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Re: dropping 32-bit host support

From: Andrew Randrianasulu
Subject: Re: dropping 32-bit host support
Date: Thu, 16 Mar 2023 10:17:38 +0300

чт, 16 мар. 2023 г., 10:05 Philippe Mathieu-Daudé <philmd@linaro.org>:
Hi Andrew,

On 16/3/23 01:57, Andrew Randrianasulu wrote:
> Looking at https://wiki.qemu.org/ChangeLog/8.0
> <https://wiki.qemu.org/ChangeLog/8.0>
> ===
> System emulation on 32-bit x86 and ARM hosts has been deprecated. The
> QEMU project no longer considers 32-bit x86 and ARM support for system
> emulation to be an effective use of its limited resources, and thus
> intends to discontinue.
>   ==
> well, I guess arguing from memory-consuption point on 32 bit x86 hosts
> (like my machine where I run 32 bit userspace on 64 bit kernel) is not

If you use a 64-bit kernel, then your host is 64-bit :)

No, I mean *kernel* is 64 bit yet userspace (glibc, X , ...) all 32bit. So, qemu naturally will be 32-bit binary on my system.

host: hardware where you run QEMU
guest: what is run within QEMU

Running 32-bit *guest* on your 64-bit *host* is still supported.

We don't plan to support running 32-bit WinXP x86 (guest) on 32-bit
Raspberry Pi 2 (host) for example.

> going anywhere, but what about 32bit userspace on Android tablets,
> either via Limbo emulator or qemu itself in Termux?

*System* emulation [on 32-bit hosts] is deprecated. User emulation
(such linux-user) is not. For example, you can still run 64-bit x86_64
Linux binaries on a 32-bit ARM Raspberry Pi.

Well, unrooted Android does not allow you to just load some perfectly fine kernel module, so user-space emulation can't do all things system-level one can. I also ran qemu-system-ppc on Huawei Matepad T8 (32 bit Android, too) for emulating old mac os 9. Yes, I can wait 10 min per guest boot. Fedora 36 armhf boots even slower on emulation!

> At least I hope it will be not *actively* (intentionally) broken, just
> ...unsupported (so users who know how to run git revert still will get
> their build for some more time).

Unsupported code almost always unintentionally end bit-rotting...

Well, sometimes simple patch restores functionality. I patched for example olive-editor to run on 32 bit, and before this intel embree (raytracing kernels for Lux renderer). So, _sometimes_ it really not that costly. While if this CI thing really runs per-commit and thrown away each result ... may be letting interested users to build things on their own machines (and share patches, if they develop them, publicly)  actually good idea.

I hope this is clearer.



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