2 # Copyright (c) 2001 John Baldwin <jhb@FreeBSD.org>
4 # Redistribution and use in source and binary forms, with or without
5 # modification, are permitted provided that the following conditions
7 # 1. Redistributions of source code must retain the above copyright
8 # notice, this list of conditions and the following disclaimer.
9 # 2. Redistributions in binary form must reproduce the above copyright
10 # notice, this list of conditions and the following disclaimer in the
11 # documentation and/or other materials provided with the distribution.
13 # THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
14 # ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 # IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
16 # ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
17 # FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
18 # DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
19 # OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
20 # HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
21 # LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
22 # OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 # This program is a freestanding boot program to load an a.out binary
30 # from a CD-ROM booted with no emulation mode as described by the El
31 # Torito standard. Due to broken BIOSen that do not load the desired
32 # number of sectors, we try to fit this in as small a space as possible.
34 # Basically, we first create a set of boot arguments to pass to the loaded
35 # binary. Then we attempt to load /boot/loader from the CD we were booted
44 .set MEM_PAGE_SIZE,0x1000 # memory page size, 4k
45 .set MEM_ARG,0x900 # Arguments at start
46 .set MEM_ARG_BTX,0xa100 # Where we move them to so the
47 # BTX client can see them
48 .set MEM_ARG_SIZE,0x18 # Size of the arguments
49 .set MEM_BTX_ADDRESS,0x9000 # where BTX lives
50 .set MEM_BTX_ENTRY,0x9010 # where BTX starts to execute
51 .set MEM_BTX_OFFSET,MEM_PAGE_SIZE # offset of BTX in the loader
52 .set MEM_BTX_CLIENT,0xa000 # where BTX clients live
56 .set AOUT_TEXT,0x04 # text segment size
57 .set AOUT_DATA,0x08 # data segment size
58 .set AOUT_BSS,0x0c # zero'd BSS size
59 .set AOUT_SYMBOLS,0x10 # symbol table
60 .set AOUT_ENTRY,0x14 # entry point
61 .set AOUT_HEADER,MEM_PAGE_SIZE # size of the a.out header
65 .set SEL_SDATA,0x8 # Supervisor data
66 .set SEL_RDATA,0x10 # Real mode data
67 .set SEL_SCODE,0x18 # PM-32 code
68 .set SEL_SCODE16,0x20 # PM-16 code
72 .set INT_SYS,0x30 # BTX syscall interrupt
74 # Constants for reading from the CD.
76 .set ERROR_TIMEOUT,0x80 # BIOS timeout on read
77 .set NUM_RETRIES,3 # Num times to retry
78 .set SECTOR_SIZE,0x800 # size of a sector
79 .set SECTOR_SHIFT,11 # number of place to shift
80 .set BUFFER_LEN,0x100 # number of sectors in buffer
81 .set MAX_READ,0x10000 # max we can read at a time
82 .set MAX_READ_SEC,MAX_READ >> SECTOR_SHIFT
83 .set MEM_READ_BUFFER,0x9000 # buffer to read from CD
84 .set MEM_VOLDESC,MEM_READ_BUFFER # volume descriptor
85 .set MEM_DIR,MEM_VOLDESC+SECTOR_SIZE # Lookup buffer
86 .set VOLDESC_LBA,0x10 # LBA of vol descriptor
