132d231605
DTLTO-related COFF LLD changes were cherry-picked to the LLVM 21 release branch in: https://github.com/llvm/llvm-project/pull/149979 This commit adds the corresponding release note, modeled after the previously added note for ELF LLD DTLTO support.
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===========================
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lld |release| Release Notes
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===========================
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.. contents::
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:local:
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.. only:: PreRelease
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.. warning::
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These are in-progress notes for the upcoming LLVM |release| 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 |release|.
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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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* Added ``-z dynamic-undefined-weak`` to make undefined weak symbols dynamic
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when the dynamic symbol table is present.
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(`#143831 <https://github.com/llvm/llvm-project/pull/143831>`_)
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* For ``-z undefs`` (default for ``-shared``), relocations referencing undefined
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strong symbols now behave like relocations referencing undefined weak symbols.
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* ``--why-live=<glob>`` prints for each symbol matching ``<glob>`` a chain of
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items that kept it live during garbage collection. This is inspired by the
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Mach-O LLD feature of the same name.
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* ``--thinlto-distributor=`` and ``--thinlto-remote-compiler=`` options are
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added to support Integrated Distributed ThinLTO.
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(`#142757 <https://github.com/llvm/llvm-project/pull/142757>`_)
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* Linker script ``OVERLAY`` descriptions now support virtual memory regions
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(e.g. ``>region``) and ``NOCROSSREFS``.
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* When the last ``PT_LOAD`` segment is executable and includes BSS sections,
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its ``p_memsz`` member is now correct.
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(`#139207 <https://github.com/llvm/llvm-project/pull/139207>`_)
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* Spurious ``ASSERT`` errors before the layout converges are now fixed.
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* For ARM and AArch64, ``--xosegment`` and ``--no-xosegment`` control whether
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to place executable-only and readable-executable sections in the same
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segment. The default option is ``--no-xosegment``.
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(`#132412 <https://github.com/llvm/llvm-project/pull/132412>`_)
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* For AArch64, added support for the ``SHF_AARCH64_PURECODE`` section flag,
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which indicates that the section only contains program code and no data.
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An output section will only have this flag set if all input sections also
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have it set. (`#125689 <https://github.com/llvm/llvm-project/pull/125689>`_,
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`#134798 <https://github.com/llvm/llvm-project/pull/134798>`_)
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* For AArch64 and ARM, added ``-zexecute-only-report``, which checks for
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missing ``SHF_AARCH64_PURECODE`` and ``SHF_ARM_PURECODE`` section flags
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on executable sections.
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(`#128883 <https://github.com/llvm/llvm-project/pull/128883>`_)
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* For AArch64, ``-z nopac-plt`` has been added.
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* For AArch64 and X86_64, added ``--branch-to-branch``, which rewrites branches
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that point to another branch instruction to instead branch directly to the
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target of the second instruction. Enabled by default at ``-O2``.
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* For AArch64, added support for ``-zgcs-report-dynamic``, enabling checks for
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GNU GCS Attribute Flags in Dynamic Objects when GCS is enabled. Inherits value
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from ``-zgcs-report`` (capped at ``warning`` level) unless user-defined,
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ensuring compatibility with GNU ld linker.
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* The default Hexagon architecture version in ELF object files produced by
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lld is changed to v68. This change is only effective when the version is
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not provided in the command line by the user and cannot be inferred from
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inputs.
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* For LoongArch, the initial-exec to local-exec TLS optimization has been implemented.
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* For LoongArch, several relaxation optimizations are supported, including relaxation for
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``R_LARCH_PCALA_HI20/LO12`` and ``R_LARCH_GOT_PC_HI20/LO12`` relocations, instruction
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relaxation for ``R_LARCH_CALL36``, TLS local-exec (``LE``)/global dynamic (``GD``)/
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local dynamic (``LD``) model relaxation, and TLSDESC code sequence relaxation.
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* For RISCV, an oscillation bug due to call relaxation is now fixed.
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(`#142899 <https://github.com/llvm/llvm-project/pull/142899>`_)
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* For x86-64, the ``.ltext`` section is now placed before ``.rodata``.
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Breaking changes
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----------------
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* Executable-only and readable-executable sections are now allowed to be placed
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in the same segment by default. Pass ``--xosegment`` to lld in order to get
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the old behavior back.
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* When using ``--no-pie`` without a ``SECTIONS`` command, the linker uses the
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target's default image base. If ``-Ttext=`` or ``--section-start`` specifies
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an output section address below this base, there will now be an error.
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``--image-base`` can be set at a lower address to fix the error.
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(`#140187 <https://github.com/llvm/llvm-project/pull/140187>`_)
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COFF Improvements
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-----------------
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* ``/thinlto-distributor`` and ``/thinlto-remote-compiler`` options
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added to support Integrated Distributed ThinLTO.
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(`#147265 <https://github.com/llvm/llvm-project/pull/147265>`_)
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MinGW Improvements
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------------------
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MachO Improvements
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------------------
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WebAssembly Improvements
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------------------------
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Fixes
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#####
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