sdk/runtime/vm/stack_frame.cc

// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

#include "vm/stack_frame.h"

#include "vm/isolate.h"
#include "vm/object.h"
#include "vm/object_store.h"
#include "vm/os.h"
#include "vm/raw_object.h"
#include "vm/stub_code.h"
#include "vm/visitor.h"

namespace dart {

bool StackFrame::FindRawCodeVisitor::FindObject(RawObject* obj) {
  return RawInstructions::ContainsPC(obj, pc_);
}


bool StackFrame::IsStubFrame() const {
  if (Dart::vm_isolate()->heap()->StubCodeContains(pc())) {
    return true;  // Common stub code is generated in the VM heap.
  }
  if (Isolate::Current()->heap()->StubCodeContains(pc())) {
    return true;  // Common stub code is generated in the VM heap.
  }
  return false;
}


void StackFrame::Print() const {
  OS::Print("[%-8s : sp(%p) ]\n", GetName(), sp());
}


RawCode* StackFrame::LookupCode(Isolate* isolate, uword pc) {
  // TODO(asiva): Need to add a data structure for storing a (pc, code
  // object) map in order to do a quick lookup and avoid having to
  // traverse the code heap.
  ASSERT(isolate != NULL);
  // We add a no gc scope to ensure that the code below does not trigger
  // a GC as we are handling raw object references here. It is possible
  // that the code is called while a GC is in progress, that is ok.
  NoGCScope no_gc;
  FindRawCodeVisitor visitor(pc);
  RawInstructions* instr = isolate->heap()->FindObjectInCodeSpace(&visitor);
  if (instr != Instructions::null()) {
    return instr->ptr()->code_;
  }
  return Code::null();
}


void ExitFrame::VisitObjectPointers(ObjectPointerVisitor* visitor) {
  // There are no objects to visit in this frame.
}


void EntryFrame::VisitObjectPointers(ObjectPointerVisitor* visitor) {
  // Visit objects between SP and (FP - callee_save_area).
  ASSERT(visitor != NULL);
  RawObject** start = reinterpret_cast<RawObject**>(sp());
  RawObject** end = reinterpret_cast<RawObject**>(
      fp() - kWordSize + ExitLinkOffset());
  visitor->VisitPointers(start, end);
}


void StackFrame::VisitObjectPointers(ObjectPointerVisitor* visitor) {
  // NOTE: This code runs while GC is in progress and runs within
  // a NoHandleScope block. Hence it is not ok to use regular Zone or
  // Scope handles. We use direct stack handles, the raw pointers in
  // these handles are not traversed. The use of handles is mainly to
  // be able to reuse the handle based code and avoid having to add
  // helper functions to the raw object interface.
  NoGCScope no_gc;
  Code code;
  code = LookupDartCode();
  if (!code.IsNull()) {
    Array maps;
    maps = Array::null();
    Stackmap map;
    map = code.GetStackmap(pc(), &maps, &map);
    if (!map.IsNull()) {
      // A stack map is present in the code object, use the stack map to visit
      // frame slots which are marked as having objects.
      intptr_t bit_offset = map.MinimumBitOffset();
      intptr_t end_bit_offset = map.MaximumBitOffset();
      while (bit_offset <= end_bit_offset) {
        uword addr = (fp() - ((bit_offset + 1) * kWordSize));
        ASSERT(addr >= sp());
        if (map.IsObject(bit_offset)) {
          visitor->VisitPointer(reinterpret_cast<RawObject**>(addr));
        }
        bit_offset += 1;
      }
      return;
    }
  }
  // No stack maps are present in the code object which means this
  // frame relies on tagged pointers and hence we visit each entry
  // on the frame between SP and FP.
  ASSERT(visitor != NULL);
  visitor->VisitPointers(reinterpret_cast<RawObject**>(sp()),
                         reinterpret_cast<RawObject**>(fp() - kWordSize));
}


RawFunction* StackFrame::LookupDartFunction() const {
  const Code& code = Code::Handle(LookupDartCode());
  if (!code.IsNull()) {
    return code.function();
  }
  return Function::null();
}


RawCode* StackFrame::LookupDartCode() const {
  // We add a no gc scope to ensure that the code below does not trigger
  // a GC as we are handling raw object references here. It is possible
  // that the code is called while a GC is in progress, that is ok.
  NoGCScope no_gc;
  Isolate* isolate = Isolate::Current();
  RawCode* code = StackFrame::LookupCode(isolate, pc());
  if ((code != Code::null()) && (code->ptr()->function_ != Function::null())) {
    return code;
  }
  return Code::null();
}


bool StackFrame::FindExceptionHandler(uword* handler_pc) const {
  const Code& code = Code::Handle(LookupDartCode());
  if (code.IsNull()) {
    return false;  // Stub frames do not have exception handlers.
  }

