[wasm] WebAssembly.Memory object can be referenced by multiple Instance objects.

src/wasm/wasm-module.cc

 // Copyright 2015 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 <memory>
 
 #include "src/base/atomic-utils.h"
 #include "src/code-stubs.h"
 
 #include "src/macro-assembler.h"
@@ skipping 538 matching lines @@
       }
       if (changed) {
         Assembler::FlushICache(isolate, code->instruction_start(),
                                code->instruction_size());
       }
     }
   }
   compiled_module->reset_memory();
 }
 
+static void MemoryInstanceFinalizer(Isolate* isolate,
+                                    WasmInstanceObject* instance) {
+  // If the memory object is destroyed, nothing needs to be done here.

[ahaas, 2016/11/23 10:25:55]

Since you have a pointer to a heap object here (I guess instance is a heap
object?), could you open a {DisallowHeapAllocation no_gc;} scope for this
function?

[gdeepti, 2016/11/23 20:01:20]

Done.

+  if (!instance->has_memory_object()) return;
+  Handle<WasmInstanceWrapper> instance_wrapper =
+      handle(instance->get_instance_wrapper());
+  DCHECK(WasmInstanceWrapper::IsWasmInstanceWrapper(*instance_wrapper));
+  DCHECK(instance_wrapper->has_instance());
+  bool has_prev = instance_wrapper->has_previous();
+  bool has_next = instance_wrapper->has_next();
+  Handle<WasmMemoryObject> memory_object(instance->get_memory_object());
+
+  if (!has_prev && !has_next) {
+    memory_object->ResetInstancesLink(isolate);
+    return;
+  } else {
+    Handle<WasmInstanceWrapper> next_wrapper, prev_wrapper;
+    if (!has_prev) {
+      Handle<WasmInstanceWrapper> next_wrapper =
+          instance_wrapper->next_wrapper();
+      next_wrapper->reset_previous_wrapper();
+      // As this is the first link in the memory object, destroying
+      // without updating memory object would corrupt the instance chain in
+      // the memory object.
+      memory_object->set_instances_link(*next_wrapper);
+    } else if (!has_next) {
+      instance_wrapper->previous_wrapper()->reset_next_wrapper();
+    } else {
+      DCHECK(has_next && has_prev);
+      Handle<WasmInstanceWrapper> prev_wrapper =
+          instance_wrapper->previous_wrapper();
+      Handle<WasmInstanceWrapper> next_wrapper =
+          instance_wrapper->next_wrapper();
+      prev_wrapper->set_next_wrapper(*next_wrapper);
+      next_wrapper->set_previous_wrapper(*prev_wrapper);
+    }
+    // Reset to avoid dangling pointers
+    instance_wrapper->reset();
+  }
+}
+
 static void InstanceFinalizer(const v8::WeakCallbackInfo<void>& data) {
   JSObject** p = reinterpret_cast<JSObject**>(data.GetParameter());

[ahaas, 2016/11/23 10:25:55]

same here

[gdeepti, 2016/11/23 20:01:20]

Done.

   WasmInstanceObject* owner = reinterpret_cast<WasmInstanceObject*>(*p);
+  Isolate* isolate = reinterpret_cast<Isolate*>(data.GetIsolate());
+  // Is a link to shared memory instances exists, update the list of memory
+  // instances before the instance is destroyed.
+  if (owner->has_instance_wrapper()) MemoryInstanceFinalizer(isolate, owner);
   WasmCompiledModule* compiled_module = owner->get_compiled_module();
   TRACE("Finalizing %d {\n", compiled_module->instance_id());
-  Isolate* isolate = reinterpret_cast<Isolate*>(data.GetIsolate());
   DCHECK(compiled_module->has_weak_wasm_module());
   WeakCell* weak_wasm_module = compiled_module->ptr_to_weak_wasm_module();
 
   // weak_wasm_module may have been cleared, meaning the module object
   // was GC-ed. In that case, there won't be any new instances created,
   // and we don't need to maintain the links between instances.
   if (!weak_wasm_module->cleared()) {
     JSObject* wasm_module = JSObject::cast(weak_wasm_module->value());
     WasmCompiledModule* current_template =
         WasmCompiledModule::cast(wasm_module->GetInternalField(0));
@@ skipping 601 matching lines @@
               ? static_cast<Address>(
                     compiled_module_->memory()->backing_store())
               : nullptr;
       RelocateMemoryReferencesInCode(code_table, old_mem_start, mem_start,
                                      old_mem_size, mem_size);
       compiled_module_->set_memory(memory_);
     } else {
       LoadDataSegments(nullptr, 0);
     }
 
