Re: [PATCH 2/2] cpu/core: Fix "help" of CPU core device types

[Eduardo Habkost]

On Fri, Apr 09, 2021 at 06:03:39PM +0200, Greg Kurz wrote:
> Calling qdev_get_machine() from a QOM instance_init function is
> fragile because we can't be sure the machine object actually
> exists. And this happens to break when passing ",help" on the
> command line to get the list of properties for a CPU core
> device types :
> 
> $ ./qemu-system-ppc64 -device power8_v2.0-spapr-cpu-core,help
> qemu-system-ppc64: ../../hw/core/machine.c:1290:
>  qdev_get_machine: Assertion `machine != NULL' failed.
> Aborted (core dumped)
> 
> This used to work before QEMU 5.0, but commit 3df261b6676b
> unwillingly introduced a subtle regression : the above command
> line needs to create an instance but the instance_init function
> of the base class calls qdev_get_machine() before
> qemu_create_machine() has been called, which is a programming bug.
> 
> Use current_machine instead. It is okay to skip the setting of
> nr_thread in this case since only its type is displayed.
> 
> Reported-by: Thomas Huth <thuth@redhat.com>
> Fixes: 3df261b6676b ("softmmu/vl.c: Handle '-cpu help' and '-device help' 
> before 'no default machine'")
> Cc: peter.maydell@linaro.org
> Signed-off-by: Greg Kurz <groug@kaod.org>

Thanks!  I'm queueing this one (without patch 1/2) for QEMU 6.0.

-- 
Eduardo