Runtime Verification with Patching and Hardware Checkers

Abstract

With this chapter we begin our discussion of the functional correctness solutions that can be pursued past the release of a new microprocessor design, when the device is already shipped and installed in an end-customer’s system. Error detection at this stage of the processor’s life cycle entails monitoring its behavior dynamically, by observing the internal state of the device with dedicated hardware components residing on the silicon die. In addition to error detection, runtime validation solutions, also called in-the-field solutions, must include an effective recovery and error bypass algorithm, to ensure minimal performance loss and forward progress of the system even in presence of bugs. To make the case for dynamic validation in this chapter, we first discuss the type, criticality and number of escaped design errors reported in several processors products.We then overview two major classes of runtime solutions: checker-based approaches and patching-based ones: themain difference between these two techniques lies in the underlying error detection mechanism. Checker-based solutions focus on verifying high-level system invariants, usually specified at design-time and then mapped to dedicated hardware components. Patching techniques address bugs of which the manufacturer becomes aware after product release and provide programmablemeans to describe these bugs so that the system can later identify their occurrence at runtime. We then contrast these two frameworks in terms of error coverage, usage flow and performance overhead, and present in detail some of the most popular academic and industrial solutions known today for each of the two classes.