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diskstart.inc

Last change on this file was e16e8f2, checked in by Edwin Eefting <edwin@datux.nl>, 3 years ago
bootstuff
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1	; -----------------------------------------------------------------------
2	;
3	; Copyright 1994-2009 H. Peter Anvin - All Rights Reserved
4	; Copyright 2009-2011 Intel Corporation; author: H. Peter Anvin
5	;
6	; This program is free software; you can redistribute it and/or modify
7	; it under the terms of the GNU General Public License as published by
8	; the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
9	; Boston MA 02110-1301, USA; either version 2 of the License, or
10	; (at your option) any later version; incorporated herein by reference.
11	;
12	; -----------------------------------------------------------------------
13
14	;
15	; diskstart.inc
16	;
17	; Common early-bootstrap code for harddisk-based Syslinux derivatives.
18	;
19
20	Sect1Ptr0_VAL equ 0xdeadbeef
21	Sect1Ptr1_VAL equ 0xfeedface
22
23	%include "diskboot.inc"
24
25	; ===========================================================================
26	; Padding after the (minimum) 512-byte boot sector so that the rest of
27	; the file has aligned sectors, even if they are larger than 512 bytes.
28	; ===========================================================================
29
30	section .init
31	align_pad zb 512
32
33	; ===========================================================================
34	; Start of LDLINUX.SYS
35	; ===========================================================================
36
37	LDLINUX_SYS equ ($-$$)+TEXT_START
38	ldlinux_sys:
39
40	early_banner db CR, LF, MY_NAME, ' ', VERSION_STR, ' ', 0
41	db CR, LF, 1Ah ; EOF if we "type" this in DOS
42
43	alignz 8
44	ldlinux_magic dd LDLINUX_MAGIC
45	dd LDLINUX_MAGIC^HEXDATE
46
47	;
48	; This area is patched by the installer. It is found by looking for
49	; LDLINUX_MAGIC, plus 8 bytes.
50	;
51	SUBVOL_MAX equ 256
52	CURRENTDIR_MAX equ FILENAME_MAX
53
54	patch_area:
55	DataSectors dw 0 ; Number of sectors (not including bootsec)
56	ADVSectors dw 0 ; Additional sectors for ADVs
57	LDLDwords dd 0 ; Total dwords starting at ldlinux_sys,
58	CheckSum dd 0 ; Checksum starting at ldlinux_sys
59	; value = LDLINUX_MAGIC - [sum of dwords]
60	MaxTransfer dw 127 ; Max sectors to transfer
61	EPAPtr dw EPA - LDLINUX_SYS ; Pointer to the extended patch area
62
63	;
64	; Extended patch area -- this is in .data16 so it doesn't occupy space in
65	; the first sector. Use this structure for anything that isn't used by
66	; the first sector itself.
67	;
68	section .data16
69	alignz 2
70	EPA:
71	ADVSecPtr dw ADVSec0 - LDLINUX_SYS
72	CurrentDirPtr dw CurrentDirName-LDLINUX_SYS ; Current directory name string
73	CurrentDirLen dw CURRENTDIR_MAX
74	SubvolPtr dw SubvolName-LDLINUX_SYS
75	SubvolLen dw SUBVOL_MAX
76	SecPtrOffset dw SectorPtrs-LDLINUX_SYS
77	SecPtrCnt dw (SectorPtrsEnd - SectorPtrs)/10
78
79	;
80	; Boot sector patch pointers
81	;
82	Sect1Ptr0Ptr dw Sect1Ptr0 - bootsec ; Pointers to Sector 1 location
83	Sect1Ptr1Ptr dw Sect1Ptr1 - bootsec
84	RAIDPatchPtr dw kaboom.again - bootsec ; Patch to INT 18h in RAID mode
85
86	;
87	; Pointer to the Syslinux banner
88	;
89	BannerPtr dw syslinux_banner - LDLINUX_SYS
90
91	;
92	; Base directory name and subvolume, if applicable.
