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1 | @c Copyright (C) 1988,1989,1992,1993,1994,1996,1998,1999,2000,2001,2002, |
2 | @c 2003 Free Software Foundation, Inc. | |
c1f7febf RK |
3 | @c This is part of the GCC manual. |
4 | @c For copying conditions, see the file gcc.texi. | |
5 | ||
fe203faf RH |
6 | @node C Implementation |
7 | @chapter C Implementation-defined behavior | |
8 | @cindex implementation-defined behavior, C language | |
9 | ||
10 | A conforming implementation of ISO C is required to document its | |
11 | choice of behavior in each of the areas that are designated | |
12 | ``implementation defined.'' The following lists all such areas, | |
13 | along with the section number from the ISO/IEC 9899:1999 standard. | |
14 | ||
15 | @menu | |
16 | * Translation implementation:: | |
17 | * Environment implementation:: | |
18 | * Identifiers implementation:: | |
19 | * Characters implementation:: | |
20 | * Integers implementation:: | |
21 | * Floating point implementation:: | |
22 | * Arrays and pointers implementation:: | |
23 | * Hints implementation:: | |
24 | * Structures unions enumerations and bit-fields implementation:: | |
25 | * Qualifiers implementation:: | |
26 | * Preprocessing directives implementation:: | |
27 | * Library functions implementation:: | |
28 | * Architecture implementation:: | |
29 | * Locale-specific behavior implementation:: | |
30 | @end menu | |
31 | ||
32 | @node Translation implementation | |
33 | @section Translation | |
34 | ||
35 | @itemize @bullet | |
36 | @item | |
37 | @cite{How a diagnostic is identified (3.10, 5.1.1.3).} | |
38 | ||
cba57c9d GK |
39 | Diagnostics consist of all the output sent to stderr by GCC. |
40 | ||
fe203faf RH |
41 | @item |
42 | @cite{Whether each nonempty sequence of white-space characters other than | |
43 | new-line is retained or replaced by one space character in translation | |
44 | phase 3 (5.1.1.2).} | |
45 | @end itemize | |
46 | ||
47 | @node Environment implementation | |
48 | @section Environment | |
49 | ||
0c688a7d | 50 | The behavior of these points are dependent on the implementation |
fe203faf RH |
51 | of the C library, and are not defined by GCC itself. |
52 | ||
53 | @node Identifiers implementation | |
54 | @section Identifiers | |
55 | ||
56 | @itemize @bullet | |
57 | @item | |
58 | @cite{Which additional multibyte characters may appear in identifiers | |
59 | and their correspondence to universal character names (6.4.2).} | |
60 | ||
61 | @item | |
62 | @cite{The number of significant initial characters in an identifier | |
63 | (5.2.4.1, 6.4.2).} | |
cba57c9d GK |
64 | |
65 | For internal names, all characters are significant. For external names, | |
66 | the number of significant characters are defined by the linker; for | |
67 | almost all targets, all characters are significant. | |
68 | ||
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69 | @end itemize |
70 | ||
71 | @node Characters implementation | |
72 | @section Characters | |
73 | ||
74 | @itemize @bullet | |
75 | @item | |
76 | @cite{The number of bits in a byte (3.6).} | |
77 | ||
78 | @item | |
79 | @cite{The values of the members of the execution character set (5.2.1).} | |
80 | ||
81 | @item | |
82 | @cite{The unique value of the member of the execution character set produced | |
83 | for each of the standard alphabetic escape sequences (5.2.2).} | |
84 | ||
85 | @item | |
86 | @cite{The value of a @code{char} object into which has been stored any | |
87 | character other than a member of the basic execution character set (6.2.5).} | |
88 | ||
89 | @item | |
90 | @cite{Which of @code{signed char} or @code{unsigned char} has the same range, | |
39ffd3cb | 91 | representation, and behavior as ``plain'' @code{char} (6.2.5, 6.3.1.1).} |
fe203faf RH |
92 | |
93 | @item | |
94 | @cite{The mapping of members of the source character set (in character | |
95 | constants and string literals) to members of the execution character | |
96 | set (6.4.4.4, 5.1.1.2).} | |
97 | ||
98 | @item | |
99 | @cite{The value of an integer character constant containing more than one | |
100 | character or containing a character or escape sequence that does not map | |
101 | to a single-byte execution character (6.4.4.4).} | |
102 | ||
103 | @item | |
104 | @cite{The value of a wide character constant containing more than one | |
105 | multibyte character, or containing a multibyte character or escape | |
106 | sequence not represented in the extended execution character set (6.4.4.4).} | |
107 | ||
108 | @item | |
109 | @cite{The current locale used to convert a wide character constant consisting | |
110 | of a single multibyte character that maps to a member of the extended | |
111 | execution character set into a corresponding wide character code (6.4.4.4).} | |
112 | ||
113 | @item | |
114 | @cite{The current locale used to convert a wide string literal into | |
115 | corresponding wide character codes (6.4.5).} | |
116 | ||
117 | @item | |
118 | @cite{The value of a string literal containing a multibyte character or escape | |
119 | sequence not represented in the execution character set (6.4.5).} | |
120 | @end itemize | |
121 | ||
122 | @node Integers implementation | |
123 | @section Integers | |
124 | ||
125 | @itemize @bullet | |
126 | @item | |
127 | @cite{Any extended integer types that exist in the implementation (6.2.5).} | |
128 | ||
129 | @item | |
130 | @cite{Whether signed integer types are represented using sign and magnitude, | |
131 | two's complement, or one's complement, and whether the extraordinary value | |
132 | is a trap representation or an ordinary value (6.2.6.2).} | |
133 | ||
cba57c9d GK |
134 | GCC supports only two's complement integer types, and all bit patterns |
135 | are ordinary values. | |
136 | ||
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137 | @item |
138 | @cite{The rank of any extended integer type relative to another extended | |
139 | integer type with the same precision (6.3.1.1).} | |
140 | ||
141 | @item | |
142 | @cite{The result of, or the signal raised by, converting an integer to a | |
143 | signed integer type when the value cannot be represented in an object of | |
144 | that type (6.3.1.3).} | |
145 | ||
146 | @item | |
147 | @cite{The results of some bitwise operations on signed integers (6.5).} | |
148 | @end itemize | |
149 | ||
150 | @node Floating point implementation | |
151 | @section Floating point | |
152 | ||
153 | @itemize @bullet | |
154 | @item | |
155 | @cite{The accuracy of the floating-point operations and of the library | |
39ffd3cb | 156 | functions in @code{<math.h>} and @code{<complex.h>} that return floating-point |
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157 | results (5.2.4.2.2).} |
158 | ||
159 | @item | |
160 | @cite{The rounding behaviors characterized by non-standard values | |
9c34dbbf ZW |
161 | of @code{FLT_ROUNDS} @gol |
162 | (5.2.4.2.2).} | |
fe203faf RH |
163 | |
164 | @item | |
165 | @cite{The evaluation methods characterized by non-standard negative | |
166 | values of @code{FLT_EVAL_METHOD} (5.2.4.2.2).} | |
167 | ||
168 | @item | |
169 | @cite{The direction of rounding when an integer is converted to a | |
170 | floating-point number that cannot exactly represent the original | |
171 | value (6.3.1.4).} | |
172 | ||
173 | @item | |
174 | @cite{The direction of rounding when a floating-point number is | |
175 | converted to a narrower floating-point number (6.3.1.5).} | |
176 | ||
177 | @item | |
178 | @cite{How the nearest representable value or the larger or smaller | |
179 | representable value immediately adjacent to the nearest representable | |
180 | value is chosen for certain floating constants (6.4.4.2).} | |
181 | ||
182 | @item | |
183 | @cite{Whether and how floating expressions are contracted when not | |
184 | disallowed by the @code{FP_CONTRACT} pragma (6.5).} | |
185 | ||
186 | @item | |
187 | @cite{The default state for the @code{FENV_ACCESS} pragma (7.6.1).} | |
188 | ||
189 | @item | |
190 | @cite{Additional floating-point exceptions, rounding modes, environments, | |
191 | and classifications, and their macro names (7.6, 7.12).} | |
192 | ||
193 | @item | |
194 | @cite{The default state for the @code{FP_CONTRACT} pragma (7.12.2).} | |
195 | ||
196 | @item | |
197 | @cite{Whether the ``inexact'' floating-point exception can be raised | |
198 | when the rounded result actually does equal the mathematical result | |
199 | in an IEC 60559 conformant implementation (F.9).} | |
200 | ||
201 | @item | |
202 | @cite{Whether the ``underflow'' (and ``inexact'') floating-point | |
203 | exception can be raised when a result is tiny but not inexact in an | |
204 | IEC 60559 conformant implementation (F.9).} | |
205 | ||
206 | @end itemize | |
207 | ||
208 | @node Arrays and pointers implementation | |
209 | @section Arrays and pointers | |
210 | ||
211 | @itemize @bullet | |
212 | @item | |
213 | @cite{The result of converting a pointer to an integer or | |
214 | vice versa (6.3.2.3).} | |
215 | ||
cbf4c36f | 216 | A cast from pointer to integer discards most-significant bits if the |
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217 | pointer representation is larger than the integer type, |
218 | sign-extends@footnote{Future versions of GCC may zero-extend, or use | |
219 | a target-defined @code{ptr_extend} pattern. Do not rely on sign extension.} | |
cbf4c36f RH |
220 | if the pointer representation is smaller than the integer type, otherwise |
221 | the bits are unchanged. | |
222 | @c ??? We've always claimed that pointers were unsigned entities. | |
223 | @c Shouldn't we therefore be doing zero-extension? If so, the bug | |
224 | @c is in convert_to_integer, where we call type_for_size and request | |
225 | @c a signed integral type. On the other hand, it might be most useful | |
226 | @c for the target if we extend according to POINTERS_EXTEND_UNSIGNED. | |
227 | ||
228 | A cast from integer to pointer discards most-significant bits if the | |
229 | pointer representation is smaller than the integer type, extends according | |
230 | to the signedness of the integer type if the pointer representation | |
231 | is larger than the integer type, otherwise the bits are unchanged. | |
232 | ||
233 | When casting from pointer to integer and back again, the resulting | |
234 | pointer must reference the same object as the original pointer, otherwise | |
235 | the behavior is undefined. That is, one may not use integer arithmetic to | |
236 | avoid the undefined behavior of pointer arithmetic as proscribed in 6.5.6/8. | |
237 | ||
fe203faf RH |
238 | @item |
239 | @cite{The size of the result of subtracting two pointers to elements | |
240 | of the same array (6.5.6).} | |
241 | ||
242 | @end itemize | |
243 | ||
244 | @node Hints implementation | |
245 | @section Hints | |
246 | ||
247 | @itemize @bullet | |
248 | @item | |
249 | @cite{The extent to which suggestions made by using the @code{register} | |
250 | storage-class specifier are effective (6.7.1).} | |
251 | ||
6fd14075 GK |
252 | The @code{register} specifier affects code generation only in these ways: |
253 | ||
254 | @itemize @bullet | |
255 | @item | |
256 | When used as part of the register variable extension, see | |
257 | @ref{Explicit Reg Vars}. | |
258 | ||
259 | @item | |
260 | When @option{-O0} is in use, the compiler allocates distinct stack | |
261 | memory for all variables that do not have the @code{register} | |
262 | storage-class specifier; if @code{register} is specified, the variable | |
263 | may have a shorter lifespan than the code would indicate and may never | |
264 | be placed in memory. | |
265 | ||
266 | @item | |
267 | On some rare x86 targets, @code{setjmp} doesn't save the registers in | |
268 | all circumstances. In those cases, GCC doesn't allocate any variables | |
269 | in registers unless they are marked @code{register}. | |
270 | ||
271 | @end itemize | |
272 | ||
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273 | @item |
274 | @cite{The extent to which suggestions made by using the inline function | |
275 | specifier are effective (6.7.4).} | |
276 | ||
cba57c9d GK |
277 | GCC will not inline any functions if the @option{-fno-inline} option is |
278 | used or if @option{-O0} is used. Otherwise, GCC may still be unable to | |
279 | inline a function for many reasons; the @option{-Winline} option may be | |
280 | used to determine if a function has not been inlined and why not. | |
281 | ||
fe203faf RH |
282 | @end itemize |
283 | ||
284 | @node Structures unions enumerations and bit-fields implementation | |
285 | @section Structures, unions, enumerations, and bit-fields | |
286 | ||
287 | @itemize @bullet | |
288 | @item | |
289 | @cite{Whether a ``plain'' int bit-field is treated as a @code{signed int} | |
290 | bit-field or as an @code{unsigned int} bit-field (6.7.2, 6.7.2.1).} | |
291 | ||
292 | @item | |
293 | @cite{Allowable bit-field types other than @code{_Bool}, @code{signed int}, | |
294 | and @code{unsigned int} (6.7.2.1).} | |
295 | ||
296 | @item | |
297 | @cite{Whether a bit-field can straddle a storage-unit boundary (6.7.2.1).} | |
298 | ||
299 | @item | |
300 | @cite{The order of allocation of bit-fields within a unit (6.7.2.1).} | |
301 | ||
302 | @item | |
303 | @cite{The alignment of non-bit-field members of structures (6.7.2.1).} | |
304 | ||
305 | @item | |
306 | @cite{The integer type compatible with each enumerated type (6.7.2.2).} | |
307 | ||
308 | @end itemize | |
309 | ||
310 | @node Qualifiers implementation | |
311 | @section Qualifiers | |
312 | ||
313 | @itemize @bullet | |
314 | @item | |
315 | @cite{What constitutes an access to an object that has volatile-qualified | |
316 | type (6.7.3).} | |
317 | ||
318 | @end itemize | |
319 | ||
320 | @node Preprocessing directives implementation | |
321 | @section Preprocessing directives | |
322 | ||
323 | @itemize @bullet | |
324 | @item | |
325 | @cite{How sequences in both forms of header names are mapped to headers | |
326 | or external source file names (6.4.7).} | |
327 | ||
328 | @item | |
329 | @cite{Whether the value of a character constant in a constant expression | |
330 | that controls conditional inclusion matches the value of the same character | |
331 | constant in the execution character set (6.10.1).} | |
332 | ||
333 | @item | |
334 | @cite{Whether the value of a single-character character constant in a | |
335 | constant expression that controls conditional inclusion may have a | |
336 | negative value (6.10.1).} | |
337 | ||
338 | @item | |
339 | @cite{The places that are searched for an included @samp{<>} delimited | |
340 | header, and how the places are specified or the header is | |
341 | identified (6.10.2).} | |
342 | ||
343 | @item | |
344 | @cite{How the named source file is searched for in an included @samp{""} | |
345 | delimited header (6.10.2).} | |
346 | ||
347 | @item | |
348 | @cite{The method by which preprocessing tokens (possibly resulting from | |
349 | macro expansion) in a @code{#include} directive are combined into a header | |
350 | name (6.10.2).} | |
351 | ||
352 | @item | |
353 | @cite{The nesting limit for @code{#include} processing (6.10.2).} | |
354 | ||
cba57c9d GK |
355 | GCC imposes a limit of 200 nested @code{#include}s. |
356 | ||
fe203faf RH |
357 | @item |
358 | @cite{Whether the @samp{#} operator inserts a @samp{\} character before | |
359 | the @samp{\} character that begins a universal character name in a | |
360 | character constant or string literal (6.10.3.2).} | |
361 | ||
362 | @item | |
363 | @cite{The behavior on each recognized non-@code{STDC #pragma} | |
364 | directive (6.10.6).} | |
365 | ||
366 | @item | |
367 | @cite{The definitions for @code{__DATE__} and @code{__TIME__} when | |
368 | respectively, the date and time of translation are not available (6.10.8).} | |
369 | ||
56da7207 ZW |
370 | If the date and time are not available, @code{__DATE__} expands to |
371 | @code{@w{"??? ?? ????"}} and @code{__TIME__} expands to | |
372 | @code{"??:??:??"}. | |
cba57c9d | 373 | |
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374 | @end itemize |
375 | ||
376 | @node Library functions implementation | |
377 | @section Library functions | |
378 | ||
0c688a7d | 379 | The behavior of these points are dependent on the implementation |
fe203faf RH |
380 | of the C library, and are not defined by GCC itself. |
381 | ||
382 | @node Architecture implementation | |
383 | @section Architecture | |
384 | ||
385 | @itemize @bullet | |
386 | @item | |
387 | @cite{The values or expressions assigned to the macros specified in the | |
39ffd3cb | 388 | headers @code{<float.h>}, @code{<limits.h>}, and @code{<stdint.h>} |
fe203faf RH |
389 | (5.2.4.2, 7.18.2, 7.18.3).} |
390 | ||
391 | @item | |
392 | @cite{The number, order, and encoding of bytes in any object | |
393 | (when not explicitly specified in this International Standard) (6.2.6.1).} | |
394 | ||
395 | @item | |
396 | @cite{The value of the result of the sizeof operator (6.5.3.4).} | |
397 | ||
398 | @end itemize | |
399 | ||
400 | @node Locale-specific behavior implementation | |
401 | @section Locale-specific behavior | |
402 | ||
0c688a7d | 403 | The behavior of these points are dependent on the implementation |
fe203faf RH |
404 | of the C library, and are not defined by GCC itself. |
405 | ||
c1f7febf RK |
406 | @node C Extensions |
407 | @chapter Extensions to the C Language Family | |
408 | @cindex extensions, C language | |
409 | @cindex C language extensions | |
410 | ||
84330467 | 411 | @opindex pedantic |
161d7b59 | 412 | GNU C provides several language features not found in ISO standard C@. |
f0523f02 | 413 | (The @option{-pedantic} option directs GCC to print a warning message if |
c1f7febf RK |
414 | any of these features is used.) To test for the availability of these |
415 | features in conditional compilation, check for a predefined macro | |
161d7b59 | 416 | @code{__GNUC__}, which is always defined under GCC@. |
c1f7febf | 417 | |
161d7b59 | 418 | These extensions are available in C and Objective-C@. Most of them are |
c1f7febf RK |
419 | also available in C++. @xref{C++ Extensions,,Extensions to the |
420 | C++ Language}, for extensions that apply @emph{only} to C++. | |
421 | ||
4b404517 JM |
422 | Some features that are in ISO C99 but not C89 or C++ are also, as |
423 | extensions, accepted by GCC in C89 mode and in C++. | |
5490d604 | 424 | |
c1f7febf RK |
425 | @menu |
426 | * Statement Exprs:: Putting statements and declarations inside expressions. | |
427 | * Local Labels:: Labels local to a statement-expression. | |
428 | * Labels as Values:: Getting pointers to labels, and computed gotos. | |
429 | * Nested Functions:: As in Algol and Pascal, lexical scoping of functions. | |
430 | * Constructing Calls:: Dispatching a call to another function. | |
c1f7febf RK |
431 | * Typeof:: @code{typeof}: referring to the type of an expression. |
432 | * Lvalues:: Using @samp{?:}, @samp{,} and casts in lvalues. | |
433 | * Conditionals:: Omitting the middle operand of a @samp{?:} expression. | |
434 | * Long Long:: Double-word integers---@code{long long int}. | |
435 | * Complex:: Data types for complex numbers. | |
6f4d7222 | 436 | * Hex Floats:: Hexadecimal floating-point constants. |
c1f7febf RK |
437 | * Zero Length:: Zero-length arrays. |
438 | * Variable Length:: Arrays whose length is computed at run time. | |
ccd96f0a NB |
439 | * Variadic Macros:: Macros with a variable number of arguments. |
440 | * Escaped Newlines:: Slightly looser rules for escaped newlines. | |
441 | * Multi-line Strings:: String literals with embedded newlines. | |
c1f7febf RK |
442 | * Subscripting:: Any array can be subscripted, even if not an lvalue. |
443 | * Pointer Arith:: Arithmetic on @code{void}-pointers and function pointers. | |
444 | * Initializers:: Non-constant initializers. | |
4b404517 | 445 | * Compound Literals:: Compound literals give structures, unions |
c1f7febf | 446 | or arrays as values. |
4b404517 | 447 | * Designated Inits:: Labeling elements of initializers. |
c1f7febf RK |
448 | * Cast to Union:: Casting to union type from any member of the union. |
449 | * Case Ranges:: `case 1 ... 9' and such. | |
4b404517 | 450 | * Mixed Declarations:: Mixing declarations and code. |
c1f7febf RK |
451 | * Function Attributes:: Declaring that functions have no side effects, |
452 | or that they can never return. | |
2c5e91d2 | 453 | * Attribute Syntax:: Formal syntax for attributes. |
c1f7febf RK |
454 | * Function Prototypes:: Prototype declarations and old-style definitions. |
455 | * C++ Comments:: C++ comments are recognized. | |
456 | * Dollar Signs:: Dollar sign is allowed in identifiers. | |
457 | * Character Escapes:: @samp{\e} stands for the character @key{ESC}. | |
458 | * Variable Attributes:: Specifying attributes of variables. | |
459 | * Type Attributes:: Specifying attributes of types. | |
460 | * Alignment:: Inquiring about the alignment of a type or variable. | |
461 | * Inline:: Defining inline functions (as fast as macros). | |
462 | * Extended Asm:: Assembler instructions with C expressions as operands. | |
463 | (With them you can define ``built-in'' functions.) | |
464 | * Constraints:: Constraints for asm operands | |
465 | * Asm Labels:: Specifying the assembler name to use for a C symbol. | |
466 | * Explicit Reg Vars:: Defining variables residing in specified registers. | |
467 | * Alternate Keywords:: @code{__const__}, @code{__asm__}, etc., for header files. | |
468 | * Incomplete Enums:: @code{enum foo;}, with details to follow. | |
469 | * Function Names:: Printable strings which are the name of the current | |
470 | function. | |
471 | * Return Address:: Getting the return or frame address of a function. | |
1255c85c | 472 | * Vector Extensions:: Using vector instructions through built-in functions. |
c5c76735 | 473 | * Other Builtins:: Other built-in functions. |
0975678f | 474 | * Target Builtins:: Built-in functions specific to particular targets. |
0168a849 | 475 | * Pragmas:: Pragmas accepted by GCC. |
b11cc610 | 476 | * Unnamed Fields:: Unnamed struct/union fields within structs/unions. |
3d78f2e9 | 477 | * Thread-Local:: Per-thread variables. |
c1f7febf | 478 | @end menu |
c1f7febf RK |
479 | |
480 | @node Statement Exprs | |
481 | @section Statements and Declarations in Expressions | |
482 | @cindex statements inside expressions | |
483 | @cindex declarations inside expressions | |
484 | @cindex expressions containing statements | |
485 | @cindex macros, statements in expressions | |
486 | ||
487 | @c the above section title wrapped and causes an underfull hbox.. i | |
488 | @c changed it from "within" to "in". --mew 4feb93 | |
489 | ||
490 | A compound statement enclosed in parentheses may appear as an expression | |
161d7b59 | 491 | in GNU C@. This allows you to use loops, switches, and local variables |
c1f7febf RK |
492 | within an expression. |
493 | ||
494 | Recall that a compound statement is a sequence of statements surrounded | |
495 | by braces; in this construct, parentheses go around the braces. For | |
496 | example: | |
497 | ||
498 | @example | |
499 | (@{ int y = foo (); int z; | |
500 | if (y > 0) z = y; | |
501 | else z = - y; | |
502 | z; @}) | |
503 | @end example | |
504 | ||
505 | @noindent | |
506 | is a valid (though slightly more complex than necessary) expression | |
507 | for the absolute value of @code{foo ()}. | |
508 | ||
509 | The last thing in the compound statement should be an expression | |
510 | followed by a semicolon; the value of this subexpression serves as the | |
511 | value of the entire construct. (If you use some other kind of statement | |
512 | last within the braces, the construct has type @code{void}, and thus | |
513 | effectively no value.) | |
514 | ||
515 | This feature is especially useful in making macro definitions ``safe'' (so | |
516 | that they evaluate each operand exactly once). For example, the | |
517 | ``maximum'' function is commonly defined as a macro in standard C as | |
518 | follows: | |
519 | ||
520 | @example | |
521 | #define max(a,b) ((a) > (b) ? (a) : (b)) | |
522 | @end example | |
523 | ||
524 | @noindent | |
525 | @cindex side effects, macro argument | |
526 | But this definition computes either @var{a} or @var{b} twice, with bad | |
527 | results if the operand has side effects. In GNU C, if you know the | |
528 | type of the operands (here let's assume @code{int}), you can define | |
529 | the macro safely as follows: | |
530 | ||
531 | @example | |
532 | #define maxint(a,b) \ | |
533 | (@{int _a = (a), _b = (b); _a > _b ? _a : _b; @}) | |
534 | @end example | |
535 | ||
536 | Embedded statements are not allowed in constant expressions, such as | |
c771326b | 537 | the value of an enumeration constant, the width of a bit-field, or |
c1f7febf RK |
538 | the initial value of a static variable. |
539 | ||
540 | If you don't know the type of the operand, you can still do this, but you | |
95f79357 | 541 | must use @code{typeof} (@pxref{Typeof}). |
c1f7febf | 542 | |
b98e139b MM |
543 | Statement expressions are not supported fully in G++, and their fate |
544 | there is unclear. (It is possible that they will become fully supported | |
545 | at some point, or that they will be deprecated, or that the bugs that | |
546 | are present will continue to exist indefinitely.) Presently, statement | |
02f52e19 | 547 | expressions do not work well as default arguments. |
b98e139b MM |
548 | |
549 | In addition, there are semantic issues with statement-expressions in | |
550 | C++. If you try to use statement-expressions instead of inline | |
551 | functions in C++, you may be surprised at the way object destruction is | |
552 | handled. For example: | |
553 | ||
554 | @example | |
555 | #define foo(a) (@{int b = (a); b + 3; @}) | |
556 | @end example | |
557 | ||
558 | @noindent | |
559 | does not work the same way as: | |
560 | ||
561 | @example | |
54e1d3a6 | 562 | inline int foo(int a) @{ int b = a; return b + 3; @} |
b98e139b MM |
563 | @end example |
564 | ||
565 | @noindent | |
566 | In particular, if the expression passed into @code{foo} involves the | |
567 | creation of temporaries, the destructors for those temporaries will be | |
568 | run earlier in the case of the macro than in the case of the function. | |
569 | ||
570 | These considerations mean that it is probably a bad idea to use | |
571 | statement-expressions of this form in header files that are designed to | |
54e1d3a6 MM |
572 | work with C++. (Note that some versions of the GNU C Library contained |
573 | header files using statement-expression that lead to precisely this | |
574 | bug.) | |
b98e139b | 575 | |
c1f7febf RK |
576 | @node Local Labels |
577 | @section Locally Declared Labels | |
578 | @cindex local labels | |
579 | @cindex macros, local labels | |
580 | ||
581 | Each statement expression is a scope in which @dfn{local labels} can be | |
582 | declared. A local label is simply an identifier; you can jump to it | |
583 | with an ordinary @code{goto} statement, but only from within the | |
584 | statement expression it belongs to. | |
585 | ||
586 | A local label declaration looks like this: | |
587 | ||
588 | @example | |
589 | __label__ @var{label}; | |
590 | @end example | |
591 | ||
592 | @noindent | |
593 | or | |
594 | ||
595 | @example | |
0d893a63 | 596 | __label__ @var{label1}, @var{label2}, /* @r{@dots{}} */; |
c1f7febf RK |
597 | @end example |
598 | ||
599 | Local label declarations must come at the beginning of the statement | |
600 | expression, right after the @samp{(@{}, before any ordinary | |
601 | declarations. | |
602 | ||
603 | The label declaration defines the label @emph{name}, but does not define | |
604 | the label itself. You must do this in the usual way, with | |
605 | @code{@var{label}:}, within the statements of the statement expression. | |
606 | ||
607 | The local label feature is useful because statement expressions are | |
608 | often used in macros. If the macro contains nested loops, a @code{goto} | |
609 | can be useful for breaking out of them. However, an ordinary label | |
610 | whose scope is the whole function cannot be used: if the macro can be | |
611 | expanded several times in one function, the label will be multiply | |
612 | defined in that function. A local label avoids this problem. For | |
613 | example: | |
614 | ||
615 | @example | |
616 | #define SEARCH(array, target) \ | |
310668e8 | 617 | (@{ \ |
c1f7febf RK |
618 | __label__ found; \ |
619 | typeof (target) _SEARCH_target = (target); \ | |
620 | typeof (*(array)) *_SEARCH_array = (array); \ | |
621 | int i, j; \ | |
622 | int value; \ | |
623 | for (i = 0; i < max; i++) \ | |
624 | for (j = 0; j < max; j++) \ | |
625 | if (_SEARCH_array[i][j] == _SEARCH_target) \ | |
310668e8 | 626 | @{ value = i; goto found; @} \ |
c1f7febf RK |
627 | value = -1; \ |
628 | found: \ | |
629 | value; \ | |
630 | @}) | |
631 | @end example | |
632 | ||
633 | @node Labels as Values | |
634 | @section Labels as Values | |
635 | @cindex labels as values | |
636 | @cindex computed gotos | |
637 | @cindex goto with computed label | |
638 | @cindex address of a label | |
639 | ||
640 | You can get the address of a label defined in the current function | |
641 | (or a containing function) with the unary operator @samp{&&}. The | |
642 | value has type @code{void *}. This value is a constant and can be used | |
643 | wherever a constant of that type is valid. For example: | |
644 | ||
645 | @example | |
646 | void *ptr; | |
0d893a63 | 647 | /* @r{@dots{}} */ |
c1f7febf RK |
648 | ptr = &&foo; |
649 | @end example | |
650 | ||
651 | To use these values, you need to be able to jump to one. This is done | |
652 | with the computed goto statement@footnote{The analogous feature in | |
653 | Fortran is called an assigned goto, but that name seems inappropriate in | |
654 | C, where one can do more than simply store label addresses in label | |
655 | variables.}, @code{goto *@var{exp};}. For example, | |
656 | ||
657 | @example | |
658 | goto *ptr; | |
659 | @end example | |
660 | ||
661 | @noindent | |
662 | Any expression of type @code{void *} is allowed. | |
663 | ||
664 | One way of using these constants is in initializing a static array that | |
665 | will serve as a jump table: | |
666 | ||
667 | @example | |
668 | static void *array[] = @{ &&foo, &&bar, &&hack @}; | |
669 | @end example | |
670 | ||
671 | Then you can select a label with indexing, like this: | |
672 | ||
673 | @example | |
674 | goto *array[i]; | |
675 | @end example | |
676 | ||
677 | @noindent | |
678 | Note that this does not check whether the subscript is in bounds---array | |
679 | indexing in C never does that. | |
680 | ||
681 | Such an array of label values serves a purpose much like that of the | |
682 | @code{switch} statement. The @code{switch} statement is cleaner, so | |
683 | use that rather than an array unless the problem does not fit a | |
684 | @code{switch} statement very well. | |
685 | ||
686 | Another use of label values is in an interpreter for threaded code. | |
687 | The labels within the interpreter function can be stored in the | |
688 | threaded code for super-fast dispatching. | |
689 | ||
02f52e19 | 690 | You may not use this mechanism to jump to code in a different function. |
47620e09 | 691 | If you do that, totally unpredictable things will happen. The best way to |
c1f7febf RK |
692 | avoid this is to store the label address only in automatic variables and |
693 | never pass it as an argument. | |
694 | ||
47620e09 RH |
695 | An alternate way to write the above example is |
696 | ||
697 | @example | |
310668e8 JM |
698 | static const int array[] = @{ &&foo - &&foo, &&bar - &&foo, |
699 | &&hack - &&foo @}; | |
47620e09 RH |
700 | goto *(&&foo + array[i]); |
701 | @end example | |
702 | ||
703 | @noindent | |
704 | This is more friendly to code living in shared libraries, as it reduces | |
705 | the number of dynamic relocations that are needed, and by consequence, | |
706 | allows the data to be read-only. | |
707 | ||
c1f7febf RK |
708 | @node Nested Functions |
709 | @section Nested Functions | |
710 | @cindex nested functions | |
711 | @cindex downward funargs | |
712 | @cindex thunks | |
713 | ||
714 | A @dfn{nested function} is a function defined inside another function. | |
715 | (Nested functions are not supported for GNU C++.) The nested function's | |
716 | name is local to the block where it is defined. For example, here we | |
717 | define a nested function named @code{square}, and call it twice: | |
718 | ||
719 | @example | |
720 | @group | |
721 | foo (double a, double b) | |
722 | @{ | |
723 | double square (double z) @{ return z * z; @} | |
724 | ||
725 | return square (a) + square (b); | |
726 | @} | |
727 | @end group | |
728 | @end example | |
729 | ||
730 | The nested function can access all the variables of the containing | |
731 | function that are visible at the point of its definition. This is | |
732 | called @dfn{lexical scoping}. For example, here we show a nested | |
733 | function which uses an inherited variable named @code{offset}: | |
734 | ||
735 | @example | |
aee96fe9 | 736 | @group |
c1f7febf RK |
737 | bar (int *array, int offset, int size) |
738 | @{ | |
739 | int access (int *array, int index) | |
740 | @{ return array[index + offset]; @} | |
741 | int i; | |
0d893a63 | 742 | /* @r{@dots{}} */ |
c1f7febf | 743 | for (i = 0; i < size; i++) |
0d893a63 | 744 | /* @r{@dots{}} */ access (array, i) /* @r{@dots{}} */ |
c1f7febf | 745 | @} |
aee96fe9 | 746 | @end group |
c1f7febf RK |
747 | @end example |
748 | ||
749 | Nested function definitions are permitted within functions in the places | |
750 | where variable definitions are allowed; that is, in any block, before | |
751 | the first statement in the block. | |
752 | ||
753 | It is possible to call the nested function from outside the scope of its | |
754 | name by storing its address or passing the address to another function: | |
755 | ||
756 | @example | |
757 | hack (int *array, int size) | |
758 | @{ | |
759 | void store (int index, int value) | |
760 | @{ array[index] = value; @} | |
761 | ||
762 | intermediate (store, size); | |
763 | @} | |
764 | @end example | |
765 | ||
766 | Here, the function @code{intermediate} receives the address of | |
767 | @code{store} as an argument. If @code{intermediate} calls @code{store}, | |
768 | the arguments given to @code{store} are used to store into @code{array}. | |
769 | But this technique works only so long as the containing function | |
770 | (@code{hack}, in this example) does not exit. | |
771 | ||
772 | If you try to call the nested function through its address after the | |
773 | containing function has exited, all hell will break loose. If you try | |
774 | to call it after a containing scope level has exited, and if it refers | |
775 | to some of the variables that are no longer in scope, you may be lucky, | |
776 | but it's not wise to take the risk. If, however, the nested function | |
777 | does not refer to anything that has gone out of scope, you should be | |
778 | safe. | |
779 | ||
9c34dbbf ZW |
780 | GCC implements taking the address of a nested function using a technique |
781 | called @dfn{trampolines}. A paper describing them is available as | |
782 | ||
783 | @noindent | |
b73b1546 | 784 | @uref{http://people.debian.org/~aaronl/Usenix88-lexic.pdf}. |
c1f7febf RK |
785 | |
786 | A nested function can jump to a label inherited from a containing | |
787 | function, provided the label was explicitly declared in the containing | |
788 | function (@pxref{Local Labels}). Such a jump returns instantly to the | |
789 | containing function, exiting the nested function which did the | |
790 | @code{goto} and any intermediate functions as well. Here is an example: | |
791 | ||
792 | @example | |
793 | @group | |
794 | bar (int *array, int offset, int size) | |
795 | @{ | |
796 | __label__ failure; | |
797 | int access (int *array, int index) | |
798 | @{ | |
799 | if (index > size) | |
800 | goto failure; | |
801 | return array[index + offset]; | |
802 | @} | |
803 | int i; | |
0d893a63 | 804 | /* @r{@dots{}} */ |
c1f7febf | 805 | for (i = 0; i < size; i++) |
0d893a63 MK |
806 | /* @r{@dots{}} */ access (array, i) /* @r{@dots{}} */ |
807 | /* @r{@dots{}} */ | |
c1f7febf RK |
808 | return 0; |
809 | ||
810 | /* @r{Control comes here from @code{access} | |
811 | if it detects an error.} */ | |
812 | failure: | |
813 | return -1; | |
814 | @} | |
815 | @end group | |
816 | @end example | |
817 | ||
818 | A nested function always has internal linkage. Declaring one with | |
819 | @code{extern} is erroneous. If you need to declare the nested function | |
820 | before its definition, use @code{auto} (which is otherwise meaningless | |
821 | for function declarations). | |
822 | ||
823 | @example | |
824 | bar (int *array, int offset, int size) | |
825 | @{ | |
826 | __label__ failure; | |
827 | auto int access (int *, int); | |
0d893a63 | 828 | /* @r{@dots{}} */ |
c1f7febf RK |
829 | int access (int *array, int index) |
830 | @{ | |
831 | if (index > size) | |
832 | goto failure; | |
833 | return array[index + offset]; | |
834 | @} | |
0d893a63 | 835 | /* @r{@dots{}} */ |
c1f7febf RK |
836 | @} |
837 | @end example | |
838 | ||
839 | @node Constructing Calls | |
840 | @section Constructing Function Calls | |
841 | @cindex constructing calls | |
842 | @cindex forwarding calls | |
843 | ||
844 | Using the built-in functions described below, you can record | |
845 | the arguments a function received, and call another function | |
846 | with the same arguments, without knowing the number or types | |
847 | of the arguments. | |
848 | ||
849 | You can also record the return value of that function call, | |
850 | and later return that value, without knowing what data type | |
851 | the function tried to return (as long as your caller expects | |
852 | that data type). | |
853 | ||
84330467 JM |
854 | @deftypefn {Built-in Function} {void *} __builtin_apply_args () |
855 | This built-in function returns a pointer to data | |
c1f7febf RK |
856 | describing how to perform a call with the same arguments as were passed |
857 | to the current function. | |
858 | ||
859 | The function saves the arg pointer register, structure value address, | |
860 | and all registers that might be used to pass arguments to a function | |
861 | into a block of memory allocated on the stack. Then it returns the | |
862 | address of that block. | |
84330467 | 863 | @end deftypefn |
c1f7febf | 864 | |
84330467 JM |
865 | @deftypefn {Built-in Function} {void *} __builtin_apply (void (*@var{function})(), void *@var{arguments}, size_t @var{size}) |
866 | This built-in function invokes @var{function} | |
867 | with a copy of the parameters described by @var{arguments} | |
868 | and @var{size}. | |
c1f7febf RK |
869 | |
870 | The value of @var{arguments} should be the value returned by | |
871 | @code{__builtin_apply_args}. The argument @var{size} specifies the size | |
872 | of the stack argument data, in bytes. | |
873 | ||
84330467 | 874 | This function returns a pointer to data describing |
c1f7febf RK |
875 | how to return whatever value was returned by @var{function}. The data |
876 | is saved in a block of memory allocated on the stack. | |
877 | ||
878 | It is not always simple to compute the proper value for @var{size}. The | |
879 | value is used by @code{__builtin_apply} to compute the amount of data | |
880 | that should be pushed on the stack and copied from the incoming argument | |
881 | area. | |
84330467 | 882 | @end deftypefn |
c1f7febf | 883 | |
84330467 | 884 | @deftypefn {Built-in Function} {void} __builtin_return (void *@var{result}) |
c1f7febf RK |
885 | This built-in function returns the value described by @var{result} from |
886 | the containing function. You should specify, for @var{result}, a value | |
887 | returned by @code{__builtin_apply}. | |
84330467 | 888 | @end deftypefn |
c1f7febf | 889 | |
c1f7febf RK |
890 | @cindex underscores in variables in macros |
891 | @cindex @samp{_} in variables in macros | |
892 | @cindex local variables in macros | |
893 | @cindex variables, local, in macros | |
894 | @cindex macros, local variables in | |
895 | ||
896 | The reason for using names that start with underscores for the local | |
897 | variables is to avoid conflicts with variable names that occur within the | |
898 | expressions that are substituted for @code{a} and @code{b}. Eventually we | |
899 | hope to design a new form of declaration syntax that allows you to declare | |
900 | variables whose scopes start only after their initializers; this will be a | |
901 | more reliable way to prevent such conflicts. | |
902 | ||
903 | @node Typeof | |
904 | @section Referring to a Type with @code{typeof} | |
905 | @findex typeof | |
906 | @findex sizeof | |
907 | @cindex macros, types of arguments | |
908 | ||
909 | Another way to refer to the type of an expression is with @code{typeof}. | |
910 | The syntax of using of this keyword looks like @code{sizeof}, but the | |
911 | construct acts semantically like a type name defined with @code{typedef}. | |
912 | ||
913 | There are two ways of writing the argument to @code{typeof}: with an | |
914 | expression or with a type. Here is an example with an expression: | |
915 | ||
916 | @example | |
917 | typeof (x[0](1)) | |
918 | @end example | |
919 | ||
920 | @noindent | |
89aed483 JM |
921 | This assumes that @code{x} is an array of pointers to functions; |
922 | the type described is that of the values of the functions. | |
c1f7febf RK |
923 | |
924 | Here is an example with a typename as the argument: | |
925 | ||
926 | @example | |
927 | typeof (int *) | |
928 | @end example | |
929 | ||
930 | @noindent | |
931 | Here the type described is that of pointers to @code{int}. | |
932 | ||
5490d604 | 933 | If you are writing a header file that must work when included in ISO C |
c1f7febf RK |
934 | programs, write @code{__typeof__} instead of @code{typeof}. |
935 | @xref{Alternate Keywords}. | |
936 | ||
937 | A @code{typeof}-construct can be used anywhere a typedef name could be | |
938 | used. For example, you can use it in a declaration, in a cast, or inside | |
939 | of @code{sizeof} or @code{typeof}. | |
940 | ||
95f79357 ZW |
941 | @code{typeof} is often useful in conjunction with the |
942 | statements-within-expressions feature. Here is how the two together can | |
943 | be used to define a safe ``maximum'' macro that operates on any | |
944 | arithmetic type and evaluates each of its arguments exactly once: | |
945 | ||
946 | @example | |
947 | #define max(a,b) \ | |
948 | (@{ typeof (a) _a = (a); \ | |
949 | typeof (b) _b = (b); \ | |
950 | _a > _b ? _a : _b; @}) | |
951 | @end example | |
952 | ||
953 | @noindent | |
954 | Some more examples of the use of @code{typeof}: | |
955 | ||
c1f7febf RK |
956 | @itemize @bullet |
957 | @item | |
958 | This declares @code{y} with the type of what @code{x} points to. | |
959 | ||
960 | @example | |
961 | typeof (*x) y; | |
962 | @end example | |
963 | ||
964 | @item | |
965 | This declares @code{y} as an array of such values. | |
966 | ||
967 | @example | |
968 | typeof (*x) y[4]; | |
969 | @end example | |
970 | ||
971 | @item | |
972 | This declares @code{y} as an array of pointers to characters: | |
973 | ||
974 | @example | |
975 | typeof (typeof (char *)[4]) y; | |
976 | @end example | |
977 | ||
978 | @noindent | |
979 | It is equivalent to the following traditional C declaration: | |
980 | ||
981 | @example | |
982 | char *y[4]; | |
983 | @end example | |
984 | ||
985 | To see the meaning of the declaration using @code{typeof}, and why it | |
986 | might be a useful way to write, let's rewrite it with these macros: | |
987 | ||
988 | @example | |
989 | #define pointer(T) typeof(T *) | |
990 | #define array(T, N) typeof(T [N]) | |
991 | @end example | |
992 | ||
993 | @noindent | |
994 | Now the declaration can be rewritten this way: | |
995 | ||
996 | @example | |
997 | array (pointer (char), 4) y; | |
998 | @end example | |
999 | ||
1000 | @noindent | |
1001 | Thus, @code{array (pointer (char), 4)} is the type of arrays of 4 | |
1002 | pointers to @code{char}. | |
1003 | @end itemize | |
1004 | ||
95f79357 ZW |
1005 | @emph{Compatibility Note:} In addition to @code{typeof}, GCC 2 supported |
1006 | a more limited extension which permitted one to write | |
1007 | ||
1008 | @example | |
1009 | typedef @var{T} = @var{expr}; | |
1010 | @end example | |
1011 | ||
1012 | @noindent | |
1013 | with the effect of declaring @var{T} to have the type of the expression | |
1014 | @var{expr}. This extension does not work with GCC 3 (versions between | |
1015 | 3.0 and 3.2 will crash; 3.2.1 and later give an error). Code which | |
1016 | relies on it should be rewritten to use @code{typeof}: | |
1017 | ||
1018 | @example | |
1019 | typedef typeof(@var{expr}) @var{T}; | |
1020 | @end example | |
1021 | ||
1022 | @noindent | |
1023 | This will work with all versions of GCC@. | |
1024 | ||
c1f7febf RK |
1025 | @node Lvalues |
1026 | @section Generalized Lvalues | |
1027 | @cindex compound expressions as lvalues | |
1028 | @cindex expressions, compound, as lvalues | |
1029 | @cindex conditional expressions as lvalues | |
1030 | @cindex expressions, conditional, as lvalues | |
1031 | @cindex casts as lvalues | |
1032 | @cindex generalized lvalues | |
1033 | @cindex lvalues, generalized | |
1034 | @cindex extensions, @code{?:} | |
1035 | @cindex @code{?:} extensions | |
1036 | Compound expressions, conditional expressions and casts are allowed as | |
1037 | lvalues provided their operands are lvalues. This means that you can take | |
1038 | their addresses or store values into them. | |
1039 | ||
1040 | Standard C++ allows compound expressions and conditional expressions as | |
1041 | lvalues, and permits casts to reference type, so use of this extension | |
1042 | is deprecated for C++ code. | |
1043 | ||
1044 | For example, a compound expression can be assigned, provided the last | |
1045 | expression in the sequence is an lvalue. These two expressions are | |
1046 | equivalent: | |
1047 | ||
1048 | @example | |
1049 | (a, b) += 5 | |
1050 | a, (b += 5) | |
1051 | @end example | |
1052 | ||
1053 | Similarly, the address of the compound expression can be taken. These two | |
1054 | expressions are equivalent: | |
1055 | ||
1056 | @example | |
1057 | &(a, b) | |
1058 | a, &b | |
1059 | @end example | |
1060 | ||
1061 | A conditional expression is a valid lvalue if its type is not void and the | |
1062 | true and false branches are both valid lvalues. For example, these two | |
1063 | expressions are equivalent: | |
1064 | ||
1065 | @example | |
1066 | (a ? b : c) = 5 | |
1067 | (a ? b = 5 : (c = 5)) | |
1068 | @end example | |
1069 | ||
1070 | A cast is a valid lvalue if its operand is an lvalue. A simple | |
1071 | assignment whose left-hand side is a cast works by converting the | |
1072 | right-hand side first to the specified type, then to the type of the | |
1073 | inner left-hand side expression. After this is stored, the value is | |
1074 | converted back to the specified type to become the value of the | |
1075 | assignment. Thus, if @code{a} has type @code{char *}, the following two | |
1076 | expressions are equivalent: | |
1077 | ||
1078 | @example | |
1079 | (int)a = 5 | |
1080 | (int)(a = (char *)(int)5) | |
1081 | @end example | |
1082 | ||
1083 | An assignment-with-arithmetic operation such as @samp{+=} applied to a cast | |
1084 | performs the arithmetic using the type resulting from the cast, and then | |
1085 | continues as in the previous case. Therefore, these two expressions are | |
1086 | equivalent: | |
1087 | ||
1088 | @example | |
1089 | (int)a += 5 | |
1090 | (int)(a = (char *)(int) ((int)a + 5)) | |
1091 | @end example | |
1092 | ||
1093 | You cannot take the address of an lvalue cast, because the use of its | |
1094 | address would not work out coherently. Suppose that @code{&(int)f} were | |
1095 | permitted, where @code{f} has type @code{float}. Then the following | |
1096 | statement would try to store an integer bit-pattern where a floating | |
1097 | point number belongs: | |
1098 | ||
1099 | @example | |
1100 | *&(int)f = 1; | |
1101 | @end example | |
1102 | ||
1103 | This is quite different from what @code{(int)f = 1} would do---that | |
1104 | would convert 1 to floating point and store it. Rather than cause this | |
1105 | inconsistency, we think it is better to prohibit use of @samp{&} on a cast. | |
1106 | ||
1107 | If you really do want an @code{int *} pointer with the address of | |
1108 | @code{f}, you can simply write @code{(int *)&f}. | |
1109 | ||
1110 | @node Conditionals | |
1111 | @section Conditionals with Omitted Operands | |
