Gentoo Embedded x86 Guide

1. Introduction

What is Gentoo Embedded? 

From the Gentoo Embedded website :

This project manages embedded system support in Gentoo. The project is responsible for overseeing the build infrastructure for creating images to be installed onto embedded systems. Also included is the support of specific types of embedded systems and development tools.

What is x86 Gentoo Embedded? 

x86 Gentoo Embedded is simply embedded Gentoo for the x86 architecture (think Intel, AMD, and Via processors). It's main purpose is for embedded SBCs (single board computers) based on the x86 architecture were a small non-volatile (flash, compact flash, DiskOnChip) footprint is needed (as low as 10 MB).

Definitions and Terms 

Overview of Process (steps) 

2. Step 1 - Prepare the development_rootfs from your system_rootfs

You must be root, and cd to the working directory (/opt). 

# su -
# cd /opt

Create development_rootfs 

Create the development_rootfs directory. I use i586 because of target is a Geode processor.

# mkdir -p /opt/i586-gentoo-uclibc-linux/usr/portage

Download stage 1 embedded Gentoo tarball. 

Download the latest stage 1 tarball. It's a stage 1 tarball utilizing uclibc.

# wget \
http://mirror.usu.edu/mirrors/gentoo/experimental/x86/embedded/stages/\
stage1-x86-uclibc-2005.0.tar.bz2

Untar stage. 

Untar the stage to the development_rootfs.

# tar -xvjpf stage1-x86-uclibc-2005.0.tar.bz2 -C /opt/i586-gentoo-uclibc-linux/

Mount needed directories. 

Mount the proc and portage directories to your development_rootfs. Makes your system_rootfs's proc and portage directory available from inside of your development_rootfs (after chrooting).

# mount --bind /proc /opt/i586-gentoo-uclibc-linux/proc/
# mount --bind /usr/portage /opt/i586-gentoo-uclibc-linux/usr/portage

Copy DNS info. 

Copy over DNS information to the development_rootfs.

# cp /etc/resolv.conf /opt/i586-gentoo-uclibc-linux/etc/resolv.conf

Chroot. 

Chroot into the development_rootfs.

# chroot /opt/i586-gentoo-uclibc-linux /bin/bash --login

3. Step 2 - Build the development_rootfs

Create new environment and load variables into memory. 

# env-update
# source /etc/profile

Modify make.conf. 

Modify make.conf file to your liking/needs. This is for my target, Geode x86 processor.

Possible values for UCLIBC_CPU : 386, 486, ELAN, 586, 586MMX, 686, PENTIUMII, PENTIUMIII, PENTIUM4, K6, K7, CRUSOE, WINCHIPC6, WINCHIP2, CYRIXIII, NEHEMIAH

# nano -w /etc/make.conf

USE="bitmap-fonts minimal truetype-fonts mmx"
CHOST="i586-gentoo-linux-uclibc"
CFLAGS="-march=i586 -Os -pipe -fomit-frame-pointer -mmmx"
CXXFLAGS="${CFLAGS}"
FEATURES="buildpkg"

VIDEO_CARDS="chips"
UCLIBC_CPU="586MMX"

Set profile to use 2.6 kernel. 

# cd /etc/
# unlink make.profile
# ln -s ../usr/portage/profiles/uclibc/x86/2005.1 make.profile

Start the bootstrap script. 

# cd /usr/portage/scripts
# ./bootstrap.sh -p -v
# ./bootstrap.sh

Workaround - bootstraping
Failure compiling uclibc (gcc-config error: Could not run/locate "gcc")?
If you get a failure while bootstrap is compiling uclibc here are the steps
to work around the problem.
# gcc-config 1
# source /etc/profile
# ./bootstrap.sh

Emerge the system ebuild for the development_rootfs. 

# emerge -e system

Workaround - emerge system
During emerge -e system, python-fchksum fails complaing about
gcc-config error: Could not run/locate "i386-gentoo-linux-uclibc-gcc"
The following commands work around this problem.
# emerge python
# emerge -e system

4. Step 3 - Build the embedded_rootfs

Create the embedded_rootfs directory. 

# mkdir /embedded_rootfs

Emerge baselayout-lite into embedded_rootfs. 

# cd /usr/portage/sys-apps/baselayout-lite/
# ROOT=/embedded_rootfs emerge baselayout-lite-1.0_pre1.ebuild

Workaround - baselayout-lite
Baselayout-lite is still beta, so a few fixes are needed.
There needs to be a directory "log" in /var.
Inittab calls for /usr/bin/tail, but it needs to /usr/bin.
# mkdir /embedded_rootfs/var/log
# nano -w /embedded_rootfs/etc/inittab
tty3::respawn:/usr/bin/tail -f /var/log/messages
tty3::respawn:/bin/tail -f /var/log/messages

Emerge uclibc into the embedded_rootfs. 

