diff --git a/src/libos/src/process/wait.rs b/src/libos/src/process/wait.rs
index e736e9d2..7cf4d37f 100644
--- a/src/libos/src/process/wait.rs
+++ b/src/libos/src/process/wait.rs
@@ -40,7 +40,7 @@ impl<D, R> Waiter<D, R>
     pub fn wait_on(&self) -> R {
         if !self.inner.lock().unwrap().has_waken {
             unsafe {
-                sgx_thread_wait_untrusted_event_ocall(self.thread);
+                wait_event(self.thread);
             }
         }
 
@@ -93,27 +93,47 @@ impl<D, R> WaitQueue<D, R>
             waiter_i.unwrap()
         };
         let del_waiter = waiters.swap_remove(del_waiter_i);
-        unsafe {
-            sgx_thread_set_untrusted_event_ocall(del_waiter.thread);
-        }
+        set_event(del_waiter.thread);
         1
     }
 }
 
+fn wait_event(thread: *const c_void) {
+    let mut ret : c_int = 0;
+    let mut sgx_ret : c_int = 0;
+    unsafe {
+        sgx_ret = sgx_thread_wait_untrusted_event_ocall(&mut ret as *mut c_int, thread);
+    }
+    if ret != 0 || sgx_ret != 0 {
+        panic!("ERROR: OCall failed!");
+    }
+}
+
+fn set_event(thread: *const c_void) {
+    let mut ret : c_int = 0;
+    let mut sgx_ret : c_int = 0;
+    unsafe {
+        sgx_ret = sgx_thread_set_untrusted_event_ocall(&mut ret as *mut c_int, thread);
+    }
+    if ret != 0 || sgx_ret != 0 {
+        panic!("ERROR: OCall failed!");
+    }
+}
+
 extern {
     fn sgx_thread_get_self() -> *const c_void;
 
     /* Go outside and wait on my untrusted event */
-    fn sgx_thread_wait_untrusted_event_ocall(self_thread: *const c_void) -> c_int;
+    fn sgx_thread_wait_untrusted_event_ocall(ret: *mut c_int, self_thread: *const c_void) -> c_int;
 
     /* Wake a thread waiting on its untrusted event */
-    fn sgx_thread_set_untrusted_event_ocall(waiter_thread: *const c_void) -> c_int;
+    fn sgx_thread_set_untrusted_event_ocall(ret: *mut c_int, waiter_thread: *const c_void) -> c_int;
 
     /* Wake a thread waiting on its untrusted event, and wait on my untrusted event */
-    fn sgx_thread_setwait_untrusted_events_ocall(
+    fn sgx_thread_setwait_untrusted_events_ocall(ret: *mut c_int,
         waiter_thread: *const c_void, self_thread: *const c_void) -> c_int;
 
     /* Wake multiple threads waiting on their untrusted events */
-    fn sgx_thread_set_multiple_untrusted_events_ocall(
+    fn sgx_thread_set_multiple_untrusted_events_ocall(ret: *mut c_int,
         waiter_threads: *const *const c_void, total: size_t ) -> c_int;
 }
diff --git a/src/libos/src/syscall/mod.rs b/src/libos/src/syscall/mod.rs
index 602c7275..4aa3c23e 100644
--- a/src/libos/src/syscall/mod.rs
+++ b/src/libos/src/syscall/mod.rs
@@ -378,7 +378,9 @@ pub extern "C" fn occlum_spawn(
 }
 
 fn do_wait4(pid: c_int, _exit_status: *mut c_int) -> Result<pid_t, Error> {
-    check_mut_ptr_from_user(_exit_status)?;
+    if _exit_status != 0 as *mut c_int {
+        check_mut_ptr_from_user(_exit_status)?;
+    }
 
     let child_process_filter = match pid {
         pid if pid < -1 => {
@@ -401,7 +403,9 @@ fn do_wait4(pid: c_int, _exit_status: *mut c_int) -> Result<pid_t, Error> {
     let mut exit_status = 0;
     match process::do_wait4(&child_process_filter, &mut exit_status) {
         Ok(pid) => {
-            unsafe { *_exit_status = exit_status; }
+            if _exit_status != 0 as *mut c_int {
+                unsafe { *_exit_status = exit_status; }
+            }
             Ok(pid)
         }
         Err(e) => {
diff --git a/test/Makefile b/test/Makefile
index 9c33b5cc..0ad8fa51 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -1,7 +1,7 @@
 CUR_DIR := $(shell dirname $(realpath $(lastword $(MAKEFILE_LIST))))
 PROJECT_DIR := $(realpath $(CUR_DIR)/../)
 
-TEST_SUITES := empty hello_world malloc getpid
+TEST_SUITES := empty hello_world malloc getpid spawn
 BUILD_TEST_SUITES := $(TEST_SUITES:%=%)
 RUN_TEST_SUITES := $(TEST_SUITES:%=run-%)
 CLEAN_TEST_SUITES := $(TEST_SUITES:%=clean-%)
diff --git a/test/getpid/main.c b/test/getpid/main.c
index 668b6d97..8636dcf3 100644
--- a/test/getpid/main.c
+++ b/test/getpid/main.c
@@ -3,7 +3,6 @@
 #include <stdio.h>
 
 int main(void) {
-    printf("pid = %d\n", getpid());
-    printf("ppid = %d\n", getppid());
+    printf("Run a new process with pid = %d and ppid = %d\n", getpid(), getppid());
     return 0;
 }
diff --git a/test/spawn/Makefile b/test/spawn/Makefile
new file mode 100644
index 00000000..b71a4d49
--- /dev/null
+++ b/test/spawn/Makefile
@@ -0,0 +1,4 @@
+include ../test_common.mk
+
+EXTRA_C_FLAGS :=
+EXTRA_LINK_FLAGS :=
diff --git a/test/spawn/main.c b/test/spawn/main.c
new file mode 100644
index 00000000..60f1b18b
--- /dev/null
+++ b/test/spawn/main.c
@@ -0,0 +1,24 @@
+#include <sys/syscall.h>
+#include <unistd.h>
+#include <stdio.h>
+
+int main(void) {
+    int ret, child_pid, status;
+    printf("Run a parent process has pid = %d and ppid = %d\n", getpid(), getppid());
+
+    ret = syscall(__NR_spawn, &child_pid, "getpid/bin.encrypted", NULL, NULL);
+    if (ret < 0) {
+        printf("ERROR: failed to spawn a child process\n");
+        return -1;
+    }
+    printf("Spawn a new proces successfully (pid = %d)\n", child_pid);
+
+    ret = syscall(__NR_wait4, -1, &status, 0);
+    if (ret < 0) {
+        printf("ERROR: failed to wait4 the child process\n");
+        return -1;
+    }
+    printf("Child process exited with status = %d\n", status);
+
+    return 0;
+}