+    DCHECK(wasm::IsWasmInstance(*instance));
+    if (instance->has_memory_object()) {
+      instance->get_memory_object()->AddInstance(isolate_, instance);
+    }
+
     //--------------------------------------------------------------------------
     // Set up the runtime support for the new instance.
     //--------------------------------------------------------------------------
     Handle<WeakCell> weak_link = factory->NewWeakCell(instance);
 
     for (int i = num_imported_functions + FLAG_skip_compiling_wasm_funcs;
          i < code_table->length(); ++i) {
       Handle<Code> code = code_table->GetValueChecked<Code>(isolate_, i);
       if (code->kind() == Code::WASM_FUNCTION) {
         Handle<FixedArray> deopt_data = factory->NewFixedArray(2, TENURED);
@@ skipping 50 matching lines @@
           compiled_module_->set_weak_wasm_module(
               original.ToHandleChecked()->weak_wasm_module());
         }
         module_object_->SetInternalField(0, *compiled_module_);
         compiled_module_->set_weak_owning_instance(link_to_owning_instance);
         GlobalHandles::MakeWeak(global_handle.location(),
                                 global_handle.location(), &InstanceFinalizer,
                                 v8::WeakCallbackType::kFinalizer);
       }
     }
-
-    DCHECK(wasm::IsWasmInstance(*instance));
-    if (instance->has_memory_object()) {
-      instance->get_memory_object()->AddInstance(*instance);
-    }
-
     //--------------------------------------------------------------------------
     // Run the start function if one was specified.
     //--------------------------------------------------------------------------
     if (module_->start_function_index >= 0) {
       HandleScope scope(isolate_);
       ModuleEnv module_env;
       module_env.module = module_;
       module_env.instance = nullptr;
       module_env.origin = module_->origin;
       int start_index = module_->start_function_index;
@@ skipping 274 matching lines @@
           break;
         }
         case kExternalMemory: {
           Handle<Object> object = result.ToHandleChecked();
           if (!WasmJs::IsWasmMemoryObject(isolate_, object)) {
             ReportFFIError("memory import must be a WebAssembly.Memory object",
                            index, module_name, function_name);
             return -1;
           }
           auto memory = Handle<WasmMemoryObject>::cast(object);
+          DCHECK(WasmJs::IsWasmMemoryObject(isolate_, memory));
           instance->set_memory_object(*memory);
           memory_ = Handle<JSArrayBuffer>(memory->get_buffer(), isolate_);
           break;
         }
         case kExternalGlobal: {
           // Global imports are converted to numbers and written into the
           // {globals_} array buffer.
           Handle<Object> object = result.ToHandleChecked();
           MaybeHandle<Object> number = Object::ToNumber(object);
           if (number.is_null()) {
@@ skipping 161 matching lines @@
             // If there was no imported WebAssembly.Memory object, create one.
             Handle<JSArrayBuffer> buffer(instance->get_memory_buffer(),
                                          isolate_);
             memory_object = WasmMemoryObject::New(
                 isolate_, buffer,
                 (module_->max_mem_pages != 0) ? module_->max_mem_pages : -1);
             instance->set_memory_object(*memory_object);
           } else {
             memory_object = Handle<WasmMemoryObject>(
                 instance->get_memory_object(), isolate_);
+            DCHECK(WasmJs::IsWasmMemoryObject(isolate_, memory_object));
+            memory_object->ResetInstancesLink(isolate_);
           }
 
           desc.set_value(memory_object);
           break;
         }
         case kExternalGlobal: {
           // Export the value of the global variable as a number.
           WasmGlobal& global = module_->globals[exp.index];
           double num = 0;
           switch (global.type) {
@@ skipping 315 matching lines @@
   ModuleResult result = DecodeWasmModule(isolate, start, end, true, origin);
   if (result.val) {
     delete result.val;
   } else {
     DCHECK(!result.ok());
   }
   return result.ok();
 }
 
