linux-kernel - Re: [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer

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Date:	Fri, 03 Apr 2009 10:21:10 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Jim Keniston <jkenisto@...ibm.com>, kvm@...r.kernel.org,
	systemtap-ml <systemtap@...rces.redhat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Vegard Nossum <vegard.nossum@...il.com>
Subject: Re: [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer

Avi Kivity wrote:
> Ingo Molnar wrote:
>> ok, the structure and concept looks quite good now, really nice!
>>
>> I'm wondering about something i suggested many moons ago: to look into
>> the KVM decoder+emulator (arch/x86/kvm/x86_emulate.c).
>>
>> I remember there were some issues with that (one problem being that
>> the KVM decoder is a special-purpose thing covering specific range of
>> execution environments - not a near-full integer-ops decoder like the
>> one we are aiming for here) - are there any other fundamental problems
>> beyond 'it has to be done' ?
>>
>> Conceptually we want just a single piece of decoder logic in
>> arch/x86/. If the KVM folks are cool with it we could factor out the
>> KVM one into arch/x86/lib/. But ... if there are compelling reasons to
>> leave the KVM one alone in its limited environment we can do that too.
>>   
> 
> kvm has three requirements not needed by kprobes:
> - it wants to execute instructions, not just decode them, including
> generating faults where appropriate
> - it is performance critical
> - it needs to support 16-bit, 32-bit, and 64-bit instructions
> simultaneously

Hmm, I'd like to know actually kvm aims to emulate all kinds of
instructions. If so, I might find some bugs in x86_emulate.c.
However, I don't know all bugs. To find all of them, we have to
port x86_emulate.c to user-space, decode binaries with it, and
compare its output with another decoder, as Jim had done with insn.c.

https://www.redhat.com/archives/utrace-devel/2009-March/msg00031.html


Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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