How to understand crash log on XCode 4

Question

I am trying to debug the cause of my app to crash. From my trial I realized that somewhere, there were leaks and I am in the middle of figuring out. I knew it because when I tried debugging using this method here, it will crash eventually as it seems the memory leaks bulking up after some time.

To find out the caused, I have now open the NSZombieEnabled to YES on XCode 4. But I didn't see anything. So now I turn to crash log. And here it is :

Thread 7 Crashed:
0   libsystem_kernel.dylib          0x31b71a1c __pthread_kill + 8
1   libsystem_c.dylib               0x35ceb3b4 pthread_kill + 52
2   libsystem_c.dylib               0x35ce3bf8 abort + 72
3   libsystem_c.dylib               0x35d1f024 free + 104
4   ImageIO                         0x32ca35f0 ImageProviderReleaseInfoCallback + 56
5   CoreGraphics                    0x31a05284 image_provider_finalize + 8
6   CoreFoundation                  0x35aad288 _CFRelease + 160
7   CoreFoundation                  0x35aad1ae CFRelease + 82
8   CoreGraphics                    0x319fe150 CGImageProviderRelease + 4
9   CoreGraphics                    0x31a00bac CGImageBlockSetRelease + 44
10  CoreGraphics                    0x31a00b70 img_blocks_destroy + 8
11  CoreGraphics                    0x319fdaae CGSImageDataUnlock + 26
12  libRIP.A.dylib                  0x309eebae ripc_ReleaseImage + 374
13  libRIP.A.dylib                  0x309ecc9c ripc_DrawImage + 536
14  CoreGraphics                    0x319f9284 CGContextDelegateDrawImage + 44
15  CoreGraphics                    0x319f9142 CGContextDrawImage + 250
16  myapp                           0x000c6a28 0x45000 + 530984
17  myapp                           0x000c6d6a 0x45000 + 531818
18  myapp                           0x000c681c 0x45000 + 530460
19  myapp                           0x000c3526 0x45000 + 517414
20  myapp                           0x000c3796 0x45000 + 518038
21  Foundation                      0x33486382 -[NSThread main] + 38
22  Foundation                      0x334f85c6 __NSThread__main__ + 966
23  libsystem_c.dylib               0x35ceb30a _pthread_start + 242
24  libsystem_c.dylib               0x35cecbb4 thread_start + 0

My question : is there any tips on how to read and understand this debug log? Maybe a link or book that cover how to debug all together. Thanks.

Answer 1

In this case,

2   libsystem_c.dylib               0x35ce3bf8 abort + 72
3   libsystem_c.dylib               0x35d1f024 free + 104

free function detected the freeing address is not in the range of heap or invalid, and then called abort function.

"Technical Note TN2239 - iOS Debugging Magic" is quite helpful document. Please take a look at "Memory Allocator" and use Malloc* environments like NSZombieEnabled. Setting breakpoint to abort function is also useful for getting the parameter for free and tracking stack.

Answer 2

That crash log is not symbolised, hence it not giving you line numbers and object names in your app. There is a process for adding this information to the crash log to give you a lot more information to help debug the crash.

See http://developer.apple.com/tools/xcode/symbolizingcrashdumps.html In particular the section on symbolising crash dumps.