For you

What is the output of this program and why?

#include <stdio.h>

void f(void) {
  printf("hax my anus\n");
  fflush(stdout);
  f();
}

int main(void) {
  f();
  return 0;
}

I think this would be undefined behavior because you're flushing stdout twice. There could be crash because you're attempting to free() more memory that what you allocate.