Fully synchronize sys/boot from FreeBSD-5.x, but add / to the module path
[dragonfly.git] / sys / boot / pc32 / boot2 / boot1.S
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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//
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16// $FreeBSD: src/sys/boot/i386/boot2/boot1.s,v 1.23 2003/08/22 01:59:28 imp Exp $
17// $DragonFly: src/sys/boot/pc32/boot2/boot1.S,v 1.3 2003/11/10 06:08:35 dillon Exp $
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19// Memory Locations
20 .set MEM_REL,0x700 // Relocation address
21 .set MEM_ARG,0x900 // Arguments
22 .set MEM_ORG,0x7c00 // Origin
23 .set MEM_BUF,0x8cec // Load area
24 .set MEM_BTX,0x9000 // BTX start
25 .set MEM_JMP,0x9010 // BTX entry point
26 .set MEM_USR,0xa000 // Client start
27 .set BDA_BOOT,0x472 // Boot howto flag
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29// Partition Constants
30 .set PRT_OFF,0x1be // Partition offset
31 .set PRT_NUM,0x4 // Partitions
32 .set PRT_BSD,0xa5 // Partition type
984263bc 33
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34// Flag Bits
35 .set FL_PACKET,0x80 // Packet mode
984263bc 36
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37// Misc. Constants
38 .set SIZ_PAG,0x1000 // Page size
39 .set SIZ_SEC,0x200 // Sector size
984263bc 40
5ee58eed 41 .set NSECT,0x10
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42 .globl start
43 .globl xread
44 .code16
45
5ee58eed 46start: jmp main // Start recognizably
984263bc 47
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48// This is the start of a standard BIOS Parameter Block (BPB). Most bootable
49// FAT disks have this at the start of their MBR. While normal BIOS's will
50// work fine without this section, IBM's El Torito emulation "fixes" up the
51// BPB by writing into the memory copy of the MBR. Rather than have data
52// written into our xread routine, we'll define a BPB to work around it.
53// The data marked with (T) indicates a field required for a ThinkPad to
54// recognize the disk and (W) indicates fields written from IBM BIOS code.
55// The use of the BPB is based on what OpenBSD and NetBSD implemented in
56// their boot code but the required fields were determined by trial and error.
57//
58// Note: If additional space is needed in boot1, one solution would be to
59// move the "prompt" message data (below) to replace the OEM ID.
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60
61 .org 0x03, 0x00
5ee58eed 62oemid: .space 0x08, 0x00 // OEM ID
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63
64 .org 0x0b, 0x00
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65bpb: .word 512 // sector size (T)
66 .byte 0 // sectors/clustor
67 .word 0 // reserved sectors
68 .byte 0 // number of FATs
69 .word 0 // root entries
70 .word 0 // small sectors
71 .byte 0 // media type (W)
72 .word 0 // sectors/fat
73 .word 18 // sectors per track (T)
74 .word 2 // number of heads (T)
75 .long 0 // hidden sectors (W)
76 .long 0 // large sectors
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77
78 .org 0x24, 0x00
5ee58eed 79ebpb: .byte 0 // BIOS physical drive number (W)
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80
81 .org 0x25,0x90
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82//
83// Trampoline used by boot2 to call read to read data from the disk via
84// the BIOS. Call with:
85//
86// %cx:%ax - long - LBA to read in
87// %es:(%bx) - caddr_t - buffer to read data into
88// %dl - byte - drive to read from
89// %dh - byte - num sectors to read
90//
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92xread: push %ss // Address
93 pop %ds // data
94//
95// Setup an EDD disk packet and pass it to read
96//
97xread.1: // Starting
98 pushl $0x0 // absolute
99 push %cx // block
100 push %ax // number
101 push %es // Address of
102 push %bx // transfer buffer
103 xor %ax,%ax // Number of
104 movb %dh,%al // blocks to
105 push %ax // transfer
106 push $0x10 // Size of packet
107 mov %sp,%bp // Packet pointer
108 callw read // Read from disk
109 lea 0x10(%bp),%sp // Clear stack
110 lret // To far caller
111//
112// Load the rest of boot2 and BTX up, copy the parts to the right locations,
113// and start it all up.
114//
984263bc 115
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116//
117// Setup the segment registers to flat addressing (segment 0) and setup the
118// stack to end just below the start of our code.
119//
120main: cld // String ops inc
121 xor %cx,%cx // Zero
122 mov %cx,%es // Address
123 mov %cx,%ds // data
124 mov %cx,%ss // Set up
125 mov $start,%sp // stack
126//
127// Relocate ourself to MEM_REL. Since %cx == 0, the inc %ch sets
128// %cx == 0x100.
