.gitignore

program
*.so

main_program.c

#include <stdlib.h>
#include <stdio.h>
#include <dlfcn.h>

void shared_lib_operation();

int main() {
  void *handle;
  void (*funptr)(void);
  char *error;


  printf("Main program executing shared library operation.\n");
  shared_lib_operation();


  printf("Loading plugin without RTLD_DEEPBIND.\n");

  handle = dlopen("libplug.so", RTLD_LAZY);
  if (!handle) {
    fprintf(stderr, "%s\n", dlerror());
    exit(EXIT_FAILURE);
  }
  dlerror();

  *(void **)(&funptr) = dlsym(handle, "execute_plugin");
  if ((error = dlerror()) != NULL)  {
    fprintf(stderr, "%s\n", error);
    exit(EXIT_FAILURE);
  }

  funptr();
  dlclose(handle);


  printf("Loading plugin with RTLD_DEEPBIND.\n");

  handle = dlopen("libplug.so", RTLD_LAZY | RTLD_DEEPBIND);
  if (!handle) {
    fprintf(stderr, "%s\n", dlerror());
    exit(EXIT_FAILURE);
  }
  dlerror();

  *(void **)(&funptr) = dlsym(handle, "execute_plugin");
  if ((error = dlerror()) != NULL)  {
    fprintf(stderr, "%s\n", error);
    exit(EXIT_FAILURE);
  }

  funptr();
  dlclose(handle);

  return 0;
}

Makefile

CFLAGS = -Wall -Wextra

all: program libplug.so libnorm.so libspec.so

program: main_program.c libspec.so
	$(CC) -o $@ $< -L. -ldl -lspec

libplug.so: plugin.c libnorm.so
	$(CC) -o $@ $< -L. -shared -fPIC -lnorm

libnorm.so: normal_shared_library.c
	$(CC) -o $@ $< -shared -fPIC

libspec.so: special_shared_library.c
	$(CC) -o $@ $< -shared -fPIC


.PHONY: clean run

run: all
	LD_LIBRARY_PATH=$$PWD ./program

clean:
	$(RM) program *.so

normal_shared_library.c

#include <stdio.h>
void shared_lib_operation() {
  printf("Normal Shared Library\n");
}

plugin.c

#include <stdio.h>
void execute_plugin() {
  printf("Plugin executing shared library operation.\n");
  shared_lib_operation();
}

special_shared_library.c

#include <stdio.h>
void shared_lib_operation() {
  printf("Special Shared Library\n");
}