Re: [PATCH v2 01/12] build: Only define OS_OBJECT_USE_OBJC with gcc

[Akihiko Odaki]

On 2023/08/31 17:12, Philippe Mathieu-Daudé wrote:
> On 30/8/23 18:14, Alexander Graf wrote:
> > Recent versions of macOS use clang instead of gcc. The OS_OBJECT_USE_OBJC
> > define is only necessary when building with gcc. Let's not define it when
> > building with clang.
> >
> > With this patch, I can successfully include GCD headers in QEMU when
> > building with clang.
> >
> > Signed-off-by: Alexander Graf <graf@amazon.com>
> > ---
> >   meson.build | 4 +++-
> >   1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/meson.build b/meson.build
> > index 98e68ef0b1..0d6a0015a1 100644
> > --- a/meson.build
> > +++ b/meson.build
> > @@ -224,7 +224,9 @@ qemu_ldflags = []
> >   if targetos == 'darwin'
> >     # Disable attempts to use ObjectiveC features in os/object.h since 
> > they
> >     # won't work when we're compiling with gcc as a C compiler.
> > -  qemu_common_flags += '-DOS_OBJECT_USE_OBJC=0'
> > +  if compiler.get_id() == 'gcc'
> > +    qemu_common_flags += '-DOS_OBJECT_USE_OBJC=0'
> > +  endif
> >   elif targetos == 'solaris'
> >     # needed for CMSG_ macros in sys/socket.h
> >     qemu_common_flags += '-D_XOPEN_SOURCE=600'
>
> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

Defining OS_OBJECT_USE_OBJC does not look like a proper solution. 
Looking at os/object.h, it seems OS_OBJECT_USE_OBJC is defined as 0 when:
!defined(OS_OBJECT_HAVE_OBJC_SUPPORT) && (!defined(__OBJC__) || 
defined(__OBJC_GC__))

This means OS_OBJECT_USE_OBJC is always 0 if Objective-C is disabled. I 
also confirmed os/object.h will not use Objective-C features when 
compiled as C code on clang with the following command:

clang -E -x -c - <<EOF
#include <os/object.h>
EOF

If compilation fails with GCC when not defining OS_OBJECT_USE_OBJC, it 
probably means GCC incorrectly treats C code as Objective-C and that is 
the problem we should solve. I cannot confirm this theory however since 
I have only an Apple Silicon Mac that is incompatible with GCC.

Regards,
Akihiko Odaki