Commit c32ee3d9 authored by Matthias Kaehlcke's avatar Matthias Kaehlcke Committed by Linus Torvalds
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bitops: avoid integer overflow in GENMASK(_ULL) 

GENMASK(_ULL) performs a left-shift of ~0UL(L), which technically
results in an integer overflow.  clang raises a warning if the overflow
occurs in a preprocessor expression.  Clear the low-order bits through a
substraction instead of the left-shift to avoid the overflow.

(akpm: no change in .text size in my testing)

Link: http://lkml.kernel.org/r/20170803212020.24939-1-mka@chromium.org


Signed-off-by: default avatarMatthias Kaehlcke <mka@chromium.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e9ef073a

include/linux/bitops.h

+3 −2
Original line number Diff line number Diff line
@@ -19,10 +19,11 @@ 
 * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000.

 */

#define GENMASK(h, l) \

	(((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h))))

	(((~0UL) - (1UL << (l)) + 1) & (~0UL >> (BITS_PER_LONG - 1 - (h))))



#define GENMASK_ULL(h, l) \

	(((~0ULL) << (l)) & (~0ULL >> (BITS_PER_LONG_LONG - 1 - (h))))

	(((~0ULL) - (1ULL << (l)) + 1) & \

	 (~0ULL >> (BITS_PER_LONG_LONG - 1 - (h))))



extern unsigned int __sw_hweight8(unsigned int w);

extern unsigned int __sw_hweight16(unsigned int w);