misc/sys/cdefs.h

   1 /* Copyright (C) 1992-2020 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #ifndef _SYS_CDEFS_H
  19 #define _SYS_CDEFS_H    1
  20
  21 /* We are almost always included from features.h. */
  22 #ifndef _FEATURES_H
  23 # include <features.h>
  24 #endif
  25
  26 /* The GNU libc does not support any K&R compilers or the traditional mode
  27    of ISO C compilers anymore.  Check for some of the combinations not
  28    anymore supported.  */
  29 #if defined __GNUC__ && !defined __STDC__
  30 # error "You need a ISO C conforming compiler to use the glibc headers"
  31 #endif
  32
  33 /* Some user header file might have defined this before.  */
  34 #undef  __P
  35 #undef  __PMT
  36
  37 #ifdef __GNUC__
  38
  39 /* All functions, except those with callbacks or those that
  40    synchronize memory, are leaf functions.  */
  41 # if __GNUC_PREREQ (4, 6) && !defined _LIBC
  42 #  define __LEAF , __leaf__
  43 #  define __LEAF_ATTR __attribute__ ((__leaf__))
  44 # else
  45 #  define __LEAF
  46 #  define __LEAF_ATTR
  47 # endif
  48
  49 /* GCC can always grok prototypes.  For C++ programs we add throw()
  50    to help it optimize the function calls.  But this works only with
  51    gcc 2.8.x and egcs.  For gcc 3.2 and up we even mark C functions
  52    as non-throwing using a function attribute since programs can use
  53    the -fexceptions options for C code as well.  */
  54 # if !defined __cplusplus && __GNUC_PREREQ (3, 3)
  55 #  define __THROW       __attribute__ ((__nothrow__ __LEAF))
  56 #  define __THROWNL     __attribute__ ((__nothrow__))
  57 #  define __NTH(fct)    __attribute__ ((__nothrow__ __LEAF)) fct
  58 #  define __NTHNL(fct)  __attribute__ ((__nothrow__)) fct
  59 # else
  60 #  if defined __cplusplus && __GNUC_PREREQ (2,8)
  61 #   if __cplusplus >= 201103L
  62 #    define __THROW     noexcept (true)
  63 #   else
  64 #    define __THROW     throw ()
  65 #   endif
  66 #   define __THROWNL    __THROW
  67 #   define __NTH(fct)   __LEAF_ATTR fct __THROW
  68 #   define __NTHNL(fct) fct __THROW
  69 #  else
  70 #   define __THROW
  71 #   define __THROWNL
  72 #   define __NTH(fct)   fct
  73 #   define __NTHNL(fct) fct
  74 #  endif
  75 # endif
  76
  77 #else   /* Not GCC.  */
  78
  79 # if (defined __cplusplus                                               \
  80       || (defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L))
  81 #  define __inline      inline
  82 # else
  83 #  define __inline              /* No inline functions.  */
  84 # endif
  85
  86 # define __THROW
  87 # define __THROWNL
  88 # define __NTH(fct)     fct
  89
  90 #endif  /* GCC.  */
  91
  92 /* Compilers that are not clang may object to
  93        #if defined __clang__ && __has_extension(...)
  94    even though they do not need to evaluate the right-hand side of the &&.  */
  95 #if defined __clang__ && defined __has_extension
  96 # define __glibc_clang_has_extension(ext) __has_extension (ext)
  97 #else
  98 # define __glibc_clang_has_extension(ext) 0
  99 #endif
 100
 101 /* These two macros are not used in glibc anymore.  They are kept here
 102    only because some other projects expect the macros to be defined.  */
 103 #define __P(args)       args
 104 #define __PMT(args)     args
 105
 106 /* For these things, GCC behaves the ANSI way normally,
 107    and the non-ANSI way under -traditional.  */
 108
 109 #define __CONCAT(x,y)   x ## y
 110 #define __STRING(x)     #x
 111
 112 /* This is not a typedef so `const __ptr_t' does the right thing.  */
 113 #define __ptr_t void *
 114
 115
 116 /* C++ needs to know that types and declarations are C, not C++.  */
 117 #ifdef  __cplusplus
 118 # define __BEGIN_DECLS  extern "C" {
 119 # define __END_DECLS    }
 120 #else
 121 # define __BEGIN_DECLS
 122 # define __END_DECLS
 123 #endif
 124
 125
 126 /* Fortify support.  */
 127 #define __bos(ptr) __builtin_object_size (ptr, __USE_FORTIFY_LEVEL > 1)
 128 #define __bos0(ptr) __builtin_object_size (ptr, 0)
 129
 130 #if __GNUC_PREREQ (4,3)
 131 # define __warndecl(name, msg) \
 132   extern void name (void) __attribute__((__warning__ (msg)))
 133 # define __warnattr(msg) __attribute__((__warning__ (msg)))
 134 # define __errordecl(name, msg) \
 135   extern void name (void) __attribute__((__error__ (msg)))
 136 #else
 137 # define __warndecl(name, msg) extern void name (void)
 138 # define __warnattr(msg)
 139 # define __errordecl(name, msg) extern void name (void)
 140 #endif
 141
 142 /* Support for flexible arrays.
