objc4-781.tar.gz

[apple/objc4.git] / runtime / objc-runtime-new.h

/*
 * Copyright (c) 2005-2007 Apple Inc.  All Rights Reserved.
 * 
 * @APPLE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this
 * file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */

#ifndef _OBJC_RUNTIME_NEW_H
#define _OBJC_RUNTIME_NEW_H

#include "PointerUnion.h"

// class_data_bits_t is the class_t->data field (class_rw_t pointer plus flags)
// The extra bits are optimized for the retain/release and alloc/dealloc paths.

// Values for class_ro_t->flags
// These are emitted by the compiler and are part of the ABI.
// Note: See CGObjCNonFragileABIMac::BuildClassRoTInitializer in clang
// class is a metaclass
#define RO_META               (1<<0)
// class is a root class
#define RO_ROOT               (1<<1)
// class has .cxx_construct/destruct implementations
#define RO_HAS_CXX_STRUCTORS  (1<<2)
// class has +load implementation
// #define RO_HAS_LOAD_METHOD    (1<<3)
// class has visibility=hidden set
#define RO_HIDDEN             (1<<4)
// class has attribute(objc_exception): OBJC_EHTYPE_$_ThisClass is non-weak
#define RO_EXCEPTION          (1<<5)
// class has ro field for Swift metadata initializer callback
#define RO_HAS_SWIFT_INITIALIZER (1<<6)
// class compiled with ARC
#define RO_IS_ARC             (1<<7)
// class has .cxx_destruct but no .cxx_construct (with RO_HAS_CXX_STRUCTORS)
#define RO_HAS_CXX_DTOR_ONLY  (1<<8)
// class is not ARC but has ARC-style weak ivar layout
#define RO_HAS_WEAK_WITHOUT_ARC (1<<9)
// class does not allow associated objects on instances
#define RO_FORBIDS_ASSOCIATED_OBJECTS (1<<10)

// class is in an unloadable bundle - must never be set by compiler
#define RO_FROM_BUNDLE        (1<<29)
// class is unrealized future class - must never be set by compiler
#define RO_FUTURE             (1<<30)
// class is realized - must never be set by compiler
#define RO_REALIZED           (1<<31)

// Values for class_rw_t->flags
// These are not emitted by the compiler and are never used in class_ro_t.
// Their presence should be considered in future ABI versions.
// class_t->data is class_rw_t, not class_ro_t
#define RW_REALIZED           (1<<31)
// class is unresolved future class
#define RW_FUTURE             (1<<30)
// class is initialized
#define RW_INITIALIZED        (1<<29)
// class is initializing
#define RW_INITIALIZING       (1<<28)
// class_rw_t->ro is heap copy of class_ro_t
#define RW_COPIED_RO          (1<<27)
// class allocated but not yet registered
#define RW_CONSTRUCTING       (1<<26)
// class allocated and registered
#define RW_CONSTRUCTED        (1<<25)
// available for use; was RW_FINALIZE_ON_MAIN_THREAD
// #define RW_24 (1<<24)
// class +load has been called
#define RW_LOADED             (1<<23)
#if !SUPPORT_NONPOINTER_ISA
// class instances may have associative references
#define RW_INSTANCES_HAVE_ASSOCIATED_OBJECTS (1<<22)
#endif
// class has instance-specific GC layout
#define RW_HAS_INSTANCE_SPECIFIC_LAYOUT (1 << 21)
// class does not allow associated objects on its instances
#define RW_FORBIDS_ASSOCIATED_OBJECTS       (1<<20)
// class has started realizing but not yet completed it
#define RW_REALIZING          (1<<19)

// class is a metaclass (copied from ro)
#define RW_META               RO_META // (1<<0)


// NOTE: MORE RW_ FLAGS DEFINED BELOW


// Values for class_rw_t->flags (RW_*), cache_t->_flags (FAST_CACHE_*),
// or class_t->bits (FAST_*).
//
// FAST_* and FAST_CACHE_* are stored on the class, reducing pointer indirection.

#if __LP64__

// class is a Swift class from the pre-stable Swift ABI
#define FAST_IS_SWIFT_LEGACY    (1UL<<0)
// class is a Swift class from the stable Swift ABI
#define FAST_IS_SWIFT_STABLE    (1UL<<1)
// class or superclass has default retain/release/autorelease/retainCount/
//   _tryRetain/_isDeallocating/retainWeakReference/allowsWeakReference
#define FAST_HAS_DEFAULT_RR     (1UL<<2)
// data pointer
#define FAST_DATA_MASK          0x00007ffffffffff8UL

#if __arm64__
// class or superclass has .cxx_construct/.cxx_destruct implementation
//   FAST_CACHE_HAS_CXX_DTOR is the first bit so that setting it in
//   isa_t::has_cxx_dtor is a single bfi
#define FAST_CACHE_HAS_CXX_DTOR       (1<<0)
#define FAST_CACHE_HAS_CXX_CTOR       (1<<1)
// Denormalized RO_META to avoid an indirection
#define FAST_CACHE_META               (1<<2)
#else
// Denormalized RO_META to avoid an indirection
#define FAST_CACHE_META               (1<<0)
// class or superclass has .cxx_construct/.cxx_destruct implementation
//   FAST_CACHE_HAS_CXX_DTOR is chosen to alias with isa_t::has_cxx_dtor
#define FAST_CACHE_HAS_CXX_CTOR       (1<<1)
#define FAST_CACHE_HAS_CXX_DTOR       (1<<2)
#endif

// Fast Alloc fields:
//   This stores the word-aligned size of instances + "ALLOC_DELTA16",
//   or 0 if the instance size doesn't fit.
//
//   These bits occupy the same bits than in the instance size, so that
//   the size can be extracted with a simple mask operation.
//
//   FAST_CACHE_ALLOC_MASK16 allows to extract the instance size rounded
//   rounded up to the next 16 byte boundary, which is a fastpath for
//   _objc_rootAllocWithZone()
#define FAST_CACHE_ALLOC_MASK         0x1ff8
#define FAST_CACHE_ALLOC_MASK16       0x1ff0
#define FAST_CACHE_ALLOC_DELTA16      0x0008

// class's instances requires raw isa
#define FAST_CACHE_REQUIRES_RAW_ISA   (1<<13)
// class or superclass has default alloc/allocWithZone: implementation
// Note this is is stored in the metaclass.
#define FAST_CACHE_HAS_DEFAULT_AWZ    (1<<14)
// class or superclass has default new/self/class/respondsToSelector/isKindOfClass
#define FAST_CACHE_HAS_DEFAULT_CORE   (1<<15)

