Support for precise stepping in functions compiled before debugging was started (step 2)

src/debug.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1709 matching lines @@
 }
 
 
 void Debug::ClearStepNext() {
   thread_local_.last_step_action_ = StepNone;
   thread_local_.last_statement_position_ = RelocInfo::kNoPosition;
   thread_local_.last_fp_ = 0;
 }
 
 
+// Compare function to compare the object pointer value of two
+// handlified objects. The handles are passed as pointers to the
+// handles.
+template <typename T>
+static int HandleObjectPointerCompare(const Handle<T>* a, const Handle<T>* b) {

[Kevin Millikin (Chromium), 2011/09/29 10:47:35]

Hmm.  There are a couple of other Compare functions in utils.h.  I don't think
this can go there, because of include dependencies, but maybe it should go in
handles.h with a comment in utils.h that it's in handles.h, and a comment in
handles.h that it's like the ones in utils.h but moved because of include
dependencies.

I'm worried someone else will just define the same function, because debug.cc is
a strange place to look for it.  Or maybe that's not a big deal.  What do you
think?

[Søren Thygesen Gjesse, 2011/09/30 08:33:22]

Good point. I moved it to utils.h together with a forward declaration of Handle.

+  return Compare<T*>(*(*a), *(*b));
+}
+
+
+// Helper function to compile full code for debugging. This code will
+// have debug break slots and deoptimization
+// information. Deoptimization information is required in case that an
+// optimized version of this function is still activated on the
+// stack. It will also make sure that the full code is compiled with
+// the same flags as the previous version - that is flags which can
+// change the code generated. The current method of mapping from
+// already compiled full code without debug break slots to full code
+// with debug break slots depends on the generated code is otherwise
+// exactly the same.
+static bool CompileFullCodeForDebugging(Handle<SharedFunctionInfo> shared,
+                                        Handle<Code> current_code) {
+  ASSERT(!current_code->has_debug_break_slots());
+
+  CompilationInfo info(shared);
+  info.MarkCompilingForDebugging(current_code);
+  ASSERT(!info.shared_info()->is_compiled());
+  ASSERT(!info.isolate()->has_pending_exception());
+
+  // Use compile lazy which will end up compiling the full code in the
+  // configuration configured above.
+  bool result = Compiler::CompileLazy(&info);
+  ASSERT(result != Isolate::Current()->has_pending_exception());
+  info.isolate()->clear_pending_exception();
+#if DEBUG
+  if (result) {
+    Handle<Code> new_code(shared->code());
+    ASSERT(new_code->has_debug_break_slots());
+    ASSERT(current_code->is_compiled_optimizable() ==
+           new_code->is_compiled_optimizable());
+    ASSERT(current_code->instruction_size() <= new_code->instruction_size());
+  }
+#endif
+  return result;
+}
+
+
 void Debug::PrepareForBreakPoints() {
   // If preparing for the first break point make sure to deoptimize all
   // functions as debugging does not work with optimized code.
   if (!has_break_points_) {
     Deoptimizer::DeoptimizeAll();
 
-    // We are going to iterate heap to find all functions without
-    // debug break slots.
-    isolate_->heap()->CollectAllGarbage(Heap::kMakeHeapIterableMask);
-
-    AssertNoAllocation no_allocation;
-    Builtins* builtins = isolate_->builtins();
-    Code* lazy_compile = builtins->builtin(Builtins::kLazyCompile);
-
-    // Find all non-optimized code functions with activation frames on
-    // the stack.
-    List<JSFunction*> active_functions(100);
-    for (JavaScriptFrameIterator it(isolate_); !it.done(); it.Advance()) {
-      JavaScriptFrame* frame = it.frame();
-      if (frame->function()->IsJSFunction()) {
-        JSFunction* function = JSFunction::cast(frame->function());
-        if (function->code()->kind() == Code::FUNCTION)
-          active_functions.Add(function);
+    Handle<Code> lazy_compile(

[Kevin Millikin (Chromium), 2011/09/29 10:47:35]

Handle<Code> lazy_compile = isolate_->builtins()->LazyCompile();

[Søren Thygesen Gjesse, 2011/09/30 08:33:22]

Done, actually

Handle<Code> lazy_compile = Handle<Code>(isolate_->builtins()->LazyCompile());

