Here is some information about KDB - the in-kernel debugger for the Linux kernel.
The KDB and KGDB official wiki: https://kgdb.wiki.kernel.org/
Jason Wessel is the current KDB maintainer. Here is a presentation from him at LinuxCon 2010 (August 2010): http://kernel.org/pub/linux/kernel/people/jwessel/dbg_webinar/State_Of_kernel_debugging_LinuxCon2010.pdf
Here are some videos showing use of KDB and KGDB:
- video 1 of 6: http://www.youtube.com/watch?v=V6Qc8ppJ_jc - example of a call to panic from a test module (without a debugger)
- video 2 of 6: http://www.youtube.com/watch?v=LqAhY8K3XzI - example of catching the panic with KDB, and looking up the source line with gdb
- video 3 of 6: http://www.youtube.com/watch?v=bBEh_UduX04 - example of a bad access request, and looking up the source line with gdb
- video 4 of 6: http://www.youtube.com/watch?v=MfJU2E0aJwg - example of using a hardware breakpoint with kdb
- video 5 of 6: http://www.youtube.com/watch?v=sWiHV5mt8_k - use an address watch (hardware watchpoint) using kgdb (data access hardware breakpoint on tp_address_ref)
- video 6 of 6: http://www.youtube.com/watch?v=nnopzcwvLTs - use of kgdb over serial - Start up the agent-proxy and connect and hit a breakpoint a sys_sync
Documentation, up-to-date as of 2010, for KDB and KGDB is at: http://kernel.org/pub/linux/kernel/people/jwessel/kdb/
See http://www.ibm.com/developerworks/linux/library/l-kdbug/ for a tutorial for the 2.4.20 kernel (from June 2003)
Here's an article from 2002 on KDB vs. KGDB: http://kerneltrap.org/node/112 It has a good discussion excerpt between Andrew Morton and Keith Owens about the relative merits of KDB versus KGDB.
Here are some questions to answer:
- What kernel versions are supported?
- 2.6.35 and on
- what kernel configs are required to be set?
- how to invoke the debugger?
- sysrq trigger ('echo g >/proc/sysrq-trigger')
- how to use agent-proxy to multiplex console and kdb (or is this only for kgdb?)
In a 2.6.35 kernel, CONFIG_KGDB=y is used to configured the kgdb (target agent) for the kernel, for gdb.
Use CONFIG_KGDB_SERIAL_CONSOLE=Y to share a serial console with kgdb. Sysrq-g must be used to break in initially.
Selecting this will automatically set CONSOLE_POLL=N and MAGIC_SYSRQ=Y.
CONFIG_KGDB_KDB=Y will include the kdb frontend for kgdb (what the heck does this mean?)