xref: /src/sys/kern/sys_sig.c

/*	$NetBSD: sys_sig.c,v 1.1.2.4 2006/11/18 21:39:23 ad Exp $	*/

/*-
 * Copyright (c) 2006 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Andrew Doran.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the NetBSD
 *	Foundation, Inc. and its contributors.
 * 4. Neither the name of The NetBSD Foundation nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * Copyright (c) 1982, 1986, 1989, 1991, 1993
 *	The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)kern_sig.c	8.14 (Berkeley) 5/14/95
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: sys_sig.c,v 1.1.2.4 2006/11/18 21:39:23 ad Exp $");

#include "opt_ptrace.h"
#include "opt_compat_netbsd.h"
#include "opt_compat_netbsd32.h"

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/signalvar.h>
#include <sys/proc.h>
#include <sys/pool.h>
#include <sys/sa.h>
#include <sys/savar.h>
#include <sys/syscallargs.h>
#include <sys/kauth.h>
#include <sys/wait.h>

#ifdef COMPAT_16
/* ARGSUSED */
int
compat_16_sys___sigaction14(struct lwp *l, void *v, register_t *retval)
{
	struct compat_16_sys___sigaction14_args /* {
		syscallarg(int)				signum;
		syscallarg(const struct sigaction *)	nsa;
		syscallarg(struct sigaction *)		osa;
	} */ *uap = v;
	struct sigaction	nsa, osa;
	int			error;

	if (SCARG(uap, nsa)) {
		error = copyin(SCARG(uap, nsa), &nsa, sizeof(nsa));
		if (error)
			return (error);
	}
	error = sigaction1(l, SCARG(uap, signum),
	    SCARG(uap, nsa) ? &nsa : 0, SCARG(uap, osa) ? &osa : 0,
	    NULL, 0);
	if (error)
		return (error);
	if (SCARG(uap, osa)) {
		error = copyout(&osa, SCARG(uap, osa), sizeof(osa));
		if (error)
			return (error);
	}
	return (0);
}
#endif

/* ARGSUSED */
int
sys___sigaction_sigtramp(struct lwp *l, void *v, register_t *retval)
{
	struct sys___sigaction_sigtramp_args /* {
		syscallarg(int)				signum;
		syscallarg(const struct sigaction *)	nsa;
		syscallarg(struct sigaction *)		osa;
		syscallarg(void *)			tramp;
		syscallarg(int)				vers;
	} */ *uap = v;
	struct sigaction nsa, osa;
	int error;

	if (SCARG(uap, nsa)) {
		error = copyin(SCARG(uap, nsa), &nsa, sizeof(nsa));
		if (error)
			return (error);
	}
	error = sigaction1(l, SCARG(uap, signum),
	    SCARG(uap, nsa) ? &nsa : 0, SCARG(uap, osa) ? &osa : 0,
	    SCARG(uap, tramp), SCARG(uap, vers));
	if (error)
		return (error);
	if (SCARG(uap, osa)) {
		error = copyout(&osa, SCARG(uap, osa), sizeof(osa));
		if (error)
			return (error);
	}
	return (0);
}

/*
 * Manipulate signal mask.  Note that we receive new mask, not pointer, and
 * return old mask as return value; the library stub does the rest.
 */
int
sys___sigprocmask14(struct lwp *l, void *v, register_t *retval)
{
	struct sys___sigprocmask14_args /* {
		syscallarg(int)			how;
		syscallarg(const sigset_t *)	set;
		syscallarg(sigset_t *)		oset;
	} */ *uap = v;
	sigset_t	nss, oss;
	int		error;

	if (SCARG(uap, set)) {
		error = copyin(SCARG(uap, set), &nss, sizeof(nss));
		if (error)
			return (error);
	}
	error = sigprocmask1(l, SCARG(uap, how),
	    SCARG(uap, set) ? &nss : 0, SCARG(uap, oset) ? &oss : 0);
	if (error)
		return (error);
	if (SCARG(uap, oset)) {
		error = copyout(&oss, SCARG(uap, oset), sizeof(oss));
		if (error)
			return (error);
	}
	return (0);
}

