linux-kernel - MIPS Function Tracer question

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Date:	Thu, 29 Nov 2012 16:04:40 -0500
From:	Alan Cooper <alcooperx@...il.com>
To:	ralf@...ux-mips.org, linux-mips@...ux-mips.org,
	linux-kernel@...r.kernel.org
Subject: MIPS Function Tracer question

I've been doing some testing of the MIPS Function Tracer functionality
on the 3.3 kernel. I was surprised to find that the option to generate
frame pointers was required for tracing. When I don't enable
FRAME_POINTER along with FUNCTION_TRACER, the kernel hangs on boot. I
also noticed that a checkin to the 3.4 kernel
(b732d439cb43336cd6d7e804ecb2c81193ef63b0) no longer forces on
FRAME_POINTER when FUNCTION_TRACER is selected. I was wondering how it
works in 3.4 and beyond, so I built a Malta kernel from the latest
MIPS tree with FUNCTION_TRACING enabled and tested it with QEMU. The
kernel hung the same way. I can think of 2 reasons for this:
1. Function tracing is broken for MIPS in 3.4 and beyond.
2. The 4.5.3 GNU C compiler I'm using is generating different code for
function tracing.
I was wondering if anyone has MIPS function tracing working in 3.4 or later?

I did figure out why it's hanging and I have some changes that will
allow the function tracer to run without frame pointers, but before I
proceed I want to rule out compiler differences.

Thanks
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