core/adv.inc

   1 ;; -----------------------------------------------------------------------
   2 ;;
   3 ;;   Copyright 2007-2008 H. Peter Anvin - All Rights Reserved
   4 ;;
   5 ;;   This program is free software; you can redistribute it and/or modify
   6 ;;   it under the terms of the GNU General Public License as published by
   7 ;;   the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
   8 ;;   Boston MA 02110-1301, USA; either version 2 of the License, or
   9 ;;   (at your option) any later version; incorporated herein by reference.
  10 ;;
  11 ;; -----------------------------------------------------------------------
  12
  13 ;;
  14 ;; adv.inc
  15 ;;
  16 ;; The auxillary data vector and its routines
  17 ;;
  18 ;; The auxillary data vector is a 512-byte aligned block that on the
  19 ;; disk-based derivatives can be part of the syslinux file itself.  It
  20 ;; exists in two copies; when written, both copies are written (with a
  21 ;; sync in between, if from the operating system.)  The first two
  22 ;; dwords are magic number and inverse checksum, then follows the data
  23 ;; area as a tagged array similar to BOOTP/DHCP, finally a tail
  24 ;; signature.
  25 ;;
  26 ;; Note that unlike BOOTP/DHCP, zero terminates the chain, and FF
  27 ;; has no special meaning.
  28 ;;
  29
  30 ;;
  31 ;; List of ADV tags...
  32 ;;
  33 ADV_BOOTONCE    equ 1
  34
  35 ;;
  36 ;; Other ADV data...
  37 ;;
  38 ADV_MAGIC1      equ 0x5a2d2fa5                  ; Head signature
  39 ADV_MAGIC2      equ 0xa3041767                  ; Total checksum
  40 ADV_MAGIC3      equ 0xdd28bf64                  ; Tail signature
  41
  42 ADV_LEN         equ 500                         ; Data bytes
  43
  44 adv_retries     equ 6                           ; Disk retries
  45
  46                 section .adv
  47                 ; Introduce the ADVs to valid but blank
  48 adv0:
  49 .head           resd 1
  50 .csum           resd 1
  51 .data           resb ADV_LEN
  52 .tail           resd 1
  53 .end            equ $
  54 adv1:
  55 .head           resd 1
  56 .csum           resd 1
  57 .data           resb ADV_LEN
  58 .tail           resd 1
  59 .end            equ $
  60                 section .text16
  61
  62                 ;
  63                 ; This is called after config file parsing, so we know
  64                 ; the intended location of the ADV
  65                 ;
  66 adv_init:
  67                 cmp byte [ADVDrive],-1
  68                 jne adv_read
  69
  70 %if IS_SYSLINUX || IS_EXTLINUX
  71                 cmp word [ADVSectors],2         ; Not present?
  72                 jb adv_verify
  73
  74                 ;
  75                 ; Update pointers to default ADVs...
  76                 ;
  77                 mov bx,[DataSectors]
  78                 shl bx,2
  79                 mov ecx,[bsHidden]
  80                 mov eax,[bx+SectorPtrs]         ; First ADV sector
  81                 mov edx,[bx+SectorPtrs+4]       ; Second ADV sector
  82                 add eax,ecx
  83                 add edx,ecx
  84                 mov [ADVSec0],eax
  85                 mov [ADVSec1],edx
  86                 mov al,[DriveNumber]
  87                 mov [ADVDrive],al
  88                 jmp adv_read
  89 %endif
  90
  91                 ;
  92                 ; Initialize the ADV data structure in memory
  93                 ;
  94 adv_verify:
  95                 cmp byte [ADVDrive],-1          ; No ADV configured, still?
