linux-kernel - Re: [PATCH -tip 0/4 V3] tracing: kprobe-based event tracer

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Date:	Thu, 2 Apr 2009 00:15:40 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	systemtap-ml <systemtap@...rces.redhat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jim Keniston <jkenisto@...ibm.com>
Subject: Re: [PATCH -tip 0/4 V3] tracing: kprobe-based event tracer

On Wed, Apr 01, 2009 at 04:51:00PM -0400, Masami Hiramatsu wrote:
> Andi Kleen wrote:
> > Masami Hiramatsu <mhiramat@...hat.com> writes:
> >> I agreed. Fortunately, Jim Keniston and I wrote an x86 instruction
> >> decoder :-) which has been made originally for uprobe andd kprobes
> >> jump-optimizer.
> >>
> >> https://www.redhat.com/archives/utrace-devel/2009-March/msg00031.html
> > 
> > An alternative would be to adapt the x86 interpreter in KVM.
> > I thought for some time that that one should be available in 
> > a more generic form in a library.
> 
> As far as I can see, KVM's instruction emulator is incomplete

That's fine for you -- you only care about a subset of instructions
anyways, don't you?

> (it doesn't cover all instructions...) and aims to emulate
> instructions, not to analyze (so I couldn't relay on it).

You can use it to analyze, just plug in the right callbacks that
do nothing. I looked at it some time ago for doing instruction
length checking for some application, but that application
then disappeared. The main obstacle with making it a library 
is that some KVM specific dependencies have crept in that would
need to be abstracted again, but I don't think it would need a lot of 
effort,

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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