Fix undefined overflow behavior when converting double to integer (#3629)

Overflows in conversions from floating-point to integer are
undefined behavior in the C99 standard. (Clause 6.3.1.4: "If the
value of the integral part cannot be represented by the integer
type, the behavior is undefined.")

When UBSAN is enabled, this gets reported at `srand()` calls. (The
random seed is usually initialized using the date port API, which
represents dates as `double`s. But `srand` takes an `unsigned int`.
A simple cast from `double` to `unsigned` becomes undefined
behavior if the value is too large. And "now" is too large
nowadays. So, effectively, all executions start with an undefined
behavior.)

This patch fixes this by casting the floating-point value of the
date to an integer through a union.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu

docs/03.API-EXAMPLE.md

@@ -1084,7 +1084,8 @@ int
 main (void)
 {
   /* Initialize srand value */
-  srand ((unsigned) jerry_port_get_current_time ());
+  union { double d; unsigned u; } now = { .d = jerry_port_get_current_time () };
+  srand (now.u);
 
   /* Generate a random number, and print it */
   const jerry_char_t script[] = "var a = Math.random (); print(a)";

jerry-main/main-unix-test.c

@@ -72,7 +72,12 @@ int
 main (int argc,
       char **argv)
 {
-  srand ((unsigned) jerry_port_get_current_time ());
+  union
+  {
+    double d;
+    unsigned u;
+  } now = { .d = jerry_port_get_current_time () };
+  srand (now.u);
   if (argc <= 1 || (argc == 2 && (!strcmp ("-h", argv[1]) || !strcmp ("--help", argv[1]))))
   {
     print_help (argv[0]);

jerry-main/main-unix.c

@@ -467,7 +467,12 @@ int
 main (int argc,
       char **argv)
 {
-  srand ((unsigned) jerry_port_get_current_time ());
+  union
+  {
+    double d;
+    unsigned u;
+  } now = { .d = jerry_port_get_current_time () };
+  srand (now.u);
   JERRY_VLA (const char *, file_names, argc);
   int files_counter = 0;
 

targets/curie_bsp/jerry_app/quark/main.c

@@ -136,7 +136,8 @@ void eval_jerry_script (int argc, char *argv[], struct tcmd_handler_ctx *ctx)
 
 void jerry_start ()
 {
-  srand ((unsigned) jerry_port_get_current_time ());
+  union { double d; unsigned u; } now = { .d = jerry_port_get_current_time () };
+  srand (now.u);
   jerry_init (JERRY_INIT_EMPTY);
   jerry_value_t global_obj_val = jerry_get_global_object ();
   jerry_value_t print_func_name_val = jerry_create_string ((jerry_char_t *) "print");

targets/esp8266/user/jerry_run.c

@@ -26,7 +26,8 @@ static const char* fn_sys_loop_name = "sysloop";
 
 void js_entry ()
 {
-  srand ((unsigned) jerry_port_get_current_time ());
+  union { double d; unsigned u; } now = { .d = jerry_port_get_current_time () };
+  srand (now.u);
 
   jerry_init (JERRY_INIT_EMPTY);
   js_register_functions ();

targets/mbedos5/jerryscript-mbed/jerryscript-mbed-launcher/source/launcher.cpp

@@ -68,7 +68,8 @@ static int load_javascript() {
 }
 
 int jsmbed_js_init() {
-    srand ((unsigned) jerry_port_get_current_time());
+    union { double d; unsigned u; } now = { .d = jerry_port_get_current_time () };
+    srand (now.u);
     jerry_init_flag_t flags = JERRY_INIT_EMPTY;
     jerry_init(flags);
 

targets/riot-stm32f4/source/main-riotos.c

@@ -98,7 +98,8 @@ const shell_command_t shell_commands[] = {
 
 int main (void)
 {
-  srand ((unsigned) jerry_port_get_current_time ());
+  union { double d; unsigned u; } now = { .d = jerry_port_get_current_time () };
+  srand (now.u);
   printf ("You are running RIOT on a(n) %s board.\n", RIOT_BOARD);
   printf ("This board features a(n) %s MCU.\n", RIOT_MCU);
 

targets/zephyr/src/main-zephyr.c

@@ -79,7 +79,8 @@ static int shell_cmd_handler (char *source_buffer)
 
 void main (void)
 {
-  srand ((unsigned) jerry_port_get_current_time ());
+  union { double d; unsigned u; } now = { .d = jerry_port_get_current_time () };
+  srand (now.u);
   uint32_t zephyr_ver = sys_kernel_version_get ();
   printf ("JerryScript build: " __DATE__ " " __TIME__ "\n");
   printf ("JerryScript API %d.%d.%d\n", JERRY_API_MAJOR_VERSION, JERRY_API_MINOR_VERSION, JERRY_API_PATCH_VERSION);

tests/unit-core/test-common.h

@@ -49,7 +49,8 @@
 #define TEST_INIT() \
 do \
 { \
-  srand ((unsigned) jerry_port_get_current_time ()); \
+  union { double d; unsigned u; } now = { .d = jerry_port_get_current_time () }; \
+  srand (now.u); \
 } while (0)
 
 /**