freebsd-dev/sys/i386/boot/biosboot/start.S
1998-07-30 02:27:41 +00:00

459 lines
11 KiB
ArmAsm

/*
* Mach Operating System
* Copyright (c) 1992, 1991 Carnegie Mellon University
* All Rights Reserved.
*
* Permission to use, copy, modify and distribute this software and its
* documentation is hereby granted, provided that both the copyright
* notice and this permission notice appear in all copies of the
* software, derivative works or modified versions, and any portions
* thereof, and that both notices appear in supporting documentation.
*
* CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
* CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
* ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
*
* Carnegie Mellon requests users of this software to return to
*
* Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
* School of Computer Science
* Carnegie Mellon University
* Pittsburgh PA 15213-3890
*
* any improvements or extensions that they make and grant Carnegie Mellon
* the rights to redistribute these changes.
*
* from: Mach, Revision 2.2 92/04/04 11:36:29 rpd
* $Id: start.S,v 1.11 1998/07/02 15:36:35 wpaul Exp $
*/
/*
Copyright 1988, 1989, 1990, 1991, 1992
by Intel Corporation, Santa Clara, California.
All Rights Reserved
Permission to use, copy, modify, and distribute this software and
its documentation for any purpose and without fee is hereby
granted, provided that the above copyright notice appears in all
copies and that both the copyright notice and this permission notice
appear in supporting documentation, and that the name of Intel
not be used in advertising or publicity pertaining to distribution
of the software without specific, written prior permission.
INTEL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE
INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS,
IN NO EVENT SHALL INTEL BE LIABLE FOR ANY SPECIAL, INDIRECT, OR
CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
LOSS OF USE, DATA OR PROFITS, WHETHER IN ACTION OF CONTRACT,
NEGLIGENCE, OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include "asm.h"
.file "start.S"
SIGNATURE= 0xaa55
LOADSZ= 15 /* size of unix boot */
PARTSTART= 0x1be /* starting address of partition table */
NUMPART= 4 /* number of partitions in partition table */
PARTSZ= 16 /* each partition table entry is 16 bytes */
BSDPART= 0xA5 /* value of boot_ind, means bootable partition */
BOOTABLE= 0x80 /* value of boot_ind, means bootable partition */
NAMEBLOCKMAGIC= 0xfadefeed /* value of magicnumebr for block2 */
/*
* This DEBUGMSG(msg) macro may be useful for debugging. Its use is
* restricted to this file since it only works in real mode.
*/
#define DEBUGMSG(msg) \
data32 ; \
mov $msg, %esi ; \
data32 ; \
call message
.text
ENTRY(boot1)
/*
* XXX I have encountered at least one machine (a no-name laptop
* with an AMI WinBIOS) that will refuse to run the bootblock
* unless this short jump and nop are here. I'm not certain, but
* this may be a case of the BIOS performing some kind of simple
* virus detection.
*/
jmp pacify_braindead_bios
nop
pacify_braindead_bios:
/*
* start (aka boot1) is loaded at 0x0:0x7c00 but we want 0x7c0:0
* ljmp to the next instruction to adjust %cs
*/
data32
ljmp $0x7c0, $start
start:
/* set up %ds */
mov %cs, %ax
mov %ax, %ds
/* set up %ss and %esp */
data32
mov $BOOTSEG, %eax
mov %ax, %ss
/*
* make a little room on the stack for
* us to save the default bootstring we might find..
* effectively, we push the bootstring.
*/
data32
mov $BOOTSTACK-64, %esp
/* set up %es, (where we will load boot2 to) */
mov %ax, %es
/* bootstrap passes us drive number in %dl */
cmpb $0x80, %dl
data32
jae hd
fd:
/*
* XXX some bootstraps don't pass the drive number in %dl.
* This is a problem mainly when we are block 0 on a floppy.
* Force drive 0 for floppies.
* XXX %dl was assumed valid in the test that led here.
