'Re: [LLVMdev] Help with PPC64 JIT'

[prev in list] [next in list] [prev in thread] [next in thread] 

List:       llvm-dev
Subject:    Re: [LLVMdev] Help with PPC64 JIT
From:       "Kaylor, Andrew" <andrew.kaylor () intel ! com>
Date:       2012-07-31 21:23:41
Message-ID: 0983E6C011D2DC4188F8761B533492DE077CD1BA () ORSMSX105 ! amr ! corp ! intel ! com
[Download RAW message or body]

Hi Adhemerval,

It looks like the default relocation model for PowerPC is "DynamicNoPIC" for the \
Darwin OS and "Static" elsewhere.  There is a command line option \
("relocation-model") to override this default in both lli and llc.  However, I'm not \
sure using this will reduce your troubles.  You may end up going down code paths that \
have not been sufficiently exercised in the past.

I don't really know anything specifically about PowerPC, but I think that you may be \
able to glean some guidance from a patch which Petar Jovanovic recently submitted to \
add MCJIT support for MIPS.  The patch (which hasn't yet been committed) is here:

http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20120723/146977.html

The big difference I see between Petar's patch and yours is that Petar added explicit \
ELFWriterInfo support for his platform.  This is outside the area of the code that I \
know well, but it looks like that might be the right direction for you to investigate \
to fix your relocation difficulties.

-Andy

-----Original Message-----
From: llvmdev-bounces@cs.uiuc.edu [mailto:llvmdev-bounces@cs.uiuc.edu] On Behalf Of \
                Adhemerval Zanella
Sent: Tuesday, July 31, 2012 7:26 AM
To: will_schmidt@vnet.ibm.com
Cc: llvmdev@cs.uiuc.edu
Subject: Re: [LLVMdev] Help with PPC64 JIT

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.

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

_______________________________________________
LLVM Developers mailing list
LLVMdev@cs.uiuc.edu         http://llvm.cs.uiuc.edu
http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

_______________________________________________
LLVM Developers mailing list
LLVMdev@cs.uiuc.edu         http://llvm.cs.uiuc.edu
http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

[prev in list] [next in list] [prev in thread] [next in thread] 