Re: [PATCH net-next v7 1/5] rust: core abstractions for network PHY drivers

Boqun Feng
2023-10-27T23:27:47Z

On Fri, Oct 27, 2023 at 10:50:45PM +0000, Benno Lossin wrote:
[...]
> >
> > Hmm... but does it mean even `set_speed()` has the similar issue?
> >
> > let phydev: *mut phy_device = self.0.get();
> > unsafe { (*phydev).speed = ...; }
>
> No that should be fine, take a look at the MIR output of the following
> code [1]:
>
> struct Foo {
> a: usize,
> b: usize,
> }
>
> fn foo(ptr: *mut Foo) {
> unsafe { (*ptr).b = 0; }
> }
>
> fn bar(ptr: *mut Foo) {
> unsafe { (&mut *ptr).b = 0; }
> }
>
> Aside from some alignment checking, foo's MIR looks like this:
>
> bb1: {
> ((*_1).1: usize) = const 0_usize;
> return;
> }
>
> And bar's MIR like this:
>
> bb1: {
> _2 = &mut (*_1);
> ((*_2).1: usize) = const 0_usize;
> return;
> }
>
> [1]: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=f7c4d87bf29a64af0acc09ff75d3716d
>
> So I think that is fine, but maybe Gary has something else to say about it.
>

Well when `-C opt-level=2`, they are the same:

https://godbolt.org/z/hxxo75YYh

Regards,
Boqun