haiku/src/system/kernel/signal.cpp

/*
 * Copyright 2002-2007, Axel Dörfler, axeld@pinc-software.de.
 * Copyright 2002, Angelo Mottola, a.mottola@libero.it.
 *
 * Distributed under the terms of the MIT License.
 */

/* POSIX signals handling routines */

#include <stddef.h>
#include <string.h>

#include <OS.h>
#include <KernelExport.h>

#include <condition_variable.h>
#include <debug.h>
#include <kernel.h>
#include <kscheduler.h>
#include <ksignal.h>
#include <sem.h>
#include <team.h>
#include <thread.h>
#include <user_debugger.h>
#include <util/AutoLock.h>


//#define TRACE_SIGNAL
#ifdef TRACE_SIGNAL
#	define TRACE(x) dprintf x
#else
#	define TRACE(x) ;
#endif


#define BLOCKABLE_SIGNALS		(~(KILL_SIGNALS | SIGNAL_TO_MASK(SIGSTOP)))
#define STOP_SIGNALS \
	(SIGNAL_TO_MASK(SIGSTOP) | SIGNAL_TO_MASK(SIGTSTP) \
	| SIGNAL_TO_MASK(SIGTTIN) | SIGNAL_TO_MASK(SIGTTOU))
#define DEFAULT_IGNORE_SIGNALS \
	(SIGNAL_TO_MASK(SIGCHLD) | SIGNAL_TO_MASK(SIGWINCH) \
	| SIGNAL_TO_MASK(SIGCONT))


const char * const sigstr[NSIG] = {
	"NONE", "HUP", "INT", "QUIT", "ILL", "CHLD", "ABRT", "PIPE",
	"FPE", "KILL", "STOP", "SEGV", "CONT", "TSTP", "ALRM", "TERM",
	"TTIN", "TTOU", "USR1", "USR2", "WINCH", "KILLTHR", "TRAP",
	"POLL", "PROF", "SYS", "URG", "VTALRM", "XCPU", "XFSZ"
};


static status_t deliver_signal(struct thread *thread, uint signal,
	uint32 flags);


/*!	Updates the thread::flags field according to what signals are pending.
	Interrupts must be disabled and the thread lock must be held.
*/
static void
update_thread_signals_flag(struct thread* thread)
{
	if (atomic_get(&thread->sig_pending) & ~atomic_get(&thread->sig_block_mask))
		atomic_or(&thread->flags, THREAD_FLAGS_SIGNALS_PENDING);
	else
		atomic_and(&thread->flags, ~THREAD_FLAGS_SIGNALS_PENDING);
}


static void
update_current_thread_signals_flag()
{
	InterruptsSpinLocker locker(thread_spinlock);

	update_thread_signals_flag(thread_get_current_thread());
}


static bool
notify_debugger(struct thread *thread, int signal, struct sigaction *handler,
	bool deadly)
{
	uint64 signalMask = SIGNAL_TO_MASK(signal);

	// first check the ignore signal masks the debugger specified for the thread

	if (atomic_get(&thread->debug_info.ignore_signals_once) & signalMask) {
		atomic_and(&thread->debug_info.ignore_signals_once, ~signalMask);
		return true;
	}

	if (atomic_get(&thread->debug_info.ignore_signals) & signalMask)
		return true;

	// deliver the event
	return user_debug_handle_signal(signal, handler, deadly);
}


/*! Actually handles the signal - ie. the thread will exit, a custom signal
	handler is prepared, or whatever the signal demands.
*/
bool
handle_signals(struct thread *thread)
{
	uint32 signalMask = atomic_get(&thread->sig_pending)
		& ~atomic_get(&thread->sig_block_mask);
	struct sigaction *handler;
	bool reschedule = false;
	bool restart = false;
	int32 i;

	// If SIGKILL[THR] are pending, we ignore other signals.
	// Otherwise check, if the thread shall stop for debugging.
	if (signalMask & KILL_SIGNALS) {
		signalMask &= KILL_SIGNALS;
	} else if (thread->debug_info.flags & B_THREAD_DEBUG_STOP) {
		user_debug_stop_thread();
	}

	if (signalMask == 0)
		return 0;

	for (i = 0; i < NSIG; i++) {
		bool debugSignal;
		int32 signal = i + 1;

		if ((signalMask & SIGNAL_TO_MASK(signal)) == 0)
			continue;

