Kernel/LibC: Implement SA_RESTART

I have been thinking how to do this for a long time but I finally
figured out a semi-clean way

kernel/include/kernel/Thread.h

@@ -53,7 +53,8 @@ namespace Kernel
 		// Returns true if pending signal can be added to thread
 		bool can_add_signal_to_execute() const;
 		bool will_execute_signal() const;
-		void handle_signal(int signal = 0);
+		// Returns true if handled signal had SA_RESTART
+		bool handle_signal(int signal = 0);
 		bool add_signal(int signal);
 
 		// blocks current thread and returns either on unblock, eintr, spuriously or after timeout

kernel/kernel/Process.cpp

@@ -2073,9 +2073,7 @@ namespace Kernel
 
 		if (act)
 		{
-			if (act->sa_flags == SA_RESTART)
+			if (act->sa_flags & ~(SA_RESTART))
-				dwarnln("FIXME: sigaction ignoring SA_RESTART", signal, act->sa_flags);
-			else if (act->sa_flags)
 			{
 				dwarnln("TODO: sigaction({}, {H})", signal, act->sa_flags);
 				return BAN::Error::from_errno(ENOTSUP);

kernel/kernel/Syscall.cpp

@@ -79,7 +79,9 @@ namespace Kernel
 
 		auto& current_thread = Thread::current();
 		if (current_thread.can_add_signal_to_execute())
-			current_thread.handle_signal();
+			if (current_thread.handle_signal())
+				if (ret.is_error() && ret.error().get_error_code() == EINTR)
+					ret = BAN::Error::from_errno(ERESTART);
 
 		ASSERT(Kernel::Thread::current().state() == Kernel::Thread::State::Executing);
 

kernel/kernel/Thread.cpp

@@ -435,7 +435,7 @@ namespace Kernel
 		return interrupt_stack.ip == (uintptr_t)signal_trampoline;
 	}
 
-	void Thread::handle_signal(int signal)
+	bool Thread::handle_signal(int signal)
 	{
 		ASSERT(&Thread::current() == this);
 		ASSERT(is_userspace());
@@ -463,10 +463,12 @@ namespace Kernel
 		}
 
 		vaddr_t signal_handler;
+		bool has_sa_restart;
 		{
 			SpinLockGuard _(m_process->m_signal_lock);
 			ASSERT(!(m_process->m_signal_handlers[signal].sa_flags & SA_SIGINFO));
 			signal_handler = (vaddr_t)m_process->m_signal_handlers[signal].sa_handler;
+			has_sa_restart = !!(m_process->m_signal_handlers[signal].sa_flags & SA_RESTART);
 		}
 
 		m_signal_pending_mask &= ~(1ull << signal);
@@ -534,6 +536,8 @@ namespace Kernel
 					ASSERT_NOT_REACHED();
 			}
 		}
+
+		return has_sa_restart;
 	}
 
 	bool Thread::add_signal(int signal)

userspace/libraries/LibC/include/errno.h

@@ -90,6 +90,7 @@ __BEGIN_DECLS
 #define EXDEV			81
 #define ENOTBLK			82
 
+#define ERESTART        0xFE /* internal errno for SA_RESTART */
 #define EUNKNOWN		0xFF
 
 #define errno (*__errno_location())

userspace/libraries/LibC/unistd.cpp

@@ -83,7 +83,10 @@ long syscall(long syscall, ...)
 
 	va_end(args);
 
-	long ret = Kernel::syscall(syscall, arg1, arg2, arg3, arg4, arg5);
+	long ret;
+	do
+		ret = Kernel::syscall(syscall, arg1, arg2, arg3, arg4, arg5);
+	while (ret == -ERESTART);
 
 	if (ret < 0)
 	{