#include <stdio.h>

void f() { printf("hello, world\n"); }

char prog[6];
typedef void (*callable)();

int main() {
        prog[0] = 0xe8;
        *(int *)(prog+1) = ((char *)f)-((char *)(prog+5));
        printf("%d\n", *(prog+1));
        prog[5] = 0xc3;
        ((callable)prog)();
}