src/debug/debug.cc

// Copyright 2012 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/debug/debug.h"

#include <memory>

#include "src/api.h"
#include "src/arguments.h"
#include "src/assembler-inl.h"
#include "src/bootstrapper.h"
#include "src/code-stubs.h"
#include "src/codegen.h"
#include "src/compilation-cache.h"
#include "src/compiler-dispatcher/optimizing-compile-dispatcher.h"
#include "src/compiler.h"
#include "src/debug/debug-evaluate.h"
#include "src/debug/liveedit.h"
#include "src/deoptimizer.h"
#include "src/execution.h"
#include "src/frames-inl.h"
#include "src/global-handles.h"
#include "src/globals.h"
#include "src/interpreter/interpreter.h"
#include "src/isolate-inl.h"
#include "src/log.h"
#include "src/messages.h"
#include "src/objects/debug-objects-inl.h"
#include "src/snapshot/natives.h"
#include "src/wasm/wasm-objects-inl.h"

#include "include/v8-debug.h"

namespace v8 {
namespace internal {

Debug::Debug(Isolate* isolate)
    : debug_context_(Handle<Context>()),
      is_active_(false),
      hook_on_function_call_(false),
      is_suppressed_(false),
      live_edit_enabled_(false),
      break_disabled_(false),
      break_points_active_(true),
      break_on_exception_(false),
      break_on_uncaught_exception_(false),
      side_effect_check_failed_(false),
      debug_info_list_(nullptr),
      feature_tracker_(isolate),
      isolate_(isolate) {
  ThreadInit();
}

BreakLocation BreakLocation::FromFrame(Handle<DebugInfo> debug_info,
                                       JavaScriptFrame* frame) {
  auto summary = FrameSummary::GetTop(frame).AsJavaScript();
  int offset = summary.code_offset();
  Handle<AbstractCode> abstract_code = summary.abstract_code();
  BreakIterator it(debug_info);
  it.SkipTo(BreakIndexFromCodeOffset(debug_info, abstract_code, offset));
  return it.GetBreakLocation();
}

void BreakLocation::AllAtCurrentStatement(
    Handle<DebugInfo> debug_info, JavaScriptFrame* frame,
    std::vector<BreakLocation>* result_out) {
  auto summary = FrameSummary::GetTop(frame).AsJavaScript();
  int offset = summary.code_offset();
  Handle<AbstractCode> abstract_code = summary.abstract_code();
  if (abstract_code->IsCode()) offset = offset - 1;
  int statement_position;
  {
    BreakIterator it(debug_info);
    it.SkipTo(BreakIndexFromCodeOffset(debug_info, abstract_code, offset));
    statement_position = it.statement_position();
  }
  for (BreakIterator it(debug_info); !it.Done(); it.Next()) {
    if (it.statement_position() == statement_position) {
      result_out->push_back(it.GetBreakLocation());
    }
  }
}

int BreakLocation::BreakIndexFromCodeOffset(Handle<DebugInfo> debug_info,
                                            Handle<AbstractCode> abstract_code,
                                            int offset) {
  // Run through all break points to locate the one closest to the address.
  int closest_break = 0;
  int distance = kMaxInt;
  DCHECK(0 <= offset && offset < abstract_code->Size());
  for (BreakIterator it(debug_info); !it.Done(); it.Next()) {
    // Check if this break point is closer that what was previously found.
    if (it.code_offset() <= offset && offset - it.code_offset() < distance) {
      closest_break = it.break_index();
      distance = offset - it.code_offset();
      // Check whether we can't get any closer.
      if (distance == 0) break;
    }
  }
  return closest_break;
}

bool BreakLocation::HasBreakPoint(Handle<DebugInfo> debug_info) const {
  // First check whether there is a break point with the same source position.
  if (!debug_info->HasBreakPoint(position_)) return false;
  // Then check whether a break point at that source position would have
  // the same code offset. Otherwise it's just a break location that we can
  // step to, but not actually a location where we can put a break point.
  DCHECK(abstract_code_->IsBytecodeArray());
  BreakIterator it(debug_info);
  it.SkipToPosition(position_);
  return it.code_offset() == code_offset_;
}

debug::BreakLocationType BreakLocation::type() const {
  switch (type_) {
    case DEBUGGER_STATEMENT:
      return debug::kDebuggerStatementBreakLocation;
    case DEBUG_BREAK_SLOT_AT_CALL:
      return debug::kCallBreakLocation;
    case DEBUG_BREAK_SLOT_AT_RETURN:
      return debug::kReturnBreakLocation;
    default:
      return debug::kCommonBreakLocation;
  }
  return debug::kCommonBreakLocation;
}

BreakIterator::BreakIterator(Handle<DebugInfo> debug_info)
    : debug_info_(debug_info),
      break_index_(-1),
      source_position_iterator_(
          debug_info->DebugBytecodeArray()->SourcePositionTable()) {
  position_ = debug_info->shared()->start_position();
  statement_position_ = position_;
  // There is at least one break location.
  DCHECK(!Done());
  Next();
}

int BreakIterator::BreakIndexFromPosition(int source_position) {
  int distance = kMaxInt;
  int closest_break = break_index();
  while (!Done()) {
    int next_position = position();
    if (source_position <= next_position &&
        next_position - source_position < distance) {
      closest_break = break_index();
      distance = next_position - source_position;
      // Check whether we can't get any closer.
      if (distance == 0) break;
    }
    Next();
  }
  return closest_break;
}

void BreakIterator::Next() {
  DisallowHeapAllocation no_gc;
  DCHECK(!Done());
  bool first = break_index_ == -1;
  while (!Done()) {
    if (!first) source_position_iterator_.Advance();
    first = false;
    if (Done()) return;
    position_ = source_position_iterator_.source_position().ScriptOffset();
    if (source_position_iterator_.is_statement()) {
      statement_position_ = position_;
    }
    DCHECK_LE(0, position_);
    DCHECK_LE(0, statement_position_);

    DebugBreakType type = GetDebugBreakType();
    if (type != NOT_DEBUG_BREAK) break;
  }
  break_index_++;
}

DebugBreakType BreakIterator::GetDebugBreakType() {
  BytecodeArray* bytecode_array = debug_info_->OriginalBytecodeArray();
  interpreter::Bytecode bytecode =
      interpreter::Bytecodes::FromByte(bytecode_array->get(code_offset()));

  if (bytecode == interpreter::Bytecode::kDebugger) {
    return DEBUGGER_STATEMENT;
  } else if (bytecode == interpreter::Bytecode::kReturn) {
    return DEBUG_BREAK_SLOT_AT_RETURN;
  } else if (interpreter::Bytecodes::IsCallOrConstruct(bytecode)) {
    return DEBUG_BREAK_SLOT_AT_CALL;
  } else if (source_position_iterator_.is_statement()) {
    return DEBUG_BREAK_SLOT;
  } else {
    return NOT_DEBUG_BREAK;
  }
}

void BreakIterator::SkipToPosition(int position) {
  BreakIterator it(debug_info_);
  SkipTo(it.BreakIndexFromPosition(position));
}

void BreakIterator::SetDebugBreak() {
  DebugBreakType debug_break_type = GetDebugBreakType();
  if (debug_break_type == DEBUGGER_STATEMENT) return;
  DCHECK(debug_break_type >= DEBUG_BREAK_SLOT);
  BytecodeArray* bytecode_array = debug_info_->DebugBytecodeArray();
  interpreter::Bytecode bytecode =
      interpreter::Bytecodes::FromByte(bytecode_array->get(code_offset()));
  if (interpreter::Bytecodes::IsDebugBreak(bytecode)) return;
  interpreter::Bytecode debugbreak =
      interpreter::Bytecodes::GetDebugBreak(bytecode);
  bytecode_array->set(code_offset(),
                      interpreter::Bytecodes::ToByte(debugbreak));
}

void BreakIterator::ClearDebugBreak() {
  DebugBreakType debug_break_type = GetDebugBreakType();
  if (debug_break_type == DEBUGGER_STATEMENT) return;
  DCHECK(debug_break_type >= DEBUG_BREAK_SLOT);
  BytecodeArray* bytecode_array = debug_info_->DebugBytecodeArray();
  BytecodeArray* original = debug_info_->OriginalBytecodeArray();
  bytecode_array->set(code_offset(), original->get(code_offset()));
}

BreakLocation BreakIterator::GetBreakLocation() {
  Handle<AbstractCode> code(
      AbstractCode::cast(debug_info_->DebugBytecodeArray()));
  return BreakLocation(code, GetDebugBreakType(), code_offset(), position_);
}


void DebugFeatureTracker::Track(DebugFeatureTracker::Feature feature) {
  uint32_t mask = 1 << feature;
  // Only count one sample per feature and isolate.
  if (bitfield_ & mask) return;
  isolate_->counters()->debug_feature_usage()->AddSample(feature);
  bitfield_ |= mask;
}


// Threading support.
void Debug::ThreadInit() {
  thread_local_.break_count_ = 0;
  thread_local_.break_id_ = 0;
  thread_local_.break_frame_id_ = StackFrame::NO_ID;
  thread_local_.last_step_action_ = StepNone;
  thread_local_.last_statement_position_ = kNoSourcePosition;
  thread_local_.last_frame_count_ = -1;
  thread_local_.fast_forward_to_return_ = false;
  thread_local_.ignore_step_into_function_ = Smi::kZero;
  thread_local_.target_frame_count_ = -1;
  thread_local_.return_value_ = Smi::kZero;
  thread_local_.async_task_count_ = 0;
  thread_local_.last_breakpoint_id_ = 0;
  clear_suspended_generator();
  thread_local_.restart_fp_ = nullptr;
  base::Relaxed_Store(&thread_local_.current_debug_scope_,
                      static_cast<base::AtomicWord>(0));
  UpdateHookOnFunctionCall();
}


char* Debug::ArchiveDebug(char* storage) {
  // Simply reset state. Don't archive anything.
  ThreadInit();
  return storage + ArchiveSpacePerThread();
}


char* Debug::RestoreDebug(char* storage) {
  // Simply reset state. Don't restore anything.
  ThreadInit();
  return storage + ArchiveSpacePerThread();
}

int Debug::ArchiveSpacePerThread() { return 0; }

void Debug::Iterate(RootVisitor* v) {
  v->VisitRootPointer(Root::kDebug, &thread_local_.return_value_);
  v->VisitRootPointer(Root::kDebug, &thread_local_.suspended_generator_);
  v->VisitRootPointer(Root::kDebug, &thread_local_.ignore_step_into_function_);
}

DebugInfoListNode::DebugInfoListNode(DebugInfo* debug_info) : next_(nullptr) {
  // Globalize the request debug info object and make it weak.
  GlobalHandles* global_handles = debug_info->GetIsolate()->global_handles();
  debug_info_ = global_handles->Create(debug_info).location();
}


DebugInfoListNode::~DebugInfoListNode() {
  if (debug_info_ == nullptr) return;
  GlobalHandles::Destroy(reinterpret_cast<Object**>(debug_info_));
  debug_info_ = nullptr;
}


bool Debug::Load() {
  // Return if debugger is already loaded.
  if (is_loaded()) return true;

