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Mach-O LLD Port
===============
LLD is a linker from the LLVM project that is a drop-in replacement
for system linkers and runs much faster than them. It also provides
features that are useful for toolchain developers. This document
will describe the Mach-O port.
Features
--------
- LLD is a drop-in replacement for Apple's Mach-O linker, ld64, that accepts the
same command line arguments.
- LLD is very fast. When you link a large program on a multicore
machine, you can expect that LLD runs more than twice as fast as the ld64
linker.
Download
--------
LLD is available as a pre-built binary by going to the `latest release <https://github.com/llvm/llvm-project/releases>`_,
downloading the appropriate bundle (``clang+llvm-<version>-<your architecture>-<your platform>.tar.xz``),
decompressing it, and locating the binary at ``bin/ld64.lld``. Note
that if ``ld64.lld`` is moved out of ``bin``, it must still be accompanied
by its sibling file ``lld``, as ``ld64.lld`` is technically a symlink to ``lld``.
Build
-----
The easiest way to build LLD is to
check out the entire LLVM projects/sub-projects from a git mirror and
build that tree. You need ``cmake`` and of course a C++ compiler.
.. code-block:: console
$ git clone https://github.com/llvm/llvm-project llvm-project
$ mkdir build
$ cd build
$ cmake -G Ninja -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS='lld' ../llvm-project/llvm
$ ninja check-lld-macho
Then you can find output binary at ``build/bin/ld64.lld``. Note
that if ``ld64.lld`` is moved out of ``bin``, it must still be accompanied
by its sibling file ``lld``, as ``ld64.lld`` is technically a symlink to ``lld``.
Using LLD
---------
LLD can be used by adding ``-fuse-ld=/path/to/ld64.lld`` to the linker flags.
For Xcode, this can be done by adding it to "Other linker flags" in the build
settings. For Bazel, this can be done with ``--linkopt`` or with
`rules_apple_linker <https://github.com/keith/rules_apple_linker>`_.
.. seealso::
:doc:`ld64-vs-lld` has more info on the differences between the two linkers.
.. toctree::
:hidden:
ld64-vs-lld
|
