isolinux.asm

linux内核

		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
		mov si,trysbm_msg
		call writemsg
		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,SECTOR_SHIFT-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:StackPtr]
		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
noinfotable_msg	db 'No boot info table, assuming single session disk...', CR, LF, 0
noinfoinspec_msg db 'Spec packet missing LBA information, trying to wing it...', CR, LF, 0
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
nothing_msg:	db 'Failed to locate CD-ROM device; boot failed.', CR, LF
trysbm_msg	db 'See http://syslinux.zytor.com/sbm for more information.', CR, LF, 0
diskerr_msg:	db 'Disk error ', 0
oncall_str:	db ', AX = ',0
ondrive_str:	db ', drive ', 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

		alignb 4, db 0
StackPtr	dw StackBuf, 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 "init.inc"
%include "cpuinit.inc"

;
; 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.
;

;
; Now, we need to sniff out the actual filesystem data structures.
; mkisofs gave us a pointer to the primary volume descriptor
; (which will be at 16 only for a single-session disk!); from the PVD
; we should be able to find the rest of what we need to know.
; 
get_fs_structures:
		mov eax,[bi_pvd]
		mov bx,trackbuf
		call getonesec

		mov eax,[trackbuf+156+2]
		mov [RootDir+dir_lba],eax
		mov [CurDir+dir_lba],eax
%ifdef DEBUG_MESSAGES
		mov si,dbg_rootdir_msg
		call writemsg
		call writehex8
		call crlf
%endif
		mov eax,[trackbuf+156+10]
		mov [RootDir+dir_len],eax		
		mov [CurDir+dir_len],eax
		add eax,SECTOR_SIZE-1
		shr eax,SECTOR_SHIFT
		mov [RootDir+dir_clust],eax
		mov [CurDir+dir_clust],eax

		; Look for an isolinux directory, and if found,
		; make it the current directory instead of the root
		; directory.
		mov di,boot_dir			; Search for /boot/isolinux
		mov al,02h
		call searchdir_iso
		jnz .found_dir
		mov di,isolinux_dir
		mov al,02h			; Search for /isolinux
		call searchdir_iso
		jz .no_isolinux_dir
.found_dir:
		mov [CurDir+dir_len],eax
		mov eax,[si+file_left]
		mov [CurDir+dir_clust],eax
		xor eax,eax			; Free this file pointer entry
		xchg eax,[si+file_sector]
		mov [CurDir+dir_lba],eax
%ifdef DEBUG_MESSAGES
		push si
		mov si,dbg_isodir_msg
		call writemsg
		pop si
		call writehex8
		call crlf
%endif
.no_isolinux_dir:

;
; Locate the configuration file
;
load_config:
%ifdef DEBUG_MESSAGES
		mov si,dbg_config_msg
		call writemsg
%endif

		mov di,isolinux_cfg
		call open
		jz no_config_file		; Not found or empty

%ifdef DEBUG_MESSAGES
		mov si,dbg_configok_msg
		call writemsg
%endif

;
; Now we have the config file open.  Parse the config file and
; run the user interface.
;
%include "ui.inc"

;
; Linux kernel loading code is common.
;
%include "runkernel.inc"

;
; COMBOOT-loading code
;
%include "comboot.inc"
%include "com32.inc"
%include "cmdline.inc"

;
; Boot sector loading code
;
%include "bootsect.inc"

;
; Enable disk emulation.  The kind of disk we emulate is dependent on the size of
; the file: 1200K, 1440K or 2880K floppy, otherwise harddisk.
;
is_disk_image:
		TRACER CR
		TRACER LF
		TRACER 'D'
		TRACER ':'

		shl edx,16
		mov dx,ax			; Set EDX <- file size
		mov di,img_table
		mov cx,img_table_count
		mov eax,[si+file_sector]	; Starting LBA of file
		mov [dsp_lba],eax		; Location of file
		mov byte [dsp_drive], 0		; 00h floppy, 80h hard disk
.search_table:
		TRACER 't'
		mov eax,[di+4]
		cmp edx,[di]
		je .type_found
		add di,8
		loop .search_table

		; Hard disk image.  Need to examine the partition table
		; in order to deduce the C/H/S geometry.  Sigh.
.hard_disk_image:
		TRACER 'h'
		cmp edx,512
		jb .bad_image

		mov bx,trackbuf
		mov cx,1			; Load 1 sector
		call getfssec
		
		cmp word [trackbuf+510],0aa55h	; Boot signature
		jne .bad_image		; Image not bootable

		mov cx,4			; 4 partition entries
		mov di,trackbuf+446		; Start of partition table

		xor ax,ax			; Highest sector(al) head(ah)

.part_scan:
		cmp byte [di+4], 0
		jz .part_loop
		lea si,[di+1]
		call .hs_check
		add si,byte 4
		call .hs_check
.part_loop:
		add di,byte 16
		loop .part_scan
		
		push eax			; H/S
		push edx			; File size
		mov bl,ah
		xor bh,bh
		inc bx				; # of heads in BX
		xor ah,ah			; # of sectors in AX
		cwde				; EAX[31:16] <- 0
		mul bx
		shl eax,9			; Convert to bytes
		; Now eax contains the number of bytes per cylinder
		pop ebx				; File size
		xor edx,edx
		div ebx
		and edx,edx
		jz .no_remainder
		inc eax				; Fractional cylinder...
		; Now (e)ax contains the number of cylinders
.no_remainder:	cmp eax,1024
		jna .ok_cyl
		mov ax,1024			; Max possible #
.ok_cyl:	dec ax				; Convert to max cylinder no
		pop ebx				; S(bl) H(bh)
		shl ah,6
		or bl,ah
		xchg ax,bx
		shl eax,16
		mov ah,bl
		mov al,4			; Hard disk boot
		mov byte [dsp_drive], 80h	; Drive 80h = hard disk

.type_found:
		TRACER 'T'
		mov bl,[sp_media]
		and bl,0F0h			; Copy controller info bits
		or al,bl
		mov [dsp_media],al		; Emulation type
		shr eax,8
		mov [dsp_chs],eax		; C/H/S geometry
		mov ax,[sp_devspec]		; Copy device spec
		mov [dsp_devspec],ax
		mov al,[sp_controller]		; Copy controller index
		mov [dsp_controller],al

		TRACER 'V'
		call vgaclearmode		; Reset video

		mov ax,4C00h			; Enable emulation and boot
		mov si,dspec_packet