99%?iOS開(kāi)發(fā)都不知道的KVO崩潰分析詳解
背景
crash 監(jiān)控發(fā)現(xiàn)有大量的新增崩潰,堆棧如下
libsystem_platform.dylib __os_unfair_lock_corruption_abort() libsystem_platform.dylib __os_unfair_lock_lock_slow() Foundation __NSSetBoolValueAndNotify()
分析堆棧
__os_unfair_lock_corruption_abort
log 翻譯:lock 已損壞
_os_unfair_lock_corruption_abort(os_ulock_value_t current) { __LIBPLATFORM_CLIENT_CRASH__(current, "os_unfair_lock is corrupt"); }
__os_unfair_lock_lock_slow
在這個(gè)方法里面 __ulock_wait 返回 EOWNERDEAD 調(diào)用 corruption abort 方法。
int ret = __ulock_wait(UL_UNFAIR_LOCK | ULF_NO_ERRNO | options, l, current, 0); if (unlikely(ret < 0)) { switch (-ret) { case EINTR: case EFAULT: continue; case EOWNERDEAD: _os_unfair_lock_corruption_abort(current); break; default: __LIBPLATFORM_INTERNAL_CRASH__(-ret, "ulock_wait failure"); } }
EOWNERDEAD 的定義
#define EOWNERDEAD 105 /* Previous owner died */
到這里猜測(cè)是 lock 的 owner 已經(jīng)野指針了,繼續(xù)向下看。
__NSSetBoolValueAndNotify
google 下這個(gè)方法是在 KVO 里面修改屬性的時(shí)候調(diào)用,偽代碼:
int __NSSetBoolValueAndNotify(int arg0, int arg1, int arg2) { r31 = r31 - 0x90; var_30 = r24; stack[-56] = r23; var_20 = r22; stack[-40] = r21; var_10 = r20; stack[-24] = r19; saved_fp = r29; stack[-8] = r30; r20 = arg2; r21 = arg1; r19 = arg0; r0 = object_getClass(arg0); r0 = object_getIndexedIvars(r0); // 理清這個(gè)崩潰的關(guān)鍵方法,這里和匯編代碼不一致,匯編代碼的入?yún)⑹?r0 + 0x20 r23 = r0; os_unfair_recursive_lock_lock_with_options(); CFDictionaryGetValue(*(r23 + 0x18), r21); r22 = _objc_msgSend$copyWithZone:(); os_unfair_recursive_lock_unlock(); if (*(int8_t *)(r23 + 0x28) != 0x0) { _objc_msgSend$willChangeValueForKey:(); (class_getMethodImplementation(*r23, r21))(r19, r21, r20); _objc_msgSend$didChangeValueForKey:(); } else { _objc_msgSend$_changeValueForKey:key:key:usingBlock:(); } var_38 = **qword_9590e8; r0 = objc_release_x22(); if (**qword_9590e8 != var_38) { r0 = __stack_chk_fail(); } return r0; }
os_unfair_recursive_lock_lock_with_options
崩潰調(diào)用棧中間還有這一層的內(nèi)聯(lián)調(diào)用 os_unfair_recursive_lock_lock_with_options。這里的 lock owner 有個(gè)比較賦值的操作,如果 oul_value 等于 OS_LOCK_NO_OWNER 則賦值 self 然后 return。崩潰時(shí)這里繼續(xù)向下執(zhí)行了,那這里的 oul_value 的取值只能是 lock->oul_value。到這里猜測(cè)崩潰的原因是 lock->oul_value 野指針了。
void os_unfair_recursive_lock_lock_with_options(os_unfair_recursive_lock_t lock, os_unfair_lock_options_t options) { os_lock_owner_t cur, self = _os_lock_owner_get_self(); _os_unfair_lock_t l = (_os_unfair_lock_t)&lock->ourl_lock; if (likely(os_atomic_cmpxchgv2o(l, oul_value, OS_LOCK_NO_OWNER, self, &cur, acquire))) { return; } if (OS_ULOCK_OWNER(cur) == self) { lock->ourl_count++; return; } return _os_unfair_lock_lock_slow(l, self, options); } OS_ALWAYS_INLINE OS_CONST static inline os_lock_owner_t _os_lock_owner_get_self(void) { os_lock_owner_t self; self = (os_lock_owner_t)_os_tsd_get_direct(__TSD_MACH_THREAD_SELF); return self; }
object_getIndexedIvars
