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a80e65e00a
This patch overhauls how we pick up the ABI library. Instead of setting ad-hoc flags, it creates interface targets that can be linked against by the rest of the build, which is easier to follow and extend to support new ABI libraries. This is intended to be a NFC change, however there are some additional simplifications and improvements we can make in the future that would require a slight behavior change. Differential Revision: https://reviews.llvm.org/D120727
581 lines
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ReStructuredText
581 lines
20 KiB
ReStructuredText
.. _BuildingLibcxx:
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===============
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Building libc++
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===============
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.. contents::
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:local:
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.. _build instructions:
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The instructions on this page are aimed at vendors who ship libc++ as part of an
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operating system distribution, a toolchain or similar shipping vehicules. If you
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are a user merely trying to use libc++ in your program, you most likely want to
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refer to your vendor's documentation, or to the general documentation for using
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libc++ :ref:`here <using-libcxx>`.
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.. warning::
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If your operating system already provides libc++, it is important to be careful
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not to replace it. Replacing your system's libc++ installation could render it
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non-functional. Use the CMake option ``CMAKE_INSTALL_PREFIX`` to select a safe
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place to install libc++.
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The default build
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=================
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The default way of building libc++, libc++abi and libunwind is to root the CMake
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invocation at ``<monorepo>/runtimes``. While those projects are under the LLVM
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umbrella, they are different in nature from other build tools, so it makes sense
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to treat them as a separate set of entities. The default build can be achieved
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with the following CMake invocation:
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.. code-block:: bash
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$ git clone https://github.com/llvm/llvm-project.git
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$ cd llvm-project
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$ mkdir build
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$ cmake -G Ninja -S runtimes -B build -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" # Configure
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$ ninja -C build cxx cxxabi unwind # Build
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$ ninja -C build check-cxx check-cxxabi check-unwind # Test
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$ ninja -C build install-cxx install-cxxabi install-unwind # Install
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.. note::
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See :ref:`CMake Options` below for more configuration options.
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After building the various ``install-XXX`` targets, shared libraries for libc++, libc++abi and
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libunwind should now be present in ``<CMAKE_INSTALL_PREFIX>/lib``, and headers in
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``<CMAKE_INSTALL_PREFIX>/include/c++/v1``. See :ref:`using an alternate libc++ installation
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<alternate libcxx>` for information on how to use this libc++ over the default one.
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In the default configuration, the runtimes will be built using the compiler available by default
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on your system. Of course, you can change what compiler is being used with the usual CMake
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variables. If you wish to build the runtimes from a just-built Clang, the bootstrapping build
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explained below makes this task easy.
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Bootstrapping build
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===================
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It is possible to build Clang and then build the runtimes using that just-built compiler in a
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single CMake invocation. This is usually the correct way to build the runtimes when putting together
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a toolchain, or when the system compiler is not adequate to build them (too old, unsupported, etc.).
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To do this, use the following CMake invocation, and in particular notice how we're now rooting the
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CMake invocation at ``<monorepo>/llvm``:
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.. code-block:: bash
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$ mkdir build
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$ cmake -G Ninja -S llvm -B build -DLLVM_ENABLE_PROJECTS="clang" \ # Configure
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-DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" \
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-DLLVM_RUNTIME_TARGETS="<target-triple>"
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$ ninja -C build runtimes # Build
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$ ninja -C build check-runtimes # Test
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$ ninja -C build install-runtimes # Install
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.. note::
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This type of build is also commonly called a "Runtimes build", but we would like to move
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away from that terminology, which is too confusing.
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Support for Windows
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===================
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libcxx supports being built with clang-cl, but not with MSVC's cl.exe, as
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cl doesn't support the ``#include_next`` extension. Furthermore, VS 2017 or
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newer (19.14) is required.
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libcxx also supports being built with clang targeting MinGW environments.
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CMake + Visual Studio
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---------------------
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Building with Visual Studio currently does not permit running tests. However,
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it is the simplest way to build.
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.. code-block:: batch
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> cmake -G "Visual Studio 16 2019" -S runtimes -B build ^
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-T "ClangCL" ^
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-DLLVM_ENABLE_RUNTIMES=libcxx ^
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-DLIBCXX_ENABLE_SHARED=YES ^
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-DLIBCXX_ENABLE_STATIC=NO ^
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-DLIBCXX_ENABLE_EXPERIMENTAL_LIBRARY=NO
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> cmake --build build
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CMake + ninja (MSVC)
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--------------------
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Building with ninja is required for development to enable tests.
