linux-kernel - Re: [PATCH v2] rust: bitops: fix missing _find

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Message-ID: <d4fc5d93-d147-4263-a672-4b6016957327@de.bosch.com>
Date: Tue, 6 Jan 2026 09:48:25 +0100
From: Dirk Behme <dirk.behme@...bosch.com>
To: Alice Ryhl <aliceryhl@...gle.com>, Yury Norov <yury.norov@...il.com>,
	Burak Emir <bqe@...gle.com>, Andreas Hindborg <a.hindborg@...nel.org>
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>, Trevor Gross
	<tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>,
	<rust-for-linux@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<stable@...r.kernel.org>
Subject: Re: [PATCH v2] rust: bitops: fix missing _find_* functions on 32-bit
 ARM

Am 1/5/2026 um 11:44 AM schrieb Alice Ryhl:
> On 32-bit ARM, you may encounter linker errors such as this one:
> 
> 	ld.lld: error: undefined symbol: _find_next_zero_bit
> 	>>> referenced by rust_binder_main.43196037ba7bcee1-cgu.0
> 	>>>               drivers/android/binder/rust_binder_main.o:(<rust_binder_main::process::Process>::insert_or_update_handle) in archive vmlinux.a
> 	>>> referenced by rust_binder_main.43196037ba7bcee1-cgu.0
> 	>>>               drivers/android/binder/rust_binder_main.o:(<rust_binder_main::process::Process>::insert_or_update_handle) in archive vmlinux.a
> 
> This error occurs because even though the functions are declared by
> include/linux/find.h, the definition is #ifdef'd out on 32-bit ARM. This
> is because arch/arm/include/asm/bitops.h contains:
> 
> 	#define find_first_zero_bit(p,sz)	_find_first_zero_bit_le(p,sz)
> 	#define find_next_zero_bit(p,sz,off)	_find_next_zero_bit_le(p,sz,off)
> 	#define find_first_bit(p,sz)		_find_first_bit_le(p,sz)
> 	#define find_next_bit(p,sz,off)		_find_next_bit_le(p,sz,off)
> 
> And the underscore-prefixed function is conditional on #ifndef of the
> non-underscore-prefixed name, but the declaration in find.h is *not*
> conditional on that #ifndef.
> 
> To fix the linker error, we ensure that the symbols in question exist
> when compiling Rust code. We do this by definining them in rust/helpers/

Just a quite minor nit: typo: definining -> defining

Dirk