iosexc-bad-accessnszombie
EXC_BAD_ACCESS, Using NSZombies to track down
I have got a EXC_BAD_ACCESS error while dismissing a view controller on device. But strangely this does not happen in simulator.
The Question: I am using the Instruments and NSZombies enabled and here is the report at the error. I am not getting heads and tails out of it. I understand that this shows the ref Count +es and -es. But where is my code that generated this error? All I see is that the responsible caller are UIVIews, CATransactions, where is my code? 
THE CRASH LOG
Thread 0:
0 libsystem_kernel.dylib 0x00000001923d5cc0 mach_msg_trap + 8
1 CoreFoundation 0x0000000185992ca8 __CFRunLoopServiceMachPort + 180
2 CoreFoundation 0x0000000185990e9c __CFRunLoopRun + 932
3 CoreFoundation 0x00000001858d1b34 CFRunLoopRunSpecific + 448
4 itunesstored 0x00000001000bfe14 0x1000b0000 + 65044
5 libdyld.dylib 0x00000001922f3a9c start + 0
Thread 1:
0 libsystem_kernel.dylib 0x00000001923d5ac8 kevent64 + 8
1 libdispatch.dylib 0x00000001922d9d74 _dispatch_mgr_thread + 48
Thread 2 name: com.apple.NSURLConnectionLoader
Thread 2:
0 libsystem_kernel.dylib 0x00000001923d5cc0 mach_msg_trap + 8
1 CoreFoundation 0x0000000185992ca8 __CFRunLoopServiceMachPort + 180
2 CoreFoundation 0x0000000185990e38 __CFRunLoopRun + 832
3 CoreFoundation 0x00000001858d1b34 CFRunLoopRunSpecific + 448
4 Foundation 0x00000001864be7f8 +[NSURLConnection(Loader) _resourceLoadLoop:] + 344
5 Foundation 0x000000018654c76c __NSThread__main__ + 996
6 libsystem_pthread.dylib 0x00000001924701ac _pthread_body + 164
7 libsystem_pthread.dylib 0x0000000192470104 _pthread_start + 136
8 libsystem_pthread.dylib 0x000000019246d7ac thread_start + 0
Thread 3 name: com.apple.CFSocket.private
Thread 3:
0 libsystem_kernel.dylib 0x00000001923ee76c select$DARWIN_EXTSN + 8
1 libsystem_pthread.dylib 0x00000001924701ac _pthread_body + 164
2 libsystem_pthread.dylib 0x0000000192470104 _pthread_start + 136
3 libsystem_pthread.dylib 0x000000019246d7ac thread_start + 0
Thread 4:
0 libsystem_kernel.dylib 0x00000001923ee394 __psynch_cvwait + 8
1 MobileSystemServices 0x000000018bc8d53c MOXPCTransportReceiveMessage + 268 2 MobileInstallation 0x000000018bc48900 perform_command + 280
3 MobileInstallation 0x000000018bc491e8 MobileInstallationLookup + 388
4 itunesstored 0x00000001000e985c 0x1000b0000 + 235612
5 libdispatch.dylib 0x00000001922d841c _dispatch_call_block_and_release + 20
6 libdispatch.dylib 0x00000001922d83dc _dispatch_client_callout + 12
7 libdispatch.dylib 0x00000001922df3f8 _dispatch_root_queue_drain + 396
