Update generated configure scripts.

[binutils.git] / etc / configure.info-1

This is configure.info, produced by makeinfo version 4.0 from
./configure.texi.

INFO-DIR-SECTION GNU admin
START-INFO-DIR-ENTRY
* configure: (configure).       The GNU configure and build system
END-INFO-DIR-ENTRY

   This file documents the GNU configure and build system.

   Copyright (C) 1998 Cygnus Solutions.

   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided that
the entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that this permission notice may be stated in a
translation approved by the Foundation.

\x1f
File: configure.info,  Node: Top,  Next: Introduction,  Up: (dir)

GNU configure and build system
******************************

   The GNU configure and build system.

* Menu:

* Introduction::                Introduction.
* Getting Started::             Getting Started.
* Files::                       Files.
* Configuration Names::         Configuration Names.
* Cross Compilation Tools::     Cross Compilation Tools.
* Canadian Cross::              Canadian Cross.
* Cygnus Configure::            Cygnus Configure.
* Multilibs::                   Multilibs.
* FAQ::                         Frequently Asked Questions.
* Index::                       Index.

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File: configure.info,  Node: Introduction,  Next: Getting Started,  Prev: Top,  Up: Top

Introduction
************

   This document describes the GNU configure and build systems.  It
describes how autoconf, automake, libtool, and make fit together.  It
also includes a discussion of the older Cygnus configure system.

   This document does not describe in detail how to use each of the
tools; see the respective manuals for that.  Instead, it describes
which files the developer must write, which files are machine generated
and how they are generated, and where certain common problems should be
addressed.

   This document draws on several sources, including the autoconf
manual by David MacKenzie (*note autoconf overview: (autoconf)Top.),
the automake manual by David MacKenzie and Tom Tromey (*note automake
overview: (automake)Top.), the libtool manual by Gordon Matzigkeit
(*note libtool overview: (libtool)Top.), and the Cygnus configure
manual by K. Richard Pixley.

* Menu:

* Goals::                       Goals.
* Tools::                       The tools.
* History::                     History.
* Building::                    Building.

\x1f
File: configure.info,  Node: Goals,  Next: Tools,  Up: Introduction

Goals
=====

   The GNU configure and build system has two main goals.

   The first is to simplify the development of portable programs.  The
system permits the developer to concentrate on writing the program,
simplifying many details of portability across Unix and even Windows
systems, and permitting the developer to describe how to build the
program using simple rules rather than complex Makefiles.

   The second is to simplify the building of programs distributed as
source code.  All programs are built using a simple, standardized, two
step process.  The program builder need not install any special tools in
order to build the program.

\x1f
File: configure.info,  Node: Tools,  Next: History,  Prev: Goals,  Up: Introduction

Tools
=====

   The GNU configure and build system is comprised of several different
tools.  Program developers must build and install all of these tools.

   People who just want to build programs from distributed sources
normally do not need any special tools beyond a Unix shell, a make
program, and a C compiler.

autoconf
     provides a general portability framework, based on testing the
     features of the host system at build time.

automake
     a system for describing how to build a program, permitting the
     developer to write a simplified `Makefile'.

libtool
     a standardized approach to building shared libraries.

gettext
     provides a framework for translation of text messages into other
     languages; not really discussed in this document.

m4
     autoconf requires the GNU version of m4; the standard Unix m4 does
     not suffice.

perl
     automake requires perl.

\x1f
File: configure.info,  Node: History,  Next: Building,  Prev: Tools,  Up: Introduction

History
=======

   This is a very brief and probably inaccurate history.

   As the number of Unix variants increased during the 1980s, it became
harder to write programs which could run on all variants.  While it was
often possible to use `#ifdef' to identify particular systems,
developers frequently did not have access to every system, and the
characteristics of some systems changed from version to version.

   By 1992, at least three different approaches had been developed:
   * The Metaconfig program, by Larry Wall, Harlan Stenn, and Raphael
     Manfredi.

   * The Cygnus configure script, by K. Richard Pixley, and the gcc
     configure script, by Richard Stallman.  These use essentially the
     same approach, and the developers communicated regularly.

   * The autoconf program, by David MacKenzie.

   The Metaconfig program is still used for Perl and a few other
programs.  It is part of the Dist package.  I do not know if it is
being developed.

   In 1994, David MacKenzie and others modified autoconf to incorporate
all the features of Cygnus configure.  Since then, there has been a
slow but steady conversion of GNU programs from Cygnus configure to
autoconf. gcc has been converted, eliminating the gcc configure script.

   GNU autoconf was regularly maintained until late 1996.  As of this
writing in June, 1998, it has no public maintainer.

   Most programs are built using the make program, which requires the
developer to write Makefiles describing how to build the programs.
Since most programs are built in pretty much the same way, this led to a
lot of duplication.

   The X Window system is built using the imake tool, which uses a
database of rules to eliminate the duplication.  However, building a
tool which was developed using imake requires that the builder have
imake installed, violating one of the goals of the GNU system.

   The new BSD make provides a standard library of Makefile fragments,
which permits developers to write very simple Makefiles.  However, this
requires that the builder install the new BSD make program.

   In 1994, David MacKenzie wrote the first version of automake, which
permitted writing a simple build description which was converted into a
Makefile which could be used by the standard make program.  In 1995, Tom
Tromey completely rewrote automake in Perl, and he continues to enhance
it.

