lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20250804164417.1612371-6-kees@kernel.org>
Date: Mon,  4 Aug 2025 09:44:02 -0700
From: Kees Cook <kees@...nel.org>
To: linux-arch@...r.kernel.org
Cc: Kees Cook <kees@...nel.org>,
	linux-kernel@...r.kernel.org,
	x86@...nel.org,
	linux-alpha@...r.kernel.org,
	linux-csky@...r.kernel.org,
	linux-hexagon@...r.kernel.org,
	linux-m68k@...ts.linux-m68k.org,
	linux-mips@...r.kernel.org,
	linux-openrisc@...r.kernel.org,
	linux-parisc@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org,
	linux-riscv@...ts.infradead.org,
	linux-s390@...r.kernel.org,
	linux-sh@...r.kernel.org,
	sparclinux@...r.kernel.org,
	llvm@...ts.linux.dev,
	linux-hardening@...r.kernel.org
Subject: [PATCH 06/17] sh: Add __attribute_const__ to ffs()-family implementations

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 SH's implementations of
__ffs() and ffz() 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=sh defconfig with GCC sh4-linux-gnu 14.2.0.

Link: https://github.com/KSPP/linux/issues/364 [1]
Signed-off-by: Kees Cook <kees@...nel.org>
---
 arch/sh/include/asm/bitops.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/sh/include/asm/bitops.h b/arch/sh/include/asm/bitops.h
index 10ceb0d6b5a9..aba3aa96a50e 100644
--- a/arch/sh/include/asm/bitops.h
+++ b/arch/sh/include/asm/bitops.h
@@ -24,7 +24,7 @@
 #include <asm-generic/bitops/non-atomic.h>
 #endif
 
-static inline unsigned long ffz(unsigned long word)
+static inline unsigned long __attribute_const__ ffz(unsigned long word)
 {
 	unsigned long result;
 
@@ -44,7 +44,7 @@ static inline unsigned long ffz(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)
 {
 	unsigned long result;
 
-- 
2.34.1


Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