		// clear the signal that we will handle
		atomic_and(&thread->sig_pending, ~SIGNAL_TO_MASK(signal));

		debugSignal = !(~atomic_get(&thread->team->debug_info.flags)
				& (B_TEAM_DEBUG_SIGNALS | B_TEAM_DEBUG_DEBUGGER_INSTALLED));

		// TODO: since sigaction_etc() could clobber the fields at any time,
		//		we should actually copy the relevant fields atomically before
		//		accessing them (only the debugger is calling sigaction_etc()
		//		right now).
		//		Update: sigaction_etc() is only used by the userland debugger
		//		support. We can just as well restrict getting/setting signal
		//		handlers to work only when the respective thread is stopped.
		//		Then sigaction() could be used instead and we could get rid of
		//		sigaction_etc().
		handler = &thread->sig_action[i];

		TRACE(("Thread 0x%lx received signal %s\n", thread->id, sigstr[signal]));

		if ((handler->sa_flags & SA_RESTART) != 0)
			restart = true;

		if (handler->sa_handler == SIG_IGN) {
			// signal is to be ignored
			// ToDo: apply zombie cleaning on SIGCHLD

			// notify the debugger
			if (debugSignal)
				notify_debugger(thread, signal, handler, false);
			continue;
		}
		if (handler->sa_handler == SIG_DFL) {
			// default signal behaviour
			switch (signal) {
				case SIGCHLD:
				case SIGWINCH:
				case SIGURG:
					// notify the debugger
					if (debugSignal)
						notify_debugger(thread, signal, handler, false);
					continue;

				case SIGCONT:
					// notify the debugger
					if (debugSignal
						&& !notify_debugger(thread, signal, handler, false))
						continue;

					// notify threads waiting for team state changes
					if (thread == thread->team->main_thread) {
						InterruptsSpinLocker locker(team_spinlock);
						team_set_job_control_state(thread->team,
							JOB_CONTROL_STATE_CONTINUED, signal, false);

						// The standard states that the system *may* send a
						// SIGCHLD when a child is continued. I haven't found
						// a good reason why we would want to, though.
					}
					continue;

				case SIGSTOP:
				case SIGTSTP:
				case SIGTTIN:
				case SIGTTOU:
					// notify the debugger
					if (debugSignal
						&& !notify_debugger(thread, signal, handler, false))
						continue;

					thread->next_state = B_THREAD_SUSPENDED;
					reschedule = true;

					// notify threads waiting for team state changes
					if (thread == thread->team->main_thread) {
						InterruptsSpinLocker locker(team_spinlock);
						team_set_job_control_state(thread->team,
							JOB_CONTROL_STATE_STOPPED, signal, false);

						// send a SIGCHLD to the parent (if it does have
						// SA_NOCLDSTOP defined)
						SpinLocker _(thread_spinlock);
						struct thread* parentThread
							= thread->team->parent->main_thread;
						struct sigaction& parentHandler
							= parentThread->sig_action[SIGCHLD - 1];
						if ((parentHandler.sa_flags & SA_NOCLDSTOP) == 0)
							deliver_signal(parentThread, SIGCHLD, 0);
					}
					continue;

				case SIGQUIT:
				case SIGILL:
				case SIGTRAP:
				case SIGABRT:
				case SIGFPE:
				case SIGSEGV:
				case SIGPOLL:
				case SIGPROF:
				case SIGSYS:
				case SIGVTALRM:
				case SIGXCPU:
				case SIGXFSZ:
					TRACE(("Shutting down thread 0x%lx due to signal #%ld\n",
						thread->id, signal));
				case SIGKILL:
				case SIGKILLTHR:
				default:
					// if the thread exited normally, the exit reason is already set
					if (thread->exit.reason != THREAD_RETURN_EXIT) {
						thread->exit.reason = THREAD_RETURN_INTERRUPTED;
						thread->exit.signal = (uint16)signal;
					}

					// notify the debugger
					if (debugSignal && signal != SIGKILL && signal != SIGKILLTHR
						&& !notify_debugger(thread, signal, handler, true))
						continue;

					thread_exit();
						// won't return
			}
		}

		// notify the debugger
		if (debugSignal && !notify_debugger(thread, signal, handler, false))
			continue;

