linux-kernel - Re: [PATCH 1/1] Allow i386 crash kernels to handle x86

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Message-Id: <1174029463.28658.25.camel@localhost.localdomain>
Date:	Fri, 16 Mar 2007 07:17:43 +0000
From:	Ian Campbell <Ian.Campbell@...Source.com>
To:	Horms <horms@...ge.net.au>
Cc:	Vivek Goyal <vgoyal@...ibm.com>, hbabu@...ibm.com,
	fastboot@...ts.osdl.org, linux-kernel@...r.kernel.org,
	Magnus Damm <magnus.damm@...il.com>
Subject: Re: [PATCH 1/1] Allow i386 crash kernels to handle x86_64 dumps

On Fri, 2007-03-16 at 08:48 +0900, Horms wrote:
> > > 
> > > Signed-off-by: Ian Campbell <ian.campbell@...source.com>
> > > 
> > > 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)
> > > +
> > 
> > Ideal place for this probably should have been arch dependent crash_dump.h
> > file. But we don't have one and no point introducing one just for this 
> > macro.
> > 
> > This change looks good to me.
> 
> Won't the above change break non i386 archtectures as
> vmcore_elf_check_arch_cross isn't defined for them?

No, because of this hunk:

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
[snip]

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