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Subject: Re: BUG: GCC-4.4.x changes the function frame on some functions
From: Steven Rostedt <rostedt@goodmis.org>
Reply-To: rostedt@goodmis.org
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: David Daney <ddaney@caviumnetworks.com>,
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Date: Thu, 19 Nov 2009 15:17:16 -0500
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On Thu, 2009-11-19 at 15:05 -0500, Steven Rostedt wrote:

> Well, other archs use a register to store the return address. But it
> would also be easy to do (pseudo arch assembly):
> 
> 	<function>:
> 		mov lr, (%sp)
> 		add 8, %sp
> 		blr __fentry__

Should be bl __fentry__ for "branch and link".

> 		sub 8, %sp
> 		mov (%sp), lr
> 
> 
> That way the lr would have the current function, and the parent would
> still be at 8(%sp)

Actually, if we add a new profiler and can make our own specification, I
would say that the add and sub lines be the responsibility of
__fentry__. Then we would have:

	<function>:
		mov lr, (%sp)
		bl __fentry__
		mov (%sp), lr

If sp points to the current content, then replace (%sp) above with 
-8(%sp).  Then the implementation of a nop __fentry__ would simply be:

	__fentry__:
		blr

For anything more elaborate, __fentry__ would be responsible for all
adjustments.

-- Steve


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