From: Masami Hiramatsu <mhiramat@redhat.com>
To: Vegard Nossum <vegard.nossum@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>, Avi Kivity <avi@redhat.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Andi Kleen <andi@firstfloor.org>,
Jim Keniston <jkenisto@us.ibm.com>,
kvm@vger.kernel.org,
systemtap-ml <systemtap@sources.redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
Pekka Paalanen <pq@iki.fi>
Subject: Re: [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer
Date: Fri, 03 Apr 2009 09:52:09 -0400 [thread overview]
Message-ID: <49D61489.9020406@redhat.com> (raw)
In-Reply-To: <19f34abd0904030616v56d66a11u7ee6054502f2922@mail.gmail.com>
Vegard Nossum wrote:
> 2009/4/3 Ingo Molnar <mingo@elte.hu>:
>> * Avi Kivity <avi@redhat.com> wrote:
>>
>>> Ingo Molnar wrote:
>>>>> 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
>>>>>
>>>>> If an arch/x86/ decoder/emulator gives me these I'll gladly switch
>>>>> to it. x86_emulate.c is high on my list of most disliked code.
>>>>>
>>>> Well, this has to be driven from the KVM side as the kprobes use
>>>> will only be for decoding so if it's modified from the kprobes
>>>> side the KVM-only functionality might regress.
>>>>
>>>> So ... we can do the library decoder for kprobes purposes, and
>>>> someone versed in the KVM emulator can then combine the two.
>>> Problem is, anyone versed in the kvm emulator will want to run as
>>> far away from this work as possible.
>> Are you suggesting that the KVM emulator should never have been
>> merged in the first place? ;-)
>>
>> Anyway, we'll make sure the kprobes/library decoder is as clean as
>> possible - so it ought to be hackable and extensible without the
>> risk of permanent brain damage. Mmiotrace and kmemcheck has decoding
>> smarts too, and i think the sw-breakpoint injection code of KGDB
>> could use it as well - so there's broader utility in all this.
>
> (Sorry in advance for jumping in -- my post may be irrelevant)
Thank you for clarify your needs :-)
> For the record, kmemcheck requirements for an instruction decoder are these:
>
> For any instruction with memory operands, we need to know which are
> the operands (so for movl %eax, (%ebx) we need to combine the
> instruction with a struct pt_regs to get the actual address
> dereferenced, i.e. the contents of %ebx), and their sizes (for movzbl,
> the source operand is 8 bits, destination operand is 32 bits). For
> things like movsb, we need to be able to get both %esi and %edi.
New decoder can give you the value of mod/rm(insn.modrm), operand size
(insn.opnd_bytes), and immediate size (insn.immediate.nbytes)
To get which register is used, you can decode modrm with MODRM_*()
macros.
> mmiotrace additionally needs to know what the actual values
> read/written were, for instructions that read/write to memory (again,
> combined with a struct pt_regs).
The decoder doesn't use any locks/shared memory, so you can
use it in interrupt context, with pt_regs.
> Maybe this doesn't really say much, since this is what a generic
> instruction decoder would be able to do anyway. But kmemcheck and
> mmiotrace both have very special-purpose decoders. I don't really know
> what other decoders look like, but what I would wish for is this: Some
> macros for iterating the operands, where each operand has a type (e.g.
> input (for reads), output (for writes), target (for jumps), immediate
> address, immediate value, etc.), a size (in bits), and a way to
> evaluate the operand. So eval(op, regs) for op=%eax, it will return
> regs->eax; for op=4(%eax), it will return regs->eax + 4; for op=4 it
> will return 4, etc.
Hmm, it's an interesting idea. I think operand classifying can be done by
evaluating opcode and mod/rm.
> Both kmemcheck and mmiotrace could gain SMP support with instruction
> emulation, though it is strictly not necessary. In that case, though,
> we would not want to emulate fault handling, etc. (i.e. the fault
> should always be generated by the CPU itself).
>
> Please do put me on Cc for future discussions, though.
Of course, thank you!
--
Masami Hiramatsu
Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division
e-mail: mhiramat@redhat.com
next prev parent reply other threads:[~2009-04-03 13:52 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-04-02 17:24 [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer Masami Hiramatsu
2009-04-03 11:26 ` Ingo Molnar
2009-04-03 11:32 ` Andi Kleen
2009-04-03 11:50 ` Avi Kivity
2009-04-03 12:12 ` Ingo Molnar
2009-04-03 12:17 ` Avi Kivity
2009-04-03 12:26 ` Ingo Molnar
2009-04-03 12:33 ` Avi Kivity
2009-04-03 13:16 ` Vegard Nossum
2009-04-03 13:40 ` Avi Kivity
2009-04-03 13:52 ` Masami Hiramatsu [this message]
2009-04-05 19:37 ` Pekka Paalanen
2009-04-06 7:53 ` Avi Kivity
2009-04-03 12:25 ` Andi Kleen
2009-04-03 14:21 ` Masami Hiramatsu
2009-04-03 14:23 ` Ingo Molnar
2009-04-03 16:55 ` Masami Hiramatsu
2009-04-03 17:59 ` Jim Keniston
2009-04-03 14:30 ` Avi Kivity
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