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linux/arch/x86_64/boot/setup.S
Steven Rostedt 51d67a488b [PATCH] x86-64: shorten the x86_64 boot setup GDT to what the comment says 
Stephen Tweedie, Herbert Xu, and myself have been struggling with a very
nasty bug in Xen.  But it also pointed out a small bug in the x86_64
kernel boot setup.

The GDT limit being setup by the initial bzImage code when entering into
protected mode is way too big.  The comment by the code states that the
size of the GDT is 2048, but the actual size being set up is much bigger
(32768). This happens simply because of one extra '0'.

Instead of setting up a 0x800 size, 0x8000 is set up.  On bare metal this
is fine because the CPU wont load any segments unless  they are
explicitly used.  But unfortunately, this breaks Xen on vmx FV, since it
(for now) blindly loads all the segments into the VMCS if they are less
than the gdt limit. Since the real mode segments are around 0x3000, we are
getting junk into the VMCS and that later causes an exception.

Stephen Tweedie has written up a patch to fix the Xen side and will be
submitting that to those folks. But that doesn't excuse the GDT limit
being a magnitude too big.

AK: changed to compute true gdt size in assembler, fixed comment

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andi Kleen <ak@suse.de>
2006-11-14 16:57:46 +01:00

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/*
* setup.S Copyright (C) 1991, 1992 Linus Torvalds
*
* setup.s is responsible for getting the system data from the BIOS,
* and putting them into the appropriate places in system memory.
* both setup.s and system has been loaded by the bootblock.
*
* This code asks the bios for memory/disk/other parameters, and
* puts them in a "safe" place: 0x90000-0x901FF, ie where the
* boot-block used to be. It is then up to the protected mode
* system to read them from there before the area is overwritten
* for buffer-blocks.
*
* Move PS/2 aux init code to psaux.c
* (troyer@saifr00.cfsat.Honeywell.COM) 03Oct92
*
* some changes and additional features by Christoph Niemann,
* March 1993/June 1994 (Christoph.Niemann@linux.org)
*
* add APM BIOS checking by Stephen Rothwell, May 1994
* (sfr@canb.auug.org.au)
*
* High load stuff, initrd support and position independency
* by Hans Lermen & Werner Almesberger, February 1996
* <lermen@elserv.ffm.fgan.de>, <almesber@lrc.epfl.ch>
*
* Video handling moved to video.S by Martin Mares, March 1996
* <mj@k332.feld.cvut.cz>
*
* Extended memory detection scheme retwiddled by orc@pell.chi.il.us (david
* parsons) to avoid loadlin confusion, July 1997
*
* Transcribed from Intel (as86) -> AT&T (gas) by Chris Noe, May 1999.
* <stiker@northlink.com>
*
* Fix to work around buggy BIOSes which don't use carry bit correctly
* and/or report extended memory in CX/DX for e801h memory size detection
* call. As a result the kernel got wrong figures. The int15/e801h docs
* from Ralf Brown interrupt list seem to indicate AX/BX should be used
* anyway. So to avoid breaking many machines (presumably there was a reason
* to orginally use CX/DX instead of AX/BX), we do a kludge to see
* if CX/DX have been changed in the e801 call and if so use AX/BX .
* Michael Miller, April 2001 <michaelm@mjmm.org>
*
* Added long mode checking and SSE force. March 2003, Andi Kleen.
*/
#include <asm/segment.h>
#include <linux/utsrelease.h>
#include <linux/compile.h>
#include <asm/boot.h>
#include <asm/e820.h>
#include <asm/page.h>
/* Signature words to ensure LILO loaded us right */
#define SIG1 0xAA55
#define SIG2 0x5A5A
INITSEG = DEF_INITSEG # 0x9000, we move boot here, out of the way
SYSSEG = DEF_SYSSEG # 0x1000, system loaded at 0x10000 (65536).
