linux-kernel - Re: [PATCH tracing/kprobes v3 4/7] tracing/kprobes: Avoid field name confliction

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Date:	Mon, 12 Oct 2009 16:22:26 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...e.hu>,
	lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>,
	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>
Subject: Re: [PATCH tracing/kprobes v3 4/7] tracing/kprobes: Avoid field	name
 confliction

Frederic Weisbecker wrote:
> On Mon, Oct 12, 2009 at 03:13:51PM -0400, Masami Hiramatsu wrote:
>> Frederic Weisbecker wrote:
>>> The conflict issue might not be obvious for a user desperately trying to set
>>> a kprobe. Even for other failcases, it might not be obvious (blacklisted
>>> symbols, syntax errors...)
>>>
>>> May be should you improve the error granularity and print a KERN_DEBUG
>>> message?
>>
>> Agreed, and kprobes error handling should be improved too (in the most cases,
>> it just returns -EINVAL).
>>
>> Thank you.
>>
>
>
> And btw, I'm enable to create a probe, neither through ftrace nor perf:
>
> 	$ sudo ./perf probe -P 'p:sys_close sys_close $retval'
> 	Adding new event: p:sys_close sys_close+0 $retval
>
> 	Error: Failed to create event: Invalid argument
>
>
> 	# echo 'p:sys_open sys_open $retval'>  /debug/tracing/kprobe_events
> 	bash: echo: write error : Invalid argument
>
> I suspect I missed something very obvious with the syntax :)

Ah, only kretprobe events can use $retval :-)
So, you should specify 'r' instead of 'p'.

-P 'r:sys_close sys_close $retval'


> I've applied your patches in:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/random-tracing.git
> 	tracing/kprobes
>
> Thanks.

Thank you!

-- 
Masami Hiramatsu

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

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

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