在XCode中调试:异常断点

Question

我正在调试一个随机的SIGTRAP崩溃,这​​只是在后台发生.这可能与某个NSManagedObjectContext地方有关.

除此之外,我正在尝试使用异常断点对其进行调试,以至少找出它的起源.唯一的问题是崩溃/断点发生在0 objc_exception_throw中,这对我没有帮助.

我得到的数据如下所示:

libobjc.A.dylib`objc_exception_throw:
0x32a3a960:  push   {r4, r5, r6, r7, lr} // breakpoint stops here
0x32a3a962:  add    r7, sp, #12
0x32a3a964:  mov    r4, r0
0x32a3a966:  movs   r0, #16
0x32a3a968:  blx    0x32a46854                ; symbol stub for: -[NSObject isEqual:]

所以我的问题是,如何创建一个异常断点来提前启动？我试图让断点发生在崩溃前的实际Objective-C代码的最后一点.

我已经尝试编辑要共享的断点,中断抛出,然后中断catch,并且在没有运气的情况下更改了Objective-C,C++和"all"之间的异常类型.

我怎样才能使异常断点更早出现？

除非有办法破译我发布的代码.如果可能的话,请给我一个简短的解释,说明它意味着什么,以及你如何破译它以便我也可以学习这样做:)

感谢大家!

如果我让程序运行...

它继续崩溃,看起来像这样:

libsystem_kernel.dylib`mach_msg_trap:
0x30830ea0:  mov    r12, sp
0x30830ea4:  push   {r4, r5, r6, r8}
0x30830ea8:  ldm    r12, {r4, r5, r6}
0x30830eac:  mvn    r12, #30
0x30830eb0:  svc    #128
0x30830eb4:  pop    {r4, r5, r6, r8} // SIGTRAP throws here
0x30830eb8:  bx     lr

运行命令"bt"作为调试器命令时的堆栈跟踪

* thread #13: tid = 0x2337, 0x32a3a960 libobjc.A.dylib`objc_exception_throw, stop reason = breakpoint 1.1
    frame #0: 0x32a3a960 libobjc.A.dylib`objc_exception_throw
    frame #1: 0x340f9fee CoreData`-[NSPersistentStoreCoordinator executeRequest:withContext:error:] + 298
    frame #2: 0x341522d2 CoreData`-[NSManagedObjectContext save:] + 730
    frame #3: 0x32054b02 UIKit`__84-[UIManagedDocument writeContents:toURL:forSaveOperation:originalContentsURL:error:]_block_invoke_0 + 30
    frame #4: 0x34155bc0 CoreData`developerSubmittedBlockToNSManagedObjectContextPerform + 88
    frame #5: 0x36e3d4b6 libdispatch.dylib`_dispatch_client_callout + 22
    frame #6: 0x36e419f6 libdispatch.dylib`_dispatch_barrier_sync_f_invoke + 30
    frame #7: 0x34155d42 CoreData`-[NSManagedObjectContext performBlockAndWait:] + 174
    frame #8: 0x32054862 UIKit`-[UIManagedDocument writeContents:toURL:forSaveOperation:originalContentsURL:error:] + 986
    frame #9: 0x3205418a UIKit`-[UIManagedDocument writeContents:andAttributes:safelyToURL:forSaveOperation:error:] + 698
    frame #10: 0x32017ce4 UIKit`__block_global_4 + 68
    frame #11: 0x32017c80 UIKit`__block_global_3 + 156
    frame #12: 0x339c767c Foundation`-[NSFileCoordinator _invokeAccessor:thenCompletionHandler:] + 144
    frame #13: 0x339c791e Foundation`__73-[NSFileCoordinator coordinateWritingItemAtURL:options:error:byAccessor:]_block_invoke_0 + 90
    frame #14: 0x339c894e Foundation`-[NSFileCoordinator(NSPrivate) _invokeAccessor:orDont:thenRelinquishAccessClaimForID:] + 202
    frame #15: 0x339c926c Foundation`-[NSFileCoordinator(NSPrivate) _coordinateWritingItemAtURL:options:error:byAccessor:] + 548
    frame #16: 0x339c78be Foundation`-[NSFileCoordinator coordinateWritingItemAtURL:options:error:byAccessor:] + 90
    frame #17: 0x32017254 UIKit`-[UIDocument _coordinateWritingItemAtURL:error:byAccessor:] + 720
    frame #18: 0x320179a0 UIKit`__59-[UIDocument saveToURL:forSaveOperation:completionHandler:]_block_invoke_0 + 284
    frame #19: 0x36e3e11e libdispatch.dylib`_dispatch_call_block_and_release + 10
    frame #20: 0x36e41ece libdispatch.dylib`_dispatch_queue_drain$VARIANT$mp + 142
    frame #21: 0x36e41dc0 libdispatch.dylib`_dispatch_queue_invoke$VARIANT$mp + 40
    frame #22: 0x36e4291c libdispatch.dylib`_dispatch_root_queue_drain + 184
    frame #23: 0x36e42ac0 libdispatch.dylib`_dispatch_worker_thread2 + 84
    frame #24: 0x33ba7a10 libsystem_c.dylib`_pthread_wqthread + 360
    frame #25: 0x33ba78a4 libsystem_c.dylib`start_wqthread + 8

查看Matt Wilding在他的回答评论中发布的链接!

Answer 1

您无法控制断点的触发位置。一旦到达断点，您就可以使用该bt命令打印当前的堆栈跟踪。

编辑：随着回溯......

看来 UIDocument 的-saveToURL:forSaveOperation:completionHandler:方法是罪魁祸首。我以前从未使用过该类，所以我无法提供太多帮助。如果您在代码中的任何位置调用该方法（例如从块中调用该方法？），您也可以在那里放置一个断点，以预防失败。