Source/WTF/wtf/WTFConfig.h

/*
 * Copyright (C) 2020 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. ``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
 * 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 <wtf/Assertions.h>
#include <wtf/Atomics.h>
#include <wtf/ExportMacros.h>
#include <wtf/PageBlock.h>
#include <wtf/PtrTag.h>
#include <wtf/StdLibExtras.h>
#include <wtf/threads/Signals.h>

#if defined(USE_SYSTEM_MALLOC) && USE_SYSTEM_MALLOC
namespace Gigacage {
constexpr size_t reservedSlotsForGigacageConfig = 0;
constexpr size_t reservedBytesForGigacageConfig = 0;
}
#else
#include <bmalloc/GigacageConfig.h>
#endif

namespace WebConfig {

using Slot = uint64_t;
extern "C" WTF_EXPORT_PRIVATE Slot g_config[];

} // namespace WebConfig

namespace WTF {

constexpr size_t ConfigSizeToProtect = CeilingOnPageSize;

struct Config {
    WTF_EXPORT_PRIVATE static void permanentlyFreeze();

    struct AssertNotFrozenScope {
        AssertNotFrozenScope();
        ~AssertNotFrozenScope();
    };

    // All the fields in this struct should be chosen such that their
    // initial value is 0 / null / falsy because Config is instantiated
    // as a global singleton.

    bool isPermanentlyFrozen;

#if OS(UNIX)
    SignalHandlers signalHandlers;
#endif
    PtrTagLookup* ptrTagLookupHead;

    uint64_t spaceForExtensions[1];
};

constexpr size_t startSlotOfWTFConfig = Gigacage::reservedSlotsForGigacageConfig;
constexpr size_t startOffsetOfWTFConfig = startSlotOfWTFConfig * sizeof(WebConfig::Slot);

constexpr size_t offsetOfWTFConfigExtension = startOffsetOfWTFConfig + offsetof(WTF::Config, spaceForExtensions);

constexpr size_t alignmentOfWTFConfig = std::alignment_of<WTF::Config>::value;

static_assert(Gigacage::reservedBytesForGigacageConfig + sizeof(WTF::Config) <= ConfigSizeToProtect);
static_assert(roundUpToMultipleOf<alignmentOfWTFConfig>(startOffsetOfWTFConfig) == startOffsetOfWTFConfig);

#define g_wtfConfig (*bitwise_cast<WTF::Config*>(&WebConfig::g_config[WTF::startSlotOfWTFConfig]))

ALWAYS_INLINE Config::AssertNotFrozenScope::AssertNotFrozenScope()
{
    RELEASE_ASSERT(!g_wtfConfig.isPermanentlyFrozen);
    compilerFence();
};

ALWAYS_INLINE Config::AssertNotFrozenScope::~AssertNotFrozenScope()
{
    compilerFence();
    RELEASE_ASSERT(!g_wtfConfig.isPermanentlyFrozen);
};

} // namespace WTF