/*
* Copyright (c) 2010-2012 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@
*/
#include "objc-private.h"
#include "NSObject.h"
#include "objc-weak.h"
#include "llvm-DenseMap.h"
#include "NSObject.h"
#include <malloc/malloc.h>
#include <stdint.h>
#include <stdbool.h>
#include <mach/mach.h>
#include <mach-o/dyld.h>
#include <mach-o/nlist.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <libkern/OSAtomic.h>
#include <Block.h>
#include <map>
#include <execinfo.h>
@interface NSInvocation
- (SEL)selector;
@end
// HACK -- the use of these functions must be after the @implementation
id bypass_msgSend_retain(NSObject *obj) asm("-[NSObject retain]");
void bypass_msgSend_release(NSObject *obj) asm("-[NSObject release]");
id bypass_msgSend_autorelease(NSObject *obj) asm("-[NSObject autorelease]");
#if TARGET_OS_MAC
// NSObject used to be in Foundation/CoreFoundation.
#define SYMBOL_ELSEWHERE_IN_3(sym, vers, n) \
OBJC_EXPORT const char elsewhere_ ##n __asm__("$ld$hide$os" #vers "$" #sym); const char elsewhere_ ##n = 0
#define SYMBOL_ELSEWHERE_IN_2(sym, vers, n) \
SYMBOL_ELSEWHERE_IN_3(sym, vers, n)
#define SYMBOL_ELSEWHERE_IN(sym, vers) \
SYMBOL_ELSEWHERE_IN_2(sym, vers, __COUNTER__)
#if __OBJC2__
# define NSOBJECT_ELSEWHERE_IN(vers) \
SYMBOL_ELSEWHERE_IN(_OBJC_CLASS_$_NSObject, vers); \
SYMBOL_ELSEWHERE_IN(_OBJC_METACLASS_$_NSObject, vers); \
SYMBOL_ELSEWHERE_IN(_OBJC_IVAR_$_NSObject.isa, vers)
#else
# define NSOBJECT_ELSEWHERE_IN(vers) \
SYMBOL_ELSEWHERE_IN(.objc_class_name_NSObject, vers)
#endif
#if TARGET_OS_IPHONE
NSOBJECT_ELSEWHERE_IN(5.1);
NSOBJECT_ELSEWHERE_IN(5.0);
NSOBJECT_ELSEWHERE_IN(4.3);
NSOBJECT_ELSEWHERE_IN(4.2);
NSOBJECT_ELSEWHERE_IN(4.1);
NSOBJECT_ELSEWHERE_IN(4.0);
NSOBJECT_ELSEWHERE_IN(3.2);
NSOBJECT_ELSEWHERE_IN(3.1);
NSOBJECT_ELSEWHERE_IN(3.0);
NSOBJECT_ELSEWHERE_IN(2.2);
NSOBJECT_ELSEWHERE_IN(2.1);
NSOBJECT_ELSEWHERE_IN(2.0);
#else
NSOBJECT_ELSEWHERE_IN(10.7);
NSOBJECT_ELSEWHERE_IN(10.6);
NSOBJECT_ELSEWHERE_IN(10.5);
NSOBJECT_ELSEWHERE_IN(10.4);
NSOBJECT_ELSEWHERE_IN(10.3);
NSOBJECT_ELSEWHERE_IN(10.2);
NSOBJECT_ELSEWHERE_IN(10.1);
NSOBJECT_ELSEWHERE_IN(10.0);
#endif
// TARGET_OS_MAC
#endif
#if SUPPORT_RETURN_AUTORELEASE
// We cannot peek at where we are returning to unless we always inline this:
__attribute__((always_inline))
static bool callerAcceptsFastAutorelease(const void * const ra0);
#endif
/***********************************************************************
* Weak ivar support
**********************************************************************/
static id defaultBadAllocHandler(Class cls)
{
_objc_fatal("attempt to allocate object of class '%s' failed",
class_getName(cls));
}
static id(*badAllocHandler)(Class) = &defaultBadAllocHandler;
static id callBadAllocHandler(Class cls)
{
// fixme add re-entrancy protection in case allocation fails inside handler
return (*badAllocHandler)(cls);
}
void _objc_setBadAllocHandler(id(*newHandler)(Class))
{
badAllocHandler = newHandler;
}
namespace {
#if TARGET_OS_EMBEDDED
# define SIDE_TABLE_STRIPE 1
#else
# define SIDE_TABLE_STRIPE 8
#endif
// should be a multiple of cache line size (64)
#define SIDE_TABLE_SIZE 128
// The order of these bits is important.
#define SIDE_TABLE_WEAKLY_REFERENCED (1<<0)
#define SIDE_TABLE_DEALLOCATING (1<<1) // MSB-ward of weak bit
#define SIDE_TABLE_RC_ONE (1<<2) // MSB-ward of deallocating bit
#define SIDE_TABLE_RC_SHIFT 2
typedef objc::DenseMap<id,size_t,true> RefcountMap;
class SideTable {
private:
static uint8_t table_buf[SIDE_TABLE_STRIPE * SIDE_TABLE_SIZE];
public:
spinlock_t slock;
RefcountMap refcnts;
weak_table_t weak_table;
SideTable() : slock(SPINLOCK_INITIALIZER)
{
memset(&weak_table, 0, sizeof(weak_table));
}
~SideTable()
{
// never delete side_table in case other threads retain during exit
assert(0);
}
static SideTable *tableForPointer(const void *p)
{
# if SIDE_TABLE_STRIPE == 1
return (SideTable *)table_buf;
# else
uintptr_t a = (uintptr_t)p;
int index = ((a >> 4) ^ (a >> 9)) & (SIDE_TABLE_STRIPE - 1);
return (SideTable *)&table_buf[index * SIDE_TABLE_SIZE];
# endif
}
static void init() {
// use placement new instead of static ctor to avoid dtor at exit
for (int i = 0; i < SIDE_TABLE_STRIPE; i++) {
new (&table_buf[i * SIDE_TABLE_SIZE]) SideTable;
}
}
};
STATIC_ASSERT(sizeof(SideTable) <= SIDE_TABLE_SIZE);
__attribute__((aligned(SIDE_TABLE_SIZE))) uint8_t
SideTable::table_buf[SIDE_TABLE_STRIPE * SIDE_TABLE_SIZE];
// Avoid false-negative reports from tools like "leaks"
#define DISGUISE(x) ((id)~(uintptr_t)(x))
// anonymous namespace
};
//
// The -fobjc-arc flag causes the compiler to issue calls to objc_{retain/release/autorelease/retain_block}
//
id objc_retainBlock(id x) {
return (id)_Block_copy(x);
}
//
// The following SHOULD be called by the compiler directly, but the request hasn't been made yet :-)
//
BOOL objc_should_deallocate(id object) {
return YES;
}
id
objc_retain_autorelease(id obj)
{
return objc_autorelease(objc_retain(obj));
}
/**
* This function stores a new value into a __weak variable. It would
* be used anywhere a __weak variable is the target of an assignment.
*
* @param location The address of the weak pointer itself
* @param newObj The new object this weak ptr should now point to
*
* @return \e newObj
*/
id
objc_storeWeak(id *location, id newObj)
{
id oldObj;
SideTable *oldTable;
SideTable *newTable;
spinlock_t *lock1;
#if SIDE_TABLE_STRIPE > 1
spinlock_t *lock2;
#endif
// Acquire locks for old and new values.
// Order by lock address to prevent lock ordering problems.
// Retry if the old value changes underneath us.
retry:
oldObj = *location;
oldTable = SideTable::tableForPointer(oldObj);
newTable = SideTable::tableForPointer(newObj);
lock1 = &newTable->slock;
#if SIDE_TABLE_STRIPE > 1
lock2 = &oldTable->slock;
if (lock1 > lock2) {
spinlock_t *temp = lock1;
lock1 = lock2;
lock2 = temp;
}
if (lock1 != lock2) spinlock_lock(lock2);
#endif
spinlock_lock(lock1);
if (*location != oldObj) {
spinlock_unlock(lock1);
#if SIDE_TABLE_STRIPE > 1
if (lock1 != lock2) spinlock_unlock(lock2);
#endif
goto retry;
}
weak_unregister_no_lock(&oldTable->weak_table, oldObj, location);
newObj = weak_register_no_lock(&newTable->weak_table, newObj, location);
// weak_register_no_lock returns nil if weak store should be rejected
// Set is-weakly-referenced bit in refcount table.
if (newObj && !newObj->isTaggedPointer()) {
newTable->refcnts[DISGUISE(newObj)] |= SIDE_TABLE_WEAKLY_REFERENCED;
}
// Do not set *location anywhere else. That would introduce a race.
*location = newObj;
spinlock_unlock(lock1);
#if SIDE_TABLE_STRIPE > 1
if (lock1 != lock2) spinlock_unlock(lock2);
#endif
return newObj;
}
id
objc_loadWeakRetained(id *location)
{
id result;
SideTable *table;
spinlock_t *lock;
retry:
result = *location;
if (!result) return nil;
table = SideTable::tableForPointer(result);
lock = &table->slock;
spinlock_lock(lock);
if (*location != result) {
spinlock_unlock(lock);
goto retry;
}
result = weak_read_no_lock(&table->weak_table, location);
spinlock_unlock(lock);
return result;
}
/**
* This loads the object referenced by a weak pointer and returns it, after
* retaining and autoreleasing the object to ensure that it stays alive
* long enough for the caller to use it. This function would be used
* anywhere a __weak variable is used in an expression.
*
* @param location The weak pointer address
*
* @return The object pointed to by \e location, or \c nil if \e location is \c nil.
*/
id
objc_loadWeak(id *location)
{
if (!*location) return nil;
return objc_autorelease(objc_loadWeakRetained(location));
}
/**
* Initialize a fresh weak pointer to some object location.
* It would be used for code like:
*
* (The nil case)
* __weak id weakPtr;
* (The non-nil case)
* NSObject *o = ...;
* __weak id weakPtr = o;
*
* @param addr Address of __weak ptr.
* @param val Object ptr.
*/
id
objc_initWeak(id *addr, id val)
{
*addr = 0;
if (!val) return nil;
return objc_storeWeak(addr, val);
}
__attribute__((noinline, used)) void
objc_destroyWeak_slow(id *addr)
{
SideTable *oldTable;
spinlock_t *lock;
id oldObj;
// No need to see weak refs, we are destroying
// Acquire lock for old value only
// retry if the old value changes underneath us
retry:
oldObj = *addr;
oldTable = SideTable::tableForPointer(oldObj);
lock = &oldTable->slock;
spinlock_lock(lock);
if (*addr != oldObj) {
spinlock_unlock(lock);
goto retry;
}
weak_unregister_no_lock(&oldTable->weak_table, oldObj, addr);
spinlock_unlock(lock);
}
/**
* Destroys the relationship between a weak pointer
* and the object it is referencing in the internal weak
* table. If the weak pointer is not referencing anything,
* there is no need to edit the weak table.
*
* @param addr The weak pointer address.
*/
void
objc_destroyWeak(id *addr)
{
if (!*addr) return;
return objc_destroyWeak_slow(addr);
}
/**
* This function copies a weak pointer from one location to another,
* when the destination doesn't already contain a weak pointer. It
* would be used for code like:
*
* __weak id weakPtr1 = ...;
* __weak id weakPtr2 = weakPtr1;
*
* @param to weakPtr2 in this ex
* @param from weakPtr1
*/
void
objc_copyWeak(id *to, id *from)
{
id val = objc_loadWeakRetained(from);
objc_initWeak(to, val);
objc_release(val);
}
/**
* Move a weak pointer from one location to another.
* Before the move, the destination must be uninitialized.
* After the move, the source is nil.
*/
void
objc_moveWeak(id *to, id *from)
{
objc_copyWeak(to, from);
objc_storeWeak(from, 0);
}
/* Autorelease pool implementation
A thread's autorelease pool is a stack of pointers.
Each pointer is either an object to release, or POOL_SENTINEL which is
an autorelease pool boundary.
A pool token is a pointer to the POOL_SENTINEL for that pool. When
the pool is popped, every object hotter than the sentinel is released.
The stack is divided into a doubly-linked list of pages. Pages are added
and deleted as necessary.
Thread-local storage points to the hot page, where newly autoreleased
objects are stored.
