[PATCH] Work around ppc64 TLS linker bug (Re: [LPM] Try again to appease powerpc64 in its self host.)

[Hal Finkel]

----- Original Message -----
> From: "Ulrich Weigand" <Ulrich.Weigand at de.ibm.com>
> To: "llvm cfe" <cfe-commits at cs.uiuc.edu>
> Cc: "Chandler Carruth" <chandlerc at gmail.com>, "Commit Messages and Patches for LLVM" <llvm-commits at cs.uiuc.edu>,
> "Rafael Espíndola" <rafael.espindola at gmail.com>, "Bill Schmidt" <wschmidt at linux.vnet.ibm.com>, "Hal Finkel"
> <hfinkel at anl.gov>
> Sent: Thursday, January 29, 2015 12:06:44 PM
> Subject: [PATCH] Work around ppc64 TLS linker bug (Re: [LPM] Try again to appease powerpc64 in its self host.)
> 
> Hal Finkel <hfinkel at anl.gov> wrote on 29.01.2015 17:13:21:
> 
> > > It's probably indeed the best to use the linker flag for now.
> > >
> > > However, I think adding them to the LLVM build flags is the wrong
> > > place; there is nothing special about compiling the LLVM code
> > > base
> > > as such.  Rather, the problem is using clang/LLVM to compile
> > > *any*
> > > coding using general-/local-dynamics TLS variables.
> > >
> > > So I think the flags should be added by the clang compiler driver
> > > whenever it invokes the linker on PowerPC.  (At least for now,
> > > and in 3.6.  They can be removed again once Bill has changed the
> > > code generation to again ensure use of r3 as expected by broken
> > > linkers ...)
> >
> > Agreed. Can you please post a patch?
> 
> I'm not completely sure if this is the correct place to add this,
> but the patch seems to work for me.  With this clang patch, I'm
> able to successfully bootstrap clang again (with the initial-exec
> TLS attribute in Chandler's latest change removed again).
> 
> OK to check in?
> 
> (See attached file: clang-ppc64-notlsopt.patch)

Yes, LGTM. We do need a test case, however (I think that something like test/Driver/Xlinker-args.c is essentially what is needed).

 -Hal

> 
> Bye,
> Ulrich

-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory