Safety of intrinsics

[fpoli]

Shouldn't mem::__llvm_memcpy_element_unordered_atomic_1 and similar functions be marked as unsafe? The following program crashes with "Segmentation fault (core dumped)".

// compiler_builtins = "=0.1.23"

extern crate compiler_builtins;

fn main() {
    compiler_builtins::mem::__llvm_memcpy_element_unordered_atomic_1(
        std::ptr::null::<u128>() as *mut u8,
        std::ptr::null(),
        1
    );
}

[alexcrichton]

Ah yeah this should be unsafe for sure, thanks for the report!

[LukasKalbertodt]

What exactly does "similar functions" mean? It seems like we should fix this issue sooner rather than later, but I unfortunately don't really know enough about this stuff to properly judge what should be unsafe and what not. I would guess that everything in mem should be unsafe, right?

[alexcrichton]

I'd interpret it the same as Rust, where safe means "impossible to cause UB regardless of arguments".

These take a raw pointer and that's unsafe since you can manufacture pointers.