2.1 General Operation

Automake works by reading a Makefile.am and generating a Makefile.in. Certain macros and targets defined in the Makefile.am instruct Automake to generate more specialized code; for instance, a ‘bin_PROGRAMS’ macro definition will cause targets for compiling and linking programs to be generated.

The macro definitions and targets in the Makefile.am are copied verbatim into the generated file. This allows you to add arbitrary code into the generated Makefile.in. For instance the Automake distribution includes a non-standard cvs-dist target, which the Automake maintainer uses to make distributions from his source control system.

Note that GNU make extensions are not recognized by Automake. Using such extensions in a Makefile.am will lead to errors or confusing behavior.

Automake tries to group comments with adjoining targets and macro definitions in an intelligent way.

A target defined in Makefile.am generally overrides any such target of a similar name that would be automatically generated by automake. Although this is a supported feature, it is generally best to avoid making use of it, as sometimes the generated rules are very particular.

Similarly, a macro defined in Makefile.am will override any definition of the macro that automake would ordinarily create. This feature is more often useful than the ability to override a target definition. Be warned that many of the macros generated by automake are considered to be for internal use only, and their names might change in future releases.

When examining a macro definition, Automake will recursively examine macros referenced in the definition. For example, if Automake is looking at the content of foo_SOURCES in this snippet

xs = a.c b.c
foo_SOURCES = c.c $(xs)

it would use the files a.c, b.c, and c.c as the contents of foo_SOURCES.

Automake also allows a form of comment which is not copied into the output; all lines beginning with ‘##’ (leading spaces allowed) are completely ignored by Automake.

It is customary to make the first line of Makefile.am read:

## Process this file with automake to produce Makefile.in

2.2 Strictness

While Automake is intended to be used by maintainers of GNU packages, it does make some effort to accommodate those who wish to use it, but do not want to use all the GNU conventions.

To this end, Automake supports three levels of strictness—the strictness indicating how stringently Automake should check standards conformance.

The valid strictness levels are:

‘foreign’

Automake will check for only those things which are absolutely required for proper operations. For instance, whereas GNU standards dictate the existence of a NEWS file, it will not be required in this mode. The name comes from the fact that Automake is intended to be used for GNU programs; these relaxed rules are not the standard mode of operation.

‘gnu’

Automake will check—as much as possible—for compliance to the GNU standards for packages. This is the default.

‘gnits’

Automake will check for compliance to the as-yet-unwritten Gnits standards. These are based on the GNU standards, but are even more detailed. Unless you are a Gnits standards contributor, it is recommended that you avoid this option until such time as the Gnits standard is actually published (which may never happen).

For more information on the precise implications of the strictness level, see The effect of --gnu and --gnits.

Automake also has a special “cygnus” mode which is similar to strictness but handled differently. This mode is useful for packages which are put into a “Cygnus” style tree (e.g., the GCC tree). For more information on this mode, see The effect of --cygnus.

2.3 The Uniform Naming Scheme

Automake macros (from here on referred to as variables) generally follow a uniform naming scheme that makes it easy to decide how programs (and other derived objects) are built, and how they are installed. This scheme also supports configure time determination of what should be built.

At make time, certain variables are used to determine which objects are to be built. The variable names are made of several pieces which are concatenated together.

The piece which tells automake what is being built is commonly called the primary. For instance, the primary PROGRAMS holds a list of programs which are to be compiled and linked.

A different set of names is used to decide where the built objects should be installed. These names are prefixes to the primary which indicate which standard directory should be used as the installation directory. The standard directory names are given in the GNU standards (see Directory Variables in The GNU Coding Standards). Automake extends this list with pkglibdir, pkgincludedir, and pkgdatadir; these are the same as the non-‘pkg’ versions, but with ‘@PACKAGE@’ appended. For instance, pkglibdir is defined as $(libdir)/@PACKAGE@.

For each primary, there is one additional variable named by prepending ‘EXTRA_’ to the primary name. This variable is used to list objects which may or may not be built, depending on what configure decides. This variable is required because Automake must statically know the entire list of objects that may be built in order to generate a Makefile.in that will work in all cases.

For instance, cpio decides at configure time which programs are built. Some of the programs are installed in bindir, and some are installed in sbindir:

EXTRA_PROGRAMS = mt rmt
bin_PROGRAMS = cpio pax
sbin_PROGRAMS = @MORE_PROGRAMS@

Defining a primary without a prefix as a variable, e.g., PROGRAMS, is an error.

Note that the common ‘dir’ suffix is left off when constructing the variable names; thus one writes ‘bin_PROGRAMS’ and not ‘bindir_PROGRAMS’.

Not every sort of object can be installed in every directory. Automake will flag those attempts it finds in error. Automake will also diagnose obvious misspellings in directory names.

Sometimes the standard directories—even as augmented by Automake— are not enough. In particular it is sometimes useful, for clarity, to install objects in a subdirectory of some predefined directory. To this end, Automake allows you to extend the list of possible installation directories. A given prefix (e.g. ‘zar’) is valid if a variable of the same name with ‘dir’ appended is defined (e.g. zardir).

For instance, until HTML support is part of Automake, you could use this to install raw HTML documentation:

htmldir = $(prefix)/html
html_DATA = automake.html

The special prefix ‘noinst’ indicates that the objects in question should not be installed at all.

The special prefix ‘check’ indicates that the objects in question should not be built until the make check command is run.

The current primary names are ‘PROGRAMS’, ‘LIBRARIES’, ‘LISP’, ‘PYTHON’, ‘JAVA’, ‘SCRIPTS’, ‘DATA’, ‘HEADERS’, ‘MANS’, and ‘TEXINFOS’.

Some primaries also allow additional prefixes which control other aspects of automake’s behavior. The currently defined prefixes are ‘dist_’, ‘nodist_’, and ‘nobase_’. These prefixes are explained later.

2.4 How derived variables are named

Sometimes a Makefile variable name is derived from some text the maintainer supplies. For instance, a program name listed in ‘_PROGRAMS’ is rewritten into the name of a ‘_SOURCES’ variable. In cases like this, Automake canonicalizes the text, so that program names and the like do not have to follow Makefile macro naming rules. All characters in the name except for letters, numbers, the strudel (@), and the underscore are turned into underscores when making macro references.

For example, if your program is named sniff-glue, the derived variable name would be sniff_glue_SOURCES, not sniff-glue_SOURCES.

The strudel is an addition, to make the use of Autoconf substitutions in macro names less obfuscating.

2.5 Variables reserved for the user

Some Makefile variables are reserved by the GNU Coding Standards for the use of the “user” – the person building the package. For instance, CFLAGS is one such variable.

Sometimes package developers are tempted to set user variables such as CFLAGS because it appears to make their job easier – they don’t have to introduce a second variable into every target.

However, the package itself should never set a user variable, particularly not to include switches which are required for proper compilation of the package. Since these variables are documented as being for the package builder, that person rightfully expects to be able to override any of these variables at build time.

To get around this problem, automake introduces an automake-specific shadow variable for each user flag variable. (Shadow variables are not introduced for variables like CC, where they would make no sense.) The shadow variable is named by prepending ‘AM_’ to the user variable’s name. For instance, the shadow variable for YFLAGS is AM_YFLAGS.

2.6 Programs automake might require

Automake sometimes requires helper programs so that the generated Makefile can do its work properly. There are a fairly large number of them, and we list them here.

ansi2knr.c

ansi2knr.1

These two files are used by the automatic de-ANSI-fication support (see Automatic de-ANSI-fication).

compile

This is a wrapper for compilers which don’t accept both ‘-c’ and ‘-o’ at the same time. It is only used when absolutely required. Such compilers are rare.

config.guess

config.sub

These programs compute the canonical triplets for the given build, host, or target architecture.

depcomp

This program understands how to run a compiler so that it will generate not only the desired output but also dependency information which is then used by the automatic dependency tracking feature.

elisp-comp

This program is used to byte-compile Emacs Lisp code.

install-sh

This is a replacement for the install program which works on platforms where install is unavailable or unusable.

mdate-sh

This script is used to generate a version.texi file. It examines a file and prints some date information about it.

missing

This wraps a number of programs which are typically only required by maintainers. If the program in question doesn’t exist, missing prints an informative warning and attempts to fix things so that the build can continue.

mkinstalldirs

This works around the fact that mkdir -p is not portable.

py-compile

This is used to byte-compile Python scripts.

texinfo.tex

Not a program, this file is required for make dvi to work when Texinfo sources are in the package.

ylwrap

This program wraps lex and yacc and ensures that, for instance, multiple yacc instances can be invoked in a single directory in parallel.

3.1 A simple example, start to finish

Let’s suppose you just finished writing zardoz, a program to make your head float from vortex to vortex. You’ve been using Autoconf to provide a portability framework, but your Makefile.ins have been ad-hoc. You want to make them bulletproof, so you turn to Automake.

The first step is to update your configure.in to include the commands that automake needs. The way to do this is to add an AM_INIT_AUTOMAKE call just after AC_INIT:

AM_INIT_AUTOMAKE(zardoz, 1.0)

Since your program doesn’t have any complicating factors (e.g., it doesn’t use gettext, it doesn’t want to build a shared library), you’re done with this part. That was easy!

