-#ifndef HEADER_LOADER_H
-#define HEADER_LOADER_H
+#ifndef THREADS_LOADER_H
+#define THREADS_LOADER_H
/* Constants fixed by the PC BIOS. */
#define LOADER_BASE 0x7c00 /* Physical address of loader's base. */
/* Kernel command line. */
#define LOADER_RAM_PAGES (LOADER_CMD_LINE - 4) /* # of pages of RAM. */
-#endif /* loader.h */
+/* 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. */
+
+#endif /* threads/loader.h */