SPARC Options
14191 @cindex SPARC options
14193 These @samp{-m} options are supported on the SPARC:
14196 @item -mno-app-regs
14198 @opindex mno-app-regs
14200 Specify @option{-mapp-regs} to generate output using the global registers
14201 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
14204 To be fully SVR4 ABI compliant at the cost of some performance loss,
14205 specify @option{-mno-app-regs}. You should compile libraries and system
14206 software with this option.
14209 @itemx -mhard-float
14211 @opindex mhard-float
14212 Generate output containing floating point instructions. This is the
14216 @itemx -msoft-float
14218 @opindex msoft-float
14219 Generate output containing library calls for floating point.
14220 @strong{Warning:} the requisite libraries are not available for all SPARC
14221 targets. Normally the facilities of the machine's usual C compiler are
14222 used, but this cannot be done directly in cross-compilation. You must make
14223 your own arrangements to provide suitable library functions for
14224 cross-compilation. The embedded targets @samp{sparc-*-aout} and
14225 @samp{sparclite-*-*} do provide software floating point support.
14227 @option{-msoft-float} changes the calling convention in the output file;
14228 therefore, it is only useful if you compile @emph{all} of a program with
14229 this option. In particular, you need to compile @file{libgcc.a}, the
14230 library that comes with GCC, with @option{-msoft-float} in order for
14233 @item -mhard-quad-float
14234 @opindex mhard-quad-float
14235 Generate output containing quad-word (long double) floating point
14238 @item -msoft-quad-float
14239 @opindex msoft-quad-float
14240 Generate output containing library calls for quad-word (long double)
14241 floating point instructions. The functions called are those specified
14242 in the SPARC ABI@. This is the default.
14244 As of this writing, there are no SPARC implementations that have hardware
14245 support for the quad-word floating point instructions. They all invoke
14246 a trap handler for one of these instructions, and then the trap handler
14247 emulates the effect of the instruction. Because of the trap handler overhead,
14248 this is much slower than calling the ABI library routines. Thus the
14249 @option{-msoft-quad-float} option is the default.
14251 @item -mno-unaligned-doubles
14252 @itemx -munaligned-doubles
14253 @opindex mno-unaligned-doubles
14254 @opindex munaligned-doubles
14255 Assume that doubles have 8 byte alignment. This is the default.
14257 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
14258 alignment only if they are contained in another type, or if they have an
14259 absolute address. Otherwise, it assumes they have 4 byte alignment.
14260 Specifying this option avoids some rare compatibility problems with code
14261 generated by other compilers. It is not the default because it results
14262 in a performance loss, especially for floating point code.
14264 @item -mno-faster-structs
14265 @itemx -mfaster-structs
14266 @opindex mno-faster-structs
14267 @opindex mfaster-structs
14268 With @option{-mfaster-structs}, the compiler assumes that structures
14269 should have 8 byte alignment. This enables the use of pairs of
14270 @code{ldd} and @code{std} instructions for copies in structure
14271 assignment, in place of twice as many @code{ld} and @code{st} pairs.
14272 However, the use of this changed alignment directly violates the SPARC
14273 ABI@. Thus, it's intended only for use on targets where the developer
14274 acknowledges that their resulting code will not be directly in line with
14275 the rules of the ABI@.
14277 @item -mimpure-text
14278 @opindex mimpure-text
14279 @option{-mimpure-text}, used in addition to @option{-shared}, tells
14280 the compiler to not pass @option{-z text} to the linker when linking a
14281 shared object. Using this option, you can link position-dependent
14282 code into a shared object.
14284 @option{-mimpure-text} suppresses the ``relocations remain against
14285 allocatable but non-writable sections'' linker error message.
14286 However, the necessary relocations will trigger copy-on-write, and the
14287 shared object is not actually shared across processes. Instead of
14288 using @option{-mimpure-text}, you should compile all source code with
14289 @option{-fpic} or @option{-fPIC}.
14291 This option is only available on SunOS and Solaris.
14293 @item -mcpu=@var{cpu_type}
14295 Set the instruction set, register set, and instruction scheduling parameters
14296 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
14297 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
14298 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
14299 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc},
14300 @samp{ultrasparc3}, @samp{niagara} and @samp{niagara2}.
14302 Default instruction scheduling parameters are used for values that select
14303 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
14304 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
14306 Here is a list of each supported architecture and their supported
14311 v8: supersparc, hypersparc
14312 sparclite: f930, f934, sparclite86x
14314 v9: ultrasparc, ultrasparc3, niagara, niagara2
14317 By default (unless configured otherwise), GCC generates code for the V7
14318 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
14319 additionally optimizes it for the Cypress CY7C602 chip, as used in the
14320 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
14321 SPARCStation 1, 2, IPX etc.
14323 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
14324 architecture. The only difference from V7 code is that the compiler emits
14325 the integer multiply and integer divide instructions which exist in SPARC-V8
14326 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
14327 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
14330 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
14331 the SPARC architecture. This adds the integer multiply, integer divide step
14332 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
14333 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
14334 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
14335 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
14336 MB86934 chip, which is the more recent SPARClite with FPU@.
14338 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
14339 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
14340 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
14341 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
14342 optimizes it for the TEMIC SPARClet chip.
14344 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
14345 architecture. This adds 64-bit integer and floating-point move instructions,
14346 3 additional floating-point condition code registers and conditional move
14347 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
14348 optimizes it for the Sun UltraSPARC I/II/IIi chips. With
14349 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
14350 Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With
14351 @option{-mcpu=niagara}, the compiler additionally optimizes it for
14352 Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler
14353 additionally optimizes it for Sun UltraSPARC T2 chips.
14355 @item -mtune=@var{cpu_type}
14357 Set the instruction scheduling parameters for machine type
14358 @var{cpu_type}, but do not set the instruction set or register set that the
14359 option @option{-mcpu=@var{cpu_type}} would.
14361 The same values for @option{-mcpu=@var{cpu_type}} can be used for
14362 @option{-mtune=@var{cpu_type}}, but the only useful values are those
14363 that select a particular cpu implementation. Those are @samp{cypress},
14364 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
14365 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc},
14366 @samp{ultrasparc3}, @samp{niagara}, and @samp{niagara2}.
14371 @opindex mno-v8plus
14372 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
14373 difference from the V8 ABI is that the global and out registers are
14374 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
14375 mode for all SPARC-V9 processors.
14381 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
14382 Visual Instruction Set extensions. The default is @option{-mno-vis}.
14385 These @samp{-m} options are supported in addition to the above
14386 on SPARC-V9 processors in 64-bit environments:
14389 @item -mlittle-endian
14390 @opindex mlittle-endian
14391 Generate code for a processor running in little-endian mode. It is only
14392 available for a few configurations and most notably not on Solaris and Linux.
