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/* -----------------------------------------------------------------------
*
* 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.
*
* ----------------------------------------------------------------------- */
/*
* Modified MBR code used on an ISO image in hybrid mode.
*
* This doesn't follow the El Torito spec at all -- it is just a stub
* loader of a hard-coded offset, but that's good enough to load
* ISOLINUX.
*/
#include "adjust.h"
.code16
.text
HYBRID_MAGIC = 0x7078c0fb
isolinux_hybrid_signature = 0x7c00+64
isolinux_start_hybrid = 0x7c00+64+4
.globl bootsec
/* Important: the top 6 words on the stack are passed to isolinux.bin */
stack = 0x7c00
partoffset = (stack-8)
driveno = (stack-14)
heads = (stack-16)
sectors = (stack-18)
ebios_flag = (stack-20)
secpercyl = (stack-24)
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:
.byte 0x33, 0xed /* xorw %bp, %bp */
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
.byte 0x33, 0xed /* xorw %bp, %bp */
cli
movw %bp, %ss
movw $stack, %sp
sti
cld
/* Check to see if we have a partition table entry */
xorl %ebx, %ebx
xorl %ecx, %ecx
#ifdef PARTITION_SUPPORT
andw %si, %si /* %si == 0 -> no partition data */
jz 1f
testb $0x7f, (%si) /* Invalid active flag field? */
jnz 1f
cmpb %cl, 4(%si) /* Partition type zero == invalid? */
je 1f
cmpl $0x58504721, %eax /* !GPT signature in EAX? */
jne 2f
cmpb $0xed, 4(%si) /* EFI partition type? */
jne 2f
/* We have GPT partition information */
movl (32+20)(%si), %ecx
movl (36+20)(%si), %ebx
jmp 1f
/* We have non-GPT partition information */
2:
movl 8(%si), %ecx
#endif
1:
/* We have no partition information */
pushl %ebx /* -4: partoffset_hi */
pushl %ecx /* -8: partoffset_lo */
pushw %es /* -10: es:di -> $PnP header */
pushw %di /* -12: es:di -> $PnP header */
movw %bp, %ds
movw %bp, %es
ADJUST_DRIVE
pushw %dx /* -14: dl -> drive number */
/* Copy down to 0:0x600 */
movw $0x7c00, %si
movw $_start, %di
movw $(512/2), %cx
rep; movsw
ljmpw $0, $next
next:
/* 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
andw $1,%cx /* Bit 0 = fixed disk subset */
jz 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)
jmp 1f
1:
popw %dx
pushw %cx /* EBIOS flag */
/* Get (C)HS geometry */
movb $0x08, %ah
int $0x13
andw $0x3f, %cx /* Sector count */
popw %bx /* EBIOS flag */
pushw %cx /* -16: Save sectors on the stack */
movzbw %dh, %ax /* dh = max head */
incw %ax /* From 0-based max to count */
pushw %ax /* -18: Save heads on the stack */
mulw %cx /* Heads*sectors -> sectors per cylinder */
pushw %bx /* -20: EBIOS flag */
/* Save sectors/cylinder on the stack */
pushw %dx /* -22: High word */
pushw %ax /* -24: Low word */
/*
* Load sectors. We do this one at a time mostly to avoid
* pitfalls and to share code with the stock MBR code.
*/
movw $0x7c00, %bx
movw $4, %cx /* Sector count */
movl (lba_offset), %eax
2:
call read_sector
jc disk_error
incl %eax
addb $(512 >> 8), %bh
loopw 2b
/*
* Okay, that actually worked... update the stack pointer
* and jump into isolinux.bin...
*/
cmpl $HYBRID_MAGIC,(isolinux_hybrid_signature)
jne bad_signature
cli
movw $ebios_flag, %sp
/*
* Use a ljmpw here to work around a bug in some unknown version
* of gas or ld when it comes to jumping to an absolute symbol...
*
* Look more closely into it if we ever are short on space.
*/
ljmpw $0, $isolinux_start_hybrid
bad_signature:
call error
.ascii "isolinux.bin missing or corrupt.\r\n"
/*
* read_sector: read a single sector pointed to by %eax to %es:%bx.
* CF is set on error. All registers saved.
*/
read_sector:
pushal
xorl %edx, %edx
addl (partoffset), %eax
adcl (partoffset+4), %edx
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
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
/* Address of pointer to isolinux.bin */
lba_offset = _start+432
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