Can't compile ath(4) into kernel

[Mikhail T.]

 My laptop's kernel config file reads:

    device          wlan            # 802.11 support
    device          ath
    device          ath_ar5212
    device          ath_rate_onoe

Config raises no objections and the compilation succeeds, but linking
the kernel breaks:

    ...
    linking kernel.debug
    ah.o(.text+0x218): In function `ath_hal_rfprobe':
    /home/mi/src/sys/dev/ath/ath_hal/ah.c:142: undefined reference to
    `__start_set_ah_rfs'
    ah.o(.text+0x21d):/home/mi/src/sys/dev/ath/ath_hal/ah.c:142:
    undefined reference to `__stop_set_ah_rfs'
    ah.o(.text+0x236):/home/mi/src/sys/dev/ath/ath_hal/ah.c:142:
    undefined reference to `__stop_set_ah_rfs'
    *** Error code 1

What could this be? All modules (including ath_hal) build correctly...
Thank you!

    -mi