[LLVMdev] Comment "FIXME" in X86MachObjectWriter::RecordX86Relocation

[Verena Beckham]

Hi Jim, Andrew,

Thanks, I read the discussions about using ELF + MCJIT + Windows and was 
hoping MachO would work just as well. Since you don't need to modify 
LLVM to be able to output MachO this was my first choice.
But are you saying MachO will not work as well as ELF?

Thanks for the patch Andrew, that will have to be my plan B in this case.

  Verena


On 29/06/2012 23:47, Kaylor, Andrew wrote:
> Can I assume we're talking about MCJIT since a file format and relocations are involved?
>
> Some changes are required in order to get MCJIT to generate ELF object files.  Eli Bendersky submitted a patch some time ago to modify the target triple code to enable this, but after a bit of discussion there didn't seem to be a consensus for accepting this proposal.
>
> If you want to try it out, the patch can be found here:
>
> http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20120130/136053.html
>
> I believe you can also find the related discussions from that post.  We've had success using this patch to generate ELF on Windows.  I don't know if any progress has been made toward a more generally acceptable solution.
>
> -Andy
>
>
> -----Original Message-----
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Jim Grosbach
> Sent: Friday, June 29, 2012 9:54 AM
> To: Verena Beckham
> Cc: llvmdev at cs.uiuc.edu
> Subject: Re: [LLVMdev] Comment "FIXME" in X86MachObjectWriter::RecordX86Relocation
>
> Hi Verena,
>
> Windows + MachO is likely to run into lots of problems once you start passing in non-trivial code. The relocation model is very tied to Darwin.
>
> I believe some folks doing JIT on Windows have had some success w/ ELF. Hopefully someone more familiar with the specifics of that will chime in.
>
> -Jim
>
> On Jun 29, 2012, at 8:58 AM, Verena Beckham<verena at codeplay.com>  wrote:
>
>> Hi,
>>
>> In X86MachObjectWriter::RecordX86Relocation I found the comment
>>
>>
>>    if (Target.isAbsolute()) { // constant
>>      // SymbolNum of 0 indicates the absolute section.
>>      //
>>      // FIXME: Currently, these are never generated (see code below). I
>> cannot
>>      // find a case where they are actually emitted.
>>      Type = macho::RIT_Vanilla;
>>    }
>>
>> Is the FIXME still true? I've got some code that hits this, and it
>> seems any code doing a function call to an absolute address (as
>> described in this bug for ELF:
>> http://llvm.org/bugs/show_bug.cgi?id=8656) would hit this. (Although I
>> haven't tried it)
>>
>> I'm using Windows 32bit x86 Mach-O, with MCJIT.
>>
>> Trying to find a bug within my program and wondered whether the code
>> is just not supported by LLVM. Let me know if you need a testcase.
>>
>> Thanks!
>>
>>
>> --
>> Verena Beckham
>>
>> Vice President Engineering
>>
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