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• Undefined symbol despite libraries being linked

  17 septembre 2020, par Areopag

  currently I'm trying to write a JNI function using ffmpeg features, but when I'm trying to run my java executable after a clean compile I get the following error :

  


  /usr/lib/jvm/java-1.11.0-openjdk-amd64/bin/java: symbol lookup error: /lib/libmediaserv_ffmpeg.so: undefined symbol: _Z19avformat_open_inputPP15AVFormatContextPKcP13AVInputFormatPP12AVDictionary


  


  I can't figure out why ffmpeg is not linked correctly.

  


  mediaserv_ffmpeg.cpp :

  


  #include <iostream>&#xA;#include <libavformat></libavformat>avformat.h>&#xA;#include <libavutil></libavutil>avutil.h>&#xA;&#xA;JNIEXPORT jobject JNICALL Java_mediaserv_ffmpeg_getMetadata&#xA;        (JNIEnv* env, jclass cls, jstring path) { ... }&#xA;</iostream>

  


  What I've tried so far is inspecting libmediaserv_ffmpeg.so :

  


   nm libmediaserv_ffmpeg.so --format=sysv | grep avformat
_Z19avformat_open_inputPP15AVFormatContextPKcP13AVInputFormatPP12AVDictionary|                |   U  |            NOTYPE|                |     |*UND*
_Z20avformat_close_inputPP15AVFormatContext|                |   U  |            NOTYPE|                |     |*UND*
_Z25avformat_find_stream_infoP15AVFormatContextPP12AVDictionary|                |   U  |            NOTYPE|                |     |*UND*


  


  Which, I think, is just another way of saying that there are undefined symbols in the .so file.

  


  The commands used to build the lib (taken from make VERBOSE=1) :

  


  /usr/bin/c++  -Dmediaserv_ffmpeg_EXPORTS -I/usr/lib/jvm/java-11-openjdk-amd64/include -I/usr/lib/jvm/java-11-openjdk-amd64/include/linux -I/mnt/g/Workspace/mediaserv/third-party/ffmpeg  -fPIC   -std=gnu++1z -o CMakeFiles/mediaserv_ffmpeg.dir/mediaserv_ffmpeg.cpp.o -c /mnt/g/Workspace/mediaserv/third-party/mediaserv_ffmpeg.cpp
/usr/bin/c++ -fPIC   -shared -Wl,-soname,libmediaserv_ffmpeg.so -o /mnt/g/Workspace/mediaserv/build/libs/libmediaserv_ffmpeg.so CMakeFiles/mediaserv_ffmpeg.dir/mediaserv_ffmpeg.cpp.o  -Wl,-rpath,/usr/lib/jvm/java-11-openjdk-amd64/lib:/usr/lib/jvm/java-11-openjdk-amd64/lib/server:/mnt/g/Workspace/mediaserv/third-party/ffmpeg/libavutil:/mnt/g/Workspace/mediaserv/third-party/ffmpeg/libavformat /usr/lib/jvm/java-11-openjdk-amd64/lib/libjawt.so /usr/lib/jvm/java-11-openjdk-amd64/lib/server/libjvm.so ../ffmpeg/libavutil/libavutil.so ../ffmpeg/libavformat/libavformat.so


  


  I've already tried to seek for errors in GCC's trace option for the linker and it lists me which libraries it tries to link / is linking but the result stays the same.

  


  /usr/bin/ld: mode elf_x86_64
/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/crti.o
/usr/lib/gcc/x86_64-linux-gnu/7/crtbeginS.o
CMakeFiles/mediaserv_ffmpeg.dir/mediaserv_ffmpeg.cpp.o
/usr/lib/jvm/java-11-openjdk-amd64/lib/libjawt.so
/usr/lib/jvm/java-11-openjdk-amd64/lib/server/libjvm.so
../ffmpeg/libavutil/libavutil.so
../ffmpeg/libavformat/libavformat.so
-lstdc++ (/usr/lib/gcc/x86_64-linux-gnu/7/libstdc++.so)
/lib/x86_64-linux-gnu/libm.so.6
/lib/x86_64-linux-gnu/libmvec.so.1
libgcc_s.so.1 (/usr/lib/gcc/x86_64-linux-gnu/7/libgcc_s.so.1)
/lib/x86_64-linux-gnu/libc.so.6
/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2
/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2
libgcc_s.so.1 (/usr/lib/gcc/x86_64-linux-gnu/7/libgcc_s.so.1)
/usr/lib/gcc/x86_64-linux-gnu/7/crtendS.o
/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/crtn.o


  


  CMakeLists.txt :

