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    SubjectRe: More on the pentium workaround - the gotchas


    On Sat, 15 Nov 1997, Linus Torvalds wrote:
    >
    >Note that you don't even need to use SMP to have problems: you can use
    >self-modifying code on a UP Pentium. Something like this is likely to
    >cause _major_ problems if the BSDi patches really do re-map the IDT (I
    >also thought that it might be a good idea to re-map the IDT to make the
    >CPU itself to the right thing, but I'm now of the opinion that trying to
    >do that is just stupid).
    >
    >movl $0xf00fc7c8,1f
    >1: int3
    >
    >which will take the int3 trap (because it has been pre-fetched), but then
    if the page fault handler notices that it was an

    Writing to the prefetch queue will flush it on Pentiums or better.
    The move 486->Pentium broke my old DOS routines which tried to detect
    whether they
    are run single-stepped :-(

    regards
    chris



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