#else

// class or superclass has .cxx_construct implementation
#define RW_HAS_CXX_CTOR       (1<<18)
// class or superclass has .cxx_destruct implementation
#define RW_HAS_CXX_DTOR       (1<<17)
// class or superclass has default alloc/allocWithZone: implementation
// Note this is is stored in the metaclass.
#define RW_HAS_DEFAULT_AWZ    (1<<16)
// class's instances requires raw isa
#if SUPPORT_NONPOINTER_ISA
#define RW_REQUIRES_RAW_ISA   (1<<15)
#endif
// class or superclass has default retain/release/autorelease/retainCount/
//   _tryRetain/_isDeallocating/retainWeakReference/allowsWeakReference
#define RW_HAS_DEFAULT_RR     (1<<14)
// class or superclass has default new/self/class/respondsToSelector/isKindOfClass
#define RW_HAS_DEFAULT_CORE   (1<<13)

// class is a Swift class from the pre-stable Swift ABI
#define FAST_IS_SWIFT_LEGACY  (1UL<<0)
// class is a Swift class from the stable Swift ABI
#define FAST_IS_SWIFT_STABLE  (1UL<<1)
// data pointer
#define FAST_DATA_MASK        0xfffffffcUL

#endif // __LP64__

// The Swift ABI requires that these bits be defined like this on all platforms.
static_assert(FAST_IS_SWIFT_LEGACY == 1, "resistance is futile");
static_assert(FAST_IS_SWIFT_STABLE == 2, "resistance is futile");


#if __LP64__
typedef uint32_t mask_t;  // x86_64 & arm64 asm are less efficient with 16-bits
#else
typedef uint16_t mask_t;
#endif
typedef uintptr_t SEL;

struct swift_class_t;

enum Atomicity { Atomic = true, NotAtomic = false };
enum IMPEncoding { Encoded = true, Raw = false };

struct bucket_t {
private:
    // IMP-first is better for arm64e ptrauth and no worse for arm64.
    // SEL-first is better for armv7* and i386 and x86_64.
#if __arm64__
    explicit_atomic<uintptr_t> _imp;
    explicit_atomic<SEL> _sel;
#else
    explicit_atomic<SEL> _sel;
    explicit_atomic<uintptr_t> _imp;
#endif

    // Compute the ptrauth signing modifier from &_imp, newSel, and cls.
    uintptr_t modifierForSEL(SEL newSel, Class cls) const {
        return (uintptr_t)&_imp ^ (uintptr_t)newSel ^ (uintptr_t)cls;
    }

    // Sign newImp, with &_imp, newSel, and cls as modifiers.
    uintptr_t encodeImp(IMP newImp, SEL newSel, Class cls) const {
        if (!newImp) return 0;
#if CACHE_IMP_ENCODING == CACHE_IMP_ENCODING_PTRAUTH
        return (uintptr_t)
            ptrauth_auth_and_resign(newImp,
                                    ptrauth_key_function_pointer, 0,
                                    ptrauth_key_process_dependent_code,
                                    modifierForSEL(newSel, cls));
#elif CACHE_IMP_ENCODING == CACHE_IMP_ENCODING_ISA_XOR
        return (uintptr_t)newImp ^ (uintptr_t)cls;
#elif CACHE_IMP_ENCODING == CACHE_IMP_ENCODING_NONE
        return (uintptr_t)newImp;
#else
#error Unknown method cache IMP encoding.
#endif
    }

public:
    inline SEL sel() const { return _sel.load(memory_order::memory_order_relaxed); }

    inline IMP imp(Class cls) const {
        uintptr_t imp = _imp.load(memory_order::memory_order_relaxed);
        if (!imp) return nil;
#if CACHE_IMP_ENCODING == CACHE_IMP_ENCODING_PTRAUTH
        SEL sel = _sel.load(memory_order::memory_order_relaxed);
        return (IMP)
            ptrauth_auth_and_resign((const void *)imp,
                                    ptrauth_key_process_dependent_code,
                                    modifierForSEL(sel, cls),
                                    ptrauth_key_function_pointer, 0);
#elif CACHE_IMP_ENCODING == CACHE_IMP_ENCODING_ISA_XOR
        return (IMP)(imp ^ (uintptr_t)cls);
#elif CACHE_IMP_ENCODING == CACHE_IMP_ENCODING_NONE
        return (IMP)imp;
#else
#error Unknown method cache IMP encoding.
#endif
    }

    template <Atomicity, IMPEncoding>
    void set(SEL newSel, IMP newImp, Class cls);
};


struct cache_t {
#if CACHE_MASK_STORAGE == CACHE_MASK_STORAGE_OUTLINED
    explicit_atomic<struct bucket_t *> _buckets;
    explicit_atomic<mask_t> _mask;
#elif CACHE_MASK_STORAGE == CACHE_MASK_STORAGE_HIGH_16
    explicit_atomic<uintptr_t> _maskAndBuckets;
    mask_t _mask_unused;
    
    // How much the mask is shifted by.
    static constexpr uintptr_t maskShift = 48;
    
    // Additional bits after the mask which must be zero. msgSend
    // takes advantage of these additional bits to construct the value
    // `mask << 4` from `_maskAndBuckets` in a single instruction.
    static constexpr uintptr_t maskZeroBits = 4;
    
    // The largest mask value we can store.
    static constexpr uintptr_t maxMask = ((uintptr_t)1 << (64 - maskShift)) - 1;
    
    // The mask applied to `_maskAndBuckets` to retrieve the buckets pointer.
    static constexpr uintptr_t bucketsMask = ((uintptr_t)1 << (maskShift - maskZeroBits)) - 1;
    
    // Ensure we have enough bits for the buckets pointer.
    static_assert(bucketsMask >= MACH_VM_MAX_ADDRESS, "Bucket field doesn't have enough bits for arbitrary pointers.");
#elif CACHE_MASK_STORAGE == CACHE_MASK_STORAGE_LOW_4
    // _maskAndBuckets stores the mask shift in the low 4 bits, and
    // the buckets pointer in the remainder of the value. The mask
    // shift is the value where (0xffff >> shift) produces the correct
    // mask. This is equal to 16 - log2(cache_size).
    explicit_atomic<uintptr_t> _maskAndBuckets;
    mask_t _mask_unused;

    static constexpr uintptr_t maskBits = 4;
    static constexpr uintptr_t maskMask = (1 << maskBits) - 1;
    static constexpr uintptr_t bucketsMask = ~maskMask;
#else
#error Unknown cache mask storage type.
#endif
    
#if __LP64__
    uint16_t _flags;
#endif
    uint16_t _occupied;

public:
    static bucket_t *emptyBuckets();
    
    struct bucket_t *buckets();
    mask_t mask();
    mask_t occupied();
    void incrementOccupied();
    void setBucketsAndMask(struct bucket_t *newBuckets, mask_t newMask);
    void initializeToEmpty();

    unsigned capacity();
    bool isConstantEmptyCache();
    bool canBeFreed();

