Makefile Conventions
********************

This chapter describes conventions for writing the Makefiles for GNU programs.

General Conventions for Makefiles
=================================

Every Makefile should contain this line:

     SHELL = /bin/sh

to avoid trouble on systems where the SHELL variable might be inherited from the environment.  (This is never a problem with GNU make.)

Don't assume that . is in the path for command execution.  When you need to run programs that are a part of your package during the make, please make sure that it uses ./ if the program is built as part of the make or $(srcdir)/ if the file is an unchanging part of the source code.  Without one of these prefixes, the current search path is used.

The distinction between ./ and $(srcdir)/ is important when using the --srcdir option to configure.  A rule of the form:

     foo.1 : foo.man sedscript
             sed -e sedscript foo.man > foo.1

will fail when the current directory is not the source directory, because foo.man and sedscript are not in the current directory.

When using GNU make, relying on VPATH to find the source file will work in the case where there is a single dependency file, since the make automatic variable $< will represent the source file wherever it is.  (Many versions of make set $< only in implicit rules.)  A makefile target like

     foo.o : bar.c
             $(CC) -I. -I$(srcdir) $(CFLAGS) -c bar.c -o foo.o

should instead be written as

     foo.o : bar.c
             $(CC) $(CFLAGS) $< -o $@

in order to allow VPATH to work correctly.  When the target has multiple dependencies, using an explicit $(srcdir) is the easiest way to make the rule work well.  For example, the target above for foo.1 is best written as:

     foo.1 : foo.man sedscript
             sed -s $(srcdir)/sedscript $(srcdir)/foo.man > foo.1

Utilities in Makefiles
======================

Write the Makefile commands (and any shell scripts, such as configure) to run in sh, not in csh.  Don't use any special features of ksh or bash.

The configure script and the Makefile rules for building and installation should not use any utilities directly except these:

     cat cmp cp echo egrep expr grep
     ln mkdir mv pwd rm rmdir sed test touch

Stick to the generally supported options for these programs.  For example, don't use mkdir -p, convenient as it may be, because most systems don't support it.

The Makefile rules for building and installation can also use compilers and related programs, but should do so via make variables so that the user can substitute alternatives.  Here are some of the programs we mean:

     ar bison cc flex install ld lex
     make makeinfo ranlib texi2dvi yacc

When you use ranlib, you should test whether it exists, and run it only if it exists, so that the distribution will work on systems that don't have ranlib.

If you use symbolic links, you should implement a fallback for systems that don't have symbolic links.

It is ok to use other utilities in Makefile portions (or scripts) intended only for particular systems where you know those utilities to exist.

Standard Targets for Users
==========================

All GNU programs should have the following targets in their Makefiles:

all
     Compile the entire program.  This should be the default target.  This target need not rebuild any documentation files; info files should normally be included in the distribution, and DVI files should be made only when explicitly asked for.

install
     Compile the program and copy the executables, libraries, and so on to the file names where they should reside for actual use.  If there is a simple test to verify that a program is properly installed then run that test.

     Use - before any command for installing a man page, so that make will ignore any errors.  This is in case there are systems that don't have the Unix man page documentation system installed.

     In the future, when we have a standard way of installing info files, install targets will be the proper place to do so.

uninstall
     Delete all the installed files that the install target would create (but not the noninstalled files such as make all would create).

clean
     Delete all files from the current directory that are normally created by building the program.  Don't delete the files that record the configuration.  Also preserve files that could be made by building, but normally aren't because the distribution comes with them.

     Delete .dvi files here if they are not part of the distribution.

distclean
     Delete all files from the current directory that are created by configuring or building the program.  If you have unpacked the source and built the program without creating any other files, make distclean should leave only the files that were in the distribution.

mostlyclean
     Like clean, but may refrain from deleting a few files that people normally don't want to recompile.  For example, the mostlyclean target for GCC does not delete libgcc.a, because recompiling it is rarely necessary and takes a lot of time.

realclean
     Delete everything from the current directory that can be reconstructed with this Makefile.  This typically includes everything deleted by distclean, plus more: C source files produced by Bison, tags tables, info files, and so on.

     One exception, however: make realclean should not delete configure even if configure can be remade using a rule in the Makefile.  More generally, make realclean should not delete anything that needs to exist in order to run configure and then begin to build the program.

