From 5febf432df1cfa5b25d99b54c32103fafbdd0eb9 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Sun, 16 Aug 2026 15:32:33 +0200 Subject: kbuild: rust: keep Rust objects out of Clang LTO with inline helpers Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit `objtool` errors such as: vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a: can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd The reason is that in such builds, the Clang invocation that compiles the combined Rust plus helpers bitcode emits LLVM bitcode (again) -- the final code generation happens in the linker's LTO step, which the `-mllvm` trap options passed to Clang do not reach. This, in turn, means that unreachable traps are missing, and the impossible paths do not merely fallthrough to the next symbol, but past the end of their own section, since LTO builds place each function in its own section. Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always emits machine code directly, with the traps in place. Assisted-by: LLM Cc: Gary Guo Cc: Boqun Feng Cc: Alice Ryhl Cc: Matthew Maurer Cc: Josh Poimboeuf Cc: Peter Zijlstra Cc: stable@vger.kernel.org Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust") Acked-by: Gary Guo Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org Signed-off-by: Miguel Ojeda --- include/asm-generic/qrwlock.h | 147 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 147 insertions(+) create mode 100644 include/asm-generic/qrwlock.h (limited to 'include/asm-generic/qrwlock.h') diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h new file mode 100644 index 000000000..75b8f4601 --- /dev/null +++ b/include/asm-generic/qrwlock.h @@ -0,0 +1,147 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ +/* + * Queue read/write lock + * + * These use generic atomic and locking routines, but depend on a fair spinlock + * implementation in order to be fair themselves. The implementation in + * asm-generic/spinlock.h meets these requirements. + * + * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P. + * + * Authors: Waiman Long + */ +#ifndef __ASM_GENERIC_QRWLOCK_H +#define __ASM_GENERIC_QRWLOCK_H + +#include +#include +#include + +#include + +/* Must be included from asm/spinlock.h after defining arch_spin_is_locked. */ + +/* + * Writer states & reader shift and bias. + */ +#define _QW_WAITING 0x100 /* A writer is waiting */ +#define _QW_LOCKED 0x0ff /* A writer holds the lock */ +#define _QW_WMASK 0x1ff /* Writer mask */ +#define _QR_SHIFT 9 /* Reader count shift */ +#define _QR_BIAS (1U << _QR_SHIFT) + +/* + * External function declarations + */ +extern void queued_read_lock_slowpath(struct qrwlock *lock); +extern void queued_write_lock_slowpath(struct qrwlock *lock); + +/** + * queued_read_trylock - try to acquire read lock of a queued rwlock + * @lock : Pointer to queued rwlock structure + * Return: 1 if lock acquired, 0 if failed + */ +static inline int queued_read_trylock(struct qrwlock *lock) +{ + int cnts; + + cnts = atomic_read(&lock->cnts); + if (likely(!(cnts & _QW_WMASK))) { + cnts = (u32)atomic_add_return_acquire(_QR_BIAS, &lock->cnts); + if (likely(!(cnts & _QW_WMASK))) + return 1; + atomic_sub(_QR_BIAS, &lock->cnts); + } + return 0; +} + +/** + * queued_write_trylock - try to acquire write lock of a queued rwlock + * @lock : Pointer to queued rwlock structure + * Return: 1 if lock acquired, 0 if failed + */ +static inline int queued_write_trylock(struct qrwlock *lock) +{ + int cnts; + + cnts = atomic_read(&lock->cnts); + if (unlikely(cnts)) + return 0; + + return likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, + _QW_LOCKED)); +} +/** + * queued_read_lock - acquire read lock of a queued rwlock + * @lock: Pointer to queued rwlock structure + */ +static inline void queued_read_lock(struct qrwlock *lock) +{ + int cnts; + + cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts); + if (likely(!(cnts & _QW_WMASK))) + return; + + /* The slowpath will decrement the reader count, if necessary. */ + queued_read_lock_slowpath(lock); +} + +/** + * queued_write_lock - acquire write lock of a queued rwlock + * @lock : Pointer to queued rwlock structure + */ +static inline void queued_write_lock(struct qrwlock *lock) +{ + int cnts = 0; + /* Optimize for the unfair lock case where the fair flag is 0. */ + if (likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED))) + return; + + queued_write_lock_slowpath(lock); +} + +/** + * queued_read_unlock - release read lock of a queued rwlock + * @lock : Pointer to queued rwlock structure + */ +static inline void queued_read_unlock(struct qrwlock *lock) +{ + /* + * Atomically decrement the reader count + */ + (void)atomic_sub_return_release(_QR_BIAS, &lock->cnts); +} + +/** + * queued_write_unlock - release write lock of a queued rwlock + * @lock : Pointer to queued rwlock structure + */ +static inline void queued_write_unlock(struct qrwlock *lock) +{ + smp_store_release(&lock->wlocked, 0); +} + +/** + * queued_rwlock_is_contended - check if the lock is contended + * @lock : Pointer to queued rwlock structure + * Return: 1 if lock contended, 0 otherwise + */ +static inline int queued_rwlock_is_contended(struct qrwlock *lock) +{ + return arch_spin_is_locked(&lock->wait_lock); +} + +/* + * Remapping rwlock architecture specific functions to the corresponding + * queued rwlock functions. + */ +#define arch_read_lock(l) queued_read_lock(l) +#define arch_write_lock(l) queued_write_lock(l) +#define arch_read_trylock(l) queued_read_trylock(l) +#define arch_write_trylock(l) queued_write_trylock(l) +#define arch_read_unlock(l) queued_read_unlock(l) +#define arch_write_unlock(l) queued_write_unlock(l) +#define arch_rwlock_is_contended(l) queued_rwlock_is_contended(l) + +#endif /* __ASM_GENERIC_QRWLOCK_H */ -- cgit v1.3.1