Now you must regenerate configure. But to do that, you’ll need to tell autoconf how to find the new macro you’ve used. The easiest way to do this is to use the aclocal program to generate your aclocal.m4 for you. But wait... you already have an aclocal.m4, because you had to write some hairy macros for your program. The aclocal program lets you put your own macros into acinclude.m4, so simply rename and then run:

mv aclocal.m4 acinclude.m4
aclocal
autoconf

Now it is time to write your Makefile.am for zardoz. Since zardoz is a user program, you want to install it where the rest of the user programs go. Additionally, zardoz has some Texinfo documentation. Your configure.in script uses AC_REPLACE_FUNCS, so you need to link against ‘@LIBOBJS@’. So here’s what you’d write:

bin_PROGRAMS = zardoz
zardoz_SOURCES = main.c head.c float.c vortex9.c gun.c
zardoz_LDADD = @LIBOBJS@

info_TEXINFOS = zardoz.texi

Now you can run automake --add-missing to generate your Makefile.in and grab any auxiliary files you might need, and you’re done!

3.2 A classic program

GNU hello is renowned for its classic simplicity and versatility. This section shows how Automake could be used with the GNU Hello package. The examples below are from the latest beta version of GNU Hello, but with all of the maintainer-only code stripped out, as well as all copyright comments.

Of course, GNU Hello is somewhat more featureful than your traditional two-liner. GNU Hello is internationalized, does option processing, and has a manual and a test suite.

Here is the configure.in from GNU Hello:

dnl Process this file with autoconf to produce a configure script.
AC_INIT(src/hello.c)
AM_INIT_AUTOMAKE(hello, 1.3.11)
AM_CONFIG_HEADER(config.h)

dnl Set of available languages.
ALL_LINGUAS="de fr es ko nl no pl pt sl sv"

dnl Checks for programs.
AC_PROG_CC
AC_ISC_POSIX

dnl Checks for libraries.

dnl Checks for header files.
AC_STDC_HEADERS
AC_HAVE_HEADERS(string.h fcntl.h sys/file.h sys/param.h)

dnl Checks for library functions.
AC_FUNC_ALLOCA

dnl Check for st_blksize in struct stat
AC_ST_BLKSIZE

dnl internationalization macros
AM_GNU_GETTEXT
AC_OUTPUT([Makefile doc/Makefile intl/Makefile po/Makefile.in \
           src/Makefile tests/Makefile tests/hello],
   [chmod +x tests/hello])

The ‘AM_’ macros are provided by Automake (or the Gettext library); the rest are standard Autoconf macros.

The top-level Makefile.am:

EXTRA_DIST = BUGS ChangeLog.O
SUBDIRS = doc intl po src tests

As you can see, all the work here is really done in subdirectories.

The po and intl directories are automatically generated using gettextize; they will not be discussed here.

In doc/Makefile.am we see:

info_TEXINFOS = hello.texi
hello_TEXINFOS = gpl.texi

This is sufficient to build, install, and distribute the GNU Hello manual.

Here is tests/Makefile.am:

TESTS = hello
EXTRA_DIST = hello.in testdata

The script hello is generated by configure, and is the only test case. make check will run this test.

Last we have src/Makefile.am, where all the real work is done:

bin_PROGRAMS = hello
hello_SOURCES = hello.c version.c getopt.c getopt1.c getopt.h system.h
hello_LDADD = @INTLLIBS@ @ALLOCA@
localedir = $(datadir)/locale
INCLUDES = -I../intl -DLOCALEDIR=\"$(localedir)\"

3.3 Building etags and ctags

Here is another, trickier example. It shows how to generate two programs (ctags and etags) from the same source file (etags.c). The difficult part is that each compilation of etags.c requires different cpp flags.

bin_PROGRAMS = etags ctags
ctags_SOURCES =
ctags_LDADD = ctags.o

etags.o: etags.c
        $(COMPILE) -DETAGS_REGEXPS -c etags.c

ctags.o: etags.c
        $(COMPILE) -DCTAGS -o ctags.o -c etags.c

Note that ctags_SOURCES is defined to be empty—that way no implicit value is substituted. The implicit value, however, is used to generate etags from etags.o.

ctags_LDADD is used to get ctags.o into the link line. ctags_DEPENDENCIES is generated by Automake.

The above rules won’t work if your compiler doesn’t accept both ‘-c’ and ‘-o’. The simplest fix for this is to introduce a bogus dependency (to avoid problems with a parallel make):

etags.o: etags.c ctags.o
        $(COMPILE) -DETAGS_REGEXPS -c etags.c

ctags.o: etags.c
        $(COMPILE) -DCTAGS -c etags.c && mv etags.o ctags.o

Also, these explicit rules do not work if the de-ANSI-fication feature is used (see Automatic de-ANSI-fication). Supporting de-ANSI-fication requires a little more work:

etags._o: etags._c ctags.o
        $(COMPILE) -DETAGS_REGEXPS -c etags.c

ctags._o: etags._c
        $(COMPILE) -DCTAGS -c etags.c && mv etags._o ctags.o

As it turns out, there is also a much easier way to do this same task. Some of the above techniques are useful enough that we’ve kept the example in the manual. However if you were to build etags and ctags in real life, you would probably use per-program compilation flags, like so:

bin_PROGRAMS = ctags etags

ctags_SOURCES = etags.c
ctags_CFLAGS = -DCTAGS

etags_SOURCES = etags.c
etags_CFLAGS = -DETAGS_REGEXPS

In this case Automake will cause etags.c to be compiled twice, with different flags. De-ANSI-fication will work automatically. In this instance, the names of the object files would be chosen by automake; they would be ctags-etags.c and etags-etags.o. (The name of the object files rarely matters.)

5.1 Configuration requirements

The one real requirement of Automake is that your configure.in call AM_INIT_AUTOMAKE. This macro does several things which are required for proper Automake operation.

Here are the other macros which Automake requires but which are not run by AM_INIT_AUTOMAKE:

AC_OUTPUT

Automake uses this to determine which files to create (see Creating Output Files in The Autoconf Manual). Listed files named Makefile are treated as Makefiles. Other listed files are treated differently. Currently the only difference is that a Makefile is removed by make distclean, while other files are removed by make clean.

You may need the following macros in some conditions, even though they are not required.

AC_CHECK_TOOL([STRIP],[strip]) ¶

Installed binaries are usually stripped using strip when you run make install-strip. However strip might not be the right tool to use in cross-compilation environments, therefore Automake will honor the STRIP environment variable to overrule the program used to perform stripping. Automake will not set STRIP itself. If your package is not setup for cross-compilation you do not have to care (strip is ok), otherwise you can set STRIP automatically by calling AC_CHECK_TOOL([STRIP],[strip]) from your configure.in.

5.2 Other things Automake recognizes

Automake will also recognize the use of certain macros and tailor the generated Makefile.in appropriately. Currently recognized macros and their effects are:

AC_CONFIG_HEADER

Automake requires the use of AM_CONFIG_HEADER, which is similar to AC_CONFIG_HEADER (see Configuration Header Files in The Autoconf Manual), but does some useful Automake-specific work.

AC_CONFIG_AUX_DIR

Automake will look for various helper scripts, such as mkinstalldirs, in the directory named in this macro invocation. If not seen, the scripts are looked for in their ‘standard’ locations (either the top source directory, or in the source directory corresponding to the current Makefile.am, whichever is appropriate). See Finding ‘configure’ Input in The Autoconf Manual. FIXME: give complete list of things looked for in this directory

AC_PATH_XTRA

Automake will insert definitions for the variables defined by AC_PATH_XTRA into each Makefile.in that builds a C program or library. See System Services in The Autoconf Manual.

AC_CANONICAL_HOST

AC_CHECK_TOOL

Automake will ensure that config.guess and config.sub exist. Also, the Makefile variables ‘host_alias’ and ‘host_triplet’ are introduced. See both Getting the Canonical System Type in The Autoconf Manual, and Generic Program Checks in The Autoconf Manual.

AC_CANONICAL_SYSTEM

This is similar to AC_CANONICAL_HOST, but also defines the Makefile variables ‘build_alias’ and ‘target_alias’. See Getting the Canonical System Type in The Autoconf Manual.

AC_FUNC_ALLOCA

AC_FUNC_GETLOADAVG

AC_FUNC_MEMCMP

AC_STRUCT_ST_BLOCKS

AC_FUNC_FNMATCH

AC_FUNC_MKTIME

AM_FUNC_STRTOD

AC_REPLACE_FUNCS

AC_REPLACE_GNU_GETOPT

AM_WITH_REGEX

Automake will ensure that the appropriate dependencies are generated for the objects corresponding to these macros. Also, Automake will verify that the appropriate source files are part of the distribution. Note that Automake does not come with any of the C sources required to use these macros, so automake -a will not install the sources. See Building a library, for more information. Also, see Particular Function Checks in The Autoconf Manual.

LIBOBJS

Automake will detect statements which put .o files into LIBOBJS, and will treat these additional files as if they were discovered via AC_REPLACE_FUNCS. See Generic Function Checks in The Autoconf Manual.

AC_PROG_RANLIB

This is required if any libraries are built in the package. See Particular Program Checks in The Autoconf Manual.

AC_PROG_CXX

This is required if any C++ source is included. See Particular Program Checks in The Autoconf Manual.

AC_PROG_F77

This is required if any Fortran 77 source is included. This macro is distributed with Autoconf version 2.13 and later. See Particular Program Checks in The Autoconf Manual.

AC_F77_LIBRARY_LDFLAGS

This is required for programs and shared libraries that are a mixture of languages that include Fortran 77 (see Mixing Fortran 77 With C and C++). See Autoconf macros supplied with Automake.

AC_PROG_LIBTOOL

Automake will turn on processing for libtool (see Introduction in The Libtool Manual).

AC_PROG_YACC

If a Yacc source file is seen, then you must either use this macro or define the variable ‘YACC’ in configure.in. The former is preferred (see Particular Program Checks in The Autoconf Manual).

