5. 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 LLVM backend of this release is to be used with LLVM 9.

5.1. 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 (#14444).

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

5.2. Full details

5.2.1. Compiler

  • A compiler crash triggered by a SPECIALISE pragma on a binding with no unfolding has been fixed (#18118).

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

  • A pair of flags, -pgmlm ⟨cmd⟩ and -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 -fbyte-code flag has been fixed (#18955).

  • A bug in the determination of source spans of post-qualified imports has been fixed #19014.

5.2.2. Runtime system

  • GHC is now more careful to respect address space limits set via ulimit` when allocating its heap (#18623).

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

  • GHC’s linker is now able to load macOS frameworks on Big Sur (#18446).

  • A soundness bug affecting programs relying on heavy mutation of MVars has been fixed (#18919).

  • The internal linker’s code unloading logic has been reenabled and now tracks object file dependencies, fixing a soundness bug (#16525).

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

5.3. Known issues

  • A long-standing bug (#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 #16893.

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

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

  • A long-standing bug (#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 ticket for mitigations.

5.4. 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.

Package Version Reason for inclusion

ghc

 8.10.4

The compiler itself

Cabal

 3.2.1.0

Dependency of ghc-pkg utility

Win32

 2.6.1.0

Dependency of ghc library

array

 0.5.4.0

Dependency of ghc library

base

 4.14.1.0

Core library

binary

 0.8.8.0

Dependency of ghc library

bytestring

 0.10.12.0

Dependency of ghc library

containers

 0.6.2.1

Dependency of ghc library

deepseq

 1.4.4.0

Dependency of ghc library

directory

 1.3.6.0

Dependency of ghc library

exceptions

 0.10.4

Dependency of haskeline library

filepath

 1.4.2.1

Dependency of ghc library

ghc-boot-th

 8.10.4

Internal compiler library

ghc-boot

 8.10.4

Internal compiler library

ghc-compact

 0.1.0.0

Core library

ghc-heap

 8.10.4

GHC heap-walking library

ghc-prim

 0.6.1

Core library

ghci

 8.10.4

The REPL interface

haskeline

 0.8.0.1

Dependency of ghci executable

hpc

 0.6.1.0

Dependency of hpc executable

integer-gmp

 1.0.3.0

Core library

libiserv

 8.10.4

Internal compiler library

mtl

 2.2.2

Dependency of Cabal library

parsec

 3.1.14.0

Dependency of Cabal library

pretty

 1.1.3.6

Dependency of ghc library

process

 1.6.9.0

Dependency of ghc library

stm

 2.5.0.0

Dependency of haskeline library

template-haskell

 2.16.0.0

Core library

terminfo

 0.4.1.4

Dependency of haskeline library

text

 1.2.4.1

Dependency of Cabal library

time

 1.9.3

Dependency of ghc library

transformers

 0.5.6.2

Dependency of ghc library

unix

 2.7.2.2

Dependency of ghc library

xhtml

 3000.2.2.1

Dependency of haddock executable