GPL-only symbol Error

[Jeff Haran]

> -----Original Message-----
> From: Bernd Petrovitsch [mailto:bernd at petrovitsch.priv.at]
> Sent: Wednesday, November 23, 2011 2:51 AM
> To: Sengottuvelan S
> Cc: Graeme Russ; Greg KH; Kernel Newbies; Jeff Haran
> Subject: RE: GPL-only symbol Error
> 
> On Die, 2011-11-22 at 17:21 -0800, Jeff Haran wrote:
> [....]
> > Perhaps, but that's not what I asked about. It seems to me the essence
> > of GPL is that it grants people the right to modify GPL sources like
> > the Linux kernel in any way they want so long as they make those
> > changes available to whoever uses the code in the future. I don't see
> 
> You forgot that you also have the hand out the same rights you have to
> other people with the (changed) source.
> You forgot that all of that also holds for all of your changes, removal
> and additions to that code (and lawyers don't care if the changes good,
> bad or ugly).

Which is what I suggested in the hypothetical scenario I described. The change to the kernel source to change an EXPORT_SYMBOL_GPL() to EXPORT_SYMBOL() would be published.
 
> >  anything in it that prohibits specific changes. So if I take a symbol
> > that in the sources from kernel.org is declared with
> > EXPORT_SYMBOL_GPL(), make a 1 line change that declares it
> > EXPORT_SYMBOL() and put that on a publically available web site, how
> > have I violated GPL?
> 
> IANAL (and there are pretty much no non-lurking lawyers on LKML), but
> you probably didn't violate the GPL as such on the kernel you downloaded
> with such a change. But that hasn't anything to do with the legal side -
> ask a lawyer if can change the legal "status" with such a change.

Just to be clear, I haven't done any of this. This thread originated with somebody else asking why he was getting this build error when he attempted to build his non-GPL module that referenced EXPORT_SYMBOL_GPL() exported symbols. I was attempting to explain to that original poster why he was getting the error.
 
> > Let's say I then ship a product that uses that custom kernel and a
> > non-GPL kernel module of my own writing that only works with the
> > custom kernel, how is that prohibited in the GPL license?
> 
> That's the actual bug: You assume that you can legally make a
> proprietary Linux kernel module by simply declaring to do so (and going
> deeper is not quite possible as we do not know the module ....).

I can clearly legally write a user space program that results in calls to kernel symbols without publishing it. To do that I load parameters into registers and onto the stack and issue a trap to generate a system call. A kernel module does almost the same thing, except instead of generating a trap, it makes a more traditional function call. The difference is technical and I don't see anything in the COPYING file that makes any reference to this difference. If I have missed that verbiage in the license, please point it out to me.

> Than you stumbled on a warning to help you to realize that (and not
> hitting such warnings or plain simply removing them doesn't change
> anything on the legal side IMHNLO).
> And you think you can "fix" the warning by simply removing it (ignoring
> the underlying issue).

Again, it I didn't stumble on this warning. The original poster did. All I did was respond to a post on a public email list.
 
> But your kernel module is very probably a derived work of the Linux
> kernel anyway and thus automatically and implicitly GPL (even if your
> whole company may want it, has been told or think otherwise).

"very probably a derived work". That is a big assumption. What in the license defines all code that makes calls into kernel symbols via the dynamic module loader mechanism different than code that calls into that code via a trap?
 
> > Not that I am planning on doing this and I've never done it in the
> > past, but technically it seems that there would be no violation here.
> 
> Technically, your module is a derived work of the Linux kernel unless
> proven otherwise.

Again, not my module, not my company's module. I was simply answering a post to this email list and asking questions around a hypothetical scenario.

Jeff Haran