ld找不到動態函式庫的除錯方法

注意是否有從C++ 呼叫C語言的函式，如果有必須要使用extern C

https://hackmd.io/@rhythm/HyOxzDkmD

https://www.airs.com/blog/archives/38

https://www.google.com/search?q=Linkers+part+site%3Ahttps%3A%2F%2Fwww.airs.com%2F&rlz=1C1GCEU_zh-TWTW902TW902&oq=Linkers+part+site%3Ahttps%3A%2F%2Fwww.airs.com%2F&gs_lcrp=EgZjaHJvbWUyBggAEEUYOdIBCDM1ODlqMGo3qAIAsAIA&sourceid=chrome&ie=UTF-8#ip=1

注意function是否為static function

c語言中的static function在function被定義的檔案以外的scope是看不到的

undefined reference to

表示必要的函式庫或是.o檔沒有被連接

1. 用nm指令確認函式確實存在.so檔裡面例如:
   nm -D libnvds_utils.so --defined-only的輸出如下，這個指令只會列出有對外開放的函式

   0000000000001470 T nvds_dependencies_version_print
   00000000000018d0 T nvds_mask_utils_resize_to_binary_argb32
   00000000000013f0 T nvds_version
   0000000000001410 T nvds_version_print
   0000000000001310 T _Z18libnvds_utils_initv
   0000000000001300 T _Z20libnvds_utils_deinitv

   https://stackoverflow.com/a/4514781

• nm不只可以用在函式庫檔，.o檔也可以用
  nm deepstream_source_bin.o --defined-only

  0000000000000000 b install_mux_eosmonitor_probe
  0000000000000010 b last_reset_time_global.31491
  0000000000000008 b mutex.31460
  00000000000030a8 t nvstreammux_eosmonitor_probe_func
  0000000000006ab0 T reset_encodebin
  00000000000065e8 T reset_source_pipeline
  000000000000133c t restart_stream_buf_prob
  0000000000002ffc t rtspsrc_monitor_probe_func
  0000000000001270 t seek_decode
  0000000000000020 t set_camera_csi_params
  00000000000000bc t set_camera_v4l2_params
  0000000000006a04 T set_source_to_playing
  0000000000002178 t smart_record_callback
  0000000000002270 t smart_record_event_generator
  0000000000002e74 t watch_source_async_state_change
  00000000000026d0 t watch_source_status
  ...

/usr/bin/ld: cannot find …

編譯過程中發現ld找不到某個函式庫例如/usr/bin/ld: cannot find -ljpeg，可以利用指令ld <函式庫> --verbose可以查看ld找了那些路徑，例如目前ld找不到-ljpeg可以利用ld -ljpeg --verbose，輸出如下

ld: mode aarch64linux
attempt to open /usr/local/lib/aarch64-linux-gnu/libjpeg.so failed
attempt to open /usr/local/lib/aarch64-linux-gnu/libjpeg.a failed
attempt to open /lib/aarch64-linux-gnu/libjpeg.so failed
attempt to open /lib/aarch64-linux-gnu/libjpeg.a failed
attempt to open /usr/lib/aarch64-linux-gnu/libjpeg.so failed
attempt to open /usr/lib/aarch64-linux-gnu/libjpeg.a failed
attempt to open /usr/local/lib/libjpeg.so failed
attempt to open /usr/local/lib/libjpeg.a failed
attempt to open /lib/libjpeg.so failed
attempt to open /lib/libjpeg.a failed
attempt to open /usr/lib/libjpeg.so failed
attempt to open /usr/lib/libjpeg.a failed
attempt to open /usr/aarch64-linux-gnu/lib/libjpeg.so failed
attempt to open /usr/aarch64-linux-gnu/lib/libjpeg.a failed
ld: cannot find -ljpeg

注意makefile的擺放順序

連接器指令放最後面
例如

gcc -I/usr/local/include -o yaml_reader yaml_reader.c  -L/usr/local/lib -lfyaml

https://stackoverflow.com/questions/22426574/gcc-undefined-reference-to

https://stackoverflow.com/questions/16710047/usr-bin-ld-cannot-find-lnameofthelibrary

注意cmake是否有把程式加入編譯

add_executable(…)內加入的cpp檔會被編譯，確認是否有將程式加入