Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
sys/boot/jumpboot.s
Version:
- FREEBSD - FREEBSD-13-STABLE - FREEBSD-13-0 - FREEBSD-12-STABLE - FREEBSD-12-0 - FREEBSD-11-STABLE - FREEBSD-11-0 - FREEBSD-10-STABLE - FREEBSD-10-0 - FREEBSD-9-STABLE - FREEBSD-9-0 - FREEBSD-8-STABLE - FREEBSD-8-0 - FREEBSD-7-STABLE - FREEBSD-7-0 - FREEBSD-6-STABLE - FREEBSD-6-0 - FREEBSD-5-STABLE - FREEBSD-5-0 - FREEBSD-4-STABLE - FREEBSD-3-STABLE - FREEBSD22 - l41 - OPENBSD - linux-2.6 - MK84 - PLAN9 - xnu-8792
SearchContext: - none - 3 - 10
SearchContext: - none - 3 - 10
1 ! jumpboot 1.0 - Jump to another bootstrap Author: Kees J. Bot 2 ! 14 Apr 1999 3 ! 4 ! This code may be placed into any free boot sector, like the first sector 5 ! of an extended partition, a file system partition other than the root, 6 ! or even the master bootstrap. It will load and run another bootstrap whose 7 ! disk, partition, and slice number (not necessarily all three) are patched 8 ! into this code by installboot. If the ALT key is held down when this code 9 ! is booted then you can type the disk, partition, and slice numbers manually. 10 ! The manual interface is default if no numbers are patched in by installboot. 11 ! 12 13 o32 = 0x66 ! This assembler doesn't know 386 extensions 14 LOADOFF = 0x7C00 ! 0x0000:LOADOFF is where this code is loaded 15 BUFFER = 0x0600 ! First free memory 16 PART_TABLE = 446 ! Location of partition table within master 17 PENTRYSIZE = 16 ! Size of one partition table entry 18 MAGIC = 510 ! Location of the AA55 magic number 19 20 ! <ibm/partition.h>: 21 MINIX_PART = 0x81 22 sysind = 4 23 lowsec = 8 24 25 26 .text 27 28 ! Find and load another bootstrap and jump to it. 29 jumpboot: 30 xor ax, ax 31 mov ds, ax 32 mov es, ax 33 cli 34 mov ss, ax ! ds = es = ss = Vector segment 35 mov sp, #LOADOFF 36 sti 37 38 ! Move this code to safety, then jump to it. 39 mov si, sp ! si = start of this code 40 mov di, #BUFFER ! di = Buffer area 41 mov cx, #512/2 ! One sector 42 cld 43 rep movs 44 jmpf BUFFER+migrate, 0 ! To safety 45 migrate: 46 47 mov bp, #BUFFER+guide ! Patched guiding characters 48 altkey: 49 movb ah, #0x02 ! Keyboard shift status 50 int 0x16 51 testb al, #0x08 ! Bit 3 = ALT key 52 jz noalt ! ALT key pressed? 53 again: 54 mov bp, #zero ! Ignore patched stuff 55 noalt: 56 57 ! Follow guide characters to find the boot partition. 58 call print 59 .ascii "d?\b\0" ! Initial greeting 60 61 ! Disk number? 62 disk: 63 movb dl, #0x80 - 0x30 ! Prepare to add an ASCII digit 64 call getch ! Get number to tell which disk 65 addb dl, al ! dl = 0x80 + (al - '0') 66 jns n0nboot ! Result should be >= 0x80 67 mov si, #BUFFER+zero-lowsec ! si = where lowsec(si) is zero 68 cmpb (bp), #0x23 ! Next guide character is '#'? 69 jne notlogical 70 lea si, 1-lowsec(bp) ! Logical sector offset follows '#' 71 notlogical: 72 call load ! Load chosen sector of chosen disk 73 cmpb (bp), #0x23 74 je boot ! Run bootstrap if a logical is chosen 75 76 call print ! Intro to partition number 77 .ascii "p?\b\0" 78 79 part: 80 call getch ! Get character to tell partition 81 call gettable ! Get partition table 82 call sort ! Sort partition table 83 call choose_load ! Compute chosen entry and load 84 85 cmpb sysind(si), #MINIX_PART ! Minix subpartition table possible? 86 jne waitboot 87 88 call print ! Intro to slice number 89 .ascii "s?\b\0" 90 91 slice: 92 call getch ! Get character to tell slice 93 call gettable ! Get partition table 94 call choose_load ! Compute chosen entry and load 95 96 waitboot: 97 call print ! Intro to nothing 98 .ascii " ?\b\0" 99 call getch ! Supposed to type RETURN now 100 n0nboot:jmp nonboot ! Sorry, can't go further 101 102 ! Get a character, either the patched-in, or one from the keyboard. 103 getch: 104 movb al, (bp) ! Get patched-in character 105 testb al, al 106 jz getkey 107 inc bp 108 jmp gotkey 109 getkey: xorb ah, ah ! Wait for keypress 110 int 0x16 111 gotkey: testb dl, dl ! Ignore CR if disk number not yet set 112 jns putch 113 cmpb al, #0x0D ! Carriage return? 114 je boot 115 !jmp putch 116 117 ! Print a character 118 putch: movb ah, #0x0E ! Print character in teletype mode 119 mov bx, #0x0001 ! Page 0, foreground color 120 int 0x10 121 ret 122 123 ! Print a message. 