Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934065AbaDIQBt (ORCPT ); Wed, 9 Apr 2014 12:01:49 -0400 Received: from gw-1.arm.linux.org.uk ([78.32.30.217]:55655 "EHLO pandora.arm.linux.org.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S933909AbaDIQBq (ORCPT ); Wed, 9 Apr 2014 12:01:46 -0400 Date: Wed, 9 Apr 2014 17:01:09 +0100 From: Russell King - ARM Linux To: Arnd Bergmann Cc: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , Jonas Jensen , "linux-arm-kernel@lists.infradead.org" , "arm@kernel.org" , "linux-kernel@vger.kernel.org" , ulli.kroll@googlemail.com, Olof Johansson Subject: Re: [PATCH] ARM: reinsert ARCH_MULTI_V4 Kconfig option Message-ID: <20140409160108.GU16119@n2100.arm.linux.org.uk> References: <1386922149-4561-1-git-send-email-jonas.jensen@gmail.com> <20140409151326.GY29751@pengutronix.de> <20140409152711.GT16119@n2100.arm.linux.org.uk> <5844640.QRALKyBQaa@wuerfel> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5844640.QRALKyBQaa@wuerfel> 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 05:50:57PM +0200, Arnd Bergmann wrote: > On Wednesday 09 April 2014 16:27:11 Russell King - ARM Linux wrote: > > If it's called from ARM code, then \reg will contain a 4-byte aligned > > address. If it's called from Thumb code, \reg will contain a 2-byte > > aligned address with bit 0 *always* set. > > Right, that is the assumption. > > > So, with the code originally quoted above, if the helper is called from > > thumb code, and CONFIG_CPU_32v4 is enabled, then we end up falling past > > the moveq to the "b ." and entering an infinite loop. > > As Uwe said, that "b ." was not meant to be in the patch used for > submission, it was to check what goes wrong when running this code > on ARMv4 -- either crash user space or hang in an infinite loop. > I forgot what the result of that experiment was. > > The trouble is that this code: > > .macro usr_ret, reg > #ifdef CONFIG_ARM_THUMB > #ifdef CONFIG_CPU_32v4 > tst \reg, #3 > moveq pc, \reg > #endif > bx \reg > #else > mov pc, \reg > #endif > .endm > > for some reason does the wrong thing running on ARMv4 (fa526) with non-thumb > user space when both CONFIG_CPU_32v4 and CONFIG_ARM_THUMB are enabled: > it still tries to do the 'bx' and triggers an invalid opcode exception. I assume this has been discussed in off-list (maybe on some irc channel somewhere), because there's nothing on-list apart from these emails... So, let's repeat the debugging which probably has already occured, but this time on-list... It would be useful to see the register state from the undefined instruction exception. That needs this patch, CONFIG_DEBUG_USER in the kernel config enabled, and user_debug=1 passed on the kernel command line. diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c index 172ee18ff124..abd2fc067736 100644 --- a/arch/arm/kernel/traps.c +++ b/arch/arm/kernel/traps.c @@ -445,6 +445,7 @@ asmlinkage void __exception do_undefinstr(struct pt_regs *regs) if (user_debug & UDBG_UNDEFINED) { printk(KERN_INFO "%s (%d): undefined instruction: pc=%p\n", current->comm, task_pid_nr(current), pc); + __show_regs(regs); dump_instr(KERN_INFO, regs); } #endif -- 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/