[musl] [bug] musl Daylight Saving Time across year bug

[musl] [bug] musl Daylight Saving Time across year bug

[wanghaitao (G)]

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Hello everyone,
I found a bug related to musl daylight saving time setting.
We are set to enter Daylight Saving Time at 10pm on the last day of 2021,
offset Daylight Saving Time by 2 hours, and end Daylight Saving Time on the first day of 2022.

However, it did not recover immediately after entering 2022, but it was delayed for more than ten hours before recovery to normal time.

We use the musl version 1.2.3
We put the TZ variable settings in /var/time/TZ and use soft links to use it.

cat /var/time/TZ
GMT-08:00DST-10:00:00,M12.5.5/18:45:0,M1.1.6/6:0:0
we have a soft link from /system/etc/TZ -> /var/time/TZ, and /etc/TZ -> /var/time/TZ
Here is our env info:
root:/# cat /proc/version
Linux version 5.10.97+ (z30045507@kwemhisprc00189) (aarch64-none-linux-gnu-gcc (
Arm GNU Toolchain 12.2.Rel1 (Build arm-12.24)) 12.2.1 20221205, GNU ld (Arm GNU
Toolchain 12.2.Rel1 (Build arm-12.24)) 2.39.0.20221210) #1 SMP PREEMPT Thu Dec 1
4 10:14:45 CST 2023

After looking at the src code I found in the src/time/__tz.c:406, there is a comment:
FIXME: may be broken if DST changes right at year boundary? Also, this could be more efficient.

I would like to ask if the current bug is the FIXME written in the comments here. Is there any solution?

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Re: [musl] [bug] musl Daylight Saving Time across year bug

[Rich Felker]

On Tue, Dec 19, 2023 at 01:52:59AM +0000, wanghaitao (G) wrote:
> Hello everyone,
> I found a bug related to musl daylight saving time setting.
> We are set to enter Daylight Saving Time at 10pm on the last day of 2021,
> offset Daylight Saving Time by 2 hours, and end Daylight Saving Time on the first day of 2022.
> 
> However, it did not recover immediately after entering 2022, but it was delayed for more than ten hours before recovery to normal time.
> 
> We use the musl version 1.2.3
> We put the TZ variable settings in /var/time/TZ and use soft links to use it.
> 
> cat /var/time/TZ
> GMT-08:00DST-10:00:00,M12.5.5/18:45:0,M1.1.6/6:0:0
> we have a soft link from /system/etc/TZ -> /var/time/TZ, and /etc/TZ -> /var/time/TZ
> Here is our env info:
> root:/# cat /proc/version
> Linux version 5.10.97+ (z30045507@kwemhisprc00189) (aarch64-none-linux-gnu-gcc (
> Arm GNU Toolchain 12.2.Rel1 (Build arm-12.24)) 12.2.1 20221205, GNU ld (Arm GNU
> Toolchain 12.2.Rel1 (Build arm-12.24)) 2.39.0.20221210) #1 SMP PREEMPT Thu Dec 1
> 4 10:14:45 CST 2023
> 
> After looking at the src code I found in the src/time/__tz.c:406, there is a comment:
> FIXME: may be broken if DST changes right at year boundary? Also, this could be more efficient.
> 
> I would like to ask if the current bug is the FIXME written in the comments here. Is there any solution?
> 
> [cid:image003.png@01DA31CC.C3E3DA30]

I looked at this briefly when you first posted it, but then I think it
slipped through the cracks. Thanks for bringing it to our attention. I
hope to follow up on it sometime after the upcoming 1.2.5 release.

BTW, is this a real timezone you're trying to make use of, or a
constructed corner case for testing purposes?

Rich