This is xnu-6153.11.26. See this file in:
/*
 * Block_private.h
 *
 * SPI for Blocks
 *
 * Copyright (c) 2008-2010 Apple Inc. All rights reserved.
 *
 * @APPLE_LLVM_LICENSE_HEADER@
 *
 */

#ifndef _BLOCK_PRIVATE_H_
#define _BLOCK_PRIVATE_H_

#include <Availability.h>
#include <AvailabilityMacros.h>
#ifndef KERNEL
#include <TargetConditionals.h>
#endif

#include <stdbool.h>
#include <stdint.h>
#ifdef KERNEL
#include <sys/systm.h>
#else
#include <stdio.h>
#endif


#ifdef KERNEL
#include <libkern/Block.h>
struct Block_byref;
#else
#include <Block.h>
#endif

#if __has_include(<ptrauth.h>)
#include <ptrauth.h>
#endif

#if __has_feature(ptrauth_calls) && __cplusplus < 201103L

// C ptrauth or old C++ ptrauth

#define _Block_set_function_pointer(field, value)                       \
    ((value)                                                            \
     ? ((field) =                                                       \
	(__typeof__(field))                                             \
	ptrauth_auth_and_resign((void*)(value),                         \
	                        ptrauth_key_function_pointer, 0,        \
	                        ptrauth_key_block_function, &(field)))  \
     : ((field) = 0))

#define _Block_get_function_pointer(field)                              \
    ((field)                                                            \
     ? (__typeof__(field))                                              \
       ptrauth_auth_function((void*)(field),                            \
	                     ptrauth_key_block_function, &(field))      \
     : (__typeof__(field))0)

#else

// C++11 ptrauth or no ptrauth

#define _Block_set_function_pointer(field, value)       \
    (field) = (value)

#define _Block_get_function_pointer(field)      \
    (field)

#endif


#if __has_feature(ptrauth_calls) && __cplusplus >= 201103L

// StorageSignedFunctionPointer<Key, Fn> stores a function pointer of type
// Fn but signed with the given ptrauth key and with the address of its
// storage as extra data.
// Function pointers inside block objects are signed this way.
template <typename Fn, ptrauth_key Key>
class StorageSignedFunctionPointer {
	uintptr_t bits;

public:

// Authenticate function pointer fn as a C function pointer.
// Re-sign it with our key and the storage address as extra data.
// DOES NOT actually write to our storage.
	uintptr_t
	prepareWrite(Fn fn) const
	{
		if (fn == nullptr) {
			return 0;
		} else {
			return (uintptr_t)
			       ptrauth_auth_and_resign(fn, ptrauth_key_function_pointer, 0,
			           Key, &bits);
		}
	}

// Authenticate otherBits at otherStorage.
// Re-sign it with our storage address.
// DOES NOT actually write to our storage.
	uintptr_t
	prepareWrite(const StorageSignedFunctionPointer& other) const
	{
		if (other.bits == 0) {
			return 0;
		} else {
			return (uintptr_t)
			       ptrauth_auth_and_resign((void*)other.bits, Key, &other.bits,
			           Key, &bits);
		}
	}

// Authenticate ptr as if it were stored at our storage address.
// Re-sign it as a C function pointer.
// DOES NOT actually read from our storage.
	Fn
	completeReadFn(uintptr_t ptr) const
	{
		if (ptr == 0) {
			return nullptr;
		} else {
			return ptrauth_auth_function((Fn)ptr, Key, &bits);
		}
	}

// Authenticate ptr as if it were at our storage address.
// Return it as a dereferenceable pointer.
// DOES NOT actually read from our storage.
	void*
	completeReadRaw(uintptr_t ptr) const
	{
		if (ptr == 0) {
			return nullptr;
		} else {
			return ptrauth_auth_data((void*)ptr, Key, &bits);
		}
	}

	StorageSignedFunctionPointer()
	{
	}

	StorageSignedFunctionPointer(Fn value)
		: bits(prepareWrite(value))
	{
	}

	StorageSignedFunctionPointer(const StorageSignedFunctionPointer& value)
		: bits(prepareWrite(value))
	{
	}

	StorageSignedFunctionPointer&
	operator =(Fn rhs)
	{
		bits = prepareWrite(rhs);
		return *this;
	}

