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Linux 386 boot代码分析 (2) setup.txt head.txt [复制链接]

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发表于 2003-02-08 20:49 |只看该作者 |倒序浏览

看到好文章为什么不能跟大家分享呢？

下面是我整理过的出自http://www.linuxforum.net/的好文章。
原文作者：feiyunw　和　raoxianhong

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读代码前先看看 raoxianhong 的中文版setup.txt ：
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1、按规定得有个头，所以一开始是惯用的JMP；
2、头里边内容很丰富，具体用法走着瞧；
3、自我检测，不知道有什么用，防伪造？防篡改？
4、如果装载程序不对，只好死掉！以下终于走入正题；
5、获取内存容量（使用了三种办法，其中的E820和E801看不明白，int 15倒是老朋友了--应该是上个世纪80年代末认识的了，真佩服十年过去了，情意依旧，不过遇上一些不守规矩的BIOS，不知道还行不行）；
6、将键盘重复键的重复率设为最大，灵敏一点？
7、检测硬盘，不懂，放这里干什么？
8、检测MCA总线（不要问我这是什么）；
9、检测PS/2鼠标，用int 11，只是不知道为何放这里；
10、检测电源管理BIOS；唉，书到用时方恨少，不懂的太多了，真不好意思；不过也没有关系，不懂的就别去动它就行了；以下要进入内核了；
11、在进入保护模式之前，可以调用一个你提供的试模式下的过程，让你最后在看她一眼，当然你要是不提供，那就有个默认的，无非是塞住耳朵闭上眼睛禁止任何中断，包括著名的NMI ；
12、设置保护模式起动后的例程地址，你可以写自己的例程，但不是代替而是把它加在setup提供的例程的前面（显示一个小鸭子？）；
13、如果内核是zImage，将它移动到0x10000处；
14、如果自己不在0x90000处，则移动到0x90000处；
15、建立idt, gdt表；
16、启动A20；
17、屏住呼吸，屏闭所有中断；
18、启动！movw $1, %ax ; lmsw %ax; 好已经进入保护模式下，马上进行局部调整；
19、jmpi 0x100000, __KERNEL_CS，终于进入内核；

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下面是　feiyunw 的代码分析：
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////////////////////////////////////////////////////////////////////
// setup.txt
// Copyright(C) 2001, Feiyun Wang
////////////////////////////////////////////////////////////////////
// analysis on linux/arch/i386/boot/setup.S (for Linux 2.2.17)
////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////
// export the margin tags for .text, .data and .bss
{
.text
begtext:
.data
begdata:
.bss
begbss:
}
////////////////////////////////////////////////////////////////////
.text
start()
SYSSEG = 0x1000
SETUPSEG = 0x9020
modelist = end of .text:
{
// if loaded by bootsect.S,
// you can assume CS=SETUPSEG (=0x9020), otherwise...
goto start_of_setup();
/*
http://lxr.linux.no/source/Documentation/i386/boot.txt
Offset/Size Proto Name Meaning
01F1/1 ALL setup_sects The size of the setup in sectors
01F2/2 ALL root_flags If set, the root is mounted readonly
01F4/2 ALL syssize DO NOT USE - for bootsect.S use only
01F6/2 ALL swap_dev DO NOT USE - obsolete
01F8/2 ALL ram_size DO NOT USE - for bootsect.S use only
01FA/2 ALL vid_mode Video mode control
01FC/2 ALL root_dev Default root device number
01FE/2 ALL boot_flag 0xAA55 magic number
0200/2 2.00+ jump Jump instruction
0202/4 2.00+ header Magic signature "HdrS"
0206/2 2.00+ version Boot protocol version supported
0208/4 2.00+ realmode_swtch Boot loader hook
020C/4 2.00+ start_sys_seg Points to kernel version string
0210/1 2.00+ type_of_loader Boot loader identifier
0211/1 2.00+ loadflags Boot protocol option flags
0212/2 2.00+ setup_move_size Move to high memory size (used with hooks)
0214/4 2.00+ code32_start Boot loader hook
0218/4 2.00+ ramdisk_image initrd load address (set by boot loader)
021C/4 2.00+ ramdisk_size initrd size (set by boot loader)
0220/4 2.00+ bootsect_kludge DO NOT USE - for bootsect.S use only
0224/4 2.01+ heap_end_ptr Free memory after setup end
0226/2 N/A pad1 Unused
0228/4 2.02+ cmd_line_ptr 32-bit pointer to the kernel command line
