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ReStructuredText
258 lines
9.0 KiB
ReStructuredText
==============
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Testing libc++
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==============
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.. contents::
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:local:
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Getting Started
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===============
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libc++ uses LIT to configure and run its tests.
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The primary way to run the libc++ tests is by using ``make check-cxx``.
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However since libc++ can be used in any number of possible
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configurations it is important to customize the way LIT builds and runs
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the tests. This guide provides information on how to use LIT directly to
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test libc++.
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Please see the `Lit Command Guide`_ for more information about LIT.
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.. _LIT Command Guide: https://llvm.org/docs/CommandGuide/lit.html
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Usage
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-----
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After building libc++, you can run parts of the libc++ test suite by simply
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running ``llvm-lit`` on a specified test or directory. If you're unsure
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whether the required libraries have been built, you can use the
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`check-cxx-deps` target. For example:
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.. code-block:: bash
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$ cd <monorepo-root>
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$ make -C <build> check-cxx-deps # If you want to make sure the targets get rebuilt
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$ <build>/bin/llvm-lit -sv libcxx/test/std/re # Run all of the std::regex tests
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$ <build>/bin/llvm-lit -sv libcxx/test/std/depr/depr.c.headers/stdlib_h.pass.cpp # Run a single test
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$ <build>/bin/llvm-lit -sv libcxx/test/std/atomics libcxx/test/std/threads # Test std::thread and std::atomic
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Sometimes you'll want to change the way LIT is running the tests. Custom options
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can be specified using the `--param=<name>=<val>` flag. The most common option
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you'll want to change is the standard dialect (ie -std=c++XX). By default the
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test suite will select the newest C++ dialect supported by the compiler and use
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that. However if you want to manually specify the option like so:
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.. code-block:: bash
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$ <build>/bin/llvm-lit -sv libcxx/test/std/containers # Run the tests with the newest -std
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$ <build>/bin/llvm-lit -sv libcxx/test/std/containers --param=std=c++03 # Run the tests in C++03
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Occasionally you'll want to add extra compile or link flags when testing.
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You can do this as follows:
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.. code-block:: bash
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$ <build>/bin/llvm-lit -sv libcxx/test --param=compile_flags='-Wcustom-warning'
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$ <build>/bin/llvm-lit -sv libcxx/test --param=link_flags='-L/custom/library/path'
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Some other common examples include:
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.. code-block:: bash
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# Specify a custom compiler.
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$ <build>/bin/llvm-lit -sv libcxx/test/std --param=cxx_under_test=/opt/bin/g++
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# Disable warnings in the test suite
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$ <build>/bin/llvm-lit -sv libcxx/test --param=enable_warnings=False
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# Use UBSAN when running the tests.
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$ <build>/bin/llvm-lit -sv libcxx/test --param=use_sanitizer=Undefined
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Using a custom site configuration
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---------------------------------
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By default, the libc++ test suite will use a site configuration that matches
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the current CMake configuration. It does so by generating a ``lit.site.cfg``
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file in the build directory from one of the configuration file templates in
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``libcxx/test/configs/``, and pointing ``llvm-lit`` (which is a wrapper around
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``llvm/utils/lit/lit.py``) to that file. So when you're running
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``<build>/bin/llvm-lit``, the generated ``lit.site.cfg`` file is always loaded
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instead of ``libcxx/test/lit.cfg.py``. If you want to use a custom site
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configuration, simply point the CMake build to it using
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``-DLIBCXX_TEST_CONFIG=<path-to-site-config>``, and that site configuration
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will be used instead. That file can use CMake variables inside it to make
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configuration easier.
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.. code-block:: bash
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$ cmake <options> -DLIBCXX_TEST_CONFIG=<path-to-site-config>
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$ make -C <build> check-cxx-deps
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$ <build>/bin/llvm-lit -sv libcxx/test # will use your custom config file
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LIT Options
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===========
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:program:`lit` [*options*...] [*filenames*...]
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Command Line Options
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--------------------
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To use these options you pass them on the LIT command line as ``--param NAME``
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or ``--param NAME=VALUE``. Some options have default values specified during
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CMake's configuration. Passing the option on the command line will override the
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default.
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.. program:: lit
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.. option:: cxx_under_test=<path/to/compiler>
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Specify the compiler used to build the tests.
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.. option:: stdlib=<stdlib name>
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**Values**: libc++, libstdc++, msvc
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Specify the C++ standard library being tested. The default is libc++ if this
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option is not provided. This option is intended to allow running the libc++
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test suite against other standard library implementations.