1112 | @cindex conditional expressions, extensions | |
1113 | @cindex omitted middle-operands | |
1114 | @cindex middle-operands, omitted | |
1115 | @cindex extensions, @code{?:} | |
1116 | @cindex @code{?:} extensions | |
1117 | ||
1118 | The middle operand in a conditional expression may be omitted. Then | |
1119 | if the first operand is nonzero, its value is the value of the conditional | |
1120 | expression. | |
1121 | ||
1122 | Therefore, the expression | |
1123 | ||
1124 | @example | |
1125 | x ? : y | |
1126 | @end example | |
1127 | ||
1128 | @noindent | |
1129 | has the value of @code{x} if that is nonzero; otherwise, the value of | |
1130 | @code{y}. | |
1131 | ||
1132 | This example is perfectly equivalent to | |
1133 | ||
1134 | @example | |
1135 | x ? x : y | |
1136 | @end example | |
1137 | ||
1138 | @cindex side effect in ?: | |
1139 | @cindex ?: side effect | |
1140 | @noindent | |
1141 | In this simple case, the ability to omit the middle operand is not | |
1142 | especially useful. When it becomes useful is when the first operand does, | |
1143 | or may (if it is a macro argument), contain a side effect. Then repeating | |
1144 | the operand in the middle would perform the side effect twice. Omitting | |
1145 | the middle operand uses the value already computed without the undesirable | |
1146 | effects of recomputing it. | |
1147 | ||
1148 | @node Long Long | |
1149 | @section Double-Word Integers | |
1150 | @cindex @code{long long} data types | |
1151 | @cindex double-word arithmetic | |
1152 | @cindex multiprecision arithmetic | |
4b404517 JM |
1153 | @cindex @code{LL} integer suffix |
1154 | @cindex @code{ULL} integer suffix | |
c1f7febf | 1155 | |
4b404517 JM |
1156 | ISO C99 supports data types for integers that are at least 64 bits wide, |
1157 | and as an extension GCC supports them in C89 mode and in C++. | |
1158 | Simply write @code{long long int} for a signed integer, or | |
c1f7febf | 1159 | @code{unsigned long long int} for an unsigned integer. To make an |
84330467 | 1160 | integer constant of type @code{long long int}, add the suffix @samp{LL} |
c1f7febf | 1161 | to the integer. To make an integer constant of type @code{unsigned long |
84330467 | 1162 | long int}, add the suffix @samp{ULL} to the integer. |
c1f7febf RK |
1163 | |
1164 | You can use these types in arithmetic like any other integer types. | |
1165 | Addition, subtraction, and bitwise boolean operations on these types | |
1166 | are open-coded on all types of machines. Multiplication is open-coded | |
1167 | if the machine supports fullword-to-doubleword a widening multiply | |
1168 | instruction. Division and shifts are open-coded only on machines that | |
1169 | provide special support. The operations that are not open-coded use | |
161d7b59 | 1170 | special library routines that come with GCC@. |
c1f7febf RK |
1171 | |
1172 | There may be pitfalls when you use @code{long long} types for function | |
1173 | arguments, unless you declare function prototypes. If a function | |
1174 | expects type @code{int} for its argument, and you pass a value of type | |
1175 | @code{long long int}, confusion will result because the caller and the | |
1176 | subroutine will disagree about the number of bytes for the argument. | |
1177 | Likewise, if the function expects @code{long long int} and you pass | |
1178 | @code{int}. The best way to avoid such problems is to use prototypes. | |
1179 | ||
1180 | @node Complex | |
1181 | @section Complex Numbers | |
1182 | @cindex complex numbers | |
4b404517 JM |
1183 | @cindex @code{_Complex} keyword |
1184 | @cindex @code{__complex__} keyword | |
c1f7febf | 1185 | |
4b404517 JM |
1186 | ISO C99 supports complex floating data types, and as an extension GCC |
1187 | supports them in C89 mode and in C++, and supports complex integer data | |
1188 | types which are not part of ISO C99. You can declare complex types | |
1189 | using the keyword @code{_Complex}. As an extension, the older GNU | |
1190 | keyword @code{__complex__} is also supported. | |
c1f7febf | 1191 | |
4b404517 | 1192 | For example, @samp{_Complex double x;} declares @code{x} as a |
c1f7febf | 1193 | variable whose real part and imaginary part are both of type |
4b404517 | 1194 | @code{double}. @samp{_Complex short int y;} declares @code{y} to |
c1f7febf RK |
1195 | have real and imaginary parts of type @code{short int}; this is not |
1196 | likely to be useful, but it shows that the set of complex types is | |
1197 | complete. | |
1198 | ||
1199 | To write a constant with a complex data type, use the suffix @samp{i} or | |
1200 | @samp{j} (either one; they are equivalent). For example, @code{2.5fi} | |
4b404517 JM |
1201 | has type @code{_Complex float} and @code{3i} has type |
1202 | @code{_Complex int}. Such a constant always has a pure imaginary | |
c1f7febf | 1203 | value, but you can form any complex value you like by adding one to a |
4b404517 JM |
1204 | real constant. This is a GNU extension; if you have an ISO C99 |
1205 | conforming C library (such as GNU libc), and want to construct complex | |
1206 | constants of floating type, you should include @code{<complex.h>} and | |
1207 | use the macros @code{I} or @code{_Complex_I} instead. | |
c1f7febf | 1208 | |
4b404517 JM |
1209 | @cindex @code{__real__} keyword |
1210 | @cindex @code{__imag__} keyword | |
c1f7febf RK |
1211 | To extract the real part of a complex-valued expression @var{exp}, write |
1212 | @code{__real__ @var{exp}}. Likewise, use @code{__imag__} to | |
4b404517 JM |
1213 | extract the imaginary part. This is a GNU extension; for values of |
1214 | floating type, you should use the ISO C99 functions @code{crealf}, | |
1215 | @code{creal}, @code{creall}, @code{cimagf}, @code{cimag} and | |
1216 | @code{cimagl}, declared in @code{<complex.h>} and also provided as | |
161d7b59 | 1217 | built-in functions by GCC@. |
c1f7febf | 1218 | |
4b404517 | 1219 | @cindex complex conjugation |
c1f7febf | 1220 | The operator @samp{~} performs complex conjugation when used on a value |
4b404517 JM |
1221 | with a complex type. This is a GNU extension; for values of |
1222 | floating type, you should use the ISO C99 functions @code{conjf}, | |
1223 | @code{conj} and @code{conjl}, declared in @code{<complex.h>} and also | |
161d7b59 | 1224 | provided as built-in functions by GCC@. |
c1f7febf | 1225 | |
f0523f02 | 1226 | GCC can allocate complex automatic variables in a noncontiguous |
c1f7febf | 1227 | fashion; it's even possible for the real part to be in a register while |
580fb356 JW |
1228 | the imaginary part is on the stack (or vice-versa). Only the DWARF2 |
1229 | debug info format can represent this, so use of DWARF2 is recommended. | |
1230 | If you are using the stabs debug info format, GCC describes a noncontiguous | |
1231 | complex variable as if it were two separate variables of noncomplex type. | |
c1f7febf RK |
1232 | If the variable's actual name is @code{foo}, the two fictitious |
1233 | variables are named @code{foo$real} and @code{foo$imag}. You can | |
1234 | examine and set these two fictitious variables with your debugger. | |
1235 | ||
6f4d7222 | 1236 | @node Hex Floats |
6b42b9ea UD |
1237 | @section Hex Floats |
1238 | @cindex hex floats | |
c5c76735 | 1239 | |
4b404517 | 1240 | ISO C99 supports floating-point numbers written not only in the usual |
6f4d7222 | 1241 | decimal notation, such as @code{1.55e1}, but also numbers such as |
4b404517 JM |
1242 | @code{0x1.fp3} written in hexadecimal format. As a GNU extension, GCC |
1243 | supports this in C89 mode (except in some cases when strictly | |
1244 | conforming) and in C++. In that format the | |
84330467 | 1245 | @samp{0x} hex introducer and the @samp{p} or @samp{P} exponent field are |
6f4d7222 | 1246 | mandatory. The exponent is a decimal number that indicates the power of |
84330467 | 1247 | 2 by which the significant part will be multiplied. Thus @samp{0x1.f} is |
aee96fe9 JM |
1248 | @tex |
1249 | $1 {15\over16}$, | |
1250 | @end tex | |
1251 | @ifnottex | |
1252 | 1 15/16, | |
1253 | @end ifnottex | |
1254 | @samp{p3} multiplies it by 8, and the value of @code{0x1.fp3} | |
6f4d7222 UD |
1255 | is the same as @code{1.55e1}. |
1256 | ||
1257 | Unlike for floating-point numbers in the decimal notation the exponent | |
1258 | is always required in the hexadecimal notation. Otherwise the compiler | |
1259 | would not be able to resolve the ambiguity of, e.g., @code{0x1.f}. This | |
84330467 | 1260 | could mean @code{1.0f} or @code{1.9375} since @samp{f} is also the |
6f4d7222 UD |
1261 | extension for floating-point constants of type @code{float}. |
1262 | ||
c1f7febf RK |
1263 | @node Zero Length |
1264 | @section Arrays of Length Zero | |
1265 | @cindex arrays of length zero | |
1266 | @cindex zero-length arrays | |
1267 | @cindex length-zero arrays | |
ffc5c6a9 | 1268 | @cindex flexible array members |
c1f7febf | 1269 | |
161d7b59 | 1270 | Zero-length arrays are allowed in GNU C@. They are very useful as the |
584ef5fe | 1271 | last element of a structure which is really a header for a variable-length |
c1f7febf RK |
1272 | object: |
1273 | ||
1274 | @example | |
1275 | struct line @{ | |
1276 | int length; | |
1277 | char contents[0]; | |
1278 | @}; | |
1279 | ||
584ef5fe RH |
1280 | struct line *thisline = (struct line *) |
1281 | malloc (sizeof (struct line) + this_length); | |
1282 | thisline->length = this_length; | |
c1f7febf RK |
1283 | @end example |
1284 | ||
3764f879 | 1285 | In ISO C90, you would have to give @code{contents} a length of 1, which |
c1f7febf RK |
1286 | means either you waste space or complicate the argument to @code{malloc}. |
1287 | ||
02f52e19 | 1288 | In ISO C99, you would use a @dfn{flexible array member}, which is |
584ef5fe RH |
1289 | slightly different in syntax and semantics: |
1290 | ||
1291 | @itemize @bullet | |
1292 | @item | |
1293 | Flexible array members are written as @code{contents[]} without | |
1294 | the @code{0}. | |
1295 | ||
1296 | @item | |
1297 | Flexible array members have incomplete type, and so the @code{sizeof} | |
1298 | operator may not be applied. As a quirk of the original implementation | |
1299 | of zero-length arrays, @code{sizeof} evaluates to zero. | |
1300 | ||
1301 | @item | |
1302 | Flexible array members may only appear as the last member of a | |
e7b6a0ee | 1303 | @code{struct} that is otherwise non-empty. |
2984fe64 JM |
1304 | |
1305 | @item | |
1306 | A structure containing a flexible array member, or a union containing | |
1307 | such a structure (possibly recursively), may not be a member of a | |
1308 | structure or an element of an array. (However, these uses are | |
1309 | permitted by GCC as extensions.) | |
ffc5c6a9 | 1310 | @end itemize |
a25f1211 | 1311 | |
ffc5c6a9 | 1312 | GCC versions before 3.0 allowed zero-length arrays to be statically |
e7b6a0ee DD |
1313 | initialized, as if they were flexible arrays. In addition to those |
1314 | cases that were useful, it also allowed initializations in situations | |
1315 | that would corrupt later data. Non-empty initialization of zero-length | |
1316 | arrays is now treated like any case where there are more initializer | |
1317 | elements than the array holds, in that a suitable warning about "excess | |
1318 | elements in array" is given, and the excess elements (all of them, in | |
1319 | this case) are ignored. | |
ffc5c6a9 RH |
1320 | |
1321 | Instead GCC allows static initialization of flexible array members. | |
1322 | This is equivalent to defining a new structure containing the original | |
1323 | structure followed by an array of sufficient size to contain the data. | |
e979f9e8 | 1324 | I.e.@: in the following, @code{f1} is constructed as if it were declared |
ffc5c6a9 | 1325 | like @code{f2}. |
a25f1211 RH |
1326 | |
1327 | @example | |
ffc5c6a9 RH |
1328 | struct f1 @{ |
1329 | int x; int y[]; | |
1330 | @} f1 = @{ 1, @{ 2, 3, 4 @} @}; | |
1331 | ||
1332 | struct f2 @{ | |
1333 | struct f1 f1; int data[3]; | |
1334 | @} f2 = @{ @{ 1 @}, @{ 2, 3, 4 @} @}; | |
1335 | @end example | |
584ef5fe | 1336 | |
ffc5c6a9 RH |
1337 | @noindent |
1338 | The convenience of this extension is that @code{f1} has the desired | |
1339 | type, eliminating the need to consistently refer to @code{f2.f1}. | |
1340 | ||
1341 | This has symmetry with normal static arrays, in that an array of | |
1342 | unknown size is also written with @code{[]}. | |
a25f1211 | 1343 | |
ffc5c6a9 RH |
1344 | Of course, this extension only makes sense if the extra data comes at |
1345 | the end of a top-level object, as otherwise we would be overwriting | |
1346 | data at subsequent offsets. To avoid undue complication and confusion | |
1347 | with initialization of deeply nested arrays, we simply disallow any | |
1348 | non-empty initialization except when the structure is the top-level | |
1349 | object. For example: | |
584ef5fe | 1350 | |
ffc5c6a9 RH |
1351 | @example |
1352 | struct foo @{ int x; int y[]; @}; | |
1353 | struct bar @{ struct foo z; @}; | |
1354 | ||
13ba36b4 JM |
1355 | struct foo a = @{ 1, @{ 2, 3, 4 @} @}; // @r{Valid.} |
1356 | struct bar b = @{ @{ 1, @{ 2, 3, 4 @} @} @}; // @r{Invalid.} | |
1357 | struct bar c = @{ @{ 1, @{ @} @} @}; // @r{Valid.} | |
1358 | struct foo d[1] = @{ @{ 1 @{ 2, 3, 4 @} @} @}; // @r{Invalid.} | |
a25f1211 | 1359 | @end example |
4b606faf | 1360 | |
c1f7febf RK |
1361 | @node Variable Length |
1362 | @section Arrays of Variable Length | |
1363 | @cindex variable-length arrays | |
1364 | @cindex arrays of variable length | |
4b404517 | 1365 | @cindex VLAs |
c1f7febf | 1366 | |
4b404517 JM |
1367 | Variable-length automatic arrays are allowed in ISO C99, and as an |
1368 | extension GCC accepts them in C89 mode and in C++. (However, GCC's | |
1369 | implementation of variable-length arrays does not yet conform in detail | |
1370 | to the ISO C99 standard.) These arrays are | |
c1f7febf RK |
1371 | declared like any other automatic arrays, but with a length that is not |
1372 | a constant expression. The storage is allocated at the point of | |
1373 | declaration and deallocated when the brace-level is exited. For | |
1374 | example: | |
1375 | ||
1376 | @example | |
1377 | FILE * | |
1378 | concat_fopen (char *s1, char *s2, char *mode) | |
1379 | @{ | |
1380 | char str[strlen (s1) + strlen (s2) + 1]; | |
1381 | strcpy (str, s1); | |
1382 | strcat (str, s2); | |
1383 | return fopen (str, mode); | |
1384 | @} | |
1385 | @end example | |
1386 | ||
1387 | @cindex scope of a variable length array | |
1388 | @cindex variable-length array scope | |
1389 | @cindex deallocating variable length arrays | |
1390 | Jumping or breaking out of the scope of the array name deallocates the | |
1391 | storage. Jumping into the scope is not allowed; you get an error | |
1392 | message for it. | |
1393 | ||
1394 | @cindex @code{alloca} vs variable-length arrays | |
1395 | You can use the function @code{alloca} to get an effect much like | |
1396 | variable-length arrays. The function @code{alloca} is available in | |
1397 | many other C implementations (but not in all). On the other hand, | |
1398 | variable-length arrays are more elegant. | |
1399 | ||
1400 | There are other differences between these two methods. Space allocated | |
1401 | with @code{alloca} exists until the containing @emph{function} returns. | |
1402 | The space for a variable-length array is deallocated as soon as the array | |
1403 | name's scope ends. (If you use both variable-length arrays and | |
1404 | @code{alloca} in the same function, deallocation of a variable-length array | |
1405 | will also deallocate anything more recently allocated with @code{alloca}.) | |
1406 | ||
1407 | You can also use variable-length arrays as arguments to functions: | |
1408 | ||
1409 | @example | |
1410 | struct entry | |
1411 | tester (int len, char data[len][len]) | |
1412 | @{ | |
0d893a63 | 1413 | /* @r{@dots{}} */ |
c1f7febf RK |
1414 | @} |
1415 | @end example | |
1416 | ||
1417 | The length of an array is computed once when the storage is allocated | |
1418 | and is remembered for the scope of the array in case you access it with | |
1419 | @code{sizeof}. | |
1420 | ||
1421 | If you want to pass the array first and the length afterward, you can | |
1422 | use a forward declaration in the parameter list---another GNU extension. | |
1423 | ||
1424 | @example | |
1425 | struct entry | |
1426 | tester (int len; char data[len][len], int len) | |
1427 | @{ | |
0d893a63 | 1428 | /* @r{@dots{}} */ |
c1f7febf RK |
1429 | @} |
1430 | @end example | |
1431 | ||
1432 | @cindex parameter forward declaration | |
1433 | The @samp{int len} before the semicolon is a @dfn{parameter forward | |
1434 | declaration}, and it serves the purpose of making the name @code{len} | |
1435 | known when the declaration of @code{data} is parsed. | |
1436 | ||
1437 | You can write any number of such parameter forward declarations in the | |
1438 | parameter list. They can be separated by commas or semicolons, but the | |
1439 | last one must end with a semicolon, which is followed by the ``real'' | |
1440 | parameter declarations. Each forward declaration must match a ``real'' | |
4b404517 JM |
1441 | declaration in parameter name and data type. ISO C99 does not support |
1442 | parameter forward declarations. | |
c1f7febf | 1443 | |
ccd96f0a NB |
1444 | @node Variadic Macros |
1445 | @section Macros with a Variable Number of Arguments. | |
c1f7febf RK |
1446 | @cindex variable number of arguments |
1447 | @cindex macro with variable arguments | |
1448 | @cindex rest argument (in macro) | |
ccd96f0a | 1449 | @cindex variadic macros |
c1f7febf | 1450 | |
ccd96f0a NB |
1451 | In the ISO C standard of 1999, a macro can be declared to accept a |
1452 | variable number of arguments much as a function can. The syntax for | |
1453 | defining the macro is similar to that of a function. Here is an | |
1454 | example: | |
c1f7febf | 1455 | |
478c9e72 | 1456 | @smallexample |
ccd96f0a | 1457 | #define debug(format, ...) fprintf (stderr, format, __VA_ARGS__) |
478c9e72 | 1458 | @end smallexample |
c1f7febf | 1459 | |
ccd96f0a NB |
1460 | Here @samp{@dots{}} is a @dfn{variable argument}. In the invocation of |
1461 | such a macro, it represents the zero or more tokens until the closing | |
1462 | parenthesis that ends the invocation, including any commas. This set of | |
1463 | tokens replaces the identifier @code{__VA_ARGS__} in the macro body | |
1464 | wherever it appears. See the CPP manual for more information. | |
1465 | ||
1466 | GCC has long supported variadic macros, and used a different syntax that | |
1467 | allowed you to give a name to the variable arguments just like any other | |
1468 | argument. Here is an example: | |
c1f7febf RK |
1469 | |
1470 | @example | |
ccd96f0a | 1471 | #define debug(format, args...) fprintf (stderr, format, args) |
c1f7febf RK |
1472 | @end example |
1473 | ||
ccd96f0a NB |
1474 | This is in all ways equivalent to the ISO C example above, but arguably |
1475 | more readable and descriptive. | |
c1f7febf | 1476 | |
ccd96f0a NB |
1477 | GNU CPP has two further variadic macro extensions, and permits them to |
1478 | be used with either of the above forms of macro definition. | |
1479 | ||
1480 | In standard C, you are not allowed to leave the variable argument out | |
1481 | entirely; but you are allowed to pass an empty argument. For example, | |
1482 | this invocation is invalid in ISO C, because there is no comma after | |
1483 | the string: | |
c1f7febf RK |
1484 | |
1485 | @example | |
ccd96f0a | 1486 | debug ("A message") |
c1f7febf RK |
1487 | @end example |
1488 | ||
ccd96f0a NB |
1489 | GNU CPP permits you to completely omit the variable arguments in this |
1490 | way. In the above examples, the compiler would complain, though since | |
1491 | the expansion of the macro still has the extra comma after the format | |
1492 | string. | |
1493 | ||
1494 | To help solve this problem, CPP behaves specially for variable arguments | |
1495 | used with the token paste operator, @samp{##}. If instead you write | |
c1f7febf | 1496 | |
478c9e72 | 1497 | @smallexample |
ccd96f0a | 1498 | #define debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__) |
478c9e72 | 1499 | @end smallexample |
c1f7febf | 1500 | |
ccd96f0a NB |
1501 | and if the variable arguments are omitted or empty, the @samp{##} |
1502 | operator causes the preprocessor to remove the comma before it. If you | |
1503 | do provide some variable arguments in your macro invocation, GNU CPP | |
1504 | does not complain about the paste operation and instead places the | |
1505 | variable arguments after the comma. Just like any other pasted macro | |
1506 | argument, these arguments are not macro expanded. | |
1507 | ||
1508 | @node Escaped Newlines | |
1509 | @section Slightly Looser Rules for Escaped Newlines | |
1510 | @cindex escaped newlines | |
1511 | @cindex newlines (escaped) | |
1512 | ||
f458d1d5 ZW |
1513 | Recently, the preprocessor has relaxed its treatment of escaped |
1514 | newlines. Previously, the newline had to immediately follow a | |
ccd96f0a NB |
1515 | backslash. The current implementation allows whitespace in the form of |
1516 | spaces, horizontal and vertical tabs, and form feeds between the | |
1517 | backslash and the subsequent newline. The preprocessor issues a | |
1518 | warning, but treats it as a valid escaped newline and combines the two | |
1519 | lines to form a single logical line. This works within comments and | |
1520 | tokens, including multi-line strings, as well as between tokens. | |
1521 | Comments are @emph{not} treated as whitespace for the purposes of this | |
1522 | relaxation, since they have not yet been replaced with spaces. | |
1523 | ||
1524 | @node Multi-line Strings | |
1525 | @section String Literals with Embedded Newlines | |
1526 | @cindex multi-line string literals | |
1527 | ||
1528 | As an extension, GNU CPP permits string literals to cross multiple lines | |
1529 | without escaping the embedded newlines. Each embedded newline is | |
1530 | replaced with a single @samp{\n} character in the resulting string | |
1531 | literal, regardless of what form the newline took originally. | |
1532 | ||
1533 | CPP currently allows such strings in directives as well (other than the | |
1534 | @samp{#include} family). This is deprecated and will eventually be | |
1535 | removed. | |
c1f7febf RK |
1536 | |
1537 | @node Subscripting | |
1538 | @section Non-Lvalue Arrays May Have Subscripts | |
1539 | @cindex subscripting | |
1540 | @cindex arrays, non-lvalue | |
1541 | ||
1542 | @cindex subscripting and function values | |
207bf485 JM |
1543 | In ISO C99, arrays that are not lvalues still decay to pointers, and |
1544 | may be subscripted, although they may not be modified or used after | |
1545 | the next sequence point and the unary @samp{&} operator may not be | |
1546 | applied to them. As an extension, GCC allows such arrays to be | |
1547 | subscripted in C89 mode, though otherwise they do not decay to | |
1548 | pointers outside C99 mode. For example, | |
4b404517 | 1549 | this is valid in GNU C though not valid in C89: |
c1f7febf RK |
1550 | |
1551 | @example | |
1552 | @group | |
1553 | struct foo @{int a[4];@}; | |
1554 | ||
1555 | struct foo f(); | |
1556 | ||
1557 | bar (int index) | |
1558 | @{ | |
1559 | return f().a[index]; | |
1560 | @} | |
1561 | @end group | |
1562 | @end example | |
1563 | ||
1564 | @node Pointer Arith | |
1565 | @section Arithmetic on @code{void}- and Function-Pointers | |
1566 | @cindex void pointers, arithmetic | |
1567 | @cindex void, size of pointer to | |
1568 | @cindex function pointers, arithmetic | |
1569 | @cindex function, size of pointer to | |
1570 | ||
1571 | In GNU C, addition and subtraction operations are supported on pointers to | |
1572 | @code{void} and on pointers to functions. This is done by treating the | |
1573 | size of a @code{void} or of a function as 1. | |
1574 | ||
1575 | A consequence of this is that @code{sizeof} is also allowed on @code{void} | |
1576 | and on function types, and returns 1. | |
1577 | ||
84330467 JM |
1578 | @opindex Wpointer-arith |
1579 | The option @option{-Wpointer-arith} requests a warning if these extensions | |
c1f7febf RK |
1580 | are used. |
1581 | ||
1582 | @node Initializers | |
1583 | @section Non-Constant Initializers | |
1584 | @cindex initializers, non-constant | |
1585 | @cindex non-constant initializers | |
1586 | ||
4b404517 | 1587 | As in standard C++ and ISO C99, the elements of an aggregate initializer for an |
161d7b59 | 1588 | automatic variable are not required to be constant expressions in GNU C@. |
c1f7febf RK |
1589 | Here is an example of an initializer with run-time varying elements: |
1590 | ||
1591 | @example | |
1592 | foo (float f, float g) | |
1593 | @{ | |
1594 | float beat_freqs[2] = @{ f-g, f+g @}; | |
0d893a63 | 1595 | /* @r{@dots{}} */ |
c1f7febf RK |
1596 | @} |
1597 | @end example | |
1598 | ||
4b404517 JM |
1599 | @node Compound Literals |
1600 | @section Compound Literals | |
c1f7febf RK |
1601 | @cindex constructor expressions |
1602 | @cindex initializations in expressions | |
1603 | @cindex structures, constructor expression | |
1604 | @cindex expressions, constructor | |
4b404517 JM |
1605 | @cindex compound literals |
1606 | @c The GNU C name for what C99 calls compound literals was "constructor expressions". | |
c1f7febf | 1607 | |
4b404517 | 1608 | ISO C99 supports compound literals. A compound literal looks like |
c1f7febf RK |
1609 | a cast containing an initializer. Its value is an object of the |
1610 | type specified in the cast, containing the elements specified in | |
db3acfa5 JM |
1611 | the initializer; it is an lvalue. As an extension, GCC supports |
1612 | compound literals in C89 mode and in C++. | |
c1f7febf RK |
1613 | |
1614 | Usually, the specified type is a structure. Assume that | |
1615 | @code{struct foo} and @code{structure} are declared as shown: | |
1616 | ||
1617 | @example | |
1618 | struct foo @{int a; char b[2];@} structure; | |
1619 | @end example | |
1620 | ||
1621 | @noindent | |
4b404517 | 1622 | Here is an example of constructing a @code{struct foo} with a compound literal: |
c1f7febf RK |
1623 | |
1624 | @example | |
1625 | structure = ((struct foo) @{x + y, 'a', 0@}); | |
1626 | @end example | |
1627 | ||
1628 | @noindent | |
1629 | This is equivalent to writing the following: | |
1630 | ||
1631 | @example | |
1632 | @{ | |
1633 | struct foo temp = @{x + y, 'a', 0@}; | |
1634 | structure = temp; | |
1635 | @} | |
1636 | @end example | |
1637 | ||
4b404517 | 1638 | You can also construct an array. If all the elements of the compound literal |
c1f7febf | 1639 | are (made up of) simple constant expressions, suitable for use in |
db3acfa5 JM |
1640 | initializers of objects of static storage duration, then the compound |
1641 | literal can be coerced to a pointer to its first element and used in | |
1642 | such an initializer, as shown here: | |
c1f7febf RK |
1643 | |
1644 | @example | |
1645 | char **foo = (char *[]) @{ "x", "y", "z" @}; | |
1646 | @end example | |
1647 | ||
4b404517 JM |
1648 | Compound literals for scalar types and union types are is |
1649 | also allowed, but then the compound literal is equivalent | |
c1f7febf RK |
1650 | to a cast. |
1651 | ||
59c83dbf JJ |
1652 | As a GNU extension, GCC allows initialization of objects with static storage |
1653 | duration by compound literals (which is not possible in ISO C99, because | |
1654 | the initializer is not a constant). | |
1655 | It is handled as if the object was initialized only with the bracket | |
1656 | enclosed list if compound literal's and object types match. | |
1657 | The initializer list of the compound literal must be constant. | |
1658 | If the object being initialized has array type of unknown size, the size is | |
ad47f1e5 | 1659 | determined by compound literal size. |
59c83dbf JJ |
1660 | |
1661 | @example | |
1662 | static struct foo x = (struct foo) @{1, 'a', 'b'@}; | |
1663 | static int y[] = (int []) @{1, 2, 3@}; | |
1664 | static int z[] = (int [3]) @{1@}; | |
1665 | @end example | |
1666 | ||
1667 | @noindent | |
1668 | The above lines are equivalent to the following: | |
1669 | @example | |
1670 | static struct foo x = @{1, 'a', 'b'@}; | |
1671 | static int y[] = @{1, 2, 3@}; | |
ad47f1e5 | 1672 | static int z[] = @{1, 0, 0@}; |
59c83dbf JJ |
1673 | @end example |
1674 | ||
4b404517 JM |
1675 | @node Designated Inits |
1676 | @section Designated Initializers | |
c1f7febf RK |
1677 | @cindex initializers with labeled elements |
1678 | @cindex labeled elements in initializers | |
1679 | @cindex case labels in initializers | |
4b404517 | 1680 | @cindex designated initializers |
c1f7febf | 1681 | |
26d4fec7 | 1682 | Standard C89 requires the elements of an initializer to appear in a fixed |
c1f7febf RK |
1683 | order, the same as the order of the elements in the array or structure |
1684 | being initialized. | |
1685 | ||
26d4fec7 JM |
1686 | In ISO C99 you can give the elements in any order, specifying the array |
1687 | indices or structure field names they apply to, and GNU C allows this as | |
1688 | an extension in C89 mode as well. This extension is not | |
c1f7febf RK |
1689 | implemented in GNU C++. |
1690 | ||
26d4fec7 | 1691 | To specify an array index, write |
c1f7febf RK |
1692 | @samp{[@var{index}] =} before the element value. For example, |
1693 | ||
1694 | @example | |
26d4fec7 | 1695 | int a[6] = @{ [4] = 29, [2] = 15 @}; |
c1f7febf RK |
1696 | @end example |
1697 | ||
1698 | @noindent | |
1699 | is equivalent to | |
1700 | ||
1701 | @example | |
1702 | int a[6] = @{ 0, 0, 15, 0, 29, 0 @}; | |
1703 | @end example | |
1704 | ||
1705 | @noindent | |
1706 | The index values must be constant expressions, even if the array being | |
1707 | initialized is automatic. | |
1708 | ||
26d4fec7 JM |
1709 | An alternative syntax for this which has been obsolete since GCC 2.5 but |
1710 | GCC still accepts is to write @samp{[@var{index}]} before the element | |
1711 | value, with no @samp{=}. | |
1712 | ||
c1f7febf | 1713 | To initialize a range of elements to the same value, write |
26d4fec7 JM |
1714 | @samp{[@var{first} ... @var{last}] = @var{value}}. This is a GNU |
1715 | extension. For example, | |
c1f7febf RK |
1716 | |
1717 | @example | |
1718 | int widths[] = @{ [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 @}; | |
1719 | @end example | |
1720 | ||
8b6a5902 JJ |
1721 | @noindent |
1722 | If the value in it has side-effects, the side-effects will happen only once, | |
1723 | not for each initialized field by the range initializer. | |
1724 | ||
c1f7febf RK |
1725 | @noindent |
1726 | Note that the length of the array is the highest value specified | |
1727 | plus one. | |
1728 | ||
1729 | In a structure initializer, specify the name of a field to initialize | |
26d4fec7 | 1730 | with @samp{.@var{fieldname} =} before the element value. For example, |
c1f7febf RK |
1731 | given the following structure, |
1732 | ||
1733 | @example | |
1734 | struct point @{ int x, y; @}; | |
1735 | @end example | |
1736 | ||
1737 | @noindent | |
1738 | the following initialization | |
1739 | ||
1740 | @example | |
26d4fec7 | 1741 | struct point p = @{ .y = yvalue, .x = xvalue @}; |
c1f7febf RK |
1742 | @end example |
1743 | ||
1744 | @noindent | |
1745 | is equivalent to | |
1746 | ||
1747 | @example | |
1748 | struct point p = @{ xvalue, yvalue @}; | |
1749 | @end example | |
1750 | ||
26d4fec7 JM |
1751 | Another syntax which has the same meaning, obsolete since GCC 2.5, is |
1752 | @samp{@var{fieldname}:}, as shown here: | |
c1f7febf RK |
1753 | |
1754 | @example | |
26d4fec7 | 1755 | struct point p = @{ y: yvalue, x: xvalue @}; |
c1f7febf RK |
1756 | @end example |
1757 | ||
4b404517 JM |
1758 | @cindex designators |
1759 | The @samp{[@var{index}]} or @samp{.@var{fieldname}} is known as a | |
1760 | @dfn{designator}. You can also use a designator (or the obsolete colon | |
1761 | syntax) when initializing a union, to specify which element of the union | |
1762 | should be used. For example, | |
c1f7febf RK |
1763 | |
1764 | @example | |
1765 | union foo @{ int i; double d; @}; | |
1766 | ||
26d4fec7 | 1767 | union foo f = @{ .d = 4 @}; |
c1f7febf RK |
1768 | @end example |
1769 | ||
1770 | @noindent | |
1771 | will convert 4 to a @code{double} to store it in the union using | |
1772 | the second element. By contrast, casting 4 to type @code{union foo} | |
1773 | would store it into the union as the integer @code{i}, since it is | |
1774 | an integer. (@xref{Cast to Union}.) | |
1775 | ||
1776 | You can combine this technique of naming elements with ordinary C | |
1777 | initialization of successive elements. Each initializer element that | |
4b404517 | 1778 | does not have a designator applies to the next consecutive element of the |
c1f7febf RK |
1779 | array or structure. For example, |
1780 | ||
1781 | @example | |
1782 | int a[6] = @{ [1] = v1, v2, [4] = v4 @}; | |
1783 | @end example | |
1784 | ||
1785 | @noindent | |
1786 | is equivalent to | |
1787 | ||
1788 | @example | |
1789 | int a[6] = @{ 0, v1, v2, 0, v4, 0 @}; | |
1790 | @end example | |
1791 | ||
1792 | Labeling the elements of an array initializer is especially useful | |
1793 | when the indices are characters or belong to an @code{enum} type. | |
1794 | For example: | |
1795 | ||
1796 | @example | |
1797 | int whitespace[256] | |
1798 | = @{ [' '] = 1, ['\t'] = 1, ['\h'] = 1, | |
1799 | ['\f'] = 1, ['\n'] = 1, ['\r'] = 1 @}; | |
1800 | @end example | |
1801 | ||
4b404517 | 1802 | @cindex designator lists |
26d4fec7 | 1803 | You can also write a series of @samp{.@var{fieldname}} and |
4b404517 | 1804 | @samp{[@var{index}]} designators before an @samp{=} to specify a |
26d4fec7 JM |
1805 | nested subobject to initialize; the list is taken relative to the |
1806 | subobject corresponding to the closest surrounding brace pair. For | |
1807 | example, with the @samp{struct point} declaration above: | |
1808 | ||
478c9e72 | 1809 | @smallexample |
26d4fec7 | 1810 | struct point ptarray[10] = @{ [2].y = yv2, [2].x = xv2, [0].x = xv0 @}; |
478c9e72 | 1811 | @end smallexample |
26d4fec7 | 1812 | |
8b6a5902 JJ |
1813 | @noindent |
1814 | If the same field is initialized multiple times, it will have value from | |
1815 | the last initialization. If any such overridden initialization has | |
1816 | side-effect, it is unspecified whether the side-effect happens or not. | |
1817 | Currently, gcc will discard them and issue a warning. | |
1818 | ||
c1f7febf RK |
1819 | @node Case Ranges |
1820 | @section Case Ranges | |
1821 | @cindex case ranges | |
1822 | @cindex ranges in case statements | |
1823 | ||
1824 | You can specify a range of consecutive values in a single @code{case} label, | |
1825 | like this: | |
1826 | ||
1827 | @example | |
1828 | case @var{low} ... @var{high}: | |
1829 | @end example | |
1830 | ||
1831 | @noindent | |
1832 | This has the same effect as the proper number of individual @code{case} | |
1833 | labels, one for each integer value from @var{low} to @var{high}, inclusive. | |
1834 | ||
1835 | This feature is especially useful for ranges of ASCII character codes: | |
1836 | ||
1837 | @example | |
1838 | case 'A' ... 'Z': | |
1839 | @end example | |
1840 | ||
1841 | @strong{Be careful:} Write spaces around the @code{...}, for otherwise | |
1842 | it may be parsed wrong when you use it with integer values. For example, | |
1843 | write this: | |
1844 | ||
1845 | @example | |
1846 | case 1 ... 5: | |
1847 | @end example | |
1848 | ||
1849 | @noindent | |
1850 | rather than this: | |
1851 | ||
1852 | @example | |
1853 | case 1...5: | |
1854 | @end example | |
1855 | ||
1856 | @node Cast to Union | |
1857 | @section Cast to a Union Type | |
1858 | @cindex cast to a union | |
1859 | @cindex union, casting to a | |
1860 | ||
1861 | A cast to union type is similar to other casts, except that the type | |
1862 | specified is a union type. You can specify the type either with | |
1863 | @code{union @var{tag}} or with a typedef name. A cast to union is actually | |
1864 | a constructor though, not a cast, and hence does not yield an lvalue like | |
4b404517 | 1865 | normal casts. (@xref{Compound Literals}.) |
c1f7febf RK |
1866 | |
1867 | The types that may be cast to the union type are those of the members | |
1868 | of the union. Thus, given the following union and variables: | |
1869 | ||
1870 | @example | |
1871 | union foo @{ int i; double d; @}; | |
1872 | int x; | |
1873 | double y; | |
1874 | @end example | |
1875 | ||
1876 | @noindent | |
aee96fe9 | 1877 | both @code{x} and @code{y} can be cast to type @code{union foo}. |
c1f7febf RK |
1878 | |
1879 | Using the cast as the right-hand side of an assignment to a variable of | |
1880 | union type is equivalent to storing in a member of the union: | |
1881 | ||
1882 | @example | |
1883 | union foo u; | |
0d893a63 | 1884 | /* @r{@dots{}} */ |
c1f7febf RK |
1885 | u = (union foo) x @equiv{} u.i = x |
1886 | u = (union foo) y @equiv{} u.d = y | |
1887 | @end example | |
1888 | ||
1889 | You can also use the union cast as a function argument: | |
1890 | ||
1891 | @example | |
1892 | void hack (union foo); | |
0d893a63 | 1893 | /* @r{@dots{}} */ |
c1f7febf RK |
1894 | hack ((union foo) x); |
1895 | @end example | |
1896 | ||
4b404517 JM |
1897 | @node Mixed Declarations |
1898 | @section Mixed Declarations and Code | |
1899 | @cindex mixed declarations and code | |
1900 | @cindex declarations, mixed with code | |
1901 | @cindex code, mixed with declarations | |
1902 | ||
1903 | ISO C99 and ISO C++ allow declarations and code to be freely mixed | |
1904 | within compound statements. As an extension, GCC also allows this in | |
1905 | C89 mode. For example, you could do: | |
1906 | ||
1907 | @example | |
1908 | int i; | |
0d893a63 | 1909 | /* @r{@dots{}} */ |
4b404517 JM |
1910 | i++; |
1911 | int j = i + 2; | |
1912 | @end example | |
1913 | ||
1914 | Each identifier is visible from where it is declared until the end of | |
1915 | the enclosing block. | |
1916 | ||
c1f7febf RK |
1917 | @node Function Attributes |
1918 | @section Declaring Attributes of Functions | |
1919 | @cindex function attributes | |
1920 | @cindex declaring attributes of functions | |
1921 | @cindex functions that never return | |
1922 | @cindex functions that have no side effects | |
1923 | @cindex functions in arbitrary sections | |
2a59078d | 1924 | @cindex functions that behave like malloc |
c1f7febf RK |
1925 | @cindex @code{volatile} applied to function |
1926 | @cindex @code{const} applied to function | |
26f6672d | 1927 | @cindex functions with @code{printf}, @code{scanf}, @code{strftime} or @code{strfmon} style arguments |
b34c7881 | 1928 | @cindex functions with non-null pointer arguments |
c1f7febf RK |
1929 | @cindex functions that are passed arguments in registers on the 386 |
1930 | @cindex functions that pop the argument stack on the 386 | |
1931 | @cindex functions that do not pop the argument stack on the 386 | |
1932 | ||
1933 | In GNU C, you declare certain things about functions called in your program | |
1934 | which help the compiler optimize function calls and check your code more | |
1935 | carefully. | |
1936 | ||
1937 | The keyword @code{__attribute__} allows you to specify special | |
1938 | attributes when making a declaration. This keyword is followed by an | |
9162542e | 1939 | attribute specification inside double parentheses. The following |
eacecf96 | 1940 | attributes are currently defined for functions on all targets: |
6aa77e6c | 1941 | @code{noreturn}, @code{noinline}, @code{always_inline}, |
39f2f3c8 | 1942 | @code{pure}, @code{const}, @code{nothrow}, |
9162542e AO |
1943 | @code{format}, @code{format_arg}, @code{no_instrument_function}, |
1944 | @code{section}, @code{constructor}, @code{destructor}, @code{used}, | |
b34c7881 JT |
1945 | @code{unused}, @code{deprecated}, @code{weak}, @code{malloc}, |
1946 | @code{alias}, and @code{nonnull}. Several other attributes are defined | |
1947 | for functions on particular target systems. Other attributes, including | |
1948 | @code{section} are supported for variables declarations | |
1949 | (@pxref{Variable Attributes}) and for types (@pxref{Type Attributes}). | |
c1f7febf RK |
1950 | |
1951 | You may also specify attributes with @samp{__} preceding and following | |
1952 | each keyword. This allows you to use them in header files without | |
1953 | being concerned about a possible macro of the same name. For example, | |
1954 | you may use @code{__noreturn__} instead of @code{noreturn}. | |
1955 | ||
2c5e91d2 JM |
1956 | @xref{Attribute Syntax}, for details of the exact syntax for using |
1957 | attributes. | |
1958 | ||
c1f7febf RK |
1959 | @table @code |
1960 | @cindex @code{noreturn} function attribute | |
1961 | @item noreturn | |
1962 | A few standard library functions, such as @code{abort} and @code{exit}, | |
f0523f02 | 1963 | cannot return. GCC knows this automatically. Some programs define |
c1f7febf RK |
1964 | their own functions that never return. You can declare them |
1965 | @code{noreturn} to tell the compiler this fact. For example, | |
1966 | ||
1967 | @smallexample | |
aee96fe9 | 1968 | @group |
c1f7febf RK |
1969 | void fatal () __attribute__ ((noreturn)); |
1970 | ||
1971 | void | |
0d893a63 | 1972 | fatal (/* @r{@dots{}} */) |
c1f7febf | 1973 | @{ |
0d893a63 | 1974 | /* @r{@dots{}} */ /* @r{Print error message.} */ /* @r{@dots{}} */ |
c1f7febf RK |
1975 | exit (1); |
1976 | @} | |
aee96fe9 | 1977 | @end group |
c1f7febf RK |
1978 | @end smallexample |
1979 | ||
1980 | The @code{noreturn} keyword tells the compiler to assume that | |
1981 | @code{fatal} cannot return. It can then optimize without regard to what | |
1982 | would happen if @code{fatal} ever did return. This makes slightly | |
1983 | better code. More importantly, it helps avoid spurious warnings of | |
1984 | uninitialized variables. | |
1985 | ||
1986 | Do not assume that registers saved by the calling function are | |
1987 | restored before calling the @code{noreturn} function. | |
1988 | ||
1989 | It does not make sense for a @code{noreturn} function to have a return | |
1990 | type other than @code{void}. | |
1991 | ||
f0523f02 | 1992 | The attribute @code{noreturn} is not implemented in GCC versions |
c1f7febf RK |
1993 | earlier than 2.5. An alternative way to declare that a function does |
1994 | not return, which works in the current version and in some older | |
1995 | versions, is as follows: | |
1996 | ||
1997 | @smallexample | |
1998 | typedef void voidfn (); | |
1999 | ||
2000 | volatile voidfn fatal; | |
2001 | @end smallexample | |
2002 | ||
9162542e AO |
2003 | @cindex @code{noinline} function attribute |
2004 | @item noinline | |
2005 | This function attribute prevents a function from being considered for | |
2006 | inlining. | |
2007 | ||
6aa77e6c AH |
2008 | @cindex @code{always_inline} function attribute |
2009 | @item always_inline | |
2010 | Generally, functions are not inlined unless optimization is specified. | |
2011 | For functions declared inline, this attribute inlines the function even | |
2012 | if no optimization level was specified. | |
2013 | ||
2a8f6b90 JH |
2014 | @cindex @code{pure} function attribute |
2015 | @item pure | |
2016 | Many functions have no effects except the return value and their | |
d4047e24 | 2017 | return value depends only on the parameters and/or global variables. |
2a8f6b90 | 2018 | Such a function can be subject |
c1f7febf RK |
2019 | to common subexpression elimination and loop optimization just as an |
2020 | arithmetic operator would be. These functions should be declared | |
2a8f6b90 | 2021 | with the attribute @code{pure}. For example, |
c1f7febf RK |
2022 | |
2023 | @smallexample | |
2a8f6b90 | 2024 | int square (int) __attribute__ ((pure)); |
c1f7febf RK |
2025 | @end smallexample |
2026 | ||
2027 | @noindent | |
2028 | says that the hypothetical function @code{square} is safe to call | |
2029 | fewer times than the program says. | |
2030 | ||
2a8f6b90 JH |
2031 | Some of common examples of pure functions are @code{strlen} or @code{memcmp}. |
2032 | Interesting non-pure functions are functions with infinite loops or those | |
2033 | depending on volatile memory or other system resource, that may change between | |
2a59078d | 2034 | two consecutive calls (such as @code{feof} in a multithreading environment). |
2a8f6b90 | 2035 | |
f0523f02 | 2036 | The attribute @code{pure} is not implemented in GCC versions earlier |
2a8f6b90 JH |
2037 | than 2.96. |
2038 | @cindex @code{const} function attribute | |
2039 | @item const | |
2040 | Many functions do not examine any values except their arguments, and | |
2041 | have no effects except the return value. Basically this is just slightly | |
84330467 | 2042 | more strict class than the @code{pure} attribute above, since function is not |
2a59078d | 2043 | allowed to read global memory. |
2a8f6b90 JH |
2044 | |
2045 | @cindex pointer arguments | |
2046 | Note that a function that has pointer arguments and examines the data | |
2047 | pointed to must @emph{not} be declared @code{const}. Likewise, a | |
2048 | function that calls a non-@code{const} function usually must not be | |
2049 | @code{const}. It does not make sense for a @code{const} function to | |
2050 | return @code{void}. | |
2051 | ||
f0523f02 | 2052 | The attribute @code{const} is not implemented in GCC versions earlier |
c1f7febf RK |
2053 | than 2.5. An alternative way to declare that a function has no side |
2054 | effects, which works in the current version and in some older versions, | |
2055 | is as follows: | |
2056 | ||
2057 | @smallexample | |
2058 | typedef int intfn (); | |
2059 | ||
2060 | extern const intfn square; | |
2061 | @end smallexample | |
2062 | ||
2063 | This approach does not work in GNU C++ from 2.6.0 on, since the language | |
2064 | specifies that the @samp{const} must be attached to the return value. | |
2065 | ||
39f2f3c8 RS |
2066 | @cindex @code{nothrow} function attribute |
2067 | @item nothrow | |
2068 | The @code{nothrow} attribute is used to inform the compiler that a | |
2069 | function cannot throw an exception. For example, most functions in | |
2070 | the standard C library can be guaranteed not to throw an exception | |
2071 | with the notable exceptions of @code{qsort} and @code{bsearch} that | |
2072 | take function pointer arguments. The @code{nothrow} attribute is not | |
2073 | implemented in GCC versions earlier than 3.2. | |
c1f7febf RK |
2074 | |
2075 | @item format (@var{archetype}, @var{string-index}, @var{first-to-check}) | |
2076 | @cindex @code{format} function attribute | |
84330467 | 2077 | @opindex Wformat |
bb72a084 | 2078 | The @code{format} attribute specifies that a function takes @code{printf}, |
26f6672d JM |
2079 | @code{scanf}, @code{strftime} or @code{strfmon} style arguments which |
2080 | should be type-checked against a format string. For example, the | |
2081 | declaration: | |
c1f7febf RK |
2082 | |
2083 | @smallexample | |
2084 | extern int | |
2085 | my_printf (void *my_object, const char *my_format, ...) | |
2086 | __attribute__ ((format (printf, 2, 3))); | |
2087 | @end smallexample | |
2088 | ||
2089 | @noindent | |
2090 | causes the compiler to check the arguments in calls to @code{my_printf} | |
2091 | for consistency with the @code{printf} style format string argument | |
2092 | @code{my_format}. | |
2093 | ||
2094 | The parameter @var{archetype} determines how the format string is | |
26f6672d JM |
2095 | interpreted, and should be @code{printf}, @code{scanf}, @code{strftime} |
2096 | or @code{strfmon}. (You can also use @code{__printf__}, | |
2097 | @code{__scanf__}, @code{__strftime__} or @code{__strfmon__}.) The | |
c1f7febf RK |
2098 | parameter @var{string-index} specifies which argument is the format |
2099 | string argument (starting from 1), while @var{first-to-check} is the | |
2100 | number of the first argument to check against the format string. For | |
2101 | functions where the arguments are not available to be checked (such as | |
2102 | @code{vprintf}), specify the third parameter as zero. In this case the | |
b722c82c JM |
2103 | compiler only checks the format string for consistency. For |
2104 | @code{strftime} formats, the third parameter is required to be zero. | |
f57a2e3a BE |
2105 | Since non-static C++ methods have an implicit @code{this} argument, the |
2106 | arguments of such methods should be counted from two, not one, when | |
2107 | giving values for @var{string-index} and @var{first-to-check}. | |
c1f7febf RK |
2108 | |
2109 | In the example above, the format string (@code{my_format}) is the second | |
2110 | argument of the function @code{my_print}, and the arguments to check | |
2111 | start with the third argument, so the correct parameters for the format | |
