[wasm] Make ActiveContinuation a root

Switching stack affects all instances, therefore make the active
continuation a root object instead of an instance field.

Bug: v8:12191
Change-Id: Ia521bf4e7c3cbca035f916e47804c2f75bbd8f18
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3268296Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77876}

src/builtins/x64/builtins-x64.cc

@@ -3696,10 +3696,7 @@ void Builtins::Generate_WasmReturnPromiseOnSuspend(MacroAssembler* masm) {
   // -------------------------------------------
   Register active_continuation = rax;
   Register foreign_jmpbuf = rbx;
-  __ LoadAnyTaggedField(
-      active_continuation,
-      FieldOperand(wasm_instance,
-                   WasmInstanceObject::kActiveContinuationOffset));
+  __ LoadRoot(active_continuation, RootIndex::kActiveContinuation);
   __ LoadAnyTaggedField(
       foreign_jmpbuf,
       FieldOperand(active_continuation, WasmContinuationObject::kJmpbufOffset));
@@ -3726,10 +3723,9 @@ void Builtins::Generate_WasmReturnPromiseOnSuspend(MacroAssembler* masm) {
   // -------------------------------------------
   MemOperand GCScanSlotPlace =
       MemOperand(rbp, BuiltinWasmWrapperConstants::kGCScanSlotCountOffset);
-  __ Move(GCScanSlotPlace, 3);
+  __ Move(GCScanSlotPlace, 2);
   __ Push(wasm_instance);
   __ Push(function_data);
-  __ Push(wasm_instance);
   __ Move(kContextRegister, Smi::zero());
   __ CallRuntime(Runtime::kWasmAllocateContinuation);
   __ Pop(function_data);
@@ -3753,10 +3749,9 @@ void Builtins::Generate_WasmReturnPromiseOnSuspend(MacroAssembler* masm) {
   // Switch stack!
   LoadJumpBuffer(masm, target_jmpbuf);
   __ movq(rbp, rsp);  // New stack, there is no frame yet.
-  __ Move(GCScanSlotPlace, 3);
+  __ Move(GCScanSlotPlace, 2);
   __ Push(wasm_instance);
   __ Push(function_data);
-  __ Push(wasm_instance);
   __ Move(kContextRegister, Smi::zero());
   __ CallRuntime(Runtime::kWasmSyncStackLimit);
   __ Pop(function_data);
@@ -3799,10 +3794,7 @@ void Builtins::Generate_WasmReturnPromiseOnSuspend(MacroAssembler* masm) {
   // Reload parent continuation.
   // -------------------------------------------
   active_continuation = rbx;
-  __ LoadAnyTaggedField(
-      active_continuation,
-      FieldOperand(wasm_instance,
-                   WasmInstanceObject::kActiveContinuationOffset));
+  __ LoadRoot(active_continuation, RootIndex::kActiveContinuation);
   Register parent = rdx;
   __ LoadAnyTaggedField(
       parent,
@@ -3813,20 +3805,7 @@ void Builtins::Generate_WasmReturnPromiseOnSuspend(MacroAssembler* masm) {
   // -------------------------------------------
   // Update instance active continuation.
   // -------------------------------------------
-  Register object = WriteBarrierDescriptor::ObjectRegister();
-  Register slot_address = WriteBarrierDescriptor::SlotAddressRegister();
-  DCHECK_EQ(object, rdi);
-  DCHECK((slot_address == rbx || slot_address == r8));
-  // Save reg clobbered by the write barrier.
-  __ movq(rax, parent);
-  __ movq(object, wasm_instance);
-  __ StoreTaggedField(
-      FieldOperand(object, WasmInstanceObject::kActiveContinuationOffset),
-      parent);
-  __ RecordWriteField(object, WasmInstanceObject::kActiveContinuationOffset,
-                      parent, slot_address, SaveFPRegsMode::kIgnore);
-  // Restore reg clobbered by the write barrier.
-  __ movq(parent, rax);
+  __ movq(masm->RootAsOperand(RootIndex::kActiveContinuation), parent);
   foreign_jmpbuf = rax;
   __ LoadAnyTaggedField(
       foreign_jmpbuf,
@@ -3838,9 +3817,8 @@ void Builtins::Generate_WasmReturnPromiseOnSuspend(MacroAssembler* masm) {
   // Switch stack!
   LoadJumpBuffer(masm, jmpbuf);
   __ leaq(rbp, Operand(rsp, (kNumSpillSlots + 1) * kSystemPointerSize));
-  __ Move(GCScanSlotPlace, 2);
+  __ Move(GCScanSlotPlace, 1);
   __ Push(wasm_instance);  // Spill.
-  __ Push(wasm_instance);  // First arg.
   __ Move(kContextRegister, Smi::zero());
   __ CallRuntime(Runtime::kWasmSyncStackLimit);
   __ Pop(wasm_instance);

