linux-kernel - Re: Anyone working on ftrace function graph support on ARM?

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Date:	Tue, 24 Mar 2009 22:57:39 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Tim Bird <tim.bird@...sony.com>,
	linux-arm-kernel <linux-arm-kernel@...ts.arm.linux.org.uk>,
	linux kernel <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Abhishek Sagar <sagar.abhishek@...il.com>,
	Russell King <rmk@....linux.org.uk>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Subject: Re: Anyone working on ftrace function graph support on ARM?

On Tue, Mar 24, 2009 at 10:48:46PM +0100, Ingo Molnar wrote:
> 
> * Frederic Weisbecker <fweisbec@...il.com> wrote:
> 
> > Well it's a very naive listing, there are sometimes some problems. 
> > For example on x86-64, I had to save even some non-scratch 
> > registers before calling the return hook, I still don't know why.
> 
> btw., which are those registers?
> 
> 	Ingo


I would expect to only save rax,rdi,rsi,rdx,rcx,r8,r9 which
are used for parameters.
And I had some crashes until I append r10 and r11 which actually are
scratch if I'm not wrong, but since they are scratch and are not used for
arguments, I thought they didn't need to be saved.

Well, I think there were some code flow cases I was missing.


The complete code is:

	movq %rax, (%rsp)
	movq %rcx, 8(%rsp)
	movq %rdx, 16(%rsp)
	movq %rsi, 24(%rsp)
	movq %rdi, 32(%rsp)
	movq %r8, 40(%rsp)
	movq %r9, 48(%rsp)
	movq %r10, 56(%rsp)
	movq %r11, 64(%rsp)

	call ftrace_return_to_handler

	movq %rax, 72(%rsp) <-- get original return value
	movq 64(%rsp), %r11
	movq 56(%rsp), %r10
	movq 48(%rsp), %r9
	movq 40(%rsp), %r8
	movq 32(%rsp), %rdi
	movq 24(%rsp), %rsi
	movq 16(%rsp), %rdx
	movq 8(%rsp), %rcx
	movq (%rsp), %rax
	addq $72, %rsp

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