http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092
--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #6)
> (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).
According to the specification this is wrong. Note that changing errno
is hindering optimization. For example
int foo (int *p)
{
*p = 1;
malloc (4);
return *p;
}
cannot CSE *p because p may point to errno. (works for float *p and
works when using posix_memalign with my patch)
