[LLVMdev] How to call a pointer that points to a C function

[David Chisnall]

There is at least one error here, possibly two.

On 27 Oct 2014, at 07:46, C K Tan <cktanx at gmail.com> wrote:

> I have a pointer to a function that I need to invoke without going
> through llvm::Module::getOrInsertFunction. This example does not work:
> 
> static int add(int x, int y);
> llvm::Value *one, *two;
> 
> llvm::Constant* addfn
>   = llvm::ConstantInt::get(JB->getIntPtrTy(DataLayout), (intptr_t)add);
> llvm::Type* args[] = { Int32Ty, Int32Ty };
> llvm::FunctionType* ftype = llvm::FunctionType::get(Int32Ty, args);

The type that you want is not the function type, but the function *pointer* type.  ftype->getPointerTo() should give you the type that you need.

> addfn = llvm::ConstantExpr::getPointerCast(addfn, ftype);

I don't remember if this will just do casts between pointers or if it can also create inttoptrs, but you might need to be more explicit and ask for an inttoptr.

David