path: root/chromium/v8/src/runtime/runtime-wasm.cc

// Copyright 2016 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// 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"
#include "src/execution/arguments-inl.h"
#include "src/execution/frame-constants.h"
#include "src/execution/frames.h"
#include "src/heap/factory.h"
#include "src/logging/counters.h"
#include "src/numbers/conversions.h"
#include "src/objects/objects-inl.h"
#include "src/runtime/runtime-utils.h"
#include "src/trap-handler/trap-handler.h"
#include "src/wasm/module-compiler.h"
#include "src/wasm/stacks.h"
#include "src/wasm/value-type.h"
#include "src/wasm/wasm-code-manager.h"
#include "src/wasm/wasm-constants.h"
#include "src/wasm/wasm-debug.h"
#include "src/wasm/wasm-engine.h"
#include "src/wasm/wasm-objects.h"
#include "src/wasm/wasm-subtyping.h"
#include "src/wasm/wasm-value.h"

namespace v8 {
namespace internal {

namespace {

template <typename FrameType>
class FrameFinder {
 public:
  explicit FrameFinder(Isolate* isolate,
                       std::initializer_list<StackFrame::Type>
                           skipped_frame_types = {StackFrame::EXIT})
      : frame_iterator_(isolate, isolate->thread_local_top()) {
    // We skip at least one frame.
    DCHECK_LT(0, skipped_frame_types.size());

    for (auto type : skipped_frame_types) {
      DCHECK_EQ(type, frame_iterator_.frame()->type());
      USE(type);
      frame_iterator_.Advance();
    }
    // Type check the frame where the iterator stopped now.
    DCHECK_NOT_NULL(frame());
  }

  FrameType* frame() { return FrameType::cast(frame_iterator_.frame()); }

 private:
  StackFrameIterator frame_iterator_;
};

WasmInstanceObject GetWasmInstanceOnStackTop(
    Isolate* isolate,
    std::initializer_list<StackFrame::Type> skipped_frame_types = {
        StackFrame::EXIT}) {
  return FrameFinder<WasmFrame>(isolate, skipped_frame_types)
      .frame()
      ->wasm_instance();
}

Context GetNativeContextFromWasmInstanceOnStackTop(Isolate* isolate) {
  return GetWasmInstanceOnStackTop(isolate).native_context();
}

class V8_NODISCARD ClearThreadInWasmScope {
 public:
  explicit ClearThreadInWasmScope(Isolate* isolate) : isolate_(isolate) {
    DCHECK_IMPLIES(trap_handler::IsTrapHandlerEnabled(),
                   trap_handler::IsThreadInWasm());
    trap_handler::ClearThreadInWasm();
  }
  ~ClearThreadInWasmScope() {
    DCHECK_IMPLIES(trap_handler::IsTrapHandlerEnabled(),
                   !trap_handler::IsThreadInWasm());
    if (!isolate_->has_pending_exception()) {
      trap_handler::SetThreadInWasm();
    }
    // Otherwise we only want to set the flag if the exception is caught in
    // wasm. This is handled by the unwinder.
  }

 private:
  Isolate* isolate_;
};

Object ThrowWasmError(Isolate* isolate, MessageTemplate message) {
  Handle<JSObject> error_obj = isolate->factory()->NewWasmRuntimeError(message);
  JSObject::AddProperty(isolate, error_obj,
                        isolate->factory()->wasm_uncatchable_symbol(),
                        isolate->factory()->true_value(), NONE);
  return isolate->Throw(*error_obj);
}
}  // namespace

RUNTIME_FUNCTION(Runtime_WasmIsValidRefValue) {
  // This code is called from wrappers, so the "thread is wasm" flag is not set.
  DCHECK_IMPLIES(trap_handler::IsTrapHandlerEnabled(),
                 !trap_handler::IsThreadInWasm());
  HandleScope scope(isolate);
  DCHECK_EQ(3, args.length());
  // 'raw_instance' can be either a WasmInstanceObject or undefined.
  Handle<Object> raw_instance = args.at(0);
  Handle<Object> value = args.at(1);
  // Make sure ValueType fits properly in a Smi.
  STATIC_ASSERT(wasm::ValueType::kLastUsedBit + 1 <= kSmiValueSize);
  int raw_type = args.smi_value_at(2);

  const wasm::WasmModule* module =
      raw_instance->IsWasmInstanceObject()
          ? Handle<WasmInstanceObject>::cast(raw_instance)->module()
          : nullptr;

  wasm::ValueType type = wasm::ValueType::FromRawBitField(raw_type);
  const char* error_message;

  bool result = internal::wasm::TypecheckJSObject(isolate, module, value, type,
                                                  &error_message);
  return Smi::FromInt(result);
}