/* ARGSUSED */
int
sys___sigpending14(struct lwp *l, void *v, register_t *retval)
{
	struct sys___sigpending14_args /* {
		syscallarg(sigset_t *)	set;
	} */ *uap = v;
	sigset_t ss;

	sigpending1(l, &ss);
	return (copyout(&ss, SCARG(uap, set), sizeof(ss)));
}

/*
 * Suspend process until signal, providing mask to be set in the meantime.
 * Note nonstandard calling convention: libc stub passes mask, not pointer,
 * to save a copyin.
 */
/* ARGSUSED */
int
sys___sigsuspend14(struct lwp *l, void *v, register_t *retval)
{
	struct sys___sigsuspend14_args /* {
		syscallarg(const sigset_t *)	set;
	} */ *uap = v;
	sigset_t	ss;
	int		error;

	if (SCARG(uap, set)) {
		error = copyin(SCARG(uap, set), &ss, sizeof(ss));
		if (error)
			return (error);
	}

	return (sigsuspend1(l, SCARG(uap, set) ? &ss : 0));
}

/* ARGSUSED */
int
sys___sigaltstack14(struct lwp *l, void *v, register_t *retval)
{
	struct sys___sigaltstack14_args /* {
		syscallarg(const struct sigaltstack *)	nss;
		syscallarg(struct sigaltstack *)	oss;
	} */ *uap = v;
	struct sigaltstack	nss, oss;
	int			error;

	if (SCARG(uap, nss)) {
		error = copyin(SCARG(uap, nss), &nss, sizeof(nss));
		if (error)
			return (error);
	}
	error = sigaltstack1(l,
	    SCARG(uap, nss) ? &nss : 0, SCARG(uap, oss) ? &oss : 0);
	if (error)
		return (error);
	if (SCARG(uap, oss)) {
		error = copyout(&oss, SCARG(uap, oss), sizeof(oss));
		if (error)
			return (error);
	}
	return (0);
}

/* ARGSUSED */
int
sys_kill(struct lwp *l, void *v, register_t *retval)
{
	struct sys_kill_args /* {
		syscallarg(int)	pid;
		syscallarg(int)	signum;
	} */ *uap = v;
	struct proc	*p;
	ksiginfo_t	ksi;
	int signum = SCARG(uap, signum);
	int error;

	if ((u_int)signum >= NSIG)
		return (EINVAL);
	KSI_INIT(&ksi);
	ksi.ksi_signo = signum;
	ksi.ksi_code = SI_USER;
	ksi.ksi_pid = l->l_proc->p_pid;
	ksi.ksi_uid = kauth_cred_geteuid(l->l_cred);
	if (SCARG(uap, pid) > 0) {
		/* kill single process */
		if ((p = p_find(SCARG(uap, pid), PFIND_UNLOCK_FAIL)) == NULL)
			return (ESRCH);
		mutex_enter(&p->p_mutex);
		error = kauth_authorize_process(l->l_cred,
		    KAUTH_PROCESS_CANSIGNAL, p, (void *)(uintptr_t)signum,
		    NULL, NULL);
		if (!error && signum) {
			mutex_enter(&p->p_smutex);
			kpsignal2(p, &ksi);
			mutex_exit(&p->p_smutex);
		}
		mutex_exit(&p->p_mutex);
		rw_exit(&proclist_lock);
		return (0);
	}
	switch (SCARG(uap, pid)) {
	case -1:		/* broadcast signal */
		return (killpg1(l, &ksi, 0, 1));
	case 0:			/* signal own process group */
		return (killpg1(l, &ksi, 0, 0));
	default:		/* negative explicit process group */
		return (killpg1(l, &ksi, -SCARG(uap, pid), 0));
	}
	/* NOTREACHED */
}

/*
 * Nonexistent system call-- signal process (may want to handle it).  Flag
 * error in case process won't see signal immediately (blocked or ignored).
 *
 * XXX This should not be here.
 */
#ifndef PTRACE
__weak_alias(sys_ptrace, sys_nosys);
#endif

