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

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Date:	Fri, 16 Mar 2007 07:28:17 +0000
From:	Ian Campbell <Ian.Campbell@...Source.com>
To:	Magnus Damm <magnus.damm@...il.com>
Cc:	Horms <horms@...ge.net.au>, Vivek Goyal <vgoyal@...ibm.com>,
	fastboot@...ts.osdl.org, linux-kernel@...r.kernel.org
Subject: Re: [Fastboot] [PATCH 1/1] Allow i386 crash kernels to handle
	x86_64 dumps

On Fri, 2007-03-16 at 11:40 +0900, Magnus Damm wrote:
> Right. And maybe it's a good idea to make sure that this feature is
> actually supported by kexec-tools before adding code to the kernel?

I sent patches to the fastboot list at the same time I sent these ones
to support differences in the underlying hypervisor architecture in the
tools.

They haven't appeared in the archives yet so I fear they have gone
astray. I'll resend when I get to the office in a bit.

The tools already have support for introducing a SHIM when kexecing
between different architectures (at least in the 64->32 direction if I
understand kexec-tools-testing/purgatory/arch/i386/compat_x86_64.S and
k-t-t.../kexec/arch/i386/compat_x86_64.S correctly). This is really just
an extension of that.

> My gut feeling about this is that you are begging for trouble. The
> kexec/kdump solution is fragile just by itself, and trying to go
> between architectures is just going to be painful.

It works fine under Xen and I think going from 64Xen+32Kernel->32Kernel
makes more sense than going from 64Xen+32Kernel->64Kernel. As I said
originally I'm not so convinced it makes sense in the native case but I
see no reason to outlaw it (people get to keep both pieces etc...)

Ian.

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