Source/JavaScriptCore/runtime/StackManager.h

/*
 * Copyright (C) 2025 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,
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#pragma once

#include <wtf/Atomics.h>
#include <wtf/Lock.h>
#include <wtf/SentinelLinkedList.h>

#if ENABLE(C_LOOP)
#include <JavaScriptCore/CLoopStack.h>
#endif

namespace JSC {

class VM;

class StackManager {
public:
    class Mirror : public BasicRawSentinelNode<Mirror> {
    public:
        void* softStackLimit() const { return m_softStackLimit; }
        void* trapAwareSoftStackLimit() const { return m_trapAwareSoftStackLimit.loadRelaxed(); }

        static constexpr ptrdiff_t offsetOfSoftStackLimit()
        {
            return OBJECT_OFFSETOF(Mirror, m_softStackLimit);
        }

    private:
        Atomic<void*> m_trapAwareSoftStackLimit { nullptr };
        void* m_softStackLimit { nullptr };

        friend class LLIntOffsetsExtractor;
        friend class StackManager;
    };

    void registerMirror(Mirror&);
    void unregisterMirror(Mirror&);

    bool hasStopRequest() { return trapAwareSoftStackLimit() == stopRequestMarker(); }
    CONCURRENT_SAFE void requestStop();
    CONCURRENT_SAFE void cancelStop();

    void* softStackLimit() const { return m_softStackLimit; }
    void* trapAwareSoftStackLimit() const { return m_trapAwareSoftStackLimit.loadRelaxed(); }

    void setStackSoftLimit(void* newLimit);

    static constexpr ptrdiff_t offsetOfSoftStackLimit()
    {
        return OBJECT_OFFSETOF(StackManager, m_softStackLimit);
    }

    void** addressOfSoftStackLimit() { return &m_softStackLimit; }

#if ENABLE(C_LOOP)
    void* cloopStackLimit() { return m_cloopStackLimit; }
    void setCLoopStackLimit(void* newStackLimit);
    ALWAYS_INLINE void* currentCLoopStackPointer() const { return m_cloopStack.currentStackPointer(); }

    CLoopStack& cloopStack() { return m_cloopStack; }
    const CLoopStack& cloopStack() const { return m_cloopStack; }

    static constexpr ptrdiff_t offsetOfCLoopStack()
    {
        return OBJECT_OFFSETOF(StackManager, m_cloopStack);
    }
#endif

    VM& vm();

    static constexpr uintptr_t StopRequestMarkerValue = std::numeric_limits<uintptr_t>::max();

private:
    static ALWAYS_INLINE void* stopRequestMarker() { return reinterpret_cast<void*>(StopRequestMarkerValue); }

    Atomic<void*> m_trapAwareSoftStackLimit { nullptr };
    void* m_softStackLimit { nullptr };

    Lock m_mirrorLock;
    SentinelLinkedList<Mirror, BasicRawSentinelNode<Mirror>> m_mirrors WTF_GUARDED_BY_LOCK(m_mirrorLock);

#if ENABLE(C_LOOP)
    void* m_cloopStackLimit { nullptr };

    // m_cloopStack must be declared after the m_mirrors list because CLoopStack
    // initialization requires calling setCLoopStackLimit() which relies on
    // m_mirrors (above) being already initialized.
    CLoopStack m_cloopStack;
#endif
    friend class LLIntOffsetsExtractor;
};

static_assert(sizeof(Atomic<void*>) == sizeof(void*), "m_trapAwareSoftStackLimit relies on this invariant");

} // namespace JSC