Missing label direction is not properly handled when using at&t syntax, with segfault on windows.

[TDecking]

I tried this code:

use std::arch::asm;

fn main() {
    println!("Hello, world!");

    unsafe {
        asm!(
            r#"
        jmp 9999
    9999:
            "#,
            options(nostack, att_syntax),
        );
    }
}

I expected to see this happen: An invalid operand for instruction error message, or something similar.

Instead, this happened: rustc segfaulted (windows). On Godbolt (Linux?), the code was accepted without error.
If att_syntax is removed, expected behaviour returns.

rustc --version --verbose:

rustc 1.73.0-nightly (03a119b0b 2023-08-07)

[asquared31415]

In the Reference it is noted that in the end it is the responsibility of the programmer to ensure that they have written valid assembly and that the compiler will not check everything. 9999 is not a valid label in att syntax: link.

Symbol names begin with a letter or with one of ._
There are ten local symbol names, which are re-used throughout the program. You may refer to them using the names 0 1 ... 9

It's very likely that the different implementations on different platforms handle this invalid syntax differently, so the assembler segfaulting is unfortunate but not surprising.

(also yes Godbolt's default host is a x86_64 (i think AMD64?) linux machine, so it would make sense to be different from windows)