nuclear@7: #include <string.h>
nuclear@7: #include "segm.h"
nuclear@10: #include "desc.h"
nuclear@7: 
nuclear@8: /* bits for the 3rd 16bt part of the descriptor */
nuclear@7: #define BIT_ACCESSED	(1 << 8)
nuclear@7: #define BIT_WR			(1 << 9)
nuclear@7: #define BIT_RD			(1 << 9)
nuclear@7: #define BIT_EXP_DOWN	(1 << 10)
nuclear@7: #define BIT_CONFORMING	(1 << 10)
nuclear@7: #define BIT_CODE		(1 << 11)
nuclear@7: #define BIT_NOSYS		(1 << 12)
nuclear@7: #define BIT_PRESENT		(1 << 15)
nuclear@29: /* TSS busy bit */
nuclear@29: #define BIT_BUSY		(1 << 9)
nuclear@7: 
nuclear@8: /* bits for the last 16bit part of the descriptor */
nuclear@7: #define BIT_BIG			(1 << 6)
nuclear@7: #define BIT_DEFAULT		(1 << 6)
nuclear@7: #define BIT_GRAN		(1 << 7)
nuclear@7: 
nuclear@7: enum {TYPE_DATA, TYPE_CODE};
nuclear@7: 
nuclear@29: #define TSS_TYPE_BITS	0x900
nuclear@29: #define TSS_BUSY		BIT_BUSY
nuclear@29: 
nuclear@7: static void segm_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl, int type);
nuclear@29: static void task_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl, unsigned int busy);
nuclear@7: 
nuclear@8: /* these functions are implemented in segm-asm.S */
nuclear@8: void setup_selectors(uint16_t code, uint16_t data);
nuclear@8: void set_gdt(uint32_t addr, uint16_t limit);
nuclear@7: 
nuclear@8: 
nuclear@8: /* our global descriptor table */
nuclear@29: static desc_t gdt[6];
nuclear@7: 
nuclear@7: 
nuclear@7: void init_segm(void)
nuclear@7: {
nuclear@7: 	memset(gdt, 0, sizeof gdt);
nuclear@7: 	segm_desc(gdt + SEGM_KCODE, 0, 0xffffffff, 0, TYPE_CODE);
nuclear@7: 	segm_desc(gdt + SEGM_KDATA, 0, 0xffffffff, 0, TYPE_DATA);
nuclear@29: 	segm_desc(gdt + SEGM_UCODE, 0, 0xffffffff, 3, TYPE_CODE);
nuclear@29: 	segm_desc(gdt + SEGM_UDATA, 0, 0xffffffff, 3, TYPE_DATA);
nuclear@47: 	task_desc(gdt + SEGM_TASK, 0, 0xffffffff, 3, TSS_BUSY);
nuclear@7: 
nuclear@7: 	set_gdt((uint32_t)gdt, sizeof gdt - 1);
nuclear@7: 
nuclear@7: 	setup_selectors(selector(SEGM_KCODE, 0), selector(SEGM_KDATA, 0));
nuclear@7: }
nuclear@7: 
nuclear@8: /* constructs a GDT selector based on index and priviledge level */
nuclear@7: uint16_t selector(int idx, int rpl)
nuclear@7: {
nuclear@7: 	return (idx << 3) | (rpl & 3);
nuclear@7: }
nuclear@7: 
nuclear@7: static void segm_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl, int type)
nuclear@7: {
nuclear@7: 	desc->d[0] = limit & 0xffff; /* low order 16bits of limit */
nuclear@7: 	desc->d[1] = base & 0xffff;  /* low order 16bits of base */
nuclear@7: 
nuclear@7: 	/* third 16bit part contains the last 8 bits of base, the 2 priviledge
nuclear@7: 	 * level bits starting on bit 13, present flag on bit 15, and type bits
nuclear@7: 	 * starting from bit 8
nuclear@7: 	 */
nuclear@7: 	desc->d[2] = ((base >> 16) & 0xff) | ((dpl & 3) << 13) | BIT_PRESENT |
nuclear@7: 		BIT_NOSYS | (type == TYPE_DATA ? BIT_WR : (BIT_RD | BIT_CODE));
nuclear@7: 
nuclear@7: 	/* last 16bit part contains the last nibble of limit, the last byte of
nuclear@7: 	 * base, and the granularity and deafult/big flags in bits 23 and 22 resp.
nuclear@7: 	 */
nuclear@7: 	desc->d[3] = ((limit >> 16) & 0xf) | ((base >> 16) & 0xff00) | BIT_GRAN | BIT_BIG;
nuclear@7: }
nuclear@29: 
nuclear@29: static void task_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl, unsigned int busy)
nuclear@29: {
nuclear@29: 	desc->d[0] = limit & 0xffff;
nuclear@29: 	desc->d[1] = base & 0xffff;
nuclear@29: 
nuclear@29: 	desc->d[2] = ((base >> 16) & 0xff) | ((dpl & 3) << 13) | BIT_PRESENT |
nuclear@29: 		TSS_TYPE_BITS | busy;
nuclear@29: 	desc->d[3] = ((limit >> 16) & 0xf) | ((base >> 16) & 0xff00) | BIT_GRAN;
nuclear@29: }