1. 背景
A、B 两个项目都依赖fmt，但是A依赖fmt8， B依赖fmt9。
系统中存在两个版本的fmt：
- apt安装的fmt8 .h头文件在/usr/include/fmt/下， .so库文件在./lib/x86_64-linux-gnu/libfmt.so.8
- 还有一个源码编译的fmt，源码在/3rdparty/fmt/下，头文件在/3rdparty/fmt/include/下, 库文件在~/3rdparty/fmt/build/下。 并且执行sudo make install进行安装， 头文件和库文件分别安装在了/usr/local/include/fmt/下和/usr/local/lib/libfmt.so.9.1。
编译时会优先选择/usr/local/下的依赖。A是长期维护的项目，B是临时项目，所以我将/usr/local/下的fmt相关依赖都删除了，保证编译A时能成功链接到fmt8版本。
现在需要解决B的依赖问题：编译B时不会自动找到fmt9的路径，会报错找不到fmt9的错误，编译失败。需要手动指定其依赖路径为源码编译的头文件和库文件路径。
2. 实施
B项目的CMakeLists.txt添加如下内容：
# 定义变量 THIRD_PARTY_ROOT，保存第三方库根目录，便于后续引用
set(THIRD_PARTY_ROOT "/home/koap/3rdparty")
# 定义变量 SPDLOG_SO和FMT_SO，为 spdlog和fmt共享库的绝对路径字符串
set(SPDLOG_SO "${THIRD_PARTY_ROOT}/spdlog/build/libspdlog.so.1.11.0")
set(FMT_SO "${THIRD_PARTY_ROOT}/fmt/build/libfmt.so.9.1.0")# 把这两个目录加入编译器的头文件搜索路径（-I），编译时能找到 spdlog/fmt 的头文件。
include_directories("${THIRD_PARTY_ROOT}/spdlog/include""${THIRD_PARTY_ROOT}/fmt/include"
)# 向 linker 添加搜索目录（-L），使得在使用未写绝对路径的库名时 linker 能在这些目录查找共享/静态库。注意：使用绝对库路径时不必依赖此项，但保留不会有害。
link_directories("${THIRD_PARTY_ROOT}/spdlog/build""${THIRD_PARTY_ROOT}/fmt/build"
)add_executable(g2oCurveFitting g2oCurveFitting.cpp)
# 为目标设置链接库
target_link_libraries(g2oCurveFitting${OpenCV_LIBS}${G2O_CORE_LIBRARY}${G2O_STUFF_LIBRARY}${FMT_SO} # link fmt (use full path)${SPDLOG_SO} # link spdlog (use full path)
)# 设置目标的 rpath（运行时库搜索路径）属性，避免运行时出现 “找不到 libfmt.so/libspdlog.so” 的错误，而无需每次手动设置 LD_LIBRARY_PATH
set_target_properties(g2oCurveFitting PROPERTIESBUILD_RPATH "${THIRD_PARTY_ROOT}/spdlog/build;${THIRD_PARTY_ROOT}/fmt/build"INSTALL_RPATH "${THIRD_PARTY_ROOT}/spdlog/build;${THIRD_PARTY_ROOT}/fmt/build"BUILD_WITH_INSTALL_RPATH TRUE
)
编译成功。
3. 问题和排查方法
运行时报错：
./g2oCurveFitting: error while loading shared libraries: libspdlog.so.1.11: cannot open shared object file: No such file or directory
排查1：查看g2oCurveFitting的依赖
koap@koap:~/workspace/slambook2/ch6/build$ ldd g2oCurveFitting linux-vdso.so.1 (0x00007fff305be000)libg2o_core.so.0.1 => /usr/local/lib/libg2o_core.so.0.1 (0x0000759b674ae000)libg2o_stuff.so.0.1 => /usr/local/lib/libg2o_stuff.so.0.1 (0x0000759b67463000)libopencv_core.so.411 => /usr/local/lib/libopencv_core.so.411 (0x0000759b66600000)libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x0000759b66200000)libm.so.6 => /usr/lib/x86_64-linux-gnu/libm.so.6 (0x0000759b66519000)libgcc_s.so.1 => /usr/lib/x86_64-linux-gnu/libgcc_s.so.1 (0x0000759b67441000)libc.so.6 => /usr/lib/x86_64-linux-gnu/libc.so.6 (0x0000759b65e00000)libspdlog.so.1.11 => not foundlibfmt.so.9 => not foundlibspdlog.so.1.11 => not foundlibfmt.so.9 => not foundlibz.so.1 => /usr/lib/x86_64-linux-gnu/libz.so.1 (0x0000759b673ef000)/lib64/ld-linux-x86-64.so.2 (0x0000759b675d5000)
libspdlog.so.1.11和libfmt.so.9都未被找到，说明是依赖的路径问题。
但明显与
set_target_properties(g2oCurveFitting PROPERTIESBUILD_RPATH "${THIRD_PARTY_ROOT}/spdlog/build;${THIRD_PARTY_ROOT}/fmt/build"INSTALL_RPATH "${THIRD_PARTY_ROOT}/spdlog/build;${THIRD_PARTY_ROOT}/fmt/build"BUILD_WITH_INSTALL_RPATH TRUE
)
的设定矛盾。
排查2：是否路径失效或者错误
指定LD路径执行：