  // Bail out if we're already in the process of compiling the native
  // JavaScript source code for the debugger.
  if (is_suppressed_) return false;
  SuppressDebug while_loading(this);

  // Disable breakpoints and interrupts while compiling and running the
  // debugger scripts including the context creation code.
  DisableBreak disable(this);
  PostponeInterruptsScope postpone(isolate_);

  // Create the debugger context.
  HandleScope scope(isolate_);
  ExtensionConfiguration no_extensions;
  // TODO(yangguo): we rely on the fact that first context snapshot is usable
  //                as debug context. This dependency is gone once we remove
  //                debug context completely.
  static const int kFirstContextSnapshotIndex = 0;
  Handle<Context> context = isolate_->bootstrapper()->CreateEnvironment(
      MaybeHandle<JSGlobalProxy>(), v8::Local<ObjectTemplate>(), &no_extensions,
      kFirstContextSnapshotIndex, v8::DeserializeEmbedderFieldsCallback(),
      DEBUG_CONTEXT);

  // Fail if no context could be created.
  if (context.is_null()) return false;

  debug_context_ = isolate_->global_handles()->Create(*context);

  feature_tracker()->Track(DebugFeatureTracker::kActive);

  return true;
}


void Debug::Unload() {
  ClearAllBreakPoints();
  ClearStepping();
  RemoveAllCoverageInfos();
  RemoveDebugDelegate();

  // Return debugger is not loaded.
  if (!is_loaded()) return;

  // Clear debugger context global handle.
  GlobalHandles::Destroy(Handle<Object>::cast(debug_context_).location());
  debug_context_ = Handle<Context>();
}

void Debug::Break(JavaScriptFrame* frame) {
  // Initialize LiveEdit.
  LiveEdit::InitializeThreadLocal(this);

  // Just continue if breaks are disabled or debugger cannot be loaded.
  if (break_disabled()) return;

  // Enter the debugger.
  DebugScope debug_scope(this);
  if (debug_scope.failed()) return;

  // Postpone interrupt during breakpoint processing.
  PostponeInterruptsScope postpone(isolate_);
  DisableBreak no_recursive_break(this);

  // Return if we fail to retrieve debug info.
  Handle<JSFunction> function(frame->function());
  Handle<SharedFunctionInfo> shared(function->shared());
  if (!EnsureBreakInfo(shared)) return;
  Handle<DebugInfo> debug_info(shared->GetDebugInfo(), isolate_);

  // Find the break location where execution has stopped.
  BreakLocation location = BreakLocation::FromFrame(debug_info, frame);

  // Find actual break points, if any, and trigger debug break event.
  MaybeHandle<FixedArray> break_points_hit =
      CheckBreakPoints(debug_info, &location);
  if (!break_points_hit.is_null()) {
    // Clear all current stepping setup.
    ClearStepping();
    // Notify the debug event listeners.
    OnDebugBreak(break_points_hit.ToHandleChecked());
    return;
  }

  // No break point. Check for stepping.
  StepAction step_action = last_step_action();
  int current_frame_count = CurrentFrameCount();
  int target_frame_count = thread_local_.target_frame_count_;
  int last_frame_count = thread_local_.last_frame_count_;

  // StepOut at not return position was requested and return break locations
  // were flooded with one shots.
  if (thread_local_.fast_forward_to_return_) {
    DCHECK(location.IsReturn());
    // We have to ignore recursive calls to function.
    if (current_frame_count > target_frame_count) return;
    ClearStepping();
    PrepareStep(StepOut);
    return;
  }

  bool step_break = false;
  switch (step_action) {
    case StepNone:
      return;
    case StepOut:
      // Step out should not break in a deeper frame than target frame.
      if (current_frame_count > target_frame_count) return;
      step_break = true;
      break;
    case StepNext:
      // Step next should not break in a deeper frame than target frame.
      if (current_frame_count > target_frame_count) return;
    // Fall through.
    case StepIn: {
      FrameSummary summary = FrameSummary::GetTop(frame);
      step_break = step_break || location.IsReturn() ||
                   current_frame_count != last_frame_count ||
                   thread_local_.last_statement_position_ !=
                       summary.SourceStatementPosition();
      break;
    }
  }

  // Clear all current stepping setup.
  ClearStepping();

  if (step_break) {
    // Notify the debug event listeners.
    OnDebugBreak(isolate_->factory()->empty_fixed_array());
  } else {
    // Re-prepare to continue.
    PrepareStep(step_action);
  }
}


// Find break point objects for this location, if any, and evaluate them.
// Return an array of break point objects that evaluated true, or an empty
// handle if none evaluated true.
MaybeHandle<FixedArray> Debug::CheckBreakPoints(Handle<DebugInfo> debug_info,
                                                BreakLocation* location,
                                                bool* has_break_points) {
  bool has_break_points_to_check =
      break_points_active_ && location->HasBreakPoint(debug_info);
  if (has_break_points) *has_break_points = has_break_points_to_check;
  if (!has_break_points_to_check) return {};

  Handle<Object> break_point_objects =
      debug_info->GetBreakPointObjects(location->position());
  return Debug::GetHitBreakPointObjects(break_point_objects);
}


bool Debug::IsMutedAtCurrentLocation(JavaScriptFrame* frame) {
  HandleScope scope(isolate_);
  // A break location is considered muted if break locations on the current
  // statement have at least one break point, and all of these break points
  // evaluate to false. Aside from not triggering a debug break event at the
  // break location, we also do not trigger one for debugger statements, nor
  // an exception event on exception at this location.
  FrameSummary summary = FrameSummary::GetTop(frame);
  DCHECK(!summary.IsWasm());
  Handle<JSFunction> function = summary.AsJavaScript().function();
  if (!function->shared()->HasBreakInfo()) return false;
  Handle<DebugInfo> debug_info(function->shared()->GetDebugInfo());
  // Enter the debugger.
  DebugScope debug_scope(this);
  if (debug_scope.failed()) return false;
  std::vector<BreakLocation> break_locations;
  BreakLocation::AllAtCurrentStatement(debug_info, frame, &break_locations);
  bool has_break_points_at_all = false;
  for (size_t i = 0; i < break_locations.size(); i++) {
    bool has_break_points;
    MaybeHandle<FixedArray> check_result =
        CheckBreakPoints(debug_info, &break_locations[i], &has_break_points);
    has_break_points_at_all |= has_break_points;
    if (has_break_points && !check_result.is_null()) return false;
  }
  return has_break_points_at_all;
}

MaybeHandle<Object> Debug::CallFunction(const char* name, int argc,
                                        Handle<Object> args[],
                                        bool catch_exceptions) {
  AllowJavascriptExecutionDebugOnly allow_script(isolate_);
  PostponeInterruptsScope no_interrupts(isolate_);
  AssertDebugContext();
  Handle<JSReceiver> holder =
      Handle<JSReceiver>::cast(isolate_->natives_utils_object());
  Handle<JSFunction> fun = Handle<JSFunction>::cast(
      JSReceiver::GetProperty(isolate_, holder, name).ToHandleChecked());
  Handle<Object> undefined = isolate_->factory()->undefined_value();
  if (catch_exceptions) {
    MaybeHandle<Object> maybe_exception;
    return Execution::TryCall(isolate_, fun, undefined, argc, args,
                              Execution::MessageHandling::kReport,
                              &maybe_exception);
  } else {
    return Execution::Call(isolate_, fun, undefined, argc, args);
  }
}


// Check whether a single break point object is triggered.
bool Debug::CheckBreakPoint(Handle<Object> break_point_object) {
  Factory* factory = isolate_->factory();
  HandleScope scope(isolate_);

  // TODO(kozyatinskiy): replace this if by DCHEK once the JS debug API has been
  // removed.
  if (break_point_object->IsBreakPoint()) {
    Handle<BreakPoint> break_point =
        Handle<BreakPoint>::cast(break_point_object);
    if (!break_point->condition()->length()) return true;
    Handle<String> condition(break_point->condition());
    Handle<Object> result;
    // Since we call CheckBreakpoint only for deoptimized frame on top of stack,
    // we can use 0 as index of inlined frame.
    if (!DebugEvaluate::Local(isolate_, break_frame_id(),
                              /* inlined_jsframe_index */ 0, condition, false)
             .ToHandle(&result)) {
      if (isolate_->has_pending_exception()) {
        isolate_->clear_pending_exception();
      }
      return false;
    }
    return result->BooleanValue();
  }

  // Ignore check if break point object is not a JSObject.
  if (!break_point_object->IsJSObject()) return true;

  // Get the break id as an object.
  Handle<Object> break_id = factory->NewNumberFromInt(Debug::break_id());

  // Call IsBreakPointTriggered.
  Handle<Object> argv[] = { break_id, break_point_object };
  Handle<Object> result;
  if (!CallFunction("IsBreakPointTriggered", arraysize(argv), argv)
           .ToHandle(&result)) {
    return false;
  }

  // Return whether the break point is triggered.
  return result->IsTrue(isolate_);
}


bool Debug::SetBreakPoint(Handle<JSFunction> function,
                          Handle<Object> break_point_object,
                          int* source_position) {
  HandleScope scope(isolate_);

  // Make sure the function is compiled and has set up the debug info.
  Handle<SharedFunctionInfo> shared(function->shared());
  if (!EnsureBreakInfo(shared)) return true;
  PrepareFunctionForBreakPoints(shared);
  Handle<DebugInfo> debug_info(shared->GetDebugInfo());
  // Source positions starts with zero.
  DCHECK_LE(0, *source_position);

  // Find the break point and change it.
  *source_position = FindBreakablePosition(debug_info, *source_position);
  DebugInfo::SetBreakPoint(debug_info, *source_position, break_point_object);
  // At least one active break point now.
  DCHECK_LT(0, debug_info->GetBreakPointCount());

  ClearBreakPoints(debug_info);
  ApplyBreakPoints(debug_info);

  feature_tracker()->Track(DebugFeatureTracker::kBreakPoint);
  return true;
}

bool Debug::SetBreakPointForScript(Handle<Script> script,
                                   Handle<Object> break_point_object,
                                   int* source_position) {
  if (script->type() == Script::TYPE_WASM) {
    Handle<WasmCompiledModule> compiled_module(
        WasmCompiledModule::cast(script->wasm_compiled_module()), isolate_);
    return WasmCompiledModule::SetBreakPoint(compiled_module, source_position,
                                             break_point_object);
  }

  HandleScope scope(isolate_);

  // Obtain shared function info for the function.
  Handle<Object> result =
      FindSharedFunctionInfoInScript(script, *source_position);
  if (result->IsUndefined(isolate_)) return false;

  // Make sure the function has set up the debug info.
  Handle<SharedFunctionInfo> shared = Handle<SharedFunctionInfo>::cast(result);
  if (!EnsureBreakInfo(shared)) return false;
  PrepareFunctionForBreakPoints(shared);

  // Find position within function. The script position might be before the
  // source position of the first function.
  if (shared->start_position() > *source_position) {
    *source_position = shared->start_position();
  }

  Handle<DebugInfo> debug_info(shared->GetDebugInfo());

