[LLVMdev] clang: call extern function using JIT

gafferuk gafferuk at gmail.com
Wed Aug 18 07:27:48 PDT 2010

Heres my full code listing, im totally stuck.

// Whistle.cpp : Defines the entry point for the console application.

#include "stdafx.h"
#include "clang/CodeGen/CodeGenAction.h"
#include "clang/Driver/Compilation.h"
#include "clang/Driver/Driver.h"
#include "clang/Driver/Tool.h"
#include "clang/Frontend/CompilerInvocation.h"
#include "clang/Frontend/CompilerInstance.h"
#include "clang/Frontend/DiagnosticOptions.h"
#include "clang/Frontend/FrontendDiagnostic.h"
#include "clang/Frontend/TextDiagnosticPrinter.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Support/TypeBuilder.h"
#include "llvm/LLVMContext.h"
#include "llvm/Module.h"
#include "llvm/Config/config.h"
#include "llvm/ADT/OwningPtr.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Config/config.h"
#include "llvm/ExecutionEngine/ExecutionEngine.h"
#include "llvm/Support/ManagedStatic.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/System/Host.h"
#include "llvm/System/Path.h"
#include "llvm/Target/TargetSelect.h"
using namespace clang;
using namespace clang::driver;

extern "C"
int yipee(int val)
	fprintf(stderr, "yipee!");

	return 1;

llvm::sys::Path GetExecutablePath(const char *Argv0) {
	// This just needs to be some symbol in the binary; C++ doesn't
	// allow taking the address of ::main however.
	void *MainAddr = (void*) (intptr_t) GetExecutablePath;
	return llvm::sys::Path::GetMainExecutable(Argv0, MainAddr);

int Execute(llvm::Module *Mod, char * const *envp) {

	std::string Error;
	llvm::OwningPtr<llvm::ExecutionEngine> EE(
		llvm::ExecutionEngine::createJIT(Mod, &Error));
	if (!EE) {
		llvm::errs() << "unable to make execution engine: " << Error << "\n";
		return 255;

	// code I have added
	llvm::FunctionType* ft =
		std::vector<const llvm::Type*>(1,
llvm::Type::getInt32Ty(llvm::getGlobalContext())), false);

	llvm::Function* F = llvm::Function::Create(ft,
llvm::Function::ExternalLinkage, "yipee", Mod);
	EE->addGlobalMapping(F, (void*)(intptr_t)yipee);
	llvm::Function *YipeeFn = Mod->getFunction("yipee");
	if (!YipeeFn) {
		llvm::errs() << "'yipee' function not found in module.\n";
		return 255;
	// end code I have added

	llvm::Function *EntryFn = Mod->getFunction("main");
	if (!EntryFn) {
		llvm::errs() << "'main' function not found in module.\n";
		return 255;

	// FIXME: Support passing arguments.
	std::vector<std::string> Args;

	return EE->runFunctionAsMain(EntryFn, Args, envp);

int main(int argc, const char **argv, char * const *envp) {
  void *MainAddr = (void*) (intptr_t) GetExecutablePath;
  llvm::sys::Path Path = GetExecutablePath(argv[0]);
  TextDiagnosticPrinter DiagClient(llvm::errs(), DiagnosticOptions());

  Diagnostic Diags(&DiagClient);
  Driver TheDriver(Path.str(), llvm::sys::getHostTriple(),
                   "a.out", /*IsProduction=*/false,
  TheDriver.setTitle("clang interpreter");

  // FIXME: This is a hack to try to force the driver to do something we can
  // recognize. We need to extend the driver library to support this use
  // (basically, exactly one input, and the operation mode is hard wired).
  llvm::SmallVector<const char *, 16> Args(argv, argv + argc);
  llvm::OwningPtr<Compilation> C(TheDriver.BuildCompilation(Args.size(),
  if (!C)
    return 0;

  // FIXME: This is copied from ASTUnit.cpp; simplify and eliminate.

  // We expect to get back exactly one command job, if we didn't something
  // failed. Extract that job from the compilation.
  const driver::JobList &Jobs = C->getJobs();
  if (Jobs.size() != 1 || !isa<driver::Command>(Jobs.begin())) {
    llvm::SmallString<256> Msg;
    llvm::raw_svector_ostream OS(Msg);
    C->PrintJob(OS, C->getJobs(), "; ", true);
    Diags.Report(diag::err_fe_expected_compiler_job) << OS.str();
    return 1;

  const driver::Command *Cmd = cast<driver::Command>(*Jobs.begin());
  if (llvm::StringRef(Cmd->getCreator().getName()) != "clang") {
    return 1;

  // Initialize a compiler invocation object from the clang (-cc1)
  const driver::ArgStringList &CCArgs = Cmd->getArguments();
  llvm::OwningPtr<CompilerInvocation> CI(new CompilerInvocation);
                                     const_cast<const char
                                     const_cast<const char
**>(CCArgs.data()) +

  // Show the invocation, with -v.
  if (CI->getHeaderSearchOpts().Verbose) {
    llvm::errs() << "clang invocation:\n";
    C->PrintJob(llvm::errs(), C->getJobs(), "\n", true);
    llvm::errs() << "\n";

  // FIXME: This is copied from cc1_main.cpp; simplify and eliminate.

  // Create a compiler instance to handle the actual work.
  CompilerInstance Clang;
  Clang.setLLVMContext(new llvm::LLVMContext);

  // Create the compilers actual diagnostics engine.
  if (!Clang.hasDiagnostics())
    return 1;

  // Infer the builtin include path if unspecified.
  if (Clang.getHeaderSearchOpts().UseBuiltinIncludes &&
    Clang.getHeaderSearchOpts().ResourceDir =
      CompilerInvocation::GetResourcesPath(argv[0], MainAddr);

  // Create and execute the frontend to generate an LLVM bitcode module.
  llvm::OwningPtr<CodeGenAction> Act(new EmitLLVMOnlyAction());
  if (!Clang.ExecuteAction(*Act))
    return 1;

  int Res = 255;
  if (llvm::Module *Module = Act->takeModule())

    Res = Execute(Module, envp);

  // Shutdown.


  return Res;

gafferuk wrote:
> I tried what you said, now I get:
> LLVM ERROR: Program used external function 'yipee' which could not be
> resolved!
> Stack dump:
> 0.      Running pass 'X86 Machine Code Emitter' on function '@main'
> did not even get as far as a breakpoint.
> Óscar Fuentes wrote:
>> gafferuk <gafferuk at gmail.com> writes:
>>> Im confused. The function i wish to call is a return type of int.
>>> Im calling it with int dd = yipee(1);
>>> What's wrong?
>> Declare the function:
>> int yipee(int);
>> int main()
>> {
>>     int dd = yipee(1);
>>     return 0;
>> }
>> If that still crashes, put a breakpoint on `yipee' and see if the
>> execution gets there, if the argument is right, if the crash happens
>> inside the function or after it returns...
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

View this message in context: http://old.nabble.com/clang%3A-call-extern-function-using-JIT-tp29449300p29471953.html
Sent from the LLVM - Dev mailing list archive at Nabble.com.

More information about the llvm-dev mailing list