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1 | @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, |
2 | @c 2000, 2001 Free Software Foundation, Inc. | |
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3 | @c This is part of the GCC manual. |
4 | @c For copying conditions, see the file gcc.texi. | |
5 | ||
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6 | @ignore |
7 | @c man begin COPYRIGHT | |
8 | Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, | |
21c7361e | 9 | 1998, 1999, 2000, 2001 Free Software Foundation, Inc. |
9d86bffc JM |
10 | |
11 | Permission is granted to make and distribute verbatim copies of this | |
12 | manual provided the copyright notice and this permission notice are | |
13 | preserved on all copies. | |
14 | ||
15 | Permission is granted to copy and distribute modified versions of this | |
16 | manual under the conditions for verbatim copying, provided also that the | |
17 | entire resulting derived work is distributed under the terms of a | |
18 | permission notice identical to this one. | |
19 | ||
20 | Permission is granted to copy and distribute translations of this manual | |
21 | into another language, under the above conditions for modified versions, | |
22 | except that this permission notice may be included in translations | |
23 | approved by the Free Software Foundation instead of in the original | |
24 | English. | |
25 | @c man end | |
26 | @c Set file name and title for the man page. | |
27 | @setfilename gcc | |
28 | @settitle GNU project C and C++ compiler | |
29 | @c man begin SYNOPSIS | |
30 | gcc [@samp{-c}|@samp{-S}|@samp{-E}] [@samp{-std=}@var{standard}] | |
31 | [@samp{-g}] [@samp{-pg}] [@samp{-O}@var{level}] | |
32 | [@samp{-W}@var{warn}...] [@samp{-pedantic}] | |
33 | [@samp{-I}@var{dir}...] [@samp{-L}@var{dir}...] | |
34 | [@samp{-D}@var{macro}[=@var{defn}]...] [@samp{-U}@var{macro}] | |
35 | [@samp{-f}@var{option}...] [@samp{-m}@var{machine-option}...] | |
36 | [@samp{-o} @var{outfile}] @var{infile}... | |
37 | ||
38 | Only the most useful options are listed here; see below for the | |
39 | remainder. @samp{g++} accepts mostly the same options as @samp{gcc}. | |
40 | @c man end | |
41 | @c man begin SEEALSO | |
42 | cpp(1), gcov(1), g77(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1) | |
43 | and the Info entries for @file{gcc}, @file{cpp}, @file{g77}, @file{as}, | |
44 | @file{ld}, @file{binutils} and @file{gdb}. | |
45 | @c man end | |
2642624b JM |
46 | @c man begin BUGS |
47 | For instructions on reporting bugs, see | |
bedc7537 | 48 | @w{@uref{http://gcc.gnu.org/bugs.html}}. Use of the @command{gccbug} |
2642624b JM |
49 | script to report bugs is recommended. |
50 | @c man end | |
51 | @c man begin AUTHOR | |
52 | See the Info entry for @file{gcc}, or | |
53 | @w{@uref{http://gcc.gnu.org/thanks.html}}, for contributors to GCC. | |
54 | @c man end | |
9d86bffc JM |
55 | @end ignore |
56 | ||
74291a4b | 57 | @node Invoking GCC |
0c2d1a2a JB |
58 | @chapter GCC Command Options |
59 | @cindex GCC command options | |
74291a4b | 60 | @cindex command options |
0c2d1a2a | 61 | @cindex options, GCC command |
74291a4b | 62 | |
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63 | @c man begin DESCRIPTION |
64 | ||
0c2d1a2a | 65 | When you invoke GCC, it normally does preprocessing, compilation, |
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66 | assembly and linking. The ``overall options'' allow you to stop this |
67 | process at an intermediate stage. For example, the @samp{-c} option | |
68 | says not to run the linker. Then the output consists of object files | |
69 | output by the assembler. | |
70 | ||
71 | Other options are passed on to one stage of processing. Some options | |
72 | control the preprocessor and others the compiler itself. Yet other | |
73 | options control the assembler and linker; most of these are not | |
74 | documented here, since you rarely need to use any of them. | |
75 | ||
76 | @cindex C compilation options | |
0c2d1a2a | 77 | Most of the command line options that you can use with GCC are useful |
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78 | for C programs; when an option is only useful with another language |
79 | (usually C++), the explanation says so explicitly. If the description | |
80 | for a particular option does not mention a source language, you can use | |
81 | that option with all supported languages. | |
82 | ||
83 | @cindex C++ compilation options | |
84 | @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special | |
85 | options for compiling C++ programs. | |
86 | ||
87 | @cindex grouping options | |
88 | @cindex options, grouping | |
bedc7537 | 89 | The @command{gcc} program accepts options and file names as operands. Many |
b192711e | 90 | options have multi-letter names; therefore multiple single-letter options |
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91 | may @emph{not} be grouped: @samp{-dr} is very different from @w{@samp{-d |
92 | -r}}. | |
93 | ||
94 | @cindex order of options | |
95 | @cindex options, order | |
96 | You can mix options and other arguments. For the most part, the order | |
97 | you use doesn't matter. Order does matter when you use several options | |
98 | of the same kind; for example, if you specify @samp{-L} more than once, | |
99 | the directories are searched in the order specified. | |
100 | ||
101 | Many options have long names starting with @samp{-f} or with | |
102 | @samp{-W}---for example, @samp{-fforce-mem}, | |
103 | @samp{-fstrength-reduce}, @samp{-Wformat} and so on. Most of | |
104 | these have both positive and negative forms; the negative form of | |
105 | @samp{-ffoo} would be @samp{-fno-foo}. This manual documents | |
106 | only one of these two forms, whichever one is not the default. | |
107 | ||
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108 | @c man end |
109 | ||
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110 | @menu |
111 | * Option Summary:: Brief list of all options, without explanations. | |
112 | * Overall Options:: Controlling the kind of output: | |
113 | an executable, object files, assembler files, | |
114 | or preprocessed source. | |
115 | * Invoking G++:: Compiling C++ programs. | |
116 | * C Dialect Options:: Controlling the variant of C language compiled. | |
117 | * C++ Dialect Options:: Variations on C++. | |
60de6385 | 118 | * Objective-C Dialect Options:: Variations on Objective-C. |
764dbbf2 | 119 | * Language Independent Options:: Controlling how diagnostics should be |
02f52e19 | 120 | formatted. |
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121 | * Warning Options:: How picky should the compiler be? |
122 | * Debugging Options:: Symbol tables, measurements, and debugging dumps. | |
123 | * Optimize Options:: How much optimization? | |
124 | * Preprocessor Options:: Controlling header files and macro definitions. | |
125 | Also, getting dependency information for Make. | |
126 | * Assembler Options:: Passing options to the assembler. | |
127 | * Link Options:: Specifying libraries and so on. | |
128 | * Directory Options:: Where to find header files and libraries. | |
129 | Where to find the compiler executable files. | |
a743d340 | 130 | * Spec Files:: How to pass switches to sub-processes. |
0c2d1a2a | 131 | * Target Options:: Running a cross-compiler, or an old version of GCC. |
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132 | * Submodel Options:: Specifying minor hardware or convention variations, |
133 | such as 68010 vs 68020. | |
134 | * Code Gen Options:: Specifying conventions for function calls, data layout | |
135 | and register usage. | |
0c2d1a2a | 136 | * Environment Variables:: Env vars that affect GCC. |
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137 | * Running Protoize:: Automatically adding or removing function prototypes. |
138 | @end menu | |
139 | ||
4bc1997b JM |
140 | @c man begin OPTIONS |
141 | ||
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142 | @node Option Summary |
143 | @section Option Summary | |
144 | ||
145 | Here is a summary of all the options, grouped by type. Explanations are | |
146 | in the following sections. | |
147 | ||
148 | @table @emph | |
149 | @item Overall Options | |
150 | @xref{Overall Options,,Options Controlling the Kind of Output}. | |
4bc1997b JM |
151 | @gccoptlist{ |
152 | -c -S -E -o @var{file} -pipe -pass-exit-codes -x @var{language} @gol | |
153 | -v --target-help --help} | |
74291a4b MM |
154 | |
155 | @item C Language Options | |
156 | @xref{C Dialect Options,,Options Controlling C Dialect}. | |
4bc1997b JM |
157 | @gccoptlist{ |
158 | -ansi -std=@var{standard} -fno-asm -fno-builtin @gol | |
159 | -fhosted -ffreestanding @gol | |
160 | -trigraphs -traditional -traditional-cpp @gol | |
161 | -fallow-single-precision -fcond-mismatch @gol | |
162 | -fsigned-bitfields -fsigned-char @gol | |
163 | -funsigned-bitfields -funsigned-char @gol | |
164 | -fwritable-strings -fshort-wchar} | |
74291a4b MM |
165 | |
166 | @item C++ Language Options | |
167 | @xref{C++ Dialect Options,,Options Controlling C++ Dialect}. | |
4bc1997b JM |
168 | @gccoptlist{ |
169 | -fno-access-control -fcheck-new -fconserve-space @gol | |
aa0cc562 JM |
170 | -fno-const-strings -fdollars-in-identifiers @gol |
171 | -fno-elide-constructors @gol | |
4bc1997b JM |
172 | -fno-enforce-eh-specs -fexternal-templates @gol |
173 | -falt-external-templates @gol | |
174 | -ffor-scope -fno-for-scope -fno-gnu-keywords -fhonor-std @gol | |
90ecce3e | 175 | -fno-implicit-templates @gol |
4bc1997b JM |
176 | -fno-implicit-inline-templates @gol |
177 | -fno-implement-inlines -fms-extensions @gol | |
aa0cc562 | 178 | -fno-nonansi-builtins -fno-operator-names @gol |
4bc1997b | 179 | -fno-optional-diags -fpermissive @gol |
aa0cc562 | 180 | -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol |
90ecce3e | 181 | -fuse-cxa-atexit -fvtable-gc -fno-weak -nostdinc++ @gol |
4bc1997b JM |
182 | -fno-default-inline -Wctor-dtor-privacy @gol |
183 | -Wnon-virtual-dtor -Wreorder @gol | |
184 | -Weffc++ -Wno-deprecated @gol | |
185 | -Wno-non-template-friend -Wold-style-cast @gol | |
186 | -Woverloaded-virtual -Wno-pmf-conversions @gol | |
187 | -Wsign-promo -Wsynth} | |
74291a4b | 188 | |
60de6385 SS |
189 | @item Objective-C Language Options |
190 | @xref{Objective-C Dialect Options,,Options Controlling Objective-C Dialect}. | |
191 | @gccoptlist{ | |
192 | -fconstant-string-class=@var{class name} @gol | |
193 | -fgnu-runtime -fnext-runtime -gen-decls | |
194 | -Wno-protocol -Wselector} | |
195 | ||
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196 | @item Language Independent Options |
197 | @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}. | |
4bc1997b JM |
198 | @gccoptlist{ |
199 | -fmessage-length=@var{n} @gol | |
200 | -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}} | |
764dbbf2 | 201 | |
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202 | @item Warning Options |
203 | @xref{Warning Options,,Options to Request or Suppress Warnings}. | |
4bc1997b JM |
204 | @gccoptlist{ |
205 | -fsyntax-only -pedantic -pedantic-errors @gol | |
206 | -w -W -Wall -Waggregate-return @gol | |
207 | -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol | |
208 | -Wconversion -Wdisabled-optimization -Werror @gol | |
209 | -Wfloat-equal -Wformat -Wformat=2 @gol | |
210 | -Wformat-nonliteral -Wformat-security @gol | |
84b77836 | 211 | -Wimplicit -Wimplicit-int @gol |
4bc1997b JM |
212 | -Wimplicit-function-declaration @gol |
213 | -Werror-implicit-function-declaration @gol | |
214 | -Wimport -Winline @gol | |
215 | -Wlarger-than-@var{len} -Wlong-long @gol | |
1f0c3120 | 216 | -Wmain -Wmissing-braces -Wmissing-declarations @gol |
4bc1997b JM |
217 | -Wmissing-format-attribute -Wmissing-noreturn @gol |
218 | -Wmultichar -Wno-format-extra-args -Wno-format-y2k @gol | |
219 | -Wno-import -Wpacked -Wpadded @gol | |
220 | -Wparentheses -Wpointer-arith -Wredundant-decls @gol | |
221 | -Wreturn-type -Wsequence-point -Wshadow @gol | |
222 | -Wsign-compare -Wswitch -Wsystem-headers @gol | |
223 | -Wtrigraphs -Wundef -Wuninitialized @gol | |
224 | -Wunknown-pragmas -Wunreachable-code @gol | |
225 | -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol | |
226 | -Wunused-value -Wunused-variable -Wwrite-strings} | |
74291a4b | 227 | |
fe50c0eb | 228 | @item C-only Warning Options |
4bc1997b JM |
229 | @gccoptlist{ |
230 | -Wbad-function-cast -Wmissing-prototypes -Wnested-externs @gol | |
231 | -Wstrict-prototypes -Wtraditional} | |
fe50c0eb | 232 | |
74291a4b MM |
233 | @item Debugging Options |
234 | @xref{Debugging Options,,Options for Debugging Your Program or GCC}. | |
4bc1997b | 235 | @gccoptlist{ |
1f0c3120 JM |
236 | -a -ax -d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol |
237 | -fdump-unnumbered -fdump-translation-unit=@var{file} @gol | |
238 | -fdump-class-layout=@var{file} -fmem-report -fpretend-float @gol | |
239 | -fprofile-arcs -ftest-coverage -ftime-report @gol | |
4bc1997b JM |
240 | -g -g@var{level} -gcoff -gdwarf -gdwarf-1 -gdwarf-1+ -gdwarf-2 @gol |
241 | -ggdb -gstabs -gstabs+ -gxcoff -gxcoff+ @gol | |
242 | -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol | |
243 | -print-prog-name=@var{program} -print-search-dirs -Q @gol | |
244 | -save-temps -time} | |
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245 | |
246 | @item Optimization Options | |
247 | @xref{Optimize Options,,Options that Control Optimization}. | |
4bc1997b JM |
248 | @gccoptlist{ |
249 | -falign-functions=@var{n} -falign-jumps=@var{n} @gol | |
250 | -falign-labels=@var{n} -falign-loops=@var{n} @gol | |
251 | -fbranch-probabilities -fcaller-saves @gol | |
252 | -fcse-follow-jumps -fcse-skip-blocks -fdata-sections -fdce @gol | |
253 | -fdelayed-branch -fdelete-null-pointer-checks @gol | |
254 | -fexpensive-optimizations -ffast-math -ffloat-store @gol | |
a13d4ebf | 255 | -fforce-addr -fforce-mem -ffunction-sections -fgcse -fgcse-lm -fgcse-sm @gol |
4bc1997b JM |
256 | -finline-functions -finline-limit=@var{n} -fkeep-inline-functions @gol |
257 | -fkeep-static-consts -fmove-all-movables @gol | |
258 | -fno-default-inline -fno-defer-pop @gol | |
de6c5979 | 259 | -fno-function-cse -fno-guess-branch-probability @gol |
454d0cc7 | 260 | -fno-inline -fno-math-errno -fno-peephole @gol |
de6c5979 | 261 | -funsafe-math-optimizations -fno-trapping-math @gol |
4bc1997b JM |
262 | -fomit-frame-pointer -foptimize-register-move @gol |
263 | -foptimize-sibling-calls -freduce-all-givs @gol | |
264 | -fregmove -frename-registers @gol | |
265 | -frerun-cse-after-loop -frerun-loop-opt @gol | |
266 | -fschedule-insns -fschedule-insns2 @gol | |
267 | -fsingle-precision-constant -fssa @gol | |
268 | -fstrength-reduce -fstrict-aliasing -fthread-jumps -ftrapv @gol | |
269 | -funroll-all-loops -funroll-loops @gol | |
3af64fd6 | 270 | --param @var{name}=@var{value} |
4bc1997b | 271 | -O -O0 -O1 -O2 -O3 -Os} |
74291a4b MM |
272 | |
273 | @item Preprocessor Options | |
274 | @xref{Preprocessor Options,,Options Controlling the Preprocessor}. | |
4bc1997b JM |
275 | @gccoptlist{ |
276 | -$ -A@var{question}=@var{answer} -A-@var{question}@r{[}=@var{answer}@r{]} @gol | |
277 | -C -dD -dI -dM -dN @gol | |
278 | -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol | |
279 | -idirafter @var{dir} @gol | |
280 | -include @var{file} -imacros @var{file} @gol | |
281 | -iprefix @var{file} -iwithprefix @var{dir} @gol | |
282 | -iwithprefixbefore @var{dir} -isystem @var{dir} -isystem-c++ @var{dir} @gol | |
283 | -M -MM -MF -MG -MP -MQ -MT -nostdinc -P -remap @gol | |
371e300b | 284 | -trigraphs -undef -U@var{macro} -Wp\,@var{option}} |
74291a4b MM |
285 | |
286 | @item Assembler Option | |
287 | @xref{Assembler Options,,Passing Options to the Assembler}. | |
4bc1997b | 288 | @gccoptlist{ |
371e300b | 289 | -Wa\,@var{option}} |
74291a4b MM |
290 | |
291 | @item Linker Options | |
292 | @xref{Link Options,,Options for Linking}. | |
4bc1997b JM |
293 | @gccoptlist{ |
294 | @var{object-file-name} -l@var{library} @gol | |
295 | -nostartfiles -nodefaultlibs -nostdlib @gol | |
296 | -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol | |
371e300b | 297 | -Wl\,@var{option} -Xlinker @var{option} @gol |
4bc1997b | 298 | -u @var{symbol}} |
74291a4b MM |
299 | |
300 | @item Directory Options | |
301 | @xref{Directory Options,,Options for Directory Search}. | |
4bc1997b JM |
302 | @gccoptlist{ |
303 | -B@var{prefix} -I@var{dir} -I- -L@var{dir} -specs=@var{file}} | |
74291a4b MM |
304 | |
305 | @item Target Options | |
306 | @c I wrote this xref this way to avoid overfull hbox. -- rms | |
307 | @xref{Target Options}. | |
4bc1997b JM |
308 | @gccoptlist{ |
309 | -b @var{machine} -V @var{version}} | |
74291a4b MM |
310 | |
311 | @item Machine Dependent Options | |
312 | @xref{Submodel Options,,Hardware Models and Configurations}. | |
74291a4b | 313 | @emph{M680x0 Options} |
4bc1997b JM |
314 | @gccoptlist{ |
315 | -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol | |
316 | -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol | |
317 | -mfpa -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol | |
318 | -malign-int -mstrict-align} | |
74291a4b | 319 | |
2856c3e3 | 320 | @emph{M68hc1x Options} |
4bc1997b JM |
321 | @gccoptlist{ |
322 | -m6811 -m6812 -m68hc11 -m68hc12 @gol | |
323 | -mauto-incdec -mshort -msoft-reg-count=@var{count}} | |
2856c3e3 | 324 | |
74291a4b | 325 | @emph{VAX Options} |
4bc1997b JM |
326 | @gccoptlist{ |
327 | -mg -mgnu -munix} | |
74291a4b MM |
328 | |
329 | @emph{SPARC Options} | |
4bc1997b JM |
330 | @gccoptlist{ |
331 | -mcpu=@var{cpu type} @gol | |
332 | -mtune=@var{cpu type} @gol | |
333 | -mcmodel=@var{code model} @gol | |
334 | -m32 -m64 @gol | |
335 | -mapp-regs -mbroken-saverestore -mcypress @gol | |
336 | -mepilogue -mfaster-structs -mflat @gol | |
337 | -mfpu -mhard-float -mhard-quad-float @gol | |
338 | -mimpure-text -mlive-g0 -mno-app-regs @gol | |
339 | -mno-epilogue -mno-faster-structs -mno-flat -mno-fpu @gol | |
340 | -mno-impure-text -mno-stack-bias -mno-unaligned-doubles @gol | |
341 | -msoft-float -msoft-quad-float -msparclite -mstack-bias @gol | |
342 | -msupersparc -munaligned-doubles -mv8} | |
74291a4b MM |
343 | |
344 | @emph{Convex Options} | |
4bc1997b JM |
345 | @gccoptlist{ |
346 | -mc1 -mc2 -mc32 -mc34 -mc38 @gol | |
347 | -margcount -mnoargcount @gol | |
348 | -mlong32 -mlong64 @gol | |
349 | -mvolatile-cache -mvolatile-nocache} | |
74291a4b MM |
350 | |
351 | @emph{AMD29K Options} | |
4bc1997b JM |
352 | @gccoptlist{ |
353 | -m29000 -m29050 -mbw -mnbw -mdw -mndw @gol | |
354 | -mlarge -mnormal -msmall @gol | |
355 | -mkernel-registers -mno-reuse-arg-regs @gol | |
356 | -mno-stack-check -mno-storem-bug @gol | |
357 | -mreuse-arg-regs -msoft-float -mstack-check @gol | |
358 | -mstorem-bug -muser-registers} | |
74291a4b MM |
359 | |
360 | @emph{ARM Options} | |
4bc1997b JM |
361 | @gccoptlist{ |
362 | -mapcs-frame -mno-apcs-frame @gol | |
363 | -mapcs-26 -mapcs-32 @gol | |
364 | -mapcs-stack-check -mno-apcs-stack-check @gol | |
365 | -mapcs-float -mno-apcs-float @gol | |
366 | -mapcs-reentrant -mno-apcs-reentrant @gol | |
367 | -msched-prolog -mno-sched-prolog @gol | |
368 | -mlittle-endian -mbig-endian -mwords-little-endian @gol | |
369 | -malignment-traps -mno-alignment-traps @gol | |
370 | -msoft-float -mhard-float -mfpe @gol | |
371 | -mthumb-interwork -mno-thumb-interwork @gol | |
247f8561 PB |
372 | -mcpu=@var{name} -march=@var{name} -mfpe=@var{name} @gol |
373 | -mstructure-size-boundary=@var{n} @gol | |
4bc1997b JM |
374 | -mbsd -mxopen -mno-symrename @gol |
375 | -mabort-on-noreturn @gol | |
376 | -mlong-calls -mno-long-calls @gol | |
4bc1997b | 377 | -msingle-pic-base -mno-single-pic-base @gol |
247f8561 PB |
378 | -mpic-register=@var{reg} @gol |
379 | -mnop-fun-dllimport @gol | |
380 | -mpoke-function-name @gol | |
381 | -mthumb -marm @gol | |
382 | -mtpcs-frame -mtpcs-leaf-frame @gol | |
383 | -mcaller-super-interworking -mcallee-super-interworking } | |
74291a4b | 384 | |
ecff22ab | 385 | @emph{MN10200 Options} |
4bc1997b JM |
386 | @gccoptlist{ |
387 | -mrelax} | |
ecff22ab | 388 | |
6d6d0fa0 | 389 | @emph{MN10300 Options} |
4bc1997b JM |
390 | @gccoptlist{ |
391 | -mmult-bug @gol | |
392 | -mno-mult-bug @gol | |
393 | -mam33 @gol | |
394 | -mno-am33 @gol | |
395 | -mrelax} | |
6d6d0fa0 | 396 | |
861bb6c1 | 397 | @emph{M32R/D Options} |
4bc1997b JM |
398 | @gccoptlist{ |
399 | -mcode-model=@var{model type} -msdata=@var{sdata type} @gol | |
400 | -G @var{num}} | |
861bb6c1 | 401 | |
74291a4b | 402 | @emph{M88K Options} |
4bc1997b JM |
403 | @gccoptlist{ |
404 | -m88000 -m88100 -m88110 -mbig-pic @gol | |
405 | -mcheck-zero-division -mhandle-large-shift @gol | |
406 | -midentify-revision -mno-check-zero-division @gol | |
407 | -mno-ocs-debug-info -mno-ocs-frame-position @gol | |
408 | -mno-optimize-arg-area -mno-serialize-volatile @gol | |
409 | -mno-underscores -mocs-debug-info @gol | |
410 | -mocs-frame-position -moptimize-arg-area @gol | |
411 | -mserialize-volatile -mshort-data-@var{num} -msvr3 @gol | |
412 | -msvr4 -mtrap-large-shift -muse-div-instruction @gol | |
413 | -mversion-03.00 -mwarn-passed-structs} | |
74291a4b MM |
414 | |
415 | @emph{RS/6000 and PowerPC Options} | |
4bc1997b JM |
416 | @gccoptlist{ |
417 | -mcpu=@var{cpu type} @gol | |
418 | -mtune=@var{cpu type} @gol | |
419 | -mpower -mno-power -mpower2 -mno-power2 @gol | |
420 | -mpowerpc -mpowerpc64 -mno-powerpc @gol | |
421 | -mpowerpc-gpopt -mno-powerpc-gpopt @gol | |
422 | -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol | |
423 | -mnew-mnemonics -mold-mnemonics @gol | |
424 | -mfull-toc -mminimal-toc -mno-fop-in-toc -mno-sum-in-toc @gol | |
425 | -m64 -m32 -mxl-call -mno-xl-call -mthreads -mpe @gol | |
426 | -msoft-float -mhard-float -mmultiple -mno-multiple @gol | |
427 | -mstring -mno-string -mupdate -mno-update @gol | |
428 | -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol | |
429 | -mstrict-align -mno-strict-align -mrelocatable @gol | |
430 | -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol | |
431 | -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol | |
432 | -mcall-aix -mcall-sysv -mprototype -mno-prototype @gol | |
433 | -msim -mmvme -mads -myellowknife -memb -msdata @gol | |
434 | -msdata=@var{opt} -mvxworks -G @var{num}} | |
74291a4b MM |
435 | |
436 | @emph{RT Options} | |
4bc1997b JM |
437 | @gccoptlist{ |
438 | -mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs @gol | |
439 | -mfull-fp-blocks -mhc-struct-return -min-line-mul @gol | |
440 | -mminimum-fp-blocks -mnohc-struct-return} | |
74291a4b MM |
441 | |
442 | @emph{MIPS Options} | |
4bc1997b | 443 | @gccoptlist{ |
84a0e7b8 | 444 | -mabicalls -mcpu=@var{cpu type} |
4bc1997b JM |
445 | -membedded-data -muninit-const-in-rodata @gol |
446 | -membedded-pic -mfp32 -mfp64 -mgas -mgp32 -mgp64 @gol | |
447 | -mgpopt -mhalf-pic -mhard-float -mint64 -mips1 @gol | |
448 | -mips2 -mips3 -mips4 -mlong64 -mlong32 -mlong-calls -mmemcpy @gol | |
449 | -mmips-as -mmips-tfile -mno-abicalls @gol | |
450 | -mno-embedded-data -mno-uninit-const-in-rodata -mno-embedded-pic @gol | |
451 | -mno-gpopt -mno-long-calls @gol | |
452 | -mno-memcpy -mno-mips-tfile -mno-rnames -mno-stats @gol | |
453 | -mrnames -msoft-float @gol | |
454 | -m4650 -msingle-float -mmad @gol | |
455 | -mstats -EL -EB -G @var{num} -nocpp @gol | |
456 | -mabi=32 -mabi=n32 -mabi=64 -mabi=eabi @gol | |
457 | -mfix7000 -mno-crt0} | |
74291a4b MM |
458 | |
459 | @emph{i386 Options} | |
4bc1997b JM |
460 | @gccoptlist{ |
461 | -mcpu=@var{cpu type} -march=@var{cpu type} @gol | |
462 | -mintel-syntax -mieee-fp -mno-fancy-math-387 @gol | |
463 | -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol | |
464 | -mno-wide-multiply -mrtd -malign-double @gol | |
3e18fdf6 | 465 | -mpreferred-stack-boundary=@var{num} @gol |
4bc1997b JM |
466 | -mthreads -mno-align-stringops -minline-all-stringops @gol |
467 | -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol | |
762e166b | 468 | -m96bit-long-double -mregparm=@var{num} -momit-leaf-frame-pointer} |
74291a4b MM |
469 | |
470 | @emph{HPPA Options} | |
4bc1997b JM |
471 | @gccoptlist{ |
472 | -march=@var{architecture type} @gol | |
473 | -mbig-switch -mdisable-fpregs -mdisable-indexing @gol | |
474 | -mfast-indirect-calls -mgas -mjump-in-delay @gol | |
475 | -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol | |
476 | -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol | |
477 | -mno-jump-in-delay -mno-long-load-store @gol | |
478 | -mno-portable-runtime -mno-soft-float @gol | |
479 | -mno-space-regs -msoft-float -mpa-risc-1-0 @gol | |
480 | -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol | |
481 | -mschedule=@var{cpu type} -mspace-regs} | |
74291a4b MM |
482 | |
483 | @emph{Intel 960 Options} | |
4bc1997b JM |
484 | @gccoptlist{ |
485 | -m@var{cpu type} -masm-compat -mclean-linkage @gol | |
486 | -mcode-align -mcomplex-addr -mleaf-procedures @gol | |
487 | -mic-compat -mic2.0-compat -mic3.0-compat @gol | |
488 | -mintel-asm -mno-clean-linkage -mno-code-align @gol | |
489 | -mno-complex-addr -mno-leaf-procedures @gol | |
490 | -mno-old-align -mno-strict-align -mno-tail-call @gol | |
491 | -mnumerics -mold-align -msoft-float -mstrict-align @gol | |
492 | -mtail-call} | |
74291a4b MM |
493 | |
494 | @emph{DEC Alpha Options} | |
4bc1997b JM |
495 | @gccoptlist{ |
496 | -mfp-regs -mno-fp-regs -mno-soft-float -msoft-float @gol | |
497 | -malpha-as -mgas @gol | |
498 | -mieee -mieee-with-inexact -mieee-conformant @gol | |
499 | -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol | |
500 | -mtrap-precision=@var{mode} -mbuild-constants @gol | |
501 | -mcpu=@var{cpu type} @gol | |
502 | -mbwx -mno-bwx -mcix -mno-cix -mmax -mno-max @gol | |
503 | -mmemory-latency=@var{time}} | |
74291a4b MM |
504 | |
505 | @emph{Clipper Options} | |
4bc1997b JM |
506 | @gccoptlist{ |
507 | -mc300 -mc400} | |
74291a4b MM |
508 | |
509 | @emph{H8/300 Options} | |
4bc1997b JM |
510 | @gccoptlist{ |
511 | -mrelax -mh -ms -mint32 -malign-300} | |
74291a4b MM |
512 | |
513 | @emph{SH Options} | |
4bc1997b JM |
514 | @gccoptlist{ |
515 | -m1 -m2 -m3 -m3e @gol | |
516 | -m4-nofpu -m4-single-only -m4-single -m4 @gol | |
517 | -mb -ml -mdalign -mrelax @gol | |
518 | -mbigtable -mfmovd -mhitachi -mnomacsave @gol | |
519 | -misize -mpadstruct -mspace @gol | |
1a66cd67 | 520 | -mprefergot |
4bc1997b | 521 | -musermode} |
74291a4b MM |
522 | |
523 | @emph{System V Options} | |
4bc1997b | 524 | @gccoptlist{ |
371e300b | 525 | -Qy -Qn -YP\,@var{paths} -Ym\,@var{dir}} |
74291a4b | 526 | |
56b2d7a7 | 527 | @emph{ARC Options} |
4bc1997b JM |
528 | @gccoptlist{ |
529 | -EB -EL @gol | |
530 | -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text section} @gol | |
531 | -mdata=@var{data section} -mrodata=@var{readonly data section}} | |
56b2d7a7 | 532 | |
282a61e6 | 533 | @emph{TMS320C3x/C4x Options} |
4bc1997b JM |
534 | @gccoptlist{ |
535 | -mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol | |
536 | -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol | |
537 | -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol | |
538 | -mparallel-insns -mparallel-mpy -mpreserve-float} | |
282a61e6 | 539 | |
f84271d9 | 540 | @emph{V850 Options} |
4bc1997b JM |
541 | @gccoptlist{ |
542 | -mlong-calls -mno-long-calls -mep -mno-ep @gol | |
543 | -mprolog-function -mno-prolog-function -mspace @gol | |
544 | -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol | |
545 | -mv850 -mbig-switch} | |
83575957 ID |
546 | |
547 | @emph{NS32K Options} | |
4bc1997b JM |
548 | @gccoptlist{ |
549 | -m32032 -m32332 -m32532 -m32081 -m32381 -mmult-add -mnomult-add @gol | |
550 | -msoft-float -mrtd -mnortd -mregparam -mnoregparam -msb -mnosb @gol | |
551 | -mbitfield -mnobitfield -mhimem -mnohimem} | |
789a3090 | 552 | |
052a4b28 | 553 | @emph{AVR Options} |
4bc1997b JM |
554 | @gccoptlist{ |
555 | -mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol | |
556 | -mcall-prologues -mno-tablejump -mtiny-stack} | |
052a4b28 | 557 | |
789a3090 | 558 | @emph{MCore Options} |
4bc1997b | 559 | @gccoptlist{ |
371e300b | 560 | -mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol |
4bc1997b JM |
561 | -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol |
562 | -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol | |
563 | -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol | |
564 | -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment} | |
f84271d9 | 565 | |
df6194d4 JW |
566 | @emph{IA-64 Options} |
567 | @gccoptlist{ | |
568 | -mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol | |
569 | -mvolatile-asm-stop -mb-step -mregister-names -mno-sdata @gol | |
570 | -mconstant-gp -mauto-pic -minline-divide-min-latency @gol | |
571 | -minline-divide-max-throughput -mno-dwarf2-asm @gol | |
572 | -mfixed-range=@var{register range}} | |
573 | ||
74291a4b MM |
574 | @item Code Generation Options |
575 | @xref{Code Gen Options,,Options for Code Generation Conventions}. | |
4bc1997b JM |
576 | @gccoptlist{ |
577 | -fcall-saved-@var{reg} -fcall-used-@var{reg} @gol | |
578 | -fexceptions -funwind-tables -ffixed-@var{reg} @gol | |
579 | -finhibit-size-directive -finstrument-functions @gol | |
580 | -fcheck-memory-usage -fprefix-function-name @gol | |
581 | -fno-common -fno-ident -fno-gnu-linker @gol | |
582 | -fpcc-struct-return -fpic -fPIC @gol | |
583 | -freg-struct-return -fshared-data -fshort-enums @gol | |
584 | -fshort-double -fvolatile -fvolatile-global -fvolatile-static @gol | |
585 | -fverbose-asm -fpack-struct -fstack-check @gol | |
586 | -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol | |
587 | -fargument-alias -fargument-noalias @gol | |
588 | -fargument-noalias-global @gol | |
589 | -fleading-underscore} | |
74291a4b MM |
590 | @end table |
591 | ||
592 | @menu | |
593 | * Overall Options:: Controlling the kind of output: | |
594 | an executable, object files, assembler files, | |
595 | or preprocessed source. | |
596 | * C Dialect Options:: Controlling the variant of C language compiled. | |
597 | * C++ Dialect Options:: Variations on C++. | |
60de6385 | 598 | * Objective-C Dialect Options:: Variations on Objective-C. |
764dbbf2 | 599 | * Language Independent Options:: Controlling how diagnostics should be |
02f52e19 | 600 | formatted. |
74291a4b MM |
601 | * Warning Options:: How picky should the compiler be? |
602 | * Debugging Options:: Symbol tables, measurements, and debugging dumps. | |
603 | * Optimize Options:: How much optimization? | |
604 | * Preprocessor Options:: Controlling header files and macro definitions. | |
605 | Also, getting dependency information for Make. | |
606 | * Assembler Options:: Passing options to the assembler. | |
607 | * Link Options:: Specifying libraries and so on. | |
608 | * Directory Options:: Where to find header files and libraries. | |
609 | Where to find the compiler executable files. | |
a743d340 | 610 | * Spec Files:: How to pass switches to sub-processes. |
0c2d1a2a | 611 | * Target Options:: Running a cross-compiler, or an old version of GCC. |
74291a4b MM |
612 | @end menu |
613 | ||
614 | @node Overall Options | |
615 | @section Options Controlling the Kind of Output | |
616 | ||
617 | Compilation can involve up to four stages: preprocessing, compilation | |
618 | proper, assembly and linking, always in that order. The first three | |
619 | stages apply to an individual source file, and end by producing an | |
620 | object file; linking combines all the object files (those newly | |
621 | compiled, and those specified as input) into an executable file. | |
622 | ||
623 | @cindex file name suffix | |
624 | For any given input file, the file name suffix determines what kind of | |
625 | compilation is done: | |
626 | ||
2642624b | 627 | @table @gcctabopt |
74291a4b MM |
628 | @item @var{file}.c |
629 | C source code which must be preprocessed. | |
630 | ||
631 | @item @var{file}.i | |
632 | C source code which should not be preprocessed. | |
633 | ||
634 | @item @var{file}.ii | |
635 | C++ source code which should not be preprocessed. | |
636 | ||
637 | @item @var{file}.m | |
638 | Objective-C source code. Note that you must link with the library | |
639 | @file{libobjc.a} to make an Objective-C program work. | |
640 | ||
b9265ec1 JM |
641 | @item @var{file}.mi |
642 | Objective-C source code which should not be preprocessed. | |
643 | ||
74291a4b MM |
644 | @item @var{file}.h |
645 | C header file (not to be compiled or linked). | |
646 | ||
647 | @item @var{file}.cc | |
b9265ec1 | 648 | @itemx @var{file}.cp |
74291a4b MM |
649 | @itemx @var{file}.cxx |
650 | @itemx @var{file}.cpp | |
b9265ec1 | 651 | @itemx @var{file}.c++ |
74291a4b MM |
652 | @itemx @var{file}.C |
653 | C++ source code which must be preprocessed. Note that in @samp{.cxx}, | |
654 | the last two letters must both be literally @samp{x}. Likewise, | |
655 | @samp{.C} refers to a literal capital C. | |
656 | ||
b9265ec1 JM |
657 | @item @var{file}.f |
658 | @itemx @var{file}.for | |
659 | @itemx @var{file}.FOR | |
660 | Fortran source code which should not be preprocessed. | |
661 | ||
662 | @item @var{file}.F | |
663 | @itemx @var{file}.fpp | |
664 | @itemx @var{file}.FPP | |
665 | Fortran source code which must be preprocessed (with the traditional | |
666 | preprocessor). | |
667 | ||
668 | @item @var{file}.r | |
669 | Fortran source code which must be preprocessed with a RATFOR | |
670 | preprocessor (not included with GCC). | |
671 | ||
672 | @xref{Overall Options,,Options Controlling the Kind of Output, g77, | |
673 | Using and Porting GNU Fortran}, for more details of the handling of | |
674 | Fortran input files. | |
675 | ||
676 | @c FIXME: Descriptions of Java file types. | |
677 | @c @var{file}.java | |
678 | @c @var{file}.class | |
679 | @c @var{file}.zip | |
680 | @c @var{file}.jar | |
681 | ||
682 | @c GCC also knows about some suffixes for languages not yet included: | |
683 | @c Ada: | |
684 | @c @var{file}.ads | |
685 | @c @var{file}.adb | |
686 | @c @var{file}.ada | |
687 | @c Pascal: | |
688 | @c @var{file}.p | |
689 | @c @var{file}.pas | |
690 | ||
691 | @item @var{file}.ch | |
692 | @itemx @var{file}.chi | |
693 | CHILL source code (preprocessed with the traditional preprocessor). | |
694 | ||
74291a4b MM |
695 | @item @var{file}.s |
696 | Assembler code. | |
697 | ||
698 | @item @var{file}.S | |
699 | Assembler code which must be preprocessed. | |
700 | ||
701 | @item @var{other} | |
702 | An object file to be fed straight into linking. | |
703 | Any file name with no recognized suffix is treated this way. | |
704 | @end table | |
705 | ||
706 | You can specify the input language explicitly with the @samp{-x} option: | |
707 | ||
2642624b | 708 | @table @gcctabopt |
74291a4b MM |
709 | @item -x @var{language} |
710 | Specify explicitly the @var{language} for the following input files | |
711 | (rather than letting the compiler choose a default based on the file | |
712 | name suffix). This option applies to all following input files until | |
713 | the next @samp{-x} option. Possible values for @var{language} are: | |
714 | @example | |
b9265ec1 JM |
715 | c c-header cpp-output |
716 | c++ c++-cpp-output | |
717 | objective-c objc-cpp-output | |
74291a4b | 718 | assembler assembler-with-cpp |
b9265ec1 JM |
719 | f77 f77-cpp-input ratfor |
720 | java chill | |
74291a4b | 721 | @end example |
b9265ec1 | 722 | @c Also f77-version, for internal use only. |
74291a4b MM |
723 | |
724 | @item -x none | |
725 | Turn off any specification of a language, so that subsequent files are | |
726 | handled according to their file name suffixes (as they are if @samp{-x} | |
727 | has not been used at all). | |
14a774a9 RK |
728 | |
729 | @item -pass-exit-codes | |
bedc7537 | 730 | Normally the @command{gcc} program will exit with the code of 1 if any |
14a774a9 | 731 | phase of the compiler returns a non-success return code. If you specify |
bedc7537 | 732 | @samp{-pass-exit-codes}, the @command{gcc} program will instead return with |
14a774a9 RK |
733 | numerically highest error produced by any phase that returned an error |
734 | indication. | |
74291a4b MM |
735 | @end table |
736 | ||
737 | If you only want some of the stages of compilation, you can use | |
bedc7537 | 738 | @samp{-x} (or filename suffixes) to tell @command{gcc} where to start, and |
74291a4b | 739 | one of the options @samp{-c}, @samp{-S}, or @samp{-E} to say where |
bedc7537 NC |
740 | @command{gcc} is to stop. Note that some combinations (for example, |
741 | @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all. | |
74291a4b | 742 | |
2642624b | 743 | @table @gcctabopt |
74291a4b MM |
744 | @item -c |
745 | Compile or assemble the source files, but do not link. The linking | |
746 | stage simply is not done. The ultimate output is in the form of an | |
747 | object file for each source file. | |
748 | ||
749 | By default, the object file name for a source file is made by replacing | |
750 | the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}. | |
751 | ||
752 | Unrecognized input files, not requiring compilation or assembly, are | |
753 | ignored. | |
754 | ||
755 | @item -S | |
756 | Stop after the stage of compilation proper; do not assemble. The output | |
757 | is in the form of an assembler code file for each non-assembler input | |
758 | file specified. | |
759 | ||
760 | By default, the assembler file name for a source file is made by | |
761 | replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}. | |
762 | ||
763 | Input files that don't require compilation are ignored. | |
764 | ||
765 | @item -E | |
766 | Stop after the preprocessing stage; do not run the compiler proper. The | |
767 | output is in the form of preprocessed source code, which is sent to the | |
768 | standard output. | |
769 | ||
770 | Input files which don't require preprocessing are ignored. | |
771 | ||
772 | @cindex output file option | |
773 | @item -o @var{file} | |
774 | Place output in file @var{file}. This applies regardless to whatever | |
775 | sort of output is being produced, whether it be an executable file, | |
776 | an object file, an assembler file or preprocessed C code. | |
777 | ||
778 | Since only one output file can be specified, it does not make sense to | |
779 | use @samp{-o} when compiling more than one input file, unless you are | |
780 | producing an executable file as output. | |
781 | ||
782 | If @samp{-o} is not specified, the default is to put an executable file | |
783 | in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in | |
784 | @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and | |
785 | all preprocessed C source on standard output.@refill | |
786 | ||
787 | @item -v | |
788 | Print (on standard error output) the commands executed to run the stages | |
789 | of compilation. Also print the version number of the compiler driver | |
790 | program and of the preprocessor and the compiler proper. | |
791 | ||
792 | @item -pipe | |
793 | Use pipes rather than temporary files for communication between the | |
794 | various stages of compilation. This fails to work on some systems where | |
795 | the assembler is unable to read from a pipe; but the GNU assembler has | |
796 | no trouble. | |
844642e6 NC |
797 | |
798 | @item --help | |
799 | Print (on the standard output) a description of the command line options | |
bedc7537 NC |
800 | understood by @command{gcc}. If the @option{-v} option is also specified |
801 | then @option{--help} will also be passed on to the various processes | |
802 | invoked by @command{gcc}, so that they can display the command line options | |
803 | they accept. If the @option{-W} option is also specified then command | |
844642e6 NC |
804 | line options which have no documentation associated with them will also |
805 | be displayed. | |
10501d8f CC |
806 | |
807 | @item --target-help | |
808 | Print (on the standard output) a description of target specific command | |
809 | line options for each tool. | |
74291a4b MM |
810 | @end table |
811 | ||
812 | @node Invoking G++ | |
813 | @section Compiling C++ Programs | |
814 | ||
815 | @cindex suffixes for C++ source | |
816 | @cindex C++ source file suffixes | |
817 | C++ source files conventionally use one of the suffixes @samp{.C}, | |
bba975d4 | 818 | @samp{.cc}, @samp{.cpp}, @samp{.c++}, @samp{.cp}, or @samp{.cxx}; |
0c2d1a2a | 819 | preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes |
bba975d4 JM |
820 | files with these names and compiles them as C++ programs even if you |
821 | call the compiler the same way as for compiling C programs (usually with | |
bedc7537 | 822 | the name @command{gcc}). |
74291a4b MM |
823 | |
824 | @findex g++ | |
825 | @findex c++ | |
826 | However, C++ programs often require class libraries as well as a | |
827 | compiler that understands the C++ language---and under some | |
828 | circumstances, you might want to compile programs from standard input, | |
829 | or otherwise without a suffix that flags them as C++ programs. | |
bedc7537 | 830 | @command{g++} is a program that calls GCC with the default language |
e5e809f4 | 831 | set to C++, and automatically specifies linking against the C++ |
bedc7537 NC |
832 | library. On many systems, @command{g++} is also |
833 | installed with the name @command{c++}. | |
74291a4b | 834 | |
bedc7537 | 835 | @cindex invoking @command{g++} |
74291a4b MM |
836 | When you compile C++ programs, you may specify many of the same |
837 | command-line options that you use for compiling programs in any | |
838 | language; or command-line options meaningful for C and related | |
839 | languages; or options that are meaningful only for C++ programs. | |
840 | @xref{C Dialect Options,,Options Controlling C Dialect}, for | |
841 | explanations of options for languages related to C. | |
842 | @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for | |
843 | explanations of options that are meaningful only for C++ programs. | |
844 | ||
845 | @node C Dialect Options | |
846 | @section Options Controlling C Dialect | |
847 | @cindex dialect options | |
848 | @cindex language dialect options | |
849 | @cindex options, dialect | |
850 | ||
851 | The following options control the dialect of C (or languages derived | |
852 | from C, such as C++ and Objective C) that the compiler accepts: | |
853 | ||
2642624b | 854 | @table @gcctabopt |
74291a4b | 855 | @cindex ANSI support |
c1030c7c | 856 | @cindex ISO support |
74291a4b | 857 | @item -ansi |
c1030c7c | 858 | In C mode, support all ISO C89 programs. In C++ mode, |
775afb25 | 859 | remove GNU extensions that conflict with ISO C++. |
74291a4b | 860 | |
c1030c7c | 861 | This turns off certain features of GCC that are incompatible with ISO |
775afb25 | 862 | C (when compiling C code), or of standard C++ (when compiling C++ code), |
0c2d1a2a | 863 | such as the @code{asm} and @code{typeof} keywords, and |
74291a4b MM |
864 | predefined macros such as @code{unix} and @code{vax} that identify the |
865 | type of system you are using. It also enables the undesirable and | |
02f52e19 | 866 | rarely used ISO trigraph feature. For the C compiler, |
0c2d1a2a | 867 | it disables recognition of C++ style @samp{//} comments as well as |
775afb25 | 868 | the @code{inline} keyword. |
74291a4b MM |
869 | |
870 | The alternate keywords @code{__asm__}, @code{__extension__}, | |
871 | @code{__inline__} and @code{__typeof__} continue to work despite | |
c1030c7c | 872 | @samp{-ansi}. You would not want to use them in an ISO C program, of |
74291a4b MM |
873 | course, but it is useful to put them in header files that might be included |
874 | in compilations done with @samp{-ansi}. Alternate predefined macros | |
875 | such as @code{__unix__} and @code{__vax__} are also available, with or | |
876 | without @samp{-ansi}. | |
877 | ||
c1030c7c | 878 | The @samp{-ansi} option does not cause non-ISO programs to be |
74291a4b MM |
879 | rejected gratuitously. For that, @samp{-pedantic} is required in |
880 | addition to @samp{-ansi}. @xref{Warning Options}. | |
881 | ||
882 | The macro @code{__STRICT_ANSI__} is predefined when the @samp{-ansi} | |
883 | option is used. Some header files may notice this macro and refrain | |
884 | from declaring certain functions or defining certain macros that the | |
c1030c7c | 885 | ISO standard doesn't call for; this is to avoid interfering with any |
74291a4b MM |
886 | programs that might use these names for other things. |
887 | ||
01702459 JM |
888 | Functions which would normally be builtin but do not have semantics |
889 | defined by ISO C (such as @code{alloca} and @code{ffs}) are not builtin | |
890 | functions with @samp{-ansi} is used. @xref{Other Builtins,,Other | |
891 | built-in functions provided by GNU CC}, for details of the functions | |
892 | affected. | |
74291a4b | 893 | |
49419c8f | 894 | @item -std= |
3043b30e | 895 | Determine the language standard. A value for this option must be provided; |
02f52e19 | 896 | possible values are |
3932261a | 897 | |
ee457005 | 898 | @table @samp |
3043b30e | 899 | @item iso9899:1990 |
bedc7537 | 900 | Same as @option{-ansi} |
3043b30e ML |
901 | |
902 | @item iso9899:199409 | |
903 | ISO C as modified in amend. 1 | |
904 | ||
49419c8f JM |
905 | @item iso9899:1999 |
906 | ISO C99. Note that this standard is not yet fully supported; see | |
2642624b | 907 | @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. |
3043b30e ML |
908 | |
909 | @item c89 | |
bedc7537 | 910 | same as @option{-std=iso9899:1990} |
3043b30e | 911 | |
49419c8f | 912 | @item c99 |
bedc7537 | 913 | same as @option{-std=iso9899:1999} |
3043b30e ML |
914 | |
915 | @item gnu89 | |
916 | default, iso9899:1990 + gnu extensions | |
917 | ||
49419c8f JM |
918 | @item gnu99 |
919 | iso9899:1999 + gnu extensions | |
920 | ||
921 | @item iso9899:199x | |
bedc7537 | 922 | same as @option{-std=iso9899:1999}, deprecated |
49419c8f JM |
923 | |
924 | @item c9x | |
bedc7537 | 925 | same as @option{-std=iso9899:1999}, deprecated |
49419c8f | 926 | |
3043b30e | 927 | @item gnu9x |
bedc7537 | 928 | same as @option{-std=gnu99}, deprecated |
49419c8f | 929 | |
ee457005 | 930 | @end table |
3043b30e ML |
931 | |
932 | Even when this option is not specified, you can still use some of the | |
933 | features of newer standards in so far as they do not conflict with | |
934 | previous C standards. For example, you may use @code{__restrict__} even | |
bedc7537 | 935 | when @option{-std=c99} is not specified. |
3932261a | 936 | |
5490d604 JM |
937 | The @option{-std} options specifying some version of ISO C have the same |
938 | effects as @option{-ansi}, except that features that were not in ISO C89 | |
939 | but are in the specified version (for example, @samp{//} comments and | |
940 | the @code{inline} keyword in ISO C99) are not disabled. | |
941 | ||
c1030c7c JM |
942 | @xref{Standards,,Language Standards Supported by GCC}, for details of |
943 | these standard versions. | |
944 | ||
74291a4b MM |
945 | @item -fno-asm |
946 | Do not recognize @code{asm}, @code{inline} or @code{typeof} as a | |
947 | keyword, so that code can use these words as identifiers. You can use | |
948 | the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__} | |
949 | instead. @samp{-ansi} implies @samp{-fno-asm}. | |
950 | ||
951 | In C++, this switch only affects the @code{typeof} keyword, since | |
952 | @code{asm} and @code{inline} are standard keywords. You may want to | |
5490d604 JM |
953 | use the @samp{-fno-gnu-keywords} flag instead, which has the same |
954 | effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this | |
955 | switch only affects the @code{asm} and @code{typeof} keywords, since | |
956 | @code{inline} is a standard keyword in ISO C99. | |
74291a4b MM |
957 | |
958 | @item -fno-builtin | |
959 | @cindex builtin functions | |
01702459 JM |
960 | Don't recognize builtin functions that do not begin with |
961 | @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in | |
962 | functions provided by GNU CC}, for details of the functions affected, | |
5490d604 JM |
963 | including those which are not builtin functions when @option{-ansi} or |
964 | @option{-std} options for strict ISO C conformance are used because they | |
965 | do not have an ISO standard meaning. | |
74291a4b MM |
966 | |
967 | GCC normally generates special code to handle certain builtin functions | |
968 | more efficiently; for instance, calls to @code{alloca} may become single | |
969 | instructions that adjust the stack directly, and calls to @code{memcpy} | |
970 | may become inline copy loops. The resulting code is often both smaller | |
971 | and faster, but since the function calls no longer appear as such, you | |
972 | cannot set a breakpoint on those calls, nor can you change the behavior | |
973 | of the functions by linking with a different library. | |
974 | ||
0b1161fc MM |
975 | In C++, @samp{-fno-builtin} is always in effect. The @samp{-fbuiltin} |
976 | option has no effect. Therefore, in C++, the only way to get the | |
977 | optimization benefits of builtin functions is to call the function | |
978 | using the @samp{__builtin_} prefix. The GNU C++ Standard Library uses | |
979 | builtin functions to implement many functions (like | |
980 | @code{std::strchr}), so that you automatically get efficient code. | |
981 | ||
861bb6c1 JL |
982 | @item -fhosted |
983 | @cindex hosted environment | |
984 | ||
985 | Assert that compilation takes place in a hosted environment. This implies | |
986 | @samp{-fbuiltin}. A hosted environment is one in which the | |
987 | entire standard library is available, and in which @code{main} has a return | |
988 | type of @code{int}. Examples are nearly everything except a kernel. | |
989 | This is equivalent to @samp{-fno-freestanding}. | |
990 | ||
991 | @item -ffreestanding | |
992 | @cindex hosted environment | |
993 | ||
994 | Assert that compilation takes place in a freestanding environment. This | |
995 | implies @samp{-fno-builtin}. A freestanding environment | |
996 | is one in which the standard library may not exist, and program startup may | |
997 | not necessarily be at @code{main}. The most obvious example is an OS kernel. | |
998 | This is equivalent to @samp{-fno-hosted}. | |
999 | ||
c1030c7c JM |
1000 | @xref{Standards,,Language Standards Supported by GCC}, for details of |
1001 | freestanding and hosted environments. | |
1002 | ||
74291a4b | 1003 | @item -trigraphs |
c1030c7c | 1004 | Support ISO C trigraphs. You don't want to know about this |
5490d604 JM |
1005 | brain-damage. The @option{-ansi} option (and @option{-std} options for |
1006 | strict ISO C conformance) implies @option{-trigraphs}. | |
74291a4b MM |
1007 | |
1008 | @cindex traditional C language | |
1009 | @cindex C language, traditional | |
1010 | @item -traditional | |
1011 | Attempt to support some aspects of traditional C compilers. | |
1012 | Specifically: | |
1013 | ||
1014 | @itemize @bullet | |
1015 | @item | |
1016 | All @code{extern} declarations take effect globally even if they | |
1017 | are written inside of a function definition. This includes implicit | |
1018 | declarations of functions. | |
1019 | ||
1020 | @item | |
1021 | The newer keywords @code{typeof}, @code{inline}, @code{signed}, @code{const} | |
1022 | and @code{volatile} are not recognized. (You can still use the | |
1023 | alternative keywords such as @code{__typeof__}, @code{__inline__}, and | |
1024 | so on.) | |
1025 | ||
1026 | @item | |
1027 | Comparisons between pointers and integers are always allowed. | |
1028 | ||
1029 | @item | |
1030 | Integer types @code{unsigned short} and @code{unsigned char} promote | |
1031 | to @code{unsigned int}. | |
1032 | ||
1033 | @item | |
1034 | Out-of-range floating point literals are not an error. | |
1035 | ||
1036 | @item | |
c1030c7c | 1037 | Certain constructs which ISO regards as a single invalid preprocessing |
74291a4b MM |
1038 | number, such as @samp{0xe-0xd}, are treated as expressions instead. |
1039 | ||
1040 | @item | |
1041 | String ``constants'' are not necessarily constant; they are stored in | |
1042 | writable space, and identical looking constants are allocated | |
1043 | separately. (This is the same as the effect of | |
1044 | @samp{-fwritable-strings}.) | |
1045 | ||
1046 | @cindex @code{longjmp} and automatic variables | |
1047 | @item | |
1048 | All automatic variables not declared @code{register} are preserved by | |
c1030c7c | 1049 | @code{longjmp}. Ordinarily, GNU C follows ISO C: automatic variables |
74291a4b MM |
1050 | not declared @code{volatile} may be clobbered. |
1051 | ||
1052 | @item | |
1053 | @kindex \x | |
1054 | @kindex \a | |
1055 | @cindex escape sequences, traditional | |
1056 | The character escape sequences @samp{\x} and @samp{\a} evaluate as the | |
1057 | literal characters @samp{x} and @samp{a} respectively. Without | |
1058 | @w{@samp{-traditional}}, @samp{\x} is a prefix for the hexadecimal | |
1059 | representation of a character, and @samp{\a} produces a bell. | |
ad299d9b | 1060 | @end itemize |
74291a4b | 1061 | |
74291a4b MM |
1062 | You may wish to use @samp{-fno-builtin} as well as @samp{-traditional} |
1063 | if your program uses names that are normally GNU C builtin functions for | |
1064 | other purposes of its own. | |
1065 | ||
1066 | You cannot use @samp{-traditional} if you include any header files that | |
c1030c7c JM |
1067 | rely on ISO C features. Some vendors are starting to ship systems with |
1068 | ISO C header files and you cannot use @samp{-traditional} on such | |
74291a4b MM |
1069 | systems to compile files that include any system headers. |
1070 | ||
e5e809f4 JL |
1071 | The @samp{-traditional} option also enables @samp{-traditional-cpp}, |
1072 | which is described next. | |
74291a4b MM |
1073 | |
1074 | @item -traditional-cpp | |
1075 | Attempt to support some aspects of traditional C preprocessors. | |
1076 | Specifically: | |
1077 | ||
1078 | @itemize @bullet | |
1079 | @item | |
1080 | Comments convert to nothing at all, rather than to a space. This allows | |
1081 | traditional token concatenation. | |
1082 | ||
1083 | @item | |
1084 | In a preprocessing directive, the @samp{#} symbol must appear as the first | |
1085 | character of a line. | |
1086 | ||
1087 | @item | |
1088 | Macro arguments are recognized within string constants in a macro | |
1089 | definition (and their values are stringified, though without additional | |
1090 | quote marks, when they appear in such a context). The preprocessor | |
1091 | always considers a string constant to end at a newline. | |
1092 | ||
1093 | @item | |
1094 | @cindex detecting @w{@samp{-traditional}} | |
1095 | The predefined macro @code{__STDC__} is not defined when you use | |
1096 | @samp{-traditional}, but @code{__GNUC__} is (since the GNU extensions | |
1097 | which @code{__GNUC__} indicates are not affected by | |
1098 | @samp{-traditional}). If you need to write header files that work | |
1099 | differently depending on whether @samp{-traditional} is in use, by | |
1100 | testing both of these predefined macros you can distinguish four | |
c1030c7c | 1101 | situations: GNU C, traditional GNU C, other ISO C compilers, and other |
74291a4b MM |
1102 | old C compilers. The predefined macro @code{__STDC_VERSION__} is also |
1103 | not defined when you use @samp{-traditional}. @xref{Standard | |
1104 | Predefined,,Standard Predefined Macros,cpp.info,The C Preprocessor}, | |
1105 | for more discussion of these and other predefined macros. | |
1106 | ||
1107 | @item | |
1108 | @cindex string constants vs newline | |
1109 | @cindex newline vs string constants | |
1110 | The preprocessor considers a string constant to end at a newline (unless | |
1111 | the newline is escaped with @samp{\}). (Without @w{@samp{-traditional}}, | |
1112 | string constants can contain the newline character as typed.) | |
1113 | @end itemize | |
1114 | ||
1115 | @item -fcond-mismatch | |
1116 | Allow conditional expressions with mismatched types in the second and | |
a7537031 JM |
1117 | third arguments. The value of such an expression is void. This option |
1118 | is not supported for C++. | |
74291a4b MM |
1119 | |
1120 | @item -funsigned-char | |
1121 | Let the type @code{char} be unsigned, like @code{unsigned char}. | |
1122 | ||
1123 | Each kind of machine has a default for what @code{char} should | |
