[llvm-dev] problem (and fix) with -fms-extensions

[Dimitry Andric via llvm-dev]

On 11 May 2017, at 20:04, Marc Espie via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> I've tried to build something that wanted ms-extensions on OpenBSD.
> Long story short, didn't work so well, because all system includes
> lead to
> 
> <machine/_types.h>
> #ifndef __cplusplus
> typedef int                     __wchar_t;
> #endif
> 
> and since ms-extensions includes __char_t as a built-in, this did fail
> abysmally.

Back in 2014 when we encountered this in FreeBSD, we just renamed our
internal type to ___wchar_t instead:

http://svnweb.freebsd.org/changeset/base/263998


> It would be simple to fix in OpenBSD, assuming clang did tell us it
> was using ms-extensions.
> 
> Would something like this be appropriate ? macro name subject to approval
> of course.
> 
> 
> Index: lib/Frontend/InitPreprocessor.cpp
> ===================================================================
> RCS file: /build/data/openbsd/cvs/src/gnu/llvm/tools/clang/lib/Frontend/InitPreprocessor.cpp,v
> retrieving revision 1.1.1.4
> diff -u -p -r1.1.1.4 InitPreprocessor.cpp
> --- lib/Frontend/InitPreprocessor.cpp	14 Mar 2017 08:07:56 -0000	1.1.1.4
> +++ lib/Frontend/InitPreprocessor.cpp	11 May 2017 17:54:41 -0000
> @@ -366,6 +366,8 @@ static void InitializeStandardPredefined
>   else
>     Builder.defineMacro("__STDC_HOSTED__");
> 
> +  if (LangOpts.MicrosoftMode)
> +    Builder.defineMacro("__ms_extensions__", 1);
>   if (!LangOpts.CPlusPlus) {
>     if (LangOpts.C11)
>       Builder.defineMacro("__STDC_VERSION__", "201112L");

Looks fine to me, though you would also have to convince the gcc authors
to do the same.  (That is, if you still want to use recent gcc's... :)

-Dimitry

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