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12.1 Using Libtool Libraries

As you have seen, It is very easy to convert automake built static libraries to automake built Libtool libraries. In order to build ‘libsic’ as a Libtool library, I have changed the name of the library from ‘libsic.a’ (the old archive name in Libtool terminology) to ‘libsic.la’ (the pseudo-library), and must use the LTLIBRARIES Automake primary:

 

Notice the ‘la’ in libsic_la_SOURCES is new too.

It is similarly easy to take advantage of Libtool convenience libraries. For the purposes of Sic, ‘libreplace’ is an ideal candidate for this treatment – I can create the library as a separate entity from selected sources in their own directory, and add those objects to ‘libsic’. This technique ensures that the installed library has all of the support functions it needs without having to link ‘libreplace’ as a separate object.

In ‘replace/Makefile.am’, I have again changed the name of the library from
libreplace.a’ to ‘libreplace.la’, and changed the automake primary from ‘LIBRARIES’ to ‘LTLIBRARIES’. Unfortunately, those changes alone are insufficient. Libtool libraries are compiled from Libtool objects (which have the ‘.lo’ suffix), so I cannot use ‘LIBOBJS’ which is a list of ‘.o’ suffixed objects(22). See section Extra Macros for Libtool, for more details. Here is ‘replace/Makefile.am’:

 

And not forgetting to set and use the ‘LTLIBOBJS’ configure substitution (see section Extra Macros for Libtool):

 

As a consequence of using libtool to build the project libraries, the increasing number of configuration files being added to the ‘config’ directory will grow to include ‘ltconfig’ and ‘ltmain.sh’. These files will be used on the installer’s machine when Sic is configured, so it is important to distribute them. The naive way to do it is to give the ‘config’ directory a ‘Makefile.am’ of its own; however, it is not too difficult to distribute these files from the top ‘Makefile.am’, and it saves clutter, as you can see here:

 
AUX_DIST                = $(ac_aux_dir)/config.guess \
                        $(ac_aux_dir)/config.sub \
                        $(ac_aux_dir)/install-sh \
                        $(ac_aux_dir)/ltconfig \
                        $(ac_aux_dir)/ltmain.sh \
                        $(ac_aux_dir)/mdate-sh \
                        $(ac_aux_dir)/missing \
                        $(ac_aux_dir)/mkinstalldirs
AUX_DIST_EXTRA          = $(ac_aux_dir)/readline.m4 \
                        $(ac_aux_dir)/sys_errlist.m4 \
                        $(ac_aux_dir)/sys_siglist.m4
EXTRA_DIST                = bootstrap

MAINTAINERCLEANFILES         = Makefile.in aclocal.m4 configure config-h.in \
                        stamp-h.in $(AUX_DIST)

dist-hook:
        (cd $(distdir) && mkdir $(ac_aux_dir))
        for file in $(AUX_DIST) $(AUX_DIST_EXTRA); do \
          cp $$file $(distdir)/$$file; \
        done

The ‘dist-hook’ rule is used to make sure the ‘config’ directory and the files it contains are correctly added to the distribution by the ‘make dist’ rules, see section Introduction to Distributions.

I have been careful to use the configure script’s location for ac_aux_dir, so that it is defined (and can be changed) in only one place. This is achieved by adding the following macro to ‘configure.in’:

 
AC_SUBST(ac_aux_dir)

There is no need to explicitly set a macro in the ‘Makefile.am’, because Automake automatically creates macros for every value that you ‘AC_SUBST’ from ‘configure.in’.

I have also added the AC_PROG_LIBTOOL macro to ‘configure.in’ in place of AC_PROG_RANLIB as described in Using GNU Libtool with ‘configure.in’ and ‘Makefile.am.

Now I can upgrade the configury to use libtool – the greater part of this is running the libtoolize script that comes with the Libtool distribution. The bootstrap script then needs to be updated to run libtoolize at the correct juncture:

 
#! /bin/sh

set -x
aclocal -I config
libtoolize --force --copy
autoheader
automake --add-missing --copy
autoconf

Now I can re-bootstrap the entire project so that it can make use of libtool:

 
$ ./bootstrap
+ aclocal -I config
+ libtoolize --force --copy
Putting files in AC_CONFIG_AUX_DIR, config.
+ autoheader
+ automake --add-missing --copy
automake: configure.in: installing config/install-sh
automake: configure.in: installing config/mkinstalldirs
automake: configure.in: installing config/missing
+ autoconf

The new macros are evident by the new output seen when the newly regenerated configure script is executed:

 
$ ./configure --with-readline
...
checking host system type... i586-pc-linux-gnu
checking build system type... i586-pc-linux-gnu
checking for ld used by GCC... /usr/bin/ld
checking if the linker (/usr/bin/ld) is GNU ld... yes
checking for /usr/bin/ld option to reload object files... -r
checking for BSD-compatible nm... /usr/bin/nm -B
checking whether ln -s works... yes
checking how to recognise dependent libraries... pass_all
checking for object suffix... o
checking for executable suffix... no
checking for ranlib... ranlib
checking for strip... strip
...
checking if libtool supports shared libraries... yes
checking whether to build shared libraries... yes
checking whether to build static libraries... yes
creating libtool
...
$ make
...
gcc -g -O2 -o .libs/sic sic.o sic_builtin.o sic_repl.o sic_syntax.o \
../sic/.libs/libsic.so -lreadline -Wl,--rpath -Wl,/usr/local/lib
creating sic
...
$ src/sic
] libtool --mode=execute ldd src/sic
    libsic.so.0 => /tmp/sic/sic/.libs/libsic.so.0 (0x40014000)
    libreadline.so.4 => /lib/libreadline.so.4 (0x4001e000)
    libc.so.6 => /lib/libc.so.6 (0x40043000)
    libncurses.so.5 => /lib/libncurses.so.5 (0x40121000)
    /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)
] exit
$

As you can see, sic is now linked against a shared library build of ‘libsic’, but not directly against the convenience library, ‘libreplace’.


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