20.1 Using gnatmake in a Makefile

Complex project organizations can be handled in a very powerful way by using GNU make combined with gnatmake. For instance, here is a Makefile which allows you to build each subsystem of a big project into a separate shared library. Such a makefile allows you to significantly reduce the link time of very big applications while maintaining full coherence at each step of the build process.

The list of dependencies are handled automatically by gnatmake. The Makefile is simply used to call gnatmake in each of the appropriate directories.

Note that you should also read the example on how to automatically create the list of directories (see Automatically Creating a List of Directories) which might help you in case your project has a lot of subdirectories.

     ## This Makefile is intended to be used with the following directory
     ## configuration:
     ##  - The sources are split into a series of csc (computer software components)
     ##    Each of these csc is put in its own directory.
     ##    Their name are referenced by the directory names.
     ##    They will be compiled into shared library (although this would also work
     ##    with static libraries
     ##  - The main program (and possibly other packages that do not belong to any
     ##    csc is put in the top level directory (where the Makefile is).
     ##       toplevel_dir __ first_csc  (sources) __ lib (will contain the library)
     ##                    \_ second_csc (sources) __ lib (will contain the library)
     ##                    \_ ...
     ## Although this Makefile is build for shared library, it is easy to modify
     ## to build partial link objects instead (modify the lines with -shared and
     ## gnatlink below)
     ##
     ## With this makefile, you can change any file in the system or add any new
     ## file, and everything will be recompiled correctly (only the relevant shared
     ## objects will be recompiled, and the main program will be re-linked).
     
     # The list of computer software component for your project. This might be
     # generated automatically.
     CSC_LIST=aa bb cc
     
     # Name of the main program (no extension)
     MAIN=main
     
     # If we need to build objects with -fPIC, uncomment the following line
     #NEED_FPIC=-fPIC
     
     # The following variable should give the directory containing libgnat.so
     # You can get this directory through 'gnatls -v'. This is usually the last
     # directory in the Object_Path.
     GLIB=...
     
     # The directories for the libraries
     # (This macro expands the list of CSC to the list of shared libraries, you
     # could simply use the expanded form:
     # LIB_DIR=aa/lib/libaa.so bb/lib/libbb.so cc/lib/libcc.so
     LIB_DIR=${foreach dir,${CSC_LIST},${dir}/lib/lib${dir}.so}
     
     ${MAIN}: objects ${LIB_DIR}
         gnatbind ${MAIN} ${CSC_LIST:%=-aO%/lib} -shared
         gnatlink ${MAIN} ${CSC_LIST:%=-l%}
     
     objects::
         # recompile the sources
         gnatmake -c -i ${MAIN}.adb ${NEED_FPIC} ${CSC_LIST:%=-I%}
     
     # Note: In a future version of GNAT, the following commands will be simplified
     # by a new tool, gnatmlib
     ${LIB_DIR}:
         mkdir -p ${dir $@ }
         cd ${dir $@ }; gcc -shared -o ${notdir $@ } ../*.o -L${GLIB} -lgnat
         cd ${dir $@ }; cp -f ../*.ali .
     
     # The dependencies for the modules
     # Note that we have to force the expansion of *.o, since in some cases
     # make won't be able to do it itself.
     aa/lib/libaa.so: ${wildcard aa/*.o}
     bb/lib/libbb.so: ${wildcard bb/*.o}
     cc/lib/libcc.so: ${wildcard cc/*.o}
     
     # Make sure all of the shared libraries are in the path before starting the
     # program
     run::
         LD_LIBRARY_PATH=`pwd`/aa/lib:`pwd`/bb/lib:`pwd`/cc/lib ./${MAIN}
     
     clean::
         ${RM} -rf ${CSC_LIST:%=%/lib}
         ${RM} ${CSC_LIST:%=%/*.ali}
         ${RM} ${CSC_LIST:%=%/*.o}
         ${RM} *.o *.ali ${MAIN}