fix: build static library as position-independent code (#224)

Author: maxday

.github/workflows/tests.yml

@@ -59,6 +59,44 @@ jobs:
         shell: bash
         run: ./ci/integ/unit-test.sh ${{ matrix.os }}
 
+  pic-check:
+    runs-on: ${{ matrix.runner }}
+    timeout-minutes: 10
+    container: ${{ matrix.container }}
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: al2023
+            container: public.ecr.aws/amazonlinux/amazonlinux:2023
+            runner: ubuntu-latest
+          - os: al2023-arm
+            container: public.ecr.aws/amazonlinux/amazonlinux:2023
+            runner: ubuntu-24.04-arm
+          - os: alpine
+            container: public.ecr.aws/docker/library/alpine:3.23
+            runner: ubuntu-latest
+
+    steps:
+      - name: Install checkout prerequisites
+        shell: sh
+        run: |
+          if command -v dnf > /dev/null 2>&1; then
+            dnf install -y tar gzip git
+          elif command -v apk > /dev/null 2>&1; then
+            apk add --no-cache bash tar git
+          fi
+
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+
+      - name: Install dependencies
+        shell: bash
+        run: ./ci/integ/install-deps.sh ${{ matrix.os }}
+
+      - name: Position-independence check
+        shell: bash
+        run: ./ci/integ/pic-check.sh ${{ matrix.os }}
+
   integration-test-oci:
     runs-on: ${{ matrix.build.runner }}
     timeout-minutes: 10

CMakeLists.txt

@@ -19,7 +19,11 @@ add_library(${PROJECT_NAME}
 
 set_target_properties(${PROJECT_NAME} PROPERTIES
     SOVERSION 0
-    VERSION ${PROJECT_VERSION}-dev)
+    VERSION ${PROJECT_VERSION}-dev
+    # Emit position-independent code so the static archive can be linked into a
+    # shared object (e.g. the Java runtime interface client's JNI .so).
+    # PIC links fine into executables too, so this is safe for all consumers.
+    POSITION_INDEPENDENT_CODE ON)
 
 target_include_directories(${PROJECT_NAME} PUBLIC
     $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>

ci/integ/docker/Dockerfile.oci-smoke

@@ -13,6 +13,13 @@ COPY main.cpp main.cpp
 
 RUN g++ -std=c++11 -O2 -Iinclude main.cpp runtime.a -lcurl -pthread -o bootstrap
 
+# Position-independence guard. The link above only proves the archive works in a
+# position-dependent executable; it stays green even for a non-PIC build. But
+# downstream consumers embed this .a in a shared object -- e.g. the Java runtime
+# interface client's JNI .so
+RUN g++ -shared -Wl,--whole-archive runtime.a -Wl,--no-whole-archive \
+        -lcurl -pthread -o /build/libaws-lambda-runtime-pic-check.so
+
 FROM public.ecr.aws/lambda/provided:al2023
 
 COPY --from=builder /build/bootstrap ${LAMBDA_RUNTIME_DIR}/bootstrap

ci/integ/pic-check.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+set -euo pipefail
+
+OS=${1:-}
+
+case "$OS" in
+  ubuntu|arch)
+    export CC=/usr/bin/clang CXX=/usr/bin/clang++
+    ;;
+esac
+
+BUILD_DIR=build-pic-check
+cmake -B "$BUILD_DIR" -GNinja -DCMAKE_BUILD_TYPE=Release
+cmake --build "$BUILD_DIR"
+
+"${CXX:-c++}" -shared \
+  -Wl,--whole-archive "$BUILD_DIR/libaws-lambda-runtime.a" -Wl,--no-whole-archive \
+  -lcurl -pthread \
+  -o "$BUILD_DIR/libaws-lambda-runtime-pic-check.so"
+
+echo "PIC check passed: static archive links into a shared object"