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Code Issues Releases Activity

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

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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).
This commit is contained in:
John Baldwin 2000-05-05 13:22:10 +00:00
parent af020b6e13
commit 773065b3b8
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=60046
2 changed files with 138 additions and 63 deletions
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1
sys/boot/i386/boot0/boot0.m4
View File

@ -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

200
sys/boot/i386/boot0/boot0.s
View File

@ -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