2112 | attribute are 2 and 3. | |
2113 | ||
84330467 | 2114 | @opindex ffreestanding |
c1f7febf | 2115 | The @code{format} attribute allows you to identify your own functions |
f0523f02 | 2116 | which take format strings as arguments, so that GCC can check the |
b722c82c | 2117 | calls to these functions for errors. The compiler always (unless |
84330467 | 2118 | @option{-ffreestanding} is used) checks formats |
b722c82c | 2119 | for the standard library functions @code{printf}, @code{fprintf}, |
bb72a084 | 2120 | @code{sprintf}, @code{scanf}, @code{fscanf}, @code{sscanf}, @code{strftime}, |
c1f7febf | 2121 | @code{vprintf}, @code{vfprintf} and @code{vsprintf} whenever such |
84330467 | 2122 | warnings are requested (using @option{-Wformat}), so there is no need to |
b722c82c JM |
2123 | modify the header file @file{stdio.h}. In C99 mode, the functions |
2124 | @code{snprintf}, @code{vsnprintf}, @code{vscanf}, @code{vfscanf} and | |
26f6672d | 2125 | @code{vsscanf} are also checked. Except in strictly conforming C |
b4c984fb KG |
2126 | standard modes, the X/Open function @code{strfmon} is also checked as |
2127 | are @code{printf_unlocked} and @code{fprintf_unlocked}. | |
b722c82c | 2128 | @xref{C Dialect Options,,Options Controlling C Dialect}. |
c1f7febf RK |
2129 | |
2130 | @item format_arg (@var{string-index}) | |
2131 | @cindex @code{format_arg} function attribute | |
84330467 | 2132 | @opindex Wformat-nonliteral |
26f6672d JM |
2133 | The @code{format_arg} attribute specifies that a function takes a format |
2134 | string for a @code{printf}, @code{scanf}, @code{strftime} or | |
2135 | @code{strfmon} style function and modifies it (for example, to translate | |
2136 | it into another language), so the result can be passed to a | |
2137 | @code{printf}, @code{scanf}, @code{strftime} or @code{strfmon} style | |
2138 | function (with the remaining arguments to the format function the same | |
2139 | as they would have been for the unmodified string). For example, the | |
2140 | declaration: | |
c1f7febf RK |
2141 | |
2142 | @smallexample | |
2143 | extern char * | |
2144 | my_dgettext (char *my_domain, const char *my_format) | |
2145 | __attribute__ ((format_arg (2))); | |
2146 | @end smallexample | |
2147 | ||
2148 | @noindent | |
26f6672d JM |
2149 | causes the compiler to check the arguments in calls to a @code{printf}, |
2150 | @code{scanf}, @code{strftime} or @code{strfmon} type function, whose | |
2151 | format string argument is a call to the @code{my_dgettext} function, for | |
2152 | consistency with the format string argument @code{my_format}. If the | |
2153 | @code{format_arg} attribute had not been specified, all the compiler | |
2154 | could tell in such calls to format functions would be that the format | |
2155 | string argument is not constant; this would generate a warning when | |
84330467 | 2156 | @option{-Wformat-nonliteral} is used, but the calls could not be checked |
26f6672d | 2157 | without the attribute. |
c1f7febf RK |
2158 | |
2159 | The parameter @var{string-index} specifies which argument is the format | |
f57a2e3a BE |
2160 | string argument (starting from one). Since non-static C++ methods have |
2161 | an implicit @code{this} argument, the arguments of such methods should | |
2162 | be counted from two. | |
c1f7febf RK |
2163 | |
2164 | The @code{format-arg} attribute allows you to identify your own | |
f0523f02 | 2165 | functions which modify format strings, so that GCC can check the |
26f6672d JM |
2166 | calls to @code{printf}, @code{scanf}, @code{strftime} or @code{strfmon} |
2167 | type function whose operands are a call to one of your own function. | |
2168 | The compiler always treats @code{gettext}, @code{dgettext}, and | |
2169 | @code{dcgettext} in this manner except when strict ISO C support is | |
84330467 JM |
2170 | requested by @option{-ansi} or an appropriate @option{-std} option, or |
2171 | @option{-ffreestanding} is used. @xref{C Dialect Options,,Options | |
26f6672d | 2172 | Controlling C Dialect}. |
c1f7febf | 2173 | |
390de769 | 2174 | @item nonnull (@var{arg-index}, @dots{}) |
b34c7881 JT |
2175 | @cindex @code{nonnull} function attribute |
2176 | The @code{nonnull} attribute specifies that some function parameters should | |
2177 | be non-null pointers. For instance, the declaration: | |
2178 | ||
2179 | @smallexample | |
2180 | extern void * | |
2181 | my_memcpy (void *dest, const void *src, size_t len) | |
2182 | __attribute__((nonnull (1, 2))); | |
2183 | @end smallexample | |
2184 | ||
2185 | @noindent | |
2186 | causes the compiler to check that, in calls to @code{my_memcpy}, | |
2187 | arguments @var{dest} and @var{src} are non-null. If the compiler | |
2188 | determines that a null pointer is passed in an argument slot marked | |
2189 | as non-null, and the @option{-Wnonnull} option is enabled, a warning | |
2190 | is issued. The compiler may also choose to make optimizations based | |
2191 | on the knowledge that certain function arguments will not be null. | |
2192 | ||
2193 | If no argument index list is given to the @code{nonnull} attribute, | |
2194 | all pointer arguments are marked as non-null. To illustrate, the | |
2195 | following declaration is equivalent to the previous example: | |
2196 | ||
2197 | @smallexample | |
2198 | extern void * | |
2199 | my_memcpy (void *dest, const void *src, size_t len) | |
2200 | __attribute__((nonnull)); | |
2201 | @end smallexample | |
2202 | ||
07417085 KR |
2203 | @item no_instrument_function |
2204 | @cindex @code{no_instrument_function} function attribute | |
84330467 JM |
2205 | @opindex finstrument-functions |
2206 | If @option{-finstrument-functions} is given, profiling function calls will | |
07417085 KR |
2207 | be generated at entry and exit of most user-compiled functions. |
2208 | Functions with this attribute will not be so instrumented. | |
2209 | ||
84330467 | 2210 | @item section ("@var{section-name}") |
c1f7febf RK |
2211 | @cindex @code{section} function attribute |
2212 | Normally, the compiler places the code it generates in the @code{text} section. | |
2213 | Sometimes, however, you need additional sections, or you need certain | |
2214 | particular functions to appear in special sections. The @code{section} | |
2215 | attribute specifies that a function lives in a particular section. | |
2216 | For example, the declaration: | |
2217 | ||
2218 | @smallexample | |
2219 | extern void foobar (void) __attribute__ ((section ("bar"))); | |
2220 | @end smallexample | |
2221 | ||
2222 | @noindent | |
2223 | puts the function @code{foobar} in the @code{bar} section. | |
2224 | ||
2225 | Some file formats do not support arbitrary sections so the @code{section} | |
2226 | attribute is not available on all platforms. | |
2227 | If you need to map the entire contents of a module to a particular | |
2228 | section, consider using the facilities of the linker instead. | |
2229 | ||
2230 | @item constructor | |
2231 | @itemx destructor | |
2232 | @cindex @code{constructor} function attribute | |
2233 | @cindex @code{destructor} function attribute | |
2234 | The @code{constructor} attribute causes the function to be called | |
2235 | automatically before execution enters @code{main ()}. Similarly, the | |
2236 | @code{destructor} attribute causes the function to be called | |
2237 | automatically after @code{main ()} has completed or @code{exit ()} has | |
2238 | been called. Functions with these attributes are useful for | |
2239 | initializing data that will be used implicitly during the execution of | |
2240 | the program. | |
2241 | ||
161d7b59 | 2242 | These attributes are not currently implemented for Objective-C@. |
c1f7febf | 2243 | |
9162542e | 2244 | @cindex @code{unused} attribute. |
c1f7febf RK |
2245 | @item unused |
2246 | This attribute, attached to a function, means that the function is meant | |
f0523f02 | 2247 | to be possibly unused. GCC will not produce a warning for this |
c1f7febf RK |
2248 | function. GNU C++ does not currently support this attribute as |
2249 | definitions without parameters are valid in C++. | |
2250 | ||
9162542e AO |
2251 | @cindex @code{used} attribute. |
2252 | @item used | |
2253 | This attribute, attached to a function, means that code must be emitted | |
2254 | for the function even if it appears that the function is not referenced. | |
2255 | This is useful, for example, when the function is referenced only in | |
2256 | inline assembly. | |
2257 | ||
e23bd218 IR |
2258 | @cindex @code{deprecated} attribute. |
2259 | @item deprecated | |
2260 | The @code{deprecated} attribute results in a warning if the function | |
2261 | is used anywhere in the source file. This is useful when identifying | |
2262 | functions that are expected to be removed in a future version of a | |
2263 | program. The warning also includes the location of the declaration | |
2264 | of the deprecated function, to enable users to easily find further | |
2265 | information about why the function is deprecated, or what they should | |
2266 | do instead. Note that the warnings only occurs for uses: | |
2267 | ||
2268 | @smallexample | |
2269 | int old_fn () __attribute__ ((deprecated)); | |
2270 | int old_fn (); | |
2271 | int (*fn_ptr)() = old_fn; | |
2272 | @end smallexample | |
2273 | ||
2274 | results in a warning on line 3 but not line 2. | |
2275 | ||
2276 | The @code{deprecated} attribute can also be used for variables and | |
2277 | types (@pxref{Variable Attributes}, @pxref{Type Attributes}.) | |
2278 | ||
c1f7febf RK |
2279 | @item weak |
2280 | @cindex @code{weak} attribute | |
2281 | The @code{weak} attribute causes the declaration to be emitted as a weak | |
2282 | symbol rather than a global. This is primarily useful in defining | |
2283 | library functions which can be overridden in user code, though it can | |
2284 | also be used with non-function declarations. Weak symbols are supported | |
2285 | for ELF targets, and also for a.out targets when using the GNU assembler | |
2286 | and linker. | |
2287 | ||
140592a0 AG |
2288 | @item malloc |
2289 | @cindex @code{malloc} attribute | |
2290 | The @code{malloc} attribute is used to tell the compiler that a function | |
2291 | may be treated as if it were the malloc function. The compiler assumes | |
2292 | that calls to malloc result in a pointers that cannot alias anything. | |
2293 | This will often improve optimization. | |
2294 | ||
84330467 | 2295 | @item alias ("@var{target}") |
c1f7febf RK |
2296 | @cindex @code{alias} attribute |
2297 | The @code{alias} attribute causes the declaration to be emitted as an | |
2298 | alias for another symbol, which must be specified. For instance, | |
2299 | ||
2300 | @smallexample | |
47bd70b5 | 2301 | void __f () @{ /* @r{Do something.} */; @} |
c1f7febf RK |
2302 | void f () __attribute__ ((weak, alias ("__f"))); |
2303 | @end smallexample | |
2304 | ||
2305 | declares @samp{f} to be a weak alias for @samp{__f}. In C++, the | |
2306 | mangled name for the target must be used. | |
2307 | ||
af3e86c2 RK |
2308 | Not all target machines support this attribute. |
2309 | ||
47bd70b5 JJ |
2310 | @item visibility ("@var{visibility_type}") |
2311 | @cindex @code{visibility} attribute | |
2312 | The @code{visibility} attribute on ELF targets causes the declaration | |
d5c4db17 | 2313 | to be emitted with default, hidden, protected or internal visibility. |
47bd70b5 JJ |
2314 | |
2315 | @smallexample | |
2316 | void __attribute__ ((visibility ("protected"))) | |
2317 | f () @{ /* @r{Do something.} */; @} | |
2318 | int i __attribute__ ((visibility ("hidden"))); | |
2319 | @end smallexample | |
2320 | ||
9e8aab55 RH |
2321 | See the ELF gABI for complete details, but the short story is |
2322 | ||
2323 | @table @dfn | |
d5c4db17 RH |
2324 | @item default |
2325 | Default visibility is the normal case for ELF. This value is | |
3bcf1b13 | 2326 | available for the visibility attribute to override other options |
d5c4db17 RH |
2327 | that may change the assumed visibility of symbols. |
2328 | ||
9e8aab55 RH |
2329 | @item hidden |
2330 | Hidden visibility indicates that the symbol will not be placed into | |
2331 | the dynamic symbol table, so no other @dfn{module} (executable or | |
2332 | shared library) can reference it directly. | |
2333 | ||
2334 | @item protected | |
2335 | Protected visibility indicates that the symbol will be placed in the | |
2336 | dynamic symbol table, but that references within the defining module | |
2337 | will bind to the local symbol. That is, the symbol cannot be overridden | |
2338 | by another module. | |
2339 | ||
2340 | @item internal | |
2341 | Internal visibility is like hidden visibility, but with additional | |
2342 | processor specific semantics. Unless otherwise specified by the psABI, | |
2343 | gcc defines internal visibility to mean that the function is @emph{never} | |
2344 | called from another module. Note that hidden symbols, while then cannot | |
2345 | be referenced directly by other modules, can be referenced indirectly via | |
2346 | function pointers. By indicating that a symbol cannot be called from | |
2347 | outside the module, gcc may for instance omit the load of a PIC register | |
2348 | since it is known that the calling function loaded the correct value. | |
2349 | @end table | |
2350 | ||
47bd70b5 JJ |
2351 | Not all ELF targets support this attribute. |
2352 | ||
dce81a1a JJ |
2353 | @item tls_model ("@var{tls_model}") |
2354 | @cindex @code{tls_model} attribute | |
2355 | The @code{tls_model} attribute sets thread-local storage model | |
2356 | (@pxref{Thread-Local}) of a particular @code{__thread} variable, | |
2357 | overriding @code{-ftls-model=} command line switch on a per-variable | |
2358 | basis. | |
2359 | The @var{tls_model} argument should be one of @code{global-dynamic}, | |
2360 | @code{local-dynamic}, @code{initial-exec} or @code{local-exec}. | |
2361 | ||
c1f7febf RK |
2362 | @item regparm (@var{number}) |
2363 | @cindex functions that are passed arguments in registers on the 386 | |
2364 | On the Intel 386, the @code{regparm} attribute causes the compiler to | |
84330467 JM |
2365 | pass up to @var{number} integer arguments in registers EAX, |
2366 | EDX, and ECX instead of on the stack. Functions that take a | |
c1f7febf RK |
2367 | variable number of arguments will continue to be passed all of their |
2368 | arguments on the stack. | |
2369 | ||
2370 | @item stdcall | |
2371 | @cindex functions that pop the argument stack on the 386 | |
2372 | On the Intel 386, the @code{stdcall} attribute causes the compiler to | |
2373 | assume that the called function will pop off the stack space used to | |
2374 | pass arguments, unless it takes a variable number of arguments. | |
2375 | ||
e91f04de CH |
2376 | @item fastcall |
2377 | @cindex functions that pop the argument stack on the 386 | |
2378 | On the Intel 386, the @code{fastcall} attribute causes the compiler to | |
2379 | pass the first two arguments in the registers ECX and EDX. Subsequent | |
2380 | arguments are passed on the stack. The called function will pop the | |
2381 | arguments off the stack. If the number of arguments is variable all | |
2382 | arguments are pushed on the stack. | |
2383 | ||
c1f7febf RK |
2384 | @item cdecl |
2385 | @cindex functions that do pop the argument stack on the 386 | |
84330467 | 2386 | @opindex mrtd |
c1f7febf RK |
2387 | On the Intel 386, the @code{cdecl} attribute causes the compiler to |
2388 | assume that the calling function will pop off the stack space used to | |
2389 | pass arguments. This is | |
84330467 | 2390 | useful to override the effects of the @option{-mrtd} switch. |
c1f7febf | 2391 | |
a5c76ee6 | 2392 | @item longcall/shortcall |
c1f7febf RK |
2393 | @cindex functions called via pointer on the RS/6000 and PowerPC |
2394 | On the RS/6000 and PowerPC, the @code{longcall} attribute causes the | |
a5c76ee6 ZW |
2395 | compiler to always call this function via a pointer, just as it would if |
2396 | the @option{-mlongcall} option had been specified. The @code{shortcall} | |
2397 | attribute causes the compiler not to do this. These attributes override | |
2398 | both the @option{-mlongcall} switch and the @code{#pragma longcall} | |
2399 | setting. | |
2400 | ||
2401 | @xref{RS/6000 and PowerPC Options}, for more information on when long | |
2402 | calls are and are not necessary. | |
c1f7febf | 2403 | |
c27ba912 DM |
2404 | @item long_call/short_call |
2405 | @cindex indirect calls on ARM | |
2406 | This attribute allows to specify how to call a particular function on | |
161d7b59 | 2407 | ARM@. Both attributes override the @option{-mlong-calls} (@pxref{ARM Options}) |
c27ba912 DM |
2408 | command line switch and @code{#pragma long_calls} settings. The |
2409 | @code{long_call} attribute causes the compiler to always call the | |
2410 | function by first loading its address into a register and then using the | |
2411 | contents of that register. The @code{short_call} attribute always places | |
2412 | the offset to the function from the call site into the @samp{BL} | |
2413 | instruction directly. | |
2414 | ||
c1f7febf RK |
2415 | @item function_vector |
2416 | @cindex calling functions through the function vector on the H8/300 processors | |
88ab0d1c | 2417 | Use this attribute on the H8/300 and H8/300H to indicate that the specified |
c1f7febf RK |
2418 | function should be called through the function vector. Calling a |
2419 | function through the function vector will reduce code size, however; | |
2420 | the function vector has a limited size (maximum 128 entries on the H8/300 | |
2421 | and 64 entries on the H8/300H) and shares space with the interrupt vector. | |
2422 | ||
2423 | You must use GAS and GLD from GNU binutils version 2.7 or later for | |
88ab0d1c | 2424 | this attribute to work correctly. |
c1f7febf | 2425 | |
6d3d9133 NC |
2426 | @item interrupt |
2427 | @cindex interrupt handler functions | |
86143814 | 2428 | Use this attribute on the ARM, AVR, C4x, M32R/D and Xstormy16 ports to indicate |
9f339dde GK |
2429 | that the specified function is an interrupt handler. The compiler will |
2430 | generate function entry and exit sequences suitable for use in an | |
2431 | interrupt handler when this attribute is present. | |
6d3d9133 | 2432 | |
b93e3893 AO |
2433 | Note, interrupt handlers for the H8/300, H8/300H and SH processors can |
2434 | be specified via the @code{interrupt_handler} attribute. | |
6d3d9133 NC |
2435 | |
2436 | Note, on the AVR interrupts will be enabled inside the function. | |
2437 | ||
2438 | Note, for the ARM you can specify the kind of interrupt to be handled by | |
2439 | adding an optional parameter to the interrupt attribute like this: | |
2440 | ||
2441 | @smallexample | |
2442 | void f () __attribute__ ((interrupt ("IRQ"))); | |
2443 | @end smallexample | |
2444 | ||
161d7b59 | 2445 | Permissible values for this parameter are: IRQ, FIQ, SWI, ABORT and UNDEF@. |
6d3d9133 | 2446 | |
b93e3893 AO |
2447 | @item interrupt_handler |
2448 | @cindex interrupt handler functions on the H8/300 and SH processors | |
88ab0d1c | 2449 | Use this attribute on the H8/300, H8/300H and SH to indicate that the |
b93e3893 AO |
2450 | specified function is an interrupt handler. The compiler will generate |
2451 | function entry and exit sequences suitable for use in an interrupt | |
2452 | handler when this attribute is present. | |
2453 | ||
2454 | @item sp_switch | |
88ab0d1c | 2455 | Use this attribute on the SH to indicate an @code{interrupt_handler} |
b93e3893 AO |
2456 | function should switch to an alternate stack. It expects a string |
2457 | argument that names a global variable holding the address of the | |
2458 | alternate stack. | |
2459 | ||
2460 | @smallexample | |
2461 | void *alt_stack; | |
aee96fe9 JM |
2462 | void f () __attribute__ ((interrupt_handler, |
2463 | sp_switch ("alt_stack"))); | |
b93e3893 AO |
2464 | @end smallexample |
2465 | ||
2466 | @item trap_exit | |
88ab0d1c | 2467 | Use this attribute on the SH for an @code{interrupt_handle} to return using |
b93e3893 AO |
2468 | @code{trapa} instead of @code{rte}. This attribute expects an integer |
2469 | argument specifying the trap number to be used. | |
2470 | ||
c1f7febf RK |
2471 | @item eightbit_data |
2472 | @cindex eight bit data on the H8/300 and H8/300H | |
88ab0d1c | 2473 | Use this attribute on the H8/300 and H8/300H to indicate that the specified |
c1f7febf RK |
2474 | variable should be placed into the eight bit data section. |
2475 | The compiler will generate more efficient code for certain operations | |
2476 | on data in the eight bit data area. Note the eight bit data area is limited to | |
2477 | 256 bytes of data. | |
2478 | ||
2479 | You must use GAS and GLD from GNU binutils version 2.7 or later for | |
88ab0d1c | 2480 | this attribute to work correctly. |
c1f7febf RK |
2481 | |
2482 | @item tiny_data | |
2483 | @cindex tiny data section on the H8/300H | |
88ab0d1c | 2484 | Use this attribute on the H8/300H to indicate that the specified |
c1f7febf RK |
2485 | variable should be placed into the tiny data section. |
2486 | The compiler will generate more efficient code for loads and stores | |
2487 | on data in the tiny data section. Note the tiny data area is limited to | |
2488 | slightly under 32kbytes of data. | |
845da534 | 2489 | |
052a4b28 DC |
2490 | @item signal |
2491 | @cindex signal handler functions on the AVR processors | |
88ab0d1c | 2492 | Use this attribute on the AVR to indicate that the specified |
052a4b28 DC |
2493 | function is an signal handler. The compiler will generate function |
2494 | entry and exit sequences suitable for use in an signal handler when this | |
767094dd | 2495 | attribute is present. Interrupts will be disabled inside function. |
052a4b28 DC |
2496 | |
2497 | @item naked | |
6d3d9133 | 2498 | @cindex function without a prologue/epilogue code |
86143814 | 2499 | Use this attribute on the ARM, AVR, C4x and IP2K ports to indicate that the |
e3223ea2 DC |
2500 | specified function do not need prologue/epilogue sequences generated by |
2501 | the compiler. It is up to the programmer to provide these sequences. | |
052a4b28 | 2502 | |
845da534 DE |
2503 | @item model (@var{model-name}) |
2504 | @cindex function addressability on the M32R/D | |
2505 | Use this attribute on the M32R/D to set the addressability of an object, | |
2506 | and the code generated for a function. | |
2507 | The identifier @var{model-name} is one of @code{small}, @code{medium}, | |
2508 | or @code{large}, representing each of the code models. | |
2509 | ||
2510 | Small model objects live in the lower 16MB of memory (so that their | |
2511 | addresses can be loaded with the @code{ld24} instruction), and are | |
2512 | callable with the @code{bl} instruction. | |
2513 | ||
02f52e19 | 2514 | Medium model objects may live anywhere in the 32-bit address space (the |
845da534 DE |
2515 | compiler will generate @code{seth/add3} instructions to load their addresses), |
2516 | and are callable with the @code{bl} instruction. | |
2517 | ||
02f52e19 | 2518 | Large model objects may live anywhere in the 32-bit address space (the |
845da534 DE |
2519 | compiler will generate @code{seth/add3} instructions to load their addresses), |
2520 | and may not be reachable with the @code{bl} instruction (the compiler will | |
2521 | generate the much slower @code{seth/add3/jl} instruction sequence). | |
2522 | ||
c1f7febf RK |
2523 | @end table |
2524 | ||
2525 | You can specify multiple attributes in a declaration by separating them | |
2526 | by commas within the double parentheses or by immediately following an | |
2527 | attribute declaration with another attribute declaration. | |
2528 | ||
2529 | @cindex @code{#pragma}, reason for not using | |
2530 | @cindex pragma, reason for not using | |
9f1bbeaa JM |
2531 | Some people object to the @code{__attribute__} feature, suggesting that |
2532 | ISO C's @code{#pragma} should be used instead. At the time | |
2533 | @code{__attribute__} was designed, there were two reasons for not doing | |
2534 | this. | |
c1f7febf RK |
2535 | |
2536 | @enumerate | |
2537 | @item | |
2538 | It is impossible to generate @code{#pragma} commands from a macro. | |
2539 | ||
2540 | @item | |
2541 | There is no telling what the same @code{#pragma} might mean in another | |
2542 | compiler. | |
2543 | @end enumerate | |
2544 | ||
9f1bbeaa JM |
2545 | These two reasons applied to almost any application that might have been |
2546 | proposed for @code{#pragma}. It was basically a mistake to use | |
2547 | @code{#pragma} for @emph{anything}. | |
2548 | ||
2549 | The ISO C99 standard includes @code{_Pragma}, which now allows pragmas | |
2550 | to be generated from macros. In addition, a @code{#pragma GCC} | |
2551 | namespace is now in use for GCC-specific pragmas. However, it has been | |
2552 | found convenient to use @code{__attribute__} to achieve a natural | |
2553 | attachment of attributes to their corresponding declarations, whereas | |
2554 | @code{#pragma GCC} is of use for constructs that do not naturally form | |
2555 | part of the grammar. @xref{Other Directives,,Miscellaneous | |
2556 | Preprocessing Directives, cpp, The C Preprocessor}. | |
c1f7febf | 2557 | |
2c5e91d2 JM |
2558 | @node Attribute Syntax |
2559 | @section Attribute Syntax | |
2560 | @cindex attribute syntax | |
2561 | ||
2562 | This section describes the syntax with which @code{__attribute__} may be | |
2563 | used, and the constructs to which attribute specifiers bind, for the C | |
161d7b59 | 2564 | language. Some details may vary for C++ and Objective-C@. Because of |
2c5e91d2 JM |
2565 | infelicities in the grammar for attributes, some forms described here |
2566 | may not be successfully parsed in all cases. | |
2567 | ||
91d231cb JM |
2568 | There are some problems with the semantics of attributes in C++. For |
2569 | example, there are no manglings for attributes, although they may affect | |
2570 | code generation, so problems may arise when attributed types are used in | |
2571 | conjunction with templates or overloading. Similarly, @code{typeid} | |
2572 | does not distinguish between types with different attributes. Support | |
2573 | for attributes in C++ may be restricted in future to attributes on | |
2574 | declarations only, but not on nested declarators. | |
2575 | ||
2c5e91d2 JM |
2576 | @xref{Function Attributes}, for details of the semantics of attributes |
2577 | applying to functions. @xref{Variable Attributes}, for details of the | |
2578 | semantics of attributes applying to variables. @xref{Type Attributes}, | |
2579 | for details of the semantics of attributes applying to structure, union | |
2580 | and enumerated types. | |
2581 | ||
2582 | An @dfn{attribute specifier} is of the form | |
2583 | @code{__attribute__ ((@var{attribute-list}))}. An @dfn{attribute list} | |
2584 | is a possibly empty comma-separated sequence of @dfn{attributes}, where | |
2585 | each attribute is one of the following: | |
2586 | ||
2587 | @itemize @bullet | |
2588 | @item | |
2589 | Empty. Empty attributes are ignored. | |
2590 | ||
2591 | @item | |
2592 | A word (which may be an identifier such as @code{unused}, or a reserved | |
2593 | word such as @code{const}). | |
2594 | ||
2595 | @item | |
2596 | A word, followed by, in parentheses, parameters for the attribute. | |
2597 | These parameters take one of the following forms: | |
2598 | ||
2599 | @itemize @bullet | |
2600 | @item | |
2601 | An identifier. For example, @code{mode} attributes use this form. | |
2602 | ||
2603 | @item | |
2604 | An identifier followed by a comma and a non-empty comma-separated list | |
2605 | of expressions. For example, @code{format} attributes use this form. | |
2606 | ||
2607 | @item | |
2608 | A possibly empty comma-separated list of expressions. For example, | |
2609 | @code{format_arg} attributes use this form with the list being a single | |
2610 | integer constant expression, and @code{alias} attributes use this form | |
2611 | with the list being a single string constant. | |
2612 | @end itemize | |
2613 | @end itemize | |
2614 | ||
2615 | An @dfn{attribute specifier list} is a sequence of one or more attribute | |
2616 | specifiers, not separated by any other tokens. | |
2617 | ||
2618 | An attribute specifier list may appear after the colon following a | |
2619 | label, other than a @code{case} or @code{default} label. The only | |
2620 | attribute it makes sense to use after a label is @code{unused}. This | |
2621 | feature is intended for code generated by programs which contains labels | |
2622 | that may be unused but which is compiled with @option{-Wall}. It would | |
2623 | not normally be appropriate to use in it human-written code, though it | |
2624 | could be useful in cases where the code that jumps to the label is | |
2625 | contained within an @code{#ifdef} conditional. | |
2626 | ||
2627 | An attribute specifier list may appear as part of a @code{struct}, | |
2628 | @code{union} or @code{enum} specifier. It may go either immediately | |
2629 | after the @code{struct}, @code{union} or @code{enum} keyword, or after | |
2630 | the closing brace. It is ignored if the content of the structure, union | |
2631 | or enumerated type is not defined in the specifier in which the | |
2632 | attribute specifier list is used---that is, in usages such as | |
2633 | @code{struct __attribute__((foo)) bar} with no following opening brace. | |
2634 | Where attribute specifiers follow the closing brace, they are considered | |
2635 | to relate to the structure, union or enumerated type defined, not to any | |
2636 | enclosing declaration the type specifier appears in, and the type | |
2637 | defined is not complete until after the attribute specifiers. | |
2638 | @c Otherwise, there would be the following problems: a shift/reduce | |
4fe9b91c | 2639 | @c conflict between attributes binding the struct/union/enum and |
2c5e91d2 JM |
2640 | @c binding to the list of specifiers/qualifiers; and "aligned" |
2641 | @c attributes could use sizeof for the structure, but the size could be | |
2642 | @c changed later by "packed" attributes. | |
2643 | ||
2644 | Otherwise, an attribute specifier appears as part of a declaration, | |
2645 | counting declarations of unnamed parameters and type names, and relates | |
2646 | to that declaration (which may be nested in another declaration, for | |
91d231cb JM |
2647 | example in the case of a parameter declaration), or to a particular declarator |
2648 | within a declaration. Where an | |
ff867905 JM |
2649 | attribute specifier is applied to a parameter declared as a function or |
2650 | an array, it should apply to the function or array rather than the | |
2651 | pointer to which the parameter is implicitly converted, but this is not | |
2652 | yet correctly implemented. | |
2c5e91d2 JM |
2653 | |
2654 | Any list of specifiers and qualifiers at the start of a declaration may | |
2655 | contain attribute specifiers, whether or not such a list may in that | |
2656 | context contain storage class specifiers. (Some attributes, however, | |
2657 | are essentially in the nature of storage class specifiers, and only make | |
2658 | sense where storage class specifiers may be used; for example, | |
2659 | @code{section}.) There is one necessary limitation to this syntax: the | |
2660 | first old-style parameter declaration in a function definition cannot | |
2661 | begin with an attribute specifier, because such an attribute applies to | |
2662 | the function instead by syntax described below (which, however, is not | |
2663 | yet implemented in this case). In some other cases, attribute | |
2664 | specifiers are permitted by this grammar but not yet supported by the | |
2665 | compiler. All attribute specifiers in this place relate to the | |
c771326b | 2666 | declaration as a whole. In the obsolescent usage where a type of |
2c5e91d2 JM |
2667 | @code{int} is implied by the absence of type specifiers, such a list of |
2668 | specifiers and qualifiers may be an attribute specifier list with no | |
2669 | other specifiers or qualifiers. | |
2670 | ||
2671 | An attribute specifier list may appear immediately before a declarator | |
2672 | (other than the first) in a comma-separated list of declarators in a | |
2673 | declaration of more than one identifier using a single list of | |
4b01f8d8 | 2674 | specifiers and qualifiers. Such attribute specifiers apply |
9c34dbbf ZW |
2675 | only to the identifier before whose declarator they appear. For |
2676 | example, in | |
2677 | ||
2678 | @smallexample | |
2679 | __attribute__((noreturn)) void d0 (void), | |
2680 | __attribute__((format(printf, 1, 2))) d1 (const char *, ...), | |
2681 | d2 (void) | |
2682 | @end smallexample | |
2683 | ||
2684 | @noindent | |
2685 | the @code{noreturn} attribute applies to all the functions | |
4b01f8d8 | 2686 | declared; the @code{format} attribute only applies to @code{d1}. |
2c5e91d2 JM |
2687 | |
2688 | An attribute specifier list may appear immediately before the comma, | |
2689 | @code{=} or semicolon terminating the declaration of an identifier other | |
2690 | than a function definition. At present, such attribute specifiers apply | |
2691 | to the declared object or function, but in future they may attach to the | |
2692 | outermost adjacent declarator. In simple cases there is no difference, | |
f282ffb3 | 2693 | but, for example, in |
9c34dbbf ZW |
2694 | |
2695 | @smallexample | |
2696 | void (****f)(void) __attribute__((noreturn)); | |
2697 | @end smallexample | |
2698 | ||
2699 | @noindent | |
2700 | at present the @code{noreturn} attribute applies to @code{f}, which | |
2701 | causes a warning since @code{f} is not a function, but in future it may | |
2702 | apply to the function @code{****f}. The precise semantics of what | |
2703 | attributes in such cases will apply to are not yet specified. Where an | |
2704 | assembler name for an object or function is specified (@pxref{Asm | |
2705 | Labels}), at present the attribute must follow the @code{asm} | |
2706 | specification; in future, attributes before the @code{asm} specification | |
2707 | may apply to the adjacent declarator, and those after it to the declared | |
2708 | object or function. | |
2c5e91d2 JM |
2709 | |
2710 | An attribute specifier list may, in future, be permitted to appear after | |
2711 | the declarator in a function definition (before any old-style parameter | |
2712 | declarations or the function body). | |
2713 | ||
0e03329a JM |
2714 | Attribute specifiers may be mixed with type qualifiers appearing inside |
2715 | the @code{[]} of a parameter array declarator, in the C99 construct by | |
2716 | which such qualifiers are applied to the pointer to which the array is | |
2717 | implicitly converted. Such attribute specifiers apply to the pointer, | |
2718 | not to the array, but at present this is not implemented and they are | |
2719 | ignored. | |
2720 | ||
2c5e91d2 JM |
2721 | An attribute specifier list may appear at the start of a nested |
2722 | declarator. At present, there are some limitations in this usage: the | |
91d231cb JM |
2723 | attributes correctly apply to the declarator, but for most individual |
2724 | attributes the semantics this implies are not implemented. | |
2725 | When attribute specifiers follow the @code{*} of a pointer | |
4b01f8d8 | 2726 | declarator, they may be mixed with any type qualifiers present. |
91d231cb | 2727 | The following describes the formal semantics of this syntax. It will make the |
2c5e91d2 JM |
2728 | most sense if you are familiar with the formal specification of |
2729 | declarators in the ISO C standard. | |
2730 | ||
2731 | Consider (as in C99 subclause 6.7.5 paragraph 4) a declaration @code{T | |
2732 | D1}, where @code{T} contains declaration specifiers that specify a type | |
2733 | @var{Type} (such as @code{int}) and @code{D1} is a declarator that | |
2734 | contains an identifier @var{ident}. The type specified for @var{ident} | |
2735 | for derived declarators whose type does not include an attribute | |
2736 | specifier is as in the ISO C standard. | |
2737 | ||
2738 | If @code{D1} has the form @code{( @var{attribute-specifier-list} D )}, | |
2739 | and the declaration @code{T D} specifies the type | |
2740 | ``@var{derived-declarator-type-list} @var{Type}'' for @var{ident}, then | |
2741 | @code{T D1} specifies the type ``@var{derived-declarator-type-list} | |
2742 | @var{attribute-specifier-list} @var{Type}'' for @var{ident}. | |
2743 | ||
2744 | If @code{D1} has the form @code{* | |
2745 | @var{type-qualifier-and-attribute-specifier-list} D}, and the | |
2746 | declaration @code{T D} specifies the type | |
2747 | ``@var{derived-declarator-type-list} @var{Type}'' for @var{ident}, then | |
2748 | @code{T D1} specifies the type ``@var{derived-declarator-type-list} | |
2749 | @var{type-qualifier-and-attribute-specifier-list} @var{Type}'' for | |
2750 | @var{ident}. | |
2751 | ||
f282ffb3 | 2752 | For example, |
9c34dbbf ZW |
2753 | |
2754 | @smallexample | |
2755 | void (__attribute__((noreturn)) ****f) (void); | |
2756 | @end smallexample | |
2757 | ||
2758 | @noindent | |
2759 | specifies the type ``pointer to pointer to pointer to pointer to | |
2760 | non-returning function returning @code{void}''. As another example, | |
2761 | ||
2762 | @smallexample | |
2763 | char *__attribute__((aligned(8))) *f; | |
2764 | @end smallexample | |
2765 | ||
2766 | @noindent | |
2767 | specifies the type ``pointer to 8-byte-aligned pointer to @code{char}''. | |
91d231cb JM |
2768 | Note again that this does not work with most attributes; for example, |
2769 | the usage of @samp{aligned} and @samp{noreturn} attributes given above | |
2770 | is not yet supported. | |
2771 | ||
2772 | For compatibility with existing code written for compiler versions that | |
2773 | did not implement attributes on nested declarators, some laxity is | |
2774 | allowed in the placing of attributes. If an attribute that only applies | |
2775 | to types is applied to a declaration, it will be treated as applying to | |
2776 | the type of that declaration. If an attribute that only applies to | |
2777 | declarations is applied to the type of a declaration, it will be treated | |
2778 | as applying to that declaration; and, for compatibility with code | |
2779 | placing the attributes immediately before the identifier declared, such | |
2780 | an attribute applied to a function return type will be treated as | |
2781 | applying to the function type, and such an attribute applied to an array | |
2782 | element type will be treated as applying to the array type. If an | |
2783 | attribute that only applies to function types is applied to a | |
2784 | pointer-to-function type, it will be treated as applying to the pointer | |
2785 | target type; if such an attribute is applied to a function return type | |
2786 | that is not a pointer-to-function type, it will be treated as applying | |
2787 | to the function type. | |
2c5e91d2 | 2788 | |
c1f7febf RK |
2789 | @node Function Prototypes |
2790 | @section Prototypes and Old-Style Function Definitions | |
2791 | @cindex function prototype declarations | |
2792 | @cindex old-style function definitions | |
2793 | @cindex promotion of formal parameters | |
2794 | ||
5490d604 | 2795 | GNU C extends ISO C to allow a function prototype to override a later |
c1f7febf RK |
2796 | old-style non-prototype definition. Consider the following example: |
2797 | ||
2798 | @example | |
2799 | /* @r{Use prototypes unless the compiler is old-fashioned.} */ | |
d863830b | 2800 | #ifdef __STDC__ |
c1f7febf RK |
2801 | #define P(x) x |
2802 | #else | |
2803 | #define P(x) () | |
2804 | #endif | |
2805 | ||
2806 | /* @r{Prototype function declaration.} */ | |
2807 | int isroot P((uid_t)); | |
2808 | ||
2809 | /* @r{Old-style function definition.} */ | |
2810 | int | |
2811 | isroot (x) /* ??? lossage here ??? */ | |
2812 | uid_t x; | |
2813 | @{ | |
2814 | return x == 0; | |
2815 | @} | |
2816 | @end example | |
2817 | ||
5490d604 | 2818 | Suppose the type @code{uid_t} happens to be @code{short}. ISO C does |
c1f7febf RK |
2819 | not allow this example, because subword arguments in old-style |
2820 | non-prototype definitions are promoted. Therefore in this example the | |
2821 | function definition's argument is really an @code{int}, which does not | |
2822 | match the prototype argument type of @code{short}. | |
2823 | ||
5490d604 | 2824 | This restriction of ISO C makes it hard to write code that is portable |
c1f7febf RK |
2825 | to traditional C compilers, because the programmer does not know |
2826 | whether the @code{uid_t} type is @code{short}, @code{int}, or | |
2827 | @code{long}. Therefore, in cases like these GNU C allows a prototype | |
2828 | to override a later old-style definition. More precisely, in GNU C, a | |
2829 | function prototype argument type overrides the argument type specified | |
2830 | by a later old-style definition if the former type is the same as the | |
2831 | latter type before promotion. Thus in GNU C the above example is | |
2832 | equivalent to the following: | |
2833 | ||
2834 | @example | |
2835 | int isroot (uid_t); | |
2836 | ||
2837 | int | |
2838 | isroot (uid_t x) | |
2839 | @{ | |
2840 | return x == 0; | |
2841 | @} | |
2842 | @end example | |
2843 | ||
9c34dbbf | 2844 | @noindent |
c1f7febf RK |
2845 | GNU C++ does not support old-style function definitions, so this |
2846 | extension is irrelevant. | |
2847 | ||
2848 | @node C++ Comments | |
2849 | @section C++ Style Comments | |
2850 | @cindex // | |
2851 | @cindex C++ comments | |
2852 | @cindex comments, C++ style | |
2853 | ||
2854 | In GNU C, you may use C++ style comments, which start with @samp{//} and | |
2855 | continue until the end of the line. Many other C implementations allow | |
f458d1d5 ZW |
2856 | such comments, and they are included in the 1999 C standard. However, |
2857 | C++ style comments are not recognized if you specify an @option{-std} | |
2858 | option specifying a version of ISO C before C99, or @option{-ansi} | |
2859 | (equivalent to @option{-std=c89}). | |
c1f7febf RK |
2860 | |
2861 | @node Dollar Signs | |
2862 | @section Dollar Signs in Identifier Names | |
2863 | @cindex $ | |
2864 | @cindex dollar signs in identifier names | |
2865 | @cindex identifier names, dollar signs in | |
2866 | ||
79188db9 RK |
2867 | In GNU C, you may normally use dollar signs in identifier names. |
2868 | This is because many traditional C implementations allow such identifiers. | |
2869 | However, dollar signs in identifiers are not supported on a few target | |
2870 | machines, typically because the target assembler does not allow them. | |
c1f7febf RK |
2871 | |
2872 | @node Character Escapes | |
2873 | @section The Character @key{ESC} in Constants | |
2874 | ||
2875 | You can use the sequence @samp{\e} in a string or character constant to | |
2876 | stand for the ASCII character @key{ESC}. | |
2877 | ||
2878 | @node Alignment | |
2879 | @section Inquiring on Alignment of Types or Variables | |
2880 | @cindex alignment | |
2881 | @cindex type alignment | |
2882 | @cindex variable alignment | |
2883 | ||
2884 | The keyword @code{__alignof__} allows you to inquire about how an object | |
2885 | is aligned, or the minimum alignment usually required by a type. Its | |
2886 | syntax is just like @code{sizeof}. | |
2887 | ||
2888 | For example, if the target machine requires a @code{double} value to be | |
2889 | aligned on an 8-byte boundary, then @code{__alignof__ (double)} is 8. | |
2890 | This is true on many RISC machines. On more traditional machine | |
2891 | designs, @code{__alignof__ (double)} is 4 or even 2. | |
2892 | ||
2893 | Some machines never actually require alignment; they allow reference to any | |
2894 | data type even at an odd addresses. For these machines, @code{__alignof__} | |
2895 | reports the @emph{recommended} alignment of a type. | |
2896 | ||
5372b3fb NB |
2897 | If the operand of @code{__alignof__} is an lvalue rather than a type, |
2898 | its value is the required alignment for its type, taking into account | |
2899 | any minimum alignment specified with GCC's @code{__attribute__} | |
2900 | extension (@pxref{Variable Attributes}). For example, after this | |
2901 | declaration: | |
c1f7febf RK |
2902 | |
2903 | @example | |
2904 | struct foo @{ int x; char y; @} foo1; | |
2905 | @end example | |
2906 | ||
2907 | @noindent | |
5372b3fb NB |
2908 | the value of @code{__alignof__ (foo1.y)} is 1, even though its actual |
2909 | alignment is probably 2 or 4, the same as @code{__alignof__ (int)}. | |
c1f7febf | 2910 | |
9d27bffe SS |
2911 | It is an error to ask for the alignment of an incomplete type. |
2912 | ||
c1f7febf RK |
2913 | @node Variable Attributes |
2914 | @section Specifying Attributes of Variables | |
2915 | @cindex attribute of variables | |
2916 | @cindex variable attributes | |
2917 | ||
2918 | The keyword @code{__attribute__} allows you to specify special | |
2919 | attributes of variables or structure fields. This keyword is followed | |
e23bd218 | 2920 | by an attribute specification inside double parentheses. Ten |
c1f7febf RK |
2921 | attributes are currently defined for variables: @code{aligned}, |
2922 | @code{mode}, @code{nocommon}, @code{packed}, @code{section}, | |
e23bd218 IR |
2923 | @code{transparent_union}, @code{unused}, @code{deprecated}, |
2924 | @code{vector_size}, and @code{weak}. Some other attributes are defined | |
2925 | for variables on particular target systems. Other attributes are | |
2926 | available for functions (@pxref{Function Attributes}) and for types | |
2927 | (@pxref{Type Attributes}). Other front ends might define more | |
2928 | attributes (@pxref{C++ Extensions,,Extensions to the C++ Language}). | |
c1f7febf RK |
2929 | |
2930 | You may also specify attributes with @samp{__} preceding and following | |
2931 | each keyword. This allows you to use them in header files without | |
2932 | being concerned about a possible macro of the same name. For example, | |
2933 | you may use @code{__aligned__} instead of @code{aligned}. | |
2934 | ||
2c5e91d2 JM |
2935 | @xref{Attribute Syntax}, for details of the exact syntax for using |
2936 | attributes. | |
2937 | ||
c1f7febf RK |
2938 | @table @code |
2939 | @cindex @code{aligned} attribute | |
2940 | @item aligned (@var{alignment}) | |
2941 | This attribute specifies a minimum alignment for the variable or | |
2942 | structure field, measured in bytes. For example, the declaration: | |
2943 | ||
2944 | @smallexample | |
2945 | int x __attribute__ ((aligned (16))) = 0; | |
2946 | @end smallexample | |
2947 | ||
2948 | @noindent | |
2949 | causes the compiler to allocate the global variable @code{x} on a | |
2950 | 16-byte boundary. On a 68040, this could be used in conjunction with | |
2951 | an @code{asm} expression to access the @code{move16} instruction which | |
2952 | requires 16-byte aligned operands. | |
2953 | ||
2954 | You can also specify the alignment of structure fields. For example, to | |
2955 | create a double-word aligned @code{int} pair, you could write: | |
2956 | ||
2957 | @smallexample | |
2958 | struct foo @{ int x[2] __attribute__ ((aligned (8))); @}; | |
2959 | @end smallexample | |
2960 | ||
2961 | @noindent | |
2962 | This is an alternative to creating a union with a @code{double} member | |
2963 | that forces the union to be double-word aligned. | |
2964 | ||
c1f7febf RK |
2965 | As in the preceding examples, you can explicitly specify the alignment |
2966 | (in bytes) that you wish the compiler to use for a given variable or | |
2967 | structure field. Alternatively, you can leave out the alignment factor | |
2968 | and just ask the compiler to align a variable or field to the maximum | |
2969 | useful alignment for the target machine you are compiling for. For | |
2970 | example, you could write: | |
2971 | ||
2972 | @smallexample | |
2973 | short array[3] __attribute__ ((aligned)); | |
2974 | @end smallexample | |
2975 | ||
2976 | Whenever you leave out the alignment factor in an @code{aligned} attribute | |
2977 | specification, the compiler automatically sets the alignment for the declared | |
2978 | variable or field to the largest alignment which is ever used for any data | |
2979 | type on the target machine you are compiling for. Doing this can often make | |
2980 | copy operations more efficient, because the compiler can use whatever | |
2981 | instructions copy the biggest chunks of memory when performing copies to | |
2982 | or from the variables or fields that you have aligned this way. | |
2983 | ||
2984 | The @code{aligned} attribute can only increase the alignment; but you | |
2985 | can decrease it by specifying @code{packed} as well. See below. | |
2986 | ||
