/*
* Copyright (c) 1999-2004 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Frank van der Linden, based on an earlier work by Wolfgang Solfrank.
* Major surgery performed by David Laight.
*
* 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.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
*/
/*
* i386 master boot code
*/
/* Compile options:
* BOOTSEL - bootselector code
* BOOT_EXTENDED - scan extended partition list (LBA reads)
* COM_PORT - do serial io to specified port number
* 0..3 => bios port, otherwise actual io_addr
* COM_BAUD - initialise serial port baud rate
*
* TERSE_ERROR - terse error messages
* NO_CHS - all reads are LBA
* NO_LBA_CHECK - no check if bios supports LBA reads
* NO_BANNER - do not output title line 'banner'
*/
#ifdef COM_PORT
#if COM_PORT < 4
/* The first 4 items in the 40:xx segment are the serial port base addresses */
#define COM_PORT_VAL (0x400 + (COM_PORT * 2))
#else
#define COM_PORT_VAL $COM_PORT
#endif
#ifdef COM_PORT
/* ASCII values for the keys */
#define KEY_ACTIVE '\r'
#define KEY_DISK1 'a'
#define KEY_PTN1 '1'
#else
/* Scan values for the various keys we use, as returned by the BIOS */
#define SCAN_ENTER 0x1c
#define SCAN_F1 0x3b
#define SCAN_1 0x2
.text
.code16
/*
* Move ourselves out of the way first.
* (to the address we are linked at)
* and zero our bss
*/
ENTRY(start)
xor %ax, %ax
mov %ax, %ss
movw $BOOTADDR, %sp
mov %ax, %es
mov %ax, %ds
movw $mbr, %di
mov $BOOTADDR + (mbr - start), %si
push %ax /* zero for %cs of lret */
push %di
movw $(bss_start - mbr), %cx
rep
movsb /* relocate code */
mov $(bss_end - bss_start + 511)/512, %ch
rep
stosw /* zero bss */
lret /* Ensures %cs == 0 */
/*
* Sanity check the drive number passed by the BIOS. Some BIOSs may not
* do this and pass garbage.
*/
mbr:
cmpb $MAXDRV, %dl /* relies on MINDRV being 0x80 */
jle 1f
movb $MINDRV, %dl /* garbage in, boot disk 0 */
1:
push %dx /* save drive number */
push %dx /* twice - for err_msg loop */
#if defined(COM_BAUD)
mov $com_args, %si
mov $num_com_args, %cl /* %ch is zero from above */
mov COM_PORT_VAL, %dx
1: lodsw
add %ah, %dl
outb %dx
loop 1b
#endif
/*
* Walk through the selector (name) table printing used entries.
*
* Register use:
* %ax temp
* %bx nametab[] boot selector menu
* %ecx base of 'extended' partition
* %edx next extended partition
* %si message ptr (etc)
* %edi sector number of this partition
* %bp parttab[] mbr partition table
*/
bootsel_menu:
movw $nametab, %bx
#ifdef BOOT_EXTENDED
xorl %ecx, %ecx /* base of extended partition */
next_extended:
xorl %edx, %edx /* for next extended partition */
#endif
lea parttab - nametab(%bx), %bp
next_ptn:
movb 4(%bp), %al /* partition type */
#ifdef NO_CHS
movl 8(%bp), %edi /* partition sector number */
#ifdef BOOT_EXTENDED
cmpb $MBR_PTYPE_EXT, %al /* Extended partition */
je 1f
cmpb $MBR_PTYPE_EXT_LBA, %al /* Extended LBA partition */
je 1f
cmpb $MBR_PTYPE_EXT_LNX, %al /* Linux extended partition */
jne 2f
1: movl %edi, %edx /* save next extended ptn */
jmp 4f
2:
#endif
addl lba_sector, %edi /* add in extended ptn base */
#endif
test %al, %al /* undefined partition */
je 4f
cmpb $0x80, (%bp) /* check for active partition */
jne 3f /* jump if not... */
#define ACTIVE (4 * ((KEY_ACTIVE - KEY_DISK1) & 0xff))
#ifdef NO_CHS
movl %edi, ptn_list + ACTIVE /* save location of active ptn */
#else
mov %bp, ptn_list + ACTIVE
#endif
#undef ACTIVE
3:
#ifdef BOOTSEL
cmpb $0, (%bx) /* check for prompt */
jz 4f
/* output menu item */
movw $prefix, %si
incb (%si)
call message /* menu number */
mov (%si), %si /* ':' << 8 | '1' + count */
