From: Miguel Ojeda ojeda@kernel.org

Similar to what was done for `Zeroable<NonNull<T>>` in commit df27cef15360 ("rust: init: fix `Zeroable` implementation for `Option<NonNull<T>>` and `Option<KBox<T>>`"), the latest Rust documentation [1] says it guarantees that `transmute::<_, Option<T>>([0u8; size_of::<T>()])` is sound and produces `Option::<T>::None` only in some cases. In particular, it says:

`Box<U>` (specifically, only `Box<U, Global>`) when `U: Sized`

Thus restrict the `impl` to `Sized`, and use similar wording as in that commit too.

Link: https://doc.rust-lang.org/stable/std/option/index.html#representation [1] Signed-off-by: Miguel Ojeda ojeda@kernel.org Link: https://github.com/Rust-for-Linux/pin-init/pull/32/commits/a6007cf555e5946bc... Fixes: 9b2299af3b92 ("rust: pin-init: add `std` and `alloc` support from the user-space version") Cc: stable@vger.kernel.org [ Adjust mentioned commit to the one from the kernel. - Benno ] Signed-off-by: Benno Lossin benno.lossin@proton.me --- rust/pin-init/src/alloc.rs | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/rust/pin-init/src/alloc.rs b/rust/pin-init/src/alloc.rs index e16baa3b434e..5017f57442d8 100644 --- a/rust/pin-init/src/alloc.rs +++ b/rust/pin-init/src/alloc.rs @@ -17,11 +17,9 @@

pub extern crate alloc;

-// SAFETY: All zeros is equivalent to `None` (option layout optimization guarantee). -// -// In this case we are allowed to use `T: ?Sized`, since all zeros is the `None` variant and there -// is no problem with a VTABLE pointer being null. -unsafe impl<T: ?Sized> ZeroableOption for Box<T> {} +// SAFETY: All zeros is equivalent to `None` (option layout optimization guarantee: +// https://doc.rust-lang.org/stable/std/option/index.html#representation). +unsafe impl<T> ZeroableOption for Box<T> {}

/// Smart pointer that can initialize memory in-place. pub trait InPlaceInit<T>: Sized {