One way to provide fault isolation among cooperating software modules is to place each in its own address space. However, for tightly-coupled modules, this solution incurs prohibitive context switch overhead. In this paper, we present a software approach to implementing fault isolation within a single address space. Our approach has two parts. First, we load the code and data for a distrusted module into its own fault domain, a logically separate portion of the application's address space. Second, we modify the object code of a distrusted module to prevent it from writing or jumping to an address outside its fault domain. Both these software operations are portable and programming language independent. Our approach poses a tradeo relative to hardware fault isolation: substantially faster communication between fault domains, at a cost of slightly increased execution time for distrusted modules. We demonstrate that for frequently communicating modules, implementing fault isolation in software rather than hardware can substantially improve end-to-end application performance.

Implementing, validating, modifying, or reengineering an object-oriented system requires an understanding of the object and class interactions which occur as a program executes. This work seeks to identify, visualize, and analyze interactions in object-oriented program executions as a means for examining and understanding dynamic behavior. We have discovered recurring interaction scenarios in program executions that can be used as abstractions in the understanding process, and have developed a means for identifying these interaction patterns. Our visualizations focus on supporting design recovery, validation, and reengineering tasks, and can be applied to both object-oriented and procedural programs.

Profile-based optimizations can be used for instruction scheduling, loop scheduling, data preloading, function in-lining, and instruction cache performance enhancement. However, these techniques have not been embraced by software vendors because programs instrumented for profiling run significantly slower, an awkward compile-run-recompile sequence is required, and a test input suite must be collected and validated for each program. This paper introduces hardware-based profiling that uses traditional branch handling hardware to generate profile information in real time. Techniques are presented for both one-level and two-level branch hardware organizations. The approach produces high accuracy with small slowdown in execution (0.4%--4.6%). This allows a program to be profiled while it is used, eliminating the need for a test input suite. With contemporary processors driven increasingly by compiler support, hardware-based profiling is important for high-performance systems. Keywords: Bran...

Many binary tools, such as disassemblers, dynamic code generation systems, and executable code rewriters, need to understand how machine instructions are encoded. Unfortunately, specifying such encodings is tedious and error-prone. Users must typically specify thousands of details of instruction layout, such as opcode and #eld locations values, legal operands, and jump o#set encodings. Wehave built a tool called derive that extracts these details from existing software: the system assembler. Users need only provide the assembly syntax for the instructions for which they want encodings. Derive automatically reverse-engineers instruction encoding knowledge from the assembler by feeding it permutations of instructions and doing equation solving on the output. Derive is robust and general. It derives instruction encodings for SPARC, MIPS, Alpha, PowerPC, ARM, and x86. In the last case, it handles variable-sized instructions, large instructions, instruction encodings determined by operan...