*/
BREAKPOINT_FUNCTION(void objc_autoreleaseNoPool(id obj));
namespace {
struct magic_t {
static const uint32_t M0 = 0xA1A1A1A1;
# define M1 "AUTORELEASE!"
static const size_t M1_len = 12;
uint32_t m[4];
magic_t() {
assert(M1_len == strlen(M1));
assert(M1_len == 3 * sizeof(m[1]));
m[0] = M0;
strncpy((char *)&m[1], M1, M1_len);
}
~magic_t() {
m[0] = m[1] = m[2] = m[3] = 0;
}
bool check() const {
return (m[0] == M0 && 0 == strncmp((char *)&m[1], M1, M1_len));
}
bool fastcheck() const {
#ifdef NDEBUG
return (m[0] == M0);
#else
return check();
#endif
}
# undef M1
};
// Set this to 1 to mprotect() autorelease pool contents
#define PROTECT_AUTORELEASEPOOL 0
class AutoreleasePoolPage
{
#define POOL_SENTINEL nil
static pthread_key_t const key = AUTORELEASE_POOL_KEY;
static uint8_t const SCRIBBLE = 0xA3; // 0xA3A3A3A3 after releasing
static size_t const SIZE =
#if PROTECT_AUTORELEASEPOOL
PAGE_SIZE; // must be multiple of vm page size
#else
PAGE_SIZE; // size and alignment, power of 2
#endif
static size_t const COUNT = SIZE / sizeof(id);
magic_t const magic;
id *next;
pthread_t const thread;
AutoreleasePoolPage * const parent;
AutoreleasePoolPage *child;
uint32_t const depth;
uint32_t hiwat;
// SIZE-sizeof(*this) bytes of contents follow
static void * operator new(size_t size) {
return malloc_zone_memalign(malloc_default_zone(), SIZE, SIZE);
}
static void operator delete(void * p) {
return free(p);
}
inline void protect() {
#if PROTECT_AUTORELEASEPOOL
mprotect(this, SIZE, PROT_READ);
check();
#endif
}
inline void unprotect() {
#if PROTECT_AUTORELEASEPOOL
check();
mprotect(this, SIZE, PROT_READ | PROT_WRITE);
#endif
}
AutoreleasePoolPage(AutoreleasePoolPage *newParent)
: magic(), next(begin()), thread(pthread_self()),
parent(newParent), child(nil),
depth(parent ? 1+parent->depth : 0),
hiwat(parent ? parent->hiwat : 0)
{
if (parent) {
parent->check();
assert(!parent->child);
parent->unprotect();
parent->child = this;
parent->protect();
}
protect();
}
~AutoreleasePoolPage()
{
check();
unprotect();
assert(empty());
// Not recursive: we don't want to blow out the stack
// if a thread accumulates a stupendous amount of garbage
assert(!child);
}
void busted(bool die = true)
{
(die ? _objc_fatal : _objc_inform)
("autorelease pool page %p corrupted\n"
" magic 0x%08x 0x%08x 0x%08x 0x%08x\n pthread %p\n",
this, magic.m[0], magic.m[1], magic.m[2], magic.m[3],
this->thread);
}
void check(bool die = true)
{
if (!magic.check() || !pthread_equal(thread, pthread_self())) {
busted(die);
}
}
void fastcheck(bool die = true)
{
if (! magic.fastcheck()) {
busted(die);
}
}
id * begin() {
return (id *) ((uint8_t *)this+sizeof(*this));
}
id * end() {
return (id *) ((uint8_t *)this+SIZE);
}
bool empty() {
return next == begin();
}
bool full() {
return next == end();
}
bool lessThanHalfFull() {
return (next - begin() < (end() - begin()) / 2);
}
id *add(id obj)
{
assert(!full());
unprotect();
*next++ = obj;
protect();
return next-1;
}
void releaseAll()
{
releaseUntil(begin());
}
void releaseUntil(id *stop)
{
// Not recursive: we don't want to blow out the stack
// if a thread accumulates a stupendous amount of garbage
while (this->next != stop) {
// Restart from hotPage() every time, in case -release
// autoreleased more objects
AutoreleasePoolPage *page = hotPage();
// fixme I think this `while` can be `if`, but I can't prove it
while (page->empty()) {
page = page->parent;
setHotPage(page);
}
page->unprotect();
id obj = *--page->next;
memset((void*)page->next, SCRIBBLE, sizeof(*page->next));
page->protect();
if (obj != POOL_SENTINEL) {
objc_release(obj);
}
}
setHotPage(this);
#ifndef NDEBUG
// we expect any children to be completely empty
for (AutoreleasePoolPage *page = child; page; page = page->child) {
assert(page->empty());
}
#endif
}
void kill()
{
// Not recursive: we don't want to blow out the stack
// if a thread accumulates a stupendous amount of garbage
AutoreleasePoolPage *page = this;
while (page->child) page = page->child;
AutoreleasePoolPage *deathptr;
do {
deathptr = page;
page = page->parent;
if (page) {
page->unprotect();
page->child = nil;
page->protect();
}
delete deathptr;
} while (deathptr != this);
}
static void tls_dealloc(void *p)
{
// reinstate TLS value while we work
setHotPage((AutoreleasePoolPage *)p);
pop(0);
setHotPage(nil);
}
static AutoreleasePoolPage *pageForPointer(const void *p)
{
return pageForPointer((uintptr_t)p);
}
static AutoreleasePoolPage *pageForPointer(uintptr_t p)
{
AutoreleasePoolPage *result;
uintptr_t offset = p % SIZE;
assert(offset >= sizeof(AutoreleasePoolPage));
result = (AutoreleasePoolPage *)(p - offset);
result->fastcheck();
return result;
}
static inline AutoreleasePoolPage *hotPage()
{
AutoreleasePoolPage *result = (AutoreleasePoolPage *)
tls_get_direct(key);
if (result) result->fastcheck();
return result;
}
static inline void setHotPage(AutoreleasePoolPage *page)
{
if (page) page->fastcheck();
tls_set_direct(key, (void *)page);
}
static inline AutoreleasePoolPage *coldPage()
{
AutoreleasePoolPage *result = hotPage();
if (result) {
while (result->parent) {
result = result->parent;
result->fastcheck();
}
}
return result;
}
static inline id *autoreleaseFast(id obj)
{
AutoreleasePoolPage *page = hotPage();
if (page && !page->full()) {
return page->add(obj);
} else {
return autoreleaseSlow(obj);
}
}
static __attribute__((noinline))
id *autoreleaseSlow(id obj)
{
AutoreleasePoolPage *page;
page = hotPage();
// The code below assumes some cases are handled by autoreleaseFast()
assert(!page || page->full());
if (!page) {
// No pool. Silently push one.
