Update stack initialization to handle overflow by allocating a second page for argument pointers

src/userprog/process.c

@@ -88,6 +88,8 @@ process_execute (const char *cmd)
   return tid;
 }
 
+
+static bool install_page (void *upage, void *kpage, bool writable);
 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)))
@@ -186,10 +188,13 @@ process_init_stack (char *cmd_saveptr, void **esp, char *file_name)
                             + return_addr_size;
 
     /* If pushing the rest of the data required for the stack would cause
-       overflow, allocate an extra page. */ 
+       overflow, allocate an extra page that is contiguous within the
+       virtual address space (below the current address range). */ 
     if (PHYS_BASE - *esp + remaining_size > PGSIZE)
       {
-        /* TODO: Allocate an extra page for the rest of the process stack. */
+        uint8_t *kpage = palloc_get_page (PAL_USER | PAL_ZERO);
+        if (!install_page (((uint8_t *) PHYS_BASE) - PGSIZE * 2, kpage, true))
+          return false;
       }
 
     /* Align stack pointer to word size before pushing argv elements for
@@ -485,8 +490,6 @@ load (const char *file_name, void (**eip) (void), void **esp)
 
 /* load() helpers. */
 
-static bool install_page (void *upage, void *kpage, bool writable);
-
 /* Checks whether PHDR describes a valid, loadable segment in
    FILE and returns true if so, false otherwise. */
 static bool