1/*
2 * Copyright (c) 1998 Robert Nordier
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms are freely
6 * permitted provided that the above copyright notice and this
7 * paragraph and the following disclaimer are duplicated in all
8 * such forms.
9 *
10 * This software is provided "AS IS" and without any express or
11 * implied warranties, including, without limitation, the implied
12 * warranties of merchantability and fitness for a particular
13 * purpose.
14 *
15 * $FreeBSD: stable/11/stand/i386/zfsboot/zfsldr.S 329192 2018-02-13 04:28:13Z kevans $
16 */
17
18/* Memory Locations */
19		.set MEM_ARG,0x900		# Arguments
20		.set MEM_ORG,0x7c00		# Origin
21		.set MEM_BUF,0x8000		# Load area
22		.set MEM_BTX,0x9000		# BTX start
23		.set MEM_JMP,0x9010		# BTX entry point
24		.set MEM_USR,0xa000		# Client start
25		.set BDA_BOOT,0x472		# Boot howto flag
26
27/* Partition Constants */
28		.set PRT_OFF,0x1be		# Partition offset
29		.set PRT_NUM,0x4		# Partitions
30		.set PRT_BSD,0xa5		# Partition type
31
32/* Misc. Constants */
33		.set SIZ_PAG,0x1000		# Page size
34		.set SIZ_SEC,0x200		# Sector size
35		.set COPY_BLKS,0x8		# Number of blocks
36						# to copy for boot2 (<= 15)
37		.set COPY_BLK_SZ,0x8000		# Copy in 32k blocks; must be
38						# a multiple of 16 bytes
39		.set NSECT,(COPY_BLK_SZ / SIZ_SEC * COPY_BLKS)
40		.globl start
41		.code16
42
43/*
44 * Load the rest of zfsboot2 and BTX up, copy the parts to the right locations,
45 * and start it all up.
46 */
47
48/*
49 * Setup the segment registers to flat addressing (segment 0) and setup the
50 * stack to end just below the start of our code.
51 */
52start:		cld				# String ops inc
53		xor %cx,%cx			# Zero
54		mov %cx,%es			# Address
55		mov %cx,%ds			#  data
56		mov %cx,%ss			# Set up
57		mov $start,%sp			#  stack
58/*
59 * Load the MBR and look for the first FreeBSD slice.  We use the fake
60 * partition entry below that points to the MBR when we call read.
61 * The first pass looks for the first active FreeBSD slice.  The
62 * second pass looks for the first non-active FreeBSD slice if the
63 * first one fails.
64 */
65		call check_edd		 	# Make sure EDD works
66		mov $part4,%si			# Dummy partition
67		xor %eax,%eax			# Read MBR
68		movl $MEM_BUF,%ebx		#  from first
69		call read			#  sector
70		mov $0x1,%cx	 		# Two passes
71main.1: 	mov $MEM_BUF+PRT_OFF,%si	# Partition table
72		movb $0x1,%dh			# Partition
73main.2: 	cmpb $PRT_BSD,0x4(%si)		# Our partition type?
74		jne main.3			# No
75		jcxz main.5			# If second pass
76		testb $0x80,(%si)		# Active?
77		jnz main.5			# Yes
78main.3: 	add $0x10,%si	 		# Next entry
79		incb %dh			# Partition
80		cmpb $0x1+PRT_NUM,%dh		# In table?
81		jb main.2			# Yes
82		dec %cx				# Do two
83		jcxz main.1			#  passes
84/*
85 * If we get here, we didn't find any FreeBSD slices at all, so print an
86 * error message and die.
