guile/lib/cdefs.h

/* Copyright (C) 1992-2021 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#ifndef	_SYS_CDEFS_H
#define	_SYS_CDEFS_H	1

/* We are almost always included from features.h. */
#ifndef _FEATURES_H
# include <features.h>
#endif

/* The GNU libc does not support any K&R compilers or the traditional mode
   of ISO C compilers anymore.  Check for some of the combinations not
   supported anymore.  */
#if defined __GNUC__ && !defined __STDC__
# error "You need a ISO C conforming compiler to use the glibc headers"
#endif

/* Some user header file might have defined this before.  */
#undef	__P
#undef	__PMT

/* Compilers that lack __has_attribute may object to
       #if defined __has_attribute && __has_attribute (...)
   even though they do not need to evaluate the right-hand side of the &&.
   Similarly for __has_builtin, etc.  */
#if (defined __has_attribute \
     && (!defined __clang_minor__ \
         || 3 < __clang_major__ + (5 <= __clang_minor__)))
# define __glibc_has_attribute(attr) __has_attribute (attr)
#else
# define __glibc_has_attribute(attr) 0
#endif
#ifdef __has_builtin
# define __glibc_has_builtin(name) __has_builtin (name)
#else
# define __glibc_has_builtin(name) 0
#endif
#ifdef __has_extension
# define __glibc_has_extension(ext) __has_extension (ext)
#else
# define __glibc_has_extension(ext) 0
#endif

#if defined __GNUC__ || defined __clang__

/* All functions, except those with callbacks or those that
   synchronize memory, are leaf functions.  */
# if __GNUC_PREREQ (4, 6) && !defined _LIBC
#  define __LEAF , __leaf__
#  define __LEAF_ATTR __attribute__ ((__leaf__))
# else
#  define __LEAF
#  define __LEAF_ATTR
# endif

/* GCC can always grok prototypes.  For C++ programs we add throw()
   to help it optimize the function calls.  But this only works with
   gcc 2.8.x and egcs.  For gcc 3.4 and up we even mark C functions
   as non-throwing using a function attribute since programs can use
   the -fexceptions options for C code as well.  */
# if !defined __cplusplus \
     && (__GNUC_PREREQ (3, 4) || __glibc_has_attribute (__nothrow__))
#  define __THROW	__attribute__ ((__nothrow__ __LEAF))
#  define __THROWNL	__attribute__ ((__nothrow__))
#  define __NTH(fct)	__attribute__ ((__nothrow__ __LEAF)) fct
#  define __NTHNL(fct)  __attribute__ ((__nothrow__)) fct
# else
#  if defined __cplusplus && (__GNUC_PREREQ (2,8) || __clang_major >= 4)
#   if __cplusplus >= 201103L
#    define __THROW	noexcept (true)
#   else
#    define __THROW	throw ()
#   endif
#   define __THROWNL	__THROW
#   define __NTH(fct)	__LEAF_ATTR fct __THROW
#   define __NTHNL(fct) fct __THROW
#  else
#   define __THROW
#   define __THROWNL
#   define __NTH(fct)	fct
#   define __NTHNL(fct) fct
#  endif
# endif

#else	/* Not GCC or clang.  */

# if (defined __cplusplus						\
      || (defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L))
#  define __inline	inline
# else
#  define __inline		/* No inline functions.  */
# endif

# define __THROW
# define __THROWNL
# define __NTH(fct)	fct

#endif	/* GCC || clang.  */

/* These two macros are not used in glibc anymore.  They are kept here
   only because some other projects expect the macros to be defined.  */
#define __P(args)	args
#define __PMT(args)	args

/* For these things, GCC behaves the ANSI way normally,
   and the non-ANSI way under -traditional.  */

#define __CONCAT(x,y)	x ## y
#define __STRING(x)	#x

/* This is not a typedef so `const __ptr_t' does the right thing.  */
#define __ptr_t void *


/* C++ needs to know that types and declarations are C, not C++.  */
#ifdef	__cplusplus
# define __BEGIN_DECLS	extern "C" {
# define __END_DECLS	}
#else
# define __BEGIN_DECLS
# define __END_DECLS
#endif