LD_LIBRARY_PATH=/home/koap/3rdparty/spdlog/build:/home/koap/3rdparty/fmt/build ./g2oCurveFitting
程序可以正常运行，说明路径本身没有问题。
当然，此方法也可以临时解决该问题，但是不够方便，而且时间久了也记不住。
排查3：打开动态链接调试，查看 loader 在哪里查找这些库
koap@koap:~/workspace/slambook2/ch6/build$ LD_DEBUG=libs ./g2oCurveFitting 2>&1 | grep -E "spdlog|fmt|search path"53197: search path=/usr/lib/glibc-hwcaps/x86-64-v3:/usr/lib/glibc-hwcaps/x86-64-v2:/usr/lib/tls/haswell/x86_64:/usr/lib/tls/haswell:/usr/lib/tls/x86_64:/usr/lib/tls:/usr/lib/haswell/x86_64:/usr/lib/haswell:/usr/lib/x86_64:/usr/lib (system search path)53197: search path=/usr/local/lib/glibc-hwcaps/x86-64-v3:/usr/local/lib/glibc-hwcaps/x86-64-v2:/usr/local/lib/tls/haswell/x86_64:/usr/local/lib/tls/haswell:/usr/local/lib/tls/x86_64:/usr/local/lib/tls:/usr/local/lib/haswell/x86_64:/usr/local/lib/haswell:/usr/local/lib/x86_64:/usr/local/lib (LD_LIBRARY_PATH)53197: search path=/usr/lib (system search path)53197: search path=/usr/local/lib (LD_LIBRARY_PATH)53197: search path=/usr/lib (system search path)53197: search path=/usr/local/lib (LD_LIBRARY_PATH)53197: search path=/usr/lib (system search path)53197: search path=/usr/local/lib (LD_LIBRARY_PATH)53197: search path=/usr/lib/x86_64-linux-gnu/glibc-hwcaps/x86-64-v3:/usr/lib/x86_64-linux-gnu/glibc-hwcaps/x86-64-v2:/usr/lib/x86_64-linux-gnu/tls/haswell/x86_64:/usr/lib/x86_64-linux-gnu/tls/haswell:/usr/lib/x86_64-linux-gnu/tls/x86_64:/usr/lib/x86_64-linux-gnu/tls:/usr/lib/x86_64-linux-gnu/haswell/x86_64:/usr/lib/x86_64-linux-gnu/haswell:/usr/lib/x86_64-linux-gnu/x86_64:/usr/lib/x86_64-linux-gnu(system search path)53197: search path=/usr/lib (system search path)53197: search path=/usr/local/lib (LD_LIBRARY_PATH)53197: search path=/usr/lib/x86_64-linux-gnu (system search path)53197: search path=/usr/lib (system search path)53197: search path=/usr/local/lib (LD_LIBRARY_PATH)53197: search path=/usr/lib/x86_64-linux-gnu (system search path)53197: search path=/usr/lib (system search path)53197: search path=/usr/local/lib (LD_LIBRARY_PATH)53197: search path=/usr/lib/x86_64-linux-gnu (system search path)53197: find library=libspdlog.so.1.11 [0]; searching53197: search path=/usr/lib (system search path)53197: trying file=/usr/lib/libspdlog.so.1.1153197: search path=/usr/local/lib (LD_LIBRARY_PATH)53197: trying file=/usr/local/lib/libspdlog.so.1.1153197: search path=/usr/lib/x86_64-linux-gnu (system search path)53197: trying file=/usr/lib/x86_64-linux-gnu/libspdlog.so.1.1153197: search path=/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/glibc-hwcaps/x86-64-v3:/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/glibc-hwcaps/x86-64-v2:/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/tls/haswell/x86_64:/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/tls/haswell:/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/tls/x86_64:/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/tls:/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/haswell/x86_64:/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/haswell:/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