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Re: [RFC PATCH] configure: deprecate 32 bit build hosts

From: Christian Borntraeger
Subject: Re: [RFC PATCH] configure: deprecate 32 bit build hosts
Date: Thu, 26 Sep 2019 15:46:00 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0

On 26.09.19 14:58, Daniel P. Berrangé wrote:
> On Thu, Sep 26, 2019 at 08:50:36AM +0100, Peter Maydell wrote:
>> On Thu, 26 Sep 2019 at 00:31, Alex Bennée <address@hidden> wrote:
>>> The 32 bit hosts are already a second class citizen especially with
>>> support for running 64 bit guests under TCG. We are also limited by
>>> testing as actual working 32 bit machines are getting quite rare in
>>> developers personal menageries. For TCG supporting newer types like
>>> Int128 is a lot harder with 32 bit calling conventions compared to
>>> their larger bit sized cousins. Fundamentally address space is the
>>> most useful thing for the translator to have even for a 32 bit guest a
>>> 32 bit host is quite constrained.
>>> As far as I'm aware 32 bit KVM users are even less numerous. Even
>>> ILP32 doesn't make much sense given the address space QEMU needs to
>>> manage.
>> For KVM we should wait until the kernel chooses to drop support,
>> I think.
> What if the kernel is waiting for QEMU to drop support too ;-P

For what its worth on kvm/s390 we never cared about implementing
32 bit. 

>>> @@ -745,19 +744,22 @@ case "$cpu" in
>>>    ;;
>>>    armv*b|armv*l|arm)
>>>      cpu="arm"
>>> -    supported_cpu="yes"
>>>    ;;
>> I'll leave others to voice opinions about their architectures,
>> but I still have 32-bit arm in my test set for builds, and
>> I'm pretty sure we have users (raspi users, for a start).
> RHEL dropped all 32-bit host support a long time ago, so Red Hat
> don't care for our products.
> Fedora has recently stopped building i686 kernels and thus also no
> long composes i686 installs. Some users complained, but ultimately
> no one cares enough to step forward as maintainers.
> That leaves armv7 as the only 32-bit arch in Fedora that is somewhat
> active & maintained. I don't have any real insight on whether any
> armv7 (Fedora) users are making much use of QEMU/KVM though, either
> system or user emulation. 
> Our preference in Fedora is to have things built on every architecture
> that the distro targets, but if upstream developers explicitly drop an
> architecture we're not going to try to add it back.
> Regards,
> Daniel

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