  // Find breakable position returns first breakable position after
  // *source_position, it can return 0 if no break location is found after
  // *source_position.
  int breakable_position = FindBreakablePosition(debug_info, *source_position);
  if (breakable_position < *source_position) return false;
  *source_position = breakable_position;

  DebugInfo::SetBreakPoint(debug_info, *source_position, break_point_object);
  // At least one active break point now.
  DCHECK_LT(0, debug_info->GetBreakPointCount());

  ClearBreakPoints(debug_info);
  ApplyBreakPoints(debug_info);

  feature_tracker()->Track(DebugFeatureTracker::kBreakPoint);
  return true;
}

int Debug::FindBreakablePosition(Handle<DebugInfo> debug_info,
                                 int source_position) {
  DCHECK(debug_info->HasDebugBytecodeArray());
  BreakIterator it(debug_info);
  it.SkipToPosition(source_position);
  return it.position();
}

void Debug::ApplyBreakPoints(Handle<DebugInfo> debug_info) {
  DisallowHeapAllocation no_gc;
  if (debug_info->break_points()->IsUndefined(isolate_)) return;
  FixedArray* break_points = debug_info->break_points();
  for (int i = 0; i < break_points->length(); i++) {
    if (break_points->get(i)->IsUndefined(isolate_)) continue;
    BreakPointInfo* info = BreakPointInfo::cast(break_points->get(i));
    if (info->GetBreakPointCount() == 0) continue;
    DCHECK(debug_info->HasDebugBytecodeArray());
    BreakIterator it(debug_info);
    it.SkipToPosition(info->source_position());
    it.SetDebugBreak();
  }
}

void Debug::ClearBreakPoints(Handle<DebugInfo> debug_info) {
  // If we attempt to clear breakpoints but none exist, simply return. This can
  // happen e.g. CoverageInfos exit but no breakpoints are set.
  if (!debug_info->HasDebugBytecodeArray()) return;

  DisallowHeapAllocation no_gc;
  for (BreakIterator it(debug_info); !it.Done(); it.Next()) {
    it.ClearDebugBreak();
  }
}

void Debug::ClearBreakPoint(Handle<Object> break_point_object) {
  HandleScope scope(isolate_);

  for (DebugInfoListNode* node = debug_info_list_; node != nullptr;
       node = node->next()) {
    Handle<Object> result =
        DebugInfo::FindBreakPointInfo(node->debug_info(), break_point_object);
    if (result->IsUndefined(isolate_)) continue;
    Handle<DebugInfo> debug_info = node->debug_info();
    if (DebugInfo::ClearBreakPoint(debug_info, break_point_object)) {
      ClearBreakPoints(debug_info);
      if (debug_info->GetBreakPointCount() == 0) {
        RemoveBreakInfoAndMaybeFree(debug_info);
      } else {
        ApplyBreakPoints(debug_info);
      }
      return;
    }
  }
}

bool Debug::SetBreakpoint(Handle<Script> script, Handle<String> condition,
                          int* offset, int* id) {
  *id = ++thread_local_.last_breakpoint_id_;
  Handle<BreakPoint> breakpoint =
      isolate_->factory()->NewBreakPoint(*id, condition);
  return SetBreakPointForScript(script, breakpoint, offset);
}

void Debug::RemoveBreakpoint(int id) {
  Handle<BreakPoint> breakpoint = isolate_->factory()->NewBreakPoint(
      id, isolate_->factory()->empty_string());
  ClearBreakPoint(breakpoint);
}

// Clear out all the debug break code.
void Debug::ClearAllBreakPoints() {
  ClearAllDebugInfos([=](Handle<DebugInfo> info) {
    ClearBreakPoints(info);
    return info->ClearBreakInfo();
  });
}

void Debug::FloodWithOneShot(Handle<SharedFunctionInfo> shared,
                             bool returns_only) {
  if (IsBlackboxed(shared)) return;
  // Make sure the function is compiled and has set up the debug info.
  if (!EnsureBreakInfo(shared)) return;
  PrepareFunctionForBreakPoints(shared);
  Handle<DebugInfo> debug_info(shared->GetDebugInfo());
  // Flood the function with break points.
  DCHECK(debug_info->HasDebugBytecodeArray());
  for (BreakIterator it(debug_info); !it.Done(); it.Next()) {
    if (returns_only && !it.GetBreakLocation().IsReturn()) continue;
    it.SetDebugBreak();
  }
}

void Debug::ChangeBreakOnException(ExceptionBreakType type, bool enable) {
  if (type == BreakUncaughtException) {
    break_on_uncaught_exception_ = enable;
  } else {
    break_on_exception_ = enable;
  }
}


bool Debug::IsBreakOnException(ExceptionBreakType type) {
  if (type == BreakUncaughtException) {
    return break_on_uncaught_exception_;
  } else {
    return break_on_exception_;
  }
}

MaybeHandle<FixedArray> Debug::GetHitBreakPointObjects(
    Handle<Object> break_point_objects) {
  DCHECK(!break_point_objects->IsUndefined(isolate_));
  if (!break_point_objects->IsFixedArray()) {
    if (!CheckBreakPoint(break_point_objects)) return {};
    Handle<FixedArray> break_points_hit = isolate_->factory()->NewFixedArray(1);
    break_points_hit->set(0, *break_point_objects);
    return break_points_hit;
  }

  Handle<FixedArray> array(FixedArray::cast(*break_point_objects));
  int num_objects = array->length();
  Handle<FixedArray> break_points_hit =
      isolate_->factory()->NewFixedArray(num_objects);
  int break_points_hit_count = 0;
  for (int i = 0; i < num_objects; ++i) {
    Handle<Object> break_point_object(array->get(i), isolate_);
    if (CheckBreakPoint(break_point_object)) {
      break_points_hit->set(break_points_hit_count++, *break_point_object);
    }
  }
  if (break_points_hit_count == 0) return {};
  break_points_hit->Shrink(break_points_hit_count);
  return break_points_hit;
}

void Debug::PrepareStepIn(Handle<JSFunction> function) {
  CHECK(last_step_action() >= StepIn);
  if (ignore_events()) return;
  if (in_debug_scope()) return;
  if (break_disabled()) return;
  Handle<SharedFunctionInfo> shared(function->shared());
  if (IsBlackboxed(shared)) return;
  if (*function == thread_local_.ignore_step_into_function_) return;
  thread_local_.ignore_step_into_function_ = Smi::kZero;
  FloodWithOneShot(Handle<SharedFunctionInfo>(function->shared(), isolate_));
}

void Debug::PrepareStepInSuspendedGenerator() {
  CHECK(has_suspended_generator());
  if (ignore_events()) return;
  if (in_debug_scope()) return;
  if (break_disabled()) return;
  thread_local_.last_step_action_ = StepIn;
  UpdateHookOnFunctionCall();
  Handle<JSFunction> function(
      JSGeneratorObject::cast(thread_local_.suspended_generator_)->function());
  FloodWithOneShot(Handle<SharedFunctionInfo>(function->shared(), isolate_));
  clear_suspended_generator();
}

void Debug::PrepareStepOnThrow() {
  if (last_step_action() == StepNone) return;
  if (ignore_events()) return;
  if (in_debug_scope()) return;
  if (break_disabled()) return;

  ClearOneShot();

  int current_frame_count = CurrentFrameCount();

  // Iterate through the JavaScript stack looking for handlers.
  JavaScriptFrameIterator it(isolate_);
  while (!it.done()) {
    JavaScriptFrame* frame = it.frame();
    if (frame->LookupExceptionHandlerInTable(nullptr, nullptr) > 0) break;
    std::vector<SharedFunctionInfo*> infos;
    frame->GetFunctions(&infos);
    current_frame_count -= infos.size();
    it.Advance();
  }

  // No handler found. Nothing to instrument.
  if (it.done()) return;

  bool found_handler = false;
  // Iterate frames, including inlined frames. First, find the handler frame.
  // Then skip to the frame we want to break in, then instrument for stepping.
  for (; !it.done(); it.Advance()) {
    JavaScriptFrame* frame = JavaScriptFrame::cast(it.frame());
    if (last_step_action() == StepIn) {
      // Deoptimize frame to ensure calls are checked for step-in.
      Deoptimizer::DeoptimizeFunction(frame->function());
    }
    std::vector<FrameSummary> summaries;
    frame->Summarize(&summaries);
    for (size_t i = summaries.size(); i != 0; i--, current_frame_count--) {
      const FrameSummary& summary = summaries[i - 1];
      if (!found_handler) {
        // We have yet to find the handler. If the frame inlines multiple
        // functions, we have to check each one for the handler.
        // If it only contains one function, we already found the handler.
        if (summaries.size() > 1) {
          Handle<AbstractCode> code = summary.AsJavaScript().abstract_code();
          CHECK_EQ(AbstractCode::INTERPRETED_FUNCTION, code->kind());
          BytecodeArray* bytecode = code->GetBytecodeArray();
          HandlerTable* table = HandlerTable::cast(bytecode->handler_table());
          int code_offset = summary.code_offset();
          HandlerTable::CatchPrediction prediction;
          int index = table->LookupRange(code_offset, nullptr, &prediction);
          if (index > 0) found_handler = true;
        } else {
          found_handler = true;
        }
      }

      if (found_handler) {
        // We found the handler. If we are stepping next or out, we need to
        // iterate until we found the suitable target frame to break in.
        if ((last_step_action() == StepNext || last_step_action() == StepOut) &&
            current_frame_count > thread_local_.target_frame_count_) {
          continue;
        }
        Handle<SharedFunctionInfo> info(
            summary.AsJavaScript().function()->shared());
        if (IsBlackboxed(info)) continue;
        FloodWithOneShot(info);
        return;
      }
    }
  }
}


void Debug::PrepareStep(StepAction step_action) {
  HandleScope scope(isolate_);

  DCHECK(in_debug_scope());

  // Get the frame where the execution has stopped and skip the debug frame if
  // any. The debug frame will only be present if execution was stopped due to
  // hitting a break point. In other situations (e.g. unhandled exception) the
  // debug frame is not present.
  StackFrame::Id frame_id = break_frame_id();
  // If there is no JavaScript stack don't do anything.
  if (frame_id == StackFrame::NO_ID) return;

  feature_tracker()->Track(DebugFeatureTracker::kStepping);

  thread_local_.last_step_action_ = step_action;

  StackTraceFrameIterator frames_it(isolate_, frame_id);
  StandardFrame* frame = frames_it.frame();

  // Handle stepping in wasm functions via the wasm interpreter.
  if (frame->is_wasm()) {
    // If the top frame is compiled, we cannot step.
    if (frame->is_wasm_compiled()) return;
    WasmInterpreterEntryFrame* wasm_frame =
        WasmInterpreterEntryFrame::cast(frame);
    wasm_frame->wasm_instance()->debug_info()->PrepareStep(step_action);
    return;
  }

  JavaScriptFrame* js_frame = JavaScriptFrame::cast(frame);
  DCHECK(js_frame->function()->IsJSFunction());

