; -*- fundamental -*- (asm-mode sucks); $Id: syslinux.asm,v 1.4 1998/02/04 09:27:54 hpa Exp $; -----------------------------------------------------------------------;   ;   Copyright 1998 H. Peter Anvin - All Rights Reserved;;   This program is free software; you can redistribute it and/or modify;   it under the terms of the GNU General Public License as published by;   the Free Software Foundation, Inc., 675 Mass Ave, Cambridge MA 02139,;   USA; either version 2 of the License, or (at your option) any later;   version; incorporated herein by reference.;; -----------------------------------------------------------------------;; syslinux.asm;;	DOS installer for SYSLINUX;		absolute 0pspInt20:		resw 1pspNextParagraph:	resw 1			resb 1		; reservedpspDispatcher:		resb 5pspTerminateVector:	resd 1pspControlCVector:	resd 1pspCritErrorVector:	resd 1			resw 11		; reservedpspEnvironment:		resw 1			resw 23		; reservedpspFCB_1:		resb 16pspFCB_2:		resb 16			resd 1		; reservedpspCommandLen:		resb 1pspCommandArg:		resb 127		section .text		org 0100h_start:				; BUG: check DOS version;; Scan command line for a drive letter followed by a colon;		xor cx,cx		mov si,pspCommandArg		mov cl,[pspCommandLen]		cmdscan1:	jcxz bad_usage			; End of command line?		lodsb				; Load character		dec cx		cmp al,' '			; White space		jbe cmdscan1		or al,020h			; -> lower case		cmp al,'a'			; Check for letter		jb bad_usage		cmp al,'z'		ja bad_usage		sub al,'a'			; Convert to zero-based index		mov [DriveNo],al		; Save away drive index		section .bssDriveNo:	resb 1		section .text;; Got the leading letter, now the next character must be a colon;got_letter:	jcxz bad_usage		lodsb		dec cx		cmp al,':'		jne bad_usage;; Got the colon; the rest better be whitespace;got_colon:	jcxz got_cmdline		lodsb		dec cx		cmp al,' '		jbe got_colon;; We end up here if the command line doesn't parse;bad_usage:	mov dx,msg_unfair		jmp die		section .datamsg_unfair:	db 'Usage: syslinux <drive>:', 0Dh, 0Ah, '$'		section .text;; Parsed the command line OK.  Check that the drive parameters are acceptable;		struc DPBdpbDrive:	resb 1dpbUnit:	resb 1dpbSectorSize:	resw 1dpbClusterMask:	resb 1dpbClusterShift: resb 1dpbFirstFAT:	resw 1dpbFATCount:	resb 1dpbRootEntries:	resw 1dpbFirstSector:	resw 1dpbMaxCluster:	resw 1dpbFATSize:	resw 1dpbDirSector:	resw 1dpbDriverAddr:	resd 1dpbMedia:	resb 1dpbFirstAccess:	resb 1dpbNextDPB:	resd 1dpbNextFree:	resw 1dpbFreeCnt:	resw 1		endstrucgot_cmdline:		mov dl,[DriveNo]		inc dl				; 1-based		mov bx,DPB		mov ah,32h		int 21h				; Get Drive Parameter Block				and al,al		jnz filesystem_error		cmp word [bx+dpbMaxCluster],4087 ; FAT16 not supported yet		ja fat16_error		cmp word [bx+dpbSectorSize],512	; Sector size = 512 required		jne sectorsize_error		cmp byte [bx+dpbClusterShift],5	; Max size = 16K = 2^5 sectors		jna read_bootsecthugeclust_error:		mov dx,msg_hugeclust_err		jmp diefilesystem_error:		mov dx,msg_filesystem_err		jmp diefat16_error:		mov dx,msg_fat16_err		jmp diesectorsize_error:		mov dx,msg_sectorsize_err		jmp die;; Good enough.  Now read the old boot sector and copy the superblock.;read_bootsect:		push cs				; Set DS == ES		pop ds		mov bx,SectorBuffer		mov al,[DriveNo]		mov cx,1			; One sector		xor dx,dx			; Absolute sector 0		int 25h				; DOS absolute disk read		add sp,byte 2			; Remove flags from stack		jc disk_read_error		mov si,SectorBuffer+11		; Offset of superblock		mov di,BootSector+11		mov cx,51			; Superblock = 51 bytes		rep movsb			; Copy the superblock;; Writing LDLINUX.SYS;		; 0. Set the correct filename		mov al,[DriveNo]		add [ldlinux_sys_str],al		; 1. If the file exists, strip its attributes and delete		xor cx,cx			; Clear attributes		mov dx,ldlinux_sys_str		mov ax,4301h			; Set file attributes		int 21h		mov dx,ldlinux_sys_str		mov ah,41h			; Delete file		int 21h		section .dataldlinux_sys_str: db 'A:\LDLINUX.SYS', 0		section .text		; 2. Create LDLINUX.SYS and write data to it		mov dx,ldlinux_sys_str		xor cx,cx			; Normal file		mov ah,3Ch			; Create file		int 21h		jc file_write_error		mov [FileHandle],ax		mov bx,ax		mov cx,ldlinux_size		mov dx,LDLinuxSYS		mov ah,40h			; Write data		int 21h		jc file_write_error		cmp ax,ldlinux_size		jne file_write_error		mov bx,[FileHandle]		mov ah,3Eh			; Close file		int 21h		section .bssFileHandle:	resw 1		section .text		; 3. Set the readonly flag on LDLINUX.SYS		mov dx,ldlinux_sys_str		mov cx,1			; Read only		mov ax,4301h			; Set attributes		int 21h;; Writing boot sector;		mov al,[DriveNo]		mov bx,BootSector		mov cx,1			; One sector		xor dx,dx			; Absolute sector 0		int 26h				; DOS absolute disk write		add sp,byte 2			; Remove flags		jc disk_write_errorall_done:	mov ax,4C00h			; Exit good status		int 21h;; Error routine jump;disk_read_error:		mov dx,msg_read_err		jmp short diedisk_write_error:file_write_error:		mov dx,msg_write_errdie:		push cs		pop ds		push dx		mov dx,msg_error		mov ah,09h		int 21h		pop dx		mov ah,09h			; Write string		int 21h		mov ax,4C01h			; Exit error status		int 21h		section .datamsg_error:		db 'ERROR: $'msg_filesystem_err:	db 'Filesystem not found on disk', 0Dh, 0Ah, '$'msg_fat16_err:		db 'FAT16 filesystems not supported at this time', 0Dh, 0Ah, '$'msg_sectorsize_err:	db 'Sector sizes other than 512 bytes not supported', 0Dh, 0Ah, '$'msg_hugeclust_err:	db 'Clusters larger than 16K not supported', 0Dh, 0Ah, '$'msg_read_err:		db 'Disk read failed', 0Dh, 0Ah, '$'msg_write_err:		db 'Disk write failed', 0Dh, 0Ah, '$'		section .data		align 4, db 0BootSector:	incbin "bootsect.bin"LDLinuxSYS:	incbin "ldlinux.sys"ldlinux_size:	equ $-LDLinuxSYS		section .bss		alignb 4SectorBuffer:	resb 512