https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118093
--- Comment #1 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:8ade3c3ea77e166f2873fb7ae57f9690e2b8d0e0 commit r15-6690-g8ade3c3ea77e166f2873fb7ae57f9690e2b8d0e0 Author: Jonathan Wakely <jwak...@redhat.com> Date: Tue Dec 17 21:32:19 2024 +0000 libstdc++: Fix std::future::wait_until for subsecond negative times [PR118093] The current check for negative times (i.e. before the epoch) only checks for a negative number of seconds. For a time 1ms before the epoch the seconds part will be zero, but the futex syscall will still fail with an EINVAL error. Extend the check to handle this case. This change adds a redundant check in the headers too, so that we avoid even calling into the library for negative times. Both checks can be marked [[unlikely]]. The check in the headers avoids the cost of splitting the time into seconds and nanoseconds and then making a PLT call. The check inside the library matches where we were checking already, and fixes existing binaries that were compiled against older headers but use a newer libstdc++.so.6 at runtime. libstdc++-v3/ChangeLog: PR libstdc++/118093 * include/bits/atomic_futex.h (_M_load_and_test_until_impl): Return false for times before the epoch. * src/c++11/futex.cc (_M_futex_wait_until): Extend check for negative times to check for subsecond times. Add unlikely attribute. (_M_futex_wait_until_steady): Likewise. * testsuite/30_threads/future/members/118093.cc: New test.
