Re: [PATCH, BFD, LD, AArch64, 0/4] Add support for AArch64 BTI and PAC in the linker

[Peter Smith <peter.smith@linaro.org>]

On Thu, 7 Mar 2019 at 14:28, Sudakshina Das <Sudi.Das@arm.com> wrote:
>
> Hi Nick
>
> On 07/03/2019 12:37, Nick Clifton wrote:
> > Hi Sudi,
> >
> >    [This is me being kind :-) ...]
>
> Thank you :)
> >
> >> We introduce a new set of command line options for the linker in order
> >> to support the correct PLTs
> >
> > Are you also planning on creating patches for GOLD and LLD to support
> > these features ?  If so, it would probably be best to submit them at
> > the same time as the BFD linker patches.
>
> I am CC'ing Peter who would be better able to answer about LLD and GOLD.

I've got LLD work on my backlog at the moment. It will likely need to
be coordinated with support for Intel CET
(https://reviews.llvm.org/D58102), which introduces .note.gnu.property
to LLD. Gold is of a lower priority right now, at least for Linaro,
with the most likely outcome that it will be worked on when a project
needs it, most likely when this feature is present in platforms that
people use gold to build applications with.

> > The document does not appear to specify what the loader should do if
> > there is more than one GNU_PROPERTY_AARCh64_FEATURE_1_AND note in an
> > executable.  (Which would be there if the executable had been linked
> > by a linker that does not know how to merge multiple GNU_PROPERTY notes).
> >
>
> Hmm I have not really considered that. I will get back to you soon on this.
>

My initial thought is that if there is more than one
.note.gnu.property section in the executable then the static linker
didn't understand the section and hence we can't assume it did any of
the required actions like producing different PLT sections. Hence I
think acting as if there were no .note.gnu.property sections present
at all would be a sensible choice.

Peter