Re: 5.0.0-rc3 : Opcode 1f 12 0f 00 (7ce003e4) leaked temporaries

[David Gibson]

On Fri, Apr 17, 2020 at 10:01:53AM +0100, Peter Maydell wrote:
> On Fri, 17 Apr 2020 at 01:43, Dennis Clarke via <address@hidden> wrote:
> >
> >
> > Very strange messages from qemu 5.0.0-rc3 wherein I try to run :
> 
> Thanks for the report. Did this work with older QEMU?
> 
> > $ /usr/local/bin/qemu-system-ppc64 --version
> > QEMU emulator version 4.2.93
> > Copyright (c) 2003-2020 Fabrice Bellard and the QEMU Project developers
> > $
> > $
> > $ /usr/local/bin/qemu-system-ppc64 \
> >  > -machine pseries-4.1 -cpu power9 -smp 4 -m 12G -accel tcg \
> >  > -drive file=/home/ppc64/ppc64le.qcow2 \
> >  > -device virtio-net-pci,netdev=usernet \
> >  > -netdev user,id=usernet,hostfwd=tcp::10000-:22 \
> >  > -serial stdio -display none -vga none
> > qemu-system-ppc64: warning: TCG doesn't support requested feature,
> > cap-cfpc=workaround
> > qemu-system-ppc64: warning: TCG doesn't support requested feature,
> > cap-sbbc=workaround
> > qemu-system-ppc64: warning: TCG doesn't support requested feature,
> > cap-ibs=workaround
> >
> >
> > SLOF **********************************************************************
> 
> [kernel boot log snipped]
> 
> 
> > root@titan:~#
> >
> >  From this point onwards I see an endless stream of :
> >
> > Opcode 1f 12 0f 00 (7ce003e4) leaked temporaries
> 
> > No idea what that is .. but it doesn't look friendly.
> >
> > Also I did compile qemu with --enable-debug --disable-strip and the
> > performance is truely horrific.  I can only assume that those options
> > are the cause. Any thoughts from anyone would be wonderful.
> 
> Well, you turned on debug and you got some warnings
> which are only emitted with debug on, so you can
> work around it by not doing that :-) And yes, debug
> is slower (it builds QEMU without optimization enabled
> so it's easier to debug QEMU in gdb, and it turns on
> various extra sanity checks.)
> 
> The warning is something we should fix -- it's a bug
> in the PPC code generation where we didn't correctly
> free a TCG temporary. The good news is that this won't
> generally have any visible bad effects, because the
> TCG common code will clean all those temporaries up
> at the end of each block anyway. The only time the leak
> is an issue is if guest code has a straight line sequence
> of hundreds of the same instruction in a row, in which
> case they'll all be in the same block and we might
> hit the limit on total temporaries. That won't happen
> unless guest code is deliberately doing something crazy.
> 
> David -- is this a known bug?

Not known to me.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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