Introduction to Linux and Makefiles

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Introduction to Linux and Makefiles

• Software Engineering 3K04/3M04
• October 17, 2005
• Prepared by M. Kinsner

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What is Linux?

• An operating system, in many ways like Windows
  and MacOS
• Free can download and installed from the
  Internet
• Countless software packages for free, and most
  very easy to install/uninstall

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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

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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 arent computer whizzes

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What is a Linux Distribution

• Collection of software prepared by a company or
  organization (e.g. Red Hat)
• Central elements of Linux (kernel, standard
  programs) are almost the same between
  distributions
• A distribution (collection of programs) will
  usually have a specific purpose in mind
• Desktop computer
• Network router/firewall

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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 no
  trace of Linux

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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

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How to acquire Linux (3)

• A middle-ground solution CYGWIN
• Installs within Windows, and allows you to use a
  Linux shell and many Linux utilities including
  the compilers from within Windows
• Not really Linux, but a collection of Linux
  programs built to work under Windows very
  useful!

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Now for some examples

• Examples of why Linux is useful for Electrical
  and Computer Engineering students

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C Compiler

• Free, and installed by default
• One of the oldest and most stable compilers
• Very powerful, with multitude of options
• Called gcc

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Compiling programs

• At first glance, harder to use than conventional
  graphical compilers
• There are graphical frontends, but the easiest
  way to get started is with the conventional
  command line
• Later we will explore Makefiles, which greatly
  simplify the compilation of programs

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Compiling programs (2)

• gcc codeFile1.c -o outputFileName
• Run the compiled program by typing
• ./outputFileName
• outputFileName is the executable program

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Compiling programs (3)

• To compile multiple files into one project
• gcc codeFile1.c codeFile2.c -o outputFileName
• - Adding multiple filenames is similar to adding
  files to a Project in a graphical development
  environment

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Compiling programs (4)

• Some useful options
• Debug symbols -g
• gcc g codeFile1.c -o outputFileName
• Allows program to be debugged with a debugger
  such as gdb
• All warnings -Wall
• gcc Wall codeFile1.c -o outputFileName
• Provides extra warnings, useful for tracking down
  some bugs

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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,
  unbelievably powerful
• Huge debates on which is better, but if you
  decide to learn one, VIM is generally considered
  best for programming

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Other advantages for power users

• Most existing programming languages are available
  under Linux
• Many very powerful scripting languages available
  such as TCL/TK
• Utilities make tasks that would be hard in other
  operating systems very easy
• Command line shells very powerful at the hands of
  an experienced user

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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 for getting
  started with Linux many of the free tutorials
  are quite good

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Makefiles

• A Makefile is the configuration file used by a
  standard program called Make
• Make is like a project manager in a graphical
  development environment, but includes many extra
  features
• Allows an entire project to be intelligently
  built with one command on the command line

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Makefiles (2)

• What do we mean by intelligent building of a
  program?
• For small programs, we dont care about
  compilation time compiling and building an
  assignment doesnt take long
• When building a large project, such as an
  operating system, the Make utility helps by
  recompiling only the files that have changed
  since the last compilation

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Dependencies

• Sometimes one file depends on another file
• e.g. a C file depends on its header files
• If a header file changes, the C files that
  include that header file should be recompiled to
  take into account the changes to the header

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Dependencies (2)
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Dependencies (3)
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Dependencies (4)
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A Simple Makefile Rule
Dependency line hello depends on hello.c

• hello hello.c
• gcc hello.c o hello
• Save this text as name Makefile in the same
  directory as the source code
• To build the project, type make
• Result is an executable named hello

Command to turn hello.c into hello
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A Simple Makefile (2)

• hello hello.c
• gcc hello.c o hello
• If hello file exists, and the file creation time
  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 the hello
  executable was created

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Generic form of a rule

• target prerequisite1 prerequisite2
• command to make target
• Target is the output file
• Prerequisites are the files that are needed by
  target (and that can cause target to be
  recompiled if they change)
• Command is the actual command to turn the
  prerequisites into the target

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Multiple Targets
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
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Multiple Targets (2)

• How does make know which target is the primary
  one?
• First target listed in the file is the master

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
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Multiple Targets (3)

• Can make non-master targets by typing, for
  example
• make main.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
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Multiple Targets (4)

• If interface.h is changed and saved, Make will
  discern that both main.o and interface.o need to
  be recompiled, followed by a build of MyProject
  from the new main.o and 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
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The clean target

• Used to remove object files that take up hard
  disk space
• In the Makefile
• clean
• rm rf ./.o
• To run make with this target, type
• make clean

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Variables

• In a large makefile, good idea to use variables
  to make later changes easy
• For example, rather than typing gcc in the
  command part of every rule, create a variable at
  the top of the Makefile
• COMPILER gcc
• Commands can then say
• COMPILER sourceFile.c o executableFile

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Variables (2)

• Our earlier example using a variable

COMPILER gcc MyProject main.o
interface.o COMPILER main.o interface.o o
MyProject main.o main.c interface.h COMPILER
c main.c o main.o interface.o interface.c
interface.h COMPILER c interface.c o
interface.o
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Only the beginning

• We wont cover more advanced topics, but
  makefiles can do much more, such as
• Automatically figure out what a files
  dependencies are (in cooperation with gcc)
• Have targets to install the program, and to do
  other non-compilation tasks
• Configure a programs compilation based on the
  libraries currently installed on the system
• And much more

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Resources

• There are resources on the Web, such as
• http//www.eng.hawaii.edu/Tutor/Make/index.html
• http//www.opussoftware.com/tutorial/TutMakefile.h
  tm
• A good book published by OReilly named
• GNU Make
• If you have Linux installed, there are many
  examples on your system since almost every Linux
  program has a Makefile