Unfortunately, the 256 MB RAM of my Raspi is barely enough to keep RetroShare running, but even a simple 'sudo apt-get update' can crash it. The RetroShare project itself is very active at the moment, bugs are constantly fixed and features added. But compiling RetroShare requires all resources, so I thought about alternatives.
"Simple", I thought, "Emulation!"
Spoiler alert: Emulating a Raspberry Pi using QEMU is slow.
I have no experience with emulation whatsoever, so there is no real reason for choosing QEMU over other emulators like VirtualBox, I just found instructions and information for this way first.
What we need to get started
The Emulator
My desktop PC is running Ubuntu 12.04, the rest of the system specifications shouldn't matter. (Yes, I know that this version is a bit outdated, but as a True Believer in Murphy's Law I tend to not change a running system.)Installing QEMU
Install the packageqemu-kvm-extras
the way you usually install packages, e.g., using aptitude
orsudo apt-get install qemu-kvm-extrasThis will also install some dependencies that are needed.
You will also need to download a QEMU-ready linux kernel for the Raspberry Pi, which you can do here:
http://xecdesign.com/downloads/linux-qemu/kernel-qemu
Alternatively, you can compile your own kernel.
Preparing the environment
Create a directory in which our experiment will take place. I chose:mkdir ~/development/raspberrypi-qemu
Raspbian Wheezy
I used newest version of Raspbian Wheezy currently available at http://www.raspberrypi.org/downloads:Torrent | 2012-12-16-wheezy-raspbian.zip.torrent |
Direct download | 2012-12-16-wheezy-raspbian.zip |
SHA-1 | 514974a5fcbbbea02151d79a715741c2159d4b0a |
Default login | Username: pi Password: raspberry |
Download it and unpack the image file into the directory you prepared in the last step.
Plan A: Running an emulated Raspberry Pi
In the directory of the image, run the following command:qemu-system-arm -kernel kernel-qemu -cpu arm1176 -m 256 -M versatilepb -no-reboot -serial stdio -append "root=/dev/sda2 panic=1" -hda 2012-10-28-wheezy-raspbian.imgThe parameters have the following functions:
- -kernel kernel-qemu
- the QEMU-ready kernel we just downloaded
- -cpu arm1176
- the CPU we want to emulate (ARM1176JZF-S (700 MHz))
- -m 256
- how much RAM should be available (in MB)
- -M versatilepb
- the machine type to emulate
- -no-reboot
- exit instead of rebooting
- -serial stdio
- redirects the serial port to the standard I/O
- -append "root=/dev/sda2 panic=1"
- where to find the root partition, depends on the image
- -hda 2012-10-28-wheezy-raspbian.img
- what should be used as hard drive, in this case our image
We also shouldn't forget to resize our image, because right now we only have about 200 MB of free space left. Again: There already are many articles on the net covering this, so I'll only quickly describe what I did.
- With QEMU not running, you can use
qemu-img
to resize an image:
qemu-img resize 2012-12-16-wheezy-raspbian.img +1G
- For other reasons, raspian's built-in functionality of growing the partition to fill the SD card won't work here, so I did it the hard way.
- Boot your emulated Raspberry Pi again using QEMU
- Resize the partition using
fdisk
sudo fdisk /dev/sda
It should look similar to this:
Device Boot Start End Blocks Id System /dev/sda1 8192 122879 57344 c W95 FAT32 (LBA) /dev/sda2 122880 5885951 2881536 83 Linux
You need to delete partition 2 and create it again with the same start, but this time with the highest allowed value for end. - Resize the filesystem using
sudo resize2fs /dev/sda2
It's too slow
Before we start compiling RetroShare again, let's check up on the speed. This is what I get from the QEMU Raspberry Pi:pi@raspberrypi:~$ cat /proc/cpuinfo | grep MIPS BogoMIPS : 565.24And this is from my actual Raspberry Pi
pi@raspberrypi:~$ cat /proc/cpuinfo | grep MIPS BogoMIPS : 697.95So, my emulated raspi running on a Intel Core i5 is actually slower than the real raspi ... which is not what I wanted. I mean, okay, if I'd have the machine running for something else anyway, that wouldn't be a problem. But I still want it to be faster.
Plan B: Architectural chroot a.k.a. chroot Voodoo
Looking for solutions to speed up QEMU, I stumbled upon another approach: architectural chroot!Now, I'm familiar with chroot (at least I though so) and I've used it hundreds of times when my Ubuntu got f*cked up because of an update or some other stuff. And I remember the difficulties when I tried to chroot into a 64 bit system from a 32 bit Live-CD. But it seems like there is a way around this. Coincidentally, we're already close to what we need: a static version of QEMU.
Install it via
apt-get
(or build it yourself)sudo apt-get install qemu-user-staticWe need to mount the image using loopback, but since the image contains multiple partitions, we require
kpartx
$ sudo kpartx -a -v 2012-12-16-wheezy-raspbian.img add map loop0p1 (252:8): 0 114688 linear /dev/loop0 8192 add map loop0p2 (252:9): 0 5763072 linear /dev/loop0 122880 $ sudo mount /dev/mapper/loop0p2 /mnt/tempNow, copy the static QEMU binary TODO and mount the special directories:
sudo cp /usr/bin/qemu-arm-static /mnt/temp/usr/bin sudo mount -o bind /dev /mnt/temp/dev sudo mount -o bind /proc /mnt/temp/proc sudo mount -o bind /sys /mnt/temp/sysBefore we can enter the chroot environment, it's time for the magic! As root (simple
sudo
won't work), do this (all in one line):echo ':arm:M::\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x28\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff:/usr/bin/qemu-arm-static:' > /proc/sys/fs/binfmt_misc/registerThis registers the static QEMU we copied as arm-interpreter to the kernel. The path specified needs to be the same on both your linux machine and the Raspberry Pi environment.
