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

5 files changed, 10 insertions, 5 deletions

diff --git a/targets/curie_bsp/jerry_app/quark/main.c b/targets/curie_bsp/jerry_app/quark/main.c
index 2aee9143..2975bbb0 100644
--- a/targets/curie_bsp/jerry_app/quark/main.c
+++ b/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");
diff --git a/targets/esp8266/user/jerry_run.c b/targets/esp8266/user/jerry_run.c
index ab70ff76..e7fff4c3 100644
--- a/targets/esp8266/user/jerry_run.c
+++ b/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 ();
diff --git a/targets/mbedos5/jerryscript-mbed/jerryscript-mbed-launcher/source/launcher.cpp b/targets/mbedos5/jerryscript-mbed/jerryscript-mbed-launcher/source/launcher.cpp
index 1acf2f16..4c70be88 100644
--- a/targets/mbedos5/jerryscript-mbed/jerryscript-mbed-launcher/source/launcher.cpp
+++ b/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);
 
diff --git a/targets/riot-stm32f4/source/main-riotos.c b/targets/riot-stm32f4/source/main-riotos.c
index d77aa274..28b9df84 100644
--- a/targets/riot-stm32f4/source/main-riotos.c
+++ b/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);
 
diff --git a/targets/zephyr/src/main-zephyr.c b/targets/zephyr/src/main-zephyr.c
index 6ea0b846..e250f9d3 100644
--- a/targets/zephyr/src/main-zephyr.c
+++ b/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);