2987 | Note that the effectiveness of @code{aligned} attributes may be limited | |
2988 | by inherent limitations in your linker. On many systems, the linker is | |
2989 | only able to arrange for variables to be aligned up to a certain maximum | |
2990 | alignment. (For some linkers, the maximum supported alignment may | |
2991 | be very very small.) If your linker is only able to align variables | |
2992 | up to a maximum of 8 byte alignment, then specifying @code{aligned(16)} | |
2993 | in an @code{__attribute__} will still only provide you with 8 byte | |
2994 | alignment. See your linker documentation for further information. | |
2995 | ||
2996 | @item mode (@var{mode}) | |
2997 | @cindex @code{mode} attribute | |
2998 | This attribute specifies the data type for the declaration---whichever | |
2999 | type corresponds to the mode @var{mode}. This in effect lets you | |
3000 | request an integer or floating point type according to its width. | |
3001 | ||
3002 | You may also specify a mode of @samp{byte} or @samp{__byte__} to | |
3003 | indicate the mode corresponding to a one-byte integer, @samp{word} or | |
3004 | @samp{__word__} for the mode of a one-word integer, and @samp{pointer} | |
3005 | or @samp{__pointer__} for the mode used to represent pointers. | |
3006 | ||
3007 | @item nocommon | |
3008 | @cindex @code{nocommon} attribute | |
84330467 | 3009 | @opindex fno-common |
f0523f02 | 3010 | This attribute specifies requests GCC not to place a variable |
c1f7febf | 3011 | ``common'' but instead to allocate space for it directly. If you |
f0523f02 | 3012 | specify the @option{-fno-common} flag, GCC will do this for all |
c1f7febf RK |
3013 | variables. |
3014 | ||
3015 | Specifying the @code{nocommon} attribute for a variable provides an | |
3016 | initialization of zeros. A variable may only be initialized in one | |
3017 | source file. | |
3018 | ||
3019 | @item packed | |
3020 | @cindex @code{packed} attribute | |
3021 | The @code{packed} attribute specifies that a variable or structure field | |
3022 | should have the smallest possible alignment---one byte for a variable, | |
3023 | and one bit for a field, unless you specify a larger value with the | |
3024 | @code{aligned} attribute. | |
3025 | ||
3026 | Here is a structure in which the field @code{x} is packed, so that it | |
3027 | immediately follows @code{a}: | |
3028 | ||
3029 | @example | |
3030 | struct foo | |
3031 | @{ | |
3032 | char a; | |
3033 | int x[2] __attribute__ ((packed)); | |
3034 | @}; | |
3035 | @end example | |
3036 | ||
84330467 | 3037 | @item section ("@var{section-name}") |
c1f7febf RK |
3038 | @cindex @code{section} variable attribute |
3039 | Normally, the compiler places the objects it generates in sections like | |
3040 | @code{data} and @code{bss}. Sometimes, however, you need additional sections, | |
3041 | or you need certain particular variables to appear in special sections, | |
3042 | for example to map to special hardware. The @code{section} | |
3043 | attribute specifies that a variable (or function) lives in a particular | |
3044 | section. For example, this small program uses several specific section names: | |
3045 | ||
3046 | @smallexample | |
3047 | struct duart a __attribute__ ((section ("DUART_A"))) = @{ 0 @}; | |
3048 | struct duart b __attribute__ ((section ("DUART_B"))) = @{ 0 @}; | |
3049 | char stack[10000] __attribute__ ((section ("STACK"))) = @{ 0 @}; | |
3050 | int init_data __attribute__ ((section ("INITDATA"))) = 0; | |
3051 | ||
3052 | main() | |
3053 | @{ | |
3054 | /* Initialize stack pointer */ | |
3055 | init_sp (stack + sizeof (stack)); | |
3056 | ||
3057 | /* Initialize initialized data */ | |
3058 | memcpy (&init_data, &data, &edata - &data); | |
3059 | ||
3060 | /* Turn on the serial ports */ | |
3061 | init_duart (&a); | |
3062 | init_duart (&b); | |
3063 | @} | |
3064 | @end smallexample | |
3065 | ||
3066 | @noindent | |
3067 | Use the @code{section} attribute with an @emph{initialized} definition | |
f0523f02 | 3068 | of a @emph{global} variable, as shown in the example. GCC issues |
c1f7febf RK |
3069 | a warning and otherwise ignores the @code{section} attribute in |
3070 | uninitialized variable declarations. | |
3071 | ||
3072 | You may only use the @code{section} attribute with a fully initialized | |
3073 | global definition because of the way linkers work. The linker requires | |
3074 | each object be defined once, with the exception that uninitialized | |
3075 | variables tentatively go in the @code{common} (or @code{bss}) section | |
84330467 JM |
3076 | and can be multiply ``defined''. You can force a variable to be |
3077 | initialized with the @option{-fno-common} flag or the @code{nocommon} | |
c1f7febf RK |
3078 | attribute. |
3079 | ||
3080 | Some file formats do not support arbitrary sections so the @code{section} | |
3081 | attribute is not available on all platforms. | |
3082 | If you need to map the entire contents of a module to a particular | |
3083 | section, consider using the facilities of the linker instead. | |
3084 | ||
593d3a34 MK |
3085 | @item shared |
3086 | @cindex @code{shared} variable attribute | |
02f52e19 AJ |
3087 | On Windows NT, in addition to putting variable definitions in a named |
3088 | section, the section can also be shared among all running copies of an | |
161d7b59 | 3089 | executable or DLL@. For example, this small program defines shared data |
84330467 | 3090 | by putting it in a named section @code{shared} and marking the section |
593d3a34 MK |
3091 | shareable: |
3092 | ||
3093 | @smallexample | |
3094 | int foo __attribute__((section ("shared"), shared)) = 0; | |
3095 | ||
3096 | int | |
3097 | main() | |
3098 | @{ | |
310668e8 JM |
3099 | /* Read and write foo. All running |
3100 | copies see the same value. */ | |
593d3a34 MK |
3101 | return 0; |
3102 | @} | |
3103 | @end smallexample | |
3104 | ||
3105 | @noindent | |
3106 | You may only use the @code{shared} attribute along with @code{section} | |
02f52e19 | 3107 | attribute with a fully initialized global definition because of the way |
593d3a34 MK |
3108 | linkers work. See @code{section} attribute for more information. |
3109 | ||
161d7b59 | 3110 | The @code{shared} attribute is only available on Windows NT@. |
593d3a34 | 3111 | |
c1f7febf RK |
3112 | @item transparent_union |
3113 | This attribute, attached to a function parameter which is a union, means | |
3114 | that the corresponding argument may have the type of any union member, | |
3115 | but the argument is passed as if its type were that of the first union | |
3116 | member. For more details see @xref{Type Attributes}. You can also use | |
3117 | this attribute on a @code{typedef} for a union data type; then it | |
3118 | applies to all function parameters with that type. | |
3119 | ||
3120 | @item unused | |
3121 | This attribute, attached to a variable, means that the variable is meant | |
f0523f02 | 3122 | to be possibly unused. GCC will not produce a warning for this |
c1f7febf RK |
3123 | variable. |
3124 | ||
e23bd218 IR |
3125 | @item deprecated |
3126 | The @code{deprecated} attribute results in a warning if the variable | |
3127 | is used anywhere in the source file. This is useful when identifying | |
3128 | variables that are expected to be removed in a future version of a | |
3129 | program. The warning also includes the location of the declaration | |
3130 | of the deprecated variable, to enable users to easily find further | |
3131 | information about why the variable is deprecated, or what they should | |
3132 | do instead. Note that the warnings only occurs for uses: | |
3133 | ||
3134 | @smallexample | |
3135 | extern int old_var __attribute__ ((deprecated)); | |
3136 | extern int old_var; | |
3137 | int new_fn () @{ return old_var; @} | |
3138 | @end smallexample | |
3139 | ||
3140 | results in a warning on line 3 but not line 2. | |
3141 | ||
3142 | The @code{deprecated} attribute can also be used for functions and | |
3143 | types (@pxref{Function Attributes}, @pxref{Type Attributes}.) | |
3144 | ||
1b9191d2 AH |
3145 | @item vector_size (@var{bytes}) |
3146 | This attribute specifies the vector size for the variable, measured in | |
3147 | bytes. For example, the declaration: | |
3148 | ||
3149 | @smallexample | |
3150 | int foo __attribute__ ((vector_size (16))); | |
3151 | @end smallexample | |
3152 | ||
3153 | @noindent | |
3154 | causes the compiler to set the mode for @code{foo}, to be 16 bytes, | |
3155 | divided into @code{int} sized units. Assuming a 32-bit int (a vector of | |
3156 | 4 units of 4 bytes), the corresponding mode of @code{foo} will be V4SI@. | |
3157 | ||
3158 | This attribute is only applicable to integral and float scalars, | |
3159 | although arrays, pointers, and function return values are allowed in | |
3160 | conjunction with this construct. | |
3161 | ||
3162 | Aggregates with this attribute are invalid, even if they are of the same | |
3163 | size as a corresponding scalar. For example, the declaration: | |
3164 | ||
3165 | @smallexample | |
ad706f54 | 3166 | struct S @{ int a; @}; |
1b9191d2 AH |
3167 | struct S __attribute__ ((vector_size (16))) foo; |
3168 | @end smallexample | |
3169 | ||
3170 | @noindent | |
3171 | is invalid even if the size of the structure is the same as the size of | |
3172 | the @code{int}. | |
3173 | ||
c1f7febf RK |
3174 | @item weak |
3175 | The @code{weak} attribute is described in @xref{Function Attributes}. | |
845da534 DE |
3176 | |
3177 | @item model (@var{model-name}) | |
3178 | @cindex variable addressability on the M32R/D | |
3179 | Use this attribute on the M32R/D to set the addressability of an object. | |
3180 | The identifier @var{model-name} is one of @code{small}, @code{medium}, | |
3181 | or @code{large}, representing each of the code models. | |
3182 | ||
3183 | Small model objects live in the lower 16MB of memory (so that their | |
3184 | addresses can be loaded with the @code{ld24} instruction). | |
3185 | ||
02f52e19 | 3186 | Medium and large model objects may live anywhere in the 32-bit address space |
845da534 DE |
3187 | (the compiler will generate @code{seth/add3} instructions to load their |
3188 | addresses). | |
3189 | ||
fe77449a DR |
3190 | @subsection i386 Variable Attributes |
3191 | ||
3192 | Two attributes are currently defined for i386 configurations: | |
3193 | @code{ms_struct} and @code{gcc_struct} | |
3194 | ||
3195 | @item ms_struct | |
3196 | @itemx gcc_struct | |
3197 | @cindex @code{ms_struct} | |
3198 | @cindex @code{gcc_struct} | |
3199 | ||
3200 | If @code{packed} is used on a structure, or if bit-fields are used | |
3201 | it may be that the Microsoft ABI packs them differently | |
3202 | than GCC would normally pack them. Particularly when moving packed | |
3203 | data between functions compiled with GCC and the native Microsoft compiler | |
3204 | (either via function call or as data in a file), it may be necessary to access | |
3205 | either format. | |
3206 | ||
3207 | Currently @option{-m[no-]ms-bitfields} is provided for the Windows X86 | |
3208 | compilers to match the native Microsoft compiler. | |
3209 | ||
c1f7febf RK |
3210 | @end table |
3211 | ||
3212 | To specify multiple attributes, separate them by commas within the | |
3213 | double parentheses: for example, @samp{__attribute__ ((aligned (16), | |
3214 | packed))}. | |
3215 | ||
3216 | @node Type Attributes | |
3217 | @section Specifying Attributes of Types | |
3218 | @cindex attribute of types | |
3219 | @cindex type attributes | |
3220 | ||
3221 | The keyword @code{__attribute__} allows you to specify special | |
3222 | attributes of @code{struct} and @code{union} types when you define such | |
3223 | types. This keyword is followed by an attribute specification inside | |
d18b1ed8 | 3224 | double parentheses. Six attributes are currently defined for types: |
e23bd218 | 3225 | @code{aligned}, @code{packed}, @code{transparent_union}, @code{unused}, |
d18b1ed8 OS |
3226 | @code{deprecated} and @code{may_alias}. Other attributes are defined for |
3227 | functions (@pxref{Function Attributes}) and for variables | |
3228 | (@pxref{Variable Attributes}). | |
c1f7febf RK |
3229 | |
3230 | You may also specify any one of these attributes with @samp{__} | |
3231 | preceding and following its keyword. This allows you to use these | |
3232 | attributes in header files without being concerned about a possible | |
3233 | macro of the same name. For example, you may use @code{__aligned__} | |
3234 | instead of @code{aligned}. | |
3235 | ||
3236 | You may specify the @code{aligned} and @code{transparent_union} | |
3237 | attributes either in a @code{typedef} declaration or just past the | |
3238 | closing curly brace of a complete enum, struct or union type | |
3239 | @emph{definition} and the @code{packed} attribute only past the closing | |
3240 | brace of a definition. | |
3241 | ||
4051959b JM |
3242 | You may also specify attributes between the enum, struct or union |
3243 | tag and the name of the type rather than after the closing brace. | |
3244 | ||
2c5e91d2 JM |
3245 | @xref{Attribute Syntax}, for details of the exact syntax for using |
3246 | attributes. | |
3247 | ||
c1f7febf RK |
3248 | @table @code |
3249 | @cindex @code{aligned} attribute | |
3250 | @item aligned (@var{alignment}) | |
3251 | This attribute specifies a minimum alignment (in bytes) for variables | |
3252 | of the specified type. For example, the declarations: | |
3253 | ||
3254 | @smallexample | |
f69eecfb JL |
3255 | struct S @{ short f[3]; @} __attribute__ ((aligned (8))); |
3256 | typedef int more_aligned_int __attribute__ ((aligned (8))); | |
c1f7febf RK |
3257 | @end smallexample |
3258 | ||
3259 | @noindent | |
d863830b | 3260 | force the compiler to insure (as far as it can) that each variable whose |
c1f7febf | 3261 | type is @code{struct S} or @code{more_aligned_int} will be allocated and |
981f6289 | 3262 | aligned @emph{at least} on a 8-byte boundary. On a SPARC, having all |
c1f7febf RK |
3263 | variables of type @code{struct S} aligned to 8-byte boundaries allows |
3264 | the compiler to use the @code{ldd} and @code{std} (doubleword load and | |
3265 | store) instructions when copying one variable of type @code{struct S} to | |
3266 | another, thus improving run-time efficiency. | |
3267 | ||
3268 | Note that the alignment of any given @code{struct} or @code{union} type | |
5490d604 | 3269 | is required by the ISO C standard to be at least a perfect multiple of |
c1f7febf RK |
3270 | the lowest common multiple of the alignments of all of the members of |
3271 | the @code{struct} or @code{union} in question. This means that you @emph{can} | |
3272 | effectively adjust the alignment of a @code{struct} or @code{union} | |
3273 | type by attaching an @code{aligned} attribute to any one of the members | |
3274 | of such a type, but the notation illustrated in the example above is a | |
3275 | more obvious, intuitive, and readable way to request the compiler to | |
3276 | adjust the alignment of an entire @code{struct} or @code{union} type. | |
3277 | ||
3278 | As in the preceding example, you can explicitly specify the alignment | |
3279 | (in bytes) that you wish the compiler to use for a given @code{struct} | |
3280 | or @code{union} type. Alternatively, you can leave out the alignment factor | |
3281 | and just ask the compiler to align a type to the maximum | |
3282 | useful alignment for the target machine you are compiling for. For | |
3283 | example, you could write: | |
3284 | ||
3285 | @smallexample | |
3286 | struct S @{ short f[3]; @} __attribute__ ((aligned)); | |
3287 | @end smallexample | |
3288 | ||
3289 | Whenever you leave out the alignment factor in an @code{aligned} | |
3290 | attribute specification, the compiler automatically sets the alignment | |
3291 | for the type to the largest alignment which is ever used for any data | |
3292 | type on the target machine you are compiling for. Doing this can often | |
3293 | make copy operations more efficient, because the compiler can use | |
3294 | whatever instructions copy the biggest chunks of memory when performing | |
3295 | copies to or from the variables which have types that you have aligned | |
3296 | this way. | |
3297 | ||
3298 | In the example above, if the size of each @code{short} is 2 bytes, then | |
3299 | the size of the entire @code{struct S} type is 6 bytes. The smallest | |
3300 | power of two which is greater than or equal to that is 8, so the | |
3301 | compiler sets the alignment for the entire @code{struct S} type to 8 | |
3302 | bytes. | |
3303 | ||
3304 | Note that although you can ask the compiler to select a time-efficient | |
3305 | alignment for a given type and then declare only individual stand-alone | |
3306 | objects of that type, the compiler's ability to select a time-efficient | |
3307 | alignment is primarily useful only when you plan to create arrays of | |
3308 | variables having the relevant (efficiently aligned) type. If you | |
3309 | declare or use arrays of variables of an efficiently-aligned type, then | |
3310 | it is likely that your program will also be doing pointer arithmetic (or | |
3311 | subscripting, which amounts to the same thing) on pointers to the | |
3312 | relevant type, and the code that the compiler generates for these | |
3313 | pointer arithmetic operations will often be more efficient for | |
3314 | efficiently-aligned types than for other types. | |
3315 | ||
3316 | The @code{aligned} attribute can only increase the alignment; but you | |
3317 | can decrease it by specifying @code{packed} as well. See below. | |
3318 | ||
3319 | Note that the effectiveness of @code{aligned} attributes may be limited | |
3320 | by inherent limitations in your linker. On many systems, the linker is | |
3321 | only able to arrange for variables to be aligned up to a certain maximum | |
3322 | alignment. (For some linkers, the maximum supported alignment may | |
3323 | be very very small.) If your linker is only able to align variables | |
3324 | up to a maximum of 8 byte alignment, then specifying @code{aligned(16)} | |
3325 | in an @code{__attribute__} will still only provide you with 8 byte | |
3326 | alignment. See your linker documentation for further information. | |
3327 | ||
3328 | @item packed | |
3329 | This attribute, attached to an @code{enum}, @code{struct}, or | |
3330 | @code{union} type definition, specified that the minimum required memory | |
3331 | be used to represent the type. | |
3332 | ||
84330467 | 3333 | @opindex fshort-enums |
c1f7febf RK |
3334 | Specifying this attribute for @code{struct} and @code{union} types is |
3335 | equivalent to specifying the @code{packed} attribute on each of the | |
84330467 | 3336 | structure or union members. Specifying the @option{-fshort-enums} |
c1f7febf RK |
3337 | flag on the line is equivalent to specifying the @code{packed} |
3338 | attribute on all @code{enum} definitions. | |
3339 | ||
3340 | You may only specify this attribute after a closing curly brace on an | |
1cd4bca9 BK |
3341 | @code{enum} definition, not in a @code{typedef} declaration, unless that |
3342 | declaration also contains the definition of the @code{enum}. | |
c1f7febf RK |
3343 | |
3344 | @item transparent_union | |
3345 | This attribute, attached to a @code{union} type definition, indicates | |
3346 | that any function parameter having that union type causes calls to that | |
3347 | function to be treated in a special way. | |
3348 | ||
3349 | First, the argument corresponding to a transparent union type can be of | |
3350 | any type in the union; no cast is required. Also, if the union contains | |
3351 | a pointer type, the corresponding argument can be a null pointer | |
3352 | constant or a void pointer expression; and if the union contains a void | |
3353 | pointer type, the corresponding argument can be any pointer expression. | |
3354 | If the union member type is a pointer, qualifiers like @code{const} on | |
3355 | the referenced type must be respected, just as with normal pointer | |
3356 | conversions. | |
3357 | ||
3358 | Second, the argument is passed to the function using the calling | |
3359 | conventions of first member of the transparent union, not the calling | |
3360 | conventions of the union itself. All members of the union must have the | |
3361 | same machine representation; this is necessary for this argument passing | |
3362 | to work properly. | |
3363 | ||
3364 | Transparent unions are designed for library functions that have multiple | |
3365 | interfaces for compatibility reasons. For example, suppose the | |
3366 | @code{wait} function must accept either a value of type @code{int *} to | |
3367 | comply with Posix, or a value of type @code{union wait *} to comply with | |
3368 | the 4.1BSD interface. If @code{wait}'s parameter were @code{void *}, | |
3369 | @code{wait} would accept both kinds of arguments, but it would also | |
3370 | accept any other pointer type and this would make argument type checking | |
3371 | less useful. Instead, @code{<sys/wait.h>} might define the interface | |
3372 | as follows: | |
3373 | ||
3374 | @smallexample | |
3375 | typedef union | |
3376 | @{ | |
3377 | int *__ip; | |
3378 | union wait *__up; | |
3379 | @} wait_status_ptr_t __attribute__ ((__transparent_union__)); | |
3380 | ||
3381 | pid_t wait (wait_status_ptr_t); | |
3382 | @end smallexample | |
3383 | ||
3384 | This interface allows either @code{int *} or @code{union wait *} | |
3385 | arguments to be passed, using the @code{int *} calling convention. | |
3386 | The program can call @code{wait} with arguments of either type: | |
3387 | ||
3388 | @example | |
3389 | int w1 () @{ int w; return wait (&w); @} | |
3390 | int w2 () @{ union wait w; return wait (&w); @} | |
3391 | @end example | |
3392 | ||
3393 | With this interface, @code{wait}'s implementation might look like this: | |
3394 | ||
3395 | @example | |
3396 | pid_t wait (wait_status_ptr_t p) | |
3397 | @{ | |
3398 | return waitpid (-1, p.__ip, 0); | |
3399 | @} | |
3400 | @end example | |
d863830b JL |
3401 | |
3402 | @item unused | |
3403 | When attached to a type (including a @code{union} or a @code{struct}), | |
3404 | this attribute means that variables of that type are meant to appear | |
f0523f02 | 3405 | possibly unused. GCC will not produce a warning for any variables of |
d863830b JL |
3406 | that type, even if the variable appears to do nothing. This is often |
3407 | the case with lock or thread classes, which are usually defined and then | |
3408 | not referenced, but contain constructors and destructors that have | |
956d6950 | 3409 | nontrivial bookkeeping functions. |
d863830b | 3410 | |
e23bd218 IR |
3411 | @item deprecated |
3412 | The @code{deprecated} attribute results in a warning if the type | |
3413 | is used anywhere in the source file. This is useful when identifying | |
3414 | types that are expected to be removed in a future version of a program. | |
3415 | If possible, the warning also includes the location of the declaration | |
3416 | of the deprecated type, to enable users to easily find further | |
3417 | information about why the type is deprecated, or what they should do | |
3418 | instead. Note that the warnings only occur for uses and then only | |
adc9fe67 | 3419 | if the type is being applied to an identifier that itself is not being |
e23bd218 IR |
3420 | declared as deprecated. |
3421 | ||
3422 | @smallexample | |
3423 | typedef int T1 __attribute__ ((deprecated)); | |
3424 | T1 x; | |
3425 | typedef T1 T2; | |
3426 | T2 y; | |
3427 | typedef T1 T3 __attribute__ ((deprecated)); | |
3428 | T3 z __attribute__ ((deprecated)); | |
3429 | @end smallexample | |
3430 | ||
3431 | results in a warning on line 2 and 3 but not lines 4, 5, or 6. No | |
3432 | warning is issued for line 4 because T2 is not explicitly | |
3433 | deprecated. Line 5 has no warning because T3 is explicitly | |
3434 | deprecated. Similarly for line 6. | |
3435 | ||
3436 | The @code{deprecated} attribute can also be used for functions and | |
3437 | variables (@pxref{Function Attributes}, @pxref{Variable Attributes}.) | |
3438 | ||
d18b1ed8 OS |
3439 | @item may_alias |
3440 | Accesses to objects with types with this attribute are not subjected to | |
3441 | type-based alias analysis, but are instead assumed to be able to alias | |
3442 | any other type of objects, just like the @code{char} type. See | |
3443 | @option{-fstrict-aliasing} for more information on aliasing issues. | |
3444 | ||
3445 | Example of use: | |
3446 | ||
478c9e72 | 3447 | @smallexample |
d18b1ed8 OS |
3448 | typedef short __attribute__((__may_alias__)) short_a; |
3449 | ||
3450 | int | |
3451 | main (void) | |
3452 | @{ | |
3453 | int a = 0x12345678; | |
3454 | short_a *b = (short_a *) &a; | |
3455 | ||
3456 | b[1] = 0; | |
3457 | ||
3458 | if (a == 0x12345678) | |
3459 | abort(); | |
3460 | ||
3461 | exit(0); | |
3462 | @} | |
478c9e72 | 3463 | @end smallexample |
d18b1ed8 OS |
3464 | |
3465 | If you replaced @code{short_a} with @code{short} in the variable | |
3466 | declaration, the above program would abort when compiled with | |
3467 | @option{-fstrict-aliasing}, which is on by default at @option{-O2} or | |
3468 | above in recent GCC versions. | |
fe77449a DR |
3469 | |
3470 | @subsection i386 Type Attributes | |
3471 | ||
3472 | Two attributes are currently defined for i386 configurations: | |
3473 | @code{ms_struct} and @code{gcc_struct} | |
3474 | ||
3475 | @item ms_struct | |
3476 | @itemx gcc_struct | |
3477 | @cindex @code{ms_struct} | |
3478 | @cindex @code{gcc_struct} | |
3479 | ||
3480 | If @code{packed} is used on a structure, or if bit-fields are used | |
3481 | it may be that the Microsoft ABI packs them differently | |
3482 | than GCC would normally pack them. Particularly when moving packed | |
3483 | data between functions compiled with GCC and the native Microsoft compiler | |
3484 | (either via function call or as data in a file), it may be necessary to access | |
3485 | either format. | |
3486 | ||
3487 | Currently @option{-m[no-]ms-bitfields} is provided for the Windows X86 | |
3488 | compilers to match the native Microsoft compiler. | |
c1f7febf RK |
3489 | @end table |
3490 | ||
3491 | To specify multiple attributes, separate them by commas within the | |
3492 | double parentheses: for example, @samp{__attribute__ ((aligned (16), | |
3493 | packed))}. | |
3494 | ||
3495 | @node Inline | |
3496 | @section An Inline Function is As Fast As a Macro | |
3497 | @cindex inline functions | |
3498 | @cindex integrating function code | |
3499 | @cindex open coding | |
3500 | @cindex macros, inline alternative | |
3501 | ||
f0523f02 | 3502 | By declaring a function @code{inline}, you can direct GCC to |
c1f7febf RK |
3503 | integrate that function's code into the code for its callers. This |
3504 | makes execution faster by eliminating the function-call overhead; in | |
3505 | addition, if any of the actual argument values are constant, their known | |
3506 | values may permit simplifications at compile time so that not all of the | |
3507 | inline function's code needs to be included. The effect on code size is | |
3508 | less predictable; object code may be larger or smaller with function | |
3509 | inlining, depending on the particular case. Inlining of functions is an | |
3510 | optimization and it really ``works'' only in optimizing compilation. If | |
84330467 | 3511 | you don't use @option{-O}, no function is really inline. |
c1f7febf | 3512 | |
4b404517 JM |
3513 | Inline functions are included in the ISO C99 standard, but there are |
3514 | currently substantial differences between what GCC implements and what | |
3515 | the ISO C99 standard requires. | |
3516 | ||
c1f7febf RK |
3517 | To declare a function inline, use the @code{inline} keyword in its |
3518 | declaration, like this: | |
3519 | ||
3520 | @example | |
3521 | inline int | |
3522 | inc (int *a) | |
3523 | @{ | |
3524 | (*a)++; | |
3525 | @} | |
3526 | @end example | |
3527 | ||
5490d604 | 3528 | (If you are writing a header file to be included in ISO C programs, write |
c1f7febf | 3529 | @code{__inline__} instead of @code{inline}. @xref{Alternate Keywords}.) |
c1f7febf | 3530 | You can also make all ``simple enough'' functions inline with the option |
84330467 | 3531 | @option{-finline-functions}. |
247b14bd | 3532 | |
84330467 | 3533 | @opindex Winline |
247b14bd RH |
3534 | Note that certain usages in a function definition can make it unsuitable |
3535 | for inline substitution. Among these usages are: use of varargs, use of | |
3536 | alloca, use of variable sized data types (@pxref{Variable Length}), | |
3537 | use of computed goto (@pxref{Labels as Values}), use of nonlocal goto, | |
84330467 | 3538 | and nested functions (@pxref{Nested Functions}). Using @option{-Winline} |
247b14bd RH |
3539 | will warn when a function marked @code{inline} could not be substituted, |
3540 | and will give the reason for the failure. | |
c1f7febf | 3541 | |
2147b154 | 3542 | Note that in C and Objective-C, unlike C++, the @code{inline} keyword |
c1f7febf RK |
3543 | does not affect the linkage of the function. |
3544 | ||
3545 | @cindex automatic @code{inline} for C++ member fns | |
3546 | @cindex @code{inline} automatic for C++ member fns | |
3547 | @cindex member fns, automatically @code{inline} | |
3548 | @cindex C++ member fns, automatically @code{inline} | |
84330467 | 3549 | @opindex fno-default-inline |
f0523f02 | 3550 | GCC automatically inlines member functions defined within the class |
c1f7febf | 3551 | body of C++ programs even if they are not explicitly declared |
84330467 | 3552 | @code{inline}. (You can override this with @option{-fno-default-inline}; |
c1f7febf RK |
3553 | @pxref{C++ Dialect Options,,Options Controlling C++ Dialect}.) |
3554 | ||
3555 | @cindex inline functions, omission of | |
84330467 | 3556 | @opindex fkeep-inline-functions |
c1f7febf RK |
3557 | When a function is both inline and @code{static}, if all calls to the |
3558 | function are integrated into the caller, and the function's address is | |
3559 | never used, then the function's own assembler code is never referenced. | |
f0523f02 | 3560 | In this case, GCC does not actually output assembler code for the |
84330467 | 3561 | function, unless you specify the option @option{-fkeep-inline-functions}. |
c1f7febf RK |
3562 | Some calls cannot be integrated for various reasons (in particular, |
3563 | calls that precede the function's definition cannot be integrated, and | |
3564 | neither can recursive calls within the definition). If there is a | |
3565 | nonintegrated call, then the function is compiled to assembler code as | |
3566 | usual. The function must also be compiled as usual if the program | |
3567 | refers to its address, because that can't be inlined. | |
3568 | ||
3569 | @cindex non-static inline function | |
3570 | When an inline function is not @code{static}, then the compiler must assume | |
3571 | that there may be calls from other source files; since a global symbol can | |
3572 | be defined only once in any program, the function must not be defined in | |
3573 | the other source files, so the calls therein cannot be integrated. | |
3574 | Therefore, a non-@code{static} inline function is always compiled on its | |
3575 | own in the usual fashion. | |
3576 | ||
3577 | If you specify both @code{inline} and @code{extern} in the function | |
3578 | definition, then the definition is used only for inlining. In no case | |
3579 | is the function compiled on its own, not even if you refer to its | |
3580 | address explicitly. Such an address becomes an external reference, as | |
3581 | if you had only declared the function, and had not defined it. | |
3582 | ||
3583 | This combination of @code{inline} and @code{extern} has almost the | |
3584 | effect of a macro. The way to use it is to put a function definition in | |
3585 | a header file with these keywords, and put another copy of the | |
3586 | definition (lacking @code{inline} and @code{extern}) in a library file. | |
3587 | The definition in the header file will cause most calls to the function | |
3588 | to be inlined. If any uses of the function remain, they will refer to | |
3589 | the single copy in the library. | |
3590 | ||
4b404517 JM |
3591 | For future compatibility with when GCC implements ISO C99 semantics for |
3592 | inline functions, it is best to use @code{static inline} only. (The | |
3593 | existing semantics will remain available when @option{-std=gnu89} is | |
3594 | specified, but eventually the default will be @option{-std=gnu99} and | |
3595 | that will implement the C99 semantics, though it does not do so yet.) | |
3596 | ||
6aa77e6c AH |
3597 | GCC does not inline any functions when not optimizing unless you specify |
3598 | the @samp{always_inline} attribute for the function, like this: | |
3599 | ||
3600 | @example | |
3601 | /* Prototype. */ | |
3602 | inline void foo (const char) __attribute__((always_inline)); | |
3603 | @end example | |
c1f7febf RK |
3604 | |
3605 | @node Extended Asm | |
3606 | @section Assembler Instructions with C Expression Operands | |
3607 | @cindex extended @code{asm} | |
3608 | @cindex @code{asm} expressions | |
3609 | @cindex assembler instructions | |
3610 | @cindex registers | |
3611 | ||
c85f7c16 JL |
3612 | In an assembler instruction using @code{asm}, you can specify the |
3613 | operands of the instruction using C expressions. This means you need not | |
3614 | guess which registers or memory locations will contain the data you want | |
c1f7febf RK |
3615 | to use. |
3616 | ||
c85f7c16 JL |
3617 | You must specify an assembler instruction template much like what |
3618 | appears in a machine description, plus an operand constraint string for | |
3619 | each operand. | |
c1f7febf RK |
3620 | |
3621 | For example, here is how to use the 68881's @code{fsinx} instruction: | |
3622 | ||
3623 | @example | |
3624 | asm ("fsinx %1,%0" : "=f" (result) : "f" (angle)); | |
3625 | @end example | |
3626 | ||
3627 | @noindent | |
3628 | Here @code{angle} is the C expression for the input operand while | |
3629 | @code{result} is that of the output operand. Each has @samp{"f"} as its | |
c85f7c16 JL |
3630 | operand constraint, saying that a floating point register is required. |
3631 | The @samp{=} in @samp{=f} indicates that the operand is an output; all | |
3632 | output operands' constraints must use @samp{=}. The constraints use the | |
3633 | same language used in the machine description (@pxref{Constraints}). | |
3634 | ||
3635 | Each operand is described by an operand-constraint string followed by | |
3636 | the C expression in parentheses. A colon separates the assembler | |
3637 | template from the first output operand and another separates the last | |
3638 | output operand from the first input, if any. Commas separate the | |
84b72302 RH |
3639 | operands within each group. The total number of operands is currently |
3640 | limited to 30; this limitation may be lifted in some future version of | |
3641 | GCC. | |
c85f7c16 JL |
3642 | |
3643 | If there are no output operands but there are input operands, you must | |
3644 | place two consecutive colons surrounding the place where the output | |
c1f7febf RK |
3645 | operands would go. |
3646 | ||
84b72302 RH |
3647 | As of GCC version 3.1, it is also possible to specify input and output |
3648 | operands using symbolic names which can be referenced within the | |
3649 | assembler code. These names are specified inside square brackets | |
3650 | preceding the constraint string, and can be referenced inside the | |
3651 | assembler code using @code{%[@var{name}]} instead of a percentage sign | |
3652 | followed by the operand number. Using named operands the above example | |
3653 | could look like: | |
3654 | ||
3655 | @example | |
3656 | asm ("fsinx %[angle],%[output]" | |
3657 | : [output] "=f" (result) | |
3658 | : [angle] "f" (angle)); | |
3659 | @end example | |
3660 | ||
3661 | @noindent | |
3662 | Note that the symbolic operand names have no relation whatsoever to | |
3663 | other C identifiers. You may use any name you like, even those of | |
3664 | existing C symbols, but must ensure that no two operands within the same | |
3665 | assembler construct use the same symbolic name. | |
3666 | ||
c1f7febf | 3667 | Output operand expressions must be lvalues; the compiler can check this. |
c85f7c16 JL |
3668 | The input operands need not be lvalues. The compiler cannot check |
3669 | whether the operands have data types that are reasonable for the | |
3670 | instruction being executed. It does not parse the assembler instruction | |
3671 | template and does not know what it means or even whether it is valid | |
3672 | assembler input. The extended @code{asm} feature is most often used for | |
3673 | machine instructions the compiler itself does not know exist. If | |
3674 | the output expression cannot be directly addressed (for example, it is a | |
f0523f02 | 3675 | bit-field), your constraint must allow a register. In that case, GCC |
c85f7c16 JL |
3676 | will use the register as the output of the @code{asm}, and then store |
3677 | that register into the output. | |
3678 | ||
f0523f02 | 3679 | The ordinary output operands must be write-only; GCC will assume that |
c85f7c16 JL |
3680 | the values in these operands before the instruction are dead and need |
3681 | not be generated. Extended asm supports input-output or read-write | |
3682 | operands. Use the constraint character @samp{+} to indicate such an | |
3683 | operand and list it with the output operands. | |
3684 | ||
3685 | When the constraints for the read-write operand (or the operand in which | |
3686 | only some of the bits are to be changed) allows a register, you may, as | |
3687 | an alternative, logically split its function into two separate operands, | |
3688 | one input operand and one write-only output operand. The connection | |
3689 | between them is expressed by constraints which say they need to be in | |
3690 | the same location when the instruction executes. You can use the same C | |
3691 | expression for both operands, or different expressions. For example, | |
3692 | here we write the (fictitious) @samp{combine} instruction with | |
3693 | @code{bar} as its read-only source operand and @code{foo} as its | |
3694 | read-write destination: | |
c1f7febf RK |
3695 | |
3696 | @example | |
3697 | asm ("combine %2,%0" : "=r" (foo) : "0" (foo), "g" (bar)); | |
3698 | @end example | |
3699 | ||
3700 | @noindent | |
c85f7c16 | 3701 | The constraint @samp{"0"} for operand 1 says that it must occupy the |
84b72302 RH |
3702 | same location as operand 0. A number in constraint is allowed only in |
3703 | an input operand and it must refer to an output operand. | |
c1f7febf | 3704 | |
84b72302 | 3705 | Only a number in the constraint can guarantee that one operand will be in |
c85f7c16 JL |
3706 | the same place as another. The mere fact that @code{foo} is the value |
3707 | of both operands is not enough to guarantee that they will be in the | |
3708 | same place in the generated assembler code. The following would not | |
3709 | work reliably: | |
c1f7febf RK |
3710 | |
3711 | @example | |
3712 | asm ("combine %2,%0" : "=r" (foo) : "r" (foo), "g" (bar)); | |
3713 | @end example | |
3714 | ||
3715 | Various optimizations or reloading could cause operands 0 and 1 to be in | |
f0523f02 | 3716 | different registers; GCC knows no reason not to do so. For example, the |
c1f7febf RK |
3717 | compiler might find a copy of the value of @code{foo} in one register and |
3718 | use it for operand 1, but generate the output operand 0 in a different | |
3719 | register (copying it afterward to @code{foo}'s own address). Of course, | |
3720 | since the register for operand 1 is not even mentioned in the assembler | |
f0523f02 | 3721 | code, the result will not work, but GCC can't tell that. |
c1f7febf | 3722 | |
84b72302 RH |
3723 | As of GCC version 3.1, one may write @code{[@var{name}]} instead of |
3724 | the operand number for a matching constraint. For example: | |
3725 | ||
3726 | @example | |
3727 | asm ("cmoveq %1,%2,%[result]" | |
3728 | : [result] "=r"(result) | |
3729 | : "r" (test), "r"(new), "[result]"(old)); | |
3730 | @end example | |
3731 | ||
c85f7c16 JL |
3732 | Some instructions clobber specific hard registers. To describe this, |
3733 | write a third colon after the input operands, followed by the names of | |
3734 | the clobbered hard registers (given as strings). Here is a realistic | |
3735 | example for the VAX: | |
c1f7febf RK |
3736 | |
3737 | @example | |
3738 | asm volatile ("movc3 %0,%1,%2" | |
3739 | : /* no outputs */ | |
3740 | : "g" (from), "g" (to), "g" (count) | |
3741 | : "r0", "r1", "r2", "r3", "r4", "r5"); | |
3742 | @end example | |
3743 | ||
c5c76735 JL |
3744 | You may not write a clobber description in a way that overlaps with an |
3745 | input or output operand. For example, you may not have an operand | |
3746 | describing a register class with one member if you mention that register | |
acb5d088 HPN |
3747 | in the clobber list. Variables declared to live in specific registers |
3748 | (@pxref{Explicit Reg Vars}), and used as asm input or output operands must | |
3749 | have no part mentioned in the clobber description. | |
3750 | There is no way for you to specify that an input | |
c5c76735 JL |
3751 | operand is modified without also specifying it as an output |
3752 | operand. Note that if all the output operands you specify are for this | |
3753 | purpose (and hence unused), you will then also need to specify | |
3754 | @code{volatile} for the @code{asm} construct, as described below, to | |
f0523f02 | 3755 | prevent GCC from deleting the @code{asm} statement as unused. |
8fe1938e | 3756 | |
c1f7febf | 3757 | If you refer to a particular hardware register from the assembler code, |
c85f7c16 JL |
3758 | you will probably have to list the register after the third colon to |
3759 | tell the compiler the register's value is modified. In some assemblers, | |
3760 | the register names begin with @samp{%}; to produce one @samp{%} in the | |
3761 | assembler code, you must write @samp{%%} in the input. | |
3762 | ||
3763 | If your assembler instruction can alter the condition code register, add | |
f0523f02 | 3764 | @samp{cc} to the list of clobbered registers. GCC on some machines |
c85f7c16 JL |
3765 | represents the condition codes as a specific hardware register; |
3766 | @samp{cc} serves to name this register. On other machines, the | |
3767 | condition code is handled differently, and specifying @samp{cc} has no | |
3768 | effect. But it is valid no matter what the machine. | |
c1f7febf RK |
3769 | |
3770 | If your assembler instruction modifies memory in an unpredictable | |
c85f7c16 | 3771 | fashion, add @samp{memory} to the list of clobbered registers. This |
f0523f02 | 3772 | will cause GCC to not keep memory values cached in registers across |
dd40655a GK |
3773 | the assembler instruction. You will also want to add the |
3774 | @code{volatile} keyword if the memory affected is not listed in the | |
3775 | inputs or outputs of the @code{asm}, as the @samp{memory} clobber does | |
3776 | not count as a side-effect of the @code{asm}. | |
c1f7febf | 3777 | |
c85f7c16 | 3778 | You can put multiple assembler instructions together in a single |
8720914b HPN |
3779 | @code{asm} template, separated by the characters normally used in assembly |
3780 | code for the system. A combination that works in most places is a newline | |
3781 | to break the line, plus a tab character to move to the instruction field | |
3782 | (written as @samp{\n\t}). Sometimes semicolons can be used, if the | |
3783 | assembler allows semicolons as a line-breaking character. Note that some | |
3784 | assembler dialects use semicolons to start a comment. | |
3785 | The input operands are guaranteed not to use any of the clobbered | |
c85f7c16 JL |
3786 | registers, and neither will the output operands' addresses, so you can |
3787 | read and write the clobbered registers as many times as you like. Here | |
3788 | is an example of multiple instructions in a template; it assumes the | |
3789 | subroutine @code{_foo} accepts arguments in registers 9 and 10: | |
c1f7febf RK |
3790 | |
3791 | @example | |
8720914b | 3792 | asm ("movl %0,r9\n\tmovl %1,r10\n\tcall _foo" |
c1f7febf RK |
3793 | : /* no outputs */ |
3794 | : "g" (from), "g" (to) | |
3795 | : "r9", "r10"); | |
3796 | @end example | |
3797 | ||
f0523f02 | 3798 | Unless an output operand has the @samp{&} constraint modifier, GCC |
c85f7c16 JL |
3799 | may allocate it in the same register as an unrelated input operand, on |
3800 | the assumption the inputs are consumed before the outputs are produced. | |
c1f7febf RK |
3801 | This assumption may be false if the assembler code actually consists of |
3802 | more than one instruction. In such a case, use @samp{&} for each output | |
c85f7c16 | 3803 | operand that may not overlap an input. @xref{Modifiers}. |
c1f7febf | 3804 | |
c85f7c16 JL |
3805 | If you want to test the condition code produced by an assembler |
3806 | instruction, you must include a branch and a label in the @code{asm} | |
3807 | construct, as follows: | |
c1f7febf RK |
3808 | |
3809 | @example | |
8720914b | 3810 | asm ("clr %0\n\tfrob %1\n\tbeq 0f\n\tmov #1,%0\n0:" |
c1f7febf RK |
3811 | : "g" (result) |
3812 | : "g" (input)); | |
3813 | @end example | |
3814 | ||
3815 | @noindent | |
3816 | This assumes your assembler supports local labels, as the GNU assembler | |
3817 | and most Unix assemblers do. | |
3818 | ||
3819 | Speaking of labels, jumps from one @code{asm} to another are not | |
c85f7c16 JL |
3820 | supported. The compiler's optimizers do not know about these jumps, and |
3821 | therefore they cannot take account of them when deciding how to | |
c1f7febf RK |
3822 | optimize. |
3823 | ||
3824 | @cindex macros containing @code{asm} | |
3825 | Usually the most convenient way to use these @code{asm} instructions is to | |
3826 | encapsulate them in macros that look like functions. For example, | |
3827 | ||
3828 | @example | |
3829 | #define sin(x) \ | |
3830 | (@{ double __value, __arg = (x); \ | |
3831 | asm ("fsinx %1,%0": "=f" (__value): "f" (__arg)); \ | |
3832 | __value; @}) | |
3833 | @end example | |
3834 | ||
3835 | @noindent | |
3836 | Here the variable @code{__arg} is used to make sure that the instruction | |
3837 | operates on a proper @code{double} value, and to accept only those | |
3838 | arguments @code{x} which can convert automatically to a @code{double}. | |
3839 | ||
c85f7c16 JL |
3840 | Another way to make sure the instruction operates on the correct data |
3841 | type is to use a cast in the @code{asm}. This is different from using a | |
c1f7febf RK |
3842 | variable @code{__arg} in that it converts more different types. For |
3843 | example, if the desired type were @code{int}, casting the argument to | |
3844 | @code{int} would accept a pointer with no complaint, while assigning the | |
3845 | argument to an @code{int} variable named @code{__arg} would warn about | |
3846 | using a pointer unless the caller explicitly casts it. | |
3847 | ||
f0523f02 | 3848 | If an @code{asm} has output operands, GCC assumes for optimization |
c85f7c16 JL |
3849 | purposes the instruction has no side effects except to change the output |
3850 | operands. This does not mean instructions with a side effect cannot be | |
3851 | used, but you must be careful, because the compiler may eliminate them | |
3852 | if the output operands aren't used, or move them out of loops, or | |
3853 | replace two with one if they constitute a common subexpression. Also, | |
3854 | if your instruction does have a side effect on a variable that otherwise | |
3855 | appears not to change, the old value of the variable may be reused later | |
3856 | if it happens to be found in a register. | |
c1f7febf RK |
3857 | |
3858 | You can prevent an @code{asm} instruction from being deleted, moved | |
3859 | significantly, or combined, by writing the keyword @code{volatile} after | |
3860 | the @code{asm}. For example: | |
3861 | ||
3862 | @example | |
310668e8 JM |
3863 | #define get_and_set_priority(new) \ |
3864 | (@{ int __old; \ | |
3865 | asm volatile ("get_and_set_priority %0, %1" \ | |
3866 | : "=g" (__old) : "g" (new)); \ | |
c85f7c16 | 3867 | __old; @}) |
24f98470 | 3868 | @end example |
c1f7febf RK |
3869 | |
3870 | @noindent | |
f0523f02 | 3871 | If you write an @code{asm} instruction with no outputs, GCC will know |
c85f7c16 | 3872 | the instruction has side-effects and will not delete the instruction or |
e71b34aa | 3873 | move it outside of loops. |
c85f7c16 | 3874 | |
e71b34aa MM |
3875 | The @code{volatile} keyword indicates that the instruction has |
3876 | important side-effects. GCC will not delete a volatile @code{asm} if | |
