LLVM MCJIT Code Samples (Working!)

mcjit.cpp

/*
 * To compile, execute on terminal:
 * g++ -o mcjit mcjit.cpp `llvm-config --cxxflags --ldflags --libs all --system-libs`
 */

#include <iostream>
#include <memory>

#include <llvm/ADT/StringRef.h>
#include <llvm/ExecutionEngine/ExecutionEngine.h>
#include <llvm/ExecutionEngine/MCJIT.h>
#include <llvm/IR/Constant.h>
#include <llvm/IR/IRBuilder.h>
#include <llvm/IR/LLVMContext.h>
#include <llvm/IR/Module.h>
#include <llvm/IR/Verifier.h>
#include <llvm/Support/DynamicLibrary.h>
#include <llvm/Support/raw_ostream.h>
#include <llvm/Support/TargetSelect.h>

void foo() {
    std::cout << "foo()\n";
}

int main() {
    llvm::InitializeNativeTarget();
    llvm::InitializeNativeTargetAsmPrinter();
    llvm::InitializeNativeTargetAsmParser();

    llvm::LLVMContext context;
    auto module = new llvm::Module("top", context);
    llvm::IRBuilder<> builder(context);

    auto footype = llvm::FunctionType::get(builder.getVoidTy(), false);
    auto foofunc = llvm::Function::Create(footype,
            llvm::Function::ExternalLinkage, "foo", module);
    // Line commented to mess up resolution of relocation and cause a jump to 0x0
    //llvm::sys::DynamicLibrary::AddSymbol("foo", reinterpret_cast<void*>(foo));

    auto functype = llvm::FunctionType::get(builder.getInt32Ty(), false);
    auto mainfunc = llvm::Function::Create(functype,
            llvm::Function::ExternalLinkage, "main", module);

    auto entryblock = llvm::BasicBlock::Create(context, "entry", mainfunc);
    builder.SetInsertPoint(entryblock);
    builder.CreateCall(foofunc);
    builder.CreateRet(llvm::ConstantInt::get(builder.getInt32Ty(), 0));

    std::string error;
    llvm::raw_string_ostream error_os(error);
    if (llvm::verifyModule(*module, &error_os)) {
        std::cerr << "Module Error: " << error << '\n';
        return 1;
    }
    module->print(llvm::errs(), nullptr);

    auto engine = llvm::EngineBuilder(std::unique_ptr<llvm::Module>(module))
                        .setErrorStr(&error)
                        .setOptLevel(llvm::CodeGenOpt::Aggressive)
                        .setEngineKind(llvm::EngineKind::JIT)
                        .create();
    if (!engine) {
        std::cerr << "EE Error: " << error << '\n';
        return 1;
    }

    engine->finalizeObject();

    typedef void (*Function)();
    Function f = reinterpret_cast<Function>(
            engine->getPointerToNamedFunction("main"));
    f();

    return 0;
}