3. Makefile Tutorial¶

Warning

Make sure to stop your Amazon instances! We only have $150 of credits and we need it to last through Homework 7. You may need to take a long break during a homework, or you might take longer to read about something on google/stackoverflow; remember to stop your instance and restart it when you are ready to continue.

In this course, we are advocating that you use a command-line workflow when you can. Of course, you can use your favorite IDE to compile your programs, (in fact, we will be using Xilinx’s IDE later in the course). Nonetheless, learning how to work from the command line is a great skill to have and can boost your productivity at times. It is great to be able to automate rebuilds so that you do not need to manually click a large number of buttons in a GUI or type a large number of commands to rebuild an output. It also serves to document how to rebuild the output so you aren’t in danger of forgetting and needing to figure it out again later.

With that, following is a short tutorial on using make to compile your C programs. If you know how to write a Makefile you can skip this section.

Clone the ese532_code repository using the following command:

git clone https://github.com/icgrp/ese532_code.git

If you already have it cloned, pull in the latest changes using:

cd ese532_code/
git pull origin master

You will find the hw1 code in the hw1 directory. The code for this tutorial is under is under hw1/tutorial.

The program has the following characteristics:

main function in App.c,
function definitions in individual .c files and declarations in App.h,
produces Output.bin output file.

These are typical characteristics of a C program, and we will show how Makefile manages compilation and cleanup of this program.

Let’s start with getting the object file of App.c. Create a file called Makefile in the extracted folder of the source code. Add the following rules in the Makefile and execute the command make in your terminal.

App.o: App.c App.h
	gcc -c App.c -o App.o

clean:
	rm -f App.o

You should now see that there is a file called App.o in your source folder. If you execute make again, it tells you make: `App.o' is up to date., since there is nothing new to compile. You can now execute make clean to remove the App.o file.

From the above example, we can learn the Makefile syntax:

targets : dependency1 dependency2 ...
   <tab> command
   <tab> command
   <tab> command

App.o is our target and App.c is the dependent file needed to produce the object file. The gcc compile command goes after that preceded by a TAB. Whenever there is change in the dependent files, make will recompile this rule.

Caution

The commands must start with a TAB character!

We don’t have an actual binary that we can execute yet. You probably have figured out—we need the object code of the other .c files and link them together in the final binary. You could write multiple rules following what we learned:

App.o: App.c App.h
	gcc -c App.c -o App.o

Compress.o: Compress.c App.h
	gcc -c Compress.c -o Compress.o

Differentiate.o: Differentiate.c App.h
	gcc -c Differentiate.c -o Differentiate.o

Filter.o: Filter.c App.h
	gcc -c Filter.c -o Filter.o

Scale.o: Scale.c App.h
	gcc -c Scale.c -o Scale.o

all: App.o Compress.o Differentiate.o Filter.o Scale.o
	gcc App.o Compress.o Differentiate.o Filter.o Scale.o -o App

clean:
	rm -f App.o Compress.o Differentiate.o Filter.o Scale.o App Output.bin

Here we are creating object files for each of the functions we have, and then linking them together in a make target called all. In addition, we updated the clean target to include the new .o files, the App executable and the output file. You can now execute ./App.

This concludes a basic introduction to writing a Makefile. You can see the Makefile we wrote is verbose. There are lots of tricks you can do to “make” it concise, e.g. implicit rules, wildcards etc. We encourage you to try those by yourselves. Following are some resources that are helpful:

Warning

Make sure to stop your Amazon instances! We only have $150 of credits and we need it to last through Homework 7. You may need to take a long break during a homework, or you might take longer to read about something on google/stackoverflow; remember to stop your instance and restart it when you are ready to continue.

ESE532 Handouts Fall 2020

3. Makefile Tutorial¶