1124 | be. It is either like @code{unsigned char} by default or like | |
1125 | @code{signed char} by default. | |
1126 | ||
1127 | Ideally, a portable program should always use @code{signed char} or | |
1128 | @code{unsigned char} when it depends on the signedness of an object. | |
1129 | But many programs have been written to use plain @code{char} and | |
1130 | expect it to be signed, or expect it to be unsigned, depending on the | |
1131 | machines they were written for. This option, and its inverse, let you | |
1132 | make such a program work with the opposite default. | |
1133 | ||
1134 | The type @code{char} is always a distinct type from each of | |
1135 | @code{signed char} or @code{unsigned char}, even though its behavior | |
1136 | is always just like one of those two. | |
1137 | ||
1138 | @item -fsigned-char | |
1139 | Let the type @code{char} be signed, like @code{signed char}. | |
1140 | ||
1141 | Note that this is equivalent to @samp{-fno-unsigned-char}, which is | |
1142 | the negative form of @samp{-funsigned-char}. Likewise, the option | |
1143 | @samp{-fno-signed-char} is equivalent to @samp{-funsigned-char}. | |
1144 | ||
1145 | You may wish to use @samp{-fno-builtin} as well as @samp{-traditional} | |
1146 | if your program uses names that are normally GNU C builtin functions for | |
1147 | other purposes of its own. | |
1148 | ||
1149 | You cannot use @samp{-traditional} if you include any header files that | |
c1030c7c JM |
1150 | rely on ISO C features. Some vendors are starting to ship systems with |
1151 | ISO C header files and you cannot use @samp{-traditional} on such | |
74291a4b MM |
1152 | systems to compile files that include any system headers. |
1153 | ||
1154 | @item -fsigned-bitfields | |
1155 | @itemx -funsigned-bitfields | |
1156 | @itemx -fno-signed-bitfields | |
1157 | @itemx -fno-unsigned-bitfields | |
1158 | These options control whether a bitfield is signed or unsigned, when the | |
1159 | declaration does not use either @code{signed} or @code{unsigned}. By | |
1160 | default, such a bitfield is signed, because this is consistent: the | |
1161 | basic integer types such as @code{int} are signed types. | |
1162 | ||
1163 | However, when @samp{-traditional} is used, bitfields are all unsigned | |
1164 | no matter what. | |
1165 | ||
1166 | @item -fwritable-strings | |
1167 | Store string constants in the writable data segment and don't uniquize | |
1168 | them. This is for compatibility with old programs which assume they can | |
1169 | write into string constants. The option @samp{-traditional} also has | |
1170 | this effect. | |
1171 | ||
1172 | Writing into string constants is a very bad idea; ``constants'' should | |
1173 | be constant. | |
1174 | ||
1175 | @item -fallow-single-precision | |
1176 | Do not promote single precision math operations to double precision, | |
1177 | even when compiling with @samp{-traditional}. | |
1178 | ||
1179 | Traditional K&R C promotes all floating point operations to double | |
1180 | precision, regardless of the sizes of the operands. On the | |
1181 | architecture for which you are compiling, single precision may be faster | |
1182 | than double precision. If you must use @samp{-traditional}, but want | |
1183 | to use single precision operations when the operands are single | |
1184 | precision, use this option. This option has no effect when compiling | |
c1030c7c | 1185 | with ISO or GNU C conventions (the default). |
74291a4b | 1186 | |
3e37bef5 JM |
1187 | @item -fshort-wchar |
1188 | Override the underlying type for @samp{wchar_t} to be @samp{short | |
1189 | unsigned int} instead of the default for the target. This option is | |
1190 | useful for building programs to run under WINE. | |
74291a4b MM |
1191 | @end table |
1192 | ||
1193 | @node C++ Dialect Options | |
1194 | @section Options Controlling C++ Dialect | |
1195 | ||
1196 | @cindex compiler options, C++ | |
1197 | @cindex C++ options, command line | |
1198 | @cindex options, C++ | |
1199 | This section describes the command-line options that are only meaningful | |
1200 | for C++ programs; but you can also use most of the GNU compiler options | |
1201 | regardless of what language your program is in. For example, you | |
1202 | might compile a file @code{firstClass.C} like this: | |
1203 | ||
1204 | @example | |
1dc5fc4b | 1205 | g++ -g -frepo -O -c firstClass.C |
74291a4b MM |
1206 | @end example |
1207 | ||
1208 | @noindent | |
1dc5fc4b | 1209 | In this example, only @samp{-frepo} is an option meant |
74291a4b | 1210 | only for C++ programs; you can use the other options with any |
0c2d1a2a | 1211 | language supported by GCC. |
74291a4b MM |
1212 | |
1213 | Here is a list of options that are @emph{only} for compiling C++ programs: | |
1214 | ||
2642624b | 1215 | @table @gcctabopt |
74291a4b MM |
1216 | @item -fno-access-control |
1217 | Turn off all access checking. This switch is mainly useful for working | |
1218 | around bugs in the access control code. | |
1219 | ||
74291a4b MM |
1220 | @item -fcheck-new |
1221 | Check that the pointer returned by @code{operator new} is non-null | |
1222 | before attempting to modify the storage allocated. The current Working | |
1223 | Paper requires that @code{operator new} never return a null pointer, so | |
1224 | this check is normally unnecessary. | |
1225 | ||
1dc5fc4b JM |
1226 | An alternative to using this option is to specify that your |
1227 | @code{operator new} does not throw any exceptions; if you declare it | |
1228 | @samp{throw()}, g++ will check the return value. See also @samp{new | |
1229 | (nothrow)}. | |
1230 | ||
74291a4b MM |
1231 | @item -fconserve-space |
1232 | Put uninitialized or runtime-initialized global variables into the | |
1233 | common segment, as C does. This saves space in the executable at the | |
1234 | cost of not diagnosing duplicate definitions. If you compile with this | |
1235 | flag and your program mysteriously crashes after @code{main()} has | |
1236 | completed, you may have an object that is being destroyed twice because | |
1237 | two definitions were merged. | |
1238 | ||
1dc5fc4b JM |
1239 | This option is no longer useful on most targets, now that support has |
1240 | been added for putting variables into BSS without making them common. | |
1241 | ||
02f52e19 | 1242 | @item -fno-const-strings |
fcca588c MM |
1243 | Give string constants type @code{char *} instead of type @code{const |
1244 | char *}. By default, G++ uses type @code{const char *} as required by | |
1245 | the standard. Even if you use @samp{-fno-const-strings}, you cannot | |
1246 | actually modify the value of a string constant, unless you also use | |
1247 | @samp{-fwritable-strings}. | |
1248 | ||
1249 | This option might be removed in a future release of G++. For maximum | |
1250 | portability, you should structure your code so that it works with | |
1251 | string constants that have type @code{const char *}. | |
1252 | ||
74291a4b MM |
1253 | @item -fdollars-in-identifiers |
1254 | Accept @samp{$} in identifiers. You can also explicitly prohibit use of | |
eb795509 RK |
1255 | @samp{$} with the option @samp{-fno-dollars-in-identifiers}. (GNU C allows |
1256 | @samp{$} by default on most target systems, but there are a few exceptions.) | |
74291a4b | 1257 | Traditional C allowed the character @samp{$} to form part of |
c1030c7c | 1258 | identifiers. However, ISO C and C++ forbid @samp{$} in identifiers. |
74291a4b | 1259 | |
1dc5fc4b JM |
1260 | @item -fno-elide-constructors |
1261 | The C++ standard allows an implementation to omit creating a temporary | |
1262 | which is only used to initialize another object of the same type. | |
1263 | Specifying this option disables that optimization, and forces g++ to | |
1264 | call the copy constructor in all cases. | |
74291a4b | 1265 | |
dd1ba632 JM |
1266 | @item -fno-enforce-eh-specs |
1267 | Don't check for violation of exception specifications at runtime. This | |
1268 | option violates the C++ standard, but may be useful for reducing code | |
1269 | size in production builds, much like defining @samp{NDEBUG}. The compiler | |
1270 | will still optimize based on the exception specifications. | |
1271 | ||
74291a4b MM |
1272 | @item -fexternal-templates |
1273 | Cause template instantiations to obey @samp{#pragma interface} and | |
1274 | @samp{implementation}; template instances are emitted or not according | |
1275 | to the location of the template definition. @xref{Template | |
1276 | Instantiation}, for more information. | |
1277 | ||
37f6b6bf MM |
1278 | This option is deprecated. |
1279 | ||
74291a4b MM |
1280 | @item -falt-external-templates |
1281 | Similar to -fexternal-templates, but template instances are emitted or | |
1282 | not according to the place where they are first instantiated. | |
1283 | @xref{Template Instantiation}, for more information. | |
1284 | ||
37f6b6bf MM |
1285 | This option is deprecated. |
1286 | ||
74291a4b | 1287 | @item -ffor-scope |
8c81598d | 1288 | @itemx -fno-for-scope |
74291a4b MM |
1289 | If -ffor-scope is specified, the scope of variables declared in |
1290 | a @i{for-init-statement} is limited to the @samp{for} loop itself, | |
34527c47 | 1291 | as specified by the C++ standard. |
74291a4b MM |
1292 | If -fno-for-scope is specified, the scope of variables declared in |
1293 | a @i{for-init-statement} extends to the end of the enclosing scope, | |
1294 | as was the case in old versions of gcc, and other (traditional) | |
1295 | implementations of C++. | |
1296 | ||
1297 | The default if neither flag is given to follow the standard, | |
1298 | but to allow and give a warning for old-style code that would | |
1299 | otherwise be invalid, or have different behavior. | |
1300 | ||
1301 | @item -fno-gnu-keywords | |
9762e8a4 | 1302 | Do not recognize @code{typeof} as a keyword, so that code can use this |
02f52e19 | 1303 | word as an identifier. You can use the keyword @code{__typeof__} instead. |
9762e8a4 | 1304 | @samp{-ansi} implies @samp{-fno-gnu-keywords}. |
74291a4b | 1305 | |
95c81fb8 ML |
1306 | @item -fhonor-std |
1307 | Treat the @code{namespace std} as a namespace, instead of ignoring | |
1308 | it. For compatibility with earlier versions of g++, the compiler will, | |
1309 | by default, ignore @code{namespace-declarations}, | |
1310 | @code{using-declarations}, @code{using-directives}, and | |
1311 | @code{namespace-names}, if they involve @code{std}. | |
1312 | ||
1dc5fc4b | 1313 | @item -fno-implicit-templates |
bba975d4 JM |
1314 | Never emit code for non-inline templates which are instantiated |
1315 | implicitly (i.e. by use); only emit code for explicit instantiations. | |
1316 | @xref{Template Instantiation}, for more information. | |
1317 | ||
1318 | @item -fno-implicit-inline-templates | |
1319 | Don't emit code for implicit instantiations of inline templates, either. | |
1320 | The default is to handle inlines differently so that compiles with and | |
1321 | without optimization will need the same set of explicit instantiations. | |
1dc5fc4b | 1322 | |
74291a4b MM |
1323 | @item -fno-implement-inlines |
1324 | To save space, do not emit out-of-line copies of inline functions | |
1325 | controlled by @samp{#pragma implementation}. This will cause linker | |
1326 | errors if these functions are not inlined everywhere they are called. | |
1327 | ||
631cf95d | 1328 | @item -fms-extensions |
32fb1fb2 PE |
1329 | Disable pedantic warnings about constructs used in MFC, such as implicit |
1330 | int and getting a pointer to member function via non-standard syntax. | |
631cf95d | 1331 | |
fcca588c MM |
1332 | @item -fno-nonansi-builtins |
1333 | Disable builtin declarations of functions that are not mandated by | |
1334 | ANSI/ISO C. These include @code{ffs}, @code{alloca}, @code{_exit}, | |
1335 | @code{index}, @code{bzero}, @code{conjf}, and other related functions. | |
1336 | ||
775afb25 ML |
1337 | @item -fno-operator-names |
1338 | Do not treat the operator name keywords @code{and}, @code{bitand}, | |
74291a4b | 1339 | @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as |
775afb25 | 1340 | synonyms as keywords. |
74291a4b | 1341 | |
4f8b4fd9 JM |
1342 | @item -fno-optional-diags |
1343 | Disable diagnostics that the standard says a compiler does not need to | |
bba975d4 JM |
1344 | issue. Currently, the only such diagnostic issued by g++ is the one for |
1345 | a name having multiple meanings within a class. | |
4f8b4fd9 | 1346 | |
8c7707b0 JM |
1347 | @item -fpermissive |
1348 | Downgrade messages about nonconformant code from errors to warnings. By | |
1349 | default, g++ effectively sets @samp{-pedantic-errors} without | |
1350 | @samp{-pedantic}; this option reverses that. This behavior and this | |
2d9f9cf1 | 1351 | option are superseded by @samp{-pedantic}, which works as it does for GNU C. |
8c7707b0 | 1352 | |
8c81598d JM |
1353 | @item -frepo |
1354 | Enable automatic template instantiation. This option also implies | |
1355 | @samp{-fno-implicit-templates}. @xref{Template Instantiation}, for more | |
1356 | information. | |
1357 | ||
8c7707b0 | 1358 | @item -fno-rtti |
a7fbfcf9 JM |
1359 | Disable generation of information about every class with virtual |
1360 | functions for use by the C++ runtime type identification features | |
1361 | (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts | |
1362 | of the language, you can save some space by using this flag. Note that | |
1363 | exception handling uses the same information, but it will generate it as | |
1364 | needed. | |
8c7707b0 | 1365 | |
fcca588c MM |
1366 | @item -fstats |
1367 | Emit statistics about front-end processing at the end of the compilation. | |
1368 | This information is generally only useful to the G++ development team. | |
1369 | ||
1dc5fc4b JM |
1370 | @item -ftemplate-depth-@var{n} |
1371 | Set the maximum instantiation depth for template classes to @var{n}. | |
1372 | A limit on the template instantiation depth is needed to detect | |
1373 | endless recursions during template class instantiation. ANSI/ISO C++ | |
1374 | conforming programs must not rely on a maximum depth greater than 17. | |
1375 | ||
fc693822 MM |
1376 | @item -fuse-cxa-atexit |
1377 | Register destructors for objects with static storage duration with the | |
1378 | @code{__cxa_atexit} function rather than the @code{atexit} function. | |
1379 | This option is required for fully standards-compliant handling of static | |
1380 | destructors, but will only work if your C library supports | |
1381 | @code{__cxa_atexit}. | |
1382 | ||
90ecce3e JM |
1383 | @item -fvtable-gc |
1384 | Emit special relocations for vtables and virtual function references | |
1385 | so that the linker can identify unused virtual functions and zero out | |
1386 | vtable slots that refer to them. This is most useful with | |
1387 | @samp{-ffunction-sections} and @samp{-Wl,--gc-sections}, in order to | |
1388 | also discard the functions themselves. | |
f5a1b0d2 | 1389 | |
90ecce3e JM |
1390 | This optimization requires GNU as and GNU ld. Not all systems support |
1391 | this option. @samp{-Wl,--gc-sections} is ignored without @samp{-static}. | |
861bb6c1 | 1392 | |
02f52e19 | 1393 | @item -fno-weak |
90ecce3e | 1394 | Do not use weak symbol support, even if it is provided by the linker. |
fcca588c MM |
1395 | By default, G++ will use weak symbols if they are available. This |
1396 | option exists only for testing, and should not be used by end-users; | |
1397 | it will result in inferior code and has no benefits. This option may | |
1398 | be removed in a future release of G++. | |
1399 | ||
74291a4b MM |
1400 | @item -nostdinc++ |
1401 | Do not search for header files in the standard directories specific to | |
1402 | C++, but do still search the other standard directories. (This option | |
e5e809f4 | 1403 | is used when building the C++ library.) |
74291a4b MM |
1404 | @end table |
1405 | ||
1406 | In addition, these optimization, warning, and code generation options | |
1407 | have meanings only for C++ programs: | |
1408 | ||
2642624b | 1409 | @table @gcctabopt |
74291a4b MM |
1410 | @item -fno-default-inline |
1411 | Do not assume @samp{inline} for functions defined inside a class scope. | |
1dc5fc4b JM |
1412 | @xref{Optimize Options,,Options That Control Optimization}. Note that these |
1413 | functions will have linkage like inline functions; they just won't be | |
1414 | inlined by default. | |
74291a4b | 1415 | |
bba975d4 JM |
1416 | @item -Wctor-dtor-privacy (C++ only) |
1417 | Warn when a class seems unusable, because all the constructors or | |
1418 | destructors in a class are private and the class has no friends or | |
1419 | public static member functions. | |
1420 | ||
1421 | @item -Wnon-virtual-dtor (C++ only) | |
1422 | Warn when a class declares a non-virtual destructor that should probably | |
1423 | be virtual, because it looks like the class will be used polymorphically. | |
1424 | ||
1425 | @item -Wreorder (C++ only) | |
1426 | @cindex reordering, warning | |
1427 | @cindex warning for reordering of member initializers | |
1428 | Warn when the order of member initializers given in the code does not | |
1429 | match the order in which they must be executed. For instance: | |
1430 | ||
1431 | @smallexample | |
1432 | struct A @{ | |
1433 | int i; | |
1434 | int j; | |
1435 | A(): j (0), i (1) @{ @} | |
1436 | @}; | |
1437 | @end smallexample | |
1438 | ||
1439 | Here the compiler will warn that the member initializers for @samp{i} | |
1440 | and @samp{j} will be rearranged to match the declaration order of the | |
1441 | members. | |
1442 | @end table | |
1443 | ||
1444 | The following @samp{-W@dots{}} options are not affected by @samp{-Wall}. | |
1445 | ||
2642624b | 1446 | @table @gcctabopt |
bba975d4 JM |
1447 | @item -Weffc++ (C++ only) |
1448 | Warn about violations of various style guidelines from Scott Meyers' | |
1449 | @cite{Effective C++} books. If you use this option, you should be aware | |
1450 | that the standard library headers do not obey all of these guidelines; | |
1451 | you can use @samp{grep -v} to filter out those warnings. | |
1452 | ||
2de45c06 ML |
1453 | @item -Wno-deprecated (C++ only) |
1454 | Do not warn about usage of deprecated features. @xref{Deprecated Features}. | |
1455 | ||
bba975d4 JM |
1456 | @item -Wno-non-template-friend (C++ only) |
1457 | Disable warnings when non-templatized friend functions are declared | |
1458 | within a template. With the advent of explicit template specification | |
1459 | support in g++, if the name of the friend is an unqualified-id (ie, | |
1460 | @samp{friend foo(int)}), the C++ language specification demands that the | |
1461 | friend declare or define an ordinary, nontemplate function. (Section | |
1462 | 14.5.3). Before g++ implemented explicit specification, unqualified-ids | |
1463 | could be interpreted as a particular specialization of a templatized | |
1464 | function. Because this non-conforming behavior is no longer the default | |
1465 | behavior for g++, @samp{-Wnon-template-friend} allows the compiler to | |
1466 | check existing code for potential trouble spots, and is on by default. | |
2228d450 MM |
1467 | This new compiler behavior can be turned off with |
1468 | @samp{-Wno-non-template-friend} which keeps the conformant compiler code | |
1469 | but disables the helpful warning. | |
bba975d4 JM |
1470 | |
1471 | @item -Wold-style-cast (C++ only) | |
1472 | Warn if an old-style (C-style) cast is used within a C++ program. The | |
1473 | new-style casts (@samp{static_cast}, @samp{reinterpret_cast}, and | |
90ecce3e JM |
1474 | @samp{const_cast}) are less vulnerable to unintended effects, and much |
1475 | easier to grep for. | |
bba975d4 JM |
1476 | |
1477 | @item -Woverloaded-virtual (C++ only) | |
1478 | @cindex overloaded virtual fn, warning | |
1479 | @cindex warning for overloaded virtual fn | |
3747f3dc MM |
1480 | Warn when a function declaration hides virtual functions from a |
1481 | base class. For example, in: | |
1482 | ||
1483 | @smallexample | |
1484 | struct A @{ | |
1485 | virtual void f(); | |
1486 | @}; | |
1487 | ||
1488 | struct B: public A @{ | |
1489 | void f(int); | |
1490 | @}; | |
1491 | @end smallexample | |
1492 | ||
1493 | the @code{A} class version of @code{f} is hidden in @code{B}, and code | |
1494 | like this: | |
1495 | ||
1496 | @smallexample | |
1497 | B* b; | |
1498 | b->f(); | |
1499 | @end smallexample | |
1500 | ||
1501 | will fail to compile. | |
bba975d4 JM |
1502 | |
1503 | @item -Wno-pmf-conversions (C++ only) | |
1504 | Disable the diagnostic for converting a bound pointer to member function | |
1505 | to a plain pointer. | |
1506 | ||
1507 | @item -Wsign-promo (C++ only) | |
1508 | Warn when overload resolution chooses a promotion from unsigned or | |
1509 | enumeral type to a signed type over a conversion to an unsigned type of | |
1510 | the same size. Previous versions of g++ would try to preserve | |
1511 | unsignedness, but the standard mandates the current behavior. | |
1512 | ||
1513 | @item -Wsynth (C++ only) | |
1514 | @cindex warning for synthesized methods | |
1515 | @cindex synthesized methods, warning | |
1516 | Warn when g++'s synthesis behavior does not match that of cfront. For | |
1517 | instance: | |
1518 | ||
1519 | @smallexample | |
1520 | struct A @{ | |
1521 | operator int (); | |
1522 | A& operator = (int); | |
1523 | @}; | |
1524 | ||
1525 | main () | |
1526 | @{ | |
1527 | A a,b; | |
1528 | a = b; | |
1529 | @} | |
1530 | @end smallexample | |
74291a4b | 1531 | |
bba975d4 JM |
1532 | In this example, g++ will synthesize a default @samp{A& operator = |
1533 | (const A&);}, while cfront will use the user-defined @samp{operator =}. | |
74291a4b MM |
1534 | @end table |
1535 | ||
60de6385 SS |
1536 | @node Objective-C Dialect Options |
1537 | @section Options Controlling Objective-C Dialect | |
1538 | ||
1539 | @cindex compiler options, Objective-C | |
1540 | @cindex Objective-C options, command line | |
1541 | @cindex options, Objective-C | |
1542 | This section describes the command-line options that are only meaningful | |
1543 | for Objective-C programs; but you can also use most of the GNU compiler | |
1544 | options regardless of what language your program is in. For example, | |
1545 | you might compile a file @code{some_class.m} like this: | |
1546 | ||
1547 | @example | |
1548 | gcc -g -fgnu-runtime -O -c some_class.m | |
1549 | @end example | |
1550 | ||
1551 | @noindent | |
1552 | In this example, only @samp{-fgnu-runtime} is an option meant only for | |
1553 | Objective-C programs; you can use the other options with any language | |
1554 | supported by GCC. | |
1555 | ||
1556 | Here is a list of options that are @emph{only} for compiling Objective-C | |
1557 | programs: | |
1558 | ||
1559 | @table @gcctabopt | |
1560 | @item -fconstant-string-class=@var{class name} | |
1561 | Use @var{class name} as the name of the class to instantiate for each | |
1562 | literal string specified with the syntax @code{@@"..."}. The default | |
1563 | class name is @code{NXConstantString}. | |
1564 | ||
1565 | @item -fgnu-runtime | |
1566 | Generate object code compatible with the standard GNU Objective-C | |
1567 | runtime. This is the default for most types of systems. | |
1568 | ||
1569 | @item -fnext-runtime | |
1570 | Generate output compatible with the NeXT runtime. This is the default | |
1571 | for NeXT-based systems, including Darwin and Mac OS X. | |
1572 | ||
1573 | @item -gen-decls | |
1574 | Dump interface declarations for all classes seen in the source file to a | |
1575 | file named @file{@var{sourcename}.decl}. | |
1576 | ||
1577 | @item -Wno-protocol | |
1578 | Do not warn if methods required by a protocol are not implemented | |
1579 | in the class adopting it. | |
1580 | ||
1581 | @item -Wselector | |
1582 | Warn if a selector has multiple methods of different types defined. | |
1583 | ||
1584 | @c not documented because only avail via -Wp | |
1585 | @c @item -print-objc-runtime-info | |
1586 | ||
1587 | @end table | |
1588 | ||
764dbbf2 GDR |
1589 | @node Language Independent Options |
1590 | @section Options to Control Diagnostic Messages Formatting | |
1591 | @cindex options to control diagnostics formatting | |
1592 | @cindex diagnostic messages | |
1593 | @cindex message formatting | |
1594 | ||
b192711e | 1595 | Traditionally, diagnostic messages have been formatted irrespective of |
764dbbf2 GDR |
1596 | the output device's aspect (e.g. its width, ...). The options described |
1597 | below can be used to control the diagnostic messages formatting | |
1598 | algorithm, e.g. how many characters per line, how often source location | |
1599 | information should be reported. Right now, only the C++ front-end can | |
1600 | honor these options. However it is expected, in the near future, that | |
02f52e19 | 1601 | the remaining front-ends would be able to digest them correctly. |
764dbbf2 | 1602 | |
2642624b | 1603 | @table @gcctabopt |
764dbbf2 GDR |
1604 | @item -fmessage-length=@var{n} |
1605 | Try to format error messages so that they fit on lines of about @var{n} | |
1606 | characters. The default is 72 characters for g++ and 0 for the rest of | |
1607 | the front-ends supported by GCC. If @var{n} is zero, then no | |
02f52e19 | 1608 | line-wrapping will be done; each error message will appear on a single |
764dbbf2 GDR |
1609 | line. |
1610 | ||
1611 | @item -fdiagnostics-show-location=once | |
b192711e | 1612 | Only meaningful in line-wrapping mode. Instructs the diagnostic messages |
764dbbf2 GDR |
1613 | reporter to emit @emph{once} source location information; that is, in |
1614 | case the message is too long to fit on a single physical line and has to | |
1615 | be wrapped, the source location won't be emitted (as prefix) again, | |
1616 | over and over, in subsequent continuation lines. This is the default | |
02f52e19 | 1617 | behaviour. |
764dbbf2 GDR |
1618 | |
1619 | @item -fdiagnostics-show-location=every-line | |
1620 | Only meaningful in line-wrapping mode. Instructs the diagnostic | |
1621 | messages reporter to emit the same source location information (as | |
1622 | prefix) for physical lines that result from the process of breaking a | |
b192711e | 1623 | a message which is too long to fit on a single line. |
764dbbf2 GDR |
1624 | |
1625 | @end table | |
1626 | ||
74291a4b MM |
1627 | @node Warning Options |
1628 | @section Options to Request or Suppress Warnings | |
1629 | @cindex options to control warnings | |
1630 | @cindex warning messages | |
1631 | @cindex messages, warning | |
1632 | @cindex suppressing warnings | |
1633 | ||
1634 | Warnings are diagnostic messages that report constructions which | |
1635 | are not inherently erroneous but which are risky or suggest there | |
1636 | may have been an error. | |
1637 | ||
1638 | You can request many specific warnings with options beginning @samp{-W}, | |
1639 | for example @samp{-Wimplicit} to request warnings on implicit | |
1640 | declarations. Each of these specific warning options also has a | |
1641 | negative form beginning @samp{-Wno-} to turn off warnings; | |
1642 | for example, @samp{-Wno-implicit}. This manual lists only one of the | |
1643 | two forms, whichever is not the default. | |
1644 | ||
0c2d1a2a | 1645 | These options control the amount and kinds of warnings produced by GCC: |
74291a4b | 1646 | |
2642624b | 1647 | @table @gcctabopt |
74291a4b MM |
1648 | @cindex syntax checking |
1649 | @item -fsyntax-only | |
1650 | Check the code for syntax errors, but don't do anything beyond that. | |
1651 | ||
1652 | @item -pedantic | |
074e95e3 JM |
1653 | Issue all the warnings demanded by strict ISO C and ISO C++; |
1654 | reject all programs that use forbidden extensions, and some other | |
1655 | programs that do not follow ISO C and ISO C++. For ISO C, follows the | |
1656 | version of the ISO C standard specified by any @samp{-std} option used. | |
74291a4b | 1657 | |
074e95e3 | 1658 | Valid ISO C and ISO C++ programs should compile properly with or without |
5490d604 JM |
1659 | this option (though a rare few will require @option{-ansi} or a |
1660 | @option{-std} option specifying the required version of ISO C). However, | |
b1d16193 JL |
1661 | without this option, certain GNU extensions and traditional C and C++ |
1662 | features are supported as well. With this option, they are rejected. | |
74291a4b MM |
1663 | |
1664 | @samp{-pedantic} does not cause warning messages for use of the | |
1665 | alternate keywords whose names begin and end with @samp{__}. Pedantic | |
1666 | warnings are also disabled in the expression that follows | |
1667 | @code{__extension__}. However, only system header files should use | |
1668 | these escape routes; application programs should avoid them. | |
1669 | @xref{Alternate Keywords}. | |
1670 | ||
074e95e3 | 1671 | Some users try to use @samp{-pedantic} to check programs for strict ISO |
74291a4b | 1672 | C conformance. They soon find that it does not do quite what they want: |
c1030c7c | 1673 | it finds some non-ISO practices, but not all---only those for which |
074e95e3 JM |
1674 | ISO C @emph{requires} a diagnostic, and some others for which |
1675 | diagnostics have been added. | |
74291a4b | 1676 | |
074e95e3 | 1677 | A feature to report any failure to conform to ISO C might be useful in |
74291a4b | 1678 | some instances, but would require considerable additional work and would |
892d0a6d AO |
1679 | be quite different from @samp{-pedantic}. We don't have plans to |
1680 | support such a feature in the near future. | |
74291a4b | 1681 | |
91ea548a JM |
1682 | Where the standard specified with @option{-std} represents a GNU |
1683 | extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a | |
1684 | corresponding @dfn{base standard}, the version of ISO C on which the GNU | |
1685 | extended dialect is based. Warnings from @option{-pedantic} are given | |
1686 | where they are required by the base standard. (It would not make sense | |
1687 | for such warnings to be given only for features not in the specified GNU | |
1688 | C dialect, since by definition the GNU dialects of C include all | |
1689 | features the compiler supports with the given option, and there would be | |
1690 | nothing to warn about.) | |
1691 | ||
74291a4b MM |
1692 | @item -pedantic-errors |
1693 | Like @samp{-pedantic}, except that errors are produced rather than | |
1694 | warnings. | |
1695 | ||
1696 | @item -w | |
1697 | Inhibit all warning messages. | |
1698 | ||
1699 | @item -Wno-import | |
1700 | Inhibit warning messages about the use of @samp{#import}. | |
1701 | ||
1702 | @item -Wchar-subscripts | |
1703 | Warn if an array subscript has type @code{char}. This is a common cause | |
1704 | of error, as programmers often forget that this type is signed on some | |
1705 | machines. | |
1706 | ||
1707 | @item -Wcomment | |
1708 | Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*} | |
1709 | comment, or whenever a Backslash-Newline appears in a @samp{//} comment. | |
1710 | ||
1711 | @item -Wformat | |
1712 | Check calls to @code{printf} and @code{scanf}, etc., to make sure that | |
1713 | the arguments supplied have types appropriate to the format string | |
26f6672d JM |
1714 | specified, and that the conversions specified in the format string make |
1715 | sense. This includes standard functions, and others specified by format | |
1716 | attributes (@pxref{Function Attributes}), in the @code{printf}, | |
1717 | @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension, | |
1718 | not in the C standard) families. | |
74291a4b | 1719 | |
8308e0b7 JM |
1720 | The formats are checked against the format features supported by GNU |
1721 | libc version 2.2. These include all ISO C89 and C99 features, as well | |
1722 | as features from the Single Unix Specification and some BSD and GNU | |
1723 | extensions. Other library implementations may not support all these | |
1724 | features; GCC does not support warning about features that go beyond a | |
1725 | particular library's limitations. However, if @samp{-pedantic} is used | |
1726 | with @samp{-Wformat}, warnings will be given about format features not | |
26f6672d JM |
1727 | in the selected standard version (but not for @code{strfmon} formats, |
1728 | since those are not in any version of the C standard). @xref{C Dialect | |
1729 | Options,,Options Controlling C Dialect}. | |
8308e0b7 | 1730 | |
4d808927 JM |
1731 | @samp{-Wformat} is included in @samp{-Wall}. For more control over some |
1732 | aspects of format checking, the options @samp{-Wno-format-y2k}, | |
c907e684 JM |
1733 | @samp{-Wno-format-extra-args}, @samp{-Wformat-nonliteral}, |
1734 | @samp{-Wformat-security} and @samp{-Wformat=2} are available, but are | |
1735 | not included in @samp{-Wall}. | |
4d808927 JM |
1736 | |
1737 | @item -Wno-format-y2k | |
1738 | If @samp{-Wformat} is specified, do not warn about @code{strftime} | |
1739 | formats which may yield only a two-digit year. | |
1740 | ||
1741 | @item -Wno-format-extra-args | |
1742 | If @samp{-Wformat} is specified, do not warn about excess arguments to a | |
1743 | @code{printf} or @code{scanf} format function. The C standard specifies | |
1744 | that such arguments are ignored. | |
1745 | ||
1746 | @item -Wformat-nonliteral | |
1747 | If @samp{-Wformat} is specified, also warn if the format string is not a | |
1748 | string literal and so cannot be checked, unless the format function | |
1749 | takes its format arguments as a @code{va_list}. | |
1750 | ||
c907e684 JM |
1751 | @item -Wformat-security |
1752 | If @samp{-Wformat} is specified, also warn about uses of format | |
1753 | functions that represent possible security problems. At present, this | |
1754 | warns about calls to @code{printf} and @code{scanf} functions where the | |
1755 | format string is not a string literal and there are no format arguments, | |
1756 | as in @code{printf (foo);}. This may be a security hole if the format | |
1757 | string came from untrusted input and contains @samp{%n}. (This is | |
1758 | currently a subset of what @samp{-Wformat-nonliteral} warns about, but | |
1759 | in future warnings may be added to @samp{-Wformat-security} that are not | |
1760 | included in @samp{-Wformat-nonliteral}.) | |
1761 | ||
4d808927 JM |
1762 | @item -Wformat=2 |
1763 | Enable @samp{-Wformat} plus format checks not included in | |
1764 | @samp{-Wformat}. Currently equivalent to @samp{-Wformat | |
c907e684 | 1765 | -Wformat-nonliteral -Wformat-security}. |
4d808927 | 1766 | |
e9a25f70 JL |
1767 | @item -Wimplicit-int |
1768 | Warn when a declaration does not specify a type. | |
1769 | ||
f5963e61 JL |
1770 | @item -Wimplicit-function-declaration |
1771 | @itemx -Werror-implicit-function-declaration | |
1772 | Give a warning (or error) whenever a function is used before being | |
1773 | declared. | |
e9a25f70 | 1774 | |
74291a4b | 1775 | @item -Wimplicit |
e5e809f4 JL |
1776 | Same as @samp{-Wimplicit-int} and @samp{-Wimplicit-function-}@* |
1777 | @samp{declaration}. | |
861bb6c1 JL |
1778 | |
1779 | @item -Wmain | |
1780 | Warn if the type of @samp{main} is suspicious. @samp{main} should be a | |
1781 | function with external linkage, returning int, taking either zero | |
1782 | arguments, two, or three arguments of appropriate types. | |
4a870dba | 1783 | |
1f0c3120 JM |
1784 | @item -Wmissing-braces |
1785 | Warn if an aggregate or union initializer is not fully bracketed. In | |
1786 | the following example, the initializer for @samp{a} is not fully | |
1787 | bracketed, but that for @samp{b} is fully bracketed. | |
1788 | ||
1789 | @smallexample | |
1790 | int a[2][2] = @{ 0, 1, 2, 3 @}; | |
1791 | int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @}; | |
1792 | @end smallexample | |
1793 | ||
4a870dba JM |
1794 | @item -Wmultichar |
1795 | Warn if a multicharacter constant (@samp{'FOOF'}) is used. Usually they | |
1796 | indicate a typo in the user's code, as they have implementation-defined | |
1797 | values, and should not be used in portable code. | |
3c12fcc2 | 1798 | |
74291a4b MM |
1799 | @item -Wparentheses |
1800 | Warn if parentheses are omitted in certain contexts, such | |
1801 | as when there is an assignment in a context where a truth value | |
1802 | is expected, or when operators are nested whose precedence people | |
1803 | often get confused about. | |
1804 | ||
e9a25f70 JL |
1805 | Also warn about constructions where there may be confusion to which |
1806 | @code{if} statement an @code{else} branch belongs. Here is an example of | |
1807 | such a case: | |
1808 | ||
1809 | @smallexample | |
1810 | @{ | |
1811 | if (a) | |
1812 | if (b) | |
1813 | foo (); | |
1814 | else | |
1815 | bar (); | |
1816 | @} | |
1817 | @end smallexample | |
1818 | ||
1819 | In C, every @code{else} branch belongs to the innermost possible @code{if} | |
1820 | statement, which in this example is @code{if (b)}. This is often not | |
1821 | what the programmer expected, as illustrated in the above example by | |
1822 | indentation the programmer chose. When there is the potential for this | |
1823 | confusion, GNU C will issue a warning when this flag is specified. | |
1824 | To eliminate the warning, add explicit braces around the innermost | |
1825 | @code{if} statement so there is no way the @code{else} could belong to | |
1826 | the enclosing @code{if}. The resulting code would look like this: | |
1827 | ||
1828 | @smallexample | |
1829 | @{ | |
1830 | if (a) | |
1831 | @{ | |
1832 | if (b) | |
1833 | foo (); | |
1834 | else | |
1835 | bar (); | |
1836 | @} | |
1837 | @} | |
1838 | @end smallexample | |
1839 | ||
bb58bec5 JM |
1840 | @item -Wsequence-point |
1841 | Warn about code that may have undefined semantics because of violations | |
1842 | of sequence point rules in the C standard. | |
1843 | ||
1844 | The C standard defines the order in which expressions in a C program are | |
1845 | evaluated in terms of @dfn{sequence points}, which represent a partial | |
1846 | ordering between the execution of parts of the program: those executed | |
1847 | before the sequence point, and those executed after it. These occur | |
1848 | after the evaluation of a full expression (one which is not part of a | |
1849 | larger expression), after the evaluation of the first operand of a | |
1850 | @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a | |
1851 | function is called (but after the evaluation of its arguments and the | |
1852 | expression denoting the called function), and in certain other places. | |
1853 | Other than as expressed by the sequence point rules, the order of | |
1854 | evaluation of subexpressions of an expression is not specified. All | |
1855 | these rules describe only a partial order rather than a total order, | |
1856 | since, for example, if two functions are called within one expression | |
1857 | with no sequence point between them, the order in which the functions | |
1858 | are called is not specified. However, the standards committee have | |
1859 | ruled that function calls do not overlap. | |
1860 | ||
1861 | It is not specified when between sequence points modifications to the | |
1862 | values of objects take effect. Programs whose behavior depends on this | |
1863 | have undefined behavior; the C standard specifies that ``Between the | |
1864 | previous and next sequence point an object shall have its stored value | |
1865 | modified at most once by the evaluation of an expression. Furthermore, | |
1866 | the prior value shall be read only to determine the value to be | |
1867 | stored.''. If a program breaks these rules, the results on any | |
1868 | particular implementation are entirely unpredictable. | |
1869 | ||
1870 | Examples of code with undefined behavior are @code{a = a++;}, @code{a[n] | |
1871 | = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not | |
1872 | diagnosed by this option, and it may give an occasional false positive | |
1873 | result, but in general it has been found fairly effective at detecting | |
1874 | this sort of problem in programs. | |
1875 | ||
1876 | The present implementation of this option only works for C programs. A | |
1877 | future implementation may also work for C++ programs. | |
1878 | ||
1879 | There is some controversy over the precise meaning of the sequence point | |
1880 | rules in subtle cases. Alternative formal definitions may be found in | |
1881 | Clive Feather's ``Annex S'' | |
2642624b | 1882 | @w{@uref{http://wwwold.dkuug.dk/JTC1/SC22/WG14/www/docs/n925.htm}} and in |
bb58bec5 | 1883 | Michael Norrish's thesis |
2642624b | 1884 | @w{@uref{http://www.cl.cam.ac.uk/users/mn200/PhD/thesis-report.ps.gz}}. |
163686bd | 1885 | Other discussions are by Raymond Mak |
2642624b | 1886 | @w{@uref{http://wwwold.dkuug.dk/JTC1/SC22/WG14/www/docs/n926.htm}} and |
163686bd | 1887 | D. Hugh Redelmeier |
2642624b | 1888 | @w{@uref{http://wwwold.dkuug.dk/JTC1/SC22/WG14/www/docs/n927.htm}}. |
bb58bec5 | 1889 | |
74291a4b | 1890 | @item -Wreturn-type |
32c4c36c ML |
1891 | Warn whenever a function is defined with a return-type that defaults to |
1892 | @code{int}. Also warn about any @code{return} statement with no | |
02f52e19 | 1893 | return-value in a function whose return-type is not @code{void}. |
32c4c36c ML |
1894 | |
1895 | For C++, a function without return type always produces a diagnostic | |
1896 | message, even when @samp{-Wno-return-type} is specified. The only | |
1897 | exceptions are @samp{main} and functions defined in system headers. | |
74291a4b MM |
1898 | |
1899 | @item -Wswitch | |
1900 | Warn whenever a @code{switch} statement has an index of enumeral type | |
1901 | and lacks a @code{case} for one or more of the named codes of that | |
1902 | enumeration. (The presence of a @code{default} label prevents this | |
1903 | warning.) @code{case} labels outside the enumeration range also | |
1904 | provoke warnings when this option is used. | |
1905 | ||
1906 | @item -Wtrigraphs | |
f2ecb02d JM |
1907 | Warn if any trigraphs are encountered that might change the meaning of |
1908 | the program (trigraphs within comments are not warned about). | |
74291a4b | 1909 | |
078721e1 AC |
1910 | @item -Wunused-function |
1911 | Warn whenever a static function is declared but not defined or a | |
1912 | non\-inline static function is unused. | |
74291a4b | 1913 | |
078721e1 AC |
1914 | @item -Wunused-label |
1915 | Warn whenever a label is declared but not used. | |
1916 | ||
1917 | To suppress this warning use the @samp{unused} attribute | |
1918 | (@pxref{Variable Attributes}). | |
1919 | ||
1920 | @item -Wunused-parameter | |
1921 | Warn whenever a function parameter is unused aside from its declaration. | |
1922 | ||
1923 | To suppress this warning use the @samp{unused} attribute | |
1924 | (@pxref{Variable Attributes}). | |
956d6950 | 1925 | |
078721e1 AC |
1926 | @item -Wunused-variable |
1927 | Warn whenever a local variable or non-constant static variable is unused | |
1928 | aside from its declaration | |
1929 | ||
1930 | To suppress this warning use the @samp{unused} attribute | |
74291a4b MM |
1931 | (@pxref{Variable Attributes}). |
1932 | ||
078721e1 AC |
1933 | @item -Wunused-value |
1934 | Warn whenever a statement computes a result that is explicitly not used. | |
1935 | ||
1936 | To suppress this warning cast the expression to @samp{void}. | |
1937 | ||
1938 | @item -Wunused | |
1939 | All all the above @samp{-Wunused} options combined. | |
1940 | ||
1941 | In order to get a warning about an unused function parameter, you must | |
b192711e | 1942 | either specify @samp{-W -Wunused} or separately specify |
078721e1 AC |
1943 | @samp{-Wunused-parameter}. |
1944 | ||
74291a4b | 1945 | @item -Wuninitialized |
c5c76735 JL |
1946 | Warn if an automatic variable is used without first being initialized or |
1947 | if a variable may be clobbered by a @code{setjmp} call. | |
74291a4b MM |
1948 | |
1949 | These warnings are possible only in optimizing compilation, | |
1950 | because they require data flow information that is computed only | |
1951 | when optimizing. If you don't specify @samp{-O}, you simply won't | |
1952 | get these warnings. | |
1953 | ||
1954 | These warnings occur only for variables that are candidates for | |
1955 | register allocation. Therefore, they do not occur for a variable that | |
1956 | is declared @code{volatile}, or whose address is taken, or whose size | |
1957 | is other than 1, 2, 4 or 8 bytes. Also, they do not occur for | |
1958 | structures, unions or arrays, even when they are in registers. | |
1959 | ||
1960 | Note that there may be no warning about a variable that is used only | |
1961 | to compute a value that itself is never used, because such | |
1962 | computations may be deleted by data flow analysis before the warnings | |
1963 | are printed. | |
1964 | ||
0c2d1a2a | 1965 | These warnings are made optional because GCC is not smart |
74291a4b MM |
1966 | enough to see all the reasons why the code might be correct |
1967 | despite appearing to have an error. Here is one example of how | |
1968 | this can happen: | |
1969 | ||
1970 | @smallexample | |
1971 | @{ | |
1972 | int x; | |
1973 | switch (y) | |
1974 | @{ | |
1975 | case 1: x = 1; | |
1976 | break; | |
1977 | case 2: x = 4; | |
1978 | break; | |
1979 | case 3: x = 5; | |
1980 | @} | |
1981 | foo (x); | |
1982 | @} | |
1983 | @end smallexample | |
1984 | ||
1985 | @noindent | |
1986 | If the value of @code{y} is always 1, 2 or 3, then @code{x} is | |
0c2d1a2a | 1987 | always initialized, but GCC doesn't know this. Here is |
74291a4b MM |
1988 | another common case: |
1989 | ||
1990 | @smallexample | |
1991 | @{ | |
1992 | int save_y; | |
1993 | if (change_y) save_y = y, y = new_y; | |
1994 | @dots{} | |
1995 | if (change_y) y = save_y; | |
1996 | @} | |
1997 | @end smallexample | |
1998 | ||
1999 | @noindent | |
2000 | This has no bug because @code{save_y} is used only if it is set. | |
2001 | ||
20300b05 | 2002 | @cindex @code{longjmp} warnings |
b192711e | 2003 | This option also warns when a non-volatile automatic variable might be |
c5c76735 JL |
2004 | changed by a call to @code{longjmp}. These warnings as well are possible |
2005 | only in optimizing compilation. | |
20300b05 GK |
2006 | |
2007 | The compiler sees only the calls to @code{setjmp}. It cannot know | |
2008 | where @code{longjmp} will be called; in fact, a signal handler could | |
2009 | call it at any point in the code. As a result, you may get a warning | |
2010 | even when there is in fact no problem because @code{longjmp} cannot | |
2011 | in fact be called at the place which would cause a problem. | |
2012 | ||
74291a4b MM |
2013 | Some spurious warnings can be avoided if you declare all the functions |
2014 | you use that never return as @code{noreturn}. @xref{Function | |
2015 | Attributes}. | |
2016 | ||
c5c76735 JL |
2017 | @item -Wreorder (C++ only) |
2018 | @cindex reordering, warning | |
2019 | @cindex warning for reordering of member initializers | |
2020 | Warn when the order of member initializers given in the code does not | |
2021 | match the order in which they must be executed. For instance: | |
2022 | ||
d300e551 NC |
2023 | @item -Wunknown-pragmas |
2024 | @cindex warning for unknown pragmas | |
2025 | @cindex unknown pragmas, warning | |
2026 | @cindex pragmas, warning of unknown | |
2027 | Warn when a #pragma directive is encountered which is not understood by | |
2028 | GCC. If this command line option is used, warnings will even be issued | |
2029 | for unknown pragmas in system header files. This is not the case if | |
2030 | the warnings were only enabled by the @samp{-Wall} command line option. | |
2031 | ||
74291a4b MM |
2032 | @item -Wall |
2033 | All of the above @samp{-W} options combined. This enables all the | |
2034 | warnings about constructions that some users consider questionable, and | |
2035 | that are easy to avoid (or modify to prevent the warning), even in | |
2036 | conjunction with macros. | |
317639a8 BC |
2037 | |
2038 | @item -Wsystem-headers | |
2039 | @cindex warnings from system headers | |
2040 | @cindex system headers, warnings from | |
2041 | Print warning messages for constructs found in system header files. | |
2042 | Warnings from system headers are normally suppressed, on the assumption | |
2043 | that they usually do not indicate real problems and would only make the | |
2044 | compiler output harder to read. Using this command line option tells | |
2045 | GCC to emit warnings from system headers as if they occurred in user | |
2046 | code. However, note that using @samp{-Wall} in conjunction with this | |
2047 | option will @emph{not} warn about unknown pragmas in system | |
2048 | headers---for that, @samp{-Wunknown-pragmas} must also be used. | |
74291a4b MM |
2049 | @end table |
2050 | ||
2051 | The following @samp{-W@dots{}} options are not implied by @samp{-Wall}. | |
2052 | Some of them warn about constructions that users generally do not | |
2053 | consider questionable, but which occasionally you might wish to check | |
2054 | for; others warn about constructions that are necessary or hard to avoid | |
2055 | in some cases, and there is no simple way to modify the code to suppress | |
2056 | the warning. | |
2057 | ||
2642624b | 2058 | @table @gcctabopt |
74291a4b MM |
2059 | @item -W |
2060 | Print extra warning messages for these events: | |
2061 | ||
2062 | @itemize @bullet | |
74291a4b MM |
2063 | @item |
2064 | A function can return either with or without a value. (Falling | |
2065 | off the end of the function body is considered returning without | |
2066 | a value.) For example, this function would evoke such a | |
2067 | warning: | |
2068 | ||
2069 | @smallexample | |
2070 | @group | |
2071 | foo (a) | |
2072 | @{ | |
2073 | if (a > 0) | |
2074 | return a; | |
2075 | @} | |
2076 | @end group | |
2077 | @end smallexample | |
2078 | ||
2079 | @item | |
2080 | An expression-statement or the left-hand side of a comma expression | |
2081 | contains no side effects. | |
2082 | To suppress the warning, cast the unused expression to void. | |
2083 | For example, an expression such as @samp{x[i,j]} will cause a warning, | |
2084 | but @samp{x[(void)i,j]} will not. | |
2085 | ||
2086 | @item | |
2087 | An unsigned value is compared against zero with @samp{<} or @samp{<=}. | |
2088 | ||
2089 | @item | |
2090 | A comparison like @samp{x<=y<=z} appears; this is equivalent to | |
2091 | @samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from | |
2092 | that of ordinary mathematical notation. | |
2093 | ||
2094 | @item | |
2095 | Storage-class specifiers like @code{static} are not the first things in | |
2096 | a declaration. According to the C Standard, this usage is obsolescent. | |
2097 | ||
e0c9fbb7 JM |
2098 | @item |
2099 | The return type of a function has a type qualifier such as @code{const}. | |
2100 | Such a type qualifier has no effect, since the value returned by a | |
2101 | function is not an lvalue. (But don't warn about the GNU extension of | |
2102 | @code{volatile void} return types. That extension will be warned about | |
2103 | if @samp{-pedantic} is specified.) | |
2104 | ||
74291a4b MM |
2105 | @item |
2106 | If @samp{-Wall} or @samp{-Wunused} is also specified, warn about unused | |
2107 | arguments. | |
2108 | ||
e9a25f70 JL |
2109 | @item |
2110 | A comparison between signed and unsigned values could produce an | |
2111 | incorrect result when the signed value is converted to unsigned. | |
e5e809f4 | 2112 | (But don't warn if @samp{-Wno-sign-compare} is also specified.) |
e9a25f70 | 2113 | |
74291a4b MM |
2114 | @item |
2115 | An aggregate has a partly bracketed initializer. | |
2116 | For example, the following code would evoke such a warning, | |
2117 | because braces are missing around the initializer for @code{x.h}: | |
2118 | ||
2119 | @smallexample | |
2120 | struct s @{ int f, g; @}; | |
2121 | struct t @{ struct s h; int i; @}; | |
2122 | struct t x = @{ 1, 2, 3 @}; | |
2123 | @end smallexample | |
dbde0d5d BH |
2124 | |
2125 | @item | |
2126 | An aggregate has an initializer which does not initialize all members. | |
2127 | For example, the following code would cause such a warning, because | |
2128 | @code{x.h} would be implicitly initialized to zero: | |
2129 | ||
2130 | @smallexample | |
2131 | struct s @{ int f, g, h; @}; | |
2132 | struct s x = @{ 3, 4 @}; | |
2133 | @end smallexample | |
74291a4b MM |
2134 | @end itemize |
2135 | ||
f793a95e JL |
2136 | @item -Wfloat-equal |
2137 | Warn if floating point values are used in equality comparisons. | |
2138 | ||
488d3985 GK |
2139 | The idea behind this is that sometimes it is convenient (for the |
2140 | programmer) to consider floating-point values as approximations to | |
2141 | infinitely precise real numbers. If you are doing this, then you need | |
2142 | to compute (by analysing the code, or in some other way) the maximum or | |
2143 | likely maximum error that the computation introduces, and allow for it | |
2144 | when performing comparisons (and when producing output, but that's a | |
2145 | different problem). In particular, instead of testing for equality, you | |
2146 | would check to see whether the two values have ranges that overlap; and | |
2147 | this is done with the relational operators, so equality comparisons are | |
2148 | probably mistaken. | |
2149 | ||
fe50c0eb | 2150 | @item -Wtraditional (C only) |
74291a4b | 2151 | Warn about certain constructs that behave differently in traditional and |
c8abc684 KG |
2152 | ISO C. Also warn about ISO C constructs that have no traditional C |
2153 | equivalent, and/or problematic constructs which should be avoided. | |
74291a4b MM |
2154 | |
2155 | @itemize @bullet | |
2156 | @item | |
da312b55 NB |
2157 | Macro parameters that appear within string literals in the macro body. |
2158 | In traditional C macro replacement takes place within string literals, | |
2159 | but does not in ISO C. | |
2160 | ||
2161 | @item | |
2162 | In traditional C, some preprocessor directives did not exist. | |
2163 | Traditional preprocessors would only consider a line to be a directive | |
2164 | if the @samp{#} appeared in column 1 on the line. Therefore | |
2165 | @samp{-Wtraditional} warns about directives that traditional C | |
2166 | understands but would ignore because the @samp{#} does not appear as the | |
2167 | first character on the line. It also suggests you hide directives like | |
2168 | @samp{#pragma} not understood by traditional C by indenting them. Some | |
2169 | traditional implementations would not recognise @samp{#elif}, so it | |
2170 | suggests avoiding it altogether. | |
2171 | ||
2172 | @item | |
2173 | A function-like macro that appears without arguments. | |
2174 | ||
2175 | @item | |
2176 | The unary plus operator. | |
2177 | ||
2178 | @item | |
2179 | The `U' integer constant suffix, or the `F' or `L' floating point | |
2180 | constant suffixes. (Traditonal C does support the `L' suffix on integer | |
2181 | constants.) Note, these suffixes appear in macros defined in the system | |
2182 | headers of most modern systems, e.g. the _MIN/_MAX macros in limits.h. | |
c8abc684 KG |
2183 | Use of these macros in user code might normally lead to spurious |
2184 | warnings, however gcc's integrated preprocessor has enough context to | |
2185 | avoid warning in these cases. | |
74291a4b MM |
2186 | |
2187 | @item | |
2188 | A function declared external in one block and then used after the end of | |
2189 | the block. | |
2190 | ||
2191 | @item | |
2192 | A @code{switch} statement has an operand of type @code{long}. | |
db838bb8 KG |
2193 | |
2194 | @item | |
2195 | A non-@code{static} function declaration follows a @code{static} one. | |
2196 | This construct is not accepted by some traditional C compilers. | |
48776cde KG |
2197 | |
2198 | @item | |
c1030c7c | 2199 | The ISO type of an integer constant has a different width or |
48776cde KG |
2200 | signedness from its traditional type. This warning is only issued if |
2201 | the base of the constant is ten. I.e. hexadecimal or octal values, which | |
2202 | typically represent bit patterns, are not warned about. | |
bb66adca KG |
2203 | |
2204 | @item | |
c1030c7c | 2205 | Usage of ISO string concatenation is detected. |
7f094a94 | 2206 | |
895ea614 KG |
2207 | @item |
2208 | Initialization of automatic aggregates. | |
2209 | ||
