Wednesday, 24 February 2016

"These Bugs Are Impossible To Fix Without rr"

Jan de Mooij and the Mozilla JS team just used rr to figure out a GC-related top-crash in Firefox Nightly. The IRC discussion starts here.

I think rr is great for most kinds of bugs, not just the really hard ones. But obviously hard bugs are where there's the most win to be had.


  1. A more permanent link to the IRC discussion:

  2. Me: What is rr? I haven’t heard of it before. (Note: I came to this blog from a link to Rewrite Everything In Rust just a few minutes ago)
    Me: That EXISTS? Why have I not heard about this before? Why have I not been using this for years? This changes everything.

    Thank you for creating such an amazing-looking tool.

  3. @Daniel because it hasn't existed for years, of course! (though I think Microsoft has something similar maybe sorta?)

    By the way, does rr work with Rust? I mean, I know it should accurately record and replay execution since I assume Rust doesn't make completely oddball syscalls or anything. I guess what I'm really asking is if *gdb* works with Rust.

    1. Yes it does. mbrubeck is apparently using rr to track down Servo intermittents.