ldlinux.asm

这是Linux环境下的bootsyslinux-1.31版本

; -*- fundamental -*- (asm-mode sucks)
; $Id: ldlinux.asm,v 1.13 1998/02/06 00:19:21 hpa Exp $
; ****************************************************************************
;
;  ldlinux.asm
;
;  A program to boot Linux kernels off an MS-DOS formatted floppy disk.	 This
;  functionality is good to have for installation floppies, where it may
;  be hard to find a functional Linux system to run LILO off.
;
;  This program allows manipulation of the disk to take place entirely
;  from MS-LOSS, and can be especially useful in conjunction with the
;  umsdos filesystem.
;
;  This file is loaded in stages; first the boot sector at offset 7C00h,
;  then the first sector (cluster, really, but we can only assume 1 sector)
;  of LDLINUX.SYS at 7E00h and finally the remainder of LDLINUX.SYS at 8000h.
;
;   Copyright (C) 1994-1998  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., 675 Mass Ave, Cambridge MA 02139,
;  USA; either version 2 of the License, or (at your option) any later
;  version; incorporated herein by reference.
; 
; ****************************************************************************

;
; Some semi-configurable constants... change on your own risk
;
max_cmd_len	equ 2047		; Must be odd; 2047 is the kernel limit
retry_count	equ 6			; How patient are we with the disk?

;
; Should be updated with every release to avoid bootsector/SYS file mismatch
;
%define	version_str	VERSION		; Must be 4 characters long!
%define date		DATE_STR	; Defined from the Makefile
%define	year		'1998'
;
; Debgging stuff
;
; %define debug 1			; Uncomment to enable debugging
;
; ID for SYSLINUX (reported to kernel)
;
syslinux_id	equ 031h		; SYSLINUX (3) version 1.x (1)
;
; Segments used by Linux
;
real_mode_seg	equ 9000h
		struc real_mode_seg_t
		resb 20h-($-$$)		; org 20h
kern_cmd_magic	resw 1			; Magic # for command line
kern_cmd_offset resw 1			; Offset for kernel command line
		resb 497-($-$$)		; org 497d
bs_setupsecs	resb 1			; Sectors for setup code (0 -> 4)
bs_rootflags	resw 1			; Root readonly flag
bs_syssize	resw 1
bs_swapdev	resw 1			; Swap device (obsolete)
bs_ramsize	resw 1			; Ramdisk flags, formerly ramdisk size
bs_vidmode	resw 1			; Video mode
bs_rootdev	resw 1			; Root device
bs_bootsign	resw 1			; Boot sector signature (0AA55h)
su_jump		resb 1			; 0EBh
su_jump2	resb 1
su_header	resd 1			; New setup code: header
su_version	resw 1			; See linux/arch/i386/boot/setup.S
su_switch	resw 1
su_setupseg	resw 1
su_startsys	resw 1
su_kver		resw 1			; Kernel version pointer
su_loader	resb 1			; Loader ID
su_loadflags	resb 1			; Load high flag
su_movesize	resw 1
su_code32start	resd 1			; Start of code loaded high
su_ramdiskat	resd 1			; Start of initial ramdisk
su_ramdisklen	equ $			; Length of initial ramdisk
su_ramdisklen1	resw 1
su_ramdisklen2	resw 1
su_bsklugeoffs	resw 1
su_bsklugeseg	resw 1
su_heapend	resw 1
		resb (8000h-12)-($-$$)	; Were bootsect.S puts it...
linux_stack	equ $
linux_fdctab	equ $
		resb 8000h-($-$$)
cmd_line_here	equ $			; Should be out of the way
		endstruc

setup_seg	equ 9020h
		struc setup_seg_t
		org 0h			; as 9020:0000, not 9000:0200
setup_entry	equ $
		endstruc

;
; Magic number of su_header field
;
HEADER_ID       equ 'HdrS'		; HdrS (in littleendian hex)
;
; Flags for the su_loadflags field
;
LOAD_HIGH	equ 01h			; Large kernel, load high
CAN_USE_HEAP    equ 80h                 ; Boot loader reports heap size
;
; The following structure is used for "virtual kernels"; i.e. LILO-style
; option labels.  The options we permit here are `kernel' and `append
; Since there is no room in the bottom 64K for up to 16 of these, we
; stick them at 8000:0000 and copy them down before we need them.
;
; Note: this structure can be added to, but must be less than 4K in size.
;
		struc vkernel
vk_vname:	resb 11			; Virtual name **MUST BE FIRST!**
		resb 3			; Alignment filler
vk_rname:	resb 11			; Real name
		resb 1			; Filler
vk_appendlen:	resw 1
vk_append:	resb max_cmd_len+1	; Command line
vk_size:	equ $
		endstruc
;
; Segment assignments in the bottom 640K
; 0000h - main code/data segment (and BIOS segment)
; 9000h - real_mode_seg
;
vk_seg          equ 8000h		; This is where we stick'em
xfer_buf_seg	equ 7000h		; Bounce buffer for I/O to high mem
fat_seg		equ 1000h		; 128K area for FAT (2x64K)

