updated

LDP/howto/docbook/Program-Library-HOWTO.sgml

@@ -7,7 +7,7 @@
 <author><firstname>David A.</firstname> <surname>Wheeler</surname>
 </author>
 <address><email>dwheeler@dwheeler.com</email></address>
-<pubdate>version 0.71, 6 September 2000</pubdate>
+<pubdate>version 0.75, 31 October 2000</pubdate>
 <abstract>
 <para>
 This HOWTO for programmers
@@ -767,6 +767,7 @@ If the library exports a routine named  _init,  then  that
 code  is  executed  before  dlopen() returns.
 You can use this fact in your own libraries to implement
 initialization routines.
+See <xref linkend="init-and-fini"> for more information.
 </para>
 </sect2>
 
@@ -830,6 +831,8 @@ until dlclose has been called on it as many times as
 dlopen has succeeded on it.
 Thus, it's not a problem for the same program
 to load the same library multiple times.
+If a library is deallocated, its function _fini is called (if it exists);
+see <xref linkend="init-and-fini"> for more information.
 </para>
 </sect2>
 
@@ -942,6 +945,37 @@ documentation locally installed at
 </para>
 </sect2>
 
+<sect2 id="init-and-fini">
+<title>Special functions _init and _fini</title>
+<para>
+Two special functions aid in initializing and finalizing a module:
+_init and _fini.
+If a function ``_init'' is exported in a library,
+then it is called whenever dllopen() is called to open the library.
+In a C program, this just means that you defined some function
+named _init.
+There is a corresponding function called _fini, which is called whenever a
+client calls dlclose() to release a library (and it's released).
+The C prototypes for these functions are:
+<programlisting>
+  void _init(void);
+  void _fini(void);
+</programlisting>
+</para>
+
+<para>
+When compiling the file into a ``.o'' file in gcc, be sure to add the
+gcc option ``-nostartfiles''.
+This keeps the C compiler from
+linking the system startup libraries against the .so file.
+Otherwise, you'll get a ``multiple-definition'' error.
+My thanks to Jim Mischel and Tim Gentry for their suggestion to add
+this discussion of _init and _fini,
+as well as help in creating it.
+</para>
+
+</sect2>
+
 <sect2>
 <title>Shared Libraries Can Be Scripts</title>
 <para>
@@ -988,6 +1022,18 @@ For more information, see its documentation at
 <ulink url="http://www.gnu.org/software/libtool/manual.html">http://www.gnu.org/software/libtool/manual.html</ulink>
 </para>
 
+</sect2>
+<sect2>
+<title>Extremely small executables</title>
+<para>
+You might find the paper
+<ulink url="http://www.muppetlabs.com/~breadbox/software/tiny/teensy.html">Whirlwind Tutorial on Creating Really Teensy ELF Executables for Linux</ulink>
+useful.
+It describes how to make a truly tiny program executable.
+Frankly, you shouldn't use most of these tricks under normal
+circumstances, but they're quite instructive in showing how
+ELF really works.
+</para>
 </sect2>
 </sect1>