Compiling kernels with envkernel.sh
This page details how to compile a kernel manually using the envkernel.sh
helper script. This workflow can be used to quickly compile and test changes to the kernel source.
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 envkernel.sh
script (for fish shell: envkernel.fish
). 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 https://github.com/LineageOS/android_kernel_oneplus_msm8974.git
$ 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
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
The envkernel.sh script is not provided, when you installed pmbootstrap from pip. You have to install pmbootstrap from git to have it. |
The envkernel.sh
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.
$ pmbootstrap init
Run the envkernel.sh
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/envkernel.sh --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 envkernel.sh
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 post-make.sh
in the kernel source directory.
#!/bin/sh
dtbTool -s 2048 -p "${srcdir}/scripts/dtc/" -o \
"${builddir}/arch/arm/boot/dt.img" \
"${builddir}/arch/arm/boot"
Run the script.
$ run-script post-make.sh
Packaging and flashing the kernel
A kernel compiled under envkernel.sh
can be packaged by pmbootstrap by using the --envkernel
build option.
$ pmbootstrap build --envkernel linux-oneplus-bacon
After compiling and packaging the kernel, it can be flashed to device using the standard pmbootstrap flash commands.
$ pmbootstrap flasher flash_kernel
See also
- !1703 optional gcc6 argument
- !1747 pmbootstrap build --envkernel
- a quick Q&A about using envkernel.sh for the Nexus 5 (if you have more questions, please open a new issue or ask in the chat).