AC_DECL_YYTEXT

This macro is required if there is Lex source in the package. See Particular Program Checks in The Autoconf Manual.

AC_PROG_LEX

If a Lex source file is seen, then this macro must be used. See Particular Program Checks in The Autoconf Manual.

AM_C_PROTOTYPES

This is required when using automatic de-ANSI-fication; see Automatic de-ANSI-fication.

AM_GNU_GETTEXT

This macro is required for packages which use GNU gettext (see Gettext). It is distributed with gettext. If Automake sees this macro it ensures that the package meets some of gettext’s requirements.

AM_MAINTAINER_MODE ¶

This macro adds a ‘--enable-maintainer-mode’ option to configure. If this is used, automake will cause ‘maintainer-only’ rules to be turned off by default in the generated Makefile.ins. This macro is disallowed in ‘Gnits’ mode (see The effect of --gnu and --gnits). This macro defines the ‘MAINTAINER_MODE’ conditional, which you can use in your own Makefile.am.

AC_SUBST

AC_CHECK_TOOL

AC_CHECK_PROG

AC_CHECK_PROGS

AC_PATH_PROG

AC_PATH_PROGS

For each of these macros, the first argument is automatically defined as a variable in each generated Makefile.in. See Setting Output Variables in The Autoconf Manual, and Generic Program Checks in The Autoconf Manual.

5.3 Auto-generating aclocal.m4

Automake includes a number of Autoconf macros which can be used in your package; some of them are actually required by Automake in certain situations. These macros must be defined in your aclocal.m4; otherwise they will not be seen by autoconf.

The aclocal program will automatically generate aclocal.m4 files based on the contents of configure.in. This provides a convenient way to get Automake-provided macros, without having to search around. Also, the aclocal mechanism is extensible for use by other packages.

At startup, aclocal scans all the .m4 files it can find, looking for macro definitions. Then it scans configure.in. Any mention of one of the macros found in the first step causes that macro, and any macros it in turn requires, to be put into aclocal.m4.

The contents of acinclude.m4, if it exists, are also automatically included in aclocal.m4. This is useful for incorporating local macros into configure.

aclocal tries to be smart about looking for new AC_DEFUNs in the files it scans. It will warn if it finds duplicates. It also tries to copy the full text of the scanned file into aclocal.m4, including both ‘#’ and ‘dnl’ comments. If you want to make a comment which will be completely ignored by aclocal, use ‘##’ as the comment leader.

aclocal accepts the following options:

--acdir=dir ¶

Look for the macro files in dir instead of the installation directory. This is typically used for debugging.

--help ¶

Print a summary of the command line options and exit.

-I dir ¶

Add the directory dir to the list of directories searched for .m4 files.

--output=file ¶

Cause the output to be put into file instead of aclocal.m4.

--print-ac-dir ¶

Prints the name of the directory which aclocal will search to find the .m4 files. When this option is given, normal processing is suppressed. This option can be used by a package to determine where to install a macro file.

--verbose ¶

Print the names of the files it examines.

--version ¶

Print the version number of Automake and exit.

5.4 Autoconf macros supplied with Automake

AM_CONFIG_HEADER

Automake will generate rules to automatically regenerate the config header. If you do use this macro, you must create the file stamp-h.in in your source directory. It can be empty.

AM_ENABLE_MULTILIB

This is used when a “multilib” library is being built. The first optional argument is the name of the Makefile being generated; it defaults to ‘Makefile’. The second option argument is used to find the top source directory; it defaults to the empty string (generally this should not be used unless you are familiar with the internals). See Support for Multilibs.

_AM_DEPENDENCIES

AM_SET_DEPDIR

AM_DEP_TRACK

AM_OUTPUT_DEPENDENCY_COMMANDS

These macros are used to implement automake’s automatic dependency tracking scheme. They are called automatically by automake when required, and there should be no need to invoke them manually.

AM_FUNC_STRTOD

If the strtod function is not available, or does not work correctly (like the one on SunOS 5.4), add strtod.o to output variable LIBOBJS.

AM_FUNC_ERROR_AT_LINE

If the function error_at_line is not found, then add error.o to LIBOBJS.

AM_FUNC_OBSTACK

Check for the GNU obstacks code; if not found, add obstack.o to ‘LIBOBJS’.

AM_C_PROTOTYPES

Check to see if function prototypes are understood by the compiler. If so, define ‘PROTOTYPES’ and set the output variables ‘U’ and ‘ANSI2KNR’ to the empty string. Otherwise, set ‘U’ to ‘_’ and ‘ANSI2KNR’ to ‘./ansi2knr’. Automake uses these values to implement automatic de-ANSI-fication.

AM_HEADER_TIOCGWINSZ_NEEDS_SYS_IOCTL

If the use of TIOCGWINSZ requires <sys/ioctl.h>, then define GWINSZ_IN_SYS_IOCTL. Otherwise TIOCGWINSZ can be found in <termios.h>.

AM_INIT_AUTOMAKE

Runs many macros that most configure.in’s need. This macro has two required arguments, the package and the version number. By default this macro AC_DEFINE’s ‘PACKAGE’ and ‘VERSION’. This can be avoided by passing in a non-empty third argument.

AM_MAKE_INCLUDE

This macro is used to discover how the user’s make handles include statements. This macro is automatically invoked when needed; there should be no need to invoke it manually.

AM_PATH_LISPDIR

Searches for the program emacs, and, if found, sets the output variable lispdir to the full path to Emacs’ site-lisp directory.

AM_PROG_AS

Use this macro when you have assembly code in your project. This will choose the assembler for you (by default the C compiler), and will set ASFLAGS if required.

AM_PROG_CC_C_O

This is like AC_PROG_CC_C_O, but it generates its results in the manner required by automake. You must use this instead of AC_PROG_CC_C_O when you need this functionality.

AM_PROG_CC_STDC

If the C compiler in not in ANSI C mode by default, try to add an option to output variable CC to make it so. This macro tries various options that select ANSI C on some system or another. It considers the compiler to be in ANSI C mode if it handles function prototypes correctly.

If you use this macro, you should check after calling it whether the C compiler has been set to accept ANSI C; if not, the shell variable am_cv_prog_cc_stdc is set to ‘no’. If you wrote your source code in ANSI C, you can make an un-ANSIfied copy of it by using the ansi2knr option (see Automatic de-ANSI-fication).

AM_PROG_LEX ¶

Like AC_PROG_LEX with AC_DECL_YYTEXT (see Particular Program Checks in The Autoconf Manual), but uses the missing script on systems that do not have lex. ‘HP-UX 10’ is one such system.

Autoconf 2.50 and higher, in order to simplify the interface, includes the body of AC_DECL_YYTEXT in AC_PROG_LEX. To ensure backward compatibility, AC_DECL_YYTEXT is nevertheless defined as an invocation of AC_PROG_LEX. Since AM_PROG_LEX invokes both, it causes an annoying but benign warning (AC_PROG_LEX invoked multiple times) which you should just ignore. In the future, once Automake requires Autoconf 2.50, this issue will be fixed, but the current compatibility with Autoconf 2.13 prevents this.

AM_PROG_GCJ

This macro finds the gcj program or causes an error. It sets ‘GCJ’ and ‘GCJFLAGS’. gcj is the Java front-end to the GNU Compiler Collection.

AM_PROG_INSTALL_STRIP

This is used to find a version of install which can be used to strip a program at installation time. This macro is automatically included when required.

AM_SANITY_CHECK

This checks to make sure that a file created in the build directory is newer than a file in the source directory. This can fail on systems where the clock is set incorrectly. This macro is automatically run from AM_INIT_AUTOMAKE.

AM_SYS_POSIX_TERMIOS ¶

Check to see if POSIX termios headers and functions are available on the system. If so, set the shell variable am_cv_sys_posix_termios to ‘yes’. If not, set the variable to ‘no’.

AM_TYPE_PTRDIFF_T ¶

Define ‘HAVE_PTRDIFF_T’ if the type ‘ptrdiff_t’ is defined in <stddef.h>.

AM_WITH_DMALLOC ¶

Add support for the dmalloc package. If the user configures with ‘--with-dmalloc’, then define WITH_DMALLOC and add ‘-ldmalloc’ to LIBS.

AM_WITH_REGEX ¶

Adds ‘--with-regex’ to the configure command line. If specified (the default), then the ‘regex’ regular expression library is used, regex.o is put into ‘LIBOBJS’, and ‘WITH_REGEX’ is defined.. If ‘--without-regex’ is given, then the ‘rx’ regular expression library is used, and rx.o is put into ‘LIBOBJS’.

5.5 Writing your own aclocal macros

The aclocal program doesn’t have any built-in knowledge of any macros, so it is easy to extend it with your own macros.

This is mostly used for libraries which want to supply their own Autoconf macros for use by other programs. For instance the gettext library supplies a macro AM_GNU_GETTEXT which should be used by any package using gettext. When the library is installed, it installs this macro so that aclocal will find it.

A file of macros should be a series of AC_DEFUN’s. The aclocal programs also understands AC_REQUIRE, so it is safe to put each macro in a separate file. See Prerequisite Macros in The Autoconf Manual, and Macro Definitions in The Autoconf Manual.

A macro file’s name should end in .m4. Such files should be installed in $(datadir)/aclocal.

