copybs.asm

   1 ; -*- fundamental -*- (asm-mode sucks)
   2 ; -----------------------------------------------------------------------
   3 ;
   4 ;   Copyright 1998-2004 H. Peter Anvin - All Rights Reserved
   5 ;
   6 ;   This program is free software; you can redistribute it and/or modify
   7 ;   it under the terms of the GNU General Public License as published by
   8 ;   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
   9 ;   Boston MA 02111-1307, USA; either version 2 of the License, or
  10 ;   (at your option) any later version; incorporated herein by reference.
  11 ;
  12 ; -----------------------------------------------------------------------
  13
  14 ;
  15 ; copybs.asm
  16 ;
  17 ; Small DOS program to copy the boot sector from a drive
  18 ; to a file
  19 ;
  20 ; Usage: copybs <drive>: <file>
  21 ;
  22
  23                 absolute 0
  24 pspInt20:               resw 1
  25 pspNextParagraph:       resw 1
  26                         resb 1          ; reserved
  27 pspDispatcher:          resb 5
  28 pspTerminateVector:     resd 1
  29 pspControlCVector:      resd 1
  30 pspCritErrorVector:     resd 1
  31                         resw 11         ; reserved
  32 pspEnvironment:         resw 1
  33                         resw 23         ; reserved
  34 pspFCB_1:               resb 16
  35 pspFCB_2:               resb 16
  36                         resd 1          ; reserved
  37 pspCommandLen:          resb 1
  38 pspCommandArg:          resb 127
  39
  40                 section .text
  41                 org 100h                        ; .COM format
  42 _start:
  43                 mov ax,3000h                    ; Get DOS version
  44                 int 21h
  45                 xchg al,ah
  46                 mov [DOSVersion],ax
  47                 cmp ax,0200h                    ; DOS 2.00 minimum
  48                 jae dosver_ok
  49                 mov dx,msg_ancient_err
  50                 jmp die
  51
  52                 section .bss
  53                 alignb 2
  54 DOSVersion:     resw 1
  55
  56                 section .text
  57 ;
  58 ; Scan command line for a drive letter followed by a colon
  59 ;
  60 dosver_ok:
  61                 xor cx,cx
  62                 mov si,pspCommandArg
  63                 mov cl,[pspCommandLen]
  64
  65 cmdscan1:       jcxz bad_usage                  ; End of command line?
  66                 lodsb                           ; Load character
  67                 dec cx
  68                 cmp al,' '                      ; White space
  69                 jbe cmdscan1
  70                 or al,020h                      ; -> lower case
  71                 cmp al,'a'                      ; Check for letter
  72                 jb bad_usage
  73                 cmp al,'z'
  74                 ja bad_usage
  75                 sub al,'a'                      ; Convert to zero-based index
  76                 mov [DriveNo],al                ; Save away drive index
  77
  78                 section .bss
  79 DriveNo:        resb 1
  80
  81                 section .text
  82 ;
  83 ; Got the leading letter, now the next character must be a colon
  84 ;
  85 got_letter:     jcxz bad_usage
  86                 lodsb
  87                 dec cx
  88                 cmp al,':'
  89                 jne bad_usage
  90 ;
  91 ; Got the colon; now we should have at least one whitespace
  92 ; followed by a filename
  93 ;
  94 got_colon:      jcxz bad_usage
  95                 lodsb
  96                 dec cx
  97                 cmp al,' '
  98                 ja bad_usage
  99
 100 skipspace:      jcxz bad_usage
 101                 lodsb
 102                 dec cx
 103                 cmp al,' '
 104                 jbe skipspace
 105
 106                 mov di,FileName
 107 copyfile:       stosb
 108                 jcxz got_cmdline
 109                 lodsb
 110                 dec cx
 111                 cmp al,' '
 112                 ja copyfile
 113                 jmp short got_cmdline
 114
 115 ;
 116 ; We end up here if the command line doesn't parse
 117 ;
 118 bad_usage:      mov dx,msg_unfair
 119                 jmp die
 120
 121                 section .data
 122 msg_unfair:     db 'Usage: copybs <drive>: <filename>', 0Dh, 0Ah, '$'
 123
 124                 section .bss
 125                 alignb 4
 126 FileName        resb 256
 127
 128 ;
 129 ; Parsed the command line OK.  Get device parameter block to get the
 130 ; sector size.
