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From: Adrian Bunk <bunk@kernel.org>
To: Ralf Baechle <ralf@linux-mips.org>
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
Subject: Re: [PATCH] Discardable strings for init and exit sections
Date: Fri, 12 Oct 2007 20:15:44 +0200	[thread overview]
Message-ID: <20071012181544.GC6476@stusta.de> (raw)
In-Reply-To: <20071012175209.GA1110@linux-mips.org>

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


  reply	other threads:[~2007-10-12 18:15 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-10-12 16:50 Maciej W. Rozycki
2007-10-12 17:19 ` Adrian Bunk
2007-10-12 17:52   ` Ralf Baechle
2007-10-12 18:15     ` Adrian Bunk [this message]
2007-10-23 16:57       ` Maciej W. Rozycki
2007-10-23 17:12         ` Adrian Bunk
2007-10-23 17:25           ` Sam Ravnborg
2007-10-12 17:45 ` Sam Ravnborg
2007-10-23 17:23   ` Maciej W. Rozycki
2007-10-23 17:27     ` Sam Ravnborg

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