Re: qemu-system-ppc64 option -smp 2 broken with commit 20b6643324a79860dcdfe811ffe4a79942bca21e

[Cédric Le Goater]

Hello Anushree,

On 6/23/23 13:09, Anushree Mathur wrote:
> Hi everyone,
>
> I was trying to boot rhel9.3 image with upstream qemu-system-ppc64 -smp 2 
> option and observed a segfault (qemu crash).
>
> qemu command line used:
>
> qemu-system-ppc64 -name Rhel9.3.ppc64le -smp 2 -m 16G -vga none -nographic 
> -machine pseries -cpu POWER10 -accel tcg -device virtio-scsi-pci -drive 
> file=/home/rh93.qcow2,if=none,format=qcow2,id=hd0 -device scsi-hd,drive=hd0 
> -boot c
>
> After doing a git bisect, I found the first bad commit which introduced this 
> issue is below:

Could you please open a gitlab issue on QEMU project ?

 https://gitlab.com/qemu-project/qemu/-/issues

Thanks,

C.

> [qemu]# git bisect good
> 20b6643324a79860dcdfe811ffe4a79942bca21e is the first bad commit
> commit 20b6643324a79860dcdfe811ffe4a79942bca21e
> Author: Richard Henderson <richard.henderson@linaro.org>
> Date:   Mon Dec 5 17:45:02 2022 -0600
>
>      tcg/ppc: Reorg goto_tb implementation
>
>      The old ppc64 implementation replaces 2 or 4 insns, which leaves a race
>      condition in which a thread could be stopped at a PC in the middle of
>      the sequence, and when restarted does not see the complete address
>      computation and branches to nowhere.
>
>      The new implemetation replaces only one insn, swapping between
>
>              b       <dest>
>      and
>              mtctr   r31
>
>      falling through to a general-case indirect branch.
>
>      Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
>      Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>
>   tcg/ppc/tcg-target.c.inc | 152 +++++++++++++----------------------------------
>   tcg/ppc/tcg-target.h     |   3 +-
>   2 files changed, 41 insertions(+), 114 deletions(-)
> [qemu]#
>
> Can someone please take a look and suggest a fix to resolve this issue?
>
> Thanks in advance.
> Regards,
> Anushree-Mathur