  96                 je .reset                       ; Then unconditionally reset
  97
  98                 mov si,adv0
  99                 call .check_adv
 100                 jz .ok                          ; Primary ADV okay
 101                 mov si,adv1
 102                 call .check_adv
 103                 jz .adv1ok
 104
 105                 ; Neither ADV is usable; initialize to blank
 106 .reset:
 107                 mov di,adv0
 108                 mov eax,ADV_MAGIC1
 109                 stosd
 110                 mov eax,ADV_MAGIC2
 111                 stosd
 112                 xor eax,eax
 113                 mov cx,ADV_LEN/4
 114                 rep stosd
 115                 mov eax,ADV_MAGIC3
 116                 stosd
 117
 118 .ok:
 119                 ret
 120
 121                 ; The primary ADV is bad, but the backup is OK
 122 .adv1ok:
 123                 mov di,adv0
 124                 mov cx,512/4
 125                 rep movsd
 126                 ret
 127
 128
 129                 ; SI points to the putative ADV; unchanged by routine
 130                 ; ZF=1 on return if good
 131 .check_adv:
 132                 push si
 133                 lodsd
 134                 cmp eax,ADV_MAGIC1
 135                 jne .done                       ; ZF=0, i.e. bad
 136                 xor edx,edx
 137                 mov cx,ADV_LEN/4+1              ; Remaining dwords
 138 .csum:
 139                 lodsd
 140                 add edx,eax
 141                 loop .csum
 142                 cmp edx,ADV_MAGIC2
 143                 jne .done
 144                 lodsd
 145                 cmp eax,ADV_MAGIC3
 146 .done:
 147                 pop si
 148                 ret
 149
 150 ;
 151 ; adv_get: find an ADV string if present
 152 ;
 153 ; Input:        DL      = ADV ID
 154 ; Output:       CX      = byte count (zero on not found)
 155 ;               SI      = pointer to data
 156 ;               DL      = unchanged
 157 ;
 158 ; Assumes CS == DS.
 159 ;
 160
 161 adv_get:
 162                 push ax
 163                 mov si,adv0.data
 164                 xor ax,ax                       ; Keep AH=0 at all times
 165 .loop:
 166                 lodsb                           ; Read ID
 167                 cmp al,dl
 168                 je .found
 169                 and al,al
 170                 jz .end
 171                 lodsb                           ; Read length
 172                 add si,ax
 173                 cmp si,adv0.tail
 174                 jb .loop
 175                 jmp .end
 176
 177 .found:
 178                 lodsb
 179                 mov cx,ax
 180                 add ax,si                       ; Make sure it fits
 181                 cmp ax,adv0.tail
 182                 jbe .ok
 183 .end:
 184                 xor cx,cx
 185 .ok:
 186                 pop ax
 187                 ret
 188
 189 ;
 190 ; adv_set: insert a string into the ADV in memory
 191 ;
 192 ; Input:        DL      = ADV ID
 193 ;               FS:BX   = input buffer
 194 ;               CX      = byte count (max = 255!)
 195 ; Output:       CF=1 on error
 196 ;               CX      clobbered
 197 ;
 198 ; Assumes CS == DS == ES.
 199 ;
 200 adv_set:
 201                 push ax
 202                 push si
 203                 push di
 204                 and ch,ch
 205                 jnz .overflow
 206
 207                 push cx
 208                 mov si,adv0.data
 209                 xor ax,ax
 210 .loop:
 211                 lodsb
 212                 cmp al,dl
 213                 je .found
 214                 and al,al
 215                 jz .endz
 216                 lodsb
 217                 add si,ax
 218                 cmp si,adv0.tail
 219                 jb .loop
 220                 jmp .end
 221
 222 .found:         ; Found, need to delete old copy
 223                 lodsb
 224                 lea di,[si-2]
 225                 push di
 226                 add si,ax
 227                 mov cx,adv0.tail
 228                 sub cx,si
 229                 jb .nukeit
 230                 rep movsb                       ; Remove the old one
 231                 mov [di],ah                     ; Termination zero
 232                 pop si
 233                 jmp .loop
 234 .nukeit:
 235                 pop si
 236                 jmp .end
 237 .endz:
 238                 dec si
 239 .end:
 240                 ; Now SI points to where we want to put our data
 241                 pop cx
 242                 mov di,si
 243                 jcxz .empty
 244                 add si,cx
 245                 cmp si,adv0.tail-2
 246                 jae .overflow                   ; CF=0
 247
 248                 mov si,bx
 249                 mov al,dl
 250                 stosb
 251                 mov al,cl
 252                 stosb
 253                 fs rep movsb
 254
 255 .empty:
 256                 mov cx,adv0.tail
 257                 sub cx,di
 258                 xor ax,ax
 259                 rep stosb                       ; Zero-fill remainder
 260
 261                 clc
 262 .done:
 263                 pop di
 264                 pop si
 265                 pop ax
 266                 ret
 267 .overflow:
 268                 stc
 269                 jmp .done
 270
 271 ;
 272 ; adv_cleanup:  checksum adv0 and copy to adv1
 273 ;               Assumes CS == DS == ES.