	StorageSignedFunctionPointer&
	operator =(const StorageSignedFunctionPointer& rhs)
	{
		bits = prepareWrite(rhs);
		return *this;
	}

	operator Fn() const {
		return completeReadFn(bits);
	}

	explicit
	operator void*() const
	{
		return completeReadRaw(bits);
	}

	explicit
	operator bool() const
	{
		return completeReadRaw(bits) != nullptr;
	}
};

using BlockCopyFunction = StorageSignedFunctionPointer
    <void (*)(void *, const void *),
    ptrauth_key_block_function>;

using BlockDisposeFunction = StorageSignedFunctionPointer
    <void (*)(const void *),
    ptrauth_key_block_function>;

using BlockInvokeFunction = StorageSignedFunctionPointer
    <void (*)(void *, ...),
    ptrauth_key_block_function>;

using BlockByrefKeepFunction = StorageSignedFunctionPointer
    <void (*)(struct Block_byref *, struct Block_byref *),
    ptrauth_key_block_function>;

using BlockByrefDestroyFunction = StorageSignedFunctionPointer
    <void (*)(struct Block_byref *),
    ptrauth_key_block_function>;

// c++11 and ptrauth_calls
#elif !__has_feature(ptrauth_calls)
// not ptrauth_calls

typedef void (*BlockCopyFunction)(void *, const void *);
typedef void (*BlockDisposeFunction)(const void *);
typedef void (*BlockInvokeFunction)(void *, ...);
typedef void (*BlockByrefKeepFunction)(struct Block_byref*, struct Block_byref*);
typedef void (*BlockByrefDestroyFunction)(struct Block_byref *);

#else
// ptrauth_calls but not c++11

typedef uintptr_t BlockCopyFunction;
typedef uintptr_t BlockDisposeFunction;
typedef uintptr_t BlockInvokeFunction;
typedef uintptr_t BlockByrefKeepFunction;
typedef uintptr_t BlockByrefDestroyFunction;

#endif


// Values for Block_layout->flags to describe block objects
enum {
	BLOCK_DEALLOCATING =      (0x0001),// runtime
	BLOCK_REFCOUNT_MASK =     (0xfffe),// runtime
	BLOCK_NEEDS_FREE =        (1 << 24),// runtime
	BLOCK_HAS_COPY_DISPOSE =  (1 << 25),// compiler
	BLOCK_HAS_CTOR =          (1 << 26),// compiler: helpers have C++ code
	BLOCK_IS_GC =             (1 << 27),// runtime
	BLOCK_IS_GLOBAL =         (1 << 28),// compiler
	BLOCK_USE_STRET =         (1 << 29),// compiler: undefined if !BLOCK_HAS_SIGNATURE
	BLOCK_HAS_SIGNATURE  =    (1 << 30),// compiler
	BLOCK_HAS_EXTENDED_LAYOUT=(1 << 31) // compiler
};

#define BLOCK_DESCRIPTOR_1 1
struct Block_descriptor_1 {
	uintptr_t reserved;
	uintptr_t size;
};

#define BLOCK_DESCRIPTOR_2 1
struct Block_descriptor_2 {
	// requires BLOCK_HAS_COPY_DISPOSE
	BlockCopyFunction copy;
	BlockDisposeFunction dispose;
};

#define BLOCK_DESCRIPTOR_3 1
struct Block_descriptor_3 {
	// requires BLOCK_HAS_SIGNATURE
	const char *signature;
	const char *layout; // contents depend on BLOCK_HAS_EXTENDED_LAYOUT
};

struct Block_layout {
	void *isa;
	volatile int32_t flags; // contains ref count
	int32_t reserved;
	BlockInvokeFunction invoke;
	struct Block_descriptor_1 *descriptor;
	// imported variables
};


// Values for Block_byref->flags to describe __block variables
enum {
	// Byref refcount must use the same bits as Block_layout's refcount.
	// BLOCK_DEALLOCATING =      (0x0001),  // runtime
	// BLOCK_REFCOUNT_MASK =     (0xfffe),  // runtime

