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    SubjectRe: [PATCH] Linux Kernel Markers
    * Martin Bligh (mbligh@google.com) wrote:
    > How about we combine all three ideas together ...
    >
    > 1. Load modified copy of the function in question.
    > 2. overwrite the first instruction of the routine with an int3 that
    > does what you say (atomically)
    > 3. Then overwrite the second instruction with a jump that's faster
    > 4. Now atomically overwrite the int3 with a nop, and let the jump
    > take over.
    >

    Very good idea.. However, overwriting the second instruction with a jump could
    be dangerous on preemptible and SMP kernels, because we never know if a thread
    has an IP in any of its contexts that would return exactly at the middle of the
    jump. I think it would be doable to overwrite a 5+ bytes instruction with a NOP
    non-atomically in all cases, but as the instructions nin the prologue seems to
    be smaller :

    prologue on x86
    0: 55 push %ebp
    1: 89 e5 mov %esp,%ebp
    epilogue on x86
    3: 5d pop %ebp
    4: c3 ret

    Then is can be a problem. Ideas are welcome.

    Mathieu


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