pure virtual problems with dlopen()

[Ralph Seguin <rpseguin at yahoo dot com>]

Hi.  I'm in the process of writing a plugin framework
and I've run into a glitch with pure virtual methods
and dlopen().  I did some searching and turned up some
similar cases, but not obvious fixes.

I've got an asbstract base class:  'base'

class base
{
public:
    virtual ~base () {}

    virtual void someMethod () = 0;
};


And a derived class: 'derived'

class derived : public base
{
public:
    // blah blah blah
    virtual void someMethod ()
    {
        // Do something here.
    }
};


When I compiled derived into an .so  (which isn't
quite working as expected either, more on that later),
nm shows derived.so as having __pure_virtual being
unresolved:

outof:rpsPlugin % nm testPlugin.so | fgrep -i pure
         U __pure_virtual


  I tracked it down in libg++.so and libgcc, but I'm
surprised that g++ isn't linking this in whilst I
compile:

g++  -shared   -Wall -I. -g -shared -c testPlugin.cpp
-o testPlugin.o
ld   -g   -Bdynamic -shared testPlugin.o -soname
testPlugin.so -o testPlugin.so

If I make base concrete by giving base::someMethod() a
body, dlopen() works (cause __pure_virtual isn't
unresolved).


For some reason:
g++ -shared -Wall -I. -g -c testPlugin.cpp -o
testPlugin.so

does NOT create something that dlopen() is comfortable
with opening, but if I use ld as above, I can dlopen()
it.

This command just doesn't work as I expect it to:
g++ -shared -Wall -I. -g -c testPlugin.cpp -o
testPlugin.so -lg++

pg++: cannot specify -o with -c or -S and multiple
compilations


Thanks.
-Ralph
rpseguin@yahoo.com


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