fbc230e42b
Split executable memory chunks into two pieces: header with all metadata (protection: RW) and body (protection: RWX). Separate header from metadata with a guard page and add a guard page after the page body. R=erik.corry@gmail.com BUG=http://crbug.com/115151 Review URL: https://chromiumcodereview.appspot.com/9452002 git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10809 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
353 lines
12 KiB
C++
353 lines
12 KiB
C++
// Copyright 2011 the V8 project authors. All rights reserved.
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following
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// disclaimer in the documentation and/or other materials provided
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// with the distribution.
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// * Neither the name of Google Inc. nor the names of its
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// contributors may be used to endorse or promote products derived
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// from this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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#ifndef V8_OBJECTS_VISITING_H_
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#define V8_OBJECTS_VISITING_H_
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#include "allocation.h"
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// This file provides base classes and auxiliary methods for defining
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// static object visitors used during GC.
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// Visiting HeapObject body with a normal ObjectVisitor requires performing
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// two switches on object's instance type to determine object size and layout
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// and one or more virtual method calls on visitor itself.
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// Static visitor is different: it provides a dispatch table which contains
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// pointers to specialized visit functions. Each map has the visitor_id
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// field which contains an index of specialized visitor to use.
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namespace v8 {
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namespace internal {
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// Base class for all static visitors.
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class StaticVisitorBase : public AllStatic {
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public:
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enum VisitorId {
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kVisitSeqAsciiString = 0,
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kVisitSeqTwoByteString,
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kVisitShortcutCandidate,
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kVisitByteArray,
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kVisitFreeSpace,
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kVisitFixedArray,
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kVisitFixedDoubleArray,
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kVisitGlobalContext,
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// For data objects, JS objects and structs along with generic visitor which
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// can visit object of any size we provide visitors specialized by
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// object size in words.
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// Ids of specialized visitors are declared in a linear order (without
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// holes) starting from the id of visitor specialized for 2 words objects
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// (base visitor id) and ending with the id of generic visitor.
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// Method GetVisitorIdForSize depends on this ordering to calculate visitor
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// id of specialized visitor from given instance size, base visitor id and
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// generic visitor's id.
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kVisitDataObject,
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kVisitDataObject2 = kVisitDataObject,
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kVisitDataObject3,
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kVisitDataObject4,
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kVisitDataObject5,
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kVisitDataObject6,
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kVisitDataObject7,
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kVisitDataObject8,
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kVisitDataObject9,
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kVisitDataObjectGeneric,
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kVisitJSObject,
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kVisitJSObject2 = kVisitJSObject,
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kVisitJSObject3,
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kVisitJSObject4,
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kVisitJSObject5,
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kVisitJSObject6,
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kVisitJSObject7,
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kVisitJSObject8,
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kVisitJSObject9,
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kVisitJSObjectGeneric,
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kVisitStruct,
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kVisitStruct2 = kVisitStruct,
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kVisitStruct3,
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kVisitStruct4,
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kVisitStruct5,
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kVisitStruct6,
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kVisitStruct7,
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kVisitStruct8,
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kVisitStruct9,
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kVisitStructGeneric,
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kVisitConsString,
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kVisitSlicedString,
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kVisitOddball,
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kVisitCode,
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kVisitMap,
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kVisitPropertyCell,
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kVisitSharedFunctionInfo,
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kVisitJSFunction,
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kVisitJSWeakMap,
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kVisitJSRegExp,
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kVisitorIdCount,
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kMinObjectSizeInWords = 2
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};
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// Visitor ID should fit in one byte.
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STATIC_ASSERT(kVisitorIdCount <= 256);
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// Determine which specialized visitor should be used for given instance type
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// and instance type.
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static VisitorId GetVisitorId(int instance_type, int instance_size);
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static VisitorId GetVisitorId(Map* map) {
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return GetVisitorId(map->instance_type(), map->instance_size());
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}
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// For visitors that allow specialization by size calculate VisitorId based
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// on size, base visitor id and generic visitor id.
