Work around portability issue with newer versions of mktime().

tglsfdc · tglsfdc · commit 73fa762417de · 2021-06-13T14:32:42.000-04:00
Recent glibc versions have made mktime() fail if tm_isdst is inconsistent with the prevailing timezone; in particular it fails for tm_isdst = 1 when the zone is UTC. (This seems wildly inconsistent with the POSIX-mandated treatment of "incorrect" values for the other fields of struct tm, so if you ask me it's a bug, but I bet they'll say it's intentional.) This has been observed to cause cosmetic problems when pg_restore'ing an archive created in a different timezone. To fix, do mktime() using the field values from the archive, and if that fails try again with tm_isdst = -1. This will give a result that's off by the UTC-offset difference from the original zone, but that was true before, too. It's not terribly critical since we don't do anything with the result except possibly print it. (Someday we should flush this entire bit of logic and record a standard-format timestamp in the archive instead. That's not okay for a back-patched bug fix, though.) Also, guard our only other use of mktime() by having initdb's build_time_t() set tm_isdst = -1 not 0. This case could only have an issue in zones that are DST year-round; but I think some do exist, or could in future. Per report from Wells Oliver. Back-patch to all supported versions, since any of them might need to run with a newer glibc. Discussion: https://postgr.es/m/CAOC+FBWDhDHO7G-i1_n_hjRzCnUeFO+H-Czi1y10mFhRWpBrew@mail.gmail.com
diff --git a/src/bin/initdb/findtimezone.c b/src/bin/initdb/findtimezone.c
@@ -195,6 +195,7 @@ build_time_t(int year, int month, int day)
 	tm.tm_mday = day;
 	tm.tm_mon = month - 1;
 	tm.tm_year = year - 1900;
+	tm.tm_isdst = -1;
 
 	return mktime(&tm);
 }
diff --git a/src/bin/pg_dump/pg_backup_archiver.c b/src/bin/pg_dump/pg_backup_archiver.c
@@ -3723,7 +3723,6 @@ ReadHead(ArchiveHandle *AH)
 				vmin,
 				vrev;
 	int			fmt;
-	struct tm	crtm;
 
 	/*
 	 * If we haven't already read the header, do so.
@@ -3791,6 +3790,8 @@ ReadHead(ArchiveHandle *AH)
 
 	if (AH->version >= K_VERS_1_4)
 	{
+		struct tm	crtm;
+
 		crtm.tm_sec = ReadInt(AH);
 		crtm.tm_min = ReadInt(AH);
 		crtm.tm_hour = ReadInt(AH);
@@ -3799,12 +3800,33 @@ ReadHead(ArchiveHandle *AH)
 		crtm.tm_year = ReadInt(AH);
 		crtm.tm_isdst = ReadInt(AH);
 
-		AH->archdbname = ReadStr(AH);
-
+		/*
+		 * Newer versions of glibc have mktime() report failure if tm_isdst is
+		 * inconsistent with the prevailing timezone, e.g. tm_isdst = 1 when
+		 * TZ=UTC.  This is problematic when restoring an archive under a
+		 * different timezone setting.  If we get a failure, try again with
+		 * tm_isdst set to -1 ("don't know").
+		 *
+		 * XXX with or without this hack, we reconstruct createDate
+		 * incorrectly when the prevailing timezone is different from
+		 * pg_dump's.  Next time we bump the archive version, we should flush
+		 * this representation and store a plain seconds-since-the-Epoch
+		 * timestamp instead.
+		 */
 		AH->createDate = mktime(&crtm);
-
 		if (AH->createDate == (time_t) -1)
-			write_msg(modulename, "WARNING: invalid creation date in header\n");
+		{
+			crtm.tm_isdst = -1;
+			AH->createDate = mktime(&crtm);
+			if (AH->createDate == (time_t) -1)
+				write_msg(modulename,
+						  "WARNING: invalid creation date in header\n");
+		}
+	}
+
+	if (AH->version >= K_VERS_1_4)
+	{
+		AH->archdbname = ReadStr(AH);
 	}
 
 	if (AH->version >= K_VERS_1_10)

Original file line number	Diff line number	Diff line change
`@@ -195,6 +195,7 @@ build_time_t(int year, int month, int day)`
`195`	`195`	`tm.tm_mday = day;`
`196`	`196`	`tm.tm_mon = month - 1;`
`197`	`197`	`tm.tm_year = year - 1900;`
	`198`	`+ tm.tm_isdst = -1;`
`198`	`199`
`199`	`200`	`return mktime(&tm);`
`200`	`201`	`}`