3877 | it is reachable. (The instruction can still be deleted if GCC can | |
3878 | prove that control-flow will never reach the location of the | |
3879 | instruction.) In addition, GCC will not reschedule instructions | |
3880 | across a volatile @code{asm} instruction. For example: | |
3881 | ||
3882 | @example | |
bd78000b | 3883 | *(volatile int *)addr = foo; |
e71b34aa MM |
3884 | asm volatile ("eieio" : : ); |
3885 | @end example | |
3886 | ||
ebb48a4d | 3887 | @noindent |
e71b34aa MM |
3888 | Assume @code{addr} contains the address of a memory mapped device |
3889 | register. The PowerPC @code{eieio} instruction (Enforce In-order | |
aee96fe9 | 3890 | Execution of I/O) tells the CPU to make sure that the store to that |
161d7b59 | 3891 | device register happens before it issues any other I/O@. |
c1f7febf RK |
3892 | |
3893 | Note that even a volatile @code{asm} instruction can be moved in ways | |
3894 | that appear insignificant to the compiler, such as across jump | |
3895 | instructions. You can't expect a sequence of volatile @code{asm} | |
3896 | instructions to remain perfectly consecutive. If you want consecutive | |
e71b34aa MM |
3897 | output, use a single @code{asm}. Also, GCC will perform some |
3898 | optimizations across a volatile @code{asm} instruction; GCC does not | |
3899 | ``forget everything'' when it encounters a volatile @code{asm} | |
3900 | instruction the way some other compilers do. | |
3901 | ||
3902 | An @code{asm} instruction without any operands or clobbers (an ``old | |
3903 | style'' @code{asm}) will be treated identically to a volatile | |
3904 | @code{asm} instruction. | |
c1f7febf RK |
3905 | |
3906 | It is a natural idea to look for a way to give access to the condition | |
3907 | code left by the assembler instruction. However, when we attempted to | |
3908 | implement this, we found no way to make it work reliably. The problem | |
3909 | is that output operands might need reloading, which would result in | |
3910 | additional following ``store'' instructions. On most machines, these | |
3911 | instructions would alter the condition code before there was time to | |
3912 | test it. This problem doesn't arise for ordinary ``test'' and | |
3913 | ``compare'' instructions because they don't have any output operands. | |
3914 | ||
eda3fbbe GB |
3915 | For reasons similar to those described above, it is not possible to give |
3916 | an assembler instruction access to the condition code left by previous | |
3917 | instructions. | |
3918 | ||
5490d604 | 3919 | If you are writing a header file that should be includable in ISO C |
c1f7febf RK |
3920 | programs, write @code{__asm__} instead of @code{asm}. @xref{Alternate |
3921 | Keywords}. | |
3922 | ||
fe0ce426 JH |
3923 | @subsection i386 floating point asm operands |
3924 | ||
3925 | There are several rules on the usage of stack-like regs in | |
3926 | asm_operands insns. These rules apply only to the operands that are | |
3927 | stack-like regs: | |
3928 | ||
3929 | @enumerate | |
3930 | @item | |
3931 | Given a set of input regs that die in an asm_operands, it is | |
3932 | necessary to know which are implicitly popped by the asm, and | |
3933 | which must be explicitly popped by gcc. | |
3934 | ||
3935 | An input reg that is implicitly popped by the asm must be | |
3936 | explicitly clobbered, unless it is constrained to match an | |
3937 | output operand. | |
3938 | ||
3939 | @item | |
3940 | For any input reg that is implicitly popped by an asm, it is | |
3941 | necessary to know how to adjust the stack to compensate for the pop. | |
3942 | If any non-popped input is closer to the top of the reg-stack than | |
3943 | the implicitly popped reg, it would not be possible to know what the | |
84330467 | 3944 | stack looked like---it's not clear how the rest of the stack ``slides |
fe0ce426 JH |
3945 | up''. |
3946 | ||
3947 | All implicitly popped input regs must be closer to the top of | |
3948 | the reg-stack than any input that is not implicitly popped. | |
3949 | ||
3950 | It is possible that if an input dies in an insn, reload might | |
3951 | use the input reg for an output reload. Consider this example: | |
3952 | ||
3953 | @example | |
3954 | asm ("foo" : "=t" (a) : "f" (b)); | |
3955 | @end example | |
3956 | ||
3957 | This asm says that input B is not popped by the asm, and that | |
c771326b | 3958 | the asm pushes a result onto the reg-stack, i.e., the stack is one |
fe0ce426 JH |
3959 | deeper after the asm than it was before. But, it is possible that |
3960 | reload will think that it can use the same reg for both the input and | |
3961 | the output, if input B dies in this insn. | |
3962 | ||
3963 | If any input operand uses the @code{f} constraint, all output reg | |
3964 | constraints must use the @code{&} earlyclobber. | |
3965 | ||
3966 | The asm above would be written as | |
3967 | ||
3968 | @example | |
3969 | asm ("foo" : "=&t" (a) : "f" (b)); | |
3970 | @end example | |
3971 | ||
3972 | @item | |
3973 | Some operands need to be in particular places on the stack. All | |
84330467 | 3974 | output operands fall in this category---there is no other way to |
fe0ce426 JH |
3975 | know which regs the outputs appear in unless the user indicates |
3976 | this in the constraints. | |
3977 | ||
3978 | Output operands must specifically indicate which reg an output | |
3979 | appears in after an asm. @code{=f} is not allowed: the operand | |
3980 | constraints must select a class with a single reg. | |
3981 | ||
3982 | @item | |
3983 | Output operands may not be ``inserted'' between existing stack regs. | |
3984 | Since no 387 opcode uses a read/write operand, all output operands | |
3985 | are dead before the asm_operands, and are pushed by the asm_operands. | |
3986 | It makes no sense to push anywhere but the top of the reg-stack. | |
3987 | ||
3988 | Output operands must start at the top of the reg-stack: output | |
3989 | operands may not ``skip'' a reg. | |
3990 | ||
3991 | @item | |
3992 | Some asm statements may need extra stack space for internal | |
3993 | calculations. This can be guaranteed by clobbering stack registers | |
3994 | unrelated to the inputs and outputs. | |
3995 | ||
3996 | @end enumerate | |
3997 | ||
3998 | Here are a couple of reasonable asms to want to write. This asm | |
3999 | takes one input, which is internally popped, and produces two outputs. | |
4000 | ||
4001 | @example | |
4002 | asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp)); | |
4003 | @end example | |
4004 | ||
4005 | This asm takes two inputs, which are popped by the @code{fyl2xp1} opcode, | |
4006 | and replaces them with one output. The user must code the @code{st(1)} | |
4007 | clobber for reg-stack.c to know that @code{fyl2xp1} pops both inputs. | |
4008 | ||
4009 | @example | |
4010 | asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)"); | |
4011 | @end example | |
4012 | ||
c1f7febf | 4013 | @include md.texi |
c1f7febf RK |
4014 | |
4015 | @node Asm Labels | |
4016 | @section Controlling Names Used in Assembler Code | |
4017 | @cindex assembler names for identifiers | |
4018 | @cindex names used in assembler code | |
4019 | @cindex identifiers, names in assembler code | |
4020 | ||
4021 | You can specify the name to be used in the assembler code for a C | |
4022 | function or variable by writing the @code{asm} (or @code{__asm__}) | |
4023 | keyword after the declarator as follows: | |
4024 | ||
4025 | @example | |
4026 | int foo asm ("myfoo") = 2; | |
4027 | @end example | |
4028 | ||
4029 | @noindent | |
4030 | This specifies that the name to be used for the variable @code{foo} in | |
4031 | the assembler code should be @samp{myfoo} rather than the usual | |
4032 | @samp{_foo}. | |
4033 | ||
4034 | On systems where an underscore is normally prepended to the name of a C | |
4035 | function or variable, this feature allows you to define names for the | |
4036 | linker that do not start with an underscore. | |
4037 | ||
0adc3c19 MM |
4038 | It does not make sense to use this feature with a non-static local |
4039 | variable since such variables do not have assembler names. If you are | |
4040 | trying to put the variable in a particular register, see @ref{Explicit | |
4041 | Reg Vars}. GCC presently accepts such code with a warning, but will | |
4042 | probably be changed to issue an error, rather than a warning, in the | |
4043 | future. | |
4044 | ||
c1f7febf RK |
4045 | You cannot use @code{asm} in this way in a function @emph{definition}; but |
4046 | you can get the same effect by writing a declaration for the function | |
4047 | before its definition and putting @code{asm} there, like this: | |
4048 | ||
4049 | @example | |
4050 | extern func () asm ("FUNC"); | |
4051 | ||
4052 | func (x, y) | |
4053 | int x, y; | |
0d893a63 | 4054 | /* @r{@dots{}} */ |
c1f7febf RK |
4055 | @end example |
4056 | ||
4057 | It is up to you to make sure that the assembler names you choose do not | |
4058 | conflict with any other assembler symbols. Also, you must not use a | |
f0523f02 JM |
4059 | register name; that would produce completely invalid assembler code. GCC |
4060 | does not as yet have the ability to store static variables in registers. | |
c1f7febf RK |
4061 | Perhaps that will be added. |
4062 | ||
4063 | @node Explicit Reg Vars | |
4064 | @section Variables in Specified Registers | |
4065 | @cindex explicit register variables | |
4066 | @cindex variables in specified registers | |
4067 | @cindex specified registers | |
4068 | @cindex registers, global allocation | |
4069 | ||
4070 | GNU C allows you to put a few global variables into specified hardware | |
4071 | registers. You can also specify the register in which an ordinary | |
4072 | register variable should be allocated. | |
4073 | ||
4074 | @itemize @bullet | |
4075 | @item | |
4076 | Global register variables reserve registers throughout the program. | |
4077 | This may be useful in programs such as programming language | |
4078 | interpreters which have a couple of global variables that are accessed | |
4079 | very often. | |
4080 | ||
4081 | @item | |
4082 | Local register variables in specific registers do not reserve the | |
4083 | registers. The compiler's data flow analysis is capable of determining | |
4084 | where the specified registers contain live values, and where they are | |
8d344fbc | 4085 | available for other uses. Stores into local register variables may be deleted |
0deaf590 JL |
4086 | when they appear to be dead according to dataflow analysis. References |
4087 | to local register variables may be deleted or moved or simplified. | |
c1f7febf RK |
4088 | |
4089 | These local variables are sometimes convenient for use with the extended | |
4090 | @code{asm} feature (@pxref{Extended Asm}), if you want to write one | |
4091 | output of the assembler instruction directly into a particular register. | |
4092 | (This will work provided the register you specify fits the constraints | |
4093 | specified for that operand in the @code{asm}.) | |
4094 | @end itemize | |
4095 | ||
4096 | @menu | |
4097 | * Global Reg Vars:: | |
4098 | * Local Reg Vars:: | |
4099 | @end menu | |
4100 | ||
4101 | @node Global Reg Vars | |
4102 | @subsection Defining Global Register Variables | |
4103 | @cindex global register variables | |
4104 | @cindex registers, global variables in | |
4105 | ||
4106 | You can define a global register variable in GNU C like this: | |
4107 | ||
4108 | @example | |
4109 | register int *foo asm ("a5"); | |
4110 | @end example | |
4111 | ||
4112 | @noindent | |
4113 | Here @code{a5} is the name of the register which should be used. Choose a | |
4114 | register which is normally saved and restored by function calls on your | |
4115 | machine, so that library routines will not clobber it. | |
4116 | ||
4117 | Naturally the register name is cpu-dependent, so you would need to | |
4118 | conditionalize your program according to cpu type. The register | |
4119 | @code{a5} would be a good choice on a 68000 for a variable of pointer | |
4120 | type. On machines with register windows, be sure to choose a ``global'' | |
4121 | register that is not affected magically by the function call mechanism. | |
4122 | ||
4123 | In addition, operating systems on one type of cpu may differ in how they | |
4124 | name the registers; then you would need additional conditionals. For | |
4125 | example, some 68000 operating systems call this register @code{%a5}. | |
4126 | ||
4127 | Eventually there may be a way of asking the compiler to choose a register | |
4128 | automatically, but first we need to figure out how it should choose and | |
4129 | how to enable you to guide the choice. No solution is evident. | |
4130 | ||
4131 | Defining a global register variable in a certain register reserves that | |
4132 | register entirely for this use, at least within the current compilation. | |
4133 | The register will not be allocated for any other purpose in the functions | |
4134 | in the current compilation. The register will not be saved and restored by | |
4135 | these functions. Stores into this register are never deleted even if they | |
4136 | would appear to be dead, but references may be deleted or moved or | |
4137 | simplified. | |
4138 | ||
4139 | It is not safe to access the global register variables from signal | |
4140 | handlers, or from more than one thread of control, because the system | |
4141 | library routines may temporarily use the register for other things (unless | |
4142 | you recompile them specially for the task at hand). | |
4143 | ||
4144 | @cindex @code{qsort}, and global register variables | |
4145 | It is not safe for one function that uses a global register variable to | |
4146 | call another such function @code{foo} by way of a third function | |
e979f9e8 | 4147 | @code{lose} that was compiled without knowledge of this variable (i.e.@: in a |
c1f7febf RK |
4148 | different source file in which the variable wasn't declared). This is |
4149 | because @code{lose} might save the register and put some other value there. | |
4150 | For example, you can't expect a global register variable to be available in | |
4151 | the comparison-function that you pass to @code{qsort}, since @code{qsort} | |
4152 | might have put something else in that register. (If you are prepared to | |
4153 | recompile @code{qsort} with the same global register variable, you can | |
4154 | solve this problem.) | |
4155 | ||
4156 | If you want to recompile @code{qsort} or other source files which do not | |
4157 | actually use your global register variable, so that they will not use that | |
4158 | register for any other purpose, then it suffices to specify the compiler | |
84330467 | 4159 | option @option{-ffixed-@var{reg}}. You need not actually add a global |
c1f7febf RK |
4160 | register declaration to their source code. |
4161 | ||
4162 | A function which can alter the value of a global register variable cannot | |
4163 | safely be called from a function compiled without this variable, because it | |
4164 | could clobber the value the caller expects to find there on return. | |
4165 | Therefore, the function which is the entry point into the part of the | |
4166 | program that uses the global register variable must explicitly save and | |
4167 | restore the value which belongs to its caller. | |
4168 | ||
4169 | @cindex register variable after @code{longjmp} | |
4170 | @cindex global register after @code{longjmp} | |
4171 | @cindex value after @code{longjmp} | |
4172 | @findex longjmp | |
4173 | @findex setjmp | |
4174 | On most machines, @code{longjmp} will restore to each global register | |
4175 | variable the value it had at the time of the @code{setjmp}. On some | |
4176 | machines, however, @code{longjmp} will not change the value of global | |
4177 | register variables. To be portable, the function that called @code{setjmp} | |
4178 | should make other arrangements to save the values of the global register | |
4179 | variables, and to restore them in a @code{longjmp}. This way, the same | |
4180 | thing will happen regardless of what @code{longjmp} does. | |
4181 | ||
4182 | All global register variable declarations must precede all function | |
4183 | definitions. If such a declaration could appear after function | |
4184 | definitions, the declaration would be too late to prevent the register from | |
4185 | being used for other purposes in the preceding functions. | |
4186 | ||
4187 | Global register variables may not have initial values, because an | |
4188 | executable file has no means to supply initial contents for a register. | |
4189 | ||
981f6289 | 4190 | On the SPARC, there are reports that g3 @dots{} g7 are suitable |
c1f7febf RK |
4191 | registers, but certain library functions, such as @code{getwd}, as well |
4192 | as the subroutines for division and remainder, modify g3 and g4. g1 and | |
4193 | g2 are local temporaries. | |
4194 | ||
4195 | On the 68000, a2 @dots{} a5 should be suitable, as should d2 @dots{} d7. | |
4196 | Of course, it will not do to use more than a few of those. | |
4197 | ||
4198 | @node Local Reg Vars | |
4199 | @subsection Specifying Registers for Local Variables | |
4200 | @cindex local variables, specifying registers | |
4201 | @cindex specifying registers for local variables | |
4202 | @cindex registers for local variables | |
4203 | ||
4204 | You can define a local register variable with a specified register | |
4205 | like this: | |
4206 | ||
4207 | @example | |
4208 | register int *foo asm ("a5"); | |
4209 | @end example | |
4210 | ||
4211 | @noindent | |
4212 | Here @code{a5} is the name of the register which should be used. Note | |
4213 | that this is the same syntax used for defining global register | |
4214 | variables, but for a local variable it would appear within a function. | |
4215 | ||
4216 | Naturally the register name is cpu-dependent, but this is not a | |
4217 | problem, since specific registers are most often useful with explicit | |
4218 | assembler instructions (@pxref{Extended Asm}). Both of these things | |
4219 | generally require that you conditionalize your program according to | |
4220 | cpu type. | |
4221 | ||
4222 | In addition, operating systems on one type of cpu may differ in how they | |
4223 | name the registers; then you would need additional conditionals. For | |
4224 | example, some 68000 operating systems call this register @code{%a5}. | |
4225 | ||
c1f7febf RK |
4226 | Defining such a register variable does not reserve the register; it |
4227 | remains available for other uses in places where flow control determines | |
4228 | the variable's value is not live. However, these registers are made | |
e5e809f4 JL |
4229 | unavailable for use in the reload pass; excessive use of this feature |
4230 | leaves the compiler too few available registers to compile certain | |
4231 | functions. | |
4232 | ||
f0523f02 | 4233 | This option does not guarantee that GCC will generate code that has |
e5e809f4 JL |
4234 | this variable in the register you specify at all times. You may not |
4235 | code an explicit reference to this register in an @code{asm} statement | |
4236 | and assume it will always refer to this variable. | |
c1f7febf | 4237 | |
8d344fbc | 4238 | Stores into local register variables may be deleted when they appear to be dead |
0deaf590 JL |
4239 | according to dataflow analysis. References to local register variables may |
4240 | be deleted or moved or simplified. | |
4241 | ||
c1f7febf RK |
4242 | @node Alternate Keywords |
4243 | @section Alternate Keywords | |
4244 | @cindex alternate keywords | |
4245 | @cindex keywords, alternate | |
4246 | ||
5490d604 | 4247 | @option{-ansi} and the various @option{-std} options disable certain |
f458d1d5 ZW |
4248 | keywords. This causes trouble when you want to use GNU C extensions, or |
4249 | a general-purpose header file that should be usable by all programs, | |
4250 | including ISO C programs. The keywords @code{asm}, @code{typeof} and | |
4251 | @code{inline} are not available in programs compiled with | |
4252 | @option{-ansi} or @option{-std} (although @code{inline} can be used in a | |
4253 | program compiled with @option{-std=c99}). The ISO C99 keyword | |
5490d604 JM |
4254 | @code{restrict} is only available when @option{-std=gnu99} (which will |
4255 | eventually be the default) or @option{-std=c99} (or the equivalent | |
bd819a4a | 4256 | @option{-std=iso9899:1999}) is used. |
c1f7febf RK |
4257 | |
4258 | The way to solve these problems is to put @samp{__} at the beginning and | |
4259 | end of each problematical keyword. For example, use @code{__asm__} | |
f458d1d5 | 4260 | instead of @code{asm}, and @code{__inline__} instead of @code{inline}. |
c1f7febf RK |
4261 | |
4262 | Other C compilers won't accept these alternative keywords; if you want to | |
4263 | compile with another compiler, you can define the alternate keywords as | |
4264 | macros to replace them with the customary keywords. It looks like this: | |
4265 | ||
4266 | @example | |
4267 | #ifndef __GNUC__ | |
4268 | #define __asm__ asm | |
4269 | #endif | |
4270 | @end example | |
4271 | ||
6e6b0525 | 4272 | @findex __extension__ |
84330467 JM |
4273 | @opindex pedantic |
4274 | @option{-pedantic} and other options cause warnings for many GNU C extensions. | |
dbe519e0 | 4275 | You can |
c1f7febf RK |
4276 | prevent such warnings within one expression by writing |
4277 | @code{__extension__} before the expression. @code{__extension__} has no | |
4278 | effect aside from this. | |
4279 | ||
4280 | @node Incomplete Enums | |
4281 | @section Incomplete @code{enum} Types | |
4282 | ||
4283 | You can define an @code{enum} tag without specifying its possible values. | |
4284 | This results in an incomplete type, much like what you get if you write | |
4285 | @code{struct foo} without describing the elements. A later declaration | |
4286 | which does specify the possible values completes the type. | |
4287 | ||
4288 | You can't allocate variables or storage using the type while it is | |
4289 | incomplete. However, you can work with pointers to that type. | |
4290 | ||
4291 | This extension may not be very useful, but it makes the handling of | |
4292 | @code{enum} more consistent with the way @code{struct} and @code{union} | |
4293 | are handled. | |
4294 | ||
4295 | This extension is not supported by GNU C++. | |
4296 | ||
4297 | @node Function Names | |
4298 | @section Function Names as Strings | |
4b404517 JM |
4299 | @cindex @code{__FUNCTION__} identifier |
4300 | @cindex @code{__PRETTY_FUNCTION__} identifier | |
4301 | @cindex @code{__func__} identifier | |
c1f7febf | 4302 | |
f0523f02 | 4303 | GCC predefines two magic identifiers to hold the name of the current |
767094dd JM |
4304 | function. The identifier @code{__FUNCTION__} holds the name of the function |
4305 | as it appears in the source. The identifier @code{__PRETTY_FUNCTION__} | |
22acfb79 NM |
4306 | holds the name of the function pretty printed in a language specific |
4307 | fashion. | |
c1f7febf RK |
4308 | |
4309 | These names are always the same in a C function, but in a C++ function | |
4310 | they may be different. For example, this program: | |
4311 | ||
4312 | @smallexample | |
4313 | extern "C" @{ | |
4314 | extern int printf (char *, ...); | |
4315 | @} | |
4316 | ||
4317 | class a @{ | |
4318 | public: | |
4319 | sub (int i) | |
4320 | @{ | |
4321 | printf ("__FUNCTION__ = %s\n", __FUNCTION__); | |
4322 | printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__); | |
4323 | @} | |
4324 | @}; | |
4325 | ||
4326 | int | |
4327 | main (void) | |
4328 | @{ | |
4329 | a ax; | |
4330 | ax.sub (0); | |
4331 | return 0; | |
4332 | @} | |
4333 | @end smallexample | |
4334 | ||
4335 | @noindent | |
4336 | gives this output: | |
4337 | ||
4338 | @smallexample | |
4339 | __FUNCTION__ = sub | |
4340 | __PRETTY_FUNCTION__ = int a::sub (int) | |
4341 | @end smallexample | |
4342 | ||
22acfb79 | 4343 | The compiler automagically replaces the identifiers with a string |
767094dd | 4344 | literal containing the appropriate name. Thus, they are neither |
22acfb79 | 4345 | preprocessor macros, like @code{__FILE__} and @code{__LINE__}, nor |
767094dd JM |
4346 | variables. This means that they catenate with other string literals, and |
4347 | that they can be used to initialize char arrays. For example | |
22acfb79 NM |
4348 | |
4349 | @smallexample | |
4350 | char here[] = "Function " __FUNCTION__ " in " __FILE__; | |
4351 | @end smallexample | |
4352 | ||
4353 | On the other hand, @samp{#ifdef __FUNCTION__} does not have any special | |
c1f7febf RK |
4354 | meaning inside a function, since the preprocessor does not do anything |
4355 | special with the identifier @code{__FUNCTION__}. | |
4356 | ||
9aa8a1df NB |
4357 | Note that these semantics are deprecated, and that GCC 3.2 will handle |
4358 | @code{__FUNCTION__} and @code{__PRETTY_FUNCTION__} the same way as | |
4359 | @code{__func__}. @code{__func__} is defined by the ISO standard C99: | |
22acfb79 NM |
4360 | |
4361 | @display | |
4362 | The identifier @code{__func__} is implicitly declared by the translator | |
4363 | as if, immediately following the opening brace of each function | |
4364 | definition, the declaration | |
4365 | ||
4366 | @smallexample | |
4367 | static const char __func__[] = "function-name"; | |
4368 | @end smallexample | |
4369 | ||
4370 | appeared, where function-name is the name of the lexically-enclosing | |
767094dd | 4371 | function. This name is the unadorned name of the function. |
22acfb79 NM |
4372 | @end display |
4373 | ||
4374 | By this definition, @code{__func__} is a variable, not a string literal. | |
4375 | In particular, @code{__func__} does not catenate with other string | |
4376 | literals. | |
4377 | ||
4378 | In @code{C++}, @code{__FUNCTION__} and @code{__PRETTY_FUNCTION__} are | |
4379 | variables, declared in the same way as @code{__func__}. | |
4380 | ||
c1f7febf RK |
4381 | @node Return Address |
4382 | @section Getting the Return or Frame Address of a Function | |
4383 | ||
4384 | These functions may be used to get information about the callers of a | |
4385 | function. | |
4386 | ||
84330467 | 4387 | @deftypefn {Built-in Function} {void *} __builtin_return_address (unsigned int @var{level}) |
c1f7febf RK |
4388 | This function returns the return address of the current function, or of |
4389 | one of its callers. The @var{level} argument is number of frames to | |
4390 | scan up the call stack. A value of @code{0} yields the return address | |
4391 | of the current function, a value of @code{1} yields the return address | |
95b1627e EC |
4392 | of the caller of the current function, and so forth. When inlining |
4393 | the expected behavior is that the function will return the address of | |
4394 | the function that will be returned to. To work around this behavior use | |
4395 | the @code{noinline} function attribute. | |
c1f7febf RK |
4396 | |
4397 | The @var{level} argument must be a constant integer. | |
4398 | ||
4399 | On some machines it may be impossible to determine the return address of | |
4400 | any function other than the current one; in such cases, or when the top | |
dd96fbc5 L |
4401 | of the stack has been reached, this function will return @code{0} or a |
4402 | random value. In addition, @code{__builtin_frame_address} may be used | |
4403 | to determine if the top of the stack has been reached. | |
c1f7febf | 4404 | |
df2a54e9 | 4405 | This function should only be used with a nonzero argument for debugging |
c1f7febf | 4406 | purposes. |
84330467 | 4407 | @end deftypefn |
c1f7febf | 4408 | |
84330467 | 4409 | @deftypefn {Built-in Function} {void *} __builtin_frame_address (unsigned int @var{level}) |
c1f7febf RK |
4410 | This function is similar to @code{__builtin_return_address}, but it |
4411 | returns the address of the function frame rather than the return address | |
4412 | of the function. Calling @code{__builtin_frame_address} with a value of | |
4413 | @code{0} yields the frame address of the current function, a value of | |
4414 | @code{1} yields the frame address of the caller of the current function, | |
4415 | and so forth. | |
4416 | ||
4417 | The frame is the area on the stack which holds local variables and saved | |
4418 | registers. The frame address is normally the address of the first word | |
4419 | pushed on to the stack by the function. However, the exact definition | |
4420 | depends upon the processor and the calling convention. If the processor | |
4421 | has a dedicated frame pointer register, and the function has a frame, | |
4422 | then @code{__builtin_frame_address} will return the value of the frame | |
4423 | pointer register. | |
4424 | ||
dd96fbc5 L |
4425 | On some machines it may be impossible to determine the frame address of |
4426 | any function other than the current one; in such cases, or when the top | |
4427 | of the stack has been reached, this function will return @code{0} if | |
4428 | the first frame pointer is properly initialized by the startup code. | |
4429 | ||
df2a54e9 | 4430 | This function should only be used with a nonzero argument for debugging |
dd96fbc5 | 4431 | purposes. |
84330467 | 4432 | @end deftypefn |
c1f7febf | 4433 | |
1255c85c BS |
4434 | @node Vector Extensions |
4435 | @section Using vector instructions through built-in functions | |
4436 | ||
4437 | On some targets, the instruction set contains SIMD vector instructions that | |
4438 | operate on multiple values contained in one large register at the same time. | |
4439 | For example, on the i386 the MMX, 3Dnow! and SSE extensions can be used | |
4440 | this way. | |
4441 | ||
4442 | The first step in using these extensions is to provide the necessary data | |
4443 | types. This should be done using an appropriate @code{typedef}: | |
4444 | ||
4445 | @example | |
4446 | typedef int v4si __attribute__ ((mode(V4SI))); | |
4447 | @end example | |
4448 | ||
4449 | The base type @code{int} is effectively ignored by the compiler, the | |
4450 | actual properties of the new type @code{v4si} are defined by the | |
4451 | @code{__attribute__}. It defines the machine mode to be used; for vector | |
80ebf43e BS |
4452 | types these have the form @code{V@var{n}@var{B}}; @var{n} should be the |
4453 | number of elements in the vector, and @var{B} should be the base mode of the | |
1255c85c BS |
4454 | individual elements. The following can be used as base modes: |
4455 | ||
4456 | @table @code | |
4457 | @item QI | |
4458 | An integer that is as wide as the smallest addressable unit, usually 8 bits. | |
4459 | @item HI | |
4460 | An integer, twice as wide as a QI mode integer, usually 16 bits. | |
4461 | @item SI | |
4462 | An integer, four times as wide as a QI mode integer, usually 32 bits. | |
4463 | @item DI | |
4464 | An integer, eight times as wide as a QI mode integer, usually 64 bits. | |
4465 | @item SF | |
4466 | A floating point value, as wide as a SI mode integer, usually 32 bits. | |
4467 | @item DF | |
4468 | A floating point value, as wide as a DI mode integer, usually 64 bits. | |
4469 | @end table | |
4470 | ||
cb2a532e AH |
4471 | Specifying a combination that is not valid for the current architecture |
4472 | will cause gcc to synthesize the instructions using a narrower mode. | |
4473 | For example, if you specify a variable of type @code{V4SI} and your | |
4474 | architecture does not allow for this specific SIMD type, gcc will | |
4475 | produce code that uses 4 @code{SIs}. | |
4476 | ||
4477 | The types defined in this manner can be used with a subset of normal C | |
4478 | operations. Currently, gcc will allow using the following operators on | |
4479 | these types: @code{+, -, *, /, unary minus}@. | |
4480 | ||
4481 | The operations behave like C++ @code{valarrays}. Addition is defined as | |
4482 | the addition of the corresponding elements of the operands. For | |
4483 | example, in the code below, each of the 4 elements in @var{a} will be | |
4484 | added to the corresponding 4 elements in @var{b} and the resulting | |
4485 | vector will be stored in @var{c}. | |
4486 | ||
4487 | @example | |
4488 | typedef int v4si __attribute__ ((mode(V4SI))); | |
4489 | ||
4490 | v4si a, b, c; | |
4491 | ||
4492 | c = a + b; | |
4493 | @end example | |
4494 | ||
4495 | Subtraction, multiplication, and division operate in a similar manner. | |
4496 | Likewise, the result of using the unary minus operator on a vector type | |
4497 | is a vector whose elements are the negative value of the corresponding | |
4498 | elements in the operand. | |
4499 | ||
4500 | You can declare variables and use them in function calls and returns, as | |
4501 | well as in assignments and some casts. You can specify a vector type as | |
4502 | a return type for a function. Vector types can also be used as function | |
4503 | arguments. It is possible to cast from one vector type to another, | |
4504 | provided they are of the same size (in fact, you can also cast vectors | |
4505 | to and from other datatypes of the same size). | |
4506 | ||
4507 | You cannot operate between vectors of different lengths or different | |
90a21764 | 4508 | signedness without a cast. |
cb2a532e AH |
4509 | |
4510 | A port that supports hardware vector operations, usually provides a set | |
4511 | of built-in functions that can be used to operate on vectors. For | |
4512 | example, a function to add two vectors and multiply the result by a | |
4513 | third could look like this: | |
1255c85c BS |
4514 | |
4515 | @example | |
4516 | v4si f (v4si a, v4si b, v4si c) | |
4517 | @{ | |
4518 | v4si tmp = __builtin_addv4si (a, b); | |
4519 | return __builtin_mulv4si (tmp, c); | |
4520 | @} | |
4521 | ||
4522 | @end example | |
4523 | ||
185ebd6c | 4524 | @node Other Builtins |
f0523f02 | 4525 | @section Other built-in functions provided by GCC |
c771326b | 4526 | @cindex built-in functions |
01702459 JM |
4527 | @findex __builtin_isgreater |
4528 | @findex __builtin_isgreaterequal | |
4529 | @findex __builtin_isless | |
4530 | @findex __builtin_islessequal | |
4531 | @findex __builtin_islessgreater | |
4532 | @findex __builtin_isunordered | |
4533 | @findex abort | |
4534 | @findex abs | |
4535 | @findex alloca | |
46847aa6 RS |
4536 | @findex atan2 |
4537 | @findex atan2f | |
4538 | @findex atan2l | |
01702459 JM |
4539 | @findex bcmp |
4540 | @findex bzero | |
b052d8ee RS |
4541 | @findex ceil |
4542 | @findex ceilf | |
4543 | @findex ceill | |
341e3d11 JM |
4544 | @findex cimag |
4545 | @findex cimagf | |
4546 | @findex cimagl | |
4547 | @findex conj | |
4548 | @findex conjf | |
4549 | @findex conjl | |
01702459 JM |
4550 | @findex cos |
4551 | @findex cosf | |
4552 | @findex cosl | |
341e3d11 JM |
4553 | @findex creal |
4554 | @findex crealf | |
4555 | @findex creall | |
01702459 JM |
4556 | @findex exit |
4557 | @findex _exit | |
796cdb65 | 4558 | @findex _Exit |
e7b489c8 RS |
4559 | @findex exp |
4560 | @findex expf | |
4561 | @findex expl | |
01702459 JM |
4562 | @findex fabs |
4563 | @findex fabsf | |
4564 | @findex fabsl | |
4565 | @findex ffs | |
b052d8ee RS |
4566 | @findex floor |
4567 | @findex floorf | |
4568 | @findex floorl | |
4569 | @findex fmod | |
4570 | @findex fmodf | |
4571 | @findex fmodl | |
18f988a0 | 4572 | @findex fprintf |
b4c984fb | 4573 | @findex fprintf_unlocked |
01702459 | 4574 | @findex fputs |
b4c984fb | 4575 | @findex fputs_unlocked |
e78f4a97 | 4576 | @findex imaxabs |
c7b6c6cd | 4577 | @findex index |
01702459 JM |
4578 | @findex labs |
4579 | @findex llabs | |
e7b489c8 RS |
4580 | @findex log |
4581 | @findex logf | |
4582 | @findex logl | |
01702459 JM |
4583 | @findex memcmp |
4584 | @findex memcpy | |
4585 | @findex memset | |
b052d8ee RS |
4586 | @findex nearbyint |
4587 | @findex nearbyintf | |
4588 | @findex nearbyintl | |
46847aa6 RS |
4589 | @findex pow |
4590 | @findex powf | |
4591 | @findex powl | |
01702459 | 4592 | @findex printf |
b4c984fb | 4593 | @findex printf_unlocked |
08291658 RS |
4594 | @findex putchar |
4595 | @findex puts | |
c7b6c6cd | 4596 | @findex rindex |
b052d8ee RS |
4597 | @findex round |
4598 | @findex roundf | |
4599 | @findex roundl | |
08291658 | 4600 | @findex scanf |
01702459 JM |
4601 | @findex sin |
4602 | @findex sinf | |
4603 | @findex sinl | |
08291658 RS |
4604 | @findex snprintf |
4605 | @findex sprintf | |
01702459 JM |
4606 | @findex sqrt |
4607 | @findex sqrtf | |
4608 | @findex sqrtl | |
08291658 | 4609 | @findex sscanf |
d118937d | 4610 | @findex strcat |
01702459 JM |
4611 | @findex strchr |
4612 | @findex strcmp | |
4613 | @findex strcpy | |
d118937d | 4614 | @findex strcspn |
01702459 | 4615 | @findex strlen |
d118937d | 4616 | @findex strncat |
da9e9f08 KG |
4617 | @findex strncmp |
4618 | @findex strncpy | |
01702459 JM |
4619 | @findex strpbrk |
4620 | @findex strrchr | |
d118937d | 4621 | @findex strspn |
01702459 | 4622 | @findex strstr |
4977bab6 ZW |
4623 | @findex trunc |
4624 | @findex truncf | |
4625 | @findex truncl | |
08291658 RS |
4626 | @findex vprintf |
4627 | @findex vscanf | |
4628 | @findex vsnprintf | |
4629 | @findex vsprintf | |
4630 | @findex vsscanf | |
185ebd6c | 4631 | |
f0523f02 | 4632 | GCC provides a large number of built-in functions other than the ones |
185ebd6c RH |
4633 | mentioned above. Some of these are for internal use in the processing |
4634 | of exceptions or variable-length argument lists and will not be | |
4635 | documented here because they may change from time to time; we do not | |
4636 | recommend general use of these functions. | |
4637 | ||
4638 | The remaining functions are provided for optimization purposes. | |
4639 | ||
84330467 | 4640 | @opindex fno-builtin |
9c34dbbf ZW |
4641 | GCC includes built-in versions of many of the functions in the standard |
4642 | C library. The versions prefixed with @code{__builtin_} will always be | |
4643 | treated as having the same meaning as the C library function even if you | |
4644 | specify the @option{-fno-builtin} option. (@pxref{C Dialect Options}) | |
4645 | Many of these functions are only optimized in certain cases; if they are | |
01702459 JM |
4646 | not optimized in a particular case, a call to the library function will |
4647 | be emitted. | |
4648 | ||
84330467 JM |
4649 | @opindex ansi |
4650 | @opindex std | |
b052d8ee RS |
4651 | Outside strict ISO C mode (@option{-ansi}, @option{-std=c89} or |
4652 | @option{-std=c99}), the functions @code{alloca}, @code{bcmp}, | |
4653 | @code{bzero}, @code{_exit}, @code{ffs}, @code{fprintf_unlocked}, | |
4654 | @code{fputs_unlocked}, @code{index}, @code{printf_unlocked}, | |
4655 | and @code{rindex} may be handled as built-in functions. | |
4656 | All these functions have corresponding versions | |
9c34dbbf ZW |
4657 | prefixed with @code{__builtin_}, which may be used even in strict C89 |
4658 | mode. | |
01702459 | 4659 | |
4977bab6 ZW |
4660 | The ISO C99 functions @code{conj}, @code{conjf}, @code{conjl}, @code{creal}, |
4661 | @code{crealf}, @code{creall}, @code{cimag}, @code{cimagf}, @code{cimagl}, | |
08291658 RS |
4662 | @code{_Exit}, @code{imaxabs}, @code{llabs}, |
4663 | @code{nearbyint}, @code{nearbyintf}, @code{nearbyintl}, | |
4664 | @code{round}, @code{roundf}, @code{roundl}, @code{snprintf}, | |
4665 | @code{trunc}, @code{truncf}, @code{truncl}, | |
4666 | @code{vscanf}, @code{vsnprintf} and @code{vsscanf} | |
4667 | are handled as built-in functions | |
b052d8ee | 4668 | except in strict ISO C90 mode (@option{-ansi} or @option{-std=c89}). |
46847aa6 RS |
4669 | |
4670 | There are also built-in versions of the ISO C99 functions @code{atan2f}, | |
4671 | @code{atan2l}, @code{ceilf}, @code{ceill}, @code{cosf}, @code{cosl}, | |
4672 | @code{expf}, @code{expl}, @code{fabsf}, @code{fabsl}, @code{floorf}, | |
b052d8ee RS |
4673 | @code{floorl}, @code{fmodf}, @code{fmodl}, |
4674 | @code{logf}, @code{logl}, @code{powf}, @code{powl}, | |
46847aa6 RS |
4675 | @code{sinf}, @code{sinl}, @code{sqrtf} and @code{sqrtl} |
4676 | that are recognized in any mode since ISO C90 reserves these names for | |
4677 | the purpose to which ISO C99 puts them. All these functions have | |
4678 | corresponding versions prefixed with @code{__builtin_}. | |
4679 | ||
b052d8ee RS |
4680 | The ISO C90 functions @code{abort}, @code{abs}, @code{atan2}, @code{ceil}, |
4681 | @code{cos}, @code{exit}, | |
4682 | @code{exp}, @code{fabs}, @code{floor}, @code{fmod}, | |
46847aa6 RS |
4683 | @code{fprintf}, @code{fputs}, @code{labs}, @code{log}, |
4684 | @code{memcmp}, @code{memcpy}, @code{memset}, @code{pow}, @code{printf}, | |
08291658 | 4685 | @code{putchar}, @code{puts}, @code{scanf}, @code{sin}, @code{snprintf}, |
efa66a74 | 4686 | @code{sprintf}, @code{sqrt}, @code{sscanf}, |
08291658 | 4687 | @code{strcat}, @code{strchr}, @code{strcmp}, |
4977bab6 | 4688 | @code{strcpy}, @code{strcspn}, @code{strlen}, @code{strncat}, @code{strncmp}, |
08291658 RS |
4689 | @code{strncpy}, @code{strpbrk}, @code{strrchr}, @code{strspn}, @code{strstr}, |
4690 | @code{vprintf} and @code{vsprintf} | |
4691 | are all recognized as built-in functions unless | |
46847aa6 RS |
4692 | @option{-fno-builtin} is specified (or @option{-fno-builtin-@var{function}} |
4693 | is specified for an individual function). All of these functions have | |
4977bab6 | 4694 | corresponding versions prefixed with @code{__builtin_}. |
9c34dbbf ZW |
4695 | |
4696 | GCC provides built-in versions of the ISO C99 floating point comparison | |
4697 | macros that avoid raising exceptions for unordered operands. They have | |
4698 | the same names as the standard macros ( @code{isgreater}, | |
4699 | @code{isgreaterequal}, @code{isless}, @code{islessequal}, | |
4700 | @code{islessgreater}, and @code{isunordered}) , with @code{__builtin_} | |
4701 | prefixed. We intend for a library implementor to be able to simply | |
4702 | @code{#define} each standard macro to its built-in equivalent. | |
185ebd6c | 4703 | |
ecbcf7b3 AH |
4704 | @deftypefn {Built-in Function} int __builtin_types_compatible_p (@var{type1}, @var{type2}) |
4705 | ||
4706 | You can use the built-in function @code{__builtin_types_compatible_p} to | |
4707 | determine whether two types are the same. | |
4708 | ||
4709 | This built-in function returns 1 if the unqualified versions of the | |
4710 | types @var{type1} and @var{type2} (which are types, not expressions) are | |
4711 | compatible, 0 otherwise. The result of this built-in function can be | |
4712 | used in integer constant expressions. | |
4713 | ||
4714 | This built-in function ignores top level qualifiers (e.g., @code{const}, | |
4715 | @code{volatile}). For example, @code{int} is equivalent to @code{const | |
4716 | int}. | |
4717 | ||
4718 | The type @code{int[]} and @code{int[5]} are compatible. On the other | |
4719 | hand, @code{int} and @code{char *} are not compatible, even if the size | |
4720 | of their types, on the particular architecture are the same. Also, the | |
4721 | amount of pointer indirection is taken into account when determining | |
4722 | similarity. Consequently, @code{short *} is not similar to | |
4723 | @code{short **}. Furthermore, two types that are typedefed are | |
4724 | considered compatible if their underlying types are compatible. | |
4725 | ||
4726 | An @code{enum} type is considered to be compatible with another | |
4727 | @code{enum} type. For example, @code{enum @{foo, bar@}} is similar to | |
4728 | @code{enum @{hot, dog@}}. | |
4729 | ||
4730 | You would typically use this function in code whose execution varies | |
4731 | depending on the arguments' types. For example: | |
4732 | ||
4733 | @smallexample | |
6e5bb5ad JM |
4734 | #define foo(x) \ |
4735 | (@{ \ | |
4736 | typeof (x) tmp; \ | |
4737 | if (__builtin_types_compatible_p (typeof (x), long double)) \ | |
4738 | tmp = foo_long_double (tmp); \ | |
4739 | else if (__builtin_types_compatible_p (typeof (x), double)) \ | |
4740 | tmp = foo_double (tmp); \ | |
4741 | else if (__builtin_types_compatible_p (typeof (x), float)) \ | |
4742 | tmp = foo_float (tmp); \ | |
4743 | else \ | |
4744 | abort (); \ | |
4745 | tmp; \ | |
ecbcf7b3 AH |
4746 | @}) |
4747 | @end smallexample | |
4748 | ||
4749 | @emph{Note:} This construct is only available for C. | |
4750 | ||
4751 | @end deftypefn | |
4752 | ||
4753 | @deftypefn {Built-in Function} @var{type} __builtin_choose_expr (@var{const_exp}, @var{exp1}, @var{exp2}) | |
4754 | ||
4755 | You can use the built-in function @code{__builtin_choose_expr} to | |
4756 | evaluate code depending on the value of a constant expression. This | |
4757 | built-in function returns @var{exp1} if @var{const_exp}, which is a | |
4758 | constant expression that must be able to be determined at compile time, | |
4759 | is nonzero. Otherwise it returns 0. | |
4760 | ||
4761 | This built-in function is analogous to the @samp{? :} operator in C, | |
4762 | except that the expression returned has its type unaltered by promotion | |
4763 | rules. Also, the built-in function does not evaluate the expression | |
4764 | that was not chosen. For example, if @var{const_exp} evaluates to true, | |
4765 | @var{exp2} is not evaluated even if it has side-effects. | |
4766 | ||
4767 | This built-in function can return an lvalue if the chosen argument is an | |
4768 | lvalue. | |
4769 | ||
4770 | If @var{exp1} is returned, the return type is the same as @var{exp1}'s | |
4771 | type. Similarly, if @var{exp2} is returned, its return type is the same | |
4772 | as @var{exp2}. | |
4773 | ||
4774 | Example: | |
4775 | ||
4776 | @smallexample | |
478c9e72 JJ |
4777 | #define foo(x) \ |
4778 | __builtin_choose_expr ( \ | |
4779 | __builtin_types_compatible_p (typeof (x), double), \ | |
4780 | foo_double (x), \ | |
4781 | __builtin_choose_expr ( \ | |
4782 | __builtin_types_compatible_p (typeof (x), float), \ | |
4783 | foo_float (x), \ | |
4784 | /* @r{The void expression results in a compile-time error} \ | |
4785 | @r{when assigning the result to something.} */ \ | |
ecbcf7b3 AH |
4786 | (void)0)) |
4787 | @end smallexample | |
4788 | ||
4789 | @emph{Note:} This construct is only available for C. Furthermore, the | |
4790 | unused expression (@var{exp1} or @var{exp2} depending on the value of | |
4791 | @var{const_exp}) may still generate syntax errors. This may change in | |
4792 | future revisions. | |
4793 | ||
4794 | @end deftypefn | |
4795 | ||
84330467 JM |
4796 | @deftypefn {Built-in Function} int __builtin_constant_p (@var{exp}) |
4797 | You can use the built-in function @code{__builtin_constant_p} to | |
185ebd6c | 4798 | determine if a value is known to be constant at compile-time and hence |
f0523f02 | 4799 | that GCC can perform constant-folding on expressions involving that |
185ebd6c RH |
4800 | value. The argument of the function is the value to test. The function |
4801 | returns the integer 1 if the argument is known to be a compile-time | |
4802 | constant and 0 if it is not known to be a compile-time constant. A | |
4803 | return of 0 does not indicate that the value is @emph{not} a constant, | |
f0523f02 | 4804 | but merely that GCC cannot prove it is a constant with the specified |
84330467 | 4805 | value of the @option{-O} option. |
185ebd6c RH |
4806 | |
4807 | You would typically use this function in an embedded application where | |
4808 | memory was a critical resource. If you have some complex calculation, | |
4809 | you may want it to be folded if it involves constants, but need to call | |
4810 | a function if it does not. For example: | |
4811 | ||
4d390518 | 4812 | @smallexample |
310668e8 JM |
4813 | #define Scale_Value(X) \ |
4814 | (__builtin_constant_p (X) \ | |
4815 | ? ((X) * SCALE + OFFSET) : Scale (X)) | |
185ebd6c RH |
4816 | @end smallexample |
4817 | ||
84330467 | 4818 | You may use this built-in function in either a macro or an inline |
185ebd6c | 4819 | function. However, if you use it in an inlined function and pass an |
f0523f02 | 4820 | argument of the function as the argument to the built-in, GCC will |
185ebd6c | 4821 | never return 1 when you call the inline function with a string constant |
4b404517 | 4822 | or compound literal (@pxref{Compound Literals}) and will not return 1 |
185ebd6c | 4823 | when you pass a constant numeric value to the inline function unless you |
84330467 | 4824 | specify the @option{-O} option. |
13104975 ZW |
4825 | |
4826 | You may also use @code{__builtin_constant_p} in initializers for static | |
4827 | data. For instance, you can write | |
4828 | ||
4829 | @smallexample | |
79323c50 | 4830 | static const int table[] = @{ |
13104975 | 4831 | __builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1, |
0d893a63 | 4832 | /* @r{@dots{}} */ |
79323c50 | 4833 | @}; |
13104975 ZW |
4834 | @end smallexample |
4835 | ||
4836 | @noindent | |
4837 | This is an acceptable initializer even if @var{EXPRESSION} is not a | |
