Re: PC-relative TLS support

[Segher Boessenkool <segher@kernel.crashing.org>]

On Fri, Aug 16, 2019 at 11:29:30AM +0930, Alan Modra wrote:
> On Thu, Aug 15, 2019 at 01:24:07PM -0500, Segher Boessenkool wrote:
> > On Thu, Aug 15, 2019 at 01:35:10PM +0930, Alan Modra wrote:
> > > Supporting TLS for -mpcrel turns out to be relatively simple, in part
> > > due to deciding that !TARGET_TLS_MARKERS with -mpcrel is silly.  No
> > > assembler that I know of supporting prefix insns lacks TLS marker
> > > support.
> > 
> > Will this stay that way?  (Or do we not care, not now anyway?)
> 
> I'd say we leave that problem to someone who wants pcrel without tls
> markers.  It's not hard to do, just extend rs6000_output_tlsargs and
> adjust IS_NOMARK_TLSGETADDR length attribute expressions.

Okay, so the latter option :-)

> > > Also, at some point powerpc gcc ought to remove
> > > !TARGET_TLS_MARKERS generally and simplify all the occurrences of
> > > IS_NOMARK_TLSGETADDR in rs6000.md rather than complicating them.
> > 
> > The last time this came up (a year ago) the conclusion was that we first
> > would have to remove AIX support.
> 
> Hmm, I wonder has that changed?  A quick look at the source says the
> AIX TLS support uses completely different patterns and shouldn't care.

https://gcc.gnu.org/ml/gcc-patches/2018-11/msg02259.html

But if you think we can remove the !TARGET_TLS_MARKERS everywhere it
is relevant at all, now is the time, patches very welcome, it would be
a nice cleanup :-)  Needs testing everywhere of course, but now is
stage 1 :-)


Segher