Go back to occupying just a single sector, reverting r1.17 - r1.20.

Taking over the sector following the MBR causes problems on some
machines, and the actual gains are fairly small in terms of how
the space is presently used.

Since we need a number of further features (eg. handling extended
partitions) that can't be readily accommodated in the basic boot0
design anyway, rather choose to implement the additional stuff
separately and concentrate on compatibility rather than features
here.

2 files changed, 82 insertions, 166 deletions

diff --git a/sys/boot/i386/boot0/Makefile b/sys/boot/i386/boot0/Makefile
index 429a62c..4d3f006 100644
--- a/sys/boot/i386/boot0/Makefile
+++ b/sys/boot/i386/boot0/Makefile
@@ -10,33 +10,23 @@ BINMODE=	444
 
 M4?=	m4
 
-# The default set of flags compiled into boot0.  This enables update (writing
-# the modified boot0 back to disk after running so that the selection made is
-# saved), packet mode (detect and use the BIOS EDD extensions if we try to
-# boot past the 1024 cylinder liimt), and booting from all valid slices.
-BOOT_BOOT0_FLAGS?=	0x8f
+B0FLAGS=0xf
+B0TICKS=0xb6
 
-# The number of timer ticks to wait for a keypress before assuming the default
-# selection.  Since there are 18.2 ticks per second, the default value of
-# 0xb6 (182d) corresponds to 10 seconds.
-BOOT_BOOT0_TICKS?=	0xb6
-
-# The base address that we the boot0 code to to run it.  Don't change this
-# unless you are glutton for punishment.
-BOOT_BOOT0_ORG?=	0x600
+ORG=	0x600
 
 boot0: boot0.o
 .if ${OBJFORMAT} == aout
-	${LD} -N -s -T ${BOOT_BOOT0_ORG} -o boot0.out boot0.o
+	${LD} -N -s -T ${ORG} -o boot0.out boot0.o
 	dd if=boot0.out of=${.TARGET} ibs=32 skip=1
 .else
-	${LD} -N -e start -Ttext ${BOOT_BOOT0_ORG} -o boot0.out boot0.o
+	${LD} -N -e start -Ttext ${ORG} -o boot0.out boot0.o
 	objcopy -S -O binary boot0.out ${.TARGET}
 .endif
 
 boot0.o: boot0.s
-	${AS} ${AFLAGS} --defsym FLAGS=${BOOT_BOOT0_FLAGS} \
-		--defsym TICKS=${BOOT_BOOT0_TICKS} ${.IMPSRC} -o ${.TARGET}
+	${AS} ${AFLAGS} --defsym FLAGS=${B0FLAGS} --defsym TICKS=${B0TICKS} \
+		${.IMPSRC} -o ${.TARGET}
 
 CLEANFILES+= boot0.out boot0.o
 
diff --git a/sys/boot/i386/boot0/boot0.s b/sys/boot/i386/boot0/boot0.s
index 90c0e5c..5c2eca2 100644
--- a/sys/boot/i386/boot0/boot0.s
+++ b/sys/boot/i386/boot0/boot0.s
@@ -15,20 +15,17 @@
 
 # $FreeBSD$
 
-# A 1024-byte boot manager.
+# A 512-byte boot manager.
 
 		.set NHRDRV,0x475		# Number of hard drives
 		.set ORIGIN,0x600		# Execution address
-		.set SECTOR_SIZE,0x200		# Length of a sector
-		.set NUM_SECTORS,2		# Total length in sectors
-
-		.set FAKE,ORIGIN+(SECTOR_SIZE*NUM_SECTORS) # Partition entry
+		.set FAKE,0x800 		# Partition entry
 		.set LOAD,0x7c00		# Load address
 
 		.set PRT_OFF,0x1be		# Partition table
 
-		.set TBL0SZ,table0_end-table0	# Table 0 size
-		.set TBL1SZ,table1_end-table1	# Table 1 size
+		.set TBL0SZ,0x3 		# Table 0 size
+		.set TBL1SZ,0xc 		# Table 1 size
 
