2e5989e814
Previously by default, when not using `--ifc=`, lld would not deduplicate string literals. This reveals reliance on undefined behavior where string literal addresses are compared instead of using string equality checks. While ideally you would be able to easily identify and eliminate the reliance on this UB, this can be difficult, especially for third party code, and increases the friction and risk of users migrating to lld. This flips the default to deduplicate strings unless `--no-deduplicate-strings` is passed, matching ld64's behavior. Differential Revision: https://reviews.llvm.org/D140517
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63 lines
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Mach-O LLD Port
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===============
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LLD is a linker from the LLVM project that is a drop-in replacement
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for system linkers and runs much faster than them. It also provides
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features that are useful for toolchain developers. This document
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will describe the Mach-O port.
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Features
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--------
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- LLD is a drop-in replacement for Apple's Mach-O linker, ld64, that accepts the
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same command line arguments.
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- LLD is very fast. When you link a large program on a multicore
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machine, you can expect that LLD runs more than twice as fast as the ld64
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linker.
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Download
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--------
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LLD is available as a pre-built binary by going to the `latest release <https://github.com/llvm/llvm-project/releases>`_,
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downloading the appropriate bundle (``clang+llvm-<version>-<your architecture>-<your platform>.tar.xz``),
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decompressing it, and locating the binary at ``bin/ld64.lld``. Note
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that if ``ld64.lld`` is moved out of ``bin``, it must still be accompanied
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by its sibling file ``lld``, as ``ld64.lld`` is technically a symlink to ``lld``.
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Build
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-----
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The easiest way to build LLD is to
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check out the entire LLVM projects/sub-projects from a git mirror and
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build that tree. You need ``cmake`` and of course a C++ compiler.
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.. code-block:: console
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$ git clone https://github.com/llvm/llvm-project llvm-project
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$ mkdir build
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$ cd build
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$ cmake -G Ninja -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS='lld' ../llvm-project/llvm
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$ ninja check-lld-macho
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Then you can find output binary at ``build/bin/ld64.lld``. Note
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that if ``ld64.lld`` is moved out of ``bin``, it must still be accompanied
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by its sibling file ``lld``, as ``ld64.lld`` is technically a symlink to ``lld``.
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Using LLD
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---------
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LLD can be used by adding ``-fuse-ld=/path/to/ld64.lld`` to the linker flags.
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For Xcode, this can be done by adding it to "Other linker flags" in the build
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settings. For Bazel, this can be done with ``--linkopt`` or with
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`rules_apple_linker <https://github.com/keith/rules_apple_linker>`_.
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.. seealso::
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:doc:`ld64-vs-lld` has more info on the differences between the two linkers.
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.. toctree::
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:hidden:
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ld64-vs-lld
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