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

From: Jakob Bohm
Subject: Re: [RFC PATCH] configure: deprecate 32 bit build hosts
Date: Thu, 26 Sep 2019 19:53:24 +0200
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On 26/09/2019 17:31, Alex Bennée wrote:
Peter Maydell <address@hidden> writes:

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
For KVM we should wait until the kernel chooses to drop support,
I think.
I can certainly do that - although I'd still like to know who actually
uses 32 bit kvm support these days.
Note that the hardware support for kvm was apparently only in 64 bit
AMD/IntelCPUs.  I don't know if early Intel Xeons with 64 bit and kvm
support ran faster in 32 bit mode, which would be a good reason to
use a 32 bit host kernel on them these days, but otherwise I see
little reason to treat 32 bit x86 kvm as a priority target.

I don't know what was used to run 32 bit ARM binaries on x86 Android
tablets with 32 bit x86 user space, but if it was qemu, it would have
been TCG, not kvm.

@@ -745,19 +744,22 @@ case "$cpu" in
-    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).
raspi is probably the most common one because of the 32 bit userspace
they use even though they are running on 64 bit chips.
Please note that not all releases of the raspi boards had 64 bit CPUs.
Raspi 0, 1 and 2 used 32 bit cores (some later production runs of Raspi
2 actually had the Raspi 3 chip).

Then there's the whole space of raspi-lookalike boards like the bananas
(mostly 32 bit A7, some boards with 64 bit A53). LeMaker Etc.

Though I don't currently run qemu on them, I happen to have some older
gen dev boards used for various things, including the BeagleBone open
hardware designs that are all based on a 32 bit Arm A8 core.

Outside of dev boards, there's also the whole theme of running qemu on
Arm based Androidsmartphonesas a way to keep the inner OS separate
from the phone OS.


Jakob Bohm, CIO, Partner, WiseMo A/S.  https://www.wisemo.com
Transformervej 29, 2860 Søborg, Denmark.  Direct +45 31 13 16 10
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