mirrors/linux
1
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2025-12-27 11:06:41 -05:00
Code Issues Packages Projects Releases Wiki Activity

openrisc: Add __attribute_const__ to ffs()-family implementations

Browse Source 
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 OpenRISC'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=openrisc defconfig with GCC or1k-linux 15.1.0.

Link: https://github.com/KSPP/linux/issues/364 [1]
Acked-by: Stafford Horne <shorne@gmail.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250804164417.1612371-10-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>
This commit is contained in:
Kees Cook
2025-08-04 09:44:06 -07:00
parent c51c26e687
commit acfab97bef
4 changed files with 4 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
arch/openrisc/include/asm/bitops/__ffs.h
View File

@@ -11,7 +11,7 @@
#ifdef CONFIG_OPENRISC_HAVE_INST_FF1
static inline unsigned long __ffs(unsigned long x)
static inline __attribute_const__ unsigned long __ffs(unsigned long x)
{
int ret;

2
arch/openrisc/include/asm/bitops/__fls.h
View File

@@ -11,7 +11,7 @@
#ifdef CONFIG_OPENRISC_HAVE_INST_FL1
static inline unsigned long __fls(unsigned long x)
static inline __attribute_const__ unsigned long __fls(unsigned long x)
{
int ret;

2
arch/openrisc/include/asm/bitops/ffs.h
View File

@@ -10,7 +10,7 @@
#ifdef CONFIG_OPENRISC_HAVE_INST_FF1
static inline int ffs(int x)
static inline __attribute_const__ int ffs(int x)
{
int ret;

2
arch/openrisc/include/asm/bitops/fls.h
View File

@@ -11,7 +11,7 @@
#ifdef CONFIG_OPENRISC_HAVE_INST_FL1
static inline int fls(unsigned int x)
static inline __attribute_const__ int fls(unsigned int x)
{
int ret;