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by tialaramex 1633 days ago
> -fsanitize=undefined.

As you yourself almost immediately mention, that's not checking for overflow.

Was the goal here to show that C and C++ programmers don't understand what overflow is?

> Yes, but this happens to be defined behavior, even if it’s what you don’t want most of the time

The defined behaviour is an overflow. Correct. So, checking for undefined behaviour does not check for overflow. See how that works?
1 comments
saagarjha 1633 days ago
Sorry, perhaps I assumed a bit too much with my response. Are you familiar with -fsanitize=unsigned-integer-overflow? Your response makes me think you might not be aware of it and I wanted you to be on the same footing in this discussion.
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tialaramex 1633 days ago
I was not. So, UBSan also "sanitizes" defined but undesirable behaviour from the language under the label "undefined". Great nomenclature there.

It also, by the looks of things, does not provide a way to say you want wrapping if that's what you did intend, you can only disable the sanitizer for the component that gets false positives. I don't know whether Zig has this, but Rust does (e.g. functions like wrapping_add() which of course inline to a single CPU instruction, and the Wrapping<> generic that implies all operations on that type are wrapping)

But you are then correct that this catches such overflows. Thanks for pointing to -fsanitize=unsigned-integer-overflow.

Since we're on the topic of sanitizers. These are great for AoC where I always run my real input under Debug anyway, but not much use in real systems where of course the edge case will inevitably happen in the uninstrumented production system and not in your unit tests...

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saagarjha 1632 days ago
> It also, by the looks of things, does not provide a way to say you want wrapping if that's what you did intend

This would be something for C/C++ to add, which they (for reasons unknown to me) failed to make progress on. I applaud Rust for having them; they're table stakes at this point.

> Since we're on the topic of sanitizers. These are great for AoC where I always run my real input under Debug anyway, but not much use in real systems where of course the edge case will inevitably happen in the uninstrumented production system and not in your unit tests...

Right, they are not perfect. They're a bandaid; a valiant effort but even then not a particularly great bandaid. As I've described elsewhere, I don't actually think this situation is going to get any better :(

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