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Date: Tue, 28 Jun 2011 14:38:00 -0000
From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>,	Yao Qi <yao@codesourcery.com>, Eric Miao <eric.y.miao@gmail.com>,	linux-arm-kernel@lists.infradead.org, gdb@sourceware.org
Subject: Re: Problem with GDB when debugging IRQ handlers
Message-ID: <20110628143758.GF21898@n2100.arm.linux.org.uk>
References: <20110627125306.GA30646@doriath.ww600.siemens.net> <20110627132735.GE16103@n2100.arm.linux.org.uk> <4E088DE1.2060809@gmail.com> <4E089AB3.1090801@codesourcery.com> <20110628103946.GC21898@n2100.arm.linux.org.uk> <BANLkTinvrJ5MAZABDmdmQk6UZHDKJQo1+A@mail.gmail.com> <20110628142045.GC7255@1n450.cable.virginmedia.net> <20110628143014.GD7255@1n450.cable.virginmedia.net>
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On Tue, Jun 28, 2011 at 03:30:14PM +0100, Catalin Marinas wrote:
> Actually since the return address is in S_PC (which maybe gdb assumes it
> would be the saved LR), this is probably not be correct. After SVC
> entry, we have he following structure on the stack:
> 
> 	ORIG_r0
> 	CPSR
> 		<--- assuming this is the Call Frame Address (SP+S_PC+4)
> 	PC	<--- CFA - 4
> 	LR	<--- don't care
> 	SP	<--- CFA - 12
> 	...

If I'm reading this correctly, it's not correct.

parent SP -->	parent context stack
		[possible empty word]
		ORIG_r0
		parent context CPSR
		parent context PC
		parent context LR
		parent context SP
		...
new SP -->	R0

That empty word may or may not be present if the parent SP is aligned to
a 64-bit boundary.