isolinux.asm

Windows上的精简Linux系统

award_loop:	push 	di			; save DI
		mov 	si,award_string		; scan for award_string
		mov	cx,7			; length of award_string = 7dw
		repz 	cmpsw			; compare
		pop 	di			; restore DI
		jcxz 	award_found		; jmp if found
		inc 	di			; not found, inc di
		jno	award_loop		; 
						;
award_failed:	pop	es			; No, not this way :-((
award_fail2:					;
						;
%ifdef DEBUG_MESSAGES				;
						;
		mov	si,award_not_fail	; display failure ...
		call	writemsg		;
%endif						;
		mov	eax,[award_oldint13]	; restore the original int
		or	eax,eax			; 13 vector if there is one
		jz	spec_query_failed	; and try other workarounds
		mov	[13h*4],eax		;
		jmp	spec_query_failed	;
						;
award_found:	mov	eax,[es:di+0eh]		; load possible int 13 addr
		pop	es			; restore ES
						;
		cmp	eax,[award_oldint13]	; give up if this is the
		jz	award_failed		; active int 13 vector,
		mov	[13h*4],eax		; otherwise change 0:13h*4
						;
						;
%ifdef DEBUG_MESSAGES				;
						;
		push	eax			; display message and 
		mov	si,award_not_new	; new vector address
		call	writemsg		;
		pop	eax			;
		call	writehex8		;
		mov	si,award_not_crlf	;
		call	writestr		;
%endif						;
		mov 	ax,4B01h		; try to read the spec packet
		mov 	dl,[DriveNo]		; now ... it should not fail
		mov 	si,spec_packet		; any longer
		int 	13h			; 
		jc	award_fail2		;
						;
%ifdef DEBUG_MESSAGES				;
						;
		mov	si,award_not_succ	; display our SUCCESS
		call	writemsg		;
%endif						;
		jmp	found_drive		; and leave error recovery code
						;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; End of BrokenAwardHack ----            10-nov-2002 [e-mail]
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;


		; INT 13h, AX=4B01h, DL=<passed in value> failed.
		; Try to scan the entire 80h-FFh from the end.

spec_query_failed:

		; some code moved to BrokenAwardHack

		mov dl,0FFh
.test_loop:	pusha
		mov ax,4B01h
		mov si,spec_packet
		mov byte [si],13		; Size of buffer
		int 13h
		popa
		jc .still_broken

		mov si,maybe_msg
		call writemsg
		mov al,dl
		call writehex2
		call crlf

		cmp byte [sp_drive],dl
		jne .maybe_broken

		; Okay, good enough...
		mov si,alright_msg
		call writemsg
		mov [DriveNo],dl
.found_drive:	jmp found_drive

		; Award BIOS 4.51 apparently passes garbage in sp_drive,
		; but if this was the drive number originally passed in
		; DL then consider it "good enough"
.maybe_broken:
		cmp byte [DriveNo],dl
		je .found_drive

.still_broken:	dec dx
		cmp dl, 80h
		jnb .test_loop

		; No spec packet anywhere.  Some particularly pathetic
		; BIOSes apparently don't even implement function
		; 4B01h, so we can't query a spec packet no matter
		; what.  If we got a drive number in DL, then try to
		; use it, and if it works, then well...
		mov dl,[DriveNo]
		cmp dl,81h			; Should be 81-FF at least
		jb fatal_error			; If not, it's hopeless

		; Write a warning to indicate we're on *very* thin ice now
		mov si,nospec_msg
		call writemsg
		mov al,dl
		call writehex2
		call crlf
		jmp .found_drive		; Pray that this works...

fatal_error:
		mov si,nothing_msg
		call writemsg

.norge:		jmp short .norge

		; Information message (DS:SI) output
		; Prefix with "isolinux: "
		;
writemsg:	push ax
		push si
		mov si,isolinux_str
		call writestr
		pop si
		call writestr
		pop ax				
		ret

;
; Write a character to the screen.  There is a more "sophisticated"
; version of this in the subsequent code, so we patch the pointer
; when appropriate.
;

writechr:
		jmp near writechr_simple	; 3-byte jump

writechr_simple:
		pushfd
		pushad
		mov ah,0Eh
		xor bx,bx
		int 10h
		popad
		popfd
		ret

;
; Get one sector.  Convenience entry point.
;
getonesec:
		mov bp,1
		; Fall through to getlinsec

