[WIP] TrapHandler 2014/11/27.

src/runtime/runtime-typedarray.cc

Index: src/runtime/runtime-typedarray.cc
diff --git a/src/runtime/runtime-typedarray.cc b/src/runtime/runtime-typedarray.cc
index cd2c0eb9fa1a3b5ca90b85b0c949b7f383c92b25..fd271fa405680040f53d08531be659448486730e 100644
--- a/src/runtime/runtime-typedarray.cc
+++ b/src/runtime/runtime-typedarray.cc
@@ -12,17 +12,34 @@
 namespace v8 {
 namespace internal {
 
+namespace {
+
+size_t MaybeUnguardArrayBuffer(Isolate* isolate, JSArrayBuffer* array_buffer) {
+  size_t allocated_length = NumberToSize(isolate, array_buffer->byte_length());
+  if (!array_buffer->is_guarded()) return allocated_length;
+  array_buffer->set_is_guarded(false);
+  size_t const page_size = base::OS::CommitPageSize();
+  CHECK(allocated_length % page_size == 0);
+  CHECK((bit_cast<uintptr_t>(array_buffer->backing_store()) % page_size) == 0);
+  isolate->RemoveGuardArea(
+      bit_cast<uint8_t*>(array_buffer->backing_store()) + allocated_length,
+      page_size);
+  return allocated_length += page_size;
+}
+
+}  // namespace
+
+
 void Runtime::FreeArrayBuffer(Isolate* isolate,
                               JSArrayBuffer* phantom_array_buffer) {
+  size_t const allocated_length =
+      MaybeUnguardArrayBuffer(isolate, phantom_array_buffer);
   if (phantom_array_buffer->should_be_freed()) {
     DCHECK(phantom_array_buffer->is_external());
     free(phantom_array_buffer->backing_store());
   }
   if (phantom_array_buffer->is_external()) return;
 
-  size_t allocated_length =
-      NumberToSize(isolate, phantom_array_buffer->byte_length());
-
   reinterpret_cast<v8::Isolate*>(isolate)
       ->AdjustAmountOfExternalAllocatedMemory(
           -static_cast<int64_t>(allocated_length));
@@ -34,7 +51,7 @@ void Runtime::FreeArrayBuffer(Isolate* isolate,
 
 void Runtime::SetupArrayBuffer(Isolate* isolate,
                                Handle<JSArrayBuffer> array_buffer,
-                               bool is_external, void* data,
+                               bool is_external, bool is_guarded, void* data,
                                size_t allocated_length) {
   DCHECK(array_buffer->GetInternalFieldCount() ==
          v8::ArrayBuffer::kInternalFieldCount);
@@ -45,6 +62,7 @@ void Runtime::SetupArrayBuffer(Isolate* isolate,
   array_buffer->set_flag(Smi::FromInt(0));
   array_buffer->set_is_external(is_external);
   array_buffer->set_is_neuterable(true);
+  array_buffer->set_is_guarded(is_guarded);
 
   Handle<Object> byte_length =
       isolate->factory()->NewNumberFromSize(allocated_length);
@@ -62,20 +80,27 @@ bool Runtime::SetupArrayBufferAllocatingData(Isolate* isolate,
                                              size_t allocated_length,
                                              bool initialize) {
   void* data;
+  bool is_guarded = false;
   CHECK(V8::ArrayBufferAllocator() != NULL);
   if (allocated_length != 0) {
-    if (initialize) {
-      data = V8::ArrayBufferAllocator()->Allocate(allocated_length);
+    const size_t page_size = base::OS::CommitPageSize();
+    if (allocated_length % page_size == 0) {
+      data = V8::ArrayBufferAllocator()->Allocate(allocated_length + page_size,
+                                                  page_size);
+      if (data == NULL) return false;
+      isolate->AddGuardArea(bit_cast<uint8_t*>(data) + allocated_length,
+                            page_size);
+      is_guarded = true;
     } else {
-      data =
-          V8::ArrayBufferAllocator()->AllocateUninitialized(allocated_length);
+      data = V8::ArrayBufferAllocator()->Allocate(allocated_length);
     }
     if (data == NULL) return false;
   } else {
     data = NULL;
   }
 
-  SetupArrayBuffer(isolate, array_buffer, false, data, allocated_length);
+  SetupArrayBuffer(isolate, array_buffer, false, is_guarded, data,
+                   allocated_length);
 
   reinterpret_cast<v8::Isolate*>(isolate)
       ->AdjustAmountOfExternalAllocatedMemory(allocated_length);
@@ -176,10 +201,11 @@ RUNTIME_FUNCTION(Runtime_ArrayBufferNeuter) {
   }
   DCHECK(!array_buffer->is_external());
   void* backing_store = array_buffer->backing_store();
-  size_t byte_length = NumberToSize(isolate, array_buffer->byte_length());
+  size_t const allocated_length =
+      MaybeUnguardArrayBuffer(isolate, *array_buffer);
   array_buffer->set_is_external(true);
   Runtime::NeuterArrayBuffer(array_buffer);
-  V8::ArrayBufferAllocator()->Free(backing_store, byte_length);
+  V8::ArrayBufferAllocator()->Free(backing_store, allocated_length);
   return isolate->heap()->undefined_value();
 }