#include <stdio.h>
#include <sys/mman.h>
#include <unistd.h>

int main ()
{
    char *p;
    int sz = 0x2000;
    int keep = 0x1000;
    int offset;
    int magic = 0x33;
    int pid;
    int rv;

    p = (char *) mmap (0, sz, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
    printf ("mmap() = %p\n", p);

#define KEEPLO
#ifdef KEEPLO
    /* keep lower chunk -> ok */
    rv = munmap (p+keep, sz-keep);
    offset = 0x42;
#else
    /* keep upper chunk -> segv */
    rv = munmap (p, keep);
    offset = keep + 0x42;
#endif

    printf ("munmap() = %d\n",rv);

    p[offset] = magic;

    pid = fork ();

    switch (pid)
    {
    case (-1):
        printf ("fork() failed\n");
        break;
    case (0):
        printf ("child touching %p\n", &(p[offset]));
        printf ("child M[%p] = 0x%x\n", &(p[offset]), p[offset]);
        break;
    default:
        printf ("parent touching %p\n", &(p[offset]));
        printf ("parent M[%p] = 0x%x\n", &(p[offset]), p[offset]);
        break;
    }

    return 0;
}