linux-kernel - Re: [PATCH] UML - Add a .note.SuSE section

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Date:	Thu, 16 Aug 2007 15:26:39 -0400
From:	Jeff Dike <jdike@...toit.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Andrew Morton <akpm@...l.org>, stable@...nel.org,
	LKML <linux-kernel@...r.kernel.org>,
	uml-devel <user-mode-linux-devel@...ts.sourceforge.net>,
	Alberto Pires de Oliveira Neto <apon1@...ra.com.br>,
	giedrius@...lt
Subject: Re: [PATCH] UML - Add a .note.SuSE section

On Thu, Aug 16, 2007 at 09:30:56AM -0700, Arjan van de Ven wrote:
> this sounds like something really stupid and bad... why would the kernel
> need to have a per-distro note section???

On Thu, Aug 16, 2007 at 09:39:06AM -0700, Chris Wright wrote:
> Huh!?  Why do we need a SuSE section?

On Thu, Aug 16, 2007 at 09:54:55AM -0700, Greg KH wrote:
> I agree, what did we mess up in the SuSE kernel to require such a hack?

Beats the crap out of me.

Drop this patch - it looks like it might just be papering over
symptoms rather than fixing the real problem - see below.

What I do know is that current UML doesn't run when built on a SuSE
host, the UML commit which caused it to break is
c35e584c087381aaa5f1ed40a28b978535c18fb2 

	http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=c35e584c087381aaa5f1ed40a28b978535c18fb2;hp=a5bd1786fb30abe663b904f6d79bba413e9ba883

and the difference between a working UML binary and a broken one is
this:

+  1 .note.ABI-tag 00000020  0000000060000254  0000000060000254  00000254  2**2
+                  CONTENTS, ALLOC, LOAD, READONLY, DATA
+  2 .note.SuSE    00000018  0000000060000274  0000000060000274  00000274  2**2
+                  CONTENTS, ALLOC, LOAD, READONLY, DATA

and the .note.SuSE section makes the difference.

Looking into it a bit further, the contents of the section are:

	objdump --section=.note.SuSE -s uml8796-linux-good

	uml8796-linux-good:     file format elf64-x86-64

	Contents of section .note.SuSE:
	 60000274 05000000 04000000 53755345 53755345  ........SuSESuSE
	 60000284 00000000 01000a02                    ........        

which seems kind of pointless, but also harmless.

The crash is in this section:

  __uml_setup_start = .;
  .uml.setup.init : { *(.uml.setup.init) }
  __uml_setup_end = .;

with &__uml_setup_start being 8 bytes before the start of the first
16-byte structure in .uml.setup.init, so the structures are misaligned
wrt the start symbol.

I don't see any connection between the presence of a section at the
start of the binary and this misalignment, so the patch is probably wrong.

				Jeff

-- 
Work email - jdike at linux dot intel dot com
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