/* ARGSUSED */
int
sys_nosys(struct lwp *l, void *v, register_t *retval)
{

	psignal(l->l_proc, SIGSYS);
	return (ENOSYS);
}

/* ARGSUSED */
int
sys_getcontext(struct lwp *l, void *v, register_t *retval)
{
	struct sys_getcontext_args /* {
		syscallarg(struct __ucontext *) ucp;
	} */ *uap = v;
	ucontext_t uc;

	getucontext(l, &uc);

	return (copyout(&uc, SCARG(uap, ucp), sizeof (*SCARG(uap, ucp))));
}

/* ARGSUSED */
int
sys_setcontext(struct lwp *l, void *v, register_t *retval)
{
	struct sys_setcontext_args /* {
		syscallarg(const ucontext_t *) ucp;
	} */ *uap = v;
	ucontext_t uc;
	int error;

	error = copyin(SCARG(uap, ucp), &uc, sizeof (uc));
	if (error)
		return (error);
	if (!(uc.uc_flags & _UC_CPU))
		return (EINVAL);
	error = setucontext(l, &uc);
	if (error)
 		return (error);

	return (EJUSTRETURN);
}

/*
 * sigtimedwait(2) system call, used also for implementation
 * of sigwaitinfo() and sigwait().
 *
 * This only handles single LWP in signal wait. libpthread provides
 * it's own sigtimedwait() wrapper to DTRT WRT individual threads.
 */
int
sys___sigtimedwait(struct lwp *l, void *v, register_t *retval)
{

	return __sigtimedwait1(l, v, retval, copyout, copyin, copyout);
}

int
sigaction1(struct lwp *l, int signum, const struct sigaction *nsa,
	struct sigaction *osa, const void *tramp, int vers)
{
	struct proc *p;
	struct sigacts *ps;
	sigset_t tset;
	int prop, error;

	if (signum <= 0 || signum >= NSIG)
		return (EINVAL);

	p = l->l_proc;
	error = 0;

	/*
	 * Trampoline ABI version 0 is reserved for the legacy kernel
	 * provided on-stack trampoline.  Conversely, if we are using a
	 * non-0 ABI version, we must have a trampoline.  Only validate the
	 * vers if a new sigaction was supplied. Emulations use legacy
	 * kernel trampolines with version 0, alternatively check for that
	 * too.
	 */
	if ((vers != 0 && tramp == NULL) ||
#ifdef SIGTRAMP_VALID
	    (nsa != NULL &&
	    ((vers == 0) ?
		(p->p_emul->e_sigcode == NULL) :
		!SIGTRAMP_VALID(vers))) ||
#endif
	    (vers == 0 && tramp != NULL)) {
		return (EINVAL);
	}

	mutex_enter(&p->p_mutex);	/* p_flag */
	mutex_enter(&p->p_smutex);

	ps = p->p_sigacts;
	if (osa)
		*osa = SIGACTION_PS(ps, signum);
	if (!nsa)
		goto out;

	prop = sigprop[signum];
	if ((nsa->sa_flags & ~SA_ALLBITS) || (prop & SA_CANTMASK)) {
		error = EINVAL;
		goto out;
	}

	SIGACTION_PS(ps, signum) = *nsa;
	ps->sa_sigdesc[signum].sd_tramp = tramp;
	ps->sa_sigdesc[signum].sd_vers = vers;
	sigminusset(&sigcantmask, &SIGACTION_PS(ps, signum).sa_mask);

	if ((prop & SA_NORESET) != 0)
		SIGACTION_PS(ps, signum).sa_flags &= ~SA_RESETHAND;

