net: wg: Support RTC with native_sim board

If running wg in native-sim, use the host clock to get the
current time. This helps to have a proper handshake when
connecting even after restarting the zephyr.exe process.

Signed-off-by: Jukka Rissanen <[email protected]>

Author: jukkar

subsys/net/lib/wireguard/CMakeLists.txt

@@ -13,3 +13,5 @@ zephyr_library_sources(crypto/refc/poly1305-donna.c)
 zephyr_library_sources(crypto/refc/blake2s.c)
 zephyr_library_sources(crypto/refc/chacha20poly1305.c)
 zephyr_library_sources(crypto/refc/x25519.c)
+
+zephyr_library_sources_ifdef(CONFIG_BOARD_NATIVE_SIM ns_rtc.c)

subsys/net/lib/wireguard/ns_rtc.c

@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) 2025 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/* Get time from host system when running on native_posix board */
+
+#include <zephyr/logging/log.h>
+LOG_MODULE_DECLARE(wireguard, CONFIG_WIREGUARD_LOG_LEVEL);
+
+#include <zephyr/kernel.h>
+#include <zephyr/net/net_core.h>
+#include <zephyr/net/wireguard.h>
+
+#include "native_rtc.h"
+
+int wireguard_get_current_time(uint64_t *seconds, uint32_t *nanoseconds)
+{
+	uint64_t timeus;
+
+	timeus = native_rtc_gettime_us(RTC_CLOCK_PSEUDOHOSTREALTIME);
+
+	*seconds = timeus / USEC_PER_SEC;
+	*nanoseconds = (timeus % USEC_PER_SEC) * NSEC_PER_USEC;
+
+	NET_DBG("Current time: %llu.%09u", *seconds, *nanoseconds);
+
+	return 0;
+}