17.5 A Simple GNU/Linux Dynamic Module

As an appetiser for working with dynamic loadable modules, here is a minimal module written for the interface used by the loader in the previous section:

#include <stdio.h> int run (const char *argument) { printf ("Hello, %s!\n", argument); return 0; }

Again, to compile on a GNU/Linux machine:

$ gcc -fPIC -c simple-module.c $ gcc -shared -o simple-module.so

Having compiled both loader and module, a test run looks like this:

$ ./simple-loader simple-module World Hello, World! => 0

If you have a GNU/Linux system, you should experiment with the simple examples from this chapter to get a feel for the relationship between a dynamic module loader and its modules -- tweak the interface a little; try writing another simple module. If you have a machine with a different dynamic loading API, try porting these examples to that machine to get a feel for the kinds of problems you would encounter if you wanted a module system that would work with both APIs.

The next chapter will do just that, and develop these examples into a fully portable module loading system with the aid of GNU Autotools. In 20.1 A Module Loading Subsystem, I will add a more realistic module loader into the Sic project last discussed in 12. A Large GNU Autotools Project.