Question

I’m writing some code that uses dynamic shared libraries as plugins.

My command line for building the shared libraries looks like:

cc -shared -fPIC -o module.so -g -Wall module.c 

Within the module, I can call functions that are in any other shared library that has been loaded within the main executable.

However I cannot access (exported) functions that are in the executable itself (I get undefined symbol errors).

My call to dlopen looks like this:

void *handle = dlopen(plugin, RTLD_NOW); 

Can anyone please advise how my module can call back to my executable, without having to put all of the executable’s utility functions into yet another shared library?

Answer 1

I’ve found the answer myself.

I had to add the --export-dynamic flags to the link options for the main executable.

When creating a dynamically linked executable, add all symbols to the dynamic symbol table. The dynamic symbol table is the set of symbols which are visible from dynamic objects at run time.

If you do not use this option, the dynamic symbol table will normally contain only those symbols which are referenced by some dynamic object mentioned in the link.

If you use ‘dlopen’ to load a dynamic object which needs to refer back to the symbols defined by the program, rather than some other dynamic object, then you will probably need to use this option when linking the program itself.