RUNTIME_FUNCTION(Runtime_WasmMemoryGrow) {
  ClearThreadInWasmScope flag_scope(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(2, args.length());
  Handle<WasmInstanceObject> instance = args.at<WasmInstanceObject>(0);
  // {delta_pages} is checked to be a positive smi in the WasmMemoryGrow builtin
  // which calls this runtime function.
  uint32_t delta_pages = args.positive_smi_value_at(1);

  int ret = WasmMemoryObject::Grow(
      isolate, handle(instance->memory_object(), isolate), delta_pages);
  // The WasmMemoryGrow builtin which calls this runtime function expects us to
  // always return a Smi.
  DCHECK(!isolate->has_pending_exception());
  return Smi::FromInt(ret);
}

RUNTIME_FUNCTION(Runtime_ThrowWasmError) {
  ClearThreadInWasmScope flag_scope(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(1, args.length());
  int message_id = args.smi_value_at(0);
  return ThrowWasmError(isolate, MessageTemplateFromInt(message_id));
}

RUNTIME_FUNCTION(Runtime_ThrowWasmStackOverflow) {
  ClearThreadInWasmScope clear_wasm_flag(isolate);
  SealHandleScope shs(isolate);
  DCHECK_LE(0, args.length());
  return isolate->StackOverflow();
}

RUNTIME_FUNCTION(Runtime_WasmThrowJSTypeError) {
  // The caller may be wasm or JS. Only clear the thread_in_wasm flag if the
  // caller is wasm, and let the unwinder set it back depending on the handler.
  if (trap_handler::IsTrapHandlerEnabled() && trap_handler::IsThreadInWasm()) {
    trap_handler::ClearThreadInWasm();
  }
  HandleScope scope(isolate);
  DCHECK_EQ(0, args.length());
  THROW_NEW_ERROR_RETURN_FAILURE(
      isolate, NewTypeError(MessageTemplate::kWasmTrapJSTypeError));
}

RUNTIME_FUNCTION(Runtime_WasmThrow) {
  ClearThreadInWasmScope clear_wasm_flag(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(2, args.length());
  isolate->set_context(GetNativeContextFromWasmInstanceOnStackTop(isolate));

  auto tag_raw = WasmExceptionTag::cast(args[0]);
  auto values_raw = FixedArray::cast(args[1]);
  // TODO(wasm): Manually box because parameters are not visited yet.
  Handle<WasmExceptionTag> tag(tag_raw, isolate);
  Handle<FixedArray> values(values_raw, isolate);
  Handle<WasmExceptionPackage> exception =
      WasmExceptionPackage::New(isolate, tag, values);
  wasm::GetWasmEngine()->SampleThrowEvent(isolate);
  return isolate->Throw(*exception);
}

RUNTIME_FUNCTION(Runtime_WasmReThrow) {
  ClearThreadInWasmScope clear_wasm_flag(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(1, args.length());
  wasm::GetWasmEngine()->SampleRethrowEvent(isolate);
  return isolate->ReThrow(args[0]);
}

RUNTIME_FUNCTION(Runtime_WasmStackGuard) {
  ClearThreadInWasmScope wasm_flag(isolate);
  SealHandleScope shs(isolate);
  DCHECK_EQ(0, args.length());

  // Check if this is a real stack overflow.
  StackLimitCheck check(isolate);
  if (check.JsHasOverflowed()) return isolate->StackOverflow();

  return isolate->stack_guard()->HandleInterrupts();
}

RUNTIME_FUNCTION(Runtime_WasmCompileLazy) {
  ClearThreadInWasmScope wasm_flag(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(2, args.length());
  Handle<WasmInstanceObject> instance = args.at<WasmInstanceObject>(0);
  int func_index = args.smi_value_at(1);