;
; Get linear sectors - EBIOS LBA addressing, 2048-byte sectors.
;
; Note that we can't always do this as a single request, because at least
; Phoenix BIOSes has a 127-sector limit.  To be on the safe side, stick
; to 32 sectors (64K) per request.
;
; Input:
;	EAX	- Linear sector number
;	ES:BX	- Target buffer
;	BP	- Sector count
;
getlinsec:
		mov si,dapa			; Load up the DAPA
		mov [si+4],bx
		mov bx,es
		mov [si+6],bx
		mov [si+8],eax
.loop:
		push bp				; Sectors left
		cmp bp,[MaxTransfer]
		jbe .bp_ok
		mov bp,[MaxTransfer]
.bp_ok:
		mov [si+2],bp
		push si
		mov dl,[DriveNo]
		mov ah,42h			; Extended Read
		call xint13
		pop si
		pop bp
		movzx eax,word [si+2]		; Sectors we read
		add [si+8],eax			; Advance sector pointer
		sub bp,ax			; Sectors left
		shl ax,SECTORSIZE_LG2-4		; 2048-byte sectors -> segment
		add [si+6],ax			; Advance buffer pointer
		and bp,bp
		jnz .loop
		mov eax,[si+8]			; Next sector
		ret

		; INT 13h with retry
xint13:		mov byte [RetryCount],retry_count
.try:		pushad
		int 13h
		jc .error
		add sp,byte 8*4			; Clean up stack
		ret
.error:
		mov [DiskError],ah		; Save error code
		popad
		mov [DiskSys],ax		; Save system call number
		dec byte [RetryCount]
		jz .real_error
		push ax
		mov al,[RetryCount]
		mov ah,[dapa+2]			; Sector transfer count
		cmp al,2			; Only 2 attempts left
		ja .nodanger
		mov ah,1			; Drop transfer size to 1
		jmp short .setsize
.nodanger:
		cmp al,retry_count-2
		ja .again			; First time, just try again
		shr ah,1			; Otherwise, try to reduce
		adc ah,0			; the max transfer size, but not to 0
.setsize:
		mov [MaxTransfer],ah
		mov [dapa+2],ah
.again:
		pop ax
		jmp .try

.real_error:	mov si,diskerr_msg
		call writemsg
		mov al,[DiskError]
		call writehex2
		mov si,oncall_str
		call writestr
		mov ax,[DiskSys]
		call writehex4
		mov si,ondrive_str
		call writestr
		mov al,dl
		call writehex2
		call crlf
		; Fall through to kaboom

;
; kaboom: write a message and bail out.  Wait for a user keypress,
;	  then do a hard reboot.
;
kaboom:
		lss sp,[cs:Stack]
		mov ax,cs
		mov ds,ax
		mov es,ax
		mov fs,ax
		mov gs,ax
		sti
		mov si,err_bootfailed
		call cwritestr
		call getchar
		cli
		mov word [BIOS_magic],0	; Cold reboot
		jmp 0F000h:0FFF0h	; Reset vector address

; -----------------------------------------------------------------------------
;  Common modules needed in the first sector
; -----------------------------------------------------------------------------

%include "writestr.inc"		; String output
writestr	equ cwritestr
%include "writehex.inc"		; Hexadecimal output

; -----------------------------------------------------------------------------
; Data that needs to be in the first sector
; -----------------------------------------------------------------------------

syslinux_banner	db CR, LF, 'ISOLINUX ', version_str, ' ', date, ' ', 0
copyright_str   db ' Copyright (C) 1994-', year, ' H. Peter Anvin'
		db CR, LF, 0
isolinux_str	db 'isolinux: ', 0
%ifdef DEBUG_MESSAGES
startup_msg:	db 'Starting up, DL = ', 0
spec_ok_msg:	db 'Loaded spec packet OK, drive = ', 0
secsize_msg:	db 'Sector size appears to be ', 0
offset_msg:	db 'Loading main image from LBA = ', 0
size_msg:	db 'Sectors to load = ', 0
loaded_msg:	db 'Loaded boot image, verifying...', CR, LF, 0
verify_msg:	db 'Image checksum verified.', CR, LF, 0
allread_msg	db 'Main image read, jumping to main code...', CR, LF, 0
%endif
spec_err_msg:	db 'Loading spec packet failed, trying to wing it...', CR, LF, 0
maybe_msg:	db 'Found something at drive = ', 0
alright_msg:	db 'Looks like it might be right, continuing...', CR, LF, 0
nospec_msg	db 'Extremely broken BIOS detected, last ditch attempt with drive = ', 0
nosecsize_msg:	db 'Failed to get sector size, assuming 0800', CR, LF, 0
diskerr_msg:	db 'Disk error ', 0
oncall_str:	db ', AX = ',0
ondrive_str:	db ', drive ', 0
nothing_msg:	db 'Failed to locate CD-ROM device; boot failed.', CR, LF, 0
checkerr_msg:	db 'Image checksum error, sorry...', CR, LF, 0

err_bootfailed	db CR, LF, 'Boot failed: press a key to retry...'
bailmsg		equ err_bootfailed
crlf_msg	db CR, LF
null_msg	db 0

