/*      $OpenBSD: dtors.c,v 1.5 2003/09/02 23:52:16 david Exp $ */
/*
 *      Written by Artur Grabowski <art@openbsd.org>, 2002 Public Domain.
 */
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/wait.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <err.h>
#include <unistd.h>

void zap(void) __attribute__((destructor));

void *destarea;

#define MAGIC "destructed"

void
zap(void)
{
        memcpy(destarea, MAGIC, sizeof(MAGIC));
}

/*
 * XXX - horrible abuse of exit(3), minherit(2) and fork(2).
 */
int
main(int argc, char **argv)
{
        int status, ch;
        int fallthru = 0;

        while ((ch = getopt(argc, argv, "f")) != -1) {
                switch(ch) {
                case 'f':
                        fallthru = 1;
                        break;
                default:
                        fprintf(stderr, "Usage: dtors [-f]\n");
                        exit(1);
                }
        }

        destarea = mmap(NULL, getpagesize(), PROT_READ|PROT_WRITE, MAP_ANON,
            -1, 0);
        if (destarea == MAP_FAILED)
                err(1, "mmap");

        if (minherit(destarea, getpagesize(), MAP_INHERIT_SHARE) != 0)
                err(1, "minherit");

        memset(destarea, 0, sizeof(MAGIC));

        switch(fork()) {
        case -1:
                err(1, "fork");
        case 0:
                /*
                 * Yes, it's exit(), not _exit(). We _want_ to run the
                 * destructors in the child.
                 */
                if (fallthru)
                        return (0);
                else
                        exit(0);
        }

        if (wait(&status) < 0)
                err(1, "wait");         /* XXX uses exit() */

        if (!WIFEXITED(status) || WEXITSTATUS(status) != 0)
                err(1, "child error");  /* XXX uses exit() */

        _exit(memcmp(destarea, MAGIC, sizeof(MAGIC)) != 0);
}