Re: [PATCH] kprobes: Mark OPTPROBES n/a for powerpc

On Sun, Jul 19, 2015 at 11:21:50AM +0900, Masami Hiramatsu wrote:

On 2015/07/16 19:56, Ananth N Mavinakayanahalli wrote:

quoted

Kprobes uses a breakpoint instruction to trap into execution flow
and the probed instruction is single-stepped from an alternate location.

On some architectures like x86, under certain conditions, the OPTPROBES
feature enables replacing the probed instruction with a jump instead,
resulting in a significant perfomance boost (one single-step exception
is bypassed for each kprobe).

The OPTPROBE is not only for bypassing the single-step exception, but also
the breakpoint exception.
Please see commit 0dc016dbd820260b (ARM: kprobes: enable OPTPROBES for ARM 32) too,
which shows how it is done on RISC processor.

Yes, will fix and send.

quoted

Powerpc has an in-kernel instruction emulator. Kprobes on powerpc uses
this emulator already and bypasses the single-step exception, with a
lot less complexity.

So, this might miss the point. Since it is impossible to do on some RISC
processor, I agree with this change, but it should be committed with
correct comments.

Sure, thanks!

Ananth