libc: support sigwait - WiP

Issue genodelabs#5343

repos/libports/lib/symbols/libc

@@ -726,6 +726,7 @@ sigsetjmp T
 sigsetmask T
 sigsuspend W
 sigvec T
+sigwait T
 sl_add T
 sl_find T
 sl_free T

repos/libports/src/lib/libc/dummies.cc

@@ -197,7 +197,6 @@ DUMMY(int, -1, thr_kill2, (pid_t pid, long id, int sig));
 __SYS_DUMMY(int, -1, sigsuspend, (const sigset_t *))
 __SYS_DUMMY(int, -1, sigtimedwait, (const sigset_t *, siginfo_t *, const struct timespec *));
 __SYS_DUMMY(int, -1, sigwaitinfo, (const sigset_t *, siginfo_t *));
-__SYS_DUMMY(int, -1, sigwait, (const sigset_t *, int *));
 __SYS_DUMMY(int, -1, thr_kill,  (long id, int sig));
 
 

repos/libports/src/lib/libc/internal/init.h

@@ -150,7 +150,7 @@ namespace Libc {
 	/**
 	 * Signal handling
 	 */
-	void init_signal(Signal &);
+	void init_signal(Signal &, Monitor &);
 
 	/**
 	 * Atexit handling

repos/libports/src/lib/libc/internal/signal.h

@@ -35,7 +35,9 @@ struct Libc::Signal : Noncopyable
 {
 	public:
 
-		struct sigaction signal_action[NSIG + 1] { };
+		struct sigaction signal_action [NSIG + 1] { };
+		unsigned         signal_count  [NSIG + 1] { };
+		bool             signal_sigwait[NSIG + 1] { };
 
 	private:
 

repos/libports/src/lib/libc/kernel.cc

@@ -504,7 +504,7 @@ Libc::Kernel::Kernel(Genode::Env &env, Genode::Allocator &heap)
 	init_select(*this);
 	init_socket_fs(*this, *this);
 	init_passwd(_passwd_config());
-	init_signal(_signal);
+	init_signal(_signal, *this);
 
 	_init_file_descriptors();
 

repos/libports/src/lib/libc/signal.cc

@@ -7,7 +7,7 @@
  */
 
 /*
- * Copyright (C) 2006-2019 Genode Labs GmbH
+ * Copyright (C) 2006-2024 Genode Labs GmbH
  *
  * This file is part of the Genode OS framework, which is distributed
  * under the terms of the GNU Affero General Public License version 3.
@@ -26,21 +26,30 @@ extern "C" {
 #include <internal/init.h>
 #include <internal/signal.h>
 #include <internal/errno.h>
+#include <internal/monitor.h>
 
 using namespace Libc;
 
 
 static Libc::Signal *_signal_ptr;
+static Monitor      *_monitor_ptr;
 
 
-void Libc::init_signal(Signal &signal)
+void Libc::init_signal(Signal &signal, Monitor &monitor)
 {
-	_signal_ptr = &signal;
+	_signal_ptr  = &signal;
+	_monitor_ptr = &monitor;
 }
 
 
-void Libc::Signal::_execute_signal_handler(unsigned n)
+void Libc::Signal::_execute_signal_handler(unsigned const n)
 {
+	signal_count[n] ++;
+
+	if (signal_sigwait[n])
+		/* the blocked thread is woken by sigwait() in monitor() */
+		return;
+
 	if (signal_action[n].sa_flags & SA_SIGINFO) {
 		signal_action[n].sa_sigaction(n, 0, 0);
 		return;
@@ -266,3 +275,70 @@ extern "C" int sigaltstack(stack_t const * const ss, stack_t * const old_ss)
 
 	return 0;
 }
+
+
+extern "C" int __libc_sigwait(const sigset_t *, int *) __attribute__((weak, alias("sigwait")));
+
+extern "C" int sigwait(const sigset_t *set, int *sig)
+{
+	if (!set || !sig)
+		return EINVAL;
+
+	if (!_signal_ptr || !_monitor_ptr)
+		return EINVAL;
+
+	auto &signals = *_signal_ptr;
+
+	auto for_each_signal_of_set = [&](sigset_t const &set, auto const &fn) {
+		for (unsigned word = 0; word < _SIG_WORDS; word++) {
+			if (!set.__bits[word])
+				continue;
+
+			unsigned signals = set.__bits[word];
+
+			/* invoke functor for all signals of set */
+			while (signals) {
+				unsigned const pos    = __builtin_ctz(signals);
+				unsigned const signal = word * 32 + pos + 1;
+
+				signals &= ~(1u << pos);
+
+				fn(signal);
+			}
+		}
+	};
+
+	unsigned signal_count_before[NSIG + 1] { };
+
+	/* mark signals to wait for */
+	for_each_signal_of_set(*set, [&](auto const signal) {
+		signals.signal_sigwait[signal] = true;
+		signal_count_before[signal]    = signals.signal_count[signal];
+	});
+
+	/* block as long none of the monitored signals are pending */
+	_monitor_ptr->monitor([&]() {
+		bool triggered = false;
+
+		for_each_signal_of_set(*set, [&](auto const signal) {
+			if (triggered)
+				return;
+
+			triggered = signals.signal_count[signal] !=
+			            signal_count_before[signal];
+
+			if (triggered)
+				*sig = signal;
+		});
+
+		return triggered ? Monitor::Function_result::COMPLETE
+		                 : Monitor::Function_result::INCOMPLETE;
+	});
+
+	/* de-mark signals we had wait for */
+	for_each_signal_of_set(*set, [&](auto const signal) {
+		signals.signal_sigwait[signal] = false;
+	});
+
+	return 0;
+}

repos/libports/src/test/libc/main.cc

@@ -39,6 +39,7 @@ extern "C" {
 }
 
 static void test_sigalt();
+static void test_sigwait();
 
 int main(int argc, char **argv)
 {
@@ -269,6 +270,7 @@ int main(int argc, char **argv)
 	} while (0);
 
 	test_sigalt();
+	test_sigwait();
 
 	exit(error_count);
 }
@@ -357,3 +359,41 @@ static void test_sigalt()
 
 	printf("%s done\n", __func__);
 }
+
+
+static void * test_sigwait_pthread(void *arg)
+{
+	sigset_t set { };
+	int      triggered_signal { };
+
+	sigemptyset(&set);
+	sigaddset  (&set, SIGBUS);
+
+	int result = sigwait(&set, &triggered_signal);
+
+	if (result)
+		abort();
+
+	return arg;
+}
+
+
+static void test_sigwait()
+{
+	pthread_t t;
+
+	if (pthread_create(&t, 0, test_sigwait_pthread, NULL)) {
+		printf("error: pthread_create() failed\n");
+		exit(-1);
+	}
+
+	/* wait for pthread to invoke sigwait */
+	sleep(3);
+
+	/* send signal to pthread */
+	kill(getpid(), SIGBUS);
+
+	pthread_join(t, NULL);
+
+	printf("%s done\n", __func__);
+}