Re: [RFC PATCH 24/24] contrib/plugins: Add cc plugin

[Akihiko Odaki]

On 2023/08/15 0:23, Alex Bennée wrote:
> Akihiko Odaki <akihiko.odaki@daynix.com> writes:
>
> > This demonstrates how to write a plugin in C++.
> >
> > Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> > ---
> >   docs/devel/tcg-plugins.rst |  8 ++++++++
> >   configure                  | 15 ++++++++++++---
> >   contrib/plugins/Makefile   |  5 +++++
> >   contrib/plugins/cc.cc      | 15 +++++++++++++++
> >   tests/tcg/Makefile.target  |  3 +++
> >   5 files changed, 43 insertions(+), 3 deletions(-)
> >   create mode 100644 contrib/plugins/cc.cc
> >
> > diff --git a/docs/devel/tcg-plugins.rst b/docs/devel/tcg-plugins.rst
> > index c9f8b27590..0a11f8036c 100644
> > --- a/docs/devel/tcg-plugins.rst
> > +++ b/docs/devel/tcg-plugins.rst
> > @@ -584,6 +584,14 @@ The plugin has a number of arguments, all of them are 
> > optional:
> >     configuration arguments implies ``l2=on``.
> >     (default: N = 2097152 (2MB), B = 64, A = 16)
> >   
> > +- contrib/plugins/cc.cc
> > +
> > +cc plugin demonstrates how to write a plugin in C++. It simply outputs
> > +"hello, world" to the plugin log::
> > +
> > +  $ qemu-system-arm $(QEMU_ARGS) \
> > +    -plugin ./contrib/plugins/libcc.so -d plugin
> > +
>
> I'm going to assume this is useful because you have some out of tree C++
> plugins? I'd drop the last two patches for now until there is a slightly
> more compelling use case.

The out-of-tree plugin is mentioned in the cover letter and available at:
https://github.com/shioya-lab/sniper/tree/akihikodaki/bb/frontend/qemu-frontend

This plugin emits a trace of execution for use in Sniper simulator. I 
believe it's useful for other people doing microarchitecture research 
since processor simulation infrastructure is often written in C++.

> The C++ compiler detection moved into meson in b485458e00 (configure,
> meson: move C++ compiler detection to meson.build) so I don't think
> there is currently a compelling reason to bring this back into
> configure.

It is necessary because TCG tests use Makefile and config-host.mak is 
emitted by configure. We can remove C++ detection from configure when 
TCG tests or the config-host.mak generation migrate to Meson.