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Magnus pushed to branch wip/mangoiv/aarch64-longjump at Glasgow Haskell Compiler / GHC

Commits:

e3df0947

by mangoiv at 2026-05-11T14:22:39+02:00

driver: enable -finter-module-far-jumps by default

this fixes a compatibility bug with certain binutils/gcc versions where
we were seeing jump offset overflow errors.
This commit can probably reverted if we stop supporting the problematic
binutils/gcc verions (2.44 and 14.2, respectively)

Reolves #26994

3 changed files:

+ changelog.d/inter-module-far-jumps-aarch64-default
compiler/GHC/Driver/DynFlags.hs
docs/users_guide/using-optimisation.rst

Changes:

changelog.d/inter-module-far-jumps-aarch64-default

 +section: driver
 +synopsis: enable -finter-module-far-jumps by default on aarch64
 +issues: #26994
 +mrs: !16016
 +description: Some binutils and gcc versions lead to jump offset erros on aarch64 profiled/dynamic ways. To mitigate this bug, we enable inter-module-far-jumps by default on this platform.

compiler/GHC/Driver/DynFlags.hs

@@ -1233,6 +1233,11 @@ defaultFlags settings
        Opt_SpecialiseIncoherents,
        Opt_WriteSelfRecompInfo
+     ]
 +    {- note(mangoiv):
 +     - on aarch64 profiled-dynamic, we are seeing jump offset overflow
 +     - errors on certain binutils versions. This can probably be deactivated
 +     - if we stop supporting binutils 2.44 / GCC 14.2 -}
 +    ++ [ Opt_InterModuleFarJumps | platformArch platform == ArchAArch64 ]
      ++ [f | (ns,f) <- optLevelFlags, 0 `elem` ns]
               -- The default -O0 options
@@ -1245,6 +1250,7 @@ defaultFlags settings
      ++ validHoleFitDefaults
      where platform = sTargetPlatform settings
 +          defaultWays = ways $ defaultDynFlags settings
  -- | These are the default settings for the display and sorting of valid hole
  --  fits in typed-hole error messages. See Note [Valid hole fits include ...]

docs/users_guide/using-optimisation.rst

@@ -732,7 +732,7 @@ as such you shouldn't need to set any of them explicitly. A flag
      :reverse: -fno-inter-module-far-jumps
      :category:
 -    :default: Off
 +    :default: on if the target platform is AArch64, off on all others
      This flag forces GHC to use far jumps instead of near jumps for all jumps
      which cross module boundries. This removes the need for jump islands/linker