Re: [RFC PATCH] configure: deprecate 32 bit build hosts

[Alistair Francis]

On Thu, Sep 26, 2019 at 8:41 AM Alex Bennée <address@hidden> wrote:
>
>
> Thomas Huth <address@hidden> writes:
>
> > On 26/09/2019 15.46, Christian Borntraeger wrote:
> >>
> >>
> >> On 26.09.19 14:58, Daniel P. Berrangé wrote:
> >>> On Thu, Sep 26, 2019 at 08:50:36AM +0100, Peter Maydell wrote:
> >>>> On Thu, 26 Sep 2019 at 00:31, Alex Bennée <address@hidden> 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 guest 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 != 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 tested.

Considering that we have enough trouble keeping the riscv32 kernel
booting it's probably ok to drop it from QEMU.

Alistair

>
> >
> >  Thomas
>
>
> --
> Alex Bennée
>