# # Copyright (c) 1998 Robert Nordier # All rights reserved. # # Redistribution and use in source and binary forms are freely # permitted provided that the above copyright notice and this # paragraph and the following disclaimer are duplicated in all # such forms. # # This software is provided "AS IS" and without any express or # implied warranties, including, without limitation, the implied # warranties of merchantability and fitness for a particular # purpose. # # $FreeBSD$ # A 512-byte boot manager. .set NHRDRV,0x475 # Number of hard drives .set ORIGIN,0x600 # Execution address .set FAKE,0x800 # Partition entry .set LOAD,0x7c00 # Load address .set PRT_OFF,0x1be # Partition table .set TBL0SZ,0x3 # Table 0 size .set TBL1SZ,0xb # Table 1 size .set MAGIC,0xaa55 # Magic: bootable .set KEY_ENTER,0x1c # Enter key scan code .set KEY_F1,0x3b # F1 key scan code # # Addresses in the sector of embedded data values. # Accessed with negative offsets from the end of the relocated sector (%ebp). # .set _NXTDRV,-0x48 # Next drive .set _OPT,-0x47 # Default option .set _SETDRV,-0x46 # Drive to force .set _FLAGS,-0x45 # Flags .set _TICKS,-0x44 # Timeout ticks .set _FAKE,0x0 # Fake partition entry .set _MNUOPT,0xc # Menu options .globl start # Entry point # # Initialise segments and registers to known values. # segments start at 0. # The stack is immediatly below the address we were loaded to. # start: cld # String ops inc xorl %eax,%eax # Zero movl %eax,%es # Address movl %eax,%ds # data movl %eax,%ss # Set up movwir(LOAD,_sp) # stack # # Copy this code to the address it was linked for # movl %esp,%esi # Source movwir(start,_di) # Destination movwir(0x100,_cx) # Word count rep # Relocate movsl # code # # Set address for variable space beyond code, and clear it. # Notice that this is also used to point to the values embedded in in the block, # by using negative offsets. # movl %edi,%ebp # Address variables movb $0x8,%cl # Words to clear rep # Zero stosl # them # # Relocate to the new copy of the code. # incb1(-0xe,_di_) # Sector number jmpnwi(main-LOAD+ORIGIN) # To relocated code # # Check what flags were loaded with us, specifically, Use a predefined Drive. # If what the bios gives us is bad, use the '0' in the block instead, as well. # main: tstbi1(0x20,_FLAGS,_bp_) # Set number drive? jnz main.1 # Yes testb %dl,%dl # Drive number valid? js main.2 # Possibly (0x80 set) main.1: movb1r(_SETDRV,_bp_,_dl) # Drive number to use # # Whatever we decided to use, now store it into the fake # partition entry that lives in the data space above us. # main.2: movbr1(_dl,_FAKE,_bp_) # Save drive number callwi(putn) # To new line pushl %edx # Save drive number # # Start out with a pointer to the 4th byte of the first table entry # so that after 4 iterations it's beyond the end of the sector. # and beyond a 256 byte boundary and thos overflowed 8 bits (see next comment). # (remember that the table starts 2 bytes earlier than you would expect # as the bootable flag is after it in the block) # movwir(partbl+0x4,_bx) # Partition table (+4) xorl %edx,%edx # Item number # # Loop around on the partition table, printing values until we # pass a 256 byte boundary. The end of loop test is at main.5. # main.3: movbr1(_ch,-0x4,_bx_) # Zero active flag (ch == 0) btwr1(_dx,_FLAGS,_bp_) # Entry enabled? jnc main.5 # No # # If any of the entries in the table are # the same as the 'type' in the slice table entry, # then this is an empty or non bootable partition. Skip it. # movb0r(_bx_,_al) # Load type movwir(tables,_di) # Lookup tables movb $TBL0SZ,%cl # Number of entries repne # Exclude scasb # partition? je main.5 # Yes # # Now scan the