 		.set MAGIC,0xaa55		# Magic: bootable
 
@@ -36,21 +33,14 @@
 		.set KEY_F1,0x3b		# F1 key scan code
 
 #
-# Flag bits
-#
-		.set FL_PACKET,0x80		# Packet mode
-		.set FL_NOUPDATE,0x40		# Don't save selection
-		.set FL_SETDRV,0x20		# Override drive number
-#
 # Addresses in the sector of embedded data values.
-# Accessed with negative offsets from the end of the relocated sectors (%bp).
-#
-		.set _PRT_END,(FAKE-(ORIGIN+SECTOR_SIZE))
-		.set _NXTDRV,-(_PRT_END+0x48)	# Next drive
-		.set _OPT,-(_PRT_END+0x47)	# Default option
-		.set _SETDRV,-(_PRT_END+0x46)	# Drive to force
-		.set _FLAGS,-(_PRT_END+0x45)	# Flags
-		.set _TICKS,-(_PRT_END+0x44)	# Timeout ticks
+# 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
 
@@ -62,48 +52,40 @@
 # segments start at 0.
 # The stack is immediately below the address we were loaded to.
 #
-# Note that this section of code is used as the first signature check in
-# boot0cfg(8).
-#
 start:		cld				# String ops inc
 		xorw %ax,%ax			# Zero
 		movw %ax,%es			# Address
 		movw %ax,%ds			#  data
 		movw %ax,%ss			# Set up
 		movw $LOAD,%sp			#  stack
-# 
-# End signature code
-# 
+	
+#
+# Copy this code to the address it was linked for
+#
+		movw %sp,%si			# Source
+		movw $start,%di			# Destination
+		movw $0x100,%cx			# Word count
+		rep				# Relocate
+		movsw				#  code
 #
 # Set address for variable space beyond code, and clear it.
 # Notice that this is also used to point to the values embedded in the block,
 # by using negative offsets.
 #
-		movw $fake,%bp			# Address variables
-		movw %bp,%di			# %di used in stosw
-		movw $0x8,%cx			# Words to clear
+		movw %di,%bp			# Address variables
+		movb $0x8,%cl			# Words to clear
 		rep				# Zero
 		stosw				#  them
-		incb -0xe(%di)			# Sector number 1
-#
-# Reload all of boot0 (including the extra sectors) into memory at the
-# relocation address.  
-#
-		push %dx			# Save drive number
-		movw $start,%bx			# Origin we were linked for
-		movw %bp,%si			# Fake PTE
-		movw $0x200+NUM_SECTORS,%ax	# Read in all
-		callw intx13			#  of boot0
-		pop %dx				# Restore
 #
 # Relocate to the new copy of the code.
 #
-		jmp main+ORIGIN-LOAD		# To relocated code
+		incb -0xe(%di)			# Sector number
+		jmp main-LOAD+ORIGIN		# To relocated code
 #
-# Check what flags were loaded with us; specifically, use a predefined Drive.
+# 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:		testb $FL_SETDRV,_FLAGS(%bp)	# Set number drive?
+main:		testb $0x20,_FLAGS(%bp)	# Set number drive?
 		jnz main.1			# Yes
 		testb %dl,%dl			# Drive number valid?
 		js main.2			# Possibly (0x80 set)
@@ -151,7 +133,7 @@ main.3: 	movb %ch,-0x4(%bx)		# Zero active flag (ch == 0)
 		jne main.4			# No
 #
 # If it matches get the matching element in the
-# next array.  If it doesn't, we are already
+# next array. if it doesn't, we are already
 # pointing at its first element which points to a "?".
 #
 		addw $TBL1SZ,%di		# Adjust
@@ -192,7 +174,7 @@ main.6: 	addb $'0'|0x80,%al		# Save next
 		callw putx			#  item
 #
 # Now that we've printed the drive (if we needed to), display a prompt.
-# Get ready for the input by noting the time.
+# Get ready for the input byt noting the time.
 #
 main.7: 	movw $prompt,%si		# Display
 		callw putstr			#  prompt
@@ -260,7 +242,7 @@ main.12:	cbtw				# Option
 # for rewriting to the disk.
 #
 		movb %al,_OPT(%bp)		# Save option
-		movw $fake,%si			# Partition for write
+		movw $FAKE,%si			# Partition for write
 		movb (%si),%dl			# Drive number
 		movw %si,%bx			# Partition for read
 		cmpb $0x4,%al			# F5 pressed?
@@ -274,10 +256,10 @@ main.12:	cbtw				# Option
 # If not asked to do a write-back (flags 0x40) don't do one.
 #
 main.13:	pushw %bx			# Save
-		testb $FL_NOUPDATE,_FLAGS(%bp)	# Skip update?
+		testb $0x40,_FLAGS(%bp)		# No updates?
 		jnz main.14			# Yes
 		movw $start,%bx			# Data to write
-		movw $0x301,%ax			# Write 1 sector
+		movb $0x3,%ah			# Write sector
 		callw intx13			#  to disk
 main.14:	popw %si			# Restore
 		popf				# Restore
@@ -292,16 +274,19 @@ main.14:	popw %si			# Restore
 # 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 %si carry?
 #
 main.15:	movw $LOAD,%bx			# Address for read
-		movw $0x201,%ax			# Read 1 sector
+		movb $0x2,%ah			# Read sector
 		callw intx13			#  from disk
 		jc main.10			# If error
 		cmpw $MAGIC,0x1fe(%bx)		# Bootable?
 		jne main.10			# No
-		callw putn			# Leave some space
+		pushw %si			# Save
+		movw $crlf,%si			# Leave some
+		callw puts			#  space
+		popw %si			# Restore
 		jmp *%bx			# Invoke bootstrap
-
 #
 # Display routines
 #
@@ -340,91 +325,28 @@ putchr: 	pushw %bx			# Save
 		retw				# To caller
 
