linux-kernel - Re: PATCH/RFC: bzImage payload as compressed ELF file.

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Date:	Tue, 29 Jan 2008 20:38:32 +0000
From:	Ian Campbell <ijc@...lion.org.uk>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: PATCH/RFC: bzImage payload as compressed ELF file.


On Tue, 2008-01-29 at 10:34 -0800, H. Peter Anvin wrote:
> Jeremy Fitzhardinge wrote:
> > H. Peter Anvin wrote:
> >> It's also easy enough to either use objdump -h or nm to extract info 
> >> from vmlinux; or for some of the simpler stuff, just parse the ELF 
> >> directly (perhaps using libelf).
> >>
> >> There is also the -R option to ld, which imports symbols from one 
> >> executable into another. 
> > 
> > Yes, I used -R, though it was necessary to generate a copy of vmlinux 
> > with a filtered symbol list to prevent collisions.  But I'm not sure any 
> > of this is necessary with Ian's approach.
> > 
> 
> Probably isn't.  He just need the start and possibly length of the 
> payload section, which should be objdump -h or equivalently reading the 
> ELF section table.

I'm currently using "objcopy --extract-symbol -w -N \* -K input_data" to
create a .o with just the symbol I'm interested in and using -R on that.
There's also an option to add a prefix to all symbols which might be
useful.

I finessed the length issue slightly since it happens that the word
before the payload is the payload's length. I'm mulling a variety of
options:
      * declare it compression scheme dependant. At least for gzip it
        knows when it has reached the end.
      * codify the length followed by data thing we happen to have now
      * add a length field to the header, using another 4 bytes (is
        there any pressure on the size of the header?).

I'd probably go with the later unless we are pressed for space in the
header.

Ian.
-- 
Ian Campbell

Man who falls in vat of molten optical glass makes spectacle of self.

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