iWatcher

Abstract

Recent impressive performance improvements in computer architecturehave not led to significant gains in ease of debugging.Software debugging often relies on inserting run-time softwarechecks. In many cases, however, it is hard to find the root causeof a bug. Moreover, program execution typically slows down significantly,often by 10-100 times.To address this problem, this paper introduces the IntelligentWatcher (iWatcher), novel architectural support to monitor dynamicexecution with minimal overhead, automatically, and flexibly.iWatcher associates program-specified monitoring functionswith memory locations. When any such location is accessed, themonitoring function is automatically triggered with low overhead.To further reduce overhead and support rollback, iWatcher canleverage Thread-Level Speculation (TLS). To test iWatcher, we useapplications with various bugs. Our results show that iWatcher detectsmany more software bugs than Valgrind, a well-known open-sourcebug detector. Moreover, iWatcher only induces a 4-80%execution overhead, which is orders of magnitude less than Valgrind.Even with 20% of the dynamic loads monitored in a program,iWatcher adds only 66-174% overhead. Finally, TLS is effective atreducing overheads for programs with substantial monitoring.