  // Get the debug info (create it if it does not exist).
  auto summary = FrameSummary::GetTop(frame).AsJavaScript();
  Handle<JSFunction> function(summary.function());
  Handle<SharedFunctionInfo> shared(function->shared());
  if (!EnsureBreakInfo(shared)) return;
  Handle<DebugInfo> debug_info(shared->GetDebugInfo());

  BreakLocation location = BreakLocation::FromFrame(debug_info, js_frame);

  // Any step at a return is a step-out and we need to schedule DebugOnFunction
  // call callback.
  if (location.IsReturn()) {
    // On StepOut we'll ignore our further calls to current function in
    // PrepareStepIn callback.
    if (last_step_action() == StepOut) {
      thread_local_.ignore_step_into_function_ = *function;
    }
    step_action = StepOut;
    thread_local_.last_step_action_ = StepIn;
  }
  UpdateHookOnFunctionCall();

  // A step-next in blackboxed function is a step-out.
  if (step_action == StepNext && IsBlackboxed(shared)) step_action = StepOut;

  thread_local_.last_statement_position_ =
      summary.abstract_code()->SourceStatementPosition(summary.code_offset());
  int current_frame_count = CurrentFrameCount();
  thread_local_.last_frame_count_ = current_frame_count;
  // No longer perform the current async step.
  clear_suspended_generator();

  switch (step_action) {
    case StepNone:
      UNREACHABLE();
      break;
    case StepOut: {
      // Clear last position info. For stepping out it does not matter.
      thread_local_.last_statement_position_ = kNoSourcePosition;
      thread_local_.last_frame_count_ = -1;
      if (!location.IsReturn() && !IsBlackboxed(shared)) {
        // At not return position we flood return positions with one shots and
        // will repeat StepOut automatically at next break.
        thread_local_.target_frame_count_ = current_frame_count;
        thread_local_.fast_forward_to_return_ = true;
        FloodWithOneShot(shared, true);
        return;
      }
      // Skip the current frame, find the first frame we want to step out to
      // and deoptimize every frame along the way.
      bool in_current_frame = true;
      for (; !frames_it.done(); frames_it.Advance()) {
        // TODO(clemensh): Implement stepping out from JS to wasm.
        if (frames_it.frame()->is_wasm()) continue;
        JavaScriptFrame* frame = JavaScriptFrame::cast(frames_it.frame());
        if (last_step_action() == StepIn) {
          // Deoptimize frame to ensure calls are checked for step-in.
          Deoptimizer::DeoptimizeFunction(frame->function());
        }
        HandleScope scope(isolate_);
        std::vector<Handle<SharedFunctionInfo>> infos;
        frame->GetFunctions(&infos);
        for (; !infos.empty(); current_frame_count--) {
          Handle<SharedFunctionInfo> info = infos.back();
          infos.pop_back();
          if (in_current_frame) {
            // We want to skip out, so skip the current frame.
            in_current_frame = false;
            continue;
          }
          if (IsBlackboxed(info)) continue;
          FloodWithOneShot(info);
          thread_local_.target_frame_count_ = current_frame_count;
          return;
        }
      }
      break;
    }
    case StepNext:
      thread_local_.target_frame_count_ = current_frame_count;
    // Fall through.
    case StepIn:
      // TODO(clemensh): Implement stepping from JS into wasm.
      FloodWithOneShot(shared);
      break;
  }
}

// Simple function for returning the source positions for active break points.
Handle<Object> Debug::GetSourceBreakLocations(
    Handle<SharedFunctionInfo> shared) {
  Isolate* isolate = shared->GetIsolate();
  if (!shared->HasBreakInfo()) {
    return isolate->factory()->undefined_value();
  }
  Handle<DebugInfo> debug_info(shared->GetDebugInfo());
  if (debug_info->GetBreakPointCount() == 0) {
    return isolate->factory()->undefined_value();
  }
  Handle<FixedArray> locations =
      isolate->factory()->NewFixedArray(debug_info->GetBreakPointCount());
  int count = 0;
  for (int i = 0; i < debug_info->break_points()->length(); ++i) {
    if (!debug_info->break_points()->get(i)->IsUndefined(isolate)) {
      BreakPointInfo* break_point_info =
          BreakPointInfo::cast(debug_info->break_points()->get(i));
      int break_points = break_point_info->GetBreakPointCount();
      if (break_points == 0) continue;
      for (int j = 0; j < break_points; ++j) {
        locations->set(count++,
                       Smi::FromInt(break_point_info->source_position()));
      }
    }
  }
  return locations;
}

void Debug::ClearStepping() {
  // Clear the various stepping setup.
  ClearOneShot();

  thread_local_.last_step_action_ = StepNone;
  thread_local_.last_statement_position_ = kNoSourcePosition;
  thread_local_.ignore_step_into_function_ = Smi::kZero;
  thread_local_.fast_forward_to_return_ = false;
  thread_local_.last_frame_count_ = -1;
  thread_local_.target_frame_count_ = -1;
  UpdateHookOnFunctionCall();
}


// Clears all the one-shot break points that are currently set. Normally this
// function is called each time a break point is hit as one shot break points
// are used to support stepping.
void Debug::ClearOneShot() {
  // The current implementation just runs through all the breakpoints. When the
  // last break point for a function is removed that function is automatically
  // removed from the list.
  for (DebugInfoListNode* node = debug_info_list_; node != nullptr;
       node = node->next()) {
    Handle<DebugInfo> debug_info = node->debug_info();
    ClearBreakPoints(debug_info);
    ApplyBreakPoints(debug_info);
  }
}

class RedirectActiveFunctions : public ThreadVisitor {
 public:
  explicit RedirectActiveFunctions(SharedFunctionInfo* shared)
      : shared_(shared) {
    DCHECK(shared->HasBytecodeArray());
  }

  void VisitThread(Isolate* isolate, ThreadLocalTop* top) {
    for (JavaScriptFrameIterator it(isolate, top); !it.done(); it.Advance()) {
      JavaScriptFrame* frame = it.frame();
      JSFunction* function = frame->function();
      if (!frame->is_interpreted()) continue;
      if (function->shared() != shared_) continue;
      InterpretedFrame* interpreted_frame =
          reinterpret_cast<InterpretedFrame*>(frame);
      BytecodeArray* debug_copy = shared_->GetDebugInfo()->DebugBytecodeArray();
      interpreted_frame->PatchBytecodeArray(debug_copy);
    }
  }

 private:
  SharedFunctionInfo* shared_;
  DisallowHeapAllocation no_gc_;
};

void Debug::DeoptimizeFunction(Handle<SharedFunctionInfo> shared) {
  // Deoptimize all code compiled from this shared function info including
  // inlining.
  if (isolate_->concurrent_recompilation_enabled()) {
    isolate_->optimizing_compile_dispatcher()->Flush(
        OptimizingCompileDispatcher::BlockingBehavior::kBlock);
  }

  // Make sure we abort incremental marking.
  isolate_->heap()->CollectAllGarbage(Heap::kMakeHeapIterableMask,
                                      GarbageCollectionReason::kDebugger);

  bool found_something = false;
  Code::OptimizedCodeIterator iterator(isolate_);
  while (Code* code = iterator.Next()) {
    if (code->Inlines(*shared)) {
      code->set_marked_for_deoptimization(true);
      found_something = true;
    }
  }

  if (found_something) {
    // Only go through with the deoptimization if something was found.
    Deoptimizer::DeoptimizeMarkedCode(isolate_);
  }
}

void Debug::PrepareFunctionForBreakPoints(Handle<SharedFunctionInfo> shared) {
  // To prepare bytecode for debugging, we already need to have the debug
  // info (containing the debug copy) upfront, but since we do not recompile,
  // preparing for break points cannot fail.
  DCHECK(shared->is_compiled());
  DCHECK(shared->HasDebugInfo());
  DCHECK(shared->HasBreakInfo());
  Handle<DebugInfo> debug_info = GetOrCreateDebugInfo(shared);
  if (debug_info->IsPreparedForBreakpoints()) return;

  DeoptimizeFunction(shared);
  // Update PCs on the stack to point to recompiled code.
  RedirectActiveFunctions redirect_visitor(*shared);
  redirect_visitor.VisitThread(isolate_, isolate_->thread_local_top());
  isolate_->thread_manager()->IterateArchivedThreads(&redirect_visitor);

  debug_info->set_flags(debug_info->flags() |
                        DebugInfo::kPreparedForBreakpoints);
}

namespace {
template <typename Iterator>
void GetBreakablePositions(Iterator* it, int start_position, int end_position,
                           std::vector<BreakLocation>* locations) {
  while (!it->Done()) {
    if (it->position() >= start_position && it->position() < end_position) {
      locations->push_back(it->GetBreakLocation());
    }
    it->Next();
  }
}

void FindBreakablePositions(Handle<DebugInfo> debug_info, int start_position,
                            int end_position,
                            std::vector<BreakLocation>* locations) {
  DCHECK(debug_info->HasDebugBytecodeArray());
  BreakIterator it(debug_info);
  GetBreakablePositions(&it, start_position, end_position, locations);
}
}  // namespace

bool Debug::GetPossibleBreakpoints(Handle<Script> script, int start_position,
                                   int end_position, bool restrict_to_function,
                                   std::vector<BreakLocation>* locations) {
  if (restrict_to_function) {
    Handle<Object> result =
        FindSharedFunctionInfoInScript(script, start_position);
    if (result->IsUndefined(isolate_)) return false;

    // Make sure the function has set up the debug info.
    Handle<SharedFunctionInfo> shared =
        Handle<SharedFunctionInfo>::cast(result);
    if (!EnsureBreakInfo(shared)) return false;

    Handle<DebugInfo> debug_info(shared->GetDebugInfo());
    FindBreakablePositions(debug_info, start_position, end_position, locations);
    return true;
  }

  while (true) {
    HandleScope scope(isolate_);
    std::vector<Handle<SharedFunctionInfo>> candidates;
    SharedFunctionInfo::ScriptIterator iterator(script);
    for (SharedFunctionInfo* info = iterator.Next(); info != nullptr;
         info = iterator.Next()) {
      if (info->end_position() < start_position ||
          info->start_position() >= end_position) {
        continue;
      }
      if (!info->IsSubjectToDebugging()) continue;
      if (!info->is_compiled() && !info->allows_lazy_compilation()) continue;
      candidates.push_back(i::handle(info));
    }

    bool was_compiled = false;
    for (const auto& candidate : candidates) {
      // Code that cannot be compiled lazily are internal and not debuggable.
      DCHECK(candidate->allows_lazy_compilation());
      if (!candidate->is_compiled()) {
        if (!Compiler::Compile(candidate, Compiler::CLEAR_EXCEPTION)) {
          return false;
        } else {
          was_compiled = true;
        }
      }
      if (!EnsureBreakInfo(candidate)) return false;
    }
    if (was_compiled) continue;

    for (const auto& candidate : candidates) {
      CHECK(candidate->HasBreakInfo());
      Handle<DebugInfo> debug_info(candidate->GetDebugInfo());
      FindBreakablePositions(debug_info, start_position, end_position,
                             locations);
    }
    return true;
  }
  UNREACHABLE();
}

void Debug::RecordGenerator(Handle<JSGeneratorObject> generator_object) {
  if (last_step_action() <= StepOut) return;

  if (last_step_action() == StepNext) {
    // Only consider this generator a step-next target if not stepping in.
    if (thread_local_.target_frame_count_ < CurrentFrameCount()) return;
  }

