/* $OpenBSD: cdbr.S,v 1.2 2004/08/24 15:24:05 tom Exp $ */
/*
* Copyright (c) 2004 Tom Cosgrove <tom.cosgrove@arches-consulting.com>
* Copyright (c) 2001 John Baldwin <jhb@FreeBSD.org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the author nor the names of any co-contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
.file "cdbr.S"
/* #include <machine/asm.h> */
/* #include <assym.h> */
/*
* This program is a CD boot sector, similar to the partition boot record
* (pbr, also called biosboot) used by hard disks. It is implemented as a
* "no-emulation" boot sector, as described in the "El Torito" Bootable
* CD-ROM Format Specification.
*
* The function of this boot sector is to load and start the next-stage
* cdboot program, which will load the kernel.
*
* The El Torito standard allows us to specify where we want to be loaded,
* but for maximum compatibility we choose the default load address of
* 0x07C00.
*
* Memory layout:
*
* 0x00000 -> 0x003FF real mode interrupt vector table
* 0x00400 -> 0x00500 BIOS data segment
*
* 0x00000 -> 0x073FF our stack (grows down) (from 29k)
* 0x07400 -> 0x07BFF we relocate to here (at 29k)
* 0x07C00 -> 0x08400 BIOS loads us here (at 31k, for 2k)
* 0x07C00 -> ... /cdboot
*
* The BIOS loads us at physical address 0x07C00. We then relocate to
* 0x07400, seg:offset 0740:0000. We then load /cdboot at seg:offset
* 07C0:0000.
*/
#define BOOTSEG 0x7c0 /* segment we're loaded to */
#define BOOTSECTSIZE 0x800 /* our size in bytes */
#define BOOTRELOCSEG 0x740 /* segment we relocate to */
#define BOOTSTACKOFF ((BOOTRELOCSEG << 4) - 4) /* starts here, grows down */
/* Constants for reading from the CD */
#define ERROR_TIMEOUT 0x80 /* BIOS timeout on read */
#define NUM_RETRIES 3 /* Num times to retry */
#define SECTOR_SIZE 0x800 /* size of a sector */
#define SECTOR_SHIFT 11 /* number of place to shift */
#define BUFFER_LEN 0x100 /* number of sectors in buffr */
#define MAX_READ 0x10000 /* max we can read at a time */
#define MAX_READ_PARAS MAX_READ >> 4
#define MAX_READ_SEC MAX_READ >> SECTOR_SHIFT
#define MEM_READ_BUFFER 0x9000 /* buffer to read from CD */
#define MEM_VOLDESC MEM_READ_BUFFER /* volume descriptor */
#define MEM_DIR MEM_VOLDESC+SECTOR_SIZE /* Lookup buffer */
#define VOLDESC_LBA 0x10 /* LBA of vol descriptor */
#define VD_PRIMARY 1 /* Primary VD */
#define VD_END 255 /* VD Terminator */
#define VD_ROOTDIR 156 /* Offset of Root Dir Record */
#define DIR_LEN 0 /* Offset of Dir Rec length */
#define DIR_EA_LEN 1 /* Offset of EA length */
#define DIR_EXTENT 2 /* Offset of 64-bit LBA */
#define DIR_SIZE 10 /* Offset of 64-bit length */
#define DIR_NAMELEN 32 /* Offset of 8-bit name len */
#define DIR_NAME 33 /* Offset of dir name */
.text
.code16
.globl start
start:
/* Set up stack */
xorw %ax, %ax
movw %ax, %ss
movw $BOOTSTACKOFF, %sp
/* Relocate so we can load cdboot where we were */
movw $BOOTSEG, %ax
movw %ax, %ds
movw $BOOTRELOCSEG, %ax
movw %ax, %es
xorw %si, %si
xorw %di, %di
movw $BOOTSECTSIZE, %cx /* Bytes in cdbr, relocate it all */
cld
rep
movsb
/* Jump to relocated self */
ljmp $BOOTRELOCSEG, $reloc
reloc:
/*
* Set up %ds and %es: %ds is our data segment (= %cs), %es is
* used to specify the segment address of the destination buffer
* for cd reads. We initially have %es = %ds.
