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[2a02:3100:ad61:5a01:743c:891f:b33c:cae7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48c71d1f8fbsm8458219f8f.33.2026.10.07.22.37.54 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Wed, 07 Oct 2026 22:37:55 -0700 (PDT) From: Karl Mehltretter To: Russell King , Miguel Ojeda Cc: Karl Mehltretter , Boqun Feng , Gary Guo , =?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?= , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , Daniel Almeida , Tamir Duberstein , Alexandre Courbot , =?UTF-8?q?Onur=20=C3=96zkan?= , Arnd Bergmann , Linus Walleij , Christian Schrefl , Bradley Morgan , "Paul E . McKenney" , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , linux-arm-kernel@lists.infradead.org, rust-for-linux@vger.kernel.org, llvm@lists.linux.dev, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 1/6] ARM: cmpxchg: always inline __arch_xchg() and __cmpxchg() Date: Thu, 8 Oct 2026 07:37:41 +0200 Message-Id: <20261008053746.49631-2-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20261008053746.49631-1-kmehltretter@gmail.com> References: <20261008053746.49631-1-kmehltretter@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit __arch_xchg(), __cmpxchg() and __cmpxchg_local() end in a default case that calls an undefined function. That turns an unsupported size into a link error. It relies on the functions being inlined, so that the compiler can drop the default case for a constant size. They are only marked inline. gcc 8.1.0 with CC_OPTIMIZE_FOR_SIZE does not inline them in rust/helpers/helpers.c, which calls xchg() and cmpxchg() from many small helpers. The out-of-line copies keep the default case and the link fails. helpers.c:(.text+0x424): undefined reference to `__bad_xchg' helpers.c:(.text+0x4ac): undefined reference to `__bad_cmpxchg' Seen with bcm2835_defconfig and CONFIG_RUST=y on v7.3-rc1. The same config links with CONFIG_RUST=n. It also links with gcc 15.2.0 and with clang. v6.19 links. Commit ab717dd98bee ("rust: helpers: Add i8/i16 atomic xchg_acquire helpers") in v7.0 triggers __bad_xchg. Commit ac8f06ade38a ("rust: sync: atomic: Add Atomic<*{mut,const} T> support") in v7.1 also triggers __bad_cmpxchg. Mark the functions __always_inline. Fixes: ab717dd98bee ("rust: helpers: Add i8/i16 atomic xchg_acquire helpers") Fixes: ac8f06ade38a ("rust: sync: atomic: Add Atomic<*{mut,const} T> support") Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Karl Mehltretter --- arch/arm/include/asm/cmpxchg.h | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h index 9beb64d30586..0ce5225af442 100644 --- a/arch/arm/include/asm/cmpxchg.h +++ b/arch/arm/include/asm/cmpxchg.h @@ -26,7 +26,7 @@ #define swp_is_buggy #endif -static inline unsigned long +static __always_inline unsigned long __arch_xchg(unsigned long x, volatile void *ptr, int size) { extern void __bad_xchg(volatile void *, int); @@ -155,8 +155,8 @@ extern void __bad_cmpxchg(volatile void *ptr, int size); * cmpxchg only support 32-bits operands on ARMv6. */ -static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old, - unsigned long new, int size) +static __always_inline unsigned long +__cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, int size) { unsigned long oldval, res; @@ -220,9 +220,9 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old, sizeof(*(ptr))); \ }) -static inline unsigned long __cmpxchg_local(volatile void *ptr, - unsigned long old, - unsigned long new, int size) +static __always_inline unsigned long +__cmpxchg_local(volatile void *ptr, unsigned long old, unsigned long new, + int size) { unsigned long ret; -- 2.39.5 (Apple Git-154)