glibc/include/alloca.h

#ifndef _ALLOCA_H

#include <stdlib/alloca.h>

# ifndef _ISOMAC

#include <elf.h>

#undef	__alloca

/* Now define the internal interfaces.  */
extern void *__alloca (size_t __size);

#ifdef	__GNUC__
# define __alloca(size)	__builtin_alloca (size)
#endif /* GCC.  */

extern int __libc_use_alloca (size_t size) __attribute__ ((const));
extern int __libc_alloca_cutoff (size_t size) __attribute__ ((const));
libc_hidden_proto (__libc_alloca_cutoff)

#define __MAX_ALLOCA_CUTOFF	65536

#include <allocalim.h>

#if defined stackinfo_get_sp && defined stackinfo_sub_sp
# define alloca_account(size, avar) \
  ({ void *old__ = stackinfo_get_sp ();					      \
     void *m__ = __alloca (size);					      \
     avar += stackinfo_sub_sp (old__);					      \
     m__; })
#else
# define alloca_account(size, avar) \
  ({ size_t s__ = (size);						      \
     avar += s__;							      \
     __alloca (s__); })
#endif

# endif /* !_ISOMAC */
#endif