dso.html.en revision e5168eeed156542fcaa4e506f01a192efc1771f1
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!--
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb This file is generated from xml source: DO NOT EDIT
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb --><title>Dynamic Shared Object (DSO) Support - Apache HTTP Server</title><link href="/style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /><link href="/style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /><link href="/style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link href="/images/favicon.ico" rel="shortcut icon" /></head><body id="manual-page"><div id="page-header"><p class="menu"><a href="/mod/">Modules</a> | <a href="/mod/directives.html">Directives</a> | <a href="/faq/">FAQ</a> | <a href="/glossary.html">Glossary</a> | <a href="/sitemap.html">Sitemap</a></p><p class="apache">Apache HTTP Server Version 2.0</p><img alt="" src="/images/feather.gif" /></div><div class="up"><a href="./"><img title="<-" alt="<-" src="/images/left.gif" /></a></div><div id="path"><a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs-project/">Documentation</a> > <a href="./">Version 2.0</a></div><div id="page-content"><div id="preamble"><h1>Dynamic Shared Object (DSO) Support</h1>
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb <p>The Apache HTTP Server is a modular program where the
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb administrator can choose the functionality to include in the
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb server by selecting a set of modules. The modules can be
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb statically compiled into the <code>httpd</code> binary when the
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb server is built. Alternatively, modules can be compiled as
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb Dynamic Shared Objects (DSOs) that exist separately from the
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb compiled at the time the server is built, or they may be
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb compiled and added at a later time using the Apache Extension
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb <p>This document describes how to use DSO modules as well as
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb the theory behind their use.</p>
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb </div><div id="quickview"><ul id="toc"><li><img alt="" src="/images/down.gif" /> <a href="#implementation">Implementation</a></li><li><img alt="" src="/images/down.gif" /> <a href="#usage">Usage Summary</a></li><li><img alt="" src="/images/down.gif" /> <a href="#background">Background</a></li><li><img alt="" src="/images/down.gif" /> <a href="#advantages">Advantages and Disadvantages</a></li></ul></div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div><div class="section"><h2><a name="implementation" id="implementation">Implementation</a></h2>
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb<table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="/mod/mod_so.html">mod_so</a></code></li></ul></td><td><ul><li><code class="directive"><a href="/mod/mod_so.html#loadmodule">LoadModule</a></code></li></ul></td></tr></table>
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb <p>The DSO support for loading individual Apache modules is based
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb on a module named <code class="module"><a href="/mod/mod_so.html">mod_so</a></code> which must be statically
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb compiled into the Apache core. It is the only module besides
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb <code class="module"><a href="/mod/core.html">core</a></code> which cannot be put into a DSO
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb itself. Practically all other distributed Apache modules can then
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb be placed into a DSO by individually enabling the DSO build for
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb <code>--enable-<em>module</em>=shared</code> option as disucussed
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb in the <a href="install.html">install documentation</a>. After a
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb module is compiled into a DSO named <code>mod_foo.so</code> you
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb can use <code class="module"><a href="/mod/mod_so.html">mod_so</a></code>'s <code class="directive"><a href="/mod/mod_so.html#loadmodule">LoadModule</a></code> command in your
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb <code>httpd.conf</code> file to load this module at server startup
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb or restart.</p>
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb <p>To simplify this creation of DSO files for Apache modules
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb (especially for third-party modules) a new support program
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb eXtenSion</em>) is available. It can be used to build DSO based
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb modules <em>outside of</em> the Apache source tree. The idea is
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb simple: When installing Apache the <code>configure</code>'s
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb <code>make install</code> procedure installs the Apache C
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb header files and puts the platform-dependent compiler and
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb linker flags for building DSO files into the <code>apxs</code>
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb program. This way the user can use <code>apxs</code> to compile
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb his Apache module sources without the Apache distribution
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb source tree and without having to fiddle with the
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb platform-dependent compiler and linker flags for DSO
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb support.</p>
