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79e8328e5a
Compiling big-endian targets with Clang produces the diagnostic:
fs/namei.c:2173:13: warning: use of bitwise '|' with boolean operands [-Wbitwise-instead-of-logical]
} while (!(has_zero(a, &adata, &constants) | has_zero(b, &bdata, &constants)));
~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
||
fs/namei.c:2173:13: note: cast one or both operands to int to silence this warning
It appears that when has_zero was introduced, two definitions were
produced with different signatures (in particular different return
types).
Looking at the usage in hash_name() in fs/namei.c, I suspect that
has_zero() is meant to be invoked twice per while loop iteration; using
logical-or would not update `bdata` when `a` did not have zeros. So I
think it's preferred to always return an unsigned long rather than a
bool than update the while loop in hash_name() to use a logical-or
rather than bitwise-or.
[ Also changed powerpc version to do the same - Linus ]
Link: https://github.com/ClangBuiltLinux/linux/issues/1832
Link: https://lore.kernel.org/lkml/20230801-bitwise-v1-1-799bec468dc4@google.com/
Fixes: 36126f8f2e ("word-at-a-time: make the interfaces truly generic")
Debugged-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
121 lines
2.8 KiB
C
121 lines
2.8 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_WORD_AT_A_TIME_H
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#define _ASM_WORD_AT_A_TIME_H
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#include <linux/kernel.h>
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#include <asm/byteorder.h>
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#ifdef __BIG_ENDIAN
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struct word_at_a_time {
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const unsigned long high_bits, low_bits;
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};
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#define WORD_AT_A_TIME_CONSTANTS { REPEAT_BYTE(0xfe) + 1, REPEAT_BYTE(0x7f) }
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/* Bit set in the bytes that have a zero */
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static inline long prep_zero_mask(unsigned long val, unsigned long rhs, const struct word_at_a_time *c)
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{
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unsigned long mask = (val & c->low_bits) + c->low_bits;
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return ~(mask | rhs);
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}
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#define create_zero_mask(mask) (mask)
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static inline long find_zero(unsigned long mask)
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{
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long byte = 0;
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#ifdef CONFIG_64BIT
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if (mask >> 32)
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mask >>= 32;
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else
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byte = 4;
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#endif
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if (mask >> 16)
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mask >>= 16;
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else
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byte += 2;
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return (mask >> 8) ? byte : byte + 1;
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}
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static inline unsigned long has_zero(unsigned long val, unsigned long *data, const struct word_at_a_time *c)
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{
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unsigned long rhs = val | c->low_bits;
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*data = rhs;
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return (val + c->high_bits) & ~rhs;
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}
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#ifndef zero_bytemask
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#define zero_bytemask(mask) (~1ul << __fls(mask))
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#endif
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#else
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/*
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* The optimal byte mask counting is probably going to be something
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* that is architecture-specific. If you have a reliably fast
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* bit count instruction, that might be better than the multiply
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* and shift, for example.
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*/
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struct word_at_a_time {
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const unsigned long one_bits, high_bits;
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};
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#define WORD_AT_A_TIME_CONSTANTS { REPEAT_BYTE(0x01), REPEAT_BYTE(0x80) }
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#ifdef CONFIG_64BIT
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/*
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* Jan Achrenius on G+: microoptimized version of
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* the simpler "(mask & ONEBYTES) * ONEBYTES >> 56"
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* that works for the bytemasks without having to
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* mask them first.
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*/
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static inline long count_masked_bytes(unsigned long mask)
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{
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return mask*0x0001020304050608ul >> 56;
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}
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#else /* 32-bit case */
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/* Carl Chatfield / Jan Achrenius G+ version for 32-bit */
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static inline long count_masked_bytes(long mask)
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{
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/* (000000 0000ff 00ffff ffffff) -> ( 1 1 2 3 ) */
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long a = (0x0ff0001+mask) >> 23;
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/* Fix the 1 for 00 case */
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return a & mask;
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}
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#endif
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/* Return nonzero if it has a zero */
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static inline unsigned long has_zero(unsigned long a, unsigned long *bits, const struct word_at_a_time *c)
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{
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unsigned long mask = ((a - c->one_bits) & ~a) & c->high_bits;
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*bits = mask;
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return mask;
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}
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static inline unsigned long prep_zero_mask(unsigned long a, unsigned long bits, const struct word_at_a_time *c)
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{
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return bits;
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}
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static inline unsigned long create_zero_mask(unsigned long bits)
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{
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bits = (bits - 1) & ~bits;
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return bits >> 7;
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}
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/* The mask we created is directly usable as a bytemask */
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#define zero_bytemask(mask) (mask)
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static inline unsigned long find_zero(unsigned long mask)
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{
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return count_masked_bytes(mask);
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}
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#endif /* __BIG_ENDIAN */
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#endif /* _ASM_WORD_AT_A_TIME_H */
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