ldlinux.asm

   1 ; -*- fundamental -*- (asm-mode sucks)
   2 ; ****************************************************************************
   3 ;
   4 ;  ldlinux.asm
   5 ;
   6 ;  A program to boot Linux kernels off an MS-DOS formatted floppy disk.  This
   7 ;  functionality is good to have for installation floppies, where it may
   8 ;  be hard to find a functional Linux system to run LILO off.
   9 ;
  10 ;  This program allows manipulation of the disk to take place entirely
  11 ;  from MS-LOSS, and can be especially useful in conjunction with the
  12 ;  umsdos filesystem.
  13 ;
  14 ;   Copyright 1994-2008 H. Peter Anvin - All Rights Reserved
  15 ;
  16 ;  This program is free software; you can redistribute it and/or modify
  17 ;  it under the terms of the GNU General Public License as published by
  18 ;  the Free Software Foundation, Inc., 53 Temple Place Ste 330,
  19 ;  Boston MA 02111-1307, USA; either version 2 of the License, or
  20 ;  (at your option) any later version; incorporated herein by reference.
  21 ;
  22 ; ****************************************************************************
  23
  24 %ifndef IS_MDSLINUX
  25 %define IS_SYSLINUX 1
  26 %endif
  27 %include "head.inc"
  28
  29 ;
  30 ; Some semi-configurable constants... change on your own risk.
  31 ;
  32 my_id           equ syslinux_id
  33 FILENAME_MAX_LG2 equ 6                  ; log2(Max filename size Including final null)
  34 FILENAME_MAX    equ (1<<FILENAME_MAX_LG2) ; Max mangled filename size
  35 NULLFILE        equ 0                   ; First char space == null filename
  36 NULLOFFSET      equ 0                   ; Position in which to look
  37 retry_count     equ 16                  ; How patient are we with the disk?
  38 %assign HIGHMEM_SLOP 0                  ; Avoid this much memory near the top
  39 LDLINUX_MAGIC   equ 0x3eb202fe          ; A random number to identify ourselves with
  40
  41 MAX_OPEN_LG2    equ 6                   ; log2(Max number of open files)
  42 MAX_OPEN        equ (1 << MAX_OPEN_LG2)
  43
  44 SECTOR_SHIFT    equ 9
  45 SECTOR_SIZE     equ (1 << SECTOR_SHIFT)
  46
  47 ;
  48 ; This is what we need to do when idle
  49 ;
  50 %macro  RESET_IDLE 0
  51         ; Nothing
  52 %endmacro
  53 %macro  DO_IDLE 0
  54         ; Nothing
  55 %endmacro
  56
  57 ;
  58 ; The following structure is used for "virtual kernels"; i.e. LILO-style
  59 ; option labels.  The options we permit here are `kernel' and `append
  60 ; Since there is no room in the bottom 64K for all of these, we
  61 ; stick them in high memory and copy them down before we need them.
  62 ;
  63                 struc vkernel
  64 vk_vname:       resb FILENAME_MAX       ; Virtual name **MUST BE FIRST!**
  65 vk_rname:       resb FILENAME_MAX       ; Real name
  66 vk_appendlen:   resw 1
  67 vk_type:        resb 1                  ; Type of file
  68                 alignb 4
  69 vk_append:      resb max_cmd_len+1      ; Command line
  70                 alignb 4
  71 vk_end:         equ $                   ; Should be <= vk_size
  72                 endstruc
  73
  74 ;
  75 ; Segment assignments in the bottom 640K
  76 ; Stick to the low 512K in case we're using something like M-systems flash
  77 ; which load a driver into low RAM (evil!!)
  78 ;
  79 ; 0000h - main code/data segment (and BIOS segment)
  80 ;
  81 real_mode_seg   equ 3000h
  82 cache_seg       equ 2000h               ; 64K area for metadata cache
  83 xfer_buf_seg    equ 1000h               ; Bounce buffer for I/O to high mem
  84 comboot_seg     equ real_mode_seg       ; COMBOOT image loading zone
  85
  86 ;
  87 ; File structure.  This holds the information for each currently open file.
  88 ;
  89                 struc open_file_t
  90 file_sector     resd 1                  ; Sector pointer (0 = structure free)
  91 file_bytesleft  resd 1                  ; Number of bytes left
  92 file_left       resd 1                  ; Number of sectors left
  93                 resd 1                  ; Unused
  94                 endstruc
  95
  96 %ifndef DEPEND
  97 %if (open_file_t_size & (open_file_t_size-1))
  98 %error "open_file_t is not a power of 2"
  99 %endif
 100 %endif
 101
 102 ; ---------------------------------------------------------------------------
 103 ;   BEGIN CODE
 104 ; ---------------------------------------------------------------------------
 105
 106 ;
 107 ; Memory below this point is reserved for the BIOS and the MBR
 108 ;
 109                 section .earlybss
 110 trackbufsize    equ 8192
 111 trackbuf        resb trackbufsize       ; Track buffer goes here
 112                 ; ends at 2800h
 113
 114                 section .bss
 115                 alignb 8
 116
 117                 ; Expanded superblock
 118 SuperInfo       equ $
 119                 resq 16                 ; The first 16 bytes expanded 8 times
 120 FAT             resd 1                  ; Location of (first) FAT
 121 RootDirArea     resd 1                  ; Location of root directory area
 122 RootDir         resd 1                  ; Location of root directory proper
 123 DataArea        resd 1                  ; Location of data area
 124 RootDirSize     resd 1                  ; Root dir size in sectors
 125 TotalSectors    resd 1                  ; Total number of sectors
 126 ClustSize       resd 1                  ; Bytes/cluster
 127 ClustMask       resd 1                  ; Sectors/cluster - 1
 128 CopySuper       resb 1                  ; Distinguish .bs versus .bss
 129 DriveNumber     resb 1                  ; BIOS drive number
 130 ClustShift      resb 1                  ; Shift count for sectors/cluster
 131 ClustByteShift  resb 1                  ; Shift count for bytes/cluster
 132
 133                 alignb open_file_t_size
 134 Files           resb MAX_OPEN*open_file_t_size
 135
 136                 section .text
 137 ;
 138 ; Some of the things that have to be saved very early are saved
 139 ; "close" to the initial stack pointer offset, in order to
 140 ; reduce the code size...
 141 ;
 142 StackBuf        equ $-44-32             ; Start the stack here (grow down - 4K)
 143 PartInfo        equ StackBuf            ; Saved partition table entry
 144 FloppyTable     equ PartInfo+16         ; Floppy info table (must follow PartInfo)
 145 OrigFDCTabPtr   equ StackBuf-8          ; The 2nd high dword on the stack
 146 OrigESDI        equ StackBuf-4          ; The high dword on the stack
 147
 148 ;
 149 ; Primary entry point.  Tempting as though it may be, we can't put the
 150 ; initial "cli" here; the jmp opcode in the first byte is part of the
 151 ; "magic number" (using the term very loosely) for the DOS superblock.
 152 ;
 153 bootsec         equ $
 154                 jmp short start         ; 2 bytes
 155                 nop                     ; 1 byte
 156 ;
 157 ; "Superblock" follows -- it's in the boot sector, so it's already
 158 ; loaded and ready for us
 159 ;
 160 bsOemName       db 'SYSLINUX'           ; The SYS command sets this, so...