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A couple of tests require Bash to be available, and a couple dozens
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of tests require other posix tools (cp, grep and similar - LLVM's tests
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require the same). Without those tools the vast majority of tests
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can still be ran successfully.
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If Git for Windows is available, that can be used to provide the bash
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shell by adding the right bin directory to the path, e.g.
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``set PATH=%PATH%;C:\Program Files\Git\usr\bin``.
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Alternatively, one can also choose to run the whole build in a MSYS2
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shell. That can be set up e.g. by starting a Visual Studio Tools Command
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Prompt (for getting the environment variables pointing to the headers and
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import libraries), and making sure that clang-cl is available in the
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path. From there, launch an MSYS2 shell via e.g.
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``C:\msys64\msys2_shell.cmd -full-path -mingw64`` (preserving the earlier
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environment, allowing the MSVC headers/libraries and clang-cl to be found).
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In either case, then run:
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.. code-block:: batch
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> cmake -G Ninja -S runtimes -B build ^
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-DCMAKE_C_COMPILER=clang-cl ^
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-DCMAKE_CXX_COMPILER=clang-cl ^
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-DLLVM_ENABLE_RUNTIMES=libcxx ^
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-DLIBCXX_ENABLE_EXPERIMENTAL_LIBRARY=NO
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> ninja -C build cxx
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> ninja -C build check-cxx
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If you are running in an MSYS2 shell and you have installed the
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MSYS2-provided clang package (which defaults to a non-MSVC target), you
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should add e.g. ``-DCMAKE_CXX_COMPILER_TARGET=x86_64-windows-msvc`` (replacing
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``x86_64`` with the architecture you're targeting) to the ``cmake`` command
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line above. This will instruct ``check-cxx`` to use the right target triple
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when invoking ``clang++``.
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Also note that if not building in Release mode, a failed assert in the tests
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pops up a blocking dialog box, making it hard to run a larger number of tests.
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CMake + ninja (MinGW)
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---------------------
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libcxx can also be built in MinGW environments, e.g. with the MinGW
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compilers in MSYS2. This requires clang to be available (installed with
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e.g. the ``mingw-w64-x86_64-clang`` package), together with CMake and ninja.
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.. code-block:: bash
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> cmake -G Ninja -S runtimes -B build \
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-DCMAKE_C_COMPILER=clang \
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-DCMAKE_CXX_COMPILER=clang++ \
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-DLLVM_ENABLE_RUNTIMES=libcxx \
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-DLIBCXX_CXX_ABI=libstdc++ \
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-DLIBCXX_TARGET_INFO="libcxx.test.target_info.MingwLocalTI"
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> ninja -C build cxx
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> cp /mingw64/bin/{libstdc++-6,libgcc_s_seh-1,libwinpthread-1}.dll lib
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> ninja -C build check-cxx
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As this build configuration ends up depending on a couple other DLLs that
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aren't available in path while running tests, copy them into the same
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directory as the tested libc++ DLL.
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(Building a libc++ that depends on libstdc++ isn't necessarily a config one
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would want to deploy, but it simplifies the config for testing purposes.)
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.. _`libc++abi`: http://libcxxabi.llvm.org/
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.. _CMake Options:
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CMake Options
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=============
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Here are some of the CMake variables that are used often, along with a
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brief explanation and LLVM-specific notes. For full documentation, check the
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CMake docs or execute ``cmake --help-variable VARIABLE_NAME``.
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**CMAKE_BUILD_TYPE**:STRING
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Sets the build type for ``make`` based generators. Possible values are
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Release, Debug, RelWithDebInfo and MinSizeRel. On systems like Visual Studio
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the user sets the build type with the IDE settings.
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**CMAKE_INSTALL_PREFIX**:PATH
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Path where LLVM will be installed if "make install" is invoked or the
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"INSTALL" target is built.
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**CMAKE_CXX_COMPILER**:STRING
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The C++ compiler to use when building and testing libc++.
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.. _libcxx-specific options:
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libc++ specific options
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-----------------------
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.. option:: LIBCXX_INSTALL_LIBRARY:BOOL
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**Default**: ``ON``
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Toggle the installation of the library portion of libc++.
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.. option:: LIBCXX_INSTALL_HEADERS:BOOL
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**Default**: ``ON``
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Toggle the installation of the libc++ headers.
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.. option:: LIBCXX_ENABLE_ASSERTIONS:BOOL
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**Default**: ``OFF``
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Build libc++ with assertions enabled in the compiled library, and enable assertions
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by default when building user code as well. Assertions can be turned off by users
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by defining ``_LIBCPP_ENABLE_ASSERTIONS=0``. For details, see
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:ref:`the documentation <assertions-mode>`.
