10 Dlopened modules

It can sometimes be confusing to discuss dynamic linking, because the term is used to refer to two different concepts:

1. Compiling and linking a program against a shared library, which is resolved automatically at run time by the dynamic linker. In this process, dynamic linking is transparent to the application.
2. The application calling functions such as dlopen that load arbitrary, user-specified modules at runtime. This type of dynamic linking is explicitly controlled by the application.

To mitigate confusion, this manual refers to the second type of dynamic linking as dlopening a module.

The main benefit to dlopening object modules is the ability to access compiled object code to extend your program, rather than using an interpreted language. In fact, dlopen calls are frequently used in language interpreters to provide an efficient way to extend the language.

As of version 2.2, libtool provides support for dlopened modules. However, you should indicate that your package is willing to use such support, by using the LT_INIT option ‘dlopen’ in configure.ac. If this option is not given, libtool will assume no dlopening mechanism is available, and will try to simulate it.

This chapter discusses how you as a dlopen application developer might use libtool to generate dlopen-accessible modules.

• Building modules: Creating dlopenable objects and libraries.
• Dlpreopening: Dlopening that works on static platforms.
• Linking with dlopened modules: Using dlopenable modules in libraries.
• Finding the dlname: Choosing the right file to dlopen.
• Dlopen issues: Unresolved problems that need your attention.