From: Alexander Weps <exander77@pm.me>
To: musl@lists.openwall.com
Cc: Daniel Gutson <danielgutson@gmail.com>,
Markus Wichmann <nullplan@gmx.net>
Subject: Re: [musl] Broken mktime calculations when crossing DST boundary
Date: Sun, 24 Mar 2024 18:00:06 +0000 [thread overview]
Message-ID: <a99XFm_NEHaIt7cSbDuCl0QKklI6qfRAfETlzuLE4Wv8F0mc21ZXJpQXbcE7Ra_s2PNz2by6gXgPF6vMx_6s7vwPvna22u1-QPRi1rzsus0=@pm.me> (raw)
In-Reply-To: <0_9-JV2MW3avVvzhE9vjqKqCX0fEZy0uUuZKIohFGEFDBY912nwZyxZe560H0cf_b8L2gD8e0eUAUp2Q3e1rmra3XEppx9HPhhFeulwLYZA=@pm.me>
So I started from:
1900-01-01 00:00:00
Adding 59 seconds each cycle (to speed things up).
And I already have some cycles in Musl even for Europe/Prague.
1946-12-01 02:59:17 CET
1946-12-01 01:00:16 CET <-- There should be: 1946-12-01 02:00:16 GMT
This looks like an issue involving negative DST change.
There were 3 STD/DST changes in 1946 in Europe/Prague:
1945-10-01 01:00:00Z +01:00:00 standard CET
1946-05-06 01:00:00Z +02:00:00 daylight CEST
1946-10-06 01:00:00Z +01:00:00 standard CET
1946-12-01 02:00:00Z +00:00:00 daylight GMT
1947-02-23 02:00:00Z +01:00:00 standard CET
And it works in glibc. I was able to run it all the way from 1900 to 2200.
Glibc correctly went from CET to GMT and then back:
1946-12-01 02:59:57 CET
1946-12-01 02:00:56 GMT
...
AW
On Sunday, March 24th, 2024 at 18:12, Alexander Weps <exander77@pm.me> wrote:
> Adding seconds cannot make time go backwards. If that is how it was interpreted, than the interpretation is erroneous.
>
> I think I will do some test.
>
> If you start with 1900-01-01 00:00:00 and start adding seconds and calling mktime, you should reliable get to 2200-12-31 59:59:59 in all timezones. Same goes for minutes, hours, days, years.
>
> If that's not the case then the interpretation in musl is wrong.
>
> This is a basic elementary functionality of mktime.
>
> There can't be any going back in time a cycles.
>
> AW
>
>
>
> On Sunday, March 24th, 2024 at 18:04, Rich Felker dalias@libc.org wrote:
>
> > On Sun, Mar 24, 2024 at 01:36:42PM +0000, Alexander Weps wrote:
> >
> > > Also thanks for the Pacific/Apia example. Not only that it fails for that date:
> > > Pattern: * * * * * *
> > > Initial: 2011-12-29_23:59:59
> > > Expected: 2011-32-31_00:00:00
> > > Actual: 2011-12-29_00:00:00
> > > My cron tool again going back in time.
> > >
> > > It fails one other test.
> > >
> > > I have to run my tests on multiple timezones.
> > >
> > > And it works in glibc.
> > >
> > > And that's after I removed tm_isdst and rewrote half the code to accommodate.
> > >
> > > Can We agree on some simple premise that with no uncertain STD/DST
> > > settings (tm_isdst = 0 or tm_isdst = 1), incrementing seconds by 1
> > > and calling mktime should never cause time to go back?
> > >
> > > Well, behold Pacific/Apia:
> > >
> > > I set 2011-12-29 23:59:59:
> > >
> > > tm_sec: 59
> > > tm_min: 59
> > > tm_hour: 23
> > > tm_mday: 29
> > > tm_mon: 11
> > > tm_year: 111
> > > tm_wday: 0
> > > tm_yday: 0
> > > tm_isdst: 1
> > > tm_gmtoff: 0
> > > tm_zone: (null)
> > >
> > > Calling mktime to see if everything is correct:
> > > mktime(&tm);
> > >
> > > before: 2011-12-29 23:59:59 -10
> > > tm_sec: 59
> > > tm_min: 59
> > > tm_hour: 23
> > > tm_mday: 29
> > > tm_mon: 11
> > > tm_year: 111
> > > tm_wday: 4
> > > tm_yday: 362
> > > tm_isdst: 1
> > > tm_gmtoff: -36000
> > > tm_zone: -10
> > >
> > > Incrementing seconds and calling mktime:
> > > tm.tm_sec += 1;
> > > mktime(&tm);
> > >
> > > after: 2011-12-29 00:00:00 -10
> > > tm_sec: 0
> > > tm_min: 0
> > > tm_hour: 0
> > > tm_mday: 29
> > > tm_mon: 11
> > > tm_year: 111
> > > tm_wday: 4
> > > tm_yday: 362
> > > tm_isdst: 1
> > > tm_gmtoff: -36000
> > > tm_zone: -10
> > > We went from:
> > > 2011-12-29 23:59:59 -10
> > > To:
> > > 2011-12-29 00:00:00 -10
> > >
> > > By adding 1 second. The tm_isdst was not set to -1.
