Question

我不确定这是从哪里来的。我在异常集上有一个断点，但它并没有告诉我真正发生了什么：

   libobjc.A.dylib`objc_exception_throw:
0x40308b9:  pushl  %ebp
0x40308ba:  movl   %esp, %ebp
0x40308bc:  pushl  %ebx
0x40308bd:  pushl  %edi
0x40308be:  pushl  %esi
0x40308bf:  subl   $0x7ec, %esp
0x40308c5:  calll  0x40308ca                 ; objc_exception_throw + 17
0x40308ca:  popl   %ebx
0x40308cb:  movl   $0x10, (%esp)
0x40308d2:  calll  0x4043698                 ; symbol stub for: __cxa_allocate_exception
0x40308d7:  movl   %eax, %esi
0x40308d9:  movl   0x8(%ebp), %eax
0x40308dc:  movl   %eax, (%esp)
0x40308df:  calll  *0x1a478a(%ebx)
0x40308e5:  movl   %eax, %edi
0x40308e7:  movl   0x1a4622(%ebx), %eax
0x40308ed:  movl   %eax, 0x4(%esp)
0x40308f1:  movl   %edi, (%esp)
0x40308f4:  calll  0x40400a4                 ; objc_msgSend
0x40308f9:  movl   %edi, (%esi)
0x40308fb:  leal   0x1a475e(%ebx), %eax
0x4030901:  movl   %eax, 0x4(%esi)
0x4030904:  movl   %edi, (%esp)
0x4030907:  calll  0x402ee20                 ; object_getClassName
0x403090c:  movl   %eax, 0x8(%esi)
0x403090f:  xorl   %eax, %eax
0x4030911:  testl  %edi, %edi
0x4030913:  je     0x4030917                 ; objc_exception_throw + 94
0x4030915:  movl   (%edi), %eax
0x4030917:  movl   %eax, 0xc(%esi)
0x403091a:  movl   0x1a37ae(%ebx), %eax
0x4030920:  movl   %eax, -0x7e0(%ebp)
0x4030926:  cmpb   $0x0, (%eax)
0x4030929:  je     0x403094d                 ; objc_exception_throw + 148
0x403092b:  movl   %edi, (%esp)
0x403092e:  calll  0x402ee20                 ; object_getClassName
0x4030933:  movl   %eax, 0xc(%esp)
0x4030937:  movl   %edi, 0x8(%esp)
0x403093b:  movl   %esi, 0x4(%esp)
0x403093f:  leal   0x141c2(%ebx), %eax
0x4030945:  movl   %eax, (%esp)
0x4030948:  calll  0x40304ad                 ; _objc_inform
0x403094d:  movl   0x1a37aa(%ebx), %eax
0x4030953:  cmpb   $0x0, (%eax)
0x4030956:  je     0x40309cd                 ; objc_exception_throw + 276
0x4030958:  movl   -0x7e0(%ebp), %eax
0x403095e:  cmpb   $0x0, (%eax)
0x4030961:  jne    0x4030985                 ; objc_exception_throw + 204
0x4030963:  movl   %edi, (%esp)
0x4030966:  calll  0x402ee20                 ; object_getClassName
0x403096b:  movl   %eax, 0xc(%esp)
0x403096f:  movl   %edi, 0x8(%esp)
0x4030973:  movl   %esi, 0x4(%esp)
0x4030977:  leal   0x141c2(%ebx), %eax
0x403097d:  movl   %eax, (%esp)
0x4030980:  calll  0x40304ad                 ; _objc_inform
0x4030985:  leal   -0x7dc(%ebp), %eax
0x403098b:  movl   %eax, (%esp)
0x403098e:  movl   $0x1f4, 0x4(%esp)
0x4030996:  calll  0x404375e                 ; symbol stub for: backtrace
0x403099b:  movl   %eax, -0x7e0(%ebp)
0x40309a1:  movl   0x1a37b6(%ebx), %eax
0x40309a7:  movl   (%eax), %eax
0x40309a9:  movl   %eax, (%esp)
0x40309ac:  calll  0x40437a0                 ; symbol stub for: fileno
0x40309b1:  movl   %eax, 0x8(%esp)
0x40309b5:  movl   -0x7e0(%ebp), %eax
0x40309bb:  movl   %eax, 0x4(%esp)
0x40309bf:  leal   -0x7dc(%ebp), %eax
0x40309c5:  movl   %eax, (%esp)
0x40309c8:  calll  0x404376a                 ; symbol stub for: backtrace_symbols_fd
0x40309cd:  movl   %ebx, -0x7e0(%ebp)
0x40309d3:  movl   %esi, %ebx
0x40309d5:  addl   $0x4, %esi
0x40309d8:  movl   %edi, (%esp)
0x40309db:  nop    
0x40309dc:  nopl   (%eax)
0x40309e0:  movl   -0x7e0(%ebp), %eax
0x40309e6:  leal   0x132(%eax), %eax
0x40309ec:  movl   %eax, 0x8(%esp)
0x40309f0:  movl   %esi, 0x4(%esp)
0x40309f4:  movl   %ebx, (%esp)
0x40309f7:  calll  0x40436bc                 ; symbol stub for: __cxa_throw

我也尝试过：

po 0x43fe068 - which shows me <null>

和

 po [(id)(0x43fe068) class] -which shows me NSNull

这是有道理的，但并没有告诉我这是怎么发生的。

Answer 1

根据你发布的内容，很难说除了明显的事实之外究竟出了什么问题。好的起点可能是在NSNull实现长度方法上添加一个类别，并设置一个断点并查看它何时被调用（可能你需要在.pch文件中导入该类别）

[NSNull length]：无法识别的选择器发送到实例0x43fe068

1 个答案: