/* -----------------------------------------------------------------------
*
* Copyright 2007-2009 H. Peter Anvin - All Rights Reserved
* Copyright 2009 Intel Corporation; author: H. Peter Anvin
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation
* files (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use,
* copy, modify, merge, publish, distribute, sublicense, and/or
* sell copies of the Software, and to permit persons to whom
* the Software is furnished to do so, subject to the following
* conditions:
*
* The above copyright notice and this permission notice shall
* be included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
* OTHER DEALINGS IN THE SOFTWARE.
*
* ----------------------------------------------------------------------- */
#include "adjust.h"
.code16
.text
.globl bootsec
stack = 0x7c00
driveno = (stack-6)
sectors = (stack-8)
secpercyl = (stack-12)
BIOS_kbdflags = 0x417
BIOS_page = 0x462
/* gas/ld has issues with doing this as absolute addresses... */
.section ".bootsec", "a", @nobits
.globl bootsec
bootsec:
.space 512
.text
.globl _start
_start:
cli
xorw %ax, %ax
movw %ax, %ds
movw %ax, %ss
movw $stack, %sp
movw %sp, %si
pushw %es /* es:di -> $PnP header */
pushw %di
movw %ax, %es
sti
cld
/* Copy down to 0:0x600 */
movw $_start, %di
movw $(512/2), %cx
rep; movsw
ljmpw $0, $next
next:
ADJUST_DRIVE
pushw %dx /* dl -> drive number */
/* Check to see if we have EBIOS */
pushw %dx /* drive number */
movb $0x41, %ah /* %al == 0 already */
movw $0x55aa, %bx
xorw %cx, %cx
xorb %dh, %dh
stc
int $0x13
jc 1f
cmpw $0xaa55, %bx
jne 1f
shrw %cx /* Bit 0 = fixed disk subset */
jnc 1f
/* We have EBIOS; patch in the following code at
read_sector_cbios: movb $0x42, %ah ; jmp read_common */
movl $0xeb42b4+((read_common-read_sector_cbios-4) << 24), \
(read_sector_cbios)
1:
popw %dx
/* Get (C)HS geometry */
movb $0x08, %ah
int $0x13
andw $0x3f, %cx /* Sector count */
pushw %cx /* Save sectors on the stack */
movzbw %dh, %ax /* dh = max head */
incw %ax /* From 0-based max to count */
mulw %cx /* Heads*sectors -> sectors per cylinder */
/* Save sectors/cylinder on the stack */
pushw %dx /* High word */
pushw %ax /* Low word */
xorl %eax, %eax /* Base */
cdq /* Root (%edx <- 0) */
call scan_partition_table
/* If we get here, we have no OS */
missing_os:
call error
.ascii "Missing operating system.\r\n"
/*
* read_sector: read a single sector pointed to by %eax to 0x7c00.
* CF is set on error. All registers saved.
*/
read_sector:
pushal
xorl %edx, %edx
movw $bootsec, %bx
pushl %edx /* MSW of LBA */
pushl %eax /* LSW of LBA */
pushw %es /* Buffer segment */
pushw %bx /* Buffer offset */
pushw $1 /* Sector count */
pushw $16 /* Size of packet */
movw %sp, %si
/* This chunk is skipped if we have ebios */
/* Do not clobber %eax before this chunk! */
/* This also relies on %bx and %edx as set up above. */
read_sector_cbios:
divl (secpercyl)
shlb $6, %ah
movb %ah, %cl
movb %al, %ch
xchgw %dx, %ax
divb (sectors)
movb %al, %dh
orb %ah, %cl
incw %cx /* Sectors are 1-based */
movw $0x0201, %ax
read_common:
movb (driveno), %dl
int $0x13
leaw 16(%si), %sp /* Drop DAPA */
popal
ret
/*
* read_partition_table:
* Read a partition table (pointed to by %eax), and copy
* the partition table into the ptab buffer.
*
* Clobbers %si, %di, and %cx, other registers preserved.
* %cx = 0 on exit.
*
* On error, CF is set and ptab is overwritten with junk.
*/
ptab = _start+446
read_partition_table:
call read_sector
movw $bootsec+446, %si
movw $ptab, %di
movw $(16*4/2), %cx
rep ; movsw
ret
/*
* scan_partition_table:
* Scan a partition table currently loaded in the partition table
* area. Preserve all registers.
*
* On entry:
* %eax - base (location of this partition table)
* %edx - root (offset from MBR, or 0 for MBR)
*
* These get pushed into stack slots:
* 28(%bp) - %eax - base
* 20(%bp) - %edx - root
*/
scan_partition_table:
pushal
movw %sp, %bp
/* Scan the primary partition table */
movw $ptab, %si
movw $4, %cx
/* Is it a primary partition table? */
andl %edx, %edx
jnz 7f
push %si
push %cx
5:
decb (partition)
jz boot
addw $16, %bx
loopw 5b
popw %cx /* %cx <- 4 */
popw %si /* %si <- ptab */
/* No primary partitions found, look for extended/logical partitions */
7:
movb 4(%si), %al
andb %al, %al
jz 12f /* Not a valid partition */
cmpb $0x0f, %al /* 0x0f = Win9x extended */
je 8f
andb $~0x80, %al /* 0x85 = Linux extended */
cmpb $0x05, %al /* 0x05 = MS-DOS extended */
jne 9f
/* It is an extended partition. Read the extended partition and
try to scan it. If the scan returns, re-load the current
partition table and resume scan. */
8:
movl 8(%si), %eax /* Partition table offset */
addl %edx, %eax /* Compute location of new ptab */
andl %edx, %edx /* Is this the MBR? */
jnz 10f
movl %eax, %edx /* Offset -> root if this was MBR */
10:
call read_partition_table
jc 11f
call scan_partition_table
11:
/* This returned, so we need to reload the current partition table */
movl 28(%bp), %eax /* "Base" */
call read_partition_table
/* fall through */
9:
/* Not an extended partition */
andl %edx, %edx /* Are we inside an extended part? */
jz 12f
/* If so, this is a logical partition */
decb (partition)
je boot
12:
addw $16, %si
loopw 7b
/* Nothing found, return */
popal
ret
/*
* boot: invoke the actual bootstrap. (%si) points to the partition
* table entry, and 28(%bp) has the partition table base.
*/
boot:
cmpb $0, 4(%si)
je missing_os
movl 8(%si), %eax
addl 28(%bp), %eax
movl %eax, 8(%si) /* Adjust in-memory partition table entry */
call read_sector
jc disk_error
cmpw $0xaa55, (bootsec+510)
jne missing_os /* Not a valid boot sector */
movw $driveno, %sp /* driveno == bootsec-6 */
popw %dx /* dl -> drive number */
popw %di /* es:di -> $PnP vector */
popw %es
cli
jmpw *%sp /* %sp == bootsec */
disk_error:
call error
.ascii "Operating system load error.\r\n"
/*
* Print error messages. This is invoked with "call", with the
* error message at the return address.
*/
error:
popw %si
2:
lodsb
movb $0x0e, %ah
movb (BIOS_page), %bh
movb $0x07, %bl
int $0x10 /* May destroy %bp */
cmpb $10, %al /* Newline? */
jne 2b
int $0x18 /* Boot failure */
die:
hlt
jmp die
/* Location of the partition configuration byte */
partition = _start + 439
