From 0903b9e2a46cb6252a13d6b19d0502da9be191cf Mon Sep 17 00:00:00 2001 From: Jubilee Young Date: Thu, 22 Aug 2024 22:03:59 -0700 Subject: [PATCH] rust: alloc: eschew `Box>::write` Upstream Rust's libs-api team has consensus for stabilizing some of `feature(new_uninit)`, but not for `Box>::write`. Instead, we can use `MaybeUninit::write`, so Rust for Linux can drop the feature after stabilization. That will happen after merging, as the FCP has completed [1]. This is required before stabilization because remaining-unstable API will be divided into new features. This code doesn't know about those yet. It can't: they haven't landed, as the relevant PR is blocked on rustc's CI testing Rust-for-Linux without this patch. [ The PR has landed [2] and will be released in Rust 1.82.0 (expected on 2024-10-17), so we could conditionally enable the new unstable feature (`box_uninit_write` [3]) instead, but just for a single `unsafe` block it is probably not worth it. For the time being, I added it to the "nice to have" section of our unstable features list. - Miguel ] Link: https://github.com/rust-lang/rust/issues/63291#issuecomment-2183022955 [1] Link: https://github.com/rust-lang/rust/pull/129416 [2] Link: https://github.com/rust-lang/rust/issues/129397 [3] Signed-off-by: Jubilee Young Reviewed-by: Alice Ryhl Reviewed-by: Trevor Gross [ Reworded slightly. - Miguel ] Signed-off-by: Miguel Ojeda --- rust/kernel/alloc/box_ext.rs | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/rust/kernel/alloc/box_ext.rs b/rust/kernel/alloc/box_ext.rs index 829cb1c1cf9e69..9f1c1c48918904 100644 --- a/rust/kernel/alloc/box_ext.rs +++ b/rust/kernel/alloc/box_ext.rs @@ -21,8 +21,10 @@ pub trait BoxExt: Sized { impl BoxExt for Box { fn new(x: T, flags: Flags) -> Result { - let b = >::new_uninit(flags)?; - Ok(Box::write(b, x)) + let mut b = >::new_uninit(flags)?; + b.write(x); + // SAFETY: We just wrote to it. + Ok(unsafe { b.assume_init() }) } #[cfg(any(test, testlib))]