Explicitly Disallow heap allocation when wasm memory references are updated

src/runtime/runtime-wasm.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/assembler.h"
 #include "src/conversions.h"
 #include "src/debug/debug.h"
 #include "src/factory.h"
 #include "src/frames-inl.h"
 #include "src/objects-inl.h"
 #include "src/v8memory.h"
 #include "src/wasm/wasm-module.h"
 
 namespace v8 {
 namespace internal {
 
 RUNTIME_FUNCTION(Runtime_WasmGrowMemory) {
   HandleScope scope(isolate);
   DCHECK_EQ(1, args.length());
   uint32_t delta_pages = 0;
   RUNTIME_ASSERT(args[0]->ToUint32(&delta_pages));
 
   // Get the module JSObject
   const Address entry = Isolate::c_entry_fp(isolate->thread_local_top());
   Address pc =
       Memory::Address_at(entry + StandardFrameConstants::kCallerPCOffset);
   Code* code = isolate->inner_pointer_to_code_cache()->GetCacheEntry(pc)->code;

[ahaas, 2016/06/29 07:13:31]

Use also "the DisallowHeapAllocation no_allocation;" scope here for the lifetime
of code, deopt_data, and obj below. These are pointers into the heap, and we
have to make sure that they are valid as long as they exist, i.e. that the GC
does not move the targeted objects away. Since the scope should not be the whole
function, you can create a sub-scope with { and }.

[gdeepti, 2016/06/29 23:38:38]

Thanks for clarifying that, used "DisallowHeapAllocation no_allocation;" for the
lifetime of code, deopt_data, and changed obj to a handle. 

   FixedArray* deopt_data = code->deoptimization_data();
   DCHECK(deopt_data->length() == 2);
-  JSObject* module_object = JSObject::cast(deopt_data->get(0));
+  Handle<JSObject> module_object(JSObject::cast(deopt_data->get(0)));
   RUNTIME_ASSERT(!module_object->IsNull(isolate));
 
   Address old_mem_start, new_mem_start;
   uint32_t old_size, new_size;
   const int kWasmMemArrayBuffer = 2;
 
   // Get mem buffer associated with module object
   Object* obj = module_object->GetInternalField(kWasmMemArrayBuffer);
 
   if (obj->IsUndefined(isolate)) {
@@ skipping 56 matching lines @@
 
   RUNTIME_ASSERT(wasm::UpdateWasmModuleMemory(
       module_object, old_mem_start, new_mem_start, old_size, new_size));
 
   return *isolate->factory()->NewNumberFromUint(old_size /
                                                 wasm::WasmModule::kPageSize);
 }
 
 }  // namespace internal
 }  // namespace v8