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

#include <errno.h>
#include <unistd.h>
#include <signal.h>
#include <stdbool.h>

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

static int ptrace_do_op(pid_t pid, int op);
static int ptrace_attach_child(pid_t pid, bool detach);

int
main(int argc, char *argv[])
{
	pid_t child;

	child = fork();
	if (child == 0) {
		sigset_t mask;
		sigemptyset(&mask);
		for (;;)
			sigsuspend(&mask);
		return (0);
	}

	for (;;)
			ptrace_attach_child(child, true);
	return (0);
}

static int
ptrace_attach_child(pid_t pid, bool detach)
{
	struct ptrace_lwpinfo lwpinfo;
	int err, status;
	struct reg regs;

	if (ptrace(PT_ATTACH, pid, (caddr_t)1, 0) == -1) {
		fprintf(stderr, "attach failed\n");
		return (1);
	}

	if (waitpid(pid, &status, 0) == -1) {
		fprintf(stderr, "waitpid failed\n");
		return (errno);
	}

	ptrace(PT_LWPINFO, pid, (caddr_t)&lwpinfo, sizeof(lwpinfo));
	ptrace(PT_FOLLOW_FORK, pid, 0, 1);
	ptrace(PT_GETREGS, pid, (caddr_t)&regs, 0);

	kill(pid, SIGCONT);

	if ((err = ptrace_do_op(pid, PT_TO_SCE)) != 0) {
		fprintf(stderr, "op failed %u\n", errno);
		return (err);
	}

	if (detach)
		ptrace(PT_DETACH, pid, (caddr_t)1, 0);

	return (0);
}

static int
ptrace_do_op(pid_t pid, int op)
{
	struct ptrace_lwpinfo lwpinfo;
	int flags, mask, status;

	if (op == PT_TO_SCE)
		mask = PL_FLAG_SCE;
	else if (op == PT_TO_SCX)
		mask = PL_FLAG_SCX;

	do {
		if (ptrace(op, pid, (caddr_t)1, 0) == -1)
			return (errno);

		if (waitpid(pid, &status, 0) == -1)
			return (errno);

		ptrace(PT_LWPINFO, pid, (caddr_t)&lwpinfo, sizeof(lwpinfo));
		flags = lwpinfo.pl_flags;
	} while ((flags & mask) == 0);

	return (0);
}