/* Fortify support.  */
#define __bos(ptr) __builtin_object_size (ptr, __USE_FORTIFY_LEVEL > 1)
#define __bos0(ptr) __builtin_object_size (ptr, 0)

/* Use __builtin_dynamic_object_size at _FORTIFY_SOURCE=3 when available.  */
#if __USE_FORTIFY_LEVEL == 3 && __glibc_clang_prereq (9, 0)
# define __glibc_objsize0(__o) __builtin_dynamic_object_size (__o, 0)
# define __glibc_objsize(__o) __builtin_dynamic_object_size (__o, 1)
#else
# define __glibc_objsize0(__o) __bos0 (__o)
# define __glibc_objsize(__o) __bos (__o)
#endif

#if __GNUC_PREREQ (4,3)
# define __warnattr(msg) __attribute__((__warning__ (msg)))
# define __errordecl(name, msg) \
  extern void name (void) __attribute__((__error__ (msg)))
#else
# define __warnattr(msg)
# define __errordecl(name, msg) extern void name (void)
#endif

/* Support for flexible arrays.
   Headers that should use flexible arrays only if they're "real"
   (e.g. only if they won't affect sizeof()) should test
   #if __glibc_c99_flexarr_available.  */
#if defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L && !defined __HP_cc
# define __flexarr	[]
# define __glibc_c99_flexarr_available 1
#elif __GNUC_PREREQ (2,97) || defined __clang__
/* GCC 2.97 and clang support C99 flexible array members as an extension,
   even when in C89 mode or compiling C++ (any version).  */
# define __flexarr	[]
# define __glibc_c99_flexarr_available 1
#elif defined __GNUC__
/* Pre-2.97 GCC did not support C99 flexible arrays but did have
   an equivalent extension with slightly different notation.  */
# define __flexarr	[0]
# define __glibc_c99_flexarr_available 1
#else
/* Some other non-C99 compiler.  Approximate with [1].  */
# define __flexarr	[1]
# define __glibc_c99_flexarr_available 0
#endif


/* __asm__ ("xyz") is used throughout the headers to rename functions
   at the assembly language level.  This is wrapped by the __REDIRECT
   macro, in order to support compilers that can do this some other
   way.  When compilers don't support asm-names at all, we have to do
   preprocessor tricks instead (which don't have exactly the right
   semantics, but it's the best we can do).

   Example:
   int __REDIRECT(setpgrp, (__pid_t pid, __pid_t pgrp), setpgid); */

#if (defined __GNUC__ && __GNUC__ >= 2) || (__clang_major__ >= 4)

# define __REDIRECT(name, proto, alias) name proto __asm__ (__ASMNAME (#alias))
# ifdef __cplusplus
#  define __REDIRECT_NTH(name, proto, alias) \
     name proto __THROW __asm__ (__ASMNAME (#alias))
#  define __REDIRECT_NTHNL(name, proto, alias) \
     name proto __THROWNL __asm__ (__ASMNAME (#alias))
# else
#  define __REDIRECT_NTH(name, proto, alias) \
     name proto __asm__ (__ASMNAME (#alias)) __THROW
#  define __REDIRECT_NTHNL(name, proto, alias) \
     name proto __asm__ (__ASMNAME (#alias)) __THROWNL
# endif
# define __ASMNAME(cname)  __ASMNAME2 (__USER_LABEL_PREFIX__, cname)
# define __ASMNAME2(prefix, cname) __STRING (prefix) cname

/*
#elif __SOME_OTHER_COMPILER__

# define __REDIRECT(name, proto, alias) name proto; \
	_Pragma("let " #name " = " #alias)
*/
#endif

/* GCC and clang have various useful declarations that can be made with
   the '__attribute__' syntax.  All of the ways we use this do fine if
   they are omitted for compilers that don't understand it.  */
#if !(defined __GNUC__ || defined __clang__)
# define __attribute__(xyz)	/* Ignore */
#endif

/* At some point during the gcc 2.96 development the `malloc' attribute
   for functions was introduced.  We don't want to use it unconditionally
   (although this would be possible) since it generates warnings.  */
#if __GNUC_PREREQ (2,96) || __glibc_has_attribute (__malloc__)
# define __attribute_malloc__ __attribute__ ((__malloc__))
#else
# define __attribute_malloc__ /* Ignore */
#endif

