将LLVM JIT代码链接到外部C ++函数

问题描述

我正在编写LLVM脚本引擎，该引擎将JIT编译为自定义语言的脚本代码.我的问题是我无法调用外部函数(甚至C99 erf()函数失败).

I'm writing a LLVM scripting engine that JIT compiles scripting code in a custom language. My problem is that I'm unable to call external functions (even the C99 erf() function is failing).

例如，如果我将erf函数"C"换成外部，

For example if I extern "C" the erf function,

extern "C" double erft(double x){
return erf(x);
}

并创建具有外部链接的功能

and create a function with external linkage

std::vector<const Type*> Double1(1,Type::getDoubleTy(getGlobalContext()));
FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),Double1,false);
Function *erft = Function::Create(FT,Function::ExternalLinkage,"erft",TheModule);

在使用erft(0.0)运行脚本时得到以下错误消息:

get the following error message when running my script with erft(0.0) :

手动进行映射

void ExecutionEngine::addGlobalMapping( const GlobalValue *  erfF, void *  erft);

会给我以下错误:

很明显，我做错了什么.任何帮助将不胜感激

Obviously I'm doing something very wrong. Any help would be much appreciated

推荐答案

假定您尚未禁用它(通过调用EE->DisableSymbolSearching())，则LLVM将使用dlsym()在JIT程序本身中查找符号.取决于您的平台，这可能意味着您需要使用-fPIC来构建JIT，或者可能根本不可用(例如在Windows上).

Assuming you haven't disabled it (by calling EE->DisableSymbolSearching()) then LLVM will use dlsym() to find the symbols in the JIT program itself. Depending on your platform, that might mean that you need to build your JIT with -fPIC, or that it might not be available at all (such as on Windows).

除了自动符号搜索外，您始终可以使用EE->addGlobalMapping(GV, &function)自己注册各个函数，其中GV =与您要调用的本机函数匹配的llvm :: Function *函数声明.在您使用ertf()的情况下，是:

Aside from automatic symbol searching, you can always register the individual functions yourself using EE->addGlobalMapping(GV, &function) where GV = the llvm::Function* function declaration that matches the native function you're calling. In your case with ertf() that's:

EE->addGlobalMapping(erft, &::erft);

请注意，您将全局函数命名为erft()，将局部变量命名为erft，因此命名为"::".下次请选择其他名称！

Note that you named the global function erft() and the local variable erft, hence the "::". Please pick different names next time!

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