	if (signum == SIGCHLD) {
		if (nsa->sa_flags & SA_NOCLDSTOP)
			p->p_sflag |= PS_NOCLDSTOP;
		else
			p->p_sflag &= ~PS_NOCLDSTOP;
		if (nsa->sa_flags & SA_NOCLDWAIT) {
			/*
			 * Paranoia: since SA_NOCLDWAIT is implemented by
			 * reparenting the dying child to PID 1 (and trust
			 * it to reap the zombie), PID 1 itself is forbidden
			 * to set SA_NOCLDWAIT.
			 */
			if (p->p_pid == 1)
				p->p_flag &= ~P_NOCLDWAIT;
			else
				p->p_flag |= P_NOCLDWAIT;
		} else
			p->p_flag &= ~P_NOCLDWAIT;

		if (nsa->sa_handler == SIG_IGN) {
			/*
			 * Paranoia: same as above.
			 */
			if (p->p_pid == 1)
				p->p_flag &= ~P_CLDSIGIGN;
			else
				p->p_flag |= P_CLDSIGIGN;
		} else
			p->p_flag &= ~P_CLDSIGIGN;
	}

	if ((nsa->sa_flags & SA_NODEFER) == 0)
		sigaddset(&SIGACTION_PS(ps, signum).sa_mask, signum);
	else
		sigdelset(&SIGACTION_PS(ps, signum).sa_mask, signum);

	/*
	 * Set bit in p_sigctx.ps_sigignore for signals that are set to
	 * SIG_IGN, and for signals set to SIG_DFL where the default is to
	 * ignore. However, don't put SIGCONT in p_sigctx.ps_sigignore, as
	 * we have to restart the process.
	 */
	if (nsa->sa_handler == SIG_IGN ||
	    (nsa->sa_handler == SIG_DFL && (prop & SA_IGNORE) != 0)) {
		/* Never to be seen again. */
		sigemptyset(&tset);
		sigaddset(&tset, signum);
		sigclearall(p, &tset);
		if (signum != SIGCONT) {
			/* Easier in psignal */
			sigaddset(&p->p_sigctx.ps_sigignore, signum);
		}
		sigdelset(&p->p_sigctx.ps_sigcatch, signum);
	} else {
		sigdelset(&p->p_sigctx.ps_sigignore, signum);
		if (nsa->sa_handler == SIG_DFL)
			sigdelset(&p->p_sigctx.ps_sigcatch, signum);
		else
			sigaddset(&p->p_sigctx.ps_sigcatch, signum);
	}

	/*
	 * Previously held signals may now have become visible.  Ensure that
	 * we check for them before returning to userspace.
	 */
	lwp_lock(l);
	signotify(l);
	lwp_unlock(l);
 out:
	mutex_exit(&p->p_smutex);
	mutex_exit(&p->p_mutex);

	return (error);
}

int
sigprocmask1(struct lwp *l, int how, const sigset_t *nss, sigset_t *oss)
{
	struct proc *p = l->l_proc;
	int more;

	mutex_enter(&p->p_smutex);

	/*
	 * If we've got pending signals that we haven't processed yet,
	 * make sure that we take them before changing the mask.
	 */
	if (sigispending(l)) {
		mutex_exit(&p->p_smutex);
		return ERESTART;
	}

	if (oss)
		*oss = *l->l_sigmask;
	if (nss) {
		switch (how) {
		case SIG_BLOCK:
			sigplusset(nss, l->l_sigmask);
			more = 0;
			break;
		case SIG_UNBLOCK:
			sigminusset(nss, l->l_sigmask);
			more = 1;
			break;
		case SIG_SETMASK:
			*l->l_sigmask = *nss;
			more = 1;
			break;
		default:
			mutex_exit(&p->p_smutex);
			return (EINVAL);
		}
		sigminusset(&sigcantmask, l->l_sigmask);
		if (more) {
			/*
			 * Grab signals from the per-process pending
			 * list that are now of interest to us.
			 */
			if ((p->p_flag & P_SA) == 0)
				sigpinch(&p->p_sigpend, l->l_sigpend,
				    l->l_sigmask);

