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Of course, the first question is: why I'm doing this. Just for fun! I'm learning more about Linux kernels and I have a virtual machine that I can replace in 15 minutes.

Getting to business, I don't know how to do this, so I went to trying to edit the makefile (trying to learn). So I started with the makefile in the path ubuntu-raring/Makefile, which is the main make file; can be found under this link:

http://pastebin.com/ms2WpQi7

And there I changed every gcc to icc, and every g++ to icpc, and every -O2 to -O3. The result is the following:

http://pastebin.com/cSwTYJ9C

I followed the instructions from this site, too:

https://help.ubuntu.com/community/Kernel/Compile

But eventually, I'm getting weird errors that seem to be caused by using gcc/g++ rather than icc/icpc. For example, I got an error in the file ubuntu-raring/include/linux/compiler-gcc.h that some macros are already defined, while this file shouldn't be included in the first place! The macro that includes it is in the file ubuntu-raring/include/linux/compiler.h, and looks like:

#ifdef __GNUC__
#include <linux/compiler-gcc.h>
#endif

/* Intel compiler defines __GNUC__. So we will overwrite implementations
 * coming from above header files here
 */
#ifdef __INTEL_COMPILER
# include <linux/compiler-intel.h>
#endif

And while I don't understand the comment written above the Intel header (sounds weird... why would you define implementations then overwrite them? Never done that in C++!), removing the include of the gcc header manually solved the problem, but other problems came up, and I have no idea whether they're related.

So now I'm confused! What did I do wrong? And should changing every gcc and g++ in the Makefile be sufficient to use a different compiler? Or are there other things to be changed that I overlooked?

Thank you for any efforts.

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1 Answer

up vote 5 down vote accepted
First learn to walk, then learn to fly.

If you want to learn, read. Have you read this instruction manual for building the kernel with the Intel C compiler? It's a rethorical question b/c this manual uses a different approach to choosing icc over gcc.

You are doing three things at once:

  • fiddle with some adopted and patched kernel to fit into the Ubuntu world (which is gcc)
  • Up the optimization from -O2 to -O3.
  • change the compiler

Start out with a vanilla Linux kernel from kernel.org. Keep everything standard and figure out how to build a kernel that works for your computer. Build a kernel that has only the drivers your computer needs, nothing more. Once you can compile and boot into your own kernel, you can start changing the build environment.

Going from -O2 to -O3 will probably never work. -O3 is like opening Pandora's box. If enabling -O3 was that easy, it would probably be the default!

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Thank you so much. I will follow those instructions, and you get a +1, unless this is the best answer, then you get the big check mark soon :) –  The Quantum Physicist Aug 31 '13 at 10:56
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