On Thu, Mar 27, 2025 at 10:15 AM Tamir Duberstein <tam...@gmail.com> wrote: > > On Wed, Mar 26, 2025 at 6:15 PM Benno Lossin <benno.los...@proton.me> wrote: > > > > On Wed Mar 26, 2025 at 11:09 PM CET, Tamir Duberstein wrote: > > > On Wed, Mar 26, 2025 at 5:09 PM Benno Lossin <benno.los...@proton.me> > > > wrote: > > >> On Wed Mar 26, 2025 at 8:06 PM CET, Tamir Duberstein wrote: > > >> > On Wed, Mar 26, 2025 at 1:36 PM Benno Lossin <benno.los...@proton.me> > > >> > wrote: > > >> >> On Wed Mar 26, 2025 at 5:57 PM CET, Tamir Duberstein wrote: > > >> >> > > > >> >> > Yeah, we should do this - but again: not relevant in this > > >> >> > discussion. > > >> >> > > >> >> I think it's pretty relevant. > > >> > > > >> > It's not relevant because we're no longer talking about transmuting > > >> > pointer to pointer. The two options are: > > >> > 1. transmute reference to reference. > > >> > 2. coerce reference to pointer, `as` cast pointer to pointer (triggers > > >> > `ptr_as_ptr`), reborrow pointer to reference. > > >> > > > >> > If anyone can help me understand why (2) is better than (1), I'd > > >> > certainly appreciate it. > > >> > > >> I am very confident that (2) is correct. With (1) I'm not sure (see > > >> above), so that's why I mentioned it. > > > > > > Can you help me understand why you're confident about (2) but not (1)? > > > > My explanation from above explains why I'm not confident about (1): > > > > For ptr-to-int transmutes, I know that they will probably remove > > provenance, hence I am a bit cautious about using them for ptr-to-ptr or > > ref-to-ref. > > > > The reason I'm confident about (2) is that that is the canonical way to > > cast the type of a reference pointing to an `!Sized` value. > > Do you have a citation, other than the transmute doc?
Turns out this appeases clippy: diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs index 80a9782b1c6e..7a6fc78fc314 100644 --- a/rust/kernel/uaccess.rs +++ b/rust/kernel/uaccess.rs @@ -240,9 +240,10 @@ pub fn read_raw(&mut self, out: &mut [MaybeUninit<u8>]) -> Result { /// Fails with [`EFAULT`] if the read happens on a bad address, or if the read goes out of /// bounds of this [`UserSliceReader`]. This call may modify `out` even if it returns an error. pub fn read_slice(&mut self, out: &mut [u8]) -> Result { + let out: *mut [u8] = out; // SAFETY: The types are compatible and `read_raw` doesn't write uninitialized bytes to // `out`. - let out = unsafe { &mut *(out as *mut [u8] as *mut [MaybeUninit<u8>]) }; + let out = unsafe { &mut *(out as *mut [MaybeUninit<u8>]) }; self.read_raw(out) } Benno, would that work for you? Same in str.rs, of course.