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    SubjectRe: framebuffer corruption due to overlapping stp instructions on arm64


    On Wed, 8 Aug 2018, Catalin Marinas wrote:

    > On Fri, Aug 03, 2018 at 01:09:02PM -0400, Mikulas Patocka wrote:
    > > while (1) {
    > > start = (unsigned)random() % (LEN + 1);
    > > end = (unsigned)random() % (LEN + 1);
    > > if (start > end)
    > > continue;
    > > for (i = start; i < end; i++)
    > > data[i] = val++;
    > > memcpy(map + start, data + start, end - start);
    > > if (memcmp(map, data, LEN)) {
    >
    > It may be worth trying to do a memcmp(map+start, data+start, end-start)
    > here to see whether the hazard logic fails when the writes are unaligned
    > but the reads are not.
    >
    > This problem may as well appear if you do byte writes and read longs
    > back (and I consider this a hardware problem on this specific board).

    I triad to insert usleep(10000) between the memcpy and memcmp, but the
    same corruption occurs. So, it can't be read-after-write hazard. It is
    caused by the improper handling of hazard between the overlapping writes
    inside memcpy.

    Mikulas

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