assert(obj != POOL_SENTINEL);
if (DebugMissingPools) {
_objc_inform("MISSING POOLS: Object %p of class %s "
"autoreleased with no pool in place - "
"just leaking - break on "
"objc_autoreleaseNoPool() to debug",
(void*)obj, object_getClassName(obj));
objc_autoreleaseNoPool(obj);
return nil;
}
push();
page = hotPage();
}
do {
if (page->child) page = page->child;
else page = new AutoreleasePoolPage(page);
} while (page->full());
setHotPage(page);
return page->add(obj);
}
public:
static inline id autorelease(id obj)
{
assert(obj);
assert(!obj->isTaggedPointer());
id *dest __unused = autoreleaseFast(obj);
assert(!dest || *dest == obj);
return obj;
}
static inline void *push()
{
if (!hotPage()) {
setHotPage(new AutoreleasePoolPage(nil));
}
id *dest = autoreleaseFast(POOL_SENTINEL);
assert(*dest == POOL_SENTINEL);
return dest;
}
static inline void pop(void *token)
{
AutoreleasePoolPage *page;
id *stop;
if (token) {
page = pageForPointer(token);
stop = (id *)token;
assert(*stop == POOL_SENTINEL);
} else {
// Token 0 is top-level pool
page = coldPage();
assert(page);
stop = page->begin();
}
if (PrintPoolHiwat) printHiwat();
page->releaseUntil(stop);
// memory: delete empty children
// hysteresis: keep one empty child if this page is more than half full
// special case: delete everything for pop(0)
// special case: delete everything for pop(top) with DebugMissingPools
if (!token ||
(DebugMissingPools && page->empty() && !page->parent))
{
page->kill();
setHotPage(nil);
} else if (page->child) {
if (page->lessThanHalfFull()) {
page->child->kill();
}
else if (page->child->child) {
page->child->child->kill();
}
}
}
static void init()
{
int r __unused = pthread_key_init_np(AutoreleasePoolPage::key,
AutoreleasePoolPage::tls_dealloc);
assert(r == 0);
}
void print()
{
_objc_inform("[%p] ................ PAGE %s %s %s", this,
full() ? "(full)" : "",
this == hotPage() ? "(hot)" : "",
this == coldPage() ? "(cold)" : "");
check(false);
for (id *p = begin(); p < next; p++) {
if (*p == POOL_SENTINEL) {
_objc_inform("[%p] ################ POOL %p", p, p);
} else {
_objc_inform("[%p] %#16lx %s",
p, (unsigned long)*p, object_getClassName(*p));
}
}
}
static void printAll()
{
_objc_inform("##############");
_objc_inform("AUTORELEASE POOLS for thread %p", pthread_self());
AutoreleasePoolPage *page;
ptrdiff_t objects = 0;
for (page = coldPage(); page; page = page->child) {
objects += page->next - page->begin();
}
_objc_inform("%llu releases pending.", (unsigned long long)objects);
for (page = coldPage(); page; page = page->child) {
page->print();
}
_objc_inform("##############");
}
static void printHiwat()
{
// Check and propagate high water mark
// Ignore high water marks under 256 to suppress noise.
AutoreleasePoolPage *p = hotPage();
uint32_t mark = p->depth*COUNT + (uint32_t)(p->next - p->begin());
if (mark > p->hiwat && mark > 256) {
for( ; p; p = p->parent) {
p->unprotect();
p->hiwat = mark;
p->protect();
}
_objc_inform("POOL HIGHWATER: new high water mark of %u "
"pending autoreleases for thread %p:",
mark, pthread_self());
void *stack[128];
int count = backtrace(stack, sizeof(stack)/sizeof(stack[0]));
char **sym = backtrace_symbols(stack, count);
for (int i = 0; i < count; i++) {
_objc_inform("POOL HIGHWATER: %s", sym[i]);
}
free(sym);
}
}
#undef POOL_SENTINEL
};
// anonymous namespace
};
// API to only be called by root classes like NSObject or NSProxy
extern "C" {
__attribute__((used,noinline,nothrow))
static id _objc_rootRetain_slow(id obj, SideTable *table);
__attribute__((used,noinline,nothrow))
static bool _objc_rootReleaseWasZero_slow(id obj, SideTable *table);
};
id
_objc_rootRetain_slow(id obj, SideTable *table)
{
spinlock_lock(&table->slock);
table->refcnts[DISGUISE(obj)] += SIDE_TABLE_RC_ONE;
spinlock_unlock(&table->slock);
return obj;
}
bool
_objc_rootTryRetain(id obj)
{
assert(obj);
assert(!UseGC);
if (obj->isTaggedPointer()) return true;
SideTable *table = SideTable::tableForPointer(obj);
// NO SPINLOCK HERE
// _objc_rootTryRetain() is called exclusively by _objc_loadWeak(),
// which already acquired the lock on our behalf.
// fixme can't do this efficiently with os_lock_handoff_s
// if (table->slock == 0) {
// _objc_fatal("Do not call -_tryRetain.");
// }
bool result = true;
RefcountMap::iterator it = table->refcnts.find(DISGUISE(obj));
if (it == table->refcnts.end()) {
table->refcnts[DISGUISE(obj)] = SIDE_TABLE_RC_ONE;
} else if (it->second & SIDE_TABLE_DEALLOCATING) {
result = false;
} else {
it->second += SIDE_TABLE_RC_ONE;
}
return result;
}
bool
_objc_rootIsDeallocating(id obj)
{
assert(obj);
assert(!UseGC);
if (obj->isTaggedPointer()) return false;
SideTable *table = SideTable::tableForPointer(obj);
// NO SPINLOCK HERE
// _objc_rootIsDeallocating() is called exclusively by _objc_storeWeak(),
// which already acquired the lock on our behalf.
