[vm, ffi] Emit the FFI callback stub as a raw blob and place it in the Fuchsia package.

Any blob in the package can be loaded as an executable VMO.

TEST=child CL
Bug: https://dartbug.com/52579
Change-Id: I61f7a84453da4da4733c5a70d4d19f0a6652581b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/496661
Commit-Queue: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Alexander Aprelev <aam@google.com>

runtime/bin/BUILD.gn

@@ -650,6 +650,20 @@ gen_snapshot_action("generate_snapshot_bin") {
   ]
 }
 
+gen_snapshot_action("ffi_callback_stub_bin") {
+  deps = [ "../vm:vm_platform_stripped" ]
+  platform_dill = "$root_out_dir/vm_platform_stripped.dill"
+  inputs = [ platform_dill ]
+  outputs = [ "$target_gen_dir/ffi_callback_stub.bin" ]
+  args = [
+    "--deterministic",
+    "--snapshot_kind=ffi-callback-stub",
+    "--ffi_callback_stub=" +
+        rebase_path("$target_gen_dir/ffi_callback_stub.bin", root_build_dir),
+    rebase_path(platform_dill, root_build_dir),
+  ]
+}
+
 # Generates an assembly file defining a given symbol with the bytes from a
 # binary file. Places the symbol in a text section if 'executable' is true,
 # otherwise places the symbol in a read-only data section.

runtime/bin/dart_api_win.c

@@ -459,6 +459,8 @@ typedef Dart_Handle (*Dart_CreateAppAOTSnapshotAndRelocatableObjectType)(
 typedef Dart_Handle (*Dart_CreateVMAOTSnapshotAsAssemblyType)(
     Dart_StreamingWriteCallback,
     void*);
+typedef Dart_Handle (*Dart_WriteCallbackStubType)(Dart_StreamingWriteCallback,
+                                                  void*);
 typedef Dart_Handle (*Dart_SortClassesType)();
 typedef Dart_Handle (*Dart_CreateAppJITSnapshotAsBlobsType)(uint8_t**,
                                                             intptr_t*,
@@ -772,6 +774,7 @@ static Dart_CreateAppAOTSnapshotAndRelocatableObjectType
     Dart_CreateAppAOTSnapshotAndRelocatableObjectFn = NULL;
 static Dart_CreateVMAOTSnapshotAsAssemblyType
     Dart_CreateVMAOTSnapshotAsAssemblyFn = NULL;
+static Dart_WriteCallbackStubType Dart_WriteCallbackStubFn = NULL;
 static Dart_SortClassesType Dart_SortClassesFn = NULL;
 static Dart_CreateAppJITSnapshotAsBlobsType Dart_CreateAppJITSnapshotAsBlobsFn =
     NULL;
@@ -1368,6 +1371,8 @@ BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved) {
     Dart_CreateVMAOTSnapshotAsAssemblyFn =
         (Dart_CreateVMAOTSnapshotAsAssemblyType)GetProcAddress(
             process, "Dart_CreateVMAOTSnapshotAsAssembly");
+    Dart_WriteCallbackStubFn = (Dart_WriteCallbackStubType)GetProcAddress(
+        process, "Dart_WriteCallbackStub");
     Dart_SortClassesFn =
         (Dart_SortClassesType)GetProcAddress(process, "Dart_SortClasses");
     Dart_CreateAppJITSnapshotAsBlobsFn =
@@ -2701,6 +2706,11 @@ Dart_Handle Dart_CreateVMAOTSnapshotAsAssembly(
   return Dart_CreateVMAOTSnapshotAsAssemblyFn(callback, callback_data);
 }
 
+Dart_Handle Dart_WriteCallbackStub(Dart_StreamingWriteCallback callback,
+                                   void* callback_data) {
+  return Dart_WriteCallbackStubFn(callback, callback_data);
+}
+
 Dart_Handle Dart_SortClasses() {
   return Dart_SortClassesFn();
 }

runtime/bin/gen_snapshot.cc

@@ -80,6 +80,7 @@ enum SnapshotKind {
   kAppAOTElf,
   kAppAOTMachODylib,
   kVMAOTAssembly,
+  kFfiCallbackStub,
 };
 static SnapshotKind snapshot_kind = kCore;
 
@@ -93,6 +94,7 @@ static const char* const kSnapshotKindNames[] = {
     "app-aot-elf",
     "app-aot-macho-dylib",
     "vm-aot-assembly",
+    "ffi-callback-stub",
     nullptr,
     // clang-format on
 };
@@ -114,7 +116,8 @@ static const char* const kSnapshotKindNames[] = {
   V(macho_object, macho_object_filename)                                       \
   V(loading_unit_manifest, loading_unit_manifest_filename)                     \
   V(save_debugging_info, debugging_info_filename)                              \
-  V(save_obfuscation_map, obfuscation_map_filename)
+  V(save_obfuscation_map, obfuscation_map_filename)                            \
+  V(ffi_callback_stub, ffi_callback_stub_filename)
 
 #define BOOL_OPTIONS_LIST(V)                                                   \
   V(compile_all, compile_all)                                                  \
@@ -142,7 +145,8 @@ DEFINE_CB_OPTION(ProcessEnvironmentOption);
 static bool IsSnapshottingForPrecompilation() {
   return (snapshot_kind == kAppAOTAssembly) || (snapshot_kind == kAppAOTElf) ||
          (snapshot_kind == kAppAOTMachODylib) ||
-         (snapshot_kind == kVMAOTAssembly);
+         (snapshot_kind == kVMAOTAssembly) ||
+         (snapshot_kind == kFfiCallbackStub);
 }
 
 // clang-format off
@@ -308,6 +312,14 @@ static int ParseArguments(int argc,
 #endif
       break;
     }
+    case kFfiCallbackStub:
+      if (ffi_callback_stub_filename == nullptr) {
+        Syslog::PrintErr(
+            "Building the FFI callback stub blob requires specifying "
+            "an output file for --ffi_callback_stub.\n\n");
+        return -1;
+      }
+      break;
   }
 
   if (!obfuscate && obfuscation_map_filename != nullptr) {
@@ -637,6 +649,13 @@ static void CreateAndWritePrecompiledSnapshot() {
     CHECK_RESULT(result);
     return;
   }
+  if (snapshot_kind == kFfiCallbackStub) {
+    File* file = OpenFile(ffi_callback_stub_filename);
+    RefCntReleaseScope<File> rs(file);
+    Dart_Handle result = Dart_WriteCallbackStub(StreamingWriteCallback, file);
+    CHECK_RESULT(result);
+    return;
+  }
 
   Dart_AotBinaryFormat format;
   const char* kind_str = nullptr;
@@ -834,6 +853,7 @@ static int CreateIsolateAndSnapshot(const CommandLineOptions& inputs) {
     case kAppAOTElf:
     case kAppAOTMachODylib:
     case kVMAOTAssembly:
+    case kFfiCallbackStub:
       CreateAndWritePrecompiledSnapshot();
       break;
     default: