Zero-cost conditional execution mechanism

It is common for kernel subsystems to conditionally include functionality, based on compile time and runtime configurations which are relatively infrequently subject to change. Typical examples include: toggling of DTrace probes, boot- time optimizations based on hardware capabilities and inclusion of additional security checks. This is often done by examining the state of a global flag and executing a block of code conditionally based on that state. When this is done in a ”hot” (i.e. frequently executed) code path, the overhead of the conditional execution can become significant. Moreover, in situations in which the state of the inspected flags changes rarely, most of the performed checks are redundant. The primary goal of this project is to design and implement a low overhead mechanism for conditional execution in contexts in which the branching condition does not change often. The mechanism will be based on runtime code patching of instructions. The second major goal is applying the developed mechanism to an existing block of kernel code.