+++ /dev/null
-/*
-pcboot - bootable PC demo/game kernel
-Copyright (C) 2018 John Tsiombikas <nuclear@member.fsf.org>
-
-This program is free software: you can redistribute it and/or modify
-it under the terms of the GNU General Public License as published by
-the Free Software Foundation, either version 3 of the License, or
-(at your option) any later version.
-
-This program is distributed in the hope that it will be useful,
-but WITHOUT ANY WARRANTY, without even the implied warranty of
-MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-GNU General Public License for more details.
-
-You should have received a copy of the GNU General Public License
-along with this program. If not, see <https://www.gnu.org/licenses/>.
-*/
-#include <stdio.h>
-#include <string.h>
-#include "segm.h"
-#include "desc.h"
-#include "tss.h"
-
-/* bits for the 3rd 16bt part of the descriptor */
-#define BIT_ACCESSED (1 << 8)
-#define BIT_WR (1 << 9)
-#define BIT_RD (1 << 9)
-#define BIT_EXP_DOWN (1 << 10)
-#define BIT_CONFORMING (1 << 10)
-#define BIT_CODE (1 << 11)
-#define BIT_NOSYS (1 << 12)
-#define BIT_PRESENT (1 << 15)
-/* TSS busy bit */
-#define BIT_BUSY (1 << 9)
-
-/* bits for the last 16bit part of the descriptor */
-#define BIT_BIG (1 << 6)
-#define BIT_DEFAULT (1 << 6)
-#define BIT_GRAN (1 << 7)
-
-enum {TYPE_DATA, TYPE_CODE};
-
-/* we need the following bit pattern at the 8th bit excluding the busy bit: 1001 */
-#define TSS_TYPE_BITS (9 << 8)
-
-static void segm_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl, int type);
-static void segm_desc16(desc_t *desc, uint32_t base, uint32_t limit, int dpl, int type);
-/*static void task_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl);*/
-
-/* these functions are implemented in segm-asm.S */
-void setup_selectors(uint16_t code, uint16_t data);
-void set_gdt(uint32_t addr, uint16_t limit);
-void set_task_reg(uint16_t tss_selector);
-
-/*
-static void dbg_print_gdt(void);
-static void print_desc(desc_t *desc);
-*/
-
-/* our global descriptor table */
-static desc_t gdt[NUM_SEGMENTS] __attribute__((aligned(8)));
-uint16_t orig_seg;
-
-void init_segm(void)
-{
- asm volatile (
- "mov %%fs, %0\n\t"
- : "=a"(orig_seg));
-
- memset(gdt, 0, sizeof gdt);
- segm_desc(gdt + SEGM_CODE, 0, 0xffffffff, 0, TYPE_CODE);
- segm_desc(gdt + SEGM_DATA, 0, 0xffffffff, 0, TYPE_DATA);
- segm_desc(gdt + SEGM_XCODE, orig_seg << 4, 0xffffffff, 0, TYPE_CODE);
- segm_desc(gdt + SEGM_XDATA, orig_seg << 4, 0xffffffff, 0, TYPE_DATA);
- segm_desc16(gdt + SEGM_CODE16, orig_seg << 4, 0xffff, 0, TYPE_CODE);
-
- set_gdt((uint32_t)gdt, sizeof gdt - 1);
-
- setup_selectors(selector(SEGM_CODE, 0), selector(SEGM_DATA, 0));
-}
-
-/* constructs a GDT selector based on index and priviledge level */
-uint16_t selector(int idx, int rpl)
-{
- return (idx << 3) | (rpl & 3);
-}
-
-/*
-void set_tss(uint32_t addr)
-{
- task_desc(gdt + SEGM_TASK, addr, sizeof(struct task_state) - 1, 3);
- set_task_reg(selector(SEGM_TASK, 0));
-}
-*/
-
-static void segm_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl, int type)
-{
- desc->d[0] = limit & 0xffff; /* low order 16bits of limit */
- desc->d[1] = base & 0xffff; /* low order 16bits of base */
-
- /* third 16bit part contains the last 8 bits of base, the 2 priviledge
- * level bits starting on bit 13, present flag on bit 15, and type bits
- * starting from bit 8
- */
- desc->d[2] = ((base >> 16) & 0xff) | ((dpl & 3) << 13) | BIT_PRESENT |
- BIT_NOSYS | (type == TYPE_DATA ? BIT_WR : (BIT_RD | BIT_CODE));
-
- /* last 16bit part contains the last nibble of limit, the last byte of
- * base, and the granularity and deafult/big flags in bits 23 and 22 resp.
- */
- desc->d[3] = ((limit >> 16) & 0xf) | ((base >> 16) & 0xff00) | BIT_GRAN | BIT_BIG;
-}
-
-static void segm_desc16(desc_t *desc, uint32_t base, uint32_t limit, int dpl, int type)
-{
- desc->d[0] = limit & 0xffff; /* low order 16bits of limit */
- desc->d[1] = base & 0xffff; /* low order 16bits of base */
-
- /* third 16bit part contains the last 8 bits of base, the 2 priviledge
- * level bits starting on bit 13, present flag on bit 15, and type bits
- * starting from bit 8
- */
- desc->d[2] = ((base >> 16) & 0xff) | ((dpl & 3) << 13) | BIT_PRESENT |
- BIT_NOSYS | (type == TYPE_DATA ? BIT_WR : (BIT_RD | BIT_CODE));
-
- /* 16bit descriptors have the upper word 0 */
- desc->d[3] = 0;
-}
-
-#if 0
-static void task_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl)
-{
- desc->d[0] = limit & 0xffff;
- desc->d[1] = base & 0xffff;
-
- desc->d[2] = ((base >> 16) & 0xff) | ((dpl & 3) << 13) | BIT_PRESENT |
- TSS_TYPE_BITS; /* XXX busy ? */
- desc->d[3] = ((limit >> 16) & 0xf) | ((base >> 16) & 0xff00) | BIT_GRAN;
-}
-
-static void dbg_print_gdt(void)
-{
- int i;
-
- printf("Global Descriptor Table\n");
- printf("-----------------------\n");
-
- for(i=0; i<NUM_SEGMENTS; i++) {
- printf("%d: ", i);
- print_desc(gdt + i);
- }
-}
-
-static void print_desc(desc_t *desc)
-{
- uint32_t base, limit;
- int dpl, g;
-
- if((desc->d[0] | desc->d[1] | desc->d[2] | desc->d[3]) == 0) {
- printf("null\n");
- }
-
- base = (uint32_t)desc->d[1] | ((uint32_t)(desc->d[2] & 0xff) << 16) | ((uint32_t)(desc->d[3] >> 8) << 24);
- limit = (uint32_t)desc->d[0] | ((uint32_t)(desc->d[3] & 0xf) << 16);
- dpl = (desc->d[2] >> 13) & 3;
- g = (desc->d[3] >> 7) & 1;
-
- if(g) limit = ((limit + 1) << 12) - 1;
-
- printf("base:%x lim:%x dpl:%d type:%s %dbit\n", base, limit, dpl,
- desc->d[2] & BIT_CODE ? "code" : "data", desc->d[3] & BIT_BIG ? 32 : 16);
-}
-#endif
projects / com32 / blobdiff