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a3fecb9160
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). For arc architecture with CONFIG_ISA_ARCV2=y, the __fls() function uses __builtin_arc_fls() which lacks GCC's const attribute, preventing compile-time constant folding, and KUnit testing of ffs/fls fails on arc[3]. A patch[2] to GCC to solve this has been sent. Add a fix for this by handling compile-time constants with the standard __builtin_clzl() builtin (which has const attribute) while preserving the optimized arc-specific builtin for runtime cases. This has the added benefit of skipping runtime calculation of compile-time constant values. Even with the GCC bug fixed (which is about "attribute const") this is a good change to avoid needless runtime costs, and should be done regardless of the state of GCC's bug. Build tested ARCH=arc allyesconfig with GCC arc-linux 15.2.0. Link: https://github.com/KSPP/linux/issues/364 [1] Link: https://gcc.gnu.org/pipermail/gcc-patches/2025-August/693273.html Reported-by: kernel test robot <lkp@intel.com> Closes: https://lore.kernel.org/oe-kbuild-all/202508031025.doWxtzzc-lkp@intel.com/ [3] Signed-off-by: Kees Cook <kees@kernel.org> Acked-by: Vineet Gupta <vgupta@kernel.org> Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
200 lines
3.8 KiB
C
200 lines
3.8 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
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*/
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#ifndef _ASM_BITOPS_H
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#define _ASM_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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#ifndef __ASSEMBLER__
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#include <linux/types.h>
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#include <linux/compiler.h>
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#ifdef CONFIG_ISA_ARCOMPACT
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/*
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* Count the number of zeros, starting from MSB
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* Helper for fls( ) friends
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* This is a pure count, so (1-32) or (0-31) doesn't apply
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* It could be 0 to 32, based on num of 0's in there
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* clz(0x8000_0000) = 0, clz(0xFFFF_FFFF)=0, clz(0) = 32, clz(1) = 31
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*/
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static inline __attribute__ ((const)) int clz(unsigned int x)
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{
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unsigned int res;
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__asm__ __volatile__(
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" norm.f %0, %1 \n"
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" mov.n %0, 0 \n"
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" add.p %0, %0, 1 \n"
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: "=r"(res)
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: "r"(x)
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: "cc");
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return res;
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}
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static inline int constant_fls(unsigned int x)
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{
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int r = 32;
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if (!x)
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return 0;
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if (!(x & 0xffff0000u)) {
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x <<= 16;
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r -= 16;
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}
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if (!(x & 0xff000000u)) {
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x <<= 8;
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r -= 8;
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}
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if (!(x & 0xf0000000u)) {
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x <<= 4;
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r -= 4;
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}
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if (!(x & 0xc0000000u)) {
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x <<= 2;
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r -= 2;
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}
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if (!(x & 0x80000000u))
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r -= 1;
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return r;
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}
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/*
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* fls = Find Last Set in word
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* @result: [1-32]
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* fls(1) = 1, fls(0x80000000) = 32, fls(0) = 0
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*/
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static inline __attribute__ ((const)) int fls(unsigned int x)
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{
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if (__builtin_constant_p(x))
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return constant_fls(x);
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return 32 - clz(x);
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}
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/*
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* __fls: Similar to fls, but zero based (0-31)
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*/
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static inline __attribute__ ((const)) unsigned long __fls(unsigned long x)
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{
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if (!x)
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return 0;
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else
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return fls(x) - 1;
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}
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/*
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* ffs = Find First Set in word (LSB to MSB)
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* @result: [1-32], 0 if all 0's
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*/
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#define ffs(x) ({ unsigned long __t = (x); fls(__t & -__t); })
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/*
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* __ffs: Similar to ffs, but zero based (0-31)
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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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if (!word)
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return word;
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return ffs(word) - 1;
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}
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#else /* CONFIG_ISA_ARCV2 */
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/*
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* fls = Find Last Set in word
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* @result: [1-32]
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* fls(1) = 1, fls(0x80000000) = 32, fls(0) = 0
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*/
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static inline __attribute__ ((const)) int fls(unsigned int x)
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{
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int n;
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asm volatile(
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" fls.f %0, %1 \n" /* 0:31; 0(Z) if src 0 */
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" add.nz %0, %0, 1 \n" /* 0:31 -> 1:32 */
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: "=r"(n) /* Early clobber not needed */
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: "r"(x)
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: "cc");
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return n;
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}
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/*
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* __fls: Similar to fls, but zero based (0-31). Also 0 if no bit set
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*/
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static inline __attribute__ ((const)) unsigned long __fls(unsigned long x)
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{
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if (__builtin_constant_p(x))
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return x ? BITS_PER_LONG - 1 - __builtin_clzl(x) : 0;
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/* FLS insn has exactly same semantics as the API */
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return __builtin_arc_fls(x);
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}
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/*
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* ffs = Find First Set in word (LSB to MSB)
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* @result: [1-32], 0 if all 0's
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*/
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static inline __attribute__ ((const)) int ffs(unsigned int x)
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{
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int n;
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asm volatile(
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" ffs.f %0, %1 \n" /* 0:31; 31(Z) if src 0 */
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" add.nz %0, %0, 1 \n" /* 0:31 -> 1:32 */
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" mov.z %0, 0 \n" /* 31(Z)-> 0 */
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: "=r"(n) /* Early clobber not needed */
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: "r"(x)
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: "cc");
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return n;
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}
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/*
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* __ffs: Similar to ffs, but zero based (0-31)
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*/
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static inline __attribute__ ((const)) unsigned long __ffs(unsigned long x)
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{
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unsigned long n;
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asm volatile(
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" ffs.f %0, %1 \n" /* 0:31; 31(Z) if src 0 */
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" mov.z %0, 0 \n" /* 31(Z)-> 0 */
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: "=r"(n)
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: "r"(x)
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: "cc");
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return n;
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}
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#endif /* CONFIG_ISA_ARCOMPACT */
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/*
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* ffz = Find First Zero in word.
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* @return:[0-31], 32 if all 1's
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*/
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#define ffz(x) __ffs(~(x))
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#include <asm-generic/bitops/hweight.h>
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#include <asm-generic/bitops/fls64.h>
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#include <asm-generic/bitops/sched.h>
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#include <asm-generic/bitops/lock.h>
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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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#include <asm-generic/bitops/le.h>
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#include <asm-generic/bitops/ext2-atomic-setbit.h>
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#endif /* !__ASSEMBLER__ */
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#endif
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