	BLOCK_BYREF_LAYOUT_MASK =       (0xf << 28),// compiler
	BLOCK_BYREF_LAYOUT_EXTENDED =   (1 << 28),// compiler
	BLOCK_BYREF_LAYOUT_NON_OBJECT = (2 << 28), // compiler
	BLOCK_BYREF_LAYOUT_STRONG =     (3 << 28),// compiler
	BLOCK_BYREF_LAYOUT_WEAK =       (4 << 28),// compiler
	BLOCK_BYREF_LAYOUT_UNRETAINED = (5 << 28), // compiler

	BLOCK_BYREF_IS_GC =             (1 << 27),// runtime

	BLOCK_BYREF_HAS_COPY_DISPOSE =  (1 << 25),// compiler
	BLOCK_BYREF_NEEDS_FREE =        (1 << 24),// runtime
};

struct Block_byref {
	void *isa;
	struct Block_byref *forwarding;
	volatile int32_t flags; // contains ref count
	uint32_t size;
};

struct Block_byref_2 {
	// requires BLOCK_BYREF_HAS_COPY_DISPOSE
	BlockByrefKeepFunction byref_keep;
	BlockByrefDestroyFunction byref_destroy;
};

struct Block_byref_3 {
	// requires BLOCK_BYREF_LAYOUT_EXTENDED
	const char *layout;
};


// Extended layout encoding.

// Values for Block_descriptor_3->layout with BLOCK_HAS_EXTENDED_LAYOUT
// and for Block_byref_3->layout with BLOCK_BYREF_LAYOUT_EXTENDED

// If the layout field is less than 0x1000, then it is a compact encoding
// of the form 0xXYZ: X strong pointers, then Y byref pointers,
// then Z weak pointers.

// If the layout field is 0x1000 or greater, it points to a
// string of layout bytes. Each byte is of the form 0xPN.
// Operator P is from the list below. Value N is a parameter for the operator.
// Byte 0x00 terminates the layout; remaining block data is non-pointer bytes.

enum {
	BLOCK_LAYOUT_ESCAPE = 0, // N=0 halt, rest is non-pointer. N!=0 reserved.
	BLOCK_LAYOUT_NON_OBJECT_BYTES = 1, // N bytes non-objects
	BLOCK_LAYOUT_NON_OBJECT_WORDS = 2, // N words non-objects
	BLOCK_LAYOUT_STRONG           = 3,// N words strong pointers
	BLOCK_LAYOUT_BYREF            = 4,// N words byref pointers
	BLOCK_LAYOUT_WEAK             = 5,// N words weak pointers
	BLOCK_LAYOUT_UNRETAINED       = 6,// N words unretained pointers
	BLOCK_LAYOUT_UNKNOWN_WORDS_7  = 7,// N words, reserved
	BLOCK_LAYOUT_UNKNOWN_WORDS_8  = 8,// N words, reserved
	BLOCK_LAYOUT_UNKNOWN_WORDS_9  = 9,// N words, reserved
	BLOCK_LAYOUT_UNKNOWN_WORDS_A  = 0xA,// N words, reserved
	BLOCK_LAYOUT_UNUSED_B         = 0xB,// unspecified, reserved
	BLOCK_LAYOUT_UNUSED_C         = 0xC,// unspecified, reserved
	BLOCK_LAYOUT_UNUSED_D         = 0xD,// unspecified, reserved
	BLOCK_LAYOUT_UNUSED_E         = 0xE,// unspecified, reserved
	BLOCK_LAYOUT_UNUSED_F         = 0xF,// unspecified, reserved
};


// Runtime support functions used by compiler when generating copy/dispose helpers

// Values for _Block_object_assign() and _Block_object_dispose() parameters
enum {
	// see function implementation for a more complete description of these fields and combinations
	BLOCK_FIELD_IS_OBJECT   =  3,// id, NSObject, __attribute__((NSObject)), block, ...
	BLOCK_FIELD_IS_BLOCK    =  7,// a block variable
	BLOCK_FIELD_IS_BYREF    =  8,// the on stack structure holding the __block variable
	BLOCK_FIELD_IS_WEAK     = 16,// declared __weak, only used in byref copy helpers
	BLOCK_BYREF_CALLER      = 128,// called from __block (byref) copy/dispose support routines.
};

enum {
	BLOCK_ALL_COPY_DISPOSE_FLAGS =
	    BLOCK_FIELD_IS_OBJECT | BLOCK_FIELD_IS_BLOCK | BLOCK_FIELD_IS_BYREF |
	    BLOCK_FIELD_IS_WEAK | BLOCK_BYREF_CALLER
};


