Fix year 2039 bug for localtime with 64-bit time_t (bug 22639)

[Joseph Myers <joseph at codesourcery dot com>]

Bug 22639 reports localtime failing to handle time offset transitions
correctly in 2039 and later on platforms with 64-bit time_t.

The problem is the use of SECSPERDAY (constant 86400) in calculations
such as

    t = ((year - 1970) * 365
	 + /* Compute the number of leapdays between 1970 and YEAR
	      (exclusive).  There is a leapday every 4th year ...  */
	 + ((year - 1) / 4 - 1970 / 4)
	 /* ... except every 100th year ... */
	 - ((year - 1) / 100 - 1970 / 100)
	 /* ... but still every 400th year.  */
	 + ((year - 1) / 400 - 1970 / 400)) * SECSPERDAY;

where t is of type time_t and year is of type int.  Before my commit
92bd70fb85bce57ac47ba5d8af008736832c955a (an update from tzcode,
included in 2.26 and later releases), SECSPERDAY was obtained from a
file imported from tzcode, where the value included a cast to
int_fast32_t.  On 64-bit platforms, glibc defines int_fast32_t to be
long int, so 64-bit, but my patch resulted in it changing to int.
(The bug would probably have existed even before my patch for x32,
which has 64-bit time_t but 32-bit int_fast32_t, but I haven't
verified that.)

This patch fixes the problem by including a cast to time_t in the
definition of SECSPERDAY.  (64-bit time support for 32-bit systems
should move such code that isn't a public interface to using the
internal 64-bit version of time_t throughout.)

Tested for x86_64 and x86.

2018-05-17  Joseph Myers  <joseph@codesourcery.com>

	[BZ #22639]
	* time/tzset.c (SECSPERDAY): Cast to time_t.
	* time/tst-y2039.c: New file.
	* time/Makefile (tests): Add tst-y2039.

diff --git a/time/Makefile b/time/Makefile
index 0db1206..ec3e39d 100644
--- a/time/Makefile
+++ b/time/Makefile
@@ -43,7 +43,7 @@ tests	:= test_time clocktest tst-posixtz tst-strptime tst_wcsftime \
 	   tst-getdate tst-mktime tst-mktime2 tst-ftime_l tst-strftime \
 	   tst-mktime3 tst-strptime2 bug-asctime bug-asctime_r bug-mktime1 \
 	   tst-strptime3 bug-getdate1 tst-strptime-whitespace tst-ftime \
-	   tst-tzname
+	   tst-tzname tst-y2039
 
 include ../Rules
 
diff --git a/time/tst-y2039.c b/time/tst-y2039.c
new file mode 100644
index 0000000..cdc6bca
--- /dev/null
+++ b/time/tst-y2039.c
@@ -0,0 +1,46 @@
+/* Test for localtime bug in year 2039 (bug 22639).
+   Copyright (C) 2017-2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <time.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <support/check.h>
+
+static int
+do_test (void)
+{
+  TEST_VERIFY_EXIT (setenv ("TZ", "PST8PDT,M3.2.0,M11.1.0", 1) == 0);
+  tzset ();
+  if (sizeof (time_t) > 4)
+    {
+      time_t ouch = (time_t) 2187810000LL;
+      char buf[500];
+      struct tm *tm = localtime (&ouch);
+      TEST_VERIFY_EXIT (tm != NULL);
+      TEST_VERIFY_EXIT (strftime (buf, sizeof buf, "%Y-%m-%d %H:%M:%S %Z", tm)
+			> 0);
+      puts (buf);
+      TEST_VERIFY (strcmp (buf, "2039-04-30 14:00:00 PDT") == 0);
+    }
+  else
+    FAIL_UNSUPPORTED ("32-bit time_t");
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/time/tzset.c b/time/tzset.c
index b517867..a828b9f 100644
--- a/time/tzset.c
+++ b/time/tzset.c
@@ -27,7 +27,7 @@
 
 #include <timezone/tzfile.h>
 
-#define SECSPERDAY 86400
+#define SECSPERDAY ((time_t) 86400)
 
 char *__tzname[2] = { (char *) "GMT", (char *) "GMT" };
 int __daylight = 0;

-- 
Joseph S. Myers
joseph@codesourcery.com