[LLVMdev] Please help with LLVM C++ integration

[Rob Grapes]

Hi Kirill,

Don't forget to add X86TargetMachine.obj (add to Additional Dependencies in Linker options, if you are using MSVS) otherwise LLVM will try and use Interpreter instead of JIT.

Hope this helps,

Rob.

> -----Original Message-----
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu]
> On Behalf Of kirill havok
> Sent: Wednesday, August 20, 2008 8:32 AM
> To: LLVM Developers Mailing List
> Subject: Re: [LLVMdev] Please help with LLVM C++ integration
>
> 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?
>
> 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
> >
> >
> > _______________________________________________
> >  LLVM Developers mailing list
> >  LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> >  http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> >
> >
>
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