1. A computer implemented method of instrumenting target code to provide changed behavior, comprising: receiving target code as input; displaying a list of functions in the target code; receiving an association of at least two of the functions on the list with a same generic wrapper function; and performing an instrumentation of the target code comprising: creating a descriptor data structure for each of the at least two functions; inserting code into each of the at least two functions, the inserted code comprising a call to the generic wrapper function with a reference to the descriptor created for that function as a call parameter.