src/heap/setup-heap-internal.cc

@@ -804,6 +804,9 @@ void Heap::CreateInitialObjects() {
   set_feedback_vectors_for_profiling_tools(roots.undefined_value());
   set_pending_optimize_for_test_bytecode(roots.undefined_value());
   set_shared_wasm_memories(roots.empty_weak_array_list());
+#ifdef V8_ENABLE_WEBASSEMBLY
+  set_active_continuation(roots.undefined_value());
+#endif  // V8_ENABLE_WEBASSEMBLY
 
   set_script_list(roots.empty_weak_array_list());
 

src/roots/roots.h

@@ -310,7 +310,8 @@ class Symbol;
   V(Object, pending_optimize_for_test_bytecode,                            \
     PendingOptimizeForTestBytecode)                                        \
   V(ArrayList, basic_block_profiling_data, BasicBlockProfilingData)        \
-  V(WeakArrayList, shared_wasm_memories, SharedWasmMemories)
+  V(WeakArrayList, shared_wasm_memories, SharedWasmMemories)               \
+  IF_WASM(V, HeapObject, active_continuation, ActiveContinuation)
 
 // Entries in this list are limited to Smis and are not visited during GC.
 #define SMI_ROOT_LIST(V)                                                       \

src/runtime/runtime-wasm.cc

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "src/base/memory.h"
+#include "src/common/assert-scope.h"
 #include "src/common/message-template.h"
 #include "src/compiler/wasm-compiler.h"
 #include "src/debug/debug.h"
@@ -705,10 +706,12 @@ namespace {
 // contains a sentinel value, and it is also thread-safe. So if an interrupt is
 // requested before, during or after this call, it will be preserved and handled
 // at the next stack check.
-void SyncStackLimit(Isolate* isolate, Handle<WasmInstanceObject> instance) {
-  auto jmpbuf = Managed<wasm::JumpBuffer>::cast(
-                    instance->active_continuation().managed_jmpbuf())
-                    .get();
+void SyncStackLimit(Isolate* isolate) {
+  DisallowGarbageCollection no_gc;
+  auto continuation = WasmContinuationObject::cast(
+      *isolate->roots_table().slot(RootIndex::kActiveContinuation));
+  auto jmpbuf =
+      Managed<wasm::JumpBuffer>::cast(continuation.managed_jmpbuf()).get();
   uintptr_t limit = reinterpret_cast<uintptr_t>(jmpbuf->stack_limit);
   isolate->stack_guard()->SetStackLimit(limit);
 }
@@ -718,22 +721,21 @@ void SyncStackLimit(Isolate* isolate, Handle<WasmInstanceObject> instance) {
 // active continuation and setting the stack limit.
 RUNTIME_FUNCTION(Runtime_WasmAllocateContinuation) {
   CHECK(FLAG_experimental_wasm_stack_switching);
-  DCHECK_EQ(1, args.length());
   HandleScope scope(isolate);
-  CONVERT_ARG_HANDLE_CHECKED(WasmInstanceObject, instance, 0);
-  auto parent = instance->active_continuation();
-  auto target = WasmContinuationObject::New(isolate, parent);
-  instance->set_active_continuation(*target);
-  SyncStackLimit(isolate, instance);
+  auto parent =
+      handle(WasmContinuationObject::cast(
+                 *isolate->roots_table().slot(RootIndex::kActiveContinuation)),
+             isolate);
+  auto target = WasmContinuationObject::New(isolate, *parent);
+  isolate->roots_table().slot(RootIndex::kActiveContinuation).store(*target);
+  SyncStackLimit(isolate);
   return *target;
 }
 