*/
movw %cs, %ax
movw %ax, %ds
movw %ax, %es
movb %dl, drive /* Store the boot drive number */
movw $signon, %si /* Say "hi", and give boot drive */
call display_string
movb drive, %al
call hex_byte
movw $crlf, %si
call display_string
/*
* Load Volume Descriptor
*/
movl $VOLDESC_LBA, %eax /* Get the sector # for vol desc */
load_vd:
pushl %eax
movb $1, %dh /* One sector */
movw $MEM_VOLDESC, %bx /* Destination */
call read /* Read it in */
popl %eax
cmpb $VD_PRIMARY, (%bx) /* Primary vol descriptor? */
je have_vd /* Yes */
inc %eax /* Try the next one */
cmpb $VD_END, (%bx) /* Is it the last one? */
jne load_vd /* No, so go try the next one */
movw $msg_novd, %si /* No pri vol descriptor */
jmp err_stop /* Panic */
have_vd: /* Have Primary VD */
/*
* Look for the next-stage loader binary at pre-defined paths (loader_paths)
*/
movw $loader_paths, %si /* Point to start of array */
lookup_path:
movw %si, loader /* remember the one we're looking for */
pushw %si /* Save file name pointer */
call lookup /* Try to find file */
popw %di /* Restore file name pointer */
jnc lookup_found /* Found this file */
xorb %al, %al /* Look for next */
movw $0xffff, %cx /* path name by */
repnz /* scanning for */
scasb /* nul char */
movw %di, %si /* Point %si at next path */
movb (%si), %al /* Get first char of next path */
orb %al, %al /* Is it double nul? */
jnz lookup_path /* No, try it */
movw $msg_failed, %si /* Failed message */
jmp err_stop /* Print it and halt */
lookup_found: /* Found a loader file */
/*
* Load the binary into the buffer. Due to real mode addressing limitations
* we have to read it in in 64k chunks.
*/
movl DIR_SIZE(%bx), %eax /* Read file length */
add $SECTOR_SIZE-1, %eax /* Convert length to sectors */
shr $SECTOR_SHIFT, %eax
cmp $BUFFER_LEN, %eax
jbe load_sizeok
movw $msg_load2big, %si /* Error message */
jmp err_stop
load_sizeok:
movzbw %al, %cx /* Num sectors to read */
movl DIR_EXTENT(%bx), %eax /* Load extent */
xorl %edx, %edx
movb DIR_EA_LEN(%bx), %dl
addl %edx, %eax /* Skip extended */
/* Use %bx to hold the segment (para) number */
movw $BOOTSEG, %bx /* We put cdboot here too */
load_loop:
movb %cl, %dh
cmpb $MAX_READ_SEC, %cl /* Truncate to max read size */
jbe load_notrunc
movb $MAX_READ_SEC, %dh
load_notrunc:
subb %dh, %cl /* Update count */
pushl %eax /* Save */
movw %bx, %es /* %bx had the segment (para) number */
xorw %bx, %bx /* %es:0000 for destination */
call read /* Read it in */
popl %eax /* Restore */
addl $MAX_READ_SEC, %eax /* Update LBA */
addw $MAX_READ_PARAS, %bx /* Update dest addr */
jcxz load_done /* Done? */
jmp load_loop /* Keep going */
load_done:
/* Now we can start the loaded program */
movw loader, %cx /* Tell cdboot where it is */
/* (Older versions of cdbr have */
/* %cx == 0 from the jcxz load_done) */
movb drive, %dl /* Get the boot drive number */
ljmp $BOOTSEG, $0 /* Go run cdboot */
/*
* Lookup the file in the path at [SI] from the root directory.
*
* Trashes: All but BX
* Returns: CF = 0 (success), BX = pointer to record
* CF = 1 (not found)
*/
lookup:
movw $VD_ROOTDIR + MEM_VOLDESC, %bx /* Root directory record */
lookup_dir:
lodsb /* Get first char of path */
cmpb $0, %al /* Are we done? */
je lookup_done /* Yes */
cmpb $'/', %al /* Skip path separator */
je lookup_dir
decw %si /* Undo lodsb side effect */
call find_file /* Lookup first path item */
jnc lookup_dir /* Try next component */
ret
lookup_done:
movw $msg_loading, %si /* Success message - say which file */
call display_string
mov loader, %si
call display_string
mov $crlf, %si
call display_string
clc /* Clear carry */
ret
/*
* Lookup file at [SI] in directory whose record is at [BX].
