libc: Export timespec_getres(3) and add tests

timespec_getres() has been declared in <time.h> and built into libc,
but never listed in a symbol map.  It is therefore local to libc.so,
and dynamically linked callers fail to link.

Reviewed by:	ziaee, fuz, des
Approved by:	fuz (mentor)
Fixes:		9b5d724cad ("libc: Add timespec_getres(3) as per C23.")
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D60799

lib/libc/gen/Symbol.map

@@ -483,6 +483,7 @@ FBSD_1.9 {
 	posix_spawnattr_getprocdescp_np;
 	posix_spawnattr_setexecfd_np;
 	posix_spawnattr_setprocdescp_np;
+	timespec_getres;
 	uexterr_set;
 };
 

lib/libc/gen/timespec_getres.3

@@ -3,7 +3,7 @@
 .\"
 .\" SPDX-License-Identifier: BSD-2-Clause
 .\"
-.Dd May 14, 2026
+.Dd October 20, 2026
 .Dt TIMESPEC_GETRES 3
 .Os
 .Sh NAME
@@ -43,7 +43,11 @@ function conforms to
 .St -isoC-2023 .
 .Sh HISTORY
 This interface first appeared in
-.Fx 14 .
+.Fx 14.0 ,
+but it was not exported from the shared C library until
+.Fx 14.6
+and
+.Fx 15.2 .
 .Sh AUTHORS
 The
 .Nm

lib/libc/tests/gen/Makefile

@@ -42,6 +42,7 @@ ATF_TESTS_C+=		scandir_blocks_test
 .endif
 ATF_TESTS_C+=		sig2str_test
 ATF_TESTS_C+=		sigsetops_test
+ATF_TESTS_C+=		timespec_getres_test
 ATF_TESTS_C+=		wordexp_test
 
 # TODO: t_closefrom, t_fmtcheck, t_randomid,

lib/libc/tests/gen/timespec_getres_test.c

@@ -0,0 +1,124 @@
+/*
+ * Copyright (c) 2026 Faraz Vahedi <kfv@FreeBSD.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+/*
+ * Tests for timespec_getres() as per ISO/IEC 9899:2024 §7.29.2.7.
+ */
+
+#include <sys/param.h>
+#include <limits.h>
+#include <time.h>
+
+#include <atf-c.h>
+
+static const struct {
+	int		base;
+	clockid_t	clock;
+} bases[] = {
+	{ TIME_UTC,		CLOCK_REALTIME },
+	{ TIME_MONOTONIC,	CLOCK_MONOTONIC },
+};
+
+static const int bad_bases[] = {
+	INT_MIN, -1, 0, INT_MAX,
+};
+
+static void
+check_res(const struct timespec *ts)
+{
+	ATF_CHECK(ts->tv_sec >= 0);
+	ATF_CHECK(ts->tv_nsec >= 0 && ts->tv_nsec < 1000000000);
+	ATF_CHECK(ts->tv_sec != 0 || ts->tv_nsec != 0);
+}
+
+ATF_TC_WITHOUT_HEAD(timespec_getres_supported);
+ATF_TC_BODY(timespec_getres_supported, tc)
+{
+	struct timespec ts;
+
+	for (size_t i = 0; i < nitems(bases); i++) {
+		ATF_CHECK_EQ(timespec_getres(&ts, bases[i].base),
+		    bases[i].base);
+		check_res(&ts);
+	}
+}
+
+ATF_TC_WITHOUT_HEAD(timespec_getres_clock);
+ATF_TC_BODY(timespec_getres_clock, tc)
+{
+	struct timespec ts, cts;
+
+	for (size_t i = 0; i < nitems(bases); i++) {
+		ATF_REQUIRE_EQ(timespec_getres(&ts, bases[i].base),
+		    bases[i].base);
+		ATF_REQUIRE_EQ(clock_getres(bases[i].clock, &cts), 0);
+		ATF_CHECK_EQ(ts.tv_sec, cts.tv_sec);
+		ATF_CHECK_EQ(ts.tv_nsec, cts.tv_nsec);
+	}
+}
+
+ATF_TC_WITHOUT_HEAD(timespec_getres_null);
+ATF_TC_BODY(timespec_getres_null, tc)
+{
+	for (size_t i = 0; i < nitems(bases); i++)
+		ATF_CHECK_EQ(timespec_getres(NULL, bases[i].base),
+		    bases[i].base);
+	for (size_t i = 0; i < nitems(bad_bases); i++)
+		ATF_CHECK_EQ(timespec_getres(NULL, bad_bases[i]), 0);
+}
+
+ATF_TC_WITHOUT_HEAD(timespec_getres_unsupported);
+ATF_TC_BODY(timespec_getres_unsupported, tc)
+{
+	struct timespec ts;
+
+	for (size_t i = 0; i < nitems(bad_bases); i++) {
+		ts.tv_sec = -1;
+		ts.tv_nsec = -1;
+		ATF_CHECK_EQ(timespec_getres(&ts, bad_bases[i]), 0);
+		ATF_CHECK_EQ(ts.tv_sec, -1);
+		ATF_CHECK_EQ(ts.tv_nsec, -1);
+	}
+}
+
+ATF_TC_WITHOUT_HEAD(timespec_getres_timespec_get);
+ATF_TC_BODY(timespec_getres_timespec_get, tc)
+{
+	struct timespec ts;
+
+	for (int base = -1; base <= TIME_MONOTONIC + 8; base++)
+		ATF_CHECK_EQ_MSG(timespec_getres(&ts, base) != 0,
+		    timespec_get(&ts, base) != 0, "base %d", base);
+}
+
+ATF_TC_WITHOUT_HEAD(timespec_getres_stable);
+ATF_TC_BODY(timespec_getres_stable, tc)
+{
+	struct timespec first, ts;
+
+	for (size_t i = 0; i < nitems(bases); i++) {
+		ATF_REQUIRE_EQ(timespec_getres(&first, bases[i].base),
+		    bases[i].base);
+		for (int n = 0; n < 100; n++) {
+			ATF_REQUIRE_EQ(timespec_getres(&ts, bases[i].base),
+			    bases[i].base);
+			ATF_CHECK_EQ(ts.tv_sec, first.tv_sec);
+			ATF_CHECK_EQ(ts.tv_nsec, first.tv_nsec);
+		}
+	}
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+	ATF_TP_ADD_TC(tp, timespec_getres_supported);
+	ATF_TP_ADD_TC(tp, timespec_getres_clock);
+	ATF_TP_ADD_TC(tp, timespec_getres_null);
+	ATF_TP_ADD_TC(tp, timespec_getres_unsupported);
+	ATF_TP_ADD_TC(tp, timespec_getres_timespec_get);
+	ATF_TP_ADD_TC(tp, timespec_getres_stable);
+
+	return (atf_no_error());
+}