Re: [PULL v2 2/3] osdep: protect qemu/osdep.h with extern "C"

[Peter Maydell <peter.maydell@linaro.org>]

On Wed, 14 Apr 2021 at 18:26, Daniel P. Berrangé <berrange@redhat.com> wrote:
>
> On Tue, Apr 13, 2021 at 06:08:49PM +0200, Paolo Bonzini wrote:
> > System headers may include templates if compiled with a C++ compiler,
> > which cause the compiler to complain if qemu/osdep.h is included
> > within a C++ source file's 'extern "C"' block.  Add
> > an 'extern "C"' block directly to qemu/osdep.h, so that
> > system headers can be kept out of it.
> >
> > There is a stray declaration early in qemu/osdep.h, which needs
> > to be special cased.  Add a definition in qemu/compiler.h to
> > make it look nice.
> >
> > config-host.h, CONFIG_TARGET, exec/poison.h and qemu/compiler.h
> > are included outside the 'extern "C"' block; that is not
> > an issue because they consist entirely of preprocessor directives.
> >
> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> > ---
> >  disas/nanomips.cpp      |  2 +-
> >  include/qemu/compiler.h |  6 ++++++
> >  include/qemu/osdep.h    | 10 +++++++++-
> >  3 files changed, 16 insertions(+), 2 deletions(-)
> >
> > diff --git a/disas/nanomips.cpp b/disas/nanomips.cpp
> > index 2b09655271..8ddef897f0 100644
> > --- a/disas/nanomips.cpp
> > +++ b/disas/nanomips.cpp
> > @@ -27,8 +27,8 @@
> >   *      Reference Manual", Revision 01.01, April 27, 2018
> >   */
> >
> > -extern "C" {
> >  #include "qemu/osdep.h"
> > +extern "C" {
> >  #include "disas/dis-asm.h"
> >  }

> This and os-posix.h both include other system headers. We don't currently
> have problem, so this is ok as the minimal fix for 6.0, but long term we
> need more work on this header to further narrow the extern {} block.

The other path where we can include system headers inside extern "C"
is that the code above still has dis-asm.h inside the extern C block,
but dis-asm.h includes qemu/bswap.h (midway down the file!) and bswap.h
in turn includes some system headers.

thanks
-- PMM