/*      $OpenBSD: stackjmp.c,v 1.3 2013/12/21 05:45:04 guenther Exp $   */
/*
 * Written by Matthew Dempsky, 2012.
 * Public domain.
 */

#include <assert.h>
#include <setjmp.h>
#include <signal.h>
#include <string.h>
#include <unistd.h>

static sigjmp_buf jb;
static char buf[SIGSTKSZ];
static volatile int handled;

static int
isaltstack()
{
        stack_t os;
        assert(sigaltstack(NULL, &os) == 0);
        return (os.ss_flags & SS_ONSTACK) != 0;
}

static void
inthandler(int signo)
{
        assert(isaltstack());
        handled = 1;
        siglongjmp(jb, 1);
}

int
main()
{
        struct sigaction sa;
        stack_t stack;

        memset(&sa, 0, sizeof(sa));
        sa.sa_handler = inthandler;
        sa.sa_flags = SA_ONSTACK;
        assert(sigaction(SIGINT, &sa, NULL) == 0);

        memset(&stack, 0, sizeof(stack));
        stack.ss_sp = buf;
        stack.ss_size = sizeof(buf);
        stack.ss_flags = 0;
        assert(sigaltstack(&stack, NULL) == 0);

        assert(!isaltstack());
        sigsetjmp(jb, 1);
        assert(!isaltstack());
        if (!handled) {
                kill(getpid(), SIGINT);
                assert(0); /* Shouldn't reach here. */
        }

        return (0);
}