chromium/chromium-111-v8-std-layout2.patch

From 916641c08de44e0a915df223d55781c6c912717c Mon Sep 17 00:00:00 2001
From: Nikolaos Papaspyrou <nikolaos@chromium.org>
Date: Thu, 19 Jan 2023 13:43:10 +0100
Subject: [PATCH] [heap] Move the Stack object from ThreadLocalTop to Isolate

Stack information is thread-specific and, until now, it was stored in a
field in ThreadLocalTop. This CL moves stack information to the isolate
and makes sure to update the stack start whenever a main thread enters
the isolate. At the same time, the Stack object is refactored and
simplified.

As a side effect, after removing the Stack object, ThreadLocalTop
satisfies the std::standard_layout trait; this fixes some issues
observed with different C++ compilers.

Bug: v8:13630
Bug: v8:13257
Change-Id: I026a35af3bc6999a09b21f277756d4454c086343

(stripped tests)
---

diff --git a/src/execution/isolate.cc b/src/execution/isolate.cc
index 31536a1..22b8492 100644
--- a/v8/src/execution/isolate.cc
+++ b/v8/src/execution/isolate.cc
@@ -3069,21 +3069,23 @@
 void Isolate::RecordStackSwitchForScanning() {
   Object current = root(RootIndex::kActiveContinuation);
   DCHECK(!current.IsUndefined());
-  thread_local_top()->stack_.ClearStackSegments();
-  wasm::StackMemory* stack = Managed<wasm::StackMemory>::cast(
-                                 WasmContinuationObject::cast(current).stack())
-                                 .get()
-                                 .get();
+  stack().ClearStackSegments();
+  wasm::StackMemory* wasm_stack =
+      Managed<wasm::StackMemory>::cast(
+          WasmContinuationObject::cast(current).stack())
+          .get()
+          .get();
   current = WasmContinuationObject::cast(current).parent();
-  heap()->SetStackStart(reinterpret_cast<void*>(stack->base()));
+  heap()->SetStackStart(reinterpret_cast<void*>(wasm_stack->base()));
   // We don't need to add all inactive stacks. Only the ones in the active chain
   // may contain cpp heap pointers.
   while (!current.IsUndefined()) {
     auto cont = WasmContinuationObject::cast(current);
-    auto* stack = Managed<wasm::StackMemory>::cast(cont.stack()).get().get();
-    thread_local_top()->stack_.AddStackSegment(
-        reinterpret_cast<const void*>(stack->base()),
-        reinterpret_cast<const void*>(stack->jmpbuf()->sp));
+    auto* wasm_stack =
+        Managed<wasm::StackMemory>::cast(cont.stack()).get().get();
+    stack().AddStackSegment(
+        reinterpret_cast<const void*>(wasm_stack->base()),
+        reinterpret_cast<const void*>(wasm_stack->jmpbuf()->sp));
     current = cont.parent();
   }
 }
@@ -3371,23 +3373,13 @@
   Isolate* saved_isolate = isolate->TryGetCurrent();
   SetIsolateThreadLocals(isolate, nullptr);
   isolate->set_thread_id(ThreadId::Current());
-  if (saved_isolate) {
-    isolate->thread_local_top()->stack_ =
-        std::move(saved_isolate->thread_local_top()->stack_);
-  } else {
-    isolate->heap()->SetStackStart(base::Stack::GetStackStart());
-  }
+  isolate->heap()->SetStackStart(base::Stack::GetStackStart());
 
   bool owns_shared_isolate = isolate->owns_shared_isolate_;
   Isolate* maybe_shared_isolate = isolate->shared_isolate_;
 
   isolate->Deinit();
 
-  // Restore the saved isolate's stack.
-  if (saved_isolate)
-    saved_isolate->thread_local_top()->stack_ =
-        std::move(isolate->thread_local_top()->stack_);
-
 #ifdef DEBUG
   non_disposed_isolates_--;
 #endif  // DEBUG
@@ -4652,6 +4644,10 @@
 void Isolate::Enter() {
   Isolate* current_isolate = nullptr;
   PerIsolateThreadData* current_data = CurrentPerIsolateThreadData();
+
+  // Set the stack start for the main thread that enters the isolate.
+  heap()->SetStackStart(base::Stack::GetStackStart());
+
   if (current_data != nullptr) {
     current_isolate = current_data->isolate_;
     DCHECK_NOT_NULL(current_isolate);
diff --git a/src/execution/isolate.h b/src/execution/isolate.h
index afc3d0b..415e476 100644
--- a/v8/src/execution/isolate.h
+++ b/v8/src/execution/isolate.h
@@ -32,6 +32,7 @@
 #include "src/execution/stack-guard.h"
 #include "src/handles/handles.h"
 #include "src/handles/traced-handles.h"
+#include "src/heap/base/stack.h"
 #include "src/heap/factory.h"
 #include "src/heap/heap.h"
 #include "src/heap/read-only-heap.h"
@@ -2028,6 +2029,8 @@
   SimulatorData* simulator_data() { return simulator_data_; }
 #endif
 
