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!!! 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.

!!! Linking fails with bootsplash 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>.

!!! 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.

!!! Other Misc 2.6 Notes

In the 2.4 series, you could read <tt>Documentation/Configure.help</tt> to see all the help for the entries you'd see in <tt>make ''foo''config</tt>. In 2.6, this has moved to individual <tt>Kconfig</tt> files in each sub-directory of the source tree.

!!! 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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