gptldr.S revision 225736 
1/*-
2 * Copyright (c) 2007 Yahoo!, Inc.
3 * All rights reserved.
4 * Written by: John Baldwin <jhb@FreeBSD.org>
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 *    notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 *    notice, this list of conditions and the following disclaimer in the
13 *    documentation and/or other materials provided with the distribution.
14 * 3. Neither the name of the author nor the names of any co-contributors
15 *    may be used to endorse or promote products derived from this software
16 *    without specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 * SUCH DAMAGE.
29 *
30 * $FreeBSD: stable/9/sys/boot/i386/gptboot/gptldr.S 173957 2007-11-26 21:29:59Z jhb $
31 *
32 * Partly from: src/sys/boot/i386/boot2/boot1.S 1.31
33 */
34
35/* Memory Locations */
36		.set MEM_REL,0x700		# Relocation address
37		.set MEM_ARG,0x900		# Arguments
38		.set MEM_ORG,0x7c00		# Origin
39		.set MEM_BUF,0x8cec		# Load area
40		.set MEM_BTX,0x9000		# BTX start
41		.set MEM_JMP,0x9010		# BTX entry point
42		.set MEM_USR,0xa000		# Client start
43		.set BDA_BOOT,0x472		# Boot howto flag
44
45/* Misc. Constants */
46		.set SIZ_PAG,0x1000		# Page size
47		.set SIZ_SEC,0x200		# Sector size
48
49		.globl start
50		.code16
51
52/*
53 * Copy BTX and boot2 to the right locations and start it all up.
54 */
55
56/*
57 * Setup the segment registers to flat addressing (segment 0) and setup the
58 * stack to end just below the start of our code.
59 */
60start:		xor %cx,%cx			# Zero
61		mov %cx,%es			# Address
62		mov %cx,%ds			#  data
63		mov %cx,%ss			# Set up
64		mov $start,%sp			#  stack
65
66/*
67 * BTX is right after us at 'end'.  We read the length of BTX out of
68 * its header to find boot2.  We need to copy boot2 to MEM_USR and BTX
69 * to MEM_BTX.  Since those might overlap, we have to copy boot2
70 * backwards first and then copy BTX.  We aren't sure exactly how long
71 * boot2 is, but we assume it can't be longer than 64k, so we just always
72 * copy 64k.
73 */
74		mov $end,%bx			# BTX
75		mov 0xa(%bx),%si		# Get BTX length and set
76		add %bx,%si			#  %si to start of boot2
77		mov %si,%ax			# Align %ds:%si on a
78		shr $4,%ax			#  paragraph boundary
79		and $0xf,%si			#  with the smallest
80		mov %ax,%ds			#  possible %si
81		add $(64 * 1024 - 16),%si
82		mov $MEM_USR/16,%ax		# Point %es:%di at end of
83		mov $(64 * 1024 - 16),%di	#  largest boot2 range
84		mov %ax,%es
85		std
86		mov %di,%cx			# Copy 64k - paragraph + 1
87		inc %cx				#  bytes
88		rep movsb
89		mov %cx,%ds			# Reset %ds and %es
90		mov %cx,%es
91		mov 0xa(%bx),%cx		# Get BTX length and set
92		mov %bx,%si			#  %si to end of BTX
93		mov $MEM_BTX,%di		# %di -> end of BTX at
94		add %cx,%si			#  MEM_BTX
95		add %cx,%di
96		dec %si
97		dec %di
98		rep movsb			# Move BTX
99		cld				# String ops inc
100/*
101 * Enable A20 so we can access memory above 1 meg.
102 * Use the zero-valued %cx as a timeout for embedded hardware which do not
103 * have a keyboard controller.
104 */
105seta20: 	cli				# Disable interrupts
106seta20.1:	dec %cx				# Timeout?
107		jz seta20.3			# Yes
108		inb $0x64,%al			# Get status
109		testb $0x2,%al			# Busy?
110		jnz seta20.1			# Yes
111		movb $0xd1,%al			# Command: Write
112		outb %al,$0x64			#  output port
113seta20.2:	inb $0x64,%al			# Get status
114		testb $0x2,%al			# Busy?
115		jnz seta20.2			# Yes
116		movb $0xdf,%al			# Enable
117		outb %al,$0x60			#  A20
118seta20.3:	sti				# Enable interrupts
119
120/*
121 * Save drive number from BIOS so boot2 can see it and start BTX.
122 */
123		movb %dl,MEM_ARG
124		jmp MEM_JMP			# Start BTX
125end:
126