boot0.S revision 128722
1128722Sru# 2128722Sru# Copyright (c) 2002 Bruce M. Simpson 3128722Sru# Copyright (c) 1998 Robert Nordier 4128722Sru# All rights reserved. 5128722Sru# 6128722Sru# Redistribution and use in source and binary forms are freely 7128722Sru# permitted provided that the above copyright notice and this 8128722Sru# paragraph and the following disclaimer are duplicated in all 9128722Sru# such forms. 10128722Sru# 11128722Sru# This software is provided "AS IS" and without any express or 12128722Sru# implied warranties, including, without limitation, the implied 13128722Sru# warranties of merchantability and fitness for a particular 14128722Sru# purpose. 15128722Sru# 16128722Sru# $FreeBSD: head/sys/boot/i386/boot0/boot0.S 128722 2004-04-28 20:49:17Z ru $ 17128722Sru# 18128722Sru 19128722Sru# A 512-byte boot manager. 20128722Sru#ifdef SIO 21128722Sru# ... using a serial console on COM1. 22128722Sru#endif /* SIO */ 23128722Sru 24128722Sru .set NHRDRV,0x475 # Number of hard drives 25128722Sru .set ORIGIN,0x600 # Execution address 26128722Sru .set FAKE,0x800 # Partition entry 27128722Sru .set LOAD,0x7c00 # Load address 28128722Sru 29128722Sru .set PRT_OFF,0x1be # Partition table 30128722Sru 31128722Sru .set TBL0SZ,0x3 # Table 0 size 32128722Sru .set TBL1SZ,0xb # Table 1 size 33128722Sru 34128722Sru .set MAGIC,0xaa55 # Magic: bootable 35128722Sru .set B0MAGIC,0xbb66 # Identification 36128722Sru 37128722Sru .set KEY_ENTER,0x1c # Enter key scan code 38128722Sru .set KEY_F1,0x3b # F1 key scan code 39128722Sru .set KEY_1,0x02 # #1 key scan code 40128722Sru 41128722Sru .set ASCII_BEL,0x07 # ASCII code for <BEL> 42128722Sru .set ASCII_CR,0x0D # ASCII code for <CR> 43128722Sru 44128722Sru# 45128722Sru# Addresses in the sector of embedded data values. 46128722Sru# Accessed with negative offsets from the end of the relocated sector (%ebp). 47128722Sru# 48128722Sru .set _NXTDRV,-0x48 # Next drive 49128722Sru .set _OPT,-0x47 # Default option 50128722Sru .set _SETDRV,-0x46 # Drive to force 51128722Sru .set _FLAGS,-0x45 # Flags 52128722Sru .set _TICKS,-0x44 # Timeout ticks 53128722Sru .set _FAKE,0x0 # Fake partition entry 54128722Sru .set _MNUOPT,0xc # Menu options 55128722Sru 56128722Sru .globl start # Entry point 57128722Sru .code16 # This runs in real mode 58128722Sru 59128722Sru# 60128722Sru# Initialise segments and registers to known values. 61128722Sru# segments start at 0. 62128722Sru# The stack is immediately below the address we were loaded to. 63128722Sru# 64128722Srustart: cld # String ops inc 65128722Sru xorw %ax,%ax # Zero 66128722Sru movw %ax,%es # Address 67128722Sru movw %ax,%ds # data 68128722Sru movw %ax,%ss # Set up 69128722Sru movw $LOAD,%sp # stack 70128722Sru 71128722Sru# 72128722Sru# Copy this code to the address it was linked for 73128722Sru# 74128722Sru movw %sp,%si # Source 75128722Sru movw $start,%di # Destination 76128722Sru movw $0x100,%cx # Word count 77128722Sru rep # Relocate 78128722Sru movsw # code 79128722Sru# 80128722Sru# Set address for variable space beyond code, and clear it. 81128722Sru# Notice that this is also used to point to the values embedded in the block, 82128722Sru# by using negative offsets. 