fix SIGSEGV inside gmmktime (VKCOM#794)

runtime/datetime/datetime_functions.cpp

@@ -12,6 +12,7 @@
 #include "runtime/critical_section.h"
 #include "runtime/datetime/timelib_wrapper.h"
 #include "runtime/string_functions.h"
+#include "server/server-log.h"
 
 extern long timezone;
 
@@ -33,7 +34,7 @@ static void set_default_timezone_id(const char *timezone_id) {
 
 static const char *suffix[] = {"st", "nd", "rd", "th"};
 
-static time_t gmmktime(struct tm *tm) {
+static time_t deprecated_gmmktime(struct tm * tm) {
   char *tz = getenv("TZ");
   setenv("TZ", "", 1);
   tzset();
@@ -50,6 +51,24 @@ static time_t gmmktime(struct tm *tm) {
   return result;
 }
 
+static time_t updated_gmmktime(struct tm * tm) {
+  return timegm(tm);
+}
+
+static time_t gmmktime(struct tm *tm) {
+  dl::CriticalSectionGuard critical_section;
+  time_t deprecated_time = deprecated_gmmktime(tm);
+  time_t updated_time = updated_gmmktime(tm);
+  if (deprecated_time != updated_time) {
+    char * tz = getenv("TZ");
+    log_server_warning("Updated gmmktime return different result. Updated value %ld. Deprecated value %ld. ENV TZ = \"%s\". "
+                       "Local tz name[0] = \"%s\", tz name[1] = \"%s\", timezone %ld, daylight %d",
+                       updated_time, deprecated_time, tz != nullptr ? tz : "null", tzname[0] != nullptr ? tzname[0] : "null",
+                       tzname[1] != nullptr ? tzname[1] : "null", timezone, daylight);
+  }
+  return deprecated_time;
+}
+
 bool f$checkdate(int64_t month, int64_t day, int64_t year) {
   return php_timelib_is_valid_date(month, day, year);
 }