#
# 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: src/sys/boot/i386/btx/btxldr/btxldr.s,v 1.8.2.2 2000/07/06 23:04:29 obrien Exp $
#
# Prototype BTX loader program, written in a couple of hours. The
# real thing should probably be more flexible, and in C.
#
#
# Memory locations.
#
.set MEM_STUB,0x600 # Real mode stub
.set MEM_ESP,0x1000 # New stack pointer
.set MEM_TBL,0x5000 # BTX page tables
.set MEM_ENTRY,0x9010 # BTX entry point
.set MEM_DATA,start+0x1000 # Data segment
#
# Segment selectors.
#
.set SEL_SCODE,0x8 # 4GB code
.set SEL_SDATA,0x10 # 4GB data
.set SEL_RCODE,0x18 # 64K code
.set SEL_RDATA,0x20 # 64K data
#
# Paging constants.
#
.set PAG_SIZ,0x1000 # Page size
.set PAG_ENT,0x4 # Page entry size
#
# Screen constants.
#
.set SCR_MAT,0x7 # Mode/attribute
.set SCR_COL,0x50 # Columns per row
.set SCR_ROW,0x19 # Rows per screen
#
# BIOS Data Area locations.
#
.set BDA_MEM,0x413 # Free memory
.set BDA_SCR,0x449 # Video mode
.set BDA_POS,0x450 # Cursor position
#
# Required by aout gas inadequacy.
#
.set SIZ_STUB,0x1a # Size of stub
#
# We expect to be loaded by boot2 at the origin defined in ./Makefile.
#
.globl start
#
# BTX program loader for ELF clients.
#
start: cld # String ops inc
movl $m_logo,%esi # Identify
call putstr # ourselves
movzwl BDA_MEM,%eax # Get base memory
shll $0xa,%eax # in bytes
movl %eax,%ebp # Base of user stack
ifdef(`BTXLDR_VERBOSE',`
movl $m_mem,%esi # Display
call hexout # amount of
call putstr # base memory
')
lgdt gdtdesc # Load new GDT
#
# Relocate caller's arguments.
#
ifdef('BTXLDR_VERBOSE',`
movl $m_esp,%esi # Display
movl %esp,%eax # caller
call hexout # stack
call putstr # pointer
movl $m_args,%esi # Format string
leal 0x4(%esp,1),%ebx # First argument
movl $0x6,%ecx # Count
start.1: movl (%ebx),%eax # Get argument and
addl $0x4,%ebx # bump pointer
call hexout # Display it
loop start.1 # Till done
call putstr # End message
')
movl $0x48,%ecx # Allocate space
subl %ecx,%ebp # for bootinfo
movl 0x18(%esp,1),%esi # Source: bootinfo
cmpl $0x0, %esi # If the bootinfo pointer
je start_null_bi # is null, don't copy it
movl %ebp,%edi # Destination
rep # Copy
movsb # it
movl %ebp,0x18(%esp,1) # Update pointer
ifdef(`BTXLDR_VERBOSE',`
movl $m_rel_bi,%esi # Display
movl %ebp,%eax # bootinfo
call hexout # relocation
call putstr # message
')
start_null_bi: movl $0x18,%ecx # Allocate space
subl %ecx,%ebp # for arguments
leal 0x4(%esp,1),%esi # Source
movl %ebp,%edi # Destination
rep # Copy
movsb # them
ifdef(`BTXLDR_VERBOSE',`
movl $m_rel_args,%esi # Display
movl %ebp,%eax # argument
call hexout # relocation
call putstr # message
')
