diff --git a/flake.nix b/flake.nix
index be80cef..0eb8860 100644
--- a/flake.nix
+++ b/flake.nix
@@ -13,77 +13,12 @@
 
   outputs = { self, genode-depot, nixpkgs, nixpkgsUpstream }:
     let
-      mkOutput = { system, localSystem, crossSystem }:
-        let thisSystem = builtins.getAttr system;
-        in rec {
-
-          lib = (nixpkgs.lib) // (import ./lib {
-            inherit system localSystem crossSystem;
-            inherit apps nixpkgs genode-depot;
-            genodepkgs = self;
-          });
-
-          legacyPackages = thisSystem nixpkgs.legacyPackages;
-          # pass thru Nixpkgs
-
-          packages = import ./packages {
-            inherit system legacyPackages apps;
-            localPackages = nixpkgsUpstream.legacyPackages.${localSystem};
-            depot = thisSystem genode-depot.packages;
-          };
-
-          devShell = let
-            pkgs = nixpkgsUpstream.legacyPackages.x86_64-linux;
-            fhs = pkgs.buildFHSUserEnv {
-              name = "genode-env";
-              targetPkgs = pkgs:
-                (with pkgs; [
-                  binutils
-                  bison
-                  expect
-                  flex
-                  git
-                  glibc.dev
-                  gnumake
-                  libxml2
-                  qemu
-                  tcl
-                  which
-                  xorriso
-                ]);
-              runScript = "bash";
-              extraBuildCommands = let
-                toolchain = pkgs.fetchzip {
-                  url = "file:///" + packages.genodeSources.toolchain.src;
-                  hash = "sha256-26rPvLUPEJm40zLSqTquwuFTJ1idTB0T4VXgaHRN+4o=";
-                };
-              in "ln -s ${toolchain}/local usr/local";
-            };
-          in pkgs.stdenv.mkDerivation {
-            name = "genode-fhs-shell";
-            nativeBuildInputs = [ fhs ];
-            shellHook = "exec genode-env";
-          };
-
-          apps = import ./apps {
-            self = self.apps.${localSystem};
-            nixpkgs = legacyPackages;
-            nixpkgsLocal = nixpkgsUpstream.legacyPackages.${localSystem};
-            inherit packages;
-          };
-
-          checks = import ./tests {
-            inherit system localSystem crossSystem;
-            inherit self nixpkgs genode-depot;
-            inherit apps lib;
-            genodepkgs = thisSystem self.packages;
-          };
-
-        };
-
       localSystems = [ "x86_64-linux" ];
       crossSystems = [ "x86_64-genode" ];
 
+      forAllLocalSystems = f:
+        nixpkgs.lib.genAttrs localSystems (system: f system);
+
       forAllCrossSystems = f:
         with builtins;
         let
@@ -97,26 +32,102 @@
           attrSet = listToAttrs list;
         in attrSet;
 
-      finalize = outputs:
-        with builtins;
+      forAllSystems = f:
+        (forAllCrossSystems f) // (forAllLocalSystems (system:
+          f {
+            inherit system;
+            localSystem = system;
+            crossSystem = system;
+          }));
+
+      nixpkgsFor = forAllSystems ({ system, localSystem, crossSystem }:
+        if localSystem == crossSystem then
+          import nixpkgsUpstream {
+            inherit system;
+            overlays = [ self.overlay ];
+          }
+        else
+          import nixpkgs {
+            inherit localSystem crossSystem;
+            config.allowUnsupportedSystem = true;
+            overlays = [ self.overlay ];
+          });
+
+    in rec {
+
+      overlay = import ./overlay;
+
+      lib = forAllCrossSystems ({ system, localSystem, crossSystem }:
+        (nixpkgs.lib) // (import ./lib {
+          inherit system localSystem crossSystem;
+          apps = self.apps.${system};
+          nixpkgs = nixpkgsFor.${system};
+          genode-depot = genode-depot.packages.${system};
+          genodepkgs = self;
+        }));
+
+      legacyPackages = forAllSystems
+        ({ system, localSystem, crossSystem }: nixpkgsFor.${system});
+      # pass thru Nixpkgs
+
+      packages = forAllCrossSystems ({ system, localSystem, crossSystem }:
+        import ./packages {
+          inherit system;
+          legacyPackages = self.legacyPackages.${system};
+          apps = self.apps.${system};
+          localPackages = nixpkgsUpstream.legacyPackages.${localSystem};
+          depot = genode-depot.packages.${system};
+        });
+
+      devShell = forAllLocalSystems (system:
         let
-          outputs' = outputs // {
-            x86_64-linux = getAttr "x86_64-linux-x86_64-genode" outputs;
+          pkgs = nixpkgsFor.${system};
+          fhs = pkgs.buildFHSUserEnv {
+            name = "genode-env";
+            targetPkgs = pkgs:
+              (with pkgs; [
+                binutils
+                bison
+                expect
+                flex
+                git
+                glibc.dev
+                gnumake
+                libxml2
+                qemu
+                tcl
+                which
+                xorriso
+              ]);
+            runScript = "bash";
+            extraBuildCommands = let
+              toolchain = pkgs.fetchzip {
+                url = "file://${packages.x86_64-linux-x86_64-genode.genodeSources.toolchain.src}";
+                hash = "sha256-26rPvLUPEJm40zLSqTquwuFTJ1idTB0T4VXgaHRN+4o=";
+              };
+            in "ln -s ${toolchain}/local usr/local";
           };
-          systems = attrNames outputs';
-          outputAttrs = attrNames (head (attrValues outputs'));
+        in pkgs.stdenv.mkDerivation {
+          name = "genode-fhs-shell";
+          nativeBuildInputs = [ fhs ];
+          shellHook = "exec genode-env";
+        });
 