#if __LP64__
    bool getBit(uint16_t flags) const {
        return _flags & flags;
    }
    void setBit(uint16_t set) {
        __c11_atomic_fetch_or((_Atomic(uint16_t) *)&_flags, set, __ATOMIC_RELAXED);
    }
    void clearBit(uint16_t clear) {
        __c11_atomic_fetch_and((_Atomic(uint16_t) *)&_flags, ~clear, __ATOMIC_RELAXED);
    }
#endif

#if FAST_CACHE_ALLOC_MASK
    bool hasFastInstanceSize(size_t extra) const
    {
        if (__builtin_constant_p(extra) && extra == 0) {
            return _flags & FAST_CACHE_ALLOC_MASK16;
        }
        return _flags & FAST_CACHE_ALLOC_MASK;
    }

    size_t fastInstanceSize(size_t extra) const
    {
        ASSERT(hasFastInstanceSize(extra));

        if (__builtin_constant_p(extra) && extra == 0) {
            return _flags & FAST_CACHE_ALLOC_MASK16;
        } else {
            size_t size = _flags & FAST_CACHE_ALLOC_MASK;
            // remove the FAST_CACHE_ALLOC_DELTA16 that was added
            // by setFastInstanceSize
            return align16(size + extra - FAST_CACHE_ALLOC_DELTA16);
        }
    }

    void setFastInstanceSize(size_t newSize)
    {
        // Set during realization or construction only. No locking needed.
        uint16_t newBits = _flags & ~FAST_CACHE_ALLOC_MASK;
        uint16_t sizeBits;

        // Adding FAST_CACHE_ALLOC_DELTA16 allows for FAST_CACHE_ALLOC_MASK16
        // to yield the proper 16byte aligned allocation size with a single mask
        sizeBits = word_align(newSize) + FAST_CACHE_ALLOC_DELTA16;
        sizeBits &= FAST_CACHE_ALLOC_MASK;
        if (newSize <= sizeBits) {
            newBits |= sizeBits;
        }
        _flags = newBits;
    }
#else
    bool hasFastInstanceSize(size_t extra) const {
        return false;
    }
    size_t fastInstanceSize(size_t extra) const {
        abort();
    }
    void setFastInstanceSize(size_t extra) {
        // nothing
    }
#endif

    static size_t bytesForCapacity(uint32_t cap);
    static struct bucket_t * endMarker(struct bucket_t *b, uint32_t cap);

    void reallocate(mask_t oldCapacity, mask_t newCapacity, bool freeOld);
    void insert(Class cls, SEL sel, IMP imp, id receiver);

    static void bad_cache(id receiver, SEL sel, Class isa) __attribute__((noreturn, cold));
};


// classref_t is unremapped class_t*
typedef struct classref * classref_t;


#ifdef __PTRAUTH_INTRINSICS__
#   define StubClassInitializerPtrauth __ptrauth(ptrauth_key_function_pointer, 1, 0xc671)
#else
#   define StubClassInitializerPtrauth
#endif
struct stub_class_t {
    uintptr_t isa;
    _objc_swiftMetadataInitializer StubClassInitializerPtrauth initializer;
};

/***********************************************************************
* entsize_list_tt<Element, List, FlagMask>
* Generic implementation of an array of non-fragile structs.
*
* Element is the struct type (e.g. method_t)
* List is the specialization of entsize_list_tt (e.g. method_list_t)
* FlagMask is used to stash extra bits in the entsize field
*   (e.g. method list fixup markers)
**********************************************************************/
template <typename Element, typename List, uint32_t FlagMask>
struct entsize_list_tt {
    uint32_t entsizeAndFlags;
    uint32_t count;
    Element first;

    uint32_t entsize() const {
        return entsizeAndFlags & ~FlagMask;
    }
    uint32_t flags() const {
        return entsizeAndFlags & FlagMask;
    }

    Element& getOrEnd(uint32_t i) const { 
        ASSERT(i <= count);
        return *(Element *)((uint8_t *)&first + i*entsize()); 
    }
    Element& get(uint32_t i) const { 
        ASSERT(i < count);
        return getOrEnd(i);
    }

    size_t byteSize() const {
        return byteSize(entsize(), count);
    }
    
    static size_t byteSize(uint32_t entsize, uint32_t count) {
        return sizeof(entsize_list_tt) + (count-1)*entsize;
    }

    List *duplicate() const {
        auto *dup = (List *)calloc(this->byteSize(), 1);
        dup->entsizeAndFlags = this->entsizeAndFlags;
        dup->count = this->count;
        std::copy(begin(), end(), dup->begin());
        return dup;
    }

    struct iterator;
    const iterator begin() const { 
        return iterator(*static_cast<const List*>(this), 0); 
    }
    iterator begin() { 
        return iterator(*static_cast<const List*>(this), 0); 
    }
    const iterator end() const { 
        return iterator(*static_cast<const List*>(this), count); 
    }
    iterator end() { 
        return iterator(*static_cast<const List*>(this), count); 
    }

    struct iterator {
        uint32_t entsize;
        uint32_t index;  // keeping track of this saves a divide in operator-
        Element* element;

        typedef std::random_access_iterator_tag iterator_category;
        typedef Element value_type;
        typedef ptrdiff_t difference_type;
        typedef Element* pointer;
        typedef Element& reference;

        iterator() { }

        iterator(const List& list, uint32_t start = 0)
            : entsize(list.entsize())
            , index(start)
            , element(&list.getOrEnd(start))
        { }

        const iterator& operator += (ptrdiff_t delta) {
            element = (Element*)((uint8_t *)element + delta*entsize);
            index += (int32_t)delta;
            return *this;
        }
        const iterator& operator -= (ptrdiff_t delta) {
            element = (Element*)((uint8_t *)element - delta*entsize);
            index -= (int32_t)delta;
            return *this;
        }
        const iterator operator + (ptrdiff_t delta) const {
            return iterator(*this) += delta;
        }
        const iterator operator - (ptrdiff_t delta) const {
            return iterator(*this) -= delta;
        }

        iterator& operator ++ () { *this += 1; return *this; }
        iterator& operator -- () { *this -= 1; return *this; }
        iterator operator ++ (int) {
            iterator result(*this); *this += 1; return result;
        }
        iterator operator -- (int) {
            iterator result(*this); *this -= 1; return result;
        }

        ptrdiff_t operator - (const iterator& rhs) const {
            return (ptrdiff_t)this->index - (ptrdiff_t)rhs.index;
        }