		// User defined signal handler
		TRACE(("### Setting up custom signal handler frame...\n"));
		arch_setup_signal_frame(thread, handler, signal, atomic_get(&thread->sig_block_mask));

		if (handler->sa_flags & SA_ONESHOT)
			handler->sa_handler = SIG_DFL;
		if ((handler->sa_flags & SA_NOMASK) == 0) {
			// Update the block mask while the signal handler is running - it
			// will be automatically restored when the signal frame is left.
			atomic_or(&thread->sig_block_mask,
				(handler->sa_mask | SIGNAL_TO_MASK(signal)) & BLOCKABLE_SIGNALS);
		}

		update_current_thread_signals_flag();

		return reschedule;
	}

	// only restart if SA_RESTART was set on at least one handler
	if (restart)
		arch_check_syscall_restart(thread);

	update_current_thread_signals_flag();

	return reschedule;
}


bool
is_kill_signal_pending(void)
{
	return (atomic_get(&thread_get_current_thread()->sig_pending)
		& KILL_SIGNALS) != 0;
}


bool
is_signal_blocked(int signal)
{
	return (atomic_get(&thread_get_current_thread()->sig_block_mask)
		& SIGNAL_TO_MASK(signal)) != 0;
}


/*!	Tries to interrupt a thread waiting for a semaphore or a condition variable.
	Interrupts must be disabled, the thread lock be held.
*/
static status_t
signal_interrupt_thread(struct thread* thread)
{
	if (thread->sem.blocking >= 0)
		return sem_interrupt_thread(thread);
	else if (thread->condition_variable_entry)
		return condition_variable_interrupt_thread(thread);
	return B_BAD_VALUE;
}


/*!	Delivers the \a signal to the \a thread, but doesn't handle the signal -
	it just makes sure the thread gets the signal, ie. unblocks it if needed.
	This function must be called with interrupts disabled and the
	thread lock held.
*/
static status_t
deliver_signal(struct thread *thread, uint signal, uint32 flags)
{
	if (flags & B_CHECK_PERMISSION) {
		// ToDo: introduce euid & uid fields to the team and check permission
	}
	
	if (signal == 0)
		return B_OK;

	if (thread->team == team_get_kernel_team()) {
		// Signals to kernel threads will only wake them up
		if (thread->state == B_THREAD_SUSPENDED) {
			thread->state = thread->next_state = B_THREAD_READY;
			scheduler_enqueue_in_run_queue(thread);
		}
		return B_OK;
	}

	atomic_or(&thread->sig_pending, SIGNAL_TO_MASK(signal));

	switch (signal) {
		case SIGKILL:
		{
			struct thread *mainThread = thread->team->main_thread;
			// Forward KILLTHR to the main thread of the team

			mainThread->sig_pending |= SIGNAL_TO_MASK(SIGKILLTHR);
			// Wake up main thread
			if (mainThread->state == B_THREAD_SUSPENDED) {
				mainThread->state = mainThread->next_state = B_THREAD_READY;
				scheduler_enqueue_in_run_queue(mainThread);
			} else if (mainThread->state == B_THREAD_WAITING)
				signal_interrupt_thread(mainThread);

			// Supposed to fall through
		}
		case SIGKILLTHR:
			// Wake up suspended threads and interrupt waiting ones
			if (thread->state == B_THREAD_SUSPENDED) {
				thread->state = thread->next_state = B_THREAD_READY;
				scheduler_enqueue_in_run_queue(thread);
			} else if (thread->state == B_THREAD_WAITING)
				signal_interrupt_thread(thread);
			break;

		case SIGCONT:
			// Wake up thread if it was suspended
			if (thread->state == B_THREAD_SUSPENDED) {
				thread->state = thread->next_state = B_THREAD_READY;
				scheduler_enqueue_in_run_queue(thread);
			}

			atomic_and(&thread->sig_pending, ~STOP_SIGNALS);
				// remove any pending stop signals
			break;

		default:
			if (thread->sig_pending
				& (~thread->sig_block_mask | SIGNAL_TO_MASK(SIGCHLD))) {
				// Interrupt thread if it was waiting
				if (thread->state == B_THREAD_WAITING)
					signal_interrupt_thread(thread);
			}
			break;
	}

	update_thread_signals_flag(thread);

	return B_OK;
}


int
send_signal_etc(pid_t id, uint signal, uint32 flags)
{
	status_t status = B_BAD_THREAD_ID;
	struct thread *thread;
	cpu_status state = 0;

	if (signal < 0 || signal > MAX_SIGNO)
		return B_BAD_VALUE;

	if ((flags & SIGNAL_FLAG_TEAMS_LOCKED) == 0)
		state = disable_interrupts();
	
	if (id > 0) {
		// send a signal to the specified thread

		GRAB_THREAD_LOCK();

		thread = thread_get_thread_struct_locked(id);
		if (thread != NULL)
			status = deliver_signal(thread, signal, flags);
	} else {
		// send a signal to the specified process group
		// (the absolute value of the id)

		struct process_group *group;
		