9.1 Building a program

• Introductory blathering
• Conditional compilations
• Linking the program

bin_PROGRAMS = hello

hello_SOURCES = hello.c version.c getopt.c getopt1.c getopt.h system.h

EXTRA_hello_SOURCES = hello-linux.c

if LINUX
hello_SOURCES = hello-linux.c
else
hello_SOURCES = hello-generic.c
endif

bin_PROGRAMS = cpio pax @MT@
libexec_PROGRAMS = @RMT@
EXTRA_PROGRAMS = mt rmt

LDADD = ../lib/libcpio.a @INTLLIBS@
rmt_LDADD =

cpio_SOURCES = …
pax_SOURCES = …
mt_SOURCES = …
rmt_SOURCES = …

9.2 Building a library

Building a library is much like building a program. In this case, the name of the primary is ‘LIBRARIES’. Libraries can be installed in libdir or pkglibdir.

See Building a Shared Library, for information on how to build shared libraries using Libtool and the ‘LTLIBRARIES’ primary.

Each ‘_LIBRARIES’ variable is a list of the libraries to be built. For instance to create a library named libcpio.a, but not install it, you would write:

noinst_LIBRARIES = libcpio.a

The sources that go into a library are determined exactly as they are for programs, via the ‘_SOURCES’ variables. Note that the library name is canonicalized (see How derived variables are named), so the ‘_SOURCES’ variable corresponding to liblob.a is ‘liblob_a_SOURCES’, not ‘liblob.a_SOURCES’.

Extra objects can be added to a library using the ‘library_LIBADD’ variable. This should be used for objects determined by configure. Again from cpio:

libcpio_a_LIBADD = @LIBOBJS@ @ALLOCA@

In addition, sources for extra objects that will not exist until configure-time must be added to the BUILT_SOURCES variable (see Built sources).

9.3 Building a Shared Library

Building shared libraries is a relatively complex matter. For this reason, GNU Libtool (see Introduction in The Libtool Manual) was created to help build shared libraries in a platform-independent way.

Automake uses Libtool to build libraries declared with the ‘LTLIBRARIES’ primary. Each ‘_LTLIBRARIES’ variable is a list of shared libraries to build. For instance, to create a library named libgettext.a and its corresponding shared libraries, and install them in ‘libdir’, write:

lib_LTLIBRARIES = libgettext.la

Note that shared libraries must be installed, so check_LTLIBRARIES is not allowed. However, noinst_LTLIBRARIES is allowed. This feature should be used for libtool “convenience libraries”.

For each library, the ‘library_LIBADD’ variable contains the names of extra libtool objects (.lo files) to add to the shared library. The ‘library_LDFLAGS’ variable contains any additional libtool flags, such as ‘-version-info’ or ‘-static’.

Where an ordinary library might include @LIBOBJS@, a libtool library must use @LTLIBOBJS@. This is required because the object files that libtool operates on do not necessarily end in .o. The libtool manual contains more details on this topic.

For libraries installed in some directory, Automake will automatically supply the appropriate ‘-rpath’ option. However, for libraries determined at configure time (and thus mentioned in EXTRA_LTLIBRARIES), Automake does not know the eventual installation directory; for such libraries you must add the ‘-rpath’ option to the appropriate ‘_LDFLAGS’ variable by hand.

Ordinarily, Automake requires that a shared library’s name start with ‘lib’. However, if you are building a dynamically loadable module then you might wish to use a "nonstandard" name. In this case, put -module into the ‘_LDFLAGS’ variable.

See The Libtool Manual in The Libtool Manual, for more information.

9.4 Program and Library Variables

Associated with each program are a collection of variables which can be used to modify how that program is built. There is a similar list of such variables for each library. The canonical name of the program (or library) is used as a base for naming these variables.

In the list below, we use the name “maude” to refer to the program or library. In your Makefile.am you would replace this with the canonical name of your program. This list also refers to “maude” as a program, but in general the same rules apply for both static and dynamic libraries; the documentation below notes situations where programs and libraries differ.

‘maude_SOURCES’

This variable, if it exists, lists all the source files which are compiled to build the program. These files are added to the distribution by default. When building the program, Automake will cause each source file to be compiled to a single .o file (or .lo when using libtool). Normally these object files are named after the source file, but other factors can change this. If a file in the ‘_SOURCES’ variable has an unrecognized extension, Automake will do one of two things with it. If a suffix rule exists for turning files with the unrecognized extension into .o files, then automake will treat this file as it will any other source file (see Support for Other Languages). Otherwise, the file will be ignored as though it were a header file.

The prefixes ‘dist_’ and ‘nodist_’ can be used to control whether files listed in a ‘_SOURCES’ variable are distributed. ‘dist_’ is redundant, as sources are distributed by default, but it can be specified for clarity if desired.

It is possible to have both ‘dist_’ and ‘nodist_’ variants of a given ‘_SOURCES’ variable at once; this lets you easily distribute some files and not others, for instance:

nodist_maude_SOURCES = nodist.c
dist_maude_SOURCES = dist-me.c

By default the output file (on Unix systems, the .o file) will be put into the current build directory. However, if the option subdir-objects is in effect in the current directory then the .o file will be put into the subdirectory named after the source file. For instance, with subdir-objects enabled, sub/dir/file.c will be compiled to sub/dir/file.o. Some people prefer this mode of operation. You can specify subdir-objects in AUTOMAKE_OPTIONS (see Changing Automake’s Behavior).

‘EXTRA_maude_SOURCES’

Automake needs to know the list of files you intend to compile statically. For one thing, this is the only way Automake has of knowing what sort of language support a given Makefile.in requires. ³ This means that, for example, you can’t put a configure substitution like ‘@my_sources@’ into a ‘_SOURCES’ variable. If you intend to conditionally compile source files and use configure to substitute the appropriate object names into, e.g., ‘_LDADD’ (see below), then you should list the corresponding source files in the ‘EXTRA_’ variable.

This variable also supports ‘dist_’ and ‘nodist_’ prefixes, e.g., ‘nodist_EXTRA_maude_SOURCES’.

‘maude_AR’

A static library is created by default by invoking $(AR) cru followed by the name of the library and then the objects being put into the library. You can override this by setting the ‘_AR’ variable. This is usually used with C++; some C++ compilers require a special invocation in order to instantiate all the templates which should go into a library. For instance, the SGI C++ compiler likes this macro set like so:

libmaude_a_AR = $(CXX) -ar -o

‘maude_LIBADD’

Extra objects can be added to a static library using the ‘_LIBADD’ variable. This should be used for objects determined by configure. Note that ‘_LIBADD’ is not used for shared libraries; there you must use ‘_LDADD’.

‘maude_LDADD’

Extra objects can be added to a shared library or a program by listing them in the ‘_LDADD’ variable. This should be used for objects determined by configure.

‘_LDADD’ is inappropriate for passing program-specific linker flags (except for ‘-l’, ‘-L’, ‘-dlopen’ and ‘-dlpreopen’). Use the ‘_LDFLAGS’ variable for this purpose.

For instance, if your configure.in uses AC_PATH_XTRA, you could link your program against the X libraries like so:

maude_LDADD = $(X_PRE_LIBS) $(X_LIBS) $(X_EXTRA_LIBS)

‘maude_LDFLAGS’

This variable is used to pass extra flags to the link step of a program or a shared library.

‘maude_LINK’

You can override the linker on a per-program basis. By default the linker is chosen according to the languages used by the program. For instance, a program that includes C++ source code would use the C++ compiler to link. The ‘_LINK’ variable must hold the name of a command which can be passed all the .o file names as arguments. Note that the name of the underlying program is not passed to ‘_LINK’; typically one uses ‘$@’:

maude_LINK = $(CCLD) -magic -o $@

‘maude_CFLAGS’

Automake allows you to set compilation flags on a per-program (or per-library) basis. A single source file can be included in several programs, and it will potentially be compiled with different flags for each program. This works for any language directly supported by Automake. The flags are ‘_CFLAGS’, ‘_CXXFLAGS’, ‘_OBJCFLAGS’, ‘_YFLAGS’, ‘_ASFLAGS’, ‘_FFLAGS’, ‘_RFLAGS’, and ‘_GCJFLAGS’.

When using a per-program compilation flag, Automake will choose a different name for the intermediate object files. Ordinarily a file like sample.c will be compiled to produce sample.o. However, if the program’s ‘_CFLAGS’ variable is set, then the object file will be named, for instance, maude-sample.o.

In compilations with per-program flags, the ordinary ‘AM_’ form of the flags variable is not automatically included in the compilation (however, the user form of the variable is included). So for instance, if you want the hypothetical maude compilations to also use the value of ‘AM_CFLAGS’, you would need to write:

maude_CFLAGS = ... your flags ... $(AM_CFLAGS)

‘maude_DEPENDENCIES’

It is also occasionally useful to have a program depend on some other target which is not actually part of that program. This can be done using the ‘_DEPENDENCIES’ variable. Each program depends on the contents of such a variable, but no further interpretation is done.

If ‘_DEPENDENCIES’ is not supplied, it is computed by Automake. The automatically-assigned value is the contents of ‘_LDADD’, with most configure substitutions, ‘-l’, ‘-L’, ‘-dlopen’ and ‘-dlpreopen’ options removed. The configure substitutions that are left in are only ‘@LIBOBJS@’ and ‘@ALLOCA@’; these are left because it is known that they will not cause an invalid value for ‘_DEPENDENCIES’ to be generated.

‘maude_SHORTNAME’

On some platforms the allowable file names are very short. In order to support these systems and per-program compilation flags at the same time, Automake allows you to set a “short name” which will influence how intermediate object files are named. For instance, if you set ‘maude_SHORTNAME’ to ‘m’, then in the above per-program compilation flag example the object file would be named m-sample.o rather than maude-sample.o. This facility is rarely needed in practice, and we recommend avoiding it until you find it is required.