   Various free packages built libraries, and by around 1995 several
included support to build shared libraries on various platforms.
However, there was no consistent approach.  In early 1996, Gordon
Matzigkeit began working on libtool, which provided a standardized
approach to building shared libraries.  This was integrated into
automake from the start.

   The development of automake and libtool was driven by the GNITS
project, a group of GNU maintainers who designed standardized tools to
help meet the GNU coding standards.

\x1f
File: configure.info,  Node: Building,  Prev: History,  Up: Introduction

Building
========

   Most readers of this document should already know how to build a
tool by running `configure' and `make'.  This section may serve as a
quick introduction or reminder.

   Building a tool is normally as simple as running `configure'
followed by `make'.  You should normally run `configure' from an empty
directory, using some path to refer to the `configure' script in the
source directory.  The directory in which you run `configure' is called
the "object directory".

   In order to use a object directory which is different from the source
directory, you must be using the GNU version of `make', which has the
required `VPATH' support.  Despite this restriction, using a different
object directory is highly recommended:
   * It keeps the files generated during the build from cluttering up
     your sources.

   * It permits you to remove the built files by simply removing the
     entire build directory.

   * It permits you to build from the same sources with several sets of
     configure options simultaneously.

   If you don't have GNU `make', you will have to run `configure' in
the source directory.  All GNU packages should support this; in
particular, GNU packages should not assume the presence of GNU `make'.

   After running `configure', you can build the tools by running `make'.

   To install the tools, run `make install'.  Installing the tools will
copy the programs and any required support files to the "installation
directory".  The location of the installation directory is controlled
by `configure' options, as described below.

   In the Cygnus tree at present, the info files are built and
installed as a separate step.  To build them, run `make info'.  To
install them, run `make install-info'.

   All `configure' scripts support a wide variety of options.  The most
interesting ones are `--with' and `--enable' options which are
generally specific to particular tools.  You can usually use the
`--help' option to get a list of interesting options for a particular
configure script.

   The only generic options you are likely to use are the `--prefix'
and `--exec-prefix' options.  These options are used to specify the
installation directory.

   The directory named by the `--prefix' option will hold machine
independent files such as info files.

   The directory named by the `--exec-prefix' option, which is normally
a subdirectory of the `--prefix' directory, will hold machine dependent
files such as executables.

   The default for `--prefix' is `/usr/local'.  The default for
`--exec-prefix' is the value used for `--prefix'.

   The convention used in Cygnus releases is to use a `--prefix' option
of `/usr/cygnus/RELEASE', where RELEASE is the name of the release, and
to use a `--exec-prefix' option of `/usr/cygnus/RELEASE/H-HOST', where
HOST is the configuration name of the host system (*note Configuration
Names::).

   Do not use either the source or the object directory as the
installation directory.  That will just lead to confusion.

\x1f
File: configure.info,  Node: Getting Started,  Next: Files,  Prev: Introduction,  Up: Top

Getting Started
***************

   To start using the GNU configure and build system with your software
package, you must write three files, and you must run some tools to
manually generate additional files.

* Menu:

* Write configure.in::          Write configure.in.
* Write Makefile.am::           Write Makefile.am.
* Write acconfig.h::            Write acconfig.h.
* Generate files::              Generate files.
* Getting Started Example::     Example.

\x1f
File: configure.info,  Node: Write configure.in,  Next: Write Makefile.am,  Up: Getting Started

Write configure.in
==================

   You must first write the file `configure.in'.  This is an autoconf
input file, and the autoconf manual describes in detail what this file
should look like.

   You will write tests in your `configure.in' file to check for
conditions that may change from one system to another, such as the
presence of particular header files or functions.

   For example, not all systems support the `gettimeofday' function.
If you want to use the `gettimeofday' function when it is available,
and to use some other function when it is not, you would check for this
by putting `AC_CHECK_FUNCS(gettimeofday)' in `configure.in'.

   When the configure script is run at build time, this will arrange to
define the preprocessor macro `HAVE_GETTIMEOFDAY' to the value 1 if the
`gettimeofday' function is available, and to not define the macro at
all if the function is not available.  Your code can then use `#ifdef'
to test whether it is safe to call `gettimeofday'.

   If you have an existing body of code, the `autoscan' program may
help identify potential portability problems, and hence configure tests
that you will want to use.  *Note Invoking autoscan: (autoconf)Invoking
autoscan.

   Another handy tool for an existing body of code is `ifnames'.  This
will show you all the preprocessor conditionals that the code already
uses.  *Note Invoking ifnames: (autoconf)Invoking ifnames.

   Besides the portability tests which are specific to your particular
package, every `configure.in' file should contain the following macros.

`AC_INIT'
     This macro takes a single argument, which is the name of a file in
     your package.  For example, `AC_INIT(foo.c)'.

`AC_PREREQ(VERSION)'
     This macro is optional.  It may be used to indicate the version of
     `autoconf' that you are using.  This will prevent users from
     running an earlier version of `autoconf' and perhaps getting an
     invalid `configure' script.  For example, `AC_PREREQ(2.12)'.

