[PATCHv2] gdb/x86: Handle kernels using compact xsave format

[Andrew Burgess]

* Pedro Alves <palves@redhat.com> [2018-05-03 18:11:15 +0100]:

> On 05/03/2018 06:06 PM, Andrew Burgess wrote:
> > This patch is a follow-up for this patch:
> > 
> >   https://sourceware.org/ml/gdb-patches/2018-03/msg00275.html
> 
> Can you summarize what changed in this version?

Of course, sorry, I should have thought to do that.

The original patch focused entirely on the fctrl register, which is
where I saw the original problem.

When I revisited the patch I realised that there's nothing special
about that register, it was _all_ of the x87 control registers, that
are broken (and mxcsr).

So the biggest change is that after this patch _no_ registers are read
from the xsave buffer unless the relevant feature is enabled.

And _no_ register will be written back to the xsave buffer unless the
value has been modified.

I did manage to remove a '{ .... }' nesting level in this patch which
means I've updated the indentation on a bunch of code.

The patch also covers gdbserver, which the original patch didn't.

Hope that helps,

Thanks,
Andrew