 MaybeHandle<JSArrayBuffer> wasm::GetInstanceMemory(
-    Isolate* isolate, Handle<WasmInstanceObject> instance) {
+    Isolate* isolate, Handle<WasmInstanceObject> object) {
+  auto instance = Handle<WasmInstanceObject>::cast(object);
   if (instance->has_memory_buffer()) {
     return Handle<JSArrayBuffer>(instance->get_memory_buffer(), isolate);
   }
   return MaybeHandle<JSArrayBuffer>();
 }
 
 void SetInstanceMemory(Handle<WasmInstanceObject> instance,
                        JSArrayBuffer* buffer) {
   DisallowHeapAllocation no_gc;
   instance->set_memory_buffer(buffer);
   instance->get_compiled_module()->set_ptr_to_memory(buffer);
 }
 
 int32_t wasm::GetInstanceMemorySize(Isolate* isolate,
                                     Handle<WasmInstanceObject> instance) {
+  DCHECK(IsWasmInstance(*instance));
   MaybeHandle<JSArrayBuffer> maybe_mem_buffer =
       GetInstanceMemory(isolate, instance);
   Handle<JSArrayBuffer> buffer;
   if (!maybe_mem_buffer.ToHandle(&buffer)) {
     return 0;
   } else {
     return buffer->byte_length()->Number() / WasmModule::kPageSize;
   }
 }
 
 uint32_t GetMaxInstanceMemorySize(Isolate* isolate,
                                   Handle<WasmInstanceObject> instance) {
   if (instance->has_memory_object()) {
     Handle<WasmMemoryObject> memory_object(instance->get_memory_object(),
                                            isolate);
 
     int maximum = memory_object->maximum_pages();
     if (maximum > 0) return static_cast<uint32_t>(maximum);
   }
   uint32_t compiled_max_pages =
       instance->get_compiled_module()->max_mem_pages();
   isolate->counters()->wasm_max_mem_pages_count()->AddSample(
       compiled_max_pages);
   if (compiled_max_pages != 0) return compiled_max_pages;
   return WasmModule::kV8MaxPages;
 }
 
-int32_t wasm::GrowInstanceMemory(Isolate* isolate,
-                                 Handle<WasmInstanceObject> instance,
-                                 uint32_t pages) {
-  if (pages == 0) return GetInstanceMemorySize(isolate, instance);
-  uint32_t max_pages = GetMaxInstanceMemorySize(isolate, instance);
-
+Handle<JSArrayBuffer> GrowMemoryBuffer(Isolate* isolate,
+                                       MaybeHandle<JSArrayBuffer> buffer,
+                                       uint32_t pages, uint32_t max_pages) {
+  Handle<JSArrayBuffer> old_buffer;
   Address old_mem_start = nullptr;
-  uint32_t old_size = 0, new_size = 0;
-
-  MaybeHandle<JSArrayBuffer> maybe_mem_buffer =
-      GetInstanceMemory(isolate, instance);
-  Handle<JSArrayBuffer> old_buffer;
-  if (!maybe_mem_buffer.ToHandle(&old_buffer) ||
-      old_buffer->backing_store() == nullptr) {
-    // If module object does not have linear memory associated with it,
-    // Allocate new array buffer of given size.
-    new_size = pages * WasmModule::kPageSize;
-    if (max_pages < pages) return -1;
-  } else {
+  uint32_t old_size = 0;
+  if (buffer.ToHandle(&old_buffer) && old_buffer->backing_store() != nullptr) {
     old_mem_start = static_cast<Address>(old_buffer->backing_store());
+    DCHECK_NOT_NULL(old_mem_start);
     old_size = old_buffer->byte_length()->Number();
-    // If the old memory was zero-sized, we should have been in the
-    // "undefined" case above.
-    DCHECK_NOT_NULL(old_mem_start);
-    DCHECK(old_size + pages * WasmModule::kPageSize <=
-           std::numeric_limits<uint32_t>::max());
-    new_size = old_size + pages * WasmModule::kPageSize;
+  }
+  DCHECK(old_size + pages * WasmModule::kPageSize <=
+         std::numeric_limits<uint32_t>::max());
+  uint32_t new_size = old_size + pages * WasmModule::kPageSize;
+  if (new_size <= old_size || max_pages * WasmModule::kPageSize < new_size ||
+      WasmModule::kV8MaxPages * WasmModule::kPageSize < new_size) {
+    return Handle<JSArrayBuffer>::null();
   }
 
