In the WO struct you use an UnsafeCell to hold the value, but UnsafeCell isn't repr(C) compatible. This causes rust to throw a warning that some struct element isn't repr(C) and should be.

I'm unsure whether or not this breaks things in practice, so what's the fix here, if any? My fork just made it work like RW structs, but would require a minor change to svd2rust (all write functions use mutable borrows).

Rust considers all references dereferencable and hence adds the dereferencable attribute. This allows the compiler to insert spurious reads from that reference. There is currently no way around that.

Some more discussions for context:

• UCG discussion
• A libstd issue caused by this behavior
• Several threads on IRLO

Unfortunately, this means the approach implemented by this crate is currently flawed: the compiler may insert spurious reads from an &RO<T> (or any of the other types, including WO).

The UCG thread is probably the best place to discuss possible solutions to this problem.

(I am not sure if this issue should be reported against this crate or vcell.)

Same as japaric/vcell#5, and maybe similar to #5
RW, RW and WO are used in ABI sensitive codes. So, it would be better to add repr(transparent) to those struct.

Ref: https://doc.rust-lang.org/nomicon/other-reprs.html