linux-kernel - Re: [PATCH -tip tracing/kprobes 0/9] tracing/kprobes, perf: perf probe and kprobe-tracer bugfixes

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Date:	Tue, 20 Oct 2009 10:38:14 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Hellwig <hch@...radead.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>
Subject: Re: [PATCH -tip tracing/kprobes 0/9] tracing/kprobes, perf: perf
 probe and kprobe-tracer bugfixes

Ingo Molnar wrote:
>>> The point is to prefer intuitive, non-mechanic, fundamentally human
>>> expressions of information above mechanic ones (absolute line numbers,
>>> addresses, ways of probing, etc.) - and to have a rich variety of them.
>>>
>>> String based pattern matching and intuitive syntax that reuses existing
>>> paradigms of arithmetics and pattern-matching is good - limited syntax
>>> and extra, arbitrary syntactic hoops to jump through is bad.
>>>
>>> If we provide all that, people will start using this stuff - and i'd
>>> only like to merge this upstream once it's clear that people like me
>>> will (be able to) use this facility for ad-hoc probe insertion.
>>>
>>> In other words: this facility has to 'live within' our source code and
>>> has to be able to interact with it on a very broad basis - for it to be
>>> maximally useful for everyday development.
>>
>> Hmm, so you mean perf-probe should work with source-code? Without 
>> source code (but with debuginfo), maybe we can't use string matching, 
>> is that OK?
> 
> Well most forms of debuginfo embedd the full source code in the 
> debuginfo, right? If it's not there (or we dont know where it is) then 
> we cannot use it, obviously.

Um, actually debuginfo doesn't have the full source code, but has
the source file path. So, only if there are source files,
we can use string-based matching. Even if there are no source files,
that means users can't change their kernel:-). So we don't care
about kernel-version dependency.

> But we obviously want the whole 'perf probe' workflow to primarily 
> operate on source code - we are humans.

Sure :-)

Thank you,

-- 
Masami Hiramatsu

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

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

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