124 print: mov cx, si ! Save si 125 pop si ! si = String following 'call print' 126 prnext: lodsb ! al = *si++ is char to be printed 127 testb al, al ! Null marks end 128 jz prdone 129 call putch 130 jmp prnext 131 prdone: xchg si, cx ! Restore si 132 jmp (cx) ! Continue after the string 133 134 ! Return typed (or in patched data) means to run the bootstrap now in core! 135 boot: 136 call print ! Make line on screen look proper 137 .ascii "\b \r\n\0" 138 jmp LOADOFF-BUFFER ! Jump to LOADOFF 139 140 ! Compute address of chosen partition entry from choice al into si, then 141 ! continue to load the boot sector of that partition. 142 choose_load: 143 subb al, #0x30 ! al -= '0' 144 cmpb al, #4 ! Only four partitions 145 ja n0nboot 146 movb ah, #PENTRYSIZE 147 mulb ah ! al *= PENTRYSIZE 148 add ax, #BUFFER+PART_TABLE 149 mov si, ax ! si = &part_table[al - '0'] 150 movb al, sysind(si) ! System indicator 151 testb al, al ! Unused partition? 152 jz n0nboot 153 !jmp load ! Continue to load boot sector 154 155 ! Load boot sector of the current partition. 156 load: 157 push dx ! Save drive code 158 push es ! Next call sets es 159 movb ah, #0x08 ! Code for drive parameters 160 int 0x13 161 pop es 162 andb cl, #0x3F ! cl = max sector number (1-origin) 163 incb dh ! dh = 1 + max head number (0-origin) 164 movb al, cl ! al = cl = sectors per track 165 mulb dh ! dh = heads, ax = heads * sectors 166 mov bx, ax ! bx = sectors per cylinder = heads * sectors 167 mov ax, lowsec+0(si) 168 mov dx, lowsec+2(si) ! dx:ax = sector within drive 169 cmp dx, #[1024*255*63-255]>>16 ! Near 8G limit? 170 jae bigdisk 171 div bx ! ax = cylinder, dx = sector within cylinder 172 xchg ax, dx ! ax = sector within cylinder, dx = cylinder 173 movb ch, dl ! ch = low 8 bits of cylinder 174 divb cl ! al = head, ah = sector (0-origin) 175 xorb dl, dl ! About to shift bits 8-9 of cylinder into dl 176 shr dx, #1 177 shr dx, #1 ! dl[6..7] = high cylinder 178 orb dl, ah ! dl[0..5] = sector (0-origin) 179 movb cl, dl ! cl[0..5] = sector, cl[6..7] = high cyl 180 incb cl ! cl[0..5] = sector (1-origin) 181 pop dx ! Restore drive code in dl 182 movb dh, al ! dh = al = head 183 mov bx, #LOADOFF ! es:bx = where sector is loaded 184 mov ax, #0x0201 ! ah = Code for read / al = one sector 185 int 0x13 186 jmp rdeval ! Evaluate read result 187 bigdisk: 188 mov bx, dx ! bx:ax = dx:ax = sector to read 189 pop dx ! Restore drive code in dl 190 push si ! Save si 191 mov si, #BUFFER+ext_rw ! si = extended read/write parameter packet 192 mov 8(si), ax ! Starting block number = bx:ax 193 mov 10(si), bx 194 movb ah, #0x42 ! Extended read 195 int 0x13 196 pop si ! Restore si to point to partition entry 197 !jmp rdeval 198 rdeval: 199 jnc rdok 200 rderr: 201 call print 202 .ascii "\r\nRead error\r\n\0" 203 jmp again 204 rdok: 205 cmp LOADOFF+MAGIC, #0xAA55 206 je sigok ! Signature ok? 207 nonboot: 208 call print 209 .ascii "\r\nNot bootable\r\n\0" 210 jmp again 211 sigok: 212 ret 213 214 ! Get the partition table into my space. 215 gettable: 216 mov si, #LOADOFF+PART_TABLE 217 mov di, #BUFFER+PART_TABLE 218 mov cx, #4*PENTRYSIZE/2 219 rep movs 220 ret 221 222 ! Sort the partition table. 223 sort: 224 mov cx, #4 ! Four times is enough to sort 225 bubble: mov si, #BUFFER+PART_TABLE ! First table entry 226 bubble1:lea di, PENTRYSIZE(si) ! Next entry 227 cmpb sysind(si), ch ! Partition type, nonzero when in use 228 jz exchg ! Unused entries sort to the end 229 inuse: mov bx, lowsec+0(di) 230 sub bx, lowsec+0(si) ! Compute di->lowsec - si->lowsec 231 mov bx, lowsec+2(di) 232 sbb bx, lowsec+2(si) 233 jae order ! In order if si->lowsec <= di->lowsec 234 exchg: movb bl, (si) 235 xchgb bl, PENTRYSIZE(si) ! Exchange entries byte by byte 236 movb (si), bl 237 inc si 238 cmp si, di 239 jb exchg 240 order: mov si, di 241 cmp si, #BUFFER+PART_TABLE+3*PENTRYSIZE 242 jb bubble1 243 loop bubble 244 ret 245 246 .data 247 248 ! Extended read/write commands require a parameter packet. 249 ext_rw: 250 .data1 0x10 ! Length of extended r/w packet 251 .data1 0 ! Reserved 252 .data2 1 ! Blocks to transfer (just one) 253 .data2 LOADOFF ! Buffer address offset 254 .data2 0 ! Buffer address segment 255 .data4 0 ! Starting block number low 32 bits (tbfi) 256 zero: .data4 0 ! Starting block number high 32 bits 257 258 .align 2 259 guide: 260 ! Guide characters and possibly a logical partition number patched here by 261 ! installboot, up to 6 bytes maximum.
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