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%include "startup-common.asm"
startup_arch:
; load protected mode GDT and IDT
cli
lgdt [gdtr]
; set protected mode bit of cr0
mov eax, cr0
or eax, 1
mov cr0, eax
; far jump to load CS with 32 bit segment
jmp gdt.kernel_code:protected_mode
USE32
protected_mode:
; load all the other segments with 32 bit data segments
mov eax, gdt.kernel_data
mov ds, eax
mov es, eax
mov fs, eax
mov gs, eax
mov ss, eax
mov esp, 0x800000 - 128
; entry point
mov eax, [args.kernel_base]
call [eax + 0x18]
.halt:
cli
hlt
jmp .halt
gdtr:
dw gdt.end + 1 ; size
dd gdt ; offset
gdt:
.null equ $ - gdt
dq 0
.kernel_code equ $ - gdt
istruc GDTEntry
at GDTEntry.limitl, dw 0xFFFF
at GDTEntry.basel, dw 0
at GDTEntry.basem, db 0
at GDTEntry.attribute, db attrib.present | attrib.user | attrib.code | attrib.readable
at GDTEntry.flags__limith, db 0xFF | flags.granularity | flags.default_operand_size
at GDTEntry.baseh, db 0
iend
.kernel_data equ $ - gdt
istruc GDTEntry
at GDTEntry.limitl, dw 0xFFFF
at GDTEntry.basel, dw 0
at GDTEntry.basem, db 0
at GDTEntry.attribute, db attrib.present | attrib.user | attrib.writable
at GDTEntry.flags__limith, db 0xFF | flags.granularity | flags.default_operand_size
at GDTEntry.baseh, db 0
iend
.end equ $ - gdt