Re: Shared library - static link specific dependency

[Bob Friesenhahn]

On Sat, 14 Jun 2008, Alon Bar-Lev wrote:
> As far as I understand, if I have PKCS#11 provider (library) with
> OpenSSL linked within it, and application loads it, there is not
> symbol mixups, as the symbols of embedded OpenSSL implementation are
> not exposted to the application. And as the interface between
> application and the library does not share any OpenSSL related
> element, it should work perfectly even if the application load
> incompatible OpenSSL library.

A fundamental precept of libtool is that it should always be possible 
to build everything static in a portable way.  Building shared 
libraries is a luxury that libtool enables (when possible).

In my experience, the popular Linux OS does not prevent duplicate 
symbols from being used.  If these similarly named symbols actually 
represent somewhat different code, then very bad things can happen.

An excellent example of this is the Ghostscript shared library which 
includes some modified libjpeg functions yet also links against shared 
libjpeg to reduce code size.  This works fine for Ghostscript but an 
application which uses both libjpeg and the Ghostscript shared library 
is likely to pick up the modified versions in Ghostscript rather than 
the expected ones in libjpeg.  I know this because it happens to my 
application (which then crashes).

Bob
======================================
Bob Friesenhahn
address@hidden, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/