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This updates llvm, clang, compiler-rt, libc++, libunwind, lld, lldb and openmp to llvmorg-12.0.0-0-gd28af7c654d8, a.k.a. 12.0.0 release. PR: 255570 MFC after: 6 weeks
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148 lines
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========================
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lld 12.0.0 Release Notes
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========================
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.. contents::
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:local:
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.. warning::
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These are in-progress notes for the upcoming LLVM 12.0.0 release.
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Release notes for previous releases can be found on
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`the Download Page <https://releases.llvm.org/download.html>`_.
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Introduction
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============
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This document contains the release notes for the lld linker, release 12.0.0.
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Here we describe the status of lld, including major improvements
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from the previous release. All lld releases may be downloaded
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from the `LLVM releases web site <https://llvm.org/releases/>`_.
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Non-comprehensive list of changes in this release
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=================================================
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ELF Improvements
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----------------
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* ``--dependency-file`` has been added. (Similar to ``cc -M -MF``.)
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(`D82437 <https://reviews.llvm.org/D82437>`_)
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* ``--error-handling-script`` has been added to allow for user-defined handlers upon
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missing libraries. (`D87758 <https://reviews.llvm.org/D87758>`_)
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* ``--exclude-libs`` can now localize defined version symbols and bitcode referenced libcall symbols.
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(`D94280 <https://reviews.llvm.org/D94280>`_)
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* ``--gdb-index`` now works with DWARF v5 and ``--icf={safe,all}``.
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(`D85579 <https://reviews.llvm.org/D85579>`_)
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(`D89751 <https://reviews.llvm.org/D89751>`_)
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* ``--gdb-index --emit-relocs`` can now be used together.
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(`D94354 <https://reviews.llvm.org/D94354>`_)
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* ``--icf={safe,all}`` conservatively no longer fold text sections with LSDA.
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Previously ICF on ``-fexceptions`` code could be unsafe.
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(`D84610 <https://reviews.llvm.org/D84610>`_)
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* ``--icf={safe,all}`` can now fold two sections with relocations referencing aliased symbols.
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(`D88830 <https://reviews.llvm.org/D88830>`_)
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* ``--lto-pseudo-probe-for-profiling`` has been added.
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(`D95056 <https://reviews.llvm.org/D95056>`_)
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* ``--no-lto-whole-program-visibility`` has been added.
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(`D92060 <https://reviews.llvm.org/D92060>`_)
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* ``--oformat-binary`` has been fixed to respect LMA.
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(`D85086 <https://reviews.llvm.org/D85086>`_)
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* ``--reproduce`` includes ``--lto-sample-profile``, ``--just-symbols``, ``--call-graph-ordering-file``, ``--retain-symbols-file`` files.
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* ``-r --gc-sections`` is now supported.
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(`D84131 <https://reviews.llvm.org/D84131>`_)
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* A ``-u`` specified symbol will no longer change the binding to ``STB_WEAK``.
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(`D88945 <https://reviews.llvm.org/D88945>`_)
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* ``--wrap`` support has been improved.
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+ If ``foo`` is not referenced, there is no longer an undefined symbol ``__wrap_foo``.
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+ If ``__real_foo`` is not referenced, there is no longer an undefined symbol ``foo``.
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* ``SHF_LINK_ORDER`` sections can now have zero ``sh_link`` values.
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* ``SHF_LINK_ORDER`` and non-``SHF_LINK_ORDER`` sections can now be mixed within an input section description.
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(`D84001 <https://reviews.llvm.org/D84001>`_)
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* ``LOG2CEIL`` is now supported in linker scripts.
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(`D84054 <https://reviews.llvm.org/D84054>`_)
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* ``DEFINED`` has been fixed to check whether the symbol is defined.
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(`D83758 <https://reviews.llvm.org/D83758>`_)
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* An input section description may now have multiple ``SORT_*``.
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The matched sections are ordered by radix sort with the keys being ``(SORT*, --sort-section, input order)``.
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(`D91127 <https://reviews.llvm.org/D91127>`_)
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* Users can now provide a GNU style linker script to convert ``.ctors`` into ``.init_array``.
