[heap] Fix setting start of stack

The stack of an isolate's main thread is kept in the isolate's heap.
This CL sets the stack's start address when the isolate's heap is set
up; it can also be set explicitly from the embedder. The CL also fixes
threaded cctests, where an isolate is shared by many "main" threads.

Bug: v8:13257
Change-Id: Ie30bbbe4130882d94f23de946cbada748f32e22d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3870923Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Nikolaos Papaspyrou <nikolaos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82973}

src/heap/cppgc-js/cpp-heap.cc

@@ -520,7 +520,6 @@ void CppHeap::AttachIsolate(Isolate* isolate) {
         &CppGraphBuilder::Run, this);
   }
   SetMetricRecorder(std::make_unique<MetricRecorderAdapter>(*this));
-  isolate_->heap()->SetStackStart(base::Stack::GetStackStart());
   oom_handler().SetCustomHandler(&FatalOutOfMemoryHandlerImpl);
   ReduceGCCapabilititesFromFlags();
   no_gc_scope_--;

src/heap/heap.cc

@@ -5481,7 +5481,7 @@ void Heap::SetUpSpaces(LinearAllocationArea& new_allocation_info,
   tracer_.reset(new GCTracer(this));
   array_buffer_sweeper_.reset(new ArrayBufferSweeper(this));
   gc_idle_time_handler_.reset(new GCIdleTimeHandler());
-  stack_ = std::make_unique<::heap::base::Stack>();
+  stack_ = std::make_unique<::heap::base::Stack>(base::Stack::GetStackStart());
   memory_measurement_.reset(new MemoryMeasurement(isolate()));
   if (!IsShared()) memory_reducer_.reset(new MemoryReducer(this));
   if (V8_UNLIKELY(TracingFlags::is_gc_stats_enabled())) {

test/cctest/test-api.cc

@@ -13014,8 +13014,12 @@ void ApiTestFuzzer::Run() {
   // When it is our turn...
   gate_.Wait();
   {
-    // ... get the V8 lock and start running the test.
+    // ... get the V8 lock
     v8::Locker locker(CcTest::isolate());
+    // ... set the isolate stack to this thread
+    CcTest::i_isolate()->heap()->SetStackStart(
+        v8::base::Stack::GetStackStart());
+    // ... and start running the test.
     CallTest();
   }
   // This test finished.
@@ -13082,6 +13086,9 @@ void ApiTestFuzzer::ContextSwitch() {
     v8::Unlocker unlocker(CcTest::isolate());
     // Wait till someone starts us again.
     gate_.Wait();
+    // Set the isolate stack to this thread.
+    CcTest::i_isolate()->heap()->SetStackStart(
+        v8::base::Stack::GetStackStart());
     // And we're off.
   }
 }

test/unittests/heap/cppgc-js/traced-reference-unittest.cc

@@ -247,8 +247,6 @@ TEST_F(TracedReferenceTest, WriteBarrierForOnStackReset) {
   if (!v8_flags.incremental_marking)
     GTEST_SKIP() << "Write barrier tests require incremental marking";
 
-  heap()->SetStackStart(base::Stack::GetStackStart());
-
   v8::Local<v8::Context> context = v8::Context::New(v8_isolate());
   v8::Context::Scope context_scope(context);
   {
@@ -290,8 +288,6 @@ TEST_F(TracedReferenceTest, WriteBarrierForOnStackCopy) {
   if (!v8_flags.incremental_marking)
     GTEST_SKIP() << "Write barrier tests require incremental marking";
 
-  heap()->SetStackStart(base::Stack::GetStackStart());
-
   v8::Local<v8::Context> context = v8::Context::New(v8_isolate());
   v8::Context::Scope context_scope(context);
   {
@@ -336,8 +332,6 @@ TEST_F(TracedReferenceTest, WriteBarrierForOnStackMove) {
   if (!v8_flags.incremental_marking)
     GTEST_SKIP() << "Write barrier tests require incremental marking";
 
-  heap()->SetStackStart(base::Stack::GetStackStart());
-
   v8::Local<v8::Context> context = v8::Context::New(v8_isolate());
   v8::Context::Scope context_scope(context);
   {

test/unittests/heap/embedder-tracing-unittest.cc

@@ -687,7 +687,17 @@ TEST_F(EmbedderTracingTest, TracedReferenceHandlesMarking) {
     heap::TemporaryEmbedderHeapTracerScope tracer_scope(v8_isolate(), &tracer);
     tracer.AddReferenceForTracing(live.get());
     const size_t initial_count = global_handles->handles_count();
+    {
+      // Conservative scanning may find stale pointers to on-stack handles.
+      // Disable scanning, assuming the slots are overwritten.
+      EmbedderStackStateScope scope =
+          EmbedderStackStateScope::ExplicitScopeForTesting(
+              reinterpret_cast<i::Isolate*>(v8_isolate())
+                  ->heap()
+                  ->local_embedder_heap_tracer(),
+              EmbedderHeapTracer::EmbedderStackState::kNoHeapPointers);
       FullGC();
+    }
     const size_t final_count = global_handles->handles_count();
     // Handles are not black allocated, so `dead` is immediately reclaimed.
     EXPECT_EQ(initial_count, final_count + 1);