#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>

void die(const char *what)
{
	perror(what);
	exit(1);
}

int main(int arg, char **argv)
{
	void *p =
	    mmap(NULL, 4096, PROT_READ | PROT_WRITE,
		 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);

	if (p == MAP_FAILED)
		die("mmap");

	/* Tickle the page. */
	((char *) p)[0] = 0;

	if (mprotect(p, 4096, PROT_NONE) != 0)
		die("mprotect");

	if (mprotect(p, 4096, PROT_READ) != 0)
		die("mprotect");

	if (munmap(p, 4096) != 0)
		die("munmap");

	return 0;
}