9.5 Special handling for LIBOBJS and ALLOCA

Automake explicitly recognizes the use of @LIBOBJS@ and @ALLOCA@, and uses this information, plus the list of LIBOBJS files derived from configure.in to automatically include the appropriate source files in the distribution (see What Goes in a Distribution). These source files are also automatically handled in the dependency-tracking scheme; see See Automatic dependency tracking.

@LIBOBJS@ and @ALLOCA@ are specially recognized in any ‘_LDADD’ or ‘_LIBADD’ variable.

9.6 Variables used when building a program

Occasionally it is useful to know which Makefile variables Automake uses for compilations; for instance you might need to do your own compilation in some special cases.

Some variables are inherited from Autoconf; these are CC, CFLAGS, CPPFLAGS, DEFS, LDFLAGS, and LIBS.

There are some additional variables which Automake itself defines:

AM_CPPFLAGS ¶

The contents of this macro are passed to every compilation which invokes the C preprocessor; it is a list of arguments to the preprocessor. For instance, ‘-I’ and ‘-D’ options should be listed here.

Automake already provides some ‘-I’ options automatically. In particular it generates ‘-I$(srcdir)’, ‘-I.’, and a ‘-I’ pointing to the directory holding config.h (if you’ve used AC_CONFIG_HEADER or AM_CONFIG_HEADER). You can disable the default ‘-I’ options using the ‘nostdinc’ option.

INCLUDES ¶

This does the same job as ‘AM_CPPFLAGS’. It is an older name for the same functionality. This macro is deprecated; we suggest using ‘AM_CPPFLAGS’ instead.

AM_CFLAGS ¶

This is the variable which the Makefile.am author can use to pass in additional C compiler flags. It is more fully documented elsewhere. In some situations, this is not used, in preference to the per-executable (or per-library) CFLAGS.

COMPILE ¶

This is the command used to actually compile a C source file. The filename is appended to form the complete command line.

LINK ¶

This is the command used to actually link a C program. It already includes ‘-o $@’ and the usual variable references (for instance, CFLAGS); it takes as “arguments” the names of the object files and libraries to link in.

9.7 Yacc and Lex support

Automake has somewhat idiosyncratic support for Yacc and Lex.

Automake assumes that the .c file generated by yacc (or lex) should be named using the basename of the input file. That is, for a yacc source file foo.y, Automake will cause the intermediate file to be named foo.c (as opposed to y.tab.c, which is more traditional).

The extension of a yacc source file is used to determine the extension of the resulting ‘C’ or ‘C++’ file. Files with the extension ‘.y’ will be turned into ‘.c’ files; likewise, ‘.yy’ will become ‘.cc’; ‘.y++’, ‘c++’; and ‘.yxx’, ‘.cxx’.

Likewise, lex source files can be used to generate ‘C’ or ‘C++’; the extensions ‘.l’, ‘.ll’, ‘.l++’, and ‘.lxx’ are recognized.

You should never explicitly mention the intermediate (‘C’ or ‘C++’) file in any ‘SOURCES’ variable; only list the source file.

The intermediate files generated by yacc (or lex) will be included in any distribution that is made. That way the user doesn’t need to have yacc or lex.

If a yacc source file is seen, then your configure.in must define the variable ‘YACC’. This is most easily done by invoking the macro ‘AC_PROG_YACC’ (see Particular Program Checks in The Autoconf Manual).

When yacc is invoked, it is passed ‘YFLAGS’ and ‘AM_YFLAGS’. The former is a user variable and the latter is intended for the Makefile.am author.

Similarly, if a lex source file is seen, then your configure.in must define the variable ‘LEX’. You can use ‘AC_PROG_LEX’ to do this (see Particular Program Checks in The Autoconf Manual). Automake’s lex support also requires that you use the ‘AC_DECL_YYTEXT’ macro—automake needs to know the value of ‘LEX_OUTPUT_ROOT’. This is all handled for you if you use the AM_PROG_LEX macro (see Autoconf macros supplied with Automake).

When yacc is invoked, it is passed ‘LFLAGS’ and ‘AM_LFLAGS’. The former is a user variable and the latter is intended for the Makefile.am author.

Automake makes it possible to include multiple yacc (or lex) source files in a single program. Automake uses a small program called ylwrap to run yacc (or lex) in a subdirectory. This is necessary because yacc’s output filename is fixed, and a parallel make could conceivably invoke more than one instance of yacc simultaneously. The ylwrap program is distributed with Automake. It should appear in the directory specified by ‘AC_CONFIG_AUX_DIR’ (see Finding ‘configure’ Input in The Autoconf Manual), or the current directory if that macro is not used in configure.in.

For yacc, simply managing locking is insufficient. The output of yacc always uses the same symbol names internally, so it isn’t possible to link two yacc parsers into the same executable.

We recommend using the following renaming hack used in gdb:

#define	yymaxdepth c_maxdepth
#define	yyparse	c_parse
#define	yylex	c_lex
#define	yyerror	c_error
#define	yylval	c_lval
#define	yychar	c_char
#define	yydebug	c_debug
#define	yypact	c_pact
#define	yyr1	c_r1
#define	yyr2	c_r2
#define	yydef	c_def
#define	yychk	c_chk
#define	yypgo	c_pgo
#define	yyact	c_act
#define	yyexca	c_exca
#define yyerrflag c_errflag
#define yynerrs	c_nerrs
#define	yyps	c_ps
#define	yypv	c_pv
#define	yys	c_s
#define	yy_yys	c_yys
#define	yystate	c_state
#define	yytmp	c_tmp
#define	yyv	c_v
#define	yy_yyv	c_yyv
#define	yyval	c_val
#define	yylloc	c_lloc
#define yyreds	c_reds
#define yytoks	c_toks
#define yylhs	c_yylhs
#define yylen	c_yylen
#define yydefred c_yydefred
#define yydgoto	c_yydgoto
#define yysindex c_yysindex
#define yyrindex c_yyrindex
#define yygindex c_yygindex
#define yytable	 c_yytable
#define yycheck	 c_yycheck
#define yyname   c_yyname
#define yyrule   c_yyrule

For each define, replace the ‘c_’ prefix with whatever you like. These defines work for bison, byacc, and traditional yaccs. If you find a parser generator that uses a symbol not covered here, please report the new name so it can be added to the list.

9.8 C++ Support

Automake includes full support for C++.

Any package including C++ code must define the output variable ‘CXX’ in configure.in; the simplest way to do this is to use the AC_PROG_CXX macro (see Particular Program Checks in The Autoconf Manual).

A few additional variables are defined when a C++ source file is seen:

CXX ¶

The name of the C++ compiler.

CXXFLAGS ¶

Any flags to pass to the C++ compiler.

AM_CXXFLAGS ¶

The maintainer’s variant of CXXFLAGS.

CXXCOMPILE ¶

The command used to actually compile a C++ source file. The file name is appended to form the complete command line.

CXXLINK ¶

The command used to actually link a C++ program.

9.9 Assembly Support

Automake includes some support for assembly code.

The variable AS holds the name of the compiler used to build assembly code. This compiler must work a bit like a C compiler; in particular it must accept ‘-c’ and ‘-o’. The value of ASFLAGS is passed to the compilation.

You are required to set AS and ASFLAGS via configure.in. The autoconf macro AM_PROG_AS will do this for you. Unless they are already set, it simply sets AS to the C compiler and ASFLAGS to the C compiler flags.

9.10 Fortran 77 Support

Automake includes full support for Fortran 77.

Any package including Fortran 77 code must define the output variable ‘F77’ in configure.in; the simplest way to do this is to use the AC_PROG_F77 macro (see Particular Program Checks in The Autoconf Manual). See Fortran 77 and Autoconf.

A few additional variables are defined when a Fortran 77 source file is seen:

F77 ¶

The name of the Fortran 77 compiler.

FFLAGS ¶

Any flags to pass to the Fortran 77 compiler.

AM_FFLAGS ¶

The maintainer’s variant of FFLAGS.

RFLAGS ¶

Any flags to pass to the Ratfor compiler.

AM_RFLAGS ¶

The maintainer’s variant of RFLAGS.

F77COMPILE ¶

The command used to actually compile a Fortran 77 source file. The file name is appended to form the complete command line.

FLINK ¶

The command used to actually link a pure Fortran 77 program or shared library.

Automake can handle preprocessing Fortran 77 and Ratfor source files in addition to compiling them⁴. Automake also contains some support for creating programs and shared libraries that are a mixture of Fortran 77 and other languages (see Mixing Fortran 77 With C and C++).

These issues are covered in the following sections.

• Preprocessing Fortran 77
• Compiling Fortran 77 Files
• Mixing Fortran 77 With C and C++
• Fortran 77 and Autoconf

bin_PROGRAMS = foo
foo_SOURCES  = main.cc foo.f
foo_LDADD    = libfoo.la @FLIBS@

pkglib_LTLIBRARIES = libfoo.la
libfoo_la_SOURCES  = bar.f baz.c zardoz.cc
libfoo_la_LIBADD   = $(FLIBS)

                     \              Linker
          source      \
           code        \     C        C++     Fortran
     -----------------  +---------+---------+---------+
                        |         |         |         |
     C                  |    x    |         |         |
                        |         |         |         |
                        +---------+---------+---------+
                        |         |         |         |
         C++            |         |    x    |         |
                        |         |         |         |
                        +---------+---------+---------+
                        |         |         |         |
               Fortran  |         |         |    x    |
                        |         |         |         |
                        +---------+---------+---------+
                        |         |         |         |
     C + C++            |         |    x    |         |
                        |         |         |         |
                        +---------+---------+---------+
                        |         |         |         |
     C +       Fortran  |         |         |    x    |
                        |         |         |         |
                        +---------+---------+---------+
                        |         |         |         |
         C++ + Fortran  |         |    x    |         |
                        |         |         |         |
                        +---------+---------+---------+
                        |         |         |         |
     C + C++ + Fortran  |         |    x    |         |
                        |         |         |         |
                        +---------+---------+---------+

9.11 Java Support

Automake includes support for compiled Java, using gcj, the Java front end to the GNU Compiler Collection.