4838 | constant expression. GCC must be more conservative about evaluating the | |
4839 | built-in in this case, because it has no opportunity to perform | |
4840 | optimization. | |
4841 | ||
4842 | Previous versions of GCC did not accept this built-in in data | |
4843 | initializers. The earliest version where it is completely safe is | |
4844 | 3.0.1. | |
84330467 | 4845 | @end deftypefn |
185ebd6c | 4846 | |
84330467 JM |
4847 | @deftypefn {Built-in Function} long __builtin_expect (long @var{exp}, long @var{c}) |
4848 | @opindex fprofile-arcs | |
02f52e19 | 4849 | You may use @code{__builtin_expect} to provide the compiler with |
994a57cd | 4850 | branch prediction information. In general, you should prefer to |
84330467 | 4851 | use actual profile feedback for this (@option{-fprofile-arcs}), as |
994a57cd | 4852 | programmers are notoriously bad at predicting how their programs |
60b6e1f5 | 4853 | actually perform. However, there are applications in which this |
994a57cd RH |
4854 | data is hard to collect. |
4855 | ||
4856 | The return value is the value of @var{exp}, which should be an | |
4857 | integral expression. The value of @var{c} must be a compile-time | |
84330467 | 4858 | constant. The semantics of the built-in are that it is expected |
994a57cd RH |
4859 | that @var{exp} == @var{c}. For example: |
4860 | ||
4861 | @smallexample | |
4862 | if (__builtin_expect (x, 0)) | |
4863 | foo (); | |
4864 | @end smallexample | |
4865 | ||
4866 | @noindent | |
4867 | would indicate that we do not expect to call @code{foo}, since | |
4868 | we expect @code{x} to be zero. Since you are limited to integral | |
4869 | expressions for @var{exp}, you should use constructions such as | |
4870 | ||
4871 | @smallexample | |
4872 | if (__builtin_expect (ptr != NULL, 1)) | |
4873 | error (); | |
4874 | @end smallexample | |
4875 | ||
4876 | @noindent | |
4877 | when testing pointer or floating-point values. | |
84330467 | 4878 | @end deftypefn |
994a57cd | 4879 | |
3bca17dd | 4880 | @deftypefn {Built-in Function} void __builtin_prefetch (const void *@var{addr}, ...) |
a9ccbb60 JJ |
4881 | This function is used to minimize cache-miss latency by moving data into |
4882 | a cache before it is accessed. | |
4883 | You can insert calls to @code{__builtin_prefetch} into code for which | |
4884 | you know addresses of data in memory that is likely to be accessed soon. | |
4885 | If the target supports them, data prefetch instructions will be generated. | |
4886 | If the prefetch is done early enough before the access then the data will | |
4887 | be in the cache by the time it is accessed. | |
4888 | ||
4889 | The value of @var{addr} is the address of the memory to prefetch. | |
e83d297b | 4890 | There are two optional arguments, @var{rw} and @var{locality}. |
a9ccbb60 | 4891 | The value of @var{rw} is a compile-time constant one or zero; one |
e83d297b JJ |
4892 | means that the prefetch is preparing for a write to the memory address |
4893 | and zero, the default, means that the prefetch is preparing for a read. | |
a9ccbb60 JJ |
4894 | The value @var{locality} must be a compile-time constant integer between |
4895 | zero and three. A value of zero means that the data has no temporal | |
4896 | locality, so it need not be left in the cache after the access. A value | |
4897 | of three means that the data has a high degree of temporal locality and | |
4898 | should be left in all levels of cache possible. Values of one and two | |
e83d297b JJ |
4899 | mean, respectively, a low or moderate degree of temporal locality. The |
4900 | default is three. | |
a9ccbb60 JJ |
4901 | |
4902 | @smallexample | |
4903 | for (i = 0; i < n; i++) | |
4904 | @{ | |
4905 | a[i] = a[i] + b[i]; | |
4906 | __builtin_prefetch (&a[i+j], 1, 1); | |
4907 | __builtin_prefetch (&b[i+j], 0, 1); | |
0d893a63 | 4908 | /* @r{@dots{}} */ |
a9ccbb60 JJ |
4909 | @} |
4910 | @end smallexample | |
4911 | ||
f282ffb3 | 4912 | Data prefetch does not generate faults if @var{addr} is invalid, but |
a9ccbb60 JJ |
4913 | the address expression itself must be valid. For example, a prefetch |
4914 | of @code{p->next} will not fault if @code{p->next} is not a valid | |
4915 | address, but evaluation will fault if @code{p} is not a valid address. | |
4916 | ||
4917 | If the target does not support data prefetch, the address expression | |
4918 | is evaluated if it includes side effects but no other code is generated | |
4919 | and GCC does not issue a warning. | |
4920 | @end deftypefn | |
4921 | ||
ab5e2615 RH |
4922 | @deftypefn {Built-in Function} double __builtin_huge_val (void) |
4923 | Returns a positive infinity, if supported by the floating-point format, | |
4924 | else @code{DBL_MAX}. This function is suitable for implementing the | |
4925 | ISO C macro @code{HUGE_VAL}. | |
4926 | @end deftypefn | |
4927 | ||
4928 | @deftypefn {Built-in Function} float __builtin_huge_valf (void) | |
4929 | Similar to @code{__builtin_huge_val}, except the return type is @code{float}. | |
4930 | @end deftypefn | |
4931 | ||
4932 | @deftypefn {Built-in Function} long double __builtin_huge_vall (void) | |
4933 | Similar to @code{__builtin_huge_val}, except the return | |
4934 | type is @code{long double}. | |
4935 | @end deftypefn | |
4936 | ||
4937 | @deftypefn {Built-in Function} double __builtin_inf (void) | |
4938 | Similar to @code{__builtin_huge_val}, except a warning is generated | |
4939 | if the target floating-point format does not support infinities. | |
4940 | This function is suitable for implementing the ISO C99 macro @code{INFINITY}. | |
4941 | @end deftypefn | |
4942 | ||
4943 | @deftypefn {Built-in Function} float __builtin_inff (void) | |
4944 | Similar to @code{__builtin_inf}, except the return type is @code{float}. | |
4945 | @end deftypefn | |
4946 | ||
4947 | @deftypefn {Built-in Function} long double __builtin_infl (void) | |
4948 | Similar to @code{__builtin_inf}, except the return | |
4949 | type is @code{long double}. | |
4950 | @end deftypefn | |
4951 | ||
1472e41c RH |
4952 | @deftypefn {Built-in Function} double __builtin_nan (const char *str) |
4953 | This is an implementation of the ISO C99 function @code{nan}. | |
4954 | ||
4955 | Since ISO C99 defines this function in terms of @code{strtod}, which we | |
c0478a66 | 4956 | do not implement, a description of the parsing is in order. The string |
1472e41c RH |
4957 | is parsed as by @code{strtol}; that is, the base is recognized by |
4958 | leading @samp{0} or @samp{0x} prefixes. The number parsed is placed | |
4959 | in the significand such that the least significant bit of the number | |
4960 | is at the least significant bit of the significand. The number is | |
4961 | truncated to fit the significand field provided. The significand is | |
4962 | forced to be a quiet NaN. | |
4963 | ||
4964 | This function, if given a string literal, is evaluated early enough | |
4965 | that it is considered a compile-time constant. | |
4966 | @end deftypefn | |
4967 | ||
4968 | @deftypefn {Built-in Function} float __builtin_nanf (const char *str) | |
4969 | Similar to @code{__builtin_nan}, except the return type is @code{float}. | |
4970 | @end deftypefn | |
4971 | ||
4972 | @deftypefn {Built-in Function} long double __builtin_nanl (const char *str) | |
4973 | Similar to @code{__builtin_nan}, except the return type is @code{long double}. | |
4974 | @end deftypefn | |
4975 | ||
4976 | @deftypefn {Built-in Function} double __builtin_nans (const char *str) | |
4977 | Similar to @code{__builtin_nan}, except the significand is forced | |
4978 | to be a signaling NaN. The @code{nans} function is proposed by | |
34bdc247 | 4979 | @uref{http://std.dkuug.dk/JTC1/SC22/WG14/www/docs/n965.htm,,WG14 N965}. |
1472e41c RH |
4980 | @end deftypefn |
4981 | ||
4982 | @deftypefn {Built-in Function} float __builtin_nansf (const char *str) | |
4983 | Similar to @code{__builtin_nans}, except the return type is @code{float}. | |
4984 | @end deftypefn | |
4985 | ||
4986 | @deftypefn {Built-in Function} long double __builtin_nansl (const char *str) | |
4987 | Similar to @code{__builtin_nans}, except the return type is @code{long double}. | |
4988 | @end deftypefn | |
4989 | ||
2928cd7a RH |
4990 | @deftypefn {Built-in Function} int __builtin_ffs (unsigned int x) |
4991 | Returns one plus the index of the least significant 1-bit of @var{x}, or | |
4992 | if @var{x} is zero, returns zero. | |
4993 | @end deftypefn | |
4994 | ||
4995 | @deftypefn {Built-in Function} int __builtin_clz (unsigned int x) | |
4996 | Returns the number of leading 0-bits in @var{x}, starting at the most | |
4997 | significant bit position. If @var{x} is 0, the result is undefined. | |
4998 | @end deftypefn | |
4999 | ||
5000 | @deftypefn {Built-in Function} int __builtin_ctz (unsigned int x) | |
5001 | Returns the number of trailing 0-bits in @var{x}, starting at the least | |
5002 | significant bit position. If @var{x} is 0, the result is undefined. | |
5003 | @end deftypefn | |
5004 | ||
5005 | @deftypefn {Built-in Function} int __builtin_popcount (unsigned int x) | |
5006 | Returns the number of 1-bits in @var{x}. | |
5007 | @end deftypefn | |
5008 | ||
5009 | @deftypefn {Built-in Function} int __builtin_parity (unsigned int x) | |
5010 | Returns the parity of @var{x}, i.@:e. the number of 1-bits in @var{x} | |
5011 | modulo 2. | |
5012 | @end deftypefn | |
5013 | ||
5014 | @deftypefn {Built-in Function} int __builtin_ffsl (unsigned long) | |
5015 | Similar to @code{__builtin_ffs}, except the argument type is | |
5016 | @code{unsigned long}. | |
5017 | @end deftypefn | |
5018 | ||
5019 | @deftypefn {Built-in Function} int __builtin_clzl (unsigned long) | |
5020 | Similar to @code{__builtin_clz}, except the argument type is | |
5021 | @code{unsigned long}. | |
5022 | @end deftypefn | |
5023 | ||
5024 | @deftypefn {Built-in Function} int __builtin_ctzl (unsigned long) | |
5025 | Similar to @code{__builtin_ctz}, except the argument type is | |
5026 | @code{unsigned long}. | |
5027 | @end deftypefn | |
5028 | ||
5029 | @deftypefn {Built-in Function} int __builtin_popcountl (unsigned long) | |
5030 | Similar to @code{__builtin_popcount}, except the argument type is | |
5031 | @code{unsigned long}. | |
5032 | @end deftypefn | |
5033 | ||
5034 | @deftypefn {Built-in Function} int __builtin_parityl (unsigned long) | |
5035 | Similar to @code{__builtin_parity}, except the argument type is | |
5036 | @code{unsigned long}. | |
5037 | @end deftypefn | |
5038 | ||
5039 | @deftypefn {Built-in Function} int __builtin_ffsll (unsigned long long) | |
5040 | Similar to @code{__builtin_ffs}, except the argument type is | |
5041 | @code{unsigned long long}. | |
5042 | @end deftypefn | |
5043 | ||
5044 | @deftypefn {Built-in Function} int __builtin_clzll (unsigned long long) | |
5045 | Similar to @code{__builtin_clz}, except the argument type is | |
5046 | @code{unsigned long long}. | |
5047 | @end deftypefn | |
5048 | ||
5049 | @deftypefn {Built-in Function} int __builtin_ctzll (unsigned long long) | |
5050 | Similar to @code{__builtin_ctz}, except the argument type is | |
5051 | @code{unsigned long long}. | |
5052 | @end deftypefn | |
5053 | ||
5054 | @deftypefn {Built-in Function} int __builtin_popcountll (unsigned long long) | |
5055 | Similar to @code{__builtin_popcount}, except the argument type is | |
5056 | @code{unsigned long long}. | |
5057 | @end deftypefn | |
5058 | ||
5059 | @deftypefn {Built-in Function} int __builtin_parityll (unsigned long long) | |
5060 | Similar to @code{__builtin_parity}, except the argument type is | |
5061 | @code{unsigned long long}. | |
5062 | @end deftypefn | |
5063 | ||
5064 | ||
0975678f JM |
5065 | @node Target Builtins |
5066 | @section Built-in Functions Specific to Particular Target Machines | |
5067 | ||
5068 | On some target machines, GCC supports many built-in functions specific | |
5069 | to those machines. Generally these generate calls to specific machine | |
5070 | instructions, but allow the compiler to schedule those calls. | |
5071 | ||
5072 | @menu | |
6d8fd7bb | 5073 | * Alpha Built-in Functions:: |
0975678f | 5074 | * X86 Built-in Functions:: |
333c8841 | 5075 | * PowerPC AltiVec Built-in Functions:: |
0975678f JM |
5076 | @end menu |
5077 | ||
6d8fd7bb RH |
5078 | @node Alpha Built-in Functions |
5079 | @subsection Alpha Built-in Functions | |
5080 | ||
5081 | These built-in functions are available for the Alpha family of | |
5082 | processors, depending on the command-line switches used. | |
5083 | ||
95b1627e | 5084 | The following built-in functions are always available. They |
6d8fd7bb RH |
5085 | all generate the machine instruction that is part of the name. |
5086 | ||
5087 | @example | |
5088 | long __builtin_alpha_implver (void) | |
5089 | long __builtin_alpha_rpcc (void) | |
5090 | long __builtin_alpha_amask (long) | |
5091 | long __builtin_alpha_cmpbge (long, long) | |
c4b50f1a RH |
5092 | long __builtin_alpha_extbl (long, long) |
5093 | long __builtin_alpha_extwl (long, long) | |
5094 | long __builtin_alpha_extll (long, long) | |
6d8fd7bb | 5095 | long __builtin_alpha_extql (long, long) |
c4b50f1a RH |
5096 | long __builtin_alpha_extwh (long, long) |
5097 | long __builtin_alpha_extlh (long, long) | |
6d8fd7bb | 5098 | long __builtin_alpha_extqh (long, long) |
c4b50f1a RH |
5099 | long __builtin_alpha_insbl (long, long) |
5100 | long __builtin_alpha_inswl (long, long) | |
5101 | long __builtin_alpha_insll (long, long) | |
5102 | long __builtin_alpha_insql (long, long) | |
5103 | long __builtin_alpha_inswh (long, long) | |
5104 | long __builtin_alpha_inslh (long, long) | |
5105 | long __builtin_alpha_insqh (long, long) | |
5106 | long __builtin_alpha_mskbl (long, long) | |
5107 | long __builtin_alpha_mskwl (long, long) | |
5108 | long __builtin_alpha_mskll (long, long) | |
5109 | long __builtin_alpha_mskql (long, long) | |
5110 | long __builtin_alpha_mskwh (long, long) | |
5111 | long __builtin_alpha_msklh (long, long) | |
5112 | long __builtin_alpha_mskqh (long, long) | |
5113 | long __builtin_alpha_umulh (long, long) | |
6d8fd7bb RH |
5114 | long __builtin_alpha_zap (long, long) |
5115 | long __builtin_alpha_zapnot (long, long) | |
5116 | @end example | |
5117 | ||
5118 | The following built-in functions are always with @option{-mmax} | |
5119 | or @option{-mcpu=@var{cpu}} where @var{cpu} is @code{pca56} or | |
5120 | later. They all generate the machine instruction that is part | |
5121 | of the name. | |
5122 | ||
5123 | @example | |
5124 | long __builtin_alpha_pklb (long) | |
5125 | long __builtin_alpha_pkwb (long) | |
5126 | long __builtin_alpha_unpkbl (long) | |
5127 | long __builtin_alpha_unpkbw (long) | |
5128 | long __builtin_alpha_minub8 (long, long) | |
5129 | long __builtin_alpha_minsb8 (long, long) | |
5130 | long __builtin_alpha_minuw4 (long, long) | |
5131 | long __builtin_alpha_minsw4 (long, long) | |
5132 | long __builtin_alpha_maxub8 (long, long) | |
5133 | long __builtin_alpha_maxsb8 (long, long) | |
5134 | long __builtin_alpha_maxuw4 (long, long) | |
5135 | long __builtin_alpha_maxsw4 (long, long) | |
5136 | long __builtin_alpha_perr (long, long) | |
5137 | @end example | |
5138 | ||
c4b50f1a RH |
5139 | The following built-in functions are always with @option{-mcix} |
5140 | or @option{-mcpu=@var{cpu}} where @var{cpu} is @code{ev67} or | |
5141 | later. They all generate the machine instruction that is part | |
5142 | of the name. | |
5143 | ||
5144 | @example | |
5145 | long __builtin_alpha_cttz (long) | |
5146 | long __builtin_alpha_ctlz (long) | |
5147 | long __builtin_alpha_ctpop (long) | |
5148 | @end example | |
5149 | ||
116b7a5e RH |
5150 | The following builtins are available on systems that use the OSF/1 |
5151 | PALcode. Normally they invoke the @code{rduniq} and @code{wruniq} | |
5152 | PAL calls, but when invoked with @option{-mtls-kernel}, they invoke | |
5153 | @code{rdval} and @code{wrval}. | |
5154 | ||
5155 | @example | |
5156 | void *__builtin_thread_pointer (void) | |
5157 | void __builtin_set_thread_pointer (void *) | |
5158 | @end example | |
5159 | ||
0975678f JM |
5160 | @node X86 Built-in Functions |
5161 | @subsection X86 Built-in Functions | |
5162 | ||
5163 | These built-in functions are available for the i386 and x86-64 family | |
5164 | of computers, depending on the command-line switches used. | |
5165 | ||
5166 | The following machine modes are available for use with MMX built-in functions | |
333c8841 AH |
5167 | (@pxref{Vector Extensions}): @code{V2SI} for a vector of two 32-bit integers, |
5168 | @code{V4HI} for a vector of four 16-bit integers, and @code{V8QI} for a | |
5169 | vector of eight 8-bit integers. Some of the built-in functions operate on | |
5170 | MMX registers as a whole 64-bit entity, these use @code{DI} as their mode. | |
0975678f JM |
5171 | |
5172 | If 3Dnow extensions are enabled, @code{V2SF} is used as a mode for a vector | |
333c8841 | 5173 | of two 32-bit floating point values. |
0975678f | 5174 | |
333c8841 AH |
5175 | If SSE extensions are enabled, @code{V4SF} is used for a vector of four 32-bit |
5176 | floating point values. Some instructions use a vector of four 32-bit | |
0975678f | 5177 | integers, these use @code{V4SI}. Finally, some instructions operate on an |
333c8841 | 5178 | entire vector register, interpreting it as a 128-bit integer, these use mode |
0975678f JM |
5179 | @code{TI}. |
5180 | ||
5181 | The following built-in functions are made available by @option{-mmmx}. | |
5182 | All of them generate the machine instruction that is part of the name. | |
5183 | ||
5184 | @example | |
5185 | v8qi __builtin_ia32_paddb (v8qi, v8qi) | |
5186 | v4hi __builtin_ia32_paddw (v4hi, v4hi) | |
5187 | v2si __builtin_ia32_paddd (v2si, v2si) | |
5188 | v8qi __builtin_ia32_psubb (v8qi, v8qi) | |
5189 | v4hi __builtin_ia32_psubw (v4hi, v4hi) | |
5190 | v2si __builtin_ia32_psubd (v2si, v2si) | |
5191 | v8qi __builtin_ia32_paddsb (v8qi, v8qi) | |
5192 | v4hi __builtin_ia32_paddsw (v4hi, v4hi) | |
5193 | v8qi __builtin_ia32_psubsb (v8qi, v8qi) | |
5194 | v4hi __builtin_ia32_psubsw (v4hi, v4hi) | |
5195 | v8qi __builtin_ia32_paddusb (v8qi, v8qi) | |
5196 | v4hi __builtin_ia32_paddusw (v4hi, v4hi) | |
5197 | v8qi __builtin_ia32_psubusb (v8qi, v8qi) | |
5198 | v4hi __builtin_ia32_psubusw (v4hi, v4hi) | |
5199 | v4hi __builtin_ia32_pmullw (v4hi, v4hi) | |
5200 | v4hi __builtin_ia32_pmulhw (v4hi, v4hi) | |
5201 | di __builtin_ia32_pand (di, di) | |
5202 | di __builtin_ia32_pandn (di,di) | |
5203 | di __builtin_ia32_por (di, di) | |
5204 | di __builtin_ia32_pxor (di, di) | |
5205 | v8qi __builtin_ia32_pcmpeqb (v8qi, v8qi) | |
5206 | v4hi __builtin_ia32_pcmpeqw (v4hi, v4hi) | |
5207 | v2si __builtin_ia32_pcmpeqd (v2si, v2si) | |
5208 | v8qi __builtin_ia32_pcmpgtb (v8qi, v8qi) | |
5209 | v4hi __builtin_ia32_pcmpgtw (v4hi, v4hi) | |
5210 | v2si __builtin_ia32_pcmpgtd (v2si, v2si) | |
5211 | v8qi __builtin_ia32_punpckhbw (v8qi, v8qi) | |
5212 | v4hi __builtin_ia32_punpckhwd (v4hi, v4hi) | |
5213 | v2si __builtin_ia32_punpckhdq (v2si, v2si) | |
5214 | v8qi __builtin_ia32_punpcklbw (v8qi, v8qi) | |
5215 | v4hi __builtin_ia32_punpcklwd (v4hi, v4hi) | |
5216 | v2si __builtin_ia32_punpckldq (v2si, v2si) | |
5217 | v8qi __builtin_ia32_packsswb (v4hi, v4hi) | |
5218 | v4hi __builtin_ia32_packssdw (v2si, v2si) | |
5219 | v8qi __builtin_ia32_packuswb (v4hi, v4hi) | |
5220 | @end example | |
5221 | ||
5222 | The following built-in functions are made available either with | |
5223 | @option{-msse}, or with a combination of @option{-m3dnow} and | |
5224 | @option{-march=athlon}. All of them generate the machine | |
5225 | instruction that is part of the name. | |
5226 | ||
5227 | @example | |
5228 | v4hi __builtin_ia32_pmulhuw (v4hi, v4hi) | |
5229 | v8qi __builtin_ia32_pavgb (v8qi, v8qi) | |
5230 | v4hi __builtin_ia32_pavgw (v4hi, v4hi) | |
5231 | v4hi __builtin_ia32_psadbw (v8qi, v8qi) | |
5232 | v8qi __builtin_ia32_pmaxub (v8qi, v8qi) | |
5233 | v4hi __builtin_ia32_pmaxsw (v4hi, v4hi) | |
5234 | v8qi __builtin_ia32_pminub (v8qi, v8qi) | |
5235 | v4hi __builtin_ia32_pminsw (v4hi, v4hi) | |
5236 | int __builtin_ia32_pextrw (v4hi, int) | |
5237 | v4hi __builtin_ia32_pinsrw (v4hi, int, int) | |
5238 | int __builtin_ia32_pmovmskb (v8qi) | |
5239 | void __builtin_ia32_maskmovq (v8qi, v8qi, char *) | |
5240 | void __builtin_ia32_movntq (di *, di) | |
5241 | void __builtin_ia32_sfence (void) | |
5242 | @end example | |
5243 | ||
5244 | The following built-in functions are available when @option{-msse} is used. | |
5245 | All of them generate the machine instruction that is part of the name. | |
5246 | ||
5247 | @example | |
5248 | int __builtin_ia32_comieq (v4sf, v4sf) | |
5249 | int __builtin_ia32_comineq (v4sf, v4sf) | |
5250 | int __builtin_ia32_comilt (v4sf, v4sf) | |
5251 | int __builtin_ia32_comile (v4sf, v4sf) | |
5252 | int __builtin_ia32_comigt (v4sf, v4sf) | |
5253 | int __builtin_ia32_comige (v4sf, v4sf) | |
5254 | int __builtin_ia32_ucomieq (v4sf, v4sf) | |
5255 | int __builtin_ia32_ucomineq (v4sf, v4sf) | |
5256 | int __builtin_ia32_ucomilt (v4sf, v4sf) | |
5257 | int __builtin_ia32_ucomile (v4sf, v4sf) | |
5258 | int __builtin_ia32_ucomigt (v4sf, v4sf) | |
5259 | int __builtin_ia32_ucomige (v4sf, v4sf) | |
5260 | v4sf __builtin_ia32_addps (v4sf, v4sf) | |
5261 | v4sf __builtin_ia32_subps (v4sf, v4sf) | |
5262 | v4sf __builtin_ia32_mulps (v4sf, v4sf) | |
5263 | v4sf __builtin_ia32_divps (v4sf, v4sf) | |
5264 | v4sf __builtin_ia32_addss (v4sf, v4sf) | |
5265 | v4sf __builtin_ia32_subss (v4sf, v4sf) | |
5266 | v4sf __builtin_ia32_mulss (v4sf, v4sf) | |
5267 | v4sf __builtin_ia32_divss (v4sf, v4sf) | |
5268 | v4si __builtin_ia32_cmpeqps (v4sf, v4sf) | |
5269 | v4si __builtin_ia32_cmpltps (v4sf, v4sf) | |
5270 | v4si __builtin_ia32_cmpleps (v4sf, v4sf) | |
5271 | v4si __builtin_ia32_cmpgtps (v4sf, v4sf) | |
5272 | v4si __builtin_ia32_cmpgeps (v4sf, v4sf) | |
5273 | v4si __builtin_ia32_cmpunordps (v4sf, v4sf) | |
5274 | v4si __builtin_ia32_cmpneqps (v4sf, v4sf) | |
5275 | v4si __builtin_ia32_cmpnltps (v4sf, v4sf) | |
5276 | v4si __builtin_ia32_cmpnleps (v4sf, v4sf) | |
5277 | v4si __builtin_ia32_cmpngtps (v4sf, v4sf) | |
5278 | v4si __builtin_ia32_cmpngeps (v4sf, v4sf) | |
5279 | v4si __builtin_ia32_cmpordps (v4sf, v4sf) | |
5280 | v4si __builtin_ia32_cmpeqss (v4sf, v4sf) | |
5281 | v4si __builtin_ia32_cmpltss (v4sf, v4sf) | |
5282 | v4si __builtin_ia32_cmpless (v4sf, v4sf) | |
0975678f JM |
5283 | v4si __builtin_ia32_cmpunordss (v4sf, v4sf) |
5284 | v4si __builtin_ia32_cmpneqss (v4sf, v4sf) | |
5285 | v4si __builtin_ia32_cmpnlts (v4sf, v4sf) | |
5286 | v4si __builtin_ia32_cmpnless (v4sf, v4sf) | |
0975678f JM |
5287 | v4si __builtin_ia32_cmpordss (v4sf, v4sf) |
5288 | v4sf __builtin_ia32_maxps (v4sf, v4sf) | |
5289 | v4sf __builtin_ia32_maxss (v4sf, v4sf) | |
5290 | v4sf __builtin_ia32_minps (v4sf, v4sf) | |
5291 | v4sf __builtin_ia32_minss (v4sf, v4sf) | |
5292 | v4sf __builtin_ia32_andps (v4sf, v4sf) | |
5293 | v4sf __builtin_ia32_andnps (v4sf, v4sf) | |
5294 | v4sf __builtin_ia32_orps (v4sf, v4sf) | |
5295 | v4sf __builtin_ia32_xorps (v4sf, v4sf) | |
5296 | v4sf __builtin_ia32_movss (v4sf, v4sf) | |
5297 | v4sf __builtin_ia32_movhlps (v4sf, v4sf) | |
5298 | v4sf __builtin_ia32_movlhps (v4sf, v4sf) | |
5299 | v4sf __builtin_ia32_unpckhps (v4sf, v4sf) | |
5300 | v4sf __builtin_ia32_unpcklps (v4sf, v4sf) | |
5301 | v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si) | |
5302 | v4sf __builtin_ia32_cvtsi2ss (v4sf, int) | |
5303 | v2si __builtin_ia32_cvtps2pi (v4sf) | |
5304 | int __builtin_ia32_cvtss2si (v4sf) | |
5305 | v2si __builtin_ia32_cvttps2pi (v4sf) | |
5306 | int __builtin_ia32_cvttss2si (v4sf) | |
5307 | v4sf __builtin_ia32_rcpps (v4sf) | |
5308 | v4sf __builtin_ia32_rsqrtps (v4sf) | |
5309 | v4sf __builtin_ia32_sqrtps (v4sf) | |
5310 | v4sf __builtin_ia32_rcpss (v4sf) | |
5311 | v4sf __builtin_ia32_rsqrtss (v4sf) | |
5312 | v4sf __builtin_ia32_sqrtss (v4sf) | |
5313 | v4sf __builtin_ia32_shufps (v4sf, v4sf, int) | |
5314 | void __builtin_ia32_movntps (float *, v4sf) | |
5315 | int __builtin_ia32_movmskps (v4sf) | |
5316 | @end example | |
5317 | ||
5318 | The following built-in functions are available when @option{-msse} is used. | |
5319 | ||
5320 | @table @code | |
5321 | @item v4sf __builtin_ia32_loadaps (float *) | |
5322 | Generates the @code{movaps} machine instruction as a load from memory. | |
5323 | @item void __builtin_ia32_storeaps (float *, v4sf) | |
5324 | Generates the @code{movaps} machine instruction as a store to memory. | |
5325 | @item v4sf __builtin_ia32_loadups (float *) | |
5326 | Generates the @code{movups} machine instruction as a load from memory. | |
5327 | @item void __builtin_ia32_storeups (float *, v4sf) | |
5328 | Generates the @code{movups} machine instruction as a store to memory. | |
5329 | @item v4sf __builtin_ia32_loadsss (float *) | |
5330 | Generates the @code{movss} machine instruction as a load from memory. | |
5331 | @item void __builtin_ia32_storess (float *, v4sf) | |
5332 | Generates the @code{movss} machine instruction as a store to memory. | |
5333 | @item v4sf __builtin_ia32_loadhps (v4sf, v2si *) | |
5334 | Generates the @code{movhps} machine instruction as a load from memory. | |
5335 | @item v4sf __builtin_ia32_loadlps (v4sf, v2si *) | |
5336 | Generates the @code{movlps} machine instruction as a load from memory | |
5337 | @item void __builtin_ia32_storehps (v4sf, v2si *) | |
5338 | Generates the @code{movhps} machine instruction as a store to memory. | |
5339 | @item void __builtin_ia32_storelps (v4sf, v2si *) | |
5340 | Generates the @code{movlps} machine instruction as a store to memory. | |
5341 | @end table | |
5342 | ||
5343 | The following built-in functions are available when @option{-m3dnow} is used. | |
5344 | All of them generate the machine instruction that is part of the name. | |
5345 | ||
5346 | @example | |
5347 | void __builtin_ia32_femms (void) | |
5348 | v8qi __builtin_ia32_pavgusb (v8qi, v8qi) | |
5349 | v2si __builtin_ia32_pf2id (v2sf) | |
5350 | v2sf __builtin_ia32_pfacc (v2sf, v2sf) | |
5351 | v2sf __builtin_ia32_pfadd (v2sf, v2sf) | |
5352 | v2si __builtin_ia32_pfcmpeq (v2sf, v2sf) | |
5353 | v2si __builtin_ia32_pfcmpge (v2sf, v2sf) | |
5354 | v2si __builtin_ia32_pfcmpgt (v2sf, v2sf) | |
5355 | v2sf __builtin_ia32_pfmax (v2sf, v2sf) | |
5356 | v2sf __builtin_ia32_pfmin (v2sf, v2sf) | |
5357 | v2sf __builtin_ia32_pfmul (v2sf, v2sf) | |
5358 | v2sf __builtin_ia32_pfrcp (v2sf) | |
5359 | v2sf __builtin_ia32_pfrcpit1 (v2sf, v2sf) | |
5360 | v2sf __builtin_ia32_pfrcpit2 (v2sf, v2sf) | |
5361 | v2sf __builtin_ia32_pfrsqrt (v2sf) | |
5362 | v2sf __builtin_ia32_pfrsqrtit1 (v2sf, v2sf) | |
5363 | v2sf __builtin_ia32_pfsub (v2sf, v2sf) | |
5364 | v2sf __builtin_ia32_pfsubr (v2sf, v2sf) | |
5365 | v2sf __builtin_ia32_pi2fd (v2si) | |
5366 | v4hi __builtin_ia32_pmulhrw (v4hi, v4hi) | |
5367 | @end example | |
5368 | ||
5369 | The following built-in functions are available when both @option{-m3dnow} | |
5370 | and @option{-march=athlon} are used. All of them generate the machine | |
5371 | instruction that is part of the name. | |
5372 | ||
5373 | @example | |
5374 | v2si __builtin_ia32_pf2iw (v2sf) | |
5375 | v2sf __builtin_ia32_pfnacc (v2sf, v2sf) | |
5376 | v2sf __builtin_ia32_pfpnacc (v2sf, v2sf) | |
5377 | v2sf __builtin_ia32_pi2fw (v2si) | |
5378 | v2sf __builtin_ia32_pswapdsf (v2sf) | |
5379 | v2si __builtin_ia32_pswapdsi (v2si) | |
5380 | @end example | |
5381 | ||
333c8841 AH |
5382 | @node PowerPC AltiVec Built-in Functions |
5383 | @subsection PowerPC AltiVec Built-in Functions | |
5384 | ||
5385 | These built-in functions are available for the PowerPC family | |
5386 | of computers, depending on the command-line switches used. | |
5387 | ||
5388 | The following machine modes are available for use with AltiVec built-in | |
5389 | functions (@pxref{Vector Extensions}): @code{V4SI} for a vector of four | |
5390 | 32-bit integers, @code{V4SF} for a vector of four 32-bit floating point | |
5391 | numbers, @code{V8HI} for a vector of eight 16-bit integers, and | |
5392 | @code{V16QI} for a vector of sixteen 8-bit integers. | |
5393 | ||
5394 | The following functions are made available by including | |
5395 | @code{<altivec.h>} and using @option{-maltivec} and | |
5396 | @option{-mabi=altivec}. The functions implement the functionality | |
5397 | described in Motorola's AltiVec Programming Interface Manual. | |
5398 | ||
90989b26 AH |
5399 | There are a few differences from Motorola's documentation and GCC's |
5400 | implementation. Vector constants are done with curly braces (not | |
5401 | parentheses). Vector initializers require no casts if the vector | |
5402 | constant is of the same type as the variable it is initializing. The | |
5403 | @code{vector bool} type is deprecated and will be discontinued in | |
5404 | further revisions. Use @code{vector signed} instead. If @code{signed} | |
5405 | or @code{unsigned} is omitted, the vector type will default to | |
8254cb45 | 5406 | @code{signed}. Lastly, all overloaded functions are implemented with macros |
90989b26 AH |
5407 | for the C implementation. So code the following example will not work: |
5408 | ||
5409 | @smallexample | |
8254cb45 | 5410 | vec_add ((vector signed int)@{1, 2, 3, 4@}, foo); |
90989b26 AH |
5411 | @end smallexample |
5412 | ||
5413 | Since vec_add is a macro, the vector constant in the above example will | |
5414 | be treated as four different arguments. Wrap the entire argument in | |
5415 | parentheses for this to work. The C++ implementation does not use | |
5416 | macros. | |
5417 | ||
ae4b4a02 AH |
5418 | @emph{Note:} Only the @code{<altivec.h>} interface is supported. |
5419 | Internally, GCC uses built-in functions to achieve the functionality in | |
5420 | the aforementioned header file, but they are not supported and are | |
5421 | subject to change without notice. | |
5422 | ||
333c8841 AH |
5423 | @smallexample |
5424 | vector signed char vec_abs (vector signed char, vector signed char); | |
5425 | vector signed short vec_abs (vector signed short, vector signed short); | |
5426 | vector signed int vec_abs (vector signed int, vector signed int); | |
5427 | vector signed float vec_abs (vector signed float, vector signed float); | |
5428 | ||
5429 | vector signed char vec_abss (vector signed char, vector signed char); | |
5430 | vector signed short vec_abss (vector signed short, vector signed short); | |
5431 | ||
5432 | vector signed char vec_add (vector signed char, vector signed char); | |
5433 | vector unsigned char vec_add (vector signed char, vector unsigned char); | |
5434 | ||
5435 | vector unsigned char vec_add (vector unsigned char, vector signed char); | |
5436 | ||
924fcc4e JM |
5437 | vector unsigned char vec_add (vector unsigned char, |
5438 | vector unsigned char); | |
333c8841 | 5439 | vector signed short vec_add (vector signed short, vector signed short); |
924fcc4e JM |
5440 | vector unsigned short vec_add (vector signed short, |
5441 | vector unsigned short); | |
5442 | vector unsigned short vec_add (vector unsigned short, | |
5443 | vector signed short); | |
6e5bb5ad JM |
5444 | vector unsigned short vec_add (vector unsigned short, |
5445 | vector unsigned short); | |
333c8841 AH |
5446 | vector signed int vec_add (vector signed int, vector signed int); |
5447 | vector unsigned int vec_add (vector signed int, vector unsigned int); | |
5448 | vector unsigned int vec_add (vector unsigned int, vector signed int); | |
5449 | vector unsigned int vec_add (vector unsigned int, vector unsigned int); | |
5450 | vector float vec_add (vector float, vector float); | |
5451 | ||
5452 | vector unsigned int vec_addc (vector unsigned int, vector unsigned int); | |
5453 | ||
924fcc4e JM |
5454 | vector unsigned char vec_adds (vector signed char, |
5455 | vector unsigned char); | |
5456 | vector unsigned char vec_adds (vector unsigned char, | |
5457 | vector signed char); | |
5458 | vector unsigned char vec_adds (vector unsigned char, | |
5459 | vector unsigned char); | |
333c8841 | 5460 | vector signed char vec_adds (vector signed char, vector signed char); |
924fcc4e JM |
5461 | vector unsigned short vec_adds (vector signed short, |
5462 | vector unsigned short); | |
5463 | vector unsigned short vec_adds (vector unsigned short, | |
5464 | vector signed short); | |
6e5bb5ad JM |
5465 | vector unsigned short vec_adds (vector unsigned short, |
5466 | vector unsigned short); | |
333c8841 AH |
5467 | vector signed short vec_adds (vector signed short, vector signed short); |
5468 | ||
5469 | vector unsigned int vec_adds (vector signed int, vector unsigned int); | |
5470 | vector unsigned int vec_adds (vector unsigned int, vector signed int); | |
5471 | vector unsigned int vec_adds (vector unsigned int, vector unsigned int); | |
5472 | ||
5473 | vector signed int vec_adds (vector signed int, vector signed int); | |
5474 | ||
5475 | vector float vec_and (vector float, vector float); | |
5476 | vector float vec_and (vector float, vector signed int); | |
5477 | vector float vec_and (vector signed int, vector float); | |
5478 | vector signed int vec_and (vector signed int, vector signed int); | |
5479 | vector unsigned int vec_and (vector signed int, vector unsigned int); | |
5480 | vector unsigned int vec_and (vector unsigned int, vector signed int); | |
5481 | vector unsigned int vec_and (vector unsigned int, vector unsigned int); | |
5482 | vector signed short vec_and (vector signed short, vector signed short); | |
924fcc4e JM |
5483 | vector unsigned short vec_and (vector signed short, |
5484 | vector unsigned short); | |
5485 | vector unsigned short vec_and (vector unsigned short, | |
5486 | vector signed short); | |
6e5bb5ad JM |
5487 | vector unsigned short vec_and (vector unsigned short, |
5488 | vector unsigned short); | |
333c8841 AH |
5489 | vector signed char vec_and (vector signed char, vector signed char); |
5490 | vector unsigned char vec_and (vector signed char, vector unsigned char); | |
5491 | ||
5492 | vector unsigned char vec_and (vector unsigned char, vector signed char); | |
5493 | ||
924fcc4e JM |
5494 | vector unsigned char vec_and (vector unsigned char, |
5495 | vector unsigned char); | |
333c8841 AH |
5496 | |
5497 | vector float vec_andc (vector float, vector float); | |
5498 | vector float vec_andc (vector float, vector signed int); | |
5499 | vector float vec_andc (vector signed int, vector float); | |
5500 | vector signed int vec_andc (vector signed int, vector signed int); | |
5501 | vector unsigned int vec_andc (vector signed int, vector unsigned int); | |
5502 | vector unsigned int vec_andc (vector unsigned int, vector signed int); | |
5503 | vector unsigned int vec_andc (vector unsigned int, vector unsigned int); | |
5504 | ||
5505 | vector signed short vec_andc (vector signed short, vector signed short); | |
5506 | ||
924fcc4e JM |
5507 | vector unsigned short vec_andc (vector signed short, |
5508 | vector unsigned short); | |
5509 | vector unsigned short vec_andc (vector unsigned short, | |
5510 | vector signed short); | |
6e5bb5ad JM |
5511 | vector unsigned short vec_andc (vector unsigned short, |
5512 | vector unsigned short); | |
333c8841 | 5513 | vector signed char vec_andc (vector signed char, vector signed char); |
924fcc4e JM |
5514 | vector unsigned char vec_andc (vector signed char, |
5515 | vector unsigned char); | |
5516 | vector unsigned char vec_andc (vector unsigned char, | |
5517 | vector signed char); | |
5518 | vector unsigned char vec_andc (vector unsigned char, | |
5519 | vector unsigned char); | |
333c8841 | 5520 | |
924fcc4e JM |
5521 | vector unsigned char vec_avg (vector unsigned char, |
5522 | vector unsigned char); | |
333c8841 | 5523 | vector signed char vec_avg (vector signed char, vector signed char); |
6e5bb5ad JM |
5524 | vector unsigned short vec_avg (vector unsigned short, |
5525 | vector unsigned short); | |
333c8841 AH |
5526 | vector signed short vec_avg (vector signed short, vector signed short); |
5527 | vector unsigned int vec_avg (vector unsigned int, vector unsigned int); | |
5528 | vector signed int vec_avg (vector signed int, vector signed int); | |
5529 | ||
5530 | vector float vec_ceil (vector float); | |
5531 | ||
5532 | vector signed int vec_cmpb (vector float, vector float); | |
5533 | ||
5534 | vector signed char vec_cmpeq (vector signed char, vector signed char); | |
924fcc4e JM |
5535 | vector signed char vec_cmpeq (vector unsigned char, |
5536 | vector unsigned char); | |
5537 | vector signed short vec_cmpeq (vector signed short, | |
5538 | vector signed short); | |
6e5bb5ad JM |
5539 | vector signed short vec_cmpeq (vector unsigned short, |
5540 | vector unsigned short); | |
333c8841 AH |
5541 | vector signed int vec_cmpeq (vector signed int, vector signed int); |
5542 | vector signed int vec_cmpeq (vector unsigned int, vector unsigned int); | |
5543 | vector signed int vec_cmpeq (vector float, vector float); | |
5544 | ||
5545 | vector signed int vec_cmpge (vector float, vector float); | |
5546 | ||
924fcc4e JM |
5547 | vector signed char vec_cmpgt (vector unsigned char, |
5548 | vector unsigned char); | |
333c8841 | 5549 | vector signed char vec_cmpgt (vector signed char, vector signed char); |
6e5bb5ad JM |
5550 | vector signed short vec_cmpgt (vector unsigned short, |
5551 | vector unsigned short); | |
924fcc4e JM |
5552 | vector signed short vec_cmpgt (vector signed short, |
5553 | vector signed short); | |
333c8841 AH |
5554 | vector signed int vec_cmpgt (vector unsigned int, vector unsigned int); |
5555 | vector signed int vec_cmpgt (vector signed int, vector signed int); | |
5556 | vector signed int vec_cmpgt (vector float, vector float); | |
5557 | ||
5558 | vector signed int vec_cmple (vector float, vector float); | |
5559 | ||
924fcc4e JM |
5560 | vector signed char vec_cmplt (vector unsigned char, |
5561 | vector unsigned char); | |
333c8841 | 5562 | vector signed char vec_cmplt (vector signed char, vector signed char); |
6e5bb5ad JM |
5563 | vector signed short vec_cmplt (vector unsigned short, |
5564 | vector unsigned short); | |
924fcc4e JM |
5565 | vector signed short vec_cmplt (vector signed short, |
5566 | vector signed short); | |
333c8841 AH |
5567 | vector signed int vec_cmplt (vector unsigned int, vector unsigned int); |
5568 | vector signed int vec_cmplt (vector signed int, vector signed int); | |
5569 | vector signed int vec_cmplt (vector float, vector float); | |
5570 | ||
5571 | vector float vec_ctf (vector unsigned int, const char); | |
5572 | vector float vec_ctf (vector signed int, const char); | |
5573 | ||
5574 | vector signed int vec_cts (vector float, const char); | |
5575 | ||
5576 | vector unsigned int vec_ctu (vector float, const char); | |
5577 | ||
5578 | void vec_dss (const char); | |
5579 | ||
5580 | void vec_dssall (void); | |
5581 | ||
5582 | void vec_dst (void *, int, const char); | |
5583 | ||
5584 | void vec_dstst (void *, int, const char); | |
5585 | ||
5586 | void vec_dststt (void *, int, const char); | |
5587 | ||
5588 | void vec_dstt (void *, int, const char); | |
5589 | ||
5590 | vector float vec_expte (vector float, vector float); | |
5591 | ||
5592 | vector float vec_floor (vector float, vector float); | |
5593 | ||
5594 | vector float vec_ld (int, vector float *); | |
5595 | vector float vec_ld (int, float *): | |
5596 | vector signed int vec_ld (int, int *); | |
5597 | vector signed int vec_ld (int, vector signed int *); | |
5598 | vector unsigned int vec_ld (int, vector unsigned int *); | |
5599 | vector unsigned int vec_ld (int, unsigned int *); | |
5600 | vector signed short vec_ld (int, short *, vector signed short *); | |
6e5bb5ad JM |
5601 | vector unsigned short vec_ld (int, unsigned short *, |
5602 | vector unsigned short *); | |
333c8841 AH |
5603 | vector signed char vec_ld (int, signed char *); |
5604 | vector signed char vec_ld (int, vector signed char *); | |
5605 | vector unsigned char vec_ld (int, unsigned char *); | |
5606 | vector unsigned char vec_ld (int, vector unsigned char *); | |
5607 | ||
5608 | vector signed char vec_lde (int, signed char *); | |
5609 | vector unsigned char vec_lde (int, unsigned char *); | |
5610 | vector signed short vec_lde (int, short *); | |
5611 | vector unsigned short vec_lde (int, unsigned short *); | |
5612 | vector float vec_lde (int, float *); | |
5613 | vector signed int vec_lde (int, int *); | |
5614 | vector unsigned int vec_lde (int, unsigned int *); | |
5615 | ||
5616 | void float vec_ldl (int, float *); | |
5617 | void float vec_ldl (int, vector float *); | |
5618 | void signed int vec_ldl (int, vector signed int *); | |
5619 | void signed int vec_ldl (int, int *); | |
5620 | void unsigned int vec_ldl (int, unsigned int *); | |
5621 | void unsigned int vec_ldl (int, vector unsigned int *); | |
5622 | void signed short vec_ldl (int, vector signed short *); | |
5623 | void signed short vec_ldl (int, short *); | |
5624 | void unsigned short vec_ldl (int, vector unsigned short *); | |
5625 | void unsigned short vec_ldl (int, unsigned short *); | |
5626 | void signed char vec_ldl (int, vector signed char *); | |
5627 | void signed char vec_ldl (int, signed char *); | |
5628 | void unsigned char vec_ldl (int, vector unsigned char *); | |
5629 | void unsigned char vec_ldl (int, unsigned char *); | |
5630 | ||
5631 | vector float vec_loge (vector float); | |
5632 | ||
5633 | vector unsigned char vec_lvsl (int, void *, int *); | |
5634 | ||
5635 | vector unsigned char vec_lvsr (int, void *, int *); | |
5636 | ||
5637 | vector float vec_madd (vector float, vector float, vector float); | |
5638 | ||
6e5bb5ad JM |
5639 | vector signed short vec_madds (vector signed short, vector signed short, |
5640 | vector signed short); | |
333c8841 AH |
5641 | |
5642 | vector unsigned char vec_max (vector signed char, vector unsigned char); | |
5643 | ||
5644 | vector unsigned char vec_max (vector unsigned char, vector signed char); | |
5645 | ||
924fcc4e JM |
5646 | vector unsigned char vec_max (vector unsigned char, |
5647 | vector unsigned char); | |
333c8841 | 5648 | vector signed char vec_max (vector signed char, vector signed char); |
924fcc4e JM |
5649 | vector unsigned short vec_max (vector signed short, |
5650 | vector unsigned short); | |
5651 | vector unsigned short vec_max (vector unsigned short, | |
5652 | vector signed short); | |
6e5bb5ad JM |
5653 | vector unsigned short vec_max (vector unsigned short, |
5654 | vector unsigned short); | |
333c8841 AH |
5655 | vector signed short vec_max (vector signed short, vector signed short); |
5656 | vector unsigned int vec_max (vector signed int, vector unsigned int); | |
5657 | vector unsigned int vec_max (vector unsigned int, vector signed int); | |
5658 | vector unsigned int vec_max (vector unsigned int, vector unsigned int); | |
5659 | vector signed int vec_max (vector signed int, vector signed int); | |
5660 | vector float vec_max (vector float, vector float); | |
5661 | ||
5662 | vector signed char vec_mergeh (vector signed char, vector signed char); | |
6e5bb5ad JM |
5663 | vector unsigned char vec_mergeh (vector unsigned char, |
5664 | vector unsigned char); | |
924fcc4e JM |
5665 | vector signed short vec_mergeh (vector signed short, |
5666 | vector signed short); | |
6e5bb5ad JM |
5667 | vector unsigned short vec_mergeh (vector unsigned short, |
5668 | vector unsigned short); | |
333c8841 AH |
5669 | vector float vec_mergeh (vector float, vector float); |
5670 | vector signed int vec_mergeh (vector signed int, vector signed int); | |
924fcc4e JM |
5671 | vector unsigned int vec_mergeh (vector unsigned int, |
5672 | vector unsigned int); | |
333c8841 AH |
5673 | |
5674 | vector signed char vec_mergel (vector signed char, vector signed char); | |
6e5bb5ad JM |
5675 | vector unsigned char vec_mergel (vector unsigned char, |
5676 | vector unsigned char); | |
924fcc4e JM |
5677 | vector signed short vec_mergel (vector signed short, |
5678 | vector signed short); | |
6e5bb5ad JM |
5679 | vector unsigned short vec_mergel (vector unsigned short, |
5680 | vector unsigned short); | |
333c8841 AH |
5681 | vector float vec_mergel (vector float, vector float); |
5682 | vector signed int vec_mergel (vector signed int, vector signed int); | |
924fcc4e JM |
5683 | vector unsigned int vec_mergel (vector unsigned int, |
5684 | vector unsigned int); | |
333c8841 AH |
5685 | |
5686 | vector unsigned short vec_mfvscr (void); | |
5687 | ||
5688 | vector unsigned char vec_min (vector signed char, vector unsigned char); | |
5689 | ||
5690 | vector unsigned char vec_min (vector unsigned char, vector signed char); | |
5691 | ||
924fcc4e JM |
5692 | vector unsigned char vec_min (vector unsigned char, |
5693 | vector unsigned char); | |
333c8841 | 5694 | vector signed char vec_min (vector signed char, vector signed char); |
924fcc4e JM |
5695 | vector unsigned short vec_min (vector signed short, |
5696 | vector unsigned short); | |
5697 | vector unsigned short vec_min (vector unsigned short, | |
5698 | vector signed short); | |
6e5bb5ad JM |
5699 | vector unsigned short vec_min (vector unsigned short, |
5700 | vector unsigned short); | |
333c8841 AH |
5701 | vector signed short vec_min (vector signed short, vector signed short); |
5702 | vector unsigned int vec_min (vector signed int, vector unsigned int); | |
5703 | vector unsigned int vec_min (vector unsigned int, vector signed int); | |
5704 | vector unsigned int vec_min (vector unsigned int, vector unsigned int); | |
5705 | vector signed int vec_min (vector signed int, vector signed int); | |
5706 | vector float vec_min (vector float, vector float); | |
5707 | ||
6e5bb5ad JM |
5708 | vector signed short vec_mladd (vector signed short, vector signed short, |
5709 | vector signed short); | |
924fcc4e JM |
5710 | vector signed short vec_mladd (vector signed short, |
5711 | vector unsigned short, | |
6e5bb5ad | 5712 | vector unsigned short); |
924fcc4e JM |
5713 | vector signed short vec_mladd (vector unsigned short, |
5714 | vector signed short, | |
6e5bb5ad JM |
5715 | vector signed short); |
5716 | vector unsigned short vec_mladd (vector unsigned short, | |
5717 | vector unsigned short, | |
5718 | vector unsigned short); | |
5719 | ||
924fcc4e JM |
5720 | vector signed short vec_mradds (vector signed short, |
5721 | vector signed short, | |
6e5bb5ad JM |
5722 | vector signed short); |
5723 | ||
924fcc4e JM |
5724 | vector unsigned int vec_msum (vector unsigned char, |
5725 | vector unsigned char, | |
6e5bb5ad JM |
5726 | vector unsigned int); |
5727 | vector signed int vec_msum (vector signed char, vector unsigned char, | |
5728 | vector signed int); | |
924fcc4e JM |
5729 | vector unsigned int vec_msum (vector unsigned short, |
5730 | vector unsigned short, | |
6e5bb5ad JM |
5731 | vector unsigned int); |
5732 | vector signed int vec_msum (vector signed short, vector signed short, | |
5733 | vector signed int); | |
5734 | ||
5735 | vector unsigned int vec_msums (vector unsigned short, | |
924fcc4e JM |
5736 | vector unsigned short, |
5737 | vector unsigned int); | |
6e5bb5ad JM |
5738 | vector signed int vec_msums (vector signed short, vector signed short, |
5739 | vector signed int); | |
333c8841 AH |
5740 | |
5741 | void vec_mtvscr (vector signed int); | |
5742 | void vec_mtvscr (vector unsigned int); | |
5743 | void vec_mtvscr (vector signed short); | |
5744 | void vec_mtvscr (vector unsigned short); | |
5745 | void vec_mtvscr (vector signed char); | |
5746 | void vec_mtvscr (vector unsigned char); | |
5747 | ||
924fcc4e JM |
5748 | vector unsigned short vec_mule (vector unsigned char, |
5749 | vector unsigned char); | |
333c8841 | 5750 | vector signed short vec_mule (vector signed char, vector signed char); |
924fcc4e JM |
5751 | vector unsigned int vec_mule (vector unsigned short, |
5752 | vector unsigned short); | |
333c8841 AH |
5753 | vector signed int vec_mule (vector signed short, vector signed short); |
5754 | ||
924fcc4e JM |
5755 | vector unsigned short vec_mulo (vector unsigned char, |
5756 | vector unsigned char); | |
333c8841 | 5757 | vector signed short vec_mulo (vector signed char, vector signed char); |
924fcc4e JM |
5758 | vector unsigned int vec_mulo (vector unsigned short, |
5759 | vector unsigned short); | |
333c8841 AH |
5760 | vector signed int vec_mulo (vector signed short, vector signed short); |
5761 | ||
5762 | vector float vec_nmsub (vector float, vector float, vector float); | |
5763 | ||
5764 | vector float vec_nor (vector float, vector float); | |
5765 | vector signed int vec_nor (vector signed int, vector signed int); | |
5766 | vector unsigned int vec_nor (vector unsigned int, vector unsigned int); | |
5767 | vector signed short vec_nor (vector signed short, vector signed short); | |
6e5bb5ad JM |
5768 | vector unsigned short vec_nor (vector unsigned short, |
5769 | vector unsigned short); | |
