linux makefile

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Introduction to Linux and

Makefiles

Software Engineering 3K04/3M04

October 17, 2005Prepared by M. Kinsner



What is Linux?

• An operating system, in many ways likeWindows and MacOS

• Free – can download and installed fromthe Internet

• Countless software packages for free, and

most very easy to install/uninstall



Should everybody use Linux?

• Certainly not

– Linux better for some people, and some tasks

• Linux great for: – People that enjoy “playing” with computers

– Programming

– Many Engineering tasks



Should everybody use Linux? (2)

• Linux NOT good for:

– Those who have trouble using Windows

– People who only want to type assignments

– Playing games

– Companies whose staff aren’t computer

whizzes



What is a Linux Distribution

• Collection of software prepared by acompany or organization (e.g. Red Hat)

• Central elements of Linux (kernel,standard programs) are almost the samebetween distributions

• A distribution (collection of programs) willusually have a specific purpose in mind:

– Desktop computer

– Network router/firewall



How to acquire Linux

• Easiest way:

– CD-based distribution (e.g. Knoppix,

Mandrake Move) – download CD from Web – Runs from CD and uses only RAM memory,

not the hard disk

– Take the CD out of computer, restart, and notrace of Linux



How to acquire Linux (2)

• Faster, but more dangerous approach:

– Install Linux to your hard disk

– Much faster to use than running from CD – Easy to damage an existing Windows install

during the Linux install process

– Recommend:• Install on an old computer, or on one where you

can afford to damage Windows

• Get help from an experienced friend



How to acquire Linux (3)

• A middle-ground solution = CYGWIN

• Installs within Windows, and allows you to

use a Linux shell and many Linux utilitiesincluding the compilers from withinWindows

• Not really Linux, but a collection of Linuxprograms built to work under Windows – very useful!



Now for some examples…

• Examples of why Linux is useful for

Electrical and Computer Engineeringstudents



C Compiler

• Free, and installed by default

• One of the oldest and most stable

compilers• Very powerful, with multitude of options

• Called: gcc



Compiling programs

• At first glance, harder to use thanconventional graphical compilers

• There are graphical frontends, but theeasiest way to get started is with theconventional command line

• Later we will explore Makefiles, whichgreatly simplify the compilation of programs



Compiling programs (2)

• gcc codeFile1.c -o outputFileName

• Run the compiled program by typing:

./outputFileName

- outputFileName is the “executable” program




• To compile multiple files into one project:

gcc codeFile1.c codeFile2.c -o outputFileName

- Adding multiple filenames is similar to addingfiles to a “Project” in a graphical developmentenvironment




• Some useful options:

• Debug symbols: -g

gcc –g codeFile1.c -o outputFileName

– Allows program to be debugged with adebugger such as gdb

• All warnings: -Wallgcc –Wall codeFile1.c -o outputFileName

– Provides extra warnings, useful for trackingdown some bugs



Editors

• Linux has many powerful text editors,loved by programmers around the world – Graphical editors are available

– Most powerful are VIM and EMACS (non-graphical)• Both have steep learning curves, and are nothing

like Windows editors

• Take days of frustration to learn how to do simple

tasks, but once good at using, unbelievablypowerful

• Huge debates on which is better, but if you decideto learn one, VIM is generally considered best for

programming



Other advantages for power users

• Most existing programming languages areavailable under Linux

• Many very powerful scripting languagesavailable such as TCL/TK

• Utilities make tasks that would be hard inother operating systems very easy

• Command line shells very powerful at thehands of an experienced user



Want more information?

• IEEE Student Branch Linux Crash Course

– You get 3 hours of hands-on introduction

– Take home a CD-based Linux distribution

• Countless resources on the Web forgetting started with Linux – many of thefree tutorials are quite good



Makefiles

• A Makefile is the configuration file used bya standard program called “Make”

• Make is like a project manager in agraphical development environment, butincludes many extra features

• Allows an entire project to be intelligently built with one command on the commandline



Makefiles (2)

• What do we mean by “intelligent” buildingof a program?

