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SubjectRe: [PATCH] rtc: fix rtc_time64_to_tm calculation
On 07/01/2016 at 13:11:50 +0100, Andrzej Hajda wrote :
> Type of local variable days has been changed recently to unsigned,
> but it can take negative values. As a result it works incorrectly for some
> arguments. The patch fixes it.
>

Yeah, I was not planning to send that patch finally because it had more
issues than expected. What you did seems good, I'll have a closer look
when I'm back from vacations. My current internet access is too limited
to be able to pull/push anything with git.

> The problem has been detected using proposed semantic patch
> scripts/coccinelle/tests/unsigned_lesser_than_zero.cocci [1].
>
> [1]: http://permalink.gmane.org/gmane.linux.kernel/2120705
>
> Fixes: cab572b82c4b ('rtc: fix overflow and incorrect calculation in rtc_time64_to_tm')
> Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
> ---
> drivers/rtc/rtc-lib.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/rtc/rtc-lib.c b/drivers/rtc/rtc-lib.c
> index cf2b23c..6323d13 100644
> --- a/drivers/rtc/rtc-lib.c
> +++ b/drivers/rtc/rtc-lib.c
> @@ -54,7 +54,7 @@ void rtc_time64_to_tm(time64_t time, struct rtc_time *tm)
> {
> unsigned int month, year;
> int secs;
> - unsigned long days;
> + unsigned long days, leaps;
>
> /*
> * time must be positive
> @@ -66,13 +66,16 @@ void rtc_time64_to_tm(time64_t time, struct rtc_time *tm)
> tm->tm_wday = (days + 4) % 7;
>
> year = 1970 + days / 365;
> - days -= (year - 1970) * 365
> - + LEAPS_THRU_END_OF(year - 1)
> - - LEAPS_THRU_END_OF(1970 - 1);
> - if (days < 0) {
> + days -= (year - 1970) * 365;
> + leaps = LEAPS_THRU_END_OF(year - 1) - LEAPS_THRU_END_OF(1970 - 1);
> +
> + while (days < leaps) {
> year -= 1;
> days += 365 + is_leap_year(year);
> }
> +
> + days -= leaps;
> +
> tm->tm_year = year - 1900;
> tm->tm_yday = days + 1;
>
> --
> 1.9.1
>

--
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com


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