// fixme can't do this efficiently with os_lock_handoff_s
// if (table->slock == 0) {
// _objc_fatal("Do not call -_isDeallocating.");
// }
RefcountMap::iterator it = table->refcnts.find(DISGUISE(obj));
return (it != table->refcnts.end()) && (it->second & SIDE_TABLE_DEALLOCATING);
}
void
objc_clear_deallocating(id obj)
{
assert(obj);
assert(!UseGC);
SideTable *table = SideTable::tableForPointer(obj);
// clear any weak table items
// clear extra retain count and deallocating bit
// (fixme warn or abort if extra retain count == 0 ?)
spinlock_lock(&table->slock);
RefcountMap::iterator it = table->refcnts.find(DISGUISE(obj));
if (it != table->refcnts.end()) {
if (it->second & SIDE_TABLE_WEAKLY_REFERENCED) {
weak_clear_no_lock(&table->weak_table, obj);
}
table->refcnts.erase(it);
}
spinlock_unlock(&table->slock);
}
bool
_objc_rootReleaseWasZero_slow(id obj, SideTable *table)
{
bool do_dealloc = false;
spinlock_lock(&table->slock);
RefcountMap::iterator it = table->refcnts.find(DISGUISE(obj));
if (it == table->refcnts.end()) {
do_dealloc = true;
table->refcnts[DISGUISE(obj)] = SIDE_TABLE_DEALLOCATING;
} else if (it->second < SIDE_TABLE_DEALLOCATING) {
// SIDE_TABLE_WEAKLY_REFERENCED may be set. Don't change it.
do_dealloc = true;
it->second |= SIDE_TABLE_DEALLOCATING;
} else {
it->second -= SIDE_TABLE_RC_ONE;
}
spinlock_unlock(&table->slock);
return do_dealloc;
}
bool
_objc_rootReleaseWasZero(id obj)
{
assert(obj);
assert(!UseGC);
if (obj->isTaggedPointer()) return false;
SideTable *table = SideTable::tableForPointer(obj);
bool do_dealloc = false;
if (spinlock_trylock(&table->slock)) {
RefcountMap::iterator it = table->refcnts.find(DISGUISE(obj));
if (it == table->refcnts.end()) {
do_dealloc = true;
table->refcnts[DISGUISE(obj)] = SIDE_TABLE_DEALLOCATING;
} else if (it->second < SIDE_TABLE_DEALLOCATING) {
// SIDE_TABLE_WEAKLY_REFERENCED may be set. Don't change it.
do_dealloc = true;
it->second |= SIDE_TABLE_DEALLOCATING;
} else {
it->second -= SIDE_TABLE_RC_ONE;
}
spinlock_unlock(&table->slock);
return do_dealloc;
}
return _objc_rootReleaseWasZero_slow(obj, table);
}
__attribute__((noinline,used))
static id _objc_rootAutorelease2(id obj)
{
if (obj->isTaggedPointer()) return obj;
return AutoreleasePoolPage::autorelease(obj);
}
uintptr_t
_objc_rootRetainCount(id obj)
{
assert(obj);
assert(!UseGC);
// XXX -- There is no way that anybody can use this API race free in a
// threaded environment because the result is immediately stale by the
// time the caller receives it.
if (obj->isTaggedPointer()) return (uintptr_t)obj;
SideTable *table = SideTable::tableForPointer(obj);
size_t refcnt_result = 1;
spinlock_lock(&table->slock);
RefcountMap::iterator it = table->refcnts.find(DISGUISE(obj));
if (it != table->refcnts.end()) {
refcnt_result += it->second >> SIDE_TABLE_RC_SHIFT;
}
spinlock_unlock(&table->slock);
return refcnt_result;
}
id
_objc_rootInit(id obj)
{
// In practice, it will be hard to rely on this function.
// Many classes do not properly chain -init calls.
return obj;
}
id
_objc_rootAllocWithZone(Class cls, malloc_zone_t *zone)
{
id obj;
#if __OBJC2__
// allocWithZone under __OBJC2__ ignores the zone parameter
(void)zone;
obj = class_createInstance(cls, 0);
#else
if (!zone || UseGC) {
obj = class_createInstance(cls, 0);
}
else {
obj = class_createInstanceFromZone(cls, 0, zone);
}
#endif
if (!obj) obj = callBadAllocHandler(cls);
return obj;
}
id
_objc_rootAlloc(Class cls)
{
#if __OBJC2__
// Skip over the +allocWithZone: call if the class doesn't override it.
if (! cls->ISA()->hasCustomAWZ()) {
id obj = class_createInstance(cls, 0);
if (!obj) obj = callBadAllocHandler(cls);
return obj;
}
#endif
return [cls allocWithZone: nil];
}
id
objc_alloc(Class cls)
{
#if __OBJC2__
// Skip over +alloc and +allocWithZone: if the class doesn't override them.
if (cls &&
cls->ISA()->isInitialized_meta() &&
! cls->ISA()->hasCustomAWZ())
{
id obj = class_createInstance(cls, 0);
if (!obj) obj = callBadAllocHandler(cls);
return obj;
}
#endif
return [cls alloc];
}
id
objc_allocWithZone(Class cls)
{
#if __OBJC2__
// Skip over the +allocWithZone: call if the class doesn't override it.
