HowTo_Chromium_OS

KEDR and Chromium OS

This guide has not been updated for a long time and may or may not be obsolete.

Here we describe how to build KEDR for Chromium OS. We assume that the readers already know how to build Chromium OS itself, how to use the special chroot environment, etc.

When building software for Chromium OS, one needs to distinguish two systems (usually, different machines):

• build system where the build is performed and
• target system where Chromium OS and that software will run.

Building

Similar to other software for Chromium OS, everything is done in chroot environment. Here we assume the working directory is /home/user/work/.

In the example described below, everything was done using the following configuration:

• Build system: Ubuntu Linux 10.04 x86-64;
• Target "board": x86-generic;
• Chromium OS kernel: version string: "3.4.0", this is the default kernel checked out at Sat Sep 22 2012;
• CMake 2.6 (should work with newer versions too);
• KEDR: version 0.2.1 (should work with newer versions too), the sources were unpacked to /home/user/work/kedr-0.2.1 inside the chroot environment.

Preliminaries

First, you need to create appropriate directories for build files and temporary installations:

cd /home/user/work/
mkdir build
mkdir install

mkdir build.kedr_gen
mkdir install.kedr_gen

Kernel build files

Chromium OS does not explicitly support building kernel modules out-of-tree, so the following is a bit of a hack. We can build the kernel once more but instruct the system to preserve the files generated during the build:

cd ~/trunk/src/scripts/
FEATURES="noclean" emerge-x86-generic -a sys-kernel/chromeos-kernel

This may take some time. The kernel will be built and installed, and the build files will be kept in /build/x86-generic/tmp/portage/sys-kernel/chromeos-kernel-9999/work/chromeos-kernel-9999/build/x86-generic. The path may be different on your system. For example, if you did not do cros_workon for the kernel, another version would be used instead of 9999. In general, just look for a directory containing vmlinux and System.map files in /build/x86-generic/tmp/portage/ tree and take the path to it.

It can be useful to make a spare copy of that directory because the contents of /build/x86-generic/tmp/portage/ may be wiped out when you build some other software for Chromium OS.

Code generation tool (kedr_gen)

KEDR build system generates the source code of some of its components using special template files. For example, the kernel modules that perform fault simulation, memory leak detection and call tracing are created this way from the descriptions of the kernel functions to be intercepted. Code generation is done by kedr_gen tool included in KEDR framework.

kedr_gen should be built before all other components of the framework. When the build and the target machines have the same architecture and use the same compiler toolchain, this is taken care of automatically. However, when building KEDR for Chromium OS, you need to build kedr_gen explicitly:

cd /home/user/work/build.kedr_gen/
cmake \
  -DCMAKE_INSTALL_PREFIX=/home/user/work/install.kedr_gen/ \
  ../kedr-0.2.1/tools/kedr_gen/
make 
make install

kedr_gen should now be available as /home/user/work/install.kedr_gen/kedr_gen

Configuring and building KEDR

Now everything is ready to configure and build KEDR itself. First you need to execute cmake from the build directory.

cd /home/user/work/build
cmake \
  -DCMAKE_TOOLCHAIN_FILE=/home/user/work/kedr-0.2.1/cmake/platform/chromiumos-x86-generic.cmake \
  -DCMAKE_SYSTEM_VERSION="2.6.37" \
  -DKBUILD_BUILD_DIR=/build/x86-generic/tmp/portage/sys-kernel/chromeos-kernel-9999/work/chromeos-kernel-9999/build/x86-generic/ \
  -DKEDR_GEN=/home/user/work/install.kedr_gen/kedr_gen \
  ../kedr-0.2.1/

As you can see, the following CMake variables are set:

CMAKE_TOOLCHAIN_FILE

The path to the toolchain file (profile). The profile for Chromium OS (x86-generic) is provided with KEDR.

CMAKE_SYSTEM_VERSION

Kernel version string. To be exact, this is what uname -r would return for the target system.

KBUILD_BUILD_DIR

Path to the build tree of the kernel (see above).

KEDR_GEN

Path to kedr_gen tool that you have created earlier.

CMake may issue the following warning:

CMake Warning:
Manually-specified variables were not used by the project:

CMAKE_TOOLCHAIN_FILE

This is a known peculiarity of CMake. CMake does use CMAKE_TOOLCHAIN_FILE variable, so you can safely ignore the warning.

If the configuration phase has completed successfully, you can now build KEDR:

make 

Note that self-testing support (make check) is currently disabled for such cross-builds. The documentation and the examples will not be installed in this case either, they are probably not necessary on the target system anyway.

Installation

It can be convenient to install KEDR using a particular directory as a root (DESTDIR):

make DESTDIR=/home/user/work/install install

After that, you can copy the contents of /home/user/work/install/usr/ to /usr directory on the target system.

Note that /etc and its subdirectories can be read-only on the target system. It is recommended to copy /home/user/work/install/etc/kedr/*.conf files somewhere else there. After that you should specify the full path to the relevant .conf files when you load KEDR, for example,

kedr start <name_of_the_target_module> \
    -f /home/chronos/user/etc/kedr/leak_check.conf \
    -f /home/chronos/user/etc/kedr/fsim.conf

Now you should be able to use KEDR on your ChromiumOS box.