Add guard pages in front of platform allocations

src/spaces.cc

Index: src/spaces.cc
===================================================================
--- src/spaces.cc	(revision 8619)
+++ src/spaces.cc	(working copy)
@@ -380,7 +380,14 @@
     if (isolate_->code_range()->exists()) {
       mem = isolate_->code_range()->AllocateRawMemory(requested, allocated);
     } else {
+#ifdef ENABLE_HEAP_PROTECTION
+      mem = OS::Allocate(requested + Page::kPageSize, allocated, true);
+      OS::Guard(mem, Page::kPageSize);
+      *allocated -= Page::kPageSize;
+      mem = static_cast<char*>(mem) + Page::kPageSize;
+#else  // ENABLE_HEAP_PROTECTION
       mem = OS::Allocate(requested, allocated, true);
+#endif  // ENABLE_HEAP_PROTECTION
     }
     // Update executable memory size.
     size_executable_ += static_cast<int>(*allocated);
@@ -407,7 +414,12 @@
   if (isolate_->code_range()->contains(static_cast<Address>(mem))) {
     isolate_->code_range()->FreeRawMemory(mem, length);
   } else {
-    OS::Free(mem, length);
+#ifdef ENABLE_HEAP_PROTECTION
+    size_t guardsize = (executable == EXECUTABLE) ? Page::kPageSize : 0;
+    OS::Free(static_cast<char*>(mem) - guardsize, length + guardsize);
+#else  // ENABLE_HEAP_PROTECTION
+    OS::Free(static_cast<char*>(mem), length);
+#endif  // ENABLE_HEAP_PROTECTION
   }
   isolate_->counters()->memory_allocated()->Decrement(static_cast<int>(length));
   size_ -= static_cast<int>(length);