 143    Headers that should use flexible arrays only if they're "real"
 144    (e.g. only if they won't affect sizeof()) should test
 145    #if __glibc_c99_flexarr_available.  */
 146 #if defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L
 147 # define __flexarr      []
 148 # define __glibc_c99_flexarr_available 1
 149 #elif __GNUC_PREREQ (2,97)
 150 /* GCC 2.97 supports C99 flexible array members as an extension,
 151    even when in C89 mode or compiling C++ (any version).  */
 152 # define __flexarr      []
 153 # define __glibc_c99_flexarr_available 1
 154 #elif defined __GNUC__
 155 /* Pre-2.97 GCC did not support C99 flexible arrays but did have
 156    an equivalent extension with slightly different notation.  */
 157 # define __flexarr      [0]
 158 # define __glibc_c99_flexarr_available 1
 159 #else
 160 /* Some other non-C99 compiler.  Approximate with [1].  */
 161 # define __flexarr      [1]
 162 # define __glibc_c99_flexarr_available 0
 163 #endif
 164
 165
 166 /* __asm__ ("xyz") is used throughout the headers to rename functions
 167    at the assembly language level.  This is wrapped by the __REDIRECT
 168    macro, in order to support compilers that can do this some other
 169    way.  When compilers don't support asm-names at all, we have to do
 170    preprocessor tricks instead (which don't have exactly the right
 171    semantics, but it's the best we can do).
 172
 173    Example:
 174    int __REDIRECT(setpgrp, (__pid_t pid, __pid_t pgrp), setpgid); */
 175
 176 #if defined __GNUC__ && __GNUC__ >= 2
 177
 178 # define __REDIRECT(name, proto, alias) name proto __asm__ (__ASMNAME (#alias))
 179 # ifdef __cplusplus
 180 #  define __REDIRECT_NTH(name, proto, alias) \
 181      name proto __THROW __asm__ (__ASMNAME (#alias))
 182 #  define __REDIRECT_NTHNL(name, proto, alias) \
 183      name proto __THROWNL __asm__ (__ASMNAME (#alias))
 184 # else
 185 #  define __REDIRECT_NTH(name, proto, alias) \
 186      name proto __asm__ (__ASMNAME (#alias)) __THROW
 187 #  define __REDIRECT_NTHNL(name, proto, alias) \
 188      name proto __asm__ (__ASMNAME (#alias)) __THROWNL
 189 # endif
 190 # define __ASMNAME(cname)  __ASMNAME2 (__USER_LABEL_PREFIX__, cname)
 191 # define __ASMNAME2(prefix, cname) __STRING (prefix) cname
 192
 193 /*
 194 #elif __SOME_OTHER_COMPILER__
 195
 196 # define __REDIRECT(name, proto, alias) name proto; \
 197         _Pragma("let " #name " = " #alias)
 198 */
 199 #endif
 200
 201 /* GCC has various useful declarations that can be made with the
 202    `__attribute__' syntax.  All of the ways we use this do fine if
 203    they are omitted for compilers that don't understand it. */
 204 #if !defined __GNUC__ || __GNUC__ < 2
 205 # define __attribute__(xyz)     /* Ignore */
 206 #endif
 207
 208 /* At some point during the gcc 2.96 development the `malloc' attribute
 209    for functions was introduced.  We don't want to use it unconditionally
 210    (although this would be possible) since it generates warnings.  */
 211 #if __GNUC_PREREQ (2,96)
 212 # define __attribute_malloc__ __attribute__ ((__malloc__))
 213 #else
 214 # define __attribute_malloc__ /* Ignore */
 215 #endif
 216
 217 /* Tell the compiler which arguments to an allocation function
 218    indicate the size of the allocation.  */
 219 #if __GNUC_PREREQ (4, 3)
 220 # define __attribute_alloc_size__(params) \
 221   __attribute__ ((__alloc_size__ params))
 222 #else
 223 # define __attribute_alloc_size__(params) /* Ignore.  */
 224 #endif
 225
 226 /* At some point during the gcc 2.96 development the `pure' attribute
