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    Subject[PATCH 5.12 211/700] random32: Fix implicit truncation warning in prandom_seed_state()
    Date
    From: Richard Fitzgerald <rf@opensource.cirrus.com>

    [ Upstream commit d327ea15a305024ef0085252fa3657bbb1ce25f5 ]

    sparse generates the following warning:

    include/linux/prandom.h:114:45: sparse: sparse: cast truncates bits from
    constant value

    This is because the 64-bit seed value is manipulated and then placed in a
    u32, causing an implicit cast and truncation. A forced cast to u32 doesn't
    prevent this warning, which is reasonable because a typecast doesn't prove
    that truncation was expected.

    Logical-AND the value with 0xffffffff to make explicit that truncation to
    32-bit is intended.

    Reported-by: kernel test robot <lkp@intel.com>
    Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
    Reviewed-by: Petr Mladek <pmladek@suse.com>
    Signed-off-by: Petr Mladek <pmladek@suse.com>
    Link: https://lore.kernel.org/r/20210525122012.6336-3-rf@opensource.cirrus.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    include/linux/prandom.h | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/include/linux/prandom.h b/include/linux/prandom.h
    index bbf4b4ad61df..056d31317e49 100644
    --- a/include/linux/prandom.h
    +++ b/include/linux/prandom.h
    @@ -111,7 +111,7 @@ static inline u32 __seed(u32 x, u32 m)
    */
    static inline void prandom_seed_state(struct rnd_state *state, u64 seed)
    {
    - u32 i = (seed >> 32) ^ (seed << 10) ^ seed;
    + u32 i = ((seed >> 32) ^ (seed << 10) ^ seed) & 0xffffffffUL;

    state->s1 = __seed(i, 2U);
    state->s2 = __seed(i, 8U);
    --
    2.30.2


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