#ifdef DEBUG
  FrameFinder<WasmCompileLazyFrame> frame_finder(isolate);
  DCHECK_EQ(*instance, frame_finder.frame()->wasm_instance());
#endif

  DCHECK(isolate->context().is_null());
  isolate->set_context(instance->native_context());
  bool success = wasm::CompileLazy(isolate, instance, func_index);
  if (!success) {
    DCHECK(isolate->has_pending_exception());
    return ReadOnlyRoots(isolate).exception();
  }

  Address entrypoint =
      instance->module_object().native_module()->GetCallTargetForFunction(
          func_index);

  return Object(entrypoint);
}

namespace {
void ReplaceWrapper(Isolate* isolate, Handle<WasmInstanceObject> instance,
                    int function_index, Handle<CodeT> wrapper_code) {
  Handle<WasmInternalFunction> internal =
      WasmInstanceObject::GetWasmInternalFunction(isolate, instance,
                                                  function_index)
          .ToHandleChecked();
  Handle<WasmExternalFunction> exported_function =
      handle(WasmExternalFunction::cast(internal->external()), isolate);
  exported_function->set_code(*wrapper_code, kReleaseStore);
  WasmExportedFunctionData function_data =
      exported_function->shared().wasm_exported_function_data();
  function_data.set_wrapper_code(*wrapper_code);
}
}  // namespace

RUNTIME_FUNCTION(Runtime_WasmCompileWrapper) {
  HandleScope scope(isolate);
  DCHECK_EQ(2, args.length());
  Handle<WasmInstanceObject> instance = args.at<WasmInstanceObject>(0);
  Handle<WasmExportedFunctionData> function_data =
      args.at<WasmExportedFunctionData>(1);
  DCHECK(isolate->context().is_null());
  isolate->set_context(instance->native_context());

  const wasm::WasmModule* module = instance->module();
  const int function_index = function_data->function_index();
  const wasm::WasmFunction& function = module->functions[function_index];
  const wasm::FunctionSig* sig = function.sig;

  // The start function is not guaranteed to be registered as
  // an exported function (although it is called as one).
  // If there is no entry for the start function,
  // the tier-up is abandoned.
  if (WasmInstanceObject::GetWasmInternalFunction(isolate, instance,
                                                  function_index)
          .is_null()) {
    DCHECK_EQ(function_index, module->start_function_index);
    return ReadOnlyRoots(isolate).undefined_value();
  }

  Handle<CodeT> wrapper_code = ToCodeT(
      wasm::JSToWasmWrapperCompilationUnit::CompileSpecificJSToWasmWrapper(
          isolate, sig, module),
      isolate);

  // Replace the wrapper for the function that triggered the tier-up.
  // This is to verify that the wrapper is replaced, even if the function
  // is implicitly exported and is not part of the export_table.
  ReplaceWrapper(isolate, instance, function_index, wrapper_code);

  // Iterate over all exports to replace eagerly the wrapper for all functions
  // that share the signature of the function that tiered up.
  for (wasm::WasmExport exp : module->export_table) {
    if (exp.kind != wasm::kExternalFunction) {
      continue;
    }
    int index = static_cast<int>(exp.index);
    const wasm::WasmFunction& exp_function = module->functions[index];
    if (exp_function.sig == sig && index != function_index) {
      ReplaceWrapper(isolate, instance, index, wrapper_code);
    }
  }

  return ReadOnlyRoots(isolate).undefined_value();
}

RUNTIME_FUNCTION(Runtime_WasmTriggerTierUp) {
  ClearThreadInWasmScope clear_wasm_flag(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(1, args.length());
  Handle<WasmInstanceObject> instance = args.at<WasmInstanceObject>(0);

  // We're reusing this interrupt mechanism to interrupt long-running loops.
  StackLimitCheck check(isolate);
  DCHECK(!check.JsHasOverflowed());
  if (check.InterruptRequested()) {
    Object result = isolate->stack_guard()->HandleInterrupts();
    if (result.IsException()) return result;
  }

