Add CI check with _GLIBCXX_USE_CXX11_ABI=0

.github/workflows/ci.yml

@@ -21,7 +21,7 @@ env:
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
-  
+
 jobs:
   linux-compat-use-openssl:
     runs-on: ubuntu-22.04 # latest
@@ -143,6 +143,18 @@ jobs:
         aws s3 cp s3://aws-crt-test-stuff/ci/${{ env.BUILDER_VERSION }}/linux-container-ci.sh ./linux-container-ci.sh && chmod a+x ./linux-container-ci.sh
         ./linux-container-ci.sh ${{ env.BUILDER_VERSION }} aws-crt-${{ env.LINUX_BASE_IMAGE }} build -p ${{ env.PACKAGE_NAME }} --compiler=${{ matrix.compiler }} --cmake-extra=-DBUILD_SHARED_LIBS=ON
 
+  linux-glibcxx-ancient-abi:
+    runs-on: ubuntu-22.04 # latest
+    strategy:
+      matrix:
+        compiler: [gcc-11] # oldest, latest
+    steps:
+        # We can't use the `uses: docker://image` version yet, GitHub lacks authentication for actions -> packages
+    - name: Build ${{ env.PACKAGE_NAME }}
+      run: |
+        aws s3 cp s3://aws-crt-test-stuff/ci/${{ env.BUILDER_VERSION }}/linux-container-ci.sh ./linux-container-ci.sh && chmod a+x ./linux-container-ci.sh
+        ./linux-container-ci.sh ${{ env.BUILDER_VERSION }} aws-crt-${{ env.LINUX_BASE_IMAGE }} build -p ${{ env.PACKAGE_NAME }} --compiler=gcc-11 --cmake-extra=-DBUILD_SHARED_LIBS=ON --cmake-extra=-DCMAKE_CXX_FLAGS=-D_GLIBCXX_USE_CXX11_ABI=0
+
   linux-openssl-static:
     runs-on: ubuntu-22.04 # latest
     steps:

CMakeLists.txt

@@ -298,9 +298,17 @@ set_target_properties(${PROJECT_NAME} PROPERTIES LINKER_LANGUAGE CXX)
 set_target_properties(${PROJECT_NAME} PROPERTIES CXX_STANDARD ${CMAKE_CXX_STANDARD})
 
 # Hide symbols by default
-# Except for ancient GCC, because it leads to crashes in shared-lib builds
-# see: https://github.com/awslabs/aws-crt-cpp/pull/675
-if(NOT (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS "5.0"))
+# Except where it causes problems...
+string(FIND "${CMAKE_CXX_FLAGS}" "-D_GLIBCXX_USE_CXX11_ABI=0" found_ancient_abi_flag)
+if(found_ancient_abi_flag GREATER -1)
+    # We've seen people set _GLIBCXX_USE_CXX11_ABI=0 which forces GCC to use it's pre-C++11 implementation.
+    # This leads to crashes on shared-lib builds.
+    message(STATUS "Cannot deal with hidden symbols when _GLIBCXX_USE_CXX11_ABI=0 is set, making everything visible")
+elseif(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS "5.0")
+    # Ancient GCC leads to crashes in shared-lib builds
+    # see: https://github.com/awslabs/aws-crt-cpp/pull/675
+    message(STATUS "Your compiler is too old to deal with hidden symbols, making everything visible")
+else()
     set_target_properties(${PROJECT_NAME} PROPERTIES CXX_VISIBILITY_PRESET hidden VISIBILITY_INLINES_HIDDEN ON)
 endif()