[PATCH] rust: clarify the language unstable features in use
From: Miguel Ojeda
Date: Thu Mar 27 2025 - 17:17:35 EST
We track the details of which Rust features we use at our usual "live
list" [1] (and its sub-lists), but in light of a discussion in the LWN
article [2], it would help to clarify it in the source code.
In particular, we are very close to rely only on stable Rust language-wise
-- essentially only two language features remain (including the `kernel`
crate).
Thus add some details in both the feature list of the `kernel` crate as
well as the list of allowed features.
This does not over every single feature, and there are quite a few
non-language features that we use too. To have the full picture, please
refer to [1].
Link: https://github.com/Rust-for-Linux/linux/issues/2 [1]
Link: https://lwn.net/Articles/1015409/ [2]
Suggested-by: Andreas Hindborg <a.hindborg@xxxxxxxxxx>
Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
---
rust/kernel/lib.rs | 27 ++++++++++++++++++++-------
scripts/Makefile.build | 8 ++++++++
2 files changed, 28 insertions(+), 7 deletions(-)
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index ba0f3b0297b2..660a3ab6f9d4 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -12,21 +12,34 @@
//! do so first instead of bypassing this crate.
#![no_std]
-#![feature(arbitrary_self_types)]
-#![cfg_attr(CONFIG_RUSTC_HAS_COERCE_POINTEE, feature(derive_coerce_pointee))]
-#![cfg_attr(not(CONFIG_RUSTC_HAS_COERCE_POINTEE), feature(coerce_unsized))]
-#![cfg_attr(not(CONFIG_RUSTC_HAS_COERCE_POINTEE), feature(dispatch_from_dyn))]
-#![cfg_attr(not(CONFIG_RUSTC_HAS_COERCE_POINTEE), feature(unsize))]
+
+// Please see https://github.com/Rust-for-Linux/linux/issues/2 for details on
+// the unstable features in use.
+
+// Stable since Rust 1.79.0.
#![feature(inline_const)]
+
+// Stable since Rust 1.81.0.
#![feature(lint_reasons)]
-// Stable in Rust 1.82
+
+// Stable since Rust 1.82.0.
#![feature(raw_ref_op)]
-// Stable in Rust 1.83
+
+// Stable since Rust 1.83.0.
#![feature(const_maybe_uninit_as_mut_ptr)]
#![feature(const_mut_refs)]
#![feature(const_ptr_write)]
#![feature(const_refs_to_cell)]
+// Expected to become stable.
+#![feature(arbitrary_self_types)]
+
+// `feature(derive_coerce_pointee)` is the one expected to become stable.
+#![cfg_attr(CONFIG_RUSTC_HAS_COERCE_POINTEE, feature(derive_coerce_pointee))]
+#![cfg_attr(not(CONFIG_RUSTC_HAS_COERCE_POINTEE), feature(coerce_unsized))]
+#![cfg_attr(not(CONFIG_RUSTC_HAS_COERCE_POINTEE), feature(dispatch_from_dyn))]
+#![cfg_attr(not(CONFIG_RUSTC_HAS_COERCE_POINTEE), feature(unsize))]
+
// Ensure conditional compilation based on the kernel configuration works;
// otherwise we may silently break things like initcall handling.
#[cfg(not(CONFIG_RUST))]
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 56be83024851..41a640990cfa 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -226,6 +226,14 @@ $(obj)/%.lst: $(obj)/%.c FORCE
# Compile Rust sources (.rs)
# ---------------------------------------------------------------------------
+# The features in this list are the ones allowed for non-`rust/` code.
+#
+# - Stable since Rust 1.81.0: `feature(lint_reasons)`.
+# - Stable since Rust 1.82.0: `feature(asm_const)`, `feature(raw_ref_op)`.
+# - Stable since Rust 1.87.0: `feature(asm_goto)`.
+#
+# Please see https://github.com/Rust-for-Linux/linux/issues/2 for details on
+# the unstable features in use.
rust_allowed_features := asm_const,asm_goto,arbitrary_self_types,lint_reasons,raw_ref_op
# `--out-dir` is required to avoid temporaries being created by `rustc` in the
base-commit: e6ea10d5dbe082c54add289b44f08c9fcfe658af
--
2.49.0