+2018-03-26 Paul Eggert <eggert@cs.ucla.edu>
+
+ time_rz: work around Mac OS X 10.6 infloop
+ * doc/posix-functions/localtime.texi:
+ * doc/posix-functions/localtime_r.texi: Mention the bug.
+ * lib/time_rz.c (localtime_rz): Work around the bug. It’d be
+ better to fix localtime and localtime_r instead, but that would be
+ more work and is not needed to fix the Emacs problem.
+ * m4/time_rz.m4 (gl_TIME_RZ): Detect the bug.
+
2018-03-24 Jim Meyering <meyering@fb.com>
test-version-etc.sh: don't use diff directly: use init.sh's compare
Portability problems not fixed by Gnulib:
@itemize
@item
+On some platforms, this function loops forever for values
+near extrema (such as the year @math{-2**31}):
+Mac OS X 10.6.
+You can use the @code{time_rz} module to work around the problem.
+@item
On some platforms, this function returns nonsense values for
unsupported arguments (like @math{2^56}), rather than failing:
FreeBSD 10.
Portability problems not fixed by Gnulib:
@itemize
-@item On some platforms, this function returns nonsense values for
+@item
+On some platforms, this function loops forever for values
+near extrema (such as the year @math{-2**31}):
+Mac OS X 10.6.
+You can use the @code{time_rz} module to work around the problem.
+@item
+On some platforms, this function returns nonsense values for
unsupported arguments (like @math{2^56}), rather than failing:
FreeBSD 10.
@end itemize
struct tm *
localtime_rz (timezone_t tz, time_t const *t, struct tm *tm)
{
+#ifdef HAVE_LOCALTIME_INFLOOP_BUG
+ /* The -67768038400665599 comes from:
+ https://lists.gnu.org/r/bug-gnulib/2017-07/msg00142.html
+ On affected platforms the greatest POSIX-compatible time_t value
+ that could return nonnull is 67768036191766798 (when
+ TZ="XXX24:59:59" it resolves to the year 2**31 - 1 + 1900, on
+ 12-31 at 23:59:59), so test for that too while we're in the
+ neighborhood. */
+ if (! (-67768038400665599 <= *t && *t <= 67768036191766798))
+ {
+ errno = EOVERFLOW;
+ return NULL;
+ }
+#endif
+
if (!tz)
return gmtime_r (t, tm);
else
AC_REQUIRE([gl_HEADER_TIME_H_DEFAULTS])
AC_REQUIRE([AC_STRUCT_TIMEZONE])
+ # Mac OS X 10.6 loops forever with some time_t values less
+ # than -67768038400665599. See Bug#27706, Bug#27736, and
+ # https://lists.gnu.org/r/bug-gnulib/2017-07/msg00142.html
+ AC_CACHE_CHECK([whether localtime loops forever near extrema],
+ [gl_cv_func_localtime_infloop_bug],
+ [gl_cv_func_localtime_infloop_bug=no
+ AC_RUN_IFELSE(
+ [AC_LANG_PROGRAM(
+ [[#include <stdlib.h>
+ #include <string.h>
+ #include <unistd.h>
+ #include <time.h>
+ ]], [[
+ time_t t = -67768038400665600;
+ struct tm *tm;
+ char *tz = getenv ("TZ");
+ if (! (tz && strcmp (tz, "QQQ0") == 0))
+ return 0;
+ alarm (2);
+ tm = localtime (&t);
+ /* Use TM and *TM to suppress over-optimization. */
+ return tm && tm->tm_isdst;
+ ]])],
+ [TZ=QQQ0 ./conftest$EXEEXT || gl_cv_func_localtime_infloop_bug=yes],
+ [],
+ [gl_cv_func_localtime_infloop_bug="guessing no"])])
+ if test "$gl_cv_func_localtime_infloop_bug" = yes; then
+ AC_DEFINE([HAVE_LOCALTIME_INFLOOP_BUG], 1,
+ [Define if localtime-like functions can loop forever on
+ extreme arguments.])
+ fi
+
AC_CHECK_TYPES([timezone_t], [], [], [[#include <time.h>]])
if test "$ac_cv_type_timezone_t" = yes; then
HAVE_TIMEZONE_T=1