  DCHECK(!has_suspended_generator());
  thread_local_.suspended_generator_ = *generator_object;
  ClearStepping();
}

class SharedFunctionInfoFinder {
 public:
  explicit SharedFunctionInfoFinder(int target_position)
      : current_candidate_(nullptr),
        current_candidate_closure_(nullptr),
        current_start_position_(kNoSourcePosition),
        target_position_(target_position) {}

  void NewCandidate(SharedFunctionInfo* shared, JSFunction* closure = nullptr) {
    if (!shared->IsSubjectToDebugging()) return;
    int start_position = shared->function_token_position();
    if (start_position == kNoSourcePosition) {
      start_position = shared->start_position();
    }

    if (start_position > target_position_) return;
    if (target_position_ > shared->end_position()) return;

    if (current_candidate_ != nullptr) {
      if (current_start_position_ == start_position &&
          shared->end_position() == current_candidate_->end_position()) {
        // If we already have a matching closure, do not throw it away.
        if (current_candidate_closure_ != nullptr && closure == nullptr) return;
        // If a top-level function contains only one function
        // declaration the source for the top-level and the function
        // is the same. In that case prefer the non top-level function.
        if (!current_candidate_->is_toplevel() && shared->is_toplevel()) return;
      } else if (start_position < current_start_position_ ||
                 current_candidate_->end_position() < shared->end_position()) {
        return;
      }
    }

    current_start_position_ = start_position;
    current_candidate_ = shared;
    current_candidate_closure_ = closure;
  }

  SharedFunctionInfo* Result() { return current_candidate_; }

  JSFunction* ResultClosure() { return current_candidate_closure_; }

 private:
  SharedFunctionInfo* current_candidate_;
  JSFunction* current_candidate_closure_;
  int current_start_position_;
  int target_position_;
  DisallowHeapAllocation no_gc_;
};


// We need to find a SFI for a literal that may not yet have been compiled yet,
// and there may not be a JSFunction referencing it. Find the SFI closest to
// the given position, compile it to reveal possible inner SFIs and repeat.
// While we are at this, also ensure code with debug break slots so that we do
// not have to compile a SFI without JSFunction, which is paifu for those that
// cannot be compiled without context (need to find outer compilable SFI etc.)
Handle<Object> Debug::FindSharedFunctionInfoInScript(Handle<Script> script,
                                                     int position) {
  for (int iteration = 0;; iteration++) {
    // Go through all shared function infos associated with this script to
    // find the inner most function containing this position.
    // If there is no shared function info for this script at all, there is
    // no point in looking for it by walking the heap.

    SharedFunctionInfo* shared;
    {
      SharedFunctionInfoFinder finder(position);
      SharedFunctionInfo::ScriptIterator iterator(script);
      for (SharedFunctionInfo* info = iterator.Next(); info != nullptr;
           info = iterator.Next()) {
        finder.NewCandidate(info);
      }
      shared = finder.Result();
      if (shared == nullptr) break;
      // We found it if it's already compiled.
      if (shared->is_compiled()) {
        Handle<SharedFunctionInfo> shared_handle(shared);
        // If the iteration count is larger than 1, we had to compile the outer
        // function in order to create this shared function info. So there can
        // be no JSFunction referencing it. We can anticipate creating a debug
        // info while bypassing PrepareFunctionForBreakpoints.
        if (iteration > 1) {
          AllowHeapAllocation allow_before_return;
          CreateBreakInfo(shared_handle);
        }
        return shared_handle;
      }
    }
    // If not, compile to reveal inner functions.
    HandleScope scope(isolate_);
    // Code that cannot be compiled lazily are internal and not debuggable.
    DCHECK(shared->allows_lazy_compilation());
    if (!Compiler::Compile(handle(shared), Compiler::CLEAR_EXCEPTION)) break;
  }
  return isolate_->factory()->undefined_value();
}


// Ensures the debug information is present for shared.
bool Debug::EnsureBreakInfo(Handle<SharedFunctionInfo> shared) {
  // Return if we already have the break info for shared.
  if (shared->HasBreakInfo()) return true;
  if (!shared->IsSubjectToDebugging()) return false;
  if (!shared->is_compiled() &&
      !Compiler::Compile(shared, Compiler::CLEAR_EXCEPTION)) {
    return false;
  }
  CreateBreakInfo(shared);
  return true;
}

void Debug::CreateBreakInfo(Handle<SharedFunctionInfo> shared) {
  HandleScope scope(isolate_);
  Handle<DebugInfo> debug_info = GetOrCreateDebugInfo(shared);

  // Initialize with break information.

  DCHECK(!debug_info->HasBreakInfo());

  Factory* factory = isolate_->factory();
  Handle<FixedArray> break_points(
      factory->NewFixedArray(DebugInfo::kEstimatedNofBreakPointsInFunction));

  // Make a copy of the bytecode array if available.
  Handle<Object> maybe_debug_bytecode_array = factory->undefined_value();
  if (shared->HasBytecodeArray()) {
    Handle<BytecodeArray> original(shared->bytecode_array());
    maybe_debug_bytecode_array = factory->CopyBytecodeArray(original);
  }

  debug_info->set_flags(debug_info->flags() | DebugInfo::kHasBreakInfo);
  debug_info->set_debug_bytecode_array(*maybe_debug_bytecode_array);
  debug_info->set_break_points(*break_points);
}

Handle<DebugInfo> Debug::GetOrCreateDebugInfo(
    Handle<SharedFunctionInfo> shared) {
  if (shared->HasDebugInfo()) return handle(shared->GetDebugInfo());

  // Create debug info and add it to the list.
  Handle<DebugInfo> debug_info = isolate_->factory()->NewDebugInfo(shared);
  DebugInfoListNode* node = new DebugInfoListNode(*debug_info);
  node->set_next(debug_info_list_);
  debug_info_list_ = node;

  return debug_info;
}

void Debug::InstallCoverageInfo(Handle<SharedFunctionInfo> shared,
                                Handle<CoverageInfo> coverage_info) {
  DCHECK(!coverage_info.is_null());

  Handle<DebugInfo> debug_info = GetOrCreateDebugInfo(shared);

  DCHECK(!debug_info->HasCoverageInfo());

  debug_info->set_flags(debug_info->flags() | DebugInfo::kHasCoverageInfo);
  debug_info->set_coverage_info(*coverage_info);
}

void Debug::RemoveAllCoverageInfos() {
  ClearAllDebugInfos(
      [=](Handle<DebugInfo> info) { return info->ClearCoverageInfo(); });
}

void Debug::FindDebugInfo(Handle<DebugInfo> debug_info,
                          DebugInfoListNode** prev, DebugInfoListNode** curr) {
  HandleScope scope(isolate_);
  *prev = nullptr;
  *curr = debug_info_list_;
  while (*curr != nullptr) {
    if ((*curr)->debug_info().is_identical_to(debug_info)) return;
    *prev = *curr;
    *curr = (*curr)->next();
  }

  UNREACHABLE();
}

void Debug::ClearAllDebugInfos(DebugInfoClearFunction clear_function) {
  DebugInfoListNode* prev = nullptr;
  DebugInfoListNode* current = debug_info_list_;
  while (current != nullptr) {
    DebugInfoListNode* next = current->next();
    Handle<DebugInfo> debug_info = current->debug_info();
    if (clear_function(debug_info)) {
      FreeDebugInfoListNode(prev, current);
      current = next;
    } else {
      prev = current;
      current = next;
    }
  }
}

void Debug::RemoveBreakInfoAndMaybeFree(Handle<DebugInfo> debug_info) {
  bool should_unlink = debug_info->ClearBreakInfo();
  if (should_unlink) {
    DebugInfoListNode* prev;
    DebugInfoListNode* node;
    FindDebugInfo(debug_info, &prev, &node);
    FreeDebugInfoListNode(prev, node);
  }
}

void Debug::FreeDebugInfoListNode(DebugInfoListNode* prev,
                                  DebugInfoListNode* node) {
  DCHECK(node->debug_info()->IsEmpty());

  // Unlink from list. If prev is nullptr we are looking at the first element.
  if (prev == nullptr) {
    debug_info_list_ = node->next();
  } else {
    prev->set_next(node->next());
  }

  // Pack debugger hints back into the SFI::debug_info field.
  Handle<DebugInfo> debug_info(node->debug_info());
  debug_info->shared()->set_debug_info(
      Smi::FromInt(debug_info->debugger_hints()));

  delete node;
}

bool Debug::IsBreakAtReturn(JavaScriptFrame* frame) {
  HandleScope scope(isolate_);

  // Get the executing function in which the debug break occurred.
  Handle<SharedFunctionInfo> shared(frame->function()->shared());

  // With no debug info there are no break points, so we can't be at a return.
  if (!shared->HasBreakInfo()) return false;

  DCHECK(!frame->is_optimized());
  Handle<DebugInfo> debug_info(shared->GetDebugInfo());
  BreakLocation location = BreakLocation::FromFrame(debug_info, frame);
  return location.IsReturn();
}

void Debug::ScheduleFrameRestart(StackFrame* frame) {
  // Set a target FP for the FrameDropperTrampoline builtin to drop to once
  // we return from the debugger.
  DCHECK(frame->is_java_script());
  // Only reschedule to a frame further below a frame we already scheduled for.
  if (frame->fp() <= thread_local_.restart_fp_) return;
  // If the frame is optimized, trigger a deopt and jump into the
  // FrameDropperTrampoline in the deoptimizer.
  thread_local_.restart_fp_ = frame->fp();

  // Reset break frame ID to the frame below the restarted frame.
  StackTraceFrameIterator it(isolate_);
  thread_local_.break_frame_id_ = StackFrame::NO_ID;
  for (StackTraceFrameIterator it(isolate_); !it.done(); it.Advance()) {
    if (it.frame()->fp() > thread_local_.restart_fp_) {
      thread_local_.break_frame_id_ = it.frame()->id();
      return;
    }
  }
}


bool Debug::IsDebugGlobal(JSGlobalObject* global) {
  return is_loaded() && global == debug_context()->global_object();
}


Handle<FixedArray> Debug::GetLoadedScripts() {
  isolate_->heap()->CollectAllGarbage(Heap::kFinalizeIncrementalMarkingMask,
                                      GarbageCollectionReason::kDebugger);
  Factory* factory = isolate_->factory();
  if (!factory->script_list()->IsWeakFixedArray()) {
    return factory->empty_fixed_array();
  }
  Handle<WeakFixedArray> array =
      Handle<WeakFixedArray>::cast(factory->script_list());
  Handle<FixedArray> results = factory->NewFixedArray(array->Length());
  int length = 0;
  {
    Script::Iterator iterator(isolate_);
    Script* script;
    while ((script = iterator.Next()) != nullptr) {
      if (script->HasValidSource()) results->set(length++, script);
    }
  }
  results->Shrink(length);
  return results;
}


