[RK_2014_0919]Linux Kernel Hacking，hacking

KernelBuild

Guide to building the Linux kernel.

Where do I find the kernel?

The latest source code for the Linux kernel is kept on kernel.org. You can either download the full source code as a tar ball (not recommended and will take forever to download), or you can check out the code from the read-only git repositories.

What tools do I need?

To build the Linux kernel from source, you need several tools: git, make, gcc, and (optionally) ctags and/or ncurses-dev. The tool packages may be called something else in your Linux distribution, so you may need to search for the package. The ncurses-dev tools are used if you "make menuconfig" or "make nconfig".

On Ubuntu, you can get these tools by running:

sudo apt-get install libncurses5-dev gcc make git exuberant-ctags

On Red Hat based systems like Fedora, Scientific Linux, and CentOS you can run:

sudo yum install gcc make git ctags ncurses-devel

Which kernel to build?

If you want to test to see if a bug is fixed then test against the latest stable kernel from kernel.org. If you are brave and your system is backed up the latest release candidate from Linus's tree is a great target. Sometimes the maintainer may want you to use an experimental branch from their own git tree. You should use the git URL they gave you instead of the git URLs below.

If you're doing development for a new feature, or trying to test a bug fix, you should use Linus' tree, or the subsystem maintainer's -next tree. Most subsystem maintainers keep their git trees on kernel.org. When in doubt, use Linus' tree.

If you don't understand what a stable or release candidate kernel is, you should read the KernelDevProcess page.

Downloading the latest stable tree

First, checkout the stable kernel git repository:

git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
cd linux-stable

Next, find the latest stable kernel tag by running

git tag -l | less

Find the latest stable kernel by looking for the largest vX.Y.Z values. For example, use the v3.1 tag over the v3.0.46 tag. If v3.1.1 is available, use that instead of v3.1. The kernel tags that end with -rcX are release candidate kernels, not stable kernels.

Now checkout the code associated with that kernel with the command

git checkout -b stable tag

Where tag is the latest vX.Y.Z tag you found.

Downloading the latest -rc tree

Check out Linus' tree:

git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
cd linux

Setting up your kernel configuration

Many kernel drivers can be turned on or off, or built as modules. The .config file in the kernel source directory determines which drivers are built. When you download the source tree, it doesn't come with a .config file. You have several options on generating a .config file. The easiest is to duplicate your current config.

Duplicating your current config

If you're trying to see if a bug is fixed, you probably want to duplicate the configuration on your running kernel. That config file is stored somewhere in /boot/. There might be several files that start with config, so you want the one associated with your running kernel. You can find that by running uname -a and finding the config file that ends with your kernel version number. Copy that file into the source directory as .config. Or just run this command:

cp /boot/config-`uname -r`* .config

Making the default config

Remember, a default config may not have the options you are currently using. Run

make defconfig

Making a minimal config

Compiling a kernel from scratch from a distribution configuration can take "forever" because the distros turn on every hardware configuration possible. For people wanting to do kernel development fast, you want to make a minimal configuration. Steve Rostedt uses ktest.pl make_min_config to get a truely minimum config, but it will take a day or two to build. Warning: make sure you have all your USB devices plugged into the system, or you won't get the drivers for them!

Changing your config

If you need to make any changes to your configuration, you can run one of the following commands. These require the curses tools to be installed.

make menuconfig

or

make nconfig

Building the kernel

Run

make

Or, if you have a multi-core processor, run

make -jX

Where X is a number like 2 or 4. If you have a dual core, 2 or 3 might be good. Quad core, 4 or 6. Do not run with really big numbers unless you want your machine to be dog-slow!

Walk away, get some coffee, lunch, or go read some comics.

Installing the kernel

To install a kernel, you will need to either manually update your GRUB configuration file, or have an installkernel script. This script installs the kernel to /boot/, installs modules to /lib/modules/X.Y.Z/ (where X.Y.Z is something like 3.1.5), and updates file /boot/grub/grub.conf. Fortunately, Ubuntu provides an installkernel script in /sbin/installkernel. The grubby RPM provides it for RPM based systems.

If you have an installkernel script, you can just run

sudo make modules_install install

Or if you don't have sudo installed, run

su -c "make modules_install install"

Running your kernel

First, make sure you know how to select a kernel at boot time. If your new kernel is broken, you want a way to boot into your old kernel. The grub bootloader usually presents users with a choice of kernels and you can reboot into a known good kernel if your new compile doesn't work. Some distros use a default grub config that hides that menu. You can usually get the menu to appear by mashing the ESC key during boot after the BIOS display disappears.

