QEMU Build Tutorial

Introduction

If you don't have a mainboard supported by LinuxBIOS don't worry: Qemu can help you to emulate one.

This nice tutorial was written by Alan Carvalho de Assis <acassis@gmail.com>, with additions by Ed Swierk <eswierk@arastra.com>.

While there are many ways to use LinuxBIOS to load and run a Linux kernel, this tutorial covers two of the most common:

• LinuxBIOS with FILO as payload, using FILO to load a Linux kernel and initramfs from a hard disk image.
• LinuxBIOS with a Linux kernel and initramfs as payload.

Requirements

You need the following software packages:

• LinuxBIOSv2 r2405 or greater
• Qemu 0.8.2 or greater
• FILO 0.4.2 or greater (if using FILO)
• mkelfImage 2.7 or greater (if not using FILO)

plus a Linux kernel and root filesystem and a working development environment (make, gcc, etc.). gcc 4.0.x and 4.1.x are known to work.

Creating FILO

Download FILO (I used filo-0.4.2.tar.bz2), decompress it, enter inside directory created.

First invocation of make creates the default Config file.

$ make   

Edit this file as you like. The default configuration worked to me.

$ vi Config   

Run make again to create filo.elf, the ELF FILO image.

$ make   

You will need this file (filo.elf) to start Linux. This is used as a payload in LinuxBIOS, when executed it can load Linux kernel.

Creating LinuxBIOS

Download LinuxBIOS source code (I used LinuxBIOSv2-2394). Decompress it.

Change to directory targets/emulation/qemu-i386 and modify Config.lb to point to your filo.elf.

Return to targets directory and execute:

$ ./buildtarget emulation/qemu-i386  

Go to targets/emulation/qemu-i386/qemu-i386 and execute:

$ make  

It will create the file "qemu-bios.rom"

Rename this file to "bios.bin" and copy to your HOME directory.

Creating your disk image

Create a empty file (~ 200MB):

# dd if=/dev/zero of=disk.img bs=1M count=200 

Format it as ext2:

# mkfs.ext2 -F disk.img 

Mount it on somewhere:

# mount disk.img /mnt/rootfs -t ext2 -o loop 

Now you need copy a root filesystem to it.

I create a directory /debian and used debootstrap command to create a basic root filesystem, but you can use any root filesystem from your distro (i.e. copy one from diskboot.img):

# cp -R /debian/* /mnt/rootfs 

Open the file /mnt/rootfs/etc/inittab and change runlevel to level 1:

id:1:initdefault: 

Change to /mnt/rootfs/boot and copy your default vmlinuz and initrd:

# cp /boot/vmlinuz-2.6.16-2-686 vmlinuz
# cp /boot/initrd.img-2.6.16-2-686 initrd

Change to /root and umount /mnt/rootfs:

# umount /mnt/rootfs

Exit of root account:

# exit

Starting LinuxBIOS in Qemu

Execute Qemu using the followings parameters:

$ qemu -L ~ -hda disk.img -nographic -no-kqemu -d in_asm,exec

When appear "boot:" text enter it:

boot: hda:/boot/vmlinuz root=/dev/hda initrd=/boot/initrd console=tty0 console=ttyS0,115200