93	;
94	%define HAVE_CURRENTDIRNAME
95	global CurrentDirName:data hidden, SubvolName:data hidden
96	CurrentDirName times CURRENTDIR_MAX db 0
97	SubvolName times SUBVOL_MAX db 0
98
99	section .init
100	ldlinux_ent:
101	;
102	; Note that some BIOSes are buggy and run the boot sector at 07C0:0000
103	; instead of 0000:7C00 and the like. We don't want to add anything
104	; more to the boot sector, so it is written to not assume a fixed
105	; value in CS, but we don't want to deal with that anymore from now
106	; on.
107	;
108	jmp 0:.next ; Normalize CS:IP
109	.next: sti ; In case of broken INT 13h BIOSes
110
111	;
112	; Tell the user we got this far
113	;
114	mov si,early_banner
115	call writestr_early
116
117	;
118	; Checksum data thus far
119	;
120	mov si,ldlinux_sys
121	mov cx,[bsBytesPerSec]
122	shr cx,2
123	mov edx,-LDLINUX_MAGIC
124	.checksum:
125	lodsd
126	add edx,eax
127	loop .checksum
128	mov [CheckSum],edx ; Save intermediate result
129	movzx ebx,si ; Start of the next sector
130
131	;
132	; Tell the user if we're using EBIOS or CBIOS
133	;
134	print_bios:
135	mov si,cbios_name
136	cmp byte [getonesec.jmp+1],(getonesec_ebios-(getonesec.jmp+2))
137	jne .cbios
138	mov si,ebios_name
139	mov byte [getlinsec.jmp+1],(getlinsec_ebios-(getlinsec.jmp+2))
140	.cbios:
141	mov [BIOSName],si
142	call writestr_early
143
144	section .earlybss
145	global BIOSName
146	alignb 2
147	%define HAVE_BIOSNAME 1
148	BIOSName resw 1
149
150	section .init
151	;
152	; Now we read the rest of LDLINUX.SYS.
153	;
154	load_rest:
155	push bx ; LSW of load address
156
157	lea esi,[SectorPtrs]
158	mov cx,[DataSectors]
159	dec cx ; Minus this sector
160
161	.get_chunk:
162	jcxz .done
163	mov eax,[si]
164	mov edx,[si+4]
165	movzx ebp,word [si+8]
166	sub cx,bp
167	push ebx
168	shr ebx,4 ; Convert to a segment
169	mov es,bx
170	xor bx,bx
171	call getlinsec
172	pop ebx
173	imul bp,[bsBytesPerSec] ; Will be < 64K
174	add ebx,ebp
175	add si,10
176	jmp .get_chunk
177
178	.done:
179
180	;
181	; All loaded up, verify that we got what we needed.
182	; Note: the checksum field is embedded in the checksum region, so
183	; by the time we get to the end it should all cancel out.
184	;
185	verify_checksum:
186	pop si ; LSW of load address
187	movzx eax,word [bsBytesPerSec]
188	shr ax,2
189	mov ecx,[LDLDwords] ; Total dwords
190	sub ecx,eax ; ... minus one sector
191	mov eax,[CheckSum]
192	.checksum:
193	add eax,[si]
194	add si,4
195	jnz .nowrap
196	; Handle segment wrap
197	mov dx,ds
198	add dx,1000h
199	mov ds,dx
200	.nowrap:
201	dec ecx
202	jnz .checksum
203
204	mov ds,cx
205
206	and eax,eax ; Should be zero
207	jz all_read ; We're cool, go for it!
208
209	;
210	; Uh-oh, something went bad...
211	;
212	mov si,checksumerr_msg
213	call writestr_early
214	jmp kaboom
215
216	;
217	; -----------------------------------------------------------------------------
218	; Subroutines that have to be in the first sector
219	; -----------------------------------------------------------------------------
220
221
222
223	;
224	; getlinsec: load a sequence of BP floppy sector given by the linear sector
225	; number in EAX into the buffer at ES:BX. We try to optimize
226	; by loading up to a whole track at a time, but the user
227	; is responsible for not crossing a 64K boundary.
228	; (Yes, BP is weird for a count, but it was available...)
229	;
230	; On return, BX points to the first byte after the transferred
231	; block.
232	;
233	; This routine assumes CS == DS.
