freebsd-dev/sys/boot/i386/cdldr/cdldr.s
Mark Peek 7684ab55c6 Allow for text section alignment to properly align the "end" symbol at the
actual end of the section. The new gas (binutils) puts in additional padding
which was misaligning the concatenated btx loader.

Reported by:	Oliver Hartmann <ohartman@klima.physik.uni-mainz.de>,
		Harti Brandt <brandt@fokus.gmd.de>
Tested by:	Oliver Hartmann <ohartman@klima.physik.uni-mainz.de>,
		David Wolfskill <dhw@whistle.com>, ps
Reviewed by:	jhb
MFC after:	1 day
2001-08-09 20:47:58 +00:00

262 lines
8.0 KiB
ArmAsm

#
# Copyright (c) 2000 John Baldwin
# 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.
#
# $FreeBSD$
#
# This simple program is a preloader for the normal boot3 loader. It is simply
# prepended to the beginning of a fully built and btxld'd loader. It then
# copies the loader to the address boot2 normally loads it, emulates the
# boot[12] environment (protected mode, a bootinfo struct, etc.), and then jumps
# to the start of btxldr to start the boot process. This method allows a stock
# /boot/loader to be used w/o having to fully rewrite boot[12] to handle the
# cd9660 file system.
#
#
# Memory locations.
#
.set MEM_PAGE_SIZE,0x1000 # memory page size, 4k
.set MEM_ARG,0x900 # Arguments at start
.set MEM_ARG_BTX,0xa100 # Where we move them to so the
# BTX client can see them
.set MEM_ARG_SIZE,0x18 # Size of the arguments
.set MEM_BTX_ADDRESS,0x9000 # where BTX lives
.set MEM_BTX_ENTRY,0x9010 # where BTX starts to execute
.set MEM_BTX_OFFSET,MEM_PAGE_SIZE # offset of BTX in the loader
.set MEM_BTX_CLIENT,0xa000 # where BTX clients live
#
# a.out header fields
#
.set AOUT_TEXT,0x04 # text segment size
.set AOUT_DATA,0x08 # data segment size
.set AOUT_BSS,0x0c # zero'd BSS size
.set AOUT_SYMBOLS,0x10 # symbol table
.set AOUT_ENTRY,0x14 # entry point
.set AOUT_HEADER,MEM_PAGE_SIZE # size of the a.out header
#
# Flags for kargs->bootflags
#
.set KARGS_FLAGS_CD,0x1 # flag to indicate booting from
# CD loader
#
# Segment selectors.
#
.set SEL_SDATA,0x8 # Supervisor data
.set SEL_RDATA,0x10 # Real mode data
.set SEL_SCODE,0x18 # PM-32 code
.set SEL_SCODE16,0x20 # PM-16 code
#
# BTX constants
#
.set INT_SYS,0x30 # BTX syscall interrupt
#
# We expect to be loaded by the BIOS at 0x7c00 (standard boot loader entry
# point)
#
.code16
.globl start
.org 0x0, 0x0
#
# BTX program loader for CD booting
#
start: cld # string ops inc
xorw %ax, %ax # zero %ax
movw %ax, %ss # setup the
movw $start, %sp # stack
pushw %dx # save the BIOS boot device in
# %dl for later
movw %ax, %ds # setup the
movw %ax, %es # data segments
movw $welcome_msg, %si # %ds:(%si) -> welcome message
callw putstr # display the welcome message
#
# Setup the arguments that the loader is expecting from boot[12]
#
movw $bootinfo_msg, %si # %ds:(%si) -> boot args message
callw putstr # display the message
movw $MEM_ARG, %bx # %ds:(%bx) -> boot args
movw %bx, %di # %es:(%di) -> boot args
xorl %eax, %eax # zero %eax
movw $(MEM_ARG_SIZE/4), %cx # Size of arguments in 32-bit
# dwords
rep # Clear the arguments
stosl # to zero
popw %dx # restore BIOS boot device
movb %dl, 0x4(%bx) # set kargs->bootdev
orb $KARGS_FLAGS_CD, 0x8(%bx) # kargs->bootflags |=
# KARGS_FLAGS_CD
#
# Turn on the A20 address line
#
callw seta20 # Turn A20 on
#
# Relocate the loader and BTX using a very lazy protected mode
#
movw $relocate_msg, %si # Display the
callw putstr # relocation message
movl end+AOUT_ENTRY, %edi # %edi is the destination
movl $(end+AOUT_HEADER), %esi # %esi is
# the start of the text
# segment
movl end+AOUT_TEXT, %ecx # %ecx = length of the text
# segment
lgdt gdtdesc # setup our own gdt
cli # turn off interrupts
movl %cr0, %eax # Turn on
orb $0x1, %al # protected
movl %eax, %cr0 # mode
ljmp $SEL_SCODE,$pm_start # long jump to clear the
# instruction pre-fetch queue
.code32
pm_start: movw $SEL_SDATA, %ax # Initialize
