1 ; ****************************************************************************
5 ; A program to boot Linux kernels off a CD-ROM using the El Torito
6 ; boot standard in "no emulation" mode, making the entire filesystem
7 ; available. It is based on the SYSLINUX boot loader for MS-DOS
10 ; Copyright (C) 1994-2001 H. Peter Anvin
12 ; This program is free software; you can redistribute it and/or modify
13 ; it under the terms of the GNU General Public License as published by
14 ; the Free Software Foundation, Inc., 675 Mass Ave, Cambridge MA 02139,
15 ; USA; either version 2 of the License, or (at your option) any later
16 ; version; incorporated herein by reference.
18 ; ****************************************************************************
20 ; THIS FILE IS A MODIFIED VERSION OF ISOLINUX.ASM
21 ; MODIFICATION DONE BY MICHAEL K TER LOUW
22 ; LAST UPDATED 3-9-2002
23 ; SEE "COPYING" FOR INFORMATION ABOUT THE LICENSE THAT APPLIES TO THIS RELEASE
25 ; ****************************************************************************
27 ; This file is a modified version of ISOLINUX.ASM.
28 ; Modification done by Eric Kohl
29 ; Last update 04-25-2002
31 ; ****************************************************************************
33 ; This file is a modified version of ISOLINUX.ASM.
34 ; (for ReactOS regression testing)
35 ; Modification done by Christoph von Wittich
36 ; Last update 08-27-2006
38 ; ****************************************************************************
41 ; Note: The Makefile builds one version with DEBUG_MESSAGES automatically.
42 ;%define DEBUG_MESSAGES ; Uncomment to get debugging messages
45 ; ---------------------------------------------------------------------------
46 ; BEGIN THE BIOS/CODE/DATA SEGMENT
47 ; ---------------------------------------------------------------------------
50 serial_base resw 4 ; Base addresses for 4 serial ports
52 BIOS_fbm resw 1 ; Free Base Memory (kilobytes)
54 BIOS_timer resw 1 ; Timer ticks
56 BIOS_magic resw 1 ; BIOS reset magic
58 BIOS_vidrows resb 1 ; Number of screen rows
61 ; Memory below this point is reserved for the BIOS and the MBR
64 trackbuf resb 8192 ; Track buffer goes here
65 trackbufsize equ $-trackbuf
66 ; trackbuf ends at 3000h
69 file_sector resd 1 ; Sector pointer (0 = structure free)
70 file_left resd 1 ; Number of sectors left
74 dir_lba resd 1 ; Directory start (LBA)
75 dir_len resd 1 ; Length in bytes
76 dir_clust resd 1 ; Length in clusters
80 MAX_OPEN_LG2 equ 2 ; log2(Max number of open files)
81 MAX_OPEN equ (1 << MAX_OPEN_LG2)
82 SECTORSIZE_LG2 equ 11 ; 2048 bytes/sector (El Torito requirement)
83 SECTORSIZE equ (1 << SECTORSIZE_LG2)
84 CR equ 13 ; Carriage Return
86 retry_count equ 6 ; How patient are we with the BIOS?
90 absolute 5000h ; Here we keep our BSS stuff
92 DriveNo resb 1 ; CD-ROM BIOS drive number
93 DiskError resb 1 ; Error code for disk I/O
94 RetryCount resb 1 ; Used for disk access retries
95 TimeoutCount resb 1 ; Timeout counter
96 ISOFlags resb 1 ; Flags for ISO directory search
97 RootDir resb dir_t_size ; Root directory
98 CurDir resb dir_t_size ; Current directory
99 ISOFileName resb 64 ; ISO filename canonicalization buffer
103 alignb open_file_t_size
104 Files resb MAX_OPEN*open_file_t_size
112 cli ; Disable interrupts
113 xor ax, ax ; ax = segment zero
114 mov ss, ax ; Initialize stack segment
115 mov sp, start ; Set up stack
116 mov ds, ax ; Initialize other segment registers
120 sti ; Enable interrupts
121 cld ; Increment pointers
123 mov cx, 2048 >> 2 ; Copy the bootsector
124 mov si, 0x7C00 ; from 0000:7C00
125 mov di, 0x7000 ; to 0000:7000
126 rep movsd ; copy the program
127 jmp 0:relocate ; jump into relocated code
130 ; Display the banner and copyright
131 %ifdef DEBUG_MESSAGES
132 mov si, isolinux_banner ; si points to hello message
133 call writestr ; display the message
138 ; check if there is a mbr on the hdd if so boot from it
147 jc .boot_cdrom ; could not read hdd
150 mov ax, word [trackbuf+510]
152 je .boot_cdrom ; no boot sector found (hopefully there are no weird bootsectors which begin with 0)
158 ; Boot first harddisk (drive 0x80)
177 ; Save and display the boot drive number
179 %ifdef DEBUG_MESSAGES
187 ; Now figure out what we're actually doing
188 ; Note: use passed-in DL value rather than 7Fh because
189 ; at least some BIOSes will get the wrong value otherwise
190 mov ax, 4B01h ; Get disk emulation status
194 jc near spec_query_failed ; Shouldn't happen (BIOS bug)
196 cmp [sp_drive], dl ; Should contain the drive number
197 jne near spec_query_failed
199 %ifdef DEBUG_MESSAGES
202 mov al, byte [sp_drive]
208 ; Get drive information
215 ; mov si, nosecsize_msg No use in reporting this
219 ; Check for the sector size (should be 2048, but
220 ; some BIOSes apparently think we're 512-byte media)
222 ; FIX: We need to check what the proper behaviour
223 ; is for getlinsec when the BIOS thinks the sector
224 ; size is 512!!! For that, we need such a BIOS, though...
