In computing, rr (usually spelled in lowercase) is a debugging tool, designed to record and reproduce execution state of a program. RR also supports reverse execution.
RR is developed by Mozilla and was originally intended as a debugging tool for Mozilla Firefox. RR later became a separate project.
Design
When the programmer runs a program with rr, the execution information of the program is remembered and saved in a file. The programmer can run the debugged program with rr multiple times until the desired effects are reproduced. Then the programmer can make rr replay the execution, which will start the debugger gdb. From that point the debugging process is mostly the same as when using gdb on its own. The main difference is that every time the execution will be identical - memory addresses will be the same, system calls will return the same results, etc.