In csky, LLVM always generates libcalls (llvm/llvm-project@ec2de74), and atomic implementations are provided by libatomic.

However, as mentioned in #115577 (comment), the atomic RMW implementation provided in libatomic.a is not lock-free.

And it violates what the standard library is intended to guarantee.

https://doc.rust-lang.org/nightly/std/sync/atomic/index.html#portability

All atomic types in this module are guaranteed to be lock-free if they’re available. This means they don’t internally acquire a global mutex.

Also, mixing lock-free load/store and non-lock-free RMW can cause data races.

To fix this, we would need to do one of the following:

• Fix libatomic to make the RMW implementation lock-free.
• Fix LLVM to generate atomic instructions instead of libcalls.

It is not impossible to fix this on our end, but it is not very realistic as it would require writing a lot of inline assembly.

cc @Dirreke (mentioned because you are target maintainer)

@rustbot label +A-atomic +I-unsound