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=== Introduction ===
=== Introduction ===


If you don't have a mainboard supported by LinuxBIOS don't worry: Qemu can help you to emulate one.
If you don't have a mainboard supported by coreboot don't worry: [http://qemu.org/ QEMU] can help you to emulate one. Using coreboot with QEMU may serve the purpose to familiarize you as a developer with coreboot and may be a reference system during development.  


This nice tutorial was written by Alan Carvalho de Assis <acassis@gmail.com>.
This nice tutorial was written by [mailto:acassis@gmail.com Alan Carvalho de Assis], with additions by [mailto:eswierk@arastra.com Ed Swierk] (but please use the [[Mailinglist|coreboot mailing list]] rather than emailing the authors directly).
 
While there are many ways to use coreboot to load and run a Linux kernel, this tutorial covers two of the most common:
 
* coreboot with [[SeaBIOS]] as payload, which is the default configuration on coreboot for Intel compatible mainboards.
* coreboot with [[FILO]] as payload, using FILO to load a Linux kernel (and optional initramfs) from a hard disk image. This approach involves a bit more mechanism (it relies on FILO's built-in disk and filesystem drivers) but it produces a tiny coreboot image.
* coreboot with a Linux kernel (and optional initramfs) as payload. This cuts FILO out of the picture, but the main challenge with this approach is squeezing the resulting coreboot image into QEMU's BIOS ROM area (currently 2 MB, but easy to extend by patching QEMU).


=== Requirements ===   
=== Requirements ===   
    
    
You need the following softwares:  
You need the following software packages:
 
 
* GCC (obvious, since you need compile FILO and LinuxBIOS)  
* [[Download_coreboot|coreboot v4]]
* Qemu 
* [http://qemu.org/ Qemu]
* FILO 
* [[FILO]] 0.6 or greater (if using FILO)
* LinuxBIOS 
 
plus a Linux kernel and root filesystem and a working development environment (make, gcc, etc.).
 
=== Building or finding a Linux kernel ===
 
If you are using FILO, you can simply grab a Linux kernel and initramfs from your favorite distribution.
 
For linux as payload, you will probably need to build a kernel and initramfs from scratch, ensuring that the final coreboot image does not exceed QEMU's BIOS size limit (2MB if qemu-bios-size patch applied, 256KB otherwise).  Building the kernel and initramfs is beyond the scope of this tutorial; how you configure them depends on your application.
 
If you plan to use kexec to chain-boot another Linux kernel, tools from these projects can help automate the process of generating a kernel and initramfs:
* [http://kboot.sourceforge.net/ kboot]
* [http://wiki.laptop.org/go/Building_LinuxBIOS OLPC buildrom]
 
=== Using SeaBIOS ===
 
Since SeaBIOS is the default payload option, you don't need to change anything in the payload section of the configuration menu, and don't need to download or prepare any source code either - the build system takes care of that.


=== Building a FILO payload ===


=== Creating FILO ===
If you plan to build your Linux kernel and root filesystem directly into coreboot, you can skip this section.


Download FILO (I used filo-0.4.2.tar.bz2), decompress it, enter inside directory created. 
Download [[FILO]], and cd to the filo directory
    
    
First invocation of make creates the default Config file.   
First invocation of make creates the config file.
$ make menuconfig
 
Run make again to create build/filo.elf, the ELF FILO image.   
  $ make   
  $ make   


Edit this file as you like. The default configuration worked to me.  
You will use this file (filo.elf) as the coreboot payload later on.
$ vi Config 


Run make again to create filo.elf, the ELF FILO image.  
=== Building a Linux kernel payload ===
$ make 
 
If you are using FILO, skip this section.


You will need this file (filo.elf) to start Linux
Specify the Linux as payload type and the Linux kernel (bzImage file), initrd and kernel command line that should be used in `make menuconfig`'s Payload section
This is used as a payload in LinuxBIOS, when executed it can load Linux kernel
 


=== Creating LinuxBIOS ===
=== Building coreboot ===


Download LinuxBIOS source code (I used LinuxBIOSv2-2394). 
See the [[Build HOWTO]] for information on how to build coreboot for this board.
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 
This creates the coreboot image (build/coreboot.rom).


Go to targets/emulation/qemu-i386/qemu-i386 and execute: 
=== Building Qemu ===
Qemu used to require patches to work with coreboot, but any current standard build (as packaged by distributions) should be good enough.


