Deriving the Worst-Case Execution Time Input Values

A Worst-Case Execution Time (WCET) analysis derives upper bounds for execution times of programs. Such bounds are crucial when designing and verifying real-time systems. A major problem with todaypsilas WCET analysis approaches is that there is no feedback on the particular values of the input variables that cause the programpsilas WCET. However, this is important information for the real-time system developer.We present a novel approach to overcome this problem. In particular, we present a method, based on a combination of input sensitive static WCET analysis and systematic search over the value space of the input variables, to derive the input value combination that causes the WCET. We also present several different approaches to speed up the search. Our evaluations show that the WCET input values can be relatively quickly derived for many type of programs, even for program with large input value spaces. We also show that the WCET estimates derived using the WCET input values often are much tighter than the WCET estimates derived when all possible input value combinations are taken into account.