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 * $FreeBSD$ 16 */ 17 18/* A 1024-byte boot manager. */ 19 20 .set NHRDRV,0x475 # Number of hard drives 21 .set ORIGIN,0x600 # Execution address 22 .set SECTOR_SIZE,0x200 # Length of a sector 23 .set NUM_SECTORS,2 # Total length in sectors 24 25 .set FAKE,ORIGIN+(SECTOR_SIZE*NUM_SECTORS) # Partition entry 26 .set LOAD,0x7c00 # Load address 27 28 .set PRT_OFF,0x1be # Partition table 29 30 .set TBL0SZ,table0_end-table0 # Table 0 size 31 .set TBL1SZ,table1_end-table1 # Table 1 size 32 33 .set MAGIC,0xaa55 # Magic: bootable 34 35 .set KEY_ENTER,0x1c # Enter key scan code 36 .set KEY_F1,0x3b # F1 key scan code 37 .set KEY_1,0x02 # #1 key scan code 38 39/* 40 * Flag bits 41 */ 42 .set FL_PACKET,0x80 # Packet mode 43 .set FL_NOUPDATE,0x40 # Don't save selection 44 .set FL_SETDRV,0x20 # Override drive number 45/* 46 * Addresses in the sector of embedded data values. 47 * Accessed with negative offsets from the end of the relocated sectors (%bp). 48 */ 49 .set _PRT_END,(FAKE-(ORIGIN+SECTOR_SIZE*(NUM_SECTORS-1))) 50 .set _NXTDRV,-(_PRT_END+0x48) # Next drive 51 .set _OPT,-(_PRT_END+0x47) # Default option 52 .set _SETDRV,-(_PRT_END+0x46) # Drive to force 53 .set _FLAGS,-(_PRT_END+0x45) # Flags 54 .set _TICKS,-(_PRT_END+0x44) # Timeout ticks 55 .set _FAKE,0x0 # Fake partition entry 56 .set _MNUOPT,0xc # Menu options 57 58 .globl start # Entry point 59 .code16 # This runs in real mode 60 61/* 62 * Initialise segments and registers to known values. 63 * segments start at 0. 64 * The stack is immediately below the address we were loaded to. 65 * 66 * Note that this section of code is used as the first signature check in 67 * boot0cfg(8). 68 */ 69start: cld # String ops inc 70 xorw %ax,%ax # Zero 71 movw %ax,%es # Address 72 movw %ax,%ds # data 73 movw %ax,%ss # Set up 74 movw $LOAD,%sp # stack 75/* 76 * End signature code 77 */ 78 79/* 80 * Set address for variable space beyond code, and clear it. 81 * Notice that this is also used to point to the values embedded in the block, 82 * by using negative offsets. 83 */ 84 movw $fake,%bp # Address variables 85 movw %bp,%di # %di used in stosw 86 movw $0x8,%cx # Words to clear 87 rep # Zero 88 stosw # them 89 incb -0xe(%di) # Sector number 1 90/* 91 * Check what flags were loaded with us; specifically, use a predefined Drive. 92 * If what the bios gives us is bad, use the '0' in the block instead, as well. 93 */ 94 testb $FL_SETDRV,LOAD+flags-start # Set number drive? 95 jnz boot.1 # Yes 96 testb %dl,%dl # Drive number valid? 97 js boot.2 # Possibly (0x80 set) 98boot.1: movb LOAD+setdrv-start,%dl # Drive number to use 99boot.2: 100/* 101 * Reload all of boot0 (including the extra sectors) into memory at the 102 * relocation address. 103 */ 104 push %dx # Save drive number 105 movw $start,%bx # Origin we were linked for 106 movw %bp,%si # Fake PTE 107 movw $0x200+NUM_SECTORS,%ax # Read in all 108 callw intx13 # of boot0 109 pop %dx # Restore 110/* 111 * Relocate to the new copy of the code. 112 */ 113 jmp main+ORIGIN-LOAD # To relocated code 114/* 115 * Whatever we decided to use, now store it into the fake 116 * partition entry that lives in the data space above us. 117 */ 118main: movb %dl,_FAKE(%bp) # Save drive number 119 callw putn # To new line 120 pushw %dx # Save drive number 121/* 122 * Start out with a pointer to the 4th byte of the first table entry 123 * so that after 4 iterations it's beyond the end of the sector. 124 * and beyond a 256 byte boundary and has overflowed 8 bits (see next comment). 125 * (remember that the table starts 2 bytes earlier than you would expect 126 * as the bootable flag is after it in the block) 127 */ 128 movw $(partbl+0x4),%bx # Partition table (+4) 129 xorw %dx,%dx # Item number 130/* 131 * Loop around on the partition table, printing values until we 132 * pass a 256 byte boundary. The end of loop test is at main.5. 