linux-kernel - Re: [RFC v3][PATCH 0/2] Make ftrace able to trace function return

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Message-ID: <y0mr65gzncc.fsf@ton.toronto.redhat.com>
Date:	Wed, 12 Nov 2008 15:44:03 -0500
From:	fche@...hat.com (Frank Ch. Eigler)
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC v3][PATCH 0/2] Make ftrace able to trace function return

Frederic Weisbecker <fweisbec@...il.com> writes:

> This patchset adds the ability for ftrace to trace the function even
> on call time and on return time. So we can now measure the time of
> execution of the most part of the functions inside the kernel with
> ftrace. [...]

By the way, one extra complication you may need to deal with, beyond
normal retprobes, is that by the time dyn-ftrace gets hold of the
function entry, some part of the function prologue will have been
executed.  Because the mcount call/sequence is not the first
instruction in the function body, is there a risk that the call frame
cannot be reliably modified because of interference from those first
few other instructions?  Maybe on some architectures/optimization
levels?

- FChE
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