  // First try to find pc descriptor for the current pc.
  intptr_t try_index = -1;
  const PcDescriptors& descriptors =
      PcDescriptors::Handle(code.pc_descriptors());
  for (intptr_t i = 0; i < descriptors.Length(); i++) {
    if (static_cast<uword>(descriptors.PC(i)) == pc() &&
        descriptors.TryIndex(i) != -1) {
      try_index = descriptors.TryIndex(i);
      break;
    }
  }
  if (try_index != -1) {
    // We found a pc descriptor, now try to see if we have an
    // exception catch handler for this try index.
    const ExceptionHandlers& handlers =
        ExceptionHandlers::Handle(code.exception_handlers());
    for (intptr_t j = 0; j < handlers.Length(); j++) {
      if (handlers.TryIndex(j) == try_index) {
        *handler_pc = handlers.HandlerPC(j);
        return true;
      }
    }
  }
  return false;
}


bool StackFrame::IsValid() const {
  if (IsEntryFrame() || IsExitFrame() || IsStubFrame()) {
    return true;
  }
  return (StackFrame::LookupCode(Isolate::Current(), pc()) != Code::null());
}


StackFrameIterator::StackFrameIterator(bool validate)
    : validate_(validate), entry_(), exit_(), current_frame_(NULL) {
  SetupLastExitFrameData();  // Setup data for last exit frame.
}


StackFrame* StackFrameIterator::NextFrame() {
  // When we are at the start of iteration after having created an
  // iterator object current_frame_ will be NULL as we haven't seen
  // any frames yet. At this point if NextFrame is called it tries
  // to set up the next exit frame by reading the top_exit_frame_info
  // from the isolate. If we do not have any dart invocations yet
  // top_exit_frame_info will be 0 and so we would return NULL.

  // current_frame_ will also be NULL, when we are at the end of having
  // iterated through all the frames. if NextFrame is called at this
  // point we will try and set up the next exit frame but since we are
  // at the end of the iteration fp_ will be 0 and we would return NULL.
  if (current_frame_ == NULL) {
    if (!HasNextFrame()) {
      return NULL;
    }
    current_frame_ = NextExitFrame();
    return current_frame_;
  }
  ASSERT((validate_ == kDontValidateFrames) || current_frame_->IsValid());
  if (current_frame_->IsEntryFrame()) {
    if (HasNextFrame()) {  // We have another chained block.
      current_frame_ = NextExitFrame();
      return current_frame_;
    }
    current_frame_ = NULL;  // No more frames.
    return current_frame_;
  }
  ASSERT(current_frame_->IsExitFrame() ||
         current_frame_->IsDartFrame() ||
         current_frame_->IsStubFrame());

  // Consume dart/stub frames using StackFrameIterator::FrameSetIterator
  // until we are out of dart/stub frames at which point we return the
  // corresponding entry frame for that set of dart/stub frames.
  current_frame_ =
      (frames_.HasNext()) ? frames_.NextFrame(validate_) : NextEntryFrame();
  return current_frame_;
}


StackFrame* StackFrameIterator::FrameSetIterator::NextFrame(bool validate) {
  StackFrame* frame;
  ASSERT(HasNext());
  frame = &stack_frame_;
  frame->sp_ = sp_;
  frame->fp_ = fp_;
  sp_ = frame->GetCallerSp();
  fp_ = frame->GetCallerFp();
  ASSERT((validate == kDontValidateFrames) || frame->IsValid());
  return frame;
}


ExitFrame* StackFrameIterator::NextExitFrame() {
  exit_.sp_ = frames_.sp_;
  exit_.fp_ = frames_.fp_;
  frames_.sp_ = exit_.GetCallerSp();
  frames_.fp_ = exit_.GetCallerFp();
  ASSERT(exit_.IsValid());
  return &exit_;
}


EntryFrame* StackFrameIterator::NextEntryFrame() {
  ASSERT(!frames_.HasNext());
  entry_.sp_ = frames_.sp_;
  entry_.fp_ = frames_.fp_;
  SetupNextExitFrameData();  // Setup data for next exit frame in chain.
  ASSERT(entry_.IsValid());
  return &entry_;
}

}  // namespace dart