+  ::heap::base::Stack& stack() { return stack_; }
+
 #ifdef V8_ENABLE_WEBASSEMBLY
   wasm::StackMemory*& wasm_stacks() { return wasm_stacks_; }
   // Update the thread local's Stack object so that it is aware of the new stack
@@ -2526,6 +2529,9 @@
   // The mutex only guards adding pages, the retrieval is signal safe.
   base::Mutex code_pages_mutex_;
 
+  // Stack information for the main thread.
+  ::heap::base::Stack stack_;
+
 #ifdef V8_ENABLE_WEBASSEMBLY
   wasm::StackMemory* wasm_stacks_;
 #endif
diff --git a/src/execution/thread-local-top.cc b/src/execution/thread-local-top.cc
index c115ae0..05cc20b 100644
--- a/v8/src/execution/thread-local-top.cc
+++ b/v8/src/execution/thread-local-top.cc
@@ -37,7 +37,6 @@
   current_embedder_state_ = nullptr;
   failed_access_check_callback_ = nullptr;
   thread_in_wasm_flag_address_ = kNullAddress;
-  stack_ = ::heap::base::Stack();
 }
 
 void ThreadLocalTop::Initialize(Isolate* isolate) {
@@ -45,12 +44,8 @@
   isolate_ = isolate;
   thread_id_ = ThreadId::Current();
 #if V8_ENABLE_WEBASSEMBLY
-  stack_.SetStackStart(base::Stack::GetStackStart(),
-                       v8_flags.experimental_wasm_stack_switching);
   thread_in_wasm_flag_address_ = reinterpret_cast<Address>(
       trap_handler::GetThreadInWasmThreadLocalAddress());
-#else
-  stack_.SetStackStart(base::Stack::GetStackStart(), false);
 #endif  // V8_ENABLE_WEBASSEMBLY
 #ifdef USE_SIMULATOR
   simulator_ = Simulator::current(isolate);
diff --git a/src/execution/thread-local-top.h b/src/execution/thread-local-top.h
index 43fec0a..989c817 100644
--- a/v8/src/execution/thread-local-top.h
+++ b/v8/src/execution/thread-local-top.h
@@ -10,7 +10,6 @@
 #include "include/v8-unwinder.h"
 #include "src/common/globals.h"
 #include "src/execution/thread-id.h"
-#include "src/heap/base/stack.h"
 #include "src/objects/contexts.h"
 #include "src/utils/utils.h"
 
@@ -30,7 +29,7 @@
   // TODO(all): This is not particularly beautiful. We should probably
   // refactor this to really consist of just Addresses and 32-bit
   // integer fields.
-  static constexpr uint32_t kSizeInBytes = 30 * kSystemPointerSize;
+  static constexpr uint32_t kSizeInBytes = 25 * kSystemPointerSize;
 
   // Does early low-level initialization that does not depend on the
   // isolate being present.
@@ -147,9 +146,6 @@
 
   // Address of the thread-local "thread in wasm" flag.
   Address thread_in_wasm_flag_address_;
-
-  // Stack information.
-  ::heap::base::Stack stack_;
 };
 
 }  // namespace internal
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index f4b7da0..6efd486 100644
--- a/v8/src/heap/heap.cc
+++ b/v8/src/heap/heap.cc
@@ -5830,9 +5830,7 @@
 #endif  // V8_ENABLE_WEBASSEMBLY
 }
 
-::heap::base::Stack& Heap::stack() {
-  return isolate_->thread_local_top()->stack_;
-}
+::heap::base::Stack& Heap::stack() { return isolate_->stack(); }
 
 void Heap::StartTearDown() {
   // Finish any ongoing sweeping to avoid stray background tasks still accessing