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SubjectRE: framebuffer corruption due to overlapping stp instructions on arm64

On Wed, 8 Aug 2018, David Laight wrote:

> From: Mikulas Patocka
> > Sent: 08 August 2018 14:47
> ...
> > The problem on ARM is that I see data corruption when the overlapping
> > unaligned writes are done just by a single core.
> Is this a sequence of unaligned writes (that shouldn't modify the
> same physical locations) or an aligned write followed by an
> unaligned one that updates part of the earlier write.
> (Or the opposite order?)
> It might be that the unaligned writes are bypassing the write-combining
> buffer (without flushing it) - so overtake the aligned write.
> Alternatively the unaligned writes go through the write-combining
> buffer but the byte-enables aren't handled in the expected way.
> It ought to be possible to work out which sequence is actually broken.
> David

All the unaligned/or aligned writes inside memcpy write the same value to
the overlapping bytes. So, the corruption can't be explained just by
reordering the writes or failing to detect hazard between them.


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