 131 ;
 132                 struc DPB
 133 dpbDrive:       resb 1
 134 dpbUnit:        resb 1
 135 dpbSectorSize:  resw 1
 136 dpbClusterMask: resb 1
 137 dpbClusterShift: resb 1
 138 dpbFirstFAT:    resw 1
 139 dpbFATCount:    resb 1
 140 dpbRootEntries: resw 1
 141 dpbFirstSector: resw 1
 142 dpbMaxCluster:  resw 1
 143 dpbFATSize:     resw 1
 144 dpbDirSector:   resw 1
 145 dpbDriverAddr:  resd 1
 146 dpbMedia:       resb 1
 147 dpbFirstAccess: resb 1
 148 dpbNextDPB:     resd 1
 149 dpbNextFree:    resw 1
 150 dpbFreeCnt:     resw 1
 151                 endstruc
 152
 153                 section .bss
 154                 alignb 2
 155 SectorSize      resw 1
 156
 157                 section .text
 158 got_cmdline:
 159                 xor al,al                       ; Zero-terminate filename
 160                 stosb
 161
 162                 mov dl,[DriveNo]
 163                 inc dl                          ; 1-based
 164                 mov ah,32h
 165                 int 21h                         ; Get Drive Parameter Block
 166
 167                 and al,al
 168                 jnz filesystem_error
 169
 170                 mov dx,[bx+dpbSectorSize]       ; Save sector size
 171 ;
 172 ; Read the boot sector.
 173 ;
 174                 section .data
 175                 align 4, db 0
 176 DISKIO          equ $
 177 diStartSector:  dd 0                            ; Absolute sector 0
 178 diSectors:      dw 1                            ; One sector
 179 diBuffer:       dw SectorBuffer                 ; Buffer offset
 180                 dw 0                            ; Buffer segment
 181
 182                 section .text
 183 read_bootsect:
 184                 mov ax,cs                       ; Set DS <- CS
 185                 mov ds,ax
 186
 187                 mov [SectorSize],dx             ; Saved sector size from above
 188
 189                 cmp word [DOSVersion],0400h     ; DOS 4.00 has a new interface
 190                 jae .new
 191 .old:
 192                 mov bx,SectorBuffer
 193                 mov cx,1                        ; One sector
 194                 jmp short .common
 195 .new:
 196                 mov [diBuffer+2],ax             ; == DS
 197                 mov bx,DISKIO
 198                 mov cx,-1
 199 .common:
 200                 xor dx,dx                       ; Absolute sector 0
 201                 mov al,[DriveNo]
 202                 int 25h                         ; DOS absolute disk read
 203                 pop ax                          ; Remove flags from stack
 204                 jc disk_read_error
 205
 206 ;
 207 ; Open the file and write the boot sector to the file.
 208 ;
 209                 mov dx,FileName
 210                 mov cx,0020h                    ; Attribute = ARCHIVE
 211                 mov ah,3Ch                      ; Create file
 212                 int 21h
 213                 jc file_write_error
 214
 215                 mov bx,ax
 216                 push ax                         ; Handle
 217
 218                 mov cx,[SectorSize]
 219                 mov dx,SectorBuffer
 220                 mov ah,40h                      ; Write file
 221                 int 21h
 222                 jc file_write_error
 223                 cmp ax,[SectorSize]
 224                 jne file_write_error
 225
 226                 pop bx                          ; Handle
 227                 mov ah,3Eh                      ; Close file
 228                 int 21h
 229                 jc file_write_error
 230 ;
 231 ; We're done!
 232 ;
 233                 mov ax,4C00h                    ; exit(0)
 234                 int 21h
 235
 236 ;
 237 ; Error routine jump
 238 ;
 239 filesystem_error:
 240                 mov dx,msg_filesystem_err
 241                 jmp short die
 242 disk_read_error:
 243                 mov dx,msg_read_err
 244                 jmp short die
 245 file_write_error:
 246                 mov dx,msg_write_err
 247 die:
 248                 push cs
 249                 pop ds
 250                 push dx
 251                 mov dx,msg_error
 252                 mov ah,09h
 253                 int 21h
 254                 pop dx
 255
 256                 mov ah,09h                      ; Write string
 257                 int 21h
 258
 259                 mov ax,4C01h                    ; Exit error status
 260                 int 21h
 261
 262                 section .data
 263 msg_error:              db 'ERROR: $'
 264 msg_ancient_err:        db 'DOS version 2.00 or later required', 0Dh, 0Ah, '$'
 265 msg_filesystem_err:     db 'Filesystem not found on disk', 0Dh, 0Ah, '$'
 266 msg_read_err:           db 'Boot sector read failed', 0Dh, 0Ah, '$'
 267 msg_write_err:          db 'File write failed', 0Dh, 0Ah, '$'
 268
 269                 section .bss
 270                 alignb 4
 271 SectorBuffer:   resb 4096