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Message-ID: <e7da93d6-b938-4558-95b2-e9d2e0194621@proton.me> Date: Sat, 28 Oct 2023 08:35:38 +0000 From: Benno Lossin <benno.lossin@...ton.me> To: Boqun Feng <boqun.feng@...il.com> Cc: FUJITA Tomonori <fujita.tomonori@...il.com>, netdev@...r.kernel.org, rust-for-linux@...r.kernel.org, andrew@...n.ch, tmgross@...ch.edu, miguel.ojeda.sandonis@...il.com, wedsonaf@...il.com Subject: Re: [PATCH net-next v7 1/5] rust: core abstractions for network PHY drivers On 28.10.23 01:26, Boqun Feng wrote: > 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 It doesn't matter what the optimizer does, `bar` is unsound in our use-case and `foo` is fine (I think). -- Cheers, Benno
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