TAGS
     Update a tags table for this program.

info
     Generate any info files needed.  The best way to write the rules is as follows:

          info:  foo.info

          foo.info: $(srcdir)/foo.texi $(srcdir)/chap1.texi $(srcdir)/chap2.texi
                  $(MAKEINFO) $(srcdir)/foo.texi

     You must define the variable MAKEINFO in the Makefile. It should run the Makeinfo program, which is part of the Texinfo2 distribution.

dvi
     Generate DVI files for all TeXinfo documentation. For example:

          dvi: foo.dvi

          foo.dvi: $(srcdir)/foo.texi $(srcdir)/chap1.texi $(srcdir)/chap2.texi
                  $(TEXI2DVI) $(srcdir)/foo.texi

     You must define the variable TEXI2DVI in the Makefile.  It should run the program texi2dvi, which is part of the Texinfo2 distribution.  Alternatively, write just the dependencies, and allow GNU Make to provide the command.

dist
     Create a distribution tar file for this program.  The tar file should be set up so that the file names in the tar file start with a subdirectory name which is the name of the package it is a distribution for.  This name can include the version number.

     For example, the distribution tar file of GCC version 1.40 unpacks into a subdirectory named gcc-1.40.

     The easiest way to do this is to create a subdirectory appropriately named, use ln or cp to install the proper files in it, and then tar that subdirectory.

     The dist target should explicitly depend on all non-source files that are in the distribution, to make sure they are up to date in the distribution. See Making Releases (GNU Coding Standards).

check
     Perform self-tests (if any).  The user must build the program before running the tests, but need not install the program; you should write the self-tests so that they work when the program is built but not installed.

The following targets are suggested as conventional names, for programs in which they are useful.

installcheck
     Perform installation tests (if any).  The user must build and install the program before running the tests.  You should not assume that $(bindir) is in the search path.

installdirs
     It's useful to add a target named installdirs to create the directories where files are installed, and their parent directories. There is a script called mkinstalldirs which is convenient for this; find it in the Texinfo package. It's in /gd/gnu/lib/mkinstalldirs. You can use a rule like this:

          # Make sure all installation directories, e.g. $(bindir) actually exist by
          # making them if necessary.
          installdirs: mkinstalldirs
                  $(srcdir)/mkinstalldirs $(bindir) $(datadir) $(libdir) \
                                          $(infodir) $(mandir)

Variables for Specifying Commands
=================================

Makefiles should provide variables for overriding certain commands, options, and so on.

In particular, you should run most utility programs via variables. Thus, if you use Bison, have a variable named BISON whose default value is set with BISON = bison, and refer to it with $(BISON) whenever you need to use Bison.

File management utilities such as ln, rm, mv, and so on, need not be referred to through variables in this way, since users don't need to replace them with other programs.

Each program-name variable should come with an options variable that is used to supply options to the program.  Append FLAGS to the program-name variable name to get the options variable name---for example, BISONFLAGS.  (The name CFLAGS is an exception to this rule, but we keep it because it is standard.)  Use CPPFLAGS in any compilation command that runs the preprocessor, and use LDFLAGS in any compilation command that does linking as well as in any direct use of ld.

If there are C compiler options that must be used for proper compilation of certain files, do not include them in CFLAGS. Users expect to be able to specify CFLAGS freely themselves. Instead, arrange to pass the necessary options to the C compiler independently of CFLAGS, by writing them explicitly in the compilation commands or by defining an implicit rule, like this:

     CFLAGS = -g
     ALL_CFLAGS = -I. $(CFLAGS)
     .c.o:
             $(CC) -c $(CPPFLAGS) $(ALL_CFLAGS) $<

Do include the -g option in CFLAGS, because that is not required for proper compilation.  You can consider it a default that is only recommended.  If the package is set up so that it is compiled with GCC by default, then you might as well include -O in the default value of CFLAGS as well.

Put CFLAGS last in the compilation command, after other variables containing compiler options, so the user can use CFLAGS to override the others.

Every Makefile should define the variable INSTALL, which is the basic command for installing a file into the system.

Every Makefile should also define variables INSTALL_PROGRAM and INSTALL_DATA.  (The default for each of these should be $(INSTALL).)  Then it should use those variables as the commands for actual installation, for executables and nonexecutables respectively.  Use these variables as follows:

     $(INSTALL_PROGRAM) foo $(bindir)/foo
     $(INSTALL_DATA) libfoo.a $(libdir)/libfoo.a

Always use a file name, not a directory name, as the second argument of the installation commands.  Use a separate command for each file to be installed.

