On 6/11/19 4:27 PM, Shuah Khan wrote:
On 6/11/19 2:50 PM, Hans Verkuil wrote:
On 6/11/19 9:42 PM, Shuah Khan wrote:
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 <sk...@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.
I would like to have this cleaned up in the public media APIs. Those
can be
used by other compilers as well and it makes sense to me not to have
undefined behavior in those headers.
Great. That is a good point. I will start looking at the public media
APIs.
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.
Sounds good.
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
I don't think it makes sense to fix this for drivers. If gcc would do
this
wrong, we'd have noticed it ages ago.
Did some research into this. We are fine with gcc, however looks like
clang had the problem which has been fixed very recently in late 2018
in 6.0 release. This will be a problem even for kernel/drivers if older
clang is used to build it.
I am sending the two header fixes (media.h, and videodev2.h) to start
with.
thanks,
-- Shuah
