Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161577AbWHDW4r (ORCPT ); Fri, 4 Aug 2006 18:56:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161576AbWHDW4r (ORCPT ); Fri, 4 Aug 2006 18:56:47 -0400 Received: from e33.co.us.ibm.com ([32.97.110.151]:6805 "EHLO e33.co.us.ibm.com") by vger.kernel.org with ESMTP id S1161574AbWHDW4q (ORCPT ); Fri, 4 Aug 2006 18:56:46 -0400 Date: Fri, 4 Aug 2006 18:56:11 -0400 From: Vivek Goyal To: "Eric W. Biederman" Cc: fastboot@osdl.org, linux-kernel@vger.kernel.org, Horms , Jan Kratochvil , "H. Peter Anvin" , Magnus Damm , Linda Wang Subject: Re: [RFC] ELF Relocatable x86 and x86_64 bzImages Message-ID: <20060804225611.GG19244@in.ibm.com> Reply-To: vgoyal@in.ibm.com References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4287 Lines: 125 On Tue, Aug 01, 2006 at 04:58:49AM -0600, Eric W. Biederman wrote: > > The problem: > > We can't always run the kernel at 1MB or 2MB, and so people who need > different addresses must build multiple kernels. The bzImage format > can't even represent loading a kernel at other than it's default address. > With kexec on panic now starting to be used by distros having a kernel > not running at the default load address is starting to become common. > Hi Eric, There seems to be a small anomaly in the current set of patches for i386. For example if one compiles the kernel with CONFIG_RELOCATABLE=y and CONFIG_PHYSICAL_START=0x400000 (4MB) and he uses grub to load the kernel then kernel would run from 1MB location. I think user would expect it to run from 4MB location. I think distro's might want to keep above config options enabled. CONFIG_RELOCATABLE=y so that kexec can load kdump kernel at a different address and CONFIG_PHYSICAL_START=non 1MB location, to extract better performance. (As we had discussions on mailing list some time back.) In principle this is a limitation on boot-loaders part but as we can not fix the boot-loaders out there, probably we can try fixing it at kernel level. What I have done here is that decompressor code will determine the final resting place of the kernel based on boot loader type. So if I have been loaded by kexec, I am supposed to run from loaded address otherwise I am supposed to run from CONFIG_PHYSICAL_START as I have been loaded at 1MB address due to boot loader limitation and that's not the intention. A prototype patch is attached with the mail. I have assumed that I can assign a boot loader type id 9 to kexec (Documentation/i386/boot.txt). Also assuming that all other boot loaders apart from kexec have got 1MB limitation. If not, its trivial to include their boot loader ids also. I have tested this patch and it works fine. What do you think about this approach ? Thanks Vivek Signed-off-by: Vivek Goyal --- arch/i386/boot/compressed/head.S | 32 ++++++++++++++++++++++++++++++-- 1 file changed, 30 insertions(+), 2 deletions(-) diff -puN arch/i386/boot/compressed/head.S~debug1-patch arch/i386/boot/compressed/head.S --- linux-2.6.18-rc3-1M/arch/i386/boot/compressed/head.S~debug1-patch 2006-08-04 18:03:02.000000000 -0400 +++ linux-2.6.18-rc3-1M-root/arch/i386/boot/compressed/head.S 2006-08-04 18:18:26.000000000 -0400 @@ -60,13 +60,32 @@ startup_32: * a relocatable kernel this is the delta to our load address otherwise * this is the delta to CONFIG_PHYSICAL start. */ + #ifdef CONFIG_RELOCTABLE + /* If loaded by non kexec boot loader, then we will be loaded + * at 1MB fixed address. But probably the intention is to run + * from a address for which kernel has been compiled which can + * be non 1MB. + */ + xorl %eax, %eax + movb 0x210(%esi), %al + + / * check boot loader type. Kexec bootloader id 9, version any */ + shrl $4, %eax + subl $0x9, %eax + jnz 1f + + /* Run kernel from the location it has been loaded at. */ movl %ebp, %ebx + jmp 2f + + /* Run the kernel from compiled destination location. */ +1: movl $(CONFIG_PHYSICAL_START - startup32), %ebx #else movl $(CONFIG_PHYSICAL_START - startup_32), %ebx #endif - /* Replace the compressed data size with the uncompressed size */ +2: /* Replace the compressed data size with the uncompressed size */ subl input_len(%ebp), %ebx movl output_len(%ebp), %eax addl %eax, %ebx @@ -95,7 +114,16 @@ startup_32: /* Compute the kernel start address. */ #ifdef CONFIG_RELOCATABLE + xorl %eax, %eax + movb 0x210(%esi), %al + / * check boot loader type. Kexec bootloader id 9, version any */ + shrl $4, %eax + subl $0x9, %eax + jnz 3f leal startup_32(%ebp), %ebp + jmp 4f +3: + movl $CONFIG_PHYSICAL_START, %ebp #else movl $CONFIG_PHYSICAL_START, %ebp #endif @@ -103,7 +131,7 @@ startup_32: /* * Jump to the relocated address. */ - leal relocated(%ebx), %eax +4: leal relocated(%ebx), %eax jmp *%eax .section ".text" relocated: _ - 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/