114 lines
3.2 KiB
NASM
114 lines
3.2 KiB
NASM
SECTION .text ; cannot use .data
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struc GDTEntry ; spell:disable-line
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.limitl resw 1
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.basel resw 1
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.basem resb 1
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.attribute resb 1
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.flags__limith resb 1
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.baseh resb 1
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endstruc
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gdt_attr:
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.present equ 1 << 7
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.ring1 equ 1 << 5
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.ring2 equ 1 << 6
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.ring3 equ 1 << 5 | 1 << 6
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.user equ 1 << 4
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;user
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.code equ 1 << 3
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; code
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.conforming equ 1 << 2
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.readable equ 1 << 1
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; data
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.expand_down equ 1 << 2
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.writable equ 1 << 1
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.accessed equ 1 << 0
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;system
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; legacy
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.tssAvailabe16 equ 0x1 ; spell:disable-line
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.ldt equ 0x2
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.tssBusy16 equ 0x3
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.call16 equ 0x4
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.task equ 0x5
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.interrupt16 equ 0x6
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.trap16 equ 0x7
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.tssAvailabe32 equ 0x9 ; spell:disable-line
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.tssBusy32 equ 0xB
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.call32 equ 0xC
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.interrupt32 equ 0xE
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.trap32 equ 0xF
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; long mode
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.ldt32 equ 0x2
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.tssAvailabe64 equ 0x9 ; spell:disable-line
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.tssBusy64 equ 0xB
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.call64 equ 0xC
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.interrupt64 equ 0xE
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.trap64 equ 0xF
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gdt_flag:
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.granularity equ 1 << 7
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.available equ 1 << 4
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;user
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.default_operand_size equ 1 << 6
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; code
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.long_mode equ 1 << 5
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; data
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.reserved equ 1 << 5
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gdtr:
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dw gdt.end + 1 ; size
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dq gdt ; offset
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gdt:
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.null equ $ - gdt
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dq 0
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; All GTD addresses are multiples of 8,
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; and thus end in three zero bits.
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;
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; Also note that all segments overlap.
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; We only need the GDT for a short time,
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; so we use the simplest possible layout.
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.pm32_code equ $ - gdt
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istruc GDTEntry
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at GDTEntry.limitl, dw 0xFFFF
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at GDTEntry.basel, dw 0
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at GDTEntry.basem, db 0
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at GDTEntry.attribute, db gdt_attr.present | gdt_attr.user | gdt_attr.code | gdt_attr.readable
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at GDTEntry.flags__limith, db 0xF | gdt_flag.granularity | gdt_flag.default_operand_size
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at GDTEntry.baseh, db 0
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iend
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.pm32_data equ $ - gdt
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istruc GDTEntry
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at GDTEntry.limitl, dw 0xFFFF
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at GDTEntry.basel, dw 0
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at GDTEntry.basem, db 0
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at GDTEntry.attribute, db gdt_attr.present | gdt_attr.user | gdt_attr.writable
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at GDTEntry.flags__limith, db 0xF | gdt_flag.granularity | gdt_flag.default_operand_size
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at GDTEntry.baseh, db 0
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iend
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.pm16_code equ $ - gdt
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istruc GDTEntry
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at GDTEntry.limitl, dw 0xFFFF
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at GDTEntry.basel, dw 0
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at GDTEntry.basem, db 0
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at GDTEntry.attribute, db gdt_attr.present | gdt_attr.user | gdt_attr.code | gdt_attr.readable
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at GDTEntry.flags__limith, db 0xF
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at GDTEntry.baseh, db 0
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iend
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.pm16_data equ $ - gdt
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istruc GDTEntry
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at GDTEntry.limitl, dw 0xFFFF
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at GDTEntry.basel, dw 0
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at GDTEntry.basem, db 0
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at GDTEntry.attribute, db gdt_attr.present | gdt_attr.user | gdt_attr.writable
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at GDTEntry.flags__limith, db 0xF
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at GDTEntry.baseh, db 0
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iend
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.end equ $ - gdt
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