i386: Allow i386 crash kernels to handle x86_64 dumps From: Ian Campbell The specific case I am encountering is kdump under Xen with a 64 bit hypervisor and 32 bit kernel/userspace. The dump created is 64 bit due to the hypervisor but the dump kernel is 32 bit for maximum compatibility. It's possibly less likely to be useful in a purely native scenario but I see no reason to disallow it. [akpm@linux-foundation.org: build fix] Signed-off-by: Ian Campbell Signed-off-by: Andi Kleen Acked-by: Vivek Goyal Cc: Horms Cc: Magnus Damm Cc: "Eric W. Biederman" Cc: Andi Kleen Signed-off-by: Andrew Morton --- fs/proc/vmcore.c | 2 +- include/asm-i386/kexec.h | 3 +++ include/linux/crash_dump.h | 8 ++++++++ 3 files changed, 12 insertions(+), 1 deletion(-) Index: linux/fs/proc/vmcore.c =================================================================== --- linux.orig/fs/proc/vmcore.c +++ linux/fs/proc/vmcore.c @@ -514,7 +514,7 @@ static int __init parse_crash_elf64_head /* 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 || Index: linux/include/asm-i386/kexec.h =================================================================== --- linux.orig/include/asm-i386/kexec.h +++ linux/include/asm-i386/kexec.h @@ -42,6 +42,9 @@ /* 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 Index: linux/include/linux/crash_dump.h =================================================================== --- linux.orig/include/linux/crash_dump.h +++ linux/include/linux/crash_dump.h @@ -14,5 +14,13 @@ extern ssize_t copy_oldmem_page(unsigned 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 +#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 */