2210 | @item | |
2211 | Identifier conflicts with labels. Traditional C lacks a separate | |
2212 | namespace for labels. | |
253b6b82 KG |
2213 | |
2214 | @item | |
2215 | Initialization of unions. If the initializer is zero, the warning is | |
2216 | omitted. This is done under the assumption that the zero initializer in | |
2217 | user code appears conditioned on e.g. @code{__STDC__} to avoid missing | |
2218 | initializer warnings and relies on default initialization to zero in the | |
2219 | traditional C case. | |
03829ad2 KG |
2220 | |
2221 | @item | |
3ed56f8a KG |
2222 | Conversions by prototypes between fixed/floating point values and vice |
2223 | versa. The absence of these prototypes when compiling with traditional | |
2224 | C would cause serious problems. This is a subset of the possible | |
2225 | conversion warnings, for the full set use @samp{-Wconversion}. | |
74291a4b MM |
2226 | @end itemize |
2227 | ||
861bb6c1 JL |
2228 | @item -Wundef |
2229 | Warn if an undefined identifier is evaluated in an @samp{#if} directive. | |
2230 | ||
74291a4b | 2231 | @item -Wshadow |
d773df5a DB |
2232 | Warn whenever a local variable shadows another local variable, parameter or |
2233 | global variable or whenever a built-in function is shadowed. | |
74291a4b | 2234 | |
74291a4b MM |
2235 | @item -Wlarger-than-@var{len} |
2236 | Warn whenever an object of larger than @var{len} bytes is defined. | |
2237 | ||
2238 | @item -Wpointer-arith | |
2239 | Warn about anything that depends on the ``size of'' a function type or | |
2240 | of @code{void}. GNU C assigns these types a size of 1, for | |
2241 | convenience in calculations with @code{void *} pointers and pointers | |
2242 | to functions. | |
2243 | ||
fe50c0eb | 2244 | @item -Wbad-function-cast (C only) |
74291a4b MM |
2245 | Warn whenever a function call is cast to a non-matching type. |
2246 | For example, warn if @code{int malloc()} is cast to @code{anything *}. | |
2247 | ||
2248 | @item -Wcast-qual | |
2249 | Warn whenever a pointer is cast so as to remove a type qualifier from | |
2250 | the target type. For example, warn if a @code{const char *} is cast | |
2251 | to an ordinary @code{char *}. | |
2252 | ||
2253 | @item -Wcast-align | |
2254 | Warn whenever a pointer is cast such that the required alignment of the | |
2255 | target is increased. For example, warn if a @code{char *} is cast to | |
2256 | an @code{int *} on machines where integers can only be accessed at | |
2257 | two- or four-byte boundaries. | |
2258 | ||
2259 | @item -Wwrite-strings | |
2260 | Give string constants the type @code{const char[@var{length}]} so that | |
2261 | copying the address of one into a non-@code{const} @code{char *} | |
2262 | pointer will get a warning. These warnings will help you find at | |
2263 | compile time code that can try to write into a string constant, but | |
2264 | only if you have been very careful about using @code{const} in | |
2265 | declarations and prototypes. Otherwise, it will just be a nuisance; | |
2266 | this is why we did not make @samp{-Wall} request these warnings. | |
2267 | ||
2268 | @item -Wconversion | |
2269 | Warn if a prototype causes a type conversion that is different from what | |
2270 | would happen to the same argument in the absence of a prototype. This | |
2271 | includes conversions of fixed point to floating and vice versa, and | |
2272 | conversions changing the width or signedness of a fixed point argument | |
2273 | except when the same as the default promotion. | |
2274 | ||
2275 | Also, warn if a negative integer constant expression is implicitly | |
2276 | converted to an unsigned type. For example, warn about the assignment | |
2277 | @code{x = -1} if @code{x} is unsigned. But do not warn about explicit | |
2278 | casts like @code{(unsigned) -1}. | |
2279 | ||
e9a25f70 JL |
2280 | @item -Wsign-compare |
2281 | @cindex warning for comparison of signed and unsigned values | |
2282 | @cindex comparison of signed and unsigned values, warning | |
2283 | @cindex signed and unsigned values, comparison warning | |
2284 | Warn when a comparison between signed and unsigned values could produce | |
2285 | an incorrect result when the signed value is converted to unsigned. | |
2286 | This warning is also enabled by @samp{-W}; to get the other warnings | |
2287 | of @samp{-W} without this warning, use @samp{-W -Wno-sign-compare}. | |
2288 | ||
74291a4b MM |
2289 | @item -Waggregate-return |
2290 | Warn if any functions that return structures or unions are defined or | |
2291 | called. (In languages where you can return an array, this also elicits | |
2292 | a warning.) | |
2293 | ||
fe50c0eb | 2294 | @item -Wstrict-prototypes (C only) |
74291a4b MM |
2295 | Warn if a function is declared or defined without specifying the |
2296 | argument types. (An old-style function definition is permitted without | |
2297 | a warning if preceded by a declaration which specifies the argument | |
2298 | types.) | |
2299 | ||
fe50c0eb | 2300 | @item -Wmissing-prototypes (C only) |
74291a4b MM |
2301 | Warn if a global function is defined without a previous prototype |
2302 | declaration. This warning is issued even if the definition itself | |
2303 | provides a prototype. The aim is to detect global functions that fail | |
2304 | to be declared in header files. | |
2305 | ||
2306 | @item -Wmissing-declarations | |
2307 | Warn if a global function is defined without a previous declaration. | |
2308 | Do so even if the definition itself provides a prototype. | |
2309 | Use this option to detect global functions that are not declared in | |
2310 | header files. | |
2311 | ||
0ca3fb0a KG |
2312 | @item -Wmissing-noreturn |
2313 | Warn about functions which might be candidates for attribute @code{noreturn}. | |
2314 | Note these are only possible candidates, not absolute ones. Care should | |
2315 | be taken to manually verify functions actually do not ever return before | |
2316 | adding the @code{noreturn} attribute, otherwise subtle code generation | |
21c7361e AJ |
2317 | bugs could be introduced. You will not get a warning for @code{main} in |
2318 | hosted C environments. | |
0ca3fb0a | 2319 | |
74ff4629 JM |
2320 | @item -Wmissing-format-attribute |
2321 | If @samp{-Wformat} is enabled, also warn about functions which might be | |
2322 | candidates for @code{format} attributes. Note these are only possible | |
2323 | candidates, not absolute ones. GCC will guess that @code{format} | |
2324 | attributes might be appropriate for any function that calls a function | |
2325 | like @code{vprintf} or @code{vscanf}, but this might not always be the | |
2326 | case, and some functions for which @code{format} attributes are | |
2327 | appropriate may not be detected. This option has no effect unless | |
2328 | @samp{-Wformat} is enabled (possibly by @samp{-Wall}). | |
2329 | ||
3c12fcc2 GM |
2330 | @item -Wpacked |
2331 | Warn if a structure is given the packed attribute, but the packed | |
02f52e19 | 2332 | attribute has no effect on the layout or size of the structure. |
3c12fcc2 GM |
2333 | Such structures may be mis-aligned for little benefit. For |
2334 | instance, in this code, the variable @code{f.x} in @code{struct bar} | |
2335 | will be misaligned even though @code{struct bar} does not itself | |
2336 | have the packed attribute: | |
2337 | ||
2338 | @smallexample | |
2339 | @group | |
2340 | struct foo @{ | |
2341 | int x; | |
2342 | char a, b, c, d; | |
2343 | @} __attribute__((packed)); | |
2344 | struct bar @{ | |
2345 | char z; | |
2346 | struct foo f; | |
2347 | @}; | |
2348 | @end group | |
2349 | @end smallexample | |
2350 | ||
2351 | @item -Wpadded | |
2352 | Warn if padding is included in a structure, either to align an element | |
2353 | of the structure or to align the whole structure. Sometimes when this | |
2354 | happens it is possible to rearrange the fields of the structure to | |
2355 | reduce the padding and so make the structure smaller. | |
2356 | ||
74291a4b MM |
2357 | @item -Wredundant-decls |
2358 | Warn if anything is declared more than once in the same scope, even in | |
2359 | cases where multiple declaration is valid and changes nothing. | |
2360 | ||
fe50c0eb | 2361 | @item -Wnested-externs (C only) |
252215a7 | 2362 | Warn if an @code{extern} declaration is encountered within a function. |
74291a4b | 2363 | |
312f6255 GK |
2364 | @item -Wunreachable-code |
2365 | Warn if the compiler detects that code will never be executed. | |
2366 | ||
2367 | This option is intended to warn when the compiler detects that at | |
2368 | least a whole line of source code will never be executed, because | |
2369 | some condition is never satisfied or because it is after a | |
2370 | procedure that never returns. | |
2371 | ||
2372 | It is possible for this option to produce a warning even though there | |
2373 | are circumstances under which part of the affected line can be executed, | |
2374 | so care should be taken when removing apparently-unreachable code. | |
2375 | ||
2376 | For instance, when a function is inlined, a warning may mean that the | |
02f52e19 | 2377 | line is unreachable in only one inlined copy of the function. |
312f6255 GK |
2378 | |
2379 | This option is not made part of @samp{-Wall} because in a debugging | |
2380 | version of a program there is often substantial code which checks | |
2381 | correct functioning of the program and is, hopefully, unreachable | |
2382 | because the program does work. Another common use of unreachable | |
2383 | code is to provide behaviour which is selectable at compile-time. | |
2384 | ||
74291a4b | 2385 | @item -Winline |
c5c76735 | 2386 | Warn if a function can not be inlined and it was declared as inline. |
74291a4b | 2387 | |
795add94 VM |
2388 | @item -Wlong-long |
2389 | Warn if @samp{long long} type is used. This is default. To inhibit | |
2390 | the warning messages, use @samp{-Wno-long-long}. Flags | |
2391 | @samp{-Wlong-long} and @samp{-Wno-long-long} are taken into account | |
2392 | only when @samp{-pedantic} flag is used. | |
2393 | ||
18424ae1 BL |
2394 | @item -Wdisabled-optimization |
2395 | Warn if a requested optimization pass is disabled. This warning does | |
2396 | not generally indicate that there is anything wrong with your code; it | |
2397 | merely indicates that GCC's optimizers were unable to handle the code | |
2398 | effectively. Often, the problem is that your code is too big or too | |
2399 | complex; GCC will refuse to optimize programs when the optimization | |
2400 | itself is likely to take inordinate amounts of time. | |
2401 | ||
74291a4b MM |
2402 | @item -Werror |
2403 | Make all warnings into errors. | |
2404 | @end table | |
2405 | ||
2406 | @node Debugging Options | |
0c2d1a2a | 2407 | @section Options for Debugging Your Program or GCC |
74291a4b MM |
2408 | @cindex options, debugging |
2409 | @cindex debugging information options | |
2410 | ||
0c2d1a2a | 2411 | GCC has various special options that are used for debugging |
74291a4b MM |
2412 | either your program or GCC: |
2413 | ||
2642624b | 2414 | @table @gcctabopt |
74291a4b MM |
2415 | @item -g |
2416 | Produce debugging information in the operating system's native format | |
2417 | (stabs, COFF, XCOFF, or DWARF). GDB can work with this debugging | |
2418 | information. | |
2419 | ||
2420 | On most systems that use stabs format, @samp{-g} enables use of extra | |
2421 | debugging information that only GDB can use; this extra information | |
2422 | makes debugging work better in GDB but will probably make other debuggers | |
2423 | crash or | |
2424 | refuse to read the program. If you want to control for certain whether | |
2425 | to generate the extra information, use @samp{-gstabs+}, @samp{-gstabs}, | |
861bb6c1 | 2426 | @samp{-gxcoff+}, @samp{-gxcoff}, @samp{-gdwarf-1+}, or @samp{-gdwarf-1} |
74291a4b MM |
2427 | (see below). |
2428 | ||
0c2d1a2a | 2429 | Unlike most other C compilers, GCC allows you to use @samp{-g} with |
74291a4b MM |
2430 | @samp{-O}. The shortcuts taken by optimized code may occasionally |
2431 | produce surprising results: some variables you declared may not exist | |
2432 | at all; flow of control may briefly move where you did not expect it; | |
2433 | some statements may not be executed because they compute constant | |
2434 | results or their values were already at hand; some statements may | |
2435 | execute in different places because they were moved out of loops. | |
2436 | ||
2437 | Nevertheless it proves possible to debug optimized output. This makes | |
2438 | it reasonable to use the optimizer for programs that might have bugs. | |
2439 | ||
0c2d1a2a | 2440 | The following options are useful when GCC is generated with the |
74291a4b MM |
2441 | capability for more than one debugging format. |
2442 | ||
2443 | @item -ggdb | |
861bb6c1 JL |
2444 | Produce debugging information for use by GDB. This means to use the |
2445 | most expressive format available (DWARF 2, stabs, or the native format | |
2446 | if neither of those are supported), including GDB extensions if at all | |
2447 | possible. | |
74291a4b MM |
2448 | |
2449 | @item -gstabs | |
2450 | Produce debugging information in stabs format (if that is supported), | |
2451 | without GDB extensions. This is the format used by DBX on most BSD | |
2452 | systems. On MIPS, Alpha and System V Release 4 systems this option | |
2453 | produces stabs debugging output which is not understood by DBX or SDB. | |
2454 | On System V Release 4 systems this option requires the GNU assembler. | |
2455 | ||
2456 | @item -gstabs+ | |
2457 | Produce debugging information in stabs format (if that is supported), | |
2458 | using GNU extensions understood only by the GNU debugger (GDB). The | |
2459 | use of these extensions is likely to make other debuggers crash or | |
2460 | refuse to read the program. | |
2461 | ||
2462 | @item -gcoff | |
2463 | Produce debugging information in COFF format (if that is supported). | |
2464 | This is the format used by SDB on most System V systems prior to | |
2465 | System V Release 4. | |
2466 | ||
2467 | @item -gxcoff | |
2468 | Produce debugging information in XCOFF format (if that is supported). | |
2469 | This is the format used by the DBX debugger on IBM RS/6000 systems. | |
2470 | ||
2471 | @item -gxcoff+ | |
2472 | Produce debugging information in XCOFF format (if that is supported), | |
2473 | using GNU extensions understood only by the GNU debugger (GDB). The | |
2474 | use of these extensions is likely to make other debuggers crash or | |
2475 | refuse to read the program, and may cause assemblers other than the GNU | |
2476 | assembler (GAS) to fail with an error. | |
2477 | ||
2478 | @item -gdwarf | |
861bb6c1 JL |
2479 | Produce debugging information in DWARF version 1 format (if that is |
2480 | supported). This is the format used by SDB on most System V Release 4 | |
2481 | systems. | |
74291a4b MM |
2482 | |
2483 | @item -gdwarf+ | |
861bb6c1 JL |
2484 | Produce debugging information in DWARF version 1 format (if that is |
2485 | supported), using GNU extensions understood only by the GNU debugger | |
2486 | (GDB). The use of these extensions is likely to make other debuggers | |
2487 | crash or refuse to read the program. | |
2488 | ||
2489 | @item -gdwarf-2 | |
2490 | Produce debugging information in DWARF version 2 format (if that is | |
2491 | supported). This is the format used by DBX on IRIX 6. | |
74291a4b MM |
2492 | |
2493 | @item -g@var{level} | |
2494 | @itemx -ggdb@var{level} | |
2495 | @itemx -gstabs@var{level} | |
2496 | @itemx -gcoff@var{level} | |
2497 | @itemx -gxcoff@var{level} | |
2498 | @itemx -gdwarf@var{level} | |
861bb6c1 | 2499 | @itemx -gdwarf-2@var{level} |
74291a4b MM |
2500 | Request debugging information and also use @var{level} to specify how |
2501 | much information. The default level is 2. | |
2502 | ||
2503 | Level 1 produces minimal information, enough for making backtraces in | |
2504 | parts of the program that you don't plan to debug. This includes | |
2505 | descriptions of functions and external variables, but no information | |
2506 | about local variables and no line numbers. | |
2507 | ||
2508 | Level 3 includes extra information, such as all the macro definitions | |
2509 | present in the program. Some debuggers support macro expansion when | |
2510 | you use @samp{-g3}. | |
2511 | ||
2512 | @cindex @code{prof} | |
2513 | @item -p | |
2514 | Generate extra code to write profile information suitable for the | |
2515 | analysis program @code{prof}. You must use this option when compiling | |
2516 | the source files you want data about, and you must also use it when | |
2517 | linking. | |
2518 | ||
2519 | @cindex @code{gprof} | |
2520 | @item -pg | |
2521 | Generate extra code to write profile information suitable for the | |
2522 | analysis program @code{gprof}. You must use this option when compiling | |
2523 | the source files you want data about, and you must also use it when | |
2524 | linking. | |
2525 | ||
2526 | @cindex @code{tcov} | |
2527 | @item -a | |
2528 | Generate extra code to write profile information for basic blocks, which will | |
2529 | record the number of times each basic block is executed, the basic block start | |
2530 | address, and the function name containing the basic block. If @samp{-g} is | |
2531 | used, the line number and filename of the start of the basic block will also be | |
2532 | recorded. If not overridden by the machine description, the default action is | |
2533 | to append to the text file @file{bb.out}. | |
2534 | ||
2535 | This data could be analyzed by a program like @code{tcov}. Note, | |
2536 | however, that the format of the data is not what @code{tcov} expects. | |
2537 | Eventually GNU @code{gprof} should be extended to process this data. | |
2538 | ||
898f531b JL |
2539 | @item -Q |
2540 | Makes the compiler print out each function name as it is compiled, and | |
2541 | print some statistics about each pass when it finishes. | |
2542 | ||
1f0c3120 JM |
2543 | @item -ftime-report |
2544 | Makes the compiler print some statistics about the time consumed by each | |
2545 | pass when it finishes. | |
2546 | ||
2547 | @item -fmem-report | |
2548 | Makes the compiler print some statistics about permanent memory | |
2549 | allocation when it finishes. | |
2550 | ||
74291a4b MM |
2551 | @item -ax |
2552 | Generate extra code to profile basic blocks. Your executable will | |
2553 | produce output that is a superset of that produced when @samp{-a} is | |
2554 | used. Additional output is the source and target address of the basic | |
2555 | blocks where a jump takes place, the number of times a jump is executed, | |
2556 | and (optionally) the complete sequence of basic blocks being executed. | |
2557 | The output is appended to file @file{bb.out}. | |
2558 | ||
2559 | You can examine different profiling aspects without recompilation. Your | |
956d6950 | 2560 | executable will read a list of function names from file @file{bb.in}. |
74291a4b MM |
2561 | Profiling starts when a function on the list is entered and stops when |
2562 | that invocation is exited. To exclude a function from profiling, prefix | |
2563 | its name with `-'. If a function name is not unique, you can | |
2564 | disambiguate it by writing it in the form | |
2565 | @samp{/path/filename.d:functionname}. Your executable will write the | |
2566 | available paths and filenames in file @file{bb.out}. | |
2567 | ||
2568 | Several function names have a special meaning: | |
2569 | @table @code | |
2570 | @item __bb_jumps__ | |
2571 | Write source, target and frequency of jumps to file @file{bb.out}. | |
2572 | @item __bb_hidecall__ | |
2573 | Exclude function calls from frequency count. | |
2574 | @item __bb_showret__ | |
2575 | Include function returns in frequency count. | |
2576 | @item __bb_trace__ | |
2577 | Write the sequence of basic blocks executed to file @file{bbtrace.gz}. | |
2578 | The file will be compressed using the program @samp{gzip}, which must | |
bedc7537 | 2579 | exist in your @env{PATH}. On systems without the @samp{popen} |
74291a4b MM |
2580 | function, the file will be named @file{bbtrace} and will not be |
2581 | compressed. @strong{Profiling for even a few seconds on these systems | |
2582 | will produce a very large file.} Note: @code{__bb_hidecall__} and | |
2583 | @code{__bb_showret__} will not affect the sequence written to | |
2584 | @file{bbtrace.gz}. | |
2585 | @end table | |
2586 | ||
2587 | Here's a short example using different profiling parameters | |
2588 | in file @file{bb.in}. Assume function @code{foo} consists of basic blocks | |
2589 | 1 and 2 and is called twice from block 3 of function @code{main}. After | |
2590 | the calls, block 3 transfers control to block 4 of @code{main}. | |
2591 | ||
2592 | With @code{__bb_trace__} and @code{main} contained in file @file{bb.in}, | |
2593 | the following sequence of blocks is written to file @file{bbtrace.gz}: | |
2594 | 0 3 1 2 1 2 4. The return from block 2 to block 3 is not shown, because | |
2595 | the return is to a point inside the block and not to the top. The | |
2596 | block address 0 always indicates, that control is transferred | |
2597 | to the trace from somewhere outside the observed functions. With | |
2598 | @samp{-foo} added to @file{bb.in}, the blocks of function | |
2599 | @code{foo} are removed from the trace, so only 0 3 4 remains. | |
2600 | ||
2601 | With @code{__bb_jumps__} and @code{main} contained in file @file{bb.in}, | |
2602 | jump frequencies will be written to file @file{bb.out}. The | |
2603 | frequencies are obtained by constructing a trace of blocks | |
2604 | and incrementing a counter for every neighbouring pair of blocks | |
2605 | in the trace. The trace 0 3 1 2 1 2 4 displays the following | |
2606 | frequencies: | |
2607 | ||
2608 | @example | |
2609 | Jump from block 0x0 to block 0x3 executed 1 time(s) | |
2610 | Jump from block 0x3 to block 0x1 executed 1 time(s) | |
2611 | Jump from block 0x1 to block 0x2 executed 2 time(s) | |
2612 | Jump from block 0x2 to block 0x1 executed 1 time(s) | |
2613 | Jump from block 0x2 to block 0x4 executed 1 time(s) | |
2614 | @end example | |
2615 | ||
2616 | With @code{__bb_hidecall__}, control transfer due to call instructions | |
2617 | is removed from the trace, that is the trace is cut into three parts: 0 | |
2618 | 3 4, 0 1 2 and 0 1 2. With @code{__bb_showret__}, control transfer due | |
2619 | to return instructions is added to the trace. The trace becomes: 0 3 1 | |
2620 | 2 3 1 2 3 4. Note, that this trace is not the same, as the sequence | |
2621 | written to @file{bbtrace.gz}. It is solely used for counting jump | |
2622 | frequencies. | |
2623 | ||
861bb6c1 JL |
2624 | @item -fprofile-arcs |
2625 | Instrument @dfn{arcs} during compilation. For each function of your | |
0c2d1a2a | 2626 | program, GCC creates a program flow graph, then finds a spanning tree |
861bb6c1 JL |
2627 | for the graph. Only arcs that are not on the spanning tree have to be |
2628 | instrumented: the compiler adds code to count the number of times that these | |
2629 | arcs are executed. When an arc is the only exit or only entrance to a | |
2630 | block, the instrumentation code can be added to the block; otherwise, a | |
2631 | new basic block must be created to hold the instrumentation code. | |
2632 | ||
2633 | Since not every arc in the program must be instrumented, programs | |
2634 | compiled with this option run faster than programs compiled with | |
2635 | @samp{-a}, which adds instrumentation code to every basic block in the | |
2636 | program. The tradeoff: since @code{gcov} does not have | |
2637 | execution counts for all branches, it must start with the execution | |
2638 | counts for the instrumented branches, and then iterate over the program | |
2639 | flow graph until the entire graph has been solved. Hence, @code{gcov} | |
2640 | runs a little more slowly than a program which uses information from | |
2641 | @samp{-a}. | |
2642 | ||
2643 | @samp{-fprofile-arcs} also makes it possible to estimate branch | |
2644 | probabilities, and to calculate basic block execution counts. In | |
2645 | general, basic block execution counts do not give enough information to | |
2646 | estimate all branch probabilities. When the compiled program exits, it | |
2647 | saves the arc execution counts to a file called | |
2648 | @file{@var{sourcename}.da}. Use the compiler option | |
2649 | @samp{-fbranch-probabilities} (@pxref{Optimize Options,,Options that | |
2650 | Control Optimization}) when recompiling, to optimize using estimated | |
2651 | branch probabilities. | |
2652 | ||
2653 | @need 2000 | |
2654 | @item -ftest-coverage | |
2655 | Create data files for the @code{gcov} code-coverage utility | |
0c2d1a2a | 2656 | (@pxref{Gcov,, @code{gcov}: a GCC Test Coverage Program}). |
861bb6c1 JL |
2657 | The data file names begin with the name of your source file: |
2658 | ||
2642624b | 2659 | @table @gcctabopt |
861bb6c1 JL |
2660 | @item @var{sourcename}.bb |
2661 | A mapping from basic blocks to line numbers, which @code{gcov} uses to | |
2662 | associate basic block execution counts with line numbers. | |
2663 | ||
2664 | @item @var{sourcename}.bbg | |
2665 | A list of all arcs in the program flow graph. This allows @code{gcov} | |
2666 | to reconstruct the program flow graph, so that it can compute all basic | |
2667 | block and arc execution counts from the information in the | |
2668 | @code{@var{sourcename}.da} file (this last file is the output from | |
2669 | @samp{-fprofile-arcs}). | |
2670 | @end table | |
2671 | ||
74291a4b MM |
2672 | @item -d@var{letters} |
2673 | Says to make debugging dumps during compilation at times specified by | |
2674 | @var{letters}. This is used for debugging the compiler. The file names | |
375e2d5c | 2675 | for most of the dumps are made by appending a pass number and a word to |
02f52e19 | 2676 | the source file name (e.g. @file{foo.c.00.rtl} or @file{foo.c.01.sibling}). |
375e2d5c | 2677 | Here are the possible letters for use in @var{letters}, and their meanings: |
74291a4b MM |
2678 | |
2679 | @table @samp | |
375e2d5c RH |
2680 | @item A |
2681 | Annotate the assembler output with miscellaneous debugging information. | |
956d6950 | 2682 | @item b |
923c2d86 | 2683 | Dump after computing branch probabilities, to @file{@var{file}.11.bp}. |
48d9ade5 | 2684 | @item B |
8bb16620 | 2685 | Dump after block reordering, to @file{@var{file}.26.bbro}. |
032713aa | 2686 | @item c |
470fc13d KH |
2687 | Dump after instruction combination, to the file @file{@var{file}.14.combine}. |
2688 | @item C | |
2689 | Dump after the first if conversion, to the file @file{@var{file}.15.ce}. | |
032713aa | 2690 | @item d |
8bb16620 | 2691 | Dump after delayed branch scheduling, to @file{@var{file}.29.dbr}. |
032713aa | 2692 | @item D |
f5963e61 JL |
2693 | Dump all macro definitions, at the end of preprocessing, in addition to |
2694 | normal output. | |
48d9ade5 RK |
2695 | @item e |
2696 | Dump after SSA optimizations, to @file{@var{file}.05.ssa} and | |
2697 | @file{@var{file}.06.ussa}. | |
470fc13d | 2698 | @item E |
8bb16620 | 2699 | Dump after the second if conversion, to @file{@var{file}.24.ce2}. |
74291a4b | 2700 | @item f |
470fc13d | 2701 | Dump after life analysis, to @file{@var{file}.13.life}. |
48d9ade5 RK |
2702 | @item F |
2703 | Dump after purging @code{ADDRESSOF} codes, to @file{@var{file}.04.addressof}. | |
74291a4b | 2704 | @item g |
470fc13d | 2705 | Dump after global register allocation, to @file{@var{file}.19.greg}. |
8bb16620 BS |
2706 | @item o |
2707 | Dump after post-reload CSE and other optimizations, to @file{@var{file}.20.postreload}. | |
02f52e19 | 2708 | @item G |
470fc13d | 2709 | Dump after GCSE, to @file{@var{file}.08.gcse}. |
48d9ade5 RK |
2710 | @item i |
2711 | Dump after sibling call optimizations, to @file{@var{file}.01.sibling}. | |
032713aa | 2712 | @item j |
470fc13d | 2713 | Dump after the first jump optimization, to @file{@var{file}.02.jump}. |
74291a4b | 2714 | @item J |
8bb16620 | 2715 | Dump after the last jump optimization, to @file{@var{file}.27.jump2}. |
74291a4b | 2716 | @item k |
470fc13d | 2717 | Dump after conversion from registers to stack, to @file{@var{file}.29.stack}. |
032713aa | 2718 | @item l |
470fc13d | 2719 | Dump after local register allocation, to @file{@var{file}.18.lreg}. |
032713aa | 2720 | @item L |
470fc13d | 2721 | Dump after loop optimization, to @file{@var{file}.09.loop}. |
032713aa NC |
2722 | @item M |
2723 | Dump after performing the machine dependent reorganisation pass, to | |
02f52e19 | 2724 | @file{@var{file}.28.mach}. |
48d9ade5 | 2725 | @item n |
470fc13d | 2726 | Dump after register renumbering, to @file{@var{file}.23.rnreg}. |
032713aa | 2727 | @item N |
470fc13d | 2728 | Dump after the register move pass, to @file{@var{file}.16.regmove}. |
032713aa | 2729 | @item r |
375e2d5c | 2730 | Dump after RTL generation, to @file{@var{file}.00.rtl}. |
032713aa | 2731 | @item R |
375e2d5c | 2732 | Dump after the second instruction scheduling pass, to |
8bb16620 | 2733 | @file{@var{file}.25.sched2}. |
032713aa NC |
2734 | @item s |
2735 | Dump after CSE (including the jump optimization that sometimes follows | |
02f52e19 | 2736 | CSE), to @file{@var{file}.03.cse}. |
032713aa | 2737 | @item S |
375e2d5c | 2738 | Dump after the first instruction scheduling pass, to |
470fc13d | 2739 | @file{@var{file}.17.sched}. |
032713aa NC |
2740 | @item t |
2741 | Dump after the second CSE pass (including the jump optimization that | |
470fc13d | 2742 | sometimes follows CSE), to @file{@var{file}.10.cse2}. |
48d9ade5 | 2743 | @item w |
8bb16620 | 2744 | Dump after the second flow pass, to @file{@var{file}.21.flow2}. |
470fc13d KH |
2745 | @item X |
2746 | Dump after dead code elimination, to @file{@var{file}.06.dce}. | |
48d9ade5 | 2747 | @item z |
470fc13d | 2748 | Dump after the peephole pass, to @file{@var{file}.22.peephole2}. |
74291a4b MM |
2749 | @item a |
2750 | Produce all the dumps listed above. | |
2751 | @item m | |
2752 | Print statistics on memory usage, at the end of the run, to | |
2753 | standard error. | |
2754 | @item p | |
2755 | Annotate the assembler output with a comment indicating which | |
f20b5577 MM |
2756 | pattern and alternative was used. The length of each instruction is |
2757 | also printed. | |
2856c3e3 SC |
2758 | @item P |
2759 | Dump the RTL in the assembler output as a comment before each instruction. | |
2760 | Also turns on @samp{-dp} annotation. | |
375e2d5c RH |
2761 | @item v |
2762 | For each of the other indicated dump files (except for | |
2763 | @file{@var{file}.00.rtl}), dump a representation of the control flow graph | |
b192711e | 2764 | suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}. |
62a1403d AS |
2765 | @item x |
2766 | Just generate RTL for a function instead of compiling it. Usually used | |
2767 | with @samp{r}. | |
032713aa NC |
2768 | @item y |
2769 | Dump debugging information during parsing, to standard error. | |
74291a4b MM |
2770 | @end table |
2771 | ||
b707b450 R |
2772 | @item -fdump-unnumbered |
2773 | When doing debugging dumps (see -d option above), suppress instruction | |
2774 | numbers and line number note output. This makes it more feasible to | |
b192711e | 2775 | use diff on debugging dumps for compiler invocations with different |
b707b450 R |
2776 | options, in particular with and without -g. |
2777 | ||
9965d119 | 2778 | @item -fdump-translation-unit=@var{file} (C and C++ only) |
f71f87f9 MM |
2779 | Dump a representation of the tree structure for the entire translation |
2780 | unit to @var{file}. | |
2781 | ||
9965d119 NS |
2782 | @item -fdump-class_layout=@var{file} (C++ only) |
2783 | @item -fdump-class_layout (C++ only) | |
2784 | Dump a representation of each class's heirarchy to @var{file}, or | |
2785 | @code{stderr} if not specified. | |
2786 | ||
74291a4b MM |
2787 | @item -fpretend-float |
2788 | When running a cross-compiler, pretend that the target machine uses the | |
2789 | same floating point format as the host machine. This causes incorrect | |
2790 | output of the actual floating constants, but the actual instruction | |
0c2d1a2a | 2791 | sequence will probably be the same as GCC would make when running on |
74291a4b MM |
2792 | the target machine. |
2793 | ||
2794 | @item -save-temps | |
2795 | Store the usual ``temporary'' intermediate files permanently; place them | |
2796 | in the current directory and name them based on the source file. Thus, | |
2797 | compiling @file{foo.c} with @samp{-c -save-temps} would produce files | |
f2ecb02d JM |
2798 | @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a |
2799 | preprocessed @file{foo.i} output file even though the compiler now | |
2800 | normally uses an integrated preprocessor. | |
74291a4b | 2801 | |
03c41c05 ZW |
2802 | @item -time |
2803 | Report the CPU time taken by each subprocess in the compilation | |
f2ecb02d JM |
2804 | sequence. For C source files, this is the compiler proper and assembler |
2805 | (plus the linker if linking is done). The output looks like this: | |
03c41c05 ZW |
2806 | |
2807 | @smallexample | |
03c41c05 ZW |
2808 | # cc1 0.12 0.01 |
2809 | # as 0.00 0.01 | |
2810 | @end smallexample | |
2811 | ||
2812 | The first number on each line is the ``user time,'' that is time spent | |
2813 | executing the program itself. The second number is ``system time,'' | |
2814 | time spent executing operating system routines on behalf of the program. | |
2815 | Both numbers are in seconds. | |
2816 | ||
74291a4b MM |
2817 | @item -print-file-name=@var{library} |
2818 | Print the full absolute name of the library file @var{library} that | |
2819 | would be used when linking---and don't do anything else. With this | |
0c2d1a2a | 2820 | option, GCC does not compile or link anything; it just prints the |
74291a4b MM |
2821 | file name. |
2822 | ||
2823 | @item -print-prog-name=@var{program} | |
2824 | Like @samp{-print-file-name}, but searches for a program such as @samp{cpp}. | |
2825 | ||
2826 | @item -print-libgcc-file-name | |
2827 | Same as @samp{-print-file-name=libgcc.a}. | |
2828 | ||
2829 | This is useful when you use @samp{-nostdlib} or @samp{-nodefaultlibs} | |
2830 | but you do want to link with @file{libgcc.a}. You can do | |
2831 | ||
2832 | @example | |
2833 | gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name` | |
2834 | @end example | |
2835 | ||
2836 | @item -print-search-dirs | |
2837 | Print the name of the configured installation directory and a list of | |
2838 | program and library directories gcc will search---and don't do anything else. | |
2839 | ||
2840 | This is useful when gcc prints the error message | |
3c0b7970 JM |
2841 | @samp{installation problem, cannot exec cpp0: No such file or directory}. |
2842 | To resolve this you either need to put @file{cpp0} and the other compiler | |
74291a4b | 2843 | components where gcc expects to find them, or you can set the environment |
bedc7537 | 2844 | variable @env{GCC_EXEC_PREFIX} to the directory where you installed them. |
74291a4b MM |
2845 | Don't forget the trailing '/'. |
2846 | @xref{Environment Variables}. | |
1f0c3120 JM |
2847 | |
2848 | @item -dumpmachine | |
2849 | Print the compiler's target machine (for example, | |
2850 | @samp{i686-pc-linux-gnu})---and don't do anything else. | |
2851 | ||
2852 | @item -dumpversion | |
2853 | Print the compiler version (for example, @samp{3.0})---and don't do | |
2854 | anything else. | |
2855 | ||
2856 | @item -dumpspecs | |
2857 | Print the compiler's built-in specs---and don't do anything else. (This | |
2858 | is used when GCC itself is being built.) @xref{Spec Files}. | |
74291a4b MM |
2859 | @end table |
2860 | ||
2861 | @node Optimize Options | |
2862 | @section Options That Control Optimization | |
2863 | @cindex optimize options | |
2864 | @cindex options, optimization | |
2865 | ||
2866 | These options control various sorts of optimizations: | |
2867 | ||
2642624b | 2868 | @table @gcctabopt |
74291a4b MM |
2869 | @item -O |
2870 | @itemx -O1 | |
2871 | Optimize. Optimizing compilation takes somewhat more time, and a lot | |
2872 | more memory for a large function. | |
2873 | ||
2874 | Without @samp{-O}, the compiler's goal is to reduce the cost of | |
2875 | compilation and to make debugging produce the expected results. | |
2876 | Statements are independent: if you stop the program with a breakpoint | |
2877 | between statements, you can then assign a new value to any variable or | |
2878 | change the program counter to any other statement in the function and | |
2879 | get exactly the results you would expect from the source code. | |
2880 | ||
2881 | Without @samp{-O}, the compiler only allocates variables declared | |
2882 | @code{register} in registers. The resulting compiled code is a little | |
2883 | worse than produced by PCC without @samp{-O}. | |
2884 | ||
2885 | With @samp{-O}, the compiler tries to reduce code size and execution | |
2886 | time. | |
2887 | ||
2888 | When you specify @samp{-O}, the compiler turns on @samp{-fthread-jumps} | |
2889 | and @samp{-fdefer-pop} on all machines. The compiler turns on | |
2890 | @samp{-fdelayed-branch} on machines that have delay slots, and | |
2891 | @samp{-fomit-frame-pointer} on machines that can support debugging even | |
2892 | without a frame pointer. On some machines the compiler also turns | |
2893 | on other flags.@refill | |
2894 | ||
2895 | @item -O2 | |
0c2d1a2a | 2896 | Optimize even more. GCC performs nearly all supported optimizations |
74291a4b MM |
2897 | that do not involve a space-speed tradeoff. The compiler does not |
2898 | perform loop unrolling or function inlining when you specify @samp{-O2}. | |
2899 | As compared to @samp{-O}, this option increases both compilation time | |
2900 | and the performance of the generated code. | |
2901 | ||
2b2a8f1f RH |
2902 | @samp{-O2} turns on all optional optimizations except for loop unrolling, |
2903 | function inlining, and register renaming. It also turns on the | |
2904 | @samp{-fforce-mem} option on all machines and frame pointer elimination | |
2905 | on machines where doing so does not interfere with debugging. | |
74291a4b MM |
2906 | |
2907 | @item -O3 | |
2908 | Optimize yet more. @samp{-O3} turns on all optimizations specified by | |
2b2a8f1f RH |
2909 | @samp{-O2} and also turns on the @samp{-finline-functions} and |
2910 | @samp{-frename-registers} options. | |
74291a4b MM |
2911 | |
2912 | @item -O0 | |
2913 | Do not optimize. | |
2914 | ||
c6aded7c AG |
2915 | @item -Os |
2916 | Optimize for size. @samp{-Os} enables all @samp{-O2} optimizations that | |
2917 | do not typically increase code size. It also performs further | |
2918 | optimizations designed to reduce code size. | |
2919 | ||
74291a4b MM |
2920 | If you use multiple @samp{-O} options, with or without level numbers, |
2921 | the last such option is the one that is effective. | |
2922 | @end table | |
2923 | ||
2924 | Options of the form @samp{-f@var{flag}} specify machine-independent | |
2925 | flags. Most flags have both positive and negative forms; the negative | |
2926 | form of @samp{-ffoo} would be @samp{-fno-foo}. In the table below, | |
2927 | only one of the forms is listed---the one which is not the default. | |
2928 | You can figure out the other form by either removing @samp{no-} or | |
2929 | adding it. | |
2930 | ||
2642624b | 2931 | @table @gcctabopt |
74291a4b MM |
2932 | @item -ffloat-store |
2933 | Do not store floating point variables in registers, and inhibit other | |
2934 | options that might change whether a floating point value is taken from a | |
2935 | register or memory. | |
2936 | ||
2937 | @cindex floating point precision | |
2938 | This option prevents undesirable excess precision on machines such as | |
2939 | the 68000 where the floating registers (of the 68881) keep more | |
2940 | precision than a @code{double} is supposed to have. Similarly for the | |
2941 | x86 architecture. For most programs, the excess precision does only | |
2942 | good, but a few programs rely on the precise definition of IEEE floating | |
6fd74494 CB |
2943 | point. Use @samp{-ffloat-store} for such programs, after modifying |
2944 | them to store all pertinent intermediate computations into variables. | |
74291a4b MM |
2945 | |
2946 | @item -fno-default-inline | |
2947 | Do not make member functions inline by default merely because they are | |
2948 | defined inside the class scope (C++ only). Otherwise, when you specify | |
2949 | @w{@samp{-O}}, member functions defined inside class scope are compiled | |
2950 | inline by default; i.e., you don't need to add @samp{inline} in front of | |
2951 | the member function name. | |
2952 | ||
2953 | @item -fno-defer-pop | |
2954 | Always pop the arguments to each function call as soon as that function | |
2955 | returns. For machines which must pop arguments after a function call, | |
2956 | the compiler normally lets arguments accumulate on the stack for several | |
2957 | function calls and pops them all at once. | |
2958 | ||
2959 | @item -fforce-mem | |
2960 | Force memory operands to be copied into registers before doing | |
2961 | arithmetic on them. This produces better code by making all memory | |
2962 | references potential common subexpressions. When they are not common | |
2963 | subexpressions, instruction combination should eliminate the separate | |
2964 | register-load. The @samp{-O2} option turns on this option. | |
2965 | ||
2966 | @item -fforce-addr | |
2967 | Force memory address constants to be copied into registers before | |
2968 | doing arithmetic on them. This may produce better code just as | |
2969 | @samp{-fforce-mem} may. | |
2970 | ||
2971 | @item -fomit-frame-pointer | |
2972 | Don't keep the frame pointer in a register for functions that | |
2973 | don't need one. This avoids the instructions to save, set up and | |
2974 | restore frame pointers; it also makes an extra register available | |
2975 | in many functions. @strong{It also makes debugging impossible on | |
2976 | some machines.} | |
2977 | ||
2978 | @ifset INTERNALS | |
2979 | On some machines, such as the Vax, this flag has no effect, because | |
2980 | the standard calling sequence automatically handles the frame pointer | |
2981 | and nothing is saved by pretending it doesn't exist. The | |
2982 | machine-description macro @code{FRAME_POINTER_REQUIRED} controls | |
2983 | whether a target machine supports this flag. @xref{Registers}.@refill | |
2984 | @end ifset | |
2985 | @ifclear INTERNALS | |
2986 | On some machines, such as the Vax, this flag has no effect, because | |
2987 | the standard calling sequence automatically handles the frame pointer | |
2988 | and nothing is saved by pretending it doesn't exist. The | |
2989 | machine-description macro @code{FRAME_POINTER_REQUIRED} controls | |
2990 | whether a target machine supports this flag. @xref{Registers,,Register | |
2991 | Usage, gcc.info, Using and Porting GCC}.@refill | |
2992 | @end ifclear | |
2993 | ||
1aaef9c1 JH |
2994 | @item -foptimize-sibling-calls |
2995 | Optimize sibling and tail recursive calls. | |
2996 | ||
91ce572a CC |
2997 | @item -ftrapv |
2998 | This option generates traps for signed overflow on addition, subtraction, | |
2999 | multiplication operations. | |
3000 | ||
74291a4b MM |
3001 | @item -fno-inline |
3002 | Don't pay attention to the @code{inline} keyword. Normally this option | |
3003 | is used to keep the compiler from expanding any functions inline. | |
3004 | Note that if you are not optimizing, no functions can be expanded inline. | |
3005 | ||
3006 | @item -finline-functions | |
3007 | Integrate all simple functions into their callers. The compiler | |
3008 | heuristically decides which functions are simple enough to be worth | |
3009 | integrating in this way. | |
3010 | ||
3011 | If all calls to a given function are integrated, and the function is | |
3012 | declared @code{static}, then the function is normally not output as | |
3013 | assembler code in its own right. | |
3014 | ||
efa3896a | 3015 | @item -finline-limit=@var{n} |
f9e814f1 TP |
3016 | By default, gcc limits the size of functions that can be inlined. This flag |
3017 | allows the control of this limit for functions that are explicitly marked as | |
02f52e19 AJ |
3018 | inline (ie marked with the inline keyword or defined within the class |
3019 | definition in c++). @var{n} is the size of functions that can be inlined in | |
f9e814f1 TP |
3020 | number of pseudo instructions (not counting parameter handling). The default |
3021 | value of n is 10000. Increasing this value can result in more inlined code at | |
3022 | the cost of compilation time and memory consumption. Decreasing usually makes | |
02f52e19 AJ |
3023 | the compilation faster and less code will be inlined (which presumably |
3024 | means slower programs). This option is particularly useful for programs that | |
f9e814f1 TP |
3025 | use inlining heavily such as those based on recursive templates with c++. |
3026 | ||
3027 | @emph{Note:} pseudo instruction represents, in this particular context, an | |
3028 | abstract measurement of function's size. In no way, it represents a count | |
3029 | of assembly instructions and as such its exact meaning might change from one | |
3030 | release to an another. | |
3031 | ||
74291a4b MM |
3032 | @item -fkeep-inline-functions |
3033 | Even if all calls to a given function are integrated, and the function | |
3034 | is declared @code{static}, nevertheless output a separate run-time | |
3035 | callable version of the function. This switch does not affect | |
3036 | @code{extern inline} functions. | |
3037 | ||
3038 | @item -fkeep-static-consts | |
3039 | Emit variables declared @code{static const} when optimization isn't turned | |
3040 | on, even if the variables aren't referenced. | |
3041 | ||
0c2d1a2a | 3042 | GCC enables this option by default. If you want to force the compiler to |
74291a4b MM |
3043 | check if the variable was referenced, regardless of whether or not |
3044 | optimization is turned on, use the @samp{-fno-keep-static-consts} option. | |
3045 | ||
3046 | @item -fno-function-cse | |
3047 | Do not put function addresses in registers; make each instruction that | |
3048 | calls a constant function contain the function's address explicitly. | |
3049 | ||
3050 | This option results in less efficient code, but some strange hacks | |
3051 | that alter the assembler output may be confused by the optimizations | |
3052 | performed when this option is not used. | |
3053 | ||
3054 | @item -ffast-math | |
de6c5979 BL |
3055 | Sets @samp{-fno-math-errno}, @samp{-funsafe-math-optimizations}, |
3056 | and @samp{-fno-trapping-math}. | |
3057 | ||
3058 | This option causes the preprocessor macro __FAST_MATH__ to be defined. | |
74291a4b MM |
3059 | |
3060 | This option should never be turned on by any @samp{-O} option since | |
3061 | it can result in incorrect output for programs which depend on | |
c1030c7c | 3062 | an exact implementation of IEEE or ISO rules/specifications for |
74291a4b | 3063 | math functions. |
9605da8a BL |
3064 | |
3065 | @item -fno-math-errno | |
3066 | Do not set ERRNO after calling math functions that are executed | |
3067 | with a single instruction, e.g., sqrt. A program that relies on | |
3068 | IEEE exceptions for math error handling may want to use this flag | |
3069 | for speed while maintaining IEEE arithmetic compatibility. | |
3070 | ||
de6c5979 BL |
3071 | This option should never be turned on by any @samp{-O} option since |
3072 | it can result in incorrect output for programs which depend on | |
3073 | an exact implementation of IEEE or ISO rules/specifications for | |
3074 | math functions. | |
3075 | ||
9605da8a BL |
3076 | The default is @samp{-fmath-errno}. The @samp{-ffast-math} option |
3077 | sets @samp{-fno-math-errno}. | |
de6c5979 BL |
3078 | |
3079 | @item -funsafe-math-optimizations | |
3080 | Allow optimizations for floating-point arithmetic that (a) assume | |
3081 | that arguments and results are valid and (b) may violate IEEE or | |
02f52e19 | 3082 | ANSI standards. |
de6c5979 BL |
3083 | |
3084 | This option should never be turned on by any @samp{-O} option since | |
3085 | it can result in incorrect output for programs which depend on | |
3086 | an exact implementation of IEEE or ISO rules/specifications for | |
3087 | math functions. | |
3088 | ||
3089 | The default is @samp{-fno-unsafe-math-optimizations}. The | |
3090 | @samp{-ffast-math} option sets @samp{-funsafe-math-optimizations}. | |
3091 | ||
3092 | @item -fno-trapping-math | |
3093 | Compile code assuming that floating-point operations cannot generate | |
3094 | user-visible traps. Setting this option may allow faster code | |
3095 | if one relies on ``non-stop'' IEEE arithmetic, for example. | |
3096 | ||
3097 | This option should never be turned on by any @samp{-O} option since | |
3098 | it can result in incorrect output for programs which depend on | |
3099 | an exact implementation of IEEE or ISO rules/specifications for | |
3100 | math functions. | |
3101 | ||
3102 | The default is @samp{-ftrapping-math}. The @samp{-ffast-math} | |
3103 | option sets @samp{-fno-trapping-math}. | |
74291a4b MM |
3104 | @end table |
3105 | ||
3106 | @c following causes underfulls.. they don't look great, but we deal. | |
3107 | @c --mew 26jan93 | |
3108 | The following options control specific optimizations. The @samp{-O2} | |
3109 | option turns on all of these optimizations except @samp{-funroll-loops} | |
3110 | and @samp{-funroll-all-loops}. On most machines, the @samp{-O} option | |
3111 | turns on the @samp{-fthread-jumps} and @samp{-fdelayed-branch} options, | |
3112 | but specific machines may handle it differently. | |
3113 | ||
3114 | You can use the following flags in the rare cases when ``fine-tuning'' | |
3115 | of optimizations to be performed is desired. | |
3116 | ||
2642624b | 3117 | @table @gcctabopt |
74291a4b MM |
3118 | @item -fstrength-reduce |
3119 | Perform the optimizations of loop strength reduction and | |
3120 | elimination of iteration variables. | |
3121 | ||
3122 | @item -fthread-jumps | |
3123 | Perform optimizations where we check to see if a jump branches to a | |
3124 | location where another comparison subsumed by the first is found. If | |
3125 | so, the first branch is redirected to either the destination of the | |
3126 | second branch or a point immediately following it, depending on whether | |
3127 | the condition is known to be true or false. | |
3128 | ||
3129 | @item -fcse-follow-jumps | |
3130 | In common subexpression elimination, scan through jump instructions | |
3131 | when the target of the jump is not reached by any other path. For | |
3132 | example, when CSE encounters an @code{if} statement with an | |
3133 | @code{else} clause, CSE will follow the jump when the condition | |
3134 | tested is false. | |
3135 | ||
3136 | @item -fcse-skip-blocks | |
3137 | This is similar to @samp{-fcse-follow-jumps}, but causes CSE to | |
3138 | follow jumps which conditionally skip over blocks. When CSE | |
3139 | encounters a simple @code{if} statement with no else clause, | |
3140 | @samp{-fcse-skip-blocks} causes CSE to follow the jump around the | |
3141 | body of the @code{if}. | |
3142 | ||
3143 | @item -frerun-cse-after-loop | |
3144 | Re-run common subexpression elimination after loop optimizations has been | |
3145 | performed. | |
3146 | ||
6d6d0fa0 JL |
3147 | @item -frerun-loop-opt |
3148 | Run the loop optimizer twice. | |
3149 | ||
7506f491 DE |
3150 | @item -fgcse |
3151 | Perform a global common subexpression elimination pass. | |
3152 | This pass also performs global constant and copy propagation. | |
3153 | ||
a13d4ebf AM |
3154 | @item -fgcse-lm |
3155 | When -fgcse-lm is enabled, global common subexpression elimination will | |
3156 | attempt to move loads which are only killed by stores into themselves. This | |
3157 | allows a loop containing a load/store sequence to be changed to a load outside | |
02f52e19 | 3158 | the loop, and a copy/store within the loop. |
a13d4ebf AM |
3159 | |
3160 | @item -fgcse-sm | |
02f52e19 | 3161 | When -fgcse-sm is enabled, A store motion pass is run after global common |
a13d4ebf AM |
3162 | subexpression elimination. This pass will attempt to move stores out of loops. |
3163 | When used in conjunction with -fgcse-lm, loops containing a load/store sequence | |
3164 | can be changed to a load before the loop and a store after the loop. | |
3165 | ||
b6d24183 JL |
3166 | @item -fdelete-null-pointer-checks |
3167 | Use global dataflow analysis to identify and eliminate useless null | |
3168 | pointer checks. Programs which rely on NULL pointer dereferences @emph{not} | |
3169 | halting the program may not work properly with this option. Use | |
3170 | -fno-delete-null-pointer-checks to disable this optimizing for programs | |
3171 | which depend on that behavior. | |
3172 | ||
74291a4b MM |
3173 | @item -fexpensive-optimizations |
3174 | Perform a number of minor optimizations that are relatively expensive. | |
3175 | ||
639726ba | 3176 | @item -foptimize-register-move |
59d40964 | 3177 | @itemx -fregmove |
9ec36da5 JL |
3178 | Attempt to reassign register numbers in move instructions and as |
3179 | operands of other simple instructions in order to maximize the amount of | |
56159047 | 3180 | register tying. This is especially helpful on machines with two-operand |
0c2d1a2a | 3181 | instructions. GCC enables this optimization by default with @samp{-O2} |
9ec36da5 JL |
3182 | or higher. |
3183 | ||
bedc7537 | 3184 | Note @option{-fregmove} and @option{-foptimize-register-move} are the same |
9ec36da5 JL |
3185 | optimization. |
3186 | ||
74291a4b MM |
3187 | @item -fdelayed-branch |
3188 | If supported for the target machine, attempt to reorder instructions | |
3189 | to exploit instruction slots available after delayed branch | |
3190 | instructions. | |
3191 | ||
3192 | @item -fschedule-insns | |
3193 | If supported for the target machine, attempt to reorder instructions to | |
3194 | eliminate execution stalls due to required data being unavailable. This | |
3195 | helps machines that have slow floating point or memory load instructions | |
3196 | by allowing other instructions to be issued until the result of the load | |
3197 | or floating point instruction is required. | |
3198 | ||
3199 | @item -fschedule-insns2 | |
3200 | Similar to @samp{-fschedule-insns}, but requests an additional pass of | |
3201 | instruction scheduling after register allocation has been done. This is | |
3202 | especially useful on machines with a relatively small number of | |
3203 | registers and where memory load instructions take more than one cycle. | |
3204 | ||
3205 | @item -ffunction-sections | |
59d40964 | 3206 | @itemx -fdata-sections |
7d0756fb CM |
3207 | Place each function or data item into its own section in the output |
3208 | file if the target supports arbitrary sections. The name of the | |
3209 | function or the name of the data item determines the section's name | |
3210 | in the output file. | |
74291a4b | 3211 | |
7d0756fb | 3212 | Use these options on systems where the linker can perform optimizations |
74291a4b MM |
3213 | to improve locality of reference in the instruction space. HPPA |
3214 | processors running HP-UX and Sparc processors running Solaris 2 have | |
3215 | linkers with such optimizations. Other systems using the ELF object format | |
3216 | as well as AIX may have these optimizations in the future. | |
3217 | ||
7d0756fb CM |
3218 | Only use these options when there are significant benefits from doing |
3219 | so. When you specify these options, the assembler and linker will | |
74291a4b MM |
3220 | create larger object and executable files and will also be slower. |
3221 | You will not be able to use @code{gprof} on all systems if you | |
3222 | specify this option and you may have problems with debugging if | |
3223 | you specify both this option and @samp{-g}. | |
3224 | ||
3225 | @item -fcaller-saves | |
3226 | Enable values to be allocated in registers that will be clobbered by | |
3227 | function calls, by emitting extra instructions to save and restore the | |
3228 | registers around such calls. Such allocation is done only when it | |
3229 | seems to result in better code than would otherwise be produced. | |
