[SOLVED] Cop4600 ex2: patches, libraries, and makefiles

Overview
In this exercise you will learn about patches, libraries and Makefiles. You will first modify the
patch you created for Project 0. You will then create a static library that will perform a simple
arithmetic operation and finally you will create a Makefile to compile that library.
Structure
The project is broken into three main parts:
1) Modify the patch file from P0.
2) Create a static library.
3) Create a Makefile to re-compile your library.
Patch Files
A patch file is a text file that contains instructions on how to update other files. In Project 0 you
modified a certain file to add your name to the boot message. You then rebuilt the kernel and
saw that your changes were applied successfully (hopefully)! Finally, you created a patch that
contained all the changes. In other words, the patch contained the differences between your
modified source and the original clean source you downloaded. You can read more about patch
files here: https://www.git-tower.com/learn/git/ebook/en/command-line/advanced-topics/diffs.
Here’s an example patch file:
The first 5 lines specify which file to modify. The remainder indicates which lines are removed
and inserted. When applying this patch file to a clean source of your file system, the patch
program will know exactly what to remove and what to add.
Patches are useful because they only keep track of changes. (Imagine if you had to export the
1.4 GB Reptilian image and upload it to Canvas every time you had to submit something!)
For this exercise you will need to do the following:
1. Create a copy of your P0 patch and modify it in a text editor to remove the message you
added in P0 and insert a new one that says “### First Last Name (Exercise 2) ###”.
NOTE: You will apply the patch to the kernel source that already contains the changes
from P0, so the patch file should remove the P0 changes and add the new changes.
2. You will apply the patch by switching to /usr/rep/src/reptilian-kernel and running:
$ git apply ex2.diff
$ make && sudo make install && sudo make modules_install
3. Take a screenshot of the boot sequence showing the modified message.
Libraries
Libraries are simply a collection of previously defined declarations and procedures. If we often
use the same subroutines, we can create a library and use it across all our projects. For example,
we can use a math library to perform matrix multiplication. You can read about different types
of libraries here: http://www.hep.wisc.edu/~pinghc/generate_your_own_library.htm
In this project you will create a simple static library using the following steps:
1. Create mean.c in /home/reptilian/math (You will need to create the math directory):
int mean(int a, int b)
{
return (a + b) / 2;
}
2. Create mean.h in /home/reptilian/math:
#pragma once
int mean(int a, int b);
3. Compile mean.c and create libmath.a:
$ cc -c mean.c
$ ar cr libmath.a mean.o
4. Create test.c in /home/reptilian:
#include <stdio.h>
#include “math/mean.h”
int main()
{
printf(“The average between 3 and 5 is %d
”, mean(3, 5));
return 0;
}
5. Compile and run test.c:
$ cc -o test test.c -L ./math -lmath
$ ./test
6. Take a screenshot of the output.
Makefiles
Makefiles are used to organize code compilation. Earlier in this exercise you manually entered
the commands to create your library… but imagine if you had to compile this and 50 other
programs! In such a circumstance, Makefiles come in handy. A Makefile contains all the
instructions needed to compile programs and can be run with the make command. For this
exercise you will create a Makefile in /home/reptilian/math that will compile the library.
In addition to compiling your code, Makefiles monitor the time stamps of your source files and
only recompile the modules of your code that have changed or depend on modules that have
changed. Your Makefile should build only when necessary and should not build if no
changes are present. Put simply, your Makefile must include dependencies for each rule!
Read about Makefiles here: http://www.cs.colby.edu/maxwell/courses/tutorials/maketutor/
To test it and make sure it works, delete libmath.a and mean.o, then run make. This should
re-create libmath.a and mean.o. Then run make again. It should say libmath.a is up to date.
Submit the Makefile on Canvas (You can add the “.txt” extension if necessary).
Submissions
You will submit the following at the end of this exercise:
⚫ Screenshot of the boot message (boot.png)
⚫ The modified patch file (ex2.diff)
⚫ Screenshot of the library output (lib.png)
⚫ Your Makefile