table of known types # movb $TBL1SZ,%cl # Number of entries repne # Known scasb # type? jne main.4 # No # # If it matches get the matching element in the # next array. if it doesn't, we are already # pointing at its first element which points to a "?". # addwir(TBL1SZ,_di) # Adjust main.4: movb0r(_di_,_cl) # Partition addl %ecx,%edi # description callwi(putx) # Display it main.5: incl %edx # Next item addb $0x10,%bl # Next entry jnc main.3 # Till done # # Passed a 256 byte boundary.. # table is finished. # Add one to the drive number and check it is valid, # popl %eax # Drive number subb $0x80-0x1,%al # Does next cmpbmr(NHRDRV,_al) # drive exist? (from BIOS?) jb main.6 # Yes # If not then if there is only one drive, # Don't display drive as an option. # decl %eax # Already drive 0? jz main.7 # Yes # If it was illegal or we cycled through them, # then go back to drive 0. # xorb %al,%al # Drive 0 # # Whatever drive we selected, make it an ascii digit and save it back # to the "next drive" location in the loaded block in case we # want to save it for next time. # This also is part of the printed drive string so add 0x80 to indicate # end of string. # main.6: addb $'0'|0x80,%al # Save next movbr1(_al,_NXTDRV,_bp_) # drive number movwir(drive,_di) # Display callwi(putx) # item # # Now that we've printed the drive (if we needed to), display a prompt. # Get ready for the input byt noting the time. # main.7: movwir(prompt,_si) # Display callwi(putstr) # prompt movb1r(_OPT,_bp_,_dl) # Display decl %esi # default callwi(putkey) # key xorb %ah,%ah # BIOS: Get int $0x1a # system time movl %edx,%edi # Ticks when addw1r(_TICKS,_bp_,_di) # timeout # # Busy loop, looking for keystrokes but # keeping one eye on the time. # main.8: movb $0x1,%ah # BIOS: Check int $0x16 # for keypress jnz main.11 # Have one xorb %ah,%ah # BIOS: Get int $0x1a # system time cmpl %edi,%edx # Timeout? jb main.8 # No # # If timed out or defaulting, come here. # main.9: movb1r(_OPT,_bp_,_al) # Load default jmp main.12 # Join common code # # User's last try was bad, beep in displeasure. # Since nothing was printed, just continue on as if the user # hadn't done anything. This gives the effect of the user getting a beep # for all bad keystrokes but no action until either the timeout # occurs or the user hits a good key. # main.10: movb $0x7,%al # Signal callwi(putchr) # error # # Get the keystroke. # main.11: xorb %ah,%ah # BIOS: Get int $0x16 # keypress movb %ah,%al # Scan code # # If it's CR act as if timed out. # cmpb $KEY_ENTER,%al # Enter pressed? je main.9 # Yes # # Otherwise check if legal # If not ask again. # subb $KEY_F1,%al # Less F1 scan code cmpb $0x4,%al # F1..F5? ja main.10 # No # # We have a selection. # but if it's a bad selection go back to complain. # The bits in MNUOPT were set when the options were printed. # Anything not printed is not an option. # main.12: cwtl # Option btwr1(_ax,_MNUOPT,_bp_) # enabled? jnc main.10 # No # # Save the info in the original tables # for rewriting to the disk. # movbr1(_al,_OPT,_bp_) # Save option movwir(FAKE,_si) # Partition for write movb0r(_si_,_dl) # Drive number movl %esi,%ebx # Partition for read cmpb $0x4,%al # F5 pressed? pushfl # Save je main.13 # Yes shlb $0x4,%al # Point to addwia(partbl) # selected xchgl %ebx,%eax # partition movbi0(0x80,_bx_) # Flag active # # If not asked to do a write-back (flags 0x40) don't do one. # main.13: pushl %ebx # Save tstbi1(0x40,_FLAGS,_bp_) # No updates? jnz main.14 # Yes movwir(start,_bx) # Data to write movb $0x3,%ah # Write sector callwi(intx13) # to disk main.14: popl %esi # Restore popfl # Restore # # If going to next drive, replace