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.. option:: LIBCXX_ENABLE_SHARED:BOOL
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**Default**: ``ON``
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Build libc++ as a shared library. Either `LIBCXX_ENABLE_SHARED` or
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`LIBCXX_ENABLE_STATIC` has to be enabled.
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.. option:: LIBCXX_ENABLE_STATIC:BOOL
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**Default**: ``ON``
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Build libc++ as a static library. Either `LIBCXX_ENABLE_SHARED` or
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`LIBCXX_ENABLE_STATIC` has to be enabled.
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.. option:: LIBCXX_LIBDIR_SUFFIX:STRING
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Extra suffix to append to the directory where libraries are to be installed.
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This option overrides `LLVM_LIBDIR_SUFFIX`.
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.. option:: LIBCXX_HERMETIC_STATIC_LIBRARY:BOOL
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**Default**: ``OFF``
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Do not export any symbols from the static libc++ library.
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This is useful when the static libc++ library is being linked into shared
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libraries that may be used in with other shared libraries that use different
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C++ library. We want to avoid exporting any libc++ symbols in that case.
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.. option:: LIBCXX_ENABLE_FILESYSTEM:BOOL
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**Default**: ``ON`` except on Windows when using MSVC.
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This option can be used to enable or disable the filesystem components on
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platforms that may not support them. For example on Windows when using MSVC.
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.. option:: LIBCXX_ENABLE_WIDE_CHARACTERS:BOOL
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**Default**: ``ON``
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This option can be used to disable support for ``wchar_t`` in the library. It also
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allows the library to work on top of a C Standard Library that does not provide
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support for ``wchar_t``. This is especially useful in embedded settings where
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C Standard Libraries don't always provide all the usual bells and whistles.
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.. option:: LIBCXX_ENABLE_INCOMPLETE_FEATURES:BOOL
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**Default**: ``ON``
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Whether to enable support for incomplete library features. Incomplete features
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are new library features under development. These features don't guarantee
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ABI stability nor the quality of completed library features. Vendors
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shipping the library may want to disable this option.
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.. option:: LIBCXX_INSTALL_LIBRARY_DIR:PATH
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**Default**: ``lib${LIBCXX_LIBDIR_SUFFIX}``
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Path where built libc++ libraries should be installed. If a relative path,
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relative to ``CMAKE_INSTALL_PREFIX``.
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.. option:: LIBCXX_INSTALL_INCLUDE_DIR:PATH
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**Default**: ``include/c++/v1``
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Path where target-agnostic libc++ headers should be installed. If a relative
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path, relative to ``CMAKE_INSTALL_PREFIX``.
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.. option:: LIBCXX_INSTALL_INCLUDE_TARGET_DIR:PATH
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**Default**: ``include/c++/v1`` or
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``include/${LLVM_DEFAULT_TARGET_TRIPLE}/c++/v1``
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Path where target-specific libc++ headers should be installed. If a relative
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path, relative to ``CMAKE_INSTALL_PREFIX``.
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.. _libc++experimental options:
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libc++experimental Specific Options
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------------------------------------
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.. option:: LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY:BOOL
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**Default**: ``ON``
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Build and test libc++experimental.a.
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.. option:: LIBCXX_INSTALL_EXPERIMENTAL_LIBRARY:BOOL
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**Default**: ``LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY AND LIBCXX_INSTALL_LIBRARY``
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Install libc++experimental.a alongside libc++.
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.. _ABI Library Specific Options:
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ABI Library Specific Options
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----------------------------
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.. option:: LIBCXX_CXX_ABI:STRING
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**Values**: ``none``, ``libcxxabi``, ``system-libcxxabi``, ``libcxxrt``, ``libstdc++``, ``libsupc++``, ``vcruntime``.
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Select the ABI library to build libc++ against.
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.. option:: LIBCXX_CXX_ABI_INCLUDE_PATHS:PATHS
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Provide additional search paths for the ABI library headers.
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.. option:: LIBCXX_CXX_ABI_LIBRARY_PATH:PATH
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Provide the path to the ABI library that libc++ should link against. This is only
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useful when linking against an out-of-tree ABI library.
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.. option:: LIBCXX_ENABLE_STATIC_ABI_LIBRARY:BOOL
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**Default**: ``OFF``
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If this option is enabled, libc++ will try and link the selected ABI library
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statically.