3230 | ||
81610a0d HPN |
3231 | This option is always enabled by default on certain machines, usually |
3232 | those which have no call-preserved registers to use instead. | |
3233 | ||
3234 | For all machines, optimization level 2 and higher enables this flag by | |
3235 | default. | |
74291a4b MM |
3236 | |
3237 | @item -funroll-loops | |
3238 | Perform the optimization of loop unrolling. This is only done for loops | |
3239 | whose number of iterations can be determined at compile time or run time. | |
1bd31d56 | 3240 | @samp{-funroll-loops} implies both @samp{-fstrength-reduce} and |
74291a4b MM |
3241 | @samp{-frerun-cse-after-loop}. |
3242 | ||
3243 | @item -funroll-all-loops | |
3244 | Perform the optimization of loop unrolling. This is done for all loops | |
3245 | and usually makes programs run more slowly. @samp{-funroll-all-loops} | |
3246 | implies @samp{-fstrength-reduce} as well as @samp{-frerun-cse-after-loop}. | |
3247 | ||
e5eb27e5 JL |
3248 | @item -fmove-all-movables |
3249 | Forces all invariant computations in loops to be moved | |
3250 | outside the loop. | |
3251 | ||
3252 | @item -freduce-all-givs | |
3253 | Forces all general-induction variables in loops to be | |
3254 | strength-reduced. | |
3255 | ||
3256 | @emph{Note:} When compiling programs written in Fortran, | |
1bd31d56 | 3257 | @samp{-fmove-all-movables} and @samp{-freduce-all-givs} are enabled |
e5eb27e5 JL |
3258 | by default when you use the optimizer. |
3259 | ||
3260 | These options may generate better or worse code; results are highly | |
3261 | dependent on the structure of loops within the source code. | |
3262 | ||
3263 | These two options are intended to be removed someday, once | |
3264 | they have helped determine the efficacy of various | |
3265 | approaches to improving loop optimizations. | |
3266 | ||
2642624b | 3267 | Please let us (@w{@email{gcc@@gcc.gnu.org}} and @w{@email{fortran@@gnu.org}}) |
e5eb27e5 JL |
3268 | know how use of these options affects |
3269 | the performance of your production code. | |
3270 | We're very interested in code that runs @emph{slower} | |
3271 | when these options are @emph{enabled}. | |
3272 | ||
74291a4b MM |
3273 | @item -fno-peephole |
3274 | Disable any machine-specific peephole optimizations. | |
861bb6c1 JL |
3275 | |
3276 | @item -fbranch-probabilities | |
3277 | After running a program compiled with @samp{-fprofile-arcs} | |
3278 | (@pxref{Debugging Options,, Options for Debugging Your Program or | |
bedc7537 | 3279 | @command{gcc}}), you can compile it a second time using |
861bb6c1 JL |
3280 | @samp{-fbranch-probabilities}, to improve optimizations based on |
3281 | guessing the path a branch might take. | |
3282 | ||
3283 | @ifset INTERNALS | |
e5e809f4 | 3284 | With @samp{-fbranch-probabilities}, GCC puts a @samp{REG_EXEC_COUNT} |
861bb6c1 JL |
3285 | note on the first instruction of each basic block, and a |
3286 | @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}. | |
3287 | These can be used to improve optimization. Currently, they are only | |
3288 | used in one place: in @file{reorg.c}, instead of guessing which path a | |
3289 | branch is mostly to take, the @samp{REG_BR_PROB} values are used to | |
3290 | exactly determine which path is taken more often. | |
3291 | @end ifset | |
8c660648 | 3292 | |
454d0cc7 AH |
3293 | @item -fno-guess-branch-probability |
3294 | Sometimes gcc will opt to guess branch probabilities when none are | |
3295 | available from either profile directed feedback (@samp{-fprofile-arcs}) | |
2bab2366 | 3296 | or @samp{__builtin_expect}. In a hard real-time system, people don't |
454d0cc7 AH |
3297 | want different runs of the compiler to produce code that has different |
3298 | behavior; minimizing non-determinism is of paramount import. This | |
3299 | switch allows users to reduce non-determinism, possibly at the expense | |
3300 | of inferior optimization. | |
3301 | ||
41472af8 MM |
3302 | @item -fstrict-aliasing |
3303 | Allows the compiler to assume the strictest aliasing rules applicable to | |
3304 | the language being compiled. For C (and C++), this activates | |
3305 | optimizations based on the type of expressions. In particular, an | |
3306 | object of one type is assumed never to reside at the same address as an | |
3307 | object of a different type, unless the types are almost the same. For | |
3308 | example, an @code{unsigned int} can alias an @code{int}, but not a | |
3309 | @code{void*} or a @code{double}. A character type may alias any other | |
02f52e19 | 3310 | type. |
41472af8 MM |
3311 | |
3312 | Pay special attention to code like this: | |
3313 | @example | |
02f52e19 | 3314 | union a_union @{ |
41472af8 MM |
3315 | int i; |
3316 | double d; | |
3317 | @}; | |
3318 | ||
3319 | int f() @{ | |
3320 | a_union t; | |
3321 | t.d = 3.0; | |
3322 | return t.i; | |
3323 | @} | |
3324 | @end example | |
3325 | The practice of reading from a different union member than the one most | |
3326 | recently written to (called ``type-punning'') is common. Even with | |
3327 | @samp{-fstrict-aliasing}, type-punning is allowed, provided the memory | |
3328 | is accessed through the union type. So, the code above will work as | |
3329 | expected. However, this code might not: | |
3330 | @example | |
02f52e19 | 3331 | int f() @{ |
41472af8 MM |
3332 | a_union t; |
3333 | int* ip; | |
3334 | t.d = 3.0; | |
3335 | ip = &t.i; | |
3336 | return *ip; | |
3337 | @} | |
3338 | @end example | |
3339 | ||
41472af8 MM |
3340 | @ifset INTERNALS |
3341 | Every language that wishes to perform language-specific alias analysis | |
3342 | should define a function that computes, given an @code{tree} | |
3343 | node, an alias set for the node. Nodes in different alias sets are not | |
3344 | allowed to alias. For an example, see the C front-end function | |
3345 | @code{c_get_alias_set}. | |
3346 | @end ifset | |
3347 | ||
efa3896a GK |
3348 | @item -falign-functions |
3349 | @itemx -falign-functions=@var{n} | |
3350 | Align the start of functions to the next power-of-two greater than | |
3351 | @var{n}, skipping up to @var{n} bytes. For instance, | |
3352 | @samp{-falign-functions=32} aligns functions to the next 32-byte | |
3353 | boundary, but @samp{-falign-functions=24} would align to the next | |
3354 | 32-byte boundary only if this can be done by skipping 23 bytes or less. | |
3355 | ||
3356 | @samp{-fno-align-functions} and @samp{-falign-functions=1} are | |
3357 | equivalent and mean that functions will not be aligned. | |
3358 | ||
3359 | Some assemblers only support this flag when @var{n} is a power of two; | |
3360 | in that case, it is rounded up. | |
3361 | ||
3362 | If @var{n} is not specified, use a machine-dependent default. | |
3363 | ||
3364 | @item -falign-labels | |
3365 | @itemx -falign-labels=@var{n} | |
3366 | Align all branch targets to a power-of-two boundary, skipping up to | |
3367 | @var{n} bytes like @samp{-falign-functions}. This option can easily | |
3368 | make code slower, because it must insert dummy operations for when the | |
3369 | branch target is reached in the usual flow of the code. | |
3370 | ||
3371 | If @samp{-falign-loops} or @samp{-falign-jumps} are applicable and | |
3372 | are greater than this value, then their values are used instead. | |
3373 | ||
3374 | If @var{n} is not specified, use a machine-dependent default which is | |
3375 | very likely to be @samp{1}, meaning no alignment. | |
3376 | ||
3377 | @item -falign-loops | |
3378 | @itemx -falign-loops=@var{n} | |
3379 | Align loops to a power-of-two boundary, skipping up to @var{n} bytes | |
3380 | like @samp{-falign-functions}. The hope is that the loop will be | |
3381 | executed many times, which will make up for any execution of the dummy | |
3382 | operations. | |
3383 | ||
3384 | If @var{n} is not specified, use a machine-dependent default. | |
3385 | ||
3386 | @item -falign-jumps | |
3387 | @itemx -falign-jumps=@var{n} | |
3388 | Align branch targets to a power-of-two boundary, for branch targets | |
3389 | where the targets can only be reached by jumping, skipping up to @var{n} | |
3390 | bytes like @samp{-falign-functions}. In this case, no dummy operations | |
3391 | need be executed. | |
3392 | ||
3393 | If @var{n} is not specified, use a machine-dependent default. | |
3394 | ||
4bae0b47 AS |
3395 | @item -fssa |
3396 | Perform optimizations in static single assignment form. Each function's | |
3397 | flow graph is translated into SSA form, optimizations are performed, and | |
90ecce3e | 3398 | the flow graph is translated back from SSA form. Users should not |
b53978a3 JO |
3399 | specify this option, since it is not yet ready for production use. |
3400 | ||
3401 | @item -fdce | |
3402 | Perform dead-code elimination in SSA form. Requires @samp{-fssa}. Like | |
3403 | @samp{-fssa}, this is an experimental feature. | |
4bae0b47 | 3404 | |
46d3a873 CC |
3405 | @item -fsingle-precision-constant |
3406 | Treat floating point constant as single precision constant instead of | |
3407 | implicitly converting it to double precision constant. | |
3408 | ||
2b2a8f1f RH |
3409 | @item -frename-registers |
3410 | Attempt to avoid false dependancies in scheduled code by making use | |
3411 | of registers left over after register allocation. This optimization | |
3412 | will most benefit processors with lots of registers. It can, however, | |
3413 | make debugging impossible, since variables will no longer stay in | |
3414 | a ``home register''. | |
3af64fd6 MM |
3415 | |
3416 | @item --param @var{name}=@var{value} | |
3417 | In some places, GCC uses various constants to control the amount of | |
3418 | optimization that is done. For example, GCC will not inline functions | |
3419 | that contain more that a certain number of instructions. You can | |
3420 | control some of these constants on the command-line using the | |
02f52e19 | 3421 | @samp{--param} option. |
3af64fd6 MM |
3422 | |
3423 | In each case, the @var{value} is a integer. The allowable choices for | |
3424 | @var{name} are given in the following table: | |
3425 | ||
3426 | @table @gcctabopt | |
1c4c47db JO |
3427 | @item max-delay-slot-insn-search |
3428 | The maximum number of instructions to consider when looking for an | |
3429 | instruction to fill a delay slot. If more than this arbitrary number of | |
3430 | instructions is searched, the time savings from filling the delay slot | |
3431 | will be minimal so stop searching. Increasing values mean more | |
3432 | aggressive optimization, making the compile time increase with probably | |
3433 | small improvement in executable run time. | |
3434 | ||
3435 | @item max-delay-slot-live-search | |
3436 | When trying to fill delay slots, the maximum number of instructions to | |
3437 | consider when searching for a block with valid live register | |
3438 | information. Increasing this arbitrarily chosen value means more | |
3439 | aggressive optimization, increasing the compile time. This parameter | |
3440 | should be removed when the delay slot code is rewritten to maintain the | |
3441 | control-flow graph. | |
33d3b05b MM |
3442 | |
3443 | @item max-gcse-memory | |
3444 | The approximate maximum amount of memory that will be allocated in | |
3445 | order to perform the global common subexpression elimination | |
3446 | optimization. If more memory than specified is required, the | |
3447 | optimization will not be done. | |
3af64fd6 | 3448 | |
1c4c47db JO |
3449 | @item max-inline-insns |
3450 | If an function contains more than this many instructions, it | |
3451 | will not be inlined. This option is precisely equivalent to | |
3452 | @samp{-finline-limit}. | |
3453 | ||
3454 | @end table | |
74291a4b MM |
3455 | @end table |
3456 | ||
3457 | @node Preprocessor Options | |
3458 | @section Options Controlling the Preprocessor | |
3459 | @cindex preprocessor options | |
3460 | @cindex options, preprocessor | |
3461 | ||
3462 | These options control the C preprocessor, which is run on each C source | |
3463 | file before actual compilation. | |
3464 | ||
3465 | If you use the @samp{-E} option, nothing is done except preprocessing. | |
3466 | Some of these options make sense only together with @samp{-E} because | |
3467 | they cause the preprocessor output to be unsuitable for actual | |
3468 | compilation. | |
3469 | ||
2642624b | 3470 | @table @gcctabopt |
74291a4b MM |
3471 | @item -include @var{file} |
3472 | Process @var{file} as input before processing the regular input file. | |
3473 | In effect, the contents of @var{file} are compiled first. Any @samp{-D} | |
3474 | and @samp{-U} options on the command line are always processed before | |
3475 | @samp{-include @var{file}}, regardless of the order in which they are | |
3476 | written. All the @samp{-include} and @samp{-imacros} options are | |
3477 | processed in the order in which they are written. | |
3478 | ||
3479 | @item -imacros @var{file} | |
3480 | Process @var{file} as input, discarding the resulting output, before | |
3481 | processing the regular input file. Because the output generated from | |
3482 | @var{file} is discarded, the only effect of @samp{-imacros @var{file}} | |
3483 | is to make the macros defined in @var{file} available for use in the | |
e582248c NB |
3484 | main input. All the @samp{-include} and @samp{-imacros} options are |
3485 | processed in the order in which they are written. | |
74291a4b MM |
3486 | |
3487 | @item -idirafter @var{dir} | |
3488 | @cindex second include path | |
3489 | Add the directory @var{dir} to the second include path. The directories | |
3490 | on the second include path are searched when a header file is not found | |
3491 | in any of the directories in the main include path (the one that | |
3492 | @samp{-I} adds to). | |
3493 | ||
3494 | @item -iprefix @var{prefix} | |
3495 | Specify @var{prefix} as the prefix for subsequent @samp{-iwithprefix} | |
3496 | options. | |
3497 | ||
3498 | @item -iwithprefix @var{dir} | |
3499 | Add a directory to the second include path. The directory's name is | |
3500 | made by concatenating @var{prefix} and @var{dir}, where @var{prefix} was | |
3501 | specified previously with @samp{-iprefix}. If you have not specified a | |
3502 | prefix yet, the directory containing the installed passes of the | |
3503 | compiler is used as the default. | |
3504 | ||
3505 | @item -iwithprefixbefore @var{dir} | |
3506 | Add a directory to the main include path. The directory's name is made | |
3507 | by concatenating @var{prefix} and @var{dir}, as in the case of | |
3508 | @samp{-iwithprefix}. | |
3509 | ||
3510 | @item -isystem @var{dir} | |
3511 | Add a directory to the beginning of the second include path, marking it | |
3512 | as a system directory, so that it gets the same special treatment as | |
3513 | is applied to the standard system directories. | |
3514 | ||
3515 | @item -nostdinc | |
3516 | Do not search the standard system directories for header files. Only | |
3517 | the directories you have specified with @samp{-I} options (and the | |
3518 | current directory, if appropriate) are searched. @xref{Directory | |
3519 | Options}, for information on @samp{-I}. | |
3520 | ||
3521 | By using both @samp{-nostdinc} and @samp{-I-}, you can limit the include-file | |
3522 | search path to only those directories you specify explicitly. | |
3523 | ||
e582248c NB |
3524 | @item -remap |
3525 | @findex -remap | |
3526 | When searching for a header file in a directory, remap file names if a | |
3527 | file named @file{header.gcc} exists in that directory. This can be used | |
3528 | to work around limitations of file systems with file name restrictions. | |
3529 | The @file{header.gcc} file should contain a series of lines with two | |
3530 | tokens on each line: the first token is the name to map, and the second | |
3531 | token is the actual name to use. | |
3532 | ||
74291a4b MM |
3533 | @item -undef |
3534 | Do not predefine any nonstandard macros. (Including architecture flags). | |
3535 | ||
3536 | @item -E | |
3537 | Run only the C preprocessor. Preprocess all the C source files | |
3538 | specified and output the results to standard output or to the | |
3539 | specified output file. | |
3540 | ||
3541 | @item -C | |
3542 | Tell the preprocessor not to discard comments. Used with the | |
3543 | @samp{-E} option. | |
3544 | ||
3545 | @item -P | |
3546 | Tell the preprocessor not to generate @samp{#line} directives. | |
3547 | Used with the @samp{-E} option. | |
3548 | ||
3549 | @cindex make | |
3550 | @cindex dependencies, make | |
3551 | @item -M | |
e582248c NB |
3552 | @findex -M |
3553 | Instead of outputting the result of preprocessing, output a rule | |
3554 | suitable for @code{make} describing the dependencies of the main source | |
3555 | file. The preprocessor outputs one @code{make} rule containing the | |
3556 | object file name for that source file, a colon, and the names of all the | |
48ce6bbb NS |
3557 | included files. Unless overridden explicitly, the object file name |
3558 | consists of the basename of the source file with any suffix replaced with | |
3559 | object file suffix. If there are many included files then the | |
3560 | rule is split into several lines using @samp{\}-newline. | |
74291a4b MM |
3561 | |
3562 | @samp{-M} implies @samp{-E}. | |
3563 | ||
e582248c NB |
3564 | @item -MM |
3565 | @findex -MM | |
3566 | Like @samp{-M}, but mention only the files included with @samp{#include | |
3567 | "@var{file}"}. System header files included with @samp{#include | |
3568 | <@var{file}>} are omitted. | |
3569 | ||
7da723ef NB |
3570 | @item -MD |
3571 | @findex -MD | |
3572 | Like @samp{-M} but the dependency information is written to a file | |
3573 | rather than stdout. @code{gcc} will use the same file name and | |
3574 | directory as the object file, but with the suffix ".d" instead. | |
3575 | ||
3576 | This is in addition to compiling the main file as specified --- | |
3577 | @samp{-MD} does not inhibit ordinary compilation the way @samp{-M} does, | |
3578 | unless you also specify @samp{-MG}. | |
3579 | ||
3580 | With Mach, you can use the utility @code{md} to merge multiple | |
3581 | dependency files into a single dependency file suitable for using with | |
3582 | the @samp{make} command. | |
3583 | ||
d396403a | 3584 | @item -MMD |
7da723ef NB |
3585 | @findex -MMD |
3586 | Like @samp{-MD} except mention only user header files, not system | |
3587 | -header files. | |
3588 | ||
e582248c NB |
3589 | @item -MF @var{file} |
3590 | @findex -MF | |
3591 | When used with @samp{-M} or @samp{-MM}, specifies a file to write the | |
3592 | dependencies to. This allows the preprocessor to write the preprocessed | |
3593 | file to stdout normally. If no @samp{-MF} switch is given, CPP sends | |
3594 | the rules to stdout and suppresses normal preprocessed output. | |
3595 | ||
74291a4b | 3596 | Another way to specify output of a @code{make} rule is by setting |
bedc7537 | 3597 | the environment variable @env{DEPENDENCIES_OUTPUT} (@pxref{Environment |
74291a4b MM |
3598 | Variables}). |
3599 | ||
74291a4b | 3600 | @item -MG |
e582248c NB |
3601 | @findex -MG |
3602 | When used with @samp{-M} or @samp{-MM}, @samp{-MG} says to treat missing | |
3603 | header files as generated files and assume they live in the same | |
3604 | directory as the source file. It suppresses preprocessed output, as a | |
3605 | missing header file is ordinarily an error. | |
3606 | ||
3607 | This feature is used in automatic updating of makefiles. | |
3608 | ||
3609 | @item -MP | |
3610 | @findex -MP | |
3611 | This option instructs CPP to add a phony target for each dependency | |
3612 | other than the main file, causing each to depend on nothing. These | |
3613 | dummy rules work around errors @code{make} gives if you remove header | |
3614 | files without updating the @code{Makefile} to match. | |
3615 | ||
3616 | This is typical output:- | |
3617 | ||
3618 | @smallexample | |
3619 | /tmp/test.o: /tmp/test.c /tmp/test.h | |
3620 | ||
3621 | /tmp/test.h: | |
3622 | @end smallexample | |
3623 | ||
3624 | @item -MQ @var{target} | |
3625 | @item -MT @var{target} | |
3626 | @findex -MQ | |
3627 | @findex -MT | |
3628 | By default CPP uses the main file name, including any path, and appends | |
3629 | the object suffix, normally ``.o'', to it to obtain the name of the | |
3630 | target for dependency generation. With @samp{-MT} you can specify a | |
3631 | target yourself, overriding the default one. | |
3632 | ||
3633 | If you want multiple targets, you can specify them as a single argument | |
3634 | to @samp{-MT}, or use multiple @samp{-MT} options. | |
3635 | ||
3636 | The targets you specify are output in the order they appear on the | |
3637 | command line. @samp{-MQ} is identical to @samp{-MT}, except that the | |
3638 | target name is quoted for Make, but with @samp{-MT} it isn't. For | |
3639 | example, -MT '$(objpfx)foo.o' gives | |
3640 | ||
3641 | @smallexample | |
3642 | $(objpfx)foo.o: /tmp/foo.c | |
3643 | @end smallexample | |
3644 | ||
3645 | but -MQ '$(objpfx)foo.o' gives | |
3646 | ||
3647 | @smallexample | |
3648 | $$(objpfx)foo.o: /tmp/foo.c | |
3649 | @end smallexample | |
3650 | ||
3651 | The default target is automatically quoted, as if it were given with | |
3652 | @samp{-MQ}. | |
74291a4b MM |
3653 | |
3654 | @item -H | |
3655 | Print the name of each header file used, in addition to other normal | |
3656 | activities. | |
3657 | ||
3658 | @item -A@var{question}(@var{answer}) | |
3659 | Assert the answer @var{answer} for @var{question}, in case it is tested | |
3660 | with a preprocessing conditional such as @samp{#if | |
3661 | #@var{question}(@var{answer})}. @samp{-A-} disables the standard | |
3662 | assertions that normally describe the target machine. | |
3663 | ||
3664 | @item -D@var{macro} | |
3665 | Define macro @var{macro} with the string @samp{1} as its definition. | |
3666 | ||
3667 | @item -D@var{macro}=@var{defn} | |
3668 | Define macro @var{macro} as @var{defn}. All instances of @samp{-D} on | |
3669 | the command line are processed before any @samp{-U} options. | |
3670 | ||
e582248c NB |
3671 | Any @samp{-D} and @samp{-U} options on the command line are processed in |
3672 | order, and always before @samp{-imacros @var{file}}, regardless of the | |
3673 | order in which they are written. | |
3674 | ||
74291a4b MM |
3675 | @item -U@var{macro} |
3676 | Undefine macro @var{macro}. @samp{-U} options are evaluated after all | |
3677 | @samp{-D} options, but before any @samp{-include} and @samp{-imacros} | |
3678 | options. | |
3679 | ||
e582248c NB |
3680 | Any @samp{-D} and @samp{-U} options on the command line are processed in |
3681 | order, and always before @samp{-imacros @var{file}}, regardless of the | |
3682 | order in which they are written. | |
3683 | ||
74291a4b MM |
3684 | @item -dM |
3685 | Tell the preprocessor to output only a list of the macro definitions | |
3686 | that are in effect at the end of preprocessing. Used with the @samp{-E} | |
3687 | option. | |
3688 | ||
3689 | @item -dD | |
3690 | Tell the preprocessing to pass all macro definitions into the output, in | |
3691 | their proper sequence in the rest of the output. | |
3692 | ||
3693 | @item -dN | |
3694 | Like @samp{-dD} except that the macro arguments and contents are omitted. | |
3695 | Only @samp{#define @var{name}} is included in the output. | |
3696 | ||
e582248c NB |
3697 | @item -dI |
3698 | @findex -dI | |
3699 | Output @samp{#include} directives in addition to the result of | |
3700 | preprocessing. | |
3701 | ||
74291a4b | 3702 | @item -trigraphs |
e582248c NB |
3703 | @findex -trigraphs |
3704 | Process ISO standard trigraph sequences. These are three-character | |
3705 | sequences, all starting with @samp{??}, that are defined by ISO C to | |
3706 | stand for single characters. For example, @samp{??/} stands for | |
3707 | @samp{\}, so @samp{'??/n'} is a character constant for a newline. By | |
3708 | default, GCC ignores trigraphs, but in standard-conforming modes it | |
3709 | converts them. See the @samp{-std} and @samp{-ansi} options. | |
3710 | ||
3711 | The nine trigraph sequences are | |
3712 | @table @samp | |
3713 | @item ??( | |
3714 | -> @samp{[} | |
3715 | ||
3716 | @item ??) | |
3717 | -> @samp{]} | |
3718 | ||
3719 | @item ??< | |
3720 | -> @samp{@{} | |
3721 | ||
3722 | @item ??> | |
3723 | -> @samp{@}} | |
3724 | ||
3725 | @item ??= | |
3726 | -> @samp{#} | |
3727 | ||
3728 | @item ??/ | |
3729 | -> @samp{\} | |
3730 | ||
3731 | @item ??' | |
3732 | -> @samp{^} | |
3733 | ||
3734 | @item ??! | |
3735 | -> @samp{|} | |
3736 | ||
3737 | @item ??- | |
3738 | -> @samp{~} | |
3739 | ||
3740 | @end table | |
3741 | ||
3742 | Trigraph support is not popular, so many compilers do not implement it | |
3743 | properly. Portable code should not rely on trigraphs being either | |
3744 | converted or ignored. | |
74291a4b | 3745 | |
371e300b | 3746 | @item -Wp\,@var{option} |
bedc7537 | 3747 | Pass @var{option} as an option to the preprocessor. If @var{option} |
74291a4b MM |
3748 | contains commas, it is split into multiple options at the commas. |
3749 | @end table | |
3750 | ||
3751 | @node Assembler Options | |
3752 | @section Passing Options to the Assembler | |
3753 | ||
3754 | @c prevent bad page break with this line | |
3755 | You can pass options to the assembler. | |
3756 | ||
2642624b | 3757 | @table @gcctabopt |
371e300b | 3758 | @item -Wa\,@var{option} |
74291a4b MM |
3759 | Pass @var{option} as an option to the assembler. If @var{option} |
3760 | contains commas, it is split into multiple options at the commas. | |
3761 | @end table | |
3762 | ||
3763 | @node Link Options | |
3764 | @section Options for Linking | |
3765 | @cindex link options | |
3766 | @cindex options, linking | |
3767 | ||
3768 | These options come into play when the compiler links object files into | |
3769 | an executable output file. They are meaningless if the compiler is | |
3770 | not doing a link step. | |
3771 | ||
2642624b | 3772 | @table @gcctabopt |
74291a4b MM |
3773 | @cindex file names |
3774 | @item @var{object-file-name} | |
3775 | A file name that does not end in a special recognized suffix is | |
3776 | considered to name an object file or library. (Object files are | |
3777 | distinguished from libraries by the linker according to the file | |
3778 | contents.) If linking is done, these object files are used as input | |
3779 | to the linker. | |
3780 | ||
3781 | @item -c | |
3782 | @itemx -S | |
3783 | @itemx -E | |
3784 | If any of these options is used, then the linker is not run, and | |
3785 | object file names should not be used as arguments. @xref{Overall | |
3786 | Options}. | |
3787 | ||
3788 | @cindex Libraries | |
3789 | @item -l@var{library} | |
4275c4c4 JS |
3790 | @itemx -l @var{library} |
3791 | Search the library named @var{library} when linking. (The second | |
3792 | alternative with the library as a separate argument is only for | |
3793 | POSIX compliance and is not recommended.) | |
74291a4b MM |
3794 | |
3795 | It makes a difference where in the command you write this option; the | |
4275c4c4 | 3796 | linker searches and processes libraries and object files in the order they |
74291a4b MM |
3797 | are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z} |
3798 | after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers | |
3799 | to functions in @samp{z}, those functions may not be loaded. | |
3800 | ||
3801 | The linker searches a standard list of directories for the library, | |
3802 | which is actually a file named @file{lib@var{library}.a}. The linker | |
3803 | then uses this file as if it had been specified precisely by name. | |
3804 | ||
3805 | The directories searched include several standard system directories | |
3806 | plus any that you specify with @samp{-L}. | |
3807 | ||
3808 | Normally the files found this way are library files---archive files | |
3809 | whose members are object files. The linker handles an archive file by | |
3810 | scanning through it for members which define symbols that have so far | |
3811 | been referenced but not defined. But if the file that is found is an | |
3812 | ordinary object file, it is linked in the usual fashion. The only | |
3813 | difference between using an @samp{-l} option and specifying a file name | |
3814 | is that @samp{-l} surrounds @var{library} with @samp{lib} and @samp{.a} | |
3815 | and searches several directories. | |
3816 | ||
3817 | @item -lobjc | |
3818 | You need this special case of the @samp{-l} option in order to | |
3819 | link an Objective C program. | |
3820 | ||
3821 | @item -nostartfiles | |
3822 | Do not use the standard system startup files when linking. | |
bedc7537 NC |
3823 | The standard system libraries are used normally, unless @option{-nostdlib} |
3824 | or @option{-nodefaultlibs} is used. | |
74291a4b MM |
3825 | |
3826 | @item -nodefaultlibs | |
3827 | Do not use the standard system libraries when linking. | |
3828 | Only the libraries you specify will be passed to the linker. | |
bedc7537 | 3829 | The standard startup files are used normally, unless @option{-nostartfiles} |
4754172c | 3830 | is used. The compiler may generate calls to memcmp, memset, and memcpy |
c1030c7c | 3831 | for System V (and ISO C) environments or to bcopy and bzero for |
4754172c CM |
3832 | BSD environments. These entries are usually resolved by entries in |
3833 | libc. These entry points should be supplied through some other | |
3834 | mechanism when this option is specified. | |
74291a4b MM |
3835 | |
3836 | @item -nostdlib | |
3837 | Do not use the standard system startup files or libraries when linking. | |
3838 | No startup files and only the libraries you specify will be passed to | |
4754172c | 3839 | the linker. The compiler may generate calls to memcmp, memset, and memcpy |
c1030c7c | 3840 | for System V (and ISO C) environments or to bcopy and bzero for |
4754172c CM |
3841 | BSD environments. These entries are usually resolved by entries in |
3842 | libc. These entry points should be supplied through some other | |
3843 | mechanism when this option is specified. | |
74291a4b MM |
3844 | |
3845 | @cindex @code{-lgcc}, use with @code{-nostdlib} | |
3846 | @cindex @code{-nostdlib} and unresolved references | |
3847 | @cindex unresolved references and @code{-nostdlib} | |
3848 | @cindex @code{-lgcc}, use with @code{-nodefaultlibs} | |
3849 | @cindex @code{-nodefaultlibs} and unresolved references | |
3850 | @cindex unresolved references and @code{-nodefaultlibs} | |
3851 | One of the standard libraries bypassed by @samp{-nostdlib} and | |
3852 | @samp{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines | |
0c2d1a2a | 3853 | that GCC uses to overcome shortcomings of particular machines, or special |
74291a4b MM |
3854 | needs for some languages. |
3855 | @ifset INTERNALS | |
0c2d1a2a | 3856 | (@xref{Interface,,Interfacing to GCC Output}, for more discussion of |
74291a4b MM |
3857 | @file{libgcc.a}.) |
3858 | @end ifset | |
3859 | @ifclear INTERNALS | |
0c2d1a2a | 3860 | (@xref{Interface,,Interfacing to GCC Output,gcc.info,Porting GCC}, |
74291a4b MM |
3861 | for more discussion of @file{libgcc.a}.) |
3862 | @end ifclear | |
3863 | In most cases, you need @file{libgcc.a} even when you want to avoid | |
3864 | other standard libraries. In other words, when you specify @samp{-nostdlib} | |
3865 | or @samp{-nodefaultlibs} you should usually specify @samp{-lgcc} as well. | |
0c2d1a2a | 3866 | This ensures that you have no unresolved references to internal GCC |
74291a4b | 3867 | library subroutines. (For example, @samp{__main}, used to ensure C++ |
bedc7537 | 3868 | constructors will be called; @pxref{Collect2,,@command{collect2}}.) |
74291a4b MM |
3869 | |
3870 | @item -s | |
3871 | Remove all symbol table and relocation information from the executable. | |
3872 | ||
3873 | @item -static | |
3874 | On systems that support dynamic linking, this prevents linking with the shared | |
3875 | libraries. On other systems, this option has no effect. | |
3876 | ||
3877 | @item -shared | |
3878 | Produce a shared object which can then be linked with other objects to | |
1d3b0e2c | 3879 | form an executable. Not all systems support this option. For predictable |
02f52e19 | 3880 | results, you must also specify the same set of options that were used to |
1d3b0e2c | 3881 | generate code (@samp{-fpic}, @samp{-fPIC}, or model suboptions) |
2642624b | 3882 | when you specify this option.@footnote{On some systems, @samp{gcc -shared} |
1d3b0e2c | 3883 | needs to build supplementary stub code for constructors to work. On |
2642624b | 3884 | multi-libbed systems, @samp{gcc -shared} must select the correct support |
1d3b0e2c ME |
3885 | libraries to link against. Failing to supply the correct flags may lead |
3886 | to subtle defects. Supplying them in cases where they are not necessary | |
3887 | is innocuous.} | |
74291a4b | 3888 | |
9db0819e RH |
3889 | @item -shared-libgcc |
3890 | @itemx -static-libgcc | |
3891 | On systems that provide @file{libgcc} as a shared library, these options | |
3892 | force the use of either the shared or static version respectively. | |
3893 | If no shared version of @file{libgcc} was built when the compiler was | |
3894 | configured, these options have no effect. | |
3895 | ||
3896 | There are several situations in which an application should use the | |
3897 | shared @file{libgcc} instead of the static version. The most common | |
3898 | of these is when the application wishes to throw and catch exceptions | |
3899 | across different shared libraries. In that case, each of the libraries | |
3900 | as well as the application itself should use the shared @file{libgcc}. | |
3901 | ||
049f6ec9 MM |
3902 | Therefore, whenever you specify the @samp{-shared} option, the GCC |
3903 | driver automatically adds @samp{-shared-libgcc}, unless you explicitly | |
3904 | specify @samp{-static-libgcc}. The G++ driver automatically adds | |
3905 | @samp{-shared-libgcc} when you build a main executable as well because | |
3906 | for C++ programs that is typically the right thing to do. | |
3907 | (Exception-handling will not work reliably otherwise.) | |
3908 | ||
3909 | However, when linking a main executable written in C, you must | |
3910 | explicitly say @samp{-shared-libgcc} if you want to use the shared | |
3911 | @file{libgcc}. | |
9db0819e | 3912 | |
74291a4b MM |
3913 | @item -symbolic |
3914 | Bind references to global symbols when building a shared object. Warn | |
3915 | about any unresolved references (unless overridden by the link editor | |
3916 | option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support | |
3917 | this option. | |
3918 | ||
3919 | @item -Xlinker @var{option} | |
3920 | Pass @var{option} as an option to the linker. You can use this to | |
0c2d1a2a | 3921 | supply system-specific linker options which GCC does not know how to |
74291a4b MM |
3922 | recognize. |
3923 | ||
3924 | If you want to pass an option that takes an argument, you must use | |
3925 | @samp{-Xlinker} twice, once for the option and once for the argument. | |
3926 | For example, to pass @samp{-assert definitions}, you must write | |
3927 | @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write | |
3928 | @samp{-Xlinker "-assert definitions"}, because this passes the entire | |
3929 | string as a single argument, which is not what the linker expects. | |
3930 | ||
371e300b | 3931 | @item -Wl\,@var{option} |
74291a4b MM |
3932 | Pass @var{option} as an option to the linker. If @var{option} contains |
3933 | commas, it is split into multiple options at the commas. | |
3934 | ||
3935 | @item -u @var{symbol} | |
3936 | Pretend the symbol @var{symbol} is undefined, to force linking of | |
3937 | library modules to define it. You can use @samp{-u} multiple times with | |
3938 | different symbols to force loading of additional library modules. | |
3939 | @end table | |
3940 | ||
3941 | @node Directory Options | |
3942 | @section Options for Directory Search | |
3943 | @cindex directory options | |
3944 | @cindex options, directory search | |
3945 | @cindex search path | |
3946 | ||
3947 | These options specify directories to search for header files, for | |
3948 | libraries and for parts of the compiler: | |
3949 | ||
2642624b | 3950 | @table @gcctabopt |
74291a4b | 3951 | @item -I@var{dir} |
861bb6c1 JL |
3952 | Add the directory @var{dir} to the head of the list of directories to be |
3953 | searched for header files. This can be used to override a system header | |
3954 | file, substituting your own version, since these directories are | |
d0a5eb32 RK |
3955 | searched before the system header file directories. However, you should |
3956 | not use this option to add directories that contain vendor-supplied | |
3957 | system header files (use @samp{-isystem} for that). If you use more than | |
3958 | one @samp{-I} option, the directories are scanned in left-to-right | |
74291a4b MM |
3959 | order; the standard system directories come after. |
3960 | ||
3961 | @item -I- | |
3962 | Any directories you specify with @samp{-I} options before the @samp{-I-} | |
3963 | option are searched only for the case of @samp{#include "@var{file}"}; | |
3964 | they are not searched for @samp{#include <@var{file}>}. | |
3965 | ||
3966 | If additional directories are specified with @samp{-I} options after | |
3967 | the @samp{-I-}, these directories are searched for all @samp{#include} | |
3968 | directives. (Ordinarily @emph{all} @samp{-I} directories are used | |
3969 | this way.) | |
3970 | ||
3971 | In addition, the @samp{-I-} option inhibits the use of the current | |
3972 | directory (where the current input file came from) as the first search | |
3973 | directory for @samp{#include "@var{file}"}. There is no way to | |
3974 | override this effect of @samp{-I-}. With @samp{-I.} you can specify | |
3975 | searching the directory which was current when the compiler was | |
3976 | invoked. That is not exactly the same as what the preprocessor does | |
3977 | by default, but it is often satisfactory. | |
3978 | ||
3979 | @samp{-I-} does not inhibit the use of the standard system directories | |
3980 | for header files. Thus, @samp{-I-} and @samp{-nostdinc} are | |
3981 | independent. | |
3982 | ||
3983 | @item -L@var{dir} | |
3984 | Add directory @var{dir} to the list of directories to be searched | |
3985 | for @samp{-l}. | |
3986 | ||
3987 | @item -B@var{prefix} | |
3988 | This option specifies where to find the executables, libraries, | |
3989 | include files, and data files of the compiler itself. | |
3990 | ||
3991 | The compiler driver program runs one or more of the subprograms | |
3992 | @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries | |
3993 | @var{prefix} as a prefix for each program it tries to run, both with and | |
3994 | without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}). | |
3995 | ||
3996 | For each subprogram to be run, the compiler driver first tries the | |
3997 | @samp{-B} prefix, if any. If that name is not found, or if @samp{-B} | |
3998 | was not specified, the driver tries two standard prefixes, which are | |
3999 | @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc-lib/}. If neither of | |
4000 | those results in a file name that is found, the unmodified program | |
4001 | name is searched for using the directories specified in your | |
bedc7537 | 4002 | @env{PATH} environment variable. |
74291a4b MM |
4003 | |
4004 | @samp{-B} prefixes that effectively specify directory names also apply | |
4005 | to libraries in the linker, because the compiler translates these | |
4006 | options into @samp{-L} options for the linker. They also apply to | |
4007 | includes files in the preprocessor, because the compiler translates these | |
4008 | options into @samp{-isystem} options for the preprocessor. In this case, | |
4009 | the compiler appends @samp{include} to the prefix. | |
4010 | ||
4011 | The run-time support file @file{libgcc.a} can also be searched for using | |
4012 | the @samp{-B} prefix, if needed. If it is not found there, the two | |
4013 | standard prefixes above are tried, and that is all. The file is left | |
4014 | out of the link if it is not found by those means. | |
4015 | ||
4016 | Another way to specify a prefix much like the @samp{-B} prefix is to use | |
bedc7537 | 4017 | the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment |
74291a4b | 4018 | Variables}. |
861bb6c1 JL |
4019 | |
4020 | @item -specs=@var{file} | |
4021 | Process @var{file} after the compiler reads in the standard @file{specs} | |
4022 | file, in order to override the defaults that the @file{gcc} driver | |
4023 | program uses when determining what switches to pass to @file{cc1}, | |
4024 | @file{cc1plus}, @file{as}, @file{ld}, etc. More than one | |
4025 | @samp{-specs=}@var{file} can be specified on the command line, and they | |
4026 | are processed in order, from left to right. | |
74291a4b MM |
4027 | @end table |
4028 | ||
ee457005 JM |
4029 | @c man end |
4030 | ||
a743d340 NC |
4031 | @node Spec Files |
4032 | @section Specifying subprocesses and the switches to pass to them | |
4033 | @cindex Spec Files | |
bedc7537 | 4034 | @command{gcc} is a driver program. It performs its job by invoking a |
a743d340 NC |
4035 | sequence of other programs to do the work of compiling, assembling and |
4036 | linking. GCC interprets its command-line parameters and uses these to | |
4037 | deduce which programs it should invoke, and which command-line options | |
4038 | it ought to place on their command lines. This behaviour is controlled | |
4039 | by @dfn{spec strings}. In most cases there is one spec string for each | |
4040 | program that GCC can invoke, but a few programs have multiple spec | |
4041 | strings to control their behaviour. The spec strings built into GCC can | |
4042 | be overridden by using the @samp{-specs=} command-line switch to specify | |
4043 | a spec file. | |
4044 | ||
4045 | @dfn{Spec files} are plaintext files that are used to construct spec | |
4046 | strings. They consist of a sequence of directives separated by blank | |
4047 | lines. The type of directive is determined by the first non-whitespace | |
4048 | character on the line and it can be one of the following: | |
4049 | ||
4050 | @table @code | |
4051 | @item %@var{command} | |
4052 | Issues a @var{command} to the spec file processor. The commands that can | |
02f52e19 | 4053 | appear here are: |
a743d340 NC |
4054 | |
4055 | @table @code | |
4056 | @item %include <@var{file}> | |
4057 | @cindex %include | |
4058 | Search for @var{file} and insert its text at the current point in the | |
4059 | specs file. | |
4060 | ||
4061 | @item %include_noerr <@var{file}> | |
4062 | @cindex %include_noerr | |
4063 | Just like @samp{%include}, but do not generate an error message if the include | |
4064 | file cannot be found. | |
4065 | ||
4066 | @item %rename @var{old_name} @var{new_name} | |
4067 | @cindex %rename | |
4068 | Rename the spec string @var{old_name} to @var{new_name}. | |
4069 | ||
4070 | @end table | |
4071 | ||
4072 | @item *[@var{spec_name}]: | |
4073 | This tells the compiler to create, override or delete the named spec | |
4074 | string. All lines after this directive up to the next directive or | |
4075 | blank line are considered to be the text for the spec string. If this | |
4076 | results in an empty string then the spec will be deleted. (Or, if the | |
4077 | spec did not exist, then nothing will happened.) Otherwise, if the spec | |
4078 | does not currently exist a new spec will be created. If the spec does | |
4079 | exist then its contents will be overridden by the text of this | |
4080 | directive, unless the first character of that text is the @samp{+} | |
4081 | character, in which case the text will be appended to the spec. | |
4082 | ||
4083 | @item [@var{suffix}]: | |
4084 | Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive | |
4085 | and up to the next directive or blank line are considered to make up the | |
02f52e19 | 4086 | spec string for the indicated suffix. When the compiler encounters an |
a743d340 NC |
4087 | input file with the named suffix, it will processes the spec string in |
4088 | order to work out how to compile that file. For example: | |
4089 | ||
4090 | @smallexample | |
4091 | .ZZ: | |
4092 | z-compile -input %i | |
4093 | @end smallexample | |
4094 | ||
4095 | This says that any input file whose name ends in @samp{.ZZ} should be | |
4096 | passed to the program @samp{z-compile}, which should be invoked with the | |
4097 | command-line switch @samp{-input} and with the result of performing the | |
4098 | @samp{%i} substitution. (See below.) | |
4099 | ||
4100 | As an alternative to providing a spec string, the text that follows a | |
4101 | suffix directive can be one of the following: | |
4102 | ||
4103 | @table @code | |
4104 | @item @@@var{language} | |
4105 | This says that the suffix is an alias for a known @var{language}. This is | |
bedc7537 | 4106 | similar to using the @option{-x} command-line switch to GCC to specify a |
a743d340 NC |
4107 | language explicitly. For example: |
4108 | ||
4109 | @smallexample | |
4110 | .ZZ: | |
4111 | @@c++ | |
4112 | @end smallexample | |
4113 | ||
4114 | Says that .ZZ files are, in fact, C++ source files. | |
4115 | ||
4116 | @item #@var{name} | |
4117 | This causes an error messages saying: | |
4118 | ||
4119 | @smallexample | |
4120 | @var{name} compiler not installed on this system. | |
4121 | @end smallexample | |
4122 | @end table | |
4123 | ||
4124 | GCC already has an extensive list of suffixes built into it. | |
4125 | This directive will add an entry to the end of the list of suffixes, but | |
4126 | since the list is searched from the end backwards, it is effectively | |
4127 | possible to override earlier entries using this technique. | |
4128 | ||
4129 | @end table | |
4130 | ||
4131 | GCC has the following spec strings built into it. Spec files can | |
4132 | override these strings or create their own. Note that individual | |
02f52e19 | 4133 | targets can also add their own spec strings to this list. |
a743d340 NC |
4134 | |
4135 | @smallexample | |
4136 | asm Options to pass to the assembler | |
4137 | asm_final Options to pass to the assembler post-processor | |
4138 | cpp Options to pass to the C preprocessor | |
4139 | cc1 Options to pass to the C compiler | |
4140 | cc1plus Options to pass to the C++ compiler | |
4141 | endfile Object files to include at the end of the link | |
4142 | link Options to pass to the linker | |
4143 | lib Libraries to include on the command line to the linker | |
4144 | libgcc Decides which GCC support library to pass to the linker | |
4145 | linker Sets the name of the linker | |
4146 | predefines Defines to be passed to the C preprocessor | |
4147 | signed_char Defines to pass to CPP to say whether @code{char} is signed by default | |
4148 | startfile Object files to include at the start of the link | |
4149 | @end smallexample | |
4150 | ||
4151 | Here is a small example of a spec file: | |
4152 | ||
4153 | @smallexample | |
4154 | %rename lib old_lib | |
4155 | ||
4156 | *lib: | |
4157 | --start-group -lgcc -lc -leval1 --end-group %(old_lib) | |
4158 | @end smallexample | |
4159 | ||
4160 | This example renames the spec called @samp{lib} to @samp{old_lib} and | |
4161 | then overrides the previous definition of @samp{lib} with a new one. | |
4162 | The new definition adds in some extra command-line options before | |
4163 | including the text of the old definition. | |
4164 | ||
4165 | @dfn{Spec strings} are a list of command-line options to be passed to their | |
4166 | corresponding program. In addition, the spec strings can contain | |
4167 | @samp{%}-prefixed sequences to substitute variable text or to | |
4168 | conditionally insert text into the command line. Using these constructs | |
4169 | it is possible to generate quite complex command lines. | |
4170 | ||
4171 | Here is a table of all defined @samp{%}-sequences for spec | |
4172 | strings. Note that spaces are not generated automatically around the | |
4173 | results of expanding these sequences. Therefore you can concatenate them | |
02f52e19 | 4174 | together or combine them with constant text in a single argument. |
a743d340 NC |
4175 | |
4176 | @table @code | |
4177 | @item %% | |
4178 | Substitute one @samp{%} into the program name or argument. | |
4179 | ||
4180 | @item %i | |
4181 | Substitute the name of the input file being processed. | |
4182 | ||
4183 | @item %b | |
4184 | Substitute the basename of the input file being processed. | |
4185 | This is the substring up to (and not including) the last period | |
4186 | and not including the directory. | |
4187 | ||
371e300b NC |
4188 | @item %B |
4189 | This is the same as @samp{%b}, but include the file suffix (text after | |
4190 | the last period). | |
4191 | ||
a743d340 NC |
4192 | @item %d |
4193 | Marks the argument containing or following the @samp{%d} as a | |
4194 | temporary file name, so that that file will be deleted if GCC exits | |
4195 | successfully. Unlike @samp{%g}, this contributes no text to the | |
02f52e19 | 4196 | argument. |
a743d340 NC |
4197 | |
4198 | @item %g@var{suffix} | |
4199 | Substitute a file name that has suffix @var{suffix} and is chosen | |
4200 | once per compilation, and mark the argument in the same way as | |
4201 | @samp{%d}. To reduce exposure to denial-of-service attacks, the file | |
02f52e19 | 4202 | name is now chosen in a way that is hard to predict even when previously |
a743d340 NC |
4203 | chosen file names are known. For example, @samp{%g.s ... %g.o ... %g.s} |
4204 | might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches | |
4205 | the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is | |
4206 | treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g} | |
4207 | was simply substituted with a file name chosen once per compilation, | |
4208 | without regard to any appended suffix (which was therefore treated | |
4209 | just like ordinary text), making such attacks more likely to succeed. | |
4210 | ||
4211 | @item %u@var{suffix} | |
4212 | Like @samp{%g}, but generates a new temporary file name even if | |
4213 | @samp{%u@var{suffix}} was already seen. | |
4214 | ||
4215 | @item %U@var{suffix} | |
4216 | Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a | |
4217 | new one if there is no such last file name. In the absence of any | |
4218 | @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share | |
4219 | the same suffix @emph{space}, so @samp{%g.s ... %U.s ... %g.s ... %U.s} | |
4220 | would involve the generation of two distinct file names, one | |
4221 | for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was | |
4222 | simply substituted with a file name chosen for the previous @samp{%u}, | |
4223 | without regard to any appended suffix. | |
4224 | ||
371e300b | 4225 | @item %j@var{SUFFIX} |
02f52e19 | 4226 | Substitutes the name of the HOST_BIT_BUCKET, if any, and if it is |
371e300b NC |
4227 | writable, and if save-temps is off; otherwise, substitute the name |
4228 | of a temporary file, just like @samp{%u}. This temporary file is not | |
4229 | meant for communication between processes, but rather as a junk | |
4230 | disposal mechanism. | |
4231 | ||
4232 | @item %.@var{SUFFIX} | |
4233 | Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args | |
4234 | when it is subsequently output with @samp{%*}. @var{SUFFIX} is | |
4235 | terminated by the next space or %. | |
4236 | ||
a743d340 NC |
4237 | @item %w |
4238 | Marks the argument containing or following the @samp{%w} as the | |
4239 | designated output file of this compilation. This puts the argument | |
4240 | into the sequence of arguments that @samp{%o} will substitute later. | |
4241 | ||
4242 | @item %o | |
4243 | Substitutes the names of all the output files, with spaces | |
4244 | automatically placed around them. You should write spaces | |
4245 | around the @samp{%o} as well or the results are undefined. | |
4246 | @samp{%o} is for use in the specs for running the linker. | |
4247 | Input files whose names have no recognized suffix are not compiled | |
4248 | at all, but they are included among the output files, so they will | |
4249 | be linked. | |
4250 | ||
4251 | @item %O | |
4252 | Substitutes the suffix for object files. Note that this is | |
4253 | handled specially when it immediately follows @samp{%g, %u, or %U}, | |
4254 | because of the need for those to form complete file names. The | |
4255 | handling is such that @samp{%O} is treated exactly as if it had already | |
4256 | been substituted, except that @samp{%g, %u, and %U} do not currently | |
4257 | support additional @var{suffix} characters following @samp{%O} as they would | |
4258 | following, for example, @samp{.o}. | |
4259 | ||
4260 | @item %p | |
4261 | Substitutes the standard macro predefinitions for the | |
4262 | current target machine. Use this when running @code{cpp}. | |
4263 | ||
4264 | @item %P | |
4265 | Like @samp{%p}, but puts @samp{__} before and after the name of each | |
4266 | predefined macro, except for macros that start with @samp{__} or with | |
c1030c7c | 4267 | @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO |
02f52e19 | 4268 | C. |
a743d340 NC |
4269 | |
4270 | @item %I | |
4271 | Substitute a @samp{-iprefix} option made from GCC_EXEC_PREFIX. | |
4272 | ||
4273 | @item %s | |
4274 | Current argument is the name of a library or startup file of some sort. | |
4275 | Search for that file in a standard list of directories and substitute | |
02f52e19 | 4276 | the full name found. |
a743d340 NC |
4277 | |
4278 | @item %e@var{str} | |
4279 | Print @var{str} as an error message. @var{str} is terminated by a newline. | |
4280 | Use this when inconsistent options are detected. | |
4281 | ||
4282 | @item %| | |
4283 | Output @samp{-} if the input for the current command is coming from a pipe. | |
4284 | ||
4285 | @item %(@var{name}) | |
4286 | Substitute the contents of spec string @var{name} at this point. | |
4287 | ||
4288 | @item %[@var{name}] | |
4289 | Like @samp{%(...)} but put @samp{__} around @samp{-D} arguments. | |
4290 | ||
4291 | @item %x@{@var{option}@} | |
4292 | Accumulate an option for @samp{%X}. | |
4293 | ||
4294 | @item %X | |
4295 | Output the accumulated linker options specified by @samp{-Wl} or a @samp{%x} | |
4296 | spec string. | |
4297 | ||
4298 | @item %Y | |
4299 | Output the accumulated assembler options specified by @samp{-Wa}. | |
4300 | ||
4301 | @item %Z | |
4302 | Output the accumulated preprocessor options specified by @samp{-Wp}. | |
4303 | ||
4304 | @item %v1 | |
4305 | Substitute the major version number of GCC. | |
4306 | (For version 2.9.5, this is 2.) | |
4307 | ||
4308 | @item %v2 | |
4309 | Substitute the minor version number of GCC. | |
4310 | (For version 2.9.5, this is 9.) | |
4311 | ||
371e300b NC |
4312 | @item %v3 |
4313 | Substitute the patch level number of GCC. | |
4314 | (For version 2.9.5, this is 5.) | |
4315 | ||
a743d340 NC |
4316 | @item %a |
4317 | Process the @code{asm} spec. This is used to compute the | |
4318 | switches to be passed to the assembler. | |
4319 | ||
4320 | @item %A | |
4321 | Process the @code{asm_final} spec. This is a spec string for | |
4322 | passing switches to an assembler post-processor, if such a program is | |
4323 | needed. | |
4324 | ||
4325 | @item %l | |
4326 | Process the @code{link} spec. This is the spec for computing the | |
4327 | command line passed to the linker. Typically it will make use of the | |
4328 | @samp{%L %G %S %D and %E} sequences. | |
4329 | ||
4330 | @item %D | |
4331 | Dump out a @samp{-L} option for each directory that GCC believes might | |
4332 | contain startup files. If the target supports multilibs then the | |
02f52e19 | 4333 | current multilib directory will be prepended to each of these paths. |
a743d340 | 4334 | |
371e300b NC |
4335 | @item %M |
4336 | Output the multilib directory with directory seperators replaced with | |
4337 | "_". If multilib directories are not set, or the multilib directory is | |
4338 | "." then this option emits nothing. | |
4339 | ||
a743d340 NC |
4340 | @item %L |
4341 | Process the @code{lib} spec. This is a spec string for deciding which | |
02f52e19 | 4342 | libraries should be included on the command line to the linker. |
a743d340 NC |