14398 Generate code for a 32-bit or 64-bit environment.
14399 The 32-bit environment sets int, long and pointer to 32 bits.
14400 The 64-bit environment sets int to 32 bits and long and pointer
14403 @item -mcmodel=medlow
14404 @opindex mcmodel=medlow
14405 Generate code for the Medium/Low code model: 64-bit addresses, programs
14406 must be linked in the low 32 bits of memory. Programs can be statically
14407 or dynamically linked.
14409 @item -mcmodel=medmid
14410 @opindex mcmodel=medmid
14411 Generate code for the Medium/Middle code model: 64-bit addresses, programs
14412 must be linked in the low 44 bits of memory, the text and data segments must
14413 be less than 2GB in size and the data segment must be located within 2GB of
14416 @item -mcmodel=medany
14417 @opindex mcmodel=medany
14418 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
14419 may be linked anywhere in memory, the text and data segments must be less
14420 than 2GB in size and the data segment must be located within 2GB of the
14423 @item -mcmodel=embmedany
14424 @opindex mcmodel=embmedany
14425 Generate code for the Medium/Anywhere code model for embedded systems:
14426 64-bit addresses, the text and data segments must be less than 2GB in
14427 size, both starting anywhere in memory (determined at link time). The
14428 global register %g4 points to the base of the data segment. Programs
14429 are statically linked and PIC is not supported.
14432 @itemx -mno-stack-bias
14433 @opindex mstack-bias
14434 @opindex mno-stack-bias
14435 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
14436 frame pointer if present, are offset by @minus{}2047 which must be added back
14437 when making stack frame references. This is the default in 64-bit mode.
14438 Otherwise, assume no such offset is present.
14441 These switches are supported in addition to the above on Solaris:
14446 Add support for multithreading using the Solaris threads library. This
14447 option sets flags for both the preprocessor and linker. This option does
14448 not affect the thread safety of object code produced by the compiler or
14449 that of libraries supplied with it.
14453 Add support for multithreading using the POSIX threads library. This
14454 option sets flags for both the preprocessor and linker. This option does
14455 not affect the thread safety of object code produced by the compiler or
14456 that of libraries supplied with it.
14460 This is a synonym for @option{-pthreads}.
14464 @subsection SPU Options
14465 @cindex SPU options
14467 These @samp{-m} options are supported on the SPU:
14471 @itemx -merror-reloc
14472 @opindex mwarn-reloc
14473 @opindex merror-reloc
14475 The loader for SPU does not handle dynamic relocations. By default, GCC
14476 will give an error when it generates code that requires a dynamic
14477 relocation. @option{-mno-error-reloc} disables the error,
14478 @option{-mwarn-reloc} will generate a warning instead.
14481 @itemx -munsafe-dma
14483 @opindex munsafe-dma
14485 Instructions which initiate or test completion of DMA must not be
14486 reordered with respect to loads and stores of the memory which is being
14487 accessed. Users typically address this problem using the volatile
14488 keyword, but that can lead to inefficient code in places where the
14489 memory is known to not change. Rather than mark the memory as volatile
14490 we treat the DMA instructions as potentially effecting all memory. With
14491 @option{-munsafe-dma} users must use the volatile keyword to protect
14494 @item -mbranch-hints
14495 @opindex mbranch-hints
14497 By default, GCC will generate a branch hint instruction to avoid
14498 pipeline stalls for always taken or probably taken branches. A hint
14499 will not be generated closer than 8 instructions away from its branch.
14500 There is little reason to disable them, except for debugging purposes,
14501 or to make an object a little bit smaller.
14505 @opindex msmall-mem
14506 @opindex mlarge-mem
14508 By default, GCC generates code assuming that addresses are never larger
14509 than 18 bits. With @option{-mlarge-mem} code is generated that assumes
14510 a full 32 bit address.
14515 By default, GCC links against startup code that assumes the SPU-style
14516 main function interface (which has an unconventional parameter list).
14517 With @option{-mstdmain}, GCC will link your program against startup
14518 code that assumes a C99-style interface to @code{main}, including a
14519 local copy of @code{argv} strings.
14521 @item -mfixed-range=@var{register-range}
14522 @opindex mfixed-range
14523 Generate code treating the given register range as fixed registers.
14524 A fixed register is one that the register allocator can not use. This is
14525 useful when compiling kernel code. A register range is specified as
14526 two registers separated by a dash. Multiple register ranges can be
14527 specified separated by a comma.
14531 @node System V Options
14532 @subsection Options for System V
14534 These additional options are available on System V Release 4 for
14535 compatibility with other compilers on those systems:
14540 Create a shared object.
14541 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
14545 Identify the versions of each tool used by the compiler, in a
14546 @code{.ident} assembler directive in the output.
14550 Refrain from adding @code{.ident} directives to the output file (this is
14553 @item -YP,@var{dirs}
14555 Search the directories @var{dirs}, and no others, for libraries
14556 specified with @option{-l}.
14558 @item -Ym,@var{dir}
14560 Look in the directory @var{dir} to find the M4 preprocessor.
14561 The assembler uses this option.
14562 @c This is supposed to go with a -Yd for predefined M4 macro files, but
14563 @c the generic assembler that comes with Solaris takes just -Ym.
14567 @subsection V850 Options
14568 @cindex V850 Options
14570 These @samp{-m} options are defined for V850 implementations:
14574 @itemx -mno-long-calls
14575 @opindex mlong-calls
14576 @opindex mno-long-calls
14577 Treat all calls as being far away (near). If calls are assumed to be
14578 far away, the compiler will always load the functions address up into a
14579 register, and call indirect through the pointer.
14585 Do not optimize (do optimize) basic blocks that use the same index
14586 pointer 4 or more times to copy pointer into the @code{ep} register, and
14587 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
14588 option is on by default if you optimize.
14590 @item -mno-prolog-function
14591 @itemx -mprolog-function
14592 @opindex mno-prolog-function
14593 @opindex mprolog-function
14594 Do not use (do use) external functions to save and restore registers
14595 at the prologue and epilogue of a function. The external functions
14596 are slower, but use less code space if more than one function saves
14597 the same number of registers. The @option{-mprolog-function} option
14598 is on by default if you optimize.
14602 Try to make the code as small as possible. At present, this just turns
14603 on the @option{-mep} and @option{-mprolog-function} options.
14605 @item -mtda=@var{n}
14607 Put static or global variables whose size is @var{n} bytes or less into
14608 the tiny data area that register @code{ep} points to. The tiny data
14609 area can hold up to 256 bytes in total (128 bytes for byte references).
14611 @item -msda=@var{n}
14613 Put static or global variables whose size is @var{n} bytes or less into
14614 the small data area that register @code{gp} points to. The small data
14615 area can hold up to 64 kilobytes.
14617 @item -mzda=@var{n}
14619 Put static or global variables whose size is @var{n} bytes or less into
14620 the first 32 kilobytes of memory.
14624 Specify that the target processor is the V850.
14627 @opindex mbig-switch
14628 Generate code suitable for big switch tables. Use this option only if
14629 the assembler/linker complain about out of range branches within a switch
14634 This option will cause r2 and r5 to be used in the code generated by
14635 the compiler. This setting is the default.
