Book tutorial results in panic: unreachable_unchecked must never be reached

[jhwgh1968]

I tried this code:

I followed the instructions of the Rust UEFI book precisely in the Tutorial chapter (which means I am using the current stable crates.io version):

#![no_main]
#![no_std]

use log::info;
use uefi::prelude::*;

#[entry]
fn main() -> Status {
    uefi::helpers::init().unwrap();
    info!("Hello world!");
    boot::stall(10_000_000);
    Status::SUCCESS
}

With the sole exception that the OVMF version I'm using renamed its files for x64 to OVMF_CODE.4m.fd and OVMF_VARS.4m.fd respectively. But everything seemed to work on the QEMU side.

I expected this to happen: the example application to run as shown in the book.

Instead, this happened: I got the following output (manually retyped so whitespace may not be accuate) and after several seconds of sleep, the VM turned itself off as expected.

[ INFO]:            [PANIC]: panicked at library/core/src/panicking.rs:218:5
unsafe precondition(s) violated: hint:unreachable_unchecked must never be reached

This indicates a bug in the program. This Undefined Behavior check is optional, and cannot be relied on for safety.

Software and Hardware

QEMU emulator version 10.0.0
Copyright (c) 2003-2025 Fabrice Bellard and the QEMU Project developers

Arch Linux:
edk2-ovmf 202411-1
linux 6.12.4-arch1-1
extra/qemu-system-x86 10.0.0-5

CPU:
vendor_id : AuthenticAMD
cpu family : 25
model : 33
model name : AMD Ryzen 9 5950X 16-Core Processor