// Function pointer accessors

static inline __typeof__(void (*)(void *, ...))
_Block_get_invoke_fn(struct Block_layout *block)
{
	return (void (*)(void *, ...))_Block_get_function_pointer(block->invoke);
}

static inline void
_Block_set_invoke_fn(struct Block_layout *block, void (*fn)(void *, ...))
{
	_Block_set_function_pointer(block->invoke, fn);
}


static inline __typeof__(void (*)(void *, const void *))
_Block_get_copy_fn(struct Block_descriptor_2 *desc)
{
	return (void (*)(void *, const void *))_Block_get_function_pointer(desc->copy);
}

static inline void
_Block_set_copy_fn(struct Block_descriptor_2 *desc,
    void (*fn)(void *, const void *))
{
	_Block_set_function_pointer(desc->copy, fn);
}


static inline __typeof__(void (*)(const void *))
_Block_get_dispose_fn(struct Block_descriptor_2 *desc)
{
	return (void (*)(const void *))_Block_get_function_pointer(desc->dispose);
}

static inline void
_Block_set_dispose_fn(struct Block_descriptor_2 *desc,
    void (*fn)(const void *))
{
	_Block_set_function_pointer(desc->dispose, fn);
}


// Other support functions


// runtime entry to get total size of a closure
BLOCK_EXPORT size_t Block_size(void *aBlock);

// indicates whether block was compiled with compiler that sets the ABI related metadata bits
BLOCK_EXPORT bool _Block_has_signature(void *aBlock)
__OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3);

// returns TRUE if return value of block is on the stack, FALSE otherwise
BLOCK_EXPORT bool _Block_use_stret(void *aBlock)
__OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3);

// Returns a string describing the block's parameter and return types.
// The encoding scheme is the same as Objective-C @encode.
// Returns NULL for blocks compiled with some compilers.
BLOCK_EXPORT const char * _Block_signature(void *aBlock)
__OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3);

// Returns a string describing the block's GC layout.
// This uses the GC skip/scan encoding.
// May return NULL.
BLOCK_EXPORT const char * _Block_layout(void *aBlock)
__OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3);

// Returns a string describing the block's layout.
// This uses the "extended layout" form described above.
// May return NULL.
BLOCK_EXPORT const char * _Block_extended_layout(void *aBlock)
__OSX_AVAILABLE_STARTING(__MAC_10_8, __IPHONE_7_0);

// Callable only from the ARR weak subsystem while in exclusion zone
BLOCK_EXPORT bool _Block_tryRetain(const void *aBlock)
__OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3);

// Callable only from the ARR weak subsystem while in exclusion zone
BLOCK_EXPORT bool _Block_isDeallocating(const void *aBlock)
__OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3);


// the raw data space for runtime classes for blocks
// class+meta used for stack, malloc, and collectable based blocks
BLOCK_EXPORT void * _NSConcreteMallocBlock[32]
__OSX_AVAILABLE_STARTING(__MAC_10_6, __IPHONE_3_2);
BLOCK_EXPORT void * _NSConcreteAutoBlock[32]
__OSX_AVAILABLE_STARTING(__MAC_10_6, __IPHONE_3_2);
BLOCK_EXPORT void * _NSConcreteFinalizingBlock[32]
__OSX_AVAILABLE_STARTING(__MAC_10_6, __IPHONE_3_2);
BLOCK_EXPORT void * _NSConcreteWeakBlockVariable[32]
__OSX_AVAILABLE_STARTING(__MAC_10_6, __IPHONE_3_2);
// declared in Block.h
// BLOCK_EXPORT void * _NSConcreteGlobalBlock[32];
// BLOCK_EXPORT void * _NSConcreteStackBlock[32];


struct Block_callbacks_RR {
	size_t  size;               // size == sizeof(struct Block_callbacks_RR)
	void  (*retain)(const void *);
	void  (*release)(const void *);
	void  (*destructInstance)(const void *);
};
typedef struct Block_callbacks_RR Block_callbacks_RR;

BLOCK_EXPORT void _Block_use_RR2(const Block_callbacks_RR *callbacks);


#endif