gdt.h

一个操作系统的源代码

/** gdt.h
 **
 ** Original Author: Kasper Verdich Lund
 ** Date: 10/11/99
 **
 ** Description:
 ** Global Descriptor Table functions
 **
 ** 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
 ** 2 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 or 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, write to the
 ** Free Software Foundation, Inc., 59 Temple Place, Suite 330,
 ** Boston, MA 02111-1307 USA
 **
 *********************************************************Apostle OS**/

#ifndef __GDT_H_
#define __GDT_H_

#include <types.h>

#define GDT_SIZE 8192
#define LIMIT_1MB 0xFFFFF
#define LIMIT_4GB 0xFFFFFFFF
#define KERNEL_CS 0x8
#define KERNEL_DS 0x10

typedef struct descriptor 
{
  /* segment limit 15:00 */
  word limit0_15; 
  /* base address 15:00 */
  word base0_15;
  /* base address 23:16 */
  byte base16_23;
  /* segment type */
  byte type : 4;
  /* descriptor type */
  byte s : 1;
  /* descriptor privilege level */
  byte dpl : 2;
  /* segment present */
  byte p : 1;
  /* segment limit 19:16 */
  byte limit16_19 : 4;
  /* available for use by system software */
  byte avl : 1;
  /* always 0 */
  byte zero : 1;
  /* default operation size */
  byte db : 1;
  /* granularity */ 
  byte g : 1;
  /* base address 31:24 */
  byte base24_31;
} __attribute__ ((packed)) descriptor;

extern descriptor *GDT;
extern void setupGDT(void);
extern void setupDescriptor(descriptor *d, dword base, dword limit, byte type, byte dpl, byte s, byte db);

#endif /* ifndef __GDT_H_ */