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SubjectRe: [PATCH v2 2/2] linux/bits.h: Add compile time sanity check of GENMASK inputs
Hi Rikard,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[cannot apply to v5.3-rc3 next-20190807]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url: https://github.com/0day-ci/linux/commits/Rikard-Falkeborn/linux-bits-h-Clarify-macro-argument-names/20190805-024030
config: x86_64-randconfig-h003-201931 (attached as .config)
compiler: gcc-7 (Debian 7.4.0-10) 7.4.0
reproduce:
# save the attached .config to linux build tree
make ARCH=x86_64

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

In file included from include/linux/bits.h:22:0,
from include/linux/bitops.h:5,
from include/linux/kernel.h:12,
from include/linux/delay.h:22,
from drivers/iio/adc/max9611.c:20:
drivers/iio/adc/max9611.c: In function 'max9611_init':
include/linux/build_bug.h:16:45: error: negative width in bit-field '<anonymous>'
#define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:(-!!(e)); }))
^
>> include/linux/bits.h:24:18: note: in expansion of macro 'BUILD_BUG_ON_ZERO'
((unsigned long)BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
^~~~~~~~~~~~~~~~~
>> include/linux/bits.h:39:3: note: in expansion of macro 'GENMASK_INPUT_CHECK'
(GENMASK_INPUT_CHECK(high, low) + __GENMASK(high, low))
^~~~~~~~~~~~~~~~~~~
>> drivers/iio/adc/max9611.c:86:28: note: in expansion of macro 'GENMASK'
#define MAX9611_TEMP_MASK GENMASK(7, 15)
^~~~~~~
>> drivers/iio/adc/max9611.c:483:17: note: in expansion of macro 'MAX9611_TEMP_MASK'
regval = ret & MAX9611_TEMP_MASK;
^~~~~~~~~~~~~~~~~
--
In file included from include/linux/bits.h:22:0,
from include/linux/bitops.h:5,
from include/linux/kernel.h:12,
from include/linux/delay.h:22,
from drivers/iio//adc/max9611.c:20:
drivers/iio//adc/max9611.c: In function 'max9611_init':
include/linux/build_bug.h:16:45: error: negative width in bit-field '<anonymous>'
#define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:(-!!(e)); }))
^
>> include/linux/bits.h:24:18: note: in expansion of macro 'BUILD_BUG_ON_ZERO'
((unsigned long)BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
^~~~~~~~~~~~~~~~~
>> include/linux/bits.h:39:3: note: in expansion of macro 'GENMASK_INPUT_CHECK'
(GENMASK_INPUT_CHECK(high, low) + __GENMASK(high, low))
^~~~~~~~~~~~~~~~~~~
drivers/iio//adc/max9611.c:86:28: note: in expansion of macro 'GENMASK'
#define MAX9611_TEMP_MASK GENMASK(7, 15)
^~~~~~~
drivers/iio//adc/max9611.c:483:17: note: in expansion of macro 'MAX9611_TEMP_MASK'
regval = ret & MAX9611_TEMP_MASK;
^~~~~~~~~~~~~~~~~

vim +/BUILD_BUG_ON_ZERO +24 include/linux/bits.h

15
16 /*
17 * Create a contiguous bitmask starting at bit position @low and ending at
18 * position @high. For example
19 * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000.
20 */
21 #ifndef __ASSEMBLY__
> 22 #include <linux/build_bug.h>
23 #define GENMASK_INPUT_CHECK(high, low) \
> 24 ((unsigned long)BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
25 __is_constexpr(high) && __is_constexpr(low), \
26 (low) > (high), UL(0))))
27 #else
28 /*
29 * BUILD_BUG_ON_ZERO and __is_constexpr() are not available in h files
30 * included from asm files, disable the input check if that is the case.
31 */
32 #define GENMASK_INPUT_CHECK(high, low) UL(0)
33 #endif
34
35 #define __GENMASK(high, low) \
36 (((~UL(0)) - (UL(1) << (low)) + 1) & \
37 (~UL(0) >> (BITS_PER_LONG - 1 - (high))))
38 #define GENMASK(high, low) \
> 39 (GENMASK_INPUT_CHECK(high, low) + __GENMASK(high, low))
40

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