*
* Trashes: All but returns
* Returns: CF = 0 (success), BX = pointer to record, SI = next path item
* CF = 1 (not found), SI = preserved
*/
find_file:
mov DIR_EXTENT(%bx), %eax /* Load extent */
xor %edx, %edx
mov DIR_EA_LEN(%bx), %dl
add %edx, %eax /* Skip extended attributes */
mov %eax, rec_lba /* Save LBA */
mov DIR_SIZE(%bx), %eax /* Save size */
mov %eax, rec_size
xor %cl, %cl /* Zero length */
push %si /* Save */
ff_namelen:
inc %cl /* Update length */
lodsb /* Read char */
cmp $0, %al /* Nul? */
je ff_namedone /* Yes */
cmp $'/', %al /* Path separator? */
jnz ff_namelen /* No, keep going */
ff_namedone:
dec %cl /* Adjust length and save */
mov %cl, name_len
pop %si /* Restore */
ff_load:
mov rec_lba, %eax /* Load LBA */
mov $MEM_DIR, %ebx /* Address buffer */
mov $1, %dh /* One sector */
call read /* Read directory block */
incl rec_lba /* Update LBA to next block */
ff_scan:
mov %ebx, %edx /* Check for EOF */
sub $MEM_DIR, %edx
cmp %edx, rec_size
ja ff_scan_1
stc /* EOF reached */
ret
ff_scan_1:
cmpb $0, DIR_LEN(%bx) /* Last record in block? */
je ff_nextblock
push %si /* Save */
movzbw DIR_NAMELEN(%bx), %si /* Find end of string */
ff_checkver:
cmpb $'0', DIR_NAME-1(%bx,%si) /* Less than '0'? */
jb ff_checkver_1
cmpb $'9', DIR_NAME-1(%bx,%si) /* Greater than '9'? */
ja ff_checkver_1
dec %si /* Next char */
jnz ff_checkver
jmp ff_checklen /* All numbers in name, so */
/* no version */
ff_checkver_1:
movzbw DIR_NAMELEN(%bx), %cx
cmp %cx, %si /* Did we find any digits? */
je ff_checkdot /* No */
cmpb $';', DIR_NAME-1(%bx,%si) /* Check for semicolon */
jne ff_checkver_2
dec %si /* Skip semicolon */
mov %si, %cx
mov %cl, DIR_NAMELEN(%bx) /* Adjust length */
jmp ff_checkdot
ff_checkver_2:
mov %cx, %si /* Restore %si to end of string */
ff_checkdot:
cmpb $'.', DIR_NAME-1(%bx,%si) /* Trailing dot? */
jne ff_checklen /* No */
decb DIR_NAMELEN(%bx) /* Adjust length */
ff_checklen:
pop %si /* Restore */
movzbw name_len, %cx /* Load length of name */
cmp %cl, DIR_NAMELEN(%bx) /* Does length match? */
je ff_checkname /* Yes, check name */
ff_nextrec:
add DIR_LEN(%bx), %bl /* Next record */
adc $0, %bh
jmp ff_scan
ff_nextblock:
subl $SECTOR_SIZE, rec_size /* Adjust size */
jnc ff_load /* If subtract ok, keep going */
ret /* End of file, so not found */
ff_checkname:
lea DIR_NAME(%bx), %di /* Address name in record */
push %si /* Save */
repe cmpsb /* Compare name */
jcxz ff_match /* We have a winner! */
pop %si /* Restore */
jmp ff_nextrec /* Keep looking */
ff_match:
add $2, %sp /* Discard saved %si */
clc /* Clear carry */
ret
/*
* Load DH sectors starting at LBA %eax into address %es:%bx.
