2 * Copyright (c) 2001 John Baldwin
5 * Redistribution and use in source and binary forms are freely
6 * permitted provided that the above copyright notice and this
7 * paragraph and the following disclaimer are duplicated in all
10 * This software is provided "AS IS" and without any express or
11 * implied warranties, including, without limitation, the implied
12 * warranties of merchantability and fitness for a particular
16 * $FreeBSD: src/sys/boot/i386/cdboot/cdboot.s,v 1.9 2001/11/07 01:20:33 jhb Exp $
17 * $DragonFly: src/sys/boot/pc32/cdboot/cdboot.S,v 1.8 2007/05/18 07:41:43 dillon Exp $
21 * This program is a freestanding boot program to load an a.out binary
22 * from a CD-ROM booted with no emulation mode as described by the El
23 * Torito standard. Due to broken BIOSen that do not load the desired
24 * number of sectors, we try to fit this in as small a space as possible.
26 * Basically, we first create a set of boot arguments to pass to the loaded
27 * binary. Then we attempt to load /boot/loader from the CD we were booted
31 #include "../bootasm.h"
36 .set AOUT_TEXT,0x04 # text segment size
37 .set AOUT_DATA,0x08 # data segment size
38 .set AOUT_BSS,0x0c # zerod BSS size
39 .set AOUT_SYMBOLS,0x10 # symbol table
40 .set AOUT_ENTRY,0x14 # entry point
41 .set AOUT_HEADER,MEM_PAGE_SIZE # size of the a.out header
44 * Flags for kargs->bootflags
46 .set KARGS_FLAGS_CD,0x1 # flag to indicate booting from
51 .set SEL_SDATA,0x8 # Supervisor data
52 .set SEL_RDATA,0x10 # Real mode data
53 .set SEL_SCODE,0x18 # PM-32 code
54 .set SEL_SCODE16,0x20 # PM-16 code
59 .set INT_SYS,0x30 # BTX syscall interrupt
62 * Constants for reading from the CD.
64 .set ERROR_TIMEOUT,0x80 # BIOS timeout on read
65 .set NUM_RETRIES,3 # Num times to retry
66 .set SECTOR_SIZE,0x800 # size of a sector
67 .set SECTOR_SHIFT,11 # number of place to shift
68 .set BUFFER_LEN,0x100 # number of sectors in buffer
69 .set MAX_READ,0x10000 # max we can read at a time
70 .set MAX_READ_SEC,MAX_READ >> SECTOR_SHIFT
71 .set MEM_READ_BUFFER,0x9000 # buffer to read from CD
72 .set MEM_VOLDESC,MEM_READ_BUFFER # volume descriptor
73 .set MEM_DIR,MEM_VOLDESC+SECTOR_SIZE # Lookup buffer
74 .set VOLDESC_LBA,0x10 # LBA of vol descriptor
75 .set VD_PRIMARY,1 # Primary VD
76 .set VD_END,255 # VD Terminator
77 .set VD_ROOTDIR,156 # Offset of Root Dir Record
78 .set DIR_LEN,0 # Offset of Dir Record length
79 .set DIR_EA_LEN,1 # Offset of EA length
80 .set DIR_EXTENT,2 # Offset of 64-bit LBA
81 .set DIR_SIZE,10 # Offset of 64-bit length
82 .set DIR_NAMELEN,32 # Offset of 8-bit name len
83 .set DIR_NAME,33 # Offset of dir name
88 * We expect to be loaded by the BIOS at 0x7c00 (standard
89 * boot loader entry point)
95 start: cld # string ops inc
96 xor %ax,%ax # zero %ax
97 mov %ax,%ss # setup the
98 mov $start,%sp # stack
99 mov %ax,%ds # setup the
100 mov %ax,%es # data segments
101 mov %dl,drive # Save BIOS boot device
102 mov $msg_welcome,%si # %ds:(%si) -> welcome message
103 call putstr # display the welcome message
106 * Setup the arguments that the loader is expecting from
109 mov $msg_bootinfo,%si # %ds:(%si) -> boot args message
110 call putstr # display the message
111 mov $MEM_ARG,%bx # %ds:(%bx) -> boot args
112 mov %bx,%di # %es:(%di) -> boot args
113 xor %eax,%eax # zero %eax
114 mov $(MEM_ARG_SIZE/4),%cx # Size of arguments in 32-bit
116 rep # Clear the arguments
118 mov drive,%dl # Store BIOS boot device
119 mov %dl,0x4(%bx) # in kargs->bootdev
120 or $KARGS_FLAGS_CD,0x8(%bx) # kargs->bootflags |=
123 * Load Volume Descriptor
125 mov $VOLDESC_LBA,%eax # Set LBA of first VD
127 mov $1,%dh # One sector
128 mov $MEM_VOLDESC,%ebx # Destination
129 call read # Read it in
130 cmpb $VD_PRIMARY,(%bx) # Primary VD?