  FrameFinder<WasmFrame> frame_finder(isolate);
  int func_index = frame_finder.frame()->function_index();
  auto* native_module = instance->module_object().native_module();

  wasm::TriggerTierUp(isolate, native_module, func_index, instance);

  return ReadOnlyRoots(isolate).undefined_value();
}

RUNTIME_FUNCTION(Runtime_WasmAtomicNotify) {
  ClearThreadInWasmScope clear_wasm_flag(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(3, args.length());
  Handle<WasmInstanceObject> instance = args.at<WasmInstanceObject>(0);
  double offset_double = args.number_value_at(1);
  uintptr_t offset = static_cast<uintptr_t>(offset_double);
  uint32_t count = NumberToUint32(args[2]);
  Handle<JSArrayBuffer> array_buffer{instance->memory_object().array_buffer(),
                                     isolate};
  // Should have trapped if address was OOB.
  DCHECK_LT(offset, array_buffer->byte_length());
  if (!array_buffer->is_shared()) return Smi::FromInt(0);
  return FutexEmulation::Wake(array_buffer, offset, count);
}

RUNTIME_FUNCTION(Runtime_WasmI32AtomicWait) {
  ClearThreadInWasmScope clear_wasm_flag(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(4, args.length());
  Handle<WasmInstanceObject> instance = args.at<WasmInstanceObject>(0);
  double offset_double = args.number_value_at(1);
  uintptr_t offset = static_cast<uintptr_t>(offset_double);
  int32_t expected_value = NumberToInt32(args[2]);
  Handle<BigInt> timeout_ns = args.at<BigInt>(3);

  Handle<JSArrayBuffer> array_buffer{instance->memory_object().array_buffer(),
                                     isolate};
  // Should have trapped if address was OOB.
  DCHECK_LT(offset, array_buffer->byte_length());

  // Trap if memory is not shared, or wait is not allowed on the isolate
  if (!array_buffer->is_shared() || !isolate->allow_atomics_wait()) {
    return ThrowWasmError(isolate, MessageTemplate::kAtomicsWaitNotAllowed);
  }
  return FutexEmulation::WaitWasm32(isolate, array_buffer, offset,
                                    expected_value, timeout_ns->AsInt64());
}

RUNTIME_FUNCTION(Runtime_WasmI64AtomicWait) {
  ClearThreadInWasmScope clear_wasm_flag(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(4, args.length());
  Handle<WasmInstanceObject> instance = args.at<WasmInstanceObject>(0);
  double offset_double = args.number_value_at(1);
  uintptr_t offset = static_cast<uintptr_t>(offset_double);
  Handle<BigInt> expected_value = args.at<BigInt>(2);
  Handle<BigInt> timeout_ns = args.at<BigInt>(3);

  Handle<JSArrayBuffer> array_buffer{instance->memory_object().array_buffer(),
                                     isolate};
  // Should have trapped if address was OOB.
  DCHECK_LT(offset, array_buffer->byte_length());

  // Trap if memory is not shared, or if wait is not allowed on the isolate
  if (!array_buffer->is_shared() || !isolate->allow_atomics_wait()) {
    return ThrowWasmError(isolate, MessageTemplate::kAtomicsWaitNotAllowed);
  }
  return FutexEmulation::WaitWasm64(isolate, array_buffer, offset,
                                    expected_value->AsInt64(),
                                    timeout_ns->AsInt64());
}

namespace {
Object ThrowTableOutOfBounds(Isolate* isolate,
                             Handle<WasmInstanceObject> instance) {
  // Handle out-of-bounds access here in the runtime call, rather
  // than having the lower-level layers deal with JS exceptions.
  if (isolate->context().is_null()) {
    isolate->set_context(instance->native_context());
  }
  return ThrowWasmError(isolate, MessageTemplate::kWasmTrapTableOutOfBounds);
}
}  // namespace

RUNTIME_FUNCTION(Runtime_WasmRefFunc) {
  ClearThreadInWasmScope flag_scope(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(2, args.length());
  Handle<WasmInstanceObject> instance = args.at<WasmInstanceObject>(0);
  uint32_t function_index = args.positive_smi_value_at(1);

  return *WasmInstanceObject::GetOrCreateWasmInternalFunction(isolate, instance,
                                                              function_index);
}

