Switch to using the .code16 as(1) directive and using 16-bit assembly

code instead of using 32-bit code and having to just "know" that it's
really 16-bit instructions when things run.  This also allows the code
to use fewer macros and more actual assembly statements, which eases
maintenance.  Unfortunately, due to as(1) brokenness, we still use m4
macros for all 16-bit addresses, and all short jumps (i.e., 8-bit
relative addresses in the jump instruction) must be wrapped in .code32
directives to avoid useless bloat by as(1).  This also fixes a few
problems that were preventing boot0 from compiling with the latest
and greatest version of as(1).

2 files changed, 138 insertions, 63 deletions

diff --git a/sys/boot/i386/boot0/boot0.m4 b/sys/boot/i386/boot0/boot0.m4
index d318d2a..7515d58 100644
--- a/sys/boot/i386/boot0/boot0.m4
+++ b/sys/boot/i386/boot0/boot0.m4
@@ -74,3 +74,4 @@ define(jmpnwi,`.byte 0xe9; .word $1 - . - 0x2')dnl
 define(tstbi1,`.byte 0xf6; .byte 0x40 | $3; .byte $2; .byte $1')dnl
 define(incb1,`.byte 0xfe; .byte 0x40 | $2; .byte $1')dnl
 define(pushw1,`.byte 0xff; .byte 0x70 | $2; .byte $1')dnl
+define(retn,`.byte 0xc3')dnl
diff --git a/sys/boot/i386/boot0/boot0.s b/sys/boot/i386/boot0/boot0.s
index 25f631d..f7a3ec2 100644
--- a/sys/boot/i386/boot0/boot0.s
+++ b/sys/boot/i386/boot0/boot0.s
@@ -45,6 +45,7 @@
 		.set _MNUOPT,0xc		# Menu options
 
