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Re: armhf multiarch tuple

On Tue, Apr 17, 2012 at 11:16:44AM -0500, Jonathan Nieder wrote:
>Steve McIntyre wrote:
>> They'll be upwardly-compatible (i.e. they'll work on v7), but not in
>> reverse. armhf is explicitly defined to be ARMv7+, using VFPv3-D16 (no
>> Neon). That's standardised across distros too.
>> There's a chance that some of the armhf binaries might run on v6, but
>> if so it's only by chance and not guaranteed.
>This is in contrast with i386-linux-gnu, where the definition is
>80386+ and actual binaries from distros and others tend to require
>something more modern like 486+ or 586+.  (In other words, for the
>sake of setting filesystem paths there is no need to be strict about
>the instruction set.)  As long as all the distros are using ARMv7+
>anyway, I don't think this will come up much, so I don't mind.

Yup. As we've switched ABI too, this allowed/required us to define a
clean break here. A hard definition of armhf is a good thing, as it's
the first time we've had any kind of agreement in the ARM distro
world. Upcoming ARM servers and other devices where people will expect
to be able to share binaries depend on this.

>The question to ask is: if someone builds an ARMv6+ library using the
>hard-float ABI, where should they place it on the filesystem?

That's a good question, and one that we haven't defined at all. It
could be as easy as installing using the arm-linux-gnueabihf multiarch
triplet dir (like armhf), but then you need to be very careful not to
install any armhf binary packages over the top. Maybe best to define
something new, but nobody has cared about it thus far.

Frankly, ARMv6 isn't a very interesting optimisation target. If the Pi
wasn't provoking so much interest then we'd probably just ignore
it. I'm not sure if we're likely to get much in the way of
cross-distro stuff, but it's a possibility. Given we've just finished
a big cross-distro discussion about v7 hard-float, I'm loath to bring
this up too, right now. Feel free to ask yourself, if you like... :-)

Steve McIntyre, Cambridge, UK.                                steve@einval.com
"The problem with defending the purity of the English language is that
 English is about as pure as a cribhouse whore. We don't just borrow words; on
 occasion, English has pursued other languages down alleyways to beat them
 unconscious and rifle their pockets for new vocabulary."  -- James D. Nicoll

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