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44 lines
1.1 KiB
44 lines
1.1 KiB
3 years ago
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; GDT
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gdt_start:
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gdt_null: ; NULL descriptor
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dd 0x0 ; 4-bytes of
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dd 0x0 ; 0x0 (0) = NULL
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gdt_code: ; Code SD
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; Range: 0x0 - 0xfffff
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; Flags1: 1001b (present:2 privilege:descriptor type)
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; Type: 1010b (code:conforming:readable:accessed)
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; Flags2: 1100b (granularity:32bit default:64bit seg:AVL)
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3 years ago
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dw 0xffff ; Limit (bits 0-15)
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dw 0x0 ; Base (bits 0-15)
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db 0x0 ; Base (bits 16-23)
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db 10011010b ; Flags1 : Type
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db 11001111b ; Flags2 : Limit (16-19)
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db 0x0 ; Base (bits 24-31)
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3 years ago
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3 years ago
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gdt_data: ; Data SD
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; Same flags as gdt_code but different type flags
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; Type: 0010b (code:expand dowm:writable:accessed)
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3 years ago
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dw 0xffff ; Limit (bits 0-15)
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dw 0x0 ; Base (bits 0-15)
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db 0x0 ; Base (bits 16-23)
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3 years ago
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db 10010010b ; Flags1 : Type
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db 11001111b ; Flags2 : Limit (16-19)
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3 years ago
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db 0x0 ; Base (bits 24-31)
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3 years ago
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gdt_end: ; Mark the end so we can get the delta-memory (size of GDT)
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; GDT descriptor
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gdt_descriptor:
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3 years ago
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dw gdt_end - gdt_start - 1 ; GDT size
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dd gdt_start ; GDT pointer
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3 years ago
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; Lazy constants
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GDT_CODE_SEG equ gdt_code - gdt_start
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GDT_DATA_SEG equ gdt_data - gdt_start
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