 161 ;
 162 ; These are the fields we actually care about.  We end up expanding them
 163 ; all to dword size early in the code, so generate labels for both
 164 ; the expanded and unexpanded versions.
 165 ;
 166 %macro          superb 1
 167 bx %+ %1        equ SuperInfo+($-superblock)*8+4
 168 bs %+ %1        equ $
 169                 zb 1
 170 %endmacro
 171 %macro          superw 1
 172 bx %+ %1        equ SuperInfo+($-superblock)*8
 173 bs %+ %1        equ $
 174                 zw 1
 175 %endmacro
 176 %macro          superd 1
 177 bx %+ %1        equ $                   ; no expansion for dwords
 178 bs %+ %1        equ $
 179                 zd 1
 180 %endmacro
 181 superblock      equ $
 182                 superw BytesPerSec
 183                 superb SecPerClust
 184                 superw ResSectors
 185                 superb FATs
 186                 superw RootDirEnts
 187                 superw Sectors
 188                 superb Media
 189                 superw FATsecs
 190                 superw SecPerTrack
 191                 superw Heads
 192 superinfo_size  equ ($-superblock)-1    ; How much to expand
 193                 superd Hidden
 194                 superd HugeSectors
 195                 ;
 196                 ; This is as far as FAT12/16 and FAT32 are consistent
 197                 ;
 198                 zb 54                   ; FAT12/16 need 26 more bytes,
 199                                         ; FAT32 need 54 more bytes
 200 superblock_len  equ $-superblock
 201
 202 SecPerClust     equ bxSecPerClust
 203 ;
 204 ; Note we don't check the constraints above now; we did that at install
 205 ; time (we hope!)
 206 ;
 207 start:
 208                 cli                     ; No interrupts yet, please
 209                 cld                     ; Copy upwards
 210 ;
 211 ; Set up the stack
 212 ;
 213                 xor ax,ax
 214                 mov ss,ax
 215                 mov sp,StackBuf         ; Just below BSS
 216                 push es                 ; Save initial ES:DI -> $PnP pointer
 217                 push di
 218                 mov es,ax
 219 ;
 220 ; DS:SI may contain a partition table entry.  Preserve it for us.
 221 ;
 222                 mov cx,8                ; Save partition info
 223                 mov di,PartInfo
 224                 rep movsw
 225
 226                 mov ds,ax               ; Now we can initialize DS...
 227
 228 ;
 229 ; Now sautee the BIOS floppy info block to that it will support decent-
 230 ; size transfers; the floppy block is 11 bytes and is stored in the
 231 ; INT 1Eh vector (brilliant waste of resources, eh?)
 232 ;
 233 ; Of course, if BIOSes had been properly programmed, we wouldn't have
 234 ; had to waste precious space with this code.
 235 ;
 236                 mov bx,fdctab
 237                 lfs si,[bx]             ; FS:SI -> original fdctab
 238                 push fs                 ; Save on stack in case we need to bail
 239                 push si
 240
 241                 ; Save the old fdctab even if hard disk so the stack layout
 242                 ; is the same.  The instructions above do not change the flags
 243                 mov [DriveNumber],dl    ; Save drive number in DL
 244                 and dl,dl               ; If floppy disk (00-7F), assume no
 245                                         ; partition table
 246                 js harddisk
 247
 248 floppy:
 249                 mov cl,6                ; 12 bytes (CX == 0)
 250                 ; es:di -> FloppyTable already
 251                 ; This should be safe to do now, interrupts are off...
 252                 mov [bx],di             ; FloppyTable
 253                 mov [bx+2],ax           ; Segment 0
 254                 fs rep movsw            ; Faster to move words
 255                 mov cl,[bsSecPerTrack]  ; Patch the sector count
 256                 mov [di-8],cl
 257                 ; AX == 0 here
 258                 int 13h                 ; Some BIOSes need this
 259
 260                 jmp short not_harddisk
 261 ;
 262 ; The drive number and possibly partition information was passed to us
 263 ; by the BIOS or previous boot loader (MBR).  Current "best practice" is to
 264 ; trust that rather than what the superblock contains.
 265 ;
 266 ; Would it be better to zero out bsHidden if we don't have a partition table?
 267 ;
 268 ; Note: di points to beyond the end of PartInfo
 269 ;
 270 harddisk:
 271                 test byte [di-16],7Fh   ; Sanity check: "active flag" should
 272                 jnz no_partition        ; be 00 or 80
 273                 mov eax,[di-8]          ; Partition offset (dword)
 274                 mov [bsHidden],eax
 275 no_partition:
 276 ;
 277 ; Get disk drive parameters (don't trust the superblock.)  Don't do this for
 278 ; floppy drives -- INT 13:08 on floppy drives will (may?) return info about
 279 ; what the *drive* supports, not about the *media*.  Fortunately floppy disks
 280 ; tend to have a fixed, well-defined geometry which is stored in the superblock.
 281 ;
 282                 ; DL == drive # still
 283                 mov ah,08h
 284                 int 13h
 285                 jc no_driveparm
 286                 and ah,ah
 287                 jnz no_driveparm
 288                 shr dx,8
 289                 inc dx                  ; Contains # of heads - 1
 290                 mov [bsHeads],dx
 291                 and cx,3fh
 292                 mov [bsSecPerTrack],cx
 293 no_driveparm:
 294 not_harddisk:
 295 ;
 296 ; Ready to enable interrupts, captain
 297 ;
 298                 sti
 299
 300 ;
 301 ; Do we have EBIOS (EDD)?
 302 ;
 303 eddcheck:
 304                 mov bx,55AAh
 305                 mov ah,41h              ; EDD existence query
 306                 mov dl,[DriveNumber]
 307                 int 13h
 308                 jc .noedd
 309                 cmp bx,0AA55h
 310                 jne .noedd
 311                 test cl,1               ; Extended disk access functionality set
 312                 jz .noedd
 313                 ;
 314                 ; We have EDD support...
 315                 ;
 316                 mov byte [getlinsec.jmp+1],(getlinsec_ebios-(getlinsec.jmp+2))
 317 .noedd:
 318
 319 ;
 320 ; Load the first sector of LDLINUX.SYS; this used to be all proper
 321 ; with parsing the superblock and root directory; it doesn't fit
 322 ; together with EBIOS support, unfortunately.
 323 ;
 324                 mov eax,[FirstSector]   ; Sector start
 325                 mov bx,ldlinux_sys      ; Where to load it
 326                 call getonesec
 327
 328                 ; Some modicum of integrity checking
 329                 cmp dword [ldlinux_magic+4],LDLINUX_MAGIC^HEXDATE
 330                 jne kaboom
 331
 332                 ; Go for it...
 333                 jmp ldlinux_ent
 334
 335 ;
 336 ; getonesec: get one disk sector
 337 ;
 338 getonesec:
 339                 mov bp,1                ; One sector
 340                 ; Fall through
 341
 342 ;
 343 ; getlinsec: load a sequence of BP floppy sector given by the linear sector
 344 ;            number in EAX into the buffer at ES:BX.  We try to optimize
 345 ;            by loading up to a whole track at a time, but the user
 346 ;            is responsible for not crossing a 64K boundary.
