有人能告诉我ndk-stack的用法么

这个是他的手册：
Usage:
   ndk-stack -sym <path> [-dump <path>]      -sym  Contains full path to the root directory for symbols.
      -dump Contains full path to the file containing the crash dump.
            This is an optional parameter. If ommited, ndk-stack will
            read input data from stdin可是我这样用:
ndk-stack -sym /system/lib
还是把手册的提示显示出来了，是我的用法有问题么