 227    for functions was introduced.  We don't want to use it unconditionally
 228    (although this would be possible) since it generates warnings.  */
 229 #if __GNUC_PREREQ (2,96)
 230 # define __attribute_pure__ __attribute__ ((__pure__))
 231 #else
 232 # define __attribute_pure__ /* Ignore */
 233 #endif
 234
 235 /* This declaration tells the compiler that the value is constant.  */
 236 #if __GNUC_PREREQ (2,5)
 237 # define __attribute_const__ __attribute__ ((__const__))
 238 #else
 239 # define __attribute_const__ /* Ignore */
 240 #endif
 241
 242 /* At some point during the gcc 3.1 development the `used' attribute
 243    for functions was introduced.  We don't want to use it unconditionally
 244    (although this would be possible) since it generates warnings.  */
 245 #if __GNUC_PREREQ (3,1)
 246 # define __attribute_used__ __attribute__ ((__used__))
 247 # define __attribute_noinline__ __attribute__ ((__noinline__))
 248 #else
 249 # define __attribute_used__ __attribute__ ((__unused__))
 250 # define __attribute_noinline__ /* Ignore */
 251 #endif
 252
 253 /* Since version 3.2, gcc allows marking deprecated functions.  */
 254 #if __GNUC_PREREQ (3,2)
 255 # define __attribute_deprecated__ __attribute__ ((__deprecated__))
 256 #else
 257 # define __attribute_deprecated__ /* Ignore */
 258 #endif
 259
 260 /* Since version 4.5, gcc also allows one to specify the message printed
 261    when a deprecated function is used.  clang claims to be gcc 4.2, but
 262    may also support this feature.  */
 263 #if __GNUC_PREREQ (4,5) \
 264     || __glibc_clang_has_extension (__attribute_deprecated_with_message__)
 265 # define __attribute_deprecated_msg__(msg) \
 266          __attribute__ ((__deprecated__ (msg)))
 267 #else
 268 # define __attribute_deprecated_msg__(msg) __attribute_deprecated__
 269 #endif
 270
 271 /* At some point during the gcc 2.8 development the `format_arg' attribute
 272    for functions was introduced.  We don't want to use it unconditionally
 273    (although this would be possible) since it generates warnings.
 274    If several `format_arg' attributes are given for the same function, in
 275    gcc-3.0 and older, all but the last one are ignored.  In newer gccs,
 276    all designated arguments are considered.  */
 277 #if __GNUC_PREREQ (2,8)
 278 # define __attribute_format_arg__(x) __attribute__ ((__format_arg__ (x)))
 279 #else
 280 # define __attribute_format_arg__(x) /* Ignore */
 281 #endif
 282
 283 /* At some point during the gcc 2.97 development the `strfmon' format
 284    attribute for functions was introduced.  We don't want to use it
 285    unconditionally (although this would be possible) since it
 286    generates warnings.  */
 287 #if __GNUC_PREREQ (2,97)
 288 # define __attribute_format_strfmon__(a,b) \
 289   __attribute__ ((__format__ (__strfmon__, a, b)))
 290 #else
 291 # define __attribute_format_strfmon__(a,b) /* Ignore */
 292 #endif
 293
 294 /* The nonull function attribute allows to mark pointer parameters which
 295    must not be NULL.  */
 296 #if __GNUC_PREREQ (3,3)
 297 # define __nonnull(params) __attribute__ ((__nonnull__ params))
 298 #else
 299 # define __nonnull(params)
 300 #endif
 301
 302 /* If fortification mode, we warn about unused results of certain
 303    function calls which can lead to problems.  */
 304 #if __GNUC_PREREQ (3,4)
 305 # define __attribute_warn_unused_result__ \
 306    __attribute__ ((__warn_unused_result__))
 307 # if __USE_FORTIFY_LEVEL > 0
 308 #  define __wur __attribute_warn_unused_result__
