[wasm] Wrap start function in a JS->WASM wrapper before calling it during initialization.

BUG=v8:5599
R=ahaas@chromium.org

Review-Url: https://codereview.chromium.org/2483193002
Cr-Commit-Position: refs/heads/master@{#40830}

src/wasm/wasm-module.cc

@@ -1233,12 +1233,18 @@ class WasmInstanceBuilder {
     //--------------------------------------------------------------------------
     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;
       Handle<Code> startup_code =
           code_table->GetValueChecked<Code>(isolate_, start_index);
       FunctionSig* sig = module_->functions[start_index].sig;
+      Handle<Code> wrapper_code = compiler::CompileJSToWasmWrapper(
+          isolate_, &module_env, startup_code, start_index);
       Handle<JSFunction> startup_fct = WrapExportCodeAsJSFunction(
-          isolate_, startup_code, factory->InternalizeUtf8String("start"), sig,
+          isolate_, wrapper_code, factory->InternalizeUtf8String("start"), sig,
           start_index, instance);
       RecordStats(isolate_, *startup_code);
       // Call the JS function.

test/mjsunit/wasm/start-function.js

@@ -62,14 +62,31 @@ assertThrows(() => {instantiate(kSig_i_v, [kExprI8Const, 0]);});
 })();
 
 
-(function testRun() {
-  print("testRun");
+(function testRun1() {
+  print("testRun1");
   var builder = new WasmModuleBuilder();
 
   builder.addMemory(12, 12, true);
 
   var func = builder.addFunction("", kSig_v_v)
-    .addBody([kExprI8Const, 0, kExprI8Const, 77, kExprI32StoreMem, 0, 0]);
+    .addBody([kExprI8Const, 0, kExprI8Const, 66, kExprI32StoreMem, 0, 0]);
+
+  builder.addStart(func.index);
+
+  var module = builder.instantiate();
+  var memory = module.exports.memory.buffer;
+  var view = new Int8Array(memory);
+  assertEquals(66, view[0]);
+})();
+
+(function testRun2() {
+  print("testRun2");
+  var builder = new WasmModuleBuilder();
+
+  builder.addMemory(12, 12, true);
+
+  var func = builder.addFunction("", kSig_v_v)
+    .addBody([kExprI8Const, 0, kExprI8Const, 22, kExprI8Const, 55, kExprI32Add, kExprI32StoreMem, 0, 0]);
 
   builder.addStart(func.index);