Messages in this thread | | | Subject | Re: [PATCH 1/2] media: v4l2-core: Shifting signed 32-bit value by 31 bits error | From | Shuah Khan <> | Date | Tue, 11 Jun 2019 13:42:12 -0600 |
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On 6/6/19 12:33 AM, Hans Verkuil wrote: > On 6/6/19 5:22 AM, Randy Dunlap wrote: >> 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@linuxfoundation.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. >>
It does build. You are right that I should have included bitops.h
>> 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> >> > > I'm not sure about this patch. '1 << 31' is used all over in the kernel, > including in public headers (e.g. media.h, videodev2.h). > > It seems arbitrary to change it only here, but not anywhere else. >
Right. We have several places in the kernel that do that.
> In this particular example for the fourcc handling I would prefer to just > use '1U << 31', both in v4l2-ioctl.c and videodev2.h. >
If you would like to take the patch, I can send v2 fixing it using 1U << 31 - This is simpler since it doesn't nee additional includes.
> A separate patch doing the same for MEDIA_ENT_ID_FLAG_NEXT in media.h would > probably be a good idea either: that way the public API at least will do > the right thing. >
I should have explained it better. I wanted to start with one or two places first to see if it is worth our time to fix these:
The full kernel cppcheck log for "Shifting signed 32-bit value by 31 bits is undefined behaviour" can be found at:
https://drive.google.com/file/d/19Xu7UqBGJ7BpzxEp92ZQYb6F8UPrk3z3/view
thanks, -- Shuah
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