        Element& operator * () const { return *element; }
        Element* operator -> () const { return element; }

        operator Element& () const { return *element; }

        bool operator == (const iterator& rhs) const {
            return this->element == rhs.element;
        }
        bool operator != (const iterator& rhs) const {
            return this->element != rhs.element;
        }

        bool operator < (const iterator& rhs) const {
            return this->element < rhs.element;
        }
        bool operator > (const iterator& rhs) const {
            return this->element > rhs.element;
        }
    };
};


struct method_t {
    SEL name;
    const char *types;
    MethodListIMP imp;

    struct SortBySELAddress :
        public std::binary_function<const method_t&,
                                    const method_t&, bool>
    {
        bool operator() (const method_t& lhs,
                         const method_t& rhs)
        { return lhs.name < rhs.name; }
    };
};

struct ivar_t {
#if __x86_64__
    // *offset was originally 64-bit on some x86_64 platforms.
    // We read and write only 32 bits of it.
    // Some metadata provides all 64 bits. This is harmless for unsigned 
    // little-endian values.
    // Some code uses all 64 bits. class_addIvar() over-allocates the 
    // offset for their benefit.
#endif
    int32_t *offset;
    const char *name;
    const char *type;
    // alignment is sometimes -1; use alignment() instead
    uint32_t alignment_raw;
    uint32_t size;

    uint32_t alignment() const {
        if (alignment_raw == ~(uint32_t)0) return 1U << WORD_SHIFT;
        return 1 << alignment_raw;
    }
};

struct property_t {
    const char *name;
    const char *attributes;
};

// Two bits of entsize are used for fixup markers.
struct method_list_t : entsize_list_tt<method_t, method_list_t, 0x3> {
    bool isUniqued() const;
    bool isFixedUp() const;
    void setFixedUp();

    uint32_t indexOfMethod(const method_t *meth) const {
        uint32_t i = 
            (uint32_t)(((uintptr_t)meth - (uintptr_t)this) / entsize());
        ASSERT(i < count);
        return i;
    }
};

struct ivar_list_t : entsize_list_tt<ivar_t, ivar_list_t, 0> {
    bool containsIvar(Ivar ivar) const {
        return (ivar >= (Ivar)&*begin()  &&  ivar < (Ivar)&*end());
    }
};

struct property_list_t : entsize_list_tt<property_t, property_list_t, 0> {
};


typedef uintptr_t protocol_ref_t;  // protocol_t *, but unremapped

// Values for protocol_t->flags
#define PROTOCOL_FIXED_UP_2     (1<<31)  // must never be set by compiler
#define PROTOCOL_FIXED_UP_1     (1<<30)  // must never be set by compiler
#define PROTOCOL_IS_CANONICAL   (1<<29)  // must never be set by compiler
// Bits 0..15 are reserved for Swift's use.

#define PROTOCOL_FIXED_UP_MASK (PROTOCOL_FIXED_UP_1 | PROTOCOL_FIXED_UP_2)

struct protocol_t : objc_object {
    const char *mangledName;
    struct protocol_list_t *protocols;
    method_list_t *instanceMethods;
    method_list_t *classMethods;
    method_list_t *optionalInstanceMethods;
    method_list_t *optionalClassMethods;
    property_list_t *instanceProperties;
    uint32_t size;   // sizeof(protocol_t)
    uint32_t flags;
    // Fields below this point are not always present on disk.
    const char **_extendedMethodTypes;
    const char *_demangledName;
    property_list_t *_classProperties;

    const char *demangledName();

    const char *nameForLogging() {
        return demangledName();
    }

    bool isFixedUp() const;
    void setFixedUp();

    bool isCanonical() const;
    void clearIsCanonical();

#   define HAS_FIELD(f) (size >= offsetof(protocol_t, f) + sizeof(f))

    bool hasExtendedMethodTypesField() const {
        return HAS_FIELD(_extendedMethodTypes);
    }
    bool hasDemangledNameField() const {
        return HAS_FIELD(_demangledName);
    }
    bool hasClassPropertiesField() const {
        return HAS_FIELD(_classProperties);
    }

#   undef HAS_FIELD

    const char **extendedMethodTypes() const {
        return hasExtendedMethodTypesField() ? _extendedMethodTypes : nil;
    }

    property_list_t *classProperties() const {
        return hasClassPropertiesField() ? _classProperties : nil;
    }
};

struct protocol_list_t {
    // count is pointer-sized by accident.
    uintptr_t count;
    protocol_ref_t list[0]; // variable-size

    size_t byteSize() const {
        return sizeof(*this) + count*sizeof(list[0]);
    }

    protocol_list_t *duplicate() const {
        return (protocol_list_t *)memdup(this, this->byteSize());
    }

    typedef protocol_ref_t* iterator;
    typedef const protocol_ref_t* const_iterator;

    const_iterator begin() const {
        return list;
    }
    iterator begin() {
        return list;
    }
    const_iterator end() const {
        return list + count;
    }
    iterator end() {
        return list + count;
    }
};

struct class_ro_t {
    uint32_t flags;
    uint32_t instanceStart;
    uint32_t instanceSize;
#ifdef __LP64__
    uint32_t reserved;
#endif

    const uint8_t * ivarLayout;
    
    const char * name;
    method_list_t * baseMethodList;
    protocol_list_t * baseProtocols;
    const ivar_list_t * ivars;

    const uint8_t * weakIvarLayout;
    property_list_t *baseProperties;

    // This field exists only when RO_HAS_SWIFT_INITIALIZER is set.
    _objc_swiftMetadataInitializer __ptrauth_objc_method_list_imp _swiftMetadataInitializer_NEVER_USE[0];

    _objc_swiftMetadataInitializer swiftMetadataInitializer() const {
        if (flags & RO_HAS_SWIFT_INITIALIZER) {
            return _swiftMetadataInitializer_NEVER_USE[0];
        } else {
            return nil;
        }
    }

    method_list_t *baseMethods() const {
        return baseMethodList;
    }

    class_ro_t *duplicate() const {
        if (flags & RO_HAS_SWIFT_INITIALIZER) {
            size_t size = sizeof(*this) + sizeof(_swiftMetadataInitializer_NEVER_USE[0]);
            class_ro_t *ro = (class_ro_t *)memdup(this, size);
            ro->_swiftMetadataInitializer_NEVER_USE[0] = this->_swiftMetadataInitializer_NEVER_USE[0];
            return ro;
        } else {
            size_t size = sizeof(*this);
            class_ro_t *ro = (class_ro_t *)memdup(this, size);
            return ro;
        }
    }
};