`AM_INIT_AUTOMAKE'
     This macro takes two arguments: the name of the package, and a
     version number.  For example, `AM_INIT_AUTOMAKE(foo, 1.0)'.  (This
     macro is not needed if you are not using automake).

`AM_CONFIG_HEADER'
     This macro names the header file which will hold the preprocessor
     macro definitions at run time.  Normally this should be
     `config.h'.  Your sources would then use `#include "config.h"' to
     include it.

     This macro may optionally name the input file for that header
     file; by default, this is `config.h.in', but that file name works
     poorly on DOS filesystems.  Therefore, it is often better to name
     it explicitly as `config.in'.

     This is what you should normally put in `configure.in':
          AM_CONFIG_HEADER(config.h:config.in)

     (If you are not using automake, use `AC_CONFIG_HEADER' rather than
     `AM_CONFIG_HEADER').

`AM_MAINTAINER_MODE'
     This macro always appears in Cygnus configure scripts.  Other
     programs may or may not use it.

     If this macro is used, the `--enable-maintainer-mode' option is
     required to enable automatic rebuilding of generated files used by
     the configure system.  This of course requires that developers be
     aware of, and use, that option.

     If this macro is not used, then the generated files will always be
     rebuilt automatically.  This will cause problems if the wrong
     versions of autoconf, automake, or others are in the builder's
     `PATH'.

     (If you are not using automake, you do not need to use this macro).

`AC_EXEEXT'
     Either this macro or `AM_EXEEXT' always appears in Cygnus configure
     files.  Other programs may or may not use one of them.

     This macro looks for the executable suffix used on the host
     system.  On Unix systems, this is the empty string.  On Windows
     systems, this is `.exe'.  This macro directs automake to use the
     executable suffix as appropriate when creating programs.  This
     macro does not take any arguments.

     The `AC_EXEEXT' form is new, and is part of a Cygnus patch to
     autoconf to support compiling with Visual C++.  Older programs use
     `AM_EXEEXT' instead.

     (Programs which do not use automake use neither `AC_EXEEXT' nor
     `AM_EXEEXT').

`AC_PROG_CC'
     If you are writing C code, you will normally want to use this
     macro.  It locates the C compiler to use.  It does not take any
     arguments.

     However, if this `configure.in' file is for a library which is to
     be compiled by a cross compiler which may not fully work, then you
     will not want to use `AC_PROG_CC'.  Instead, you will want to use a
     variant which does not call the macro `AC_PROG_CC_WORKS'.  Examples
     can be found in various `configure.in' files for libraries that are
     compiled with cross compilers, such as libiberty or libgloss.
     This is essentially a bug in autoconf, and there will probably be
     a better workaround at some point.

`AC_PROG_CXX'
     If you are writing C++ code, you will want to use this macro.  It
     locates the C++ compiler to use.  It does not take any arguments.
     The same cross compiler comments apply as for `AC_PROG_CC'.

`AM_PROG_LIBTOOL'
     If you want to build libraries, and you want to permit them to be
     shared, or you want to link against libraries which were built
     using libtool, then you will need this macro.  This macro is
     required in order to use libtool.

     By default, this will cause all libraries to be built as shared
     libraries.  To prevent this-to change the default-use
     `AM_DISABLE_SHARED' before `AM_PROG_LIBTOOL'.  The configure
     options `--enable-shared' and `--disable-shared' may be used to
     override the default at build time.

`AC_DEFINE(_GNU_SOURCE)'
     GNU packages should normally include this line before any other
     feature tests.  This defines the macro `_GNU_SOURCE' when
     compiling, which directs the libc header files to provide the
     standard GNU system interfaces including all GNU extensions.  If
     this macro is not defined, certain GNU extensions may not be
     available.

`AC_OUTPUT'
     This macro takes a list of file names which the configure process
     should produce.  This is normally a list of one or more `Makefile'
     files in different directories.  If your package lives entirely in
     a single directory, you would use simply `AC_OUTPUT(Makefile)'.
     If you also have, for example, a `lib' subdirectory, you would use
     `AC_OUTPUT(Makefile lib/Makefile)'.

   If you want to use locally defined macros in your `configure.in'
file, then you will need to write a `acinclude.m4' file which defines
them (if not using automake, this file is called `aclocal.m4').
Alternatively, you can put separate macros in an `m4' subdirectory, and
put `ACLOCAL_AMFLAGS = -I m4' in your `Makefile.am' file so that the
`aclocal' program will be able to find them.

   The different macro prefixes indicate which tool defines the macro.
Macros which start with `AC_' are part of autoconf.  Macros which start
with `AM_' are provided by automake or libtool.

\x1f
File: configure.info,  Node: Write Makefile.am,  Next: Write acconfig.h,  Prev: Write configure.in,  Up: Getting Started

Write Makefile.am
=================

   You must write the file `Makefile.am'.  This is an automake input
file, and the automake manual describes in detail what this file should
look like.

   The automake commands in `Makefile.am' mostly look like variable
assignments in a `Makefile'.  automake recognizes special variable
names, and automatically add make rules to the output as needed.

   There will be one `Makefile.am' file for each directory in your
package.  For each directory with subdirectories, the `Makefile.am'
file should contain the line
     SUBDIRS = DIR DIR ...

where each DIR is the name of a subdirectory.

