Re: Can we link an application with different libstdc++.so.x version?

[Paul Pluzhnikov]

praks <praks.world@gmail.com> writes:

> We want to build an application which requires 3rd party libraries.
> The 3rd party shared libraries strictly require "libstdc++.so.5" and
> we don't have source code of these libs

In this case, you *have* to use the same version of GCC which was
used to link these 3rd party libraries: C++ code compiled with
different compilers is not link compatible, and gcc-3.3 and 3.4
are different enough.

> We are using gcc 3.4.x to build main application.

The result of such build is undefined, and should generally not work.

> We have been able to build and link main
> application with these libraries by using following gcc options:
> #g++ -rdynamic -g -o app /usr/lib/librt.so /usr/lib/libdl.so /usr/lib/
> libcrypt.so /usr/lib/libpthread.so /usr/lib/libstdc++.so.5 -
> l3rdPartyLib1

This command line is largely screwed up, and in fact it's very hard
to believe that that command produces a runnable application. Don't
you have any objects to link in? Where is main() coming from?

> It builds and runs fine on my dev ( rhel 4.0 )  machine.

It shouldn't run fine, but for some reason you got (un)lucky.

> But it
> doesn't work in the build that we gave to QA, we are getting a segv in
> static initialization of objects.

That's the expected outcome.

> This seems to stem from the fact
> that we have two versions of libstdc++ linked in the application viz.
> "libstdc++.so.5" (explicitly linked for 3rd party libs) and "libstdc+
> +.so.6" (from the complier we are using).

Yes, that's likely the cause.

> Is it fine to use 2 different libstdc++ in same application?

No, it isn't.

You may try to figure out exactly what's different between the QA
and development box, by comparing the result of running:

  env LD_DEBUG=symbols,bindings ./app

on the two machines. But even if you figure out the difference,
you are still in "undefined behavior" territory.

Cheers,
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