diff --git a/sdk/xtdk/amd64/ketypes.h b/sdk/xtdk/amd64/ketypes.h
index c177871..91097bc 100644
--- a/sdk/xtdk/amd64/ketypes.h
+++ b/sdk/xtdk/amd64/ketypes.h
@@ -13,6 +13,45 @@
 #include <xttypes.h>
 
 
+/* Selector masks */
+#define MODE_MASK                                 0x0001
+#define RPL_MASK                                  0x0003
+
+/* GDT selector names */
+#define KGDT_NULL                                 0x0000
+#define KGDT_R0_CODE                              0x0010
+#define KGDT_R0_DATA                              0x0018
+#define KGDT_R3_CMCODE                            0x0020
+#define KGDT_R3_DATA                              0x0028
+#define KGDT_R3_CODE                              0x0030
+#define KGDT_SYS_TSS                              0x0040
+#define KGDT_R3_CMTEB                             0x0050
+#define KGDT_R0_LDT                               0x0060
+
+/* GDT descriptor privilege levels */
+#define KGDT_DPL_SYSTEM                           0
+#define KGDT_DPL_USER                             3
+
+/* GDT descriptor properties */
+#define KGDT_DESCRIPTOR_ACCESSED                  0x01
+#define KGDT_DESCRIPTOR_READ_WRITE                0x02
+#define KGDT_DESCRIPTOR_EXECUTE_READ              0x02
+#define KGDT_DESCRIPTOR_EXPAND_DOWN               0x04
+#define KGDT_DESCRIPTOR_CONFORMING                0x04
+#define KGDT_DESCRIPTOR_CODE                      0x08
+
+/* GDT descriptor type codes */
+#define KGDT_TYPE_CODE                            (0x10 | KGDT_DESCRIPTOR_CODE | KGDT_DESCRIPTOR_EXECUTE_READ)
+#define KGDT_TYPE_DATA                            (0x10 | KGDT_DESCRIPTOR_READ_WRITE)
+
+/* AMD64 Segment Types */
+#define AMD64_TASK_GATE                           0x5
+#define AMD64_TSS                                 0x9
+#define AMD64_ACTIVE_TSS                          0xB
+#define AMD64_CALL_GATE                           0xC
+#define AMD64_INTERRUPT_GATE                      0xE
+#define AMD64_TRAP_GATE                           0xF
+
 /* Size of the exception area */
 #define EXCEPTION_AREA_SIZE               64