133 cmpb $VD_END,(%bx) # Last VD?
134 jne load_vd # No, read next
135 mov $msg_novd,%si # No VD
137 have_vd: # Have Primary VD
140 * Lookup the loader binary.
142 mov $loader_path,%si # File to lookup
143 call lookup # Try to find it
146 * Load the binary into the buffer. Due to real mode
147 * addressing limitations we have to read it in in 64k
150 mov DIR_SIZE(%bx),%eax # Read file length
151 add $SECTOR_SIZE-1,%eax # Convert length to sectors
155 mov $msg_load2big,%si # Error message
157 load_sizeok: movzbw %al,%cx # Num sectors to read
158 mov DIR_EXTENT(%bx),%eax # Load extent
160 mov DIR_EA_LEN(%bx),%dl
161 add %edx,%eax # Skip extended
162 mov $MEM_READ_BUFFER,%ebx # Read into the buffer
163 load_loop: mov %cl,%dh
164 cmp $MAX_READ_SEC,%cl # Truncate to max read size
166 mov $MAX_READ_SEC,%dh
167 load_notrunc: sub %dh,%cl # Update count
168 call read # Read it in
169 add $MAX_READ_SEC,%eax # Update LBA
170 add $MAX_READ,%ebx # Update dest addr
171 jcxz load_done # Done?
172 jmp load_loop # Keep going
175 * Turn on the A20 address line.
177 call seta20 # Turn A20 on
180 * Relocate the loader and BTX using a very lazy
183 mov $msg_relocate,%si # Display the
184 call putstr # relocation message
185 mov MEM_READ_BUFFER+AOUT_ENTRY,%edi # %edi is the destination
186 mov $(MEM_READ_BUFFER+AOUT_HEADER),%esi # %esi is
187 # the start of the text
189 mov MEM_READ_BUFFER+AOUT_TEXT,%ecx # %ecx = length of the text
191 push %edi # Save entry point for later
192 lgdt gdtdesc # setup our own gdt
193 cli # turn off interrupts
194 mov %cr0,%eax # Turn on
195 or $0x1,%al # protected
197 ljmp $SEL_SCODE,$pm_start # long jump to clear the
198 # instruction pre-fetch queue
200 pm_start: mov $SEL_SDATA,%ax # Initialize
201 mov %ax,%ds # %ds and
202 mov %ax,%es # %es to a flat selector
205 add $(MEM_PAGE_SIZE - 1),%edi # pad %edi out to a new page
206 and $~(MEM_PAGE_SIZE - 1),%edi # for the data segment
207 mov MEM_READ_BUFFER+AOUT_DATA,%ecx # size of the data segment
210 mov MEM_READ_BUFFER+AOUT_BSS,%ecx # size of the bss
211 xor %eax,%eax # zero %eax
212 add $3,%cl # round %ecx up to
213 shr $2,%ecx # a multiple of 4
216 mov MEM_READ_BUFFER+AOUT_ENTRY,%esi # %esi -> relocated loader
217 add $MEM_BTX_LDR_OFF,%esi # %esi -> BTX in the loader
218 mov $MEM_BTX_ORG,%edi # %edi -> where BTX needs to go
219 movzwl 0xa(%esi),%ecx # %ecx -> length of BTX
222 ljmp $SEL_SCODE16,$pm_16 # Jump to 16-bit PM
224 pm_16: mov $SEL_RDATA,%ax # Initialize
225 mov %ax,%ds # %ds and
226 mov %ax,%es # %es to a real mode selector
227 mov %cr0,%eax # Turn off
228 and $~0x1,%al # protected
230 ljmp $0,$pm_end # Long jump to clear the
231 # instruction pre-fetch queue
232 pm_end: sti # Turn interrupts back on now
235 * Copy the BTX client to MEM_BTX_USR.
237 xor %ax,%ax # zero %ax and set
238 mov %ax,%ds # %ds and %es
239 mov %ax,%es # to segment 0
240 mov $MEM_BTX_USR,%di # Prepare to relocate
241 mov $btx_client,%si # the simple btx client
242 mov $(btx_client_end-btx_client),%cx # length of btx client
244 movsb # simple BTX client
247 * Copy the boot[12] args to where the BTX client
250 mov $MEM_ARG,%si # where the args are at now
251 mov $MEM_BTX_USR_ARG,%di # where the args are moving to
252 mov $(MEM_ARG_SIZE/4),%cx # size of the arguments in longs
257 * Save the entry point so the client can get to it
260 pop %eax # Restore saved entry point
261 stosl # and add it to the end of
264 * Now we just start up BTX and let it do the rest
266 mov $msg_jump,%si # Display the
267 call putstr # jump message
268 ljmp $0,$MEM_BTX_ENTRY # Jump to the BTX entry point
271 * Lookup the file in the path at [SI] from the root
274 * Trashes: All but BX
275 * Returns: BX = pointer to record
277 lookup: mov $VD_ROOTDIR+MEM_VOLDESC,%bx # Root directory record
279 mov $msg_lookup,%si # Display lookup message
287 lookup_dir: lodsb # Get first char of path
288 cmp $0,%al # Are we done?
