/* * Copyright (c) Meta Platforms, Inc. and affiliates. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ #include #include #include #include #include namespace folly { namespace detail { namespace { constexpr long linux_syscall_nr_(long nr, long def) { return nr == -1 ? def : nr; } // __NR_membarrier or -1; always defined as v.s. __NR_membarrier #if defined(__NR_membarrier) constexpr long linux_syscall_nr_membarrier_ = __NR_membarrier; #else constexpr long linux_syscall_nr_membarrier_ = -1; #endif // __NR_membarrier with hardcoded fallback where available or -1 constexpr long linux_syscall_nr_membarrier = kIsArchAmd64 && !kIsMobile && kIsLinux // ? linux_syscall_nr_(linux_syscall_nr_membarrier_, 324) : -1; // linux_membarrier_cmd // // Backport from the linux header, since older versions of the header may // define the enum but not all of the enum constants that we require. // // mimic: membarrier_cmd, linux/membarrier.h enum linux_membarrier_cmd { MEMBARRIER_CMD_QUERY = 0, MEMBARRIER_CMD_PRIVATE_EXPEDITED = (1 << 3), MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED = (1 << 4), }; FOLLY_ERASE int call_membarrier(int cmd, unsigned int flags = 0) { if (linux_syscall_nr_membarrier < 0) { errno = ENOSYS; return -1; } return linux_syscall(linux_syscall_nr_membarrier, cmd, flags); } } // namespace bool sysMembarrierPrivateExpeditedAvailable() { constexpr auto flags = 0 // | MEMBARRIER_CMD_PRIVATE_EXPEDITED // | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED; auto const r = call_membarrier(MEMBARRIER_CMD_QUERY); return r != -1 && (r & flags) == flags; } int sysMembarrierPrivateExpedited() { if (0 == call_membarrier(MEMBARRIER_CMD_PRIVATE_EXPEDITED)) { return 0; } switch (errno) { case EINVAL: case ENOSYS: return -1; } assert(errno == EPERM); if (-1 == call_membarrier(MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED)) { return -1; } return call_membarrier(MEMBARRIER_CMD_PRIVATE_EXPEDITED); } } // namespace detail } // namespace folly