Flashba k: A Lightweight Extension for Rollba k and Deterministi Replay for Software Debugging

Software robustness has signi ant impa t on system availability. Unfortunately, nding software bugs is a very hallenging task be ause many bugs are hard to re-produ e. While debugging a program, it would be very useful to rollba k a rashed program to a previous exe u-tion point and deterministi ally re-exe ute the \buggy" ode region. However, most previous work on rollba k and replay support was designed to survive hardware or operating system failures, and is therefore too heavy-weight for the ne-grained rollba k and replay needed for software debugging. This paper presents Flashba k, a lightweight OS ex-tension that provides ne-grained rollba k and replay to help debug software. Flashba k uses shadow pro esses to eÆ iently roll ba k in-memory state of a pro ess, and logs a pro ess ' intera tions with the system to support deterministi replay. Both shadow pro esses and logging of system alls are implemented in a lightweight fashion spe i ally designed for the purpose of software debug-ging. We have implemented a prototype of Flashba k in the Linux operating system. Our experimental results with mi ro-ben hmarks and real appli ations show that Flashba k adds little overhead and an qui kly roll ba k a debugged program to a previous exe ution point and deterministi ally replay from that point. 1 Introdu tion As rapid advan es in omputing hardware have led to dramati improvements in omputer performan e, issues of reliability, maintainability, and ost of ownership are be oming in reasingly important. Unfortunately, soft-ware bugs are as frequent as ever, a ounting for as mu h as 40 % of omputer system failures [45℄. Softwar