GNU ld linker wrapping

GNU ld linker wrapping

[Shawn Yarbrough]

I'm hoping to use the linker to "protect" me from closed-source
third-party libraries I can't get rid of.  Some are static and some
are shared.  Some of the libraries use old versions of gcc/g++ such
as g++-3.2.2.

My first idea, not yet attempted, is to use a thin C library to wrap
the third-party 3.2.2 C++ library, only wrapping the few functions I
need and ignoring all others, and then link the resulting C library
against my own 3.4.5 ABI C++ code.

The third-party 3.2.2 library uses the older, version 5, C++ standard
library that was normal for g++ 3.2.2.  My code uses version 6.  How
would I tell the linker to use version 5 only for linking the
third-party library, and use version 6 for linking everything else in
my app?

Related to this I'm also wondering how to pull the third-party
library into my wrapper library so that I only have to distribute one
file.

Suggestions for better ways to attack this problem would also be
welcome.

Thanks,

Shawn Yarbrough
Senior E-Trading Developer
Gelber Group, LLC
syarbrough@gelbergroup.com

Re: GNU ld linker wrapping

[Alan Modra]

On Fri, Jun 02, 2006 at 04:33:49PM -0500, Shawn Yarbrough wrote:
> The third-party 3.2.2 library uses the older, version 5, C++ standard
> library that was normal for g++ 3.2.2.  My code uses version 6.  How
> would I tell the linker to use version 5 only for linking the
> third-party library, and use version 6 for linking everything else in
> my app? 

For shared libraries without versioned symbols, I think you are out of
luck.  The linker can't help you as the libs are already finally linked,
so there isn't any possibility of "wrapping" them as you imagine.
Instead, you need some magic in the dynamic linker, ld.so.  Modifying
ld.so symbol resolution would be possible, but you likely won't find
much help, at least for free, if you attempt this.  Failing that, you'd
need to edit dynamic symbols so that references in the proprietary lib
are changed to only be satisfied by a similarly changed old libstdc++.
Note that objcopy doesn't allow renaming of dynamic syms, one reason
being that the sections describing dyamic symbols are loadable and thus
can't increase in size without affecting other loaded sections.  You'd
also need to adjust symbol hashes.

For static libs, you might be able to do something with ld -r.  Link the
proprietary static lib against the static version of the old libstdc++.
Then use objcopy to remove all the syms you don't want.  The resulting
.o might then be usable, but I suspect there will be some horrible
details that will bite you.

Frankly, I wouldn't try any of this myself.  You would be better off
using the same old version of g++ as that used to compile the
proprietary libs, or pressing your vendor for new libs.

-- 
Alan Modra
IBM OzLabs - Linux Technology Centre

GNU ld linker wrapping

[Shawn Yarbrough]

Is this the right place to ask linking questions?

I'm hoping to use the linker to "protect" me from closed-source third-party libraries I can't get rid of.  Some are static and some are shared.  Some of the libraries use old versions of gcc/g++ such as g++-3.2.2.

My first idea, not yet attempted, is to use a thin C library to wrap the third-party 3.2.2 C++ library, only wrapping the few functions I need and ignoring all others, and then link the resulting C library against my own 3.4.5 ABI C++ code.

The third-party 3.2.2 library uses the older, version 5, C++ standard library that was normal for g++ 3.2.2.  My code uses version 6.  How would I tell the linker to use version 5 only for linking the third-party library, and use version 6 for linking everything else in my app?

Related to this I'm also wondering how to pull the third-party library into my wrapper library so that I only have to distribute one file.

Suggestions for better ways to attack this problem would also be welcome.

Thanks,

Shawn Yarbrough
Senior E-Trading Developer
Gelber Group, LLC
syarbrough@gelbergroup.com