linux-kernel - [crng-random:jd/get_random_u32_below 23/26] include/linux/random.h:64:77: sparse: sparse: cast truncates bits from constant value (5dc becomes dc)

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Message-ID: <202210111552.nyQfJ2TY-lkp@intel.com>
Date:   Tue, 11 Oct 2022 15:11:14 +0800
From:   kernel test robot <lkp@...el.com>
To:     "Jason A. Donenfeld" <zx2c4@...nel.org>
Cc:     kbuild-all@...ts.01.org, zx2c4@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [crng-random:jd/get_random_u32_below 23/26]
 include/linux/random.h:64:77: sparse: sparse: cast truncates bits from
 constant value (5dc becomes dc)

tree:   git://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git jd/get_random_u32_below
head:   64e577cf130af4c0a0cb0dcc9cd64de6525ab80f
commit: dbc0933c6b1d8c21eb938d44038ae0ffaf930c0c [23/26] random: use rejection sampling for uniform bounded random integers
config: s390-randconfig-s031-20221010
compiler: s390-linux-gcc (GCC) 12.1.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # apt-get install sparse
        # sparse version: v0.6.4-39-gce1a6720-dirty
        # https://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git/commit/?id=dbc0933c6b1d8c21eb938d44038ae0ffaf930c0c
        git remote add crng-random git://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git
        git fetch --no-tags crng-random jd/get_random_u32_below
        git checkout dbc0933c6b1d8c21eb938d44038ae0ffaf930c0c
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=s390 SHELL=/bin/bash fs/ext4/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@...el.com>

sparse warnings: (new ones prefixed by >>)
   fs/ext4/super.c: note: in included file (through include/linux/nodemask.h, include/linux/mmzone.h, include/linux/gfp.h, ...):
>> include/linux/random.h:64:77: sparse: sparse: cast truncates bits from constant value (5dc becomes dc)
>> include/linux/random.h:64:77: sparse: sparse: cast truncates bits from constant value (5dc becomes dc)

vim +64 include/linux/random.h

    53	
    54	u32 __get_random_u32_below(u32 ceil);
    55	/* Returns a random integer in the interval [0, ceil), with uniform distribution. */
    56	static inline u32 get_random_u32_below(u32 ceil)
    57	{
    58		if (!__builtin_constant_p(ceil))
    59			return __get_random_u32_below(ceil);
    60	
    61		for (;;) {
    62			if (ceil <= 1U << 8) {
    63				u32 mult = ceil * get_random_u8();
  > 64				if (is_power_of_2(ceil) || (u8)mult >= -(__force u8)ceil % ceil)
    65					return mult >> 8;
    66			} else if (ceil <= 1U << 16) {
    67				u32 mult = ceil * get_random_u16();
    68				if (is_power_of_2(ceil) || (u16)mult >= -(__force u16)ceil % ceil)
    69					return mult >> 16;
    70			} else {
    71				u64 mult = (u64)ceil * get_random_u32();
    72				if (is_power_of_2(ceil) || (u32)mult >= -ceil % ceil)
    73					return mult >> 32;
    74			}
    75		}
    76	}
    77	

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp

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