src/Makefile.build

@@ -63,6 +63,7 @@ userprog_SRC += userprog/tss.c		# TSS management.
 
 # Virtual memory code.
 vm_SRC += devices/swap.c		# Swap block manager.
+vm_SRC += vm/stackgrowth.c
 #vm_SRC = vm/file.c			# Some other file.
 
 # Filesystem code.

src/userprog/exception.c

@@ -4,6 +4,7 @@
 #include "userprog/gdt.h"
 #include "threads/interrupt.h"
 #include "threads/thread.h"
+#include "vm/stackgrowth.h"
 
 /* Number of page faults processed. */
 static long long page_fault_cnt;
@@ -145,6 +146,12 @@ page_fault (struct intr_frame *f)
   write = (f->error_code & PF_W) != 0;
   user = (f->error_code & PF_U) != 0;
 
+   if (user && needs_new_page (fault_addr, f->esp))
+     {
+       if (grow_stack (fault_addr))
+        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. */

src/vm/stackgrowth.c

@@ -0,0 +1,38 @@
+#include <stdio.h>
+#include "stackgrowth.h"
+#include "threads/palloc.h"
+#include "threads/thread.h"
+#include "threads/vaddr.h"
+#include "userprog/pagedir.h"
+
+/* Validates a given address for being <=32 bytes away from the stack pointer or
+   above the stack */
+bool needs_new_page (void *addr, void *esp)
+{
+    return (is_user_vaddr (addr) &&
+            (uint32_t*)addr >= ((uint32_t*)esp - 32) &&
+                    ((PHYS_BASE - pg_round_down (addr))
+                                  <= MAX_STACK_SIZE));
+}
+
+/* Extends the stack by the necessary number of pages */
+bool grow_stack (void *addr)
+{
+  struct thread *t = thread_current ();
+  void *last_page = pg_round_down (addr);
+
+  uint8_t *new_page = palloc_get_page (PAL_USER | PAL_ZERO);
+  if ( new_page == NULL)
+    return false;
+
+  bool added_page = pagedir_get_page (t->pagedir, last_page) == NULL
+                    && pagedir_set_page (t->pagedir, last_page, new_page, true);
+
+  if (!added_page) {
+    palloc_free_page (new_page);
+    return false;
+  }
+  return true;
+
+
+}

src/vm/stackgrowth.h

@@ -0,0 +1,11 @@
+#ifndef GROWSTACK_H
+#define GROWSTACK_H
+
+#include <stdio.h>
+
+#define MAX_STACK_SIZE 8388608 // (8MB)
+
+bool needs_new_page (void *addr, void *esp);
+bool grow_stack (void *addr);
+
+#endif //GROWSTACK_H