   For each `Makefile.am', there should be a corresponding `Makefile'
in the `AC_OUTPUT' macro in `configure.in'.

   Every `Makefile.am' written at Cygnus should contain the line
     AUTOMAKE_OPTIONS = cygnus

This puts automake into Cygnus mode.  See the automake manual for
details.

   You may to include the version number of `automake' that you are
using on the `AUTOMAKE_OPTIONS' line.  For example,
     AUTOMAKE_OPTIONS = cygnus 1.3

This will prevent users from running an earlier version of `automake'
and perhaps getting an invalid `Makefile.in'.

   If your package builds a program, then in the directory where that
program is built you will normally want a line like
     bin_PROGRAMS = PROGRAM

where PROGRAM is the name of the program.  You will then want a line
like
     PROGRAM_SOURCES = FILE FILE ...

where each FILE is the name of a source file to link into the program
(e.g., `foo.c').

   If your package builds a library, and you do not want the library to
ever be built as a shared library, then in the directory where that
library is built you will normally want a line like
     lib_LIBRARIES = libNAME.a

where `libNAME.a' is the name of the library.  You will then want a
line like
     libNAME_a_SOURCES = FILE FILE ...

where each FILE is the name of a source file to add to the library.

   If your package builds a library, and you want to permit building the
library as a shared library, then in the directory where that library is
built you will normally want a line like
     lib_LTLIBRARIES = libNAME.la
   The use of `LTLIBRARIES', and the `.la' extension, indicate a
library to be built using libtool.  As usual, you will then want a line
like
     libNAME_la_SOURCES = FILE FILE ...

   The strings `bin' and `lib' that appear above in `bin_PROGRAMS' and
`lib_LIBRARIES' are not arbitrary.  They refer to particular
directories, which may be set by the `--bindir' and `--libdir' options
to `configure'.  If those options are not used, the default values are
based on the `--prefix' or `--exec-prefix' options to `configure'.  It
is possible to use other names if the program or library should be
installed in some other directory.

   The `Makefile.am' file may also contain almost anything that may
appear in a normal `Makefile'.  automake also supports many other
special variables, as well as conditionals.

   See the automake manual for more information.

\x1f
File: configure.info,  Node: Write acconfig.h,  Next: Generate files,  Prev: Write Makefile.am,  Up: Getting Started

Write acconfig.h
================

   If you are generating a portability header file, (i.e., you are using
`AM_CONFIG_HEADER' in `configure.in'), then you will have to write a
`acconfig.h' file.  It will have to contain the following lines.

     /* Name of package.  */
     #undef PACKAGE
     
     /* Version of package.  */
     #undef VERSION

   This requirement is really a bug in the system, and the requirement
may be eliminated at some later date.

   The `acconfig.h' file will also similar comment and `#undef' lines
for any unusual macros in the `configure.in' file, including any macro
which appears in a `AC_DEFINE' macro.

   In particular, if you are writing a GNU package and therefore include
`AC_DEFINE(_GNU_SOURCE)' in `configure.in' as suggested above, you will
need lines like this in `acconfig.h':
     /* Enable GNU extensions.  */
     #undef _GNU_SOURCE

   Normally the `autoheader' program will inform you of any such
requirements by printing an error message when it is run.  However, if
you do anything particular odd in your `configure.in' file, you will
have to make sure that the right entries appear in `acconfig.h', since
otherwise the results of the tests may not be available in the
`config.h' file which your code will use.

   (Thee `PACKAGE' and `VERSION' lines are not required if you are not
using automake, and in that case you may not need a `acconfig.h' file
at all).

\x1f
File: configure.info,  Node: Generate files,  Next: Getting Started Example,  Prev: Write acconfig.h,  Up: Getting Started

Generate files
==============

   Once you have written `configure.in', `Makefile.am', `acconfig.h',
and possibly `acinclude.m4', you must use autoconf and automake
programs to produce the first versions of the generated files.  This is
done by executing the following sequence of commands.

     aclocal
     autoconf
     autoheader
     automake

   The `aclocal' and `automake' commands are part of the automake
package, and the `autoconf' and `autoheader' commands are part of the
autoconf package.

   If you are using a `m4' subdirectory for your macros, you will need
to use the `-I m4' option when you run `aclocal'.

   If you are not using the Cygnus tree, use the `-a' option when
running `automake' command in order to copy the required support files
into your source directory.

   If you are using libtool, you must build and install the libtool
package with the same `--prefix' and `--exec-prefix' options as you
used with the autoconf and automake packages.  You must do this before
running any of the above commands.  If you are not using the Cygnus
tree, you will need to run the `libtoolize' program to copy the libtool
support files into your directory.

   Once you have managed to run these commands without getting any
errors, you should create a new empty directory, and run the `configure'
script which will have been created by `autoconf' with the
`--enable-maintainer-mode' option.  This will give you a set of
Makefiles which will include rules to automatically rebuild all the
generated files.

   After doing that, whenever you have changed some of the input files
and want to regenerated the other files, go to your object directory
and run `make'.  Doing this is more reliable than trying to rebuild the
files manually, because there are complex order dependencies and it is
easy to forget something.

\x1f
File: configure.info,  Node: Getting Started Example,  Prev: Generate files,  Up: Getting Started

Example
=======

   Let's consider a trivial example.

