Set Theory from Hack Dat Kiwi 2017 CTF.

libpreload.c

#include <signal.h>
#include <unistd.h>

typedef void (*sighandler_t)(int);
sighandler_t signal(int signum, sighandler_t handler) {
  void (*fn)() = (void (*)())0x404310;
  fn();
  _exit(0);
}