1 /*
2 * Copyright (C) 2018 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "membarrier.h"
18
19 #include <errno.h>
20 #include <stdio.h>
21
22 #if !defined(_WIN32)
23 #include <sys/syscall.h>
24 #include <sys/utsname.h>
25 #include <unistd.h>
26 #endif
27 #include "macros.h"
28
29 #if __has_include(<linux/membarrier.h>)
30
31 #include <linux/membarrier.h>
32
33 #define CHECK_MEMBARRIER_CMD(art_value, membarrier_value) \
34 static_assert(static_cast<int>(art_value) == (membarrier_value), "Bad value for " # art_value)
35 CHECK_MEMBARRIER_CMD(art::MembarrierCommand::kQuery, MEMBARRIER_CMD_QUERY);
36 CHECK_MEMBARRIER_CMD(art::MembarrierCommand::kGlobal, MEMBARRIER_CMD_SHARED);
37 CHECK_MEMBARRIER_CMD(art::MembarrierCommand::kPrivateExpedited, MEMBARRIER_CMD_PRIVATE_EXPEDITED);
38 CHECK_MEMBARRIER_CMD(art::MembarrierCommand::kRegisterPrivateExpedited,
39 MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED);
40 CHECK_MEMBARRIER_CMD(art::MembarrierCommand::kPrivateExpedited, MEMBARRIER_CMD_PRIVATE_EXPEDITED);
41 #undef CHECK_MEMBARRIER_CMD
42
43 #endif // __has_include(<linux/membarrier.h>)
44
45 namespace art {
46
47 #if defined(__linux__)
48
IsMemBarrierSupported()49 static bool IsMemBarrierSupported() {
50 // Check kernel version supports membarrier(2).
51 // MEMBARRIER_CMD_QUERY is supported since Linux 4.3.
52 // MEMBARRIER_CMD_PRIVATE_EXPEDITED is supported since Linux 4.14.
53 // MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE is supported since Linux 4.16.
54 // Lowest Linux version useful for ART is 4.14.
55 static constexpr int kRequiredMajor = 4;
56 static constexpr int kRequiredMinor = 14;
57 struct utsname uts;
58 int major, minor;
59 if (uname(&uts) != 0 ||
60 strcmp(uts.sysname, "Linux") != 0 ||
61 sscanf(uts.release, "%d.%d", &major, &minor) != 2 ||
62 (major < kRequiredMajor || (major == kRequiredMajor && minor < kRequiredMinor))) {
63 return false;
64 }
65 #if defined(__BIONIC__)
66 // Avoid calling membarrier on older Android versions where membarrier may be barred by seccomp
67 // causing the current process to be killed. The probing here could be considered expensive so
68 // endeavour not to repeat too often.
69 int api_level = android_get_device_api_level();
70 if (api_level < __ANDROID_API_Q__) {
71 return false;
72 }
73 #endif // __BIONIC__
74 return true;
75 }
76
membarrier(MembarrierCommand command)77 int membarrier(MembarrierCommand command) {
78 static const bool membarrier_supported = IsMemBarrierSupported();
79 if (UNLIKELY(!membarrier_supported)) {
80 errno = ENOSYS;
81 return -1;
82 }
83 return syscall(__NR_membarrier, static_cast<int>(command), 0);
84 }
85
86 #else // __linux__
87
88 int membarrier([[maybe_unused]] MembarrierCommand command) {
89 errno = ENOSYS;
90 return -1;
91 }
92
93 #endif // __linux__
94
95 } // namespace art
96