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[88.187.86.199]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-438bd5730a6sm161596195e9.35.2025.01.28.02.02.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 28 Jan 2025 02:02:57 -0800 (PST) Message-ID: <9bf6d4b0-7a89-4110-a1e1-46bbdb2fc793@linaro.org> Date: Tue, 28 Jan 2025 11:02:56 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/1] meson: Deprecate 32-bit host systems From: =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= To: =?UTF-8?Q?Daniel_P=2E_Berrang=C3=A9?= Cc: =?UTF-8?Q?Alex_Benn=C3=A9e?= , Thomas Huth , Richard Henderson , qemu-devel@nongnu.org, peter.maydell@linaro.org, stefanha@redhat.com, pbonzini@redhat.com, mark.cave-ayland@ilande.co.uk, Liviu Ionescu References: <20250128004254.33442-1-richard.henderson@linaro.org> <9a280789-9248-4eca-b50c-048fc58e3f53@redhat.com> <87plk72tvr.fsf@draig.linaro.org> <8c0eea44-d0bf-4b86-9b1b-1c2082ab2df9@linaro.org> Content-Language: en-US In-Reply-To: <8c0eea44-d0bf-4b86-9b1b-1c2082ab2df9@linaro.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::329; envelope-from=philmd@linaro.org; helo=mail-wm1-x329.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 28/1/25 11:01, Philippe Mathieu-Daudé wrote: > On 28/1/25 10:27, Daniel P. Berrangé wrote: >> On Tue, Jan 28, 2025 at 10:17:33AM +0100, Philippe Mathieu-Daudé wrote: >>> On 28/1/25 10:02, Alex Bennée wrote: >>>> Thomas Huth writes: >>>> >>>>> On 28/01/2025 01.42, Richard Henderson wrote: >>>>>> Time for our biennial attempt to kill ancient hosts. >>>>>> I've been re-working the tcg code generator a bit over the holidays. >>>>>> One place that screams for a bit of cleanup is with 64-bit guest >>>>>> addresses on 32-bit hosts.  Of course the best "cleanup" is to not >>>>>> have to handle such silliness at all. >>>>>> Two years after Thomas' last attempt, >>>>>>      https://lore.kernel.org/qemu-devel/20230130114428.1297295-1- >>>>>> thuth@redhat.com/ >>>>>> which resulted only in deprecation of i686 host for system >>>>>> emulation. >>>>>> By itself, this just isn't enough for large-scale cleanups. >>>>>> I'll note that we've separately deprecated mips32, set to expire >>>>>> with the end of Debian bookworm, set to enter LTS in June 2026. >>>>>> I'll note that there is *already* no Debian support for ppc32, >>>>>> and that I am currently unable to cross-compile that host at all. >>>>> >>>>> IIRC the biggest pushback that I got two years ago was with regards to >>>>> 32-bit arm: The recommended version of Raspberry Pi OS is still >>>>> 32-bit: >>>>> >>>>>    https://lore.kernel.org/qemu-devel/ >>>>> F852C238-77B8-4E24-9494-8D060EB78F9F@livius.net/ >>>>> >>>>> And looking at https://www.raspberrypi.com/software/operating-systems/ >>>>> this still seems to be the case... >>>>> >>>>> So I guess the main question is now: Would it be ok to kill support >>>>> for 32-bit Raspberry Pi OS nowadays? >>>> >>>> I would argue yes for a few reasons. >>>> >>>>     - you can't buy 32 bit only Pi's AFAICT, even the Pi Zero 2W can >>>> work >>>>       with a 64 bit OS. >>>> >>>>     - It's not like the versions shipping in bullseye and bookworm will >>>>       stop working. >>>> >>>>     - Even if we deprecate now there will likely be one more Debian >>>>       release cycle that gets 32 bit host support. >>>> >>>>>> Showing my hand a bit, I am willing to limit deprecation to >>>>>> 64-bit guests on 32-bit hosts.  But I'd prefer to go the whole hog: >>>>>> unconditional support for TCG_TYPE_I64 would remove a *lot* of >>>>>> 32-bit fallback code. >>>> >>>> I support going the whole hog. I would be curious what use cases still >>>> exist for an up to date 32-on-32 QEMU based emulation? >>> >>> Current maintainers don't have spare time to support the 32-on-32 >>> emulation. If there is interest in the community for such niche, >>> someone needs to step forward, willing to maintain it. >> >> I'm not sure that's the case here. >> >> 32-on-32 is already effectively unmaintained, so we're not suffering >> in terms of keeping the 32-on-32 code reliable. >> >> We're suffering from the complexity that 32-on-32 code places on the >> rest of the XX-on-64 code that we do care about. >> >> IOW if someone volunteered to maintain 32-on-32 that's not actually >> solving the complexity problem, just perpetuating it. >> >> The current maintainers only interested in XX-on-64 will still suffer >> ongoing burden from the code complexity caused by 32-on-32 merely >> existing. >> >> So again lets be clear... >> >> Either we... >> >>   * ...want to kill 32-on-32 code to reduce the complexity on the >>     main XX-on-64 codebase regardless of interest in 32-on-32 >> >> Or >> >>   * ...want to kill 32-on-32 code because it is buggy due to lack >>     of maintainers, but would welcome someone to step forward to >>     maintain it >> >> It sounded like we were wanting the former, not the latter. > > Yes, we want to former. But as Thomas pointed out, last time > someone showed up, and while the maintainers weren't willing to > keep 32-on-32 [*], they kept maintaining it at the price of restricting > XX-on-64. > > [*] back then we proved system emulation XX-on-32 wasn't really useful > anymore, and user emulation 64-on-32 was partly broken, so only > 32-on-32 user emulation was functional. So it seems reasonable to deprecate and ask interested 32-on-32 user emulation users to use QEMU 10.1 release.