129//
130 mov %sp,%si // Source
131 mov $MEM_REL,%di // Destination
132 incb %ch // Word count
133 rep // Copy
134 movsw // code
135//
136// If we are on a hard drive, then load the MBR and look for the first
137// FreeBSD slice. We use the fake partition entry below that points to
138// the MBR when we call nread. The first pass looks for the first active
139// FreeBSD slice. The second pass looks for the first non-active FreeBSD
140// slice if the first one fails.
141//
142 mov $part4,%si // Partition
143 cmpb $0x80,%dl // Hard drive?
144 jb main.4 // No
145 movb $0x1,%dh // Block count
146 callw nread // Read MBR
147 mov $0x1,%cx // Two passes
148main.1: mov $MEM_BUF+PRT_OFF,%si // Partition table
149 movb $0x1,%dh // Partition
150main.2: cmpb $PRT_BSD,0x4(%si) // Our partition type?
151 jne main.3 // No
152 jcxz main.5 // If second pass
153 testb $0x80,(%si) // Active?
154 jnz main.5 // Yes
155main.3: add $0x10,%si // Next entry
156 incb %dh // Partition
157 cmpb $0x1+PRT_NUM,%dh // In table?
158 jb main.2 // Yes
159 dec %cx // Do two
160 jcxz main.1 // passes
161//
162// If we get here, we didn't find any FreeBSD slices at all, so print an
163// error message and die.
164//
165 mov $msg_part,%si // Message
166 jmp error // Error
167//
168// Floppies use partition 0 of drive 0.
169//
170main.4: xor %dx,%dx // Partition:drive
171//
172// Ok, we have a slice and drive in %dx now, so use that to locate and load
173// boot2. %si references the start of the slice we are looking for, so go
174// ahead and load up the first 16 sectors (boot1 + boot2) from that. When
175// we read it in, we conveniently use 0x8cec as our transfer buffer. Thus,
176// boot1 ends up at 0x8cec, and boot2 starts at 0x8cec + 0x200 = 0x8eec.
177// The first part of boot2 is the disklabel, which is 0x114 bytes long.
178// The second part is BTX, which is thus loaded into 0x9000, which is where
179// it also runs from. The boot2.bin binary starts right after the end of
180// BTX, so we have to figure out where the start of it is and then move the
181// binary to 0xc000. Normally, BTX clients start at MEM_USR, or 0xa000, but
182// when we use btxld to create boot2, we use an entry point of 0x2000. That
183// entry point is relative to MEM_USR; thus boot2.bin starts at 0xc000.
184//
185main.5: mov %dx,MEM_ARG // Save args
186 movb $NSECT,%dh // Sector count
187 callw nread // Read disk
188 mov $MEM_BTX,%bx // BTX
189 mov 0xa(%bx),%si // Get BTX length and set
190 add %bx,%si // %si to start of boot2.bin
191 mov $MEM_USR+SIZ_PAG*2,%di // Client page 2
192 mov $MEM_BTX+(NSECT-1)*SIZ_SEC,%cx // Byte
193 sub %si,%cx // count
194 rep // Relocate
195 movsb // client
196 sub %di,%cx // Byte count
197 xorb %al,%al // Zero assumed bss from
198 rep // the end of boot2.bin
199 stosb // up to 0x10000
200 callw seta20 // Enable A20
201 jmp start+MEM_JMP-MEM_ORG // Start BTX
202//
203// Enable A20 so we can access memory above 1 meg.
204//
205seta20: cli // Disable interrupts
206seta20.1: inb $0x64,%al // Get status
207 testb $0x2,%al // Busy?
208 jnz seta20.1 // Yes
209 movb $0xd1,%al // Command: Write
210 outb %al,$0x64 // output port
211seta20.2: inb $0x64,%al // Get status
212 testb $0x2,%al // Busy?
213 jnz seta20.2 // Yes
214 movb $0xdf,%al // Enable
215 outb %al,$0x60 // A20
216 sti // Enable interrupts
217 retw // To caller
218//
219// Trampoline used to call read from within boot1.
220//
221nread: mov $MEM_BUF,%bx // Transfer buffer
222 mov 0x8(%si),%ax // Get
223 mov 0xa(%si),%cx // LBA
224 push %cs // Read from
225 callw xread.1 // disk
226 jnc return // If success, return
227 mov $msg_read,%si // Otherwise, set the error
228 // message and fall through to
229 // the error routine
230//
231// Print out the error message pointed to by %ds:(%si) followed
232// by a prompt, wait for a keypress, and then reboot the machine.
233//
234error: callw putstr // Display message
235 mov $prompt,%si // Display
236 callw putstr // prompt
237 xorb %ah,%ah // BIOS: Get
238 int $0x16 // keypress
239 movw $0x1234, BDA_BOOT // Do a warm boot
240 ljmp $0xffff,$0x0 // reboot the machine
241//
242// Display a null-terminated string using the BIOS output.