+        isolate_->builtins()->builtin(Builtins::kLazyCompile));
+
+    // Keep the list of activated functions in a handlified list as it
+    // is used both in GC and non-GC code.
+    List<Handle<JSFunction> > active_functions(100);
+
+    {
+      // Ensure no GC in this scope as we are comparing raw pointer
+      // values and performing a heap iteration.
+      AssertNoAllocation no_allocation;
+
+      // Find all non-optimized code functions with activation frames on
+      // the stack.
+      for (JavaScriptFrameIterator it(isolate_); !it.done(); it.Advance()) {
+        JavaScriptFrame* frame = it.frame();
+        if (frame->function()->IsJSFunction()) {
+          JSFunction* function = JSFunction::cast(frame->function());
+          if (function->code()->kind() == Code::FUNCTION &&
+              !function->code()->has_debug_break_slots())
+            active_functions.Add(Handle<JSFunction>(function));
+        }
+      }
+      // Sort the functions on the object pointer value to prepare for
+      // the binary search below.
+      active_functions.Sort(HandleObjectPointerCompare<JSFunction>);
+
+      // Scan the heap for all non-optimized functions which has no
+      // debug break slots.
+      HeapIterator iterator;
+      HeapObject* obj = NULL;
+      while (((obj = iterator.next()) != NULL)) {

[Kevin Millikin (Chromium), 2011/09/29 10:47:35]

Maybe it doesn't matter, but should you avoid scanning map, code, and data
spaces?

[Søren Thygesen Gjesse, 2011/09/30 08:33:22]

Currently there is no space filtering in the heap iterator. I will prepare one
as a separate change.

