VM: Support bootstrapping core libraries from Kernel binaries instead of source.

runtime/bin/main.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
 
 #include "include/dart_api.h"
 #include "include/dart_tools_api.h"
@@ skipping 781 matching lines @@
 #else
   // Always create the service isolate in DEBUG and RELEASE modes for profiling,
   // even if we don't need it for loading.
   const bool run_service_isolate = true;
 #endif  // PRODUCT
   if (!run_service_isolate &&
       (strcmp(script_uri, DART_VM_SERVICE_ISOLATE_NAME) == 0)) {
     return NULL;
   }
 
+  // If the script is a Kernel binary, then we will try to bootstrap from the
+  // script.
+  const uint8_t* kernel_file = NULL;
+  intptr_t kernel_length = -1;
+  const bool is_kernel =
+      !run_app_snapshot &&
+      TryReadKernel(script_uri, &kernel_file, &kernel_length);
+
   IsolateData* isolate_data =
       new IsolateData(script_uri, package_root, packages_config);
-  Dart_Isolate isolate = Dart_CreateIsolate(
-      script_uri, main, isolate_snapshot_buffer, flags, isolate_data, error);
+  Dart_Isolate isolate =
+      is_kernel ? Dart_CreateIsolateFromKernel(script_uri, main, kernel_file,
+                                               kernel_length, flags,
+                                               isolate_data, error)
+                : Dart_CreateIsolate(script_uri, main, isolate_snapshot_buffer,
+                                     flags, isolate_data, error);
+  if (is_kernel) {
+    free(const_cast<uint8_t*>(kernel_file));
+  }
+
   if (isolate == NULL) {
     delete isolate_data;
     return NULL;
   }
 
   Dart_EnterScope();
 
-  if (isolate_snapshot_buffer != NULL) {
+  // Set up the library tag handler for this isolate.
+  Dart_Handle result = Dart_SetLibraryTagHandler(Loader::LibraryTagHandler);
+  CHECK_RESULT(result);
+
+  if (is_kernel) {
+    // TODO(27590): We should not read the kernel file again!
+    if (!TryReadKernel(script_uri, &kernel_file, &kernel_length)) {
+      FATAL("Failed to read kernel second time");
+    }
+    Dart_Handle result = Dart_LoadKernel(kernel_file, kernel_length);

[siva, 2016/11/16 05:49:34]

The TODO says do not read the kernel file again, does that also include
not having to do a Dat_LoadKernel here, i.e. I am wondering if the
isolate can be created with the kernel file similar to how we create
an isolate from an application snapshot.

[Vyacheslav Egorov (Google), 2016/11/16 12:47:46]

There is a difference between snapshots we have and Kernel in a sense that
Kernel is simultaneously application snapshot *and* isolate snapshot. That's why
it ends up loaded twice. 

We will fix it after landing.  

+    free(const_cast<uint8_t*>(kernel_file));
+    CHECK_RESULT(result);
+  }
+  if (is_kernel || (isolate_snapshot_buffer != NULL)) {
     // Setup the native resolver as the snapshot does not carry it.
     Builtin::SetNativeResolver(Builtin::kBuiltinLibrary);
     Builtin::SetNativeResolver(Builtin::kIOLibrary);
   }
   if (run_app_snapshot) {
     Dart_Handle result = Loader::ReloadNativeExtensions();
     CHECK_RESULT(result);
   }
 
-  // Set up the library tag handler for this isolate.
-  Dart_Handle result = Dart_SetLibraryTagHandler(Loader::LibraryTagHandler);
-  CHECK_RESULT(result);
-
   if (Dart_IsServiceIsolate(isolate)) {
     // If this is the service isolate, load embedder specific bits and return.
     bool skip_library_load = run_app_snapshot;
     if (!VmService::Setup(vm_service_server_ip, vm_service_server_port,
                           skip_library_load, vm_service_dev_mode)) {
       *error = strdup(VmService::GetErrorMessage());
       return NULL;
     }
     if (compile_all) {
       result = Dart_CompileAll();
@@ skipping 28 matching lines @@
 
   if (run_app_snapshot) {
     result = DartUtils::SetupIOLibrary(script_uri);
     CHECK_RESULT(result);
     Loader::InitForSnapshot(script_uri);
   } else {
     // Load the specified application script into the newly created isolate.
     Dart_Handle uri =
         DartUtils::ResolveScript(Dart_NewStringFromCString(script_uri));
     CHECK_RESULT(uri);
-    result = Loader::LibraryTagHandler(Dart_kScriptTag, Dart_Null(), uri);
-    CHECK_RESULT(result);
+    if (!is_kernel) {
+      result = Loader::LibraryTagHandler(Dart_kScriptTag, Dart_Null(), uri);
+      CHECK_RESULT(result);
+    }
 
     Dart_TimelineEvent("LoadScript", Dart_TimelineGetMicros(),
                        Dart_GetMainPortId(), Dart_Timeline_Event_Async_End, 0,
                        NULL, NULL);
 
     result = DartUtils::SetupIOLibrary(script_uri);
     CHECK_RESULT(result);
   }
 
   // Make the isolate runnable so that it is ready to handle messages.
@@ skipping 1031 matching lines @@
   Platform::Exit(Process::GlobalExitCode());
 }
 
 }  // namespace bin
 }  // namespace dart
 
 int main(int argc, char** argv) {
   dart::bin::main(argc, argv);
   UNREACHABLE();
 }