234	;
235	global getlinsec:function hidden
236	getlinsec:
237	pushad
238	add eax,[Hidden] ; Add partition offset
239	adc edx,[Hidden+4]
240	.jmp: jmp strict short getlinsec_cbios
241
242	;
243	; getlinsec_ebios:
244	;
245	; getlinsec implementation for EBIOS (EDD)
246	;
247	getlinsec_ebios:
248	.loop:
249	push bp ; Sectors left
250	.retry2:
251	call maxtrans ; Enforce maximum transfer size
252	movzx edi,bp ; Sectors we are about to read
253	mov cx,retry_count
254	.retry:
255
256	; Form DAPA on stack
257	push edx
258	push eax
259	push es
260	push bx
261	push di
262	push word 16
263	mov si,sp
264	pushad
265	mov ah,42h ; Extended Read
266	push ds
267	push ss
268	pop ds
269	call xint13
270	pop ds
271	popad
272	lea sp,[si+16] ; Remove DAPA
273	jc .error
274	pop bp
275	add eax,edi ; Advance sector pointer
276	adc edx,0
277	sub bp,di ; Sectors left
278	imul di,[bsBytesPerSec]
279	add bx,di ; Advance buffer pointer
280	and bp,bp
281	jnz .loop
282
283	popad
284	ret
285
286	.error:
287	; Some systems seem to get "stuck" in an error state when
288	; using EBIOS. Doesn't happen when using CBIOS, which is
289	; good, since some other systems get timeout failures
290	; waiting for the floppy disk to spin up.
291
292	pushad ; Try resetting the device
293	xor ax,ax
294	call xint13
295	popad
296	loop .retry ; CX-- and jump if not zero
297
298	;shr word [MaxTransfer],1 ; Reduce the transfer size
299	;jnz .retry2
300
301	; Total failure. Try falling back to CBIOS.
302	mov byte [getlinsec.jmp+1],(getlinsec_cbios-(getlinsec.jmp+2))
303	;mov byte [MaxTransfer],63 ; Max possibe CBIOS transfer
304
305	pop bp
306	; ... fall through ...
307
308	;
309	; getlinsec_cbios:
310	;
311	; getlinsec implementation for legacy CBIOS
312	;
313	getlinsec_cbios:
314	.loop:
315	push edx
316	push eax
317	push bp
318	push bx
319
320	movzx esi,word [bsSecPerTrack]
321	movzx edi,word [bsHeads]
322	;
323	; Dividing by sectors to get (track,sector): we may have
324	; up to 2^18 tracks, so we need to use 32-bit arithmetric.
325	;
326	div esi
327	xor cx,cx
328	xchg cx,dx ; CX <- sector index (0-based)
329	; EDX <- 0
330	; eax = track #
331	div edi ; Convert track to head/cyl
332
333	cmp eax,1023 ; Outside the CHS range?
334	ja kaboom
335
336	;
337	; Now we have AX = cyl, DX = head, CX = sector (0-based),
338	; BP = sectors to transfer, SI = bsSecPerTrack,
339	; ES:BX = data target
340	;
341
342	call maxtrans ; Enforce maximum transfer size
343
344	; Must not cross track boundaries, so BP <= SI-CX
345	sub si,cx
346	cmp bp,si
347	jna .bp_ok
348	mov bp,si
349	.bp_ok:
350
351	shl ah,6 ; Because IBM was STOOPID
352	; and thought 8 bits were enough
353	; then thought 10 bits were enough...
354	inc cx ; Sector numbers are 1-based, sigh
355	or cl,ah
356	mov ch,al
357	mov dh,dl
358	xchg ax,bp ; Sector to transfer count
359	mov ah,02h ; Read sectors
360	mov bp,retry_count
361	.retry:
362	pushad
363	call xint13
364	popad
365	jc .error
366	.resume:
367	movzx ecx,al ; ECX <- sectors transferred
368	imul ax,[bsBytesPerSec] ; Convert sectors in AL to bytes in AX
369	pop bx
370	add bx,ax
371	pop bp
372	pop eax
373	pop edx
374	add eax,ecx
375	sub bp,cx
376	jnz .loop
377	popad
378	ret
379
380	.error:
381	dec bp
382	jnz .retry
383
384	xchg ax,bp ; Sectors transferred <- 0
385	shr word [MaxTransfer],1
386	jnz .resume
387	jmp kaboom
388
389	maxtrans:
390	cmp bp,[MaxTransfer]
391	jna .ok
392	mov bp,[MaxTransfer]
393	.ok: ret
394
395	;
396	;
397	; writestr_early: write a null-terminated string to the console
398	; This assumes we're on page 0. This is only used for early
399	; messages, so it should be OK.
