Ping. On Tue, Sep 18, 2012 at 6:47 PM, Richard Smith <[email protected]>wrote:
> On Mon, Sep 17, 2012 at 4:11 PM, Eli Friedman <[email protected]>wrote: > >> On Sat, Sep 15, 2012 at 1:05 AM, Richard Smith <[email protected]> >> wrote: >> > >> > >> > On Fri, Sep 14, 2012 at 8:17 PM, Eli Friedman <[email protected]> >> > wrote: >> >> >> >> On Fri, Sep 14, 2012 at 7:48 PM, Richard Smith <[email protected]> >> >> wrote: >> >> > Hi, >> >> > >> >> > The attached patch adds an implementation of <stdatomic.h> to the >> set of >> >> > headers provided by Clang. Since this header is so >> compiler-dependent, >> >> > it >> >> > seems that we are the most rational component to be providing this >> >> > header >> >> > (even though, for instance, some flavors of BSD already provide their >> >> > own). >> >> > Please review! >> >> >> >> +// Clang allows memory_order_consume ordering for __c11_atomic_store, >> >> +// even though C11 doesn't allow it for atomic_store. >> >> >> >> That looks like a bug... >> > >> > >> > Possibly it's a bug in the specification for atomic_flag_clear? >> > memory_order_consume doesn't seem to have any meaning for a store >> operation. >> > >> >> >> >> Please put the new warning in a separate commit. >> > >> > >> > r163964. >> > >> >> It looks like standard requires that we expose functions named >> >> atomic_thread_fence, atomic_signal_fence, atomic_flag_test_and_set, >> >> atomic_flag_test_and_set_explicit, and atomic_flag_clear; your version >> >> of stdatomic.h doesn't include declarations for these functions (which >> >> is required by C11 7.1.4p1). >> > >> > >> > Ugh. And C11 7.1.2/6 requires them to have external linkage. I don't >> want >> > these functions to require linking to a library. We could emit them >> weak and >> > inline, but then we'll get a weak copy in every TU which includes this >> > header, which seems fairly egregious. Is there currently any way to >> emit a >> > function as linkonce_odr from C? Do you have any suggestions as to how >> to >> > proceed? >> >> There isn't any way to get linkonce_odr from C at the moment; patches >> welcome. I don't see any issues with that from the standpoint of the >> standard; I'm a little worried about ABI-compat issues, though. >> (Specifically, if the system provides the header, having our own >> linkonce_odr version could cause strange linker errors.) >> >> We could put it into compiler-rt, and say that if someone tries to use >> the function instead of the macro without linking in compiler-rt, >> that's an error. Not particularly satisfying either, but somewhat >> simpler. > > > After some discussion with Chandler, we think the best approach is to say > that the definition of these functions belongs in libc, and to provide only > declarations of them. A patch for that approach is attached. >
_______________________________________________ cfe-commits mailing list [email protected] http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