225 %ifdef DEBUG_MESSAGES
235 ; Clear Files structures
238 mov cx, (MAX_OPEN*open_file_t_size)/4
243 ; Now, we need to sniff out the actual filesystem data structures.
244 ; mkisofs gave us a pointer to the primary volume descriptor
245 ; (which will be at 16 only for a single-session disk!); from the PVD
246 ; we should be able to find the rest of what we need to know.
249 mov eax, 16 ; Primary Volume Descriptor (sector 16)
253 mov eax, [trackbuf+156+2]
254 mov [RootDir+dir_lba],eax
255 mov [CurDir+dir_lba],eax
256 %ifdef DEBUG_MESSAGES
263 mov eax,[trackbuf+156+10]
264 mov [RootDir+dir_len],eax
265 mov [CurDir+dir_len],eax
266 %ifdef DEBUG_MESSAGES
273 shr eax,SECTORSIZE_LG2
274 mov [RootDir+dir_clust],eax
275 mov [CurDir+dir_clust],eax
276 %ifdef DEBUG_MESSAGES
283 ; Look for the "REACTOS" directory, and if found,
284 ; make it the current directory instead of the root
287 mov al,02h ; Search for a directory
295 mov [CurDir+dir_len],eax
296 mov eax,[si+file_left]
297 mov [CurDir+dir_clust],eax
298 xor eax,eax ; Free this file pointer entry
299 xchg eax,[si+file_sector]
300 mov [CurDir+dir_lba],eax
303 mov di, isolinux_bin ; di points to Isolinux filename
304 call searchdir ; look for the file
305 jnz .isolinux_opened ; got the file
306 mov si, no_isolinux_msg ; si points to error message
307 call writemsg ; display the message
308 jmp kaboom ; fail boot
311 mov di, si ; save file pointer
313 %ifdef DEBUG_MESSAGES
320 mov ecx, eax ; calculate sector count
327 %ifdef DEBUG_MESSAGES
335 mov bx, 0x8000 ; bx = load address
336 mov si, di ; restore file pointer
337 mov cx, 0xFFFF ; load the whole file
338 call getfssec ; get the whole file
340 %ifdef DEBUG_MESSAGES
346 mov dl, [DriveNo] ; dl = boot drive
347 mov dh, 0 ; dh = boot partition
348 jmp 0:0x8000 ; jump into OSLoader
362 ; DX:AX or EAX = file length in bytes
368 ; searchdir_iso is a special entry point for ISOLINUX only. In addition
369 ; to the above, searchdir_iso passes a file flag mask in AL. This is useful
370 ; for searching for directories.
380 call allocate_file ; Temporary file structure for directory
386 cmp byte [di],'\' ; If filename begins with slash
388 inc di ; Skip leading slash
389 mov si,RootDir ; Reference root directory instead
391 mov eax,[si+dir_clust]
392 mov [bx+file_left],eax
394 mov [bx+file_sector],eax
406 mov [di-1],byte 0 ; Terminate at directory name
407 mov cl,02h ; Search for directory
411 push word .resume ; Where to "return" to
417 ; Get a chunk of the directory
421 mov cx,1 ; load one sector
426 movzx eax, byte [si] ; Length of directory entry
431 test cl, byte 8Eh ; Unwanted file attributes!
434 movzx cx, byte [si+32] ; File identifier length
435 add si, byte 33 ; File identifier offset
436 call iso_compare_names
440 sub edx, eax ; Decrease bytes left
442 add si, ax ; Advance pointer
445 ; Did we finish the buffer?
