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changeset 16923:0bce099a6479

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mktime: fix integer overflow in 'configure'-time test * m4/mktime.m4 (gl_FUNC_MKTIME): Do not rely on undefined behavior after integer overflow. Problem reported by Rich Felker in <http://lists.gnu.org/archive/html/bug-gnulib/2012-06/msg00257.html>. Also, don't look for further instances of a bug if we've already found one instance; this helps 'configure' run faster.
author Paul Eggert <eggert@cs.ucla.edu>
date Thu, 21 Jun 2012 01:49:15 -0700
parents 937fc0f34278
children 84f589f56820
files ChangeLog m4/mktime.m4
diffstat 2 files changed, 23 insertions(+), 11 deletions(-) [+]
line wrap: on
line diff
--- a/ChangeLog	Wed Jun 20 23:30:48 2012 +0200
+++ b/ChangeLog	Thu Jun 21 01:49:15 2012 -0700
@@ -1,3 +1,12 @@
+2012-06-21  Paul Eggert  <eggert@cs.ucla.edu>
+
+	mktime: fix integer overflow in 'configure'-time test
+	* m4/mktime.m4 (gl_FUNC_MKTIME): Do not rely on undefined behavior
+	after integer overflow.  Problem reported by Rich Felker in
+	<http://lists.gnu.org/archive/html/bug-gnulib/2012-06/msg00257.html>.
+	Also, don't look for further instances of a bug if we've already
+	found one instance; this helps 'configure' run faster.
+
 2012-06-20  John Darrington  <john@darrington.wattle.id.au>  (tiny change)
 
 	tmpfile, clean-temp: Fix invocation of GetVersionEx.
--- a/m4/mktime.m4	Wed Jun 20 23:30:48 2012 +0200
+++ b/m4/mktime.m4	Thu Jun 21 01:49:15 2012 -0700
@@ -1,4 +1,4 @@
-# serial 21
+# serial 22
 dnl Copyright (C) 2002-2003, 2005-2007, 2009-2012 Free Software Foundation,
 dnl Inc.
 dnl This file is free software; the Free Software Foundation
@@ -192,20 +192,23 @@
       if (tz_strings[i])
         putenv (tz_strings[i]);
 
-      for (t = 0; t <= time_t_max - delta; t += delta)
+      for (t = 0; t <= time_t_max - delta && (result & 1) == 0; t += delta)
         if (! mktime_test (t))
           result |= 1;
-      if (! (mktime_test ((time_t) 1)
-             && mktime_test ((time_t) (60 * 60))
-             && mktime_test ((time_t) (60 * 60 * 24))))
+      if ((result & 2) == 0
+          && ! (mktime_test ((time_t) 1)
+                && mktime_test ((time_t) (60 * 60))
+                && mktime_test ((time_t) (60 * 60 * 24))))
         result |= 2;
 
-      for (j = 1; ; j <<= 1)
-        if (! bigtime_test (j))
-          result |= 4;
-        else if (INT_MAX / 2 < j)
-          break;
-      if (! bigtime_test (INT_MAX))
+      for (j = 1; (result & 4) == 0; j <<= 1)
+        {
+          if (! bigtime_test (j))
+            result |= 4;
+          if (INT_MAX / 2 < j)
+            break;
+        }
+      if ((result & 8) == 0 && ! bigtime_test (INT_MAX))
         result |= 8;
     }
   if (! irix_6_4_bug ())