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    SubjectRe: [PATCH 3/4] x86_64: Fold pda into per cpu area
    Mike Travis wrote:
    > Jeremy Fitzhardinge wrote:
    >> Mike Travis wrote:
    >>> * Declare the pda as a per cpu variable.
    >>> * Make the x86_64 per cpu area start at zero.
    >>> * Since the pda is now the first element of the per_cpu area, cpu_pda()
    >>> is no longer needed and per_cpu() can be used instead. This also
    >>> makes
    >>> the _cpu_pda[] table obsolete.
    >>> * Since %gs is pointing to the pda, it will then also point to the
    >>> per cpu
    >>> variables and can be accessed thusly:
    >>> %gs:[&per_cpu_xxxx - __per_cpu_start]
    > The above is only a partial story (I folded the two patches but didn't
    > update the comments correctly.] The variables are already offset from
    > __per_cpu_start by virtue of the .data.percpu section being based at
    > zero. Therefore only the %gs register needs to be set to the base of
    > each cpu's percpu section to resolve the target address:
    > %gs:&per_cpu_xxxx

    Oh, good. I'd played with trying to make that work at one point, and
    got lost in linker bugs and/or random version-specific strangeness.


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