 347 ;            (Yes, BP is weird for a count, but it was available...)
 348 ;
 349 ;            On return, BX points to the first byte after the transferred
 350 ;            block.
 351 ;
 352 ;            This routine assumes CS == DS, and trashes most registers.
 353 ;
 354 ; Stylistic note: use "xchg" instead of "mov" when the source is a register
 355 ; that is dead from that point; this saves space.  However, please keep
 356 ; the order to dst,src to keep things sane.
 357 ;
 358 getlinsec:
 359                 add eax,[bsHidden]              ; Add partition offset
 360                 xor edx,edx                     ; Zero-extend LBA (eventually allow 64 bits)
 361
 362 .jmp:           jmp strict short getlinsec_cbios
 363
 364 ;
 365 ; getlinsec_ebios:
 366 ;
 367 ; getlinsec implementation for EBIOS (EDD)
 368 ;
 369 getlinsec_ebios:
 370 .loop:
 371                 push bp                         ; Sectors left
 372 .retry2:
 373                 call maxtrans                   ; Enforce maximum transfer size
 374                 movzx edi,bp                    ; Sectors we are about to read
 375                 mov cx,retry_count
 376 .retry:
 377
 378                 ; Form DAPA on stack
 379                 push edx
 380                 push eax
 381                 push es
 382                 push bx
 383                 push di
 384                 push word 16
 385                 mov si,sp
 386                 pushad
 387                 mov dl,[DriveNumber]
 388                 push ds
 389                 push ss
 390                 pop ds                          ; DS <- SS
 391                 mov ah,42h                      ; Extended Read
 392                 int 13h
 393                 pop ds
 394                 popad
 395                 lea sp,[si+16]                  ; Remove DAPA
 396                 jc .error
 397                 pop bp
 398                 add eax,edi                     ; Advance sector pointer
 399                 sub bp,di                       ; Sectors left
 400                 shl di,SECTOR_SHIFT             ; 512-byte sectors
 401                 add bx,di                       ; Advance buffer pointer
 402                 and bp,bp
 403                 jnz .loop
 404
 405                 ret
 406
 407 .error:
 408                 ; Some systems seem to get "stuck" in an error state when
 409                 ; using EBIOS.  Doesn't happen when using CBIOS, which is
 410                 ; good, since some other systems get timeout failures
 411                 ; waiting for the floppy disk to spin up.
 412
 413                 pushad                          ; Try resetting the device
 414                 xor ax,ax
 415                 mov dl,[DriveNumber]
 416                 int 13h
 417                 popad
 418                 loop .retry                     ; CX-- and jump if not zero
 419
 420                 ;shr word [MaxTransfer],1       ; Reduce the transfer size
 421                 ;jnz .retry2
 422
 423                 ; Total failure.  Try falling back to CBIOS.
 424                 mov byte [getlinsec.jmp+1],(getlinsec_cbios-(getlinsec.jmp+2))
 425                 ;mov byte [MaxTransfer],63      ; Max possibe CBIOS transfer
 426
 427                 pop bp
 428                 ; ... fall through ...
 429
 430 ;
 431 ; getlinsec_cbios:
 432 ;
 433 ; getlinsec implementation for legacy CBIOS
 434 ;
 435 getlinsec_cbios:
 436 .loop:
 437                 push edx
 438                 push eax
 439                 push bp
 440                 push bx
 441
 442                 movzx esi,word [bsSecPerTrack]
 443                 movzx edi,word [bsHeads]
 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                 ; We should test this, but it doesn't fit...
 456                 ; cmp eax,1023
 457                 ; ja .error
 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                 call maxtrans                   ; Enforce maximum transfer size
 466
 467                 ; Must not cross track boundaries, so BP <= SI-CX
 468                 sub si,cx
 469                 cmp bp,si
 470                 jna .bp_ok
 471                 mov bp,si
 472 .bp_ok:
 473
 474                 shl ah,6                ; Because IBM was STOOPID
 475                                         ; and thought 8 bits were enough
 476                                         ; then thought 10 bits were enough...
 477                 inc cx                  ; Sector numbers are 1-based, sigh
 478                 or cl,ah
 479                 mov ch,al
 480                 mov dh,dl
 481                 mov dl,[DriveNumber]
 482                 xchg ax,bp              ; Sector to transfer count
 483                 mov ah,02h              ; Read sectors
 484                 mov bp,retry_count
 485 .retry:
 486                 pushad
 487                 int 13h
 488                 popad
 489                 jc .error
 490 .resume:
 491                 movzx ecx,al            ; ECX <- sectors transferred
 492                 shl ax,SECTOR_SHIFT     ; Convert sectors in AL to bytes in AX
 493                 pop bx
 494                 add bx,ax
 495                 pop bp
 496                 pop eax
 497                 pop edx
 498                 add eax,ecx
 499                 sub bp,cx
 500                 jnz .loop
 501                 ret
 502
 503 .error:
 504                 dec bp
 505                 jnz .retry
 506
 507                 xchg ax,bp              ; Sectors transferred <- 0
 508                 shr word [MaxTransfer],1
 509                 jnz .resume
 510                 ; Fall through to disk_error
 511
 512 ;
 513 ; kaboom: write a message and bail out.
 514 ;
 515 disk_error:
 516 kaboom:
 517                 xor si,si
 518                 mov ss,si
 519                 mov sp,StackBuf-4       ; Reset stack
 520                 mov ds,si               ; Reset data segment
 521                 pop dword [fdctab]      ; Restore FDC table
 522 .patch:                                 ; When we have full code, intercept here
 523                 mov si,bailmsg
 524
 525                 ; Write error message, this assumes screen page 0
 526 .loop:          lodsb
 527                 and al,al
 528                 jz .done
 529                 mov ah,0Eh              ; Write to screen as TTY
 530                 mov bx,0007h            ; Attribute
 531                 int 10h
 532                 jmp short .loop
 533 .done:
 534                 cbw                     ; AH <- 0
 535 .again:         int 16h                 ; Wait for keypress
 536                                         ; NB: replaced by int 18h if
 537                                         ; chosen at install time..
 538                 int 19h                 ; And try once more to boot...
 539 .norge:         jmp short .norge        ; If int 19h returned; this is the end
 540
 541 ;
 542 ; Truncate BP to MaxTransfer
 543 ;
 544 maxtrans:
 545                 cmp bp,[MaxTransfer]
 546                 jna .ok
 547                 mov bp,[MaxTransfer]
 548 .ok:            ret
 549
 550 ;
 551 ; Error message on failure
 552 ;
 553 bailmsg:        db 'Boot error', 0Dh, 0Ah, 0
 554
 555                 ; This fails if the boot sector overflows
 556                 zb 1F8h-($-$$)
 557
 558 FirstSector     dd 0xDEADBEEF                   ; Location of sector 1
 559 MaxTransfer     dw 0x007F                       ; Max transfer size
 560
 561 ; This field will be filled in 0xAA55 by the installer, but we abuse it
 562 ; to house a pointer to the INT 16h instruction at
 563 ; kaboom.again, which gets patched to INT 18h in RAID mode.
