.. _release-8-10-2:

Release notes for version 8.10.2
================================

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
----------

- A few important correctness fixes for the low-latency garbage collector.
  Users of :rts-flag:`--nonmoving-gc` are strongly encouraged to upgrade
  promptly.

- Fixes a bug in process creation on Windows (:ghc-ticket:`17926`).

- Works around a Linux kernel bug in the implementation of ``timerfd``\s
  (:ghc-ticket:`18033`).

- Fixes a few specialiser regressions (:ghc-ticket:`17810`,
  :ghc-ticket:`18120`) as well introduces a variety of miscellaneous
  specialiser improvements (:ghc-ticket:`16473`, :ghc-ticket:`17930`,
  :ghc-ticket:`17966`)

- Fixes a potential loss of sharing due to left operator sections
  (:ghc-ticket:`18151`).

- Fix bootstrapping of GHC with the LLVM backend on x86-64 (:ghc-ticket:`17920`).

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

Compiler
~~~~~~~~

 - A simplifier panic manifesting when DWARF debug information is enabled has
   been fixed (:ghc-ticket:`18162`, :ghc-ticket:`17619`)


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

 - The RTS now supports a flag, :rts-flag:`--copying-gc`, to counter-act the
   effect of :rts-flag:`--nonmoving-gc`.

 - The RTS now allows the user to specify a minimum time between idle GCs with
   the :rts-flag:`-Iw ⟨seconds⟩` flag. 8.10.1 contained a users guide reference
   to this flag but did not include the associated implementation.

 - A memory leak in the cost-center profiler has been fixed
   (:ghc-ticket:`18348`)

 - A potential integer overflow in the compact normal form import logic has
   been fixed (:ghc-ticket:`16992`)

 - We now workaround a Linux kernel bug in the implementation of timerfd which
   could previously result in program crashes (:ghc-ticket:`18033`)

 - The cost center profiler's JSON output backend now escapes backslashes
   correctly (:ghc-ticket:`18438`)

 - A variety of linker issues on ARM platforms have been fixed.


``base`` library
~~~~~~~~~~~~~~~~

- Fix a precision issue in the implementation of ``log1mexp``
  (:ghc-ticket:`17125`)


Build system
~~~~~~~~~~~~

 - Fix a bug wherein GHC would link against the non-thread-safe unique supply
   implementation when bootstrapping with an unregisterised compiler
   (:ghc-ticket:`18024`)

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.

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