1 files changed, 56 insertions, 0 deletions
diff --git a/src/kernel/gdt/gdt.c b/src/kernel/gdt/gdt.c
new file mode 100644
index 0000000..4886dc3
--- /dev/null
+++ b/src/kernel/gdt/gdt.c
@@ -0,0 +1,56 @@
+#include "gdt.h"
+#include <stdint.h>
+
+GDT_t *table = 0x0;
+extern GDTR_t gdtr;
+void get_gdtr() {
+    uint32_t base = 0x0000;
+
+    *table = (GDT_t){
+        // NULL
+        make_descriptor(0, 0, 0),
+        // Code segment, read
+        make_descriptor(base, 0x8FFFF, make_code(0, 0, 1)),
+        // Data segment, read write
+        make_descriptor(base, 0x8FFFF, make_data(0, 0, 1)),
+    };
+    gdtr.size = sizeof(Segment_Descriptor_t) * 3 - 1;
+    gdtr.offset = base;
+}
+
+uint16_t make_code(uint8_t priv, uint8_t dc, uint8_t rw) {
+    uint16_t access = 0;
+    access |= (1 << 7);
+    access |= (priv << 5);
+    access |= (0b11 << 3);
+    access |= (dc << 2);
+    access |= (rw << 1); // 10
+    access <<= 8;
+    access |= FLAG;
+    return access;
+}
+
+uint16_t make_data(uint8_t priv, uint8_t dc, uint8_t rw) {
+    uint16_t access = 0;
+    access |= (1 << 7);
+    access |= (priv << 5);
+    access |= (0b10 << 3);
+    access |= (dc << 2);
+    access |= (rw << 1); // 10
+    access <<= 8;
+    access |= FLAG;
+    return access;
+}
+
+Segment_Descriptor_t make_descriptor(uint32_t base, uint32_t limit,
+                                     uint16_t access_flag) {
+    uint16_t lim_low = limit;
+    uint16_t base_low = base;
+    uint8_t base_mid = (base >> 16);
+    uint8_t access_byte = access_flag >> 8;
+    uint8_t lim_flag = ((access_flag << 4) | (limit >> 16));
+    uint8_t base_high = (base >> 24);
+    return (Segment_Descriptor_t){
+        lim_low, base_low, base_mid, access_byte, lim_flag, base_high,
+    };
+}