+        if (obj->IsJSFunction()) {
+          JSFunction* function = JSFunction::cast(obj);
+          if (function->shared()->allows_lazy_compilation() &&
+              function->shared()->script()->IsScript() &&
+              function->code()->kind() == Code::FUNCTION &&
+              !function->code()->has_debug_break_slots()) {
+            bool has_activation =
+                SortedListBSearch<Handle<JSFunction> >(
+                    active_functions,
+                    Handle<JSFunction>(function),
+                    HandleObjectPointerCompare<JSFunction>) != -1;
+            if (!has_activation) {
+              function->set_code(*lazy_compile);
+              function->shared()->set_code(*lazy_compile);
+            }
+          }
+        }
       }
     }
-    active_functions.Sort();
-
-    // Scan the heap for all non-optimized functions which has no
-    // debug break slots.
-    HeapIterator iterator;
-    HeapObject* obj = NULL;
-    while (((obj = iterator.next()) != NULL)) {
-      if (obj->IsJSFunction()) {
-        JSFunction* function = JSFunction::cast(obj);
-        if (function->shared()->allows_lazy_compilation() &&
-            function->shared()->script()->IsScript() &&
-            function->code()->kind() == Code::FUNCTION &&
-            !function->code()->has_debug_break_slots()) {
-          bool has_activation =
-              SortedListBSearch<JSFunction*>(active_functions, function) != -1;
-          if (!has_activation) {
-            function->set_code(lazy_compile);
-            function->shared()->set_code(lazy_compile);
+
+    // Now the non-GC scope is left, and the sorting of the functions
+    // in active_function is not ensured any more. The code below does
+    // not rely on it.
+
+    // Now recompile all functions with activation frames and and
+    // patch the return address to run in the new compiled code.
+    for (int i = 0; i < active_functions.length(); i++) {
+      Handle<JSFunction> function = active_functions[i];
+      Handle<SharedFunctionInfo> shared(function->shared());
+      // If recompilation is not possible just skip it.
+      if (shared->is_toplevel() ||
+          !shared->allows_lazy_compilation() ||
+          shared->code()->kind() == Code::BUILTIN) {
+        continue;
+      }
+
+      // Make sure that the shared full code is compiled with debug
+      // break slots.
+      Handle<Code> current_code(function->code());
+      if (shared->code()->has_debug_break_slots()) {
+        // if the code is already recompiled to have break slots skip
+        // recompilation.
+        ASSERT(!function->code()->has_debug_break_slots());
+      } else {
+        // Try to compile the full code with debug break slots. If it
+        // fails just keep the current code.
+        ASSERT(shared->code() == *current_code);
+        ZoneScope zone_scope(isolate_, DELETE_ON_EXIT);
+        shared->set_code(*lazy_compile);
+        bool prev_force_debugger_active =
+            isolate_->debugger()->force_debugger_active();
+        isolate_->debugger()->set_force_debugger_active(true);
+        CompileFullCodeForDebugging(shared, current_code);
+        isolate_->debugger()->set_force_debugger_active(
+            prev_force_debugger_active);
+        if (!shared->is_compiled()) {
+          shared->set_code(*current_code);
+          continue;
+        }
+      }
+      Handle<Code> new_code(shared->code());
+
+      // Find the function and patch return address.
+      for (JavaScriptFrameIterator it(isolate_); !it.done(); it.Advance()) {
+        JavaScriptFrame* frame = it.frame();
+        // If the current frame is for this function in its
+        // non-optimized form rewrite the return address to continue
+        // in the newly compiled full code with debug break slots.
+        if (frame->function()->IsJSFunction() &&
+            frame->function() == *function &&
+            frame->LookupCode()->kind() == Code::FUNCTION) {
+          int delta = frame->pc() - current_code->instruction_start();
+          int debug_break_slot_count = 0;
+          int mask = RelocInfo::ModeMask(RelocInfo::DEBUG_BREAK_SLOT);
+          for (RelocIterator it(*new_code, mask); !it.done(); it.next()) {
+            // Check if the pc in the new code with debug break
+            // slots is before this slot.
+            RelocInfo* info = it.rinfo();
+            int debug_break_slot_bytes =
+                debug_break_slot_count * Assembler::kDebugBreakSlotLength;
+            int new_delta =
+                info->pc() -
+                new_code->instruction_start() -
+                debug_break_slot_bytes;
+            if (new_delta > delta) {
+              break;
+            }
+
+            // Passed a debug break slot in the full code with debug
+            // break slots.
+            debug_break_slot_count++;
           }
+          int debug_break_slot_bytes =
+              debug_break_slot_count * Assembler::kDebugBreakSlotLength;
+          if (FLAG_trace_deopt) {
+            PrintF("Replacing code %08" V8PRIxPTR " - %08" V8PRIxPTR " (%d) "
+                   "with %08" V8PRIxPTR " - %08" V8PRIxPTR " (%d) "
+                   "for debugging, "
+                   "changing pc from %08" V8PRIxPTR " to %08" V8PRIxPTR "\n",
+                   reinterpret_cast<intptr_t>(
+                       current_code->instruction_start()),
+                   reinterpret_cast<intptr_t>(
+                       current_code->instruction_start()) +
+                       current_code->instruction_size(),
+                   current_code->instruction_size(),
+                   reinterpret_cast<intptr_t>(new_code->instruction_start()),
+                   reinterpret_cast<intptr_t>(new_code->instruction_start()) +
+                       new_code->instruction_size(),
+                   new_code->instruction_size(),
+                   reinterpret_cast<intptr_t>(frame->pc()),
+                   reinterpret_cast<intptr_t>(new_code->instruction_start()) +
+                       delta + debug_break_slot_bytes);
+          }
+
+          // Patch the return address to return into the code with
+          // debug break slots.
+          frame->set_pc(
+              new_code->instruction_start() + delta + debug_break_slot_bytes);
         }
       }
     }
   }
 }
 
 
 // Ensures the debug information is present for shared.
 bool Debug::EnsureDebugInfo(Handle<SharedFunctionInfo> shared) {
   // Return if we already have the debug info for shared.
@@ skipping 1050 matching lines @@
   // Set the debug command break flag to have the command processed.
   if (!isolate_->debug()->InDebugger()) {
     isolate_->stack_guard()->DebugCommand();
   }
 }
 
 
 bool Debugger::IsDebuggerActive() {
   ScopedLock with(debugger_access_);
 
-  return message_handler_ != NULL || !event_listener_.is_null();
+  return message_handler_ != NULL ||
+      !event_listener_.is_null() ||
+      force_debugger_active_;
 }
 
 
 Handle<Object> Debugger::Call(Handle<JSFunction> fun,
                               Handle<Object> data,
                               bool* pending_exception) {
   // When calling functions in the debugger prevent it from beeing unloaded.
   Debugger::never_unload_debugger_ = true;
 
   // Enter the debugger.
@@ skipping 377 matching lines @@
     {
       Locker locker;
       Isolate::Current()->debugger()->CallMessageDispatchHandler();
     }
   }
 }
 
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 } }  // namespace v8::internal