83128722Sru# 84128722Sru movw %di,%bp # Address variables 85128722Sru movb $0x8,%cl # Words to clear 86128722Sru rep # Zero 87128722Sru stosw # them 88128722Sru# 89128722Sru# Relocate to the new copy of the code. 90128722Sru# 91128722Sru incb -0xe(%di) # Sector number 92128722Sru jmp main-LOAD+ORIGIN # To relocated code 93128722Sru 94128722Srumain: 95128722Sru#ifdef SIO 96128722Sru# 97128722Sru# Initialize the serial port. 98128722Sru# Must save DX (contains drive number) 99128722Sru# 100128722Sru pushw %dx # Save 101128722Sru xorw %dx,%dx # Port: COM1 102128722Sru movb COMSPEED,%al # defined by Makefile 103128722Sru movb $0x00,%ah # BIOS: Set COM Port 104128722Sru int $0x14 # Parameters 105128722Sru popw %dx # Restore 106128722Sru#endif /* SIO */ 107128722Sru# 108128722Sru# Check what flags were loaded with us, specifically, Use a predefined Drive. 109128722Sru# If what the bios gives us is bad, use the '0' in the block instead, as well. 110128722Sru# 111128722Sru testb $0x20,_FLAGS(%bp) # Set number drive? 112128722Sru jnz main.1 # Yes 113128722Sru testb %dl,%dl # Drive number valid? 114128722Sru js main.2 # Possibly (0x80 set) 115128722Srumain.1: movb _SETDRV(%bp),%dl # Drive number to use 116128722Sru# 117128722Sru# Whatever we decided to use, now store it into the fake 118128722Sru# partition entry that lives in the data space above us. 119128722Sru# 120128722Srumain.2: movb %dl,_FAKE(%bp) # Save drive number 121128722Sru callw putn # To new line 122128722Sru pushw %dx # Save drive number 123128722Sru# 124128722Sru# Start out with a pointer to the 4th byte of the first table entry 125128722Sru# so that after 4 iterations it's beyond the end of the sector. 126128722Sru# and beyond a 256 byte boundary and has overflowed 8 bits (see next comment). 127128722Sru# (remember that the table starts 2 bytes earlier than you would expect 128128722Sru# as the bootable flag is after it in the block) 129128722Sru# 130128722Sru movw $(partbl+0x4),%bx # Partition table (+4) 131128722Sru xorw %dx,%dx # Item number 132128722Sru# 133128722Sru# Loop around on the partition table, printing values until we 134128722Sru# pass a 256 byte boundary. The end of loop test is at main.5. 135128722Sru# 136128722Srumain.3: movb %ch,-0x4(%bx) # Zero active flag (ch == 0) 137128722Sru btw %dx,_FLAGS(%bp) # Entry enabled? 138128722Sru jnc main.5 # No 139128722Sru# 140128722Sru# If any of the entries in the table are 141128722Sru# the same as the 'type' in the slice table entry, 142128722Sru# then this is an empty or non bootable partition. Skip it. 143128722Sru# 144128722Sru movb (%bx),%al # Load type 145128722Sru movw $tables,%di # Lookup tables 146128722Sru movb $TBL0SZ,%cl # Number of entries 147128722Sru repne # Exclude 148128722Sru scasb # partition? 149128722Sru je main.5 # Yes 150128722Sru# 151128722Sru# Now scan the table of known types 152128722Sru# 153128722Sru movb $TBL1SZ,%cl # Number of entries 154128722Sru repne # Known 155128722Sru scasb # type? 156128722Sru jne main.4 # No 157128722Sru# 158128722Sru# If it matches get the matching element in the 159128722Sru# next array. if it doesn't, we are already 160128722Sru# pointing at its first element which points to a "?". 