CMake版本的细微差异导致find_package(GTest)不能发现GTest的全部库
在Orin上用CMake编译某个程序时，总是报错:
-- Found GTest: /usr/lib/aarch64-linux-gnu/libgtest.a
-- Configuring done
CMake Error at tests/CMakeLists.txt:8 (add_executable):
Target "rb_test" links to target "GTest::gtest_main" but the target was
not found. Perhaps a find_package() call is missing for an IMPORTED
target, or an ALIAS target is missing?
Call Stack (most recent call first):
tests/rb_test/CMakeLists.txt:1 (add_target_test)
/usr/bin/ld: cannot find -lGTest::gtest_main
collect2: error: ld returned 1 exit status
make[2]: *** [tests/rb_test/CMakeFiles/rb_test.dir/build.make:85: tests/rb_test/rb_test] Error 1
make[1]: *** [CMakeFiles/Makefile2:992: tests/rb_test/CMakeFiles/rb_test.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
GTest实际上有两个库:/usr/lib/aarch64-linux-gnu/libgtest.a和/usr/lib/aarch64-linux-gnu/libgtest_main.a
上面的错误信息表明发现了/usr/lib/aarch64-linux-gnu/libgtest.a，不知为何就是发现不了/usr/lib/aarch64-linux-gnu/libgtest_main.a，但是/usr/lib/aarch64-linux-gnu/pkgconfig/gtest_main.pc /usr/lib/aarch64-linux-gnu/libgtest_main.a和/usr/lib/aarch64-linux-gnu/pkgconfig/gtest.pc /usr/lib/aarch64-linux-gnu/libgtest.a 一样都是存在的，按理能发现libgtest 也应该能发现libgtest_main.a，但是就是莫名其妙地报上面的错。
发现在同样的程序在另一个Orin上编译时却能顺利成功，但是对比了一下两个环境的libgtest-dev和cmake版本都是一模一样的！抱着试试看的心态继续对比了一下两个环境下cmake用于发现GTest模块的文件: /usr/share/cmake-3.16/Modules/FindGTest.cmake, 没想到发现两个环境下这个文件的内容还真不一样，能顺利编译成功的环境下的FindGTest.cmake里内容要多得多！看来虽然cmake版本一样，但是支持的module还是有差别，于是再仔细对比了一下cmake相关的包发现有差异:
ii cmake 3.16.3-1ubuntu1 arm64 cross-platform, open-source make system
ii cmake-data 3.16.3-1ubuntu1 all CMake data files (modules, templates and documentation)
ii cmake 3.16.3-1ubuntu1.20.04.1 arm64 cross-platform, open-source make system
ii cmake-data 3.16.3-1ubuntu1.20.04.1 all CMake data files (modules, templates and documentation)
很显然，编译报错的环境下的cmake和cmake-data的版本号里没有20.04.1，于是试着安装cmake:
sudo apt-get install cmake
出现了需要升级cmake 和cmake-data的提示！这表明编译出错的环境下的cmake 3.16.3还不是最新的！
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
cmake-data
Suggested packages:
cmake-doc ninja-build
The following packages will be upgraded:
cmake cmake-data
2 upgraded, 0 newly installed, 0 to remove and 354 not upgraded.
Need to get 4,725 kB of archives.
After this operation, 38.9 kB of additional disk space will be used.
Do you want to continue? [Y/n] Y
Get:1 http://mirrors.aliyun.com/ubuntu-ports focal-updates/main arm64 cmake arm64 3.16.3-1ubuntu1.20.04.1 [3,112 kB]
Get:2 http://mirrors.aliyun.com/ubuntu-ports focal-updates/main arm64 cmake-data all 3.16.3-1ubuntu1.20.04.1 [1,613 kB]
Fetched 4,725 kB in 1s (3,622 kB/s)
debconf: delaying package configuration, since apt-utils is not installed
(Reading database ... 214219 files and directories currently installed.)
Preparing to unpack .../cmake_3.16.3-1ubuntu1.20.04.1_arm64.deb ...
Unpacking cmake (3.16.3-1ubuntu1.20.04.1) over (3.16.3-1ubuntu1) ...
Preparing to unpack .../cmake-data_3.16.3-1ubuntu1.20.04.1_all.deb ...
Unpacking cmake-data (3.16.3-1ubuntu1.20.04.1) over (3.16.3-1ubuntu1) ...
Setting up cmake-data (3.16.3-1ubuntu1.20.04.1) ...
Setting up cmake (3.16.3-1ubuntu1.20.04.1) ...
Processing triggers for man-db (2.9.1-1) ...升级完后，cmake的版本里也有了ubuntu20.04.1，然后编译程序就不再报错了！难怪两个环境下的/usr/share/cmake-3.16/Modules/FindGTest.cmake有差异，cmake-data里包括module的文件，cmake-data版本不一样，module的文件内容自然有差异了。
另外记录一个小问题，在编译gtest测试应用程序时，在脚本里加了个-shared
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -shared -fPIC")忘了删除，编译出来的测试应用程序在运行时总是崩溃:
CMake Error at /usr/share/cmake-3.16/Modules/GoogleTestAddTests.cmake:40 (message):
Error running test executable.
Path: '/home/nvidia/workspace/alg_common-development/build/tests/rb_test/rb_test'
Result: Segmentation fault
Output:用gdb看又看不出和测试应用程序本身有关:
Program received signal SIGSEGV, Segmentation fault.
0x0000fffff7ec0438 in testing::internal::FormatCxxExceptionMessage(char const*, char const*) ()
(gdb) bt
#0 0x0000fffff7ec0438 in testing::internal::FormatCxxExceptionMessage(char const*, char const*) ()应该是gtest主程序googletest-1.10.0/googletest/src/gtest_main.cc里问题，但是重装了libgtest-dev和 googletest
ii libgtest-dev:arm64 1.10.0-2 arm64 Google's framework for writing C++ tests
ii googletest 1.10.0-2 all Google's C++ test framework sources后仍然没效果，后来再想想莫非主程序装载测试应用时有问题，检查了一下CMakeLists.txt脚本，去掉了之前实验时给CMAKE_CXX_FLAGS加的 -shared后再编译后运行，测试程序立即可以正常运行了！