System and method for monitoring library software

A method and system for enabling the monitoring of a shared library of software programs for executing on a computer system. The system enables monitor instrumentation of the library without recompiling the source code of the programs. Encapsulation of the library routines does not disrupt the relative addressing of the library routines since an instruction is simply replaced. A single demultiplexor entry for each library routine provides access to common instrumentation code and to user specified entry and exit routines for the particular library routine. Common instrumentation code and user specified entry and exit routines are not replicated when used to monitor a number of software programs. No instructions are added to the library routine. User specified entry and exit routines are used to collect selected performance and system state data. Instrumentation code is provided to link the library routines to the user specified entry and exit routines. The standard link interface allows the entry and exit routines to be written in high level languages.