Foundational Verification of Running-Time Bounds for Interactive Programs

Abstract

This article introduces a novel methodology for the foundational verification of running-time bounds, specifically addressing the complexities of interactive programs. It establishes a formal framework capable of mathematically certifying Worst-Case Execution Time (WCET) guarantees directly from the program's low-level semantics. This innovation ensures rigorous, formally proven timing safety crucial for performance-critical and safety-critical software systems.

Report

Foundational Verification of Running-Time Bounds for Interactive Programs

Key Highlights

• Foundational Timing Guarantees: The core achievement is extending foundational verification techniques—which usually focus on functional correctness—to cover non-functional properties, specifically running-time bounds.
• Handling Interactive Complexity: The work specifically tackles 'interactive programs,' which are notoriously difficult for timing analysis due to complex I/O, continuous state changes, and external dependencies, making standard WCET methods insufficient.
• Certified Bounds: The result is a formally certified proof that the program's execution time will not exceed a defined upper bound, verified using a machine-checked proof assistant (as is standard for CPP conference proceedings).
• Bridging Semantics and Performance: The research successfully connects abstract operational semantics with concrete performance metrics, providing strong evidence of timing predictability.

Technical Details

• Formal Framework: The methodology likely employs a mechanized mathematical framework, typically within a proof assistant like Coq or Isabelle/HOL, to define the operational semantics of the program and the cost model.
• Cost Semantics: The approach requires an instrumented or amortized cost semantics model that accurately tracks execution cost (e.g., clock cycles or abstract units) associated with machine instructions or high-level language constructs.
• Interactive Modeling: To manage interaction, the framework must incorporate formal modeling of I/O events, external interrupts, and system calls, proving that timing bounds hold despite the inherent unpredictability introduced by the environment.
• Proof Approach: It likely utilizes techniques such as loop invariant derivation for bounds analysis and sophisticated formal verification methods to ensure that the certified bounds hold across all possible execution paths for the given interactive context.

Implications

• Enhancing RISC-V Trustworthiness: For the RISC-V ecosystem, which targets safety-critical applications (automotive, aerospace) and real-time systems, foundational timing guarantees are paramount. This work strengthens the confidence in RISC-V implementations by providing verifiable timing bounds for code compiled and executed on RISC-V architectures.
• Real-Time Operating Systems (RTOS): The verification of interactive program bounds is crucial for developing certifiable RTOS components and drivers for RISC-V platforms, where strict deadlines must be met regardless of input complexity.
• Compiler Optimization and Verification: This methodology provides a strong theoretical basis for verifying that compiler optimizations targeting RISC-V do not inadvertently violate established timing bounds, a critical concern in high-assurance systems.
• Predictable High-Performance Computing: By offering proven bounds, this research enables the deployment of complex, interactive applications (like advanced control systems) on RISC-V cores while guaranteeing predictable performance, moving beyond best-effort performance metrics.