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In the GNU Build System, packages can be nested to arbitrary depth. This means that a package can embedded other packages with their own configure, Makefiles, etc.
These other packages should just appear as subdirectories of their
parent package. They must be listed in SUBDIRS
like other
ordinary directories. However the subpackage’s Makefiles
should be output by its own configure script, not by the
parent’s configure. This is achieved using the
AC_CONFIG_SUBDIRS
Autoconf macro (see Configuring Other Packages in Subdirectories in The Autoconf Manual).
Here is an example package for an arm
program that links with
an hand
library that is a nested package in subdirectory
hand/.
arm
’s configure.ac:
AC_INIT([arm], [1.0]) AC_CONFIG_AUX_DIR([.]) AM_INIT_AUTOMAKE AC_PROG_CC AC_CONFIG_FILES([Makefile]) # Call hand's ./configure script recursively. AC_CONFIG_SUBDIRS([hand]) AC_OUTPUT
arm
’s Makefile.am:
# Build the library in the hand subdirectory first. SUBDIRS = hand # Include hand's header when compiling this directory. AM_CPPFLAGS = -I$(srcdir)/hand bin_PROGRAMS = arm arm_SOURCES = arm.c # link with the hand library. arm_LDADD = hand/libhand.a
Now here is hand
’s hand/configure.ac:
AC_INIT([hand], [1.2]) AC_CONFIG_AUX_DIR([.]) AM_INIT_AUTOMAKE AC_PROG_CC AC_PROG_RANLIB AC_CONFIG_FILES([Makefile]) AC_OUTPUT
and its hand/Makefile.am:
lib_LIBRARIES = libhand.a libhand_a_SOURCES = hand.c
When make dist
is run from the top-level directory it will
create an archive arm-1.0.tar.gz that contains the arm
code as well as the hand subdirectory. This package can be
built and installed like any ordinary package, with the usual
./configure && make && make install
sequence (the hand
subpackage will be built and installed by the process).
When make dist
is run from the hand directory, it will create a
self-contained hand-1.2.tar.gz archive. So although it appears
to be embedded in another package, it can still be used separately.
The purpose of the AC_CONFIG_AUX_DIR([.])
instruction is to
force Automake and Autoconf into search auxiliary script in the
current directory. For instance this means that there will be two
copies of install-sh: one in the top-level of the arm
package, and another one in the hand/ subdirectory for the
hand
package.
The historical default is to search these auxiliary scripts in the
immediate parent and grand-parent directories. So if the
AC_CONFIG_AUX_DIR([.])
line was removed from
hand/configure.ac, that subpackage would share the auxiliary
script of the arm
package. This may looks like a gain in size
(a few kilobytes), but it is actually a loss of modularity as the
hand
subpackage is no longer self-contained (make dist
in the subdirectory will not work anymore).
Packages that do not use Automake need more work to be integrated this way. See Third-Party Makefiles.
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