src/userprog/exception.c

@@ -157,30 +157,33 @@ page_fault (struct intr_frame *f)
   write = (f->error_code & PF_W) != 0;
   user = (f->error_code & PF_U) != 0;
 
-  if (!user || !not_present)
+  /* Select the appropriate stack pointer based on the context of the fault. */
+  void *esp = user ? f->esp : thread_current()->curr_esp;
+
+  /* If the fault address is in a user page that is not present, then it might
+   be just that the stack needs to grow or that it needs to be lazily loaded.
+   So we attempt to grow the stack. If this does not work, we check our SPT to
+   see if the page is expected to have data loaded in memory. */
+  void *upage = pg_round_down (fault_addr);
+  if (not_present && is_user_vaddr (upage) && upage != NULL)
+    {
+      if (is_valid_stack_access (fault_addr, esp))
+          if (grow_stack (upage))
+            return;
+
+      if (try_fetch_page (upage, write))
+        return;
+    }
+
+  /* If the page fault occurred in kernel mode,  then we intentionally indicate
+     a fault (for get_user() etc). */
+  if (!user)
   {
     f->eip = (void *)f->eax;
     f->eax = 0xffffffff;
     return;
   }
 
-  /* If the fault address is in a user page that is not present, then it might
-   be just that the stack needs to grow or that it needs to be lazily loaded.
-   So we attempt to grow the stack. If this does not work, we check our SPT to see if the page
-     is expected to have data loaded in memory. */
-  void *upage = pg_round_down (fault_addr);
-  if (not_present && is_user_vaddr (upage) && upage != NULL)
-    {
-      if (is_valid_stack_access (fault_addr, f->esp))
-        {
-          if (grow_stack (upage))
-            return;
-        }
-
-      if (try_fetch_page (upage, write))
-        return;
-    }
-
   /* To implement virtual memory, delete the rest of the function
      body, and replace it with code that brings in the page to
      which fault_addr refers. */