DragonFly BSD
DragonFly kernel List (threaded) for 2012-03
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AMD cpu bug update -- AMD confirms!

From: Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>
Date: Mon, 5 Mar 2012 11:27:44 -0800 (PST)

    AMD has confirmed the cpu bug that I analyzed.  I am going to quote
    the first paragraph.  They gave me some more info and will be updating
    their revision guide.  To avoid any confusion (so they can finalize their
    wording for the entry they will be putting in the revision guide) I'm
    just including the confirmation here.


    "AMD has taken your example and also analyzed the segmentation fault and
    the fill_sons_in_loop code. We confirm that you have found an erratum
    with som e AMD processor families. The specific compiled version of
    the fill_sons_in_loop code, through a very specific sequence of
    consecutive back-to-back pops and (near) return instructions, can
    create a condition where the process or incorrectly updates the
    stack pointer."


    We exchanged a few emails to try to come up with a good test case.
    Owing to the difficulty of reproducing the bug I constructed a
    fully bootable DFly operating system & test case USB image and
    verified that the bug was present on my test box using that image.
    AMD was then able to reproduce the bug using that image on their own
    machines.  Over the last few months they have been working through
    the possibilities and today emailed me the confirmation that it was,
    indeed, a cpu bug.

    I'm pretty stoked... it isn't every day that a guy like me gets to
    find an honest-to-god hardware bug in a major cpu!

					Matthew Dillon 

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