The rust atomic crate was recently uploaded to Debian, unfortunately on a number of Debian architectures it's tests failed.

---- tests::atomic_i16 stdout ----
thread 'tests::atomic_i16' panicked at 'assertion failed: `(left == right)`
  left: `-25`,
 right: `30`', src/lib.rs:448:9

---- tests::atomic_i8 stdout ----
thread 'tests::atomic_i8' panicked at 'assertion failed: `(left == right)`
  left: `-25`,
 right: `30`', src/lib.rs:428:9

The debian architectures where it failed and the corresponding rust architectures are listed below.

armel -> armv5te-unknown-linux-gnueabi
mips64el -> mips64el-unknown-linux-gnuabi64
mipsel -> mipsel-unknown-linux-gnu
powerpc -> powerpc-unknown-linux-gnu

My guess is that this is a bug in fallback code used when the architecture does not natively support 8 and 16 bit atomics.

I produced the following testcase to confirm this was not a problem in the atomic crate, but instead an issue in either the compiler or the standard library. I tested this on Debian armel.

use std::sync::atomic::Ordering::SeqCst;
use std::sync::atomic::AtomicI8;
use std::sync::atomic::AtomicI16;
use std::sync::atomic::AtomicI32;
fn main() {
    let a = AtomicI8::new(30);
    println!("{}",a.fetch_max(-25,SeqCst));
    println!("{}",a.load(SeqCst));
    let a = AtomicI16::new(30);
    println!("{}",a.fetch_max(-25,SeqCst));
    println!("{}",a.load(SeqCst));
    let a = AtomicI32::new(30);
    println!("{}",a.fetch_max(-25,SeqCst));
    println!("{}",a.load(SeqCst));
}

I expected this to print 30 six times, but the second and fourth lines of the output are instead -25, this shows fetch_max is not being implemented correctly for AtomicI8 and AtomicI16 (but is being implemented correctly for AtomicI32).

I've only tested this with Debian's rustc so far, I may try to test with upstream rustc but this is complicated by the fact that I don't think upstream offers binaries for armv5te-unknown-linux-gnueabi

Meta

rustc --version --verbose:

rustc 1.59.0
binary: rustc
commit-hash: unknown
commit-date: unknown
host: armv5te-unknown-linux-gnueabi
release: 1.59.0
LLVM version: 13.0.1