[vlovich123]

I don't know if it's technically UB or well defined. The crash is a SEGFAULT and not a panic/abort, but it's probably a SEGFAULT due to guard pages. Still, it's possible to evade guard pages so if you access var[X] such that X points to the heap, it's possible you're reading aliased memory which would be UB in safe Rust.

EDIT: Going to take it back. I'm unable to create a situation where I create a large stack array that doesn't result in an immediate stack overflow. I even tried nightly MaybeUninit::uninit_array but that crashed explicitly with a "fatal runtime error: stack overflow" so it seems like the standard library has improved reporting instead of the old SEGFAULT. So no UB.

[Kranar]

Panics are not quite the same as an abort in Rust. Most notably a panic can be caught and execution can resume so as to gracefully terminate the application, but an abort is an immediate termination, a go to jail do not pass go kind of situation.

An out of bounds access in Rust will result in a panic but a stack overflow is an abort.

[vlovich123]

A segfault would imply it's not an abort either although it seems like it has been converted to a proper abort in newer versions of Rust.

[SAI_Peregrinus]

Panics can be aborts if set in cargo.toml.