A software instruction counter

Abstract

Although several recent papers have proposed architectural support for program debugging and profiling, most processors do not yet provide even basic facilities, such as an instruction counter. As a result, system developers have been forced to invent software solutions. This paper describes our implementation of a software instruction counter for program debugging. We show that an instruction counter can be reasonably implemented in software, often with less than 10% execution overhead. Our experience suggests that a hardware instruction counter is not necessary for a practical implementation of watch-points and reverse execution, however it will make program instrumentation much easier for the system developer.