https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69179
--- Comment #1 from Jack Howarth <howarth.at.gcc at gmail dot com> --- Note that weak_import was added by Geoffrey Keating in... https://gcc.gnu.org/ml/gcc-patches/2004-10/msg02441.html and tweaked in... https://gcc.gnu.org/ml/gcc-patches/2005-01/msg00146.html The last time Geoff referenced it in a patch, he claimed it was 'effectively deprecated' in gcc... https://gcc.gnu.org/ml/gcc-patches/2005-12/msg00378.html It might be worth checking with the Apple clang developers to see what their current position is on the feature. I would note that http://clang.llvm.org/docs/AttributeReference.html has... A declaration can be used even when deploying back to a platform version prior to when the declaration was introduced. When this happens, the declaration is weakly linked, as if the weak_import attribute were added to the declaration. A weakly-linked declaration may or may not be present a run-time, and a program can determine whether the declaration is present by checking whether the address of that declaration is non-NULL. in the section describing the availability attribute so I guess they still intend to support into the future.