290 cmp $'/',%al # Skip path separator.
292 dec %si # Undo lodsb side effect
293 call find_file # Lookup first path item
294 jnc lookup_dir # Try next component
295 mov $msg_lookupfail,%si # Not found.
297 lookup_done: mov $msg_lookupok,%si # Success message
302 * Lookup file at [SI] in directory whose record is at [BX].
304 * Trashes: All but returns
306 * Returns: CF = 0 (success)
307 * BX = pointer to record,
308 * SX = next path item
312 find_file: mov DIR_EXTENT(%bx),%eax # Load extent
314 mov DIR_EA_LEN(%bx),%dl
315 add %edx,%eax # Skip extended attributes
316 mov %eax,rec_lba # Save LBA
317 mov DIR_SIZE(%bx),%eax # Save size
319 xor %cl,%cl # Zero length
321 ff.namelen: inc %cl # Update length
325 cmp $'/',%al # Path separator?
326 jnz ff.namelen # No, keep going
327 ff.namedone: dec %cl # Adjust length and save
330 ff.load: mov rec_lba,%eax # Load LBA
331 mov $MEM_DIR,%ebx # Address buffer
332 mov $1,%dh # One sector
333 call read # Read directory block
334 incl rec_lba # Update LBA to next block
335 ff.scan: mov %ebx,%edx # Check for EOF
341 ff.scan.1: cmpb $0,DIR_LEN(%bx) # Last record in block?
344 movzbw DIR_NAMELEN(%bx),%si # Find end of string
345 ff.checkver: cmpb $'0',DIR_NAME-1(%bx,%si) # Less than '0'?
347 cmpb $'9',DIR_NAME-1(%bx,%si) # Greater than '9'?
351 jmp ff.checklen # All numbers in name, so
353 ff.checkver.1: movzbw DIR_NAMELEN(%bx),%cx
354 cmp %cx,%si # Did we find any digits?
356 cmpb $';',DIR_NAME-1(%bx,%si) # Check for semicolon
358 dec %si # Skip semicolon
360 mov %cl,DIR_NAMELEN(%bx) # Adjust length
362 ff.checkver.2: mov %cx,%si # Restore %si to end of string
363 ff.checkdot: cmpb $'.',DIR_NAME-1(%bx,%si) # Trailing dot?
365 decb DIR_NAMELEN(%bx) # Adjust length
366 ff.checklen: pop %si # Restore
367 movzbw name_len,%cx # Load length of name
368 cmp %cl,DIR_NAMELEN(%bx) # Does length match?
369 je ff.checkname # Yes, check name
370 ff.nextrec: add DIR_LEN(%bx),%bl # Next record
373 ff.nextblock: subl $SECTOR_SIZE,rec_size # Adjust size
374 jnc ff.load # If subtract ok, keep going
375 ret # End of file, so not found
376 ff.checkname: lea DIR_NAME(%bx),%di # Address name in record
378 repe cmpsb # Compare name
379 jcxz ff.match # We have a winner!
381 jmp ff.nextrec # Keep looking.
382 ff.match: add $2,%sp # Discard saved %si
387 * Load DH sectors starting at LBA EAX into [EBX]. No
388 * registers are destroyed. Don't trust the BIOS, especially
389 * with regards to the msb 16 bits of our registers.
391 read: pushal # dont screw around
392 mov %eax,edd_lba # LBA to read from
393 mov %ebx,%eax # Convert address
394 shr $4,%eax # to segment
395 mov %ax,edd_addr+0x2 # and store
396 read.retry: call twiddle # Entertain the user
398 mov $edd_packet,%si # Address Packet
399 mov %dh,edd_len # Set length
400 mov drive,%dl # BIOS Device
401 mov $0x42,%ah # BIOS: Extended Read
402 int $0x13 # Call BIOS
404 jc read.fail # Worked?
407 read.fail: cmp $ERROR_TIMEOUT,%ah # Timeout?
408 je read.retry # Yes, Retry.