400	;
401	writestr_early:
402	pushad
403	.loop: lodsb
404	and al,al
405	jz .return
406	mov ah,0Eh ; Write to screen as TTY
407	mov bx,0007h ; Attribute
408	int 10h
409	jmp short .loop
410	.return: popad
411	ret
412
413	;
414	; Checksum error message
415	;
416	checksumerr_msg db ' Load error - ', 0 ; Boot failed appended
417
418	;
419	; BIOS type string
420	;
421	cbios_name db 'CHS', 0 ; CHS/CBIOS
422	ebios_name db 'EDD', 0 ; EDD/EBIOS
423
424	;
425	; Debug routine
426	;
427	%ifdef debug
428	safedumpregs:
429	cmp word [Debug_Magic],0D00Dh
430	jnz nc_return
431	jmp dumpregs
432	%endif
433
434	rl_checkpt equ $ ; Must be <= 8000h
435
436	rl_checkpt_off equ $-ldlinux_sys
437	%ifndef DEPEND
438	%if rl_checkpt_off > 512-10 ; Need minimum one extent
439	%assign rl_checkpt_overflow rl_checkpt_off - (512-10)
440	%error Sector 1 overflow by rl_checkpt_overflow bytes
441	%endif
442	%endif
443
444	;
445	; Extent pointers... each extent contains an 8-byte LBA and an 2-byte
446	; sector count. In most cases, we will only ever need a handful of
447	; extents, but we have to assume a maximally fragmented system where each
448	; extent contains only one sector.
449	;
450	alignz 2
451	MaxInitDataSize equ 96 << 10
452	MaxLMA equ LDLINUX_SYS+MaxInitDataSize
453	SectorPtrs zb 10*(MaxInitDataSize >> MIN_SECTOR_SHIFT)
454	SectorPtrsEnd equ $
455
456	; ----------------------------------------------------------------------------
457	; End of code and data that have to be in the first sector
458	; ----------------------------------------------------------------------------
459
460	section .text16
461	all_read:
462	; We enter here with ES scrambled...
463	xor ax,ax
464	mov es,ax
465	;
466	; Let the user (and programmer!) know we got this far. This used to be
467	; in Sector 1, but makes a lot more sense here.
468	;
469	mov si,late_banner
470	call writestr_early
471
472	mov si,copyright_str
473	call writestr_early
474
475
476	;
477	; Insane hack to expand the DOS superblock to dwords
478	;
479	expand_super:
480	xor eax,eax
481	mov si,superblock
482	mov di,SuperInfo
483	mov cx,superinfo_size
484	.loop:
485	lodsw
486	dec si
487	stosd ; Store expanded word
488	xor ah,ah
489	stosd ; Store expanded byte
490	loop .loop
491
492
493	;
494	; Common initialization code
495	;
496	%include "init.inc"
497
498	pushad
499	mov eax,ROOT_FS_OPS
500	movzx dx,byte [DriveNumber]
501	; DH = 0: we are boot from disk not CDROM
502	mov ecx,[Hidden]
503	mov ebx,[Hidden+4]
504	mov si,[bsHeads]
505	mov di,[bsSecPerTrack]
506	movzx ebp,word [MaxTransfer]
507	pm_call pm_fs_init
508	pm_call load_env32
509	popad
510
511	section .bss16
512	SuperInfo resq 16 ; The first 16 bytes expanded 8 times
513
514	;
515	; Banner information not needed in sector 1
516	;
517	section .data16
518	global syslinux_banner
519	syslinux_banner db CR, LF, MY_NAME, ' ', VERSION_STR
520	late_banner db ' ', DATE_STR, 0
521
522	section .text16

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