From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mailout.stusta.mhn.de ([141.84.69.5]:56359 "EHLO mailhub.stusta.mhn.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1758096AbXJLSPQ (ORCPT ); Fri, 12 Oct 2007 14:15:16 -0400 Date: Fri, 12 Oct 2007 20:15:44 +0200 From: Adrian Bunk Subject: Re: [PATCH] Discardable strings for init and exit sections Message-ID: <20071012181544.GC6476@stusta.de> References: <20071012171938.GB6476@stusta.de> <20071012175209.GA1110@linux-mips.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20071012175209.GA1110@linux-mips.org> Sender: linux-arch-owner@vger.kernel.org To: Ralf Baechle Cc: "Maciej W. Rozycki" , Franck Bui-Huu , linux-arch@vger.kernel.org, linux-mips@linux-mips.org, Andrew Morton , linux-kernel@vger.kernel.org List-ID: On Fri, Oct 12, 2007 at 06:52:10PM +0100, Ralf Baechle wrote: > 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. - Most of the string annotations are (naturally) dev{init,exit} annotations, and bugs there are therefore in configurations that have only extremely low testing coverage during -rc. - I'm counting 22 annotations in the driver Maciej converted as an example. When estimating the number of possible annotations based on the number of C files in the kernel I'm getting a six digit number. No matter how hard it would be to teach gcc about it, when thinking of the amount of __*init*/__*exit* bugs we already have I simply can't imagine the string annotations as a maintainable solution. > Ralf cu Adrian -- "Is there not promise of rain?" Ling Tan asked suddenly out of the darkness. There had been need of rain for many days. "Only a promise," Lao Er said. Pearl S. Buck - Dragon Seed