[LLVMdev] Help with PPC64 JIT

[Duncan Sands]

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.

Ciao, Duncan.
> I am currently working with PPC64 JIT support for LLVM. So far I could make function calls
> work by adding function descriptors in 'lib/Target/PowerPC/PPCJITInfo.h' and adding a
> virtual method at 'LLVM::TargetJITInfo' that is called within 'JITEmitter::finishFunction'
> just after 'sys::Memory::InvalidateInstructionCache' to update the Global Mapping with
> function descriptor instead of the function address. The JIT function descriptor is
> loaded correctly in 'JIT::runFunction', instead of assuming the JIT function code is
> an ODP.
>
> Now I'm trying to make the relocation work properly. Using the testcase '2003-01-04-ArgumentBug'
> the assembly generated for main functions is the following:
>
> .L.main:
> # BB#0:
>          mflr 0
>          std 0, 16(1)
>          stdu 1, -112(1)
>          lis 3, .LCPI1_0 at ha
>          li 4, 1
>          lfs 1, .LCPI1_0 at l(3)
>          li 3, 0
>          bl foo
>          nop
>          addi 1, 1, 112
>          ld 0, 16(1)
>          mtlr 0
>          blr
>
> Which is correct, however for the JIT one generated in memory the relocations generate some issues.
>
> First the 'lis 3, .LCPI1_0 at ha' can possible overflow which will generate an wrong relocation.
> Since the const data will be place just before the function code in JIT generation, my first
> approach was to point the functions descriptor TOC to the JIT function base, so the 'lis' relocation
> could be rewritten as 'addis 3,2,.LCPI1 at TOC@ha'.
>
> And there where I could use some help: is it the best approach? Where is the best place to make this
> kind of analysis? Is there another way to make code adjustments for JIT?
>
> At fist I though to put the logic at 'lib/Target/PowerPC/PPCJITInfo.cpp', but from what I could
> understand the 'relocate' function method is indeed just to operate on the relocation
> addresses, not to change the upcode.
>
> Any advices/tips/suggestion would be appreciated.
>