Variables for Installation Directories
======================================

Installation directories should always be named by variables, so it is easy to install in a nonstandard place.  The standard names for these variables are:

prefix
     A prefix used in constructing the default values of the variables listed below.  The default value of prefix should be /usr/local (at least for now).

exec_prefix
     A prefix used in constructing the default values of the some of the variables listed below.  The default value of exec_prefix should be $(prefix).

     Generally, $(exec_prefix) is used for directories that contain machine-specific files (such as executables and subroutine libraries), while $(prefix) is used directly for other directories.

bindir
     The directory for installing executable programs that users can run. This should normally be /usr/local/bin, but write it as $(exec_prefix)/bin.

libdir
     The directory for installing executable files to be run by the program rather than by users.  Object files and libraries of object code should also go in this directory.  The idea is that this directory is used for files that pertain to a specific machine architecture, but need not be in the path for commands.  The value of libdir should normally be /usr/local/lib, but write it as $(exec_prefix)/lib.

datadir
     The directory for installing read-only data files which the programs refer to while they run.  This directory is used for files which are independent of the type of machine being used.  This should normally be /usr/local/lib, but write it as $(prefix)/lib.

statedir
     The directory for installing data files which the programs modify while they run.  These files should be independent of the type of machine being used, and it should be possible to share them among machines at a network installation.  This should normally be /usr/local/lib, but write it as $(prefix)/lib.

includedir
     The directory for installing header files to be included by user programs with the C #include preprocessor directive.  This should normally be /usr/local/include, but write it as $(prefix)/include.

     Most compilers other than GCC do not look for header files in /usr/local/include.  So installing the header files this way is only useful with GCC.  Sometimes this is not a problem because some libraries are only really intended to work with GCC.  But some libraries are intended to work with other compilers.  They should install their header files in two places, one specified by includedir and one specified by oldincludedir.

oldincludedir
     The directory for installing #include header files for use with compilers other than GCC.  This should normally be /usr/include.

     The Makefile commands should check whether the value of oldincludedir is empty.  If it is, they should not try to use it; they should cancel the second installation of the header files.

     A package should not replace an existing header in this directory unless the header came from the same package.  Thus, if your Foo package provides a header file foo.h, then it should install the header file in the oldincludedir directory if either (1) there is no foo.h there or (2) the foo.h that exists came from the Foo package.

     The way to tell whether foo.h came from the Foo package is to put a magic string in the file---part of a comment---and grep for that string.

mandir
     The directory for installing the man pages (if any) for this package. It should include the suffix for the proper section of the manual---usually 1 for a utility.

man1dir
     The directory for installing section 1 man pages.

man2dir
     The directory for installing section 2 man pages.

...
     Use these names instead of mandir if the package needs to install man pages in more than one section of the manual.

     Don't make the primary documentation for any GNU software be a man page.  Write a manual in Texinfo instead.  Man pages are just for the sake of people running GNU software on Unix, which is a secondary application only.

manext
     The file name extension for the installed man page.  This should contain a period followed by the appropriate digit.

infodir
     The directory for installing the info files for this package.  By default, it should be /usr/local/info, but it should be written as $(prefix)/info.

srcdir
     The directory for the sources being compiled.  The value of this variable is normally inserted by the configure shell script.

For example:

     # Common prefix for installation directories.
     # NOTE: This directory must exist when you start the install.
     prefix = /usr/local
     exec_prefix = $(prefix)
     # Where to put the executable for the command `gcc'.
     bindir = $(exec_prefix)/bin
     # Where to put the directories used by the compiler.
     libdir = $(exec_prefix)/lib
     # Where to put the Info files.
     infodir = $(prefix)/info

If your program installs a large number of files into one of the standard user-specified directories, it might be useful to group them into a subdirectory particular to that program.  If you do this, you should write the install rule to create these subdirectories.

Do not expect the user to include the subdirectory name in the value of any of the variables listed above.  The idea of having a uniform set of variable names for installation directories is to enable the user to specify the exact same values for several different GNU packages.  In order for this to be useful, all the packages must be designed so that they will work sensibly when the user does so.