4343 | |
4344 | @item %G | |
4345 | Process the @code{libgcc} spec. This is a spec string for deciding | |
02f52e19 | 4346 | which GCC support library should be included on the command line to the linker. |
a743d340 NC |
4347 | |
4348 | @item %S | |
4349 | Process the @code{startfile} spec. This is a spec for deciding which | |
4350 | object files should be the first ones passed to the linker. Typically | |
02f52e19 | 4351 | this might be a file named @file{crt0.o}. |
a743d340 NC |
4352 | |
4353 | @item %E | |
4354 | Process the @code{endfile} spec. This is a spec string that specifies | |
02f52e19 | 4355 | the last object files that will be passed to the linker. |
a743d340 NC |
4356 | |
4357 | @item %C | |
4358 | Process the @code{cpp} spec. This is used to construct the arguments | |
4359 | to be passed to the C preprocessor. | |
4360 | ||
4361 | @item %c | |
4362 | Process the @code{signed_char} spec. This is intended to be used | |
02f52e19 | 4363 | to tell cpp whether a char is signed. It typically has the definition: |
a743d340 NC |
4364 | @smallexample |
4365 | %@{funsigned-char:-D__CHAR_UNSIGNED__@} | |
4366 | @end smallexample | |
4367 | ||
4368 | @item %1 | |
4369 | Process the @code{cc1} spec. This is used to construct the options to be | |
4370 | passed to the actual C compiler (@samp{cc1}). | |
4371 | ||
4372 | @item %2 | |
4373 | Process the @code{cc1plus} spec. This is used to construct the options to be | |
4374 | passed to the actual C++ compiler (@samp{cc1plus}). | |
4375 | ||
4376 | @item %* | |
4377 | Substitute the variable part of a matched option. See below. | |
4378 | Note that each comma in the substituted string is replaced by | |
4379 | a single space. | |
4380 | ||
4381 | @item %@{@code{S}@} | |
4382 | Substitutes the @code{-S} switch, if that switch was given to GCC. | |
4383 | If that switch was not specified, this substitutes nothing. Note that | |
4384 | the leading dash is omitted when specifying this option, and it is | |
4385 | automatically inserted if the substitution is performed. Thus the spec | |
4386 | string @samp{%@{foo@}} would match the command-line option @samp{-foo} | |
4387 | and would output the command line option @samp{-foo}. | |
4388 | ||
4389 | @item %W@{@code{S}@} | |
4390 | Like %@{@code{S}@} but mark last argument supplied within as a file to be | |
02f52e19 | 4391 | deleted on failure. |
a743d340 NC |
4392 | |
4393 | @item %@{@code{S}*@} | |
4394 | Substitutes all the switches specified to GCC whose names start | |
4395 | with @code{-S}, but which also take an argument. This is used for | |
4396 | switches like @samp{-o, -D, -I}, etc. GCC considers @samp{-o foo} as being | |
4397 | one switch whose names starts with @samp{o}. %@{o*@} would substitute this | |
02f52e19 | 4398 | text, including the space. Thus two arguments would be generated. |
a743d340 NC |
4399 | |
4400 | @item %@{^@code{S}*@} | |
4401 | Like %@{@code{S}*@}, but don't put a blank between a switch and its | |
4402 | argument. Thus %@{^o*@} would only generate one argument, not two. | |
4403 | ||
371e300b NC |
4404 | @item %@{@code{S}*&@code{T}*@} |
4405 | Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options | |
4406 | (the order of @code{S} and @code{T} in the spec is not significant). | |
4407 | There can be any number of ampersand-separated variables; for each the | |
4408 | wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}. | |
4409 | ||
d630442f | 4410 | @item %@{<@code{S}@} |
50c57e7b | 4411 | Remove all occurrences of @code{-S} from the command line. Note - this |
d630442f | 4412 | command is position dependent. @samp{%} commands in the spec string |
50c57e7b | 4413 | before this option will see @code{-S}, @samp{%} commands in the spec |
d630442f NC |
4414 | string after this option will not. |
4415 | ||
a743d340 NC |
4416 | @item %@{@code{S}*:@code{X}@} |
4417 | Substitutes @code{X} if one or more switches whose names start with | |
4418 | @code{-S} are specified to GCC. Note that the tail part of the | |
4419 | @code{-S} option (i.e. the part matched by the @samp{*}) will be substituted | |
02f52e19 | 4420 | for each occurrence of @samp{%*} within @code{X}. |
a743d340 NC |
4421 | |
4422 | @item %@{@code{S}:@code{X}@} | |
4423 | Substitutes @code{X}, but only if the @samp{-S} switch was given to GCC. | |
4424 | ||
4425 | @item %@{!@code{S}:@code{X}@} | |
4426 | Substitutes @code{X}, but only if the @samp{-S} switch was @emph{not} given to GCC. | |
4427 | ||
4428 | @item %@{|@code{S}:@code{X}@} | |
4429 | Like %@{@code{S}:@code{X}@}, but if no @code{S} switch, substitute @samp{-}. | |
4430 | ||
4431 | @item %@{|!@code{S}:@code{X}@} | |
4432 | Like %@{!@code{S}:@code{X}@}, but if there is an @code{S} switch, substitute @samp{-}. | |
4433 | ||
4434 | @item %@{.@code{S}:@code{X}@} | |
4435 | Substitutes @code{X}, but only if processing a file with suffix @code{S}. | |
4436 | ||
4437 | @item %@{!.@code{S}:@code{X}@} | |
4438 | Substitutes @code{X}, but only if @emph{not} processing a file with suffix @code{S}. | |
4439 | ||
4440 | @item %@{@code{S}|@code{P}:@code{X}@} | |
4441 | Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC. This may be | |
4442 | combined with @samp{!} and @samp{.} sequences as well, although they | |
4443 | have a stronger binding than the @samp{|}. For example a spec string | |
4444 | like this: | |
4445 | ||
4446 | @smallexample | |
4447 | %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@} | |
4448 | @end smallexample | |
4449 | ||
4450 | will output the following command-line options from the following input | |
4451 | command-line options: | |
4452 | ||
4453 | @smallexample | |
4454 | fred.c -foo -baz | |
4455 | jim.d -bar -boggle | |
4456 | -d fred.c -foo -baz -boggle | |
4457 | -d jim.d -bar -baz -boggle | |
4458 | @end smallexample | |
4459 | ||
4460 | @end table | |
4461 | ||
4462 | The conditional text @code{X} in a %@{@code{S}:@code{X}@} or | |
4463 | %@{!@code{S}:@code{X}@} construct may contain other nested @samp{%} constructs | |
4464 | or spaces, or even newlines. They are processed as usual, as described | |
02f52e19 | 4465 | above. |
a743d340 NC |
4466 | |
4467 | The @samp{-O, -f, -m, and -W} switches are handled specifically in these | |
4468 | constructs. If another value of @samp{-O} or the negated form of a @samp{-f, -m, or | |
4469 | -W} switch is found later in the command line, the earlier switch | |
4470 | value is ignored, except with @{@code{S}*@} where @code{S} is just one | |
4471 | letter, which passes all matching options. | |
4472 | ||
4473 | The character @samp{|} at the beginning of the predicate text is used to indicate | |
4474 | that a command should be piped to the following command, but only if @samp{-pipe} | |
4475 | is specified. | |
4476 | ||
4477 | It is built into GCC which switches take arguments and which do not. | |
4478 | (You might think it would be useful to generalize this to allow each | |
4479 | compiler's spec to say which switches take arguments. But this cannot | |
4480 | be done in a consistent fashion. GCC cannot even decide which input | |
4481 | files have been specified without knowing which switches take arguments, | |
4482 | and it must know which input files to compile in order to tell which | |
02f52e19 | 4483 | compilers to run). |
a743d340 NC |
4484 | |
4485 | GCC also knows implicitly that arguments starting in @samp{-l} are to be | |
4486 | treated as compiler output files, and passed to the linker in their | |
4487 | proper position among the other output files. | |
4488 | ||
ee457005 JM |
4489 | @c man begin OPTIONS |
4490 | ||
74291a4b MM |
4491 | @node Target Options |
4492 | @section Specifying Target Machine and Compiler Version | |
4493 | @cindex target options | |
4494 | @cindex cross compiling | |
4495 | @cindex specifying machine version | |
4496 | @cindex specifying compiler version and target machine | |
4497 | @cindex compiler version, specifying | |
4498 | @cindex target machine, specifying | |
4499 | ||
0c2d1a2a | 4500 | By default, GCC compiles code for the same type of machine that you |
74291a4b MM |
4501 | are using. However, it can also be installed as a cross-compiler, to |
4502 | compile for some other type of machine. In fact, several different | |
0c2d1a2a | 4503 | configurations of GCC, for different target machines, can be |
74291a4b MM |
4504 | installed side by side. Then you specify which one to use with the |
4505 | @samp{-b} option. | |
4506 | ||
0c2d1a2a | 4507 | In addition, older and newer versions of GCC can be installed side |
74291a4b MM |
4508 | by side. One of them (probably the newest) will be the default, but |
4509 | you may sometimes wish to use another. | |
4510 | ||
2642624b | 4511 | @table @gcctabopt |
74291a4b MM |
4512 | @item -b @var{machine} |
4513 | The argument @var{machine} specifies the target machine for compilation. | |
0c2d1a2a | 4514 | This is useful when you have installed GCC as a cross-compiler. |
74291a4b MM |
4515 | |
4516 | The value to use for @var{machine} is the same as was specified as the | |
0c2d1a2a | 4517 | machine type when configuring GCC as a cross-compiler. For |
74291a4b MM |
4518 | example, if a cross-compiler was configured with @samp{configure |
4519 | i386v}, meaning to compile for an 80386 running System V, then you | |
4520 | would specify @samp{-b i386v} to run that cross compiler. | |
4521 | ||
4522 | When you do not specify @samp{-b}, it normally means to compile for | |
4523 | the same type of machine that you are using. | |
4524 | ||
4525 | @item -V @var{version} | |
0c2d1a2a | 4526 | The argument @var{version} specifies which version of GCC to run. |
74291a4b | 4527 | This is useful when multiple versions are installed. For example, |
0c2d1a2a | 4528 | @var{version} might be @samp{2.0}, meaning to run GCC version 2.0. |
74291a4b MM |
4529 | |
4530 | The default version, when you do not specify @samp{-V}, is the last | |
0c2d1a2a | 4531 | version of GCC that you installed. |
74291a4b MM |
4532 | @end table |
4533 | ||
4534 | The @samp{-b} and @samp{-V} options actually work by controlling part of | |
4535 | the file name used for the executable files and libraries used for | |
0c2d1a2a | 4536 | compilation. A given version of GCC, for a given target machine, is |
74291a4b MM |
4537 | normally kept in the directory @file{/usr/local/lib/gcc-lib/@var{machine}/@var{version}}.@refill |
4538 | ||
4539 | Thus, sites can customize the effect of @samp{-b} or @samp{-V} either by | |
4540 | changing the names of these directories or adding alternate names (or | |
4541 | symbolic links). If in directory @file{/usr/local/lib/gcc-lib/} the | |
4542 | file @file{80386} is a link to the file @file{i386v}, then @samp{-b | |
4543 | 80386} becomes an alias for @samp{-b i386v}. | |
4544 | ||
4545 | In one respect, the @samp{-b} or @samp{-V} do not completely change | |
bedc7537 | 4546 | to a different compiler: the top-level driver program @command{gcc} |
74291a4b MM |
4547 | that you originally invoked continues to run and invoke the other |
4548 | executables (preprocessor, compiler per se, assembler and linker) | |
4549 | that do the real work. However, since no real work is done in the | |
4550 | driver program, it usually does not matter that the driver program | |
8c7b74b9 JM |
4551 | in use is not the one for the specified target. It is common for the |
4552 | interface to the other executables to change incompatibly between | |
4553 | compiler versions, so unless the version specified is very close to that | |
4554 | of the driver (for example, @samp{-V 3.0} with a driver program from GCC | |
4555 | version 3.0.1), use of @samp{-V} may not work; for example, using | |
4556 | @samp{-V 2.95.2} will not work with a driver program from GCC 3.0. | |
74291a4b MM |
4557 | |
4558 | The only way that the driver program depends on the target machine is | |
4559 | in the parsing and handling of special machine-specific options. | |
4560 | However, this is controlled by a file which is found, along with the | |
4561 | other executables, in the directory for the specified version and | |
4562 | target machine. As a result, a single installed driver program adapts | |
8c7b74b9 JM |
4563 | to any specified target machine, and sufficiently similar compiler |
4564 | versions. | |
74291a4b MM |
4565 | |
4566 | The driver program executable does control one significant thing, | |
4567 | however: the default version and target machine. Therefore, you can | |
4568 | install different instances of the driver program, compiled for | |
4569 | different targets or versions, under different names. | |
4570 | ||
bedc7537 NC |
4571 | For example, if the driver for version 2.0 is installed as @command{ogcc} |
4572 | and that for version 2.1 is installed as @command{gcc}, then the command | |
4573 | @command{gcc} will use version 2.1 by default, while @command{ogcc} will use | |
74291a4b MM |
4574 | 2.0 by default. However, you can choose either version with either |
4575 | command with the @samp{-V} option. | |
4576 | ||
4577 | @node Submodel Options | |
4578 | @section Hardware Models and Configurations | |
4579 | @cindex submodel options | |
4580 | @cindex specifying hardware config | |
4581 | @cindex hardware models and configurations, specifying | |
4582 | @cindex machine dependent options | |
4583 | ||
4584 | Earlier we discussed the standard option @samp{-b} which chooses among | |
4585 | different installed compilers for completely different target | |
4586 | machines, such as Vax vs. 68000 vs. 80386. | |
4587 | ||
4588 | In addition, each of these target machine types can have its own | |
4589 | special options, starting with @samp{-m}, to choose among various | |
4590 | hardware models or configurations---for example, 68010 vs 68020, | |
4591 | floating coprocessor or none. A single installed version of the | |
4592 | compiler can compile for any model or configuration, according to the | |
4593 | options specified. | |
4594 | ||
4595 | Some configurations of the compiler also support additional special | |
4596 | options, usually for compatibility with other compilers on the same | |
4597 | platform. | |
4598 | ||
4599 | @ifset INTERNALS | |
4600 | These options are defined by the macro @code{TARGET_SWITCHES} in the | |
4601 | machine description. The default for the options is also defined by | |
4602 | that macro, which enables you to change the defaults. | |
4603 | @end ifset | |
4604 | ||
4605 | @menu | |
4606 | * M680x0 Options:: | |
2856c3e3 | 4607 | * M68hc1x Options:: |
74291a4b MM |
4608 | * VAX Options:: |
4609 | * SPARC Options:: | |
4610 | * Convex Options:: | |
4611 | * AMD29K Options:: | |
4612 | * ARM Options:: | |
ecff22ab | 4613 | * MN10200 Options:: |
6d6d0fa0 | 4614 | * MN10300 Options:: |
861bb6c1 | 4615 | * M32R/D Options:: |
74291a4b MM |
4616 | * M88K Options:: |
4617 | * RS/6000 and PowerPC Options:: | |
4618 | * RT Options:: | |
4619 | * MIPS Options:: | |
4620 | * i386 Options:: | |
4621 | * HPPA Options:: | |
4622 | * Intel 960 Options:: | |
4623 | * DEC Alpha Options:: | |
4624 | * Clipper Options:: | |
4625 | * H8/300 Options:: | |
4626 | * SH Options:: | |
4627 | * System V Options:: | |
282a61e6 | 4628 | * TMS320C3x/C4x Options:: |
f84271d9 | 4629 | * V850 Options:: |
56b2d7a7 | 4630 | * ARC Options:: |
83575957 | 4631 | * NS32K Options:: |
052a4b28 DC |
4632 | * AVR Options:: |
4633 | * MCore Options:: | |
df6194d4 | 4634 | * IA-64 Options:: |
e8ad90e5 | 4635 | * D30V Options:: |
74291a4b MM |
4636 | @end menu |
4637 | ||
4638 | @node M680x0 Options | |
4639 | @subsection M680x0 Options | |
4640 | @cindex M680x0 options | |
4641 | ||
4642 | These are the @samp{-m} options defined for the 68000 series. The default | |
4643 | values for these options depends on which style of 68000 was selected when | |
4644 | the compiler was configured; the defaults for the most common choices are | |
4645 | given below. | |
4646 | ||
2642624b | 4647 | @table @gcctabopt |
74291a4b MM |
4648 | @item -m68000 |
4649 | @itemx -mc68000 | |
4650 | Generate output for a 68000. This is the default | |
4651 | when the compiler is configured for 68000-based systems. | |
4652 | ||
74cf1c6d RK |
4653 | Use this option for microcontrollers with a 68000 or EC000 core, |
4654 | including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356. | |
4655 | ||
74291a4b MM |
4656 | @item -m68020 |
4657 | @itemx -mc68020 | |
4658 | Generate output for a 68020. This is the default | |
4659 | when the compiler is configured for 68020-based systems. | |
4660 | ||
4661 | @item -m68881 | |
4662 | Generate output containing 68881 instructions for floating point. | |
4663 | This is the default for most 68020 systems unless @samp{-nfp} was | |
4664 | specified when the compiler was configured. | |
4665 | ||
4666 | @item -m68030 | |
4667 | Generate output for a 68030. This is the default when the compiler is | |
4668 | configured for 68030-based systems. | |
4669 | ||
4670 | @item -m68040 | |
4671 | Generate output for a 68040. This is the default when the compiler is | |
4672 | configured for 68040-based systems. | |
4673 | ||
4674 | This option inhibits the use of 68881/68882 instructions that have to be | |
74cf1c6d RK |
4675 | emulated by software on the 68040. Use this option if your 68040 does not |
4676 | have code to emulate those instructions. | |
74291a4b MM |
4677 | |
4678 | @item -m68060 | |
4679 | Generate output for a 68060. This is the default when the compiler is | |
4680 | configured for 68060-based systems. | |
4681 | ||
4682 | This option inhibits the use of 68020 and 68881/68882 instructions that | |
74cf1c6d RK |
4683 | have to be emulated by software on the 68060. Use this option if your 68060 |
4684 | does not have code to emulate those instructions. | |
4685 | ||
4686 | @item -mcpu32 | |
4687 | Generate output for a CPU32. This is the default | |
4688 | when the compiler is configured for CPU32-based systems. | |
4689 | ||
4690 | Use this option for microcontrollers with a | |
4691 | CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334, | |
4692 | 68336, 68340, 68341, 68349 and 68360. | |
74291a4b MM |
4693 | |
4694 | @item -m5200 | |
4695 | Generate output for a 520X "coldfire" family cpu. This is the default | |
4696 | when the compiler is configured for 520X-based systems. | |
4697 | ||
02f52e19 | 4698 | Use this option for microcontroller with a 5200 core, including |
74cf1c6d RK |
4699 | the MCF5202, MCF5203, MCF5204 and MCF5202. |
4700 | ||
74291a4b MM |
4701 | |
4702 | @item -m68020-40 | |
4703 | Generate output for a 68040, without using any of the new instructions. | |
4704 | This results in code which can run relatively efficiently on either a | |
4705 | 68020/68881 or a 68030 or a 68040. The generated code does use the | |
4706 | 68881 instructions that are emulated on the 68040. | |
4707 | ||
861bb6c1 JL |
4708 | @item -m68020-60 |
4709 | Generate output for a 68060, without using any of the new instructions. | |
4710 | This results in code which can run relatively efficiently on either a | |
4711 | 68020/68881 or a 68030 or a 68040. The generated code does use the | |
4712 | 68881 instructions that are emulated on the 68060. | |
4713 | ||
74291a4b MM |
4714 | @item -mfpa |
4715 | Generate output containing Sun FPA instructions for floating point. | |
4716 | ||
4717 | @item -msoft-float | |
4718 | Generate output containing library calls for floating point. | |
4719 | @strong{Warning:} the requisite libraries are not available for all m68k | |
4720 | targets. Normally the facilities of the machine's usual C compiler are | |
4721 | used, but this can't be done directly in cross-compilation. You must | |
4722 | make your own arrangements to provide suitable library functions for | |
4723 | cross-compilation. The embedded targets @samp{m68k-*-aout} and | |
4724 | @samp{m68k-*-coff} do provide software floating point support. | |
4725 | ||
4726 | @item -mshort | |
4727 | Consider type @code{int} to be 16 bits wide, like @code{short int}. | |
4728 | ||
4729 | @item -mnobitfield | |
74cf1c6d RK |
4730 | Do not use the bit-field instructions. The @samp{-m68000}, @samp{-mcpu32} |
4731 | and @samp{-m5200} options imply @w{@samp{-mnobitfield}}. | |
74291a4b MM |
4732 | |
4733 | @item -mbitfield | |
4734 | Do use the bit-field instructions. The @samp{-m68020} option implies | |
4735 | @samp{-mbitfield}. This is the default if you use a configuration | |
4736 | designed for a 68020. | |
4737 | ||
4738 | @item -mrtd | |
4739 | Use a different function-calling convention, in which functions | |
4740 | that take a fixed number of arguments return with the @code{rtd} | |
4741 | instruction, which pops their arguments while returning. This | |
4742 | saves one instruction in the caller since there is no need to pop | |
4743 | the arguments there. | |
4744 | ||
4745 | This calling convention is incompatible with the one normally | |
4746 | used on Unix, so you cannot use it if you need to call libraries | |
4747 | compiled with the Unix compiler. | |
4748 | ||
4749 | Also, you must provide function prototypes for all functions that | |
4750 | take variable numbers of arguments (including @code{printf}); | |
4751 | otherwise incorrect code will be generated for calls to those | |
4752 | functions. | |
4753 | ||
4754 | In addition, seriously incorrect code will result if you call a | |
4755 | function with too many arguments. (Normally, extra arguments are | |
4756 | harmlessly ignored.) | |
4757 | ||
4758 | The @code{rtd} instruction is supported by the 68010, 68020, 68030, | |
74cf1c6d | 4759 | 68040, 68060 and CPU32 processors, but not by the 68000 or 5200. |
861bb6c1 JL |
4760 | |
4761 | @item -malign-int | |
4762 | @itemx -mno-align-int | |
02f52e19 | 4763 | Control whether GCC aligns @code{int}, @code{long}, @code{long long}, |
861bb6c1 JL |
4764 | @code{float}, @code{double}, and @code{long double} variables on a 32-bit |
4765 | boundary (@samp{-malign-int}) or a 16-bit boundary (@samp{-mno-align-int}). | |
4766 | Aligning variables on 32-bit boundaries produces code that runs somewhat | |
4767 | faster on processors with 32-bit busses at the expense of more memory. | |
4768 | ||
0c2d1a2a | 4769 | @strong{Warning:} if you use the @samp{-malign-int} switch, GCC will |
861bb6c1 JL |
4770 | align structures containing the above types differently than |
4771 | most published application binary interface specifications for the m68k. | |
4772 | ||
fb868474 DL |
4773 | @item -mpcrel |
4774 | Use the pc-relative addressing mode of the 68000 directly, instead of | |
4775 | using a global offset table. At present, this option implies -fpic, | |
4776 | allowing at most a 16-bit offset for pc-relative addressing. -fPIC is | |
4777 | not presently supported with -mpcrel, though this could be supported for | |
4778 | 68020 and higher processors. | |
4779 | ||
b71733d5 GM |
4780 | @item -mno-strict-align |
4781 | @itemx -mstrict-align | |
4782 | @kindex -mstrict-align | |
4783 | Do not (do) assume that unaligned memory references will be handled by | |
4784 | the system. | |
4785 | ||
74291a4b MM |
4786 | @end table |
4787 | ||
2856c3e3 SC |
4788 | @node M68hc1x Options |
4789 | @subsection M68hc1x Options | |
4790 | @cindex M68hc1x options | |
4791 | ||
4792 | These are the @samp{-m} options defined for the 68hc11 and 68hc12 | |
02f52e19 | 4793 | microcontrollers. The default values for these options depends on |
2856c3e3 SC |
4794 | which style of microcontroller was selected when the compiler was configured; |
4795 | the defaults for the most common choices are given below. | |
4796 | ||
2642624b | 4797 | @table @gcctabopt |
2856c3e3 SC |
4798 | @item -m6811 |
4799 | @itemx -m68hc11 | |
4800 | Generate output for a 68HC11. This is the default | |
4801 | when the compiler is configured for 68HC11-based systems. | |
4802 | ||
4803 | @item -m6812 | |
4804 | @itemx -m68hc12 | |
4805 | Generate output for a 68HC12. This is the default | |
4806 | when the compiler is configured for 68HC12-based systems. | |
4807 | ||
4808 | @item -mauto-incdec | |
4809 | Enable the use of 68HC12 pre and post auto-increment and auto-decrement | |
4810 | addressing modes. | |
4811 | ||
4812 | @item -mshort | |
4813 | Consider type @code{int} to be 16 bits wide, like @code{short int}. | |
4814 | ||
4815 | @item -msoft-reg-count=@var{count} | |
4816 | Specify the number of pseudo-soft registers which are used for the | |
4817 | code generation. The maximum number is 32. Using more pseudo-soft | |
4818 | register may or may not result in better code depending on the program. | |
4819 | The default is 4 for 68HC11 and 2 for 68HC12. | |
4820 | ||
4821 | @end table | |
4822 | ||
74291a4b MM |
4823 | @node VAX Options |
4824 | @subsection VAX Options | |
4825 | @cindex VAX options | |
4826 | ||
4827 | These @samp{-m} options are defined for the Vax: | |
4828 | ||
2642624b | 4829 | @table @gcctabopt |
74291a4b MM |
4830 | @item -munix |
4831 | Do not output certain jump instructions (@code{aobleq} and so on) | |
4832 | that the Unix assembler for the Vax cannot handle across long | |
4833 | ranges. | |
4834 | ||
4835 | @item -mgnu | |
4836 | Do output those jump instructions, on the assumption that you | |
4837 | will assemble with the GNU assembler. | |
4838 | ||
4839 | @item -mg | |
4840 | Output code for g-format floating point numbers instead of d-format. | |
4841 | @end table | |
4842 | ||
4843 | @node SPARC Options | |
4844 | @subsection SPARC Options | |
4845 | @cindex SPARC options | |
4846 | ||
4847 | These @samp{-m} switches are supported on the SPARC: | |
4848 | ||
2642624b | 4849 | @table @gcctabopt |
74291a4b MM |
4850 | @item -mno-app-regs |
4851 | @itemx -mapp-regs | |
4852 | Specify @samp{-mapp-regs} to generate output using the global registers | |
4853 | 2 through 4, which the SPARC SVR4 ABI reserves for applications. This | |
4854 | is the default. | |
4855 | ||
4856 | To be fully SVR4 ABI compliant at the cost of some performance loss, | |
4857 | specify @samp{-mno-app-regs}. You should compile libraries and system | |
4858 | software with this option. | |
4859 | ||
4860 | @item -mfpu | |
4861 | @itemx -mhard-float | |
4862 | Generate output containing floating point instructions. This is the | |
4863 | default. | |
4864 | ||
4865 | @item -mno-fpu | |
4866 | @itemx -msoft-float | |
4867 | Generate output containing library calls for floating point. | |
4868 | @strong{Warning:} the requisite libraries are not available for all SPARC | |
4869 | targets. Normally the facilities of the machine's usual C compiler are | |
4870 | used, but this cannot be done directly in cross-compilation. You must make | |
4871 | your own arrangements to provide suitable library functions for | |
4872 | cross-compilation. The embedded targets @samp{sparc-*-aout} and | |
4873 | @samp{sparclite-*-*} do provide software floating point support. | |
4874 | ||
4875 | @samp{-msoft-float} changes the calling convention in the output file; | |
4876 | therefore, it is only useful if you compile @emph{all} of a program with | |
4877 | this option. In particular, you need to compile @file{libgcc.a}, the | |
0c2d1a2a | 4878 | library that comes with GCC, with @samp{-msoft-float} in order for |
74291a4b MM |
4879 | this to work. |
4880 | ||
4881 | @item -mhard-quad-float | |
4882 | Generate output containing quad-word (long double) floating point | |
4883 | instructions. | |
4884 | ||
4885 | @item -msoft-quad-float | |
4886 | Generate output containing library calls for quad-word (long double) | |
4887 | floating point instructions. The functions called are those specified | |
4888 | in the SPARC ABI. This is the default. | |
4889 | ||
4890 | As of this writing, there are no sparc implementations that have hardware | |
4891 | support for the quad-word floating point instructions. They all invoke | |
4892 | a trap handler for one of these instructions, and then the trap handler | |
4893 | emulates the effect of the instruction. Because of the trap handler overhead, | |
4894 | this is much slower than calling the ABI library routines. Thus the | |
4895 | @samp{-msoft-quad-float} option is the default. | |
4896 | ||
4897 | @item -mno-epilogue | |
4898 | @itemx -mepilogue | |
4899 | With @samp{-mepilogue} (the default), the compiler always emits code for | |
4900 | function exit at the end of each function. Any function exit in | |
4901 | the middle of the function (such as a return statement in C) will | |
4902 | generate a jump to the exit code at the end of the function. | |
4903 | ||
4904 | With @samp{-mno-epilogue}, the compiler tries to emit exit code inline | |
4905 | at every function exit. | |
4906 | ||
4907 | @item -mno-flat | |
4908 | @itemx -mflat | |
4909 | With @samp{-mflat}, the compiler does not generate save/restore instructions | |
4910 | and will use a "flat" or single register window calling convention. | |
4911 | This model uses %i7 as the frame pointer and is compatible with the normal | |
4912 | register window model. Code from either may be intermixed. | |
4913 | The local registers and the input registers (0-5) are still treated as | |
4914 | "call saved" registers and will be saved on the stack as necessary. | |
4915 | ||
4916 | With @samp{-mno-flat} (the default), the compiler emits save/restore | |
4917 | instructions (except for leaf functions) and is the normal mode of operation. | |
4918 | ||
4919 | @item -mno-unaligned-doubles | |
4920 | @itemx -munaligned-doubles | |
4921 | Assume that doubles have 8 byte alignment. This is the default. | |
4922 | ||
0c2d1a2a | 4923 | With @samp{-munaligned-doubles}, GCC assumes that doubles have 8 byte |
74291a4b MM |
4924 | alignment only if they are contained in another type, or if they have an |
4925 | absolute address. Otherwise, it assumes they have 4 byte alignment. | |
4926 | Specifying this option avoids some rare compatibility problems with code | |
4927 | generated by other compilers. It is not the default because it results | |
4928 | in a performance loss, especially for floating point code. | |
4929 | ||
c219ddf7 BK |
4930 | @item -mno-faster-structs |
4931 | @itemx -mfaster-structs | |
4932 | With @samp{-mfaster-structs}, the compiler assumes that structures | |
4933 | should have 8 byte alignment. This enables the use of pairs of | |
4934 | @code{ldd} and @code{std} instructions for copies in structure | |
4935 | assignment, in place of twice as many @code{ld} and @code{st} pairs. | |
4936 | However, the use of this changed alignment directly violates the Sparc | |
4937 | ABI. Thus, it's intended only for use on targets where the developer | |
4938 | acknowledges that their resulting code will not be directly in line with | |
4939 | the rules of the ABI. | |
4940 | ||
74291a4b MM |
4941 | @item -mv8 |
4942 | @itemx -msparclite | |
4943 | These two options select variations on the SPARC architecture. | |
4944 | ||
4945 | By default (unless specifically configured for the Fujitsu SPARClite), | |
4946 | GCC generates code for the v7 variant of the SPARC architecture. | |
4947 | ||
4948 | @samp{-mv8} will give you SPARC v8 code. The only difference from v7 | |
4949 | code is that the compiler emits the integer multiply and integer | |
4950 | divide instructions which exist in SPARC v8 but not in SPARC v7. | |
4951 | ||
4952 | @samp{-msparclite} will give you SPARClite code. This adds the integer | |
4953 | multiply, integer divide step and scan (@code{ffs}) instructions which | |
4954 | exist in SPARClite but not in SPARC v7. | |
4955 | ||
0c2d1a2a | 4956 | These options are deprecated and will be deleted in a future GCC release. |
74291a4b MM |
4957 | They have been replaced with @samp{-mcpu=xxx}. |
4958 | ||
4959 | @item -mcypress | |
4960 | @itemx -msupersparc | |
4961 | These two options select the processor for which the code is optimised. | |
4962 | ||
4963 | With @samp{-mcypress} (the default), the compiler optimizes code for the | |
4964 | Cypress CY7C602 chip, as used in the SparcStation/SparcServer 3xx series. | |
4965 | This is also appropriate for the older SparcStation 1, 2, IPX etc. | |
4966 | ||
4967 | With @samp{-msupersparc} the compiler optimizes code for the SuperSparc cpu, as | |
4968 | used in the SparcStation 10, 1000 and 2000 series. This flag also enables use | |
4969 | of the full SPARC v8 instruction set. | |
4970 | ||
0c2d1a2a | 4971 | These options are deprecated and will be deleted in a future GCC release. |
74291a4b MM |
4972 | They have been replaced with @samp{-mcpu=xxx}. |
4973 | ||
4974 | @item -mcpu=@var{cpu_type} | |
c0498f43 DE |
4975 | Set the instruction set, register set, and instruction scheduling parameters |
4976 | for machine type @var{cpu_type}. Supported values for @var{cpu_type} are | |
4977 | @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite}, | |
ad6843d7 RH |
4978 | @samp{hypersparc}, @samp{sparclite86x}, @samp{f930}, @samp{f934}, |
4979 | @samp{sparclet}, @samp{tsc701}, @samp{v9}, and @samp{ultrasparc}. | |
c0498f43 DE |
4980 | |
4981 | Default instruction scheduling parameters are used for values that select | |
4982 | an architecture and not an implementation. These are @samp{v7}, @samp{v8}, | |
4983 | @samp{sparclite}, @samp{sparclet}, @samp{v9}. | |
4984 | ||
4985 | Here is a list of each supported architecture and their supported | |
4986 | implementations. | |
4987 | ||
4988 | @smallexample | |
4989 | v7: cypress | |
ad6843d7 RH |
4990 | v8: supersparc, hypersparc |
4991 | sparclite: f930, f934, sparclite86x | |
c0498f43 DE |
4992 | sparclet: tsc701 |
4993 | v9: ultrasparc | |
4994 | @end smallexample | |
74291a4b MM |
4995 | |
4996 | @item -mtune=@var{cpu_type} | |
4997 | Set the instruction scheduling parameters for machine type | |
c0498f43 DE |
4998 | @var{cpu_type}, but do not set the instruction set or register set that the |
4999 | option @samp{-mcpu=}@var{cpu_type} would. | |
5000 | ||
5001 | The same values for @samp{-mcpu=}@var{cpu_type} are used for | |
e5e809f4 | 5002 | @samp{-mtune=}@*@var{cpu_type}, though the only useful values are those that |
c0498f43 | 5003 | select a particular cpu implementation: @samp{cypress}, @samp{supersparc}, |
ad6843d7 RH |
5004 | @samp{hypersparc}, @samp{f930}, @samp{f934}, @samp{sparclite86x}, |
5005 | @samp{tsc701}, @samp{ultrasparc}. | |
74291a4b MM |
5006 | |
5007 | @end table | |
5008 | ||
5009 | These @samp{-m} switches are supported in addition to the above | |
5010 | on the SPARCLET processor. | |
5011 | ||
2642624b | 5012 | @table @gcctabopt |
74291a4b MM |
5013 | @item -mlittle-endian |
5014 | Generate code for a processor running in little-endian mode. | |
5015 | ||
5016 | @item -mlive-g0 | |
5017 | Treat register @code{%g0} as a normal register. | |
5018 | GCC will continue to clobber it as necessary but will not assume | |
5019 | it always reads as 0. | |
5020 | ||
5021 | @item -mbroken-saverestore | |
5022 | Generate code that does not use non-trivial forms of the @code{save} and | |
5023 | @code{restore} instructions. Early versions of the SPARCLET processor do | |
5024 | not correctly handle @code{save} and @code{restore} instructions used with | |
5025 | arguments. They correctly handle them used without arguments. A @code{save} | |
5026 | instruction used without arguments increments the current window pointer | |
5027 | but does not allocate a new stack frame. It is assumed that the window | |
5028 | overflow trap handler will properly handle this case as will interrupt | |
5029 | handlers. | |
5030 | @end table | |
5031 | ||
5032 | These @samp{-m} switches are supported in addition to the above | |
02f52e19 | 5033 | on SPARC V9 processors in 64-bit environments. |
74291a4b | 5034 | |
2642624b | 5035 | @table @gcctabopt |
74291a4b MM |
5036 | @item -mlittle-endian |
5037 | Generate code for a processor running in little-endian mode. | |
5038 | ||
ded17aad DE |
5039 | @item -m32 |
5040 | @itemx -m64 | |
02f52e19 AJ |
5041 | Generate code for a 32-bit or 64-bit environment. |
5042 | The 32-bit environment sets int, long and pointer to 32 bits. | |
5043 | The 64-bit environment sets int to 32 bits and long and pointer | |
ded17aad DE |
5044 | to 64 bits. |
5045 | ||
5046 | @item -mcmodel=medlow | |
5047 | Generate code for the Medium/Low code model: the program must be linked | |
5048 | in the low 32 bits of the address space. Pointers are 64 bits. | |
5049 | Programs can be statically or dynamically linked. | |
5050 | ||
5051 | @item -mcmodel=medmid | |
5052 | Generate code for the Medium/Middle code model: the program must be linked | |
5053 | in the low 44 bits of the address space, the text segment must be less than | |
5054 | 2G bytes, and data segment must be within 2G of the text segment. | |
5055 | Pointers are 64 bits. | |
5056 | ||
5057 | @item -mcmodel=medany | |
5058 | Generate code for the Medium/Anywhere code model: the program may be linked | |
5059 | anywhere in the address space, the text segment must be less than | |
5060 | 2G bytes, and data segment must be within 2G of the text segment. | |
5061 | Pointers are 64 bits. | |
5062 | ||
5063 | @item -mcmodel=embmedany | |
5064 | Generate code for the Medium/Anywhere code model for embedded systems: | |
02f52e19 | 5065 | assume a 32-bit text and a 32-bit data segment, both starting anywhere |
ded17aad | 5066 | (determined at link time). Register %g4 points to the base of the |
02f52e19 | 5067 | data segment. Pointers are still 64 bits. |
ded17aad | 5068 | Programs are statically linked, PIC is not supported. |
74291a4b MM |
5069 | |
5070 | @item -mstack-bias | |
5071 | @itemx -mno-stack-bias | |
0c2d1a2a | 5072 | With @samp{-mstack-bias}, GCC assumes that the stack pointer, and |
74291a4b MM |
5073 | frame pointer if present, are offset by -2047 which must be added back |
5074 | when making stack frame references. | |
5075 | Otherwise, assume no such offset is present. | |
5076 | @end table | |
5077 | ||
5078 | @node Convex Options | |
5079 | @subsection Convex Options | |
5080 | @cindex Convex options | |
5081 | ||
5082 | These @samp{-m} options are defined for Convex: | |
5083 | ||
2642624b | 5084 | @table @gcctabopt |
74291a4b MM |
5085 | @item -mc1 |
5086 | Generate output for C1. The code will run on any Convex machine. | |
5087 | The preprocessor symbol @code{__convex__c1__} is defined. | |
5088 | ||
5089 | @item -mc2 | |
5090 | Generate output for C2. Uses instructions not available on C1. | |
5091 | Scheduling and other optimizations are chosen for max performance on C2. | |
5092 | The preprocessor symbol @code{__convex_c2__} is defined. | |
5093 | ||
5094 | @item -mc32 | |
5095 | Generate output for C32xx. Uses instructions not available on C1. | |
5096 | Scheduling and other optimizations are chosen for max performance on C32. | |
5097 | The preprocessor symbol @code{__convex_c32__} is defined. | |
5098 | ||
5099 | @item -mc34 | |
5100 | Generate output for C34xx. Uses instructions not available on C1. | |
5101 | Scheduling and other optimizations are chosen for max performance on C34. | |
5102 | The preprocessor symbol @code{__convex_c34__} is defined. | |
5103 | ||
5104 | @item -mc38 | |
5105 | Generate output for C38xx. Uses instructions not available on C1. | |
5106 | Scheduling and other optimizations are chosen for max performance on C38. | |
5107 | The preprocessor symbol @code{__convex_c38__} is defined. | |
5108 | ||
5109 | @item -margcount | |
5110 | Generate code which puts an argument count in the word preceding each | |
5111 | argument list. This is compatible with regular CC, and a few programs | |
5112 | may need the argument count word. GDB and other source-level debuggers | |
5113 | do not need it; this info is in the symbol table. | |
5114 | ||
5115 | @item -mnoargcount | |
5116 | Omit the argument count word. This is the default. | |
5117 | ||
5118 | @item -mvolatile-cache | |
5119 | Allow volatile references to be cached. This is the default. | |
5120 | ||
5121 | @item -mvolatile-nocache | |
5122 | Volatile references bypass the data cache, going all the way to memory. | |
5123 | This is only needed for multi-processor code that does not use standard | |
5124 | synchronization instructions. Making non-volatile references to volatile | |
5125 | locations will not necessarily work. | |
5126 | ||
5127 | @item -mlong32 | |
5128 | Type long is 32 bits, the same as type int. This is the default. | |
5129 | ||
5130 | @item -mlong64 | |
5131 | Type long is 64 bits, the same as type long long. This option is useless, | |
5132 | because no library support exists for it. | |
5133 | @end table | |
5134 | ||
5135 | @node AMD29K Options | |
5136 | @subsection AMD29K Options | |
5137 | @cindex AMD29K options | |
5138 | ||
5139 | These @samp{-m} options are defined for the AMD Am29000: | |
5140 | ||
2642624b | 5141 | @table @gcctabopt |
74291a4b MM |
5142 | @item -mdw |
5143 | @kindex -mdw | |
5144 | @cindex DW bit (29k) | |
5145 | Generate code that assumes the @code{DW} bit is set, i.e., that byte and | |
5146 | halfword operations are directly supported by the hardware. This is the | |
5147 | default. | |
5148 | ||
5149 | @item -mndw | |
5150 | @kindex -mndw | |
5151 | Generate code that assumes the @code{DW} bit is not set. | |
5152 | ||
5153 | @item -mbw | |
5154 | @kindex -mbw | |
5155 | @cindex byte writes (29k) | |
5156 | Generate code that assumes the system supports byte and halfword write | |
5157 | operations. This is the default. | |
5158 | ||
5159 | @item -mnbw | |
5160 | @kindex -mnbw | |
5161 | Generate code that assumes the systems does not support byte and | |
5162 | halfword write operations. @samp{-mnbw} implies @samp{-mndw}. | |
5163 | ||
5164 | @item -msmall | |
5165 | @kindex -msmall | |
5166 | @cindex memory model (29k) | |
5167 | Use a small memory model that assumes that all function addresses are | |
5168 | either within a single 256 KB segment or at an absolute address of less | |
5169 | than 256k. This allows the @code{call} instruction to be used instead | |
5170 | of a @code{const}, @code{consth}, @code{calli} sequence. | |
5171 | ||
5172 | @item -mnormal | |
5173 | @kindex -mnormal | |
5174 | Use the normal memory model: Generate @code{call} instructions only when | |
5175 | calling functions in the same file and @code{calli} instructions | |
5176 | otherwise. This works if each file occupies less than 256 KB but allows | |
5177 | the entire executable to be larger than 256 KB. This is the default. | |
5178 | ||
5179 | @item -mlarge | |
5180 | Always use @code{calli} instructions. Specify this option if you expect | |
5181 | a single file to compile into more than 256 KB of code. | |
5182 | ||
5183 | @item -m29050 | |
5184 | @kindex -m29050 | |
5185 | @cindex processor selection (29k) | |
5186 | Generate code for the Am29050. | |
5187 | ||
5188 | @item -m29000 | |
5189 | @kindex -m29000 | |
5190 | Generate code for the Am29000. This is the default. | |
5191 | ||
5192 | @item -mkernel-registers | |
5193 | @kindex -mkernel-registers | |
5194 | @cindex kernel and user registers (29k) | |
5195 | Generate references to registers @code{gr64-gr95} instead of to | |
5196 | registers @code{gr96-gr127}. This option can be used when compiling | |
5197 | kernel code that wants a set of global registers disjoint from that used | |
5198 | by user-mode code. | |
5199 | ||
5200 | Note that when this option is used, register names in @samp{-f} flags | |
5201 | must use the normal, user-mode, names. | |
5202 | ||
5203 | @item -muser-registers | |
5204 | @kindex -muser-registers | |
5205 | Use the normal set of global registers, @code{gr96-gr127}. This is the | |
5206 | default. | |
5207 | ||
5208 | @item -mstack-check | |
5209 | @itemx -mno-stack-check | |
5210 | @kindex -mstack-check | |
5211 | @cindex stack checks (29k) | |
5212 | Insert (or do not insert) a call to @code{__msp_check} after each stack | |
5213 | adjustment. This is often used for kernel code. | |
5214 | ||
5215 | @item -mstorem-bug | |
5216 | @itemx -mno-storem-bug | |
5217 | @kindex -mstorem-bug | |
5218 | @cindex storem bug (29k) | |
5219 | @samp{-mstorem-bug} handles 29k processors which cannot handle the | |
5220 | separation of a mtsrim insn and a storem instruction (most 29000 chips | |
5221 | to date, but not the 29050). | |
5222 | ||
5223 | @item -mno-reuse-arg-regs | |
5224 | @itemx -mreuse-arg-regs | |
5225 | @kindex -mreuse-arg-regs | |
5226 | @samp{-mno-reuse-arg-regs} tells the compiler to only use incoming argument | |
5227 | registers for copying out arguments. This helps detect calling a function | |
5228 | with fewer arguments than it was declared with. | |
5229 | ||
861bb6c1 JL |
5230 | @item -mno-impure-text |
5231 | @itemx -mimpure-text | |
5232 | @kindex -mimpure-text | |
5233 | @samp{-mimpure-text}, used in addition to @samp{-shared}, tells the compiler to | |
5234 | not pass @samp{-assert pure-text} to the linker when linking a shared object. | |
5235 | ||
74291a4b MM |
5236 | @item -msoft-float |
5237 | @kindex -msoft-float | |
5238 | Generate output containing library calls for floating point. | |
0c2d1a2a | 5239 | @strong{Warning:} the requisite libraries are not part of GCC. |
74291a4b MM |
5240 | Normally the facilities of the machine's usual C compiler are used, but |
5241 | this can't be done directly in cross-compilation. You must make your | |
5242 | own arrangements to provide suitable library functions for | |
5243 | cross-compilation. | |
4e8d7ddc JW |
5244 | |
5245 | @item -mno-multm | |
5246 | @kindex -mno-multm | |
5247 | Do not generate multm or multmu instructions. This is useful for some embedded | |
5248 | systems which do not have trap handlers for these instructions. | |
74291a4b MM |
5249 | @end table |
5250 | ||
5251 | @node ARM Options | |
5252 | @subsection ARM Options | |
5253 | @cindex ARM options | |
5254 | ||
5255 | These @samp{-m} options are defined for Advanced RISC Machines (ARM) | |
5256 | architectures: | |
5257 | ||
2642624b | 5258 | @table @gcctabopt |
74291a4b MM |
5259 | @item -mapcs-frame |
5260 | @kindex -mapcs-frame | |
5261 | Generate a stack frame that is compliant with the ARM Procedure Call | |
5262 | Standard for all functions, even if this is not strictly necessary for | |
157a620e NC |
5263 | correct execution of the code. Specifying @samp{-fomit-frame-pointer} |
5264 | with this option will cause the stack frames not to be generated for | |
5265 | leaf functions. The default is @samp{-mno-apcs-frame}. | |
5266 | ||
5267 | @item -mapcs | |
5268 | @kindex -mapcs | |
5269 | This is a synonym for @samp{-mapcs-frame}. | |
74291a4b MM |
5270 | |
5271 | @item -mapcs-26 | |
5272 | @kindex -mapcs-26 | |
5273 | Generate code for a processor running with a 26-bit program counter, | |
5274 | and conforming to the function calling standards for the APCS 26-bit | |
5275 | option. This option replaces the @samp{-m2} and @samp{-m3} options | |
5276 | of previous releases of the compiler. | |
5277 | ||
5278 | @item -mapcs-32 | |
5279 | @kindex -mapcs-32 | |
5280 | Generate code for a processor running with a 32-bit program counter, | |
5281 | and conforming to the function calling standards for the APCS 32-bit | |
5282 | option. This option replaces the @samp{-m6} option of previous releases | |
5283 | of the compiler. | |
5284 | ||
247f8561 PB |
5285 | @ignore |
5286 | @c not currently implemented | |
157a620e NC |
5287 | @item -mapcs-stack-check |
5288 | @kindex -mapcs-stack-check | |
5289 | @kindex -mno-apcs-stack-check | |
5290 | Generate code to check the amount of stack space available upon entry to | |
5291 | every function (that actually uses some stack space). If there is | |
5292 | insufficient space available then either the function | |
5293 | @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be | |
5294 | called, depending upon the amount of stack space required. The run time | |
5295 | system is required to provide these functions. The default is | |
5296 | @samp{-mno-apcs-stack-check}, since this produces smaller code. | |
5297 | ||
247f8561 | 5298 | @c not currently implemented |
157a620e NC |
5299 | @item -mapcs-float |
5300 | @kindex -mapcs-float | |
5301 | @kindex -mno-apcs-float | |
5302 | Pass floating point arguments using the float point registers. This is | |
ed0e6530 | 5303 | one of the variants of the APCS. This option is recommended if the |
157a620e NC |
5304 | target hardware has a floating point unit or if a lot of floating point |
5305 | arithmetic is going to be performed by the code. The default is | |
5306 | @samp{-mno-apcs-float}, since integer only code is slightly increased in | |
5307 | size if @samp{-mapcs-float} is used. | |
5308 | ||
247f8561 | 5309 | @c not currently implemented |
157a620e NC |
5310 | @item -mapcs-reentrant |
5311 | @kindex -mapcs-reentrant | |
5312 | @kindex -mno-apcs-reentrant | |
247f8561 | 5313 | Generate reentrant, position independent code. The default is |
157a620e | 5314 | @samp{-mno-apcs-reentrant}. |
247f8561 | 5315 | @end ignore |
157a620e NC |
5316 | |
5317 | @item -mthumb-interwork | |
5318 | @kindex -mthumb-interwork | |
5319 | @kindex -mno-thumb-interwork | |
247f8561 | 5320 | Generate code which supports calling between the ARM and Thumb |
157a620e NC |
5321 | instruction sets. Without this option the two instruction sets cannot |
5322 | be reliably used inside one program. The default is | |
5323 | @samp{-mno-thumb-interwork}, since slightly larger code is generated | |
5324 | when @samp{-mthumb-interwork} is specified. | |
5325 | ||
5326 | @item -mno-sched-prolog | |
5327 | @kindex -mno-sched-prolog | |
5328 | @kindex -msched-prolog | |
5329 | Prevent the reordering of instructions in the function prolog, or the | |
5330 | merging of those instruction with the instructions in the function's | |
ed0e6530 PB |
5331 | body. This means that all functions will start with a recognizable set |
5332 | of instructions (or in fact one of a choice from a small set of | |
157a620e NC |
5333 | different function prologues), and this information can be used to |
5334 | locate the start if functions inside an executable piece of code. The | |
5335 | default is @samp{-msched-prolog}. | |
5336 | ||
74291a4b MM |
5337 | @item -mhard-float |
5338 | Generate output containing floating point instructions. This is the | |
5339 | default. | |
5340 | ||
5341 | @item -msoft-float | |
5342 | Generate output containing library calls for floating point. | |
5343 | @strong{Warning:} the requisite libraries are not available for all ARM | |
5344 | targets. Normally the facilities of the machine's usual C compiler are | |
5345 | used, but this cannot be done directly in cross-compilation. You must make | |
5346 | your own arrangements to provide suitable library functions for | |
5347 | cross-compilation. | |
5348 | ||
5349 | @samp{-msoft-float} changes the calling convention in the output file; | |
5350 | therefore, it is only useful if you compile @emph{all} of a program with | |
5351 | this option. In particular, you need to compile @file{libgcc.a}, the | |
0c2d1a2a | 5352 | library that comes with GCC, with @samp{-msoft-float} in order for |
74291a4b MM |
5353 | this to work. |
5354 | ||
5355 | @item -mlittle-endian | |
5356 | Generate code for a processor running in little-endian mode. This is | |
5357 | the default for all standard configurations. | |
5358 | ||
5359 | @item -mbig-endian | |
5360 | Generate code for a processor running in big-endian mode; the default is | |
5361 | to compile code for a little-endian processor. | |
5362 | ||
5363 | @item -mwords-little-endian | |
5364 | This option only applies when generating code for big-endian processors. | |
5365 | Generate code for a little-endian word order but a big-endian byte | |
5366 | order. That is, a byte order of the form @samp{32107654}. Note: this | |
5367 | option should only be used if you require compatibility with code for | |
5368 | big-endian ARM processors generated by versions of the compiler prior to | |
5369 | 2.8. | |
5370 | ||
5f1e6755 NC |
5371 | @item -malignment-traps |
5372 | @kindex -malignment-traps | |
5373 | Generate code that will not trap if the MMU has alignment traps enabled. | |
5374 | On ARM architectures prior to ARMv4, there were no instructions to | |
5375 | access half-word objects stored in memory. However, when reading from | |
5376 | memory a feature of the ARM architecture allows a word load to be used, | |
5377 | even if the address is unaligned, and the processor core will rotate the | |
5378 | data as it is being loaded. This option tells the compiler that such | |
5379 | misaligned accesses will cause a MMU trap and that it should instead | |
5380 | synthesise the access as a series of byte accesses. The compiler can | |
5381 | still use word accesses to load half-word data if it knows that the | |
5382 | address is aligned to a word boundary. | |
5383 | ||
5384 | This option is ignored when compiling for ARM architecture 4 or later, | |
5385 | since these processors have instructions to directly access half-word | |
02f52e19 AJ |
5386 | objects in memory. |
5387 | ||
5f1e6755 NC |
5388 | @item -mno-alignment-traps |
5389 | @kindex -mno-alignment-traps | |
5390 | Generate code that assumes that the MMU will not trap unaligned | |
5391 | accesses. This produces better code when the target instruction set | |
247f8561 | 5392 | does not have half-word memory operations (i.e. implementations prior to |
02f52e19 | 5393 | ARMv4). |
5f1e6755 NC |
5394 | |
5395 | Note that you cannot use this option to access unaligned word objects, | |
5396 | since the processor will only fetch one 32-bit aligned object from | |
02f52e19 | 5397 | memory. |
5f1e6755 NC |
5398 | |
5399 | The default setting for most targets is -mno-alignment-traps, since | |
5400 | this produces better code when there are no half-word memory | |
02f52e19 | 5401 | instructions available. |
5f1e6755 | 5402 | |
74291a4b | 5403 | @item -mshort-load-bytes |
247f8561 | 5404 | @itemx -mno-short-load-words |
74291a4b | 5405 | @kindex -mshort-load-bytes |
247f8561 PB |
5406 | @kindex -mno-short-load-words |
5407 | These are deprecated aliases for @samp{-malignment-traps}. | |
74291a4b MM |
5408 | |
5409 | @item -mno-short-load-bytes | |
247f8561 | 5410 | @itemx -mshort-load-words |
74291a4b | 5411 | @kindex -mno-short-load-bytes |
157a620e | 5412 | @kindex -mshort-load-words |
247f8561 | 5413 | This are deprecated aliases for @samp{-mno-alignment-traps}. |
157a620e | 5414 | |
74291a4b MM |
5415 | @item -mbsd |
5416 | @kindex -mbsd | |
5417 | This option only applies to RISC iX. Emulate the native BSD-mode | |
5418 | compiler. This is the default if @samp{-ansi} is not specified. | |
5419 | ||
5420 | @item -mxopen | |
5421 | @kindex -mxopen | |
5422 | This option only applies to RISC iX. Emulate the native X/Open-mode | |
5423 | compiler. | |
5424 | ||
5425 | @item -mno-symrename | |
5426 | @kindex -mno-symrename | |
5427 | This option only applies to RISC iX. Do not run the assembler | |
5428 | post-processor, @samp{symrename}, after code has been assembled. | |
5429 | Normally it is necessary to modify some of the standard symbols in | |
5430 | preparation for linking with the RISC iX C library; this option | |
5431 | suppresses this pass. The post-processor is never run when the | |
5432 | compiler is built for cross-compilation. | |
157a620e NC |
5433 | |
5434 | @item -mcpu=<name> | |
5435 | @kindex -mcpu= | |
5436 | This specifies the name of the target ARM processor. GCC uses this name | |
247f8561 | 5437 | to determine what kind of instructions it can emit when generating |
ed0e6530 | 5438 | assembly code. Permissible names are: arm2, arm250, arm3, arm6, arm60, |
157a620e NC |
5439 | arm600, arm610, arm620, arm7, arm7m, arm7d, arm7dm, arm7di, arm7dmi, |
5440 | arm70, arm700, arm700i, arm710, arm710c, arm7100, arm7500, arm7500fe, | |
f5a1b0d2 | 5441 | arm7tdmi, arm8, strongarm, strongarm110, strongarm1100, arm8, arm810, |
247f8561 PB |
5442 | arm9, arm9e, arm920, arm920t, arm940t, arm9tdmi, arm10tdmi, arm1020t, |
5443 | xscale. | |
62b10bbc NC |
5444 | |
5445 | @itemx -mtune=<name> | |
5446 | @kindex -mtune= | |
5447 | This option is very similar to the @samp{-mcpu=} option, except that | |
5448 | instead of specifying the actual target processor type, and hence | |
5449 | restricting which instructions can be used, it specifies that GCC should | |
5450 | tune the performance of the code as if the target were of the type | |
5451 | specified in this option, but still choosing the instructions that it | |