 # One-sector disk I/O routine
-#
-# Calling conventions: (assumes %si -> partition table entry)
-#
-# 0x1(%si)	- byte - head
-# 0x2(%si)	- word - cylinder/sector
-# 0x8(%si)	- long - LBA to use if needed
-# %ah		- byte - operation, 2 = read, 3 = write
-# %al		- byte - sector count
-# %dl		- byte - drive number
-# %es:(%bx)	- void - buffer to use for transfer
-#
-# If the head == 0xff, and cylinder/sector == 0xffff, then try
-# to use the EDD stuff with the LBA offset instead of CHS.  However,
-# use CHS if at all possible.
 
 intx13: 	movb 0x1(%si),%dh		# Load head
 		movw 0x2(%si),%cx		# Load cylinder:sector
+		movb $0x1,%al			# Sector count
 		pushw %si			# Save
 		movw %sp,%di			# Save
-		cmpb $0xff,%dh			# Might we need LBA?
-		jne intx13.2			# No, just use CHS
-		cmpw $0xffff,%cx		# Do we need LBA?
-		jne intx13.2			# No
-		testb $FL_PACKET,_FLAGS(%bp)	# Try the packet interface?
-		jz intx13.2			# No
-		pushw %cx			# Save
-		pushw %bx			# Save
-		movw $0x55aa,%bx		# Magic
-		pushw %ax			# Save
-		movb $0x41,%ah			# BIOS: EDD extensions
-		int $0x13			#  present?
-		popw %ax			# Restore
-		jc intx13.1			# Not present, use CHS
-		cmpw $0xaa55,%bx		# Magic?
-		jne intx13.1			# Not present, use CHS
-		testb $0x1,%cl			# Packet mode available?
-		jz intx13.1			# No, use CHS
-		orb $0x40,%ah			# Use disk packet
-intx13.1:	popw %bx			# Restore
-		popw %cx			# Restore
-		testb $0x40,%ah			# Using packet mode?
-		jz intx13.2			# No, so skip the rest
+		testb $0x80,_FLAGS(%bp)		# Use packet interface?
+		jz intx13.1			# No
 		pushl $0x0			# Set the
 		pushl 0x8(%si)			# LBA address
 		pushw %es			# Set the transfer
 		pushw %bx			#  buffer address
-		push $0x0			# Punch a hole in the stack
-		push $0x10			# Packet size
+		push  $0x1			# Block count
+		push  $0x10			# Packet size
 		movw %sp,%si			# Packet pointer
-		xchgb %al,0x2(%si)		# Set the block count in the
-						#  packet and zero %al,
-						#  turning verify off for writes
-intx13.2:	int $0x13			# BIOS: Disk I/O
+		decw %ax			# Verify off
+		orb $0x40,%ah			# Use disk packet
+intx13.1:	int $0x13			# BIOS: Disk I/O
 		movw %di,%sp			# Restore
 		popw %si			# Restore
 		retw				# To caller
 