*
* Preserves %bx, %cx, %dx, %si, %es
* Trashes %eax
*/
read:
pushw %si /* Save */
pushw %cx /* Save since some BIOSs trash */
movl %eax, edd_lba /* LBA to read from */
movw %es, %ax /* Get the segment */
movw %ax, edd_addr + 2 /* and store */
movw %bx, edd_addr /* Store offset too */
read_retry:
call twiddle /* Entertain the user */
pushw %dx /* Save */
movw $edd_packet, %si /* Address Packet */
movb %dh, edd_len /* Set length */
movb drive, %dl /* BIOS Device */
movb $0x42, %ah /* BIOS: Extended Read */
int $0x13 /* Call BIOS */
popw %dx /* Restore */
jc read_fail /* Worked? */
popw %cx /* Restore */
popw %si
ret /* Return */
read_fail:
cmpb $ERROR_TIMEOUT, %ah /* Timeout? */
je read_retry /* Yes, Retry */
read_error:
pushw %ax /* Save error */
movw $msg_badread, %si /* "Read error: 0x" */
call display_string
popw %ax /* Retrieve error code */
movb %ah, %al /* Into %al */
call hex_byte /* Display error code */
jmp stay_stopped /* ... then hang */
/*
* Display the ASCIZ error message in %esi then halt
*/
err_stop:
call display_string
stay_stopped:
sti /* Ensure Ctl-Alt-Del will work */
hlt /* (don't require power cycle) */
jmp stay_stopped /* (Just to make sure) */
/*
* Output the "twiddle"
*/
twiddle:
push %ax /* Save */
push %bx /* Save */
mov twiddle_index, %al /* Load index */
mov twiddle_chars, %bx /* Address table */
inc %al /* Next */
and $3, %al /* char */
mov %al, twiddle_index /* Save index for next call */
xlat /* Get char */
call display_char /* Output it */
mov $8, %al /* Backspace */
call display_char /* Output it */
pop %bx /* Restore */
pop %ax /* Restore */
ret
/*
* Display the ASCIZ string pointed to by %si.
*
* Destroys %si, possibly others.
*/
display_string:
pushw %ax
cld
1:
lodsb /* %al = *%si++ */
testb %al, %al
jz 1f
call display_char
jmp 1b
/*
* Write out value in %eax in hex
*/
hex_long:
pushl %eax
shrl $16, %eax
call hex_word
popl %eax
/* fall thru */
/*
* Write out value in %ax in hex
*/
hex_word:
pushw %ax
mov %ah, %al
call hex_byte
popw %ax
/* fall thru */
/*
* Write out value in %al in hex
*/
hex_byte:
pushw %ax
shrb $4, %al
call hex_nibble
popw %ax
/* fall thru */
/* Write out nibble in %al */
hex_nibble:
and $0x0F, %al
add $'0', %al
cmpb $'9', %al
jbe display_char
addb $'A'-'9'-1, %al
/* fall thru to display_char */
/*
* Display the character in %al
*/
display_char:
pushw %ax
pushw %bx
movb $0x0e, %ah
movw $1, %bx
int $0x10
popw %bx
1: popw %ax
ret
/*
* Data
*/
drive: .byte 0 /* Given to us by the BIOS */
signon: .asciz "CD-ROM: "
crlf: .asciz "\r\n"
msg_load2big: .asciz "File too big"
msg_badread: .asciz "Read error: 0x"
msg_novd: .asciz "No Primary Volume Descriptor"
msg_loading: .asciz "Loading "
/* State for searching dir */
rec_lba: .long 0x0 /* LBA (adjusted for EA) */
rec_size: .long 0x0 /* File size */
name_len: .byte 0x0 /* Length of current name */
twiddle_index: .byte 0x0
twiddle_chars: .ascii "|/-\\"
/* Packet for LBA (CD) read */
edd_packet: .byte 0x10 /* Length */
.byte 0 /* Reserved */
edd_len: .byte 0x0 /* Num to read */
.byte 0 /* Reserved */
edd_addr: .word 0x0, 0x0 /* Seg:Off */
edd_lba: .quad 0x0 /* LBA */
/* The data from here must be last in the file, only followed by 0x00 bytes */
loader: .word 0 /* The path we end up using */
msg_failed: .ascii "Can't find " /* This string runs into... */
/* loader_paths is a list of ASCIZ strings followed by a term NUL byte */
loader_paths: .asciz "/cdboot"
.asciz "/CDBOOT"
.ascii "/", OSREV, "/", MACH, "/cdboot"
.byte 0 /* NUL-term line above */
.ascii "/", OSREV, "/", MACH_U, "/CDBOOT"
.byte 0 /* NUL-term line above */
.byte 0 /* Terminate the list */
. = BOOTSECTSIZE
.end
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