87 .set VD_PRIMARY,1 # Primary VD
88 .set VD_END,255 # VD Terminator
89 .set VD_ROOTDIR,156 # Offset of Root Dir Record
90 .set DIR_LEN,0 # Offset of Dir Record length
91 .set DIR_EA_LEN,1 # Offset of EA length
92 .set DIR_EXTENT,2 # Offset of 64-bit LBA
93 .set DIR_SIZE,10 # Offset of 64-bit length
94 .set DIR_NAMELEN,32 # Offset of 8-bit name len
95 .set DIR_NAME,33 # Offset of dir name
97 # We expect to be loaded by the BIOS at 0x7c00 (standard boot loader entry
106 start: cld # string ops inc
107 xor %ax,%ax # zero %ax
108 mov %ax,%ss # setup the
109 mov $start,%sp # stack
110 mov %ax,%ds # setup the
111 mov %ax,%es # data segments
112 mov %dl,drive # Save BIOS boot device
113 mov $msg_welcome,%si # %ds:(%si) -> welcome message
114 call putstr # display the welcome message
116 # Setup the arguments that the loader is expecting from boot[12]
118 mov $msg_bootinfo,%si # %ds:(%si) -> boot args message
119 call putstr # display the message
120 mov $MEM_ARG,%bx # %ds:(%bx) -> boot args
121 mov %bx,%di # %es:(%di) -> boot args
122 xor %eax,%eax # zero %eax
123 mov $(MEM_ARG_SIZE/4),%cx # Size of arguments in 32-bit
125 rep # Clear the arguments
127 mov drive,%dl # Store BIOS boot device
128 mov %dl,0x4(%bx) # in kargs->bootdev
129 orb $KARGS_FLAGS_CD,0x8(%bx) # kargs->bootflags |=
132 # Load Volume Descriptor
134 mov $VOLDESC_LBA,%eax # Set LBA of first VD
135 load_vd: push %eax # Save %eax
136 mov $1,%dh # One sector
137 mov $MEM_VOLDESC,%ebx # Destination
138 call read # Read it in
139 cmpb $VD_PRIMARY,(%bx) # Primary VD?
141 pop %eax # Prepare to
143 cmpb $VD_END,(%bx) # Last VD?
144 jne load_vd # No, read next
145 mov $msg_novd,%si # No VD
147 have_vd: # Have Primary VD
149 # Try to look up the loader binary using the paths in the loader_paths
152 mov $loader_paths,%si # Point to start of array
153 lookup_path: push %si # Save file name pointer
154 call lookup # Try to find file
155 pop %di # Restore file name pointer
156 jnc lookup_found # Found this file
157 xor %al,%al # Look for next
158 mov $0xffff,%cx # path name by
161 mov %di,%si # Point %si at next path
162 mov (%si),%al # Get first char of next path
163 or %al,%al # Is it double nul?
164 jnz lookup_path # No, try it.
165 mov $msg_failed,%si # Failed message
167 lookup_found: # Found a loader file
169 # Load the binary into the buffer. Due to real mode addressing limitations
170 # we have to read it in 64k chunks.
172 mov DIR_SIZE(%bx),%eax # Read file length
173 add $SECTOR_SIZE-1,%eax # Convert length to sectors
174 shr $SECTOR_SHIFT,%eax
177 mov $msg_load2big,%si # Error message
179 load_sizeok: movzbw %al,%cx # Num sectors to read
180 mov DIR_EXTENT(%bx),%eax # Load extent
182 mov DIR_EA_LEN(%bx),%dl
183 add %edx,%eax # Skip extended
184 mov $MEM_READ_BUFFER,%ebx # Read into the buffer
185 load_loop: mov %cl,%dh
186 cmp $MAX_READ_SEC,%cl # Truncate to max read size
188 mov $MAX_READ_SEC,%dh
189 load_notrunc: sub %dh,%cl # Update count
191 call read # Read it in
193 add $MAX_READ_SEC,%eax # Update LBA
194 add $MAX_READ,%ebx # Update dest addr
195 jcxz load_done # Done?