 564 bootsignature   dw kaboom.again-bootsec
 565
 566 ;
 567 ; ===========================================================================
 568 ;  End of boot sector
 569 ; ===========================================================================
 570 ;  Start of LDLINUX.SYS
 571 ; ===========================================================================
 572
 573 ldlinux_sys:
 574
 575 syslinux_banner db 0Dh, 0Ah
 576 %if IS_MDSLINUX
 577                 db 'MDSLINUX '
 578 %else
 579                 db 'SYSLINUX '
 580 %endif
 581                 db version_str, ' ', date, ' ', 0
 582                 db 0Dh, 0Ah, 1Ah        ; EOF if we "type" this in DOS
 583
 584                 align 8, db 0
 585 ldlinux_magic   dd LDLINUX_MAGIC
 586                 dd LDLINUX_MAGIC^HEXDATE
 587
 588 ;
 589 ; This area is patched by the installer.  It is found by looking for
 590 ; LDLINUX_MAGIC, plus 8 bytes.
 591 ;
 592 patch_area:
 593 LDLDwords       dw 0            ; Total dwords starting at ldlinux_sys
 594 LDLSectors      dw 0            ; Number of sectors - (bootsec+this sec)
 595 CheckSum        dd 0            ; Checksum starting at ldlinux_sys
 596                                 ; value = LDLINUX_MAGIC - [sum of dwords]
 597
 598 ; Space for up to 64 sectors, the theoretical maximum
 599 SectorPtrs      times 64 dd 0
 600
 601 ldlinux_ent:
 602 ;
 603 ; Note that some BIOSes are buggy and run the boot sector at 07C0:0000
 604 ; instead of 0000:7C00 and the like.  We don't want to add anything
 605 ; more to the boot sector, so it is written to not assume a fixed
 606 ; value in CS, but we don't want to deal with that anymore from now
 607 ; on.
 608 ;
 609                 jmp 0:.next
 610 .next:
 611
 612 ;
 613 ; Tell the user we got this far
 614 ;
 615                 mov si,syslinux_banner
 616                 call writestr
 617
 618 ;
 619 ; Tell the user if we're using EBIOS or CBIOS
 620 ;
 621 print_bios:
 622                 mov si,cbios_name
 623                 cmp byte [getlinsec.jmp+1],(getlinsec_ebios-(getlinsec.jmp+2))
 624                 jne .cbios
 625                 mov si,ebios_name
 626 .cbios:
 627                 mov [BIOSName],si
 628                 call writestr
 629
 630                 section .bss
 631 %define HAVE_BIOSNAME 1
 632 BIOSName        resw 1
 633
 634                 section .text
 635 ;
 636 ; Now we read the rest of LDLINUX.SYS.  Don't bother loading the first
 637 ; sector again, though.
 638 ;
 639 load_rest:
 640                 mov si,SectorPtrs
 641                 mov bx,7C00h+2*SECTOR_SIZE      ; Where we start loading
 642                 mov cx,[LDLSectors]
 643
 644 .get_chunk:
 645                 jcxz .done
 646                 xor bp,bp
 647                 lodsd                           ; First sector of this chunk
 648
 649                 mov edx,eax
 650
 651 .make_chunk:
 652                 inc bp
 653                 dec cx
 654                 jz .chunk_ready
 655                 inc edx                         ; Next linear sector
 656                 cmp [si],edx                    ; Does it match
 657                 jnz .chunk_ready                ; If not, this is it
 658                 add si,4                        ; If so, add sector to chunk
 659                 jmp short .make_chunk
 660
 661 .chunk_ready:
 662                 call getlinsecsr
 663                 shl bp,SECTOR_SHIFT
 664                 add bx,bp
 665                 jmp .get_chunk
 666
 667 .done:
 668
 669 ;
 670 ; All loaded up, verify that we got what we needed.
 671 ; Note: the checksum field is embedded in the checksum region, so
 672 ; by the time we get to the end it should all cancel out.
 673 ;
 674 verify_checksum:
 675                 mov si,ldlinux_sys
 676                 mov cx,[LDLDwords]
 677                 mov edx,-LDLINUX_MAGIC
 678 .checksum:
 679                 lodsd
 680                 add edx,eax
 681                 loop .checksum
 682
 683                 and edx,edx                     ; Should be zero
 684                 jz all_read                     ; We're cool, go for it!
 685
 686 ;
 687 ; Uh-oh, something went bad...
 688 ;
 689                 mov si,checksumerr_msg
 690                 call writestr
 691                 jmp kaboom
 692
 693 ;
 694 ; -----------------------------------------------------------------------------
 695 ; Subroutines that have to be in the first sector
 696 ; -----------------------------------------------------------------------------
 697
 698 ;
 699 ;
 700 ; writestr: write a null-terminated string to the console
 701 ;           This assumes we're on page 0.  This is only used for early
 702 ;           messages, so it should be OK.
 703 ;
 704 writestr:
 705 .loop:          lodsb
 706                 and al,al
 707                 jz .return
 708                 mov ah,0Eh              ; Write to screen as TTY
 709                 mov bx,0007h            ; Attribute
 710                 int 10h
 711                 jmp short .loop
 712 .return:        ret
 713
 714
 715 ; getlinsecsr: save registers, call getlinsec, restore registers
 716 ;
 717 getlinsecsr:    pushad
 718                 call getlinsec
 719                 popad
 720                 ret
 721
 722 ;
 723 ; Checksum error message
 724 ;
 725 checksumerr_msg db ' Load error - ', 0  ; Boot failed appended
 726
 727 ;
 728 ; BIOS type string
 729 ;
 730 cbios_name      db 'CBIOS', 0
 731 ebios_name      db 'EBIOS', 0
 732
 733 ;
 734 ; Debug routine
 735 ;
 736 %ifdef debug
 737 safedumpregs:
 738                 cmp word [Debug_Magic],0D00Dh
 739                 jnz nc_return
 740                 jmp dumpregs
 741 %endif
 742
 743 rl_checkpt      equ $                           ; Must be <= 8000h
 744
 745 rl_checkpt_off  equ ($-$$)
 746 %ifndef DEPEND
 747 %if rl_checkpt_off > 400h
 748 %error "Sector 1 overflow"
 749 %endif
 750 %endif
 751
 752 ; ----------------------------------------------------------------------------
 753 ;  End of code and data that have to be in the first sector
 754 ; ----------------------------------------------------------------------------
 755
 756 all_read:
 757 ;
 758 ; Let the user (and programmer!) know we got this far.  This used to be
 759 ; in Sector 1, but makes a lot more sense here.
 760 ;
 761                 mov si,copyright_str
 762                 call writestr
 763
 764
 765 ;
 766 ; Insane hack to expand the superblock to dwords
 767 ;
 768 expand_super:
 769                 xor eax,eax
 770                 mov si,superblock
 771                 mov di,SuperInfo
 772                 mov cx,superinfo_size
 773 .loop:
 774                 lodsw
 775                 dec si
 776                 stosd                           ; Store expanded word
 777                 xor ah,ah
 778                 stosd                           ; Store expanded byte
 779                 loop .loop
 780
 781 ;
 782 ; Compute some information about this filesystem.
