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/* $Id$ */
/* ----------------------------------------------------------------------- *
*
* Copyright 2001 H. Peter Anvin - All Rights Reserved
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, Inc., 53 Temple Place Ste 330,
* Bostom MA 02111-1307, USA; either version 2 of the License, or
* (at your option) any later version; incorporated herein by reference.
*
* ----------------------------------------------------------------------- */
/*
* init.S
*
* memdisk initialization code
*
* This module *MUST* get linked first into the image
*/
.text
.code16
/*
* The header derives directly from the Linux kernel and must be first
* in the binary, hence section .init
*/
.org 497
setup_sects: .byte 0 # Filled in later
root_flags: .word 0
syssize: .word 0
swap_dev: .word 0
ram_size: .word 0
vid_mode: .word 0
root_dev: .word 0
boot_flag: .word 0xAA55
.globl _start
_start:
jmp start
# This is the setup header, and it must start at %cs:2 (old 0x9020:2)
.ascii "HdrS" # header signature
.word 0x0203 # header version number (>= 0x0105)
# or else old loadlin-1.5 will fail)
realmode_swtch: .word 0, 0 # default_switch, SETUPSEG
start_sys_seg: .word 0
.word kernel_version # pointing to kernel version string
# above section of header is compatible
# with loadlin-1.5 (header v1.5).
type_of_loader: .byte 0 # = 0, old one (LILO, Loadlin,
# Bootlin, SYSLX, bootsect...)
# See Documentation/i386/boot.txt for
# assigned ids
# flags, unused bits must be zero (RFU) bit within loadflags
loadflags:
LOADED_HIGH = 1 # If set, the kernel is loaded high
CAN_USE_HEAP = 0x80 # If set, the loader also has set
# heap_end_ptr to tell how much
# space behind setup.S can be used for
# heap purposes.
# Only the loader knows what is free
.byte LOADED_HIGH # Dont force the loader to move
# us to 0x90000
setup_move_size: .word 0 # Unused
code32_start: # here loaders can put a different
# start address for 32-bit code.
.long 0x100000 # 0x100000 = default for big kernel
ramdisk_image: .long 0 # address of loaded ramdisk image
# Here the loader puts the 32-bit
# address where it loaded the image.
# This only will be read by the kernel.
ramdisk_size: .long 0 # its size in bytes
bootsect_kludge:
.word 0, 0
heap_end_ptr: .word 0 # (Header version 0x0201 or later)
# space from here (exclusive) down to
# end of setup code can be used by setup
# for local heap purposes.
pad1: .word 0
cmd_line_ptr: .long 0 # (Header version 0x0202 or later)
# If nonzero, a 32-bit pointer
# to the kernel command line.
# The command line should be
# located between the start of
# setup and the end of low
# memory (0xa0000), or it may
# get overwritten before it
# gets read. If this field is
# used, there is no longer
# anything magical about the
# 0x90000 segment; the setup
# can be located anywhere in
# low memory 0x10000 or higher.
ramdisk_max: .long 0xffffffff # Load ramdisk as high as
# absolutely possible
/* ------------------- End of setup header --------------------------- */
LOWSEG = 0x0800 # 0x8000 physical
/*
* Move ourselves down in memory to reduce the risk of conflicts;
* the canonicalize CS to match the other segments...
*
* The C code uses 32-bit registers to make sure the high part of
* %esp is zero.
*
* The C code expects %cs == %ds == %es == %ss, and %fs == 0.
*/
start:
movw $LOWSEG,%ax
movw %ax,%es
movzbw setup_sects,%cx
inc %cx # Add one for the boot sector
shlw $7,%cx # Convert to dwords
xorw %si,%si
xorw %di,%di
movw %si,%fs # %fs -> zero segment
cld
rep ; movsl %ds:(%si),%es:(%di)
movw %ax,%ds
movw %ax,%ss
xorl %esp,%esp # Stack at the top of the segment
ljmp $LOWSEG, $startc
startc:
/*
* Copy the command line, if there is one
*/
xorw %di,%di # Bottom of our own segment
movl cmd_line_ptr, %eax
andl %eax,%eax
jz endcmd # No command line?
movw %ax,%si
shrl $4,%eax # Convert to a segment address
andw $0x000F,%si # Starting offset
movw %ax,%gs
movw $496,%cx # Maximum number of bytes
copycmd:
lodsb %gs:(%si),%al
andb %al,%al # Make sure we're null-terminated
jz endcmd
stosb %al,%es:(%di)
loopw copycmd
endcmd:
xorb %al,%al
stosb %al,%es:(%di)
/*
* Jump to C code
*/
sti # Maybe not?
calll setup # Call the C code
# The setup function returns the drive number,
# which should be returned in %dl
movw %ax,%dx
# If the C code returns, we are good to go, and the
# new boot sector is already loaded
cli
movw $0x7c00,%sp
xorw %si,%si # Not a partition BS - SI <- 0
movw %si,%ds
movw %si,%es
movw %si,%fs
movw %si,%gs
movw %si,%ss
ljmp $0,$0x7c00 # Entrypoint at 0000:7C00
.section ".rodata", "a"
kernel_version: .ascii "MEMDISK ..."
.byte 0
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