llvm JIT add library to module

问题

I am working on a JIT that uses LLVM. The language has a small run-time written in C++ which I compile down to LLVM IR using clang

clang++ runtime.cu --cuda-gpu-arch=sm_50 -c -emit-llvm

and then load the *.bc files, generate additional IR, and execute on the fly. The reason for the CUDA stuff is that I want to add some GPU acceleration to the runtime. However, this introduces CUDA specific external functions which gives errors such as:

LLVM ERROR: Program used external function 'cudaSetupArgument' which could not be resolved!

As discussed here, this is usually solved by including the appropriate libraries when compiling the program:

g++ main.c cmal.o -L/usr/local/cuda/lib64 -lcudart

However, I am not sure how to include libraries in JITed modules using LLVM. I found this question which suggested that is used to be possible to add libraries to modules in the JIT like this:

[your module]->addLibrary("m");

Unfortunately, this has been deprecated. Can anyone tell me the best way to do this now? Let me know if I need to provide more information!

Furthermore, I am not really sure if this is the best way to be incorporating GPU offloading into my JIT, so if anyone can point me to a better method then please do :)

Thanks!

EDIT: I am using LLVM 5.0 and the JIT engine I am using is from llvm/ExecutionEngine/ExecutionEngine.h, more specifically I create it like this:

EngineBuilder EB(std::move(module));
ExecutionEngine *EE = EB.create(targetMachine);

回答1:

You need to teach your JIT engine about other symbols explicitly.

If they are in a dynamic library (dylib, so, dll) then you can just call

sys::DynamicLibrary::LoadLibraryPermanently("path_to_some.dylib")

with a path to the dynamic library.

If the symbols are in an object file or an archive, then it requires a bit more work: you would need to load them into memory and add to the ExecutionEngine using its APIs.

Here is an example for an object file:

std::string objectFileName("some_object_file.o");

ErrorOr<std::unique_ptr<MemoryBuffer>> buffer =
  MemoryBuffer::getFile(objectFileName.c_str());

if (!buffer) {
  // handle error
}

Expected<std::unique_ptr<ObjectFile>> objectOrError =
  ObjectFile::createObjectFile(buffer.get()->getMemBufferRef());

if (!objectOrError) {
  // handle error
}

std::unique_ptr<ObjectFile> objectFile(std::move(objectOrError.get()));

auto owningObject = OwningBinary<ObjectFile>(std::move(objectFile),
                                             std::move(buffer.get()));

executionEngine.addObjectFile(std::move(owningObject));

For archives replace template types ObjectFile with Archive, and call

executionEngine.addArchive(std::move(owningArchive));

at the end.

来源：https://stackoverflow.com/questions/48105342/llvm-jit-add-library-to-module

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