RUNTIME_FUNCTION(Runtime_WasmFunctionTableGet) {
  ClearThreadInWasmScope flag_scope(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(3, args.length());
  Handle<WasmInstanceObject> instance = args.at<WasmInstanceObject>(0);
  uint32_t table_index = args.positive_smi_value_at(1);
  uint32_t entry_index = args.positive_smi_value_at(2);
  DCHECK_LT(table_index, instance->tables().length());
  auto table = handle(
      WasmTableObject::cast(instance->tables().get(table_index)), isolate);
  // We only use the runtime call for lazily initialized function references.
  DCHECK(
      table->instance().IsUndefined()
          ? table->type() == wasm::kWasmFuncRef
          : IsSubtypeOf(table->type(), wasm::kWasmFuncRef,
                        WasmInstanceObject::cast(table->instance()).module()));

  if (!WasmTableObject::IsInBounds(isolate, table, entry_index)) {
    return ThrowWasmError(isolate, MessageTemplate::kWasmTrapTableOutOfBounds);
  }

  return *WasmTableObject::Get(isolate, table, entry_index);
}

RUNTIME_FUNCTION(Runtime_WasmFunctionTableSet) {
  ClearThreadInWasmScope flag_scope(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(4, args.length());
  Handle<WasmInstanceObject> instance = args.at<WasmInstanceObject>(0);
  uint32_t table_index = args.positive_smi_value_at(1);
  uint32_t entry_index = args.positive_smi_value_at(2);
  Object element_raw = args[3];
  // TODO(wasm): Manually box because parameters are not visited yet.
  Handle<Object> element(element_raw, isolate);
  DCHECK_LT(table_index, instance->tables().length());
  auto table = handle(
      WasmTableObject::cast(instance->tables().get(table_index)), isolate);
  // We only use the runtime call for function references.
  DCHECK(
      table->instance().IsUndefined()
          ? table->type() == wasm::kWasmFuncRef
          : IsSubtypeOf(table->type(), wasm::kWasmFuncRef,
                        WasmInstanceObject::cast(table->instance()).module()));

  if (!WasmTableObject::IsInBounds(isolate, table, entry_index)) {
    return ThrowWasmError(isolate, MessageTemplate::kWasmTrapTableOutOfBounds);
  }
  WasmTableObject::Set(isolate, table, entry_index, element);
  return ReadOnlyRoots(isolate).undefined_value();
}

RUNTIME_FUNCTION(Runtime_WasmTableInit) {
  ClearThreadInWasmScope flag_scope(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(6, args.length());
  Handle<WasmInstanceObject> instance = args.at<WasmInstanceObject>(0);
  uint32_t table_index = args.positive_smi_value_at(1);
  uint32_t elem_segment_index = args.positive_smi_value_at(2);
  static_assert(
      wasm::kV8MaxWasmTableSize < kSmiMaxValue,
      "Make sure clamping to Smi range doesn't make an invalid call valid");
  uint32_t dst = args.positive_smi_value_at(3);
  uint32_t src = args.positive_smi_value_at(4);
  uint32_t count = args.positive_smi_value_at(5);

  DCHECK(!isolate->context().is_null());

  bool oob = !WasmInstanceObject::InitTableEntries(
      isolate, instance, table_index, elem_segment_index, dst, src, count);
  if (oob) return ThrowTableOutOfBounds(isolate, instance);
  return ReadOnlyRoots(isolate).undefined_value();
}

RUNTIME_FUNCTION(Runtime_WasmTableCopy) {
  ClearThreadInWasmScope flag_scope(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(6, args.length());
  Handle<WasmInstanceObject> instance = args.at<WasmInstanceObject>(0);
  uint32_t table_dst_index = args.positive_smi_value_at(1);
  uint32_t table_src_index = args.positive_smi_value_at(2);
  static_assert(
      wasm::kV8MaxWasmTableSize < kSmiMaxValue,
      "Make sure clamping to Smi range doesn't make an invalid call valid");
  uint32_t dst = args.positive_smi_value_at(3);
  uint32_t src = args.positive_smi_value_at(4);
  uint32_t count = args.positive_smi_value_at(5);

