linux-kernel - [PATCH] rust: bitops: add helpers for _find

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Message-ID: <20251203-bitops-find-helper-v1-1-5193deb57766@google.com>
Date: Wed, 03 Dec 2025 15:42:06 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Yury Norov <yury.norov@...il.com>, Burak Emir <bqe@...gle.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Alice Ryhl <aliceryhl@...gle.com>
Subject: [PATCH] rust: bitops: add helpers for _find_* functions

On 32-bit ARM, _find_next_bit does not exist because ARM provides that
function through a #define instead. This means that Rust, which calls
the underscored version, fails to find it. This triggers errors:

	ld.lld: error: undefined symbol: _find_next_bit
	>>> referenced by bitmap.rs:459 (rust/kernel/bitmap.rs:459)
	>>>               rust/kernel.o:(kernel::bitmap::tests::kunit_rust_wrapper_bitmap_borrow) in archive vmlinux.a
	>>> referenced by bitmap.rs:459 (rust/kernel/bitmap.rs:459)
	>>>               rust/kernel.o:(kernel::bitmap::tests::kunit_rust_wrapper_bitmap_set_clear_find) in archive vmlinux.a
	>>> referenced by bitmap.rs:459 (rust/kernel/bitmap.rs:459)
	>>>               rust/kernel.o:(kernel::bitmap::tests::kunit_rust_wrapper_bitmap_set_clear_find) in archive vmlinux.a
	>>> referenced 10 more times

	ld.lld: error: undefined symbol: _find_next_zero_bit
	>>> referenced by bitmap.rs:479 (rust/kernel/bitmap.rs:479)
	>>>               rust/kernel.o:(kernel::bitmap::tests::kunit_rust_wrapper_bitmap_copy) in archive vmlinux.a
	>>> referenced by bitmap.rs:479 (rust/kernel/bitmap.rs:479)
	>>>               rust/kernel.o:(kernel::bitmap::tests::kunit_rust_wrapper_bitmap_set_clear_find) in archive vmlinux.a
	>>> referenced by bitmap.rs:479 (rust/kernel/bitmap.rs:479)
	>>>               rust/kernel.o:(kernel::bitmap::tests::kunit_rust_wrapper_owned_bitmap_out_of_bounds) in archive vmlinux.a
	>>> referenced 6 more times

To fix this, add Rust helpers in this particular case.

Fixes: 6cf93a9ed39e ("rust: add bindings for bitops.h")
Reported-by: Andreas Hindborg <a.hindborg@...nel.org>
Closes: https://rust-for-linux.zulipchat.com/#narrow/channel/x/topic/x/near/561677301
Tested-by: Andreas Hindborg <a.hindborg@...nel.org>
Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
---
 rust/helpers/bitops.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/rust/helpers/bitops.c b/rust/helpers/bitops.c
index 5d0861d29d3f0d705a014ae4601685828405f33b..84061af591a261f7268ffe6535282bf3c7608e2d 100644
--- a/rust/helpers/bitops.c
+++ b/rust/helpers/bitops.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include <linux/bitops.h>
+#include <linux/find.h>
 
 void rust_helper___set_bit(unsigned long nr, unsigned long *addr)
 {
@@ -21,3 +22,34 @@ void rust_helper_clear_bit(unsigned long nr, volatile unsigned long *addr)
 {
 	clear_bit(nr, addr);
 }
+
+/*
+ * Rust normally calls the single-underscore-prefixed version of these
+ * functions, which are not inlined. However, on some platforms, they do not
+ * exist. In those cases, provide a rust helper for the underscored version.
+ */
+#ifdef find_next_zero_bit
+__rust_helper unsigned long
+rust_helper__find_next_zero_bit(const unsigned long *addr, unsigned long size,
+				unsigned long offset)
+{
+	return find_next_zero_bit(addr, size, offset);
+}
+#endif /* find_next_zero_bit */
+
+#ifdef find_next_bit
+__rust_helper unsigned long
+rust_helper__find_next_bit(const unsigned long *addr, unsigned long size,
+			   unsigned long offset)
+{
+	return find_next_bit(addr, size, offset);
+}
+#endif /* find_next_bit */
+
+#ifdef find_last_bit
+__rust_helper unsigned long
+rust_helper__find_last_bit(const unsigned long *addr, unsigned long size)
+{
+	return find_last_bit(addr, size);
+}
+#endif /* find_last_bit */

---
base-commit: 54e3eae855629702c566bd2e130d9f40e7f35bde
change-id: 20251203-bitops-find-helper-25ed1bbae700

Best regards,
-- 
Alice Ryhl <aliceryhl@...gle.com>