How can a shared library (.so) call a function that is implemented in its loading program?

Question

I have a shared library that I implemented and want the .so to call a function that\'s implemented in the main program which loads the library.

Let\'s say I have mai

Answer 1

You'll need make a register function in your .so so that the executable can give a function pointer to your .so for it's later use.

Like this:

void in_main_func () {
// this is the function that need to be called from a .so
}

void (*register_function)(void(*)());
void *handle = dlopen("libmylib.so");

register_function = dlsym(handle, "register_function");

register_function(in_main_func);

the register_function needs to store the function pointer in a variable in the .so where the other function in the .so can find it.

Your mylib.c would the need to look something like this:

void (*callback)() = NULL;

void register_function( void (*in_main_func)())
{
    callback = in_main_func();
}

void function_needing_callback() 
{
     callback();
}