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

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
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