On 3/10/24 00:57, Maíra Canal wrote:
> There are cases where we need to check the alignment of the pointers
> returned by `into_foreign`. Currently, this is not possible to be done
> at build time. Therefore, add a property to the trait ForeignOwnable,
> which specifies the alignment of the pointers returned by
> `into_foreign`.
>
> Suggested-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> Signed-off-by: Maíra Canal <mcanal@xxxxxxxxxx>
> Reviewed-by: Andreas Hindborg <a.hindborg@xxxxxxxxxxx>
> Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> ---
> rust/kernel/sync/arc.rs | 2 ++
> rust/kernel/types.rs | 7 +++++++
> 2 files changed, 9 insertions(+)
>
> diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
> index 7d4c4bf58388..da5c8cc325b6 100644
> --- a/rust/kernel/sync/arc.rs
> +++ b/rust/kernel/sync/arc.rs
> @@ -274,6 +274,8 @@ pub fn ptr_eq(this: &Self, other: &Self) -> bool {
> }
>
> impl<T: 'static> ForeignOwnable for Arc<T> {
> + const FOREIGN_ALIGN: usize = core::mem::align_of::<ArcInner<T>>();
> +
> type Borrowed<'a> = ArcBorrow<'a, T>;
>
> fn into_foreign(self) -> *const core::ffi::c_void {
> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> index aa77bad9bce4..76cd4226dd35 100644
> --- a/rust/kernel/types.rs
> +++ b/rust/kernel/types.rs
> @@ -20,6 +20,9 @@
> /// This trait is meant to be used in cases when Rust objects are stored in C objects and
> /// eventually "freed" back to Rust.
> pub trait ForeignOwnable: Sized {
> + /// The alignment of pointers returned by `into_foreign`.
> + const FOREIGN_ALIGN: usize;
> +
I think we need to make the trait `unsafe`, since we want `unsafe` code
to be able to rely on this value being correct.
--
Cheers,
Benno
> /// Type of values borrowed between calls to [`ForeignOwnable::into_foreign`] and
> /// [`ForeignOwnable::from_foreign`].
> type Borrowed<'a>;
> @@ -68,6 +71,8 @@ unsafe fn try_from_foreign(ptr: *const core::ffi::c_void) -> Option<Self> {
> }
>
> impl<T: 'static> ForeignOwnable for Box<T> {
> + const FOREIGN_ALIGN: usize = core::mem::align_of::<T>();
> +
> type Borrowed<'a> = &'a T;
>
> fn into_foreign(self) -> *const core::ffi::c_void {
> @@ -90,6 +95,8 @@ unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
> }
>
> impl ForeignOwnable for () {
> + const FOREIGN_ALIGN: usize = core::mem::align_of::<()>();
> +
> type Borrowed<'a> = ();
>
> fn into_foreign(self) -> *const core::ffi::c_void {
> --
> 2.43.0
>
