From 44f2e626cbf777f3035aef7fa379ce34bf2f57e8 Mon Sep 17 00:00:00 2001 From: Alice Ryhl Date: Thu, 15 Feb 2024 10:46:01 +0000 Subject: rust: kernel: stop using ptr_metadata feature The `byte_sub` method was stabilized in Rust 1.75.0. By using that method, we no longer need the unstable `ptr_metadata` feature for implementing `Arc::from_raw`. This brings us one step closer towards not using unstable compiler features. Reviewed-by: Benno Lossin Reviewed-by: Martin Rodriguez Reboredo Reviewed-by: Trevor Gross Signed-off-by: Alice Ryhl Link: https://lore.kernel.org/r/20240215104601.1267763-1-aliceryhl@google.com [ Reworded title. ] Signed-off-by: Miguel Ojeda --- rust/kernel/sync/arc.rs | 16 +++++++--------- 1 file changed, 7 insertions(+), 9 deletions(-) (limited to 'rust/kernel/sync') diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs index 936bc549a082..7d4c4bf58388 100644 --- a/rust/kernel/sync/arc.rs +++ b/rust/kernel/sync/arc.rs @@ -30,7 +30,7 @@ use core::{ mem::{ManuallyDrop, MaybeUninit}, ops::{Deref, DerefMut}, pin::Pin, - ptr::{NonNull, Pointee}, + ptr::NonNull, }; use macros::pin_data; @@ -239,22 +239,20 @@ impl Arc { // binary, so its layout is not so large that it can trigger arithmetic overflow. let val_offset = unsafe { refcount_layout.extend(val_layout).unwrap_unchecked().1 }; - let metadata: ::Metadata = core::ptr::metadata(ptr); - // SAFETY: The metadata of `T` and `ArcInner` is the same because `ArcInner` is a struct - // with `T` as its last field. + // Pointer casts leave the metadata unchanged. This is okay because the metadata of `T` and + // `ArcInner` is the same since `ArcInner` is a struct with `T` as its last field. // // This is documented at: // . - let metadata: as Pointee>::Metadata = - unsafe { core::mem::transmute_copy(&metadata) }; + let ptr = ptr as *const ArcInner; + // SAFETY: The pointer is in-bounds of an allocation both before and after offsetting the // pointer, since it originates from a previous call to `Arc::into_raw` and is still valid. - let ptr = unsafe { (ptr as *mut u8).sub(val_offset) as *mut () }; - let ptr = core::ptr::from_raw_parts_mut(ptr, metadata); + let ptr = unsafe { ptr.byte_sub(val_offset) }; // SAFETY: By the safety requirements we know that `ptr` came from `Arc::into_raw`, so the // reference count held then will be owned by the new `Arc` object. - unsafe { Self::from_inner(NonNull::new_unchecked(ptr)) } + unsafe { Self::from_inner(NonNull::new_unchecked(ptr.cast_mut())) } } /// Returns an [`ArcBorrow`] from the given [`Arc`]. -- cgit v1.2.3