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SECTION .text ; cannot use .data
struc GDTEntry
.limitl resw 1
.basel resw 1
.basem resb 1
.attribute resb 1
.flags__limith resb 1
.baseh resb 1
endstruc
gdt_attr:
.present equ 1 << 7
.ring1 equ 1 << 5
.ring2 equ 1 << 6
.ring3 equ 1 << 5 | 1 << 6
.user equ 1 << 4
;user
.code equ 1 << 3
; code
.conforming equ 1 << 2
.readable equ 1 << 1
; data
.expand_down equ 1 << 2
.writable equ 1 << 1
.accessed equ 1 << 0
;system
; legacy
.tssAvailabe16 equ 0x1
.ldt equ 0x2
.tssBusy16 equ 0x3
.call16 equ 0x4
.task equ 0x5
.interrupt16 equ 0x6
.trap16 equ 0x7
.tssAvailabe32 equ 0x9
.tssBusy32 equ 0xB
.call32 equ 0xC
.interrupt32 equ 0xE
.trap32 equ 0xF
; long mode
.ldt32 equ 0x2
.tssAvailabe64 equ 0x9
.tssBusy64 equ 0xB
.call64 equ 0xC
.interrupt64 equ 0xE
.trap64 equ 0xF
gdt_flag:
.granularity equ 1 << 7
.available equ 1 << 4
;user
.default_operand_size equ 1 << 6
; code
.long_mode equ 1 << 5
; data
.reserved equ 1 << 5
gdtr:
dw gdt.end + 1 ; size
dd gdt ; offset
gdt:
.null equ $ - gdt
dq 0
.lm64_code equ $ - gdt
istruc GDTEntry
at GDTEntry.limitl, dw 0
at GDTEntry.basel, dw 0
at GDTEntry.basem, db 0
at GDTEntry.attribute, db gdt_attr.present | gdt_attr.user | gdt_attr.code
at GDTEntry.flags__limith, db gdt_flag.long_mode
at GDTEntry.baseh, db 0
iend
.lm64_data equ $ - gdt
istruc GDTEntry
at GDTEntry.limitl, dw 0
at GDTEntry.basel, dw 0
at GDTEntry.basem, db 0
; AMD System Programming Manual states that the writeable bit is ignored in long mode, but ss can not be set to this descriptor without it
at GDTEntry.attribute, db gdt_attr.present | gdt_attr.user | gdt_attr.writable
at GDTEntry.flags__limith, db 0
at GDTEntry.baseh, db 0
iend
.pm32_code equ $ - gdt
istruc GDTEntry
at GDTEntry.limitl, dw 0xFFFF
at GDTEntry.basel, dw 0
at GDTEntry.basem, db 0
at GDTEntry.attribute, db gdt_attr.present | gdt_attr.user | gdt_attr.code | gdt_attr.readable
at GDTEntry.flags__limith, db 0xF | gdt_flag.granularity | gdt_flag.default_operand_size
at GDTEntry.baseh, db 0
iend
.pm32_data equ $ - gdt
istruc GDTEntry
at GDTEntry.limitl, dw 0xFFFF
at GDTEntry.basel, dw 0
at GDTEntry.basem, db 0
at GDTEntry.attribute, db gdt_attr.present | gdt_attr.user | gdt_attr.writable
at GDTEntry.flags__limith, db 0xF | gdt_flag.granularity | gdt_flag.default_operand_size
at GDTEntry.baseh, db 0
iend
.pm16_code equ $ - gdt
istruc GDTEntry
at GDTEntry.limitl, dw 0xFFFF
at GDTEntry.basel, dw 0
at GDTEntry.basem, db 0
at GDTEntry.attribute, db gdt_attr.present | gdt_attr.user | gdt_attr.code | gdt_attr.readable
at GDTEntry.flags__limith, db 0xF
at GDTEntry.baseh, db 0
iend
.pm16_data equ $ - gdt
istruc GDTEntry
at GDTEntry.limitl, dw 0xFFFF
at GDTEntry.basel, dw 0
at GDTEntry.basem, db 0
at GDTEntry.attribute, db gdt_attr.present | gdt_attr.user | gdt_attr.writable
at GDTEntry.flags__limith, db 0xF
at GDTEntry.baseh, db 0
iend
.end equ $ - gdt