The Makefile utility
(Extract from the slides by
Terrance E. Boult
http://vast.uccs.edu/~tboult/)
Motivation
Small programs single file
“Not so small” programs :
– Many lines of code
– Multiple components
– More than one programmer
Motivation – continued
Problems:
– Long files are harder to manage
(for both programmers and machines)
– Every change requires long compilation
– Many programmers can not modify the
same file simultaneously
– Division to components is desired
Motivation – continued
Solution : divide project to multiple files
Targets:
– Good division to components
– Minimum compilation when something is
changed
– Easy maintenance of project structure,
dependencies and creation
Project maintenance
Done in Unix by the Makefile mechanism
A makefile is a file (script) containing :
– Project structure (files, dependencies)
– Instructions for files creation
The make command reads a makefile,
understands the project structure and
makes up the executable
Note that the Makefile mechanism is not
limited to C programs
Project structure
Project structure and dependencies can be
represented as a DAG (= Directed Acyclic
Graph)
Example :
– Program contains 3 files
– main.c., sum.c, sum.h
– sum.h included in both .c files
– Executable should be the file sum
sum (exe)
main.o sum.o
main.c sum.h sum.c sum.h
makefile
sum: main.o sum.o
gcc –o sum main.o sum.o
main.o: main.c sum.h
gcc –c main.c
sum.o: sum.c sum.h
gcc –c sum.c
Rule syntax
main.o: main.c sum.h
Rule
gcc –c main.c
tab
dependency action
Equivalent makefiles
.o depends (by default) on corresponding
.c file. Therefore, equivalent makefile is:
sum: main.o sum.o
gcc –o sum main.o sum.o
main.o: sum.h
gcc –c main.c
sum.o: sum.h
gcc –c sum.c
Equivalent makefiles - continued
We can compress identical dependencies
and use built-in macros to get another
(shorter) equivalent makefile :
sum: main.o sum.o
gcc –o $@ main.o sum.o
main.o sum.o: sum.h
gcc –c $*.c
$@ name of the target
$* name of each target without extension
make operation
Project dependencies tree is constructed
Target of first rule should be created
We go down the tree to see if there is a target
that should be recreated. This is the case when
the target file is older than one of its
dependencies
In this case we recreate the target file according
to the action specified, on our way up the tree.
Consequently, more files may need to be
recreated
If something is changed, linking is usually
necessary
make operation - continued
make operation ensures minimum
compilation, when the project structure is
written properly
Do not write something like:
prog: main.c sum1.c sum2.c
gcc –o prog main.c sum1.c sum2.c
which requires compilation of all project when
something is changed
Another makefile example
# Makefile to compare sorting routines
BASE = /home/blufox/base
CC = gcc
CFLAGS = -O –Wall
EFILE = $(BASE)/bin/compare_sorts
INCLS = -I$(LOC)/include
LIBS = $(LOC)/lib/g_lib.a \
$(LOC)/lib/h_lib.a
LOC = /usr/local
OBJS = main.o another_qsort.o chk_order.o \
compare.o quicksort.o
$(EFILE): $(OBJS)
@echo “linking …”
@$(CC) $(CFLAGS) –o $@ $(OBJS) $(LIBS)
# @command suppresses the echoing of the command
$(OBJS): compare_sorts.h
$(CC) $(CFLAGS) $(INCLS) –c $*.c
# Clean intermediate files
clean:
rm $(OBJS)
Example - continued
We can define multiple targets in a makefile
Target clean – has an empty set of
dependencies. Used to clean intermediate
files.
make
– Will create the compare_sorts executable
make clean
– Will remove intermediate files
Make: Advanced Options
Pattern rules
– Uses a pattern in the target with % as wildcard
– Matched % can be used in dependencies as well
– Simple Example:
%.o : %.cc
<tab>command …
Pattern rules with automatic variables
– $< first dependency
– Advanced Example:
%.o : %.cc
<tab>$(CC) $(CCFLAGS) –c $< $(INCPATHS)
Make: A Simple Example
CC=g++ # Compiler to use
FLAGS=-g # Compile flags
MASLAB_ROOT=maslab-software # Maslab software root directory
LIB_DIR=$(MASLAB_ROOT)/liborc # orc-related library directory
INC_DIR=$(MASLAB_ROOT)/liborc # orc-related include directory
LIBS=-lm –lpthread -lorc # Library files
# note –l gcc option
all : helloworld
helloworld.o : helloworld.cc
$(CC) $(FLAGS) –c $*.cc –o $@ -I$(INC_DIR)
# note –I gcc option
helloworld: helloworld.o
$(CC) -o helloworld helloworld.o $(LIBS) –L$(LIB_DIR)
# note –L gcc option
clean:
rm -f *.o helloworld
The real Problem
How do we handle platform specific issues?
– Providing a different Makefile for each architecture
– Using Autoconf, Automake and Libtool
The installer needs only
– Bourne shell
– C compilers
– Make program
Some advantages when using GNU
autotools
The installation of a program is straightforward:
./configure; make; make install
This procedure checks for system parameters, libraries,
location of programs, availability of functions and writes
a Makefile
./configure supports many options to overwrite
defaults settings
– /configure --prefix=… (default /usr/local)
GNU autoconf
Source Code configure.ac
(configure.in)
aclocal
autoscan autoconf
configure.scan configure
GNU automake
Makefile.am Makefile.in
automake configure
Makefile
configure.ac
dnl Comment … …
AC_INIT(project_name, 1.2.8)
AM_INIT_AUTOMAKE
AC_PROG_CC it locates the C (C++) compiler
AC_HEADER_STDC it checks for standard headers
AC_CHECK_HEADERS(sys/time.h /header.h) it checks for headers availability
AC_CHECK_LIB(crypto SSLeay_version) it checks for libraries availability
AC_CHECK_FUNCS(ctime) it checks for functions availability
AC_PROG_INSTALL it checks for BSD compatible install utility
AC_OUTPUT
Makefile.am
bin_PROGRAMS = foo
foo_SOURCES=foo.c foo.h
noist_PROGRAMS=test
(make compiles, make install does nothing)
EXTRA_DIST=disclaimer.txt
Example
foo.c :
#include <stdio.h>
main()
{
printf(“Cum grano salis\n");
}
Makefile.am :
bin_PROGRAMS = foo
foo_SOURCES = foo.c
configure.ac :
AC_INIT(foo.c)
AM_INIT_AUTOMAKE(latin_words, 0.9)
AC_PROG_CC
AC_HEADER_STDC
AC_PROG_INSTALL
AC_OUTPUT([Makefile])
Summary
Source Code, configure.ac, Makefile.am
autoscan; aclocal; autoconf
Create NEWS README AUTHORS ChangeLog
automake –add-missing
./configure; make; make dist
Result: project_name-2.10.tar.gz
aclocal.m4 autom4te-2.53.cache ChangeLog config.status
configure.in COPYING install-sh Makefile.am missing NEWS
README AUTHORS autoscan.log config.log configure
configure.scan INSTALL Makefile.in mkinstalldirs code.c
References
GNU Autoconf, Automake, and Libtool
http://sources.redhat.com/autobook/autobook/autobook_toc.html
GNU Autoconf Manual
http://www.gnu.org/manual/autoconf
GNU Automake Manual
http://www.gnu.org/manual/automake
GNU Libtool Manual
http://www.gnu.org/manual/libtool
Learning the GNU development tools
http://autotoolset.sourceforge.net/tutorial.html
The GNU configure and build system
http://www.airs.com/ian/configure/configure_toc.html
GNU macro processor (GNU m4)
http://www.gnu.org/manual/m4-1.4/m4.html
