linux-kernel - Re: /proc/kallsyms broken in 2.6.26-rc1-git6

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Message-ID: <20080512100809.GH31954@one.firstfloor.org>
Date:	Mon, 12 May 2008 12:08:09 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Paulo Marques <pmarques@...popie.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: /proc/kallsyms broken in 2.6.26-rc1-git6

> So, the only difference is the filter made by that "grep -v" to exclude 
> a few classes of symbols.
> 
> Maybe I lost myself in that expression, but it doesn't seem like it 
> would be able to filter out the symbols you're seeing. Are you sure the 
> same symbols don't appear in System.map?

They do, but that's also new.

> 
> >They didn't use to be there and don't
> >make any sense because they don't have any valid kernel addresses.
> 
> I don't know enough about the markers infrastructure but I guess these 
> "addresses" are more like an "offset" into a markers structure that is 
> automatically produced by putting these symbols into a special section 
> that starts at offset 0.

I don't know too much about the markers implementation either and
if it's caused by then.

> Well, my first suspects would be these:
> 
> CONFIG_KPROBES=y
> CONFIG_KRETPROBES=y
> CONFIG_HAVE_KPROBES=y
> CONFIG_HAVE_KRETPROBES=y

I've always had those enabled and afaik they don't generate any 
magic symbols.

> 
> >
> >It's the other way round -- kallsyms changed and that change will likely
> >break programs.
> 
> I don't have the time right now to try your configuration and pinpoint 
> the problem, but if you can come up with a plan, like: "we need to 
> filter out symbols from the output of "nm" whose type is 'N'", I'll be 
> more than happy to provide a patch to fix it...

man nm says

 "N" The symbol is a debugging symbol.

while I'm not 100% sure what a debugging symbol is I suppose we don't
need those so yes please filter those out (both
out of System.map and out of kallsyms) 

-Andi
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