Sean Silva | 3872b46 | 2012-12-12 23:44:55 +0000 | [diff] [blame] | 1 | ThreadSanitizer |
| 2 | =============== |
| 3 | |
| 4 | Introduction |
| 5 | ------------ |
| 6 | |
| 7 | ThreadSanitizer is a tool that detects data races. It consists of a compiler |
| 8 | instrumentation module and a run-time library. Typical slowdown introduced by |
Dmitry Vyukov | c092cba | 2012-12-17 07:16:54 +0000 | [diff] [blame] | 9 | ThreadSanitizer is about **5x-15x**. Typical memory overhead introduced by |
| 10 | ThreadSanitizer is about **5x-10x**. |
Sean Silva | 3872b46 | 2012-12-12 23:44:55 +0000 | [diff] [blame] | 11 | |
| 12 | How to build |
| 13 | ------------ |
| 14 | |
Stephen Hines | 0e2c34f | 2015-03-23 12:09:02 -0700 | [diff] [blame] | 15 | Build LLVM/Clang with `CMake <http://llvm.org/docs/CMake.html>`_. |
Sean Silva | 3872b46 | 2012-12-12 23:44:55 +0000 | [diff] [blame] | 16 | |
| 17 | Supported Platforms |
| 18 | ------------------- |
| 19 | |
Stephen Hines | 651f13c | 2014-04-23 16:59:28 -0700 | [diff] [blame] | 20 | ThreadSanitizer is supported on Linux x86_64 (tested on Ubuntu 12.04). |
| 21 | Support for other 64-bit architectures is possible, contributions are welcome. |
| 22 | Support for 32-bit platforms is problematic and is not planned. |
Sean Silva | 3872b46 | 2012-12-12 23:44:55 +0000 | [diff] [blame] | 23 | |
| 24 | Usage |
| 25 | ----- |
| 26 | |
Peter Collingbourne | 52ca70d | 2013-04-09 04:35:11 +0000 | [diff] [blame] | 27 | Simply compile and link your program with ``-fsanitize=thread``. To get a |
| 28 | reasonable performance add ``-O1`` or higher. Use ``-g`` to get file names |
| 29 | and line numbers in the warning messages. |
Sean Silva | 3872b46 | 2012-12-12 23:44:55 +0000 | [diff] [blame] | 30 | |
| 31 | Example: |
| 32 | |
| 33 | .. code-block:: c++ |
| 34 | |
Dmitry Vyukov | c092cba | 2012-12-17 07:16:54 +0000 | [diff] [blame] | 35 | % cat projects/compiler-rt/lib/tsan/lit_tests/tiny_race.c |
Sean Silva | 3872b46 | 2012-12-12 23:44:55 +0000 | [diff] [blame] | 36 | #include <pthread.h> |
| 37 | int Global; |
| 38 | void *Thread1(void *x) { |
| 39 | Global = 42; |
| 40 | return x; |
| 41 | } |
| 42 | int main() { |
| 43 | pthread_t t; |
| 44 | pthread_create(&t, NULL, Thread1, NULL); |
| 45 | Global = 43; |
| 46 | pthread_join(t, NULL); |
| 47 | return Global; |
| 48 | } |
| 49 | |
Peter Collingbourne | 52ca70d | 2013-04-09 04:35:11 +0000 | [diff] [blame] | 50 | $ clang -fsanitize=thread -g -O1 tiny_race.c |
Sean Silva | 3872b46 | 2012-12-12 23:44:55 +0000 | [diff] [blame] | 51 | |
| 52 | If a bug is detected, the program will print an error message to stderr. |
| 53 | Currently, ThreadSanitizer symbolizes its output using an external |
| 54 | ``addr2line`` process (this will be fixed in future). |
| 55 | |
| 56 | .. code-block:: bash |
| 57 | |
Dmitry Vyukov | c092cba | 2012-12-17 07:16:54 +0000 | [diff] [blame] | 58 | % ./a.out |
Sean Silva | 3872b46 | 2012-12-12 23:44:55 +0000 | [diff] [blame] | 59 | WARNING: ThreadSanitizer: data race (pid=19219) |
Dmitry Vyukov | c092cba | 2012-12-17 07:16:54 +0000 | [diff] [blame] | 60 | Write of size 4 at 0x7fcf47b21bc0 by thread T1: |
Sean Silva | 3872b46 | 2012-12-12 23:44:55 +0000 | [diff] [blame] | 61 | #0 Thread1 tiny_race.c:4 (exe+0x00000000a360) |
Dmitry Vyukov | c092cba | 2012-12-17 07:16:54 +0000 | [diff] [blame] | 62 | |
Sean Silva | 3872b46 | 2012-12-12 23:44:55 +0000 | [diff] [blame] | 63 | Previous write of size 4 at 0x7fcf47b21bc0 by main thread: |
| 64 | #0 main tiny_race.c:10 (exe+0x00000000a3b4) |
Dmitry Vyukov | c092cba | 2012-12-17 07:16:54 +0000 | [diff] [blame] | 65 | |
| 66 | Thread T1 (running) created at: |
| 67 | #0 pthread_create tsan_interceptors.cc:705 (exe+0x00000000c790) |
Sean Silva | 3872b46 | 2012-12-12 23:44:55 +0000 | [diff] [blame] | 68 | #1 main tiny_race.c:9 (exe+0x00000000a3a4) |
| 69 | |
Dmitry Vyukov | 728e212 | 2012-12-17 08:52:05 +0000 | [diff] [blame] | 70 | ``__has_feature(thread_sanitizer)`` |
| 71 | ------------------------------------ |
| 72 | |
| 73 | In some cases one may need to execute different code depending on whether |
| 74 | ThreadSanitizer is enabled. |
| 75 | :ref:`\_\_has\_feature <langext-__has_feature-__has_extension>` can be used for |
| 76 | this purpose. |
| 77 | |
| 78 | .. code-block:: c |
| 79 | |
Kostya Serebryany | 85aee96 | 2013-02-26 06:58:27 +0000 | [diff] [blame] | 80 | #if defined(__has_feature) |
| 81 | # if __has_feature(thread_sanitizer) |
Dmitry Vyukov | 728e212 | 2012-12-17 08:52:05 +0000 | [diff] [blame] | 82 | // code that builds only under ThreadSanitizer |
Kostya Serebryany | 85aee96 | 2013-02-26 06:58:27 +0000 | [diff] [blame] | 83 | # endif |
Dmitry Vyukov | 728e212 | 2012-12-17 08:52:05 +0000 | [diff] [blame] | 84 | #endif |
| 85 | |
Kostya Serebryany | 85aee96 | 2013-02-26 06:58:27 +0000 | [diff] [blame] | 86 | ``__attribute__((no_sanitize_thread))`` |
| 87 | ----------------------------------------------- |
| 88 | |
| 89 | Some code should not be instrumented by ThreadSanitizer. |
| 90 | One may use the function attribute |
| 91 | :ref:`no_sanitize_thread <langext-thread_sanitizer>` |
| 92 | to disable instrumentation of plain (non-atomic) loads/stores in a particular function. |
Dmitry Vyukov | 39dc016 | 2013-10-17 08:06:19 +0000 | [diff] [blame] | 93 | ThreadSanitizer still instruments such functions to avoid false positives and |
| 94 | provide meaningful stack traces. |
Kostya Serebryany | 85aee96 | 2013-02-26 06:58:27 +0000 | [diff] [blame] | 95 | This attribute may not be |
| 96 | supported by other compilers, so we suggest to use it together with |
Evgeniy Stepanov | fa203cf | 2013-08-15 13:57:11 +0000 | [diff] [blame] | 97 | ``__has_feature(thread_sanitizer)``. |
Kostya Serebryany | 85aee96 | 2013-02-26 06:58:27 +0000 | [diff] [blame] | 98 | |
Alexey Samsonov | 05654ff | 2013-08-07 08:23:32 +0000 | [diff] [blame] | 99 | Blacklist |
| 100 | --------- |
| 101 | |
| 102 | ThreadSanitizer supports ``src`` and ``fun`` entity types in |
| 103 | :doc:`SanitizerSpecialCaseList`, that can be used to suppress data race reports in |
Dmitry Vyukov | 39dc016 | 2013-10-17 08:06:19 +0000 | [diff] [blame] | 104 | the specified source files or functions. Unlike functions marked with |
| 105 | :ref:`no_sanitize_thread <langext-thread_sanitizer>` attribute, |
| 106 | blacklisted functions are not instrumented at all. This can lead to false positives |
| 107 | due to missed synchronization via atomic operations and missed stack frames in reports. |
Alexey Samsonov | 05654ff | 2013-08-07 08:23:32 +0000 | [diff] [blame] | 108 | |
Sean Silva | 3872b46 | 2012-12-12 23:44:55 +0000 | [diff] [blame] | 109 | Limitations |
| 110 | ----------- |
| 111 | |
| 112 | * ThreadSanitizer uses more real memory than a native run. At the default |
Dmitry Vyukov | c092cba | 2012-12-17 07:16:54 +0000 | [diff] [blame] | 113 | settings the memory overhead is 5x plus 1Mb per each thread. Settings with 3x |
| 114 | (less accurate analysis) and 9x (more accurate analysis) overhead are also |
| 115 | available. |
Sean Silva | 3872b46 | 2012-12-12 23:44:55 +0000 | [diff] [blame] | 116 | * ThreadSanitizer maps (but does not reserve) a lot of virtual address space. |
| 117 | This means that tools like ``ulimit`` may not work as usually expected. |
Dmitry Vyukov | c092cba | 2012-12-17 07:16:54 +0000 | [diff] [blame] | 118 | * Libc/libstdc++ static linking is not supported. |
Peter Collingbourne | 52ca70d | 2013-04-09 04:35:11 +0000 | [diff] [blame] | 119 | * Non-position-independent executables are not supported. Therefore, the |
| 120 | ``fsanitize=thread`` flag will cause Clang to act as though the ``-fPIE`` |
| 121 | flag had been supplied if compiling without ``-fPIC``, and as though the |
| 122 | ``-pie`` flag had been supplied if linking an executable. |
Sean Silva | 3872b46 | 2012-12-12 23:44:55 +0000 | [diff] [blame] | 123 | |
| 124 | Current Status |
| 125 | -------------- |
| 126 | |
Dmitry Vyukov | c092cba | 2012-12-17 07:16:54 +0000 | [diff] [blame] | 127 | ThreadSanitizer is in beta stage. It is known to work on large C++ programs |
| 128 | using pthreads, but we do not promise anything (yet). C++11 threading is |
Dmitry Vyukov | 61dde19 | 2012-12-17 13:07:35 +0000 | [diff] [blame] | 129 | supported with llvm libc++. The test suite is integrated into CMake build |
Dmitry Vyukov | c092cba | 2012-12-17 07:16:54 +0000 | [diff] [blame] | 130 | and can be run with ``make check-tsan`` command. |
Sean Silva | 3872b46 | 2012-12-12 23:44:55 +0000 | [diff] [blame] | 131 | |
| 132 | We are actively working on enhancing the tool --- stay tuned. Any help, |
| 133 | especially in the form of minimized standalone tests is more than welcome. |
| 134 | |
| 135 | More Information |
| 136 | ---------------- |
| 137 | `http://code.google.com/p/thread-sanitizer <http://code.google.com/p/thread-sanitizer/>`_. |
| 138 | |