maptest.c

#include <assert.h>
#include <stdio.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <fcntl.h>

int main() {
    int fd = open("doesnotexist", O_CREAT);
    assert(fd > 0);
    void* map = mmap(NULL, 65536, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
    assert((long long)map != -1);
    ((char*)map)[4095] = 1;
}