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div><div class="section"><h2><a name="usage" id="usage">Usage Summary</a></h2>
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb <p>To give you an overview of the DSO features of Apache 2.0,
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb here is a short and concise summary:</p>
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb Build and install a <em>distributed</em> Apache module, say
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb$ /configure --prefix=/path/to/install --enable-foo=shared<br />
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb$ make install
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb Build and install a <em>third-party</em> Apache module, say
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb$ /configure --add-module=module_type:/path/to/3rdparty/mod_foo.c --enable-foo=shared<br />
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb$ make install
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb Configure Apache for <em>later installation</em> of shared
f888346b48f5e5b5e3f0a47dedb8cefd2759a4e2gregames$ make install
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb Build and install a <em>third-party</em> Apache module, say
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb source tree using <a href="programs/apxs.html">apxs</a>:
d4abb06ac220bb280ae996b6d21bbd257db51bb1jerenkrantz$ apxs -i -a -n foo mod_foo.la
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb <p>In all cases, once the shared module is compiled, you must
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb use a <code class="directive"><a href="/mod/mod_so.html#loadmodule">LoadModule</a></code>
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb directive in <code>httpd.conf</code> to tell Apache to activate
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb the module.</p>
a2a0abd88b19e042a3eb2a9fa1702c25ad51303dwrowe</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div><div class="section"><h2><a name="background" id="background">Background</a></h2>
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb <p>On modern Unix derivatives there exists a nifty mechanism
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb usually called dynamic linking/loading of <em>Dynamic Shared
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb Objects</em> (DSO) which provides a way to build a piece of
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb program code in a special format for loading it at run-time
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb into the address space of an executable program.</p>
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb <p>This loading can usually be done in two ways: Automatically
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb executable program is started or manually from within the
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb executing program via a programmatic system interface to the
b38846b15c8891c6dec44dcc4f96ca40721bf663rbb Unix loader through the system calls
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe <p>In the first way the DSO's are usually called <em>shared
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe <code>libfoo.so</code> or <code>libfoo.so.1.2</code>. They
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe reside in a system directory (usually <code>/usr/lib</code>)
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe and the link to the executable program is established at
c2cf53a40a9814eb91db2cdf820f97d943f21628coar build-time by specifying <code>-lfoo</code> to the linker
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe command. This hard-codes library references into the executable
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe program file so that at start-time the Unix loader is able to
731344ed8f3677d1661c261ca5fcdd2ee3dbc74ccoar locate <code>libfoo.so</code> in <code>/usr/lib</code>, in
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe paths hard-coded via linker-options like <code>-R</code> or in
731344ed8f3677d1661c261ca5fcdd2ee3dbc74ccoar paths configured via the environment variable
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe <code>LD_LIBRARY_PATH</code>. It then resolves any (yet
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe unresolved) symbols in the executable program which are
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe available in the DSO.</p>
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe <p>Symbols in the executable program are usually not referenced
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe by the DSO (because it's a reusable library of general code)
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe and hence no further resolving has to be done. The executable
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe program has no need to do anything on its own to use the
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe symbols from the DSO because the complete resolving is done by
3e392a5afd51526de3cb15d57ee46d8cb160ae65gregames the Unix loader. (In fact, the code to invoke
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe <code>ld.so</code> is part of the run-time startup code which
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe is linked into every executable program which has been bound
ea512a4af20e6b6e6931de4929d54d93f03a0139ianh non-static). The advantage of dynamic loading of common library
ea512a4af20e6b6e6931de4929d54d93f03a0139ianh code is obvious: the library code needs to be stored only once,
9e2e5b9bccb45b4a1bb9b747f15c7355e43be916ianh in a system library like <code>libc.so</code>, saving disk
cbd8d35ca8d9780f1081f30ebfe4abda44cab7ebianh space for every program.</p>
ea512a4af20e6b6e6931de4929d54d93f03a0139ianh <p>In the second way the DSO's are usually called <em>shared
ea512a4af20e6b6e6931de4929d54d93f03a0139ianh objects</em> or <em>DSO files</em> and can be named with an
ea512a4af20e6b6e6931de4929d54d93f03a0139ianh arbitrary extension (although the canonical name is
ea512a4af20e6b6e6931de4929d54d93f03a0139ianh <code>foo.so</code>). These files usually stay inside a
ea512a4af20e6b6e6931de4929d54d93f03a0139ianh program-specific directory and there is no automatically
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe established link to the executable program where they are used.
