DISE: Implementing Application Meta-Features via Software-Programmable Decoding

Dynamic Instruction Stream Editing (DISE) is a cooperative software-hardware scheme for efficiently adding meta-features—e.g., safety/security checking, profiling, and dynamic code decompression—to an application. DISE implements meta-features by providing a programmable processor decoder that macro-expands certain instructions into parameterized instruction sequences. The technique is similar in spirit to programmable microcode and exploits the macro-expansion-style decoding technology already present in many of today’ s processors. DISE is a single facility that unifies the implementation of a large class of meta-features previously requiring either special-purpose hardware widgets or software-only tools like binary rewriters. Meta-features implemented via DISE require no new hardware widgets and avoid many of the costs of binary rewriting, primarily static code bloat and the fix ed overhead of the rewriting process itself. The dynamic character of DISE makes it appropriate for meta-features with fine grain intermittent usage patterns (e.g., sampled profiling) as well as applications that have no natural software implementations (e.g., dynamic code decompression). In this paper, we introduce DISE and show how it can be used to formulate three meta-features: path profiling, memory fault isolation, and dynamic code decompression. We find DISE to be general, powerful, and efficient. We describe the requirements of a DISE implementation and show one particular design. We also discuss the implications of DISE on all facets of a system. Using cycle-level simulation we show that DISE-implemented meta-features have competitive raw performance and a profitable dynamic cost structure.