First of all, ensure you've built the custom 5.4 kernel and that all the required kernel debug config options enabled (again, look back to Chapter 5, Writing Your First Kernel Module – LKMs Part 2, the Configuring a debug kernel section if you need to). Then, boot off your debug kernel (here, it's named 5.4.0-llkd-dbg). Now, build the driver (in ch12/2_miscdrv_rdwr_spinlock/) against this debug kernel (the usual make within the driver's directory should do this; you might find that, on the debug kernel, the build is noticeably slower!):
$ lsb_release -a 2>/dev/null | grep "^Description" ; uname -r
Description: Ubuntu 20.04.1 LTS
5.4.0-llkd-dbg
$ make
[ ... ]
$ modinfo ./miscdrv_rdwr_spinlock.ko
filename: /home/llkd/llkd_src/ch12/2_miscdrv_rdwr_spinlock/./miscdrv_rdwr_spinlock.ko
[ ... ]
description: LLKD book:ch12/2_miscdrv_rdwr_spinlock: simple misc char driver rewritten with spinlocks
[...