Ubuntu: To make the grub menu always appear on boot under Ubuntu, remove the GRUB_HIDDEN_TIMEOUT_QUIET line from /etc/default/grub. You may want to increase the GRUB_DEFAULT timeout from 0 to 15 seconds or more. After you've finished editing the grub file you may need to update your grub file.

sudo update-grub2

You will (usually) need to reboot into your new kernel.

Patching your kernel

There are several ways to apply a patch to your kernel. Usually the maintainer will send you a patch as attachment, or inline in the mail. You should either save the file, or copy and paste the patch into a new file.

To apply the patch, go to the base kernel directory and run

git am patchfile

Where patchfile is the file you saved. If patch fails, you can run:

git am --abort
git reset --hard HEAD
git am -3 patchfile

This applies the patch, and attempts to run a three-way merge if the patch application fails. If all else fails, you can attempt to duplicate the patch changes by hand.

Then you need to re-build your kernel and reboot.

(Note: the older way of manually patching the kernel with patch -p1 <patchfile does not create any git history, which makes it hard to revert and retry different patches. You will often have to go through several patches with a maintainer to find the right fix for a bug, so having the git history is useful.)

Reverting a patch

If a maintainer wants you to revert a patch you have applied, and try a different patch, you can use git to reset the history to the point before the patch was applied.

If git log shows the patch to be removed is the first log entry, you can run

git reset --hard HEAD^

If you need to revert several patches, you can use git log to find the commit ID of the first commit before those patches. For instance, say you have applied two patches to the stable tree 3.4.17, and you want to revert those patches. git log will look like this:

$ git log --pretty=oneline --abbrev-commit
8901234 Testing patch 2
1234567 Testing patch 1
5390967 Linux 3.4.17
1f94bd4 drm/i915: no lvds quirk for Zotac ZDBOX SD ID12/ID13
0187c24 x86, mm: Use memblock memory loop instead of e820_RAM
a0419ca staging: comedi: amplc_pc236: fix invalid register access during detach

To reset your tree to 3.4.17, you can run:

git reset --hard 5390967

If you look at the commits with gitk you will notice that the 3.4.17 commit is also tagged as v3.4.17. You can reset by tag as well:

git reset --hard v3.4.17

Tips and Tricks

If you have a driver installed as a module, you can recompile just that driver. This saves time, because the kernel build system doesn't have to look for changes across the entire kernel tree or compile any of the built-in code.

All module files end with .ko. The kernel make system will compile just one .ko file if you give it the full path to the file:

make drivers/usb/host/xhci-hcd.ko

Note you will need to be in the base kernel source directory for this to work. You can't make from a different directory.

You can also reload drivers without rebooting your kernel. For example, I can remove the xHCI driver and reload it with

sudo rmmod xhci-hcd && sudo insmod drivers/usb/host/xhci-hcd.ko

Make sure that you understand the consequences of unloading your driver! For instance, if you unload the USB core driver in order to try out changes, your USB mouse and keyboard aren't going to work until the USB core driver is reloaded.

You may have to unload other drivers that depend on your driver before you can reload it. Use lsmod to find which drivers that are loaded depend on your driver. E.g.

$ lsmod | grep usb
usbnet                 26596  2 rndis_host,cdc_ether
mii                     5198  1 usbnet
btusb                  16575  0 
usbhid                 44621  1 hid_logitech
usbcore               191078  9 xhci_hcd,rndis_host,cdc_ether,usbnet,btusb,uvcvideo,usbhid,ehci_hcd
usb_common              1093  1 usbcore

In this case, usbcore is used by xhci_hcd, rndis_host, cdc_ether, usbnet, btusb, uvcvideo, usbhid, and ehci_hcd. I would have to unload all those drivers in order to reload the usbcore module.

http://kernelnewbies.org/KernelHacking

二、网址

http://www.cnblogs.com/tom-and-jerry/articles/3978090.html 

                       

内核配置注意事项

如果打算自己编译内核的话（内核源代码可以到ftp://ftp.kernel.org/pub/kernel/ 下载，国内下载可以到ftp://ftp.cn.kernel.org/pub/kernel/ 这样下载速度更快），在编译之前一般都要先用make menuconfig或make xconfig配置内核。我的系统中没有xconfig，所以只能用menuconfig。在我的Compaq Presario V3414TX laptop上编译2.6.23.x内核时，以下选项是必须要注意的：

