kernel: add header files

arch/x86_64/include/kernel/machine/thread.h

@@ -0,0 +1,31 @@
+#ifndef KERNEL_X86_64_THREAD_H_
+#define KERNEL_X86_64_THREAD_H_
+
+#include <kernel/sched.h>
+
+struct ml_cpu_context;
+
+/* switch from one thread to another. the stack of the `to` thread must have
+ * been prepared in one of two ways:
+ *  1) a previous call to ml_thread_switch where it was the `from` thread.
+ *  2) a call to ml_thread_prepare_kernel_context
+ * the switch occurs entirely with kernel mode. a further return from an
+ * interrupt context is then used to return to usermode if necessary.
+ */
+extern void ml_thread_switch(struct thread *from, struct thread *to);
+
+/* perform the initial transition to userspace. the stack must be prepared using
+ * ml_thread_prepare_user_context before this function can be used */
+extern void ml_thread_switch_user(void);
+/* prepare the stack so that ml_thread_switch can jump to the specified IP/SP */
+extern void ml_thread_prepare_kernel_context(uintptr_t ip, uintptr_t *sp);
+/* prepare the stack so that ml_thread_switch_user can jump to usermode
+ * with the specified IP/user SP */
+extern kern_status_t ml_thread_prepare_user_context(
+	virt_addr_t ip,
+	virt_addr_t user_sp,
+	virt_addr_t *kernel_sp,
+	const uintptr_t *args,
+	size_t nr_args);
+
+#endif