Fix DST bug in aon_timer_get_time for rp2040 (#2409)

If you set the timezone, aon_timer_get_time can wrongly apply a
daylight saving time adjustment based on the stack contents. This can
make it appear that time has gone backwards.

Make sure datetime_to_tm initialises tm_isdst to -1.

Fixes #2374

Author: peterharperuk

src/common/pico_util/datetime.c

@@ -63,6 +63,7 @@ void datetime_to_tm(const datetime_t *dt, struct tm *tm) {
     tm->tm_hour = dt->hour;
     tm->tm_min = dt->min;
     tm->tm_sec = dt->sec;
+    tm->tm_isdst  = -1;
 }
 
 void tm_to_datetime(const struct tm *tm, datetime_t *dt) {

test/pico_time_test/pico_time_test.c

@@ -85,6 +85,7 @@ static int issue_1953_test(void);
 static int issue_2118_test(void);
 static int issue_2148_test(void);
 static int issue_2186_test(void);
+static int issue_2374_test(void);
 
 int main() {
     setup_default_uart();
@@ -263,6 +264,8 @@ int main() {
 
     issue_2186_test();
 
+    issue_2374_test();
+
     PICOTEST_END_TEST();
 }
 
@@ -421,3 +424,42 @@ static int issue_2148_test(void) {
 #endif
     return 0;
 }
+
+static void fill_stack(int val) {
+    uint8_t array[50];
+    memset(array, val, sizeof(array));
+}
+
+// aon_timer_get_time called aon_timer_get_time_calendar which called datetime_to_tm
+// which didn't initialise tm_isdst
+static int issue_2374_test(void) {
+#if HAS_RP2040_RTC && !__clang__
+    PICOTEST_START_SECTION("Issue #2374 defect - time goes backwards");
+    setenv("TZ", "PST8PDT7,M3.2.0/2,M11.1.0/02:00:00", 1);
+    tzset();
+
+    struct timespec ts = { .tv_sec = 1743055938, .tv_nsec = 0 };
+    aon_timer_start(&ts);
+
+    struct timespec ts1;
+    fill_stack(1); // Setting tm_isdst if it's uninitialised
+    hard_assert(aon_timer_get_time(&ts1));
+
+    sleep_ms(1000);
+
+    struct timespec ts2;
+    fill_stack(0); // Setting tm_isdst if it's uninitialised
+    hard_assert(aon_timer_get_time(&ts2));
+
+    // Check time hasn't been adjusted due to dst
+    hard_assert(ts1.tv_sec == ts2.tv_sec - 1);
+
+    setenv("TZ", "", 1);
+    tzset();
+
+    aon_timer_stop();
+
+    PICOTEST_END_SECTION();
+#endif
+    return 0;
+}