Re: ARM tunings was Re: [PATCH 3/7] conf/machine/include: Cleanup MIPS tunings to match README

[Phil Blundell <philb@gnu.org>]

On Mon, 2012-04-09 at 16:21 -0500, Mark Hatle wrote:
> I do, and thus the hell that is ARM.  I could not currently generate a single 
> package feed that work would on a variety of devices (like a traditional 
> workstaton/server Linux OS would.) 

Well, actually, you could in fact do exactly that.  What you couldn't
necessarily do with the tunings as they exist right now is generate a
package feed which is optimised for (as opposed to "works on") all those
devices.  But it isn't clear to me that you could do that with a
"traditional workstaton/server" kind of distribution either.  In the x86
world, for example, the majority of the big distros do not bother to
ship individually-tuned binaries for different processor types,
certainly not for the entire distribution.

>Add in to that one of the tunings -- not indicated by the package arch
>of thumb enabled or not

There are multiple reasons why this isn't indicated by the PACKAGE_ARCH.
Firstly, it's irrelevant: on v5T or newer, the question of whether a
given package is using Thumb-state or not has no ABI impact and there is
no reason for anyone to care at a compatibility level.  Second, it may
be unpredictable: the compiler is at liberty (although current versions
of gcc don't exploit this latitude) to switch arbitrarily between
ARM-state and Thumb-state as it sees fit to get the best performance.
And thirdly, it's just another piece of distro policy in the same way as
compiling for -O2 vs -Os (which we also don't encode into PACKAGE_ARCH)
is.

p.