-  if (new_size <= old_size || max_pages * WasmModule::kPageSize < new_size ||
-      WasmModule::kV8MaxPages * WasmModule::kPageSize < new_size) {
-    return -1;
-  }
-
-  Handle<JSArrayBuffer> buffer;
-
+  Handle<JSArrayBuffer> new_buffer;
   if (!old_buffer.is_null() && old_buffer->has_guard_region()) {
     // We don't move the backing store, we simply change the protection to make
     // more of it accessible.
     base::OS::Unprotect(old_buffer->backing_store(), new_size);
     reinterpret_cast<v8::Isolate*>(isolate)
         ->AdjustAmountOfExternalAllocatedMemory(pages * WasmModule::kPageSize);
     Handle<Object> new_size_object =
         isolate->factory()->NewNumberFromSize(new_size);
     old_buffer->set_byte_length(*new_size_object);
-
-    SetInstanceMemory(instance, *old_buffer);
-    Handle<FixedArray> code_table =
-        instance->get_compiled_module()->code_table();
-    RelocateMemoryReferencesInCode(code_table, old_mem_start, old_mem_start,
-                                   old_size, new_size);
-    buffer = old_buffer;
+    new_buffer = old_buffer;
   } else {
     const bool enable_guard_regions = false;
-    buffer = NewArrayBuffer(isolate, new_size, enable_guard_regions);
-    if (buffer.is_null()) return -1;
-    Address new_mem_start = static_cast<Address>(buffer->backing_store());
+    new_buffer = NewArrayBuffer(isolate, new_size, enable_guard_regions);
+    if (new_buffer.is_null()) return new_buffer;
+    Address new_mem_start = static_cast<Address>(new_buffer->backing_store());
     if (old_size != 0) {
       memcpy(new_mem_start, old_mem_start, old_size);
     }
-    SetInstanceMemory(instance, *buffer);
-    Handle<FixedArray> code_table =
-        instance->get_compiled_module()->code_table();
-    RelocateMemoryReferencesInCode(code_table, old_mem_start, new_mem_start,
-                                   old_size, new_size);
   }
+  return new_buffer;
+}
 
-  SetInstanceMemory(instance, *buffer);
-  if (instance->has_memory_object()) {
-    instance->get_memory_object()->set_buffer(*buffer);
+void UncheckedUpdateInstanceMemory(Isolate* isolate,
+                                   Handle<WasmInstanceObject> instance,
+                                   Address old_mem_start, uint32_t old_size) {
+  DCHECK(instance->has_memory_buffer());
+  Handle<JSArrayBuffer> new_buffer(instance->get_memory_buffer());
+  uint32_t new_size = new_buffer->byte_length()->Number();
+  DCHECK(new_size <= std::numeric_limits<uint32_t>::max());
+  Address new_mem_start = static_cast<Address>(new_buffer->backing_store());
+  DCHECK_NOT_NULL(new_mem_start);
+  Handle<FixedArray> code_table = instance->get_compiled_module()->code_table();
+  RelocateMemoryReferencesInCode(code_table, old_mem_start, new_mem_start,
+                                 old_size, new_size);
+}
+
+int32_t wasm::GrowWebAssemblyMemory(Isolate* isolate, Handle<Object> receiver,
+                                    uint32_t pages) {
+  DCHECK(WasmJs::IsWasmMemoryObject(isolate, receiver));
+  Handle<WasmMemoryObject> memory_object(WasmMemoryObject::cast(*receiver));

[ahaas, 2016/11/23 10:25:55]

Could you just say
Handle<WasmMemoryObject> memory_object =
Handle<WasmMemoryObject>::cast(receiver);?

[gdeepti, 2016/11/23 20:01:20]

Done.

