let's see if we can just use the qemu-user stuff...

Author: RalfJung

.github/workflows/ci.yml

@@ -31,6 +31,11 @@ jobs:
             os: ubuntu-24.04-arm
             multiarch: armhf
             gcc_cross: arm-linux-gnueabihf
+          - host_target: s390x-unknown-linux-gnu
+            os: ubuntu-latest
+            multiarch: s390x
+            gcc_cross: s390x-linux-gnu
+            qemu: true
           - host_target: aarch64-apple-darwin
             os: macos-latest
           - host_target: i686-pc-windows-msvc
@@ -40,9 +45,23 @@ jobs:
       HOST_TARGET: ${{ matrix.host_target }}
     steps:
       - uses: actions/checkout@v4
-      - name: multiarch setup
+      - name: install qemu
+        if: ${{ matrix.qemu }}
+        run: sudo apt install qemu-user qemu-user-binfmt
+      - name: install multiarch
         if: ${{ matrix.multiarch != '' }}
         run: |
+          # Some multiarch architectures seem to be missing from security.ubuntu.com... so try to disable that.
+          echo "Sources before patch:"
+          cat /etc/apt/sources.list.d/*
+          echo
+          sudo sed -i -E 's/(Suites:.*security$)/\1\nArchitectures:/' /etc/apt/sources.list.d/ubuntu.sources
+          sudo bash -c "echo 'https://ports.ubuntu.com/	priority:4' >> /etc/apt/apt-mirrors.txt"
+          echo "Sources after patch:"
+          cat /etc/apt/sources.list.d/*
+          echo
+          cat /etc/apt/apt-mirrors.txt
+          # Add architecture and install base packages.
           sudo dpkg --add-architecture ${{ matrix.multiarch }}
           sudo apt update
           sudo apt install $(echo "libatomic1: zlib1g-dev:" | sed 's/:/:${{ matrix.multiarch }}/g')
@@ -52,7 +71,7 @@ jobs:
 
       # We set up the cross-compiler *after* the basic setup as setting CC would otherwise
       # cause confusion.
-      - name: gcc-cross setup
+      - name: install gcc-cross
         if: ${{ matrix.gcc_cross != '' }}
         run: |
           sudo apt install gcc-${{ matrix.gcc_cross }}