kern/gdt.c

#include "types.h"

#define __GDT__
#include "gdt.h"

void *memcpy(char *dst, char *src, int n)
{
        char *p = dst;
        while (n--)
                *dst++ = *src++;
        return p;
}
/*
 * 'init_desc' init a segment descriptor which is in gdt or ldt.
 * 'desc' is the linear address of the descriptor to init
 */
void init_gdt_desc(u32 base, u32 limite, u8 acces, u8 other,
           struct gdtdesc *desc)
{
    desc->lim0_15 = (limite & 0xffff);
    desc->base0_15 = (base & 0xffff);
    desc->base16_23 = (base & 0xff0000) >> 16;
    desc->acces = acces;
    desc->lim16_19 = (limite & 0xf0000) >> 16;
    desc->other = (other & 0xf);
    desc->base24_31 = (base & 0xff000000) >> 24;
    return;
}

/*
 * this function init the GDT after the kernel has been loaded into RAM
 */
void init_gdt(void)
{

    /* init some segments descriptors */
    init_gdt_desc(0x0, 0x0, 0x0, 0x0, &kgdt[0]);
    init_gdt_desc(0x0, 0xFFFFF, 0x9B, 0x0D, &kgdt[1]);  /* code */
    init_gdt_desc(0x0, 0xFFFFF, 0x93, 0x0D, &kgdt[2]);  /* data */
    init_gdt_desc(0x0, 0x0, 0x97, 0x0D, &kgdt[3]);      /* stack */

    /* init GDTR struct*/
    kgdtr.limite = GDTSIZE * 8;
    kgdtr.base = GDTBASE;

    memcpy((char *) kgdtr.base, (char *) kgdt, kgdtr.limite);

    /* load gdtr */
    asm("lgdtl (kgdtr)");

    /* init segments */
    asm("   movw $0x10, %ax \n \
            movw %ax, %ds   \n \
            movw %ax, %es   \n \
            movw %ax, %fs   \n \
            movw %ax, %gs   \n \
            ljmp $0x08, $next   \n \
            next:       \n");
}