Refactor process_init_stack to reduce code duplication

src/userprog/process.c

@@ -90,6 +90,7 @@ process_execute (const char *cmd)
 
 static bool process_init_stack (char *cmd_saveptr, void **esp, char *file_name);
 static void *push_to_stack (void **esp, void *data, size_t data_size);
+#define push_var_to_stack(esp, var) (push_to_stack (esp, &var, sizeof (var)))
 
 /* Make the current thread execute 'cmd', passing in a copy of the
    command string used for processing, the saveptr used by strtok_r
@@ -196,11 +197,8 @@ process_init_stack (char *cmd_saveptr, void **esp, char *file_name)
     *esp -= align_size;
     
     /* Push a null pointer sentinel inside argv. */
-    *esp -= sizeof (char *);
-    *(char *) *esp = 0;
-    
-    /* Push pointer to the process file name to the stack. */
-    char **argv;
+    char *null_sentinel = NULL;
+    push_var_to_stack (esp, null_sentinel); 
 
     /* Push pointers to process arguments from argument linked list */
     struct list_elem *e = list_begin (&arg_list);
@@ -209,21 +207,21 @@ process_init_stack (char *cmd_saveptr, void **esp, char *file_name)
       {
         struct arg_elem *arg_elem = list_entry (e, struct arg_elem, elem);
         
-        argv = push_to_stack (esp, &arg_elem->arg, sizeof (arg_elem->arg));
+        push_var_to_stack(esp, arg_elem->arg);
         
         e = list_next (e);
         free (arg_elem);
       }
 
     /* Push pointer to the start of argv array. */
-    push_to_stack (esp, &argv, sizeof(argv));
+    char **argv = *esp;
+    push_var_to_stack(esp, argv);
 
     /* Push the number of arguments to the stack. */
-    push_to_stack (esp, &arg_count, sizeof (arg_count));
+    push_var_to_stack(esp, arg_count);
 
     /* Push fake return address (null pointer). */
-    *esp -= sizeof (char *);
-    *(char *) *esp = 0;
+    push_var_to_stack (esp, null_sentinel); 
 
     return true;
  }