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.. option:: LIBCXX_ENABLE_ABI_LINKER_SCRIPT:BOOL
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**Default**: ``ON`` by default on UNIX platforms other than Apple unless
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'LIBCXX_ENABLE_STATIC_ABI_LIBRARY' is ON. Otherwise the default value is ``OFF``.
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This option generate and installs a linker script as ``libc++.so`` which
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links the correct ABI library.
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.. option:: LIBCXXABI_USE_LLVM_UNWINDER:BOOL
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**Default**: ``OFF``
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Build and use the LLVM unwinder. Note: This option can only be used when
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libc++abi is the C++ ABI library used.
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libc++ Feature Options
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----------------------
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.. option:: LIBCXX_ENABLE_EXCEPTIONS:BOOL
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**Default**: ``ON``
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Build libc++ with exception support.
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.. option:: LIBCXX_ENABLE_RTTI:BOOL
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**Default**: ``ON``
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Build libc++ with run time type information.
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.. option:: LIBCXX_INCLUDE_TESTS:BOOL
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**Default**: ``ON`` (or value of ``LLVM_INCLUDE_TESTS``)
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Build the libc++ tests.
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.. option:: LIBCXX_INCLUDE_BENCHMARKS:BOOL
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**Default**: ``ON``
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Build the libc++ benchmark tests and the Google Benchmark library needed
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to support them.
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.. option:: LIBCXX_BENCHMARK_TEST_ARGS:STRING
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**Default**: ``--benchmark_min_time=0.01``
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A semicolon list of arguments to pass when running the libc++ benchmarks using the
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``check-cxx-benchmarks`` rule. By default we run the benchmarks for a very short amount of time,
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since the primary use of ``check-cxx-benchmarks`` is to get test and sanitizer coverage, not to
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get accurate measurements.
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.. option:: LIBCXX_BENCHMARK_NATIVE_STDLIB:STRING
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**Default**:: ``""``
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**Values**:: ``libc++``, ``libstdc++``
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Build the libc++ benchmark tests and Google Benchmark library against the
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specified standard library on the platform. On Linux this can be used to
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compare libc++ to libstdc++ by building the benchmark tests against both
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standard libraries.
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.. option:: LIBCXX_BENCHMARK_NATIVE_GCC_TOOLCHAIN:STRING
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Use the specified GCC toolchain and standard library when building the native
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stdlib benchmark tests.
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.. option:: LIBCXX_HIDE_FROM_ABI_PER_TU_BY_DEFAULT:BOOL
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**Default**: ``OFF``
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Pick the default for whether to constrain ABI-unstable symbols to
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each individual translation unit. This setting controls whether
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`_LIBCPP_HIDE_FROM_ABI_PER_TU_BY_DEFAULT` is defined by default --
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see the documentation of that macro for details.
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libc++ ABI Feature Options
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--------------------------
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The following options allow building libc++ for a different ABI version.
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.. option:: LIBCXX_ABI_VERSION:STRING
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**Default**: ``1``
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Defines the target ABI version of libc++.
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.. option:: LIBCXX_ABI_UNSTABLE:BOOL
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**Default**: ``OFF``
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Build the "unstable" ABI version of libc++. Includes all ABI changing features
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on top of the current stable version.
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.. option:: LIBCXX_ABI_NAMESPACE:STRING
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**Default**: ``__n`` where ``n`` is the current ABI version.
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This option defines the name of the inline ABI versioning namespace. It can be used for building
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custom versions of libc++ with unique symbol names in order to prevent conflicts or ODR issues
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with other libc++ versions.
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.. warning::
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When providing a custom namespace, it's the user's responsibility to ensure the name won't cause
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conflicts with other names defined by libc++, both now and in the future. In particular, inline
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namespaces of the form ``__[0-9]+`` could cause conflicts with future versions of the library,
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and so should be avoided.
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.. option:: LIBCXX_ABI_DEFINES:STRING
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**Default**: ``""``
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A semicolon-separated list of ABI macros to persist in the site config header.
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See ``include/__config`` for the list of ABI macros.
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.. _LLVM-specific variables:
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LLVM-specific options
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---------------------
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.. option:: LLVM_LIBDIR_SUFFIX:STRING
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Extra suffix to append to the directory where libraries are to be
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installed. On a 64-bit architecture, one could use ``-DLLVM_LIBDIR_SUFFIX=64``
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to install libraries to ``/usr/lib64``.
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.. option:: LLVM_BUILD_32_BITS:BOOL
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Build 32-bits executables and libraries on 64-bits systems. This option is
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available only on some 64-bits Unix systems. Defaults to OFF.
