rr Record and Replay Debugger

rr is a lightweight tool for recording and replaying execution of applications, developed by Mozilla Research (originally by Robert O'Callahan and Chris Jones). With over 9,500 stars as of 2026, rr transforms debugging by enabling bidirectional debugging: stepping backwards through execution, examining program state at any point, and resuming from earlier checkpoints. Key features include: record and replay (recording full execution including all system calls, signals, and thread scheduling, then replaying deterministically), reverse execution (reverse-continue, reverse-step, reverse-next, reverse-finish for finding root causes by going backwards), deterministic replay (exact reproduction of race conditions and multi-threading bugs), GDB integration (working as a GDB stub with all standard capabilities plus reverse debugging), efficient recording (using performance counters with typical 1.2-2x slowdown during recording and near-native speed during replay), checkpointing (creating checkpoints during replay to jump back to interesting states), chaos mode (randomizing thread scheduling to increase probability of reproducing race conditions), multiprocess and multithread support (recording complex applications like web browsers with multiple processes and threads), system call recording (intercepting and recording all system calls with return values for faithful replay of file I/O, network operations, and IPC), and x86/x86-64 Linux support.