[PATCH] time_rz: work around Mac OS X 10.6 infloop

[Paul Eggert]

* 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.
---
ChangeLog | 10 ++++++++++
doc/posix-functions/localtime.texi | 5 +++++
doc/posix-functions/localtime_r.texi | 8 +++++++-
lib/time_rz.c | 15 +++++++++++++++
m4/time_rz.m4 | 32 ++++++++++++++++++++++++++++++++
5 files changed, 69 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index 4b0890876..99f219c26 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
[phone] Paul 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 <***@fb.com>

test-version-etc.sh: don't use diff directly: use init.sh's compare
diff --git a/doc/posix-functions/localtime.texi b/doc/posix-functions/localtime.texi
index 02d069cc1..c8a2b83b0 100644
--- a/doc/posix-functions/localtime.texi
+++ b/doc/posix-functions/localtime.texi
@@ -16,6 +16,11 @@ when the environment variable @code{TZ} has been set by Cygwin.
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.
diff --git a/doc/posix-functions/localtime_r.texi b/doc/posix-functions/localtime_r.texi
index 6ca2aed6c..4862cbfd6 100644
--- a/doc/posix-functions/localtime_r.texi
+++ b/doc/posix-functions/localtime_r.texi
@@ -22,7 +22,13 @@ HP-UX 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
diff --git a/lib/time_rz.c b/lib/time_rz.c
index 4682beb57..f9262c172 100644
--- a/lib/time_rz.c
+++ b/lib/time_rz.c
@@ -286,6 +286,21 @@ revert_tz (timezone_t tz)
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
diff --git a/m4/time_rz.m4 b/m4/time_rz.m4
index 437814897..af9fa02b5 100644
--- a/m4/time_rz.m4
+++ b/m4/time_rz.m4
@@ -13,6 +13,38 @@ AC_DEFUN([gl_TIME_RZ],
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