linux-kernel - Re: [PATCH -tip v5 07/10] kprobes/x86: Support kprobes jump optimization on x86

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Date:	Wed, 25 Nov 2009 11:12:57 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Jason Baron <jbaron@...hat.com>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>,
	Jim Keniston <jkenisto@...ibm.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Anders Kaseorg <andersk@...lice.com>,
	Tim Abbott <tabbott@...lice.com>,
	Andi Kleen <andi@...stfloor.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Subject: Re: [PATCH -tip v5 07/10] kprobes/x86: Support kprobes jump	optimization
 on x86

Masami Hiramatsu wrote:
> Jason Baron wrote:
>> Also, with multiple users we don't want to trample over each others code
>> patching. Thus, if each sub-system could register some type of
>> 'is_reserved()' callback, and then we can call all these call backs from
>> the '__multibyte_poke()' routine before we do any patching to make sure
>> that we aren't trampling on each others code. After a successful
>> patching, each sub-system can update its reserved set of code as
>> appropriate. I can code a prototype here, if this makes sense.
>
> Hmm, we have to implement it carefully, because here kprobes already
> inserted int3 and optprobe rewrites the int3 again. If is_reserved()
> returns 1 and multibyte_poke returns error, we can't optimize it anymore.

IMHO, all text-modifiers except kprobes provide is_reserved() callback
and kprobes cancels probing if its target address is reserved, since
only kprobes changes texts anywhere while others changes texts at
fixed addresses.

Anyway, I think this will be another bugfix for current kprobes/alternative.

Thank you,
-- 
Masami Hiramatsu

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

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

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