LLVM JIT:通过JIT代码将C++异常传递回主机应用程序

Question

我正在开发一个项目,我使用clang生成一些LLVM IR,然后JIT编译并在我的宿主应用程序中运行它.JIT代码调用宿主应用程序中的一些函数,这些函数可能会抛出异常.我希望通过JIT代码抛出异常并回到主机应用程序中.AFAIK这应该与LLVM一起使用,但不幸的是我的测试应用程序总是崩溃"在抛出'int'实例后调用终止".让我举一些简单的例子.

我使用clang 3.5将以下简单程序编译成LLVM IR:

extern void test() ;

extern "C" void exec(void*) {
        test();
}

同

./clang -O0 -S -emit-llvm test.cpp -c

结果是test.ll.

; ModuleID = 'test.cpp'
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

; Function Attrs: uwtable
define void @exec(i8*) #0 {
  %2 = alloca i8*, align 8
  store i8* %0, i8** %2, align 8
  call void @_Z4testv()
  ret void
}

declare void @_Z4testv() #1

attributes #0 = { uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #1 = { "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }

!llvm.ident = !{!0}

!0 = metadata !{metadata !"clang version 3.5.0 (224841)"}

我的主机应用程序如下所示:

static void test() {
    throw 1;
}

int main(int, const char **) {
    llvm::InitializeNativeTarget();
    llvm::InitializeNativeTargetAsmPrinter();
    llvm::InitializeNativeTargetAsmParser();

    llvm::LLVMContext &Context = llvm::getGlobalContext();
    llvm::SMDiagnostic Err;
    llvm::Module *Mod = llvm::ParseIRFile("test.ll", Err, Context);

    llvm::ExecutionEngine* m_EE = llvm::EngineBuilder(Mod)
            .setEngineKind(llvm::EngineKind::JIT)
            .create();

    llvm::Function* f = Mod->getFunction("_Z4testv");
    m_EE->addGlobalMapping(f, reinterpret_cast<void*>(test));

    f = Mod->getFunction("exec");

    void* poi = m_EE->getPointerToFunction(f);
    void (*exec)(void*) = reinterpret_cast<void (*)(void*)>(poi);

    try {
        exec(NULL);
    } catch (...) {
        std::cout << "catched exception" << std::endl;
    }

    return 0;
}

我使用我用cmake编译的LLVM 3.5.我设置LLVM_ENABLE_EH = ON和LLVM_ENABLE_RTTI = ON.编译LLVM或主机应用程序代码错误时我是否遗漏了什么？

谢谢!

Answer 1

最后它起作用,这里有一些解决问题所必需的东西.

首先,确保包含MCJIT.h非常重要,否则MCJIT不会被链接.不幸的是,如果MCJIT.h未被包含,则LLVM默默地回退到旧的JIT实现,即使已明确请求MCJIT:

llvm::EngineBuilder factory(Mod);
factory.setEngineKind(llvm::EngineKind::JIT);
factory.setUseMCJIT(true);

只有MCJIT支持propper异常处理.

在我使用的问题的例子中

Execution::Engine::addGlobalMapping()

哪个不适用于MCJIT.必须通过以下方式重新输入外部功能

llvm::sys::DynamicLibrary::AddSymbol()

按照完整的例子:

static void test() {
    throw 1;
}

int main(int, const char **) {
    llvm::InitializeNativeTarget();
    llvm::InitializeNativeTargetAsmPrinter();
    llvm::InitializeNativeTargetAsmParser();

    llvm::LLVMContext &Context = llvm::getGlobalContext();
    llvm::SMDiagnostic Err;
    llvm::Module *Mod = llvm::ParseIRFile("test.ll", Err, Context);

    std::unique_ptr<llvm::RTDyldMemoryManager> MemMgr(new llvm::SectionMemoryManager());

    // Build engine with JIT
    std::string err;
    llvm::EngineBuilder factory(Mod);
    factory.setErrorStr(&err);
    factory.setEngineKind(llvm::EngineKind::JIT);
    factory.setUseMCJIT(true);
    factory.setMCJITMemoryManager(MemMgr.release());
    llvm::ExecutionEngine *m_EE = factory.create();

    llvm::sys::DynamicLibrary::AddSymbol("_Z4testv", reinterpret_cast<void*>(test));

    llvm::Function* f = Mod->getFunction("exec");

    m_EE->finalizeObject();

    void* poi = m_EE->getPointerToFunction(f);
    void (*exec)(void*) = reinterpret_cast<void (*)(void*)>(poi); 

    try {
        exec(NULL);
    } catch (int e) {
        std::cout << "catched " << e << std::endl;
    }
    return 0;
}

此外,您现在还可以通过添加以下内容获取JIT代码的调试符号:

Opts.JITEmitDebugInfo = true;