[PATCH] Don't write beyond destination in __mempcpy_avx512_no_vzeroupper (bug 23196)

[Florian Weimer]

On 05/22/2018 04:12 PM, Andreas Schwab wrote:
> On Mai 22 2018, Florian Weimer <fweimer@redhat.com> wrote:
> 
>> My test machine had an L2 cache size of 1 MiB.
> 
> Then you should be safe, a 64K mempcpy is enough to trigger it.

Our memcpy has:


L(512bytesormore):
#ifdef SHARED_CACHE_SIZE_HALF
         mov     $SHARED_CACHE_SIZE_HALF, %r8
#else
         mov     __x86_64_shared_cache_size_half(%rip), %r8
#endif
         cmp     %r8, %rdx
         jae     L(preloop_large)
         cmp     $1024, %rdx
         ja      L(1024bytesormore)

And with the original reproducer, we wouldn't hit preloop_large, where 
the bug is.

Thanks,
Florian