MaybeHandle<Object> Debug::MakeExecutionState() {
  // Create the execution state object.
  Handle<Object> argv[] = { isolate_->factory()->NewNumberFromInt(break_id()) };
  return CallFunction("MakeExecutionState", arraysize(argv), argv);
}


MaybeHandle<Object> Debug::MakeBreakEvent(Handle<Object> break_points_hit) {
  // Create the new break event object.
  Handle<Object> argv[] = { isolate_->factory()->NewNumberFromInt(break_id()),
                            break_points_hit };
  return CallFunction("MakeBreakEvent", arraysize(argv), argv);
}


MaybeHandle<Object> Debug::MakeExceptionEvent(Handle<Object> exception,
                                              bool uncaught,
                                              Handle<Object> promise) {
  // Create the new exception event object.
  Handle<Object> argv[] = { isolate_->factory()->NewNumberFromInt(break_id()),
                            exception,
                            isolate_->factory()->ToBoolean(uncaught),
                            promise };
  return CallFunction("MakeExceptionEvent", arraysize(argv), argv);
}


MaybeHandle<Object> Debug::MakeCompileEvent(Handle<Script> script,
                                            v8::DebugEvent type) {
  // Create the compile event object.
  Handle<Object> script_wrapper = Script::GetWrapper(script);
  Handle<Object> argv[] = { script_wrapper,
                            isolate_->factory()->NewNumberFromInt(type) };
  return CallFunction("MakeCompileEvent", arraysize(argv), argv);
}

MaybeHandle<Object> Debug::MakeAsyncTaskEvent(
    v8::debug::PromiseDebugActionType type, int id) {
  // Create the async task event object.
  Handle<Object> argv[] = {Handle<Smi>(Smi::FromInt(type), isolate_),
                           Handle<Smi>(Smi::FromInt(id), isolate_)};
  return CallFunction("MakeAsyncTaskEvent", arraysize(argv), argv);
}


void Debug::OnThrow(Handle<Object> exception) {
  if (in_debug_scope() || ignore_events()) return;
  // Temporarily clear any scheduled_exception to allow evaluating
  // JavaScript from the debug event handler.
  HandleScope scope(isolate_);
  Handle<Object> scheduled_exception;
  if (isolate_->has_scheduled_exception()) {
    scheduled_exception = handle(isolate_->scheduled_exception(), isolate_);
    isolate_->clear_scheduled_exception();
  }
  OnException(exception, isolate_->GetPromiseOnStackOnThrow());
  if (!scheduled_exception.is_null()) {
    isolate_->thread_local_top()->scheduled_exception_ = *scheduled_exception;
  }
  PrepareStepOnThrow();
}

void Debug::OnPromiseReject(Handle<Object> promise, Handle<Object> value) {
  if (in_debug_scope() || ignore_events()) return;
  HandleScope scope(isolate_);
  // Check whether the promise has been marked as having triggered a message.
  Handle<Symbol> key = isolate_->factory()->promise_debug_marker_symbol();
  if (!promise->IsJSObject() ||
      JSReceiver::GetDataProperty(Handle<JSObject>::cast(promise), key)
          ->IsUndefined(isolate_)) {
    OnException(value, promise);
  }
}

namespace {
v8::Local<v8::Context> GetDebugEventContext(Isolate* isolate) {
  Handle<Context> context = isolate->debug()->debugger_entry()->GetContext();
  // Isolate::context() may have been nullptr when "script collected" event
  // occurred.
  if (context.is_null()) return v8::Local<v8::Context>();
  Handle<Context> native_context(context->native_context());
  return v8::Utils::ToLocal(native_context);
}
}  // anonymous namespace

bool Debug::IsExceptionBlackboxed(bool uncaught) {
  // Uncaught exception is blackboxed if all current frames are blackboxed,
  // caught exception if top frame is blackboxed.
  StackTraceFrameIterator it(isolate_);
  while (!it.done() && it.is_wasm()) it.Advance();
  bool is_top_frame_blackboxed =
      !it.done() ? IsFrameBlackboxed(it.javascript_frame()) : true;
  if (!uncaught || !is_top_frame_blackboxed) return is_top_frame_blackboxed;
  return AllFramesOnStackAreBlackboxed();
}

bool Debug::IsFrameBlackboxed(JavaScriptFrame* frame) {
  HandleScope scope(isolate_);
  std::vector<Handle<SharedFunctionInfo>> infos;
  frame->GetFunctions(&infos);
  for (const auto& info : infos) {
    if (!IsBlackboxed(info)) return false;
  }
  return true;
}

void Debug::OnException(Handle<Object> exception, Handle<Object> promise) {
  // We cannot generate debug events when JS execution is disallowed.
  // TODO(5530): Reenable debug events within DisallowJSScopes once relevant
  // code (MakeExceptionEvent and ProcessDebugEvent) have been moved to C++.
  if (!AllowJavascriptExecution::IsAllowed(isolate_)) return;

  Isolate::CatchType catch_type = isolate_->PredictExceptionCatcher();

  // Don't notify listener of exceptions that are internal to a desugaring.
  if (catch_type == Isolate::CAUGHT_BY_DESUGARING) return;

  bool uncaught = catch_type == Isolate::NOT_CAUGHT;
  if (promise->IsJSObject()) {
    Handle<JSObject> jspromise = Handle<JSObject>::cast(promise);
    // Mark the promise as already having triggered a message.
    Handle<Symbol> key = isolate_->factory()->promise_debug_marker_symbol();
    JSObject::SetProperty(jspromise, key, key, LanguageMode::kStrict).Assert();
    // Check whether the promise reject is considered an uncaught exception.
    uncaught = !isolate_->PromiseHasUserDefinedRejectHandler(jspromise);
  }

  if (!debug_delegate_) return;

  // Bail out if exception breaks are not active
  if (uncaught) {
    // Uncaught exceptions are reported by either flags.
    if (!(break_on_uncaught_exception_ || break_on_exception_)) return;
  } else {
    // Caught exceptions are reported is activated.
    if (!break_on_exception_) return;
  }

  {
    JavaScriptFrameIterator it(isolate_);
    // Check whether the top frame is blackboxed or the break location is muted.
    if (!it.done() && (IsMutedAtCurrentLocation(it.frame()) ||
                       IsExceptionBlackboxed(uncaught))) {
      return;
    }
    if (it.done()) return;  // Do not trigger an event with an empty stack.
  }

  DebugScope debug_scope(this);
  if (debug_scope.failed()) return;
  HandleScope scope(isolate_);
  PostponeInterruptsScope postpone(isolate_);
  DisableBreak no_recursive_break(this);

  // Create the execution state.
  Handle<Object> exec_state;
  // Bail out and don't call debugger if exception.
  if (!MakeExecutionState().ToHandle(&exec_state)) return;

  debug_delegate_->ExceptionThrown(
      GetDebugEventContext(isolate_),
      v8::Utils::ToLocal(Handle<JSObject>::cast(exec_state)),
      v8::Utils::ToLocal(exception), v8::Utils::ToLocal(promise), uncaught);
}

void Debug::OnDebugBreak(Handle<FixedArray> break_points_hit) {
  DCHECK(!break_points_hit.is_null());
  // The caller provided for DebugScope.
  AssertDebugContext();
  // Bail out if there is no listener for this event
  if (ignore_events()) return;

#ifdef DEBUG
  PrintBreakLocation();
#endif  // DEBUG

  if (!debug_delegate_) return;
  HandleScope scope(isolate_);
  PostponeInterruptsScope no_interrupts(isolate_);
  DisableBreak no_recursive_break(this);

  // Create the execution state.
  Handle<Object> exec_state;
  // Bail out and don't call debugger if exception.
  if (!MakeExecutionState().ToHandle(&exec_state)) return;

  std::vector<int> inspector_break_points_hit;
  int inspector_break_points_count = 0;
  // This array contains breakpoints installed using JS debug API.
  for (int i = 0; i < break_points_hit->length(); ++i) {
    Object* break_point = break_points_hit->get(i);
    if (break_point->IsBreakPoint()) {
      inspector_break_points_hit.push_back(BreakPoint::cast(break_point)->id());
      ++inspector_break_points_count;
    } else {
      break_points_hit->set(i - inspector_break_points_count, break_point);
    }
  }
  int break_points_length =
      break_points_hit->length() - inspector_break_points_count;
  Handle<Object> break_points;
  if (break_points_length) {
    break_points_hit->Shrink(break_points_length);
    break_points = isolate_->factory()->NewJSArrayWithElements(
        break_points_hit, PACKED_ELEMENTS, break_points_length);
  } else {
    break_points = isolate_->factory()->undefined_value();
  }

  debug_delegate_->BreakProgramRequested(
      GetDebugEventContext(isolate_),
      v8::Utils::ToLocal(Handle<JSObject>::cast(exec_state)),
      v8::Utils::ToLocal(break_points), inspector_break_points_hit);
}


void Debug::OnCompileError(Handle<Script> script) {
  ProcessCompileEvent(v8::CompileError, script);
}


// Handle debugger actions when a new script is compiled.
void Debug::OnAfterCompile(Handle<Script> script) {
  ProcessCompileEvent(v8::AfterCompile, script);
}

namespace {
// In an async function, reuse the existing stack related to the outer
// Promise. Otherwise, e.g. in a direct call to then, save a new stack.
// Promises with multiple reactions with one or more of them being async
// functions will not get a good stack trace, as async functions require
// different stacks from direct Promise use, but we save and restore a
// stack once for all reactions.
//
// If this isn't a case of async function, we return false, otherwise
// we set the correct id and return true.
//
// TODO(littledan): Improve this case.
int GetReferenceAsyncTaskId(Isolate* isolate, Handle<JSPromise> promise) {
  Handle<Symbol> handled_by_symbol =
      isolate->factory()->promise_handled_by_symbol();
  Handle<Object> handled_by_promise =
      JSObject::GetDataProperty(promise, handled_by_symbol);
  if (!handled_by_promise->IsJSPromise()) {
    return isolate->debug()->NextAsyncTaskId(promise);
  }
  Handle<JSPromise> handled_by_promise_js =
      Handle<JSPromise>::cast(handled_by_promise);
  Handle<Symbol> async_stack_id_symbol =
      isolate->factory()->promise_async_stack_id_symbol();
  Handle<Object> async_task_id =
      JSObject::GetDataProperty(handled_by_promise_js, async_stack_id_symbol);
  if (!async_task_id->IsSmi()) {
    return isolate->debug()->NextAsyncTaskId(promise);
  }
  return Handle<Smi>::cast(async_task_id)->value();
}
}  //  namespace

void Debug::RunPromiseHook(PromiseHookType type, Handle<JSPromise> promise,
                           Handle<Object> parent) {
  if (!debug_delegate_) return;
  int id = GetReferenceAsyncTaskId(isolate_, promise);
  switch (type) {
    case PromiseHookType::kInit:
      OnAsyncTaskEvent(debug::kDebugPromiseCreated, id,
                       parent->IsJSPromise()
                           ? GetReferenceAsyncTaskId(
                                 isolate_, Handle<JSPromise>::cast(parent))
                           : 0);
      return;
    case PromiseHookType::kResolve:
      // We can't use this hook because it's called before promise object will
      // get resolved status.
      return;
    case PromiseHookType::kBefore:
      OnAsyncTaskEvent(debug::kDebugWillHandle, id, 0);
      return;
    case PromiseHookType::kAfter:
      OnAsyncTaskEvent(debug::kDebugDidHandle, id, 0);
      return;
  }
}

