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source: bootcd/isolinux/syslinux-6.03/core/isolinux.asm

Last change on this file was e16e8f2, checked in by Edwin Eefting <edwin@datux.nl>, 3 years ago
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1	; -- fundamental -- (asm-mode sucks)
2	; ****************************************************************************
3	;
4	; isolinux.asm
5	;
6	; A program to boot Linux kernels off a CD-ROM using the El Torito
7	; boot standard in "no emulation" mode, making the entire filesystem
8	; available. It is based on the SYSLINUX boot loader for MS-DOS
9	; floppies.
10	;
11	; Copyright 1994-2009 H. Peter Anvin - All Rights Reserved
12	; Copyright 2009 Intel Corporation; author: H. Peter Anvin
13	;
14	; This program is free software; you can redistribute it and/or modify
15	; it under the terms of the GNU General Public License as published by
16	; the Free Software Foundation, Inc., 53 Temple Place Ste 330,
17	; Boston MA 02111-1307, USA; either version 2 of the License, or
18	; (at your option) any later version; incorporated herein by reference.
19	;
20	; ****************************************************************************
21
22	%define IS_ISOLINUX 1
23	%include "head.inc"
24
25	;
26	; Some semi-configurable constants... change on your own risk.
27	;
28	my_id equ isolinux_id
29	NULLFILE equ 0 ; Zero byte == null file name
30	NULLOFFSET equ 0 ; Position in which to look
31	retry_count equ 6 ; How patient are we with the BIOS?
32	%assign HIGHMEM_SLOP 128*1024 ; Avoid this much memory near the top
33	SECTOR_SHIFT equ 11 ; 2048 bytes/sector (El Torito requirement)
34	SECTOR_SIZE equ (1 << SECTOR_SHIFT)
35
36	ROOT_DIR_WORD equ 0x002F
37
38	; ---------------------------------------------------------------------------
39	; BEGIN CODE
40	; ---------------------------------------------------------------------------
41
42	;
43	; Memory below this point is reserved for the BIOS and the MBR
44	;
45	section .earlybss
46	global trackbuf
47	trackbufsize equ 8192
48	trackbuf resb trackbufsize ; Track buffer goes here
49	; ends at 2800h
50
51	; Some of these are touched before the whole image
52	; is loaded. DO NOT move this to .bss16/.uibss.
53	section .earlybss
54	global BIOSName
55	alignb 4
56	FirstSecSum resd 1 ; Checksum of bytes 64-2048
57	ImageDwords resd 1 ; isolinux.bin size, dwords
58	InitStack resd 1 ; Initial stack pointer (SS:SP)
59	DiskSys resw 1 ; Last INT 13h call
60	ImageSectors resw 1 ; isolinux.bin size, sectors
61	; These following two are accessed as a single dword...
62	GetlinsecPtr resw 1 ; The sector-read pointer
63	BIOSName resw 1 ; Display string for BIOS type
64	%define HAVE_BIOSNAME 1
65	global BIOSType
66	BIOSType resw 1
67	DiskError resb 1 ; Error code for disk I/O
68	global DriveNumber
69	DriveNumber resb 1 ; CD-ROM BIOS drive number
70	ISOFlags resb 1 ; Flags for ISO directory search
71	RetryCount resb 1 ; Used for disk access retries
72
73	alignb 8
74	global Hidden
75	Hidden resq 1 ; Used in hybrid mode
76	bsSecPerTrack resw 1 ; Used in hybrid mode
77	bsHeads resw 1 ; Used in hybrid mode
78
79
80	;
81	; El Torito spec packet
82	;
83
84	alignb 8
85	_spec_start equ $
86	global spec_packet
87	spec_packet: resb 1 ; Size of packet
88	sp_media: resb 1 ; Media type
89	sp_drive: resb 1 ; Drive number
90	sp_controller: resb 1 ; Controller index
91	sp_lba: resd 1 ; LBA for emulated disk image
92	sp_devspec: resw 1 ; IDE/SCSI information
93	sp_buffer: resw 1 ; User-provided buffer
94	sp_loadseg: resw 1 ; Load segment
95	sp_sectors: resw 1 ; Sector count
96	sp_chs: resb 3 ; Simulated CHS geometry
97	sp_dummy: resb 1 ; Scratch, safe to overwrite
98
99	;
100	; EBIOS drive parameter packet
101	;
102	alignb 8
103	drive_params: resw 1 ; Buffer size
104	dp_flags: resw 1 ; Information flags
105	dp_cyl: resd 1 ; Physical cylinders
106	dp_head: resd 1 ; Physical heads
107	dp_sec: resd 1 ; Physical sectors/track
108	dp_totalsec: resd 2 ; Total sectors
109	dp_secsize: resw 1 ; Bytes per sector
110	dp_dpte: resd 1 ; Device Parameter Table
111	dp_dpi_key: resw 1 ; 0BEDDh if rest valid
112	dp_dpi_len: resb 1 ; DPI len
113	resb 1
114	resw 1
115	dp_bus: resb 4 ; Host bus type
116	dp_interface: resb 8 ; Interface type
117	db_i_path: resd 2 ; Interface path
118	db_d_path: resd 2 ; Device path
119	resb 1
120	db_dpi_csum: resb 1 ; Checksum for DPI info
121
122	;
123	; EBIOS disk address packet
124	;
125	alignb 8
126	dapa: resw 1 ; Packet size
127	.count: resw 1 ; Block count
128	.off: resw 1 ; Offset of buffer
129	.seg: resw 1 ; Segment of buffer
130	.lba: resd 2 ; LBA (LSW, MSW)
131
132	;
133	; Spec packet for disk image emulation
134	;
135	alignb 8
136	dspec_packet: resb 1 ; Size of packet
137	dsp_media: resb 1 ; Media type
138	dsp_drive: resb 1 ; Drive number
139	dsp_controller: resb 1 ; Controller index
140	dsp_lba: resd 1 ; LBA for emulated disk image
141	dsp_devspec: resw 1 ; IDE/SCSI information
142	dsp_buffer: resw 1 ; User-provided buffer
143	dsp_loadseg: resw 1 ; Load segment
144	dsp_sectors: resw 1 ; Sector count
145	dsp_chs: resb 3 ; Simulated CHS geometry
146	dsp_dummy: resb 1 ; Scratch, safe to overwrite
147
148	alignb 4
149	_spec_end equ $
150	_spec_len equ _spec_end - _spec_start
151
152	section .init
153	;;
154	;; Primary entry point. Because BIOSes are buggy, we only load the first
155	;; CD-ROM sector (2K) of the file, so the number one priority is actually
156	;; loading the rest.
