How to rebuild a single kernel module¶

If you have a patch for a specific kernel driver and want to test it quickly, you can rebuild just that module out-of-tree instead of rebuilding the entire kernel. This approach is significantly faster and is well suited for iterating on a driver fix.

Important

Modules built using this method are not intended for use in production. For managing kernel modules across kernel upgrades, consider using dkms(8) instead.

Prerequisites¶

The kernel version for which you are rebuilding the module must match the running kernel (uname -r).
The driver patch you intent to apply.

Install required packages¶

sudo apt update && sudo apt install -y linux-source build-essential

Obtain and patch the kernel source¶

Install the kernel source package and extract it to your working directory:

sudo apt install -y linux-source
tar xjf /usr/src/linux-source-$(uname -r | cut -d- -f1).tar.bz2

Note

The tarball name uses the base kernel version (e.g. linux-source-6.8.0.tar.bz2), not the full ABI version string reported by uname -r.

Apply your patch to the extracted source tree:

cd linux-source-$(uname -r | cut -d- -f1)
patch -p1 < /path/to/your.patch

Set up the out-of-tree build directory¶

Create a separate build directory and populate it with the build artefacts from the running kernel:

cd ~
mkdir build_module

cp /lib/modules/$(uname -r)/build/.config    ./build_module/
cp /lib/modules/$(uname -r)/build/Module.symvers ./build_module/
cp /lib/modules/$(uname -r)/build/Makefile   ./build_module/

Prepare the build environment¶

From inside the kernel source tree, prepare the out-of-tree build directory:

cd linux-source-$(uname -r | cut -d- -f1)

make O=../build_module outputmakefile
make O=../build_module archprepare

Note

If archprepare fails with an error, run make mrproper in the source directory, re-copy the three files from /lib/modules/$(uname -r)/build/ as shown in the previous step, then retry rerunning from make O=../build_module outputmakefile.

Complete the build preparation:

make O=../build_module prepare
make O=../build_module M=scripts

Build the module¶

Build only the driver subdirectory containing your change. Replace drivers/<path/to/driver> with the actual path relative to the kernel source root (for example, drivers/net/ethernet/intel/e1000e):

make O=../build_module M=drivers/<path/to/driver> modules

The compiled module file (<driver>.ko) will appear inside build_module/drivers/<path/to/driver>/.

Install the module¶

Copy the new .ko file over the existing one in the live module tree:

sudo cp build_module/drivers/<path/to/driver>/<driver>.ko \
    /lib/modules/$(uname -r)/kernel/drivers/<path/to/driver>/

Load and test the module¶

Unload the old module if it is currently loaded, then load the new one:

sudo modprobe -r <driver>
sudo modprobe <driver>

Confirm the module loaded successfully:

lsmod | grep <driver>
dmesg | tail -20

Test and verify that your patch is working as intended.