linux-kernel - Re: Fast LKM symbol resolution with SysV ELH hash table

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Message-ID: <9b2b86520910191346n305a52e6x311b38577d84eaf3@mail.gmail.com>
Date:	Mon, 19 Oct 2009 21:46:20 +0100
From:	Alan Jenkins <sourcejedi.lkml@...glemail.com>
To:	Greg KH <greg@...ah.com>
Cc:	Carmelo Amoroso <carmelo73@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kbuild <linux-kbuild@...r.kernel.org>
Subject: Re: Fast LKM symbol resolution with SysV ELH hash table

On 10/19/09, Greg KH <greg@...ah.com> wrote:
> On Mon, Oct 19, 2009 at 05:02:51PM +0200, Carmelo Amoroso wrote:
>> 2009/10/19 Greg KH <greg@...ah.com>:
>> > On Mon, Oct 19, 2009 at 01:45:20PM +0200, Carmelo Amoroso wrote:
>> >> Just a few other notes. The current implementation I did based on SysV
>> >> has a drawback that is not backward compatible, so you cannot use old
>> >> modules with a kernel with the option enabled due to changes on struct
>> >> kernel_symbol.
>> >
>> > Why would this be a problem? ?Whenever making a kernel config change,
>> > you should be able to rebuild everything, as lots of other configuration
>> > options are that way.
>> >
>>
>> This is not always true... there could be cases in which you cannot
>> recompile old modules (e.g vendors that provide non GPL modules)
>
> But we do not care at all about that kind of thing, sorry.
>
>> >> Anyway I've just figured out how to change it to remove this
>> >> limitation.
>> >> I need some time to review these patches. ?Further, the newer
>> >> implementation based on GNU hash which we are working on right now,
>> >> will not require the extra .undef.hash ELF sections because hash
>> >> values are already embedded into the GNU hash table, with a reduction
>> >> in terms of footprint.
>> >
>> > Footprint in the memory for the loaded module, or just in the footprint
>> > for the module on the disk?
>> >
>>
>> both
>
> Why would the already-loaded module size increase?
>
> I guess I'll just wait to see the code before worrying about this :)

Modules export symbols, as well as importing them :).
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