196 jmp load_loop # Keep going
199 # Turn on the A20 address line
201 call seta20 # Turn A20 on
203 # Relocate the loader and BTX using a very lazy protected mode
205 mov $msg_relocate,%si # Display the
206 call putstr # relocation message
207 mov MEM_READ_BUFFER+AOUT_ENTRY,%edi # %edi is the destination
208 mov $(MEM_READ_BUFFER+AOUT_HEADER),%esi # %esi is
209 # the start of the text
211 mov MEM_READ_BUFFER+AOUT_TEXT,%ecx # %ecx = length of the text
213 push %edi # Save entry point for later
214 lgdt gdtdesc # setup our own gdt
215 cli # turn off interrupts
216 mov %cr0,%eax # Turn on
217 or $0x1,%al # protected
219 ljmp $SEL_SCODE,$pm_start # long jump to clear the
220 # instruction pre-fetch queue
222 pm_start: mov $SEL_SDATA,%ax # Initialize
223 mov %ax,%ds # %ds and
224 mov %ax,%es # %es to a flat selector
227 add $(MEM_PAGE_SIZE - 1),%edi # pad %edi out to a new page
228 and $~(MEM_PAGE_SIZE - 1),%edi # for the data segment
229 mov MEM_READ_BUFFER+AOUT_DATA,%ecx # size of the data segment
232 mov MEM_READ_BUFFER+AOUT_BSS,%ecx # size of the bss
233 xor %eax,%eax # zero %eax
234 add $3,%cl # round %ecx up to
235 shr $2,%ecx # a multiple of 4
238 mov MEM_READ_BUFFER+AOUT_ENTRY,%esi # %esi -> relocated loader
239 add $MEM_BTX_OFFSET,%esi # %esi -> BTX in the loader
240 mov $MEM_BTX_ADDRESS,%edi # %edi -> where BTX needs to go
241 movzwl 0xa(%esi),%ecx # %ecx -> length of BTX
244 ljmp $SEL_SCODE16,$pm_16 # Jump to 16-bit PM
246 pm_16: mov $SEL_RDATA,%ax # Initialize
247 mov %ax,%ds # %ds and
248 mov %ax,%es # %es to a real mode selector
249 mov %cr0,%eax # Turn off
250 and $~0x1,%al # protected
252 ljmp $0,$pm_end # Long jump to clear the
253 # instruction pre-fetch queue
254 pm_end: sti # Turn interrupts back on now
256 # Copy the BTX client to MEM_BTX_CLIENT
258 xor %ax,%ax # zero %ax and set
259 mov %ax,%ds # %ds and %es
260 mov %ax,%es # to segment 0
261 mov $MEM_BTX_CLIENT,%di # Prepare to relocate
262 mov $btx_client,%si # the simple btx client
263 mov $(btx_client_end-btx_client),%cx # length of btx client
265 movsb # simple BTX client
267 # Copy the boot[12] args to where the BTX client can see them
269 mov $MEM_ARG,%si # where the args are at now
270 mov $MEM_ARG_BTX,%di # where the args are moving to
271 mov $(MEM_ARG_SIZE/4),%cx # size of the arguments in longs
275 # Save the entry point so the client can get to it later on
277 pop %eax # Restore saved entry point
278 stosl # and add it to the end of
281 # Now we just start up BTX and let it do the rest
283 mov $msg_jump,%si # Display the
284 call putstr # jump message
285 ljmp $0,$MEM_BTX_ENTRY # Jump to the BTX entry point
288 # Lookup the file in the path at [SI] from the root directory.
290 # Trashes: All but BX
291 # Returns: CF = 0 (success), BX = pointer to record
294 lookup: mov $VD_ROOTDIR+MEM_VOLDESC,%bx # Root directory record
296 mov $msg_lookup,%si # Display lookup message
304 lookup_dir: lodsb # Get first char of path
305 cmp $0,%al # Are we done?
307 cmp $'/',%al # Skip path separator.
309 dec %si # Undo lodsb side effect
310 call find_file # Lookup first path item
311 jnc lookup_dir # Try next component
312 mov $msg_lookupfail,%si # Not found message
317 lookup_done: mov $msg_lookupok,%si # Success message
323 # Lookup file at [SI] in directory whose record is at [BX].
