[cfe-dev] Clang inconsistency with gcc on Windows

[Edward Diener]

On 5/31/2015 3:26 PM, Yaron Keren wrote:
> Maybe gcc is more fogiving with checking redeclarations or some compiler
> predefine is not the same. You can check this in depth by looking at
> preprocess output (-E) and comparing how both compilers expand the
> GetSystemTimeAsFileTime declaration.

Both compilers expand the different GetSystemTimeAsFileTime declaration 
in the internal Boost winapi headers and the mingw headers in exactly 
the same way.

The preprocessed expansion in the internal Boost winapi header is:

      __attribute__((dllimport)) void __attribute__((__stdcall__))
          GetSystemTimeAsFileTime(FILETIME_* lpFileTime);

and the preprocessed expansion in the mingw headers is:

      void __attribute__((__stdcall__)) GetSystemTimeAsFileTime(LPFILETIME);

where FILETIME_ and LPFILETIME are the same structure.

The gcc compiler sees these declarations as the same but the clang 
compiler sees them as different and therefore an error.

>
>
> 2015-05-31 21:50 GMT+03:00 Edward Diener
> <eldlistmailingz at tropicsoft.com
> <mailto:eldlistmailingz at tropicsoft.com>>:
>
>     On 5/31/2015 2:05 PM, Yaron Keren wrote:
>
>         Boost tries to supplies its own version of the Windows API to avoid
>         including WIndows.h
>         Boost version of the API is not strictly identical to Windows.h,
>         so if
>         Windows.h do get included somehow such errors happen. I always
>         -DBOOST_USE_WINDOWS_H to force Boost to use Windows.h instead of
>         its own.
>
>
>     Thanks, that does work.
>
>     I still would like to know why clang is giving errors in the
>     situation I describe in my OP and gcc is not. I am not saying that
>     clang is wrong to do so but clearly it is not being compatible with
>     gcc in this area.
>
>
>
>
>         2015-05-31 20:48 GMT+03:00 Edward Diener
>         <eldlistmailingz at tropicsoft.com
>         <mailto:eldlistmailingz at tropicsoft.com>
>         <mailto:eldlistmailingz at tropicsoft.com
>         <mailto:eldlistmailingz at tropicsoft.com>>>:
>
>
>              Compiling some Boost library code the latest clang has
>         produced an
>              inconsistency with gcc on Windows that is making it
>         impossible to
>              build Boost libraries successfully.
>
>              The code in question, where clang is given an error:
>
>                  clang-linux.compile.c++.without-pth
>
>         ..\..\..\bin.v2\libs\context\build\clang-linux-3.7.0\debug\threading-multi\windows\stack_traits.obj
>                  In file included from
>                  ..\..\..\libs\context\src\windows\stack_traits.cpp:24:
>                  In file included from ..\..\..\boost/thread.hpp:13:
>                  In file included from ..\..\..\boost/thread/thread.hpp:12:
>                  In file included from
>         ..\..\..\boost/thread/thread_only.hpp:15:
>                  In file included from
>                  ..\..\..\boost/thread/win32/thread_data.hpp:10:
>                  In file included from
>         ..\..\..\boost/thread/thread_time.hpp:10:
>                  In file included from
>                  ..\..\..\boost/date_time/microsec_time_clock.hpp:23:
>                  ..\..\..\boost/date_time/filetime_functions.hpp:57:46:
>         error:
>                  conflicting types for 'GetSystemTimeAsFileTime'
>                           __declspec(dllimport) void __stdcall
>                  GetSystemTimeAsFileTime(FILETIME* lpFileTime);
>                                                                ^
>                  /mingw/include\winbase.h:1397:24: note: previous
>         declaration is here
>                  WINBASEAPI void WINAPI GetSystemTimeAsFileTime(LPFILETIME);
>
>                                        ^
>
>              and more of the same in many places building Boost
>         libraries with clang.
>
>              This is with the latest clang, which I build with
>         mingw/gcc-4.8.1 on
>              Windows.
>
>              With gcc-4.8.1:
>
>                  gcc.compile.c++
>
>         ..\..\..\bin.v2\libs\context\build\gcc-mingw-4.8.1\debug\threading-multi\windows\stack_traits.o
>
>
>              With gcc-4.9.2
>
>                  gcc.compile.c++
>
>         ..\..\..\bin.v2\libs\context\build\gcc-mingw-4.9.2\debug\threading-multi\windows\stack_traits.o
>
>
>              This is happening extensively in Boost code which uses the
>         Windows
>              API when compiling under Windows.
>
>              I do not know what WINBASEAPI is supposed to resove to
>         under mingw,
>              but clearly it should not be different for gcc and clang under
>              Windows and gcc has no problems with this.