1 files changed, 84 insertions, 79 deletions

diff --git a/gl/mktime.c b/gl/mktime.c
index c704f415..4218fca6 100644
--- a/gl/mktime.c
+++ b/gl/mktime.c
@@ -1,5 +1,5 @@
 /* Convert a 'struct tm' to a time_t value.
-   Copyright (C) 1993-2024 Free Software Foundation, Inc.
+   Copyright (C) 1993-2025 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Paul Eggert <eggert@twinsun.com>.
 
@@ -51,7 +51,6 @@
 #include <string.h>
 
 #include <intprops.h>
-#include <verify.h>
 
 #ifndef NEED_MKTIME_INTERNAL
 # define NEED_MKTIME_INTERNAL 0
@@ -63,6 +62,9 @@
 # define NEED_MKTIME_WORKING 0
 #endif
 
+#ifdef _LIBC
+# include <tzset.h>
+#endif
 #include "mktime-internal.h"
 
 #if !defined _LIBC && (NEED_MKTIME_WORKING || NEED_MKTIME_WINDOWS)
@@ -99,8 +101,8 @@ my_tzset (void)
   tzset ();
 # endif
 }
-# undef __tzset
-# define __tzset() my_tzset ()
+# undef tzset
+# define tzset() my_tzset ()
 #endif
 
 #if defined _LIBC || NEED_MKTIME_WORKING || NEED_MKTIME_INTERNAL
@@ -119,12 +121,12 @@ my_tzset (void)
    __time64_t values that mktime can generate even on platforms where
    __time64_t is wider than the int components of struct tm.  */
 
-#if INT_MAX <= LONG_MAX / 4 / 366 / 24 / 60 / 60
+# if INT_MAX <= LONG_MAX / 4 / 366 / 24 / 60 / 60
 typedef long int long_int;
-#else
+# else
 typedef long long int long_int;
-#endif
-verify (INT_MAX <= TYPE_MAXIMUM (long_int) / 4 / 366 / 24 / 60 / 60);
+# endif
+static_assert (INT_MAX <= TYPE_MAXIMUM (long_int) / 4 / 366 / 24 / 60 / 60);
 
 /* Shift A right by B bits portably, by dividing A by 2**B and
    truncating towards minus infinity.  B should be in the range 0 <= B
@@ -155,9 +157,9 @@ static long_int const mktime_max
   = (TYPE_MAXIMUM (long_int) < TYPE_MAXIMUM (__time64_t)
      ? TYPE_MAXIMUM (long_int) : TYPE_MAXIMUM (__time64_t));
 
-#define EPOCH_YEAR 1970
-#define TM_YEAR_BASE 1900
-verify (TM_YEAR_BASE % 100 == 0);
+# define EPOCH_YEAR 1970
+# define TM_YEAR_BASE 1900
+static_assert (TM_YEAR_BASE % 100 == 0);
 
 /* Is YEAR + TM_YEAR_BASE a leap year?  */
 static bool
@@ -172,9 +174,9 @@ leapyear (long_int year)
 }
 
 /* How many days come before each month (0-12).  */
-#ifndef _LIBC
+# ifndef _LIBC
 static
-#endif
+# endif
 const unsigned short int __mon_yday[2][13] =
   {
     /* Normal years.  */
@@ -206,7 +208,7 @@ static long_int
 ydhms_diff (long_int year1, long_int yday1, int hour1, int min1, int sec1,
             int year0, int yday0, int hour0, int min0, int sec0)
 {
-  verify (-1 / 2 == 0);
+  static_assert (-1 / 2 == 0);
 
   /* Compute intervening leap days correctly even if year is negative.
      Take care to avoid integer overflow here.  */
@@ -251,29 +253,34 @@ tm_diff (long_int year, long_int yday, int hour, int min, int sec,
                      tp->tm_hour, tp->tm_min, tp->tm_sec);
 }
 
-/* Use CONVERT to convert T to a struct tm value in *TM.  T must be in
-   range for __time64_t.  Return TM if successful, NULL (setting errno) on
-   failure.  */
+#ifndef _LIBC
+/* Convert T to a struct tm value in *TM.  Use localtime64_r if LOCAL,
+   otherwise gmtime64_r.  T must be in range for __time64_t.  Return
+   TM if successful, NULL (setting errno) on failure.  */
 static struct tm *
-convert_time (struct tm *(*convert) (const __time64_t *, struct tm *),
-              long_int t, struct tm *tm)
+convert_time (long_int t, bool local, struct tm *tm)
 {
   __time64_t x = t;
-  return convert (&x, tm);
+  if (local)
+    return __localtime64_r (&x, tm);
+  else
+    return __gmtime64_r (&x, tm);
 }
+# define __tz_convert convert_time
+#endif
 
