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

[CK Tan]

Does anyone have a sample code on calling a c function thru pointer? Thanks.

> On Oct 27, 2014, at 1:37 AM, David Chisnall <David.Chisnall at cl.cam.ac.uk> wrote:
> 
> 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