 		.globl start			# Entry point
+		.code16				# This runs in real mode
 
 #
 # Initialise segments and registers to known values.
@@ -52,49 +53,59 @@
 # 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
+		xorw %ax,%ax			# Zero
+		movw %ax,%es			# Address
+		movw %ax,%ds			#  data
+		movw %ax,%ss			# Set up
+		movw $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
+		movw %sp,%si			# Source
+		movw $start,%di			# Destination
+		movw $0x100,%cx			# Word count
 		rep				# Relocate
-		movsl				#  code
+		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 in the block,
 # by using negative offsets.
 #
-		movl %edi,%ebp			# Address variables
+		movw %di,%bp			# Address variables
 		movb $0x8,%cl			# Words to clear
 		rep				# Zero
-		stosl				#  them
+		stosw				#  them
 #
 # Relocate to the new copy of the code.
 #
 		incb1(-0xe,_di_)		# Sector number
+		/* incb $-0xe(%di) */
 		jmpnwi(main-LOAD+ORIGIN)	# To relocated code
+		/* jmp main-LOAD+ORIGIN */
 #
 # 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?
+		/* testb $(0x20+_FLAGS)(%bp) */
+		.code32
 		jnz main.1			# Yes
+		.code16
 		testb %dl,%dl			# Drive number valid?
+		.code32
 		js main.2			# Possibly (0x80 set)
+		.code16
 main.1: 	movb1r(_SETDRV,_bp_,_dl)	# Drive number to use
+		/* movb $_SETDRV(%bp),%dl */
 #
 # Whatever we decided to use, now store it into the fake
 # partition entry that lives in the data space above us.
 #
 main.2: 	movbr1(_dl,_FAKE,_bp_)		# Save drive number
+		/* movb %dl,$_FAKE(%bp) */
 		callwi(putn)			# To new line
-		pushl %edx			# Save drive number
+		pushw %dx			# 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.
@@ -102,59 +113,75 @@ main.2: 	movbr1(_dl,_FAKE,_bp_)		# Save drive number
 # (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
+		movw $(partbl+0x4),%bx		# Partition table (+4)
+		xorw %dx,%dx			# Item number
 #
 # Loop around on the partition table, printing values until we
 # pass a 256 byte boundary. The end of loop test is at main.5.
 #
 main.3: 	movbr1(_ch,-0x4,_bx_)		# Zero active flag (ch == 0)
+	 	/* movb %ch,$-0x4(%bx) */
 		btwr1(_dx,_FLAGS,_bp_)		# Entry enabled?
+		/* bt %dx,$_FLAGS(%bp) */
+		.code32
 		jnc main.5			# No
+		.code16
 #
 # 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 (%bx),%al */
+		movw $tables,%di		# Lookup tables
 		movb $TBL0SZ,%cl		# Number of entries
 		repne				# Exclude
 		scasb				#  partition?
+		.code32
 		je main.5			# Yes
+		.code16
 #
 # Now scan the table of known types
 #
 		movb $TBL1SZ,%cl		# Number of entries
 		repne				# Known
 		scasb				#  type?
+		.code32
 		jne main.4			# No
+		.code16
 #
 # 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
+		addw $TBL1SZ,%di		# Adjust
+main.4: 	movb0r(_di_,_cl)		# Partition
+		/* movb (%di),%cl */
+		addw %cx,%di			#  description
 		callwi(putx)			# Display it
-main.5: 	incl %edx			# Next item 
+main.5: 	incw %dx			# Next item 
 		addb $0x10,%bl			# Next entry
+		.code32
 		jnc main.3			# Till done
+		.code16
 #
 # Passed a 256 byte boundary..
 # table is finished.
 # Add one to the drive number and check it is valid, 
 #
-		popl %eax			# Drive number
+		popw %ax			# Drive number
 		subb $0x80-0x1,%al		# Does next
-		cmpbmr(NHRDRV,_al)		#  drive exist? (from BIOS?)
+		cmpb NHRDRV,%al			#  drive exist? (from BIOS?)
+		.code32
 		jb main.6			# Yes
+		.code16
 # If not then if there is only one drive,
 # Don't display drive as an option.
 #
-		decl %eax			# Already drive 0?
+		decw %ax			# Already drive 0?
+		.code32
 		jz main.7			# Yes
+		.code16
 # If it was illegal or we cycled through them,
 # then go back to drive 0.
 #
@@ -168,37 +195,47 @@ main.5: 	incl %edx			# Next item
 #
 main.6: 	addb $'0'|0x80,%al		# Save next
 		movbr1(_al,_NXTDRV,_bp_)	#  drive number
-		movwir(drive,_di)		# Display
+		/* movb %al,$NXTDRV(%bp) */
+		movw $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
+main.7: 	movw $prompt,%si		# Display
 		callwi(putstr)			#  prompt
 		movb1r(_OPT,_bp_,_dl)		# Display
-		decl %esi			#  default
+		/* movb $_OPT(%bp),%dl */
+		decw %si			#  default
 		callwi(putkey)			#  key
 		xorb %ah,%ah			# BIOS: Get
 		int $0x1a			#  system time
-		movl %edx,%edi			# Ticks when
+		movw %dx,%di			# Ticks when
 		addw1r(_TICKS,_bp_,_di) 	#  timeout
+		/* addw $_TICKS(%bp),%di */
 # 
 # Busy loop, looking for keystrokes but
 # keeping one eye on the time.
 #
 main.8: 	movb $0x1,%ah			# BIOS: Check
 		int $0x16			#  for keypress
+		.code32
 		jnz main.11			# Have one
+		.code16
 		xorb %ah,%ah			# BIOS: Get
 		int $0x1a			#  system time
-		cmpl %edi,%edx			# Timeout?
+		cmpw %di,%dx			# Timeout?
+		.code32
 		jb main.8			# No
+		.code16
 #
 # If timed out or defaulting, come here.
 #
 main.9: 	movb1r(_OPT,_bp_,_al)		# Load default
+		/* movb $_OPT(%bp),%al */
+		.code32
 		jmp main.12			# Join common code
+		.code16
 #
 # User's last try was bad, beep in displeasure.
 # Since nothing was printed, just continue on as if the user
@@ -218,74 +255,99 @@ main.11:	xorb %ah,%ah			# BIOS: Get
 # If it's CR act as if timed out.
 #
 		cmpb $KEY_ENTER,%al		# Enter pressed?
+		.code32
 		je main.9			# Yes
+		.code16
 #
 # Otherwise check if legal
 # If not ask again.
 #
 		subb $KEY_F1,%al		# Less F1 scan code
 		cmpb $0x4,%al			# F1..F5?
+		.code32
 		ja main.10			# No
+		.code16
 #
 # We have a selection.
 # but if it's a bad selection go back to complain.
 # The bits in MNUOPT were set when the options were printed.
 # Anything not printed is not an option.
 #
-main.12:	cwtl				# Option
+main.12:	cbtw				# Option
 		btwr1(_ax,_MNUOPT,_bp_) 	#  enabled?
+		/* btw %ax,$_MNUOPT(%bp) */
+		.code32
 		jnc main.10			# No
+		.code16
 #
 # Save the info in the original tables
 # for rewriting to the disk.
 #
 		movbr1(_al,_OPT,_bp_)		# Save option
-		movwir(FAKE,_si)		# Partition for write
+		/* movb %al,$OPT(%bp) */
+		movw $FAKE,%si			# Partition for write
 		movb0r(_si_,_dl)		# Drive number
-		movl %esi,%ebx			# Partition for read
+		/* movb (%si),%dl */
+		movw %si,%bx			# Partition for read
 		cmpb $0x4,%al			# F5 pressed?
-		pushfl				# Save
+		pushf				# Save
+		.code32
 		je main.13			# Yes
+		.code16
 		shlb $0x4,%al			# Point to
-		addwia(partbl)			#  selected
-		xchgl %ebx,%eax 		#  partition
+		addw $partbl,%ax		#  selected
+		xchgw %bx,%ax	 		#  partition
 		movbi0(0x80,_bx_)		# Flag active
+		/* movb $0x80,(%bx) */
 #
 # If not asked to do a write-back (flags 0x40) don't do one.
 #
-main.13:	pushl %ebx			# Save
+main.13:	pushw %bx			# Save
 		tstbi1(0x40,_FLAGS,_bp_)	# No updates?
+		/* testb $0x40,$_FLAGS(%bp) */
+		.code32
 		jnz main.14			# Yes
-		movwir(start,_bx)		# Data to write
+		.code16
+		movw $start,%bx			# Data to write
 		movb $0x3,%ah			# Write sector
 		callwi(intx13)			#  to disk
-main.14:	popl %esi			# Restore
-		popfl				# Restore
+main.14:	popw %si			# Restore
+		popf				# Restore
 #
 # If going to next drive, replace drive with selected one.
 # Remember to un-ascii it. Hey 0x80 is already set, cool!
 #
+		.code32
 		jne main.15			# If not F5
+		.code16
 		movb1r(_NXTDRV,_bp_,_dl)	# Next drive
+		/* movb $_NXTDRV(%bp),%dl */
 		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?
+# XXX what does %si carry?
 #
-main.15:	movwir(LOAD,_bx)		# Address for read
+main.15:	movw $LOAD,%bx			# Address for read
 		movb $0x2,%ah			# Read sector
 		callwi(intx13)			#  from disk
+		.code32
 		jc main.10			# If error
+		.code16
 		cmpwi2(MAGIC,0x1fe,_bx_)	# Bootable?
+		/* cmpw $MAGIC,$0x1fe(%bx) */
+		.code32
 		jne main.10			# No
-		pushl %esi			# Save
-		movwir(crlf,_si)		# Leave some
+		.code16
+		pushw %si			# Save
+		movw $crlf,%si			# Leave some
 		callwi(puts)			#  space
-		popl %esi			# Restore
+		popw %si			# Restore
+		.code32
 		jmp *%ebx			# Invoke bootstrap
-
+		/* jmp *%bx */
+		.code16
 #
 # Display routines
 #
@@ -294,59 +356,71 @@ putkey: 	movb $'F',%al			# Display
 		callwi(putchr)			#  'F'
 		movb $'1',%al			# Prepare
 		addb %dl,%al			#  digit
+		.code32
 		jmp putstr.1			# Display the rest
+		.code16
 
