Here is gdb up 12. It looks like the script variable is ":" which seem odd.
(gdb) up 12
#12 NsTclConnChanProc (UNUSED_sock=24, arg=0x7f11b03c01d0, why=1) at connchan.c:551
551 servPtr = cbPtr->connChanPtr->sockPtr->servPtr;
(gdb) print *cbPtr
$1 = {connChanPtr = 0x7f11b035f410, threadName = 0x7f11b0000080 "\340V\003(\020\177", when = 13, scriptLength = 98, scriptCmdNameLength = 17, script = ":"}