8 libdispatch.dylib 0x00000001922df634 _dispatch_worker_thread2 + 72
9 libsystem_pthread.dylib 0x000000019246d914 _pthread_wqthread + 352
10 libsystem_pthread.dylib 0x000000019246d7a4 start_wqthread + 0
Thread 5:
0 libsystem_kernel.dylib 0x00000001923eee74 __workq_kernreturn + 8
1 libsystem_pthread.dylib 0x000000019246d7a4 start_wqthread + 0
Thread 6:
0 libsystem_kernel.dylib 0x00000001923d5cc0 mach_msg_trap + 8
1 CoreFoundation 0x0000000185992ca8 __CFRunLoopServiceMachPort + 180
2 CoreFoundation 0x0000000185990e38 __CFRunLoopRun + 832
3 CoreFoundation 0x00000001858d1b34 CFRunLoopRunSpecific + 448
4 iTunesStore 0x00000001903c2a58 -[ISOperation runRunLoopUntilStopped] + 200
5 iTunesStore 0x00000001903c9f84 -[ISURLOperation _runRequestWithURL:] + 1256
6 iTunesStore 0x00000001903c9a30 -[ISURLOperation _run] + 428
7 iTunesStore 0x00000001903c5588 -[ISURLOperation run] + 328
8 iTunesStore 0x00000001903d2324 -[ISStoreURLOperation _runURLOperation] + 696
9 iTunesStore 0x00000001903d0b68 -[ISStoreURLOperation run] + 568
10 iTunesStore 0x00000001903c4214 -[ISOperation _main:] + 304
11 iTunesStore 0x00000001903c35cc -[ISOperation main] + 548
12 iTunesStore 0x00000001903c2b94 -[ISOperation runSubOperation:returningError:] + 220
13 iTunesStore 0x00000001903ce928 -[ISLoadURLBagOperation run] + 884
14 iTunesStore 0x00000001903c4214 -[ISOperation _main:] + 304
15 iTunesStore 0x00000001903c35cc -[ISOperation main] + 548
16 iTunesStore 0x00000001903c2b94 -[ISOperation runSubOperation:returningError:] + 220
17 iTunesStore 0x00000001903d1f74 -[ISStoreURLOperation _resolvedURLInBagContext:URLBag:] + 104
18 iTunesStore 0x00000001903d20e4 -[ISStoreURLOperation _runURLOperation] + 120
19 iTunesStore 0x00000001903d0b68 -[ISStoreURLOperation run] + 568
20 iTunesStore 0x00000001903c4214 -[ISOperation _main:] + 304
21 iTunesStore 0x00000001903c35cc -[ISOperation main] + 548
22 Foundation 0x0000000186474d34 -[__NSOperationInternal _start:] + 640
23 Foundation 0x0000000186536d78 __NSOQSchedule_f + 72
24 libdispatch.dylib 0x00000001922d83dc _dispatch_client_callout + 12
25 libdispatch.dylib 0x00000001922dd92c _dispatch_async_redirect_invoke + 148
26 libdispatch.dylib 0x00000001922d83dc _dispatch_client_callout + 12
27 libdispatch.dylib 0x00000001922df3f8 _dispatch_root_queue_drain + 396
28 libdispatch.dylib 0x00000001922df634 _dispatch_worker_thread2 + 72
29 libsystem_pthread.dylib 0x000000019246d914 _pthread_wqthread + 352
30 libsystem_pthread.dylib 0x000000019246d7a4 start_wqthread + 0
Thread 7 name: Data corruption: Malformed Mach message or kernel bug.
