From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 12324 invoked by alias); 17 Dec 2009 19:49:07 -0000 Received: (qmail 12305 invoked by uid 22791); 17 Dec 2009 19:49:04 -0000 X-SWARE-Spam-Status: No, hits=-2.6 required=5.0 tests=AWL,BAYES_00 X-Spam-Check-By: sourceware.org Received: from caramon.arm.linux.org.uk (HELO caramon.arm.linux.org.uk) (78.32.30.218) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Thu, 17 Dec 2009 19:49:00 +0000 Received: from n2100.arm.linux.org.uk ([2002:4e20:1eda:1:214:fdff:fe10:4f86]) by caramon.arm.linux.org.uk with esmtpsa (TLSv1:AES256-SHA:256) (Exim 4.69) (envelope-from ) id 1NLML1-00020y-E1; Thu, 17 Dec 2009 19:48:39 +0000 Received: from linux by n2100.arm.linux.org.uk with local (Exim 4.69) (envelope-from ) id 1NLMKz-0003nc-Gv; Thu, 17 Dec 2009 19:48:37 +0000 Date: Thu, 17 Dec 2009 19:49:00 -0000 From: Russell King - ARM Linux To: Jamie Lokier Cc: Joe Buck , 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: <20091217194837.GD4440@n2100.arm.linux.org.uk> 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> <20091217193826.GE362@shareable.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091217193826.GE362@shareable.org> User-Agent: Mutt/1.5.18 (2008-05-17) Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-owner@gcc.gnu.org X-SW-Source: 2009-12/txt/msg00265.txt.bz2 On Thu, Dec 17, 2009 at 07:38:26PM +0000, Jamie Lokier wrote: > 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 was going to say the following in a different reply but discarded it because it wasn't relevant to the GCC list. I regard ARM nommu as highly experimental, especially as the maintainer vanished half way through merging it into mainline. I know that there are some parts of ARM nommu that are highly buggy - such as ARM940 support invalidating the entire data cache on any DMA transaction... say goodbye stacked return addresses. As such, I would not be surprised if the ARM nommu kernel has _lots_ of weird and wonderful bugs. I am not surprised that NULL pointer dereferences don't work - its actually something I'd expect given that they have a protection unit which the kernel doesn't apparently touch. Maybe the protection unit code never got merged? I've no idea. As I say, uclinux support got as far as being half merged and that's roughly the state it's remained in ever since. We don't even have any no-MMU configurations which the kernel builder automatically tests for us. Given the lack of progress/bug reporting on ARM uclinux, the lack of platform support and the lack of configurations, my view is that there is no one actually using it. I know that I don't particularly take any care with respect to uclinux when making changes to the MMU based kernels. Why bother if apparantly no one's using it?