rr debugger on GitHub

rr is a time travel debugger that runs native programs with only about a 50% overhead

it uses GDB for its interface

Mason Jones uses it as he's been weeding out bugs in jimtcl

I [Mason] start by setting a breakpoint at the segfault or panic, see what value is messed up, set a watchpoint, and run it backwards until I hit that watchpoint. Then it's a matter of alternating forwards and backwards until I find the exact spot

For example, it's kinda amazing to do watch -l someObj->refCount, use rc to run backwards, and find exactly where the refCount was last set