Improve syscall definitions

- Allow constant id specification
- Define function signature in SYSCALL macro
- Move implementation into src/kernel/syscalls/*.cpp

src/kernel/syscalls/exit.cpp

@@ -0,0 +1,17 @@
+#include "log.h"
+#include "scheduler.h"
+
+namespace syscalls {
+
+void
+exit(int64_t status)
+{
+	auto &s = scheduler::get();
+	auto *p = s.current();
+	log::debug(logs::syscall, "Process %d exiting with code %d", p->pid, status);
+
+	p->exit(status);
+	s.schedule();
+}
+
+} // namespace syscalls

src/kernel/syscalls/getpid.cpp

@@ -0,0 +1,14 @@
+#include "log.h"
+#include "scheduler.h"
+
+namespace syscalls {
+
+pid_t
+getpid()
+{
+	auto &s = scheduler::get();
+	auto *p = s.current();
+	return p->pid;
+}
+
+} // namespace syscalls

src/kernel/syscalls/message.cpp

@@ -0,0 +1,14 @@
+#include "log.h"
+#include "scheduler.h"
+
+namespace syscalls {
+
+void
+message(const char *message)
+{
+	auto &s = scheduler::get();
+	auto *p = s.current();
+	log::info(logs::syscall, "Message[%d]: %s", p->pid, message);
+}
+
+} // namespace syscalls

src/kernel/syscalls/noop.cpp

@@ -0,0 +1,14 @@
+#include "log.h"
+#include "scheduler.h"
+
+namespace syscalls {
+
+void
+noop()
+{
+	auto &s = scheduler::get();
+	auto *p = s.current();
+	log::debug(logs::syscall, "Process %d called noop syscall.", p->pid);
+}
+
+} // namespace syscalls

src/kernel/syscalls/pause.cpp

@@ -0,0 +1,15 @@
+#include "log.h"
+#include "scheduler.h"
+
+namespace syscalls {
+
+void
+pause()
+{
+	auto &s = scheduler::get();
+	auto *p = s.current();
+	p->wait_on_signal(-1ull);
+	s.schedule();
+}
+
+} // namespace syscalls

src/kernel/syscalls/sleep.cpp

@@ -0,0 +1,17 @@
+#include "log.h"
+#include "scheduler.h"
+
+namespace syscalls {
+
+void
+sleep(uint64_t til)
+{
+	auto &s = scheduler::get();
+	auto *p = s.current();
+	log::debug(logs::syscall, "Process %d sleeping until %d", p->pid, til);
+
+	p->wait_on_time(til);
+	s.schedule();
+}
+
+} // namespace syscalls