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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: Portable Library Design</TITLE><META NAME="description" CONTENT="Autoconf, Automake, and Libtool: Portable Library Design"><META NAME="keywords" CONTENT="Autoconf, Automake, and Libtool: Portable Library Design"><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; if (navigator.appVersion.charAt(0)>=4) return true; 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If you do accidentally use any of these features, youprobably won't find out about it until someone first tries to use yourproject on an older or less featureful host.</P><P>I have already used the <SAMP>`-module'</SAMP> and <SAMP>`-avoid-version'</SAMP>libtool linking options when compiling the libltdl module in thelast section, the others are useful to know also. All of these are usedwith the <SAMP>`link'</SAMP> mode of <CODE>libtool</CODE> (<SAMP>`libtool--mode=link'</SAMP>): </P><P><DL COMPACT><DT><SAMP>`-module'</SAMP><DD>This option tells <CODE>libtool</CODE> that the target is a dynamicallyloadable module (as opposed to a conventional shared library) and assuch need not have the <SAMP>`lib'</SAMP> prefix.<P><DT><SAMP>`-avoid-version'</SAMP><DD>When linking a dynamic module, this option can be used instead of the<SAMP>`-version-info'</SAMP> option, so that the module is not subject to theusual shared library version number suffixes.<P><DT><SAMP>`-no-undefined'</SAMP><DD>This is an extremely important option when you are aiming for maximumportability. It declares that all of the symbols required by the targetare resolved at link time. Some shared library architectures do notallow undefined symbols by default (Tru64 Unix), and others do not allowthem at all (AIX). By using this switch, and ensuring that allsymbols really are resolved at link time, your libraries will work oneven these platforms. See section <A HREF="autobook_88.html#SEC88">11.2.1 Creating Libtool Libraries with Automake</A>.<P><DT><SAMP>`-export-dynamic'</SAMP><DD>Almost the opposite of <SAMP>`-no-undefined'</SAMP>, this option will compilethe target so that the symbols it exports can be used to satisfyunresolved symbols in subsequently loaded modules. Not all sharedlibrary architectures support this feature, and many that do support it,do so by default regardless of whether this option is supplied. If yourely on this feature, then you should use this option, in the knowledgethat you project will not work correctly on architectures that have nosupport for the feature. For maximum portability, you should neitherrely on this feature nor use the <SAMP>`-export-dynamic'</SAMP> option -- but,on the occasions you do need the feature, this option is necessary toensure that the linker is called correctly.</DL><P>When you have the option to do so, I recommend that you design yourproject so that each of the libraries and modules is self contained,except for minimal number of dependent libraries, arranged in adirectional graph shaped like a tree. That is, by relying onback-linking, or mutual or cyclic dependencies you reduce theportability of your project.In the diagrams below, an arrow indicates that the compilation objectrelies on symbols from the objects that it points to:</P><P><TABLE width=100%><tr><td> </td><td class=example bgcolor=#6688aa><br><pre> main .---> main main | | | | .----+----, | .----+----, .----+----, v v | v v v v liba libb liba libb liba<-----libb | | | ^ v v v | libc libc libc-------' Tree: good Backlinking: bad Cyclic: bad</pre></td></tr></table></P><P><A NAME="dlpreopen Loading"></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>⌨️ 快捷键说明
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