Re: [PATCH] Kprobe:multi kprobe posthandler for booster

[Masami Hiramatsu <hiramatu at sdl dot hitachi dot co dot jp>]

Hi, Andrew

Andrew Morton wrote:
> OK...  But you didn't provide me with sufficient information with which I
> can gauge the seriousness of this problem.  Show-stopper bug?  Minor
> performance problem?  Hard to tell, and I do need that information to be
> able to judge whether patches should do into -rc or into the next kernel
> cycle, as well as being backported into -stable.

I'm sorry not to provide detail information.
I described it below.

> I currently have four patches:
> 
> kprobe-boost-2byte-opcodes-on-i386.patch

This is an enhancement patch of kprobe-booster on i386.
In the previous patch
(http://marc.theaimsgroup.com/?l=linux-kernel&m=114104159911612&w=4),
I decided that the first booster patch didn't boost the 2bytes
opcodes and prefixes, because of simplicity of the patch.

In this patch, I identified "boostable" 2 byte instructions as below;
- Conditional jumps can not be boost.
- WRMSR, RDMSR, CPUID, RSM, and RDPMC may have unexpected side effects.
  Thus these can not be boost.
- Extended Groups are including some undefined opcodes. Thus
  these can not be boost.
- Invalid opcode, UD2 and other undefined opcodes can not be boost.
- other defined opcodes can be boost.

I also identified prefixes again:
- Address size prefix(0x67) and CS segment override(0x2e) may change
  valid address range. So these can not be boost.
- If there is other prefixes, there is a chance to boost it.

> kprobe-fix-resume-execution-on-i386.patch

This patch enables kprobe's resume_execution() to handle
iret(0xcf) and absolute-call(0x9a) correctly.
It handles those operations as below;
- iret
 After the "iret" was executed, the value of eip register
was restored from the stack. Thus resume_execution() handles
it as same as "ret".
- absolute-call
 The target address of the "absolute-call" is specified as an
absolute address. Thus no need to fix eip.


Best regards,

-- 
Masami HIRAMATSU
2nd Research Dept.
Hitachi, Ltd., Systems Development Laboratory
E-mail: hiramatu@sdl.hitachi.co.jp