14637 @item -mno-app-regs
14638 @opindex mno-app-regs
14639 This option will cause r2 and r5 to be treated as fixed registers.
14643 Specify that the target processor is the V850E1. The preprocessor
14644 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
14645 this option is used.
14649 Specify that the target processor is the V850E@. The preprocessor
14650 constant @samp{__v850e__} will be defined if this option is used.
14652 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
14653 are defined then a default target processor will be chosen and the
14654 relevant @samp{__v850*__} preprocessor constant will be defined.
14656 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
14657 defined, regardless of which processor variant is the target.
14659 @item -mdisable-callt
14660 @opindex mdisable-callt
14661 This option will suppress generation of the CALLT instruction for the
14662 v850e and v850e1 flavors of the v850 architecture. The default is
14663 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
14668 @subsection VAX Options
14669 @cindex VAX options
14671 These @samp{-m} options are defined for the VAX:
14676 Do not output certain jump instructions (@code{aobleq} and so on)
14677 that the Unix assembler for the VAX cannot handle across long
14682 Do output those jump instructions, on the assumption that you
14683 will assemble with the GNU assembler.
14687 Output code for g-format floating point numbers instead of d-format.
14690 @node VxWorks Options
14691 @subsection VxWorks Options
14692 @cindex VxWorks Options
14694 The options in this section are defined for all VxWorks targets.
14695 Options specific to the target hardware are listed with the other
14696 options for that target.
14701 GCC can generate code for both VxWorks kernels and real time processes
14702 (RTPs). This option switches from the former to the latter. It also
14703 defines the preprocessor macro @code{__RTP__}.
14706 @opindex non-static
14707 Link an RTP executable against shared libraries rather than static
14708 libraries. The options @option{-static} and @option{-shared} can
14709 also be used for RTPs (@pxref{Link Options}); @option{-static}
14716 These options are passed down to the linker. They are defined for
14717 compatibility with Diab.
14720 @opindex Xbind-lazy
14721 Enable lazy binding of function calls. This option is equivalent to
14722 @option{-Wl,-z,now} and is defined for compatibility with Diab.
14726 Disable lazy binding of function calls. This option is the default and
14727 is defined for compatibility with Diab.
14730 @node x86-64 Options
14731 @subsection x86-64 Options
14732 @cindex x86-64 options
14734 These are listed under @xref{i386 and x86-64 Options}.
14736 @node Xstormy16 Options
14737 @subsection Xstormy16 Options
14738 @cindex Xstormy16 Options
14740 These options are defined for Xstormy16:
14745 Choose startup files and linker script suitable for the simulator.
14748 @node Xtensa Options
14749 @subsection Xtensa Options
14750 @cindex Xtensa Options
14752 These options are supported for Xtensa targets:
14756 @itemx -mno-const16
14758 @opindex mno-const16
14759 Enable or disable use of @code{CONST16} instructions for loading
14760 constant values. The @code{CONST16} instruction is currently not a
14761 standard option from Tensilica. When enabled, @code{CONST16}
14762 instructions are always used in place of the standard @code{L32R}
14763 instructions. The use of @code{CONST16} is enabled by default only if
14764 the @code{L32R} instruction is not available.
14767 @itemx -mno-fused-madd
14768 @opindex mfused-madd
14769 @opindex mno-fused-madd
14770 Enable or disable use of fused multiply/add and multiply/subtract
14771 instructions in the floating-point option. This has no effect if the
14772 floating-point option is not also enabled. Disabling fused multiply/add
14773 and multiply/subtract instructions forces the compiler to use separate
14774 instructions for the multiply and add/subtract operations. This may be
14775 desirable in some cases where strict IEEE 754-compliant results are
14776 required: the fused multiply add/subtract instructions do not round the
14777 intermediate result, thereby producing results with @emph{more} bits of
14778 precision than specified by the IEEE standard. Disabling fused multiply
14779 add/subtract instructions also ensures that the program output is not
14780 sensitive to the compiler's ability to combine multiply and add/subtract
14783 @item -mserialize-volatile
14784 @itemx -mno-serialize-volatile
14785 @opindex mserialize-volatile
14786 @opindex mno-serialize-volatile
14787 When this option is enabled, GCC inserts @code{MEMW} instructions before
14788 @code{volatile} memory references to guarantee sequential consistency.
14789 The default is @option{-mserialize-volatile}. Use
14790 @option{-mno-serialize-volatile} to omit the @code{MEMW} instructions.
14792 @item -mtext-section-literals
14793 @itemx -mno-text-section-literals
14794 @opindex mtext-section-literals
14795 @opindex mno-text-section-literals
14796 Control the treatment of literal pools. The default is
14797 @option{-mno-text-section-literals}, which places literals in a separate
14798 section in the output file. This allows the literal pool to be placed
14799 in a data RAM/ROM, and it also allows the linker to combine literal
14800 pools from separate object files to remove redundant literals and
14801 improve code size. With @option{-mtext-section-literals}, the literals
14802 are interspersed in the text section in order to keep them as close as
14803 possible to their references. This may be necessary for large assembly
14806 @item -mtarget-align
14807 @itemx -mno-target-align
14808 @opindex mtarget-align
14809 @opindex mno-target-align
14810 When this option is enabled, GCC instructs the assembler to
14811 automatically align instructions to reduce branch penalties at the
14812 expense of some code density. The assembler attempts to widen density
14813 instructions to align branch targets and the instructions following call
14814 instructions. If there are not enough preceding safe density
14815 instructions to align a target, no widening will be performed. The
14816 default is @option{-mtarget-align}. These options do not affect the
14817 treatment of auto-aligned instructions like @code{LOOP}, which the
14818 assembler will always align, either by widening density instructions or
14819 by inserting no-op instructions.
14822 @itemx -mno-longcalls
14823 @opindex mlongcalls
14824 @opindex mno-longcalls
14825 When this option is enabled, GCC instructs the assembler to translate
14826 direct calls to indirect calls unless it can determine that the target
14827 of a direct call is in the range allowed by the call instruction. This
14828 translation typically occurs for calls to functions in other source
14829 files. Specifically, the assembler translates a direct @code{CALL}
14830 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
14831 The default is @option{-mno-longcalls}. This option should be used in
14832 programs where the call target can potentially be out of range. This
14833 option is implemented in the assembler, not the compiler, so the
14834 assembly code generated by GCC will still show direct call
14835 instructions---look at the disassembled object code to see the actual
14836 instructions. Note that the assembler will use an indirect call for
14837 every cross-file call, not just those that really will be out of range.
14840 @node zSeries Options
14841 @subsection zSeries Options
14842 @cindex zSeries options
14844 These are listed under @xref{S/390 and zSeries Options}.
14846 @node Code Gen Options
14847 @section Options for Code Generation Conventions
14848 @cindex code generation conventions
14849 @cindex options, code generation
14850 @cindex run-time options
14852 These machine-independent options control the interface conventions
14853 used in code generation.