if (cls &&
cls->ISA()->isInitialized_meta() &&
! cls->ISA()->hasCustomAWZ())
{
id obj = class_createInstance(cls, 0);
if (!obj) obj = callBadAllocHandler(cls);
return obj;
}
#endif
return [cls allocWithZone: nil];
}
void
_objc_rootDealloc(id obj)
{
assert(obj);
assert(!UseGC);
if (obj->isTaggedPointer()) return;
object_dispose(obj);
}
void
_objc_rootFinalize(id obj __unused)
{
assert(obj);
assert(UseGC);
if (UseGC) {
return;
}
_objc_fatal("_objc_rootFinalize called with garbage collection off");
}
malloc_zone_t *
_objc_rootZone(id obj)
{
(void)obj;
if (gc_zone) {
return gc_zone;
}
#if __OBJC2__
// allocWithZone under __OBJC2__ ignores the zone parameter
return malloc_default_zone();
#else
malloc_zone_t *rval = malloc_zone_from_ptr(obj);
return rval ? rval : malloc_default_zone();
#endif
}
uintptr_t
_objc_rootHash(id obj)
{
if (UseGC) {
return _object_getExternalHash(obj);
}
return (uintptr_t)obj;
}
// make CF link for now
void *_objc_autoreleasePoolPush(void) { return objc_autoreleasePoolPush(); }
void _objc_autoreleasePoolPop(void *ctxt) { objc_autoreleasePoolPop(ctxt); }
void *
objc_autoreleasePoolPush(void)
{
if (UseGC) return nil;
return AutoreleasePoolPage::push();
}
void
objc_autoreleasePoolPop(void *ctxt)
{
if (UseGC) return;
// fixme rdar://9167170
if (!ctxt) return;
AutoreleasePoolPage::pop(ctxt);
}
void
_objc_autoreleasePoolPrint(void)
{
if (UseGC) return;
AutoreleasePoolPage::printAll();
}
#if SUPPORT_RETURN_AUTORELEASE
/*
Fast handling of returned autoreleased values.
The caller and callee cooperate to keep the returned object
out of the autorelease pool.
Caller:
ret = callee();
objc_retainAutoreleasedReturnValue(ret);
// use ret here
Callee:
// compute ret
[ret retain];
return objc_autoreleaseReturnValue(ret);
objc_autoreleaseReturnValue() examines the caller's instructions following
the return. If the caller's instructions immediately call
objc_autoreleaseReturnValue, then the callee omits the -autorelease and saves
the result in thread-local storage. If the caller does not look like it
cooperates, then the callee calls -autorelease as usual.
objc_autoreleaseReturnValue checks if the returned value is the same as the
one in thread-local storage. If it is, the value is used directly. If not,
the value is assumed to be truly autoreleased and is retained again. In
either case, the caller now has a retained reference to the value.
Tagged pointer objects do participate in the fast autorelease scheme,
because it saves message sends. They are not entered in the autorelease
pool in the slow case.
*/
# if __x86_64__
static bool callerAcceptsFastAutorelease(const void * const ra0)
{
const uint8_t *ra1 = (const uint8_t *)ra0;
const uint16_t *ra2;
const uint32_t *ra4 = (const uint32_t *)ra1;
const void **sym;
#define PREFER_GOTPCREL 0
#if PREFER_GOTPCREL
// 48 89 c7 movq %rax,%rdi
// ff 15 callq *symbol@GOTPCREL(%rip)
if (*ra4 != 0xffc78948) {
return false;
}
if (ra1[4] != 0x15) {
return false;
}
ra1 += 3;
#else
// 48 89 c7 movq %rax,%rdi
// e8 callq symbol
if (*ra4 != 0xe8c78948) {
return false;
}
ra1 += (long)*(const int32_t *)(ra1 + 4) + 8l;
ra2 = (const uint16_t *)ra1;
// ff 25 jmpq *symbol@DYLDMAGIC(%rip)
if (*ra2 != 0x25ff) {
return false;
}
#endif
ra1 += 6l + (long)*(const int32_t *)(ra1 + 2);
sym = (const void **)ra1;
if (*sym != objc_retainAutoreleasedReturnValue)
{
return false;
}
return true;
}
// __x86_64__
# elif __arm__
static bool callerAcceptsFastAutorelease(const void *ra)
{
// if the low bit is set, we're returning to thumb mode
if ((uintptr_t)ra & 1) {
// 3f 46 mov r7, r7
// we mask off the low bit via subtraction
if (*(uint16_t *)((uint8_t *)ra - 1) == 0x463f) {
return true;
}
} else {
// 07 70 a0 e1 mov r7, r7
if (*(uint32_t *)ra == 0xe1a07007) {
return true;
}
}
return false;
}
// __arm__
# elif __i386__ && TARGET_IPHONE_SIMULATOR
static bool callerAcceptsFastAutorelease(const void *ra)
{
return false;
}
// __i386__ && TARGET_IPHONE_SIMULATOR
# else
#warning unknown architecture
static bool callerAcceptsFastAutorelease(const void *ra)
{
return false;
}
# endif
// SUPPORT_RETURN_AUTORELEASE
#endif
id
objc_autoreleaseReturnValue(id obj)
{
#if SUPPORT_RETURN_AUTORELEASE
assert(tls_get_direct(AUTORELEASE_POOL_RECLAIM_KEY) == nil);
if (callerAcceptsFastAutorelease(__builtin_return_address(0))) {
tls_set_direct(AUTORELEASE_POOL_RECLAIM_KEY, obj);
return obj;
}
#endif
return objc_autorelease(obj);
}
id
objc_retainAutoreleaseReturnValue(id obj)
{
return objc_autoreleaseReturnValue(objc_retain(obj));
}
id
objc_retainAutoreleasedReturnValue(id obj)
{
#if SUPPORT_RETURN_AUTORELEASE
if (obj == tls_get_direct(AUTORELEASE_POOL_RECLAIM_KEY)) {
tls_set_direct(AUTORELEASE_POOL_RECLAIM_KEY, 0);
return obj;
}
#endif
return objc_retain(obj);
}
void
objc_storeStrong(id *location, id obj)
{
// XXX FIXME -- GC support?
id prev = *location;
if (obj == prev) {
return;
}
objc_retain(obj);
*location = obj;
objc_release(prev);
}
id
objc_retainAutorelease(id obj)
{
return objc_autorelease(objc_retain(obj));
}
void
_objc_deallocOnMainThreadHelper(void *context)
{
id obj = (id)context;
[obj dealloc];
}
#undef objc_retainedObject
#undef objc_unretainedObject
#undef objc_unretainedPointer
// convert objc_objectptr_t to id, callee must take ownership.
id objc_retainedObject(objc_objectptr_t pointer) { return (id)pointer; }
// convert objc_objectptr_t to id, without ownership transfer.
id objc_unretainedObject(objc_objectptr_t pointer) { return (id)pointer; }
// convert id to objc_objectptr_t, no ownership transfer.
