Experiments with Buildroot
The contents are as follows:
From http://www.buildroot.org/
Buildroot is a simple, efficient and easy-to-use tool to generate embedded Linux systems through cross-compilation
Pull the source code as follows:
$ git clone git://git.busybox.net/buildroot
Unlike many linux projects, does not require root access or the use of sudo:
No need to run as root, Buildroot is designed to be executed with normal user privileges.
And:
Running as root is even strongly discouraged!
Offers many options:
| Command | Requirements | Packages |
|---|---|---|
| make menuconfig | ncurses | 'ncurses-devel' or 'libncurses-dev' depending on distro |
| make nconfig | ncurses | 'ncurses-devel' or 'libncurses-dev' depending on distro |
| make xconfig | Qt | Qt 4.8 or Qt 5.x |
| make gconfig | Gtk | gtk+-2.0, glib-2.0 and libglade-2.0 |
'ncurses' is the lightest framework so we will use that; on Ubuntu this requires 'libncurses5-dev'.
Both make menuconfig and make nconfig are now options; my preference is for make nconfig.
More importantly Buildroot offers a staggering number of predefined configurations:
$ ls -al ./configs/
total 808
drwxrwxr-x 2 owner owner 12288 May 25 12:11 .
drwxrwxr-x 16 owner owner 4096 May 25 12:14 ..
-rw-rw-r-- 1 owner owner 1002 May 25 12:11 aarch64_efi_defconfig
...
<snip>
...
-rw-rw-r-- 1 owner owner 1084 May 25 12:11 zynq_zed_defconfig
$[The options include arm, bananapi, beaglebone, chromebook, raspberrypi and many others.]
Linux is what is known as a microkernel architecture. The kernel is the bare minimum required to run the computer so that accessing hardware requires loading device drivers.
Device drivers generally run in kernel space (as opposed to user space, sometimes referred to as userland) as this is generally needed to deliver the level of performance modern applications require.
For additional performance, compiling needed device drivers into a kernel is fairly trivial.
The difficulty comes in specifying the device drivers to compile into the kernel so as to deliver increased performance under a normal workload. There can be what seem like hundreds of options to specify, as well as dependencies to sort through.
This is where Buildroot really shines, as it offers a rich selection of predefined configurations.
This is a simple as make savedefconfig, for instance:
$ make beaglebone_defconfig
mkdir -p /home/owner/Documents/Linux/Buildroot/buildroot/output/build/buildroot-config/lxdialog
PKG_CONFIG_PATH="" make CC="/usr/bin/gcc" HOSTCC="/usr/bin/gcc" \
obj=/home/owner/Documents/Linux/Buildroot/buildroot/output/build/buildroot-config -C support/kconfig -f Makefile.br conf
/usr/bin/gcc -D_GNU_SOURCE -DCURSES_LOC="<ncurses.h>" -DLOCALE -I/home/owner/Documents/Linux/Buildroot/buildroot/output/build/buildroot-config -DCONFIG_=\"\" /home/owner/Documents/Linux/Buildroot/buildroot/output/build/buildroot-config/conf.o /home/owner/Documents/Linux/Buildroot/buildroot/output/build/buildroot-config/zconf.tab.o -o /home/owner/Documents/Linux/Buildroot/buildroot/output/build/buildroot-config/conf
#
# configuration written to /home/owner/Documents/Linux/Buildroot/buildroot/.config
#
$The full configuration for a beaglebone has now been written to the default .config file.
Now that our configuration options are defined, this is as simple as running make.
Of course, if you wish to keep a log of the build that can be done as follows:
$ make 2>&1 | tee build.log
[Expect the initial build to take quite some time. Over a slow internet connection, it will really take some time.]
The built kernel image, bootloader image, and root filesystem image(s) will be in output/images/.
$ ls -alh output/images/
total 118M
drwxr-xr-x 2 owner owner 4.0K May 25 15:08 .
drwxrwxr-x 6 owner owner 4.0K May 25 15:08 ..
-rw-r--r-- 1 owner owner 36K May 25 15:08 am335x-boneblack.dtb
-rw-r--r-- 1 owner owner 35K May 25 15:08 am335x-bone.dtb
-rw-r--r-- 1 owner owner 35K May 25 15:08 am335x-bonegreen.dtb
-rw-r--r-- 1 owner owner 41K May 25 15:08 am335x-evm.dtb
-rw-r--r-- 1 owner owner 40K May 25 15:08 am335x-evmsk.dtb
-rw-r--r-- 1 owner owner 16M May 25 15:08 boot.vfat
-rw-r--r-- 1 owner owner 79K May 25 15:02 MLO
-rw-r--r-- 1 owner owner 60M May 25 15:08 rootfs.ext2
lrwxrwxrwx 1 owner owner 11 May 25 15:08 rootfs.ext4 -> rootfs.ext2
-rw-r--r-- 1 owner owner 15M May 25 15:08 rootfs.tar
-rw-r--r-- 1 owner owner 77M May 25 15:08 sdcard.img
-rw-r--r-- 1 owner owner 654K May 25 15:02 u-boot.img
-rw-r--r-- 1 owner owner 376 May 25 15:08 uEnv.txt
-rw-r--r-- 1 owner owner 5.3M May 25 15:08 zImage
$Various useful websites are listed below.
The home page can be found here:
http://www.buildroot.org/
The source code can be found here:
http://git.busybox.net/buildroot/
The user manual can be found at:
http://buildroot.org/downloads/manual/manual.html
Buildroot Training:
http://bootlin.com/doc/training/buildroot
[These documents change frequently so it is worth checking back often for the most up-to-date version.]
The source for these materials can be found at:
http://github.com/bootlin/training-materials/
[Pull requests can be submitted here also.]