You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
36 lines
1.0 KiB
36 lines
1.0 KiB
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
|