 783 ;
 784
 785 ; First, generate the map of regions
 786 genfatinfo:
 787                 mov edx,[bxSectors]
 788                 and dx,dx
 789                 jnz .have_secs
 790                 mov edx,[bsHugeSectors]
 791 .have_secs:
 792                 mov [TotalSectors],edx
 793
 794                 mov eax,[bxResSectors]
 795                 mov [FAT],eax                   ; Beginning of FAT
 796                 mov edx,[bxFATsecs]
 797                 and dx,dx
 798                 jnz .have_fatsecs
 799                 mov edx,[bootsec+36]            ; FAT32 BPB_FATsz32
 800 .have_fatsecs:
 801                 imul edx,[bxFATs]
 802                 add eax,edx
 803                 mov [RootDirArea],eax           ; Beginning of root directory
 804                 mov [RootDir],eax               ; For FAT12/16 == root dir location
 805
 806                 mov edx,[bxRootDirEnts]
 807                 add dx,SECTOR_SIZE/32-1
 808                 shr dx,SECTOR_SHIFT-5
 809                 mov [RootDirSize],edx
 810                 add eax,edx
 811                 mov [DataArea],eax              ; Beginning of data area
 812
 813 ; Next, generate a cluster size shift count and mask
 814                 mov eax,[bxSecPerClust]
 815                 bsr cx,ax
 816                 mov [ClustShift],cl
 817                 push cx
 818                 add cl,SECTOR_SHIFT
 819                 mov [ClustByteShift],cl
 820                 pop cx
 821                 dec ax
 822                 mov [ClustMask],eax
 823                 inc ax
 824                 shl eax,SECTOR_SHIFT
 825                 mov [ClustSize],eax
 826
 827 ;
 828 ; FAT12, FAT16 or FAT28^H^H32?  This computation is fscking ridiculous.
 829 ;
 830 getfattype:
 831                 mov eax,[TotalSectors]
 832                 sub eax,[DataArea]
 833                 shr eax,cl                      ; cl == ClustShift
 834                 mov cl,nextcluster_fat12-(nextcluster+2)
 835                 cmp eax,4085                    ; FAT12 limit
 836                 jb .setsize
 837                 mov cl,nextcluster_fat16-(nextcluster+2)
 838                 cmp eax,65525                   ; FAT16 limit
 839                 jb .setsize
 840                 ;
 841                 ; FAT32, root directory is a cluster chain
 842                 ;
 843                 mov cl,[ClustShift]
 844                 mov eax,[bootsec+44]            ; Root directory cluster
 845                 sub eax,2
 846                 shl eax,cl
 847                 add eax,[DataArea]
 848                 mov [RootDir],eax
 849                 mov cl,nextcluster_fat28-(nextcluster+2)
 850 .setsize:
 851                 mov byte [nextcluster+1],cl
 852
 853 ;
 854 ; Common initialization code
 855 ;
 856 %include "cpuinit.inc"
 857 %include "init.inc"
 858
 859 ;
 860 ; Initialize the metadata cache
 861 ;
 862                 call initcache
 863
 864 ;
 865 ; Now, everything is "up and running"... patch kaboom for more
 866 ; verbosity and using the full screen system
 867 ;
 868                 ; E9 = JMP NEAR
 869                 mov dword [kaboom.patch],0e9h+((kaboom2-(kaboom.patch+3)) << 8)
 870
 871 ;
 872 ; Now we're all set to start with our *real* business.  First load the
 873 ; configuration file (if any) and parse it.
 874 ;
 875 ; In previous versions I avoided using 32-bit registers because of a
 876 ; rumour some BIOSes clobbered the upper half of 32-bit registers at
 877 ; random.  I figure, though, that if there are any of those still left
 878 ; they probably won't be trying to install Linux on them...
 879 ;
 880 ; The code is still ripe with 16-bitisms, though.  Not worth the hassle
 881 ; to take'm out.  In fact, we may want to put them back if we're going
 882 ; to boot ELKS at some point.
 883 ;
 884
 885 ;
 886 ; Load configuration file
 887 ;
 888                 mov si,config_name      ; Save configuration file name
 889                 mov di,ConfigName
 890                 call strcpy
 891
 892                 mov di,syslinux_cfg1
 893                 call open
 894                 jnz .config_open
 895                 mov di,syslinux_cfg2
 896                 call open
 897                 jnz .config_open
 898                 mov di,syslinux_cfg3
 899                 call open
 900                 jz no_config_file
 901 .config_open:
 902                 mov eax,[PrevDir]       ; Make the directory with syslinux.cfg ...
 903                 mov [CurrentDir],eax    ; ... the current directory
 904
 905 ;
 906 ; Now we have the config file open.  Parse the config file and
 907 ; run the user interface.
 908 ;
 909 %include "ui.inc"
 910
 911 ;
 912 ; allocate_file: Allocate a file structure
 913 ;
 914 ;               If successful:
 915 ;                 ZF set
 916 ;                 BX = file pointer
 917 ;               In unsuccessful:
 918 ;                 ZF clear
 919 ;
 920 allocate_file:
 921                 TRACER 'a'
 922                 push cx
 923                 mov bx,Files
 924                 mov cx,MAX_OPEN
 925 .check:         cmp dword [bx], byte 0
 926                 je .found
 927                 add bx,open_file_t_size         ; ZF = 0
 928                 loop .check
 929                 ; ZF = 0 if we fell out of the loop
 930 .found:         pop cx
 931                 ret
 932
 933 ;
 934 ; search_dos_dir:
 935 ;            Search a specific directory for a pre-mangled filename in
 936 ;            MangledBuf, in the directory starting in sector EAX.
 937 ;
 938 ;            NOTE: This file considers finding a zero-length file an
 939 ;            error.  This is so we don't have to deal with that special
 940 ;            case elsewhere in the program (most loops have the test
 941 ;            at the end).
 942 ;
 943 ;            Assumes DS == ES == CS.
 944 ;
 945 ;            If successful:
 946 ;               ZF clear
 947 ;               SI      = file pointer
 948 ;               EAX     = file length (MAY BE ZERO!)
 949 ;               DL      = file attributes
 950 ;            If unsuccessful
 951 ;               ZF set
 952 ;
 953
 954 search_dos_dir:
 955                 push bx
 956                 call allocate_file
 957                 jnz .alloc_failure
 958
 959                 push cx
 960                 push gs
 961                 push es
 962                 push ds
 963                 pop es                          ; ES = DS
 964
 965 .scansector:
 966                 ; EAX <- directory sector to scan
 967                 call getcachesector
 968                 ; GS:SI now points to this sector
 969
 970                 mov cx,SECTOR_SIZE/32           ; 32 == directory entry size
 971 .scanentry:
 972                 cmp byte [gs:si],0
 973                 jz .failure                     ; Hit directory high water mark
 974                 test byte [gs:si+11],8          ; Ignore volume labels and
 975                                                 ; VFAT long filename entries
 976                 jnz .nomatch
 977                 push cx
 978                 push si
 979                 push di
 980                 mov di,MangledBuf
 981                 mov cx,11
 982                 gs repe cmpsb
 983                 pop di
 984                 pop si
 985                 pop cx
 986                 jz .found
 987 .nomatch:
 988                 add si,32
 989                 loop .scanentry
 990
 991                 call nextsector
 992                 jnc .scansector                 ; CF is set if we're at end
 993
 994                 ; If we get here, we failed
 995 .failure:
 996                 pop es
 997                 pop gs
 998                 pop cx
 999 .alloc_failure:
1000                 pop bx
1001                 xor eax,eax                     ; ZF <- 1
1002                 ret
1003 .found:
1004                 mov eax,[gs:si+28]              ; File size
1005                 add eax,SECTOR_SIZE-1
1006                 shr eax,SECTOR_SHIFT
1007                 mov [bx+4],eax                  ; Sector count
1008
1009                 mov cl,[ClustShift]
1010                 mov dx,[gs:si+20]               ; High cluster word
1011                 shl edx,16
1012                 mov dx,[gs:si+26]               ; Low cluster word
1013                 sub edx,2
1014                 shl edx,cl
1015                 add edx,[DataArea]
1016                 mov [bx],edx                    ; Starting sector
1017
1018                 mov eax,[gs:si+28]              ; File length again
1019                 mov dl,[gs:si+11]               ; File attribute
1020                 mov si,bx                       ; File pointer...