-		.org PRT_OFF-0xe,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.
-#
-# Note that the 'drive' string variable is used as the second signature
-# check in boot0cfg(8).
-#
-version_minor:	.byte 0x1			# minor version
-version_major:	.byte 0x1			# major version	
-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
-
-#
-# start of sector two.. ugh
-#
-		.org SECTOR_SIZE,0x90
 # Menu strings
 
 item:		.ascii "  ";	     .byte ' '|0x80
@@ -437,14 +359,12 @@ tables:
 #
 # These entries identify invalid or NON BOOT types and partitions.
 #
-table0:		.byte 0x0, 0x5, 0xf
-table0_end:
+		.byte 0x0, 0x5, 0xf
 #
 # These values indicate bootable types we know the names of
 #
-table1:		.byte 0x1, 0x4, 0x6, 0x7, 0xb, 0xc, 0xe, 0x63, 0x83
+		.byte 0x1, 0x4, 0x6, 0xb, 0xc, 0xe, 0x63, 0x83
 		.byte 0x9f, 0xa5, 0xa6, 0xa9
-table1_end:
 #
 # These are offsets that match the known names above and point to the strings
 # that will be printed.
@@ -453,35 +373,41 @@ table1_end:
 		.byte os_dos-.			# DOS
 		.byte os_dos-.			# DOS
 		.byte os_dos-.			# DOS
-		.byte os_nt-.			# NT or OS/2
-		.byte os_windows-.		# Windows
-		.byte os_windows-.		# Windows
-		.byte os_windows-.		# Windows
+		.byte os_dos-.			# Windows
+		.byte os_dos-.			# Windows
+		.byte os_dos-.			# Windows
 		.byte os_unix-. 		# UNIX
 		.byte os_linux-.		# Linux
-		.byte os_bsdos-.		# BSD/OS
+		.byte os_bsd-.			# BSD/OS
 		.byte os_freebsd-.		# FreeBSD
-		.byte os_openbsd-.		# OpenBSD
-		.byte os_netbsd-.		# NetBSD
+		.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 "Unknow";	.byte 'n'|0x80
-os_dos: 	.ascii "DO";		.byte 'S'|0x80
-os_nt:		.ascii "Windows N";	.byte 'T'|0x80
-os_windows: 	.ascii "Window";	.byte 's'|0x80
-os_unix:	.ascii "UNI";		.byte 'X'|0x80
-os_linux:	.ascii "Linu";		.byte 'x'|0x80
-os_freebsd:	.ascii "FreeBS";	.byte 'D'|0x80
-os_openbsd:	.ascii "OpenBS";	.byte 'D'|0x80
-os_netbsd:	.ascii "NetBS";		.byte 'D'|0x80
-os_bsdos:	.ascii "BSD/O";		.byte 'S'|0x80
+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
 #
-# Fake partition entry created at the end of the table used when loading
-# boot0 at the very beginning and when loading an MBR from another disk when
-# F5 is pressed.
+# 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.
 #
-		.org SECTOR_SIZE*NUM_SECTORS, 0x0
-fake:
+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