From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933536AbXCOMXH (ORCPT ); Thu, 15 Mar 2007 08:23:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933537AbXCOMXH (ORCPT ); Thu, 15 Mar 2007 08:23:07 -0400 Received: from 207.47.60.147.static.nextweb.net ([207.47.60.147]:48671 "EHLO webmail.xensource.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S933536AbXCOMXD (ORCPT ); Thu, 15 Mar 2007 08:23:03 -0400 Subject: Re: [PATCH 1/1] Allow i386 crash kernels to handle x86_64 dumps From: Ian Campbell To: vgoyal@in.ibm.com Cc: Horms , hbabu@us.ibm.com, fastboot@lists.osdl.org, linux-kernel@vger.kernel.org, Magnus Damm In-Reply-To: <20070315054726.GC6766@in.ibm.com> References: <1173891609.8591.41.camel@localhost.localdomain> <20070315014635.GC28396@verge.net.au> <20070315045536.GA6766@in.ibm.com> <20070315050754.GB22329@verge.net.au> <20070315054726.GC6766@in.ibm.com> Content-Type: text/plain Date: Thu, 15 Mar 2007 12:22:57 +0000 Message-Id: <1173961378.8591.63.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.6.3 Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 15 Mar 2007 12:23:01.0985 (UTC) FILETIME=[ACC6CD10:01C766FC] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2007-03-15 at 11:17 +0530, Vivek Goyal wrote: > > > But I think changing this macro might run into issues. It is > > > being used at few places in kernel, for example while loading > > > module. This will essentially mean that we allow loading 64bit > > > x86_64 modules on 32bit i386 systems? Yes, not sure how I missed that fact... > Kexec will also not allow loading an x86_64 kernel on a 32bit machine. For crash kernel only or for regular kexec too? > So how about something like vmcore_elf_allowed_cross_arch()? Vmcore > code can continue to check elf_check_arch() and if that fails it can > invoke vmcore_elf_allowed_cross_arch() to find out what cross arch are > allowed for vmcore. Something like this? Ian. --- Allow i386 crash kernels to handle x86_64 dumps. The specific case I am encountering is kdump under Xen with a 64 bit hypervisor and 32 bit kernel/userspace. The dump created is a 64 bit due to the hypervisor but the dump kernel is 32 bit in for maximum compatibility. It's possibly less likely to be useful in a purely native scenario but I see no reason to disallow it. Signed-off-by: Ian Campbell diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c index d960507..523e109 100644 --- a/fs/proc/vmcore.c +++ b/fs/proc/vmcore.c @@ -514,7 +514,7 @@ static int __init parse_crash_elf64_headers(void) /* Do some basic Verification. */ if (memcmp(ehdr.e_ident, ELFMAG, SELFMAG) != 0 || (ehdr.e_type != ET_CORE) || - !elf_check_arch(&ehdr) || + !vmcore_elf_check_arch(&ehdr) || ehdr.e_ident[EI_CLASS] != ELFCLASS64 || ehdr.e_ident[EI_VERSION] != EV_CURRENT || ehdr.e_version != EV_CURRENT || diff --git a/include/asm-i386/kexec.h b/include/asm-i386/kexec.h index 4dfc9f5..c76737e 100644 --- a/include/asm-i386/kexec.h +++ b/include/asm-i386/kexec.h @@ -47,6 +47,9 @@ /* The native architecture */ #define KEXEC_ARCH KEXEC_ARCH_386 +/* We can also handle crash dumps from 64 bit kernel. */ +#define vmcore_elf_check_arch_cross(x) ((x)->e_machine == EM_X86_64) + #define MAX_NOTE_BYTES 1024 /* CPU does not save ss and esp on stack if execution is already diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h index 3250365..db60dac 100644 --- a/include/linux/crash_dump.h +++ b/include/linux/crash_dump.h @@ -14,5 +14,13 @@ extern ssize_t copy_oldmem_page(unsigned long, char *, size_t, extern const struct file_operations proc_vmcore_operations; extern struct proc_dir_entry *proc_vmcore; +/* Architecture code defines this if there are other possible ELF + * machine types, e.g. on bi-arch capable hardware. */ +#ifndef vmcore_elf_check_arch_cross(x) +#define vmcore_elf_check_arch_cross(x) 0 +#endif + +#define vmcore_elf_check_arch(x) (elf_check_arch(x) || vmcore_elf_check_arch_cross(x)) + #endif /* CONFIG_CRASH_DUMP */ #endif /* LINUX_CRASHDUMP_H */