linux-kernel - Re: [PATCH] reduce export symbol CRC table size on 64-bit archs

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Message-ID: <20090630220932.GE1241@elte.hu>
Date:	Wed, 1 Jul 2009 00:09:32 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jan Beulich <JBeulich@...ell.com>
Cc:	tony.luck@...el.com, Thomas Gleixner <tglx@...utronix.de>,
	Rusty Russell <rusty@...tcorp.com.au>, hpa@...or.com,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] reduce export symbol CRC table size on 64-bit archs


* Jan Beulich <JBeulich@...ell.com> wrote:

> Since these CRCs are really only 32-bit quantities, there's no 
> need to store them in 64-bit slots. Since, however, gcc doesn't 
> allow respective initializations, asm() constructs get used to 
> create the CRC tables (and its for that reason that the patch only 
> makes x86-64 and ia64 utilize that functionality, as I can't 
> verify this doesn't break in some subtle way elsewhere).
> 
> Observed size reduction (x86-64):
> - 16k kernel resident size
> - 2k module resident size
> - 1M vmlinux image size
> 
> If the asm() construct could be extended to all architectures, and 
> if modpost would guarantee generation of CRCs for all exported, 
> then the __crc_* symbols wouldn't need to be declared weak 
> anymore, could hence remain local to the exporting object. By 
> adding -Wa,-strip-local-absolute to the second compilation step 
> the __crc_* symbols could even be prevented from making it into 
> any object file at all.
> 
> Signed-off-by: Jan Beulich <jbeulich@...ell.com>

> 
> ---
>  arch/ia64/include/asm/module.h |    2 ++
>  arch/x86/include/asm/module.h  |    1 +
>  include/linux/module.h         |   41 ++++++++++++++++++++++++++---------------
>  include/linux/moduleparam.h    |   10 +++++++++-
>  kernel/module.c                |   26 +++++++++++++-------------
>  scripts/genksyms/genksyms.c    |   16 ++++++++--------
>  6 files changed, 59 insertions(+), 37 deletions(-)

No objections to the (minor) x86 bits.

	Ingo
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