[Bug]: POSIX Timezone offset incorectly on T-Echo - but correct on a Haltec v3

[OrByR]

Category

Other

Hardware

T-Echo

Firmware Version

2.3.9.0afe2d4

Description

Using the correct CST6CDT,M3.2.0,M11.1.0 time zone code on a T-Echo results in the time being off by 1hr on the device.
If I change it to a wrong code of CST5CDT,M3.2.0,M11.1.0 then it shows correctly on the device.
Using the correct time zone code CST6CDT,M3.2.0,M11.1.0 on a Haltec v3 shows the correct time.
All devices tested on 2.3.9.0afe2d4, I also tested via both GPS and phone provided time - both were affected.

Relevant log output

No response

[todd-herbert]

I have a funny feeling that I've seen the same behavior on my devices.
As far as I'm aware, the time zones are handled at a deeper layer than the Meshtastic code, using platform specific implementations of tzset(), time(), gmtime(). It seems like the version the T-Echo is built with might have an issue with the tm:tm_isdt() function?

I'm not sure what the options to correct / mitigate might be.
It'd be good to hear what @caveman99 thinks of the situation; I know he's worked with these functions before and probably has much better insight here.

[caveman99]

I'm swamped right now with other things but will try to look into this later this week. TZ is indeed handled by the underlying toolchain.