linux-kernel - Re: [PATCH 1/2] media: v4l2-core: Shifting signed 32-bit value by 31 bits error

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Date:   Wed, 5 Jun 2019 20:22:55 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Shuah Khan <skhan@...uxfoundation.org>, mchehab@...nel.org,
        hverkuil-cisco@...all.nl, sakari.ailus@...ux.intel.com,
        niklas.soderlund+renesas@...natech.se, ezequiel@...labora.com,
        paul.kocialkowski@...tlin.com
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] media: v4l2-core: Shifting signed 32-bit value by 31
 bits error

On 6/5/19 2:53 PM, Shuah Khan wrote:
> Fix the following cppcheck error:
> 
> Checking drivers/media/v4l2-core/v4l2-ioctl.c ...
> [drivers/media/v4l2-core/v4l2-ioctl.c:1370]: (error) Shifting signed 32-bit value by 31 bits is undefined behaviour
> 
> Signed-off-by: Shuah Khan <skhan@...uxfoundation.org>
> ---
>  drivers/media/v4l2-core/v4l2-ioctl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 6859bdac86fe..333e387bafeb 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -1364,7 +1364,7 @@ static void v4l_fill_fmtdesc(struct v4l2_fmtdesc *fmt)
>  					(char)((fmt->pixelformat >> 8) & 0x7f),
>  					(char)((fmt->pixelformat >> 16) & 0x7f),
>  					(char)((fmt->pixelformat >> 24) & 0x7f),
> -					(fmt->pixelformat & (1 << 31)) ? "-BE" : "");
> +					(fmt->pixelformat & BIT(31)) ? "-BE" : "");
>  			break;
>  		}
>  	}
> 

If this builds, I guess #define BIT(x) got pulled in indirectly
since bits.h nor bitops.h is currently #included in that source file.

Documentation/process/submit-checklist.rst rule #1 says:
1) If you use a facility then #include the file that defines/declares
   that facility.  Don't depend on other header files pulling in ones
   that you use.

Please add #include <linux/bits or bitops.h>

-- 
~Randy