int Debug::NextAsyncTaskId(Handle<JSObject> promise) {
  LookupIterator it(promise, isolate_->factory()->promise_async_id_symbol());
  Maybe<bool> maybe = JSReceiver::HasProperty(&it);
  if (maybe.ToChecked()) {
    MaybeHandle<Object> result = Object::GetProperty(&it);
    return Handle<Smi>::cast(result.ToHandleChecked())->value();
  }
  Handle<Smi> async_id =
      handle(Smi::FromInt(++thread_local_.async_task_count_), isolate_);
  Object::SetProperty(&it, async_id, LanguageMode::kSloppy,
                      Object::MAY_BE_STORE_FROM_KEYED)
      .ToChecked();
  return async_id->value();
}

namespace {
debug::Location GetDebugLocation(Handle<Script> script, int source_position) {
  Script::PositionInfo info;
  Script::GetPositionInfo(script, source_position, &info, Script::WITH_OFFSET);
  // V8 provides ScriptCompiler::CompileFunctionInContext method which takes
  // expression and compile it as anonymous function like (function() ..
  // expression ..). To produce correct locations for stmts inside of this
  // expression V8 compile this function with negative offset. Instead of stmt
  // position blackboxing use function start position which is negative in
  // described case.
  return debug::Location(std::max(info.line, 0), std::max(info.column, 0));
}
}  // namespace

bool Debug::IsBlackboxed(Handle<SharedFunctionInfo> shared) {
  if (!debug_delegate_) return !shared->IsSubjectToDebugging();
  if (!shared->computed_debug_is_blackboxed()) {
    bool is_blackboxed =
        !shared->IsSubjectToDebugging() || !shared->script()->IsScript();
    if (!is_blackboxed) {
      SuppressDebug while_processing(this);
      HandleScope handle_scope(isolate_);
      PostponeInterruptsScope no_interrupts(isolate_);
      DisableBreak no_recursive_break(this);
      DCHECK(shared->script()->IsScript());
      Handle<Script> script(Script::cast(shared->script()));
      DCHECK(script->IsUserJavaScript());
      debug::Location start =
          GetDebugLocation(script, shared->start_position());
      debug::Location end = GetDebugLocation(script, shared->end_position());
      is_blackboxed = debug_delegate_->IsFunctionBlackboxed(
          ToApiHandle<debug::Script>(script), start, end);
    }
    shared->set_debug_is_blackboxed(is_blackboxed);
    shared->set_computed_debug_is_blackboxed(true);
  }
  return shared->debug_is_blackboxed();
}

bool Debug::AllFramesOnStackAreBlackboxed() {
  HandleScope scope(isolate_);
  for (StackTraceFrameIterator it(isolate_); !it.done(); it.Advance()) {
    if (!IsFrameBlackboxed(it.javascript_frame())) return false;
  }
  return true;
}

bool Debug::SetScriptSource(Handle<Script> script, Handle<String> source,
                            bool preview, bool* stack_changed) {
  DebugScope debug_scope(this);
  set_live_edit_enabled(true);
  Handle<Object> script_wrapper = Script::GetWrapper(script);
  Handle<Object> argv[] = {script_wrapper, source,
                           isolate_->factory()->ToBoolean(preview),
                           isolate_->factory()->NewJSArray(0)};
  Handle<Object> result;
  if (!CallFunction("SetScriptSource", arraysize(argv), argv, false)
           .ToHandle(&result)) {
    isolate_->OptionalRescheduleException(false);
    set_live_edit_enabled(false);
    return false;
  }
  set_live_edit_enabled(false);
  Handle<Object> stack_changed_value =
      JSReceiver::GetProperty(isolate_, Handle<JSObject>::cast(result),
                              "stack_modified")
          .ToHandleChecked();
  *stack_changed = stack_changed_value->IsTrue(isolate_);
  return true;
}

void Debug::OnAsyncTaskEvent(debug::PromiseDebugActionType type, int id,
                             int parent_id) {
  if (in_debug_scope() || ignore_events()) return;
  if (!debug_delegate_) return;
  SuppressDebug while_processing(this);
  PostponeInterruptsScope no_interrupts(isolate_);
  DisableBreak no_recursive_break(this);
  bool created_by_user = false;
  if (type == debug::kDebugPromiseCreated) {
    JavaScriptFrameIterator it(isolate_);
    // We need to skip top frame which contains instrumentation.
    it.Advance();
    created_by_user =
        !it.done() &&
        !IsFrameBlackboxed(it.frame());
  }
  debug_delegate_->PromiseEventOccurred(type, id, parent_id, created_by_user);
}

void Debug::ProcessCompileEvent(v8::DebugEvent event, Handle<Script> script) {
  // Attach the correct debug id to the script. The debug id is used by the
  // inspector to filter scripts by native context.
  script->set_context_data(isolate_->native_context()->debug_context_id());
  if (ignore_events()) return;
  if (!script->IsUserJavaScript() && script->type() != i::Script::TYPE_WASM) {
    return;
  }
  if (!debug_delegate_) return;
  SuppressDebug while_processing(this);
  DebugScope debug_scope(this);
  if (debug_scope.failed()) return;
  HandleScope scope(isolate_);
  PostponeInterruptsScope postpone(isolate_);
  DisableBreak no_recursive_break(this);
  AllowJavascriptExecution allow_script(isolate_);
  debug_delegate_->ScriptCompiled(ToApiHandle<debug::Script>(script),
                                  live_edit_enabled(),
                                  event != v8::AfterCompile);
}


Handle<Context> Debug::GetDebugContext() {
  if (!is_loaded()) return Handle<Context>();
  DebugScope debug_scope(this);
  if (debug_scope.failed()) return Handle<Context>();
  // The global handle may be destroyed soon after.  Return it reboxed.
  return handle(*debug_context(), isolate_);
}

int Debug::CurrentFrameCount() {
  StackTraceFrameIterator it(isolate_);
  if (break_frame_id() != StackFrame::NO_ID) {
    // Skip to break frame.
    DCHECK(in_debug_scope());
    while (!it.done() && it.frame()->id() != break_frame_id()) it.Advance();
  }
  int counter = 0;
  while (!it.done()) {
    if (it.frame()->is_optimized()) {
      std::vector<SharedFunctionInfo*> infos;
      OptimizedFrame::cast(it.frame())->GetFunctions(&infos);
      counter += infos.size();
    } else {
      counter++;
    }
    it.Advance();
  }
  return counter;
}

void Debug::SetDebugDelegate(debug::DebugDelegate* delegate,
                             bool pass_ownership) {
  RemoveDebugDelegate();
  debug_delegate_ = delegate;
  owns_debug_delegate_ = pass_ownership;
  UpdateState();
}

void Debug::RemoveDebugDelegate() {
  if (debug_delegate_ == nullptr) return;
  if (owns_debug_delegate_) {
    owns_debug_delegate_ = false;
    delete debug_delegate_;
  }
  debug_delegate_ = nullptr;
}

void Debug::UpdateState() {
  bool is_active = debug_delegate_ != nullptr;
  if (is_active || in_debug_scope()) {
    // Note that the debug context could have already been loaded to
    // bootstrap test cases.
    isolate_->compilation_cache()->Disable();
    is_active = Load();
  } else if (is_loaded()) {
    isolate_->compilation_cache()->Enable();
    Unload();
  }
  is_active_ = is_active;
  isolate_->DebugStateUpdated();
}

void Debug::UpdateHookOnFunctionCall() {
  STATIC_ASSERT(LastStepAction == StepIn);
  hook_on_function_call_ = thread_local_.last_step_action_ == StepIn ||
                           isolate_->needs_side_effect_check();
}

MaybeHandle<Object> Debug::Call(Handle<Object> fun, Handle<Object> data) {
  AllowJavascriptExecutionDebugOnly allow_script(isolate_);
  DebugScope debug_scope(this);
  if (debug_scope.failed()) return isolate_->factory()->undefined_value();

  // Create the execution state.
  Handle<Object> exec_state;
  if (!MakeExecutionState().ToHandle(&exec_state)) {
    return isolate_->factory()->undefined_value();
  }

  Handle<Object> argv[] = { exec_state, data };
  return Execution::Call(
      isolate_,
      fun,
      Handle<Object>(debug_context()->global_proxy(), isolate_),
      arraysize(argv),
      argv);
}

void Debug::HandleDebugBreak(IgnoreBreakMode ignore_break_mode) {
  // Initialize LiveEdit.
  LiveEdit::InitializeThreadLocal(this);
  // Ignore debug break during bootstrapping.
  if (isolate_->bootstrapper()->IsActive()) return;
  // Just continue if breaks are disabled.
  if (break_disabled()) return;
  // Ignore debug break if debugger is not active.
  if (!is_active()) return;

  StackLimitCheck check(isolate_);
  if (check.HasOverflowed()) return;

  { JavaScriptFrameIterator it(isolate_);
    DCHECK(!it.done());
    Object* fun = it.frame()->function();
    if (fun && fun->IsJSFunction()) {
      HandleScope scope(isolate_);
      Handle<JSFunction> function(JSFunction::cast(fun), isolate_);
      // Don't stop in builtin and blackboxed functions.
      Handle<SharedFunctionInfo> shared(function->shared(), isolate_);
      bool ignore_break = ignore_break_mode == kIgnoreIfTopFrameBlackboxed
                              ? IsBlackboxed(shared)
                              : AllFramesOnStackAreBlackboxed();
      if (ignore_break) {
        // Inspector uses pause on next statement for asynchronous breakpoints.
        // When breakpoint is fired we try to break on first not blackboxed
        // statement. To achieve this goal we need to deoptimize current
        // function and don't clear requested DebugBreak even if it's blackboxed
        // to be able to break on not blackboxed function call.
        // TODO(yangguo): introduce break_on_function_entry since current
        // implementation is slow.
        if (isolate_->stack_guard()->CheckDebugBreak()) {
          Deoptimizer::DeoptimizeFunction(*function);
        }
        return;
      }
      JSGlobalObject* global = function->context()->global_object();
      // Don't stop in debugger functions.
      if (IsDebugGlobal(global)) return;
      // Don't stop if the break location is muted.
      if (IsMutedAtCurrentLocation(it.frame())) return;
    }
  }

  isolate_->stack_guard()->ClearDebugBreak();

  // Clear stepping to avoid duplicate breaks.
  ClearStepping();

  HandleScope scope(isolate_);
  DebugScope debug_scope(this);
  if (debug_scope.failed()) return;