157	;;
158	global StackBuf
159	StackBuf equ STACK_TOP-44 ; 44 bytes needed for
160	; the bootsector chainloading
161	; code!
162	global OrigESDI
163	OrigESDI equ StackBuf-4 ; The high dword on the stack
164	StackHome equ OrigESDI
165
166	bootsec equ $
167
168	_start: ; Far jump makes sure we canonicalize the address
169	cli
170	jmp 0:_start1
171	times 8-($-$$) nop ; Pad to file offset 8
172
173	; This table hopefully gets filled in by mkisofs using the
174	; -boot-info-table option. If not, the values in this
175	; table are default values that we can use to get us what
176	; we need, at least under a certain set of assumptions.
177	global iso_boot_info
178	iso_boot_info:
179	bi_pvd: dd 16 ; LBA of primary volume descriptor
180	bi_file: dd 0 ; LBA of boot file
181	bi_length: dd 0xdeadbeef ; Length of boot file
182	bi_csum: dd 0xdeadbeef ; Checksum of boot file
183	bi_reserved: times 10 dd 0xdeadbeef ; Reserved
184	bi_end:
185
186	; Custom entry point for the hybrid-mode disk.
187	; The following values will have been pushed onto the
188	; entry stack:
189	; - partition offset (qword)
190	; - ES
191	; - DI
192	; - DX (including drive number)
193	; - CBIOS Heads
194	; - CBIOS Sectors
195	; - EBIOS flag
196	; (top of stack)
197	;
198	; If we had an old isohybrid, the partition offset will
199	; be missing; we can check for that with sp >= 0x7c00.
200	; Serious hack alert.
201	%ifndef DEBUG_MESSAGES
202	_hybrid_signature:
203	dd 0x7078c0fb ; An arbitrary number...
204
205	_start_hybrid:
206	pop cx ; EBIOS flag
207	pop word [cs:bsSecPerTrack]
208	pop word [cs:bsHeads]
209	pop dx
210	pop di
211	pop es
212	xor eax,eax
213	xor ebx,ebx
214	cmp sp,7C00h
215	jae .nooffset
216	pop eax
217	pop ebx
218	.nooffset:
219	mov si,bios_cbios
220	jcxz _start_common
221	mov si,bios_ebios
222	jmp _start_common
223	%endif
224
225	_start1:
226	mov si,bios_cdrom
227	xor eax,eax
228	xor ebx,ebx
229	_start_common:
230	mov [cs:InitStack],sp ; Save initial stack pointer
231	mov [cs:InitStack+2],ss
232	xor cx,cx
233	mov ss,cx
234	mov sp,StackBuf ; Set up stack
235	push es ; Save initial ES:DI -> $PnP pointer
236	push di
237	mov ds,cx
238	mov es,cx
239	mov fs,cx
240	mov gs,cx
241	sti
242	cld
243
244	mov [Hidden],eax
245	mov [Hidden+4],ebx
246
247	mov [BIOSType],si
248	mov eax,[si]
249	mov [GetlinsecPtr],eax
250
251	; Show signs of life
252	mov si,syslinux_banner
253	call writestr_early
254	%ifdef DEBUG_MESSAGES
255	mov si,copyright_str
256	%else
257	mov si,[BIOSName]
258	%endif
259	call writestr_early
260
261	;
262	; Before modifying any memory, get the checksum of bytes
263	; 64-2048
264	;
265	initial_csum: xor edi,edi
266	mov si,bi_end
267	mov cx,(SECTOR_SIZE-64) >> 2
268	.loop: lodsd
269	add edi,eax
270	loop .loop
271	mov [FirstSecSum],edi
272
273	mov [DriveNumber],dl
274	%ifdef DEBUG_MESSAGES
275	mov si,startup_msg
276	call writemsg
277	mov al,dl
278	call writehex2
279	call crlf_early
280	%endif
281	;
282	; Initialize spec packet buffers
283	;
284	mov di,_spec_start
285	mov cx,_spec_len >> 2
286	xor eax,eax
287	rep stosd
288
289	; Initialize length field of the various packets
290	mov byte [spec_packet],13h
291	mov byte [drive_params],30
292	mov byte [dapa],16
293	mov byte [dspec_packet],13h
294
295	; Other nonzero fields
296	inc word [dsp_sectors]
297
298	; Are we just pretending to be a CD-ROM?