Use the -K option because we don't get the extra files created by the build/emerge process into our embedded rootfs which needs to be as small as possible.

# ROOT=/embedded_rootfs emerge -K uclibc

Emerge busybox into the embedded_rootfs. 

First you must emerge it into your development_rootfs. This does not create the symlinks in our development embedded rootfs.

# emerge busybox
# ROOT=/embedded_rootfs emerge -K busybox

Create the symlinks for busybox in the embedded_rootfs. 

# mkdir /embedded_rootfs/proc
# mount -o bind /proc/ /embedded_rootfs/proc/
# chroot /embedded_rootfs /bin/busybox --install -s
# umount /embedded_rootfs/proc

Set time zone in your embedded_rootfs. 

# nano -w /embedded_rootfs/etc/TZ
CST6CDT

Install a boot loader (usually grub or lilo). 

Once you copy/deploy your embedded_rootfs to your target SBC you will have to run grub on the command line to write to the master boot record (MBR). For some reason not all of /boot/grub is copied over to the embedded_rootfs, so a extra manual copy step is needed. The --nodeps gets rip of the run time need of ncurses.

# emerge --nodeps grub
# ROOT=/embedded_rootfs emerge -K --nodeps grub
# cp -R /boot/grub /embedded_rootfs/boot/

Modify your boot configure file. The example below is for a gurb, for a boot partition on /dev/hda1 and only one partition on the target SBC system.

# nano -w /embedded_rootfs/boot/grub/grub.conf
default 0
timeout 10
splashimage=(hd0,0)/boot/grub/splash.xpm.gz

title=Linux 2.6.x
root (hd0,0)
kernel /vmlinuz-2.6.x root=/dev/hda1 vga=792

Set root password for the embedded_rootfs. 

# chroot /embedded_rootfs /bin/sh
# passwd
# exit
# rm /embedded_rootfs/etc/passwd-

Modify fstab. 

Below is mine, yours may vary.

# nano -w /embedded_rootfs/etc/fstab
/dev/hda1     reiserfs  defaults  0 0
none/proc     proc      defaults  0 0
none/sys      sysfs     defaults  0 0
none/dev/shm  tmpfs     defaults  0 0

Clean up the embedded_rootfs. 

Need to clean up extra files generated by portage that we don't need.

rm -R /embedded_rootfs/var/db/pkg/*
rm -R /embedded_rootfs/var/lib/portage/

5. Step 4 - Build and install non-system programs to the embedded_rootfs

Emerge other software you need for you embedded target. This is very wildly depending on your needs. Also your proprietary application will be done here.

# emerge foo*
# ROOT=/embedded_rootfs emerge -K foo*

6. Step 5 - Build and install a kernel to the embedded_rootfs

Install a kernel into embedded_rootfs. 

First we will emerge it into our development_rootfs, then configure and build it.

# emerge vanilla-sources
# cd /usr/src/
# cd linux
# make menuconfig

Configure your kernel for your TARGET SBC here. I HIGHLY suggest you configure the kernel to compile everything into the kernel, and nothing as a module.

# make
# make INSTALL_MOD_PATH=/embedded_rootfs modules_install
# cp /usr/src/linux/arch/i386/boot/bzImage /embedded_rootfs/boot/vmlinuz-2.6.x

A few notes on compiling your kernel. If deploying to a compact flash/DiskOnChip/SD use ext2, as the journaling filing systems "write" far to much for a flash device. If deploying to a hard drive use a journaling filing system, such as ext3 or reiserfs.

7. Step 6 - Deploy embedded_rootfs to target

Prepare a Gentoo (or any Linux distro) system on the target SBC using a harddrive. This is known as the target development rootfs. We will create a partition (/embedded_rootfs) that will server as our "test" partition to deploy our embedded_rootfs that we generate on our development_system.

Copy over your embedded_rootfs from you development system to your target system and the directory /embedded_rootfs. This needs to be done via NFS as need to preserve the permissions.

The following commands are done from the target development rootfs.

# mount -t reiserfs /dev/hda1 /mnt/embedded_rootfs
# mount -t nfs\
# 192.168.0.10:/opt/i586-gentoo-uclibc-linux/embedded_rootfs\
# /mnt/nfs_embedded_rootfs
# cp -adpR /mnt/nfs_embedded_rootfs/* /mnt/embedded_rootfs

Modify your target system's gurb.conf (or lilo.conf) for allow you to boot to the embedded_rootfs partition.

Reboot, and if all goes well you'll be greeted with a login prompt.

Fin.