feat: Add s390x architecture support via cross-compilation

.semaphore/semaphore.yml

@@ -227,6 +227,36 @@ blocks:
             - packaging/tools/build-release-artifacts.sh --disable-gssapi alpine:3.16.9 artifacts/librdkafka.tgz
 
 
+  - name: 'Linux s390x: release artifact cross-compilation builds'
+    dependencies: []
+    run:
+      # TODO: Remove branch condition after testing - only keep tag condition for production
+      when: "tag =~ '^v[0-9]\\.' or branch = 'feat/s390x-cross-compilation'"
+    task:
+      agent:
+        machine:
+          type: s1-prod-ubuntu24-04-amd64-1
+      prologue:
+        commands:
+          # Setup QEMU for s390x emulation (for verification only)
+          - docker run --rm --privileged multiarch/qemu-user-static --reset -p yes
+          # Setup buildx for cross-compilation
+          - docker buildx create --name s390x-builder --use || docker buildx use s390x-builder
+          - docker buildx inspect --bootstrap
+          - '[[ -z $DOCKERHUB_APIKEY ]] || docker login --username $DOCKERHUB_USER --password $DOCKERHUB_APIKEY'
+      epilogue:
+        commands:
+          - '[[ -z $SEMAPHORE_GIT_TAG_NAME ]] || artifact push workflow artifacts/ --destination artifacts/${ARTIFACT_KEY}/'
+      jobs:
+        # TODO: For testing only - running single job. Add back both variants for production.
+        - name: 'Build: cross-compiled s390x (test)'
+          env_vars:
+            - name: ARTIFACT_KEY
+              value: p-librdkafka__plat-linux__dist-ubuntu__arch-s390x__lnk-all
+          commands:
+            - packaging/tools/build-s390x-cross.sh artifacts/librdkafka.tgz
+
+
   - name: 'Windows x64: MinGW-w64'
     dependencies: []
     run:
@@ -313,6 +343,7 @@ blocks:
       - 'OSX x64'
       - 'Linux x64: release artifact docker builds'
       - 'Linux arm64: release artifact docker builds'
+      - 'Linux s390x: release artifact cross-compilation builds'
       - 'Windows x64: MinGW-w64'
       - 'Windows x64: Windows SDK 10.0 / MSVC v142 / VS 2019'
     run:

packaging/tools/Dockerfile.s390x

@@ -0,0 +1,80 @@
+# syntax=docker/dockerfile:1
+#
+# Cross-compilation Dockerfile for building librdkafka for s390x architecture
+# Uses BuildKit cross-compilation with tonistiigi/xx toolkit to avoid QEMU slowness
+#
+
+ARG BASE_IMAGE=ubuntu:24.04
+
+# Cross-compilation helpers
+FROM --platform=$BUILDPLATFORM tonistiigi/xx:1.5.0 AS xx
+
+# Build stage runs on native platform (AMD64), outputs s390x binaries
+FROM --platform=$BUILDPLATFORM ${BASE_IMAGE} AS builder
+
+COPY --from=xx / /
+
+ARG TARGETPLATFORM
+ARG LIBRDKAFKA_VERSION
+
+# Install native build tools and cross-compilation toolchain
+RUN NEEDRESTART_MODE=a apt-get update && apt-get install -y \
+    wget curl python3 git build-essential \
+    clang lld pkg-config \
+    && rm -rf /var/lib/apt/lists/*
+
+# Install cross-compilation toolchain for s390x
+RUN xx-apt-get install -y \
+    gcc g++ libc6-dev \
+    libssl-dev \
+    libsasl2-dev \
+    libcurl4-openssl-dev \
+    zlib1g-dev \
+    libzstd-dev \
+    liblz4-dev
+
+# Set up cross-compilation environment
+ENV PKG_CONFIG_PATH=/usr/lib/$(xx-info)-linux-gnu/pkgconfig
+
+WORKDIR /build
+
+# Copy source code
+COPY . /build/
+
+# Configure for cross-compilation
+# --host tells configure we're cross-compiling for s390x
+# --enable-static builds static libraries
+# We use system packages for dependencies (installed via xx-apt-get above)
+# Must explicitly set CC, AR, etc. as configure doesn't pick up ENV vars reliably
+RUN CC=$(xx-info)-gcc \
+    CXX=$(xx-info)-g++ \
+    AR=$(xx-info)-ar \
+    RANLIB=$(xx-info)-ranlib \
+    STRIP=$(xx-info)-strip \
+    ./configure \
+    --host=$(xx-info) \
+    --prefix=/usr/local \
+    --enable-static \
+    --enable-strip \
+    --enable-ssl \
+    --enable-sasl \
+    --enable-zstd \
+    --enable-lz4-ext
+
+# Build librdkafka
+RUN make -j$(nproc)
+
+# Run examples to verify build (using QEMU for this step)
+RUN xx-verify --static src/librdkafka.a
+RUN xx-verify src/librdkafka.so.1
+
+# Install to staging directory
+RUN DESTDIR=/artifacts make install
+
+# Show what was built
+RUN ls -lh /artifacts/usr/local/lib/
+RUN file /artifacts/usr/local/lib/librdkafka.so.1
+
+# Final stage: Package the artifacts
+FROM scratch AS artifacts
+COPY --from=builder /artifacts /

packaging/tools/build-s390x-cross.sh

@@ -0,0 +1,63 @@
+#!/bin/bash
+#
+# Build librdkafka for s390x using cross-compilation
+#
+# This script uses Docker BuildKit with cross-compilation to build
+# s390x binaries on AMD64 hosts, avoiding QEMU emulation issues.
+#
+# Usage:
+# packaging/tools/build-s390x-cross.sh <output-tarball-path.tgz>
+#
+# Requirements:
+# - Docker with BuildKit support
+# - QEMU binfmt support (for verification only)
+#
+
+set -e
+
+if [ $# -ne 1 ]; then
+    echo "Usage: $0 <output-path.tgz>"
+    echo ""
+    echo "Example:"
+    echo "  $0 artifacts/librdkafka-s390x.tgz"
+    exit 1
+fi
+
+output="$1"
+output_dir=$(dirname "$output")
+output_file=$(basename "$output")
+
+# Ensure output directory exists
+mkdir -p "$output_dir"
+
+# Get absolute path for output
+output_abs=$(cd "$output_dir" && pwd)/$output_file
+
+echo "Building librdkafka for s390x using cross-compilation..."
+echo "Output will be: $output_abs"
+
+# Enable Docker BuildKit
+export DOCKER_BUILDKIT=1
+
+# Build using cross-compilation Dockerfile
+docker buildx build \
+    --platform linux/s390x \
+    --file packaging/tools/Dockerfile.s390x \
+    --target artifacts \
+    --output type=local,dest=/tmp/librdkafka-s390x-build \
+    .
+
+# Package the artifacts
+echo "Packaging artifacts..."
+cd /tmp/librdkafka-s390x-build
+tar czf "$output_abs" .
+cd -
+
+# Clean up
+rm -rf /tmp/librdkafka-s390x-build
+
+# Emit SHA256 for verification
+echo ""
+echo "Build complete!"
+echo "SHA256 $output:"
+sha256sum "$output"