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From: Segher Boessenkool <segher@kernel.crashing.org>
Subject: Re: [Cbe-oss-dev] [RFC, PATCH] selection of CPU optimization
Date: Fri, 13 Apr 2007 20:43:02 +0200
To: Arnd Bergmann <arnd@arndb.de>
Cc: linuxppc-dev@ozlabs.org, cbe-oss-dev@ozlabs.org
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> My understanding at this point is that we can always fall back
> to -mcpu=powerpc or -mcpu=powerpc64,

Yes.  With perhaps and added -mno-string or similar if
some supported CPU really needs it.


>  and also

[SNIP]

> So if we select e.g. power6 and cell, it needs to fall back to power4,
> which is the common subset. Selecting both 403 and 405 would result
> in falling back to -mcpu=powerpc, because they don't have any larger
> subset.

This is way complicated.  Also, it is not unique to the
kernel; you'd be better off adding this logic to the
compiler itself.  OTOH, it's such a niche market, maybe
the distros that want it (if any do) should do this in
their RPM build scripts or similar.


Segher