325 # Trashes: All but returns
326 # Returns: CF = 0 (success), BX = pointer to record, SI = next path item
327 # CF = 1 (not found), SI = preserved
329 find_file: mov DIR_EXTENT(%bx),%eax # Load extent
331 mov DIR_EA_LEN(%bx),%dl
332 add %edx,%eax # Skip extended attributes
333 mov %eax,rec_lba # Save LBA
334 mov DIR_SIZE(%bx),%eax # Save size
336 xor %cl,%cl # Zero length
338 ff.namelen: inc %cl # Update length
342 cmp $'/',%al # Path separator?
343 jnz ff.namelen # No, keep going
344 ff.namedone: dec %cl # Adjust length and save
347 ff.load: mov rec_lba,%eax # Load LBA
348 mov $MEM_DIR,%ebx # Address buffer
349 mov $1,%dh # One sector
350 call read # Read directory block
351 incl rec_lba # Update LBA to next block
352 ff.scan: mov %ebx,%edx # Check for EOF
358 ff.scan.1: cmpb $0,DIR_LEN(%bx) # Last record in block?
361 movzbw DIR_NAMELEN(%bx),%si # Find end of string
362 ff.checkver: cmpb $'0',DIR_NAME-1(%bx,%si) # Less than '0'?
364 cmpb $'9',DIR_NAME-1(%bx,%si) # Greater than '9'?
368 jmp ff.checklen # All numbers in name, so
370 ff.checkver.1: movzbw DIR_NAMELEN(%bx),%cx
371 cmp %cx,%si # Did we find any digits?
373 cmpb $';',DIR_NAME-1(%bx,%si) # Check for semicolon
375 dec %si # Skip semicolon
377 mov %cl,DIR_NAMELEN(%bx) # Adjust length
379 ff.checkver.2: mov %cx,%si # Restore %si to end of string
380 ff.checkdot: cmpb $'.',DIR_NAME-1(%bx,%si) # Trailing dot?
382 decb DIR_NAMELEN(%bx) # Adjust length
383 ff.checklen: pop %si # Restore
384 movzbw name_len,%cx # Load length of name
385 cmp %cl,DIR_NAMELEN(%bx) # Does length match?
386 je ff.checkname # Yes, check name
387 ff.nextrec: add DIR_LEN(%bx),%bl # Next record
390 ff.nextblock: subl $SECTOR_SIZE,rec_size # Adjust size
391 jnc ff.load # If subtract ok, keep going
392 ret # End of file, so not found
393 ff.checkname: lea DIR_NAME(%bx),%di # Address name in record
395 repe cmpsb # Compare name
396 je ff.match # We have a winner!
398 jmp ff.nextrec # Keep looking.
399 ff.match: add $2,%sp # Discard saved %si
404 # Load DH sectors starting at LBA EAX into [EBX].
408 read: push %si # Save
409 push %cx # Save since some BIOSs trash
410 mov %eax,edd_lba # LBA to read from
411 mov %ebx,%eax # Convert address
412 shr $4,%eax # to segment
413 mov %ax,edd_addr+0x2 # and store
414 read.retry: call twiddle # Entertain the user
416 mov $edd_packet,%si # Address Packet
417 mov %dh,edd_len # Set length
418 mov drive,%dl # BIOS Device
419 mov $0x42,%ah # BIOS: Extended Read
420 int $0x13 # Call BIOS
422 jc read.fail # Worked?
426 read.fail: cmp $ERROR_TIMEOUT,%ah # Timeout?
427 je read.retry # Yes, Retry.
428 read.error: mov %ah,%al # Save error
429 mov $hex_error,%di # Format it
431 mov $msg_badread,%si # Display Read error message
434 # Display error message at [SI] and halt.
436 error: call putstr # Display message
441 # Display a null-terminated string.
445 putstr: push %bx # Save
446 putstr.load: lodsb # load %al from %ds:(%si)
447 test %al,%al # stop at null
448 jnz putstr.putc # if the char != null, output it
450 ret # return when null is hit
451 putstr.putc: call putc # output char
452 jmp putstr.load # next char
455 # Display a single char.
