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    Subject[PATCH v4 2/2] arch/powerpc: Optimize kprobe in kretprobe_trampoline
    Date
    Kprobe placed on the  kretprobe_trampoline during boot time can be 
    optimized, since the instruction at probe point is a 'nop'.

    Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
    Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
    ---
    arch/powerpc/kernel/kprobes.c | 8 ++++++++
    arch/powerpc/kernel/optprobes.c | 7 +++----
    2 files changed, 11 insertions(+), 4 deletions(-)

    diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
    index e785cc9..5b0fd07 100644
    --- a/arch/powerpc/kernel/kprobes.c
    +++ b/arch/powerpc/kernel/kprobes.c
    @@ -282,6 +282,7 @@ asm(".global kretprobe_trampoline\n"
    ".type kretprobe_trampoline, @function\n"
    "kretprobe_trampoline:\n"
    "nop\n"
    + "blr\n"
    ".size kretprobe_trampoline, .-kretprobe_trampoline\n");

    /*
    @@ -334,6 +335,13 @@ static int __kprobes trampoline_probe_handler(struct kprobe *p,

    kretprobe_assert(ri, orig_ret_address, trampoline_address);
    regs->nip = orig_ret_address;
    + /*
    + * Make LR point to the orig_ret_address.
    + * When the 'nop' inside the kretprobe_trampoline
    + * is optimized, we can do a 'blr' after executing the
    + * detour buffer code.
    + */
    + regs->link = orig_ret_address;

    reset_current_kprobe();
    kretprobe_hash_unlock(current, &flags);
    diff --git a/arch/powerpc/kernel/optprobes.c b/arch/powerpc/kernel/optprobes.c
    index ecba221..5e4c254 100644
    --- a/arch/powerpc/kernel/optprobes.c
    +++ b/arch/powerpc/kernel/optprobes.c
    @@ -72,12 +72,11 @@ static unsigned long can_optimize(struct kprobe *p)

    /*
    * kprobe placed for kretprobe during boot time
    - * is not optimizing now.
    - *
    - * TODO: Optimize kprobe in kretprobe_trampoline
    + * has a 'nop' instruction, which can be emulated.
    + * So further checks can be skipped.
    */
    if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
    - return 0;
    + return (unsigned long)p->addr + sizeof(kprobe_opcode_t);

    /*
    * We only support optimizing kernel addresses, but not
    --
    2.7.4
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