		// TODO: handle -1 correctly
		if (id == 0 || id == -1) {
			// send a signal to the current team
			id = thread_get_current_thread()->team->id;
		} else
			id = -id;

		if ((flags & SIGNAL_FLAG_TEAMS_LOCKED) == 0)
			GRAB_TEAM_LOCK();

		group = team_get_process_group_locked(NULL, id);
		if (group != NULL) {
			struct team *team, *next;

			// Send a signal to all teams in this process group

			for (team = group->teams; team != NULL; team = next) {
				next = team->group_next;
				id = team->id;

				GRAB_THREAD_LOCK();

				thread = thread_get_thread_struct_locked(id);
				if (thread != NULL) {
					// we don't stop because of an error sending the signal; we
					// rather want to send as much signals as possible
					status = deliver_signal(thread, signal, flags);
				}

				RELEASE_THREAD_LOCK();
			}
		}

		if ((flags & SIGNAL_FLAG_TEAMS_LOCKED) == 0)
			RELEASE_TEAM_LOCK();

		GRAB_THREAD_LOCK();
	}		

	// ToDo: maybe the scheduler should only be invoked if there is reason to do it?
	//	(ie. deliver_signal() moved some threads in the running queue?)
	if ((flags & (B_DO_NOT_RESCHEDULE | SIGNAL_FLAG_TEAMS_LOCKED)) == 0)
		scheduler_reschedule();

	RELEASE_THREAD_LOCK();

	if ((flags & SIGNAL_FLAG_TEAMS_LOCKED) == 0)
		restore_interrupts(state);

	return status;
}


int
send_signal(pid_t threadID, uint signal)
{
	// The BeBook states that this function wouldn't be exported
	// for drivers, but, of course, it's wrong.
	return send_signal_etc(threadID, signal, 0);
}


int
has_signals_pending(void *_thread)
{
	struct thread *thread = (struct thread *)_thread;
	if (thread == NULL)
		thread = thread_get_current_thread();

	return atomic_get(&thread->sig_pending) & ~atomic_get(&thread->sig_block_mask);
}


int
sigprocmask(int how, const sigset_t *set, sigset_t *oldSet)
{
	struct thread *thread = thread_get_current_thread();
	sigset_t oldMask = atomic_get(&thread->sig_block_mask);

	if (set != NULL) {
		switch (how) {
			case SIG_BLOCK:
				atomic_or(&thread->sig_block_mask, *set & BLOCKABLE_SIGNALS);
				break;
			case SIG_UNBLOCK:
				atomic_and(&thread->sig_block_mask, ~*set);
				break;
			case SIG_SETMASK:
				atomic_set(&thread->sig_block_mask, *set & BLOCKABLE_SIGNALS);
				break;
			default:
				return B_BAD_VALUE;
		}

		update_current_thread_signals_flag();
	}

	if (oldSet != NULL)
		*oldSet = oldMask;

	return B_OK;
}


/**	\brief sigaction() for the specified thread.
 *
 *	A \a threadID is < 0 specifies the current thread.
 *
 */

int
sigaction_etc(thread_id threadID, int signal, const struct sigaction *act,
	struct sigaction *oldAction)
{
	struct thread *thread;
	cpu_status state;
	status_t error = B_OK;

	if (signal < 1 || signal > MAX_SIGNO
		|| (SIGNAL_TO_MASK(signal) & ~BLOCKABLE_SIGNALS) != 0)
		return B_BAD_VALUE;

	state = disable_interrupts();
	GRAB_THREAD_LOCK();

	thread = (threadID < 0
		? thread_get_current_thread()
		: thread_get_thread_struct_locked(threadID));

	if (thread) {
		if (oldAction) {
			// save previous sigaction structure
			memcpy(oldAction, &thread->sig_action[signal - 1],
				sizeof(struct sigaction));
		}

		if (act) {
			// set new sigaction structure
			memcpy(&thread->sig_action[signal - 1], act,
				sizeof(struct sigaction));
			thread->sig_action[signal - 1].sa_mask &= BLOCKABLE_SIGNALS;
		}

		if (act && act->sa_handler == SIG_IGN) {
			// remove pending signal if it should now be ignored
			atomic_and(&thread->sig_pending, ~SIGNAL_TO_MASK(signal));
		} else if (act && act->sa_handler == SIG_DFL
			&& (SIGNAL_TO_MASK(signal) & DEFAULT_IGNORE_SIGNALS) != NULL) {
			// remove pending signal for those signals whose default
			// action is to ignore them
			atomic_and(&thread->sig_pending, ~SIGNAL_TO_MASK(signal));
		}
	} else
		error = B_BAD_THREAD_ID;