/* Tell the compiler which arguments to an allocation function
   indicate the size of the allocation.  */
#if __GNUC_PREREQ (4, 3)
# define __attribute_alloc_size__(params) \
  __attribute__ ((__alloc_size__ params))
#else
# define __attribute_alloc_size__(params) /* Ignore.  */
#endif

/* At some point during the gcc 2.96 development the `pure' attribute
   for functions was introduced.  We don't want to use it unconditionally
   (although this would be possible) since it generates warnings.  */
#if __GNUC_PREREQ (2,96) || __glibc_has_attribute (__pure__)
# define __attribute_pure__ __attribute__ ((__pure__))
#else
# define __attribute_pure__ /* Ignore */
#endif

/* This declaration tells the compiler that the value is constant.  */
#if __GNUC_PREREQ (2,5) || __glibc_has_attribute (__const__)
# define __attribute_const__ __attribute__ ((__const__))
#else
# define __attribute_const__ /* Ignore */
#endif

#if defined __STDC_VERSION__ && 201710L < __STDC_VERSION__
# define __attribute_maybe_unused__ [[__maybe_unused__]]
#elif __GNUC_PREREQ (2,7) || __glibc_has_attribute (__unused__)
# define __attribute_maybe_unused__ __attribute__ ((__unused__))
#else
# define __attribute_maybe_unused__ /* Ignore */
#endif

/* At some point during the gcc 3.1 development the `used' attribute
   for functions was introduced.  We don't want to use it unconditionally
   (although this would be possible) since it generates warnings.  */
#if __GNUC_PREREQ (3,1) || __glibc_has_attribute (__used__)
# define __attribute_used__ __attribute__ ((__used__))
# define __attribute_noinline__ __attribute__ ((__noinline__))
#else
# define __attribute_used__ __attribute__ ((__unused__))
# define __attribute_noinline__ /* Ignore */
#endif

/* Since version 3.2, gcc allows marking deprecated functions.  */
#if __GNUC_PREREQ (3,2) || __glibc_has_attribute (__deprecated__)
# define __attribute_deprecated__ __attribute__ ((__deprecated__))
#else
# define __attribute_deprecated__ /* Ignore */
#endif

/* Since version 4.5, gcc also allows one to specify the message printed
   when a deprecated function is used.  clang claims to be gcc 4.2, but
   may also support this feature.  */
#if __GNUC_PREREQ (4,5) \
    || __glibc_has_extension (__attribute_deprecated_with_message__)
# define __attribute_deprecated_msg__(msg) \
	 __attribute__ ((__deprecated__ (msg)))
#else
# define __attribute_deprecated_msg__(msg) __attribute_deprecated__
#endif

/* At some point during the gcc 2.8 development the `format_arg' attribute
   for functions was introduced.  We don't want to use it unconditionally
   (although this would be possible) since it generates warnings.
   If several `format_arg' attributes are given for the same function, in
   gcc-3.0 and older, all but the last one are ignored.  In newer gccs,
   all designated arguments are considered.  */
#if __GNUC_PREREQ (2,8) || __glibc_has_attribute (__format_arg__)
# define __attribute_format_arg__(x) __attribute__ ((__format_arg__ (x)))
#else
# define __attribute_format_arg__(x) /* Ignore */
#endif

/* At some point during the gcc 2.97 development the `strfmon' format
   attribute for functions was introduced.  We don't want to use it
   unconditionally (although this would be possible) since it
   generates warnings.  */
#if __GNUC_PREREQ (2,97) || __glibc_has_attribute (__format__)
# define __attribute_format_strfmon__(a,b) \
  __attribute__ ((__format__ (__strfmon__, a, b)))
#else
# define __attribute_format_strfmon__(a,b) /* Ignore */
#endif

