BACKGROUND Deterministic replay in a virtual machine creates an execu tion that is
logically equivalent to an original execution of interest. Two executions are logically
equivalent if they con tain the same set of dynamic instructions, each dynamic instruction
computes the same result in the two executions, and the two executions compute the same
final state of the system (processor, memory and devices). Virtual machines are software
abstractions of physical computer systems, gen erally using virtualization Software which is …

The output of a non-deterministic instruction is handled during record and replay in a virtual
machine. An output of a non-deterministic instruction is stored to a buffer during record mode
and retrieved from a buffer during replay mode without exiting to the hypervisor. At least part
of the contents of the buffer can be stored to a log when the buffer is full during record mode,
and the buffer can be replenished from a log when the buffer is empty during replay mode.