   Suppose we want to write a simple version of `touch'.  Our program,
which we will call `poke', will take a single file name argument, and
use the `utime' system call to set the modification and access times of
the file to the current time.  We want this program to be highly
portable.

   We'll first see what this looks like without using autoconf and
automake, and then see what it looks like with them.

* Menu:

* Getting Started Example 1::           First Try.
* Getting Started Example 2::           Second Try.
* Getting Started Example 3::           Third Try.
* Generate Files in Example::           Generate Files.

\x1f
File: configure.info,  Node: Getting Started Example 1,  Next: Getting Started Example 2,  Up: Getting Started Example

First Try
---------

   Here is our first try at `poke.c'.  Note that we've written it
without ANSI/ISO C prototypes, since we want it to be highly portable.

     #include <stdio.h>
     #include <stdlib.h>
     #include <sys/types.h>
     #include <utime.h>
     
     int
     main (argc, argv)
          int argc;
          char **argv;
     {
       if (argc != 2)
         {
           fprintf (stderr, "Usage: poke file\n");
           exit (1);
         }
     
       if (utime (argv[1], NULL) < 0)
         {
           perror ("utime");
           exit (1);
         }
     
       exit (0);
     }

   We also write a simple `Makefile'.

     CC = gcc
     CFLAGS = -g -O2
     
     all: poke
     
     poke: poke.o
        $(CC) -o poke $(CFLAGS) $(LDFLAGS) poke.o

   So far, so good.

   Unfortunately, there are a few problems.

   On older Unix systems derived from BSD 4.3, the `utime' system call
does not accept a second argument of `NULL'.  On those systems, we need
to pass a pointer to `struct utimbuf' structure.  Unfortunately, even
older systems don't define that structure; on those systems, we need to
pass an array of two `long' values.

   The header file `stdlib.h' was invented by ANSI C, and older systems
don't have a copy.  We included it above to get a declaration of `exit'.

   We can find some of these portability problems by running
`autoscan', which will create a `configure.scan' file which we can use
as a prototype for our `configure.in' file.  I won't show the output,
but it will notice the potential problems with `utime' and `stdlib.h'.

   In our `Makefile', we don't provide any way to install the program.
This doesn't matter much for such a simple example, but a real program
will need an `install' target.  For that matter, we will also want a
`clean' target.

\x1f
File: configure.info,  Node: Getting Started Example 2,  Next: Getting Started Example 3,  Prev: Getting Started Example 1,  Up: Getting Started Example

Second Try
----------

   Here is our second try at this program.

   We modify `poke.c' to use preprocessor macros to control what
features are available.  (I've cheated a bit by using the same macro
names which autoconf will use).

     #include <stdio.h>
     
     #ifdef STDC_HEADERS
     #include <stdlib.h>
     #endif
     
     #include <sys/types.h>
     
     #ifdef HAVE_UTIME_H
     #include <utime.h>
     #endif
     
     #ifndef HAVE_UTIME_NULL
     
     #include <time.h>
     
     #ifndef HAVE_STRUCT_UTIMBUF
     
     struct utimbuf
     {
       long actime;
       long modtime;
     };
     
     #endif
     
     static int
     utime_now (file)
          char *file;
     {
       struct utimbuf now;
     
       now.actime = now.modtime = time (NULL);
       return utime (file, &now);
     }
     
     #define utime(f, p) utime_now (f)
     
     #endif /* HAVE_UTIME_NULL  */
     
     int
     main (argc, argv)
          int argc;
          char **argv;
     {
       if (argc != 2)
         {
           fprintf (stderr, "Usage: poke file\n");
           exit (1);
         }
     
       if (utime (argv[1], NULL) < 0)
         {
           perror ("utime");
           exit (1);
         }
     
       exit (0);
     }

   Here is the associated `Makefile'.  We've added support for the
preprocessor flags we use.  We've also added `install' and `clean'
targets.

     # Set this to your installation directory.
     bindir = /usr/local/bin
     
     # Uncomment this if you have the standard ANSI/ISO C header files.
     # STDC_HDRS = -DSTDC_HEADERS
     
     # Uncomment this if you have utime.h.
     # UTIME_H = -DHAVE_UTIME_H
     
     # Uncomment this if utime (FILE, NULL) works on your system.
     # UTIME_NULL = -DHAVE_UTIME_NULL
     
     # Uncomment this if struct utimbuf is defined in utime.h.
     # UTIMBUF = -DHAVE_STRUCT_UTIMBUF
     
     CC = gcc
     CFLAGS = -g -O2
     
     ALL_CFLAGS = $(STDC_HDRS) $(UTIME_H) $(UTIME_NULL) $(UTIMBUF) $(CFLAGS)
     
     all: poke
     
     poke: poke.o
        $(CC) -o poke $(ALL_CFLAGS) $(LDFLAGS) poke.o
     
     .c.o:
        $(CC) -c $(ALL_CFLAGS) poke.c
     
     install: poke
        cp poke $(bindir)/poke
     
     clean:
        rm poke poke.o

   Some problems with this approach should be clear.

   Users who want to compile poke will have to know how `utime' works
on their systems, so that they can uncomment the `Makefile' correctly.

   The installation is done using `cp', but many systems have an
`install' program which may be used, and which supports optional
features such as stripping debugging information out of the installed
binary.