Any package including Java code to be compiled must define the output variable ‘GCJ’ in configure.in; the variable ‘GCJFLAGS’ must also be defined somehow (either in configure.in or Makefile.am). The simplest way to do this is to use the AM_PROG_GCJ macro.

By default, programs including Java source files are linked with gcj.

As always, the contents of ‘AM_GCJFLAGS’ are passed to every compilation invoking gcj (in its role as an ahead-of-time compiler – when invoking it to create .class files, ‘AM_JAVACFLAGS’ is used instead). If it is necessary to pass options to gcj from Makefile.am, this macro, and not the user macro ‘GCJFLAGS’, should be used.

gcj can be used to compile .java, .class, .zip, or .jar files.

9.12 Support for Other Languages

Automake currently only includes full support for C, C++ (see C++ Support), Fortran 77 (see Fortran 77 Support), and Java (see Java Support). There is only rudimentary support for other languages, support for which will be improved based on user demand.

Some limited support for adding your own languages is available via the suffix rule handling; see Handling new file extensions.

9.13 Automatic de-ANSI-fication

Although the GNU standards allow the use of ANSI C, this can have the effect of limiting portability of a package to some older compilers (notably the SunOS C compiler).

Automake allows you to work around this problem on such machines by de-ANSI-fying each source file before the actual compilation takes place.

If the Makefile.am variable AUTOMAKE_OPTIONS (see Changing Automake’s Behavior) contains the option ansi2knr then code to handle de-ANSI-fication is inserted into the generated Makefile.in.

This causes each C source file in the directory to be treated as ANSI C. If an ANSI C compiler is available, it is used. If no ANSI C compiler is available, the ansi2knr program is used to convert the source files into K&R C, which is then compiled.

The ansi2knr program is simple-minded. It assumes the source code will be formatted in a particular way; see the ansi2knr man page for details.

Support for de-ANSI-fication requires the source files ansi2knr.c and ansi2knr.1 to be in the same package as the ANSI C source; these files are distributed with Automake. Also, the package configure.in must call the macro AM_C_PROTOTYPES (see Autoconf macros supplied with Automake).

Automake also handles finding the ansi2knr support files in some other directory in the current package. This is done by prepending the relative path to the appropriate directory to the ansi2knr option. For instance, suppose the package has ANSI C code in the src and lib subdirs. The files ansi2knr.c and ansi2knr.1 appear in lib. Then this could appear in src/Makefile.am:

AUTOMAKE_OPTIONS = ../lib/ansi2knr

If no directory prefix is given, the files are assumed to be in the current directory.

Files mentioned in LIBOBJS which need de-ANSI-fication will not be automatically handled. That’s because configure will generate an object name like regex.o, while make will be looking for regex_.o (when de-ANSI-fying). Eventually this problem will be fixed via autoconf magic, but for now you must put this code into your configure.in, just before the AC_OUTPUT call:

# This is necessary so that .o files in LIBOBJS are also built via
# the ANSI2KNR-filtering rules.
LIBOBJS=`echo $LIBOBJS|sed 's/\.o /\$U.o /g;s/\.o$/\$U.o/'`

Note that automatic de-ANSI-fication will not work when the package is being built for a different host architecture. That is because automake currently has no way to build ansi2knr for the build machine.

9.14 Automatic dependency tracking

As a developer it is often painful to continually update the Makefile.in whenever the include-file dependencies change in a project. Automake supplies a way to automatically track dependency changes.

Automake always uses complete dependencies for a compilation, including system headers. Automake’s model is that dependency computation should be a side effect of the build. To this end, dependencies are computed by running all compilations through a special wrapper program called depcomp. depcomp understands how to coax many different C and C++ compilers into generating dependency information in the format it requires. automake -a will install depcomp into your source tree for you. If depcomp can’t figure out how to properly invoke your compiler, dependency tracking will simply be disabled for your build.

Experience with earlier versions of Automake ⁶ taught us that it is not reliable to generate dependencies only on the maintainer’s system, as configurations vary too much. So instead Automake implements dependency tracking at build time.

Automatic dependency tracking can be suppressed by putting no-dependencies in the variable AUTOMAKE_OPTIONS. Or, you can invoke automake with the -i option. Dependency tracking is enabled by default.

The person building your package also can choose to disable dependency tracking by configuring with --disable-dependency-tracking.

9.15 Support for executable extensions

On some platforms, such as Windows, executables are expected to have an extension such as ‘.exe’. On these platforms, some compilers (GCC among them) will automatically generate foo.exe when asked to generate foo.

Automake provides mostly-transparent support for this. Unfortunately the support isn’t completely transparent; if you want your package to support these platforms then you must assist.

One thing you must be aware of is that, internally, Automake rewrites something like this:

bin_PROGRAMS = liver

to this:

bin_PROGRAMS = liver$(EXEEXT)

The targets Automake generates are likewise given the ‘$(EXEEXT)’ extension. EXEEXT

However, Automake cannot apply this rewriting to configure substitutions. This means that if you are conditionally building a program using such a substitution, then your configure.in must take care to add ‘$(EXEEXT)’ when constructing the output variable.

With Autoconf 2.13 and earlier, you must explicitly use AC_EXEEXT to get this support. With Autoconf 2.50, AC_EXEEXT is run automatically if you configure a compiler (say, through AC_PROG_CC).

Sometimes maintainers like to write an explicit link rule for their program. Without executable extension support, this is easy—you simply write a target with the same name as the program. However, when executable extension support is enabled, you must instead add the ‘$(EXEEXT)’ suffix.

Unfortunately, due to the change in Autoconf 2.50, this means you must always add this extension. However, this is a problem for maintainers who know their package will never run on a platform that has executable extensions. For those maintainers, the no-exeext option (see Changing Automake’s Behavior) will disable this feature. This works in a fairly ugly way; if no-exeext is seen, then the presence of a target named foo in Makefile.am will override an automake-generated target of the form foo$(EXEEXT). Without the no-exeext option, this use will give an error.

10.1 Executable Scripts

It is possible to define and install programs which are scripts. Such programs are listed using the ‘SCRIPTS’ primary name. Automake doesn’t define any dependencies for scripts; the Makefile.am should include the appropriate rules.

Automake does not assume that scripts are derived objects; such objects must be deleted by hand (see What Gets Cleaned).

The automake program itself is a Perl script that is generated at configure time from automake.in. Here is how this is handled:

bin_SCRIPTS = automake

Since automake appears in the AC_OUTPUT macro, a target for it is automatically generated.

Script objects can be installed in bindir, sbindir, libexecdir, or pkgdatadir.

10.2 Header files

Header files are specified by the ‘HEADERS’ family of variables. Generally header files are not installed, so the noinst_HEADERS variable will be the most used. ⁷

All header files must be listed somewhere; missing ones will not appear in the distribution. Often it is clearest to list uninstalled headers with the rest of the sources for a program. See Building a program. Headers listed in a ‘_SOURCES’ variable need not be listed in any ‘_HEADERS’ variable.

Headers can be installed in includedir, oldincludedir, or pkgincludedir.

10.3 Architecture-independent data files

Automake supports the installation of miscellaneous data files using the ‘DATA’ family of variables.

Such data can be installed in the directories datadir, sysconfdir, sharedstatedir, localstatedir, or pkgdatadir.

By default, data files are not included in a distribution. Of course, you can use the ‘dist_’ prefix to change this on a per-variable basis.

Here is how Automake installs its auxiliary data files:

pkgdata_DATA = clean-kr.am clean.am …

10.4 Built sources

Occasionally a file which would otherwise be called ‘source’ (e.g. a C ‘.h’ file) is actually derived from some other file. Such files should be listed in the BUILT_SOURCES variable.

BUILT_SOURCES is actually a bit of a misnomer, as any file which must be created early in the build process can be listed in this variable.

A source file listed in BUILT_SOURCES is created before the other all targets are made. However, such a source file is not compiled unless explicitly requested by mentioning it in some other ‘_SOURCES’ variable.

So, for instance, if you had header files which were created by a script run at build time, then you would list these headers in BUILT_SOURCES, to ensure that they would be built before any other compilations (perhaps ones using these headers) were started.

11.1 Emacs Lisp

Automake provides some support for Emacs Lisp. The ‘LISP’ primary is used to hold a list of .el files. Possible prefixes for this primary are ‘lisp_’ and ‘noinst_’. Note that if lisp_LISP is defined, then configure.in must run AM_PATH_LISPDIR (see Autoconf macros supplied with Automake).

By default Automake will byte-compile all Emacs Lisp source files using the Emacs found by AM_PATH_LISPDIR. If you wish to avoid byte-compiling, simply define the variable ELCFILES to be empty. Byte-compiled Emacs Lisp files are not portable among all versions of Emacs, so it makes sense to turn this off if you expect sites to have more than one version of Emacs installed. Furthermore, many packages don’t actually benefit from byte-compilation. Still, we recommend that you leave it enabled by default. It is probably better for sites with strange setups to cope for themselves than to make the installation less nice for everybody else.

11.2 Gettext

If AM_GNU_GETTEXT is seen in configure.in, then Automake turns on support for GNU gettext, a message catalog system for internationalization (see GNU Gettext in GNU gettext utilities).

The gettext support in Automake requires the addition of two subdirectories to the package, intl and po. Automake insures that these directories exist and are mentioned in SUBDIRS.