457 putc: mov $0x7,%bx # attribute for output
458 mov $0xe,%ah # BIOS: put_char
459 int $0x10 # call BIOS, print char in %al
460 ret # Return to caller
463 # Output the "twiddle"
465 twiddle: push %ax # Save
467 mov twiddle_index,%al # Load index
468 mov $twiddle_chars,%bx # Address table
471 mov %al,twiddle_index # Save index for next call
473 call putc # Output it
474 mov $8,%al # Backspace
475 call putc # Output it
481 # Enable A20. Put an upper limit on the amount of time we wait for the
482 # keyboard controller to get ready (65K x ISA access time). If
483 # we wait more than that amount, the hardware is probably
484 # legacy-free and simply doesn't have a keyboard controller.
485 # Thus, the A20 line is already enabled.
487 seta20: cli # Disable interrupts
489 seta20.1: inc %cx # Increment, overflow?
491 in $0x64,%al # Get status
492 test $0x2,%al # Busy?
494 mov $0xd1,%al # Command: Write
495 out %al,$0x64 # output port
496 seta20.2: in $0x64,%al # Get status
497 test $0x2,%al # Busy?
499 mov $0xdf,%al # Enable
501 seta20.3: sti # Enable interrupts
505 # Convert AL to hex, saving the result to [EDI].
507 hex8: pushl %eax # Save
508 shrb $0x4,%al # Do upper
511 hex8.1: andb $0xf,%al # Get lower 4
512 cmpb $0xa,%al # Convert
513 sbbb $0x69,%al # to hex
515 orb $0x20,%al # To lower case
520 # BTX client to start btxldr
523 btx_client: mov $(MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE-4), %esi
526 mov $(MEM_ARG_SIZE/4),%ecx # Number of words to push
528 push_arg: lodsl # Read argument
529 push %eax # Push it onto the stack
530 loop push_arg # Push all of the arguments
531 cld # In case anyone depends on this
532 pushl MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE # Entry point of
534 push %eax # Emulate a near call
535 mov $0x1,%eax # 'exec' system call
536 int $INT_SYS # BTX system call
542 # Global descriptor table.
544 gdt: .word 0x0,0x0,0x0,0x0 # Null entry
545 .word 0xffff,0x0,0x9200,0xcf # SEL_SDATA
546 .word 0xffff,0x0,0x9200,0x0 # SEL_RDATA
547 .word 0xffff,0x0,0x9a00,0xcf # SEL_SCODE (32-bit)
548 .word 0xffff,0x0,0x9a00,0x8f # SEL_SCODE16 (16-bit)
551 # Pseudo-descriptors.
553 gdtdesc: .word gdt.1-gdt-1 # Limit
558 edd_packet: .byte 0x10 # Length
560 edd_len: .byte 0x0 # Num to read
562 edd_addr: .word 0x0,0x0 # Seg:Off
563 edd_lba: .quad 0x0 # LBA
568 # State for searching dir
570 rec_lba: .long 0x0 # LBA (adjusted for EA)
571 rec_size: .long 0x0 # File size
572 name_len: .byte 0x0 # Length of current name
574 twiddle_index: .byte 0x0
576 msg_welcome: .asciz "CD Loader 1.2\r\n\n"
577 msg_bootinfo: .asciz "Building the boot loader arguments\r\n"
578 msg_relocate: .asciz "Relocating the loader and the BTX\r\n"
579 msg_jump: .asciz "Starting the BTX loader\r\n"
580 msg_badread: .ascii "Read Error: 0x"
581 hex_error: .asciz "00\r\n"
582 msg_novd: .asciz "Could not find Primary Volume Descriptor\r\n"
583 msg_lookup: .asciz "Looking up "
584 msg_lookup2: .asciz "... "
585 msg_lookupok: .asciz "Found\r\n"
586 msg_lookupfail: .asciz "File not found\r\n"
587 msg_load2big: .asciz "File too big\r\n"
588 msg_failed: .asciz "Boot failed\r\n"
589 twiddle_chars: .ascii "|/-\\"
590 loader_paths: .asciz "/BOOT/LOADER"
591 .asciz "/boot/loader"