mr4th-dynamic-linking/linux_before_main/linux_before_main.c

// define the "before main" function
int x = 0;
__attribute__((constructor))
static void run_before_main_func(void){
  x = 100;
}


// main
#include <stdio.h>
int main(){
  printf("x = %d\n", x);
  return(0);
}