objc_objectptr_t objc_unretainedPointer(id object) { return object; }
void arr_init(void)
{
AutoreleasePoolPage::init();
SideTable::init();
}
@implementation NSObject
+ (void)load {
if (UseGC) gc_init2();
}
+ (void)initialize {
}
+ (id)self {
return (id)self;
}
- (id)self {
return self;
}
+ (Class)class {
return self;
}
- (Class)class {
return object_getClass(self);
}
+ (Class)superclass {
return self->superclass;
}
- (Class)superclass {
return [self class]->superclass;
}
+ (BOOL)isMemberOfClass:(Class)cls {
return object_getClass((id)self) == cls;
}
- (BOOL)isMemberOfClass:(Class)cls {
return [self class] == cls;
}
+ (BOOL)isKindOfClass:(Class)cls {
for (Class tcls = object_getClass((id)self); tcls; tcls = tcls->superclass) {
if (tcls == cls) return YES;
}
return NO;
}
- (BOOL)isKindOfClass:(Class)cls {
for (Class tcls = [self class]; tcls; tcls = tcls->superclass) {
if (tcls == cls) return YES;
}
return NO;
}
+ (BOOL)isSubclassOfClass:(Class)cls {
for (Class tcls = self; tcls; tcls = tcls->superclass) {
if (tcls == cls) return YES;
}
return NO;
}
+ (BOOL)isAncestorOfObject:(NSObject *)obj {
for (Class tcls = [obj class]; tcls; tcls = tcls->superclass) {
if (tcls == self) return YES;
}
return NO;
}
+ (BOOL)instancesRespondToSelector:(SEL)sel {
if (!sel) return NO;
return class_respondsToSelector(self, sel);
}
+ (BOOL)respondsToSelector:(SEL)sel {
if (!sel) return NO;
return class_respondsToSelector(object_getClass((id)self), sel);
}
- (BOOL)respondsToSelector:(SEL)sel {
if (!sel) return NO;
return class_respondsToSelector([self class], sel);
}
+ (BOOL)conformsToProtocol:(Protocol *)protocol {
if (!protocol) return NO;
for (Class tcls = self; tcls; tcls = tcls->superclass) {
if (class_conformsToProtocol(tcls, protocol)) return YES;
}
return NO;
}
- (BOOL)conformsToProtocol:(Protocol *)protocol {
if (!protocol) return NO;
for (Class tcls = [self class]; tcls; tcls = tcls->superclass) {
if (class_conformsToProtocol(tcls, protocol)) return YES;
}
return NO;
}
+ (NSUInteger)hash {
return _objc_rootHash(self);
}
- (NSUInteger)hash {
return _objc_rootHash(self);
}
+ (BOOL)isEqual:(id)obj {
return obj == (id)self;
}
- (BOOL)isEqual:(id)obj {
return obj == self;
}
+ (BOOL)isFault {
return NO;
}
- (BOOL)isFault {
return NO;
}
+ (BOOL)isProxy {
return NO;
}
- (BOOL)isProxy {
return NO;
}
+ (IMP)instanceMethodForSelector:(SEL)sel {
if (!sel) [self doesNotRecognizeSelector:sel];
return class_getMethodImplementation(self, sel);
}
+ (IMP)methodForSelector:(SEL)sel {
if (!sel) [self doesNotRecognizeSelector:sel];
return object_getMethodImplementation((id)self, sel);
}
- (IMP)methodForSelector:(SEL)sel {
if (!sel) [self doesNotRecognizeSelector:sel];
return object_getMethodImplementation(self, sel);
}
+ (BOOL)resolveClassMethod:(SEL)sel {
return NO;
}
+ (BOOL)resolveInstanceMethod:(SEL)sel {
return NO;
}
// Replaced by CF (throws an NSException)
+ (void)doesNotRecognizeSelector:(SEL)sel {
_objc_fatal("+[%s %s]: unrecognized selector sent to instance %p",
class_getName(self), sel_getName(sel), self);
}
// Replaced by CF (throws an NSException)
- (void)doesNotRecognizeSelector:(SEL)sel {
_objc_fatal("-[%s %s]: unrecognized selector sent to instance %p",
object_getClassName(self), sel_getName(sel), self);
}
+ (id)performSelector:(SEL)sel {
if (!sel) [self doesNotRecognizeSelector:sel];
return ((id(*)(id, SEL))objc_msgSend)((id)self, sel);
}
+ (id)performSelector:(SEL)sel withObject:(id)obj {
if (!sel) [self doesNotRecognizeSelector:sel];
return ((id(*)(id, SEL, id))objc_msgSend)((id)self, sel, obj);
}
+ (id)performSelector:(SEL)sel withObject:(id)obj1 withObject:(id)obj2 {
if (!sel) [self doesNotRecognizeSelector:sel];
return ((id(*)(id, SEL, id, id))objc_msgSend)((id)self, sel, obj1, obj2);
}
- (id)performSelector:(SEL)sel {
if (!sel) [self doesNotRecognizeSelector:sel];
return ((id(*)(id, SEL))objc_msgSend)(self, sel);
}
- (id)performSelector:(SEL)sel withObject:(id)obj {
if (!sel) [self doesNotRecognizeSelector:sel];
return ((id(*)(id, SEL, id))objc_msgSend)(self, sel, obj);
}
- (id)performSelector:(SEL)sel withObject:(id)obj1 withObject:(id)obj2 {
if (!sel) [self doesNotRecognizeSelector:sel];
return ((id(*)(id, SEL, id, id))objc_msgSend)(self, sel, obj1, obj2);
}
// Replaced by CF (returns an NSMethodSignature)
+ (NSMethodSignature *)instanceMethodSignatureForSelector:(SEL)sel {
_objc_fatal("+[NSObject instanceMethodSignatureForSelector:] "
"not available without CoreFoundation");
}
// Replaced by CF (returns an NSMethodSignature)
+ (NSMethodSignature *)methodSignatureForSelector:(SEL)sel {
_objc_fatal("+[NSObject methodSignatureForSelector:] "
"not available without CoreFoundation");
}
// Replaced by CF (returns an NSMethodSignature)
- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel {
_objc_fatal("-[NSObject methodSignatureForSelector:] "
"not available without CoreFoundation");
}
+ (void)forwardInvocation:(NSInvocation *)invocation {
[self doesNotRecognizeSelector:(invocation ? [invocation selector] : 0)];
}
- (void)forwardInvocation:(NSInvocation *)invocation {
