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<HTML><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><!-- Created on September, 12  2004 by texi2html 1.64 --><!-- Written by: Lionel Cons <Lionel.Cons@cern.ch> (original author)            Karl Berry  <karl@freefriends.org>            Olaf Bachmann <obachman@mathematik.uni-kl.de>            and many others.Maintained by: Olaf Bachmann <obachman@mathematik.uni-kl.de>Send bugs and suggestions to <texi2html@mathematik.uni-kl.de> --><HEAD><TITLE>Autoconf, Automake, and Libtool: Creating Libtool Libraries with Automake</TITLE><META NAME="description" CONTENT="Autoconf, Automake, and Libtool: Creating Libtool Libraries with Automake"><META NAME="keywords" CONTENT="Autoconf, Automake, and Libtool: Creating Libtool Libraries with Automake"><META NAME="resource-type" CONTENT="document"><META NAME="distribution" CONTENT="global"><META NAME="Generator" CONTENT="texi2html 1.64"><script language="Javascript"><!--    // Check the browser version.    function checkVersion() {      if (navigator.appVersion.charAt(0)>=3) return true; 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<TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_90.html#SEC90" onMouseover="img_act('back')" onMouseout="img_inact('back')"><IMG SRC="back.png" BORDER="0" ALT="FastBack: Using libtoolize" ALIGN="MIDDLE" NAME="back"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_87.html#SEC87" onMouseover="img_act('up')" onMouseout="img_inact('up')"><IMG SRC="up.png" BORDER="0" ALT="Up: Integration with Makefile.am" ALIGN="MIDDLE" NAME="up"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_90.html#SEC90" onMouseover="img_act('forward')" onMouseout="img_inact('forward')"><IMG SRC="forward.png" BORDER="0" ALT="FastForward: Using libtoolize" ALIGN="MIDDLE" NAME="forward"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook.html#SEC_Top" onMouseover="img_act('home')" onMouseout="img_inact('home')"><IMG SRC="home.png" BORDER="0" ALT="Top: Autoconf, Automake, and Libtool" ALIGN="MIDDLE" NAME="home"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_toc.html#SEC_Contents" onMouseover="img_act('toc')" onMouseout="img_inact('toc')"><IMG SRC="toc.png" BORDER="0" ALT="Contents: Table of Contents" ALIGN="MIDDLE" NAME="toc"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_285.html#SEC285" onMouseover="img_act('index')" onMouseout="img_inact('index')"><IMG SRC="index.png" BORDER="0" ALT="Index: Index" ALIGN="MIDDLE" NAME="index"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_abt.html#SEC_About" onMouseover="img_act('help')" onMouseout="img_inact('help')"><IMG SRC="help.png" BORDER="0" ALT="About: About this document" ALIGN="MIDDLE" NAME="help"></A></TD></TR></TABLE></TD><TD ALIGN="LEFT"><H3> 11.2.1 Creating Libtool Libraries with Automake </H3><!--docid::SEC88::--><P>Continuing in the spirit of making Libtool library management look likenative static archive management, converting a <TT>`Makefile.am'</TT> fromstatic archive use to Libtool library use is a matter of changing thename of the library, and adding a Libtool prefix somewhere.  Forexample, a <TT>`Makefile.am'</TT> for building a static archive might be:</P><P><TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>lib_LIBRARIES      = libshell.alibshell_a_SOURCES = object.c subr.c symbol.c</pre></td></tr></table></P><P>This would build a static archive called <TT>`libshell.a'</TT> consisting ofthe objects <TT>`object.o'</TT>, <TT>`subr.o'</TT> and <TT>`bar.o'</TT>.  To buildan equivalent Libtool library from the same objects, you change this to:</P><P><TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>lib_LTLIBRARIES     = libshell.lalibshell_la_SOURCES = object.c subr.c symbol.c</pre></td></tr></table></P><P>The only changes are that the library is now named with a <CODE>.la</CODE>suffix,  and the Automake primary is now <SAMP>`LTLIBRARIES'</SAMP>.Note that since the name of the library has changed, you also need touse <SAMP>`libshell_la_SOURCES'</SAMP>, and similarly for any other Automakemacros which used to refer to the old archive.  As for native libraries,Libtool library names should begin with the letters <SAMP>`lib'</SAMP>, so thatthe linker will be able to find them when passed <SAMP>`-l'</SAMP> options.</P><P>Often you will need to add extra objects to the library as determined by<CODE>configure</CODE>, but this is also a mechanical process.  Whenbuilding native libraries, the <TT>`Makefile.am'</TT> would have contained:</P><P><TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>libshell_a_LDADD = xmalloc.o @LIBOBJS@</pre></td></tr></table></P><P>To add the same objects to an equivalent Libtool library would require:</P><P><TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>libshell_la_LDADD = xmalloc.lo @LTLIBOBJS@</pre></td></tr></table></P><P>That is, objects added to a Libtool library must be Libtool objects(with a <CODE>.lo</CODE>) suffix.  You should add code to <TT>`configure.in'</TT>to ensure that <SAMP>`LTALLOCA'</SAMP> and <SAMP>`LTLIBOBJS'</SAMP> are setappropriately, See section <A HREF="autobook_86.html#SEC86">11.1.2 Extra Macros for Libtool</A>.  Automake willtake care of generating appropriate rules for building the Libtoolobjects mentioned in an <SAMP>`LDADD'</SAMP> macro.</P><P>If you want to pass any additional flags to <CODE>libtool</CODE> when it isbuilding, you use the <SAMP>`LDFLAGS'</SAMP> macro for that library, like this:</P><P><TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>libshell_la_LDFLAGS = -version-info 1:0:1</pre></td></tr></table></P><P>For a detailed list of all the available options, see section `Link mode' in <CITE>The Libtool Manual</CITE>.