Compiling kernels with

From postmarketOS

This page details how to compile a kernel manually using the helper script as well as how to package and install a locally compiled kernel. This workflow can be used to quickly iterate and test during kernel development by using the existing kernel packaging and upgrade process to install a development kernel.

Usually when compiling a kernel, you would install all dependencies and a cross compiler in your host system. To make it easier, we have the script (for fish shell: It sets up an Alpine Linux chroot with all the dependencies by using pmbootstrap internally, exports the environment variables to use the right cross compiler and creates an alias to make. This means, whenever you type make after sourcing that script, it will actually run make in the chroot.

Selecting a kernel

This section details how to fetch the kernel source of an existing postmarketOS device. Existing kernel aports can be found in the aports/device directory.

In the following example we will use the oneplus-bacon device. The kernel aport is in the aports/device/linux-oneplus-bacon directory. Within the APKBUILD is the source variable which lists the kernel source repository.

After determining the kernel you want to work with, download the source code.

$ git clone
$ cd android_kernel_oneplus_msm8974

Preparing the source directory

To compile the current version of the kernel, check out the git revision found in the APKBUILD.

$ git checkout dd65620ba04a8c6ba0e30553c9c95388daefae02 # example

Applying patches

Some kernel aports have patches applied on top of the remote source. You may want to apply these patches if they aren't in the source tree you have checked out.

For example oneplus-bacon has a patch which isn't in the git revision in the prior example.

$ git apply /code/pmboostrap/aports/device/linux-oneplus-bacon/02_gpu-msm-fix-gcc5-compile.patch

Kernels which can only be compiled with older GCC versions may need the compiler-gcc6.h. If this header exists in the kernel aport then copy it to the kernel source directory.

$ cp /code/pmboostrap/aports/device/linux-oneplus-bacon/compiler-gcc6.h include/linux/

Compile the kernel

Note The script is not provided when you installed pmbootstrap from pip. You have to install pmbootstrap from git to have it.

The script will set up a build environment based on the target device configured for pmbootstrap.

In this example we are using the oneplus-bacon device. So we should be sure to have run pmbootstrap init and select oneplus-bacon as the target device. Most devices should include a link to their kernel package at the bottom of their wiki page.

$ pmbootstrap init

Run the script once in the kernel source directory to initialize the build environment. If the kernel can only be compiled with GCC6 then pass the --gcc6 flag.

$ source /code/pmbootstrap/helpers/ --gcc6

Copy the defconfig from the kernel aport to the kernel source directory.

$ cp /code/pmboostrap/aports/device/testing/linux-oneplus-bacon/config-oneplus-bacon.armv7 arch/arm/configs/oneplus_bacon_defconfig

Build the defconfig and kernel with the following commands.

$ make oneplus_bacon_defconfig
$ make

Run the kernel

Post make scripts

Some kernels require extra packaging steps such as dtbtool. The build environment works within the pmbootstrap chroots. The run-script alias can be used to execute scripts within the source or build directory in the chroot.

In this example we are using the oneplus-bacon which requires dtbtool. Create a script with the dtbtool command named in the kernel source directory.

dtbTool -s 2048 -p "${srcdir}/scripts/dtc/" -o \
	"${builddir}/arch/arm/boot/dt.img" \

Run the script.

$ run-script

Packaging and flashing the kernel

A kernel compiled under can be packaged by pmbootstrap by using the --envkernel build option.

$ pmbootstrap build --envkernel linux-oneplus-bacon

Usually if the device boots to SSH with USB networking and has support for kernel upgrades, you can install the new kernel by sideloading.

$ pmbootstrap sideload linux-oneplus-bacon

After compiling and packaging the kernel, it can be flashed to device using the standard pmbootstrap flash commands. Note that if your kernel includes kernel modules (most mainline kernels do) these will not be installed and some features might break when you boot back up. In this case you can sideload as above once you have a booting kernel.

$ pmbootstrap flasher flash_kernel

Packaging kernels built without envkernel

As of !2175 the envkernel packaging logic can be used to package kernels built directly on the host. This is intended to allow folks who prefer to set up their own kernel building environment to still make use of pmbootstrap for packaging and sideloading the new kernel.

Currently this requires that you use .output as your output directory (add O=.output as an argument to make). With that done just build your kernel as normal and follow the packaging/flashing steps above.

See also