14855 Most of them have both positive and negative forms; the negative form
14856 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
14857 one of the forms is listed---the one which is not the default. You
14858 can figure out the other form by either removing @samp{no-} or adding
14862 @item -fbounds-check
14863 @opindex fbounds-check
14864 For front-ends that support it, generate additional code to check that
14865 indices used to access arrays are within the declared range. This is
14866 currently only supported by the Java and Fortran front-ends, where
14867 this option defaults to true and false respectively.
14871 This option generates traps for signed overflow on addition, subtraction,
14872 multiplication operations.
14876 This option instructs the compiler to assume that signed arithmetic
14877 overflow of addition, subtraction and multiplication wraps around
14878 using twos-complement representation. This flag enables some optimizations
14879 and disables others. This option is enabled by default for the Java
14880 front-end, as required by the Java language specification.
14883 @opindex fexceptions
14884 Enable exception handling. Generates extra code needed to propagate
14885 exceptions. For some targets, this implies GCC will generate frame
14886 unwind information for all functions, which can produce significant data
14887 size overhead, although it does not affect execution. If you do not
14888 specify this option, GCC will enable it by default for languages like
14889 C++ which normally require exception handling, and disable it for
14890 languages like C that do not normally require it. However, you may need
14891 to enable this option when compiling C code that needs to interoperate
14892 properly with exception handlers written in C++. You may also wish to
14893 disable this option if you are compiling older C++ programs that don't
14894 use exception handling.
14896 @item -fnon-call-exceptions
14897 @opindex fnon-call-exceptions
14898 Generate code that allows trapping instructions to throw exceptions.
14899 Note that this requires platform-specific runtime support that does
14900 not exist everywhere. Moreover, it only allows @emph{trapping}
14901 instructions to throw exceptions, i.e.@: memory references or floating
14902 point instructions. It does not allow exceptions to be thrown from
14903 arbitrary signal handlers such as @code{SIGALRM}.
14905 @item -funwind-tables
14906 @opindex funwind-tables
14907 Similar to @option{-fexceptions}, except that it will just generate any needed
14908 static data, but will not affect the generated code in any other way.
14909 You will normally not enable this option; instead, a language processor
14910 that needs this handling would enable it on your behalf.
14912 @item -fasynchronous-unwind-tables
14913 @opindex fasynchronous-unwind-tables
14914 Generate unwind table in dwarf2 format, if supported by target machine. The
14915 table is exact at each instruction boundary, so it can be used for stack
14916 unwinding from asynchronous events (such as debugger or garbage collector).
14918 @item -fpcc-struct-return
14919 @opindex fpcc-struct-return
14920 Return ``short'' @code{struct} and @code{union} values in memory like
14921 longer ones, rather than in registers. This convention is less
14922 efficient, but it has the advantage of allowing intercallability between
14923 GCC-compiled files and files compiled with other compilers, particularly
14924 the Portable C Compiler (pcc).
14926 The precise convention for returning structures in memory depends
14927 on the target configuration macros.
14929 Short structures and unions are those whose size and alignment match
14930 that of some integer type.
14932 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
14933 switch is not binary compatible with code compiled with the
14934 @option{-freg-struct-return} switch.
14935 Use it to conform to a non-default application binary interface.
14937 @item -freg-struct-return
14938 @opindex freg-struct-return
14939 Return @code{struct} and @code{union} values in registers when possible.
14940 This is more efficient for small structures than
14941 @option{-fpcc-struct-return}.
14943 If you specify neither @option{-fpcc-struct-return} nor
14944 @option{-freg-struct-return}, GCC defaults to whichever convention is
14945 standard for the target. If there is no standard convention, GCC
14946 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
14947 the principal compiler. In those cases, we can choose the standard, and
14948 we chose the more efficient register return alternative.
14950 @strong{Warning:} code compiled with the @option{-freg-struct-return}
14951 switch is not binary compatible with code compiled with the
14952 @option{-fpcc-struct-return} switch.
14953 Use it to conform to a non-default application binary interface.
14955 @item -fshort-enums
14956 @opindex fshort-enums
14957 Allocate to an @code{enum} type only as many bytes as it needs for the
14958 declared range of possible values. Specifically, the @code{enum} type
14959 will be equivalent to the smallest integer type which has enough room.
14961 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
14962 code that is not binary compatible with code generated without that switch.
14963 Use it to conform to a non-default application binary interface.
14965 @item -fshort-double
14966 @opindex fshort-double
14967 Use the same size for @code{double} as for @code{float}.
14969 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
14970 code that is not binary compatible with code generated without that switch.
14971 Use it to conform to a non-default application binary interface.
14973 @item -fshort-wchar
14974 @opindex fshort-wchar
14975 Override the underlying type for @samp{wchar_t} to be @samp{short
14976 unsigned int} instead of the default for the target. This option is
14977 useful for building programs to run under WINE@.
14979 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
14980 code that is not binary compatible with code generated without that switch.
14981 Use it to conform to a non-default application binary interface.
14984 @opindex fno-common
14985 In C, allocate even uninitialized global variables in the data section of the
14986 object file, rather than generating them as common blocks. This has the
14987 effect that if the same variable is declared (without @code{extern}) in
14988 two different compilations, you will get an error when you link them.
14989 The only reason this might be useful is if you wish to verify that the
14990 program will work on other systems which always work this way.
14994 Ignore the @samp{#ident} directive.
14996 @item -finhibit-size-directive
14997 @opindex finhibit-size-directive
14998 Don't output a @code{.size} assembler directive, or anything else that
14999 would cause trouble if the function is split in the middle, and the
15000 two halves are placed at locations far apart in memory. This option is
15001 used when compiling @file{crtstuff.c}; you should not need to use it
15004 @item -fverbose-asm
15005 @opindex fverbose-asm
15006 Put extra commentary information in the generated assembly code to
15007 make it more readable. This option is generally only of use to those
15008 who actually need to read the generated assembly code (perhaps while
15009 debugging the compiler itself).
15011 @option{-fno-verbose-asm}, the default, causes the
15012 extra information to be omitted and is useful when comparing two assembler
15015 @item -frecord-gcc-switches
15016 @opindex frecord-gcc-switches
15017 This switch causes the command line that was used to invoke the
15018 compiler to be recorded into the object file that is being created.
15019 This switch is only implemented on some targets and the exact format
15020 of the recording is target and binary file format dependent, but it
15021 usually takes the form of a section containing ASCII text. This
15022 switch is related to the @option{-fverbose-asm} switch, but that
15023 switch only records information in the assembler output file as
15024 comments, so it never reaches the object file.
15028 @cindex global offset table
15030 Generate position-independent code (PIC) suitable for use in a shared
15031 library, if supported for the target machine. Such code accesses all
15032 constant addresses through a global offset table (GOT)@. The dynamic
15033 loader resolves the GOT entries when the program starts (the dynamic
15034 loader is not part of GCC; it is part of the operating system). If
15035 the GOT size for the linked executable exceeds a machine-specific
15036 maximum size, you get an error message from the linker indicating that
15037 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
15038 instead. (These maximums are 8k on the SPARC and 32k
15039 on the m68k and RS/6000. The 386 has no such limit.)
