Incorrect local-dynamic TLS linker optimization with clang-generated code on PowerPC

[Chandler Carruth]

And FYI, I've removed the attribute to try to force TLS models in r227511.

Thanks to everyone tracking down this twisty maze of interactions.

On Thu, Jan 29, 2015 at 6:44 AM, Ulrich Weigand <Ulrich.Weigand at de.ibm.com>
wrote:

> Alan Modra <amodra at gmail.com> wrote on 29.01.2015 03:50:58:
> > On Thu, Jan 29, 2015 at 08:28:17AM +1030, Alan Modra wrote:
> > > On Wed, Jan 28, 2015 at 05:02:06PM +0100, Ulrich Weigand wrote:
> > > > Note how the original instruction marked with R_PPC64_GOT_TLSLD16_LO
> sets
> > > > register r29, while the linker-generated replacement sets r3.
> Looking at
> > > > the linker code, the addis "r3, r13, ..." seems to be simply
> hard-coded,
> > > > which works only if the original instruction sets register r3.
> > >
> > > Ouch.  Will fix.
> >
> > Fixed with https://sourceware.org/ml/binutils/2015-01/msg00318.html
>
> Thanks!
>
> > > > There is also a linker optimination for the general-dynamic case, but
> > > > from reading the BFD sources this seems to work correctly for any
> > > > target register and doesn't just assume r3.  Alan, is that right?
> > >
> > > No, I think that is also broken.
> >
> > Actually, looking at it again after I'd woken up properly, the general
> > dynamic case is good.
>
> Actually, experiment shows that it was broken after all :-)
>
> More specifically, the general-dynamic to *local-exec* optimization
> was broken, since it uses the same code path as the local-dynamic
> to local-exec optimization.  There is a separate general-dynamic to
> initial-exec optimization, which ought to be fine.
>
> But with Chandler's change, the linker actually used the general-dynamic
> to local-exec optimization (since the output is an executable file, and
> not a shared library), and thus it is still broken.
>
>
> Bye,
> Ulrich
>
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