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Kernel/arch/i386/cpu/gdt.hpp
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Kernel/arch/i386/cpu/gdt.hpp
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/*
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This file is part of Fennix Kernel.
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Fennix Kernel is free software: you can redistribute it and/or
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modify it under the terms of the GNU General Public License as
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published by the Free Software Foundation, either version 3 of
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the License, or (at your option) any later version.
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Fennix Kernel is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with Fennix Kernel. If not, see <https://www.gnu.org/licenses/>.
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*/
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#ifndef __FENNIX_KERNEL_GDT_H__
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#define __FENNIX_KERNEL_GDT_H__
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#include <types.h>
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namespace GlobalDescriptorTable
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{
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struct TaskStateSegmentEntry
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{
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/* LOW */
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uint16_t Limit;
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uint16_t BaseLow;
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uint8_t BaseMiddle;
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union GlobalDescriptorTableAccess
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{
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struct
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{
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/** @brief Access bit.
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* @note The CPU sets this bit to 1 when the segment is accessed.
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*/
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uint8_t A : 1;
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/** @brief Readable bit for code segments, writable bit for data segments.
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* @details For code segments, this bit must be 1 for the segment to be readable.
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* @details For data segments, this bit must be 1 for the segment to be writable.
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*/
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uint8_t RW : 1;
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/** @brief Direction bit for data segments, conforming bit for code segments.
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* @details For data segments, this bit must be 1 for the segment to grow up (higher addresses).
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* @details For code segments, this bit must be 1 for code in the segment to be able to be executed from an equal or lower privilege level.
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*/
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uint8_t DC : 1;
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/** @brief Executable bit.
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* @details This bit must be 1 for code-segment descriptors.
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* @details This bit must be 0 for data-segment and system descriptors.
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*/
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uint8_t E : 1;
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/** @brief Descriptor type.
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* @details This bit must be 0 for system descriptors.
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* @details This bit must be 1 for code or data segment descriptor.
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*/
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uint8_t S : 1;
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/** @brief Descriptor privilege level.
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* @details This field determines the privilege level of the segment.
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* @details 0 = kernel mode, 3 = user mode.
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*/
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uint8_t DPL : 2;
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/** @brief Present bit.
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* @details This bit must be 1 for all valid descriptors.
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*/
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uint8_t P : 1;
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} __packed;
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uint8_t Raw : 8;
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} Access;
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uint8_t Granularity;
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uint8_t BaseHigh;
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/* HIGH */
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uint32_t BaseUpper;
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uint32_t Reserved;
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} __packed;
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struct TaskStateSegment
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{
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uint32_t Reserved0 __aligned(16);
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uint64_t StackPointer[3];
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uint64_t Reserved1;
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uint64_t InterruptStackTable[7];
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uint64_t Reserved2;
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uint16_t Reserved3;
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uint16_t IOMapBaseAddressOffset;
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} __packed;
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struct GlobalDescriptorTableEntry
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{
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/** @brief Limit 0:15 */
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uint16_t Limit0 : 16;
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/** @brief Low Base 0:15 */
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uint16_t BaseLow : 16;
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/** @brief Middle Base 16:23 */
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uint8_t BaseMiddle : 8;
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/** @brief Access */
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union GlobalDescriptorTableAccess
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{
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struct
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{
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/** @brief Access bit.
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* @note The CPU sets this bit to 1 when the segment is accessed.
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*/
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uint8_t A : 1;
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/** @brief Readable bit for code segments, writable bit for data segments.
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* @details For code segments, this bit must be 1 for the segment to be readable.
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* @details For data segments, this bit must be 1 for the segment to be writable.
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*/
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uint8_t RW : 1;
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/** @brief Direction bit for data segments, conforming bit for code segments.
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* @details For data segments, this bit must be 1 for the segment to grow up (higher addresses).
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* @details For code segments, this bit must be 1 for code in the segment to be able to be executed from an equal or lower privilege level.
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*/
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uint8_t DC : 1;
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/** @brief Executable bit.
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* @details This bit must be 1 for code-segment descriptors.
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* @details This bit must be 0 for data-segment and system descriptors.
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*/
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uint8_t E : 1;
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/** @brief Descriptor type.
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* @details This bit must be 0 for system descriptors.
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* @details This bit must be 1 for code or data segment descriptor.
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*/
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uint8_t S : 1;
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/** @brief Descriptor privilege level.
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* @details This field determines the privilege level of the segment.
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* @details 0 = kernel mode, 3 = user mode.
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*/
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uint8_t DPL : 2;
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/** @brief Present bit.
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* @details This bit must be 1 for all valid descriptors.
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*/
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uint8_t P : 1;
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} __packed;
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uint8_t Raw : 8;
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} Access;
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// /** @brief Limit 16:19 */
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// uint16_t Limit1 : 4;
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/** @brief Flags */
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union GlobalDescriptorTableFlags
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{
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struct
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{
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uint8_t Reserved : 4; /* FIXME: Without this, the kernel crashes. */
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/** @brief Available bit.
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* @details This bit is available for use by system software.
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*/
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uint8_t AVL : 1;
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/** @brief Long mode.
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* @details If the long mode bit is clear, the segment is in 32-bit protected mode.
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* @details If the long mode bit is set, the segment is in 64-bit long mode.
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*/
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uint8_t L : 1;
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/** @brief Size flag.
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* @details If the size bit is clear, the segment is in 16-bit protected mode.
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* @details If the size bit is set, the segment is in 32-bit protected mode.
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*/
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uint8_t DB : 1;
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/** @brief Granularity bit.
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* @details If the granularity bit is clear, the segment limit is in 1 B blocks.
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* @details If the granularity bit is set, the segment limit is in 4 KiB blocks.
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*/
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uint8_t G : 1;
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} __packed;
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uint8_t Raw : 8;
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} Flags;
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/** @brief High Base 24:31 */
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uint8_t BaseHigh : 8;
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} __packed;
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struct GlobalDescriptorTableEntries
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{
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GlobalDescriptorTableEntry Null;
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GlobalDescriptorTableEntry Code;
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GlobalDescriptorTableEntry Data;
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GlobalDescriptorTableEntry UserData;
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GlobalDescriptorTableEntry UserCode;
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TaskStateSegmentEntry TaskStateSegment;
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} __packed;
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struct GlobalDescriptorTableDescriptor
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{
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/** @brief GDT entries length */
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uint16_t Length;
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/** @brief GDT entries address */
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GlobalDescriptorTableEntries *Entries;
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} __packed;
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extern void *CPUStackPointer[];
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extern TaskStateSegment tss[];
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void Init(int Core);
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void SetKernelStack(void *Stack);
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void *GetKernelStack();
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}
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#define GDT_KERNEL_CODE offsetof(GlobalDescriptorTable::GlobalDescriptorTableEntries, Code)
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#define GDT_KERNEL_DATA offsetof(GlobalDescriptorTable::GlobalDescriptorTableEntries, Data)
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#define GDT_USER_CODE (offsetof(GlobalDescriptorTable::GlobalDescriptorTableEntries, UserCode) | 3)
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#define GDT_USER_DATA (offsetof(GlobalDescriptorTable::GlobalDescriptorTableEntries, UserData) | 3)
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#define GDT_TSS (offsetof(GlobalDescriptorTable::GlobalDescriptorTableEntries, TaskStateSegment) | 3)
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#endif // !__FENNIX_KERNEL_GDT_H__
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