We define multiple configuration dimensions and assign code fragments to the appropriate dimensions. The kernel build system combines code fragments for the specific configuration. While this approach avoids the run-time costs of a full-blown object-oriented design, it does not avoid code duplication.

To address the code duplication problem, we model the code selection with class hierarchies using multiple inheritance and polymorphism. However, the run-time overhead of virtual functions results in a serious (2x) performance hit for the time-critical kernel functionality.

To address this latter problem, we apply class flattening to completely eliminate the overhead of virtual function calls. Our evaluation shows that a kernel with flattened class hierarchies performs as fast as one without class hierarchies. Thus, advanced object-oriented programming techniques need no longer be avoided in performance-focused microkernels.