Thread 7 Crashed:
0 libxpc.dylib 0x0000000192488f9c _xpc_connection_mach_event + 1992
1 libdispatch.dylib 0x00000001922d84b0 _dispatch_client_callout4 + 12
2 libdispatch.dylib 0x00000001922dabdc _dispatch_mach_msg_invoke + 148
3 libdispatch.dylib 0x00000001922de698 _dispatch_queue_drain + 456
4 libdispatch.dylib 0x00000001922da620 _dispatch_mach_invoke + 104
5 libdispatch.dylib 0x00000001922dd8d0 _dispatch_async_redirect_invoke + 56
6 libdispatch.dylib 0x00000001922d83dc _dispatch_client_callout + 12
7 libdispatch.dylib 0x00000001922df3f8 _dispatch_root_queue_drain + 396
8 libdispatch.dylib 0x00000001922df634 _dispatch_worker_thread2 + 72
9 libsystem_pthread.dylib 0x000000019246d914 _pthread_wqthread + 352
10 libsystem_pthread.dylib 0x000000019246d7a4 start_wqthread + 0
Thread 8:
0 libsystem_kernel.dylib 0x00000001923ee3dc __psynch_mutexwait + 8
1 Foundation 0x000000018645b958 -[NSLock lock] + 152
2 iTunesStore 0x00000001903e7760 ISUniqueOperationLock + 228
3 iTunesStore 0x00000001903c3408 -[ISOperation main] + 96
4 iTunesStore 0x00000001903c2b94 -[ISOperation runSubOperation:returningError:] + 220
5 iTunesStore 0x00000001903cf438 -[ISOperation(ISLoadURLBagAdditions) loadURLBagWithContext:returningError:] + 112
6 itunesstored 0x00000001001046e0 0x1000b0000 + 345824
7 iTunesStore 0x00000001903c4214 -[ISOperation _main:] + 304
8 iTunesStore 0x00000001903c35cc -[ISOperation main] + 548
9 Foundation 0x0000000186474d34 -[__NSOperationInternal _start:] + 640
10 Foundation 0x0000000186536d78 __NSOQSchedule_f + 72
11 libdispatch.dylib 0x00000001922d83dc _dispatch_client_callout + 12
12 libdispatch.dylib 0x00000001922dd92c _dispatch_async_redirect_invoke + 148
13 libdispatch.dylib 0x00000001922d83dc _dispatch_client_callout + 12
14 libdispatch.dylib 0x00000001922df3f8 _dispatch_root_queue_drain + 396
15 libdispatch.dylib 0x00000001922df634 _dispatch_worker_thread2 + 72
16 libsystem_pthread.dylib 0x000000019246d914 _pthread_wqthread + 352
17 libsystem_pthread.dylib 0x000000019246d7a4 start_wqthread + 0
Thread 9:
0 libsystem_kernel.dylib 0x00000001923eee74 __workq_kernreturn + 8
1 libsystem_pthread.dylib 0x000000019246d7a4 start_wqthread + 0
Thread 10:
0 libsystem_kernel.dylib 0x00000001923eee74 __workq_kernreturn + 8
1 libsystem_pthread.dylib 0x000000019246d7a4 start_wqthread + 0
Thread 7 crashed with ARM Thread State (64-bit):
x0: 0x0000000000000036 x1: 0x0000000000000037 x2: 0x00000001924a516e x3: 0x0000000000000037
x4: 0x0000000102263bc8 x5: 0x0000000000000036 x6: 0x0000000000000000 x7: 0x0000000000000110
x8: 0x7300ae44061c0155 x9: 0x7300ae44061c0155 x10: 0x0000000102263bc8 x11: 0x0000000000000000
x12: 0x000000000000006f x13: 0x000000019239e3d1 x14: 0x000000000000005f x15: 0x000000019239be4b
x16: 0x0000000192468e90 x17: 0x0021c35bf1cc0111 x18: 0x0000000000000000 x19: 0x0000000147db6140
x20: 0x0000000147e999f0 x21: 0x0000000147e34d80 x22: 0x000000001000000c x23: 0x0000000147d8aa00
x24: 0x00000001022640e0 x25: 0x0000000147d436d0 x26: 0x0000000000020001 x27: 0x000000000000000a
x28: 0x00000001022640e0 fp: 0x0000000102263d50 lr: 0x0000000192488f9c sp: 0x0000000102263c80
pc: 0x0000000192488f9c cpsr: 0x60000000
Solution
Your application is crashing with the message “Data corruption: Malformed Mach message or kernel bug”. Either that means what it says (in which case the bug is most likely not yours), or (more likely IMO) you’re tramping on memory you don’t own. Finding memory overwrites is hard, but Apple provides tools to help you — see TN2124.
I’d try enabling MallocGuardEdges et al in the simulator and see if you crash (you can do this from Xcode in the Scheme configuration.) Alternatively, you could try enabling Guard Malloc and that might also help.
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