  OnDebugBreak(isolate_->factory()->empty_fixed_array());
}

#ifdef DEBUG
void Debug::PrintBreakLocation() {
  if (!FLAG_print_break_location) return;
  HandleScope scope(isolate_);
  StackTraceFrameIterator iterator(isolate_);
  if (iterator.done()) return;
  StandardFrame* frame = iterator.frame();
  FrameSummary summary = FrameSummary::GetTop(frame);
  int source_position = summary.SourcePosition();
  Handle<Object> script_obj = summary.script();
  PrintF("[debug] break in function '");
  summary.FunctionName()->PrintOn(stdout);
  PrintF("'.\n");
  if (script_obj->IsScript()) {
    Handle<Script> script = Handle<Script>::cast(script_obj);
    Handle<String> source(String::cast(script->source()));
    Script::InitLineEnds(script);
    int line =
        Script::GetLineNumber(script, source_position) - script->line_offset();
    int column = Script::GetColumnNumber(script, source_position) -
                 (line == 0 ? script->column_offset() : 0);
    Handle<FixedArray> line_ends(FixedArray::cast(script->line_ends()));
    int line_start = line == 0 ? 0 : Smi::ToInt(line_ends->get(line - 1)) + 1;
    int line_end = Smi::ToInt(line_ends->get(line));
    DisallowHeapAllocation no_gc;
    String::FlatContent content = source->GetFlatContent();
    if (content.IsOneByte()) {
      PrintF("[debug] %.*s\n", line_end - line_start,
             content.ToOneByteVector().start() + line_start);
      PrintF("[debug] ");
      for (int i = 0; i < column; i++) PrintF(" ");
      PrintF("^\n");
    } else {
      PrintF("[debug] at line %d column %d\n", line, column);
    }
  }
}
#endif  // DEBUG

DebugScope::DebugScope(Debug* debug)
    : debug_(debug),
      prev_(debug->debugger_entry()),
      save_(debug_->isolate_),
      no_termination_exceptons_(debug_->isolate_,
                                StackGuard::TERMINATE_EXECUTION) {
  // Link recursive debugger entry.
  base::Relaxed_Store(&debug_->thread_local_.current_debug_scope_,
                      reinterpret_cast<base::AtomicWord>(this));

  // Store the previous break id, frame id and return value.
  break_id_ = debug_->break_id();
  break_frame_id_ = debug_->break_frame_id();

  // Create the new break info. If there is no proper frames there is no break
  // frame id.
  StackTraceFrameIterator it(isolate());
  bool has_frames = !it.done();
  debug_->thread_local_.break_frame_id_ =
      has_frames ? it.frame()->id() : StackFrame::NO_ID;
  debug_->SetNextBreakId();

  debug_->UpdateState();
  // Make sure that debugger is loaded and enter the debugger context.
  // The previous context is kept in save_.
  failed_ = !debug_->is_loaded();
  if (!failed_) isolate()->set_context(*debug->debug_context());
}


DebugScope::~DebugScope() {
  // Leaving this debugger entry.
  base::Relaxed_Store(&debug_->thread_local_.current_debug_scope_,
                      reinterpret_cast<base::AtomicWord>(prev_));

  // Restore to the previous break state.
  debug_->thread_local_.break_frame_id_ = break_frame_id_;
  debug_->thread_local_.break_id_ = break_id_;

  debug_->UpdateState();
}

ReturnValueScope::ReturnValueScope(Debug* debug) : debug_(debug) {
  return_value_ = debug_->return_value_handle();
}

ReturnValueScope::~ReturnValueScope() {
  debug_->set_return_value(*return_value_);
}

bool Debug::PerformSideEffectCheck(Handle<JSFunction> function) {
  DCHECK(isolate_->needs_side_effect_check());
  DisallowJavascriptExecution no_js(isolate_);
  if (!function->is_compiled() &&
      !Compiler::Compile(function, Compiler::KEEP_EXCEPTION)) {
    return false;
  }
  Deoptimizer::DeoptimizeFunction(*function);
  if (!function->shared()->HasNoSideEffect()) {
    if (FLAG_trace_side_effect_free_debug_evaluate) {
      PrintF("[debug-evaluate] Function %s failed side effect check.\n",
             function->shared()->DebugName()->ToCString().get());
    }
    side_effect_check_failed_ = true;
    // Throw an uncatchable termination exception.
    isolate_->TerminateExecution();
    return false;
  }
  return true;
}

bool Debug::PerformSideEffectCheckForCallback(Address function) {
  DCHECK(isolate_->needs_side_effect_check());
  if (DebugEvaluate::CallbackHasNoSideEffect(function)) return true;
  side_effect_check_failed_ = true;
  // Throw an uncatchable termination exception.
  isolate_->TerminateExecution();
  isolate_->OptionalRescheduleException(false);
  return false;
}

void LegacyDebugDelegate::PromiseEventOccurred(
    v8::debug::PromiseDebugActionType type, int id, int parent_id,
    bool created_by_user) {
  DebugScope debug_scope(isolate_->debug());
  if (debug_scope.failed()) return;
  HandleScope scope(isolate_);
  Handle<Object> event_data;
  if (isolate_->debug()->MakeAsyncTaskEvent(type, id).ToHandle(&event_data)) {
    ProcessDebugEvent(v8::AsyncTaskEvent, Handle<JSObject>::cast(event_data));
  }
}

void LegacyDebugDelegate::ScriptCompiled(v8::Local<v8::debug::Script> script,
                                         bool is_live_edited,
                                         bool is_compile_error) {
  Handle<Object> event_data;
  v8::DebugEvent event = is_compile_error ? v8::CompileError : v8::AfterCompile;
  if (isolate_->debug()
          ->MakeCompileEvent(v8::Utils::OpenHandle(*script), event)
          .ToHandle(&event_data)) {
    ProcessDebugEvent(event, Handle<JSObject>::cast(event_data));
  }
}

void LegacyDebugDelegate::BreakProgramRequested(
    v8::Local<v8::Context> paused_context, v8::Local<v8::Object> exec_state,
    v8::Local<v8::Value> break_points_hit,
    const std::vector<debug::BreakpointId>&) {
  Handle<Object> event_data;
  if (isolate_->debug()
          ->MakeBreakEvent(v8::Utils::OpenHandle(*break_points_hit))
          .ToHandle(&event_data)) {
    ProcessDebugEvent(
        v8::Break, Handle<JSObject>::cast(event_data),
        Handle<JSObject>::cast(v8::Utils::OpenHandle(*exec_state)));
  }
}

void LegacyDebugDelegate::ExceptionThrown(v8::Local<v8::Context> paused_context,
                                          v8::Local<v8::Object> exec_state,
                                          v8::Local<v8::Value> exception,
                                          v8::Local<v8::Value> promise,
                                          bool is_uncaught) {
  Handle<Object> event_data;
  if (isolate_->debug()
          ->MakeExceptionEvent(v8::Utils::OpenHandle(*exception), is_uncaught,
                               v8::Utils::OpenHandle(*promise))
          .ToHandle(&event_data)) {
    ProcessDebugEvent(
        v8::Exception, Handle<JSObject>::cast(event_data),
        Handle<JSObject>::cast(v8::Utils::OpenHandle(*exec_state)));
  }
}

void LegacyDebugDelegate::ProcessDebugEvent(v8::DebugEvent event,
                                            Handle<JSObject> event_data) {
  Handle<Object> exec_state;
  if (isolate_->debug()->MakeExecutionState().ToHandle(&exec_state)) {
    ProcessDebugEvent(event, event_data, Handle<JSObject>::cast(exec_state));
  }
}

JavaScriptDebugDelegate::JavaScriptDebugDelegate(Isolate* isolate,
                                                 Handle<JSFunction> listener,
                                                 Handle<Object> data)
    : LegacyDebugDelegate(isolate) {
  GlobalHandles* global_handles = isolate->global_handles();
  listener_ = global_handles->Create(*listener);
  data_ = global_handles->Create(*data);
}

JavaScriptDebugDelegate::~JavaScriptDebugDelegate() {
  GlobalHandles::Destroy(Handle<Object>::cast(listener_).location());
  GlobalHandles::Destroy(data_.location());
}

void JavaScriptDebugDelegate::ProcessDebugEvent(v8::DebugEvent event,
                                                Handle<JSObject> event_data,
                                                Handle<JSObject> exec_state) {
  AllowJavascriptExecutionDebugOnly allow_script(isolate_);
  Handle<Object> argv[] = {Handle<Object>(Smi::FromInt(event), isolate_),
                           exec_state, event_data, data_};
  Handle<JSReceiver> global = isolate_->global_proxy();
  // Listener must not throw.
  Execution::Call(isolate_, listener_, global, arraysize(argv), argv)
      .ToHandleChecked();
}

NativeDebugDelegate::NativeDebugDelegate(Isolate* isolate,
                                         v8::Debug::EventCallback callback,
                                         Handle<Object> data)
    : LegacyDebugDelegate(isolate), callback_(callback) {
  data_ = isolate->global_handles()->Create(*data);
}

NativeDebugDelegate::~NativeDebugDelegate() {
  GlobalHandles::Destroy(data_.location());
}

NativeDebugDelegate::EventDetails::EventDetails(DebugEvent event,
                                                Handle<JSObject> exec_state,
                                                Handle<JSObject> event_data,
                                                Handle<Object> callback_data)
    : event_(event),
      exec_state_(exec_state),
      event_data_(event_data),
      callback_data_(callback_data) {}

DebugEvent NativeDebugDelegate::EventDetails::GetEvent() const {
  return event_;
}

v8::Local<v8::Object> NativeDebugDelegate::EventDetails::GetExecutionState()
    const {
  return v8::Utils::ToLocal(exec_state_);
}

v8::Local<v8::Object> NativeDebugDelegate::EventDetails::GetEventData() const {
  return v8::Utils::ToLocal(event_data_);
}

v8::Local<v8::Context> NativeDebugDelegate::EventDetails::GetEventContext()
    const {
  return GetDebugEventContext(exec_state_->GetIsolate());
}

v8::Local<v8::Value> NativeDebugDelegate::EventDetails::GetCallbackData()
    const {
  return v8::Utils::ToLocal(callback_data_);
}

v8::Isolate* NativeDebugDelegate::EventDetails::GetIsolate() const {
  return reinterpret_cast<v8::Isolate*>(exec_state_->GetIsolate());
}

void NativeDebugDelegate::ProcessDebugEvent(v8::DebugEvent event,
                                            Handle<JSObject> event_data,
                                            Handle<JSObject> exec_state) {
  EventDetails event_details(event, exec_state, event_data, data_);
  Isolate* isolate = isolate_;
  callback_(event_details);
  CHECK(!isolate->has_scheduled_exception());
}

NoSideEffectScope::~NoSideEffectScope() {
  if (isolate_->needs_side_effect_check() &&
      isolate_->debug()->side_effect_check_failed_) {
    DCHECK(isolate_->has_pending_exception());
    DCHECK_EQ(isolate_->heap()->termination_exception(),
              isolate_->pending_exception());
    // Convert the termination exception into a regular exception.
    isolate_->CancelTerminateExecution();
    isolate_->Throw(*isolate_->factory()->NewEvalError(
        MessageTemplate::kNoSideEffectDebugEvaluate));
  }
  isolate_->set_needs_side_effect_check(old_needs_side_effect_check_);
  isolate_->debug()->UpdateHookOnFunctionCall();
  isolate_->debug()->side_effect_check_failed_ = false;
}

}  // namespace internal
}  // namespace v8