[PATCH v3 2/2] elf: Add GNU_PROPERTY_1_NEEDED check

[Florian Weimer]

* H. J. Lu:

> If GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS is set on any input
> relocatable files:
>
> 1. Don't generate copy relocations.
> 2. Turn off extern_protected_data since it implies
> GNU_PROPERTY_NO_COPY_ON_PROTECTED.
> 3. Treate reference to protected symbols with indirect external access
> as local.
> 4. Set GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS on output.
> 5. When generating executable, clear this bit when there are non-GOT or
> non-PLT relocations in input relocatable files without the bit set.
> 6. Add -z [no]indirect-extern-access to control indirect external access.

Should the property be used just for error checking?  We would flip the
default unconditionally.  Such a behavioral change simply based on some
input file is quite surprising.

For (4), I think we need to set a different flag (or perhaps even
flags), and be really careful about what we do.  I think an output file
that is an executable will never require indirect-extern-access, but it
can be incompatible with indirect-extern-access objects at run time.
Shared objects as output files may themselves depend on
indirect-extern-access objects at run time.  Ideally, markup would be
applied to the relocations that are affected by the changes in the ABI.

Thanks,
Florian