[gentoo-user] "universal" CFLAGS/CXXFLAGS/CHOST for 64bit (AMD64 & EMT64T)?

[Jarry <mr.jarry@gmail.com>]

Hi,
how should I change/set CFLAGS/CXXFLAGS/CHOST if I want to have
system which can be easily migrated between AMD64 and Intel/Core
without recompilation? I have a few virtual servers which I can
not move from one arch to the other, as they have hw-specific
CFLAGS (different host-server hardware, both AMD64 and EM64T):

I have systems with Athlon64/X2 and Core2Quad, with settings:
CFLAGS="-march=athlon64 -O2 -pipe"
CFLAGS="-march=core2 -O2 -pipe"
CHOST is always "x86_64-pc-linux-gnu".

I'm not sure "-mtune=generic" is the right solution, because
it would generate code for IA32/AMD64/EM64T (if I understand
gcc manual correctly, for both 32bit as well as 64bit HW).

What I'm looking for are some generic 64bit settings only for
AMD64/EM64T (not 32bit/IA32) similar as for distros with binary
distributions (i.e. I can download Ubuntu either 32bit or 64bit
version, no other hardware-specific difference). I know with
"universal" 64bit binaries I'm going to loose some pefrormance,
but for me flexibility with migration would overweight this
disadvantage...

Jarry

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