$ make 
<!--
==== Building Qemu on FreeBSD ====
Qemu can easily be installed using FreeBSD's Ports tree. The Qemu port lives in emulators/qemu. However, as of version 0.9.1 the FreeBSD port can unfortunately no longer be used with coreboot. The latest working version is 0.9.0 which can be retrieved from the FreeBSD CVS repository. For your convenience, an archive of the last working port version has been uploaded to this wiki. You can download the archive from [http://www.coreboot.org/Image:FreeBSD-Qemu-0.9.0.tgz here]. For some reason, the downloaded archive cannot be extracted with tar only, so use these steps to extract the archive:


It will create the file "qemu-bios.rom"  
$ gunzip FreeBSD-Qemu-0.9.0.tgz
 
  $ tar -xvf FreeBSD-Qemu.0.9.0.tar
Rename this file to "bios.bin" and copy to your HOME directory.
 


=== Creating your disk image ===
To build and install the port, do this:
Create a empty file (~ 200MB):  


  # dd if=/dev/zero of=disk.img bs=1M count=200
  $ cd qemu
$ make clean install


Format it as ext2:  
Make sure you load the aio(4) kernel module before starting QEMU. Also, QEMU can be build with the kqemu kernel module that enhances QEMU's performance. To load both kernel modules at boot time, add the following lines to <tt>/boot/loader.conf</tt>:


# mkfs.ext2 -F disk.img
<pre>
aio_load="YES"
kqemu_load="YES"
</pre>


Mount it on somewhere:
You can now use the Qemu binary located in <tt>/usr/local/bin</tt>.
-->
=== Creating a hard disk image ===


# mount disk.img /mnt/rootfs -t ext2 -o loop
If you are using FILO, you must create a hard disk image containing the Linux kernel and optional initramfs that FILO loads.


Now you need copy a root filesystem to it.  
Whether or not you use FILO, you may also wish to populate the disk image with the root filesystem of whatever Linux distribution you want to run.


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):
Create an empty disk image:
$ qemu-img create -f raw disk.img 200M


  # cp -R /debian/* /mnt/rootfs
Format it:
  $ mkfs.ext2 -F disk.img


Open the file /mnt/rootfs/etc/inittab and change runlevel to level 1:
The remaining steps must be performed as root.  Create a temporary mountpoint and mount the image:
# mkdir /mnt/rootfs
# mount -o loop disk.img /mnt/rootfs


  id:1:initdefault:
Create a boot directory and copy your Linux kernel (vmlinuz) and initramfs (initrd) to it:
# mkdir /mnt/rootfs/boot
# cp vmlinuz /mnt/rootfs/boot/vmlinuz
  # cp initrd /mnt/rootfs/boot/initrd


Change to /mnt/rootfs/boot and copy your default vmlinuz and initrd:
At this point, you can also copy a complete root filesystem to the disk image.
# cp -R /* /mnt/rootfs  


  # cp /boot/vmlinuz-2.6.16-2-686 vmlinuz
Alternatively, with Debian you can use the debootstrap command to create a basic root filesystem:
# cp /boot/initrd.img-2.6.16-2-686 initrd
  # debootstrap --arch i386 sarge /mnt/rootfs http://ftp.debian.org/debian/  


Change to /root and umount /mnt/rootfs:
If you are using a debootstrap filesystem, open the file /mnt/rootfs/etc/inittab and change runlevel to level 1:
id:1:initdefault:  


cd out of /mnt/rootfs and umount it:
  # umount /mnt/rootfs
  # umount /mnt/rootfs


Exit of root account:
Exit from the root account:
# exit


  # exit
=== Starting coreboot in QEMU ===
 
Execute QEMU using the following parameters:
  $ qemu -bios path/to/coreboot.rom -hda disk.img -nographic


The -bios option tells QEMU to use path/to/coreboot.rom as its BIOS.  The -nographic option suppresses the graphical VGA display and connects the virtual machine's serial port to your console. If you want to keep VGA display, you can use "-serial stdio" instead, which only redirects serial to the console.


=== Starting LinuxBIOS in Qemu ===
You should now see all sorts of interesting coreboot messages, followed by Linux kernel boot messages or a FILO prompt.


Execute Qemu using the followings parameters:
If you are using FILO, enter at the boot: prompt:


  $ qemu -L ~ -hda disk.img -nographic -no-kqemu -d in_asm,exec
  kernel hda:/boot/vmlinuz root=/dev/hda
initrd hda:/boot/initrd
boot console=ttyS0


When appear "boot:" text enter it:
Example:


boot: hda:/boot/vmlinuz root=/dev/hda initrd=/boot/initrd console=tty0 console=ttyS0,115200
[[Image:Screenshot linuxbios boots qemu.png]]

Latest revision as of 17:17, 29 May 2015

Introduction

If you don't have a mainboard supported by coreboot don't worry: QEMU can help you to emulate one. Using coreboot with QEMU may serve the purpose to familiarize you as a developer with coreboot and may be a reference system during development.