SETUPSEG = DEF_SETUPSEG # 0x9020, this is the current segment
# ... and the former contents of CS
DELTA_INITSEG = SETUPSEG - INITSEG # 0x0020
.code16
.globl begtext, begdata, begbss, endtext, enddata, endbss
.text
begtext:
.data
begdata:
.bss
begbss:
.text
start:
jmp trampoline
# This is the setup header, and it must start at %cs:2 (old 0x9020:2)
.ascii "HdrS" # header signature
.word 0x0204 # header version number (>= 0x0105)
# or else old loadlin-1.5 will fail)
realmode_swtch: .word 0, 0 # default_switch, SETUPSEG
start_sys_seg: .word SYSSEG
.word kernel_version # pointing to kernel version string
# above section of header is compatible
# with loadlin-1.5 (header v1.5). Don't
# change it.
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
#ifndef __BIG_KERNEL__
.byte 0
#else
.byte LOADED_HIGH
#endif
setup_move_size: .word 0x8000 # size to move, when setup is not
# loaded at 0x90000. We will move setup
# to 0x90000 then just before jumping
# into the kernel. However, only the
# loader knows how much data behind
# us also needs to be loaded.
code32_start: # here loaders can put a different
# start address for 32-bit code.
#ifndef __BIG_KERNEL__
.long 0x1000 # 0x1000 = default for zImage
#else
.long 0x100000 # 0x100000 = default for big kernel
#endif
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:
.long 0 # obsolete
heap_end_ptr: .word modelist+1024 # (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
trampoline: call start_of_setup
.align 16
# The offset at this point is 0x240
.space (0xeff-0x240+1) # E820 & EDD space (ending at 0xeff)
# End of setup header #####################################################
start_of_setup:
# Bootlin depends on this being done early
movw $0x01500, %ax
movb $0x81, %dl
int $0x13
#ifdef SAFE_RESET_DISK_CONTROLLER
# Reset the disk controller.
movw $0x0000, %ax
movb $0x80, %dl
int $0x13
#endif
# Set %ds = %cs, we know that SETUPSEG = %cs at this point
movw %cs, %ax # aka SETUPSEG
movw %ax, %ds
# Check signature at end of setup
cmpw $SIG1, setup_sig1
jne bad_sig
cmpw $SIG2, setup_sig2
jne bad_sig
jmp good_sig1
# Routine to print asciiz string at ds:si
prtstr:
lodsb
andb %al, %al
jz fin
call prtchr
jmp prtstr
fin: ret
# Space printing
prtsp2: call prtspc # Print double space
prtspc: movb $0x20, %al # Print single space (note: fall-thru)
prtchr:
pushw %ax
pushw %cx
movw $0007,%bx
movw $0x01, %cx
movb $0x0e, %ah
int $0x10
popw %cx
popw %ax
ret
beep: movb $0x07, %al
jmp prtchr
no_sig_mess: .string "No setup signature found ..."
good_sig1:
jmp good_sig
# We now have to find the rest of the setup code/data
bad_sig:
movw %cs, %ax # SETUPSEG
subw $DELTA_INITSEG, %ax # INITSEG
movw %ax, %ds
xorb %bh, %bh
movb (497), %bl # get setup sect from bootsect
subw $4, %bx # LILO loads 4 sectors of setup
shlw $8, %bx # convert to words (1sect=2^8 words)
movw %bx, %cx
shrw $3, %bx # convert to segment
addw $SYSSEG, %bx
movw %bx, %cs:start_sys_seg
# Move rest of setup code/data to here
movw $2048, %di # four sectors loaded by LILO
subw %si, %si
movw %cs, %ax # aka SETUPSEG
movw %ax, %es
movw $SYSSEG, %ax
movw %ax, %ds
rep
movsw
movw %cs, %ax # aka SETUPSEG
movw %ax, %ds
cmpw $SIG1, setup_sig1
jne no_sig
cmpw $SIG2, setup_sig2
jne no_sig
jmp good_sig
no_sig:
lea no_sig_mess, %si
call prtstr
no_sig_loop:
jmp no_sig_loop
good_sig:
movw %cs, %ax # aka SETUPSEG
subw $DELTA_INITSEG, %ax # aka INITSEG
movw %ax, %ds
# Check if an old loader tries to load a big-kernel
testb $LOADED_HIGH, %cs:loadflags # Do we have a big kernel?
jz loader_ok # No, no danger for old loaders.
cmpb $0, %cs:type_of_loader # Do we have a loader that
# can deal with us?
jnz loader_ok # Yes, continue.
pushw %cs # No, we have an old loader,
popw %ds # die.