446 cmp si, trackbuf+trackbufsize
447 jb .compare ; No, keep going
449 jmp short .getsome ; Get some more directory
452 ; Advance to the beginning of next sector
453 lea ax, [si+SECTORSIZE-1]
454 and ax, ~(SECTORSIZE-1)
456 jmp short .not_file ; We still need to do length checks
459 %ifdef DEBUG_MESSAGES
464 xor eax, eax ; ZF = 1
465 mov [bx+file_sector], eax
470 mov eax, [si+2] ; Location of extent
471 mov [bx+file_sector], eax
472 mov eax, [si+10] ; Data length
474 add eax, SECTORSIZE-1
475 shr eax, SECTORSIZE_LG2
476 mov [bx+file_left], eax
486 ; We get here if we were only doing part of a lookup
487 ; This relies on the fact that .success returns bx == si
488 xchg edx, eax ; Directory length in edx
489 pop cx ; Old ISOFlags
490 pop di ; Next filename pointer
492 mov byte [di-1], '\' ; restore the backslash in the filename
494 mov [ISOFlags], cl ; Restore the flags
495 jz .failure ; Did we fail? If so fail for real!
496 jmp .look_for_slash ; Otherwise, next level
499 ; allocate_file: Allocate a file structure
512 cmp dword [bx], byte 0
514 add bx, open_file_t_size ; ZF = 0
516 ; ZF = 0 if we fell out of the loop
523 ; Compare the names DS:SI and DS:DI and report if they are
524 ; equal from an ISO 9660 perspective. SI is the name from
525 ; the filesystem; CX indicates its length, and ';' terminates.
526 ; DI is expected to end with a null.
528 ; Note: clobbers AX, CX, SI, DI; assumes DS == ES == base segment
531 ; First, terminate and canonicalize input filename
543 cmp di, ISOFileNameEnd-1 ; Guard against buffer overrun
548 cmp byte [di-1], '.' ; Remove terminal dots
553 mov [di], byte 0 ; Null-terminate string
561 jz .success ; End of string for both
562 and al, al ; Is either one end of string?
563 jz .failure ; If so, failure
566 or ax, 2020h ; Convert to lower case
570 and ax, ax ; ZF = 0 (at least one will be nonzero)
581 ; getfssec: Get multiple clusters from a file, given the file pointer.
586 ; CX -> Cluster count; 0FFFFh = until end of file
588 ; SI -> File pointer (or 0 on EOF)
592 cmp cx, [si+file_left]
594 mov cx, [si+file_left]
600 mov eax, [si+file_sector]
606 add [si+file_sector], ecx
607 sub [si+file_left], ecx
611 mov [si+file_sector], ecx ; Mark as unused
620 ; INT 13h, AX=4B01h, DL=<passed in value> failed.
621 ; Try to scan the entire 80h-FFh from the end.
631 mov byte [si], 13 ; Size of buffer
642 cmp byte [sp_drive], dl
645 ; Okay, good enough...
652 ; Award BIOS 4.51 apparently passes garbage in sp_drive,
653 ; but if this was the drive number originally passed in
654 ; DL then consider it "good enough"
656 cmp byte [DriveNo], dl
673 ; Information message (DS:SI) output
674 ; Prefix with "isolinux: "
687 ; crlf: Print a newline
694 ; writestr: write a null-terminated string to the console, saving
695 ; registers on entry.
713 ; writehex[248]: Write a hex number in (AL, AX, EAX) to the console
720 jmp short writehex_common
726 jmp short writehex_common
752 ; Write a character to the screen. There is a more "sophisticated"
753 ; version of this in the subsequent code, so we patch the pointer
768 ; Get one sector. Convenience entry point.
772 ; Fall through to getlinsec
775 ; Get linear sectors - EBIOS LBA addressing, 2048-byte sectors.
777 ; Note that we can't always do this as a single request, because at least
778 ; Phoenix BIOSes has a 127-sector limit. To be on the safe side, stick
779 ; to 32 sectors (64K) per request.
782 ; EAX - Linear sector number
783 ; ES:BX - Target buffer
787 mov si,dapa ; Load up the DAPA
793 push bp ; Sectors left
801 mov ah,42h ; Extended Read
805 movzx eax,word [si+2] ; Sectors we read
806 add [si+8],eax ; Advance sector pointer
807 sub bp,ax ; Sectors left
808 shl ax,SECTORSIZE_LG2-4 ; 2048-byte sectors -> segment
809 add [si+6],ax ; Advance buffer pointer
812 mov eax,[si+8] ; Next sector
817 mov byte [RetryCount], retry_count
822 add sp, byte 8*4 ; Clean up stack
825 mov [DiskError], ah ; Save error code
827 dec byte [RetryCount]
831 mov ah,[dapa+2] ; Sector transfer count
832 cmp al,2 ; Only 2 attempts left
834 mov ah,1 ; Drop transfer size to 1
838 ja .again ; First time, just try again
839 shr ah,1 ; Otherwise, try to reduce
840 adc ah,0 ; the max transfer size, but not to 0
858 ; Fall through to kaboom
861 ; kaboom: write a message and bail out. Wait for a user keypress,
862 ; then do a hard reboot.
