[LLVMdev] Instrumenting virtual function calls

[Chris Lattner]

On Feb 10, 2008, at 5:33 AM, Robert Zeh wrote:

> I'm attempting to instrument virtual function calls in my code.   
> After each virtual call I'm calling my own registerMethod function,  
> with an integer marking the location of the call and a pointer to  
> the function that was called.
>
> However, and this is where I get confused, the function pointer  
> doesn't match any of the functions in my module.  I'd hoped to call  
> ExecutionEngine::getGlobalValueAtAddress to get a Function* for the  
> virtual function, but ExecutionEngine::getGlobalValueAtAddress  
> returns null.
>
> If I look up the virtual function that is getting called (with  
> ExeuctionEngine::getPointerToFunction) it doesn't match the  
> arguments being passed to my instrumentation. What's a little  
> strange is that the pointers are somewhat close:  
> getPointerToFunction returns 0x47829a0, but my instrumentation gets  
> 0x477fc10.

This should basically work.  You'll have to walk through the various  
code that populates the maps.  It could be that the start of the  
function is actually a constant pool or jump table or something, not  
the first instruction of the function.

-Chris