299	cmp word [BIOSType],bios_cdrom
300	jne found_drive ; If so, no spec packet...
301
302	; Now figure out what we're actually doing
303	; Note: use passed-in DL value rather than 7Fh because
304	; at least some BIOSes will get the wrong value otherwise
305	mov ax,4B01h ; Get disk emulation status
306	mov dl,[DriveNumber]
307	mov si,spec_packet
308	call int13
309	jc award_hack ; changed for BrokenAwardHack
310	mov dl,[DriveNumber]
311	cmp [sp_drive],dl ; Should contain the drive number
312	jne spec_query_failed
313
314	%ifdef DEBUG_MESSAGES
315	mov si,spec_ok_msg
316	call writemsg
317	mov al,byte [sp_drive]
318	call writehex2
319	call crlf_early
320	%endif
321
322	found_drive:
323	; Alright, we have found the drive. Now, try to find the
324	; boot file itself. If we have a boot info table, life is
325	; good; if not, we have to make some assumptions, and try
326	; to figure things out ourselves. In particular, the
327	; assumptions we have to make are:
328	; - single session only
329	; - only one boot entry (no menu or other alternatives)
330
331	cmp dword [bi_file],0 ; Address of code to load
332	jne found_file ; Boot info table present :)
333
334	%ifdef DEBUG_MESSAGES
335	mov si,noinfotable_msg
336	call writemsg
337	%endif
338
339	; No such luck. See if the spec packet contained one.
340	mov eax,[sp_lba]
341	and eax,eax
342	jz set_file ; Good enough
343
344	%ifdef DEBUG_MESSAGES
345	mov si,noinfoinspec_msg
346	call writemsg
347	%endif
348
349	; No such luck. Get the Boot Record Volume, assuming single
350	; session disk, and that we're the first entry in the chain.
351	mov eax,17 ; Assumed address of BRV
352	mov bx,trackbuf
353	call getonesec
354
355	mov eax,[trackbuf+47h] ; Get boot catalog address
356	mov bx,trackbuf
357	call getonesec ; Get boot catalog
358
359	mov eax,[trackbuf+28h] ; First boot entry
360	; And hope and pray this is us...
361
362	; Some BIOSes apparently have limitations on the size
363	; that may be loaded (despite the El Torito spec being very
364	; clear on the fact that it must all be loaded.) Therefore,
365	; we load it ourselves, and bleep the BIOS.
366
367	set_file:
368	mov [bi_file],eax
369
370	found_file:
371	; Set up boot file sizes
372	mov eax,[bi_length]
373	sub eax,SECTOR_SIZE-3 ; ... minus sector loaded
374	shr eax,2 ; bytes->dwords
375	mov [ImageDwords],eax ; boot file dwords
376	add eax,((SECTOR_SIZE-1) >> 2)
377	shr eax,SECTOR_SHIFT-2 ; dwords->sectors
378	mov [ImageSectors],ax ; boot file sectors
379
380	mov eax,[bi_file] ; Address of code to load
381	inc eax ; Don't reload bootstrap code
382	%ifdef DEBUG_MESSAGES
383	mov si,offset_msg
384	call writemsg
385	call writehex8
386	call crlf_early
387	%endif
388
389	; Load the rest of the file. However, just in case there
390	; are still BIOSes with 64K wraparound problems, we have to
391	; take some extra precautions. Since the normal load
392	; address (TEXT_START) is not 2K-sector-aligned, we round
393	; the target address upward to a sector boundary,
394	; and then move the entire thing down as a unit.
395	MaxLMA equ 384*1024 ; Reasonable limit (384K)
396
397	mov bx,((TEXT_START+2*SECTOR_SIZE-1) & ~(SECTOR_SIZE-1)) >> 4
398	mov bp,[ImageSectors]
399	push bx ; Load segment address
400
401	.more:
402	push bx ; Segment address
403	push bp ; Sector count
404	mov es,bx
405	mov cx,0xfff
406	and bx,cx
407	inc cx
408	sub cx,bx
409	shr cx,SECTOR_SHIFT - 4
410	jnz .notaligned
411	mov cx,0x10000 >> SECTOR_SHIFT ; Full 64K segment possible
412	.notaligned:
413	cmp bp,cx
414	jbe .ok
415	mov bp,cx
416	.ok:
417	xor bx,bx
418	push bp
419	push eax
420	call getlinsec
421	pop eax
422	pop cx
423	movzx edx,cx
424	pop bp
425	pop bx
426
427	shl cx,SECTOR_SHIFT - 4
428	add bx,cx
429	add eax,edx
430	sub bp,dx
431	jnz .more
432
433	; Move the image into place, and also verify the
434	; checksum
435	pop ax ; Load segment address
436	mov bx,(TEXT_START + SECTOR_SIZE) >> 4
437	mov ecx,[ImageDwords]
438	mov edi,[FirstSecSum] ; First sector checksum
439	xor si,si
440
441	move_verify_image:
442	.setseg:
443	mov ds,ax
444	mov es,bx
445	.loop:
446	mov edx,[si]
447	add edi,edx
448	dec ecx
449	mov [es:si],edx
450	jz .done
451	add si,4
452	jnz .loop
453	add ax,1000h
454	add bx,1000h
455	jmp .setseg
456	.done:
457	mov ax,cs
458	mov ds,ax
459	mov es,ax
460
461	; Verify the checksum on the loaded image.
