cos2000v2/lib/gdt.c

#include "gdt.h"
#include "asm.h"
#include "types.h"


 /* registre gdt */
static struct gdtr gdtreg;

/* table de GDT */
static gdtdes gdt[SIZEGDT];

/* TSS */
static struct tss tss0;

/*******************************************************************************/

/* Initialise la GDT */

void initgdt(u32 offset)
{
	makegdtdes(0x0, 0x00000, 0x00, 0x00, &gdt[0]);  /* descripteur nul         */
	makegdtdes(0x0, 0xFFFFF, 0x9B, 0x0D, &gdt[1]);	/* code -> SEL_KERNEL_CODE */
	makegdtdes(0x0, 0x00000, 0x97, 0x0D, &gdt[2]);  /* pile -> SEL_KERNEL_STACK */
	makegdtdes(0x0, 0xFFFFF, 0xFF, 0x0D, &gdt[3]);	/* code -> SEL_USER_CODE */
	makegdtdes(0x0, 0x00000, 0xF7, 0x0D, &gdt[4]);  /* pile -> SEL_USER_STACK */
	makegdtdes(0x0, 0xFFFFF, 0x93, 0x0D, &gdt[5]);	/* data -> SEL_KERNEL_DATA */
	makegdtdes(0x0, 0xFFFFF, 0xF3, 0x0D, &gdt[6]);	/* data -> SEL_USER_DATA */

	tss0.trapflag = 0x00;
	tss0.iomap = 0x00;
	tss0.esp0 = 0x1FFF0;
	tss0.ss0 = SEL_TSS;

	makegdtdes(&tss0, 0x67, 0xE9, 0x00, &gdt[7]);	/* descripteur de tss */

	/* initialise le registre gdt */
	gdtreg.limite = SIZEGDT * 8;
	gdtreg.base = BASEGDT;
	/* recopie de la GDT a son adresse */
	memcpy(&gdt, (u8 *) gdtreg.base, gdtreg.limite, 1);
	/* chargement du registre GDT */
	lgdt(&gdtreg);
	/* initialisation des segments */
	initselectors(offset);
}

/*******************************************************************************/

/* Initialise le registre de t<>che (TSR) */

void inittr(void) 
{
    ltr(SEL_TSS);
}

/*******************************************************************************/

/* Initialise les selecteurs avec la GDT */

void initselectors(u32 executingoffset)
{
asm("   movw %[data], %%ax	\n \
            movw %%ax, %%ds	\n \
            movw %%ax, %%es	\n \
            movw %%ax, %%fs	\n \
            movw %%ax, %%gs   \n \
            movl %[offset], %%ebx \n \
            movw %[stack], %%ax \n \
            movw %%ax, %%ss \n \
            movl %[stackoff], %%esp \n \
            ljmp %[code], $raz	\n \
            raz:		\n \
            pushl %%ebx \n \
            ret\n"::[data] "i"(SEL_KERNEL_DATA),[code] "i"(SEL_KERNEL_CODE), [stack] "i"(SEL_KERNEL_STACK), [stackoff] "i"(STACK_OFFSET), [offset] "m"(executingoffset));
}

/*******************************************************************************/

/* Cr<43><72> un descripteur GDT */

void makegdtdes(u32 base, u32 limite, u8 acces, u8 flags, gdtdes *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->flags = (flags & 0xf);
        desc->base24_31 = (base & 0xff000000) >> 24;
        return;
}