2、输入"gdb hello"；
屏幕上应该会出现类似：最后出现done字样，表示可以使用gdb调试；
gdb hello
GNU gdb (GDB) 7.7.1
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Reading symbols from hello...Reading symbols from /Users/chenchen/Desktop/Retail/sus/gcc/hello.dSYM/Contents/Resources/DWARF/hello...done.
done.
(gdb)