/***********************************************************************
* list_array_tt<Element, List>
* Generic implementation for metadata that can be augmented by categories.
*
* Element is the underlying metadata type (e.g. method_t)
* List is the metadata's list type (e.g. method_list_t)
*
* A list_array_tt has one of three values:
* - empty
* - a pointer to a single list
* - an array of pointers to lists
*
* countLists/beginLists/endLists iterate the metadata lists
* count/begin/end iterate the underlying metadata elements
**********************************************************************/
template <typename Element, typename List>
class list_array_tt {
    struct array_t {
        uint32_t count;
        List* lists[0];

        static size_t byteSize(uint32_t count) {
            return sizeof(array_t) + count*sizeof(lists[0]);
        }
        size_t byteSize() {
            return byteSize(count);
        }
    };

 protected:
    class iterator {
        List * const *lists;
        List * const *listsEnd;
        typename List::iterator m, mEnd;

     public:
        iterator(List *const *begin, List *const *end)
            : lists(begin), listsEnd(end)
        {
            if (begin != end) {
                m = (*begin)->begin();
                mEnd = (*begin)->end();
            }
        }

        const Element& operator * () const {
            return *m;
        }
        Element& operator * () {
            return *m;
        }

        bool operator != (const iterator& rhs) const {
            if (lists != rhs.lists) return true;
            if (lists == listsEnd) return false;  // m is undefined
            if (m != rhs.m) return true;
            return false;
        }

        const iterator& operator ++ () {
            ASSERT(m != mEnd);
            m++;
            if (m == mEnd) {
                ASSERT(lists != listsEnd);
                lists++;
                if (lists != listsEnd) {
                    m = (*lists)->begin();
                    mEnd = (*lists)->end();
                }
            }
            return *this;
        }
    };

 private:
    union {
        List* list;
        uintptr_t arrayAndFlag;
    };

    bool hasArray() const {
        return arrayAndFlag & 1;
    }

    array_t *array() const {
        return (array_t *)(arrayAndFlag & ~1);
    }

    void setArray(array_t *array) {
        arrayAndFlag = (uintptr_t)array | 1;
    }

 public:
    list_array_tt() : list(nullptr) { }
    list_array_tt(List *l) : list(l) { }

    uint32_t count() const {
        uint32_t result = 0;
        for (auto lists = beginLists(), end = endLists(); 
             lists != end;
             ++lists)
        {
            result += (*lists)->count;
        }
        return result;
    }

    iterator begin() const {
        return iterator(beginLists(), endLists());
    }

    iterator end() const {
        List * const *e = endLists();
        return iterator(e, e);
    }


    uint32_t countLists() {
        if (hasArray()) {
            return array()->count;
        } else if (list) {
            return 1;
        } else {
            return 0;
        }
    }

    List* const * beginLists() const {
        if (hasArray()) {
            return array()->lists;
        } else {
            return &list;
        }
    }

    List* const * endLists() const {
        if (hasArray()) {
            return array()->lists + array()->count;
        } else if (list) {
            return &list + 1;
        } else {
            return &list;
        }
    }

    void attachLists(List* const * addedLists, uint32_t addedCount) {
        if (addedCount == 0) return;

        if (hasArray()) {
            // many lists -> many lists
            uint32_t oldCount = array()->count;
            uint32_t newCount = oldCount + addedCount;
            setArray((array_t *)realloc(array(), array_t::byteSize(newCount)));
            array()->count = newCount;
            memmove(array()->lists + addedCount, array()->lists, 
                    oldCount * sizeof(array()->lists[0]));
            memcpy(array()->lists, addedLists, 
                   addedCount * sizeof(array()->lists[0]));
        }
        else if (!list  &&  addedCount == 1) {
            // 0 lists -> 1 list
            list = addedLists[0];
        } 
        else {
            // 1 list -> many lists
            List* oldList = list;
            uint32_t oldCount = oldList ? 1 : 0;
            uint32_t newCount = oldCount + addedCount;
            setArray((array_t *)malloc(array_t::byteSize(newCount)));
            array()->count = newCount;
            if (oldList) array()->lists[addedCount] = oldList;
            memcpy(array()->lists, addedLists, 
                   addedCount * sizeof(array()->lists[0]));
        }
    }

    void tryFree() {
        if (hasArray()) {
            for (uint32_t i = 0; i < array()->count; i++) {
                try_free(array()->lists[i]);
            }
            try_free(array());
        }
        else if (list) {
            try_free(list);
        }
    }

    template<typename Result>
    Result duplicate() {
        Result result;

        if (hasArray()) {
            array_t *a = array();
            result.setArray((array_t *)memdup(a, a->byteSize()));
            for (uint32_t i = 0; i < a->count; i++) {
                result.array()->lists[i] = a->lists[i]->duplicate();
            }
        } else if (list) {
            result.list = list->duplicate();
        } else {
            result.list = nil;
        }

        return result;
    }
};


class method_array_t : 
    public list_array_tt<method_t, method_list_t> 
{
    typedef list_array_tt<method_t, method_list_t> Super;

 public:
    method_array_t() : Super() { }
    method_array_t(method_list_t *l) : Super(l) { }

    method_list_t * const *beginCategoryMethodLists() const {
        return beginLists();
    }
    
    method_list_t * const *endCategoryMethodLists(Class cls) const;

    method_array_t duplicate() {
        return Super::duplicate<method_array_t>();
    }
};


class property_array_t : 
    public list_array_tt<property_t, property_list_t> 
{
    typedef list_array_tt<property_t, property_list_t> Super;

 public:
    property_array_t() : Super() { }
    property_array_t(property_list_t *l) : Super(l) { }

    property_array_t duplicate() {
        return Super::duplicate<property_array_t>();
    }
};


class protocol_array_t : 
    public list_array_tt<protocol_ref_t, protocol_list_t> 
{
    typedef list_array_tt<protocol_ref_t, protocol_list_t> Super;

 public:
    protocol_array_t() : Super() { }
    protocol_array_t(protocol_list_t *l) : Super(l) { }

    protocol_array_t duplicate() {
        return Super::duplicate<protocol_array_t>();
    }
};

struct class_rw_ext_t {
    const class_ro_t *ro;
    method_array_t methods;
    property_array_t properties;
    protocol_array_t protocols;
    char *demangledName;
    uint32_t version;
};

struct class_rw_t {
    // Be warned that Symbolication knows the layout of this structure.
    uint32_t flags;
    uint16_t witness;
#if SUPPORT_INDEXED_ISA
    uint16_t index;
#endif

    explicit_atomic<uintptr_t> ro_or_rw_ext;

    Class firstSubclass;
    Class nextSiblingClass;

private:
    using ro_or_rw_ext_t = objc::PointerUnion<const class_ro_t *, class_rw_ext_t *>;

    const ro_or_rw_ext_t get_ro_or_rwe() const {
        return ro_or_rw_ext_t{ro_or_rw_ext};
    }

    void set_ro_or_rwe(const class_ro_t *ro) {
        ro_or_rw_ext_t{ro}.storeAt(ro_or_rw_ext, memory_order_relaxed);
    }

    void set_ro_or_rwe(class_rw_ext_t *rwe, const class_ro_t *ro) {
        // the release barrier is so that the class_rw_ext_t::ro initialization
        // is visible to lockless readers
        rwe->ro = ro;
        ro_or_rw_ext_t{rwe}.storeAt(ro_or_rw_ext, memory_order_release);
    }

    class_rw_ext_t *extAlloc(const class_ro_t *ro, bool deep = false);

public:
    void setFlags(uint32_t set)
    {
        __c11_atomic_fetch_or((_Atomic(uint32_t) *)&flags, set, __ATOMIC_RELAXED);
    }

    void clearFlags(uint32_t clear) 
    {
        __c11_atomic_fetch_and((_Atomic(uint32_t) *)&flags, ~clear, __ATOMIC_RELAXED);
    }

