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    SubjectRe: [RFC 00/15] x86_64: Optimize percpu accesses
    On Wed, 09 Jul 2008 13:00:19 -0700
    ebiederm@xmission.com (Eric W. Biederman) wrote:

    >
    > I just took a quick look at how stack_protector works on x86_64.
    > Unless there is some deep kernel magic that changes the segment
    > register to %gs from the ABI specified %fs CC_STACKPROTECTOR is
    > totally broken on x86_64. We access our pda through %gs.

    and so does gcc in kernel mode.

    >
    > Further -fstack-protector-all only seems to detect against buffer
    > overflows and thus corruption of the stack. Not stack overflows. So
    > it doesn't appear especially useful.

    stopping buffer overflows and other return address corruption is not
    useful? Excuse me?

    >
    > So we don't we kill the broken CONFIG_CC_STACKPROTECTOR. Stop trying
    > to figure out how to use a zero based percpu area.

    So why don't we NOT do that and fix instead what you're trying to do?

    >
    > That should allow us to make the current pda a per cpu variable, and
    > use %gs with a large offset to access the per cpu area.

    and what does that gain us?


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