lea loader_panic_mess, %si
call prtstr
jmp no_sig_loop
loader_panic_mess: .string "Wrong loader, giving up..."
loader_ok:
/* check for long mode. */
/* we have to do this before the VESA setup, otherwise the user
can't see the error message. */
pushw %ds
movw %cs,%ax
movw %ax,%ds
/* minimum CPUID flags for x86-64 */
/* see http://www.x86-64.org/lists/discuss/msg02971.html */
#define SSE_MASK ((1<<25)|(1<<26))
#define REQUIRED_MASK1 ((1<<0)|(1<<3)|(1<<4)|(1<<5)|(1<<6)|(1<<8)|\
(1<<13)|(1<<15)|(1<<24))
#define REQUIRED_MASK2 (1<<29)
pushfl /* standard way to check for cpuid */
popl %eax
movl %eax,%ebx
xorl $0x200000,%eax
pushl %eax
popfl
pushfl
popl %eax
cmpl %eax,%ebx
jz no_longmode /* cpu has no cpuid */
movl $0x0,%eax
cpuid
cmpl $0x1,%eax
jb no_longmode /* no cpuid 1 */
xor %di,%di
cmpl $0x68747541,%ebx /* AuthenticAMD */
jnz noamd
cmpl $0x69746e65,%edx
jnz noamd
cmpl $0x444d4163,%ecx
jnz noamd
mov $1,%di /* cpu is from AMD */
noamd:
movl $0x1,%eax
cpuid
andl $REQUIRED_MASK1,%edx
xorl $REQUIRED_MASK1,%edx
jnz no_longmode
movl $0x80000000,%eax
cpuid
cmpl $0x80000001,%eax
jb no_longmode /* no extended cpuid */
movl $0x80000001,%eax
cpuid
andl $REQUIRED_MASK2,%edx
xorl $REQUIRED_MASK2,%edx
jnz no_longmode
sse_test:
movl $1,%eax
cpuid
andl $SSE_MASK,%edx
cmpl $SSE_MASK,%edx
je sse_ok
test %di,%di
jz no_longmode /* only try to force SSE on AMD */
movl $0xc0010015,%ecx /* HWCR */
rdmsr
btr $15,%eax /* enable SSE */
wrmsr
xor %di,%di /* don't loop */
jmp sse_test /* try again */
no_longmode:
call beep
lea long_mode_panic,%si
call prtstr
no_longmode_loop:
jmp no_longmode_loop
long_mode_panic:
.string "Your CPU does not support long mode. Use a 32bit distribution."
.byte 0
sse_ok:
popw %ds
# tell BIOS we want to go to long mode
movl $0xec00,%eax # declare target operating mode
movl $2,%ebx # long mode
int $0x15
# Get memory size (extended mem, kB)
xorl %eax, %eax
movl %eax, (0x1e0)
#ifndef STANDARD_MEMORY_BIOS_CALL
movb %al, (E820NR)
# Try three different memory detection schemes. First, try
# e820h, which lets us assemble a memory map, then try e801h,
# which returns a 32-bit memory size, and finally 88h, which
# returns 0-64m
# method E820H:
# the memory map from hell. e820h returns memory classified into
# a whole bunch of different types, and allows memory holes and
# everything. We scan through this memory map and build a list
# of the first 32 memory areas, which we return at [E820MAP].
# This is documented at http://www.acpi.info/, in the ACPI 2.0 specification.
#define SMAP 0x534d4150
meme820:
xorl %ebx, %ebx # continuation counter
movw $E820MAP, %di # point into the whitelist
# so we can have the bios
# directly write into it.
jmpe820:
movl $0x0000e820, %eax # e820, upper word zeroed
movl $SMAP, %edx # ascii 'SMAP'
movl $20, %ecx # size of the e820rec
pushw %ds # data record.