-/* Use CONVERT to convert *T to a broken down time in *TP.
-   If *T is out of range for conversion, adjust it so that
-   it is the nearest in-range value and then convert that.
-   A value is in range if it fits in both __time64_t and long_int.
-   Return TP on success, NULL (setting errno) on failure.  */
+/* Convert *T to a broken down time in *TP (as if by localtime if
+   LOCAL, otherwise as if by gmtime).  If *T is out of range for
+   conversion, adjust it so that it is the nearest in-range value and
+   then convert that.  A value is in range if it fits in both
+   __time64_t and long_int.  Return TP on success, NULL (setting
+   errno) on failure.  */
 static struct tm *
-ranged_convert (struct tm *(*convert) (const __time64_t *, struct tm *),
-                long_int *t, struct tm *tp)
+ranged_convert (bool local, long_int *t, struct tm *tp)
 {
   long_int t1 = (*t < mktime_min ? mktime_min
                  : *t <= mktime_max ? *t : mktime_max);
-  struct tm *r = convert_time (convert, t1, tp);
+  struct tm *r = __tz_convert (t1, local, tp);
   if (r)
     {
       *t = t1;
@@ -294,7 +301,7 @@ ranged_convert (struct tm *(*convert) (const __time64_t *, struct tm *),
       long_int mid = long_int_avg (ok, bad);
       if (mid == ok || mid == bad)
         break;
-      if (convert_time (convert, mid, tp))
+      if (__tz_convert (mid, local, tp))
         ok = mid, oktm = *tp;
       else if (errno != EOVERFLOW)
         return NULL;
@@ -310,29 +317,38 @@ ranged_convert (struct tm *(*convert) (const __time64_t *, struct tm *),
 }
 
 
-/* Convert *TP to a __time64_t value, inverting
-   the monotonic and mostly-unit-linear conversion function CONVERT.
-   Use *OFFSET to keep track of a guess at the offset of the result,
+/* Convert *TP to a __time64_t value.  If LOCAL, the reverse mapping
+   is performed as if localtime, otherwise as if by gmtime.  Use
+   *OFFSET to keep track of a guess at the offset of the result,
    compared to what the result would be for UTC without leap seconds.
-   If *OFFSET's guess is correct, only one CONVERT call is needed.
-   If successful, set *TP to the canonicalized struct tm;
+   If *OFFSET's guess is correct, only one reverse mapping call is
+   needed.  If successful, set *TP to the canonicalized struct tm;
    otherwise leave *TP alone, return ((time_t) -1) and set errno.
-   This function is external because it is used also by timegm.c.  */
+   This function is external because it is used also by timegm.c.
+
+   If _LIBC, the caller must lock __tzset_lock.  */
 __time64_t
-__mktime_internal (struct tm *tp,
-                   struct tm *(*convert) (const __time64_t *, struct tm *),
-                   mktime_offset_t *offset)
+__mktime_internal (struct tm *tp, bool local, mktime_offset_t *offset)
 {
   struct tm tm;
 
-  /* The maximum number of probes (calls to CONVERT) should be enough
-     to handle any combinations of time zone rule changes, solar time,
-     leap seconds, and oscillations around a spring-forward gap.
-     POSIX.1 prohibits leap seconds, but some hosts have them anyway.  */
+  /* The maximum number of probes should be enough to handle any
+     combinations of time zone rule changes, solar time, leap seconds,
+     and oscillations around a spring-forward gap.  POSIX.1 prohibits
+     leap seconds, but some hosts have them anyway.  */
   int remaining_probes = 6;
 
-  /* Time requested.  Copy it in case CONVERT modifies *TP; this can
-     occur if TP is localtime's returned value and CONVERT is localtime.  */
+#ifndef _LIBC
+  /* Gnulib mktime doesn't lock the tz state, so it may need to probe
+     more often if some other thread changes local time while
+     __mktime_internal is probing.  Double the number of probes; this
+     should suffice for practical cases that are at all likely.  */
+  remaining_probes *= 2;
+#endif
+
+  /* Time requested.  Copy it in case gmtime/localtime modify *TP;
+     this can occur if TP is localtime's returned value and CONVERT is
+     localtime.  */
   int sec = tp->tm_sec;
   int min = tp->tm_min;
   int hour = tp->tm_hour;
@@ -341,8 +357,8 @@ __mktime_internal (struct tm *tp,
   int year_requested = tp->tm_year;
   int isdst = tp->tm_isdst;
 
-  /* 1 if the previous probe was DST.  */
-  int dst2 = 0;
+  /* True if the previous probe was DST.  */
+  bool dst2 = false;
 
   /* Ensure that mon is in range, and set year accordingly.  */
   int mon_remainder = mon % 12;
@@ -390,7 +406,7 @@ __mktime_internal (struct tm *tp,
 
   while (true)
     {
-      if (! ranged_convert (convert, &t, &tm))
+      if (! ranged_convert (local, &t, &tm))
         return -1;
       long_int dt = tm_diff (year, yday, hour, min, sec, &tm);
       if (dt == 0)
@@ -431,13 +447,10 @@ __mktime_internal (struct tm *tp,
 