movw %ax, %ds # %ds and
movw %ax, %es # %es to a flat selector
rep # Relocate the
movsb # text segment
addl $(MEM_PAGE_SIZE - 1), %edi # pad %edi out to a new page
andl $~(MEM_PAGE_SIZE - 1), %edi # for the data segment
movl end+AOUT_DATA, %ecx # size of the data segment
rep # Relocate the
movsb # data segment
movl end+AOUT_BSS, %ecx # size of the bss
xorl %eax, %eax # zero %eax
addb $3, %cl # round %ecx up to
shrl $2, %ecx # a multiple of 4
rep # zero the
stosl # bss
movl end+AOUT_ENTRY, %esi # %esi -> relocated loader
addl $MEM_BTX_OFFSET, %esi # %esi -> BTX in the loader
movl $MEM_BTX_ADDRESS, %edi # %edi -> where BTX needs to go
movzwl 0xa(%esi), %ecx # %ecx -> length of BTX
rep # Relocate
movsb # BTX
ljmp $SEL_SCODE16,$pm_16 # Jump to 16-bit PM
.code16
pm_16: movw $SEL_RDATA, %ax # Initialize
movw %ax, %ds # %ds and
movw %ax, %es # %es to a real mode selector
movl %cr0, %eax # Turn off
andb $~0x1, %al # protected
movl %eax, %cr0 # mode
ljmp $0,$pm_end # Long jump to clear the
# instruction pre-fetch queue
pm_end: sti # Turn interrupts back on now
#
# Copy the BTX client to MEM_BTX_CLIENT
#
xorw %ax, %ax # zero %ax and set
movw %ax, %ds # %ds and %es
movw %ax, %es # to segment 0
movw $MEM_BTX_CLIENT, %di # Prepare to relocate
movw $btx_client, %si # the simple btx client
movw $(btx_client_end-btx_client), %cx # length of btx client
rep # Relocate the
movsb # simple BTX client
#
# Copy the boot[12] args to where the BTX client can see them
#
movw $MEM_ARG, %si # where the args are at now
movw $MEM_ARG_BTX, %di # where the args are moving to
movw $(MEM_ARG_SIZE/4), %cx # size of the arguments in longs
rep # Relocate
movsl # the words
#
# Save the entry point so the client can get to it later on
#
movl end+AOUT_ENTRY, %eax # load the entry point
stosl # add it to the end of the
# arguments
#
# Now we just start up BTX and let it do the rest
#
movw $jump_message, %si # Display the
callw putstr # jump message
ljmp $0,$MEM_BTX_ENTRY # Jump to the BTX entry point
#
# Display a null-terminated string
#
putstr: lodsb # load %al from %ds:(%si)
testb %al,%al # stop at null
jnz putc # if the char != null, output it
retw # return when null is hit
putc: movw $0x7,%bx # attribute for output
movb $0xe,%ah # BIOS: put_char
int $0x10 # call BIOS, print char in %al
jmp putstr # keep looping
#
# Enable A20
#
seta20: cli # Disable interrupts
seta20.1: inb $0x64,%al # Get status
testb $0x2,%al # Busy?
jnz seta20.1 # Yes
movb $0xd1,%al # Command: Write
outb %al,$0x64 # output port
seta20.2: inb $0x64,%al # Get status
testb $0x2,%al # Busy?
jnz seta20.2 # Yes
movb $0xdf,%al # Enable
outb %al,$0x60 # A20
sti # Enable interrupts
retw # To caller
#
# BTX client to start btxldr
#
.code32
btx_client: movl $(MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE-4), %esi
# %ds:(%esi) -> end
# of boot[12] args
movl $(MEM_ARG_SIZE/4), %ecx # Number of words to push
std # Go backwards
push_arg: lodsl # Read argument
pushl %eax # Push it onto the stack
loop push_arg # Push all of the arguments
cld # In case anyone depends on this
pushl MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE # Entry point of
# the loader
pushl %eax # Emulate a near call
movl $0x1, %eax # 'exec' system call
int $INT_SYS # BTX system call
btx_client_end:
.code16
.p2align 4
#
# Global descriptor table.
#
gdt: .word 0x0,0x0,0x0,0x0 # Null entry
.word 0xffff,0x0,0x9200,0xcf # SEL_SDATA
.word 0xffff,0x0,0x9200,0x0 # SEL_RDATA
.word 0xffff,0x0,0x9a00,0xcf # SEL_SCODE (32-bit)
.word 0xffff,0x0,0x9a00,0x8f # SEL_SCODE16 (16-bit)
gdt.1:
#
# Pseudo-descriptors.
#
gdtdesc: .word gdt.1-gdt-1 # Limit
.long gdt # Base
welcome_msg: .asciz "CD Loader 1.00\r\n\n"
bootinfo_msg: .asciz "Building the boot loader arguments\r\n"
relocate_msg: .asciz "Relocating the loader and the BTX\r\n"
jump_message: .asciz "Starting the BTX loader\r\n"
.p2align 4
end: