[Qt-interest] Difficulties with statically linking plugins

[Atlant Schmidt]

Folks:

  I'm trying to statically link my Qt application and running into
  several problem with plugins:

  I'm following the instructions here:

    http://doc.trolltech.com/4.6.2/plugins-howto.html#static-plugins

  And using the qgif plugin as my example. I've built Qt 4.6.2 with
  -static added to and -shared removed from the configuration
  command line and the result was all the expected .a libraries in
  my tree. (Oddly enough, the .../plugins/... directories all
  contain both .so and .a versions of the plugins even though Qt
  was rebuilt from distclean up.)

 -=-=-=-=-=-

  If I simply follow the instructions on that web page, my application
  won't link, complaining:

> /eldk/usr/bin/../lib/gcc/powerpc-linux/4.2.2/../../../../powerpc-linux/bin/ld: cannot find -lqgif
> collect2: ld returned 1 exit status

  That makes a sort of sense, given that the -L line that qmake
  included into the Makefile was:

> -L/usr/lib/qtopia/plugins/imageformats

  and the Qt build procedure certainly doesn't push any of the created libraries
  into my /usr/lib/ directory (and I wouldn't want it to). This sounds like bug in
  qmake; for everything else, it includes -L lines that point to the .../lib/
  directory within my Qt tree.

 -=-=-=-=-=-

  So I tried adding the following strings to the .pro file, first:

> LIBS += -L../plugins/imageformats/

  And later:

> LIBS += -L../plugins/imageformats/ -lqgif


  These both got farther. Qmake built an appropriate -L line into my
  Makefile:

> -L../plugins/imageformats/

  and it built it into the command line appropriately "early" so this time,
  the linker found libqgif.a, but with either version of the line in the
  .pro file, the linker couldn't find the necessary routine within the library,
  so it now reported:

> .obj/release-static-emb-powerpc/my_qt_app.o: In function `__static_initialization_and_destruction_0(int, int)':
> my_qt_app.cpp:(.text+0x32): undefined reference to `qt_plugin_instance_qgif()'
> my_qt_app.cpp:(.text+0x36): undefined reference to `qt_plugin_instance_qgif()'
> collect2: ld returned 1 exit status

 -=-=-=-=-=-

  I then simply moved a copy of libqgif.a into my .../lib/
  directory and with that change, my application built fine!

  So why does the linker get in trouble when the libqgif.a file is
  coming from the directory where Qt built it?

 -=-=-=-=-=-

  Second part of the question:

  We also have our own plugin (for an Epson framebuffer chip).
  AFAIK, it was built exactly the same as the qgif plugin and
  at the same time. But with our plugin, even when I put its
  .a file into my .../lib/ directory, I still get:

> .obj/release-static-emb-powerpc/my_qt_app.o: In function `__static_initialization_and_destruction_0(int, int)':
> my_qt_app.cpp:(.text+0x32): undefined reference to `qt_plugin_instance_qscreenlinuxfbepson()'
> my_qt_app.cpp:(.text+0x36): undefined reference to `qt_plugin_instance_qscreenlinuxfbepson()'
> collect2: ld returned 1 exit status

  similar to when I was trying to access libqgif.a from the
  result directory. In other words, in this case, my "move
  the library" work-around didn't work.

  (FYI: This plug-in has been working okay when dynamically
  loaded.)

  Does anyone know why these things are behaving as they are?

                                      Atlant


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