Re: [PATCH v9 23/23] plugins: Support C++

[Daniel P . Berrangé]

On Wed, Oct 11, 2023 at 04:03:09PM +0900, Akihiko Odaki wrote:
> Make qemu-plugin.h consumable for C++ platform.
> 
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
>  docs/devel/tcg-plugins.rst |  4 ++++
>  meson.build                |  2 +-
>  include/qemu/qemu-plugin.h |  4 ++++
>  tests/plugin/cc.cc         | 16 ++++++++++++++++
>  tests/plugin/meson.build   |  5 +++++
>  tests/tcg/Makefile.target  |  3 +--
>  6 files changed, 31 insertions(+), 3 deletions(-)
>  create mode 100644 tests/plugin/cc.cc
> 
> diff --git a/docs/devel/tcg-plugins.rst b/docs/devel/tcg-plugins.rst
> index c9f8b27590..984d8012e9 100644
> --- a/docs/devel/tcg-plugins.rst
> +++ b/docs/devel/tcg-plugins.rst
> @@ -283,6 +283,10 @@ run::
>    160          1      0
>    135          1      0
>  
> +- contrib/plugins/cc.cc
> +
> +A pure test plugin to ensure that the plugin API is compatible with C++.
> +

IMHO we don't need to be adding a test just to prove the
existance of the G_BEGIN_DECLS/G_END_DECLS macros in the
plugin header.

>  - contrib/plugins/hotblocks.c
>  
>  The hotblocks plugin allows you to examine the where hot paths of
> diff --git a/meson.build b/meson.build
> index 9f4c4f2f1e..c289bb8948 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -20,7 +20,7 @@ config_host = keyval.load(meson.current_build_dir() / 
> 'config-host.mak')
>  
>  cc = meson.get_compiler('c')
>  all_languages = ['c']
> -if targetos == 'windows' and add_languages('cpp', required: false, native: 
> false)
> +if add_languages('cpp', required: false, native: false)
>    all_languages += ['cpp']
>    cxx = meson.get_compiler('cpp')
>  endif

Our goal has been to entirely eliminate C++ from our build system,
even the Windows piece will ideally go away eventually. So I'm
loathe to see us expand where we use C++ again, even if only for
a unit test.

> diff --git a/include/qemu/qemu-plugin.h b/include/qemu/qemu-plugin.h
> index 40aae8db68..55f514ca6c 100644
> --- a/include/qemu/qemu-plugin.h
> +++ b/include/qemu/qemu-plugin.h
> @@ -16,6 +16,8 @@
>  #include <stdbool.h>
>  #include <stddef.h>
>  
> +G_BEGIN_DECLS
> +
>  /*
>   * For best performance, build the plugin with -fvisibility=hidden so that
>   * QEMU_PLUGIN_LOCAL is implicit. Then, just mark qemu_plugin_install with
> @@ -710,4 +712,6 @@ int qemu_plugin_find_register(unsigned int vcpu_index, 
> int file,
>   */
>  int qemu_plugin_read_register(GByteArray *buf, int reg);
>  
> +G_END_DECLS
> +
>  #endif /* QEMU_QEMU_PLUGIN_H */
> diff --git a/tests/plugin/cc.cc b/tests/plugin/cc.cc
> new file mode 100644
> index 0000000000..297a7e4f3f
> --- /dev/null
> +++ b/tests/plugin/cc.cc
> @@ -0,0 +1,16 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +
> +#include <qemu-plugin.h>
> +
> +extern "C" {
> +
> +QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
> +
> +QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
> +                                           const qemu_info_t *info, int argc,
> +                                           char **argv)
> +{
> +    return 0;
> +}
> +
> +};
> diff --git a/tests/plugin/meson.build b/tests/plugin/meson.build
> index 322cafcdf6..fed14aa0c2 100644
> --- a/tests/plugin/meson.build
> +++ b/tests/plugin/meson.build
> @@ -5,6 +5,11 @@ if get_option('plugins')
>                         include_directories: '../../include/qemu',
>                         dependencies: glib)
>    endforeach
> +  if 'cpp' in all_languages
> +    t += shared_module('cc', files('cc.cc'),
> +                       include_directories: '../../include/qemu',
> +                       dependencies: glib)
> +  endif
>  endif
>  if t.length() > 0
>    alias_target('test-plugins', t)
> diff --git a/tests/tcg/Makefile.target b/tests/tcg/Makefile.target
> index 462289f47c..66a20d0f2c 100644
> --- a/tests/tcg/Makefile.target
> +++ b/tests/tcg/Makefile.target
> @@ -145,10 +145,9 @@ RUN_TESTS=$(patsubst %,run-%, $(TESTS))
>  
>  # If plugins exist also include those in the tests
>  ifeq ($(CONFIG_PLUGIN),y)
> -PLUGIN_SRC=$(SRC_PATH)/tests/plugin
>  PLUGIN_LIB=../../plugin
>  VPATH+=$(PLUGIN_LIB)
> -PLUGINS=$(patsubst %.c, lib%.so, $(notdir $(wildcard $(PLUGIN_SRC)/*.c)))
> +PLUGINS=$(notdir $(wildcard $(PLUGIN_LIB)/*.so))
>  
>  # We need to ensure expand the run-plugin-TEST-with-PLUGIN
>  # pre-requistes manually here as we can't use stems to handle it. We
> -- 
> 2.42.0
> 

With regards,
Daniel
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