__NSSetBoolValueAndNotify 里面的獲取 lock 的方法,這個(gè)函數(shù)非常關(guān)鍵。
/** * Returns a pointer to any extra bytes allocated with an instance given object. * * @param obj An Objective-C object. * * @return A pointer to any extra bytes allocated with \e obj. If \e obj was * not allocated with any extra bytes, then dereferencing the returned pointer is undefined. * * @note This function returns a pointer to any extra bytes allocated with the instance * (as specified by \c class_createInstance with extraBytes>0). This memory follows the * object's ordinary ivars, but may not be adjacent to the last ivar. * @note The returned pointer is guaranteed to be pointer-size aligned, even if the area following * the object's last ivar is less aligned than that. Alignment greater than pointer-size is never * guaranteed, even if the area following the object's last ivar is more aligned than that. * @note In a garbage-collected environment, the memory is scanned conservatively. /** * Returns a pointer immediately after the instance variables declared in an * object. This is a pointer to the storage specified with the extraBytes * parameter given when allocating an object. */ void *object_getIndexedIvars(id obj) { uint8_t *base = (uint8_t *)obj; if (_objc_isTaggedPointerOrNil(obj)) return nil; if (!obj->isClass()) return base + obj->ISA()->alignedInstanceSize(); Class cls = (Class)obj; if (!cls->isAnySwift()) return base + sizeof(objc_class); swift_class_t *swcls = (swift_class_t *)cls; return base - swcls->classAddressOffset + word_align(swcls->classSize); }
上層調(diào)用 __NSSetBoolValueAndNotify 里面:
r0 = object_getClass(arg0),arg0 是實(shí)例對(duì)象,r0 是類(lèi)對(duì)象,因?yàn)檫@里是個(gè) KVO 的調(diào)用,那正常情況下r0 是 NSKVONotifying_xxx。
對(duì)于 KVO 類(lèi),object_getIndexedIvars 返回的地址是 (uint8_t *)obj + sizeof(objc_class)。根據(jù)函數(shù)的注釋?zhuān)@個(gè)地址指向創(chuàng)建類(lèi)時(shí)附在類(lèi)空間后 extraBytes 大小的一塊內(nèi)存。
debug 調(diào)試
object_getIndexedIvars
__NSSetBoolValueAndNotify 下的調(diào)用
object_getIndexedIvars 入?yún)⑹?NSKVONotifying_KVObject,object_getClass 獲取的是 KVO Class。
objc_allocateClassPair
動(dòng)態(tài)創(chuàng)建 KVO 類(lèi)的方法。
thread #8, queue = 'com.apple.root.default-qos', stop reason = breakpoint 1.1 * frame #0: 0x000000018143a088 libobjc.A.dylib`objc_allocateClassPair frame #1: 0x000000018259cd94 Foundation`_NSKVONotifyingCreateInfoWithOriginalClass + 152 frame #2: 0x00000001825b8fd0 Foundation`_NSKeyValueContainerClassGetNotifyingInfo + 56 frame #3: 0x000000018254b7dc Foundation`-[NSKeyValueUnnestedProperty _isaForAutonotifying] + 44 frame #4: 0x000000018254b504 Foundation`-[NSKeyValueUnnestedProperty isaForAutonotifying] + 88 frame #5: 0x000000018254b32c Foundation`-[NSObject(NSKeyValueObserverRegistration) _addObserver:forProperty:options:context:] + 404 frame #6: 0x000000018254b054 Foundation`-[NSObject(NSKeyValueObserverRegistration) addObserver:forKeyPath:options:context:] + 