; -*- fundamental -*- (asm-mode sucks); $Id: ldlinux.asm,v 1.13 1998/02/06 00:19:21 hpa Exp $; ****************************************************************************;;  ldlinux.asm;;  A program to boot Linux kernels off an MS-DOS formatted floppy disk.	 This;  functionality is good to have for installation floppies, where it may;  be hard to find a functional Linux system to run LILO off.;;  This program allows manipulation of the disk to take place entirely;  from MS-LOSS, and can be especially useful in conjunction with the;  umsdos filesystem.;;  This file is loaded in stages; first the boot sector at offset 7C00h,;  then the first sector (cluster, really, but we can only assume 1 sector);  of LDLINUX.SYS at 7E00h and finally the remainder of LDLINUX.SYS at 8000h.;;   Copyright (C) 1994-1998  H. Peter Anvin;;  This program is free software; you can redistribute it and/or modify;  it under the terms of the GNU General Public License as published by;  the Free Software Foundation, Inc., 675 Mass Ave, Cambridge MA 02139,;  USA; either version 2 of the License, or (at your option) any later;  version; incorporated herein by reference.; ; ****************************************************************************;; Some semi-configurable constants... change on your own risk;max_cmd_len	equ 2047		; Must be odd; 2047 is the kernel limitretry_count	equ 6			; How patient are we with the disk?;; Should be updated with every release to avoid bootsector/SYS file mismatch;%define	version_str	VERSION		; Must be 4 characters long!%define date		DATE_STR	; Defined from the Makefile%define	year		'1998';; Debgging stuff;; %define debug 1			; Uncomment to enable debugging;; ID for SYSLINUX (reported to kernel);syslinux_id	equ 031h		; SYSLINUX (3) version 1.x (1);; Segments used by Linux;real_mode_seg	equ 9000h		struc real_mode_seg_t		resb 20h-($-$$)		; org 20hkern_cmd_magic	resw 1			; Magic # for command linekern_cmd_offset resw 1			; Offset for kernel command line		resb 497-($-$$)		; org 497dbs_setupsecs	resb 1			; Sectors for setup code (0 -> 4)bs_rootflags	resw 1			; Root readonly flagbs_syssize	resw 1bs_swapdev	resw 1			; Swap device (obsolete)bs_ramsize	resw 1			; Ramdisk flags, formerly ramdisk sizebs_vidmode	resw 1			; Video modebs_rootdev	resw 1			; Root devicebs_bootsign	resw 1			; Boot sector signature (0AA55h)su_jump		resb 1			; 0EBhsu_jump2	resb 1su_header	resd 1			; New setup code: headersu_version	resw 1			; See linux/arch/i386/boot/setup.Ssu_switch	resw 1su_setupseg	resw 1su_startsys	resw 1su_kver		resw 1			; Kernel version pointersu_loader	resb 1			; Loader IDsu_loadflags	resb 1			; Load high flagsu_movesize	resw 1su_code32start	resd 1			; Start of code loaded highsu_ramdiskat	resd 1			; Start of initial ramdisksu_ramdisklen	equ $			; Length of initial ramdisksu_ramdisklen1	resw 1su_ramdisklen2	resw 1su_bsklugeoffs	resw 1su_bsklugeseg	resw 1su_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		endstrucsetup_seg	equ 9020h		struc setup_seg_t		org 0h			; as 9020:0000, not 9000:0200setup_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 highCAN_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 vkernelvk_vname:	resb 11			; Virtual name **MUST BE FIRST!