system/boot at master · Glam0rgan/system · GitHub

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%include "pm.inc"
org 07c00h
	jmp LABEL_BEGIN
[SECTION .gdt]
LABEL_GDT: 			Descriptor       0,                0,	0
LABEL_DESC_CODE32:  Descriptor       0, SegCode32Len - 1,	DA_C + DA_32
LABEL_DESC_VIDEO:   Descriptor 0B8000h, 		 	   0ffffh,	DA_DRW
GdtLen equ $ - LABEL_GDT
GdtPtr dw GdtLen-1
	   dd 0
SelectorCode32 equ LABEL_DESC_CODE32	- LABEL_GDT
SelectorVideo equ LABEL_DESC_VIDEO	- LABEL_GDT
[SECTION .s16]
[BITS   16]
LABEL_BEGIN:
	mov ax,cs
	mov ds,ax
	mov es,ax
	mov ss,ax
	mov sp,0100h
	xor eax,eax
	mov ax,cs
	shl eax,4
	add eax,LABEL_SEG_CODE32
	mov word [LABEL_DESC_CODE32+2],ax
	shr eax,16
	mov byte [LABEL_DESC_CODE32+4],al
	mov byte [LABEL_DESC_CODE32+7],ah
	xor eax,eax
	mov ax,ds
	shl eax,4
	add eax,LABEL_GDT
	mov dword [GdtPtr+2],eax
	lgdt [GdtPtr]
	cli
	in al,92h
	or al,00000010b
	out 92h,al
	mov eax,cr0
	or eax,1
	mov cr0,eax
	jmp dword SelectorCode32:0
[SECTION .s32]
[BITS 32]
LABEL_SEG_CODE32:
		mov ax,SelectorVideo
		mov gs,ax
		mov edi,(80 * 11 + 79) * 2
		mov ah,0Ch
		mov al,'P'
		mov [gs:edi],ax
		jmp $
SegCode32Len equ $-LABEL_SEG_CODE32