serenity/DevTools/UserspaceEmulator/ValueWithShadow.h

/*
 * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
 * 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 THE COPYRIGHT HOLDERS AND 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 THE COPYRIGHT HOLDER OR 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.
 */

#include <AK/Format.h>
#include <AK/Platform.h>

#pragma once

namespace UserspaceEmulator {

template<typename T>
class ValueAndShadowReference;

template<typename T>
class ValueWithShadow {
public:
    using ValueType = T;

    ValueWithShadow(T value, T shadow)
        : m_value(value)
        , m_shadow(shadow)
    {
    }

    ValueWithShadow(const ValueAndShadowReference<T>&);

    T value() const { return m_value; }
    T shadow() const { return m_shadow; }

    bool is_uninitialized() const
    {
        if constexpr (sizeof(T) == 4)
            return (m_shadow & 0x01010101) != 0x01010101;
        if constexpr (sizeof(T) == 2)
            return (m_shadow & 0x0101) != 0x0101;
        if constexpr (sizeof(T) == 1)
            return (m_shadow & 0x01) != 0x01;
    }

    void set_initialized()
    {
        if constexpr (sizeof(T) == 4)
            m_shadow = 0x01010101;
        if constexpr (sizeof(T) == 2)
            m_shadow = 0x0101;
        if constexpr (sizeof(T) == 1)
            m_shadow = 0x01;
    }

private:
    T m_value;
    T m_shadow;
};

template<typename T>
class ValueAndShadowReference {
public:
    using ValueType = T;

    ValueAndShadowReference(T& value, T& shadow)
        : m_value(value)
        , m_shadow(shadow)
    {
    }

    bool is_uninitialized() const
    {
        if constexpr (sizeof(T) == 4)
            return (m_shadow & 0x01010101) != 0x01010101;
        if constexpr (sizeof(T) == 2)
            return (m_shadow & 0x0101) != 0x0101;
        if constexpr (sizeof(T) == 1)
            return (m_shadow & 0x01) != 0x01;
    }

    void operator=(const ValueWithShadow<T>&);

    T& value() { return m_value; }
    T& shadow() { return m_shadow; }

    const T& value() const { return m_value; }
    const T& shadow() const { return m_shadow; }

private:
    T& m_value;
    T& m_shadow;
};

template<typename T>
ALWAYS_INLINE ValueWithShadow<T> shadow_wrap_as_initialized(T value)
{
    if constexpr (sizeof(T) == 8)
        return { value, 0x01010101'01010101LLU };
    if constexpr (sizeof(T) == 4)
        return { value, 0x01010101 };
    if constexpr (sizeof(T) == 2)
        return { value, 0x0101 };
    if constexpr (sizeof(T) == 1)
        return { value, 0x01 };
}

template<typename T, typename U>
ALWAYS_INLINE ValueWithShadow<T> shadow_wrap_with_taint_from(T value, const U& taint_a)
{
    if (taint_a.is_uninitialized())
        return { value, 0 };
    return shadow_wrap_as_initialized(value);
}

template<typename T, typename U, typename V>
ALWAYS_INLINE ValueWithShadow<T> shadow_wrap_with_taint_from(T value, const U& taint_a, const V& taint_b)
{
    if (taint_a.is_uninitialized() || taint_b.is_uninitialized())
        return { value, 0 };
    return shadow_wrap_as_initialized(value);
}

template<typename T, typename U, typename V, typename X>
ALWAYS_INLINE ValueWithShadow<T> shadow_wrap_with_taint_from(T value, const U& taint_a, const V& taint_b, const X& taint_c)
{
    if (taint_a.is_uninitialized() || taint_b.is_uninitialized() || taint_c.is_uninitialized())
        return { value, 0 };
    return shadow_wrap_as_initialized(value);
}

template<typename T>
inline ValueWithShadow<T>::ValueWithShadow(const ValueAndShadowReference<T>& other)
    : m_value(other.value())
    , m_shadow(other.shadow())
{
}

template<typename T>
inline void ValueAndShadowReference<T>::operator=(const ValueWithShadow<T>& other)
{
    m_value = other.value();
    m_shadow = other.shadow();
}

}

template<typename T>
struct AK::Formatter<UserspaceEmulator::ValueWithShadow<T>> : AK::Formatter<T> {
    void format(TypeErasedFormatParams& params, FormatBuilder& builder, UserspaceEmulator::ValueWithShadow<T> value)
    {
        return Formatter<T>::format(params, builder, value.value());
    }
};