	RELEASE_THREAD_LOCK();
	restore_interrupts(state);

	return error;
}


int
sigaction(int signal, const struct sigaction *act, struct sigaction *oldAction)
{
	return sigaction_etc(-1, signal, act, oldAction);
}


/** Triggers a SIGALRM to the thread that issued the timer and reschedules */

static int32
alarm_event(timer *t)
{
	// The hook can be called from any context, but we have to
	// deliver the signal to the thread that originally called
	// set_alarm().
	// Since thread->alarm is this timer structure, we can just
	// cast it back - ugly but it works for now
	struct thread *thread = (struct thread *)((uint8 *)t - offsetof(struct thread, alarm));
		// ToDo: investigate adding one user parameter to the timer structure to fix this hack

	TRACE(("alarm_event: thread = %p\n", thread));
	send_signal_etc(thread->id, SIGALRM, B_DO_NOT_RESCHEDULE);

	return B_INVOKE_SCHEDULER;
}


/** Sets the alarm timer for the current thread. The timer fires at the
 *	specified time in the future, periodically or just once, as determined
 *	by \a mode.
 *	\return the time left until a previous set alarm would have fired.
 */

bigtime_t
set_alarm(bigtime_t time, uint32 mode)
{
	struct thread *thread = thread_get_current_thread();
	bigtime_t remainingTime = 0;

	ASSERT(B_ONE_SHOT_RELATIVE_ALARM == B_ONE_SHOT_RELATIVE_TIMER);
		// just to be sure no one changes the headers some day

	TRACE(("set_alarm: thread = %p\n", thread));

	if (thread->alarm.period)
		remainingTime = (bigtime_t)thread->alarm.entry.key - system_time();

	cancel_timer(&thread->alarm);

	if (time != B_INFINITE_TIMEOUT)
		add_timer(&thread->alarm, &alarm_event, time, mode);
	else {
		// this marks the alarm as canceled (for returning the remaining time)
		thread->alarm.period = 0;
	}

	return remainingTime;
}


/**	Replace the current signal block mask and wait for any event to happen.
 *	Before returning, the original signal block mask is reinstantiated.
 */

int
sigsuspend(const sigset_t *mask)
{
	struct thread *thread = thread_get_current_thread();
	sigset_t oldMask = atomic_get(&thread->sig_block_mask);
	cpu_status state;

	// set the new block mask and suspend ourselves - we cannot use
	// SIGSTOP for this, as signals are only handled upon kernel exit

	atomic_set(&thread->sig_block_mask, *mask);

	while (true) {
		thread->next_state = B_THREAD_SUSPENDED;

		state = disable_interrupts();
		GRAB_THREAD_LOCK();

		update_thread_signals_flag(thread);

		scheduler_reschedule();

		RELEASE_THREAD_LOCK();
		restore_interrupts(state);

		if (has_signals_pending(thread))
			break;
	}

	// restore the original block mask
	atomic_set(&thread->sig_block_mask, oldMask);

	update_current_thread_signals_flag();

	// we're not supposed to actually succeed
	// ToDo: could this get us into trouble with SA_RESTART handlers?
	return B_INTERRUPTED;
}


int
sigpending(sigset_t *set)
{
	struct thread *thread = thread_get_current_thread();

	if (set == NULL)
		return B_BAD_VALUE;

	*set = atomic_get(&thread->sig_pending);	
	return B_OK;
}


//	#pragma mark -


bigtime_t
_user_set_alarm(bigtime_t time, uint32 mode)
{
	syscall_64_bit_return_value();

	return set_alarm(time, mode);
}


status_t
_user_send_signal(pid_t team, uint signal)
{
	return send_signal_etc(team, signal, B_CHECK_PERMISSION);
}


status_t
_user_sigprocmask(int how, const sigset_t *userSet, sigset_t *userOldSet)
{
	sigset_t set, oldSet;
	status_t status;

	if ((userSet != NULL && user_memcpy(&set, userSet, sizeof(sigset_t)) < B_OK)
		|| (userOldSet != NULL && user_memcpy(&oldSet, userOldSet,
				sizeof(sigset_t)) < B_OK))
		return B_BAD_ADDRESS;

	status = sigprocmask(how, userSet ? &set : NULL,
		userOldSet ? &oldSet : NULL);

