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Joined 11 months ago
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Cake day: July 27th, 2023

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  • This is a use-after-free, which should be impossible in safe Rust due to the borrow checker. The only way for this to happen would be incorrect unsafe code (still possible, but dramatically reduced code surface to worry about) or a compiler bug. To allocate heap space in safe Rust, you have to use types provided by the language like Box, Rc, Vec, etc. To free that space (in Rust terminology, dropping it by using drop() or letting it go out of scope) you must be the owner of it and there may be current borrows (i.e. no references may exist). Once the variable is droped, the variable is dead so accessing it is a compiler error, and the compiler/std handles freeing the memory.

    There’s some extra semantics to some of that but that’s pretty much it. These kind of memory bugs are basically Rust’s raison d’etre - it’s been carefully designed to make most memory bugs impossible without using unsafe. If you’d like more information I’d be happy to provide!





  • I was very intrigued by a follow-up to the recent numberphile video about divergent series. It was a return to the idea that the sum of the integers greater than zero can be assigned the value -1/12. There were some places this could be used, but as far as I know it was viewed as shaky math by a lot of experts.

    As far as I recall the story goes something like this: now, using a new technique Terrence Tao found, a team was seemingly able to “fix” previous infinities in quantum field theory - there’s a certain way to make at least some divergent series work out to being a real number, and the presenter proposed that this can be explained as the universe “protecting us” from the infinities inherent in the math.

    It made me think about other places infinities show up in modern physics (namely, singularities in general relativity) and whether a technique something like this could “solve” them without a whole new framework like string theory is.
















  • The issue is not just that a bad update went out. Freak accidents can happen. Software is complicated and you can never be 100% sure. The problem is the specifics. A fat finger should never be able to push a bad update to a system in customers’ hands, forget a system easily capable of killing people in a multitude of ways. I’m not quite as critical as the above commentor but this is a serious issue that should raise major questions about their culture and procedures.

    This isn’t just some website where a fat finger at worst means the site is down for a while (assuming you do the bare minimum and back up your db). This is a vehicle. That’s what they meant about the CAN bus - not that that’s really a concern when the infotainment system just gets bricked, but that they have such lax procedures around software that touches a safety-critical system.

    Having systems in place to ensure only tested, known good builds are pushed is pretty damn basic safety practice. Swiss cheese model. If they can’t even handle the basics, what other bad practices do they have?

    Again, not that I think this is necessarily as bad as the other person - perhaps this is the only mistake they’ve made in their safety procedures and otherwise they’re industry leaders - we don’t know that yet. But this is extremely concerning and until proven otherwise should be investigated and treated as a very serious safety violation. Safety first.