2 * Copyright (c) 2003,2004 The DragonFly Project. All rights reserved.
4 * This code is derived from software contributed to The DragonFly Project
5 * by Matthew Dillon <dillon@backplane.com>
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in
15 * the documentation and/or other materials provided with the
17 * 3. Neither the name of The DragonFly Project nor the names of its
18 * contributors may be used to endorse or promote products derived
19 * from this software without specific, prior written permission.
21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
22 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
23 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
24 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
25 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
26 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
27 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
28 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
29 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
30 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
31 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * Copyright (c) 1998 Robert Nordier
35 * All rights reserved.
37 * Redistribution and use in source and binary forms are freely
38 * permitted provided that the above copyright notice and this
39 * paragraph and the following disclaimer are duplicated in all
42 * This software is provided "AS IS" and without any express or
43 * implied warranties, including, without limitation, the implied
44 * warranties of merchantability and fitness for a particular
47 * $FreeBSD: src/sys/boot/i386/boot2/boot1.s,v 1.23 2003/08/22 01:59:28 imp Exp $
48 * $DragonFly: src/sys/boot/pc32/boot2/boot1.S,v 1.10 2008/09/13 11:45:45 corecode Exp $
51 #include "../bootasm.h"
53 // Partition Constants
54 .set PRT_OFF,0x1be // Partition offset
55 .set PRT_NUM,0x4 // Partitions
56 .set PRT_BSD,0xa5 // Partition type
59 .set FL_PACKET,0x80 // Packet mode
62 .set SIZ_PAG,0x1000 // Page size
63 .set SIZ_SEC,0x200 // Sector size
72 start: jmp main // Start recognizably
74 // This is the start of a standard BIOS Parameter Block (BPB). Most bootable
75 // FAT disks have this at the start of their MBR. While normal BIOS's will
76 // work fine without this section, IBM's El Torito emulation "fixes" up the
77 // BPB by writing into the memory copy of the MBR. Rather than have data
78 // written into our xread routine, we'll define a BPB to work around it.
79 // The data marked with (T) indicates a field required for a ThinkPad to
80 // recognize the disk and (W) indicates fields written from IBM BIOS code.
81 // The use of the BPB is based on what OpenBSD and NetBSD implemented in
82 // their boot code but the required fields were determined by trial and error.
84 // Note: If additional space is needed in boot1, one solution would be to
85 // move the "prompt" message data (below) to replace the OEM ID.
88 oemid: .space 0x08, 0x00 // OEM ID
91 bpb: .word 512 // sector size (T)
92 .byte 0 // sectors/clustor
93 .word 0 // reserved sectors
94 .byte 0 // number of FATs
95 .word 0 // root entries
96 .word 0 // small sectors
97 .byte 0 // media type (W)
98 .word 0 // sectors/fat
99 .word 18 // sectors per track (T)
100 .word 2 // number of heads (T)
101 .long 0 // hidden sectors (W)
102 .long 0 // large sectors
105 ebpb: .byte 0 // BIOS physical drive number (W)
109 // Trampoline used by boot2 to call read to read data from the disk via
110 // the BIOS. Call with:
112 // %cx:%ax - long - LBA to read in
113 // %es:(%bx) - caddr_t - buffer to read data into
114 // %dl - byte - drive to read from
115 // %dh - byte - num sectors to read
118 xread: push %ss // Address
121 // Setup an EDD disk packet and pass it to read
124 pushl $0x0 // absolute
127 push %es // Address of
128 push %bx // transfer buffer
129 xor %ax,%ax // Number of
130 movb %dh,%al // blocks to
132 push $0x10 // Size of packet
133 mov %sp,%bp // Packet pointer
134 callw read // Read from disk
135 lea 0x10(%bp),%sp // Clear stack
136 lret // To far caller
138 // Load the rest of boot2 and BTX up, copy the parts to the right locations,
139 // and start it all up.
143 // Setup the segment registers to flat addressing (segment 0) and setup the
144 // stack to end just below the start of our code.
146 // XXX note - our origin (start) points to the MEM_BIOS_LADDR. We run
147 // from there but boot2 later on calls xread at BOOT1_ORIGIN.
149 main: cld // String ops inc
151 mov %cx,%es // Address
153 mov %cx,%ss // Set up
154 mov $start,%sp // stack
156 // Relocate ourself to BOOT1_ORIGIN. Since %cx == 0, the inc %ch sets
157 // %cx == 0x100 (256 words == 512 bytes).