;
; For our convenience: define macros for jump-over-unconditinal jumps
;
%macro	jmpz	1
	jnz %%skip
	jmp %1
%%skip:
%endmacro

%macro	jmpnz	1
	jz %%skip
	jmp %1
%%skip:
%endmacro

%macro	jmpe	1
	jne %%skip
	jmp %1
%%skip:
%endmacro

%macro	jmpne	1
	je %%skip
	jmp %1
%%skip:
%endmacro

%macro	jmpc	1
	jnc %%skip
	jmp %1
%%skip:
%endmacro

%macro	jmpnc	1
	jc %%skip
	jmp %1
%%skip:
%endmacro

%macro	jmpb	1
	jnb %%skip
	jmp %1
%%skip:
%endmacro

%macro	jmpnb	1
	jb %%skip
	jmp %1
%%skip:
%endmacro

;
; Macros similar to res[bwd], but which works in the code segment (after
; section .text)
;
%macro	zb	1
	times %1 db 0
%endmacro

%macro	zw	1
	times %1 dw 0
%endmacro

%macro	zd	1
	times %1 dd 0
%endmacro

; ---------------------------------------------------------------------------
;   BEGIN THE BIOS/CODE/DATA SEGMENT
; ---------------------------------------------------------------------------
		absolute 4*1Eh		; In the interrupt table
fdctab		equ $
fdctab1		resw 1
fdctab2		resw 1

%ifdef debug
		org 0100h
..start:	
;
; Hook for debugger stuff.  This gets automatically removed when
; generating the real thing.
;
; Initialize the registers for debugger operation
;
		cli
		mov ax,cs
		mov ds,ax
		mov es,ax
		mov ss,ax
		mov sp,StackBuf
		sti
		cld
;
; Load the actual boot sector so we can copy the data block
;
		xor ax,ax		; Reset floppy
		xor dx,dx
		int 13h
		mov cx,6		; Retry count...
debug_tryloop:	push cx
		mov bx,trackbuf
		mov cx,0001h
		xor dx,dx
		mov ax,0201h
		int 13h
		pop cx
		jnc debug_okay
		loop debug_tryloop
		int 3			; Halt! (Breakpoint)
debug_okay:	mov si,trackbuf+0bh
		mov di,bsBytesPerSec
		mov cx,33h
		rep movsb
;
; Save bogus "BIOS floppy block" info to the stack in case we hit kaboom
;
		push si
		push si
		push si			; Writing to the trackbuf is harmless
;
; Copy the BIOS data area
;
                push ds
                xor ax,ax
                mov ds,ax
                mov si,0400h
                mov di,si
                mov cx,0100h
                rep movsw
                pop ds
;
;
; A NOP where we can breakpoint, then jump into the code *after*
; the segment register initialization section
;
		nop
		jmp debugentrypt
%endif

                absolute 0484h
BIOS_vidrows    resb 1                    ; Number of screen rows

		absolute 0600h
trackbuf	equ $			; Track buffer goes here
trackbufsize	equ 16384		; Safe size of track buffer
;		trackbuf ends at 4600h

                absolute 6000h          ; Here we keep our BSS stuff
StackBuf	equ $			; Start the stack here (grow down)
VKernelBuf:	resb vk_size		; "Current" vkernel
		alignb 4
AppendBuf       resb max_cmd_len+1	; append=
FKeyName	resb 10*16		; File names for F-key help
NumBuf		resb 16			; Buffer to load number
NumBufEnd	equ NumBuf+15		; Pointer to last byte in NumBuf
RootDir		equ $			; Location of root directory
RootDir1	resw 1
RootDir2	resw 1
DataArea	equ $			; Location of data area
DataArea1	resw 1
DataArea2	resw 1
FBytes		equ $			; Used by open/getc
FBytes1		resw 1
FBytes2		resw 1
RootDirSize	resw 1			; Root dir size in sectors
DirScanCtr	resw 1			; Used while searching directory
DirBlocksLeft	resw 1			; Ditto
EndofDirSec	resw 1			; = trackbuf+bsBytesPerSec-31
RunLinClust	resw 1			; Cluster # for LDLINUX.SYS
ClustSize	resw 1			; Bytes/cluster
SecPerClust	resw 1			; Same as bsSecPerClust, but a word
BufSafe		resw 1			; Clusters we can load into trackbuf
BufSafeSec	resw 1			; = how many sectors?
BufSafeBytes	resw 1			; = how many bytes?
EndOfGetCBuf	resw 1			; = getcbuf+BufSafeBytes
HighMemSize	resw 1			; High memory (K)
KernelClust	resw 1			; Kernel size in clusters
KernelK		resw 1			; Kernel size in kilobytes
InitRDClust	resw 1			; Ramdisk size in clusters
InitRDat	resw 1			; Load address (x256)
ClustPerMoby	resw 1			; Clusters per 64K
FClust		resw 1			; Number of clusters in open/getc file
FNextClust	resw 1			; Pointer to next cluster in d:o
FPtr		resw 1			; Pointer to next char in buffer
CmdOptPtr       resw 1			; Pointer to first option on cmd line
KernelCNameLen  resw 1			; Length of unmangled kernel name
InitRDCNameLen  resw 1			; Length of unmangled initrd name
NextCharJump    resw 1			; Routine to interpret next print char
HiLoadAddr      resw 1			; Address pointer for high load loop
SetupSecs	resw 1			; Number of setup sectors
TextAttrBX      equ $
TextAttribute   resb 1			; Text attribute for message file
TextPage        resb 1			; Active display page
CursorDX        equ $
CursorCol       resb 1			; Cursor column for message file
CursorRow       resb 1			; Cursor row for message file
ScreenSize      equ $
VidCols         resb 1			; Columns on screen-1
VidRows         resb 1			; Rows on screen-1
RetryCount      resb 1			; Used for disk access retries
KbdFlags	resb 1			; Check for keyboard escapes
MNameBuf        resb 11            	; Generic mangled file name buffer
KernelName      resb 11		        ; Mangled name for kernel
InitRD          resb 11                 ; initrd= mangled name
KernelCName     resb 13                 ; Unmangled kernel name
InitRDCName     resb 13            	; Unmangled initrd name