1、Networking -->

Wireless LAN -->

[M]Generic IEEE 802.11 Networking Stack (mac80211)

这是Linux当前使用的网络栈模块。如果想要使用无线网卡（我的是Intel PRO/3945 ABG），就要将此选项编为模块（或者编入内核也可以，那样启动时就会自动加载mac80211模块）。否则到时候就要自己去intellinuxwireless.org下载该模块进行安装。

2、Device Drivers -->

Network Drivers -->

Wireless LAN-->

[M]Intel PRO/Wireless 3945ABG Network Connection

Intel PRO/Wireless 3945ABG Network Connection这一项可以换成你的任何无线网卡。同样，如果你想使用无线网卡的话，这一项也是要编为模块的。但是我最后编译的2.6.23.14内核中没有这一项，因此就必须到intellinuxwireless.org下载3495ABG的驱动了。

3、File System -->

DOS/FAT/NT Filesystems -->

<*> VFAT (Windows-95) fs support

(437) Default codepage for FAT (NEW)

(utf8) Default iocharset for FAT (NEW)

将 VFAT (Windows-95) fs support 选为y是为了让内核能支持FAT格式硬盘的挂载。这里codepage要用437；在网上很多文章都说要用936，这样才能让FAT硬盘的文件名显示支持中文，但事实上我这么做之后，在挂载FAT分区时却被新内核提示无法挂载，系统日志显示找不到codepage 936——可是我已经将codepage 936编进内核了啊（下文会说明），因此在这一点上我相当困惑。后来发现FAT分区的中文文件名能否正确显示是取决于 Default iocharset for FAT 这一项，其字符编码要使用utf8才行。原因上，也许是因为Windows的FAT分区默认的字符编码是ascii或gb2312，而Linux默认的是utf8编码，认不得gb2312……这个地方我也不太明白。

4、File System -->

Native Language Support -->

[M]Simplified Chinese charset (CP936, GB2312)

想要中文支持的话，当然要选上这一项（......余下全文>>
 

内核，是一个操作系统的核心。它负责管理系统的进程、内存、设备驱动程序、文件和网络系统，决定着系统的性能和稳定性。Linux作为一个自由软件，
在广大爱好者的支持下，内核版本不断更新。新的内核修订了旧内核的bug，并增加了许多新的特性。如果用户想要使用这些新特性，或想根据自己的系统度身定
制一个更高效，更稳定的内核，就需要重新编译内核。本文将以RedHat Linux 6.0（kernel
2.2.5）为操作系统平台，介绍在Linux上进行内核编译的方法。

　　一、 下载新内核的源代码

　　目前，在Internet上提供Linux源代码的站点有很多，读者可以选择一个速度较快的站点下载。笔者是从站点www.kernelnotes.org上下载了Linux的最新开发版内核2.3.14的源代码，全部代码被压缩到一个名叫Linux-2.3.14.tar.gz的文件中。

　　二、 释放内核源代码

　　由于源代码放在一个压缩文件中，因此在配置内核之前，要先将源代码释放到指定的目录下。首先以root帐号登录，然后进入/usr/src子目录。如果用户在安装Linux时，安装了内核的源代码，则会发现一个linux-2.2.5的子目录。该目录下存放着内核2.2.5的源代码。此外，还会发现一个指向该目录的链接linux。删除该连接，然后将新内核的源文件拷贝到/usr/src目录中。

　　（一）、用tar命令释放内核源代码

　　# cd /usr/src

　　# tar zxvf Linux-2.3.14.tar.gz

　　文件释放成功后，在/usr/src目录下会生成一个linux子目录。其中包含了内核2.3.14的全部源代码。

　　（二）、将/usr/include/asm、/usr/inlude/linux、/usr/include/scsi链接到/usr/src/linux/include目录下的对应目录中。

　　# cd /usr/include

　　# rm -Rf asm linux

　　# ln -s /usr/src/linux/include/asm-i386 asm

　　# ln -s /usr/src/linux/include/linux linux

　　# ln -s /usr/src/linux/include/scsi scsi

　　（三）、删除源代码目录中残留的.o文件和其它从属文件。

　　# cd /usr/src/linux

　　# make mrproper

　　三、 配置内核

　　（一）、启动内核配置程序。

　　# cd /usr/src/linux

　　# make config

　　除了上面的命令，用户还可以使用make menuconfig命令启动一个菜单模式的配置界面。如果用户安装了X window系统，还可以执......余下全文>>