> > >
> > > This is totally unreliable.
> >
> > From what I understand, you've set the input to a time that doesn't
> > exist in the local timezone: 2011-12-30 00:00:00. This could be either
> > 1 second after 2011-12-29 23:59:59, as you intended, or 1 day before
> > 2011-12-31 00:00:00. The latter is how it was interpreted. However, it
> > does not seem to have correctly set tm_gmtoff to reflect how it was
> > interpreted. We should check this out because that's probably an
> > actual bug.
> >
> > Rich
next prev parent reply other threads:[~2024-03-24 18:00 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-24 13:36 Alexander Weps
2024-03-24 16:59 ` Alexander Weps
2024-03-24 17:04 ` Rich Felker
2024-03-24 17:12 ` Alexander Weps
2024-03-24 18:00 ` Alexander Weps [this message]
2024-03-24 18:02 ` Rich Felker
2024-03-24 18:16 ` Alexander Weps
2024-03-24 18:24 ` Rich Felker
2024-03-24 18:36 ` Alexander Weps
2024-03-24 19:01 ` Joakim Sindholt
2024-03-24 19:05 ` Alexander Weps
2024-03-24 19:06 ` Alexander Weps
2024-03-24 19:13 ` Alexander Weps
2024-03-24 19:13 ` Alexander Weps
2024-03-24 19:22 ` Rich Felker
2024-03-24 19:57 ` Alexander Weps
2024-03-24 20:22 ` Rich Felker
2024-03-24 20:50 ` Alexander Weps
2024-03-24 21:43 ` Alexander Weps
2024-03-24 23:51 ` Thorsten Glaser
2024-03-25 0:36 ` Alexander Weps
2024-03-25 11:52 ` Alexander Weps
2024-03-25 12:21 ` Rich Felker
2024-03-25 12:55 ` Alexander Weps
2024-03-25 13:08 ` Rich Felker
2024-03-25 13:13 ` Alexander Weps
2024-03-25 13:13 ` Rich Felker
2024-03-25 13:24 ` Alexander Weps
2024-03-25 13:42 ` Rich Felker
2024-03-25 13:48 ` Alexander Weps
2024-03-25 13:50 ` Alexander Weps
2024-03-25 18:02 ` Rich Felker
2024-03-25 18:28 ` Alexander Weps
2024-03-25 18:53 ` Rich Felker
2024-03-25 18:57 ` Alexander Weps
2024-03-25 19:38 ` Rich Felker
2024-03-25 19:47 ` Rich Felker
2024-03-25 20:05 ` Alexander Weps
2024-03-25 20:12 ` Alexander Weps
2024-03-25 20:00 ` Alexander Weps
2024-03-25 20:23 ` Rich Felker
2024-03-25 20:31 ` Rich Felker
2024-03-25 23:19 ` Thorsten Glaser
2024-03-25 23:16 ` Thorsten Glaser
2024-03-25 13:44 ` Alexander Weps
2024-03-25 22:40 ` Thorsten Glaser
2024-03-25 22:59 ` Alexander Weps
2024-03-25 23:34 ` Thorsten Glaser
2024-03-26 12:45 ` Alexander Weps
2024-03-26 21:59 ` Thorsten Glaser
2024-03-27 0:14 ` Alexander Weps
2024-03-27 0:38 ` Alexander Weps
2024-03-27 1:35 ` Thorsten Glaser
2024-03-27 2:45 ` Alexander Weps
2024-03-27 4:42 ` Thorsten Glaser
2024-03-26 18:56 ` Alexander Weps
2024-03-25 23:13 ` Rich Felker
-- strict thread matches above, loose matches on Subject: below --
2024-03-22 19:56 Alexander Weps
2024-03-23 6:41 ` Markus Wichmann
[not found] ` <528SeRFaPfDw7fA4kqKDlio1U4RB_t9nmUemPcWw9_t1e2hBDpXYFmOqxAC37szgYvAVtmTuXWsmT64SSN3cSQFVdrQqXUAgkdTMPZQ0bg0=@pm.me>
2024-03-23 10:38 ` Markus Wichmann
2024-03-23 11:59 ` Alexander Weps
2024-03-23 12:00 ` Alexander Weps
2024-03-23 12:31 ` Rich Felker
2024-03-23 13:49 ` Alexander Weps
2024-03-23 15:31 ` Rich Felker
2024-03-23 16:54 ` Alexander Weps
2024-03-23 18:57 ` Alexander Weps
2024-03-23 19:33 ` Alexander Weps
2024-03-23 20:18 ` Rich Felker
2024-03-23 20:40 ` Alexander Weps
2024-03-24 0:36 ` Eric Pruitt
2024-03-24 2:04 ` Rich Felker
2024-03-24 3:32 ` Daniel Gutson
2024-03-24 11:05 ` Alexander Weps
2024-03-24 13:24 ` Alexander Weps
2024-03-23 12:01 ` Alexander Weps
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