memdisk.asm

linux内核

; -*- fundamental -*- (asm-mode sucks)
; $Id$
; ****************************************************************************
;
;  memdisk.asm
;
;  A program to emulate an INT 13h disk BIOS from a "disk" in extended
;  memory.
;
;   Copyright (C) 2001-2005  H. Peter Anvin
;
;  This program is free software; you can redistribute it and/or modify
;  it under the terms of the GNU General Public License as published by
;  the Free Software Foundation, Inc., 53 Temple Place Ste 330,
;  Boston MA 02111-1307, USA; either version 2 of the License, or
;  (at your option) any later version; incorporated herein by reference.
; 
; ****************************************************************************

%ifndef DEPEND
%include	"../version.gen"
%endif

; %define DEBUG_TRACERS			; Uncomment to get debugging tracers

%ifdef WITH_EDD
%define EDD 1
%else
%define EDD 0
%endif

%ifdef DEBUG_TRACERS

%macro TRACER	1
	call debug_tracer
	db %1
%endmacro

%else	; DEBUG_TRACERS

%macro	TRACER	1
%endmacro

%endif	; DEBUG_TRACERS

%define CONFIG_READONLY	0x01
%define CONFIG_RAW	0x02
%define CONFIG_BIGRAW	0x08		; MUST be 8!

		org 0h

%define SECTORSIZE_LG2	9		; log2(sector size)
%define	SECTORSIZE	(1 << SECTORSIZE_LG2)

		; Parameter registers definition; this is the definition
		; of the stack frame.
%define		P_DS		word [bp+34]
%define		P_ES		word [bp+32]
%define		P_EAX		dword [bp+28]
%define		P_HAX		word [bp+30]
%define		P_AX		word [bp+28]
%define		P_AL		byte [bp+28]
%define		P_AH		byte [bp+29]
%define		P_ECX		dword [bp+24]
%define		P_HCX		word [bp+26]
%define		P_CX		word [bp+24]
%define		P_CL		byte [bp+24]
%define		P_CH		byte [bp+25]
%define		P_EDX		dword [bp+20]
%define		P_HDX		word [bp+22]
%define		P_DX		word [bp+20]
%define		P_DL		byte [bp+20]
%define		P_DH		byte [bp+21]
%define		P_EBX		dword [bp+16]
%define		P_HBX		word [bp+18]
%define		P_HBXL		byte [bp+18]
%define		P_BX		word [bp+16]
%define		P_BL		byte [bp+16]
%define		P_BH		byte [bp+17]
%define		P_EBP		dword [bp+8]
%define		P_BP		word [bp+8]
%define		P_ESI		dword [bp+4]
%define		P_SI		word [bp+4]
%define		P_EDI		dword [bp]
%define		P_DI		word [bp]

		section .text
		; These pointers are used by the installer and
		; must be first in the binary
Pointers:	dw Int13Start
		dw Int15Start
		dw PatchArea
		dw TotalSize

Int13Start:
		; Swap stack
		mov [cs:Stack],esp
		mov [cs:SavedAX],ax
		mov ax,ss
		mov [cs:Stack+4],ax
		mov ax,cs
		mov ss,ax
		mov sp,[cs:MyStack]

		; See if DL points to our class of device (FD, HD)
		push dx
		push dx
		xor dl,[cs:DriveNo]
		pop dx
		js .nomatch		; If SF=0, we have a class match here
		jz .our_drive		; If ZF=1, we have an exact match
		cmp dl,[cs:DriveNo]
		jb .nomatch		; Drive < Our drive
		dec dl			; Drive > Our drive, adjust drive #
.nomatch:
		mov ax,[cs:SavedAX]
		pushf
		call far [cs:OldInt13]
		pushf
		push bp
		mov bp,sp
		cmp byte [cs:SavedAX+1],08h
		je .norestoredl
		cmp byte [cs:SavedAX+1],15h
		jne .restoredl
		test byte [bp+4],80h	; Hard disk?
		jnz .norestoredl
.restoredl:
		mov dl,[bp+4]
.norestoredl:
		push ax
		push ebx
		push ds
		mov ax,[bp+2]		; Flags
		lds ebx,[cs:Stack]
		mov [bx+4],al		; Arithmetric flags
		pop ds
		pop ebx
		pop ax
		pop bp
		lss esp,[cs:Stack]
		iret