 274 ;
 275 adv_cleanup:
 276                 pushad
 277                 mov si,adv0.data
 278                 mov cx,ADV_LEN/4
 279                 xor edx,edx
 280 .loop:
 281                 lodsd
 282                 add edx,eax
 283                 loop .loop
 284                 mov eax,ADV_MAGIC2
 285                 sub eax,edx
 286                 lea di,[si+4]                   ; adv1
 287                 mov si,adv0
 288                 mov [si+4],eax                  ; Store checksum
 289                 mov cx,(ADV_LEN+12)/4
 290                 rep movsd
 291                 popad
 292                 ret
 293
 294 ;
 295 ; adv_write:    write the ADV to disk.
 296 ;
 297 ;               Location is in memory variables.
 298 ;               Assumes CS == DS == ES.
 299 ;
 300 ;               Returns CF=1 if the ADV cannot be written.
 301 ;
 302 adv_write:
 303                 cmp dword [ADVSec0],0
 304                 je .bad
 305                 cmp dword [ADVSec1],0
 306                 je .bad
 307                 cmp byte [ADVDrive],-1
 308                 je .bad
 309
 310                 push ax
 311                 call adv_cleanup
 312                 mov ah,3                        ; Write
 313                 call adv_read_write
 314                 pop ax
 315
 316                 clc
 317                 ret
 318 .bad:                                           ; No location for ADV set
 319                 stc
 320                 ret
 321
 322 ;
 323 ; adv_read:     read the ADV from disk
 324 ;
 325 ;               Location is in memory variables.
 326 ;               Assumes CS == DS == ES.
 327 ;
 328 adv_read:
 329                 push ax
 330                 mov ah,2                        ; Read
 331                 call adv_read_write
 332                 call adv_verify
 333                 pop ax
 334                 ret
 335
 336 ;
 337 ; adv_read_write: disk I/O for the ADV
 338 ;
 339 ;               On input, AH=2 for read, AH=3 for write.
 340 ;               Assumes CS == DS == ES.
 341 ;
 342 adv_read_write:
 343                 mov [ADVOp],ah
 344                 pushad
 345
 346                 ; Check for EDD
 347                 mov bx,55AAh
 348                 mov ah,41h                      ; EDD existence query
 349                 mov dl,[ADVDrive]
 350                 int 13h
 351                 mov si,.cbios
 352                 jc .noedd
 353                 cmp bx,0AA55h
 354                 jne .noedd
 355                 test cl,1
 356                 jz .noedd
 357                 mov si,.ebios
 358 .noedd:
 359
 360                 mov eax,[ADVSec0]
 361                 mov bx,adv0
 362                 call .doone
 363
 364                 mov eax,[ADVSec1]
 365                 mov bx,adv1
 366                 call .doone
 367
 368                 popad
 369                 ret
 370
 371 .doone:
 372                 xor edx,edx                     ; Zero-extend LBA
 373                 push si
 374                 jmp si
 375
 376 .ebios:
 377                 mov cx,adv_retries
 378 .eb_retry:
 379                 ; Form DAPA on stack
 380                 push edx
 381                 push eax
 382                 push es
 383                 push bx
 384                 push word 1                     ; Sector count
 385                 push word 16                    ; DAPA size
 386                 mov si,sp
 387                 pushad
 388                 mov dl,[ADVDrive]
 389                 mov ax,4000h
 390                 or ah,[ADVOp]
 391                 push ds
 392                 push ss
 393                 pop ds
 394                 int 13h
 395                 pop ds
 396                 popad
 397                 lea sp,[si+16]                  ; Remove DAPA
 398                 jc .eb_error
 399                 pop si
 400                 ret
 401 .eb_error:
 402                 loop .eb_retry
 403                 stc
 404                 pop si
 405                 ret
 406
 407 .cbios:
 408                 push edx
 409                 push eax
 410                 push bp
 411
 412                 mov dl,[ADVDrive]
 413                 and dl,dl
 414                 ; Floppies: can't trust INT 13h 08h, we better know
 415                 ; the geometry a priori, which means it better be our
 416                 ; boot device...
