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

[Marcos Pividori via Phabricator via llvm-commits]

mpividori added a comment.

@aizatsky I updated the code 2 minutes before your comment.

I think the two macros that I am defining: `WEAK_DEF()` and `WEAK_INTERFACE_DECL()` are very simple to understand and simplify the code removing redundant code.

The solution that you propose has some disadvantages:

- For Linux, we don't need to define a different function for the default implementation.  So, with your proposed solution we have 2 approaches:

+) or we define the default function and we create a weak alias in linux too:

    SANITIZER_INTERFACE_ATTRIBUTE const char *__ubsan_options__def() { return ""; }
  #ifdef SANITIZER_WINDOWS
    SANITIZER_INTERFACE_ATTRIBUTE const char *__ubsan_options();
    WIN_WEAK_ALIAS(__ubsan_options, __ubsan_options__def);
  #else
    SANITIZER_INTERFACE_ATTRIBUTE const char *__ubsan_options()  __attribute__ ((weak, alias ("___ubsan_options__def")));;
  #endif

(I guess weak aliases also work for APPLE)
 We could generalize the weak alias in a macro to avoid the #ifdefs .

+) Or we can use some `#ifdef ` to define the default function only for Windows:

  #ifdef SANITIZER_WINDOWS
    SANITIZER_INTERFACE_ATTRIBUTE const char *__ubsan_options__def() { return ""; }
    SANITIZER_INTERFACE_ATTRIBUTE const char *__ubsan_options();
    WIN_WEAK_ALIAS(__ubsan_options, __ubsan_options__def);
  #else
    SANITIZER_INTERFACE_ATTRIBUTE SANITIZER_WEAK_ATTRIBUTE const char *__ubsan_options(){ return ""; }
  #endif

In this case we have to duplicate the code for the default implementation.

With the macro `WEAK_DEF()` that I define, you can see that I simply the code, since we don't need any special code for different platforms:

  WEAK_DEF(const char *, __ubsan_options, ()) { return ""; }

This works fine for Windows and other platforms.

- Also, we need to export default functions but only on Windows, with your approach, this means I should write this code in the header file:

  #ifdef SANITIZER_WINDOWS
    const char *__ubsan_options();
    SANITIZER_INTERFACE_ATTRIBUTE const char *__ubsan_options__def();
  #else
    SANITIZER_INTERFACE_ATTRIBUTE const char *__ubsan_options();
  #endif

Which I achieve with the macro `WEAK_INTERFACE_DECL()`, and simplifies that code to:

  WEAK_INTERFACE_DECL(const char *, __ubsan_options, ());




https://reviews.llvm.org/D28596