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Code: Select all

; vim: ft=nasm noet ts=4 sw=4 sts=0

[bits 32]

[global bit16_init]
[global bit16_int]

; copy the 16bit codes into 0000:7c00h
;;;; this works correctly.
bit16_init:
	mov		edi, 7c00h
	mov		esi, do16_int
	mov		ecx, do16_int_len
	repnz	movsb
	ret

bit16_int:
	cli
	jmp		18h:7c00h		; 3 * 8h = 4th descriptor in gdt = code 16-bit
	ret




[bits 16]

do16_int:
	mov		eax, cr0
	xor		al, 1
	mov		cr0, eax

	jmp		dword 0:.real - do16_int + 7c00h  ;; no `org' directive can be used in elf

.real:
	mov		ax, cs
	mov		ds, ax
	mov		es, ax
	mov		ss, ax
	mov		sp, 7c00h - 1

	; disable A20
	in		al, 92h
	xor		al, 10b
	out		92h, al

	sti

	mov		ax, 0b800h
	mov		gs, ax

	mov		al, 'A'
	mov		ah, 01110000b
	mov		[gs:0], ax

;;;; things work fine till here

; read key, just for testing the bios call
	xor		ah, ah
	int		16h 
;;;; both qemu and bochs crashed before reaching here
	mov		[gs:0], ax

	jmp		$

do16_int_len	equ		$-do16_int

Code: Select all

;*********************************************************************
;*                       Setup real mode                             *
;*********************************************************************
macro	hardware_realmode
{
		USE32
		call			near hardware_realmodefunc
		USE16
}
		USE32
hardware_realmodefunc:
		cli
		;get return address
		pop			ebp
		;save stack pointer
		mov			dword [hardware_protstack], esp
		jmp			CODE_BOOT:.back		;load 16 bit mode segment into cs
		USE16
.back:
		mov			eax, CR0
		and			al, 0FEh				;switching back to real mode
		mov			CR0, eax
		xor			ax, ax
		mov			ds, ax				;load registers 2nd turn
		mov			es, ax
		mov			ss, ax
		jmp			0:.back2
.back2:
		mov			sp, word [hardware_realstack]
		sti
		jmp			bp

;*********************************************************************
;*   Call a hardware api (BIOS call) to read a sector in prot mode   *
;*********************************************************************
;edx:eax sector, edi:pointer
macro	hardware_readsector
{
		call			hardware_readsectorfunc
}
		USE32
hardware_readsectorfunc:
		push			esi
		push			edi
		;load sector somewhere in low memory (first 64k)
		add			eax, dword [bda_bootsec]
		adc			edx, dword [bda_bootsec+4]
		mov			dword [lbapacket.sect0], eax
		mov			dword [lbapacket.sect1], edx
		hardware_realmode
		mov			ah, byte 42h
		mov			dl, byte [bda_bootdev]
		mov			si, lbapacket
		int			13h
		hardware_protmode
		pop			edi
		push		      edi
		;and copy to addr where it wanted to be (maybe in high memory)
		mov			esi, dword [lbapacket.addr0]
		mov			ecx, 128
		repnz		 movsd
		pop			edi
		pop			esi
		ret
		USE16

Code: Select all

include "desc.inc"
include "misc.inc"

MBH_MAGIC equ 1BADB002h
MBH_FLAGS equ 10000h
MBH_LOAD_ADDR equ 100000h

MBF_BOOTDEV equ 2

struc MBINFO
{
  .flags dd ?
  .basemem dd ?
  .highmem dd ?
  .bootdev dd ?
  .paramstr dd ?
  .modcount dd ?
  .modlist dd ?
}

virtual at 0
MBINFO MBINFO
end virtual

	org 8000h

	xor bx,bx
	cli
	mov ss,bx
	mov sp,$$
	sti
	mov ds,bx
	jmp 0:@f

	align 4
header:
	dd MBH_MAGIC
	dd MBH_FLAGS
	dd -MBH_MAGIC-MBH_FLAGS
	dd MBH_LOAD_ADDR-$$+header
	dd MBH_LOAD_ADDR
	dd MBH_LOAD_ADDR-$$+FS_IMAGE
	dd MBH_LOAD_ADDR-$$+FS_IMAGE
	dd MBH_LOAD_ADDR-$$+entry32
entry16:
	mov ax,DATA16
	mov ds,ax
	mov es,ax
	mov fs,ax
	mov gs,ax
	mov ss,ax

	lidt [IDTR]

	mov eax,cr0
	and al,0FEh
	mov cr0,eax

	jmp 0:$$
@@:
; mov ax,3
; int 10h

	call putstr
	db 13,10,"Hello World!",32,0
@@:
	mov bx,7
	mov ah,0Eh
	push si
	int 10h
putstr:
	pop si
	mov al,[si]
	inc si
	and al,al
	jg short @b
@@:
	hlt
	jmp @b

	use32
entry32:
; sub eax,2BADB002h
; jnz $

	xor edx,edx
	test byte [ebx+MBINFO.flags],MBF_BOOTDEV
	jz @f
	mov dx,word [ebx+MBINFO.bootdev+2]
	xchg dl,dh
	inc dh
@@:
	cld
	mov esi,MBH_LOAD_ADDR
	mov edi,$$
	mov ecx,(FS_IMAGE-$$)/4
	rep movsd

	lgdt [GDTR]

	jmp CODE16:entry16

	align 2
GDTR:
	dw GDT_SIZE-1
	dd GDT
IDTR:
	dw 3FFh
	dd 0

	align 8
GDT:
	dq 0

	set CODE16,$-GDT
	desc 0,0FFFFh,DF_CODE+DF_DUALACTION

	set DATA16,$-GDT
	desc 0,0FFFFh,DF_DATA+DF_DUALACTION

	set GDT_SIZE,$-GDT

	rb 3FFh - ($+1) and 3FFh
	dw 0AA55h

	label FS_IMAGE