159 mov %sp,%si // Source
160 mov $BOOT1_ORIGIN,%di // Destination
161 incb %ch // Word count
165 // If we are on a hard drive, then load the MBR and look for the first
168 // Note, we can't use the fake partition entry (part4), as it may contain
169 // garbage if this is a normal boot1 on a slice, verses a dangerously
170 // dedicated disk. Hardwire sector 0 to acquire the MBR
174 cmpb $0x80,%dl // Hard drive?
176 movb $0x1,%dh // Block count
177 callw nread_alt // Read MBR
178 mov $0x1,%cx // Two passes
179 main.1: mov $BOOT2_LOAD_BUF+PRT_OFF,%si // Partition table
180 movb $0x1,%dh // Partition
181 main.2: cmpb $PRT_BSD,0x4(%si) // Our partition type?
183 jcxz main.5 // If second pass
184 testb $0x80,(%si) // Active?
186 main.3: add $0x10,%si // Next entry
187 incb %dh // Partition
188 cmpb $0x1+PRT_NUM,%dh // In table?
191 jcxz main.1 // passes
193 // If we get here, we didn't find any FreeBSD slices at all, so print an
194 // error message and die.
196 mov $msg_part,%si // Message
199 // Floppies use partition 0 of drive 0.
201 main.4: xor %dx,%dx // Partition:drive
203 // Ok, we have a slice and drive in %dx now, so use that to locate and load
204 // boot2. %si references the start of the slice we are looking for, so go
205 // ahead and load up the first N sectors (boot1 + boot2) from that.
207 // N is 16 for boot1 in a disklabel32 and up to 32 in a disklabel64. The
208 // disklabel64 can hold up to 64 sectors but MEM_BTX_USR+BOOT2_VORIGIN
209 // will overflow the segment if we use more then 32 sectors.
211 // When we read it in, we conveniently use BOOT2_LOAD_BUF (0x8c00) as our
212 // transfer buffer. Thus, boot1 ends up at 0x8c00, and boot2 starts at
213 // 0x8c00 + 0x200 = 0x8e00.
215 // The first part of boot2 is the disklabel, which is 0x200 bytes long.
216 // The second part is BTX, which is thus loaded into 0x9000, which is where
217 // it also runs from. The boot2.bin binary starts right after the end of
218 // BTX, so we have to figure out where the start of it is and then move the
219 // binary to 0xc000. Normally, BTX clients start at MEM_BTX_USR, or 0xa000,
220 // but when we use btxld to create boot2, we use an entry point of 0x2000.
221 // That entry point is relative to MEM_BTX_USR; thus boot2.bin starts
224 // MEM_BTX_USR_ARG will be overwritten by the disk read and the relocation
225 // loop, so we must store the argument after completing said loops.
227 main.5: pushw %dx // Save args
228 movb $NSECT,%dh // Sector count
230 // In disklabel64 boot2 starts
231 addl $7,0x8(%si) // offset 0x1000.
233 callw nread // Read disk
234 mov $MEM_BTX_ORG,%bx // Base of BTX header
235 mov 0xa(%bx),%si // Get BTX text length (btx.S)
236 add %bx,%si // %si = start of boot2.bin
237 // %di = relocation target
238 mov $MEM_BTX_USR+BOOT2_VORIGIN,%di
239 mov $MEM_BTX_ORG+(NSECT-1)*SIZ_SEC,%cx
240 sub %si,%cx // %cx = Size of boot2 client
241 rep // Relocate boot2
243 popw MEM_BTX_USR_ARG // save (disk,slice) for boot2
246 // XXX DISABLED. This makes incorrect assumptions about
247 // where BSS begins, potentially leaving garbage in the BSS
248 // space. The BSS zeroing code has been moved to
249 // btx/lib/btxcsu.S (BTX client startup code) where we have
250 // more definitive knowledge about where BSS resides.
252 // %cx now contains 0. Calculate 0x[1]0000 - %di to get a
253 // count of assumed BSS bytes from the end of boot2.bin up
254 // to 0x10000, then zero it out.
261 callw seta20 // Enable A20
264 pushw $MEM_BTX_ENTRY // Start BTX
267 // Enable A20 so we can access memory above 1 meg.
269 seta20: cli // Disable interrupts
270 seta20.1: inb $0x64,%al // Get status
271 testb $0x2,%al // Busy?
273 movb $0xd1,%al // Command: Write
274 outb %al,$0x64 // output port
275 seta20.2: inb $0x64,%al // Get status
276 testb $0x2,%al // Busy?
278 movb $0xdf,%al // Enable
279 outb %al,$0x60 // A20
280 sti // Enable interrupts
283 // Trampoline used to call read from within boot1.
