How to build *.so module in Automake and a libtool-using project?

One thing that could work according to the libtool documentation for LT_INIT is to partition your build into two packages: the main application and the plugins. That way you could (in theory) invoke:

./configure --enable-shared=plugins

and things would work the way you would expect.

I've solved a similar problem using the noinst_LTLIBRARIES macro.

The noinst_LTLIBRARIES macro creates static, non installable libraries to be only used internally. all noinst_LTLIBRARIES static libraries are created also if you specify the --disable-static configure option.

lib_LTLIBRARIES = libtokenclient.la
noinst_LTLIBRARIES = libtokenclient_static.la 

libtokenclient_la_SOURCES = $(TOKEN_SERVER_CLIENT_SOURCES) cDynlib.c cDynlib.h token_mod.h
libtokenclient_la_CFLAGS = @BASE_CFLAGS@
libtokenclient_la_CXXFLAGS = $(libtokenclient_la_CFLAGS)
libtokenclient_la_LIBADD = @B_BASE_OS_LIBS@
libtokenclient_la_LDFLAGS = @LT_PLUGIN_LIBS_FLAGS@ @LIBS_FLAGS@ $(TOKEN_SERVER_CLIENT_EXPORT_SYMBOLS)

libtokenclient_static_la_SOURCES = $(libtokenclient_la_SOURCES)
libtokenclient_static_la_CFLAGS = $(libtokenclient_la_CFLAGS)
libtokenclient_static_la_CXXFLAGS = $(libtokenclient_static_la_CFLAGS)

token_test_SOURCES = $(TEST_SOURCES)
token_test_LDADD = @B_BASE_OS_LIBS@ libtokenclient_static.la
token_test_CFLAGS = @BASE_CFLAGS@
token_test_CXXFLAGS = $(token_test_CFLAGS)

I use noinst_LTLIBRARIES static libraries for 2 reasons:

1. to speed up compile time I create static libraries to be used as intermediate containers for code that shall be linked against more than once: the code is compiled just once, otherwise automake would compile same source files once for each target
2. to statically link the code to some executable

What you are looking for is called a module. You can tell Autotools to create a static binary (executable) by adding -all-static to the LDFLAGS of the application. I think this is the preferred way over using --disable-shared configure flag (which really is aimed at the libraries rather than the executable)

Something like this should do the trick:

AM_CPPFLAGS=-I$(top_srcdir)/include

lib_LTLIBRARIES = module.la
module_la_LDFLAGS = -module -avoid-version -shared
module_la_SOURCES = mm_cpp_logger.cpp

bin_PROGRAMS = application
application_LDFLAGS = -all-static
application_SOURCES = main.cpp

The .so file will (as usual) end up in the .libs/ subdirectory (unless you install it, of course).

And you can build both your application and plugins in one go (even with a single Makefile.am), so there is no need to call configure multiple times.

The use of -fPIC (and friends) should be auto-detected by Autotools.

---

Update: here's a little trick to make the shared-libraries available where you expect them. Since all shlibs end up in .libs/, it is sometimes nice to have them in a non-hidden directory.

The following makefile snippet creates convenience links (on platforms that support symlinks; otherwise they are copied). Simply adding the snippet to your makefile (i usually use an -include convenience-link.mk) should be enough (you might need an AC_PROG_LN_S in your configure.ac)

.PHONY: convenience-link clean-convenience-link

convenience-link: $(lib_LTLIBRARIES)
    @for soname in `echo | $(EGREP) "^dlname=" $^ | $(SED) -e "s|^dlname='\(.*\)'|\1|"`; do  \
        echo "$$soname: creating convenience link from $(abs_builddir)/.libs to $(top_builddir)"; \
        rm -f $(top_builddir)/$$soname ; \
        test -e $(abs_builddir)/.libs/$$soname && \
        cd $(top_builddir) && \
        $(LN_S) $(abs_builddir)/.libs/$$soname $$soname || true;\
    done 

clean-convenience-link:
    @for soname in `echo | $(EGREP) "^dlname=" $(lib_LTLIBRARIES) | $(SED) -e "s|^dlname='\(.*\)'|\1|"`; do  \
        echo "$$soname: cleaning convenience links"; \
        test -L $(top_builddir)/$$soname && rm -f $(top_builddir)/$$soname || true; \
    done 
        
all-local:: convenience-link

clean-local:: clean-convenience-link