Re: qemuarm: should it really have TUNE_ARCH armv5te?

[Phil Blundell <philb@gnu.org>]

On Thu, 2012-09-13 at 11:47 -0500, Mark Hatle wrote:
> ARM seems to be the one exception, where you have three levels.. ABI 
> (EABI/hf-EABI), processor family (armv4, armv5, armv7, cortext....), and then 
> CPU optimization.  This seems to cause additional confusion, as the CPU 
> optimizations are not being captured in the current package ARCH, which makes it 
> difficult to optimize on a feed.

I guess that by "processor family" you mean ISA.  (I'm not aware of an
ARM ISA variant named "cortext", though I haven't really been keeping up
with the latest developments there so I could imagine that one might
exist.)

Anyway, the basic three-way scenario (ISA, ABI, optimisation) that you
describe above isn't in any sense unique to ARM; the concept of
per-cpu-model optimisation/tuning applies equally to other architectures
(x86 for example) as well.  It's probably less of an issue for MIPS but
I suspect that's more a reflection of gcc's weaker optimisation
capabilities on that architecture rather than a homogeous CPU
population.  I don't know PowerPC well enough to make any comment about
that.

There's no particular reason that the per-cpu tuning couldn't be
captured in PACKAGE_ARCH if one wanted to do it.  But the decision about
how to structure a binary feed is clearly one for the DISTRO and the
question of how to map that into PACKAGE_ARCH is, equally clearly, one
that the distro ought to be solving.  Since oe-core itself doesn't build
any feeds, I don't think there's any reason for it to make heroic
efforts to sort out the package architectures that would go into them.

p.