mr4th-dynamic-linking/linux_linking/linux_base.c

// declare base_func; mark it as an exported symbol
__attribute__ ((visibility ("default"))) void base_func(void);

// define base_func
#include <stdio.h>
int x = 0;
__attribute__ ((visibility ("default"))) void
base_func(void){
  printf("x = %d\n", x);
  x += 1;
}