Messages in this thread | | | Date | Sun, 11 Nov 2007 17:05:04 +0100 | From | Adrian Bunk <> | Subject | Re: [PATCH 1/6] Suppress A.OUT library support if !CONFIG_BINFMT_AOUT [try #5] |
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On Sun, Nov 11, 2007 at 04:46:26PM +0100, Andi Kleen wrote: > > > My thoughts go more into the direction that we have hundreds of similar > > cases where e.g. a VFS function might currently only by used by OCFS2 > > and therefore be dead code for most users, and the only maintainable > > solution will be to solve these at the compiler and/or linker level. > > -ffunction-sections can mostly do it, but only for non modular kernels > > One problem is that EXPORT_SYMBOL always creates a reference to the function > even when nothing uses it. > > We would need a weak EXPORT_SYMBOL and some way to check references > over main kernel and modules. I suppose it could be done as part of modpost > and then generating a custom linker script that only includes the function > sections referenced by anybody. But to make this work it would require > putting all the EXPORT_SYMBOLs into own sections too, but I suppose > that would be possible. > > In the past we had trouble that the explicit linker scripts mentioning every > function section made the linker very slow, but perhaps that's fixed now.
I don't remember the technical details, but Denys Vlasenko posted some patches that implemented -ffunction-sections while retaining exports.
Another approach would be calling gcc with "-combine -fwhole-program".
David Woodhouse once sent a whacky patch that implemented this on a per-module basis retaining exports.
Much harder, but with the biggest possible savings, would be a CONFIG_MODULES=n kernel built with one gcc call.
>... > The question is if it would be still have a large enough user base without the > distribution kernels. If it would be only used by a few users I don't think > the maintenance overhead would be worth it. >...
You forget the big embedded userbase - some even stay at kernel 2.4 since kernel 2.6 is much bigger.
> -Andi
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
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