[self doesNotRecognizeSelector:(invocation ? [invocation selector] : 0)];
}
+ (id)forwardingTargetForSelector:(SEL)sel {
return nil;
}
- (id)forwardingTargetForSelector:(SEL)sel {
return nil;
}
// Replaced by CF (returns an NSString)
+ (NSString *)description {
return nil;
}
// Replaced by CF (returns an NSString)
- (NSString *)description {
return nil;
}
+ (NSString *)debugDescription {
return [self description];
}
- (NSString *)debugDescription {
return [self description];
}
+ (id)new {
return [[self alloc] init];
}
+ (id)retain {
return (id)self;
}
// Replaced by ObjectAlloc
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wmismatched-method-attributes"
- (id)retain
__attribute__((aligned(16)))
{
if (((id)self)->isTaggedPointer()) return self;
SideTable *table = SideTable::tableForPointer(self);
if (spinlock_trylock(&table->slock)) {
table->refcnts[DISGUISE(self)] += SIDE_TABLE_RC_ONE;
spinlock_unlock(&table->slock);
return self;
}
return _objc_rootRetain_slow(self, table);
}
#pragma clang diagnostic pop
+ (BOOL)_tryRetain {
return YES;
}
// Replaced by ObjectAlloc
- (BOOL)_tryRetain {
return _objc_rootTryRetain(self);
}
+ (BOOL)_isDeallocating {
return NO;
}
- (BOOL)_isDeallocating {
return _objc_rootIsDeallocating(self);
}
+ (BOOL)allowsWeakReference {
return YES;
}
+ (BOOL)retainWeakReference {
return YES;
}
- (BOOL)allowsWeakReference {
return ! [self _isDeallocating];
}
- (BOOL)retainWeakReference {
return [self _tryRetain];
}
+ (oneway void)release {
}
// Replaced by ObjectAlloc
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wmismatched-method-attributes"
- (oneway void)release
__attribute__((aligned(16)))
{
// tagged pointer check is inside _objc_rootReleaseWasZero().
if (_objc_rootReleaseWasZero(self) == false) {
return;
}
[self dealloc];
}
#pragma clang diagnostic pop
+ (id)autorelease {
return (id)self;
}
// Replaced by ObjectAlloc
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wmismatched-method-attributes"
- (id)autorelease
__attribute__((aligned(16)))
{
// no tag check here: tagged pointers DO use fast autoreleasing
#if SUPPORT_RETURN_AUTORELEASE
assert(tls_get_direct(AUTORELEASE_POOL_RECLAIM_KEY) == nil);
if (callerAcceptsFastAutorelease(__builtin_return_address(0))) {
tls_set_direct(AUTORELEASE_POOL_RECLAIM_KEY, self);
return self;
}
#endif
return _objc_rootAutorelease2(self);
}
#pragma clang diagnostic pop
+ (NSUInteger)retainCount {
return ULONG_MAX;
}
- (NSUInteger)retainCount {
return _objc_rootRetainCount(self);
}
+ (id)alloc {
return _objc_rootAlloc(self);
}
// Replaced by ObjectAlloc
+ (id)allocWithZone:(struct _NSZone *)zone {
return _objc_rootAllocWithZone(self, (malloc_zone_t *)zone);
}
// Replaced by CF (throws an NSException)
+ (id)init {
return (id)self;
}
- (id)init {
return _objc_rootInit(self);
}
// Replaced by CF (throws an NSException)
+ (void)dealloc {
}
// Replaced by NSZombies
- (void)dealloc {
_objc_rootDealloc(self);
}
// Replaced by CF (throws an NSException)
+ (void)finalize {
}
- (void)finalize {
_objc_rootFinalize(self);
}
+ (struct _NSZone *)zone {
return (struct _NSZone *)_objc_rootZone(self);
}
- (struct _NSZone *)zone {
return (struct _NSZone *)_objc_rootZone(self);
}
+ (id)copy {
return (id)self;
}
+ (id)copyWithZone:(struct _NSZone *)zone {
return (id)self;
}
- (id)copy {
return [(id)self copyWithZone:nil];
}
+ (id)mutableCopy {
return (id)self;
}
+ (id)mutableCopyWithZone:(struct _NSZone *)zone {
return (id)self;
}
- (id)mutableCopy {
return [(id)self mutableCopyWithZone:nil];
}
@end
__attribute__((aligned(16)))
id
objc_retain(id obj)
{
if (!obj || obj->isTaggedPointer()) {
goto out_slow;
}
#if __OBJC2__
if (((Class)obj->isa)->hasCustomRR()) {
return [obj retain];
}
return bypass_msgSend_retain(obj);
#else
return [obj retain];
#endif
out_slow:
// clang really wants to reorder the "mov %rdi, %rax" early
// force better code gen with a data barrier
asm volatile("");
return obj;
}
__attribute__((aligned(16)))
void
objc_release(id obj)
{
if (!obj || obj->isTaggedPointer()) {
return;
}
#if __OBJC2__
if (((Class)obj->isa)->hasCustomRR()) {
return (void)[obj release];
}
return bypass_msgSend_release(obj);
#else
[obj release];
#endif
}
__attribute__((aligned(16)))
id
objc_autorelease(id obj)
{
if (!obj || obj->isTaggedPointer()) {
goto out_slow;
}
#if __OBJC2__
if (((Class)obj->isa)->hasCustomRR()) {
return [obj autorelease];
}
return bypass_msgSend_autorelease(obj);
#else
return [obj autorelease];
#endif
out_slow:
// clang really wants to reorder the "mov %rdi, %rax" early
// force better code gen with a data barrier
asm volatile("");
return obj;
}
id
_objc_rootRetain(id obj)
{
assert(obj);
assert(!UseGC);
if (obj->isTaggedPointer()) return obj;
return bypass_msgSend_retain(obj);
}
void
_objc_rootRelease(id obj)
{
assert(obj);
assert(!UseGC);
if (obj->isTaggedPointer()) return;
bypass_msgSend_release(obj);
}
id
_objc_rootAutorelease(id obj)
{
assert(obj); // root classes shouldn't get here, since objc_msgSend ignores nil
// assert(!UseGC);
if (UseGC) {
return obj;
}
// no tag check here: tagged pointers DO use fast autoreleasing
return bypass_msgSend_autorelease(obj);
}