Re: [PATCH v12 1/3] rust: io: add resource abstraction

[Alice Ryhl <aliceryhl@google.com>]

On Tue, Jul 08, 2025 at 02:43:33PM -0300, Daniel Almeida wrote:
> > What you wrote is not equivalent. (*inner) is a place expression, but
> > when you write `unsafe { <place expr> }` that turns it into a value
> > expression by reading the value. So this code copies the entire struct
> > to the stack, and then you read `start` from the copy on the stack.
> 
> To be honest, I've seen a bug where the opposite was going on, a field was
> being written on the value that was copied to the stack, leaving the original unchanged.
> 
> In any case, I thought this would be optimized away by the compiler. Also, IMHO
> there should be a lint for this, because it does not make sense to copy a struct
> just to read a field if we can just read the original location.
> 
> Thanks for catching that though, I will fix it on the next iteration :)

Yes, it is probably optimized out. However, the main problem is that
when you read the entire struct, that could be a data race of another
field which may be UB.

Alice