87 */
88		mov $msg_part,%si		# Message
89		jmp error			# Error
90
91/*
92 * Ok, we have a slice and drive in %dx now, so use that to locate and
93 * load boot2.  %si references the start of the slice we are looking
94 * for, so go ahead and load up the COPY_BLKS*COPY_BLK_SZ/SIZ_SEC sectors
95 * starting at sector 1024 (i.e. after the two vdev labels).  We don't
96 * have do anything fancy here to allow for an extra copy of boot1 and
97 * a partition table (compare to this section of the UFS bootstrap) so we
98 * just load it all at 0x9000. The first part of boot2 is BTX, which wants
99 * to run at 0x9000. The boot2.bin binary starts right after the end of BTX,
100 * so we have to figure out where the start of it is and then move the
101 * binary to 0xc000.  Normally, BTX clients start at MEM_USR, or 0xa000,
102 * but when we use btxld to create zfsboot2, we use an entry point of
103 * 0x2000.  That entry point is relative to MEM_USR; thus boot2.bin
104 * starts at 0xc000.
105 *
106 * The load area and the target area for the client overlap so we have
107 * to use a decrementing string move. We also play segment register
108 * games with the destination address for the move so that the client
109 * can be larger than 16k (which would overflow the zero segment since
110 * the client starts at 0xc000).
111 */
112main.5: 	mov %dx,MEM_ARG			# Save args
113		mov $NSECT,%cx			# Sector count
114		movl $1024,%eax			# Offset to boot2
115		mov $MEM_BTX,%ebx		# Destination buffer
116main.6:		pushal				# Save params
117		call read			# Read disk
118		popal				# Restore
119		incl %eax			# Advance to
120		add $SIZ_SEC,%ebx		#  next sector
121		loop main.6			# If not last, read another
122
123		mov $MEM_BTX,%bx		# BTX
124		mov 0xa(%bx),%si		# Get BTX length and set
125		add %bx,%si			#  %si to start of boot2
126		dec %si				# Set %ds:%si to point at the
127		mov %si,%ax			# last byte we want to copy
128		shr $4,%ax			# from boot2, with %si made as
129		add $(COPY_BLKS*COPY_BLK_SZ/16),%ax	# small as possible.
130		and $0xf,%si			#
131		mov %ax,%ds			#
132		mov $(MEM_USR+2*SIZ_PAG)/16,%ax # Set %es:(-1) to point at
133		add $(COPY_BLKS*COPY_BLK_SZ/16),%ax	# the last byte we
134		mov %ax,%es			# want to copy boot2 into.
135		mov $COPY_BLKS,%bx		# Copy COPY_BLKS 32k blocks
136copyloop:
137		add $COPY_BLK_SZ,%si		# Adjust %ds:%si to point at
138		mov %ds,%ax			# the end of the next 32k to
139		sub $COPY_BLK_SZ/16,%ax		# copy from boot2
140		mov %ax,%ds
141		mov $COPY_BLK_SZ-1,%di		# Adjust %es:%di to point at
142		mov %es,%ax			# the end of the next 32k into
143		sub $COPY_BLK_SZ/16,%ax		# which we want boot2 copied
144		mov %ax,%es
145		mov $COPY_BLK_SZ,%cx		# Copy 32k
146		std
147		rep movsb
148		dec %bx
149		jnz copyloop
150		mov %cx,%ds			# Reset %ds and %es
151		mov %cx,%es
152		cld				# Back to increment
153
154/*
155 * Enable A20 so we can access memory above 1 meg.
156 * Use the zero-valued %cx as a timeout for embedded hardware which do not
157 * have a keyboard controller.
158 */
159seta20: 	cli				# Disable interrupts
160seta20.1:	dec %cx				# Timeout?
161		jz seta20.3			# Yes
162		inb $0x64,%al			# Get status
163		testb $0x2,%al			# Busy?
164		jnz seta20.1			# Yes
165		movb $0xd1,%al			# Command: Write
166		outb %al,$0x64			#  output port
167seta20.2:	inb $0x64,%al			# Get status
168		testb $0x2,%al			# Busy?
169		jnz seta20.2			# Yes
170		movb $0xdf,%al			# Enable
171		outb %al,$0x60			#  A20
172seta20.3:	sti				# Enable interrupts
173
174		jmp start+MEM_JMP-MEM_ORG	# Start BTX
175
176
177/*
178 * Read a sector from the disk.  Sets up an EDD packet on the stack
179 * and passes it to read.  We assume that the destination address is
180 * always segment-aligned.
