[PATCH,RFC] - make /proc/vmcore accesable on x86_64

[Jiri Olsa]

hi,

I was playing around with preserve context feature on x86_64
and was not able to get the /proc/vmcore in the kexec-ed
kernel until I aplied attached patch.

I'm not at all sure this is right fix ;) but it seems
that /proc/vmcore is not loaded since the machine field in the
elf header is wrong.


If the x86_64 arch returns 0 (KEXEC_ARCH_DEFAULT) then following
condition in load_crashdump_segments function will fill 386 as the
machine for the vmcore elf header..

...

        if ((info->kexec_flags & KEXEC_ARCH_MASK) == KEXEC_ARCH_X86_64)
        {
                elf_info.machine = EM_X86_64;
        } else {
                elf_info.machine       = EM_386;
                elf_info.lowmem_limit  = X86_MAXMEM;
                elf_info.get_note_info = get_crash_notes;
        }
...

ending with kexec-ed kernel failing check for the machine,
and disabling vmcore interface...


I'm guessing that the reason is the load_crashdump_segments function
being shared among 32 and 64 bits.. but again, not sure ;)


My goal is to share data within the host and kexec-ed kernel,
so I'd like to use the /proc/vmcore for that.. any other
ideas are welcome :)


thanks,
jirka
---
diff --git a/kexec/arch/i386/crashdump-x86.c b/kexec/arch/i386/crashdump-x86.c
index 06e5ae9..40f989a 100644
--- a/kexec/arch/i386/crashdump-x86.c
+++ b/kexec/arch/i386/crashdump-x86.c
@@ -691,6 +691,8 @@ int load_crashdump_segments(struct kexec_info *info, char* mod_cmdline,
 	struct memory_range *mem_range, *memmap_p;
 	struct crash_elf_info elf_info;
 
+	memset(&elf_info, 0x0, sizeof(elf_info));
+
 	/* Constant parts of the elf_info */
 	elf_info.data             = ELFDATA2LSB;
 	elf_info.backup_src_start = BACKUP_SRC_START;
diff --git a/kexec/arch/x86_64/kexec-x86_64.c b/kexec/arch/x86_64/kexec-x86_64.c
index 3092643..c34fd92 100644
--- a/kexec/arch/x86_64/kexec-x86_64.c
+++ b/kexec/arch/x86_64/kexec-x86_64.c
@@ -134,10 +134,7 @@ int arch_process_options(int argc, char **argv)
 }
 
 const struct arch_map_entry arches[] = {
-	/* For compatibility with older patches
-	 * use KEXEC_ARCH_DEFAULT instead of KEXEC_ARCH_X86_64 here.
-	 */
-	{ "x86_64", KEXEC_ARCH_DEFAULT },
+	{ "x86_64", KEXEC_ARCH_X86_64 },
 	{ NULL, 0 },
 };