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- gdt_start: ; don't remove the labels, they're needed to compute sizes and jumps
- ; the GDT starts with a null 8-byte
- dd 0x0 ; 4 byte
- dd 0x0 ; 4 byte
- ; GDT for code segment. base = 0x00000000, length = 0xfffff
- ; for flags, refer to os-dev.pdf document, page 36
- gdt_code:
- dw 0xffff ; segment length, bits 0-15
- dw 0x0 ; segment base, bits 0-15
- db 0x0 ; segment base, bits 16-23
- db 10011010b ; flags (8 bits)
- db 11001111b ; flags (4 bits) + segment length, bits 16-19
- db 0x0 ; segment base, bits 24-31
- ; GDT for data segment. base and length identical to code segment
- ; some flags changed, again, refer to os-dev.pdf
- gdt_data:
- dw 0xffff
- dw 0x0
- db 0x0
- db 10010010b
- db 11001111b
- db 0x0
- gdt_end:
- ; GDT descriptor
- gdt_descriptor:
- dw gdt_end - gdt_start - 1 ; size (16 bit), always one less of its true size
- dd gdt_start ; address (32 bit)
- ; define some constants for later use
- CODE_SEG equ gdt_code - gdt_start
- DATA_SEG equ gdt_data - gdt_start
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