1 files changed, 77 insertions, 0 deletions
diff --git a/src/core/gdt.h b/src/core/gdt.h
new file mode 100644
index 0000000..f010891
--- /dev/null
+++ b/src/core/gdt.h
@@ -0,0 +1,77 @@
+#ifndef GDT_H
+#define GDT_H
+
+#include "types.h"
+
+#define GDT_MAX_ENTRIES 8
+
+// Access byte
+#define GDT_AC 1            // Access bit
+#define GDT_RW 1 << 1       // Read/Write bit
+#define GDT_DC 1 << 2       // Direction bit/Conforming bit
+#define GDT_EXEC 1 << 3     // Executable bit
+#define GDT_S 1 << 4        // Descriptor type
+#define GDT_PRVL_0 0        // Privilege (from 0 to 3)
+#define GDT_PRVL_1 1 << 5
+#define GDT_PRVL_2 2 << 5
+#define GDT_PRVL_3 3 << 5
+#define GDT_PR 1 << 7       // Present Bit
+
+// Flags
+#define GDT_SZ 1 << 2       // Size bit
+#define GDT_GR 1 << 3       // Granularity bit
+
+typedef struct GDT_ENTRY {
+  u32 base;
+  u32 limit;
+  u8 flags;
+  u8 access;
+} GDT_ENTRY;
+
+struct GDT_REGISTER {
+  u16 limit;
+  u32 base;
+} __attribute__((packed));
+
+typedef struct GDT_TSS {
+  u16 previous_task,previous_task_unused;
+  u32 esp0;
+  u16 ss0, ss0_unused;
+  u32 esp1;
+  u16 ss1, ss1_unused;
+  u32 esp2;
+  u16 ss2, ss2_unused;
+  u32 cr3;
+  u32 eip;
+  u32 eflags;
+  u32 eax;
+  u32 ecx;
+  u32 edx;
+  u32 ebx;
+  u32 esp;
+  u32 ebp;
+  u32 esi;
+  u32 edi;
+  u16 es, es_reserved;
+  u16 cs, cs_reserved;
+  u16 ss, ss_reserved;
+  u16 ds, ds_reserved;
+  u16 fs, fs_reserved;
+  u16 gs, gs_reserved;
+  u16 ldtss, ldtss_reserved;
+  u16 t_reserved, io_map;
+} __attribute__((packed)) GDT_TSS;
+
+/**
+ * Copy GDT in memory
+ */
+void gdt_memcpy();
+
+/**
+ * Write a GDT entry at address addr
+ */
+void gdt_write_entry(GDT_ENTRY entry, u32 id);
+
+int gdt_user_ds_base();
+
+#endif