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

[Alexander Graf <graf@amazon.com>]

On 31.08.23 10:53, Akihiko Odaki wrote:
>
>
> 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.


My take on this was to make the gcc hack be a "legacy" thing that we put 
into its own corner, so that in a few years we can just drop it 
altogether. I don't really think it's worth wasting much time on this 
workaround and its potential compatibility with old macOS versions.


Alex





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