	// copy old set if asked for
	if (status >= B_OK && userOldSet != NULL
		&& user_memcpy(userOldSet, &oldSet, sizeof(sigset_t)) < B_OK)
		return B_BAD_ADDRESS;

	return status;
}


status_t
_user_sigaction(int signal, const struct sigaction *userAction,
	struct sigaction *userOldAction)
{
	struct sigaction act, oact;
	status_t status;

	if ((userAction != NULL && user_memcpy(&act, userAction,
				sizeof(struct sigaction)) < B_OK)
		|| (userOldAction != NULL && user_memcpy(&oact, userOldAction,
				sizeof(struct sigaction)) < B_OK))
		return B_BAD_ADDRESS;

	status = sigaction(signal, userAction ? &act : NULL,
		userOldAction ? &oact : NULL);

	// only copy the old action if a pointer has been given
	if (status >= B_OK && userOldAction != NULL
		&& user_memcpy(userOldAction, &oact, sizeof(struct sigaction)) < B_OK)
		return B_BAD_ADDRESS;

	return status;
}


status_t
_user_sigsuspend(const sigset_t *userMask)
{
	sigset_t mask;

	if (userMask == NULL)
		return B_BAD_VALUE;
	if (user_memcpy(&mask, userMask, sizeof(sigset_t)) < B_OK)
		return B_BAD_ADDRESS;

	return sigsuspend(&mask);
}


status_t
_user_sigpending(sigset_t *userSet)
{
	sigset_t set;
	int status;

	if (userSet == NULL)
		return B_BAD_VALUE;
	if (!IS_USER_ADDRESS(userSet))
		return B_BAD_ADDRESS;

	status = sigpending(&set);
	if (status == B_OK
		&& user_memcpy(userSet, &set, sizeof(sigset_t)) < B_OK)
		return B_BAD_ADDRESS;

	return status;
}


status_t
_user_set_signal_stack(const stack_t *newUserStack, stack_t *oldUserStack)
{
	struct thread *thread = thread_get_current_thread();
	struct stack_t newStack, oldStack;
	bool onStack = false;

	if ((newUserStack != NULL && user_memcpy(&newStack, newUserStack,
				sizeof(stack_t)) < B_OK)
		|| (oldUserStack != NULL && user_memcpy(&oldStack, oldUserStack,
				sizeof(stack_t)) < B_OK))
		return B_BAD_ADDRESS;

	if (thread->signal_stack_enabled) {
		// determine wether or not the user thread is currently
		// on the active signal stack
		onStack = arch_on_signal_stack(thread);
	}

	if (oldUserStack != NULL) {
		oldStack.ss_sp = (void *)thread->signal_stack_base;
		oldStack.ss_size = thread->signal_stack_size;
		oldStack.ss_flags = (thread->signal_stack_enabled ? 0 : SS_DISABLE)
			| (onStack ? SS_ONSTACK : 0);
	}

	if (newUserStack != NULL) {
		// no flags other than SS_DISABLE are allowed
		if ((newStack.ss_flags & ~SS_DISABLE) != 0)
			return B_BAD_VALUE;

		if ((newStack.ss_flags & SS_DISABLE) == 0) {
			// check if the size is valid
			if (newStack.ss_size < MINSIGSTKSZ)
				return B_NO_MEMORY;
			if (onStack)
				return B_NOT_ALLOWED;
			if (!IS_USER_ADDRESS(newStack.ss_sp))
				return B_BAD_VALUE;

			thread->signal_stack_base = (addr_t)newStack.ss_sp;
			thread->signal_stack_size = newStack.ss_size;
			thread->signal_stack_enabled = true;
		} else
			thread->signal_stack_enabled = false;
	}

	// only copy the old stack info if a pointer has been given
	if (oldUserStack != NULL
		&& user_memcpy(oldUserStack, &oldStack, sizeof(stack_t)) < B_OK)
		return B_BAD_ADDRESS;

	return B_OK;
}