MS Compat: interpose vadefs.h to fix definitions of _crt_va_{start,end,arg} (PR21247)

[hans]

Summary

Please take a look.

[rnk]

lib/Headers/vadefs.h

25

I'd wordsmith this to "Only include this if we're aiming for MSVC compatibility."

33

Should we only do this if __has_include(<vadefs.h>) ?

35

I think we should do "#ifndef _crt_va_start #undef _crt_va_start" to avoid warnings with -Wsystem-headers.

[hans]

lib/Headers/vadefs.h

25

Done.

33

I think we should always do it. If the user is including vadefs.h, she's expecting to get the system one, and we should just always try to forward to it.

35

Done.

[hans]

Addressing rnk's comments.

I tried this on a small program with -Wsystem-headers, and it was clean.

[rnk]

lgtm

[hans]

Closed by commit rL219740 (authored by @hans).

lib/Headers/CMakeLists.txt

set(files
   stddef.h
   __stddef_max_align_t.h
   stdint.h
   stdnoreturn.h
   tbmintrin.h
   tgmath.h
   tmmintrin.h
   varargs.h
+  vadefs.h
   wmmintrin.h
   __wmmintrin_aes.h
   __wmmintrin_pclmul.h
   x86intrin.h
   xmmintrin.h
   xopintrin.h
   cpuid.h
   unwind.h

lib/Headers/vadefs.h

+/* ===-------- vadefs.h ---------------------------------------------------===
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ *===-----------------------------------------------------------------------===
+ */
+
+/* Only include this if we are aiming for MSVC compatibility. */
+#ifndef _MSC_VER
+#include_next <vadefs.h>
+#else
+
+#ifndef __clang_vadefs_h
+#define __clang_vadefs_h
+
+#include_next <vadefs.h>
+
+/* Override macros from vadefs.h with definitions that work with Clang. */
+#ifdef _crt_va_start
+#undef _crt_va_start
+#endif
+#ifdef _crt_va_end
+#undef _crt_va_end
+#endif
+#ifdef _crt_va_arg
+#undef _crt_va_arg
+#endif
+
+#define _crt_va_start(ap, param) __builtin_va_start(ap, param)
+#define _crt_va_end(ap)          __builtin_va_end(ap)
+#define _crt_va_arg(ap, type)    __builtin_va_arg(ap, type)
+
+#endif
+#endif