Getting Started with Akaros

Barret Rhoden

Last thorough update: 2013-02-07

Most everyone wants KFS turned on (Filesystems --> KFS filesystem). This is the in-memory filesystem that the kernel uses. The kernel build scripts will look at the "KFS/Initramfs paths" string and take any of those directories and add them to a CPIO archive that will eventually become the root filesystem when Akaros runs. These settings are set by default when you do a make defconfig.

There are also settings for ext2. If you turn on ext2 support, you need to point to an img file that has been formatted with ext2 and has files in it. If you aren't messing with filesystems at all, feel free to ignore this. It's an in-memory filesystem, like KFS (linked to the end of the kernel), so you won't gain much by using it for now.

3.1 Cross compiler (and glibc)

The second step is to build the cross compiler, which lives in tools/compilers/gcc-glibc

$ cd tools/compilers/gcc-glibc

You should already have set your AKAROS_TOOLCHAINS to some place where you want the cross compiler installed. I have a directory named akaros-gcc-glibc for this. My bash environment variables are -

export AKAROS_ROOT=/home/brho/classes/akaros/akaros-kernel
export AKAROS_TOOLCHAINS=/home/brho/classes/akaros/akaros-gcc-glibc

You can also set up MAKE_JOBS, so you don't over or under load your system when building. I have a 2 core laptop, so I use MAKE_JOBS := 3

At this point, you can build (for example):

$ make x86_64

This might take a while (10-20 minutes for me on a 2007 era laptop).

Next you will need to add bin directories to your PATH where the cross compiler was installed. This will vary based on the architecture you built the toolchain for. Refer below for updating your PATH -

For riscv, add $AKAROS_TOOLCHAINS/riscv-ucb-akaros-gcc/bin to your PATH.
For x86_64, add $AKAROS_TOOLCHAINS/x86_64-ucb-akaros-gcc/bin to your PATH.
For x86_64 native, add $AKAROS_TOOLCHAINS/x86_64-ucb-akaros-gcc-native/bin to your PATH.

Just to double check everything installed correctly, you should be able to run x86_64-ucb-akaros-gcc from your shell.

Now, you have a cross compiler ready, and you can start to build Akaros.

3.2 Kernel

cd back into the repo root.

Like the cross compiler, the kernel has its own Makelocal.

$ cp Makelocal.template Makelocal

This file is used to set up custom make targets that are not part of the default Makefile, but fit nicely into your personal workflow. This file is not under version control and can be made to contain just about anything.

Now you're ready to build the kernel:

$ make

So the kernel built, but you can't do much with it, and you probably have no programs.

Notice that we didn't have to set the ARCH variable this time. The make system knows what architecture we are set up for and will always build for that architecture until a new ARCH is selected (i.e. via make ARCH=xxx defconfig etc.)

3.3 Userspace

First, you'll need to build a few common applications and libraries:

$ make apps-install

Then you can build the tests and small utility programs:

$ make tests

You now have programs and libraries, and need to put them in KFS. To do this, we provide a fill-kfs make target.

$ make fill-kfs

The fill-kfs target copies your cross compiler's shared libraries and all test binaries into the first "KFS/Initramfs path" you set during configuration (or kern/kfs/lib if you just kept the default).

Now that you've changed the contents of KFS's source, remake the kernel. You should see something like the following before the kernel links. If you don't see this, then you probably didn't actually fill KFS properly.

	Building initramfs:
	Adding kern/kfs to initramfs...

3.4 Building and Loading a Virtual Machine Image

At this point, you probably have a runnable kernel with programs in KFS. It should be sitting at obj/kern/akaros-kernel. When running in a VM, you can either run the kernel directly from qemu, or put it in a virtual machine image file.

If you don't want to bother with the image, skip this section. I tend to run my images off an image file, since qemu acts more like hardware (as far as multiboot goes). The downside is the boot up is slower, especially if you have a large kernel (>100MB). It also takes some effort to set up the VM image.