136 frame #7: 0x00000001040d1860 Test`__29-[ViewController viewDidLoad]_block_invoke(.block_descriptor=0x0000000282a55170) at ViewController.m:28:13 frame #8: 0x00000001043d05a8 libdispatch.dylib`_dispatch_call_block_and_release + 32 frame #9: 0x00000001043d205c libdispatch.dylib`_dispatch_client_callout + 20 frame #10: 0x00000001043d4b94 libdispatch.dylib`_dispatch_queue_override_invoke + 1052 frame #11: 0x00000001043e6478 libdispatch.dylib`_dispatch_root_queue_drain + 408 frame #12: 0x00000001043e6e74 libdispatch.dylib`_dispatch_worker_thread2 + 196 frame #13: 0x00000001d515fdbc libsystem_pthread.dylib`_pthread_wqthread + 228
_NSKVONotifyingCreateInfoWithOriginalClass
objc_allocateClassPair 的上層調(diào)用。 allocate 之前的 context w2 是個(gè)固定值 0x30,即創(chuàng)建 KVO Class 入?yún)?extraBytes 的大小是 0x30
0x18259cd78 <+124>: mov x1, x21 0x18259cd7c <+128>: mov x2, x22 0x18259cd80 <+132>: bl 0x188097080 0x18259cd84 <+136>: mov x0, x20 0x18259cd88 <+140>: mov x1, x19 0x18259cd8c <+144>: mov w2, #0x30 0x18259cd90 <+148>: bl 0x1880961f0 // objc_allocateClassPair 0x18259cd94 <+152>: cbz x0, 0x18259ce24 ; <+296> 0x18259cd98 <+156>: mov x21, x0 0x18259cd9c <+160>: bl 0x188096410 // objc_registerClassPair 0x18259cda0 <+164>: mov x0, x19 0x18259cda4 <+168>: bl 0x182b45f44 ; symbol stub for: free 0x18259cda8 <+172>: mov x0, x21 0x18259cdac <+176>: bl 0x1880967e0 // object_getIndexedIvars 0x18259cdb0 <+180>: mov x19, x0 0x18259cdb4 <+184>: stp x20, x21, [x0]
_NSKVONotifyingCreateInfoWithOriginalClass+184 處將 x20 和 x21 寫(xiě)入 [x0],此時(shí) x0 指向的是大小為 extraBytes 的內(nèi)存,打印 x20 和 x21 的值
x20 = 0x00000001117caa10 (void *)0x00000001117caa38: KVObject(向上回溯這個(gè)值取自 _NSKVONotifyingCreateInfoWithOriginalClass 的入?yún)?x0)
x21 NSKVONotifying_KVObject
根據(jù)這里可以看出 object_getIndexedIvars 返回的地址,依次存儲(chǔ)了 KVObject(origin Class) 和 NSKVONotifying_KVObject(KVO Class)。
查看 _NSKVONotifyingCreateInfoWithOriginalClass 的偽代碼,對(duì) [x0] 有 5 次寫(xiě)入的操作,并且最終這個(gè)方法返回的是 x0 的地址。
function __NSKVONotifyingCreateInfoWithOriginalClass { r31 = r31 - 0x50; stack[32] = r22; stack[40] = r21; stack[48] = r20; stack[56] = r19; stack[64] = r29; stack[72] = r30; r20 = r0; if (*(int8_t *)0x993e78 != 0x0) { os_unfair_lock_assert_owner(0x993e7c); } r0 = class_getName(r20); r22 = strlen(r0) + 0x10; r0 = malloc(r22); r19 = r0; strlcpy(r0, "NSKVONotifying_", r22); strlcat(r19, r21, r22); r0 = objc_allocateClassPair(r20, r19, 0x30); if (r0 != 0x0) { objc_registerClassPair(r0); free(r19); r0 = object_getIndexedIvars(r21); r19 = r0; *(int128_t *)r0 = r20; // 第一次寫(xiě)入 Class *(int128_t *)(r0 + 0x8) = r21; // 第二次寫(xiě)入 Class *(r19 + 0x10) = CFSetCreateMutable(0x0, 0x0, *qword_9592d8); // 第三次寫(xiě)入 CFSet *(int128_t *)(r19 + 0x18) = CFDictionaryCreateMutable(0x0, 0x0, 0x0, *qword_959598); // 第四次寫(xiě)入 CFDictionary *(int128_t *)(r19 + 0x20) = 0x0; // 第五次寫(xiě)入空值 if (*qword_9fc560 != -0x1) { dispatch_once(0x9fc560, 0x8eaf98); } if (class_getMethodImplementation(*r19, @selector(willChangeValueForKey:)) != *qword_9fc568) { r8 = 0x1; } else { r0 = *r19; r0 = class_getMethodImplementation(r0, @selector(didChangeValueForKey:)); r8 = *qword_9fc570; if (r0 != r8) { r8 = *qword_9fc570; if (CPU_FLAGS & NE) { r8 = 0x1; } } } *(int8_t *)(r19 + 0x28) = r8; _NSKVONotifyingSetMethodImplementation(r19, @selector(_isKVOA), 0x44fab4, 0x0); _NSKVONotifyingSetMethodImplementation(r19, @selector(dealloc), 0x44fabc, 0x0); _NSKVONotifyingSetMethodImplementation(r19, @selector(class), 0x44fd2c, 0x0); } else { if (*qword_9fc558 != -0x1) { dispatch_once(0x9fc558, 0x8eaf78); } if (os_log_type_enabled(*0x9fc550, 0x10) != 0x0) { _os_log_error_impl(0x0, *0x9fc550, 0x10, "KVO failed to allocate class pair for name %s, automatic key-value observing will not work for this class", &stack[0], 0xc); } free(r19); r19 = 0x0; } if (**qword_9590e8 == **qword_9590e8) { r0 = r19; } else { r0 = __stack_chk_fail(); } return r0; }
_NSKVONotifyingCreateInfoWithOriginalClass 的上層調(diào)用,入?yún)⑹?[x19, #0x8],返回的參數(shù)寫(xiě)入 [x19, #0x28]
0x1825b8fc0 <+40>: ldr x0, [x19, #0x28] 0x1825b8fc4 <+44>: b 0x1825b8fd4 ; <+60> 0x1825b8fc8 <+48>: ldr x0, [x19, #0x8] -> 0x1825b8fcc <+52>: bl 0x18259ccfc ; _NSKVONotifyingCreateInfoWithOriginalClass 0x1825b8fd0 <+56>: str x0, [x19, #0x28] 0x1825b8fd4 <+60>: ldp x29, x30, [sp, #0x10] 0x1825b8fd8 <+64>: ldp x20, x19, [sp], #0x20
打印 x19 是一個(gè) NSKeyValueContainerClass 類(lèi)型的實(shí)例對(duì)象,這個(gè)對(duì)象類(lèi)的 ivars layout
ivars 0x99f3c0 __OBJC_$_INSTANCE_VARIABLES_NSKeyValueContainerClass entsize 32 count 5 offset 0x9e6048 _OBJC_IVAR_$_NSKeyValueContainerClass._originalClass 8 name 0x90bd27 _originalClass type 0x929ae6 # alignment 3 size 8 offset 0x9e6050 _OBJC_IVAR_$_NSKeyValueContainerClass._cachedObservationInfoImplementation 16 name 0x90bd36 _cachedObservationInfoImplementation type 0x92bb88 ^? alignment 3 size 8 offset 0x9e6058 _OBJC_IVAR_$_NSKeyValueContainerClass._cachedSetObservationInfoImplementation 24 name 0x90bd5b _cachedSetObservationInfoImplementation type 0x92bb88 ^? alignment 3 size 8 offset 0x9e6060 _OBJC_IVAR_$_NSKeyValueContainerClass._cachedSetObservationInfoTakesAnObject 32 name 0x90bd83 _cachedSetObservationInfoTakesAnObject type 0x92a01a B alignment 0 size 1 offset 0x9e6068 _OBJC_IVAR_$_NSKeyValueContainerClass._notifyingInfo 40 name 0x90bdaa _notifyingInfo type 0x92bdd7 ^{?=##^{__CFSet}^{__CFDictionary}{os_unfair_recursive_lock_s={os_unfair_lock_s=I}I}B} alignment 3 size 8
offset 0x8 name:_originalClass type:Class
offset 0x28 name:_notifyingInfo type:struct
_notifyingInfo 結(jié)構(gòu)體
{ Class, Class, __CFSet, __CFDictionary, os_unfair_recursive_lock_s }
type encoding:
developer.apple.com/library/arc…
從 context 可以看出_NSKVONotifyingCreateInfoWithOriginalClass 這個(gè)方法入?yún)⑹?OBJC_IVAR_NSKeyValueContainerClass._originalClass。