shl $2, %si /* const + count * 4 */
#define CONST (4 * ((':' << 8) + '1' - ((KEY_PTN1 - KEY_DISK1) & 0xff)))
#ifdef NO_CHS
movl %edi, ptn_list - CONST(%si) /* sector to read */
#else
mov %bp, ptn_list - CONST(%si) /* partition info */
#endif
#undef CONST
mov %bx, %si
call message_crlf /* prompt */
#endif
4:
add $0x10, %bp
add $TABENTRYSIZE, %bx
cmpb $(nametab - start - 0x100) + 4 * TABENTRYSIZE, %bl
jne next_ptn
#ifdef BOOT_EXTENDED
/*
* Now check extended partition chain
*/
testl %edx, %edx
je wait_key
testl %ecx, %ecx
jne 1f
xchg %ecx, %edx /* save base of ext ptn chain */
1: addl %ecx, %edx /* sector to read */
movl %edx, lba_sector
movw $lba_info, %si
movb $0x42, %ah
pop %dx /* recover drive # */
push %dx /* save drive */
int $0x13
movw $BOOTADDR + (nametab - start), %bx
jnc next_extended /* abort menu on read fail */
#endif
/*
* The non-bootsel code traverses this code path, it needs the
* correct keycode to select the active partition.
*/
#ifndef BOOTSEL
mov $(KEY_ACTIVE - KEY_DISK1) & 0xff, %ax
#else
/*
* Get the initial time value for the timeout comparison. It is returned
* by int 1a in cx:dx. We do sums modulo 2^16 so it doesn't matter if
* the counter wraps (which it does every hour) - so we can safely
* ignore 'cx'.
*
* Loop around checking for a keypress until we have one, or timeout is
* reached.
*/
wait_key:
xorb %ah, %ah
int $0x1a
mov %dx, %di /* start time to di */
3:
#ifdef COM_PORT_VAL
mov COM_PORT_VAL, %dx
push %dx
add $5, %dx
inb %dx
pop %dx
test $1, %al
jz 1f
inb %dx
jmp check_key
#else
movb $1, %ah /* looks to see if a */
int $0x16 /* key has been pressed */
jz 1f
get_key:
xorb %ah, %ah
int $0x16 /* 'read key', code ah, ascii al */
shr $8, %ax /* code in %al, %ah zero */
jmp check_key
#endif
1: xorb %ah, %ah
int $0x1a /* current time to cx:dx */
sub %di, %dx
cmpw timeout, %dx /* always wait for 1 tick... */
jbe 3b /* 0xffff means never timeout */
def_key:
mov defkey, %al /* timedout - we need %ah to still be zero! */
/*
* We have a keycode, see what it means.
* If we don't know we generate error '?' and go ask again
*/
check_key:
/*
* F1-F10 -> boot disk 0-9. Check if the requested disk isn't above
* the number of disks actually in the system as stored in 0:0475 by
* the BIOS.
* If we trust loc 475, we needn't check the upper bound on the keystroke
* This is always sector 0, so always read using chs.
*/
subb $KEY_DISK1, %al
cmpb 0x0475, %al
jae boot_ptn
addb $0x80, %al
pop %dx /* dump saved drive # */
push %ax /* replace with new */
#ifdef NO_CHS
xorl %ebp, %ebp /* read sector number 0 */
jmp boot_lba
#else
movw $chs_zero, %si /* chs read sector zero info */
jmp read_chs
#endif
#endif /* BOOTSEL */
/*
* Boot requested partition.
* Use keycode to index the table we generated when we scanned the mbr
* while generating the menu.
*
* We very carfully saved the values in the correct part of the table.
*/
/* Something went wrong...
* Output error code,
* reset disk subsystem - needed after read failure,
* and wait for user key
*/
err_msg:
#ifdef TERSE_ERROR
movb %al, errcod
movw $errtxt, %si
call message
#else
push %ax
movw $errtxt, %si
call message
pop %si
call message_crlf
#endif
pop %dx /* drive we errored on */
xor %ax,%ax /* only need %ah = 0 */
int $0x13 /* reset disk subsystem */
#ifdef BOOTSEL
pop %dx /* original drive number */
push %dx
push %dx
#ifdef COM_PORT_VAL
jmp wait_key /* Read with timeout (again) */
#else
jmp get_key /* Blocking read */
#endif
#else
int $0x18 /* BIOS might ask for a key */
/* press and retry boot seq. */
1: sti
hlt
jmp 1b
#endif
#ifndef NO_CHS
/*
* Active partition pointed to by si.
