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.. _full_cross_build:
================
Full Cross Build
================
.. contents:: Table of Contents
:depth: 1
:local:
In this document, we will present a recipe to cross build a full libc. When we
say *cross build* a full libc, we mean that we will build the libc for a target
system which is not the same as the system on which the libc is being built.
For example, you could be building for a bare metal aarch64 *target* on a Linux
x86_64 *host*.
Configure the full cross build of the libc
==========================================
Below is a simple recipe to configure the libc for a cross build.
.. code-block:: sh
$> cd llvm-project # The llvm-project checkout
$> mkdir build
$> cd build
$> cmake ../llvm \
-G Ninja \ # Generator
-DLLVM_ENABLE_PROJECTS=libc \ # Enable the libc project
-DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ \
-DLLVM_LIBC_FULL_BUILD=ON \ # We are building the full libc
-DLIBC_TARGET_TRIPLE=<Your target triple>
We will go over the special options passed to the ``cmake`` command above.
* **Enabled Projects** - Since we want to build the libc project, we list
``libc`` as the enabled project.
* **The full build option** - Since we want to build the full libc, we pass
``-DLLVM_LIBC_FULL_BUILD=ON``.
* **The target triple** - This is the target triple of the target for which
we are building the libc. For example, for a Linux 32-bit Arm target,
one can specify it as ``arm-linux-eabi``.
Build and install
=================
After configuring the build with the above ``cmake`` command, one can build the
the libc for the target with the following command:
.. code-block:: sh
$> ninja libc
The above ``ninja`` command will build the ``libc.a`` static archive for the
target specified with ``-DLIBC_TARGET_TRIPLE`` to the ``cmake`` command.
Building for bare metal
=======================
To build for bare metal, all one has to do is to specify the
`system <https://clang.llvm.org/docs/CrossCompilation.html#target-triple>`_
component of the target triple as ``none``. For example, to build for a
32-bit arm target on bare metal, one can use a target triple like
``arm-none-eabi``.
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