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#ifndef GDT_H
#define GDT_H
#include <typedefs.h>
#include <string.h>
#define GDT_ENTRY_SIZE 0x8
#define GDT_NULL_SEGMENT 0x0
#define GDT_KERNEL_CODE_SEGMENT 0x1
#define GDT_KERNEL_DATA_SEGMENT 0x2
#define GDT_USERMODE_CODE_SEGMENT 0x3
#define GDT_USERMODE_DATA_SEGMENT 0x4
#define GDT_TSS_SEGMENT 0x5
struct GDT_Entry
{
u16 limit_low;
u32 base_low : 24;
u32 accessed : 1;
u32 read_write : 1; // readable for code, writable for data
u32 conforming_expand_down : 1; // conforming for code, expand down for data
u32 code : 1; // 1 for code, 0 for data
u32 code_data_segment : 1; // should be 1 for everything but TSS and LDT
u32 DPL : 2; // privilege level
u32 present : 1;
u32 limit_high : 4;
u32 available : 1; // only used in software; has no effect on hardware
u32 long_mode : 1;
u32 big : 1; // 32-bit opcodes for code, u32 stack for data
u32 gran : 1; // 1 to use 4k page addressing, 0 for byte addressing
u8 base_high;
}__attribute__((packed));
typedef struct GDT_Pointer
{
u16 size;
u32 offset;
}__attribute__((packed)) GDT_Pointer;
struct tss_entry_struct
{
u32 prev_tss; // The previous TSS - with hardware task switching these form a kind of backward linked list.
u32 esp0; // The stack pointer to load when changing to kernel mode.
u32 ss0; // The stack segment to load when changing to kernel mode.
// Everything below here is unused.
u32 esp1; // esp and ss 1 and 2 would be used when switching to rings 1 or 2.
u32 ss1;
u32 esp2;
u32 ss2;
u32 cr3;
u32 eip;
u32 eflags;
u32 eax;
u32 ecx;
u32 edx;
u32 ebx;
u32 esp;
u32 ebp;
u32 esi;
u32 edi;
u32 es;
u32 cs;
u32 ss;
u32 ds;
u32 fs;
u32 gs;
u32 ldt;
u16 trap;
u16 iomap_base;
} __attribute__((packed));
void gdt_init();
u8 gen_access_byte(u8 priv, u8 s, u8 ex, u8 dc, u8 rw);
u64 gen_gdt_entry(u32 base, u32 limit, u8 access_byte, u8 flag);
u8 gen_flag(u8 gr, u8 sz);
#endif
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