181 *
182 * %eax		- int     - LBA to read in relative to partition start
183 * %ebx		- ptr	  - destination address
184 * %dl		- byte    - drive to read from
185 * %si		- ptr     - MBR partition entry
186 */
187read:		xor %ecx,%ecx			# Get
188		addl 0x8(%si),%eax		#  LBA
189		adc $0,%ecx
190		pushl %ecx			# Starting absolute block
191		pushl %eax			#  block number
192		shr $4,%ebx			# Convert to segment
193		push %bx			# Address of
194		push $0				#  transfer buffer
195		push $0x1			# Read 1 sector
196		push $0x10			# Size of packet
197		mov %sp,%si			# Packet pointer
198		mov $0x42,%ah			# BIOS: Extended
199		int $0x13			#  read
200		jc read.1			# If error, fail
201		lea 0x10(%si),%sp		# Clear stack
202		ret				# If success, return
203read.1:		mov %ah,%al			# Format
204		mov $read_err,%di		#  error
205		call hex8			#  code
206		mov $msg_read,%si		# Set the error message and
207						#  fall through to the error
208						#  routine
209/*
210 * Print out the error message pointed to by %ds:(%si) followed
211 * by a prompt, wait for a keypress, and then reboot the machine.
212 */
213error:		callw putstr			# Display message
214		mov $prompt,%si			# Display
215		callw putstr			#  prompt
216		xorb %ah,%ah			# BIOS: Get
217		int $0x16			#  keypress
218		movw $0x1234, BDA_BOOT		# Do a warm boot
219		ljmp $0xffff,$0x0		# reboot the machine
220/*
221 * Display a null-terminated string using the BIOS output.
222 */
223putstr.0:	mov $0x7,%bx	 		# Page:attribute
224		movb $0xe,%ah			# BIOS: Display
225		int $0x10			#  character
226putstr: 	lodsb				# Get char
227		testb %al,%al			# End of string?
228		jne putstr.0			# No
229		ret				# To caller
230/*
231 * Check to see if the disk supports EDD.  zfsboot requires EDD and does not
232 * support older C/H/S disk I/O.
233 */
234check_edd:	cmpb $0x80,%dl			# Hard drive?
235		jb check_edd.1 			# No, fail to boot
236		mov $0x55aa,%bx			# Magic
237		push %dx			# Save
238		movb $0x41,%ah			# BIOS: Check
239		int $0x13			#  extensions present
240		pop %dx				# Restore
241		jc check_edd.1			# If error, fail
242		cmp $0xaa55,%bx			# Magic?
243		jne check_edd.1			# No, so fail
244		testb $0x1,%cl			# Packet interface?
245		jz check_edd.1			# No, so fail
246		ret				# EDD ok, keep booting
247check_edd.1:	mov $msg_chs,%si		# Warn that CHS is
248		jmp error			#  unsupported and fail
249/*
250 * AL to hex, saving the result to [EDI].
251 */
252hex8:		push %ax			# Save
253		shrb $0x4,%al			# Do upper
254		call hex8.1			#  4
255		pop %ax				# Restore
256hex8.1: 	andb $0xf,%al			# Get lower 4
257		cmpb $0xa,%al			# Convert
258		sbbb $0x69,%al			#  to hex
259		das				#  digit
260		orb $0x20,%al			# To lower case
261		stosb				# Save char
262		ret				# (Recursive)
263
264/* Messages */
265
266msg_chs:	.asciz "CHS not supported"
267msg_read:	.ascii "Read error: "
268read_err:	.asciz "XX"
269msg_part:	.asciz "Boot error"
270
271prompt: 	.asciz "\r\n"
272
273		.org PRT_OFF,0x90
274
275/* Partition table */
276
277		.fill 0x30,0x1,0x0
278part4:		.byte 0x80, 0x00, 0x01, 0x00
279		.byte 0xa5, 0xfe, 0xff, 0xff
280		.byte 0x00, 0x00, 0x00, 0x00
281		.byte 0x50, 0xc3, 0x00, 0x00	# 50000 sectors long, bleh
282
283		.word 0xaa55			# Magic number
284