An Execution Backtracking Approach to Program Debugging

An execution backtracking facility in interactive source debuggers allows users to mirror their thought processes while debugging --- working backwards from the location where an error is manifested and determining the conditions under which the error occurred. Such a facility also allows a user to change program characteristics and reexecute from arbitrary points within the program under examination --- a "what-if" capability. This paper describes an experimental debugger that provides such a backtracking function. We describe why the facility is useful, and why other current techniques are inadequate. We show how execution backtracking can be efficiently implemented by saving only the latest values of variables modified by a statement, and allowing backtracking only over complete program statements. We also describe how this approach relates to our work on dynamic program slicing. Keywords: debugging, backtracking, reverse execution. 1 Introduction The importance of good debugging t..