太神奇了，居然可以查看可执行文件里面的符号

用nm命令，查看a.out文件内部，居然可以看到如下内容：

0000000000601058 B TIME

0000000000600e48 d _DYNAMIC

0000000000600fe8 d _GLOBAL_OFFSET_TABLE_

00000000004007a8 R _IO_stdin_used

                 w _Jv_RegisterClasses

0000000000600e28 d __CTOR_END__

0000000000600e20 d __CTOR_LIST__

0000000000600e38 D __DTOR_END__

0000000000600e30 d __DTOR_LIST__

0000000000400890 r __FRAME_END__

0000000000600e40 d __JCR_END__

0000000000600e40 d __JCR_LIST__

0000000000601040 A __bss_start

                 U __cxa_atexit@@GLIBC_2.2.5

0000000000601030 D __data_start

0000000000400760 t __do_global_ctors_aux

00000000004005e0 t __do_global_dtors_aux

0000000000601038 d __dso_handle

0000000000400580 T __gmon_start__

0000000000600e1c d __init_array_end

0000000000600e1c d __init_array_start

00000000004006a0 T __libc_csu_fini

00000000004006b0 T __libc_csu_init

                 U __libc_start_main@@GLIBC_2.2.5

                 U __monstartup@@GLIBC_2.2.5

0000000000601040 A _edata

0000000000601060 A _end

0000000000400798 T _fini

00000000004004c8 T _init

                 U _mcleanup@@GLIBC_2.2.5

0000000000400550 T _start

0000000000400740 T atexit

00000000004005c0 t call_gmon_start

0000000000601040 b called.3815

0000000000601048 b completed.7424

0000000000601030 W data_start

0000000000601050 b dtor_idx.7426

00000000004007a6 A etext

0000000000400650 t frame_dummy

0000000000400674 T main

                 U mcount@@GLIBC_2.2.5

                 U printf@@GLIBC_2.2.5

一个汇编语言的程序段

it so amazing！