Release 2025c - 2025-12-10 14:42:37 -0800

Briefly:
Several code changes for compatibility with FreeBSD.

Changes to code

An unset TZ is no longer invalid when /etc/localtime is missing,
and is abbreviated "UTC" not "-00". This reverts to 2024b behavior.
(Problem and patch reported by Dag-Erling Smørgrav.)

New function offtime_r, short for fixed-offset localtime_rz.
It is defined if STD_INSPIRED is defined.
(Patch from Dag-Erling Smørgrav.)

tzset etc. are now more cautious about questionable TZ settings.
Privileged programs now reject TZ settings that start with '/',
unless they are TZDEFAULT (default "/etc/localtime") or
start with TZDIR then '/' (default "/usr/share/zoneinfo/").
Unprivileged programs now require files to be regular files
and reject relative names containing ".." directory components;
formerly, only privileged programs did those two things.
These changes were inspired by similar behavior in FreeBSD.
On NetBSD, unprivileged programs now use O_REGULAR to check
whether a TZ setting starting with '/' names a regular file,
avoiding a minor security race still present elsewhere.
TZ strings taken from tzalloc arguments are now treated with
no less caution than TZ strings taken from the environment, as
the old undocumented behavior would have been hard to explain.
tzset etc. no longer use the 'access' system call to check access;
instead they now use the system calls issetugid, getauxval,
getresuid/getresgid, and geteuid/getegid/getuid/getgid (whichever
first works) to test whether a program is privileged.
Compile with -DHAVE_SYS_AUXV_H=[01] to enable or disable
<sys/auxv.h> which (if it defines AT_SECURE) enables getauxval,
and compile with -DHAVE_ISSETUGID=[01], -DHAVE_GETRESUID=[01], and
-DHAVE_GETEUID=[01] to enable or disable the other calls' use.

The new CFLAGS option -DTZ_CHANGE_INTERVAL=N makes tzset etc.
check for TZif file changes if the in-memory data are N seconds
old or more, and are derived from the TZ environment variable.
This is intended for platforms that want tzset etc. to reflect
changes to whatever file TZ selects (including changes to
/etc/localtime if TZ is unset). If N is negative (the default)
these checks are omitted; this is the traditional behavior.

The new CFLAGS options -DHAVE_STRUCT_STAT_ST_CTIM=0 and
-DHAVE_STRUCT_TIMESPEC=0 port to non-POSIX.1-2008 platforms
that lack st_ctim and struct timespec, respectively.

tzset etc. now treat ' ' like '_' in time zone abbreviations,
just as they treat other invalid bytes. This continues the
transition begun in release 96k, which removed spaces in tzdata
because the spaces break time string parsers.

The new CFLAGS option -DTHREAD_PREFER_SINGLE causes tzcode
in single-threaded processes to avoid locks, as FreeBSD does.
This can save time in single-threaded apps. The threadedness
testing costs CPU time and energy in multi-threaded apps.
New options -DHAVE___ISTHREADED and -DHAVE_SYS_SINGLE_THREADED_H
can help configure how to test for single-threadedness.

The new CFLAGS option -DTHREAD_RWLOCK uses read-write locks, as
macOS does, instead of mutexes. This saves real time when TZ is
rarely changing and many threads call tzcode simultaneously.
It costs more CPU time and energy.

The new CFLAGS option -TTHREAD_TM_MULTI causes localtime to return
a pointer to thread-specific memory, as FreeBSD does, instead of
to the same memory in all threads. This supports unportable
programs that incorrectly use localtime instead of localtime_r.
This option affects gmtime and offtime similarly to localtime.
Because the corresponding storage is freed on thread exit, this
option is incompatible with POSIX.1-2024 and earlier. It also
costs CPU time and memory.

tzfree now preserves errno, consistently with POSIX.1-2024 'free'.

tzcode now uses mempcpy if available, guessing its availability.
Compile with -DHAVE_MEMPCPY=1 or 0 to override the guess.

tzcode now uses strnlen to improve asymptotic performance a bit.
Compile with -DHAVE_STRNLEN=0 if your platform lacks it.

tzcode now hand-declares unistd.h-provided symbols like getopt
if HAVE_UNISTD_H=0, not if HAVE_POSIX_DECLS=0.

tzset etc. now have an experimental OPENAT_TZDIR option;
see Makefile and localtime.c for details.

