License issues

[Steve Langasek]

On Tue, 29 May 2001, Alex Larsson wrote:

> > IANAL either, but the 'conventional' understanding of the GPL (i.e., the one
> > spearheaded by RMS) holds that if you link to a library that's GPLed, you're
> > required to release your application's source under the GPL if you
> > redistribute said app.  The exception is if the GPL library exports an ABI
> > that's also provided by some other, non-GPL library.  It may also apply to
> > libs that export the same API; RMS makes this explicit so that developers are
> > not discouraged from using GPL'ed versions of essential system libraries.

> What if the ABI is provided by several other non-GPLd libraries, but they
> do slightly different things, like talk nfs instead of smb.

I suspect that it makes no difference -- if the libraries are truly
binary-compatible, then there's no way to prove, in a court of law or
elsewhere, that your application is linked against the GPL library and not the
non-GPL library; all the linking is done at runtime, at which point there's no
GPL violation because the GPL only places restrictions on redistribution of
the derivative work.  To be safe, you can even compile your app against the
headers from the non-GPL library, and dynamically link it against the non-GPL
library; and then if someone later uses it with the GPLed library instead,
that's ok.

Steve Langasek
postmodern programmer