Re: [PATCH v2] hw/misc: use extract64 instead of 1 << i

[Richard Henderson]

On 12/27/24 02:46, Tigran Sogomonian wrote:
> 1 << i is casted to uint64_t while bitwise and with val.
> So this value may become 0xffffffff80000000 but only
> 31th "start" bit is required.
> Use the bitfield extract() API instead.

Again, I < 32.  There is no overflow.  The type of value is irrelevant.


> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> Signed-off-by: Tigran Sogomonian <tsogomonian@astralinux.ru>
> ---
>   hw/misc/mps2-fpgaio.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/misc/mps2-fpgaio.c b/hw/misc/mps2-fpgaio.c
> index d07568248d..04a3da5db0 100644
> --- a/hw/misc/mps2-fpgaio.c
> +++ b/hw/misc/mps2-fpgaio.c
> @@ -198,7 +198,7 @@ static void mps2_fpgaio_write(void *opaque, hwaddr offset, 
> uint64_t value,
>   
>               s->led0 = value & MAKE_64BIT_MASK(0, s->num_leds);
>               for (i = 0; i < s->num_leds; i++) {
> -                led_set_state(s->led[i], value & (1 << i));
> +                led_set_state(s->led[i], extract64(value, i, 1));
>               }
>           }
>           break;