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

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Message-ID: <4A5CB5B3.2060002@zytor.com>
Date:	Tue, 14 Jul 2009 12:43:31 -0400
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jon Masters <jonathan@...masters.org>
CC:	Jan Beulich <JBeulich@...ell.com>, Michal Marek <mmarek@...e.cz>,
	Ingo Molnar <mingo@...e.hu>, tony.luck@...el.com,
	Thomas Gleixner <tglx@...utronix.de>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-modules@...r.kernel.org
Subject: Re: [PATCH] reduce export symbol CRC table size on 64-bit	 archs

Jon Masters wrote:
> On Mon, 2009-07-13 at 09:44 +0100, Jan Beulich wrote:
>>>>> Michal Marek <mmarek@...e.cz> 13.07.09 10:11 >>>
>>> Jan Beulich napsal(a):
>>>> Actually I meanwhile think that module-init-tools can easily detect the changed
>>>> layout without any further kernel side adjustments: Since it is known that a
>>>> CRC always is a 32-bit value, simply checking whether the so-far-used 64-bit
>>>> value has more than 32 significant bits should suffice: If so, the new layout
>>>> is being used (with the symbol name starting at offset 4), else the old one is
>>>> in effect (name at offset 8). This ought to be a pretty trivial change to that
>>>> code.
>>> But old module-init-tools will continue reading garbage in this case.
> 
> Most of the distros can fix that with a dependency on the kernel package
> in the absolute worst case, not that I love that idea, but it happens. I
> assume for now we are going with detecting the two possibilities because
> it doesn't really hurt in any case to have this support.
> 

It would seem to me that reading garbage is worse than reading nothing, 
unless I'm missing something fundamental.

	-hpa

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