Re: PT_NOTE alignment, NT_GNU_PROPERTY_TYPE_0, glibc and gold

[Mark Wielaard <mark at klomp dot org>]

On Wed, Aug 22, 2018 at 11:39:02AM +0200, Florian Weimer wrote:
> glibc 2.28 assumes that no 4-byte-aligned PT_NOTE segments contain GNU
> property notes and will search for such notes in 8-byte aligned segments
> only.  The glibc changes were formally reviewed and checked for
> interoperability with BFD ld.  I think we have (had) community consensus for
> them.

I think there was actually consensus that they were a bad idea.
There is a bug and a fix for BFD ld:
https://sourceware.org/bugzilla/show_bug.cgi?id=22749

Unfortunately it didn't make it before the binutils release:
https://sourceware.org/ml/binutils/2018-01/msg00354.html
Which might have given the impression it wasn't a simple bug.
Sorry about that. I have raised the issue a couple of time,
but apparently not clearly enough.

I think the best thing forward is to actually apply and backport
the fix now (and fix cet.h) to generate proper GNU ELF notes.
It is unfortunate there are a few binaries out there with
these bad notes. But they haven't hit any long term distros
yet. And they should impact only CET, which isnt really
supported anywhere yet because there isn't any hardware
for it.

I understand the appeal of introducing a new section and
segment type for storing these properties, but I fear that
will be much more effort and coordination.

Cheers,

Mark