Building the Linux Kernel
This page covers the process of configuring and compiling the Linux kernel using the EMAC kernel build script. This process assumes that you have already acquired the following software:
- EMAC Software Development Kit OE 4 or OE 5
- Linux kernel source for target hardware (provided via EMAC public GIT server )
- Kernel build script
The example below will assume that a kernel image for the SoM-9x25 module will be created, although the instructions apply to other hardware as well assuming that the correct SDK, kernel tree, and build script is used.
The steps below assume that the
kernel-build-cross.sh script is
located in the same directory as the kernel tree. Be sure to modify the
environment.cfg.sh script for the correct
architecture and EMAC OE version.
Configuring the Kernel
The first step for building the kernel is to configure it as desired. It is recommended to start with the kernel configuration file used by EMAC to build the kernel for the target device. Starting with EMAC OE 5, the kernel configuration can be
obtained on a running board from /proc/config.gz. Please contact EMAC support
for earlier EMAC OE versions.
The following are steps to configure the kernel:
Copy the default configuration file to the same directory as the kernel source tree and kernel-build-cross.sh and rename it defconfig.
The kernel-build-cross script accepts the SOURCE_TREE as the first argument and either config or build as the second argument. Optionally, a third argument, BUILD_SUFFIX may be supplied as a suffix to add to the build directory. BUILD_SUFFIX is commonly used to add a date tag or machine name to a build.
The kernel menu-driven configuration utility will be displayed. Features can be selected/deselected to be built into the kernel. Some features can be built as a loadable module, denoted by < >, and not built directly into the kernel.
WARNING! Disabling or modularizing some kernel features may prevent the kernel from starting correctly or at all.
Use the space bar to select an option or the 'm' key to configure the selected option as a module. Select
Exitto close the kernel configuration menu and save the configuration to the newly created build directory. When the same build-suffix is used for subsequent builds, this configuration will be used.
Building the Kernel
Run the kernel-build-cross script again with the build option, this time using the same build-suffix used in the configuration step.
The kernel will begin compiling now. This will take several minutes to complete depending on the kernel configuration and the speed of the development machine. Only move on to the next step if the build completes with no errors.
The new kernel image will be in the
build-3.10.0-som9x25/Install/bootdirectory. For the 3.10 and later device tree enabled ARM kernels, the image name will be a zImage. Also, the desired device tree blob (*.dtb) needs to be appended to the kernel. For earlier versions of the kernel, a uImage will be generated that can be loaded directly from U-Boot. X86 boards use a bzImage.
This is the image that will get loaded onto the board and executed by the bootloader. To load the new kernel onto the target machine, see the Loading Linux Kernels Onto a Board page.
The build script will also create an archive of all of the modules created during the build process and place it in the
build-3.10.0-som9x25/Install/directory. The archive will be called
Loading Kernel Modules
If the kernel is recompiled without changing the configuration or source code for any modules, it is not necessary to reload the modules archive. Alternatively, if a module was modified or added, it is only necessary to reload the modules archive. To reload the modules:
Copy the archive to the root of the filesystem of the target machine
Log onto the target machine
Extract the kernel modules archive and force the kernel to reload the modules. Make sure that the root flash is mounted read/write before extracting.