vsyscall

gistfile1.c

#include <stdio.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int (*gettod)(int *) = (void *)0xffffffffff600000;

static void
vsyscall()
{
        char buf[256];
        int now, rval;

        rval = gettod(&now);
        snprintf(buf, sizeof (buf), "result of gettod is %d\n", now);
        write(1, buf, strlen(buf) + 1);
}

int
main(int argc, char **argv)
{
        struct sigaction act;

        (void) sigemptyset(&act.sa_mask);

        act.sa_flags = SA_SIGINFO;
        act.sa_handler = NULL;

        if (sigaction(SIGSEGV, &act, NULL) != 0) {
                perror("sigaction");
                exit(EXIT_FAILURE);
        }

        vsyscall();
}