extern void _loadgdt();

struct gdt_entry
{
    unsigned short limit_low;
    unsigned short base_low;
    unsigned char base_middle;
    unsigned char access;
    unsigned char granularity;
    unsigned char base_high;
} __attribute__((packed));

struct gdt_entry gdt[3];

void gdt_set_gate(int num, unsigned long base, unsigned long limit, unsigned char access, unsigned char gran)
{
    /* Ustawianie adres bazowy segmentu */
    gdt[num].base_low = (base & 0xFFFF);
    gdt[num].base_middle = (base >> 16) & 0xFF;
    gdt[num].base_high = (base >> 24) & 0xFF;

    /* Ustawianie limtu segmentu */
    gdt[num].limit_low = (limit & 0xFFFF);
    gdt[num].granularity = ((limit >> 16) & 0x0F);

    /* Ustaw rodzaj deskryptora oraz informacje o segmencie */
    gdt[num].granularity |= (gran & 0xF0);
    gdt[num].access = access;
}

struct gdt_ptr
{
    unsigned short limit; // Limit GDT
    unsigned int base; // Adres bazowy GDT
} __attribute__((packed));

struct gdt_ptr _gdtptr;

void gdt_install()
{
    /* Ustaw wskaźnik */

    _gdtptr.limit = (sizeof(struct gdt_entry) * 3) - 1;
    _gdtptr.base = (unsigned int)&gdt;

    /* Deskryptor zerowy */

    gdt_set_gate(0, 0, 0, 0, 0);

    /* Deskryptor segmentu kodu:
        G = 1, D/B = 1, P = 1, DPL = 0, S=1, TYPE = 0x0A
        Adres bazowy: 0x0, Limit: 0xFFFFFFFF */

    gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);

    /* Deskryptor segmentu danych:
        G = 1, D/B = 1, P = 1, DPL = 0, S=1, TYPE = 0x02
        Adres bazowy: 0x0, Limit: 0xFFFFFFFF */

    gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);

   /* Zaktualizuj rejestr GDTR */

    _loadgdt();
}