[CMake] detecting __attribute__((weak)) support

[Laurent Demailly]

Pending (possible) built-in support in cmake, looks like I could use

check_cxx_source_compiles(
"extern \"C\" void cmkcheckweak() __attribute__((weak));
int main(int argc, char** argv) {
  return cmkcheckweak == nullptr; // works with (void*)0;
}" HAVE_WEAK_SYMBOLS)



But that doesn't work because check_cxx_source_compiles doesn't (by
default - how do I tell it to?) use the compiler flags (like -std=gnu++11)
needed to compile this (while in this case there is an easy workaround -
how do I do this in general)

Filled the 2 issues:
http://public.kitware.com/Bug/view.php?id=15359 for weak symbol knowledge
by cmake
http://public.kitware.com/Bug/view.php?id=15361 for
check_cxx_source_compiles

Thanks!
Laurent


On 1/19/15, 1:35 PM, "Laurent Demailly" <ldemailly at fb.com> wrote:

>I searched and didn't find yet ­ would it be reasonable to have built in
>support in cmake for knowing if the platform/compiler supports weak
>symbols ?
>
>I'm porting the following autconf fragment:
>
>AC_CACHE_CHECK(
>  [for weak symbol support],
>  [folly_cv_prog_cc_weak_symbols],
>  [AC_LINK_IFELSE(
>    [AC_LANG_SOURCE[
>      extern "C" void configure_link_extern_weak_test()
>__attribute__((weak));
>      int main(int argc, char** argv) {
>          return configure_link_extern_weak_test == nullptr;
>      }]],
>    [folly_cv_prog_cc_weak_symbols="yes"],
>    [folly_cv_prog_cc_weak_symbols="no"])])
>
>if test "$folly_cv_prog_cc_weak_symbols" = yes; then
>  AC_DEFINE([HAVE_WEAK_SYMBOLS], [1],
>            [Define to 1 if the linker supports weak symbols.])
>fi
>
>And I'm not sure what's the best way to do such recipe in Cmake ?
>(by hand for now pending possible support in 3.2+ maybe)
>
>
>Laurent