161128722Sru# 162128722Sru addw $TBL1SZ,%di # Adjust 163128722Srumain.4: movb (%di),%cl # Partition 164128722Sru addw %cx,%di # description 165128722Sru callw putx # Display it 166128722Srumain.5: incw %dx # Next item 167128722Sru addb $0x10,%bl # Next entry 168128722Sru jnc main.3 # Till done 169128722Sru# 170128722Sru# Passed a 256 byte boundary.. 171128722Sru# table is finished. 172128722Sru# Add one to the drive number and check it is valid, 173128722Sru# 174128722Sru popw %ax # Drive number 175128722Sru subb $0x80-0x1,%al # Does next 176128722Sru cmpb NHRDRV,%al # drive exist? (from BIOS?) 177128722Sru jb main.6 # Yes 178128722Sru# 179128722Sru# If not then if there is only one drive, 180128722Sru# Don't display drive as an option. 181128722Sru# 182128722Sru decw %ax # Already drive 0? 183128722Sru jz main.7 # Yes 184128722Sru# 185128722Sru# If it was illegal or we cycled through them, 186128722Sru# then go back to drive 0. 187128722Sru# 188128722Sru xorb %al,%al # Drive 0 189128722Sru# 190128722Sru# Whatever drive we selected, make it an ascii digit and save it back 191128722Sru# to the "next drive" location in the loaded block in case we 192128722Sru# want to save it for next time. 193128722Sru# This also is part of the printed drive string so add 0x80 to indicate 194128722Sru# end of string. 195128722Sru# 196128722Srumain.6: addb $'0'|0x80,%al # Save next 197128722Sru movb %al,_NXTDRV(%bp) # drive number 198128722Sru movw $drive,%di # Display 199128722Sru callw putx # item 200128722Sru# 201128722Sru# Now that we've printed the drive (if we needed to), display a prompt. 202128722Sru# Get ready for the input by noting the time. 203128722Sru# 204128722Srumain.7: movw $prompt,%si # Display 205128722Sru callw putstr # prompt 206128722Sru movb _OPT(%bp),%dl # Display 207128722Sru decw %si # default 208128722Sru callw putkey # key 209128722Srumain.7_1: 210128722Sru xorb %ah,%ah # BIOS: Get 211128722Sru int $0x1a # system time 212128722Sru#ifndef SIO 213128722Sru movw %dx,%di # Ticks when 214128722Sru addw _TICKS(%bp),%di # timeout 215128722Sru#else /* SIO */ 216128722Sru movw %dx,%si # Ticks when 217128722Sru addw _TICKS(%bp),%si # timeout 218128722Sru#endif /* SIO */ 219128722Sru# 220128722Sru# Busy loop, looking for keystrokes but 221128722Sru# keeping one eye on the time. 222128722Sru# 223128722Srumain.8: 224128722Sru#ifndef SIO 225128722Sru movb $0x1,%ah # BIOS: Check 226128722Sru int $0x16 # for keypress 227128722Sru jnz main.11 # Have one 228128722Sru#else /* SIO */ 229128722Sru xorw %dx,%dx # Use COM1 230128722Sru movb $0x03,%ah # BIOS: Read COM 231128722Sru int $0x14 # Status 232128722Sru testb $0x01,%ah # Check line status 233128722Sru jnz main.11 # (bit 1 indicates input) 234128722Sru#endif /* SIO */ 235128722Sru xorb %ah,%ah # BIOS: Get 236128722Sru int $0x1a # system time 237128722Sru#ifndef SIO 238128722Sru cmpw %di,%dx # Timeout? 