133 */ 134main.3: movb %ch,-0x4(%bx) # Zero active flag (ch == 0) 135 btw %dx,_FLAGS(%bp) # Entry enabled? 136 jnc main.5 # No 137/* 138 * If any of the entries in the table are 139 * the same as the 'type' in the slice table entry, 140 * then this is an empty or non bootable partition. Skip it. 141 */ 142 movb (%bx),%al # Load type 143 movw $tables,%di # Lookup tables 144 movb $TBL0SZ,%cl # Number of entries 145 repne # Exclude 146 scasb # partition? 147 je main.5 # Yes 148/* 149 * Now scan the table of known types 150 */ 151 movb $TBL1SZ,%cl # Number of entries 152 repne # Known 153 scasb # type? 154 jne main.4 # No 155/* 156 * If it matches get the matching element in the 157 * next array. If it doesn't, we are already 158 * pointing at its first element which points to a "?". 159 */ 160 addw $TBL1SZ,%di # Adjust 161main.4: movb (%di),%cl # Partition 162 addw %cx,%di # description 163 callw putx # Display it 164main.5: incw %dx # Next item 165 addb $0x10,%bl # Next entry 166 jnc main.3 # Till done 167/* 168 * Passed a 256 byte boundary.. 169 * table is finished. 170 * Add one to the drive number and check it is valid, 171 */ 172 popw %ax # Drive number 173 subb $0x80-0x1,%al # Does next 174 cmpb NHRDRV,%al # drive exist? (from BIOS?) 175 jb main.6 # Yes 176/* 177 * If not then if there is only one drive, 178 * Don't display drive as an option. 179 */ 180 decw %ax # Already drive 0? 181 jz main.7 # Yes 182/* 183 * If it was illegal or we cycled through them, 184 * then go back to drive 0. 185 */ 186 xorb %al,%al # Drive 0 187/* 188 * Whatever drive we selected, make it an ascii digit and save it back 189 * to the "next drive" location in the loaded block in case we 190 * want to save it for next time. 191 * This also is part of the printed drive string so add 0x80 to indicate 192 * end of string. 193 */ 194main.6: addb $'0'|0x80,%al # Save next 195 movb %al,_NXTDRV(%bp) # drive number 196 movw $drive,%di # Display 197 callw putx # item 198/* 199 * Now that we've printed the drive (if we needed to), display a prompt. 200 * Get ready for the input by noting the time. 201 */ 202main.7: movw $prompt,%si # Display 203 callw putstr # prompt 204 movb _OPT(%bp),%dl # Display 205 decw %si # default 206 callw putkey # key 207 xorb %ah,%ah # BIOS: Get 208 int $0x1a # system time 209 movw %dx,%di # Ticks when 210 addw _TICKS(%bp),%di # timeout 211/* 212 * Busy loop, looking for keystrokes but 213 * keeping one eye on the time. 214 */ 215main.8: movb $0x1,%ah # BIOS: Check 216 int $0x16 # for keypress 217 jnz main.11 # Have one 218 xorb %ah,%ah # BIOS: Get 219 int $0x1a # system time 220 cmpw %di,%dx # Timeout? 221 jb main.8 # No 222/* 223 * If timed out or defaulting, come here. 224 */ 225main.9: movb _OPT(%bp),%al # Load default 226 jmp main.12 # Join common code 227/* 228 * User's last try was bad, beep in displeasure. 229 * Since nothing was printed, just continue on as if the user 230 * hadn't done anything. This gives the effect of the user getting a beep 231 * for all bad keystrokes but no action until either the timeout 232 * occurs or the user hits a good key. 233 */ 234main.10: movb $0x7,%al # Signal 235 callw putchr # error 236/* 237 * Get the keystroke. 238 */ 239main.11: xorb %ah,%ah # BIOS: Get 240 int $0x16 # keypress 241 movb %ah,%al # Scan code 242/* 243 * If it's CR act as if timed out. 244 */ 245 cmpb $KEY_ENTER,%al # Enter pressed? 246 je main.9 # Yes 247/* 248 * Otherwise check if legal 249 * If not ask again. 250 */ 251 subb $KEY_F1,%al # Less F1 scan code 252 cmpb $0x4,%al # F1..F5? 