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

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Message-ID: <20070315050754.GB22329@verge.net.au>
Date:	Thu, 15 Mar 2007 14:07:56 +0900
From:	Horms <horms@...ge.net.au>
To:	Vivek Goyal <vgoyal@...ibm.com>
Cc:	Ian Campbell <Ian.Campbell@...Source.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 Thu, Mar 15, 2007 at 10:25:36AM +0530, Vivek Goyal wrote:
> On Thu, Mar 15, 2007 at 10:46:38AM +0900, Horms wrote:
> > On Wed, Mar 14, 2007 at 05:00:09PM +0000, Ian Campbell wrote:
> > > 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 to match the domain 0
> > > kernel.
> > > 
> > > It's possibly less likely to be useful in a purely native scenario but I
> > > see no reason to disallow it.
> > 
> > For native Linux, would this cover the case where the pre-crash kernel
> > is 64bit and the crashdump (post-crash) kernel is 32bit?
> > 
> 
> I think so. Though I have never tried this.
> 
> > > Signed-off-by: Ian Campbell <ian.campbell@...source.com>
> > > 
> > > --- pristine-linux-2.6.18/include/asm-i386/elf.h	2006-09-20 04:42:06.000000000 +0100
> > > +++ linux-2.6.18-xen/include/asm-i386/elf.h	2007-03-14 16:42:30.000000000 +0000
> > > @@ -36,7 +36,7 @@
> > >   * This is used to ensure we don't load something for the wrong architecture.
> > >   */
> > >  #define elf_check_arch(x) \
> > > -	(((x)->e_machine == EM_386) || ((x)->e_machine == EM_486))
> > > +	(((x)->e_machine == EM_386) || ((x)->e_machine == EM_486) || ((x)->e_machine == EM_X86_64))
> 
> 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?
> 
> Similarly, load_elf_interp() is using it, again will we allow loading a 
> interp written for X86_64 on a 32bit i386 machine?
> 
> Should we create a separate macro something like elf_check_allowed_arch(),
> to take care of such corner cases?

That sounds reasonable to me. Though perhaps it could just be
kexec_elf_check_arch() for now, as I don't think there are any
other consumers of it.

-- 
Horms
  H: http://www.vergenet.net/~horms/
  W: http://www.valinux.co.jp/en/

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