// 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_CODE_MEMORY_ACCESS_H_

#define V8_COMMON_CODE_MEMORY_ACCESS_H_

#include "src/base/build_config.h"

#include "src/base/macros.h"

namespace v8 {

namespace internal {

class CodePageCollectionMemoryModificationScope;

class CodePageMemoryModificationScope;

class CodeSpaceMemoryModificationScope;

class RwxMemoryWriteScopeForTesting;

namespace wasm {

class CodeSpaceWriteScope;

}

// This scope is a wrapper for APRR/MAP_JIT machinery on MacOS on ARM64

// ("Apple M1"/Apple Silicon) with respective semantics.

// See pthread_jit_write_protect_np() for details.

// On other platforms the scope is a no-op.

//

// The semantics is the following: the scope switches permissions between

// writable and executable for all the pages allocated with RWX permissions.

// Only current thread is affected. This achieves "real" W^X and it's fast.

// By default it is assumed that the state is executable.

//

// The scope is reentrant and thread safe.

class V8_NODISCARD RwxMemoryWriteScope final {

public:

V8_INLINE RwxMemoryWriteScope();

V8_INLINE ~RwxMemoryWriteScope();

// Disable copy constructor and copy-assignment operator, since this manages

// a resource and implicit copying of the scope can yield surprising errors.

RwxMemoryWriteScope(const RwxMemoryWriteScope&) = delete;

RwxMemoryWriteScope& operator=(const RwxMemoryWriteScope&) = delete;

private:

friend class CodePageCollectionMemoryModificationScope;

friend class CodePageMemoryModificationScope;

friend class CodeSpaceMemoryModificationScope;

friend class RwxMemoryWriteScopeForTesting;

friend class wasm::CodeSpaceWriteScope;

// {SetWritable} and {SetExecutable} implicitly enters/exits the scope.

// These methods are exposed only for the purpose of implementing other

// scope classes that affect executable pages permissions.

V8_INLINE static void SetWritable();

V8_INLINE static void SetExecutable();

#if V8_HAS_PTHREAD_JIT_WRITE_PROTECT

// This counter is used for supporting scope reentrance.

static thread_local int code_space_write_nesting_level_;

#endif // V8_HAS_PTHREAD_JIT_WRITE_PROTECT

};

// Same as the RwxMemoryWriteScope but without inlining the code.

// This is a workaround for component build issue (crbug/1316800), when

// a thread_local value can't be properly exported.

class V8_NODISCARD RwxMemoryWriteScopeForTesting final {

public:

#if V8_HAS_PTHREAD_JIT_WRITE_PROTECT

V8_EXPORT_PRIVATE RwxMemoryWriteScopeForTesting();

V8_EXPORT_PRIVATE ~RwxMemoryWriteScopeForTesting();

#else

V8_INLINE RwxMemoryWriteScopeForTesting() {

// Define a constructor to avoid unused variable warnings.

}

#endif // V8_HAS_PTHREAD_JIT_WRITE_PROTECT

// Disable copy constructor and copy-assignment operator, since this manages

// a resource and implicit copying of the scope can yield surprising errors.

RwxMemoryWriteScopeForTesting(const RwxMemoryWriteScopeForTesting&) = delete;

RwxMemoryWriteScopeForTesting& operator=(

const RwxMemoryWriteScopeForTesting&) = delete;

};

} // namespace internal

} // namespace v8

#endif // V8_COMMON_CODE_MEMORY_ACCESS_H_