On platforms like GNU/Hurd that do not define PATH_MAX,
exceedingly long TZ strings no longer fail merely because they
exceed an arbitrary file name length limit imposed by tzcode.

zic has new options inspired by FreeBSD. '-D' skips creation of
output ancestor directories, '-m MODE' sets output files' mode,
and '-u OWNER[:GROUP]' sets output files' owner and group.

zic now uses the fdopen function, which was standardized by
POSIX.1-1988 and is now safe to use in portable code.
This replaces its use of the older umask function, which
complicated maintenance.

Welcome to 2022b:

zic has a new option '-R @N' to output explicit transitions < N.
(Need suggested by Almaz Mingaleev.)

'zic -r @N' no longer outputs bad data when N < first transition.
(Problem introduced in 2021d and reported by Peter Krefting.)

zic now checks its input for NUL bytes and unterminated lines, and
now supports input line lengths up to 2048 (not 512) bytes.

gmtime and related code now use the abbreviation "UTC" not "GMT".
POSIX is being revised to require this.

When tzset and related functions set vestigial static variables
like tzname, they now prefer specified timestamps to unspecified ones.
(Problem reported by Almaz Mingaleev.)

zic no longer complains "can't determine time zone abbreviation to
use just after until time" when a transition to a new standard
time occurs simultanously with the first DST fallback transition.

Welcome to 2017c:

zic and the reference runtime now reject multiple leap seconds
within 28 days of each other, or leap seconds before the Epoch.
As a result, support for double leap seconds, which was
obsolescent and undocumented, has been removed. Double leap
seconds were an error in the C89 standard; they have never existed
in civil timekeeping. (Thanks to Robert Elz and Bradley White for
noticing glitches in the code that uncovered this problem.)

zic now warns about use of the obsolescent and undocumented -y
option, and about use of the obsolescent TYPE field of Rule lines.

zic now allows unambiguous abbreviations like "Sa" and "Su" for
weekdays; formerly it rejected them due to a bug. Conversely, zic
no longer considers non-prefixes to be abbreviations; for example,
it no longer accepts "lF" as an abbreviation for "lastFriday".
Also, zic warns about the undocumented usage with a "last-"
prefix, e.g., "last-Fri".

Similarly, zic now accepts the unambiguous abbreviation "L" for
"Link" in ordinary context and for "Leap" in leap-second context.
Conversely, zic no longer accepts non-prefixes such as "La" as
abbreviations for words like "Leap".

zic no longer accepts leap second lines in ordinary input, or
ordinary lines in leap second input. Formerly, zic sometimes
warned about this undocumented usage and handled it incorrectly.

The new macro HAVE_TZNAME governs whether the tzname external
variable is exported, instead of USG_COMPAT. USG_COMPAT now
governs only the external variables "timezone" and "daylight".
This change is needed because the three variables are not in the
same category: although POSIX requires tzname, it specifies the
other two variables as optional. Also, USG_COMPAT is now 1 or 0:
if not defined, the code attempts to guess it from other macros.

localtime.c and difftime.c no longer require stdio.h, and .c files
other than zic.c no longer require sys/wait.h.

zdump.c no longer assumes snprintf. (Reported by Jonathan Leffler.)

Calculation of time_t extrema works around a bug in GCC 4.8.4
(Reported by Stan Shebs and Joseph Myers.)

zic.c no longer mistranslates formats of line numbers in non-English
locales. (Problem reported by Benno Schulenberg.)

Several minor changes have been made to the code to make it a
bit easier to port to MS-Windows and Solaris. (Thanks to Kees
Dekker for reporting the problems.)

Changes to documentation and commentary

The two new files 'theory.html' and 'calendars' contain the
contents of the removed file 'Theory'. The goal is to document
tzdb theory more accessibly.

The zic man page now documents abbreviation rules.

tz-link.htm now covers how to apply tzdata changes to clients.
(Thanks to Jorge Fábregas for the AIX link.) It also mentions MySQL.

The leap-seconds.list URL has been updated to something that is
more reliable for tzdb. (Thanks to Tim Parenti and Brian Inglis.)