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Message-ID: <20240205091842.2858516-1-aliceryhl@google.com>
Date: Mon, 5 Feb 2024 09:18:42 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Miguel Ojeda <ojeda@...nel.org>
Cc: Wedson Almeida Filho <wedsonaf@...il.com>, Alex Gaynor <alex.gaynor@...il.com>,
Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>,
Alice Ryhl <aliceryhl@...gle.com>, rust-for-linux@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH] rust: 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.
Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
---
This patch is based on rust-next because it depends on the patch [1]
that upgrades to Rust 1.75.0.
[1]: https://lore.kernel.org/all/20231224172128.271447-1-ojeda@kernel.org/
rust/kernel/lib.rs | 1 -
rust/kernel/sync/arc.rs | 10 ++++------
2 files changed, 4 insertions(+), 7 deletions(-)
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index b89ecf4e97a0..b8d4c8167a29 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -17,7 +17,6 @@
#![feature(dispatch_from_dyn)]
#![feature(new_uninit)]
#![feature(offset_of)]
-#![feature(ptr_metadata)]
#![feature(receiver_trait)]
#![feature(unsize)]
diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 77cdbcf7bd2e..16309c3a9a01 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -30,7 +30,7 @@
mem::{ManuallyDrop, MaybeUninit},
ops::{Deref, DerefMut},
pin::Pin,
- ptr::{NonNull, Pointee},
+ ptr::NonNull,
};
use macros::pin_data;
@@ -239,18 +239,16 @@ pub unsafe fn from_raw(ptr: *const T) -> Self {
// 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: <T as Pointee>::Metadata = core::ptr::metadata(ptr);
// SAFETY: The metadata of `T` and `ArcInner<T>` is the same because `ArcInner` is a struct
// with `T` as its last field.
//
// This is documented at:
// <https://doc.rust-lang.org/std/ptr/trait.Pointee.html>.
- let metadata: <ArcInner<T> as Pointee>::Metadata =
- unsafe { core::mem::transmute_copy(&metadata) };
+ let ptr = ptr as *mut ArcInner<T>;
+
// 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.
base-commit: f090f0d0eea9666a96702b29bc9a64cbabee85c5
--
2.43.0.594.gd9cf4e227d-goog
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