#include <sys/types.h>
#include <sys/ptrace.h>
#include <sys/wait.h>

#include <err.h>
#include <signal.h>
#include <stdio.h>
#include <unistd.h>

static void
sighup(int sig)
{
}

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

	pid = fork();
	if (pid < 0)
		err(1, "fork");
	if (pid == 0) {
		act.sa_handler = sighup;
		act.sa_flags = 0;
		sigemptyset(&act.sa_mask);
		if (sigaction(SIGHUP, &act, NULL) != 0)
			err(1, "sigaction");
		while (1) {
			sleep(1);
		}
	} else {
		sleep(1); /* give the child a chance to call sigaction */

		if (kill(pid, SIGSTOP) != 0)
			err(1, "kill(SIGSTOP)");

		printf("waiting for child to stop...\n");
		if (waitpid(pid, &status, WUNTRACED) != pid)
			err(1, "waitpid");
		if (!WIFSTOPPED(status) || WSTOPSIG(status) != SIGSTOP)
			errx(1, "unexpected status %d after SIGSTOP", status);

		if (kill(pid, SIGHUP) != 0)
			err(1, "kill(SIGHUP)");

		if (ptrace(PT_ATTACH, pid, NULL, 0) != 0)
			err(1, "ptrace(PT_ATTACH)");
		if (waitpid(pid, &status, WUNTRACED) != pid)
			err(1, "waitpid");
		if (!WIFSTOPPED(status))
			errx(1, "unexpected status %d after PT_ATTACH", status);
		printf("stopping signal is %d\n", WSTOPSIG(status));
		if (ptrace(PT_DETACH, pid, NULL, 0) != 0)
			err(1, "ptrace(PT_DETACH)");

		/* if ptrace works as expected, we'll block here */
		printf("waiting on child...\n");
		if (waitpid(pid, &status, WUNTRACED) != pid)
			err(1, "waitpid");
		if (!WIFSTOPPED(status))
			errx(1, "unexpected status %d after PT_DETACH", status);
		printf("child is stopped after detach (sig %d)\n",
		    WSTOPSIG(status));
	}

	return (0);
}