linux-kernel - Re: [PATCH] ARM: reinsert ARCH_MULTI

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Date:	Fri, 13 Dec 2013 11:39:03 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Jonas Jensen <jonas.jensen@...il.com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"arm@...nel.org" <arm@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	ulli.kroll@...glemail.com, Arnd Bergmann <arnd@...db.de>,
	Olof Johansson <olof@...om.net>
Subject: Re: [PATCH] ARM: reinsert ARCH_MULTI_V4 Kconfig option

On Fri, Dec 13, 2013 at 11:51:09AM +0100, Jonas Jensen wrote:
> On 13 December 2013 10:56, Russell King - ARM Linux
> <linux@....linux.org.uk> wrote:
> > So, having these symbols enabled (provided the right ones for FA526 are
> > also enabled) makes no difference.  So I don't buy your explanation.
> 
> The explanation is indeed false, CPU_FA526 and CPU_ARM920T get along just fine.
> That's not where the problem is.
> 
> Panic goes away after removing CONFIG_ARM_THUMB=y.
> 
> I assume this is what should happen on processors without thumb?

I see what's causing this: the kuser helpers are using "bx lr" to return
which will be undefined on non-Thumb CPUs.  We generally cope fine with
non-Thumb CPUs, conditionalising where necessary on HWCAP_THUMB or the
T bit in the PSR being set.

However, it looks like the kuser helpers got missed.  As a check, please
look at arch/arm/kernel/entry-armv.S, find the line with:

	.macro	usr_ret, reg

and ensure that the mov pc, \reg case always gets used.  Please report
back.

Thanks.
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