/* The nonnull function attribute marks pointer parameters that
   must not be NULL.  */
#ifndef __attribute_nonnull__
# if __GNUC_PREREQ (3,3) || __glibc_has_attribute (__nonnull__)
#  define __attribute_nonnull__(params) __attribute__ ((__nonnull__ params))
# else
#  define __attribute_nonnull__(params)
# endif
#endif
#ifndef __nonnull
# define __nonnull(params) __attribute_nonnull__ (params)
#endif

/* If fortification mode, we warn about unused results of certain
   function calls which can lead to problems.  */
#if __GNUC_PREREQ (3,4) || __glibc_has_attribute (__warn_unused_result__)
# define __attribute_warn_unused_result__ \
   __attribute__ ((__warn_unused_result__))
# if defined __USE_FORTIFY_LEVEL && __USE_FORTIFY_LEVEL > 0
#  define __wur __attribute_warn_unused_result__
# endif
#else
# define __attribute_warn_unused_result__ /* empty */
#endif
#ifndef __wur
# define __wur /* Ignore */
#endif

/* Forces a function to be always inlined.  */
#if __GNUC_PREREQ (3,2) || __glibc_has_attribute (__always_inline__)
/* The Linux kernel defines __always_inline in stddef.h (283d7573), and
   it conflicts with this definition.  Therefore undefine it first to
   allow either header to be included first.  */
# undef __always_inline
# define __always_inline __inline __attribute__ ((__always_inline__))
#else
# undef __always_inline
# define __always_inline __inline
#endif

/* Associate error messages with the source location of the call site rather
   than with the source location inside the function.  */
#if __GNUC_PREREQ (4,3) || __glibc_has_attribute (__artificial__)
# define __attribute_artificial__ __attribute__ ((__artificial__))
#else
# define __attribute_artificial__ /* Ignore */
#endif

/* GCC 4.3 and above with -std=c99 or -std=gnu99 implements ISO C99
   inline semantics, unless -fgnu89-inline is used.  Using __GNUC_STDC_INLINE__
   or __GNUC_GNU_INLINE is not a good enough check for gcc because gcc versions
   older than 4.3 may define these macros and still not guarantee GNU inlining
   semantics.

   clang++ identifies itself as gcc-4.2, but has support for GNU inlining
   semantics, that can be checked for by using the __GNUC_STDC_INLINE_ and
   __GNUC_GNU_INLINE__ macro definitions.  */
#if (!defined __cplusplus || __GNUC_PREREQ (4,3) \
     || (defined __clang__ && (defined __GNUC_STDC_INLINE__ \
			       || defined __GNUC_GNU_INLINE__)))
# if defined __GNUC_STDC_INLINE__ || defined __cplusplus
#  define __extern_inline extern __inline __attribute__ ((__gnu_inline__))
#  define __extern_always_inline \
  extern __always_inline __attribute__ ((__gnu_inline__))
# else
#  define __extern_inline extern __inline
#  define __extern_always_inline extern __always_inline
# endif
#endif

#ifdef __extern_always_inline
# define __fortify_function __extern_always_inline __attribute_artificial__
#endif

/* GCC 4.3 and above allow passing all anonymous arguments of an
   __extern_always_inline function to some other vararg function.  */
#if __GNUC_PREREQ (4,3)
# define __va_arg_pack() __builtin_va_arg_pack ()
# define __va_arg_pack_len() __builtin_va_arg_pack_len ()
#endif

/* It is possible to compile containing GCC extensions even if GCC is
   run in pedantic mode if the uses are carefully marked using the
   `__extension__' keyword.  But this is not generally available before
   version 2.8.  */
#if !(__GNUC_PREREQ (2,8) || defined __clang__)
# define __extension__		/* Ignore */
#endif

/* __restrict is known in EGCS 1.2 and above, and in clang.
   It works also in C++ mode (outside of arrays), but only when spelled
   as '__restrict', not 'restrict'.  */
#if !(__GNUC_PREREQ (2,92) || __clang_major__ >= 3)
# if defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L
#  define __restrict	restrict
# else
#  define __restrict	/* Ignore */
# endif
#endif

