From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-3.0 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL autolearn=ham autolearn_force=no version=3.4.4 Received: from second.openwall.net (second.openwall.net [193.110.157.125]) by inbox.vuxu.org (Postfix) with SMTP id 74F82224C2 for ; Mon, 25 Mar 2024 14:42:47 +0100 (CET) Received: (qmail 22431 invoked by uid 550); 25 Mar 2024 13:38:01 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 22377 invoked from network); 25 Mar 2024 13:38:01 -0000 Date: Mon, 25 Mar 2024 09:42:53 -0400 From: Rich Felker To: Alexander Weps Cc: musl@lists.openwall.com Message-ID: <20240325134252.GE4163@brightrain.aerifal.cx> References: <20240324192258.GY4163@brightrain.aerifal.cx> <-svm5EdX4OFN9hKzgS2FP6N1lgUGjT7edQONkAfCywgsRitwT6Vw22W3sUUGY_pnKGIXBKlujMZhPCDkJAMCYbBA5uF-IYgzhj8WB0wBE-A=@pm.me> <4YlR0YRqzZlDIOVv6SP8UDoop89n8u7BvQl_7eXNTvDZnogXMxG1z-TLGIBf-O4edUphddXGfADbk_d7Uzb37g5JoH7vOIvvNRMFDxPWZok=@pm.me> <20240325122113.GB4163@brightrain.aerifal.cx> <20240325131318.GD4163@brightrain.aerifal.cx> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="YvxfeT9y/1FRS2+9" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Subject: Re: [musl] Broken mktime calculations when crossing DST boundary --YvxfeT9y/1FRS2+9 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Mon, Mar 25, 2024 at 01:24:57PM +0000, Alexander Weps wrote: > See below. > > AW > > > On Monday, March 25th, 2024 at 14:13, Rich Felker wrote: > > > On Mon, Mar 25, 2024 at 12:55:28PM +0000, Alexander Weps wrote: > > > > > > If you take your test program and switch it to initialize with > > > > tm_mday=31, then do -=1 instead of +=1, you'll find that it gives > > > > 2011-12-29 01:00:00 -10 as well, only now it seems like the correct, > > > > expected thing to happen. Any change to "fix" the case you're > > > > complaining about would necessarily break this case. > > > > > > So (- day, +day): > > > > > > Musl: > > > 2011-12-31 01:00:00 +14 > > > 2011-12-29 01:00:00 -10 > > > 2011-12-29 01:00:00 -10 > > > > > > Glibc: > > > 2012-01-01 01:00:00 +14 > > > 2011-12-31 01:00:00 +14 > > > 2012-01-01 01:00:00 +14 > > > > > > Seems like musl doesn't even interpret the initial struct tm > > > correctly in that case. It is off by day. > > > > > > Because December only had 30 days, 31s day after normalization is > > > January 1st. > > > > > > This is nonsense. December has a day 31, which you can clearly see > > from the glibc output. For this particular year in this zone, with the > > zone rule change, there are "only 30 days" in December, but they are > > numbered 1-29 and 31, not 1-30. > > You confuse day of month which is represented in tm_mday with > calendar day that is interpreted by strftime. > > You said to set tm_mday = 31, which would be January 1st after normalization. > December 31s is 30th day of month represented as tm_mday = 30. OK, I meant tm_mday=31-1. > > What did you do that got glibc to output 2012-01-01? I guess you wrote > > code to do some wacky arithmetic after the original code you already > > had, rather than changing the code to start with 2011-12-31 as I > > suggested to get a look at what's happening. > > > > > > In any case, the core issue you're hitting here is that time zones are > > > > HARD to work with and that there is inherent complexity that libc > > > > cannot save you from. You only got lucky that what you were trying to > > > > do "worked" with glibc because you were iterating days forward; if you > > > > were doing reverse, it would break exactly the same way. > > > > > > I am not really commenting on this, until you sort out the above > > > inconsistencies. > > > > > > I already have but you refuse to look. > > It was addressed, do didn't scroll at the end of the e-mail. Run the attached passing the starting date to check as the first/only argument, and these test dates: - "2011-12-29 00:00:00" - "2011-12-31 00:00:00" Hopefully that will clarify things for you. On musl you will see: normalized input: 2011-12-29 00:00:00 -10 +1day per mktime: 2011-12-29 00:00:00 -10 +1day via time_t: 2011-12-31 00:00:00 +14 -1day per mktime: 2011-12-28 00:00:00 -10 -1day via time_t: 2011-12-28 00:00:00 -10 normalized input: 2011-12-31 00:00:00 +14 +1day per mktime: 2012-01-01 00:00:00 +14 +1day via time_t: 2012-01-01 00:00:00 +14 -1day per mktime: 2011-12-29 00:00:00 -10 -1day via time_t: 2011-12-29 00:00:00 -10 You can see what you get on glibc. Rich --YvxfeT9y/1FRS2+9 Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename="mktime_rel.c" #include #include #include #include int main(int argc, char **argv) { struct tm tm = { .tm_isdst = -1 }; if (!strptime(argv[1], "%Y-%m-%d %H:%M:%S", &tm)) { perror("strptime"); return 1; } errno = 0; time_t t = mktime(&tm); if (t==-1 && errno) { perror("mktime"); return 1; } char buf[100]; strftime(buf, sizeof buf, "%Y-%m-%d %H:%M:%S %Z", &tm); printf("normalized input: %s\n", buf); struct tm tm2 = tm; tm2.tm_mday++; errno = 0; if (mktime(&tm2)==-1 && errno) { perror("mktime day+1"); } else { strftime(buf, sizeof buf, "%Y-%m-%d %H:%M:%S %Z", &tm2); printf("+1day per mktime: %s\n", buf); } localtime_r(&(time_t){t+86400}, &tm2); strftime(buf, sizeof buf, "%Y-%m-%d %H:%M:%S %Z", &tm2); printf("+1day via time_t: %s\n", buf); tm2 = tm; tm2.tm_mday--; errno = 0; if (mktime(&tm2)==-1 && errno) { perror("mktime day-1"); } else { strftime(buf, sizeof buf, "%Y-%m-%d %H:%M:%S %Z", &tm2); printf("-1day per mktime: %s\n", buf); } localtime_r(&(time_t){t-86400}, &tm2); strftime(buf, sizeof buf, "%Y-%m-%d %H:%M:%S %Z", &tm2); printf("-1day via time_t: %s\n", buf); } --YvxfeT9y/1FRS2+9--