obl
Joined 11 years ago
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Comment · 1 year ago
Comment · 2 years ago
Weird that this treats uninitialized variables as unknown values. For example in ex3.c, the program
int main(){
int x;
if (x <= 42){
assert(x != 12345);
}
}
(even in O1 clang gets rid of the whole function, including even the ret instruction, I'm surprised it does not at least leave an ud2 for an empty function to help debugging since it would not cost anything https://godbolt.org/z/eK8cz3EPe )
Comment · 3 years ago
This is memory safe if you never re-use a (generational index, address) pair.
They seem to use 64 bit ones so this means that to overflow a single memory cell you would have to allocate and free it every cycle (!) at 4 ghz for about 150 years.
Basically as long as you accept this incredibly small "memory leak" you're fine.
You can think of it as the rather classic "Vec of struct + numeric IDs" that is used a lot e.g. in Rust to represent complex graph-like structures.
This combined with bound checking is absolutely memory safe. It has a bunch of correctness issue that can arise due to index confusion but those are not safety issues. When combined with some kind of generational counters those correctness issue also go away but are only caught at runtime not at compile time (and they incur a runtime cost).
Rust's memory safety is about avoiding liveness issues (that become type confusions since all memory allocators will reuse memory for different types), nothing more, nothing less.