From mboxrd@z Thu Jan 1 00:00:00 1970 From: Catalin Marinas Subject: Re: [PATCH v3 02/31] arm64: Kernel booting and initialisation Date: Mon, 10 Sep 2012 15:53:29 +0100 Message-ID: <20120910145329.GE27042@arm.com> References: <1347035226-18649-1-git-send-email-catalin.marinas@arm.com> <201209101353.34325.arnd@arndb.de> <201209101448.20745.arnd@arndb.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:43000 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753060Ab2IJOyL (ORCPT ); Mon, 10 Sep 2012 10:54:11 -0400 Content-Disposition: inline In-Reply-To: <201209101448.20745.arnd@arndb.de> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Arnd Bergmann Cc: Nicolas Pitre , Jean-Christophe PLAGNIOL-VILLARD , "linux-arch@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" On Mon, Sep 10, 2012 at 03:48:20PM +0100, Arnd Bergmann wrote: > On Monday 10 September 2012, Nicolas Pitre wrote: > > On Mon, 10 Sep 2012, Arnd Bergmann wrote: > > > On Monday 10 September 2012, Catalin Marinas wrote: > > > > On Mon, Sep 10, 2012 at 06:53:39AM +0100, Jean-Christophe PLAGNIOL-VILLARD wrote: > > > I think a bunch of other architectures can have relocatable kernels, which > > > is useful e.g. for kdump. It does imply a small runtime cost and may have > > > other disadvantages though. > > > > Relocatable in physical space is what kdump actually needs, and that's > > what we already have here (as well as on ARM32 for that matter with > > CONFIG_ARM_PATCH_PHYS_VIRT). Relocatable in the virtual space is costly > > and we shouldn't need to go there. > > Ah, I see. I thought that the other architectures (powerpc and x86) > doing this were actually building with -fPIC, but they do the same > kind of early patching that we do. On arm64 I don't have run-time code patching (yet) but a PHYS_OFFSET variable set at boot time. It may prove useful to have run-time code patching but that's just an optimisation that can be added later. -- Catalin From mboxrd@z Thu Jan 1 00:00:00 1970 From: catalin.marinas@arm.com (Catalin Marinas) Date: Mon, 10 Sep 2012 15:53:29 +0100 Subject: [PATCH v3 02/31] arm64: Kernel booting and initialisation In-Reply-To: <201209101448.20745.arnd@arndb.de> References: <1347035226-18649-1-git-send-email-catalin.marinas@arm.com> <201209101353.34325.arnd@arndb.de> <201209101448.20745.arnd@arndb.de> Message-ID: <20120910145329.GE27042@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Sep 10, 2012 at 03:48:20PM +0100, Arnd Bergmann wrote: > On Monday 10 September 2012, Nicolas Pitre wrote: > > On Mon, 10 Sep 2012, Arnd Bergmann wrote: > > > On Monday 10 September 2012, Catalin Marinas wrote: > > > > On Mon, Sep 10, 2012 at 06:53:39AM +0100, Jean-Christophe PLAGNIOL-VILLARD wrote: > > > I think a bunch of other architectures can have relocatable kernels, which > > > is useful e.g. for kdump. It does imply a small runtime cost and may have > > > other disadvantages though. > > > > Relocatable in physical space is what kdump actually needs, and that's > > what we already have here (as well as on ARM32 for that matter with > > CONFIG_ARM_PATCH_PHYS_VIRT). Relocatable in the virtual space is costly > > and we shouldn't need to go there. > > Ah, I see. I thought that the other architectures (powerpc and x86) > doing this were actually building with -fPIC, but they do the same > kind of early patching that we do. On arm64 I don't have run-time code patching (yet) but a PHYS_OFFSET variable set at boot time. It may prove useful to have run-time code patching but that's just an optimisation that can be added later. -- Catalin