[wasm] Resume suspender on resolved promise

Implement the WasmResume builtin, which resumes a wasm suspender
when the corresponding JS promise resolves.

Drive-by 1: Fix detection of empty stacks in the stack frame iterator.
Drive-by 2: Add a stack ID for better tracing.

R=ahaas@chromium.org
CC=​fgm@chromium.org

Bug: v8:12191
Change-Id: Ifa3f00c4259f802292b04d426c739e9b551f87b9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3420827Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78842}

src/builtins/x64/builtins-x64.cc

@@ -3847,15 +3847,26 @@ void Builtins::Generate_WasmReturnPromiseOnSuspend(MacroAssembler* masm) {
   // -------------------------------------------
   active_continuation = rbx;
   __ LoadRoot(active_continuation, RootIndex::kActiveContinuation);
+  // Set a null pointer in the jump buffer's SP slot to indicate to the stack
+  // frame iterator that this stack is empty.
+  foreign_jmpbuf = rcx;
+  __ LoadAnyTaggedField(
+      foreign_jmpbuf,
+      FieldOperand(active_continuation, WasmContinuationObject::kJmpbufOffset));
+  jmpbuf = foreign_jmpbuf;
+  __ LoadExternalPointerField(
+      jmpbuf, FieldOperand(foreign_jmpbuf, Foreign::kForeignAddressOffset),
+      kForeignForeignAddressTag, rdx);
+  __ movq(Operand(jmpbuf, wasm::kJmpBufSpOffset), Immediate(kNullAddress));
   Register parent = rdx;
   __ LoadAnyTaggedField(
       parent,
       FieldOperand(active_continuation, WasmContinuationObject::kParentOffset));
   active_continuation = no_reg;
-  // live: [rsi]
+  // live: [rsi, rdx]
 
   // -------------------------------------------
-  // Update instance active continuation.
+  // Update active continuation.
   // -------------------------------------------
   __ movq(masm->RootAsOperand(RootIndex::kActiveContinuation), parent);
   foreign_jmpbuf = rax;
@@ -4019,10 +4030,122 @@ void Builtins::Generate_WasmSuspend(MacroAssembler* masm) {
   __ ret(0);
 }
 