#
# Set up BTX kernel.
#
movl $MEM_ESP,%esp # Set up new stack
movl $MEM_DATA,%ebx # Data segment
movl $m_vers,%esi # Display BTX
call putstr # version message
movb 0x5(%ebx),%al # Get major version
addb $'0',%al # Display
call putchr # it
movb $'.',%al # And a
call putchr # dot
movb 0x6(%ebx),%al # Get minor
xorb %ah,%ah # version
movb $0xa,%dl # Divide
divb %dl,%al # by 10
addb $'0',%al # Display
call putchr # tens
movb %ah,%al # Get units
addb $'0',%al # Display
call putchr # units
call putstr # End message
movl %ebx,%esi # BTX image
movzwl 0x8(%ebx),%edi # Compute
orl $PAG_SIZ/PAG_ENT-1,%edi # the
incl %edi # BTX
shll $0x2,%edi # load
addl $MEM_TBL,%edi # address
pushl %edi # Save load address
movzwl 0xa(%ebx),%ecx # Image size
ifdef(`BTXLDR_VERBOSE',`
pushl %ecx # Save image size
')
rep # Relocate
movsb # BTX
movl %esi,%ebx # Keep place
ifdef(`BTXLDR_VERBOSE',`
movl $m_rel_btx,%esi # Restore
popl %eax # parameters
call hexout # and
')
popl %ebp # display
ifdef(`BTXLDR_VERBOSE',`
movl %ebp,%eax # the
call hexout # relocation
call putstr # message
')
addl $PAG_SIZ,%ebp # Display
ifdef(`BTXLDR_VERBOSE',`
movl $m_base,%esi # the
movl %ebp,%eax # user
call hexout # base
call putstr # address
')
#
# Set up ELF-format client program.
#
cmpl $0x464c457f,(%ebx) # ELF magic number?
je start.3 # Yes
movl $e_fmt,%esi # Display error
call putstr # message
start.2: jmp start.2 # Hang
start.3:
ifdef(`BTXLDR_VERBOSE',`
movl $m_elf,%esi # Display ELF
call putstr # message
movl $m_segs,%esi # Format string
')
movl $0x2,%edi # Segment count
movl 0x1c(%ebx),%edx # Get e_phoff
addl %ebx,%edx # To pointer
movzwl 0x2c(%ebx),%ecx # Get e_phnum
start.4: cmpl $0x1,(%edx) # Is p_type PT_LOAD?
jne start.6 # No
ifdef(`BTXLDR_VERBOSE',`
movl 0x4(%edx),%eax # Display
call hexout # p_offset
movl 0x8(%edx),%eax # Display
call hexout # p_vaddr
movl 0x10(%edx),%eax # Display
call hexout # p_filesz
movl 0x14(%edx),%eax # Display
call hexout # p_memsz
call putstr # End message
')
pushl %esi # Save
pushl %edi # working
pushl %ecx # registers
movl 0x4(%edx),%esi # Get p_offset
addl %ebx,%esi # as pointer
movl 0x8(%edx),%edi # Get p_vaddr
addl %ebp,%edi # as pointer
movl 0x10(%edx),%ecx # Get p_filesz
rep # Set up
movsb # segment
movl 0x14(%edx),%ecx # Any bytes
subl 0x10(%edx),%ecx # to zero?
jz start.5 # No
xorb %al,%al # Then
rep # zero
stosb # them
start.5: popl %ecx # Restore
popl %edi # working
popl %esi # registers
decl %edi # Segments to do
je start.7 # If none
start.6: addl $0x20,%edx # To next entry
loop start.4 # Till done
start.7:
ifdef(`BTXLDR_VERBOSE',`
movl $m_done,%esi # Display done
call putstr # message
')
movl $start.8,%esi # Real mode stub
movl $MEM_STUB,%edi # Destination
movl $start.9-start.8,%ecx # Size
rep # Relocate
movsb # it
ljmp $SEL_RCODE,$MEM_STUB # To 16-bit code
.code16
start.8: xorw %ax,%ax # Data
movb $SEL_RDATA,%al # selector
movw %ax,%ss # Reload SS
movw %ax,%ds # Reset
movw %ax,%es # other
movw %ax,%fs # segment
movw %ax,%gs # limits
movl %cr0,%eax # Switch to
decw %ax # real
movl %eax,%cr0 # mode
ljmp $0,$MEM_ENTRY # Jump to BTX entry point
start.9:
.code32
#
# Output message [ESI] followed by EAX in hex.
#
hexout: pushl %eax # Save
call putstr # Display message
popl %eax # Restore
pushl %esi # Save
pushl %edi # caller's
movl $buf,%edi # Buffer
pushl %edi # Save
call hex32 # To hex
xorb %al,%al # Terminate
stosb # string
popl %esi # Restore
hexout.1: lodsb # Get a char
cmpb $'0',%al # Leading zero?
je hexout.1 # Yes
testb %al,%al # End of string?
jne hexout.2 # No
decl %esi # Undo
hexout.2: decl %esi # Adjust for inc
call putstr # Display hex
popl %edi # Restore
popl %esi # caller's
ret # To caller
#
# Output zero-terminated string [ESI] to the console.
#
putstr.0: call putchr # Output char
putstr: lodsb # Load char
testb %al,%al # End of string?