 309 # endif
 310 #else
 311 # define __attribute_warn_unused_result__ /* empty */
 312 #endif
 313 #ifndef __wur
 314 # define __wur /* Ignore */
 315 #endif
 316
 317 /* Forces a function to be always inlined.  */
 318 #if __GNUC_PREREQ (3,2)
 319 /* The Linux kernel defines __always_inline in stddef.h (283d7573), and
 320    it conflicts with this definition.  Therefore undefine it first to
 321    allow either header to be included first.  */
 322 # undef __always_inline
 323 # define __always_inline __inline __attribute__ ((__always_inline__))
 324 #else
 325 # undef __always_inline
 326 # define __always_inline __inline
 327 #endif
 328
 329 /* Associate error messages with the source location of the call site rather
 330    than with the source location inside the function.  */
 331 #if __GNUC_PREREQ (4,3)
 332 # define __attribute_artificial__ __attribute__ ((__artificial__))
 333 #else
 334 # define __attribute_artificial__ /* Ignore */
 335 #endif
 336
 337 /* GCC 4.3 and above with -std=c99 or -std=gnu99 implements ISO C99
 338    inline semantics, unless -fgnu89-inline is used.  Using __GNUC_STDC_INLINE__
 339    or __GNUC_GNU_INLINE is not a good enough check for gcc because gcc versions
 340    older than 4.3 may define these macros and still not guarantee GNU inlining
 341    semantics.
 342
 343    clang++ identifies itself as gcc-4.2, but has support for GNU inlining
 344    semantics, that can be checked for by using the __GNUC_STDC_INLINE_ and
 345    __GNUC_GNU_INLINE__ macro definitions.  */
 346 #if (!defined __cplusplus || __GNUC_PREREQ (4,3) \
 347      || (defined __clang__ && (defined __GNUC_STDC_INLINE__ \
 348                                || defined __GNUC_GNU_INLINE__)))
 349 # if defined __GNUC_STDC_INLINE__ || defined __cplusplus
 350 #  define __extern_inline extern __inline __attribute__ ((__gnu_inline__))
 351 #  define __extern_always_inline \
 352   extern __always_inline __attribute__ ((__gnu_inline__))
 353 # else
 354 #  define __extern_inline extern __inline
 355 #  define __extern_always_inline extern __always_inline
 356 # endif
 357 #endif
 358
 359 #ifdef __extern_always_inline
 360 # define __fortify_function __extern_always_inline __attribute_artificial__
 361 #endif
 362
 363 /* GCC 4.3 and above allow passing all anonymous arguments of an
 364    __extern_always_inline function to some other vararg function.  */
 365 #if __GNUC_PREREQ (4,3)
 366 # define __va_arg_pack() __builtin_va_arg_pack ()
 367 # define __va_arg_pack_len() __builtin_va_arg_pack_len ()
 368 #endif
 369
 370 /* It is possible to compile containing GCC extensions even if GCC is
 371    run in pedantic mode if the uses are carefully marked using the
 372    `__extension__' keyword.  But this is not generally available before
 373    version 2.8.  */
 374 #if !__GNUC_PREREQ (2,8)
 375 # define __extension__          /* Ignore */
 376 #endif
 377
 378 /* __restrict is known in EGCS 1.2 and above. */
 379 #if !__GNUC_PREREQ (2,92)
 380 # if defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L
 381 #  define __restrict    restrict
 382 # else
 383 #  define __restrict    /* Ignore */
 384 # endif
 385 #endif
 386
 387 /* ISO C99 also allows to declare arrays as non-overlapping.  The syntax is
 388      array_name[restrict]
 389    GCC 3.1 supports this.  */
 390 #if __GNUC_PREREQ (3,1) && !defined __GNUG__
 391 # define __restrict_arr __restrict
 392 #else
 393 # ifdef __GNUC__
 394 #  define __restrict_arr        /* Not supported in old GCC.  */
 395 # else
