Message-ID: <4B0D5789.3000303@redhat.com>
Date: Wed, 25 Nov 2009 11:12:57 -0500
From: Masami Hiramatsu <mhiramat@redhat.com>
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To: Jason Baron <jbaron@redhat.com>
CC: Frederic Weisbecker <fweisbec@gmail.com>, Ingo Molnar <mingo@elte.hu>,
       Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
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       Anders Kaseorg <andersk@ksplice.com>, Tim Abbott <tabbott@ksplice.com>,
       Andi Kleen <andi@firstfloor.org>,
       Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Subject: Re: [PATCH -tip v5 07/10] kprobes/x86: Support kprobes jump	optimization
 on x86
References: <20091123232115.22071.71558.stgit@dhcp-100-2-132.bos.redhat.com> <20091123232211.22071.58974.stgit@dhcp-100-2-132.bos.redhat.com> <20091124162708.GA29995@redhat.com> <4B0C1BF8.9060408@redhat.com>
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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@redhat.com

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