.our_drive:
		; Set up standard entry frame
		push ds
		push es
		mov ds,ax
		mov es,ax
		mov ax,[SavedAX]
		pushad
		mov bp,sp		; Point BP to the entry stack frame
		TRACER 'F'
		; Note: AH == P_AH here
		cmp ah,Int13FuncsMax
		jae Invalid_jump
		xor al,al		; AL = 0 is standard entry condition
		mov di,ax
		shr di,7		; Convert AH to an offset in DI
		call [Int13Funcs+di]

Done:		; Standard routine for return
		mov P_AX,ax
DoneWeird:
		TRACER 'D'
		xor bx,bx
		mov es,bx
		mov bx,[StatusPtr]
		mov [es:bx],ah		; Save status
		and ah,ah

		lds ebx,[Stack]
		; This sets the low byte (the arithmetric flags) of the
		; FLAGS on stack to either 00h (no flags) or 01h (CF)
		; depending on if AH was zero or not.
		setnz [bx+4]		; Set CF iff error
		popad
		pop es
		pop ds
		lss esp,[cs:Stack]
		iret

Reset:
		; Reset affects multiple drives, so we need to pass it on
		TRACER 'R'
		xor ax,ax		; Bottom of memory
		mov es,ax
		test dl,dl		; Always pass it on if we are resetting HD
		js .hard_disk		; Bit 7 set
		; Some BIOSes get very unhappy if we pass a reset floppy
		; command to them and don't actually have any floppies.
		; This is a bug, but we have to deal with it nontheless.
		; Therefore, if we are the *ONLY* floppy drive, and the
		; user didn't request HD reset, then just drop the command.
		; BIOS equipment byte, top two bits + 1 == total # of floppies
		test byte [es:0x410],0C0h
		jz success
		jmp .pass_on		; ... otherwise pass it to the BIOS
.hard_disk:
		; ... same thing for hard disks, sigh ...
		cmp byte [es:0x475],1	; BIOS variable for number of hard disks
		jbe success

.pass_on:
		pop ax			; Drop return address
		popad			; Restore all registers
		pop es
		pop ds
		lss esp,[cs:Stack]	; Restore the stack
		and dl,80h		; Clear all but the type bit
		jmp far [cs:OldInt13]


Invalid:
		pop dx			; Drop return address
Invalid_jump:
		TRACER 'I'
		mov ah,01h		; Unsupported function
		jmp short Done

GetDriveType:
		test byte [DriveNo],80h
		mov bl,02h		; Type 02h = floppy with changeline
		jz .floppy
		; Hard disks only...
		inc bx			; Type = 03h
		mov dx,[DiskSize]	; Return the disk size in sectors
		mov P_DX,dx
		mov cx,[DiskSize+2]
		mov P_CX,cx
.floppy:
		mov P_AH,bl		; 02h floppy, 03h hard disk
		pop ax			; Drop return address
		xor ax,ax		; Success...
		jmp DoneWeird		; But don't stick it into P_AX

GetStatus:
		xor ax,ax
		mov es,ax
		mov bx,[StatusPtr]
		mov ah,[bx]		; Copy last status
		ret

ReadMult:
		TRACER 'm'
Read:
		TRACER 'R'
		call setup_regs
do_copy:
		TRACER '<'
		call bcopy
		TRACER '>'
		movzx ax,P_AL		; AH = 0, AL = transfer count
		ret

WriteMult:
		TRACER 'M'
Write:
		TRACER 'W'
		test byte [ConfigFlags],CONFIG_READONLY
		jnz .readonly
		call setup_regs
		xchg esi,edi		; Opposite direction of a Read!
		jmp short do_copy
.readonly:	mov ah,03h		; Write protected medium
		ret

		; Verify integrity; just bounds-check
Seek:
Verify:
		call setup_regs		; Returns error if appropriate
		; And fall through to success

CheckIfReady:				; These are always-successful noop functions
Recalibrate:
InitWithParms:
DetectChange:
SetMode:
success:
		xor ax,ax		; Always successful
		ret

GetParms:
		TRACER 'G'
		mov dl,[DriveCnt]	; Cached data
		mov P_DL,dl
		test byte [DriveNo],80h
		jnz .hd
		mov P_DI,DPT
		mov P_ES,cs
		mov bl,[DriveType]
		mov P_BL,bl
.hd:
		mov ax,[Cylinders]
		dec ax			; We report the highest #, not the count
		xchg al,ah
		shl al,6
		or al,[Sectors]
		mov P_CX,ax
		mov ax,[Heads]
		dec ax
		mov P_DH,al

