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Message-ID: <4702EA68.3090900@zytor.com>
Date: Tue, 02 Oct 2007 18:03:36 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Jeremy Fitzhardinge <jeremy@...p.org>
CC: Rusty Russell <rusty@...tcorp.com.au>,
lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
Vivek Goyal <vgoyal@...ibm.com>, lguest <lguest@...abs.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH 0/5] Boot protocol changes
Jeremy Fitzhardinge wrote:
> H. Peter Anvin wrote:
>> I'm proposing that the existing bzImage format be retained, but that
>> the payload of the decompressor (already a gzip file) simply be
>> vmlinux.gz -- i.e. a gzip compressed ELF file, notes and all. A
>> pointer in the header will point to the offset of the payload (this is
>> new, obviously.)
>>
>> The decompression stub is adjusted to expect an ELF image, instead of
>> a raw binary.
>
> It could, or just treat it as a raw binary at 1M+offset to skip the headers.
It would be cleaner to actually parse the ELF; it's only a handful of
lines of code (we don't have to support arbitrary placement of sections,
obviously, which makes the problem simpler.)
>> Existing bootloaders (16- or 32-bit) simply load the bzImage the way
>> they do now; new bootloaders have the option of accessing the
>> vmlinux.gz directly if they either want to load it themselves or want
>> to examine the notes.
>
> OK, but that has the same problem as making the payload an ELF file:
> 32-bit bootloaders which simply jump to 1M will be jumping into data
> rather than code - and I got the impression from taking to Eric at KS
> that there are such bootloaders.
Uhm, no it doesn't. Those bootloaders jump to the decompressor, not to
the payload. The decompressor interface hasn't changed.
> If that's not an issue, then I still think the payload should be a plain
> ELF file (possibly self-decompressing, or just a plain uncompressed
> vmlinux, if that's what's desired). Still think making a protected-mode
> bootloader do the decompression is the wrong way to go about this; ELF
> is enough.
It doesn't have to if it doesn't want to; it only needs to do so if it
wants to access the kernel as an ELF. Again, it has the advantage that
the ELF is the real vmlinux, no funnies.
-hpa
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