mr4th-dynamic-linking/linux_linking/linux_main.c

// declare base_func; no mark -> load-time imported symbol
void base_func(void);


// setup plugin_func as a function pointer so that it can be linked at run time
typedef void PLUGIN_Func(void);
PLUGIN_Func *plugin_func = 0;


// need to include for dlopen and dlsym
#include <dlfcn.h>

// helper macro for dlsym that handles the casting of function pointers
#define GET_PROC(var,mod,name) *((void**)(&(var))) = dlsym((mod),(name))


int main(){
  
  // functions linked by load-time linking can be called directly without further setup
  base_func();
  
  
  // to call a function with run-time linking, we must manually load and link it
  void *module = dlopen("$ORIGIN/linux_plugin.so", RTLD_NOW);
  if (module != 0){
    GET_PROC(plugin_func, module, "plugin_func");
  }
  
  
  // calls to plugin_func only work after the "plugin" loaded successfully
  if (plugin_func != 0){
    plugin_func();
  }
  
  
  // demonstration: the data structures contained in the 'base' are not duplicated in each binary
  base_func();
}