A Linux Kernel Module is loadable at runtime. This keeps the kernel itself smaller and removes the need to recompile the whole kernel when functionality is added.

A notable use of Kernel Modules are Device Drivers.

Main Tools and Commands

Install necessary tools:

sudo apt-get install build-essential kmod

To list modules that are currently loaded in th kernel use lsmod or cat /proc/modules.

Building Kernel Modules

The kernel build system kbuild is used to build kernel modules. It supports also out-of-tree build of modules.

See documentation.

Useful Kernel Config Settings

CONFIG_DEBUG_INFO: Add debug symbols (for gdb, addr2line, and objdump). CONFIG_KASAN: Enable Kernel Address Sanitizer (detect out-of-bounds, use-after-free, and other memory errors). CONFIG_LOCKDEP: Enable lock dependency checker (detect potential deadlocks). CONFIG_DEBUG_ATOMIC_SLEEP: Flags attempts to sleep in atomic context (catches the most common spinlock misuse). CONFIG_MODULE_FORCE_UNLOAD: Allows rmmod -f as a last resort during development.

Dynamic Debug Logs

• Compile kernel with CONFIG_DYNAMIC_DEBUG: pr_debug() calls are compiled but disabled.
• Enable logs: echo "module <my-module> +p" > /sys/kernel/debug/dynamic_debug/control.

See documentation.

Resources

The Linux Kernel Module Programming Guide