  DCHECK(!isolate->context().is_null());

  bool oob = !WasmInstanceObject::CopyTableEntries(
      isolate, instance, table_dst_index, table_src_index, dst, src, count);
  if (oob) return ThrowTableOutOfBounds(isolate, instance);
  return ReadOnlyRoots(isolate).undefined_value();
}

RUNTIME_FUNCTION(Runtime_WasmTableGrow) {
  ClearThreadInWasmScope flag_scope(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(4, args.length());
  Handle<WasmInstanceObject> instance = args.at<WasmInstanceObject>(0);
  uint32_t table_index = args.positive_smi_value_at(1);
  Object value_raw = args[2];
  // TODO(wasm): Manually box because parameters are not visited yet.
  Handle<Object> value(value_raw, isolate);
  uint32_t delta = args.positive_smi_value_at(3);

  Handle<WasmTableObject> table(
      WasmTableObject::cast(instance->tables().get(table_index)), isolate);
  int result = WasmTableObject::Grow(isolate, table, delta, value);

  return Smi::FromInt(result);
}

RUNTIME_FUNCTION(Runtime_WasmTableFill) {
  ClearThreadInWasmScope flag_scope(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(5, args.length());
  Handle<WasmInstanceObject> instance = args.at<WasmInstanceObject>(0);
  uint32_t table_index = args.positive_smi_value_at(1);
  uint32_t start = args.positive_smi_value_at(2);
  Object value_raw = args[3];
  // TODO(wasm): Manually box because parameters are not visited yet.
  Handle<Object> value(value_raw, isolate);
  uint32_t count = args.positive_smi_value_at(4);

  Handle<WasmTableObject> table(
      WasmTableObject::cast(instance->tables().get(table_index)), isolate);

  uint32_t table_size = table->current_length();

  if (start > table_size) {
    return ThrowTableOutOfBounds(isolate, instance);
  }

  // Even when table.fill goes out-of-bounds, as many entries as possible are
  // put into the table. Only afterwards we trap.
  uint32_t fill_count = std::min(count, table_size - start);
  if (fill_count < count) {
    return ThrowTableOutOfBounds(isolate, instance);
  }
  WasmTableObject::Fill(isolate, table, start, value, fill_count);

  return ReadOnlyRoots(isolate).undefined_value();
}

RUNTIME_FUNCTION(Runtime_WasmDebugBreak) {
  ClearThreadInWasmScope flag_scope(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(0, args.length());
  FrameFinder<WasmFrame> frame_finder(
      isolate, {StackFrame::EXIT, StackFrame::WASM_DEBUG_BREAK});
  WasmFrame* frame = frame_finder.frame();
  auto instance = handle(frame->wasm_instance(), isolate);
  auto script = handle(instance->module_object().script(), isolate);
  auto* debug_info = instance->module_object().native_module()->GetDebugInfo();
  isolate->set_context(instance->native_context());

  // Stepping can repeatedly create code, and code GC requires stack guards to
  // be executed on all involved isolates. Proactively do this here.
  StackLimitCheck check(isolate);
  if (check.InterruptRequested()) {
    Object interrupt_object = isolate->stack_guard()->HandleInterrupts();
    // Interrupt handling can create an exception, including the
    // termination exception.
    if (interrupt_object.IsException(isolate)) return interrupt_object;
    DCHECK(interrupt_object.IsUndefined(isolate));
  }

  // Enter the debugger.
  DebugScope debug_scope(isolate->debug());
  bool paused_on_instrumentation = false;
  // Check for instrumentation breakpoint.
  DCHECK_EQ(script->break_on_entry(), !!instance->break_on_entry());
  if (script->break_on_entry()) {
    MaybeHandle<FixedArray> maybe_on_entry_breakpoints =
        WasmScript::CheckBreakPoints(isolate, script,
                                     WasmScript::kOnEntryBreakpointPosition,
                                     frame->id());
    script->set_break_on_entry(false);
    // Update the "break_on_entry" flag on all live instances.
    i::WeakArrayList weak_instance_list = script->wasm_weak_instance_list();
    for (int i = 0; i < weak_instance_list.length(); ++i) {
      if (weak_instance_list.Get(i)->IsCleared()) continue;
      i::WasmInstanceObject::cast(weak_instance_list.Get(i)->GetHeapObject())
          .set_break_on_entry(false);
    }
    DCHECK(!instance->break_on_entry());
    if (!maybe_on_entry_breakpoints.is_null()) {
      isolate->debug()->OnInstrumentationBreak();
      paused_on_instrumentation = true;
    }
  }

