Re: [PATCH] Linux Kernel Markers

[Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>]

Hi Karim,

Karim Yaghmour wrote:
> Martin Bligh wrote:
>> be that many? Still doesn't fix the problem Matieu just pointed
>> out though. Humpf.
> 
> There's one possibility if we're willing to insert a placeholder
> at function entry that allows to essentially do what Andrew
> suggests without much impact. Specifically, if you need a 5-byte
> operation to jump to the alternate instrumented function, you
> can then do something like:

This method is very similar to the djprobe.
And I had gotten the same idea to support preemptive kernel.

> 1- At build time insert 5-byte unconditional jump to instruction
> right after placeholder.

This means the below code, doesn't this?
---
	jmp 1f /* short jump consumes 2 bytes */
	nop
	nop
	nop
1:
---

> 2- At runtime for diverting flow:
>    - Replace first byte with int3 (atomically)
>    - Replace next 4 bytes with instrumented function destination

     - Serialize all processor's cache by using IPI and cpuid.

>    - Replace first byte
> 3- At runtime for returning flow:
>    - Do #2 but for the original placeholder jump.


I think the djprobe can provide most of functionalities which
your idea requires.
I'll update the djprobe against for 2.6.17 or later as soon as
possible. Would you try to use it?

Thanks,

-- 
Masami HIRAMATSU
2nd Research Dept.
Hitachi, Ltd., Systems Development Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com