LLVM JIT编译的程序找不到外部函数 [英] LLVM JIT-compiled program cannot find external functions

问题描述

我的程序JIT编译LLVM IR模块并调用定义的函数 foo 在运行时如果 foo 使用外部定义的函数：

My program which JIT compiles a LLVM IR module and calls a function foo defined therein fails at runtime if foo uses an externally-defined function:

LLVM ERROR: Program used external function 'glutInit' which could not be resolved!

我的程序：

// foo1.cpp
#include <GL/glut.h>

extern "C" void foo()
{
  glutInit(0,0);
}

// foo2.cpp
#include <iostream>
#include <fstream>
#include <string>

#include <llvm/Support/raw_ostream.h>
#include <llvm/LLVMContext.h>
#include <llvm/Support/TargetSelect.h>
#include <llvm/Support/IRReader.h>
#include <llvm/ExecutionEngine/ExecutionEngine.h>
#include <llvm/Support/MemoryBuffer.h>
#include <llvm/ExecutionEngine/JIT.h>
#include <llvm/ExecutionEngine/RuntimeDyld.h>

int main(int argc, char **argv)
{
  using namespace llvm;
  InitializeNativeTarget();

  LLVMContext context;
  SMDiagnostic error;

  std::ifstream ir_file("foo1.s");
  std::string ir((std::istreambuf_iterator<char>(ir_file)),
                 (std::istreambuf_iterator<char>()));

  Module *m = ParseIR(MemoryBuffer::getMemBuffer(StringRef(ir)), error, context);
  if(!m)
  {
    error.print(argv[0], errs());
  }

  ExecutionEngine *ee = ExecutionEngine::create(m);

  Function *func = ee->FindFunctionNamed("foo");
  if(func == 0)
  {
    std::cerr << "Couldn't find Function foo" << std::endl;
    std::exit(-1);
  }

  typedef void (*fcn_ptr)();
  fcn_ptr foo = reinterpret_cast<fcn_ptr>(ee->getPointerToFunction(func));
  foo();
  delete ee;

  return 0;
}

这是我如何构建我的程序：

Here's how I build my program:

$ clang -S -emit-llvm foo1.cpp
$ g++ -rdynamic foo2.cpp `llvm-config --cxxflags` `llvm-config --libs` `llvm-config --ldflags` -lglut

输出：

$ ./a.out 
LLVM ERROR: Program used external function 'glutInit' which could not be resolved!

无论何时我尝试使用外部定义的函数， C ++标准库（例如 printf ， malloc ，& free 没有问题）。我做错了什么？

It fails with a similar error any time I try to use an externally-defined function which is not in the C++ standard library (e.g., printf, malloc, & free are no problem). What am I doing wrong?

推荐答案

确保 glutInit 到 a.out 。如果你的主机代码（执行JIT的东西）没有调用它，它可能已经由链接器混合。如果是这样，你必须添加一个虚拟引用或使用链接器脚本/标志。

Make sure that glutInit was linked into a.out. If your host code (the thing executing the JIT) didn't call it, it could have been nixed by the linker. If that's the case, you have to add a dummy reference to it or use linker scripts / flags.

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