diff --git a/sys/boot/i386/boot0/boot0.s b/sys/boot/i386/boot0/boot0.s index 00c63914604a..69146c2c1159 100644 --- a/sys/boot/i386/boot0/boot0.s +++ b/sys/boot/i386/boot0/boot0.s @@ -1,5 +1,8 @@ # -# Copyright (c) 1998 Robert Nordier +# Copyright (c) 1998 Robert NordierSince 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. # All rights reserved. # # Redistribution and use in source and binary forms are freely @@ -32,6 +35,10 @@ .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 @@ -42,65 +49,134 @@ .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 + 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 - movwir(partbl+0x4,_bx) # Partition table +# +# 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 -main.3: movbr1(_ch,-0x4,_bx_) # Zero active flag +# +# 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 +main.4: movb0r(_di_,_cl) # Partition addl %ecx,%edi # description callwi(putx) # Display it -main.5: incl %edx # Next item +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? + 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 @@ -110,6 +186,10 @@ main.7: movwir(prompt,_si) # Display 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 @@ -117,21 +197,51 @@ main.8: movb $0x1,%ah # BIOS: Check 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 @@ -143,6 +253,9 @@ main.12: cwtl # Option 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 @@ -151,9 +264,19 @@ main.13: pushl %ebx # Save 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 @@ -166,7 +289,9 @@ main.15: movwir(LOAD,_bx) # Address for read popl %esi # Restore jmp *%ebx # Invoke bootstrap +# # Display routines +# putkey: movb $'F',%al # Display callwi(putchr) # 'F' @@ -174,6 +299,10 @@ putkey: movb $'F',%al # Display 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 @@ -231,11 +360,19 @@ 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 @@ -248,7 +385,10 @@ tables: .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 @@ -257,7 +397,11 @@ 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 @@ -265,5 +409,8 @@ 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