For this course we will be writing code for a small but complete OS named

CastorOS to implement real$-$world OS mechanisms. CastorOS is an educational

OS that runs on real hardware or as a VM using virtualization $[12].$ In the

course of the assignments we will write code to boot and run CastorOS, and

then add critical system calls to it to implement important OS functionality like

threading, scheduling, and file systems.

We will be running CastorOS using the QEMU emulator $[1]$ that runs the

entire OS inside a userspace process. QEMU emulates $[4]$ real hardware using

code, so the OS runs as if on bare metal. QEMU is available on Linux and

MacOS $,$ and on Windows through WSL $[11].$

In this assigment we set up CastorOS and fill in the code enough to make

it boot into userspace. The OS is missing parts of the Spawn call that is needed

to run applications and pass arguments to them. Booting up the system thus

leads to a crash when the kernel tries to set up the init process. CastorOS's

loader is incomplete and cannot load the program into the process. The loader

also does not have code for copying the process' command line arguments into

its memory. We will implement argument passing so that we can run userspace

processes like shells.

$1$ Setting up the CS$350$ Client

We will be using the

client.py command line tool to interact with the CS$350$

submission server. The tool is a script that we use to retrieve the source, submit

our work, and check the status of our submission.

$1\mathrm{.}1$ Setting Up the Submission Client

We first add our credentials to the

client.py tool. To access the server we need

to add our username and hex magic string to allow the script to authenticate

with the server. The username is our $8-$character UW ID$.$ The magic hex string

is a hex string that we receive via email from

cs$350-$noreply@uwaterloo.ca$.$

We directly modify in a text editor the

client.py Python script provided in the

course website. We change the values of the script's STUDENT and MAGIC variables

from None to our username and magic string respectively. To test whether we

have entered our credentials correctly we run:

$ python

client.py ping

We first use the

client.py ping command to confirm that the submission

server is accessible from our machine. After we ensure we can ping the server

we run

client.py status to ensure we have the proper credentials. If we have

properly added our credentials to the client the server will respond with our

last active submission and our active grade. In this case we have not submitted

anything yet, so there are no active submissions or grades.

$1\mathrm{.}2$ Downloading Castor OS

Next we download the newest version of the CastorOS source:

$ python

client.py download

The command requests CastorOS's source from the submission server and

places it in the current directory. We use tar to unpack the source into a Cas$-$

torOS directory that we will be developing our solutions in$.$

$ tar zxvf castoros$-$latest.tar.gz

The starter code will be in the castoros directory.