Design and implementation of a backward-in-time debugger

Abstract

Traditional debugging and stepping execution trace are well-accepted techniques to understand deep internals about a program. However in many cases navigating the stack trace is not enough to find bugs, since the cause of a bug is often not in the stack trace anymore and old state is lost, so out of reach from the debugger. In this paper, we present the design and implementation of a backward-in-time debugger for a dynamic language, i.e., a debugger that allows one to navigate back the history of the application. We present the design and implementation of a backward-in-time debugger called UNSTUCK and show our solution to key implementation challenges.