That make sense. nmea uses UTC. UTC does not use daylight saving. So we should set tm_isdst to zero or negative. I think zero is better as UTC should not use daylight saving.
Sound like a good ground for a patch Erez From: Lars Munch <l...@segv.dk> Sent: Wednesday, 21 April 2021 15:01 To: Geva, Erez (ext) (DI PA DCP R&D 3) <erez.geva....@siemens.com> Cc: Richard Cochran <richardcoch...@gmail.com>; linuxptp-devel@lists.sourceforge.net Subject: Re: [Linuxptp-devel] [PATCH] Fix uninitialized variable in nmea_scan_rmc My Arch system does indeed have daylight saving set, but nmea.c forces the TZ to UTC where a positive value of tm_isdst does not make sense. On Wed, Apr 21, 2021 at 1:51 PM Geva, Erez <erez.geva....@siemens.com<mailto:erez.geva....@siemens.com>> wrote: Looks like the man page is not accurate. Looking in https://pubs.opengroup.org/onlinepubs/009695399/functions/mktime.html<https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpubs.opengroup.org%2Fonlinepubs%2F009695399%2Ffunctions%2Fmktime.html&data=04%7C01%7Cerez.geva.ext%40siemens.com%7Cda8de2bf9a9b49318d0b08d904c59709%7C38ae3bcd95794fd4addab42e1495d55a%7C1%7C0%7C637546069391715822%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=%2F7zfn0tJyfjfQRFOJTRUMa4pxhfSeWh%2FR4ikHOK%2BPeU%3D&reserved=0> A positive or 0 value for tm_isdst shall cause mktime() to presume initially that Daylight Savings Time, respectively, is or is not in effect for the specified time. A negative value for tm_isdst shall cause mktime() to attempt to determine whether Daylight Savings Time is in effect for the specified time. My guess is that on Lars new system the daylight is NOT set, then the mktime fail to determine the Daylight Savings and return error (-1). Erez -----Original Message----- From: Richard Cochran <richardcoch...@gmail.com<mailto:richardcoch...@gmail.com>> Sent: Tuesday, 20 April 2021 16:05 To: Lars Munch <l...@segv.dk<mailto:l...@segv.dk>> Cc: linuxptp-devel@lists.sourceforge.net<mailto:linuxptp-devel@lists.sourceforge.net> Subject: Re: [Linuxptp-devel] [PATCH] Fix uninitialized variable in nmea_scan_rmc 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 _______________________________________________ Linuxptp-devel mailing list Linuxptp-devel@lists.sourceforge.net<mailto:Linuxptp-devel@lists.sourceforge.net> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.sourceforge.net%2Flists%2Flistinfo%2Flinuxptp-devel&data=04%7C01%7Cerez.geva.ext%40siemens.com%7C6b9d88bf27584b2d9eb508d9040556d6%7C38ae3bcd95794fd4addab42e1495d55a%7C1%7C0%7C637545243247255579%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=wHxP0yERXKP6unOP1ZPV%2F87BVduutafEUIOl8jH%2Bud4%3D&reserved=0<https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.sourceforge.net%2Flists%2Flistinfo%2Flinuxptp-devel&data=04%7C01%7Cerez.geva.ext%40siemens.com%7Cda8de2bf9a9b49318d0b08d904c59709%7C38ae3bcd95794fd4addab42e1495d55a%7C1%7C0%7C637546069391725818%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=fAigqGaS7r%2FSyDhqtebI4bmYmfHq0Mp0evVhlko7M9c%3D&reserved=0>
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