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

From: Eric W. Biederman
Date: Thu Nov 09 2006 - 09:03:13 EST


Magnus Damm <magnus@xxxxxxxxxxxxx> 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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