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124 lines
4.8 KiB
ReStructuredText
124 lines
4.8 KiB
ReStructuredText
.. _full_host_build:
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===============
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Full Host Build
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===============
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.. contents:: Table of Contents
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:depth: 1
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:local:
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In this document, we will present a recipe to build the full libc for the host.
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When we say *build the libc for the host*, the goal is to build the libc for
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the same system on which the libc is being built. Also, we will take this
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opportunity to demonstrate how one can set up a *sysroot* (see the documentation
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of the ``--sysroot`` option here:
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`<https://gcc.gnu.org/onlinedocs/gcc/Directory-Options.html>`_) which includes
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not only the components of LLVM's libc, but also a full LLVM only toolchain
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consisting of the `clang <https://clang.llvm.org/>`_ compiler, the
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`lld <https://lld.llvm.org/>`_ linker and the
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`compiler-rt <https://compiler-rt.llvm.org/>`_ runtime libraries. LLVM's libc is
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not yet complete enough to allow using and linking a C++ application against
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a C++ standard library (like libc++). Hence, we do not include
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`libc++ <https://libcxx.llvm.org/>`_ in the sysroot.
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.. note:: When the libc is complete enough, we should be able to include
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`libc++ <https://libcxx.llvm.org/>`_, libcxx-abi and libunwind in the
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LLVM only toolchain and use them to build and link C++ applications.
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Configure the full libc build
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===============================
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Below is the list of commands for a simple recipe to build and install the
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libc components along with other components of an LLVM only toolchain. In this
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we've set the Ninja generator, enabled a full compiler suite, set the build
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type to "Debug", and enabled the Scudo allocator. The build also tells clang
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to use the freshly built lld and compiler-rt.
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.. code-block:: sh
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$> cd llvm-project # The llvm-project checkout
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$> mkdir build
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$> cd build
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$> SYSROOT=/path/to/sysroot # Remember to set this!
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$> cmake ../llvm \
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-G Ninja \
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-DLLVM_ENABLE_PROJECTS="clang;libc;lld;compiler-rt" \
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-DCMAKE_BUILD_TYPE=Debug \
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-DCMAKE_C_COMPILER=clang \
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-DCMAKE_CXX_COMPILER=clang++ \
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-DLLVM_LIBC_FULL_BUILD=ON \
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-DLLVM_LIBC_INCLUDE_SCUDO=ON \
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-DCOMPILER_RT_BUILD_SCUDO_STANDALONE_WITH_LLVM_LIBC=ON \
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-DCOMPILER_RT_BUILD_GWP_ASAN=OFF \
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-DCOMPILER_RT_SCUDO_STANDALONE_BUILD_SHARED=OFF \
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-DCLANG_DEFAULT_LINKER=lld \
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-DCLANG_DEFAULT_RTLIB=compiler-rt \
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-DDEFAULT_SYSROOT=$SYSROOT \
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-DCMAKE_INSTALL_PREFIX=$SYSROOT
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We will go over some of the special options passed to the ``cmake`` command
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above.
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* **Enabled Projects** - Since we want to build and install clang, lld
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and compiler-rt along with the libc, we specify
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``clang;libc;lld;compiler-rt`` as the list of enabled projects.
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* **The full build option** - Since we want to do build the full libc, we pass
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``-DLLVM_LIBC_FULL_BUILD=ON``.
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* **Scudo related options** - LLVM's libc uses
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`Scudo <https://llvm.org/docs/ScudoHardenedAllocator.html>`_ as its allocator.
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So, when building the full libc, we should specify that we want to include
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Scudo in the libc. Since the libc currently only supports static linking, we
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also specify that we do not want to build the Scudo shared library.
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* **Default sysroot and install prefix** - This is the path to the tool chain
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install directory. This is the directory where you intend to set up the sysroot.
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Build and install
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=================
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After configuring the build with the above ``cmake`` command, one can build and
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install the libc, clang (and its support libraries and builtins), lld and
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compiler-rt, with the following command:
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.. code-block:: sh
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$> ninja install-clang install-builtins install-compiler-rt \
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install-core-resource-headers install-libc install-lld
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Once the above command completes successfully, the ``$SYSROOT`` directory you
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have specified with the CMake configure step above will contain a full LLVM-only
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toolchain with which you can build practical/real-world C applications. See
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`<https://github.com/llvm/llvm-project/tree/main/libc/examples>`_ for examples
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of how to start using this new toolchain.
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Linux Headers
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=============
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If you are using the full libc on Linux, then you will also need to install
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Linux headers in your sysroot. The way to do this varies per system.
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These instructions should work on a Debian-based x86_64 system:
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.. code-block:: sh
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$> apt download linux-libc-dev
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$> dpkg -x linux-libc-dev*deb .
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$> mv usr/include/* /path/to/sysroot/include
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$> rm -rf usr linux-libc-dev*deb
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$> ln -s x86_64-linux-gnu/asm ~/Programming/sysroot/include/asm
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Using your newly built libc
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===========================
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You can now use your newly built libc nearly like you would use any compiler
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invocation:
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.. code-block:: sh
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$> /path/to/sysroot/bin/clang -static main.c
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.. warning::
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Because the libc does not yet support dynamic linking, the -static parameter
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must be added to all clang invocations.
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