5452 | will generate based on the cpu specified by a @samp{-mcpu=} option. | |
247f8561 | 5453 | For some ARM implementations better performance can be obtained by using |
62b10bbc | 5454 | this option. |
157a620e NC |
5455 | |
5456 | @item -march=<name> | |
5457 | @kindex -march= | |
5458 | This specifies the name of the target ARM architecture. GCC uses this | |
247f8561 | 5459 | name to determine what kind of instructions it can emit when generating |
157a620e | 5460 | assembly code. This option can be used in conjunction with or instead |
ed0e6530 | 5461 | of the @samp{-mcpu=} option. Permissible names are: armv2, armv2a, |
247f8561 | 5462 | armv3, armv3m, armv4, armv4t, armv5, armv5t, armv5te. |
157a620e NC |
5463 | |
5464 | @item -mfpe=<number> | |
59d40964 | 5465 | @itemx -mfp=<number> |
157a620e | 5466 | @kindex -mfpe= |
f5a1b0d2 | 5467 | @kindex -mfp= |
b192711e | 5468 | This specifies the version of the floating point emulation available on |
ed0e6530 | 5469 | the target. Permissible values are 2 and 3. @samp{-mfp=} is a synonym |
247f8561 | 5470 | for @samp{-mfpe=}, for compatibility with older versions of GCC. |
157a620e NC |
5471 | |
5472 | @item -mstructure-size-boundary=<n> | |
5473 | @kindex -mstructure-size-boundary | |
5474 | The size of all structures and unions will be rounded up to a multiple | |
ed0e6530 | 5475 | of the number of bits set by this option. Permissible values are 8 and |
157a620e NC |
5476 | 32. The default value varies for different toolchains. For the COFF |
5477 | targeted toolchain the default value is 8. Specifying the larger number | |
ed0e6530 | 5478 | can produce faster, more efficient code, but can also increase the size |
157a620e NC |
5479 | of the program. The two values are potentially incompatible. Code |
5480 | compiled with one value cannot necessarily expect to work with code or | |
5481 | libraries compiled with the other value, if they exchange information | |
247f8561 | 5482 | using structures or unions. |
157a620e | 5483 | |
f5a1b0d2 NC |
5484 | @item -mabort-on-noreturn |
5485 | @kindex -mabort-on-noreturn | |
5486 | @kindex -mnoabort-on-noreturn | |
247f8561 PB |
5487 | Generate a call to the function @code{abort} at the end of a |
5488 | @code{noreturn} function. It will be executed if the function tries to | |
5489 | return. | |
f5a1b0d2 | 5490 | |
c27ba912 DM |
5491 | @item -mlong-calls |
5492 | @itemx -mno-long-calls | |
5493 | Tells the compiler to perform function calls by first loading the | |
5494 | address of the function into a register and then performing a subroutine | |
5495 | call on this register. This switch is needed if the target function | |
5496 | will lie outside of the 64 megabyte addressing range of the offset based | |
02f52e19 | 5497 | version of subroutine call instruction. |
c27ba912 DM |
5498 | |
5499 | Even if this switch is enabled, not all function calls will be turned | |
5500 | into long calls. The heuristic is that static functions, functions | |
5501 | which have the @samp{short-call} attribute, functions that are inside | |
5502 | the scope of a @samp{#pragma no_long_calls} directive and functions whose | |
5503 | definitions have already been compiled within the current compilation | |
5504 | unit, will not be turned into long calls. The exception to this rule is | |
b192711e | 5505 | that weak function definitions, functions with the @samp{long-call} |
c27ba912 DM |
5506 | attribute or the @samp{section} attribute, and functions that are within |
5507 | the scope of a @samp{#pragma long_calls} directive, will always be | |
5508 | turned into long calls. | |
5509 | ||
5510 | This feature is not enabled by default. Specifying | |
247f8561 | 5511 | @samp{-mno-long-calls} will restore the default behaviour, as will |
c27ba912 DM |
5512 | placing the function calls within the scope of a @samp{#pragma |
5513 | long_calls_off} directive. Note these switches have no effect on how | |
5514 | the compiler generates code to handle function calls via function | |
02f52e19 | 5515 | pointers. |
c27ba912 | 5516 | |
62b10bbc NC |
5517 | @item -mnop-fun-dllimport |
5518 | @kindex -mnop-fun-dllimport | |
247f8561 | 5519 | Disable support for the @emph{dllimport} attribute. |
62b10bbc | 5520 | |
ed0e6530 PB |
5521 | @item -msingle-pic-base |
5522 | @kindex -msingle-pic-base | |
5523 | Treat the register used for PIC addressing as read-only, rather than | |
5524 | loading it in the prologue for each function. The run-time system is | |
5525 | responsible for initialising this register with an appropriate value | |
5526 | before execution begins. | |
5527 | ||
5528 | @item -mpic-register=<reg> | |
5529 | @kindex -mpic-register= | |
5530 | Specify the register to be used for PIC addressing. The default is R10 | |
5531 | unless stack-checking is enabled, when R9 is used. | |
5532 | ||
247f8561 PB |
5533 | @item -mpoke-function-name |
5534 | @kindex -mpoke-function-name | |
5535 | Write the name of each function into the text section, directly | |
5536 | preceding the function prologue. The generated code is similar to this: | |
74291a4b | 5537 | |
247f8561 PB |
5538 | @smallexample |
5539 | t0 | |
5540 | .ascii "arm_poke_function_name", 0 | |
5541 | .align | |
5542 | t1 | |
5543 | .word 0xff000000 + (t1 - t0) | |
5544 | arm_poke_function_name | |
5545 | mov ip, sp | |
5546 | stmfd sp!, @{fp, ip, lr, pc@} | |
5547 | sub fp, ip, #4 | |
5548 | @end smallexample | |
157a620e | 5549 | |
247f8561 PB |
5550 | When performing a stack backtrace, code can inspect the value of |
5551 | @code{pc} stored at @code{fp + 0}. If the trace function then looks at | |
5552 | location @code{pc - 12} and the top 8 bits are set, then we know that | |
5553 | there is a function name embedded immediately preceding this location | |
5554 | and has length @code{((pc[-3]) & 0xff000000)}. | |
157a620e | 5555 | |
247f8561 PB |
5556 | @item -mthumb |
5557 | @kindex -mthumb | |
5558 | Generate code for the 16-bit Thumb instruction set. The default is to | |
5559 | use the 32-bit ARM instruction set. | |
157a620e NC |
5560 | |
5561 | @item -mtpcs-frame | |
5562 | @kindex -mtpcs-frame | |
5563 | @kindex -mno-tpcs-frame | |
5564 | Generate a stack frame that is compliant with the Thumb Procedure Call | |
5565 | Standard for all non-leaf functions. (A leaf function is one that does | |
247f8561 | 5566 | not call any other functions.) The default is @samp{-mno-tpcs-frame}. |
157a620e NC |
5567 | |
5568 | @item -mtpcs-leaf-frame | |
5569 | @kindex -mtpcs-leaf-frame | |
5570 | @kindex -mno-tpcs-leaf-frame | |
5571 | Generate a stack frame that is compliant with the Thumb Procedure Call | |
5572 | Standard for all leaf functions. (A leaf function is one that does | |
247f8561 | 5573 | not call any other functions.) The default is @samp{-mno-apcs-leaf-frame}. |
62b10bbc NC |
5574 | |
5575 | @item -mcallee-super-interworking | |
5576 | @kindex -mcallee-super-interworking | |
5577 | Gives all externally visible functions in the file being compiled an ARM | |
5578 | instruction set header which switches to Thumb mode before executing the | |
5579 | rest of the function. This allows these functions to be called from | |
5580 | non-interworking code. | |
5581 | ||
5582 | @item -mcaller-super-interworking | |
5583 | @kindex -mcaller-super-interworking | |
5584 | Allows calls via function pointers (including virtual functions) to | |
5585 | execute correctly regardless of whether the target code has been | |
5586 | compiled for interworking or not. There is a small overhead in the cost | |
4bdc1ac7 PB |
5587 | of executing a function pointer if this option is enabled. |
5588 | ||
157a620e NC |
5589 | @end table |
5590 | ||
ecff22ab JL |
5591 | @node MN10200 Options |
5592 | @subsection MN10200 Options | |
5593 | @cindex MN10200 options | |
5594 | These @samp{-m} options are defined for Matsushita MN10200 architectures: | |
2642624b | 5595 | @table @gcctabopt |
ecff22ab JL |
5596 | |
5597 | @item -mrelax | |
5598 | Indicate to the linker that it should perform a relaxation optimization pass | |
5599 | to shorten branches, calls and absolute memory addresses. This option only | |
5600 | has an effect when used on the command line for the final link step. | |
5601 | ||
02f52e19 | 5602 | This option makes symbolic debugging impossible. |
ecff22ab | 5603 | @end table |
157a620e | 5604 | |
6d6d0fa0 JL |
5605 | @node MN10300 Options |
5606 | @subsection MN10300 Options | |
5607 | @cindex MN10300 options | |
5608 | These @samp{-m} options are defined for Matsushita MN10300 architectures: | |
5609 | ||
2642624b | 5610 | @table @gcctabopt |
6d6d0fa0 JL |
5611 | @item -mmult-bug |
5612 | Generate code to avoid bugs in the multiply instructions for the MN10300 | |
5613 | processors. This is the default. | |
5614 | ||
5615 | @item -mno-mult-bug | |
5616 | Do not generate code to avoid bugs in the multiply instructions for the | |
5617 | MN10300 processors. | |
ecff22ab | 5618 | |
705ac34f JL |
5619 | @item -mam33 |
5620 | Generate code which uses features specific to the AM33 processor. | |
5621 | ||
5622 | @item -mno-am33 | |
5623 | Do not generate code which uses features specific to the AM33 processor. This | |
5624 | is the default. | |
5625 | ||
ecff22ab JL |
5626 | @item -mrelax |
5627 | Indicate to the linker that it should perform a relaxation optimization pass | |
5628 | to shorten branches, calls and absolute memory addresses. This option only | |
5629 | has an effect when used on the command line for the final link step. | |
5630 | ||
02f52e19 | 5631 | This option makes symbolic debugging impossible. |
6d6d0fa0 JL |
5632 | @end table |
5633 | ||
ecff22ab | 5634 | |
861bb6c1 JL |
5635 | @node M32R/D Options |
5636 | @subsection M32R/D Options | |
5637 | @cindex M32R/D options | |
5638 | ||
5639 | These @samp{-m} options are defined for Mitsubishi M32R/D architectures: | |
5640 | ||
2642624b | 5641 | @table @gcctabopt |
861bb6c1 JL |
5642 | @item -mcode-model=small |
5643 | Assume all objects live in the lower 16MB of memory (so that their addresses | |
5644 | can be loaded with the @code{ld24} instruction), and assume all subroutines | |
5645 | are reachable with the @code{bl} instruction. | |
5646 | This is the default. | |
5647 | ||
5648 | The addressability of a particular object can be set with the | |
5649 | @code{model} attribute. | |
5650 | ||
5651 | @item -mcode-model=medium | |
02f52e19 | 5652 | Assume objects may be anywhere in the 32-bit address space (the compiler |
861bb6c1 JL |
5653 | will generate @code{seth/add3} instructions to load their addresses), and |
5654 | assume all subroutines are reachable with the @code{bl} instruction. | |
5655 | ||
5656 | @item -mcode-model=large | |
02f52e19 | 5657 | Assume objects may be anywhere in the 32-bit address space (the compiler |
861bb6c1 JL |
5658 | will generate @code{seth/add3} instructions to load their addresses), and |
5659 | assume subroutines may not be reachable with the @code{bl} instruction | |
5660 | (the compiler will generate the much slower @code{seth/add3/jl} | |
5661 | instruction sequence). | |
5662 | ||
5663 | @item -msdata=none | |
5664 | Disable use of the small data area. Variables will be put into | |
5665 | one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the | |
5666 | @code{section} attribute has been specified). | |
5667 | This is the default. | |
5668 | ||
5669 | The small data area consists of sections @samp{.sdata} and @samp{.sbss}. | |
5670 | Objects may be explicitly put in the small data area with the | |
5671 | @code{section} attribute using one of these sections. | |
5672 | ||
5673 | @item -msdata=sdata | |
5674 | Put small global and static data in the small data area, but do not | |
5675 | generate special code to reference them. | |
5676 | ||
5677 | @item -msdata=use | |
5678 | Put small global and static data in the small data area, and generate | |
5679 | special instructions to reference them. | |
5680 | ||
5681 | @item -G @var{num} | |
5682 | @cindex smaller data references | |
5683 | Put global and static objects less than or equal to @var{num} bytes | |
5684 | into the small data or bss sections instead of the normal data or bss | |
5685 | sections. The default value of @var{num} is 8. | |
5686 | The @samp{-msdata} option must be set to one of @samp{sdata} or @samp{use} | |
5687 | for this option to have any effect. | |
5688 | ||
5689 | All modules should be compiled with the same @samp{-G @var{num}} value. | |
5690 | Compiling with different values of @var{num} may or may not work; if it | |
5691 | doesn't the linker will give an error message - incorrect code will not be | |
5692 | generated. | |
5693 | ||
5694 | @end table | |
5695 | ||
74291a4b MM |
5696 | @node M88K Options |
5697 | @subsection M88K Options | |
5698 | @cindex M88k options | |
5699 | ||
5700 | These @samp{-m} options are defined for Motorola 88k architectures: | |
5701 | ||
2642624b | 5702 | @table @gcctabopt |
74291a4b MM |
5703 | @item -m88000 |
5704 | @kindex -m88000 | |
5705 | Generate code that works well on both the m88100 and the | |
5706 | m88110. | |
5707 | ||
5708 | @item -m88100 | |
5709 | @kindex -m88100 | |
5710 | Generate code that works best for the m88100, but that also | |
5711 | runs on the m88110. | |
5712 | ||
5713 | @item -m88110 | |
5714 | @kindex -m88110 | |
5715 | Generate code that works best for the m88110, and may not run | |
5716 | on the m88100. | |
5717 | ||
5718 | @item -mbig-pic | |
5719 | @kindex -mbig-pic | |
5720 | Obsolete option to be removed from the next revision. | |
5721 | Use @samp{-fPIC}. | |
5722 | ||
5723 | @item -midentify-revision | |
5724 | @kindex -midentify-revision | |
5725 | @kindex ident | |
5726 | @cindex identifying source, compiler (88k) | |
5727 | Include an @code{ident} directive in the assembler output recording the | |
5728 | source file name, compiler name and version, timestamp, and compilation | |
5729 | flags used. | |
5730 | ||
5731 | @item -mno-underscores | |
5732 | @kindex -mno-underscores | |
5733 | @cindex underscores, avoiding (88k) | |
5734 | In assembler output, emit symbol names without adding an underscore | |
5735 | character at the beginning of each name. The default is to use an | |
5736 | underscore as prefix on each name. | |
5737 | ||
5738 | @item -mocs-debug-info | |
5739 | @itemx -mno-ocs-debug-info | |
5740 | @kindex -mocs-debug-info | |
5741 | @kindex -mno-ocs-debug-info | |
5742 | @cindex OCS (88k) | |
5743 | @cindex debugging, 88k OCS | |
5744 | Include (or omit) additional debugging information (about registers used | |
5745 | in each stack frame) as specified in the 88open Object Compatibility | |
5746 | Standard, ``OCS''. This extra information allows debugging of code that | |
5747 | has had the frame pointer eliminated. The default for DG/UX, SVr4, and | |
5748 | Delta 88 SVr3.2 is to include this information; other 88k configurations | |
5749 | omit this information by default. | |
5750 | ||
5751 | @item -mocs-frame-position | |
5752 | @kindex -mocs-frame-position | |
5753 | @cindex register positions in frame (88k) | |
5754 | When emitting COFF debugging information for automatic variables and | |
5755 | parameters stored on the stack, use the offset from the canonical frame | |
5756 | address, which is the stack pointer (register 31) on entry to the | |
5757 | function. The DG/UX, SVr4, Delta88 SVr3.2, and BCS configurations use | |
5758 | @samp{-mocs-frame-position}; other 88k configurations have the default | |
5759 | @samp{-mno-ocs-frame-position}. | |
5760 | ||
5761 | @item -mno-ocs-frame-position | |
5762 | @kindex -mno-ocs-frame-position | |
5763 | @cindex register positions in frame (88k) | |
5764 | When emitting COFF debugging information for automatic variables and | |
5765 | parameters stored on the stack, use the offset from the frame pointer | |
5766 | register (register 30). When this option is in effect, the frame | |
5767 | pointer is not eliminated when debugging information is selected by the | |
5768 | -g switch. | |
5769 | ||
5770 | @item -moptimize-arg-area | |
5771 | @itemx -mno-optimize-arg-area | |
5772 | @kindex -moptimize-arg-area | |
5773 | @kindex -mno-optimize-arg-area | |
5774 | @cindex arguments in frame (88k) | |
5775 | Control how function arguments are stored in stack frames. | |
5776 | @samp{-moptimize-arg-area} saves space by optimizing them, but this | |
5777 | conflicts with the 88open specifications. The opposite alternative, | |
5778 | @samp{-mno-optimize-arg-area}, agrees with 88open standards. By default | |
0c2d1a2a | 5779 | GCC does not optimize the argument area. |
74291a4b MM |
5780 | |
5781 | @item -mshort-data-@var{num} | |
5782 | @kindex -mshort-data-@var{num} | |
5783 | @cindex smaller data references (88k) | |
5784 | @cindex r0-relative references (88k) | |
5785 | Generate smaller data references by making them relative to @code{r0}, | |
5786 | which allows loading a value using a single instruction (rather than the | |
5787 | usual two). You control which data references are affected by | |
5788 | specifying @var{num} with this option. For example, if you specify | |
5789 | @samp{-mshort-data-512}, then the data references affected are those | |
5790 | involving displacements of less than 512 bytes. | |
5791 | @samp{-mshort-data-@var{num}} is not effective for @var{num} greater | |
5792 | than 64k. | |
5793 | ||
5794 | @item -mserialize-volatile | |
5795 | @kindex -mserialize-volatile | |
5796 | @itemx -mno-serialize-volatile | |
5797 | @kindex -mno-serialize-volatile | |
5798 | @cindex sequential consistency on 88k | |
5799 | Do, or don't, generate code to guarantee sequential consistency | |
5800 | of volatile memory references. By default, consistency is | |
5801 | guaranteed. | |
5802 | ||
5803 | The order of memory references made by the MC88110 processor does | |
5804 | not always match the order of the instructions requesting those | |
5805 | references. In particular, a load instruction may execute before | |
5806 | a preceding store instruction. Such reordering violates | |
5807 | sequential consistency of volatile memory references, when there | |
5808 | are multiple processors. When consistency must be guaranteed, | |
5809 | GNU C generates special instructions, as needed, to force | |
5810 | execution in the proper order. | |
5811 | ||
5812 | The MC88100 processor does not reorder memory references and so | |
5813 | always provides sequential consistency. However, by default, GNU | |
5814 | C generates the special instructions to guarantee consistency | |
5815 | even when you use @samp{-m88100}, so that the code may be run on an | |
5816 | MC88110 processor. If you intend to run your code only on the | |
5817 | MC88100 processor, you may use @samp{-mno-serialize-volatile}. | |
5818 | ||
5819 | The extra code generated to guarantee consistency may affect the | |
5820 | performance of your application. If you know that you can safely | |
5821 | forgo this guarantee, you may use @samp{-mno-serialize-volatile}. | |
5822 | ||
5823 | @item -msvr4 | |
5824 | @itemx -msvr3 | |
5825 | @kindex -msvr4 | |
5826 | @kindex -msvr3 | |
5827 | @cindex assembler syntax, 88k | |
5828 | @cindex SVr4 | |
5829 | Turn on (@samp{-msvr4}) or off (@samp{-msvr3}) compiler extensions | |
5830 | related to System V release 4 (SVr4). This controls the following: | |
5831 | ||
5832 | @enumerate | |
5833 | @item | |
5834 | Which variant of the assembler syntax to emit. | |
5835 | @item | |
5836 | @samp{-msvr4} makes the C preprocessor recognize @samp{#pragma weak} | |
5837 | that is used on System V release 4. | |
5838 | @item | |
0c2d1a2a | 5839 | @samp{-msvr4} makes GCC issue additional declaration directives used in |
74291a4b MM |
5840 | SVr4. |
5841 | @end enumerate | |
5842 | ||
5843 | @samp{-msvr4} is the default for the m88k-motorola-sysv4 and | |
5844 | m88k-dg-dgux m88k configurations. @samp{-msvr3} is the default for all | |
5845 | other m88k configurations. | |
5846 | ||
5847 | @item -mversion-03.00 | |
5848 | @kindex -mversion-03.00 | |
5849 | This option is obsolete, and is ignored. | |
5850 | @c ??? which asm syntax better for GAS? option there too? | |
5851 | ||
5852 | @item -mno-check-zero-division | |
5853 | @itemx -mcheck-zero-division | |
5854 | @kindex -mno-check-zero-division | |
5855 | @kindex -mcheck-zero-division | |
5856 | @cindex zero division on 88k | |
5857 | Do, or don't, generate code to guarantee that integer division by | |
5858 | zero will be detected. By default, detection is guaranteed. | |
5859 | ||
5860 | Some models of the MC88100 processor fail to trap upon integer | |
5861 | division by zero under certain conditions. By default, when | |
5862 | compiling code that might be run on such a processor, GNU C | |
5863 | generates code that explicitly checks for zero-valued divisors | |
5864 | and traps with exception number 503 when one is detected. Use of | |
5865 | mno-check-zero-division suppresses such checking for code | |
5866 | generated to run on an MC88100 processor. | |
5867 | ||
5868 | GNU C assumes that the MC88110 processor correctly detects all | |
5869 | instances of integer division by zero. When @samp{-m88110} is | |
5870 | specified, both @samp{-mcheck-zero-division} and | |
5871 | @samp{-mno-check-zero-division} are ignored, and no explicit checks for | |
5872 | zero-valued divisors are generated. | |
5873 | ||
5874 | @item -muse-div-instruction | |
5875 | @kindex -muse-div-instruction | |
5876 | @cindex divide instruction, 88k | |
5877 | Use the div instruction for signed integer division on the | |
5878 | MC88100 processor. By default, the div instruction is not used. | |
5879 | ||
5880 | On the MC88100 processor the signed integer division instruction | |
5881 | div) traps to the operating system on a negative operand. The | |
5882 | operating system transparently completes the operation, but at a | |
5883 | large cost in execution time. By default, when compiling code | |
5884 | that might be run on an MC88100 processor, GNU C emulates signed | |
5885 | integer division using the unsigned integer division instruction | |
5886 | divu), thereby avoiding the large penalty of a trap to the | |
5887 | operating system. Such emulation has its own, smaller, execution | |
5888 | cost in both time and space. To the extent that your code's | |
5889 | important signed integer division operations are performed on two | |
5890 | nonnegative operands, it may be desirable to use the div | |
5891 | instruction directly. | |
5892 | ||
5893 | On the MC88110 processor the div instruction (also known as the | |
5894 | divs instruction) processes negative operands without trapping to | |
5895 | the operating system. When @samp{-m88110} is specified, | |
5896 | @samp{-muse-div-instruction} is ignored, and the div instruction is used | |
5897 | for signed integer division. | |
5898 | ||
5899 | Note that the result of dividing INT_MIN by -1 is undefined. In | |
5900 | particular, the behavior of such a division with and without | |
5901 | @samp{-muse-div-instruction} may differ. | |
5902 | ||
5903 | @item -mtrap-large-shift | |
5904 | @itemx -mhandle-large-shift | |
5905 | @kindex -mtrap-large-shift | |
5906 | @kindex -mhandle-large-shift | |
5907 | @cindex bit shift overflow (88k) | |
5908 | @cindex large bit shifts (88k) | |
5909 | Include code to detect bit-shifts of more than 31 bits; respectively, | |
0c2d1a2a | 5910 | trap such shifts or emit code to handle them properly. By default GCC |
74291a4b MM |
5911 | makes no special provision for large bit shifts. |
5912 | ||
5913 | @item -mwarn-passed-structs | |
5914 | @kindex -mwarn-passed-structs | |
5915 | @cindex structure passing (88k) | |
5916 | Warn when a function passes a struct as an argument or result. | |
5917 | Structure-passing conventions have changed during the evolution of the C | |
5918 | language, and are often the source of portability problems. By default, | |
0c2d1a2a | 5919 | GCC issues no such warning. |
74291a4b MM |
5920 | @end table |
5921 | ||
5922 | @node RS/6000 and PowerPC Options | |
5923 | @subsection IBM RS/6000 and PowerPC Options | |
5924 | @cindex RS/6000 and PowerPC Options | |
5925 | @cindex IBM RS/6000 and PowerPC Options | |
5926 | ||
5927 | These @samp{-m} options are defined for the IBM RS/6000 and PowerPC: | |
2642624b | 5928 | @table @gcctabopt |
74291a4b MM |
5929 | @item -mpower |
5930 | @itemx -mno-power | |
5931 | @itemx -mpower2 | |
5932 | @itemx -mno-power2 | |
5933 | @itemx -mpowerpc | |
5934 | @itemx -mno-powerpc | |
5935 | @itemx -mpowerpc-gpopt | |
5936 | @itemx -mno-powerpc-gpopt | |
5937 | @itemx -mpowerpc-gfxopt | |
5938 | @itemx -mno-powerpc-gfxopt | |
7fe90e7b DE |
5939 | @itemx -mpowerpc64 |
5940 | @itemx -mno-powerpc64 | |
74291a4b MM |
5941 | @kindex -mpower |
5942 | @kindex -mpower2 | |
5943 | @kindex -mpowerpc | |
5944 | @kindex -mpowerpc-gpopt | |
5945 | @kindex -mpowerpc-gfxopt | |
7fe90e7b | 5946 | @kindex -mpowerpc64 |
0c2d1a2a | 5947 | GCC supports two related instruction set architectures for the |
74291a4b MM |
5948 | RS/6000 and PowerPC. The @dfn{POWER} instruction set are those |
5949 | instructions supported by the @samp{rios} chip set used in the original | |
5950 | RS/6000 systems and the @dfn{PowerPC} instruction set is the | |
5951 | architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and | |
861bb6c1 | 5952 | the IBM 4xx microprocessors. |
74291a4b MM |
5953 | |
5954 | Neither architecture is a subset of the other. However there is a | |
5955 | large common subset of instructions supported by both. An MQ | |
5956 | register is included in processors supporting the POWER architecture. | |
5957 | ||
5958 | You use these options to specify which instructions are available on the | |
5959 | processor you are using. The default value of these options is | |
0c2d1a2a | 5960 | determined when configuring GCC. Specifying the |
74291a4b MM |
5961 | @samp{-mcpu=@var{cpu_type}} overrides the specification of these |
5962 | options. We recommend you use the @samp{-mcpu=@var{cpu_type}} option | |
5963 | rather than the options listed above. | |
5964 | ||
0c2d1a2a | 5965 | The @samp{-mpower} option allows GCC to generate instructions that |
74291a4b | 5966 | are found only in the POWER architecture and to use the MQ register. |
0c2d1a2a | 5967 | Specifying @samp{-mpower2} implies @samp{-power} and also allows GCC |
74291a4b MM |
5968 | to generate instructions that are present in the POWER2 architecture but |
5969 | not the original POWER architecture. | |
5970 | ||
0c2d1a2a | 5971 | The @samp{-mpowerpc} option allows GCC to generate instructions that |
74291a4b MM |
5972 | are found only in the 32-bit subset of the PowerPC architecture. |
5973 | Specifying @samp{-mpowerpc-gpopt} implies @samp{-mpowerpc} and also allows | |
0c2d1a2a | 5974 | GCC to use the optional PowerPC architecture instructions in the |
74291a4b | 5975 | General Purpose group, including floating-point square root. Specifying |
0c2d1a2a | 5976 | @samp{-mpowerpc-gfxopt} implies @samp{-mpowerpc} and also allows GCC to |
74291a4b MM |
5977 | use the optional PowerPC architecture instructions in the Graphics |
5978 | group, including floating-point select. | |
5979 | ||
0c2d1a2a | 5980 | The @samp{-mpowerpc64} option allows GCC to generate the additional |
7fe90e7b | 5981 | 64-bit instructions that are found in the full PowerPC64 architecture |
0c2d1a2a | 5982 | and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to |
7fe90e7b DE |
5983 | @samp{-mno-powerpc64}. |
5984 | ||
0c2d1a2a | 5985 | If you specify both @samp{-mno-power} and @samp{-mno-powerpc}, GCC |
74291a4b MM |
5986 | will use only the instructions in the common subset of both |
5987 | architectures plus some special AIX common-mode calls, and will not use | |
5988 | the MQ register. Specifying both @samp{-mpower} and @samp{-mpowerpc} | |
0c2d1a2a | 5989 | permits GCC to use any instruction from either architecture and to |
74291a4b MM |
5990 | allow use of the MQ register; specify this for the Motorola MPC601. |
5991 | ||
5992 | @item -mnew-mnemonics | |
5993 | @itemx -mold-mnemonics | |
5994 | @kindex -mnew-mnemonics | |
5995 | @kindex -mold-mnemonics | |
5996 | Select which mnemonics to use in the generated assembler code. | |
5997 | @samp{-mnew-mnemonics} requests output that uses the assembler mnemonics | |
5998 | defined for the PowerPC architecture, while @samp{-mold-mnemonics} | |
5999 | requests the assembler mnemonics defined for the POWER architecture. | |
6000 | Instructions defined in only one architecture have only one mnemonic; | |
0c2d1a2a | 6001 | GCC uses that mnemonic irrespective of which of these options is |
74291a4b MM |
6002 | specified. |
6003 | ||
0c2d1a2a | 6004 | GCC defaults to the mnemonics appropriate for the architecture in |
7fe90e7b DE |
6005 | use. Specifying @samp{-mcpu=@var{cpu_type}} sometimes overrides the |
6006 | value of these option. Unless you are building a cross-compiler, you | |
6007 | should normally not specify either @samp{-mnew-mnemonics} or | |
74291a4b MM |
6008 | @samp{-mold-mnemonics}, but should instead accept the default. |
6009 | ||
6010 | @item -mcpu=@var{cpu_type} | |
7fe90e7b | 6011 | @kindex -mcpu |
74291a4b MM |
6012 | Set architecture type, register usage, choice of mnemonics, and |
6013 | instruction scheduling parameters for machine type @var{cpu_type}. | |
5f59ecb7 DE |
6014 | Supported values for @var{cpu_type} are @samp{rios}, @samp{rios1}, |
6015 | @samp{rsc}, @samp{rios2}, @samp{rs64a}, @samp{601}, @samp{602}, | |
6016 | @samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620}, | |
6017 | @samp{630}, @samp{740}, @samp{750}, @samp{power}, @samp{power2}, | |
6018 | @samp{powerpc}, @samp{403}, @samp{505}, @samp{801}, @samp{821}, | |
6019 | @samp{823}, and @samp{860} and @samp{common}. @samp{-mcpu=power}, | |
6020 | @samp{-mcpu=power2}, @samp{-mcpu=powerpc}, and @samp{-mcpu=powerpc64} | |
6021 | specify generic POWER, POWER2, pure 32-bit PowerPC (i.e., not MPC601), | |
6022 | and 64-bit PowerPC architecture machine types, with an appropriate, | |
bef84347 | 6023 | generic processor model assumed for scheduling purposes.@refill |
74291a4b | 6024 | |
02f52e19 | 6025 | Specifying any of the following options: |
74291a4b | 6026 | @samp{-mcpu=rios1}, @samp{-mcpu=rios2}, @samp{-mcpu=rsc}, |
02f52e19 AJ |
6027 | @samp{-mcpu=power}, or @samp{-mcpu=power2} |
6028 | enables the @samp{-mpower} option and disables the @samp{-mpowerpc} option; | |
74291a4b | 6029 | @samp{-mcpu=601} enables both the @samp{-mpower} and @samp{-mpowerpc} options. |
5f59ecb7 DE |
6030 | All of @samp{-mcpu=rs64a}, @samp{-mcpu=602}, @samp{-mcpu=603}, |
6031 | @samp{-mcpu=603e}, @samp{-mcpu=604}, @samp{-mcpu=620}, @samp{-mcpu=630}, | |
6032 | @samp{-mcpu=740}, and @samp{-mcpu=750} | |
02f52e19 | 6033 | enable the @samp{-mpowerpc} option and disable the @samp{-mpower} option. |
74291a4b | 6034 | Exactly similarly, all of @samp{-mcpu=403}, |
02f52e19 | 6035 | @samp{-mcpu=505}, @samp{-mcpu=821}, @samp{-mcpu=860} and @samp{-mcpu=powerpc} |
74291a4b | 6036 | enable the @samp{-mpowerpc} option and disable the @samp{-mpower} option. |
02f52e19 | 6037 | @samp{-mcpu=common} disables both the |
74291a4b | 6038 | @samp{-mpower} and @samp{-mpowerpc} options.@refill |
74291a4b MM |
6039 | |
6040 | AIX versions 4 or greater selects @samp{-mcpu=common} by default, so | |
5f59ecb7 | 6041 | that code will operate on all members of the RS/6000 POWER and PowerPC |
0c2d1a2a | 6042 | families. In that case, GCC will use only the instructions in the |
74291a4b | 6043 | common subset of both architectures plus some special AIX common-mode |
0c2d1a2a | 6044 | calls, and will not use the MQ register. GCC assumes a generic |
74291a4b MM |
6045 | processor model for scheduling purposes. |
6046 | ||
6047 | Specifying any of the options @samp{-mcpu=rios1}, @samp{-mcpu=rios2}, | |
6048 | @samp{-mcpu=rsc}, @samp{-mcpu=power}, or @samp{-mcpu=power2} also | |
6049 | disables the @samp{new-mnemonics} option. Specifying @samp{-mcpu=601}, | |
6050 | @samp{-mcpu=602}, @samp{-mcpu=603}, @samp{-mcpu=603e}, @samp{-mcpu=604}, | |
5f59ecb7 DE |
6051 | @samp{-mcpu=620}, @samp{-mcpu=630}, @samp{-mcpu=403}, @samp{-mcpu=505}, |
6052 | @samp{-mcpu=821}, @samp{-mcpu=860} or @samp{-mcpu=powerpc} also enables | |
6053 | the @samp{new-mnemonics} option.@refill | |
74291a4b MM |
6054 | |
6055 | Specifying @samp{-mcpu=403}, @samp{-mcpu=821}, or @samp{-mcpu=860} also | |
6056 | enables the @samp{-msoft-float} option. | |
6057 | ||
6058 | @item -mtune=@var{cpu_type} | |
6059 | Set the instruction scheduling parameters for machine type | |
6060 | @var{cpu_type}, but do not set the architecture type, register usage, | |
6061 | choice of mnemonics like @samp{-mcpu=}@var{cpu_type} would. The same | |
6062 | values for @var{cpu_type} are used for @samp{-mtune=}@var{cpu_type} as | |
6063 | for @samp{-mcpu=}@var{cpu_type}. The @samp{-mtune=}@var{cpu_type} | |
6064 | option overrides the @samp{-mcpu=}@var{cpu_type} option in terms of | |
6065 | instruction scheduling parameters. | |
6066 | ||
6067 | @item -mfull-toc | |
6068 | @itemx -mno-fp-in-toc | |
6069 | @itemx -mno-sum-in-toc | |
6070 | @itemx -mminimal-toc | |
7fe90e7b | 6071 | @kindex -mminimal-toc |
74291a4b MM |
6072 | Modify generation of the TOC (Table Of Contents), which is created for |
6073 | every executable file. The @samp{-mfull-toc} option is selected by | |
0c2d1a2a JB |
6074 | default. In that case, GCC will allocate at least one TOC entry for |
6075 | each unique non-automatic variable reference in your program. GCC | |
74291a4b MM |
6076 | will also place floating-point constants in the TOC. However, only |
6077 | 16,384 entries are available in the TOC. | |
6078 | ||
6079 | If you receive a linker error message that saying you have overflowed | |
6080 | the available TOC space, you can reduce the amount of TOC space used | |
6081 | with the @samp{-mno-fp-in-toc} and @samp{-mno-sum-in-toc} options. | |
0c2d1a2a JB |
6082 | @samp{-mno-fp-in-toc} prevents GCC from putting floating-point |
6083 | constants in the TOC and @samp{-mno-sum-in-toc} forces GCC to | |
74291a4b MM |
6084 | generate code to calculate the sum of an address and a constant at |
6085 | run-time instead of putting that sum into the TOC. You may specify one | |
0c2d1a2a | 6086 | or both of these options. Each causes GCC to produce very slightly |
74291a4b MM |
6087 | slower and larger code at the expense of conserving TOC space. |
6088 | ||
6089 | If you still run out of space in the TOC even when you specify both of | |
6090 | these options, specify @samp{-mminimal-toc} instead. This option causes | |
0c2d1a2a JB |
6091 | GCC to make only one TOC entry for every file. When you specify this |
6092 | option, GCC will produce code that is slower and larger but which | |
74291a4b MM |
6093 | uses extremely little TOC space. You may wish to use this option |
6094 | only on files that contain less frequently executed code. @refill | |
6095 | ||
fa06229f GK |
6096 | @item -maix64 |
6097 | @itemx -maix32 | |
6098 | @kindex -maix64 | |
6099 | @kindex -maix32 | |
6100 | Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit | |
7fe90e7b | 6101 | @code{long} type, and the infrastructure needed to support them. |
fa06229f GK |
6102 | Specifying @samp{-maix64} implies @samp{-mpowerpc64} and |
6103 | @samp{-mpowerpc}, while @samp{-maix32} disables the 64-bit ABI and | |
6104 | implies @samp{-mno-powerpc64}. GCC defaults to @samp{-maix32}. | |
7fe90e7b | 6105 | |
74291a4b MM |
6106 | @item -mxl-call |
6107 | @itemx -mno-xl-call | |
7fe90e7b | 6108 | @kindex -mxl-call |
74291a4b MM |
6109 | On AIX, pass floating-point arguments to prototyped functions beyond the |
6110 | register save area (RSA) on the stack in addition to argument FPRs. The | |
6111 | AIX calling convention was extended but not initially documented to | |
6112 | handle an obscure K&R C case of calling a function that takes the | |
6113 | address of its arguments with fewer arguments than declared. AIX XL | |
7fe90e7b DE |
6114 | compilers access floating point arguments which do not fit in the |
6115 | RSA from the stack when a subroutine is compiled without | |
74291a4b MM |
6116 | optimization. Because always storing floating-point arguments on the |
6117 | stack is inefficient and rarely needed, this option is not enabled by | |
6118 | default and only is necessary when calling subroutines compiled by AIX | |
6119 | XL compilers without optimization. | |
6120 | ||
861bb6c1 | 6121 | @item -mthreads |
7fe90e7b | 6122 | @kindex -mthreads |
861bb6c1 JL |
6123 | Support @dfn{AIX Threads}. Link an application written to use |
6124 | @dfn{pthreads} with special libraries and startup code to enable the | |
6125 | application to run. | |
6126 | ||
6127 | @item -mpe | |
7fe90e7b | 6128 | @kindex -mpe |
861bb6c1 JL |
6129 | Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE). Link an |
6130 | application written to use message passing with special startup code to | |
6131 | enable the application to run. The system must have PE installed in the | |
6132 | standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file | |
6133 | must be overridden with the @samp{-specs=} option to specify the | |
6134 | appropriate directory location. The Parallel Environment does not | |
6135 | support threads, so the @samp{-mpe} option and the @samp{-mthreads} | |
6136 | option are incompatible. | |
6137 | ||
74291a4b MM |
6138 | @item -msoft-float |
6139 | @itemx -mhard-float | |
7fe90e7b | 6140 | @kindex -msoft-float |
74291a4b MM |
6141 | Generate code that does not use (uses) the floating-point register set. |
6142 | Software floating point emulation is provided if you use the | |
0c2d1a2a | 6143 | @samp{-msoft-float} option, and pass the option to GCC when linking. |
74291a4b MM |
6144 | |
6145 | @item -mmultiple | |
6146 | @itemx -mno-multiple | |
6147 | Generate code that uses (does not use) the load multiple word | |
6148 | instructions and the store multiple word instructions. These | |
6149 | instructions are generated by default on POWER systems, and not | |
6150 | generated on PowerPC systems. Do not use @samp{-mmultiple} on little | |
6151 | endian PowerPC systems, since those instructions do not work when the | |
bef84347 VM |
6152 | processor is in little endian mode. The exceptions are PPC740 and |
6153 | PPC750 which permit the instructions usage in little endian mode. | |
74291a4b MM |
6154 | |
6155 | @item -mstring | |
6156 | @itemx -mno-string | |
7fe90e7b | 6157 | @kindex -mstring |
bef84347 VM |
6158 | Generate code that uses (does not use) the load string instructions |
6159 | and the store string word instructions to save multiple registers and | |
6160 | do small block moves. These instructions are generated by default on | |
6161 | POWER systems, and not generated on PowerPC systems. Do not use | |
6162 | @samp{-mstring} on little endian PowerPC systems, since those | |
6163 | instructions do not work when the processor is in little endian mode. | |
6164 | The exceptions are PPC740 and PPC750 which permit the instructions | |
6165 | usage in little endian mode. | |
74291a4b | 6166 | |
861bb6c1 JL |
6167 | @item -mupdate |
6168 | @itemx -mno-update | |
7fe90e7b | 6169 | @kindex -mupdate |
861bb6c1 JL |
6170 | Generate code that uses (does not use) the load or store instructions |
6171 | that update the base register to the address of the calculated memory | |
6172 | location. These instructions are generated by default. If you use | |
6173 | @samp{-mno-update}, there is a small window between the time that the | |
6174 | stack pointer is updated and the address of the previous frame is | |
6175 | stored, which means code that walks the stack frame across interrupts or | |
6176 | signals may get corrupted data. | |
6177 | ||
6178 | @item -mfused-madd | |
6179 | @itemx -mno-fused-madd | |
7fe90e7b | 6180 | @kindex -mfused-madd |
861bb6c1 JL |
6181 | Generate code that uses (does not use) the floating point multiply and |
6182 | accumulate instructions. These instructions are generated by default if | |
6183 | hardware floating is used. | |
6184 | ||
74291a4b MM |
6185 | @item -mno-bit-align |
6186 | @itemx -mbit-align | |
7fe90e7b | 6187 | @kindex -mbit-align |
74291a4b MM |
6188 | On System V.4 and embedded PowerPC systems do not (do) force structures |
6189 | and unions that contain bit fields to be aligned to the base type of the | |
6190 | bit field. | |
6191 | ||
6192 | For example, by default a structure containing nothing but 8 | |
6193 | @code{unsigned} bitfields of length 1 would be aligned to a 4 byte | |
6194 | boundary and have a size of 4 bytes. By using @samp{-mno-bit-align}, | |
6195 | the structure would be aligned to a 1 byte boundary and be one byte in | |
6196 | size. | |
6197 | ||
6198 | @item -mno-strict-align | |
6199 | @itemx -mstrict-align | |
7fe90e7b | 6200 | @kindex -mstrict-align |
74291a4b MM |
6201 | On System V.4 and embedded PowerPC systems do not (do) assume that |
6202 | unaligned memory references will be handled by the system. | |
6203 | ||
6204 | @item -mrelocatable | |
6205 | @itemx -mno-relocatable | |
7fe90e7b | 6206 | @kindex -mrelocatable |
74291a4b MM |
6207 | On embedded PowerPC systems generate code that allows (does not allow) |
6208 | the program to be relocated to a different address at runtime. If you | |
6209 | use @samp{-mrelocatable} on any module, all objects linked together must | |
6210 | be compiled with @samp{-mrelocatable} or @samp{-mrelocatable-lib}. | |
6211 | ||
6212 | @item -mrelocatable-lib | |
6213 | @itemx -mno-relocatable-lib | |
6214 | On embedded PowerPC systems generate code that allows (does not allow) | |
6215 | the program to be relocated to a different address at runtime. Modules | |
956d6950 | 6216 | compiled with @samp{-mrelocatable-lib} can be linked with either modules |
74291a4b MM |
6217 | compiled without @samp{-mrelocatable} and @samp{-mrelocatable-lib} or |
6218 | with modules compiled with the @samp{-mrelocatable} options. | |
6219 | ||
6220 | @item -mno-toc | |
6221 | @itemx -mtoc | |
6222 | On System V.4 and embedded PowerPC systems do not (do) assume that | |
6223 | register 2 contains a pointer to a global area pointing to the addresses | |
6224 | used in the program. | |
6225 | ||
74291a4b MM |
6226 | @item -mlittle |
6227 | @itemx -mlittle-endian | |
6228 | On System V.4 and embedded PowerPC systems compile code for the | |
6229 | processor in little endian mode. The @samp{-mlittle-endian} option is | |
6230 | the same as @samp{-mlittle}. | |
6231 | ||
6232 | @item -mbig | |
6233 | @itemx -mbig-endian | |
6234 | On System V.4 and embedded PowerPC systems compile code for the | |
6235 | processor in big endian mode. The @samp{-mbig-endian} option is | |
6236 | the same as @samp{-mbig}. | |
6237 | ||
6238 | @item -mcall-sysv | |
6239 | On System V.4 and embedded PowerPC systems compile code using calling | |
6240 | conventions that adheres to the March 1995 draft of the System V | |
6241 | Application Binary Interface, PowerPC processor supplement. This is the | |
6242 | default unless you configured GCC using @samp{powerpc-*-eabiaix}. | |
6243 | ||
6244 | @item -mcall-sysv-eabi | |
6245 | Specify both @samp{-mcall-sysv} and @samp{-meabi} options. | |
6246 | ||
6247 | @item -mcall-sysv-noeabi | |
6248 | Specify both @samp{-mcall-sysv} and @samp{-mno-eabi} options. | |
6249 | ||
6250 | @item -mcall-aix | |
6251 | On System V.4 and embedded PowerPC systems compile code using calling | |
6252 | conventions that are similar to those used on AIX. This is the | |
6253 | default if you configured GCC using @samp{powerpc-*-eabiaix}. | |
6254 | ||
6255 | @item -mcall-solaris | |
6256 | On System V.4 and embedded PowerPC systems compile code for the Solaris | |
6257 | operating system. | |
6258 | ||
6259 | @item -mcall-linux | |
861bb6c1 JL |
6260 | On System V.4 and embedded PowerPC systems compile code for the |
6261 | Linux-based GNU system. | |
74291a4b MM |
6262 | |
6263 | @item -mprototype | |
e9a25f70 | 6264 | @itemx -mno-prototype |
74291a4b MM |
6265 | On System V.4 and embedded PowerPC systems assume that all calls to |
6266 | variable argument functions are properly prototyped. Otherwise, the | |
6267 | compiler must insert an instruction before every non prototyped call to | |
6268 | set or clear bit 6 of the condition code register (@var{CR}) to | |
6269 | indicate whether floating point values were passed in the floating point | |
6270 | registers in case the function takes a variable arguments. With | |
6271 | @samp{-mprototype}, only calls to prototyped variable argument functions | |
6272 | will set or clear the bit. | |
6273 | ||
6274 | @item -msim | |
6275 | On embedded PowerPC systems, assume that the startup module is called | |
6276 | @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and | |
6277 | @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}. | |
6278 | configurations. | |
6279 | ||
6280 | @item -mmvme | |
6281 | On embedded PowerPC systems, assume that the startup module is called | |
e9a25f70 JL |
6282 | @file{crt0.o} and the standard C libraries are @file{libmvme.a} and |
6283 | @file{libc.a}. | |
6284 | ||
6285 | @item -mads | |
6286 | On embedded PowerPC systems, assume that the startup module is called | |
6287 | @file{crt0.o} and the standard C libraries are @file{libads.a} and | |
6288 | @file{libc.a}. | |
6289 | ||
6290 | @item -myellowknife | |
6291 | On embedded PowerPC systems, assume that the startup module is called | |
6292 | @file{crt0.o} and the standard C libraries are @file{libyk.a} and | |
74291a4b MM |
6293 | @file{libc.a}. |
6294 | ||
bff46771 GK |
6295 | @item -mvxworks |
6296 | On System V.4 and embedded PowerPC systems, specify that you are | |
6297 | compiling for a VxWorks system. | |
6298 | ||
74291a4b MM |
6299 | @item -memb |
6300 | On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags | |
6301 | header to indicate that @samp{eabi} extended relocations are used. | |
6302 | ||
6303 | @item -meabi | |
6304 | @itemx -mno-eabi | |
6305 | On System V.4 and embedded PowerPC systems do (do not) adhere to the | |
6306 | Embedded Applications Binary Interface (eabi) which is a set of | |
bedc7537 | 6307 | modifications to the System V.4 specifications. Selecting @option{-meabi} |
74291a4b MM |
6308 | means that the stack is aligned to an 8 byte boundary, a function |
6309 | @code{__eabi} is called to from @code{main} to set up the eabi | |
6310 | environment, and the @samp{-msdata} option can use both @code{r2} and | |
6311 | @code{r13} to point to two separate small data areas. Selecting | |
bedc7537 | 6312 | @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary, |
74291a4b MM |
6313 | do not call an initialization function from @code{main}, and the |
6314 | @samp{-msdata} option will only use @code{r13} to point to a single | |
6315 | small data area. The @samp{-meabi} option is on by default if you | |
6316 | configured GCC using one of the @samp{powerpc*-*-eabi*} options. | |
6317 | ||
6318 | @item -msdata=eabi | |
6319 | On System V.4 and embedded PowerPC systems, put small initialized | |
6320 | @code{const} global and static data in the @samp{.sdata2} section, which | |
6321 | is pointed to by register @code{r2}. Put small initialized | |
6322 | non-@code{const} global and static data in the @samp{.sdata} section, | |
6323 | which is pointed to by register @code{r13}. Put small uninitialized | |
6324 | global and static data in the @samp{.sbss} section, which is adjacent to | |
6325 | the @samp{.sdata} section. The @samp{-msdata=eabi} option is | |
6326 | incompatible with the @samp{-mrelocatable} option. The | |
6327 | @samp{-msdata=eabi} option also sets the @samp{-memb} option. | |
6328 | ||
6329 | @item -msdata=sysv | |
6330 | On System V.4 and embedded PowerPC systems, put small global and static | |
6331 | data in the @samp{.sdata} section, which is pointed to by register | |
6332 | @code{r13}. Put small uninitialized global and static data in the | |
6333 | @samp{.sbss} section, which is adjacent to the @samp{.sdata} section. | |
6334 | The @samp{-msdata=sysv} option is incompatible with the | |
6335 | @samp{-mrelocatable} option. | |
6336 | ||
6337 | @item -msdata=default | |
6338 | @itemx -msdata | |
6339 | On System V.4 and embedded PowerPC systems, if @samp{-meabi} is used, | |
6340 | compile code the same as @samp{-msdata=eabi}, otherwise compile code the | |
6341 | same as @samp{-msdata=sysv}. | |
6342 | ||
6343 | @item -msdata-data | |
6344 | On System V.4 and embedded PowerPC systems, put small global and static | |
6345 | data in the @samp{.sdata} section. Put small uninitialized global and | |
6346 | static data in the @samp{.sbss} section. Do not use register @code{r13} | |
6347 | to address small data however. This is the default behavior unless | |
6348 | other @samp{-msdata} options are used. | |
6349 | ||
6350 | @item -msdata=none | |
6351 | @itemx -mno-sdata | |
6352 | On embedded PowerPC systems, put all initialized global and static data | |
6353 | in the @samp{.data} section, and all uninitialized data in the | |
6354 | @samp{.bss} section. | |
6355 | ||
6356 | @item -G @var{num} | |
6357 | @cindex smaller data references (PowerPC) | |
6358 | @cindex .sdata/.sdata2 references (PowerPC) | |
956d6950 | 6359 | On embedded PowerPC systems, put global and static items less than or |
74291a4b MM |
6360 | equal to @var{num} bytes into the small data or bss sections instead of |
6361 | the normal data or bss section. By default, @var{num} is 8. The | |
6362 | @samp{-G @var{num}} switch is also passed to the linker. | |
6363 | All modules should be compiled with the same @samp{-G @var{num}} value. | |
6364 | ||
6365 | @item -mregnames | |
6366 | @itemx -mno-regnames | |
6367 | On System V.4 and embedded PowerPC systems do (do not) emit register | |
6368 | names in the assembly language output using symbolic forms. | |
f5a1b0d2 | 6369 | |
74291a4b | 6370 | @end table |
f5a1b0d2 | 6371 | |
74291a4b MM |
6372 | @node RT Options |
6373 | @subsection IBM RT Options | |
6374 | @cindex RT options | |
6375 | @cindex IBM RT options | |
6376 | ||
6377 | These @samp{-m} options are defined for the IBM RT PC: | |
6378 | ||
2642624b | 6379 | @table @gcctabopt |
74291a4b MM |
6380 | @item -min-line-mul |
6381 | Use an in-line code sequence for integer multiplies. This is the | |
6382 | default. | |
6383 | ||
6384 | @item -mcall-lib-mul | |
6385 | Call @code{lmul$$} for integer multiples. | |
6386 | ||
6387 | @item -mfull-fp-blocks | |
6388 | Generate full-size floating point data blocks, including the minimum | |
6389 | amount of scratch space recommended by IBM. This is the default. | |
6390 | ||
6391 | @item -mminimum-fp-blocks | |
6392 | Do not include extra scratch space in floating point data blocks. This | |
6393 | results in smaller code, but slower execution, since scratch space must | |
6394 | be allocated dynamically. | |
6395 | ||
6396 | @cindex @file{varargs.h} and RT PC | |
6397 | @cindex @file{stdarg.h} and RT PC | |
6398 | @item -mfp-arg-in-fpregs | |
6399 | Use a calling sequence incompatible with the IBM calling convention in | |
6400 | which floating point arguments are passed in floating point registers. | |
6401 | Note that @code{varargs.h} and @code{stdargs.h} will not work with | |
6402 | floating point operands if this option is specified. | |
6403 | ||
6404 | @item -mfp-arg-in-gregs | |
6405 | Use the normal calling convention for floating point arguments. This is | |
6406 | the default. | |
6407 | ||
6408 | @item -mhc-struct-return | |
6409 | Return structures of more than one word in memory, rather than in a | |
6410 | register. This provides compatibility with the MetaWare HighC (hc) | |
6411 | compiler. Use the option @samp{-fpcc-struct-return} for compatibility | |
6412 | with the Portable C Compiler (pcc). | |
6413 | ||
6414 | @item -mnohc-struct-return | |
6415 | Return some structures of more than one word in registers, when | |
6416 | convenient. This is the default. For compatibility with the | |
6417 | IBM-supplied compilers, use the option @samp{-fpcc-struct-return} or the | |
6418 | option @samp{-mhc-struct-return}. | |
6419 | @end table | |
6420 | ||
6421 | @node MIPS Options | |
6422 | @subsection MIPS Options | |
6423 | @cindex MIPS options | |
6424 | ||
6425 | These @samp{-m} options are defined for the MIPS family of computers: | |
6426 | ||
2642624b | 6427 | @table @gcctabopt |
74291a4b MM |
6428 | @item -mcpu=@var{cpu type} |
6429 | Assume the defaults for the machine type @var{cpu type} when scheduling | |
6430 | instructions. The choices for @var{cpu type} are @samp{r2000}, @samp{r3000}, | |
8b9243df JJ |
6431 | @samp{r3900}, @samp{r4000}, @samp{r4100}, @samp{r4300}, @samp{r4400}, |
6432 | @samp{r4600}, @samp{r4650}, @samp{r5000}, @samp{r6000}, @samp{r8000}, | |
6433 | and @samp{orion}. Additionally, the @samp{r2000}, @samp{r3000}, | |
6434 | @samp{r4000}, @samp{r5000}, and @samp{r6000} can be abbreviated as | |
6435 | @samp{r2k} (or @samp{r2K}), @samp{r3k}, etc. While picking a specific | |
6436 | @var{cpu type} will schedule things appropriately for that particular | |
6437 | chip, the compiler will not generate any code that does not meet level 1 | |
6438 | of the MIPS ISA (instruction set architecture) without a @samp{-mipsX} | |
6439 | or @samp{-mabi} switch being used. | |
74291a4b MM |
6440 | |
6441 | @item -mips1 | |
6442 | Issue instructions from level 1 of the MIPS ISA. This is the default. | |
6443 | @samp{r3000} is the default @var{cpu type} at this ISA level. | |
6444 | ||
6445 | @item -mips2 | |
6446 | Issue instructions from level 2 of the MIPS ISA (branch likely, square | |
6447 | root instructions). @samp{r6000} is the default @var{cpu type} at this | |
6448 | ISA level. | |
6449 | ||
6450 | @item -mips3 | |
02f52e19 | 6451 | Issue instructions from level 3 of the MIPS ISA (64-bit instructions). |
74291a4b | 6452 | @samp{r4000} is the default @var{cpu type} at this ISA level. |
74291a4b | 6453 | |
3398f47f | 6454 | @item -mips4 |
8b9243df JJ |
6455 | Issue instructions from level 4 of the MIPS ISA (conditional move, |
6456 | prefetch, enhanced FPU instructions). @samp{r8000} is the default | |
6457 | @var{cpu type} at this ISA level. | |
3398f47f | 6458 | |
74291a4b MM |
6459 | @item -mfp32 |
6460 | Assume that 32 32-bit floating point registers are available. This is | |
6461 | the default. | |
6462 | ||
6463 | @item -mfp64 | |
6464 | Assume that 32 64-bit floating point registers are available. This is | |
6465 | the default when the @samp{-mips3} option is used. | |
6466 | ||
6467 | @item -mgp32 | |
6468 | Assume that 32 32-bit general purpose registers are available. This is | |
6469 | the default. | |
6470 | ||
6471 | @item -mgp64 | |
6472 | Assume that 32 64-bit general purpose registers are available. This is | |
6473 | the default when the @samp{-mips3} option is used. | |
6474 | ||
6475 | @item -mint64 | |
3ce1ba83 GRK |
6476 | Force int and long types to be 64 bits wide. See @samp{-mlong32} for an |
6477 | explanation of the default, and the width of pointers. | |
74291a4b MM |
6478 | |
6479 | @item -mlong64 | |
3ce1ba83 GRK |
6480 | Force long types to be 64 bits wide. See @samp{-mlong32} for an |
6481 | explanation of the default, and the width of pointers. | |
fb1bf66d | 6482 | |
3ce1ba83 GRK |
6483 | @item -mlong32 |
6484 | Force long, int, and pointer types to be 32 bits wide. | |
6485 | ||
6486 | If none of @samp{-mlong32}, @samp{-mlong64}, or @samp{-mint64} are set, | |
b192711e | 6487 | the size of ints, longs, and pointers depends on the ABI and ISA chosen. |
3ce1ba83 GRK |
6488 | For @samp{-mabi=32}, and @samp{-mabi=n32}, ints and longs are 32 bits |
6489 | wide. For @samp{-mabi=64}, ints are 32 bits, and longs are 64 bits wide. | |
6490 | For @samp{-mabi=eabi} and either @samp{-mips1} or @samp{-mips2}, ints | |
6491 | and longs are 32 bits wide. For @samp{-mabi=eabi} and higher ISAs, ints | |
6492 | are 32 bits, and longs are 64 bits wide. The width of pointer types is | |
6493 | the smaller of the width of longs or the width of general purpose | |
6494 | registers (which in turn depends on the ISA). | |
74291a4b | 6495 | |
62a1403d | 6496 | @item -mabi=32 |
8b9243df | 6497 | @itemx -mabi=o64 |
3398f47f MM |
6498 | @itemx -mabi=n32 |
6499 | @itemx -mabi=64 | |
6500 | @itemx -mabi=eabi | |
8b9243df JJ |
