gh-111758: Run UBSan in GitHub Actions

.github/workflows/build.yml

@@ -527,6 +527,14 @@ jobs:
       config_hash: ${{ needs.build-context.outputs.config-hash }}
       free-threading: ${{ matrix.free-threading }}
 
+  build-ubsan:
+    name: Undefined behavior sanitizer
+    needs: build-context
+    if: needs.build-context.outputs.run-tests == 'true'
+    uses: ./.github/workflows/reusable-ubsan.yml
+    with:
+      config_hash: ${{ needs.build-context.outputs.config-hash }}
+
   cross-build-linux:
     name: Cross build Linux
     runs-on: ubuntu-latest

.github/workflows/reusable-ubsan.yml

@@ -0,0 +1,74 @@
+name: Reusable Undefined Behavior Sanitizer
+
+on:
+  workflow_call:
+    inputs:
+      config_hash:
+        required: true
+        type: string
+
+env:
+  FORCE_COLOR: 1
+
+jobs:
+  build-ubsan-reusable:
+    name: 'Undefined behavior sanitizer'
+    runs-on: ubuntu-24.04
+    timeout-minutes: 60
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        persist-credentials: false
+    - name: Runner image version
+      run: echo "IMAGE_OS_VERSION=${ImageOS}-${ImageVersion}" >> "$GITHUB_ENV"
+    - name: Restore config.cache
+      uses: actions/cache@v4
+      with:
+        path: config.cache
+        key: ${{ github.job }}-${{ env.IMAGE_OS_VERSION }}-${{ inputs.config_hash }}
+    - name: Install dependencies
+      run: |
+        sudo ./.github/workflows/posix-deps-apt.sh
+        # Install clang-20
+        wget https://apt.llvm.org/llvm.sh
+        chmod +x llvm.sh
+        sudo ./llvm.sh 20
+    - name: UBSAN option setup
+      run: |
+        echo "UBSAN_OPTIONS=halt_on_error=1:abort_on_error=1:print_summary=1:print_stacktrace=1" >> "$GITHUB_ENV"
+        echo "CC=clang" >> "$GITHUB_ENV"
+        echo "CXX=clang++" >> "$GITHUB_ENV"
+    - name: Add ccache to PATH
+      run: |
+        echo "PATH=/usr/lib/ccache:$PATH" >> "$GITHUB_ENV"
+    - name: Configure ccache action
+      uses: hendrikmuhs/[email protected]
+      with:
+        save: ${{ github.event_name == 'push' }}
+        max-size: "200M"
+    - name: Configure CPython
+      run: >-
+        ./configure
+        --config-cache
+        --with-undefined-behavior-sanitizer
+        --with-pydebug
+    - name: Set up UBSAN log after configuration
+      run: |
+        echo "UBSAN_OPTIONS=${UBSAN_OPTIONS}:log_path=${GITHUB_WORKSPACE}/ubsan_log" >> "$GITHUB_ENV"
+    - name: Build CPython
+      run: make -j4
+    - name: Display build info
+      run: make pythoninfo
+    - name: Tests
+      run: ./python -m test -j4
+    - name: Display UBSAN logs
+      if: always()
+      run: find "${GITHUB_WORKSPACE}" -name 'ubsan_log.*' | xargs head -n 1000
+    - name: Archive UBSAN logs
+      if: always()
+      uses: actions/upload-artifact@v4
+      with:
+        name: >-
+          ubsan-logs
+        path: ubsan_log.*
+        if-no-files-found: ignore