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    SubjectRe: [tip:x86/urgent] x86: Add memory modify constraints to xchg() and cmpxchg()
    On 07/28/2010 08:45 AM, Linus Torvalds wrote:
    > On Tue, Jul 27, 2010 at 10:33 PM, tip-bot for H. Peter Anvin
    > <hpa@zytor.com> wrote:
    >>
    >> x86: Add memory modify constraints to xchg() and cmpxchg()
    >
    > Ack. I assume this doesn't really change the code generated? At least
    > not with a gcc that honors the whole memory clobber thing properly?
    >
    > I also suspect that we can/should get rid of the __xg() thing - it was
    > there just to make sure gcc didn't see the memory read as a single
    > word and tried to optimize it. With the "+m" it probably doesn't
    > matter any more (don't know if it ever did)
    >

    For what it's worth, it fairly heavily preturbs code around
    __set_64bit(), which implies it actually does something useful in that
    case. The rest of the code looks similar enough.

    -hpa



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