linux-kernel - Re: [RFC] ELF Relocatable x86 and x86

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Date:	Tue, 8 Aug 2006 13:57:10 +0900
From:	"Magnus Damm" <magnus.damm@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Horms <horms@...ge.net.au>,
	"Eric W. Biederman" <ebiederm@...ssion.com>, vgoyal@...ibm.com,
	fastboot@...l.org, linux-kernel@...r.kernel.org,
	"Jan Kratochvil" <lace@...kratochvil.net>,
	"Linda Wang" <lwang@...hat.com>
Subject: Re: [RFC] ELF Relocatable x86 and x86_64 bzImages

On 8/8/06, H. Peter Anvin <hpa@...or.com> wrote:
> Horms wrote:
> >
> > I also agree that it is non-intitive. But I wonder if a cleaner
> > fix would be to remove CONFIG_PHYSICAL_START all together. Isn't
> > it just a work around for the kernel not being relocatable, or
> > are there uses for it that relocation can't replace?
> >
>
> Yes, booting with the 2^n existing bootloaders.
>
> Relocation, as far as I've understood this patch, refers to loaded
> address, not runtime address.

I believe Erics patch implements the following (correct me if I'm wrong):

vmlinux:
vmlinux is extended to contain relocation information. Absolute
symbols are used for non-relocatable symbols, and section-relative
symbols are used for relocatable symbols.

bzImage loader:
The bzImage loader code is no longer required to be loaded at a fixed
address. The bzImage file contains vmlinux relocation information and
the bzImage loader adjusts the relocations in vmlinux before executing
it.

So I would say that the runtime address of symbols in vmlinux are
changed by the bzImage loader. Or maybe I'm misunderstanding?

/ magnus
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