Kernel debug notes

control printk with /proc/sys/kernel/printk

/proc/sys/kernel/printk
The four values in this file are
console_loglevel,
default_message_loglevel,
minimum_console_level and
default_console_loglevel.

These values influence printk() behavior when
printing or logging error messages. See syslog(2) for more info
on the different loglevels. Messages with a higher priority
than console_loglevel will be printed to the console. Messages
without an explicit priority will be printed with priority
default_message_level.

minimum_console_loglevel is the minimum
(highest) value to which console_loglevel can be set.
default_console_loglevel is the default value for con-
sole_loglevel.

example:
echo "4 4 1 4" > /proc/sys/kernel/printk"

gdb mini howto
http://linux.bytesex.org/gdb.html