1 files changed, 51 insertions, 29 deletions

diff --git a/userprog/exception.c b/userprog/exception.c
index 54621fa..debe7f0 100644
--- a/userprog/exception.c
+++ b/userprog/exception.c
@@ -2,6 +2,8 @@
 #include <inttypes.h>
 #include <stdio.h>
 #include "userprog/gdt.h"
+#include "userprog/process.h"
+#include "userprog/syscall.h"
 #include "threads/interrupt.h"
 #include "threads/thread.h"
 #include "threads/vaddr.h"
@@ -128,7 +130,8 @@ page_fault (struct intr_frame *f)
   bool write;        /* True: access was write, false: access was read. */
   bool user;         /* True: access by user, false: access by kernel. */
   void *fault_addr;  /* Fault address. */
-  struct page_table_entry *pte;
+  void *sp;          /* Stack pointer. */
+  struct page_table_entry *pte; /* Page table entry. */
 
   /* Obtain faulting address, the virtual address that was
      accessed to cause the fault.  It may point to code or to
@@ -151,38 +154,57 @@ page_fault (struct intr_frame *f)
   write = (f->error_code & PF_W) != 0;
   user = (f->error_code & PF_U) != 0;
 
-  /* To implement virtual memory, adapt the rest of the function
-     body, adding code that brings in the page to
-     which fault_addr refers. */
-  if (is_user_vaddr(fault_addr)) {
-    pte = page_table_fetch (&thread_current ()->page_table, pg_round_down (fault_addr));
-    if (pte != NULL)
-      page_load (pte);
-    else
+  /* accessing r/o page is always wrong */
+  if (!not_present)
+    thread_exit ();
+
+  if (is_user_vaddr (fault_addr))
     {
-      printf ("Page fault %p\n", pte);
-      kill (f);
-    }
+      /* if page fault occurs during syscall, use saved stack pointer */
+      sp = (!user) ? syscall_sp : f->esp;
+
+      /* try to fetch page entry */
+      pte = page_table_fetch (&thread_current ()->page_table,
+          pg_round_down (fault_addr));
+
+      /* we got a page entry so try to load the page */
+      if (pte != NULL)
+        {
+          if (page_load (pte))
+            return;
+          printf ("Unable to load page at %p in %s context.\n",
+            fault_addr, user ? "user" : "kernel");
+        }
+      /* there's no page in our page table but we might still have an valid
+         stack access and need to expand our stack. so just check for that.
+         the maxium offset we consider as a valid access is caused by the PUSHA
+         instruction. it's 32 bytes below the current stack pointer */
+      else if (fault_addr >= (sp - 32) && (PHYS_BASE - fault_addr) <= STACK_SIZE)
+        {
+          if (process_grow_stack (pg_round_down (fault_addr)))
+            return;
+          printf ("Unable to grow stack %p in %s context.\n",
+            fault_addr, user ? "user" : "kernel");
+        }
 
-    //TODO
-#if 0
-    if (! user) {
       /* syscall exception; set eax and eip */
-      f->eip = (void*)f->eax;
-      f->eax = 0xFFFFFFFF;
-      return;
-    } else {
+      if (!user)
+        {
+          f->eip = (void*)f->eax;
+          f->eax = 0xFFFFFFFF;
+          return;
+        }
+
       /* user process access violation */
-      thread_exit();
+      thread_exit ();
+      return;
     }
-#endif
-  } else {
-    printf ("Page fault at %p: %s error %s page in %s context.\n",
-            fault_addr,
-            not_present ? "not present" : "rights violation",
-            write ? "writing" : "reading",
-            user ? "user" : "kernel");
-    kill (f);
-  }
+
+  printf ("Page fault at %p: %s error %s page in %s context.\n",
+          fault_addr,
+          not_present ? "not present" : "rights violation",
+          write ? "writing" : "reading",
+          user ? "user" : "kernel");
+  kill (f);
 }