*/
.ascii "HdrS"
.word 0x0201
realmode_swtch: // boot loader hook
.word 0, 0
start_sys_seg: // pointer to kernel version string
.word SYSSEG
.word kernel_version
type_of_loader:
.byte 0
loadflags:
#ifndef __BIG_KERNEL__
.byte 0x00
#else
.byte LOADED_HIGH = 1
#endif
setup_move_size:
.word 0x8000
code32_start: // boot loader hook
#ifndef __BIG_KERNEL__
.long 0x1000
#else
.long 0x100000
#endif
ramdisk_image: // initrd load address (set by boot loader)
.long 0
ramdisk_size: // initrd size (set by boot loader)
.long 0
bootsect_kludge: // DO NOT USE - for bootsect.S use only
.word bootsect_helper(), SETUPSEG
heap_end_ptr: // free memory after setup end
.word modelist+1024
}
////////////////////////////////////////////////////////////////////
// check signature to see if all code loaded
start_of_setup()
{
// get disk type, bootlin depends on this
// http://www.ctyme.com/intr/rb-0639.htm
int13h/AH=15h(AL=0, DL=0x81);
#ifdef SAFE_RESET_DISK_CONTROLLER
int13h/AH=0(AL=0, DL=0x80); // reset hd0
#endif
// check signature at the end of setup code
if (setup_sig1!=SIG1 || setup_sig2!=SIG2) {
// since size of setup may >; 4 sectors,
// the rest code may be loaded at SYSSEG
goto bad_sig;
}
goto goodsig1;
}
////////////////////////////////////////////////////////////////////
// some small functions
prtstr() { /* ... print ASCIIz string at DS:SI */}
prtsp2() { /* ... print double space */ }
prtspc() { /* ... print single space */ }
prtchr() { /* ... print ASCII AL */ }
beep() { /* ... beep */ }
////////////////////////////////////////////////////////////////////
goodsig1() { goto goodsig; } // making near jumps
////////////////////////////////////////////////////////////////////
// move rest setup code from SYSSEG:0 to CS:0800
// TODO: it won't work if image loaded at 0x100000?
bad_sig()
DELTA_INITSEG = 0x0020 (= SETUPSEG - INITSEG)
SYSSEG = 0x1000
{
BX = (CS-DELTA_INITSEG):[497]; // i.e. setup_sects
// first 4 sectors have been loaded
CX = (BX - 4) << 8; // rest code in words
start_sys_seg = (CX >;>; 3) + SYSSEG; // real system code start
move SYSSEG:0 to CS:0800 (CX*2 bytes);
if (setup_sig1!=SIG1 || setup_sig2!=SIG2) {
prtstr("No setup signature found ...");
halt;
}
}
////////////////////////////////////////////////////////////////////
// check if loader compatible with image
good_sig()
LOADHIGH = 1
{
if ((loadflags & LOADHIGH) && (!type_of_loader)) {
// Nope, old loader want to load big kernel
prtstr("Wrong loader: giving up.");
halt;
}
}
////////////////////////////////////////////////////////////////////
// get memory size
// set the keyboard repeat rate to max
// check video adapter
// get hd0 & hd1 data
// check for Micro Channel (MCA) bus
// check for PS/2 pointing device
// check for APM BIOS
// move code to INITSEG/SETUPSEG
// load IDT and GDT
// enable and test A20
// reset coprocessor
// reprogram the interrupts
// switch to protected mode
// goto KERNEL
loader_ok()
SETUPSET = 0x9020
INITSEG = 0x9000
DELTA_INITSEG = 0x20
{
// DS = CS - DELTA_INITSEG when entering this function
// get memory size
#ifndef STANDARD_MEMORY_BIOS_CALL
(double word)DS:[0x1E0] = 0;
try {
// get memory size for >;64M configurations
