1 files changed, 46 insertions, 0 deletions
diff --git a/include/03.gdt/gdt.c b/include/03.gdt/gdt.c
new file mode 100644
index 0000000..e3d2b4c
--- /dev/null
+++ b/include/03.gdt/gdt.c
@@ -0,0 +1,46 @@
+#include<types.h>
+
+struct gdt_entry
+{
+    uint16_t limit;
+    uint16_t base1;
+    uint8_t base2;
+    uint8_t access;
+    uint8_t limit_flags;
+    uint8_t base3;
+} __attribute__((packed));
+
+struct gdt_pointer
+{
+    uint16_t size;
+    uint32_t offset;
+} __attribute__((packed));
+
+extern void load_gdt(struct gdt_pointer *gdtp);
+
+struct gdt_entry gdt[5];
+struct gdt_pointer gdtp;
+
+void init_gdt_entry(size_t num, uint32_t limit, uint32_t base, uint8_t access, uint8_t limit_flags)
+{
+    gdt[num].limit=limit;
+    gdt[num].base1=(base & 0xffff);
+    gdt[num].base2=(base & 0xff0000) >> 16;
+    gdt[num].access=access;
+    gdt[num].limit_flags=limit_flags;
+    gdt[num].base3=(base & 0xff000000) >> 24;
+}
+
+void init_gdt_table()
+{
+    gdtp.size=sizeof(gdt)-1;
+    gdtp.offset=(uint32_t)&gdt;
+
+    init_gdt_entry(0,0,0,0,0);                              // null segment
+    init_gdt_entry(1,0xffffffff,0,0b10011010,0b11001111);   // code segment
+    init_gdt_entry(2,0xffffffff,0,0b10010010,0b11001111);   // data segment
+    init_gdt_entry(3,0xffffffff,0,0b11111010,0b11001111);   // user mode code segment
+    init_gdt_entry(4,0xffffffff,0,0b11110010,0b11001111);   // user mode data segment
+
+    load_gdt(&gdtp);
+}