  if (debug_info->IsStepping(frame)) {
    debug_info->ClearStepping(isolate);
    StepAction step_action = isolate->debug()->last_step_action();
    isolate->debug()->ClearStepping();
    isolate->debug()->OnDebugBreak(isolate->factory()->empty_fixed_array(),
                                   step_action);
    return ReadOnlyRoots(isolate).undefined_value();
  }

  // Check whether we hit a breakpoint.
  Handle<FixedArray> breakpoints;
  if (WasmScript::CheckBreakPoints(isolate, script, frame->position(),
                                   frame->id())
          .ToHandle(&breakpoints)) {
    debug_info->ClearStepping(isolate);
    StepAction step_action = isolate->debug()->last_step_action();
    isolate->debug()->ClearStepping();
    if (isolate->debug()->break_points_active()) {
      // We hit one or several breakpoints. Notify the debug listeners.
      isolate->debug()->OnDebugBreak(breakpoints, step_action);
    }
    return ReadOnlyRoots(isolate).undefined_value();
  }

  // We only hit the instrumentation breakpoint, and there is no other reason to
  // break.
  if (paused_on_instrumentation) {
    return ReadOnlyRoots(isolate).undefined_value();
  }

  // We did not hit a breakpoint. If we are in stepping code, but the user did
  // not request stepping, clear this (to save further calls into this runtime
  // function).
  debug_info->ClearStepping(frame);

  return ReadOnlyRoots(isolate).undefined_value();
}

namespace {
inline void* ArrayElementAddress(Handle<WasmArray> array, uint32_t index,
                                 int element_size_bytes) {
  return reinterpret_cast<void*>(array->ptr() + WasmArray::kHeaderSize -
                                 kHeapObjectTag + index * element_size_bytes);
}
}  // namespace

// Assumes copy ranges are in-bounds and copy length > 0.
RUNTIME_FUNCTION(Runtime_WasmArrayCopy) {
  ClearThreadInWasmScope flag_scope(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(5, args.length());
  Handle<WasmArray> dst_array = args.at<WasmArray>(0);
  uint32_t dst_index = args.positive_smi_value_at(1);
  Handle<WasmArray> src_array = args.at<WasmArray>(2);
  uint32_t src_index = args.positive_smi_value_at(3);
  uint32_t length = args.positive_smi_value_at(4);
  DCHECK_GT(length, 0);
  bool overlapping_ranges =
      dst_array->ptr() == src_array->ptr() &&
      (dst_index < src_index ? dst_index + length > src_index
                             : src_index + length > dst_index);
  wasm::ValueType element_type = src_array->type()->element_type();
  if (element_type.is_reference()) {
    ObjectSlot dst_slot = dst_array->ElementSlot(dst_index);
    ObjectSlot src_slot = src_array->ElementSlot(src_index);
    if (overlapping_ranges) {
      isolate->heap()->MoveRange(*dst_array, dst_slot, src_slot, length,
                                 UPDATE_WRITE_BARRIER);
    } else {
      isolate->heap()->CopyRange(*dst_array, dst_slot, src_slot, length,
                                 UPDATE_WRITE_BARRIER);
    }
  } else {
    int element_size_bytes = element_type.value_kind_size();
    void* dst = ArrayElementAddress(dst_array, dst_index, element_size_bytes);
    void* src = ArrayElementAddress(src_array, src_index, element_size_bytes);
    size_t copy_size = length * element_size_bytes;
    if (overlapping_ranges) {
      MemMove(dst, src, copy_size);
    } else {
      MemCopy(dst, src, copy_size);
    }
  }
  return ReadOnlyRoots(isolate).undefined_value();
}

