Hi Laurent,
On Tue, Aug 18, 2020 at 8:54 PM Laurent Pinchart
<laurent.pinchart@xxxxxxxxxxxxxxxx> wrote:
> No, the issue is that bits is equal to -7, 1LL won't change that.
>
> Once bits become negative, the loop stops, and the mask value isn't used
> afterwards. This would only cause an issue if a shift with a negative
> value generated side effects (such as a trap for instance) on top of
> producing an incorrect result. Can this happen ? I suppose we should
> silence the warning even if it's a false positive, as it doesn't look
> good in the kernel log.
Yes, you are right.
One way to avoid the negative shift:
--- a/drivers/media/usb/uvc/uvc_ctrl.c
+++ b/drivers/media/usb/uvc/uvc_ctrl.c
@@ -778,7 +778,8 @@ static s32 uvc_get_le_value(struct
uvc_control_mapping *mapping,
value |= offset > 0 ? (byte >> offset) : (byte << (-offset));
bits -= 8 - (offset > 0 ? offset : 0);
offset -= 8;
- mask = (1 << bits) - 1;
+ if (bits > 0)
+ mask = (1 << bits) - 1;
}
/* Sign-extend the value if needed. */
Just saw your patch where you quit the while(1) if bits <=0. Thanks!