 // Update the stack limit after a stack switch, and preserve pending interrupts.
 RUNTIME_FUNCTION(Runtime_WasmSyncStackLimit) {
   CHECK(FLAG_experimental_wasm_stack_switching);
-  HandleScope scope(isolate);
-  CONVERT_ARG_HANDLE_CHECKED(WasmInstanceObject, instance, 0);
-  SyncStackLimit(isolate, instance);
+  SyncStackLimit(isolate);
   return ReadOnlyRoots(isolate).undefined_value();
 }
 

src/runtime/runtime.h

@@ -593,8 +593,8 @@ namespace internal {
   F(WasmDebugBreak, 0, 1)             \
   F(WasmAllocateRtt, 3, 1)            \
   F(WasmArrayCopy, 5, 1)              \
-  F(WasmAllocateContinuation, 1, 1)   \
-  F(WasmSyncStackLimit, 1, 1)
+  F(WasmAllocateContinuation, 0, 1)   \
+  F(WasmSyncStackLimit, 0, 1)
 
 #define FOR_EACH_INTRINSIC_WASM_TEST(F, I) \
   F(DeserializeWasmModule, 2, 1)           \

src/wasm/wasm-js.cc

@@ -2830,6 +2830,13 @@ void WasmJs::Install(Isolate* isolate, bool exposed_on_global_object) {
         WasmSuspenderObject::kHeaderSize, "WebAssembly.Suspender");
     InstallFunc(isolate, suspender_proto, "returnPromiseOnSuspend",
                 WebAssemblySuspenderReturnPromiseOnSuspend, 1);
+    std::unique_ptr<wasm::StackMemory> stack(
+        wasm::StackMemory::GetCurrentStackView(isolate));
+    auto continuation = WasmContinuationObject::New(isolate, std::move(stack));
+    isolate->heap()
+        ->roots_table()
+        .slot(RootIndex::kActiveContinuation)
+        .store(*continuation);
   }
 
   // Setup Function

src/wasm/wasm-objects-inl.h

@@ -227,8 +227,6 @@ PRIMITIVE_ACCESSORS(WasmInstanceObject, hook_on_function_call_address, Address,
                     kHookOnFunctionCallAddressOffset)
 PRIMITIVE_ACCESSORS(WasmInstanceObject, num_liftoff_function_calls_array,
                     uint32_t*, kNumLiftoffFunctionCallsArrayOffset)
-ACCESSORS(WasmInstanceObject, active_continuation, WasmContinuationObject,
-          kActiveContinuationOffset)
 PRIMITIVE_ACCESSORS(WasmInstanceObject, break_on_entry, uint8_t,
                     kBreakOnEntryOffset)
 

src/wasm/wasm-objects.cc

@@ -1208,15 +1208,6 @@ Handle<WasmInstanceObject> WasmInstanceObject::New(
       module_object->native_module()->num_liftoff_function_calls_array());
   instance->set_break_on_entry(module_object->script().break_on_entry());
 
-  if (FLAG_experimental_wasm_stack_switching) {
-    // TODO(thibaudm): If there is already a continuation object for the current
-    // execution context, re-use that instead of creating a new one.
-    std::unique_ptr<wasm::StackMemory> stack(
-        wasm::StackMemory::GetCurrentStackView(isolate));
-    auto continuation = WasmContinuationObject::New(isolate, std::move(stack));
-    instance->set_active_continuation(*continuation);
-  }
-
   // Insert the new instance into the scripts weak list of instances. This list
   // is used for breakpoints affecting all instances belonging to the script.
   if (module_object->script().type() == Script::TYPE_WASM) {

src/wasm/wasm-objects.h

@@ -353,7 +353,6 @@ class V8_EXPORT_PRIVATE WasmInstanceObject : public JSObject {
   DECL_PRIMITIVE_ACCESSORS(dropped_elem_segments, byte*)
   DECL_PRIMITIVE_ACCESSORS(hook_on_function_call_address, Address)
   DECL_PRIMITIVE_ACCESSORS(num_liftoff_function_calls_array, uint32_t*)
-  DECL_ACCESSORS(active_continuation, WasmContinuationObject)
   DECL_PRIMITIVE_ACCESSORS(break_on_entry, uint8_t)
 
   // Clear uninitialized padding space. This ensures that the snapshot content
@@ -410,7 +409,6 @@ class V8_EXPORT_PRIVATE WasmInstanceObject : public JSObject {
   V(kWasmExternalFunctionsOffset, kTaggedSize)                            \
   V(kManagedObjectMapsOffset, kTaggedSize)                                \
   V(kFeedbackVectorsOffset, kTaggedSize)                                  \
-  V(kActiveContinuationOffset, kTaggedSize)                               \
   V(kBreakOnEntryOffset, kUInt8Size)                                      \
   /* More padding to make the header pointer-size aligned */              \
   V(kHeaderPaddingOffset, POINTER_SIZE_PADDING(kHeaderPaddingOffset))     \