		section .text
                org 7C00h
bootsec		equ $
		jmp short start		; 2 bytes
		nop			; 1 byte
;
; "Superblock" follows -- it's in the boot sector, so it's already
; loaded and ready for us
;
bsOemName	db 'SYSLINUX'		; The SYS command sets this, so...
bsBytesPerSec	zw 1
bsSecPerClust	zb 1
bsResSectors	zw 1
bsFATs		zb 1
bsRootDirEnts	zw 1
bsSectors	zw 1
bsMedia		zb 1
bsFATsecs	zw 1
bsSecPerTrack	zw 1
bsHeads		zw 1
bsHiddenSecs	equ $
bsHidden1	zw 1
bsHidden2	zw 1
bsHugeSectors	equ $
bsHugeSec1	zw 1
bsHugeSec2	zw 1
bsDriveNumber	zb 1
bsReserved1	zb 1
bsBootSignature zb 1			; 29h if the following fields exist
bsVolumeID	zd 1
bsVolumeLabel	zb 11
bsFileSysType	zb 8			; Must be FAT12 for this version
;
; Note we don't check the constraints above now; we did that at install
; time (we hope!)
;

floppy_table	equ $			; No sense in wasting memory, overwrite start

start:
		cli			; No interrupts yet, please
		xor ax,ax
		mov es,ax
		mov ss,ax
		mov sp,StackBuf		; Just below BSS
;
; Now sautee the BIOS floppy info block to that it will support decent-
; size transfers; the floppy block is 11 bytes and is stored in the
; INT 1Eh vector (brilliant waste of resources, eh?)
;
; Of course, if BIOSes had been properly programmed, we wouldn't have
; had to waste precious boot sector space with this code.
;
		mov bx,fdctab
		lds si,[ss:bx]		; DS:SI -> original
		push ds			; Save on stack in case
		push si			; we have to bail
		push bx
		mov cx,6		; 12 bytes
		mov di,floppy_table
		push di
		cld
		rep movsw		; Faster to move words
		pop di
		mov ds,ax		; Now we can point DS to here, too
		mov cl,[bsSecPerTrack]  ; Patch the sector count
		mov [di+4],cl
;		 mov byte ptr [di+9],0Fh ; I have no clue what this does???
		mov [bx+2],ax		; Segment 0
		mov [bx],di		; offset floppy_block
;
; Ready to enable interrupts, captain
;
		sti
;
; Reset floppy system to load new parameter block
;
		xor dx,dx
		int 13h			; AH = 00h already
;
; Now we have to do some arithmetric to figure out where things are located.
; If Microsoft had had brains they would already have done this for us,
; and stored it in the superblock at format time, but here we go,
; wasting precious boot sector space again...
;
debugentrypt:
		mov al,[bsFATs]		; Number of FATs
		jmpc kaboom		; If the floppy init failed
					; (too far to be above the mov)
		cbw			; Clear AH (we WILL have < 128 FATs)
		mul word [bsFATsecs]	; Get the size of the FAT area
		add ax,[bsHidden1]	; Add hidden sectors
		adc dx,[bsHidden2]
		add ax,[bsResSectors]	; And reserved sectors (why two?)
		adc dx,byte 0

		mov [RootDir1],ax	; Location of root directory
		mov [RootDir2],dx
		mov [DataArea1],ax
		mov [DataArea2],dx
		push ax
		push dx

		mov ax,32		; Size of a directory entry
		mul word [bsRootDirEnts]
		mov bx,[bsBytesPerSec]
		add ax,bx		; Round up, not down
		dec ax