linux-kernel - Re: Size of kernel modules

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Date:	Wed, 6 Jun 2007 17:51:24 +0200
From:	"Jesper Juhl" <jesper.juhl@...il.com>
To:	"Christoph Pleger" <Christoph.Pleger@...uni-dortmund.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Size of kernel modules

On 06/06/07, Christoph Pleger <Christoph.Pleger@...uni-dortmund.de> wrote:
> Hello,
>
> I have a machine here which I installed with Ubuntu 7.04. Immediately
> after the installation had been finished, I installed the Ubuntu package
> which contains the Ubuntu-modified sources of the linux kernel. I
> extracted the resulting tar.bz2-file, copied the configuration of the
> currently running kernel to .config and created a file localversion-irb
> which contains the line "-irb" and then called "make menuconfig".

You forgot "make oldconfig". When you copy in a .config file from a
different kernel, always do oldconfig (just get in the habbit, if the
.config from the same kernel it's harmless).

> In the
> menu, I changed the CPU type from 586 to Pentium Pro and entered "-686"
> as the localversion. Finally, I used the Ubuntu tool make-kpkg with
> option "--initrd" to create a new kernel. The option "--initrd" causes
> the installation scripts of the kernel package to automatically create
> an initial ramdisk for the kernel.
>
> After the new kernel package had been created, I installed it. After
> that, I looked into the directory /boot and was very surprised: The
> initial ramdisk of the new kernel was much larger than the initrd of the
> old kernel. To find out the cause for this, I investigated how
> directories /lib/modules/$old and /lib/modules/$new differ. I found out
> that the filenames are the same, but the size of the files differs very
> much. I found a module file in the new directory that was almost five
> times as large as the file with the same name in the old directory.
>
> So, my question is the follwing: Is it an expected feature that the file
> sizes of modules grow so much only because of a different cpu type and a
> different localversion, or is there probably a bug in my build tools?
>
Compiling for a different CPU type will often change object file size,
but what you describe sounds extreme. I would have suspected something
along the lines of some debug options having been enabled - that would
more easily explain the large size difference.

-- 
Jesper Juhl <jesper.juhl@...il.com>
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