   The use of `Makefile' variables like `CC', `CFLAGS' and `LDFLAGS'
follows the requirements of the GNU standards.  This is convenient for
all packages, since it reduces surprises for users.  However, it is
easy to get the details wrong, and wind up with a slightly nonstandard
distribution.

\x1f
File: configure.info,  Node: Getting Started Example 3,  Next: Generate Files in Example,  Prev: Getting Started Example 2,  Up: Getting Started Example

Third Try
---------

   For our third try at this program, we will write a `configure.in'
script to discover the configuration features on the host system, rather
than requiring the user to edit the `Makefile'.  We will also write a
`Makefile.am' rather than a `Makefile'.

   The only change to `poke.c' is to add a line at the start of the
file:
     #include "config.h"

   The new `configure.in' file is as follows.

     AC_INIT(poke.c)
     AM_INIT_AUTOMAKE(poke, 1.0)
     AM_CONFIG_HEADER(config.h:config.in)
     AC_PROG_CC
     AC_HEADER_STDC
     AC_CHECK_HEADERS(utime.h)
     AC_EGREP_HEADER(utimbuf, utime.h, AC_DEFINE(HAVE_STRUCT_UTIMBUF))
     AC_FUNC_UTIME_NULL
     AC_OUTPUT(Makefile)

   The first four macros in this file, and the last one, were described
above; see *Note Write configure.in::.  If we omit these macros, then
when we run `automake' we will get a reminder that we need them.

   The other macros are standard autoconf macros.

`AC_HEADER_STDC'
     Check for standard C headers.

`AC_CHECK_HEADERS'
     Check whether a particular header file exists.

`AC_EGREP_HEADER'
     Check for a particular string in a particular header file, in this
     case checking for `utimbuf' in `utime.h'.

`AC_FUNC_UTIME_NULL'
     Check whether `utime' accepts a NULL second argument to set the
     file change time to the current time.

   See the autoconf manual for a more complete description.

   The new `Makefile.am' file is as follows.  Note how simple this is
compared to our earlier `Makefile'.

     bin_PROGRAMS = poke
     
     poke_SOURCES = poke.c

   This means that we should build a single program name `poke'.  It
should be installed in the binary directory, which we called `bindir'
earlier.  The program `poke' is built from the source file `poke.c'.

   We must also write a `acconfig.h' file.  Besides `PACKAGE' and
`VERSION', which must be mentioned for all packages which use automake,
we must include `HAVE_STRUCT_UTIMBUF', since we mentioned it in an
`AC_DEFINE'.

     /* Name of package.  */
     #undef PACKAGE
     
     /* Version of package.  */
     #undef VERSION
     
     /* Whether utime.h defines struct utimbuf.  */
     #undef HAVE_STRUCT_UTIMBUF

\x1f
File: configure.info,  Node: Generate Files in Example,  Prev: Getting Started Example 3,  Up: Getting Started Example

Generate Files
--------------

   We must now generate the other files, using the following commands.

     aclocal
     autoconf
     autoheader
     automake

   When we run `autoheader', it will remind us of any macros we forgot
to add to `acconfig.h'.

   When we run `automake', it will want to add some files to our
distribution.  It will add them automatically if we use the
`--add-missing' option.

   By default, `automake' will run in GNU mode, which means that it
will want us to create certain additional files; as of this writing, it
will want `NEWS', `README', `AUTHORS', and `ChangeLog', all of which
are files which should appear in a standard GNU distribution.  We can
either add those files, or run `automake' with the `--foreign' option.

   Running these tools will generate the following files, all of which
are described in the next chapter.

   * `aclocal.m4'

   * `configure'

   * `config.in'

   * `Makefile.in'

   * `stamp-h.in'

\x1f
File: configure.info,  Node: Files,  Next: Configuration Names,  Prev: Getting Started,  Up: Top

Files
*****

   As was seen in the previous chapter, the GNU configure and build
system uses a number of different files.  The developer must write a
few files.  The others are generated by various tools.

   The system is rather flexible, and can be used in many different
ways.  In describing the files that it uses, I will describe the common
case, and mention some other cases that may arise.

* Menu:

* Developer Files::             Developer Files.
* Build Files::                 Build Files.
* Support Files::               Support Files.

\x1f
File: configure.info,  Node: Developer Files,  Next: Build Files,  Up: Files

Developer Files
===============

   This section describes the files written or generated by the
developer of a package.

* Menu:

* Developer Files Picture::     Developer Files Picture.
* Written Developer Files::     Written Developer Files.
* Generated Developer Files::   Generated Developer Files.

\x1f
File: configure.info,  Node: Developer Files Picture,  Next: Written Developer Files,  Up: Developer Files

Developer Files Picture
-----------------------

   Here is a picture of the files which are written by the developer,
the generated files which would be included with a complete source
distribution, and the tools which create those files.  The file names
are plain text and the tool names are enclosed by `*' characters (e.g.,
`autoheader' is the name of a tool, not the name of a file).

   acconfig.h       configure.in                 Makefile.am
       |                |                           |
       |  --------------+----------------------     |
       |  |             |                     |     |
       v  v             |    acinclude.m4     |     |
   *autoheader*         |         |           v     v
       |                |         v      --->*automake* 
       v                |--->*aclocal*   |       |      
   config.in            |         |      |       v      
                        |         v      |   Makefile.in
                        |    aclocal.m4---
                        |     |
                        v     v
                       *autoconf*
                           |
                           v
                       configure

\x1f
File: configure.info,  Node: Written Developer Files,  Next: Generated Developer Files,  Prev: Developer Files Picture,  Up: Developer Files

Written Developer Files
-----------------------

   The following files would be written by the developer.

