HARE: Hardware assisted reverse execution

Bidirectional execution is a powerful debugging technique that allows program execution to proceed both forward and in reverse. Many software-only techniques and tools have emerged that use checkpointing and replay to provide the effect of reverse execution, although with considerable performance overheads in both forward and reverse execution. Recent hardware proposals for checkpointing and execution replay minimize these performance overheads, but in a way that prevents checkpoint consolidation, a key technique for reducing memory use while retaining the ability to reverse long periods of execution. This paper presents HARE, a hardware technique that efficiently supports both checkpointing and consolidation. Our experiments show that on average HARE incurs <3% performace overheads even when creating tens of checkpoints per second, provides reverse execution times similar to forward execution times, and reduces the total space used by checkpoints by a factor of 36 on average (this factor gets better for longer runs) relative to prior consolidation-less hardware checkpointing schemes.