Now we can chroot:
sudo chroot /mnt/tempDid it work?
$ uname -a Linux localhost 2.6.32 #58-Ubuntu SMP Thu Jan 24 15:28:10 UTC 2013 armv7l GNU/Linux
Hooray! Welcome to your (much faster) Raspberry Pi environment! Now, let's do some compiling ;)
Cleaning up
To avoid inconsistencies, make sure you never use QEMU and chroot at the same time! Even more, you need to completely unmount the image before you start QEMU. Otherwise you might see some undesireable side effects.sudo umount /mnt/temp/dev sudo umount /mnt/temp/proc sudo umount /mnt/temp/sys sudo umount /mnt/temp
sudo kpartx -d -v 2012-12-16-wheezy-raspbian.img
Acknowledgements
I also want to give credit to the following articles that helped me doing this:- http://xecdesign.com/qemu-emulating-raspberry-pi-the-easy-way/
- http://www.smallbulb.net/2012/225-emulating-raspberry-pi
- http://xecdesign.com/compiling-a-kernel/
- http://www.frambozenbier.org/index.php/raspi-distribution-news/11474-jojopi-on-fedora-arm-on-raspberry-pi
- http://www.darrinhodges.com/chroot-voodoo/
Thank you for this article. Very well done and helpful.
ReplyDeleteThank you very much for this article. It works up to the point where I want to do anything with it :(
ReplyDeleteI wrote a little bash script that does each of your steps and I run it as root [not sudo] the problem is when I try to do an apt-get or whatever it core dumps.
root@jool:/# uname -a
Linux jool 2.6.32 #28-Ubuntu SMP Tue Oct 9 19:31:23 UTC 2012 armv7l GNU/Linux
root@jool:/# cd /devel
root@jool:/devel# ls
root@jool:/devel# apt-get install git-core
qemu: uncaught target signal 4 (Illegal instruction) - core dumped
Illegal instruction (core dumped)
Am I missing something? do I need to make a working rasbian from my unit, then dd it to an image and use that?
Hi TheQuestor,
Deletethanks for the feedback! Now let's see if we can solve your problem ;)
Are you executing those commands from the architectural chroot? If yes, there is the problem. I haven't exactly figured out how so resolve this, but some things won't work in this environment.
Whenever I wanted to install something using apt-get or even just download something with wget, I had to use QEMU.
I've described some of those issues in my other article (http://sentryytech.blogspot.de/2013/02/compiling-retroshare-for-raspberry-pi.html), please see if this helps you. If not, I will investigate.
From: http://xecdesign.com/qemu-emulating-raspberry-pi-the-easy-way/
DeleteYou need to edit /etc/ld.so.preload in the image and comment out the one and only line with a #.
Florian, to fix your broken internet access inside the chroot environment, copy /etc/resolv.conf to /mnt/temp/etc/resolv.conf
DeleteThx, I will try that next time.
DeleteHi all,
ReplyDeleteIf anyone is interested, I have put together a script which chroot's and un-chroot's an image:
https://github.com/jeffery/raspbian-tools/blob/master/raspbian-chroot.sh
This works on opensuse 12.3 but looking for feedback on how it runs on other distros.
Works fine on ubuntu 12.04.
DeleteThanks
Good article. easy to follow. But, as a newby to qemu and on booting qemu-system-arm.....etc, I keep getting "scsi: 0.0.1.0" re-occurring and incrementing ie. scsi: 0.0.2.0. At the end of each attempt I get "sym0: scsi bus has reset". Is there a way to stop this from happening. Cheers!
ReplyDeleteHow to copy any data from base system to chroot raspberry system?
ReplyDeleteYou just copy the files like you would do it in any other situation. But you have to copy it from outside the chroot environment into the folder of the chroot.
DeleteAlso, if you need to build something that needs a lot of space to build and find you are running out of room, I typically do a bind mount of a working directory as well.
ReplyDeletesudo mount -o bind /home/me/src/WebKit /mnt/temp/home/rPi/src/WebKit
Cool stuff, tnx for sharing.
ReplyDeleteWill this run in a virtualbox environment, too?
I have no idea, but I think it should and you can probably find something about it already on the net. All I did here was gather information already available in a way that I found useful, so go ahead ;)
DeleteWhy didnt you use a buildroot, toolchain? cross-compiling is absurdly fast compared to this, you can actually compile using your own computer clock speed, instead of emulating
ReplyDeleteWhat do you mean? The architectural chroot is no emulation, it compiles with yout own computers clock speed, multiple cores and all the RAM. Can you elaborate more?
DeleteMaybe Marcus was explaining the CHROOTed QEMU system translate every piece of ARM to the corrispondent of x86 or whatever the host machine is.
DeleteSo it slowdown the effective comparison between architectural chroot and the HOST CPU power when using cross-toolchain.
If you install distcc on the architectural chroot _AND_ the toolchain for cross-compiling in the HOST system you will speed up of a magnitude faster!!! Only linking must be done in the architectural chroot environment...
If you use qemu 2.8, they have a bugfix so you don't need to comment the line in /etc/ld.so.preload any more.
ReplyDeleteI'm busy with life and can't test that or write an updated article. But thanks for the update, much appreciated :)
DeleteIndeed - but thought I'd go round passing this on after I persuaded qemu to fix it.
DeleteAt some time I'd like to understand a little more about KVM, and how it can speed up emulating ARM chips, probably need to ask Qemu devs.
This comment has been removed by the author.
ReplyDelete