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static VisitorId GetVisitorIdForSize(VisitorId base,
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VisitorId generic,
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int object_size) {
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ASSERT((base == kVisitDataObject) ||
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(base == kVisitStruct) ||
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(base == kVisitJSObject));
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ASSERT(IsAligned(object_size, kPointerSize));
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ASSERT(kMinObjectSizeInWords * kPointerSize <= object_size);
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ASSERT(object_size < Page::kMaxNonCodeHeapObjectSize);
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const VisitorId specialization = static_cast<VisitorId>(
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base + (object_size >> kPointerSizeLog2) - kMinObjectSizeInWords);
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return Min(specialization, generic);
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}
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};
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template<typename Callback>
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class VisitorDispatchTable {
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public:
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void CopyFrom(VisitorDispatchTable* other) {
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// We are not using memcpy to guarantee that during update
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// every element of callbacks_ array will remain correct
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// pointer (memcpy might be implemented as a byte copying loop).
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for (int i = 0; i < StaticVisitorBase::kVisitorIdCount; i++) {
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NoBarrier_Store(&callbacks_[i], other->callbacks_[i]);
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}
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}
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inline Callback GetVisitorById(StaticVisitorBase::VisitorId id) {
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return reinterpret_cast<Callback>(callbacks_[id]);
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}
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inline Callback GetVisitor(Map* map) {
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return reinterpret_cast<Callback>(callbacks_[map->visitor_id()]);
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}
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void Register(StaticVisitorBase::VisitorId id, Callback callback) {
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ASSERT(id < StaticVisitorBase::kVisitorIdCount); // id is unsigned.
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callbacks_[id] = reinterpret_cast<AtomicWord>(callback);
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}
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template<typename Visitor,
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StaticVisitorBase::VisitorId base,
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StaticVisitorBase::VisitorId generic,
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int object_size_in_words>
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void RegisterSpecialization() {
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static const int size = object_size_in_words * kPointerSize;
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Register(StaticVisitorBase::GetVisitorIdForSize(base, generic, size),
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&Visitor::template VisitSpecialized<size>);
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}
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template<typename Visitor,
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StaticVisitorBase::VisitorId base,
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StaticVisitorBase::VisitorId generic>
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void RegisterSpecializations() {
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STATIC_ASSERT(
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(generic - base + StaticVisitorBase::kMinObjectSizeInWords) == 10);
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RegisterSpecialization<Visitor, base, generic, 2>();
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RegisterSpecialization<Visitor, base, generic, 3>();
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RegisterSpecialization<Visitor, base, generic, 4>();
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RegisterSpecialization<Visitor, base, generic, 5>();
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RegisterSpecialization<Visitor, base, generic, 6>();
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RegisterSpecialization<Visitor, base, generic, 7>();
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RegisterSpecialization<Visitor, base, generic, 8>();
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RegisterSpecialization<Visitor, base, generic, 9>();
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Register(generic, &Visitor::Visit);
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}
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private:
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AtomicWord callbacks_[StaticVisitorBase::kVisitorIdCount];
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};
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template<typename StaticVisitor>
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class BodyVisitorBase : public AllStatic {
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public:
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INLINE(static void IteratePointers(Heap* heap,
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HeapObject* object,
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int start_offset,
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int end_offset)) {
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Object** start_slot = reinterpret_cast<Object**>(object->address() +
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start_offset);
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Object** end_slot = reinterpret_cast<Object**>(object->address() +
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end_offset);
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StaticVisitor::VisitPointers(heap, start_slot, end_slot);
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}
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};
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template<typename StaticVisitor, typename BodyDescriptor, typename ReturnType>
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class FlexibleBodyVisitor : public BodyVisitorBase<StaticVisitor> {
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public:
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static inline ReturnType Visit(Map* map, HeapObject* object) {
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int object_size = BodyDescriptor::SizeOf(map, object);
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BodyVisitorBase<StaticVisitor>::IteratePointers(
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map->GetHeap(),
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object,
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BodyDescriptor::kStartOffset,
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object_size);
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return static_cast<ReturnType>(object_size);
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}
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template<int object_size>
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static inline ReturnType VisitSpecialized(Map* map, HeapObject* object) {
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ASSERT(BodyDescriptor::SizeOf(map, object) == object_size);
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BodyVisitorBase<StaticVisitor>::IteratePointers(
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map->GetHeap(),
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object,
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BodyDescriptor::kStartOffset,
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object_size);
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return static_cast<ReturnType>(object_size);
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}
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};
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template<typename StaticVisitor, typename BodyDescriptor, typename ReturnType>
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class FixedBodyVisitor : public BodyVisitorBase<StaticVisitor> {
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public:
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static inline ReturnType Visit(Map* map, HeapObject* object) {
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BodyVisitorBase<StaticVisitor>::IteratePointers(
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map->GetHeap(),
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object,
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BodyDescriptor::kStartOffset,
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BodyDescriptor::kEndOffset);
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return static_cast<ReturnType>(BodyDescriptor::kSize);
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}
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};
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// Base class for visitors used for a linear new space iteration.
