Merge stack growth functions

src/vm/stackgrowth.c

@@ -0,0 +1,50 @@
+#include <stdio.h>
+#include "stackgrowth.h"
+#include "threads/palloc.h"
+#include "threads/thread.h"
+#include "threads/vaddr.h"
+#include "userprog/pagedir.h"
+
+#define MAX_STACK_ACCESS_DIST 32
+
+static bool needs_new_page (const void *addr, const void *esp);
+static bool grow_stack (const void *addr);
+
+bool
+try_alloc_new_page (const void *ptr, const void *esp)
+{
+  return needs_new_page (ptr, esp) && grow_stack (ptr);
+}
+
+/* Validates a given address for being a stack query and not a generic erroneous
+   address
+ */
+static bool
+needs_new_page (const void *addr, const void *esp)
+{
+    return (is_user_vaddr (addr) &&
+            (uint32_t*)addr >= ((uint32_t*)esp - MAX_STACK_ACCESS_DIST) &&
+            ((PHYS_BASE - pg_round_down (addr))
+                          <= MAX_STACK_SIZE));
+}
+
+/* Extends the stack by the necessary number of pages */
+static bool
+grow_stack (const 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 +1,10 @@
+#ifndef VM_GROWSTACK_H
+#define VM_GROWSTACK_H
+
+#include <stdio.h>
+
+#define MAX_STACK_SIZE 8388608 // (8MB)
+
+bool try_alloc_new_page (const void *ptr, const void *esp);
+
+#endif /* vm/frame.h */