/x86_64:/usr/lib/x86_64-linux-gnu/gazebo-11/plugins:/opt/ros/humble/opt/rviz_ogre_vendor/lib/glibc-hwcaps/x86-64-v3:/opt/ros/humble/opt/rviz_ogre_vendor/lib/glibc-hwcaps/x86-64-v2:/opt/ros/humble/opt/rviz_ogre_vendor/lib/tls/haswell/x86_64:/opt/ros/humble/opt/rviz_ogre_vendor/lib/tls/haswell:/opt/ros/humble/opt/rviz_ogre_vendor/lib/tls/x86_64:/opt/ros/humble/opt/rviz_ogre_vendor/lib/tls:/opt/ros/humble/opt/rviz_ogre_vendor/lib/haswell/x86_64:/opt/ros/humble/opt/rviz_ogre_vendor/lib/haswell:/opt/ros/humble/opt/rviz_ogre_vendor/lib/x86_64:/opt/ros/humble/opt/rviz_ogre_vendor/lib:/opt/ros/humble/lib/x86_64-linux-gnu/glibc-hwcaps/x86-64-v3:/opt/ros/humble/lib/x86_64-linux-gnu/glibc-hwcaps/x86-64-v2:/opt/ros/humble/lib/x86_64-linux-gnu/tls/haswell/x86_64:/opt/ros/humble/lib/x86_64-linux-gnu/tls/haswell:/opt/ros/humble/lib/x86_64-linux-gnu/tls/x86_64:/opt/ros/humble/lib/x86_64-linux-gnu/tls:/opt/ros/humble/lib/x86_64-linux-gnu/haswell/x86_64:/opt/ros/humble/lib/x86_64-linux-gnu/haswell:/opt/ros/humble/lib/x86_64-linux-gnu/x86_64:/opt/ros/humble/lib/x86_64-linux-gnu:/opt/ros/humble/lib/glibc-hwcaps/x86-64-v3:/opt/ros/humble/lib/glibc-hwcaps/x86-64-v2:/opt/ros/humble/lib/tls/haswell/x86_64:/opt/ros/humble/lib/tls/haswell:/opt/ros/humble/lib/tls/x86_64:/opt/ros/humble/lib/tls:/opt/ros/humble/lib/haswell/x86_64:/opt/ros/humble/lib/haswell:/opt/ros/humble/lib/x86_64:/opt/ros/humble/lib (LD_LIBRARY_PATH)53197: trying file=/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/glibc-hwcaps/x86-64-v3/libspdlog.so.1.1153197: trying file=/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/glibc-hwcaps/x86-64-v2/libspdlog.so.1.1153197: trying file=/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/tls/haswell/x86_64/libspdlog.so.1.1153197: trying file=/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/tls/haswell/libspdlog.so.1.1153197: trying file=/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/tls/x86_64/libspdlog.so.1.1153197: trying file=/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/tls/libspdlog.so.1.1153197: trying file=/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/haswell/x86_64/libspdlog.so.1.1153197: trying file=/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/haswell/libspdlog.so.1.1153197: trying file=/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/x86_64/libspdlog.so.1.1153197: trying file=/usr/lib/x86_64-linux-gnu/gazebo-11/plugins/libspdlog.so.1.1153197: trying file=/opt/ros/humble/opt/rviz_ogre_vendor/lib/glibc-hwcaps/x86-64-v3/libspdlog.so.1.1153197: trying file=/opt/ros/humble/opt/rviz_ogre_vendor/lib/glibc-hwcaps/x86-64-v2/libspdlog.so.1.1153197: trying file=/opt/ros/humble/opt/rviz_ogre_vendor/lib/tls/haswell/x86_64/libspdlog.so.1.1153197: trying file=/opt/ros/humble/opt/rviz_ogre_vendor/lib/tls/haswell/libspdlog.so.1.1153197: trying file=/opt/ros/humble/opt/rviz_ogre_vendor/lib/tls/x86_64/libspdlog.so.1.1153197: trying file=/opt/ros/humble/opt/rviz_ogre_vendor/lib/tls/libspdlog.so.1.1153197: trying