[LLVMdev] Please help with LLVM C++ integration

[kirill havok]

Hi John,
Unfortunately this did not help :-(

2008/8/19, John Criswell <criswell at cs.uiuc.edu>:
> kirill havok wrote:
>  > Hi Gordon,
>  > I wrote a small example, but while running I get an error("Tied to
>  > execute an unknown external function"), where I am wrong?
>  >
>
> I think the problem is that some_test_func() is a C++ function, so its
>  name is being mangled during compilation.
>
>  To fix it, I think you want to add a declaration telling the compiler to
>  treat some_test_func() as a C function.  Something like the below will work:
>
>  extern "C" {
>     int some_test_func(int);
>
> }
>
>  int some_test_func (int) {
>
>     <code for function here>
>     ...
>  }
>
>  -- John T.
>
>
>  > Thanks in advance.
>  > Kirill.
>  >
>  > int some_test_func( int ){
>  >         std::cout << "!!!!" << std::endl;
>  >         return 8848;
>  > }
>  >
>  > int _tmain(int argc, _TCHAR* argv[]){
>  >
>  >         Module *M = new Module("test");
>  >         ExistingModuleProvider* MP = new ExistingModuleProvider(M);
>  >         ExecutionEngine* EE = ExecutionEngine::create(MP, false);
>  >
>  >         std::vector<const Type *> func_args;
>  >         func_args.push_back(Type::Int32Ty);
>  >         FunctionType * func_type = FunctionType::get(Type::Int32Ty, func_args, false);
>  >         Function * my_function = Function::Create( func_type,
>  > Function::ExternalLinkage, "some_test_func", M );
>  >         EE->addGlobalMapping( my_function, (void*)&some_test_func );
>  >
>  >         Function *FooF = cast<Function>(M->getOrInsertFunction("foo",
>  > Type::Int32Ty, (Type *)0));
>  >         BasicBlock * BB = BasicBlock::Create("EntryBlock", FooF);
>  >         Value *Ten = ConstantInt::get(Type::Int32Ty, 10);
>  >         CallInst *Add1CallRes = CallInst::Create(my_function, Ten,
>  > "some_test_func", BB);
>  >         Add1CallRes->setTailCall(true);
>  >
>  >         ReturnInst::Create(Add1CallRes, BB);
>  >
>  >         std::cout << "We just constructed this LLVM module:\n\n" << *M;
>  >         std::cout << "\n\nRunning foo: " << std::flush;
>  >
>  >         std::vector<GenericValue> noargs;
>  >         GenericValue gv = EE->runFunction(FooF, noargs);
>  >
>  >         std::cout << "Result: " << gv.IntVal.toStringUnsigned(10) << "\n";
>  >         return 0;
>  > }
>  >
>  >
>  >
>  > 2008/8/19, Gordon Henriksen <gordonhenriksen at me.com>:
>  >
>  >> On Aug 19, 2008, at 13:36, kirill havok wrote:
>  >>
>  >> I got very interested in LLVM project, and I decided to start writing my own
>  >> scripting language based on it. By studying the documentation, I could not
>  >> find how to call external function, written in C. That is, I have a set of
>  >> functions written in C/C++, I generate code, using LLVM C++ interface, how
>  >> can I call(or register in machine in run-time) my external functions? Maybe
>  >> I just missed something. Please, give in which direction to search.
>  >>
>  >> Hi Kirill,
>  >>
>  >> Since LLVM goes to the bare metal, there is no need for an "FFI" or bindings
>  >> to call native code. Simply create a declaration for the function—a Function
>  >> with no body—and call it as any other function in your program. (Also, of
>  >> course, link with a library to define the symbols.) It might be instructive
>  >> to examine the llvm-gcc -S -emit-llvm output of a program like this:
>  >>
>  >> int MyExternalFn(int, int, int);
>  >>
>  >> int main(int, const char**, const char**) {
>  >>   return MyExternalFn(1, 2, 3);
>  >> }
>  >>
>  >>
>  >> Where you tweak MyExternalFn to have the desired prototype.
>  >>
>  >> To create a function declaration:
>  >>
>  >>
>  >> From C++, simply call Function::Create and then do not add any basic blocks.
>  >> From LLVM assembly, use the keyword "declare" instead of "define":
>  >> http://llvm.org/docs/LangRef.html#functionstructure
>  >>
>  >>
>  >> If you're using the JIT, you'll need to do the above, but also may need to
>  >> register your functions using
>  >> ExecutionEngine::addGlobalMapping.
>  >>
>  >> http://llvm.org/doxygen/classllvm_1_1ExecutionEngine.html#a8
>  >>
>  >>
>  >> Note that the C calling convention do not map directly to LLVM IR for many
>  >> cases, so it's best to stick to simple parameter types (pointers and ints,
>  >> for example) and also to verify that the LLVM FunctionTypes you use are
>  >> correct on each platform you support.
>  >>
>  >> Good luck!
>  >>
>  >> — Gordon
>  >>
>  >>
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>  >>
>  >>
>  >
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