linux-kernel - Re: Re : [PATCH] Compressed ia32 ELF file generation for loading by Gujin 1/3

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Message-ID: <20070207064432.GB12170@in.ibm.com>
Date:	Wed, 7 Feb 2007 12:14:32 +0530
From:	Vivek Goyal <vgoyal@...ibm.com>
To:	Etienne Lorrain <etienne_lorrain@...oo.fr>
Cc:	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: Re : [PATCH] Compressed ia32 ELF file generation for loading by Gujin 1/3

On Tue, Feb 06, 2007 at 01:12:05PM +0000, Etienne Lorrain wrote:
> > Building real mode code with kernel binary (vmlinux) has got another
> > disadvantage that it breaks using vmlinux for kdump purposes. One compiles
> > the kernel binary to execute from a different address but real mode code/data
> > will continue to be at virtual/physical addr 0 and kexec can not load it
> > as that physical memory is not available at all. Kdump skips the real mode
> > code execution.
> 
>  But that is exactly what you want and need for kdump, isn't it?
>  The ELF file did not change, the program header has the last index at
> address 0 that you do not want to load because you do not want to
> execute the real-mode code. Load the rest and provide the 4 Kbytes
> parameter page - it should work.

How do I know which program header is real mode code and the boot loader
is not supposed to load it? May be PT_LOAD header with physical addr 0?
What happens if changes happen and down the line we start compiling 
real mode code for non-zero address? Hence I think keeping real mode
code out of vmlinux might prove to be a good idea.

Secondly, if you compile real mode code with vmlinux, what would be the
entry point for this ELF file? Real mode entry? Then I have not way to
find out from ELF headers where is the protected mode entry point and
I can not do use this vmlinux with kexec/kdump. 

OTOH, now bzImage is relocatable. Is this image going to be relocatable?
How do we take care of that?

Thanks
Vivek
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