An API for Runtime Code Patching

We present a post-compiler program manipulation tool called Dyninst which provides a C++ class library for program instrumentation. Using this library, it is possible to instrument and modify application programs during execution. A unique feature of this library is that it permits machine-independent binary instrumentation programs to be written. We describe the interface that a tool sees when using this library. We also discuss three simple tools built using this interface: a utility to count the number of times a function is called, a program to capture the output of an already running program to a file, and an implementation of conditional break points. For the conditional breakpoint example, we show that by using our interface compared with gdb we are able to execute a program with conditional breakpoints up to 900 times faster.