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    SubjectRe: [BUG] x86 kenel won't boot under Virtual PC


    On Fri, 5 Sep 2008, Jan Beulich wrote:
    >
    > I disagree here: If I configure a 686+ kernel, I expect these NOPs to be
    > that way (and to work). If you want to run on something that's not
    > compliant, you just shouldn't configure your kernel that way.

    Well, if you actually do a

    git grep 'ASM_NOP[0-9]'

    you'll find that just the _definitions_ of those things are the bulk of it
    BY FAR, and that there doesn't seem to be a single user that cares even
    remotely about performance.

    So I actually think that the whole thing is a waste of time. We should
    probably

    - pick a single set of NOP's per 32-bit/64-bit (since the good nops in
    32-bit aren't 64-bit instructions at all, so we do want different nops
    depending on _that_)

    The whole static choice by microarchitecture is pure garbage.

    - Probably also just declare that those default nops are single
    instructions, just so that we never even have to think about it from a
    dynamic replacement angle.

    Look at the uses again, and realize that it really is just pure garbage
    to have this kind of complex and subtle stuff going on.

    - Move the optimized nop definitions (K7_NOPx etc) to the only place that
    cares - asm/x86/kernel/alternative.c. When we do things _dynamically_,
    it can actually make sense to pick a nop more precisely, but for this
    whole static thing it's just a pain.

    IOW, if it actually _worked_ reasonably, I wouldn't care. But clearly it
    doesn't. And once it's not working reasonably, it should be fixed.

    Linus


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