 396 #  if defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L
 397 #   define __restrict_arr       restrict
 398 #  else
 399 /* Some other non-C99 compiler.  */
 400 #   define __restrict_arr       /* Not supported.  */
 401 #  endif
 402 # endif
 403 #endif
 404
 405 #if __GNUC__ >= 3
 406 # define __glibc_unlikely(cond) __builtin_expect ((cond), 0)
 407 # define __glibc_likely(cond)   __builtin_expect ((cond), 1)
 408 #else
 409 # define __glibc_unlikely(cond) (cond)
 410 # define __glibc_likely(cond)   (cond)
 411 #endif
 412
 413 #ifdef __has_attribute
 414 # define __glibc_has_attribute(attr)    __has_attribute (attr)
 415 #else
 416 # define __glibc_has_attribute(attr)    0
 417 #endif
 418
 419 #if (!defined _Noreturn \
 420      && (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0) < 201112 \
 421      &&  !__GNUC_PREREQ (4,7))
 422 # if __GNUC_PREREQ (2,8)
 423 #  define _Noreturn __attribute__ ((__noreturn__))
 424 # else
 425 #  define _Noreturn
 426 # endif
 427 #endif
 428
 429 #if __GNUC_PREREQ (8, 0)
 430 /* Describes a char array whose address can safely be passed as the first
 431    argument to strncpy and strncat, as the char array is not necessarily
 432    a NUL-terminated string.  */
 433 # define __attribute_nonstring__ __attribute__ ((__nonstring__))
 434 #else
 435 # define __attribute_nonstring__
 436 #endif
 437
 438 /* Undefine (also defined in libc-symbols.h).  */
 439 #undef __attribute_copy__
 440 #if __GNUC_PREREQ (9, 0)
 441 /* Copies attributes from the declaration or type referenced by
 442    the argument.  */
 443 # define __attribute_copy__(arg) __attribute__ ((__copy__ (arg)))
 444 #else
 445 # define __attribute_copy__(arg)
 446 #endif
 447
 448 #if (!defined _Static_assert && !defined __cplusplus \
 449      && (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0) < 201112 \
 450      && (!__GNUC_PREREQ (4, 6) || defined __STRICT_ANSI__))
 451 # define _Static_assert(expr, diagnostic) \
 452     extern int (*__Static_assert_function (void)) \
 453       [!!sizeof (struct { int __error_if_negative: (expr) ? 2 : -1; })]
 454 #endif
 455
 456 #include <bits/wordsize.h>
 457 #include <bits/long-double.h>
 458
 459 #if __LDOUBLE_REDIRECTS_TO_FLOAT128_ABI == 1
 460 # ifdef __REDIRECT
 461
 462 /* Alias name defined automatically.  */
 463 #  define __LDBL_REDIR(name, proto) ... unused__ldbl_redir
 464 #  define __LDBL_REDIR_DECL(name) \
 465   extern __typeof (name) name __asm (__ASMNAME ("__" #name "ieee128"));
 466
 467 /* Alias name defined automatically, with leading underscores.  */
 468 #  define __LDBL_REDIR2_DECL(name) \
 469   extern __typeof (__##name) __##name \
 470     __asm (__ASMNAME ("__" #name "ieee128"));
 471
 472 /* Alias name defined manually.  */
 473 #  define __LDBL_REDIR1(name, proto, alias) ... unused__ldbl_redir1
 474 #  define __LDBL_REDIR1_DECL(name, alias) \
 475   extern __typeof (name) name __asm (__ASMNAME (#alias));
 476
 477 #  define __LDBL_REDIR1_NTH(name, proto, alias) \
 478   __REDIRECT_NTH (name, proto, alias)
 479 #  define __REDIRECT_NTH_LDBL(name, proto, alias) \
 480   __LDBL_REDIR1_NTH (name, proto, __##alias##ieee128)
 481
 482 /* Unused.  */
 483 #  define __REDIRECT_LDBL(name, proto, alias) ... unused__redirect_ldbl
 484 #  define __LDBL_REDIR_NTH(name, proto) ... unused__ldbl_redir_nth
 485
 486 # else
 487 _Static_assert (0, "IEEE 128-bits long double requires redirection on this platform");
 488 # endif
 489 #elif defined __LONG_DOUBLE_MATH_OPTIONAL && defined __NO_LONG_DOUBLE_MATH
 490 # define __LDBL_COMPAT 1
