diff --git a/builder/hspkg-builder.nix b/builder/hspkg-builder.nix
index ffa1a9da52..d8d5ced2fb 100644
--- a/builder/hspkg-builder.nix
+++ b/builder/hspkg-builder.nix
@@ -23,7 +23,14 @@ assert (if ghc.isHaskellNixCompiler or false then true
     + pkgs.lib.optionalString (name != null) (" for " + name)));
 
 let
-  cabalFile = if revision == null || revision == 0 then null else
+  # Some packages bundled with GHC are not the same as they are in hackage.
+  bundledSrc = {
+      # These are problematic because the hackage versions will not install and are part of LTS.
+      "ghc902/stm-2.5.0.0" = "/libraries/stm";
+      "ghc902/filepath-1.4.2.1" = "/libraries/filepath";
+    }."${compiler-nix-name}/${name}" or null;
+  src = if bundledSrc == null then pkg.src else ghc.configured-src + bundledSrc;
+  cabalFile = if revision == null || revision == 0 || bundledSrc != null then null else
     fetchurl {
       name = "${name}-${toString revision}.cabal";
       url = "https://hackage.haskell.org/package/${name}/revision/${toString revision}.cabal";
@@ -94,7 +101,8 @@ let
       synopsis = null;
       license = "MIT";
     };
-    src = null; cleanSrc = buildPackages.runCommand "default-Setup-src" {} ''
+    src = null;
+    cleanSrc = buildPackages.runCommand "default-Setup-src" {} ''
       mkdir $out
       cat ${defaultSetupSrc} > $out/Setup.hs
     '';
diff --git a/builder/make-config-files.nix b/builder/make-config-files.nix
index 94650bffa9..928f91722b 100644
--- a/builder/make-config-files.nix
+++ b/builder/make-config-files.nix
@@ -3,6 +3,10 @@
 { identifier, component, fullName, flags ? {}, needsProfiling ? false, enableDWARF ? false, chooseDrv ? drv: drv, nonReinstallablePkgs ? defaults.nonReinstallablePkgs }:
 
 let
+  # Sort and remove duplicates from nonReinstallablePkgs.
+  # That way changes to the order of nonReinstallablePkgs does not require rebuilds.
+  nonReinstallablePkgs' = __attrNames (lib.genAttrs nonReinstallablePkgs (x: x));
+
   ghc = if enableDWARF then defaults.ghc.dwarf else defaults.ghc;
 
   flagsAndConfig = field: xs: lib.optionalString (xs != []) ''
@@ -93,7 +97,7 @@ let
     ghc=${ghc}
     ${ # Copy over the nonReinstallablePkgs from the global package db.
     ''
-      for p in ${lib.concatStringsSep " " nonReinstallablePkgs}; do
+      for p in ${lib.concatStringsSep " " nonReinstallablePkgs'}; do
         find $ghc/lib/${ghc.name}/package.conf.d -name $p'*.conf' -exec cp -f {} $out/${packageCfgDir} \;
       done
     ''}
@@ -152,13 +156,13 @@ let
         cat $p/exactDep/cabal.config >> $out/cabal.config
       ''}
     done
-    for p in ${lib.concatStringsSep " " (lib.remove "ghc" nonReinstallablePkgs)}; do
+    for p in ${lib.concatStringsSep " " (lib.remove "ghc" nonReinstallablePkgs')}; do
       if [ -e $ghc/envDeps/$p ]; then
         cat $ghc/envDeps/$p >> $out/ghc-environment
       fi
     done
   '' + lib.optionalString component.doExactConfig ''
-    for p in ${lib.concatStringsSep " " nonReinstallablePkgs}; do
+    for p in ${lib.concatStringsSep " " nonReinstallablePkgs'}; do
       if [ -e $ghc/exactDeps/$p ]; then
         cat $ghc/exactDeps/$p/configure-flags >> $out/configure-flags
         cat $ghc/exactDeps/$p/cabal.config >> $out/cabal.config
diff --git a/ci.nix b/ci.nix
index dff87df1c9..8283772409 100644
--- a/ci.nix
+++ b/ci.nix
@@ -44,10 +44,16 @@
       ghc810420210212 = false;
     });
   systems = nixpkgsName: nixpkgs: compiler-nix-name: nixpkgs.lib.genAttrs (
-    nixpkgs.lib.filter (v: v != "aarch64-darwin" || (
-      # aarch64-darwin requires ghc 8.10.7 and does not work on older nixpkgs
-         !__elem compiler-nix-name ["ghc865" "ghc884" "ghc8104" "ghc810420210212" "ghc8105" "ghc8106" "ghc901"]
-      && !__elem nixpkgsName ["R2105"])) supportedSystems) (v: v);
+    nixpkgs.lib.filter (v:
+        # We have less x86_64-darwin build capacity so build fewer GhC versions and no R2105
+        (v != "x86_64-darwin" || (
+           !__elem compiler-nix-name ["ghc8104" "ghc810420210212" "ghc8105" "ghc8106" "ghc901" "ghc921"]
+        && !__elem nixpkgsName ["R2105"]))
+      &&
+        # aarch64-darwin requires ghc 8.10.7 and does not work on older nixpkgs
+        (v != "aarch64-darwin" || (
+           !__elem compiler-nix-name ["ghc865" "ghc884" "ghc8104" "ghc810420210212" "ghc8105" "ghc8106" "ghc901" "ghc921"]
+        && !__elem nixpkgsName ["R2105"]))) supportedSystems) (v: v);
   crossSystems = nixpkgsName: nixpkgs: compiler-nix-name: system:
     # We need to use the actual nixpkgs version we're working with here, since the values
     # of 'lib.systems.examples' are not understood between all versions
diff --git a/compiler/ghc/default.nix b/compiler/ghc/default.nix
index e18a88a487..7c15b51eb6 100644
--- a/compiler/ghc/default.nix
+++ b/compiler/ghc/default.nix
@@ -288,7 +288,7 @@ stdenv.mkDerivation (rec {
         $i
     done
 