/* ISO C99 also allows to declare arrays as non-overlapping.  The syntax is
     array_name[restrict]
   GCC 3.1 and clang support this.
   This syntax is not usable in C++ mode.  */
#if (__GNUC_PREREQ (3,1) || __clang_major__ >= 3) && !defined __cplusplus
# define __restrict_arr	__restrict
#else
# ifdef __GNUC__
#  define __restrict_arr	/* Not supported in old GCC.  */
# else
#  if defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L
#   define __restrict_arr	restrict
#  else
/* Some other non-C99 compiler.  */
#   define __restrict_arr	/* Not supported.  */
#  endif
# endif
#endif

#if (__GNUC__ >= 3) || __glibc_has_builtin (__builtin_expect)
# define __glibc_unlikely(cond)	__builtin_expect ((cond), 0)
# define __glibc_likely(cond)	__builtin_expect ((cond), 1)
#else
# define __glibc_unlikely(cond)	(cond)
# define __glibc_likely(cond)	(cond)
#endif

#if (!defined _Noreturn \
     && (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0) < 201112 \
     &&  !(__GNUC_PREREQ (4,7) \
           || (3 < __clang_major__ + (5 <= __clang_minor__))))
# if __GNUC_PREREQ (2,8)
#  define _Noreturn __attribute__ ((__noreturn__))
# else
#  define _Noreturn
# endif
#endif

#if __GNUC_PREREQ (8, 0)
/* Describes a char array whose address can safely be passed as the first
   argument to strncpy and strncat, as the char array is not necessarily
   a NUL-terminated string.  */
# define __attribute_nonstring__ __attribute__ ((__nonstring__))
#else
# define __attribute_nonstring__
#endif

/* Undefine (also defined in libc-symbols.h).  */
#undef __attribute_copy__
#if __GNUC_PREREQ (9, 0)
/* Copies attributes from the declaration or type referenced by
   the argument.  */
# define __attribute_copy__(arg) __attribute__ ((__copy__ (arg)))
#else
# define __attribute_copy__(arg)
#endif

#if (!defined _Static_assert && !defined __cplusplus \
     && (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0) < 201112 \
     && (!(__GNUC_PREREQ (4, 6) || __clang_major__ >= 4) \
         || defined __STRICT_ANSI__))
# define _Static_assert(expr, diagnostic) \
    extern int (*__Static_assert_function (void)) \
      [!!sizeof (struct { int __error_if_negative: (expr) ? 2 : -1; })]
#endif

/* The #ifndef lets Gnulib avoid including these on non-glibc
   platforms, where the includes typically do not exist.  */
#ifndef __WORDSIZE
# include <bits/wordsize.h>
# include <bits/long-double.h>
#endif

#if __LDOUBLE_REDIRECTS_TO_FLOAT128_ABI == 1
# ifdef __REDIRECT

/* Alias name defined automatically.  */
#  define __LDBL_REDIR(name, proto) ... unused__ldbl_redir
#  define __LDBL_REDIR_DECL(name) \
  extern __typeof (name) name __asm (__ASMNAME ("__" #name "ieee128"));

/* Alias name defined automatically, with leading underscores.  */
#  define __LDBL_REDIR2_DECL(name) \
  extern __typeof (__##name) __##name \
    __asm (__ASMNAME ("__" #name "ieee128"));

/* Alias name defined manually.  */
#  define __LDBL_REDIR1(name, proto, alias) ... unused__ldbl_redir1
#  define __LDBL_REDIR1_DECL(name, alias) \
  extern __typeof (name) name __asm (__ASMNAME (#alias));

#  define __LDBL_REDIR1_NTH(name, proto, alias) \
  __REDIRECT_NTH (name, proto, alias)
#  define __REDIRECT_NTH_LDBL(name, proto, alias) \
  __LDBL_REDIR1_NTH (name, proto, __##alias##ieee128)

/* Unused.  */
#  define __REDIRECT_LDBL(name, proto, alias) ... unused__redirect_ldbl
#  define __LDBL_REDIR_NTH(name, proto) ... unused__ldbl_redir_nth

