linux-kernel - Re: RFC: bug in load_elf

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Message-ID: <46EAD121.5080804@goop.org>
Date:	Fri, 14 Sep 2007 11:21:21 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Chris Friesen <cfriesen@...tel.com>
CC:	linux-kernel@...r.kernel.org, Andi Kleen <ak@...e.de>,
	Andrew Morton <akpm@...l.org>,
	James Bottomley <James.Bottomley@...eleye.com>,
	bapper@...atehaven.org, aaw@...gle.com
Subject: Re: RFC: bug in load_elf_binary?

Chris Friesen wrote:
> I believe that's correct.  It's basically the equivalent of BSS, but
> used for an emulated OS (the app in question is an emulator).

Right.

>> Well, you could make the p_offset the same as the first segment with a
>> non-zero filesz.  That should satisfy the elf loader, though it might
>> still confuse things.
>
> Interesting idea.  Worth a try.
>
> However, this doesn't address the kernel side of things.  Am I correct
> in thinking that the kernel is making an invalid assumption that it
> can find the load_addr based on the first segment?

God, that code is such a tangle.  I'm not sure why it particularly cares
about the offset, though perhaps its making sure that (offset %
pagesize) == (vaddr % pagesize), which only matters for filesz>0.

It's not too surprising it falls over with more unconventional ELF files.

>> Why can't you create this mapping at runtime?
>
> Our emulated OS wants to put stuff at fixed addresses in this range,
> so we're trying to keep the loader from allocating stuff there before
> our program gets a chance to start up.

Hm, you might want to have a look at how valgrind gets itself started.

    J
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