linux2.6内核研读笔记一

/*

* BIG FAT NOTE: We're in real mode using 64k segments.  Therefore segment

 * addresses must be multiplied by 16 to obtain their respective linear

 * addresses. To avoid confusion, linear addresses are written using leading

 * hex while segment addresses are written as segment:offset.

 *

 */

我们处于实模式下，使用64k个段，因此段地址必须是16的倍数，为避免冲突，线性地址用16进制头书写，段地址作为偏移书写

#include <asm/segment.h>

#include <linux/utsrelease.h>

#include <asm/boot.h>

#include <asm/e820.h>

#include <asm/page_types.h>

#include <asm/setup.h>

#include "boot.h"

#include "offsets.h"

 

BOOTSEG            = 0x07C0              /* original address of boot-sector */

SYSSEG        = 0x1000        /* historical load address >> 4 */

 

#ifndef SVGA_MODE

#define SVGA_MODE ASK_VGA

#endif

 

#ifndef RAMDISK

#define RAMDISK 0

#endif

 

#ifndef ROOT_RDONLY

#define ROOT_RDONLY 1

#endif

 

       .code16

       .section ".bstext", "ax"

 

       .global bootsect_start

bootsect_start:

 

       # Normalize the start address

       ljmp $BOOTSEG, $start2 跳到0x07c000start2的地方

 

start2:

       movw     %cs, %ax

       movw     %ax, %ds

       movw     %ax, %es

       movw     %ax, %ss

       xorw       %sp, %sp

       sti允许中断

       cld

 

       movw     $bugger_off_msg, %si

                              

msg_loop:

       lodsb将DS:[si]中的内容取到AL中，由于前边的cld，si开始递减

       andb       %al, %al

       jz     bs_die 如果bug信息打完，则跳转

       AL－显示ASCII字符
       BH－页号(在我们要进行的工作中，它一直是0x00)
       BL－文本属性(在我们将进行的工作中，它一直是0x07) 通过更改它的值可以选择不同  的颜色等。

       movb      $0xe, %ah显示字符

       movw     $7, %bx

       int    $0x10 INT 0x10是BIOS视频中断

       jmp  msg_loop

 

bs_die:

       # Allow the user to press a key, then reboot

       xorw       %ax, %ax清零

       int    $0x16按任意键重启

16

1

读键盘缓冲区字符

ZF=0 AL=字符码      AH=扫描码 ZF=1 缓冲区空

 

       int    $0x19

       重新启动系统

       # int 0x19 should never return.  In case it does anyway,

       # invoke the BIOS reset code...

       ljmp $0xf000,$0xfff0跳转到f000,fff0

bios的重置码

       .section ".bsdata", "a"

bugger_off_msg:

       .ascii       "Direct booting from floppy is no longer supported./r/n"

       .ascii       "Please use a boot loader program instead./r/n"

       .ascii       "/n"

       .ascii       "Remove disk and press any key to reboot . . ./r/n"

       .byte       0