Source code of a golden version and a next version of a program is received in which procedure calls are modified to call from an entry point table (EPT) with index numbers corresponding to procedure memory addresses. An executable defect-free golden version program and next version program with a defect are received. A first entry point table (first EPT) for the new version program and a second EPT for the golden version program are generated. A series of substitutions of procedures from the second EPT to the first EPT is performed and an order of substitutions includes: a module set, a module of the module set, a procedure set of the module, and a procedure of the procedure set. The defect producing procedure is identified by substituting in order until the defect is absent and proceeding to the next substitution in order.