From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8375128642B; Mon, 4 Aug 2025 16:44:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754325858; cv=none; b=M9DHg7BzfmUrF9Cc5XWW58gFWTG6rgnkn3++J1KPJnUryJwVCe5mEroHSC6+QLN0kOFex9WRld4JKnXjRueKHGBclH9+/QQT5PyIHOHdYLtWkxJoGXmNkMkuurYxfRmM8ADrNnjqtQZV+Yur3I4YUsPkMMmqxMWyRn2FIsM6xwM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754325858; c=relaxed/simple; bh=Blko/RG2lvaODf864DzTpEKxwCgrc6vWtsbWwn+kegM=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=Y8vUr/HuFDQG1BTK4DhYGkbhs7PfAI7GJ+IReLtu9NjanMih9bqPETt/TLUsb2ipByXOaD/FbLLnK/YtfnghgjGQw2XrqAk50L+wwb38pWyOxAdq7yo7YKZFoIXsefB85TE+Aa1hWojnIbFnf2f2jVYVF1pHvn4HaQwEr9GwNcA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=RKm7fStn; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="RKm7fStn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 38944C4CEFA; 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=Blko/RG2lvaODf864DzTpEKxwCgrc6vWtsbWwn+kegM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=RKm7fStnT2f/O9WTNiGO7vEnfTrtD2BjrdbvAqXYGVLzrvGMKRZpwNljrVdV5Yc7F ms/UkNjaUp45VzaxYml1V2nd8lcIp45AXVOtEcUonr/GGOlwTuoYIbgkvoQhFG/wN6 WKZh/vtDzYFHTHdBEIoe7UUh+2ifIrTv4JkUwkgI3r31kXpv/+gCV57tdSm5RVB+/O k/FFqo6u0bVzkLRl1/HE6qUBw2RV4HQjdVjWVDfm2DbICcjzwJ+2AIF2V6qq7UvY2s 1GPhzwrTFl0I2J3UaB6SO0WN6XerugMXmpU92vxpkjKRJ1CQhkGFuh0FEX4P7zr0Pl YCvaKu3TYXMJw== 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 05/17] powerpc: Add __attribute_const__ to ffs()-family implementations Date: Mon, 4 Aug 2025 09:44:01 -0700 Message-Id: <20250804164417.1612371-5-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> Precedence: bulk X-Mailing-List: sparclinux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=1894; i=kees@kernel.org; h=from:subject; bh=Blko/RG2lvaODf864DzTpEKxwCgrc6vWtsbWwn+kegM=; b=owGbwMvMwCVmps19z/KJym7G02pJDBkTHkf8q+aJtHjfkMxRZhbRVyTe91hepyc95ULUY4Nmo RcSm190lLIwiHExyIopsgTZuce5eLxtD3efqwgzh5UJZAgDF6cATOTwfUaGT12nXSZdEFMMv1jN WH1s+TYRodUWp2689y1ICF67snCjFiPDy4IrLHkZtyc8f2I0KUiD65L66soy16kWMewJ/B3xN0J 4AA== X-Developer-Key: i=kees@kernel.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: 8bit 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 PowerPC's implementations of fls() function. 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=powerpc defconfig with GCC powerpc-linux-gnu 14.2.0. Link: https://github.com/KSPP/linux/issues/364 [1] Signed-off-by: Kees Cook --- arch/powerpc/include/asm/bitops.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/powerpc/include/asm/bitops.h b/arch/powerpc/include/asm/bitops.h index 671ecc6711e3..0d0470cd5ac3 100644 --- a/arch/powerpc/include/asm/bitops.h +++ b/arch/powerpc/include/asm/bitops.h @@ -276,7 +276,7 @@ static inline void arch___clear_bit_unlock(int nr, volatile unsigned long *addr) * fls: find last (most-significant) bit set. * Note fls(0) = 0, fls(1) = 1, fls(0x80000000) = 32. */ -static __always_inline int fls(unsigned int x) +static __always_inline __attribute_const__ int fls(unsigned int x) { int lz; @@ -294,7 +294,7 @@ static __always_inline int fls(unsigned int x) * 32-bit fls calls. */ #ifdef CONFIG_PPC64 -static __always_inline int fls64(__u64 x) +static __always_inline __attribute_const__ int fls64(__u64 x) { int lz; -- 2.34.1