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// IterateBody returns size of visited object.
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// Certain types of objects (i.e. Code objects) are not handled
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// by dispatch table of this visitor because they cannot appear
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// in the new space.
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//
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// This class is intended to be used in the following way:
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//
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// class SomeVisitor : public StaticNewSpaceVisitor<SomeVisitor> {
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// ...
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// }
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//
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// This is an example of Curiously recurring template pattern
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// (see http://en.wikipedia.org/wiki/Curiously_recurring_template_pattern).
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// We use CRTP to guarantee aggressive compile time optimizations (i.e.
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// inlining and specialization of StaticVisitor::VisitPointers methods).
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template<typename StaticVisitor>
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class StaticNewSpaceVisitor : public StaticVisitorBase {
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public:
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static void Initialize();
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static inline int IterateBody(Map* map, HeapObject* obj) {
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return table_.GetVisitor(map)(map, obj);
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}
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static inline void VisitPointers(Heap* heap, Object** start, Object** end) {
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for (Object** p = start; p < end; p++) StaticVisitor::VisitPointer(heap, p);
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}
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private:
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static inline int VisitByteArray(Map* map, HeapObject* object) {
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return reinterpret_cast<ByteArray*>(object)->ByteArraySize();
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}
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static inline int VisitFixedDoubleArray(Map* map, HeapObject* object) {
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int length = reinterpret_cast<FixedDoubleArray*>(object)->length();
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return FixedDoubleArray::SizeFor(length);
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}
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static inline int VisitJSObject(Map* map, HeapObject* object) {
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return JSObjectVisitor::Visit(map, object);
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}
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static inline int VisitSeqAsciiString(Map* map, HeapObject* object) {
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return SeqAsciiString::cast(object)->
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SeqAsciiStringSize(map->instance_type());
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}
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static inline int VisitSeqTwoByteString(Map* map, HeapObject* object) {
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return SeqTwoByteString::cast(object)->
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SeqTwoByteStringSize(map->instance_type());
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}
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static inline int VisitFreeSpace(Map* map, HeapObject* object) {
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return FreeSpace::cast(object)->Size();
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}
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class DataObjectVisitor {
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public:
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template<int object_size>
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static inline int VisitSpecialized(Map* map, HeapObject* object) {
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return object_size;
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}
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static inline int Visit(Map* map, HeapObject* object) {
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return map->instance_size();
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}
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};
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typedef FlexibleBodyVisitor<StaticVisitor,
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StructBodyDescriptor,
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int> StructVisitor;
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typedef FlexibleBodyVisitor<StaticVisitor,
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JSObject::BodyDescriptor,
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int> JSObjectVisitor;
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typedef int (*Callback)(Map* map, HeapObject* object);
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static VisitorDispatchTable<Callback> table_;
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};
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template<typename StaticVisitor>
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VisitorDispatchTable<typename StaticNewSpaceVisitor<StaticVisitor>::Callback>
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StaticNewSpaceVisitor<StaticVisitor>::table_;
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} } // namespace v8::internal
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#endif // V8_OBJECTS_VISITING_H_
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