[libc] test: cover settimeofday() field validation

Requested in the review of #11928: add a utest for the narrowing fix.

The case walks the values whose byte range collides with INT32_MAX, so it only
proves something on targets where time_t is wider than long. Instead of silently
passing elsewhere it reports the sizes and skips:

    sizeof(time_t)=8 is not wider than sizeof(long)=4, skipping

Cases, all against the on-board rtc device:

    tv_sec = 2147483648   INT32_MAX + 1, first value the old cast broke
    tv_sec = 2208988800   2040-01-01, the value from #11922
    tv_sec = 4294967295   2106-02-07
    tv_usec = -1          must keep being rejected with EINVAL

The clock is saved before the first write and restored afterwards.

Without the fix in the previous commit the three large timestamps fail, while the
negative tv_usec case still passes:

    [E/utest] tv_sec = INT32_MAX + 1     ((settimeofday(&tv, 0)) not == (0))
    [E/utest] tv_sec = 2208988800 ...    ((settimeofday(&tv, 0)) not == (0))
    [E/utest] tv_sec = 4294967295 ...    ((settimeofday(&tv, 0)) not == (0))
    [I/utest] tv_usec = -1 must be rejected
    [E/utest] [  FAILED  ] components.libc.settimeofday

Verified on bsp/qemu-vexpress-a9 (RT_USING_RTC, on-board rtc device):
  with the fix    : PASSED
  without the fix : FAILED, the three boundary assertions listed above

Registered under its own Kconfig symbol rather than the existing time_tc.c, since
it depends on RT_USING_RTC while that case depends on RT_USING_POSIX_CLOCK.

Refs #11922
Refs #11928

Author: Yunlk

components/libc/compilers/common/utest/Kconfig

@@ -5,4 +5,9 @@ config RT_UTEST_LIBC_TIME
     default n
     depends on RT_USING_POSIX_CLOCK
 
+config RT_UTEST_LIBC_SETTIMEOFDAY
+    bool "settimeofday() field validation Test"
+    default n
+    depends on RT_USING_RTC
+
 endmenu

components/libc/compilers/common/utest/SConscript

@@ -8,6 +8,9 @@ CPPPATH = [cwd]
 if GetDepend(['RT_UTEST_LIBC_TIME']):
     src += ['time_tc.c']
 
+if GetDepend(['RT_UTEST_LIBC_SETTIMEOFDAY']):
+    src += ['settimeofday_tc.c']
+
 group = DefineGroup('utestcases', src, depend = ['RT_USING_UTESTCASES'], CPPPATH = CPPPATH)
 
 Return('group')

components/libc/compilers/common/utest/settimeofday_tc.c

@@ -0,0 +1,108 @@
+/*
+ * Copyright (c) 2006-2026, RT-Thread Development Team
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * Test Case Name: settimeofday() field validation
+ *
+ * Test Objectives:
+ * - Verify that timestamps above INT32_MAX are accepted on time64/long32 targets.
+ * - Verify that a negative tv_usec is still rejected.
+ * - Prevent regression of GitHub Issue #11922.
+ *
+ * Note: the rejections exercised here only happen when time_t is wider than long,
+ * which is the time64/long32 configuration. On targets where the two are the same
+ * width the old narrowing cast could not change the result, so the case would not
+ * prove anything; it reports that and skips.
+ */
+
+#include <rtthread.h>
+#include <rtdevice.h>
+#include <sys/time.h>
+#include <errno.h>
+#include "utest.h"
+
+/* Run settimeofday() against the boundary values, then restore the clock. */
+static void settimeofday_time64_test(void)
+{
+    struct timeval tv;
+    struct timeval saved = { 0, 0 };
+    rt_device_t rtc;
+    int ret;
+
+    rtc = rt_device_find("rtc");
+    if (rtc == RT_NULL)
+    {
+        LOG_I("no rtc device, skipping");
+        return;
+    }
+
+    if (sizeof(time_t) <= sizeof(long))
+    {
+        LOG_I("sizeof(time_t)=%d is not wider than sizeof(long)=%d, skipping",
+              (int)sizeof(time_t), (int)sizeof(long));
+        return;
+    }
+
+    /* remember the current time so the rtc can be put back afterwards */
+    if (gettimeofday(&saved, RT_NULL) != 0)
+    {
+        saved.tv_sec  = 0;
+        saved.tv_usec = 0;
+    }
+
+    /* INT32_MAX + 1: the first value the old (long) cast turned negative */
+    tv.tv_sec  = (time_t)2147483647 + 1;
+    tv.tv_usec = 0;
+    LOG_I("tv_sec = INT32_MAX + 1");
+    uassert_int_equal(settimeofday(&tv, RT_NULL), 0);
+
+    /* 2040-01-01, the value reported in #11922 */
+    tv.tv_sec  = (time_t)2208988800;
+    tv.tv_usec = 0;
+    LOG_I("tv_sec = 2208988800 (2040-01-01)");
+    uassert_int_equal(settimeofday(&tv, RT_NULL), 0);
+
+    /* 2106-02-07, UINT32_MAX */
+    tv.tv_sec  = (time_t)4294967295U;
+    tv.tv_usec = 0;
+    LOG_I("tv_sec = 4294967295 (2106-02-07)");
+    uassert_int_equal(settimeofday(&tv, RT_NULL), 0);
+
+    /* a negative tv_usec is still invalid and must keep being rejected */
+    tv.tv_sec  = (time_t)1000000000;
+    tv.tv_usec = -1;
+    LOG_I("tv_usec = -1 must be rejected");
+    errno = 0;
+    ret = settimeofday(&tv, RT_NULL);
+    uassert_int_equal(ret, -1);
+    uassert_int_equal(errno, EINVAL);
+
+    /* put the clock back */
+    if (settimeofday(&saved, RT_NULL) != 0)
+    {
+        LOG_W("failed to restore the rtc");
+    }
+}
+
+/* Initialize the settimeofday test. */
+static rt_err_t utest_tc_init(void)
+{
+    return RT_EOK;
+}
+
+/* Clean up the settimeofday test. */
+static rt_err_t utest_tc_cleanup(void)
+{
+    return RT_EOK;
+}
+
+/* Run the settimeofday test case. */
+static void testcase(void)
+{
+    UTEST_UNIT_RUN(settimeofday_time64_test);
+}
+
+UTEST_TC_EXPORT(testcase, "components.libc.settimeofday", utest_tc_init, utest_tc_cleanup, 10);