From mboxrd@z Thu Jan 1 00:00:00 1970 From: Russell King - ARM Linux Subject: Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig Date: Tue, 22 Apr 2014 19:12:52 +0100 Message-ID: <20140422181252.GX24070@n2100.arm.linux.org.uk> References: <534D0D91.8020406@linaro.org> <534EAD6C.3040502@codeaurora.org> <534EF153.5050603@codeaurora.org> <53501E87.6070307@codeaurora.org> <20140417203521.GB22411@obsidianresearch.com> <535681A4.1080402@monstr.eu> <20140422171141.GW24070@n2100.arm.linux.org.uk> <20140422175325.GD23955@obsidianresearch.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from gw-1.arm.linux.org.uk ([78.32.30.217]:44161 "EHLO pandora.arm.linux.org.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750974AbaDVSNs (ORCPT ); Tue, 22 Apr 2014 14:13:48 -0400 Content-Disposition: inline In-Reply-To: <20140422175325.GD23955@obsidianresearch.com> Sender: linux-arm-msm-owner@vger.kernel.org List-Id: linux-arm-msm@vger.kernel.org To: Jason Gunthorpe Cc: Michal Simek , Nicolas Pitre , Peter Maydell , Daniel Thompson , Joel Fernandes , linux-arm-msm@vger.kernel.org, Stephen Boyd , Peter Crosthwaite , QEMU Developers , Christopher Covington , linux-arm-kernel@lists.infradead.org On Tue, Apr 22, 2014 at 11:53:25AM -0600, Jason Gunthorpe wrote: > On Tue, Apr 22, 2014 at 06:11:42PM +0100, Russell King - ARM Linux wrote: > > > Put another way, if your platform is part of the multi-platform kernel > > then you are *excluded* from being able to use this... unless you hack > > the Kconfig, and then also provide a constant value for PHYS_OFFSET, > > thereby _tying_ the kernel you built to a _single_ platform. > > That is exactly right. To get a fixed LMA you must commit to a > non-relocatable kernel image. > > Realistically this patch would need to be accompanied by something > that makes ARM_PATCH_PHYS_VIRT optional for multiplatform based on > EXPERT or similar. > > The best usecase seems to be to support ELF tooling for low level > debugging activities, a non-relocatable image isn't a blocker for that > case. Let's not forget that if you want to debug, it's because you've hit a problem in the kernel you're running. To get an ELF image you can debug, you have to turn ARM_PATCH_PHYS_VIRT off, which changes the generated code - which can in itself cause bugs to hide themselves. Unfortunately, those kinds of bugs are not as rare as you might think. > Since the patch is a no-op if LOAD_OFFSET isn't set, is there a > downside I don't see? It leads people into thinking that we support booting an ELF file. We don't. -- FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly improving, and getting towards what was expected from it.