strange build failure when kconfig symbol is bool but not when tristate

[Randy Dunlap <rdunlap@xenotime.net>]

(my turn)

I have seen this randconfig build error 2-3 times in the past 3 months:
(this one is from linux-next of 20111014.)

net/built-in.o: In function `unregister_8022_client':
(.text+0x26157): undefined reference to `llc_sap_close'
net/built-in.o: In function `register_8022_client':
(.text+0x261b6): undefined reference to `llc_sap_open'
net/built-in.o: In function `p8022_request':
p8022.c:(.text+0x261e5): undefined reference to `llc_build_and_send_ui_pkt'
net/built-in.o: In function `snap_request':
psnap.c:(.text+0x26487): undefined reference to `llc_build_and_send_ui_pkt'
net/built-in.o: In function `snap_init':
psnap.c:(.init.text+0xb22): undefined reference to `llc_sap_open'
net/built-in.o: In function `snap_exit':
psnap.c:(.exit.text+0x16): undefined reference to `llc_sap_close'

I finally found that if I change drivers/net/tokenring/Kconfig
symbol TR from bool to tristate, the build completes successfully,
but I don't understand why this is happening.


---
 drivers/net/tokenring/Kconfig |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- next-2011-1014.orig/drivers/net/tokenring/Kconfig
+++ next-2011-1014/drivers/net/tokenring/Kconfig
@@ -4,7 +4,7 @@
 
 # So far, we only have PCI, ISA, and MCA token ring devices
 menuconfig TR
-	bool "Token Ring driver support"
+	tristate "Token Ring driver support"
 	depends on NETDEVICES && !UML
 	depends on (PCI || ISA || MCA || CCW || PCMCIA)
 	select LLC

> make oldconfig

> diff -u .config.old .config
--- .config.old	2011-10-14 15:17:45.000000000 -0700
+++ .config	2011-10-14 15:24:45.000000000 -0700
@@ -876,7 +876,7 @@
 # CONFIG_MDIO_BITBANG is not set
 # CONFIG_PPP is not set
 # CONFIG_SLIP is not set
-CONFIG_TR=y
+CONFIG_TR=m
 CONFIG_PCMCIA_IBMTR=m


voila.  build works cleanly.

ideas?

thanks,
-- 
~Randy
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