#define _GNU_SOURCE
#include <err.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/prctl.h>
#include <sys/wait.h>
#include <sys/mman.h>

#define SYSCHK(x) ({          \
  typeof(x) __res = (x);      \
  if (__res == (typeof(x))-1) \
    err(1, "SYSCHK(" #x ")"); \
  __res;                      \
})

int main(void) {
  int fd = SYSCHK(memfd_create("foo", 0));
  SYSCHK(ftruncate(fd, 0x2000));
  char *map1 = SYSCHK(mmap((void*)(0x40000000-0x1000), 0x2000, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_FIXED_NOREPLACE, fd, 0));
  ((volatile char *)map1)[0] = 'A';
  ((volatile char *)map1)[0x1000] = 'B';

  char *map2 = map1 + 0x1000;
  SYSCHK(mmap(map2, 0x1000, PROT_READ, MAP_SHARED|MAP_FIXED, fd, 0));
  ((volatile char *)map2)[0];
  //SYSCHK(mprotect(map2, 0x1000, PROT_READ));

  /*
  int pipefds[2];
  SYSCHK(pipe(pipefds));
  */

  if (SYSCHK(fork()) == 0) {
    SYSCHK(munmap(map1, 0x2000));
    sleep(1);
    SYSCHK(prctl(PR_SET_NAME, "SLOWME2"));
    SYSCHK(ftruncate(fd, 0x1000)); // rmap walk
    SYSCHK(prctl(PR_SET_NAME, "task2"));
    exit(0);
  }

  //system("cat /proc/$PPID/maps");
  SYSCHK(prctl(PR_SET_NAME, "SLOWME1"));
  SYSCHK(mmap(map2, 0x1000, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_FIXED, fd, 0x1000));
  SYSCHK(prctl(PR_SET_NAME, "task1"));
  //system("cat /proc/$PPID/maps");

  /*
  for (int i=0; i<8; i++) {
    char buf[0x1000];
    memset(buf, 'A', 0x1000);
    SYSCHK(write(pipefds[1], buf, 0x1000));
  }
  */

  int wstatus;
  SYSCHK(wait(&wstatus));
  return 0;
}