file=/opt/ros/humble/opt/rviz_ogre_vendor/lib/haswell/x86_64/libspdlog.so.1.1153197: trying file=/opt/ros/humble/opt/rviz_ogre_vendor/lib/haswell/libspdlog.so.1.1153197: trying file=/opt/ros/humble/opt/rviz_ogre_vendor/lib/x86_64/libspdlog.so.1.1153197: trying file=/opt/ros/humble/opt/rviz_ogre_vendor/lib/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/x86_64-linux-gnu/glibc-hwcaps/x86-64-v3/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/x86_64-linux-gnu/glibc-hwcaps/x86-64-v2/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/x86_64-linux-gnu/tls/haswell/x86_64/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/x86_64-linux-gnu/tls/haswell/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/x86_64-linux-gnu/tls/x86_64/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/x86_64-linux-gnu/tls/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/x86_64-linux-gnu/haswell/x86_64/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/x86_64-linux-gnu/haswell/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/x86_64-linux-gnu/x86_64/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/x86_64-linux-gnu/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/glibc-hwcaps/x86-64-v3/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/glibc-hwcaps/x86-64-v2/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/tls/haswell/x86_64/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/tls/haswell/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/tls/x86_64/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/tls/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/haswell/x86_64/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/haswell/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/x86_64/libspdlog.so.1.1153197: trying file=/opt/ros/humble/lib/libspdlog.so.1.1153197: search path=/lib/x86_64-linux-gnu/glibc-hwcaps/x86-64-v3:/lib/x86_64-linux-gnu/glibc-hwcaps/x86-64-v2:/lib/x86_64-linux-gnu/tls/haswell/x86_64:/lib/x86_64-linux-gnu/tls/haswell:/lib/x86_64-linux-gnu/tls/x86_64:/lib/x86_64-linux-gnu/tls:/lib/x86_64-linux-gnu/haswell/x86_64:/lib/x86_64-linux-gnu/haswell:/lib/x86_64-linux-gnu/x86_64:/lib/x86_64-linux-gnu:/usr/lib/x86_64-linux-gnu:/lib/glibc-hwcaps/x86-64-v3:/lib/glibc-hwcaps/x86-64-v2:/lib/tls/haswell/x86_64:/lib/tls/haswell:/lib/tls/x86_64:/lib/tls:/lib/haswell/x86_64:/lib/haswell:/lib/x86_64:/lib:/usr/lib (system search path)53197: trying file=/lib/x86_64-linux-gnu/glibc-hwcaps/x86-64-v3/libspdlog.so.1.1153197: trying file=/lib/x86_64-linux-gnu/glibc-hwcaps/x86-64-v2/libspdlog.so.1.1153197: trying file=/lib/x86_64-linux-gnu/tls/haswell/x86_64/libspdlog.so.1.1153197: trying file=/lib/x86_64-linux-gnu/tls/haswell/libspdlog.so.1.1153197: trying file=/lib/x86_64-linux-gnu/tls/x86_64/libspdlog.so.1.1153197: trying file=/lib/x86_64-linux-gnu/tls/libspdlog.so.1.1153197: trying file=/lib/x86_64-linux-gnu/haswell/x86_64/libspdlog.so.1.1153197: trying file=/lib/x86_64-linux-gnu/haswell/libspdlog.so.1.1153197: trying file=/lib/x86_64-linux-gnu/x86_64/libspdlog.so.1.1153197: trying