</P><P><BLOCKQUOTE>Libtool's use of <SAMP>`-rpath'</SAMP> has been a point of contention for someusers, since it prevents you from moving shared libraries to anotherlocation in the library search path.  Or, at least, if you do, all ofthe executables that were linked with <SAMP>`-rpath'</SAMP> set to the oldlocation will need to be relinked.<P>We (the Libtool maintainers) assert that always using <SAMP>`-rpath'</SAMP> isa good thing:  Mainly because you can guarantee that any executablelinked with <SAMP>`-rpath'</SAMP> will find the correct version of thelibrary, in the rpath directory, that was intended when the executablewas linked.  Library versions can still be managed correctly, and willbe found by the run time loader, by installing newer versions to thesame directory.  Additionally, it is much harder for a malicious user toleave a modified copy of system library in a directory that someonemight wish to list in their <SAMP>`LD_LIBRARY_PATH'</SAMP> in the hope that somecode they have written will be executed unexpectedly.</P><P>The argument against <SAMP>`-rpath'</SAMP> was instigated when one of theGNU/Linux distributions moved some important system libraries toanother directory to make room for a different version, and discoveredthat all of the executables that relied on these libraries and werelinked with Libtool no longer worked.  Doing this was, arguably, badsystem management -- the new libraries should have been placed in a newdirectory, and the old libraries left alone.  Refusing to use<SAMP>`-rpath'</SAMP> in case you want to restructure the system librarydirectories is a very weak argument.</BLOCKQUOTE><P>The <SAMP>`-rpath'</SAMP> option (which is required for Libtool libraries) isautomatically supplied by <CODE>automake</CODE> based on the installationdirectory specified with the library primary.</P><P><TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>lib_LTLIBRARIES = libshell.la</pre></td></tr></table></P><P>The example would use the value of the make macro <CODE>$(libdir)</CODE> asthe argument to <SAMP>`-rpath'</SAMP>, since that is where the library will beinstalled.</P><P>A few of the other options you can use in the library <SAMP>`LDFLAGS'</SAMP> are:</P><P><DL COMPACT><DT><SAMP>`-no-undefined'</SAMP><DD>Modern architectures allow us to create shared libraries with undefinedsymbols, provided those symbols are resolved (usually by the executablewhich loads the library) at runtime.  Unfortunately, there are somearchitectures (notably AIX and Windows) which require that<EM>all</EM> symbols are resolved when the library is linked.  If you knowthat your library has no unresolved symbols at link time, then addingthis option tells <CODE>libtool</CODE> that it will be able to build ashared library, even on architectures which have this requirement.<P><DT><SAMP>`-static'</SAMP><DD>Using this option will force <CODE>libtool</CODE> to build only a staticarchive for this library.<P><DT><SAMP>`-release'</SAMP><DD>On occasion, it is desirable to encode the release number of a libraryinto its name.  By specifying the release number with this option,<CODE>libtool</CODE> will build a library that does this, but will breakbinary compatibility for each change of the release number.  By breakingbinary compatibility this way, you negate the possibility of fixing bugsin installed programs by installing an updated shared library.  Youshould probably be using <SAMP>`-version-info'</SAMP> instead.<P><TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>libshell_la_LDFLAGS = -release 27</pre></td></tr></table></P><P>The above fragment might create a library called<TT>`libshell-27.so.0.0.0'</TT> for example.</P><P><DT><SAMP>`-version-info'</SAMP><DD>Set the version number of the library according to the native versioningrules based on the numbers supplied, See section <A HREF="autobook_91.html#SEC91">11.4 Library Versioning</A>.  Youneed to be aware that the library version number is for the use of theruntime loader, and is completely unrelated to the release number ofyour project.  If you really want to encode the project release into thelibrary, you can use <SAMP>`-release'</SAMP> to do it.<P>If this option is not supplied explicitly, it defaults to<SAMP>`-version-info 0:0:0'</SAMP>.</DL><P><BLOCKQUOTE>Historically, the default behaviour of Libtool was as if<SAMP>`-no-undefined'</SAMP> was always passed on the command line, but itproved to be annoying to developers who had to constantly turn it off sothat  their ELF libraries could be featureful.  Now it has to bedefined explicitly if you need it.<P>There are is a tradeoff:</P><P><UL><LI>If you don't specify <SAMP>`-no-undefined'</SAMP>, then Libtool will not buildshared libraries on platforms which don't allow undefined symbols atlink time for such a library.<P><LI>It is only safe to specify this flag when you know for certain that<EM>all</EM> of the libraries symbols are defined at link time, otherwisethe <SAMP>`-no-undefined'</SAMP> link will appear to work until it is tried ona platform which requires all symbols to be defined.  Libtool will tryto link the shared library in this case (because you told it that youhave not left any undefined symbols), but the link will fail, becausethere <STRONG>are</STRONG> undefined symbols in spite of what you told Libtool.</UL><P>For more information about this topic, see <A HREF="autobook_172.html#SEC172">18.3 Portable Library Design</A>.</BLOCKQUOTE><P><A NAME="Linking against Libtool Libraries with Automake"></A></TR></TABLE><BR>  <FONT SIZE="-1">This document was generatedby <I>Gary V. Vaughan</I> on <I>September, 12  2004</I>using <A HREF="http://www.mathematik.uni-kl.de/~obachman/Texi2html"><I>texi2html</I></A></BODY></HTML>
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