[Debugger] Hold a strong reference to debug bytecode from DebugInfo.

With BytecodeArray flushing the SFI->BytecodeArray pointer will become pseudo weak.
In order to prevent instrumented bytecode from being flushed while the function is
being debugged, hold onto the instrumented bytecode strongly.

BUG=v8:8395

Change-Id: Ie346732b77833afa0595a84a4956295e50855392
Reviewed-on: https://chromium-review.googlesource.com/c/1312849Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57569}

src/debug/debug.cc

@@ -1205,6 +1205,7 @@ void Debug::PrepareFunctionForDebugExecution(
         handle(shared->GetBytecodeArray(), isolate_);
     Handle<BytecodeArray> debug_bytecode_array =
         isolate_->factory()->CopyBytecodeArray(original_bytecode_array);
+    debug_info->set_debug_bytecode_array(*debug_bytecode_array);
     shared->SetDebugBytecodeArray(*debug_bytecode_array);
     maybe_original_bytecode_array = original_bytecode_array;
   }

src/heap/factory.cc

@@ -3632,6 +3632,7 @@ Handle<DebugInfo> Factory::NewDebugInfo(Handle<SharedFunctionInfo> shared) {
   debug_info->set_script(shared->script_or_debug_info());
   debug_info->set_original_bytecode_array(
       ReadOnlyRoots(heap).undefined_value());
+  debug_info->set_debug_bytecode_array(ReadOnlyRoots(heap).undefined_value());
   debug_info->set_break_points(ReadOnlyRoots(heap).empty_fixed_array());
 
   // Link debug info to function.

src/objects-printer.cc

@@ -2184,6 +2184,7 @@ void DebugInfo::DebugInfoPrint(std::ostream& os) {  // NOLINT
   os << "\n - shared: " << Brief(shared());
   os << "\n - script: " << Brief(script());
   os << "\n - original bytecode array: " << Brief(original_bytecode_array());
+  os << "\n - debug bytecode array: " << Brief(debug_bytecode_array());
   os << "\n - break_points: ";
   break_points()->FixedArrayPrint(os);
   os << "\n - coverage_info: " << Brief(coverage_info());

src/objects/debug-objects-inl.h

@@ -27,6 +27,7 @@ SMI_ACCESSORS(DebugInfo, debugger_hints, kDebuggerHintsOffset)
 ACCESSORS(DebugInfo, script, Object, kScriptOffset)
 ACCESSORS(DebugInfo, original_bytecode_array, Object,
           kOriginalBytecodeArrayOffset)
+ACCESSORS(DebugInfo, debug_bytecode_array, Object, kDebugBytecodeArrayOffset)
 ACCESSORS(DebugInfo, break_points, FixedArray, kBreakPointsStateOffset)
 ACCESSORS(DebugInfo, coverage_info, Object, kCoverageInfoOffset)
 
@@ -46,7 +47,9 @@ SMI_ACCESSORS(BreakPoint, id, kIdOffset)
 ACCESSORS(BreakPoint, condition, String, kConditionOffset)
 
 bool DebugInfo::HasInstrumentedBytecodeArray() {
-  return original_bytecode_array()->IsBytecodeArray();
+  DCHECK_EQ(debug_bytecode_array()->IsBytecodeArray(),
+            original_bytecode_array()->IsBytecodeArray());
+  return debug_bytecode_array()->IsBytecodeArray();
 }
 
 BytecodeArray* DebugInfo::OriginalBytecodeArray() {
@@ -56,7 +59,8 @@ BytecodeArray* DebugInfo::OriginalBytecodeArray() {
 
 BytecodeArray* DebugInfo::DebugBytecodeArray() {
   DCHECK(HasInstrumentedBytecodeArray());
-  return shared()->GetDebugBytecodeArray();
+  DCHECK_EQ(shared()->GetDebugBytecodeArray(), debug_bytecode_array());
+  return BytecodeArray::cast(debug_bytecode_array());
 }
 
 }  // namespace internal

src/objects/debug-objects.cc

@@ -30,6 +30,7 @@ void DebugInfo::ClearBreakInfo(Isolate* isolate) {
     // array.
     shared()->SetDebugBytecodeArray(OriginalBytecodeArray());
     set_original_bytecode_array(ReadOnlyRoots(isolate).undefined_value());
+    set_debug_bytecode_array(ReadOnlyRoots(isolate).undefined_value());
   }
   set_break_points(ReadOnlyRoots(isolate).empty_fixed_array());
 

src/objects/debug-objects.h

@@ -85,6 +85,10 @@ class DebugInfo : public Struct, public NeverReadOnlySpaceObject {
   // points - the instrumented bytecode is held in the shared function info.
   DECL_ACCESSORS(original_bytecode_array, Object)
 
+  // The debug instrumented bytecode array for functions with break points
+  // - also pointed to by the shared function info.
+  DECL_ACCESSORS(debug_bytecode_array, Object)
+
   // Fixed array holding status information for each active break point.
   DECL_ACCESSORS(break_points, FixedArray)
 
@@ -167,8 +171,10 @@ class DebugInfo : public Struct, public NeverReadOnlySpaceObject {
       kSharedFunctionInfoOffset + kPointerSize;
   static const int kScriptOffset = kDebuggerHintsOffset + kPointerSize;
   static const int kOriginalBytecodeArrayOffset = kScriptOffset + kPointerSize;
-  static const int kBreakPointsStateOffset =
+  static const int kDebugBytecodeArrayOffset =
       kOriginalBytecodeArrayOffset + kPointerSize;
+  static const int kBreakPointsStateOffset =
+      kDebugBytecodeArrayOffset + kPointerSize;
   static const int kFlagsOffset = kBreakPointsStateOffset + kPointerSize;
   static const int kCoverageInfoOffset = kFlagsOffset + kPointerSize;
   static const int kSize = kCoverageInfoOffset + kPointerSize;