  


  cmake_minimum_required(VERSION 3.17)
project(mediaserv_ffmpeg)

set(CMAKE_CXX_STANDARD 17)
set(BUILD_SHARED_LIBS ON)
add_library(${PROJECT_NAME} SHARED mediaserv_ffmpeg.cpp mediaserv_ffmpeg.h)

find_package(JNI REQUIRED)

find_path(AVUTIL_INCLUDE_DIR libavutil/avutil.h HINTS ffmpeg REQUIRED)
find_library(AVUTIL_LIBRARY avutil HINTS ${PROJECT_SOURCE_DIR}/ffmpeg/libavutil PATHS REQUIRED)

find_path(AVFORMAT_INCLUDE_DIR libavformat/avformat.h HINTS ffmpeg REQUIRED)
find_library(AVFORMAT_LIBRARY avformat HINTS ${PROJECT_SOURCE_DIR}/ffmpeg/libavformat REQUIRED)

target_include_directories(${PROJECT_NAME} PRIVATE ${JNI_INCLUDE_DIRS} ${AVUTIL_INCLUDE_DIR} ${AVFORMAT_INCLUDE_DIR})

target_link_libraries(${PROJECT_NAME} ${JNI_LIBRARIES} ${AVUTIL_LIBRARY} ${AVFORMAT_LIBRARY})


  


  Neither ffmpeg taken from the official ubuntu bionic repository nor a self-compiled version with configure --enable-shared works for me.

  


  Where is my mistake or what could I still inspect ?

  


  Thanks in advance.

  


• Piwik Developer Guides : helping you make the most of the Piwik platform

  16 avril 2015, par Piwik Core Team — Community, Development, Plugins

  At Piwik we are creating the leading open analytics platform that gives every user full control over their data. Today we are excited to announce the official launch of the Piwik Developer Guides at developer.piwik.org. The Developer Guides complement existing User Guides and more than 250 FAQs.

  Piwik Developer Guides

  The Developer guides will help you whenever you need to :

  • Integrate Piwik analytics in your website or application — Integration guides explain (1) how to track users of your apps (with JavaScript Tracking or other Tracking API Clients) and (2) how to query Piwik’s reporting data to integrate it into your application (Accessing Piwik data).
  • Develop a new Plugin for Piwik — Plugin development guides introduce the Piwik Platform and explain how to get started with creating a new plugin to extend and customise Piwik.
  • Piwik API references — API References include the references for Tracking API, Analytics API, JavaScript Tracking API and the Database schema.
  • See what’s changed in the platform — Changelog for Piwik platform developers lists all changes to our HTTP API’s, Plugins, Themes, etc.

  Helping Developers innovate with Piwik

  Piwik is an open platform – it is open because users control their data, users control the Piwik software (it is Free/libre software) and also because users can extend the platform via the powerful plugins architecture. Piwik users can already choose from 49 plugins available on the Marketplace ! (as of 2015 April 16th)

  Now that developer guides are officially released, we are hopeful that even more talented developers will be able to create Plugins and distribute them on the Marketplace.

  Share your feedback

  We are committed to providing excellent Developer Guides and to achieve this, we need to hear your feedback and suggestions. To send us a message, click on the “Give Feedback” link in the footer of pages (we are listening !).

  What’s coming next ?

  • Platform Developer Changelog will continue to list all changes to the Piwik Platform and APIs.
  • We will regularly update the guides when there are changes in the platform.
  • We will improve existing guides based on users’ feedback and suggestions (tasks are tracked in this issue tracker on Github.)

  We hope you find the guides useful, and thank you for being part of the Piwik community !

  

• Piwik Developer Guides : helping you make the most of the Piwik platform

  16 avril 2015, par Piwik Core Team — Community, Development, Plugins

  At Piwik we are creating the leading open analytics platform that gives every user full control over their data. Today we are excited to announce the official launch of the Piwik Developer Guides at developer.piwik.org. The Developer Guides complement existing User Guides and more than 250 FAQs.

  Piwik Developer Guides

  The Developer guides will help you whenever you need to :

  • Integrate Piwik analytics in your website or application — Integration guides explain (1) how to track users of your apps (with JavaScript Tracking or other Tracking API Clients) and (2) how to query Piwik’s reporting data to integrate it into your application (Accessing Piwik data).
  • Develop a new Plugin for Piwik — Plugin development guides introduce the Piwik Platform and explain how to get started with creating a new plugin to extend and customise Piwik.
  • Piwik API references — API References include the references for Tracking API, Analytics API, JavaScript Tracking API and the Database schema.
  • See what’s changed in the platform — Changelog for Piwik platform developers lists all changes to our HTTP API’s, Plugins, Themes, etc.

  Helping Developers innovate with Piwik

  Piwik is an open platform – it is open because users control their data, users control the Piwik software (it is Free/libre software) and also because users can extend the platform via the powerful plugins architecture. Piwik users can already choose from 49 plugins available on the Marketplace ! (as of 2015 April 16th)

  Now that developer guides are officially released, we are hopeful that even more talented developers will be able to create Plugins and distribute them on the Marketplace.

  Share your feedback

  We are committed to providing excellent Developer Guides and to achieve this, we need to hear your feedback and suggestions. To send us a message, click on the “Give Feedback” link in the footer of pages (we are listening !).

  What’s coming next ?

  • Platform Developer Changelog will continue to list all changes to the Piwik Platform and APIs.
  • We will regularly update the guides when there are changes in the platform.
  • We will improve existing guides based on users’ feedback and suggestions (tasks are tracked in this issue tracker on Github.)

  We hope you find the guides useful, and thank you for being part of the Piwik community !