drive with selected one. # Remember to un-ascii it. Hey 0x80 is already set, cool! # jne main.15 # If not F5 movb1r(_NXTDRV,_bp_,_dl) # Next drive subb $'0',%dl # number # # load selected bootsector to the LOAD location in RAM. # If it fails to read or isn't marked bootable, treat it # as a bad selection. # XXX what does %esi carry? # main.15: movwir(LOAD,_bx) # Address for read movb $0x2,%ah # Read sector callwi(intx13) # from disk jc main.10 # If error cmpwi2(MAGIC,0x1fe,_bx_) # Bootable? jne main.10 # No pushl %esi # Save movwir(crlf,_si) # Leave some callwi(puts) # space popl %esi # Restore jmp *%ebx # Invoke bootstrap # # Display routines # putkey: movb $'F',%al # Display callwi(putchr) # 'F' movb $'1',%al # Prepare addb %dl,%al # digit jmp putstr.1 # Display the rest # # Display the option and note that it is a valid option. # That last point is a bit tricky.. # putx: btswr1(_dx,_MNUOPT,_bp_) # Enable menu option movwir(item,_si) # Display callwi(putkey) # key movl %edi,%esi # Display the rest puts: callwi(putstr) # Display string putn: movwir(crlf,_si) # To next line putstr: lodsb # Get byte testb $0x80,%al # End of string? jnz putstr.2 # Yes putstr.1: callwi(putchr) # Display char jmp putstr # Continue putstr.2: andb $~0x80,%al # Clear MSB putchr: pushl %ebx # Save movwir(0x7,_bx) # Page:attribute movb $0xe,%ah # BIOS: Display int $0x10 # character popl %ebx # Restore ret # To caller # One-sector disk I/O routine intx13: movb1r(0x1,_si_,_dh) # Load head movw1r(0x2,_si_,_cx) # Load cylinder:sector movb $0x1,%al # Sector count pushl %esi # Save movl %esp,%edi # Save tstbi1(0x80,_FLAGS,_bp_) # Use packet interface? jz intx13.1 # No o16 # Set pushb $0x0 # the o16 # LBA pushw1(0x8,_si_) # address pushl %es # Set the transfer pushl %ebx # buffer address pushb $0x1 # Block count pushb $0x10 # Packet size movl %esp,%esi # Packet pointer decl %eax # Verify off orb $0x40,%ah # Use disk packet intx13.1: int $0x13 # BIOS: Disk I/O movl %edi,%esp # Restore popl %esi # Restore ret # To caller # Menu strings item: .ascii " "; .byte ' '|0x80 prompt: .ascii "\nDefault:"; .byte ' '|0x80 crlf: .ascii "\r"; .byte '\n'|0x80 # Partition type tables tables: # # These entries identify invalid or NON BOOT types and partitions. # .byte 0x0, 0x5, 0xf # # These valuse indicate botable types we know the names of # .byte 0x1, 0x4, 0x6, 0xb, 0xc, 0xe, 0x63, 0x83 .byte 0xa5, 0xa6, 0xa9 # # These are offsets that match the known names above and point to the strings # that will be printed. # .byte os_misc-. # Unknown .byte os_dos-. # DOS .byte os_dos-. # DOS .byte os_dos-. # DOS .byte os_dos-. # Windows .byte os_dos-. # Windows .byte os_dos-. # Windows .byte os_unix-. # UNIX .byte os_linux-. # Linux .byte os_freebsd-. # FreeBSD .byte os_bsd-. # OpenBSD .byte os_bsd-. # NetBSD # # And here are the strings themselves. 0x80 or'd into a byte indicates # the end of the string. (not so great for Russians but...) # os_misc: .ascii "?"; .byte '?'|0x80 os_dos: .ascii "DO"; .byte 'S'|0x80 os_unix: .ascii "UNI"; .byte 'X'|0x80 os_linux: .ascii "Linu"; .byte 'x'|0x80 os_freebsd: .ascii "Free" os_bsd: .ascii "BS"; .byte 'D'|0x80 .org PRT_OFF-0xc,0x90 # # These values are sometimes changed before writing back to the drive # Be especially careful that nxtdrv: must come after drive:, as it # is part of the same string. # drive: .ascii "Drive " nxtdrv: .byte 0x0 # Next drive number opt: .byte 0x0 # Option setdrv: .byte 0x80 # Drive to force flags: .byte FLAGS # Flags ticks: .word TICKS # Delay # # here is the 64 byte partition table that fdisk would fiddle with. # partbl: .fill 0x40,0x1,0x0 # Partition table .word MAGIC # Magic number