 417                 jns .noparm                     ; Floppy drive... urk
 418
 419                 mov ah,08h                      ; Get disk parameters
 420                 int 13h
 421                 jc .noparm
 422                 and ah,ah
 423                 jnz .noparm
 424                 shr dx,8
 425                 inc dx
 426                 movzx edi,dx                    ; EDI = heads
 427                 and cx,3fh
 428                 movzx esi,cx                    ; ESI = sectors/track
 429                 jmp .parmok
 430
 431 .noparm:
 432                 ; No CHS info... this better be our boot drive, then
 433 %if IS_SYSLINUX || IS_EXTLINUX
 434                 cmp dl,[DriveNumber]
 435                 jne .cb_overflow                ; Fatal error!
 436                 movzx esi,word [bsSecPerTrack]
 437                 movzx edi,word [bsHeads]
 438 %else
 439                 ; Not a disk-based derivative... there is no hope
 440                 jmp .cb_overflow
 441 %endif
 442
 443 .parmok:
 444                 ;
 445                 ; Dividing by sectors to get (track,sector): we may have
 446                 ; up to 2^18 tracks, so we need to use 32-bit arithmetric.
 447                 ;
 448                 div esi
 449                 xor cx,cx
 450                 xchg cx,dx              ; CX <- sector index (0-based)
 451                                         ; EDX <- 0
 452                 ; eax = track #
 453                 div edi                 ; Convert track to head/cyl
 454
 455                 ; Watch out for overflow, we might be writing!
 456                 cmp eax,1023
 457                 ja .cb_overflow
 458
 459                 ;
 460                 ; Now we have AX = cyl, DX = head, CX = sector (0-based),
 461                 ; BP = sectors to transfer, SI = bsSecPerTrack,
 462                 ; ES:BX = data target
 463                 ;
 464
 465                 shl ah,6                ; Because IBM was STOOPID
 466                                         ; and thought 8 bits were enough
 467                                         ; then thought 10 bits were enough...
 468                 inc cx                  ; Sector numbers are 1-based, sigh
 469                 or cl,ah
 470                 mov ch,al
 471                 mov dh,dl
 472                 mov dl,[ADVDrive]
 473                 mov al,01h              ; Transfer one sector
 474                 mov ah,[ADVOp]          ; Operation
 475
 476                 mov bp,adv_retries
 477 .cb_retry:
 478                 pushad
 479                 int 13h
 480                 popad
 481                 jc .cb_error
 482
 483 .cb_done:
 484                 pop bp
 485                 pop eax
 486                 pop edx
 487                 pop si
 488                 ret
 489
 490 .cb_error:
 491                 dec bp
 492                 jnz .cb_retry
 493 .cb_overflow:
 494                 stc
 495                 jmp .cb_done
 496
 497                 section .data16
 498                 alignz 4
 499 ADVSec0         dd 0                    ; Not specified
 500 ADVSec1         dd 0                    ; Not specified
 501 ADVDrive        db -1                   ; No ADV defined
 502 ADVCHSInfo      db -1                   ; We have CHS info for this drive
 503
 504                 section .bss16
 505 ADVOp           resb 1
 506
 507                 section .text16