286 mov 0x8(%si),%ax // Get
287 mov 0xa(%si),%cx // LBA
289 mov $BOOT2_LOAD_BUF,%bx // Transfer buffer
290 push %cs // Read from
291 callw xread.1 // disk
292 jnc return // If success, return
293 mov $msg_read,%si // Otherwise, set the error
294 // message and fall through to
297 // Print out the error message pointed to by %ds:(%si) followed
298 // by a prompt, wait for a keypress, and then reboot the machine.
300 error: callw putstr // Display message
301 mov $prompt,%si // Display
302 callw putstr // prompt
303 xorb %ah,%ah // BIOS: Get
304 int $0x16 // keypress
305 movw $0x1234, BDA_BOOT // Do a warm boot
306 ljmp $0xffff,$0x0 // reboot the machine
308 // Display a null-terminated string using the BIOS output.
310 putstr.0: mov $0x7,%bx // Page:attribute
311 movb $0xe,%ah // BIOS: Display
312 int $0x10 // character
313 putstr: lodsb // Get char
314 testb %al,%al // End of string?
318 // Overused return code. ereturn is used to return an error from the
319 // read function. Since we assume putstr succeeds, we (ab)use the
320 // same code when we return from putstr.
322 ereturn: movb $0x1,%ah // Invalid
324 return: retw // To caller
326 // Reads sectors from the disk. If EDD is enabled, then check if it is
327 // installed and use it if it is. If it is not installed or not enabled, then
328 // fall back to using CHS. Since we use a LBA, if we are using CHS, we have to
329 // fetch the drive parameters from the BIOS and divide it out ourselves.
332 // %dl - byte - drive number
333 // stack - 10 bytes - EDD Packet
337 * Try EDD mode first. If not enabled or no BIOS support
338 * exists, fall back to CHS mode.
340 testb $FL_PACKET,%cs:BOOT1_ORIGIN+flags-start
344 * BIOS: check extensions present
351 jc read.1 /* BIOS error return */
352 cmp $0xaa55,%bx /* check for proper magic */
354 testb $0x1,%cl /* packet interface support? */
358 * Issue packet command.
359 * BIOS: Extended read command
367 * Fallback to CHS mode
371 movb $0x8,%ah // BIOS: Get drive
372 int $0x13 // parameters
373 movb %dh,%ch // Max head number
375 jc return // If error
376 andb $0x3f,%cl // Sectors per track
377 jz ereturn // If zero
378 cli // Disable interrupts
379 mov 0x8(%bp),%eax // Get LBA
381 movzbl %cl,%ebx // Divide by
382 xor %edx,%edx // sectors
383 div %ebx // per track
384 movb %ch,%bl // Max head number
385 movb %dl,%ch // Sector number
387 xorb %dl,%dl // number
389 movb %dl,%bh // Head number
391 cmpl $0x3ff,%eax // Cylinder number supportable?
392 sti // Enable interrupts
393 ja ereturn // No, failed
394 xchgb %al,%ah // Set up cylinder
395 rorb $0x2,%al // number
398 xchg %ax,%cx // number
399 movb %bh,%dh // Head number
400 subb %ah,%al // Sectors this track
401 mov 0x2(%bp),%ah // Blocks to read
402 cmpb %ah,%al // To read
404 #ifdef TRACK_AT_A_TIME
405 movb %ah,%al // track
407 movb $1,%al // one sector
409 read.2: mov $0x5,%di // Try count
410 read.3: les 0x4(%bp),%bx // Transfer buffer
412 movb $0x2,%ah // BIOS: Read
413 int $0x13 // from disk
415 jnc read.4 // If success
418 xorb %ah,%ah // BIOS: Reset
419 int $0x13 // disk system
420 xchg %bx,%ax // Block count
421 jmp read.3 // Continue
422 read.4: movzbw %bl,%ax // Sectors read
423 add %ax,0x8(%bp) // Adjust
425 incw 0xa(%bp) // transfer
426 read.5: shlb %bl // buffer
427 add %bl,0x5(%bp) // pointer,
428 sub %al,0x2(%bp) // block count
429 ja read.1 // If not done
430 read.6: retw // To caller
434 msg_read: .asciz "Read"
435 msg_part: .asciz "Boot"
437 prompt: .asciz " error\r\n"
439 flags: .byte FLAGS // Flags
445 // THIS MAY NOT BE WRITTEN OUT TO THE BOOT1 AREA OF THE DISKLABEL. This
446 // section is only written out when the disklabel is placed on the raw
447 // disk instead of in a slice, when creating a dangerously dedicated disk.
450 part4: .byte 0x80, 0x00, 0x01, 0x00
451 .byte 0xa5, 0xfe, 0xff, 0xff
452 .byte 0x00, 0x00, 0x00, 0x00
453 .byte 0x50, 0xc3, 0x00, 0x00 // 50000 sectors long, bleh
455 .word 0xaa55 // Magic number