[kernel] Add userspace threading

Implement the syscalls necessary for threads to create other threads in
their same process. This involved rearranging a number of syscalls, as
well as implementing object_wait and a basic implementation of a
process' list of handles.

src/kernel/syscalls/object.cpp

@@ -2,24 +2,32 @@
 #include "j6/types.h"
 
 #include "log.h"
+#include "objects/process.h"
+#include "objects/thread.h"
 #include "scheduler.h"
 
 namespace syscalls {
 
 j6_status_t
-object_noop()
+object_wait(j6_handle_t handle, j6_signal_t mask, j6_signal_t *sigs)
 {
-	auto &s = scheduler::get();
-	TCB *tcb = s.current();
-	thread *th = thread::from_tcb(tcb);
-	log::debug(logs::syscall, "Thread %llx called noop syscall.", th->koid());
-	return j6_status_ok;
-}
+	scheduler &s = scheduler::get();
+	thread *th = thread::from_tcb(s.current());
+	process &p = th->parent();
 
-j6_status_t
-object_wait(j6_handle_t, j6_signal_t, j6_signal_t*)
-{
-	return j6_err_nyi;
+	kobject *obj = p.lookup_handle(handle);
+	if (!obj)
+		return j6_err_invalid_arg;
+
+	obj->add_blocked_thread(th);
+	th->wait_on_signals(obj, mask);
+	s.schedule();
+
+	j6_status_t result = th->get_wait_result();
+	if (result == j6_status_ok) {
+		*sigs = th->get_wait_data();
+	}
+	return result;
 }
 
 } // namespace syscalls