file=/lib/x86_64-linux-gnu/libspdlog.so.1.1153197: trying file=/usr/lib/x86_64-linux-gnu/libspdlog.so.1.1153197: trying file=/lib/glibc-hwcaps/x86-64-v3/libspdlog.so.1.1153197: trying file=/lib/glibc-hwcaps/x86-64-v2/libspdlog.so.1.1153197: trying file=/lib/tls/haswell/x86_64/libspdlog.so.1.1153197: trying file=/lib/tls/haswell/libspdlog.so.1.1153197: trying file=/lib/tls/x86_64/libspdlog.so.1.1153197: trying file=/lib/tls/libspdlog.so.1.1153197: trying file=/lib/haswell/x86_64/libspdlog.so.1.1153197: trying file=/lib/haswell/libspdlog.so.1.1153197: trying file=/lib/x86_64/libspdlog.so.1.1153197: trying file=/lib/libspdlog.so.1.1153197: trying file=/usr/lib/libspdlog.so.1.11
./g2oCurveFitting: error while loading shared libraries: libspdlog.so.1.11: cannot open shared object file: No such file or directory
并没有去指定路径查找。说明可能这些库不是程序的直接依赖，而是二级依赖。
排查4：查看一个可执行文件的“动态库依赖链”（递归依赖）
ldd 默认只显示第一层依赖，不会自动展开二级、三级库的链条。
在网上查找到了工具lddtree，它可以：
自动展开所有层级依赖；
显示每个库的实际路径；
用树形结构展示依赖关系。
sudo apt install pax-utils # apt即可安装koap@koap:~/workspace/slambook2/ch6/build$ lddtree g2oCurveFitting
g2oCurveFitting => ./g2oCurveFitting (interpreter => /lib64/ld-linux-x86-64.so.2)libg2o_core.so.0.1 => /usr/local/lib/libg2o_core.so.0.1libspdlog.so.1.11 => not foundlibfmt.so.9 => not foundlibg2o_stuff.so.0.1 => /usr/local/lib/libg2o_stuff.so.0.1libopencv_core.so.411 => /usr/local/lib/libopencv_core.so.411libz.so.1 => /usr/lib/x86_64-linux-gnu/libz.so.1libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6ld-linux-x86-64.so.2 => /lib64/ld-linux-x86-64.so.2libm.so.6 => /usr/lib/x86_64-linux-gnu/libm.so.6libgcc_s.so.1 => /usr/lib/x86_64-linux-gnu/libgcc_s.so.1libc.so.6 => /usr/lib/x86_64-linux-gnu/libc.so.6
发现spdlog和fmt是libg2o_core.so.0.1的依赖，相当于是可执行文件g2oCurveFitting的二级依赖。
定位到原因：
可执行文件有 RUNPATH，但 libg2o_core.so（位于 /usr/local/lib）是直接依赖 libspdlog/libfmt 的共享库。动态链接器在解析 libg2o_core.so 的依赖时，会优先使用 libg2o_core.so 自身的 rpath/runpath（以及系统搜索路径），不会使用可执行文件的 RUNPATH 来满足“来自另一个共享库的依赖”。所以尽管 g2oCurveFitting 有 runpath，加载 libg2o_core.so 时仍找不到 libspdlog/libfmt。
4. 解决
给 libg2o_core 设置 rpath：
sudo apt install patchelfsudo patchelf --set-rpath /home/koap/3rdparty/spdlog/build:/home/koap/3rdparty/fmt/build /usr/local/lib/libg2o_core.so.0.1
sudo ldconfig
然后可以看到依赖都满足了：
koap@koap:~/workspace/slambook2/ch6/build$ lddtree g2oCurveFitting
g2oCurveFitting => ./g2oCurveFitting (interpreter => /lib64/ld-linux-x86-64.so.2)libg2o_core.so.0.1 => /usr/local/lib/libg2o_core.so.0.1libspdlog.so.1.11 => /home/koap/3rdparty/spdlog/build/libspdlog.so.1.11ld-linux-x86-64.so.2 => /lib64/ld-linux-x86-64.so.2libfmt.so.9 => /home/koap/3rdparty/fmt/build/libfmt.so.9libg2o_stuff.so.0.1 => /usr/local/lib/libg2o_stuff.so.0.1libopencv_core.so.411 => /usr/local/lib/libopencv_core.so.411libz.so.1 => /usr/lib/x86_64-linux-gnu/libz.so.1libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6libm.so.6 => /usr/lib/x86_64-linux-gnu/libm.so.6libgcc_s.so.1 => /usr/lib/x86_64-linux-gnu/libgcc_s.so.1libc.so.6 => /usr/lib/x86_64-linux-gnu/libc.so.6
程序也可以正常运行了。
不过链接中使用了绝对路径，迁移到其他设备时需要注意修改路径。