問題來源

嘗試在UE5中使用本地編譯的aws-sdk-cpp，并需要在UE的windows編輯器里，交叉編譯linux版本。

編譯aws-sdk-cpp的方法參照了Build the AWS SDK for C++ on Linux/macOS，在UE項目中引入庫的方法，參照了How to Integrate the AWS C++ SDK with Unreal Engine。

在Windows編輯器中編譯正常，打包Windows也正常，但交叉編譯linux版本時出現(xiàn)鏈接錯誤，提示undefined symbol: Aws::Utils::DateTime::DateTime，如下

[2023.09.14-01.59.44:568][655]UATHelper: Packaging (Linux): ld.lld: error: undefined symbol: Aws::Utils::DateTime::DateTime(std::__1::chrono::time_point<std::__1::chrono::system_clock, std::__1::chrono::duration<long long, std::__1::ratio<1l, 1000000l> > > const&)
[2023.09.14-01.59.44:568][655]UATHelper: Packaging (Linux): >>> referenced by AWSCredentials.h:36 (D:/Projects/DT/MapEditorUE/ThirdParty/AWS/Include\aws/core/auth\AWSCredentials.h:36)

解決方案

嘗試了各種動態(tài)庫，靜態(tài)庫，均報同樣錯誤。

最終發(fā)現(xiàn)，編譯aws-sdk-cpp時，需要使用clang，而非gcc，因為Unreal的交叉編譯使用的就是clang（似乎還是定制過的），一些c++標(biāo)準(zhǔn)的函數(shù)符號似乎存在差異，導(dǎo)致了這個問題。

使用clang編譯可在cmake前用環(huán)境變量指定，并需要設(shè)定-DCMAKE_CXX_FLAGS="-stdlib=libc++"，否則找不到libc++庫

# 指定使用clang作為編譯器
export CXX=/path/to/clang++
export CC=/path/to/clang

# cmake時指定-DCMAKE_CXX_FLAGS="-stdlib=libc++"
cmake ../../aws-sdk-cpp -DCMAKE_BUILD_TYPE=Release -DCMAKE_PREFIX_PATH=/usr/local/ -DCMAKE_INSTALL_PREFIX=/usr/local/ -DBUILD_SHARED_LIBS=ON -DCMAKE_CXX_FLAGS="-stdlib=libc++"

# make
make -j 8

TIP

如果不設(shè)定-DCMAKE_CXX_FLAGS="-stdlib=libc++"，cmake可能會報如下錯誤，因為clang默認(rèn)不會取找gcc的庫

CMake Error at /usr/local/share/cmake-3.22/Modules/CMakeTestCXXCompiler.cmake:62 (message):
  The C++ compiler

    "/usr/bin/clang++"

  is not able to compile a simple test program.

  It fails with the following output:

    Change Dir: /home/SENSETIME/sunxia/Develop/Programs/aws-sdk-cpp-build/test/CMakeFiles/CMakeTmp
   
    Run Build Command(s):/bin/make -f Makefile cmTC_fba77/fast && /bin/make  -f CMakeFiles/cmTC_fba77.dir/build.make CMakeFiles/cmTC_fba77.dir/build
    make[1]: Entering directory '/home/SENSETIME/sunxia/Develop/Programs/aws-sdk-cpp-build/test/CMakeFiles/CMakeTmp'
    Building CXX object CMakeFiles/cmTC_fba77.dir/testCXXCompiler.cxx.o
    /usr/bin/clang++    -MD -MT CMakeFiles/cmTC_fba77.dir/testCXXCompiler.cxx.o -MF CMakeFiles/cmTC_fba77.dir/testCXXCompiler.cxx.o.d -o CMakeFiles/cmTC_fba77.dir/testCXXCompiler.cxx.o -c /home/SENSETIME/sunxia/Develop/Programs/aws-sdk-cpp-build/test/CMakeFiles/CMakeTmp/testCXXCompiler.cxx
    Linking CXX executable cmTC_fba77
    /usr/local/bin/cmake -E cmake_link_script CMakeFiles/cmTC_fba77.dir/link.txt --verbose=1
    /usr/bin/clang++ -rdynamic CMakeFiles/cmTC_fba77.dir/testCXXCompiler.cxx.o -o cmTC_fba77
    /usr/bin/ld: cannot find -lstdc++
    clang: error: linker command failed with exit code 1 (use -v to see invocation)
    make[1]: *** [CMakeFiles/cmTC_fba77.dir/build.make:100: cmTC_fba77] Error 1
    make[1]: Leaving directory '/home/SENSETIME/sunxia/Develop/Programs/aws-sdk-cpp-build/test/CMakeFiles/CMakeTmp'
    make: *** [Makefile:127: cmTC_fba77/fast] Error 2
   
   

 

  CMake will not be able to correctly generate this project.
Call Stack (most recent call first):
  CMakeLists.txt:152 (project)