 491 # ifdef __REDIRECT
 492 #  define __LDBL_REDIR1(name, proto, alias) __REDIRECT (name, proto, alias)
 493 #  define __LDBL_REDIR(name, proto) \
 494   __LDBL_REDIR1 (name, proto, __nldbl_##name)
 495 #  define __LDBL_REDIR1_NTH(name, proto, alias) __REDIRECT_NTH (name, proto, alias)
 496 #  define __LDBL_REDIR_NTH(name, proto) \
 497   __LDBL_REDIR1_NTH (name, proto, __nldbl_##name)
 498 #  define __LDBL_REDIR2_DECL(name) \
 499   extern __typeof (__##name) __##name __asm (__ASMNAME ("__nldbl___" #name));
 500 #  define __LDBL_REDIR1_DECL(name, alias) \
 501   extern __typeof (name) name __asm (__ASMNAME (#alias));
 502 #  define __LDBL_REDIR_DECL(name) \
 503   extern __typeof (name) name __asm (__ASMNAME ("__nldbl_" #name));
 504 #  define __REDIRECT_LDBL(name, proto, alias) \
 505   __LDBL_REDIR1 (name, proto, __nldbl_##alias)
 506 #  define __REDIRECT_NTH_LDBL(name, proto, alias) \
 507   __LDBL_REDIR1_NTH (name, proto, __nldbl_##alias)
 508 # endif
 509 #endif
 510 #if (!defined __LDBL_COMPAT && __LDOUBLE_REDIRECTS_TO_FLOAT128_ABI == 0) \
 511     || !defined __REDIRECT
 512 # define __LDBL_REDIR1(name, proto, alias) name proto
 513 # define __LDBL_REDIR(name, proto) name proto
 514 # define __LDBL_REDIR1_NTH(name, proto, alias) name proto __THROW
 515 # define __LDBL_REDIR_NTH(name, proto) name proto __THROW
 516 # define __LDBL_REDIR2_DECL(name)
 517 # define __LDBL_REDIR_DECL(name)
 518 # ifdef __REDIRECT
 519 #  define __REDIRECT_LDBL(name, proto, alias) __REDIRECT (name, proto, alias)
 520 #  define __REDIRECT_NTH_LDBL(name, proto, alias) \
 521   __REDIRECT_NTH (name, proto, alias)
 522 # endif
 523 #endif
 524
 525 /* __glibc_macro_warning (MESSAGE) issues warning MESSAGE.  This is
 526    intended for use in preprocessor macros.
 527
 528    Note: MESSAGE must be a _single_ string; concatenation of string
 529    literals is not supported.  */
 530 #if __GNUC_PREREQ (4,8) || __glibc_clang_prereq (3,5)
 531 # define __glibc_macro_warning1(message) _Pragma (#message)
 532 # define __glibc_macro_warning(message) \
 533   __glibc_macro_warning1 (GCC warning message)
 534 #else
 535 # define __glibc_macro_warning(msg)
 536 #endif
 537
 538 /* Generic selection (ISO C11) is a C-only feature, available in GCC
 539    since version 4.9.  Previous versions do not provide generic
 540    selection, even though they might set __STDC_VERSION__ to 201112L,
 541    when in -std=c11 mode.  Thus, we must check for !defined __GNUC__
 542    when testing __STDC_VERSION__ for generic selection support.
 543    On the other hand, Clang also defines __GNUC__, so a clang-specific
 544    check is required to enable the use of generic selection.  */
 545 #if !defined __cplusplus \
 546     && (__GNUC_PREREQ (4, 9) \
 547         || __glibc_clang_has_extension (c_generic_selections) \
 548         || (!defined __GNUC__ && defined __STDC_VERSION__ \
 549             && __STDC_VERSION__ >= 201112L))
 550 # define __HAVE_GENERIC_SELECTION 1
 551 #else
 552 # define __HAVE_GENERIC_SELECTION 0
 553 #endif
 554
 555 #if __GNUC_PREREQ (10, 0)
 556 /* Designates a 1-based positional argument ref-index of pointer type
 557    that can be used to access size-index elements of the pointed-to
 558    array according to access mode, or at least one element when
 559    size-index is not provided:
 560      access (access-mode, <ref-index> [, <size-index>])  */
 561 #define __attr_access(x) __attribute__ ((__access__ x))
 562 #else
 563 #  define __attr_access(x)
 564 #endif
 565
 566 #endif   /* sys/cdefs.h */