View Source: KernelNotes - Waikato Linux Users Group

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!!! Updating the [Kernel] SourceCode without reconfiguring from scratch

Download and unpack the latest [Kernel] TarBall (ie from [http://kernel.org/]). Copy the <tt>.config</tt> file from the previous [Kernel]'s directory to the fresh one. From the new directory, run <tt>make oldconfig</tt> to pick up the old configuration, then <tt>make menuconfig</tt> to change any options for the new [Kernel].

To update the symlink:

<pre>
ls -l /usr/src/linux
rm /usr/src/linux
cd /usr/src
ln -s linux-''version'' linux
</pre>

DebianLinux users will want to read KernelPackageNotes for information on using make-kpkg(1) to build a [Kernel] [Deb]. If not, they can follow the same steps, using

<pre>
apt-cache search kernel-source # to find out the latest version
apt-get kernel-source-''version''
</pre>

to download the latest source.

!!! Updating your source tree to the latest version

patch-2.6.17 applies against 2.6.16, so if you have 2.6.16.n, you'll have to first remove the 2.6.16.n patch.

Use [ketchup|http://kerneltrap.org/node/2976], a [Python] utility to handle this patching for you.

A good command line for [NZ] users:

<pre>
ketchup -G -k ftp://ftp.nz.kernel.org/pub/linux/kernel -r 2.6
</pre>

Only use <tt>-G</tt> if you trust the mirror!

!!! Compiler Version

The [Kernel] can be sensitive to the version of [GCC] in use. F.ex. 2.4 and early 2.6 kernels did not work with [GCC] 3.x. They contained the following snippet in <tt>README</tt>:

  <verbatim>
  COMPILING the kernel:

   - Make sure you have gcc 2.95.3 available.  gcc 2.91.66 (egcs-1.1.2) may
     also work but is not as safe, and *gcc 2.7.2.3 is no longer supported*.
  </verbatim>

OTOH kernels since about 2.6.15 require [GCC] 3.x. Read the file  to find the versions of compilers and other tools you need. Make sure to check the <tt>README</tt> and <tt>Documentation/Changes</tt> files to find out which version you need. Of course you always read the compile instructions for software you download, right? :)

To compile a kernel with a specific compiler, you can say eg. <tt>make CC=gcc-2.95 bzImage</tt> to make the <tt>bzImage</tt> target using the <tt>gcc-2.95</tt> compiler. See also [DistCC]

!!! Linking fails with <tt>bootsplash</tt> compiled into your kernel

Compiling aborts with the following message:

 <verbatim>
   LD      .tmp_vmlinux1
 drivers/built-in.o(.text+0xa898a): In function `splash_getraw':
 : undefined reference to `con2fb_map'
 drivers/built-in.o(.text+0xa918c): In function `splash_verbose':
 : undefined reference to `con2fb_map'
 drivers/built-in.o(.text+0xa9670): In function `splash_status':
 : undefined reference to `con2fb_map'
 drivers/built-in.o(.text+0xa97a4): In function `splash_read_proc':
 : undefined reference to `con2fb_map'
 drivers/built-in.o(.text+0xa997d): In function `splash_write_proc':
 : undefined reference to `con2fb_map'
 make: *** [.tmp_vmlinux1] Error 1
 </verbatim>

You need to have framebuffer console support compiled in. It can't be a module! Set <tt>CONFIG_FRAMEBUFFER_CONSOLE=y</tt> in the <tt>.config</tt>. NB This sounds like a one off bug that has probably been long fixed.

!!! ModuleInitTools

Starting with 2.5.51, modules have a different format. The extension has also changed from <tt>.o</tt> to <tt>.ko</tt>, for kernel object. To work with modules, you need a completely rewritten set of module tools (modprobe(8), insmod(8), lsmod(8)), collectively called <tt>module-init-tools</tt>. They can coexist with the 2.4.x-specific tools. __Note, however__ that <tt>module-init-tools</tt> no longer reads <tt>modules.conf</tt> and instead uses a new file called modprobe.conf(5) which has a different syntax. <tt>man 5 modprobe.conf</tt> will be your friend here. It's possible to set <tt>modprobe.conf</tt> to handle modules for both 2.4.x and 2.5.x kernels, which is pretty cool if you're a dual-booter.

!!! nVidia and LinuxKernel 2.6

[nVidia drivers|http://www.nvidia.com/linux] version 1.0-6106 and up support all 2.4 and 2.6 kernels, including kernels with the new 2.6 option for 4k stacks.

!!! Kconfig files

These are kernel configuration files. When the kernel configuration application is run, it reads the main kernel configuration file, located in /source/dir/arch/<your architecture>/Kconfig. This main configuration file then includes other configuration files from the different subdirectories in the kernel directory tree.

Don't edit these Kconfig files directly unless you are doing [KernelDevelopment]. These files are driven from .config file mentioned earlier in this article.

In the 2.4 series, you could read <tt>Documentation/Configure.help</tt> to get the equivalent information.

!!! See also

* TroubleshootingStartUp has help for some problems while booting kernels
* KernelTweaking
* [Safe remote kernel install howto | http://groups.google.com/group/fa.linux.kernel/msg/75497a47b0dd2b6b] describes a strategy for testing a new kernel on a remote machine without shutting yourself out even if it doesn't work

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CategoryKernel
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Last edited on Tuesday, June 12, 2007 8:40:44 am by IanMcDonald
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