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe Instead the executable program manually loads the DSO at
d4abb06ac220bb280ae996b6d21bbd257db51bb1jerenkrantz run-time into its address space via <code>dlopen()</code>. At
d4abb06ac220bb280ae996b6d21bbd257db51bb1jerenkrantz this time no resolving of symbols from the DSO for the
d4abb06ac220bb280ae996b6d21bbd257db51bb1jerenkrantz executable program is done. But instead the Unix loader
d4abb06ac220bb280ae996b6d21bbd257db51bb1jerenkrantz automatically resolves any (yet unresolved) symbols in the DSO
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe from the set of symbols exported by the executable program and
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe its already loaded DSO libraries (especially all symbols from
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe the ubiquitous <code>libc.so</code>). This way the DSO gets
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe knowledge of the executable program's symbol set as if it had
3e392a5afd51526de3cb15d57ee46d8cb160ae65gregames been statically linked with it in the first place.</p>
3e392a5afd51526de3cb15d57ee46d8cb160ae65gregames <p>Finally, to take advantage of the DSO's API the executable
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe program has to resolve particular symbols from the DSO via
731344ed8f3677d1661c261ca5fcdd2ee3dbc74ccoar <code>dlsym()</code> for later use inside dispatch tables
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe <em>etc.</em> In other words: The executable program has to
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe manually resolve every symbol it needs to be able to use it.
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe The advantage of such a mechanism is that optional program
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe parts need not be loaded (and thus do not spend memory) until
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe they are needed by the program in question. When required,
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe these program parts can be loaded dynamically to extend the
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe base program's functionality.</p>
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe <p>Although this DSO mechanism sounds straightforward there is
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe at least one difficult step here: The resolving of symbols from
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe the executable program for the DSO when using a DSO to extend a
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe program (the second way). Why? Because "reverse resolving" DSO
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe symbols from the executable program's symbol set is against the
c2cf53a40a9814eb91db2cdf820f97d943f21628coar library design (where the library has no knowledge about the
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe programs it is used by) and is neither available under all
4775dfc34c90fada8c7c4d6a57ed8a3114d55c2dtrawick platforms nor standardized. In practice the executable
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe program's global symbols are often not re-exported and thus not
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe available for use in a DSO. Finding a way to force the linker
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe to export all global symbols is the main problem one has to
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe solve when using DSO for extending a program at run-time.</p>
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe <p>The shared library approach is the typical one, because it
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe is what the DSO mechanism was designed for, hence it is used
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe for nearly all types of libraries the operating system
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe provides. On the other hand using shared objects for extending
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe a program is not used by a lot of programs.</p>
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe <p>As of 1998 there are only a few software packages available
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe which use the DSO mechanism to actually extend their
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe functionality at run-time: Perl 5 (via its XS mechanism and the
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe DynaLoader module), Netscape Server, <em>etc.</em> Starting
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe with version 1.3, Apache joined the crew, because Apache
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe already uses a module concept to extend its functionality and
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe internally uses a dispatch-list-based approach to link external
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe modules into the Apache core functionality. So, Apache is
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe really predestined for using DSO to load its modules at
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe run-time.</p>
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div><div class="section"><h2><a name="advantages" id="advantages">Advantages and Disadvantages</a></h2>