409 read.error: mov %ah,%al # Save error
410 mov $hex_error,%di # Format it
412 mov $msg_badread,%si # Display Read error message
415 * Display error message at [SI] and halt.
417 error: call putstr # Display message
422 * Display a null-terminated string.
427 putstr.load: lodsb # load %al from %ds:(%si)
428 test %al,%al # stop at null
429 jnz putstr.putc # if the char != null, output it
430 ret # return when null is hit
431 putstr.putc: call putc # output char
432 jmp putstr.load # next char
435 * Display a single char(%al). Don't trust the bios to save
439 mov $0x7,%bx # attribute for output
440 mov $0xe,%ah # BIOS: put_char
441 int $0x10 # call BIOS, print char in %al
443 ret # Return to caller
446 * Output the "twiddle"
448 twiddle: push %ax # Save
450 mov twiddle_index,%al # Load index
451 mov $twiddle_chars,%bx # Address table
454 mov %al,twiddle_index # Save index for next call
456 call putc # Output it
457 mov $8,%al # Backspace
458 call putc # Output it
464 * Enable A20. Put upper limit on amount of time we wait for the
465 * keyboard controller to get ready (65K x ISA access time). If
466 * we wait more than that amount it's likely that the hardware
467 * is legacy-free and simply doesn't have keyboard controller
468 * and don't need enabling A20 at all.
470 seta20: cli # Disable interrupts
472 seta20.1: inc %cx # Increment, overflow?
474 in $0x64,%al # Get status
475 test $0x2,%al # Busy?
477 mov $0xd1,%al # Command: Write
478 out %al,$0x64 # output port
479 seta20.2: in $0x64,%al # Get status
480 test $0x2,%al # Busy?
482 mov $0xdf,%al # Enable
484 seta20.3: sti # Enable interrupts
488 * Convert AL to hex, saving the result to [EDI].
490 hex8: pushl %eax # Save
491 shrb $0x4,%al # Do upper
494 hex8.1: andb $0xf,%al # Get lower 4
495 cmpb $0xa,%al # Convert
496 sbbb $0x69,%al # to hex
498 orb $0x20,%al # To lower case
503 * BTX client to start btxldr
506 btx_client: mov $(MEM_BTX_USR_ARG-MEM_BTX_USR+MEM_ARG_SIZE-4), %esi
509 mov $(MEM_ARG_SIZE/4),%ecx # Number of words to push
511 push_arg: lodsl # Read argument
512 push %eax # Push it onto the stack
513 loop push_arg # Push all of the arguments
514 cld # In case anyone depends on this
515 pushl MEM_BTX_USR_ARG-MEM_BTX_USR+MEM_ARG_SIZE # Entry point of
517 push %eax # Emulate a near call
518 mov $0x1,%eax # "exec" system call
519 int $INT_SYS # BTX system call
526 * Global descriptor table.
528 gdt: .word 0x0,0x0,0x0,0x0 # Null entry
529 .word 0xffff,0x0,0x9200,0xcf # SEL_SDATA
530 .word 0xffff,0x0,0x9200,0x0 # SEL_RDATA
531 .word 0xffff,0x0,0x9a00,0xcf # SEL_SCODE (32-bit)
532 .word 0xffff,0x0,0x9a00,0x8f # SEL_SCODE16 (16-bit)
536 * Pseudo-descriptors.
538 gdtdesc: .word gdt.1-gdt-1 # Limit
544 edd_packet: .byte 0x10 # Length
546 edd_len: .byte 0x0 # Num to read
548 edd_addr: .word 0x0,0x0 # Seg:Off
549 edd_lba: .quad 0x0 # LBA
554 * State for searching dir
556 rec_lba: .long 0x0 # LBA (adjusted for EA)
557 rec_size: .long 0x0 # File size
558 name_len: .byte 0x0 # Length of current name
560 twiddle_index: .byte 0x0
562 msg_welcome: .asciz "CD Loader 1.01\r\n\n"
563 msg_bootinfo: .asciz "Building the boot loader arguments\r\n"
564 msg_relocate: .asciz "Relocating the loader and the BTX\r\n"
565 msg_jump: .asciz "Starting the BTX loader\r\n"
566 msg_badread: .ascii "Read Error: 0x"
567 hex_error: .ascii "00\r\n"
568 msg_novd: .asciz "Could not find Primary Volume Descriptor\r\n"
569 msg_lookup: .asciz "Looking up "
570 msg_lookup2: .asciz "... "
571 msg_lookupok: .asciz "Found\r\n"
572 msg_lookupfail: .asciz "File not found\r\n"
573 msg_load2big: .asciz "File too big\r\n"
574 loader_path: .asciz "/BOOT/LOADER"
575 twiddle_chars: .ascii "|/-\\"