* Read the first sector.
*
* We can either do a CHS (Cylinder Head Sector) or an LBA (Logical
* Block Address) read. Always doing the LBA one
* would be nice - unfortunately not all systems support it.
* Also some may contain a separate (eg SCSI) bios that doesn't
* support it even when the main bios does.
*
* There is also the additional problem that the CHS values may be wrong
* (eg if fdisk was run on a different system that used different BIOS
* geometry). We convert the CHS value to a LBA sector number using
* the geometry from the BIOS, if the number matches we do a CHS read.
*/
boot_si:
movl 8(%si), %ebp /* get sector # */
pop %dx /* collect saved drive... */
push %dx /* ...number to dl */
movb $8, %ah
int $0x13 /* chs info */
/*
* Validate geometry, if the CHS sector number doesn't match the LBA one
* we'll do an LBA read.
* calc: (cylinder * number_of_heads + head) * number_of_sectors + sector
* and compare against LBA sector number.
* Take a slight 'flier' and assume we can just check 16bits (very likely
* to be true because the number of sectors per track is 63).
*/
movw 2(%si), %ax /* cylinder + sector */
push %ax /* save for sector */
shr $6, %al
xchgb %al, %ah /* 10 bit cylinder number */
shr $8, %dx /* last head */
inc %dx /* number of heads */
mul %dx
mov 1(%si), %dl /* head we want */
add %dx, %ax
and $0x3f, %cx /* number of sectors */
mul %cx
pop %dx /* recover sector we want */
and $0x3f, %dx
add %dx, %ax
dec %ax
cmp %bp, %ax
je read_chs
#ifndef NO_LBA_CHECK
/*
* Determine whether we have int13-extensions, by calling int 13, function 41.
* Check for the magic number returned, and the disk packet capability.
*/
movw $0x55aa, %bx
movb $0x41, %ah
pop %dx
push %dx
int $0x13
set_err(ERR_NO_LBA)
jc err_msg /* no int13 extensions */
cmpw $0xaa55, %bx
jnz err_msg
testb $1, %cl
jz err_msg
#endif /* NO_LBA_CHECK */
#endif /* NO_CHS */
/*
* Save sector number (passed in %ebp) into lba parameter block,
* read the sector and leap into it.
*/
boot_lba:
movl %ebp, lba_sector /* save sector number */
movw $lba_info, %si
movb $0x42, %ah
pop %dx /* recover drive # */
do_read:
push %dx /* save drive */
int $0x13
/* We pass the sector number through to the next stage boot.
* It doesn't have to use it (indeed no other mbr code will generate) it,
* but it does let us have a NetBSD pbr that can identify where it was
* read from! This lets us use this code to select between two
* NetBSD system on the same physical driver.
* (If we've read the mbr of a different disk, it gets a random number
* - but it wasn't expecting anything...)
*/
movl %ebp, %esi
pop %dx /* recover drive # */
jmp BOOTADDR
/*
* I hate #including source files, but the stuff below has to be at
* the correct absolute address.
* Clearly this could be done with a linker script.
*/
/*
* Stuff from here on is overwritten by fdisk - the offset must not change...
*
* Get amount of space to makefile can report it.
* (Unfortunately I can't seem to get the value reported when it is -ve)
*/
mbr_space = defkey - .
. = start + MBR_BS_OFFSET
/*
* Default action, as a keyvalue we'd normally read from the BIOS.
*/
defkey:
.byte KEY_ACTIVE /* ps/2 code */
#ifndef BOOTSEL_FLAGS
#define BOOTSEL_FLAGS 0
#endif
flags: .byte MBR_BS_NEWMBR | BOOTSEL_FLAGS
/*
* Timeout value. ~65536 ticks per hour, which is ~18.2 times per second.
* 0xffff means never timeout.
*/
timeout:
.word 182 /* default to 10 seconds */
/*
* mbr_bootsel
*/
nametab:
.fill MBR_PART_COUNT * (MBR_BS_PARTNAMESIZE + 1), 0x01, 0x00
/* space for mbr_dsn */
. = start + MBR_DSN_OFFSET
.long 0
