Question

通过 llvm 教程我实现了 JIT ，发现我的 REPL 意外地因segfault而失败。调试器显示运算符throw导致此段错误。但是只有在抛出异常之前使用 JIT 编译某些代码时才会发生崩溃。来自this的代码可以使用一些修改来重现问题：

#include <string>
#include <vector>
#include <iostream>

#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Verifier.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ExecutionEngine/ExecutionEngine.h"
#include "llvm/ExecutionEngine/RTDyldMemoryManager.h"
#include "llvm/ExecutionEngine/RuntimeDyld.h"
#include "llvm/ExecutionEngine/SectionMemoryManager.h"
#include "llvm/ExecutionEngine/Orc/CompileUtils.h"
#include "llvm/ExecutionEngine/Orc/IRCompileLayer.h"
#include "llvm/ExecutionEngine/Orc/LambdaResolver.h"
#include "llvm/ExecutionEngine/Orc/ObjectLinkingLayer.h"
#include "llvm/ExecutionEngine/JITSymbol.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Mangler.h"
#include "llvm/Support/DynamicLibrary.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/TargetSelect.h"

using namespace llvm;
typedef orc::ObjectLinkingLayer<> ObjLayerT;
typedef orc::IRCompileLayer<ObjLayerT> CompileLayerT;

static LLVMContext Context;
static auto MyModule = make_unique<Module>("my compiler", Context);

Function *createFunc(IRBuilder<> &Builder, std::string Name) {
    std::vector<Type*> Integers(2, Builder.getInt32Ty());
    auto *funcType = FunctionType::get(Builder.getInt32Ty(), Integers, false);
    auto *fooFunc = Function::Create(funcType, Function::ExternalLinkage, Name, MyModule.get());
    return fooFunc;
};

void updateBody(Function *fooFunc, IRBuilder<> &Builder) {
    auto *entry = BasicBlock::Create(Context, "entry", fooFunc);
    Builder.SetInsertPoint(entry);
    auto args = fooFunc->arg_begin();
    Value *arg1 = &(*args);
    args = std::next(args);
    Value *arg2 = &(*args);
    auto *sum = Builder.CreateAdd(arg1, arg2, "tmp");
    Builder.CreateRet(sum);
};

int main(int argc, char* argv[]) {
    // Prepare the module
    static IRBuilder<> Builder(Context);
    auto *fooFunc = createFunc(Builder, "sum");
    updateBody(fooFunc, Builder);
    verifyFunction(*fooFunc);

    // Initilaze native target
    InitializeNativeTarget();
    InitializeNativeTargetAsmPrinter();
    InitializeNativeTargetAsmParser();

    // Prepare jit layer
    ObjLayerT ObjectLayer;
    std::unique_ptr<TargetMachine> TM(EngineBuilder().selectTarget());
    DataLayout DL(TM->createDataLayout());
    CompileLayerT CompileLayer(ObjectLayer, orc::SimpleCompiler(*TM));
    auto Resolver = orc::createLambdaResolver(
        [&](const std::string &Name) {
            if (auto Sym = CompileLayer.findSymbol(Name, false))
                return Sym;
            return JITSymbol(nullptr);
        },
        [](const std::string &S) { return nullptr; }
    );

    // Add MyModule to the jit layer
    std::vector<std::unique_ptr<Module>> Modules;
    Modules.push_back(std::move(MyModule));
    auto handle = CompileLayer.addModuleSet(std::move(Modules),
                        make_unique<SectionMemoryManager>(),
                        std::move(Resolver));

    // Retrieve the foo symbol
    std::string MangledName;
    raw_string_ostream MangledNameStream(MangledName);
    Mangler::getNameWithPrefix(MangledNameStream, "sum", DL);
    auto Sym = CompileLayer.findSymbol(MangledNameStream.str(), true);

    // Cast to function
    auto func = (int(*)(int, int))Sym.getAddress();

    // Try it
    std::cout << func(5, 7) << std::endl;

    CompileLayer.removeModuleSet(handle);

    try {
      throw std::runtime_error("Whoops!");
    } catch (const std::runtime_error& e) {
      std::cout << "Exception: " << e.what() << '\n';
    }

    return 0;
}

编译：

$ clang++ -std=c++11 -lLLVM code.cpp -o jittest

提供以下输出：

$ ./jittest 
12
Segmentation fault (core dumped)

如何正确使用LLVM JIT的异常？

0 个答案: