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/*
* bubbl
* Copyright (C) 2024-2025 Raghuram Subramani <raghus2247@gmail.com>
*
* 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 <http://www.gnu.org/licenses/>.
*/
#ifndef __boot_gdt_h
#define __boot_gdt_h
#include <common.h>
#include <stdint.h>
/* Access Flags:
* 7 PRESENT
* 6 PRIVILEGE
* 5 PRIVILEGE
* 4 TYPE
* 3 EXECUTABLE
* 2 DIRECTION/CONFORMING
* 1 READABLE/WRITABLE
* 0 ACCESSED
*/
#define PRESENT(x) (x << 7)
#define PRIVILEGE(x) (x << 5)
#define TYPE(x) (x << 4)
#define EXECUTABLE(x) (x << 3)
#define DIRECTION_CONFORMING(x) (x << 2)
#define READABLE_WRITABLE(x) (x << 1)
#define ACCESSED(x) x
#define CODE_SEGMENT_ACCESS_FLAGS(privilege) \
PRESENT(1) | PRIVILEGE(privilege) | TYPE(1) | EXECUTABLE(1) \
| DIRECTION_CONFORMING(0) | READABLE_WRITABLE(1) | ACCESSED(0)
#define DATA_SEGMENT_ACCESS_FLAGS(privilege) \
PRESENT(1) | PRIVILEGE(privilege) | TYPE(1) | EXECUTABLE(0) \
| DIRECTION_CONFORMING(0) | READABLE_WRITABLE(1) | ACCESSED(0)
#define KERNEL_CODE_SEGMENT_ACCESS_FLAGS CODE_SEGMENT_ACCESS_FLAGS(0)
#define KERNEL_DATA_SEGMENT_ACCESS_FLAGS DATA_SEGMENT_ACCESS_FLAGS(0)
#define USER_CODE_SEGMENT_ACCESS_FLAGS CODE_SEGMENT_ACCESS_FLAGS(3)
#define USER_DATA_SEGMENT_ACCESS_FLAGS DATA_SEGMENT_ACCESS_FLAGS(3)
/* Other Flags:
* 3 GRANULARITY
* 2 SIZE
* 1 LONGMODE
* 0 RESERVED
*/
#define GRANULARITY (1 << 3)
#define SIZE (1 << 2)
#define LONGMODE (0 << 1)
#define RESERVED 0
#define FLAGS (GRANULARITY | SIZE | LONGMODE | RESERVED)
#define FLAGS_LIMIT_HIGH(flags, limit_high) ((flags << 4) | limit_high)
/* GDT Entry:
* BASE FLAGS LIMIT ACCESS_FLAGS BASE BASE LIMIT
* 8bit 4bit 4bit 8bit 8bit 16bit 16bit
*/
#define GDT_ENTRY(base, limit, access_flags, flags) \
{ \
(limit & 0xffff), /* limit_low */ \
(base & 0xffff), /* base_low */ \
((base >> 16) & 0xff), /* base_mid */ \
access_flags, /* access_flags */ \
FLAGS_LIMIT_HIGH(flags, ((limit >> 16) & 0xff)), /* flags_limit_high */ \
((base >> 24) & 0xff) /* base_high */ \
}
#define GDT_KERNEL_CODE_OFFSET 0x8
#define GDT_KERNEL_DATA_OFFSET 0x10
namespace GDT
{
typedef struct {
uint16_t limit_low;
uint16_t base_low;
uint8_t base_mid;
uint8_t access_flags;
uint8_t flags_limit_high;
uint8_t base_high;
} PACKED entry_t;
typedef struct {
uint16_t limit; /* sizeof(GDT) - 1 */
entry_t *ptr; /* Address of GDT */
} PACKED descriptor_t;
extern "C" void _GDT_flush(descriptor_t *descriptor);
void initialize(void);
void load(void);
}
#endif
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