lib: posix: semaphore: use consistent timebase in sem_timedwait

In the Zephyr implementation, `sem_timedwait()` uses a
potentially wildly different timebase for comparison via
`k_uptime_get()` (uptime in ms).

The standard specifies `CLOCK_REALTIME`. However, the real-time
clock can be modified to an arbitrary value via clock_settime()
and there is no guarantee that it will always reflect uptime.

This change ensures that `sem_timedwait()` uses a more
consistent timebase for comparison.

Fixes #46807

Signed-off-by: Christopher Friedt <chrisfriedt@gmail.com>
(cherry picked from commit 9d433c89a2)

lib/posix/Kconfig

@@ -19,6 +19,7 @@ config POSIX_API
 config PTHREAD_IPC
 	bool "POSIX pthread IPC API"
 	default y if POSIX_API
+	depends on POSIX_CLOCK
 	help
 	  This enables a mostly-standards-compliant implementation of
 	  the pthread mutex, condition variable and barrier IPC

lib/posix/semaphore.c

@@ -91,6 +91,7 @@ int sem_post(sem_t *semaphore)
 int sem_timedwait(sem_t *semaphore, struct timespec *abstime)
 {
 	int32_t timeout;
+	struct timespec current;
 	int64_t current_ms, abstime_ms;
 
 	__ASSERT(abstime, "abstime pointer NULL");
@@ -100,8 +101,12 @@ int sem_timedwait(sem_t *semaphore, struct timespec *abstime)
 		return -1;
 	}
 
-	current_ms = (int64_t)k_uptime_get();
+	if (clock_gettime(CLOCK_REALTIME, &current) < 0) {
+		return -1;
+	}
+
 	abstime_ms = (int64_t)_ts_to_ms(abstime);
+	current_ms = (int64_t)_ts_to_ms(&current);
 
 	if (abstime_ms <= current_ms) {
 		timeout = 0;

samples/net/sockets/socketpair/prj.conf

@@ -12,4 +12,5 @@ CONFIG_TEST_RANDOM_GENERATOR=y
 
 # Use Portable threads
 CONFIG_PTHREAD_IPC=y
+CONFIG_POSIX_CLOCK=y
 CONFIG_NET_SOCKETS_POSIX_NAMES=y