;
; El Torito spec packet
;
		align 8, db 0
spec_packet:	db 13h				; Size of packet
sp_media:	db 0				; Media type
sp_drive:	db 0				; Drive number
sp_controller:	db 0				; Controller index
sp_lba:		dd 0				; LBA for emulated disk image
sp_devspec:	dw 0				; IDE/SCSI information
sp_buffer:	dw 0				; User-provided buffer
sp_loadseg:	dw 0				; Load segment
sp_sectors:	dw 0				; Sector count
sp_chs:		db 0,0,0			; Simulated CHS geometry
sp_dummy:	db 0				; Scratch, safe to overwrite

;
; Spec packet for disk image emulation
;
		align 8, db 0
dspec_packet:	db 13h				; Size of packet
dsp_media:	db 0				; Media type
dsp_drive:	db 0				; Drive number
dsp_controller:	db 0				; Controller index
dsp_lba:	dd 0				; LBA for emulated disk image
dsp_devspec:	dw 0				; IDE/SCSI information
dsp_buffer:	dw 0				; User-provided buffer
dsp_loadseg:	dw 0				; Load segment
dsp_sectors:	dw 1				; Sector count
dsp_chs:	db 0,0,0			; Simulated CHS geometry
dsp_dummy:	db 0				; Scratch, safe to overwrite

;
; EBIOS drive parameter packet
;
		align 8, db 0
drive_params:	dw 30				; Buffer size
dp_flags:	dw 0				; Information flags
dp_cyl:		dd 0				; Physical cylinders
dp_head:	dd 0				; Physical heads
dp_sec:		dd 0				; Physical sectors/track
dp_totalsec:	dd 0,0				; Total sectors
dp_secsize:	dw 0				; Bytes per sector
dp_dpte:	dd 0				; Device Parameter Table
dp_dpi_key:	dw 0				; 0BEDDh if rest valid
dp_dpi_len:	db 0				; DPI len
		db 0
		dw 0
dp_bus:		times 4 db 0			; Host bus type
dp_interface:	times 8 db 0			; Interface type
db_i_path:	dd 0,0				; Interface path
db_d_path:	dd 0,0				; Device path
		db 0
db_dpi_csum:	db 0				; Checksum for DPI info

;
; EBIOS disk address packet
;
		align 8, db 0
dapa:		dw 16				; Packet size
.count:		dw 0				; Block count
.off:		dw 0				; Offset of buffer
.seg:		dw 0				; Segment of buffer
.lba:		dd 0				; LBA (LSW)
		dd 0				; LBA (MSW)

		alignb 4, db 0
Stack		dw _start, 0			; SS:SP for stack reset
MaxTransfer	dw 32				; Max sectors per transfer

rl_checkpt	equ $				; Must be <= 800h

rl_checkpt_off	equ ($-$$)
%ifndef DEPEND
%if rl_checkpt_off > 0x800
%error "Sector 0 overflow"
%endif
%endif

; ----------------------------------------------------------------------------
;  End of code and data that have to be in the first sector
; ----------------------------------------------------------------------------

all_read:
;
; Initialize screen (if we're using one)
;
		; Now set up screen parameters
		call adjust_screen

		; Wipe the F-key area
		mov al,NULLFILE
		mov di,FKeyName
		mov cx,10*(1 << FILENAME_MAX_LG2)
		rep stosb

		; Patch the writechr routine to point to the full code
		mov word [writechr+1], writechr_full-(writechr+3)

; Tell the user we got this far...
%ifndef DEBUG_MESSAGES			; Gets messy with debugging on
		mov si,copyright_str
		call writestr
%endif

; Test tracers
		TRACER 'T'
		TRACER '>'

;
; Common initialization code
;
%include "cpuinit.inc"

;
; Clear Files structures
;
		mov di,Files
		mov cx,(MAX_OPEN*open_file_t_size)/4
		xor eax,eax
		rep stosd

;
; Now we're all set to start with our *real* business.	First load the
; configuration file (if any) and parse it.
;
; In previous versions I avoided using 32-bit registers because of a
; rumour some BIOSes clobbered the upper half of 32-bit registers at
; random.  I figure, though, that if there are any of those still left
; they probably won't be trying to install Linux on them...
;
; The code is still ripe with 16-bitisms, though.  Not worth the hassle
; to take'm out.  In fact, we may want to put them back if we're going
; to boot ELKS at some point.
;
		mov si,linuxauto_cmd		; Default command: "linux auto"
		mov di,default_cmd
                mov cx,linuxauto_len
		rep movsb

		mov di,KbdMap			; Default keymap 1:1