11.3 Libtool

Automake provides support for GNU Libtool (see Introduction in The Libtool Manual) with the ‘LTLIBRARIES’ primary. See Building a Shared Library.

11.4 Java

Automake provides some minimal support for Java compilation with the ‘JAVA’ primary.

Any .java files listed in a ‘_JAVA’ variable will be compiled with JAVAC at build time. By default, .class files are not included in the distribution.

Currently Automake enforces the restriction that only one ‘_JAVA’ primary can be used in a given Makefile.am. The reason for this restriction is that, in general, it isn’t possible to know which .class files were generated from which .java files – so it would be impossible to know which files to install where. For instance, a .java file can define multiple classes; the resulting .class file names cannot be predicted without parsing the .java file.

There are a few variables which are used when compiling Java sources:

JAVAC ¶

The name of the Java compiler. This defaults to ‘javac’.

JAVACFLAGS ¶

The flags to pass to the compiler. This is considered to be a user variable (see Variables reserved for the user).

AM_JAVACFLAGS ¶

More flags to pass to the Java compiler. This, and not JAVACFLAGS, should be used when it is necessary to put Java compiler flags into Makefile.am.

JAVAROOT ¶

The value of this variable is passed to the ‘-d’ option to javac. It defaults to ‘$(top_builddir)’.

CLASSPATH_ENV ¶

This variable is an sh expression which is used to set the CLASSPATH environment variable on the javac command line. (In the future we will probably handle class path setting differently.)

11.5 Python

Automake provides support for Python modules. Automake will turn on Python support if the AM_PATH_PYTHON macro is used in configure.in. The ‘PYTHON’ primary is used to hold a list of .py files. Possible prefixes for this primary are ‘python_’ and ‘noinst_’. Note that if python_PYTHON is defined, then configure.in must run AM_PATH_PYTHON. Python source files are included in the distribution by default.

AM_PATH_PYTHON takes a single optional argument. This argument, if present, is the minimum version of Python which can be used for this package. If the version of Python found on the system is older than the required version, then AM_PATH_PYTHON will cause an error.

AM_PATH_PYTHON creates several output variables based on the Python installation found during configuration.

PYTHON ¶

The name of the Python executable.

PYTHON_VERSION ¶

The Python version number, in the form major.minor (e.g. ‘1.5’). This is currently the value of sys.version[:3].

PYTHON_PREFIX ¶

The string $prefix. This term may be used in future work which needs the contents of Python’s sys.prefix, but general consensus is to always use the value from configure.

PYTHON_EXEC_PREFIX ¶

The string $exec_prefix. This term may be used in future work which needs the contents of Python’s sys.exec_prefix, but general consensus is to always use the value from configure.

PYTHON_PLATFORM ¶

The canonical name used by Python to describe the operating system, as given by sys.platform. This value is sometimes needed when building Python extensions.

pythondir ¶

The directory name for the site-packages subdirectory of the standard Python install tree.

pkgpythondir ¶

This is is the directory under pythondir which is named after the package. That is, it is ‘$(pythondir)/$(PACKAGE)’. It is provided as a convenience.

pyexecdir ¶

This is the directory where Python extension modules (shared libraries) should be installed.

pkgpyexecdir ¶

This is a convenience variable which is defined as ‘$(pyexecdir)/$(PACKAGE)’.

By default Automake will byte-compile all Python source files to both .pyc and .pyo forms. If you wish to avoid generating the optimized byte-code files, simply define the variable PYOFILES to be empty. Similarly, if you don’t wish to generate the standard byte-compiled files, define the variable PYCFILES to be empty.

12.1 Texinfo

If the current directory contains Texinfo source, you must declare it with the ‘TEXINFOS’ primary. Generally Texinfo files are converted into info, and thus the info_TEXINFOS macro is most commonly used here. Any Texinfo source file must end in the .texi, .txi, or .texinfo extension. We recommend .texi for new manuals.

If the .texi file @includes version.texi, then that file will be automatically generated. The file version.texi defines four Texinfo macros you can reference:

EDITION

VERSION

Both of these macros hold the version number of your program. They are kept separate for clarity.

UPDATED

This holds the date the primary .texi file was last modified.

UPDATED-MONTH

This holds the name of the month in which the primary .texi file was last modified.

The version.texi support requires the mdate-sh program; this program is supplied with Automake and automatically included when automake is invoked with the --add-missing option.

If you have multiple Texinfo files, and you want to use the version.texi feature, then you have to have a separate version file for each Texinfo file. Automake will treat any include in a Texinfo file that matches ‘vers*.texi’ just as an automatically generated version file.

When an info file is rebuilt, the program named by the MAKEINFO variable is used to invoke it. If the makeinfo program is found on the system then it will be used by default; otherwise missing will be used instead. The flags in the variables MAKEINFOFLAGS and AM_MAKEINFOFLAGS will be passed to the makeinfo invocation; the first of these is intended for use by the user (see Variables reserved for the user) and the second by the Makefile.am writer.

Sometimes an info file actually depends on more than one .texi file. For instance, in GNU Hello, hello.texi includes the file gpl.texi. You can tell Automake about these dependencies using the texi_TEXINFOS variable. Here is how GNU Hello does it:

info_TEXINFOS = hello.texi
hello_TEXINFOS = gpl.texi

By default, Automake requires the file texinfo.tex to appear in the same directory as the Texinfo source. However, if you used AC_CONFIG_AUX_DIR in configure.in (see Finding ‘configure’ Input in The Autoconf Manual), then texinfo.tex is looked for there. Automake supplies texinfo.tex if ‘--add-missing’ is given.

If your package has Texinfo files in many directories, you can use the variable TEXINFO_TEX to tell Automake where to find the canonical texinfo.tex for your package. The value of this variable should be the relative path from the current Makefile.am to texinfo.tex:

TEXINFO_TEX = ../doc/texinfo.tex

The option ‘no-texinfo.tex’ can be used to eliminate the requirement for texinfo.tex. Use of the variable TEXINFO_TEX is preferable, however, because that allows the dvi target to still work.

Automake generates an install-info target; some people apparently use this. By default, info pages are installed by ‘make install’. This can be prevented via the no-installinfo option.

12.2 Man pages

A package can also include man pages (but see the GNU standards on this matter, Man Pages in The GNU Coding Standards.) Man pages are declared using the ‘MANS’ primary. Generally the man_MANS macro is used. Man pages are automatically installed in the correct subdirectory of mandir, based on the file extension.

File extensions such as ‘.1c’ are handled by looking for the valid part of the extension and using that to determine the correct subdirectory of mandir. Valid section names are the digits ‘0’ through ‘9’, and the letters ‘l’ and ‘n’.

Sometimes developers prefer to name a man page something like foo.man in the source, and then rename it to have the correct suffix, e.g. foo.1, when installing the file. Automake also supports this mode. For a valid section named SECTION, there is a corresponding directory named ‘manSECTIONdir’, and a corresponding ‘_MANS’ variable. Files listed in such a variable are installed in the indicated section. If the file already has a valid suffix, then it is installed as-is; otherwise the file suffix is changed to match the section.

For instance, consider this example:

man1_MANS = rename.man thesame.1 alsothesame.1c

In this case, rename.man will be renamed to rename.1 when installed, but the other files will keep their names.

By default, man pages are installed by ‘make install’. However, since the GNU project does not require man pages, many maintainers do not expend effort to keep the man pages up to date. In these cases, the no-installman option will prevent the man pages from being installed by default. The user can still explicitly install them via ‘make install-man’.

Here is how the man pages are handled in GNU cpio (which includes both Texinfo documentation and man pages):

man_MANS = cpio.1 mt.1
EXTRA_DIST = $(man_MANS)

Man pages are not currently considered to be source, because it is not uncommon for man pages to be automatically generated. Therefore they are not automatically included in the distribution. However, this can be changed by use of the ‘dist_’ prefix.

The ‘nobase_’ prefix is meaningless for man pages and is disallowed.

13.1 Basics of installation

Naturally, Automake handles the details of actually installing your program once it has been built. All files named by the various primaries are automatically installed in the appropriate places when the user runs make install.

A file named in a primary is installed by copying the built file into the appropriate directory. The base name of the file is used when installing.

bin_PROGRAMS = hello subdir/goodbye

In this example, both ‘hello’ and ‘goodbye’ will be installed in $(bindir).

Sometimes it is useful to avoid the basename step at install time. For instance, you might have a number of header files in subdirectories of the source tree which are laid out precisely how you want to install them. In this situation you can use the ‘nobase_’ prefix to suppress the base name step. For example:

nobase_include_HEADERS = stdio.h sys/types.h

Will install stdio.h in $(includedir) and types.h in $(includedir)/sys.

13.2 The two parts of install

Automake generates separate install-data and install-exec targets, in case the installer is installing on multiple machines which share directory structure—these targets allow the machine-independent parts to be installed only once. install-exec installs platform-dependent files, and install-data installs platform-independent files. The install target depends on both of these targets. While Automake tries to automatically segregate objects into the correct category, the Makefile.am author is, in the end, responsible for making sure this is done correctly.

Variables using the standard directory prefixes ‘data’, ‘info’, ‘man’, ‘include’, ‘oldinclude’, ‘pkgdata’, or ‘pkginclude’ (e.g. ‘data_DATA’) are installed by ‘install-data’.

Variables using the standard directory prefixes ‘bin’, ‘sbin’, ‘libexec’, ‘sysconf’, ‘localstate’, ‘lib’, or ‘pkglib’ (e.g. ‘bin_PROGRAMS’) are installed by ‘install-exec’.

