mcfTRaptor: Toward unobtrusive on-the-fly control-flow tracing in multicores

Software testing and debugging has become the most critical aspect of the development of modern embedded systems, mainly driven by growing software and hardware complexity, increasing integration, and tightening time-to-market deadlines. Software developers increasingly rely on on-chip trace and debug infrastructure to locate software bugs faster. However, the existing infrastructure offers limited visibility or relies on hefty on-chip buffers and wide trace ports that significantly increase system cost. This paper introduces a new technique called mcfTRaptor for capturing and compressing functional and time-stamped control-flow traces on-the-fly in modern multicore systems. It relies on private on-chip predictor structures and corresponding software modules in the debugger to significantly reduce the number of events that needs to be streamed out of the target platform. Our experimental evaluation explores the effectiveness of mcfTRaptor as a function of the number of cores, encoding mechanisms, and predictor configurations. When compared to the Nexus-like control-flow tracing, mcfTRaptor reduces the trace port bandwidth in the range from 14 to 23.8 times for functional traces and 10.8–18.6 times for time-stamped traces.