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<p><FONT class=normalfont><B><font color=blue>读核日记</font></B></FONT><BR><FONT class=smallfont color=#ff9900>2004-04-23 15:18 pm</FONT><BR><FONT class=normalfont>作者：sunmoon<br>来自：Linux知识宝库<br>联系方式：无名<br><br>读核日记(一) <br>
本文出自:http://os.silversand.net 作者: sunmoon (2001-08-31 10:00:00) <br>
今天开始我的读核罹难记.第一次读内核,整整上学时的考试前.胡里胡涂的就过去了,没甚收获.这次我发誓要彻底读一次.<br>
<br>
面对近50 m 的源码,困惑是难免的所以我决定先从大面上把握,再在某一些具体的点上切入.这样一来linux 的启动过程便十分重要,因此我先用dmesg命令察看一下linux启动时打出的消息.(我想源文件应在/usr/src/linux/init/main.c中) <br>
<br>
内核的启动最后是到 start_kernel ( in /init/main.c )也就是说启动的过程是从 head.S ( arch/i386/boot/ ) 一直运行到 main.c(start_kernel) .它的作用是完成开机后的设置与内核的初始化,然后,系统究竟入一个无限的循环中等待用户的输入,调用fork来产生子进程.从而达到交互式操作系统的设计要求.<br>
<br>
第一部分 : 内核初始化以及启动.<br>
<br>
.启动系统.当PC机加电开始启动时，80X86的处理器(CPU)在实模式下自检，开始执行物理地址0xFFFF0即ROM-BIOS的起始地址处的代码。PC机的BIOS进行系统自检，初始化中断向量表到物理地址0x0。然后把引导设备的第一个扇区加载到地址0x7C00，执行此处的指令。到这里与linux无关,x86系列的硬件设置如此.<br>
<br>
linux的内核本身是不能自举的,所以lilo和loadlin的作用就是加载系统内核.有关lilo的原理可以参考lilo的readme.从加电到内核加载的过程是:加电->执行BIOS->加载第一扇区->lilo->加载内核<br>
<br>
Linux内核的最初部分代码是用汇编语言写的（文件是boot/bootsect.s)。(我的汇编水平有限,暂且不看），它首先把自身这部分代码移到绝对地址0x90000，把下面的2K代码从引导设备加载到地址0x90200上，内核的其余部分加载到地址0x10000处。在加载系统时显示“loading...”. 然后，程序控制权交给另一个实模式汇编程序（boot/Setup.S）。接下来，此程序把整个系统从地址0x10000移到地址0x1000，进入保护模式。程序控制转给系统的其余部分即地址0x1000。<br>
<br>
下一个步骤是系统内核的解压过程，这部分代码在地址0x1000（文件/Boot/head.S），该段程序初始化寄存器，然后执行decompress_kernel()，这个函数源于zBoot/inflate.c、zBoot/unzip.c和zBoot/misc.c三个文件<br>
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