Hybrid binary rewriting for memory access instrumentation

Abstract

Memory access instrumentation is fundamental to many applications such as software transactional memory systems, profiling tools and race detectors. We examine the problem of efficiently instrumenting memory accesses in x86 machine code to support software transactional memory and profiling. We aim to automatically instrument all shared memory accesses in critical sections of x86 binaries, while achieving overhead close to that obtained when performing manual instrumentation at the source code level. The two primary options in building such an instrumentation system are static and dynamic binary rewriting: the former instruments binaries at link time before execution, while the latter binary rewriting instruments binaries at runtime. Static binary rewriting offers extremely low overhead but is hampered by the limits of static analysis. Dynamic binary rewriting is able to use runtime information but typically incurs higher overhead. This paper proposes an alternative: hybrid binary rewriting. Hybrid binary rewriting is built around the idea of a persistent instrumentation cache (PIC) that is associated with a binary and contains instrumented code from it. It supports two execution modes when using instrumentation: active and passive modes. In the active execution mode, a dynamic binary rewriting engine (PIN) is used to intercept execution, and generate instrumentation into the PIC, which is an on-disk file. This execution mode can take full advantage of runtime information. Later, passive execution can be used where instrumented code is executed out of the PIC. This allows us to attain overheads similar to those incurred with static binary rewriting. This instrumentation methodology enables a variety of static and dynamic techniques to be applied. For example, in passive mode, execution occurs directly from the original executable save for regions that require instrumentation. This has allowed us to build a low-overhead transactional memory profiler. We also demonstrate how we can use the combination of static and dynamic techniques to eliminate instrumentation for accesses to locations that are thread-private.