[H-GEN] GPL question

[Anthony Towns]

On Tue, Jan 06, 2004 at 11:14:21AM +1000, Paul Gearon wrote:
> Now linking against a dynamic library involves reading it to determine 
> the offsets of each symbol, but that's it.  It doesn't involve copying, 
> distribution or modification of the library.  

You have a shared library licensed under the GPL, called libgpl. You have
a program, foo, that you don't want to license under the GPL. Distributing
the library requires you to obey the GPL, and especially if you distribute
libgpl and foo together, it's hard to claim that the entire work is
"mere aggregation" rather than a derived work of libgpl, and thus must
be licensed under the GPL in its entirety.

If you're not distributing libgpl though -- maybe "libgpl" is actually
Qt, and is already installed everywhere -- the only ways you could
be misbehaving is by your program nevertheless being a derived work
of libgpl -- and that's not unreasonable, considering you probably had
libgpl around when developing and compiling foo, you said -lgpl on the gcc
command line eg -- or if you're encouraging people to act infringingly,
and can get done for contributory infringement.

The analogy that's usually drawn is that if static linking is illegal,
then dynamic linking will leave you just as liable, since you're just
using it as a technical measure to try to avoid culpability. I'm not sure
that sort of reasoning holds up, though [0].

> Sure, linking against a 
> *static* library involves copying a portion of the library into the 
> resulting binary, so I can see the problem there, but I can't see that 
> there's an issue with dynamic libraries.

I think it's pretty questionable too, personally, but I'm not a lawyer.
The FSF stands by its legal arguments, and Trolltech seem to have been
convinced enough to be willing to risk licensing Qt under the GPL and
losing the revenue they get from proprietary software that wants to
link to Qt. And I don't think there's been anyone convinced enough
that it's not a problem that they've been willing to try it and risk
the consequences.

Cheers,
aj

[0] "I'm making a citizen's arrest for shoplifting! You only handed
     over that money as an attempt to employ a technical measure to
     avoid culpability!"

-- 
Anthony Towns <aj at humbug.org.au> <http://azure.humbug.org.au/~aj/>
I don't speak for anyone save myself. GPG signed mail preferred.

               Linux.conf.au 2004 -- Because we can.
           http://conf.linux.org.au/ -- Jan 12-17, 2004
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