871 mov si, err_bootfailed
875 mov word [BIOS_magic], 0 ; Cold reboot
876 jmp 0F000h:0FFF0h ; Reset vector address
880 mov ah, 1 ; Poll keyboard
884 xor ax, ax ; Get keyboard input
890 isolinux_banner db CR, LF, 'Loading IsoBoot...', CR, LF, 0
891 copyright_str db ' Copyright (C) 1994-2002 H. Peter Anvin', CR, LF, 0
892 presskey_msg db 'Press any key to boot from CD', 0
895 %ifdef DEBUG_MESSAGES
896 startup_msg: db 'Starting up, DL = ', 0
897 spec_ok_msg: db 'Loaded spec packet OK, drive = ', 0
898 secsize_msg: db 'Sector size appears to be ', 0
899 rootloc_msg: db 'Root directory location: ', 0
900 rootlen_msg: db 'Root directory length: ', 0
901 rootsect_msg: db 'Root directory length(sectors): ', 0
902 fileloc_msg: db 'SETUPLDR.SYS location: ', 0
903 filelen_msg: db 'SETUPLDR.SYS length: ', 0
904 filesect_msg: db 'SETUPLDR.SYS length(sectors): ', 0
905 findfail_msg: db 'Failed to find file!', 0
906 startldr_msg: db 'Starting SETUPLDR.SYS', 0
909 nosecsize_msg: db 'Failed to get sector size, assuming 0800', CR, LF, 0
910 spec_err_msg: db 'Loading spec packet failed, trying to wing it...', CR, LF, 0
911 maybe_msg: db 'Found something at drive = ', 0
912 alright_msg: db 'Looks like it might be right, continuing...', CR, LF, 0
913 nothing_msg: db 'Failed to locate CD-ROM device; boot failed.', CR, LF, 0
914 isolinux_str db 'IsoBoot: ', 0
915 crlf_msg db CR, LF, 0
916 diskerr_msg: db 'Disk error ', 0
917 ondrive_str: db ', drive ', 0
918 err_bootfailed db CR, LF, 'Boot failed: press a key to retry...'
919 isolinux_dir db '\LOADER', 0
920 no_dir_msg db 'Could not find the LOADER directory.', CR, LF, 0
921 isolinux_bin db 'SETUPLDR.SYS', 0
922 no_isolinux_msg db 'Could not find SETUPLDR.SYS.', CR, LF, 0
925 ; El Torito spec packet
928 spec_packet: db 13h ; Size of packet
929 sp_media: db 0 ; Media type
930 sp_drive: db 0 ; Drive number
931 sp_controller: db 0 ; Controller index
932 sp_lba: dd 0 ; LBA for emulated disk image
933 sp_devspec: dw 0 ; IDE/SCSI information
934 sp_buffer: dw 0 ; User-provided buffer
935 sp_loadseg: dw 0 ; Load segment
936 sp_sectors: dw 0 ; Sector count
937 sp_chs: db 0,0,0 ; Simulated CHS geometry
938 sp_dummy: db 0 ; Scratch, safe to overwrite
941 ; EBIOS drive parameter packet
944 drive_params: dw 30 ; Buffer size
945 dp_flags: dw 0 ; Information flags
946 dp_cyl: dd 0 ; Physical cylinders
947 dp_head: dd 0 ; Physical heads
948 dp_sec: dd 0 ; Physical sectors/track
949 dp_totalsec: dd 0,0 ; Total sectors
950 dp_secsize: dw 0 ; Bytes per sector
951 dp_dpte: dd 0 ; Device Parameter Table
952 dp_dpi_key: dw 0 ; 0BEDDh if rest valid
953 dp_dpi_len: db 0 ; DPI len
956 dp_bus: times 4 db 0 ; Host bus type
957 dp_interface: times 8 db 0 ; Interface type
958 db_i_path: dd 0,0 ; Interface path
959 db_d_path: dd 0,0 ; Device path
961 db_dpi_csum: db 0 ; Checksum for DPI info
964 ; EBIOS disk address packet
967 dapa: dw 16 ; Packet size
968 .count: dw 0 ; Block count
969 .off: dw 0 ; Offset of buffer
970 .seg: dw 0 ; Segment of buffer
971 .lba: dd 0 ; LBA (LSW)
975 MaxTransfer dw 2 ;32 ; Max sectors per transfer
977 times 2046-($-$$) db 0 ; Pad to file offset 2046
978 dw 0aa55h ; BootSector signature