253 jna main.12 # Yes 254 subb $(KEY_1 - KEY_F1),%al # Less #1 scan code 255 cmpb $0x4,%al # #1..#5? 256 ja main.10 # No 257/* 258 * We have a selection. 259 * but if it's a bad selection go back to complain. 260 * The bits in MNUOPT were set when the options were printed. 261 * Anything not printed is not an option. 262 */ 263main.12: cbtw # Option 264 btw %ax,_MNUOPT(%bp) # enabled? 265 jnc main.10 # No 266/* 267 * Save the info in the original tables 268 * for rewriting to the disk. 269 */ 270 movb %al,_OPT(%bp) # Save option 271 movw $fake,%si # Partition for write 272 movb (%si),%dl # Drive number 273 movw %si,%bx # Partition for read 274 cmpb $0x4,%al # F5/#5 pressed? 275 pushf # Save 276 je main.13 # Yes 277 shlb $0x4,%al # Point to 278 addw $partbl,%ax # selected 279 xchgw %bx,%ax # partition 280 movb $0x80,(%bx) # Flag active 281/* 282 * If not asked to do a write-back (flags 0x40) don't do one. 283 */ 284main.13: pushw %bx # Save 285 testb $FL_NOUPDATE,_FLAGS(%bp) # Skip update? 286 jnz main.14 # Yes 287 movw $start,%bx # Data to write 288 movw $0x301,%ax # Write 1 sector 289 callw intx13 # to disk 290main.14: popw %si # Restore 291 popf # Restore 292/* 293 * If going to next drive, replace drive with selected one. 294 * Remember to un-ascii it. Hey 0x80 is already set, cool! 295 */ 296 jne main.15 # If not F5/#5 297 movb _NXTDRV(%bp),%dl # Next drive 298 subb $'0',%dl # number 299/* 300 * load selected bootsector to the LOAD location in RAM. 301 * If it fails to read or isn't marked bootable, treat it 302 * as a bad selection. 303 */ 304main.15: movw $LOAD,%bx # Address for read 305 movw $0x201,%ax # Read 1 sector 306 callw intx13 # from disk 307 jc main.10 # If error 308 cmpw $MAGIC,0x1fe(%bx) # Bootable? 309 jne main.10 # No 310 callw putn # Leave some space 311 jmp *%bx # Invoke bootstrap 312 313/* 314 * Display routines 315 */ 316 317putkey: movb $'F',%al # Display 318 callw putchr # 'F' 319 movb $'1',%al # Prepare 320 addb %dl,%al # digit 321 jmp putstr.1 # Display the rest 322 323/* 324 * Display the option and note that it is a valid option. 325 * That last point is a bit tricky.. 326 */ 327putx: btsw %dx,_MNUOPT(%bp) # Enable menu option 328 movw $item,%si # Display 329 callw putkey # key 330 movw %di,%si # Display the rest 331 332puts: callw putstr # Display string 333 334putn: movw $crlf,%si # To next line 335 336putstr: lodsb # Get byte 337 testb $0x80,%al # End of string? 338 jnz putstr.2 # Yes 339putstr.1: callw putchr # Display char 340 jmp putstr # Continue 341putstr.2: andb $~0x80,%al # Clear MSB 342 343putchr: pushw %bx # Save 344 movw $0x7,%bx # Page:attribute 345 movb $0xe,%ah # BIOS: Display 346 int $0x10 # character 347 popw %bx # Restore 348 retw # To caller 349 350/* 351 * One-sector disk I/O routine 352 * 353 * Calling conventions: (assumes %si -> partition table entry) 354 * 355 * 0x1(%si) - byte - head 356 * 0x2(%si) - word - cylinder/sector 357 * 0x8(%si) - long - LBA to use if needed 358 * %ah - byte - operation, 2 = read, 3 = write 359 * %al - byte - sector count 360 * %dl - byte - drive number 361 * %es:(%bx) - void - buffer to use for transfer 362 * 363 * If the head == 0xff, and cylinder/sector == 0xffff, then try 364 * to use the EDD stuff with the LBA offset instead of CHS. However, 365 * use CHS if at all possible. 366 */ 367 368intx13: movb 0x1(%si),%dh # Load head 369 movw 0x2(%si),%cx # Load cylinder:sector 370 pushw %si # Save 371 movw %sp,%di # Save 372 cmpb $0xff,%dh # Might we need LBA? 373 jne intx13.2 # No, just use CHS 374 cmpw $0xffff,%cx # Do we need LBA? 375 jne intx13.2 # No 376 testb $FL_PACKET,_FLAGS(%bp) # Try the packet interface? 377 jz intx13.2 # No 378 pushw %cx # Save 379 pushw %bx # Save 380 movw $0x55aa,%bx # Magic 381 pushw %ax # Save 382 movb $0x41,%ah # BIOS: EDD extensions 383 int $0x13 # present? 384 popw %ax # Restore 385 jc intx13.1 # Not present, use CHS 386 cmpw $0xaa55,%bx # Magic? 387 jne intx13.1 # Not present, use CHS 388 testb $0x1,%cl # Packet mode available? 389 jz intx13.1 # No, use CHS 390 orb $0x40,%ah # Use disk packet 391intx13.1: popw %bx # Restore 392 popw %cx # Restore 393 testb $0x40,%ah # Using packet mode? 394 jz intx13.2 # No, so skip the rest 395 pushl $0x0 # Set the 396 pushl 0x8(%si) # LBA address 397 pushw %es # Set the transfer 398 pushw %bx # buffer address 399 push $0x0 # Punch a hole in the stack 400 push $0x10 # Packet size 401 movw %sp,%si # Packet pointer 402 xchgb %al,0x2(%si) # Set the block count in the 403 # packet and zero %al, 404 # turning verify off for writes 405intx13.2: int $0x13 # BIOS: Disk I/O 406 movw %di,%sp # Restore 407 popw %si # Restore 408 retw # To caller 409 410 .org PRT_OFF-0xe,0x90 411/* 412 * These values are sometimes changed before writing back to the drive 413 * Be especially careful that nxtdrv: must come after drive:, as it 414 * is part of the same string. 415 * 416 * Note that the 'drive' string variable is used as the second signature 417 * check in boot0cfg(8). 418 */ 419version_minor: .byte 0x1 # minor version 420version_major: .byte 0x1 # major version 421drive: .ascii "Drive " 422nxtdrv: .byte 0x0 # Next drive number 423opt: .byte 0x0 # Option 424setdrv: .byte 0x80 # Drive to force 425flags: .byte FLAGS # Flags 426ticks: .word TICKS # Delay 427 428/* 429 * here is the 64 byte partition table that fdisk would fiddle with. 430 */ 431partbl: .fill 0x40,0x1,0x0 # Partition table 432 .word MAGIC # Magic number 433 434/* 435 * start of sector two.. ugh 436 */ 437 .org SECTOR_SIZE,0x90 438 439/* Menu strings */ 440 441item: .ascii " "; .byte ' '|0x80 442prompt: .ascii "\nDefault:"; .byte ' '|0x80 443crlf: .ascii "\r"; .byte '\n'|0x80 444 445/* Partition type tables */ 446 447tables: 448/* 449 * These entries identify invalid or NON BOOT types and partitions. 450 */ 451table0: .byte 0x0, 0x5, 0xf 452table0_end: 453/* 454 * These values indicate bootable types we know the names of 455 */ 456table1: .byte 0x1, 0x4, 0x6, 0x7, 0xb, 0xc, 0xe, 0x42, 0x63, 0x83 457 .byte 0x9f, 0xa5, 0xa6, 0xa9 458table1_end: 459/* 460 * These are offsets that match the known names above and point to the strings 461 * that will be printed. 462 */ 463 .byte os_misc-. # Unknown 464 .byte os_dos-. # DOS 465 .byte os_dos-. # DOS 466 .byte os_dos-. # DOS 467 .byte os_nt-. # NT/XP or OS/2 468 .byte os_windows-. # Windows 32-bit FAT 469 .byte os_windows-. # Windows 32-bit FAT ext int 13 470 .byte os_windows-. # Windows 471 .byte os_windows-. # Windows 2000 dyn ext 472 .byte os_unix-. # UNIX 473 .byte os_linux-. # Linux 474 .byte os_bsdos-. # BSD/OS 475 .byte os_freebsd-. # FreeBSD 476 .byte os_openbsd-. # OpenBSD 477 .byte os_netbsd-. # NetBSD 478/* 479 * And here are the strings themselves. 0x80 or'd into a byte indicates 480 * the end of the string. (not so great for Russians but...) 481 */ 482os_misc: .ascii "Unknow"; .byte 'n'|0x80 483os_dos: .ascii "DO"; .byte 'S'|0x80 484os_nt: .ascii "Windows NT/X"; .byte 'P'|0x80 485os_windows: .ascii "Window"; .byte 's'|0x80 486os_unix: .ascii "UNI"; .byte 'X'|0x80 487os_linux: .ascii "Linu"; .byte 'x'|0x80 488os_freebsd: .ascii "FreeBS"; .byte 'D'|0x80 489os_openbsd: .ascii "OpenBS"; .byte 'D'|0x80 490os_netbsd: .ascii "NetBS"; .byte 'D'|0x80 491os_bsdos: .ascii "BSD/O"; .byte 'S'|0x80 492 493/* 494 * Fake partition entry created at the end of the table used when loading 495 * boot0 at the very beginning and when loading an MBR from another disk when 496 * F5 is pressed. 497 */ 498 .org SECTOR_SIZE*NUM_SECTORS, 0x0 499fake: 500