[vm/ffi] Fix FfiTrampolineData GC bug

This lets the GC visit FfiTrampolineData::c_signature again.

https://dart-review.googlesource.com/c/sdk/+/272201 stopped adding
FfiTrampolineData::c_signature to snapshots. However, instead of
skipping it manually in app_shapshot.cc, we skipped it in
raw_object.h, which also caused the GC to skip it.
This CL adds it back in as we need it in JIT snapshots. This way we
keep it consistent between AOT/JIT snapshots.

TEST=tests/ffi/regress_b_261224444_test.dart

The c signatures of FFI trampolines were not properly traced in the
precompiler, causing us to hit an assert when the classes mentioned in
those types where only referenced from a signature and not retained
for any other reason.

TEST=tests/ffi/native_assets/process_test.dart (dartkp)

Closes: #50678
Bug: b/261224444
Change-Id: I84fc880744c2045ea3e2ef4f37df454b80b2faeb
Cq-Include-Trybots: luci.dart.try:vm-precomp-ffi-qemu-linux-release-arm-try,vm-ffi-android-debug-arm-try,vm-ffi-android-debug-arm64c-try,vm-kernel-reload-rollback-linux-debug-x64-try,vm-kernel-reload-linux-debug-x64-try,app-kernel-linux-debug-x64-try,vm-kernel-precomp-linux-debug-x64c-try,vm-kernel-precomp-linux-debug-x64-try,vm-kernel-nnbd-linux-debug-x64-try,vm-kernel-linux-debug-x64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/274387
Reviewed-by: Martin Kustermann <[email protected]>
Auto-Submit: Daco Harkes <[email protected]>
Commit-Queue: Daco Harkes <[email protected]>

Author: dcharkes

runtime/lib/object.cc

@@ -330,7 +330,8 @@ DEFINE_NATIVE_ENTRY(Internal_nativeEffect, 0, 1) {
 }
 
 DEFINE_NATIVE_ENTRY(Internal_collectAllGarbage, 0, 0) {
-  isolate->group()->heap()->CollectAllGarbage(GCReason::kDebugging);
+  isolate->group()->heap()->CollectAllGarbage(GCReason::kDebugging,
+                                              /*compact=*/true);
   return Object::null();
 }
 

runtime/vm/compiler/aot/precompiler.cc

@@ -1043,6 +1043,7 @@ void Precompiler::AddCalleesOfHelper(const Object& entry,
         if (!callback_target.IsNull()) {
           AddFunction(callback_target, RetainReasons::kFfiCallbackTarget);
         }
+        AddTypesOf(target);
       }
       break;
     }
@@ -1109,6 +1110,10 @@ void Precompiler::AddTypesOf(const Function& function) {
   const Class& owner = Class::Handle(Z, function.Owner());
   AddTypesOf(owner);
 
+  if (function.IsFfiTrampoline()) {
+    AddType(FunctionType::Handle(Z, function.FfiCSignature()));
+  }
+
   const auto& parent_function = Function::Handle(Z, function.parent_function());
   if (parent_function.IsNull()) {
     return;

runtime/vm/raw_object.h

@@ -1404,13 +1404,11 @@ class UntaggedFfiTrampolineData : public UntaggedObject {
  private:
   RAW_HEAP_OBJECT_IMPLEMENTATION(FfiTrampolineData);
 
-  // Not traced. We don't need this info after precompilation, and FFI
-  // trampolines are not supported in JIT snapshots.
-  COMPRESSED_POINTER_FIELD(FunctionTypePtr, c_signature)
-
   COMPRESSED_POINTER_FIELD(TypePtr, signature_type)
   VISIT_FROM(signature_type)
 
+  COMPRESSED_POINTER_FIELD(FunctionTypePtr, c_signature)
+
   // Target Dart method for callbacks, otherwise null.
   COMPRESSED_POINTER_FIELD(FunctionPtr, callback_target)
 

tests/ffi/regress_b_261224444_test.dart

@@ -0,0 +1,19 @@
+// Copyright (c) 2022, 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.
+
+import 'dart:ffi';
+
+import 'ffi_test_helpers.dart';
+
+main() {
+  // Ensure we have FfiTrampolineData in heap.
+  final foo = DynamicLibrary.process()
+      .lookup<NativeFunction<Pointer<Void> Function(IntPtr)>>("malloc")
+      .asFunction<Pointer<Void> Function(int)>();
+  print(foo);
+
+  triggerGc();
+
+  print(foo(100).address);
+}

tests/ffi_2/regress_b_261224444_test.dart

@@ -0,0 +1,21 @@
+// Copyright (c) 2022, 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.
+
+// @dart=2.9
+
+import 'dart:ffi';
+
+import 'ffi_test_helpers.dart';
+
+main() {
+  // Ensure we have FfiTrampolineData in heap.
+  final foo = DynamicLibrary.process()
+      .lookup<NativeFunction<Pointer<Void> Function(IntPtr)>>("malloc")
+      .asFunction<Pointer<Void> Function(int)>();
+  print(foo);
+
+  triggerGc();
+
+  print(foo(100).address);
+}