INSTALL-xv6.md

Install Notes

To get xv6 up and running on your machine, you'll need a few tools installed. Here, we'll walk you through what you need to do.

The xv6 Source Code

To obtain the xv6 source code, just clone it from github:

prompt> git clone https://github.com/mit-pdos/xv6-public
loning into 'xv6-public'...
remote: Enumerating objects: 13974, done.
remote: Total 13974 (delta 0), reused 0 (delta 0), pack-reused 13974
Receiving objects: 100% (13974/13974), 17.15 MiB | 2.73 MiB/s, done.
Resolving deltas: 100% (9534/9534), done.
prompt> cd xv6-public

There! Now you have completed the easiest part.

MacOS Build Environment for xv6

To play with xv6 on a Mac, you'll need to install two pieces of software. The first is the qemu machine emulation environment.

To learn more about what emulation is, read this page. The short story is that an emulator is just another computer program, but one that is a realistic facsimile of a particular computer system. In this case, we'll use qemu to pretend we are running an x86 computer system; on this pretend x86 system, we'll boot our xv6 kernel.

Now you might ask: why not just run xv6 on a real machine? You could do that, but it would make running and debugging xv6 slower and more painful. With a realistic emulator like qemu, you can quickly run your kernel but not have the pain of rebooting the actual system you are using. Further, if you make a mistake, your entire machine doesn't lock up, just the emulator, which you can exit or kill. It just makes your life much better than doing the real thing.

To install qemu on a Mac, just do the following:

prompt> sudo port install qemu

This will take a little while, so pour yourself a cup of coffee and enjoy.

This command assumes you have MacPorts installed. If you don't, go to the MacPorts install page and follow instructions first.

Th command further assumes that the path to port (usually /opt/local/bin) is in your path. You should probably add this directory to your path anyhow; the qemu software will get installed there too.

When finished, you should be able to run the qemu software. To run the x86 version (which is what is needed for xv6), type the following command:

prompt> qemu-system-x86_64 -nographic

This will run the qemu emulator, but with no kernel to boot! Alas, not that useful.

To quit qemu, type C-a x (that is, hold down control and while doing so, press a, then let go of control, then press x).

The second piece of software you'll need is the gcc cross-compilation toolchain. To install these pieces of software, type:

prompt> sudo port install i386-elf-gcc gdb

When you're done, you're ready to try to build and run xv6. Change into the xv6-public directory, and type:

prompt> make TOOLPREFIX=i386-elf- qemu-nox

If all has worked well, you'll see something like:

Booting from Hard Disk..xv6...
cpu1: starting 1
cpu0: starting 0
sb: size 1000 nblocks 941 ninodes 200 nlog 30 logstart 2 inodestart 32 bmap
sta8
init: starting sh
$

The $ is the shell command prompt: who-hoo!

Remember to type C-a x to quit the emulation.

A couple of quick edits might be useful to the xv6 Makefile. First, change the TOOLPREFIX line to uncommented, and to look as follows:

TOOLPREFIX = i386-elf-

This will all you to type the following simpler make command:

prompt> make qemu-nox

Note: qemu-nox is the way this Makefile allows you to build and run xv6 without spinning up a separate window, but rather running qemu directly within your terminal, which we prefer. If you want the new window to pop up instead, just run make qemu.

We also usually edit the Makefile to use one CPU (not two). Look for the line that says:

CPUS := 2

and change it to:

CPUS := 1

Now, time to go do the projects!

Linux

TBD.