Re: [musl] Broken mktime calculations when crossing DST boundary

[Markus Wichmann <nullplan@gmx.net>]

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