From: Alexander Weps <exander77@pm.me>
To: Markus Wichmann <nullplan@gmx.net>
Cc: musl@lists.openwall.com
Subject: Re: [musl] Broken mktime calculations when crossing DST boundary
Date: Sat, 23 Mar 2024 11:59:56 +0000 [thread overview]
Message-ID: <Yf9tAroDB-Og6dyI5Ccs_aEwhmPuBXvmzllVAtyGCZSlAij_zgUHJyojz0fF-c9kudgI5mSVbFv6iwiPTeywz0lRgtUnLkoQJGw4It22YLg=@pm.me> (raw)
In-Reply-To: <Zf6xNpDVhTL7CdeP@voyager>
> You don't need to set yday or the others before calling mktime().
I thought that too, but wanted to test it on exactly the same struct tm. No change in behavior.
So I have found a minimal example:
void test()
{
time_t t;
struct tm tm = {0};
char buf[64];
tm.tm_year = 2024 - 1900;
tm.tm_mon = 3 - 1;
tm.tm_mday = 31;
tm.tm_hour = 1;
tm.tm_min = 59;
tm.tm_sec = 2;
print_tm(&tm);
mktime(&tm);
strftime(buf, sizeof buf, "%F %T %Z", &tm);
printf("before: %s\n", buf);
tm.tm_isdst = -1; // This is the cause.
tm.tm_min += 1;
mktime(&tm);
strftime(buf, sizeof buf, "%F %T %Z", &tm);
printf("after: %s\n", buf);
}
Setting tm_isdst to -1 after first mktime and before second mktime causes the issue.
AW
On Saturday, March 23rd, 2024 at 11:38, Markus Wichmann <nullplan@gmx.net> wrote:
> Am Sat, Mar 23, 2024 at 09:26:00AM +0000 schrieb Alexander Weps:
>
> > This works for me as well even after changes to match struct tm in my
> > app (setting tm_yday, __tm_gtmoff a __tm_zone):
>
>
> You don't need to set yday or the others before calling mktime().
> mktime() is defined to only use year, mon, mday, hour, min, sec, and
> isdst as input, normalize them, and calculate the others (and also the
> UNIX time stamp).
>
> > Any idea how could a previous calculation mess with musl internals so
> > it would start producing bad results? Because otherwise, I don't see
> > how this could be happening if you completely extract it out of the
> > code and it works.
>
>
> The only thing that means is that the isolated code works, and the bug
> is elsewhere. I'm sorry, but you are going to have to debug this
> yourself. There may be some static memory getting corrupted (e.g. the TZ
> and rule caches), but honestly this is just speculation.
>
> > And when I compile under glibc, everything is fine.
>
>
> That tends to indicate some undefined behavior. Not that that helps you
> find the reason. You are going to have to debug it. Finding a minimum
> reproducer may help in that, or you directly apply liberal amounts of
> gdb.
>
> You seem to have dropped the list from CC, so I'm adding it back.
>
> Ciao,
> Markus
next prev parent reply other threads:[~2024-03-23 12:00 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
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 [this message]
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
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
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
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