Linux Kernel Module Cheat

2.6.2. Prebuilt setup getting started

Checkout to the latest tag and use the Ubuntu packaged QEMU to boot Linux:

sudo apt-get install qemu-system-x86
git clone https://github.com/cirosantilli/linux-kernel-module-cheat
cd linux-kernel-module-cheat
git checkout "$(git rev-list --tags --max-count=1)"
./release-download-latest
unzip lkmc-*.zip
./run --qemu-which host

You have to checkout to the latest tag to ensure that the scripts match the release format: https://stackoverflow.com/questions/1404796/how-to-get-the-latest-tag-name-in-current-branch-in-git

This is known not to work for aarch64 on an Ubuntu 16.04 host with QEMU 2.5.0, presumably because QEMU is too old, the terminal does not show any output. I haven’t investigated why.

Or to run a baremetal example instead:

./run \
  --arch aarch64 \
  --baremetal userland/c/hello.c \
  --qemu-which host \
;

Be saner and use our custom built QEMU instead:

./setup
./build --download-dependencies qemu
./run

To build the kernel modules as in Your first kernel module hack do:

git submodule update --depth 1 --init --recursive "$(./getvar linux_source_dir)"
./build-linux --no-modules-install -- modules_prepare
./build-modules --gcc-which host
./run

TODO: for now the only way to test those modules out without building Buildroot is with 9p, since we currently rely on Buildroot to manipulate the root filesystem.

Command explanation:

modules_prepare does the minimal build procedure required on the kernel for us to be able to compile the kernel modules, and is way faster than doing a full kernel build. A full kernel build would also work however.
--gcc-which host selects your host Ubuntu packaged GCC, since you don’t have the Buildroot toolchain
--no-modules-install is required otherwise the make modules_install target we run by default fails, since the kernel wasn’t built

To modify the Linux kernel, build and use it as usual:

git submodule update --depth 1 --init --recursive "$(./getvar linux_source_dir)"
./build-linux
./run