Bug in qemu-system-ppc running fedora 12 ppc guest

Bug in qemu-system-ppc running fedora 12 ppc guest

[Howard Spoelstra]

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Hi,

Qemu-system-ppc built from current master can no longer run Fedora 12 ppc
as guest. (This the only ppc distro I tested.) Host is Fedora 34. Please
see screen shot attached.
Booting from both an installation DVD and from an installed system fail.

To reproduce:
compile qemu-system-ppc from current master and run:

./qemu-system-ppc \
-M mac99,via=pmu \
-m 1024 \
-L pc-bios \
-boot d \
-cdrom Fedora-12-ppc-DVD.iso \
-g 1024x768x8

I tracked the issue down to this commit:

8f0a4b6a9b40e18116a2bb6bbcc00feb8119c792 is the first bad commit
commit 8f0a4b6a9b40e18116a2bb6bbcc00feb8119c792
Author: Matheus Ferst <matheus.ferst@eldorado.org.br>
Date:   Tue Jun 1 16:35:28 2021 -0300

    target/ppc: Move cmp/cmpi/cmpl/cmpli to decodetree

    Additionally, REQUIRE_64BIT when L=1 to match what is specified in The
    Programming Environments Manual:

    "For 32-bit implementations, the L field must be cleared, otherwise the
    instruction form is invalid."

    Some CPUs are known to deviate from this specification by ignoring the
    L bit [1]. The stricter behavior, however, can help users that test
    software with qemu, making it more likely to detect bugs that would
    otherwise be silent.

    If deemed necessary, a future patch can adapt this behavior based on
    the specific CPU model.

    [1] The 601 manual is the only one I've found that explicitly states
    that the L bit is ignored, but we also observe this behavior in a 7447A
    v1.2.

    Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
    Message-Id: <20210601193528.2533031-15-matheus.ferst@eldorado.org.br>
    Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
    [dwg: Corrected whitespace error]
    Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

 target/ppc/insn32.decode                   | 14 ++++++++
 target/ppc/translate.c                     | 52
------------------------------
 target/ppc/translate/fixedpoint-impl.c.inc | 31 ++++++++++++++++++
 3 files changed, 45 insertions(+), 52 deletions(-)

Best,
Howard

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Re: Bug in qemu-system-ppc running fedora 12 ppc guest

[BALATON Zoltan]

Hello,

On Thu, 29 Jul 2021, Howard Spoelstra wrote:
> Hi,
>
> Qemu-system-ppc built from current master can no longer run Fedora 12 ppc
> as guest. (This the only ppc distro I tested.) Host is Fedora 34. Please
> see screen shot attached.
> Booting from both an installation DVD and from an installed system fail.
>
> To reproduce:
> compile qemu-system-ppc from current master and run:
>
> ./qemu-system-ppc \
> -M mac99,via=pmu \
> -m 1024 \
> -L pc-bios \
> -boot d \
> -cdrom Fedora-12-ppc-DVD.iso \
> -g 1024x768x8
>
> I tracked the issue down to this commit:
>
> 8f0a4b6a9b40e18116a2bb6bbcc00feb8119c792 is the first bad commit
> commit 8f0a4b6a9b40e18116a2bb6bbcc00feb8119c792

There's a fix for a similar problem I've seen with AROS and pegasos2 
firmware 1.2 that's in today's pull request:

https://lists.nongnu.org/archive/html/qemu-ppc/2021-07/msg00281.html

That should likely fixes this. Can you try with that (either once it's 
merged or from David's for-6.1 branch).

Regards,
BALATON Zoltan

> Author: Matheus Ferst <matheus.ferst@eldorado.org.br>
> Date:   Tue Jun 1 16:35:28 2021 -0300
>
>    target/ppc: Move cmp/cmpi/cmpl/cmpli to decodetree
>
>    Additionally, REQUIRE_64BIT when L=1 to match what is specified in The
>    Programming Environments Manual:
>
>    "For 32-bit implementations, the L field must be cleared, otherwise the
>    instruction form is invalid."
>
>    Some CPUs are known to deviate from this specification by ignoring the
>    L bit [1]. The stricter behavior, however, can help users that test
>    software with qemu, making it more likely to detect bugs that would
>    otherwise be silent.
>
>    If deemed necessary, a future patch can adapt this behavior based on
>    the specific CPU model.
>
>    [1] The 601 manual is the only one I've found that explicitly states
>    that the L bit is ignored, but we also observe this behavior in a 7447A
>    v1.2.
>
>    Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
>    Message-Id: <20210601193528.2533031-15-matheus.ferst@eldorado.org.br>
>    Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
>    [dwg: Corrected whitespace error]
>    Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
>
> target/ppc/insn32.decode                   | 14 ++++++++
> target/ppc/translate.c                     | 52
> ------------------------------
> target/ppc/translate/fixedpoint-impl.c.inc | 31 ++++++++++++++++++
> 3 files changed, 45 insertions(+), 52 deletions(-)
>
> Best,
> Howard
>
> [image: Qemu-system-ppc-Fedora-Crashing.png]
>

Re: Bug in qemu-system-ppc running fedora 12 ppc guest

[Howard Spoelstra]

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On Thu, Jul 29, 2021 at 12:07 PM BALATON Zoltan <balaton@eik.bme.hu> wrote:

> Hello,
>
> On Thu, 29 Jul 2021, Howard Spoelstra wrote:
> > Hi,
> >
> > Qemu-system-ppc built from current master can no longer run Fedora 12 ppc
> > as guest. (This the only ppc distro I tested.) Host is Fedora 34. Please
> > see screen shot attached.
> > Booting from both an installation DVD and from an installed system fail.
> >
> > To reproduce:
> > compile qemu-system-ppc from current master and run:
> >
> > ./qemu-system-ppc \
> > -M mac99,via=pmu \
> > -m 1024 \
> > -L pc-bios \
> > -boot d \
> > -cdrom Fedora-12-ppc-DVD.iso \
> > -g 1024x768x8
> >
> > I tracked the issue down to this commit:
> >
> > 8f0a4b6a9b40e18116a2bb6bbcc00feb8119c792 is the first bad commit
> > commit 8f0a4b6a9b40e18116a2bb6bbcc00feb8119c792
>
> There's a fix for a similar problem I've seen with AROS and pegasos2
> firmware 1.2 that's in today's pull request:
>
> https://lists.nongnu.org/archive/html/qemu-ppc/2021-07/msg00281.html
>
> That should likely fixes this. Can you try with that (either once it's
> merged or from David's for-6.1 branch).
>
> Regards,
> BALATON Zoltan
>

Thanks, this issue is indeed fixed by
https://github.com/qemu/qemu/commit/2d1154bd95a8bfea30cc59de8e080e5a016a9bee

Best,
Howard

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