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Re: [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer
- From: Masami Hiramatsu <mhiramat at redhat dot com>
- To: Avi Kivity <avi at redhat dot com>
- Cc: Ingo Molnar <mingo at elte dot hu>, "H. Peter Anvin" <hpa at zytor dot com>, Frederic Weisbecker <fweisbec at gmail dot com>, Steven Rostedt <rostedt at goodmis dot org>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Andrew Morton <akpm at linux-foundation dot org>, Andi Kleen <andi at firstfloor dot org>, Jim Keniston <jkenisto at us dot ibm dot com>, kvm at vger dot kernel dot org, systemtap-ml <systemtap at sources dot redhat dot com>, LKML <linux-kernel at vger dot kernel dot org>, Vegard Nossum <vegard dot nossum at gmail dot com>
- Date: Fri, 03 Apr 2009 10:21:10 -0400
- Subject: Re: [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer
- References: <49D4F4B5.9040107@redhat.com> <20090403112639.GC31399@elte.hu> <49D5F80B.7000305@redhat.com>
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@redhat.com