333c8841 | 5770 | vector signed char vec_nor (vector signed char, vector signed char); |
924fcc4e JM |
5771 | vector unsigned char vec_nor (vector unsigned char, |
5772 | vector unsigned char); | |
333c8841 AH |
5773 | |
5774 | vector float vec_or (vector float, vector float); | |
5775 | vector float vec_or (vector float, vector signed int); | |
5776 | vector float vec_or (vector signed int, vector float); | |
5777 | vector signed int vec_or (vector signed int, vector signed int); | |
5778 | vector unsigned int vec_or (vector signed int, vector unsigned int); | |
5779 | vector unsigned int vec_or (vector unsigned int, vector signed int); | |
5780 | vector unsigned int vec_or (vector unsigned int, vector unsigned int); | |
5781 | vector signed short vec_or (vector signed short, vector signed short); | |
924fcc4e JM |
5782 | vector unsigned short vec_or (vector signed short, |
5783 | vector unsigned short); | |
5784 | vector unsigned short vec_or (vector unsigned short, | |
5785 | vector signed short); | |
5786 | vector unsigned short vec_or (vector unsigned short, | |
5787 | vector unsigned short); | |
333c8841 AH |
5788 | vector signed char vec_or (vector signed char, vector signed char); |
5789 | vector unsigned char vec_or (vector signed char, vector unsigned char); | |
5790 | vector unsigned char vec_or (vector unsigned char, vector signed char); | |
924fcc4e JM |
5791 | vector unsigned char vec_or (vector unsigned char, |
5792 | vector unsigned char); | |
333c8841 AH |
5793 | |
5794 | vector signed char vec_pack (vector signed short, vector signed short); | |
6e5bb5ad JM |
5795 | vector unsigned char vec_pack (vector unsigned short, |
5796 | vector unsigned short); | |
333c8841 | 5797 | vector signed short vec_pack (vector signed int, vector signed int); |
924fcc4e JM |
5798 | vector unsigned short vec_pack (vector unsigned int, |
5799 | vector unsigned int); | |
333c8841 | 5800 | |
924fcc4e JM |
5801 | vector signed short vec_packpx (vector unsigned int, |
5802 | vector unsigned int); | |
333c8841 | 5803 | |
6e5bb5ad JM |
5804 | vector unsigned char vec_packs (vector unsigned short, |
5805 | vector unsigned short); | |
333c8841 AH |
5806 | vector signed char vec_packs (vector signed short, vector signed short); |
5807 | ||
924fcc4e JM |
5808 | vector unsigned short vec_packs (vector unsigned int, |
5809 | vector unsigned int); | |
333c8841 AH |
5810 | vector signed short vec_packs (vector signed int, vector signed int); |
5811 | ||
6e5bb5ad JM |
5812 | vector unsigned char vec_packsu (vector unsigned short, |
5813 | vector unsigned short); | |
924fcc4e JM |
5814 | vector unsigned char vec_packsu (vector signed short, |
5815 | vector signed short); | |
5816 | vector unsigned short vec_packsu (vector unsigned int, | |
5817 | vector unsigned int); | |
333c8841 AH |
5818 | vector unsigned short vec_packsu (vector signed int, vector signed int); |
5819 | ||
924fcc4e JM |
5820 | vector float vec_perm (vector float, vector float, |
5821 | vector unsigned char); | |
6e5bb5ad JM |
5822 | vector signed int vec_perm (vector signed int, vector signed int, |
5823 | vector unsigned char); | |
5824 | vector unsigned int vec_perm (vector unsigned int, vector unsigned int, | |
5825 | vector unsigned char); | |
5826 | vector signed short vec_perm (vector signed short, vector signed short, | |
5827 | vector unsigned char); | |
5828 | vector unsigned short vec_perm (vector unsigned short, | |
5829 | vector unsigned short, | |
5830 | vector unsigned char); | |
5831 | vector signed char vec_perm (vector signed char, vector signed char, | |
5832 | vector unsigned char); | |
924fcc4e JM |
5833 | vector unsigned char vec_perm (vector unsigned char, |
5834 | vector unsigned char, | |
6e5bb5ad | 5835 | vector unsigned char); |
333c8841 AH |
5836 | |
5837 | vector float vec_re (vector float); | |
5838 | ||
5839 | vector signed char vec_rl (vector signed char, vector unsigned char); | |
924fcc4e JM |
5840 | vector unsigned char vec_rl (vector unsigned char, |
5841 | vector unsigned char); | |
333c8841 AH |
5842 | vector signed short vec_rl (vector signed short, vector unsigned short); |
5843 | ||
924fcc4e JM |
5844 | vector unsigned short vec_rl (vector unsigned short, |
5845 | vector unsigned short); | |
333c8841 AH |
5846 | vector signed int vec_rl (vector signed int, vector unsigned int); |
5847 | vector unsigned int vec_rl (vector unsigned int, vector unsigned int); | |
5848 | ||
5849 | vector float vec_round (vector float); | |
5850 | ||
5851 | vector float vec_rsqrte (vector float); | |
5852 | ||
5853 | vector float vec_sel (vector float, vector float, vector signed int); | |
5854 | vector float vec_sel (vector float, vector float, vector unsigned int); | |
6e5bb5ad JM |
5855 | vector signed int vec_sel (vector signed int, vector signed int, |
5856 | vector signed int); | |
5857 | vector signed int vec_sel (vector signed int, vector signed int, | |
5858 | vector unsigned int); | |
5859 | vector unsigned int vec_sel (vector unsigned int, vector unsigned int, | |
5860 | vector signed int); | |
5861 | vector unsigned int vec_sel (vector unsigned int, vector unsigned int, | |
5862 | vector unsigned int); | |
5863 | vector signed short vec_sel (vector signed short, vector signed short, | |
5864 | vector signed short); | |
5865 | vector signed short vec_sel (vector signed short, vector signed short, | |
5866 | vector unsigned short); | |
5867 | vector unsigned short vec_sel (vector unsigned short, | |
924fcc4e JM |
5868 | vector unsigned short, |
5869 | vector signed short); | |
6e5bb5ad JM |
5870 | vector unsigned short vec_sel (vector unsigned short, |
5871 | vector unsigned short, | |
5872 | vector unsigned short); | |
5873 | vector signed char vec_sel (vector signed char, vector signed char, | |
5874 | vector signed char); | |
5875 | vector signed char vec_sel (vector signed char, vector signed char, | |
5876 | vector unsigned char); | |
924fcc4e JM |
5877 | vector unsigned char vec_sel (vector unsigned char, |
5878 | vector unsigned char, | |
6e5bb5ad | 5879 | vector signed char); |
924fcc4e JM |
5880 | vector unsigned char vec_sel (vector unsigned char, |
5881 | vector unsigned char, | |
6e5bb5ad | 5882 | vector unsigned char); |
333c8841 AH |
5883 | |
5884 | vector signed char vec_sl (vector signed char, vector unsigned char); | |
924fcc4e JM |
5885 | vector unsigned char vec_sl (vector unsigned char, |
5886 | vector unsigned char); | |
333c8841 AH |
5887 | vector signed short vec_sl (vector signed short, vector unsigned short); |
5888 | ||
924fcc4e JM |
5889 | vector unsigned short vec_sl (vector unsigned short, |
5890 | vector unsigned short); | |
333c8841 AH |
5891 | vector signed int vec_sl (vector signed int, vector unsigned int); |
5892 | vector unsigned int vec_sl (vector unsigned int, vector unsigned int); | |
5893 | ||
5894 | vector float vec_sld (vector float, vector float, const char); | |
6e5bb5ad JM |
5895 | vector signed int vec_sld (vector signed int, vector signed int, |
5896 | const char); | |
5897 | vector unsigned int vec_sld (vector unsigned int, vector unsigned int, | |
5898 | const char); | |
5899 | vector signed short vec_sld (vector signed short, vector signed short, | |
5900 | const char); | |
5901 | vector unsigned short vec_sld (vector unsigned short, | |
5902 | vector unsigned short, const char); | |
5903 | vector signed char vec_sld (vector signed char, vector signed char, | |
5904 | const char); | |
924fcc4e JM |
5905 | vector unsigned char vec_sld (vector unsigned char, |
5906 | vector unsigned char, | |
6e5bb5ad | 5907 | const char); |
333c8841 AH |
5908 | |
5909 | vector signed int vec_sll (vector signed int, vector unsigned int); | |
5910 | vector signed int vec_sll (vector signed int, vector unsigned short); | |
5911 | vector signed int vec_sll (vector signed int, vector unsigned char); | |
5912 | vector unsigned int vec_sll (vector unsigned int, vector unsigned int); | |
924fcc4e JM |
5913 | vector unsigned int vec_sll (vector unsigned int, |
5914 | vector unsigned short); | |
333c8841 AH |
5915 | vector unsigned int vec_sll (vector unsigned int, vector unsigned char); |
5916 | ||
5917 | vector signed short vec_sll (vector signed short, vector unsigned int); | |
924fcc4e JM |
5918 | vector signed short vec_sll (vector signed short, |
5919 | vector unsigned short); | |
333c8841 AH |
5920 | vector signed short vec_sll (vector signed short, vector unsigned char); |
5921 | ||
924fcc4e JM |
5922 | vector unsigned short vec_sll (vector unsigned short, |
5923 | vector unsigned int); | |
6e5bb5ad JM |
5924 | vector unsigned short vec_sll (vector unsigned short, |
5925 | vector unsigned short); | |
924fcc4e JM |
5926 | vector unsigned short vec_sll (vector unsigned short, |
5927 | vector unsigned char); | |
333c8841 AH |
5928 | vector signed char vec_sll (vector signed char, vector unsigned int); |
5929 | vector signed char vec_sll (vector signed char, vector unsigned short); | |
5930 | vector signed char vec_sll (vector signed char, vector unsigned char); | |
924fcc4e JM |
5931 | vector unsigned char vec_sll (vector unsigned char, |
5932 | vector unsigned int); | |
5933 | vector unsigned char vec_sll (vector unsigned char, | |
5934 | vector unsigned short); | |
5935 | vector unsigned char vec_sll (vector unsigned char, | |
5936 | vector unsigned char); | |
333c8841 AH |
5937 | |
5938 | vector float vec_slo (vector float, vector signed char); | |
5939 | vector float vec_slo (vector float, vector unsigned char); | |
5940 | vector signed int vec_slo (vector signed int, vector signed char); | |
5941 | vector signed int vec_slo (vector signed int, vector unsigned char); | |
5942 | vector unsigned int vec_slo (vector unsigned int, vector signed char); | |
5943 | vector unsigned int vec_slo (vector unsigned int, vector unsigned char); | |
5944 | ||
5945 | vector signed short vec_slo (vector signed short, vector signed char); | |
5946 | vector signed short vec_slo (vector signed short, vector unsigned char); | |
5947 | ||
924fcc4e JM |
5948 | vector unsigned short vec_slo (vector unsigned short, |
5949 | vector signed char); | |
5950 | vector unsigned short vec_slo (vector unsigned short, | |
5951 | vector unsigned char); | |
333c8841 AH |
5952 | vector signed char vec_slo (vector signed char, vector signed char); |
5953 | vector signed char vec_slo (vector signed char, vector unsigned char); | |
5954 | vector unsigned char vec_slo (vector unsigned char, vector signed char); | |
5955 | ||
924fcc4e JM |
5956 | vector unsigned char vec_slo (vector unsigned char, |
5957 | vector unsigned char); | |
333c8841 AH |
5958 | |
5959 | vector signed char vec_splat (vector signed char, const char); | |
5960 | vector unsigned char vec_splat (vector unsigned char, const char); | |
5961 | vector signed short vec_splat (vector signed short, const char); | |
5962 | vector unsigned short vec_splat (vector unsigned short, const char); | |
5963 | vector float vec_splat (vector float, const char); | |
5964 | vector signed int vec_splat (vector signed int, const char); | |
5965 | vector unsigned int vec_splat (vector unsigned int, const char); | |
5966 | ||
5967 | vector signed char vec_splat_s8 (const char); | |
5968 | ||
5969 | vector signed short vec_splat_s16 (const char); | |
5970 | ||
5971 | vector signed int vec_splat_s32 (const char); | |
5972 | ||
5973 | vector unsigned char vec_splat_u8 (const char); | |
5974 | ||
5975 | vector unsigned short vec_splat_u16 (const char); | |
5976 | ||
5977 | vector unsigned int vec_splat_u32 (const char); | |
5978 | ||
5979 | vector signed char vec_sr (vector signed char, vector unsigned char); | |
924fcc4e JM |
5980 | vector unsigned char vec_sr (vector unsigned char, |
5981 | vector unsigned char); | |
333c8841 AH |
5982 | vector signed short vec_sr (vector signed short, vector unsigned short); |
5983 | ||
924fcc4e JM |
5984 | vector unsigned short vec_sr (vector unsigned short, |
5985 | vector unsigned short); | |
333c8841 AH |
5986 | vector signed int vec_sr (vector signed int, vector unsigned int); |
5987 | vector unsigned int vec_sr (vector unsigned int, vector unsigned int); | |
5988 | ||
5989 | vector signed char vec_sra (vector signed char, vector unsigned char); | |
924fcc4e JM |
5990 | vector unsigned char vec_sra (vector unsigned char, |
5991 | vector unsigned char); | |
5992 | vector signed short vec_sra (vector signed short, | |
5993 | vector unsigned short); | |
6e5bb5ad JM |
5994 | vector unsigned short vec_sra (vector unsigned short, |
5995 | vector unsigned short); | |
333c8841 AH |
5996 | vector signed int vec_sra (vector signed int, vector unsigned int); |
5997 | vector unsigned int vec_sra (vector unsigned int, vector unsigned int); | |
5998 | ||
5999 | vector signed int vec_srl (vector signed int, vector unsigned int); | |
6000 | vector signed int vec_srl (vector signed int, vector unsigned short); | |
6001 | vector signed int vec_srl (vector signed int, vector unsigned char); | |
6002 | vector unsigned int vec_srl (vector unsigned int, vector unsigned int); | |
924fcc4e JM |
6003 | vector unsigned int vec_srl (vector unsigned int, |
6004 | vector unsigned short); | |
333c8841 AH |
6005 | vector unsigned int vec_srl (vector unsigned int, vector unsigned char); |
6006 | ||
6007 | vector signed short vec_srl (vector signed short, vector unsigned int); | |
924fcc4e JM |
6008 | vector signed short vec_srl (vector signed short, |
6009 | vector unsigned short); | |
333c8841 AH |
6010 | vector signed short vec_srl (vector signed short, vector unsigned char); |
6011 | ||
924fcc4e JM |
6012 | vector unsigned short vec_srl (vector unsigned short, |
6013 | vector unsigned int); | |
6e5bb5ad JM |
6014 | vector unsigned short vec_srl (vector unsigned short, |
6015 | vector unsigned short); | |
924fcc4e JM |
6016 | vector unsigned short vec_srl (vector unsigned short, |
6017 | vector unsigned char); | |
333c8841 AH |
6018 | vector signed char vec_srl (vector signed char, vector unsigned int); |
6019 | vector signed char vec_srl (vector signed char, vector unsigned short); | |
6020 | vector signed char vec_srl (vector signed char, vector unsigned char); | |
924fcc4e JM |
6021 | vector unsigned char vec_srl (vector unsigned char, |
6022 | vector unsigned int); | |
6023 | vector unsigned char vec_srl (vector unsigned char, | |
6024 | vector unsigned short); | |
6025 | vector unsigned char vec_srl (vector unsigned char, | |
6026 | vector unsigned char); | |
333c8841 AH |
6027 | |
6028 | vector float vec_sro (vector float, vector signed char); | |
6029 | vector float vec_sro (vector float, vector unsigned char); | |
6030 | vector signed int vec_sro (vector signed int, vector signed char); | |
6031 | vector signed int vec_sro (vector signed int, vector unsigned char); | |
6032 | vector unsigned int vec_sro (vector unsigned int, vector signed char); | |
6033 | vector unsigned int vec_sro (vector unsigned int, vector unsigned char); | |
6034 | ||
6035 | vector signed short vec_sro (vector signed short, vector signed char); | |
6036 | vector signed short vec_sro (vector signed short, vector unsigned char); | |
6037 | ||
924fcc4e JM |
6038 | vector unsigned short vec_sro (vector unsigned short, |
6039 | vector signed char); | |
6040 | vector unsigned short vec_sro (vector unsigned short, | |
6041 | vector unsigned char); | |
333c8841 AH |
6042 | vector signed char vec_sro (vector signed char, vector signed char); |
6043 | vector signed char vec_sro (vector signed char, vector unsigned char); | |
6044 | vector unsigned char vec_sro (vector unsigned char, vector signed char); | |
6045 | ||
924fcc4e JM |
6046 | vector unsigned char vec_sro (vector unsigned char, |
6047 | vector unsigned char); | |
333c8841 AH |
6048 | |
6049 | void vec_st (vector float, int, float *); | |
6050 | void vec_st (vector float, int, vector float *); | |
6051 | void vec_st (vector signed int, int, int *); | |
6052 | void vec_st (vector signed int, int, unsigned int *); | |
6053 | void vec_st (vector unsigned int, int, unsigned int *); | |
6054 | void vec_st (vector unsigned int, int, vector unsigned int *); | |
6055 | void vec_st (vector signed short, int, short *); | |
6056 | void vec_st (vector signed short, int, vector unsigned short *); | |
6057 | void vec_st (vector signed short, int, vector signed short *); | |
6058 | void vec_st (vector unsigned short, int, unsigned short *); | |
6059 | void vec_st (vector unsigned short, int, vector unsigned short *); | |
6060 | void vec_st (vector signed char, int, signed char *); | |
6061 | void vec_st (vector signed char, int, unsigned char *); | |
6062 | void vec_st (vector signed char, int, vector signed char *); | |
6063 | void vec_st (vector unsigned char, int, unsigned char *); | |
6064 | void vec_st (vector unsigned char, int, vector unsigned char *); | |
6065 | ||
6066 | void vec_ste (vector signed char, int, unsigned char *); | |
6067 | void vec_ste (vector signed char, int, signed char *); | |
6068 | void vec_ste (vector unsigned char, int, unsigned char *); | |
6069 | void vec_ste (vector signed short, int, short *); | |
6070 | void vec_ste (vector signed short, int, unsigned short *); | |
6071 | void vec_ste (vector unsigned short, int, void *); | |
6072 | void vec_ste (vector signed int, int, unsigned int *); | |
6073 | void vec_ste (vector signed int, int, int *); | |
6074 | void vec_ste (vector unsigned int, int, unsigned int *); | |
6075 | void vec_ste (vector float, int, float *); | |
6076 | ||
6077 | void vec_stl (vector float, int, vector float *); | |
6078 | void vec_stl (vector float, int, float *); | |
6079 | void vec_stl (vector signed int, int, vector signed int *); | |
6080 | void vec_stl (vector signed int, int, int *); | |
6081 | void vec_stl (vector signed int, int, unsigned int *); | |
6082 | void vec_stl (vector unsigned int, int, vector unsigned int *); | |
6083 | void vec_stl (vector unsigned int, int, unsigned int *); | |
6084 | void vec_stl (vector signed short, int, short *); | |
6085 | void vec_stl (vector signed short, int, unsigned short *); | |
6086 | void vec_stl (vector signed short, int, vector signed short *); | |
6087 | void vec_stl (vector unsigned short, int, unsigned short *); | |
6088 | void vec_stl (vector unsigned short, int, vector signed short *); | |
6089 | void vec_stl (vector signed char, int, signed char *); | |
6090 | void vec_stl (vector signed char, int, unsigned char *); | |
6091 | void vec_stl (vector signed char, int, vector signed char *); | |
6092 | void vec_stl (vector unsigned char, int, unsigned char *); | |
6093 | void vec_stl (vector unsigned char, int, vector unsigned char *); | |
6094 | ||
6095 | vector signed char vec_sub (vector signed char, vector signed char); | |
6096 | vector unsigned char vec_sub (vector signed char, vector unsigned char); | |
6097 | ||
6098 | vector unsigned char vec_sub (vector unsigned char, vector signed char); | |
6099 | ||
924fcc4e JM |
6100 | vector unsigned char vec_sub (vector unsigned char, |
6101 | vector unsigned char); | |
333c8841 | 6102 | vector signed short vec_sub (vector signed short, vector signed short); |
924fcc4e JM |
6103 | vector unsigned short vec_sub (vector signed short, |
6104 | vector unsigned short); | |
6105 | vector unsigned short vec_sub (vector unsigned short, | |
6106 | vector signed short); | |
6e5bb5ad JM |
6107 | vector unsigned short vec_sub (vector unsigned short, |
6108 | vector unsigned short); | |
333c8841 AH |
6109 | vector signed int vec_sub (vector signed int, vector signed int); |
6110 | vector unsigned int vec_sub (vector signed int, vector unsigned int); | |
6111 | vector unsigned int vec_sub (vector unsigned int, vector signed int); | |
6112 | vector unsigned int vec_sub (vector unsigned int, vector unsigned int); | |
6113 | vector float vec_sub (vector float, vector float); | |
6114 | ||
6115 | vector unsigned int vec_subc (vector unsigned int, vector unsigned int); | |
6116 | ||
924fcc4e JM |
6117 | vector unsigned char vec_subs (vector signed char, |
6118 | vector unsigned char); | |
6119 | vector unsigned char vec_subs (vector unsigned char, | |
6120 | vector signed char); | |
6121 | vector unsigned char vec_subs (vector unsigned char, | |
6122 | vector unsigned char); | |
333c8841 | 6123 | vector signed char vec_subs (vector signed char, vector signed char); |
924fcc4e JM |
6124 | vector unsigned short vec_subs (vector signed short, |
6125 | vector unsigned short); | |
6126 | vector unsigned short vec_subs (vector unsigned short, | |
6127 | vector signed short); | |
6e5bb5ad JM |
6128 | vector unsigned short vec_subs (vector unsigned short, |
6129 | vector unsigned short); | |
333c8841 AH |
6130 | vector signed short vec_subs (vector signed short, vector signed short); |
6131 | ||
6132 | vector unsigned int vec_subs (vector signed int, vector unsigned int); | |
6133 | vector unsigned int vec_subs (vector unsigned int, vector signed int); | |
6134 | vector unsigned int vec_subs (vector unsigned int, vector unsigned int); | |
6135 | ||
6136 | vector signed int vec_subs (vector signed int, vector signed int); | |
6137 | ||
924fcc4e JM |
6138 | vector unsigned int vec_sum4s (vector unsigned char, |
6139 | vector unsigned int); | |
333c8841 AH |
6140 | vector signed int vec_sum4s (vector signed char, vector signed int); |
6141 | vector signed int vec_sum4s (vector signed short, vector signed int); | |
6142 | ||
6143 | vector signed int vec_sum2s (vector signed int, vector signed int); | |
6144 | ||
6145 | vector signed int vec_sums (vector signed int, vector signed int); | |
6146 | ||
6147 | vector float vec_trunc (vector float); | |
6148 | ||
6149 | vector signed short vec_unpackh (vector signed char); | |
6150 | vector unsigned int vec_unpackh (vector signed short); | |
6151 | vector signed int vec_unpackh (vector signed short); | |
6152 | ||
6153 | vector signed short vec_unpackl (vector signed char); | |
6154 | vector unsigned int vec_unpackl (vector signed short); | |
6155 | vector signed int vec_unpackl (vector signed short); | |
6156 | ||
6157 | vector float vec_xor (vector float, vector float); | |
6158 | vector float vec_xor (vector float, vector signed int); | |
6159 | vector float vec_xor (vector signed int, vector float); | |
6160 | vector signed int vec_xor (vector signed int, vector signed int); | |
6161 | vector unsigned int vec_xor (vector signed int, vector unsigned int); | |
6162 | vector unsigned int vec_xor (vector unsigned int, vector signed int); | |
6163 | vector unsigned int vec_xor (vector unsigned int, vector unsigned int); | |
6164 | vector signed short vec_xor (vector signed short, vector signed short); | |
924fcc4e JM |
6165 | vector unsigned short vec_xor (vector signed short, |
6166 | vector unsigned short); | |
6167 | vector unsigned short vec_xor (vector unsigned short, | |
6168 | vector signed short); | |
6e5bb5ad JM |
6169 | vector unsigned short vec_xor (vector unsigned short, |
6170 | vector unsigned short); | |
333c8841 AH |
6171 | vector signed char vec_xor (vector signed char, vector signed char); |
6172 | vector unsigned char vec_xor (vector signed char, vector unsigned char); | |
6173 | ||
6174 | vector unsigned char vec_xor (vector unsigned char, vector signed char); | |
6175 | ||
924fcc4e JM |
6176 | vector unsigned char vec_xor (vector unsigned char, |
6177 | vector unsigned char); | |
333c8841 AH |
6178 | |
6179 | vector signed int vec_all_eq (vector signed char, vector unsigned char); | |
6180 | ||
6181 | vector signed int vec_all_eq (vector signed char, vector signed char); | |
6182 | vector signed int vec_all_eq (vector unsigned char, vector signed char); | |
6183 | ||
924fcc4e JM |
6184 | vector signed int vec_all_eq (vector unsigned char, |
6185 | vector unsigned char); | |
6186 | vector signed int vec_all_eq (vector signed short, | |
6187 | vector unsigned short); | |
333c8841 AH |
6188 | vector signed int vec_all_eq (vector signed short, vector signed short); |
6189 | ||
924fcc4e JM |
6190 | vector signed int vec_all_eq (vector unsigned short, |
6191 | vector signed short); | |
6192 | vector signed int vec_all_eq (vector unsigned short, | |
6193 | vector unsigned short); | |
333c8841 AH |
6194 | vector signed int vec_all_eq (vector signed int, vector unsigned int); |
6195 | vector signed int vec_all_eq (vector signed int, vector signed int); | |
6196 | vector signed int vec_all_eq (vector unsigned int, vector signed int); | |
6197 | vector signed int vec_all_eq (vector unsigned int, vector unsigned int); | |
6198 | ||
6199 | vector signed int vec_all_eq (vector float, vector float); | |
6200 | ||
6201 | vector signed int vec_all_ge (vector signed char, vector unsigned char); | |
6202 | ||
6203 | vector signed int vec_all_ge (vector unsigned char, vector signed char); | |
6204 | ||
924fcc4e JM |
6205 | vector signed int vec_all_ge (vector unsigned char, |
6206 | vector unsigned char); | |
333c8841 | 6207 | vector signed int vec_all_ge (vector signed char, vector signed char); |
924fcc4e JM |
6208 | vector signed int vec_all_ge (vector signed short, |
6209 | vector unsigned short); | |
6210 | vector signed int vec_all_ge (vector unsigned short, | |
6211 | vector signed short); | |
6212 | vector signed int vec_all_ge (vector unsigned short, | |
6213 | vector unsigned short); | |
333c8841 AH |
6214 | vector signed int vec_all_ge (vector signed short, vector signed short); |
6215 | ||
6216 | vector signed int vec_all_ge (vector signed int, vector unsigned int); | |
6217 | vector signed int vec_all_ge (vector unsigned int, vector signed int); | |
6218 | vector signed int vec_all_ge (vector unsigned int, vector unsigned int); | |
6219 | ||
6220 | vector signed int vec_all_ge (vector signed int, vector signed int); | |
6221 | vector signed int vec_all_ge (vector float, vector float); | |
6222 | ||
6223 | vector signed int vec_all_gt (vector signed char, vector unsigned char); | |
6224 | ||
6225 | vector signed int vec_all_gt (vector unsigned char, vector signed char); | |
6226 | ||
924fcc4e JM |
6227 | vector signed int vec_all_gt (vector unsigned char, |
6228 | vector unsigned char); | |
333c8841 | 6229 | vector signed int vec_all_gt (vector signed char, vector signed char); |
924fcc4e JM |
6230 | vector signed int vec_all_gt (vector signed short, |
6231 | vector unsigned short); | |
f282ffb3 | 6232 | vector signed int vec_all_gt (vector unsigned short, |
924fcc4e JM |
6233 | vector signed short); |
6234 | vector signed int vec_all_gt (vector unsigned short, | |
6235 | vector unsigned short); | |
333c8841 AH |
6236 | vector signed int vec_all_gt (vector signed short, vector signed short); |
6237 | ||
6238 | vector signed int vec_all_gt (vector signed int, vector unsigned int); | |
6239 | vector signed int vec_all_gt (vector unsigned int, vector signed int); | |
6240 | vector signed int vec_all_gt (vector unsigned int, vector unsigned int); | |
6241 | ||
6242 | vector signed int vec_all_gt (vector signed int, vector signed int); | |
6243 | vector signed int vec_all_gt (vector float, vector float); | |
6244 | ||
6245 | vector signed int vec_all_in (vector float, vector float); | |
6246 | ||
6247 | vector signed int vec_all_le (vector signed char, vector unsigned char); | |
6248 | ||
6249 | vector signed int vec_all_le (vector unsigned char, vector signed char); | |
6250 | ||
924fcc4e JM |
6251 | vector signed int vec_all_le (vector unsigned char, |
6252 | vector unsigned char); | |
333c8841 | 6253 | vector signed int vec_all_le (vector signed char, vector signed char); |
924fcc4e JM |
6254 | vector signed int vec_all_le (vector signed short, |
6255 | vector unsigned short); | |
6256 | vector signed int vec_all_le (vector unsigned short, | |
6257 | vector signed short); | |
6258 | vector signed int vec_all_le (vector unsigned short, | |
6259 | vector unsigned short); | |
333c8841 AH |
6260 | vector signed int vec_all_le (vector signed short, vector signed short); |
6261 | ||
6262 | vector signed int vec_all_le (vector signed int, vector unsigned int); | |
6263 | vector signed int vec_all_le (vector unsigned int, vector signed int); | |
6264 | vector signed int vec_all_le (vector unsigned int, vector unsigned int); | |
6265 | ||
6266 | vector signed int vec_all_le (vector signed int, vector signed int); | |
6267 | vector signed int vec_all_le (vector float, vector float); | |
6268 | ||
6269 | vector signed int vec_all_lt (vector signed char, vector unsigned char); | |
6270 | ||
6271 | vector signed int vec_all_lt (vector unsigned char, vector signed char); | |
6272 | ||
924fcc4e JM |
6273 | vector signed int vec_all_lt (vector unsigned char, |
6274 | vector unsigned char); | |
333c8841 | 6275 | vector signed int vec_all_lt (vector signed char, vector signed char); |
924fcc4e JM |
6276 | vector signed int vec_all_lt (vector signed short, |
6277 | vector unsigned short); | |
6278 | vector signed int vec_all_lt (vector unsigned short, | |
6279 | vector signed short); | |
6280 | vector signed int vec_all_lt (vector unsigned short, | |
6281 | vector unsigned short); | |
333c8841 AH |
6282 | vector signed int vec_all_lt (vector signed short, vector signed short); |
6283 | ||
6284 | vector signed int vec_all_lt (vector signed int, vector unsigned int); | |
6285 | vector signed int vec_all_lt (vector unsigned int, vector signed int); | |
6286 | vector signed int vec_all_lt (vector unsigned int, vector unsigned int); | |
6287 | ||
6288 | vector signed int vec_all_lt (vector signed int, vector signed int); | |
6289 | vector signed int vec_all_lt (vector float, vector float); | |
6290 | ||
6291 | vector signed int vec_all_nan (vector float); | |
6292 | ||
6293 | vector signed int vec_all_ne (vector signed char, vector unsigned char); | |
6294 | ||
6295 | vector signed int vec_all_ne (vector signed char, vector signed char); | |
6296 | vector signed int vec_all_ne (vector unsigned char, vector signed char); | |
6297 | ||
924fcc4e JM |
6298 | vector signed int vec_all_ne (vector unsigned char, |
6299 | vector unsigned char); | |
6300 | vector signed int vec_all_ne (vector signed short, | |
6301 | vector unsigned short); | |
333c8841 AH |
6302 | vector signed int vec_all_ne (vector signed short, vector signed short); |
6303 | ||
924fcc4e JM |
6304 | vector signed int vec_all_ne (vector unsigned short, |
6305 | vector signed short); | |
6306 | vector signed int vec_all_ne (vector unsigned short, | |
6307 | vector unsigned short); | |
333c8841 AH |
6308 | vector signed int vec_all_ne (vector signed int, vector unsigned int); |
6309 | vector signed int vec_all_ne (vector signed int, vector signed int); | |
6310 | vector signed int vec_all_ne (vector unsigned int, vector signed int); | |
6311 | vector signed int vec_all_ne (vector unsigned int, vector unsigned int); | |
6312 | ||
6313 | vector signed int vec_all_ne (vector float, vector float); | |
6314 | ||
6315 | vector signed int vec_all_nge (vector float, vector float); | |
6316 | ||
6317 | vector signed int vec_all_ngt (vector float, vector float); | |
6318 | ||
6319 | vector signed int vec_all_nle (vector float, vector float); | |
6320 | ||
6321 | vector signed int vec_all_nlt (vector float, vector float); | |
6322 | ||
6323 | vector signed int vec_all_numeric (vector float); | |
6324 | ||
6325 | vector signed int vec_any_eq (vector signed char, vector unsigned char); | |
6326 | ||
6327 | vector signed int vec_any_eq (vector signed char, vector signed char); | |
6328 | vector signed int vec_any_eq (vector unsigned char, vector signed char); | |
6329 | ||
924fcc4e JM |
6330 | vector signed int vec_any_eq (vector unsigned char, |
6331 | vector unsigned char); | |
6332 | vector signed int vec_any_eq (vector signed short, | |
6333 | vector unsigned short); | |
333c8841 AH |
6334 | vector signed int vec_any_eq (vector signed short, vector signed short); |
6335 | ||
924fcc4e JM |
6336 | vector signed int vec_any_eq (vector unsigned short, |
6337 | vector signed short); | |
6338 | vector signed int vec_any_eq (vector unsigned short, | |
6339 | vector unsigned short); | |
333c8841 AH |
6340 | vector signed int vec_any_eq (vector signed int, vector unsigned int); |
6341 | vector signed int vec_any_eq (vector signed int, vector signed int); | |
6342 | vector signed int vec_any_eq (vector unsigned int, vector signed int); | |
6343 | vector signed int vec_any_eq (vector unsigned int, vector unsigned int); | |
6344 | ||
6345 | vector signed int vec_any_eq (vector float, vector float); | |
6346 | ||
6347 | vector signed int vec_any_ge (vector signed char, vector unsigned char); | |
6348 | ||
6349 | vector signed int vec_any_ge (vector unsigned char, vector signed char); | |
6350 | ||
924fcc4e JM |
6351 | vector signed int vec_any_ge (vector unsigned char, |
6352 | vector unsigned char); | |
333c8841 | 6353 | vector signed int vec_any_ge (vector signed char, vector signed char); |
924fcc4e JM |
6354 | vector signed int vec_any_ge (vector signed short, |
6355 | vector unsigned short); | |
6356 | vector signed int vec_any_ge (vector unsigned short, | |
6357 | vector signed short); | |
6358 | vector signed int vec_any_ge (vector unsigned short, | |
6359 | vector unsigned short); | |
333c8841 AH |
6360 | vector signed int vec_any_ge (vector signed short, vector signed short); |
6361 | ||
6362 | vector signed int vec_any_ge (vector signed int, vector unsigned int); | |
6363 | vector signed int vec_any_ge (vector unsigned int, vector signed int); | |
6364 | vector signed int vec_any_ge (vector unsigned int, vector unsigned int); | |
6365 | ||
6366 | vector signed int vec_any_ge (vector signed int, vector signed int); | |
6367 | vector signed int vec_any_ge (vector float, vector float); | |
6368 | ||
6369 | vector signed int vec_any_gt (vector signed char, vector unsigned char); | |
6370 | ||
6371 | vector signed int vec_any_gt (vector unsigned char, vector signed char); | |
6372 | ||
924fcc4e JM |
6373 | vector signed int vec_any_gt (vector unsigned char, |
6374 | vector unsigned char); | |
333c8841 | 6375 | vector signed int vec_any_gt (vector signed char, vector signed char); |
924fcc4e JM |
6376 | vector signed int vec_any_gt (vector signed short, |
6377 | vector unsigned short); | |
6378 | vector signed int vec_any_gt (vector unsigned short, | |
6379 | vector signed short); | |
6380 | vector signed int vec_any_gt (vector unsigned short, | |
6381 | vector unsigned short); | |
333c8841 AH |
6382 | vector signed int vec_any_gt (vector signed short, vector signed short); |
6383 | ||
6384 | vector signed int vec_any_gt (vector signed int, vector unsigned int); | |
6385 | vector signed int vec_any_gt (vector unsigned int, vector signed int); | |
6386 | vector signed int vec_any_gt (vector unsigned int, vector unsigned int); | |
6387 | ||
6388 | vector signed int vec_any_gt (vector signed int, vector signed int); | |
6389 | vector signed int vec_any_gt (vector float, vector float); | |
6390 | ||
6391 | vector signed int vec_any_le (vector signed char, vector unsigned char); | |
6392 | ||
6393 | vector signed int vec_any_le (vector unsigned char, vector signed char); | |
6394 | ||
924fcc4e JM |
6395 | vector signed int vec_any_le (vector unsigned char, |
6396 | vector unsigned char); | |
333c8841 | 6397 | vector signed int vec_any_le (vector signed char, vector signed char); |
924fcc4e JM |
6398 | vector signed int vec_any_le (vector signed short, |
6399 | vector unsigned short); | |
6400 | vector signed int vec_any_le (vector unsigned short, | |
6401 | vector signed short); | |
6402 | vector signed int vec_any_le (vector unsigned short, | |
6403 | vector unsigned short); | |
333c8841 AH |
6404 | vector signed int vec_any_le (vector signed short, vector signed short); |
6405 | ||
6406 | vector signed int vec_any_le (vector signed int, vector unsigned int); | |
6407 | vector signed int vec_any_le (vector unsigned int, vector signed int); | |
6408 | vector signed int vec_any_le (vector unsigned int, vector unsigned int); | |
6409 | ||
6410 | vector signed int vec_any_le (vector signed int, vector signed int); | |
6411 | vector signed int vec_any_le (vector float, vector float); | |
6412 | ||
6413 | vector signed int vec_any_lt (vector signed char, vector unsigned char); | |
6414 | ||
6415 | vector signed int vec_any_lt (vector unsigned char, vector signed char); | |
6416 | ||
924fcc4e JM |
6417 | vector signed int vec_any_lt (vector unsigned char, |
6418 | vector unsigned char); | |
333c8841 | 6419 | vector signed int vec_any_lt (vector signed char, vector signed char); |
924fcc4e JM |
6420 | vector signed int vec_any_lt (vector signed short, |
6421 | vector unsigned short); | |
6422 | vector signed int vec_any_lt (vector unsigned short, | |
6423 | vector signed short); | |
6424 | vector signed int vec_any_lt (vector unsigned short, | |
6425 | vector unsigned short); | |
333c8841 AH |
6426 | vector signed int vec_any_lt (vector signed short, vector signed short); |
6427 | ||
6428 | vector signed int vec_any_lt (vector signed int, vector unsigned int); | |
6429 | vector signed int vec_any_lt (vector unsigned int, vector signed int); | |
6430 | vector signed int vec_any_lt (vector unsigned int, vector unsigned int); | |
6431 | ||
6432 | vector signed int vec_any_lt (vector signed int, vector signed int); | |
6433 | vector signed int vec_any_lt (vector float, vector float); | |
6434 | ||
6435 | vector signed int vec_any_nan (vector float); | |
6436 | ||
6437 | vector signed int vec_any_ne (vector signed char, vector unsigned char); | |
6438 | ||
6439 | vector signed int vec_any_ne (vector signed char, vector signed char); | |
6440 | vector signed int vec_any_ne (vector unsigned char, vector signed char); | |
6441 | ||
924fcc4e JM |
6442 | vector signed int vec_any_ne (vector unsigned char, |
6443 | vector unsigned char); | |
6444 | vector signed int vec_any_ne (vector signed short, | |
6445 | vector unsigned short); | |
333c8841 AH |
6446 | vector signed int vec_any_ne (vector signed short, vector signed short); |
6447 | ||
924fcc4e JM |
6448 | vector signed int vec_any_ne (vector unsigned short, |
6449 | vector signed short); | |
6450 | vector signed int vec_any_ne (vector unsigned short, | |
6451 | vector unsigned short); | |
333c8841 AH |
6452 | vector signed int vec_any_ne (vector signed int, vector unsigned int); |
6453 | vector signed int vec_any_ne (vector signed int, vector signed int); | |
6454 | vector signed int vec_any_ne (vector unsigned int, vector signed int); | |
6455 | vector signed int vec_any_ne (vector unsigned int, vector unsigned int); | |
6456 | ||
6457 | vector signed int vec_any_ne (vector float, vector float); | |
6458 | ||
6459 | vector signed int vec_any_nge (vector float, vector float); | |
6460 | ||
6461 | vector signed int vec_any_ngt (vector float, vector float); | |
6462 | ||
6463 | vector signed int vec_any_nle (vector float, vector float); | |
6464 | ||
6465 | vector signed int vec_any_nlt (vector float, vector float); | |
6466 | ||
6467 | vector signed int vec_any_numeric (vector float); | |
6468 | ||
6469 | vector signed int vec_any_out (vector float, vector float); | |
6470 | @end smallexample | |
6471 | ||
0168a849 SS |
6472 | @node Pragmas |
6473 | @section Pragmas Accepted by GCC | |
6474 | @cindex pragmas | |
6475 | @cindex #pragma | |
6476 | ||
6477 | GCC supports several types of pragmas, primarily in order to compile | |
6478 | code originally written for other compilers. Note that in general | |
6479 | we do not recommend the use of pragmas; @xref{Function Attributes}, | |
6480 | for further explanation. | |
6481 | ||
6482 | @menu | |
6483 | * ARM Pragmas:: | |
a5c76ee6 | 6484 | * RS/6000 and PowerPC Pragmas:: |
0168a849 | 6485 | * Darwin Pragmas:: |
41c64394 RH |
6486 | * Solaris Pragmas:: |
6487 | * Tru64 Pragmas:: | |
0168a849 SS |
6488 | @end menu |
6489 | ||
6490 | @node ARM Pragmas | |
6491 | @subsection ARM Pragmas | |
6492 | ||
6493 | The ARM target defines pragmas for controlling the default addition of | |
6494 | @code{long_call} and @code{short_call} attributes to functions. | |
6495 | @xref{Function Attributes}, for information about the effects of these | |
6496 | attributes. | |
6497 | ||
6498 | @table @code | |
6499 | @item long_calls | |
6500 | @cindex pragma, long_calls | |
6501 | Set all subsequent functions to have the @code{long_call} attribute. | |
6502 | ||
6503 | @item no_long_calls | |
6504 | @cindex pragma, no_long_calls | |
6505 | Set all subsequent functions to have the @code{short_call} attribute. | |
6506 | ||
6507 | @item long_calls_off | |
6508 | @cindex pragma, long_calls_off | |
6509 | Do not affect the @code{long_call} or @code{short_call} attributes of | |
6510 | subsequent functions. | |
6511 | @end table | |
6512 | ||
a5c76ee6 ZW |
6513 | @node RS/6000 and PowerPC Pragmas |
6514 | @subsection RS/6000 and PowerPC Pragmas | |
6515 | ||
6516 | The RS/6000 and PowerPC targets define one pragma for controlling | |
6517 | whether or not the @code{longcall} attribute is added to function | |
6518 | declarations by default. This pragma overrides the @option{-mlongcall} | |
95b1627e | 6519 | option, but not the @code{longcall} and @code{shortcall} attributes. |
a5c76ee6 ZW |
6520 | @xref{RS/6000 and PowerPC Options}, for more information about when long |
6521 | calls are and are not necessary. | |
6522 | ||
6523 | @table @code | |
6524 | @item longcall (1) | |
6525 | @cindex pragma, longcall | |
6526 | Apply the @code{longcall} attribute to all subsequent function | |
6527 | declarations. | |
6528 | ||
6529 | @item longcall (0) | |
6530 | Do not apply the @code{longcall} attribute to subsequent function | |
6531 | declarations. | |
6532 | @end table | |
6533 | ||
0168a849 SS |
6534 | @c Describe c4x pragmas here. |
6535 | @c Describe h8300 pragmas here. | |
6536 | @c Describe i370 pragmas here. | |
6537 | @c Describe i960 pragmas here. | |
6538 | @c Describe sh pragmas here. | |
6539 | @c Describe v850 pragmas here. | |
6540 | ||
6541 | @node Darwin Pragmas | |
6542 | @subsection Darwin Pragmas | |
6543 | ||
6544 | The following pragmas are available for all architectures running the | |
6545 | Darwin operating system. These are useful for compatibility with other | |
6546 | MacOS compilers. | |
6547 | ||
6548 | @table @code | |
6549 | @item mark @var{tokens}@dots{} | |
6550 | @cindex pragma, mark | |
6551 | This pragma is accepted, but has no effect. | |
6552 | ||
6553 | @item options align=@var{alignment} | |
6554 | @cindex pragma, options align | |
6555 | This pragma sets the alignment of fields in structures. The values of | |
6556 | @var{alignment} may be @code{mac68k}, to emulate m68k alignment, or | |
6557 | @code{power}, to emulate PowerPC alignment. Uses of this pragma nest | |
6558 | properly; to restore the previous setting, use @code{reset} for the | |
6559 | @var{alignment}. | |
6560 | ||
6561 | @item segment @var{tokens}@dots{} | |
6562 | @cindex pragma, segment | |
6563 | This pragma is accepted, but has no effect. | |
6564 | ||
6565 | @item unused (@var{var} [, @var{var}]@dots{}) | |
6566 | @cindex pragma, unused | |
6567 | This pragma declares variables to be possibly unused. GCC will not | |
6568 | produce warnings for the listed variables. The effect is similar to | |
6569 | that of the @code{unused} attribute, except that this pragma may appear | |
6570 | anywhere within the variables' scopes. | |
6571 | @end table | |
6572 | ||
41c64394 RH |
6573 | @node Solaris Pragmas |
6574 | @subsection Solaris Pragmas | |
6575 | ||
6576 | For compatibility with the SunPRO compiler, the following pragma | |
6577 | is supported. | |
6578 | ||
6579 | @table @code | |
6580 | @item redefine_extname @var{oldname} @var{newname} | |
6581 | @cindex pragma, redefine_extname | |
6582 | ||
6583 | This pragma gives the C function @var{oldname} the assembler label | |
6584 | @var{newname}. The pragma must appear before the function declaration. | |
6585 | This pragma is equivalent to the asm labels extension (@pxref{Asm | |
6586 | Labels}). The preprocessor defines @code{__PRAGMA_REDEFINE_EXTNAME} | |
6587 | if the pragma is available. | |
6588 | @end table | |
6589 | ||
6590 | @node Tru64 Pragmas | |
6591 | @subsection Tru64 Pragmas | |
6592 | ||
6593 | For compatibility with the Compaq C compiler, the following pragma | |
6594 | is supported. | |
6595 | ||
6596 | @table @code | |
6597 | @item extern_prefix @var{string} | |
6598 | @cindex pragma, extern_prefix | |
6599 | ||
6600 | This pragma renames all subsequent function and variable declarations | |
6601 | such that @var{string} is prepended to the name. This effect may be | |
95b1627e | 6602 | terminated by using another @code{extern_prefix} pragma with the |
41c64394 RH |
6603 | empty string. |
6604 | ||
6605 | This pragma is similar in intent to to the asm labels extension | |
6606 | (@pxref{Asm Labels}) in that the system programmer wants to change | |
6607 | the assembly-level ABI without changing the source-level API. The | |
f8dc212b RO |
6608 | preprocessor defines @code{__PRAGMA_EXTERN_PREFIX} if the pragma is |
6609 | available. | |
41c64394 RH |
6610 | @end table |
6611 | ||
3e96a2fd DD |
6612 | @node Unnamed Fields |
6613 | @section Unnamed struct/union fields within structs/unions. | |
6614 | @cindex struct | |
6615 | @cindex union | |
6616 | ||
6617 | For compatibility with other compilers, GCC allows you to define | |
6618 | a structure or union that contains, as fields, structures and unions | |
6619 | without names. For example: | |
6620 | ||
6621 | @example | |
6622 | struct @{ | |
6623 | int a; | |
6624 | union @{ | |
6625 | int b; | |
6626 | float c; | |
6627 | @}; | |
6628 | int d; | |
6629 | @} foo; | |
6630 | @end example | |
6631 | ||
6632 | In this example, the user would be able to access members of the unnamed | |
6633 | union with code like @samp{foo.b}. Note that only unnamed structs and | |
6634 | unions are allowed, you may not have, for example, an unnamed | |
6635 | @code{int}. | |
6636 | ||
6637 | You must never create such structures that cause ambiguous field definitions. | |
6638 | For example, this structure: | |
6639 | ||
6640 | @example | |
6641 | struct @{ | |
6642 | int a; | |
6643 | struct @{ | |
6644 | int a; | |
6645 | @}; | |
6646 | @} foo; | |
6647 | @end example | |
6648 | ||
6649 | It is ambiguous which @code{a} is being referred to with @samp{foo.a}. | |
6650 | Such constructs are not supported and must be avoided. In the future, | |
6651 | such constructs may be detected and treated as compilation errors. | |
6652 | ||
3d78f2e9 RH |
6653 | @node Thread-Local |
6654 | @section Thread-Local Storage | |
6655 | @cindex Thread-Local Storage | |
9217ef40 | 6656 | @cindex @acronym{TLS} |
3d78f2e9 RH |
6657 | @cindex __thread |
6658 | ||
9217ef40 RH |
6659 | Thread-local storage (@acronym{TLS}) is a mechanism by which variables |
6660 | are allocated such that there is one instance of the variable per extant | |
3d78f2e9 RH |
6661 | thread. The run-time model GCC uses to implement this originates |
6662 | in the IA-64 processor-specific ABI, but has since been migrated | |
6663 | to other processors as well. It requires significant support from | |
6664 | the linker (@command{ld}), dynamic linker (@command{ld.so}), and | |
6665 | system libraries (@file{libc.so} and @file{libpthread.so}), so it | |
9217ef40 | 6666 | is not available everywhere. |
3d78f2e9 RH |
6667 | |
6668 | At the user level, the extension is visible with a new storage | |
6669 | class keyword: @code{__thread}. For example: | |
6670 | ||
6671 | @example | |
6672 | __thread int i; | |
6673 | extern __thread struct state s; | |
6674 | static __thread char *p; | |
6675 | @end example | |
6676 | ||
6677 | The @code{__thread} specifier may be used alone, with the @code{extern} | |
6678 | or @code{static} specifiers, but with no other storage class specifier. | |
6679 | When used with @code{extern} or @code{static}, @code{__thread} must appear | |
6680 | immediately after the other storage class specifier. | |
6681 | ||
6682 | The @code{__thread} specifier may be applied to any global, file-scoped | |
244c2241 RH |
6683 | static, function-scoped static, or static data member of a class. It may |
6684 | not be applied to block-scoped automatic or non-static data member. | |
3d78f2e9 RH |
6685 | |
6686 | When the address-of operator is applied to a thread-local variable, it is | |
6687 | evaluated at run-time and returns the address of the current thread's | |
6688 | instance of that variable. An address so obtained may be used by any | |
6689 | thread. When a thread terminates, any pointers to thread-local variables | |
6690 | in that thread become invalid. | |
6691 | ||
6692 | No static initialization may refer to the address of a thread-local variable. | |
6693 | ||
244c2241 RH |
6694 | In C++, if an initializer is present for a thread-local variable, it must |
6695 | be a @var{constant-expression}, as defined in 5.19.2 of the ANSI/ISO C++ | |
6696 | standard. | |
3d78f2e9 RH |
6697 | |
