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Thu, 26 Sep 2019 09:16:03 -0700 (PDT) MIME-Version: 1.0 References: <20190925233013.6449-1-alex.bennee@linaro.org> <20190926125817.GB19660@redhat.com> <19efe3ee-a532-cf66-a5a7-03a7c053737c@redhat.com> <87d0fn9ix8.fsf@linaro.org> In-Reply-To: <87d0fn9ix8.fsf@linaro.org> From: Alistair Francis Date: Thu, 26 Sep 2019 09:11:17 -0700 Message-ID: Subject: Re: [RFC PATCH] configure: deprecate 32 bit build hosts To: =?UTF-8?B?QWxleCBCZW5uw6ll?= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.85.208.194 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 , Thomas Huth , =?UTF-8?Q?Daniel_P=2E_Berrang=C3=A9?= , Richard Henderson , QEMU Developers , qemu-discuss , Christian Borntraeger , qemu-s390x , qemu-arm , "open list:New World" , "open list:RISC-V" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Sep 26, 2019 at 8:41 AM Alex Benn=C3=A9e w= rote: > > > Thomas Huth writes: > > > On 26/09/2019 15.46, Christian Borntraeger wrote: > >> > >> > >> On 26.09.19 14:58, Daniel P. Berrang=C3=A9 wrote: > >>> On Thu, Sep 26, 2019 at 08:50:36AM +0100, Peter Maydell wrote: > >>>> On Thu, 26 Sep 2019 at 00:31, Alex Benn=C3=A9e 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 gues= t 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 > >>>>> manage. > >>>> > >>>> For KVM we should wait until the kernel chooses to drop support, > >>>> I think. > >>> > >>> What if the kernel is waiting for QEMU to drop support too ;-P > >> > >> For what its worth on kvm/s390 we never cared about implementing > >> 32 bit. > > > > Looking at tcg/s390/tcg-target.inc.c : > > > > ... > > /* We only support generating code for 64-bit mode. */ > > #if TCG_TARGET_REG_BITS !=3D 64 > > #error "unsupported code generation mode" > > #endif > > ... > > > > ... it seems to me that TCG does not support 32-bit on s390 either. I > > think we can remove s390 (32-bit) from the list completely? > > It's the same for riscv32 I think. I think riscv32 host *should* work, although I don't think it was ever test= ed. Considering that we have enough trouble keeping the riscv32 kernel booting it's probably ok to drop it from QEMU. Alistair > > > > > Thomas > > > -- > Alex Benn=C3=A9e >