llvm dev - Jun 2009 - [LLVMdev] Referring to an argument in another function

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();
      if (ait) {
        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?

Thanks,
Scott

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?

On Thu, Jun 18, 2009 at 12:41 PM, Frits van Bommel<fvbommel at wxs.nl>
wrote:
> 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.
>
Thanks!

CallSite is what I needed. I ended up getting P with CS.getArgument(0)
instead of an arg_iterator, but only because I first check that it is
an externally linked call to free with 1 argument.

Scott