返回值 x0 是 _OBJC_IVAR__NSKeyValueContainerClass._notifyingInfo。5 次對(duì) [x0] 的寫(xiě)入是在初始化 _notifyingInfo。
崩潰時(shí)的 context:
0x1825231f0 <+56>: bl 0x1880967c0 // object_getClass 0x1825231f4 <+60>: bl 0x1880967e0 // object_getIndexedIvars 0x1825231f8 <+64>: mov x23, x0 // x0 == _notifyingInfo 0x1825231fc <+68>: add x24, x0, #0x20 // x24 == os_unfair_recursive_lock_s 0x182523200 <+72>: mov x0, x24 0x182523204 <+76>: mov w1, #0x0 0x182523208 <+80>: bl 0x188096910 // os_unfair_recursive_lock_lock_with_options crash 調(diào)用棧
調(diào)用 object_getClass 獲取 Class,調(diào)用 object_getIndexedIvars 獲取到 _notifyingInfo,_notifyingInfo + 偏移量 0x20 獲取 os_unfair_recursive_lock_s,崩潰的原因是這把鎖的 owner 損壞了,lock 也是一個(gè)結(jié)構(gòu)體,ower 也是根據(jù) offset 獲取的。
結(jié)論
從崩潰的上下文來(lái)看,最可能出問(wèn)題的是獲取 _notifyingInfo,因?yàn)橹挥?KVO Class 才能獲取到 _notifyingInfo 這個(gè)結(jié)構(gòu)體,如果在調(diào)用 __NSSetBoolValueAndNotify 的過(guò)程中,在其它線(xiàn)程監(jiān)聽(tīng)被移除,此時(shí) object_getClass 取到的不是 KVO Class 那后續(xù)再根據(jù) offset 去取 lock,這個(gè)時(shí)候就有可能發(fā)生上述崩潰。
線(xiàn)下暴力復(fù)現(xiàn)驗(yàn)證了上述猜測(cè)。
- (void)start { __block KVObject *obj = [KVObject new]; dispatch_async(dispatch_get_global_queue(0, 0x0), ^{ for (int i = 0; i < 100000; i++) { [obj addObserver:self forKeyPath:@"value" options:0x7 context:nil]; [obj removeObserver:self forKeyPath:@"value"]; } }); dispatch_async(dispatch_get_global_queue(0, 0x0), ^{ for (int i = 0; i < 100000; i++) { obj.value = YES; obj.value = NO; } }); } - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context {}
解決這個(gè)問(wèn)題的思路就是保證線(xiàn)程安全,我們?cè)诰€(xiàn)上斷點(diǎn)找到了 removeObserver 的代碼,將 removeObserver 和觸發(fā)監(jiān)聽(tīng)的代碼放在了同一個(gè)串行隊(duì)列。當(dāng)然如果 removeObserver 在 dealloc 里面,理論上也不會(huì)出現(xiàn)這類(lèi)問(wèn)題。
__NSSetxxxValueAndNotify 系列方法都有可能會(huì)觸發(fā)這個(gè)崩潰,類(lèi)似的問(wèn)題可以按照相同的思路解決。
00000000004e05cd t __NSSetBoolValueAndNotify 00000000004e0707 t __NSSetCharValueAndNotify 00000000004e097b t __NSSetDoubleValueAndNotify 00000000004e0abc t __NSSetFloatValueAndNotify 00000000004e0bfd t __NSSetIntValueAndNotify 00000000004e10e7 t __NSSetLongLongValueAndNotify 00000000004e0e6f t __NSSetLongValueAndNotify 00000000004e0491 t __NSSetObjectValueAndNotify 00000000004e15d5 t __NSSetPointValueAndNotify 00000000004e1734 t __NSSetRangeValueAndNotify 00000000004e188a t __NSSetRectValueAndNotify 00000000004e135f t __NSSetShortValueAndNotify 00000000004e19e8 t __NSSetSizeValueAndNotify 00000000004e0841 t __NSSetUnsignedCharValueAndNotify 00000000004e0d36 t __NSSetUnsignedIntValueAndNotify 00000000004e1223 t __NSSetUnsignedLongLongValueAndNotify 00000000004e0fab t __NSSetUnsignedLongValueAndNotify 00000000004e149a t __NSSetUnsignedShortValueAndNotify 00000000004de834 t __NSSetValueAndNotifyForKeyInIvar
以上就是99% iOS開(kāi)發(fā)都不知道的KVO崩潰分析詳解的詳細(xì)內(nèi)容,更多關(guān)于iOS開(kāi)發(fā)KVO崩潰的資料請(qǐng)關(guān)注腳本之家其它相關(guān)文章!