Any variable using a user-defined directory prefix with ‘exec’ in the name (e.g. ‘myexecbin_PROGRAMS’ is installed by ‘install-exec’. All other user-defined prefixes are installed by ‘install-data’.

13.3 Extending installation

It is possible to extend this mechanism by defining an install-exec-local or install-data-local target. If these targets exist, they will be run at ‘make install’ time. These rules can do almost anything; care is required.

Automake also supports two install hooks, install-exec-hook and install-data-hook. These hooks are run after all other install rules of the appropriate type, exec or data, have completed. So, for instance, it is possible to perform post-installation modifications using an install hook.

13.4 Staged installs

Automake generates support for the ‘DESTDIR’ variable in all install rules. ‘DESTDIR’ is used during the ‘make install’ step to relocate install objects into a staging area. Each object and path is prefixed with the value of ‘DESTDIR’ before being copied into the install area. Here is an example of typical DESTDIR usage:

make DESTDIR=/tmp/staging install

This places install objects in a directory tree built under /tmp/staging. If /gnu/bin/foo and /gnu/share/aclocal/foo.m4 are to be installed, the above command would install /tmp/staging/gnu/bin/foo and /tmp/staging/gnu/share/aclocal/foo.m4.

This feature is commonly used to build install images and packages. For more information, see Makefile Conventions in The GNU Coding Standards.

Support for ‘DESTDIR’ is implemented by coding it directly into the install rules. If your Makefile.am uses a local install rule (e.g., install-exec-local) or an install hook, then you must write that code to repsect ‘DESTDIR’.

13.5 Rules for the user

Automake also generates an uninstall target, an installdirs target, and an install-strip target.

Automake supports uninstall-local and uninstall-hook. There is no notion of separate uninstalls for “exec” and “data”, as that does not make sense.

Note that uninstall is not meant as a replacement for a real packaging tool.

15.1 Basics of distribution

The dist target in the generated Makefile.in can be used to generate a gzip’d tar file for distribution. The tar file is named based on the ‘PACKAGE’ and ‘VERSION’ variables; more precisely it is named ‘package-version.tar.gz’. You can use the make variable ‘GZIP_ENV’ to control how gzip is run. The default setting is ‘--best’.

For the most part, the files to distribute are automatically found by Automake: all source files are automatically included in a distribution, as are all Makefile.ams and Makefile.ins. Automake also has a built-in list of commonly used files which, if present in the current directory, are automatically included. This list is printed by ‘automake --help’. Also, files which are read by configure (i.e. the source files corresponding to the files specified in the AC_OUTPUT invocation) are automatically distributed.

Still, sometimes there are files which must be distributed, but which are not covered in the automatic rules. These files should be listed in the EXTRA_DIST variable. You can mention files from subdirectories in EXTRA_DIST.

You can also mention a directory in EXTRA_DIST; in this case the entire directory will be recursively copied into the distribution. Please note that this will also copy everything in the directory, including CVS/RCS version control files. We recommend against using this feature.

15.2 Fine-grained distribution control

Sometimes you need tighter control over what does not go into the distribution; for instance you might have source files which are generated and which you do not want to distribute. In this case Automake gives fine-grained control using the ‘dist’ and ‘nodist’ prefixes. Any primary or ‘_SOURCES’ variable can be prefixed with ‘dist_’ to add the listed files to the distribution. Similarly, ‘nodist_’ can be used to omit the files from the distribution.

As an example, here is how you would cause some data to be distributed while leaving some source code out of the distribution:

dist_data_DATA = distribute-this
bin_PROGRAMS = foo
nodist_foo_SOURCES = do-not-distribute.c

15.3 The dist hook

Another way to to use this is for removing unnecessary files that get recursively included by specifying a directory in EXTRA_DIST:

EXTRA_DIST = doc

dist-hook:
	rm -rf `find $(distdir)/doc -name CVS`

If you define SUBDIRS, Automake will recursively include the subdirectories in the distribution. If SUBDIRS is defined conditionally (see Conditionals), Automake will normally include all directories that could possibly appear in SUBDIRS in the distribution. If you need to specify the set of directories conditionally, you can set the variable DIST_SUBDIRS to the exact list of subdirectories to include in the distribution.

Occasionally it is useful to be able to change the distribution before it is packaged up. If the dist-hook target exists, it is run after the distribution directory is filled, but before the actual tar (or shar) file is created. One way to use this is for distributing files in subdirectories for which a new Makefile.am is overkill:

dist-hook:
        mkdir $(distdir)/random
        cp -p $(srcdir)/random/a1 $(srcdir)/random/a2 $(distdir)/random

15.4 Checking the distribution

Automake also generates a distcheck target which can be of help to ensure that a given distribution will actually work. distcheck makes a distribution, and then tries to do a VPATH build.

If the target distcheck-hook is defined in your Makefile.am, then it will be invoked by distcheck after the new distribution has been unpacked, but before the unpacked copy is configured and built. Your distcheck-hook can do almost anything, though as always caution is advised. Generally this hook is used to check for potential distribution errors not caught by the standard mechanism.

15.5 The types of distributions

By default Automake generates a ‘.tar.gz’ file when asked to create a distribution. However, some projects prefer different packaging formats. Automake accomodates most of these using options; Changing Automake’s Behavior.

Automake also generates a dist-all target which can be used to make all the requested packaged distributions at once.

16.1 Simple Tests

If the variable TESTS is defined, its value is taken to be a list of programs to run in order to do the testing. The programs can either be derived objects or source objects; the generated rule will look both in srcdir and .. Programs needing data files should look for them in srcdir (which is both an environment variable and a make variable) so they work when building in a separate directory (see Build Directories in The Autoconf Manual), and in particular for the distcheck target (see What Goes in a Distribution).

The number of failures will be printed at the end of the run. If a given test program exits with a status of 77, then its result is ignored in the final count. This feature allows non-portable tests to be ignored in environments where they don’t make sense.

The variable TESTS_ENVIRONMENT can be used to set environment variables for the test run; the environment variable srcdir is set in the rule. If all your test programs are scripts, you can also set TESTS_ENVIRONMENT to an invocation of the shell (e.g. ‘$(SHELL) -x’); this can be useful for debugging the tests.

You may define the variable XFAIL_TESTS to a list of tests (usually a subset of TESTS) that are expected to fail. This will reverse the result of those tests.

Automake ensures that each program listed in TESTS is built before any tests are run; you can list both source and derived programs in TESTS. For instance, you might want to run a C program as a test. To do this you would list its name in TESTS and also in check_PROGRAMS, and then specify it as you would any other program.

16.2 DejaGNU Tests

If ‘dejagnu’ appears in AUTOMAKE_OPTIONS, then a dejagnu-based test suite is assumed. The variable DEJATOOL is a list of names which are passed, one at a time, as the --tool argument to runtest invocations; it defaults to the name of the package.

The variable RUNTESTDEFAULTFLAGS holds the --tool and --srcdir flags that are passed to dejagnu by default; this can be overridden if necessary.

The variables EXPECT and RUNTEST can also be overridden to provide project-specific values. For instance, you will need to do this if you are testing a compiler toolchain, because the default values do not take into account host and target names.

The contents of the variable RUNTESTFLAGS are passed to the runtest invocation. This is considered a “user variable” (see Variables reserved for the user). If you need to set runtest flags in Makefile.am, you can use AM_RUNTESTFLAGS instead.

In either case, the testing is done via ‘make check’.

18.1 Interfacing to etags

Automake will generate rules to generate TAGS files for use with GNU Emacs under some circumstances.

If any C, C++ or Fortran 77 source code or headers are present, then tags and TAGS targets will be generated for the directory.

At the topmost directory of a multi-directory package, a tags target file will be generated which, when run, will generate a TAGS file that includes by reference all TAGS files from subdirectories.

The tags target will also be generated if the variable ETAGS_ARGS is defined. This variable is intended for use in directories which contain taggable source that etags does not understand.

Here is how Automake generates tags for its source, and for nodes in its Texinfo file:

ETAGS_ARGS = automake.in --lang=none \
 --regex='/^@node[ \t]+\([^,]+\)/\1/' automake.texi

If you add filenames to ‘ETAGS_ARGS’, you will probably also want to set ‘TAGS_DEPENDENCIES’. The contents of this variable are added directly to the dependencies for the tags target.

Automake will also generate an ID target which will run mkid on the source. This is only supported on a directory-by-directory basis.

Automake also supports the GNU Global Tags program. The GTAGS target runs Global Tags automatically and puts the result in the top build directory. The variable GTAGS_ARGS holds arguments which are passed to gtags.

18.2 Handling new file extensions

It is sometimes useful to introduce a new implicit rule to handle a file type that Automake does not know about. If this is done, you must notify GNU Make of the new suffixes. This can be done by putting a list of new suffixes in the SUFFIXES variable.

For instance, suppose you had a compiler which could compile ‘.foo’ files to ‘.o’ files. Then you would add ‘.foo’ to your suffix list:

SUFFIXES = .foo

Then you could directly use a ‘.foo’ file in a ‘_SOURCES’ variable and expect the correct results:

bin_PROGRAMS = doit
doit_SOURCES = doit.foo

Any given SUFFIXES go at the start of the generated suffixes list, followed by automake generated suffixes not already in the list.

18.3 Support for Multilibs

Automake has support for an obscure feature called multilibs. A multilib is a library which is built for multiple different ABIs at a single time; each time the library is built with a different target flag combination. This is only useful when the library is intended to be cross-compiled, and it is almost exclusively used for compiler support libraries.

The multilib support is still experimental. Only use it if you are familiar with multilibs and can debug problems you might encounter.