On 11/10/06, Horms <[email protected]> wrote:
On Thu, Nov 09, 2006 at 07:00:22AM -0700, Eric W. Biederman wrote:
> Magnus Damm <[email protected]> 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.
Or perhaps a spec that hasn't been implemented correctly.
I guess that the real question is, what padding is correct?
I see no point in aligning to 32-bit boundaries on 64-bit platforms.
Their intention was most likely to align to the word size IMO, so this
is most likely a "thinko" left over from whoever ported the code from
32-bit to 64-bit.
How we chose to align on 64-bit platforms is another issue, either we
fix it soon or live with the fact that we are not following the 64-bit
draft spec. Either way is fine with me.
/ magnus
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