From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:43608 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965676AbeBMU7G (ORCPT ); Tue, 13 Feb 2018 15:59:06 -0500 Date: Tue, 13 Feb 2018 21:59:00 +0100 From: Pavel Machek To: Hans Verkuil Cc: "Gustavo A. R. Silva" , Mauro Carvalho Chehab , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" Subject: Re: [PATCH v2 8/8] platform: vivid-cec: use 64-bit arithmetic instead of 32-bit Message-ID: <20180213205900.GB6185@amd> References: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="WYTEVAkct0FjGQmd" Content-Disposition: inline In-Reply-To: Sender: linux-media-owner@vger.kernel.org List-ID: --WYTEVAkct0FjGQmd Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon 2018-02-05 22:29:41, Hans Verkuil wrote: > On 02/05/2018 09:36 PM, Gustavo A. R. Silva wrote: > > Add suffix ULL to constant 10 in order to give the compiler complete > > information about the proper arithmetic to use. Notice that this > > constant is used in a context that expects an expression of type > > u64 (64 bits, unsigned). > >=20 > > The expression len * 10 * CEC_TIM_DATA_BIT_TOTAL is currently being > > evaluated using 32-bit arithmetic. > >=20 > > Also, remove unnecessary parentheses and add a code comment to make it > > clear what is the reason of the code change. > >=20 > > Addresses-Coverity-ID: 1454996 > > Signed-off-by: Gustavo A. R. Silva > > --- > > Changes in v2: > > - Update subject and changelog to better reflect the proposed code cha= nges. > > - Add suffix ULL to constant instead of casting a variable. > > - Remove unncessary parentheses. >=20 > unncessary -> unnecessary >=20 > > - Add code comment. > >=20 > > drivers/media/platform/vivid/vivid-cec.c | 11 +++++++++-- > > 1 file changed, 9 insertions(+), 2 deletions(-) > >=20 > > diff --git a/drivers/media/platform/vivid/vivid-cec.c b/drivers/media/p= latform/vivid/vivid-cec.c > > index b55d278..614787b 100644 > > --- a/drivers/media/platform/vivid/vivid-cec.c > > +++ b/drivers/media/platform/vivid/vivid-cec.c > > @@ -82,8 +82,15 @@ static void vivid_cec_pin_adap_events(struct cec_ada= pter *adap, ktime_t ts, > > =20 > > if (adap =3D=3D NULL) > > return; > > - ts =3D ktime_sub_us(ts, (CEC_TIM_START_BIT_TOTAL + > > - len * 10 * CEC_TIM_DATA_BIT_TOTAL)); > > + > > + /* > > + * Suffix ULL on constant 10 makes the expression > > + * CEC_TIM_START_BIT_TOTAL + 10ULL * len * CEC_TIM_DATA_BIT_TOTAL > > + * be evaluated using 64-bit unsigned arithmetic (u64), which > > + * is what ktime_sub_us expects as second argument. > > + */ >=20 > That's not really the comment that I was looking for. It still doesn't > explain *why* this is needed at all. How about something like this: >=20 > /* > * Add the ULL suffix to the constant 10 to work around a false Coverity > * "Unintentional integer overflow" warning. Coverity isn't smart enough > * to understand that len is always <=3D 16, so there is no chance of an > * integer overflow. > */ Or maybe it would be better to add comment about Coverity having false-positive and not to modify the code? Hmm. Could we do something like BUG_ON(len > 16) to make Coverity understand the ranges? Pavel --=20 (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo= g.html --WYTEVAkct0FjGQmd Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iEYEARECAAYFAlqDUZQACgkQMOfwapXb+vJPCACffW74HBAdGlWkCS5bplte9NVo e1wAn3KhUE81CDM5QDwzULA1mkqj9/Wf =aAcH -----END PGP SIGNATURE----- --WYTEVAkct0FjGQmd--