If you are still reading, you'll need an image file that looks like a hard disk to boot qemu off of. I put one similar to mine at: http://akaros.cs.berkeley.edu/files/hdd268mb.img

It's around 268MB (256MiB, or whatever). If you want to make your own, check out Documentation/howtos/make-bootable-grub-hdd.txt. That's actually the original document I made back when I first figured it out back in 2009, which was updated again in 2013. In between, I wrote it up online at http://www.omninerd.com/articles/Installing_GRUB_on_a_Hard_Disk_Image_File, which has some other tidbits in the comments. Both methods still use grub1.

Anyway, I put that img in AKAROS-ROOT/mnt/, and make a folder next to it: AKAROS-ROOT/mnt/hdd. mnt/hdd is the mount point where I mount hdd.img (Note I don't call it hdd64mb.img on my dev machine).

Personally, I always have hdd.img mounted. Some of the other devs have make targets that mount and umount it. Whenever I reboot my development machine, I run a script (as root) that mounts the image file and sets up a few things for networking. I put a script I use for this in scripts/kvm-up.sh. You'll likely want to copy it to the directory above the akaros root directory and edit it accordingly. Feel free to comment out the networking stuff. That's for using networking in qemu.

Now that your image file is mounted at mnt/hdd, you'll want to copy your freshly built kernel to the root of the image. I have a make target in my makelocal for this, so that whenever I do a make kvm, it builds the kernel and copies it to my hdd.img.

I added edited versions of my KVM (and USB) make targets to the Makelocal.template. Uncomment the KVM one (at least).

Incidentally, I also have the following in my Makelocal, so that make (and make all) also make kvm:

all: kvm

Now, make kvm. You should be able to see the new kernel in mnt/hdd/ (do an ls -l and check the timestamp).

3.5 Running Qemu

Here is the command I use to run qemu/kvm. It's evolved over the years, and it will vary based on your linux distribution. Don't run it just yet:

$ qemu-system-x86_64 -s -enable-kvm -cpu kvm64 -smp 8 -m 4096 -nographic -monitor /dev/pts/3 -net nic,model=e1000 -net user,hostfwd=tcp::5555-:22 -net dump,file=/tmp/vm.pcap -drive file=mnt/hdd.img,index=0,media=disk,format=raw

If you skipped making a virtual machine image or want to run the kernel directly without emulating a disk, replace the "-drive" parameter (all the way to format=raw) with "-kernel obj/kern/akaros-kernel".

The -monitor is the qemu monitor, which is a CLI for qemu. Pick a tab/terminal/pty in Linux that you will only use for qemu monitoring, and enter 'tty'. Whatever it tells you, put in place of /dev/pts/3. I've been using the same tab for about 4 years now. In that tab, enter 'sleep 999999999'. Qemu will still access it, but you won't have to worry about bash trying to handle your inputs.

-nographic allows qemu to work in the terminal you run qemu from, instead of spawning off a fake cpu crt/monitor.

The command as written uses qemu's user networking. It's emulated and a little slow. The example I have alo forwards port 5555 on the host to port 22 on the guest. Customize it according to your needs.

Another option for networking is to set up a tun/tap device. I use this on some machines, and the kvm-up script has some commands to set it up. It's tricky, and may vary for your distribution. If you do use the tun/tap networking, replace the "-net user" section with:

-net tap,ifname=tap0,script=no

The "-net dump" option saves a pcap trace of the network traffic. This is very useful for debugging, but probably not needed for most people.

Feel free to pick different values for the number of cpus and RAM (8 and 4096 in the example).

Once you finally run it, you can stop the VM by entering 'q' to the qemu monitor (or just killing the process).. Other help commands from the monitor include 'info cpus', 'info registers', 'x', and 'help'.

