vlmillet / llvm-jit-pdb Goto Github PK

Hi, thank you very much for releasing the code for this library. I found a link pointing to here from some LLVM mailing list.

I managed to make it work with clang EmitLLVMOnlyAction+MCJIT. I figured out that your code makes a fundamental assumption about the module passed to it that each section (.text, .debug$T/S, etc) is only emitted once. With a handwritten module like the one in your example code it might be true. However, comprehensive codegen like clang emits every global symbol marked as COMDAT, which allows the linker to erase unused code from the final object. Consequently, each global symbol creates a dedicated section in the output COFF object stream, which is not handled in your code.

I found that this can be overcome by removing the COMDAT pointer from each global symbol and manually update their linking type (otherwise they all become weak symbols) before passing the module to ExecutionEngine, so that when emitting object, the sections will be reused.

for(auto &o : module->globals())
{
    o.setComdat(nullptr);
    o.setLinkage(llvm::GlobalValue::ExternalLinkage);
}
for(auto &o : module->global_objects())
{
    o.setComdat(nullptr);
    o.setLinkage(llvm::GlobalValue::ExternalLinkage);
}
for(auto &o : module->functions())
{
    o.setComdat(nullptr);
    o.setLinkage(llvm::GlobalValue::ExternalLinkage);
}

I would like to try out your tool with a 32-bit process. Can you post the source code for jitmemgen.exe? Thanks.