[wasm] Disable trap handlers within the same NativeModule

The current implementation allocates a new {NativeModule} if trap
handlers are disabled. Afterwards, all export wrappers need to be
patched to call to the code objects in this new native module (this
patching is done in {CodeSpecialization}).
With the jump table, we want to get rid of this patching, hence we need
to reuse the same jump table, hence we cannot allocate a new
{NativeModule}. Instead, we should update the existing one with the new
code.

R=mstarzinger@chromium.org
CC=eholk@chromium.org

Bug: v8:7143, v8:7758
Change-Id: If2f395d462752b9084ed1e5f0a81f71d400ccfca
Reviewed-on: https://chromium-review.googlesource.com/1095262
Reviewed-by: Eric Holk <eholk@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53645}

src/wasm/module-compiler.cc

@@ -1635,29 +1635,18 @@ MaybeHandle<WasmInstanceObject> InstanceBuilder::Build() {
       TRACE("Recompiling module without bounds checks\n");
       constexpr bool allow_trap_handler = false;
       ModuleEnv env = CreateDefaultModuleEnv(module_, allow_trap_handler);
-      Handle<WasmCompiledModule> compiled_module(
+      // Disable trap handlers on this native module.
-          module_object_->compiled_module(), isolate_);
+      NativeModule* native_module =
-      // Create a new native module...
+          module_object_->compiled_module()->GetNativeModule();
-      auto native_module =
+      native_module->DisableTrapHandler();
-          isolate_->wasm_engine()->code_manager()->NewNativeModule(*module_,
-                                                                   env);
-      Handle<Foreign> native_module_wrapper =
-          Managed<wasm::NativeModule>::FromUniquePtr(
-              isolate_,
-              0,  // TODO(eholk): estimate size
-              std::move(native_module));
-      compiled_module->set_native_module(*native_module_wrapper);
-      compiled_module->GetNativeModule()->SetRuntimeStubs(isolate_);
 
-      // ...and then compile it.
+      // Recompile all functions in this native module.
       ErrorThrower thrower(isolate_, "recompile");
       CompileNativeModule(isolate_, &thrower, module_object_, module_, &env);
       if (thrower.error()) {
         return {};
       }
-      DCHECK(!module_object_->compiled_module()
+      DCHECK(!native_module->use_trap_handler());
-                  ->GetNativeModule()
-                  ->use_trap_handler());
     }
   }
 

src/wasm/wasm-code-manager.cc

@@ -801,6 +801,20 @@ void NativeModule::ReleaseProtectedInstructions() {
   }
 }
 
+void NativeModule::DisableTrapHandler() {
+  // Switch {use_trap_handler_} from true to false.
+  DCHECK(use_trap_handler_);
+  use_trap_handler_ = false;
+
+  // Clear the code table (just to increase the chances to hit an error if we
+  // forget to re-add all code).
+  uint32_t num_wasm_functions = num_functions_ - num_imported_functions_;
+  memset(code_table_.get(), 0, num_wasm_functions * sizeof(WasmCode*));
+
+  // TODO(clemensh): Actually free the owned code, such that the memory can be
+  // recycled.
+}
+
 NativeModule::~NativeModule() {
   TRACE_HEAP("Deleting native module: %p\n", reinterpret_cast<void*>(this));
   // Clear the handle at the beginning of destructor to make it robust against

src/wasm/wasm-code-manager.h

@@ -291,6 +291,14 @@ class V8_EXPORT_PRIVATE NativeModule final {
   void UnpackAndRegisterProtectedInstructions();
   void ReleaseProtectedInstructions();
 
+  // Transition this module from code relying on trap handlers (i.e. without
+  // explicit memory bounds checks) to code that does not require trap handlers
+  // (i.e. code with explicit bounds checks).
+  // This method must only be called if {use_trap_handler()} is true (it will be
+  // false afterwards). All code in this {NativeModule} needs to be re-added
+  // after calling this method.
+  void DisableTrapHandler();
+
   // Returns the instruction start of code suitable for indirect or import calls
   // for the given function index. If the code at the given index is the lazy
   // compile stub, it will clone a non-anonymous lazy compile stub for the
@@ -395,7 +403,7 @@ class V8_EXPORT_PRIVATE NativeModule final {
   size_t committed_code_space_ = 0;
   int modification_scope_depth_ = 0;
   bool can_request_more_memory_;
-  bool use_trap_handler_;
+  bool use_trap_handler_ = false;
   bool is_executable_ = false;
   bool lazy_compile_frozen_ = false;