-          list = map (attr: {
-            name = attr;
-            value = listToAttrs (map (system: {
-              name = system;
-              value = getAttr attr (getAttr system outputs');
-            }) systems);
-          }) outputAttrs;
+      apps = forAllCrossSystems ({ system, localSystem, crossSystem }:
+        import ./apps {
+          self = self.apps.${system};
+          nixpkgs = self.legacyPackages.${system};
+          nixpkgsLocal = nixpkgsFor.${localSystem};
+          packages = self.packages.${system};
+        });
 
-        in listToAttrs list;
-
-      final = finalize (forAllCrossSystems mkOutput);
-
-    in final;
+      checks = forAllCrossSystems ({ system, localSystem, crossSystem }:
+        import ./tests {
+          inherit system localSystem crossSystem;
+          inherit self nixpkgs genode-depot;
+          apps = self.apps.${system};
+          lib = self.lib.${system};
+          genodepkgs = self.packages.${system};
+        });
+    };
 }
diff --git a/lib/default.nix b/lib/default.nix
index 9fc69a3..725a58e 100644
--- a/lib/default.nix
+++ b/lib/default.nix
@@ -22,7 +22,7 @@ in {
     '';
 
   mergeManifests = inputs:
-    nixpkgs.legacyPackages.${localSystem}.writeTextFile {
+    nixpkgs.writeTextFile {
       name = "manifest.dhall";
       text = with builtins;
         let
diff --git a/overlay/default.nix b/overlay/default.nix
new file mode 100644
index 0000000..633b687
--- /dev/null
+++ b/overlay/default.nix
@@ -0,0 +1,3 @@
+final: prev: {
+
+}
diff --git a/packages/default.nix b/packages/default.nix
index 1327e4e..6a3444a 100644
--- a/packages/default.nix
+++ b/packages/default.nix
@@ -33,9 +33,11 @@ let
       "echo REPOSITORIES += ${genodeWorld} >> build/etc/build.conf";
   });
 
+  genodeTupRules = ./Tuprules.tup;
+
 in rec {
   inherit (legacyPackages) stdenv;
-  inherit (genodeLabs) genodeSources;
+  inherit (genodeLabs) genodeSources; # toolchain;
 
   base-hw-pc = buildUpstream {
     name = "base-hw-pc";
@@ -111,5 +113,4 @@ in rec {
   sotest-producer = callPackage' ./sotest-producer { };
 
   stdcxx = callPackage' ./stdcxx { };
-
 }
diff --git a/tests/driver-hw.nix b/tests/driver-hw.nix
index dd298e7..182093d 100644
--- a/tests/driver-hw.nix
+++ b/tests/driver-hw.nix
@@ -46,7 +46,6 @@ let
       testConfig' = "${./test-wrapper.dhall} ${testConfig} (toMap ${manifest})";
       testEnv' = {
         DHALL_GENODE = "${testPkgs.dhallGenode}/source.dhall";
-        MANIFEST = manifest;
         XDG_CACHE_HOME = "/tmp";
       } // testEnv;
 
diff --git a/tests/driver-linux.nix b/tests/driver-linux.nix
index 36228e1..6d7e4b3 100644
--- a/tests/driver-linux.nix
+++ b/tests/driver-linux.nix
@@ -43,7 +43,6 @@ let
       testConfig' = "${./test-wrapper.dhall} ${testConfig} (toMap ${manifest})";
       env' = {
         DHALL_GENODE = "${testPkgs.dhallGenode}/source.dhall";
-        MANIFEST = manifest;
         XDG_CACHE_HOME = "/tmp";
       } // env;
 
diff --git a/tests/driver-nova.nix b/tests/driver-nova.nix
index 0aa3b9f..9662bd8 100644
--- a/tests/driver-nova.nix
+++ b/tests/driver-nova.nix
@@ -46,7 +46,6 @@ let
       testConfig' = "${./test-wrapper.dhall} ${testConfig} (toMap ${manifest})";
       testEnv' = {
         DHALL_GENODE = "${testPkgs.dhallGenode}/source.dhall";
-        MANIFEST = manifest;
         XDG_CACHE_HOME = "/tmp";
       } // testEnv;