Re: [PATCH 2/5] lib: div64: use abs64() for the 64-bit operands of div64_s64()

On 2026-07-30T18:40:37, Alexey Charkov <[email protected]> wrote:
> lib: div64: use abs64() for the 64-bit operands of div64_s64()
>
> Both operands of div64_s64() are s64, but U-Boot's abs() is not 64-bit
> safe. Unlike its Linux counterpart, which dispatches on the argument
> type down to long long, U-Boot's abs() evaluates its argument as int
> whenever sizeof(x) != sizeof(long) and yields a long.
>
> The header even says so: "abs() should not be used for 64-bit types
> (s64, u64, long long) - use abs64() for those."
>
> So on BITS_PER_LONG == 32 both operands are silently truncated to 32
> bits before the division. Simulating the macro with long narrowed to
> 32 bits shows what reaches div64_u64():
>
>   x=         -4294967296  abs()=          0  abs64()=         4294967296
>   x=         -5000000000  abs()=  705032704  abs64()=         5000000000
>   x=-9223372036854775807  abs()=          1  abs64()= 9223372036854775807
>
> A zero from the first case makes the subsequent division a divide by
> zero rather than merely imprecise.
>
> div64_s64() has no in-tree callers today, so this is a latent bug and
> not a regression. Note that the abs() in div_s64_rem() is correct as-is
> and deliberately left alone.
>
> Fixes: 0342e335ba88 ("lib: div64: sync with Linux")
> Signed-off-by: Alexey Charkov <[email protected]>
>
> lib/div64.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)

Reviewed-by: Simon Glass <[email protected]>