[erlang-patches] leap-second-enabled FreeBSD doesn't work right with R12B4 erts/emulator/beam/erl_time_sup.c; correction patch included
Sun Sep 14 03:41:11 CEST 2008
A patch to correct erlang:universaltime_to_localtime/1
for FreeBSD running leap-second-enabled timezone
by Kenji Rikitake <>
This patch fixes the time calculation problem of
FreeBSD 6.x and 7.x, which has the internal leap-second
This patch is tested with Erlang/OTP R12B-4 source distribution.
Without this patch,
are not symmetric and will break
* Example of symptom:
(under where local time is GMT + 9 hours)
(Note that as of September 1, 2008, TAI - UTC = 33 seconds.
UNIX time_t with TAI correction is 10 seconds ahead of UTC.
So the 23-second difference occurs when the leap-second
correction is NOT performed, as in the C function of
univ_to_local() in erts/emulator/beam/erl_time_sup.c)
* Workaround in this patch
This patch changes the operation of
so that the "universaltime" is handled properly
with leap-year correction.
(Note: OS time_t is in TAI)
See FreeBSD man time2posix(3) and
for the further details.
This patch will NOT affect a FreeBSD machine without
leap-year correction; posix2time() will do nothing
in such a situation. (NOT tested though)
* Caveats, TODO and suggestions
There is no portable way to do this among UNIX-derived OSes
HAVE_POSIX2TIME should be set by configure
A Linux patch for leap-second supported systems is highly desired
(I found posix2time() is also available on Linux, but I'm not sure)
Should I rather do this using timegm(3) and throw away
the rather naive computation algorithm in univ_to_local()?
(Note that this is not necessarily portable either)
* How to apply this patch
Apply this at Erlang R12B4 source tree's directory under:
--- erl_time_sup.c.FCS 2008-04-07 22:57:50.000000000 +0900
+++ erl_time_sup.c 2008-09-14 09:56:10.000000000 +0900
@@ -71,6 +71,10 @@
+/* FreeBSD internal leap year correction function */
+/* define this for FreeBSD 6.x and 7.x */
# include "config.h"
@@ -686,6 +690,18 @@
the_clock = *second + 60 * (*minute + 60 * (*hour + 24 *
gregday(*year, *month, *day)));
+ * leap-second correction performed
+ * if system is configured so;
+ * do nothing if not
+ * See FreeBSD 6.x and 7.x
+ * /usr/src/lib/libc/stdtime/localtime.c
+ * for the details
+ the_clock = posix2time(the_clock);
localtime_r(&the_clock, (tm = &tmbuf));
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