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

To: David Daney <ddaney@caviumnetworks.com>
Subject: Re: [PATCH -v4 9/9] tracing: add function graph tracer support for MIPS
From: Steven Rostedt <rostedt@goodmis.org>
Date: Thu, 22 Oct 2009 12:11:56 -0400
Cc: wuzhangjin@gmail.com, linux-kernel@vger.kernel.org, linux-mips@linux-mips.org, Thomas Gleixner <tglx@linutronix.de>, Ralf Baechle <ralf@linux-mips.org>, Nicholas Mc Guire <der.herr@hofr.at>
In-reply-to: <4AE08173.7070500@caviumnetworks.com>
Organization: Kihon Technologies Inc.
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <028867b99ec532b84963a35e7d552becc783cafc.1256135456.git.wuzhangjin@gmail.com> <2f73eae542c47ac5bbb9f7280e6c0271d193e90d.1256135456.git.wuzhangjin@gmail.com> <3f0d3515f74a58f4cfd11e61b62a129fdc21e3a7.1256135456.git.wuzhangjin@gmail.com> <ea8aa927fbd184b54941e4c2ae0be8ea0b4f6b8a.1256135456.git.wuzhangjin@gmail.com> <96110ea5dd4d3d54eb97d0bb708a5bd81c7a50b5.1256135456.git.wuzhangjin@gmail.com> <5dda13e8e3a9c9dba4bb7179183941bda502604f.1256135456.git.wuzhangjin@gmail.com> <af3ec1b5cd06b6f6a461c9fa7d09a51fabccb08d.1256135456.git.wuzhangjin@gmail.com> <a6f2959a69b6a77dd32cc36a5c8202f97d524f1e.1256135456.git.wuzhangjin@gmail.com> <53bdfdd95ec4fa00d4cc505bb5972cf21243a14d.1256135456.git.wuzhangjin@gmail.com> <1256141540.18347.3118.camel@gandalf.stny.rr.com> <4ADF38D5.9060100@caviumnetworks.com> <1256143568.18347.3169.camel@gandalf.stny.rr.com> <4ADF3FE0.5090104@caviumnetworks.com> <1256145813.18347.3210.camel@gandalf.stny.rr.com> <1256211516.3852.47.camel@falcon> <4AE08173.7070500@caviumnetworks.com>
Reply-to: rostedt@goodmis.org
Sender: linux-mips-bounce@linux-mips.org
On Thu, 2009-10-22 at 08:59 -0700, David Daney wrote:

> This is what I was talking about up-thread.  Leaf functions may have no 
> function prolog.  If you do code scanning you will fail.  While scanning 
> backwards, there is no way to know when you have entered a new function. 
>   Looking for function return sequences 'jr ra' doesn't work as there 
> may be functions with multiple return sites, functions that never 
> return, or arbitrary data before the function.  I think you have to 
> force a frame pointer to be established if you want this to work.

Functions that run off into another function?? I guess the compiler
could do that, but with -pg enable, I would think is broken.

-- Steve



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