+// Resume the suspender stored in the closure.
 void Builtins::Generate_WasmResume(MacroAssembler* masm) {
   __ EnterFrame(StackFrame::STACK_SWITCH);
+
+  Register param_count = rax;
+  Register closure = kJSFunctionRegister;  // rdi
+  __ subq(rsp, Immediate(ReturnPromiseOnSuspendFrameConstants::kSpillAreaSize));
+
+  // This slot is not used in this builtin. But when we return from the resumed
+  // continuation, we return to the ReturnPromiseOnSuspend code, which expects
+  // this slot to be set.
+  __ movq(
+      MemOperand(rbp, ReturnPromiseOnSuspendFrameConstants::kParamCountOffset),
+      param_count);
+  param_count = no_reg;
+
+  // -------------------------------------------
+  // Load suspender from closure.
+  // -------------------------------------------
+  Register sfi = closure;
+  __ LoadAnyTaggedField(
+      sfi,
+      MemOperand(
+          closure,
+          wasm::ObjectAccess::SharedFunctionInfoOffsetInTaggedJSFunction()));
+  Register function_data = sfi;
+  __ LoadAnyTaggedField(
+      function_data,
+      FieldOperand(sfi, SharedFunctionInfo::kFunctionDataOffset));
+  Register suspender = rax;
+  __ LoadAnyTaggedField(
+      suspender,
+      FieldOperand(function_data, WasmOnFulfilledData::kSuspenderOffset));
+  // Check the suspender state.
+  Label suspender_is_suspended;
+  Register state = rdx;
+  __ LoadTaggedSignedField(
+      state, FieldOperand(suspender, WasmSuspenderObject::kStateOffset));
+  __ SmiCompare(state, Smi::FromInt(WasmSuspenderObject::Suspended));
+  __ j(equal, &suspender_is_suspended);
+  __ Trap();  // TODO(thibaudm): Throw a wasm trap.
+  closure = no_reg;
+  sfi = no_reg;
+
+  __ bind(&suspender_is_suspended);
+  // -------------------------------------------
+  // Save current state.
+  // -------------------------------------------
+  Label suspend;
+  Register active_continuation = r9;
+  __ LoadRoot(active_continuation, RootIndex::kActiveContinuation);
+  Register current_jmpbuf = rdi;
+  __ LoadAnyTaggedField(
+      current_jmpbuf,
+      FieldOperand(active_continuation, WasmContinuationObject::kJmpbufOffset));
+  __ LoadExternalPointerField(
+      current_jmpbuf,
+      FieldOperand(current_jmpbuf, Foreign::kForeignAddressOffset),
+      kForeignForeignAddressTag, rdx);
+  FillJumpBuffer(masm, current_jmpbuf, &suspend);
+  current_jmpbuf = no_reg;
+
+  // -------------------------------------------
+  // Set suspender's parent to active continuation.
+  // -------------------------------------------
+  __ StoreTaggedSignedField(
+      FieldOperand(suspender, WasmSuspenderObject::kStateOffset),
+      Smi::FromInt(WasmSuspenderObject::Active));
+  Register target_continuation = rdi;
+  __ LoadAnyTaggedField(
+      target_continuation,
+      FieldOperand(suspender, WasmSuspenderObject::kContinuationOffset));
+  Register slot_address = WriteBarrierDescriptor::SlotAddressRegister();
+  __ StoreTaggedField(
+      FieldOperand(target_continuation, WasmContinuationObject::kParentOffset),
+      active_continuation);
+  __ RecordWriteField(
+      target_continuation, WasmContinuationObject::kParentOffset,
+      active_continuation, slot_address, SaveFPRegsMode::kIgnore);
+  active_continuation = no_reg;
+
+  // -------------------------------------------
+  // Update roots.
+  // -------------------------------------------
+  __ movq(masm->RootAsOperand(RootIndex::kActiveContinuation),
+          target_continuation);
+  __ movq(masm->RootAsOperand(RootIndex::kActiveSuspender), suspender);
+  suspender = no_reg;
+
+  MemOperand GCScanSlotPlace =
+      MemOperand(rbp, BuiltinWasmWrapperConstants::kGCScanSlotCountOffset);
+  __ Move(GCScanSlotPlace, 1);
+  __ Push(target_continuation);
+  __ Move(kContextRegister, Smi::zero());
+  __ CallRuntime(Runtime::kWasmSyncStackLimit);
+  __ Pop(target_continuation);
+
+  // -------------------------------------------
+  // Load state from target jmpbuf (longjmp).
+  // -------------------------------------------
+  Register target_jmpbuf = target_continuation;
+  __ LoadAnyTaggedField(
+      target_jmpbuf,
+      FieldOperand(target_continuation, WasmContinuationObject::kJmpbufOffset));
+  __ LoadExternalPointerField(
+      target_jmpbuf,
+      FieldOperand(target_jmpbuf, Foreign::kForeignAddressOffset),
+      kForeignForeignAddressTag, rax);
+  // Move resolved value to return register.
+  __ movq(kReturnRegister0, Operand(rbp, 3 * kSystemPointerSize));
+  __ Move(GCScanSlotPlace, 0);
+  LoadJumpBuffer(masm, target_jmpbuf, true);
+  __ Trap();
+  __ bind(&suspend);
   __ LeaveFrame(StackFrame::STACK_SWITCH);
-  __ ret(0);
+  __ ret(3);
 }
 
 void Builtins::Generate_WasmOnStackReplace(MacroAssembler* masm) {

src/execution/frames.cc

@@ -162,8 +162,9 @@ void StackFrameIterator::Reset(ThreadLocalTop* top) {
 
 #if V8_ENABLE_WEBASSEMBLY
 void StackFrameIterator::Reset(ThreadLocalTop* top, wasm::StackMemory* stack) {
-  if (stack->jmpbuf()->sp == stack->base()) {
-    // Empty stack.
+  if (stack->jmpbuf()->sp == kNullAddress) {
+    // A null SP indicates that the computation associated with this stack has
+    // returned, leaving the stack segment empty.
     return;
   }
   StackFrame::State state;

src/runtime/runtime-wasm.cc

@@ -731,6 +731,9 @@ void SyncStackLimit(Isolate* isolate) {
   auto continuation = WasmContinuationObject::cast(
       *isolate->roots_table().slot(RootIndex::kActiveContinuation));
   auto stack = Managed<wasm::StackMemory>::cast(continuation.stack()).get();
+  if (FLAG_trace_wasm_stack_switching) {
+    PrintF("Switch to stack #%d\n", stack->id());
+  }
   uintptr_t limit = reinterpret_cast<uintptr_t>(stack->jmpbuf()->stack_limit);
   isolate->stack_guard()->SetStackLimit(limit);
 }

src/wasm/stacks.h

@@ -44,7 +44,7 @@ class StackMemory {
 
   ~StackMemory() {
     if (FLAG_trace_wasm_stack_switching) {
-      PrintF("Delete stack (sp: %p)\n", reinterpret_cast<void*>(jmpbuf_.sp));
+      PrintF("Delete stack #%d\n", id_);
     }
     PageAllocator* allocator = GetPlatformPageAllocator();
     if (owned_) allocator->DecommitPages(limit_, size_);
@@ -59,6 +59,7 @@ class StackMemory {
   void* jslimit() const { return limit_ + kJSLimitOffsetKB; }
   Address base() const { return reinterpret_cast<Address>(limit_ + size_); }
   JumpBuffer* jmpbuf() { return &jmpbuf_; }
+  int id() { return id_; }
 
