Autoconf and automake for libraries

In this article, I explain how to use autotools, also known and the GNU build system, to create portable shared libraries that can be easily built and used in various unix/linux systems.

autoconf/automake

The first we need is to have the functions exported by the library implemented. We need to implement a .c file and a .h file. Lets assume our library offers list manipulation functions. We would then implement list manipulation functions in list.c and define the function prototypes in test.h

Apart from these source files, we need to prepare a couple of other files. These files are as follows :

This file will be converted by autotools to Makefile.am which will be later converted to a Makefile by the configure script for compiling and building the library.

This is the content of our Makefile.am

# General settings
lib_LTLIBRARIES = liblist.la
liblhs_la_SOURCES = list.c test.c
liblhs_la_LDFLAGS = -version-info 1:0:0
include_HEADERS = list.h

# Specify some flags to be passed to the compiler
AM_CFLAGS = -I/some/include/path -L/some/lib/path

# Specify distributable binaries
bin_PROGRAMS = test
test_SOURCES = test.c

# Name of the static library
LDADDBASE = liblist.la

# Specify the libraries to compile our library and the accompanying binaries (change these according to your needs)
LDADD = $(LDADDBASE)  -lcrypto -lcrypt -lkrb5 -lroken -lasn1

If our library had more source files, the name of these files must be added to the liblhs_la_SOURCES and include_HEADERS variables accordingly.

This file will generate the configure script that checks for system resources and prepares for the compilation and building of our library. The configure script

The contents of this file are pretty generic. You just need to customized it by changing in the first section “General stuff”. You may also add checks for particular programs or other dependencies. In our example, we check for the library libmm (memory mapping).

#General stuff
AC_INIT(liblist, 1.0, yourname@yourdomain.com)
AM_INIT_AUTOMAKE(liblist, 1.0)
AC_CONFIG_SRCDIR([list.c])
AC_CONFIG_HEADER([config.h])

# Checks for programs.
AC_PROG_CXX
AC_PROG_CC
AC_PROG_CPP
AC_PROG_INSTALL
AC_PROG_LN_S
AC_PROG_MAKE_SET
AC_PROG_LIBTOOL

# Checks for header files.
AC_HEADER_STDC
AC_HEADER_SYS_WAIT
AC_CHECK_HEADERS([fcntl.h limits.h memory.h stdlib.h string.h strings.h sys/file.h sys/param.h unistd.h])

# Checks for typedefs, structures, and compiler characteristics.
AC_C_CONST
AC_TYPE_UID_T
AC_TYPE_MODE_T
AC_TYPE_OFF_T
AC_TYPE_PID_T
AC_TYPE_SIZE_T

# Checks for library functions.
AC_FUNC_CHOWN
AC_FUNC_FORK
AC_FUNC_MALLOC
AC_FUNC_MMAP
AC_CHECK_FUNCS([ftruncate getpagesize memset munmap strerror])

# Check if libmm is installed and whether the MM_malloc function is defined
AC_CHECK_LIB([mm], [MM_malloc])


AC_OUTPUT([Makefile])

For more information on configure.ac, check my previous article Autotools by example

Now that we have prepared the Makefile.am and the configure.ac files, we need to run autotools to build the Makefile.in file and the configure script.

This script does this job and adds other additional files.

#!/bin/sh
# Function to test and add generic files
function Check_And_Add {
if ! test -f $1
then
    echo Creating New file $1
    touch $1
fi
 
}
 
# Generate aclocal.m4 macros from configure.in
# these M4 macros will be used by autoconf to
# create the configure script
 
aclocal
 
# Generate the configure script
 
autoconf
 
Check_And_Add INSTALL
Check_And_Add COPYING
Check_And_Add NEWS
Check_And_Add README
Check_And_Add AUTHORS
Check_And_Add ChangeLog
 
# Creates a config.h.in, useful when we want the code to depend on
# information provided by configure
 
autoheader
 
# Create Makefile.in from Makefile.am
 
automake -a -c -i --gnu

Now, we can configure and compile the library.

$./configure
$make

Once we checked that the library is compiling fine, we can create a .tar.gz for distribution.

$make dist

Labels: coding, howto, unix