Make max_align_t respect _Float128 [version 2]

[Bernd Schmidt]

On 09/06/2016 11:11 AM, Florian Weimer wrote:

> I think this change is only safe because nothing relies on it.
> max_align_t is a committee invention with no actual users.

I tried to verify that and ran grep over all the packages in 
/usr/portage/distfiles. That did get a number of matches, fairly obvious 
and expected ones like gcc and glibc, and several more which match only 
because gnulib seems to try to provide a default, but I also found a few 
real uses:

grep-2.25/lib/fts.c:
         /* Align the allocation size so that it works for FTSENT,
            so that trailing padding may be referenced by direct access
            to the flexible array members, without triggering undefined 
behavior
            by accessing bytes beyond the heap allocation.  This 
implicit access
            was seen for example with ISDOT() and GCC 5.1.1 at -O2.
            Do not use alignof (FTSENT) here, since C11 prohibits
            taking the alignment of a structure containing a flexible
            array member.  */
         len += alignof (max_align_t) - 1;
         len &= ~ (alignof (max_align_t) - 1);


libvpx-v1.3.0/nestegg/halloc/src/halloc.c:
/*
  *      block control header
  */
typedef struct hblock
{
#ifndef NDEBUG
#define HH_MAGIC    0x20040518L
         long          magic;
#endif
         hlist_item_t  siblings; /* 2 pointers */
         hlist_head_t  children; /* 1 pointer  */
         max_align_t   data[1];  /* not allocated, see below */

} hblock_t;


Bernd