		;
		; Is this MEMDISK installation check?
		;
		cmp P_HAX,'ME'
		jne .notic
		cmp P_HCX,'MD'
		jne .notic
		cmp P_HDX,'IS'
		jne .notic
		cmp P_HBX,'K?'
		jne .notic

		; MEMDISK installation check...
		mov P_HAX,'!M'
		mov P_HCX,'EM'
		mov P_HDX,'DI'
		mov P_HBX,'SK'
		mov P_ES,cs
		mov P_DI,MemDisk_Info

.notic:
		xor ax,ax
		ret
;
; EDD functions -- only if enabled
;
%if EDD
EDDPresence:
		TRACER 'E'
		TRACER 'c'

		cmp P_BX,55AAh
		jne Invalid
		mov P_BX,0AA55h		; EDD signature
		mov P_AX,02100h		; EDD 1.1
		mov P_CX,0001h		; Fixed disk access subset
		pop ax			; Drop return address
		xor ax,ax		; Success
		jmp DoneWeird		; Success, but AH != 0, sigh...

EDDRead:
		TRACER 'E'
		TRACER 'r'

		call edd_setup_regs
		call bcopy
		xor ax,ax
		ret

EDDWrite:
		TRACER 'E'
		TRACER 'w'

		call edd_setup_regs
		xchg esi,edi
		call bcopy
		xor ax,ax
		ret

EDDVerify:
EDDSeek:
		call edd_setup_regs	; Just bounds checking
		xor ax,ax
		ret

EDDGetParms:
		TRACER 'E'
		TRACER 'p'

		mov es,P_DS
		mov di,P_SI
		mov cx,30		; Length of our DPT
		cmp [es:di],cx
		jae .oksize

		mov cx,26
		cmp [es:di],cx
		jb .overrun


.oksize:
		mov [si],cx

		; This should be done by the installer...
		mov eax,[DiskSize]
		mov [si+16],eax

		mov si,EDD_DPT
		rep movsb

		xor ax,ax
		ret

.overrun:
		mov ax,0100h
		ret
%endif ; EDD

		; Set up registers as for a "Read", and compares against disk size.
		; WARNING: This fails immediately, even if we can transfer some
		; sectors.  This isn't really the correct behaviour.
setup_regs:

		; Convert a CHS address in P_CX/P_DH into an LBA in eax
		; CH = cyl[7:0]
		; CL[0:5] = sector (1-based)  CL[7:6] = cyl[9:8]
		; DH = head
		movzx ecx,P_CX
		movzx ebx,cl		; Sector number
		and bl,3Fh
		dec ebx			; Sector number is 1-based
		cmp bx,[Sectors]
		jae .overrun
		movzx edi,P_DH		; Head number
		movzx eax,word [Heads]
		cmp di,ax
		jae .overrun
		shr cl,6
		xchg cl,ch		; Now (E)CX <- cylinder number
		mul ecx			; eax <- Heads*cyl# (edx <- 0)
		add eax,edi
		mul dword [Sectors]
		add eax,ebx
		; Now eax = LBA, edx = 0

		;
		; setup_regs continues...
		;
		; Note: edi[31:16] and ecx[31:16] = 0 already
		mov di,P_BX		; Get linear address of target buffer
		mov cx,P_ES
		shl ecx,4
		add edi,ecx		; EDI = address to fetch to
		movzx ecx,P_AL		; Sector count
		mov esi,eax
		add eax,ecx		; LBA of final sector + 1
		shl esi,SECTORSIZE_LG2	; LBA -> byte offset
		add esi,[DiskBuf]	; Get address in high memory
		cmp eax,[DiskSize]	; Check the high mark against limit
		ja .overrun
		shl ecx,SECTORSIZE_LG2-2 ; Convert count to dwords
		ret

.overrun:	pop ax			; Drop setup_regs return address
		mov ax,0200h		; Missing address mark
		ret			; Return to Done

		; Set up registers as for an EDD Read, and compares against disk size.
%if EDD
edd_setup_regs:
		push es
		mov si,P_SI		; DS:SI -> DAPA
		mov es,P_DS

		mov dx,[es:si]
		cmp dx,16
		jb .baddapa

		cmp dword [es:si+4],-1
		je .linear_address

		movzx esi,word [es:si+4]	; Offset