linux-kernel - Re: [PATCH 1/2] x86_64: Reflect the relocatability of the kernel in the ELF header.

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Message-ID: <m14pmx18ey.fsf@ebiederm.dsl.xmission.com>
Date:	Mon, 30 Apr 2007 22:20:53 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	vgoyal@...ibm.com
Cc:	Andi Kleen <ak@...e.de>,
	Kexec Mailing List <kexec@...ts.infradead.org>,
	linux-kernel@...r.kernel.org, Jurriaan <thunder7@...all.nl>,
	Helge Hafting <helgehaf@...el.hist.no>,
	Horms <horms@...ge.net.au>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] x86_64: Reflect the relocatability of the kernel in the ELF header.

Vivek Goyal <vgoyal@...ibm.com> writes:

> On Mon, Apr 30, 2007 at 05:17:07PM +0200, Andi Kleen wrote:
>> On Monday 30 April 2007 17:12:39 Eric W. Biederman wrote:
>> > 
>> > Currently because vmlinux does not reflect that the kernel is relocatable
>> > we still have to support CONFIG_PHYSICAL_START.  So this patch adds a small
>> > c program to do what we cannot do with a linker script set the elf header
>> > type to ET_DYN.
>> > 
>> > Since last time I have fixed the type to be in my code ET_DYN (oops),
>> > and verified this works with kexec.  I realized while testing that we
>> > don't have anyway of identifying a kernel vmlinux as linux so we
>> > probably want to add an ELF note but that will be another patch.
>> 
>> The patch is ok for me, but does it pass Vivek's usual testing?
>
> I am facing one issue with this patch. gdb can not analyze the
> resulting kernel core file. Looks like gdb treats vmlinux differently if
> ELF header type is "ET_DYN". It reads the symbol values incorrectly.

Weird.

> For example, symbol value of "panic_timeout" is 0xffffffff808a1fa8 but
> gdb somehow things that it is 0xffffffff008aaebf. Looks like it is
> performing some relocation.
>
> I am using GNU gdb Red Hat Linux (6.5-5.fc6rh).

Does it take a kernel core file to reproduce this problem?
Or can you just open up gdb on a vmlinux and look at the symbol
address?

At least without a core file it is working on with gdb 6.4.

Eric
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