*/
mov $0x0, %dl
/* reset the disk system */
movb $0x0, %ah
int $0x13
data32
mov $0x0001, %ecx /* cyl 0, sector 1 */
movb $0, %dh /* head */
data32
jmp load
hd: /**** load sector 0 into the BOOTSEG ****/
data32
mov $0x0201, %eax
xor %ebx, %ebx /* %bx = 0 */
data32
mov $0x0001, %ecx
data32
andl $0xff, %edx
/*mov $0x0080, %edx*/
int $0x13
data32
jb read_error
/* find the first 386BSD partition */
data32
mov $PARTSTART, %ebx
data32
mov $NUMPART, %ecx
again:
addr32
movb %es:4(%ebx), %al
cmpb $BSDPART, %al
data32
je found
data32
add $PARTSZ, %ebx
data32
loop again
data32
mov $enoboot, %esi
data32
jmp err_stop
/*
* BIOS call "INT 0x13 Function 0x2" to read sectors from disk into memory
* Call with %ah = 0x2
* %al = number of sectors
* %ch = cylinder
* %cl = sector
* %dh = head
* %dl = drive (0x80 for hard disk, 0x0 for floppy disk)
* %es:%bx = segment:offset of buffer
* Return:
* %al = 0x0 on success; err code on failure
*/
found:
addr32
movb %es:1(%ebx), %dh /* head */
addr32
movl %es:2(%ebx), %ecx /*sect, cyl (+ 2 bytes junk in top word) */
load:
#ifdef NAMEBLOCK
/*
* Load the second sector and see if it is a boot instruction block.
* If it is then scan the contents for the first valid string and copy it to
* the location of the default boot string.. then zero it out.
* Finally write the block back to disk with the zero'd out entry..
* I hate writing at this stage but we need this to be persistant.
* If the boot fails, then the next boot will get the next string.
* /etc/rc will regenerate a complete block2 iff the boot succeeds.
*
* Format of block 2 is:
* [NAMEBLOCKMAGIC] <--0xdeafc0de
* [nulls]
* [bootstring]NULL <---e.g. 0:wd(0,a)/kernel.experimental
* [bootstring]NULL <---e.g. 0:wd(0,a)/kernel.old
* ....
* [bootstring]NULL <---e.g. 0:wd(0,f)/kernel
* FF FF FF
*/
where:
/*
* save things we might smash
* (that are not smashed immedatly after us anyway.)
*/
data32
push %ecx /* preserve 'cyl,sector ' */
data32
push %edx
/*
* Load the second sector
* BIOS call "INT 0x13 Function 0x2" to read sectors from disk into memory
* Call with %ah = 0x2
* %al = number of sectors
* %ch = cylinder
* %cl = sector
* %dh = head
* %dl = drive (0x80 for hard disk, 0x0 for floppy disk)
* %es:%bx = segment:offset of buffer
* Return:
* %al = 0x0 on success; err code on failure
*/
data32
movl $0x0201, %eax /function 2 (read) 1 sector */
xor %ebx, %ebx /* %bx = 0 */ /* buffer address (ES:0) */
data32
movl $0x0002, %ecx /* sector 2, cylinder 0 */
data32
andl $0x00ff, %edx /* head 0, drive N */
int $0x13
data32
jb read_error
/*
* confirm that it is one for us
*/
data32
xorl %ebx, %ebx /* magic number at start of buffer */
data32
addr32
movl %es:(%ebx), %eax
data32
cmpl $NAMEBLOCKMAGIC, %eax
data32
jne notours /* not ours so return to caller */
/*
* scan for a bootstring
* Skip the magic number, and scan till we find a non-null,
* or a -1
*/
incl %ebx /* quicker and smaller */
incl %ebx
incl %ebx
scan:
incl %ebx
addr32
movb %es:(%ebx), %al /* load the next byte */
testb %al, %al /* and if it is null */
data32 /* keep scanning (past deleted entries) */
jz scan
incb %al /* now look for -1 */
data32
jz notours /* if we reach the 0xFF then we have finished */
/*
* save our settings.. we need them twice..
*/
data32
push %ebx
/*
* copy it to the default string location
* which is just above the stack for 64 bytes.
