# $Id: Makefile.am,v 1.15 2007/10/15 04:53:59 rocky Exp $ # # Copyright (C) 2003, 2004, 2005, 2006, 2007 # Rocky Bernstein # # This program is free software; you can redistribute it and/or modify # it under the terms of the GNU General Public License as published by # the Free Software Foundation; either version 2 of the License, or # (at your option) any later version. # # This program is distributed in the hope that it will be useful, # but WITHOUT ANY WARRANTY; without even the implied warranty of # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the # GNU General Public License for more details. # # You should have received a copy of the GNU General Public License # along with this program; if not, write to the Free Software # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA # 02110-1301 USA. # ######################################################## # Things to make the libiso9660 library ######################################################## # # From libtool documentation amended with guidance from N. Boullis: # # 1. Start with version information of `0:0:0' for each libtool library. # # 2. It is probably not a good idea to update the version information # several times between public releases, but rather once per public # release. (This seems to be more an aesthetic consideration than # a hard technical one.) # # 3. If the library source code has changed at all since the last # update, then increment REVISION (`C:R:A' becomes `C:R+1:A'). # # 4. If any interfaces have been added, removed, or changed since the # last update, increment CURRENT, and set REVISION to 0. # # 5. If any interfaces have been added since the last public release, # then increment AGE. # # 6. If any interfaces have been removed or changed since the last # public release, then set AGE to 0. A changed interface means an # incompatibility with previous versions. libiso9660_la_CURRENT = 6 libiso9660_la_REVISION = 0 libiso9660_la_AGE = 1 EXTRA_DIST = libiso9660.sym noinst_HEADERS = iso9660_private.h lib_LTLIBRARIES = libiso9660.la if ENABLE_ROCK rock_src = rock.c else rock_src = endif libiso9660_la_SOURCES = \ iso9660.c \ iso9660_private.h \ iso9660_fs.c \ $(rock_src) \ xa.c libiso9660_la_LIBADD = @LIBCDIO_LIBS@ libiso9660_la_ldflags = -version-info $(libiso9660_la_CURRENT):$(libiso9660_la_REVISION):$(libiso9660_la_AGE) libiso9660_la_dependencies = libcdio.la INCLUDES = $(LIBCDIO_CFLAGS) ######################################################## # Things to version the symbols in the libraries ######################################################## # An explanation of the versioning problem from Nicolas Boullis and # the versioned symbol solution he uses below... # # Currently, libvcdinfo uses the cdio_open function from libcdio. # Let's imagine a program foobar that uses both the vcdinfo_open # function from libvcdinfo and the cdio_open function from libcdio. # Currently, libcdio has SONAME libcdio.so.0, libvcdinfo has SONAME # libvcdinfo.so.0 and requires libcdio.so.0, and foobar requires both # libvcdinfo.so.0 and libcdio.so.0. Everything looks fine. # # Now, for some reason, you decide to change the cdio_open function. # That's your right, but you have to bump the CURRENT version and (if I # understand it correctly, athough this is not that clear in libtool's # documentation) set the AGE to 0. Anyway, this bumps the SONAME, which is # sane since the interface changes incompatibly. # Now, you have a new libcdio with SONAME libcdio.so.1. But libvcdinfo and # foobar still require libcdio.so.0. Everything is still fine. # Now, after some minor changes, the author of foobar recompiles foobar. # Then, foobar now requires libvcdinfo.so.0 and libcdio.so.1. And foobar # now segfaults... # What is happening? When you run foobar, if brings both libvcdinfo.so.0 # and libcdio.so.1, but libvcdinfo.so.0 also brings libcdio.so.0. So you # have both libcdio.so.0 and libcdio.so.1 that bring their symbols to the # global namespace. Hence, you have to incompatible versions of the # cdio_open function in the name space. When foobar calls cdio_open, it # may choose the wrong function, and segfaults... # With versioned symbols, the cdio_open function from libcdio.so.0 may be # known as (something that looks like) cdio_open@@CDIO_0. An the cdio_open # function from libcdio.so.1 as cdio_open@@CDIO_1. Both versions of # libcdio would still be brought in by the most recent foobar, but foobar # (and libvcdinfo) know which versioned function to use and then use the # good one. # This is some simple versioning where every symbol is versioned with # something that looks like the SONAME of the library. More complex (and # better) versioning is possible; it is for example what is used by glibc. # But good complex versioning is something that requires much more # work... # The below is a impliments symbol versioning. First of all, I # compute MAJOR as CURENT - AGE; that is what is used within libtool # (at least on GNU/Linux systems) for the number in the SONAME. The # nm command gives the list of symbols known in each of the object # files that will be part of the shared library. And the sed command # extracts from this list those symbols that will be shared. (This sed # command comes from libtool.) libiso9660_la_MAJOR = $(shell expr $(libiso9660_la_CURRENT) - $(libiso9660_la_AGE)) if BUILD_VERSIONED_LIBS libiso9660_la_LDFLAGS = $(libiso9660_la_ldflags) -Wl,--version-script=libiso9660.la.ver libiso9660_la_DEPENDENCIES = $(libcdio9660_la_dependencies) libiso9660.la.ver libiso9660.la.ver: $(libiso9660_la_OBJECTS) $(srcdir)/libiso9660.sym echo 'ISO9660_$(libiso9660_la_MAJOR) {' > $@ objs=`for obj in $(libiso9660_la_OBJECTS); do sed -ne "s/^pic_object='\(.*\)'$$/\1/p" $$obj; done`; if test -n "$$objs" ; then \ nm $${objs} | sed -n -e 's/^.*[ ][ABCDGIRSTW][ABCDGIRSTW]*[ ][ ]*\([_A-Za-z][_A-Za-z0-9]*\)$$/\1/p' | sort -u | { first=true; while read symbol; do if grep -q "^$${symbol}\$$" $(srcdir)/libiso9660.sym; then if test $$first = true; then echo " global:"; first=false; fi; echo " $${symbol};"; fi; done; } >> $@; \ nm $${objs} | sed -n -e 's/^.*[ ][ABCDGIRSTW][ABCDGIRSTW]*[ ][ ]*\([_A-Za-z][_A-Za-z0-9]*\)$$/\1/p' | sort -u | { first=true; while read symbol; do if grep -q "^$${symbol}\$$" $(srcdir)/libiso9660.sym; then :; else if test $$first = true; then echo " local:"; first=false; fi; echo " $${symbol};"; fi; done; } >> $@; \ fi echo '};' >> $@ MOSTLYCLEANFILES = libiso9660.la.ver else libiso9660_la_LDFLAGS = $(libiso9660_la_ldflags) libiso9660_la_DEPENDENCIES = $(libcdio9660_la_dependencies) endif