// http://www.ctyme.com/intr/rb-1739.htm
int15h/AX=E801h;
// AX = extended memory between 1M and 16M, in KB
// BX = extended memory above 16M, in 64K blocks
(double word)DS:[0x1E0] = ((EBX & 0xFFFF) << 6)
+ (EAX & 0xFFFF);
}
#else
(double word)DS:[0x1E0] = 0;
#endif
// get extended memory size
// http://www.ctyme.com/intr/rb-1529.htm
int15h/AH=88h;
DS:[2] = AX; // KB of contiguous memory from 100000h
// set the keyboard repeat rate to max
// http://www.ctyme.com/intr/rb-1757.htm
int16h/AX=0305h(BX=0);
// check video adapter and its parameters, see video.S
video();
// get hd0 & hd1 data
// http://www.ctyme.com/intr/rb-6135.htm
// http://www.ctyme.com/intr/rb-6184.htm
// pointers in 0:0104 & 0:0118 respectively
move hd0 data to CS-DELTA_INITSEG:0080 (16 bytes);
move hd1 data to CS-DELTA_INITSEG:0090 (16 bytes);
// get disk type, check if hd1 exists
// http://www.ctyme.com/intr/rb-0639.htm
int13h/AH=15h(AL=0, DL=0x81);
if (failed || AH!=03h) { // AH=03h if is a hard disk
clear CS-DELTA_INITSEG:0090 (16 bytes);
}
// check for Micro Channel (MCA) bus
DS:[0xA0] = 0; // set table length to 0
try {
// get system configuration
// http://www.ctyme.com/intr/rb-1594.htm
int15h/AH=C0h; // ES:BX = ROM configuration table
move ROM configuration table to CS-DELTA_INITSEG:00A0;
// first 16 bytes only
}
// check PS/2 pointing device
DS:[0x1FF] = 0;
// get equipment list
// http://www.ctyme.com/intr/rb-0575.htm
int11h();
if (has psmouse) {
DS:[0x1FF] = 0xAA;
}
#ifdef CONFIG_APM
// check for APM BIOS
DS:[0x40] = 0;
// Advanced Power Management v1.0+ - installation check
// http://www.ctyme.com/intr/rb-1394.htm
int15h/AX=5300h(BX=0);
// check both CF and BX for APM support
if (APM && 32-bit protected mode interface supported) {
int15h/AX=5304h(BX=0); // disconnect interface
try {
// clear return values first
clear EBX, CX, DX, ESI, DI;
// connect 32bit protect mode APM interface
// http://www.ctyme.com/intr/rb-1397.htm
int15h/AX=5303h(BX=0);
if (supported) {
DS:[0x42] = 32-bit code segment base address;
DS:[0x44] = offset of entry point;
DS:[0x48] = 16-bit code segment base address;
DS:[0x4A] = 16-bit data segment base address;
DS:[0x4E] = APM BIOS code segment length;
DS:[0x52] = APM BIOS data segment length;
int15h/AX=5300h(BX=0); // check again
if (APM supported) {
INITSET:[0x40] = APM version;
INITSET:[0x4C] = APM flags;
}
else { // should not happen
// disconnect interface
int15h/AX=5304h(BX=0);
}
}
else {
// clear 32bit support
INITSET:[0x4C] &= ~0x0002;
}
}
}
#endif
// call mode switch
if (realmode_swtch) {
far realmode_swtch(); // mode switch hook
}
else {
far default_switch(); // see below
}
// set code32: 0x100000 for big kernel, otherwise 0x1000
(double word) code32 = code32_start;
if (!(loadflags & LOADED_HIGH)) {
// normal low loaded zImage
move start_sys_seg:0 to (0100:0 ... CS-DELTA_INITSEG:0);
// move 0x1000 bytes each time
}
if (CS!=SETUPSEG) {
cli; // disable interrupts
// store new SS in DX
DX = SS;
AX = CS - DELTA_INITSEG;
if (DX>;=AX) {
DX = DX + INITSEG - AX; // i.e. SS-CS+SETUPSEG
}
// move CS-DELTA_INITSEG:0 to INITSEG:0 (setup_move_size bytes)
// TODO: why not do this in one step?