462	cmp [bi_csum],edi
463	je integrity_ok
464
465	mov si,checkerr_msg
466	call writemsg
467	jmp kaboom
468
469	integrity_ok:
470	%ifdef DEBUG_MESSAGES
471	mov si,allread_msg
472	call writemsg
473	%endif
474	jmp all_read ; Jump to main code
475
476	;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
477	;; Start of BrokenAwardHack --- 10-nov-2002 Knut_Petersen@t-online.de
478	;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
479	;;
480	;; There is a problem with certain versions of the AWARD BIOS ...
481	;; the boot sector will be loaded and executed correctly, but, because the
482	;; int 13 vector points to the wrong code in the BIOS, every attempt to
483	;; load the spec packet will fail. We scan for the equivalent of
484	;;
485	;; mov ax,0201h
486	;; mov bx,7c00h
487	;; mov cx,0006h
488	;; mov dx,0180h
489	;; pushf
490	;; call <direct far>
491	;;
492	;; and use <direct far> as the new vector for int 13. The code above is
493	;; used to load the boot code into ram, and there should be no reason
494	;; for anybody to change it now or in the future. There are no opcodes
495	;; that use encodings relativ to IP, so scanning is easy. If we find the
496	;; code above in the BIOS code we can be pretty sure to run on a machine
497	;; with an broken AWARD BIOS ...
498	;;
499	;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
500	;;
501	%ifdef DEBUG_MESSAGES ;;
502	;;
503	award_notice db "Trying BrokenAwardHack first ...",CR,LF,0 ;;
504	award_not_orig db "BAH: Original Int 13 vector : ",0 ;;
505	award_not_new db "BAH: Int 13 vector changed to : ",0 ;;
506	award_not_succ db "BAH: SUCCESS",CR,LF,0 ;;
507	award_not_fail db "BAH: FAILURE" ;;
508	award_not_crlf db CR,LF,0 ;;
509	;;
510	%endif ;;
511	;;
512	award_oldint13 dd 0 ;;
513	award_string db 0b8h,1,2,0bbh,0,7ch,0b9h,6,0,0bah,80h,1,09ch,09ah ;;
514	;;
515	;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
516	award_hack: mov si,spec_err_msg ; Moved to this place from
517	call writemsg ; spec_query_failed
518	;
519	%ifdef DEBUG_MESSAGES ;
520	;
521	mov si,award_notice ; display our plan
522	call writemsg ;
523	mov si,award_not_orig ; display original int 13
524	call writemsg ; vector
525	%endif ;
526	mov eax,[13h*4] ;
527	mov [award_oldint13],eax ;
528	;
529	%ifdef DEBUG_MESSAGES ;
530	;
531	call writehex8 ;
532	mov si,award_not_crlf ;
533	call writestr_early ;
534	%endif ;
535	push es ; save ES
536	mov ax,0f000h ; ES = BIOS Seg
537	mov es,ax ;
538	cld ;
539	xor di,di ; start at ES:DI = f000:0
540	award_loop: push di ; save DI
541	mov si,award_string ; scan for award_string
542	mov cx,7 ; length of award_string = 7dw
543	repz cmpsw ; compare
544	pop di ; restore DI
545	jcxz award_found ; jmp if found
546	inc di ; not found, inc di
547	jno award_loop ;
548	;
549	award_failed: pop es ; No, not this way :-((
550	award_fail2: ;
551	;
552	%ifdef DEBUG_MESSAGES ;
553	;
554	mov si,award_not_fail ; display failure ...
555	call writemsg ;
556	%endif ;
557	mov eax,[award_oldint13] ; restore the original int
558	or eax,eax ; 13 vector if there is one
559	jz spec_query_failed ; and try other workarounds
560	mov [13h*4],eax ;
561	jmp spec_query_failed ;
562	;
563	award_found: mov eax,[es:di+0eh] ; load possible int 13 addr
564	pop es ; restore ES
565	;
566	cmp eax,[award_oldint13] ; give up if this is the
567	jz award_failed ; active int 13 vector,
568	mov [13h4],eax ; otherwise change 0:13h4
569	;
570	;
571	%ifdef DEBUG_MESSAGES ;
572	;
573	push eax ; display message and
574	mov si,award_not_new ; new vector address
575	call writemsg ;
576	pop eax ;
577	call writehex8 ;
578	mov si,award_not_crlf ;
579	call writestr_early ;
580	%endif ;
581	mov ax,4B01h ; try to read the spec packet
582	mov dl,[DriveNumber] ; now ... it should not fail
583	mov si,spec_packet ; any longer
584	int 13h ;
585	jc award_fail2 ;
586	;
587	%ifdef DEBUG_MESSAGES ;
588	;
589	mov si,award_not_succ ; display our SUCCESS
590	call writemsg ;
591	%endif ;
592	jmp found_drive ; and leave error recovery code
593	;
594	;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
595	;; End of BrokenAwardHack ---- 10-nov-2002 Knut_Petersen@t-online.de
596	;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
597
598
599	; INT 13h, AX=4B01h, DL=<passed in value> failed.
600	; Try to scan the entire 80h-FFh from the end.
601
602	spec_query_failed:
603
604	; some code moved to BrokenAwardHack
605
606	mov dl,0FFh
607	.test_loop: pusha
608	mov ax,4B01h
609	mov si,spec_packet
610	mov byte [si],13h ; Size of buffer
611	call int13
612	popa
613	jc .still_broken
614
615	mov si,maybe_msg
616	call writemsg
617	mov al,dl
618	call writehex2
619	call crlf_early
620
621	cmp byte [sp_drive],dl
622	jne .maybe_broken
623
624	; Okay, good enough...
625	mov si,alright_msg
626	call writemsg
627	.found_drive0: mov [DriveNumber],dl
628	.found_drive: jmp found_drive
629
630	; Award BIOS 4.51 apparently passes garbage in sp_drive,
631	; but if this was the drive number originally passed in
632	; DL then consider it "good enough"
633	.maybe_broken:
634	mov al,[DriveNumber]
635	cmp al,dl
636	je .found_drive
637
638	; Intel Classic R+ computer with Adaptec 1542CP BIOS 1.02
639	; passes garbage in sp_drive, and the drive number originally
640	; passed in DL does not have 80h bit set.
641	or al,80h
642	cmp al,dl
643	je .found_drive0
644
645	.still_broken: dec dx
646	cmp dl, 80h
647	jnb .test_loop
648
649	; No spec packet anywhere. Some particularly pathetic
650	; BIOSes apparently don't even implement function
651	; 4B01h, so we can't query a spec packet no matter
652	; what. If we got a drive number in DL, then try to
653	; use it, and if it works, then well...
654	mov dl,[DriveNumber]
655	cmp dl,81h ; Should be 81-FF at least
656	jb fatal_error ; If not, it's hopeless
657
658	; Write a warning to indicate we're on very thin ice now
659	mov si,nospec_msg
660	call writemsg
661	mov al,dl
662	call writehex2
663	call crlf_early
664	mov si,trysbm_msg
665	call writemsg
666	jmp .found_drive ; Pray that this works...
667
668	fatal_error:
669	mov si,nothing_msg
670	call writemsg
671
672	.norge: jmp short .norge
673
674	; Information message (DS:SI) output
675	; Prefix with "isolinux: "
676	;
677	writemsg: push ax
678	push si
679	mov si,isolinux_str
680	call writestr_early
681	pop si
682	call writestr_early
683	pop ax
684	ret
685
686	writestr_early:
687	pushfd
688	pushad
689	.top: lodsb
690	and al,al
691	jz .end
692	call writechr
693	jmp short .top
694	.end: popad
695	popfd
696	ret
697
698	crlf_early: push ax
699	mov al,CR
700	call writechr
701	mov al,LF
702	call writechr
703	pop ax
704	ret
705
706	;
707	; Write a character to the screen. There is a more "sophisticated"
708	; version of this in the subsequent code, so we patch the pointer
709	; when appropriate.
710	;
711
712	writechr:
713	.simple:
714	pushfd
715	pushad
716	mov ah,0Eh
717	xor bx,bx
718	int 10h
719	popad
720	popfd
721	ret
722
723	;
724	; int13: save all the segment registers and call INT 13h.
725	; Some CD-ROM BIOSes have been found to corrupt segment registers
726	; and/or disable interrupts.
727	;
728	int13:
729	pushf
730	push bp
731	push ds
732	push es
733	push fs
734	push gs
735	int 13h
736	mov bp,sp
737	setc [bp+10] ; Propagate CF to the caller
738	pop gs
739	pop fs
740	pop es
741	pop ds
742	pop bp
743	popf
744	ret
745
746	;
747	; Get one sector. Convenience entry point.
748	;
749	getonesec:
750	mov bp,1
751	; Fall through to getlinsec
752
753	;
754	; Get linear sectors - EBIOS LBA addressing, 2048-byte sectors.
755	;
756	; Input:
757	; EAX - Linear sector number
758	; ES:BX - Target buffer
759	; BP - Sector count
760	;
761	global getlinsec
762	getlinsec: jmp word [cs:GetlinsecPtr]
763
764	%ifndef DEBUG_MESSAGES
765
766	;
767	; First, the variants that we use when actually loading off a disk
768	; (hybrid mode.) These are adapted versions of the equivalent routines
769	; in ldlinux.asm.