-    # Save generated files for needed when building ghcjs
+    # Save generated files for needed when building ghc and ghcjs
     mkdir -p $generated/includes/dist-derivedconstants/header
     cp includes/dist-derivedconstants/header/GHCConstantsHaskell*.hs \
        $generated/includes/dist-derivedconstants/header
@@ -299,6 +299,15 @@ stdenv.mkDerivation (rec {
     fi
     mkdir -p $generated/compiler/stage2/build
     cp compiler/stage2/build/Config.hs $generated/compiler/stage2/build || true
+    if [[ -f compiler/stage2/build/GHC/Platform/Constants.hs ]]; then
+      mkdir -p $generated/compiler/stage2/build/GHC/Platform
+      cp compiler/stage2/build/GHC/Platform/Constants.hs $generated/compiler/stage2/build/GHC/Platform
+    fi
+    if [[ -f compiler/stage2/build/GHC/Settings/Config.hs ]]; then
+      mkdir -p $generated/compiler/stage2/build/GHC/Settings
+      cp compiler/stage2/build/GHC/Settings/Config.hs $generated/compiler/stage2/build/GHC/Settings
+    fi
+    cp compiler/stage2/build/*.hs-incl $generated/compiler/stage2/build || true
     mkdir -p $generated/rts/build
     cp rts/build/config.hs-incl $generated/rts/build || true
 
diff --git a/modules/component-driver.nix b/modules/component-driver.nix
index 90a257b3f8..34af70a98e 100644
--- a/modules/component-driver.nix
+++ b/modules/component-driver.nix
@@ -54,7 +54,7 @@ in
   # without reinstallable-lib:ghc, this is significantly larger.
 
   config.nonReinstallablePkgs =
-    [ "rts" "ghc-heap" "ghc-prim" "integer-gmp" "integer-simple" "base"
+    [ "rts" "ghc-prim" "integer-gmp" "integer-simple" "base"
       "deepseq" "array" "ghc-boot-th" "pretty" "template-haskell"
       # ghcjs custom packages
       "ghcjs-prim" "ghcjs-th"
@@ -72,6 +72,9 @@ in
       "mtl" "parsec" "process" "text" "time" "transformers"
       "unix" "xhtml" "terminfo"
       # "stm"
+    ]
+    ++ lib.optionals (!config.reinstallableLibGhc || __elem config.compiler.nix-name ["ghc865"]) [
+      "ghc-heap"
     ];
 
