FreeBSD, enabling kernel debugging.

07 Apr 2017

Create a new configuration file for kernel and add KDB and DDB options to it.

bash
cd /usr/src/sys/amd64/conf
cp GENERIC DBG
cat <<EOS >> DBG
options KDB
options DDB
EOS

Compile and install kernel. After that reboot.

cd ../../../
make buildkernel KERNCONF=DBG
make installkernel KERNCONF=DBG
reboot

If your /usr/src is newer than ports tree you may need to update ports. For This please follow the handbook guide.

You may need to enable debugger by issuing the command sysctl debug.debugger_on_panic=1.

At kernel panic the ddb prompt will arise. You can use bt command for getting a stack backtrace. You may need to enable debugger by issuing the command sysctl debug.debugger_on_panic=1.

Tested on: FreeBSD 10.3-STABLE #0 r316608.

References: http://www.freebsd.org/doc/en/books/developers-handbook/kerneldebug-online-ddb.html https://www.freebsd.org/cgi/man.cgi?ddb(4)