1021                 and si,si                       ; ZF <- 0
1022
1023                 pop es
1024                 pop gs
1025                 pop cx
1026                 pop bx
1027                 ret
1028
1029 ;
1030 ; close_file:
1031 ;            Deallocates a file structure (pointer in SI)
1032 ;            Assumes CS == DS.
1033 ;
1034 close_file:
1035                 and si,si
1036                 jz .closed
1037                 mov dword [si],0                ; First dword == file_sector
1038                 xor si,si
1039 .closed:        ret
1040
1041 ;
1042 ; searchdir:
1043 ;
1044 ;       Open a file
1045 ;
1046 ;            On entry:
1047 ;               DS:DI   = filename
1048 ;            If successful:
1049 ;               ZF clear
1050 ;               SI              = file pointer
1051 ;               EAX             = file length in bytes
1052 ;            If unsuccessful
1053 ;               ZF set
1054 ;
1055 ; Assumes CS == DS == ES, and trashes BX and CX.
1056 ;
1057 searchdir:
1058                 mov eax,[CurrentDir]
1059                 cmp byte [di],'/'       ; Root directory?
1060                 jne .notroot
1061                 mov eax,[RootDir]
1062                 inc di
1063 .notroot:
1064
1065 .pathwalk:
1066                 push eax                ; <A> Current directory sector
1067                 mov si,di
1068 .findend:
1069                 lodsb
1070                 cmp al,' '
1071                 jbe .endpath
1072                 cmp al,'/'
1073                 jne .findend
1074 .endpath:
1075                 xchg si,di
1076                 pop eax                 ; <A> Current directory sector
1077
1078                 mov [PrevDir],eax       ; Remember last directory searched
1079
1080                 push di
1081                 call mangle_dos_name    ; MangledBuf <- component
1082                 call search_dos_dir
1083                 pop di
1084                 jz .notfound            ; Pathname component missing
1085
1086                 cmp byte [di-1],'/'     ; Do we expect a directory
1087                 je .isdir
1088
1089                 ; Otherwise, it should be a file
1090 .isfile:
1091                 test dl,18h             ; Subdirectory|Volume Label
1092                 jnz .badfile            ; If not a file, it's a bad thing
1093
1094                 ; SI and EAX are already set
1095                 mov [si+file_bytesleft],eax
1096                 push eax
1097                 add eax,SECTOR_SIZE-1
1098                 shr eax,SECTOR_SHIFT
1099                 mov [si+file_left],eax  ; Sectors left
1100                 pop eax
1101                 and eax,eax             ; EAX != 0
1102                 jz .badfile
1103                 ret                     ; Done!
1104
1105                 ; If we expected a directory, it better be one...
1106 .isdir:
1107                 test dl,10h             ; Subdirectory
1108                 jz .badfile
1109
1110                 xor eax,eax
1111                 xchg eax,[si+file_sector] ; Get sector number and free file structure
1112                 jmp .pathwalk           ; Walk the next bit of the path
1113
1114 .badfile:
1115                 xor eax,eax
1116                 mov [si],eax            ; Free file structure
1117
1118 .notfound:
1119                 xor eax,eax
1120                 ret
1121
1122                 section .bss
1123                 alignb 4
1124 CurrentDir      resd 1                  ; Current directory
1125 PrevDir         resd 1                  ; Last scanned directory
1126
1127                 section .text
1128
1129 ;
1130 ;
1131 ; kaboom2: once everything is loaded, replace the part of kaboom
1132 ;          starting with "kaboom.patch" with this part
1133
1134 kaboom2:
1135                 mov si,err_bootfailed
1136                 call cwritestr
1137                 cmp byte [kaboom.again+1],18h   ; INT 18h version?
1138                 je .int18
1139                 call getchar
1140                 call vgaclearmode
1141                 int 19h                 ; And try once more to boot...
1142 .norge:         jmp short .norge        ; If int 19h returned; this is the end
1143 .int18:
1144                 call vgaclearmode
1145                 int 18h
1146 .noreg:         jmp short .noreg        ; Nynorsk
1147
1148 ;
1149 ; mangle_name: Mangle a filename pointed to by DS:SI into a buffer pointed
1150 ;              to by ES:DI; ends on encountering any whitespace.
1151 ;              DI is preserved.
1152 ;
1153 ;              This verifies that a filename is < FILENAME_MAX characters,
1154 ;              doesn't contain whitespace, zero-pads the output buffer,
1155 ;              and removes trailing dots and redundant slashes, plus changes
1156 ;              backslashes to forward slashes,
1157 ;              so "repe cmpsb" can do a compare, and the path-searching routine
1158 ;              gets a bit of an easier job.
1159 ;
1160 ;
1161 mangle_name:
1162                 push di
1163                 push bx
1164                 xor ax,ax
1165                 mov cx,FILENAME_MAX-1
1166                 mov bx,di
1167
1168 .mn_loop:
1169                 lodsb
1170                 cmp al,' '                      ; If control or space, end
1171                 jna .mn_end
1172                 cmp al,'\'                      ; Backslash?
1173                 jne .mn_not_bs
1174                 mov al,'/'                      ; Change to forward slash
1175 .mn_not_bs:
1176                 cmp al,ah                       ; Repeated slash?
1177                 je .mn_skip
1178                 xor ah,ah
1179                 cmp al,'/'
1180                 jne .mn_ok
1181                 mov ah,al
1182 .mn_ok          stosb
1183 .mn_skip:       loop .mn_loop
1184 .mn_end:
1185                 cmp bx,di                       ; At the beginning of the buffer?
1186                 jbe .mn_zero
1187                 cmp byte [es:di-1],'.'          ; Terminal dot?
1188                 je .mn_kill
1189                 cmp byte [es:di-1],'/'          ; Terminal slash?
1190                 jne .mn_zero
1191 .mn_kill:       dec di                          ; If so, remove it
1192                 inc cx
1193                 jmp short .mn_end
1194 .mn_zero:
1195                 inc cx                          ; At least one null byte
1196                 xor ax,ax                       ; Zero-fill name
1197                 rep stosb
1198                 pop bx
1199                 pop di
1200                 ret                             ; Done
1201
1202 ;
1203 ; unmangle_name: Does the opposite of mangle_name; converts a DOS-mangled
1204 ;                filename to the conventional representation.  This is needed
1205 ;                for the BOOT_IMAGE= parameter for the kernel.
