[LLVMdev] Referring to an argument in another function

[Frits van Bommel]

Scott Ricketts wrote:
> I would like to instrument certain function calls with a function call
> of my own that takes some of the same arguments. For example, I would
> like to instrument calls to free with some function foo, so the C code
> would look like:
> 
> foo(myarg1, myarg2, ptr);
> free(ptr);
> 
> The problem occurs when I grab the arg from the free function and try
> to pass it to foo...
> 
>   if (isCallToFree(&I)) {
>     Value* P;
>     if (Function *F = I.getCalledFunction()) {
>       Function::arg_iterator ait = F->arg_begin();

You want to look at the operands of the call/invoke/free instruction, not the 
arguments of the function being called.
So if you're sure it's a call or invoke (not a 'free' instruction), try 
something like this:

#include "llvm/Support/CallSite.h"
// ...
         CallSite CS(&I);
         CallSite::arg_iterator ait = CS.arg_begin(), aend = CS.arg_end();

>       if (ait) {

You want
         if (ait != aend) {
here.

>         P = &(*ait);
>       }
>       createCallInst(mem_fcall, &I, 3, getOpcodeValue(I),
>                      getInstrIDValue(), P);
>     }
>   }
> 
> createCallInst is my own wrapper. The error thrown during the pass is:
> 
> "Referring to an argument in another function!"
> 
> Any suggestions?