From: Udo de Boer <udo.de.boer@ubero.nl>
To: newlib@sourceware.org
Subject: Bug in UTC -> localtime conversion after 2038
Date: Wed, 4 Nov 2020 12:36:45 +0100 [thread overview]
Message-ID: <5d87b235-f246-1bab-f225-484c6fd93b4d@ubero.nl> (raw)
Hi,
UTC time to local timezone conversion did not work for years after 2038.
Daylight saving in the timezone was not recognized. Tested on 32bit
xtensa architecture with GCC 8.4 (esp32) and with 64bit time_t enabled.
The struct tm is filled correct. So year, day etc are all filled with
the correct values. But the tm.tm_isdst is 0 and no daylight saving is
applied.
It was caused by the following calculation in time/tzcalc_limits.c at
line 68
/* store the change-over time in GMT form by adding offset */
tz->__tzrule[i].change = days * SECSPERDAY +
tz->__tzrule[i].s + tz->__tzrule[i].offset;
Here tz->__tzrule[i].change is a time_t (64bit). For some reason the
compiler does the calculation in 32 bit. All variables used in the
calculation are 32bit.
I solved this locally by changing the lines to.
/* store the change-over time in GMT form by adding offset */
tz->__tzrule[i].change = (time_t)days * SECSPERDAY +
tz->__tzrule[i].s + tz->__tzrule[i].offset;
Adding the cast time_t should not cause a problem when time_t is still
32bit.
I don't know if this is correct solution. I also only needed this
function. So more bugs like this could be hidden away in the time code.
next reply other threads:[~2020-11-04 11:36 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-04 11:36 Udo de Boer [this message]
2020-11-04 12:59 ` Richard Damon
2020-11-04 16:20 ` Ivan Grokhotkov
2020-11-04 18:37 ` Jeff Johnston
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