Building with the attached random configuration file,

drivers/built-in.o: In function `smssdio_remove':
smssdio.c:(.text+0x14751c): undefined reference to `smscore_putbuffer'
smssdio.c:(.text+0x147526): undefined reference to `smscore_unregister_device'
drivers/built-in.o: In function `smssdio_interrupt':
smssdio.c:(.text+0x1475aa): undefined reference to `smscore_getbuffer'
smssdio.c:(.text+0x147695): undefined reference to `smscore_putbuffer'
smssdio.c:(.text+0x1476f3): undefined reference to `smscore_putbuffer'
smssdio.c:(.text+0x14772a): undefined reference to `smsendian_handle_rx_message'
smssdio.c:(.text+0x147737): undefined reference to `smscore_onresponse'
drivers/built-in.o: In function `smssdio_sendrequest':
smssdio.c:(.text+0x14776c): undefined reference to `smsendian_handle_tx_message'
drivers/built-in.o: In function `smssdio_probe':
smssdio.c:(.text+0x14786c): undefined reference to `sms_get_board'
smssdio.c:(.text+0x14788a): undefined reference to `smscore_register_device'
smssdio.c:(.text+0x1478a1): undefined reference to `smscore_set_board_id'
smssdio.c:(.text+0x1478fa): undefined reference to `smscore_start_device'
smssdio.c:(.text+0x14792d): undefined reference to `smscore_unregister_device'
make: *** [vmlinux] Error 1