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- ; GDT
- gdt_start:
- gdt_null:
- dd 0x0 ; the mandatory null-descriptor
- dd 0x0
- gdt_code: ; code segment of descriptor
- dw 0xFFFF ; Limit (bits 0-15)
- dw 0x0 ; Base (bits 0-15)
- db 0x0 ; Base (bits 16-23
- ; 1st flags: (present)1, (privilege)00, (descriptor type)1 -> 1001b
- ; type flags: (code)1, (conforming)0, (readable)1, (accessed)0 -> 1010b
- ; 2nd flags: (granularity)1, (32-bit default)1, (64-bit seg)0, (AVL)0 -> 1100b
- db 10011010b ; 1st flags and type flags
- db 11001111b ; 2nd flags and Limit (bits 16-19)
- db 0x0 ; Base (bits 24-31)
- gdt_data:
- ; type flags: (code)0, (expand down)0, (writable)1, (accessed)0 -> 0010b
- dw 0xFFFF ; Limit (bits 0-15)
- dw 0x0 ; Base (bits 0-15)
- db 0x0 ; Base (bits 16-23)
- db 10010010b ; 1st flags and type flags
- db 11001111b ; 2nd flags and Limit (bits 16-19)
- db 0x0 ; Base (bits 24-31)
- gdt_end: ; for calculating size of the gdt
- gdt_descriptor:
- dw gdt_end - gdt_start - 1 ; size of our GDT, always decrement true size by one
- dd gdt_start ; start address of our GDT
- ;;;
- ; Constants used for GDT segment offsets
- GDT_CODE_SEG: equ gdt_code - gdt_start
- GDT_DATA_SEG: equ gdt_data - gdt_start
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