[gentoo-dev] Gentoo i486 support

[Ben Kohler <bkohler@gentoo.org>]

Hi guys,

For some time now, we've been shipping broken i486 stage3s that do not 
run on pre-i686 hardware [1].  Due to a change in catalyst [2], we no 
longer set CXXFLAGS in the default make.conf, so the x86 profiles' (imho 
wrong/broken) defaults [3] kick in.

I'd like to get this fixed, and I see 3 possible solutions, listed in 
order of my own preference:

1) Adjust x86 profile defaults to drop the problematic -march=i686. 
This would be more in line with amd64 profiles (et al), which set no 
-march value so it can run on any hardware for this arch.

2) Patch catalyst to start setting CXXFLAGS again.  Rather than roll 
back to exactly CXXFLAGS="${CFLAGS}" again, it's been suggested that we 
start setting COMMON_FLAGS, and CFLAGS="${COMMON_FLAGS}" 
CXXFLAGS=${COMMON_FLAGS}" etc.  I prepared such a patch a while back 
[4], which seems to work but may need a bit of updating.

3) Drop i486 support.  We're only pretending to have support now, we 
could officially stop building these broken stages completely.

Personally I think #1 is the most technically correct and least amount 
of work.  The only result will be slightly less optimized builds for 
people who choose not to customize *FLAGS at all in make.conf.  But this 
is correct behavior.  What we have now is akin to setting -march=core2 
on amd64 stage3 and saying "oops it doesn't work on early 64bit AMD 
cpus, but oh well most people have newer and will appreciate the 
optimization".

Thoughts?

-Ben

[1] https://bugs.gentoo.org/654080
[2] 
https://gitweb.gentoo.org/proj/catalyst.git/commit/?id=b409bd9bb4b50f69a555e4e148057ade86a7ed16
[3] 
https://gitweb.gentoo.org/repo/gentoo.git/tree/profiles/arch/x86/make.defaults
[4] https://bugs.gentoo.org/575446#c4