Hi Hans,
Quoting Hans Verkuil <hverkuil@xxxxxxxxx>:
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 <gustavo@xxxxxxxxxxxxxx>
---
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
Thanks for this.
- 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:
In MHO the reason for the change is simply the discrepancy between the
arithmetic expected by
the function ktime_sub_us and the arithmetic in which the expression
is being evaluated. And this
has nothing to do with any particular tool.
/*
* 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.
*/
:P
In my opinion it is not a good idea to tie the code to a particular tool.
There are only three appearances of the word 'Coverity' in the whole
code base, and, honestly I don't want to add more.
So I think I will document this issue as a FP in the Coverity platform.
Thanks!
--
Gustavo
Regards,
Hans
+ ts = ktime_sub_us(ts, CEC_TIM_START_BIT_TOTAL +
+ 10ULL * len * CEC_TIM_DATA_BIT_TOTAL);
cec_queue_pin_cec_event(adap, false, ts);
ts = ktime_add_us(ts, CEC_TIM_START_BIT_LOW);
cec_queue_pin_cec_event(adap, true, ts);
