Re: [PULL 11/24] tcg/optimize: Use tcg_constant_internal with constant folding

[Richard W.M. Jones]

On Thu, Feb 04, 2021 at 05:04:22PM +0100, Philippe Mathieu-Daudé wrote:
> On 2/4/21 10:37 AM, David Hildenbrand wrote:
> > On 04.02.21 10:29, Richard W.M. Jones wrote:
> >>>> commit 8f17a975e60b773d7c366a81c0d9bbe304f30859
> >>>> Author: Richard Henderson <richard.henderson@linaro.org>
> >>>> Date:   Mon Mar 30 19:52:02 2020 -0700
> >>>>
> >>>>      tcg/optimize: Adjust TempOptInfo allocation
> >>>>
> >>>> The image boots just fine on s390x/TCG as well.
> >>>
> >>> Let me try this in a minute on my original test machine.
> >>
> >> I got the wrong end of the stick as David pointed out in the other email.
> >>
> >> However I did test things again this morning (all on s390 host), and
> >> current head (1ed9228f63ea4b) fails same as before ("mount" command
> >> fails).
> >>
> >> Also I downloaded:
> >>
> >>   
> >> https://dl.fedoraproject.org/pub/fedora-secondary/releases/33/Cloud/s390x/images/Fedora-Cloud-Base-33-1.2.s390x.qcow2
> >>
> >>
> >> and booted it on 1ed9228f63ea4b using this command:
> >>
> >>    $ ~/d/qemu/build/s390x-softmmu/qemu-system-s390x -machine accel=tcg
> >> -m 2048 -drive
> >> file=Fedora-Cloud-Base-33-1.2.s390x.qcow2,format=qcow2,if=virtio
> >> -serial stdio
> >>
> >> Lots of core dumps inside the guest, same as David saw.
> >>
> >> I then reset qemu back to 8f17a975e60b773d ("tcg/optimize: Adjust
> >> TempOptInfo allocation"), rebuilt qemu, tested the same command and
> >> cloud image, and that booted up much happier with no failures or core
> >> dumps.
> >>
> >> Isn't it kind of weird that this would only affect an s390 host?  I
> >> don't understand why the host would make a difference if we're doing
> >> TCG.
> > 
> > I assume an existing BUG in the s390x TCG backend ... which makes it
> > harder to debug :)
> 
> This seems to fix it:
> 
> -- >8 --
> diff --git a/tcg/s390/tcg-target.c.inc b/tcg/s390/tcg-target.c.inc
> index 8517e552323..32d03dbfbaf 100644
> --- a/tcg/s390/tcg-target.c.inc
> +++ b/tcg/s390/tcg-target.c.inc
> @@ -1094,10 +1094,16 @@ static int tgen_cmp(TCGContext *s, TCGType type,
> TCGCond c, TCGReg r1,
>                  op = (is_unsigned ? RIL_CLFI : RIL_CFI);
>                  tcg_out_insn_RIL(s, op, r1, c2);
>                  goto exit;
> -            } else if (c2 == (is_unsigned ? (uint32_t)c2 : (int32_t)c2)) {
> -                op = (is_unsigned ? RIL_CLGFI : RIL_CGFI);
> -                tcg_out_insn_RIL(s, op, r1, c2);
> -                goto exit;
> +            } else if (is_unsigned) {
> +                if (c2 == (uint32_t)c2) {
> +                    tcg_out_insn_RIL(s, RIL_CLGFI, r1, c2);
> +                    goto exit;
> +                }
> +            } else {
> +                if (c2 == (int32_t)c2) {
> +                    tcg_out_insn_RIL(s, RIL_CGFI, r1, c2);
> +                    goto exit;
> +                }
>              }
>          }

Thanks - can confirm this fixes both observed problems here.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-builder quickly builds VMs from scratch
http://libguestfs.org/virt-builder.1.html