770	;
771
772	;
773	; getlinsec_ebios:
774	;
775	; getlinsec implementation for floppy/HDD EBIOS (EDD)
776	;
777	getlinsec_ebios:
778	xor edx,edx
779	shld edx,eax,2
780	shl eax,2 ; Convert to HDD sectors
781	add eax,[Hidden]
782	adc edx,[Hidden+4]
783	shl bp,2
784
785	.loop:
786	push bp ; Sectors left
787	.retry2:
788	call maxtrans ; Enforce maximum transfer size
789	movzx edi,bp ; Sectors we are about to read
790	mov cx,retry_count
791	.retry:
792
793	; Form DAPA on stack
794	push edx
795	push eax
796	push es
797	push bx
798	push di
799	push word 16
800	mov si,sp
801	pushad
802	mov dl,[DriveNumber]
803	push ds
804	push ss
805	pop ds ; DS <- SS
806	mov ah,42h ; Extended Read
807	call int13
808	pop ds
809	popad
810	lea sp,[si+16] ; Remove DAPA
811	jc .error
812	pop bp
813	add eax,edi ; Advance sector pointer
814	adc edx,0
815	sub bp,di ; Sectors left
816	shl di,9 ; 512-byte sectors
817	add bx,di ; Advance buffer pointer
818	and bp,bp
819	jnz .loop
820
821	ret
822
823	.error:
824	; Some systems seem to get "stuck" in an error state when
825	; using EBIOS. Doesn't happen when using CBIOS, which is
826	; good, since some other systems get timeout failures
827	; waiting for the floppy disk to spin up.
828
829	pushad ; Try resetting the device
830	xor ax,ax
831	mov dl,[DriveNumber]
832	call int13
833	popad
834	loop .retry ; CX-- and jump if not zero
835
836	;shr word [MaxTransfer],1 ; Reduce the transfer size
837	;jnz .retry2
838
839	; Total failure. Try falling back to CBIOS.
840	mov word [GetlinsecPtr], getlinsec_cbios
841	;mov byte [MaxTransfer],63 ; Max possibe CBIOS transfer
842
843	pop bp
844	jmp getlinsec_cbios.loop
845
846	;
847	; getlinsec_cbios:
848	;
849	; getlinsec implementation for legacy CBIOS
850	;
851	getlinsec_cbios:
852	xor edx,edx
853	shl eax,2 ; Convert to HDD sectors
854	add eax,[Hidden]
855	shl bp,2
856
857	.loop:
858	push edx
859	push eax
860	push bp
861	push bx
862
863	movzx esi,word [bsSecPerTrack]
864	movzx edi,word [bsHeads]
865	;
866	; Dividing by sectors to get (track,sector): we may have
867	; up to 2^18 tracks, so we need to use 32-bit arithmetric.
868	;
869	div esi
870	xor cx,cx
871	xchg cx,dx ; CX <- sector index (0-based)
872	; EDX <- 0
873	; eax = track #
874	div edi ; Convert track to head/cyl
875
876	; We should test this, but it doesn't fit...
877	; cmp eax,1023
878	; ja .error
879
880	;
881	; Now we have AX = cyl, DX = head, CX = sector (0-based),
882	; BP = sectors to transfer, SI = bsSecPerTrack,
883	; ES:BX = data target
884	;
885
886	call maxtrans ; Enforce maximum transfer size
887
888	; Must not cross track boundaries, so BP <= SI-CX
889	sub si,cx
890	cmp bp,si
891	jna .bp_ok
892	mov bp,si
893	.bp_ok:
894
895	shl ah,6 ; Because IBM was STOOPID
896	; and thought 8 bits were enough
897	; then thought 10 bits were enough...
898	inc cx ; Sector numbers are 1-based, sigh
899	or cl,ah
900	mov ch,al
901	mov dh,dl
902	mov dl,[DriveNumber]
903	xchg ax,bp ; Sector to transfer count
904	mov ah,02h ; Read sectors
905	mov bp,retry_count
906	.retry:
907	pushad
908	call int13
909	popad
910	jc .error
911	.resume:
912	movzx ecx,al ; ECX <- sectors transferred
913	shl ax,9 ; Convert sectors in AL to bytes in AX
914	pop bx
915	add bx,ax
916	pop bp
917	pop eax
918	pop edx
919	add eax,ecx
920	sub bp,cx
921	jnz .loop
922	ret
923
924	.error:
925	dec bp
926	jnz .retry
927
928	xchg ax,bp ; Sectors transferred <- 0
929	shr word [MaxTransfer],1
930	jnz .resume
931	jmp disk_error
932
933	;
934	; Truncate BP to MaxTransfer
935	;
936	maxtrans:
937	cmp bp,[MaxTransfer]
938	jna .ok
939	mov bp,[MaxTransfer]
940	.ok: ret
941
942	%endif
943
944	;
945	; This is the variant we use for real CD-ROMs:
946	; LBA, 2K sectors, some special error handling.