 #
 # 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
+		/* btsw %dx,$_MNUOPT(%bp) */
+		movw $item,%si			# Display
 		callwi(putkey)			#  key
-		movl %edi,%esi			# Display the rest
+		movw %di,%si			# Display the rest
 
 puts:		callwi(putstr)			# Display string
 
-putn:		movwir(crlf,_si)		# To next line
+putn:		movw $crlf,%si			# To next line
 
 putstr: 	lodsb				# Get byte
 		testb $0x80,%al 		# End of string?
+		.code32
 		jnz putstr.2			# Yes
+		.code16
 putstr.1:	callwi(putchr)			# Display char
+		.code32
 		jmp putstr			# Continue
+		.code16
 putstr.2:	andb $~0x80,%al 		# Clear MSB
 
-putchr: 	pushl %ebx			# Save
-		movwir(0x7,_bx) 		# Page:attribute
+putchr: 	pushw %bx			# Save
+		movw $0x7,%bx	 		# Page:attribute
 		movb $0xe,%ah			# BIOS: Display
 		int $0x10			#  character
-		popl %ebx			# Restore
-		ret				# To caller
+		popw %bx			# Restore
+		retn				# To caller
 
 # One-sector disk I/O routine
 
 intx13: 	movb1r(0x1,_si_,_dh)		# Load head
+		/* movb $0x1(%si),%dh */
 		movw1r(0x2,_si_,_cx)		# Load cylinder:sector
+		/* movw $0x2(%si),%cx */
 		movb $0x1,%al			# Sector count
-		pushl %esi			# Save
-		movl %esp,%edi			# Save
+		pushw %si			# Save
+		movw %sp,%di			# Save
 		tstbi1(0x80,_FLAGS,_bp_)	# Use packet interface?
+		/* testb $0x80,$_FLAGS(%bp) */
+		.code32
 		jz intx13.1			# No
-		o16				# Set
-		pushb $0x0			#  the
+		.code16
+		pushl $0x0			# Set 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
+		/* pushl $0x8(%si) */
+		pushw %es			# Set the transfer
+		pushw %bx			#  buffer address
+		push  $0x1			# Block count
+		push  $0x10			# Packet size
+		movw %sp,%si			# Packet pointer
+		decw %ax			# 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
+		movw %di,%sp			# Restore
+		popw %si			# Restore
+		retn				# To caller
 
 # Menu strings