Re: [PATCH 1/2] qga/vss-win32: Fix ConvertStringToBSTR redefinition with newer MinGW

[Kostiantyn Kostiuk <kkostiuk@redhat.com>]

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Hi

On Tue, Dec 16, 2025 at 8:26 AM Marc-André Lureau <
marcandre.lureau@redhat.com> wrote:

> Hi
>
> On Mon, Dec 15, 2025 at 8:57 PM <phind.uet@gmail.com> wrote:
>
>> From: Nguyen Dinh Phi <phind.uet@gmail.com>
>>
>> Newer versions of MinGW-w64 provide ConvertStringToBSTR() in the
>> _com_util namespace via <comutil.h>. This causes a redefinition
>> error when building qemu-ga on Windows with these toolchains.
>>
>> Add a meson check to detect whether ConvertStringToBSTR is already
>> available, and conditionally compile our fallback implementation
>> only when the system does not provide one.
>>
>> Signed-off-by: Nguyen Dinh Phi <phind.uet@gmail.com>
>> ---
>>  meson.build               | 12 ++++++++++++
>>  qga/vss-win32/install.cpp |  2 ++
>>  2 files changed, 14 insertions(+)
>>
>> diff --git a/meson.build b/meson.build
>> index c5710a6a47..60a980e610 100644
>> --- a/meson.build
>> +++ b/meson.build
>> @@ -3299,6 +3299,18 @@ endif
>>  # Detect host pointer size for the target configuration loop.
>>  host_long_bits = cc.sizeof('void *') * 8
>>
>> +# Detect if ConvertStringToBSTR has been defined in _com_util namespace
>> +if host_os == 'windows'
>> +  has_convert_string_to_bstr = cxx.compiles('''
>> +    #include <comutil.h>
>> +    int main() {
>> +        BSTR b = _com_util::ConvertStringToBSTR("test");
>> +        return b ? 0 : 1;
>> +    }
>> +  ''')
>> +  config_host_data.set('CONFIG_CONVERT_STRING_TO_BSTR',
>> has_convert_string_to_bstr)
>> +endif
>> +
>>  ########################
>>  # Target configuration #
>>  ########################
>> diff --git a/qga/vss-win32/install.cpp b/qga/vss-win32/install.cpp
>> index 7b25d9098b..5b7a8e9bc5 100644
>> --- a/qga/vss-win32/install.cpp
>> +++ b/qga/vss-win32/install.cpp
>> @@ -549,6 +549,7 @@ STDAPI DllUnregisterServer(void)
>>
>>
>>  /* Support function to convert ASCII string into BSTR (used in _bstr_t)
>> */
>> +#ifndef CONFIG_CONVERT_STRING_TO_BSTR
>>
>
> I wonder if it could check __MINGW64_VERSION_MAJOR >= 14 instead of adding
> a configure-time check.
>

@Peter Maydell <peter.maydell@linaro.org> preferred to avoid specific
version-number checks.
See: https://gitlab.com/qemu-project/qemu/-/issues/3217#note_2935451782

I also preferred the idea of checking the real function present instead of
the version of the component.

Reviewed-by: Kostiantyn Kostiuk <kkostiuk@redhat.com>


>
> lgtm anyway
> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
>
>  namespace _com_util
>>  {
>>      BSTR WINAPI ConvertStringToBSTR(const char *ascii) {
>> @@ -566,6 +567,7 @@ namespace _com_util
>>          return bstr;
>>      }
>>  }
>> +#endif
>>
>>  /* Stop QGA VSS provider service using Winsvc API  */
>>  STDAPI StopService(void)
>> --
>> 2.43.0
>>
>>

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