15041 Position-independent code requires special support, and therefore works
15042 only on certain machines. For the 386, GCC supports PIC for System V
15043 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
15044 position-independent.
15046 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
15051 If supported for the target machine, emit position-independent code,
15052 suitable for dynamic linking and avoiding any limit on the size of the
15053 global offset table. This option makes a difference on the m68k,
15054 PowerPC and SPARC@.
15056 Position-independent code requires special support, and therefore works
15057 only on certain machines.
15059 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
15066 These options are similar to @option{-fpic} and @option{-fPIC}, but
15067 generated position independent code can be only linked into executables.
15068 Usually these options are used when @option{-pie} GCC option will be
15069 used during linking.
15071 @option{-fpie} and @option{-fPIE} both define the macros
15072 @code{__pie__} and @code{__PIE__}. The macros have the value 1
15073 for @option{-fpie} and 2 for @option{-fPIE}.
15075 @item -fno-jump-tables
15076 @opindex fno-jump-tables
15077 Do not use jump tables for switch statements even where it would be
15078 more efficient than other code generation strategies. This option is
15079 of use in conjunction with @option{-fpic} or @option{-fPIC} for
15080 building code which forms part of a dynamic linker and cannot
15081 reference the address of a jump table. On some targets, jump tables
15082 do not require a GOT and this option is not needed.
15084 @item -ffixed-@var{reg}
15086 Treat the register named @var{reg} as a fixed register; generated code
15087 should never refer to it (except perhaps as a stack pointer, frame
15088 pointer or in some other fixed role).
15090 @var{reg} must be the name of a register. The register names accepted
15091 are machine-specific and are defined in the @code{REGISTER_NAMES}
15092 macro in the machine description macro file.
15094 This flag does not have a negative form, because it specifies a
15097 @item -fcall-used-@var{reg}
15098 @opindex fcall-used
15099 Treat the register named @var{reg} as an allocable register that is
15100 clobbered by function calls. It may be allocated for temporaries or
15101 variables that do not live across a call. Functions compiled this way
15102 will not save and restore the register @var{reg}.
15104 It is an error to used this flag with the frame pointer or stack pointer.
15105 Use of this flag for other registers that have fixed pervasive roles in
15106 the machine's execution model will produce disastrous results.
15108 This flag does not have a negative form, because it specifies a
15111 @item -fcall-saved-@var{reg}
15112 @opindex fcall-saved
15113 Treat the register named @var{reg} as an allocable register saved by
15114 functions. It may be allocated even for temporaries or variables that
15115 live across a call. Functions compiled this way will save and restore
15116 the register @var{reg} if they use it.
15118 It is an error to used this flag with the frame pointer or stack pointer.
15119 Use of this flag for other registers that have fixed pervasive roles in
15120 the machine's execution model will produce disastrous results.
15122 A different sort of disaster will result from the use of this flag for
15123 a register in which function values may be returned.
15125 This flag does not have a negative form, because it specifies a
15128 @item -fpack-struct[=@var{n}]
15129 @opindex fpack-struct
15130 Without a value specified, pack all structure members together without
15131 holes. When a value is specified (which must be a small power of two), pack
15132 structure members according to this value, representing the maximum
15133 alignment (that is, objects with default alignment requirements larger than
15134 this will be output potentially unaligned at the next fitting location.
15136 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
15137 code that is not binary compatible with code generated without that switch.
15138 Additionally, it makes the code suboptimal.
15139 Use it to conform to a non-default application binary interface.
15141 @item -finstrument-functions
15142 @opindex finstrument-functions
15143 Generate instrumentation calls for entry and exit to functions. Just
15144 after function entry and just before function exit, the following
15145 profiling functions will be called with the address of the current
15146 function and its call site. (On some platforms,
15147 @code{__builtin_return_address} does not work beyond the current
15148 function, so the call site information may not be available to the
15149 profiling functions otherwise.)
15152 void __cyg_profile_func_enter (void *this_fn,
15154 void __cyg_profile_func_exit (void *this_fn,
15158 The first argument is the address of the start of the current function,
15159 which may be looked up exactly in the symbol table.
15161 This instrumentation is also done for functions expanded inline in other
15162 functions. The profiling calls will indicate where, conceptually, the
15163 inline function is entered and exited. This means that addressable
15164 versions of such functions must be available. If all your uses of a
15165 function are expanded inline, this may mean an additional expansion of
15166 code size. If you use @samp{extern inline} in your C code, an
15167 addressable version of such functions must be provided. (This is
15168 normally the case anyways, but if you get lucky and the optimizer always
15169 expands the functions inline, you might have gotten away without
15170 providing static copies.)
15172 A function may be given the attribute @code{no_instrument_function}, in
15173 which case this instrumentation will not be done. This can be used, for
15174 example, for the profiling functions listed above, high-priority
15175 interrupt routines, and any functions from which the profiling functions
15176 cannot safely be called (perhaps signal handlers, if the profiling
15177 routines generate output or allocate memory).
15179 @item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}
15180 @opindex finstrument-functions-exclude-file-list
15182 Set the list of functions that are excluded from instrumentation (see
15183 the description of @code{-finstrument-functions}). If the file that
15184 contains a function definition matches with one of @var{file}, then
15185 that function is not instrumented. The match is done on substrings:
15186 if the @var{file} parameter is a substring of the file name, it is
15187 considered to be a match.
15190 @code{-finstrument-functions-exclude-file-list=/bits/stl,include/sys}
15191 will exclude any inline function defined in files whose pathnames
15192 contain @code{/bits/stl} or @code{include/sys}.
15194 If, for some reason, you want to include letter @code{','} in one of
15195 @var{sym}, write @code{'\,'}. For example,
15196 @code{-finstrument-functions-exclude-file-list='\,\,tmp'}
15197 (note the single quote surrounding the option).
15199 @item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{}
15200 @opindex finstrument-functions-exclude-function-list
15202 This is similar to @code{-finstrument-functions-exclude-file-list},
15203 but this option sets the list of function names to be excluded from
15204 instrumentation. The function name to be matched is its user-visible
15205 name, such as @code{vector<int> blah(const vector<int> &)}, not the
15206 internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The
15207 match is done on substrings: if the @var{sym} parameter is a substring
15208 of the function name, it is considered to be a match.
15210 @item -fstack-check
15211 @opindex fstack-check
15212 Generate code to verify that you do not go beyond the boundary of the
15213 stack. You should specify this flag if you are running in an
15214 environment with multiple threads, but only rarely need to specify it in
15215 a single-threaded environment since stack overflow is automatically
15216 detected on nearly all systems if there is only one stack.