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe <p>The above DSO based features have the following
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe advantages:</p>
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe <li>The server package is more flexible at run-time because
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe the actual server process can be assembled at run-time via
d4abb06ac220bb280ae996b6d21bbd257db51bb1jerenkrantz <code class="directive"><a href="/mod/mod_so.html#loadmodule">LoadModule</a></code>
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe <code>httpd.conf</code> configuration commands instead of
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe <code>configure</code> options at build-time. For instance
731344ed8f3677d1661c261ca5fcdd2ee3dbc74ccoar this way one is able to run different server instances
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe (standard & SSL version, minimalistic & powered up
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe version [mod_perl, PHP3], <em>etc.</em>) with only one Apache
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe installation.</li>
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe <li>The server package can be easily extended with
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe third-party modules even after installation. This is at least
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe a great benefit for vendor package maintainers who can create
c2cf53a40a9814eb91db2cdf820f97d943f21628coar a Apache core package and additional packages containing
c2cf53a40a9814eb91db2cdf820f97d943f21628coar extensions like PHP3, mod_perl, mod_fastcgi,
d4abb06ac220bb280ae996b6d21bbd257db51bb1jerenkrantz <li>Easier Apache module prototyping because with the
d4abb06ac220bb280ae996b6d21bbd257db51bb1jerenkrantz DSO/<code>apxs</code> pair you can both work outside the
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe Apache source tree and only need an <code>apxs -i</code>
c2cf53a40a9814eb91db2cdf820f97d943f21628coar command followed by an <code>apachectl restart</code> to
c2cf53a40a9814eb91db2cdf820f97d943f21628coar bring a new version of your currently developed module into
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe the running Apache server.</li>
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe <li>The DSO mechanism cannot be used on every platform
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe because not all operating systems support dynamic loading of
d4abb06ac220bb280ae996b6d21bbd257db51bb1jerenkrantz code into the address space of a program.</li>
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe <li>The server is approximately 20% slower at startup time
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe because of the symbol resolving overhead the Unix loader now
d4abb06ac220bb280ae996b6d21bbd257db51bb1jerenkrantz has to do.</li>
d4abb06ac220bb280ae996b6d21bbd257db51bb1jerenkrantz <li>The server is approximately 5% slower at execution time
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe under some platforms because position independent code (PIC)
c2cf53a40a9814eb91db2cdf820f97d943f21628coar sometimes needs complicated assembler tricks for relative
c2cf53a40a9814eb91db2cdf820f97d943f21628coar addressing which are not necessarily as fast as absolute
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe addressing.</li>
d4abb06ac220bb280ae996b6d21bbd257db51bb1jerenkrantz <li>Because DSO modules cannot be linked against other
d4abb06ac220bb280ae996b6d21bbd257db51bb1jerenkrantz DSO-based libraries (<code>ld -lfoo</code>) on all platforms
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe (for instance a.out-based platforms usually don't provide
c2cf53a40a9814eb91db2cdf820f97d943f21628coar this functionality while ELF-based platforms do) you cannot
c2cf53a40a9814eb91db2cdf820f97d943f21628coar use the DSO mechanism for all types of modules. Or in other
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe words, modules compiled as DSO files are restricted to only
d4abb06ac220bb280ae996b6d21bbd257db51bb1jerenkrantz use symbols from the Apache core, from the C library
d4abb06ac220bb280ae996b6d21bbd257db51bb1jerenkrantz (<code>libc</code>) and all other dynamic or static libraries
d4abb06ac220bb280ae996b6d21bbd257db51bb1jerenkrantz used by the Apache core, or from static library archives
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe (<code>libfoo.a</code>) containing position independent code.
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe The only chances to use other code is to either make sure the
fa06de8a28a737e8fbaad76d7f3ff67aaa5e4a09wrowe Apache core itself already contains a reference to it or
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe loading the code yourself via <code>dlopen()</code>.</li>
83a8dc5a596a8a1b9d14f063268287d123b9ed7ewrowe</div></div><div id="footer"><p class="apache">Maintained by the <a href="http://httpd.apache.org/docs-project/">Apache HTTP Server Documentation Project</a></p><p class="menu"><a href="/mod/">Modules</a> | <a href="/mod/directives.html">Directives</a> | <a href="/faq/">FAQ</a> | <a href="/glossary.html">Glossary</a> | <a href="/sitemap.html">Sitemap</a></p></div></body></html>