`configure.in'
     This is the configuration script.  This script contains
     invocations of autoconf macros.  It may also contain ordinary
     shell script code.  This file will contain feature tests for
     portability issues.  The last thing in the file will normally be
     an `AC_OUTPUT' macro listing which files to create when the
     builder runs the configure script.  This file is always required
     when using the GNU configure system.  *Note Write configure.in::.

`Makefile.am'
     This is the automake input file.  It describes how the code should
     be built.  It consists of definitions of automake variables.  It
     may also contain ordinary Makefile targets.  This file is only
     needed when using automake (newer tools normally use automake, but
     there are still older tools which have not been converted, in
     which the developer writes `Makefile.in' directly).  *Note Write
     Makefile.am::.

`acconfig.h'
     When the configure script creates a portability header file, by
     using `AM_CONFIG_HEADER' (or, if not using automake,
     `AC_CONFIG_HEADER'), this file is used to describe macros which are
     not recognized by the `autoheader' command.  This is normally a
     fairly uninteresting file, consisting of a collection of `#undef'
     lines with comments.  Normally any call to `AC_DEFINE' in
     `configure.in' will require a line in this file. *Note Write
     acconfig.h::.

`acinclude.m4'
     This file is not always required.  It defines local autoconf
     macros.  These macros may then be used in `configure.in'.  If you
     don't need any local autoconf macros, then you don't need this
     file at all.  In fact, in general, you never need local autoconf
     macros, since you can put everything in `configure.in', but
     sometimes a local macro is convenient.

     Newer tools may omit `acinclude.m4', and instead use a
     subdirectory, typically named `m4', and define `ACLOCAL_AMFLAGS =
     -I m4' in `Makefile.am' to force `aclocal' to look there for macro
     definitions.  The macro definitions are then placed in separate
     files in that directory.

     The `acinclude.m4' file is only used when using automake; in older
     tools, the developer writes `aclocal.m4' directly, if it is needed.

\x1f
File: configure.info,  Node: Generated Developer Files,  Prev: Written Developer Files,  Up: Developer Files

Generated Developer Files
-------------------------

   The following files would be generated by the developer.

   When using automake, these files are normally not generated manually
after the first time.  Instead, the generated `Makefile' contains rules
to automatically rebuild the files as required.  When
`AM_MAINTAINER_MODE' is used in `configure.in' (the normal case in
Cygnus code), the automatic rebuilding rules will only be defined if
you configure using the `--enable-maintainer-mode' option.

   When using automatic rebuilding, it is important to ensure that all
the various tools have been built and installed on your `PATH'.  Using
automatic rebuilding is highly recommended, so much so that I'm not
going to explain what you have to do if you don't use it.

`configure'
     This is the configure script which will be run when building the
     package.  This is generated by `autoconf' from `configure.in' and
     `aclocal.m4'.  This is a shell script.

`Makefile.in'
     This is the file which the configure script will turn into the
     `Makefile' at build time.  This file is generated by `automake'
     from `Makefile.am'.  If you aren't using automake, you must write
     this file yourself.  This file is pretty much a normal `Makefile',
     with some configure substitutions for certain variables.

`aclocal.m4'
     This file is created by the `aclocal' program, based on the
     contents of `configure.in' and `acinclude.m4' (or, as noted in the
     description of `acinclude.m4' above, on the contents of an `m4'
     subdirectory).  This file contains definitions of autoconf macros
     which `autoconf' will use when generating the file `configure'.
     These autoconf macros may be defined by you in `acinclude.m4' or
     they may be defined by other packages such as automake, libtool or
     gettext.  If you aren't using automake, you will normally write
     this file yourself; in that case, if `configure.in' uses only
     standard autoconf macros, this file will not be needed at all.

`config.in'
     This file is created by `autoheader' based on `acconfig.h' and
     `configure.in'.  At build time, the configure script will define
     some of the macros in it to create `config.h', which may then be
     included by your program.  This permits your C code to use
     preprocessor conditionals to change its behaviour based on the
     characteristics of the host system.  This file may also be called
     `config.h.in'.

`stamp.h-in'
     This rather uninteresting file, which I omitted from the picture,
     is generated by `automake'.  It always contains the string
     `timestamp'.  It is used as a timestamp file indicating whether
     `config.in' is up to date.  Using a timestamp file means that
     `config.in' can be marked as up to date without actually changing
     its modification time.  This is useful since `config.in' depends
     upon `configure.in', but it is easy to change `configure.in' in a
     way which does not affect `config.in'.

\x1f
File: configure.info,  Node: Build Files,  Next: Support Files,  Prev: Developer Files,  Up: Files

Build Files
===========

   This section describes the files which are created at configure and
build time.  These are the files which somebody who builds the package
will see.

