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• Including objects to a shared library from a C++ archive (.a)

  1er septembre 2021, par El Sampsa

  I am trying to include some object files into a shared library I am building. Take the following command (things in [ETC] have been omitted for brevity) :

  



  


  /usr/bin/c++ -fPIC -std=c++14 -pthread -Iinclude/ext/liveMedia -Iinclude/ext/groupsock [ETC] -g -shared -Wl,-soname,libValkka.so -o lib/libValkka.so CMakeFiles/Valkka.dir/src/avthread.cpp.o CMakeFiles/Valkka.dir/src/opengl.cpp.o [ETC] CMakeFiles/Valkka.dir/src/decoders.cpp.o -lX11 -lGLEW -lGLU -lGL -Wl,—whole-archive lib/libavcodec.a -Wl,—no-whole-archive

  


  



  So basically I am just creating a shared library where most of the objects come from my own source code (i.e. CMakeFiles/Valkka.dir/src/*.o), but some of them come from an external static library, located at "lib/libavcodec.a". I get the following error :

  



  


  /usr/bin/ld : lib/libavcodec.a(h264_cabac.o) : relocation R_X86_64_PC32 against symbol 'ff_h264_cabac_tables' can not be used when making a shared object ; recompile with -fPIC
 /usr/bin/ld : final link failed : Bad value
 collect2 : error : ld returned 1 exit status

  


  



  But that is so untrue ! I can extract "libavcodec.a" with

  



  ar x libavcodec.a


  



  And after that check that

  



  readelf --relocs h264_cabac.o | egrep '(GOT|PLT|JU?MP_SLOT)' 


  



  does give some **it :

  



  


  00000000175d 003100000004 R_X86_64_PLT32 0000000000000000 __stack_chk_fail - 4
 000000001926 003100000004 R_X86_64_PLT32 0000000000000000 __stack_chk_fail - 4

  
 


  ...

  


  



  As does

  



  objdump -r h264_cabac.o | grep -i "relocation"


  



  So, indeed, the object files in "libavcodec.a" have been compiled to get PIC (position independent code).

  



  Why does the linker believe otherwise !?

  



  Related links :

  



  How to include all objects of an archive in a shared object ?

  



  Linking archives (.a) into shared object (.so)

  



  Is there a way to determine that a .a or .so library has been compiled as position indepenent code ?

  



  How can I tell, with something like objdump, if an object file has been built with -fPIC ?

  


• Anomalie #3748 (Fermé) : La fonction recuperer_lapage est obsolète ; à remplacer par recuperer_url

  10 mars 2016

  Après la release de 3.1.1, en local et chez OVH, la détection de version de SPIP affichée en pied du backoffice ne fonctionnait plus.
  Je n’avais pas l’annonce "La mise à jour 3.1.1 de SPIP est disponible" même après lancement du genie mise_a_jour.

  En local mon /tmp/cache/xml/archives.xml restait vide

  Apparement le problème vient de :
  genie/mise_a_jour.php
  $res = recuperer_lapage($url, false, ’GET’, _COPIE_LOCALE_MAX_SIZE, ’’, false, $a) ;
  qui ne renvoie rien
  en remplacant par la fonction non obsolète
  $res = recuperer_url($url) ;
  on récupère bien l’archive et résout le bug

• vdpau : add helper for surface chroma type and size

  19 décembre 2014, par Rémi Denis-Courmont

  vdpau : add helper for surface chroma type and size
  Since the VDPAU pixel format does not distinguish between different
  
  VDPAU video surface chroma types, we need another way to pass this
  
  data to the application.
  Originally VDPAU in libavcodec only supported decoding to 8-bits YUV
  
  with 4:2:0 chroma sampling. Correspondingly, applications assumed that
  
  libavcodec expected VDP_CHROMA_TYPE_420 video surfaces for output.
  
  However some of the new HEVC profiles proposed for addition to VDPAU
  
  would require different depth and/or sampling :
  
  http://lists.freedesktop.org/archives/vdpau/2014-July/000167.html
  
  ...as would lossless AVC profiles :
  
  http://lists.freedesktop.org/archives/vdpau/2014-November/000241.html
  To preserve backward binary compatibility with existing applications,
  
  a new av_vdpau_bind_context() flag is introduced in a further change.
  Signed-off-by : Rémi Denis-Courmont <remi@remlab.net>
  
  Signed-off-by : Anton Khirnov <anton@khirnov.net>
  

  • [DBH] doc/APIchanges
  • [DBH] libavcodec/vdpau.c
  • [DBH] libavcodec/vdpau.h
  • [DBH] libavcodec/version.h