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

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Message-Id: <JMVTP7$E1B1C27F58AFF22330472C8DFD9A4C5B@multidominios>
Date:	Thu, 16 Aug 2007 16:48:43 -0300
From:	"Alberto Pires de Oliveira Neto" <apon1@...ra.com.br>
To:	"jdike" <jdike@...toit.com>
Cc:	"arjan" <arjan@...radead.org>, "akpm" <akpm@...l.org>,
	"stable" <stable@...nel.org>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	"user-mode-linux-devel" <user-mode-linux-devel@...ts.sourceforge.net>,
	"giedrius" <giedrius@...lt>
Subject: Re:[Spam] Re: [PATCH] UML - Add a .note.SuSE section

Hi Jeff,

  I'm really sorry, but I forget to mention, that I had the same problems on a RedHat RH4 (x86_64) too. 

> 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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