243//
244putstr.0: mov $0x7,%bx // Page:attribute
245 movb $0xe,%ah // BIOS: Display
246 int $0x10 // character
247putstr: lodsb // Get char
248 testb %al,%al // End of string?
249 jne putstr.0 // No
984263bc 250
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251//
252// Overused return code. ereturn is used to return an error from the
253// read function. Since we assume putstr succeeds, we (ab)use the
254// same code when we return from putstr.
255//
256ereturn: movb $0x1,%ah // Invalid
257 stc // argument
258return: retw // To caller
259//
260// Reads sectors from the disk. If EDD is enabled, then check if it is
261// installed and use it if it is. If it is not installed or not enabled, then
262// fall back to using CHS. Since we use a LBA, if we are using CHS, we have to
263// fetch the drive parameters from the BIOS and divide it out ourselves.
264// Call with:
265//
266// %dl - byte - drive number
267// stack - 10 bytes - EDD Packet
268//
269read: push %dx // Save
270 movb $0x8,%ah // BIOS: Get drive
271 int $0x13 // parameters
272 movb %dh,%ch // Max head number
273 pop %dx // Restore
274 jc return // If error
275 andb $0x3f,%cl // Sectors per track
276 jz ereturn // If zero
277 cli // Disable interrupts
278 mov 0x8(%bp),%eax // Get LBA
279 push %dx // Save
280 movzbl %cl,%ebx // Divide by
281 xor %edx,%edx // sectors
282 div %ebx // per track
283 movb %ch,%bl // Max head number
284 movb %dl,%ch // Sector number
285 inc %bx // Divide by
286 xorb %dl,%dl // number
287 div %ebx // of heads
288 movb %dl,%bh // Head number
289 pop %dx // Restore
290 cmpl $0x3ff,%eax // Cylinder number supportable?
291 sti // Enable interrupts
292 ja read.7 // No, try EDD
293 xchgb %al,%ah // Set up cylinder
294 rorb $0x2,%al // number
295 orb %ch,%al // Merge
296 inc %ax // sector
297 xchg %ax,%cx // number
298 movb %bh,%dh // Head number
299 subb %ah,%al // Sectors this track
300 mov 0x2(%bp),%ah // Blocks to read
301 cmpb %ah,%al // To read
302 jb read.2 // this
303#ifdef TRACK_AT_A_TIME
304 movb %ah,%al // track
305#else
306 movb $1,%al // one sector
307#endif
308read.2: mov $0x5,%di // Try count
309read.3: les 0x4(%bp),%bx // Transfer buffer
310 push %ax // Save
311 movb $0x2,%ah // BIOS: Read
312 int $0x13 // from disk
313 pop %bx // Restore
314 jnc read.4 // If success
315 dec %di // Retry?
316 jz read.6 // No
317 xorb %ah,%ah // BIOS: Reset
318 int $0x13 // disk system
319 xchg %bx,%ax // Block count
320 jmp read.3 // Continue
321read.4: movzbw %bl,%ax // Sectors read
322 add %ax,0x8(%bp) // Adjust
323 jnc read.5 // LBA,
324 incw 0xa(%bp) // transfer
325read.5: shlb %bl // buffer
326 add %bl,0x5(%bp) // pointer,
327 sub %al,0x2(%bp) // block count
328 ja read // If not done
329read.6: retw // To caller
330read.7: testb $FL_PACKET,%cs:MEM_REL+flags-start // LBA support enabled?
331 jz ereturn // No, so return an error
332 mov $0x55aa,%bx // Magic
333 push %dx // Save
334 movb $0x41,%ah // BIOS: Check
335 int $0x13 // extensions present
336 pop %dx // Restore
337 jc return // If error, return an error
338 cmp $0xaa55,%bx // Magic?
339 jne ereturn // No, so return an error
340 testb $0x1,%cl // Packet interface?
341 jz ereturn // No, so return an error
342 mov %bp,%si // Disk packet
343 movb $0x42,%ah // BIOS: Extended
344 int $0x13 // read
345 retw // To caller
984263bc 346
5ee58eed 347// Messages
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348
349msg_read: .asciz "Read"
350msg_part: .asciz "Boot"
351
352prompt: .asciz " error\r\n"
353
5ee58eed 354flags: .byte FLAGS // Flags
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355
356 .org PRT_OFF,0x90
357
5ee58eed 358// Partition table
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359
360 .fill 0x30,0x1,0x0
361part4: .byte 0x80, 0x00, 0x01, 0x00
5ee58eed 362 .byte 0xa5, 0xfe, 0xff, 0xff
984263bc 363 .byte 0x00, 0x00, 0x00, 0x00
5ee58eed 364 .byte 0x50, 0xc3, 0x00, 0x00 // 50000 sectors long, bleh
984263bc 365
5ee58eed 366 .word 0xaa55 // Magic number