Reliability of WCET Analysis

International audienceAll contemporary safety standards require to demonstrate the absence of functional and non-functional safety hazards. In real-time systems this includes demonstrating the absence of critical timing hazards. To meet this verification objective it is necessary to show the correctness of the timing behavior with adequate confidence. Adequate confidence means that the evidence provided can be trusted beyond reasonable doubt. There are two main sources of doubt: the logical doubt associated with the validity of the reasoning and the epistemic doubt associated with uncertainty about the underlying assumptions. A fundamental timing property is the per-task worst-case execution (WCET). It is an ingredient for determining all higher level timing concepts like worst-case response times, and system-wide end-to-end times. This article gives an overview of the challenges in ensuring timeliness of real-time software focusing on the worst-case execution time problem. It describes the principles of abstract interpretation-based WCET analysis and summarizes the confidence argument for applying it in the certification process of safety-critical software, addressing both logical and epistemic doubt