volatile

So, Rust actually ships, today, what you'd actually want, a pair of generic intrinsics for volatile reads and writes. Provide a suitably aligned pointer and you can read, or write, any implemented data type. Rust promises this read (or write) doesn't tear and won't get re-ordered, duplicated, optimised out etc. since performing the read (or write) has side effects invisible to the compiler (except that ZSTs can be elided because, fancy as MMIO is, reading or writing *nothing* does not have side effects). On most systems, of course, the intrinsic evaluates to a single machine code instruction.

This is roughly what Paul and co. have asked for in P1382R1 for C++ which makes sense because, as I said, it's what you'd actually want.

But what jumps out at me is that although Rust provides this intrinsic, which is exactly what you'd want here, Paul apparently proposes that what Rust ought to do instead is wrap the Linux kernel features that try to coerce a C compiler into doing what you want despite the C language standard not promising anything useful. Why? Is it because Paul didn't know these intrinsics already exist?