1206 ;                NOTE: A 13-byte buffer is mandatory, even if the string is
1207 ;                known to be shorter.
1208 ;
1209 ;                DS:SI -> input mangled file name
1210 ;                ES:DI -> output buffer
1211 ;
1212 ;                On return, DI points to the first byte after the output name,
1213 ;                which is set to a null byte.
1214 ;
1215 unmangle_name:  call strcpy
1216                 dec di                          ; Point to final null byte
1217                 ret
1218
1219 ;
1220 ; mangle_dos_name:
1221 ;               Mangle a DOS filename component pointed to by DS:SI
1222 ;               into [MangledBuf]; ends on encountering any whitespace or slash.
1223 ;               Assumes CS == DS == ES.
1224 ;
1225
1226 mangle_dos_name:
1227                 pusha
1228                 mov di,MangledBuf
1229
1230                 mov cx,11                       ; # of bytes to write
1231 .loop:
1232                 lodsb
1233                 cmp al,' '                      ; If control or space, end
1234                 jna .end
1235                 cmp al,'/'                      ; Slash, too
1236                 je .end
1237                 cmp al,'.'                      ; Period -> space-fill
1238                 je .is_period
1239                 cmp al,'a'
1240                 jb .not_lower
1241                 cmp al,'z'
1242                 ja .not_uslower
1243                 sub al,020h
1244                 jmp short .not_lower
1245 .is_period:     mov al,' '                      ; We need to space-fill
1246 .period_loop:   cmp cx,3                        ; If <= 3 characters left
1247                 jbe .loop                       ; Just ignore it
1248                 stosb                           ; Otherwise, write a period
1249                 loop .period_loop               ; Dec CX and (always) jump
1250 .not_uslower:   cmp al,ucase_low
1251                 jb .not_lower
1252                 cmp al,ucase_high
1253                 ja .not_lower
1254                 mov bx,ucase_tab-ucase_low
1255                 xlatb
1256 .not_lower:     stosb
1257                 loop .loop                      ; Don't continue if too long
1258 .end:
1259                 mov al,' '                      ; Space-fill name
1260                 rep stosb                       ; Doesn't do anything if CX=0
1261                 popa
1262                 ret                             ; Done
1263
1264                 section .bss
1265 MangledBuf      resb 11
1266
1267                 section .text
1268 ;
1269 ; Case tables for extended characters; this is technically code page 865,
1270 ; but code page 437 users will probably not miss not being able to use the
1271 ; cent sign in kernel images too much :-)
1272 ;
1273 ; The table only covers the range 129 to 164; the rest we can deal with.
1274 ;
1275                 section .data
1276
1277 ucase_low       equ 129
1278 ucase_high      equ 164
1279 ucase_tab       db 154, 144, 'A', 142, 'A', 143, 128, 'EEEIII'
1280                 db 142, 143, 144, 146, 146, 'O', 153, 'OUUY', 153, 154
1281                 db 157, 156, 157, 158, 159, 'AIOU', 165
1282
1283                 section .text
1284 ;
1285 ; getfssec_edx: Get multiple sectors from a file
1286 ;
1287 ;       This routine makes sure the subtransfers do not cross a 64K boundary,
1288 ;       and will correct the situation if it does, UNLESS *sectors* cross
1289 ;       64K boundaries.
1290 ;
1291 ;       ES:BX   -> Buffer
1292 ;       EDX     -> Current sector number
1293 ;       CX      -> Sector count (0FFFFh = until end of file)
1294 ;                  Must not exceed the ES segment
1295 ;       Returns EDX=0, CF=1 on EOF (not necessarily error)
1296 ;       All arguments are advanced to reflect data read.
1297 ;
1298 getfssec_edx:
1299                 push ebp
1300                 push eax
1301 .getfragment:
1302                 xor ebp,ebp                     ; Fragment sector count
1303                 push edx                        ; Starting sector pointer
1304 .getseccnt:
1305                 inc bp
1306                 dec cx
1307                 jz .do_read
1308                 xor eax,eax
1309                 mov ax,es
1310                 shl ax,4
1311                 add ax,bx                       ; Now AX = how far into 64K block we are
1312                 not ax                          ; Bytes left in 64K block
1313                 inc eax
1314                 shr eax,SECTOR_SHIFT            ; Sectors left in 64K block
1315                 cmp bp,ax
1316                 jnb .do_read                    ; Unless there is at least 1 more sector room...
1317                 mov eax,edx                     ; Current sector
1318                 inc edx                         ; Predict it's the linearly next sector
1319                 call nextsector
1320                 jc .do_read
1321                 cmp edx,eax                     ; Did it match?
1322                 jz .getseccnt
1323 .do_read:
1324                 pop eax                         ; Starting sector pointer
1325                 call getlinsecsr
1326                 lea eax,[eax+ebp-1]             ; This is the last sector actually read
1327                 shl bp,9
1328                 add bx,bp                       ; Adjust buffer pointer
1329                 call nextsector
1330                 jc .eof
1331                 mov edx,eax
1332                 and cx,cx
1333                 jnz .getfragment
1334 .done:
1335                 pop eax
1336                 pop ebp
1337                 ret
1338 .eof:
1339                 xor edx,edx
1340                 stc
1341                 jmp .done
1342
1343 ;
1344 ; getfssec: Get multiple sectors from a file
1345 ;
1346 ;       Same as above, except SI is a pointer to a open_file_t
1347 ;
1348 ;       ES:BX   -> Buffer
1349 ;       DS:SI   -> Pointer to open_file_t
1350 ;       CX      -> Sector count (0FFFFh = until end of file)
1351 ;                  Must not exceed the ES segment
1352 ;       Returns CF=1 on EOF (not necessarily error)
1353 ;       ECX returns number of bytes read.
1354 ;       All arguments are advanced to reflect data read.
1355 ;
1356 getfssec:
1357                 push edx
1358                 movzx edx,cx
1359                 push edx                ; Zero-extended CX
1360                 cmp edx,[si+file_left]
1361                 jbe .sizeok
1362                 mov edx,[si+file_left]
1363                 mov cx,dx
1364 .sizeok:
1365                 sub [si+file_left],edx
1366                 mov edx,[si+file_sector]
1367                 call getfssec_edx
1368                 mov [si+file_sector],edx
1369                 pop ecx                 ; Sectors requested read
1370                 shl ecx,SECTOR_SHIFT
1371                 cmp ecx,[si+file_bytesleft]
1372                 ja .eof
1373 .noteof:
1374                 sub [si+file_bytesleft],ecx     ; CF <- 0
1375                 pop edx
1376                 ret
1377 .eof:
1378                 mov ecx,[si+file_bytesleft]
1379                 call close_file
1380                 pop edx
1381                 stc
1382                 ret
1383
1384 ;
1385 ; nextcluster: Advance a cluster pointer in EDI to the next cluster
1386 ;              pointed at in the FAT tables.  CF=0 on return if end of file.
