Building the Ubuntu kernel: fakeroot debian/rules
=================================================

Before submitting any patch, make sure it builds inside the devel chroot (e.g. Lunar):

.. code-block:: shell

        $ schroot -c lunar-amd64
        (lunar-amd64)$ fakeroot debian/rules clean
        (lunar-amd64)$ debian/rules build
        # building takes some time, be patient
        (lunar-amd64)$ fakeroot debian/rules binary

Depending on your build box resources (cpus, memory, disk, etc) the process could
take minutes or hours, be patient.

If the build is successful, a set of .deb binary packages will be present in the parent directory: you can install these (``sudo dpkg -i linux-generic-...deb linux-modules-...deb``) to test the resulting kernel.

Cross compilation
-----------------

Cross compiling is a matter of setting the target ``dpkg-architecture`` before starting the build (e.g. to cross-compile an arm64 kernel):

.. code-block:: shell

        $ schroot -c lunar-amd64
        (lunar-amd64)$ export $(dpkg-architecture -aarm64)
        (lunar-amd64)$ fakeroot debian/rules clean
        (lunar-amd64)$ debian/rules build
        # build time...
        (lunar-amd64)$ fakeroot debian/rules binary

These are the available ``dpkg-architecture`` targets, and the corresponding
Kbuild vars:

+---------------------+----------+----------------------+-------------------+
| Target architecture | ARCH     | CROSS_COMPILE        | dpkg-architecture |
+=====================+==========+======================+===================+
| arm64               | arm64    | aarch64-linux-gnu-   | arm64             |
+---------------------+----------+----------------------+-------------------+
| armhf               | arm      | aarch64-linux-gnu-   | armhf             |
+---------------------+----------+----------------------+-------------------+
| ppc64el             | powerpc  | aarch64-linux-gnu-   | ppc64el           |
+---------------------+----------+----------------------+-------------------+
| riscv64             | riscv    | aarch64-linux-gnu-   | riscv64           |
+---------------------+----------+----------------------+-------------------+
| s390x               | s390x    | aarch64-linux-gnu-   | s390x             |
+---------------------+----------+----------------------+-------------------+