Why does linker fail to resolve dependencies within the same .a file?

["Christian Convey" <christian dot convey at gmail dot com>]

On 2/28/07, Nick Clifton <nickc@redhat.com> wrote:
> Hi Christian,
>
> > /usr/bin/c++ -fPIC "CMakeFiles/simpleIO.dir/main_IO.o" -o
> > simpleIO -rdynamic
> > -L/home/cjc/csc583-svn/uriVisionLib/trunk/Development/Source/C++ -lGL
> > -lglut -Wl,-Bstatic -luriVision -luriVision -Wl,-Bdynamic
> > -Wl,-rpath,/home/cjc/csc583-svn/uriVisionLib/trunk/Development/Source/C++
>
> Note: Placing "-luriVision" twice on the command line next to each other
> like that will not actually gain you anything.  The only reason to
> include a library more than once on a linker command line is if it
> contains symbols that are referenced by files that are placed after the
> first occurrence of the library on the command line.  eg:
>
>    foo.o -lbar baz.o -lbar
>
> The second "-lbar" is only needed if baz.o includes references to
> symbols that are defined in libbar.a which will not be pulled in when
> resolving the references made by foo.o.

I'm not so sure that's true, because someone said that putting "bar.a"
on the linker command line is pretty much identical in effect to
listing, on the command line, the files that got bundled up into
bar.a.  So if bar.a is made up of x.o, y.o and z.o, and z.o contains a
function that depends on a function in x.o, then I really do need to
list bar.a twice in order to resolve that dependency. No?

> > In function `uriVideoSources::ImageReader::getFrame(bool,
> > uriBase::RasterImage*)':
> > ImageReader.cpp:(.text+0x90): undefined reference to
> > `uriVideoSources::ImageReader_gen::getFrame_(bool,
> > uriBase::RasterImage*)'
>
> > cjc@peace:~$ nm --demangle
> > /home/cjc/csc583-svn/uriVisionLib/trunk/Development/Source/C++/liburiVision.a
> > | grep outputFrame
>
> As has already been pointed out you are greping for 'outputFrame' when
> the error message you have reported was for a missing 'getFrame_'
> symbol.  I assume therefore that you are also getting error messages
> about a missing reference to 'outputFrame_' ?

I pasted an irrelevant example by accident, but I really am seeing the
problem in question (I think).  Here's the link command and my first
error message from it:

cd /home/cjc/csc583-svn/uriVisionLib/trunk/SDK/Demos/C++/Basic/Simple_IO
&& /usr/bin/c++      -fPIC "CMakeFiles/simpleIO.dir/main_IO.o"   -o
simpleIO -rdynamic
-L/home/cjc/csc583-svn/uriVisionLib/trunk/Development/Source/C++ -lGL
-lglut -Wl,-Bstatic -luriVision -luriVision -Wl,-Bdynamic
-Wl,-rpath,/home/cjc/csc583-svn/uriVisionLib/trunk/Development/Source/C++
/home/cjc/csc583-svn/uriVisionLib/trunk/Development/Source/C++/liburiVision.a(ImageReader.o):
In function `uriVideoSources::ImageReader::getFrame(bool,
uriBase::RasterImage*)':
ImageReader.cpp:(.text+0x90): undefined reference to
`uriVideoSources::ImageReader_gen::getFrame_(bool,
uriBase::RasterImage*)'

and here's the (hopefully) telling nm/grep statement:

cjc@peace:~$ nm --demangle
/home/cjc/csc583-svn/uriVisionLib/trunk/Development/Source/C++/liburiVision.a
| grep "uriVideoSources::ImageReader_gen::getFrame"
        U uriVideoSources::ImageReader_gen::getFrame_(bool)
        U uriVideoSources::ImageReader_gen::getFrame_(bool,
uriBase::RasterImage*)