From 592c61f3bfceaa29f8275696bd67c3dfad7ef72e Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Thu, 12 Mar 2026 12:10:14 +0100 Subject: [PATCH] rust: kbuild: allow `unused_features` Starting with the upcoming Rust 1.96.0 (to be released 2026-05-28), `rustc` introduces the new lint `unused_features` [1], which warns [2]: warning: feature `used_with_arg` is declared but not used --> :1:93 | 1 | #![feature(asm_const,asm_goto,arbitrary_self_types,lint_reasons,offset_of_nested,raw_ref_op,used_with_arg)] | ^^^^^^^^^^^^^ | = note: `#[warn(unused_features)]` (part of `#[warn(unused)]`) on by default The original goal of using `-Zcrate-attr` automatically was that there is a consistent set of features enabled and managed globally for all Rust kernel code (modulo exceptions like the `rust/` crated). While we could require crates to enable features manually (even if we still keep the `-Zallow-features=` list, i.e. removing the `-Zcrate-attr` list), it is not really worth making all developers worry about it just for a new lint. The features are expected to eventually become stable anyway (most already did), and thus having to remove features in every file that may use them is not worth it either. Thus just allow the new lint globally. The lint actually existed for a long time, which is why `rustc` does not complain about an unknown lint in the stable versions we support, but it was "disabled" years ago [3], and now it was made to work again. For extra context, the new implementation of the lint has already been improved to avoid linting about features that became stable thanks to Benno's report and the ensuing discussion [4] [5], but while that helps, it is still the case that we may have features enabled that are not used for one reason or another in a particular crate. Cc: stable@vger.kernel.org # Needed in 6.12.y and later (Rust is pinned in older LTSs). Link: https://github.com/rust-lang/rust/pull/152164 [1] Link: https://github.com/Rust-for-Linux/pin-init/pull/114 [2] Link: https://github.com/rust-lang/rust/issues/44232 [3] Link: https://github.com/rust-lang/rust/issues/153523 [4] Link: https://github.com/rust-lang/rust/pull/153610 [5] Reviewed-by: Benno Lossin Reviewed-by: Gary Guo Link: https://patch.msgid.link/20260312111014.74198-1-ojeda@kernel.org Signed-off-by: Miguel Ojeda --- Makefile | 1 + 1 file changed, 1 insertion(+) diff --git a/Makefile b/Makefile index 73a39592f112..587345f16c97 100644 --- a/Makefile +++ b/Makefile @@ -476,6 +476,7 @@ KBUILD_USERLDFLAGS := $(USERLDFLAGS) export rust_common_flags := --edition=2021 \ -Zbinary_dep_depinfo=y \ -Astable_features \ + -Aunused_features \ -Dnon_ascii_idents \ -Dunsafe_op_in_unsafe_fn \ -Wmissing_docs \