[llvm-dev] ORC v2 question

[Dibyendu Majumdar via llvm-dev]

Hi Lang,

On Tue, 13 Aug 2019 at 23:26, Lang Hames <lhames at gmail.com> wrote:
>> I also get this message:
>> JIT session error: Symbols not found: { raise_error }
>
>
> Ahh -- I see the problem. The DynamicLibrarySearchGenerator is using the getAddressOfSymbol method, which (under the hood) is basically issuing an appropriate dlsym lookup, and that does not find explicitly added symbols. To find explicitly added symbols you need to call DynamicLibrary::SearchForAddressOfSymbol instead, but unfortunately that method's behavior is not a good fit for what DynamicLibrarySearchGenerator is trying to do.
>
> There are two ways you could tackle this:
> (1) Write your own generator that calls sys::DynamicLibrary::SearchforAddressOfSymbol, or
> (2) Add the symbols up-front using the absoluteSymbols function.
>
> I would be inclined to do the latter: it's more explicit, and easier to limit searches to exactly the symbols you want.
>

Okay I will look into this. Thank you for all the help.

> > CodeGen optimization seems a more likely culprit: JITTargetMachineBuilder and ExecutionEngineBuilder have different defaults for their CodeGen opt-level. JITTargetMachineBuilder defaults to CodeGenOpt::None, and ExecutionEngineBuilder default to CodeGenOpt::Default.
> >
> > What happens if you make the following modification to your setup?
> >
> > auto JTMB = llvm::orc::JITTargetMachineBuilder::detectHost();
> > JTMB->setCodeGenOptLevel(CodeGenOpt::Default); // <-- Explicitly set Codegen opt level
> > auto dataLayout = JTMB->getDefaultDataLayoutForTarget();
>
> I am not sure what to make of that. What happens if you print TM->getOptLevel() right before running CodeGen? Once your have explicitly set it I would expect them to be the same for ORCv1 and ORCv2. If they're not then it's a plumbing issue.
>

I explicitly set TM->Options anyway so maybe I don't need this?


Regards
Dibyendu