Looks like you daylight time is broken on Arch Linux and Ubuntu 20.04.
-1 is error by mktime.
Why do you think it is related here?
Fix you daylight time setting in your system and open a bug report in the
relevant packages/systems.
Erez
From: Lars Munch <l...@segv.dk>
Sent: Tuesday, 20 April 2021 22:24
To: Michael Galassi <mich...@galassi.us>
Cc: linuxptp-devel@lists.sourceforge.net
Subject: Re: [Linuxptp-devel] [PATCH] Fix uninitialized variable in
nmea_scan_rmc
Sorry for the noise. In my previous example I had by accident pasted a huge
number into the example. New example:
#include <stdio.h>
#include <time.h>
#include <stdlib.h>
int main()
{
struct tm t;
time_t now = time((void*)0);
localtime_r(&now, &t);
setenv("TZ", "UTC", 1);
t.tm_isdst = 1;
printf("%ld\n", mktime(&t));
t.tm_isdst = 0;
printf("%ld\n", mktime(&t));
t.tm_isdst = -1;
printf("%ld\n", mktime(&t));
}
Gives:
-1
1618956512
1618956512
This is on my up-to-date Arch Linux and Ubuntu 20.04.
On my Ubuntu 18.04 it's fine.
On Tue, Apr 20, 2021 at 5:55 PM Lars Munch <l...@segv.dk<mailto:l...@segv.dk>>
wrote:
Ok, so mktime is forced to return in time UTC time scale earlier in the code:
#include <stdio.h>
#include <time.h>
#include <stdlib.h>
int main()
{
struct tm t;
time_t now = time((void*)0);
localtime_r(&now, &t);
setenv("TZ", "UTC", 1);
t.tm_isdst = 4000000001;
printf("%ld\n", mktime(&t));
t.tm_isdst = 0;
printf("%ld\n", mktime(&t));
t.tm_isdst = -1;
printf("%ld\n", mktime(&t));
}
1618941220
1618941220
1618941220
So my problem might come from the fact that I do not have any timezone database
on my system.
On Tue, Apr 20, 2021 at 5:30 PM Lars Munch <l...@segv.dk<mailto:l...@segv.dk>>
wrote:
Indeed, any positive random number in tm.tm_isdst will set DST in effect it
seems.
On my stripped down ARM system with no timezone information, it will simply
return -1.
On Tue, Apr 20, 2021 at 4:26 PM Michael Galassi
<mich...@galassi.us<mailto:mich...@galassi.us>> wrote:
Somewhere lies a bug. The following code snippet:
#include <stdio.h>
#include <time.h>
int main()
{
struct tm t;
time_t now = time((void*)0);
localtime_r(&now, &t);
t.tm_isdst = 1;
printf("%ld\n", mktime(&t));
t.tm_isdst = 0;
printf("%ld\n", mktime(&t));
t.tm_isdst = -1;
printf("%ld\n", mktime(&t));
}
Yields:
1618928503
1618932103
1618932103
This is true on FreeBSD 13 and Ubuntu 18.04, both fully patched.
-michael
On Tue, Apr 20, 2021 at 7:04 AM Richard Cochran
<richardcoch...@gmail.com<mailto:richardcoch...@gmail.com>> wrote:
On Tue, Apr 20, 2021 at 11:44:06AM +0200, Lars Munch wrote:
> tm_isdst needs to be initialized to make sure mktime does not fail
> or calculates the wrong time.
No, take a look at the mktime(3) man page. There you will read the
following.
The mktime() function modifies the fields of the tm structure as fol‐
lows: tm_wday and tm_yday are set to values determined from the con‐
tents of the other fields; if structure members are outside their
valid interval, they will be normalized (so that, for example, 40 Oc‐
tober is changed into 9 November); tm_isdst is set (regardless of its
initial value) to a positive value or to 0, respectively, to indicate
whether DST is or is not in effect at the specified time.
Thanks,
Richard
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