			/*
			 * Check for pending signals on return to user.
			 */
			lwp_lock(l);
			signotify(l);
			lwp_unlock(l);
		}
	}

	mutex_exit(&p->p_smutex);

	return (0);
}

void
sigpending1(struct lwp *l, sigset_t *ss)
{
	struct proc *p = l->l_proc;

	mutex_enter(&p->p_smutex);
	*ss = l->l_sigpend->sp_set;
	sigminusset(l->l_sigmask, ss);
	mutex_exit(&p->p_smutex);
}

int
sigsuspend1(struct lwp *l, const sigset_t *ss)
{
	struct proc *p;
	struct sigacts *ps;

	p = l->l_proc;
	ps = p->p_sigacts;

	mutex_enter(&p->p_smutex);

	/*
	 * If we've got pending signals that we haven't processed yet,
	 * make sure that we take them before changing the mask.
	 */
	if (sigispending(l)) {
		mutex_exit(&p->p_smutex);
		return ERESTART;
	}

	if (ss) {
		/*
		 * When returning from sigpause, we want
		 * the old mask to be restored after the
		 * signal handler has finished.  Thus, we
		 * save it here and mark the sigctx structure
		 * to indicate this.
		 */
		l->l_sigoldmask = *l->l_sigmask;
		l->l_sigrestore = 1;
		*l->l_sigmask = *ss;
		sigminusset(&sigcantmask, l->l_sigmask);

		/*
		 * Pinch any signals from the per-process pending
		 * list that are now of interest to us.
		 */
		if ((p->p_flag & P_SA) == 0)
			sigpinch(&p->p_sigpend, l->l_sigpend, l->l_sigmask);

		lwp_lock(l);
		signotify(l);
		lwp_unlock(l);
	}

	while (mtsleep((caddr_t) ps, PPAUSE|PCATCH, "pause", 0,
	    &p->p_smutex) == 0)
		/* void */;

	mutex_exit(&p->p_smutex);

	/* always return EINTR rather than ERESTART... */
	return (EINTR);
}

int
sigaltstack1(struct lwp *l, const struct sigaltstack *nss,
	     struct sigaltstack *oss)
{
	struct proc *p = l->l_proc;
	int error = 0;

	mutex_enter(&p->p_smutex);

	if (oss)
		*oss = *l->l_sigstk;

	if (nss) {
		if (nss->ss_flags & ~SS_ALLBITS)
			error = EINVAL;
		else if (nss->ss_flags & SS_DISABLE) {
			if (l->l_sigstk->ss_flags & SS_ONSTACK)
				error = EINVAL;
		} else if (nss->ss_size < MINSIGSTKSZ)
			error = ENOMEM;

		if (!error)
			*l->l_sigstk = *nss;
	}

	mutex_exit(&p->p_smutex);

	return (error);
}

int
__sigtimedwait1(struct lwp *l, void *v, register_t *retval,
    copyout_t put_info, copyin_t fetch_timeout, copyout_t put_timeout)
{
	struct sys___sigtimedwait_args /* {
		syscallarg(const sigset_t *) set;
		syscallarg(siginfo_t *) info;
		syscallarg(struct timespec *) timeout;
	} */ *uap = v;
	sigset_t *waitset;
	struct proc *p = l->l_proc;
	int error, signum;
	int timo = 0;
	struct timespec ts, tsstart, tsnow;
	ksiginfo_t *ksi;

	memset(&tsstart, 0, sizeof tsstart);	 /* XXX gcc */

	/*
	 * Calculate timeout, if it was specified.
	 */
	if (SCARG(uap, timeout)) {
		uint64_t ms;

		if ((error = (*fetch_timeout)(SCARG(uap, timeout), &ts, sizeof(ts))))
			return (error);

		ms = (ts.tv_sec * 1000) + (ts.tv_nsec / 1000000);
		timo = mstohz(ms);
		if (timo == 0 && ts.tv_sec == 0 && ts.tv_nsec > 0)
			timo = 1;
		if (timo <= 0)
			return (EAGAIN);

		/*
		 * Remember current uptime, it would be used in
		 * ECANCELED/ERESTART case.
		 */
		getnanouptime(&tsstart);
	}

	MALLOC(waitset, sigset_t *, sizeof(sigset_t), M_TEMP, M_WAITOK);
	if ((error = copyin(SCARG(uap, set), waitset, sizeof(sigset_t)))) {
		FREE(waitset, M_TEMP);
		return (error);
	}