popw %es
int $0x15 # make the call
jc bail820 # fall to e801 if it fails
cmpl $SMAP, %eax # check the return is `SMAP'
jne bail820 # fall to e801 if it fails
# cmpl $1, 16(%di) # is this usable memory?
# jne again820
# If this is usable memory, we save it by simply advancing %di by
# sizeof(e820rec).
#
good820:
movb (E820NR), %al # up to 128 entries
cmpb $E820MAX, %al
jae bail820
incb (E820NR)
movw %di, %ax
addw $20, %ax
movw %ax, %di
again820:
cmpl $0, %ebx # check to see if
jne jmpe820 # %ebx is set to EOF
bail820:
# method E801H:
# memory size is in 1k chunksizes, to avoid confusing loadlin.
# we store the 0xe801 memory size in a completely different place,
# because it will most likely be longer than 16 bits.
# (use 1e0 because that's what Larry Augustine uses in his
# alternative new memory detection scheme, and it's sensible
# to write everything into the same place.)
meme801:
stc # fix to work around buggy
xorw %cx,%cx # BIOSes which don't clear/set
xorw %dx,%dx # carry on pass/error of
# e801h memory size call
# or merely pass cx,dx though
# without changing them.
movw $0xe801, %ax
int $0x15
jc mem88
cmpw $0x0, %cx # Kludge to handle BIOSes
jne e801usecxdx # which report their extended
cmpw $0x0, %dx # memory in AX/BX rather than
jne e801usecxdx # CX/DX. The spec I have read
movw %ax, %cx # seems to indicate AX/BX
movw %bx, %dx # are more reasonable anyway...
e801usecxdx:
andl $0xffff, %edx # clear sign extend
shll $6, %edx # and go from 64k to 1k chunks
movl %edx, (0x1e0) # store extended memory size
andl $0xffff, %ecx # clear sign extend
addl %ecx, (0x1e0) # and add lower memory into
# total size.
# Ye Olde Traditional Methode. Returns the memory size (up to 16mb or
# 64mb, depending on the bios) in ax.
mem88:
#endif
movb $0x88, %ah
int $0x15
movw %ax, (2)
# Set the keyboard repeat rate to the max
movw $0x0305, %ax
xorw %bx, %bx
int $0x16
# Check for video adapter and its parameters and allow the
# user to browse video modes.
call video # NOTE: we need %ds pointing
# to bootsector
# Get hd0 data...
xorw %ax, %ax
movw %ax, %ds
ldsw (4 * 0x41), %si
movw %cs, %ax # aka SETUPSEG
subw $DELTA_INITSEG, %ax # aka INITSEG
pushw %ax
movw %ax, %es
movw $0x0080, %di
movw $0x10, %cx
pushw %cx
cld
rep
movsb
# Get hd1 data...
xorw %ax, %ax
movw %ax, %ds
ldsw (4 * 0x46), %si
popw %cx
popw %es
movw $0x0090, %di
rep
movsb
# Check that there IS a hd1 :-)
movw $0x01500, %ax
movb $0x81, %dl
int $0x13
jc no_disk1
cmpb $3, %ah
je is_disk1
no_disk1:
movw %cs, %ax # aka SETUPSEG
subw $DELTA_INITSEG, %ax # aka INITSEG
movw %ax, %es
movw $0x0090, %di
movw $0x10, %cx
xorw %ax, %ax
cld
rep
stosb
is_disk1:
# Check for PS/2 pointing device
movw %cs, %ax # aka SETUPSEG
subw $DELTA_INITSEG, %ax # aka INITSEG
movw %ax, %ds
movb $0, (0x1ff) # default is no pointing device
int $0x11 # int 0x11: equipment list
testb $0x04, %al # check if mouse installed
jz no_psmouse
movb $0xAA, (0x1ff) # device present
no_psmouse:
#include "../../i386/boot/edd.S"
# Now we want to move to protected mode ...
cmpw $0, %cs:realmode_swtch
jz rmodeswtch_normal
lcall *%cs:realmode_swtch
jmp rmodeswtch_end
rmodeswtch_normal:
pushw %cs
call default_switch
rmodeswtch_end:
# we get the code32 start address and modify the below 'jmpi'
# (loader may have changed it)
movl %cs:code32_start, %eax
movl %eax, %cs:code32
# Now we move the system to its rightful place ... but we check if we have a
# big-kernel. In that case we *must* not move it ...
testb $LOADED_HIGH, %cs:loadflags
jz do_move0 # .. then we have a normal low
# loaded zImage
# .. or else we have a high
# loaded bzImage
jmp end_move # ... and we skip moving
do_move0:
movw $0x100, %ax # start of destination segment
movw %cs, %bp # aka SETUPSEG
subw $DELTA_INITSEG, %bp # aka INITSEG
movw %cs:start_sys_seg, %bx # start of source segment
cld
do_move:
movw %ax, %es # destination segment
incb %ah # instead of add ax,#0x100
movw %bx, %ds # source segment
addw $0x100, %bx
subw %di, %di
subw %si, %si
movw $0x800, %cx
rep
movsw
cmpw %bp, %bx # assume start_sys_seg > 0x200,
# so we will perhaps read one
# page more than needed, but
# never overwrite INITSEG
# because destination is a
# minimum one page below source
jb do_move
end_move:
# then we load the segment descriptors
movw %cs, %ax # aka SETUPSEG
movw %ax, %ds
# Check whether we need to be downward compatible with version <=201
cmpl $0, cmd_line_ptr
jne end_move_self # loader uses version >=202 features
cmpb $0x20, type_of_loader
je end_move_self # bootsect loader, we know of it
# Boot loader doesnt support boot protocol version 2.02.
# If we have our code not at 0x90000, we need to move it there now.
# We also then need to move the params behind it (commandline)
# Because we would overwrite the code on the current IP, we move
# it in two steps, jumping high after the first one.
movw %cs, %ax
cmpw $SETUPSEG, %ax
je end_move_self
cli # make sure we really have
# interrupts disabled !
# because after this the stack
# should not be used
subw $DELTA_INITSEG, %ax # aka INITSEG
movw %ss, %dx
cmpw %ax, %dx
jb move_self_1
addw $INITSEG, %dx
subw %ax, %dx # this will go into %ss after
# the move
move_self_1:
movw %ax, %ds
movw $INITSEG, %ax # real INITSEG
movw %ax, %es
movw %cs:setup_move_size, %cx
std # we have to move up, so we use
# direction down because the
# areas may overlap
movw %cx, %di
decw %di
movw %di, %si
subw $move_self_here+0x200, %cx
rep
movsb
ljmp $SETUPSEG, $move_self_here
move_self_here:
movw $move_self_here+0x200, %cx
rep
movsb
movw $SETUPSEG, %ax
movw %ax, %ds
movw %dx, %ss
end_move_self: # now we are at the right place
lidt idt_48 # load idt with 0,0
xorl %eax, %eax # Compute gdt_base
movw %ds, %ax # (Convert %ds:gdt to a linear ptr)
shll $4, %eax
addl $gdt, %eax
movl %eax, (gdt_48+2)
lgdt gdt_48 # load gdt with whatever is
# appropriate
# that was painless, now we enable a20
call empty_8042
movb $0xD1, %al # command write
outb %al, $0x64
call empty_8042
movb $0xDF, %al # A20 on
outb %al, $0x60
call empty_8042
#
# You must preserve the other bits here. Otherwise embarrasing things
# like laptops powering off on boot happen. Corrected version by Kira
# Brown from Linux 2.2
#
inb $0x92, %al #
orb $02, %al # "fast A20" version
outb %al, $0x92 # some chips have only this
# wait until a20 really *is* enabled; it can take a fair amount of
# time on certain systems; Toshiba Tecras are known to have this
# problem. The memory location used here (0x200) is the int 0x80
# vector, which should be safe to use.
xorw %ax, %ax # segment 0x0000
movw %ax, %fs
decw %ax # segment 0xffff (HMA)
movw %ax, %gs
a20_wait:
incw %ax # unused memory location <0xfff0
movw %ax, %fs:(0x200) # we use the "int 0x80" vector
cmpw %gs:(0x210), %ax # and its corresponding HMA addr
je a20_wait # loop until no longer aliased
# make sure any possible coprocessor is properly reset..
xorw %ax, %ax
outb %al, $0xf0
call delay
outb %al, $0xf1
call delay
# well, that went ok, I hope. Now we mask all interrupts - the rest
# is done in init_IRQ().
movb $0xFF, %al # mask all interrupts for now
outb %al, $0xA1
call delay
movb $0xFB, %al # mask all irq's but irq2 which
outb %al, $0x21 # is cascaded
# Well, that certainly wasn't fun :-(. Hopefully it works, and we don't
# need no steenking BIOS anyway (except for the initial loading :-).
# The BIOS-routine wants lots of unnecessary data, and it's less
# "interesting" anyway. This is how REAL programmers do it.
#
# Well, now's the time to actually move into protected mode. To make
# things as simple as possible, we do no register set-up or anything,
# we let the gnu-compiled 32-bit programs do that. We just jump to
# absolute address 0x1000 (or the loader supplied one),
# in 32-bit protected mode.
#
# Note that the short jump isn't strictly needed, although there are
# reasons why it might be a good idea. It won't hurt in any case.
movw $1, %ax # protected mode (PE) bit
lmsw %ax # This is it!