    // set and clear must not overlap
    void changeFlags(uint32_t set, uint32_t clear) 
    {
        ASSERT((set & clear) == 0);

        uint32_t oldf, newf;
        do {
            oldf = flags;
            newf = (oldf | set) & ~clear;
        } while (!OSAtomicCompareAndSwap32Barrier(oldf, newf, (volatile int32_t *)&flags));
    }

    class_rw_ext_t *ext() const {
        return get_ro_or_rwe().dyn_cast<class_rw_ext_t *>();
    }

    class_rw_ext_t *extAllocIfNeeded() {
        auto v = get_ro_or_rwe();
        if (fastpath(v.is<class_rw_ext_t *>())) {
            return v.get<class_rw_ext_t *>();
        } else {
            return extAlloc(v.get<const class_ro_t *>());
        }
    }

    class_rw_ext_t *deepCopy(const class_ro_t *ro) {
        return extAlloc(ro, true);
    }

    const class_ro_t *ro() const {
        auto v = get_ro_or_rwe();
        if (slowpath(v.is<class_rw_ext_t *>())) {
            return v.get<class_rw_ext_t *>()->ro;
        }
        return v.get<const class_ro_t *>();
    }

    void set_ro(const class_ro_t *ro) {
        auto v = get_ro_or_rwe();
        if (v.is<class_rw_ext_t *>()) {
            v.get<class_rw_ext_t *>()->ro = ro;
        } else {
            set_ro_or_rwe(ro);
        }
    }

    const method_array_t methods() const {
        auto v = get_ro_or_rwe();
        if (v.is<class_rw_ext_t *>()) {
            return v.get<class_rw_ext_t *>()->methods;
        } else {
            return method_array_t{v.get<const class_ro_t *>()->baseMethods()};
        }
    }

    const property_array_t properties() const {
        auto v = get_ro_or_rwe();
        if (v.is<class_rw_ext_t *>()) {
            return v.get<class_rw_ext_t *>()->properties;
        } else {
            return property_array_t{v.get<const class_ro_t *>()->baseProperties};
        }
    }

    const protocol_array_t protocols() const {
        auto v = get_ro_or_rwe();
        if (v.is<class_rw_ext_t *>()) {
            return v.get<class_rw_ext_t *>()->protocols;
        } else {
            return protocol_array_t{v.get<const class_ro_t *>()->baseProtocols};
        }
    }
};


struct class_data_bits_t {
    friend objc_class;

    // Values are the FAST_ flags above.
    uintptr_t bits;
private:
    bool getBit(uintptr_t bit) const
    {
        return bits & bit;
    }

    // Atomically set the bits in `set` and clear the bits in `clear`.
    // set and clear must not overlap.
    void setAndClearBits(uintptr_t set, uintptr_t clear)
    {
        ASSERT((set & clear) == 0);
        uintptr_t oldBits;
        uintptr_t newBits;
        do {
            oldBits = LoadExclusive(&bits);
            newBits = (oldBits | set) & ~clear;
        } while (!StoreReleaseExclusive(&bits, oldBits, newBits));
    }

    void setBits(uintptr_t set) {
        __c11_atomic_fetch_or((_Atomic(uintptr_t) *)&bits, set, __ATOMIC_RELAXED);
    }

    void clearBits(uintptr_t clear) {
        __c11_atomic_fetch_and((_Atomic(uintptr_t) *)&bits, ~clear, __ATOMIC_RELAXED);
    }

public:

    class_rw_t* data() const {
        return (class_rw_t *)(bits & FAST_DATA_MASK);
    }
    void setData(class_rw_t *newData)
    {
        ASSERT(!data()  ||  (newData->flags & (RW_REALIZING | RW_FUTURE)));
        // Set during realization or construction only. No locking needed.
        // Use a store-release fence because there may be concurrent
        // readers of data and data's contents.
        uintptr_t newBits = (bits & ~FAST_DATA_MASK) | (uintptr_t)newData;
        atomic_thread_fence(memory_order_release);
        bits = newBits;
    }

    // Get the class's ro data, even in the presence of concurrent realization.
    // fixme this isn't really safe without a compiler barrier at least
    // and probably a memory barrier when realizeClass changes the data field
    const class_ro_t *safe_ro() {
        class_rw_t *maybe_rw = data();
        if (maybe_rw->flags & RW_REALIZED) {
            // maybe_rw is rw
            return maybe_rw->ro();
        } else {
            // maybe_rw is actually ro
            return (class_ro_t *)maybe_rw;
        }
    }

    void setClassArrayIndex(unsigned Idx) {
#if SUPPORT_INDEXED_ISA
        // 0 is unused as then we can rely on zero-initialisation from calloc.
        ASSERT(Idx > 0);
        data()->index = Idx;
#endif
    }

    unsigned classArrayIndex() {
#if SUPPORT_INDEXED_ISA
        return data()->index;
#else
        return 0;
#endif
    }

    bool isAnySwift() {
        return isSwiftStable() || isSwiftLegacy();
    }

    bool isSwiftStable() {
        return getBit(FAST_IS_SWIFT_STABLE);
    }
    void setIsSwiftStable() {
        setAndClearBits(FAST_IS_SWIFT_STABLE, FAST_IS_SWIFT_LEGACY);
    }

    bool isSwiftLegacy() {
        return getBit(FAST_IS_SWIFT_LEGACY);
    }
    void setIsSwiftLegacy() {
        setAndClearBits(FAST_IS_SWIFT_LEGACY, FAST_IS_SWIFT_STABLE);
    }

    // fixme remove this once the Swift runtime uses the stable bits
    bool isSwiftStable_ButAllowLegacyForNow() {
        return isAnySwift();
    }

    _objc_swiftMetadataInitializer swiftMetadataInitializer() {
        // This function is called on un-realized classes without
        // holding any locks.
        // Beware of races with other realizers.
        return safe_ro()->swiftMetadataInitializer();
    }
};


struct objc_class : objc_object {
    // Class ISA;
    Class superclass;
    cache_t cache;             // formerly cache pointer and vtable
    class_data_bits_t bits;    // class_rw_t * plus custom rr/alloc flags

    class_rw_t *data() const {
        return bits.data();
    }
    void setData(class_rw_t *newData) {
        bits.setData(newData);
    }

    void setInfo(uint32_t set) {
        ASSERT(isFuture()  ||  isRealized());
        data()->setFlags(set);
    }

    void clearInfo(uint32_t clear) {
        ASSERT(isFuture()  ||  isRealized());
        data()->clearFlags(clear);
    }

    // set and clear must not overlap
    void changeInfo(uint32_t set, uint32_t clear) {
        ASSERT(isFuture()  ||  isRealized());
        ASSERT((set & clear) == 0);
        data()->changeFlags(set, clear);
    }

#if FAST_HAS_DEFAULT_RR
    bool hasCustomRR() const {
        return !bits.getBit(FAST_HAS_DEFAULT_RR);
    }
    void setHasDefaultRR() {
        bits.setBits(FAST_HAS_DEFAULT_RR);
    }
    void setHasCustomRR() {
        bits.clearBits(FAST_HAS_DEFAULT_RR);
    }
#else
    bool hasCustomRR() const {
        return !(bits.data()->flags & RW_HAS_DEFAULT_RR);
    }
    void setHasDefaultRR() {
        bits.data()->setFlags(RW_HAS_DEFAULT_RR);
    }
    void setHasCustomRR() {
        bits.data()->clearFlags(RW_HAS_DEFAULT_RR);
    }
#endif

#if FAST_CACHE_HAS_DEFAULT_AWZ
    bool hasCustomAWZ() const {
        return !cache.getBit(FAST_CACHE_HAS_DEFAULT_AWZ);
    }
    void setHasDefaultAWZ() {
        cache.setBit(FAST_CACHE_HAS_DEFAULT_AWZ);
    }
    void setHasCustomAWZ() {
        cache.clearBit(FAST_CACHE_HAS_DEFAULT_AWZ);
    }
#else
    bool hasCustomAWZ() const {
        return !(bits.data()->flags & RW_HAS_DEFAULT_AWZ);
    }
    void setHasDefaultAWZ() {
        bits.data()->setFlags(RW_HAS_DEFAULT_AWZ);
    }
    void setHasCustomAWZ() {
        bits.data()->clearFlags(RW_HAS_DEFAULT_AWZ);
    }
#endif

#if FAST_CACHE_HAS_DEFAULT_CORE
    bool hasCustomCore() const {
        return !cache.getBit(FAST_CACHE_HAS_DEFAULT_CORE);
    }
    void setHasDefaultCore() {
        return cache.setBit(FAST_CACHE_HAS_DEFAULT_CORE);
    }
    void setHasCustomCore() {
        return cache.clearBit(FAST_CACHE_HAS_DEFAULT_CORE);
    }
#else
    bool hasCustomCore() const {
        return !(bits.data()->flags & RW_HAS_DEFAULT_CORE);
    }
    void setHasDefaultCore() {
        bits.data()->setFlags(RW_HAS_DEFAULT_CORE);
    }
    void setHasCustomCore() {
        bits.data()->clearFlags(RW_HAS_DEFAULT_CORE);
    }
#endif

#if FAST_CACHE_HAS_CXX_CTOR
    bool hasCxxCtor() {
        ASSERT(isRealized());
        return cache.getBit(FAST_CACHE_HAS_CXX_CTOR);
    }
    void setHasCxxCtor() {
        cache.setBit(FAST_CACHE_HAS_CXX_CTOR);
    }
#else
    bool hasCxxCtor() {
        ASSERT(isRealized());
        return bits.data()->flags & RW_HAS_CXX_CTOR;
    }
    void setHasCxxCtor() {
        bits.data()->setFlags(RW_HAS_CXX_CTOR);
    }
#endif

#if FAST_CACHE_HAS_CXX_DTOR
    bool hasCxxDtor() {
        ASSERT(isRealized());
        return cache.getBit(FAST_CACHE_HAS_CXX_DTOR);
    }
    void setHasCxxDtor() {
        cache.setBit(FAST_CACHE_HAS_CXX_DTOR);
    }
#else
    bool hasCxxDtor() {
        ASSERT(isRealized());
        return bits.data()->flags & RW_HAS_CXX_DTOR;
    }
    void setHasCxxDtor() {
        bits.data()->setFlags(RW_HAS_CXX_DTOR);
    }
#endif

#if FAST_CACHE_REQUIRES_RAW_ISA
    bool instancesRequireRawIsa() {
        return cache.getBit(FAST_CACHE_REQUIRES_RAW_ISA);
    }
    void setInstancesRequireRawIsa() {
        cache.setBit(FAST_CACHE_REQUIRES_RAW_ISA);
    }
#elif SUPPORT_NONPOINTER_ISA
    bool instancesRequireRawIsa() {
        return bits.data()->flags & RW_REQUIRES_RAW_ISA;
    }
    void setInstancesRequireRawIsa() {
        bits.data()->setFlags(RW_REQUIRES_RAW_ISA);
    }
#else
    bool instancesRequireRawIsa() {
        return true;
    }
    void setInstancesRequireRawIsa() {
        // nothing
    }
#endif
    void setInstancesRequireRawIsaRecursively(bool inherited = false);
    void printInstancesRequireRawIsa(bool inherited);

    bool canAllocNonpointer() {
        ASSERT(!isFuture());
        return !instancesRequireRawIsa();
    }

    bool isSwiftStable() {
        return bits.isSwiftStable();
    }

    bool isSwiftLegacy() {
        return bits.isSwiftLegacy();
    }

    bool isAnySwift() {
        return bits.isAnySwift();
    }

    bool isSwiftStable_ButAllowLegacyForNow() {
        return bits.isSwiftStable_ButAllowLegacyForNow();
    }

    bool isStubClass() const {
        uintptr_t isa = (uintptr_t)isaBits();
        return 1 <= isa && isa < 16;
    }

    // Swift stable ABI built for old deployment targets looks weird.
    // The is-legacy bit is set for compatibility with old libobjc.
    // We are on a "new" deployment target so we need to rewrite that bit.
    // These stable-with-legacy-bit classes are distinguished from real
    // legacy classes using another bit in the Swift data
    // (ClassFlags::IsSwiftPreStableABI)

    bool isUnfixedBackwardDeployingStableSwift() {
        // Only classes marked as Swift legacy need apply.
        if (!bits.isSwiftLegacy()) return false;

        // Check the true legacy vs stable distinguisher.
        // The low bit of Swift's ClassFlags is SET for true legacy
        // and UNSET for stable pretending to be legacy.
        uint32_t swiftClassFlags = *(uint32_t *)(&bits + 1);
        bool isActuallySwiftLegacy = bool(swiftClassFlags & 1);
        return !isActuallySwiftLegacy;
    }

    void fixupBackwardDeployingStableSwift() {
        if (isUnfixedBackwardDeployingStableSwift()) {
            // Class really is stable Swift, pretending to be pre-stable.
            // Fix its lie.
            bits.setIsSwiftStable();
        }
    }