15218 Note that this switch does not actually cause checking to be done; the
15219 operating system must do that. The switch causes generation of code
15220 to ensure that the operating system sees the stack being extended.
15222 @item -fstack-limit-register=@var{reg}
15223 @itemx -fstack-limit-symbol=@var{sym}
15224 @itemx -fno-stack-limit
15225 @opindex fstack-limit-register
15226 @opindex fstack-limit-symbol
15227 @opindex fno-stack-limit
15228 Generate code to ensure that the stack does not grow beyond a certain value,
15229 either the value of a register or the address of a symbol. If the stack
15230 would grow beyond the value, a signal is raised. For most targets,
15231 the signal is raised before the stack overruns the boundary, so
15232 it is possible to catch the signal without taking special precautions.
15234 For instance, if the stack starts at absolute address @samp{0x80000000}
15235 and grows downwards, you can use the flags
15236 @option{-fstack-limit-symbol=__stack_limit} and
15237 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
15238 of 128KB@. Note that this may only work with the GNU linker.
15240 @cindex aliasing of parameters
15241 @cindex parameters, aliased
15242 @item -fargument-alias
15243 @itemx -fargument-noalias
15244 @itemx -fargument-noalias-global
15245 @itemx -fargument-noalias-anything
15246 @opindex fargument-alias
15247 @opindex fargument-noalias
15248 @opindex fargument-noalias-global
15249 @opindex fargument-noalias-anything
15250 Specify the possible relationships among parameters and between
15251 parameters and global data.
15253 @option{-fargument-alias} specifies that arguments (parameters) may
15254 alias each other and may alias global storage.@*
15255 @option{-fargument-noalias} specifies that arguments do not alias
15256 each other, but may alias global storage.@*
15257 @option{-fargument-noalias-global} specifies that arguments do not
15258 alias each other and do not alias global storage.
15259 @option{-fargument-noalias-anything} specifies that arguments do not
15260 alias any other storage.
15262 Each language will automatically use whatever option is required by
15263 the language standard. You should not need to use these options yourself.
15265 @item -fleading-underscore
15266 @opindex fleading-underscore
15267 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
15268 change the way C symbols are represented in the object file. One use
15269 is to help link with legacy assembly code.
15271 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
15272 generate code that is not binary compatible with code generated without that
15273 switch. Use it to conform to a non-default application binary interface.
15274 Not all targets provide complete support for this switch.
15276 @item -ftls-model=@var{model}
15277 @opindex ftls-model
15278 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
15279 The @var{model} argument should be one of @code{global-dynamic},
15280 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
15282 The default without @option{-fpic} is @code{initial-exec}; with
15283 @option{-fpic} the default is @code{global-dynamic}.
15285 @item -fvisibility=@var{default|internal|hidden|protected}
15286 @opindex fvisibility
15287 Set the default ELF image symbol visibility to the specified option---all
15288 symbols will be marked with this unless overridden within the code.
15289 Using this feature can very substantially improve linking and
15290 load times of shared object libraries, produce more optimized
15291 code, provide near-perfect API export and prevent symbol clashes.
15292 It is @strong{strongly} recommended that you use this in any shared objects
15295 Despite the nomenclature, @code{default} always means public ie;
15296 available to be linked against from outside the shared object.
15297 @code{protected} and @code{internal} are pretty useless in real-world
15298 usage so the only other commonly used option will be @code{hidden}.
15299 The default if @option{-fvisibility} isn't specified is
15300 @code{default}, i.e., make every
15301 symbol public---this causes the same behavior as previous versions of
15304 A good explanation of the benefits offered by ensuring ELF
15305 symbols have the correct visibility is given by ``How To Write
15306 Shared Libraries'' by Ulrich Drepper (which can be found at
15307 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
15308 solution made possible by this option to marking things hidden when
15309 the default is public is to make the default hidden and mark things
15310 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
15311 and @code{__attribute__ ((visibility("default")))} instead of
15312 @code{__declspec(dllexport)} you get almost identical semantics with
15313 identical syntax. This is a great boon to those working with
15314 cross-platform projects.
15316 For those adding visibility support to existing code, you may find
15317 @samp{#pragma GCC visibility} of use. This works by you enclosing
15318 the declarations you wish to set visibility for with (for example)
15319 @samp{#pragma GCC visibility push(hidden)} and
15320 @samp{#pragma GCC visibility pop}.
15321 Bear in mind that symbol visibility should be viewed @strong{as
15322 part of the API interface contract} and thus all new code should
15323 always specify visibility when it is not the default ie; declarations
15324 only for use within the local DSO should @strong{always} be marked explicitly
15325 as hidden as so to avoid PLT indirection overheads---making this
15326 abundantly clear also aids readability and self-documentation of the code.
15327 Note that due to ISO C++ specification requirements, operator new and
15328 operator delete must always be of default visibility.
15330 Be aware that headers from outside your project, in particular system
15331 headers and headers from any other library you use, may not be
15332 expecting to be compiled with visibility other than the default. You
15333 may need to explicitly say @samp{#pragma GCC visibility push(default)}
15334 before including any such headers.
15336 @samp{extern} declarations are not affected by @samp{-fvisibility}, so
15337 a lot of code can be recompiled with @samp{-fvisibility=hidden} with
15338 no modifications. However, this means that calls to @samp{extern}
15339 functions with no explicit visibility will use the PLT, so it is more
15340 effective to use @samp{__attribute ((visibility))} and/or
15341 @samp{#pragma GCC visibility} to tell the compiler which @samp{extern}
15342 declarations should be treated as hidden.
15344 Note that @samp{-fvisibility} does affect C++ vague linkage
15345 entities. This means that, for instance, an exception class that will
15346 be thrown between DSOs must be explicitly marked with default
15347 visibility so that the @samp{type_info} nodes will be unified between
15350 An overview of these techniques, their benefits and how to use them
15351 is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}.
15357 @node Environment Variables
15358 @section Environment Variables Affecting GCC
15359 @cindex environment variables
15361 @c man begin ENVIRONMENT
15362 This section describes several environment variables that affect how GCC
15363 operates. Some of them work by specifying directories or prefixes to use
15364 when searching for various kinds of files. Some are used to specify other
15365 aspects of the compilation environment.
15367 Note that you can also specify places to search using options such as
15368 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
15369 take precedence over places specified using environment variables, which
15370 in turn take precedence over those specified by the configuration of GCC@.
15371 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
15372 GNU Compiler Collection (GCC) Internals}.
15377 @c @itemx LC_COLLATE
15379 @c @itemx LC_MONETARY
15380 @c @itemx LC_NUMERIC
15385 @c @findex LC_COLLATE
15386 @findex LC_MESSAGES
15387 @c @findex LC_MONETARY
15388 @c @findex LC_NUMERIC
15392 These environment variables control the way that GCC uses
15393 localization information that allow GCC to work with different
15394 national conventions. GCC inspects the locale categories
15395 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
15396 so. These locale categories can be set to any value supported by your
15397 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
15398 Kingdom encoded in UTF-8.
15400 The @env{LC_CTYPE} environment variable specifies character
15401 classification. GCC uses it to determine the character boundaries in
15402 a string; this is needed for some multibyte encodings that contain quote
15403 and escape characters that would otherwise be interpreted as a string
15406 The @env{LC_MESSAGES} environment variable specifies the language to
15407 use in diagnostic messages.
