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    SubjectRe: [PATCH 12/17] x86-64: Use absolute displacements for per-cpu accesses.

    * Brian Gerst <brgerst@gmail.com> wrote:

    > On Sat, Jan 17, 2009 at 11:22 PM, Tejun Heo <tj@kernel.org> wrote:
    >
    > > Hello, Brian.
    > >
    > > Brian Gerst wrote:
    > > > Accessing memory through %gs should not use rip-relative addressing.
    > > > Adding a P prefix for the argument tells gcc to not add (%rip) to
    > > > the memory references.
    > >
    > > Nice catch. I dind't know about the P prefix thing. It also is used
    > > in other places too. Hmmm... I can't find anything about the P
    > > argument prefix in the gcc info page (4.3). Any ideas where I can
    > > find some information about it? It's a bit weird that it's not a
    > > constraint prefix but an argument one.
    >
    > The only place I could confirm that it works is in the gcc source
    > itself, and even there it's not well documented.

    does %P support go back as far as gcc 3.2 (the earliest GCC we still
    support)?

    Ingo


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