   // Insert a stack in the linked list after this stack.
   void Add(StackMemory* stack) {
@@ -82,6 +83,8 @@ class StackMemory {
 
   // This constructor allocates a new stack segment.
   explicit StackMemory(Isolate* isolate) : isolate_(isolate), owned_(true) {
+    static int next_id = 1;
+    id_ = next_id++;
     PageAllocator* allocator = GetPlatformPageAllocator();
     int kJsStackSizeKB = 4;
     size_ = (kJsStackSizeKB + kJSLimitOffsetKB) * KB;
@@ -89,8 +92,9 @@ class StackMemory {
     limit_ = static_cast<byte*>(
         allocator->AllocatePages(nullptr, size_, allocator->AllocatePageSize(),
                                  PageAllocator::kReadWrite));
-    if (FLAG_trace_wasm_stack_switching)
-      PrintF("Allocate stack (sp: %p, limit: %p)\n", limit_ + size_, limit_);
+    if (FLAG_trace_wasm_stack_switching) {
+      PrintF("Allocate stack #%d\n", id_);
+    }
   }
 
   // Overload to represent a view of the libc stack.
@@ -98,13 +102,16 @@ class StackMemory {
       : isolate_(isolate),
         limit_(limit),
         size_(reinterpret_cast<size_t>(limit)),
-        owned_(false) {}
+        owned_(false) {
+    id_ = 0;
+  }
 
   Isolate* isolate_;
   byte* limit_;
   size_t size_;
   bool owned_;
   JumpBuffer jmpbuf_;
+  int id_;
   // Stacks form a circular doubly linked list per isolate.
   StackMemory* next_ = this;
   StackMemory* prev_ = this;

test/mjsunit/wasm/stack-switching.js

@@ -48,6 +48,49 @@ load("test/mjsunit/wasm/wasm-module-builder.js");
   let wrapped_export = suspender.returnPromiseOnSuspend(instance.exports.test);
   let combined_promise = wrapped_export();
   assertEquals(0, instance.exports.g.value);
+  combined_promise.then(_ => assertEquals(42, instance.exports.g.value));
+})();
+
+// Check that we can suspend back out of a resumed computation.
+(function TestStackSwitchSuspendLoop() {
+  print(arguments.callee.name);
+  let builder = new WasmModuleBuilder();
+  builder.addGlobal(kWasmI32, true).exportAs('g');
+  import_index = builder.addImport('m', 'import', kSig_i_v);
+  // Pseudo-code for the wasm function:
+  // for (i = 0; i < 5; ++i) {
+  //   g = g + import();
+  // }
+  builder.addFunction("test", kSig_v_v)
+      .addLocals(kWasmI32, 1)
+      .addBody([
+          kExprI32Const, 5,
+          kExprLocalSet, 0,
+          kExprLoop, kWasmVoid,
+            kExprCallFunction, import_index, // suspend
+            kExprGlobalGet, 0, // resume
+            kExprI32Add,
+            kExprGlobalSet, 0,
+            kExprLocalGet, 0,
+            kExprI32Const, 1,
+            kExprI32Sub,
+            kExprLocalTee, 0,
+            kExprBrIf, 0,
+          kExprEnd,
+      ]).exportFunc();
+  let suspender = new WebAssembly.Suspender();
+  let i = 0;
+  // The n-th call to the import returns a promise that resolves to n.
+  function js_import() {
+    return new Promise((resolve) => { resolve(++i); });
+  };
+  let wasm_js_import = new WebAssembly.Function({parameters: [], results: ['i32']}, js_import);
+  let suspending_wasm_js_import = suspender.suspendOnReturnedPromise(wasm_js_import);
+  let instance = builder.instantiate({m: {import: suspending_wasm_js_import}});
+  let wrapped_export = suspender.returnPromiseOnSuspend(instance.exports.test);
+  let chained_promise = wrapped_export();
+  assertEquals(0, instance.exports.g.value);
+  chained_promise.then(_ => assertEquals(15, instance.exports.g.value));
 })();
 
 (function TestStackSwitchGC() {