slackware11 下gdb 不认得coredump 文件 ？？

#gdb ./test2 core.test2
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This GDB was configured as "i686-pc-linux-gnu"...Using host libthread_db library "/lib/tls/libthread_db.so.1".

"/root/core.test2" is not a core dump: 不可识别的文件格式
(gdb)
:ask :ask :ask :ask :ask :ask

无论是构造浮点错误还是地址越界的程序，gdb都无法读coredump文件