From f90244c970dbc053cee0fdb9b73eb98493d65fde Mon Sep 17 00:00:00 2001
From: sternenseemann <0rpkxez4ksa01gb3typccl0i@systemli.org>
Date: Mon, 17 May 2021 17:22:47 +0200
Subject: [PATCH 1/2] haskell.compiler.ghcHEAD: disable DWARF on non x86

The broken build of ghcHEAD on aarch64-linux results from rts/Libdw.c
not supporting that platform. Seemingly this particular file is only
relevant for DWARF support in GHC, so we disable that on unsupported
platforms.
---
 pkgs/development/compilers/ghc/head.nix | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/pkgs/development/compilers/ghc/head.nix b/pkgs/development/compilers/ghc/head.nix
index 60371ec5a1b..8a2a6397257 100644
--- a/pkgs/development/compilers/ghc/head.nix
+++ b/pkgs/development/compilers/ghc/head.nix
@@ -10,7 +10,9 @@
 , # GHC can be built with system libffi or a bundled one.
   libffi ? null
 
-, enableDwarf ? !stdenv.targetPlatform.isDarwin &&
+  # Libdw.c only supports x86_64, i686 and s390x
+, enableDwarf ? stdenv.targetPlatform.isx86 &&
+                !stdenv.targetPlatform.isDarwin &&
                 !stdenv.targetPlatform.isWindows
 , elfutils # for DWARF support
 
@@ -258,10 +260,7 @@ stdenv.mkDerivation (rec {
     homepage = "http://haskell.org/ghc";
     description = "The Glasgow Haskell Compiler";
     maintainers = with lib.maintainers; [ marcweber andres peti ];
-    inherit (ghc.meta) license;
-    # GHC-HEAD does not appear to compile on aarch64.
-    broken = stdenv.isAarch64;
-    platforms = builtins.filter (p: p != "aarch64-linux") ghc.meta.platforms;
+    inherit (ghc.meta) license platforms;
   };
 
   dontStrip = (targetPlatform.useAndroidPrebuilt || targetPlatform.isWasm);

From 29e029da1c568aacdbe94409314263f6bb568f71 Mon Sep 17 00:00:00 2001
From: sternenseemann <0rpkxez4ksa01gb3typccl0i@systemli.org>
Date: Mon, 17 May 2021 22:08:56 +0200
Subject: [PATCH 2/2] haskell.compiler.ghcHEAD: bootstrap using GHC 9.0

They use matching LLVM versions which should alleviate some warnings.
---
 pkgs/top-level/haskell-packages.nix | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pkgs/top-level/haskell-packages.nix b/pkgs/top-level/haskell-packages.nix
index af4125d6713..8bea40efe64 100644
--- a/pkgs/top-level/haskell-packages.nix
+++ b/pkgs/top-level/haskell-packages.nix
@@ -86,7 +86,7 @@ in {
       llvmPackages = pkgs.llvmPackages_10;
     };
     ghcHEAD = callPackage ../development/compilers/ghc/head.nix {
-      bootPkgs = packages.ghc8104; # no binary yet
+      bootPkgs = packages.ghc901; # no binary yet
       inherit (buildPackages.python3Packages) sphinx;
       buildLlvmPackages = buildPackages.llvmPackages_10;
       llvmPackages = pkgs.llvmPackages_10;