Move BootGDT definition to C

src/kernel/cpu/gdt.c

@@ -0,0 +1,28 @@
+#include <stdint.h>
+#include <cpu.h>
+
+#define GDT_CODE      (3<<11)
+#define GDT_DPL(lvl)  ((lvl)<<13)
+#define GDT_PRESENT   (1<<15)
+#define GDT_LONG      (1<<21)
+
+
+struct gdt
+{
+  uint32_t _;
+  uint32_t flags;
+}__attribute__((packed));
+
+struct gdtp
+{
+  uint16_t len;
+  struct gdt *gdt;
+}__attribute__((packed));
+
+
+struct gdt BootGDT[] = {
+  {0, 0},
+  {0, GDT_PRESENT | GDT_DPL(0) | GDT_CODE | GDT_LONG}
+};
+
+struct gdtp GDTp = {2*8-1, BootGDT};