linux-kernel - Re: [PATCH 12/12] i386 boot: Add an ELF header to bzImage

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Date:	Wed, 04 Oct 2006 08:18:07 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	vgoyal@...ibm.com, Andrew Morton <akpm@...l.org>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Reloc Kernel List <fastboot@...ts.osdl.org>, ak@...e.de,
	horms@...ge.net.au, lace@...kratochvil.net, magnus.damm@...il.com,
	lwang@...hat.com, dzickus@...hat.com, maneesh@...ibm.com
Subject: Re: [PATCH 12/12] i386 boot: Add an ELF header to bzImage

Eric W. Biederman wrote:
> 
>> The entrypoint is going to be a major headache, since the standard kernel is
>> entered in real mode, whereas an ELF file will typically be entered in protected
>> mode, quite possibly using the C calling convention to pass the command line as
>> (argc, argv).  God only knows how they're going to deal with an initrd.
>>
>> It may very well be that the ELF magic number has to be obfuscated.
> 
> The entry point that is exported is the kernels protected mode entry point
> that is used after the real mode code has been run.  This is to allow
> bootloaders like kexec where running the real-mode code is insane or
> impossible to be used.  
> 
> The calling conventions though are not changed, this is just formalizing
> something that various groups have been doing for years.  Since it is
> all in the bzImage we still only have a single file format to support,
> so any bootloader that can load a standard bzImage and run the kernels
> real mode code should still do it that way but.  If you can't the
> rest of the information is available.
> 

Well, it doesn't help if what you end up with for some bootloader is a 
nonfunctioning kernel.

	-hpa
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