15409 If the @env{LC_ALL} environment variable is set, it overrides the value
15410 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
15411 and @env{LC_MESSAGES} default to the value of the @env{LANG}
15412 environment variable. If none of these variables are set, GCC
15413 defaults to traditional C English behavior.
15417 If @env{TMPDIR} is set, it specifies the directory to use for temporary
15418 files. GCC uses temporary files to hold the output of one stage of
15419 compilation which is to be used as input to the next stage: for example,
15420 the output of the preprocessor, which is the input to the compiler
15423 @item GCC_EXEC_PREFIX
15424 @findex GCC_EXEC_PREFIX
15425 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
15426 names of the subprograms executed by the compiler. No slash is added
15427 when this prefix is combined with the name of a subprogram, but you can
15428 specify a prefix that ends with a slash if you wish.
15430 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
15431 an appropriate prefix to use based on the pathname it was invoked with.
15433 If GCC cannot find the subprogram using the specified prefix, it
15434 tries looking in the usual places for the subprogram.
15436 The default value of @env{GCC_EXEC_PREFIX} is
15437 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to
15438 the installed compiler. In many cases @var{prefix} is the value
15439 of @code{prefix} when you ran the @file{configure} script.
15441 Other prefixes specified with @option{-B} take precedence over this prefix.
15443 This prefix is also used for finding files such as @file{crt0.o} that are
15446 In addition, the prefix is used in an unusual way in finding the
15447 directories to search for header files. For each of the standard
15448 directories whose name normally begins with @samp{/usr/local/lib/gcc}
15449 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
15450 replacing that beginning with the specified prefix to produce an
15451 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
15452 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
15453 These alternate directories are searched first; the standard directories
15454 come next. If a standard directory begins with the configured
15455 @var{prefix} then the value of @var{prefix} is replaced by
15456 @env{GCC_EXEC_PREFIX} when looking for header files.
15458 @item COMPILER_PATH
15459 @findex COMPILER_PATH
15460 The value of @env{COMPILER_PATH} is a colon-separated list of
15461 directories, much like @env{PATH}. GCC tries the directories thus
15462 specified when searching for subprograms, if it can't find the
15463 subprograms using @env{GCC_EXEC_PREFIX}.
15466 @findex LIBRARY_PATH
15467 The value of @env{LIBRARY_PATH} is a colon-separated list of
15468 directories, much like @env{PATH}. When configured as a native compiler,
15469 GCC tries the directories thus specified when searching for special
15470 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
15471 using GCC also uses these directories when searching for ordinary
15472 libraries for the @option{-l} option (but directories specified with
15473 @option{-L} come first).
15477 @cindex locale definition
15478 This variable is used to pass locale information to the compiler. One way in
15479 which this information is used is to determine the character set to be used
15480 when character literals, string literals and comments are parsed in C and C++.
15481 When the compiler is configured to allow multibyte characters,
15482 the following values for @env{LANG} are recognized:
15486 Recognize JIS characters.
15488 Recognize SJIS characters.
15490 Recognize EUCJP characters.
15493 If @env{LANG} is not defined, or if it has some other value, then the
15494 compiler will use mblen and mbtowc as defined by the default locale to
15495 recognize and translate multibyte characters.
15499 Some additional environments variables affect the behavior of the
15502 @include cppenv.texi
15506 @node Precompiled Headers
15507 @section Using Precompiled Headers
15508 @cindex precompiled headers
15509 @cindex speed of compilation
15511 Often large projects have many header files that are included in every
15512 source file. The time the compiler takes to process these header files
15513 over and over again can account for nearly all of the time required to
15514 build the project. To make builds faster, GCC allows users to
15515 `precompile' a header file; then, if builds can use the precompiled
15516 header file they will be much faster.
15518 To create a precompiled header file, simply compile it as you would any
15519 other file, if necessary using the @option{-x} option to make the driver
15520 treat it as a C or C++ header file. You will probably want to use a
15521 tool like @command{make} to keep the precompiled header up-to-date when
15522 the headers it contains change.
15524 A precompiled header file will be searched for when @code{#include} is
15525 seen in the compilation. As it searches for the included file
15526 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
15527 compiler looks for a precompiled header in each directory just before it
15528 looks for the include file in that directory. The name searched for is
15529 the name specified in the @code{#include} with @samp{.gch} appended. If
15530 the precompiled header file can't be used, it is ignored.
15532 For instance, if you have @code{#include "all.h"}, and you have
15533 @file{all.h.gch} in the same directory as @file{all.h}, then the
15534 precompiled header file will be used if possible, and the original
15535 header will be used otherwise.
15537 Alternatively, you might decide to put the precompiled header file in a
15538 directory and use @option{-I} to ensure that directory is searched
15539 before (or instead of) the directory containing the original header.
15540 Then, if you want to check that the precompiled header file is always
15541 used, you can put a file of the same name as the original header in this
15542 directory containing an @code{#error} command.
15544 This also works with @option{-include}. So yet another way to use
15545 precompiled headers, good for projects not designed with precompiled
15546 header files in mind, is to simply take most of the header files used by
15547 a project, include them from another header file, precompile that header
15548 file, and @option{-include} the precompiled header. If the header files
15549 have guards against multiple inclusion, they will be skipped because
15550 they've already been included (in the precompiled header).
15552 If you need to precompile the same header file for different
15553 languages, targets, or compiler options, you can instead make a
15554 @emph{directory} named like @file{all.h.gch}, and put each precompiled
15555 header in the directory, perhaps using @option{-o}. It doesn't matter
15556 what you call the files in the directory, every precompiled header in
15557 the directory will be considered. The first precompiled header
15558 encountered in the directory that is valid for this compilation will
15559 be used; they're searched in no particular order.
15561 There are many other possibilities, limited only by your imagination,
15562 good sense, and the constraints of your build system.
15564 A precompiled header file can be used only when these conditions apply:
15568 Only one precompiled header can be used in a particular compilation.
15571 A precompiled header can't be used once the first C token is seen. You
15572 can have preprocessor directives before a precompiled header; you can
15573 even include a precompiled header from inside another header, so long as
15574 there are no C tokens before the @code{#include}.
15577 The precompiled header file must be produced for the same language as
15578 the current compilation. You can't use a C precompiled header for a C++
15582 The precompiled header file must have been produced by the same compiler
15583 binary as the current compilation is using.
15586 Any macros defined before the precompiled header is included must
15587 either be defined in the same way as when the precompiled header was
15588 generated, or must not affect the precompiled header, which usually
15589 means that they don't appear in the precompiled header at all.
