[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/drivers/nulldrv/main.cpp

@@ -3,32 +3,53 @@
 
 #include "j6/types.h"
 #include "j6/errors.h"
+#include "j6/signals.h"
 
 extern "C" {
-	j6_status_t get_process_koid(j6_koid_t *koid);
-	j6_status_t sleep(uint64_t til);
-	j6_status_t debug();
-	j6_status_t message(const char *msg);
+	j6_status_t system_log(const char *msg);
+
+	j6_status_t object_wait(j6_handle_t obj, j6_signal_t sig, j6_signal_t *out);
+
+	j6_status_t process_koid(j6_koid_t *koid);
+
+	j6_status_t thread_koid(j6_koid_t *koid);
+	j6_status_t thread_create(void (*koid)(), j6_handle_t *handle);
+	j6_status_t thread_sleep(uint64_t til);
+	j6_status_t thread_exit(int64_t status);
 
 	int main(int, const char **);
 }
 
+void
+thread_proc()
+{
+	system_log("sub thread starting");
+	for (int i = 1; i < 5; ++i)
+		thread_sleep(i*10);
+
+	system_log("sub thread exiting");
+	thread_exit(0);
+}
 
 int
 main(int argc, const char **argv)
 {
-	uint64_t pid = 0;
-	uint64_t child = 0;
-	j6_koid_t process = 0;
+	j6_handle_t child = 0;
+	j6_signal_t out = 0;
 
-	j6_status_t result = get_process_koid(&process);
+	system_log("main thread starting");
+
+	j6_status_t result = thread_create(&thread_proc, &child);
 	if (result != j6_status_ok)
 		return result;
 
-	message("hello from nulldrv!");
+	system_log("main thread waiting on child");
 
-	for (int i = 1; i < 5; ++i)
-		sleep(i*10);
+	result = object_wait(child, -1ull, &out);
+	if (result != j6_status_ok)
+		return result;
 
-	return pid;
+	system_log("main thread done, exiting");
+	return 0;
 }
+