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4251f58f62
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] Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20250804164417.1612371-6-kees@kernel.org Signed-off-by: Kees Cook <kees@kernel.org>
73 lines
1.6 KiB
C
73 lines
1.6 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __ASM_SH_BITOPS_H
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#define __ASM_SH_BITOPS_H
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#ifndef _LINUX_BITOPS_H
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#error only <linux/bitops.h> can be included directly
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#endif
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/* For __swab32 */
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#include <asm/byteorder.h>
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#include <asm/barrier.h>
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#ifdef CONFIG_GUSA_RB
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#include <asm/bitops-grb.h>
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#elif defined(CONFIG_CPU_SH2A)
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#include <asm-generic/bitops/atomic.h>
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#include <asm/bitops-op32.h>
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#elif defined(CONFIG_CPU_SH4A)
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#include <asm/bitops-llsc.h>
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#elif defined(CONFIG_CPU_J2) && defined(CONFIG_SMP)
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#include <asm/bitops-cas.h>
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#else
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#include <asm-generic/bitops/atomic.h>
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#include <asm-generic/bitops/non-atomic.h>
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#endif
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static inline unsigned long __attribute_const__ ffz(unsigned long word)
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{
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unsigned long result;
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__asm__("1:\n\t"
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"shlr %1\n\t"
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"bt/s 1b\n\t"
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" add #1, %0"
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: "=r" (result), "=r" (word)
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: "0" (~0L), "1" (word)
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: "t");
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return result;
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}
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/**
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* __ffs - find first bit in word.
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* @word: The word to search
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*
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* Undefined if no bit exists, so code should check against 0 first.
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*/
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static inline __attribute_const__ unsigned long __ffs(unsigned long word)
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{
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unsigned long result;
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__asm__("1:\n\t"
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"shlr %1\n\t"
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"bf/s 1b\n\t"
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" add #1, %0"
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: "=r" (result), "=r" (word)
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: "0" (~0L), "1" (word)
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: "t");
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return result;
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}
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#include <asm-generic/bitops/ffs.h>
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#include <asm-generic/bitops/hweight.h>
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#include <asm-generic/bitops/lock.h>
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#include <asm-generic/bitops/sched.h>
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#include <asm-generic/bitops/ext2-atomic.h>
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#include <asm-generic/bitops/fls.h>
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#include <asm-generic/bitops/__fls.h>
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#include <asm-generic/bitops/fls64.h>
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#include <asm-generic/bitops/le.h>
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#endif /* __ASM_SH_BITOPS_H */
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