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). > > > > The expression len * 10 * CEC_TIM_DATA_BIT_TOTAL is currently being > > evaluated using 32-bit arithmetic. > > > > Also, remove unnecessary parentheses and add a code comment to make it > > clear what is the reason of the code change. > > > > Addresses-Coverity-ID: 1454996 > > Signed-off-by: Gustavo A. R. Silva <gust...@embeddedor.com> > > --- > > Changes in v2: > > - Update subject and changelog to better reflect the proposed code changes. > > - Add suffix ULL to constant instead of casting a variable. > > - Remove unncessary parentheses. > > unncessary -> unnecessary > > > - Add code comment. > > > > drivers/media/platform/vivid/vivid-cec.c | 11 +++++++++-- > > 1 file changed, 9 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/media/platform/vivid/vivid-cec.c > > b/drivers/media/platform/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_adapter > > *adap, ktime_t ts, > > > > if (adap == NULL) > > return; > > - ts = 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. > > + */ > > 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: > > /* > * 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 <= 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
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