ES = INITSEG;
move _DOWNWARD_ from CS-DELTA_INITSEG:setup_move_size-1 to
(INITSEG:setup_move_size-1
... INITSEG:move_self_here+0x200);
// setup_move_size-move_self_here-0x200 bytes
// INITSEG:move_self_here+0x200 = SETUPSEG:move_self_here
goto SETUPSEG:move_self_here;
move_self_here:
move the rest to INITSEG:move_self_here+0x200-1 ... INITSEG:0;
// move_self_here+0x200 bytes
DS = SETUPSEG;
SS = DX;
}
// CS==SETUPSEG is true now
// Protected Mode Basics
// http://x86.ddj.com/articles/pmbasics/tspec_a1_doc.htm
lidt idt_48; // load idt with 0, 0;
// new code added here in Linux 2.4
lgdt gdt_48; // load gdt with whatever appropriate;
// enable A20
empty_8042();
outportb(0x64, 0xD1); // command write
empty_8042();
outportb(0x60, 0xDF); // A20 on
empty_8042();
#define TEST_ADDR 0x7C
// test A20
GS = AX = 0xFFFF;
BX = 0:[TEST_ADDR];
do {
0:[TEST_ADDR] = ++AX;
} while (AX==GS:[TEST_ADDR+0x10]);
0:[TEST_ADDR] = BX;
// reset coprocessor
outportb(0xF0, 0);
delay();
outportb(0xF1, 0);
delay();
// reprogram the interrupts
outportb(0x20, 0x11); // initialize 8259A-1
delay();
outportb(0xA0, 0x11); // initialize 8259A-2
delay();
outportb(0x21, 0x20); // start of hardware int's (0x20)
delay();
outportb(0xA1, 0x28); // start of hardware int's 2 (0x28)
delay();
outportb(0x21, 0x04); // 8259-1 is master
delay();
outportb(0xA1, 0x02); // 8259-2 is slave
delay();
outportb(0x21, 0x01); // 8086 mode
delay();
outportb(0xA1, 0x01); // 8086 mode
delay();
outportb(0xA1, 0xFF); // mask off all interrupts for now
delay();
outportb(0x21, 0xFB); // mask all irq's but irq2, which is cascaded
// protected mode!
mov ax, #1;
lmsw ax;
jmp flush_instr;
flush_instr:
xor bx, bx;
}
////////////////////////////////////////////////////////////////////
{
db 0x66, 0xea
code32:
dd 0x1000
dw __KERNEL_CS // 0x10, defined in asm-i386/segment.h
// goto 10:1000 or 10:100000
kernel_version:
.ascii UTS_RELEASE // defined in makefile
.ascii "("
.ascii LINUX_COMPILE_BY
.ascii "@"
.ascii LINUX_COMPILE_HOST
.ascii ")"
.ascii UTS_VERSION
db 0
}
////////////////////////////////////////////////////////////////////
// default real mode switch routine
far default_switch()
{
cli;
outportb(0x70, 0x80); // disable NMI
}
////////////////////////////////////////////////////////////////////
// get called when using bootsect loader _AND_ have bzImage to load
far bootsect_helper(ES)
{
if (bootsect_es==0) {
type_of_loader = 0x20; // bootsect-loader, version 0
AX = ES >;>; 4;
CS:[bootsect_src_base+2] = AH;
bootsect_es = ES;
AX = ES - SYSSEG;
}
else {
if (BX==0) { // 64K aligned
// copy extended memory
// http://www.ctyme.com/intr/rb-1527.htm
try {
int15h/AX=87h(CX=0x8000,
ES:SI=CS:bootsect_gdt);
}
catch {
bootsect_panic:
prtstr("INT15 refuses to access high memory."