   options.bootPkgs = lib.mkOption {
@@ -80,7 +83,6 @@ in
 
   config.bootPkgs =  [
       "rts" "ghc-boot-th"
-      "ghc-heap" # since ghc 8.6.
       "ghcjs-prim"
    ] ++ lib.optional (!config.reinstallableLibGhc) "ghc"
     ++ lib.optionals (
diff --git a/overlays/ghc-packages.nix b/overlays/ghc-packages.nix
index 20bc3bf61c..94ac2f2a98 100644
--- a/overlays/ghc-packages.nix
+++ b/overlays/ghc-packages.nix
@@ -106,24 +106,42 @@ let
 in rec {
   ghc-boot-packages-src-and-nix = builtins.mapAttrs
     (ghcName: ghc: builtins.mapAttrs
-      (pkgName: dir: rec {
+      (pkgName: subDir: rec {
         src =
           # Add in the generated files needed by ghc-boot
-          if dir == "libraries/ghc-boot"
-            then final.evalPackages.runCommand "ghc-boot-src" {} ''
-              cp -Lr ${ghc.passthru.configured-src}/${dir} $out
-              chmod -R +w $out
-              cp -Lr ${ghc.generated}/libraries/ghc-boot/dist-install/build/GHC/* $out/GHC
+          if subDir == "libraries/ghc-boot"
+            then final.evalPackages.runCommand "ghc-boot-src" { nativeBuildInputs = [final.evalPackages.xorg.lndir]; } ''
+              mkdir $out
+              lndir -silent ${ghc.passthru.configured-src}/${subDir} $out
+              lndir -silent ${ghc.generated}/libraries/ghc-boot/dist-install/build/GHC $out/GHC
             ''
-            else if dir == "compiler"
-            then final.evalPackages.runCommand "ghc-src" {} ''
-              cp -Lr ${ghc.passthru.configured-src}/${dir} $out
-              chmod -R +w $out
-              if [[ -f ${ghc.generated}/compiler/stage2/build/Config.hs ]]; then
-                cp -Lr ${ghc.generated}/compiler/stage2/build/Config.hs $out
-              fi
-            ''
-            else "${ghc.passthru.configured-src}/${dir}";
+          else if subDir == "compiler"
+            then final.haskell-nix.haskellLib.cleanSourceWith {
+              src = final.evalPackages.runCommand "ghc-src" { nativeBuildInputs = [final.evalPackages.xorg.lndir]; } ''
+                mkdir $out
+                lndir -silent ${ghc.passthru.configured-src} $out
+                if [[ -f ${ghc.generated}/libraries/ghc-boot/dist-install/build/GHC/Version.hs ]]; then
+                  ln -s ${ghc.generated}/libraries/ghc-boot/dist-install/build/GHC/Version.hs $out/libraries/ghc-boot/GHC
+                fi
+                if [[ -f ${ghc.generated}/libraries/ghc-boot/dist-install/build/GHC/Platform/Host.hs ]]; then
+                  ln -s ${ghc.generated}/libraries/ghc-boot/dist-install/build/GHC/Platform/Host.hs $out/libraries/ghc-boot/GHC/Platform
+                fi
+                if [[ -f ${ghc.generated}/compiler/stage2/build/Config.hs ]]; then
+                  ln -s ${ghc.generated}/compiler/stage2/build/Config.hs $out/compiler
+                fi
+                if [[ -f ${ghc.generated}/compiler/stage2/build/GHC/Platform/Constants.hs ]]; then
+                  ln -s ${ghc.generated}/compiler/stage2/build/GHC/Platform/Constants.hs $out/compiler/GHC/Platform
+                fi
+                if [[ -f ${ghc.generated}/compiler/stage2/build/GHC/Settings/Config.hs ]]; then
+                  ln -s ${ghc.generated}/compiler/stage2/build/GHC/Settings/Config.hs $out/compiler/GHC/Settings
+                fi
+                ln -s ${ghc.generated}/includes/dist-derivedconstants/header/* $out/compiler
+                ln -s ${ghc.generated}/compiler/stage2/build/*.hs-incl $out/compiler
+              '';
+              inherit subDir;
+              includeSiblings = true;
+            }
+            else "${ghc.passthru.configured-src}/${subDir}";
         nix = callCabal2Nix ghcName "${ghcName}-${pkgName}" src;
       }) (ghc-extra-pkgs ghc.version))
     final.buildPackages.haskell-nix.compiler;
diff --git a/test/setup-deps/default.nix b/test/setup-deps/default.nix
index 3d23cd0a65..c2f0be5f5b 100644
--- a/test/setup-deps/default.nix
+++ b/test/setup-deps/default.nix
@@ -17,15 +17,13 @@ let
 
   meta = {
     platforms = platforms.unix;
-    # Building reinstallable lib GHC is broken on 8.10, and we require lib ghc so this won't work with cross-compiling.
+    # We require lib ghc so this won't work with cross-compiling.
     # Moreover, even building the plan doesn't seem to work in these circumstances.
-    disabled = stdenv.buildPlatform != stdenv.hostPlatform || stdenv.hostPlatform.isMusl || __elem compiler-nix-name ["ghc8101" "ghc8102" "ghc8103" "ghc8104" "ghc8105" "ghc8106" "ghc8107" "ghc810420210212"];
+    disabled = stdenv.buildPlatform != stdenv.hostPlatform || stdenv.hostPlatform.isMusl;
   };
 in 
 
 recurseIntoAttrs ({
-  meta.disabled = __elem compiler-nix-name ["ghc901" "ghc902" "ghc921" "ghc922"];
-
   ifdInputs = {
     plan-nix = addMetaAttrs meta project.plan-nix;
   };
diff --git a/test/setup-deps/pkg/Setup.hs b/test/setup-deps/pkg/Setup.hs
index 81aebe61a8..69c4f08c20 100644
--- a/test/setup-deps/pkg/Setup.hs
+++ b/test/setup-deps/pkg/Setup.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 import Distribution.Simple
 
 -- https://github.com/snoyberg/conduit#readme
@@ -7,7 +8,11 @@ import System.Directory (removeFile)
 
 -- Make sure Cabal and ghc were included
 import Distribution.Package ()
+#if MIN_VERSION_ghc(9,0,0)
+import GHC.SysTools.Ar ()
+#else
 import Ar ()
+#endif
 
 example = do
     -- Pure operations: summing numbers.