// Returns
// - the new array if the operation succeeds,
// - Smi(0) if the requested array length is too large,
// - Smi(1) if the data segment ran out-of-bounds.
RUNTIME_FUNCTION(Runtime_WasmArrayInitFromData) {
  ClearThreadInWasmScope flag_scope(isolate);
  HandleScope scope(isolate);
  DCHECK_EQ(5, args.length());
  Handle<WasmInstanceObject> instance = args.at<WasmInstanceObject>(0);
  uint32_t data_segment = args.positive_smi_value_at(1);
  uint32_t offset = args.positive_smi_value_at(2);
  uint32_t length = args.positive_smi_value_at(3);
  Handle<Map> rtt = args.at<Map>(4);
  uint32_t element_size = WasmArray::DecodeElementSizeFromMap(*rtt);
  uint32_t length_in_bytes = length * element_size;

  if (length > static_cast<uint32_t>(WasmArray::MaxLength(element_size))) {
    return Smi::FromInt(wasm::kArrayInitFromDataArrayTooLargeErrorCode);
  }
  // The check above implies no overflow.
  DCHECK_EQ(length_in_bytes / element_size, length);
  if (!base::IsInBounds<uint32_t>(
          offset, length_in_bytes,
          instance->data_segment_sizes()[data_segment])) {
    return Smi::FromInt(wasm::kArrayInitFromDataSegmentOutOfBoundsErrorCode);
  }

  Address source = instance->data_segment_starts()[data_segment] + offset;
  return *isolate->factory()->NewWasmArrayFromMemory(length, rtt, source);
}

namespace {
// Synchronize the stack limit with the active continuation for stack-switching.
// This can be done before or after changing the stack pointer itself, as long
// as we update both before the next stack check.
// {StackGuard::SetStackLimit} doesn't update the value of the jslimit if it
// 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) {
  DisallowGarbageCollection no_gc;
  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);
}
}  // namespace

// Allocate a new continuation, and prepare for stack switching by updating the
// active continuation, active suspender and stack limit.
RUNTIME_FUNCTION(Runtime_WasmAllocateContinuation) {
  CHECK(FLAG_experimental_wasm_stack_switching);
  HandleScope scope(isolate);
  Handle<WasmSuspenderObject> suspender = args.at<WasmSuspenderObject>(0);

  // Update the continuation state.
  auto parent =
      handle(WasmContinuationObject::cast(
                 *isolate->roots_table().slot(RootIndex::kActiveContinuation)),
             isolate);
  Handle<WasmContinuationObject> target =
      WasmContinuationObject::New(isolate, parent);
  auto target_stack =
      Managed<wasm::StackMemory>::cast(target->stack()).get().get();
  isolate->wasm_stacks()->Add(target_stack);
  isolate->roots_table().slot(RootIndex::kActiveContinuation).store(*target);

  // Update the suspender state.
  FullObjectSlot active_suspender_slot =
      isolate->roots_table().slot(RootIndex::kActiveSuspender);
  suspender->set_parent(HeapObject::cast(*active_suspender_slot));
  if (!(*active_suspender_slot).IsUndefined()) {
    WasmSuspenderObject::cast(*active_suspender_slot)
        .set_state(WasmSuspenderObject::Inactive);
  }
  suspender->set_state(WasmSuspenderObject::State::Active);
  suspender->set_continuation(*target);
  active_suspender_slot.store(*suspender);

  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);
  SyncStackLimit(isolate);
  return ReadOnlyRoots(isolate).undefined_value();
}

// Takes a promise and a suspender, and returns promise.then(onFulfilled), where
// onFulfilled resumes the suspender.
RUNTIME_FUNCTION(Runtime_WasmCreateResumePromise) {
  CHECK(FLAG_experimental_wasm_stack_switching);
  HandleScope scope(isolate);
  Handle<Object> promise = args.at(0);
  Handle<WasmSuspenderObject> suspender = args.at<WasmSuspenderObject>(1);

  i::Handle<i::Object> argv[] = {handle(suspender->resume(), isolate)};
  i::Handle<i::Object> result;
  bool has_pending_exception =
      !i::Execution::CallBuiltin(isolate, isolate->promise_then(), promise,
                                 arraysize(argv), argv)
           .ToHandle(&result);
  // TODO(thibaudm): Propagate exception.
  CHECK(!has_pending_exception);
  return *result;
}

}  // namespace internal
}  // namespace v8