42 lines
1.5 KiB
C
42 lines
1.5 KiB
C
#pragma once
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#include <stdint.h>
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#define GDT_ADDRESS 0x00000800
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#define GDT_SIZE 7
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// https://wiki.osdev.org/Global_Descriptor_Table#GDTR
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struct gdt_descriptor {
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uint16_t size;
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uint32_t base;
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} __attribute__((packed));
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void init_gdt();
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#define GDT_FLAG_64BIT_MODE 0b0010
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#define GDT_FLAG_32BIT_MODE 0b0100
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#define GDT_FLAG_PAGE_MODE 0b1000
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#define GDT_FLAG_BYTE_MODE 0b1000
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#define GDT_ACCESS_P_VALID 0b10000000
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#define GDT_ACCESS_DPL_KERNEL_MODE 0b00000000
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#define GDT_ACCESS_DPL_USER_MODE 0b01100000
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#define GDT_ACCESS_S_CODE_OR_DATA 0b00010000
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#define GDT_ACCESS_S_SYSTEM_SEGMENT 0b00010000
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#define GDT_ACCESS_E_EXECUTABLE 0b00001000
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#define GDT_ACCESS_E_NOT_EXECUTABLE 0b00000000
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#define GDT_ACCESS_DC_CONFORM 0b00000100 // TODO UNDERSTAND THIS BIT
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#define GDT_ACCESS_DC_NOT_CONFORM 0b00000000
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#define GDT_ACCESS_RW_READABLE_FOR_CODE_WRITABLE_FOR_DATA 0b00000010
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#define GDT_ACCESS_A_ACCESSED 0b00000001
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#define GDT_ACCESS_A_NOT_ACCESSED 0b00000000
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extern uint8_t gdt_entries[GDT_SIZE * 8];
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#define GDT_OFFSET_KERNEL_CODE 0x08
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#define GDT_OFFSET_KERNEL_DATA 0x10
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#define GDT_OFFSET_KERNEL_STACK 0x18
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#define GDT_OFFSET_USER_CODE 0x20
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#define GDT_OFFSET_USER_DATA 0x28
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#define GDT_OFFSET_USER_STACK 0x30
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