gdt.c

#include "gdt.h"

typedef unsigned long uint64_t;

typedef unsigned short uint16_t;

#define GDT_ENTRIES 5

#define GDT_FLAG_DATASEG 0x02

#define GDT_FLAG_CODESEG 0x0a

#define GDT_FLAG_TSS     0x09

#define GDT_FLAG_SEGMENT 0x10

#define GDT_FLAG_RING0   0x00

#define GDT_FLAG_RING3   0x60

#define GDT_FLAG_PRESENT 0x80

#define GDT_FLAG_4K_GRAN 0x800

#define GDT_FLAG_32_BIT  0x400

uint64_t gdt[GDT_ENTRIES];

void set_gdt_entry(int i, unsigned int base, unsigned int limit, int flags)

{

    gdt[i] = limit & 0xffffLL;

    gdt[i] |= (base & 0xffffffLL) << 16;

    gdt[i] |= (flags & 0xffLL) << 40;

    gdt[i] |= ((limit >> 16) & 0xfLL) << 48;

    gdt[i] |= ((flags >> 8 )& 0xffLL) << 52;

    gdt[i] |= ((base >> 24) & 0xffLL) << 56;

}

void init_gdt()

{

    set_gdt_entry(0, 0, 0, 0);

    set_gdt_entry(1, 0, 0xfffff, GDT_FLAG_SEGMENT | GDT_FLAG_32_BIT |

        GDT_FLAG_CODESEG | GDT_FLAG_4K_GRAN | GDT_FLAG_PRESENT);

    set_gdt_entry(2, 0, 0xfffff, GDT_FLAG_SEGMENT | GDT_FLAG_32_BIT |

        GDT_FLAG_DATASEG | GDT_FLAG_4K_GRAN | GDT_FLAG_PRESENT);

    set_gdt_entry(3, 0, 0xfffff, GDT_FLAG_SEGMENT | GDT_FLAG_32_BIT |

        GDT_FLAG_CODESEG | GDT_FLAG_4K_GRAN | GDT_FLAG_PRESENT | GDT_FLAG_RING3);

    set_gdt_entry(4, 0, 0xfffff, GDT_FLAG_SEGMENT | GDT_FLAG_32_BIT |

        GDT_FLAG_DATASEG | GDT_FLAG_4K_GRAN | GDT_FLAG_PRESENT | GDT_FLAG_RING3);

}

struct 

{

    uint16_t limit;

    unsigned int pointer;

} __attribute__((packed)) gdtp = 

{

    .limit = GDT_ENTRIES * 12 - 1, //vorher  *8

    .pointer = &gdt,

};

void install_gdt()

{

  init_gdt();

  asm volatile("lgdt %0" : : "m" (gdtp));

  loadseg();

}