Very simple threading and context switching.

src/kernel/include/thread.h

@@ -0,0 +1,43 @@
+#pragma once
+#include <memory.h>
+
+
+struct tcb
+{
+  uintptr_t stack_ptr;
+  uint64_t tid;
+  uint64_t state;
+};
+
+#define TCB_OFFSET (PAGE_SIZE - sizeof(struct tcb))
+#define SWTCH_STACK_SIZE (0x8*8)
+
+struct thread
+{
+  union {
+    uint8_t stack[TCB_OFFSET];
+    struct {
+      uint8_t _stck[TCB_OFFSET-SWTCH_STACK_SIZE];
+      uint64_t RBP;
+      uint64_t RBX;
+      uint64_t R12;
+      uint64_t R13;
+      uint64_t R14;
+      uint64_t R15;
+      uint64_t RBP2;
+      uint64_t ret;
+    };
+  };
+  struct tcb tcb;
+};
+
+extern struct thread *threads[];
+int current_tid;
+
+#define CURRENT_THREAD() (threads[current_tid])
+
+struct thread *new_thread(void (*function)());
+void yield();
+int get_tid();
+
+void swtch(void *, void *);