GDT

include/boot/gdt.h

struct gdt_entry

struct gdt_entry {
    uint16_t  limit_low;
    uint16_t  base_low;
    uint8_t   base_middle;
    uint8_t   access;
    uint8_t   granularity;
    uint8_t   base_high;
};

struct gdt_ptr

struct gdt_ptr {
    uint16_t  limit;
    uint64_t  base;
};

struct gdt_entry_tss

struct gdt_entry_tss {
    uint16_t  limit_low;
    uint16_t  base_low;
    uint8_t   base_middle;
    uint8_t   access;
    uint8_t   granularity;
    uint8_t   base_high;
    uint32_t  base_upper;
    uint32_t  reserved;
};

Defines

ACCESS_CODE_RING0

#define ACCESS_CODE_RING0 0x9A // exec/read, ring 0

ACCESS_DATA_RING0

#define ACCESS_DATA_RING0 0x92 // read/write, ring 0

ACCESS_CODE_RING3

#define ACCESS_CODE_RING3 0xFA // exec/read, ring 3

ACCESS_DATA_RING3

#define ACCESS_DATA_RING3 0xF2 // read/write, ring 3

GRAN_CODE

#define GRAN_CODE 0xAF // G=1, D/B=0, L=1, AVL=0

GRAN_DATA

#define GRAN_DATA 0xAF // G=1, D/B=0, L=0, AVL=0

GDT_KERNEL_CODE

#define GDT_KERNEL_CODE 0x08 // index 1

GDT_KERNEL_DATA

#define GDT_KERNEL_DATA 0x10 // index 2

KERNEL_CS

#define KERNEL_CS GDT_KERNEL_CODE

KERNEL_DS

#define KERNEL_DS GDT_KERNEL_DATA

GDT_USER_CODE

#define GDT_USER_CODE 0x28 // index 5 << 3

GDT_USER_DATA

#define GDT_USER_DATA 0x30 // index 6 << 3

USER_CS

#define USER_CS (GDT_USER_CODE | 0x3) // == 0x2B

USER_DS

#define USER_DS (GDT_USER_DATA | 0x3) // == 0x33

USER_SS

#define USER_SS USER_DS

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