需求: 加断点这块，按照书上操作的，提示如下错误：
使用的是XCode9.3的LLDB
步骤：加完断点，之后使用br com add 1预设了命令，然后执行c，操作notes.app，就出现下面的错误
代码：
(lldb) c
Process 2854 resuming
(lldb) po $r2
error: Aborting reading of commands after command #0: ‘po $r2’ failed with error: use of undeclared identifier ‘$r2’
Process 2854 stopped
- thread #1, queue = ‘com.apple.main-thread’, stop reason = breakpoint 1.1
frame #0: 0x00000001000e34ec MobileNotes_mh_execute_header + 95468 MobileNotes_mh_execute_header:
→ 0x1000e34ec <+95468>: nop
0x1000e34f0 <+95472>: nop
0x1000e34f4 <+95476>: ldr x1, #0x4cbd4 ; “reloadSearchedTermHighlight”
0x1000e34f8 <+95480>: b 0x100107bf4 ; symbol stub for: objc_msgSend
Target 0: (MobileNotes) stopped.