239128722Sru#else /* SIO */ 240128722Sru cmpw %si,%dx # Timeout? 241128722Sru#endif /* SIO */ 242128722Sru jb main.8 # No 243128722Sru# 244128722Sru# If timed out or defaulting, come here. 245128722Sru# 246128722Srumain.9: movb _OPT(%bp),%al # Load default 247128722Sru jmp main.12 # Join common code 248128722Sru# 249128722Sru# User's last try was bad, beep in displeasure. 250128722Sru# Since nothing was printed, just continue on as if the user 251128722Sru# hadn't done anything. This gives the effect of the user getting a beep 252128722Sru# for all bad keystrokes but no action until either the timeout 253128722Sru# occurs or the user hits a good key. 254128722Sru# 255128722Srumain.10: movb $ASCII_BEL,%al # Signal 256128722Sru callw putchr # error 257128722Sru#ifdef SIO 258128722Sru jmp main.7_1 # Go back 259128722Sru#endif /* SIO */ 260128722Sru# 261128722Sru# Get the keystroke. 262128722Sru# 263128722Srumain.11: 264128722Sru#ifndef SIO 265128722Sru xorb %ah,%ah # BIOS: Get 266128722Sru int $0x16 # keypress 267128722Sru movb %ah,%al # Scan code 268128722Sru#else /* SIO */ 269128722Sru movb $0x02,%ah # BIOS: Receive 270128722Sru int $0x14 # COM Byte 271128722Sru#endif /* SIO */ 272128722Sru# 273128722Sru# If it's CR act as if timed out. 274128722Sru# 275128722Sru#ifndef SIO 276128722Sru cmpb $KEY_ENTER,%al # Enter pressed? 277128722Sru#else /* SIO */ 278128722Sru cmpb $ASCII_CR,%al # Enter pressed? 279128722Sru#endif /* SIO */ 280128722Sru je main.9 # Yes 281128722Sru# 282128722Sru# Otherwise check if legal 283128722Sru# If not ask again. 284128722Sru# 285128722Sru#ifndef SIO 286128722Sru subb $KEY_F1,%al # Less F1 scan code 287128722Sru cmpb $0x4,%al # F1..F5? 288128722Sru jna main.12 # Yes 289128722Sru subb $(KEY_1 - KEY_F1),%al # Less #1 scan code 290128722Sru#else /* SIO */ 291128722Sru subb $'1',%al # Less '1' ascii character 292128722Sru#endif /* SIO */ 293128722Sru cmpb $0x4,%al # #1..#5? 294128722Sru ja main.10 # No 295128722Sru# 296128722Sru# We have a selection. 297128722Sru# but if it's a bad selection go back to complain. 298128722Sru# The bits in MNUOPT were set when the options were printed. 299128722Sru# Anything not printed is not an option. 300128722Sru# 301128722Srumain.12: cbtw # Option 302128722Sru btw %ax,_MNUOPT(%bp) # enabled? 303128722Sru jnc main.10 # No 304128722Sru# 305128722Sru# Save the info in the original tables 306128722Sru# for rewriting to the disk. 307128722Sru# 308128722Sru movb %al,_OPT(%bp) # Save option 309128722Sru movw $FAKE,%si # Partition for write 310128722Sru movb (%si),%dl # Drive number 311128722Sru movw %si,%bx # Partition for read 312128722Sru cmpb $0x4,%al # F5/#5 pressed? 313128722Sru pushf # Save 314128722Sru je main.13 # Yes 315128722Sru shlb $0x4,%al # Point to 316128722Sru addw $partbl,%ax # selected 317128722Sru xchgw %bx,%ax # partition 318128722Sru movb $0x80,(%bx) # Flag active 319128722Sru# 320128722Sru# If not asked to do a write-back (flags 0x40) don't do one. 321128722Sru# 322128722Srumain.13: pushw %bx # Save 323128722Sru testb $0x40,_FLAGS(%bp) # No updates? 324128722Sru jnz main.14 # Yes 325128722Sru movw $start,%bx # Data to write 326128722Sru movb $0x3,%ah # Write sector 327128722Sru callw intx13 # to disk 328128722Srumain.14: popw %si # Restore 329128722Sru popf # Restore 330128722Sru# 331128722Sru# If going to next drive, replace drive with selected one. 332128722Sru# Remember to un-ascii it. Hey 0x80 is already set, cool! 333128722Sru# 334128722Sru jne main.15 # If not F5/#5 335128722Sru movb _NXTDRV(%bp),%dl # Next drive 336128722Sru subb $'0',%dl # number 337128722Sru# 338128722Sru# load selected bootsector to the LOAD location in RAM. 339128722Sru# If it fails to read or isn't marked bootable, treat it 340128722Sru# as a bad selection. 341128722Sru# XXX what does %si carry? 342128722Sru# 343128722Srumain.15: movw $LOAD,%bx # Address for read 344128722Sru movb $0x2,%ah # Read sector 345128722Sru callw intx13 # from disk 346128722Sru jc main.10 # If error 347128722Sru cmpw $MAGIC,0x1fe(%bx) # Bootable? 348128722Sru jne main.10 # No 349128722Sru pushw %si # Save 350128722Sru movw $crlf,%si # Leave some 351128722Sru callw puts # space 352128722Sru popw %si # Restore 353128722Sru jmp *%bx # Invoke bootstrap 354128722Sru 355128722Sru# 356128722Sru# Display routines 357128722Sru# 358128722Sruputkey: 359128722Sru#ifndef SIO 360128722Sru movb $'F',%al # Display 361128722Sru callw putchr # 'F' 362128722Sru#endif /* SIO */ 363128722Sru movb $'1',%al # Prepare 364128722Sru addb %dl,%al # digit 365128722Sru jmp putstr.1 # Display the rest 366128722Sru 367128722Sru# 368128722Sru# Display the option and note that it is a valid option. 369128722Sru# That last point is a bit tricky.. 370128722Sru# 371128722Sruputx: btsw %dx,_MNUOPT(%bp) # Enable menu option 372128722Sru movw $item,%si # Display 373128722Sru callw putkey # key 374128722Sru movw %di,%si # Display the rest 375128722Sru 376128722Sruputs: callw putstr # Display string 377128722Sru 378128722Sruputn: movw $crlf,%si # To next line 379128722Sru 380128722Sruputstr: lodsb # Get byte 381128722Sru testb $0x80,%al # End of string? 382128722Sru jnz putstr.2 # Yes 383128722Sruputstr.1: callw putchr # Display char 384128722Sru jmp putstr # Continue 385128722Sruputstr.2: andb $~0x80,%al # Clear MSB 386128722Sru 387128722Sruputchr: 388128722Sru#ifndef SIO 389128722Sru pushw %bx # Save 390128722Sru movw $0x7,%bx # Page:attribute 391128722Sru movb $0xe,%ah # BIOS: Display 392128722Sru int $0x10 # character 393128722Sru popw %bx # Restore 394128722Sru#else /* SIO */ 395128722Sru pushw %dx # Save 396128722Sru xorw %dx,%dx # Use COM1 397128722Sru xorw %cx,%cx # No timeout 398128722Sru movb $0x01,%ah # BIOS: Send 399128722Sru int $0x14 # Character 400128722Sru popw %dx # Restore 401128722Sru#endif /* SIO */ 402128722Sru retw # To caller 403128722Sru 404128722Sru# One-sector disk I/O routine 405128722Sru 406128722Sruintx13: movb 0x1(%si),%dh # Load head 407128722Sru movw 0x2(%si),%cx # Load cylinder:sector 408128722Sru movb $0x1,%al # Sector count 409128722Sru pushw %si # Save 410128722Sru movw %sp,%di # Save 411128722Sru testb $0x80,_FLAGS(%bp) # Use packet interface? 412128722Sru jz intx13.1 # No 413128722Sru pushl $0x0 # Set the 414128722Sru pushl 0x8(%si) # LBA address 415128722Sru pushw %es # Set the transfer 416128722Sru pushw %bx # buffer address 417128722Sru push $0x1 # Block count 418128722Sru push $0x10 # Packet size 419128722Sru movw %sp,%si # Packet pointer 420128722Sru decw %ax # Verify off 421128722Sru orb $0x40,%ah # Use disk packet 422128722Sruintx13.1: int $0x13 # BIOS: Disk I/O 423128722Sru movw %di,%sp # Restore 424128722Sru popw %si # Restore 425128722Sru retw # To caller 426128722Sru 427128722Sru# Menu strings 428128722Sru 429128722Sru#ifndef SIO 430128722Sruitem: .ascii " "; .byte ' '|0x80 431128722Sruprompt: .ascii "\nDefault:"; .byte ' '|0x80 432128722Sru#else /* SIO */ 433128722Sruitem: .ascii " "; .byte ' '|0x80 434128722Sruprompt: .ascii "\nDef:"; .byte ' '|0x80 435128722Sru#endif /* SIO */ 436128722Srucrlf: .ascii "\r"; .byte '\n'|0x80 437128722Sru 438128722Sru# Partition type tables 439128722Sru 440128722Srutables: 441128722Sru# 442128722Sru# These entries identify invalid or NON BOOT types and partitions. 443128722Sru# 444128722Sru .byte 0x0, 0x5, 0xf 445128722Sru# 446128722Sru# These values indicate bootable types we know the names of 447128722Sru# 448128722Sru .byte 0x1, 0x4, 0x6, 0xb, 0xc, 0xe, 0x83 449128722Sru .byte 0x9f, 0xa5, 0xa6, 0xa9 450128722Sru# 451128722Sru# These are offsets that match the known names above and point to the strings 452128722Sru# that will be printed. 453128722Sru# 454128722Sru .byte os_misc-. # Unknown 455128722Sru .byte os_dos-. # DOS 456128722Sru .byte os_dos-. # DOS 457128722Sru .byte os_dos-. # DOS 458128722Sru .byte os_dos-. # Windows 459128722Sru .byte os_dos-. # Windows 460128722Sru .byte os_dos-. # Windows 461128722Sru .byte os_linux-. # Linux 462128722Sru .byte os_bsd-. # BSD/OS 463128722Sru .byte os_freebsd-. # FreeBSD 464128722Sru .byte os_bsd-. # OpenBSD 465128722Sru .byte os_bsd-. # NetBSD 466128722Sru# 467128722Sru# And here are the strings themselves. 0x80 or'd into a byte indicates 468128722Sru# the end of the string. (not so great for Russians but...) 469128722Sru# 470128722Sruos_misc: .ascii "?"; .byte '?'|0x80 471128722Sruos_dos: .ascii "DO"; .byte 'S'|0x80 472128722Sruos_linux: .ascii "Linu"; .byte 'x'|0x80 473128722Sruos_freebsd: .ascii "Free" 474128722Sruos_bsd: .ascii "BS"; .byte 'D'|0x80 475128722Sru 476128722Sru .org PRT_OFF-0xe,0x90 477128722Sru 478128722Sru .word B0MAGIC # Magic number 479128722Sru 480128722Sru# 481128722Sru# These values are sometimes changed before writing back to the drive 482128722Sru# Be especially careful that nxtdrv: must come after drive:, as it 483128722Sru# is part of the same string. 484128722Sru# 485128722Srudrive: .ascii "Drive " 486128722Srunxtdrv: .byte 0x0 # Next drive number 487128722Sruopt: .byte 0x0 # Option 488128722Srusetdrv: .byte 0x80 # Drive to force 489128722Sruflags: .byte FLAGS # Flags 490128722Sruticks: .word TICKS # Delay 491128722Sru 492128722Sru# 493128722Sru# here is the 64 byte partition table that fdisk would fiddle with. 494128722Sru# 495128722Srupartbl: .fill 0x40,0x1,0x0 # Partition table 496128722Sru .word MAGIC # Magic number 497