[LLVMdev] Help with PPC64 JIT

[Adhemerval Zanella]

On 07/31/2012 11:26 AM, Adhemerval Zanella wrote:
> On 07/20/2012 10:35 AM, Will Schmidt wrote:
>> On Fri, 2012-07-20 at 08:36 +0200, Duncan Sands wrote:
>>> Hi Adhemerval Zanella, the old JIT infrastructure is going away, to be replaced
>>> by "MC-JIT" (try passing -use-mcjit to lli).  It sounds like you are working on
>>> the old JIT, so I suggest you work instead on getting MC-JIT working on powerpc.
>> Hi Duncan, 
>>    Thanks for the pointers.  We hadn't stumbled across the MC-JIT refs
>> in our digging so far.  (LLVM GettingStarted.html doesn't mention it,
>> and (FIXME: T.B.D.) under llvm/lib/mc, so I suppose the MC jit is fairly
>> recent?)
>> Are we safe to assume the old JIT infrastructure will be completely
>> replaced, or are there likely to be 'users' that may still need
>> functionality?
>> I imagine since the old jit is where Adhemerval was focused, the
>> build/test steps must still be referencing it.
>>
>> Thanks, 
>> -Will 
> Thanks for the reply Duncan, I shifted my focus fo MCJIT. So far I could check there are basically
> two issues with MCJIT relating to PPC64 support:
>
> 1. Looks like LLVM does not generate PPC64 PIC code with TOC references. Using the testcase
> '2003-01-04-ArgumentBug.ll' I tried to invoke the llc with '-march=ppc64 -mcpu=ppc64 -mattr=64bit'
> and still uses the 32-bits relocations (@ha/@l(3)) where TOC would be expected (@toc). I did some
> adjustments to JIT code and function calling is correct (the function ODP is created and called),
> but BSS access is still not right since the 64-bits relocations are not done correctly.
> Could someone point where should I focus my efforts to add TOC support on PowerPC backend?
>
> 2. Relocations: I could add some support for PPC32 relocations by implementing some functions at
> 'RuntimeDyldELF.cpp', but then I fall back again in 1. (the PPC64 support is incomplete). 
>
> Is my analysis correct or I am issuing llc/lli wrongly and not activating the PPC64 PIC support?
> Anyone to advice me on this one? Any help would be appreciated.
>
The modifications I have done so far are in attachments. Basically it adds the PPC64 machine
name in Target, add some relocation support in Elf Runtime class. I'm still figuring out a
lot of internal llvm and the patch is still WIP.


-- 
Adhemerval Zanella Netto
  Software Engineer
  Linux Technology Center Brazil
  Toolchain / GLIBC on Power Architecture
  azanella at linux.vnet.ibm.com / azanella at br.ibm.com
  +55 61 8642-9890

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