Hardware and software support for efficient exception handling

Abstract

Program-synchronous exceptions, for example, breakpoints, watch points, illegal opcodes, and memory access violations, provide information about exceptional conditions, interrupting the program and vectoring to an operating system handler. Over the last decade, however, programs and run-time systems have increasingly employed these mechanisms as a performance optimization to detect normal and expected conditions. Unfortunately, current architecture and operating system structures are designed for exceptional or erroneous conditions, where performance is of secondary importance, rather than normal conditions. Consequently, this has limited the practicality of such hardware-based detection mechanisms. We propose both hardware and software structures that permit efficient handling of synchronous exceptions by user-level code. We demonstrate a software implementation that reduces exceptiondelivery cost by an order-of-magnitude on current RISC processors, and show the performance benefits of that mechanism for several example applications.