https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89864
--- Comment #25 from Erik Schnetter <schnetter at gmail dot com> --- > On Thu, Apr 4, 2019 at 5:43 AM iains at gcc dot gnu.org < > gcc-bugzi...@gcc.gnu.org> wrote: > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89864 > > > > --- Comment #22 from Iain Sandoe <iains at gcc dot gnu.org> --- > > (In reply to Erik Schnetter from comment #21) > > > https://gcc.gnu.org/ml/gcc-patches/2019-04/msg00162.html > > > > Additional to the comments on list. > > > > Perhaps this is just unfixable :( > > > > I suspect that Apple will want to re-release the SDK, and the best real > > fix is > > to use the SDK from the previous Xcode command line tools (you can still > > use > > the latest tools from XC10.2 - just install the older version somewhere and > > then use --with-sysroot= and/or --sysroot=) > > > > (a) there's no guarantee that _Atomic u_long has the same size or > > alignment as > > volatile u_long. > > > > C11: 6.2.5 Types > > ... > > 27 ... The size, representation, and alignment of an atomic type need not > > be > > the same as those of the corresponding unqualified type. > > ... > > > > .. although it *probably* is for simple types for which there are direct > > atomic > > ops. > > > > This is for Apple systems, where they presumably control the ABI, or are at > least aware of the ABI when writing header files. > > (b) If we hack around it with "volatile" (assuming that the type happens to > > have the same size and alignment), this will silently fail in any case it's > > used. > > > > _Atomic is used only in a single struct, which is marked "this structure > should not be used outside the kernel", and protected by a "#ifdef > __APPLE_API_UNSTABLE" (which unfortunately defaults to being defined). To > my knowledge, no part of GCC will use this structure. > > (c) the <atomic> header is only available from C++11, AFAIR, and GCC is > > supposed to be boot-strappable with C++98. Iff Apple were to elect to > > declare > > that the OS *requires* C++11 to operate, then we should fix the > > configuration > > for Darwin to ensure that this is enforced. > > > > The header file works for all versions of C and C++. It uses _Atomic for > C11, _Atomic for C++11 (the bug we're seeing), and volatile in all other > cases. There is no requirement for C++11. > > (d) In any case, is there any guarantee that the representation of the > > u_long > > as a C++ atomic is the same size and align as its C11 counterpart? (I've > > not > > checked this). > > > > This seems to be an ABI question, and I assume Apple checked this on their > ABIs (probably only Intel and ARM). I assume that this is generally the > case as C11 and C++11 atomics were designed at the same time, so the ABI > designers will want to ensure sure. > > -erik
