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

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Date:	Wed, 21 Oct 2009 13:23:33 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	David Daney <ddaney@...iumnetworks.com>
Cc:	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>,
	Nicholas Mc Guire <der.herr@...r.at>
Subject: Re: [PATCH -v4 9/9] tracing: add function graph tracer support for
 MIPS

On Wed, 2009-10-21 at 10:07 -0700, David Daney wrote:

> I have not used -pg, so I don't know for sure, I think all it does is 
> add the calls to _mcount.  Someone could investigate 
> -fno-omit-frame-pointer, with that you may be able to use:

Note, -pg assumes -fno-omit-frame-pointer, since -fomit-frame-pointer
and -pg are incompatible.

> 
>     move    s8,sp
> 
> To identify function prologs, but it would still be ad hoc, as modern 
> versions of GCC will reorder instructions in the prolog for better 
> scheduling.

I'll have to search the ABI documentation about calling _mcount in MIPS.
There are assumptions with _mcount that are made. It may very well be
safe to assume that the move s8,sp will always be there before an mcount
call.

-- Steve


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