Perl DynaLoader hack using .bs files

I needed to install a perl extension from a third-party. It’s an interface to a shared library, a .so file, that they also supply.

Normally I’d add the directory containing the shared library to the LD_LIBRARY_PATH environment variable. Then when the extension is loaded the system dynamic loader can find it.

For various reasons I didn’t want to do that in this case.

An alternative approach is to pre-load the shared library with a flag to make it’s symbols globally available for later linking. (The flag is called RTLD_GLOBAL on Linux, Solaris and other systems that use dlopen(). This hack may not work on other systems.)

But how to pre-load the shared library, only when needed, and without changing any existing perl code? This is where the pesky little .bs files that get installed with perl extensions come in handy.

They’re known as ‘bootstrap’ files. If the .bs file for an extension not empty then DynaLoader (and XSLoader) will execute the contents just before loading the shared object for the extension.

So I put code like this into the .bs file for the extension:

    use DynaLoader;
    DynaLoader::dl_load_file("$ENV{...}/", 1)
	    or die DynaLoader::dl_error();

Not a recommended approach, but neat and handy for me in this case.