          Heuristic: probe the adjacent timestamps in both directions,
          looking for the desired isdst.  If none is found within a
-         reasonable duration bound, assume a one-hour DST difference.
+         reasonable duration bound, ignore the disagreement.
          This should work for all real time zone histories in the tz
          database.  */
 
-      /* +1 if we wanted standard time but got DST, -1 if the reverse.  */
-      int dst_difference = (isdst == 0) - (tm.tm_isdst == 0);
-
       /* Distance between probes when looking for a DST boundary.  In
          tzdata2003a, the shortest period of DST is 601200 seconds
          (e.g., America/Recife starting 2000-10-08 01:00), and the
@@ -447,21 +460,17 @@ __mktime_internal (struct tm *tp,
          periods when probing.  */
       int stride = 601200;
 
-      /* In TZDB 2021e, the longest period of DST (or of non-DST), in
-         which the DST (or adjacent DST) difference is not one hour,
-         is 457243209 seconds: e.g., America/Cambridge_Bay with leap
-         seconds, starting 1965-10-31 00:00 in a switch from
-         double-daylight time (-05) to standard time (-07), and
-         continuing to 1980-04-27 02:00 in a switch from standard time
-         (-07) to daylight time (-06).  */
-      int duration_max = 457243209;
-
-      /* Search in both directions, so the maximum distance is half
-         the duration; add the stride to avoid off-by-1 problems.  */
-      int delta_bound = duration_max / 2 + stride;
+      /* Do not probe too far away from the requested time,
+         by striding until at least a year has passed, but then giving up.
+         This helps avoid unexpected results in (for example) Asia/Kolkata,
+         for which today's users expect to see no DST even though it
+         did observe DST long ago.  */
+      int year_seconds_bound = 366 * 24 * 60 * 60 + 1;
+      int delta_bound = year_seconds_bound + stride;
 
       int delta, direction;
 
+      /* Search in both directions, closest first.  */
       for (delta = stride; delta < delta_bound; delta += stride)
         for (direction = -1; direction <= 1; direction += 2)
           {
@@ -469,7 +478,7 @@ __mktime_internal (struct tm *tp,
             if (! ckd_add (&ot, t, delta * direction))
               {
                 struct tm otm;
-                if (! ranged_convert (convert, &ot, &otm))
+                if (! ranged_convert (local, &ot, &otm))
                   return -1;
                 if (! isdst_differ (isdst, otm.tm_isdst))
                   {
@@ -479,7 +488,7 @@ __mktime_internal (struct tm *tp,
                                                 &otm);
                     if (mktime_min <= gt && gt <= mktime_max)
                       {
-                        if (convert_time (convert, gt, &tm))
+                        if (__tz_convert (gt, local, &tm))
                           {
                             t = gt;
                             goto offset_found;
@@ -491,13 +500,8 @@ __mktime_internal (struct tm *tp,
               }
           }
 
-      /* No unusual DST offset was found nearby.  Assume one-hour DST.  */
-      t += 60 * 60 * dst_difference;
-      if (mktime_min <= t && t <= mktime_max && convert_time (convert, t, &tm))
-        goto offset_found;
-
-      __set_errno (EOVERFLOW);
-      return -1;
+      /* No probe with the requested tm_isdst was found nearby.
+         Ignore the requested tm_isdst.  */
     }
 
  offset_found:
@@ -520,7 +524,7 @@ __mktime_internal (struct tm *tp,
           __set_errno (EOVERFLOW);
           return -1;
         }
-      if (! convert_time (convert, t, &tm))
+      if (! __tz_convert (t, local, &tm))
         return -1;
     }
 
@@ -536,18 +540,19 @@ __mktime_internal (struct tm *tp,
 __time64_t
 __mktime64 (struct tm *tp)
 {
-  /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
-     time zone names contained in the external variable 'tzname' shall
-     be set as if the tzset() function had been called.  */
-  __tzset ();
+  __libc_lock_lock (__tzset_lock);
+  __tzset_unlocked ();
 
 # if defined _LIBC || NEED_MKTIME_WORKING
   static mktime_offset_t localtime_offset;
-  return __mktime_internal (tp, __localtime64_r, &localtime_offset);
+  __time64_t result = __mktime_internal (tp, true, &localtime_offset);
 # else
 #  undef mktime
-  return mktime (tp);
+  __time64_t result = mktime (tp);
 # endif
+
+  __libc_lock_unlock (__tzset_lock);
+  return result;
 }
 #endif /* _LIBC || NEED_MKTIME_WORKING || NEED_MKTIME_WINDOWS */