Preface：之前已经做了一部分MIT-6.828了，后来要考托福就搁置了，现在重新捡起来。
顺便把所有的博客迁移到我的域名www.shaojintian.cn下
Sources:xv6 book && xv6 source codes
Exercise1:
看懂x86 的32bit汇编,参见xv6 book附录A
Exercise2:
Use GDB’ssi(Step Instruction) command to trace into the ROM BIOS for a few more instructions, and try to guess what it might be doing.
答案：依照提示使用GDB si
Exercise 3.
阅读bootloader的源码，回答问题
1：At what point does the processor start executing 32-bit code? What exactly causes the switch from 16- to 32-bit mode?
答案：
ljmp to 0x7c32 从i8086->i386（16bit->32bit)
2：What is the last instruction of the boot loader executed, and what is the first instruction of the kernel it just loaded?
答案：
last instruction:
查阅xv6 book, boot loader call bootmain() to call kernel and run kernel
所以去boot.asm 找bootmain的位置
然后去找此汇编中bootmain（）最后一条语句为
((void (*)(void)) (ELFHDR->e_entry))();
找到此语句汇编的指向为
call *0x10018
kernel 第一个instruction：
从boot.asm找到最后一条指令的SI为0x7d6b
打上断点
movw $0x1234, 0x472
反汇编
objdump -d obj/kern/kernel 验证了这个结果
3：Where is the first instruction of the kernel?
答案：
0x10000c
4：How does the boot loader decide how many sectors it must read in order to fetch the entire kernel from disk? Where does it find this information?
答案：
xv6 book chapter2 说明kernel是ELF文件
kernel的大小包含在ELF的文件program header中
Exercise 4
Download the code for pointers.c, run it, and make sure you understand where all of the printed values come from.