   Of course, the developer will also build the package.  The
distinction between developer files and build files is not that the
developer does not see the build files, but that somebody who only
builds the package does not have to worry about the developer files.

* Menu:

* Build Files Picture::         Build Files Picture.
* Build Files Description::     Build Files Description.

\x1f
File: configure.info,  Node: Build Files Picture,  Next: Build Files Description,  Up: Build Files

Build Files Picture
-------------------

   Here is a picture of the files which will be created at build time.
`config.status' is both a created file and a shell script which is run
to create other files, and the picture attempts to show that.

   config.in        *configure*      Makefile.in
      |                  |               |
      |                  v               |
      |             config.status        |
      |                  |               |
   *config.status*<======+==========>*config.status*
      |                                  |
      v                                  v
   config.h                          Makefile

\x1f
File: configure.info,  Node: Build Files Description,  Prev: Build Files Picture,  Up: Build Files

Build Files Description
-----------------------

   This is a description of the files which are created at build time.

`config.status'
     The first step in building a package is to run the `configure'
     script.  The `configure' script will create the file
     `config.status', which is itself a shell script.  When you first
     run `configure', it will automatically run `config.status'.  An
     `Makefile' derived from an automake generated `Makefile.in' will
     contain rules to automatically run `config.status' again when
     necessary to recreate certain files if their inputs change.

`Makefile'
     This is the file which make will read to build the program.  The
     `config.status' script will transform `Makefile.in' into
     `Makefile'.

`config.h'
     This file defines C preprocessor macros which C code can use to
     adjust its behaviour on different systems.  The `config.status'
     script will transform `config.in' into `config.h'.

`config.cache'
     This file did not fit neatly into the picture, and I omitted it.
     It is used by the `configure' script to cache results between
     runs.  This can be an important speedup.  If you modify
     `configure.in' in such a way that the results of old tests should
     change (perhaps you have added a new library to `LDFLAGS'), then
     you will have to remove `config.cache' to force the tests to be
     rerun.

     The autoconf manual explains how to set up a site specific cache
     file.  This can speed up running `configure' scripts on your
     system.

`stamp.h'
     This file, which I omitted from the picture, is similar to
     `stamp-h.in'.  It is used as a timestamp file indicating whether
     `config.h' is up to date.  This is useful since `config.h' depends
     upon `config.status', but it is easy for `config.status' to change
     in a way which does not affect `config.h'.

\x1f
File: configure.info,  Node: Support Files,  Prev: Build Files,  Up: Files

Support Files
=============

   The GNU configure and build system requires several support files to
be included with your distribution.  You do not normally need to concern
yourself with these.  If you are using the Cygnus tree, most are already
present.  Otherwise, they will be installed with your source by
`automake' (with the `--add-missing' option) and `libtoolize'.

   You don't have to put the support files in the top level directory.
You can put them in a subdirectory, and use the `AC_CONFIG_AUX_DIR'
macro in `configure.in' to tell `automake' and the `configure' script
where they are.

   In this section, I describe the support files, so that you can know
what they are and why they are there.

`ABOUT-NLS'
     Added by automake if you are using gettext.  This is a
     documentation file about the gettext project.

`ansi2knr.c'
     Used by an automake generated `Makefile' if you put `ansi2knr' in
     `AUTOMAKE_OPTIONS' in `Makefile.am'.  This permits compiling ANSI
     C code with a K&R C compiler.

`ansi2knr.1'
     The man page which goes with `ansi2knr.c'.

`config.guess'
     A shell script which determines the configuration name for the
     system on which it is run.

`config.sub'
     A shell script which canonicalizes a configuration name entered by
     a user.

`elisp-comp'
     Used to compile Emacs LISP files.

`install-sh'
     A shell script which installs a program.  This is used if the
     configure script can not find an install binary.

`ltconfig'
     Used by libtool.  This is a shell script which configures libtool
     for the particular system on which it is used.

`ltmain.sh'
     Used by libtool.  This is the actual libtool script which is used,
     after it is configured by `ltconfig' to build a library.

`mdate-sh'
     A shell script used by an automake generated `Makefile' to pretty
     print the modification time of a file.  This is used to maintain
     version numbers for texinfo files.

`missing'
     A shell script used if some tool is missing entirely.  This is
     used by an automake generated `Makefile' to avoid certain sorts of
     timestamp problems.

`mkinstalldirs'
     A shell script which creates a directory, including all parent
     directories.  This is used by an automake generated `Makefile'
     during installation.

`texinfo.tex'
     Required if you have any texinfo files.  This is used when
     converting Texinfo files into DVI using `texi2dvi' and TeX.

`ylwrap'
     A shell script used by an automake generated `Makefile' to run
     programs like `bison', `yacc', `flex', and `lex'.  These programs
     default to producing output files with a fixed name, and the
     `ylwrap' script runs them in a subdirectory to avoid file name
     conflicts when using a parallel make program.

\x1f
File: configure.info,  Node: Configuration Names,  Next: Cross Compilation Tools,  Prev: Files,  Up: Top

Configuration Names
*******************

   The GNU configure system names all systems using a "configuration
name".  All such names used to be triplets (they may now contain four
parts in certain cases), and the term "configuration triplet" is still
seen.

* Menu:

* Configuration Name Definition::       Configuration Name Definition.
* Using Configuration Names::           Using Configuration Names.