jne putstr.0 # No
ret # To caller
#
# Output character AL to the console.
#
putchr: pusha # Save
xorl %ecx,%ecx # Zero for loops
movb $SCR_MAT,%ah # Mode/attribute
movl $BDA_POS,%ebx # BDA pointer
movw (%ebx),%dx # Cursor position
movl $0xb8000,%edi # Regen buffer (color)
cmpb %ah,BDA_SCR-BDA_POS(%ebx) # Mono mode?
jne putchr.1 # No
xorw %di,%di # Regen buffer (mono)
putchr.1: cmpb $0xa,%al # New line?
je putchr.2 # Yes
xchgl %eax,%ecx # Save char
movb $SCR_COL,%al # Columns per row
mulb %dh # * row position
addb %dl,%al # + column
adcb $0x0,%ah # position
shll %eax # * 2
xchgl %eax,%ecx # Swap char, offset
movw %ax,(%edi,%ecx,1) # Write attr:char
incl %edx # Bump cursor
cmpb $SCR_COL,%dl # Beyond row?
jb putchr.3 # No
putchr.2: xorb %dl,%dl # Zero column
incb %dh # Bump row
putchr.3: cmpb $SCR_ROW,%dh # Beyond screen?
jb putchr.4 # No
leal 2*SCR_COL(%edi),%esi # New top line
movw $(SCR_ROW-1)*SCR_COL/2,%cx # Words to move
rep # Scroll
movsl # screen
movb $' ',%al # Space
movb $SCR_COL,%cl # Columns to clear
rep # Clear
stosw # line
movb $SCR_ROW-1,%dh # Bottom line
putchr.4: movw %dx,(%ebx) # Update position
popa # Restore
ret # To caller
#
# Convert EAX, AX, or AL to hex, saving the result to [EDI].
#
hex32: pushl %eax # Save
shrl $0x10,%eax # Do upper
call hex16 # 16
popl %eax # Restore
hex16: call hex16.1 # Do upper 8
hex16.1: xchgb %ah,%al # Save/restore
hex8: pushl %eax # Save
shrb $0x4,%al # Do upper
call hex8.1 # 4
popl %eax # Restore
hex8.1: andb $0xf,%al # Get lower 4
cmpb $0xa,%al # Convert
sbbb $0x69,%al # to hex
das # digit
orb $0x20,%al # To lower case
stosb # Save char
ret # (Recursive)
.data
.p2align 4
#
# Global descriptor table.
#
gdt: .word 0x0,0x0,0x0,0x0 # Null entry
.word 0xffff,0x0,0x9a00,0xcf # SEL_SCODE
.word 0xffff,0x0,0x9200,0xcf # SEL_SDATA
.word 0xffff,0x0,0x9a00,0x0 # SEL_RCODE
.word 0xffff,0x0,0x9200,0x0 # SEL_RDATA
gdt.1:
gdtdesc: .word gdt.1-gdt-1 # Limit
.long gdt # Base
#
# Messages.
#
m_logo: .asciz " \nBTX loader 1.00 "
m_vers: .asciz "BTX version is \0\n"
e_fmt: .asciz "Error: Client format not supported\n"
ifdef(`BTXLDR_VERBOSE',`
m_mem: .asciz "Starting in protected mode (base mem=\0)\n"
m_esp: .asciz "Arguments passed (esp=\0):\n"
m_args: .asciz"<howto="
.asciz" bootdev="
.asciz" junk="
.asciz" "
.asciz" "
.asciz" bootinfo=\0>\n"
m_rel_bi: .asciz "Relocated bootinfo (size=48) to \0\n"
m_rel_args: .asciz "Relocated arguments (size=18) to \0\n"
m_rel_btx: .asciz "Relocated kernel (size=\0) to \0\n"
m_base: .asciz "Client base address is \0\n"
m_elf: .asciz "Client format is ELF\n"
m_segs: .asciz "text segment: offset="
.asciz " vaddr="
.asciz " filesz="
.asciz " memsz=\0\n"
.asciz "data segment: offset="
.asciz " vaddr="
.asciz " filesz="
.asciz " memsz=\0\n"
m_done: .asciz "Loading complete\n"
')
#
# Uninitialized data area.
#
buf: # Scratch buffer
