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Re: [PATCH] Discardable strings for init and exit sections

To: Adrian Bunk <bunk@kernel.org>
Subject: Re: [PATCH] Discardable strings for init and exit sections
From: Ralf Baechle <ralf@linux-mips.org>
Date: Fri, 12 Oct 2007 18:52:10 +0100
Cc: "Maciej W. Rozycki" <macro@linux-mips.org>, Franck Bui-Huu <vagabon.xyz@gmail.com>, linux-arch@vger.kernel.org, linux-mips@linux-mips.org, Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org
In-reply-to: <20071012171938.GB6476@stusta.de>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <Pine.LNX.4.64N.0710121711120.21684@blysk.ds.pg.gda.pl> <20071012171938.GB6476@stusta.de>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.5.14 (2007-02-12)
On Fri, Oct 12, 2007 at 07:19:38PM +0200, Adrian Bunk wrote:

> I have an objection against this approach:
> 
> Our __*init*/__*exit* annotations are already a constant source of bugs, 
> and adding more pifalls (e.g. forgotten removal of _i()/_e() when a 
> function is no longer __*init*/__*exit*) doesn't sound like a good plan.
> 
> Shouldn't it be possible to automatically determine where to put the 
> strings? I don't know enough gcc/ld voodoo for being able to tell 
> whether it is currently possible, and if yes how, but doing it 
> automatically sounds like the only solution that wouldn't result in an
> unmaintainable mess.

gcc tends to place data such as strings or jump tables generated from
switches not into a place were it would be easily discardable.  The
latter is the reason that on MIPS we can't discard __exit functions
at all - a switch table in .rodata might be referencing discarded code
in .exit.text which makes ld fail.  When I discussed this with some gcc
people a while ago nobody really had a good suggestion to solve this.

  Ralf

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