From: Frederic Weisbecker <fweisbec@gmail.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: "Abhishek Sagar" <sagar.abhishek@gmail.com>,
"Tim Bird" <tim.bird@am.sony.com>,
linux-arm-kernel <linux-arm-kernel@lists.arm.linux.org.uk>,
"linux kernel" <linux-kernel@vger.kernel.org>,
"Steven Rostedt" <rostedt@goodmis.org>,
"Ingo Molnar" <mingo@redhat.com>,
"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Subject: Re: Anyone working on ftrace function graph support on ARM?
Date: Wed, 25 Mar 2009 12:41:31 +0100 [thread overview]
Message-ID: <20090325114129.GA5976@nowhere> (raw)
In-Reply-To: <20090325084248.GF4697@n2100.arm.linux.org.uk>
On Wed, Mar 25, 2009 at 08:42:48AM +0000, Russell King - ARM Linux wrote:
> On Tue, Mar 24, 2009 at 11:48:58PM +0100, Frederic Weisbecker wrote:
> > On Tue, Mar 24, 2009 at 06:29:03PM -0400, Abhishek Sagar wrote:
> > > Instead of just restoring the old backed-up args, lr can be fixed up
> > > inside the entry hook to point to the return hook. So when the traced
> > > function returns, it actually returns to the return hook (where we can
> > > restore the original return address). This means that
> > > -finstrument-functions is not required at all. This is analogous to how
> > > kretprobes work. The only difference here is that instead of planting a
> > > kprobe at the function entry and redirecting the function return to the
> > > profiling exit routine, we can use mcount. This is slightly more
> > > complicated to implement but can be a very efficient alternative to
> > > kretprobes.
> > > --
> > > Abhishek
> > >
> >
> > Indeed, you need to override lr, that even the only solution.
> > I was still thinking in an x86 way with its on stack return address.
>
> As pointed out in my previous mail, identifying where on the stack the
> return address is stored is only possible for OABI with frame pointers.
>
> EABI will probably be possible with the stack unwinding code, but it
> probably won't be cheap. The EABI unwinder is scheduled for merging
> during the present now-open merge window.
Hm, if I'm not wrong, the function tracer already depends on frame pointer,
this is necessary to retrieve the parent of the caller.
next prev parent reply other threads:[~2009-03-25 11:41 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-24 19:38 Anyone working on ftrace function graph support on ARM? Tim Bird
2009-03-24 20:25 ` Ingo Molnar
2009-03-24 20:48 ` Tim Bird
2009-03-24 20:38 ` Uwe Kleine-König
2009-03-24 21:36 ` Frederic Weisbecker
2009-03-24 21:40 ` Tim Bird
2009-03-24 21:48 ` Ingo Molnar
2009-03-24 21:57 ` Frederic Weisbecker
2009-03-24 22:14 ` Ingo Molnar
2009-03-24 22:54 ` Frederic Weisbecker
2009-03-25 8:36 ` Russell King - ARM Linux
2009-03-25 16:00 ` Steven Rostedt
2009-03-25 17:13 ` Frederic Weisbecker
2009-03-25 20:27 ` [PATCH][GIT PULL] x86, function-graph: only save return values on x86_64 Steven Rostedt
2009-03-25 20:45 ` Jaswinder Singh Rajput
2009-03-25 21:26 ` Steven Rostedt
2009-04-08 16:09 ` Ingo Molnar
2009-04-08 16:37 ` Steven Rostedt
2009-04-08 16:41 ` Ingo Molnar
2009-04-08 17:40 ` Frederic Weisbecker
2009-03-24 22:29 ` Anyone working on ftrace function graph support on ARM? Abhishek Sagar
2009-03-24 22:48 ` Frederic Weisbecker
2009-03-25 8:42 ` Russell King - ARM Linux
2009-03-25 8:54 ` Ingo Molnar
2009-03-25 9:57 ` Russell King - ARM Linux
2009-03-25 10:45 ` Uwe Kleine-König
2009-03-25 11:21 ` Russell King - ARM Linux
2009-03-25 12:09 ` Uwe Kleine-König
2009-03-25 16:41 ` Tim Bird
2009-03-25 11:41 ` Frederic Weisbecker [this message]
2009-03-25 16:34 ` Tim Bird
2009-03-25 17:05 ` Uwe Kleine-König
2009-03-25 17:17 ` Russell King - ARM Linux
2009-03-25 18:37 ` Tim Bird
2009-03-25 18:41 ` Steven Rostedt
2009-03-27 12:58 ` Catalin Marinas
2009-04-09 15:29 ` Daniel Jacobowitz
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