Bug#680096: ATLAS on PowerPC

[brian m. carlson]

On Wed, Jul 04, 2012 at 07:26:00PM +0200, Sébastien Villemot wrote:
> [please keep the bug in Cc:, I’m not subscribed to the list]
> 
> Dear PowerPC porters,
> 
> As a co-maintainer of atlas, I intend to force a specific PowerPC CPU
> architecture when the package is built on buildds (in order to fix
> #680096).
> 
> Atlas gives me the following options: POWER3, POWER4, POWER5, POWER6,
> POWER7, PPCG4, PPCG5.
> 
> I would like to know which one of these is the most generic
> architecture, so that the atlas package thus modified will work on all
> supported machines. I guess this is either POWER3 or PPCG4, but it is
> unclear to me which one is more generic. Or maybe none of the two
> encompasses the other, in which case I would like to know which one
> would be the best choice from your point of view.

POWER3 is 64-bit.  PPCG4 is 32-bit, but it requires the use of Altivec
instructions, which G3 processors do not have.  So the answer is that
neither of these is acceptable by default.  For example, neither of
these would work on my iBook.  Is there a reason that you cannot use the
defaults of the compiler?

Also, POWER and PowerPC are two very similar architectures.  In general,
they each have a few instructions that the other does not, but there is
a large common subset that is generally what Debian uses.  POWER 3 and
newer support all of the PowerPC instruction set.  However, if you use a
POWER setting, you need to be sure that it does not include instructions
that only POWER processors have, or it will not work on PowerPC
processors.

> BTW, if you could answer the same question concerning the ppc64 and
> powerpcspe ports, that would be great.

I don't know enough here to have an opinion, sorry.

-- 
brian m. carlson / brian with sandals: Houston, Texas, US
+1 832 623 2791 | http://www.crustytoothpaste.net/~bmc | My opinion only
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