**		resb 3			; Alignment fillervk_rname:	resb 11			; Real name		resb 1			; Fillervk_appendlen:	resw 1vk_append:	resb max_cmd_len+1	; Command linevk_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'emxfer_buf_seg	equ 7000h		; Bounce buffer for I/O to high memfat_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 tablefdctab		equ $fdctab1		resw 1fdctab2		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 0484hBIOS_vidrows    resb 1                    ; Number of screen rows		absolute 0600htrackbuf	equ $			; Track buffer goes heretrackbufsize	equ 16384		; Safe size of track buffer;		trackbuf ends at 4600h                absolute 6000h          ; Here we keep our BSS stuffStackBuf	equ $			; Start the stack here (grow down)VKernelBuf:	resb vk_size		; "Current" vkernel		alignb 4AppendBuf       resb max_cmd_len+1	; append=FKeyName	resb 10*16		; File names for F-key helpNumBuf		resb 16			; Buffer to load numberNumBufEnd	equ NumBuf+15		; Pointer to last byte in NumBufRootDir		equ $			; Location of root directoryRootDir1	resw 1RootDir2	resw 1DataArea	equ $			; Location of data areaDataArea1	resw 1DataArea2	resw 1FBytes		equ $			; Used by open/getcFBytes1		resw 1FBytes2		resw 1RootDirSize	resw 1			; Root dir size in sectorsDirScanCtr	resw 1			; Used while searching directoryDirBlocksLeft	resw 1			; DittoEndofDirSec	resw 1			; = trackbuf+bsBytesPerSec-31RunLinClust	resw 1			; Cluster # for LDLINUX.SYSClustSize	resw 1			; Bytes/clusterSecPerClust	resw 1			; Same as bsSecPerClust, but a wordBufSafe		resw 1			; Clusters we can load into trackbufBufSafeSec	resw 1			; = how many sectors?BufSafeBytes	resw 1			; = how many bytes?EndOfGetCBuf	resw 1			; = getcbuf+BufSafeBytesHighMemSize	resw 1			; High memory (K)KernelClust	resw 1			; Kernel size in clustersKernelK		resw 1			; Kernel size in kilobytesInitRDClust	resw 1			; Ramdisk size in clustersInitRDat	resw 1			; Load address (x256)ClustPerMoby	resw 1			; Clusters per 64KFClust		resw 1			; Number of clusters in open/getc fileFNextClust	resw 1			; Pointer to next cluster in d:oFPtr		resw 1			; Pointer to next char in bufferCmdOptPtr       resw 1			; Pointer to first option on cmd lineKernelCNameLen  resw 1			; Length of unmangled kernel nameInitRDCNameLen  resw 1			; Length of unmangled initrd nameNextCharJump    resw 1			; Routine to interpret next print charHiLoadAddr      resw 1			; Address pointer for high load loopSetupSecs	resw 1			; Number of setup sectorsTextAttrBX      equ $TextAttribute   resb 1			; Text attribute for message fileTextPage        resb 1			; Active display pageCursorDX        equ $CursorCol       resb 1			; Cursor column for message fileCursorRow       resb 1			; Cursor row for message fileScreenSize      equ $VidCols         resb 1			; Columns on screen-1VidRows         resb 1			; Rows on screen-1RetryCount      resb 1			; Used for disk access retriesKbdFlags	resb 1			; Check for keyboard escapesMNameBuf        resb 11            	; Generic mangled file name bufferKernelName      resb 11		        ; Mangled name for kernelInitRD          resb 11                 ; initrd= mangled nameKernelCName     resb 13                 ; Unmangled kernel nameInitRDCName     resb 13            	; Unmangled initrd name		section .text                org 7C00hbootsec		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 1bsSecPerClust	zb 1bsResSectors	zw 1bsFATs		zb 1bsRootDirEnts	zw 1bsSectors	zw 1bsMedia		zb 1bsFATsecs	zw 1bsSecPerTrack	zw 1bsHeads		zw 1bsHiddenSecs	equ $bsHidden1	zw 1bsHidden2	zw 1bsHugeSectors	equ $bsHugeSec1	zw 1bsHugeSec2	zw 1bsDriveNumber	zb 1bsReserved1	zb 1bsBootSignature zb 1			; 29h if the following fields existbsVolumeID	zd 1bsVolumeLabel	zb 11bsFileSysType	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 startstart:		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