947	;
948	getlinsec_cdrom:
949	mov si,dapa ; Load up the DAPA
950	mov [si+4],bx
951	mov [si+6],es
952	mov [si+8],eax
953	.loop:
954	push bp ; Sectors left
955	cmp bp,[MaxTransferCD]
956	jbe .bp_ok
957	mov bp,[MaxTransferCD]
958	.bp_ok:
959	mov [si+2],bp
960	push si
961	mov dl,[DriveNumber]
962	mov ah,42h ; Extended Read
963	call xint13
964	pop si
965	pop bp
966	movzx eax,word [si+2] ; Sectors we read
967	add [si+8],eax ; Advance sector pointer
968	sub bp,ax ; Sectors left
969	shl ax,SECTOR_SHIFT-4 ; 2048-byte sectors -> segment
970	add [si+6],ax ; Advance buffer pointer
971	and bp,bp
972	jnz .loop
973	mov eax,[si+8] ; Next sector
974	ret
975
976	; INT 13h with retry
977	xint13: mov byte [RetryCount],retry_count
978	.try: pushad
979	call int13
980	jc .error
981	add sp,byte 8*4 ; Clean up stack
982	ret
983	.error:
984	mov [DiskError],ah ; Save error code
985	popad
986	mov [DiskSys],ax ; Save system call number
987	dec byte [RetryCount]
988	jz .real_error
989	push ax
990	mov al,[RetryCount]
991	mov ah,[dapa+2] ; Sector transfer count
992	cmp al,2 ; Only 2 attempts left
993	ja .nodanger
994	mov ah,1 ; Drop transfer size to 1
995	jmp short .setsize
996	.nodanger:
997	cmp al,retry_count-2
998	ja .again ; First time, just try again
999	shr ah,1 ; Otherwise, try to reduce
1000	adc ah,0 ; the max transfer size, but not to 0
1001	.setsize:
1002	mov [MaxTransferCD],ah
1003	mov [dapa+2],ah
1004	.again:
1005	pop ax
1006	jmp .try
1007
1008	.real_error: mov si,diskerr_msg
1009	call writemsg
1010	mov al,[DiskError]
1011	call writehex2
1012	mov si,oncall_str
1013	call writestr_early
1014	mov ax,[DiskSys]
1015	call writehex4
1016	mov si,ondrive_str
1017	call writestr_early
1018	mov al,dl
1019	call writehex2
1020	call crlf_early
1021	; Fall through to kaboom
1022
1023	;
1024	; kaboom: write a message and bail out. Wait for a user keypress,
1025	; then do a hard reboot.
1026	;
1027	global kaboom
1028	disk_error:
1029	kaboom:
1030	RESET_STACK_AND_SEGS AX
1031	mov si,bailmsg
1032	pm_call pm_writestr
1033	pm_call pm_getchar
1034	cli
1035	mov word [BIOS_magic],0 ; Cold reboot
1036	jmp 0F000h:0FFF0h ; Reset vector address
1037
1038	; -----------------------------------------------------------------------------
1039	; Common modules needed in the first sector
1040	; -----------------------------------------------------------------------------
1041
1042	%include "writehex.inc" ; Hexadecimal output
1043
1044	; -----------------------------------------------------------------------------
1045	; Data that needs to be in the first sector
1046	; -----------------------------------------------------------------------------
1047
1048	global syslinux_banner, copyright_str
1049	syslinux_banner db CR, LF, MY_NAME, ' ', VERSION_STR, ' ', DATE_STR, ' ', 0
1050	copyright_str db ' Copyright (C) 1994-'
1051	asciidec YEAR
1052	db ' H. Peter Anvin et al', CR, LF, 0
1053	isolinux_str db 'isolinux: ', 0
1054	%ifdef DEBUG_MESSAGES
1055	startup_msg: db 'Starting up, DL = ', 0
1056	spec_ok_msg: db 'Loaded spec packet OK, drive = ', 0
1057	secsize_msg: db 'Sector size ', 0
1058	offset_msg: db 'Main image LBA = ', 0
1059	verify_msg: db 'Image csum verified.', CR, LF, 0
1060	allread_msg db 'Image read, jumping to main code...', CR, LF, 0
1061	%endif
1062	noinfotable_msg db 'No boot info table, assuming single session disk...', CR, LF, 0
1063	noinfoinspec_msg db 'Spec packet missing LBA information, trying to wing it...', CR, LF, 0
1064	spec_err_msg: db 'Loading spec packet failed, trying to wing it...', CR, LF, 0
1065	maybe_msg: db 'Found something at drive = ', 0
1066	alright_msg: db 'Looks reasonable, continuing...', CR, LF, 0
1067	nospec_msg db 'Extremely broken BIOS detected, last attempt with drive = ', 0
1068	nothing_msg: db 'Failed to locate CD-ROM device; boot failed.', CR, LF
1069	trysbm_msg db 'See http://syslinux.zytor.com/sbm for more information.', CR, LF, 0
1070	diskerr_msg: db 'Disk error ', 0
1071	oncall_str: db ', AX = ',0
1072	ondrive_str: db ', drive ', 0
1073	checkerr_msg: db 'Image checksum error, sorry...', CR, LF, 0
1074
1075	err_bootfailed db CR, LF, 'Boot failed: press a key to retry...'
