From: Alexander Weps <exander77@pm.me>
To: musl@lists.openwall.com
Subject: Re: [musl] Broken mktime calculations when crossing DST boundary
Date: Mon, 25 Mar 2024 00:36:49 +0000 [thread overview]
Message-ID: <4YlR0YRqzZlDIOVv6SP8UDoop89n8u7BvQl_7eXNTvDZnogXMxG1z-TLGIBf-O4edUphddXGfADbk_d7Uzb37g5JoH7vOIvvNRMFDxPWZok=@pm.me> (raw)
In-Reply-To: <Pine.BSM.4.64L.2403242340310.10180@herc.mirbsd.org>
I have no problem with the POSIX (Issue 8) or ISO C standard.
I agree it doesn't mandate mktime making correct calculations, but I would assume it is expected.
AW
On Monday, March 25th, 2024 at 00:51, Thorsten Glaser <tg@mirbsd.de> wrote:
> Alexander Weps dixit:
>
> > You are describing the musl behavior, more specifically what I see in mktime & __tm_to_secs.
> > I don't think this is correct behavior.
>
>
> This is what POSIX (Issue 8) and AFAIR also the next ISO C standard
> mandate, though:
>
> 1.–6. struct tm is normalised from seconds or minutes up to year
> 7. struct tm is converted to time_t (wrongly written down as
> “the number of seconds since the epoch” as it omits leap
> seconds)
> 8. timezone corrections for standard time at the moment in
> time calculated in step 7 is applied
> 9. if the timezone has DST:
> + if tm_isdst is positive, the time is adjusted by the offset
> + if tm_isdst is negative, the result is either the same as
> if it were 0 or the same as if it were 1; if the struct tm
> specifies a gap or repeated segment, which of the two is
> used is explicitly unspecified, i.e. the caller cannot rely
> on the libc to guess his intent if he sets tm_isdst to -1.
> 10. (not numbered) for gaps or repeats, mktime uses either the value
> from before the gap/repeat or the one after, choice again
> unspecified
>
> Tough luck there.
>
> The wording in this part is interesting though:
>
> | If tm_isdst is positive, mktime() shall further adjust the seconds
> | since the Epoch by the DST offset.
>
> But I guess that if you call with tm_isdst=1 and a broken-down time
> that clearly corresponds to nōn-DST, the DST offset for it is just 0
> and it’ll work out the obvious way.
>
> bye,
> //mirabilos
> --
> “It is inappropriate to require that a time represented as
> seconds since the Epoch precisely represent the number of
> seconds between the referenced time and the Epoch.”
> -- IEEE Std 1003.1b-1993 (POSIX) Section B.2.2.2
next prev parent reply other threads:[~2024-03-25 0:37 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
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 [this message]
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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