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
@@ -40,26 +45,32 @@ 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: |
+          # s390x, ppc64el need Ubuntu Ports to be in the mirror list
+          sudo bash -c "echo 'https://ports.ubuntu.com/	priority:4' >> /etc/apt/apt-mirrors.txt"
+          # Add architecture
           sudo dpkg --add-architecture ${{ matrix.multiarch }}
           sudo apt update
+          # Install needed packages
           sudo apt install $(echo "libatomic1: zlib1g-dev:" | sed 's/:/:${{ matrix.multiarch }}/g')
       - uses: ./.github/workflows/setup
         with:
           toolchain_flags: "--host ${{ matrix.host_target }}"
 
       # 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 }}
-          echo "CC=${{ matrix.gcc_cross }}-gcc" >> $GITHUB_ENV
-          mkdir -p .cargo
-          echo '[target.${{ matrix.host_target }}]' >> .cargo/config.toml
-          echo 'linker = "${{ matrix.gcc_cross }}-gcc"' >> .cargo/config.toml
+          echo "CC=${{ matrix.gcc_cross }}-gcc" | tee -a $GITHUB_ENV
+          TARGET_UPPERCASE=$(echo ${{ matrix.host_target }} | tr '[:lower:]-' '[:upper:]_')
+          echo "CARGO_TARGET_${TARGET_UPPERCASE}_LINKER=${{ matrix.gcc_cross }}-gcc" | tee -a $GITHUB_ENV
 
       - name: Test Miri
         run: ./ci/ci.sh

ci/ci.sh

@@ -169,6 +169,9 @@ case $HOST_TARGET in
     # Host
     GC_STRESS=1 MIR_OPT=1 MANY_SEEDS=64 TEST_BENCH=1 CARGO_MIRI_ENV=1 run_tests
     ;;
+  s390x-unknown-linux-gnu)
+    # Build-only runner; this is quite slow due to emulation.
+    ;;
   aarch64-apple-darwin)
     # Host
     GC_STRESS=1 MIR_OPT=1 MANY_SEEDS=64 TEST_BENCH=1 CARGO_MIRI_ENV=1 run_tests