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

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Date:	Tue, 6 Feb 2007 13:12:05 +0000 (GMT)
From:	Etienne Lorrain <etienne_lorrain@...oo.fr>
To:	vgoyal@...ibm.com, "H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re : [PATCH] Compressed ia32 ELF file generation for loading by Gujin 1/3

> 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.

> I don't know much about Gujin, but advantage here seems to be that it has
> capability to load elf files and that's why the attempt to turn kernel binary
> into a compressed elf image. Why don't we then simply add an ELF header to
> bzImage and Gujin and any ELF loader including Gujin, should be able to load
> it? (As Eric had done in one of the implementations in the past?) Why to 
>create the new infrastructure?

 Because I think when a program evolves it has to get simpler to generate,
run and maintain/debug - while doing more stuff. The number of assembler
lines has to reduce because they are difficult to maintain.
 Removing a ELF header to modify the binary and stick another ELF header
is not exactly what I think simpler - a bit like linking at a fix address and
then modifying the whole set.

HPA wrote:
> Well, Gujin wants additional code too.
> Putting an ELF header on bzImage broke some bootloaders (GRUB, I believe),
> so that's not going to happen again. See the relocatable bzImage thread...

  I also refuses to load a big file at a fixed address before asking the BIOS
 for information, I only crash once the memory when I am pretty sure everything
 seems alright, interruption disabled, just before jumping to the kernel
 entry point. Cannot do that with bzImage. Cannot easily debug without
 this feature.

> Thanks
> Vivek

  Thanks for you comment.
 Etienne.

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