linux-kernel - Re: [PATCH -tip 10/10] perf probe: Accessing members in data structures

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Message-ID: <20100323162719.GG4066@ghostprotocols.net>
Date:	Tue, 23 Mar 2010 13:27:19 -0300
From:	Arnaldo Carvalho de Melo <acme@...radead.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Mark Wielaard <mjw@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>,
	Paul Mackerras <paulus@...ba.org>,
	Mike Galbraith <efault@....de>
Subject: Re: [PATCH -tip 10/10] perf probe: Accessing members in data
	structures

Em Tue, Mar 23, 2010 at 04:55:13PM +0100, Peter Zijlstra escreveu:
> On Thu, 2010-03-18 at 04:28 +0100, Frederic Weisbecker wrote:
> > On Wed, Mar 17, 2010 at 03:14:43PM -0400, Masami Hiramatsu wrote:
> > > Mark Wielaard wrote:
> > > > 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.

> > And lets people use what is common for them: expressions that follow
> > C rules in the context.

> > And those who will be more familiar with perf probe will know they can
> > use the simplified "." based scheme.

> I'd expect a syntax error when I mix up '.' and '->'.

Yup, I'd stick with following the C language rules.

- Arnaldo
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