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Received: from dfw.source.kernel.org ([2604:1380:4641:c500::1]) by desiato.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1uiyIa-0000000DsSX-05zH for linux-riscv@lists.infradead.org; Mon, 04 Aug 2025 16:44:34 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id D5B615C5C4F; Mon, 4 Aug 2025 16:44:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6CA43C4AF09; Mon, 4 Aug 2025 16:44:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1754325858; bh=Lvi+SOjPyvnPy8ciTq59tLtKnNheCboKdQcwuoaKmUM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Ctp3G9AgiSCKLRp3GaS8h8tJ0qd2GiWi29AWYoW9OphEKR9uxRpx+tVuZ37fpfpsL IIiqsW+BqW+QyimiyTxqwluC3gBj0itLpMcnGvSkUJW+Jtvtu0G8zJm4JEpeAv07ho 5p6x/9qjLA5BPlYqTiJ+ItnXGdxvcaVtNEU6C921kzwAdklU0oJOrywzY/43+qATyc qkCMHpUPQU7oHixjqmmc6E/rz2akCtU5V8u3ok+s8qmQdwYEwufDL+M7FaTtHByKcC AuS5qqztdOQXGV87h2P9OWbRhnDlzJPeEZsfRqWu0o2aRbkYyxMYY+FjPb1Q+fYa9A LXmNT4G4CjwRQ== From: Kees Cook To: linux-arch@vger.kernel.org Cc: Kees Cook , linux-kernel@vger.kernel.org, x86@kernel.org, linux-alpha@vger.kernel.org, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-openrisc@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, llvm@lists.linux.dev, linux-hardening@vger.kernel.org Subject: [PATCH 14/17] s390: Add __attribute_const__ to ffs()-family implementations Date: Mon, 4 Aug 2025 09:44:10 -0700 Message-Id: <20250804164417.1612371-14-kees@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20250804163910.work.929-kees@kernel.org> References: <20250804163910.work.929-kees@kernel.org> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2996; i=kees@kernel.org; h=from:subject; bh=Lvi+SOjPyvnPy8ciTq59tLtKnNheCboKdQcwuoaKmUM=; b=owGbwMvMwCVmps19z/KJym7G02pJDBkTHkdP80i3EZa0WqNV8fMHixWbmEZHeZVc662+q3+e/ xLYYFLfUcrCIMbFICumyBJk5x7n4vG2Pdx9riLMHFYmkCEMXJwCMBGxaIa/knsDtxWE2YZe7I7U 3WXadmPtRbMlWjOOFS4Pyt5xp698FyPDCXntuf8OrPNQnv7aqHOTUcK6qfbFbx5JC57KYzE7e+8 jOwA= X-Developer-Key: i=kees@kernel.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250804_174432_525598_32265840 X-CRM114-Status: GOOD ( 12.41 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org While tracking down a problem where constant expressions used by BUILD_BUG_ON() suddenly stopped working[1], we found that an added static initializer was convincing the compiler that it couldn't track the state of the prior statically initialized value. Tracing this down found that ffs() was used in the initializer macro, but since it wasn't marked with __attribute__const__, the compiler had to assume the function might change variable states as a side-effect (which is not true for ffs(), which provides deterministic math results). Add missing __attribute_const__ annotations to S390's implementations of ffs(), __ffs(), fls(), and __fls() functions. These are pure mathematical functions that always return the same result for the same input with no side effects, making them eligible for compiler optimization. Build tested ARCH=s390 defconfig with GCC s390x-linux-gnu 14.2.0. Link: https://github.com/KSPP/linux/issues/364 [1] Signed-off-by: Kees Cook --- arch/s390/include/asm/bitops.h | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/arch/s390/include/asm/bitops.h b/arch/s390/include/asm/bitops.h index a5ca0a947691..fbcc3e1cc776 100644 --- a/arch/s390/include/asm/bitops.h +++ b/arch/s390/include/asm/bitops.h @@ -179,7 +179,7 @@ static inline unsigned char __flogr(unsigned long word) * * Undefined if no bit exists, so code should check against 0 first. */ -static inline unsigned long __ffs(unsigned long word) +static inline __attribute_const__ unsigned long __ffs(unsigned long word) { return __flogr(-word & word) ^ (BITS_PER_LONG - 1); } @@ -191,7 +191,7 @@ static inline unsigned long __ffs(unsigned long word) * This is defined the same way as the libc and * compiler builtin ffs routines (man ffs). */ -static inline int ffs(int word) +static inline __attribute_const__ int ffs(int word) { unsigned long mask = 2 * BITS_PER_LONG - 1; unsigned int val = (unsigned int)word; @@ -205,7 +205,7 @@ static inline int ffs(int word) * * Undefined if no set bit exists, so code should check against 0 first. */ -static inline unsigned long __fls(unsigned long word) +static inline __attribute_const__ unsigned long __fls(unsigned long word) { return __flogr(word) ^ (BITS_PER_LONG - 1); } @@ -221,7 +221,7 @@ static inline unsigned long __fls(unsigned long word) * set bit if value is nonzero. The last (most significant) bit is * at position 64. */ -static inline int fls64(unsigned long word) +static inline __attribute_const__ int fls64(unsigned long word) { unsigned long mask = 2 * BITS_PER_LONG - 1; @@ -235,7 +235,7 @@ static inline int fls64(unsigned long word) * This is defined the same way as ffs. * Note fls(0) = 0, fls(1) = 1, fls(0x80000000) = 32. */ -static inline int fls(unsigned int word) +static inline __attribute_const__ int fls(unsigned int word) { return fls64(word); } -- 2.34.1 _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv