I'll answer with my own hypothetical. If I write a program that dynamically links a library performing the same GPL'd fluid sim calculations, it is presumably forced to be GPL, because it links to it. What if someone comes along and runs the program but at runtime uses LD_PRELOAD to override the dynamic linker, linking it to an alternative library that presents the same interface. Is the program still required to be GPL?
I don't really have an answer to your specific proposed loophole, it's pretty clever and is a very good question; but I don't think the calling mechanism is part of the issue. You could make the same argument whether you are talking about a "program" or a library. The calling convention is a meaningless detail imho.
I think you are specifically responding to my "does not work without" interpretation overly literally. Clearly if the program is written for and tested against a specific interface of a GPL'd program, it is intended to work with that program.
On the other hand if it's written to call into some kind of standard interface, it no longer requires that GPL program specifically, but could work with any program implementing that interface. And I will admit that whether a program is written only to work with a GPL program/library/whatever, or is more general, may be up to interpretation, what is considered "standard", etc., but that is exactly my point -- law is nuanced. If it were possible to codify laws perfectly with overly simple rules like "the copyright applies because it's a DLL and not a program", then we wouldn't need lawyers.
In law, intent is important. If I write a non-GPL program that depends on the functionality of a GPL library, I can go find all sorts of ways to not "link" to it but still use it, e.g., as a program, a service, etc. -- and it happens -- but the intent, which was to find a way to use GPL software without adhering to its license, is still quite clear.
> I'll answer with my own hypothetical. If I write a program that dynamically links a library performing the same GPL'd fluid sim calculations, it is presumably forced to be GPL, because it links to it. What if someone comes along and runs the program but at runtime uses LD_PRELOAD to override the dynamic linker, linking it to an alternative library that presents the same interface. Is the program still required to be GPL?
I've never believed that linking made your code necessarily GPL in the first place. I don't care what the FSF says, they're not exactly unbiased.
> I think you are specifically responding to my "does not work without" interpretation overly literally. Clearly if the program is written for and tested against a specific interface of a GPL'd program, it is intended to work with that program.
> On the other hand if it's written to call into some kind of standard interface, it no longer requires that GPL program specifically, but could work with any program implementing that interface.
Well that's basically how the standard already works. If your code is using a specialized enough interface, sharing data structures you got from the GPL code, then it's derivative of the GPL code and needs to follow the GPL.
So while "process boundary" is an inexact tool, your suggestion of "does not work without" doesn't seem significantly better to me.
Yeah, I think you make some great points and I'll give you that; you probably did show here why my idea is not correct. I don't know the right answer, I'm certainly no lawyer ;)
I just know that, to me, "dynamic linking" seems like an arbitrary and imprecise way to define "derivative work". And, I'm not sure whether it's really something that _can_ be defined and possible to determine without consider it on a case by case basis. It's a good "right hand rule", perhaps, but doesn't strike me as either necessary or sufficient to really define it. We'll never really know, I guess, until someone makes that actual argument in court.
Depends on what you mean by changing the dependency. Let me lay out the scenario in more detail.
The program is still exactly the same. It asks to be pointed at a fluid sim program, and then uses that for some of the math it needs.
When it was coded, the only dependency it could use was GPL.
Now there's a new non-GPL dependency it could be pointed at, with the same API.
Now it's possible to run the program without using any GPL code. Does that make the program no longer GPL, even though it didn't change?