Genode on the OKL4 microkernel

OKl4 is a microkernel developed and distributed by Open Kernel Labs. It is focused on embedded devices. Genode support the OKL4 kernel version 2.1 on the x86_32 platform.

This document provides brief instructions about downloading, building and booting the OKL4 version of Genode.

Prerequisites

You need Python 2.4 to use the OKL4 build system. On Debian/Ubuntu systems simply type:

 apt-get install python2.4

Since Ubuntu 10.04, the python2.4 package is no longer part of the official repositories. However, you can manually add the repository via:

 add-apt-repository ppa:python24-team/python24
 apt-get update

Moreover, you need to download and install the tool-chain used by Genode. Have a look at this page:

Downloading and building the OKL4 kernel

To download the OKL4 source code, issue the following command:

 <genode-dir>/tool/ports/prepare_port okl4

It will take care of downloading the kernel's source code and applying the patches found at base-okl4/patches.

For the VESA driver on x86, the x86emu library is required and can be downloaded and prepared by invoking the following command:

 <genode-dir>/tool/ports/prepare_port x86emu

To create a build directory for Genode running on OKL4, use the create_builddir tool:

 <genode-dir>/tool/create_builddir okl4_x86

Once you have created the build directory at <genode-dir>/build/okl4_x86, the OKL4 kernel can be built from within the build directory via

 make kernel

Running the Genode demonstration scenario

For a quick test drive of the OKL4 kernel, issue make run/demo from the build directory.

Manually building a boot image

This section is not needed when using Genode's run-script mechanism. The manual steps described below are automatically executed via the OKL4 run environment as found at tool/run/boot_dir/okl4.

To practically use the OKL4 kernel and applications running on top of it, Open Kernel Labs provide a tool called elfweaver, that is used to merge different application binaries and the kernel itself into one single elf binary that can be executed by your bootloader, e.g. Grub.

To configure elfweaver to merge the appropriated elf binaries you have to provide an XML file. A good starting point is the weaver_x86.xml file that includes the Genode demo example. Simply copy that file to your Genode build directory and adapt the file attribute of the kernel tag to the absolute path of the OKL4 kernel we build previously.

 cp <path_to_genode_src>/base-okl4/tool/weaver_x86.xml weaver.xml

The corresponding line in your weaver.xml should look like this:

 <kernel file="<path_to_okl4_src>/build/pistachio/bin/kernel" xip="false" >

Before creating the image, we need to supply a Genode config file as well. For a quick start, you can copy and rename the template provided os/config/demo to <buil-ddir>/bin/config. Alternatively, you can assign another file to the filename of the memsection declaration for the config file in weaver.xml. Now, we can use elfweaver to create the image. Go to the bin directory in the Genode build directory that contains all the binaries and invoke the script.

 cd bin
 <path_to_okl4_src>/tools/pyelf/elfweaver merge --output=weaver.elf ../weaver.xml
 strip weaver.elf

Note: the given paths to the resulting elf file and the input xml file have to be relative.

Bug alert: Elfweaver triggers an assertion when too many memsections are declared in the weaver.xml file and just outputs the following message

 An error occurred:

Apparently, elfweaver has a problem with calculating the size of the boot info section. As a quick fix, you can increase the value of BOOTINFO_GUESS_OPS in <okl4-dir>/tools/pyelf/weaver/bootinfo.py.

The resulting elf image can be loaded by GRUB now.

Further Information