+/* Sizes of loader data structures. */
+#define LOADER_SIG_LEN 2
+#define LOADER_PARTS_LEN 64
+#define LOADER_ARGS_LEN 128
+#define LOADER_ARG_CNT_LEN 4
+
+/* GDT selectors defined by loader.
+ More selectors are defined by userprog/gdt.h. */
+#define SEL_NULL 0x00 /* Null selector. */
+#define SEL_KCSEG 0x08 /* Kernel code selector. */
+#define SEL_KDSEG 0x10 /* Kernel data selector. */
+
+#ifndef __ASSEMBLER__
+#include <stdint.h>