We have developed a facility for run-time optimization of a commodity operating system kernel. This facility is a first step towards an evolving operating system, one that adapts and changes over time without need for rebooting. Our infrastructure, currently implemented on UltraSPARC Solaris 7, includes the ability to do a detailed analysis of the running kernel's binary code, dynamically insert and remove code patches, and dynamically install new versions of kernel functions. As a first use of this technology, we have implemented a run-time kernel version of the code positioning I-cache optimizations, and obtained noticeable speedups in kernel performance. As a first case study, we performed run-time code positioning on the kernel's TCP read-side processing routine while running a Web client benchmark. We found that the code positioning optimizations reduced this function's execution time by 17.6%, resulting in an end-to-end benchmark speedup of 7%. The primary contributions of this paper are the first run-time kernel implementation of code positioning, and an infrastructure for turning an unmodified commodity kernel into an evolving one. Two further contributions are made in kernel performance measurement. First, we provide a simple and effective algorithm for deriving control flow edge execution counts from basic block execution counts, which contradicts the widely held belief that edge counts cannot be derived from block counts. Second, we describe a means for converting wall time instrumentation-based kernel measurements into virtual (i.e., CPU) time measurements via instrumentation of the kernel's context switch handlers. 1

Evaluation of statement coverage is the problem of identifying the statements of a program that execute in one or more runs of a program. The traditional approach for statement coverage tools is to use static code instrumentation. In this paper we present a new approach to dynamically insert and remove instrumentation code to reduce the runtime overhead of statement coverage measurement. We also explore the use of dominator tree information to reduce the number of instrumentation points needed. Our experiments show that our approach reduces runtime overhead by 38-90 % compared with purecov, a commercial statement coverage tool. Our tool is fully automated and available for download from the Internet. 1.

SPEC-VALUE, a rigorous scenario-driven approach for the description and validation of complex system functionalities at the early stages of design, is presented. It is based on two notations. The first notation, called Use Case Maps (UCMs), is used to capture functional requirements. UCMs can help reasoning about system-wide functionalities at a high level of abstraction before a prototype is generated. The second notation is the formal specification language LOTOS. UCM scenarios are translated into LOTOS specifications, which animate UCMs with the help of tools. LOTOS-based techniques, especially specification-level testing, can be used to validate designs. It is shown how SPEC-VALUE can help to produce better-quality designs and standards and to improve human understanding with reduced time and costs. A real-life case study is provided: the Group Call service of the mobile data system General Packet Radio Services (GPRS). KEY WORDS: Causal Scenarios, LOTOS, Telecommunications Standa...