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    SubjectRe: [PATCH 2/3] x86-64: Unify x86_*_percpu() functions.
    Brian Gerst wrote:
    > Merge the 32-bit and 64-bit versions of these functions. Unlike 32-bit,
    > the segment base is the current cpu's PDA instead of the offset from the
    > original per-cpu area. This is because GCC hardcodes the stackprotector
    > canary at %gs:40. Since the assembler is incapable of relocating against
    > multiple symbols, the code ends up looking like:
    > movq $per_cpu__var, reg
    > subq $per_cpu__pda, reg
    > movq %gs:(reg), reg
    > This is still atomic since the offset is a constant (just calculated at
    > runtime) and not dependant on the cpu number.

    Yeah, it's a real pity we can't convince the linker to do this simple
    computation as a single %gs:ADDR addressing mode. On the other hand, if
    the compiler can reuse the computation of %reg 2-3 times, then the
    generated code could well end up being denser.


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