Re: [kdevops PATCH] qemu-build: Add a configuration option for enabling qemu debug

[Fan Ni <fan.ni@gmx.us>]

On Thu, Aug 24, 2023 at 02:29:04PM -0700, Luis Chamberlain wrote:
> On Thu, Aug 24, 2023 at 02:08:05PM -0700, fan.ni@gmx.us wrote:
> > From: Fan Ni <fan.ni@gmx.us>
> >
> > Currently, qemu will always be compiled without enabling debug, however,
> > enabling qemu debug is important for debug purpose. A new Kconfig
> > option is added to allow user to enable debug when configuring qemu. By
> > default, it is disabled.
> >
> > Signed-off-by: Fan Ni <fan.ni@samsung.com>
> > ---
>
> Thanks Fan, I've Cc'd kdevops@lists.linux.dev. Please use that
> mailing list for future patches. My review below.
>
Thaks Luis for the review. See below.

> >  Makefile.build_qemu                          | 4 ++++
> >  playbooks/roles/build_qemu/defaults/main.yml | 1 +
> >  playbooks/roles/build_qemu/tasks/main.yml    | 2 +-
> >  vagrant/Kconfig                              | 7 +++++++
> >  4 files changed, 13 insertions(+), 1 deletion(-)
> >
> > diff --git a/Makefile.build_qemu b/Makefile.build_qemu
> > index 7addd2f0..3f50f949 100644
> > --- a/Makefile.build_qemu
> > +++ b/Makefile.build_qemu
> > @@ -19,6 +19,10 @@ ifeq (y,$(CONFIG_TARGET_ARCH_PPC64LE))
> >  QEMU_BUILD_SETUP_ARGS += qemu_target="ppc64-softmmu"
> >  endif
> >
> > +ifeq (y,$(CONFIG_QEMU_WITH_DEBUG_ENABLED))
> > +QEMU_BUILD_SETUP_ARGS += qemu_debug="--enable-debug"
> > +endif
>
> This is a build debug thing.
Will fix in the next version.
>
> > +
> >  qemu: $(KDEVOPS_EXTRA_VARS)
> >  	@$(Q)ansible-playbook $(ANSIBLE_VERBOSE) --connection=local \
> >  		--inventory localhost, \
> > diff --git a/playbooks/roles/build_qemu/defaults/main.yml b/playbooks/roles/build_qemu/defaults/main.yml
> > index 006d669c..c8e12759 100644
> > --- a/playbooks/roles/build_qemu/defaults/main.yml
> > +++ b/playbooks/roles/build_qemu/defaults/main.yml
> > @@ -12,3 +12,4 @@ qemu_git: "https://github.com/qemu/qemu.git"
> >  qemu_version: "v7.2.0-rc4"
> >  qemu_build_dir: "{{ qemu_data }}/build"
> >  qemu_target: "x86_64-softmmu"
> > +qemu_debug: False
>
> this should be qemu_build_debug
Will fix in the next version.
>
> > diff --git a/playbooks/roles/build_qemu/tasks/main.yml b/playbooks/roles/build_qemu/tasks/main.yml
> > index 448714b2..a4b4bba9 100644
> > --- a/playbooks/roles/build_qemu/tasks/main.yml
> > +++ b/playbooks/roles/build_qemu/tasks/main.yml
> > @@ -74,7 +74,7 @@
> >      - build_qemu_now|bool
> >
> >  - name: Run configure for QEMU
> > -  command: "./configure --target-list={{ qemu_target }} --disable-download"
> > +  command: "./configure --target-list={{ qemu_target }} --disable-download {{qemu_debug}}"
> >    tags: [ 'qemu', 'configure' ]
> >    args:
> >      chdir: "{{ qemu_data }}"
> > diff --git a/vagrant/Kconfig b/vagrant/Kconfig
> > index 68b14a0b..68986295 100644
> > --- a/vagrant/Kconfig
> > +++ b/vagrant/Kconfig
> > @@ -266,6 +266,13 @@ endif # !QEMU_BUILD
> >
> >  if QEMU_BUILD
> >
> > +config QEMU_WITH_DEBUG_ENABLED
>
> And so this should be QEMU_BUILD_WITH_DEBUG_ENABLED
Will fix in the next version.
>
> > +	bool "enable debug for qemu"
> > +	default n
> > +	help
> > +	  Enable this will add "--enable-debug" option when configuring qemu. This
> > +	  is useful for debugging and testing qemu code.
>
> This should clarify when it's useful. Is it only a build thing?
>
> Are there options for runtime debug? Is that also useful to you?
> Could those be added dynamically, so that perhaps one could enable them
> on the fly ? If so check DYNAMIC_RUNTIME_VARS on
> workflows/fstests/Makefile for an exmaple of how one can for example for
> example add specific arguments at the end of a make target to extend
> variables dynamically. Likewise we have the use of ANSIBLE_VERBOSE which
> might help for run time things too.
>
> In so far as dynamic run time though, running qemu though is done
> through vagrant and that just sets up and uses libvirt, but I suppose
> the above might still be useful somehow if one perhaps wanted to somehow
> extend debug dynamic parameters somewhere.
>
>   Luis

Yes, this is a build thing. Currently, qemu is built without debug,
which means we cannot use gdb for debugging the qemu code.
Once its compiled and installed, we cannot dynamically enable it.
I just use the change to debug qemu and locate a bug in qemu.

Fan