What is Copyleft?

[Ian Lance Taylor]

Dave J Woolley <david.woolley at bts.co.uk> writes:

> I had a look over the LGPL and it seems to have some interesting
> restrictions on derivative works that are almost certainly 
> violated more often than obeyed, at least for the glibc.
> It seems to require that limited licesnses be given to modify 
> the code and to reverse engineer it to aid in modifying it. There
> are also requirements with regard to notifying the library copyright.
> 
> As I read it, if you want to completely avoid restrictions, you
> must distribute the proprietory code as unlinked object files
> and let the end user create the final executable.  (This only
> works for the LGPL as it contains exemptions for common uses of
> header files.)

The LGPL, unlike the GPL, was intended to permit linking against
dynamic libraries covered by the LGPL without thereby bringing the
program which is linking against the dynamic library under the [L]GPL.
That is, in the case of an LGPL dynamic library, you can provide the
unlinked object files in the form of an executable which is linked to
the dynamic library by the dynamic linker (i.e., by the end user).

So, since glibc is available as a dynamic library, most uses of glibc
do not conflict with the LGPL.  The only way to conflict would be link
against the static version of glibc and distribute the resulting
binary without distributing the unlinked objects.

Ian