相關(guān)文章
iOS應(yīng)用腳本重簽名的實(shí)現(xiàn)方法
這篇文章主要介紹了iOS應(yīng)用腳本重簽名的實(shí)現(xiàn)方法,文中通過(guò)示例代碼介紹的非常詳細(xì),對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值,需要的朋友們下面隨著小編來(lái)一起學(xué)習(xí)學(xué)習(xí)吧2019-01-01詳解iOS開(kāi)發(fā) - 用AFNetworking實(shí)現(xiàn)https單向驗(yàn)證,雙向驗(yàn)證
這篇文章主要介紹了詳解iOS開(kāi)發(fā) - 用AFNetworking實(shí)現(xiàn)https單向驗(yàn)證,雙向驗(yàn)證,具有一定的參考價(jià)值,感興趣的小伙伴們可以參考一下。2016-12-12iOS UIBezierPath實(shí)現(xiàn)餅狀圖
這篇文章主要為大家詳細(xì)介紹了iOS UIBezierPath實(shí)現(xiàn)餅狀圖,文中示例代碼介紹的非常詳細(xì),具有一定的參考價(jià)值,感興趣的小伙伴們可以參考一下2021-03-03iOS中將個(gè)別頁(yè)面強(qiáng)制橫屏其他頁(yè)面豎屏
這篇文章主要介紹了iOS中將個(gè)別頁(yè)面強(qiáng)制橫屏其他頁(yè)面豎屏的實(shí)現(xiàn)思路,需要的朋友參考下吧2016-12-12舉例講解Objective-C中@property屬性的用法
這篇文章主要介紹了Objective-C中@property屬性的用法,包括@property的屬性關(guān)鍵字的整理,需要的朋友可以參考下2016-03-03IOS 開(kāi)發(fā)之讀取addressbook的實(shí)現(xiàn)實(shí)例
這篇文章主要介紹了IOS 開(kāi)發(fā)之讀取addressbook的實(shí)現(xiàn)實(shí)例的相關(guān)資料,希望通過(guò)本文大家能夠掌握這樣的內(nèi)容,需要的朋友可以參考下2017-09-09關(guān)于iOS屏幕旋轉(zhuǎn)的一些注意事項(xiàng)
這篇文章主要給大家介紹了關(guān)于iOS屏幕旋轉(zhuǎn)的一些注意事項(xiàng),文中通過(guò)一步步的步驟介紹的很詳細(xì),相信對(duì)大家的學(xué)習(xí)或者工作具有一定的參考借鑒價(jià)值,有需要的朋友可以參考學(xué)習(xí),下面來(lái)一起看看吧。2017-01-01iOS中多線(xiàn)程的經(jīng)典崩潰總結(jié)大全
這篇文章主要給大家介紹了關(guān)于iOS中多線(xiàn)程的一些經(jīng)典崩潰的相關(guān)資料,文中通過(guò)示例代碼介紹的非常詳細(xì),對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值,需要的朋友們下面隨著小編來(lái)一起學(xué)習(xí)學(xué)習(xí)吧。2017-12-12