diff --git a/environments/hlrs/spack.yaml b/environments/hlrs/spack.yaml
index b020bdd..38eacec 100644
--- a/environments/hlrs/spack.yaml
+++ b/environments/hlrs/spack.yaml
@@ -1,10 +1,25 @@
-# This is a Spack Environment file.
-#
-# It describes a set of packages to be installed, along with
-# configuration settings.
+# This is a Spack Environment file fot he main HLRS software stack
 spack:
+#  definitions:
+#    core_compiler: [gcc@7.5]
+#    compilers: [gcc@13.2, cce@18.0]    
+  packages:
+#    all:
+#      compiler: [gcc@13.2, cce@18.0]
+ # force OS related libs to use core compiler
+    libdwarf:
+      require:
+      - '%gcc@7.5'
   # add package specs to the `specs` list
-  specs: []
+  specs:
+    - matrix:    # modules for low-level tools
+      - [libunwind, papi]
+      - ['%gcc@7.5']
+#      - [$%core_compiler]
+    - matrix:
+      - [mpip, extrae]
+      - [^mpi]
+      - ['%gcc@13.2', '%cce@18.0']  # mpip and extrae fail with implicit function declaration when using %cce -> is it actually using cce? 
   view: false
   concretizer:
     unify: when_possible