15591 The @option{-D} option is one way to define a macro before a
15592 precompiled header is included; using a @code{#define} can also do it.
15593 There are also some options that define macros implicitly, like
15594 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
15597 @item If debugging information is output when using the precompiled
15598 header, using @option{-g} or similar, the same kind of debugging information
15599 must have been output when building the precompiled header. However,
15600 a precompiled header built using @option{-g} can be used in a compilation
15601 when no debugging information is being output.
15603 @item The same @option{-m} options must generally be used when building
15604 and using the precompiled header. @xref{Submodel Options},
15605 for any cases where this rule is relaxed.
15607 @item Each of the following options must be the same when building and using
15608 the precompiled header:
15610 @gccoptlist{-fexceptions -funit-at-a-time}
15613 Some other command-line options starting with @option{-f},
15614 @option{-p}, or @option{-O} must be defined in the same way as when
15615 the precompiled header was generated. At present, it's not clear
15616 which options are safe to change and which are not; the safest choice
15617 is to use exactly the same options when generating and using the
15618 precompiled header. The following are known to be safe:
15620 @gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol
15621 -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol
15622 -fsched-verbose=<number> -fschedule-insns -fvisibility= @gol
15627 For all of these except the last, the compiler will automatically
15628 ignore the precompiled header if the conditions aren't met. If you
15629 find an option combination that doesn't work and doesn't cause the
15630 precompiled header to be ignored, please consider filing a bug report,
15633 If you do use differing options when generating and using the
15634 precompiled header, the actual behavior will be a mixture of the
15635 behavior for the options. For instance, if you use @option{-g} to
15636 generate the precompiled header but not when using it, you may or may
15637 not get debugging information for routines in the precompiled header.
15639 @node Running Protoize
15640 @section Running Protoize
15642 The program @code{protoize} is an optional part of GCC@. You can use
15643 it to add prototypes to a program, thus converting the program to ISO
15644 C in one respect. The companion program @code{unprotoize} does the
15645 reverse: it removes argument types from any prototypes that are found.
15647 When you run these programs, you must specify a set of source files as
15648 command line arguments. The conversion programs start out by compiling
15649 these files to see what functions they define. The information gathered
15650 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
15652 After scanning comes actual conversion. The specified files are all
15653 eligible to be converted; any files they include (whether sources or
15654 just headers) are eligible as well.
15656 But not all the eligible files are converted. By default,
15657 @code{protoize} and @code{unprotoize} convert only source and header
15658 files in the current directory. You can specify additional directories
15659 whose files should be converted with the @option{-d @var{directory}}
15660 option. You can also specify particular files to exclude with the
15661 @option{-x @var{file}} option. A file is converted if it is eligible, its
15662 directory name matches one of the specified directory names, and its
15663 name within the directory has not been excluded.
15665 Basic conversion with @code{protoize} consists of rewriting most
15666 function definitions and function declarations to specify the types of
15667 the arguments. The only ones not rewritten are those for varargs
15670 @code{protoize} optionally inserts prototype declarations at the
15671 beginning of the source file, to make them available for any calls that
15672 precede the function's definition. Or it can insert prototype
15673 declarations with block scope in the blocks where undeclared functions
15676 Basic conversion with @code{unprotoize} consists of rewriting most
15677 function declarations to remove any argument types, and rewriting
15678 function definitions to the old-style pre-ISO form.
15680 Both conversion programs print a warning for any function declaration or
15681 definition that they can't convert. You can suppress these warnings
15684 The output from @code{protoize} or @code{unprotoize} replaces the
15685 original source file. The original file is renamed to a name ending
15686 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
15687 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
15688 for DOS) file already exists, then the source file is simply discarded.
15690 @code{protoize} and @code{unprotoize} both depend on GCC itself to
15691 scan the program and collect information about the functions it uses.
15692 So neither of these programs will work until GCC is installed.
15694 Here is a table of the options you can use with @code{protoize} and
15695 @code{unprotoize}. Each option works with both programs unless
15699 @item -B @var{directory}
15700 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
15701 usual directory (normally @file{/usr/local/lib}). This file contains
15702 prototype information about standard system functions. This option
15703 applies only to @code{protoize}.
15705 @item -c @var{compilation-options}
15706 Use @var{compilation-options} as the options when running @command{gcc} to
15707 produce the @samp{.X} files. The special option @option{-aux-info} is
15708 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
15710 Note that the compilation options must be given as a single argument to
15711 @code{protoize} or @code{unprotoize}. If you want to specify several
15712 @command{gcc} options, you must quote the entire set of compilation options
15713 to make them a single word in the shell.
15715 There are certain @command{gcc} arguments that you cannot use, because they
15716 would produce the wrong kind of output. These include @option{-g},
15717 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
15718 the @var{compilation-options}, they are ignored.
15721 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
15722 systems) instead of @samp{.c}. This is convenient if you are converting
15723 a C program to C++. This option applies only to @code{protoize}.
15726 Add explicit global declarations. This means inserting explicit
15727 declarations at the beginning of each source file for each function
15728 that is called in the file and was not declared. These declarations
15729 precede the first function definition that contains a call to an
15730 undeclared function. This option applies only to @code{protoize}.
15732 @item -i @var{string}
15733 Indent old-style parameter declarations with the string @var{string}.
15734 This option applies only to @code{protoize}.
15736 @code{unprotoize} converts prototyped function definitions to old-style
15737 function definitions, where the arguments are declared between the
15738 argument list and the initial @samp{@{}. By default, @code{unprotoize}
15739 uses five spaces as the indentation. If you want to indent with just
15740 one space instead, use @option{-i " "}.
15743 Keep the @samp{.X} files. Normally, they are deleted after conversion
15747 Add explicit local declarations. @code{protoize} with @option{-l} inserts
15748 a prototype declaration for each function in each block which calls the
15749 function without any declaration. This option applies only to
15753 Make no real changes. This mode just prints information about the conversions
15754 that would have been done without @option{-n}.
15757 Make no @samp{.save} files. The original files are simply deleted.
15758 Use this option with caution.
15760 @item -p @var{program}
15761 Use the program @var{program} as the compiler. Normally, the name
15762 @file{gcc} is used.
15765 Work quietly. Most warnings are suppressed.
15768 Print the version number, just like @option{-v} for @command{gcc}.
15771 If you need special compiler options to compile one of your program's
15772 source files, then you should generate that file's @samp{.X} file
15773 specially, by running @command{gcc} on that source file with the
15774 appropriate options and the option @option{-aux-info}. Then run
15775 @code{protoize} on the entire set of files. @code{protoize} will use
15776 the existing @samp{.X} file because it is newer than the source file.
15780 gcc -Dfoo=bar file1.c -aux-info file1.X
15785 You need to include the special files along with the rest in the
15786 @code{protoize} command, even though their @samp{.X} files already
15787 exist, because otherwise they won't get converted.
15789 @xref{Protoize Caveats}, for more information on how to use
15790 @code{protoize} successfully.