1 files changed, 69 insertions, 0 deletions
diff --git a/arch/i386/include/gdt.h b/arch/i386/include/gdt.h
new file mode 100644
index 0000000..4ffa155
--- /dev/null
+++ b/arch/i386/include/gdt.h
@@ -0,0 +1,69 @@
+#ifndef GDT_H
+#define GDT_H
+
+#include <stdint.h>
+
+#define SEG_DESCTYPE(x) ((x) << 0x04)
+#define SEG_PRES(x)     ((x) << 0x07)
+#define SEG_SAVL(x)     ((x) << 0x0C)
+#define SEG_LONG(x)     ((x) << 0x0D)
+#define SEG_SIZE(x)     ((x) << 0x0E)
+#define SEG_GRAN(x)     ((x) << 0x0F)
+#define SEG_PRIV(x)     (((x) & 0x03) << 0x05)
+
+#define SEG_DATA_RD             0x00
+#define SEG_DATA_RDA            0x01
+#define SEG_DATA_RDWR           0x02
+#define SEG_DATA_RDWRA          0x03
+#define SEG_DATA_RDEXPD         0x04
+#define SEG_DATA_RDEXPDA        0x05
+#define SEG_DATA_RDWREXD        0x06
+#define SEG_DATA_RDWREXDA       0x07
+#define SEG_CODE_EX             0x08
+#define SEG_CODE_EXA            0x09
+#define SEG_CODE_EXRD           0x0A
+#define SEG_CODE_EXRDA          0x0B
+#define SEG_CODE_EXC            0x0C
+#define SEG_CODE_EXCA           0x0D
+#define SEG_CODE_EXRDC          0x0E
+#define SEG_CODE_EXRDCA         0x0F
+
+#define GDT_CODE_PL0    SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
+                        SEG_LONG(0)     | SEG_SIZE(1) | SEG_GRAN(1) | \
+                        SEG_PRIV(0)     | SEG_CODE_EXRD
+
+#define GDT_DATA_PL0    SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
+                        SEG_LONG(0)     | SEG_SIZE(1) | SEG_GRAN(1) | \
+                        SEG_PRIV(0)     | SEG_CODE_RDWR
+
+#define GDT_CODE_PL3    SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
+                        SEG_LONG(0)     | SEG_SIZE(1) | SEG_GRAN(1) | \
+                        SEG_PRIV(3)     | SEG_DATA_EXRD
+
+#define GDT_DATA_PL3    SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
+                        SEG_LONG(0)     | SEG_SIZE(1) | SEG_GRAN(1) | \
+                        SEG_PRIV(3)     | SEG_DATA_RDWR
+
+struct gdt {
+        uint16_t size;
+        uint32_t offset;
+} __attribute__((packed));
+
+void flush_gdt(void);
+
+uint64_t create_descriptor(uint32_t base, uint32_t limit, uint16_t flag) {
+        uint64_t descriptor;
+
+        descriptor = limit              & 0x000F0000;
+        descriptor |= (flag << 8)       & 0x00F0FF00;
+        descriptor |= (base >> 16)      & 0x000000FF;
+        descriptor |= base              & 0xFF000000;
+
+        descriptor <<= 32;
+        descriptor |= base << 16;
+        descriptor |= limit & 0x0000FFFF;
+
+        return descriptor;
+}
+
+#endif