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    SubjectRe: [PATCH] Subject: kprobes-x86: correct post-eip value in post_hander()

    * Ananth N Mavinakayanahalli <ananth@in.ibm.com> wrote:

    > > thanks, i've added your patch to the .26 bucket of x86.git, but it
    > > would be nice to get an Ack/Nack from a kprobes person as well.
    >
    > Ingo,
    >
    > I've tested Yakov's more comprehensive patch on powerpc too. This has
    > my ack.
    >
    > Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>

    thanks, i've queued up the x86-only patch below for .26 merging. (that
    is all that is needed for x86, and no .25 urgency, right?)

    Ingo

    ------------------>
    Subject: x86, kprobes: correct post-eip value in post_hander()
    From: "Yakov Lerner" <iler.ml@gmail.com>
    Date: Sun, 16 Mar 2008 03:21:21 -0500

    I was trying to get the address of instruction to be executed
    next after the kprobed instruction. But regs->eip in post_handler()
    contains value which is useless to the user. It's pre-corrected value.
    This value is difficult to use without access to resume_execution(), which
    is not exported anyway.
    I moved the invocation of post_handler() to *after* resume_execution().
    Now regs->eip contains meaningful value in post_handler().

    I do not think this change breaks any backward-compatibility.
    To make meaning of the old value, post_handler() would need access to
    resume_execution() which is not exported. I have difficulty to believe
    that previous, uncorrected, regs->eip can be meaningfully used in
    post_handler().

    Signed-off-by: Yakov Lerner <iler.ml@gmail.com>
    Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    arch/x86/kernel/kprobes.c | 8 ++++----
    1 file changed, 4 insertions(+), 4 deletions(-)

    Index: linux-x86.q/arch/x86/kernel/kprobes.c
    ===================================================================
    --- linux-x86.q.orig/arch/x86/kernel/kprobes.c
    +++ linux-x86.q/arch/x86/kernel/kprobes.c
    @@ -858,15 +858,15 @@ static int __kprobes post_kprobe_handler
    if (!cur)
    return 0;

    + resume_execution(cur, regs, kcb);
    + regs->flags |= kcb->kprobe_saved_flags;
    + trace_hardirqs_fixup_flags(regs->flags);
    +
    if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
    kcb->kprobe_status = KPROBE_HIT_SSDONE;
    cur->post_handler(cur, regs, 0);
    }

    - resume_execution(cur, regs, kcb);
    - regs->flags |= kcb->kprobe_saved_flags;
    - trace_hardirqs_fixup_flags(regs->flags);
    -
    /* Restore back the original saved kprobes variables and continue. */
    if (kcb->kprobe_status == KPROBE_REENTER) {
    restore_previous_kprobe(kcb);

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