    _objc_swiftMetadataInitializer swiftMetadataInitializer() {
        return bits.swiftMetadataInitializer();
    }

    // Return YES if the class's ivars are managed by ARC, 
    // or the class is MRC but has ARC-style weak ivars.
    bool hasAutomaticIvars() {
        return data()->ro()->flags & (RO_IS_ARC | RO_HAS_WEAK_WITHOUT_ARC);
    }

    // Return YES if the class's ivars are managed by ARC.
    bool isARC() {
        return data()->ro()->flags & RO_IS_ARC;
    }


    bool forbidsAssociatedObjects() {
        return (data()->flags & RW_FORBIDS_ASSOCIATED_OBJECTS);
    }

#if SUPPORT_NONPOINTER_ISA
    // Tracked in non-pointer isas; not tracked otherwise
#else
    bool instancesHaveAssociatedObjects() {
        // this may be an unrealized future class in the CF-bridged case
        ASSERT(isFuture()  ||  isRealized());
        return data()->flags & RW_INSTANCES_HAVE_ASSOCIATED_OBJECTS;
    }

    void setInstancesHaveAssociatedObjects() {
        // this may be an unrealized future class in the CF-bridged case
        ASSERT(isFuture()  ||  isRealized());
        setInfo(RW_INSTANCES_HAVE_ASSOCIATED_OBJECTS);
    }
#endif

    bool shouldGrowCache() {
        return true;
    }

    void setShouldGrowCache(bool) {
        // fixme good or bad for memory use?
    }

    bool isInitializing() {
        return getMeta()->data()->flags & RW_INITIALIZING;
    }

    void setInitializing() {
        ASSERT(!isMetaClass());
        ISA()->setInfo(RW_INITIALIZING);
    }

    bool isInitialized() {
        return getMeta()->data()->flags & RW_INITIALIZED;
    }

    void setInitialized();

    bool isLoadable() {
        ASSERT(isRealized());
        return true;  // any class registered for +load is definitely loadable
    }

    IMP getLoadMethod();

    // Locking: To prevent concurrent realization, hold runtimeLock.
    bool isRealized() const {
        return !isStubClass() && (data()->flags & RW_REALIZED);
    }

    // Returns true if this is an unrealized future class.
    // Locking: To prevent concurrent realization, hold runtimeLock.
    bool isFuture() const {
        return data()->flags & RW_FUTURE;
    }

    bool isMetaClass() {
        ASSERT(this);
        ASSERT(isRealized());
#if FAST_CACHE_META
        return cache.getBit(FAST_CACHE_META);
#else
        return data()->flags & RW_META;
#endif
    }

    // Like isMetaClass, but also valid on un-realized classes
    bool isMetaClassMaybeUnrealized() {
        static_assert(offsetof(class_rw_t, flags) == offsetof(class_ro_t, flags), "flags alias");
        static_assert(RO_META == RW_META, "flags alias");
        return data()->flags & RW_META;
    }

    // NOT identical to this->ISA when this is a metaclass
    Class getMeta() {
        if (isMetaClass()) return (Class)this;
        else return this->ISA();
    }

    bool isRootClass() {
        return superclass == nil;
    }
    bool isRootMetaclass() {
        return ISA() == (Class)this;
    }

    const char *mangledName() { 
        // fixme can't assert locks here
        ASSERT(this);

        if (isRealized()  ||  isFuture()) {
            return data()->ro()->name;
        } else {
            return ((const class_ro_t *)data())->name;
        }
    }
    
    const char *demangledName(bool needsLock);
    const char *nameForLogging();

    // May be unaligned depending on class's ivars.
    uint32_t unalignedInstanceStart() const {
        ASSERT(isRealized());
        return data()->ro()->instanceStart;
    }

    // Class's instance start rounded up to a pointer-size boundary.
    // This is used for ARC layout bitmaps.
    uint32_t alignedInstanceStart() const {
        return word_align(unalignedInstanceStart());
    }

    // May be unaligned depending on class's ivars.
    uint32_t unalignedInstanceSize() const {
        ASSERT(isRealized());
        return data()->ro()->instanceSize;
    }

    // Class's ivar size rounded up to a pointer-size boundary.
    uint32_t alignedInstanceSize() const {
        return word_align(unalignedInstanceSize());
    }

    size_t instanceSize(size_t extraBytes) const {
        if (fastpath(cache.hasFastInstanceSize(extraBytes))) {
            return cache.fastInstanceSize(extraBytes);
        }

        size_t size = alignedInstanceSize() + extraBytes;
        // CF requires all objects be at least 16 bytes.
        if (size < 16) size = 16;
        return size;
    }

    void setInstanceSize(uint32_t newSize) {
        ASSERT(isRealized());
        ASSERT(data()->flags & RW_REALIZING);
        auto ro = data()->ro();
        if (newSize != ro->instanceSize) {
            ASSERT(data()->flags & RW_COPIED_RO);
            *const_cast<uint32_t *>(&ro->instanceSize) = newSize;
        }
        cache.setFastInstanceSize(newSize);
    }

    void chooseClassArrayIndex();

    void setClassArrayIndex(unsigned Idx) {
        bits.setClassArrayIndex(Idx);
    }

    unsigned classArrayIndex() {
        return bits.classArrayIndex();
    }
};


struct swift_class_t : objc_class {
    uint32_t flags;
    uint32_t instanceAddressOffset;
    uint32_t instanceSize;
    uint16_t instanceAlignMask;
    uint16_t reserved;

    uint32_t classSize;
    uint32_t classAddressOffset;
    void *description;
    // ...

    void *baseAddress() {
        return (void *)((uint8_t *)this - classAddressOffset);
    }
};


struct category_t {
    const char *name;
    classref_t cls;
    struct method_list_t *instanceMethods;
    struct method_list_t *classMethods;
    struct protocol_list_t *protocols;
    struct property_list_t *instanceProperties;
    // Fields below this point are not always present on disk.
    struct property_list_t *_classProperties;

    method_list_t *methodsForMeta(bool isMeta) {
        if (isMeta) return classMethods;
        else return instanceMethods;
    }

    property_list_t *propertiesForMeta(bool isMeta, struct header_info *hi);
    
    protocol_list_t *protocolsForMeta(bool isMeta) {
        if (isMeta) return nullptr;
        else return protocols;
    }
};

struct objc_super2 {
    id receiver;
    Class current_class;
};

struct message_ref_t {
    IMP imp;
    SEL sel;
};


extern Method protocol_getMethod(protocol_t *p, SEL sel, bool isRequiredMethod, bool isInstanceMethod, bool recursive);

#endif