Deductive Verification for Earliest Deadline First Scheduler Implementations

2026-07-29

AI Summary

This work addresses the critical need for rigorous assurance that implementations of Earliest Deadline First (EDF) schedulers in real-time operating systems adhere precisely to their intended scheduling semantics, rather than relying solely on abstract analyses. The paper presents the first general, property-driven formal verification framework specifically tailored for EDF implementations, explicitly defining three core correctness properties and conducting deductive verification using the Frama-C/ACSL platform. The framework has been successfully applied to EDF extensions in RTEMS 5, RTEMS 6, and FreeRTOS, demonstrating that three architecturally distinct scheduler implementations all satisfy the essential correctness properties. This approach effectively resolves the semantic fidelity challenges arising from reusing fixed-priority kernel infrastructure and substantially enhances the trustworthiness of EDF scheduler implementations in safety-critical systems.

Abstract

Real-Time Operating Systems (RTOSes) rely on scheduler implementations to provide predictable task execution. For safety-critical systems, it is therefore not sufficient to reason only about the abstract scheduling policy; the concrete implementation must also preserve the intended scheduling semantics. This is particularly challenging for Earliest Deadline First (EDF) scheduling, because EDF introduces dynamic, deadline-derived priorities that are often realized by reusing kernel infrastructure originally designed for fixed-priority scheduling. In this work, we formalize EDF correctness through three essential properties that any implementation of the Earliest Deadline First (EDF) scheduler must satisfy. Based on these properties, we propose a framework utilizing deductive verification, that applies to any EDF-based scheduler realization. We instantiate the framework in Frama-C/ACSL and apply it to three structurally different EDF scheduler realizations: RTEMS 5, RTEMS 6, and an EDF extension of FreeRTOS.

Problem

• Earliest Deadline First
• scheduler implementation
• real-time operating systems
• scheduling semantics
• safety-critical systems

Innovation

• deductive verification
• Earliest Deadline First
• scheduler correctness
• formal verification
• real-time operating systems