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    SubjectRe: [RFC, PATCHv1 15/28] x86: detect 5-level paging support
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    On 12/08/16 12:20, Borislav Petkov wrote:
    > On Thu, Dec 08, 2016 at 12:08:53PM -0800, Linus Torvalds wrote:
    >> Especially since that's some of the ugliest inline asm ever due to the
    >> nasty BX handling.
    >
    > Yeah, about that: why doesn't gcc handle that for us like it would
    > handle a clobbered register? I mean, it *should* know that BX is live
    > when building with -fPIC... The .ifnc thing looks really silly.
    >

    When compiling with -fPIC gcc treats ebx as a "fixed register". A fixed
    register can't be spilled, and so a clobber of a fixed register is a
    fatal error.

    Like it or not, it's how it works.

    -hpa

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