1076	bailmsg equ err_bootfailed
1077	crlf_msg db CR, LF
1078	null_msg db 0
1079
1080	bios_cdrom_str db 'ETCD', 0
1081	%ifndef DEBUG_MESSAGES
1082	bios_cbios_str db 'CHDD', 0
1083	bios_ebios_str db 'EHDD' ,0
1084	%endif
1085
1086	alignz 4
1087	global bios_cdrom
1088	bios_cdrom: dw getlinsec_cdrom, bios_cdrom_str
1089	%ifndef DEBUG_MESSAGES
1090	bios_cbios: dw getlinsec_cbios, bios_cbios_str
1091	bios_ebios: dw getlinsec_ebios, bios_ebios_str
1092	%endif
1093
1094	; Maximum transfer size
1095	MaxTransfer dw 127 ; Hard disk modes
1096	MaxTransferCD dw 32 ; CD mode
1097
1098	rl_checkpt equ $ ; Must be <= 800h
1099
1100	; This pads to the end of sector 0 and errors out on
1101	; overflow.
1102	times 2048-($-$$) db 0
1103
1104	; ----------------------------------------------------------------------------
1105	; End of code and data that have to be in the first sector
1106	; ----------------------------------------------------------------------------
1107
1108	section .text16
1109
1110	all_read:
1111
1112	; Test tracers
1113	TRACER 'T'
1114	TRACER '>'
1115
1116	;
1117	; Common initialization code
1118	;
1119	%include "init.inc"
1120
1121	; Tell the user we got this far...
1122	%ifndef DEBUG_MESSAGES ; Gets messy with debugging on
1123	mov si,copyright_str
1124	pm_call pm_writestr
1125	%endif
1126
1127	;
1128	; Now we're all set to start with our real business. First load the
1129	; configuration file (if any) and parse it.
1130	;
1131	; In previous versions I avoided using 32-bit registers because of a
1132	; rumour some BIOSes clobbered the upper half of 32-bit registers at
1133	; random. I figure, though, that if there are any of those still left
1134	; they probably won't be trying to install Linux on them...
1135	;
1136	; The code is still ripe with 16-bitisms, though. Not worth the hassle
1137	; to take'm out. In fact, we may want to put them back if we're going
1138	; to boot ELKS at some point.
1139	;
1140
1141	;
1142	; Now, we need to sniff out the actual filesystem data structures.
1143	; mkisofs gave us a pointer to the primary volume descriptor
1144	; (which will be at 16 only for a single-session disk!); from the PVD
1145	; we should be able to find the rest of what we need to know.
1146	;
1147	init_fs:
1148	pushad
1149	mov eax,ROOT_FS_OPS
1150	mov dl,[DriveNumber]
1151	cmp word [BIOSType],bios_cdrom
1152	sete dh ; 1 for cdrom, 0 for hybrid mode
1153	jne .hybrid
1154	movzx ebp,word [MaxTransferCD]
1155	jmp .common
1156	.hybrid:
1157	movzx ebp,word [MaxTransfer]
1158	.common:
1159	mov ecx,[Hidden]
1160	mov ebx,[Hidden+4]
1161	mov si,[bsHeads]
1162	mov di,[bsSecPerTrack]
1163	pm_call pm_fs_init
1164	pm_call load_env32
1165	enter_command:
1166	auto_boot:
1167	jmp kaboom ; load_env32() should never return. If
1168	; it does, then kaboom!
1169	popad
1170
1171	section .rodata
1172	alignz 4
1173	ROOT_FS_OPS:
1174	extern iso_fs_ops
1175	dd iso_fs_ops
1176	dd 0
1177
1178	section .text16
1179
1180	%ifdef DEBUG_TRACERS
1181	;
1182	; debug hack to print a character with minimal code impact
1183	;
1184	debug_tracer: pushad
1185	pushfd
1186	mov bp,sp
1187	mov bx,[bp+9*4] ; Get return address
1188	mov al,[cs:bx] ; Get data byte
1189	inc word [bp+9*4] ; Return to after data byte
1190	call writechr
1191	popfd
1192	popad
1193	ret
1194	%endif ; DEBUG_TRACERS
1195
1196	section .bss16
1197	alignb 4
1198	ThisKbdTo resd 1 ; Temporary holder for KbdTimeout
1199	ThisTotalTo resd 1 ; Temporary holder for TotalTimeout
1200	KernelExtPtr resw 1 ; During search, final null pointer
1201	FuncFlag resb 1 ; Escape sequences received from keyboard
1202	KernelType resb 1 ; Kernel type, from vkernel, if known
1203	global KernelName
1204	KernelName resb FILENAME_MAX ; Mangled name for kernel
1205
1206	section .text16
1207	;
1208	; COM32 vestigial data structure
1209	;
1210	%include "com32.inc"
1211
1212	;
1213	; Common local boot code
1214	;
1215	%include "localboot.inc"
1216
1217	; -----------------------------------------------------------------------------
1218	; Common modules
1219	; -----------------------------------------------------------------------------
1220
1221	%include "common.inc" ; Universal modules
1222
1223	; -----------------------------------------------------------------------------
1224	; Begin data section
1225	; -----------------------------------------------------------------------------
1226
1227	section .data16
1228	err_disk_image db 'Cannot load disk image (invalid file)?', CR, LF, 0
1229
1230	section .bss16
1231	global OrigFDCTabPtr
1232	OrigFDCTabPtr resd 1 ; Keep bios_cleanup_hardware() honest

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