On Tue, Apr 20, 2021 at 8:23 PM Thomas Rodgers <rodg...@appliantology.com> wrote: > > On 2021-04-20 17:09, David Edelsohn wrote: > > On Tue, Apr 20, 2021 at 7:52 PM Thomas Rodgers > <rodg...@appliantology.com> wrote: > > > On 2021-04-20 15:25, David Edelsohn via Gcc wrote: > > On Tue, Apr 20, 2021 at 12:43 PM Jakub Jelinek via Gcc <gcc@gcc.gnu.org> > wrote: > > > The first release candidate for GCC 11.1 is available from > > https://gcc.gnu.org/pub/gcc/snapshots/11.1.0-RC-20210420/ > ftp://gcc.gnu.org/pub/gcc/snapshots/11.1.0-RC-20210420 > > and shortly its mirrors. It has been generated from git revision > r11-8265-g246abba01f302eb453475b650ba839ec905be76d. > > I have so far bootstrapped and tested the release candidate on > x86_64-linux and i686-linux. Please test it and report any issues to > bugzilla. > > If all goes well, I'd like to release 11.1 on Tuesday, April 27th. > > > As I have reported in Bugzilla, the last minute > > libstdc++: Refactor/cleanup of C++20 atomic wait implementation > > has severely regressed libstdc++ on AIX due to changes to > bits/semaphore_base.h header. > > - David > > > I posted a patch to BZ that should disable <semaphore> entirely for AIX (and > other targets where there's not a supported implementation strategy). > > This patch isn't the best way of addressing this for a variety of reasons, > but this support is intended as experimental for GCC11 anyway. Unfortunately > I can't test it on AIX because it would seem that my ssh keys never landed on > the AIX cfarm machines. > > > I am testing the patch on an AIX system inside IBM. > > But it seems that you are disabling semaphore entirely on AIX, which > is an unnecessary regression. AIX has POSIX semaphores. libstdc++ > configure defines > > _GLIBCXX_HAVE_POSIX_SEMAPHORE > > I don't understand your comments about disabling semaphore on AIX > while the comment about experimental for GCC11 implies that this is > some new, experimental feature. I could understand disabling the > experimental feature, but not disabling all semaphore support. > > Thanks, David > > > The #error would not be hit if _GLIBCXX_HAVE_POSIX_SEMAPHORE were defined, > but it shows up in your error report.
You now have pinpointed the problem. It's not that AIX doesn't have semaphore, but that the code previously had a fallback that hid a bug in the macros: #if defined _GLIBCXX_HAVE_LINUX_FUTEX && !_GLIBCXX_REQUIRE_POSIX_SEMAPHORE // Use futex if available and didn't force use of POSIX using __fast_semaphore = __atomic_semaphore<__detail::__platform_wait_t>; #elif _GLIBCXX_HAVE_POSIX_SEMAPHORE using __fast_semaphore = __platform_semaphore; #else using __fast_semaphore = __atomic_semaphore<ptrdiff_t>; #endif The problem is that libstdc++ configure defines _GLIBCXX_HAVE_POSIX_SEMAPHORE in config.h. libstdc++ uses sed to rewrite config.h to c++config.h and prepends _GLIBCXX_, so c++config.h contains #define _GLIBCXX__GLIBCXX_HAVE_POSIX_SEMAPHORE 1 And bits/semaphore_base.h is not testing that corrupted macro. Either semaphore_base.h needs to test for the corrupted macro, or libtsdc++ configure needs to define HAVE_POSIX_SEMAPHORE without itself prepending _GLIBCXX_ so that the c++config.h rewriting works correctly and defines the correct macro for semaphore_base.h. Thanks, David
