https://peertube.watch/videos/watch/aab90c3b-fd18-4eb1-a471-21df2846e3d1 Keeping the false positive rate under control The ongoing work to improve the accuracy of definedness tracking in the face of newer more aggressively optimizing compilers. Valgrind's Memcheck tool reports various kinds of errors. One of the most important ones are those where an if-conditions or a memory address uses undefined data. To do this, it tracks the definedness of every bit in the process, and "follows" any undefinedness through arithmetic operations (Add, Sub, Mul, Or, Xor, etc). This tracking is expensive and so Memcheck makes compromises, trading off exactness for speed. That has worked well for many years. However, as compilers become more aggressive, this works less and less well. In particular, Memcheck now often reports false errors in optimised code from GCC 6, Clang 4, and later versions. This is a problem because one of Memcheck's main strengths is the accuracy of its analyses. In this talk I'll present my ongoing work to improve accuracy of definedness tracking. I'll mostly talk about various examples involving integer addition and comparisons, and will avoid gory details of Memcheck's internals. I'll also show two problems to which I have no solution. The talk should be accessible to anyone with some familiarity of basic integer arithmetic (add, sub, and/or/xor, etc) and is curious about how undefinedness "flows" through these operations. If you like maths and proving simple theorems, you might enjoy this talk too -- and we'd like to talk to you! Speaker: Julian Seward, Track: Debugging tools, Room: AW1.121, When: Saturday 3 February 2018, 11:30–12:10 (Brussels time), Schedule: FOSDEM 2018 event page, Licence: Creative Commons Attribution 2.0 Belgium (CC BY 2.0 BE) (as stated in the FOSDEM video archive). Attribution: “Valgrind's Memcheck tool vs Optimising Compilers” by Julian Seward, FOSDEM 2018. Original recording: 2018/AW1.121/debugging_tools_memcheck.webm from the FOSDEM video archive. This channel is an unofficial mirror; FOSDEM is a free and non-commercial event organised by the community for the community. Sat, 10 Oct 2026 00:31:01 GMT https://validator.w3.org/feed/docs/rss2.html PeerTube - https://peertube.watch https://peertube.watch/lazy-static/avatars/3b284627-b75f-409e-ac2e-10f4c2946f43.png https://peertube.watch/videos/watch/aab90c3b-fd18-4eb1-a471-21df2846e3d1 All rights reserved, unless otherwise specified in the terms specified at https://peertube.watch/about and potential licenses granted by each content's rightholder.