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Re: [PATCH -tip 10/10] perf probe: Accessing members in data structures
- From: Masami Hiramatsu <mhiramat at redhat dot com>
- To: Mark Wielaard <mjw at redhat dot com>
- Cc: Ingo Molnar <mingo at elte dot hu>, lkml <linux-kernel at vger dot kernel dot org>, systemtap <systemtap at sources dot redhat dot com>, DLE <dle-develop at lists dot sourceforge dot net>, Frederic Weisbecker <fweisbec at gmail dot com>, Arnaldo Carvalho de Melo <acme at redhat dot com>, Paul Mackerras <paulus at samba dot org>, Mike Galbraith <efault at gmx dot de>, Peter Zijlstra <a dot p dot zijlstra at chello dot nl>
- Date: Wed, 17 Mar 2010 15:14:43 -0400
- Subject: Re: [PATCH -tip 10/10] perf probe: Accessing members in data structures
- References: <20100316220515.32050.82185.stgit@localhost6.localdomain6> <20100316220626.32050.57552.stgit@localhost6.localdomain6> <1268821537.6022.12.camel@springer.wildebeest.org>
Mark Wielaard wrote:
> On Tue, 2010-03-16 at 18:06 -0400, Masami Hiramatsu wrote:
>> Support accessing members in the data structures. With this,
>> perf-probe accepts data-structure members(IOW, it now accepts
>> dot '.' and arrow '->' operators) as probe arguemnts.
>>
>> e.g.
>>
>> ./perf probe --add 'schedule:44 rq->curr'
>>
>> ./perf probe --add 'vfs_read file->f_op->read file->f_path.dentry'
>>
>> Note that '>' can be interpreted as redirection in command-line.
>
> If you find that a problem then you can do like SystemTap does and allow
> '.' in place of '->'. In the code you already use the
> perf_probe_arg_field ref flag only to check that the DIE gives you the
> same information. So you could just drop that and use any separator.
> Then you decide based on whether you see a DW_TAG_pointer_type. This
> gives the user some extra flexibility by letting them not having to care
> about specifying extra type information already available elsewhere.
Thanks, when designing this feature, I considered it too.
Since perf probe already support displaying source code by --line option,
users will read the probed code itself and try to probe it. In that case,
I think they naturally use '.' and '->' as they read (they might try to
copy & paste it).
So, I think that it would be good to support both of '.' and '->' as
they are used in the code, because it will not confuse users.
Thank you,
--
Masami Hiramatsu
e-mail: mhiramat@redhat.com