1387 ;
1388 nextcluster:
1389                 jmp strict short nextcluster_fat28      ; This gets patched
1390
1391 nextcluster_fat12:
1392                 push eax
1393                 push edx
1394                 push bx
1395                 push cx
1396                 push si
1397                 mov edx,edi
1398                 shr edi,1
1399                 pushf                   ; Save the shifted-out LSB (=CF)
1400                 add edx,edi
1401                 mov eax,edx
1402                 shr eax,9
1403                 call getfatsector
1404                 mov bx,dx
1405                 and bx,1FFh
1406                 mov cl,[gs:si+bx]
1407                 inc edx
1408                 mov eax,edx
1409                 shr eax,9
1410                 call getfatsector
1411                 mov bx,dx
1412                 and bx,1FFh
1413                 mov ch,[gs:si+bx]
1414                 popf
1415                 jnc .even
1416                 shr cx,4
1417 .even:          and cx,0FFFh
1418                 movzx edi,cx
1419                 cmp di,0FF0h
1420                 pop si
1421                 pop cx
1422                 pop bx
1423                 pop edx
1424                 pop eax
1425                 ret
1426
1427 ;
1428 ; FAT16 decoding routine.
1429 ;
1430 nextcluster_fat16:
1431                 push eax
1432                 push si
1433                 push bx
1434                 mov eax,edi
1435                 shr eax,SECTOR_SHIFT-1
1436                 call getfatsector
1437                 mov bx,di
1438                 add bx,bx
1439                 and bx,1FEh
1440                 movzx edi,word [gs:si+bx]
1441                 cmp di,0FFF0h
1442                 pop bx
1443                 pop si
1444                 pop eax
1445                 ret
1446 ;
1447 ; FAT28 ("FAT32") decoding routine.
1448 ;
1449 nextcluster_fat28:
1450                 push eax
1451                 push si
1452                 push bx
1453                 mov eax,edi
1454                 shr eax,SECTOR_SHIFT-2
1455                 call getfatsector
1456                 mov bx,di
1457                 add bx,bx
1458                 add bx,bx
1459                 and bx,1FCh
1460                 mov edi,dword [gs:si+bx]
1461                 and edi,0FFFFFFFh       ; 28 bits only
1462                 cmp edi,0FFFFFF0h
1463                 pop bx
1464                 pop si
1465                 pop eax
1466                 ret
1467
1468 ;
1469 ; nextsector:   Given a sector in EAX on input, return the next sector
1470 ;               of the same filesystem object, which may be the root
1471 ;               directory or a cluster chain.  Returns  EOF.
1472 ;
1473 ;               Assumes CS == DS.
1474 ;
1475 nextsector:
1476                 push edi
1477                 push edx
1478                 mov edx,[DataArea]
1479                 mov edi,eax
1480                 sub edi,edx
1481                 jae .isdata
1482
1483                 ; Root directory
1484                 inc eax
1485                 cmp eax,edx
1486                 cmc
1487                 jmp .done
1488
1489 .isdata:
1490                 not edi
1491                 test edi,[ClustMask]
1492                 jz .endcluster
1493
1494                 ; It's not the final sector in a cluster
1495                 inc eax
1496                 jmp .done
1497
1498 .endcluster:
1499                 push gs                 ; nextcluster trashes gs
1500                 push cx
1501                 not edi
1502                 mov cl,[ClustShift]
1503                 shr edi,cl
1504                 add edi,2
1505
1506                 ; Now EDI contains the cluster number
1507                 call nextcluster
1508                 cmc
1509                 jc .exit                ; There isn't anything else...
1510
1511                 ; New cluster number now in EDI
1512                 sub edi,2
1513                 shl edi,cl              ; CF <- 0, unless something is very wrong
1514                 lea eax,[edi+edx]
1515 .exit:
1516                 pop cx
1517                 pop gs
1518 .done:
1519                 pop edx
1520                 pop edi
1521                 ret
1522
1523 ;
1524 ; getfatsector: Check for a particular sector (in EAX) in the FAT cache,
1525 ;               and return a pointer in GS:SI, loading it if needed.
1526 ;
1527 ;               Assumes CS == DS.
1528 ;
1529 getfatsector:
1530                 add eax,[FAT]           ; FAT starting address
1531                 jmp getcachesector
1532
1533 ; -----------------------------------------------------------------------------
1534 ;  Common modules
1535 ; -----------------------------------------------------------------------------
1536
1537 %include "getc.inc"             ; getc et al
1538 %include "conio.inc"            ; Console I/O
1539 %include "plaincon.inc"         ; writechr
1540 %include "writestr.inc"         ; String output
1541 %include "configinit.inc"       ; Initialize configuration
1542 %include "parseconfig.inc"      ; High-level config file handling
1543 %include "parsecmd.inc"         ; Low-level config file handling
1544 %include "bcopy32.inc"          ; 32-bit bcopy
1545 %include "loadhigh.inc"         ; Load a file into high memory
1546 %include "font.inc"             ; VGA font stuff
1547 %include "graphics.inc"         ; VGA graphics
1548 %include "highmem.inc"          ; High memory sizing
1549 %include "strcpy.inc"           ; strcpy()
1550 %include "cache.inc"            ; Metadata disk cache
1551 %include "adv.inc"              ; Auxillary Data Vector
1552
1553 ; -----------------------------------------------------------------------------
1554 ;  Begin data section
1555 ; -----------------------------------------------------------------------------
1556
1557                 section .data
1558 copyright_str   db ' Copyright (C) 1994-', year, ' H. Peter Anvin'
1559                 db CR, LF, 0
1560 err_bootfailed  db CR, LF, 'Boot failed: please change disks and press '
1561                 db 'a key to continue.', CR, LF, 0
1562 syslinux_cfg1   db '/boot'                      ; /boot/syslinux/syslinux.cfg
1563 syslinux_cfg2   db '/syslinux'                  ; /syslinux/syslinux.cfg
1564 syslinux_cfg3   db '/'                          ; /syslinux.cfg
1565 config_name     db 'syslinux.cfg', 0            ; syslinux.cfg
1566
1567 ;
1568 ; Command line options we'd like to take a look at
1569 ;
1570 ; mem= and vga= are handled as normal 32-bit integer values
1571 initrd_cmd      db 'initrd='
1572 initrd_cmd_len  equ 7
1573
1574 ;
1575 ; Config file keyword table
1576 ;
1577 %include "keywords.inc"
1578
1579 ;
1580 ; Extensions to search for (in *forward* order).
1581 ;
1582 exten_table:    db '.cbt'               ; COMBOOT (specific)
1583                 db '.bss'               ; Boot Sector (add superblock)
1584                 db '.bs', 0             ; Boot Sector
1585                 db '.com'               ; COMBOOT (same as DOS)
1586                 db '.c32'               ; COM32
1587 exten_table_end:
1588                 dd 0, 0                 ; Need 8 null bytes here
1589
1590 ;
1591 ; Misc initialized (data) variables
1592 ;
1593 %ifdef debug                            ; This code for debugging only
1594 debug_magic     dw 0D00Dh               ; Debug code sentinel
1595 %endif
1596
1597                 alignb 4, db 0
1598 BufSafe         dw trackbufsize/SECTOR_SIZE     ; Clusters we can load into trackbuf
1599 BufSafeBytes    dw trackbufsize         ; = how many bytes?
1600 %ifndef DEPEND
1601 %if ( trackbufsize % SECTOR_SIZE ) != 0
1602 %error trackbufsize must be a multiple of SECTOR_SIZE
1603 %endif
1604 %endif