From: Theo Buehler <tb@theobuehler.org>
Subject: time.h: const correct tm_zone
To: tech@openbsd.org
Date: Tue, 18 Nov 2025 09:32:21 +0100

POSIX.1-2024 standardized struct tm's tm_zone as a const char *:
https://austingroupbugs.net/view.php?id=1533

Avoid casting away const and fix some warnings introduced in
strptime.c r1.32 when moving gmt[] and utc[] to rodata:

/usr/src/lib/libc/time/strptime.c:423:17: warning: assigning to 'char *' from 'const char[4]' discards qualifiers [-Wincompatible-pointer-types-discards-qualifiers]
  423 |                                 tm->tm_zone = gmt;
      |                                             ^ ~~~

This diff went through an amd64 bulk with no fallout.

Index: include/time.h
===================================================================
RCS file: /cvs/src/include/time.h,v
diff -u -p -r1.32 time.h
--- include/time.h	25 Oct 2022 16:30:30 -0000	1.32
+++ include/time.h	15 Nov 2025 16:50:37 -0000
@@ -106,7 +106,7 @@ struct tm {
 	int	tm_yday;	/* days since January 1 [0-365] */
 	int	tm_isdst;	/* Daylight Saving Time flag */
 	long	tm_gmtoff;	/* offset from UTC in seconds */
-	char	*tm_zone;	/* timezone abbreviation */
+	const char *tm_zone;	/* timezone abbreviation */
 };
 
 __BEGIN_DECLS
Index: lib/libc/time/ctime.3
===================================================================
RCS file: /cvs/src/lib/libc/time/ctime.3,v
diff -u -p -r1.49 ctime.3
--- lib/libc/time/ctime.3	23 Jun 2025 13:53:11 -0000	1.49
+++ lib/libc/time/ctime.3	15 Nov 2025 20:21:39 -0000
@@ -241,7 +241,7 @@ includes the following fields:
 	int tm_yday;	/* day of year (0 \- 365) */
 	int tm_isdst;	/* is summer time in effect? */
 	long tm_gmtoff;	/* offset from UT in seconds */
-	char *tm_zone;	/* abbreviation of timezone name */
+	const char *tm_zone;	/* abbreviation of timezone name */
 .Ed
 .Pp
 The
Index: lib/libc/time/localtime.c
===================================================================
RCS file: /cvs/src/lib/libc/time/localtime.c,v
diff -u -p -r1.71 localtime.c
--- lib/libc/time/localtime.c	17 Aug 2025 08:42:21 -0000	1.71
+++ lib/libc/time/localtime.c	15 Nov 2025 21:19:52 -0000
@@ -1356,7 +1356,7 @@ gmtsub(const time_t *timep, int_fast32_t
 		tmp->tm_zone = wildabbr;
 	else {
 		if (gmtptr == NULL)
-			tmp->tm_zone = (char *)gmt;
+			tmp->tm_zone = gmt;
 		else
 			tmp->tm_zone = gmtptr->chars;
 	}
Index: lib/libc/time/strptime.c
===================================================================
RCS file: /cvs/src/lib/libc/time/strptime.c,v
diff -u -p -r1.33 strptime.c
--- lib/libc/time/strptime.c	26 Aug 2025 22:30:42 -0000	1.33
+++ lib/libc/time/strptime.c	15 Nov 2025 21:19:07 -0000
@@ -484,7 +484,7 @@ literal:
 				ep = _find_string(bp, &i, nast, NULL, 4);
 				if (ep != NULL) {
 					tm->tm_gmtoff = (-5 - i) * SECSPERHOUR;
-					tm->tm_zone = (char *)nast[i];
+					tm->tm_zone = nast[i];
 					bp = ep;
 					continue;
 				}
@@ -492,7 +492,7 @@ literal:
 				if (ep != NULL) {
 					tm->tm_isdst = 1;
 					tm->tm_gmtoff = (-4 - i) * SECSPERHOUR;
-					tm->tm_zone = (char *)nadt[i];
+					tm->tm_zone = nadt[i];
 					bp = ep;
 					continue;
 				}
Index: usr.bin/finger/lprint.c
===================================================================
RCS file: /cvs/src/usr.bin/finger/lprint.c,v
diff -u -p -r1.13 lprint.c
--- usr.bin/finger/lprint.c	26 Apr 2018 12:42:51 -0000	1.13
+++ usr.bin/finger/lprint.c	15 Nov 2025 20:16:24 -0000
@@ -72,7 +72,7 @@ lprint(PERSON *pn)
 	int cpr, len, maxlen;
 	struct tm *tp;
 	int oddfield;
-	char *t, *tzn;
+	const char *t, *tzn;
 
 	cpr = 0;
 	/*