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    SubjectRe: [GIT PULL] x86/kaslr for v3.14

    * Linus Torvalds <torvalds@linux-foundation.org> wrote:

    > On Mon, Jan 20, 2014 at 2:54 PM, Linus Torvalds
    > <torvalds@linux-foundation.org> wrote:
    > > So I pulled this, but one question:
    >
    > .. oh, and since I decided to test it, and was looking for problems:
    > enabling kaslr breaks "perf". The *profile* looks fine, but the
    > disassembly doesn't work.
    >
    > I'm not entirely surprised. I decided I wanted to test it for a
    > reason, after all. So it's not unexpected, but perhaps people hadn't
    > thought about it, and clearly hadn't tested it.
    >
    > Kernel modules disassemble fine, so clearly perf knows about code
    > that moves around, but apparently it gets surprised when the core
    > vmlinux file disassembly doesn't match addresses.

    Hm, live annotation of the kernel image is a relatively new perf
    feature, and KASLR predated that (by years) - which would at least in
    part explain why it went unnoticed. (Although it does not excuse the
    lack of testing.)

    I've Cc:-ed Adrian Hunter, the author of the /proc/kcore annotation
    feature.

    Adrian: enabling x86 KASLR in Linus's latestest kernel via
    CONFIG_RANDOMIZE_BASE=y [this is also present in the -tip tree] breaks
    /proc/kcore annotation, because the kernel image position is now per
    bootup randomized and perf's annotation code gets surprised by that.

    Thanks,

    Ingo


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