.. _release-8-10-3:

Release notes for version 8.10.3
================================

The significant changes to the various parts of the compiler are listed in the
following sections.

Like previous releases in the 8.10 series, the :ghc-flag:`LLVM backend <-fllvm>`
of this release is to be used with LLVM 9.

Highlights
----------

- Numerous stability improvements on Windows.

- GHC now has far more robust support for architectures with weak memory
  ordering guarantees.

- GHC can split up dynamic objects to mitigate the macOS ``RPATH`` size
  limitation when building large projects (:ghc-ticket:`14444`).

- Several significant correctness bugs in the low-latency garbage collector have
  been fixed.  Users of :rts-flag:`--nonmoving-gc` are strongly encouraged to
  upgrade promptly.


Full details
------------

Compiler
~~~~~~~~

* A compiler crash triggered by a ``SPECIALISE`` pragma on a binding with
  no unfolding has been fixed (:ghc-ticket:`18118`).

* GHC now supports a command-line flag, :ghc-flag:`-pgmc-supports-no-pie`,
  allowing the user to indicate that the C compiler supplied via
  :ghc-flag:`-pgmc ⟨cmd⟩` supports ``-no-pie``.

* A pair of flags, :ghc-flag:`-pgmlm ⟨cmd⟩` and :ghc-flag:`-optlm ⟨option⟩`,
  allowing the user to override the linker used to be join GHCi object files
  has been added.

* A regression in the treatment of the :ghc-flag:`-fbyte-code` flag has been
  fixed (:ghc-ticket:`18955`).

- A bug in the determination of source spans of post-qualified imports has been
  fixed :ghc-ticket:`19014`.


Runtime system
~~~~~~~~~~~~~~

- GHC is now more careful to respect address space limits set via `ulimit``
  when allocating its heap (:ghc-ticket:`18623`).

- Numerous fixes on Windows. These include a bug in stack allocation
  triggering Windows' stack verifier (:ghc-ticket:`18601`), various linker bugs
  (:ghc-ticket:`15808`, :ghc-ticket:`18991`), and a bug where ``libc`` may be
  called during image initialization resulting in undefined behavior
  (:ghc-ticket:`18548`).

- GHC's linker is now able to load macOS frameworks on Big Sur
  (:ghc-ticket:`18446`).

- A soundness bug affecting programs relying on heavy mutation of ``MVar``\ s
  has been fixed (:ghc-ticket:`18919`).

- The internal linker's code unloading logic has been reenabled and now tracks
  object file dependencies, fixing a soundness bug (:ghc-ticket:`16525`).

- A linker bug relying in the misalignment of loaded ``.rodata`` sections has
  been fixed.


Known issues
------------

- A long-standing bug (:ghc-ticket:`16893`) which can cause some applications
  of ``unsafeCoerce`` to segmentation fault is only partially fixed in this
  release. This release only avoids this issue in the uses of ``unsafeCoerce``
  in ``Data.Typeable.Internal``, which was the proximate cause of
  :ghc-ticket:`16893`.

  However, it is possible that this bug could manifest in user-code using
  ``unsafeCoerce`` to perform dynamic type checks. See the :ghc-ticket:`ticket
  <16893>` for details.

  We expect that this issue will be fixed in the next major release of GHC.

- A long-standing bug (:ghc-ticket:`17760`) where some uses of the ``touch#``
  primop can be dropped by the simplifier is present in this release. This bug
  will be fixed in GHC 9.0.1. In the meantime, see the :ghc-ticket:`ticket
  <17760>` for mitigations.


Included libraries
------------------

The package database provided with this distribution also contains a number of
packages other than GHC itself. See the changelogs provided with these packages
for further change information.

.. ghc-package-list::

    libraries/array/array.cabal:             Dependency of ``ghc`` library
    libraries/base/base.cabal:               Core library
    libraries/binary/binary.cabal:           Dependency of ``ghc`` library
    libraries/bytestring/bytestring.cabal:   Dependency of ``ghc`` library
    libraries/Cabal/Cabal/Cabal.cabal:       Dependency of ``ghc-pkg`` utility
    libraries/containers/containers/containers.cabal:   Dependency of ``ghc`` library
    libraries/deepseq/deepseq.cabal:         Dependency of ``ghc`` library
    libraries/directory/directory.cabal:     Dependency of ``ghc`` library
    libraries/exceptions/exceptions.cabal:   Dependency of ``haskeline`` library
    libraries/filepath/filepath.cabal:       Dependency of ``ghc`` library
    compiler/ghc.cabal:                      The compiler itself
    libraries/ghci/ghci.cabal:               The REPL interface
    libraries/ghc-boot/ghc-boot.cabal:       Internal compiler library
    libraries/ghc-boot-th/ghc-boot-th.cabal: Internal compiler library
    libraries/ghc-compact/ghc-compact.cabal: Core library
    libraries/ghc-heap/ghc-heap.cabal:       GHC heap-walking library
    libraries/ghc-prim/ghc-prim.cabal:       Core library
    libraries/haskeline/haskeline.cabal:     Dependency of ``ghci`` executable
    libraries/hpc/hpc.cabal:                 Dependency of ``hpc`` executable
    libraries/integer-gmp/integer-gmp.cabal: Core library
    libraries/libiserv/libiserv.cabal:       Internal compiler library
    libraries/mtl/mtl.cabal:                 Dependency of ``Cabal`` library
    libraries/parsec/parsec.cabal:           Dependency of ``Cabal`` library
    libraries/pretty/pretty.cabal:           Dependency of ``ghc`` library
    libraries/process/process.cabal:         Dependency of ``ghc`` library
    libraries/stm/stm.cabal:                 Dependency of ``haskeline`` library
    libraries/template-haskell/template-haskell.cabal:     Core library
    libraries/terminfo/terminfo.cabal:       Dependency of ``haskeline`` library
    libraries/text/text.cabal:               Dependency of ``Cabal`` library
    libraries/time/time.cabal:               Dependency of ``ghc`` library
    libraries/transformers/transformers.cabal: Dependency of ``ghc`` library
    libraries/unix/unix.cabal:               Dependency of ``ghc`` library
    libraries/Win32/Win32.cabal:             Dependency of ``ghc`` library
    libraries/xhtml/xhtml.cabal:             Dependency of ``haddock`` executable