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[83.35.25.14]) by smtp.gmail.com with ESMTPSA id c7sm3759781wmq.13.2021.09.15.01.51.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 15 Sep 2021 01:51:57 -0700 (PDT) Subject: Re: Deprecate 32-bit hosts? (was: Re: [PULL 14/14] hw/arm/aspeed: Add Fuji machine type) To: =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , Thomas Huth References: <20210913161304.3805652-1-clg@kaod.org> <20210913161304.3805652-15-clg@kaod.org> <88c26520-6b87-e7a2-ac78-c1c92477c814@kaod.org> <1949e204-1bce-f15b-553b-1b42b41e3e08@linaro.org> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: Date: Wed, 15 Sep 2021 10:51:56 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::32f; envelope-from=philippe.mathieu.daude@gmail.com; helo=mail-wm1-x32f.google.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FORGED_FROMDOMAIN=0.249, FREEMAIL_FROM=0.001, HEADER_FROM_DIFFERENT_DOMAINS=0.25, NICE_REPLY_A=-1.969, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Samuel Thibault , Andrew Jeffery , Michael Tokarev , Richard Henderson , "qemu-devel@nongnu.org" , "Richard W.M. Jones" , "qemu-arm@nongnu.org" , Joel Stanley , Peter Delevoryas , Paolo Bonzini , Stefan Weil , =?UTF-8?Q?C=c3=a9dric_Le_Goater?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 9/15/21 10:37 AM, Daniel P. Berrangé wrote: > On Wed, Sep 15, 2021 at 09:42:48AM +0200, Thomas Huth wrote: >> On 14/09/2021 17.22, Richard Henderson wrote: >>> On 9/14/21 5:26 AM, Peter Maydell wrote: >>>> (2) RAM blocks should have a length that fits inside a >>>>      signed 32-bit type on 32-bit hosts (at least I assume this >>>>      is where the 2047MB limit is coming from; in theory this ought >>>>      to be improveable but auditing the code for mishandling of >>>>      RAMblock sizes to ensure we weren't accidentally stuffing >>>>      their size into a signed 'long' somewhere would be kind >>>>      of painful) >>> >>> Recalling that the win64 abi model is p64, i.e. 'long' is still 32-bit >>> while pointers are 64-bit, how close do we think we are to this being >>> fixed already? >>> >>>> Even if we did fix (2) we'd need to compromise on (3) >>>> sometimes still -- if a board has 4GB of RAM that's >>>> not going to fit in 32 bits regardless. But we would be >>>> able to let boards with 2GB have 2GB. >>> >>> I'm not opposed to deprecating 32-bit hosts...  ;-) >> >> I think we should consider this again, indeed. Plain 32-bit CPUs are quite >> seldom these days, aren't they? And I think we urgently need to decrease the >> amount of things that we have to test and maintain in our CI and developer >> branches... So is there still a really really compelling reason to keep >> 32-bit host support alive? > > I think it probably depends on the architecture to some extent. > > i386 is possibly getting rare enough to consider dropping, though > IIUC, KVM in the kernel still supports it. Would feel odd to drop > it in QEMU if the kernel still thinks it is popular enough to keep > KVM support. > > armv7 feels like it is relatively common as 64-bit didn't arrive > in widespread use until relatively recent times compared to x86_64. > KVM dropped armv7, but then hardware for that was never widespread, > so armv7 was always TCG dominated > > Other 32-bit arches were/are always rare. While I could understand there are rare uses of system emulation on 32-bit hosts, I still believe user-emulation is used, but would like to be proven to the contrary. With that in mind, I'm not sure removing sysemu on 32-bit hosts is worthful. Maybe we should ask distribution maintainers first, then eventually poll the community? Or start with a deprecation warning? >> Could we maybe also decrease the amount of targets, i.e. merge >> qemu-system-x86_64 and qemu-system-i386, merge qemu-system-ppc64 and >> qemu-system-ppc, etc. where it makes sense (i.e. where one of the binaries >> is a superset of the other)? > > Regards, > Daniel >