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(libtool.info)Modules for libltdl

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Creating modules that can be `dlopen'ed
=======================================

   Libtool modules are like normal libtool libraries with a few
exceptions:

   You have to link the module with libtool's `-module' switch, and you
should link any program that is intended to dlopen the module with
`-dlopen modulename.la' so that libtool can dlpreopen the module on
platforms which don't support dlopening.  If the module depends on any
other libraries, make sure you specify them either when you link the
module or when you link programs that dlopen it.  If you want to
disable Note: Versioning for a specific module you should link it
with the `-avoid-version' switch.  Note that libtool modules don't need
to have a "lib" prefix.  However, automake 1.4 or higher is required to
build such modules.

   Usually a set of modules provide the same interface, i.e, exports
the same symbols, so that a program can dlopen them without having to
know more about their internals.  In order to avoid symbol conflicts
all exported symbols must be prefixed with "modulename_LTX_"
(`modulename' is the name of the module).  Internal symbols must be
named in such a way that they won't conflict with other modules, for
example, by prefixing them with "_modulename_".  Although some
platforms support having the same symbols defined more than once it is
generally not portable and it makes it impossible to dlpreopen such
modules.  libltdl will automatically cut the prefix off to get the real
name of the symbol.  Additionally, it supports modules which don't use
a prefix so that you can also dlopen non-libtool modules.

   `foo1.c' gives an example of a portable libtool module.  Exported
symbols are prefixed with "foo1_LTX_", internal symbols with "_foo1_".
Aliases are defined at the beginning so that the code is more readable.

     /* aliases for the exported symbols */
     #define foo	foo1_LTX_foo
     #define bar	foo1_LTX_bar
     
     /* a global variable definition */
     int bar = 1;
     
     /* a private function */
     int _foo1_helper() {
       return bar;
     }
     
     /* an exported function */
     int foo() {
       return _foo1_helper();
     }

The `Makefile.am' contains the necessary rules to build the module
`foo1.la':

     ...
     lib_LTLIBRARIES = foo1.la
     
     foo1_la_SOURCES = foo1.c
     foo1_la_LDFLAGS = -module
     ...