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发信人: jjksam (欢迎光临荔园晨风Linux版, InstallBBS版!), 信区: Linux
标 题: [转载] 我对linux启动的一点分析(三)
发信站: 荔园晨风BBS站 (Sun Dec 9 13:15:46 2001), 转信
【 以下文字转载自 jjksam 的信箱 】
【 原文由 jjksam@smth.org 所发表 】
发信人: babyant (云淡风清), 信区: KernelTech
标 题: [转载] 我对linux启动的一点分析(三)
发信站: BBS 水木清华站 (Sat Dec 8 08:45:12 2001)
setup.s
/*
* 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 dont 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 reaso
n
* 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>
*
*/
#include <linux/config.h>
#include <asm/segment.h>
#include <linux/version.h>
#include <linux/compile.h>
#include <asm/boot.h>
#include <asm/e820.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 0x0202 # 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: ;由bootsect.s调用9020h:bootsect_help
er,这个子过程
;原本属于bootsect.s,但他只有512B,因此
放不下
.word bootsect_helper, SETUPSEG
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.
trampoline: call start_of_setup
.space 1024
# End of setup header #####################################################
start_of_setup:
# Bootlin depends on this being done early
movw $0x01500, %ax
movb $0x81, %dl
int $0x13 ;get disk type
#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 ;如果不是用bootsect.s启动，而是lilo,他只会load
setup.s的头4个扇区
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)
# Part of above routine, this one just prints ascii al
prtchr: pushw %ax
pushw %cx
xorb %bh, %bh
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 = 9020h
subw $DELTA_INITSEG, %ax ;INITSEG = 9000h
movw %ax, %ds
xorb %bh, %bh
movb (497), %bl ;get setup sect from bootsect,即使用lilo启动，也少不了加载
bootsect.s
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 ;实际压缩内核的起始段，??可见syssize=k
ernelsize + setupsize - 4才能保证压缩内核被完全加载到了内存,大内核覆盖了1000
:0又怎么办？
# 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: ;无标志则死机
jmp no_sig_loop
good_sig:
movw %cs, %ax ;aka SETUPSEG
subw $DELTA_INITSEG, %ax ;aka INITSEG
movw %ax, %ds ;ds = 9000h
# 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:
;取内存容量到9000:0002，设置键盘的拍发速率MAX(30)及延迟时间为0，调用子过
程video(在video模块中，其源程序是video.S)检查显卡及其参数；
;将第一个硬盘参数表读入9000:0080；
;检查有无第二个硬盘，有则将其参数表读入9000:0090，无则此段内存清零；
;检查有无PS/2鼠标，无则将9000:01FF字节清零，有则将0xAA填入；
;检查有无BIOS增强电源管理，无则9000:0064清零，有则在9000:0064 ~ 0080填入
相应值
# 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.teleport.com/~acpi/acpihtml/topic245.htm
#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 32 entries
cmpb $E820MAX, %al
jnl 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 dont 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 Micro Channel (MCA) bus
movw %cs, %ax # aka SETUPSEG
subw $DELTA_INITSEG, %ax # aka INITSEG
movw %ax, %ds
xorw %ax, %ax
movw %ax, (0xa0) # set table length to 0
movb $0xc0, %ah
stc
int $0x15 # moves feature table to es:bx
jc no_mca
pushw %ds
movw %es, %ax
movw %ax, %ds
movw %cs, %ax # aka SETUPSEG
subw $DELTA_INITSEG, %ax # aka INITSEG
movw %ax, %es
movw %bx, %si
movw $0xa0, %di
movw (%si), %cx
addw $2, %cx # table length is a short
cmpw $0x10, %cx
jc sysdesc_ok
movw $0x10, %cx # we keep only first 16 bytes
sysdesc_ok:
rep
movsb
popw %ds
no_mca:
# Check for PS/2 pointing device
movw %cs, %ax # aka SETUPSEG
subw $DELTA_INITSEG, %ax # aka INITSEG
movw %ax, %ds
movw $0, (0x1ff) # default is no pointing device
int $0x11 # int 0x11: equipment list
testb $0x04, %al # check if mouse installed
jz no_psmouse
movw $0xAA, (0x1ff) # device present
no_psmouse:
#if defined(CONFIG_APM) || defined(CONFIG_APM_MODULE)
# Then check for an APM BIOS...
# %ds points to the bootsector
movw $0, 0x40 # version = 0 means no APM BIOS
movw $0x05300, %ax # APM BIOS installation check
xorw %bx, %bx
int $0x15
jc done_apm_bios # Nope, no APM BIOS
cmpw $0x0504d, %bx # Check for "PM" signature
jne done_apm_bios # No signature, no APM BIOS
andw $0x02, %cx # Is 32 bit supported?
je done_apm_bios # No 32-bit, no (good) APM BIOS
movw $0x05304, %ax # Disconnect first just in case
xorw %bx, %bx
int $0x15 # ignore return code
movw $0x05303, %ax # 32 bit connect
xorl %ebx, %ebx
xorw %cx, %cx # paranoia :-)
xorw %dx, %dx # ...
xorl %esi, %esi # ...
xorw %di, %di # ...
int $0x15
jc no_32_apm_bios # Ack, error.