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.. option:: std=<standard version>
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**Values**: c++03, c++11, c++14, c++17, c++2a
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Change the standard version used when building the tests.
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.. option:: cxx_headers=<path/to/headers>
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Specify the c++ standard library headers that are tested. By default the
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headers in the source tree are used.
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.. option:: cxx_library_root=<path/to/lib/>
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Specify the directory of the libc++ library to be tested. By default the
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library folder of the build directory is used.
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.. option:: cxx_runtime_root=<path/to/lib/>
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Specify the directory of the libc++ library to use at runtime. This directory
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is not added to the linkers search path. This can be used to compile tests
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against one version of libc++ and run them using another. The default value
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for this option is `cxx_library_root`.
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.. option:: use_system_cxx_lib=<bool>
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**Default**: False
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Enable or disable testing against the installed version of libc++ library.
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This impacts whether the ``with_system_cxx_lib`` Lit feature is defined or
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not. The ``cxx_library_root`` and ``cxx_runtime_root`` parameters should
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still be used to specify the path of the library to link to and run against,
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respectively.
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.. option:: debug_level=<level>
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**Values**: 0, 1
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Enable the use of debug mode. Level 0 enables assertions and level 1 enables
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assertions and debugging of iterator misuse.
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.. option:: use_sanitizer=<sanitizer name>
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**Values**: Memory, MemoryWithOrigins, Address, Undefined
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Run the tests using the given sanitizer. If LLVM_USE_SANITIZER was given when
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building libc++ then that sanitizer will be used by default.
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.. option:: llvm_unwinder
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Enable the use of LLVM unwinder instead of libgcc.
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.. option:: builtins_library
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Path to the builtins library to use instead of libgcc.
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Writing Tests
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-------------
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When writing tests for the libc++ test suite, you should follow a few guidelines.
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This will ensure that your tests can run on a wide variety of hardware and under
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a wide variety of configurations. We have several unusual configurations such as
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building the tests on one host but running them on a different host, which add a
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few requirements to the test suite. Here's some stuff you should know:
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- All tests are run in a temporary directory that is unique to that test and
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cleaned up after the test is done.
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- When a test needs data files as inputs, these data files can be saved in the
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repository (when reasonable) and referenced by the test as
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``// FILE_DEPENDENCIES: <path-to-dependencies>``. Copies of these files or
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directories will be made available to the test in the temporary directory
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where it is run.
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- You should never hardcode a path from the build-host in a test, because that
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path will not necessarily be available on the host where the tests are run.
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- You should try to reduce the runtime dependencies of each test to the minimum.
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For example, requiring Python to run a test is bad, since Python is not
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necessarily available on all devices we may want to run the tests on (even
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though supporting Python is probably trivial for the build-host).
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Benchmarks
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==========
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Libc++ contains benchmark tests separately from the test of the test suite.
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The benchmarks are written using the `Google Benchmark`_ library, a copy of which
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is stored in the libc++ repository.
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For more information about using the Google Benchmark library see the
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`official documentation <https://github.com/google/benchmark>`_.
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.. _`Google Benchmark`: https://github.com/google/benchmark
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Building Benchmarks
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-------------------
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The benchmark tests are not built by default. The benchmarks can be built using
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the ``cxx-benchmarks`` target.
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An example build would look like:
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.. code-block:: bash
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$ cd build
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$ cmake [options] <path to libcxx sources>
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$ make cxx-benchmarks
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This will build all of the benchmarks under ``<libcxx-src>/benchmarks`` to be
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built against the just-built libc++. The compiled tests are output into
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``build/benchmarks``.
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The benchmarks can also be built against the platforms native standard library
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using the ``-DLIBCXX_BUILD_BENCHMARKS_NATIVE_STDLIB=ON`` CMake option. This
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is useful for comparing the performance of libc++ to other standard libraries.
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The compiled benchmarks are named ``<test>.libcxx.out`` if they test libc++ and
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``<test>.native.out`` otherwise.
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Also See:
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* :ref:`Building Libc++ <build instructions>`
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* :ref:`CMake Options`
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Running Benchmarks
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------------------
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The benchmarks must be run manually by the user. Currently there is no way
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to run them as part of the build.
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For example:
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.. code-block:: bash
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$ cd build/benchmarks
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$ make cxx-benchmarks
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$ ./algorithms.libcxx.out # Runs all the benchmarks
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$ ./algorithms.libcxx.out --benchmark_filter=BM_Sort.* # Only runs the sort benchmarks
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For more information about running benchmarks see `Google Benchmark`_.
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