Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965485AbZLQTim (ORCPT ); Thu, 17 Dec 2009 14:38:42 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965471AbZLQTik (ORCPT ); Thu, 17 Dec 2009 14:38:40 -0500 Received: from mail2.shareable.org ([80.68.89.115]:56039 "EHLO mail2.shareable.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965464AbZLQTij (ORCPT ); Thu, 17 Dec 2009 14:38:39 -0500 Date: Thu, 17 Dec 2009 19:38:26 +0000 From: Jamie Lokier To: Joe Buck Cc: Russell King - ARM Linux , Richard Guenther , David Daney , "gcc@gcc.gnu.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Subject: Re: [PATCH] ARM: Convert BUG() to use unreachable() Message-ID: <20091217193826.GE362@shareable.org> References: <1260266138-17684-1-git-send-email-u.kleine-koenig@pengutronix.de> <20091217150120.GD24967@shareable.org> <4B2A65C6.7080009@caviumnetworks.com> <84fc9c000912170917y4b2772d0n47bb4dabc74b91ef@mail.gmail.com> <20091217181718.GA4440@n2100.arm.linux.org.uk> <20091217183517.GC10707@synopsys.com> <20091217190613.GB4440@n2100.arm.linux.org.uk> <20091217191401.GD10707@synopsys.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091217191401.GD10707@synopsys.com> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1411 Lines: 32 Joe Buck wrote: > On Thu, Dec 17, 2009 at 11:06:13AM -0800, Russell King - ARM Linux wrote: > > On Thu, Dec 17, 2009 at 10:35:17AM -0800, Joe Buck wrote: > > > Besides, didn't I see a whole bunch of kernel security patches related > > > to null pointer dereferences lately? If page 0 can be mapped, you > > > suddenly won't get your trap. > > > > Page 0 can not be mapped on ARM kernels since the late 1990s, and this > > protection is independent of the generic kernel. > > > > Milage may vary on other architectures, but that's not a concern here. It does not trap on at least one ARM-nommu kernel... > I don't understand, though, why you would want to implement a generally > useful facility (make the kernel trap so you can do a post-mortem > analysis) in a way that's only safe for the ARM port. The patch under discussion, which led to these questions and Cc gcc@gcc.gnu.org, is specific to the ARM architecture and that is Russell's focus, as ARM kernel maintainer. But yes, the whole principle of how to trap and whether it's safe to follow a null pointer dereference with __builtin_unreachable() applies to all the other architectures too. -- Jamie -- 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/