In more recent versions of qemu, CTRL-C will not get sent to the guest; instead it will kill the VM. If this gets annoying, you can remap "interrupt" to something other than CTRL-C in the terminal where you run qemu:

$ stty intr ^]

To change it back:

$ stty intr ^c

3.6 Running on Hardware

I have a few bootable USB sticks with grub set up to run Akaros. The make usb target (example in Makelocal.template) will copy freshly made kernels to your USB device. You'll need to adjust those paths according to your distro. My usb sticks are usually /dev/sdc, for instance (some odd USB device in the last couple of years has taken over /dev/sdb. Probably something to do with udev changing over the years).

Anyway, you'll need to mess around a bit to get that working. Or I can dd one for you (I have 4GB disks in my office that I use). If you make your own, the critical part is getting grub to pick the right device (from what I remember), and its fairly similar to installing grub on any old hard drive (since it's just a bloc device). Much easier than a hard disk image file.

3.7 Hello World

So now you can run the kernel. It's time to edit a program (or make your own). In this, I'll go through my workflow for making changes.

$ vi tests/hello.c
(edit, save)

$ make tests
(new version in obj/tests/hello)

$ make fill-kfs
(updates kfs)

$ make
(rebuilds kernel with the new KFS)

$ qemu...

(following commands are in Akaros)
Shift-G (to get to the kernel monitor)

ROS(Core 0)> bb (to run busybox)

/ $ hello
(Should print your message)

3.8 Other Dev Workflow Stuff

One thing to note is that while we use dynamic linking for libc, parlib libraries are statically linked with applications. In fact, nowadays all Akaros programs need to be linked againt parlib (used to be that single-core processes (SCPs) didn't need it).

The makefiles won't notice if you change a file in parlib and then remake a binary. So if you edit user/parlib/uthread.c for example, tests/pthread_test won't get rebuilt. Here's what I do:

$ vi user/parlib/uthread.c (make awesome change)

$ touch tests/pthread_test.c ; make tests

This will force the rebuild of pthread_test. Older, untouched binaries (e.g. block_test), won't get rebuilt. I actually want this in some cases (different versions of parlib when I'm running certain tests). Anyway, just pay attention to what you're building. There's not much output in the console, so you should be able to see what's going on all the time. (unlike when building glibc...).

Oh, and don't forget to:

$ make fill-kfs

to make sure you run the new pthread_test.

Additionally, when switching between 32 and 64 bit x86, make objclean before filling KFS. This is the easiest way to make sure you get the appropriate libraries loaded in KFS.

Early on as a dev, there are lots of times where you accidentally don't run the right program (or kernel) and won't understand why your change isn't happening. A few printk("WTF\n")'s later, you realize you didn't have the hdd.img mounted, or you didn't fill KFS, or you didn't relink your binaries, or you forgot to save all files in vi (and not just the current buffer). But after doing a couple hello worlds, you're set.

Alternatively, you could have a make target to run qemu, which also touches all binaries (or otherwise enforces a rebuild), auto-fills KFS, remakes the kernel, and mounts/copies/unmounts your hdd.img. Personally, I like to keep track of what is going on under the hood, esp if I want to do something a little differently (like with testing ext2, having different versions of parlib with some binaries, or being picky about my mount/umounts).

RISCV

TODO.

For now, you need a 64 bit distro to build the RISCV stuff, so I don't do it very often. I'll eventually sync up with Andrew and we'll get this part sorted out.

Other Developer's Stuff

Nothing for now...

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

GETTING_STARTED.md

GETTING_STARTED.md

Getting Started with Akaros

Contents

3.1 Cross compiler (and glibc)

3.2 Kernel

3.3 Userspace

3.4 Building and Loading a Virtual Machine Image

3.5 Running Qemu

3.6 Running on Hardware

3.7 Hello World

3.8 Other Dev Workflow Stuff

Files

GETTING_STARTED.md

Latest commit

History

GETTING_STARTED.md

File metadata and controls

Getting Started with Akaros

Contents

3.1 Cross compiler (and glibc)

3.2 Kernel

3.3 Userspace

3.4 Building and Loading a Virtual Machine Image

3.5 Running Qemu

3.6 Running on Hardware

3.7 Hello World

3.8 Other Dev Workflow Stuff