jmp flush_instr
flush_instr:
xorw %bx, %bx # Flag to indicate a boot
xorl %esi, %esi # Pointer to real-mode code
movw %cs, %si
subw $DELTA_INITSEG, %si
shll $4, %esi # Convert to 32-bit pointer
# NOTE: For high loaded big kernels we need a
# jmpi 0x100000,__KERNEL_CS
#
# but we yet haven't reloaded the CS register, so the default size
# of the target offset still is 16 bit.
# However, using an operand prefix (0x66), the CPU will properly
# take our 48 bit far pointer. (INTeL 80386 Programmer's Reference
# Manual, Mixing 16-bit and 32-bit code, page 16-6)
.byte 0x66, 0xea # prefix + jmpi-opcode
code32: .long 0x1000 # will be set to 0x100000
# for big kernels
.word __KERNEL_CS
# Here's a bunch of information about your current kernel..
kernel_version: .ascii UTS_RELEASE
.ascii " ("
.ascii LINUX_COMPILE_BY
.ascii "@"
.ascii LINUX_COMPILE_HOST
.ascii ") "
.ascii UTS_VERSION
.byte 0
# This is the default real mode switch routine.
# to be called just before protected mode transition
default_switch:
cli # no interrupts allowed !
movb $0x80, %al # disable NMI for bootup
# sequence
outb %al, $0x70
lret
# This routine checks that the keyboard command queue is empty
# (after emptying the output buffers)
#
# Some machines have delusions that the keyboard buffer is always full
# with no keyboard attached...
#
# If there is no keyboard controller, we will usually get 0xff
# to all the reads. With each IO taking a microsecond and
# a timeout of 100,000 iterations, this can take about half a
# second ("delay" == outb to port 0x80). That should be ok,
# and should also be plenty of time for a real keyboard controller
# to empty.
#
empty_8042:
pushl %ecx
movl $100000, %ecx
empty_8042_loop:
decl %ecx
jz empty_8042_end_loop
call delay
inb $0x64, %al # 8042 status port
testb $1, %al # output buffer?
jz no_output
call delay
inb $0x60, %al # read it
jmp empty_8042_loop
no_output:
testb $2, %al # is input buffer full?
jnz empty_8042_loop # yes - loop
empty_8042_end_loop:
popl %ecx
ret
# Read the cmos clock. Return the seconds in al
gettime:
pushw %cx
movb $0x02, %ah
int $0x1a
movb %dh, %al # %dh contains the seconds
andb $0x0f, %al
movb %dh, %ah
movb $0x04, %cl
shrb %cl, %ah
aad
popw %cx
ret
# Delay is needed after doing I/O
delay:
outb %al,$0x80
ret
# Descriptor tables
gdt:
.word 0, 0, 0, 0 # dummy
.word 0, 0, 0, 0 # unused
.word 0xFFFF # 4Gb - (0x100000*0x1000 = 4Gb)
.word 0 # base address = 0
.word 0x9A00 # code read/exec
.word 0x00CF # granularity = 4096, 386
# (+5th nibble of limit)
.word 0xFFFF # 4Gb - (0x100000*0x1000 = 4Gb)
.word 0 # base address = 0
.word 0x9200 # data read/write
.word 0x00CF # granularity = 4096, 386
# (+5th nibble of limit)
gdt_end:
idt_48:
.word 0 # idt limit = 0
.word 0, 0 # idt base = 0L
gdt_48:
.word gdt_end-gdt-1 # gdt limit
.word 0, 0 # gdt base (filled in later)
# Include video setup & detection code
#include "video.S"
# Setup signature -- must be last
setup_sig1: .word SIG1
setup_sig2: .word SIG2
# After this point, there is some free space which is used by the video mode
# handling code to store the temporary mode table (not used by the kernel).
modelist:
.text
endtext:
.data
enddata:
.bss
endbss:
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