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.. option:: LLVM_LIT_ARGS:STRING
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Arguments given to lit. ``make check`` and ``make clang-test`` are affected.
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By default, ``'-sv --no-progress-bar'`` on Visual C++ and Xcode, ``'-sv'`` on
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others.
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Using Alternate ABI libraries
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=============================
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In order to implement various features like exceptions, RTTI, ``dynamic_cast`` and
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more, libc++ requires what we refer to as an ABI library. Typically, that library
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implements the `Itanium C++ ABI <https://itanium-cxx-abi.github.io/cxx-abi/abi.html>`_.
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By default, libc++ uses libc++abi as an ABI library. However, it is possible to use
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other ABI libraries too.
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Using libsupc++ on Linux
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------------------------
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You will need libstdc++ in order to provide libsupc++.
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Figure out where the libsupc++ headers are on your system. On Ubuntu this
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is ``/usr/include/c++/<version>`` and ``/usr/include/c++/<version>/<target-triple>``
|
|
|
|
You can also figure this out by running
|
|
|
|
.. code-block:: bash
|
|
|
|
$ echo | g++ -Wp,-v -x c++ - -fsyntax-only
|
|
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
|
|
ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../x86_64-linux-gnu/include"
|
|
#include "..." search starts here:
|
|
#include <...> search starts here:
|
|
/usr/include/c++/4.7
|
|
/usr/include/c++/4.7/x86_64-linux-gnu
|
|
/usr/include/c++/4.7/backward
|
|
/usr/lib/gcc/x86_64-linux-gnu/4.7/include
|
|
/usr/local/include
|
|
/usr/lib/gcc/x86_64-linux-gnu/4.7/include-fixed
|
|
/usr/include/x86_64-linux-gnu
|
|
/usr/include
|
|
End of search list.
|
|
|
|
Note that the first two entries happen to be what we are looking for. This
|
|
may not be correct on all platforms.
|
|
|
|
We can now run CMake:
|
|
|
|
.. code-block:: bash
|
|
|
|
$ cmake -G Ninja -S runtimes -B build \
|
|
-DLLVM_ENABLE_RUNTIMES="libcxx" \
|
|
-DLIBCXX_CXX_ABI=libstdc++ \
|
|
-DLIBCXX_CXX_ABI_INCLUDE_PATHS="/usr/include/c++/4.7/;/usr/include/c++/4.7/x86_64-linux-gnu/"
|
|
$ ninja -C build install-cxx
|
|
|
|
|
|
You can also substitute ``-DLIBCXX_CXX_ABI=libsupc++``
|
|
above, which will cause the library to be linked to libsupc++ instead
|
|
of libstdc++, but this is only recommended if you know that you will
|
|
never need to link against libstdc++ in the same executable as libc++.
|
|
GCC ships libsupc++ separately but only as a static library. If a
|
|
program also needs to link against libstdc++, it will provide its
|
|
own copy of libsupc++ and this can lead to subtle problems.
|
|
|
|
Using libcxxrt on Linux
|
|
------------------------
|
|
|
|
You will need to keep the source tree of `libcxxrt`_ available
|
|
on your build machine and your copy of the libcxxrt shared library must
|
|
be placed where your linker will find it.
|
|
|
|
We can now run CMake like:
|
|
|
|
.. code-block:: bash
|
|
|
|
$ cmake -G Ninja -S runtimes -B build \
|
|
-DLLVM_ENABLE_RUNTIMES="libcxx" \
|
|
-DLIBCXX_CXX_ABI=libcxxrt \
|
|
-DLIBCXX_CXX_ABI_INCLUDE_PATHS=path/to/libcxxrt-sources/src
|
|
$ ninja -C build install-cxx
|
|
|
|
Unfortunately you can't simply run clang with "-stdlib=libc++" at this point, as
|
|
clang is set up to link for libc++ linked to libsupc++. To get around this
|
|
you'll have to set up your linker yourself (or patch clang). For example,
|
|
|
|
.. code-block:: bash
|
|
|
|
$ clang++ -stdlib=libc++ helloworld.cpp \
|
|
-nodefaultlibs -lc++ -lcxxrt -lm -lc -lgcc_s -lgcc
|
|
|
|
Alternately, you could just add libcxxrt to your libraries list, which in most
|
|
situations will give the same result:
|
|
|
|
.. code-block:: bash
|
|
|
|
$ clang++ -stdlib=libc++ helloworld.cpp -lcxxrt
|
|
|
|
.. _`libcxxrt`: https://github.com/libcxxrt/libcxxrt
|