Re: [PATCH v2 2/2] linux/bits.h: Add compile time sanity check of GENMASK inputs

[kbuild test robot]

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@xxxxxxxxx>

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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