# else
_Static_assert (0, "IEEE 128-bits long double requires redirection on this platform");
# endif
#elif defined __LONG_DOUBLE_MATH_OPTIONAL && defined __NO_LONG_DOUBLE_MATH
# define __LDBL_COMPAT 1
# ifdef __REDIRECT
#  define __LDBL_REDIR1(name, proto, alias) __REDIRECT (name, proto, alias)
#  define __LDBL_REDIR(name, proto) \
  __LDBL_REDIR1 (name, proto, __nldbl_##name)
#  define __LDBL_REDIR1_NTH(name, proto, alias) __REDIRECT_NTH (name, proto, alias)
#  define __LDBL_REDIR_NTH(name, proto) \
  __LDBL_REDIR1_NTH (name, proto, __nldbl_##name)
#  define __LDBL_REDIR2_DECL(name) \
  extern __typeof (__##name) __##name __asm (__ASMNAME ("__nldbl___" #name));
#  define __LDBL_REDIR1_DECL(name, alias) \
  extern __typeof (name) name __asm (__ASMNAME (#alias));
#  define __LDBL_REDIR_DECL(name) \
  extern __typeof (name) name __asm (__ASMNAME ("__nldbl_" #name));
#  define __REDIRECT_LDBL(name, proto, alias) \
  __LDBL_REDIR1 (name, proto, __nldbl_##alias)
#  define __REDIRECT_NTH_LDBL(name, proto, alias) \
  __LDBL_REDIR1_NTH (name, proto, __nldbl_##alias)
# endif
#endif
#if (!defined __LDBL_COMPAT && __LDOUBLE_REDIRECTS_TO_FLOAT128_ABI == 0) \
    || !defined __REDIRECT
# define __LDBL_REDIR1(name, proto, alias) name proto
# define __LDBL_REDIR(name, proto) name proto
# define __LDBL_REDIR1_NTH(name, proto, alias) name proto __THROW
# define __LDBL_REDIR_NTH(name, proto) name proto __THROW
# define __LDBL_REDIR2_DECL(name)
# define __LDBL_REDIR_DECL(name)
# ifdef __REDIRECT
#  define __REDIRECT_LDBL(name, proto, alias) __REDIRECT (name, proto, alias)
#  define __REDIRECT_NTH_LDBL(name, proto, alias) \
  __REDIRECT_NTH (name, proto, alias)
# endif
#endif

/* __glibc_macro_warning (MESSAGE) issues warning MESSAGE.  This is
   intended for use in preprocessor macros.

   Note: MESSAGE must be a _single_ string; concatenation of string
   literals is not supported.  */
#if __GNUC_PREREQ (4,8) || __glibc_clang_prereq (3,5)
# define __glibc_macro_warning1(message) _Pragma (#message)
# define __glibc_macro_warning(message) \
  __glibc_macro_warning1 (GCC warning message)
#else
# define __glibc_macro_warning(msg)
#endif

/* Generic selection (ISO C11) is a C-only feature, available in GCC
   since version 4.9.  Previous versions do not provide generic
   selection, even though they might set __STDC_VERSION__ to 201112L,
   when in -std=c11 mode.  Thus, we must check for !defined __GNUC__
   when testing __STDC_VERSION__ for generic selection support.
   On the other hand, Clang also defines __GNUC__, so a clang-specific
   check is required to enable the use of generic selection.  */
#if !defined __cplusplus \
    && (__GNUC_PREREQ (4, 9) \
	|| __glibc_has_extension (c_generic_selections) \
	|| (!defined __GNUC__ && defined __STDC_VERSION__ \
	    && __STDC_VERSION__ >= 201112L))
# define __HAVE_GENERIC_SELECTION 1
#else
# define __HAVE_GENERIC_SELECTION 0
#endif

#if __GNUC_PREREQ (10, 0)
/* Designates a 1-based positional argument ref-index of pointer type
   that can be used to access size-index elements of the pointed-to
   array according to access mode, or at least one element when
   size-index is not provided:
     access (access-mode, <ref-index> [, <size-index>])  */
#define __attr_access(x) __attribute__ ((__access__ x))
#else
#  define __attr_access(x)
#endif

/* Specify that a function such as setjmp or vfork may return
   twice.  */
#if __GNUC_PREREQ (4, 1)
# define __attribute_returns_twice__ __attribute__ ((__returns_twice__))
#else
# define __attribute_returns_twice__ /* Ignore.  */
#endif

#endif	 /* sys/cdefs.h */