Wrong package configuration file for aws-c-common

[marco-ceriani]

Confirm by changing [ ] to [x] below to ensure that it's a bug:

• I've gone though Developer Guide and API reference
• I've searched for previous similar issues and didn't find any solution

Describe the bug
In one of the products I work on I'm using the aws-encryption-sdk-c library to encrypt data, which is another library provided by AWS, which depends on the aws-sdk-cpp. Hence, I wrote a CMake file to build both libraries as shared libraries.
However, since a recent release, the aws-c-common is compiled as a static library, ignoring the variable BUILD_SHARED_LIB. This is fine for the compilation of aws-sdk-cpp. But when I try to use it inside aws-encryption-sdk-c, that build fails, with this message

[ 61%] Performing configure step for 'encryption_sdk'
CMake Error at <install_prefix>/aws-c-common/cmake/aws-c-common-config.cmake:8 (include):
  include could not find load file:

    <install_prefix>/aws-c-common/cmake/shared/aws-c-common-targets.cmake
Call Stack (most recent call first):
  CMakeLists.txt:38 (find_package)

I've looked at that file, and the issue is that it uses the variable BUILD_SHARED_LIBS to choose wether to include static/aws-c-common-targets.cmake or shared/aws-c-common-targets.cmake. But now aws-c-common is always built as a static library. Hence, the folder shared does not exist. Since the compilation of the common c libraries is now independent from the variable BUILD_SHARED_LIBS, then also the config.cmake should be modified accordingly.

SDK version number
1.9.39

Platform/OS/Hardware/Device
CentOS 7.9

To Reproduce (observed behavior)
Steps to reproduce the behavior (please share code)

Expected behavior
A clear and concise description of what you expected to happen.

[KaibaLopez]

Hi @marco-ceriani ,
Can you share how you are trying to link the cpp sdk? It should be doing the linking correctly if you are using find_package() but it is kind of hard to see what is going on without knowing how it is being linked.

[marco-ceriani]

I'm building both aws-sdk-cpp and aws-encryption-sdk using a CMakeLIsts.txt with two external projects

ExternalProject_Add(aws-sdk-cpp
    PREFIX          ${SDK_ROOT}
    GIT_REPOSITORY  https://github.com/aws/aws-sdk-cpp.git
    GIT_TAG         ${AWS_SDK_VERSION}
    LIST_SEPARATOR  "|"
    CMAKE_ARGS      -DBUILD_ONLY=kms
                    -DBUILD_SHARED_LIBS=ON
                    -DENABLE_TESTING=OFF
                    -DENABLE_UNITY_BUILD=ON
                    -DCMAKE_INSTALL_PREFIX=<INSTALL_DIR>
                    -DCMAKE_INSTALL_LIBDIR=${CMAKE_INSTALL_LIBDIR}
                    -DCMAKE_CXX_FLAGS=-Wno-stringop-overflow
    BUILD_COMMAND   make install
    TEST_COMMAND    ""
)

# Download Encryption SDK
ExternalProject_Add(encryption_sdk
    PREFIX          ${SDK_ROOT}
    GIT_REPOSITORY  https://github.com/aws/aws-encryption-sdk-c.git
    GIT_TAG         ${ENCRYPTION_SDK_VERSION}
    LIST_SEPARATOR  "|"
    CMAKE_ARGS      -DBUILD_SHARED_LIBS=ON
                    -DBUILD_DOC=${BUILD_DOC}
                    -DBUILD_AWS_ENC_SDK_CPP=ON
                    -DCMAKE_PREFIX_PATH=${CMAKE_PREFIX_PATH}
                    -DCMAKE_INSTALL_PREFIX=<INSTALL_DIR>
                    -DCMAKE_INSTALL_LIBDIR=${CMAKE_INSTALL_LIBDIR}
    BUILD_COMMAND   make install ${DOC_TARGET}
    TEST_COMMAND    ""
)
add_dependencies(encryption_sdk aws-sdk-cpp)

I'm also doing other things to prepare a package with all the libraries, but it's irrelevant for this issue.

The complete build script for the aws-encryption-sdk is in their project. The piece that breaks down is indeed a find_package(aws-c-common CONFIG REQUIRED) at line 38.

list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")

# Make sure we can pick up Cmake modules installed by dependencies
# both when they are in the CMAKE_INSTALL_PREFIX directory
# and in the CMAKE_PREFIX_PATH list.
list(APPEND CMAKE_MODULE_PATH "${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}/cmake")
foreach(prefix ${CMAKE_PREFIX_PATH})
    list(APPEND CMAKE_MODULE_PATH "${prefix}/${CMAKE_INSTALL_LIBDIR}/cmake")
endforeach(prefix)

# Including AwsSharedLibSetup depends on aws-c-common being installed already.
# Putting this ahead of that include line for a more meaningful error when missing.
find_package(aws-c-common CONFIG REQUIRED)

The build of aws-sdk-cpp completes correctly, and it produces the file <install_prefix>/lib/aws-c-common/cmake/aws-c-common-config.cmake, with this content

set(THREADS_PREFER_PTHREAD_FLAG ON)

if(WIN32 OR UNIX OR APPLE)
    find_package(Threads REQUIRED)
endif()

if (BUILD_SHARED_LIBS)
    include(${CMAKE_CURRENT_LIST_DIR}/shared/aws-c-common-targets.cmake)
else()
    include(${CMAKE_CURRENT_LIST_DIR}/static/aws-c-common-targets.cmake)
endif()

While building the other library, the variable BUILD_SHARED_LIBS is again ON, and I assume that this triggers the search on the path /shared/aws-c-common-targets.cmake that does not exist, since the aws-c-common library is now compiled statically.

I have two questions

1. is it possible to use the find_package, if half the libraries are linked as dynamic objects and half as static ones, given that the same variable BUILD_SHARED_LIBS is used in all cmake files?
2. I could try to build again aws-c-common as dynamic library. In that case, given that the cpp sdk will contain some of the functions of c-common, will there be issues when linking both libaws-cpp-sdk-core.so and libaws-c-common.so in my application?

[alex-chew]

Hi @KaibaLopez, any updates on this? I'm able to use a workaround on the aws-encryption-sdk-c side [1], but it's preferable if the aws-sdk-cpp fixes the root cause.

[1] aws/aws-encryption-sdk-c#719

[jmklix]

We have been working on some updates to the build/configurations of this sdk. You can track the progress here