Introduction

This file contains information for installing and running xv6. Please read this for your respective operating system if you were not able to previously obtain xv6 and get it running in the QEMU emulator. I strongly recommend following the instructions for linux (thus running on a Linux machine or within virtual box).

Task 1 - Install an emulator and Build xv6

For this lab we need to install an emulator that can emulate an operating system. We are using an emulator because we do not want to dedicate our personal machines to installing xv6 (although we could!). You will install this emulator on your local machines.

1. The first step is to install QEMU by navigating to https://www.qemu.org/download/#linux. You may follow the directions here, or I have highlighted them below for several platforms.

Linux or Linux VM (the easiest choice!)

• Run the following on the terminal: sudo apt-get install qemu-system-x86

See: https://www.qemu.org/download/#linux for the official instructions.

Windows 7 or earlier. (probably not many of these around anymore)

(If you have Windows 10, you can skip these steps and navigate below to ‘Install xv6’)

• Download the appropriate binary from: https://www.qemu.org/download/#windows
  • Run the installer with the default settings.
  • You can launch the executable to test it out (e.g. from C:Files-system-x86_64w.exe)
    • However, we do not have xv6 installed quite yet! Keep reading.

See: https://www.qemu.org/download/#windows for the official instructions.

Modern Macs

1. Install Homebrew (if not already installed)
2. Install QEMU: brew install qemu

See: https://www.qemu.org/download/#macos for the official instructions.

Building from source

If none of the above options work, you can try to build from source for your architecture. This is a good skill to have, but may take some time and additional configuring. See https://www.qemu.org/download/#source for directions.

Task 2 - Install xv6

(The official instructions are here: https://pdos.csail.mit.edu/6.828/2017/xv6.html)

We are going to run xv6 in an emulator–specifically the QEMU emulator that you built above. What this means is we now need to compile the xv6 operating system into a format that our emulator understands. If you are using linux, this is relatively straight forward. If you are not using Linux, then we need to ‘cross-compile’ the binary.

Cross-compiling means to generate a binary file that is not necessarily for our native platform. That is, if you are windows normally when you compile, executables are generaetd that run on windows. So what is different if we are on windows, is we want to generate a binary that actually is of the ELF format (which windows does not understand, but our emulator will).

Proceed to the directions below.

Obtaining xv6

xv6 lives in a github repository for the MIT operating systems class.

• Obtain the repository here: git clone https://github.com/mit-pdos/xv6-public.git or git clone git@github.com:mit-pdos/xv6-public.git

Modifying the Makefile for a recent GCC

This most likely applies to you if you’re building on WSL2 (and keep the Linux within updated), macOS with Homebrew, or a recent Linux distro. So almost always.

If you’re building with a recent version of GCC, after cloning xv6, update the Makefile as follows

Locate the line containing

CFLAGS = -fno-pic -static -fno-builtin -fno-strict-aliasing -O2 -Wall -MD -ggdb -m32 -Werror -fno-omit-frame-pointer

(should be line 79) and change it to

CFLAGS = -fno-pic -static -fno-builtin -fno-strict-aliasing -O2 -Wall -MD -ggdb -m32 -Werror -fno-omit-frame-pointer -Wno-stringop-overflow -Wno-error=array-bounds -Wno-error=infinite-recursion

Save the Makefile.

Building xv6 on Linux or on a Linux VM (one again the simplest path)

1. Once the repository has downloaded run navigate inside the public-xv6 folder.
2. Type make within the public-xv6 repository you have downloaded and wait a few seconds for the OS to compile.

Building xv6 on Mac

3. Install a GCC cross-compiler: brew install i686-elf-gcc

4. Clone xv6, cd xv6-public

5. Edit the Makefile and find the line containing TOOLPREFIX=. It may be commented out, uncomment it. Make sure that it says the following:

   TOOLPREFIX = i686-elf-

6. (Make sure to also update CFLAGS as shown above.)

7. make and make qemu-nox

To use gdb with xv6, i.e., make qemu-nox-gdb, you need a version of gdb that understands ELF binaries. Install an ELF-compatible gdb, brew install i386-elf-gdb. The installed binary is i386-elf-gdb.

Building xv6 on Windows

If you have Windows 10 64-bit follow the directions below.

• Follow the instructions here: https://gcallah.github.io/OperatingSystems/xv6Install.html (I have also written them below)

1. From within Bash on on windows(https://www.howtogeek.com/249966/how-to-install-and-use-the-linux-bash-shell-on-windows-10/) type the following: sudo apt-get update && sudo apt-get install git nasm build-essential qemu gdb
2. Then within the Makefile in the directory modify QEMUOPTS = -hdb fs.img xv6.img -smp $(CPUS) -m 512 $(QEMUEXTRA) to QEMUOPTS = -hdb fs.img xv6.img -smp $(CPUS) -m 512 $(QEMUEXTRA) -display none

If you have Windows 7 or earlier, you will need to install cygwin or some other terminal, and follow similar instructions to the Mac.

After building xv6 – Actually running xv6

Okay great, what did we achieve? After building xv6 you should see the fs.img and xv6.img This is an ‘image’ of your operating system. In other words, you whole operating system wrapped up into a single file. The emulator (qemu) will then boot up the operating system from within this image file, and host it in a virtualized environment.

Okay, final step from whatever terminal you are working in.

• If you are working in Unix, or on Mac, it should be as simple as typing make qemu-nox and the operating system will begin in your current shell! (If for some reason that does not work, you can try make qemu)

• If you are running in the Windows Linux subsystem run: make qemu fs.img

• To exit XV6, press Ctrl-a immediately followed x to terminate the QEMU emulator.