linux-kernel - Re: [PATCH 02/02] Elf: Align elf notes properly

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Message-ID: <m1psbwzpmx.fsf@ebiederm.dsl.xmission.com>
Date:	Thu, 09 Nov 2006 07:00:22 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Magnus Damm <magnus@...inux.co.jp>
Cc:	linux-kernel@...r.kernel.org, Vivek Goyal <vgoyal@...ibm.com>,
	Andi Kleen <ak@....de>, magnus.damm@...il.com,
	fastboot@...ts.osdl.org, Horms <horms@...ge.net.au>,
	Dave Anderson <anderson@...hat.com>
Subject: Re: [PATCH 02/02] Elf: Align elf notes properly

Magnus Damm <magnus@...inux.co.jp> writes:

> elf: Align elf notes properly
>
> The kernel currently contains several elf note aligment implementations. Most
> implementations follow the spec on 32-bit platforms, but none current aligns
> the notes correctly on 64-bit platforms. This patch tries to fix this by
> interpreting the 64-bit and 32-bit elf specs as the following:
>
> offset bytes name
> 0      4     n_namesz -+                  -+
> 4      4     n_descsz  | elf note header   |
> 8      4     n_type   -+                   | elf note entry size - N4
> 12     N1    name                          |
> N2     N3    desc                         -+
>
> WS = word size in bytes (4 for 32 bit, 8 for 64 bit)
> N1 = roundup(n_namesz + sizeof(elf note header), WS) - sizeof(elf note header)
> N2 = sizeof(elf note header) + N1
> N3 = roundup(n_descsz, WS)
> N4 = sizeof(elf note header) + N1 + N2
>
> The elf note header contains three 32-bit values on 32-bit and 64-bit systems. 
> The header is followed by name and desc data together with padding. The 
> alignment and padding varies depending on the word size.

I see your point and I disagree.  The notes in a kernel generated 
core dump do not vary in size.  Find me some implementation evidence that
anyone ever added the extra 4 bytes of alignment to the description and the
padding fields and I will be ready to consider this.  Currently this
just appears to be reading a draft spec that doesn't match reality.

Eric
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