6501 | Generate code for the indicated ABI. The default instruction level is |
6502 | @samp{-mips1} for @samp{32}, @samp{-mips3} for @samp{n32}, and | |
6503 | @samp{-mips4} otherwise. Conversely, with @samp{-mips1} or | |
6504 | @samp{-mips2}, the default ABI is @samp{32}; otherwise, the default ABI | |
6505 | is @samp{64}. | |
3398f47f | 6506 | |
74291a4b MM |
6507 | @item -mmips-as |
6508 | Generate code for the MIPS assembler, and invoke @file{mips-tfile} to | |
6509 | add normal debug information. This is the default for all | |
6510 | platforms except for the OSF/1 reference platform, using the OSF/rose | |
6511 | object format. If the either of the @samp{-gstabs} or @samp{-gstabs+} | |
6512 | switches are used, the @file{mips-tfile} program will encapsulate the | |
6513 | stabs within MIPS ECOFF. | |
6514 | ||
6515 | @item -mgas | |
6516 | Generate code for the GNU assembler. This is the default on the OSF/1 | |
861bb6c1 JL |
6517 | reference platform, using the OSF/rose object format. Also, this is |
6518 | the default if the configure option @samp{--with-gnu-as} is used. | |
6519 | ||
6520 | @item -msplit-addresses | |
6521 | @itemx -mno-split-addresses | |
6522 | Generate code to load the high and low parts of address constants separately. | |
6523 | This allows @code{gcc} to optimize away redundant loads of the high order | |
6524 | bits of addresses. This optimization requires GNU as and GNU ld. | |
6525 | This optimization is enabled by default for some embedded targets where | |
6526 | GNU as and GNU ld are standard. | |
74291a4b MM |
6527 | |
6528 | @item -mrnames | |
6529 | @itemx -mno-rnames | |
6530 | The @samp{-mrnames} switch says to output code using the MIPS software | |
6531 | names for the registers, instead of the hardware names (ie, @var{a0} | |
6532 | instead of @var{$4}). The only known assembler that supports this option | |
6533 | is the Algorithmics assembler. | |
6534 | ||
6535 | @item -mgpopt | |
6536 | @itemx -mno-gpopt | |
6537 | The @samp{-mgpopt} switch says to write all of the data declarations | |
6538 | before the instructions in the text section, this allows the MIPS | |
6539 | assembler to generate one word memory references instead of using two | |
6540 | words for short global or static data items. This is on by default if | |
6541 | optimization is selected. | |
6542 | ||
6543 | @item -mstats | |
6544 | @itemx -mno-stats | |
6545 | For each non-inline function processed, the @samp{-mstats} switch | |
6546 | causes the compiler to emit one line to the standard error file to | |
6547 | print statistics about the program (number of registers saved, stack | |
6548 | size, etc.). | |
6549 | ||
6550 | @item -mmemcpy | |
6551 | @itemx -mno-memcpy | |
6552 | The @samp{-mmemcpy} switch makes all block moves call the appropriate | |
6553 | string function (@samp{memcpy} or @samp{bcopy}) instead of possibly | |
6554 | generating inline code. | |
6555 | ||
6556 | @item -mmips-tfile | |
6557 | @itemx -mno-mips-tfile | |
6558 | The @samp{-mno-mips-tfile} switch causes the compiler not | |
6559 | postprocess the object file with the @file{mips-tfile} program, | |
6560 | after the MIPS assembler has generated it to add debug support. If | |
6561 | @file{mips-tfile} is not run, then no local variables will be | |
6562 | available to the debugger. In addition, @file{stage2} and | |
6563 | @file{stage3} objects will have the temporary file names passed to the | |
6564 | assembler embedded in the object file, which means the objects will | |
6565 | not compare the same. The @samp{-mno-mips-tfile} switch should only | |
6566 | be used when there are bugs in the @file{mips-tfile} program that | |
6567 | prevents compilation. | |
6568 | ||
6569 | @item -msoft-float | |
6570 | Generate output containing library calls for floating point. | |
0c2d1a2a | 6571 | @strong{Warning:} the requisite libraries are not part of GCC. |
74291a4b MM |
6572 | Normally the facilities of the machine's usual C compiler are used, but |
6573 | this can't be done directly in cross-compilation. You must make your | |
6574 | own arrangements to provide suitable library functions for | |
6575 | cross-compilation. | |
6576 | ||
6577 | @item -mhard-float | |
6578 | Generate output containing floating point instructions. This is the | |
6579 | default if you use the unmodified sources. | |
6580 | ||
6581 | @item -mabicalls | |
6582 | @itemx -mno-abicalls | |
6583 | Emit (or do not emit) the pseudo operations @samp{.abicalls}, | |
6584 | @samp{.cpload}, and @samp{.cprestore} that some System V.4 ports use for | |
6585 | position independent code. | |
6586 | ||
6587 | @item -mlong-calls | |
6588 | @itemx -mno-long-calls | |
6589 | Do all calls with the @samp{JALR} instruction, which requires | |
6590 | loading up a function's address into a register before the call. | |
6591 | You need to use this switch, if you call outside of the current | |
6592 | 512 megabyte segment to functions that are not through pointers. | |
6593 | ||
6594 | @item -mhalf-pic | |
6595 | @itemx -mno-half-pic | |
6596 | Put pointers to extern references into the data section and load them | |
6597 | up, rather than put the references in the text section. | |
6598 | ||
6599 | @item -membedded-pic | |
6600 | @itemx -mno-embedded-pic | |
69fa83cf JW |
6601 | Generate PIC code suitable for some embedded systems. All calls are |
6602 | made using PC relative address, and all data is addressed using the $gp | |
6603 | register. No more than 65536 bytes of global data may be used. This | |
6604 | requires GNU as and GNU ld which do most of the work. This currently | |
6605 | only works on targets which use ECOFF; it does not work with ELF. | |
74291a4b MM |
6606 | |
6607 | @item -membedded-data | |
6608 | @itemx -mno-embedded-data | |
6609 | Allocate variables to the read-only data section first if possible, then | |
6610 | next in the small data section if possible, otherwise in data. This gives | |
6611 | slightly slower code than the default, but reduces the amount of RAM required | |
6612 | when executing, and thus may be preferred for some embedded systems. | |
6613 | ||
919509ce DN |
6614 | @item -muninit-const-in-rodata |
6615 | @itemx -mno-uninit-const-in-rodata | |
6616 | When used together with -membedded-data, it will always store uninitialized | |
6617 | const variables in the read-only data section. | |
02f52e19 | 6618 | |
74291a4b MM |
6619 | @item -msingle-float |
6620 | @itemx -mdouble-float | |
6621 | The @samp{-msingle-float} switch tells gcc to assume that the floating | |
6622 | point coprocessor only supports single precision operations, as on the | |
6623 | @samp{r4650} chip. The @samp{-mdouble-float} switch permits gcc to use | |
6624 | double precision operations. This is the default. | |
6625 | ||
6626 | @item -mmad | |
6627 | @itemx -mno-mad | |
6628 | Permit use of the @samp{mad}, @samp{madu} and @samp{mul} instructions, | |
6629 | as on the @samp{r4650} chip. | |
6630 | ||
6631 | @item -m4650 | |
6632 | Turns on @samp{-msingle-float}, @samp{-mmad}, and, at least for now, | |
6633 | @samp{-mcpu=r4650}. | |
6634 | ||
8b9243df JJ |
6635 | @item -mips16 |
6636 | @itemx -mno-mips16 | |
6637 | Enable 16-bit instructions. | |
6638 | ||
6639 | @item -mentry | |
6640 | Use the entry and exit pseudo ops. This option can only be used with | |
6641 | @samp{-mips16}. | |
6642 | ||
74291a4b MM |
6643 | @item -EL |
6644 | Compile code for the processor in little endian mode. | |
6645 | The requisite libraries are assumed to exist. | |
6646 | ||
6647 | @item -EB | |
6648 | Compile code for the processor in big endian mode. | |
6649 | The requisite libraries are assumed to exist. | |
6650 | ||
6651 | @item -G @var{num} | |
6652 | @cindex smaller data references (MIPS) | |
6653 | @cindex gp-relative references (MIPS) | |
6654 | Put global and static items less than or equal to @var{num} bytes into | |
6655 | the small data or bss sections instead of the normal data or bss | |
6656 | section. This allows the assembler to emit one word memory reference | |
6657 | instructions based on the global pointer (@var{gp} or @var{$28}), | |
6658 | instead of the normal two words used. By default, @var{num} is 8 when | |
6659 | the MIPS assembler is used, and 0 when the GNU assembler is used. The | |
6660 | @samp{-G @var{num}} switch is also passed to the assembler and linker. | |
6661 | All modules should be compiled with the same @samp{-G @var{num}} | |
6662 | value. | |
6663 | ||
6664 | @item -nocpp | |
9ec36da5 | 6665 | Tell the MIPS assembler to not run its preprocessor over user |
74291a4b | 6666 | assembler files (with a @samp{.s} suffix) when assembling them. |
63357d93 | 6667 | |
1e387156 CM |
6668 | @item -mfix7000 |
6669 | Pass an option to gas which will cause nops to be inserted if | |
6670 | the read of the destination register of an mfhi or mflo instruction | |
6671 | occurs in the following two instructions. | |
6672 | ||
63357d93 GRK |
6673 | @item -no-crt0 |
6674 | Do not include the default crt0. | |
74291a4b MM |
6675 | @end table |
6676 | ||
6677 | @ifset INTERNALS | |
6678 | These options are defined by the macro | |
6679 | @code{TARGET_SWITCHES} in the machine description. The default for the | |
6680 | options is also defined by that macro, which enables you to change the | |
6681 | defaults. | |
6682 | @end ifset | |
6683 | ||
6684 | @node i386 Options | |
6685 | @subsection Intel 386 Options | |
6686 | @cindex i386 Options | |
6687 | @cindex Intel 386 Options | |
6688 | ||
6689 | These @samp{-m} options are defined for the i386 family of computers: | |
6690 | ||
2642624b | 6691 | @table @gcctabopt |
a9f3e1a4 JL |
6692 | @item -mcpu=@var{cpu type} |
6693 | Assume the defaults for the machine type @var{cpu type} when scheduling | |
9d86bffc JM |
6694 | instructions. The choices for @var{cpu type} are @samp{i386}, |
6695 | @samp{i486}, @samp{i586}, @samp{i686}, @samp{pentium}, | |
b4e89e2d | 6696 | @samp{pentiumpro}, @samp{pentium4}, @samp{k6}, and @samp{athlon} |
6f670fde RH |
6697 | |
6698 | While picking a specific @var{cpu type} will schedule things appropriately | |
6699 | for that particular chip, the compiler will not generate any code that | |
6700 | does not run on the i386 without the @samp{-march=@var{cpu type}} option | |
7001ee2d | 6701 | being used. @samp{i586} is equivalent to @samp{pentium} and @samp{i686} |
6ca3ad1b | 6702 | is equivalent to @samp{pentiumpro}. @samp{k6} and @samp{athlon} are the |
b4e89e2d | 6703 | AMD chips as opposed to the Intel ones. |
a9f3e1a4 JL |
6704 | |
6705 | @item -march=@var{cpu type} | |
6706 | Generate instructions for the machine type @var{cpu type}. The choices | |
02f52e19 | 6707 | for @var{cpu type} are the same as for @samp{-mcpu}. Moreover, |
6f670fde | 6708 | specifying @samp{-march=@var{cpu type}} implies @samp{-mcpu=@var{cpu type}}. |
a9f3e1a4 JL |
6709 | |
6710 | @item -m386 | |
6711 | @itemx -m486 | |
6712 | @itemx -mpentium | |
6713 | @itemx -mpentiumpro | |
6714 | Synonyms for -mcpu=i386, -mcpu=i486, -mcpu=pentium, and -mcpu=pentiumpro | |
7001ee2d | 6715 | respectively. These synonyms are deprecated. |
74291a4b | 6716 | |
04e149ab KC |
6717 | @item -mintel-syntax |
6718 | Emit assembly using Intel syntax opcodes instead of AT&T syntax. | |
6719 | ||
74291a4b MM |
6720 | @item -mieee-fp |
6721 | @itemx -mno-ieee-fp | |
6722 | Control whether or not the compiler uses IEEE floating point | |
6723 | comparisons. These handle correctly the case where the result of a | |
6724 | comparison is unordered. | |
6725 | ||
6726 | @item -msoft-float | |
6727 | Generate output containing library calls for floating point. | |
0c2d1a2a | 6728 | @strong{Warning:} the requisite libraries are not part of GCC. |
74291a4b MM |
6729 | Normally the facilities of the machine's usual C compiler are used, but |
6730 | this can't be done directly in cross-compilation. You must make your | |
6731 | own arrangements to provide suitable library functions for | |
6732 | cross-compilation. | |
6733 | ||
6734 | On machines where a function returns floating point results in the 80387 | |
6735 | register stack, some floating point opcodes may be emitted even if | |
6736 | @samp{-msoft-float} is used. | |
6737 | ||
6738 | @item -mno-fp-ret-in-387 | |
6739 | Do not use the FPU registers for return values of functions. | |
6740 | ||
6741 | The usual calling convention has functions return values of types | |
6742 | @code{float} and @code{double} in an FPU register, even if there | |
6743 | is no FPU. The idea is that the operating system should emulate | |
6744 | an FPU. | |
6745 | ||
6746 | The option @samp{-mno-fp-ret-in-387} causes such values to be returned | |
6747 | in ordinary CPU registers instead. | |
6748 | ||
6749 | @item -mno-fancy-math-387 | |
6750 | Some 387 emulators do not support the @code{sin}, @code{cos} and | |
6751 | @code{sqrt} instructions for the 387. Specify this option to avoid | |
6752 | generating those instructions. This option is the default on FreeBSD. | |
6753 | As of revision 2.6.1, these instructions are not generated unless you | |
de6c5979 | 6754 | also use the @samp{-funsafe-math-optimizations} switch. |
74291a4b MM |
6755 | |
6756 | @item -malign-double | |
6757 | @itemx -mno-align-double | |
0c2d1a2a | 6758 | Control whether GCC aligns @code{double}, @code{long double}, and |
74291a4b MM |
6759 | @code{long long} variables on a two word boundary or a one word |
6760 | boundary. Aligning @code{double} variables on a two word boundary will | |
6761 | produce code that runs somewhat faster on a @samp{Pentium} at the | |
6762 | expense of more memory. | |
6763 | ||
2b589241 JH |
6764 | @item -m128bit-long-double |
6765 | @itemx -m128bit-long-double | |
6766 | Control the size of @code{long double} type. i386 application binary interface | |
6767 | specify the size to be 12 bytes, while modern architectures (Pentium and newer) | |
6768 | preffer @code{long double} aligned to 8 or 16 byte boundary. This is | |
6769 | impossible to reach with 12 byte long doubles in the array accesses. | |
6770 | ||
6771 | @strong{Warning:} if you use the @samp{-m128bit-long-double} switch, the | |
6772 | structures and arrays containing @code{long double} will change their size as | |
6773 | well as function calling convention for function taking @code{long double} | |
02f52e19 | 6774 | will be modified. |
2b589241 JH |
6775 | |
6776 | @item -m96bit-long-double | |
6777 | @itemx -m96bit-long-double | |
0a75e5c3 | 6778 | Set the size of @code{long double} to 96 bits as required by the i386 |
2b589241 | 6779 | application binary interface. This is the default. |
74291a4b MM |
6780 | |
6781 | @item -msvr3-shlib | |
6782 | @itemx -mno-svr3-shlib | |
0c2d1a2a | 6783 | Control whether GCC places uninitialized locals into @code{bss} or |
74291a4b MM |
6784 | @code{data}. @samp{-msvr3-shlib} places these locals into @code{bss}. |
6785 | These options are meaningful only on System V Release 3. | |
6786 | ||
6787 | @item -mno-wide-multiply | |
6788 | @itemx -mwide-multiply | |
0c2d1a2a | 6789 | Control whether GCC uses the @code{mul} and @code{imul} that produce |
02f52e19 | 6790 | 64-bit results in @code{eax:edx} from 32-bit operands to do @code{long |
74291a4b MM |
6791 | long} multiplies and 32-bit division by constants. |
6792 | ||
6793 | @item -mrtd | |
6794 | Use a different function-calling convention, in which functions that | |
6795 | take a fixed number of arguments return with the @code{ret} @var{num} | |
6796 | instruction, which pops their arguments while returning. This saves one | |
6797 | instruction in the caller since there is no need to pop the arguments | |
6798 | there. | |
6799 | ||
6800 | You can specify that an individual function is called with this calling | |
6801 | sequence with the function attribute @samp{stdcall}. You can also | |
6802 | override the @samp{-mrtd} option by using the function attribute | |
0b433de6 | 6803 | @samp{cdecl}. @xref{Function Attributes}. |
74291a4b MM |
6804 | |
6805 | @strong{Warning:} this calling convention is incompatible with the one | |
6806 | normally used on Unix, so you cannot use it if you need to call | |
6807 | libraries compiled with the Unix compiler. | |
6808 | ||
6809 | Also, you must provide function prototypes for all functions that | |
6810 | take variable numbers of arguments (including @code{printf}); | |
6811 | otherwise incorrect code will be generated for calls to those | |
6812 | functions. | |
6813 | ||
6814 | In addition, seriously incorrect code will result if you call a | |
6815 | function with too many arguments. (Normally, extra arguments are | |
6816 | harmlessly ignored.) | |
6817 | ||
74291a4b MM |
6818 | @item -mregparm=@var{num} |
6819 | Control how many registers are used to pass integer arguments. By | |
6820 | default, no registers are used to pass arguments, and at most 3 | |
6821 | registers can be used. You can control this behavior for a specific | |
0b433de6 JL |
6822 | function by using the function attribute @samp{regparm}. |
6823 | @xref{Function Attributes}. | |
74291a4b MM |
6824 | |
6825 | @strong{Warning:} if you use this switch, and | |
6826 | @var{num} is nonzero, then you must build all modules with the same | |
6827 | value, including any libraries. This includes the system libraries and | |
6828 | startup modules. | |
6829 | ||
3af4bd89 JH |
6830 | @item -mpreferred-stack-boundary=@var{num} |
6831 | Attempt to keep the stack boundary aligned to a 2 raised to @var{num} | |
6832 | byte boundary. If @samp{-mpreferred-stack-boundary} is not specified, | |
6833 | the default is 4 (16 bytes or 128 bits). | |
6834 | ||
6835 | The stack is required to be aligned on a 4 byte boundary. On Pentium | |
6836 | and PentiumPro, @code{double} and @code{long double} values should be | |
6837 | aligned to an 8 byte boundary (see @samp{-malign-double}) or suffer | |
6838 | significant run time performance penalties. On Pentium III, the | |
b192711e | 6839 | Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar |
3af4bd89 JH |
6840 | penalties if it is not 16 byte aligned. |
6841 | ||
6842 | To ensure proper alignment of this values on the stack, the stack boundary | |
02f52e19 | 6843 | must be as aligned as that required by any value stored on the stack. |
3af4bd89 JH |
6844 | Further, every function must be generated such that it keeps the stack |
6845 | aligned. Thus calling a function compiled with a higher preferred | |
6846 | stack boundary from a function compiled with a lower preferred stack | |
6847 | boundary will most likely misalign the stack. It is recommended that | |
6848 | libraries that use callbacks always use the default setting. | |
6849 | ||
6850 | This extra alignment does consume extra stack space. Code that is sensitive | |
6851 | to stack space usage, such as embedded systems and operating system kernels, | |
6852 | may want to reduce the preferred alignment to | |
6853 | @samp{-mpreferred-stack-boundary=2}. | |
f22a97d2 | 6854 | |
f73ad30e JH |
6855 | @item -mpush-args |
6856 | @kindex -mpush-args | |
6857 | Use PUSH operations to store outgoing parameters. This method is shorter | |
6858 | and usually equally fast as method using SUB/MOV operations and is enabled | |
6859 | by default. In some cases disabling it may improve performance because of | |
6860 | improved scheduling and reduced dependencies. | |
6861 | ||
6862 | @item -maccumulate-outgoing-args | |
6863 | @kindex -maccumulate-outgoing-args | |
6864 | If enabled, the maximum amount of space required for outgoing arguments will be | |
6865 | computed in the function prologue. This in faster on most modern CPUs | |
b192711e | 6866 | because of reduced dependencies, improved scheduling and reduced stack usage |
f73ad30e JH |
6867 | when preferred stack boundary is not equal to 2. The drawback is a notable |
6868 | increase in code size. This switch implies -mno-push-args. | |
6869 | ||
f22a97d2 MK |
6870 | @item -mthreads |
6871 | @kindex -mthreads | |
02f52e19 AJ |
6872 | Support thread-safe exception handling on @samp{Mingw32}. Code that relies |
6873 | on thread-safe exception handling must compile and link all code with the | |
6874 | @samp{-mthreads} option. When compiling, @samp{-mthreads} defines | |
6875 | @samp{-D_MT}; when linking, it links in a special thread helper library | |
f22a97d2 | 6876 | @samp{-lmingwthrd} which cleans up per thread exception handling data. |
79f05c19 JH |
6877 | |
6878 | @item -mno-align-stringops | |
6879 | @kindex -mno-align-stringops | |
6880 | Do not align destination of inlined string operations. This switch reduces | |
6881 | code size and improves performance in case the destination is already aligned, | |
6882 | but gcc don't know about it. | |
6883 | ||
6884 | @item -minline-all-stringops | |
6885 | @kindex -minline-all-stringops | |
6886 | By default GCC inlines string operations only when destination is known to be | |
6887 | aligned at least to 4 byte boundary. This enables more inlining, increase code | |
6888 | size, but may improve performance of code that depends on fast memcpy, strlen | |
6889 | and memset for short lengths. | |
762e166b AJ |
6890 | |
6891 | @item -momit-leaf-frame-pointer | |
6892 | @kindex -momit-leaf-frame-pointer | |
6893 | Don't keep the frame pointer in a register for leaf functions. This | |
6894 | avoids the instructions to save, set up and restore frame pointers and | |
6895 | makes an extra register available in leaf functions. The option | |
6896 | @samp{-fomit-frame-pointer} removes the frame pointer for all functions | |
6897 | which might make debugging harder. | |
3af4bd89 JH |
6898 | @end table |
6899 | ||
74291a4b MM |
6900 | @node HPPA Options |
6901 | @subsection HPPA Options | |
6902 | @cindex HPPA Options | |
6903 | ||
6904 | These @samp{-m} options are defined for the HPPA family of computers: | |
6905 | ||
2642624b | 6906 | @table @gcctabopt |
ea3bfbfe JQ |
6907 | @item -march=@var{architecture type} |
6908 | Generate code for the specified architecture. The choices for | |
6909 | @var{architecture type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA | |
6910 | 1.1, and @samp{2.0} for PA 2.0 processors. Refer to | |
6911 | @file{/usr/lib/sched.models} on an HP-UX system to determine the proper | |
6912 | architecture option for your machine. Code compiled for lower numbered | |
6913 | architectures will run on higher numbered architectures, but not the | |
6914 | other way around. | |
6915 | ||
6916 | PA 2.0 support currently requires gas snapshot 19990413 or later. The | |
6917 | next release of binutils (current is 2.9.1) will probably contain PA 2.0 | |
02f52e19 | 6918 | support. |
74291a4b | 6919 | |
ea3bfbfe | 6920 | @item -mpa-risc-1-0 |
62a1403d AS |
6921 | @itemx -mpa-risc-1-1 |
6922 | @itemx -mpa-risc-2-0 | |
ea3bfbfe | 6923 | Synonyms for -march=1.0, -march=1.1, and -march=2.0 respectively. |
74291a4b | 6924 | |
861bb6c1 JL |
6925 | @item -mbig-switch |
6926 | Generate code suitable for big switch tables. Use this option only if | |
6927 | the assembler/linker complain about out of range branches within a switch | |
6928 | table. | |
6929 | ||
74291a4b MM |
6930 | @item -mjump-in-delay |
6931 | Fill delay slots of function calls with unconditional jump instructions | |
6932 | by modifying the return pointer for the function call to be the target | |
6933 | of the conditional jump. | |
6934 | ||
6935 | @item -mdisable-fpregs | |
6936 | Prevent floating point registers from being used in any manner. This is | |
6937 | necessary for compiling kernels which perform lazy context switching of | |
6938 | floating point registers. If you use this option and attempt to perform | |
6939 | floating point operations, the compiler will abort. | |
6940 | ||
6941 | @item -mdisable-indexing | |
6942 | Prevent the compiler from using indexing address modes. This avoids some | |
6943 | rather obscure problems when compiling MIG generated code under MACH. | |
6944 | ||
6945 | @item -mno-space-regs | |
6946 | Generate code that assumes the target has no space registers. This allows | |
6947 | GCC to generate faster indirect calls and use unscaled index address modes. | |
6948 | ||
6949 | Such code is suitable for level 0 PA systems and kernels. | |
6950 | ||
6951 | @item -mfast-indirect-calls | |
6952 | Generate code that assumes calls never cross space boundaries. This | |
6953 | allows GCC to emit code which performs faster indirect calls. | |
6954 | ||
b192711e | 6955 | This option will not work in the presence of shared libraries or nested |
74291a4b MM |
6956 | functions. |
6957 | ||
74291a4b MM |
6958 | @item -mlong-load-store |
6959 | Generate 3-instruction load and store sequences as sometimes required by | |
6960 | the HP-UX 10 linker. This is equivalent to the @samp{+k} option to | |
6961 | the HP compilers. | |
6962 | ||
6963 | @item -mportable-runtime | |
6964 | Use the portable calling conventions proposed by HP for ELF systems. | |
6965 | ||
6966 | @item -mgas | |
6967 | Enable the use of assembler directives only GAS understands. | |
6968 | ||
6969 | @item -mschedule=@var{cpu type} | |
6970 | Schedule code according to the constraints for the machine type | |
02f52e19 AJ |
6971 | @var{cpu type}. The choices for @var{cpu type} are @samp{700} |
6972 | @samp{7100}, @samp{7100LC}, @samp{7200}, and @samp{8000}. Refer to | |
732135bf JL |
6973 | @file{/usr/lib/sched.models} on an HP-UX system to determine the |
6974 | proper scheduling option for your machine. | |
74291a4b MM |
6975 | |
6976 | @item -mlinker-opt | |
6977 | Enable the optimization pass in the HPUX linker. Note this makes symbolic | |
6978 | debugging impossible. It also triggers a bug in the HPUX 8 and HPUX 9 linkers | |
6979 | in which they give bogus error messages when linking some programs. | |
6980 | ||
6981 | @item -msoft-float | |
6982 | Generate output containing library calls for floating point. | |
6983 | @strong{Warning:} the requisite libraries are not available for all HPPA | |
6984 | targets. Normally the facilities of the machine's usual C compiler are | |
6985 | used, but this cannot be done directly in cross-compilation. You must make | |
6986 | your own arrangements to provide suitable library functions for | |
6987 | cross-compilation. The embedded target @samp{hppa1.1-*-pro} | |
6988 | does provide software floating point support. | |
6989 | ||
6990 | @samp{-msoft-float} changes the calling convention in the output file; | |
6991 | therefore, it is only useful if you compile @emph{all} of a program with | |
6992 | this option. In particular, you need to compile @file{libgcc.a}, the | |
0c2d1a2a | 6993 | library that comes with GCC, with @samp{-msoft-float} in order for |
74291a4b MM |
6994 | this to work. |
6995 | @end table | |
6996 | ||
6997 | @node Intel 960 Options | |
6998 | @subsection Intel 960 Options | |
6999 | ||
7000 | These @samp{-m} options are defined for the Intel 960 implementations: | |
7001 | ||
2642624b | 7002 | @table @gcctabopt |
74291a4b MM |
7003 | @item -m@var{cpu type} |
7004 | Assume the defaults for the machine type @var{cpu type} for some of | |
7005 | the other options, including instruction scheduling, floating point | |
7006 | support, and addressing modes. The choices for @var{cpu type} are | |
7007 | @samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf}, | |
7008 | @samp{sa}, and @samp{sb}. | |
7009 | The default is | |
7010 | @samp{kb}. | |
7011 | ||
7012 | @item -mnumerics | |
7013 | @itemx -msoft-float | |
7014 | The @samp{-mnumerics} option indicates that the processor does support | |
7015 | floating-point instructions. The @samp{-msoft-float} option indicates | |
7016 | that floating-point support should not be assumed. | |
7017 | ||
7018 | @item -mleaf-procedures | |
7019 | @itemx -mno-leaf-procedures | |
7020 | Do (or do not) attempt to alter leaf procedures to be callable with the | |
7021 | @code{bal} instruction as well as @code{call}. This will result in more | |
7022 | efficient code for explicit calls when the @code{bal} instruction can be | |
7023 | substituted by the assembler or linker, but less efficient code in other | |
7024 | cases, such as calls via function pointers, or using a linker that doesn't | |
7025 | support this optimization. | |
7026 | ||
7027 | @item -mtail-call | |
7028 | @itemx -mno-tail-call | |
7029 | Do (or do not) make additional attempts (beyond those of the | |
7030 | machine-independent portions of the compiler) to optimize tail-recursive | |
7031 | calls into branches. You may not want to do this because the detection of | |
7032 | cases where this is not valid is not totally complete. The default is | |
7033 | @samp{-mno-tail-call}. | |
7034 | ||
7035 | @item -mcomplex-addr | |
7036 | @itemx -mno-complex-addr | |
7037 | Assume (or do not assume) that the use of a complex addressing mode is a | |
7038 | win on this implementation of the i960. Complex addressing modes may not | |
7039 | be worthwhile on the K-series, but they definitely are on the C-series. | |
7040 | The default is currently @samp{-mcomplex-addr} for all processors except | |
7041 | the CB and CC. | |
7042 | ||
7043 | @item -mcode-align | |
7044 | @itemx -mno-code-align | |
7045 | Align code to 8-byte boundaries for faster fetching (or don't bother). | |
7046 | Currently turned on by default for C-series implementations only. | |
7047 | ||
7048 | @ignore | |
7049 | @item -mclean-linkage | |
7050 | @itemx -mno-clean-linkage | |
7051 | These options are not fully implemented. | |
7052 | @end ignore | |
7053 | ||
7054 | @item -mic-compat | |
7055 | @itemx -mic2.0-compat | |
7056 | @itemx -mic3.0-compat | |
7057 | Enable compatibility with iC960 v2.0 or v3.0. | |
7058 | ||
7059 | @item -masm-compat | |
7060 | @itemx -mintel-asm | |
7061 | Enable compatibility with the iC960 assembler. | |
7062 | ||
7063 | @item -mstrict-align | |
7064 | @itemx -mno-strict-align | |
7065 | Do not permit (do permit) unaligned accesses. | |
7066 | ||
7067 | @item -mold-align | |
7068 | Enable structure-alignment compatibility with Intel's gcc release version | |
861bb6c1 | 7069 | 1.3 (based on gcc 1.37). This option implies @samp{-mstrict-align}. |
eaa4b44c VM |
7070 | |
7071 | @item -mlong-double-64 | |
7072 | Implement type @samp{long double} as 64-bit floating point numbers. | |
7073 | Without the option @samp{long double} is implemented by 80-bit | |
7074 | floating point numbers. The only reason we have it because there is | |
7075 | no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it | |
7076 | is only useful for people using soft-float targets. Otherwise, we | |
7077 | should recommend against use of it. | |
7078 | ||
74291a4b MM |
7079 | @end table |
7080 | ||
7081 | @node DEC Alpha Options | |
7082 | @subsection DEC Alpha Options | |
7083 | ||
7084 | These @samp{-m} options are defined for the DEC Alpha implementations: | |
7085 | ||
2642624b | 7086 | @table @gcctabopt |
74291a4b MM |
7087 | @item -mno-soft-float |
7088 | @itemx -msoft-float | |
7089 | Use (do not use) the hardware floating-point instructions for | |
bedc7537 | 7090 | floating-point operations. When @option{-msoft-float} is specified, |
7857f134 | 7091 | functions in @file{libgcc.a} will be used to perform floating-point |
74291a4b MM |
7092 | operations. Unless they are replaced by routines that emulate the |
7093 | floating-point operations, or compiled in such a way as to call such | |
7094 | emulations routines, these routines will issue floating-point | |
7095 | operations. If you are compiling for an Alpha without floating-point | |
7096 | operations, you must ensure that the library is built so as not to call | |
7097 | them. | |
7098 | ||
7099 | Note that Alpha implementations without floating-point operations are | |
7100 | required to have floating-point registers. | |
7101 | ||
7102 | @item -mfp-reg | |
7103 | @itemx -mno-fp-regs | |
7104 | Generate code that uses (does not use) the floating-point register set. | |
bedc7537 | 7105 | @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point |
74291a4b MM |
7106 | register set is not used, floating point operands are passed in integer |
7107 | registers as if they were integers and floating-point results are passed | |
7108 | in $0 instead of $f0. This is a non-standard calling sequence, so any | |
7109 | function with a floating-point argument or return value called by code | |
bedc7537 | 7110 | compiled with @option{-mno-fp-regs} must also be compiled with that |
74291a4b MM |
7111 | option. |
7112 | ||
7113 | A typical use of this option is building a kernel that does not use, | |
7114 | and hence need not save and restore, any floating-point registers. | |
7115 | ||
7116 | @item -mieee | |
7117 | The Alpha architecture implements floating-point hardware optimized for | |
7118 | maximum performance. It is mostly compliant with the IEEE floating | |
7119 | point standard. However, for full compliance, software assistance is | |
7120 | required. This option generates code fully IEEE compliant code | |
7121 | @emph{except} that the @var{inexact flag} is not maintained (see below). | |
7122 | If this option is turned on, the CPP macro @code{_IEEE_FP} is defined | |
7123 | during compilation. The option is a shorthand for: @samp{-D_IEEE_FP | |
7124 | -mfp-trap-mode=su -mtrap-precision=i -mieee-conformant}. The resulting | |
7125 | code is less efficient but is able to correctly support denormalized | |
7126 | numbers and exceptional IEEE values such as not-a-number and plus/minus | |
7127 | infinity. Other Alpha compilers call this option | |
bedc7537 | 7128 | @option{-ieee_with_no_inexact}. |
74291a4b MM |
7129 | |
7130 | @item -mieee-with-inexact | |
7131 | @c overfull hbox here --bob 22 jul96 | |
7132 | @c original text between ignore ... end ignore | |
7133 | @ignore | |
7134 | This is like @samp{-mieee} except the generated code also maintains the | |
7135 | IEEE @var{inexact flag}. Turning on this option causes the generated | |
7136 | code to implement fully-compliant IEEE math. The option is a shorthand | |
7137 | for @samp{-D_IEEE_FP -D_IEEE_FP_INEXACT} plus @samp{-mieee-conformant}, | |
7138 | @samp{-mfp-trap-mode=sui}, and @samp{-mtrap-precision=i}. On some Alpha | |
7139 | implementations the resulting code may execute significantly slower than | |
7140 | the code generated by default. Since there is very little code that | |
7141 | depends on the @var{inexact flag}, you should normally not specify this | |
7142 | option. Other Alpha compilers call this option | |
7143 | @samp{-ieee_with_inexact}. | |
7144 | @end ignore | |
7145 | @c changed paragraph | |
7146 | This is like @samp{-mieee} except the generated code also maintains the | |
7147 | IEEE @var{inexact flag}. Turning on this option causes the generated | |
7148 | code to implement fully-compliant IEEE math. The option is a shorthand | |
7149 | for @samp{-D_IEEE_FP -D_IEEE_FP_INEXACT} plus the three following: | |
7150 | @samp{-mieee-conformant}, | |
02f52e19 AJ |
7151 | @samp{-mfp-trap-mode=sui}, |
7152 | and @samp{-mtrap-precision=i}. | |
74291a4b MM |
7153 | On some Alpha implementations the resulting code may execute |
7154 | significantly slower than the code generated by default. Since there | |
7155 | is very little code that depends on the @var{inexact flag}, you should | |
7156 | normally not specify this option. Other Alpha compilers call this | |
7157 | option @samp{-ieee_with_inexact}. | |
7158 | @c end changes to prevent overfull hboxes | |
7159 | ||
7160 | @item -mfp-trap-mode=@var{trap mode} | |
7161 | This option controls what floating-point related traps are enabled. | |
7162 | Other Alpha compilers call this option @samp{-fptm }@var{trap mode}. | |
7163 | The trap mode can be set to one of four values: | |
7164 | ||
7165 | @table @samp | |
7166 | @item n | |
7167 | This is the default (normal) setting. The only traps that are enabled | |
7168 | are the ones that cannot be disabled in software (e.g., division by zero | |
7169 | trap). | |
7170 | ||
7171 | @item u | |
7172 | In addition to the traps enabled by @samp{n}, underflow traps are enabled | |
7173 | as well. | |
7174 | ||
7175 | @item su | |
7176 | Like @samp{su}, but the instructions are marked to be safe for software | |
7177 | completion (see Alpha architecture manual for details). | |
7178 | ||
7179 | @item sui | |
7180 | Like @samp{su}, but inexact traps are enabled as well. | |
7181 | @end table | |
7182 | ||
7183 | @item -mfp-rounding-mode=@var{rounding mode} | |
7184 | Selects the IEEE rounding mode. Other Alpha compilers call this option | |
7185 | @samp{-fprm }@var{rounding mode}. The @var{rounding mode} can be one | |
7186 | of: | |
7187 | ||
7188 | @table @samp | |
7189 | @item n | |
7190 | Normal IEEE rounding mode. Floating point numbers are rounded towards | |
7191 | the nearest machine number or towards the even machine number in case | |
7192 | of a tie. | |
7193 | ||
7194 | @item m | |
7195 | Round towards minus infinity. | |
7196 | ||
7197 | @item c | |
7198 | Chopped rounding mode. Floating point numbers are rounded towards zero. | |
7199 | ||
7200 | @item d | |
7201 | Dynamic rounding mode. A field in the floating point control register | |
7202 | (@var{fpcr}, see Alpha architecture reference manual) controls the | |
7203 | rounding mode in effect. The C library initializes this register for | |
7204 | rounding towards plus infinity. Thus, unless your program modifies the | |
ec4b2ecb CB |
7205 | @var{fpcr}, @samp{d} corresponds to round towards plus infinity. |
7206 | @end table | |
74291a4b MM |
7207 | |
7208 | @item -mtrap-precision=@var{trap precision} | |
7209 | In the Alpha architecture, floating point traps are imprecise. This | |
7210 | means without software assistance it is impossible to recover from a | |
7211 | floating trap and program execution normally needs to be terminated. | |
0c2d1a2a | 7212 | GCC can generate code that can assist operating system trap handlers |
74291a4b MM |
7213 | in determining the exact location that caused a floating point trap. |
7214 | Depending on the requirements of an application, different levels of | |
7215 | precisions can be selected: | |
7216 | ||
7217 | @table @samp | |
7218 | @item p | |
7219 | Program precision. This option is the default and means a trap handler | |
7220 | can only identify which program caused a floating point exception. | |
7221 | ||
7222 | @item f | |
7223 | Function precision. The trap handler can determine the function that | |
7224 | caused a floating point exception. | |
7225 | ||
7226 | @item i | |
7227 | Instruction precision. The trap handler can determine the exact | |
7228 | instruction that caused a floating point exception. | |
7229 | @end table | |
7230 | ||
7231 | Other Alpha compilers provide the equivalent options called | |
7232 | @samp{-scope_safe} and @samp{-resumption_safe}. | |
7233 | ||
7234 | @item -mieee-conformant | |
7235 | This option marks the generated code as IEEE conformant. You must not | |
7236 | use this option unless you also specify @samp{-mtrap-precision=i} and either | |
7237 | @samp{-mfp-trap-mode=su} or @samp{-mfp-trap-mode=sui}. Its only effect | |
7238 | is to emit the line @samp{.eflag 48} in the function prologue of the | |
7239 | generated assembly file. Under DEC Unix, this has the effect that | |
7240 | IEEE-conformant math library routines will be linked in. | |
7241 | ||
7242 | @item -mbuild-constants | |
0c2d1a2a | 7243 | Normally GCC examines a 32- or 64-bit integer constant to |
74291a4b MM |
7244 | see if it can construct it from smaller constants in two or three |
7245 | instructions. If it cannot, it will output the constant as a literal and | |
956d6950 | 7246 | generate code to load it from the data segment at runtime. |
74291a4b | 7247 | |
0c2d1a2a | 7248 | Use this option to require GCC to construct @emph{all} integer constants |
74291a4b MM |
7249 | using code, even if it takes more instructions (the maximum is six). |
7250 | ||
7251 | You would typically use this option to build a shared library dynamic | |
7252 | loader. Itself a shared library, it must relocate itself in memory | |
7253 | before it can find the variables and constants in its own data segment. | |
956d6950 JL |
7254 | |
7255 | @item -malpha-as | |
7256 | @itemx -mgas | |
7257 | Select whether to generate code to be assembled by the vendor-supplied | |
7258 | assembler (@samp{-malpha-as}) or by the GNU assembler @samp{-mgas}. | |
7259 | ||
7260 | @item -mbwx | |
7261 | @itemx -mno-bwx | |
7262 | @itemx -mcix | |
7263 | @itemx -mno-cix | |
7264 | @itemx -mmax | |
7265 | @itemx -mno-max | |
0c2d1a2a | 7266 | Indicate whether GCC should generate code to use the optional BWX, |
956d6950 JL |
7267 | CIX, and MAX instruction sets. The default is to use the instruction sets |
7268 | supported by the CPU type specified via @samp{-mcpu=} option or that | |
0c2d1a2a | 7269 | of the CPU on which GCC was built if none was specified. |
956d6950 | 7270 | |
956d6950 JL |
7271 | @item -mcpu=@var{cpu_type} |
7272 | Set the instruction set, register set, and instruction scheduling | |
7273 | parameters for machine type @var{cpu_type}. You can specify either the | |
0c2d1a2a | 7274 | @samp{EV} style name or the corresponding chip number. GCC |
956d6950 JL |
7275 | supports scheduling parameters for the EV4 and EV5 family of processors |
7276 | and will choose the default values for the instruction set from | |
7277 | the processor you specify. If you do not specify a processor type, | |
0c2d1a2a | 7278 | GCC will default to the processor on which the compiler was built. |
956d6950 JL |
7279 | |
7280 | Supported values for @var{cpu_type} are | |
7281 | ||
7282 | @table @samp | |
7283 | @item ev4 | |
7284 | @itemx 21064 | |
7285 | Schedules as an EV4 and has no instruction set extensions. | |
7286 | ||
7287 | @item ev5 | |
7288 | @itemx 21164 | |
7289 | Schedules as an EV5 and has no instruction set extensions. | |
7290 | ||
7291 | @item ev56 | |
7292 | @itemx 21164a | |
7293 | Schedules as an EV5 and supports the BWX extension. | |
7294 | ||
7295 | @item pca56 | |
4f69985c | 7296 | @itemx 21164pc |
956d6950 JL |
7297 | @itemx 21164PC |
7298 | Schedules as an EV5 and supports the BWX and MAX extensions. | |
7299 | ||
7300 | @item ev6 | |
7301 | @itemx 21264 | |
7302 | Schedules as an EV5 (until Digital releases the scheduling parameters | |
7303 | for the EV6) and supports the BWX, CIX, and MAX extensions. | |
4f69985c RH |
7304 | @end table |
7305 | ||
7306 | @item -mmemory-latency=@var{time} | |
7307 | Sets the latency the scheduler should assume for typical memory | |
7308 | references as seen by the application. This number is highly | |
b192711e | 7309 | dependent on the memory access patterns used by the application |
4f69985c RH |
7310 | and the size of the external cache on the machine. |
7311 | ||
7312 | Valid options for @var{time} are | |
7313 | ||
7314 | @table @samp | |
7315 | @item @var{number} | |
7316 | A decimal number representing clock cycles. | |
7317 | ||
7318 | @item L1 | |
7319 | @itemx L2 | |
7320 | @itemx L3 | |
7321 | @itemx main | |
7322 | The compiler contains estimates of the number of clock cycles for | |
7323 | ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches | |
7324 | (also called Dcache, Scache, and Bcache), as well as to main memory. | |
7325 | Note that L3 is only valid for EV5. | |
7326 | ||
956d6950 | 7327 | @end table |
74291a4b MM |
7328 | @end table |
7329 | ||
7330 | @node Clipper Options | |
7331 | @subsection Clipper Options | |
7332 | ||
7333 | These @samp{-m} options are defined for the Clipper implementations: | |
7334 | ||
2642624b | 7335 | @table @gcctabopt |
74291a4b MM |
7336 | @item -mc300 |
7337 | Produce code for a C300 Clipper processor. This is the default. | |
7338 | ||
62a1403d | 7339 | @item -mc400 |
74291a4b MM |
7340 | Produce code for a C400 Clipper processor i.e. use floating point |
7341 | registers f8..f15. | |
7342 | @end table | |
7343 | ||
7344 | @node H8/300 Options | |
7345 | @subsection H8/300 Options | |
7346 | ||
7347 | These @samp{-m} options are defined for the H8/300 implementations: | |
7348 | ||
2642624b | 7349 | @table @gcctabopt |
74291a4b MM |
7350 | @item -mrelax |
7351 | Shorten some address references at link time, when possible; uses the | |
7352 | linker option @samp{-relax}. @xref{H8/300,, @code{ld} and the H8/300, | |
7353 | ld.info, Using ld}, for a fuller description. | |
7354 | ||
7355 | @item -mh | |
7356 | Generate code for the H8/300H. | |
7357 | ||
dcb9d1f0 JL |
7358 | @item -ms |
7359 | Generate code for the H8/S. | |
7360 | ||
17f0f8fa KH |
7361 | @item -ms2600 |
7362 | Generate code for the H8/S2600. This switch must be used with -ms. | |
7363 | ||
74291a4b MM |
7364 | @item -mint32 |
7365 | Make @code{int} data 32 bits by default. | |
7366 | ||
7367 | @item -malign-300 | |
2c54abce KH |
7368 | On the H8/300H and H8/S, use the same alignment rules as for the H8/300. |
7369 | The default for the H8/300H and H8/S is to align longs and floats on 4 | |
7370 | byte boundaries. | |
74291a4b | 7371 | @samp{-malign-300} causes them to be aligned on 2 byte boundaries. |
2c54abce | 7372 | This option has no effect on the H8/300. |
74291a4b MM |
7373 | @end table |
7374 | ||
7375 | @node SH Options | |
7376 | @subsection SH Options | |
7377 | ||
7378 | These @samp{-m} options are defined for the SH implementations: | |
7379 | ||
2642624b | 7380 | @table @gcctabopt |
74291a4b MM |
7381 | @item -m1 |
7382 | Generate code for the SH1. | |
7383 | ||
7384 | @item -m2 | |
7385 | Generate code for the SH2. | |
7386 | ||
7387 | @item -m3 | |
7388 | Generate code for the SH3. | |
7389 | ||
7390 | @item -m3e | |
7391 | Generate code for the SH3e. | |
7392 | ||
3cadd778 AO |
7393 | @item -m4-nofpu |
7394 | Generate code for the SH4 without a floating-point unit. | |
7395 | ||
7396 | @item -m4-single-only | |
7397 | Generate code for the SH4 with a floating-point unit that only | |
7398 | supports single-precision arithmentic. | |
7399 | ||
7400 | @item -m4-single | |
7401 | Generate code for the SH4 assuming the floating-point unit is in | |
7402 | single-precision mode by default. | |
7403 | ||
7404 | @item -m4 | |
7405 | Generate code for the SH4. | |
7406 | ||
74291a4b MM |
7407 | @item -mb |
7408 | Compile code for the processor in big endian mode. | |
7409 | ||
7410 | @item -ml | |
7411 | Compile code for the processor in little endian mode. | |
7412 | ||
3d5a0820 | 7413 | @item -mdalign |
02f52e19 | 7414 | Align doubles at 64-bit boundaries. Note that this changes the calling |
3d5a0820 R |
7415 | conventions, and thus some functions from the standard C library will |
7416 | not work unless you recompile it first with -mdalign. | |
7417 | ||
74291a4b MM |
7418 | @item -mrelax |
7419 | Shorten some address references at link time, when possible; uses the | |
7420 | linker option @samp{-relax}. | |
3cadd778 AO |
7421 | |
7422 | @item -mbigtable | |
7423 | Use 32-bit offsets in @code{switch} tables. The default is to use | |
7424 | 16-bit offsets. | |
7425 | ||
7426 | @item -mfmovd | |
7427 | Enable the use of the instruction @code{fmovd}. | |
7428 | ||
7429 | @item -mhitachi | |
7430 | Comply with the calling conventions defined by Hitachi. | |
7431 | ||
7432 | @item -mnomacsave | |
7433 | Mark the @code{MAC} register as call-clobbered, even if | |
bedc7537 | 7434 | @option{-mhitachi} is given. |
3cadd778 AO |
7435 | |
7436 | @item -misize | |
7437 | Dump instruction size and location in the assembly code. | |
7438 | ||
7439 | @item -mpadstruct | |
7440 | This option is deprecated. It pads structures to multiple of 4 bytes, | |
7441 | which is incompatible with the SH ABI. | |
7442 | ||
7443 | @item -mspace | |
bedc7537 | 7444 | Optimize for space instead of speed. Implied by @option{-Os}. |
1a66cd67 AO |
7445 | |
7446 | @item -mprefergot | |
7447 | When generating position-independent code, emit function calls using | |
7448 | the Global Offset Table instead of the Procedure Linkage Table. | |
93ca1662 NY |
7449 | |
7450 | @item -musermode | |
7451 | Generate a library function call to invalidate instruction cache | |
7452 | entries, after fixing up a trampoline. This library function call | |
7453 | doesn't assume it can write to the whole memory address space. This | |
7454 | is the default when the target is @code{sh-*-linux*}. | |
74291a4b MM |
7455 | @end table |
7456 | ||
7457 | @node System V Options | |
7458 | @subsection Options for System V | |
7459 | ||
7460 | These additional options are available on System V Release 4 for | |
7461 | compatibility with other compilers on those systems: | |
7462 | ||
2642624b | 7463 | @table @gcctabopt |
74291a4b MM |
7464 | @item -G |
7465 | Create a shared object. | |
7466 | It is recommended that @samp{-symbolic} or @samp{-shared} be used instead. | |
7467 | ||
7468 | @item -Qy | |
7469 | Identify the versions of each tool used by the compiler, in a | |
7470 | @code{.ident} assembler directive in the output. | |
7471 | ||
7472 | @item -Qn | |
7473 | Refrain from adding @code{.ident} directives to the output file (this is | |
7474 | the default). | |
7475 | ||
371e300b | 7476 | @item -YP\,@var{dirs} |
74291a4b MM |
7477 | Search the directories @var{dirs}, and no others, for libraries |
7478 | specified with @samp{-l}. | |
7479 | ||
371e300b | 7480 | @item -Ym\,@var{dir} |
bedc7537 | 7481 | Look in the directory @var{dir} to find the M4 preprocessor. |
74291a4b MM |
7482 | The assembler uses this option. |
7483 | @c This is supposed to go with a -Yd for predefined M4 macro files, but | |
7484 | @c the generic assembler that comes with Solaris takes just -Ym. | |
7485 | @end table | |
7486 | ||
282a61e6 MH |
7487 | @node TMS320C3x/C4x Options |
7488 | @subsection TMS320C3x/C4x Options | |
7489 | @cindex TMS320C3x/C4x Options | |
7490 | ||
7491 | These @samp{-m} options are defined for TMS320C3x/C4x implementations: | |
7492 | ||
2642624b | 7493 | @table @gcctabopt |
282a61e6 MH |
7494 | |
7495 | @item -mcpu=@var{cpu_type} | |
7496 | Set the instruction set, register set, and instruction scheduling | |
7497 | parameters for machine type @var{cpu_type}. Supported values for | |
7498 | @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and | |
7499 | @samp{c44}. The default is @samp{c40} to generate code for the | |
7500 | TMS320C40. | |
7501 | ||
7502 | @item -mbig-memory | |
7503 | @item -mbig | |
7504 | @itemx -msmall-memory | |
7505 | @itemx -msmall | |
7506 | Generates code for the big or small memory model. The small memory | |
7507 | model assumed that all data fits into one 64K word page. At run-time | |
7508 | the data page (DP) register must be set to point to the 64K page | |
7509 | containing the .bss and .data program sections. The big memory model is | |
7510 | the default and requires reloading of the DP register for every direct | |
7511 | memory access. | |
7512 | ||
7513 | @item -mbk | |
7514 | @itemx -mno-bk | |
7515 | Allow (disallow) allocation of general integer operands into the block | |
02f52e19 | 7516 | count register BK. |
282a61e6 MH |
7517 | |
7518 | @item -mdb | |
7519 | @itemx -mno-db | |
7520 | Enable (disable) generation of code using decrement and branch, | |
7521 | DBcond(D), instructions. This is enabled by default for the C4x. To be | |
7522 | on the safe side, this is disabled for the C3x, since the maximum | |
7523 | iteration count on the C3x is 2^23 + 1 (but who iterates loops more than | |
7524 | 2^23 times on the C3x?). Note that GCC will try to reverse a loop so | |
7525 | that it can utilise the decrement and branch instruction, but will give | |
7526 | up if there is more than one memory reference in the loop. Thus a loop | |
7527 | where the loop counter is decremented can generate slightly more | |
7528 | efficient code, in cases where the RPTB instruction cannot be utilised. | |
7529 | ||
7530 | @item -mdp-isr-reload | |
7531 | @itemx -mparanoid | |
7532 | Force the DP register to be saved on entry to an interrupt service | |
7533 | routine (ISR), reloaded to point to the data section, and restored on | |
7534 | exit from the ISR. This should not be required unless someone has | |
7535 | violated the small memory model by modifying the DP register, say within | |
7536 | an object library. | |
7537 | ||
7538 | @item -mmpyi | |
7539 | @itemx -mno-mpyi | |
7540 | For the C3x use the 24-bit MPYI instruction for integer multiplies | |
7541 | instead of a library call to guarantee 32-bit results. Note that if one | |
7542 | of the operands is a constant, then the multiplication will be performed | |
7543 | using shifts and adds. If the -mmpyi option is not specified for the C3x, | |
7544 | then squaring operations are performed inline instead of a library call. | |
7545 | ||
7546 | @item -mfast-fix | |
7547 | @itemx -mno-fast-fix | |
7548 | The C3x/C4x FIX instruction to convert a floating point value to an | |
7549 | integer value chooses the nearest integer less than or equal to the | |
7550 | floating point value rather than to the nearest integer. Thus if the | |
7551 | floating point number is negative, the result will be incorrectly | |
7552 | truncated an additional code is necessary to detect and correct this | |
7553 | case. This option can be used to disable generation of the additional | |
7554 | code required to correct the result. | |
7555 | ||
7556 | @item -mrptb | |
7557 | @itemx -mno-rptb | |
7558 | Enable (disable) generation of repeat block sequences using the RPTB | |
7559 | instruction for zero overhead looping. The RPTB construct is only used | |
7560 | for innermost loops that do not call functions or jump across the loop | |
7561 | boundaries. There is no advantage having nested RPTB loops due to the | |
7562 | overhead required to save and restore the RC, RS, and RE registers. | |
7563 | This is enabled by default with -O2. | |
7564 | ||
7565 | @item -mrpts=@var{count} | |
7566 | @itemx -mno-rpts | |
7567 | Enable (disable) the use of the single instruction repeat instruction | |
7568 | RPTS. If a repeat block contains a single instruction, and the loop | |
7569 | count can be guaranteed to be less than the value @var{count}, GCC will | |
7570 | emit a RPTS instruction instead of a RPTB. If no value is specified, | |
7571 | then a RPTS will be emitted even if the loop count cannot be determined | |
7572 | at compile time. Note that the repeated instruction following RPTS does | |
7573 | not have to be reloaded from memory each iteration, thus freeing up the | |
b192711e | 7574 | CPU buses for operands. However, since interrupts are blocked by this |
282a61e6 MH |
7575 | instruction, it is disabled by default. |
7576 | ||
7577 | @item -mloop-unsigned | |
7578 | @itemx -mno-loop-unsigned | |
7579 | The maximum iteration count when using RPTS and RPTB (and DB on the C40) | |
7580 | is 2^31 + 1 since these instructions test if the iteration count is | |
7581 | negative to terminate the loop. If the iteration count is unsigned | |
7582 | there is a possibility than the 2^31 + 1 maximum iteration count may be | |
7583 | exceeded. This switch allows an unsigned iteration count. | |
7584 | ||
7585 | @item -mti | |
7586 | Try to emit an assembler syntax that the TI assembler (asm30) is happy | |
7587 | with. This also enforces compatibility with the API employed by the TI | |
7588 | C3x C compiler. For example, long doubles are passed as structures | |
7589 | rather than in floating point registers. | |
7590 | ||
7591 | @item -mregparm | |
7592 | @itemx -mmemparm | |
7593 | Generate code that uses registers (stack) for passing arguments to functions. | |
7594 | By default, arguments are passed in registers where possible rather | |
7595 | than by pushing arguments on to the stack. | |
7596 | ||
7597 | @item -mparallel-insns | |
7598 | @itemx -mno-parallel-insns | |
7599 | Allow the generation of parallel instructions. This is enabled by | |
7600 | default with -O2. | |
7601 | ||
7602 | @item -mparallel-mpy | |
7603 | @itemx -mno-parallel-mpy | |
7604 | Allow the generation of MPY||ADD and MPY||SUB parallel instructions, | |
7605 | provided -mparallel-insns is also specified. These instructions have | |
7606 | tight register constraints which can pessimize the code generation | |
7607 | of large functions. | |
7608 | ||
7609 | @end table | |
7610 | ||
f84271d9 JL |
7611 | @node V850 Options |
7612 | @subsection V850 Options | |
7613 | @cindex V850 Options | |
7614 | ||
7615 | These @samp{-m} options are defined for V850 implementations: | |