" Giving up.");
halt;
}
ES = bootsect_es;
CS:[bootsect_dst_base+2]++;
}
AH = CS:[bootsect_dst_base+2] << 4;
AL = 0;
}
}
////////////////////////////////////////////////////////////////////
{
bootsect_gdt:
.word 0, 0, 0, 0
.word 0, 0, 0, 0
bootsect_src:
.word 0xFFFF
bootsect_src_base:
.byte 0, 0, 1 ! base = 0x010000
.byte 0x93 ! typbyte
.word 0 ! limit16, base24 =0
bootsect_dst:
.word 0xFFFF
bootsect_dst_base:
.byte 0, 0, 0x10 ! base = 0x100000
.byte 0x93 ! typbyte
.word 0 ! limit16, base24 =0
.word 0, 0, 0, 0 ! used by BIOS
.word 0, 0, 0, 0
bootsect_es:
.word 0
}
////////////////////////////////////////////////////////////////////
// check that the keyboard command queue is empty
empty_8042()
{
timeout = 0xFFFFFF; // local variable
for (;;) {
if (--timeout==0) return;
delay();
inportb(0x64, AL); // 8042 status port
if (AL & 1) { // output buffer
delay();
inportb(0x60, .);
continue;
}
if (!(AL & 2)) return; // input buffer
}
}
////////////////////////////////////////////////////////////////////
// read the CMOS clock, return the seconds in AL
gettime()
{
// get real-time clock time
// http://www.ctyme.com/intr/rb-2273.htm
int1Ah/AH=02h(); // DH = seconds (in BCD)
AL = DH & 0x0F;
AH = DH >;>; 4;
AAD;
}
////////////////////////////////////////////////////////////////////
delay() { /* needed after doing I/O */ }
////////////////////////////////////////////////////////////////////
{
gdt:
.word 0,0,0,0 ! dummy
.word 0,0,0,0 ! unused
.word 0xFFFF ! 4Gb - (0x100000*0x1000 = 4Gb)
.word 0x0000 ! base address=0
.word 0x9A00 ! code read/exec
.word 0x00CF ! granularity=4096, 386 (+5th nibble of limit)
.word 0xFFFF ! 4Gb - (0x100000*0x1000 = 4Gb)
.word 0x0000 ! 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 0x800 ! gdt limit=2048, 256 GDT entries
.word 512+gdt, 0x9 ! gdt base = 0x9XXXX
// +512 because of bootsect
}
////////////////////////////////////////////////////////////////////
// Included video setup & detection code "video.S"
/*
Positions of various video parameters passed to the kernel
(see also include/linux/tty.h)
CS-DELTA_INITSEG segment
#define PARAM_CURSOR_POS 0x00
#define PARAM_VIDEO_PAGE 0x04
#define PARAM_VIDEO_MODE 0x06
#define PARAM_VIDEO_COLS 0x07
#define PARAM_VIDEO_EGA_BX 0x0a
#define PARAM_VIDEO_LINES 0x0e
#define PARAM_HAVE_VGA 0x0f
#define PARAM_FONT_POINTS 0x10
#define PARAM_LFB_WIDTH 0x12
#define PARAM_LFB_HEIGHT 0x14
#define PARAM_LFB_DEPTH 0x16
#define PARAM_LFB_BASE 0x18
#define PARAM_LFB_SIZE 0x1c
#define PARAM_LFB_LINELENGTH 0x24
#define PARAM_LFB_COLORS 0x26
#define PARAM_VESAPM_SEG 0x2e
#define PARAM_VESAPM_OFF 0x30
#define PARAM_LFB_PAGES 0x32
*/
video()
{
FS = DS;
DS = ES = CS;
GS = 0;
basic_detect();
#ifdef CONFIG_VIDEO_SELECT
if (FS:[0x1FA]!=ASK_VGA) {
// ASK_VGA=0xFFFD, defined in asm-i386/boot.h
mode_set();
if (failed) {
prtstr("You passed an undefined mode number.");
}
}
else {
mode_menu();
}
#ifdef CONFIG_VIDEO_RETAIN
restore_screen();
#endif
#endif
mode_params();
}
////////////////////////////////////////////////////////////////////
SIG1 = 0xAA55
SIG2 = 0x5A5A
{
setup_sig1: .word SIG1
setup_sig2: .word SIG2
modelist:
.text
endtext:
.data
enddata:
.bss
endbss:
}
////////////////////////////////////////////////////////////////////
// end of file

复制代码

---------------------------------------------------------------------------
再看　feiyunw 的代码分析：
---------------------------------------------------------------------------