What am I doing wrong here...

I'm getting a 'function arguments must be value types' assertion from the following (abridged) code. Basically, I'm writing a pass that inserts llvm.frameaddress intrinsic calls everywhere 'interesting' that passes on the result by calling the C function void mcp_trace_stack(char *ptr). First I grab the functions themselves:

  Constant *MCPTraceStack, *LLVMFrameAddress;
     std::vector<const Type*> argstype;
         FunctionType *FT = FunctionType::get(Type::VoidTy, argstype, false);
  MCPTraceStack = M.getOrInsertFunction("mcp_trace_stack", FT);

  std::vector<const Type*> frargstype;

  FunctionType *FA = FunctionType::get(PointerType::get(Type::Int8Ty), frargstype, false);
  LLVMFrameAddress = M.getOrInsertFunction("llvm.frameaddress", FA);

then (in the pass itself) I use a code fragment like the following:

  CallInst *faddr = new CallInst(LLVMFrameAddress, "", np);
  new CallInst(MCPTraceStack, faddr, "", np);

which compiles fine, but at run-time (under opt) the pass aborts with an assertion. I realise I've probably done something subtly wrong, but I've been prodding at this for ages now and I just can't find it.

Thank you in advance,

  CallInst *faddr = new CallInst(LLVMFrameAddress, "", np);
  new CallInst(MCPTraceStack, faddr, "", np);

Fixed it myself. I should have been passing in an int32 to llvm.frameaddress. Me = stupid.