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List:       gentoo-dev
Subject:    Re: [gentoo-dev] {bi,multi}arch support for all x86/amd64/ppc/sparc systems
From:       Mike Frysinger <vapier () gentoo ! org>
Date:       2012-01-27 21:00:15
Message-ID: 201201271600.15986.vapier () gentoo ! org
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On Wednesday 07 December 2011 17:15:47 Mike Frysinger wrote:
> the advantage is that it should obsolete the separate kgcc64 package for
> most people.  and i think it might help out with the multilib bootstrap
> issue: you can't build multilib gcc without a multilib glibc, and can't
> build a multilib glibc without a multilib gcc, but i think you should be
> able to build a multilib glibc with a multiarch gcc, and then a multilib
> gcc after that.

a followup: have glibc always install headers for all possible ABIs.  this 
might sound like a lot, but in practice, it amounts to only a handful as glibc 
by default includes support for all ABIs in common headers.

the most common example:
 - amd64 ABI has one unshared header: gnu/stubs-64.h
 - x86 ABI has three unshared headers: gnu/stubs-32.h sys/elf.h sys/vm86.h

so the overhead we're talking about here is that nomultilib amd64 systems will 
have 3 additional headers installed, and nomultilib x86 systems will have one 
extra header.  i suspect the overhead will be very similar for all arches.

the reason for doing this is to try and make multilib migration simpler.  with 
this change in place, you should be able to "upgrade" from a nomultilib amd64 
profile to a multilib amd64 profile with:
	USE='-*' emerge sys-devel/gcc
	emerge sys-libs/glibc
	emerge sys-devel/gcc

still not as automatic as i'd like, but getting closer ...
-mike

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