This nice tutorial was written by Alan Carvalho de Assis, with additions by Ed Swierk (but please use the coreboot mailing list rather than emailing the authors directly).

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

  • coreboot with SeaBIOS as payload, which is the default configuration on coreboot for Intel compatible mainboards.
  • coreboot with FILO as payload, using FILO to load a Linux kernel (and optional initramfs) from a hard disk image. This approach involves a bit more mechanism (it relies on FILO's built-in disk and filesystem drivers) but it produces a tiny coreboot image.
  • coreboot with a Linux kernel (and optional initramfs) as payload. This cuts FILO out of the picture, but the main challenge with this approach is squeezing the resulting coreboot image into QEMU's BIOS ROM area (currently 2 MB, but easy to extend by patching QEMU).

Requirements

You need the following software packages:

plus a Linux kernel and root filesystem and a working development environment (make, gcc, etc.).

Building or finding a Linux kernel

If you are using FILO, you can simply grab a Linux kernel and initramfs from your favorite distribution.

For linux as payload, you will probably need to build a kernel and initramfs from scratch, ensuring that the final coreboot image does not exceed QEMU's BIOS size limit (2MB if qemu-bios-size patch applied, 256KB otherwise). Building the kernel and initramfs is beyond the scope of this tutorial; how you configure them depends on your application.

If you plan to use kexec to chain-boot another Linux kernel, tools from these projects can help automate the process of generating a kernel and initramfs:

Using SeaBIOS

Since SeaBIOS is the default payload option, you don't need to change anything in the payload section of the configuration menu, and don't need to download or prepare any source code either - the build system takes care of that.

Building a FILO payload

If you plan to build your Linux kernel and root filesystem directly into coreboot, you can skip this section.

Download FILO, and cd to the filo directory

First invocation of make creates the config file.

$ make menuconfig

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

$ make   

You will use this file (filo.elf) as the coreboot payload later on.

Building a Linux kernel payload

If you are using FILO, skip this section.

Specify the Linux as payload type and the Linux kernel (bzImage file), initrd and kernel command line that should be used in `make menuconfig`'s Payload section

Building coreboot

See the Build HOWTO for information on how to build coreboot for this board.

This creates the coreboot image (build/coreboot.rom).

Building Qemu

Qemu used to require patches to work with coreboot, but any current standard build (as packaged by distributions) should be good enough.

Creating a hard disk image

If you are using FILO, you must create a hard disk image containing the Linux kernel and optional initramfs that FILO loads.

Whether or not you use FILO, you may also wish to populate the disk image with the root filesystem of whatever Linux distribution you want to run.

Create an empty disk image:

$ qemu-img create -f raw disk.img 200M

Format it:

$ mkfs.ext2 -F disk.img 

The remaining steps must be performed as root. Create a temporary mountpoint and mount the image:

# mkdir /mnt/rootfs
# mount -o loop disk.img /mnt/rootfs

Create a boot directory and copy your Linux kernel (vmlinuz) and initramfs (initrd) to it:

# mkdir /mnt/rootfs/boot
# cp vmlinuz /mnt/rootfs/boot/vmlinuz
# cp initrd /mnt/rootfs/boot/initrd

At this point, you can also copy a complete root filesystem to the disk image.

# cp -R /* /mnt/rootfs 

Alternatively, with Debian you can use the debootstrap command to create a basic root filesystem:

# debootstrap --arch i386 sarge /mnt/rootfs http://ftp.debian.org/debian/ 

If you are using a debootstrap filesystem, open the file /mnt/rootfs/etc/inittab and change runlevel to level 1:

id:1:initdefault: 

cd out of /mnt/rootfs and umount it:

# umount /mnt/rootfs

Exit from the root account:

# exit

Starting coreboot in QEMU

Execute QEMU using the following parameters:

$ qemu -bios path/to/coreboot.rom -hda disk.img -nographic

The -bios option tells QEMU to use path/to/coreboot.rom as its BIOS. The -nographic option suppresses the graphical VGA display and connects the virtual machine's serial port to your console. If you want to keep VGA display, you can use "-serial stdio" instead, which only redirects serial to the console.

You should now see all sorts of interesting coreboot messages, followed by Linux kernel boot messages or a FILO prompt.

If you are using FILO, enter at the boot: prompt:

kernel hda:/boot/vmlinuz root=/dev/hda
initrd hda:/boot/initrd
boot console=ttyS0

Example: