Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964810AbaDIPHS (ORCPT ); Wed, 9 Apr 2014 11:07:18 -0400 Received: from gw-1.arm.linux.org.uk ([78.32.30.217]:55558 "EHLO pandora.arm.linux.org.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S933372AbaDIPHQ (ORCPT ); Wed, 9 Apr 2014 11:07:16 -0400 Date: Wed, 9 Apr 2014 16:06:40 +0100 From: Russell King - ARM Linux To: Jonas Jensen Cc: "linux-arm-kernel@lists.infradead.org" , "arm@kernel.org" , "linux-kernel@vger.kernel.org" , ulli.kroll@googlemail.com, Arnd Bergmann , Olof Johansson , u.kleine-koenig@pengutronix.de Subject: Re: [PATCH] ARM: reinsert ARCH_MULTI_V4 Kconfig option Message-ID: <20140409150640.GQ16119@n2100.arm.linux.org.uk> References: <1386922149-4561-1-git-send-email-jonas.jensen@gmail.com> <20131213095655.GB4360@n2100.arm.linux.org.uk> <20131213113903.GE4360@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 09, 2014 at 04:54:16PM +0200, Jonas Jensen wrote: > On 13 December 2013 12:39, Russell King - ARM Linux > wrote: > > 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. > > Uwe and Arnd came up with a solution except it doesn't work when I test it. > > The suggested patch is: > > diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S > index 1879e8d..de15bfd 100644 > --- a/arch/arm/kernel/entry-armv.S > +++ b/arch/arm/kernel/entry-armv.S > @@ -739,6 +739,18 @@ ENDPROC(__switch_to) > > .macro usr_ret, reg > #ifdef CONFIG_ARM_THUMB > + /* > + * Having CONFIG_ARM_THUMB isn't a guarantee that the cpu has support > + * for Thumb and so the bx instruction. Use a mov if the address to > + * jump to is 32 bit aligned. (Note that this code is compiled in ARM > + * mode, so this is the right test.) > + */ > +#if defined(CONFIG_CPU_32v4) > + tst \reg, #3 > + moveq pc, \reg > + b . > +#endif > + > bx \reg What's wrong with: tst \reg, #3 moveq pc, \reg bx \reg rather than ending in an infinite loop? -- FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly improving, and getting towards what was expected from it. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/