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(`D91187 <https://reviews.llvm.org/D91187>`_)
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* An empty output section can now be discarded even if it is assigned to a program header.
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(`D92301 <https://reviews.llvm.org/D92301>`_)
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* Non-``SHF_ALLOC`` sections now have larger file offsets than ``SHF_ALLOC`` sections.
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(`D85867 <https://reviews.llvm.org/D85867>`_)
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* Some symbol versioning improvements.
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+ Defined ``foo@@v1`` now resolve undefined ``foo@v1`` (`D92259 <https://reviews.llvm.org/D92259>`_)
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+ Undefined ``foo@v1`` now gets an error (`D92260 <https://reviews.llvm.org/D92260>`_)
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* The AArch64 port now has support for ``STO_AARCH64_VARIANT_PCS`` and ``DT_AARCH64_VARIANT_PCS``.
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(`D93045 <https://reviews.llvm.org/D93045>`_)
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* The AArch64 port now has support for ``R_AARCH64_LD64_GOTPAGE_LO15``.
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* The PowerPC64 port now detects missing R_PPC64_TLSGD/R_PPC64_TLSLD and disables TLS relaxation.
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This allows linking with object files produced by very old IBM XL compilers.
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(`D92959 <https://reviews.llvm.org/D92959>`_)
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* Many PowerPC PC-relative relocations are now supported.
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* ``R_PPC_ADDR24`` and ``R_PPC64_ADDR16_HIGH`` are now supported.
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* powerpcle is now supported. Tested with FreeBSD loader and freestanding.
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(`D93917 <https://reviews.llvm.org/D93917>`_)
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* RISC-V: the first ``SHT_RISCV_ATTRIBUTES`` section is now retained.
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(`D86309 <https://reviews.llvm.org/D86309>`_)
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* LTO pipeline now defaults to the new PM if the CMake variable ``ENABLE_EXPERIMENTAL_NEW_PASS_MANAGER`` is on.
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(`D92885 <https://reviews.llvm.org/D92885>`_)
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Breaking changes
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----------------
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* A COMMON symbol can now cause the fetch of an archive providing a ``STB_GLOBAL`` definition.
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This behavior follows GNU ld newer than December 1999.
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If you see ``duplicate symbol`` errors with the new behavior, check out `PR49226 <https://bugs.llvm.org//show_bug.cgi?id=49226>`_.
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(`D86142 <https://reviews.llvm.org/D86142>`_)
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COFF Improvements
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-----------------
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* Error out clearly if creating a DLL with too many exported symbols.
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(`D86701 <https://reviews.llvm.org/D86701>`_)
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MinGW Improvements
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------------------
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* Enabled dynamicbase by default. (`D86654 <https://reviews.llvm.org/D86654>`_)
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* Tolerate mismatches between COMDAT section sizes with different amount of
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padding (produced by binutils) by inspecting the aux section definition.
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(`D86659 <https://reviews.llvm.org/D86659>`_)
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* Support setting the subsystem version via the subsystem argument.
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(`D88804 <https://reviews.llvm.org/D88804>`_)
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* Implemented the GNU -wrap option.
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(`D89004 <https://reviews.llvm.org/D89004>`_,
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`D91689 <https://reviews.llvm.org/D91689>`_)
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* Handle the ``--demangle`` and ``--no-demangle`` options.
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(`D93950 <https://reviews.llvm.org/D93950>`_)
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Mach-O Improvements
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------------------
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We've gotten the new implementation of LLD for Mach-O to the point where it is
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able to link large x86_64 programs, and we'd love to get some alpha testing on
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it. The new Darwin back-end can be invoked as follows:
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.. code-block::
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clang -fuse-ld=lld.darwinnew /path/to/file.c
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To reach this point, we implemented numerous features, and it's easier to list
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the major features we *haven't* yet completed:
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* LTO support
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* Stack unwinding for exceptions
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* Support for arm64, arm, and i386 architectures
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If you stumble upon an issue and it doesn't fall into one of these categories,
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please file a bug report!
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WebAssembly Improvements
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------------------------
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