linux-kernel - Re: [PATCH 0/2] do not select KALLSYMS

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Date:	Fri, 01 Apr 2011 17:40:33 +0300
From:	Artem Bityutskiy <dedekind1@...il.com>
To:	Paulo Marques <pmarques@...popie.com>
Cc:	Randy Dunlap <randy.dunlap@...cle.com>,
	MTD list <linux-mtd@...ts.infradead.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] do not select KALLSYMS_ALL

On Thu, 2011-03-31 at 15:18 +0100, Paulo Marques wrote:
> Artem Bityutskiy wrote:
> > [...]
> > I personally think KALLSYMS_ALL should be just merged with KALLSYMS and
> > disappear - we should have only one option. CONFIG_KALLSYMS_EXTRA_PASS should
> > die as well.
> 
> That sounds a little too extreme...
> 
> KALLSYMS is useful for most kernels, since it provides nice readable
> stack dumps for panics and BUG's.
> 
> KALLSYMS_ALL adds a lot of extra symbols that can be useful mostly to
> development kernels and shouldn't be used to add unnecessary bloat to
> user kernels.

OK, thanks.

> Now as for CONFIG_KALLSYMS_EXTRA_PASS: to build the kallsyms table, the
> build process first links a kernel image with an empty kallsyms table
> and use that to fetch information for all the symbols.
> 
> It then uses that information to build the table with the right size,
> and links it again. If everything goes ok, this new version as all the
> symbols in the correct places and the final table can be built with the
> correct addresses.
> 
> The final linking should produce the same result as only the data on the
> kallsyms table changed, but not its size.
> 
> However, there have been bugs in the past with section alignments and
> symbol reordering for symbols with the same address, etc., etc. that
> make this final table not have the exact same size, and the build fails
> with an inconsistent kallsyms data message. At this point, the user can
> turn on the CONFIG_KALLSYMS_EXTRA_PASS and temporarily solve the problem
> while the developers find the correct fix. Without this option, in this
> situation the kernel would simply fail the compilation.
> 
> All this has been stable for a while and this option hasn't been needed
> recently (AFAIK), but if there is some bug in some new binutils or
> something, the option might be needed again.

Thanks for explanation!

But... why on earth this option is in Kconfig then, if this is only
about extra pass during the kernel _compilation_ ? This and the vague
help message in Kconfig help section are very misleading. This should
not be in Kconfig at all then, it should be purely a Makefile thing!

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

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