chromium/v8/src/common/ptr-compr.h

// Copyright 2022 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.

#ifndef V8_COMMON_PTR_COMPR_H_
#define V8_COMMON_PTR_COMPR_H_

#include "src/base/memory.h"
#include "src/common/globals.h"

namespace v8::internal {

class IsolateGroup;

// This is just a collection of common compression scheme related functions.
// Each pointer compression cage then has its own compression scheme, which
// mainly differes in the cage base address they use.
template <typename Cage>
class V8HeapCompressionSchemeImpl { … };

// The main pointer compression cage, used for most objects.
class MainCage : public AllStatic { … };
V8HeapCompressionScheme;

#ifdef V8_ENABLE_SANDBOX
// Compression scheme used for compressed pointers between trusted objects in
// the trusted heap space, outside of the sandbox.
class TrustedCage : public AllStatic { … };
TrustedSpaceCompressionScheme;
#else
// The trusted cage does not exist in this case.
using TrustedSpaceCompressionScheme = V8HeapCompressionScheme;
#endif  // V8_ENABLE_SANDBOX

// A compression scheme which can be passed if the only objects we ever expect
// to see are Smis (e.g. for {TaggedField<Smi, 0, SmiCompressionScheme>}).
class SmiCompressionScheme : public AllStatic { … };

#ifdef V8_EXTERNAL_CODE_SPACE
// Compression scheme used for fields containing InstructionStream objects
// (namely for the Code::code field). Same as
// V8HeapCompressionScheme but with a different base value.
// TODO(ishell): consider also using V8HeapCompressionSchemeImpl here unless
// this becomes a different compression scheme that allows crossing the 4GB
// boundary.
class ExternalCodeCompressionScheme { … };

#endif  // V8_EXTERNAL_CODE_SPACE

// Accessors for fields that may be unaligned due to pointer compression.

template <typename V>
static inline V ReadMaybeUnalignedValue(Address p) { … }

template <typename V>
static inline void WriteMaybeUnalignedValue(Address p, V value) { … }

// When multi-cage pointer compression mode is enabled this scope object
// saves current cage's base values and sets them according to given Isolate.
// For all other configurations this scope object is a no-op.
class PtrComprCageAccessScope final { … };

}  // namespace v8::internal

#endif  // V8_COMMON_PTR_COMPR_H_