movw %ax, (66) # BIOS code segment
movl %ebx, (68) # BIOS entry point offset
movw %cx, (72) # BIOS 16 bit code segment
movw %dx, (74) # BIOS data segment
movl %esi, (78) # BIOS code segment lengths
movw %di, (82) # BIOS data segment length
# Redo the installation check as the 32 bit connect
# modifies the flags returned on some BIOSs
movw $0x05300, %ax # APM BIOS installation check
xorw %bx, %bx
xorw %cx, %cx # paranoia
int $0x15
jc apm_disconnect # error -> shouldn't happen
cmpw $0x0504d, %bx # check for "PM" signature
jne apm_disconnect # no sig -> shouldn't happen
movw %ax, (64) # record the APM BIOS version
movw %cx, (76) # and flags
jmp done_apm_bios
apm_disconnect: # Tidy up
movw $0x05304, %ax # Disconnect
xorw %bx, %bx
int $0x15 # ignore return code
jmp done_apm_bios
no_32_apm_bios:
andw $0xfffd, (76) # remove 32 bit support bit
done_apm_bios:
#endif
# Now we want to move to protected mode ...
cmpw $0, %cs:realmode_swtch
jz rmodeswtch_normal
lcall %cs:realmode_swtch ;9020h:default_switch
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: ;普通内核-->0100:0h
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=4k
movw %bx, %ds ;source segment
addw $0x100, %bx
subw %di, %di
subw %si, %si
movw $0x800, %cx ;4k bytes
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 ;fs=0h
decw %ax ;segment 0xffff (HMA)
movw %ax, %gs ;gs=ffffh
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! 切换保护模式有两种 mov cr0,1 ; lmsw 1
jmp flush_instr ;清CPU指令预取队列
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 operant 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 = jmpi code32 10h(__Kernel_cs)
code32: .long 0x1000 ;will be set to 0x100000
;for big kernels
.word __KERNEL_CS ;10h,16 bit CS segment selector: the
2nd entry of GDT
# 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 only gets called, if we get loaded by the simple
# bootsect loader _and_ have a bzImage to load.
# Because there is no place left in the 512 bytes of the boot sector,
# we must emigrate to code space here.
bootsect_helper: ;入口参数：ES:BX为当前段和偏
移
cmpw $0, %cs:bootsect_es ;第一次bootsect_es = 0,表1000:0h还未读
压缩内核
jnz bootsect_second
movb $0x20, %cs:type_of_loader ;Loader is bootsect
movw %es, %ax ;es = 1000h
shrw $4, %ax
movb %ah, %cs:bootsect_src_base+2 ;bootsect_src_base = 10000h
movw %es, %ax
movw %ax, %cs:bootsect_es ;bootsect_es = 1000h
subw $SYSSEG, %ax
lret ;nothing else to do for now
bootsect_second: ;读压缩内核了
pushw %cx
pushw %si
pushw %bx
testw %bx, %bx ;64K full?
jne bootsect_ex
movw $0x8000, %cx ;full 64K, INT15 moves words
pushw %cs
popw %es
movw $bootsect_gdt, %si
movw $0x8700, %ax
int $0x15 ;10000h --> 100000h
jc bootsect_panic ;this, if INT15 fails,死机
movw %cs:bootsect_es, %es ;恢复ES,第一次后永远是1000h，因为每读一个64k就进
行搬移,此时bx=0
incb %cs:bootsect_dst_base+2 ;增加64K
bootsect_ex: ;not 64K full
movb %cs:bootsect_dst_base+2, %ah
shlb $4, %ah ;we now have the number of
;moved frames in %ax？？？
xorb %al, %al
popw %bx
popw %si
popw %cx
lret
;Format of global descriptor
table
bootsect_gdt: ;全0,由BIOS使用
.word 0, 0, 0, 0
.word 0, 0, 0, 0
bootsect_src: ;source segment length in by
tes
.word 0xffff
bootsect_src_base: ;24-bit linear source addres
s, low byte first
.byte 0x00, 0x00, 0x01 ;base = 0x010000
.byte 0x93 ;typbyte,source segment access rights (93h)
.word 0 ;limit16,base24 =0,386mode
bootsect_dst:
.word 0xffff ;dest. segment length in bytes
bootsect_dst_base:
.byte 0x00, 0x00, 0x10 ;base = 0x100000
.byte 0x93 ;typbyte
.word 0 ;limit16,base24 =0
.word 0, 0, 0, 0 ;BIOS CS
.word 0, 0, 0, 0 ;BIOS DS
;end of global description t
able
bootsect_es:
.word 0
bootsect_panic:
pushw %cs
popw %ds
cld
leaw bootsect_panic_mess, %si
call prtstr
bootsect_panic_loop:
jmp bootsect_panic_loop
bootsect_panic_mess:
.string "INT15 refuses to access high mem, giving up."
# 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)
idt_48:
.word 0 # idt limit = 0
.word 0, 0 # idt base = 0L
gdt_48:
.word 0x8000 # gdt limit=2048,
# 256 GDT entries
.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:
1.检查setup模块结尾处的完整性标记setup_sig1和setup_sig2
2.setup完整加载后，start_sys_seg:0000被设置为真正的压缩内核始址
3.利用BIOS提供的功能，取内存容量到9000:0002，设置键盘的拍发速率MAX(30)及延迟
时间为0，调用子过程video(在video模块中，其源程序是video.S)检查显卡及其参数；
将第一个硬盘参数表读入9000:0080；
检查有无第二个硬盘，有则将其参数表读入9000:0090，无则此段内存清零；
检查有无PS/2鼠标，无则将9000:01FF字节清零，有则将0xAA填入；
检查有无BIOS增强电源管理，无则9000:0064清零，有则在9000:0064 ~ 0080填入相应值
4.检查标识realmode_swtch，做实模式切换准备
5.对大内核设置相应code32的值,普通内核则从当前位置SYSSEG segment移至0x100 seg
ment
6.初始化IDTR和GDTR
7.enable A20; 设协处理器
8.设置CR0的PE位，进入保护模式
9．跳转到压缩内核，继续运行
--
※ 来源:·BBS 水木清华站 smth.org·[FROM: 137.194.8.113]
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