	/*
	 * Silently ignore SA_CANTMASK signals. psignal1() would ignore
	 * SA_CANTMASK signals in waitset, we do this only for the below
	 * siglist check.
	 */
	sigminusset(&sigcantmask, waitset);

	/*
	 * Allocate a ksi up front.  We can't sleep with the mutex held.
	 */
	if ((ksi = ksiginfo_alloc(p, NULL, PR_WAITOK)) == NULL) {
		FREE(waitset, M_TEMP);
		return (ENOMEM);
	}

	mutex_enter(&p->p_smutex);

	/*
	 * If we've got pending signals that we haven't processed yet,
	 * make sure that we take them before changing the mask.
	 */
	if ((error = sigispending(l)) != 0) {
		mutex_exit(&p->p_smutex);
		goto out;
	}

	/*
	 * SA processes can have no more than 1 sigwaiter.
	 */
	if ((p->p_flag & P_SA) != 0 && !LIST_EMPTY(&p->p_sigwaiters)) {
		mutex_exit(&p->p_smutex);
		error = EINVAL;
		goto out;
	}

	if ((signum = sigget(&p->p_sigpend, ksi, 0, waitset)) == 0)
		if ((p->p_flag & P_SA) == 0)
			signum = sigget(l->l_sigpend, ksi, 0, waitset);

	if (signum != 0) {
		/*
		 * We found a pending signal - copy it out to the user.
		 */
		mutex_exit(&p->p_smutex);
		goto out;
	}

	/*
	 * Set up the sigwait list. Pass pointer to malloced memory here;
	 * it's not possible to pass pointer to a structure on current
	 * process's stack, the current LWP might be swapped out when the
	 * when the signal is delivered.
	 */
	l->l_sigwaited = ksi;
	l->l_sigwait = waitset;
	LIST_INSERT_HEAD(&p->p_sigwaiters, l, l_sigwaiter);

	/*
	 * Wait for signal to arrive. We can either be woken up or time out.
	 */
	error = mtsleep(&l->l_sigwait, PPAUSE|PCATCH, "sigwait", timo,
	    &p->p_smutex);

	/*
	 * Need to find out if we woke as a result of lwp_wakeup() or a
	 * signal outside our wait set.
	 */
	if (l->l_sigwaited != NULL) {
		if (error == EINTR) {
			/* wakeup via _lwp_wakeup() */
			error = ECANCELED;
		} else if (!error) {
			/* spurious wakeup - arrange for syscall restart */
			error = ERESTART;
		}
	}

	/*
	 * Clear the sigwait indication and unlock.
	 */
	l->l_sigwait = NULL;
	l->l_sigwaited = NULL;
	LIST_REMOVE(l, l_sigwaiter);
	mutex_exit(&p->p_smutex);

	/*
	 * If the sleep was interrupted (either by signal or wakeup), update
	 * the timeout and copyout new value back.  It would be used when
	 * the syscall would be restarted or called again.
	 */
	if (timo && (error == ERESTART || error == ECANCELED)) {
		getnanouptime(&tsnow);

		/* compute how much time has passed since start */
		timespecsub(&tsnow, &tsstart, &tsnow);
		/* substract passed time from timeout */
		timespecsub(&ts, &tsnow, &ts);

		if (ts.tv_sec < 0)
			error = EAGAIN;
		else {
			/* copy updated timeout to userland */
			error = (*put_timeout)(&ts, SCARG(uap, timeout),
			    sizeof(ts));
		}
	}

	/*
	 * If a signal from the wait set arrived, copy it to userland.
	 * Copy only the used part of siginfo, the padding part is
	 * left unchanged (userland is not supposed to touch it anyway).
	 */
 out:
	FREE(waitset, M_TEMP);
	ksiginfo_free(ksi);

	if (error == 0)
		error = (*put_info)(&ksi->ksi_info, SCARG(uap, info),
		    sizeof(ksi->ksi_info));

	return error;
}