[PATCH] D28596: [compiler-rt] General definition for weak functions.

[Zachary Turner via Phabricator via llvm-commits]

zturner added a comment.

In https://reviews.llvm.org/D28596#649978, @mpividori wrote:

> > 2. Having a macro only around the function name, i.e.: `WEAK_ATTRIBUTE void WEAK_NAME(OnPrint)(const char *str) { code }`.
>
> I can't do that because not only I need to change the name, I also need to add a linker pragma `WIN_WEAK_ALIAS(OnPrint, OnPrint__def)` and declare `OnPrint`.
>  I mean, for non-windows `OnPrint` definition will be:
>
>   void OnPrint(const char *str) {
>     // Default implementation
>   }
>   
>
> And for Windows, it will be:
>
>   void OnPrint__def(const char *str) {
>     // Default implementation
>   }
>   void OnPrint(const char *str);
>   WIN_WEAK_ALIAS(OnPrint, OnPrint__def)
>   
>
> Thanks.


What if instead of getting it all into one line, we settle for this:

  void WEAK_FN_DEF(OnPrint)(const char *str) {
  }
  WEAK_FN_ALIAS(OnPrint)

The macro `WEAK_FN_ALIAS` could look like this:

  #define WEAK_FN_ALIAS(Fn) \
    decltype(Fn##__def) Fn; \
    WIN_WEAK_ALIAS(Fn, Fn##__def)

On non-Windows platforms, it would just do nothing.  Apparently the crazy decltype magic works and should give you a definition named `OnPrint__def` and a forward declaration named `OnPrint`.


https://reviews.llvm.org/D28596