One successful case of using rr to track down a subtle bug in LuaJIT's JIT compiler

Robert O'Callahan robert at ocallahan.org
Mon Feb 11 02:46:31 UTC 2019


On Sat, Feb 9, 2019 at 11:46 AM Yichun Zhang <yichun at openresty.com> wrote:

> Not sure if this is the right mailing list for such things (if not,
> please let me know). rocallahan once asked to me share some good
> experiences of using rr to debug LuaJIT bugs, and below is such a
> case:
>
>
> https://www.freelists.org/post/luajit/Patch-to-fix-a-Assertion-nslots-250-failed-assertion-failure-in-LuaJIT-v21
>
> It's not really a blog post but a mailing list email. Still I think it
> has enough details to make this case interesting for some others in
> the rr user community (if any of you needs more details, please let me
> know).
>
> Many thanks for creating and improving rr! In the past, debugging such
> bugs can take a notoriously long period of time and a lot of hacks to
> gather needed information in the execution process. This is because
> it's very hard to prepare minimal examples for such bugs and even for
> big ones it is not always reproducible due to inherent nondeterminism
> in the JIT compiler's runtime heuristics. Now it becomes fun rr
> exercises for just tens of minutes as long as we can reproduce it for
> at least once :)
>

Thanks for letting us know!

Rob
-- 
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mialcorp ew dna, ti ot yfitset dna ti nees evah ew; deraeppa efil eht. Efil
fo Drow eht gninrecnoc mialcorp ew siht - dehcuot evah sdnah ruo dna ta
dekool evah ew hcihw, seye ruo htiw nees evah ew hcihw, draeh evah ew
hcihw, gninnigeb eht morf saw hcihw taht.
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