Source/JavaScriptCore/runtime/Scribble.h

/*
 * Copyright (C) 2019 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. 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 with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGE.
 */

#pragma once

#include "JSCJSValue.h"
#include "JSCell.h"
#include "Options.h"

namespace JSC {

inline bool scribbleFreeCells()
{
    return ASSERT_ENABLED || Options::scribbleFreeCells();
}

#define SCRIBBLE_WORD static_cast<intptr_t>(0xbadbeef0)

inline bool isScribbledValue(JSValue value)
{
    return JSValue::encode(value) == JSValue::encode(bitwise_cast<JSCell*>(SCRIBBLE_WORD));
}

inline void scribble(void* base, size_t size)
{
    for (size_t i = size / sizeof(EncodedJSValue); i--;) {
        // Use a 16-byte aligned value to ensure that it passes the cell check.
        static_cast<EncodedJSValue*>(base)[i] = JSValue::encode(bitwise_cast<JSCell*>(SCRIBBLE_WORD));
    }
}

}