Developing changes for OPTEE-OS

Developing with Buildroot

Because Buildroot is meant as more of a deployment than a development system, making changes to the components requires some work. We will be following the Buildroot documentation.

  1. First, clone the repositories of the components you want to in a separate directory. Let’s use <changes-dir> for this example.

  2. Create a file in <project-dir>/output called local.mk and add the following lines for each component that you cloned locally (in this case OPTEE-OS and Linux):

    OPTEE_OS_OVERRIDE_SRCDIR = <changes-dir>/optee_os
LINUX_OVERRIDE_SRCDIR = <changes-dir>/linux

    This will tell Buildroot that it should not pull the build files from the remote repositories, but should instead use the locally cloned files.

  3. Then issue the following command after every change you made to these files (again for OPTEE-OS and Linux):

    make BR2_JLEVEL="$(nproc)" optee-os-rebuild linux-rebuild all

    This will copy the files from the local clones to <project-dir>/output/build/...

    It might be necessary to first run

    make optee-os-dirclean linux-dirclean

    to remove the current build files. This will remove all files in <project-dir>/output/build/..., so make sure that any changes are backed up first.

Debugging

Debugging Linux on hardware boards is pretty difficult. printk statements can be used to print execution flow and memory values to the console. Otherwise, a hardware J-Link debugger may be used. We do not explain how to use that here.