linux-kernel - Re: [PATCH -v4 9/9] tracing: add function graph tracer support for MIPS

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Message-ID: <20091021181705.GA5218@opentech.at>
Date:	Wed, 21 Oct 2009 20:17:05 +0200
From:	Nicholas Mc Guire <der.herr@...r.at>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	David Daney <ddaney@...iumnetworks.com>,
	Wu Zhangjin <wuzhangjin@...il.com>,
	linux-kernel@...r.kernel.org, linux-mips@...ux-mips.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [PATCH -v4 9/9] tracing: add function graph tracer support for
	MIPS

> 
> 
> We're not doing back traces. We need to modify the return of the
> function being called. Note, the above functions that end with ";" are
> leaf functions. Non leaf functions show "{" and end with "}".
> 
> The trick here is to find a reliable way to modify the return address.
>
would it not more or less be the same thing if you used -finstrument-functions
then and provide a stub __cyg_profile_func_enter/exit initialized to an empty
function until you replace it during tracing. This does give you an overhead
when you are not tracing - but it would make the tracer implementation quite
generic.

hofrat 
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