6698 | See @uref{http://people.redhat.com/drepper/tls.pdf, | |
6699 | ELF Handling For Thread-Local Storage} for a detailed explanation of | |
6700 | the four thread-local storage addressing models, and how the run-time | |
6701 | is expected to function. | |
6702 | ||
9217ef40 RH |
6703 | @menu |
6704 | * C99 Thread-Local Edits:: | |
6705 | * C++98 Thread-Local Edits:: | |
6706 | @end menu | |
6707 | ||
6708 | @node C99 Thread-Local Edits | |
6709 | @subsection ISO/IEC 9899:1999 Edits for Thread-Local Storage | |
6710 | ||
6711 | The following are a set of changes to ISO/IEC 9899:1999 (aka C99) | |
6712 | that document the exact semantics of the language extension. | |
6713 | ||
6714 | @itemize @bullet | |
6715 | @item | |
6716 | @cite{5.1.2 Execution environments} | |
6717 | ||
6718 | Add new text after paragraph 1 | |
6719 | ||
6720 | @quotation | |
6721 | Within either execution environment, a @dfn{thread} is a flow of | |
6722 | control within a program. It is implementation defined whether | |
6723 | or not there may be more than one thread associated with a program. | |
6724 | It is implementation defined how threads beyond the first are | |
6725 | created, the name and type of the function called at thread | |
6726 | startup, and how threads may be terminated. However, objects | |
6727 | with thread storage duration shall be initialized before thread | |
6728 | startup. | |
6729 | @end quotation | |
6730 | ||
6731 | @item | |
6732 | @cite{6.2.4 Storage durations of objects} | |
6733 | ||
6734 | Add new text before paragraph 3 | |
6735 | ||
6736 | @quotation | |
6737 | An object whose identifier is declared with the storage-class | |
6738 | specifier @w{@code{__thread}} has @dfn{thread storage duration}. | |
6739 | Its lifetime is the entire execution of the thread, and its | |
6740 | stored value is initialized only once, prior to thread startup. | |
6741 | @end quotation | |
6742 | ||
6743 | @item | |
6744 | @cite{6.4.1 Keywords} | |
6745 | ||
6746 | Add @code{__thread}. | |
6747 | ||
6748 | @item | |
6749 | @cite{6.7.1 Storage-class specifiers} | |
6750 | ||
6751 | Add @code{__thread} to the list of storage class specifiers in | |
6752 | paragraph 1. | |
6753 | ||
6754 | Change paragraph 2 to | |
6755 | ||
6756 | @quotation | |
6757 | With the exception of @code{__thread}, at most one storage-class | |
6758 | specifier may be given [@dots{}]. The @code{__thread} specifier may | |
6759 | be used alone, or immediately following @code{extern} or | |
6760 | @code{static}. | |
6761 | @end quotation | |
6762 | ||
6763 | Add new text after paragraph 6 | |
6764 | ||
6765 | @quotation | |
6766 | The declaration of an identifier for a variable that has | |
6767 | block scope that specifies @code{__thread} shall also | |
6768 | specify either @code{extern} or @code{static}. | |
6769 | ||
6770 | The @code{__thread} specifier shall be used only with | |
6771 | variables. | |
6772 | @end quotation | |
6773 | @end itemize | |
6774 | ||
6775 | @node C++98 Thread-Local Edits | |
6776 | @subsection ISO/IEC 14882:1998 Edits for Thread-Local Storage | |
6777 | ||
6778 | The following are a set of changes to ISO/IEC 14882:1998 (aka C++98) | |
6779 | that document the exact semantics of the language extension. | |
6780 | ||
6781 | @itemize @bullet | |
8d23a2c8 | 6782 | @item |
9217ef40 RH |
6783 | @b{[intro.execution]} |
6784 | ||
6785 | New text after paragraph 4 | |
6786 | ||
6787 | @quotation | |
6788 | A @dfn{thread} is a flow of control within the abstract machine. | |
6789 | It is implementation defined whether or not there may be more than | |
6790 | one thread. | |
6791 | @end quotation | |
6792 | ||
6793 | New text after paragraph 7 | |
6794 | ||
6795 | @quotation | |
95b1627e | 6796 | It is unspecified whether additional action must be taken to |
9217ef40 RH |
6797 | ensure when and whether side effects are visible to other threads. |
6798 | @end quotation | |
6799 | ||
6800 | @item | |
6801 | @b{[lex.key]} | |
6802 | ||
6803 | Add @code{__thread}. | |
6804 | ||
6805 | @item | |
6806 | @b{[basic.start.main]} | |
6807 | ||
6808 | Add after paragraph 5 | |
6809 | ||
6810 | @quotation | |
6811 | The thread that begins execution at the @code{main} function is called | |
95b1627e | 6812 | the @dfn{main thread}. It is implementation defined how functions |
9217ef40 RH |
6813 | beginning threads other than the main thread are designated or typed. |
6814 | A function so designated, as well as the @code{main} function, is called | |
6815 | a @dfn{thread startup function}. It is implementation defined what | |
6816 | happens if a thread startup function returns. It is implementation | |
6817 | defined what happens to other threads when any thread calls @code{exit}. | |
6818 | @end quotation | |
6819 | ||
6820 | @item | |
6821 | @b{[basic.start.init]} | |
6822 | ||
6823 | Add after paragraph 4 | |
6824 | ||
6825 | @quotation | |
6826 | The storage for an object of thread storage duration shall be | |
c0478a66 | 6827 | statically initialized before the first statement of the thread startup |
9217ef40 RH |
6828 | function. An object of thread storage duration shall not require |
6829 | dynamic initialization. | |
6830 | @end quotation | |
6831 | ||
6832 | @item | |
6833 | @b{[basic.start.term]} | |
6834 | ||
6835 | Add after paragraph 3 | |
6836 | ||
6837 | @quotation | |
244c2241 RH |
6838 | The type of an object with thread storage duration shall not have a |
6839 | non-trivial destructor, nor shall it be an array type whose elements | |
6840 | (directly or indirectly) have non-trivial destructors. | |
9217ef40 RH |
6841 | @end quotation |
6842 | ||
6843 | @item | |
6844 | @b{[basic.stc]} | |
6845 | ||
6846 | Add ``thread storage duration'' to the list in paragraph 1. | |
6847 | ||
6848 | Change paragraph 2 | |
6849 | ||
6850 | @quotation | |
6851 | Thread, static, and automatic storage durations are associated with | |
6852 | objects introduced by declarations [@dots{}]. | |
6853 | @end quotation | |
6854 | ||
6855 | Add @code{__thread} to the list of specifiers in paragraph 3. | |
6856 | ||
6857 | @item | |
6858 | @b{[basic.stc.thread]} | |
6859 | ||
6860 | New section before @b{[basic.stc.static]} | |
6861 | ||
6862 | @quotation | |
6863 | The keyword @code{__thread} applied to an non-local object gives the | |
6864 | object thread storage duration. | |
6865 | ||
6866 | A local variable or class data member declared both @code{static} | |
6867 | and @code{__thread} gives the variable or member thread storage | |
6868 | duration. | |
6869 | @end quotation | |
6870 | ||
6871 | @item | |
6872 | @b{[basic.stc.static]} | |
6873 | ||
6874 | Change paragraph 1 | |
6875 | ||
6876 | @quotation | |
6877 | All objects which have neither thread storage duration, dynamic | |
6878 | storage duration nor are local [@dots{}]. | |
6879 | @end quotation | |
6880 | ||
6881 | @item | |
6882 | @b{[dcl.stc]} | |
6883 | ||
6884 | Add @code{__thread} to the list in paragraph 1. | |
6885 | ||
6886 | Change paragraph 1 | |
6887 | ||
6888 | @quotation | |
6889 | With the exception of @code{__thread}, at most one | |
6890 | @var{storage-class-specifier} shall appear in a given | |
6891 | @var{decl-specifier-seq}. The @code{__thread} specifier may | |
6892 | be used alone, or immediately following the @code{extern} or | |
6893 | @code{static} specifiers. [@dots{}] | |
6894 | @end quotation | |
6895 | ||
6896 | Add after paragraph 5 | |
6897 | ||
6898 | @quotation | |
6899 | The @code{__thread} specifier can be applied only to the names of objects | |
6900 | and to anonymous unions. | |
6901 | @end quotation | |
6902 | ||
6903 | @item | |
6904 | @b{[class.mem]} | |
6905 | ||
6906 | Add after paragraph 6 | |
6907 | ||
6908 | @quotation | |
6909 | Non-@code{static} members shall not be @code{__thread}. | |
6910 | @end quotation | |
6911 | @end itemize | |
6912 | ||
c1f7febf RK |
6913 | @node C++ Extensions |
6914 | @chapter Extensions to the C++ Language | |
6915 | @cindex extensions, C++ language | |
6916 | @cindex C++ language extensions | |
6917 | ||
6918 | The GNU compiler provides these extensions to the C++ language (and you | |
6919 | can also use most of the C language extensions in your C++ programs). If you | |
6920 | want to write code that checks whether these features are available, you can | |
6921 | test for the GNU compiler the same way as for C programs: check for a | |
6922 | predefined macro @code{__GNUC__}. You can also use @code{__GNUG__} to | |
6923 | test specifically for GNU C++ (@pxref{Standard Predefined,,Standard | |
6924 | Predefined Macros,cpp.info,The C Preprocessor}). | |
6925 | ||
6926 | @menu | |
c1f7febf | 6927 | * Min and Max:: C++ Minimum and maximum operators. |
02cac427 | 6928 | * Volatiles:: What constitutes an access to a volatile object. |
49419c8f | 6929 | * Restricted Pointers:: C99 restricted pointers and references. |
7a81cf7f | 6930 | * Vague Linkage:: Where G++ puts inlines, vtables and such. |
c1f7febf | 6931 | * C++ Interface:: You can use a single C++ header file for both |
e6f3b89d | 6932 | declarations and definitions. |
c1f7febf | 6933 | * Template Instantiation:: Methods for ensuring that exactly one copy of |
e6f3b89d | 6934 | each needed template instantiation is emitted. |
0ded1f18 JM |
6935 | * Bound member functions:: You can extract a function pointer to the |
6936 | method denoted by a @samp{->*} or @samp{.*} expression. | |
e6f3b89d | 6937 | * C++ Attributes:: Variable, function, and type attributes for C++ only. |
1f730ff7 | 6938 | * Java Exceptions:: Tweaking exception handling to work with Java. |
e6f3b89d PE |
6939 | * Deprecated Features:: Things might disappear from g++. |
6940 | * Backwards Compatibility:: Compatibilities with earlier definitions of C++. | |
c1f7febf RK |
6941 | @end menu |
6942 | ||
c1f7febf RK |
6943 | @node Min and Max |
6944 | @section Minimum and Maximum Operators in C++ | |
6945 | ||
6946 | It is very convenient to have operators which return the ``minimum'' or the | |
6947 | ``maximum'' of two arguments. In GNU C++ (but not in GNU C), | |
6948 | ||
6949 | @table @code | |
6950 | @item @var{a} <? @var{b} | |
6951 | @findex <? | |
6952 | @cindex minimum operator | |
6953 | is the @dfn{minimum}, returning the smaller of the numeric values | |
6954 | @var{a} and @var{b}; | |
6955 | ||
6956 | @item @var{a} >? @var{b} | |
6957 | @findex >? | |
6958 | @cindex maximum operator | |
6959 | is the @dfn{maximum}, returning the larger of the numeric values @var{a} | |
6960 | and @var{b}. | |
6961 | @end table | |
6962 | ||
6963 | These operations are not primitive in ordinary C++, since you can | |
6964 | use a macro to return the minimum of two things in C++, as in the | |
6965 | following example. | |
6966 | ||
6967 | @example | |
6968 | #define MIN(X,Y) ((X) < (Y) ? : (X) : (Y)) | |
6969 | @end example | |
6970 | ||
6971 | @noindent | |
6972 | You might then use @w{@samp{int min = MIN (i, j);}} to set @var{min} to | |
6973 | the minimum value of variables @var{i} and @var{j}. | |
6974 | ||
6975 | However, side effects in @code{X} or @code{Y} may cause unintended | |
6976 | behavior. For example, @code{MIN (i++, j++)} will fail, incrementing | |
95f79357 ZW |
6977 | the smaller counter twice. The GNU C @code{typeof} extension allows you |
6978 | to write safe macros that avoid this kind of problem (@pxref{Typeof}). | |
6979 | However, writing @code{MIN} and @code{MAX} as macros also forces you to | |
6980 | use function-call notation for a fundamental arithmetic operation. | |
6981 | Using GNU C++ extensions, you can write @w{@samp{int min = i <? j;}} | |
6982 | instead. | |
c1f7febf RK |
6983 | |
6984 | Since @code{<?} and @code{>?} are built into the compiler, they properly | |
6985 | handle expressions with side-effects; @w{@samp{int min = i++ <? j++;}} | |
6986 | works correctly. | |
6987 | ||
02cac427 NS |
6988 | @node Volatiles |
6989 | @section When is a Volatile Object Accessed? | |
6990 | @cindex accessing volatiles | |
6991 | @cindex volatile read | |
6992 | @cindex volatile write | |
6993 | @cindex volatile access | |
6994 | ||
767094dd JM |
6995 | Both the C and C++ standard have the concept of volatile objects. These |
6996 | are normally accessed by pointers and used for accessing hardware. The | |
8117da65 | 6997 | standards encourage compilers to refrain from optimizations |
02cac427 | 6998 | concerning accesses to volatile objects that it might perform on |
767094dd JM |
6999 | non-volatile objects. The C standard leaves it implementation defined |
7000 | as to what constitutes a volatile access. The C++ standard omits to | |
02cac427 | 7001 | specify this, except to say that C++ should behave in a similar manner |
767094dd | 7002 | to C with respect to volatiles, where possible. The minimum either |
8117da65 | 7003 | standard specifies is that at a sequence point all previous accesses to |
02cac427 | 7004 | volatile objects have stabilized and no subsequent accesses have |
767094dd | 7005 | occurred. Thus an implementation is free to reorder and combine |
02cac427 | 7006 | volatile accesses which occur between sequence points, but cannot do so |
767094dd | 7007 | for accesses across a sequence point. The use of volatiles does not |
02cac427 NS |
7008 | allow you to violate the restriction on updating objects multiple times |
7009 | within a sequence point. | |
7010 | ||
7011 | In most expressions, it is intuitively obvious what is a read and what is | |
767094dd | 7012 | a write. For instance |
02cac427 NS |
7013 | |
7014 | @example | |
c771326b JM |
7015 | volatile int *dst = @var{somevalue}; |
7016 | volatile int *src = @var{someothervalue}; | |
02cac427 NS |
7017 | *dst = *src; |
7018 | @end example | |
7019 | ||
7020 | @noindent | |
7021 | will cause a read of the volatile object pointed to by @var{src} and stores the | |
767094dd | 7022 | value into the volatile object pointed to by @var{dst}. There is no |
02cac427 NS |
7023 | guarantee that these reads and writes are atomic, especially for objects |
7024 | larger than @code{int}. | |
7025 | ||
7026 | Less obvious expressions are where something which looks like an access | |
767094dd | 7027 | is used in a void context. An example would be, |
02cac427 NS |
7028 | |
7029 | @example | |
c771326b | 7030 | volatile int *src = @var{somevalue}; |
02cac427 NS |
7031 | *src; |
7032 | @end example | |
7033 | ||
7034 | With C, such expressions are rvalues, and as rvalues cause a read of | |
f0523f02 | 7035 | the object, GCC interprets this as a read of the volatile being pointed |
767094dd | 7036 | to. The C++ standard specifies that such expressions do not undergo |
02cac427 | 7037 | lvalue to rvalue conversion, and that the type of the dereferenced |
767094dd | 7038 | object may be incomplete. The C++ standard does not specify explicitly |
02cac427 | 7039 | that it is this lvalue to rvalue conversion which is responsible for |
767094dd JM |
7040 | causing an access. However, there is reason to believe that it is, |
7041 | because otherwise certain simple expressions become undefined. However, | |
f0523f02 | 7042 | because it would surprise most programmers, G++ treats dereferencing a |
02cac427 | 7043 | pointer to volatile object of complete type in a void context as a read |
767094dd | 7044 | of the object. When the object has incomplete type, G++ issues a |
02cac427 NS |
7045 | warning. |
7046 | ||
7047 | @example | |
7048 | struct S; | |
7049 | struct T @{int m;@}; | |
c771326b JM |
7050 | volatile S *ptr1 = @var{somevalue}; |
7051 | volatile T *ptr2 = @var{somevalue}; | |
02cac427 NS |
7052 | *ptr1; |
7053 | *ptr2; | |
7054 | @end example | |
7055 | ||
7056 | In this example, a warning is issued for @code{*ptr1}, and @code{*ptr2} | |
767094dd | 7057 | causes a read of the object pointed to. If you wish to force an error on |
02cac427 NS |
7058 | the first case, you must force a conversion to rvalue with, for instance |
7059 | a static cast, @code{static_cast<S>(*ptr1)}. | |
7060 | ||
f0523f02 | 7061 | When using a reference to volatile, G++ does not treat equivalent |
02cac427 | 7062 | expressions as accesses to volatiles, but instead issues a warning that |
767094dd | 7063 | no volatile is accessed. The rationale for this is that otherwise it |
02cac427 NS |
7064 | becomes difficult to determine where volatile access occur, and not |
7065 | possible to ignore the return value from functions returning volatile | |
767094dd | 7066 | references. Again, if you wish to force a read, cast the reference to |
02cac427 NS |
7067 | an rvalue. |
7068 | ||
535233a8 NS |
7069 | @node Restricted Pointers |
7070 | @section Restricting Pointer Aliasing | |
7071 | @cindex restricted pointers | |
7072 | @cindex restricted references | |
7073 | @cindex restricted this pointer | |
7074 | ||
49419c8f | 7075 | As with gcc, g++ understands the C99 feature of restricted pointers, |
535233a8 | 7076 | specified with the @code{__restrict__}, or @code{__restrict} type |
767094dd | 7077 | qualifier. Because you cannot compile C++ by specifying the @option{-std=c99} |
535233a8 NS |
7078 | language flag, @code{restrict} is not a keyword in C++. |
7079 | ||
7080 | In addition to allowing restricted pointers, you can specify restricted | |
7081 | references, which indicate that the reference is not aliased in the local | |
7082 | context. | |
7083 | ||
7084 | @example | |
7085 | void fn (int *__restrict__ rptr, int &__restrict__ rref) | |
7086 | @{ | |
0d893a63 | 7087 | /* @r{@dots{}} */ |
535233a8 NS |
7088 | @} |
7089 | @end example | |
7090 | ||
7091 | @noindent | |
7092 | In the body of @code{fn}, @var{rptr} points to an unaliased integer and | |
7093 | @var{rref} refers to a (different) unaliased integer. | |
7094 | ||
7095 | You may also specify whether a member function's @var{this} pointer is | |
7096 | unaliased by using @code{__restrict__} as a member function qualifier. | |
7097 | ||
7098 | @example | |
7099 | void T::fn () __restrict__ | |
7100 | @{ | |
0d893a63 | 7101 | /* @r{@dots{}} */ |
535233a8 NS |
7102 | @} |
7103 | @end example | |
7104 | ||
7105 | @noindent | |
7106 | Within the body of @code{T::fn}, @var{this} will have the effective | |
767094dd | 7107 | definition @code{T *__restrict__ const this}. Notice that the |
535233a8 NS |
7108 | interpretation of a @code{__restrict__} member function qualifier is |
7109 | different to that of @code{const} or @code{volatile} qualifier, in that it | |
767094dd | 7110 | is applied to the pointer rather than the object. This is consistent with |
535233a8 NS |
7111 | other compilers which implement restricted pointers. |
7112 | ||
7113 | As with all outermost parameter qualifiers, @code{__restrict__} is | |
767094dd | 7114 | ignored in function definition matching. This means you only need to |
535233a8 NS |
7115 | specify @code{__restrict__} in a function definition, rather than |
7116 | in a function prototype as well. | |
7117 | ||
7a81cf7f JM |
7118 | @node Vague Linkage |
7119 | @section Vague Linkage | |
7120 | @cindex vague linkage | |
7121 | ||
7122 | There are several constructs in C++ which require space in the object | |
7123 | file but are not clearly tied to a single translation unit. We say that | |
7124 | these constructs have ``vague linkage''. Typically such constructs are | |
7125 | emitted wherever they are needed, though sometimes we can be more | |
7126 | clever. | |
7127 | ||
7128 | @table @asis | |
7129 | @item Inline Functions | |
7130 | Inline functions are typically defined in a header file which can be | |
7131 | included in many different compilations. Hopefully they can usually be | |
7132 | inlined, but sometimes an out-of-line copy is necessary, if the address | |
7133 | of the function is taken or if inlining fails. In general, we emit an | |
7134 | out-of-line copy in all translation units where one is needed. As an | |
7135 | exception, we only emit inline virtual functions with the vtable, since | |
7136 | it will always require a copy. | |
7137 | ||
7138 | Local static variables and string constants used in an inline function | |
7139 | are also considered to have vague linkage, since they must be shared | |
7140 | between all inlined and out-of-line instances of the function. | |
7141 | ||
7142 | @item VTables | |
7143 | @cindex vtable | |
7144 | C++ virtual functions are implemented in most compilers using a lookup | |
7145 | table, known as a vtable. The vtable contains pointers to the virtual | |
7146 | functions provided by a class, and each object of the class contains a | |
7147 | pointer to its vtable (or vtables, in some multiple-inheritance | |
7148 | situations). If the class declares any non-inline, non-pure virtual | |
7149 | functions, the first one is chosen as the ``key method'' for the class, | |
7150 | and the vtable is only emitted in the translation unit where the key | |
7151 | method is defined. | |
7152 | ||
7153 | @emph{Note:} If the chosen key method is later defined as inline, the | |
7154 | vtable will still be emitted in every translation unit which defines it. | |
7155 | Make sure that any inline virtuals are declared inline in the class | |
7156 | body, even if they are not defined there. | |
7157 | ||
7158 | @item type_info objects | |
7159 | @cindex type_info | |
7160 | @cindex RTTI | |
7161 | C++ requires information about types to be written out in order to | |
7162 | implement @samp{dynamic_cast}, @samp{typeid} and exception handling. | |
7163 | For polymorphic classes (classes with virtual functions), the type_info | |
7164 | object is written out along with the vtable so that @samp{dynamic_cast} | |
7165 | can determine the dynamic type of a class object at runtime. For all | |
7166 | other types, we write out the type_info object when it is used: when | |
7167 | applying @samp{typeid} to an expression, throwing an object, or | |
7168 | referring to a type in a catch clause or exception specification. | |
7169 | ||
7170 | @item Template Instantiations | |
7171 | Most everything in this section also applies to template instantiations, | |
7172 | but there are other options as well. | |
7173 | @xref{Template Instantiation,,Where's the Template?}. | |
7174 | ||
7175 | @end table | |
7176 | ||
7177 | When used with GNU ld version 2.8 or later on an ELF system such as | |
7178 | Linux/GNU or Solaris 2, or on Microsoft Windows, duplicate copies of | |
7179 | these constructs will be discarded at link time. This is known as | |
7180 | COMDAT support. | |
7181 | ||
7182 | On targets that don't support COMDAT, but do support weak symbols, GCC | |
7183 | will use them. This way one copy will override all the others, but | |
7184 | the unused copies will still take up space in the executable. | |
7185 | ||
7186 | For targets which do not support either COMDAT or weak symbols, | |
7187 | most entities with vague linkage will be emitted as local symbols to | |
7188 | avoid duplicate definition errors from the linker. This will not happen | |
7189 | for local statics in inlines, however, as having multiple copies will | |
7190 | almost certainly break things. | |
7191 | ||
7192 | @xref{C++ Interface,,Declarations and Definitions in One Header}, for | |
7193 | another way to control placement of these constructs. | |
7194 | ||
c1f7febf RK |
7195 | @node C++ Interface |
7196 | @section Declarations and Definitions in One Header | |
7197 | ||
7198 | @cindex interface and implementation headers, C++ | |
7199 | @cindex C++ interface and implementation headers | |
7200 | C++ object definitions can be quite complex. In principle, your source | |
7201 | code will need two kinds of things for each object that you use across | |
7202 | more than one source file. First, you need an @dfn{interface} | |
7203 | specification, describing its structure with type declarations and | |
7204 | function prototypes. Second, you need the @dfn{implementation} itself. | |
7205 | It can be tedious to maintain a separate interface description in a | |
7206 | header file, in parallel to the actual implementation. It is also | |
7207 | dangerous, since separate interface and implementation definitions may | |
7208 | not remain parallel. | |
7209 | ||
7210 | @cindex pragmas, interface and implementation | |
7211 | With GNU C++, you can use a single header file for both purposes. | |
7212 | ||
7213 | @quotation | |
7214 | @emph{Warning:} The mechanism to specify this is in transition. For the | |
7215 | nonce, you must use one of two @code{#pragma} commands; in a future | |
7216 | release of GNU C++, an alternative mechanism will make these | |
7217 | @code{#pragma} commands unnecessary. | |
7218 | @end quotation | |
7219 | ||
7220 | The header file contains the full definitions, but is marked with | |
7221 | @samp{#pragma interface} in the source code. This allows the compiler | |
7222 | to use the header file only as an interface specification when ordinary | |
7223 | source files incorporate it with @code{#include}. In the single source | |
7224 | file where the full implementation belongs, you can use either a naming | |
7225 | convention or @samp{#pragma implementation} to indicate this alternate | |
7226 | use of the header file. | |
7227 | ||
7228 | @table @code | |
7229 | @item #pragma interface | |
7230 | @itemx #pragma interface "@var{subdir}/@var{objects}.h" | |
7231 | @kindex #pragma interface | |
7232 | Use this directive in @emph{header files} that define object classes, to save | |
7233 | space in most of the object files that use those classes. Normally, | |
7234 | local copies of certain information (backup copies of inline member | |
7235 | functions, debugging information, and the internal tables that implement | |
7236 | virtual functions) must be kept in each object file that includes class | |
7237 | definitions. You can use this pragma to avoid such duplication. When a | |
7238 | header file containing @samp{#pragma interface} is included in a | |
7239 | compilation, this auxiliary information will not be generated (unless | |
7240 | the main input source file itself uses @samp{#pragma implementation}). | |
7241 | Instead, the object files will contain references to be resolved at link | |
7242 | time. | |
7243 | ||
7244 | The second form of this directive is useful for the case where you have | |
7245 | multiple headers with the same name in different directories. If you | |
7246 | use this form, you must specify the same string to @samp{#pragma | |
7247 | implementation}. | |
7248 | ||
7249 | @item #pragma implementation | |
7250 | @itemx #pragma implementation "@var{objects}.h" | |
7251 | @kindex #pragma implementation | |
7252 | Use this pragma in a @emph{main input file}, when you want full output from | |
7253 | included header files to be generated (and made globally visible). The | |
7254 | included header file, in turn, should use @samp{#pragma interface}. | |
7255 | Backup copies of inline member functions, debugging information, and the | |
7256 | internal tables used to implement virtual functions are all generated in | |
7257 | implementation files. | |
7258 | ||
7259 | @cindex implied @code{#pragma implementation} | |
7260 | @cindex @code{#pragma implementation}, implied | |
7261 | @cindex naming convention, implementation headers | |
7262 | If you use @samp{#pragma implementation} with no argument, it applies to | |
7263 | an include file with the same basename@footnote{A file's @dfn{basename} | |
7264 | was the name stripped of all leading path information and of trailing | |
7265 | suffixes, such as @samp{.h} or @samp{.C} or @samp{.cc}.} as your source | |
7266 | file. For example, in @file{allclass.cc}, giving just | |
7267 | @samp{#pragma implementation} | |
7268 | by itself is equivalent to @samp{#pragma implementation "allclass.h"}. | |
7269 | ||
7270 | In versions of GNU C++ prior to 2.6.0 @file{allclass.h} was treated as | |
7271 | an implementation file whenever you would include it from | |
7272 | @file{allclass.cc} even if you never specified @samp{#pragma | |
7273 | implementation}. This was deemed to be more trouble than it was worth, | |
7274 | however, and disabled. | |
7275 | ||
7276 | If you use an explicit @samp{#pragma implementation}, it must appear in | |
7277 | your source file @emph{before} you include the affected header files. | |
7278 | ||
7279 | Use the string argument if you want a single implementation file to | |
7280 | include code from multiple header files. (You must also use | |
7281 | @samp{#include} to include the header file; @samp{#pragma | |
7282 | implementation} only specifies how to use the file---it doesn't actually | |
7283 | include it.) | |
7284 | ||
7285 | There is no way to split up the contents of a single header file into | |
7286 | multiple implementation files. | |
7287 | @end table | |
7288 | ||
7289 | @cindex inlining and C++ pragmas | |
7290 | @cindex C++ pragmas, effect on inlining | |
7291 | @cindex pragmas in C++, effect on inlining | |
7292 | @samp{#pragma implementation} and @samp{#pragma interface} also have an | |
7293 | effect on function inlining. | |
7294 | ||
7295 | If you define a class in a header file marked with @samp{#pragma | |
7296 | interface}, the effect on a function defined in that class is similar to | |
7297 | an explicit @code{extern} declaration---the compiler emits no code at | |
7298 | all to define an independent version of the function. Its definition | |
7299 | is used only for inlining with its callers. | |
7300 | ||
84330467 | 7301 | @opindex fno-implement-inlines |
c1f7febf RK |
7302 | Conversely, when you include the same header file in a main source file |
7303 | that declares it as @samp{#pragma implementation}, the compiler emits | |
7304 | code for the function itself; this defines a version of the function | |
7305 | that can be found via pointers (or by callers compiled without | |
7306 | inlining). If all calls to the function can be inlined, you can avoid | |
84330467 | 7307 | emitting the function by compiling with @option{-fno-implement-inlines}. |
c1f7febf RK |
7308 | If any calls were not inlined, you will get linker errors. |
7309 | ||
7310 | @node Template Instantiation | |
7311 | @section Where's the Template? | |
7312 | ||
7313 | @cindex template instantiation | |
7314 | ||
7315 | C++ templates are the first language feature to require more | |
7316 | intelligence from the environment than one usually finds on a UNIX | |
7317 | system. Somehow the compiler and linker have to make sure that each | |
7318 | template instance occurs exactly once in the executable if it is needed, | |
7319 | and not at all otherwise. There are two basic approaches to this | |
7320 | problem, which I will refer to as the Borland model and the Cfront model. | |
7321 | ||
7322 | @table @asis | |
7323 | @item Borland model | |
7324 | Borland C++ solved the template instantiation problem by adding the code | |
469b759e JM |
7325 | equivalent of common blocks to their linker; the compiler emits template |
7326 | instances in each translation unit that uses them, and the linker | |
7327 | collapses them together. The advantage of this model is that the linker | |
7328 | only has to consider the object files themselves; there is no external | |
7329 | complexity to worry about. This disadvantage is that compilation time | |
7330 | is increased because the template code is being compiled repeatedly. | |
7331 | Code written for this model tends to include definitions of all | |
7332 | templates in the header file, since they must be seen to be | |
7333 | instantiated. | |
c1f7febf RK |
7334 | |
7335 | @item Cfront model | |
7336 | The AT&T C++ translator, Cfront, solved the template instantiation | |
7337 | problem by creating the notion of a template repository, an | |
469b759e JM |
7338 | automatically maintained place where template instances are stored. A |
7339 | more modern version of the repository works as follows: As individual | |
7340 | object files are built, the compiler places any template definitions and | |
7341 | instantiations encountered in the repository. At link time, the link | |
7342 | wrapper adds in the objects in the repository and compiles any needed | |
7343 | instances that were not previously emitted. The advantages of this | |
7344 | model are more optimal compilation speed and the ability to use the | |
7345 | system linker; to implement the Borland model a compiler vendor also | |
c1f7febf | 7346 | needs to replace the linker. The disadvantages are vastly increased |
469b759e JM |
7347 | complexity, and thus potential for error; for some code this can be |
7348 | just as transparent, but in practice it can been very difficult to build | |
c1f7febf | 7349 | multiple programs in one directory and one program in multiple |
469b759e JM |
7350 | directories. Code written for this model tends to separate definitions |
7351 | of non-inline member templates into a separate file, which should be | |
7352 | compiled separately. | |
c1f7febf RK |
7353 | @end table |
7354 | ||
469b759e | 7355 | When used with GNU ld version 2.8 or later on an ELF system such as |
a4b3b54a JM |
7356 | Linux/GNU or Solaris 2, or on Microsoft Windows, g++ supports the |
7357 | Borland model. On other systems, g++ implements neither automatic | |
7358 | model. | |
469b759e JM |
7359 | |
7360 | A future version of g++ will support a hybrid model whereby the compiler | |
7361 | will emit any instantiations for which the template definition is | |
7362 | included in the compile, and store template definitions and | |
7363 | instantiation context information into the object file for the rest. | |
7364 | The link wrapper will extract that information as necessary and invoke | |
7365 | the compiler to produce the remaining instantiations. The linker will | |
7366 | then combine duplicate instantiations. | |
7367 | ||
7368 | In the mean time, you have the following options for dealing with | |
7369 | template instantiations: | |
c1f7febf RK |
7370 | |
7371 | @enumerate | |
d863830b | 7372 | @item |
84330467 JM |
7373 | @opindex frepo |
7374 | Compile your template-using code with @option{-frepo}. The compiler will | |
d863830b JL |
7375 | generate files with the extension @samp{.rpo} listing all of the |
7376 | template instantiations used in the corresponding object files which | |
7377 | could be instantiated there; the link wrapper, @samp{collect2}, will | |
7378 | then update the @samp{.rpo} files to tell the compiler where to place | |
7379 | those instantiations and rebuild any affected object files. The | |
7380 | link-time overhead is negligible after the first pass, as the compiler | |
7381 | will continue to place the instantiations in the same files. | |
7382 | ||
7383 | This is your best option for application code written for the Borland | |
7384 | model, as it will just work. Code written for the Cfront model will | |
7385 | need to be modified so that the template definitions are available at | |
7386 | one or more points of instantiation; usually this is as simple as adding | |
7387 | @code{#include <tmethods.cc>} to the end of each template header. | |
7388 | ||
7389 | For library code, if you want the library to provide all of the template | |
7390 | instantiations it needs, just try to link all of its object files | |
7391 | together; the link will fail, but cause the instantiations to be | |
7392 | generated as a side effect. Be warned, however, that this may cause | |
7393 | conflicts if multiple libraries try to provide the same instantiations. | |
7394 | For greater control, use explicit instantiation as described in the next | |
7395 | option. | |
7396 | ||
c1f7febf | 7397 | @item |
84330467 JM |
7398 | @opindex fno-implicit-templates |
7399 | Compile your code with @option{-fno-implicit-templates} to disable the | |
c1f7febf RK |
7400 | implicit generation of template instances, and explicitly instantiate |
7401 | all the ones you use. This approach requires more knowledge of exactly | |
7402 | which instances you need than do the others, but it's less | |
7403 | mysterious and allows greater control. You can scatter the explicit | |
7404 | instantiations throughout your program, perhaps putting them in the | |
7405 | translation units where the instances are used or the translation units | |
7406 | that define the templates themselves; you can put all of the explicit | |
7407 | instantiations you need into one big file; or you can create small files | |
7408 | like | |
7409 | ||
7410 | @example | |
7411 | #include "Foo.h" | |
7412 | #include "Foo.cc" | |
7413 | ||
7414 | template class Foo<int>; | |
7415 | template ostream& operator << | |
7416 | (ostream&, const Foo<int>&); | |
7417 | @end example | |
7418 | ||
7419 | for each of the instances you need, and create a template instantiation | |
7420 | library from those. | |
7421 | ||
7422 | If you are using Cfront-model code, you can probably get away with not | |
84330467 | 7423 | using @option{-fno-implicit-templates} when compiling files that don't |
c1f7febf RK |
7424 | @samp{#include} the member template definitions. |
7425 | ||
7426 | If you use one big file to do the instantiations, you may want to | |
84330467 | 7427 | compile it without @option{-fno-implicit-templates} so you get all of the |
c1f7febf RK |
7428 | instances required by your explicit instantiations (but not by any |
7429 | other files) without having to specify them as well. | |
7430 | ||
7431 | g++ has extended the template instantiation syntax outlined in the | |
03d0f4af | 7432 | Working Paper to allow forward declaration of explicit instantiations |
4003d7f9 | 7433 | (with @code{extern}), instantiation of the compiler support data for a |
e979f9e8 | 7434 | template class (i.e.@: the vtable) without instantiating any of its |
4003d7f9 JM |
7435 | members (with @code{inline}), and instantiation of only the static data |
7436 | members of a template class, without the support data or member | |
7437 | functions (with (@code{static}): | |
c1f7febf RK |
7438 | |
7439 | @example | |
7440 | extern template int max (int, int); | |
c1f7febf | 7441 | inline template class Foo<int>; |
4003d7f9 | 7442 | static template class Foo<int>; |
c1f7febf RK |
7443 | @end example |
7444 | ||
7445 | @item | |
7446 | Do nothing. Pretend g++ does implement automatic instantiation | |
7447 | management. Code written for the Borland model will work fine, but | |
7448 | each translation unit will contain instances of each of the templates it | |
7449 | uses. In a large program, this can lead to an unacceptable amount of code | |
7450 | duplication. | |
7451 | ||
c1f7febf RK |
7452 | @xref{C++ Interface,,Declarations and Definitions in One Header}, for |
7453 | more discussion of these pragmas. | |
7454 | @end enumerate | |
7455 | ||
0ded1f18 JM |
7456 | @node Bound member functions |
7457 | @section Extracting the function pointer from a bound pointer to member function | |
7458 | ||
7459 | @cindex pmf | |
7460 | @cindex pointer to member function | |
7461 | @cindex bound pointer to member function | |
7462 | ||
7463 | In C++, pointer to member functions (PMFs) are implemented using a wide | |
7464 | pointer of sorts to handle all the possible call mechanisms; the PMF | |
7465 | needs to store information about how to adjust the @samp{this} pointer, | |
7466 | and if the function pointed to is virtual, where to find the vtable, and | |
7467 | where in the vtable to look for the member function. If you are using | |
7468 | PMFs in an inner loop, you should really reconsider that decision. If | |
7469 | that is not an option, you can extract the pointer to the function that | |
7470 | would be called for a given object/PMF pair and call it directly inside | |
7471 | the inner loop, to save a bit of time. | |
7472 | ||
7473 | Note that you will still be paying the penalty for the call through a | |
7474 | function pointer; on most modern architectures, such a call defeats the | |
161d7b59 | 7475 | branch prediction features of the CPU@. This is also true of normal |
0ded1f18 JM |
7476 | virtual function calls. |
7477 | ||
7478 | The syntax for this extension is | |
7479 | ||
7480 | @example | |
7481 | extern A a; | |
7482 | extern int (A::*fp)(); | |
7483 | typedef int (*fptr)(A *); | |
7484 | ||
7485 | fptr p = (fptr)(a.*fp); | |
7486 | @end example | |
7487 | ||
e979f9e8 | 7488 | For PMF constants (i.e.@: expressions of the form @samp{&Klasse::Member}), |
767094dd | 7489 | no object is needed to obtain the address of the function. They can be |
0fb6bbf5 ML |
7490 | converted to function pointers directly: |
7491 | ||
7492 | @example | |
7493 | fptr p1 = (fptr)(&A::foo); | |
7494 | @end example | |
7495 | ||
84330467 JM |
7496 | @opindex Wno-pmf-conversions |
7497 | You must specify @option{-Wno-pmf-conversions} to use this extension. | |
0ded1f18 | 7498 | |
5c25e11d PE |
7499 | @node C++ Attributes |
7500 | @section C++-Specific Variable, Function, and Type Attributes | |
7501 | ||
7502 | Some attributes only make sense for C++ programs. | |
7503 | ||
7504 | @table @code | |
7505 | @item init_priority (@var{priority}) | |
7506 | @cindex init_priority attribute | |
7507 | ||
7508 | ||
7509 | In Standard C++, objects defined at namespace scope are guaranteed to be | |
7510 | initialized in an order in strict accordance with that of their definitions | |
7511 | @emph{in a given translation unit}. No guarantee is made for initializations | |
7512 | across translation units. However, GNU C++ allows users to control the | |
3844cd2e | 7513 | order of initialization of objects defined at namespace scope with the |
5c25e11d PE |
7514 | @code{init_priority} attribute by specifying a relative @var{priority}, |
7515 | a constant integral expression currently bounded between 101 and 65535 | |
7516 | inclusive. Lower numbers indicate a higher priority. | |
7517 | ||
7518 | In the following example, @code{A} would normally be created before | |
7519 | @code{B}, but the @code{init_priority} attribute has reversed that order: | |
7520 | ||
478c9e72 | 7521 | @smallexample |
5c25e11d PE |
7522 | Some_Class A __attribute__ ((init_priority (2000))); |
7523 | Some_Class B __attribute__ ((init_priority (543))); | |
478c9e72 | 7524 | @end smallexample |
5c25e11d PE |
7525 | |
7526 | @noindent | |
7527 | Note that the particular values of @var{priority} do not matter; only their | |
7528 | relative ordering. | |
7529 | ||
60c87482 BM |
7530 | @item java_interface |
7531 | @cindex java_interface attribute | |
7532 | ||
02f52e19 | 7533 | This type attribute informs C++ that the class is a Java interface. It may |
60c87482 | 7534 | only be applied to classes declared within an @code{extern "Java"} block. |
02f52e19 AJ |
7535 | Calls to methods declared in this interface will be dispatched using GCJ's |
7536 | interface table mechanism, instead of regular virtual table dispatch. | |
60c87482 | 7537 | |
5c25e11d PE |
7538 | @end table |
7539 | ||
1f730ff7 ZW |
7540 | @node Java Exceptions |
7541 | @section Java Exceptions | |
7542 | ||
7543 | The Java language uses a slightly different exception handling model | |
7544 | from C++. Normally, GNU C++ will automatically detect when you are | |
7545 | writing C++ code that uses Java exceptions, and handle them | |
7546 | appropriately. However, if C++ code only needs to execute destructors | |
7547 | when Java exceptions are thrown through it, GCC will guess incorrectly. | |
9c34dbbf | 7548 | Sample problematic code is: |
1f730ff7 | 7549 | |
478c9e72 | 7550 | @smallexample |
1f730ff7 | 7551 | struct S @{ ~S(); @}; |
9c34dbbf | 7552 | extern void bar(); // is written in Java, and may throw exceptions |
1f730ff7 ZW |
7553 | void foo() |
7554 | @{ | |
7555 | S s; | |
7556 | bar(); | |
7557 | @} | |
478c9e72 | 7558 | @end smallexample |
1f730ff7 ZW |
7559 | |
7560 | @noindent | |
7561 | The usual effect of an incorrect guess is a link failure, complaining of | |
7562 | a missing routine called @samp{__gxx_personality_v0}. | |
7563 | ||
7564 | You can inform the compiler that Java exceptions are to be used in a | |
7565 | translation unit, irrespective of what it might think, by writing | |
7566 | @samp{@w{#pragma GCC java_exceptions}} at the head of the file. This | |
7567 | @samp{#pragma} must appear before any functions that throw or catch | |
7568 | exceptions, or run destructors when exceptions are thrown through them. | |
7569 | ||
7570 | You cannot mix Java and C++ exceptions in the same translation unit. It | |
7571 | is believed to be safe to throw a C++ exception from one file through | |
9c34dbbf ZW |
7572 | another file compiled for the Java exception model, or vice versa, but |
7573 | there may be bugs in this area. | |
1f730ff7 | 7574 | |
e6f3b89d PE |
7575 | @node Deprecated Features |
7576 | @section Deprecated Features | |
7577 | ||
7578 | In the past, the GNU C++ compiler was extended to experiment with new | |
767094dd | 7579 | features, at a time when the C++ language was still evolving. Now that |
e6f3b89d | 7580 | the C++ standard is complete, some of those features are superseded by |
767094dd JM |
7581 | superior alternatives. Using the old features might cause a warning in |
7582 | some cases that the feature will be dropped in the future. In other | |
e6f3b89d PE |
7583 | cases, the feature might be gone already. |
7584 | ||
7585 | While the list below is not exhaustive, it documents some of the options | |
7586 | that are now deprecated: | |
7587 | ||
7588 | @table @code | |
7589 | @item -fexternal-templates | |
7590 | @itemx -falt-external-templates | |
7591 | These are two of the many ways for g++ to implement template | |
767094dd | 7592 | instantiation. @xref{Template Instantiation}. The C++ standard clearly |
e6f3b89d | 7593 | defines how template definitions have to be organized across |
767094dd | 7594 | implementation units. g++ has an implicit instantiation mechanism that |
e6f3b89d PE |
7595 | should work just fine for standard-conforming code. |
7596 | ||
7597 | @item -fstrict-prototype | |
7598 | @itemx -fno-strict-prototype | |
7599 | Previously it was possible to use an empty prototype parameter list to | |
7600 | indicate an unspecified number of parameters (like C), rather than no | |
767094dd | 7601 | parameters, as C++ demands. This feature has been removed, except where |
e6f3b89d PE |
7602 | it is required for backwards compatibility @xref{Backwards Compatibility}. |
7603 | @end table | |
7604 | ||
ad1a6d45 NS |
7605 | The named return value extension has been deprecated, and is now |
7606 | removed from g++. | |
e6f3b89d | 7607 | |
82c18d5c | 7608 | The use of initializer lists with new expressions has been deprecated, |
ad1a6d45 NS |
7609 | and is now removed from g++. |
7610 | ||
7611 | Floating and complex non-type template parameters have been deprecated, | |
7612 | and are now removed from g++. | |
7613 | ||
7614 | The implicit typename extension has been deprecated and will be removed | |
05713b80 | 7615 | from g++ at some point. In some cases g++ determines that a dependent |
ad1a6d45 NS |
7616 | type such as @code{TPL<T>::X} is a type without needing a |
7617 | @code{typename} keyword, contrary to the standard. | |
82c18d5c | 7618 | |
e6f3b89d PE |
7619 | @node Backwards Compatibility |
7620 | @section Backwards Compatibility | |
7621 | @cindex Backwards Compatibility | |
7622 | @cindex ARM [Annotated C++ Reference Manual] | |
7623 | ||
aee96fe9 | 7624 | Now that there is a definitive ISO standard C++, G++ has a specification |
767094dd | 7625 | to adhere to. The C++ language evolved over time, and features that |
e6f3b89d | 7626 | used to be acceptable in previous drafts of the standard, such as the ARM |
767094dd | 7627 | [Annotated C++ Reference Manual], are no longer accepted. In order to allow |
aee96fe9 | 7628 | compilation of C++ written to such drafts, G++ contains some backwards |
767094dd | 7629 | compatibilities. @emph{All such backwards compatibility features are |
aee96fe9 | 7630 | liable to disappear in future versions of G++.} They should be considered |
e6f3b89d PE |
7631 | deprecated @xref{Deprecated Features}. |
7632 | ||
7633 | @table @code | |
7634 | @item For scope | |
7635 | If a variable is declared at for scope, it used to remain in scope until | |
7636 | the end of the scope which contained the for statement (rather than just | |
aee96fe9 | 7637 | within the for scope). G++ retains this, but issues a warning, if such a |
e6f3b89d PE |
7638 | variable is accessed outside the for scope. |
7639 | ||
ad1a6d45 | 7640 | @item Implicit C language |
630d3d5a | 7641 | Old C system header files did not contain an @code{extern "C" @{@dots{}@}} |
767094dd JM |
7642 | scope to set the language. On such systems, all header files are |
7643 | implicitly scoped inside a C language scope. Also, an empty prototype | |
e6f3b89d PE |
7644 | @code{()} will be treated as an unspecified number of arguments, rather |
7645 | than no arguments, as C++ demands. | |
7646 | @end table |