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

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Message-ID: <m1fycrjn99.fsf@ebiederm.dsl.xmission.com>
Date:	Fri, 10 Nov 2006 09:10:42 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	vgoyal@...ibm.com
Cc:	Magnus Damm <magnus.damm@...il.com>,
	Magnus Damm <magnus@...inux.co.jp>,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@....de>,
	fastboot@...ts.osdl.org, Horms <horms@...ge.net.au>,
	Dave Anderson <anderson@...hat.com>
Subject: Re: [PATCH 02/02] Elf: Align elf notes properly

Vivek Goyal <vgoyal@...ibm.com> writes:
>
> IMHO, I think we should go by the specs (8byte boundary alignment on 64bit
> platforms) until and unless it can be proven that specs are wrong. This
> probably will mean that we will break things for sometime (until and unless
> it is fixed in tool chain and probably will also break the capability to use
> an older kernel for capturing dump). But that's unavoidable if we want to be
> compliant to specs.

I just looked a little more, and the notes gcc generates on x86_64 are only 4
byte aligned. (.note.ABI-tag)

The linux kernel gcc, gdb.  I think that is enough to say that notes need to
be 4 byte aligned on Linux.   The core ELF spec also calls out 4 byte alignment
(although it does not mention ELFCLASS64).

I think the evidence is that someone intended to the alignment to go to 8 bytes
with the move to 64bits but it did not catch on in the real world.

So yes I believe the evidence is quite strong that the spec is wrong. 
(Not on some rare platforms certainly but in general).

Eric
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