[RFC, Darwin, PPC] Fix PR 65342.

[Alan Modra]

On Sat, Oct 12, 2019 at 05:39:51PM -0500, Segher Boessenkool wrote:
> On Sat, Oct 12, 2019 at 10:13:16PM +0100, Iain Sandoe wrote:
> > For 32bit cases this isn't a problem since we can load/store to unaligned
> > addresses using D-mode insns.
> 
> Can you?  -m32 -mpowerpc64?  We did have a bug with this before, maybe
> six years ago or so...  Alan, do you remember?  It required some assembler
> work IIRC.

Yes, the ppc32 ABI doesn't have the relocs to support DS fields.
Rather than defining a whole series of _DS (and _DQ!) relocs, the
linker inspects the instruction being relocated and complains if the
relocation would modify opcode bits.  See is_insn_ds_form in
bfd/elf32-ppc.c.  We do the same on ppc64 for DQ field insns.

> I'll have another looke through this (esp. the generic part) when I'm fresh
> awake (but not before coffee!).  Alan, can you have a look as well please?

It looks reasonable to me.

-- 
Alan Modra
Australia Development Lab, IBM