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Re: dropping 32-bit host support

From: Philippe Mathieu-Daudé
Subject: Re: dropping 32-bit host support
Date: Thu, 16 Mar 2023 08:36:55 +0100
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.8.0

On 16/3/23 08:17, Andrew Randrianasulu wrote:

чт, 16 мар. 2023 г., 10:05 Philippe Mathieu-Daudé <philmd@linaro.org <mailto: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.
     > QEMU project no longer considers 32-bit x86 and ARM support for
     > 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
     > (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.

This configuration is still supported!

Thomas, should we clarify yet again? Maybe adding examples?

    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!

Huawei MatePad T8 is based on a MediaTek MT8768 CPU which contains
ARM Cortex-A53 cores. These cores implements the ARMv8-A 64-bit ISA,
so theoretically it is able to run a 64-bit Android.

     > At least I hope it will be not *actively* (intentionally) broken,
     > ...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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