Understanding the kernel code, and CR3 register

Recently, I was working on the kernel code and CR3 register. This article is going to record what I have learn.

First Question: How can we get the kernel code of Operating System?

Get Virtual Address of kernel code:

$ cat /boot/System.map-2.6.32-33-generic | grep text

c0100000 T_text

The first one is start virtual address of kernel code

Get Physical Address of kernel code:

$ cat /proc/iomem

00100000-00590de6 : Kernel Code

More info: please see

http://fengweizhang.blogspot.com/2010/12/boot-cat-system.html

http://jianggmulab.blogspot.com/2009/09/blog-post.html

Second Question: How to translate virtual address to physical address? 

Control Register 3 (CR3) stores the base address of Page Directory Table. More info please see page 47 in ULK book. 

Third Question: Which CR3 I should use to translate VA to PA of kernel code?

Any CR3. For each process, it has its own address spaces and CR3. No matter which processes the operating system is running, the virtual address and physical address of kernel code will never change. Although the CR3 is different depends on the running process, same VA will map to same PA by CR3.

Each process has its own address space. From the virtual address point of view, it has some address space at 0-3G region, and it also has some address space at 3-4G region (this is for kernel mode). All Processes get same mappings for the kernel address space (3-4G). Each process also has its own page directory table and page tables. CR3 is the base address of page directory table. The address space at 3-4G region must have its own translation entries in page directory table and page tables. These entries are always same in different page directory table and page tables. 

Process 1 has virtual address space from 0xc0100000-0xc0590de6 (kernel code), translate to physical address is 0x00100000-0x00590de6

Process 2 has virtual address space from 0xc0100000-0xc0590de6 (kernel code), translate to physical address is 0x00100000-0x00590de6

Thus, process 1 and process 2 has same kernel memory mappings. (CR3 is different)

cat /proc/iomem

This is command shows the io memory map
This is the virtual address (linear address in Linux).
For example, it tells you the virtual address of kernel code.
If you want to get the kernel code, you could write a kenel module, and read the code out.


[root@localhost fengweiWorkSpace]# cat /proc/iomem
00010000-0009e3ff : System RAM
000a0000-000bffff : Video RAM area
000c0000-000cefff : Video ROM
000d3800-000d3fff : Adapter ROM
000f0000-000fffff : System ROM
00100000-7ddff7ff : System RAM
  00400000-00620dc5 : Kernel code
  00620dc6-007039fb : Kernel data
7ddff800-7de53bff : ACPI Non-volatile Storage
7de53c00-7de55bff : ACPI Tables
7de55c00-7dffffff : reserved
80000000-800fffff : PCI Bus #01
  80000000-8001ffff : 0000:01:00.0
  80020000-8002ffff : 0000:01:00.0
80100000-801fffff : PCI Bus #03
  80100000-8010ffff : 0000:03:00.0
  80110000-80110fff : 0000:03:02.0
80200000-8021ffff : 0000:00:19.0
  80200000-8021ffff : e1000e
80220000-80223fff : 0000:00:1b.0
  80220000-80223fff : ICH HD audio
80224000-80224fff : 0000:00:03.3
80225000-80225fff : 0000:00:19.0
  80225000-80225fff : e1000e
80226000-802263ff : 0000:00:1a.7
  80226000-802263ff : ehci_hcd
80226400-802264ff : 0000:00:1f.3
d0000000-dfffffff : PCI Bus #01
  d0000000-dfffffff : 0000:01:00.0
e0000000-fed003ff : reserved
fed20000-fed9ffff : reserved
fedad000-fedad00f : 0000:00:03.0
fee00000-feefffff : reserved
ff970000-ff9707ff : 0000:00:1f.2
  ff970000-ff9707ff : ahci
ff980800-ff980bff : 0000:00:1d.7
  ff980800-ff980bff : ehci_hcd
ffb00000-ffffffff : reserved

latex tip

If there is not make file in the latex directory, use pdflatex tool output PDF from latex.
If it is missing reference, run bibtex tool.

Latex comments: 


1). line comment: %

2). paragraph comment:
add \usepackage{comment} in the main.tex

\begin{comment}

\end{comment}

NAND and NOR Flash

NOR flash used as main memory
NAND flash used as secondary memroy.

In embeded device:
used as main memory: ROM, EPROM, NOR flash, SRAM, DRAM
used as secondary memory: NAND flash, SD, DOC(disk on chip).

NOR and NAND flash differ in two important ways:

• the connections of the individual memory cells are different
• the interface provided for reading and writing the memory is different (NOR allows random-access for reading, NAND allows only page access)

http://en.wikipedia.org/wiki/Flash_memory#Distinction_between_NOR_and_NAND_flash

Get MAC address of Windows

ipconfig \all

set domain in XP

My computer -> Properties -> System properties -> Comupter Name -> Change Domain

For exmaple, you are in a Company, after you install a new OS, you need to set the correct domain of your company. You add it form here, then restart your machine.

After you restart your machine, you need to add your comany account into administor account.
Go to Control panel -> account -> add account

Then you can switch user. Logout, and login use your company username and password

Note: this is for my expeirence on XP

WinCE Development Tool

http://bbs.pediy.com/showthread.php?p=557435