7616 | ||
2642624b | 7617 | @table @gcctabopt |
f84271d9 JL |
7618 | @item -mlong-calls |
7619 | @itemx -mno-long-calls | |
7620 | Treat all calls as being far away (near). If calls are assumed to be | |
7621 | far away, the compiler will always load the functions address up into a | |
7622 | register, and call indirect through the pointer. | |
7623 | ||
7624 | @item -mno-ep | |
bd762873 | 7625 | @itemx -mep |
f84271d9 JL |
7626 | Do not optimize (do optimize) basic blocks that use the same index |
7627 | pointer 4 or more times to copy pointer into the @code{ep} register, and | |
7628 | use the shorter @code{sld} and @code{sst} instructions. The @samp{-mep} | |
7629 | option is on by default if you optimize. | |
7630 | ||
7631 | @item -mno-prolog-function | |
7632 | @itemx -mprolog-function | |
7633 | Do not use (do use) external functions to save and restore registers at | |
7634 | the prolog and epilog of a function. The external functions are slower, | |
7635 | but use less code space if more than one function saves the same number | |
7636 | of registers. The @samp{-mprolog-function} option is on by default if | |
7637 | you optimize. | |
7638 | ||
7639 | @item -mspace | |
7640 | Try to make the code as small as possible. At present, this just turns | |
7641 | on the @samp{-mep} and @samp{-mprolog-function} options. | |
7642 | ||
7643 | @item -mtda=@var{n} | |
7644 | Put static or global variables whose size is @var{n} bytes or less into | |
7645 | the tiny data area that register @code{ep} points to. The tiny data | |
7646 | area can hold up to 256 bytes in total (128 bytes for byte references). | |
7647 | ||
7648 | @item -msda=@var{n} | |
7649 | Put static or global variables whose size is @var{n} bytes or less into | |
7650 | the small data area that register @code{gp} points to. The small data | |
7651 | area can hold up to 64 kilobytes. | |
7652 | ||
7653 | @item -mzda=@var{n} | |
7654 | Put static or global variables whose size is @var{n} bytes or less into | |
7655 | the first 32 kilobytes of memory. | |
02f52e19 | 7656 | |
48f0be1b SC |
7657 | @item -mv850 |
7658 | Specify that the target processor is the V850. | |
7659 | ||
e9a25f70 JL |
7660 | @item -mbig-switch |
7661 | Generate code suitable for big switch tables. Use this option only if | |
7662 | the assembler/linker complain about out of range branches within a switch | |
7663 | table. | |
f84271d9 JL |
7664 | @end table |
7665 | ||
56b2d7a7 JL |
7666 | @node ARC Options |
7667 | @subsection ARC Options | |
7668 | @cindex ARC Options | |
7669 | ||
7670 | These options are defined for ARC implementations: | |
7671 | ||
2642624b | 7672 | @table @gcctabopt |
56b2d7a7 JL |
7673 | @item -EL |
7674 | Compile code for little endian mode. This is the default. | |
7675 | ||
7676 | @item -EB | |
7677 | Compile code for big endian mode. | |
7678 | ||
7679 | @item -mmangle-cpu | |
7680 | Prepend the name of the cpu to all public symbol names. | |
7681 | In multiple-processor systems, there are many ARC variants with different | |
7682 | instruction and register set characteristics. This flag prevents code | |
7683 | compiled for one cpu to be linked with code compiled for another. | |
7684 | No facility exists for handling variants that are "almost identical". | |
7685 | This is an all or nothing option. | |
7686 | ||
7687 | @item -mcpu=@var{cpu} | |
7688 | Compile code for ARC variant @var{cpu}. | |
7689 | Which variants are supported depend on the configuration. | |
7690 | All variants support @samp{-mcpu=base}, this is the default. | |
7691 | ||
7692 | @item -mtext=@var{text section} | |
59d40964 AS |
7693 | @itemx -mdata=@var{data section} |
7694 | @itemx -mrodata=@var{readonly data section} | |
56b2d7a7 JL |
7695 | Put functions, data, and readonly data in @var{text section}, |
7696 | @var{data section}, and @var{readonly data section} respectively | |
7697 | by default. This can be overridden with the @code{section} attribute. | |
0b433de6 | 7698 | @xref{Variable Attributes}. |
56b2d7a7 JL |
7699 | |
7700 | @end table | |
7701 | ||
83575957 ID |
7702 | @node NS32K Options |
7703 | @subsection NS32K Options | |
7704 | @cindex NS32K options | |
7705 | ||
7706 | These are the @samp{-m} options defined for the 32000 series. The default | |
7707 | values for these options depends on which style of 32000 was selected when | |
7708 | the compiler was configured; the defaults for the most common choices are | |
7709 | given below. | |
7710 | ||
2642624b | 7711 | @table @gcctabopt |
83575957 ID |
7712 | @item -m32032 |
7713 | @itemx -m32032 | |
7714 | Generate output for a 32032. This is the default | |
7715 | when the compiler is configured for 32032 and 32016 based systems. | |
7716 | ||
7717 | @item -m32332 | |
7718 | @itemx -m32332 | |
7719 | Generate output for a 32332. This is the default | |
7720 | when the compiler is configured for 32332-based systems. | |
7721 | ||
7722 | @item -m32532 | |
7723 | @itemx -m32532 | |
7724 | Generate output for a 32532. This is the default | |
7725 | when the compiler is configured for 32532-based systems. | |
7726 | ||
7727 | @item -m32081 | |
7728 | Generate output containing 32081 instructions for floating point. | |
7729 | This is the default for all systems. | |
7730 | ||
7731 | @item -m32381 | |
7732 | Generate output containing 32381 instructions for floating point. This | |
7733 | also implies @samp{-m32081}. The 32381 is only compatible with the 32332 | |
7734 | and 32532 cpus. This is the default for the pc532-netbsd configuration. | |
7735 | ||
7736 | @item -mmulti-add | |
7737 | Try and generate multiply-add floating point instructions @code{polyF} | |
7738 | and @code{dotF}. This option is only available if the @samp{-m32381} | |
7739 | option is in effect. Using these instructions requires changes to to | |
7740 | register allocation which generally has a negative impact on | |
7741 | performance. This option should only be enabled when compiling code | |
7742 | particularly likely to make heavy use of multiply-add instructions. | |
7743 | ||
7744 | @item -mnomulti-add | |
7745 | Do not try and generate multiply-add floating point instructions | |
7746 | @code{polyF} and @code{dotF}. This is the default on all platforms. | |
7747 | ||
7748 | @item -msoft-float | |
7749 | Generate output containing library calls for floating point. | |
7750 | @strong{Warning:} the requisite libraries may not be available. | |
7751 | ||
7752 | @item -mnobitfield | |
7753 | Do not use the bit-field instructions. On some machines it is faster to | |
7754 | use shifting and masking operations. This is the default for the pc532. | |
7755 | ||
7756 | @item -mbitfield | |
7757 | Do use the bit-field instructions. This is the default for all platforms | |
7758 | except the pc532. | |
7759 | ||
7760 | @item -mrtd | |
7761 | Use a different function-calling convention, in which functions | |
7762 | that take a fixed number of arguments return pop their | |
7763 | arguments on return with the @code{ret} instruction. | |
7764 | ||
7765 | This calling convention is incompatible with the one normally | |
7766 | used on Unix, so you cannot use it if you need to call libraries | |
7767 | compiled with the Unix compiler. | |
7768 | ||
7769 | Also, you must provide function prototypes for all functions that | |
7770 | take variable numbers of arguments (including @code{printf}); | |
7771 | otherwise incorrect code will be generated for calls to those | |
7772 | functions. | |
7773 | ||
7774 | In addition, seriously incorrect code will result if you call a | |
7775 | function with too many arguments. (Normally, extra arguments are | |
7776 | harmlessly ignored.) | |
7777 | ||
7778 | This option takes its name from the 680x0 @code{rtd} instruction. | |
7779 | ||
7780 | ||
7781 | @item -mregparam | |
7782 | Use a different function-calling convention where the first two arguments | |
7783 | are passed in registers. | |
7784 | ||
7785 | This calling convention is incompatible with the one normally | |
7786 | used on Unix, so you cannot use it if you need to call libraries | |
7787 | compiled with the Unix compiler. | |
7788 | ||
7789 | @item -mnoregparam | |
7790 | Do not pass any arguments in registers. This is the default for all | |
7791 | targets. | |
7792 | ||
7793 | @item -msb | |
7794 | It is OK to use the sb as an index register which is always loaded with | |
7795 | zero. This is the default for the pc532-netbsd target. | |
7796 | ||
7797 | @item -mnosb | |
7798 | The sb register is not available for use or has not been initialized to | |
7799 | zero by the run time system. This is the default for all targets except | |
7800 | the pc532-netbsd. It is also implied whenever @samp{-mhimem} or | |
7801 | @samp{-fpic} is set. | |
7802 | ||
7803 | @item -mhimem | |
7804 | Many ns32000 series addressing modes use displacements of up to 512MB. | |
7805 | If an address is above 512MB then displacements from zero can not be used. | |
7806 | This option causes code to be generated which can be loaded above 512MB. | |
7807 | This may be useful for operating systems or ROM code. | |
7808 | ||
7809 | @item -mnohimem | |
7810 | Assume code will be loaded in the first 512MB of virtual address space. | |
7811 | This is the default for all platforms. | |
7812 | ||
7813 | ||
7814 | @end table | |
7815 | ||
052a4b28 DC |
7816 | @node AVR Options |
7817 | @subsection AVR Options | |
7818 | @cindex AVR Options | |
7819 | ||
7820 | These options are defined for AVR implementations: | |
7821 | ||
2642624b | 7822 | @table @gcctabopt |
052a4b28 | 7823 | @item -mmcu=@var{mcu} |
3a69a7d5 MM |
7824 | Specify ATMEL AVR instruction set or MCU type. |
7825 | ||
7826 | Instruction set avr1 is for the minimal AVR core, not supported by the C | |
7827 | compiler, only for assembler programs (MCU types: at90s1200, attiny10, | |
7828 | attiny11, attiny12, attiny15, attiny28). | |
7829 | ||
7830 | Instruction set avr2 (default) is for the classic AVR core with up to | |
7831 | 8K program memory space (MCU types: at90s2313, at90s2323, attiny22, | |
7832 | at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515, | |
7833 | at90c8534, at90s8535). | |
7834 | ||
7835 | Instruction set avr3 is for the classic AVR core with up to 128K program | |
7836 | memory space (MCU types: atmega103, atmega603). | |
7837 | ||
7838 | Instruction set avr4 is for the enhanced AVR core with up to 8K program | |
7839 | memory space (MCU types: atmega83, atmega85). | |
7840 | ||
7841 | Instruction set avr5 is for the enhanced AVR core with up to 128K program | |
7842 | memory space (MCU types: atmega161, atmega163, atmega32, at94k). | |
052a4b28 DC |
7843 | |
7844 | @item -msize | |
3a69a7d5 | 7845 | Output instruction sizes to the asm file. |
052a4b28 DC |
7846 | |
7847 | @item -minit-stack=@var{N} | |
3a69a7d5 MM |
7848 | Specify the initial stack address, which may be a symbol or numeric value, |
7849 | __stack is the default. | |
052a4b28 DC |
7850 | |
7851 | @item -mno-interrupts | |
7852 | Generated code is not compatible with hardware interrupts. | |
7853 | Code size will be smaller. | |
7854 | ||
7855 | @item -mcall-prologues | |
7856 | Functions prologues/epilogues expanded as call to appropriate | |
7857 | subroutines. Code size will be smaller. | |
3a69a7d5 MM |
7858 | |
7859 | @item -mno-tablejump | |
7860 | Do not generate tablejump insns which sometimes increase code size. | |
7861 | ||
7862 | @item -mtiny-stack | |
7863 | Change only the low 8 bits of the stack pointer. | |
052a4b28 DC |
7864 | @end table |
7865 | ||
789a3090 NC |
7866 | @node MCore Options |
7867 | @subsection MCore Options | |
7868 | @cindex MCore options | |
7869 | ||
7870 | These are the @samp{-m} options defined for the Motorola M*Core | |
02f52e19 | 7871 | processors. |
789a3090 | 7872 | |
2642624b | 7873 | @table @gcctabopt |
789a3090 NC |
7874 | |
7875 | @item -mhardlit | |
7876 | @itemx -mhardlit | |
7877 | @itemx -mno-hardlit | |
7878 | Inline constants into the code stream if it can be done in two | |
7879 | instructions or less. | |
7880 | ||
7881 | @item -mdiv | |
7882 | @itemx -mdiv | |
7883 | @itemx -mno-div | |
7884 | Use the divide instruction. (Enabled by default). | |
7885 | ||
7886 | @item -mrelax-immediate | |
7887 | @itemx -mrelax-immediate | |
7888 | @itemx -mno-relax-immediate | |
b192711e | 7889 | Allow arbitrary sized immediates in bit operations. |
789a3090 NC |
7890 | |
7891 | @item -mwide-bitfields | |
7892 | @itemx -mwide-bitfields | |
7893 | @itemx -mno-wide-bitfields | |
7894 | Always treat bitfields as int-sized. | |
7895 | ||
7896 | @item -m4byte-functions | |
7897 | @itemx -m4byte-functions | |
7898 | @itemx -mno-4byte-functions | |
b192711e | 7899 | Force all functions to be aligned to a four byte boundary. |
789a3090 NC |
7900 | |
7901 | @item -mcallgraph-data | |
7902 | @itemx -mcallgraph-data | |
7903 | @itemx -mno-callgraph-data | |
7904 | Emit callgraph information. | |
7905 | ||
7906 | @item -mslow-bytes | |
7907 | @itemx -mslow-bytes | |
7908 | @itemx -mno-slow-bytes | |
7909 | Prefer word access when reading byte quantities. | |
7910 | ||
7911 | @item -mlittle-endian | |
7912 | @itemx -mlittle-endian | |
7913 | @itemx -mbig-endian | |
b192711e | 7914 | Generate code for a little endian target. |
789a3090 NC |
7915 | |
7916 | @item -m210 | |
7917 | @itemx -m210 | |
7918 | @itemx -m340 | |
7919 | Generate code for the 210 processor. | |
789a3090 | 7920 | @end table |
83575957 | 7921 | |
df6194d4 JW |
7922 | @node IA-64 Options |
7923 | @subsection IA-64 Options | |
7924 | @cindex IA-64 Options | |
7925 | ||
7926 | These are the @samp{-m} options defined for the Intel IA-64 architecture. | |
7927 | ||
7928 | @table @gcctabopt | |
7929 | @item -mbig-endian | |
7930 | Generate code for a big endian target. This is the default for HPUX. | |
7931 | ||
7932 | @item -mlittle-endian | |
7933 | Generate code for a little endian target. This is the default for AIX5 | |
7934 | and Linux. | |
7935 | ||
7936 | @item -mgnu-as | |
7937 | @itemx -mno-gnu-as | |
15d3a111 JW |
7938 | Generate (or don't) code for the GNU assembler. This is the default. |
7939 | @c Also, this is the default if the configure option @samp{--with-gnu-as} | |
7940 | @c is used. | |
df6194d4 JW |
7941 | |
7942 | @item -mgnu-ld | |
7943 | @itemx -mno-gnu-ld | |
15d3a111 JW |
7944 | Generate (or don't) code for the GNU linker. This is the default. |
7945 | @c Also, this is the default if the configure option @samp{--with-gnu-ld} | |
7946 | @c is used. | |
df6194d4 JW |
7947 | |
7948 | @item -mno-pic | |
15d3a111 JW |
7949 | Generate code that does not use a global pointer register. The result |
7950 | is not position independent code, and violates the IA-64 ABI. | |
df6194d4 JW |
7951 | |
7952 | @item -mvolatile-asm-stop | |
7953 | @itemx -mno-volatile-asm-stop | |
15d3a111 JW |
7954 | Generate (or don't) a stop bit immediately before and after volatile asm |
7955 | statements. | |
df6194d4 JW |
7956 | |
7957 | @item -mb-step | |
7958 | Generate code that works around Itanium B step errata. | |
7959 | ||
7960 | @item -mregister-names | |
7961 | @itemx -mno-register-names | |
15d3a111 JW |
7962 | Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for |
7963 | the stacked registers. This may make assembler output more readable. | |
df6194d4 JW |
7964 | |
7965 | @item -mno-sdata | |
7966 | @itemx -msdata | |
15d3a111 JW |
7967 | Disable (or enable) optimizations that use the small data section. This may |
7968 | be useful for working around optimizer bugs. | |
df6194d4 JW |
7969 | |
7970 | @item -mconstant-gp | |
7971 | Generate code that uses a single constant global pointer value. This is | |
7972 | useful when compiling kernel code. | |
7973 | ||
7974 | @item -mauto-pic | |
7975 | Generate code that is self-relocatable. This implies @samp{-mconstant-gp}. | |
7976 | This is useful when compiling firmware code. | |
7977 | ||
7978 | @item -minline-divide-min-latency | |
7979 | Generate code for inline divides using the minimum latency algorithm. | |
7980 | ||
7981 | @item -minline-divide-max-throughput | |
7982 | Generate code for inline divides using the maximum throughput algorithm. | |
7983 | ||
7984 | @item -mno-dwarf2-asm | |
7985 | @itemx -mdwarf2-asm | |
15d3a111 JW |
7986 | Don't (or do) generate assembler code for the DWARF2 line number debugging |
7987 | info. This may be useful when not using the GNU assembler. | |
df6194d4 JW |
7988 | |
7989 | @item -mfixed-range=@var{register range} | |
7990 | Generate code treating the given register range as fixed registers. | |
7991 | A fixed register is one that the register allocator can not use. This is | |
7992 | useful when compiling kernel code. A register range is specified as | |
7993 | two registers separated by a dash. Multiple register ranges can be | |
7994 | specified separated by a comma. | |
7995 | @end table | |
7996 | ||
e8ad90e5 MM |
7997 | @node D30V Options |
7998 | @subsection D30V Options | |
7999 | @cindex D30V Options | |
8000 | ||
8001 | These @samp{-m} options are defined for D30V implementations: | |
8002 | ||
2642624b | 8003 | @table @gcctabopt |
e8ad90e5 MM |
8004 | @item -mextmem |
8005 | Link the @samp{.text}, @samp{.data}, @samp{.bss}, @samp{.strings}, | |
8006 | @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into external | |
8007 | memory, which starts at location @code{0x80000000}. | |
8008 | ||
8009 | @item -mextmemory | |
8010 | Same as the @samp{-mextmem} switch. | |
8011 | ||
8012 | @item -monchip | |
8013 | Link the @samp{.text} section into onchip text memory, which starts at | |
8014 | location @code{0x0}. Also link @samp{.data}, @samp{.bss}, | |
8015 | @samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections | |
8016 | into onchip data memory, which starts at location @code{0x20000000}. | |
8017 | ||
8018 | @item -mno-asm-optimize | |
8019 | @itemx -masm-optimize | |
8020 | Disable (enable) passing @samp{-O} to the assembler when optimizing. | |
8021 | The assembler uses the @samp{-O} option to automatically parallelize | |
8022 | adjacent short instructions where possible. | |
8023 | ||
8024 | @item -mbranch-cost=@var{n} | |
8025 | Increase the internal costs of branches to @var{n}. Higher costs means | |
8026 | that the compiler will issue more instructions to avoid doing a branch. | |
8027 | The default is 2. | |
8028 | ||
8029 | @item -mcond-exec=@var{n} | |
8030 | Specify the maximum number of conditionally executed instructions that | |
8031 | replace a branch. The default is 4. | |
8032 | @end table | |
56b2d7a7 | 8033 | |
74291a4b MM |
8034 | @node Code Gen Options |
8035 | @section Options for Code Generation Conventions | |
8036 | @cindex code generation conventions | |
8037 | @cindex options, code generation | |
8038 | @cindex run-time options | |
8039 | ||
8040 | These machine-independent options control the interface conventions | |
8041 | used in code generation. | |
8042 | ||
8043 | Most of them have both positive and negative forms; the negative form | |
8044 | of @samp{-ffoo} would be @samp{-fno-foo}. In the table below, only | |
8045 | one of the forms is listed---the one which is not the default. You | |
8046 | can figure out the other form by either removing @samp{no-} or adding | |
8047 | it. | |
8048 | ||
2642624b | 8049 | @table @gcctabopt |
956d6950 | 8050 | @item -fexceptions |
89ed4e9d | 8051 | Enable exception handling. Generates extra code needed to propagate |
c5c76735 JL |
8052 | exceptions. For some targets, this implies GNU CC will generate frame |
8053 | unwind information for all functions, which can produce significant data | |
8054 | size overhead, although it does not affect execution. If you do not | |
8055 | specify this option, GNU CC will enable it by default for languages like | |
90ecce3e | 8056 | C++ which normally require exception handling, and disable it for |
c5c76735 JL |
8057 | languages like C that do not normally require it. However, you may need |
8058 | to enable this option when compiling C code that needs to interoperate | |
8059 | properly with exception handlers written in C++. You may also wish to | |
8060 | disable this option if you are compiling older C++ programs that don't | |
8061 | use exception handling. | |
956d6950 | 8062 | |
14a774a9 | 8063 | @item -funwind-tables |
bedc7537 | 8064 | Similar to @option{-fexceptions}, except that it will just generate any needed |
14a774a9 RK |
8065 | static data, but will not affect the generated code in any other way. |
8066 | You will normally not enable this option; instead, a language processor | |
8067 | that needs this handling would enable it on your behalf. | |
8068 | ||
74291a4b MM |
8069 | @item -fpcc-struct-return |
8070 | Return ``short'' @code{struct} and @code{union} values in memory like | |
8071 | longer ones, rather than in registers. This convention is less | |
8072 | efficient, but it has the advantage of allowing intercallability between | |
0c2d1a2a | 8073 | GCC-compiled files and files compiled with other compilers. |
74291a4b MM |
8074 | |
8075 | The precise convention for returning structures in memory depends | |
8076 | on the target configuration macros. | |
8077 | ||
8078 | Short structures and unions are those whose size and alignment match | |
8079 | that of some integer type. | |
8080 | ||
8081 | @item -freg-struct-return | |
8082 | Use the convention that @code{struct} and @code{union} values are | |
8083 | returned in registers when possible. This is more efficient for small | |
8084 | structures than @samp{-fpcc-struct-return}. | |
8085 | ||
8086 | If you specify neither @samp{-fpcc-struct-return} nor its contrary | |
0c2d1a2a JB |
8087 | @samp{-freg-struct-return}, GCC defaults to whichever convention is |
8088 | standard for the target. If there is no standard convention, GCC | |
8089 | defaults to @samp{-fpcc-struct-return}, except on targets where GCC | |
74291a4b MM |
8090 | is the principal compiler. In those cases, we can choose the standard, |
8091 | and we chose the more efficient register return alternative. | |
8092 | ||
8093 | @item -fshort-enums | |
8094 | Allocate to an @code{enum} type only as many bytes as it needs for the | |
8095 | declared range of possible values. Specifically, the @code{enum} type | |
8096 | will be equivalent to the smallest integer type which has enough room. | |
8097 | ||
8098 | @item -fshort-double | |
8099 | Use the same size for @code{double} as for @code{float}. | |
8100 | ||
8101 | @item -fshared-data | |
8102 | Requests that the data and non-@code{const} variables of this | |
8103 | compilation be shared data rather than private data. The distinction | |
8104 | makes sense only on certain operating systems, where shared data is | |
8105 | shared between processes running the same program, while private data | |
8106 | exists in one copy per process. | |
8107 | ||
8108 | @item -fno-common | |
90ecce3e | 8109 | In C, allocate even uninitialized global variables in the data section of the |
74291a4b MM |
8110 | object file, rather than generating them as common blocks. This has the |
8111 | effect that if the same variable is declared (without @code{extern}) in | |
8112 | two different compilations, you will get an error when you link them. | |
8113 | The only reason this might be useful is if you wish to verify that the | |
8114 | program will work on other systems which always work this way. | |
8115 | ||
8116 | @item -fno-ident | |
8117 | Ignore the @samp{#ident} directive. | |
8118 | ||
8119 | @item -fno-gnu-linker | |
8120 | Do not output global initializations (such as C++ constructors and | |
8121 | destructors) in the form used by the GNU linker (on systems where the GNU | |
8122 | linker is the standard method of handling them). Use this option when | |
8123 | you want to use a non-GNU linker, which also requires using the | |
bedc7537 NC |
8124 | @command{collect2} program to make sure the system linker includes |
8125 | constructors and destructors. (@command{collect2} is included in the GCC | |
8126 | distribution.) For systems which @emph{must} use @command{collect2}, the | |
8127 | compiler driver @command{gcc} is configured to do this automatically. | |
74291a4b MM |
8128 | |
8129 | @item -finhibit-size-directive | |
8130 | Don't output a @code{.size} assembler directive, or anything else that | |
8131 | would cause trouble if the function is split in the middle, and the | |
8132 | two halves are placed at locations far apart in memory. This option is | |
8133 | used when compiling @file{crtstuff.c}; you should not need to use it | |
8134 | for anything else. | |
8135 | ||
8136 | @item -fverbose-asm | |
8137 | Put extra commentary information in the generated assembly code to | |
8138 | make it more readable. This option is generally only of use to those | |
8139 | who actually need to read the generated assembly code (perhaps while | |
8140 | debugging the compiler itself). | |
8141 | ||
c85f7c16 | 8142 | @samp{-fno-verbose-asm}, the default, causes the |
74291a4b MM |
8143 | extra information to be omitted and is useful when comparing two assembler |
8144 | files. | |
8145 | ||
8146 | @item -fvolatile | |
8147 | Consider all memory references through pointers to be volatile. | |
8148 | ||
8149 | @item -fvolatile-global | |
8150 | Consider all memory references to extern and global data items to | |
0c2d1a2a | 8151 | be volatile. GCC does not consider static data items to be volatile |
ab87f8c8 JL |
8152 | because of this switch. |
8153 | ||
8154 | @item -fvolatile-static | |
8155 | Consider all memory references to static data to be volatile. | |
74291a4b MM |
8156 | |
8157 | @item -fpic | |
8158 | @cindex global offset table | |
8159 | @cindex PIC | |
8160 | Generate position-independent code (PIC) suitable for use in a shared | |
8161 | library, if supported for the target machine. Such code accesses all | |
861bb6c1 JL |
8162 | constant addresses through a global offset table (GOT). The dynamic |
8163 | loader resolves the GOT entries when the program starts (the dynamic | |
0c2d1a2a | 8164 | loader is not part of GCC; it is part of the operating system). If |
861bb6c1 JL |
8165 | the GOT size for the linked executable exceeds a machine-specific |
8166 | maximum size, you get an error message from the linker indicating that | |
8167 | @samp{-fpic} does not work; in that case, recompile with @samp{-fPIC} | |
8168 | instead. (These maximums are 16k on the m88k, 8k on the Sparc, and 32k | |
8169 | on the m68k and RS/6000. The 386 has no such limit.) | |
74291a4b MM |
8170 | |
8171 | Position-independent code requires special support, and therefore works | |
0c2d1a2a | 8172 | only on certain machines. For the 386, GCC supports PIC for System V |
74291a4b MM |
8173 | but not for the Sun 386i. Code generated for the IBM RS/6000 is always |
8174 | position-independent. | |
8175 | ||
74291a4b MM |
8176 | @item -fPIC |
8177 | If supported for the target machine, emit position-independent code, | |
8178 | suitable for dynamic linking and avoiding any limit on the size of the | |
8179 | global offset table. This option makes a difference on the m68k, m88k, | |
8180 | and the Sparc. | |
8181 | ||
8182 | Position-independent code requires special support, and therefore works | |
8183 | only on certain machines. | |
8184 | ||
8185 | @item -ffixed-@var{reg} | |
8186 | Treat the register named @var{reg} as a fixed register; generated code | |
8187 | should never refer to it (except perhaps as a stack pointer, frame | |
8188 | pointer or in some other fixed role). | |
8189 | ||
8190 | @var{reg} must be the name of a register. The register names accepted | |
8191 | are machine-specific and are defined in the @code{REGISTER_NAMES} | |
8192 | macro in the machine description macro file. | |
8193 | ||
8194 | This flag does not have a negative form, because it specifies a | |
8195 | three-way choice. | |
8196 | ||
8197 | @item -fcall-used-@var{reg} | |
956d6950 | 8198 | Treat the register named @var{reg} as an allocable register that is |
74291a4b MM |
8199 | clobbered by function calls. It may be allocated for temporaries or |
8200 | variables that do not live across a call. Functions compiled this way | |
8201 | will not save and restore the register @var{reg}. | |
8202 | ||
cb2fdc84 GRK |
8203 | It is an error to used this flag with the frame pointer or stack pointer. |
8204 | Use of this flag for other registers that have fixed pervasive roles in | |
8205 | the machine's execution model will produce disastrous results. | |
74291a4b MM |
8206 | |
8207 | This flag does not have a negative form, because it specifies a | |
8208 | three-way choice. | |
8209 | ||
8210 | @item -fcall-saved-@var{reg} | |
956d6950 | 8211 | Treat the register named @var{reg} as an allocable register saved by |
74291a4b MM |
8212 | functions. It may be allocated even for temporaries or variables that |
8213 | live across a call. Functions compiled this way will save and restore | |
8214 | the register @var{reg} if they use it. | |
8215 | ||
cb2fdc84 GRK |
8216 | It is an error to used this flag with the frame pointer or stack pointer. |
8217 | Use of this flag for other registers that have fixed pervasive roles in | |
8218 | the machine's execution model will produce disastrous results. | |
74291a4b MM |
8219 | |
8220 | A different sort of disaster will result from the use of this flag for | |
8221 | a register in which function values may be returned. | |
8222 | ||
8223 | This flag does not have a negative form, because it specifies a | |
8224 | three-way choice. | |
8225 | ||
8226 | @item -fpack-struct | |
8227 | Pack all structure members together without holes. Usually you would | |
8228 | not want to use this option, since it makes the code suboptimal, and | |
8229 | the offsets of structure members won't agree with system libraries. | |
8230 | ||
861bb6c1 | 8231 | @item -fcheck-memory-usage |
0c2d1a2a | 8232 | Generate extra code to check each memory access. GCC will generate |
861bb6c1 | 8233 | code that is suitable for a detector of bad memory accesses such as |
7d384cc0 | 8234 | @file{Checker}. |
861bb6c1 | 8235 | |
d3111037 CB |
8236 | Normally, you should compile all, or none, of your code with this option. |
8237 | ||
8238 | If you do mix code compiled with and without this option, | |
8239 | you must ensure that all code that has side effects | |
8240 | and that is called by code compiled with this option | |
8241 | is, itself, compiled with this option. | |
8242 | If you do not, you might get erroneous messages from the detector. | |
8243 | ||
861bb6c1 | 8244 | If you use functions from a library that have side-effects (such as |
d3111037 | 8245 | @code{read}), you might not be able to recompile the library and |
861bb6c1 | 8246 | specify this option. In that case, you can enable the |
0c2d1a2a | 8247 | @samp{-fprefix-function-name} option, which requests GCC to encapsulate |
861bb6c1 JL |
8248 | your code and make other functions look as if they were compiled with |
8249 | @samp{-fcheck-memory-usage}. This is done by calling ``stubs'', | |
8250 | which are provided by the detector. If you cannot find or build | |
d3111037 | 8251 | stubs for every function you call, you might have to specify |
861bb6c1 JL |
8252 | @samp{-fcheck-memory-usage} without @samp{-fprefix-function-name}. |
8253 | ||
7d384cc0 | 8254 | If you specify this option, you can not use the @code{asm} or |
c5c76735 JL |
8255 | @code{__asm__} keywords in functions with memory checking enabled. GNU |
8256 | CC cannot understand what the @code{asm} statement may do, and therefore | |
8257 | cannot generate the appropriate code, so it will reject it. However, if | |
ee457005 JM |
8258 | you specify the function attribute @code{no_check_memory_usage} |
8259 | (@pxref{Function Attributes}), GNU CC will disable memory checking within a | |
c5c76735 JL |
8260 | function; you may use @code{asm} statements inside such functions. You |
8261 | may have an inline expansion of a non-checked function within a checked | |
8262 | function; in that case GNU CC will not generate checks for the inlined | |
8263 | function's memory accesses. | |
8264 | ||
8265 | If you move your @code{asm} statements to non-checked inline functions | |
8266 | and they do access memory, you can add calls to the support code in your | |
7d384cc0 KR |
8267 | inline function, to indicate any reads, writes, or copies being done. |
8268 | These calls would be similar to those done in the stubs described above. | |
8269 | ||
861bb6c1 | 8270 | @item -fprefix-function-name |
0c2d1a2a JB |
8271 | Request GCC to add a prefix to the symbols generated for function names. |
8272 | GCC adds a prefix to the names of functions defined as well as | |
861bb6c1 | 8273 | functions called. Code compiled with this option and code compiled |
d3111037 | 8274 | without the option can't be linked together, unless stubs are used. |
861bb6c1 JL |
8275 | |
8276 | If you compile the following code with @samp{-fprefix-function-name} | |
8277 | @example | |
8278 | extern void bar (int); | |
8279 | void | |
8280 | foo (int a) | |
8281 | @{ | |
8282 | return bar (a + 5); | |
861bb6c1 JL |
8283 | @} |
8284 | @end example | |
8285 | ||
8286 | @noindent | |
0c2d1a2a | 8287 | GCC will compile the code as if it was written: |
861bb6c1 JL |
8288 | @example |
8289 | extern void prefix_bar (int); | |
8290 | void | |
8291 | prefix_foo (int a) | |
8292 | @{ | |
8293 | return prefix_bar (a + 5); | |
8294 | @} | |
8295 | @end example | |
8296 | This option is designed to be used with @samp{-fcheck-memory-usage}. | |
8297 | ||
07417085 KR |
8298 | @item -finstrument-functions |
8299 | Generate instrumentation calls for entry and exit to functions. Just | |
8300 | after function entry and just before function exit, the following | |
8301 | profiling functions will be called with the address of the current | |
8302 | function and its call site. (On some platforms, | |
8303 | @code{__builtin_return_address} does not work beyond the current | |
8304 | function, so the call site information may not be available to the | |
8305 | profiling functions otherwise.) | |
8306 | ||
8307 | @example | |
8308 | void __cyg_profile_func_enter (void *this_fn, void *call_site); | |
8309 | void __cyg_profile_func_exit (void *this_fn, void *call_site); | |
8310 | @end example | |
8311 | ||
8312 | The first argument is the address of the start of the current function, | |
8313 | which may be looked up exactly in the symbol table. | |
8314 | ||
8315 | This instrumentation is also done for functions expanded inline in other | |
8316 | functions. The profiling calls will indicate where, conceptually, the | |
8317 | inline function is entered and exited. This means that addressable | |
8318 | versions of such functions must be available. If all your uses of a | |
8319 | function are expanded inline, this may mean an additional expansion of | |
8320 | code size. If you use @samp{extern inline} in your C code, an | |
8321 | addressable version of such functions must be provided. (This is | |
8322 | normally the case anyways, but if you get lucky and the optimizer always | |
8323 | expands the functions inline, you might have gotten away without | |
8324 | providing static copies.) | |
8325 | ||
8326 | A function may be given the attribute @code{no_instrument_function}, in | |
8327 | which case this instrumentation will not be done. This can be used, for | |
8328 | example, for the profiling functions listed above, high-priority | |
8329 | interrupt routines, and any functions from which the profiling functions | |
8330 | cannot safely be called (perhaps signal handlers, if the profiling | |
8331 | routines generate output or allocate memory). | |
8332 | ||
861bb6c1 JL |
8333 | @item -fstack-check |
8334 | Generate code to verify that you do not go beyond the boundary of the | |
8335 | stack. You should specify this flag if you are running in an | |
8336 | environment with multiple threads, but only rarely need to specify it in | |
8337 | a single-threaded environment since stack overflow is automatically | |
8338 | detected on nearly all systems if there is only one stack. | |
8339 | ||
a157febd GK |
8340 | Note that this switch does not actually cause checking to be done; the |
8341 | operating system must do that. The switch causes generation of code | |
8342 | to ensure that the operating system sees the stack being extended. | |
8343 | ||
8344 | @item -fstack-limit-register=@var{reg} | |
8345 | @itemx -fstack-limit-symbol=@var{sym} | |
8346 | @itemx -fno-stack-limit | |
8347 | Generate code to ensure that the stack does not grow beyond a certain value, | |
8348 | either the value of a register or the address of a symbol. If the stack | |
8349 | would grow beyond the value, a signal is raised. For most targets, | |
8350 | the signal is raised before the stack overruns the boundary, so | |
8351 | it is possible to catch the signal without taking special precautions. | |
8352 | ||
8353 | For instance, if the stack starts at address @samp{0x80000000} and grows | |
8354 | downwards you can use the flags | |
8355 | @samp{-fstack-limit-symbol=__stack_limit} | |
8356 | @samp{-Wl,--defsym,__stack_limit=0x7ffe0000} which will enforce a stack | |
8357 | limit of 128K. | |
8358 | ||
e5eb27e5 JL |
8359 | @cindex aliasing of parameters |
8360 | @cindex parameters, aliased | |
8361 | @item -fargument-alias | |
04afd9d6 JL |
8362 | @itemx -fargument-noalias |
8363 | @itemx -fargument-noalias-global | |
e5eb27e5 JL |
8364 | Specify the possible relationships among parameters and between |
8365 | parameters and global data. | |
8366 | ||
8367 | @samp{-fargument-alias} specifies that arguments (parameters) may | |
8368 | alias each other and may alias global storage. | |
8369 | @samp{-fargument-noalias} specifies that arguments do not alias | |
8370 | each other, but may alias global storage. | |
8371 | @samp{-fargument-noalias-global} specifies that arguments do not | |
8372 | alias each other and do not alias global storage. | |
8373 | ||
8374 | Each language will automatically use whatever option is required by | |
8375 | the language standard. You should not need to use these options yourself. | |
19283265 RH |
8376 | |
8377 | @item -fleading-underscore | |
8378 | This option and its counterpart, -fno-leading-underscore, forcibly | |
8379 | change the way C symbols are represented in the object file. One use | |
8380 | is to help link with legacy assembly code. | |
8381 | ||
8382 | Be warned that you should know what you are doing when invoking this | |
8383 | option, and that not all targets provide complete support for it. | |
74291a4b MM |
8384 | @end table |
8385 | ||
ee457005 JM |
8386 | @c man end |
8387 | ||
74291a4b | 8388 | @node Environment Variables |
0c2d1a2a | 8389 | @section Environment Variables Affecting GCC |
74291a4b MM |
8390 | @cindex environment variables |
8391 | ||
ee457005 JM |
8392 | @c man begin ENVIRONMENT |
8393 | ||
0c2d1a2a JB |
8394 | This section describes several environment variables that affect how GCC |
8395 | operates. Some of them work by specifying directories or prefixes to use | |
56f48ce9 | 8396 | when searching for various kinds of files. Some are used to specify other |
46103ab4 | 8397 | aspects of the compilation environment. |
74291a4b MM |
8398 | |
8399 | @ifclear INTERNALS | |
8400 | Note that you can also specify places to search using options such as | |
8401 | @samp{-B}, @samp{-I} and @samp{-L} (@pxref{Directory Options}). These | |
8402 | take precedence over places specified using environment variables, which | |
0c2d1a2a JB |
8403 | in turn take precedence over those specified by the configuration of GCC. |
8404 | ||
74291a4b MM |
8405 | @end ifclear |
8406 | @ifset INTERNALS | |
8407 | Note that you can also specify places to search using options such as | |
8408 | @samp{-B}, @samp{-I} and @samp{-L} (@pxref{Directory Options}). These | |
8409 | take precedence over places specified using environment variables, which | |
0c2d1a2a JB |
8410 | in turn take precedence over those specified by the configuration of GCC. |
8411 | @xref{Driver}. | |
74291a4b MM |
8412 | @end ifset |
8413 | ||
bedc7537 | 8414 | @table @env |
ab87f8c8 JL |
8415 | @item LANG |
8416 | @itemx LC_CTYPE | |
8417 | @c @itemx LC_COLLATE | |
8418 | @itemx LC_MESSAGES | |
8419 | @c @itemx LC_MONETARY | |
8420 | @c @itemx LC_NUMERIC | |
8421 | @c @itemx LC_TIME | |
8422 | @itemx LC_ALL | |
8423 | @findex LANG | |
8424 | @findex LC_CTYPE | |
8425 | @c @findex LC_COLLATE | |
8426 | @findex LC_MESSAGES | |
8427 | @c @findex LC_MONETARY | |
8428 | @c @findex LC_NUMERIC | |
8429 | @c @findex LC_TIME | |
8430 | @findex LC_ALL | |
8431 | @cindex locale | |
0c2d1a2a JB |
8432 | These environment variables control the way that GCC uses |
8433 | localization information that allow GCC to work with different | |
8434 | national conventions. GCC inspects the locale categories | |
bedc7537 | 8435 | @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do |
ab87f8c8 JL |
8436 | so. These locale categories can be set to any value supported by your |
8437 | installation. A typical value is @samp{en_UK} for English in the United | |
8438 | Kingdom. | |
8439 | ||
bedc7537 | 8440 | The @env{LC_CTYPE} environment variable specifies character |
0c2d1a2a | 8441 | classification. GCC uses it to determine the character boundaries in |
ab87f8c8 JL |
8442 | a string; this is needed for some multibyte encodings that contain quote |
8443 | and escape characters that would otherwise be interpreted as a string | |
8444 | end or escape. | |
8445 | ||
bedc7537 | 8446 | The @env{LC_MESSAGES} environment variable specifies the language to |
ab87f8c8 JL |
8447 | use in diagnostic messages. |
8448 | ||
bedc7537 NC |
8449 | If the @env{LC_ALL} environment variable is set, it overrides the value |
8450 | of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE} | |
8451 | and @env{LC_MESSAGES} default to the value of the @env{LANG} | |
0c2d1a2a | 8452 | environment variable. If none of these variables are set, GCC |
ab87f8c8 JL |
8453 | defaults to traditional C English behavior. |
8454 | ||
74291a4b MM |
8455 | @item TMPDIR |
8456 | @findex TMPDIR | |
bedc7537 | 8457 | If @env{TMPDIR} is set, it specifies the directory to use for temporary |
0c2d1a2a | 8458 | files. GCC uses temporary files to hold the output of one stage of |
74291a4b MM |
8459 | compilation which is to be used as input to the next stage: for example, |
8460 | the output of the preprocessor, which is the input to the compiler | |
8461 | proper. | |
8462 | ||
8463 | @item GCC_EXEC_PREFIX | |
8464 | @findex GCC_EXEC_PREFIX | |
bedc7537 | 8465 | If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the |
74291a4b MM |
8466 | names of the subprograms executed by the compiler. No slash is added |
8467 | when this prefix is combined with the name of a subprogram, but you can | |
8468 | specify a prefix that ends with a slash if you wish. | |
8469 | ||
bedc7537 | 8470 | If @env{GCC_EXEC_PREFIX} is not set, GNU CC will attempt to figure out |
0deb20df TT |
8471 | an appropriate prefix to use based on the pathname it was invoked with. |
8472 | ||
0c2d1a2a | 8473 | If GCC cannot find the subprogram using the specified prefix, it |
74291a4b MM |
8474 | tries looking in the usual places for the subprogram. |
8475 | ||
bedc7537 | 8476 | The default value of @env{GCC_EXEC_PREFIX} is |
74291a4b MM |
8477 | @file{@var{prefix}/lib/gcc-lib/} where @var{prefix} is the value |
8478 | of @code{prefix} when you ran the @file{configure} script. | |
8479 | ||
8480 | Other prefixes specified with @samp{-B} take precedence over this prefix. | |
8481 | ||
8482 | This prefix is also used for finding files such as @file{crt0.o} that are | |
8483 | used for linking. | |
8484 | ||
8485 | In addition, the prefix is used in an unusual way in finding the | |
8486 | directories to search for header files. For each of the standard | |
8487 | directories whose name normally begins with @samp{/usr/local/lib/gcc-lib} | |
bedc7537 | 8488 | (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries |
74291a4b | 8489 | replacing that beginning with the specified prefix to produce an |
0c2d1a2a | 8490 | alternate directory name. Thus, with @samp{-Bfoo/}, GCC will search |
74291a4b MM |
8491 | @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}. |
8492 | These alternate directories are searched first; the standard directories | |
8493 | come next. | |
8494 | ||
8495 | @item COMPILER_PATH | |
8496 | @findex COMPILER_PATH | |
bedc7537 NC |
8497 | The value of @env{COMPILER_PATH} is a colon-separated list of |
8498 | directories, much like @env{PATH}. GCC tries the directories thus | |
74291a4b | 8499 | specified when searching for subprograms, if it can't find the |
bedc7537 | 8500 | subprograms using @env{GCC_EXEC_PREFIX}. |
74291a4b MM |
8501 | |
8502 | @item LIBRARY_PATH | |
8503 | @findex LIBRARY_PATH | |
bedc7537 NC |
8504 | The value of @env{LIBRARY_PATH} is a colon-separated list of |
8505 | directories, much like @env{PATH}. When configured as a native compiler, | |
0c2d1a2a | 8506 | GCC tries the directories thus specified when searching for special |
bedc7537 | 8507 | linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking |
0c2d1a2a | 8508 | using GCC also uses these directories when searching for ordinary |
74291a4b MM |
8509 | libraries for the @samp{-l} option (but directories specified with |
8510 | @samp{-L} come first). | |
8511 | ||
8512 | @item C_INCLUDE_PATH | |
8513 | @itemx CPLUS_INCLUDE_PATH | |
8514 | @itemx OBJC_INCLUDE_PATH | |
8515 | @findex C_INCLUDE_PATH | |
8516 | @findex CPLUS_INCLUDE_PATH | |
8517 | @findex OBJC_INCLUDE_PATH | |
8518 | @c @itemx OBJCPLUS_INCLUDE_PATH | |
8519 | These environment variables pertain to particular languages. Each | |
8520 | variable's value is a colon-separated list of directories, much like | |
bedc7537 | 8521 | @env{PATH}. When GCC searches for header files, it tries the |
74291a4b MM |
8522 | directories listed in the variable for the language you are using, after |
8523 | the directories specified with @samp{-I} but before the standard header | |
8524 | file directories. | |
8525 | ||
8526 | @item DEPENDENCIES_OUTPUT | |
8527 | @findex DEPENDENCIES_OUTPUT | |
8528 | @cindex dependencies for make as output | |
8529 | If this variable is set, its value specifies how to output dependencies | |
8530 | for Make based on the header files processed by the compiler. This | |
8531 | output looks much like the output from the @samp{-M} option | |
8532 | (@pxref{Preprocessor Options}), but it goes to a separate file, and is | |
8533 | in addition to the usual results of compilation. | |
8534 | ||
bedc7537 | 8535 | The value of @env{DEPENDENCIES_OUTPUT} can be just a file name, in |
74291a4b MM |
8536 | which case the Make rules are written to that file, guessing the target |
8537 | name from the source file name. Or the value can have the form | |
8538 | @samp{@var{file} @var{target}}, in which case the rules are written to | |
8539 | file @var{file} using @var{target} as the target name. | |
56f48ce9 DB |
8540 | |
8541 | @item LANG | |
8542 | @findex LANG | |
8543 | @cindex locale definition | |
8544 | This variable is used to pass locale information to the compiler. One way in | |
8545 | which this information is used is to determine the character set to be used | |
8546 | when character literals, string literals and comments are parsed in C and C++. | |
8547 | When the compiler is configured to allow multibyte characters, | |
bedc7537 | 8548 | the following values for @env{LANG} are recognized: |
56f48ce9 | 8549 | |
2642624b | 8550 | @table @samp |
56f48ce9 DB |
8551 | @item C-JIS |
8552 | Recognize JIS characters. | |
8553 | @item C-SJIS | |
8554 | Recognize SJIS characters. | |
8555 | @item C-EUCJP | |
8556 | Recognize EUCJP characters. | |
8557 | @end table | |
8558 | ||
bedc7537 | 8559 | If @env{LANG} is not defined, or if it has some other value, then the |
56f48ce9 DB |
8560 | compiler will use mblen and mbtowc as defined by the default locale to |
8561 | recognize and translate multibyte characters. | |
74291a4b MM |
8562 | @end table |
8563 | ||
9d86bffc JM |
8564 | @c man end |
8565 | ||
74291a4b MM |
8566 | @node Running Protoize |
8567 | @section Running Protoize | |
8568 | ||
8569 | The program @code{protoize} is an optional part of GNU C. You can use | |
c1030c7c | 8570 | it to add prototypes to a program, thus converting the program to ISO |
74291a4b MM |
8571 | C in one respect. The companion program @code{unprotoize} does the |
8572 | reverse: it removes argument types from any prototypes that are found. | |
8573 | ||
8574 | When you run these programs, you must specify a set of source files as | |
8575 | command line arguments. The conversion programs start out by compiling | |
8576 | these files to see what functions they define. The information gathered | |
8577 | about a file @var{foo} is saved in a file named @file{@var{foo}.X}. | |
8578 | ||
8579 | After scanning comes actual conversion. The specified files are all | |
8580 | eligible to be converted; any files they include (whether sources or | |
8581 | just headers) are eligible as well. | |
8582 | ||
8583 | But not all the eligible files are converted. By default, | |
8584 | @code{protoize} and @code{unprotoize} convert only source and header | |
8585 | files in the current directory. You can specify additional directories | |
8586 | whose files should be converted with the @samp{-d @var{directory}} | |
8587 | option. You can also specify particular files to exclude with the | |
8588 | @samp{-x @var{file}} option. A file is converted if it is eligible, its | |
8589 | directory name matches one of the specified directory names, and its | |
8590 | name within the directory has not been excluded. | |
8591 | ||
8592 | Basic conversion with @code{protoize} consists of rewriting most | |
8593 | function definitions and function declarations to specify the types of | |
8594 | the arguments. The only ones not rewritten are those for varargs | |
8595 | functions. | |
8596 | ||
8597 | @code{protoize} optionally inserts prototype declarations at the | |
8598 | beginning of the source file, to make them available for any calls that | |
8599 | precede the function's definition. Or it can insert prototype | |
8600 | declarations with block scope in the blocks where undeclared functions | |
8601 | are called. | |
8602 | ||
8603 | Basic conversion with @code{unprotoize} consists of rewriting most | |
8604 | function declarations to remove any argument types, and rewriting | |
c1030c7c | 8605 | function definitions to the old-style pre-ISO form. |
74291a4b MM |
8606 | |
8607 | Both conversion programs print a warning for any function declaration or | |
8608 | definition that they can't convert. You can suppress these warnings | |
8609 | with @samp{-q}. | |
8610 | ||
8611 | The output from @code{protoize} or @code{unprotoize} replaces the | |
8612 | original source file. The original file is renamed to a name ending | |
02f52e19 | 8613 | with @samp{.save} (for DOS, the saved filename ends in @samp{.sav} |
a7db8bbb MK |
8614 | without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav} |
8615 | for DOS) file already exists, then the source file is simply discarded. | |
74291a4b | 8616 | |
0c2d1a2a | 8617 | @code{protoize} and @code{unprotoize} both depend on GCC itself to |
74291a4b | 8618 | scan the program and collect information about the functions it uses. |
0c2d1a2a | 8619 | So neither of these programs will work until GCC is installed. |
74291a4b MM |
8620 | |
8621 | Here is a table of the options you can use with @code{protoize} and | |
8622 | @code{unprotoize}. Each option works with both programs unless | |
8623 | otherwise stated. | |
8624 | ||
8625 | @table @code | |
8626 | @item -B @var{directory} | |
8627 | Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the | |
8628 | usual directory (normally @file{/usr/local/lib}). This file contains | |
8629 | prototype information about standard system functions. This option | |
8630 | applies only to @code{protoize}. | |
8631 | ||
8632 | @item -c @var{compilation-options} | |
8633 | Use @var{compilation-options} as the options when running @code{gcc} to | |
8634 | produce the @samp{.X} files. The special option @samp{-aux-info} is | |
8635 | always passed in addition, to tell @code{gcc} to write a @samp{.X} file. | |
8636 | ||
8637 | Note that the compilation options must be given as a single argument to | |
8638 | @code{protoize} or @code{unprotoize}. If you want to specify several | |
8639 | @code{gcc} options, you must quote the entire set of compilation options | |
8640 | to make them a single word in the shell. | |
8641 | ||
8642 | There are certain @code{gcc} arguments that you cannot use, because they | |
8643 | would produce the wrong kind of output. These include @samp{-g}, | |
8644 | @samp{-O}, @samp{-c}, @samp{-S}, and @samp{-o} If you include these in | |
8645 | the @var{compilation-options}, they are ignored. | |
8646 | ||
8647 | @item -C | |
a7db8bbb | 8648 | Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file |
02f52e19 | 8649 | systems) instead of @samp{.c}. This is convenient if you are converting |
ee77eda5 | 8650 | a C program to C++. This option applies only to @code{protoize}. |
74291a4b MM |
8651 | |
8652 | @item -g | |
8653 | Add explicit global declarations. This means inserting explicit | |
8654 | declarations at the beginning of each source file for each function | |
8655 | that is called in the file and was not declared. These declarations | |
8656 | precede the first function definition that contains a call to an | |
8657 | undeclared function. This option applies only to @code{protoize}. | |
8658 | ||
8659 | @item -i @var{string} | |
8660 | Indent old-style parameter declarations with the string @var{string}. | |
8661 | This option applies only to @code{protoize}. | |
8662 | ||
8663 | @code{unprotoize} converts prototyped function definitions to old-style | |
8664 | function definitions, where the arguments are declared between the | |
8665 | argument list and the initial @samp{@{}. By default, @code{unprotoize} | |
8666 | uses five spaces as the indentation. If you want to indent with just | |
8667 | one space instead, use @samp{-i " "}. | |
8668 | ||
8669 | @item -k | |
8670 | Keep the @samp{.X} files. Normally, they are deleted after conversion | |
8671 | is finished. | |
8672 | ||
8673 | @item -l | |
8674 | Add explicit local declarations. @code{protoize} with @samp{-l} inserts | |
8675 | a prototype declaration for each function in each block which calls the | |
8676 | function without any declaration. This option applies only to | |
8677 | @code{protoize}. | |
8678 | ||
8679 | @item -n | |
8680 | Make no real changes. This mode just prints information about the conversions | |
8681 | that would have been done without @samp{-n}. | |
8682 | ||
8683 | @item -N | |
8684 | Make no @samp{.save} files. The original files are simply deleted. | |
8685 | Use this option with caution. | |
8686 | ||
8687 | @item -p @var{program} | |
8688 | Use the program @var{program} as the compiler. Normally, the name | |
8689 | @file{gcc} is used. | |
8690 | ||
8691 | @item -q | |
8692 | Work quietly. Most warnings are suppressed. | |
8693 | ||
8694 | @item -v | |
8695 | Print the version number, just like @samp{-v} for @code{gcc}. | |
8696 | @end table | |
8697 | ||
8698 | If you need special compiler options to compile one of your program's | |
8699 | source files, then you should generate that file's @samp{.X} file | |
8700 | specially, by running @code{gcc} on that source file with the | |
8701 | appropriate options and the option @samp{-aux-info}. Then run | |
8702 | @code{protoize} on the entire set of files. @code{protoize} will use | |
8703 | the existing @samp{.X} file because it is newer than the source file. | |
8704 | For example: | |
8705 | ||
8706 | @example | |
8707 | gcc -Dfoo=bar file1.c -aux-info | |
8708 | protoize *.c | |
8709 | @end example | |
8710 | ||
8711 | @noindent | |
8712 | You need to include the special files along with the rest in the | |
8713 | @code{protoize} command, even though their @samp{.X} files already | |
8714 | exist, because otherwise they won't get converted. | |
8715 | ||
8716 | @xref{Protoize Caveats}, for more information on how to use | |
8717 | @code{protoize} successfully. |