+  Handle<WasmInstanceWrapper> instance_wrapper(
+      memory_object->get_instances_link());
+  DCHECK(WasmInstanceWrapper::IsWasmInstanceWrapper(*instance_wrapper));
+  DCHECK(instance_wrapper->has_instance());
+  Handle<WasmInstanceObject> instance = instance_wrapper->instance_object();
+  DCHECK(IsWasmInstance(*instance));
+  if (pages == 0) return GetInstanceMemorySize(isolate, instance);
+  uint32_t max_pages = GetMaxInstanceMemorySize(isolate, instance);
+
+  // Grow memory object buffer and update instances associated with it.
+  MaybeHandle<JSArrayBuffer> memory_buffer =
+      handle(memory_object->get_buffer());
+  Handle<JSArrayBuffer> old_buffer;
+  uint32_t old_size = 0;
+  Address old_mem_start = nullptr;
+  if (memory_buffer.ToHandle(&old_buffer) &&
+      old_buffer->backing_store() != nullptr) {
+    old_size = old_buffer->byte_length()->Number();
+    old_mem_start = static_cast<Address>(old_buffer->backing_store());
   }
-
+  Handle<JSArrayBuffer> new_buffer =
+      GrowMemoryBuffer(isolate, memory_buffer, pages, max_pages);
+  if (new_buffer.is_null()) return -1;
+  DCHECK(!instance_wrapper->has_previous());
+  SetInstanceMemory(instance, *new_buffer);
+  UncheckedUpdateInstanceMemory(isolate, instance, old_mem_start, old_size);
+  while (instance_wrapper->has_next()) {
+    instance_wrapper = instance_wrapper->next_wrapper();
+    DCHECK(WasmInstanceWrapper::IsWasmInstanceWrapper(*instance_wrapper));
+    Handle<WasmInstanceObject> instance = instance_wrapper->instance_object();
+    DCHECK(IsWasmInstance(*instance));
+    SetInstanceMemory(instance, *new_buffer);
+    UncheckedUpdateInstanceMemory(isolate, instance, old_mem_start, old_size);
+  }
+  memory_object->set_buffer(*new_buffer);
   DCHECK(old_size % WasmModule::kPageSize == 0);
   return (old_size / WasmModule::kPageSize);
 }
 
+int32_t wasm::GrowMemory(Isolate* isolate, Handle<WasmInstanceObject> instance,
+                         uint32_t pages) {
+  if (!IsWasmInstance(*instance)) return -1;
+  if (pages == 0) return GetInstanceMemorySize(isolate, instance);
+  Handle<WasmInstanceObject> instance_obj(WasmInstanceObject::cast(*instance));
+  if (!instance_obj->has_memory_object()) {
+    // No other instances to grow, grow just the one.
+    MaybeHandle<JSArrayBuffer> instance_buffer =
+        GetInstanceMemory(isolate, instance);
+    Handle<JSArrayBuffer> old_buffer;
+    uint32_t old_size = 0;
+    Address old_mem_start = nullptr;
+    if (instance_buffer.ToHandle(&old_buffer) &&
+        old_buffer->backing_store() != nullptr) {
+      old_size = old_buffer->byte_length()->Number();
+      old_mem_start = static_cast<Address>(old_buffer->backing_store());
+    }
+    uint32_t max_pages = GetMaxInstanceMemorySize(isolate, instance_obj);
+    Handle<JSArrayBuffer> buffer =
+        GrowMemoryBuffer(isolate, instance_buffer, pages, max_pages);
+    if (buffer.is_null()) return -1;
+    SetInstanceMemory(instance, *buffer);
+    UncheckedUpdateInstanceMemory(isolate, instance, old_mem_start, old_size);
+    DCHECK(old_size % WasmModule::kPageSize == 0);
+    return (old_size / WasmModule::kPageSize);
+  } else {
+    return GrowWebAssemblyMemory(
+        isolate, handle(instance_obj->get_memory_object()), pages);
+  }
+}
+
 void testing::ValidateInstancesChain(Isolate* isolate,
                                      Handle<WasmModuleObject> module_obj,
                                      int instance_count) {
   CHECK_GE(instance_count, 0);
   DisallowHeapAllocation no_gc;
   WasmCompiledModule* compiled_module = module_obj->get_compiled_module();
   CHECK_EQ(JSObject::cast(compiled_module->ptr_to_weak_wasm_module()->value()),
            *module_obj);
   Object* prev = nullptr;
   int found_instances = compiled_module->has_weak_owning_instance() ? 1 : 0;
@@ skipping 65 matching lines @@
 MaybeHandle<String> WasmCompiledModule::GetFunctionName(
     Handle<WasmCompiledModule> compiled_module, uint32_t func_index) {
   DCHECK_LT(func_index, compiled_module->module()->functions.size());
   WasmFunction& function = compiled_module->module()->functions[func_index];
   Isolate* isolate = compiled_module->GetIsolate();
   MaybeHandle<String> string = ExtractStringFromModuleBytes(
       isolate, compiled_module, function.name_offset, function.name_length);
   if (!string.is_null()) return string.ToHandleChecked();
   return {};
 }