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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
Date: Thu, 06 Feb 2014 13:13:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Marc Glisse from comment #4)
> Hack: when the return value of posix_memalign is ignored, if the platform
> supports it, replace with a call to aligned_alloc (C11), which has an easier
> interface.

The question is if posix_memalign is allowed to change errno.  If it is, then
making glibc contains say something like:

extern int __REDIRECT_NTH (__posix_memalign_alias,
                           (void ** __ptr, size_t __alignment, size_t __size),
                           posix_memalign) __nonnull ((1)) __wur;
extern void *__REDIRECT_NTH (__memalign_alias,
                           (size_t __alignment, size_t __size),
                           memalign)  __attribute__ ((__malloc__,
__alloc_size__ (2)));

__extern_inline int
posix_memalign (void **__ptr, size_t __alignment, size_t __size)
{
  if (__builtin_constant_p (__alignment))
    {
      if (__alignment == 0
          || __alignment & (__alignment - 1)) != 0
          || __alignment % sizeof (void *))
        return EINVAL;
      void *__res = __memalign_alias (__alignment, __size);
      if (__res == NULL)
        return ENOMEM;
      *__ptr = __res;
      return 0;
    }
  return __posix_memalign_alias (__ptr, __alignment, __size);
}

But looking at glibc sources, even posix_memalign actually changes errno.
Tbe problem with this inline version is that user aliasing bugs will trigger
people more often, and that some hack will need to be find out for the EINVAL
and ENOMEM values (because, stdlib.h is not supposed to include errno.h I
guess, so it would need to be some __EINVAL/__ENOMEM value determined by
configure or something).