diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index cf353cc..98c9dd4 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -116,10 +116,15 @@ syscall_exit (int status)
 }
 
 static pid_t
-syscall_exec (const char *cmd_line UNUSED)
+syscall_exec (const char *cmd_line)
 {
-  //TODO
-  return 0;
+  validate_user_pointer (cmd_line, 1);
+
+  lock_acquire (&filesys_lock);
+  pid_t pid = process_execute(cmd_line);
+  lock_release (&filesys_lock);
+
+  return pid;
 }
 
 static int