*/
data32
movl $BOOTSTACK-64, %ecx /* 64 bytes at the top of the stack */
nxtbyte:
addr32
movb %es:(%ebx), %al /* get the next byte in */
addr32
movb %al, %es:(%ecx) /* and transfer it to the name buffer */
incl %ebx /* get on with the next byte */
incl %ecx /* get on with the next byte */
testb %al, %al /* if it was 0 then quit this */
data32
jnz nxtbyte /* and looop if more to do */
/*
* restore the saved settings and
* zero it out so next time we don't try it again
*/
data32
pop %ebx /* get back our starting location */
#ifdef NAMEBLOCK_WRITEBACK
nxtbyte2:
addr32
movb %es:(%ebx), %al /* get the byte */
addr32
movb $0, %es:(%ebx) /* zero it out */
data32
incl %ebx /* point to the next byte */
testb %al, %al /* check if we have finished.. */
data32
jne nxtbyte2
/*
* Write the second sector back
* Load the second sector
* BIOS call "INT 0x13 Function 0x3" to write sectors from memory to disk
* Call with %ah = 0x3
* %al = number of sectors
* %ch = cylinder
* %cl = sector
* %dh = head
* %dl = drive (0x80 for hard disk, 0x0 for floppy disk)
* %es:%bx = segment:offset of buffer
* Return:
* %al = 0x0 on success; err code on failure
*/
data32
movl $0x0301, %eax /* write 1 sector */
xor %ebx, %ebx /* buffer is at offset 0 */
data32
movl $0x0002, %ecx /* block 2 */
data32
andl $0xff, %edx /* head 0 */
int $0x13
data32
jnb notours
data32
mov $eread, %esi
jmp err_stop
#endif /* NAMEBLOCK_WRITEBACK */
/*
* return to the main-line
*/
notours:
data32
pop %edx
data32
pop %ecx
#endif
movb $0x2, %ah /* function 2 */
movb $LOADSZ, %al /* number of blocks */
xor %ebx, %ebx /* %bx = 0, put it at 0 in the BOOTSEG */
int $0x13
data32
jb read_error
/*
* ljmp to the second stage boot loader (boot2).
* After ljmp, %cs is BOOTSEG and boot1 (512 bytes) will be used
* as an internal buffer "intbuf".
*/
data32
ljmp $BOOTSEG, $ EXT(boot2)
/*
* read_error
*/
read_error:
data32
mov $eread, %esi
err_stop:
data32
call message
data32
jmp stop
/*
* message: write the error message in %ds:%esi to console
*/
message:
/*
* Use BIOS "int 10H Function 0Eh" to write character in teletype mode
* %ah = 0xe %al = character
* %bh = page %bl = foreground color (graphics modes)
*/
data32
push %eax
data32
push %ebx
data32
mov $0x0001, %ebx
cld
nextb:
lodsb /* load a byte into %al */
cmpb $0x0, %al
data32
je done
movb $0xe, %ah
int $0x10 /* display a byte */
data32
jmp nextb
done:
data32
pop %ebx
data32
pop %eax
data32
ret
stop: hlt
data32
jmp stop /* halt doesnt actually halt forever */
/* error messages */
#ifdef DEBUG
one: String "1-\0"
two: String "2-\0"
three: String "3-\0"
four: String "4-\0"
#endif DEBUG
#ifdef NAMEBLOCK_WRITEBACK
ewrite: String "Write error\r\n\0"
#endif /* NAMEBLOCK_WRITEBACK */
eread: String "Read error\r\n\0"
enoboot: String "No bootable partition\r\n\0"
endofcode:
/*
* Dummy partition table in case we are block 0. The ending c/h/s values
* of the non-null partition are almost arbitary. The length of this
* partition is bogus for backwards compatibility and as a signature.
* A real partition table shouldn't be as weird and broken as this one,
* and the isa slice initialization routine interprets this table as
* saying that the whole disk is used for FreeBSD.
*/
/* flag, head, sec, cyl, typ, ehead, esect, ecyl, start, len */
. = EXT(boot1) + PARTSTART
strttbl:
.byte 0x0,0,0,0,0,0,0,0
.long 0,0
.byte 0x0,0,0,0,0,0,0,0
.long 0,0
.byte 0x0,0,0,0,0,0,0,0
.long 0,0
.byte BOOTABLE,0,1,0,BSDPART,255,255,255
.long 0,50000
/* the last 2 bytes in the sector 0 contain the signature */
. = EXT(boot1) + 0x1fe
.value SIGNATURE
ENTRY(disklabel)
. = EXT(boot1) + 0x400