[llvm-commits] [PATCH, RFC] 64-bit PowerPC ELF support for Initial Exec TLS model

[Hal Finkel]

Bill,

Thanks for working on this!

One quick comment: please add triples to the test cases (otherwise the Darwin ppc builtbots may complain).

 -Hal

----- Original Message -----
> From: "Bill Schmidt" <wschmidt at linux.vnet.ibm.com>
> To: llvm-commits at cs.uiuc.edu
> Sent: Monday, December 3, 2012 2:09:05 PM
> Subject: [llvm-commits] [PATCH,	RFC] 64-bit PowerPC ELF support for Initial Exec TLS model
> 
> Here's some incremental progress on thread-local storage.  I've
> verified
> it introduces no regressions.  Thought I'd open it up to comments
> before
> committing in case there's anything obvious I've missed.
> 
> I've had one comment that the lib/Target/PowerPC/PPC.h changes could
> be
> a separate patch.  I'm not sure if that's useful, since there isn't
> any
> new testable function by doing that.  But I don't feel strongly
> either
> way.
> 
> Thanks,
> Bill
> --
> Bill Schmidt, Ph.D.
> IBM Advance Toolchain for PowerLinux
> IBM Linux Technology Center
> wschmidt at linux.vnet.ibm.com
> wschmidt at us.ibm.com
> 
> --------------------------------------------------------------------------
> This patch introduces initial-exec model support for thread-local
> storage
> on 64-bit PowerPC ELF.
> 
> The patch includes code to handle external assembly and MC output
> with the
> integrated assembler.  It intentionally does not support the "old"
> JIT.
> 
> For the initial-exec TLS model, the ABI requires the following to
> calculate
> the address of external thread-local variable x:
> 
>  Code sequence            Relocation                  Symbol
>   ld 9,x at got@tprel(2)      R_PPC64_GOT_TPREL16_DS      x
>   add 9,9,x at tls            R_PPC64_TLS                 x
> 
> The register 9 is arbitrary here.  The linker will replace
> x at got@tprel
> with the offset relative to the thread pointer to the generated GOT
> entry for symbol x.  It will replace x at tls with the thread-pointer
> register (13).
> 
> The two test cases verify correct assembly output and relocation
> output
> as just described.
> 
> PowerPC-specific selection node variants are added for the two
> instructions above:  LD_GOT_TPREL and ADD_TLS.  These are inserted
> when an initial-exec global variable is encountered by
> PPCTargetLowering::LowerGlobalTLSAddress(), and later lowered to
> machine instructions LDgotTPREL and ADD8TLS.  LDgotTPREL is a pseudo
> that uses the same LDrs support added for medium code model's LDtocL,
> with a different relocation type.
> 
> The rest of the processing is (relatively) straightforward.
> 
> 
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-- 
Hal Finkel
Postdoctoral Appointee
Leadership Computing Facility
Argonne National Laboratory