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/* $OpenBSD: biosboot.S,v 1.9 1997/05/29 04:31:48 mickey Exp $ */
.file "bootbios.S"
#include <machine/asm.h>
#include <machine/specialreg.h>
#define _LOCORE
#include <machine/segments.h>
#undef _LOCORE
#define addr32 .byte 0x67
#define data32 .byte 0x66
/* Better use 32, 48 does not seem to compile */
#define BLKCNT 20 /* Max without colliding with the partition table */
#define BOOTSEG 0x07c0 /* boot loaded here */
#define BOOTSTACK 0xfffc /* stack starts here */
#define ZMAGIC 0x0b01 /* ZMAGIC */
/*
* Partition table values
*/
BOOTABLE= 0x80 # value of boot_ind, means bootable partition
OPENBSDPART= 0xA6 # OpenBSD partition type
#ifdef DEBUG
#define DBGMSG(msg) \
movb $msg, %al; \
data32; \
call chr
#define GO_RELOC 'R' /* running relocated code */
#define REAL2PROT 'P' /* switch to protected mode */
#else /* !DEBUG */
#define DBGMSG(msg)
#endif /* !DEBUG */
.text
.globl start
start:
/* set up stack (%ss:%esp) */
cli /* disable interrupts w/o stack */
# movw $BOOTREL, %ax
.byte 0xb8
.word BOOTREL
movl %ax, %ss
movl %ax, %es /* relocate there */
data32
movl $BOOTSTACK, %esp
sti /* we have stack, do ints */
# movw $BOOTSEG, %ax /* we are here */
.byte 0xb8
.word BOOTSEG
movl %ax, %ds
xorl %si, %si
xorl %di, %di
# movw $0x100, %cx /* 512 bytes to move */
.byte 0xb9
.word 0x100
cld
rep; movsl
/* jump to relocated code */
data32
ljmp $BOOTREL, $2f
1: .asciz "loading /boot"
2: DBGMSG(GO_RELOC)
/* set up %ds */
pushl %cs
popl %ds
/* set up %es, (where we will load /boot to) */
# movw $(START >> 4), %ax
.byte 0xb8
.word START >> 4
movl %ax, %es
#ifdef SERIAL
# Initialize the serial port to 9600 baud, 8N1.
pushl %dx
# movw $0x00e3, %ax
.byte 0xb8
.word 0x00e3
# movw SERIAL, %dx
.byte 0xba
.word SERIAL
int $0x14
popl %dx
#endif
data32
movl $1b, %esi
data32
call message
data32
xorl %ebx, %ebx /* put it at %es:0 */
addr32
movb _block_count, %cl /* how many to read */
movzbl %cl, %ecx
# movw $_block_table, %si
.byte 0xbe
.word _block_table
1:
pushl %cx
cld
lodsl /* word */ /* cylinder/sector */
movl %ax, %cx
lodsb /* head */
movb %al, %dh
lodsb /* # of sectors to load */
movb $0x2, %ah
pushl %ax
int $0x13
jnc 3f
/* read error */
data32
movl $2f, %esi
jmp halt
2: .asciz "\r\nRead error\r\n"
3: /* read next block */
movb $'.', %al
data32
call chr /* show progress indicator */
popl %ax
movzbl %al, %ax
shll $9, %ax /* 512 bytes sectors */
addl %ax, %bx
popl %cx
loop 1b
data32
movl $2f, %esi /* new line */
data32
call message
xorl %si, %si
cld
/* check /boot magic */
es;lodsl;es;lodsl /* no need for high word */
# cmpw $ZMAGIC, %ax
.byte 0x3d
.word ZMAGIC
je 3f
data32
movl $1f, %esi
halt:
data32
call message
cli
hlt
1: .ascii "Bad magic"
2: .asciz "\r\n"
3:
#if notdef
data32;es;lodsl /* text size */
data32;es;lodsl /* data size */
data32;es;lodsl /* bss size */
data32;es;lodsl /* syms size */
#endif
data32
addl 16(%esi), %edi /* entry */
DBGMSG(REAL2PROT)
/* change to protected mode */
/* guarantee that interrupts are disabled when in prot mode */
cli
/* load the gdtr */
addr32
data32
lgdt Gdtr
/* set the PE bit of CR0 */
movl %cr0, %eax
data32
orl $CR0_PE, %eax
movl %eax, %cr0
/*
* make intrasegment jump to flush the processor pipeline and
* reload CS register
*/
data32
ljmp $8, $1f+(BOOTREL << 4)
1: /*
* 32bit mode
* set up %ds, %ss, %es
*/
movw $0x10, %eax
movl %ax, %ds
movl %ax, %ss
movl $BOOTSTACK, %esp
#ifdef DEBUG
movl $0xb8004, %ebx
movl $0x074f0747, (%ebx)
#endif
movzbl %dl, %eax /* drive number is in the lowest byte */
pushl %eax
pushl $BOOTMAGIC /* use some magic */
/* jmp /boot */
ljmp $8, $(START + 0x20)
/* not reached */
#
# chr: write the character in %al to console
#
chr:
data32
pushl %eax
#ifndef SERIAL
data32
pushl %ebx
movb $0x0e, %ah
xorl %bx, %bx
incl %bx /* movw $0x01, %bx */
int $0x10
data32
popl %ebx
#else
data32
pushl %edx
movb $0x01, %ah
xorl %dx, %dx
movb SERIAL, %dl
int $0x14
data32
popl %edx
#endif
data32
popl %eax
data32
ret
/*
* Display string
*/
message:
data32
pushl %eax
cld
1:
lodsb # load a byte into %al
testb %al, %al
jz 1f
data32
call chr
jmp 1b
1:
data32
popl %eax
data32
ret
.align 3
gdt: /* 0x00 : null */
.long 0, 0
/* 0x08 : flat code */
.word 0xFFFF # lolimit
.word 0 # lobase
.byte 0 # midbase
.byte SDT_MEMERAC | 0 | 0x80 # RWXAC, dpl = 0, present
.byte 0xf | 0 | 0x40 | 0x80 # hilimit, xx, 32bit, 4k granularity
.byte 0 # hibase
/* 0x10 : flat data */
.word 0xFFFF # lolimit
.word 0 # lobase
.byte 0 # midbase
.byte SDT_MEMRWA | 0 | 0x80 # RWA, dpl = 0, present
.byte 0xf | 0 | 0x40 | 0x80 # hilimit, xx, 32bit, 4k granularity
.byte 0 # hibase
Gdtr: .word . - gdt
.long (BOOTREL << 4) + gdt
.globl _block_table
_block_table:
.word 0 /* cyllinder/sector */
.byte 0 /* head */
.byte 0 /* nsect */
. = _block_table + BLKCNT*4
.globl _block_count
_block_count:
.byte BLKCNT /* entries in _block_table */
. = 0x1b8
.space 4, 0 /* NT registry offset from James C. Cortilier III */
. = 446
.globl _partitions
/* throw in a partition in case we are block0 as well */
/* flag, head, sec, cyl, typ, ehead, esect, ecyl, start, len */
_partitions:
.byte BOOTABLE, 0, 1, 0,OPENBSDPART, 255, 255, 255
.long 0,50000
.byte 0,0,0,0,0,0,0,0
.long 0,0
.byte 0,0,0,0,0,0,0,0
.long 0,0
.byte 0,0,0,0,0,0,0,0
.long 0,0
. = 0x200 - 2
/* a little signature */
.word 0xaa55
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