– For small programs, we don’t care aboutcompilation time – compiling and building anassignment doesn’t take long

– When building a large project, such as an

operating system, the Make utility helps byrecompiling only the files that have changedsince the last compilation



Dependencies

• Sometimes one file depends on anotherfile

– e.g. a C file depends on its header files

– If a header file changes, the C files that

#include that header file should berecompiled to take into account the changesto the header



Dependencies (2)

Final executable file(MyProject.exe)

main.o interface.o

main.c interface.h interface.c



Dependencies (3)


main.o interface.o




Dependencies (4)


main.o interface.o




A Simple Makefile “Rule”

hello: hello.c

gcc hello.c –o hello

• Save this text as name “Makefile” in thesame directory as the source code

• To build the project, type “make”

• Result is an executable named hello

Dependency line – hellodepends on hello.c

Command to turn hello.c into hello



A Simple Makefile (2)

hello: hello.c

gcc hello.c –o hello

• If hello file exists, and the file creationtime is newer than hello.c, what should

“make” do? – Does nothing, since there have been no

changes to hello.c since the last time that thehello executable was created



Generic form of a rule

target: prerequisite1 prerequisite2 …

command to make target

– Target is the output file

– Prerequisites are the files that are needed bytarget (and that can cause target to be

recompiled if they change) – Command is the actual command to turn the

prerequisites into the target



Multiple TargetsFinal executable file

(MyProject.exe)

main.o interface.o


MyProject: main.o interface.o

gcc main.o interface.o –o MyProject

main.o: main.c interface.h

gcc –c main.c –o main.o

interface.o: interface.c interface.h

gcc –c interface.c –o interface.o



Multiple Targets (2)



main.o: main.c interface.hgcc –c main.c –o main.o



• How does make know which target is theprimary one?

– First target listed in the file is the master






main.o: main.c interface.hgcc –c main.c –o main.o



• Can make non-master targets by typing,for example:

make main.o





gcc main.o interface.o –o MyProjectmain.o: main.c interface.h

gcc –c main.c –o main.o



• If interface.h is changed and saved, Makewill discern that both main.o andinterface.o need to be recompiled,followed by a build of MyProject from thenew main.o and interface.o



The “clean” target

• Used to remove object files that take up harddisk space

• In the Makefile:

clean:

rm –rf ./*.o

To run make with this target, type:

make clean



Variables

• In a large makefile, good idea to usevariables to make later changes easy

– For example, rather than typing “gcc” in thecommand part of every rule, create a variableat the top of the Makefile:

COMPILER = gcc

• Commands can then say:

${COMPILER} sourceFile.c –o executableFile



Variables (2)

• Our earlier example using a variable:

COMPILER = gcc


${COMPILER} main.o interface.o –o MyProject

main.o: main.c interface.h

${COMPILER} –c main.c –o main.o


${COMPILER} –c interface.c –o interface.o



Only the beginning…

• We won’t cover more advanced topics, butmakefiles can do much more, such as:

– Automatically figure out what a file’sdependencies are (in cooperation with gcc)

– Have targets to install the program, and to doother non-compilation tasks

– Configure a program’s compilation based onthe libraries currently installed on the system

– And much more…



Resources

• There are resources on the Web, such as: – http://www.eng.hawaii.edu/Tutor/Make/index.html

– http://www.opussoftware.com/tutorial/TutMakefile.htm

• A good book published by O’Reilly named:

– GNU Make

• If you have Linux installed, there are manyexamples on your system since almost everyLinux program has a Makefile

http://www.eng.hawaii.edu/Tutor/Make/index.html

http://www.opussoftware.com/tutorial/TutMakefile.htm

http://www.opussoftware.com/tutorial/TutMakefile.htm

http://www.eng.hawaii.edu/Tutor/Make/index.html

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