lld/docs/ReleaseNotes.rst

===========================
lld |release| Release Notes
===========================

.. contents::
    :local:

.. only:: PreRelease

  .. warning::
     These are in-progress notes for the upcoming LLVM |release| release.
     Release notes for previous releases can be found on
     `the Download Page <https://releases.llvm.org/download.html>`_.

Introduction
============

This document contains the release notes for the lld linker, release |release|.
Here we describe the status of lld, including major improvements
from the previous release. All lld releases may be downloaded
from the `LLVM releases web site <https://llvm.org/releases/>`_.

Non-comprehensive list of changes in this release
=================================================

ELF Improvements
----------------

* ``--export-dynamic-symbol-list`` has been added.
  (`D107317 <https://reviews.llvm.org/D107317>`_)
* ``--why-extract`` has been added to query why archive members/lazy object files are extracted.
  (`D109572 <https://reviews.llvm.org/D109572>`_)
* If ``-Map`` is specified, ``--cref`` will be printed to the specified file.
  (`D114663 <https://reviews.llvm.org/D114663>`_)
* ``-z bti-report`` and ``-z cet-report`` are now supported.
  (`D113901 <https://reviews.llvm.org/D113901>`_)
* ``--lto-pgo-warn-mismatch`` has been added.
  (`D104431 <https://reviews.llvm.org/D104431>`_)
* Archives without an index (symbol table) are now supported and work with
  ``--warn-backrefs``. One may build such an archive with ``llvm-ar rcS
  [--thin]`` to save space.
  (`D117284 <https://reviews.llvm.org/D117284>`_)
  The archive index may be `entirely ignored <https://reviews.llvm.org/D119074>`_
  in a future release.
* No longer deduplicate local symbol names at the default optimization level of ``-O1``.
  This results in a larger ``.strtab`` (usually less than 1%) but a faster link
  time. Use optimization level ``-O2`` to restore the deduplication. The ``-O2``
  deduplication may be dropped in the future to help parallel ``.symtab`` write.
* In relocatable output, relocations to discarded symbols now use tombstone
  values.
  (`D116946 <https://reviews.llvm.org/D116946>`_)
* Orphan section placement now picks a more suitable segment. Previously the
  algorithm might pick a readonly segment for a writable orphan section and make
  the segment writable.
  (`D111717 <https://reviews.llvm.org/D111717>`_)
* An empty output section moved by an ``INSERT`` comment now gets appropriate
  flags.
  (`D118529 <https://reviews.llvm.org/D118529>`_)
* Negation in a memory region attribute is now correctly handled.
  (`D113771 <https://reviews.llvm.org/D113771>`_)
* ``--compress-debug-sections=zlib`` is now run in parallel. ``{clang,gcc} -gz`` link
  actions are significantly faster.
  (`D117853 <https://reviews.llvm.org/D117853>`_)
* "relocation out of range" diagnostics and a few uncommon diagnostics
  now report an object file location beside a source file location.
  (`D112518 <https://reviews.llvm.org/D117853>`_)
* The write of ``.rela.dyn`` and ``SHF_MERGE|SHF_STRINGS`` sections (e.g.
  ``.debug_str``) is now run in parallel.

Architecture specific changes:

* The AArch64 port now supports adrp+ldr and adrp+add optimizations.
  ``--no-relax`` can suppress the optimization.
  (`D112063 <https://reviews.llvm.org/D112063>`_)
  (`D117614 <https://reviews.llvm.org/D117614>`_)
* The x86-32 port now supports TLSDESC (``-mtls-dialect=gnu2``).
  (`D112582 <https://reviews.llvm.org/D112582>`_)
* The x86-64 port now handles non-RAX/non-adjacent ``R_X86_64_GOTPC32_TLSDESC``
  and ``R_X86_64_TLSDESC_CALL`` (``-mtls-dialect=gnu2``).
  (`D114416 <https://reviews.llvm.org/D114416>`_)
* The x86-32 and x86-64 ports now support mixed TLSDESC and TLS GD, i.e. mixing
  objects compiled with and without ``-mtls-dialect=gnu2`` referencing the same
  TLS variable is now supported.
  (`D114416 <https://reviews.llvm.org/D114416>`_)
* For x86-64, ``--no-relax`` now suppresses ``R_X86_64_GOTPCRELX`` and
  ``R_X86_64_REX_GOTPCRELX`` GOT optimization
  (`D113615 <https://reviews.llvm.org/D113615>`_)
* ``R_X86_64_PLTOFF64`` is now supported.
  (`D112386 <https://reviews.llvm.org/D112386>`_)
* ``R_AARCH64_NONE``, ``R_PPC_NONE``, and ``R_PPC64_NONE`` in input REL
  relocation sections are now supported.

Breaking changes
----------------

* ``e_entry`` no longer falls back to the address of ``.text`` if the entry symbol does not exist.
  Instead, a value of 0 will be written.
  (`D110014 <https://reviews.llvm.org/D110014>`_)
* ``--lto-pseudo-probe-for-profiling`` has been removed. In LTO, the compiler
  enables this feature automatically.
  (`D110209 <https://reviews.llvm.org/D110209>`_)
* Use of ``--[no-]define-common``, ``-d``, ``-dc``, and ``-dp`` will now get a
  warning. They will be removed or ignored in 15.0.0.
  (`llvm-project#53660 <https://github.com/llvm/llvm-project/issues/53660>`_)

COFF Improvements
-----------------

* Correctly handle a signed immediate offset in ARM64 adr/adrp relocations.
  (`D114347 <https://reviews.llvm.org/D114347>`_)

* Omit section and label symbols from the symbol table.
  (`D113866 <https://reviews.llvm.org/D113866>`_)

MinGW Improvements
------------------

* ``--heap`` is now handled.
  (`D118405 <https://reviews.llvm.org/D118405>`_)

Mach-O Improvements
-------------------

* The ``ld64.lld.darwinnew`` symlink has been removed. Use ``ld64.lld`` to
  invoke the Mach-O backend from now on. Moreover, the symlink
  ``ld64.lld.darwinold`` -- and the old Mach-O LLD code that it pointed to --
  have been removed. (`D114842 <https://reviews.llvm.org/D114842>`_)
* The "cannot export hidden symbol" error has been downgraded to a warning.
  (`D107011 <https://reviews.llvm.org/D107011>`_)
* Common bitcode symbols are now supported.
  (`D107027 <https://reviews.llvm.org/D107027>`_)
* Weak references in bitcode are now supported.
  (`D115949 <https://reviews.llvm.org/D115949>`_)
* Thunk insertion now works more reliably.
  (`D108897 <https://reviews.llvm.org/D108897>`_,
  `D108924 <https://reviews.llvm.org/D108924>`_,
  `D109079  <https://reviews.llvm.org/D109079>`_,
  `D116705 <https://reviews.llvm.org/D116705>`_)
* ``-ObjC`` now loads archive members before the symbol resolution phase.
  (`D108781 <https://reviews.llvm.org/D108781>`_)
* ``-oso_prefix`` is now supported.
  (`D112291 <https://reviews.llvm.org/D112291>`_)
* Properly encode binaries with zero exported symbols. Tools like
  ``codesign_allocate`` no longer choke on those binaries.
  (`D112589 <https://reviews.llvm.org/D112589>`_)
* We no longer treat architecture mismatches as a fatal error. Use
  ``-arch_errors_fatal`` if that behavior is still desired.
  (`D113082 <https://reviews.llvm.org/D113082>`_)
* Several performance improvements were done to speed LLD up on projects with
  a lot of framework flags and library lookups. Large Swift-based projects
  will benefit significantly.
  (`D113073 <https://reviews.llvm.org/D113073>`_,
  `D113063 <https://reviews.llvm.org/D113063>`_,
  `D113153 <https://reviews.llvm.org/D113153>`_,
  `D113235 <https://reviews.llvm.org/D113235>`_)
* Several memory-reduction optimizations were done to reduce LLD's RSS
  footprint.
  (`D113813 <https://reviews.llvm.org/D113813>`_,
  `D113818 <https://reviews.llvm.org/D113818>`_)
* Symbol patterns from ``-[un]exported_symbols_list`` are now processed in
  parallel. (`D113820 <https://reviews.llvm.org/D113820>`_)
* ``.weak_def_can_be_hidden`` symbols can now be exported.
  (`D113167 <https://reviews.llvm.org/D113167>`_)
* ``-S`` -- to omit debug info -- is now handled.
  (`D112594 <https://reviews.llvm.org/D112594>`_)
* ``-v`` now writes to stderr instead of stdout.
  (`D113020 <https://reviews.llvm.org/D113020>`_)
* Private externs with GOT relocations are now marked as LOCAL in the indirect
  symbol table. This allows ``strip -x`` to remove more symbols.
  (`D111852 <https://reviews.llvm.org/D111852>`_)
* We no longer generate bogus addresses when ``__TEXT,__gcc_except_tab`` is
  renamed. (`D113582 <https://reviews.llvm.org/D113582>`_)
* Unreferenced weak dylib symbols no longer trigger fetches from an archive.
  (`D115092 <https://reviews.llvm.org/D115092>`_)
* ``$ld$hide`` symbols are now supported.
  (`D115775 <https://reviews.llvm.org/D115775>`_)
* Symbols imported via ``-weak_framework`` are now properly marked as weak refs.
  (`D114397 <https://reviews.llvm.org/D114397>`_)
* ``--warn-dylib-install-name`` and ``--no-warn-dylib-install-name`` were added
  to toggle LLD-specific warnings around the use of ``-install_name``.
  (`D113534 <https://reviews.llvm.org/D113534>`_)
* Passing both ``--icf=all`` and ``-no_deduplicate`` no longer results in a
  warning. (`D110672 <https://reviews.llvm.org/D110672>`_)
* ICF now deduplicates functions with (identical) unwind info too.
  (`D109946 <https://reviews.llvm.org/D109946>`_)
* We now support ordering sections based on call graph profile data.
  (`D112164 <https://reviews.llvm.org/D112164>`_)
* Map file output now proceeds in parallel with output of the binary.
  (`D117069 <https://reviews.llvm.org/D117069>`_)
* The map file now contains dead-stripped symbols too.
  (`D114737  <https://reviews.llvm.org/D114737>`_)
* Multiple TLV sections with different alignments are now handled properly.
  (`D116263 <https://reviews.llvm.org/D116263>`_)
* ``--start-lib`` and ``--end-lib`` are now supported.
  (`D116913  <https://reviews.llvm.org/D116913>`_)
* ``-noall_load`` is now supported.
  (`D117629 <https://reviews.llvm.org/D117629>`_)
* ``-add_empty_section`` is now supported.
  (`D117749 <https://reviews.llvm.org/D117749>`_)

WebAssembly Improvements
------------------------